GB2201681A

GB2201681A - Heat and pressure activated adhesive compositions

Info

Publication number: GB2201681A
Application number: GB08805263A
Authority: GB
Inventors: George Cecil Thomas
Original assignee: HB Fuller Adhesives Ltd
Current assignee: HB Fuller Adhesives Ltd
Priority date: 1987-03-06
Filing date: 1988-03-04
Publication date: 1988-09-07
Also published as: GB8805263D0; GB8705288D0

Abstract

Adhesive compositions comprise a blocking adhesive with incorporated therein a particulate anti-blocking component, e.g. liquid-filled hollow polymer beads, which is degradable under the action of heat and pressure. The composition is particularly suited for use in labeling operations and especially in in-mould labeling as labels may be dispensed from stacks of ready-coated labels as the adhesive is not activated until the labels are subjected to heat and pressure.

Description

HEAT AND PRESSURE ACTIVATED ADHESIVE COMPOSITIONS This invention relates to adhesive compositions, and in particular to heat and pressure activated adhesive compositions, and to the use of such compositions, especially in labelling.

In product labelling, particularly in the labelling of containers, for example drinks bottles, the labels are conventionally supplied in stacks or bundles from which they are individually removed, provided with a coat or patch of a wet adhesive composition and then applied directly to the product surface. By a wet adhesive composition in this context is meant a composition capable without further activation of adhering the label to the product. Thus for example in the case of a waterbased adhesive composition, such as a starch or dextrin, the composition would be in fluid form whereas in the case of a non-aqueous hot melt adhesive the composition would be in melt form.

Product labelling might thus be made simpler and more economic if the labels could be pre-provided with an adhesive coat. Such labels are of course already known. However the known labels carrying non-blocking adhesives, i.e. adhesives which do not cause adjacent labels within a stack to stick together, generally require an extra activation step, for example moistening if the adhesive is a water-soluble gum, before application of the label to the product. Labels pre-provided with a blocking adhesive, for example a pressure sensitive adhesive, are also well known but in this case each label must be provided with a protective cover for example a release paper, which must be removed before the label can be applied.

Thus there is the need for an adhesive composition which is non-blocking under ambient conditions but which can be readily or automatically activated in use.

In container labelling it is often the case that the surface to which the label is applied is at an elevated temperature and equally it is often the case that the labelling apparatus is conventionally arranged to press the labels against the product surface.

It is an object of the present invention to provide an adhesive composition which is activated, i.e. made capable of adhering one surface to another, by elevated heat and pressure, for example the conditions attainable in some labelling operations.

We have now found that such an adhesive composition may be produced by incorporation within an adhesive composition which is otherwise blocking under ambient conditions of a particulate, polymeric anti-blocking component the particles of which collapse or otherwise degrade under the application of heat and pressure.

Accordingly, in one aspect, the present invention provides an adhesive composition comprising a blocking adhesive with incorporated therein a particulate, polymeric anti-blocking component which is degradeable under the application of heat and pressure, said composition optionally being dissolved or dispersed in a solvent vehicle.

The particulate anti-blocking component of the composition of the invention preferably comprises a polymer which is compatible with the blocking adhesive. It is particularly preferred that the particles of the anti-blocking component are of a polymer having a relatively low softening temperature (for example 75 to 1100C, e.g. 75 to 950C) for example an acrylic polymer. The polymeric material of such particles is thus able to participate in the adhesive bonding once degradation under heat and pressure has occured and thus adherency will not be reduced as a result of the incorporation of the anti-blocking component as might for example be the case were the particles to be of an inert organic material.Nor, unlike waxes, will the polymeric anti-blocking agents be released from the adhesive at elevated temperatures to cause staining of material, e.g. labels, in contact with adhesive. Furthermore, it may be possible to vary the conditions of heat and pressure necessary for the degradation of the polymeric anti blocking particles to occur by incorporating within the composition of the invention a plasticiser for their polymeric material.

