Note: Descriptions are shown in the official language in which they were submitted.
BLENDS OF AN ACRYLIC POLYMER
AND IMPACT RESISTANT INTERPOLYMER
Background of the Invention
Field of the Invention
The present invention relates to blends of an
acrylic polymer, such as polymethyl methacrylate resin,
and an impact resistant interpolymer. The resulting
blends can be used to form weatherable, impact resis-
tant articles.
Description of the Prior Art
Acrylic polymers, such as polymethyl methacrylate
resins, have good optical quality, excellent weather-
ability and good tensile and flexural strength. They
find use in a wide variety of applications including
building panels and trim, external vehicle components,
outdoor furniture, swimming pool parts, and so forth.
The impact resistance of unmodified acrylic resins is,
however, very low and precludes the use of those
resins in certain applications where a higher degree
of impact resistance is also desired.
Recently, it has been proposed in U.S. Patent No.
3,655,826 to R. P. Fellmann et al. to blend various
thermoplastic polymers (including acrylic resins, see
Col. 8, lines 11-13) and a three-stage acrylic elasto-
mer impact resistant interpolymer. This prior art
reference indicates that the selection of the third
phase of the interpolymer is crucial, and it suggests
that when impact modification is desired, the third
stage should be a methacrylate or acrylate (see Col~
5, lines 65-70).
C-6035
Summary of the Present Invention
The present invention relates to a weatherable,
impact resistant blend of: (1) an acrylic polymer,
such as, polymethyl methacrylate resin; and (2) an
impact resistant interpolymer comprising crosslinked
(meth)acrylate, crosslinked styrene-acrylonitrile,
and uncrosslinked s-tyrene-acrylonitrile polymer com-
ponents. This type of interpolymer is more fully
described in U.S. Patent No. 3,944,631 to A. J. Yu et
al. It has been described in the prior art as being
a suitable additlve for polycarbonate resins (U.S.
Patent No. 4,148,842 to A. J. Yu et al.), for blends
of chlorinated vinyl chloride polymer and vinyl
chloride polymer (U.S. Patent No. 4,160,793 to P.
Kraft et al.), and for vinyl chloride polymers (U.S.
Patent No. 4,168,285).
Description of Preferred Embodiments
The blends of the present invention comprise:
(1) an acrylic resin; and (2) an impact resistant
interpol~mer comprising crosslinked (meth)acrylate,
crosslinked styrene-acrylonitrile,and uncrosslinked
styrene-acrylonitrile polymeric components.
The term "acrylic resin", as used herein, is
intended to encompass those acrylic resins which are
made by the polymerization of acrylic ester monomers.
Details regarding the structure of these polymeric
materials as well as the processes for forming them
are available from a number of sources including
Modern Plastics Encyclopedia (1977-1978 ~dition) pp.
9-lQ; Handbook of Plastics and Elastomers, C. A.
C-6035
~ $~ ~
Harper, ed., McGraw-Hill, Inc. 1975, pp. 1-71 to 1-75;
and Polymers and Resins by B. Golding, Van Nostrand
Co., 1959, pp. 448-462. Representative polymers
which are included in this class of acrylic resins
or plastics include: polymethyl methacrylate, poly-
ethyl acrylate and polybutyl acrylate. Copolymers
of these acrylic esters with minor amounts of one or
more copolymerizable monomers are also intended to
be encompassed, e.g., the copolymer of methyl meth-
acrylate with styrene and acrylonitrile. Commer-
cially available acrylic resins include those sold
under the following trademarks: LUCITE (E.I. duPont
de Nemours and Co.); and PLEXIGLAS (Rohm and Haas
Co . ) -
The terminology "impact resistant interpolymer
comprising crosslinked (meth)acrylate, crosslinked
styrene-acrylonitrile, and uncrosslinked styrene-
acrylonitrile components" is meant to encompass the
type of interpolymer compositions described in U.S.
Patent No. 3,944,631 to A. ~. YU et al. These inter-
polymer compositions are formed by the following type
of three-step, sequential polymerization process:
1. emulsion polymerizing a monomer charge (here-
in designated "(meth)acrylate", for the purposes of
the presen-t invention), of at least one C2-C10 alkyl
acrylate, C8-C22 alkyl methacrylate or compatible
mixtures thereof, in an aqueous polymerization medium
in the presence of an effective amount of a suitable
di- or polyethylenically unsaturated crosslinking
3Q agent for such a type of monomer, with the C~-C8
alkyl acrylates being the preferred (meth)acrylate
monomers for use in this step;
C-6035
2. emulsion polymerizing a monomer charge of
styrene and acrylonitrile in an aqueous polymeriza-
tion medium, also in the presence of an effective
amoun~ of a suitable di- or polyethylenically unsat-
urated crosslinking agent for such monomers, saidpolymerization being carried out in the presence of
the product from Step 1 so that the crosslinked
(meth)acrylate and crosslinked styrene-acrylo-
nitrile components form an interpolymer wherein the
respective phases surround and penetrate one another;
and
3. either emulsion or suspension polymerizing
a monomer charge of styrene and acrylonitrile, in the
absence of a crosslinking agent, in the presence of
the product resulting from Step ~. If desired, Steps
1 and 2 can be reversed in the above-described pro-
cedure.
