PL187362B1 - Injection moulding - Google Patents

Abstract

In the present invention, there is disclosed a process for producing elastic thin-walled articles comprising the steps of: 1) selecting a polymer blend having an environmental stress crack resistance(ESCR) of greater than 10 hours; 2) melting said polymer blend; 3) ramming the molten polymer blend into a mold, said mold having a cavity which produces a thin-walled article having a thin section less than 1 mm in thickness and wherein the thin section is substantially continuous for greater distance than 50 mm in the direction of flow of the molten polymer blend in the mould; and 4) removing from the mold the thin-walled article formed from the polymer blend.

Description

The subject of the invention is a method of manufacturing a thin-walled flexible product.

This relates in particular to an injection molding method, in particular a method for injection molding articles having thin fragments, such as thin-walled cylindrical containers, in particular tubes, which are used in the cosmetics industry for lotions, moisturizers and the like.

Thin-walled cylindrical containers, such as those used in the cosmetics industry, are currently made by a process that uses a combination of extrusion, injection molding and heat sealing (commonly referred to herein as an extrusion process). The tube body is extruded into a continuous cylinder which is then cut to the desired length to form a container body. In a separate injection molding operation, the "head and shoulders" of the tube are manufactured. The resulting injection molding "head and shoulders" is then welded to the extruded tube to form a container. Once the container has been filled with product, the rear end of the container is sealed by an additional sealing operation. This method of producing tubes has a number of limitations, the main limitations being the high cost of equipment, the limitations of the variety of tube shapes that can be produced by this method, the inability to provide surface finishes with varying textures or embossed patterns in an operation that is integral to the manufacturing process, and the inability to introducing supplementary elements and components such as closures and hooks during the manufacturing process.

The preferred polymer for making the tube is polyethylene with a low MFI (MFI typically below 2) because it typically provides the tactile and flexibility properties required by buyers and is extrusion processable. Furthermore, low MFI polyethylene has adequate product resistance and barrier properties, making it suitable for most products currently packaged in tubes. It is commonly used when the barrier properties of polyethylene are unsuitable for certain applications

187 362 medium density polyethylene (MDPE), high density polyethylene (HDPE), polypropylene (PP) and multilayer polymer films.

In U.S. Patent No. 5,451,450, plastomers are disclosed as copolymers of ethylene and α-olefins (including ethylene / α-olefin / polyene copolymers), the molecular weight distribution of which, determined by the ratio Mw / M /, is in the range of 1.5- 30, preferably in the range 1.8-10 and more preferably in the range 2-4.

Typically, plastomeric polymers that contain ethylene homopolymers and ethylene interpolymers with at least one α-C 3-20 olefin copolymer are particularly preferred.

The term "interpolymer" is used herein to indicate a copolymer or terpolymer or the like. That is, at least one other comonomer is copolymerized with ethylene to form an interpolymer. Typically, the α-olefins that are copolymerized with ethylene to form plastomers contain from about 2 to about 20 carbon atoms, preferably from about 3 to about 16 carbon atoms, and most preferably from about 3 to about 8 carbon atoms. Non-limiting examples illustrating such α-olefins include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and 1-dodecene.

Plastomers and "substantially linear polyethylenes" are mainly made using metallocene catalysts. U.S. Patent No. 5,281,679 discloses a method of producing homopolymers and metallocene copolymers having a broad molecular weight distribution, typically in the range of 3-30, which have improved tensile strength and impact strength over polymers made using Ziegler-Natta catalysts. They also have much narrower short chain branching distributions and are less extractable in hexane.

The method of producing VLDPE polyethylenes is generally described in EP 120503.

Flexible, substantially linear olefinic polymers have been disclosed in a number of patents, including US Patent Nos. 5,272,236, 5,278,272, 5,380,810, 5,525,695, and 5,665,800. As an example of a flexible substantially linear olefin polymer, U.S. Patent No. 5,578,272 describes one type of polymer as having an amount of critical slip resistance at the beginning of elastic surface turbulence that is at least 50% greater than the amount of critical slip resistance at the beginning. elastic surface turbulence of an olefinic polymer having the same I2 and Mw / M /. The processing index (PI) of these polymers is also lower than or equal to that of the comparable linear olefin polymer, with the same values of I2 and M _w / M /.

The term "substantially linear" when referring to polymers means that the polymer backbone is substituted with from about 0.01 to about 3 per 1000 carbon atoms long side chains, most preferably it is substituted with 0.01 long side chains. up to 1 in 1,000 carbon atoms. The term "linear olein polymer" means that the polymer does not have long side chains, such as those of traditional linear low density polyethylene or linear high density polyethylene obtained by Ziegler polymerization (e.g., disclosed in U.S. Patent Nos. 4,076,698). and No. 3,645,992).

U.S. Patent No. 5,525,695 describes a process for making "substantially linear polyethylenes" and characterizes these polyethylenes as having:

A. a density from about 0.85 g / cm ³ to about 0.97 g / cm ³ ;

B. Honey 0.01 min. To 1000 g / 10 min;

C. 1 preferably sUssma ^ k junction ^ ^ cm of alloy I ₁₀ / Ii from ^ t ^ t ^ r ^ r ^ o 20 1 and

D. mass order M _w / M. _A value of less than 5 1 or less than

3.5 and most preferably from about 1.5 to 2.5.

Flexible, substantially linear, olefinic polymers can be made with broader molecular weight distributions by appropriate selection of polymerization catalysts, as taught in US Patent No. 5,278,272. Material with a wider MDW has a higher value of slip resistance or a relationship

187 362 from shear stress. In other words, usually a wider MWD results in a higher effective MFI with high slip resistance and therefore better processing properties.

As discussed in US Patent No. 5,281,679, extending the molecular weight distribution of a polymer, particularly polyethylene and its copolymers, increases the tensile strength and impact strength of products made from these polymers. The main reason for the high I10 / I2 in the polymer is the presence of both high molecular weight (MW) and low molecular weight molecules in the polymer. It is assumed that the high molecular weight fraction of the molecule contributes significantly to the improvement of the ESCR properties of the polymer, while the low molecular weight fraction of the molecule contributes to the improvement of the processability of the polymer by increasing the slip sensitivity of the polymer and thus allowing the formation of tubes from this polymer despite the relatively low MFI of the polymer (usually measured as I2).

U.S. Patent No. 5,539,076 discloses a single reactor process to produce bi- or multimodal polyethylene polymers having densities ranging from 0.89 to 0.97.

Various aspects of the method of making and cross-linking various silane-based polymer compositions are described in U.S. Patent Nos. 5,055,249, 4,117,063, 4,117,195, 4,413,066, 4,975,488, and 3,646,155.

It is known that poly-2-oxazoline compounds and fluoroelastomers are suitable for use as compatible polymers. U.S. Patent No. 4,474,928 teaches that the inclusion of 1 to 40%, preferably 2 to 20% of the poly-2-oxazoline compounds improves the ESCR of the polymers.

From U.S. Patent 4,244,910, a method of forming resin blends containing polyolefin and inorganic filler is known to form a thin article, wherein said resin blend is injected into a mold at such a speed that its flow rate through the mold injection opening is at least 100 m. / s, which reduces the occurrence of insufficient mold filling, the occurrence of ejection from the mold and allows the product to be formed in a short time.

This method produces moldings with increased stiffness, suitable for high-quality food containers, household items and precision parts whose high stiffness is required for their functionality.

US patent 5346732 discloses a method of shaping and formulating products such as thin-walled pans and lids for which rigidity, not flexibility, is important. The product is hot-formed by extruding a blend containing at least one linear ethylene polymer with specified ranges of properties, allowing the formation of a rigid product, preferably a thin-walled lid, container or bowl.

While it has been proposed to injection mold articles such as thin walled containers, it has hitherto not been possible to injection mold such articles having relatively long, thin parts that are not prone to damage and are salable and practical. The main problems with polymers used for injection molding of the tubes are that the process of forming cylindrical or other shaped tubes requires that the polymer also have a high MFI to allow the polymer to flow downward through a long, narrow and curved path dictated by the shape of the tube. without applying excessive pressures during injection, so that it still exhibits sufficient, good mechanical properties to resist manipulation and resistance to stress cracking caused by the many products that may be packaged therein. In order to injection mold the tube, traditional methods require a polymer whose flow properties allow it to form extruded parts with curves and with a length / thickness ratio of 100 and often greater than 100. Punching a "standard" polymer to flow in a mold of this size. it introduces strong stresses to the polymer which are "frozen" in the product thus produced when the polymer is rapidly cooled below its crystallization temperature before these stresses are removed. These stresses result in the tube being unexpectedly different

187 362 and degraded properties relative to other products of the same polymer formed under less stringent molding conditions.

Additional stresses are introduced into the tubes as they are filled with product and then kneaded and sealed - most often by heat sealing or ultrasonic welding. The process involves bending the "open" end of the tube back to the side through an angle of 180 ° to form an overlap at the seal edge. This overlap is made in the direction of flow of the polymer, which direction has been shown to be the direction of maximum weakening of the molded product. This "folded and sealed" area where the tube has to be deformed in order to obtain a sealing effect is an area of the injection-molded tube particularly susceptible to stress and bending cracking.

