Note: Descriptions are shown in the official language in which they were submitted.
4 6 9
LO~-GLOSS POLYACETAL RESIN COMPOSITION AND MOLDED
ARTICLE
[Field of Industrial Application]
The present invention relates to a polyacetal
resin composition which is lowered in surface gloss
and exhibits excellent weathering ~light) resistance.
More particularly, the present invention pxovides a
polyacetal resin composition which comprises a
polyacetal resin, a specific silicone yraft copolymer
and, if necessary, a weathering (light) stabilizer and
which is lowered in surface gloss and improved in
weathering resistance without impairing the well-
balanced mechanical properties inherent in a
polyacetal resin, and a molded article thereof.
[Prior Art
As well known, a polyacetal rewin has recently
been used in various fields as an engineering plastic
excellent both in physical characteristics such as
mechanical and electrical properties and in chemical
characteristics such as resistance~ to chemicals and
heat. As the field of use of a pol~acetal resin has
been enlaxged, however, the resin has been frequently
required to exhibit more special properties as
materials.
One of such properties is low glossiness, i.e.,
low light reflectivity, which is requixed in the
fields of automotive trim parts and optical
;~ 2~4~
instruments for the purpose of reducing the
irritations to the eye due to the reflection of light,
inhibiting the malfunction of devices and imparting a
high-grade appearance. Meanwhile chances of using two
or more materials combined depending upon the object
have also increased in the fields of electrical
appliances and building materials. In such cases, a
polyacetal resin exhibits a higher surface gloss than
those of other conventional resin materials, so that
when an article is produced by assembling the parts
made from various materials including a polyacetal
resin, the polyacetal resin is inharmonious with the
other materials. Therefore, the use of a polyacetal
resin has been restricted not a little from the
standpoint of surface appearance. A process for
adding an inorganic filler such as calcium carbonate
or talc to a polyacetal resin has been known as means
for meeting the abo~e requirement of low surface
glossiness.
According to this process, however, a large
amount of talc or the like must be added in order to
attain a desirable gloss-lowering effect, so that the
resulting composition has another disadvantage that
the mechanical characteristics, particularly
elongation and toughness, are lowered to become liable
2~64~
to be broken by the stress applied during the post-
processing or assembling of a molded article or the
impact made on a molded article when, e.g., it is
dropped during the handling thereof. Further, the
polyacetal resin composition prepared according to the
above process has another disadvantage that a molded
article made therefrom causes surface deterioration
(such as crack and discoloration) when exposed to
sunlight (ultraviolet xays), rain and so on outdoors
for a long period of time, because of the poor
weathering resistance of the composition. Under these
circumstances, the development of a polyacetal resin
exhibiting lowered surface gloss and excellent
weathering (light) resistance has been expected.
( Summary of the Invention )
,
The inventors of the present invention have
intensively studied for the purpose of lowering the
surface gloss of a polyacetal resin and improving the
weathering (light~ resistance thereof in the outdoor
use without impairing the characteristics inherent in
polyacetal resin and have accomplished the present
invention.
Namely, the present invention provides a
low-gloss polyacetal resin composition which comprises
(A) 100 parts by weight of a polyacetal rasin and (B)
o ~
0.1 to 40 parts by weight of a silicone graft
copolymer prepared by the radical copolymerization of
(a) an acrylic-modified silicone with (b) a radical-
polymerizable monomer, another polyacetal resin
composition which further contains (C) 0.01 to 5 parts
by weight of a weathering (light) stabilizer in
addition to the above essential components and which
is lowered in surface gloss and exhibits excellent
weathering resistance, and a low-gloss molded article
made therefrom.
The constitution of the present invention will
now be described in more detail.
First, the polyacetal resin (A) to be used in the
pr sent invention is a high-molecular compound mainly
composed of oxymethylene (-CH20-) units which may be
either a polyoxymethylene homopolymer or a copolymer,
terpolymer or block copolymer containing a small
amount of other monomer(s) in addition to oxymethylene
unitsO These (co)polymers may be linear, branched or
crosslinked and the degree of polymerization thereof
is not particularly limited.
