CA2118779A1 - Radiation-curable poly(.alpha.-olefin) adhesives containing pendant olefinic functionality - Google Patents

Abstract

ABSTRACT

The invention relates to adhesive compositions comprising terpolymers C6-C10 unsaturated .alpha.-olefin monomers, C2-C5 .alpha.-olefin monomers, and polyene monomers and an effective amount of photoactive crosslinking agent to crosslink composition upon exposure to a source of radiation.

Description

RADIATION-CURABLE POLY(~-OLEFIN) ADHESIVES
CONTAINING PENDANT OLEFINIC F~NCTIONALITY
FIELD OF THE INVENTION
This invention relates to poly(~-olefin) compositions having enhanced radiation curability to provide adhesives having a superior balance of peel 10 adhesion and cohesive strength at both ambient and elevated temperatures.

BACKGROUND OF THE INVENTION
A continuing need in the pressure-sensitive 15 adhesive (PSA) art is the achievement of better control over various mechanical and process properties so that adhesives can be made specifically for highly demanding end use applications such as packaging, medical, and masking tapes. These applications require a proper 20 balance of properties that changes with the particular end use.
Among the earliest polymers to provide a reasonable balance of the properties required for satisfactory PSA performance were the natural and 25 synthetic rubbers. However, these PSAs had poor aging properties, and the art quickly recognized the need to eliminate ethylenically unsaturated groups from the polymer backbone of rubber adhesives in order to ~-improve their oxidative stability.
The discovery of Ziegler-Natta (ZN) catalysts made possible polymerization of ~olefin monomers to high molecular weights. The homopolymers of the C6-Clo ~-olefins were naturally tacky and also had low toxicity, good aging and favorable environmental 35 stability (i.e., low oxidation). These homopolymers were chemically inert, resistant to plasticizer migration, and relatively inexpensive. However, they had poor cohesive strength and therefore, lacked the shear adhesion necessary for high performance PSAs.
40 Use of ZN catalysts to make homopolymers from ~-olefin ~`` - 2 - 21~ 8 7 79 monomers and to make copolymers from mixtures of ~-olefin and nonconjugated polyene monomers is known in the art and is succinctly summarized in Odian, G., "Principles of Polymerization", Ch. 8.4 (Second Edition -5 J. Wiley & Sons, New York, 1981). For a more detailed discussion of the polymerization of ~-olefins, see Boor, J., "Ziegler-Natta Catalysts and Polymerizations", Ch. 19 (Academic Press, NY, 1979).
Adhesives derived primarily from C6 or higher 10 ~-olefins are also known. U.S. Patent No. 3,542,717 - -~
describes poly(~-olefin) adhesive compositions comprising mixtures of polyolefin copolymers derived from olefin monomers with different molecular weights (i.e., copolymers from one ~-olefin monomer having 11 15 to 20 carbon atoms and another having 4 to 20 carbon atoms.) U.S. Patent No. 3,635,755 describes polyolefin PSAs suitable for use as a single component PSA for surgical tapes that are substantially non-allergenic. -~
20 Such adhesives can be made from homopolymers of the C6 to C~ ~-olefins or from interpolymers of C2 to C~
~-olefins having an intrinsic viscosity of 1.5 to 7.0, a Williams plasticity of 0.8 to 4.0, and an ~-acetone/heptane soluble fraction of less than 25% by 25 weight. This patent does not teach radiation curing of these poly-olefin compounds.
U.S. Patent Nos. 3,954,697 and 4,072,812 describe hot melt adhesives based respectively on propylene/C6-Cl0 1-olefins wherein the C6-CI0 l-olefins comprise 40 to 60 30 mole percent of the composition and l-butene/C6-C~0 1-olefins wherein the C6-CI0 1-olefins comprise 40 to 60 mole percent of the composition. These compositions have no detectable crystallinity by differen~ial scanning calorimetry. These two patents also teach 35 that copolymers containing only minor amounts of propylene or butylene (e.g. 5 to 20 wt%) are permanently tacky. Moreover, they teach that _ 3 _ 211 8 7~9 copolymexs containing only minor amounts of propylene or butylene have little static shear and fail in the static shear test after less than 100 minutes. In addition, neither teaches the use of polyene monomers.
U.S. Patent No. 4,178,272 describes hot melt adhesives based on a blend of poly(propylene-co-higher 1-olefin) containing 35 to 65 mole percent higher l-olefins. A tackifying resin and crystalline polypropylene are added. Without the crystalline ~ -~
10 polypropylene homopolymer, the adhesive exhibits ~ ;
excessive creep under load.
U.S. Patent No. 4,259,470 describes hot melt adhesives containing propylene, l-butene or l-pentene ~ -and 3 to 14 mole percent of at least one C6-ClO linear 15 ~-olefin. Tackifying resins and plasticizing oils are added to the hot-melt compositions.
U.S. Patent No. 4,2~8,358 describes hot-melt ` -~-adhesive compositions containing terpolymers of 10 to ~:
55 mole percent propylene, 15 to 60 mole percent 20 l-butene or 1-pentene, and 5 to 39 mole percent higher ~ -1-olefins, i.e., C6-C~0 ~-olefins. Tackifying resins and plasticizing oils are added to the hot-melt compositions.
~.S. Patent No. 5,112,882 describes a radiation 25 curable poly(d-olefin)-containing adhesive composition that is pressure sensitive at room temperature which upon cure yields an adhesive film having superior balance of peel and shear adhesion. The adhesive composition comprises (a) C6-C~0 ~-olefin monomer(s) and 30 0 to 15 mole percent polyene monomers and (b) sufficient photoactive crosslinking agent to crosslink the composition upon irradiation. The radiation must be sufficient energy to generate free radicals so as to crosslink the composition.