The following examples illustrate the specific problems associated with injection molding such tubes. The tubes were injection molded using Du Pont's 2020T polymer, which Du Pont's polymer is described as "especially suited to an injection molded and extruded tube closure where flexibility and maximum resistance to external fracture are required". These tubes were formed under extreme difficulties, which forced the use of very high injection pressures and temperatures to obtain the usual filling of the mold with 2020T polymer. Significant degrees of core displacement / flexure were noted with each molding, no doubt caused by the extremely high injection pressures that were required. It has further been found that the tubes are not actually resistant to bending in the flow direction of the material, breaking significantly with fewer than 5 hand presses on the tube. Cracking under the influence of external factors of the same tubes was investigated, and despite the requirements of "maximum resistance" to cracking caused by external stress, it was found that when thin-walled tubes are injection-molded, they do not meet the requirements.

In another illustration of the difficulties associated with injection molding the tubes, the Dow brochure on Dowlex LLDPE states that LLDPE has significantly better ESCR properties than the corresponding high pressure LDPE. To illustrate the difference, the brochure states that, according to one comparative test, Dowlex High Flowability LLDPE has ESCR properties in oil slightly over 80 times better than those of high pressure LDPE of similar density and MFI (5700 hours in compared to 70 hours), additionally, the ESCR properties were found to be approximately 10 times better than LDPE when immersed in a 10% Teric solution at 50 ° C (225 hours vs.26 hours). However, contrary to these observations, we found that when these polymers are formed into thin wall tubes and then tested for their ESCR properties using a specially developed test method to evaluate the ESCR properties of the tube, both Dow LLDPE 2517 Dowlex and Kemcor LD 8153 ( high pressure LDPE with a similar MFI and density) poorly met the test conditions in 10% of Teric N9 and both polymers were damaged within 20 minutes, clearly demonstrating their unsuitable for the manufacture of tubes by injection molding. This poor result is highly illustrated by the remarkable and difficult physical nature of producing commercially accepted tubes using the injection molding method.

We have now found that it is possible to injection mold flexible thin walled articles having relatively long thin wall parts by selecting polymers used in the injection molding process and having a failure time greater than 10 hours when tested according to the following procedure:

i) a plurality (preferably 6 or more) of the strips of polymer blend derived from any post shaping treatment of the final article, the cross-sectional dimensions of which are 0.65 mm thick and 10 mm wide, injection molded under high shear and high shear forces. flow distances, similar to those used in the manufacture of flexible thin walled articles;

187 362 ii) the strips are folded back over each other and stapled 3 mm from the bend;

iii) the bent strips are immersed in a solution of a stress cracking agent such as nonylphenol ethoxylate, for example in 10% Teric N9 (9 mole ethylene oxide nonylphenol - Orica Australia Pty Ltd) solution and held at 50 ° C;

(iv) the strips are observed for signs of breakage, with any sign of breakage being taken as damage; and

(v) failure time is the time when 50% of the strips show signs of failure.

A method of producing a flexible thin-walled article, especially a tube having a thin portion 1 mm or less in thickness and substantially continuous over 50 mm in length, in which the polymer blend is melted, the molten polymer blend is injected into the mold and the thin-walled article produced is removed from the mold. from a polymer blend, the invention is characterized in that the polymer blend has an ESCR stress cracking resistance value in excess of 10 hours as determined by a test carried out according to the following procedure: many, preferably 6 or more, strips of the polymer blend derived from any one post-shaping treatments, the cross-sectional dimensions of which are as follows: thickness 0.65 mm and width 10 mm, are injection molded under conditions of high shear forces and long flow distances, similar to those used in the production of flexible thin-walled product the stripes are bent to back on itself and stapled 3 mm from the bend, the bent strips are immersed in a solution of a stress cracking agent such as nonylphenol ethoxylate, e.g. 10% solution of Teric N9 - nonylphenol ethoxylated using 9 moles of ethylene oxide from Orica Australia Pty Ltd. and held at 50 ° C, the strips are observed for signs of cracking to appear, any symptom of breakage being taken as a failure; and the failure time is the time when 50% of the strips show signs of failure.

Preferably, at least one polymer of the polymer blend has a melt flow index MFI greater than 10.

Preferably, at least one polymer of the polymer blend has a melt flow index MFI greater than 20.

Preferably, at least one polymer of the polymer blend has a melt flow index MFI greater than 30.

Preferably, the ESCR value of the polymer blend is greater than 100 hours.

Preferably, the ESCR value of the polymer blend is greater than 200 hours.

Preferably, the ESCR value of the polymer blend is greater than 360 hours.

Preferably, the polymer blend comprises at least one polymer and at least one compatible agent and / or at least one nucleating agent.

Preferably, the at least one polymer is selected from the group consisting of plastomers, polyethylenes, copolymers of ethylene and at least one unsaturated olefin, plastomers, substantially linear polyethylenes, branched polyethylenes, polymers and copolymers of ethylene prepared using metallocene or other catalysts that result in copolymers characterized by a highly disordered arrangement of comonomers within polymer chains, polypropylenes, copolymers of propylene and at least one of ethylene and unsaturated olefins, polymers and copolymers of propylene made using metallocene or other catalysts, resulting in copolymers having highly disordered polymer chains in order to comonomer , polylactic acid polymers, silane polymers, and mixtures thereof.

Preferably, the at least one compatible agent is selected from the group consisting of ethylene / vinyl acetate copolymer, ethylene / vinyl alcohol copolymer, plasticized polyvinyl acetate and polyvinyl alcohol, alkyl carboxy substituted polyolefins, organic acid anhydride copolymers, copolymers containing groups epoxy, chlorinated polyethylene, ethylene / propylene / butylene copolymers, polyethylene

187 362 custom low density polyethylene, very low density polyethylene, low density polyethylene, medium density polyethylene and high density polyethylene, polypropylene, polybutylene and their copolymers, polyester ethers, poly (ether esters), acrylonitrile / methacrylate copolymers, block copolymers having styrene end blocks, half esters, amine and alkoxysilane grafted polyethylenes, vinyl addition polymers, styrene / butadiene block copolymers, acid grafted polyolefins, vinyl pyrrolidine grafted polyolefins, block copolymers of dihydroxy monomers, polyethylenes modified with polyolefenic unsaturated or polypropylene grafted with polyolefinates C2-6 acyloxy functional groups, polyoxazoline; fluoroelastomers, from other compatible polymeric substances suitable for use with polyolefins, particles coated with any of the above, and mixtures thereof.

Preferably, the at least one nucleating agent is selected from the group consisting of talc, mica, various metal compounds, including oxides and silicates, as well as various organic compounds including various dyes and pigments.

Preferably, at least one polymer is a polyethylene-based polymer and at least one compatible agent is a polypropylene-based polymer.

Preferably, the at least one polymer is a linear, substantially linear or branched polyethylene or copolymer characterized by a highly disordered arrangement of comonomers within the polymer chains, and the at least one compatible agent is a polypropylene based polymer.

By the term "substantially continuous", it is understood by those skilled in the art that the thickness of the thin portion of the article is typically kept below 1 mm, although some variations to increase the thickness are allowed when, for example, a patterned surface finish is incorporated into the article. texture or relief.

The term thickness refers to the thickness of the layer of the polymer blend described above and excludes any additional layers that may be included as components of the multi-layer laminate. In applications where the blend is foamed, the term thickness refers to the thickness of the non-foamed material which can be readily determined from the density of the polymer blend.

It is understood that throughout the specification and the claims that follow, the term "polymer blend" refers to compositions comprising at least one polymer and optionally incorporated additional ingredients, such as are described herein.

It is understood that throughout the specification and the claims that follow, the term "copolymer" refers to polymers into which two or more monomers are incorporated.

For the selection of an appropriate polymer blend suitable for the production of thin-walled articles, it is essential that the above defined ESCR of the polymer blend be greater than 10 hours. Preferably, the ESCR of the polymer blend is greater than 100 hours, more preferably greater than 200 hours, and most preferably greater than 360 hours. When the thin-walled product is a tube or other container used to package compositions such as a moisturizer or shampoo, which may be highly aggressive to the thin-walled product and may degrade its properties over time, it is necessary to select a polymer blend having such a sufficiently high ESCR that the thin-walled article formed from the blend is able to withstand the harsh conditions of use despite any deterioration in properties resulting from the aggressive nature of the materials contained within the thin walled article. When a thin wall article is used to package a relatively inert material, lower ESCR values may be allowed.

The ESCR test as defined above can be performed using a variety of stress crack agents. A preferred stress crack agent is Teric N9 (nonylphenol ethoxylated with 9 moles of ethylene oxide from Orica Australia Pty Ltd), while other nonylphenol ethoxylates may also be advantageously used. Other stress crack agents may be used and may be selected for the desired end use. For other causing agents

Stress cracks include mineral oils, cationic surfactants, solvents, and other agents that are readily apparent to those skilled in the art.

Preferably, the above-described EsCr test is carried out under forming conditions similar to those used in the production of thin-walled articles. For example, when one intends to produce a thin walled article using oscillating melt-forcing techniques, it is preferable to perform ESCR tests on wafers made from shapes made by oscillating melt-forcing techniques.

