GB2136003A - Contact adhesives - Google Patents

Abstract

Contact adhesives comprise aqueous emulsions having the following dry component compositions by weight: (1) 100 parts polymer component comprising a terpolymer containing a chlorinated monomer, an acrylic monomer without a reactive functional group and an acrylic monomer having a reactive functional group, the polymer component having a glass transition temperature in the range - 18 DEG C to +10 DEG C, (2) 10 to 50 parts resin component comprising at least one of: an alkyl phenolic resin, a liquid addition product of an alkyl phenol and formaldehyde, and a terpene phenolic resin, (3) 0.1 to 10 parts emulsifier and (4) 0.01 to 10 parts stabiliser. A crosslinking agent may be included. The contact adhesives are prepared by blending an aqueous emulsion of the polymer component with the resin component in a liquid state, either molten or in solution. The solvent may subsequently be removed by evaporation.

Description

SPECIFICATION Contact adhesives A contact adhesive is a liquid or paste which can be applied to a surface, for example by brushing or spreading, and will set to form a substantially dry film, and for a certain time thereafter, known as the "open" time, if two such dry films are broughttogetherthey will coalesce. Usually, only light pressure is required to bring aboutthis coalescence, which occurs at ambienttemperatures, but contact adhesives are known which require heat activation and/or substantial pressureto be applied.

Many contact adhesives are, or include, solutions in organic solvents, and their setting toform the substantiallydryfilm depends upon evaporation of the solvent. One example isthat produced bythe Applicants and sold under their Registered Trade Mark "Evo-Stik" with the reference number 528, which is a solvent-borne polychloroprene contact adhesive. The growing awareness ofthe narcotic and other properties of some ofthe solvents used in these adhesives, and the practice of solvent abuse by inhalation, have given rise to a demand for contact adhesives which have a lower proportion of, or do not include, such solvents. However, contact adhesives which have so far been developed in response to this demand have not matched the performance ofthose containing organic solvents.

U.S. Patent Specification No. 3,222,419 describes pressure-sensitive adhesives made by blending a non-crosslinking resin with a crosslinkable resin.

Amongstthe non-crosslinking resins exemplified are copolymers of vinylidene chloride with alkyl esters of acrylicormethacrylicacid with the alkyl group containing 2 to 8 carbon atoms. The crosslinkable resins are polymers ofthe monomeric components of the non-crosslinking resins with a crosslinkable monomer. In producing the pressure-sensitive adhesives, the two resins are dissolved in organic solvents and the solutions are blended. Alternatively, it is proposed that water be added to one or both solutions with vigorous agitation to produce an oil-in-water emulsion before blending and then the solvent may be removed by vacuum distillation to produce a waterbased adhesive.

Pressure-sensitive adhesives, when spread and allowed to dry, form films which are tacky to the touch and will adhereto other surfaces. The primary object described in the above-mentioned U.S. Specification is to prepare pressure-sensitive adhesives which display (inter alia) effective properties of tack and tack retention, with ready adhesion to a wide variety of substrates.

In contrast,thedryfilms produced with contact adhesives, as mentioned above, should not be tacky to thetouch and should not adhere to other surfaces.

Such properties are, indeed, undesirable in contact adhesives, the dry films of which are required only to adhere to likefilms, by coalescing as described.

According to this invention, a contact adhesive comprises an aqueous emulsion of a resin component and apolymercomponent, havingthefollowing dry componentcomposition by weight: polymer component 100 resin component 10to50 emulsifier 0.1 to 10 stabiliser 0.01 to 10 the polymer component comprising aterpolymer containing a chlorinated monomer, an acrylic monomerwithouta reactivefunctional group and an acrylic monomer having a reactive functional group, the polymer component having a glass transition temperature in the range -1 80C to +1 0 C and the resin component comprising at least one of: an alkyl phenolic resin, a liquid addition product of an alkyl phenol and formaldehyde, and a terpene phenolic resin.

Acrosslinking agent may be included if desired.

