U.S. patent application number 09/983337 was filed with the patent office on 2002-05-02 for rubber-containing sytrenic resin and process for producing the same.
This patent application is currently assigned to Daicel Chemical Industries, Ltd.. Invention is credited to Asada, Takeshi, Sekiguchi, Junichi, Teranishi, Tadashi, Umemoto, Koichi, Yanagita, Soko.
Application Number | 20020052447 09/983337 |
Document ID | / |
Family ID | 26554198 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020052447 |
Kind Code |
A1 |
Asada, Takeshi ; et
al. |
May 2, 2002 |
Rubber-containing sytrenic resin and process for producing the
same
Abstract
The rubber-containing styrenic resin of the present invention
comprises a styrenic resin matrix and a rubber component dispersed
in particles. In the resin, the graft ratio of a styrenic monomer
relative to the rubber component is not less than 1, the particle
size of the dispersed rubber component is 0.1 to 3 .mu.m, and the
following equation (1) is satisfied: Mn=aT+b (1) wherein Mn is the
number average molecular weight of the matrix resin; T is the
conversion of the styrenic monomer; a is a constant greater than 0;
and b is a constant of 0 or greater. The rubber component may be a
butadiene-series rubber. The particle-size distribution of the
dispersed rubber component may have, for example, two peaks. Such
styrenic resin can be produced by, in the presence of a rubber
component, polymerizing at least a styrenic monomer at a graft
ratio of not less than 1 under such conditions that the
relationship between the conversion T of the styrenic monomer and
the number average molecular weight Mn of the polymer can be
approximated by a linear equation. According to the present
invention, the morphology and the particle size of rubber particles
dispersed in a styrenic resin are controllable.
Inventors: |
Asada, Takeshi; (Himeji-shi,
JP) ; Sekiguchi, Junichi; (Himeji-shi, JP) ;
Teranishi, Tadashi; (Himeji-shi, JP) ; Umemoto,
Koichi; (Himeji-shi, JP) ; Yanagita, Soko;
(Himeji-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Daicel Chemical Industries,
Ltd.
|
Family ID: |
26554198 |
Appl. No.: |
09/983337 |
Filed: |
October 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09983337 |
Oct 24, 2001 |
|
|
|
09440930 |
Nov 16, 1999 |
|
|
|
Current U.S.
Class: |
525/232 ;
525/240 |
Current CPC
Class: |
C08F 279/02 20130101;
C08F 279/02 20130101; C08F 212/06 20130101 |
Class at
Publication: |
525/232 ;
525/240 |
International
Class: |
C08L 009/00; C08L
023/00; C08L 023/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 20, 1998 |
JP |
331478/1998 |
Oct 1, 1999 |
JP |
281461/1999 |
Claims
What is claimed is:
1. A process for producing a rubber-containing styrenic resin,
which comprises polymerizing at least a styrenic monomer in the
presence of a rubber component at a graft ratio of not less than 1
under such conditions that the relationship between the conversion
T of the styrenic monomer and the number average molecular weight
Mn of the resultant polymer can be approximated by a linear
equation.
2. A process according to claim 1 which provides a
rubber-containing styrenic resin in which the rubber component
having a mean particle size of 0.1 to 3 .mu.m is dispersed.
3. A process according to claim 1, wherein the polymerization is
carried out in the presence of a polymerization initiator and/or at
least one additive selected from the group consisting of a
hydroxyamine, a nitroso compound and a nitrone compound represented
by the following formulae (2) to (4) respectively: 3wherein R.sup.1
to R.sup.5 are the same or different from each other, each
representing a hydrogen atom, an alkyl group, an alkoxy group, an
acyl group, an alkenyl group, a cycloalkyl group, an aryl group, or
an aralkyl group; the groups R.sup.1 and R.sup.2 and the groups
R.sup.4 and R.sup.5 may bond together to form rings individually;
and R.sup.3 may be a group represented by the following formula
(3a): 4wherein R.sup.3a to R.sup.3c are the same or different from
each other, each representing a hydrogen atom, an alkyl group, or
an aryl group; and at least two of the groups R.sup.3a to R.sup.3c
may bond together to form a ring.
4. A process according to claim 3, wherein the additive is at least
one member selected from the group consisting of an
N,N-diC.sub.1-4alkylhydro- xylamine, an aromatic dicarboxylic acid
imide, a compound shown by the formula (3a) in which at least two
of the groups R.sup.3a to R.sup.3c are the same or different alkyl
groups, a nitroso-t-alkane, nitrosobenzene, a dimer of a nitroso
compound, an N-t-C.sub.4-8alkyl-.alpha.-arylnitrone, a
pyrroline-N-oxide, and a pyridine-N-oxide.
5. A process according to claim 3, wherein the ratio of the
additive to the polymerization initiator is the former/the latter
(molar ratio)=0.01/1 to 100/1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a rubber-containing
styrenic resin of which the rubber component dispersed therein is
controllable in its morphology and particle size, and to a process
for producing the same.
BACKGROUND OF THE INVENTION
[0002] As a means for improving the impact resistance of a styrenic
resin, there has been proposed a styrenic resin containing a rubber
component (styrene-butadiene rubber, polybutadiene rubber) such as
high impact resistant polystyrene HIPS. Various techniques have
been adopted to improve the impact resistance, in which a rubber
dispersed in a HIPS is increased in particle size or the rubber
content is raised. According to such methods, while the impact
resistance of a shaped article is improved to some extent, the
surface gloss thereof or other characteristics are deteriorated. On
the other hand, a rubber component of smaller particle size or a
lower rubber content improves the surface gloss of a shaped article
but deteriorates the impact resistance. Therefore, the external
appearance and impact resistance cannot both be held at high
levels.
[0003] Control of the morphology of the rubber component dispersed
in particles in the resin (morphology of particles) is suggested to
improve the impact resistance or characteristics related to
external appearance such as surface gloss. For example, a rubber
particle formed such as to have a small particle size and a
microdomain structure of the core/shell type (core/shell structure)
is useful for improving the surface gloss of a styrenic resin.
However, the formation of a styrenic resin having a core/shell
morphology requires a rubber component to be efficiently dispersed
in a styrenic resin matrix, consequently limiting the range of
rubber components available therefor [e.g., rubber components
highly compatible with styrenic resins (styrene-butadiene rubber,
etc.)]. Therefore, a styrenic resin having a core/shell structure
cannot be produced with a conventional diene rubber. Moreover, when
a diene rubber is used, the morphology of the resultant resin is a
salami structure with a large particle size, and hence no
improvement in the surface gloss of a shaped article thereof.
[0004] Moreover, for improvements in both surface gloss and impact
resistance, there has been proposed an idea of using a HIPS
containing small rubber particles having a core/shell structure in
combination with a HIPS containing larger rubber particles having a
salami structure. However, this method requires specific and
peculiar polymerization conditions and a blending step, and hence
the operation much complicated.
[0005] On the other hand, there has been known a living radical
polymerization process which is a combination method of a living
polymerization method whereby a primary structure of a polymer
(e.g., molecular weight, molecular-weight distribution) is easily
controllable and a radical polymerization method which is less
sensitive to impurities or solvents. Though the living radical
polymerization process is a radical polymerization, this process
enables control of the molecular weight and provides a polymer
having a narrow molecular-weight distribution.
[0006] Japanese Patent Publication No. 6537/1993 (JP-B-5-6537)
corresponding to USP or WO discloses a compound as an initiator for
the living radical polymerization of an unsaturated monomer.
Japanese Patent Application Laid-Open No. 199916/1994
(JP-A-6-199916) corresponding to USP or WO discloses a
polymerization method for a thermoplastic resin having a narrow
polydispersity, comprising a step of heating a free radical
initiator, a stable free radical agent and a polymerizable monomer
compound.
[0007] Further, Japanese Patent Application Laid-Open No.
239434/1996 (JP-A-8-239434) corresponding to USP or WO discloses a
process for producing a composition containing a vinyl aromatic
polymer and a rubber, comprising a step of polymerizing a vinyl
aromatic monomer in the presence of a rubber. The literature
teaches the presence of a stabilized free radical in the
polymerization step. However, considering the amount of the rubber
used, the degree of improvement in impact resistance in this
process, in other words, rubber efficiency, is low.
SUMMARY OF THE INVENTION
[0008] Thus, an object of the present invention is to provide a
rubber-containing or rubber-modified styrenic resin of which the
dispersed rubber is easily controllable in its particle morphology
and size according to the intended use, and a process for producing
the same.
[0009] Another object of the present invention is to provide a
rubber-containing or rubber-modified styrenic resin having surface
gloss and impact resistance both at high levels, and a process for
producing the same.
[0010] Still another object of the present invention is to provide
a rubber-containing or rubber-modified styrenic resin which is
excellent in rubber efficiency, and a process for producing the
same.
[0011] Another object of the present invention is to provide a
rubber-containing or rubber-modified styrenic resin having a
microdomain structure of the core/shell type even if the rubber
component contained therein is a diene rubber such as
polybutadiene, and a process for producing the same.
[0012] The inventors of the present invention did intensive and
extensive studies to achieve the above objects and found that the
morphology or particle size of a rubber component dispersed in a
polymer and the molecular weight of a styrenic resin forming a
matrix can be controlled by, in the presence of a rubber component,
radical-polymerizing a styrenic monomer in a specific manner. The
present invention was accomplished based on the above findings.
