Note: Descriptions are shown in the official language in which they were submitted.
. CA 02218167 1997-11-04
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ACRYLONITRILE/SlY~N~/AC~YLATE COP31YMERS WITH IMPROVED STAIN
RESISTANCE
Field of the Invention
The present invention relates to acrylonitrile -styrene -
acrylate (ASA) copolymers with improved stain-resistance and
methods for improving the stain resistance of ASA copolymers.
Background of the Invention
Acrylonitrile/styrene/acrylate (ASA) copolymers are
weatherable, W -resistant thermoplastic polymers that retain
color and property stability in outdoor exposure. These
copolymers have many applications in automotive, construction,
and recreational markets. For example, ASA copolymers are
used in production of automotive body moldings, exterior and
interior trim parts, bumper parts, pickup truck caps, and
recreational vehicle components; in home siding and trim,
gutters and downspouts, shutters, and window frames; and in
swimming pool and pump components, outdoor furniture, bath
tubs, shower stalls, and spas. In general, ASA copolymers are
excellent candidates for fabricating articles that will be
used outdoors because the copolymers exhibit good weathering
properties.
In some applications for which ASA copolymers are
suitable, the formed article may be brought into contact with
CA 02218167 1997-11-04
water, solvents, or other substances that might damage the
surface of the article. For example, ASA copolymers are used
for the fabrication of automotive grills such as the cowl vent
grill below the windshield. One concern for a cowl vent grill
is the resistance of the plastic to water and/or the chemicals
in windshield washer solution or other products that may come
lnto contact with the plastic grill. Products of concern
including cleaning and polishing materials. Traditional ASA
has been found to stain in such applications.
Staining of ASA may also be observed in other ASA end use
applications involving exposure to water or aqueous mixtures
of other agents. For example, hot tub spas have been found to
show stains. Pigments, dyestuffs, and water treatment
chemicals have been suspected of contributing to the staining
of ASA in these applications.
"Staining," as used herein, includes discoloration,
blushing, loss of gloss, weathering and/or whitening, which is
perceived as a surface imperfection. Such staining or
weathering typically results from exposure to water or
mixtures of water and other agents such as chemicals,
solvents, pigments and dyes. Staining can be manifested via
the appearance of water spot-like markc on the polymer
surface. Although staining can occur at any time, parts which
have been exposed outdoors or weathered have been found to be
more likely to show stains.
CA 02218167 1997-11-04
The appearance of staining in weathered parts is highly
disadvantageous, because many articles that may potentially be
manufactured using ASA copolymers would likely come into
contact with water or products containing the agents described
above. Thus, it is highly desirable to produce ASA articles
that are resistant to staining and other appearance problems
that could develop during use.
It has been discovered that ASA copolymer compositions
that include certain fluorine- or silicon-based additives have
a high degree of stain, spotting and weathering resistance.
Detailed Description
The compositions of the invention comprise both
ASA copolymers and a fluorine or silicon-based additive, or a
mixture of these additives, in an amount sufficient to improve
the stain resistance of the composition. An effective amount
is an amount that demonstrates a measurable or observable
difference. The fluorine-based additive is a fluorinated
compound, preferably a fluorosurfactant. The silicon-based
additive is a polymeric silicon material, preferabty a
polysiloxane. Materials that are hydrophobic, nonionic
compounds compounds that can migrate through the ASA matrix to
t~.e surface of the formed article are preferred.
The ASA copolymers of the invention are known in the art
and may be produced by known processes, for example, according
to the methods described in U.S. Pat. Nos. 3,944,631;
CA 02218167 1997-11-04
4,111,876; 4,528,328; 4,537,933; 5,068,285j and 5,070,142, the
disclosures of each being incorporated herein by reference.
ASA copolymers comprise at least a styrene-acrylonitrile
copolymer matrix containing acrylic rubber particles. The
styrene portion may comprise vinyl aromatic monomers selected
from styrene and alkyl styrenes, such as alpha methyl styrene,
p-methyl styrene, ethyl styrene, isopropyl styrene, and the
like, and halogenated substituted styrenes such as
chlorostyrene and the like, and mixtures thereof. Copolymer
matrices of acrylonitrile and alpha-methyl styrene are
preferred. ASA copolymers are generally random amorphous
terpolymer produced either by a mass copolymerization or
emulsion copolymerization process or by grafting styrene-
acrylonitrile to the acrylic elastomer backbone.