Second, the silicone graft copolymer (B) to be
used in the present invention is a high-molecular
compound prepared by the radical copolymerization of
(a) an acrylic-modified silicone with (b) a radical-
;, 2~6~
polymerizable monomer. The acrylic-modified silicone
(a) constituting the silicone graft copolymer (B) is a
product of the condensation of a silicone represented
by the following general formula (1) with an acryllc
compound represented by the following general formula
~2):
R~
(1) HO ~ Si -D ~ H
R2
wherein R1 and R2 are each an aliphatic
hydrocarbyl group having 1 to 10 carbon atoms, a
phenyl group or a halogenated hydrocarbyl group;
and n is an integer of 2 or above,
R3
(2) CHa=C~C~O~CH~HaCHa- Si(Ri) 2X
O
and/or
Ra
CH2=C-C-O-CHzCH~CH~ ~ SiX3
wherein R3 is a hydrogen atom or a methyl group;
2 ~ 6 ~
R4 is a methyl, ethyl or phenyl group; and X is an
alkoxy group having 1 to 10 carbon atoms, an
acetoxy group or a chlorine atom.
The substituents R1 and R2 bonded to the silicon
atom of the silicone represented by the above general
formula (1) are each an aliphatic hydrocarbyl group
having 1 to 10 carbon atoms, a phenyl group or a
halogenated hydrocarbyl group, preferably a methyl
group.
The acrylic compound represented by the above
general formula (2) includes ~-methacryloxypropyl-
dimethylchlorosilane, ~-methacryloxypropyldiethoxy-
silane, ~-methacryloxypropyldiethylchlorosilane, ~-
acryloxypropyldimethylchlorosilane, ~-methacryloxy-
propyltrichlorosilane and ~-methacryloxypropyltri-
ethoxysilane.
Preferable examples of the acrylic-modified
silicone (a) include condensation products of a,~
dihydroxypolydimethylsiloxane with ~-methacryloxy-
propyldimethylchlorosilane and with ~-methacryloxy-
propyltrichlorosilane.
N xt, the radical-polymerizable monomer (b)
constituting the silicone graft copolymer (B) includes
methacrylic acid, methyl methacrylate, ethyl
methacrylate, butyl methacrylate, 2-ethylhexyl
2 ~ 6 ~
methacrylate, cyclohexyl methacrylate, acrylic acid,
methyl acrylate, ethyl acrylate, butyl acrylate,
styrene, vinyl esters of organic acids such as vinyl
acetate and low-molecular-weight, straight-chain
hydrocarbons such as ethylene and propylene.
Among the monomers listed above, it is preferable
to use acrylic or methacrylic acid or an ester
thereof, still preferably acrylic acid, methyl
acrylate, methacrylic acid or methyl methacrylate.
Among silicone graft copolymers prepared from the
components as described above, it is particularly
preferable to use one prepared by the radical
copolymerization of (a) a condensation product of u,~
dihydroxypolydimethylsiloxane with ~-methacryloxy-
propyldimethylchlorosilane with (b) methyl acrylate or
methyl methacrylate.
The silicone graft copolymer (B) to be used in
the present invention is characterized in that the
acrylic-modified silicone polymer (a) and the radical-
polymerizable monomer or polymer thereof (b), both of
which constitute the main backbone chain of the
copolymer (B), are used not each alone but as a graft
copolymer of the both. As will be descrlbed below,
remarbale effect can be attained in the present
invention by virtue of this graft structure, whereas
2~6~9
the effect cannot be attained b~ the addition of the
component (a) or (b) alone.
Although the process for the preparation of the
graft copolymer is not particularly limited, for
example, the acrylic-modified silicone (a)
constituting the sillcone graft copolymer (B) can be
very easily prepared by a conventional condensation
process. That is, when an acrylic compound
represented by the general formula (2) whereln X is a
chlorine atom is used, the condensation may be
conducted through dehydrochlorination in the presence
of an acid acceptor, while when an acrylic compound
represented by the general formula (2) wherein X is a
methoxy or ethoxy group is used, the condensation may
be conducted through elimination of an alcohol-
molecule. In the condensation, the compound
represented by the general formula (2) and the
silicone represented by the general formula (1) may be
used in such amounts as to give an e~uivalent ratio of
the Si-X group to the SiOH group of between 0O25 and
1. When the amount of the compound (2) is too large,
the resulting silicone graft copolymer (B) will be
liable to gel easily, while when the ratio is less
than 0.25, a large amount o~ unreacted silicone will
remain unfavorably.