[0013] Thus, the rubber-containing styrenic resin of the present
invention comprises a matrix of a styrenic resin and a rubber
component in particle form dispersed in the matrix, wherein the
graft ratio of a styrenic monomer relative to the rubber component
is not less than 1, and the mean particle size of the dispersed
rubber component is 0.1 to 3 .mu.m, satisfying the following
equation (1):
Mn=aT+b (1)
[0014] wherein Mn is the number average molecular weight of the
matrix resin; T is the conversion of the styrenic monomer; a is a
constant greater than 0; and b is a constant of not less than
0.
[0015] The present invention further includes a styrenic resin
comprising a styrenic resin matrix and a rubber component dispersed
therein in particles, in which the graft ratio of a styrenic
monomer relative to the rubber component is not less than 2.5 and
the mean particle size of the dispersed rubber component is about
0.3 to 3 .mu.m.
[0016] The above-mentioned rubber component may be a
butadiene-series rubber (e.g., a diene rubber). The particle-size
distribution of the dispersed rubber component may show, for
example, a plurality of peaks (i.e., the particle-size distribution
having a plurality of peaks, particularly two peaks) or a
single-peak, and the morphology (microdomain structure) of the
dispersed rubber component may for example be of the salami type
(salami strcture), core/shell type (core/shell structure), or a
mixed or complex type thereof.
[0017] The present invention further includes a process for
producing a rubber-containing styrenic resin in which, under such
conditions that the relationship between the conversion T of a
styrenic monomer and the number average molecular weight Mn of the
resulting polymer can be approximated by a linear equation, at
least a styrenic monomer is polymerized in the presence of a rubber
component at a graft ratio of not less than 1.
[0018] In this specification, acrylic monomers and methacrylic
monomers are collectively referred to as "(meth)acrylic
monomer.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The rubber-containing styrenic resin of the present
invention comprises a matrix of a styrenic resin and a rubber
component dispersed in the matrix, and the graft ratio of the
styrenic monomer relative to the rubber component is not less than
1.
[0020] The styrenic resin forming the matrix may comprises a
homopolymer or copolymer of a styrenic monomer, a copolymer of a
styrenic monomer and a copolymerizable vinyl monomer, or the
like.
[0021] As the styrenic monomer, there may be mentioned, for
example, styrene, alkylstyrenes [e.g., monoalkylstyrens such as
vinyltoluenes (e.g., o-, m-, p-methylstyrenes), vinylxylenes (e.g.,
2,4-dimethylstyrene), and alkyl-substituted styrenes (e.g.,
C.sub.1-4alkylstyrenes) such as ethylstyrene, p-isopropylstyrene,
butylstyrene, and p-t-butylstyrene; dialkylstyrenes
(diC.sub.1-4alkylstyrenes such as 2,4-dimethylstyrene);
.alpha.-alkyl-substituted styrenes (e.g.,
.alpha.-C.sub.1-2alkylstyrenes such as a-methylstyrene and
.alpha.-methyl-p-methylstyrene], alkoxystyrenes (e.g.,
C.sub.1-4alkoxystyrenes such as o-methoxystyrene, m-methoxystyrene,
p-methoxystyrene, p-t-butoxystyrene), halostyrenes (e.g., o-, m-,
and p-chlorostyrenes, p-bromostyrene), styrene sulfonic acid and
alkaline metal salts thereof. These styrenic monomers can be used
either singly or in combination. These styrenic monomers can be
used either singly or in combinaion. The preferred styrenic monomer
includes styrene, vinyltoluenes, and .alpha.-methylstyrene, with
styrene particularly preferred.
[0022] As the copolymerizable vinyl monomer, there may be
exemplified .alpha.,.beta.-unsaturated nitriles [e.g, vinyl
cyanides such as (meth)acrylonitrile, halogenated
(meth)acrylonitrile (chloro(meth)acrylnitrile, etc.)],
.alpha.,.beta.-unsaturated carboxylates (particularly, alkylesters)
[e.g., (meth)acrylic acid alkylesters; (meth)acrylic acid
C.sub.5-7cycloalkylesters such as cyclohexyl (meth)acrylate;
(meth)acrylic acid C.sub.6-12aryl esters such as phenyl
(meth)acrylate; (meth)acrylic acid C.sub.7-14aralkyl esters such as
benzyl (meth)acrylate; or maleic acidmono- or dialkylester, fumaric
acid mono- or dialkylesters, and itaconic acid mono- or
dialkylesters corresponding to these (meth)acrylic acid esters],
vinyl ester-series monomers [e.g., carboxylic acid vinyl esters
such as C.sub.1-10 carboxylic vinyl esters typified by vinyl
formate, vinyl acetate, vinyl propionate, vinyl pivalate
(particularly, C.sub.1-6 carboxylic acid vinyl esters)], hydroxyl
group-containing monomers [e.g., hydroxyalkyl(meth)acrylates such
as hydroxyethyl(meth)acyrlate and hydroxypropyl(meth)acrylate
(e.g., hydroxyC.sub.1-10alkyl(meth)acrylates, preferably,
hydroxyC.sub.1-4alkyl(meth)acrylates)], glycidyl group-containing
monomers [e.g., glycidyl (meth)acrylate], carboxyl group-containing
monomers [e.g., .alpha.,.beta.-unsaturated monocarboxylic acids
such as (meth)acrylic acid; .alpha.,.beta.-unsaturat- ed
polycarboxylic acids such as maleic acid, fumaric acid, and
itaconic acid; or acid anhydrides thereof (e.g., maleic anhydride,
fumaric anhydride)], amino group-containing monomers [e.g.,
N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminopropyl
(meth)acrylate], amide-series monomers [e.g., (meth)acrylamide, or
derivatives thereof (e.g., N-methyl(meth)acrylamide,
N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide), or
fumaric acid amides correponding thereto (e.g., fumaramide,
fumaramic acid, or derivatives thereof)], imide-series monomers
(e.g., maleimide, N--C.sub.1-4alkyl maleimides such as
N-methylmaleimide, N-phenylmaleimide), conjugated diene-series
monomers [e.g., C.sub.4-16dienes such as butadiene, isoprene,
chloroprene, neoprene, 1,3-pentadiene, 1-chlorobutadiene,
2,3-dimethyl-1,3-butadiene, 3-butyl-1,3-octadiene, and
phenyl-1,3-butadiene (preferably, C.sub.4-10 dienes)], olefinic
monomers [e.g., C.sub.2-10 alkenes such as ethylene, propylene,
butene (e.g., isobutene)], vinyl halides (e.g., vinyl fluoride,
vinyl chloride, vinyl bromide, vinyl iodide), and vinylidene
halides (e.g., vinylidene fluoride, vinylidene chloride, vinylidene
bromide, vinylidene iodide). The (meth)acrylic acid alkylester
includes (meth)acrylic acid C.sub.1-20alkyl esters such as methyl
(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, t-butyl
(meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate,
2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate (preferably,
(meth)acrylic acid C.sub.1-14alkyl esters).
[0023] The preferred vinyl-series monomer includes (meth)acrylic
monomers [e.g., (meth)acrylic acid, (meth)acrylates (particularly,
methyl methacrylate, acrylic acid C.sub.2-10alkyl esters),
(meth)acrylonitrile].
[0024] These vinyl monomers can be used either singly or in
combination. The amount of such copolymerizable monomer can be
selected from the range of, e.g., about 0 to 50% by weight and
preferably of about 0 to 30% by weight.
[0025] The weight average molecular weight Mw of the matrix resin
comprised of a styrenic resin is about 100,000 to 500,000,
preferably about 150,000 to 300,000. A Mw smaller than 100,000
leads to poor rigidity, and a Mw exceeding 500,000 might cause
deterioration in fluidity and moldability.
[0026] As the rubber component, use can be made of a variety of
rubbery polymers (e.g., diene rubbers such as butadiene rubber and
isoprene rubber; sytrene-diene copolymerized rubbers such as
styrene-butadiene rubber and styrene-isoprene rubber;
ethylene-vinyl acetate copolymer, acrylic rubber,
ethylene-propylene rubber (EPDM)). Preferred as the rubber
component is a diene-series rubber component (e.g., a conjugated
1,3-diene rubber and a derivative thereof, such as butadiene,
isoprene, 2-chloro-1,3-butadiene, and 1-chloro-1,3-butadiene).
Particularly preferred is a butadiene-series rubber (a diene rubber
typified by butadiene rubber). These rubber components can be used
either singly or in combination.
[0027] The weight average molecular weight of the rubber component
is about 1.times.10.sup.4 to 2.times.10.sup.6, preferably about
5.times.10.sup.4 to 1.times.10.sup.6, and more preferably about
1.times.10.sup.5 to 5.times.10.sup.5.
[0028] As the rubber-modified styrenic resin, there may be
exemplified high impact resistance polystyrenes (HIPS),
styrene-butadiene-styrene (SBS resin), styrene-isoprene-styrene
(SIS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin),
acrylonitrile-acrylic rubber-styrene copolymer (AAS resin),
acrylonitrile-(ethylene-propylene rubber)-styrene copolymer,
acrylonitrile-EPDM-styrene copolymer (AES resin), and methyl
methacrylate-butadiene-styrene copolymer (MBS resin), with HIPS and
ABS resin particularly preferred.
