GB2041949A - Pressure Sensitive Adhesive Composition and Article - Google Patents

Abstract

High strength pressure sensitive calenderable, adhesive compositions comprise (1) a rubbery copolymer of ethylene, a C3-14 monoolefin and optionally a non-conjugated diene, the copolymer optionally being partially cross linked, (2) 10 to 100% by weight based on said copolymer of a crystalline ethylene or propylene polymer and (3) a tackifying agent, preferably resinous, in amounts sufficient to yield a tackifier: rubbery copolymer weight ratio of 1.2:1 to 8:1.

Description

SPECIFICATION Pressure Sensitive Adhesive Composition and Article The present invention relates in general to pressure sensitive calenderable, adhesives and in particular to such adhesives based on thermoplastic rubbers having improved strength characteristics, processability, as well as outstanding tack and adhesion, and low creep, etc. properties.

As is known in the art and practiced industrially, relatively effective pressure sensitive adhesives, hereinafter also designated p.s.a. can be prepared from various types of organic, synthetic, polymeric substances such as triblock copolymers, e.g. styrene-diolefin-styrene types and available commercially in the form of styrene-isoprene-styrene and styrene-butadiene-styrene triblock polymers.

The former type is usually preferred for use as a contact adhesive while the latter type is preferably used for heat activated adhesives. In general, the base elastomer materials used in adhesive formulations, whether of the synthetic or natural rubber type are not of the cross linked type and are accordingly soluble in the usual solvents employed in adhesives manufacture. Being of an essentially amorphous nature, however, the strength as well as other important properties characterising the product upon blending with the usual additives is often inadquate for the adhesion problem at hand.

Fairly recent developments in polymer technology have enabled the preparation of unusually high strength resinous materials which are highly crystalline. Polymers of this type as typified by crystalline homo- and copolymers of ethylene and propylene in combination with rubbery alpha-olefin copolymers to produce thermoplastic rubbers which may or may not be partially cured, are described for uses not relevant to the present application in the U.S. patents 3,758,643; 3,806,558 and 3,835,201.

U.S. patent 4,072,735 discloses hot melt adhesives based on an ethylene-propylene rubber with tackifying resin and a large amount of polybutylene.

In accordance with the present invention, it has been discovered that polymer compositions of a thermoplastic "crystalline" olefinic polymer component combined with a rubbery olefin copolymer component can, in accordance with the limitations to be hereinafter discussed in detail, be utilised in the preparation of pressure sensitive adhesive compositions having manifold beneficial properties and particularly, tack, adhesion, creep and the like. and in addition are readily calenderable.

Thus, paramount among the objects of the present invention is to provide an adhesive composition having the aforementioned as well as other improved properties, the product adhesive having significantly improved overall functionally and thus eminently suitable for use in a wide variety of environments under diverse conditions of heat, humidity, physical stress and the like.

Attainment of the foregoing objects is made possible in accordance with the present invention which in its broader aspects provides a pressure sensitive adhesive, calenderable composition comprising a rubbery copolymer of ethylene and at least one other copolymerisable monoolefin of the formula CH2=CHR wherein R is alkyl of 1 to 1 2 carbons with or without at least one copolymerisable polyene, said rubbery copolymer containing from about 10 to 100% by weight based on the copolymer, of crystalline polymer of ethylene, propylene or crystalline copolymers of ethylene and propylene and sufficient tackifying agent to provide a tackifier: rubbery copolymer weight ratio of from about 1.2:1 to 8:1.

In a further aspect, the invention provides an adhesive article comprising the composition coated on a base such as a flexible, film forming polymeric substance including thermoplastic resins such as poiyethylene polyester, etc.

One of the truly surprising aspects of the present invention is the fact that the aforedescribed composition of rubbery and crystalline polymer components could be formulated to provide effective adhesive having the highly desirable strength properties normally characteristic of a crystalline thermoplastic polymeric material and yet the ease of processability, and superior tack, adhesion and creep properties normally characteristic of a rubber, essentially amorphous polymeric material. The use, in an adhesive composition, of a thermoplastic polymeric substance having a significant degree of crystallinity and particularly in the relatively large amounts prescribed herein, would normally be contraindicated, primarily due to the inertness and insolubility ordinarily attributed to such materials.It was thus unexpected to find that the "thermoplastic rubber" described herein could be effectively plasticised with tackifying agents as will be described to provide a truly superior adhesive product.

