KR920000757B1 - Paper product prepared with structured latex - Google Patents

Abstract

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Description

Paper products made of latex particles with reinforcement and opacity and methods for preparing the same

In general, the present invention relates to a method for producing high quality lightweight paper with increased opacity. This method uses a structural latex that is both reinforcing and opaque.

In producing paper, especially lightweight paper, the main aspect is the opacity of the paper. In general, opacity is provided by conventional fillers such as clay, calcium carbonate and titanium dioxide. Unfortunately, these fillers can adversely affect the mechanical properties of the paper if too many fillers are incorporated to achieve the desired opacity.

Attempts have been made to offset the reduction in mechanical properties using various formulations of latex with increased strength. However, improved methods of achieving good opacity and light scattering without reducing mechanical properties have been continually explored. This problem is difficult to solve because opacity and strength are generally inversely proportional. In particular, this problem becomes more difficult for lightweight papers that minimize the amount of material that can be used to make paper.

In particular, we have identified structural latex particles with core / shell morphology that can satisfy both opacity and mechanical strength. This is to produce latex particles by providing the paper with a limit of the opacity of the particles themselves to reinforce or bind the components of the paper as well as to scatter light.

The present invention provides structural latex particles suitable for use in the preparation of latex-containing products comprising increased depth of opacity and strength so that Tg is greater than 80 ° C. with light scattering and outer regions with Tg less than 25 ° C. It is. The size of these structural latex particles is 1,400 to 0,000 kPa (140 to 400 nm).

In one embodiment, the structural latex particles have a homopolymer deep portion of styrene and an outer portion of styrene / butadiene / atrylic acid.

The present invention also provides a paper product made from the structural latex particles described above. The latex particles are most useful for making lightweight papers with the desired degree of opacity and mechanical strength. Such structural latex particles are characterized by providing opacity and reinforcement in order to reduce fillers such as TiO2 in the manufacture of the product. That is, the structural latex particles are allowed to reduce or eliminate expensive opaque fillers in the product without compromising the corresponding opacity.

The preparation of the product of the present invention requires starting latexes comprising structural latex morphology of deep / outer morphology with a secondary transition temperature (Tg) of greater than or equal to 80 ° C. and less than or equal to 25 ° C. of the outer area. Such structural latex particles are suitable for use in the production of paper products having good opacity and mechanical strength properties. Such latex is preferred and most usefully used to produce lightweight paper having the desired good opacity and mechanical strength.

The term “opaque” is defined as a property that blocks the passage of light by neither being transparent nor translucent. Opacity can be measured by measuring the brightness, light scattering or reflectance of reflected light, and opacity (TAPPI Standard T-425 om 81). “Mechanical strength” means tensile strength, modulus, burst strength, and other physical properties that are generally recognized as a source of mechanical strength in the art.

The production of structural latexes is well known but does not form part of the invention except as modified by the compositional requirements of the invention. Generally, particles of starting latex are encapsulated with additional monomers thereby polymerized. This can be conveniently done by an emulsion that polymerizes the desired outer monomers in the presence of the latex in the state of the desired deep composition. Thus, the polymerization is a conventional emulsion polymerization of the latex, but the polymerization of the outer monomer sites is carried out in the presence of already existing latex particles which represent the deep sites of the final latex product.

Emulsion polymerization is generally used in which the feed of monomer is added stepwise or continuously. Examples of such techniques are described in detail in US Pat. Nos. 4,156,669 and 4,017,442.

The structural latex particles of the present invention require deep light scattering regions. Generally, such light scattering properties are provided by polymerizers or copolymers of ethylenically unsaturated monomers having a Tg of 80 ° C or higher. Tg in the deep region is important for maintaining the homogeneity (ie, size and distribution) of the deep, which causes light scattering of the latex. On the contrary, when Tg is low, light-scattering property will fall because a deep part is joined at the time of paper manufacture.

Bifunctional monomers generally useful as crosslinking agents can be used at the deep sites to increase the Tg of the deep sites. Examples of good crosslinkers are allyl or crotyl acrylate with methacrylate and divinyl benzene. Preferred polymer depth compositions are monovinyl aromatic polymers such as styrene and copolymers or derivatives thereof having a Tg of at least 80 ° C. More preferred deep sites are homopolymers of styrene.