[0029] In the rubber-modified styrenic resin, the content of the
rubber component such as polybutadiene is about 1 to 20% by weight
(e.g., 3 to 20% by weight), preferably about 2 to 15% by weight
(e.g., 5 to 15% by weight). When the rubber component content is
not more than 1% by weight, the impact resistance is insufficient
for practical use, and a rubber component content exceeding 20% by
weight makes the rubber-modified styrenic resin prone to suffer
from deterioration in surface gloss and rigidity.
[0030] In the rubber-containing styrenic resin of the present
invention, the most efficient use can be made of the rubber
component (high rubber efficiency), and therefor, the
rubber-containing styrenic resin presents a high surface gloss even
if the particle size of the rubber component dispersed therein is
large and shows excellent impact strength even with a low rubber
content. These characteristics are due to the graft ratio thereof
being high.
[0031] The graft ratio (g-value) is the ratio of the amount of the
styrenic monomer relative to that of the rubber component and
measured in the following manner. 1 g of a styrenic resin is
dissolved in 35 ml of a mixed solvent [methyl ethyl ketone/acetone
(1/1 v/v)], and the mixture is subjected to a centrifuge to give an
insoluble portion or matter, and the weight fraction (on solid
basis) of the insoluble portion is defined as a "gel portion". The
weight fraction of the rubber contained in 1 g of the styrenic
resin measured according to the iodometry is defined as a "rubber
content". The graft ratio is represented by the following
equation.
Graft ratio=[gel portion (g)-rubber content (g)]/rubber content
(g)
[0032] The g-value is an index representing the degree of grafting
of the styrenic monomer relative to the rubber component, and the
g-value is not less than 1 (e.g., not less than 2), preferably
about 1 to 5, and more preferably about 1.5 to 3 (e.g., 2 to 3). A
g-value smaller than 1 means that the proportion of the grafted
styrenic monomer is small relative to the rubber content, which
leads to a reduction in rubber efficiency and deterioration in
impact resistance. Moreover, a g-value exceeding 5 causes
deterioration in rigidity, and hence ill-balanced physical
properties insufficient for practical use.
[0033] In the rubber-containing styrenic resin, the rubber
component is dispersed in the styrenic resin matrix in
particles.
[0034] Both of the surface gloss and impact strength of the
styrenic resin are influenced by the particle size of the rubber
component dispersed in the styrenic resin matrix. The particle size
of the dispersed rubber is an average value calculated in the
following manner. A transmission electron photomicrograph of an
ultra-thin slice cut from the styrenic resin is taken, and
measurements of the particle size are made for 1000 particles of
the rubbery polymer regarded as of spheres. The mean particle size
is represented by the following formula:
Mean particle
size=(.SIGMA.n.sub.iD.sub.i.sup.4)/(.SIGMA.n.sub.iD.sub.i.su-
p.3)
[0035] In the equation, n.sub.i represents the number of rubbery
polymer particles regarded as of spheres having a particle size Di
(.mu.m).
[0036] The mean particle size of the dispersed rubber is about 0.1
to 3 .mu.m, preferably 0.3 to 2 .mu.m, more preferably about 0.3 to
1.5 .mu.m, and usually about 0.2 to 2 .mu.m. A mean particle size
smaller than 0.1 .mu.m deteriorates the impact resistance, and a
mean particle size exceeding 3 .mu.m degrades the surface
gloss.
[0037] From the rubber-containing styrenic resin of the present
invention can be obtained a highly glossy shaped article even if
the mean particle size of the dispersed rubber is relatively large,
and it may be due to its high graft ratio. For example, a shaped
article having a high gloss can be obtained even though the mean
particle size is 0.3 to 2 .mu.m (e.g., 0.5 to 2 .mu.m), preferably
about 0.4 to 1.5 .mu.m, and 0.5 to 1.2 .mu.m.
[0038] The morphology of the dispersed rubber particle (the
microdomain structure of the rubber-containing styrenic resin) may
be a core/shell structure (e.g., a structure in which a single
styrenic resin phase is contained or confined within one rubber
particle) or a salami structure (e.g., a structure in which a
plurality of styrenic resin phases are confined within one rubber
particle, and the styrenic resin phases are partitioned from each
other by the rubber phase), or a mixed or complex structure
thereof.
[0039] In the core/shell structure, the mean particle size of the
dispersed rubber component is about 0.1 to 1 .mu.m, preferably
about 0.2 to 0.8 .mu.m, and more preferably about 0.3 to 0.7 .mu.m.
As can be understood from the above, even if a diene rubber (e.g.,
polybutadiene) is employed, the present invention can provide not
only a rubber-containing styrenic resin having a core/shell
structure and a small mean particle size but also a
rubber-containing styrenic resin containing constant and fine
rubber component particles, 90% (by volume) and more (preferably
95% and more) of the rubber particles each containing three
occlusions or less. Since the resin having a core/shell structure
can be formed even with a butadiene rubber which is inexpensive, a
styrenic resin of high surface gloss can be manufactured at low
cost. The core/shell structure seems to improve the gloss,
transmittance and transparency.
[0040] According to the present invention, since rubber particles
can be formed with a polymer solution of relatively low viscosity,
as will later be described, the rubber particle can be formed not
only such as to have a core/shell structure and a relatively small
mean particle size as was described above but also such as to have
a core/shell structure and a larger particle size, such large
particle size having been difficult to achieve. As for the large
particles with the core/shell structure, the mean particle size of
the dispersed rubber component is about 0.5 to 3 .mu.m, preferably
about 0.7 to 2.5 .mu.m. The resin containing large rubber particles
of core/shell structure is highly glossy and excellent in impact
strength and therefore can be used as a base resin for an
alloy.
[0041] In the salami structure, the mean particle size of the
dispersed rubber component is about 0.3 to 3 .mu.m, preferably
about 0.5 to 2.5 .mu.m (e.g., 0.7 to 2.5 .mu.m).
[0042] The particle-size distribution of the dispersed rubber
component may have a single peak or a plurality of peaks as in the
case with a bimodal structure [i.e., the particle-size distribution
has two peaks (e.g., rubber particles with a core/shell structure
and those with a salami structure are contained in mixture].
[0043] The rubber-containing styrenic resin having the bimodal
structure is excellent in impact strength as compared to a
single-peak styrenic resin having a core/shell structure, and the
surface gloss thereof is substantially comparable to a single-peak
resin.
[0044] When the microdomain structure is of the salami type (salami
structure) or bimodal type (bimodal structure), further control of
the particle size makes it possible to apply the rubber-containing
styrenic resin of the present invention for uses requiring a higher
gloss, improves the rubber efficiency, and reduces the cost.
[0045] In the case of the bimodal structure, the particle-size
distribution of the dispersed rubber particles may for example has
two peaks: one for core/shell rubber particles and salami rubber
particles (salami rubber particles containing not more than three
occlusions) having mean particle sizes in the range of about 0.1 to
1 .mu.m (preferably 0.1 to 0.5 .mu.m) and the other for salami
rubber particles having a mean particle size in the range of about
0.5 to 5 .mu.m (preferably, 1 to 3 .mu.m). When the mean particle
size of the small particles is smaller than 0.1 .mu.m or that of
the large particles is smaller than 0.5 .mu.m, the impact
resistance of the resin is insufficient. When the mean particle
size of the small particles exceeds 1 .mu.m or that of the large
particles exceeds 5 .mu.m, the surface gloss of the resin is
degraded. Particularly, when the mean particle size of the large
particles is outside the above-mentioned range, the impact
resistance or surface gloss is adversely affected.
[0046] In the rubber-containing styrenic resin having the bimodal
structure, suitable control of the conditions mentioned above
allows the rubber component in small particles and large particles
to be present in mixture in desired proportions. The proportions
thereof are not particularly restricted, and the ratio of the small
rubber particles to the large rubber particles is, for example,
about 40/60 to 95/5 (volume ratio), preferably about60/40 to 90/10
(volume ratio). A ratio smaller than 40/60 might lead to
deterioration in surface gloss and a ratio greater than 95/5 might
lower the impact resistance, and therefore, the resin cannot have
well-balanced surface gloss and impact resistance both at high
levels.
[0047] In the case of a rubber-containing styrenic resin having the
bimodal structure, the volume ratio of the small rubber particle to
the large rubber particle is obtained by figuring out the volumes
of the large rubber particle and the small rubber particle
individually from the particle sizes obtained from measurements
made for 1000 or more rubber polymer particles regarded as of
spheres which are randomly chosen from transmission type electron
photomicrographs, and then calculating from the number of large
particles, that of small particles and the volumes obtained above
with the following equation. A core/shell rubber particle and a
salami rubber particle (a particle containing not more than three
occlusions) each having a particle size of about 0.1 to 1 .mu.m are
defined as small rubber particles, and a salami rubber particle
having a particle size of about 1 to 5 .mu.m is defined as a large
rubber particle.
Volume ratio=.rho.p.sub.iV.sub.i/.SIGMA.q.sub.iW.sub.i
[0048] In the equation, p.sub.i is the number of small rubbery
polymer particles having a volume V.sub.i; q.sub.i is the number of
large rubbery polymer particles having a volume W.sub.i.