" 2n~4~
The acrylic-modified silicone (a) prepared by the
above process can be very smoothly copolymerized with
a conventional radical-polymerlzable monomer to give a
sllicone graft copolymer (B). It is desirable that
the amounts of the components (a) and (b) constituting
the silicone graft copolymer (B) be selected so as to
give a silicone graft copolymer having a silicone
content of 5 to 80% by weight, preferably 10 to 70% by
weight.
Although the molecular weight of the graft
copolymer thus prepared is not particularly limited,
it is generally 1000 to 200000, preferably 5000 to
lS0000.
According to the present invention, the amount of
the component (B) to be used is 0.1 to 40 parts by
weight, preferably 5 to 20 parts by weight per 100
parts by weight of the component (A). When the amount
of the component (B) is too small, the surface gloss-
lowering effect will not sufficiently be attained,
while when it is too large, the mechanical properties
and/or the heat stability will be adversely affected
and economic disadvantage will be brought about.
A molded article made from a composition
comprising a polyacetal resin (A) and the silicone
graft copolymer (B) is uniformly lGwered in surface
i~
gloss to acquire a profound and high grade appearance
and is sufficiently improved in weathering (light)
resistance. The reasons why the surface gloss is
lowered are thought to be that part of the silicone
graft copolymer (B) dispersed in the molded article in
the form of a particle having a size of 0.5 to 2 ~m
reaches the surface of the article to roughen the
surface, thus lowering the gloss thereof and that the
silicone moiety uniformly dispersed in the surface
area covers the polyacetal resin to lower the surface
gloss. A practically desirable surface gloss is 40%
or below, still preferably 15% or below as determined
by the process which will be described below, though
the surface gloss varies depending upon molding
conditions and the degree of mold surface finishing.
Although the composition of the present invention
exhibits low gloss and excellent weathering resistance
even when used as such, the additional use of a
weathering (light) stabilizer (C) is more effective in
improving the weathering (light) resistance,
particularly inhibiting the crack of the surface of
the molded article and the discoloration thereof.
The weathering (light) stabilizer to be
preferably used in the present invention is one or
more members selected from the group consisting of (1)
i i 2~B~
benzotriazoles, (2) benzophenones, (3) oxanilides, (4)
aromatic benzoates, (5) cyanoacrylates and (6)
hindered amines.
Examples of the stabilizer are as follows.
Namely, examples of the benzotriazole (1) include
2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-
hydroxy-3',5'-di-t-butylphenyl)benzotriazole, 2-(3,5-
di-t-amyl-2-hydroxyphenyl)benzotriazole, 2-(2'-
hydroxy-3',5'-diisoamylphenyl)benzotriazole,
2-[2-hydroxy-3,5-bis( a, a-dimethylbenzyl)phenyl]-
benzotriazole and 2-(2'-hydroxy-4'-octoxyphenyl)-
benzotriazole.
Examples of the benzophenones (2) include 2,4-
dihydroxybenzophenone, 2-hydroxy-4-methoxy-
benzophenone, 2-hydroxy-4-octoxybenzophenone,
2-hydroxy-4-dodecyloxy benzophenone, 2,2'-dihydroxy-
4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-
benzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone
and 2-hydroxy-4-oxybenzylbenzophenone.
Examples of the oxanilindes (3) include N-(2-
ethylphenyl)-N'-(2-ethoxy-5-t-butylphenyl)oxanilide
and N-(2-ethylphenyl)-N'-(2-ethoxyphenyl)oxanilide.
Examples of the aromatic benzoates (4) include
p-t-butylphenyl salicylate and p-octylphenyl
salicylate.
2 ~ 9
Examples of the cyanoacrylates (5) include
2-ethylhexyl 2-cyano 3,3-diphenylacrylate and ethyl
2-cyano-3,3-diphenylacrylate.
