Stock material or miscellaneous articles – Composite – Including interfacial reaction product of adjacent layers
Patent
1998-01-13
2000-06-13
Cano, Milton
Stock material or miscellaneous articles
Composite
Including interfacial reaction product of adjacent layers
156310, 1563317, 2641761, 2642101, 426106, 426127, B32B 704
Patent
active
060747552
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the preparation of a laminate. Furthermore, the invention relates to a laminate obtainable by the process mentioned, as well as the use of said laminate for the packaging of food. Finally, the invention relates to a packaging material comprising the said laminate.
Plastic film is a frequently used material for the packaging of numerous articles and products. Within many fields of application, the requirements for such plastic films are of a character that cannot be met by one film alone. Consequently, various laminates of films have been developed with properties that in many respects meet the requirements better.
Usually, adhesives are used to attach separate films to each other, thus generating a laminate. Various requirements are made for such adhesives, e.g. adherence, heat resistance, transparency etc., and it has been proved that, inter alia, polyurethane-containing adhesives may be used for the adhesion of the separate films of a laminate, thus obtaining the requested properties of the laminate.
As far as polyurethane adhesives are concerned, it is problematic, however, that the curing time is long and that a laminate has to age, possibly at a comparatively high temperature and in a properly ventilated room, to ensure the adhesive curing.
In order to reduce the curing time of the adhesives, various procedures have been instituted, including the addition of a catalyst for the curing reaction.
When using a catalyst, the simplest way to accelerate the curing of a polyurethane adhesive is to add the catalyst directly into the polyurethane adhesive, immediately before the adhesive is applied to a film that is to be attached onto a secondary film. On an industrial scale, this is not efficient, however, since to some extent the adhesive composition will have cured before use. The curing will result in a viscosity enhancement and a subsequently more difficult application onto the film, where the application quantity is uncontrollable. The time period, within which the adhesive composition may be administered, the so-called pot-time, is thus restricted, and in case of production break-downs may cause glue vessels and application devices having to be cleared of cured adhesives.
To overcome the said problem of the low pot-time, in EP-A1-0152102 it is suggested to use a urethane adhesive containing micro capsules with a catalyst for the curing. Such micro capsules will be destroyed when the laminate film is attached by means of pressure rollers, which releases the encapsulated catalyst.
When using this process, the disadvantage is that a homogenous distribution of the catalyst in the glue layer cannot be obtained, as the catalyst concentration will peak in the immediate vicinity of the destroyed capsule. Furthermore, such capsules will remain in the adhesive as a suspension and thus precipitate when stored.
Another suggestion to bring a polyurethane adhesive in contact with the catalyst is described in EP-AL-0586843. In this, a process for preparing a laminate film is disclosed, wherein at least two films are attached by a polyurethane adhesive, the adhesive layer or the adhesive free film being humidified with an aqueous solution bearing at least one catalyst, which accelerates the curing reaction of polyurethane adhesives. The catalyst solution humidification is problematic, however, since it will be difficult to obtain a homogenous distribution of the solution on a film, of e.g. polyethylene or polypropylene, even when using a surfactant in the solution. Inter alia the reason is, that a suitable equipment for a homogenous application of the catalyst solution all over the film is not available, which means, that in certain sections of the prepared laminate water will accumulate, which results in a decomposition of isocyanate to the corresponding amine compound, thus involving the risk of a subsequent amine compound migration. Therefore, whenever preparing a laminate as disclosed in EP-A1-058-6843, it will be necessary to age the laminate before use, especially wh
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Rasmussen Janne
Rasmussen Max Otto Henri
Rasmussen Peter Max
Cano Milton
Curex APS
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