[0049] The present invention further includes a rubber-containing
styrenic resin having a g-value of as high as not less than 2.5
(e.g., 2.5 to 5), preferably about 3 to 5, and a mean particle size
of a rubber component dispersed therein of about 0.3 to 3 .mu.m,
preferably 0.4 to 2 .mu.m. In such styrenic resin, a diene rubber
(particularly, polybutadiene) is a preferred rubber component.
[0050] In the rubber-containing styrenic resin of the present
invention, there is a relationship between the number average
molecular weight Mn of the sytrenic matrix resin and the conversion
T of the styrenic monomer, which is represented by the following
equation (1):
Mn=aT+b (1)
[0051] wherein Mn is the number average molecular weight of the
matrix resin; T is the conversion of the styrenic monomer; a is a
constant greater than 0, b is a constant of 0 or greater; and the
number average molecular weight Mn represents the number average
molecular weight of the matrix resin calculated based on a gel
permeation chromatography measurement made of a solubilized portion
of 1 g of the rubber-containing styrenic resin dissolved in 35 mL
of a mixed solvent [methyl ethyl ketone/acetone (1/1 v/v)].
[0052] In other words, in the polymerization of the sytrenic
monomer, since the relationship between the conversion T of the
styrenic monomer and the number average molecular weight Mn of the
styrenic resin forming the matrix can be approximated with a linear
equation, the molecular weight of the matrix resin is controllable
with accuracy by controlling the conversion. In the above equation
(1), the constants "a" and "b" respectively represent the slope and
the intercept of the approximated straight line obtained by
plotting the relationship between the number average molecular
weight Mn and the conversion T. The constant "a" is greater than 0,
and b is 0 or greater.
[0053] Accordingly, the above-mentioned rubber-containing styrenic
resin can be produced by polymerizing at least the styrenic monomer
in the presence of the rubber component at a graft ratio of not
less than 1 under such conditions that the relationship between the
conversion T of the styrenic monomer and the number average
molecular weight Mn can be approximated by a linear equation.
[0054] The system in which the polymerization reaction is carried
out is not limited to a batch or semi-batch system. Even when
polymerizing in a continuous system, the relationship between the
conversion T and the number average molecular weight Mn can be
approximated with a linear equation by extrapolating the values of
the conversion T and the number average molecular weight Mn
measured at a plurality of points (e.g., two points) in the course
of the polymerization process (or route).
[0055] In the polymerization, when the conversion T of the styrenic
monomer is 10 to 80%, the Mn of the matrix resin is usually about
20,000 to 300,000 (e.g., 20,000 to 200,000), preferably about
50,000 to 200,000. A Mn (T) on phase inversion or transformation (a
Mn measured at the time where rubber particles are being formed
from the liquid phase as the polymerization reaction proceeds)
smaller than 20,000 renders the dispersed rubber particles after
the phase inversion (or phase transformation) unstable, resulting
in difficulty in retaining the particle size. A Mn (T) on phase
inversion exceeding 200,000 or a Mn (L) on completion of the
reaction exceeding 300,000 raises the viscosity of the
polymerization system too much, thus making it difficult to
efficiently disperse the rubber component. Incidentally, the phrase
"on phase inversion (or transformation)" means "the time rubber
particles are being produced from the liquid phase as the
polymerization proceeds, corresponding to the time the conversion
reaches about 10 to about 20% by weight", and the phrase "on
completion of the reaction" means, though it depends on reaction
conditions, "the time the rate of polymerization reaches a
predetermined value, corresponding to the time the conversion
reaches about 60 to about 90%".
[0056] The above-mentioned Japanese Patent Application Laid-Open
No. 199916/1994 (JP-A-6-199916) discloses that the thermoplastic
resin is obtained by heating a mixture of a free radical initiator,
a stable free radical agent, and a polymerizable monomer such as
styrene. In this system, however, since the number average
molecular weight in the initial stage of the polymerization is as
small as about 2000, it is difficult to disperse a rubber component
in particles.
[0057] When polymerizing according to the bulk polymerization
method, the Mn (T) of the matrix resin on phase inversion (a
conversion of about 10% to about 20%) is about 20,000 to 200,000,
and the Mn (L) of the matrix resin on completion of the reaction (a
conversion of about 60% to about 90%) is about 50,000 to 300,000.
In so far as the number average molecular weight is in the
above-mentioned range, the particle size can be controlled such as
to be within a suitable range, thus providing a styrenic resin of
excellent impact strength. Moreover, the value Mn (L) is 1.5 times
the value Mn (T) or more (e.g., about 1.5 to 15 times), and
preferably 1.7 times the value Mn (T) or more (about 1.7 to 15
times). A Mn (L) smaller than a value of 1.5 times the Mn (T) might
not sufficiently improve the impact resistance due to the dispersed
rubber particle size being too small. When the conversion is
practically lower than about 60%, it is desirable that the number
average molecular weight is in the range mentioned above by
extrapolating the approximation equation (linear equation)
representing the relationship between the conversion and the number
average molecular weight.
[0058] To be more specific, the Mn (L) of a rubber-containing
styrenic resin with a bimodal microdomain structure is, for
example, about 1.5 to 15 times and preferably about 1.7 to 15 times
the value of the Mn (T) [Mn(L)/Mn(T)]. When the ratio Mn (L)/Mn (T)
is smaller than 1.5, the resin sometimes cannot have a bimodal
structure. A Mn (L) exceeding fifteen times the value Mn (T) raises
the molecular weight of a matrix resin as the polymerization
reaction proceeds, with an increase in the viscosity of the
reaction system. This leads to a decrease in operating efficiency
and deterioration in the flowability and moldability of the
resulting resin.
[0059] When examined with an electron microscope, the rubber phase
in the microdomain structure of the rubber-containing styrenic
resin is observed to be thin. The further the graft-polymerization
proceeds, the stronger tendency toward the core/shell microdomain
structure the rubber-containing styrenic resin has, but it might
sometimes be of the salami type (salami structure) under certain
conditions (e.g., shearing, viscosity). Moreover, according to the
present invention, since the radical reaction proceeds in a
specific manner, the polymerization can be effected even if the
viscosity of the polymerization system during the initial stages of
the polymerization is relatively low as compared to that in a
conventional radical polymerization reaction. Therefore,
application of a larger shearing force allows the rubber component
to have a core/shell structure.
[0060] In the polymerization reaction, a polymerization initiator
may be added. Addition of a polymerization initiator provides a
higher g-value. As the polymerization initiator, use can be made of
conventional ones, such as organic peroxides represented by ketone
peroxides (e. g., cyclohexanone peroxide,
3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone
peroxide); peroxyketals (e.g.,
2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane,
1,1-bis(t-butylperoxy)-3,- 3,5-trimethylcyclohexane,
1,1-bis(t-butylperoxy)cyclohexane,
n-butyl-4,4-bis(t-butylperoxy)valate; hydroperoxides (e.g., cumene
hydroperoxide, diisopropylbenzene hydroperoxide,
2,5-dimethylhexane-2,5-d- ihydroperoxide); dialkyl peroxides (e.g.,
di-t-butyl peroxide, dicumyl peroxide, t-butyl cumyl peroxide,
.alpha.,.alpha.'-bis(t-butylperoxy-m-is- opropyl)benzene,
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3); diacyl peroxides
(e.g., benzoyl peroxide, decanoyl peroxide, lauroyl peroxide,
2,4-dichlorobenzoyl peroxide); peroxycarbonates (e.g.,
bis(t-butylcyclohexyl)peroxydicarbonate); peroxy acid esters
(t-butyl peroxy benzoate, 2,5-dimethyl-2,5-di(benzoyl
peroxy)hexane), inorganic peroxides such as hydrogen peroxide,
persulfates (e.g., potassium persulfate, ammonium persulfate), and
mixtures thereof (e.g., substituted benzoyl peroxide mixtures, such
as m-toluyl & benzoyl peroxide (trade name: Niper
BMT-K40)].
[0061] As the polymerization initiator, an azo compound may be
used, and examples of which are azobisnitriles [e.g.,
2,2'-azobisbutylonitriles typified by 2,2'-azobisisobutylonitrile
(AIBN) and 2,2'-azobis(2-methylbutylonitrile);
2,2'-azobisvaleronitriles typified by
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and
2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitriles
such as 2,2'-azobis(2-hydroxymethylpropionitrile);
1,1'-azobis-1-alkanenitriles such as
1,1'-azobis(cyclohexane-1-carbonitrile), particularly
1,1'-azobis-1-cycloalkanenitriles (e.g.,
1,1'-azobis-1-C.sub.5-8cycloalka- nenitrile); azobiscyanocarboxylic
acids typified by 4,4'-azobis(4-cyanovaleric acid);
azobutyronitriles typified by azonitrile
[2-(carbamoylazo)isobutyronitrile; azovaleronitriles typified by
2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile; azobisalkanes
[e.g., 2,2'-azobisC.sub.3-10alkanes typified by
2,2'-azobis(2-methylpropane) and
2,2'-azobis(2,4,4-trimethylpentane); and dimethyl
2,2'-azobisisobutylate.
[0062] These polymerization initiators can be used either singly or
in combination.
[0063] The ratio of the polymerization initiator to the styrenic
monomer is about 0.001/100 to 10/100 (molar ratio), and preferably
about 0.01/100 to 1/100 (molar ratio). A ratio smaller than
0.001/100 (molar ratio) may lower the rate of polymerization and
the g-value. Further, a ratio exceeding 10/100 (molar ratio)
accelerates the rate of polymerization too much, hence difficulty
in controlling the polymerization reaction.