The degradation under heat and pressure of the anti-blocking particles preferably involves a collapse of the macrostructure of the particles and thus it is particularly preferred that the particles should contain voids to allow such a collapse to occur, for example under the application of pressure as the particles soften due to the application of heat.

In order to reduce the blocking in an adhesive layer of a depth conventional for product labelling, the particle size of the anti-blocking component of the composition of the invention is prefereably in the micron range, for example 0.1 to 10 microns, especially preferably about 0.2 to 5 microns.

However, particles of sizes outside these preferred ranges might be used for other applications of the adhesive composition of the invention.

Especially suitable as the particulate antiblocking component are hollow polymeric beads or microspheres comprising a polymeric shell surrounding a central void. Beads of this nature of a polymeric material having a softening temperature of about 1020C are supplied by Rohm and Haas Company, for example under the trade name ROPAQUE OP-62, for use as non-pigmentary hiding additives for paint as they allow the quantity of titanium dioxide pigment in a paint to be reduced.

The acrylic/styrene ROPAQUE beads, which have an average size of about 0.4 microns, initially have the central void filled with water. However, after application of a composition containing these beads, the water diffuses permanently out to leave the central void empty. The initial presence of water within the beads is thus particularly advantageous as the beads may readily be dispersed within an adhesive composition during formulation without significant settling out problems being encountered.

The preparation of void containing polymeric microparticles is discussed in EP-A-119054 (Rohm and Haas Company) and in the prior literature referred to therein.

The concentration of the particulate antiblocking component within the adhesive composition of the present invention will of course be dependent primarily on the nature of the blocking adhesive and on the level of tackiness acceptable for the applied but unactivated adhesive. In general however, expressed as the weight percentage of total dry solids within the adhesive composition, the antiblocking component will conveniently constitute from 3 to 45%, preferably 5 to 20% and especially preferably 7 to 15%.

In a particularly preferred formulation, an aqueous emulsion of ROPAQUE OP-62 (approximately 37.5% by weight solids) may form 5 to 50%, preferably 10 to 20%, by weight of the total adhesive formulation, the balance being provided by an aqueous emulsion containing 40 to 70%, preferably 50 to 60%, by weight solids of a polymeric adhesive.

The solvent vehicle, which may if required be incorporated to bring the adhesive composition to a viscosity suitable for application, may as in the preferred embodiment discussed above comprise water; alternatively, organic solvents, such as for example l,l,l-trichloroethane or toluene, can of course be used although for environmental and economic reasons their use is generally less preferable.

Where the adhesive composition of the present invention is formulated as a dispersion or emulsion of adhesive and anti-blocking particles within a solvent vehicle, the adhesive particle size should preferably be smaller than the anti-blocking component particle size so that on application to a substrate and evaporation of the solvent vehicle the antiblocking component will cause the exposed dried surface to be less blocking or non-blocking.

The blocking adhesive in the adhesive compositions of the present invention is particularly preferably a polymer which is compatable with the material of the anti-blocking component. Conventional polymeric adhesives may be used as the blocking adhesive and in this respect mention may be made for example of the following adhesive polymers: vinyl ester homo and copolymers (e.g. polyvinyl acetate, vinyl acetate ethylene, carboxylated vinyl acetate ethylene, vinyl acetate acrylate, and vinyl acetate dibutyl maleate), (meth)acrylic polymers (e.g. acrylate styrene), and latexes (e.g. neoprene latex and styrene butadiene latex); adhesive vinyl acetate/ethylene copolymers, e.g. MOWILITH LDM 1900 (available from Harlow Chemical Company Ltd. of Harlow Essex are especially preferred.Such blocking adhesives are particularly conveniently incorporated within the compositions of the invention in the form of aqueous emulsions.