The acrylic monomer having a reactive functional group may have hydroxyl or carboxylic acid functionality. Suitable examples are hydroxy alkyl acrylates, hydroxy alkyl methacrylates and acrylic acid.

The polymer component may be a physical blend of a terpolymer as described above with one or more other polymers. Such other polymers need not contain a chlorinated monomer. Examples are styrene acrylate copolymers, acrylic copolymers, vinyl acetate ethylene copolymers (which could include a third monomer), polychloroprene, polyvinyl acetate and vinyl acetate copolymers. The inclusion of one or more of such other polymers enables contact adhesives with improved properties to be obtained. In particular, improvements may be obtained in contactability, water resistance and adhesion to particular substrates.

The contact adhesive is produced by blending an aqueous emulsion of the polymer component with the resin component in a liquid state, as will be described.

We have found that best results are obtained by using polymers produced by emulsion polymerisation. Polymers produced by other means, such as bulk or solution polymerisation, and converted into emulsions by stirring solvent solutions with water and then removing the solvent, produce less satisfactory results and are preferably not used.

The emulsifier and/or the stabiliser may be included in the aqueous emulsion of the polymer component during the emulsion polymerisation process or may be added immediately priorto blending with the resin.

They improve the thermal and mechanical stability of the emulsions. Even when an emulsifier and/or a stabiliser has been included during emulsion polymerisation, a further emulsifier and/or stabiliser, not necessarily the same as already present, may be added prior to blending.

Additionally, the contact adhesive may contain one or more ofthefollowing: thickener Oto5 plasticiser Oto40 solvent Oto30 Some ofthe resins which may form, or be included in,the resin component are available in the form of an aqueous dispersion, or emulsion, and these can readily be blended with emulsions ofthe polymer components by stirring. Emulsion blends produced in this way do not perform very satisfactorily as contact adhesives. However, when the resin component is a liquid addition product of an alkyl phenol and formaldehyde, it may be incorporated with the polymer component emulsion by stirring, with satisfactory results.Since such liquid addition products are heat-advancing, contact adhesives in which they form, or are included in, the resin component produce adhesive bonds which are improved by heat or ageing, particularly when a suitable cross-linking agent is included.

Rosin esters, hydrogenated rosins and hydrocarbon resins, sometimes used to improve tack insolvent- based adhesives, do not produce satisfactory contact adhesives when incorporated in aqueous emulsions ofthe polymer components specified.

The invention further includes a method of manufacture of a contact adhesive as described, comprising the steps of rendering the resincomponentliquid by heating if necessary and adding an aqueous emulsion of the polymer component (which includes the emulsifier and the colloid stabiliser) with vigorous agitation. As the first portion ofthe polymer emulsion is added, a water-in-oil emulsion is formed with the resin component as the continuous phase. Inversion occurs as more polymer emulsion is added until finallythe resin and polymer components are dispersed ina continuous aqueous phase.

If the resin component is such that heating to a temperature above 100"C is required to render it liquid, the method must be carried out under pressure sufficientto elevate the boiling point of water above that temperature.

A solvent or plasticiser may be added to the resin componentto reduce the melting point in a known manner. Alternatively, the resin component may be rendered into a liquid form by dissolving in a solvent.

The amount of solvent required for such purposes is substantially less than is used in solvent-based contact adhesives. In most cases, it is advantageous to keepthe resin componentina liquid form, either molten or solution, throughout the inversion process.

Forthis purpose, the polymer emulsion may be pre-heated and/orthe whole system may be heated.

The solvent, or a substantial proportion of it, may be removed by evaporation once the inversion of the emulsion has been achieved.

In a preferred method, particularly beneficial when the polymer emulsion is stable in a low pH (i.e. less than 7) environment, the emulsion of the polymer component is divided into two portions. Ammonia is added to both portions to adjust the pH of the first portion to a level between 7.5 and 9, preferably 8.5, and ofthe second portion to a level between 4 and 5, preferably between 4 and 4.5. The first portion is added to the liquid resin component with vigorous agitation. Initially, the aqueous emulsion ofthe polymer component is dispersed in the resin compo nentasawater-in-oil emulsion, but, on continued agitation, inversion ofthe emulsion occurs as previously mentioned. The second portion is then added with further vigorous agitation.The proportions of the firstandsecond portions should be such thatthe pH of the resulting product is in the range 5 to 6.