As defined above, the ESCR test allows the selection of various polymer blends that are suitable for injection molding to form thin-walled articles.

A wide variety of polymers can be used as the basis of the blend which meets the requirements of the ESCR test as defined above or functions as at least one polymer. These polymers include olefinic homopolymers and copolymers, preferably ethylene or polypropylene homopolymers and copolymers with α- or P-Cs-olefins and / or polyenes, preferably α- or β-Cs-s-olefins, the density of such polymers being ranges from very low to high density (density ranges from 0.85 g / cm ³ to 0.97 g / cm3). Also suitable for use in the present invention are copolymers of ethylene, propylene and butene with vinyl end groups and copolymers of ethylene, propylene and butene containing more than 50% ethylene, propylene or butylene, which are copolymerized with comonomers such as methyl acrylates, ethyl acrylates, acid acrylic and methacrylic acid, styrene-ethylene / butene-styrene ABA ionomers and copolymers. These polymers can be made using a variety of methods, including high and low pressure processes, using a variety of catalysts such as the Ziegler-Natta catalyst and metallocenes and have molecular structures ranging from linear to highly branched, including polymers such as LDPE, MDPE and HDPE. Particularly suitable for use in the present invention are plastomers, "substantially linear" and branched polyethylenes or polypropylenes, copolymers of propylene and ethylene or one or more α-olefins, terpolymers of ethylene and propylene or one or more α-olefins (exemplified by are Catalloy polymers by Montell) and propylene polymers and copolymers produced using metallocene catalysts. Other polymers that can be used in the present invention include polylactic acid polymers.

We have found that plastomers, "substantially linear polyethylenes", branched chain metallocene polyethylene copolymers, propylene-α-olefin interpolymers, and metallocene polymers and propylene interpolymers, are preferred for use in the invention in the manufacture of thin-walled articles, particularly in the manufacture of flexible tubes. A key characteristic of plastomers, "substantially linear polyethylenes", branched chain metallocene copolymers of polyethylene, propylene-α-olefin interpolymers, and metallocene polymers and propylene interpolymers is the distribution of their constituents, i.e. homogeneity of the comonomer distribution within and between polymer molecules.

Plastomers, "substantially linear polyethylenes", branched-chain metallocene polyethylene copolymers, propylene-α-olefin interpolymers, and metallocene polymers and propylene interpolymers, are usually made using metallocene catalysts, which are known to introduce comonomer very evenly between and along polymer molecules that are formed with their participation. Thus, most particles of a particular plastomer, "substantially linear polyethylenes", branched chain metallocene polyethylene copolymers, propylene-α-olefin interpolymers, and metallocene polymers and propylene interpolymers, will have approximately the same comonomer content and within each particle the comonomer will be distributed in utterly chaotic. Typically, Ziegler-Natta catalysts produce copolymers having a much broader component distribution - especially the comonomer distribution in the polymers so produced will vary widely among the polymer particles and within a given particle the distribution will also be less random.

187 362

Polyene comonomers suitable for copolymerization with ethylene to form plastomers suitable for the present invention contain, in the backbone, from about 3 to about 20 carbon atoms, preferably from about 4 to about 20 carbon atoms, and most preferably from about 4 to about 15 carbon atoms. coal. In one embodiment, the polyene is a diene that contains from about 3 to about 20 carbon atoms and may be straight or branched chain or may be a cyclic hydrocarbon diene. A preferred diene is an unconjugated diene. Non-limiting examples of ethylene / α-olefin plastomers suitable in the present invention include ethylene / butene-1 copolymers. ethylene / hexene-1, ethylene / octene-1 and ethylene / propylene. Non-limiting examples of terpolymer plastomers suitable for the present invention include ethylene / propylene / 1,4-hexadiene and ethylene / octene-1 / 1,4-hexadiene terpolymers.

Suitable metallocene homopolymers and copolymers having a broad molecular weight distribution, typically in the range 3-30, having improved tensile strength and impact strength, and narrower short chain branching distributions are suitable for use in the present invention.

With regard to density, the plastomers which are advantageously suitable for use in the process of the present invention are comparable to VLDPE and ULDPE, which are also copolymers of ethylene with α-olefins such as butene, hexene or octene. They are typically defined as copolymers of ethylene and α-olefins with densities ranging from 0.86 to about 0.915. Plastomers, even those whose density is the same as that of VLDPE polyethylenes, have significantly different physical properties due to differences in the production method - mainly due to the use of metallocene catalysts. Typically, VLDPE compared to a plastomer of similar density has a much higher melting point and softening point, a molecular weight / dimension distribution greater than 3 and a higher level of crystallinity.

Flexible, substantially linear olefinic polymers including ethylene homopolymers and ethylene interpolymers with at least one of the α-C3-20 olefinic copolymers are particularly preferred. The term "interpolymer" is used in the present invention to denote a copolymer or a terpolymer. That is, at least one other comonomer is copolymerized with ethylene to form an interpolymer.

The SCBDI index (Short Side Chain Distribution Index) is defined as the weight percent of the particles having a comonomer content within 15 *% of the median total mole comonomer content. The SCBDI of the substantially linear polymers suitable for the present invention is preferably greater than about 30%, particularly greater than 50%.

A unique feature of the substantially linear polymers of the present invention is a highly unexpected flowability where the I10 / I2 value is substantially independent of the polydispersity index (i.e., M _w / Mn). This contrasts with traditional polyethylene resins having rheological properties such as polydispersity index, the I10 / I2 value is increased.

The density of the ethylene or ethylene / α-olefin essentially linear olefin polymers of the present invention is typically from about 0.85 g / cm ³ to about 0.97 g / cm ³ , preferably from about 0.85 g / cm 3 to 0 .92 g / cnt '.

The substantially linear polymers preferred for use in the process of the present invention have a processability similar to that of high pressure LDPE, while exhibiting strength and other physical properties similar to those of traditional LLDPE, without the support of special adhesion promoters (e.g. processing additives such as Yiton fluoroelastomers manufactured by Du Pont).

"Substantially linear olein polymers", plastomers and branched metallocene polyethylenes with a broad molecular weight distribution are particularly suitable for making the tubes of the present invention.

We have further found that certain types of polymers, particularly unsaturated polymers such as polyvinyl chloride and polystyrene, more preferably polyolefins and even more preferably plastomers, "substantially linear polyethylene", copolymers of branched metallocene polyethylene and polypropylene, and most preferably plastomers and copolymers of polymers " essentially linear polyethylene "and polypropylene, the densities of which are in the range 0.87 to 0.92 and whose MFI values are above 10, preferably above 20 and most preferably above 30, with the addition of only nucleating agents to improve Tubes' ESCR properties, can be used to make tubes suitable for the packaging of some less aggressive products. However, the addition of compatible polymers such as polypropylene and polypropylene copolymers to these polymers, in addition to nucleating agents, results in better overall ESCR resistance and is usually preferred.

It has been established that polymers, but especially plastomers and essentially linear polyolefins having higher than normal I10 / I2 values that are essentially independent of the polydispersity index (i.e. M _w / M _n ), and metallocene homopolymers and polypropylene copolymers, are particularly suitable for the preparation of by injection molding of tubes and other thin-walled products with good ESCR properties and other physicochemical properties.

The high I10 / I2 ratio polymers suitable for use in the present invention can be made by a variety of methods. These methods include:

1) homogeneously blending two or more polymers having different molecular weights, in suitable mixing equipment;

2) preparation of 1β- or mutimroclh^^h polymers with a high I10II2 ratio, using "tandem" reactors (one after the other); and

3) preparation of bi-modal polymers with a high I ₁₀ / I2 ratio in a single reactor using appropriate catalysts.

The catalysts used to prepare bi- or multimodal polymers with a high WI2 ratio may be selected to produce:

2) polymers - with a broad molecular weight order (e.g. with a molecular weight distribution in the range of 3-30, or

And 3) Efficiently producing two or more polymers with T i i c c c albo posiada albo albo albo albo albo albo albo albo albo albo albo albo albo either narrow or broad molecular weight distribution as desired.

Other polymers suitable for injection molding the tubes are silane grafted or copolymerized polymers. Such polymers can be cross-linked after their manufacture, resulting in mouldable / processable cross-linked polymer compounds that facilitate the processing and design / manufacture of relatively low-viscosity polymers while simultaneously achieving the strength and other benefits of copolymers and cross-linked polymers. These polymers also eliminate the need to extend cycle times and elevated temperatures to achieve crosslinking in the mold.

Many such silane-based polymer compositions are suitable for use in the present invention.