2ll877~9 : - 4 -SUMMARY OF THE INVENTION
The present invention provides radiation curable poly(~-olefin) adhesive compositions with enhanced curability to adhesive films that have a superior 5 balance of peel adhesion and cohesive strength at . :;
elevated temperatures comprising:
a. an ~-olefin polymer comprising about 45 to 98 mole percent of an ethanediyl repeat unit ~:
having a pendent hydrocarbyl group having 4 to 8 carbon atoms, from about 1 to 40 mole percent of an ethanediyl repeat unit selected from ethylene or units having a pendent ~::
hydrocarbyl group having 1 to 3 carbon atoms, and from about 1 to 15 mole percent of an ethanediyl repeat unit comprising an ethylenically-unsaturated group; and b. an effective amount of a photoactive crosslinking agent to crosslink the composition upon exposure to a source of actinic radiation.
The present invention also provides a method of ::
preparing a radiation cured adhesive composition comprising the steps:
a. providing one or more C6-CIo ~-olefin monomers, one or more C2-C5 ~-olefin monomers and at least one non-conjugated polyene monomer selected from the group consisting of 1) a linear or branched polyene having 5 to 18 carbon atoms, 2) a monocyclic polyene having 6-20 or more carbon atoms, 3) a polycyclic polyene having 7 to 20 carbon atoms or a combination of one or more of the foregoing, b. adding an effective amount of a photoactive crosslinking agent, c. subjecting the admixture to sufficient actinic radiation to provide a cross-linked polymer, 2ll8~79 \ :

said polymer comprising about 45 to 98 mole percent of C6-ClO ~-olefin repeat units, about 1 to 40 mole percent C2-C5 ~olefin repeat units, and about 1 to 15 mole percent non-conjugated polyene repeat units;
In another aspect, the present invention provides a method of preparing a radiation curable adhesive composition comprising the steps~
a. polymerizing a C6-C~o ~-olefin monomer with at ~ i least one lower ~-olefin monomer using a -..
Ziegler-Natta catalyst to produce a saturated ~ -homopolymer or a copolymer, b. reacting the resulting ~-olefin polymer with ;~
maleic anhydride in the presence of an initiator such as a peroxide and preferably ;
an electron donor (e.g., triphenyl phosphite or triethyl phosphate) to produce a polyolefin adduct, c. reacting the maleated ~ olefin polymer adduct with an ethylenically-unsaturated primary amine or isocyanate having 3 to 20 carbon atoms, and d. optionally, adding an effective amount of a photoactive cross-linking agent.
Compositions with improved PSA properties may be 25 obtained by blending two or more polymers of the invention or by blending one or more polymers with tackifying resins, preferably 1 to 150 parts by weight (pbw) of tackifying resin per 100 pbw polymer.
The adhesives of the present invention can be 30 applied to appropriate substrate surfaces by a wide range of processes, i.e., solution coating, solution spraying, hot-melt extrusion, emulsion coating, etcO, to make adhesive tapes and adhesive transfer films.
Unless otherwise indicated, the ~ollowing 35 definitions apply in this application:
''C6-C~0 ~-olefin monomer" means a linear or branched organic compound having 6 to 10 carbon atoms and one ,. 2l~-8779 terminal ethylenically-unsaturated group and no other functional group;
"polymer" means a homopolymer or a polymer, either random or blocked, derived from more than one monomer (e.g., copolymer, terpolymer, tetrapolymer, etc.);
"polyene monomer" means a hydrocarbon of five or more carbon atoms containing two or more non-conjugated ethylenically unsaturated groups which may also contain ;
1 to 5 unitary heteroatoms selected from the group 10 consisting of oxygen and silicon;
"photoactive crosslinking agent" means a compound which, under the influence of suitable actinic radiation, initiates free radical formation and subsequent interchain crosslinking and which may or may 15 not become incorporated therein, thus increasing the cohesive strength of the adhesive.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The ethylenically-unsaturated ~-olefin polymer of 20 the PSA composition preferably has the formula:

~ M1)~ ( M2 ~ M3~ I
wherein:
x, y, and z are numbers designating the relative molar amounts of Ml, M2, and M3 units that are randomly located in the backbone chain of the polymer such that the polymer has a weight average molecular weight in the range of 50,000 to 3.5 million, x is at least 45 30 mole percent of (x~y), y is 1 to 40 mole percent of (x+y), and z is 0.1 to 15 mole percent of (x+y+z);
Ml, is an ethanediyl repeat unit having a pendent hydrocarbyl group having 4 to 8 carbon atoms;
M2 is an ethanediyl repeat unit, different Prom Ml, 35 selected from ethylene and units having a pendent hydrocarbyl group selected from linear and branched alkyl groups having 1 to 3 carbon atoms; and 211~77,~
, _ 7 _ M3 is an ethanediyl repeat unit having a pendent, non-conjugated ethylenically-unsaturated aliphatic or aryl group selected from the group consisting of 1) linear and branched mono- and polyethylenically- -5 unsaturated hydrocarbyl groups having 3 to 18 carbon atoms, 2) aryl groups substituted by mono- or polyethylenically-unsaturated groups having a total of 7 to 18 carbon atoms, and 3) cycloalkylene groups having 6 to 18 carbon atoms wherein the cyclic group 10 has at least 6 carbon atoms in the ring, provided that the ethylenically-unsaturated (C=C) moiety is not . ~-~
bonded directly to a backbone carbon atom.
Most preferably, the ethylenically-unsaturated ~-olefin random polymers have the formula~
Rs ~CH2 IH ~ CH2-IH- ~ -CH)z, ( Rl R2 R~ R3 HC~
O=C\ /C=o 15 wherein x, y, z' and z" are numbers designating the relative molar amounts of monomer units comprising the backbone chain of the polymer such that the polymer has a weight average molecular weight in the range of 20 50,000 to 3.5 million, x is at least 45 mole percent of (x+y), y is 1 to 40 mole percent of the sum (x+y), and (z'+z") is 0.1 to 15 mole percent of (x+y+z'+z") and either z' or z" can be zero (z of Formula I equals the sum of (z'+z") of Formula II);
Rl is an alkyl group having 4 to 8 carbon atoms, preferably 4 to 6 atoms;