Alternatively, if the polymer emulsion is stable in a high pH environment (i.e. greaterthan 7), then all the emulsion can be adjustedtoan appropriate pH level prior to adding to the liquid resin.

If desired, other additives requiredforvarious purposes, such as thickeners, biocides, antioxidants and crosslinking agents may be added immediately afterthe addition of the second portion of the polymer component emulsion.

Polymer components having glass transition temperatures within the specified range of - 18"C to + 1 0'C provide contact adhesive with good autohesive characteristics. Polymers with glass transition temperatures belowthis range, being more rubbery in character, produce undesirabletackiness in the dried films and have inadequate strength characteristics to perform as contact adhesives. Polymers with higher glass transition temperatures, on the other hand, would require highertemperatureand/or pressure to promote coalescence ofthe dried films than would normally be expected for contact adhesives.

The resin component is the essential contributor towards the autohesive characteristics of the adhesives. It also improves the adhesion ofthe driedfilms to various substrates.

The inclusion of a crosslinking agent may improve the final strength characteristics ofthefinal bond produced bythecoalesceddryfilmsand may give improved heat resistance, peel strength and water resistance. A crosslinking agent may promote crosslinking ofthe acrylic monomer having a reactive functional group, inthe aqueous emulsion orwhen the adhesive is spread as a film and allowed to dry or in the final bond. Heat may be required in the latter case. As previously mentioned, improvements may similarly be obtained when the resin component is, or includes, a liquid addition product of an alkyl phenol and formaldehyde.

Terpolymer emulsions suitable for producing contact adhesives according to the invention are produced by Imperial Chemical Industries p.l.c. and identified by the Registered Trade Mark"Haloflex" with various suffices and by Scott Bader p.l.c. under the Registered Trade Mark"Polidene". Emulsions sold underthe Trade Mark"Haloflex" include terpolymers containing vinylidene chloride, vinyl chloride and one or more alkyl acrylates or alkyl methacrylates and may include an unsaturated carboxylic acid monomer. They are described in the Specifications of British Patent No.1,558,441, U.S.Patent No.4,341,679 and European PatentApplication No. 0030080. Not all the terpolymers described in those Specifications are suitable for use in performing the present invention, but we have found that by selection amongstthese terpolymers a range of contact adhesives can be produced to provide properties comparable with or superiorto those of solvent-borne contact adhesives.

Particularly useful are the Haloflex "ECL" and "ST" grades, which includeterpolymers having molar masses in excess of 1,000,000, compared with figures around 25,000 for other grades.

Suitable crosslinking agents include organicspecies, for example hexamethoxymethyl melamines such as Cymel 303 our glycol urils such as Cymel 1172.

("Cymel" is a Registered Trade MarkofCyanamid Corporation.) Alternatively, crosslinking agents including metal salts or complexes may be used. Zinc or zirconium, in both cation and anion complexes, are preferred. For example, zinc ammonium carbonate, zinc oxide, zirconium oxychloride orzirconium ammonium carbonate.Adhesives including such crosslinking agents can have a usable life in excess of one month. Other crosslinking agents can produce adhesives with shorter usable lives, such as a few hours, and in these cases the crosslinking agent may be added immediatelybefore use. Forsuch adhesives the adhesive and the crosslinking agent may be supplied separately as a two-pack adhesive, for mixing by the user.One example of a crosslinking agent suitablefor such a two-pack adhesive is DesmodurKA8267,which has isocyanatefunctionality. "Desmodur" is a Registered Trade Mark of Bayer AG.

The invention is illustrated bythefollowing examples. All compositions are given in parts by weight.

