IE45405B1 - Thermoformed laminate article - Google Patents

Abstract

The present invention relates to a complex material for the realization of objects with thermoforming comprising a material support not thermoformable (for example, vinyl polychloride) covered of an adhesive and assembled to a metallized polyester film. [FR2364118A1]

Description

patent application by (71) la cellophane, a french body corporate OF, 110 BOULEVARD HAUSSMANN, 75008 PARIS, FRANCE.

Price I2|p - 2 4540S The present invention relates to an article produced from a thermoformable laminate.

Laminated polymer sheets are used in foodstuff packaging, the advantage of such laminates being in particular that they allow good preservation of the packaged foodstuffs because of their impermeability to certain gases. Xt is known, for example, that polyethylene has a low permeability to water vapour but a high permeability to gases such as oxygen, nitrogen and sulphur dioxide, whereas polyethylene glycol terephthalate possesses converse properties, so that it is advantageous to use laminates of these two materials. Such laminates are not, however, thermoformable.

A solution to this problem has already been proposed in French Patent 2,259,696 and consists of using a laminate of non-stretched polyethylene and non-stretched polyethylene glycol terephthalate having a crystallisation temperature of at least 150°C. It is quite obvious that such a complex is thermoformable because polyethylene is naturally thermoformable whilst the polyester of crystallisation temperature above 150° will also be thermoformable· provided the thermoforming is carried out at a lower temperature. This solution, however, is Ί 54(-5 - 3 applicable to only the one type of polyester. Many more polyesters are commercially available in the form of films (generally biaxially stretched films) which are not thermoformable and therefore cannot be used as described above.

Tin-: present invention makes it possible to avoid these disadvantages.

The invention provides an article produced by thermoforming a laminate comprising a carrier of thermoformable plastics material laminated by means of polyurethane-based adhesive to a film of intrinsically non-thermoformable plastics material, the carrier or the film being coated with a thin metallic layer of at least 0.01 microns thickness,which metallic layer is sandwiched within the laminate.

It is difficult to define exactly whether or not a given polymer film is thermoformable. Satisfactory thermoformability depends on the degree of which a film or laminate conforms to the contours of an article or mould around which it is thermoformed, but normally skilled operators in this field can readily tell in practice whether or not a particular material is thermoformable in the sense of conforming sufficiently to produce acceptable definitions.

It has surprisingly been found that the presence of the metallic layer between the film and the carrier ^S-10 5 - 4 makes the laminate perfectly thermoformable, notwithstanding the presence of the film (e.g. the aforementioned stretched polyesters) which is not in itself thermoformable.

Preferably, the metallic layer is deposited on 5 the carrier or on the film by vacuum vapour deposition, but any other convenient method may be used. The film and the carrier are then laminated, preferably in accordance with the process described in U.S. Patent No. 2,702,580.

Any type of thermoformable plastics carrier can 10 be suitable, the most commonly used carriers being, for example, polyvinyl chloride, polystyrene, polyethylene, aerylonitrile/styrene/butadiene copolymers and methyl methacrylate/styrene/butadiene copolymers.

As examples of the non-thermoformable films of 15 plastics, it is possible to use any polyester film (for example biaxially stretched polyethylene glycol terephthalate or polyethylene glycol naphthalenate), polypropylene film, or biaxially stretched nylon film.

Any metals can be used which can be deposited 20 on a plastics substrate or film as a thin layer of a few microns thickness. For example, it is known to deposit, by vacuum metallisation, various metals such as aluminium, zinc, gold, silver and chromium, as well as certain of their alloys. A suitable vacuum metallisation process is described, for example, in U.S. Patents Nos. 2,665,224 to 2,665,229. It is also possible to deposit metals on - 5 plastics in general by electroplating techniques, the surface of the plastics material being made capable of conducting electricity by chemical treatment with a palladium salt and a resin. This technique is applied, in particular, in the field of printed circuits, and permits metal·? such as copper, zinc, tin, nickel, chromium, silver, and gold and their alloys to be deposited as very thin layers on virtually any insulating carrier. It is also possible to use techniques of precipitation from a metal salt, such as zinc, tin, nickel or silver salt.

In all cases, the thickness of the metal layer must not be less than Ο.ΟΙμ, since below this thickness it is in fact not possible to obtain a layer which is sufficiently uniform to impart the desired thermoformability to the laminate. The total thickness of the metal-coated film is preferably less than 100 microns.