The adhesive composition of the invention may also contain further optional ingredients, such as for example pH adjusting agents, surfactants antifoaming agents (e.g. NOPCO, ANTIFOAM FD, etc.) and plasticizers (e.g. dibutyl phthalate). These optional ingredients will generally be present in minor quantities: thus for example the anti foaming agent if used might be present at up to about 0.28 by weight, e.g. 0.1% by weight, and the plasticizer might be present at up to about 30% weight, e.g 5 to 20%, relative to total dry solids.

Although the adhesive compositions of the invention may be used for a wide range of heat seal applications, they are particularly suited to use in product labelling, in heat sealing (e.g.

to difficult surfaces, such as heat sealing of paper to polyethylene or polypropylene) and in the preparation of laminated barrier films (e.g.

polyethylene, polypropylene, polyvinylchloride or polyethylene terephthalate films) for use for example as packaging films, and in another aspect the invention provides such use.

In a yet further aspect, the present invention also provides a method of product labelling comprising bringing a product into contact under elevated temperature and pressure with a label provided with a layer of an adhesive composition according to the invention containing a particulate antiblocking component degradable by said elevated temperature and pressure whereby to cause said label to adhere to said product.

The products labelled using the method of the invention may take any convenient form but the method is particularly suited to the labelling of containers, such as for example glass or plastics bottles. In such applications, the label will generally be pressed against the product surface and heated there by the application of external heat and/or by the surface of the container itself where the container being labelled is at an elevated temperature as is often the case in bottling or container forming operations.

In the method of the invention, the adhesive composition is conveniently brought to a temperature of or contacted by a product surface at a temperature of at least 600C, e.g. 60-2000C, preferably at least 800C, for example 80-1800C, under an elevated pressure of for example at least 0.14 MPa (20 psi), conveniently about 0.14 to 0.62 MPa. (20-60 psi), preferably about 0.28 MPa (40 psi). The heat and pressure are preferably maintained for a period of seconds, e.g. 1 to 60 seconds, preferably 2 to 20 seconds, before pressure and temperature are allowed to drop back to ambient. The time for which elevated temperature and/or pressure should be maintained will of course generally be lower the higher the elevated temperature and/or pressure.

In another aspect, the present invention also provides a web, e.g. a label or a polymer film, provided on a major surface thereof with a coating of an adhesive composition of the invention.

Polymer films provided with a coating of the adhesive composition of the invention may be stored in rolls and may for example be used as or in the preparation of laminated barrier films.

Labels provided with the adhesive layer may particularly conveniently be stored in stacks, for example in magazines, from which they may be removed one at a time. In conventional labelling techniques, labels are picked from one end of a labelling magazine by a suction means applied to the exposed label surface. To avoid labels being picked up more than one at a time, which can occur even with labels bearing no adhesive whatsoever, it is again possible to direct a stream of gas, usually air, across the edges of the labels at the label dispensing end of the magazine.Using the adhesive composition of the present invention, such air blow separation may be assisted by the non-planar surface of the dried adhesive which results from the projection out of the adhesive surface of the particulate anti-blocking component - this partly raised surface should thus allow air to pass more readily between adjacent labels.

Use of the adhesive composition of the invention for labels may also allow a more porous substrate, such as unfilled or incompletely filled paper, to be used as the particulate anti-blocking component may also serve on application of the adhesive to the label to fill the pores of the substrate and so reduce the extent to which the substrate absorbs or is penetrated by the adhesive.

The method of the present invention is particularly suitable for the labelling technique known as inmould labelling where the label is placed inside the mould for the product, a plastics container, and the product is then blown inside the mould.

This form of labelling is particularly attractive and effective since the label is pressed into the hot surface of the material from which the product is being blown so that in the finished product the outer surface of the label is flush with the exposed outer surface of the product. A brief description of the technique of in-mould labelling may be found for example in Packaging News Extra, page 18, January 1984.

