Blends of ethylene-vinyl acetate copolymer rubbers with elastomers

The Mooney viscosity and green strength of ethylene-vinyl acetate (EVA) copolymer gum stock is improved by the addition thereto of a suitable elastomer such as: high viscosity ethylene propylene rubber (EPR); nitrile rubber; polychloroprene; polyacrylate rubber; polyurethane; chlorinated polyethylene; polyester; ethylene-propylene diene monomer (EPDM) terpolymer; and other elastomers such as ethylene-methyl acrylate, ethylene butyl acrylate and acrylonitrile types.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the field of polymer blends, or alloys, and in 
particular, this invention relates to blends of rubbery EVA copolymer and 
at least one other elastomer. 
2. Description of the Prior Art 
EVA copolymers constitute a well-known class of synthetic resins 
demonstrating a broad range of properties depending upon the relative 
quantities of copolymerized ethylene and vinyl acetate (and other 
ethylenic monomers which may be present) in the copolymer chain. Rubbery 
amorphous EVA gum stocks contain from about 40% to about 70% vinyl acetate 
by weight randomly distributed throughout the copolymer chain and, when 
crosslinked, for example, by a peroxide crosslinking agent, possess 
properties which make them especially useful as elastomers for rubber 
compounding, as base copolymers for adhesive formulations and as impact 
modifiers for polyvinyl chloride (PVC). Among the physical and chemical 
properties which make the rubbery EVA copolymers attractive for such 
applications are the following: heat aging resistance; oil and solvent 
resistance; low compression set; good low temperature performance; 
excellent weatherability and ozone resistance; resistance to natural 
light; transparent or white-to-black vulcanizates; high loadability; 
receptance to dielectric heating; and high dampening characteristics. 
Thus, the rubbery EVA copolymers are excellent candidates for such 
automotive applications as gaskets, seals and O-rings, wire insulation, 
radiator tubing and hose, bumper strips and auto body filler panels and 
are ideal for other demanding applications as well such as machinery 
mounts, weather stripping, washing machine hose, refrigerator gaskets, 
hydraulic hose, and the like. 
It has been observed that, as synthesized by the high pressure process, the 
ethylene-vinyl acetate copolymers of this invention exhibit Mooney 
viscosities of only about 8-12, and although it has been found that these 
values can be approximately doubled by a suitable thermal working process 
(U.S. Pat. No. 3,968,091) the resulting worked gum stocks are still 
deficient in Mooney viscosity and green strength for many applications in 
the rubber industry. Accordingly, successful processing of EVA gum stocks 
of from about 40% to about 70% copolymerized vinyl acetate by weight 
requires that the Mooney viscosity and green strength be suitably 
increased, without, however, detracting to any appreciable extent from the 
desirable characteristics of rubbery EVA copolymers enumerated above. 
While it is known that EVA copolymers and graft copolymers of EVA with 
another monomer such as vinyl chloride can be blended with one or more 
other elastomers (cf. U.S. Pat. Nos. 3,282,035; 3,322,858; 3,361,850; 
3,361,852; 3,374,198; 3,422,055; 3,549,727; 3,600,461; 3,644,577; 
3,718,711; 3,758,661; 3,808,047; 3,821,333; 3,941,859; and 4,102,855), 
heretofore there has been no recognition or appreciation that the Mooney 
viscosity and green strength of EVA gum stocks containing from about 40% 
to about 70% vinyl acetate by weight can be significantly increased upon 
the addition of certain elastomers as hereinafter described. 
SUMMARY OF THE INVENTION 
It has now been discovered that the addition of from about 10% to about 40% 
by weight of an elastomer having a Mooney viscosity within the range of 
from about 65 to about 115 ML.sub.1+4 at 100.degree. C. to from 90% to 
about 60% by weight of an amorphous EVA gum stock containing from about 
40% to about 70% copolymerized vinyl acetate by weight results in a 
significant increase in Mooney viscosity and green strength of the EVA gum 
stock without negatively affecting the physical and chemical properties of 
the EVA copolymer in any appreciable way. 
The improved EVA rubbers of this invention can be easily processed 
employing known and conventional machinery and techniques and are suitable 
for injection molding, compression molding, transfer molding and profile 
extrusion. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The useful EVA gum stocks herein contain from about 40% to about 70% 
copolymerized vinyl acetate by weight and are amorphous in nature, and the 
constituent monomers are randomly distributed throughout the copolymer 
chain. The most significant improvement in Mooney viscosity and green 
strength in accordance with this invention is achieved with EVA gum stocks 
having a vinyl acetate content of from about 50% to about 60% by weight. 
In addition to the two principal monomers, ethylene and vinyl acetate, the 
EVA gum stocks of this invention can contain small quantities, generally 
not exceeding about 10% by weight, of one or more other ethylenically 
unsaturated monomers copolymerizable therewith. Examples of such monomers 
include (meth) acrylate ester, e.g., ethyl acrylate, butyl methacrylate, 
2-hydroxy ethyl acrylate, and the like; vinyl esters, e.g., vinyl 
stearate, vinyl versatate, vinyl benzoate, and the like; vinyl ethers, 
e.g., ethyl vinyl ether, hexyl vinyl ether, and the like; and, carbon 
monoxide. The preferred EVA gum stocks herein are the VYNATHENE.RTM. 
resins (U.S. Industrial Chemicals Co., Division of National Distillers and 
Chemical Corporation) whose typical physical properties are given in Table 
I as follows: 
TABLE I 
______________________________________ 
Typical Physical Properties of VYNATHENE EVA Elastomers 
(Raw Gum Stock) 
EY 903 EY 904 EY 906 HY 907 
______________________________________ 
Vinyl acetate content 
45% 52% 55% 60% 
Density 0.948 0.986 1.00 1.02 
Mooney Viscosity 
(ml 1 + 4 at 100.degree. C.) 