/', .'~. ~, , ., ' ' , , ' ' ' '~ .. ,:, " " ' :: : ' 8 ~
R2 is hydrogen or a hydrocarbyl group, preferably selected from linear and branched alkyl groups having 1 : ~-to 3 carbon atoms;
R3 is an unsaturated aliphatic hydrocarbyl group 5 having 3 to 18 carbon atoms, the unsaturated group of which is separated from the -CH-CH- of the ~-olefin polymer backbone by at least one carbon atom, preferably selected from linear and branched alkenyl 10 groups having 3 to 18 carbon atoms, non-conjugated polyethylenically-unsaturated aliphatic groups having 6 to 18 carbon atoms, cyclic alkenyl groups having 5 to : :
18 carbon atoms, and cyclic non-conjugated polyethylenically-unsaturated groups having 6 to 18 15 carbon atoms, or R3 can also be -Q-R7, wherein R7 is a C2 to C~0 mo~ovalent hydrocarbyl group containing one or more ethylenically unsaturated groups and Q is a divalent radical, -O-, or -si-25 wherein R8 and R9 are the same or different C~ to C~2 monovalent organic groups selected from alkyl, cycloalkyl, alkaryl, alkoxy, and aryloxy groups; and R4 is hydrogen or R4 together with R3 and the carbon atoms to which they are attached forms an unsaturated 30 or non-conjugated polyunsaturated monocyclic ring system having 6 to 18 carbon atoms, the unsaturated groups of which are separated from the -C~-CH- of the I I . . ' ~-olefin polymer backbone by at least one carbon atom;
R5 is hydrogen, a linear or branched alkyl group having 1 to 18 carpon atoms, or cyclic alkyl group having 5 to 18 carbon atoms; and R6 is a linear or branched ethylenically- or non-conjugated polyethylenically-unsaturated aliphatic 40 hydrocarbon group having 3 to 18 carbon atoms, or a ..

221~779 , . , g cyclic ethylenically or non-conjugated polyethvlenically-unsaturated aliphatic hydrocarbyl group having 5 to 18 carbon atoms.
The ~-olefin polvmers of the present invention 5 have terminating groups, the identity of which depends upon the catalyst and components in the polymerizing composition. The terminating groups, because of their insignificant concentration, do not affect the essential properties of the polymers of the present 10 invention.
When Rl contains from 4 to 8 carbon atoms, the ethylenically-unsaturated ~-olefin polymers are tacky PSAs at room temperature (i.e., 20 to 25~C).
Preferably, the ethylenically-unsaturated ~-olefin 15 polymer of the present invention has a glass transition -~
temperature (T~) not higher than about 0C, more preferably not hiqher than about -lO~C. Indeed, its Tg can be as low as -70C. PSA crosslinked ~-olefin polymers of the present invention that have low Tg's 20 tend to have superior adhesion. Furthermore, a crosslinked ~-olefin polymer with a lower Tg can be blended with larger amounts of tackifying resin to make coatings that exhibit less shocky peel adhesion. -The ethylenically-unsaturated ~-olefin polymers 25 have inherent viscosities (IV) in the range of 0.5 to 5 dl/g, preferably from 0.5 to 4 dl/g, at concentrations of 0.5 g/dl in toluene at 25C, which values roughly correspond to average molecular weights of from 50,000 to 2,500,000, preferably 50,000 to 2,000,000, 30 respectively. At an IV substantially below that preferred xange, the ethylenically-unsaturated ~-olefin polymer can be less lik~ly to attain high internal or -cohesive strengtK, especially at elevated temperatures.
At viscosities substantially higher than 4 dl/g, the 35 ethylenically-unsaturated ~-olefin polymers preferably are coated from solution or hot melt extrusion.

::

. ~118'~7~
" -- 1 0 --The ethylenically-unsaturated ~-olefin polymer can .
be produced by the following methods. In a first method, a C6-C~0 ~-olefin monomer is polymerized with a C2-Cs ~-olefin monomer and a non-conjugated polyene 5 selected from 1) a linear or branched polyene having 5 to 18 carbon atoms, 2) a monocyclic polyene having 6 to 20 or more carbon atoms, or 3) a polycyclic polyene having 7 to 20 or more carbon atoms, using a Z-N
catalyst to produce a terpolymer containing ethylenic 10 unsaturation. In the terpolymer produced by this first method, M3 of formula I, has, for example, structures such as III, IV and V (below) when the diene is linear, and structures such as VI, VII, and VIII (below) when the diene is cyclic, ~H2~ ~H2~ H2~
(~) s(CH2) t CH3 IlH CH/

m IV v :;
' ' :

--CH2-~H ~ CH--CH - ---CH-CH

N~C ~CH~HC = CU ~2 VI VII vm 2 1 1 ~ r~ 7 9 ' -- 1 1 -- , wherein s is an integer from 1 to 14, preferably 2 to 4, and t is an integer from 1 to 14, preferably 2 to 4.
A second method involves the steps of~
a. polymerizing a C6 to C~0 ~-olefin monomer with at least one lower ~-olefin monomer using a -~
Z-N catalyst to produce a saturated homopolymer or a copolymer, b. reacting the resulting ~-olefin polymer with maleic anhydride in the presence of an initiator such as a peroxide and preferably an electron donor (e.g., triphenyl phosphite or triethyl phosphate) to produce a maleated ~-olefin polymer adduct, c. reacting the maleated ~-olefin polymer adduct with an ethylenically-unsaturated primary amine or isocyanate having 3 to 20 carbon atoms, either in solution or in a melt, (e.g., in an extruder) to produce an ethylenically-unsaturated ~-olefin polymer, and d. optionally, adding an effective amount of a photoactive crosslinking agent.
In the resulting ~-olefin polymer, M3 of Formula I has structures such as IX and X.
Alpha-olefin monomers that can be used in the preparation of the ethylenically-unsaturated ~-ole~in polymers of the present invention can have from 2 to 20 carbon atoms. Representative examples include, but are not limited to, ethylene, propylene, l-butene, 1-30 pentene, 1-hexene, 1-heptene, 1-octene, and 1-tetradecene; branched olefins such as 3-methyl-1-butene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, and 3-ethyl-1-pentene; cyclic olefins such as cyclopentene, cyclohexene, 3-methylcyclopentene, 4-n-35 butylcyclohexene, bicyclo[2.2.1]hept-2-ene, 1,7,7-trimethylbicyclo[2.2.1]hept-2-ene (bornylene) bicyclo[3.2.0]hept-2-ene, bicyclo[3.2.0]hept-6-ene, ::