The acrylic rubber particles may be, and preferably are,
grafted to the styrene-acrylonitrile copolymer matrix. During
the polymerization, the acrylic rubber particles may be
grafted to the polystyrene/acrylonitrile (SAN) matrix by
reaction of unsaturation remaining in the rubber or grafted to
~he SAN matrix after polymerization by a further
The ASA copolymer preferably has a weight average
molecular wei~ht, as measured against a polystyrene standard,
of from about 50,000 to about 120,000.
The acrylic rubber particles may be, and preferably are,
at least partially crosslinked. In one embodiment of the
- CA 02218167 1997-11-04
invention, the ASA polymer may be made by first emulsion
polymerization of an alkyl acrylate or methacrylate or
mixtures thereof, with at least one crosslinking monomer to
form a crosslinked acrylate elastomer, followed by emulsion
polymerization of a mixture of the styrene monomer, the
acrylonitrile, and the acrylate rubber. The sequence of the
first two steps may be reversed, so that the acrylic elastomer
is polymerized in the presence of the already-formed
crosslinked styrene-acrylonitrile copolymer.
In general, in forming the acrylic rubber, the acrylate
and/or methacrylate monomers are chosen from alkyl acrylates
and methacrylates having alkyl groups of Cl to C12, preferably
C4 to C~0. The C4 to C~ alkyl acrylates and mixtures of these
acrylates with other acrylates or methacrylates are preferred.
lS Examples of useful acrylic monomers include, without
limitation, ethyl acrylate, isopropyl acrylate, propyl
acrylate, n-butyl acrylate, hexyl acrylate, 2-ethylhexyl
acrylate, dodecyl acrylate, 3-methyl-1-butyl acrylate,
isobutyl acrylate, isodecyl acrylate, and the corresponding
methacrylates. The crosslinking monomer is a
polyethylenically unsaturated monomer, preferably a divinyl,
diacrylate, t iacrylate, or tetraacrylate monomer.
The crosslinking monomers of the acrylic polymerizations
preferably comprise from about 0.05 to about 10 percent, and
most preferably 0.1 to 5 percent, by weight of the respective
CA 02218167 1997-11-04
monomer mixtures. Examples of suitable crosslinking monomers
include, without limitation, divinyl benzene, trimethylol
triacrylate, allyl methacrylate, diallyl fumarate, diallyl
maleate, 1,3-butylene dimethacrylate, diethylene
dimethacrylate, ethylene glycol dimethacrylate,
trimethylolpropane trimethacrylate, trimethylolpropane
triacrylate, diethylene glycol diacrylate, divinyl ether,
diallyl phthalate, divinyl sorbitol, triethylene glycol
dimethacrylate, trimethylene glycol diacrylate, butylene
glycol diacrylate, pentamethylene glycol diacrylate, glyceryl
triacrylate, and the tetraacrylate ester of pentaerythritol.
The emulsion polymerizations may be carried out in the
manner usual for the art, for example with anionic, nonionic,
or cationic emulsifiers in amounts of from about 0.5 to about
5~ by weight of the emulsion. Conventional initiators and
chain transfer agents may be employed, including, without
limitation, hydrogen peroxide and organic peroxides and redox
catalysts may be used. Initiators may be used in amounts of
from about 0.005 to about 2 percent by weight, based on the
weight of the monomers.
The polymerization of styrene and acrylonitrile provides
a hard matrix component. The preferred ratio of acrylonitrile
to styrene is from about 1 to 3 acrylonitrile to about 1 to 7
styrene, by weight. The acrylonitrile-styrene matrix should
be in the range of from about 20 to about 60 percent by weight
CA 02218167 1997-11-04
of the ASA copolymer, preferably from about 20 to about 40
percent by weight of the ASA copolymer. Compositions with oc-
methyl styrene are preferred.
The ASA copolymer preferably comprises from about 5 to
about 95 percent by weight of the acrylic elastomer, from 0 to
about 35 percent by weight of the crosslinked styrene-
acrylonitrile copolymer, and from about 5 to about 95 percent
by weight of the uncrosslinked styrene-acrylonitrile copolymer
matrix. The acrylic rubber particles may contain
thermoplastic polymer occlusions, such as, for example, when
mass polymerization is used to prepare the ASA copolymer.