The improvements described herein obtain where the rubbery copolymer is any one of those described in U.S. patents 3,758,643; 3,806,558 and 3,835,201 and whether the rubbery copolymer as provided for incorporation with the crystalline polymer is or is not partially cured. The disclosures of said three patients are incorporated herein by reference. Thus, in U.S. 3,758,643, the amorphous rubbery copolymer is prepared by copolymerising two or more monoolefins of the formula CH2=CHR wherein R is alkyl of 1 to 12 carbons. A small amount of at least one copolymerisable polymer may be added to provide unsaturation in the copolymer. The polyene may be a conjugated or preferably nonconjugated diene such as dicyclo-pentadiene as described in U.S. 3,758,643. Moreover, trienes as well as dienes may be used. The polyene may be used in amounts up to about 20% by weight of the copolymer rubber.Partial curing of the rubbery copolymer, effected with the usual curatives of the free radical or cross linking type as explained in column 3 of the patent, is carried out to a gel, i.e. insolubles content at least 1 0% in excess of the original gel content of the rubber and preferably at least 20% in excess and more preferably at least 30% in excess as measured in cyclohexane. In general, the gel content will be at least 30% but less than 90%. The gel is that portion of the rubber which is insoluble in the cyclohexane and is measured by immersing a sample of the material in the solvent for 48 hours at 730F (22.80C), taking an aliquot of the solution and determining the concentration of solute by evaporating the solvent.The partially cured rubber can be blended with the crystalline polymer material e.g. poiy-propylene on a roll mill, in a Banbury mixer or in an extruder. As explained in the patent, poly propylene is somewhat superior having highly crystalline isotactic and syndiotactic form.

As described in U.S. 3,806,558, the aforedescribed procedure can be modified to a one step process by effecting partial cure of the rubber in the presence of the crystalline polymer component while the blend is undergoing mastication.

As described in U.S. 3,835,201 treatment of the copolymer rubber with curative is rendered unnecessary provided the copolymer rubber be typified in having certain specified rheological characteristics, specifically a relatively high value of a viscosity parameter designated "zero shear viscosity". The latter, also called steady flow viscosity, is defined as the melt viscosity at zero shear rate and can be determined from stress relaxation data or from shear creep data in the manner fully described in U.S. 3,835,201. The patent further describes "branching index" as a further qualifying test.

In any event, any of the thermoplastic rubber composition described in the foregoing 3,758,643; 3,806,553 and 3,835,201 patents may be used to advantage herein.

Tackifiers useful herein include hydrocarbon resins such as amorphous polypropylene; poly terpenes such as those commercially available under the trade name designations, Wingtack supplied by Goodyear, e.g. Wingtack 10 and Wingtack 95; hydrogenated rosin esters such as those commercially available from Hercules under the trade name designation Hercolyn D; the glycerol or pentaerythritol esters of rosin acids available commercially from Hercules under the trade name designations, respectively, Permalyn-xA-1 1 5 and Foral 85 and the zinc salts of rosin acids such as Pexate resins available commercially from Hercules. Many of the foregoing tackifiers are available in various grades, differing, for example, in molecular weight, softening point etc.In any event, the characteristics of the product adhesive will differ somewhat depending upon the nature and quantity of the tackifier used. In accordance with a particularly preferred embodiment of the invention, the tackifiers are used in combination comprising two or more thereof. Particularly, worthy of mention in this regard are the combination of different polyterpenes and specifically those available commercially as Wingtack 10 and Wingtack 95 in approximately equal weight amounts as well as combinations of hydrogenated rosin esters (Hercolyn D) and polyterpenes (Wingtack 95) respectively in weight ratios of, for example 83:71,82:99 and 62:134.

The tackifier is added in amounts sufficient to yield a tackifier: rubbery copolymer weight ratio of from about 1.2:1 to 8:1 and preferably from about 1.2:1 to 6:1 with a range of 1.5:1 to 4.5:1 being most preferred.

The compositions herein can be conveniently prepared by mixing the thermoplastic rubber material and tackifier on a rubber mill the rolls being preheated to elevated temperature, e.g. 275- 3500F (1 3 5--1 77 OC). As blending occurs, the roll temperature is preferably reduced to less than about 2000F (940 C) e.g. 1 750F (79.50C). The resultant adhesive composition can be applied to a suitable base by pressing same to the desired thickness between a piece of Mylar film, for example, and a release paper sheet to produce an adhesive article. Alternatively, the thermoplastic rubber may be blended with minor amounts of the tackifier in a Banbury mill, completion of the compounding being thereafter effected by adding the remaining tackifier on the rubber mill.Since the present adhesive compositions are readily calenderable, compounding on the rubber mill is greatly facilitated.

The following examples are given for purposes of illustration only and are not to be interpreted as necessarily limiting the invention. All quantities are by weight unless otherwise indicated.

Example 1 The thermoplastic rubber (TPR) used in this example is that described in Example 1, run no. 4 of US.

3,758,643 comprising partially cured ethylene-propylene copolymer rubber, 90 parts, (masterbatch) combined with 10 parts of crystalline polypropylene.

A mixture of 200 parts of the above TPR, 250 parts Wingtack 95 and 250 parts Wingtack 10 are mixed on a rubber mill with rolls preheated to 31 00F (154.50C). As the tackifier level increases during the blending, the rolls are lowered in temperature to 1 700F (76.60C). A sample of the final mixture, containing 72% tackifier by weight is pressed between a piece of Mylar film and a sheet of release paper at 1 700F (76.60C) to obtain a film of about 2 mils thickness. The adhesive gives a Probe Tack value (100 g load, 0.1 second) of 720.