2~18 ~719 ~ - 12 -., CH3 C4~ ~
`
HC~-CH~ HC--CH~2 0~ /C=O ~ /C=O
\N \N/
/ ~ \

H2 HC\\ / ~2 X

bicyclo[2.2.2]oct-2-ene, and bicyclo[3.2.2]non-6-ene; ~-and aromatic olefins such as allylbenzene, lH-indene, ;
3-methyl-lH-indene, and styrene.
Non-conjugated dienes that can be used in the 5 preparation of the ~-olefin polymers of the present invention have 5 to 20 carbon atoms. Representative examples include, but are not limited to, 1,4~
pentadiene, 1,5-hexadiene, ~,6-heptadiene, 1,7-octadiene, and 1,13-tetradecadiene; cyclic dienes such 10 as 1,4-cyclohexadiene, bicyclo[2.2.1]hept-2,5-diene, bicyclo[2.2.2~oct-2,5-diene, ;
bicyclo[2.2.2]oct-2,6-diene, 1,7,7-trimethylbicyclo[2.2.1~hept-2,5-diene, 5-allylbicyclo[2.2.1]hept-2-ene, and 15 1,5-cyclooctadiene; and aromatic dienes such as bis(~-alkenyl)benzenes such as 1,4-diallylbenzene, and 4-allyl-lH-indene.
Suitable polyene monomers useful in the practice of the present invention are comprised of hydrocarbons 20 containing two to four ethylenically unsaturated 2 1 1 8 7 7 9 : :

groups. 5-ethylidene-2-norbornene, dicyclopentadiene, limonene, beta-pinene, methylene-norbornene and various alkenyl-norbornenes with the structure:

~ ~ )mCH=CH2 10 where m is an integer from l to 18.
Other suitable polyene monomers useful in the practice of the p~esent invention~are diallyl ether, di(3-butenyl) ether, 4-(2-propenyl)-1-benzene, diallylbenzene, 3-butenylethenyldimethylsilane, 15 dimethyldi(2-propenyl)silane, tetra(3-butenyl)silane, tetravinylsilane, diethenyldimethylsilane, di(3-butenyl) dimethylsilane, di(3-butenyl)-dimethoxysilane and diethenyldiethoxysilane.
The ~-olefin polymers of the present invention can 20 be either random co-, ter-, tetra-polymers; or blocks of homopoly(~-olefins) interspersed with polyene units, depending upon the relative reactivities of the various monomers. When the reactivity at each end of the alpha, omega dienes are about equal, gel-permeation 25 chromatographic analysis (with low-angle light scattering detector) of polymers containing these monomers show more branching than observed with monomers having double bonds of unequal reactivity. -~ ;
When diene monomers in which the reactivities of the 30 double bonds are unequal are polymerized, as i6 the case with 7-octenyldimethylvinylsilane, essentially linear polymers are formed during ZN polymerization.
The unsaturated ~-olefin polymers of the present invention preferably have a T~ in the range of from ~-35 about -70C to about 0C and more preferably, in the range of from about -60C to about -10C. Also, the IV
of the unsaturated copolymers preferably range from ".~ :: :~ . : . . .. : , , ~ , , .

about 0.5 to 9.0 dl/g, more preferably from about 0.5 to 6.0 dl/g. The number average molecular weights of the copolymers are preferably in the range of 50~000 to 5,000,000, more preferably in the range from about 5 50,000 to 3,000,000.
The ~-olefin and polyene monomers can be polymerized in the presence of Ziegler-Natta catalysts over a wide range of temperatures, e.g., 0 to 140C, preferably 30 to 90C. The polymerization can be done 10 in bulk or in inert solvents. Suitable examples of inert solvents include, but are not limited to, the aliphatic, aromatic, and cycloaliphatic hydrocarbon solvents, i.e., pentane, hexane, heptane, benzene, toluene, cyclopentane, and cyclohexane. The amount of 15 catalyst used is preferably in the range of 0.1 g to 5 g per kg of monomer, more preferably 0.2 to 3 g per kg of monomer, and most preferably, 0.5 to 2 g per kg of monomer. ZN catalysts are well known in the art and are disclosed, for example, in Odian, G., supra. and 20 Boor, J., supra.
Suitable photo crosslinking agents for use in the compositions of the invention, which are free of elemental sulfur include, but are not limited to~
:: .: .
aldehydes, such as benzaldehyde, acetaldehyde, and 25 their substituted derivatives; ketones such as acetophenone, benzophenone and their substituted derivatives; quinones such as the benzoquinones, anthraquinone and their substituted derivatives;
thioxanthones such as 2-isopropylthioxanthone and 2-30 dodecylthioxanthone; and certain chromophore-substituted vinyl halomethyl-sym-triazines such as 2,4-bis-(trichloromethyl)-6-(3',4'-dimethoxyphenyl)-sym-triazine. The concentration of photoactive crosslinking agent is in the range of 0.05 to 6.0% (by 35 wt.), preferably 0.1 to 2% (by wt.), and more preferably 0.5 to 1.5% (by wt.).