[0064] When polymerizing, an additive (or controlling agent or
compound) may be added to control the molecular weight, etc. In so
far as the above-mentioned equation is satisfied, the additive
(controlling compound) is not particularly restricted, but a
hydroxyamine, a nitroso compound and a nitrone compound
respectively shown by the following formulae (2) to (4) are
preferred. 1
[0065] wherein R.sup.1 to R.sup.5 are the same or different, each
representing a hydrogen atom, an alkyl group, an alkoxy group, an
acyl group, an alkenyl group, an cycloalkyl group, an aryl group,
or an aralkyl group group; the groups R.sup.1 and R.sup.2, and the
groups R.sup.4 and R.sup.5 may individually bond together to form
rings.
[0066] Examples of the alkyl groups represented by the groups
R.sup.1 to R.sup.5 are straight- or branched C.sub.1-10alkyl groups
such as methyl, ethyl, propyl, isopropyl, 1-ethylpropyl, butyl,
isobutyl, s-butyl, t-butyl, pentyl, t-pentyl, isopentyl, hexyl,
1,1-diethylpropyl, octyl, isooctyl, and decyl.
[0067] As the alkoxy group, there may be exemplified
C.sub.1-10alkoxy groups such as methoxy, ethoxy, propoxy,
isopropoxy, butoxy, isobutoxy, s-butoxy, t-butoxy, pentyloxy, and
hexyloxy.
[0068] As the acyl group, there may be exemplified C.sub.2-10acyl
groups such as acetyl, propionyl, butyryl, isobutyryl, valeryl, and
hexanoyl.
[0069] As the alkenyl group, there may be exemplified
C.sub.2-10alkenyl groups such as vinyl, 1-propenyl, 2-propenyl,
isopropenyl, 2-butenyl, and 2-hexenyl.
[0070] As the cycloalkyl group, there may be exemplified
C.sub.4-10cycloalkyl groups such as cyclobutyl, cyclopentyl,
cyclohexyl, cycloheptyl, and cyclooctyl (particularly,
C.sub.5-8cycloalkyl groups such as cyclopentyl group or cyclohexyl
group). Examples of aryl group are C.sub.6-10aryl groups such as
phenyl group and naphthyl group. As the aralkyl group, there may be
mentioned, for example, C.sub.6-10aryl-C.sub.1-4alkyl groups such
as benzyl, phenethyl, and naphthylmethyl group.
[0071] In the formulae (2) to (4), each of R.sup.1 and R.sup.2 is
preferably an alkyl group (e.g., a C.sub.1-6 alkyl group,
particularly a C.sub.1-4 alkyl group), an alkoxy group (e.g., a
C.sub.1-4 alkoxy group), or an acyl group (e.g., a C.sub.1-4 acyl
group), and R.sup.3 is preferably an aryl group (e.g., a C.sub.6-12
aryl group), an aralkyl group (e.g., a C.sub.7-14 aralkyl group),
or a group represented by the following formula (3a): 2
[0072] wherein R.sup.3a to R.sup.3c are the same or different from
each other, each representing a hydrogen atom, an alkyl group, or
an aryl group; and at least two of the groups R.sup.3a to R.sup.3c
may bond together to form a ring. Each of R.sup.3a to R.sup.3c is
preferably an alkyl group (e.g., a C.sub.1-4 alkyl group).
[0073] Each of R.sup.4 and R.sup.5 is preferably an alkyl group
[e.g., a C.sub.1-10 alkyl group, preferably a C.sub.1-8 alkyl
group, more preferably a branched alkyl group such as a
t-C.sub.4-8alkyl group (particularly, t-butyl group)], or an aryl
group [e.g., a C.sub.6-12 aryl group (particularly phenyl group)].
Moreover, the groups R.sup.1 and R.sup.2, and the groups R.sup.4
and R.sup.5 may individually bond together to form rings
(preferably 4- to 8-membered rings), and at least two of the groups
R.sup.3a to R.sup.3c may bond together to form a ring (preferably a
4- to 8-membered ring), such as heterocycles such as azepine,
pyrroline, pyrrolenine, pyridine, azepine, azocine, Preferred as
the heterocycle is a 5- or 6-membered ring containing a nitrogen
atom as a hetero atom, such as pyrroline and pyridine. The ring may
be any one of aromatic, non-aromatic ring, and condensed rings
(e.g., quinoline, isoquinoline, indoline). Moreover, the same or
different carbon atoms each constituting the ring may be
substituted with one or a plurality of substituents such as an
alkyl group(s) (e.g., C.sub.1-4 alkyl groups such as methyl, ethyl,
propyl, isopropyl, and butyl groups).
[0074] The groups R.sup.1 to R.sup.5 each may have a substituent.
Examples of the substituent are alkyl groups (e.g., C.sub.1-6 alkyl
groups such as methyl, ethyl, propyl, isopropyl, and butyl groups);
aryl groups (e.g., C.sub.6-10 aryl groups such as phenyl and
naphthyl groups); amino group; N-monoalkyl-substituted amino group
(e.g., mono-C.sub.1-6alkyl-substitute- d amino groups such as
methylamino group and ethylamino group); N,N-dialkyl-substituted
amino group (di-C.sub.1-6alkyl-substituted amino groups such as
dimethylamino group and diethyl amino group); acylamino (e.g.,
C.sub.1-6acylamino groups such as formylamino and acetylamino);
halogen atoms; halogenated alkyl groups; carbonyl groups; and
hydroxy group.
[0075] Examples of the hydroxyamine (2) are linear hydroxylamines
typified by hydroxylamines which may have a substituent such as an
alkyl group, an alkoxy group, an alkenyl group, an aryl group, or
an aralkyl group (e.g., N-mono-substituted hydroxylamines such as
C.sub.1-6alkylhydroxylamines typified by methylhydroxylamine and
ethylhydroxylamine, C.sub.1-6alkoxyhydroxylamines,
methoxyhydroxylamine; C.sub.6-12arylhydroxylamines typified by
phenylhydroxylamine; N,N-di-substituted hydroxylamines such as
diC.sub.1-6alkylhydroxylamines typified by dimethylhydroxylamine,
diethylhydroxylamine, and methylethylhydroxylamine,
C.sub.1-6alkyl-C.sub.1-6alkoxyhydroxylamines typified by
ethylmethoxyhydroxylamine); N-hydroxyimides of aliphatic
dicarboxylic acids (e.g., N-hydroxysuccinic acid imide,
N-hydroxymaleimide); and cyclic hydroxylamines such as
N-hydroxyimides of non-aromatic cyclic dicarboxylic acids (e.g.,
N-hydroxytetrahydrophthalim- ide, N-hydroxyhexahydrophthalimide);
crosslinked cyclic dicarboxylic acid imides (e.g., N-hydroxyhetic
acid imide, N-hydroxyhimic acid imide), and aromatic dicarboxylic
imides (e.g., N-hydroxyphthalic imide, N-hydroxytrimellitic acid,
N-hydroxy-methylcyclohexene tricarboxylic acid imide) with
N,N-di-C.sub.1-4alkylhydroxylamines and aromatic dicarboxylic acid
imides (e.g., N-hydroxyphthalimide) particularly preferred.
[0076] The hydroxyamines (2) can be used either singly or in
combination.
[0077] As the nitroso compound (3), there may be mentioned, e.g.,
nitrosoalkanes which may be substituted with a substituent selected
from those mentioned above (e.g., nitrosoC.sub.1-10alkanes,
preferably nitrosoC.sub.2-10alkanes such as nitrosomethane,
nitrosoethane, 1-nitrosopropane, 2-nitrosopropane, 2-nitrosobutane,
2-methyl-1-nitrosopropane, 2-methyl-2-nitrosopropane (BNO),
2-methyl-2-nitrosobutane, 3-methyl-3-nitrosopentane,
3-ethyl-3-nitrosopentane, 3-methyl-3-nitrosohexane,
3-ethyl-3-nitrosohexane, 3-ethyl-3-nitrosoheptane,
4-ethyl-4-nitrosoheptane, 4-propyl-4-nitrosoheptane);
nitrosocycloalkanes (e.g., nitrosoC.sub.4-8 cycloalkanes such as
nitrosocyclopentane and nitrosocyclohexane); nitrosobenzenes which
may have a substituent (e.g., nitrosobenzene (NB), nitrosotoluene
(o-, m-, p-body), di-C.sub.1-4alkylamino-nitrosobenzens such as
p-dimethylamino-nitrosobenz- ene (DMNA); and nitrosonaphthalene.
Examples of the preferred N-substituted nitroso compound are
compounds in which at least two of the groups R.sup.3a to R.sup.3c
in the formula (3a) are the same or different from each other each
representing an alkyl group (particularly, a C.sub.1-3 alkyl
group), nitroso-t-alkanes (e.g., 2-alkyl-2-nitrosopropane- ), and
nitrosobenzenes. These nitroso compounds (3) can be used either
singly or in combination.
[0078] Incidentally, the nitroso compound (3) can be used not only
in the form of a monomer but also in the form of a dimer.
