Vinyl chloride resin elastomer composition

A vinyl chloride resin elastomer composition comprising, as main components, 100 parts by weight of a vinyl chloride resin, from 10 to 200 parts by weight of an acrylic rubber containing a tetrahydrofuran-insoluble cross-linking component, from 1 to 50 parts by weight of an acrylic resin and from 30 to 300 parts by weight of a plasticizer.

The present invention relates to a vinyl chloride resin elastomer 
composition excellent in compression set, creep resistance, weather 
resistance, tear strength and thermal aging resistance, which is useful 
for gaskets, for which airtight sealing properties are required, for 
example, for application to automobiles, such as weather strips, glass 
runs, packings for trunks or roofmoles, or for application to electrical 
equipments or buildings, such as packings or joint filling materials. 
With respect to elastomer materials, there has been an increasing demand 
for improvement of their properties year by year. Particularly, in the 
field of automobiles, excellent compression set is demanded for materials 
of e.g. glass runs and weather strips. 
Heretofore, soft vinyl chloride resins have been widely used as such 
materials, since they have flexible rubber-like texture and they are 
superior to vulcanized rubber in the moldability, weather resistance and 
tinting properties, and they have an advantage also from the viewpoint of 
costs. However, they are inferior to vulcanized rubber in the compression 
set, and their softening point is low, whereby their application for use 
at high temperatures has been limited. Under these circumstances, an 
attempt has been made for improvement by modifying the vinyl chloride 
resins to have high degrees of polymerization, but no satisfactory results 
have been obtained. 
A technique of improving the compression set by adding a partially 
cross-linked acrylonitrile-butadiene rubber (hereinafter referred to as 
NBR) is disclosed, for example, in Japanese Unexamined Patent Publications 
No. 115342/1981 and No. 187341/1982. However, such a technique employs NBR 
as the rubber component and thus has a drawback that the composition is 
poor in the weather resistance and is not durable for use for a long 
period of time. 
The above-mentioned Japanese Unexamined Patent Publication No. 115341/1981 
discloses use of an acrylic rubber, and Japanese Unexamined Patent 
Publication No. 256554/1989 discloses a composition comprising a vinyl 
chloride resin, an acrylic rubber containing a component insoluble in 
tetrahydrofuran (hereinafter referred to as THF), and a plasticizer, for 
the purpose of improving a high temperature shape-maintaining property and 
weather resistance. However, such a composition has had drawbacks that, 
when used for a long period of time, it is poor in the thermal aging 
resistance, and the tear strength is low, since the plasticizer is one 
commonly used, and no acrylic resin is incorporated. 
The present inventors have conducted an extensive research with an aim to 
obtain a composition excellent in thermal aging resistance and tear 
strength without impairing compression set, creep resistance and weather 
resistance with an elastomer composition comprising, as the main 
components, a vinyl chloride resin, a rubber material and a plasticizer. 
As a result, they have found it possible to accomplish the above object 
with a composition having an acrylic rubber containing a THF-insoluble 
cross-linking component, an acrylic resin and a plasticizer having a 
relatively high weight average molecular weight incorporated to a vinyl 
chloride resin. The present invention has been accomplished on the basis 
of this discovery. 
Namely, it is an object of the present invention to provide a vinyl 
chloride resin elastomer composition excellent in various physical 
properties such as compression set, creep resistance, weather resistance, 
thermal aging resistance and tear strength. 
The present invention provides a vinyl chloride resin elastomer composition 
comprising, as main components, 100 parts by weight of a vinyl chloride 
resin, from 10 to 200 parts by weight of an acrylic rubber containing a 
tetrahydrofuran-insoluble cross-linking component, from 1 to 50 parts by 
weight of an acrylic resin and from 30 to 300 parts by weight of a 
plasticizer, and a method for its production. 
Now, the present invention will be described in detail. 