The hindered amines (6) are piperidine
derivatives each having a sterically hindering group
and examples thereof include 4-acetoxy-2,2,6,6-
tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-
tetramethylpiperidine, 4-acryloyloxy-2,2,6,6,-
tetramethylpiperidine, 4-methoxy-2,2,6,6-
tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-
tetramethylpiperidine, 4-cyclohexyloxy-2,2,6,6-tetra-
methylpiperidine, 4-phenoxy-2,2,6,6-tetramethyl-
piperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine,
4-(phenylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine,
bis(2,.2,6,6-tetramethyl-4-piperidyl) oxalate,
bis(2,2,6,6-tetramethyl-4-piperidyl) malonate,
bis(2,2,6,6-tetramethyl-4-piperidyl) adipate,
bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate,
bis(1,2,2,6,6-peptamethyl-4-piperidyl) sebacate,
bis(2,2,6,6-tetramethyl-4-piperidyl) terephthalate,
1,2-bis(2,2,6,6-tetramethyl-4-piperidyloxy)ethane,
bis(2,2,6,6-tetramethyl-4-piperidyl) hexamethylene-
1,6-dicarbamate, bis(1-methyl-2,2,6,6-tetramethyl-
4-piperidyl) adipate and tris(2,2,6,6-tetramethyl-
4-piperidyl) benzene-1,3,5-tricarboxylate. Further,
1 ~ 2 ~ 9
high-molecular polycondensates of piperidine
derivatives, such as dimethyl succinate-l-
(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-
piperidine polycondensate, are effectively used.
According to the present invention, one or more
of the above weathering (light) stabilizers may be
used. Particularly, the simultaneous use of one of
the above stabilizers(l) to (5) with a hindered amine
(6) is effective and, more particularly, the
simultaneous use of a benzotriazole (1) with a
hindered amine (6) is most effective.
The weathering (light) stabilizer (C) may be used
in an amount of 0.01 to 5 parts by weight, preferably
0.02 to 3 parts by weight, per 100 parts by weight of
the component (A). When the amount of the stabilizer
(C) is too small, no effect will be attained, while
the use thereof in too large an amount will bring
about not only an economic disadvantage but also
lowering in the mechanical properties or pollution of
a mold.
Although even a composition prepared by adding a
weathering (light) stabilizer (C) alone to a
polyacetal resin exhibits fairly excellent weathexing
resistance, the weathering resistance is not enough to
withstand the long-term exposure to sunllght
1 ~ 2~
(ultraviolet rays) or rain outdoors. The use of a
weathering (light) stabilizer together with the
silicone graft copolymer (B) can give a molded article
exhibiting low surface gloss and more improved
weathering resistance. Further, it is desirable that
the composition of the present invention further
contain various known stabilizers in order to improve
the heat stability and so on. For this purpose, it is
desirable to use one or more members selected from
among known antioxidants, nitrogenous compounds and
alkali and alkaline earth metal compounds.
Furthermore, the composition of the present
invention may be arbitrarily colored by the addition
of various carbon blacks or other dyes or pigments.
Particularly, the use of carbon black is
effective in further improving the weathering (light)
resistance of the composition~
The composition of the present invention may
further contain one or more conventional additives in
order to impart desirable characteristics thereto
depending upon the object and examples of the
additives include lubricant, nucleating agent, mold
release agent, anbistatic agent, other surfactant,
organic high-molecular materials other than the
component (B) and inorganic or organic, fibrous,
l ;j 2 ~ 9
granular, powdery or flaky fillers.
The additlonal use of a known additive having a
gloss-lowering effect (for example~ talc, calcium
carbonate or aluminum silicate) is somewhat effective.
The composition of the present invention can be
prepared by a conventional process for the preparation
of a synthetic resin composition with conventional
equipment therefor. Namely, necessary components are
mixed together and kneaded and extruded with a single-
or twin-screw extruder to give pellets, followed by
the molding of the pellets. Alternatively, the
preparation of the composition may be conducted in a
molding machine simultaneously with the molding
thereof. Further, a process which comprises
pulverizing a part or the whole of the resin
components, mixing the pulverized components with the
residual components, melt-extruding the obtained
mixture to give pellets and molding the pellets may be
employed.