According to the invention, for the production of a flexible thin-walled product, a blend is used, all the ingredients of which can be mixed in a single step, immediately before injection molding. The blend consists of one or more types of polymers such as acrylates or metallocene catalyzed branched α-olefin plastomers, which are reacted with an organosilane compound such as vinyltrimethoxysilane in the presence of a peroxide such as cumyl peroxide to form a silane grafted polymer this reactive processing takes place in the cylinder of the injection molding machine. Thereafter, a catalyst such as dibutyltin dilaurate is introduced into the silane grafted polymer in the barrel of the injection molding machine just prior to injection of the silane graft polymer into the mold and mixed to ensure the catalyst and the graft polymer are homogeneously mixed. The catalyst facilitates post-formation crosslinking of the main chains by the silane components, in the presence of moisture, by condensation of the hydrolysable silane groups with the various polymer backbones, resulting in a new polymer that possesses properties that combine the properties of the individual polymers from which they were formed. polymers produced

187 362 silane grafted, as well as the properties imparted by the higher molecular weight polymer molecules which result from the above cross-linking. The end properties of the new polymer can be varied by changing the proportions of the different polymers, by changing the properties of one or both of the polymers (e.g. by using polymers containing additional functional groups such as vinyl acetate and / or by varying the properties of the silane-containing polymer by, for example, changing the type of polyethylene and / or a type of silane chemically bonded to the polymer). The final properties can be further altered by the addition of other compounds / additives such as fillers, plasticizers and antioxidants which are well known to those skilled in the preparation of polymer blends.

An alternative method of making silane grafted polymers which may be used in the present invention is to graft the silane onto the polymer in the presence of peroxide or other free radical generator in a suitable reactor such as an extruder, this grafting being a separate step, followed by packaging the resulting material. polymer grafted into a packaging that is resistant to moisture, intended for later use. If desired, the grafted polymer may be introduced into the injection molding machine together with a suitable amount of condensation catalyst, the two components being mixed together in the injection molding machine and then injection molded, followed by crosslinking.

The silane-containing polymer typically has from 0.1% to 15% of a hydrolysable silane. The most common hydrolysable silanes that are used to make silane-containing polymers are vinyltrimethoxysilane and vinyltriethoxysilane, but can be any hydrolyzable silane that can be incorporated into another polymer to form a silane-containing polymer.

The at least one compatible agent is preferably a polymer and, when mixed with at least one polymer, results in a blend which, when mixed and used to form thin-walled articles such as injection molded flexible tubes, has properties superior to those of the original ingredients or polymers without admixtures. The at least one compatible agent may be selected from the group consisting of ethylene / vinyl acetate copolymer; ethylene / vinyl alcohol copolymer; plasticized polyvinyl acetate and polyvinyl alcohol; alkylcarboxy substituted polyolefins; organic acid anhydride copolymers; epoxy-containing copolymers; chlorinated polyethylene; ethylene / propylene / butylene copolymer and the like copolymers; extremely low-density polyethylene, very low-density polyethylene, low-density polyethylene, medium-density polyethylene and high-density polyethylene; polypropylene, polybutylene and their copolymers; polyester ethers; poly (ether) esters (such as the Hytrel product group from Du Pont); acrylonitrile / methacrylate copolymers; block copolymers having styrene end blocks; half esters; amine and alkoxysilane grafted polyethylenes; vinyl addition polymers; styrene butadiene block copolymers; acid grafted polyolefins; vinylpyrrolidine grafted polyolefins; block copolymers of dihydric monomers; propylene grafted unsaturated esters; modified polyolefins containing amide, epoxy, hydroxyl or C2-6 acyloxy functional groups, from other compatible polymeric substances suitable for use with polyolefins; particles coated with any of the above substances; and mixtures thereof. In the above compatible agents, functional groups are typically incorporated into the modified polyolefin as part of the unsaturated monomer that is either copolymerized with the olefin monomer or grafted into the polyolefin to form the modified polyolefin.

Alkyl carboxyl-substituted polyolefins include substituted polyolefins in which the carboxy groups are derived from acids, esters, anhydrides, and their salts. Carboxylate salts include neutralized acids, which are often referred to as ionomers (e.g., Surlyn). Commonly, acids, anhydrides, and esters include methacrylic acid, acrylic acid, ethacrylic acid, glycidyl maleate, 2-hydroxyacrylate, diethyl maleate, maleic anhydride, maleic acid, dicarboxylic acid esters, and the like. Preferred examples include copolymers of ethylenically unsaturated acids

187,362 carboxylic acid compounds such as polyethylene / methacrylic acid copolymer and polyethylene / acrylic acid copolymer and salts thereof.

Organic acid anhydride copolymers include maleic anhydride copolymers as well as cyclic anhydride copolymers.

Poly-2-oxazoline compounds are also suitable for use as compatible agents. It is preferred to include from 1% to 40%, more preferably from 2% to 20% of the poly-2-oxazoline compounds. These compatible agents improve the adhesion of the PE blend to various substrates which may make it suitable for printing and labeling. The compatibilizing agent comprises an α-olefinic copolymer substrate grafted with an amount of a monovinylidene aromatic polymer. Preferably, the alpha-olefin copolymer support is a terpolymer of ethylene, propylene and unconjugated diolefins.

Many ethylene copolymers are also useful as compatible agents in the process of the present invention. For example, single-site catalyzed polymers such as metallocene catalyzed polyethylene may be used as compatible agents in the present invention.

Polypropylene suitable for use in the process of the present invention as a compatible agent includes isotactic, syndiotactic and atactic polypropylene and syndiotactic polypropylene with different MFI values, densities and crystallinity that will achieve the desired properties in the products formed by the process of the present invention. Particularly when blended with low molecular weight plastomers, a variety of polypropylene polymers having a wide range of MFI values (from 1 to greater than 200), densities and crystallinity, will provide blends suitable for use in the process of the present invention.

The polyethylene that can be used in the process of the present invention as a compatible agent includes polyethylenes having different MFI values, densities and crystallinity which will allow obtaining the desired properties in the products formed by the process of the present invention. They include very low, low, medium and high density polyethylene. Particularly when blended with low molecular weight plastomers, substantially linear polyethylenes, and branched chain metallocene polyethylene polymers, a variety of polyethylene polymers having a wide range of MFI values (from 1 to over 200), densities and crystallinity will provide blends suitable for for use in the method of the present invention.

Many monomers have been copolymerized with propylene to obtain propylene copolymers. Many of these copolymers are suitable for use in the present invention as compatible agents. Examples of ethylene / propylene copolymers include Montell's SMD6100P and XMA6170P copolymers. Further examples of polypropylene copolymers include the Catalloy KS-084P and KS-357P copolymers from Montell, which products are believed to be propylene, ethylene and butene terpolymers. Other such copolymers and terpolymers can be used.

When such compatible agents as ionomers are combined with plastomers, an essentially linear polymer, and branched chain polyethylenes as at least one polymer, particular advantages are obtained. The ionomers are usually copolymers of ethylene and acrylic and methacrylic acids that have been neutralized with metal ions such as sodium, lithium or zinc. An example of one group of ethylene copolymers, called ionomers, are the commercial products Surlyn (manufactured by Du Pont). At ambient temperature, ionomers tend to behave similarly to cross-linked polymers, i.e. they are stiff and hard, however, they can be processed at elevated temperatures. A blend of plastomers and ionomers is particularly preferred as such a blend enables polymers with enhanced barrier properties to be obtained.

Block copolymers of dihydric monomers include block copolymers of dihydric phenol monomers, a carbamate precursor, and a polyoxypropylene resin.

The compatible agent is used in an amount at least sufficient to improve the resistance of the polymer blend to external cracking. Stan14

Standard tests for determining the toughness to cracking by external factors are of little value in determining the behavior of individual polymer blends when processed into thin-walled products such as tubes. Without wishing to be bound by theory, it is believed that injection molding of thin walled articles such as tubes introduces and freezes extreme stresses in the formed articles. The degree and orientation of stresses in articles such as injection molded tubes make them susceptible to cracking under the influence of external factors. Accordingly, the test described above was developed in accordance with the present invention to demonstrate an improvement in the toughness against external stress cracking.

In some compositions, 2% or less of the compatible agent is sufficient to improve the external crack resistance of the polymer blend relative to the external crack resistance of the plastomer.

The compatible agent may also be used in excess of the amounts required to make the polymer blend compatible, in order to improve the viscosity properties of the polymer blend so as to optimize the molding properties of the polymer blend and / or overall properties of the molded products such as softness and flexibility. Typically, the compatible agent is used in an amount of from about 2% to about 98% by weight of the polymer blend, although smaller amounts may be used in some polymer blends. The optimal amount for a particular composition will depend on the properties required and can be determined experimentally. In addition, it has been found that increasing the percentage of compatible agent above the amount necessary to increase the resistance to cracking of the polymer blend to external factors often also allows the properties of the polymer blend to be improved, such as tear strength and impact strength, barrier properties, chemical resistance, processability and properties. associated with the tactile sensation. For example, introducing a greater than necessary percentage of excess polypropylene to improve the resistance to external cracking of the polyethylene blend to a desired level, can improve chemical resistance and reduce the transmission of water vapor and water through the polymer blend relative to polymer blends containing minimal the amount of polypropylene required to improve only the toughness against environmental cracking. It has furthermore been found that the incorporation of a greater than necessary percentage of the compatible agent may allow the incorporation of a greater percentage of other polymers than otherwise would be compatible with the present invention. Thus, the use of a compatible agent in such amounts may allow for the incorporation of more than otherwise possible amounts of such advantageous, substantially incompatible other polymers such as nylons and EVOH, with accompanying improvements in properties such as tear strength and tear strength. impact, chemical resistance, barrier properties and tactile properties.