EXAMPLE 1 Haloflex ST 296, with pH adjusted to8withammonia 350 Haloflex ST 296, with pH adjusted to4withammonia 378 Resin SP 12 (amyl phenolic resin) 130 Butyl Ethoxyl (solvent) 25 880 Ammonia 1 20% Synperonic Np 30 in water (emulsifier) 20 Collacral VL (thickener) 12 Haloflex ST 296 has glass transition temperature (Tg) (measured by differential scanning calorimetry) of 7 C+ 1 Candsolidscontent51% +1.

EXAMPLE 2 Composition as in Example 1 but with the amyl phenolic resin SP 12 replaced by 130 parts of Resin SMD 5205. This is a terpene phenolic resin with softening point + 3 C.

EXAMPLE 3 Haloflex ECL 220 with PH adjusted to8withammonia 100 Resin SMD 5224 (circa 70% terpene phenolic resin solution in xylene) 27 20% Ammonium Zirconium Carbonate solution (crosslinking agent) 6 ViscalexAT 55 (inverse emulsion thickener) 1 Haloflex ECL 220 has Tg of -7"C + 1"C and solids content 55% 11.

EXAMPLE 4 HaloflexECL220,with pH adjusted to8withammonia 100 Haloflex ST 302, with pH adjusted to 8 with ammonia 6 Resin SMD 5224 27 20% Ammonia Zirconium Carbonate solution 6 Viscalex AT 55 2 Haloflex ST302 has Tg of -7 C + 1"C and solids content 61 % + 2.

EXAMPLE 5 Haloflex ST 304/362 with pH adjusted to 8 with ammonia 103 Resin SMD 5224 27 20% Ammonium Zirconium Carbonate solution 6 Viscalex AT 55 3 Haloflex ST 304/362 hasTg of -9"C + 1"C and solids content 53% + 1.

The resins SP 12, SMD 5205 and SMD 5224 are supplied bySchenectadyMidland Limited,"Ethoxyl" and "Synperonic" are Registered Trade Marks of Imperial Chemical Industries p.l.c., "Collacral" is a Registered Trade Mark of Badische Anilin & Soda Fabrik., "Viscalex" is a Registered Trade Mark of Allied Colloids.

In all the examples, the adhesive compositions were prepared by adding the Haloflexterpolymercompo- nent emulsions to the resin component when the latter was in a liquid state with vigorous agitation, as previously described. In examples 1,2 and 4, in which two Haloflex emulsions were included,theywere added to the resin component in the order indicated in the tables of components.

In orderto assess the performance of these examples of contact adhesives according to the invention, the following tests were performed and the results compared with the results of similartests performed with the solvent-borne polychloroprene adhesive "Evo-Stik 528": TESTPROCEDURES 1. PEEL TEST: A brush coat of adhesive was applied uniformlyto a piece of fabric duck and the volatile carrierwas allowed to evaporate at ambient temperature for 1 hour. A second coat of adhesive was then applied and after a further drying period of 1 hour two pieces of coated duckwere laminated together using the following techniques: Cold blend 30 seconds under a pressure of 60 p.s.i. (approximately 4.2Kg/cm2).

Heat activation-the coated pieces were heatedfor 10 seconds under a radiant heater so thatthe adhesive surfaces reached 70 80 Cfollowed by pressing togetherfor30 seconds at 60 p.s.i.

25mmwidth specimenswerethen aged for7days at 20 - 250C prior to testing in a SATRA peel tester (900 peel test). Results are in Newtons/25mm width of bonded specimen.

2. CREEP TEST: Laminated pieces prepared as for the Peel Test were conditioned for7 days at 20 25 C.The bonded specimens were then conditioned in an oven at60 + 1"C for 30 minutes priorto suspending static weights in a T peel configuration.

The length of bond (in mm) which separated in one minute is recorded (width of bond 25mm).