The above stabilizers and additives may be added
in any arbitrary step and, of course, even just before
the production of a final molded article.
The resin composition of the present invention
may be molded by extrusion, injection, compression,
vacuum blow or expansion molding.
lt~ 20~69
As described above, the composition of the
present invention comprising a polyacetal resin and a
specific silicone graft copolymer exhibits an effect
of giving a molded article which is remarkably lowered
in surface gloss without impairing the well-balanced
mechanical properties inherent in a polyacetal resin.
Further, the composition containing a weathering
(light) stabilizer in addition to the above components
is further improved in weathering resistance which has
been problematic when an inorganic filler (such as
talc or calcium carbonate) is used. Particularly, it
exhibits a remarkably lengthened crack initiation time
and reduced discoloration.
Accordingly, the low-gloss polyacetal resin
composition of the present invention can be favorably
used in the production of various molded articles
necessitating high-grade appearances and high
weathering (light) resistance, i.e., automotive
internal trim parts (such as inner handle, regulator
handle and trim clip) and in the fields which are
required to have a profound appearance in spite of
long-term exposure to sunlight and rain, for example,
automotive exterior trim parts (such as outer handle
and fuel lid), electrical appliances, building
materials, cameras and housewares.
2 0 ~ 9
[Exarnple]
The present invention wi~l now be described by
referring to the following Examples, though the
present invention is not limited by them.
In the Examples, characteristic values such as
surface appearance, weathering (light) resistance and
so on were determined by the following methods.
(1) Surface appearance
The surface appearance was ranked according to
the following four criteria based on the dullness and
uniformity of the surface, wherein a smaller numeral
represents a state of more excellent dullness and
uniformity.
l...when a sample was irradiated with a
fluorescent lamp, no outlines of the lamp
were recognized on the surface of a sample
and the surface was uniformly rough.
2...the surface of a sample was ununiformly rough
though no outlines of a fluorescent lamp were
recognized on the surface.
3...the outlines of a fluorescent lamp were
recognized on the surface of a sample, though
they were indistinct.
4...distinct outlines of a fluorescent lamp were
recognlzed on the surface and the surace was
4 ~
nearly smooth.
(2) Surface gloss
The gloss of a test piece (70 mm x 40 mm x 3 mm)
prepared by molding under the followlng conditions was
determined according to the method of JIS K 7105 with
a variable angle digital glossmeter (mfd. by Suga Test
Instruments Co., Ltd.; UGV-40) at 45-45 reflection.
O molding machine: mfd. by Toshiba Corporation,
IS80
O moldinq conditions:
nozzle Cl C2 C3
cylinder temp. 200 190 180 160 (C)
injection 650 (kgtcm2)
pressure
injection 1.0 (m/min)
speed
mold temp. 80 (C)
(3) Weathering test
A test piece was irradiated with ultraviolet rays
in a weathermeter (mfd. by Suga Test Instruments Co.,
Ltd., WBL-SUN-HCH type) under the conditions of a
black panel temperature of 63C and weathering
(including the spray with rain) to determine the crack
initiation time and the change in the surface
appearance.
~ crack initiation time
1~ 2~646~
A test piece was irradiated with ultraviolet rays
under the above conditions. The sur~ace of the test
piece was observed with a 10 x magnifier to determine
the time elapsed until crack was recognized ~or the
first time. This time was regarded as the crack
initiation time. A higher value means a better
weathering resistance.
~ change in the surface appearance
A test piece was irradiated with ultraviolet rays
under the above conditions for a predetermined time
(600, 1000 or 2000 hours) to observe changes in the
hue of the test piece before and after the irradiation
and the crack. The observed changes were indicated by
five ranks. A smaller numeral means less changes,
i.e., less discoloration and less crack.
(4) Tensile test
The tensile strength and tensile elongation were
determined according to ASTM D 638.