~ll877y The adhesive composition of the present invention can be coated from solution by any of the coating processes known in the art, such as knife coating, roll coating, gravure coating, curtain coating, etc. Useful 5 coating thicknesses for the present invention are in the range of 0.5 to 15 mg/cm2, preferably from 2.0 to 7.0 mg/cm2. Furthermore, some of the compositions of the invention can be applied by extrusion coating with no solvent present, thereby eliminating environmental 10 and toxicity problems associated with solution coating processes.
In addition, the adhesive composition can be cured using a source of actinic radiation of sufficient energy (i.e., wavelength range) to generate free 15 radicals when incident upon the particular photoactive crosslinking agent selected for use in the composition.
The preferred wavelength range for the photoactive crosslinking agents disclosed above is 400 to 250 nm.
The radiant energy in this preferred range of -~
20 wavelengths required to crosslink the adhesive film of the invention is 100 to 1500 mJ/cm2, more preferably 200 to 800 mJ/cm2. Additional details of the photocure process are disclosed in U.S. Patent Nos. 4,181,752 and 4,329,384.
The adhesive compositions of the present invention, with or without a photoactive crosslinking agent, may be cured by electron beam irradiation.
The crosslinked adhesive films preferably have a ~
gel content in the range of from 2 to 95% thy wt.) ~;
30 percent, more preferably from 30 to 80% tby wt.), and most preferably from 50 to 70% tby wt.) when the gel content has been corrected for soluble tackifying resins and other additives as hereinafter described.
Adding one or more tackifying resins to the 35 inventive composition can provide a PSA having improved tack, lower viscosity, improved coatability, good heat stability, and improved peel adhesion. The shear ~ 18779 - 16 ~
adhesion of the tackified compositions can be enhanced by radiation cure with no loss of peel adhesion. The resulting adhesives have the high internal or cohesive strength required for box cealing tape or masking tape 5 applications.
Compatible tackifying resins useful in the radiation curable adhesive compositions of the invention include resins derived by polymerization of C5-C9 unsaturated hydrocarbon monomers, polyterpenes, 10 synthetic polyterpenes, and the like. Hydrocarbon tackifying resins can be prepared by polymerization of -monomers consisting primarily of olefins and diolefins and includ~, for example, residual byproduct monomers of the isoprene manufacturing process. These ;;
15 hydrocarbon tackifying resins typically exhibit Ball and Ring Softening Points (ASTM D465-s9) of from about 80C to 145C; acid numbers of from about o to 2, and saponification values of less than one.
Examples of such commercially available resins 20 based on a C5-C9 olefin fraction of this type are WingtackTM 95, WingtackTM 115 and WingtackTM Plus tackifying resins (Goodyear Tire and Rubber Co.; Akron, OH); RegalrezTM 1078 and RegalrezTM 1126 reins (Hercules Chemical Co. Inc., Wilmington, DE); Arkon resins, such 25 as ArkonTM P115 (Arakawa Forest Chemical Industries;
Chicago IL); and EscorezTM resins (Exxon Chemical Co.;
Newark, NJ).
Other suitable resins include the terpene polymers ! such as polymeric resinous materials obtained 30 by polymerization and/or copolymerization of terpene hydrocarbons such as their mixtures, including carene, isomerized pinene, terpinene, terpentene, and various other terpenes. Commerically available resins of the terpene type include the ZonarezTM B and 7000 terpene 35 series (Arizona Chemical Corp., Wayne, NJ). Typical properties reported for the ZonarezTM terpene resins include Ball and Ring Softening of less than one, and . :, , :

211~'~79 Saponification Numbers (ASTM D464-59) of less than one.
The terpene resin used in examples below is a poly(beta-pinene) resin, PiccolyteTM A115 (Hercules Chemical Co. Inc.), which has a Ball and Ring Softening 5 Point of 115C, an Acid Number 4 of one, and Iodine Number 4 of 190.
The tackifying resins may contain ethylenic unsaturation; however, saturated tackifying resins are preferred for those applications where oxidation 10 resistance is important. The total amount of tackifying resins in the composition ranges up to about 150 pbw, more preferably 5 to 50 pbw, and most preferably 25 to 35 pbw, per 100 pbw of polymer.
Saturated tackifying resins such as RegalrezTM 1078 and -~
15 ArkonTM P115 are preferred because they yield a higher gel content upon equivalent treatment by an activated ; ~
crosslinking agent. - ~ -Minor amounts of additives can also be included in the composition to provide adhesives for special end 20 uses. Such additives may include pigments, dyes, plasticizers, fillers, stabilizers, ultraviolet absorbers, antioxidants, processing oils, and the like.
The weight percentages of these additives can vary from 0.1 to 50% depending on the end use desired.
The adhesive composition of the present invention can be coated onto a wid~ range of substrate materials such as polymer films (e.g., polyethylene terephthalate (PET) and biaxially oriented polypropylene (BOPP));
woven and non-woven fabrics; metals and metal foils 30 such as aluminum, copper, lead, gold and the like;
paper; glass; ceramics; and composite materials comprised of laminates of one or more of these materials.
The present invention provides ~-olefin polymers 35 containing adhesive compositions that are radiation curable to yield adhesive films with an improved balance of peel adhesion and cohesive strength, ~118779 especially at elevated temperatures. The peel adhesion and cohesive strength values are capable of being varied independently to achieve desired values.
Adhesive films of the invention preferably have peel 5 values in the range of 2 to 100 N/dm and shear values in the range of 1 to 10,000 or more minutes.
The present invention provides PSA that have good cohesive strength at elevated temperatures. The PSA
tapes of the invention are ideally suited for 10 automotive masking tape applications as well as other ;
tape applications which require good cohesive strength at elevated temperatures and yet be readily removed from painted or other surfaces leaving essentially no adhesive residue.
Another embodiment of the invention comprises a laminated structure of at least a first and a second substrate, the substrates being joined by a layer of the adhesive composition of the invention. At least one of the substrates is capable of transmitting 20 actinic or electron beam radiation so that the adhesive film may be cured.
In some applications primers may be useful for improving the adhesion of the adhesive to some substrates. Useful primers for the practice of the 25 present invention include a triblock copolymer of styrene-ethylene/butylene-styrene grafted with maleic anhydride, both alone and in combination with amorphous polypropylene (such as are described in U.S. Patent Nos. 4,386,135, 3,957,724, and 2,532,011). These form 30 a special class of substrates on which the composition of the invention can be coated and subsequently radiation cured to form adhesive transfer films.
, TEST METHODS:
The test procedures used in the examples to evaluate and compare the properties of the PSA
compositions and tapes made from them are industry 211 ~779 -standard tests. These tests are described in detail in various publications of the American Society for -Testing Materials (ASTM) (Philadelphia, PA) and the Pressure Sensitive Tape Council (PSTC) (Glenview, IL).
5 References to these standards are also given.
Shear Stren~th (ASTM D-3654-78: PSTC-7) -Shear strength is a measure of the cohesiveness or internal strength of an adhesive. It is based upon the ~-amount of force required to pull an adhesive strip from 10 a standard flat surface in a direction parallel to the surface to which it has been affixed with a definite -~
pressure. It is measured in units of time(minutes) required to pull a standard area of PSA coated sheet - -material from a stainless steel test panel under stress 15 of a constant, standard load.
The tests were conducted on adhesive coated strips applied to a stainless steel panel such that a 12.7 mm by 12.7 mm portion of each strip was in firm contact with the panel with one end portion of the tape being 20 free. The panel with coated strip attached was held in a rack such that the coated surface of the panel forms an angle of 182 with the vertical tape free end which is then tensioned by application of a force of one kilogram applied as a hanging weight from the free end 25 of the coated strip. The 182 angle is used to negate peel forces thus insuring that only the shear forces are measured, thereby more accurately determining the holding power of the tape being tested. The time elapsed for each test specimen to separate from the 30 steel panel is recorded as the shear strength.
Mode of Failure (MOF) ;
The time at which the mass falls is called "Shear Test" and is reported as "5000+" if the tape has nok failed after 5000 minutes. With each Shear is 35 indicated the mode of failure as follows:
po = pop-off, i.e., 75-100~i adhesive failure from steelplate:
-Y, , , - - , - ., . -.. ,, . . ,, . , .. ~ .. ,. . ,,, , ,,, ~, ,.,, ,, ~ .