This product, which is used as the impact resis-
tant interpolymer component in the blends of the pres-
ent invention generally comprises from about 5% toabout S0~, by weight, of the above-identified cross-
linked ~meth)acrylate component, from about 5% to
about 35~, by weight, of the crosslinked styrene-
acrylonitrile component and from about 15~ to about
90~, by weight, of the uncrosslinked styrene-acrylo-
nitrile component. It contains little graft polymer-
ization between the styrene-acrylonitrile copolymer
components and the crosslinked (meth)acrylate poly-
meric component. Further details regarding this type
of polymer composition can be found in U.S. Patent No.
- 3,944,631 to A. J. Yu et al.
C-6035
f~
5 -
The blends of the present invention can be formu-
la-ted in weight ratios of acrylic resin to in-terpolymer
additive of from about 75:25 to about 5:95, depending
upon the precise physical properties desired in the
5 end product. A preferred range is from &0:40 to 20:80.
Blenaing can be achieved by any of the well-known
polymer blending techniques, such as a two-roll or
Branbury mixing, single or multiple screw extrusion,
or any other method which applies sufficient heat
(e.g., 175 to 300C., preferably 200 to 250C.) and
shear to the respective polymeric ingredients (acrylic
resin and interpolymer additive) to obtain a satis-
factory blend in accordance with the present inventionO
The blends of the present invention can also con-
tain any conventional functional additives normally
used with acrylic polymer compositions, including
fillers, colorants, lubricants, flame retardants, and
the like.
The present invention is further illustrated by
the Examples which follow.
C-6035
EXAMPLE 1
This Example illustrates the impact resistance,
hardness, tensile and flexural properties for a number
of blends of a commercially available polymethyl meth-
acrylate (PMMA), LUCITE 147K brand from E.I. duPont
de Nemours and Co., and the impact resistant inter-
polymer described heretofore (abbreviated "Interpoly-
mer"). The interpolymer comprised 32~, by weight,
crosslinked polybutyl acrylate, 10%, by weight, cross-
linked styrene-acrylonitrile, and 58~, by weight,
uncrosslinked styrene-acrylonitrile.
Sample Nos. 2-5 listed below were extrusion com-
pounded at temperatures o~ 221-232C. at 90 rpm in
a conventional extrusion apparatus using a 2:1 com-
pression ratio single stage screw. Sample Nos. 1 and
6 were the control samples.
Sample Composition (~ by weight)
20 1 100~ Interpolymer
2 20% P~ ~ /80% Interpolymer
3 40~ P~/60~ Interpolymer
4 50% PMMA/50% Interpolymer
60% PMMA/40~ Interpolymer
25 6 100% PMMA
Sample Nos. 1-6 were then dried overnight at 90C.
and were injection molded (on a 28 gm. capacity in-
jection machine available from Boy Company) at 190-
30 200C. with the mold temperature set at 54C. The
screw speed was set on "slow", the back pressure was
moderate, and the injection pressure setting was "34".
The cycle had an injection hold time of 10 sec. and a
screw return time of 20 sec.
C-6035
-- 7 --
The produced test plaques were tested and the
following physical properties were noted:
IMPACT RESISTANCE
_ _
Falling Dart (1) Izod Impact (2)
Sample% PMMA(J/m) (J/m)
~_ .
1 0 9P6410 641
2 20 ~6410 395
3 40 5230 176
10 4 50 2030 85
1180 64
6 100 ~e 800 21
(1) Test performed by dropping 1.8 kg. dart with 1.60
cm. diameter tip from variable heights upon 0.32
cm. thick injection molded plaque over a 2.22 cm.
diameter support. Mean failure energy was then
calculated.
(2) ASTM D-256, Method A, using 0.32 cm. thick speci-
men.
_ IMPACT RESISTANCE
Rev. Notch Izod
Impact (3~ Tensile Impact (4)
Sample % PMMA ~J/m) ~KJ/m2)
1 0 2355 435
2 20 1484 174
3 40 769 202
4 50 475 80
406 61
6 100 176 27
(3) ASTM D-256, Method E using 0.32 cm. thick speci-
mens.