3. SUBJECTIVETEST: Athin uniform film of adhesive was applied to 150mm x 150mm pieces of chipboard and "Formica" laminated plastic sheet and allowed to dryfor one hour. The adhesive surfaces were broughttogether using light hand pressure. The strength ofthe bonded assembly was assessed immediately using the subjective scale 0 = no coalescence 10 = verystrong bond,substrate failure before adhesive failure RESULTS Evo-Stik 528 Examples (Control) 1 2 3 4 5 Peel Test Cold Bond 120 - 100 100 90 Peel Test HeatActivation 130 130 120 - - Creeps 0.5kg 0.2 0.5 2 0.4 0 G Creeps 1.5kg 3.4 5 5 3.6 3 1 Creeps 2.5kg 8.6 10 7 8.0 11 6 Subjective 8-9 1 1 8 7-8 8 NB Examples 1 and 2 were used as contact adhe sives under heat activation conditions.

NB Examples 3-5 were used under cold blend conditions.

Claims (18)

1. A contact adhesive comprising an aqueous emulsion of a resin component and a polymer component, having the following dry component composition by weight: polymer component 100 resin component 10 to 50 emulsifier 0.1 to 10 stabiliser 0.01 to 10 the polymercomponentcomprising aterpolymer containing a chlorinated monomer, an acrylic monomerwithouta reactivefunctionalgroupandan acrylic monomer having a reactive functional group, the polymer component having a glass transition temperature in the ra nge - 1 8"C to +1 00C and the resin component comprising at least one of: an alkyl phenolic resin, a liquid addition product of an alkyl phenol and formaldehyde, and a terpene phenolic resin.

2. Acontact adhesive as claimed in Claim 1 including a crosslinking agent.

3. A contact adhesive as claimed in Claim 2 wherein the crosslinking agent is of an organic species.

4. A contact adhesive as claimed in Claim 2 wherein the crosslinking agent comprises a metal salt orcomplex.

5. A contact adhesive as claimed in Claim 4 wherein the crosslinking agent comprises zinc ammonium carbonate or zirconium ammonium carbonate.

6. Acontactadhesive as claimed in any preceding claim wherein the acrylic monomer having a reactive functional group has hydroxyl or carboxylic acid functionality.

7. Acontact adhesive as claimed in any preceding claim wherein the polymer component comprises a blend of a saidtermpolymerand at least one other polymer.

8. A contact adhesive asclaimed in Claim 7 wherein the said other polymer is selected from styrene acrylate copolymers, acrylic copolymers, vinyl acetate ethylene copolymers (which may include a third monomer), polychloroprene, and polyvinyl acetate and vinyl acetate copolymers.

9. A contact adhesive substantially as hereinbefore desonbedwith reference to any one ofthe Examples.

10. Method of manufacture of a contact adhesive as claimed in any preceding claim comprising the steps of rendering the resin componentlíquid if necessary and adding an aqueous emulsion of the polymer component with vigorous agitation,

11. Method as claimed in Claim 10 comprising the steps ofdividing an aqueous emulsion of ttwpolymer component into two portions, adding ammoniato the first of the portions to adjustthe pH to a level between 7.5 and 9, adding ammonia to the second ofthe portions to adjustthe pH to a level between 4 and 5, addingthefirstportion tothe resin with vigorous agitation andthereafter adding the second portion with continued vigorous agitation, the proportions of thefirst and second portions being such that the resulting ing product has a pH level in the range 5 to 6.

12. Method as claimed in Claim 10 or Claim 11 wherein the resin is rendered liquid by heating.

13. Method as claimed in Claim 10 or Claim 11 whereinthe resin is rendered liquid by dissolving in an organic solvent.

14. Method as claimed in Claim 13 including the final step of removing a substantial proportion of the organicsolvent by evaporation.

15. Method as claimed in any of Claims 11 to 14 wherein the pK of the first portion is adjusted to 8.5.

16. Method as claimed in any of Claims 11 to 14 wherein the pH ofthe second portion is adjustedto a level between 4and 4.5.

17. Method of manufacture of a contact adhesive substantially as hereinbefore described.

18. A contact adhesive as claimed in any offClaims I to 9 made bythe method claimed in any of Claims 10 to 17.