CA1146299A

CA1146299A - Pressure sensitive adhesive composition and article

Info

Publication number: CA1146299A
Application number: CA000345168A
Authority: CA
Inventors: Samuel C. Temin
Original assignee: Kendall Co
Current assignee: Kendall Co
Priority date: 1979-02-07
Filing date: 1980-02-06
Publication date: 1983-05-10
Also published as: DE3004377A1; AU5506780A; IE800226L; GB2041949A; IT1141361B; FR2448563B1; IE49382B1; FR2448563A1; MX151229A; JPS6358195B2; GB2041949B; NZ192810A; JPS55106277A; AU532615B2; BE881576A; ZA80527B; IT8019763A0

Abstract

ABSTRACT OF THE DISCLOSURE
Improved, high strength pressure sensitive calender-able, adhesive compositions are provided comprising (1) a rubbery copolymer of e.g. ethylene and propylene and optionally, a non-conjugated diene wherein the copolymer may or may not be partially cross linked to the copolymer containing by weight from 10 to 100% and preferably from about 25% to 67% by weight based on said copolymer of crystalline polymer of ethylene, pro-pylene or copolymer thereof and (2) tackifying agent, preferably resinous, in amounts sufficient to yield a tackifier: rubbery copolymer weight ratio of about 1.2:1 to 8:1.

Description

1~6~9~

sAcKGRouND OF THE INVENTION
The present invention relates in ~eneral 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 con-tact 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 amorphorus nature, however, the strength as well as other important properties characteriz-ing the product upon blending with the usual additives is often inadequate for the adhesion problem at hand.
PRIOR ART
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 these in combination with rubbery alpha-olefin copolymers to produce thermoplastic rubbers which may or may not be partially cured, are described for uses not reIevant to the ~ -- 1 -- .
~ .

3~ 29~

present application in the United States patents 3,758,643;
3,B06,558 and 3,835,201.
United States patent 4,072,735 discloses hot melt ad-h~sives based on an ethylene-propylene rubber with tackifying resin and a large amount of polybutylene GENERAL DESCRIPTION OF THF. INVENTION
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 car, in accordance with the limitations to be hereinafter discussed in detail, be utilized in the prepar-ation 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 inven-: .
tion is to provide an adhesive composition having the aforemen-tioned as well as other improved properties, the product adhesive having significantly improved overall functionally and

- 2 -, 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, calendarable composition comprising a rubbery copolymer of ethylene and at least one other copolymerizable mono~lefin of the formula CH2=CHR wherein R is alkyl of 1 to 12 carbons with or without at least one copolymer-izable polyene, said rubbery copolymer containing from about 10 to 100% by weight, preferably from 20 - 67% 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 polyethylene, 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 character-istic of a rubbery, essentially amorphous polymeric material.

~6~99 The use, in an adhesive composition, of a thermoplastic polymeric substance having a significant degree of crystallinity and par-ticularly 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 fine that the "thermoplastic rubber"
described herein could be effectively plasticized 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 United States 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. Thus, in United States

3,758,643, the amorphous rubbery copolymer is prepared by copolymerizing 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 non-conjugated diene such as dicyclo-pentadiene as described in United States 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 B

z~9 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 10% 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 o~ the material in the solvent for 48 hours at 73F, taking an aliquot of the solution and determining the concentration of solute by evapor-ating the solvent. The partially cured rubber can be blended with the crystalline polymex material e.g. poly-propylene on a roll mill, in a Banbury mixer or in an extruder. As explained in the patent, polypropylene is somewhat superior having highly crystalline isotactic and syndiotactic form.
As described in United States 3,806,558, the afore-described procedure can be modified to a one step process by effecting partial cure of the rubber in the presence of the ~0 crystalline polymer component while the blend is undergoing masti-cation As described in United States 3~835~201 treatment of the copolymer rubber with curative is rendered unnecessary pro-vided the copolymer rubber be typified in having certain speci-fied rheological characteristics, specifically a relatively high value of a viscosity parameter designated "zero shear viscosity".

~62~

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 United States 3,835,201. The patent further describes "branching index" as a further qualifying test.
In any event, any of the thermoplastic rubber compo-sition described in the foregoing 3,758,643; 3,806,558 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, eg. Wingtack 10, 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, PermalynxA-115* and Foral*85 and the zinc salts of rosin acids such as Pexate resins available commercially from Hercules. ~any 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 tacki-fiers are used in combination comprising two or more thereof.