[0079] As the nitrone compound (4), there may be exemplified linear
nitrone compounds such as
N--C.sub.1-8alkyl-.alpha.-C.sub.1-8alkylnitrone- s (e.g.,
N-methyl-.alpha.-methylnitrone, N-methyl-.alpha.-ethylnitrone),
N--C.sub.1-8alkyl-.alpha.-C.sub.6-12arylnitrones (e.g.,
N-methyl-.alpha.-phenylnitrone, N-ethyl-.alpha.-phenylnitrone,
N-isopropyl-.alpha.-phenylnitrone,
N-isobutyl-.alpha.-phenylnitrone, N-s-butyl-.alpha.-phenylnitrone,
N-t-butyl-.alpha.-phenylnitrone (PBN),
N-t-pentyl-.alpha.-phenylnitrone),
N--C.sub.1-10alkyl-.alpha.-C.sub.5-8cy- cloalkylnitrones (e.g.,
compounds corresponding to the N-alkyl-.alpha.-arylnitrones listed
above such as N-isopropyl-.alpha.-cyc- lohexylnitrone,
N-isobutyl-.alpha.-cyclohexylnitrone,
N-s-butyl-.alpha.-cyclohexylnitrone,
N-t-butyl-.alpha.-cyclohexylnitrone, and
N-t-pentyl-.alpha.-cyclohexylnitrone), N-aryl-.alpha.-arylnitrones
(e.g., N-phenyl-.alpha.-phenylnitrone); and cyclic nitrone
compounds such as pyrroline-N-oxides (e.g., 1-pyrroline-N-oxide,
5,5-dimethyl-1-pyrrolin- e-N-oxide (DMPO),
5,5-diethyl-1-pyrroline-N-oxide, 4,4-diethyl-1-pyrroline- -N-oxide,
3,3-dimethyl-1-pyrroline-N-oxide), pyrrole-N-oxide,
pyridine-N-oxide (PO), and piperazine-N-oxide.
N-t-C.sub.4-8alkyl-.alpha.- -arylnitrones such as
N-t-butyl-.alpha.-phenylnitrone (PBN), pyrroline-N-oxides such as
5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and pyridine N-oxide are
particularly preferred.
[0080] These nitrone compounds (4) can be used either singly or in
combination.
[0081] These additives (2) to (4) can be used either singly or in
combination.
[0082] The ratio of the additive (controlling agent) to the
polymerization initiator is about 0.01/1 to 100/1 (molar ratio),
preferably about 0.01/1 to 10/1 (molar ratio), more preferably
about 0.1/1 to 10/1 (e.g., 0.1/1 to 5/1), and particularly about
0.1/1 to 2/1. When the ratio is smaller than 0.01/1 (molar ratio),
it is difficult to precisely control the molecular weight, and a
ratio exceeding 100/1 (molar ratio) might lower the rate of
polymerization.
[0083] In Japanese Patent Application Laid-Open No. 239434/1996
(JP-A-8-239434), 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) is
used as a free radical stabilizer, which corresponds to an additive
used in the present invention. However, the g-value of this system
is smaller than 1, and hence low rubber efficiency. Moreover, in
Japanese Patent Publication No. 6537/1993 (JP-B-5-6537), a compound
which, upon thermal decomposition, produces a free radical capable
of initiating a polymerization and a nitroxide group is used as a
reversible terminating agent for a radical polymerization. However,
in this system, it is difficult to efficiently control the
molecular weight.
[0084] The polymerization method of the styrenic monomer is not
particularly limited, and may be a conventional one (e.g., bulk
polymerization, solution polymerization, suspension polymerization,
emulsion polymeization, bulk-suspension polymerization).
[0085] Particularly preferred is a bulk polymerization or
bulk-suspension polymerization in which a rubber component
dissolved in a styrenic monomer is bulk-polymerized and then, if
necessary, suspension-polymerized. Moreover, the polymerization can
be initiated by, e.g., heating the system or irradiating the system
with light or radiations.
[0086] In the bulk-polymerization method which is advantageous in
industrial production, a solvent may be added. The species of the
solvent is not particularly limited, and a conventional one may be
used. Examples of which are aromatic hydrocarbons (e.g., benzene,
toluene, ethylbenzene, xylene), alicyclic hydrocarbons (e.g.,
cyclohexane), and aliphatic hydrocarbons (e.g., hexane, octane),
ketones (e.g., methyl ethyl ketone), esters (e.g., ethyl acetate),
and ethers (e.g., 1,4-dioxane).
[0087] The amount of the solvent can be selected from the range of,
relative to the total amount of the reaction mixture, about 0 to
30% by weight, preferably of 5 to 20% by weight. When the
proportion of the solvent exceeds 30% by weight, there arises the
need for the recovery of the solvent. This might lead to a decrease
in economical efficiency.
[0088] The polymerization may be conducted under atmospheric
pressure or applied pressure.
[0089] The polymerization temperature can be selected from the
range of about 80 to 180.degree. C. and preferably of about 90 to
150.degree. C., depending on the polymerization method, the
constituent(s) of the polymerization initiating system, the rate of
polymerization, etc. A polymerization temperature below 80.degree.
C. lowers the productivity. A temperature above 180.degree. C.
might reduce the molecular weight of the resin, leading to
deterioration in impact resistance, or it accelerates the reaction
rate, making it difficult to control the polymerization
reaction.
[0090] Usually, the polymerization may be carried out in an
atmosphere of an inert gas typified by nitrogen, helium, argon, for
example, under a stream of an inert gas.
[0091] The polymerization may be carried out in any system selected
from a batch system, a semi-batch system, and a continuous system.
For example, the polymerization may be carried out according to a
continuous polymerization method, such as a multistage bath
continuous polymerization method, a multistage column continuous
polymerization method, or a combination thereof.
[0092] According to the process of the present invention, the
morphology of a rubber-containing styrenic resin is easily
controllable with accuracy. For example, a rubber-containing
styrenic resin mainly having a core/shell structure can be prepared
by, in the above-polymerization reaction, carring on shearing
(steering) a resin composition until the conversion becomes
relatively high, or adding (admixing) a styrenic monomer at the
point where the molecular weiht of the matrix resin gets relatively
high, under such conditions that shearing force efficiently acts on
the rubber component, such as the molecular weight of the matrix
resin being relatively high (a relatively small difference between
the matrix resin and the rubber component in viscosity). Suitably
selected conditions allows the rubber component of the
rubber-containing styrenic resin to have a single peak
particle-size distribution. When preparing a rubber-containing
styrenic resin with the core/shell structure, a polymerization
reaction may be carried out initially at a suitable stirring speed
(e.g., about 70 to 100 rpm), then at a lower stirring speed (e.g.,
about 15 to 30 rpm) decreased at the time where the conversion of a
styrenic monomer reaches about 25 to 50%. Thereafter, the
composition may further be polymerized, or may further be
polymerized after being additionally mixed with a styrenic monomer
to temporarily decrease the viscosity of the polymerization system.
Incidentally, if no styrenic monomer is further added, it may be
possible to provide a rubber-containing styrenic resin having a
morphology of the salami type.
[0093] The rubber-containing styrenic resin having a bimodal
morphology comprised of both salami and core/shell structures can
be prepared by, under such conditions that the shearing force
applied to the rubber component is reduced, e.g., the molecular
weight of the matrix resin being relatively low (a relatively large
difference between the matrix resin and the rubber component in
viscosity), decreasing the shearing speed at a relatively early
stage of the polymerization, or further adding a styrenic monomer
at a stage where the molecular weight of the matrix resin is low.
When preparing the rubber-containing styrenic resin having the
bimodal structure, for example, a resin composition may be
polymerized at a suitable stirring speed (e.g., about 70 to 100
rpm, then at a lower stirring speed (e.g., about 15 to 30 rpm)
decreased at the point the conversion of the styrenic monomer is
about 20 to 40%, and, optionally, further polymerized or further
polymerized after being mixed with an additional styrenic monomer
thereby to temporarily decrease the viscosity of the polymerization
system.
[0094] When adding a styrenic monomer to the polymerization system,
in so far as the relationship between the conversion T.sub.1 of the
styrenic monomer before being added and the molecular weight
Mn.sub.1 of the matrix resin and the relationship between the
conversion T.sub.2 of the styrenic monomer after being added and
the molecular weight Mn.sub.2 of the matrix resin can be
approximated by linear equations individually, the time to add the
monomer and the amount thereof are not particularly restricted. The
amount of the styrenic monomer added is, for example, about 5 to
50% by weight (e.g., about 10 to 40% by weight) relative to the
total amount of the styrenic monomer.
[0095] As was described above, suitable control of the conditions
enables one to produce a resin having a salami or core/shell
structure according to the intended use, and also to vary the ratio
of the rubber particles with a core/shell structure to those with a
salami structure. To summarize, according to the process of the
present invention, the microdomain structure (e.g., the morphology
(configuration), particle size of the dispersed rubber particles)
of a rubber-containing structure is controllable.
[0096] The rubber-containing styrenic resin obtained by the above
reaction may optionally be separated or purified by diluting with a
solvent and then precipitating in a poor solvent or removing a
volatile matter such as the monomer or solvent.