The vinyl chloride resin as the main resin component of the elastomer 
composition of the present invention may be any resin produced by 
subjecting vinyl chloride, or a mixture of vinyl chloride with a comonomer 
copolymerizable therewith to a conventional polymerization method such as 
suspension polymerization, bulk polymerization, microsuspension 
polymerization or emulsion polymerization. The comonomer may, for example, 
be a vinyl ester such as vinyl acetate, vinyl propionate or vinyl laurate, 
an acrylic acid ester such as methyl acrylate, ethyl acrylate or butyl 
acrylate, a methacrylic acid ester such as methyl methacrylate or ethyl 
methacrylate, a maleic acid ester such as dibutyl maleate or diethyl 
maleate, a fumaric acid ester such as dibutyl fumarate or diethyl 
fumarate, a vinyl ether such as vinyl methyl ether, vinyl butyl ether or 
vinyl octyl ether, a vinyl cyanide such as acrylonitrile or 
methacrylonitrile, an .alpha.-olefin such as ethylene, propylene or 
styrene, a vinylidene halide or vinyl halide other than vinyl chloride, 
such as vinylidene chloride or vinyl bromide, or a polyfunctional monomer 
such as diallylphthalate or ethylene glycol dimethacrylate. The comonomer 
is of course not restricted to the above specific examples. The comonomer 
is used in an amount of not more than 30% by weight, preferably not more 
than 20% by weight, in the constituting components of the vinyl chloride 
resin. 
The average polymerization degree of the vinyl chloride resin is not 
particularly limited, but is preferably within a range of from 700 to 
8,000, more preferably from 1,000 to 4,000, most preferably from 1,300 to 
3,500, from the viewpoint of processability and moldability. 
The acrylic rubber contained in the elastomer composition of the present 
invention is a synthetic rubber containing an acrylic acid ester such as 
an alkyl acrylate or an alkoxyalkyl acrylate, as the main component. Such 
a synthetic rubber includes in its scope a copolymer comprising an acrylic 
acid derivative as the main component which is copolymerized with a 
functional monomer such as an alkyl methacrylate, acrylonitrile or a 
styrene. The acrylic rubber is required to contain a cross-linking 
component insoluble in tetrahydrofuran (THF). It preferably contains at 
least 30 wt %, preferably at least 50 wt %, of the cross-linking 
component. To introduce the cross-linking component to the acrylic rubber, 
a cross-linkable monomer such as divinylbenzene, ethylene glycol 
diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate or 
propylene glycol dimethacrylate, may, for example, be reacted. If the 
amount of the THF-insoluble cross-linking component is small, the 
compression set property of the elastomer composition tends to be poor. 
The amount of the acrylic rubber is selected usually within a range of from 
10 to 200 parts by weight, preferably from 20 to 150 parts by weight, most 
preferably from 30 to 120 parts by weight, per 100 parts by weight of the 
vinyl chloride resin. If the amount of the acrylic rubber is less than 10 
parts by weight, the effect to improve the compression set tends to be 
small, and if it exceeds 200 parts by weight, deterioration of the 
physical properties such as tear strength, elongation and thermal aging 
resistance, tends to be substantial. 
The above THF-insoluble cross-linking component is determined in such a 
manner that 0.5 g of the acrylic rubber is introduced into 30 ml of THF 
with stirring, left to stand at 23.degree. C. for 24 hours to dissolve a 
THF-soluble component, and then subjected to filtration by means of a 
glass fiber filter paper. The insoluble residue is dried, and the dried 
weight is determined, whereupon the content of the cross-linking component 
is calculated. 