Suitable ASA copolymer materials are commercially
available. Preferred among the commercial products is LURAN~
S 778T, commercially available from BASF Corporation, 3000
Continental Drive North, Mt. Olive, New Jersey 07828.
Preferred fluorine-based additives are hydrophobic
fluorosurfactants. Fluorosurfactants are characterized in
that they have a hydrophobic portion ~CnF2n~1 and a hydrophilic
portion. The fluorosurfactant are preferably noniohic. An
especially preferred fluorosurfactant has a fluorocarbyl
radical with F(CF2CFX)n, wherein n is 3 to 8.
The hydrophobic fluorosurfactants may be added to the ASA
copolymer composition in amounts of up to about 0.5 percent by
weight, preferably from about 0.005 to about 0.15 percent by
23 weight, and particularly preferably from about .08 to about
CA 02218167 1997-11-04
.12 percent by weight. Fluorosurfactants are available
commercially, for example from DuPont Specialty Chemicals,
Wilmington, Delaware, under the tradename ZONYL~. Particularly
preferred among these are ZONYL~ FSN 100 and FSO 100.
Preferred silicon-based additives are silicone fluids and
greases. Among these, polydimethylsiloxanes,
polyphenylmethylsiloxanes, and polydiphenylsiloxanes are
especially useful. Particularly preferred are
polyphenylmethylsiloxanes.
The silicone materials of the invention may have
viscosities of between about 50 and about 250,000 centistokes.
It is particularly preferred to use polysiloxanes that have
viscosities of from about 50,000 to about 150,000 centistokes.
Such silicones are available commercially, for example from
Dow Corning Corp., Midland, Michigan and General Electric,
Scenectady, New York. Preferred among these is 710 Fluid,
available from Dow Corning.
The silicone materials may be added to the ASA copolymer
composition in amounts of up to about 5 percent by weight,
preferably from about .1 to about 3 percent by weight, and
particularly preferably from about .1 to about 1 percent by
weight.
In addition to the ASA copolymer and the fluorine- or
silicon-based additive, the ASA copolymer compositions of the
invention may include further polymer components or additives.
CA 02218167 1997-11-04
For example, the ASA copolymer may be blen~ed with one or more
different thermoplastic polymers, including, without
limitation, blends with polystyrenes, polycarbonates,
unmodified styrene-acrylonitrile copolymers, polyvinyl
chloride, polymethylmethacrylate, and pblyesters such as
polybutylene terephthalate and polyethylene terephthalate.
Further additives that may be incorporated into the ASA
copolymer compositions of the invention include, without
limitation, hindered amine stabilizers (HALS), benzotriazole
W absorbers, organic and inorganic pigments, dyes, and
fillers, thermal stabilizers, antioxidants, lubricants,
processing aids, and plasticizers such as phenyl dicarboxylic
esters of C7 to Cl1 alcohols, such as di-octyl phthalate and
di-isononyl phthalate. Preferably, the compositions of the
invention include from about 0.1 to about 1.0 percent by
weight of a HALS or a mixture of HALS.
The ASA compositions may be blended or compounded in any
manner known in the art. For example, and without any
limitation, polymer blends may be prepared by mixing in a
single- or twin-screw extruder, milling in a roll mill or
Banbury mixer at an elevated temperature, continuous melt
blending, or by calendering. All such blend preparations may
be preceded by mixing in, for example, a Herschel type mixer.
Blending can be carried out in the same equipment being used
to produce the final article, e.g., in a screw-type extruder.
CA 02218167 1997-11-04
Alternatively, the blend may be produced as pellets for later
thermoforming by, for example, melt mixing or extrusion
molding techniques. Compounding and pelletizing may be done
by any of various means known in the art.
The compositions of the invention may be processed by any
thermoforming technique, for example by injection molding,
compression molding, and extrusion molding techniques.
Molding conditions may be the same as conditions usually
employed for molding ASA copolymer compositions. Molding
conditions for particular compounds and equipment may be
optimized by straightforward testing according to the usual
methods.