* Trade Mark Particularly, worthy of mention in this regard are the combina-tion of different polyterpenes and specifically those available commercially as Wingtack 10 and Wingtack 95 in approximately equal weight amounts as we11 as combinations of hydrogenated rosin esters (Hercolyn D) and polyterpenes (Wingtack 95) respecti~ely in weight ratios of, for example 83:71 82:99 and 62:134.
The tackiEier 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. 275-350F. As blending occurs, the roll temperature is preferably reduced to less than about 200F e.g. 175F. 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 pro-duce 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 e~fected by adding the remaining tackifier on the rubber mill.
Since the present adhesive compositions are readily calender-able, compounding on the rubber mill is greatly facilitated.

* Trade Mark i'Z99 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.

-The thermoplastic rubber (TPR) used in this example is that described in Example 1, run no. 4 of United States 3,758,643 comprising partially cured ethylene-propylene copoly-mer 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 310F. As the tackifier level increases during the blending, the rolls are lowered in temper-ature to 170F. 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 170F 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 United States 3,758,643 comprising partially cured ethylene-propylene copolymer rubber, 70 parts (masterbatch) combined ~ith 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 complet~
ing the compounding by adding additional tackifier on the rubber mill.

~6'~99 The compositions of the products and the physical properties obtained when coated on Mylar film to thickness of 2.3, l.9 and 1.6 mil respectively are given below:

Composition Properties Adhes~lon ExampleTPR Hercolyn D Wingtack 95 T (a)TO Steel(b~reeP(C) No. (parts)(parts) (parts) 2.) lO0 83 71 386 46 lO0 3.) lO0 82 99 480 54 83

4.) lO0 62 134 252 65 50 (a) tested under ASTM-D 2979 (b) tested under AST~l-D 1000 (c) tested by flat bar heated to 150F; adhere 1 in2 of end of adhesive tape to flat bar in vertical position and attach l kilogram weight to free end of tape; creep det~rmined electronically and given as time in hours for tape to move down bar 0.5 inches.
EXAMPLE~ 5 ~ .
The TPR used in this Example is that described in United States 3,806,558, Example l, run no. 8, comprising ethy-lenepropylene copolymer, 60 parts combined with crystalline poly-propylene, 40 parts. An adhesive prepared as in Examples 2-4 has the following composition.

Ingredient Parts Wingtack-lO 88 Wingtack 95 78 X _ g ~46~99 This adhesive, spread to a thickness of 2.2 mils on ~ylar back-ing gives the following values when tested as described in the previous Examples:

tack: 202 ashesion to steel: 40 creep: 66 EXA~IPLE 6 The TPR used in this Example is that described in United States 3,835,201. Example ~o. 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:

IngredientParts l~ingtack 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.

ashesion to steel: 78 ounces/inch flat bar creep time: 72 hours/0.5 in.
Results similar to those described in the preceding Examples are obtained when the procedures described therein are repeated utilizing other tackifiers and TPR materials described herein and varying the concentrations thereof within the limits herein-~0 before delineated.

~ .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pressure-sensitive, calenderable adhesive composi-tion comprising a rubbery copolymer of ethylene and at least one other copolymerizable monolefin of the formula CH2 = CHR wherein R represents alkyl of 1 to 12 carbon atoms with or without at least one copolymerizable polyene, said rubbery copolymer con-taining, 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 tacki-fying agent is pentaerythritol 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 Claim 2 wherein the ratio of tackifier to rubbery copolymer is 1.2:1 to 6:1.

8. A composition according to Claim 2 wherein the ratio of tackifier to rubbery copolymer is 1.5:1 to 4.5:1.

9. A composition according to Claim 2 wherein the amount of crystalline polymer is from 20 to 67% by weight of said rubbery copolymer.

10. A composition according to Claim 1 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 73°F.

11. A composition according to Claim 1 wherein said rubbery copolymer has a zero shear viscosity of at least 1 x 109 poises determined from sheer creep data at 135°C.

12. A composition according to Claim 1 wherein said co-polymerizable monoolefin is propylene.

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

14. A composition according to Claim 13 wherein said non-conjugated diene is dicyclopentadiene.

15. An adhesive article comprising the composition of Claim 1 coated on a base.

16. An adhesive article comprising the composition of Claim 2 coated on a base.

17. An adhesive article according to Claim 15 wherein said base is a film-forming, organic, polymeric resinous material.