The plasticizer to be used for the elastomer composition of the present 
invention is not particularly limited. However, its weight average 
molecular weight is preferably at least 430. With a plasticizer having a 
weight average molecular weight (MW) of less than 430, the effect of 
improving the tear strength is low, and the thermal aging resistance tends 
to be poor for an extended period of time. Such a plasticizer may, for 
example, be a plasticizer of a phthalic acid ester of a higher alcohol 
such as di-2-ethylhexyl phthalate (MW391), diisononyl phthalate (MW418), 
diisodecyl phthalate (MW447) or diundecyl phthalate (MW475), a phosphoric 
acid ester plasticizer such as tris(2-ethylhexyl) phosphate (MW435) or 
trisdichloropropyl phosphate (MW431), an adipic acid ester plasticizer 
such as di-2-ethylhexyl adipate (MW370) or dibutyl diglycol adipate 
(MW435), a trimellitic acid ester plasticizer such as 
tri(2-ethylhexyl)trimellitate (MW547), or a polyester plasticizer obtained 
by esterifying an aliphatic dibasic acid such as adipic acid, sebacic acid 
or azelaic acid, or an aromatic dibasic acid such as phthalic acid, with 
an aliphatic glycol such as 1,2-propanediol, 1,2-butanediol, 
1,3-butandiol, 1,4-butandiol, 2,2-dimethyl-1,3-propanediol, 
1,6-hexanediol, 1,8-octanediol or trimethylhexanediol. Among such 
plasticizers, a polyester plasticizer, or a mixture of a polyester 
plasticizer with other plasticizers, is preferred. The polyester 
plasticizer should preferably have a weight average molecular weight of up 
to 8,000, more preferably from 1,000 to 5,000, particularly preferably 
from 1,000 to 2,000. 
It is also possible to use an epoxy fatty acid ester (MW400 to 500) or an 
epoxidized oil plasticizer (MW about 1,000) in combination. 
The amount of the plasticizer varies depending upon the type and the amount 
of the vinyl chloride resin or the acrylic rubber, the presence or absence 
of the filler. However, it is usually selected within a range of from 30 
to 300 parts by weight, preferably from 40 to 200 parts by weight, per 100 
parts by weight of the vinyl chloride resin. 
The acrylic resin to be incorporated to the elastomer composition of the 
present invention means a resin obtained by polymerization of acrylic acid 
or its derivative, and it may, for example, be a polymer or a copolymer of 
e.g. acrylic acid, an acrylic acid ester, acrylamide, acrylonitrile, 
methacrylic acid or a methacrylic acid ester. For the elastomer 
composition of the present invention, it is particularly preferred to use 
a copolymer of methyl methacrylate with an alkyl acrylate, wherein the 
methyl methacrylate is at least 60% by weight, preferably from 70 to 90% 
by weight, and the alkyl acrylate is at most 40% by weight, preferably 
from 10 to 30% by weight. The acrylic resin is incorporated within a range 
of from 1 to 50 parts by weight, preferably from 3 to 30 parts by weight, 
per 100 parts by weight of the vinyl chloride resin. If the amount of the 
acrylic resin is less than 1 part by weight, the effect of improving the 
tear strength of the elastomer composition tends to be small, and if it 
exceeds 50 parts by weight, the composition tends to be hard, and the 
elasticity tends to be lost, although such may depend also on the type and 
the amount of the plasticizer. 
It is preferred to incorporate a filler to the elastomer composition of the 
present invention to such an extent not to impair the compression set or 
other physical properties. The filler has a function to absorb an excess 
amount of a plasticizer and to facilitate the kneading and molding. The 
filler may, for example, be carbon black, calcium carbonate, titanium 
oxide, talc, aluminum hydroxide, magnesium hydroxide, hydrotalcite, clay, 
silica or white carbon. The filler is incorporated usually within a range 
of not more than 150 parts by weight, preferably from 10 to 100 parts by 
weight, per 100 parts by weight of the vinyl chloride resin. If the amount 
of the filler is too small, the effect of improving the kneading and 
molding properties tends to be small. On the other hand, if it exceeds 150 
parts by weight, the moldability tends to be poor, and it is advisable to 
incorporate the filler within a range not to impair the moldability also 
from the economical viewpoint. 