Barrier resins can be incorporated into the polymer blends of the present invention. Barrier resins that may be compatible with at least one polymer include: condensation polymers such as polyamides, polycarbonates, and various esters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), poly (naphthalate) ethylene) (PEN); polyvinyl chloride (PVC); poly (t1-vinylidene) (pVDc); ethylene / vinyl alcohol (EVOH); polyvinyl alcohol (PVOH); ethylene vinyl acetate (EVA); EMA, EMAA, EEA; ionomers; aromatic monovidylidene polymers and copolymers; ethylene, propylene and butylene copolymers; chlorosulfonated polyethylene, polyisoprene and polychloroprene, polyalkalene phenylene ester and ether; phenylformaldehyde; polyacrylate; polyester ethers; acrylonitrile-methacrylate copolymers; nitrile copolymers; polyacrylonitrile; polyurethane and polyacetals. It is obvious that some barrier polymers will be more or less compatible with at least one polymer than with others. For example, EVOH, with sufficiently high ethylene content, will be compatible with at least one polymer, especially when that polymer is an ethylene copolymer such as a plastomer, although EVOH

187 362 relatively low ethylene content will be substantially incompatible. The barrier properties of the polymer blends of the present invention can be further improved by adding additives capable of reacting with or absorbing harmful chemicals such as oxygen or other gases.

The polymer blend can also contain various other additives. Examples of these supplementary additives also include polymers, pigments, dyes, fillers, antioxidants, plasticizers, UV-protectants, viscosity modifiers, additives capable of reacting with or absorbing harmful chemicals such as oxygen or other gases, and among others, mold release agents and alloy concentration modifiers. These additives may be added to one or more of the components of the polymer blend or to the polymer blend as a whole prior to its formation, in order to modify the properties of the blend to suit specific applications or to achieve specific effects in the final product.

In order to achieve the desired barrier properties when using a substantially incompatible polymer and without pre-orienting the polymers prior to injection molding, it is preferred that the melt flow rate of the disperse phase is slightly greater than that of the continuous phase for the same amount of slip resistance. Specifically, the melt flow index of the barrier resin (usually in the dispersed phase) ranges from 1.1 to 3.5 times that of the continuous phase. For optimal barrier properties, it is assumed that the droplets of the disperse phase should distort to form lamellae (lamellar structures) when subjected to stresses associated with the injection operation. However, if the melt flow rate of the dispersed phase is much lower than that of the continuous phase, the droplets of the dispersed phase tend to resist distortion and will not form the lamellar structure necessary for optimal barrier properties. On the other hand, if the melt flow rate of the dispersed phase is greater than that of the continuous phase, they have a greater tendency to break under shear stress during mixing, thereby leading to finer dispersion and thus forming smaller platelets of the barrier material, thereby reducing same barrier action.

It is also preferred that the polymer blend, including the barrier polymer, is not subjected to more mixing prior to molding than necessary to achieve uniform mixing. Excessive shear forces may reduce the barrier properties. Those skilled in the art will be able to determine the desired mixing amounts necessary to obtain an optimal balance of properties. An additional advantage of the formation of these lamellar structures in the polymer blends of the present invention is that the mold can be designed to facilitate the flow of the polymer melt across the mold as well as directly down the core. It is believed that this mold design facilitates biaxial stretching of the barrier materials to form lamellar structures that further improve the barrier properties of the molded articles.

Another method by which the formation of a lamellar / multilayer structure of polymers for use in the present invention can be promoted is to pre-blend the polymers into a composite stream and inject this stream into a mold to form articles containing largely discontinuous, usually flat and parallel layers. This can be achieved in a number of ways, including co-extruding a complex stream of discontinuous, usually planar and parallel layers of different polymer components of the blends of the present invention, manipulating this complex stream as necessary to form a second composite stream having an increased number of layers of substantially uniform thickness. and then direct injection molding the final stream so as to form a multilayer plastic article.

In a particularly preferred embodiment of the present invention, the polymer blend comprises at least one plastomer and at least one ionomer. These polymer blends may advantageously incorporate an additional polymer to impart a specific blend

187 362 barrier properties. For example, incorporating nylon into such a blend and selecting the appropriate mixing and molding conditions greatly reduces the hydrocarbon and gas permeability of the plastomer. It is believed that the high degree of directional orientation caused by the molding operation contributes to imparting highly desirable barrier properties that can be introduced by the addition of nylon and other substantially incompatible polymers. The nylon itself must be stretched and oriented to form lamellar structures to optimize barrier properties. By incorporating the nylon into the plastomer and ionomer blend, the blend can be injection molded to form components having barrier properties that are believed to be incorporated with the nylon while maintaining resistance to external stress cracking.

Without wishing to be bound by theory, we have found that at least one polymer has the property of interacting with at least one compatible agent whereby the properties of both the at least one polymer and the at least one compatible agent are significantly and unexpectedly altered to cause the production so produced. the polymer blend was suitable for the production of thin-walled products.

It is believed that the interaction between the at least one polymer and the at least one compatible agent results in the formation of areas within the molded articles which may be referred to as "joints". As it turns out, these "joints" absorb or dissipate stresses in articles made of the polymer blend. The presence of these "joints" dispersed within the article causes the stress to be absorbed or dissipated which would otherwise degrade the physical properties. These so-called "joints" are considered to be the result of one or more of the following mechanisms:

(i) polymer and compatible interact to increase the number of amorphous regions within the polymer;

(ii) χνν ^ ερυίε a negative reaction between the polymer and the compatible agent resulting in a significant localized reduction in crystallinity, that is, the formation of relatively amorphous regions at the interface between the polymer and the compatible agent; and (iii) there is a mutual reaction between the polymer and the agent i ^ tmi {^: ip ^ dilh ^; ^ mi which, while not reducing the crystallinity and hence more amorphous areas, nevertheless creates an interface area between the polymer and the agent compatible that has a greater ability to absorb or dissipate stresses.

In particular, it has been found that when the at least one polymer is a copolymer or homopolymer of ethylene, preferably a plastomer or a substantially linear polymer, said polymer is capable of interacting with propylene and with many of its copolymers, and the crystallinity of the polymer is reduced as a result.

The polypropylene polymers are believed to act as crystallizing agents for the at least one polymer and as a result the number of amorphous regions within the at least one polymer is increased. DSC analysis showed that they also caused a significant reduction in the overall crystallinity of the ethylene polymer, especially plastomers and substantially linear polyethylene polymers. It is also believed that these amorphous regions, along with the interfacial interaction between the at least one polymer and the propylene polymer, act to reduce or dissipate stresses in the molded part generated during molding, thereby increasing its ESCR. At the same time, the at least one polymer interacts with the at least one plastomer or substantially linear polymer and as a result significantly reduces the crystallinity of the at least one plastomer.

It is believed that the plurality of polymer blends form a co-continuous lamellar structure and that the interface between the at least one polymer and the at least one compatible agent is characterized by an abutting interlacing of the at least one polymer and the at least one compatible agent at the croscopic level. In other words, the at least one compatible agent is assumed to function as an interactive filler. It is believed that due to this contiguous interlacing between the at least one polymer and the at least one compatible agent, the overall properties of the polymer blend improve. Particularly when the at least one polymer is low molecular weight plastomers and substantially linear polyethylenes, other polymers previously contemplated as being substantially incompatible with polyethylene may now become compatible and blends thereof may have a range of properties that will permit the production of acceptable articles. by the market, which until now were not commercially available.

It has been found that many compounds known for their ability to nucleate polymers, especially olefin polymers and copolymers, and especially ethylene polymers and copolymers, improve the ESCR properties of polymers for use in the present invention. Depending on the physical nature of the individual polymer (s), the nucleating agents themselves (i.e. without the addition of compatible agents) are capable of increasing the ESCR of the polymer (s) to a level that makes the polymer (s) suitable for making tubes by injection molding. Nucleating agents are believed to increase the ESCR of polymers during tube production by causing more small crystals to form than would otherwise be the case. This greater number of small crystals increases the number of amorphous regions within the polymer that are capable of absorbing or dissipating the stresses introduced into the molded tubes during injection molding, thereby increasing the ESCR and flexural strength of the product. Suitable nucleating agents for use in making tubes include inorganic compounds such as talc, mica, various metal compounds such as oxides and silicates, as well as various organic compounds including various dyes and pigments. However, for the best results when injection molding the tubes, it is preferable to use nucleating agents in combination with compatible polymers.

Compounds known to be capable of reducing the glass transition temperature (Tg) of at least one polymer according to the present invention, particularly olefinic copolymers and polymers, especially ethylene copolymers and polymers, have been found to improve the ESCR properties of the polymers to be used in the present invention.

Depending on the physical nature of the individual polymer (s), the Tg lowering agents alone (i.e. without the addition of compatible agents, nucleating agents or "high thermal density agents") are capable of increasing the ESCR of the polymer (s) to a level that causes that the polymer (s) are suitable for the manufacture of tubes by injection molding. Tg lowering agents are believed to increase the ESCR of polymers used to make tubes by effectively increasing the time for which the crystallinity of the polymer is reduced, thereby increasing the time available for the polymer particles to self-convert so as to reduce stresses in the molded article. This causes the molded part to have less stress than it would have been if the Tg had not been lowered, resulting in a molded product having better ESCR properties. A suitable Tg reducing agent is polypropylene. However, for best results when injection molding the tubes, it is preferable to use Tg lowering agents together with compatible agents, unless the Tg lowering agent is itself a compatible agent.