The polyurethane-based adhesive may be any which will withstand the temperature used for thermoforming the laminate without causing delamination of its layers.

In this regard, the present inventors have found that substantially any of the broad range of commercially available two-component polyurethane or polyisocyanate base adhesives can withstand the normal operating conditions (e.g. 250°C for at least 10 seconds) used for heat-forming the composite assembly into shaped articles for packaging of foodstuffs or for other applications. As is well known - 6 in the art, the two-component adhesives include a crosslinkable or hardenable urethane or isocyanate base and a cross-linking or hardening agent or catalyst.

The amount of adhesive composition is also not particularly critical so long as a uniform distribution over the entire film surface is obtained. Generally, the amount of coating, <·η a dry basis, is at least about one gram per square metre (Ig/m ) and preferably is on the 2 order of about 3g/m to about 4 g/m · Adhesives in which the two components are supplied as a single premixed composition may be used. A preferred adhesive is that sold by Messrs. Henkel under the name UK 3640 with a cross-linking agent UK 6000, but other examples of suitable adhesives include Adcote C 310A and all those of the same family (a product of Morton William Conpany), Pentacoil ET 691 and Lunoflex E (a monoconponent adhesive whose elements are premixed and which react in situ) (products of Wilkolin Polymer), EPS 71 (a product of Herberts), Holdenite 10 13 18 A (product of Holden Europe).

The results obtained with such laminates are particularly satisfactory. If the film of non4 510 5 - 7 thermoformable material is transparent, thermoforming of the laminate gives articles which have the appearance of stainless steel or a mirror whilst having the advantageous properties of the materials of which they consist. The laminate can be thermoformed to produce packagings, especially foodstuff packagings with the foodstuffs in contact with the film, whieh in that case is preferably made of polyester. It can also be thermoformed for decorative purposes, for example, in gramophone record sleeves or other decorative objects having relief patterns of metallic appearance.

Before lamination of the carrier with the film, the metallic layer can, if desired, be completely or partially coated with a coloured layer deposited by photogravure printing to obtain a final thermoformed article having a metallised appearance of the desired colour.

A particularly important advantage of the articles obtained by thermoforming of the laminate according to the invention, is that containers formed in this way have a heat retention capability much superior to that of containers obtained by thermoforming the corresponding carrier alone. This is particularly valuable in foodstuff packaging, it being possible directly to package provisions which are at a high temperature, such as jams, or tomato concentrates. Embodiments of the invention will now be 4^5 - 8 described in more detail in the following Exanples.

EXAMPLE I An adhesive based on polyurethane dissolved in ethyl acetate, sold by Messrs. Henkel under the name UK 3640, with a.cross-linking agent UK 6000 is deposited by photogravure on a polyvinyl chloride carrier 300μ thick. The adhesive is dried, and the carrier is then laminated with a 12μ thick metallised polyester film sold under the trademark CLARYL, the metallised face of the polyester being against the adhesive. Further details of the laminating process may be obtained by reference to U.S. Patent 2,702,580.

This laminate is vacuum-thermoformed by means of a thermoforming machine from Messrs. Illig, type SB 53, equipped with a positive rectangular mould of size 35 cm x 25 cm, with a depth of 2.5 cm, the machine being equipped with a heating element having a power of 5kW.

Depending on the heating temperature and on the heated face, the following results were obtained: *5403 Heated face Heating time in seconds Results obtained Metallised polyester 12 Insufficient thermoforming film 17 Good thermoforming 18 N 20 II 22 H 25 II 28 Limit of heating 30 Film breaking Polyvinyl chloride Mediocre thermoforming carrier 20 The results'obtained for heating times of between 17 and 28 seconds, under the experimental conditions cited, are particularly good. In particular it proved possible, under the same conditions, using appropriate moulds optionally provided with plug-assist, to obtain packagings such as pots for packaging butter, jam and the like, which pots have a particularly well-finished appearance.

EXAMPLE II Following the same procedure as in Exanple I, on the same machine equipped with the same mould, a laminate composed of a 300μ polystyrene carrier coated with the aforesaid adhesive UK 3640 and a 12μ metallised polyester film sold under the trademark CLARYL was thermoformed. On heating the polyester face of the laminate for 12 seconds, ,5402 ·- 10 it was found that very good thermoforming was achieved. EXAMPLE III A laminate is produced by the process described in Example I, using an 80μ thick polyethylene carrier coated with the Henkel UK 3640 adhesive and the 12μ CLARYL film is produced. Packagings for cold meats, the packagings having a maximum depth of 20mm, are produced by means of a Multivac M 72 machine, having only an upper heating plate of 6kW power, and operating at a speed of 20 cycles/minutes (20 thermoformed objects per minute).