Further, various additives such as a stabilizer, a lubricant, an 
antioxidant, an ultraviolet absorber, a blowing agent, a flame retardant, 
a pigment, an impact resistance-improving agent, and a thermoplastic resin 
and a rubber other than those mentioned above, may be added to the 
elastomer composition of the present invention, as the case requires. 
As such a thermoplastic resin and a rubber, a methyl 
methacrylate-butadiene-styrene rubber (MBS), an acrylic rubber (AR) 
soluble in THF, a butadiene rubber (BR), a styrene-butadiene rubber (SBR), 
an acrylonitrile-butadiene-styrene rubber (ABS), an isoprene rubber (IR), 
a chloroprene rubber (CR), an ethylene-propylene rubber (EPR), an 
ethylene-vinyl acetate copolymer (EVA), a thermoplastic polyurethane (TPU) 
and nylon may, for example, be mentioned. 
The vinyl chloride resin elastomer composition of the present invention can 
be prepared by a method which comprises introducing predetermined amounts 
of the vinyl chloride resin, the acrylic rubber containing the 
THF-insoluble cross-linking component, the plasticizer and the acrylic 
resin as well as various additives such as a filler into a mixer or a 
kneader and mixing and kneading the components uniformly under heating at 
a temperature of from 100.degree. to 230.degree. C., preferably from 
130.degree. to 230.degree. C. From the operational viewpoint or with a 
view to obtaining a uniformly kneaded composition, it is preferred to 
prepare the elastomer composition of the present invention, for example, 
by the following method. Namely, a blend comprising the respective 
components such as the vinyl chloride resin, the acrylic resin and the 
plasticizer other than the acrylic rubber, is preliminarily dry-blended, 
and then the dry-blended product and the acrylic rubber containing the 
THF-insoluble cross-linking component are mixed and kneaded under heating 
at a temperature of from 100.degree. to 230.degree. C. After the kneading, 
the kneaded composition is usually formed into pellets by a sheet cutting 
method or a hot cutting method, and such pellets are supplied to the next 
step of molding. Other additives such as a filler may, of course, be 
incorporated at the time of mixing and kneading the acrylic rubber. If the 
mixing and kneading temperature is lower than 100.degree. C. it takes a 
long time for kneading, whereby the productivity tends to be poor. On the 
other hand, if it is higher than 230.degree. C., the elastomer composition 
tends to be decomposed. 
An apparatus to be used for mixing the above blend components, may be any 
apparatus so long as it is capable of uniformly mixing them. For example, 
it may be a Henschel mixer, a ribbon blender or a planetary mixer. To 
knead the mixture, an apparatus capable of kneading it under a shearing 
force under heating, such as an extruder, a roll mill, a Banbury mixer or 
a kneader, can be used. To prepare the elastomer composition, it is 
preferred to employ a closed type kneader such as a Banbury mixer, an 
intensive mixer or a pressure kneader, or an equidirectional twin-screw 
extruder in view of the greater kneading effects. 
The elastomer composition thus prepared is continuously extruded in a 
continuous length with a profile by a profile extrusion machine such as an 
extruder to form a gasket or the like. The cross-sectional shape is not 
particularly limited, and may be any desired shape, for example, a 
T-shape, an L-shape, an F-shape, an E-shape or a hollow shape, or a 
combination of these shapes. 
Further, the above composition may be combined with a metal or a hard resin 
to form a composite gasket. The hard resin may, for example, a chlorinated 
vinyl chloride resin, a hard vinyl chloride resin, or an 
acrylonitrile-butadiene-styrene resin. The metal may, for example, be 
iron, steel, stainless steel, brass or aluminum. As a method for combining 
the vinyl chloride resin elastomer composition with a hard material such 
as a metal or a hard resin, it is possible to employ a method wherein the 
vinyl chloride resin elastomer composition is extruded and coated over the 
entire surface or a part of the surface of the hard material of a strip 
shape, a plate shape or a rod shape, a method wherein the both materials 
are co-extruded by means of a plurality of extruders, and they are 
combined in an extruding die or in the vicinity thereof, or a method 
wherein the two materials are formed into molded products by various 
molding methods, and the molded products are bonded by heat fusion or by 
means of an adhesive. 