The deep portions of the structural latex particles make up 40 to 90% of the total particles. Preferred depth / outer polymer weight ratios are 50/50 to 90/10, respectively.

Since the particle size of the present structural latex is important for total light scattering, a particle size of 1,400 to 4,000 kPa (140 to 400 nm) is preferred. More preferable average particle diameter is 2,000-3,500 kPa (200-350 nm).

The outer portion of the structural latex particles of the present invention consists of a polymer or copolymer of ethylenically unsaturated monomers having a Tg of 25 ° C. or less. In general, the outer composition may contain monomers used in the deep portion. Thus, usefully used outer compositions are various mixtures of polymerization monomers such as monovinyl aromatics, aliphatic conjugated dienes, monoethylenically unsaturated carboxylic acids, vinyl or vinylidene halides or acrylates. Optionally, it may contain reactive monomers such as N-methylol acrylamide and glycidyl methacrylate.

(여기서, R은 수소 또는 C₁내지 C₄의 저급 알킬이다)의 라디칼과 함께 이러한 단량체를 포함한다는 것을 의미하며, 방향족 핵은 알킬 또는 할로겐 치환체로 치환된다. 바람직한 단량체는 스티렌이다.The term "monovinyl aromatic monomer" used in the present invention is a general formula directly attached to the aromatic nucleus of C ₆ to C ₁₀

Which includes such monomers together with a radical of hydrogen or lower alkyl of C ₁ to C ₄ , wherein the aromatic nucleus is substituted with an alkyl or halogen substituent. Preferred monomer is styrene.

As used herein, the term “aliphatic conjugated diene” refers to 1,3-butadiene, 2-methyl-1,3butadiene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3butadiene, Compounds such as piperylene (1,3-pentadiene), and other hydrocarbon analogs of 1,3-butadiene.

As used herein, “monoethylenically unsaturated carboxylic acid monomer” means monocarboxylic monomers such as acrylic acid and methacrylic acid, dicarboxylic monomers such as itaconic acid, fumaric acid, and maleic acid and monoesters thereof. Preferred acid monomers are acrylic acid.

Vinylidene halides and vinyl halides suitable for the present invention are vinylidene chloride and vinyl chloride, with vinyl chloride being preferred. Vinylidene bromide and vinyl bromide can also be used.

As used herein, "acrylate" refers to monomers in acrylate or methacrylate form. Acrylate may also include acids, esters, amides, and substituted derivatives thereof. In general, preferred acrylates are C ₁ -C ₈ alkyl acrylates or methacrylates. Examples of such acrylates are butyl acrylate, 4-biphenyl acrylate, hexyl acrylate, secondary-butyl acrylate, tert-butyl acrylate, methyl methacrylate, butyl methacrylate, lauryl methacrylate. , Hexyl methacrylate, isobutyl methacrylate, and isopropyl methacrylate.

The outer portion preferably consists of a polymer mixture containing styrene, butadiene and acrylic acid. It has been found that this particular mixture has the desired physical properties and is miscible with the preferred depth composition of styrene. In general, the styrene / butadiene / acrylic acid ratios of the outer composition are 49/49/2 to 47/47/6, 49/49/2 to 69/29/2 and 69/29/2 to 67/27/6, respectively.

Structural latex particles produced by this method are usefully used as paper coatings or fillers that require good opacity and mechanical properties. More particularly, paper products made of such structural particle latex will increase opacity and strength than similar papers made in the absence of structural particle latex. Without being limited to the paper sector, these latexes may also be used as fillers or ingredients in other applications where latex may be used as a protective or decorative coating (such as paint). Such structural latexes are used as latex binders or as partial substitutes for latex binders in the manufacture of lightweight or fine paper of good quality. Lightweight paper is generally defined as less than 34 lb / 3300 ft ² or less than about 50 g / m 2.

These and other advantages will be readily apparent in the following examples.