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2~1~779 f = cohesive failure (both surfaces completely ~-covered by adhesive);
The pop-off failure mode is preferred because it -is indicative of adhesive failure of the adhesive/steel 5 interfacial bond as opposed to cohesive failure of the adhesive. Adhesives of various shear adhesions, all within the range of the present invention (1 to 10,000 minutes), are preferred depending on end-use applications.
Two specimens of each tape were tested and the shear tests were averaged to obtain the shear value.
Peel Adhesion ~ASTM D 3330-78: PSTC-1(11/75~]
Peel adhesion is the force required to remove a PSA coated test specimen from a test panel measured at 15 a specific angle and rate of removal. In the examples, this force is expressed in Newtons per decimeter (N/dm) width of coated sheet. The procedure followed is:
(1) A 25.4 mm x 150 mm test specimen was applied to a horizontally positioned clean glass test plate 20 such that 12. 7 mm of the specimen extended beyond the plate. A 2. 3 kg rubber roller was rolled over the test specimen twice to insure good contact between the specimen and the test plate.
(2) The free end of the specimen is doubled b~lck 25 nearly touching itself so the angle of removal is 1~0.
The free end is attached to the adhesion tester scale.
(3) The glass test plate is clamped in the jaws of tensile testing machine which is capable of moving the plate away from the scale at a constant rate of 2.3 30 meters per minute.
(4) The scale reading in Newtons is noted as the tape is peeled from the glass surface, and the average, peak, and vall~y reading from the entire length of peeled tape specimén are recorded.

2 ~ r~ 9 Inherent Viscosity [ASTM D 2857-70 (Reapproved -1977)~
In order to understand the benefits derived from the teaching of this invention, it is necessary to 5 relate the improvements in shear strength and processability to the molecular weight of the PSA. The inherent viscosity of 10 ml sample of a 0.5 g/dl solution of the sample in toluene is measured using a Cannon-Fenske #50 viscometer in a water bath controlled 10 at 25C. The solvent used is specified in the examples.
. :-Percent Gel Test [ASTM D 3616-821 The percent gel is used as an indication of cure level. The tapes containing tackifying resins are 15 corrected to the actual percent gel. The corrected percent gel is 100 times the gelled mass divided by the total mass of material that is capable of forming a gelled network. Soluble materials such as tackifiers are subtracted out when determining the gel fraction.
Crosslinking by radiation improves the creep and ~;
shear resistance of pressure-sensitive adhesives.
Many important properties of crosslinked PSAs vary with the gel content. Hence, determination of the gel content provides a means for controlling the proce~;s 25 and thereby raising the quality of the tape.
Extraction tests permit verification of the proper gel content of polyolefin PSAs and they also permit comparison between different crosslinked adhesives and their speci~ic end uses.
Gel Content Determination A square test specimen (3.81 cm x 3.81 cm) containing approximately 0.06 g of PSA is cut from the tape and placed in a 120-mesh stainless steel basket measuring approximately 4.4 x 4.4. x 1.3 cm. The 35 contents are weighed to the nearest 0.1 mg and then immersed in a capped beaker containing sufficient toluene to cover the specimen. After extraction for 24 ~" 2ll8779 - 22 - ~-to 48 hours, the basket (containing the specimen) is removed, drained, and placed in an oven at 93C. The basket and specimen are dried to a constant weight and the gel content is determined as follows:
5 Extract ~ = weiqht lost durina extraction x loo weight of original specimen Gel content = 100 - percent extract The gel content of the adhesive was determined after 10 correcting for the tackifier. (and backing for a tape construction).
Two specimens of each tape were tested and the results were averagsd to obtain the gel content value.
Percent Residue Test An aluminum panel painted with an automotive basecoat/clearcoat (BC/CC) acrylic enamel paint system or the automotive 50J~ acrylic enamel paint (Ford Motor Co.; Detroit, Mi) is used as a test panel for the percent residue test. -Tapes are applied at room temperature to the test surface followed by rolling the test specimen with two passes of a 2 Kg rubber-coated metal roller. After one hour in an air-circulating oven at either 121C or 150C, the tape is peeled back, while hot, at an angle 25 of 135 at an approximate rate of 1.9 m/min across half of the panel. Thereafter, the test panel is allowed to cool to room temperature and the tape samples are peeled from the remainder of the test panel at an angle of 45 peel and a rate of approximately 1.9 m/min. The 30 panel is then visually examined for any adhesive residue.
This invention is further illustrated by the following examples of preferred embodiments thereof, although it will be understood that these examples are 35 included merely for purposes of illustration and are not intended to limit the scope of the inventio~ unless otherwise specifically indicated.

2~18779 :.

Unsaturated ~-olefin copolymers -l-Hexene/propylene/4-vinylcyclohex-1-ene copolymer ru-l ) A reaction vessel equipped with a mechanical 5 stirrer, reflux condenser and temperature controller was dried and filled with nitrogen. The vessel was charged with 300 ml 1-hexene, 300 ml toluene, 7.5 ml 4-vinylcyclohex-1-ene, and 1.1 ml diethyl aluminum chloride. The reactor was heated to 60C, 0.21 g 10 Aluminum Activated Reduced titanium trichloride, AATiCl3 (Stauffer Chemical Co.; Hartford, CT) was introduced, and propylene was bubbled into the reaction mixture at a rate of about 60 cm3/min for about 2 hours. Methanol was added to the reaction mixture to terminate the 15 polymerization. The reactor was cooled to room temperature, excess methanol was added to precipitate the polymer, and the precipitated polymer was washed twice with methanol.
Reaction product of maleated ~olyolefin (NPO~ and isocyanatoethyl methacrylate (U-2) 52.0 g of 1.2 mole percent maleated hexene/propylene (60/40) copolymer having a melt viscosity of 7680 cp at 190C (available from Eastman Chemical Co. as TX-P1824-013) was dried in a vacuum at 25 70C for about 16 hours and dissolved in 250 ml toluene. The solution was refluxed under nitrogen, and about 50 ml toluene was distilled out to ensure recyclization of diacid grafts and to remove residual water in the polymer. To this was added 0.63 g 30 isocyanatoethyl methacrylate (IEM), and the reaction mixture was gently refluxed ~or about 3 hours. IR ~ -analysis showed that all isocyanate groups were consumed indicating completion of the reaction. The ~ -copolymér was concentrated to a viscosity suitable for 35 coating on PET backing (approximately 25 to 30%
solids).

