Stock material or miscellaneous articles – Composite – Including interfacial reaction product of adjacent layers
Reexamination Certificate
1999-01-08
2002-09-24
Gallagher, John J. (Department: 1733)
Stock material or miscellaneous articles
Composite
Including interfacial reaction product of adjacent layers
C106S031130, C156S310000, C156S315000, C426S075000
Reexamination Certificate
active
06455164
ABSTRACT:
The present invention relates to a method for the preparation of a quick-curing laminate and a laminate obtainable thereby.
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, 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 employed, various methods have been used, 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 to another 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 cause an increased viscosity and a subsequently more difficult application to the film, whereby the application quantity cannot be controlled. A limited space of time is available for the administration so the adhesive composition, the so-called pot-life, and, in consequence, production disturbances may cause glue vessels and application devices having to be cleared of cured adhesives.
To overcome said problem of the low pot-life, 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, whereby the encapsulated catalyst will be released.
The disadvantage of this method is that a homogenous distribution of the catalyst in the glue layer cannot be obtained, since 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 therefore precipitate when stored.
Another suggestion to bring a polyurethane adhesive into contact with the catalyst is disclosed in EP-A1-0586843. In this, a method for the preparation of a laminate film is disclosed, wherein at least two films are attached to each other by means of 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, e.g. a polyethylene or polypropylene film, even when using a surfactant in the solution, inter alia, because suitable equipment for a homogenous application of the catalyst solution all over the film is not available, so that in certain sections of the prepared laminate water will accumulate, which leads to an isocyanate conversion to the corresponding amine compound, thus involving the risk of subsequent amine compound migration. Therefore, whenever preparing a laminate according to the method disclosed in EP-A1-0586843, it is necessary to age the said laminate before use, in particular when foreseen for the packaging of food.
In international patent application No. PCT/DK 96/00319, publication No. WO-A-97/03821 (which was not available to the public on the priority date of the present application), the present applicant suggested to bring the catalyst into contact with the adhesive by incorporating the catalyst in one of the films to be attached to each other by means of the adhesive. Although this reduces the curing time considerably and results in a low migration of amine compounds so far as laminates with no ink between the films are concerned, the suggestion is not recommendable when the catalyst-containing film has to be printed with ink, because the layer of ink will prevent a diffusion of catalyst from the film to the adhesive.
The object of the present invention is to provide a method for the preparation of a laminate having ink on one or both films to be attached to each other, whereby the laminate is ready for further treatment comparatively soon after its preparation, without any long-lasting ageing period.
According to the invention, this is achieved by
a) providing an ink comprising a catalyst suitable for accelerating the curing of an adhesive for films,
b) applying to a first film one or more completely or partially covering layers of the said ink,
c) laminating a second film to the first film inked surface, using an adhesive, the curing of which is accelerated by the catalyst.
The present invention relates to the laminate obtainable by this method as well. Furthermore, the invention relates to the film being coated with one or more entirely or partially covering layers of ink obtainable after step b) of the method.
Soon after the preparation of the laminate according to he invention, the measurable amine migration is comparatively low, and, in addition, a fairly satisfactory mutual adherence of the films is obtained shortly after the preparation of the laminate. Due to the quick-curing of the adhesive used as well as the low amine migration, the laminate prepared needs no or only moderate ageing before further treatment. Especially within the food industry a low amine migration is in great demand, and, when in use, the laminate should show no amine migration at all. The fact that the laminate prepared may be exposed to further treatment shortly after its preparation is advantageous from a producer's point of view, inter alia, because this will reduce the need for storage room, and, sales of the laminate prepared can start sooner after production.
Moreover, a laminate according to the invention has a reduced tendency to telescoping, i.e. shear of the films relative to each other.
The term “ink” used in the present description and claims refers to both pigmented and un-pigmented inks and varnishes as well as clear and coloured varnishes. For the application of the inks methods known from the prior art, e.g. gravure, flexography or offset printing, may be used.
The ink employed may be of any suitable type, e.g. nitrocellulose, PVB, acrylic, acrylate or combinations thereof. In addition, the inks may be offset inks, e.g. oil-based or water-based. The ink may have any colour or be uncoloured.
The inks may be based on any solvent, in particular, they may be dilutable in ethanol, isopropanol, ethylacetate, methylethylketone, acetone, water or combinations thereof. Furthermore, solvent-free inks may be used.
The inks used according to the invention may be single-component, dual-component and/or even three-component inks. Single-component inks are immediately employable for printing, possibly after having been diluted by a suitable solvent. Dual-component inks are foreseen to be mixed immediately before use, whereby the first component comprises a standard ink and the second component the catalyst suitable for accelerating the curing of an adhesive for films.
Any adhesive curing in the presence of a catalyst may be used. Preferred adhesives are of the polyurethane type and alcohol-based or water-based imine-epoxy systems. Polyurethane adhesives may be single-component systems or dual-component systems. A polyurethane adhesive comprises at least one organic polyisocyanate and at least one polyol, the polyisocyana
Gallagher John J.
Jacobson & Holman PLLC
LandOfFree
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