Example 1

Structural latex is prepared as follows. 80 parts by weight per 100 parts of the comonomer charge of an aqueous medium containing 0.01 parts by weight of pentasodium salt of diethylenetriaminepentacetic acid and 0.52 parts by weight of a styrene / acrylic acid copolymer particle latex in a 97/3 weight ratio for 2.8 hours. 100 parts by weight of styrene monomer feed are added continuously with stirring. An aqueous effluent containing 40 parts of deionized water, 40 parts by weight sodium dodecyldiphenyl ether disulfonate, 0.5 parts by weight sodium persulfate and 0.1 parts by weight sodium hydroxide is added at 90 ° C. for 4.5 hours with styrene feed. After the styrene feed is added, a 49/49/2 weight ratio of styrene / butadiene / acrylic acid comonomer feed is added continuously with stirring for 1.2 hours. The comonomer feed also contains 0.15% by weight tertiary dodecylmercaptan.

Upon completion, the resulting latex had a total solids content of about 43% at pH 3, an average particle diameter of structural latex particles of 1550Å (155 nm), and a polystyrene deep layer (Tg of about 100 ° C) versus styrene / butadiene / acrylic acid (25 ° C). The ratio of Tg) below is 70/30.

Example 2

A structural latex particle was prepared as in Example 1 except that the depth / contour ratio was 50/50.

Example 3

Paper compositions using the latexes prepared in Examples 1 and 2 as reinforcing opacifiers were prepared. 7.5 parts (based on polymer solids) of the latexes of Examples 1 and 2 are mixed with the individual samples of the aqueous paper composition. 6,424 parts of an aqueous suspension containing 92.5 parts (based on dry weight) of bleached kraft wood fibers (50/50 dry weight hardwood / softwood), 100 parts of 2% by weight aqueous aluminum sulfate octadecahydrate, And 3.5 parts of a high molecular weight polyacrylamide aqueous solution of 0.1% by weight.

The suspensions described above are used to produce paper handsheets having a basis weight of 40 lb / 3300 ft ² (59.2 g / m 2) on Noble and Wood paper machines. The structural particle latex content of each paper is determined by pyrolysis-gas chromatography. The opacity, lightness, tensile strength and elongation of the handsheets were measured and shown below with comparative paper examples prepared in the absence of the structural latex particles of the present invention.

¹ is not an example of the present invention.

² Opacity is TAPPI Standard T-425 om 81.

^Three persons are TAPPI Standard T-452 om 83.

⁴ Scattering coefficient obtained from Kubelka-Munk eqnation

The results show that small additions of the structural latex particles of the invention increase the opacity while increasing the strength, in fact, without decreasing the strength than the comparative paper sheet containing no structural latex particles. These results are significant because opacity and intensity are generally inversely related. This shows that the properties can be further increased by increasing the degree of latex composition, but tend to increase the total cost of the paper. In general, such latexes may be contained in a dry composition of 1 to 20% by weight based on the paper composition. Preferred latex content of the paper is 2 to 10% by weight.

Claims (10)

By containing structural latex particles comprising (1) a light scattering deep portion having a Tg of 80 ° C. or more and (2) an outer portion of Tg of 25 ° C. or less, paper opacity and strength are increased compared to a paper product prepared in the absence of latex particles. Lightweight paper product characterized. The paper product of claim 1, wherein the structural latex particles comprise 1-20 dry weight percent of the paper. The paper product of claim 1, wherein the deep portion comprises a monovinyl aromatic polymer, copolymer, or derivative thereof. The paper product of claim 3 wherein the monovinyl aromatic polymer is styrene. The paper product of claim 1, wherein the structural particle latex has a homopolymer deep portion of styrene. The paper product of claim 3, wherein the depth site further contains a bifunctional monomer that contributes to increasing the Tg of the depth. The paper product of claim 6, wherein the bifunctional monomer comprises allyl or crotyl acrylate and / or methacrylate, or divinyl benzene. The paper product of claim 1, wherein the structural particle latex has an outer portion containing a polymer mixture of styrene / butadiene / acrylic acid. The method of claim 8, wherein the ratio of styrene / butadiene / acrylic acid is 49/49/2 to 47/47/6, 49/49/2 to 69/29/2 and 69/29/2 to 67/27/6, respectively. Paper product. (a) providing a structural latex particle comprising (1) a light scattering deep portion having a Tg of 80 ° C. or higher and (2) an outer portion of a Tg of 25 ° C. or lower, and (b) mixing the structural latex particles with an aqueous paper composition, (c) forming the mixture into a paper product.