The adhesive composition of the present invention may particularly advantageously be used in in-mould labelling since the technique involves labels being pressed against a heated substrate, an action which will automatically activate the adhesive composition by degrading the anti-blocking component. Thus, for example, in in-mould labelling of polyethylene terephthalate or high density polyethylene containers, the container surface contacts the label within the mould at an elevated temperature (e.g. 60 to 2O00C) and at an elevated pressure (e.g. about 0.14-0.62 MPa(20-9Opsi)) for a short period (e.g about 9 to 20 seconds).

In in-mould labelling, the use of the adhesive compositions of the present invention is also advantageous since they need not contain the resin and wax components of conventional hot melt adhesives which can cause label staining in such an application.

The labels of the present invention can conveniently be prepared by applying the adhesive composition to a web substrate (generally at a viscosity of about 2 Pa.s(20 poise) although this is not critical and the preferred viscosity will depend on the particular applicator used), cutting the web into labels of the desired shape and size, stacking the coated labels and, optionally, loading stacks of coated labels into dispensing magazines. The adhesive composition will generally be applied at a coverage of about 3 to 15 g/m2 to give a layer thickness, when dry, of about 2 to 10, preferably about 3 to 6, microns.The application of the adhesive composition may for example be by conventional printing techniques (for example roller coating, gravure, letter press, etc.) or by draw down bar, and where the composition has included a solvent vehicle the adhesive may be dried either under ambient or forced conditions, for example in a drying oven, before being cut and stacked.

The following Examples are provided to illustrate the invention further without restricting the scope of protection sought therefor: Examples 1 - 6 Six aqueous adhesive compositions according to the invention were prepared by intimately mixing their components in the relative quantities set forth in the Table below. All six compositions, on activation by heat and pressure, gave acceptable bonding of paper labels to polymer substrates (the compositions of Examples 1 to 6 were tested on poly-ethylene terephthalate substrates and the composition of Example 6 has also been tested on polyethylene substrates).

Table Example No. 1 2 3 4 5 6 Component Concentration (% by weight) ROPAQUE OP-621 10 10 50 10 40 15 MOWILITH DS52 90 30 MOWILITH LDM 1900 75 4 VINNAPAS EV2 30 90 DOW DL 221E5 20 REVACRYL 383 30 20 7 REVACRYL 491 50 20 FOAMASTER DF-l24-L8 0.2 WATER 9.8 1. 37.58 solids, aqueous emulsion of hollow acrylic/styrene beads available from Rohm and Haas Company of Philadelphia.

2. 56% solids, cellulose ether stabilized, vinyl acetate/dibutyl maleate copolymer emulsion available from Harlow Chemical Co., Ltd. of Harlow, Essex.

3. 50% solids, vinyl acetate/ethylene copolymer avalable from Harlow Chemical Co., Ltd.

4. 50% solids, unplasticized, vinyl acetate/ethylene copolymer emulsion available from Wacker-Chemie GmbH of Munich.

5. 43% solids, carboxylated styrene butadiene copolymer latex available from The Dow Chemical Company.

6. 55% solids, styrene acrylate copolymer available from Harlow Chemical Co., Ltd.

7. 58t solids, colloid stabilized, acrylic ester copolymer emulsion available from Harlow Chemical Co., Ltd.

8. Liquid coating defoamer available from Diamond Shamrock Process Chemicals Ltd. of Manchester.

Example 7 The reduction in blocking level by the inclusion of an anti-blocking component in an otherwise blocking adhesive is illustrated in the accompanying Figure which is a graph of peel strength in g/25mm, measured on an Instron tensometer at 230C and 50% relative humidity, for MELINEX polyester sheets bearing a series of adhesive compositions each comprising x% by weight ROPAQUE OP-62 and 100-x% by weight REVACRYL-491.

Example 8 The reduction in blocking level by the inclusion of an anti-blocking component in an otherwise blocking adhesive was also demonstrated by the subjection of a stack of labels (each comprising a clay coated paper sheet coated on one side with the composition of Example 6 and allowed to dry) to a pressure of 327 Pa (1 kg weight over 300 cm2) for a period of 24 hours at 230C and 50% relative humidity followed by 24 hours at 400C and 70% relative humidity no blocking, i.e. adhesion of adjacent labels, occurred.