Examples 1 to 19 and Comparative Examples 1 to 17
As shown in Table 1, a polyacetal resin (A) [a
product of Polyplastics; trade name "Duracon (MgO)~
was mixed with a silicone graft copolymer (B) alone or
together with a weathering (light) stabilizer (C) and,
if necessary, carbon black. The obtained mixture was
melt-kneaded with a 30-mm twin-screw extruder to give
~()
a pelletized composition. Thls composition was molded
into a test piece with an lnjection molding machlne.
This test piece was examined for gloss, weathering
resistance and other characterlstics. For comparison,
the same procedure as that described above was
repeated except that ungrafted silicone oil, an
acrylic resin, a weathering (light) stabilizer and/or
a conventional additive having a gloss-lowering effect
were used instead of the component (B) as specified in
Table 2. The results are given in Tables 1 and 2.
2 ~ 9
~1
_ O O m O ~ ~ ~. ~ _ _ _ _ L I Ln o ~' _ _ ~D O
-0 ~ ; 1~ Un' _ _ _ _ N- _ ~ ~
O O .1 O I O L L`~ r-~ O N ~ ~ ~') O Ln
_ O ~1 C~ '.'.10 _ __ -_ L O-_ _ _~ .,
Z ~/1 O O O O r L ~ N .-1 N _ .-1 L/~
g ~
~' ~
2 ~ 9
_~ ~ o~ ~ __ _ o, _ ~ ~ _ _ _ ~I ~
~ ~ , ~
'~0 EQ' ~ ~ i ~ ~ ~ ___ _ , ~ ~ ~ ~ ~
~1 O l O t.) O t.) O _ _ _ _ ~ o _ N _ ~_ o
4 ~ ~ ~
V V Q. O J~J 3 _ ~ 3 V V ~ JJ C "
e I .a 4 ,4 1:: ''I a) C . .~
_ ~ _, ~ ~ P. ~ ~ ~ O ~ ~ a~ ~ o ~ ~
_I tJ~ ~ h 3 ~1 ~r
o . ~_ ,~ ~ ,~: j a v
_ _ o ---- ~ ----~ . _ ~ L L ~
~ i ~ ~ ~
_ ~ ~ `
_ r o _ -- ~ o tJ o _ _ o o N N N _ Itl _ _ N
~D O _ _ ~.) O ~ O N O _ O _ r o _ _ _ r1 N
Z u~ o _ _ C.)~ ~o _ o _ _ _ r o N _ _ It> O
X ~r o 1~ o ~.) o o N 0 O 'r It) "_, 0:1 N
:' _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
O ~ ~ O t.) O ~ O N O ~ r o ~r u~ ~ ~ N
~.1 ~3 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
N N O ~ O O O N ~r U~ N 1-~ Il) 1~1 r o
~0 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
,~ o t~ o ~ o ~ r o ~7 u~ u~ r N
o o _ ~ o~ L _r o---- _ ~ _
~1 N ~ V O C O E
3 o ~:L o O ~ ~ ~ ~ o n 4~ q~ a
~ 3 3 A 3 ~ a
C O v Q. ~ ~ 0 o nl S~ ~ 0 O
~J
~\ O . N :~ O A m o .r~
_ _ 3 u~-- o ~ ~ ~ u o I J ."
~ ~ ~ .~ _ 0 m o ,1 3 C) O
note 1)
B-1: copolymer comprising methyl methacrylate
and an acrylic-modified silicone prepared
from a,~-dihydroxypolydimethylsiloxane and
~-methacryloxypropyldimethylchlorosilane
B-2: copolymer comprising methyl methacrylate
and an acrylic-modified silicone prepared
from a,~fdihydroxypolydimethylsiloxane and
~-methacryloxypropyltrichlorosilane
note 2)
C-1: 2-[2-hydroxy-3,5-bis(a,a-dimethylbenzyl)-
phenyl]benzotriazole
C-2: 2-hydroxy-4-oxybenzylbenzophenone
C-3: bis(2,2,6,6-tetramethyl-4-piperidyl)
sebacate
C-4: dimethyl succinate-1-(2-hydroxyethyl)-
4-hydroxy-2,2,6,6-tetramethylpiperidine
polycondensate