Poly-2-oxazoline compounds and fluoroelastomers are also suitable for use as compatible polymers. The incorporation of 1% to 40%, preferably 2% to 20% of the poly-2-oxazoline compounds improves the ESCR of the polymers. These compatible polymers also improve the adhesion of the PE blend to various substrates which may make them suitable for making PE for printing or labeling.

While the ESCR-enhancing effect of additives such as nucleating agents and Tg-lowering agents is not particularly noticeable in "normal" molded articles, it is believed that in such molded articles as thin walled tubes, where the polymer is subjected to rapid cooling, high injection rates, high

Due to injection pressures, long, narrow and rounded flow paths (and resulting high levels of induced stress), the performance can be significant even at low additive levels. It has been found that such additives can improve the ESCR of certain polymers to the extent that at least one polymer and an appropriate amount of the additive itself may be suitable for production by vacuum forming.

According to the invention, at least one compatible agent may be incorporated into at least one polymer. For example, a polymer having monomers introducing compatible agent groups can be copolymerized with other monomers to form a polymer that contains the compatible agent. For example, a monomer having methacrylic acid groups can be added to the polymerization mixture of at least one polymer to form an elastomer that contains a compatible agent. Alternatively, compatible agent groups can be grafted onto the polymer. Preferably, the polymer having compatible agent groups grafted thereon is a plastomer or a substantially linear polymer.

The polymer blend can be produced by extruding some or all of the components of the polymer blend, and the resultant chopped extrusion can be used in the injection molding process of the present invention. Alternatively, the polymer blend may be provided as separate components and blended prior to and during the melting of the polymer blend in the process of the present invention.

The polymer blend can be melted by any conventional means. It is particularly convenient to melt the polymer mixture in a conventional injection molding machine in which the screw rotating in a heated cylinder both melts the polymer mixture and forces the molten polymer mixture into the mold. The molded articles of the polymer blend can be easily removed from the mold by conventional methods.

The injection molding process of the present invention makes it possible to produce injection molded articles having surprisingly thin parts while maintaining the mechanical properties of the polymer blend. We have found that products with section thicknesses ranging from 0.3 mm to 0.7 mm can be injection molded and that the thin wall length of these thin walled products may exceed 50 mm. These articles can be easily manufactured without substantially deteriorating the mechanical properties of the plastic used.

The polymer blends of the present invention, which allow for injection molding of articles having thin parts, provide a number of advantages that otherwise cannot be achieved due to technical limitations. These technical limitations are best illustrated in the manufacture of thin walled tubes. These tubes, which are a very important commercial product, are obtained by extrusion, which excludes the use of regulation and changing the wall thickness to enable the production of tubes with adjustable and variable wall thickness. In accordance with the present invention, it is envisaged to produce articles having thin parts, the thickness of which can be adjusted and varied. For example, in one variation of an injection molded tube, the thickness of the walls of the tube may vary along its length. The wall thickness may be made greater at the neck of the tube in order to obtain increased flexibility at the end of the tube. The method according to the present invention also makes it possible to introduce an embossing on the thin walls of the tube. The embossing may take the form of logos, trademarks, various texts, as well as textures or such a surface finish as leather grain or undulations.

An additional advantage of the present invention, which cannot otherwise be achieved due to technical limitations, is the use of "in-mold" labeling to decorate the thin walled tubes. Extruded tubes cannot be decorated by in-mold labeling, which necessitates any labeling of such tubes in a separate and costly manufacturing package. The tubes made by the method of the present invention can be labeled in-mold in a one-step forming operation to avoid a separate and costly additional manufacturing operation. The positioning of the labels in the mold cavity can be accomplished in a variety of ways, including placing the label on the core while the mold is open, closing the mold, and transferring the label from the core to the cavity.

187 362 using various methods, just prior to injection of the polymer to form the tube labeled in the mold.

An additional advantage of the present invention is that a barrier sheath can be applied to all or part of the core prior to the formation of the barrier sheath that is transferred to the molded article prior to the molding operation, in order to impart improved barrier properties or other advantageous properties to the tubes of the present invention. An additional advantage of the present invention is the possibility of applying a coating prior to molding either on the core or on the core or on the core and the mold cavity, which in turn is transferred during the molding operation to a suitable surface of the molded article. This operation results in a coating either on the outer or inner surface of the tubes obtained by the process of the present invention. Such coatings can fulfill a variety of functions, including decorative and covering functions.

The method of manufacturing thin-walled articles by injection molding according to the invention allows for a number of variations in the shape and configuration of the articles, which otherwise could not be obtained due to the technical difficulties associated with the production of thin-walled articles. Referring again to the example of a thin walled tube, various closures, hooks or flaps can be incorporated into its structure. Hitherto, the incorporation of such additional components has required separate components to be prepared and then welded or otherwise attached to the tubes, which has significantly increased the overall cost of the tube. In accordance with the present invention, the use of a suitably designed tool and / or a dual injection molding machine enables a one-step production of tubes having integrated closures, hooks, flaps or other accessories made of the same or different polymers.

A number of modifications to standard tube making tooling can be made to facilitate the manufacture of unitary tube / accessory molded articles, particularly unitary tube / closure molded articles. If required, such unitary tube / closure molded articles may have a variety of pressed hinges (including retaining hinges), dispensing spouts, and other aids, each pressed in during the molding operation. In case the polymer used to form the unitary tube / closure article is inadequately rigid to allow the formation of a conventional hinge with a "self-closing" or "snap-on" mechanism, the hinge itself may be designed with a roundness. Provided the polymer has sufficient flexibility, the roundness combined with the elasticity of the polymer should result in a self-latching closure.

An additional advantage of the method of the present invention is that by allowing the production of tubes with special contours designed to engage with the handles, a relatively cheap and easy attachment of convenient components such as self-sealing valves is achieved. A typical tube / self-closing closure combination consists of at least four, and often five individual components - a two-piece tube (tube body and head / arm), body closure, self-sealing valve, locking device that secures the valve to the body, and often a valve protector to prevent contents leakage, especially during packing and delivery to retail outlets. At least three parts of the self-sealing closure are folded separately and then attached to the tube. The method of the present invention allows for the production of a one piece tube / valve holder / flip-top assembly to which a valve and a locking device can be easily attached. This reduces the number of parts required to be manufactured, as well as the complexity and number of assembly steps, and as a result reduces the cost of such a tube and closure assembly significantly.

In an additional variant, the use of at least one compatible polymer according to the present invention allows the production of articles such as tubes, which may have protective or barrier coatings applied directly to the inner or outer thin-walled parts, without the need for pre-treatment such as discharge.

187 362 non-corona or flame treated. For example, the incorporation of polyoxazoline compounds can improve the adhesion of varnishes and varnishes to eliminate the need for such pretreatment. This can be particularly advantageous for containers used for food or containing substances that require special coatings for their storage.

Alternatively, suitable barrier and other coatings can be applied by conventional methods such as dipping, spraying, printing, vapor deposition or vacuum deposition, the latter process being particularly useful for applying barrier materials with special properties such as metallic or non-metallic oxides / nitrides ( e.g. silicon oxide) or fluorine as well as carbon and / or organic groups with useful properties. In addition, certain coatings, such as those made by reacting the tube polymer with fluorine, may be further reacted with monomers containing various preferred functional groups to further improve the properties of the coatings. For example, hydroxy-containing monomers can be reacted with a fluorinated polyethylene coating to form a hydroxy-containing coating.

By their very nature, tubes have thin, soft and flexible walls. This lack of rigidity in the molded tube makes it difficult to push the molded part out of the mold core by common mechanical means commonly used in injection molding and compression molding, such as stripper plates and injector pins, without potentially damaging the molded articles. An additional disadvantage is the slow ejection rates, often necessary to minimize the possibility of damage to the tube during ejection.

We have found that the use of the pressurized gas that accompanies the ejection minimizes the possibility of damage to the tube during ejection and also allows for a quick ejection. Once the tube has been formed in the mold cavity and has a position suitable for removal from the mold cavity, the male and female mold portions are separated by telescopically moving the male core part away from the female part. At the same time or sequentially, the formed tube may be separated by injecting pressurized gas from the inside of the male core portion and to allow the compressed air to communicate with the inner surface of the end portion of the formed tube, most preferably by tearing the end of the core away from the main portion of the core just prior to air injection, at to remove the seal that often exists between the formed tube and the core to facilitate removal of the formed tube. This end detachment as well as the generation of overpressure under the end portion enables the formed tube and the male core part to be separated by moving the formed tube and the male end part to one another. In order to participate in the separation, the male core part may have a very slightly swollen outer surface such that the diameter is greater at the end of the tube remote from the end part.

Also, the outer surface of the male core portion may be formed or treated such that the surface is slightly rough, which would be suitable for inhibiting the formation of a vacuum seal between the molded body and the male core portion when pressurized gas is introduced. That is, the degree of surface roughness allows the compressed air to flow along the outer surface of the male core portion and slightly expand the formed tube to separate the tube from the core.