(4) ASTM D-1822, specimen Type L.
C-6035
a ~
-- 8 --
These data illustrate that for Sample Nos. 2-5,
an increase in the amoun-t of interpolymer (and a cor-
responding decrease in the amount of polymethyl meth-
acrylate) yields a composite blend having improved
impact resistance.
BARCOL HARDNESS (5)
Samp~e % PMMA Instantaneous After lO sec.
l 0 48 28
2 20 60 43
3 40 66 55
4 5~ 75 66
- lO0 92 87
(5) tested on a Barcol Impressor Hardness tester
(Model No. GYZJ 935) as per the procedure sug-
gested in the instruction manual published by
Barber-Coleman Co.,. Rockford, Ill.
These data illustrate that the presence o~ poly-
methyl methacrylate contributes to the hardness of the
blend.
C-6035
qJ! I !~ ~.D ~_~
- 9 -
_ TENSILE PROPERTIES
Tens. Str.
at Yield (6) Ultimate
Sample ~PMMA (MPa) Elong. (%) (6)
1 0 32.4 120
2 20 42.7 120
3 40 49.6 130
4 50 55.1 120
59,9 9~
6 100 N.A. N.A.
(6) ASTM D~638, Type I specimen.
The presence of polymethyl methacrylate con-
tributes to the strength of the blend. The readings
for Example No. 6 were not considered reliable due to
rupture at the clamping area arising from brittleness
of the specimens.
FLEXURAL PROPERTIES
Flex. Str. (7) Flex. Mod. (7)
Sample ~P~A (MPa) (GPa)
1 0 52.7 1.69
2 20 69.6 2.07
3 40 81~3 2.56
4 50 90.9 2,54
~9.9 2.72
6 100 131.6 3.36
(7) ASTM D-790, Method I, Procedure B.
Greater flexural strength and modulus (stiff-
ness) are exhibited when the percentage of polymethyl
methacrylate is increased in the blends.
C-6035
~ 10 -
EXAMPLE 2
This Example illustrates the effect of blending
conditions such as stock temperature and mixing shear
on the impact resistance, as measured by the Izod
impact test, of a blend of 70%, by weight, impact re-
sistant interpolymer and 30%, by weight, polymethyl
methacrylate (LUCITE 40 brand from DuPont). The
respective blends in 250 gm. portions were melt fluxed
in a small batch mixer (the PREP MIXERT from Brabender
Co.) under the conditions described below. The mixing
time was varied inversely with the rpm values to keep
the number of total revolutions constant.
Total Mixing TimeEquilibrium
Sample RPMtMin.) Stock T~mp. (C.)
1 50 7 205
2 50 7 232
3 50 7 258
20 ~ 25 14 235
4.6 250
Equilibrium Torque Izod Impact
Sample (m-gm.)_ (J/m)
1 13,200 112
25 2 7,000 80
3 3,600 75
4 4,600 85
6,700 96
3 These data indicate that in a high shear batch
mixing process of the type used in the above -test,
overly severe temperature conditions during mixing
C-6035
.~. d ~P~
tend -to be detrimental to the Izod impact strength of
the blend. Varying the shear rate does not show this
effect, however, when the total number of revolutions
is held constant.
C-6035
- 12 -
EXAMPLE 3
This Example tests the ultraviolet induced dis-
coloration of the blends o the present invention
including those pigmented with titanium dioxide.
The samples were prepared by compounding the
materials at 200C. and 50 rpm for 10 minutes in a
small batch mixer apparatus and then pressed to form
homogeneous test plaques which also comprised rutile
Tio2 pigment at six parts by weight per one hundred
parts by weight o~ sample. The samples were placed
in a high intensity (30 watt) germicidal lamp appar-
atus at a distance of 3.2 cm. from the lamp for
various lengths of time, as reported below, at the
end of which time the change in color agains~ an un-
exposed control specimen from the same sample was
~easured on a Hunter Color Meter. Lower values indi-
cate a less discolored specimen.
Color Change With Respect to
Unexposed Spe~imen (1)
.
Sample 1 day 4 days 5 days
100% Inter-
polymer 13.7 17.4 19.2
20% PMMA/æO%
Interpolyme~**12.2 -- 18.1
50% PMMA/50~
Interpolymer* 9.913.2 --
50~ PM~/50%
Interpolymer** 10.0 12.9 --
50% PMMA/50~
Interpolymer*** 9.6 13.3 --
*TiO2 was added to interpolymer phase before it was
mixed with PMMA.