[0097] To the rubber-containing styrenic resin of the present
invention may be added a conventional additive, such as a
stabilizer [e.g., an antioxidant (phenolic antioxidant, phosphoric
antioxidant, and the like), an ultraviolet ray absorber,
thermostabilizer], a flame retardant, a lubricant (zinc stearate,
calcium stearate, ethylenebisstearylamide, and the like), a mold
lubricant or parting agent, an antistatic agent, a filler, a
colorant (titanium oxide, red iron oxide, colorants of azo
compounds, perylene, phthalocyanine, and heterocyclic-series
compounds, and the like), a plasticizer, and a spreading agent (or
texture) (e.g., polyethylene glycol, mineral oil).
[0098] The rubber-containing styrenic resin of the present
invention may be used as a resin composition (e.g., polymer blend
or polymer alloy) by being used in combination with a variety of
resins (e.g., thermoplastic resins, thermosetting resins,
thermoplastic elastomers). For example, the rubber-containing
styrenic resin of the present invention may be melt-mixed with a
polystyrenic resin to be used as a polymer blend, or may be mixed
or melt-mixed with a resin other than polystyrenes (e.g.,
styrene-butadiene rubber, polyphenylene ether resin,
polycarbonates, polyesters) to be used as a polymer blend.
[0099] According to the present invention, a rubber-containing
styrenic resin is produced by a specific radical polymerzation, and
this allows one to easily control the morphology and the particle
size of the dispersed rubber according the intended use, realizes a
high rubber efficiency, and gives highly improved surface gloss and
impact resistance to the styrenic resin. The styrenic resin is
excellent in surface gloss even if the particle size of the
dispersed rubber is large. Moreover, even with a low rubber
content, the styrenic resin is excellent in impact resistance.
Furthermore, the present invention makes it possible to allow a
rubber-containing styrenic resin to have a microdomain structure of
the core/shell type, even if a diene rubber is employed as a rubber
component.
EXAMPLES
[0100] Hereinafter, the present invention will be described in
further detail with reference to the following-examples and should
by no means be construed as defining the scope of the
invention.
[0101] In the following Examples and Comparative Examples, unless
specifically stated otherwise, all operations were conducted under
a stream of nitrogen gas with a polymerization apparatus composed
of a 20 L reactor equipped with a stirrer and a deaerating
apparatus-equipped biaxial extruder connected to the reactor.
[0102] The Izod impact strength, rigidity, surface appearance, the
rate of polymerization, molecular weight, the constants a and b,
and the content of particles with a core/shell structure of the
styrenic resins obtained in Examples and Comparative Example were
measured in accordance with the following methods.
[0103] [Izod Impact Strength]
[0104] Measured in accordance with JIS (Japanese Industrial
standards) K7710
[0105] [Rigidity (Modulus of Bending Elasticity]
[0106] Measured in accordance with JIS K7203
[0107] [Surface Appearance (Degree of Gloss]]
[0108] The gloss (degree of gloss) was measured, at an incidence
angle of 60.degree., in accordance with JIS K7105.
[0109] [Rate of Polymerization (Conversion)]
[0110] The monomer remaining in the reaction solution obtained by
the polymerization was determined using a gas chromatography (GC,
manufactured by Shimazu Seisakusho, Co., Ltd., column: PEG 20M) in
accordance with the internal standard method (internal standard
reagent: dimethylformamide), and the decrement of the monomer was
calculated as the conversion (the rate of polymerization) to the
polymer.
[0111] [Molecular Weight]
[0112] The number average molecular weight Mn (T) and Mn (L) and
the weight average molecular weights (Mw) upon phase inversion (the
time the conversion to the matrix resin reaches about 10% to about
20%) and completion of the reaction (the time the conversion to the
matrix resin reaches about 60 to about 90%) were measured with a
gel permeation chromatography (manufactured by Shimazu Seisakusho,
Co., Ltd.) under the following conditions.
[0113] Column: Shodex K-806L, three columns arranged in line
[0114] Solvent: THF
[0115] Column temperature: 40.degree. C.
[0116] Detector: differential refractometer (RI)
[0117] Flow rate: 0.8 mL/min.
[0118] [Constants "a" and "b"]
[0119] The constants "a" and "b" were calculated from the obtained
number average molecular weight Mn and the conversion using the
equation (1).
[0120] [Content of Core/shell Structure Particle (Small
Particles)]
[0121] A transmission-type electron photomicrograph of the
composition was taken using an ultra-thin slice cut therefrom and,
of about 1000 rubbery polymer particles, the percentage by volume
of the particles each containing three or less occlusions was
calculated.
Example 1
[0122] In 150 mol of styrene monomer were dissolved 1.3 kg of
polybutadiene (manufactured by Asahi Chemical Industry, Co., Ltd.,
Diene 35A), 150 mmol of a polymerization initiator (manufactured by
NOF Corporation, Niper BMT-K40) and 75 mmol of an additive
[diethylhydroxylamine (Daicel Chemical Industries, Co., Ltd.], and
the solution was fed to the reactor. The solution was polymerized
at 95.degree. C. and a stirring speed of 85 rpm for 3.5 hours, then
at a temperature raised up to 130.degree. C. for further
polymerization. At the point where the conversion reached about
30%, the stirring speed was decreased down to 20 rpm and the
polymerization was allowed to proceed further. Thereafter, at the
point of a conversion exceeding 70%, the monomer left unreacted was
removed at 230.degree. C. with the extruder equipped with the
deaerating apparatus. The melt strand extruded from the extruder
was cooled and cut to give a sample in pellet form. The physical
properties of the sample was measured, and the results are shown in
Tables 1 and 2.
Example 2
[0123] In 100 mol of styrene monomer were dissolved 1.3 kg of
polybutadiene (manufactured by Asahi Chemical Industry, Co., Ltd.,
Diene 35A), 75 mmol of a polymerization initiator (manufactured by
NOF Corporation, Niper BMT-K40) and 37.5 mmol of an additive
(manufactured by Daicel Chemical Industries, Co., Ltd.,
diethylhydroxylamine), and the solution was fed to the reactor. The
solution was polymerized at a stirring speed of 85 rpm and
95.degree. C. for 3.5 hours, then at a temperature raised up to
130.degree. C. for further polymerization. When the conversion was
about 40%, 50 mol of a styrene monomer was added. When the
conversion of the entire polymerization system reached about 40%
again, the stirring speed was decreased down to 20 rpm and the
polymerization was allowed to proceed further. At the point where
the conversion exceeded 70%, the monomer left unreacted was removed
at 230.degree. C. with the extruder equipped with the deaerating
apparatus. The melt strand obtained was cooled and cut to give a
sample in pellet form. The physical properties of the sample were
measured, and the results are shown in Tables 1 and 2.
Example 3
[0124] In 150 mol of styrene monomer were dissolved 1.3 kg of
polybutadiene (Asahi Chemical Industry Co., Ltd., Diene 35A), 100
mmol of a polymerization initiator (Niper BMT-K40, manufactured by
NOF Corporation) and 50 mmol of an additive (manufactured by Tokyo
Kasei, Co., Ltd., 2-methyl-2-nitrosopropane), and the solution was
fed to the reactor. The solution was polymerized at a stirring
speed of 85 rpm and 95.degree. C. for 3.5 hours, then at
130.degree. C. and the polymerization was allowed to proceed
further. When the conversion reached about 30%, the stirring speed
was decreased down to 20 rpm and the polymerization was allowed to
proceed further. At the point of a conversion exceeding 70%, the
monomer left unreacted was removed at 230.degree. C. with the
extruder equipped with the deaerating apparatus. The melt strand
obtained was cooled and cut to give a sample in pellet form. The
physical properties of the sample were measured, and the results
are shown in Tables 1 and 2.
Comparative Example 1
[0125] In a 150 mol of styrene monomer were dissolved 1.3 kg of
polybutadiene (Asahi Chemical Industry Co., Ltd., Diene 35A), 150
mmol of a polymerization initiator [Niper BMT-K40, manufactured by
NOF Corporation] and 180 mmol of TEMPO (manufactured by Aldrich
Chemical Company, Inc.), and the solution was fed to the reactor.
The solution was polymerized at a temperature of 95.degree. C. and
a stirring speed of 85 rpm for 3.5 hours, then at a temperature
raised up to 130.degree. C. for further polymerization. At the
point of a conversion of about 30%, the stirring speed was
decreased down to 20 rpm and the polymerization was allowed to
proceed further. At the point of a conversion exceeding 70% , the
monomer left unreacted was removed at 230.degree. C. with the
extruder equipped with the deaerating apparatus. The melt strand
extruded from the extruder was cooled and cut to give a sample in
pellet form. The physical properties of the sample were measured,
and the results are shown in Tables 1 and 2.
Comparative Example 2
[0126] In a 150 mol of styrene monomer were dissolved 1.3 kg of
polybutadiene (Asahi Chemical Industry Co., Ltd., Diene 35A), 15
mmol of a polymerization initiator [Niper BMT-K40, manufactured by
NOF Corporation] and 45 mmol of TEMPO (manufactured by Aldrich
Chemical Company, Inc.), and the solution was fed to the reactor.
The solution was polymerized at a temperature of 95.degree. C. and
a stirring speed of 85 rpm for 3.5 hours, then at a temperature
raised up to 130.degree. C. for further polymerization. At the
point the conversion was about 30%, the stirring speed was
decreased down to 20 rpm and the polymerization was allowed to
proceed further. At the point of a conversion exceeding 70% , the
monomer left unreacted was removed at 230.degree. C. with the
extruder equipped with the deaerating apparatus. The melt strand
obtained was first cooled and then cut to give a sample in pellet
form. The physical properties of the sample were measured, and the
results are shown in Tables 1 and 2.