In an additional refinement to assist in removing the molded part from the pocket, pressurized gas may be injected into the mold just before or during the separation of the core from the socket such that gas flows between the outer surface of the molded part and the inner surface of the socket, thereby assisting in separating the molded part from the cavity and subsequently removing it from the cavity while it is on the mold core.

A vacuum may be applied to the cavity just prior to and during injection of the polymer to facilitate the flow of polymer into the cavity to form a thin-walled article during the injection operation. Mold filling may be further assisted by balancing the flow inside the mold by cutting longitudinal and transverse grooves in either the core or

187 362 in the cavity or core and cavity to direct and / or accelerate the flow of polymer to selected areas within the mold.

The invention also makes it possible to use in the form of expandable cores that facilitate the release of the thin walled product from the mold, and it also enables the production of thin walled containers having wide portions adjacent to the head and shoulder area in a way that has not hitherto been possible.

The invention will be further described with reference to the following non-limiting examples and drawing

The subject of the invention is illustrated in the drawing in which Fig. 1 is a view of a thin-walled container in the form of a double-tube, made of a polymer blend according to the method of the invention, Fig. 2 is a view of a thin-walled container in the form of a tube with one end bent upwards and provided with a hole for hanging it, made of a polymer mixture according to the invention, fig. 3 a view of a thin-walled container in the form of a tube symmetrically expanding from the mouth to an arched end, made of a polymer mixture according to the invention, fig. 4 - a view of a thin-walled container in the form of a tube with a cap closure arched from the closure towards the concave end made of a polymer blend according to the method of the invention, Fig. 5 is a view of a thin-walled container made of a polymer blend by the method of the invention, connected to a hook integrally formed with the container. The hook may be conveniently replaced with a spatula or other desired convenience tool, Fig. 6 - View of a thin walled container made of a polymer blend according to the method of the invention coupled to a flange having an opening adapted to be hung on a hook or hanger at the point of sale, Fig. 7 - a view of a thin-walled container made of a polymer blend according to the method of the invention connected to a hook adapted to hang the container at a point of sale on a hook or hanger, fig. 8 - view of a thin-walled container with a cut end made of a polymer blend by the method of the invention and having a barrier coating on the inside surface of the container, Fig. 9 is a view of a unitary tube / closure arrangement, Figs. 10 (a) and Fig. 10 (b) are views of a tube with a pocket for receiving articles such as product samples, toothbrushes or combs, Figs. 11-14 show details of some of the support mechanisms for a unitary tube / accessory system, particularly a unitary tube / closure system, and some of the mold design modifications that can be used to form a unitary tube / accessory moldings.

Figures 1 to 10 show various configurations of thin-walled tubular containers 6 made by the method of the invention, which illustrate the wide range of possibilities for changes both in the shape of the tube, its closure and the additional elements that make up the manufacturing method according to the invention.

Figure 11a shows a longitudinal section of a mold with an unsupported core 4 that can be used to form a unitary tube / closure system.

In the case of a unitary tube / accessory system where there will be no core bending or transverse movement of the core if the core is not supported (for example large diameter tubes made of high MFl materials).

The mold has a channel 1 for feeding the molten polymer, a core 4 and a "pop" mushroom valve 3 with a shaft 5. Fig. 11 (a) also shows the location of the tube 6 with a "living" hinge 7 and a "flip-top" closure 2 in as a hinged lid.

Figure 11 (b) shows the form in section a plane along the line XX in Figure 11 (a) showing channels 8 to improve the flow of polymer into the sidewalls of the tube and a groove 9 to improve polymer flow down the sidewall of the tube, Fig. 11 (b) ) is an alternative section XX to section YY in Figs. and 1 (a). In a further refinement of the base design of the tool, the tool may have a slot along the line X-X1 (or XX ₂ ) such that the part of the tool defined by XX! (or XX ₂ ) and YY may be separated from the tool part defined by XX through ZZ. You can replace it with

187 362 alternate tool part Χ-Χ1 (or Χ-Χ2) to Y-Y, [see Fig. 11 (c)], introducing different designs or types of closure to enable the manufacture of a tube containing different closures. The same principle can be extended to other types of add-ons. The possibilities of this general mold design can be easily modified with "interchangeable parts" to form tubes with different or different attachments, and also allow, if necessary and using suitable "interchangeable parts", to form tubes containing no elements. additional, that is, "standard" tubes with "head and shoulders".

In cases of a homogeneous tube / accessory arrangement where it is possible to bend the core if the core is unsupported, a number of designs are able to stabilize the core against lateral movement (and hence varying wall thicknesses) while allowing a uniform tube / accessory arrangement to form.

Figure 12 illustrates a tool design in which the core is stabilized against bending by the use of one or more support members 10a, 10b extending from the top of the female half of the mold and pressing down on the pop valve on the male mold core during polymer injection. to form the product. As the polymer is injected to fill the mold but before closing the cylinder valve, the support members are raised to allow the polymer to flow into the gaps left by the support members to ensure a complete molded article is formed.

Figure 12 (a) shows a support member 10b positioned on the poppet valve 3 of core 4 and a support member 10a in the raised position to allow polymer to flow into the gaps left by the raised support member 10a. If appropriate, the support may be positioned in the support member location 11 on the poppet valve. 3 Fig. 12 (b) is a section along line Χ-showing a series of locations 11 on the poppet valve 3 of the support members 10a, 10b.

Figure 13 illustrates a tool construction in which the core 4 is stabilized against bending by the use of one or more support elements 12 (a) and 12 (b) which protrude from the seat to support the core 4 laterally during polymer injection to forming the product. An advantageous feature of the support element 12 (a) is that it also presses the mushroom valve 3 firmly against the core 4, thereby minimizing the chance of it rising under the injection pressure. Once the polymer has been injected to fill the mold, before closing the cylinder valve, the support members 12a, 12b are retracted to allow the polymer to flow into the voids left by the members to ensure a complete molded article is formed.

Figure 14 illustrates a tool design in which there are expandable support members 13, 15 inside the core 4, the support 15 being shown expanded and supported in the encompassing mold portion to "anchor" the core 4 to prevent the core 4 from being transverse. When pcOiim ^ e · is injected to fill the mold, before closing the cylinder valve, the support members 13, 15 are retracted to allow the polymer to flow into the spaces left by these components to ensure the formation of a complete molded article. A variation of the above mechanism is to slide the entire core 4 up to be placed in the mold-containing part and when the polymer is injected to fill the mold, but before the cylinder valve is closed, the entire core 4 retracts to allow the polymer to flow into the new cavity left by the withdrawn core to ensure the formation of a complete molded article. Another advantage of this arrangement (i.e. not placing the core in the center of the molded closure) is that the center of the closure is not limited by retaining devices. This enables complete closures (for example with spouts and membranes that allow the contents of the tube to be effectively "cut off"), as in medicated bottles. In an additional variation, the mold can be designed to form very thin films across the end of the closure opening to protect against "undesirable opening".

187 362

Among the main advantages of the stabilizing mechanisms as shown in Figs. 12-14 is that the core support members are positioned "off center", which allows the injection point to be positioned in the center position without the danger of flow inhibition. This allows the formation of "centrally located" auxiliary elements such as openings and flow regulating mechanisms that would otherwise have to be located "off center". If the positioning of openings and other additional elements "off center" is permissible or required, it is possible to centrally locate the support elements through a series of mechanisms that are well known to those skilled in the art.

Example 1

A polymer blend made of 50% Exact 4038, 20% Cataloy KS059P and 30% Montell 6100P was injection molded to form a cylindrical container, the body of which was in the form of a continuous cylinder with a diameter of 35 mm and a length of 150 mm, and a neck and arm part adapted to be connected to a nut. The thickness of the continuous cylinder varied from 0.8 mm in the region adjacent to the neck and shoulder to 0.5 mm in the distal end. The cylindrical container was found to have properties suitable for use in, for example, the cosmetics industry.

Example 2

A polymer blend made of 60% Exact 4038 and 40% Montell 6100P was injection molded to form a cylindrical container, the body of which was in the form of a continuous cylinder 35 mm in diameter and 150 mm long, and a neck and arm portion adapted to be joined with a cap. The thickness of the continuous cylinder varied from 0.8 mm in the region adjacent to the neck and shoulder to 0.5 mm in the distal end. The cylindrical container was found to have properties suitable for use in, for example, the cosmetics industry.

Example 3

A polymer blend made of 24% Exact 4038, 56% Affinity 1350 and 20% Surlyn 9970 was injection molded to form a cylindrical container, the body of which was in the form of a continuous cylinder with a diameter of 35 mm and a length of 150 mm, and a neck and arm part adapted to be joined with a cap. The thickness of the continuous cylinder varied from 0.8 mm in the region adjacent to the neck and shoulder to 0.5 mm in the distal end. The cylindrical container was found to have properties suitable for use in, for example, the cosmetics industry.