**TiO2 was added to the P~ phase before mixing
with the interpolymer.
***TiO2 was added a~ter the interpolymer and PMMA
were mixed.
C-6Q35
L ~ ~ ~..J
- 13 -
(1) measured on a HUNTERLAB color difference meter
(Model No. D ~5D2) in accordance with ASTM D-1925,
except that these values express color change (~)
rather than the yellowness index units suggested
in the above ASTM method.
These data indicate that polymethyl methacrylate
improves the ultraviolet light resistance of the blend
to discoloration and that the phase to which the TiO2
pigment is added does not significantly affect the
ultraviolet resistance of the blend.
C-6035
- 14 -
EXAMPLE 4
This Example illustrates the effect of processing
conditions on the impact resistance properties of a
blend of 70~, by weight, impact resistant interpolymer
and 30~, by weight, polymethyl methacrylate (LUCITE
147I~ brand from DuPont).
The blends were prepared by extrusion at various
barrel temperatures in the range of 177-265C. and
various screw speeds (40-120 xpm). A single stage
2:1 compression screw having a diameter of 1 inch was
used. The extruded specimens were then injection
molded at 200-220C. into a 54C. mold. The injection
machine described in Example 1 was used. No back pres-
sure was applied to the melt, and the cycle time
totaled 30 seconds.
Screw SpeedBarrel Temp.
Sample (RPM) (C.)
20 1 80 177
2 80 199
3 40 221
~ 60 221
221
25 6 100 221
7 120 221
8 80 243
9 80 265
C-6035
- 15 -
Falling Dart* Izod Impact*
Sample (J/m) (J/m)
1 2510 123
2 3200 128
3 2830 123
4 3680 139
4320 166
6 4380 155
7 4010 187
8 3790 187
9 3260 187
Reverse Izod Impact*Tensile Imp.*
Sample ~J/m) _ (KJ/m~)
1 481 114
2 908 105
3 491 124
4 561 122
587 120
6 539 111
7 705 130
8 833 132
9 732 120
* The same test procedures reported for the corres-
ponding tests in Example 1 were employed.
These data illustrate that for the tested blends
under extrusion conditions the general trend is for
impact strength to be optimum at moderate to high tem-
peratures and screw speeds and that insufficient levels
of temperature and shear do not allow the blend to
develop its full impact strength potential.
C-6035
- 16 -
EXAMPLE S
This Example illustrates the gloss and color char-
acteristics o~ a blend of 50%, by weight, of the impact
S resistant interpolymer and 50%, by weight, of poly-
methyl methacrylate (LUCITE 147 brand from DuPont)
which had been additionally pigmented with six parts
by weight of TiO~ to one hundred parts by weight of
the interpolymer and polymethyl methacrylate.
The test specimens of the blend were formed by
compression molding at 188C to 0.08 cm. thickness
after the blend had been mixed at 220C. and 30 rpm
in a small batch mixer. The compression molded speci-
mens were exposed in a xenon-arc WEATHER-OMETER brand
accelerated aging apparatus at 50~ relative humidity
with 18 minutes of water spray every 2 hours. The
Table sets forth the readings in the color change for
the sample with the passage of time as compared to a
commercially available impact grade acrylic of differ-
ing chemical composition.
C-6035
Color Change
With Respect to y~oQed-specinlen ~
Hours Interpolymer/P~5MA Blend Commercial Acrylic
46 0.8 0.7
5209 1.2 0.7
378 1.0 1.0
515 1.1 1.0
682 1.1 1.2
851 1.4 1.3
101014 1.1 1.6
1301 1.3 1.9
2052 1.4 l.g
~1) measured on a HUNTERLAB color difference meter
(Model No. D25D2) in accordance with ASTM D-1925,
1 except that these values express color change
( F) rather than the yellowness index units sug-
gested in the above standard method.
These data indicate that the blend has color re-
tention properties equivalent to the commercial
acrylic material.
60 Gloss Lost (%3 (2)
Hours Interpolymer/PM~SA Blend Commercial Acrylic
46 1 0
209 5 6
25378 10 10
515 12 1~
682 15 15
851 19 21
1014 26 38
301301 28 60
2052 39 76
(2) measured with a GARDNER Gloss Meter (GLOSSGARD
SYSTEM 60) in accordance with ASTM D-523.
C-6035
- 18 -
These data illustrate that the loss of gloss is
greater for the commercial acrylic after more than
about one thousand hours of exposure under the de-
scribed test conditions.
The foregoing Examples set forth certain embodi-
ments of the present invention but should not be con-
strued in a limiting manner. The scope of protection
for the present invention is set forth in the claims
which follow.
C-6035