Claims

CLAIMS:

1. An adhesive composition comprising a blocking adhesive with incorporated therein a particulate, polymeric anti-blocking component which is degradable under the application of heat and pressure.

2. An adhesive composition as claimed in claim 1 wherein said blocking adhesive and said antiblocking component are dissolved or dispersed in a solvent.

3. An adhesive composition as claimed in claim 2 wherein said solvent comprises water.

4. An adhesive composition as claimed in any one of claims 1 to 3 wherein said anti-blocking component comprises a polymeric material having a softening temperature in the range 75 to 1100C,

5. An adhesive composition as claimed in any one of claims 1 to 3 wherein said anti-blocking component comprises a polymeric material having a softening temperature of about 1020C.

6. An adhesive composition as claimed in any one of claims 1 to 5 further comprising a plasticizer.

7. An adhesive composition as claimed in any one of claims 1 to 6 wherein said anti-blocking component comprises void-containing polymeric particles.

8. An adhesive composition as claimed in claim 7 wherein said anti-blocking component comprises liquid containing polymeric beads.

9. An adhesive composition as claimed in any one of claims 1 to 8 wherein said anti-blocking component comprises particles of 0.1 to 10 micrometers in size.

10. An adhesive composition as claimed in claim 9 wherein the average particle size of said antiblocking component is 0.2 to 5 micrometers.

11. An adhesive composition as claimed in any one of claims 1 to 10 wherein said anti-blocking component constitutes from 3 to 45%, on a dry solid basis, of the total composition weight.

12. An adhesive composition as claimed in any one of claims 1 to 11 comprising a solvent, an anti-foaming agent, a polymeric blocking adhesive and an anti-blocking component comprising liquidcontaining polymer particles.

13. An adhesive composition as claimed in any one of claims 1 to 12 wherein said anti-blocking component comprises particles of an acrylic/styrene polymer and said blocking adhesive comprises an adhesive vinyl acetate/ethylene polymer.

14. A particulate anti-blocking agent containing adhesive composition substantially as herein described.

15. A particulate anti-blocking agent containing adhesive composition substantially as herein described in any one of the Examples.

16. The use of an adhesive composition as claimed in any one of the preceding claims in product labelling, heat sealing or in the preparation of laminated barrier films.

17. A method of product labelling comprising bringing a product into contact under elevated temperature and pressure with a label provided with a layer of an adhesive composition comprising a blocking adhesive with incorporated therein a particulate, polymeric anti-blocking component which is degradable by said elevated temperature and pressure whereby to cause said label to adhere to said product.

18. A method as claimed in claim 17 wherein said label is pressed against a surface of said product which is at an elevated temperature.

19. A method as claimed in either one of claims 17 and 18 wherein said product is a container.

20. A method as claimed in any one of claims 17 to 19 wherein a said label is placed within a mould and wherein a said product is thereafter formed by blow moulding within said mould.

21. A method as claimed in claim 20 wherein said product is a plastics container.

22. A method as claimed in any one of claims 17 to 21 wherin said label is contacted with said product at a temperature of 60 to 2000C and a pressure of 0.14 to 0.62 MPa.

23. A method as claimed in claim 22 wherein said label is contacted with said product at a temperature of 80 to 1800C and a pressure of 0.14 to 0.42 MPa.

24. A web provided on a major surface thereof with a coating of an adhesive composition comprising a blocking adhesive with incorporated therein a particulate, polymeric anti-blocking component which is degradable under the application of heat and pressure.

25. A web as claimed in claim 24 wherein the dry thickness of said coating is 2 to 10 micrometers.

26. A web as claimed in either one of claims 24 and 25 in the form of a label.

27. A web as claimed in any one of claims 24 to 26 comprising a polymer film provided on a major surface thereof with a said coating of an adhesive composition.