EXAMPLE IV A laminate identical to that described in Example I is produced. Wall decoration articles are produced by means of a machine from Messrs. Illig, having an upper heating element of 7kW and a lower heating element of 4kW, with a mould of 50 cm x 50 cm. With the polyester arranged facing the upper heating element, a thermoforming depth of as much as 8 cm can be obtained, the heating time of the two elements being of the order of 20 seconds. Juxtaposing these thermoformed articles on a partition makes it possible to obtain a decorative effect highly sought-after in shop fitting, for example, because of the metallic appearance of these articles.

EXAMPLE V a first circular container of 15 cm diameter and cm depth, made of polyvinyl chloride, is compared with 4 0 5 - 11 a second container of the same size, produced from a laminate as described in Example I, with the polyester face constituting the hollow part of the container. These two containers are subjected to the following heat resistance test : each container is filled with oil sold under the name FLUITHERMA, at a defined temperature, for 5 minutes. When the temperature of the oil reaches 80°C, the first container deforms and yellows. It is necessary to reach an oil temperature of 150®C in order to produce a slight deformation of the second container, the outer shell of which does not yellow. A third container, produced from the laminate of Example I, with the polyvinyl chloride face constituting the cavity of the container, does not deform up to 130°C, and the p.lyvinyl chloride does not yellow up to this temperature.

British Patent Specification No. 1,556,803 describes and claims a laminate plastics mirror produced by a process for the manufacture of a laminate plastics mirror comprising assembling a Support consisting of thermoplastics material, an adhesive layer and a film of transparent plastics material metallised on one face and not more than 100 microns in thickness, so that the support and film respectively are superposed on opposite surfaces of the adhesive layer with the metallised face of the film against the adhesive, introducing the resulting assembly between a pair of heated pressuring meinbers having pressing surfaces 4 0 5 - 12 of substantially mirror finish smoothness, pressing said assembly therebetween (a) for 10 to 20 minutes at a pressure of not more than 20 bars but suffice to deform the support with the temperature of the pressing members above the Vicat point of the thermoplastics support and thereafter (not necassarily immediately) (b) for more than 20 minutes at a pressure within the range from 25 to 90 bars while the pressing members are being cooled to ambient temperature. The following claims are to be interpreted as excluding that which is claimed in British Patent

Claims (11)

1. CLAIMS:1. An article produced by thermoforming a laminate comprising a carrier of thermoformable plastics material laminated by means of polyurethane-based adhesive to a film of intrinsically non-thermoformable plastics material, the carrier or the film being coated with a thin metallic layer of at least 0.01 microns thickness, which metallic layer is sandwiched within the laminate.

2. An article according to Claim 1, wherein the metallic layer has been deposited on the film by vacuum vapour deposition, electroplating, or precipitation, before assembling the film with the carrier.

3. An article according to Claim 1, wherein the metallic layer has been deposited on the carrier by vacuum vapour deposition, electroplating, or precipitation, before assembling the carrier with the film.

4. An article according to any one of Claims 1 to 3, wherein the carrier consists of polyvinyl chloride, polystyrene, polyethylene, acrylonitrile/styrene/butadiene copolymers, or methyl methacrylate/styrene/butadiene copolymers.

5. An article according to any one of Claims 1 to 4, wherein the film consists of biaxially stretched polyester, polypropylene or biaxially stretched nylon.

6. An article according to any one of Claims 1 to 5, wherein the metallised layer has been coloured by photogravure printing before lamination of the film and the carrier. Λ j5 4 OS - 14

7. An article according to any one of Claims 1 to 6, wherein a metal coated film is used which is less than 100 microns in total thickness.

8. An article according to any one of the 5 preceding claims, wherein the film consists of biaxially stretched polyethylene terephthalate coated with vacuumdeposited aluminium, and the carrier consists of polyvinyl chloride.

9. An article according to Claim 1 substantially 10. As described in any one of the foregoing Examples I to V.

10. An article according to any one of the preceding claims in the form of packaging for provisions, the film of intrinsically non-thermormable plastics material being arranged to be in contact with the said

11. 15 provisions when said provisions are in said packaging.