-............................................. , 2118779 Reaction product of MPO and isocyanatoethyl methacrvlate (U3) 53 g of 2.6 mole percent maleated hexane/propylene (60/40) copolymer having a melt viscosity of 9840 cp at 5 190C (available from Eastman Chemical Co. ais TX-1768-85) was dissolved in 250 ml toluene. The solution was refluxed under nitrogen, and about 50 ml toluene was distilled to ensure recyclization of the acid grafts and to remove residual water in the polymer. To this 10 was added 2.03 g of isocyanatoethyl methacrylate (IEM), and the reaction mixture gently refluxed for about 3 hours. Progress of the reaction was monitored as described above. The copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30 percent solids).
Reaction ~roduct of MP0 and 4-aminostyrene (U4) 17 g of 4.4 mole percent maleated hexene/propylene (60/40) copolymer having melt viscosity 4700 cp at 190C (available from Eastman Chemical Co. as TX P1824-20 011) was dissolved in 150 ml toluene. The polymersolution was refluxed under nitrogen and about 20 ml toluene was distilled out to ensure recyclization of the acid grafts and to remove residual water from the polymer. To this was added 1.24 g of 4-aminostyrene (PAS), and the mixture was gently refluxed for about 3 hours. Progress of the reaction was monitored as described above. The copolymer was concentrated to a viscosity suitable for coating on PET backing (approximately 25 to 30% solids).
Reaction product of MPO and 4-aminostyrene (U5) 15 g of 4.4 mole percent maleated hexene/propylene (60/40) copolymer as described in the preparation of U4 was dissolved in 150 ml toluene. The solution was refluxed under nitrogen to ensure recyclization of the 35 acid grafts and about 20 ml toluene was distilled out ;
to remove residual water in the polymer. To this was added 0.53 g of PAS, and the reaction mixture gently ~ ;
'''",' , ' ' ' - 2118779 ~ :

refluxed for about 3 hours. Progress of the reaction was monitored as described above. TXe copolymer was concentrated to a viscosity suitable for coating on PET
backing (approximately 25 to 30% solids). --~
Reaction product of MPO and 4-aminostyrene (U6) 16.7 g of 4.4 mole percent maleated ~, hexene/propylene (60/40) copolymer as described in the ~
preparation of U4 was dissolved in 150 ml toluene. The - , solution was refluxed under nitrogen, and about 20 ml 10 toluene was distilled out to ensure recyclization of the acid grafts and to remove residual water in the polymer. To this mixture was added 0.30 g of PAS, and the reaction mixture was gently refluxed for about 3 hours. Progress of the reaction was monitored as 15 described above. The copolymer was concentrated to a viscosity suitable for coating on PET backing - ~ '' (approximately 25 to 30% solids).
Reaction product of MP0 and allylamine (U7) 27.1 g o~ 4.4 mole percent maleated 20 hexene/propylene (60/40) copolymer as described in the preparation of U4 was dissolved in 150 ml toluene. The solution was refluxed under nitrogen to recyclize the acid,grafts, and about 20 ml toluene was distilled out to remove residual water in the polymer. To this was 25 added 0.94 g of allyl amine, and the reaction mixture gently refluxed for about 3 hours. Progress of the reaction was monitored as describ2d above. At the end of the reaction, the copolymer was concentrat~d to a , ' viscosity suitable for coating on PET backing (approximately 25 to 30% solids).

Examples 1-19 Pressure Sensitive AdhesiYes From Unsaturated Polyolefins Blends of 100 parts of unsaturated ~-ole~in ~
copolymers U-1, U-2, U-3, U-4, U-5, U-6, and U-7, with ' and without 33 phr (parts per 100 parts) by weight ~

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2ll8779 tackifier resin, 1.0 phr of photoinitiator, and 0.25 phr IrganoxTM 1010 photoinitiator in toluene were knife coated to yield a dry adhesive coating thickness of 38 ~m on a 57 ~m thick biaxially oriented poly(ethylene 5 terephthalate)(PET) film. Each coating was dried for 5 minutes at 70C and exposed to doses of 300 to 1200 mJ/cm2 from medium pressure mercury lamps. The compositions prepared and the test results obtained for each are recorded in Table I.
10 Comparative Examples C1, C2, C3, C4, C5, C6 and C7 Control PSA construction consisted of untackified and uncured samples of the unsaturated a-olefin polymers (U-1, U-2, U-3, U-4, U-5, U-6, and U-7, as previously described) which were solution coated onto a 15 57 ~m biaxially oriented PET film to produce dry PSA
films having a nominal thickness of 38 ~m. The coating conditions and subsequent test protocol was the same as described for Examples 1-19.

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The data in Table I reveals that unsaturated polyolefin PSA compositions containing propylene as the C2-Cs ~-olefin monomer, when irradiated with ultraviolet light, leave less than 5% residue in the Percent -~
5 Residue test and, particularly, that where the unsaturation is introduced into propylene-containing polyolefin by maleation followed by reaction with an amino or isocyanate group substituted unsaturated compound, excellent shear values at 25C are obtained 10 and less than 5% adhesive residue (in most cases no adhesive residue) is left in the Percent Residue Test.
The samples of the comparative examples leave 25 to 100% adhesive residue.
In summary, novel adhesive compositions have been :
15 described. Although specific embodiments and examples have been disclosed herein, it should be borne in mind that these have been provided by way of explanation and illustration and the present invention is not limited thereby. Certainly, modifications which are within the ~ -20 ordinary skill in the art are considered to lie within the scope of this invention as defined by the following claims including all equivalents.
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Claims (10)

1. A composition radiation curable to an adhesive comprising:
a. an .alpha.-olefin polymer comprising 45 to 98 mole percent of an ethanediyl repeat unit having a pendent hydrocarbyl group having 4 to 8 carbon atoms, from 1 to 40 mole percent of an ethanediyl repeat unit selected from ethylene and units having a pendent hydrocarbyl group having 1 to 3 carbon atoms, and from 1 to 15 mole percent of an ethanediyl repeat unit comprising an ethylenically-unsaturated group; and b. an effective amount of a photoactive crosslinking agent to crosslink the composition upon exposure to a source of actinic radiation.