Now, the present invention will be described in further detail with 
reference to Examples. However, it should be understood that the present 
invention is by no means restricted by such specific Examples. 
Evaluation of the quality of the vinyl chloride resin elastomer 
compositions and gaskets were conducted as follows, and the results are 
shown in Table 1. 
Compression set: Measured in accordance with JIS K6301 at 70.degree. C. for 
22 hours under a compression of 25%. 
Tear strength: Measured in accordance with JIS K6301. 
Weather resistance test: An elastomer composition was formed into a sheet 
by a roll mill, and from the sheet, a press sheet was prepared. Then, test 
specimens of 5 cm.times.5 cm were punched out and subjected to a weather 
resistance test, whereby the weather resistance was evaluated by the color 
difference before and after the weather resistance test. The weather 
resistance test conditions and the color difference measurement conditions 
were as follows. 
Weather resistance test conditions 
Sunshine Weather Meter (manufactured by Suga Shikenki) was used. 
Black panel: 83.degree. C. 
Spray cycle: 60 min/12 min (water spray for 12 minutes in 60 minutes) 
Period of time: 450 hours. 
Color difference measuring conditions 
Photometer AUCOLOR VP-1 (manufactured by Kurashiki Boseki) was used. Light 
was irradiated to the surface of a test specimen, and the reflected light 
was measured by a spectrophotometer. The difference in the intensity of 
the reflected light from the surface of the test specimen before and after 
the test was taken as the color difference. The greater the numerical 
value, the greater the color change. 
Elongation: Measured in accordance with JIS K6723. 
Thermal aging resistance: In accordance with JIS K6723,elongation after 
thermal aging under a heating condition of 100.degree. C. for 500 hours, 
was measured, and the elongation remaining ratio was determined by the 
following formula. 
Elongation remaining ratio (%)=elongation after aging/elongation before 
aging).times.100 
Gasket deformation ratio: In accordance with JIS K6301, the deformation 
ratio of a gasket having a length of 5 cm was measured under a condition 
of 70.degree. C. for 22 hours under a compression of 50%.

EXAMPLES 1 TO 8 AND COMATIVE EXAMPLES 1 TO 5 
Preparation of compositions 
To 100 parts by weight of a vinyl chloride resin having an average 
polymerization degree of 2,350, a plasticizer and an acrylic resin of the 
types and the amounts (parts by weight) as identified in Table 1, as well 
as 3 parts by weight of a Ba-Zn type composite stabilizer, 1 part by 
weight of a phosphite type chelator, 0.4 part by weight of a lubricant, 1 
part by weight of an ultraviolet absorber and 30 parts by weight of 
calcium carbonate were mixed in a beaker, and an acrylic rubber or NBR of 
the type and the amount as identified in Table 1, was further added and 
mixed thereto. The mixture was kneaded by a 8 inch mill roll at a surface 
temperature of 160.degree. C. for 5 minutes. From a roll sheet obtained by 
the kneading, a press sheet was prepared, from which test specimens were 
punched out. 
Preparation of a gasket 
A roll sheet prepared as described above, was pelletized by a sheet cut 
method. Pellets were extruded by a 20 mm.cent. extruder to obtain a molded 
product of a tubular shape having an outer diameter of 16.5 mm and an 
inner diameter of 13.5 mm. 
The tubular molded product was bonded on a stainless steel plate having a 
thickness of 1 mm to obtain a gasket. 