20 20 20 20 
Color Water Water Water Water 
White White White White 
Form Pellets Pellets Slabs Slabs 
Volatiles Less than 
Less than 
Less than 
Less than 
0.3% 0.3% 0.3% 0.3% 
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As previously stated, from about 60% to about 90% by weight of EVA gum 
stock is blended with from 40% to about 10% by weight of at least one 
other elastomer having a Mooney viscosity of from about 65 to about 115 
ML.sub.1+4 at 100.degree. C. Examples of elastomers which are useful for 
addition to EVA gum stock to improve the Mooney viscosity and green 
strength of the latter are high viscosity ethylene propylene rubber (EPR); 
polychloroprene; polyacrylate rubber; polyurethane; chlorinated 
polyethylene; polyester; ethylene-propylene diene monomer (EPDM) 
terpolymer; acrylate copolymers such as ethylene-methyl acrylate and 
ethylene-butyl acrylate copolymers and acrylonitrile. The foregoing 
elastomers can be prepared to include additional quantities of other 
copolymerizable monomer as long as the Mooney viscosity of the resulting 
resins do not exceed the range, supra. 
Increases of as little as 10% over the original Mooney viscosity of the 
unalloyed EVA gum stock result in an observable improvement in the 
processing characteristics of EVA rubbers. In accordance with this 
invention, the addition of an elastomer of the aforesaid type will provide 
at least about a 10% increase in Mooney viscosity and increases of nearly 
100% are readily attainable. 
To prepare the polymer blends of this invention, the EVA gum stock and 
modifying elastomer together with a crosslinking (vulcanizing) agent and 
optional ingredients such as fillers, antioxidants and any other known 
elastomer additives are combined in conventional mixing equipment, 
typified by a two roll rubber mill, a mixing extruder or, preferably, a 
high shear internal mixer such as a Banbury mixer, until a homogeneous 
blend is obtained. Upon completion of the mixing stage, the resin blend is 
processed into any of several forms convenient for subsequent 
manufacturing operations, for example, pellets formed by an underwater 
pelletizer, strand cut, etc. 
The crosslinking agents which can be used herein include such peroxides as: 
t-butyl perbenzoate, dicumyl peroxide; 2,5-dimethyl-2,5-di(t-butyl 
peroxy)hexane; 2,5-dimethyl-2,5-di(t-butyl peroxy)hexyne-3; 
1,3,5-tris[alpha,alpha-dimethyl-alpha-(t-butyl peroxy)]-methyl benzene; 
alpha,alpha'-bis(t-butyl peroxy)diisopropyl benzene; and, 
n-butyl-4,4-bis(t-butyl peroxy)valerate. These crosslinking agents can be 
used alone or in combination with any of several polyfunctional auxiliary 
crosslinking agents such as triallyl phosphate, trimethylol propane 
triacrylate; diallyl fumarate; triallyl cyanurate; triallyl isocyanurate; 
pentaerythritol tetraacrylate; trimethylol propane trimethacrylate; 
1,3-butylene glycol dimethacrylate; allyl methacrylate; ethylene glycol 
dimethacrylate; and, 1,3-butylene glycol diacrylate. A preferred curing 
agent for use herein is Vul-Cup 40 KE (40% alpha,alpha'-bis(t-butyl 
peroxy)diisopropyl benzene on Burgess KE obtained from Hercules Inc.) The 
amount of peroxide crosslinking agent can range from about 1.0 to about 
10.0 parts, and preferably from about 2.0 parts to about 5.0 parts per 
hundred parts of EVA copolymer. The polyfunctional auxiliary crosslinking 
agents are useful within the range of from about 0.1 to about 3.0 parts 
per hundred parts of EVA gum stock. 
Examples of fillers which can advantageously be employed herein are: Hydral 
710, an alumina trihydrate obtained from Alcoa; Hi-Sil EP and Hi-Sil 233, 
amorphous precipitated hydrated silicas obtained from PPG Industries, 
Inc.; Cab-O-Sil, a fumed silica obtained from Cabot Corporation; Mistron 
Monomix, a talc (magnesium silicate) from Cyprus Industrial Minerals 
Company; Burgess KE, a surface treated (silane) calcined kaolin clay 
(anhydrous aluminum silicate) obtained from the Burgess Pigment Company; 
and, antimony oxide. As is appreciated by those skilled in the art, the 
amounts of filler incorporated into a polymer blend of this invention will 
depend on the nature of the filler and the properties desired of the final 
product. Non-reinforcing fillers such as alumina trihydrate can be used in 
amounts ranging from about 5.0 parts to about 400.0 parts and preferably 
from about 100.0 parts to about 150.0 parts, per hundred parts of polymer 
blend. Reinforcing fillers such as hydrated silica, carbon black and 
sintered colloidal silica are useful in the range of from about 5 parts to 
about 100 parts per hundred parts of polymer blend but the useful upper 
range is limited by the high viscosity imparted by fillers of this type. 
The preferred amounts of these reinforcing fillers range from about 20 
parts to about 80 parts per hundred parts of polymer blend for hydrated 
silica and carbon black and from about 10 parts to about 50 parts per 
hundred parts of polymer blend for sintered colloidal silica. 
Any of several known and conventional antioxidants can be incorporated into 
the polymer blends herein at from about 0.1 parts to about 4.0 parts, and 
preferably at about 1.0 part, per hundred parts of resin. Agerite MA (R. 
T. Vanderbilt Company, Inc.), a polymerized trimethyl dihydroquinoline 
antioxidant, has been used with good results.