Comparative Example 3
[0127] In 150 mol of styrene monomer were dissolved 1.3 kg of a
styrene-butadiene copolymerized rubber (manufactured by Nippon Zeon
Co., Ltd., NS-312) and 15 mmol of a polymerization initiator
(Perbutyl Z, manufactured by NOF Corporation), and the solution was
fed to the reactor. The solution was polymerized at 110.degree. C.
and a stirring speed of 20 rpm. At the point of a conversion of
about 40%, the stirring speed was decreased down to 10 rpm, and the
polymerization was allowed to proceed further. Thereafter, at the
point the conversion exceeded 70%, the monomer left unreacted was
removed with the extruder equipped with the deaerating apparatus at
230.degree. C. The melt strand extruded from the extruder was
cooled and cut to give a sample in pellet form. The physical
properties of the sample were measured, and the results are shown
in Tables 1 and 2.
Example 4
[0128] In 150 mol of styrene monomer were dissolved 1.3 kg of
polybutadiene (manufactured by Asahi Chemical Industry Co., Ltd.,
Diene 35A), 200 mmol of a polymerization initiator (Niper BMT-K40,
manufactured by NOF Corporation) and 100 mmol of an additive
(diethylhydroxylamine, manufactured by Daicel Chemical Industries,
Co., LTd.), and the solution was fed to the reactor. The solution
was polymerized at a stirring speed of 85 rpm and 95.degree. C. for
3.5 hours, then at a temperature raised up to 130.degree. C. for
further polymerization. At the point the conversion reached about
30%, the stirring speed was decreased down to 20 rpm, and the
polymerization was allowed to proceed further. Thereafter, at the
point of a conversion exceeding 70%, the monomer left unreacted was
removed at 230.degree. C. with the extruder equipped with the
deaerating apparatus. The obtained melt strand was cooled and cut
to give a sample in pellet form. The physical properties of this
sample were measured, and the results are shown in Tables 1 and
2.
Example 5
[0129] In 100 mol of styrene monomer were dissolved 1.3 kg of
polybutadiene (manufactured by Asahi Chemical Industry, Co., Ltd.,
Diene 35A) were dissolved 100 mmol of a polymerization initiator
(Niper BMT-K40, manufactured by NOF Corporation), and 50 mmol of an
additive (diethylhydroxylamine, manufactured by Daicel Chemical
Industries, Co., Ltd.), and the solution was fed to the reactor.
The polymerization was carried out at a stirring speed of 85 rpm
and 95.degree. C. for 3.5 hours, then at a temperature raised up to
130.degree. C. for further polymerization. At the point the
conversion was about 30%, 50 mol of a monomer were added. When the
conversion of the entire polymerization system reached about 30%
again, the stirring speed was decreased down to 20 rpm, and the
polymerization was allowed to proceed further. At the point of a
conversion exceeding 70%, the monomer left unreacted was removed
with an extruder equipped with a deaerating apparatus at
230.degree. C. The obtained melt strand was cooled and cut to give
a sample in pellet form. The physical properties of the sample were
measured, and the results are shown in Tables 1 and 2.
Example 6
[0130] In a mixture of 50 mol of acrylonitrile monomer and 87 mol
of styrene monomer were dissolved 1.3 kg of polybutadiene
(manufactured by Asahi Chemical Industry Co., Ltd., Diene 35A), 328
mmol of a polymerization initiator (Niper BMT-K40, manufactured by
NOF Corporation) and 328 mmol of an additive (diethylhydroxylamine,
manufactured by Daicel Chemical Industries, Co., Ltd.), and the
solution and 3.25 kg of ethylbenzene were fed to the reactor. The
mixed solution was polymerized at a steering speed of 85 rpm and
80.degree. C. for 3.5 hours, then at a temperature raised up to
130.degree. C. for further polymerization. When the conversion of
the entire polymerization system reached about 40%, the steering
speed was decreased down to 25 rpm, and the polymerization was
allowed to proceed further. At the point of a conversion exceeding
65%, the monomer left unreaced was removed at 230.degree. C. with
the extruder equipped with the deaerating apparatus. The melt
strand obtained was cooled and cut to give a sample in pellet form
The physical properties of the sample were measured, and the
results are shown in Tables 1 and 2.
Example 7
[0131] In a mixture of 50 mol of acrylonitrile monomer and 87 mol
of styrene monomer were dissolved 1.3 kg of polybutadiene
(manufactured by Asahi Chemical Industry Co., Ltd., Diene 35A), 328
mmol of a polymerization initiator (Niper BMT-K40, manufactured by
NOF Corporation) and 820 mmol of an additive (diethylhydroxylamine,
manufactured by Daicel Chemical Industries, Co., Ltd.), and the
solution and 3.25 kg of ethylbenzene were fed to the reactor. A
polymerization was carried out at a stirring speed of 85 rpm and
80.degree. C. for 3.5 hours, then at a temperature raised up to
130.degree. C. for further polymerization. When the conversion of
the entire polymerization system reached about 40%, the stirring
speed was decreased down to 25 rpm, and the polymerization was
allowed to further proceed to further. At the point of a conversion
exceeding 65%, the monomer left unreacted was removed at
230.degree. C. with the extruder equipped with the deaerating
apparatus. The melt strand obtained were cooled and cut to give a
sample in pellet form. The physical properties of the sample were
measured, and the results are shown in Tables 1 and 2.
[0132] Incidentally, in Table 1, the Mn (T) and Mn (L) stand for
the number average molecular weight of the matrix resin upon phase
inversion (a conversion of the styrenic monomer of about 10% to
about 20%) and that upon completion of the reaction (a conversion
of the styrenic monomer of about 60 to about 90%), respectively,
and Mw represents the weight average molecular weight of the pellet
so obtained.
1 TABLE 1 Mn(T) (.times.10.sup.-4) Mn(L) (.times.10.sup.-4)
Mn(L)/Mn(T) a b Mw (pellet) (.times.10.sup.-4) Ex. 1 5.2 12.5 2.53
1084 40176 20.2 Ex. 2 6.1 13.2 2.16 900* 42500* 781* 67322* 23.8
Ex. 3 3.5 11.8 3.37 1296 14992 18.7 Comp. Ex. 1 1.2 7.1 5.92 918
707 13.0 Comp. Ex. 2 5.5 12.2 2.22 1039 37963 20.6 Comp. Ex. 3 13.2
14.8 1.12 214 127739 24.6 Ex. 4 4.0 10.1 2.53 988 24291 24.8 Ex. 5
5.0 14.3 2.86 1000* 29667* 1313* 38919* 23.5 Ex. 6 5.1 8.5 1.67 680
37400 15.6 Ex. 7 3.5 5.7 1.63 440 26200 9.8
[0133]
2 TABLE 2 Modulus of Degree Mean Core/shell Izod Impact Bending of
Particle Particle Strength Elasticity Gloss Size (.mu.m) Content
(%)*** g-value (kgf .multidot. cm/cm.sup.2) (kgf/cm.sup.2) (%) Ex.
1 0.8 7.0 2.7 7.5 21,500 98 Ex. 2 0.5 95.8 2.8 5.8 22,300 104 Ex. 3
1.1 2.0 2.5 6.8 21,100 97 Comp. Ex. 1 3.5 -- 1.3 5.5 16,200 35
Comp. Ex. 2 2.2 1.8 0.9 4.5 17,500 50 Comp. Ex. 3 0.2 98.3 3.6 4.8
21,500 105 Ex. 4 0.2 (80.2%)** 100 3.1 9.5 19,700 92 1.1 (19.8%)**
small particle Ex. 5 0.2 (88.6%)** 100 2.9 8.2 20,500 95 1.3
(11.4%)** small particle Ex. 6 0.6 -- 1.8 16.5 22,800 85 Ex. 7 1.0
-- 2.0 16.0 23,000 78
[0134] In Tables, an upper figure with the symbol "*" is the value
before the further addition of the monomer, and a lower figure is
the value after the further addition of the monomer. An upper
figure with the symbol "**" is the mean particle size of the small
particles in the bimodal morphology, and a figure within a round
bracket ( ) is the percentage of the small particles being present
in the resin (the small rubber particles expressed by percent by
volume relative to the entire rubbery polymer). A lower figure is
the mean particle size of the large particles in the bimodal
morphology, and a figure in a bracket ( ) is the percentage of the
large particles being present in the resin (the large rubber
particles expressed by percent by volume relative to the entire
rubbery polymer). The symbol "***" is the content (volume %) of
particles each containing three or less occlusions.
[0135] As obvious from Tables, the Izod impact strength, modulus of
bending elasticity, and the degree of gloss in every Example were
all more excellent than those in Comparative Examples 1 with a
dispersed rubber particle size exceeding 3 .mu.m and Comparative
Example 2 with a g-value smaller than 1, and the impact strength
and rubber efficiency in each Example were high even if the
particle size was small. Moreover, the rubber-containing styrenic
resins with a core/shell structure of Examples 1 to 2 presented the
gloss of substantially the same degree as that of the
styrene-butadiene rubber-employed resin in Comparative Example 3
despite the facts that their dispersed rubber particles had larger
particle sizes and that the resins had higher impact resistance
than in Comparative Example 3.
* * * * *