TABLE 1 
__________________________________________________________________________ 
Examples 
1 2 3 4 5 6 7 8 
__________________________________________________________________________ 
Plasti- 
Phthalic acid type 1 
100 
cizer 
Polyester type 1 
100 
Polyester type 2 
100 
100 
50 
DOP 50 100 
DINP 100 
50 
Adipic acid type 1 50 
Acrylic resin 10 10 10 5 10 10 10 10 
Rubber 
Acrylic rubber 1 
50 50 50 50 50 50 50 50 
Acrylic rubber 2 
NBR 
Gasket deformation ratio (%) 
45 47 48 -- 47 46 -- 46 
Compression set (%) 
47 48 49 49 48 47 48 47 
Tear strength (kg/cm) 
26 26 29 28 27 23 23 23 
Color difference 
2.6 
2.6 
2.7 
2.7 
2.6 
2.7 
2.7 
2.7 
Elongation before aging (%) 
315 
320 
320 
315 
320 
315 
310 
305 
Elongation remaining ratio 
95 98 98 98 96 55 75 65 
after aging (%) 
__________________________________________________________________________ 
Comparative Examples 
1 2 3 4 5 
__________________________________________________________________________ 
Plasti- Phthalic acid type 1 
cizer Polyester type 1 
Polyester type 2 
100 
100 100 
DOP 100 100 
DINP 
Adipic acid type 1 
Acrylic resin 10 10 10 10 
Rubber Acrylic rubber 1 
50 300 
Acrylic rubber 2 
50 
NBR 50 
Gasket deformation ratio (%) 
45 78 46 58 -- 
Compression set (%) 
46 83 47 60 32 
Tear strength (kg/cm) 
20 25 29 35 8 
Color difference 2.8 2.6 
48.8 2.0 
2.7 
Elongation before aging (%) 
310 800 
420 400 
90 
Elongation remaining ratio 
54 95 96 95 65 
after aging (%) 
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The materials in Table 1 used in the Examples are as follows. 
Plasticizer 
Phthalic acid type 1: MW452, phthalic acid dialkyl ester (alkyl groups: 
mixture of C.sub.9-11) 
Polyester type 1: MW1300, polyester of adipic acid with butanediol 
(terminal: 2-ethylhexanol) 
Polyester type 2: MW1800, polyester of adipic acid with butanediol 
(terminal: 2-ethylhexanol) 
DOP: Di-2-ethylhexyl phthalate (MW391) 
DINP: Diisononyl phthalate (MW418) 
Adipic acid type 1: MW387, adipic acid dialkyl ester (alkyl groups: mixture 
of C.sub.7-11) 
Acrylic resin Methyl methacrylate/alkyl acrylate=70 to 90/30 to 10 wt % 
Rubber material 
Acrylic rubber 1: THF-insoluble cross-linking component: 93.9 wt % 
(prepared) 
Acrylic rubber 2: THF-insoluble cross-linking component: nil (commercial 
product) 
NBR: THF-insoluble cross-linking component: 89.4 wt % 
Acrylonitrile content: 30 wt % 
The vinyl chloride resin elastomer composition of the present invention 
comprises a vinyl chloride resin, an acrylic rubber containing a 
THF-insoluble cross-linking component, an acrylic resin and a plasticizer, 
particularly a plasticizer having a weight average molecular weight of at 
least 430, whereby it is excellent in thermal aging resistance and tear 
strength, and when compared with a vinyl chloride resin elastomer 
containing cross-linked NBR, it has equivalent physical properties with 
respect to the compression set, creep resistance, moldability, bleed 
resistance, blocking resistance and low temperature flexibility. Thus, it 
can be used as a material for not only extrusion molding but also calender 
processing, injection molding, inflation molding or compression molding, 
whereby a molded product having an optional or predetermined shape can be 
obtained. 
The vinyl chloride resin elastomer composition of the present invention is 
useful in a wide range of industrial, automobile and building 
applications, for example, for weather strips, glass runs, packings, 
gaskets, hoses, sheets, grips, rolls, grommets, duct boots and cushion 
materials.