Example 4

A polymer blend made of 24% WSM 168 (Orica Australia Pty Ltd), 56% Affinity 1350 and 20% Surlyn 9970 was injection molded to form a cylindrical container whose body was a continuous cylinder 35 mm in diameter and 150 mm long, and a neck and part of the arm suitable for connection with a nut. The thickness of the continuous cylinder varied from 0.8 mm in the region adjacent to the neck and shoulder to 0.5 mm in the distal end. The cylindrical container was found to have properties suitable for use in, for example, the cosmetics industry.

ESCR test

Six thin parts of a polymer blend 0.65 mm thick were used to determine the resistance to cracking under the influence of external factors. 10 mm wide parts were cut across the main flow direction of the polymer blend in the mold and then processed as desired after molding. Each part was folded back on itself and stapled at a distance of 3 mm from the bend. The bent parts were immersed in a 10% Teric N9 solution at 50 ° C (Teric is a trademark of Orica Australia Pty Ltd). The strips were then inspected regularly for signs of cracking. Any symptom of cracking is considered a failure. The time it takes 50% (3) of the parts to fail is considered the failure time of the polymer blend. The test is completed after 360 hours if the polymer has not yet been damaged.

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Comparative example A.

The Dow Affinity plastomer, which had a crystallinity of approximately 34%, was injection molded, and then six parts were cut from the molded article and subjected to the ESCR test. The results are shown in Table 1.

Examples from 5 to 7

The Dow Affinity Plastomer, which had a crystallinity of 34%, was mixed with ADP 126 polypropylene (Montell) in the amounts shown in Table 1. The compounds were injection molded and six parts were cut from the molded article and subjected to the ESCR test. The results are shown in Table 1.

Table 1

Example Dow Plastomer Affinity Polypropylene ADP 126 ESCR test (hours) Comparative example A. 100% 7 5 97.5% 2.5% thirty 6 95% 5% 60 7 60% 40% Over 360

Examples 8 to 10

The Dow Affinity Plastomer, which had a crystallinity of 34%, was mixed with Surlyn (Du Pont) in the amounts shown in Table 2. The compounds were injection molded and then six parts were cut from the molded article and subjected to the ESCR test. The results are shown in Table 2.

Table 2

Example Dow Plastomer Affinity Surlyn 9970 by Du Pont ESCR test (hours) Comparative example A. 100% 7 8 97.5% 2.5% 15 9 95% 5% thirty 10 70% thirty% Over 360

Example 11

A polymer blend was made up of 80% Dow Affinity plastomer (34% crystallinity), 19% Nylon B3 (BASF) and 1.2% Surlyn 9970. The ESCR test result of this polymer blend is over 360 hours.

Examples 12 and 13

A polymer blend was made of 79% Dow Affinity (approximately 34% crystallinity) and 30% Surlyn 9970 and injection molded to form a thin walled tube. A second polymer blend was made of 76% Dow Affinity plastomer (24% crystallinity), 20% Nylon B3 (BASF) and 4% Surlyn and injection molded to form a thin walled container. The thin-walled containers were filled with gasoline and tightly closed. The polymer blend, containing 20% nylon and 4% Surlyn, showed about twenty times lower gasoline permeability than the blend containing plastomer and only Surlyn.

Example 14

Dow Affinity Plastomer, which had a crystallinity of 34%, was mixed with the amount of TiO2 shown in Table 3 below. The compounds were injection molded and then six parts were cut from the molded article and subjected to the ESCR test. The results are shown in Table 3.

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Table 3

Example Dow Plastomer Affinity TiO2 ESCR test (hours) AND 100% 0% 7 14 96.5% 3.5% 22

It will be apparent to those skilled in the art that variations and modifications to the invention disclosed herein other than those specifically described are possible. It is also understood that the invention covers all such changes and modifications which fall within the scope and spirit of the invention. The invention also includes all the steps, features, compositions and compounds mentioned in this specification and referred to in this specification individually or collectively, and includes any and all combinations of any two or more of the steps or features.

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List of references

1st channel for feeding molten polymer,

2. "flip-top" closure in the form of a hinged lid,

3. "pop" mushroom valve,

4. core,

5. "pop" valve stem,

6.thin-walled tube,

7. "living" hinge,

8. channels improving the flow of polymer to the side walls of the tube,

9. groove to improve the polymer flow down to the thin walls of the tube,

10 (a) a support located on the globe valve,

10 (b) support shown in retracted position,

11.the area where the support element is located on the globe valve,

12 (a) a support element located both on the core and on the mushroom valve,

12 (b) a support located on the side of the core,

13.expandable core support, shown in extended position

14.supporting element placed on the mold part,

15. expandable core support, shown unexpanded

FIG. 3

FIG 4

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FIG 5

FIG 6

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FIG. 10 (b)

FIG. 10 (a)

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FIG 11 (a)

FIG.lKc)

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FIG.12 (b)

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FIG.14

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Publishing Department of the UP RP. Circulation of 70 copies. Price PLN 6.00.

Claims (13)

Patent claims A method for producing a thin-walled flexible article, especially a tube, having a thin portion 1 mm or less in thickness and substantially continuous over 50 mm in length, in which the polymer blend is melted, the molten polymer blend is injected into the mold and the article is removed from the mold. thin-walled made of a polymer blend, characterized in that the polymer blend has an ESCR stress cracking resistance value exceeding 10 hours, determined by a test carried out according to the following procedure: many, preferably 6 or more, strips of the polymer blend derived from any treatment after shaping the final product, the cross-sectional dimensions of which are as follows - thickness 0.65 mm and width 10 mm, are injection molded under conditions of high shear forces and long flow distances, similar to those used in the production of a flexible thin-walled product, the straps are bent back over each other and tightened at a distance of 3 mm from the bend, the bent strips are immersed in a solution of a stress crack agent such as Nonylphenol Ethoxylated - 10% Teric N9-Nonylphenol Ethoxylated solution using 9 moles of ethylene oxide from Orica Australia Pty Ltd. and kept at 50 ° C, the strips are observed for signs of breakage, any sign of breakage being taken as damage; and the failure time is the time when 50% of the strips show signs of failure. 2. The method according to p. The process of claim 1, wherein the at least one polymer of the polymer blend has a melt flow index MFI greater than 10. 3. The method according to p. The process of claim 1, wherein the at least one polymer of the polymer blend has a melt flow index MFI greater than 20. 4. The method according to p. The process of claim 1, wherein the at least one polymer of the polymer blend has a melt flow index MFI greater than 30. 5. The method according to p. The process of claim 1, wherein the ESCR value of the polymer blend is greater than 100 hours. 6. The method according to p. The process of claim 1, wherein the ESCR value of the polymer blend is greater than 200 hours. 7. The method according to p. The process of claim 1, wherein the ESCR value of the polymer blend is greater than 360 hours. 8. The method according to p. The process of claim 1, wherein the polymer blend comprises at least one polymer and at least one compatible agent and / or at least one nucleating agent. 9. The method according to p. The process of claim 8, wherein the at least one polymer is selected from the group consisting of plastomers, polyethylenes, copolymers of ethylene and at least one unsaturated olefin, plastomers, substantially linear polyethylenes, branched polyethylenes, polymers and copolymers of ethylene prepared using metallocene or other catalysts. resulting in copolymers having a highly disordered arrangement of comonomers within polymer chains, polypropylenes, copolymers of propylene and at least one of ethylene and unsaturated olefins, polymers and copolymers of propylene made using metallocene or other catalysts resulting in highly disordered copolymers intra-polymeric comonomers, polylactic acid polymers, silane polymers, and mixtures thereof. 10. The method according to p. 8. The process of claim 8, characterized in that the at least one compatible agent is selected from the group consisting of ethylene / vinyl acetate copolymer, ethylene / vinyl alcohol copolymer, plasticized polyvinyl acetate and polyvinyl alcohol), alkyl carboxy substituted polyolefins, copolymers of acid anhydrides orga187 362 other copolymers containing epoxy groups, chlorinated polyethylene, ethylene / propylene / butylene copolymers, extremely low density polyethylene, very low density polyethylene, low density polyethylene, medium density polyethylene and high density polyethylene, polypropylene, polybutylene and the same copolymers, polyester ethers, poly (ether esters), acrylonitrile / methacrylate copolymers, block copolymers with styrene end blocks, half esters, amine and alkoxysilane grafted polyethylenes, vinyl addition polymers, styrene / butadiene block copolymers, acid grafted polyolefinylsilinated polymers ± block copolymers of dihydric monomers, unsaturated ester grafted propylene, modified polyolefins comprising amide, epoxy, hydroxy or _C2 6-acyloxy functional groups, polyoxazoline; fluoroelastomers, from other compatible polymeric substances suitable for use with polyolefins, particles coated with any of the above, and mixtures thereof. 11. The method according to p. The process of claim 8, wherein the at least one nucleating agent is selected from the group consisting of shake, mica, compounds of various metals, including oxides and silicates, as well as various organic compounds including various dyes and pigments. 12. The method according to p. The process of claim 8, wherein the at least one polymer is a polyethylene-based polymer and the at least one compatible agent is a polypropylene-based polymer. 13. The method according to p. The process of claim 12, wherein the at least one polymer is a linear, substantially linear or branched polyethylene or a copolymer characterized by a highly disordered arrangement of comonomers within the polymer chains, and the at least one compatible agent is a polypropylene-based polymer.