2. The composition of claim 1 wherein the .alpha.-olefin polymer(s) has a Tg less than about 0°C.

3. The composition of claim 1 wherein the .alpha.-olefin polymer(s) has the general formula:
I
wherein:
x, y, and z are numbers designating the relative molar amounts of M1, M2, and M3 units that are randomly located in the backbone chain of the polymer such that the polymer has a weight average molecular weight in the range of 50,000 to 3.5 million, x is at least 45 mole percent of (x+y), y is from about 1 to 40 mole percent of (x+y) and z is 0.1 to 15 mole percent of (x+y+z).
M1, is an ethanediyl repeat unit having a pendent hydrocarbyl group having 4 to 8 carbon atoms;
M2 is an ethanediyl repeat unit, different from M1, selected from ethylene or units having a pendent hydrocarbyl group selected from linear and branched alkyl groups having 1 to 3 carbon atoms.
M3 is an ethanediyl repeat unit having a pendent, non-conjugated ethylenically-unsaturated aliphatic or aryl group selected from the group consisting of 1) linear and branched mono- and polyethylenically-unsaturated hydrocarbyl groups having 3 to 18 carbon atoms, 2) aryl groups substituted by mono- or polyethylenically-unsaturated groups having a total of 7 to 18 carbon atoms, and 3) cycloalkylene groups having 6 to 18 carbon atoms wherein the cyclic group has at least 6 carbon atoms in the ring, provided that the ethylenically-unsaturated moiety is not bonded directly to a backbone carbon atom.

4. The composition of claim 3 wherein the .alpha.-olefin polymers have the general formula:
II
wherein x, y, z' and z" are numbers designating the relative molar amounts of monomer units comprising the backbone chain of the polymer such that the polymer has a weight average molecular weight in the range of 50,000 to 3,500,000, x is at least 45 mole percent of (x+y), y is from about 1 to 40 mole percent of (x+y), and (z'+z") is 0.1 to 15 mole percent of (x+y+z'+z") and either of z' or z" can be zero; z of Formula I
equals (z'+z") of Formula II;
R1 is an alkyl group having 4 to 8 carbon atoms;
R2 is hydrogen or a hydrocarbyl group, preferably selected from linear and branched alkyl groups having 1 to 3 carbon atoms;
R3 is an unsaturated aliphatic hydrocarbyl group having 3 to 18 carbon atoms, the unsaturated group of which is separated from the -?H-?H- of the .alpha.-olefin polymer backbone by at least one carbon atom, preferably selected from linear and branched alkenyl groups having 3 to 18 carbon atoms, non-conjugated polyethylenically-unsaturated aliphatic groups having 6 to 18 carbon atoms, cyclic alkenyl groups having 5 to 18 carbon atoms, and cyclic non-conjugated polyethylenically-unsaturated groups having 6 to 18 carbon atoms, or R3 can also be -Q-R7, wherein R7 is a C2 to C10 monovalent hydrocarbyl group containing one or more ethylenically unsaturated groups and Q is a divalent radical, -O- or wherein R8 and R9 are the same or different C1 to C12 monovalent organic groups selected from alkyl, cycloalkyl, alkaryl, alkoxy, and aryloxy groups; and R4 is hydrogen or R4 together with R3 and the carbon atoms to which they are attached forms an unsaturated or non-conjugated polyunsaturated monocyclic ring system having 6 to 18 carbon atoms, the unsaturated groups of which are separated from the -?H-?H- of the .alpha.-olefin polymer backbone by at least one carbon atom;
R5 is hydrogen or a linear or branched alkyl group having 1 to 18 carbon atoms or cyclic alkyl group having 5 to 18 carbon atoms; and R6 is a linear or branched ethylenically- or non-conjugated polyethylenically-unsaturated aliphatic hydrocarbon group having 3 to 18 carbon atoms, or a cyclic ethylenically or non-conjugated polyethylenically-unsaturated aliphatic hydrocarbyl group having 5 to 18 carbon atoms.

5. The adhesive composition of claims 1 to 4 wherein said photoactive crosslinking agent is selected from the group consisting of aldehydes, ketones, quinones, thioxanthones and s-triazines.

6. The adhesive composition of claims 1 to 5 further comprising a tackifying resin.

7. The adhesive composition of claims 1 to 6 wherein said composition has been crosslinked.

8. An article comprising the adhesive composition of claim 1 coated on a substrate, said composition optionally being crosslinked.

9. A method of preparing a radiation cured adhesive composition comprising the steps:
a. providing one or more C6-C10 .alpha.-olefin monomers, one or more C2-C5 .alpha.-olefin monomers, and at least one non-conjugated polyene monomer selected from the group consisting of 1) a linear or branched polyene having 5 to 18 carbon atoms, 2) a monocyclic polyene having 6-20 or more carbon atoms, 3) a polycyclic polyene having 7 to 20 carbon atoms or a combination of one or more of the foregoing;
wherein said resultant polymer comprises 45 to 98 mole percent of C6-C10 .alpha.-olefin repeat units, 1 to 40 mole percent C2-C5 .alpha.-olefin repeat units and 1 to 15 mole percent non-conjugated polyene repeat units; and then adding an effective amount of a photoactive cross-linking agent; and b. subjecting the admixture to sufficient actinic radiation to provide a cross-linked polymer.

10. A method of preparing a radiation curable adhesive composition comprising the steps of:
a. polymerizing a C6-C10 .alpha.-olefin monomer with at least one lower .alpha.-olefin monomer using a Ziegler-Natt catalyst to produce a saturated homopolymer or a copolymer, b. reacting the resulting .alpha.-olefin polymer with maleic anhydride in the presence of an initiator such as a peroxide and preferably an electron donor (e.g., triphenyl phosphite or triethyl phosphate) to produce a polyolefin adduct, c. reacting the maleated .alpha.-olefin polymer adduct with an ethylenically unsaturated primary amine or isocyanate having 3 to 20 carbon atoms, and d. optionally, adding an effective amount of a photoactive cross-linking agent.