Examples 2,3 and 4 The TPR used in these Examples is that described in Example 1, run no. 8 of U.S. 3,758,643 comprising partially cured ethylene-propylene copolymer rubber, 70 parts (masterbatch) combined with 30 parts of crystalline polypropylene. A series of adhesives is prepared by initially blending the TPR with minor amounts of tackifiers on the rubber and then completing the compounding by adding additional tackifier on the rubber mill.The compositions of the products and the physical properties obtained when coated on Mylar film to thickness of 2.3, 1.9 and 1.6 mil respectively are given below: Composition Properties Example TPR Hercolyn D Wingtack 95 Adhesion No. (parts) (parts) (parts) Tack(a) To Steer' Creep (C) 2.) 100 83 71 386 46 100 3.) 100 82 99 480 54 83 4.) 100 62 134 252 65 50 (a) tested under ASTM-D 2979 (b) tested under ASTM-D 1000 (c) tested by flat bar heated to 1 500F (65.50C); adhere 1 in2 (2.54 cm2) of end of adhesive tape to flat bar in vertical position and attach 1 kilogram weight to free end of tape; creep determined electronically and given as time in hours for tape to move down bar 0.5 inches (1.27 cm).

Example 5 The TPR used in this Example is that described in U.S. 3,806,558. Example 1, run no. 8, comprising ethylenepropylene copolymer, 60 parts combined with crystalline polypropylene, 40 parts.

An adhesive prepared as in Example 2-4 has the following composition.

Ingredient Parts TPR 100 Wingtack 10 88 Wingtack 95 78 This adhesive, spread to a thickness of 2.2 mils on Mylar backing gives the following values when tested as described in the previous exxamples: tack: 202 adhesion to steel: 40 creep: 66 Example 6 The TPR used in this Example is that described in U.S. 3,835,201. Example No. 1 comprising an 80/20 blend of monoolefin copolymer elastomer with crystalline polypropylene. An adhesive is prepared as described in Examples 2-4 of the following composition: Ingredient Parts TPR 100 Wingtack 10 77 Foral 85 66 This composition when tested as described in the foregoing examples at a mass thickness of 3.2 mils gives the following results.

adhesion to steel: 78 ounces/inch (2211.3 grm/2.54 cm or 870.6 grm/cm) flat bar creep time: 72 hours/0.5. in (1.27 cm) Results similar to those described in the preceding examples are obtained when the procedures described therein are repeated utilising other tackifiers and TPR materials described herein and varying the concentrations thereof within the limits hereinbefore delineated.

Claims (14)

Claims

1. A pressure-sensitive, calenderable adhesive composition comprising rubbery copolymer of ethylene and at least one other copolymerisable monoolefin of the formula CH2=CHR wherein R represents alkyl of 1 to 1 2 carbon atoms with or without at least one copolymerisable polyene, said rubbery copolymer containing from about 10 to 100% by weight based on said copolymer of crystalline polyethylene, polypropylene or copolymers of ethylene and propylene and sufficient tackifying agent to provide a tackifier: rubbery copolymer weight ratio of from about 1.2:1 to 8:1.

2. A composition according to Claim 1 wherein said tackifying agent is at least one member selected from the group consisting of hydrocarbon resins, polyterpenes, rosin esters and zinc salts of rosin acids.

3. A composition according to Claim 2 wherein said tackifying agent is glycerol ester of rosin acid.

4. A composition according to Claim 2 wherein said tackifying agent is pentaerythritoi ester of rosin acid.

5. A composition according to Claim 2 wherein said tackifying agent is amorphous polypropylene.

6. A composition according to Claim 2 wherein said tackifying agent is hydrogenated rosin ester.

7. A composition according to any one of Claims 2 to 6 wherein the ratio of tackifier to rubbery copolymer is 1.2:1 to 6:1.

8. A composition according to Claim 7 wherein the ratio of tackifier to rubbery copolymer is 1.5:1 to 4.5:1.

9. A composition according to any one of the preceding Claims wherein the amount of crystalline polymer is from 20 to 67% by weight of said rubbery copolymer.

10. A composition according to any one of the preceding Claims wherein said rubbery copolymer as provided is partially cross linked to a gel content of at least about 30% but less than about 90% by weight measured by immersion in cyclohexane for 48 hours at about 730F (22.80C).

11. A composition according to any one of the preceding Claims wherein said rubbery copolymer has a zero shear viscosity of at least 1 x109 poises determined from sheer creep data at 1 550C.

12. A composition according to any one of the preceding Claims wherein said copolymerisable monoolefin is propylene.

13. A composition according to any one of Claims 1 to 11 wherein said rubber copolymer is an unsaturated terpolymer of ethylene, propylene and from a small amount up to about 20% by weight based on said rubber copolymer of at least one copolymerisable, non-conjugated diene.

14. A composition according to Claim 1 3 wherein said non-conjugated diene is dicyclopentadiene.

1 5. A composition according to Claim 1 substantially as hereinbefore described.

1 6. An adhesive article comprising a composition as claimed in any one of Claims 1 to 1 5 coated on a base.

1 7. An adhesive article according to Claim 1 6 wherein said base is a film-forming, organic, polymeric resinous material.

1 8. The features as herein disclosed, or their equivalents, in any novel selection.