The compositions of the invention may be used to
advantageously make automotive vehicle components such as cowl
vent grills and the like as well as construction components,
parts for outdoor articles and articles exposed to water such
as tubs, showers, and spas.
The invention is illustrated by the following examples.
The examples are merely illustrative and do not in any way
limit the scope of the invention as described and claimed.
All parts are parts by weight unless otherwise noted.
EXAMPLE 1
The present invention was testing according to Ford Motor
Company Test Procedure No. 84-52509. A commercially available
ASA from BASF Corporation, LURAN~ S 778T, was employed as the
CA 02218167 1997-11-04
ASA with a standard W stabilizer package.' The same material
without the standard W stabilizer package was used as the ASA
without W stabilizer. All samples contained carbon black
according to BASF Corporation's Color Code BLK-31261. Varying
S amounts of the fluoro surfactant or silicone-containing
additives of the invention were added to the identified ASA.
The ingredients of the composition were mixed in a Herschel-
type mixer and subsequently compounded in a twin screw 4Omm
extruder.
IO Sample plaques were made out of the samples below using
standard injectin molding techniques. After a 24 hour ambient
aging period, the plaques where placed in a Xenon Arc
Weatherometer per SAE J1960 procedure. After 2500 kJ/m2, the
following staining tests were performed.
CA 02218167 1997~ 04
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TABLE 1
COMPOSITION ASA WITH W ASA WITHOUT ADDITIVE AMOUNT
PACKAGE UV PACKAGE
A X -0- -0-
X --O-- --O--
C X DUPONT 0.1
ZONYL~ FSO
100
D X DUPONT 0.1
ZONYL~ FSO
100
E X DUPONT 0.1
ZONYL~ FSO
100
F' X . DUPONT 0.1
ZONYL~ FSO
100
G X DUPONT 0.1
ZONYL~ FSO
100
H X FS0 100 0.1
I X -0- -~-
J X~ FSO 100 0.1
K X DOW CORNING 0.5
SILICONE
710 FLUID
L X FSN 100 O.l
1 = 1/2 OF STANDARD W PACKAGE
2 = CARBON BLACK INTRODUCED VIA MASTERBATCH CONCENTRATE RATHER
THAN EXTRUSION.
12
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..
TABLE 2
~S~-k~ATIONS TAx~~ WHI~ ~POTS WERE ~ TEST PANEL
Using a pipette, one spot each ~f Ford Motor Company
commercially ~v~ilable ~nd~hield wa~her fluid, win~ ield
washer fluid with rubber ~bbing extract, and ~indshield
.w~sher fl~i~ with nylon ~U~ing extract, was dropped on a
prepared s~mple panel. The appearance of ~he pipetted liquid
spo~ was observe~ ~fter th~ee (3~ minutes,
SAMPLE A PE~ ~RANC E; O ' SPOI 'S ON PANEL
P~ S OT DO~" ~ PREA~ OUT
B S OT DO~-' T PREA~ OUT
C SPOT ~JERY UNIFORM; LITTI-E SPRE~D
D SPOT SPREA~ OUT AN~ COUPL,ED 1'0 EACH
OTHER, OILY APPEARANCE OF SPOTS
( R~INBOW ~
E SPOTS SPREAl:) OUT AND COUPLE;D TO EACH
OTHER (~AINE3OW)
F SPOTS SPRE;AD OUT ANl~ C:OUPLED TO EACH
OTHER ~ SLIGHT RP-INB0~0 ~
G SPOTS ARE ~IOMOGENOUS ~D VERY LITTLE
SP~ DING AS IN CONTROL B lNO E~AINBOW)
H SPOTS SPREAD OUT INTERMEDIATE~Y
l~LIG~T RAIN~O~)
I ~POTS SPREAD OU~ SIGNIFICANTLY BUT
RETAINED ROUNP SHAPE (RAI~OW)
J SPO~S SPREAD OUT SIGNIFICANTLY
(~A.r~Bow)
K SPO~ RETAI~ SHAPE: ~XD NOT SPREAD OUT
L SPO ", SPREAD SIGNIFIC~TLYi HI~H
TE~PERA~U~E tRAINBOW)
13
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TABLE 3
OBSERVATIONS OF PANEL APPEARANCE SUBSEQUENT TO
REMOVAL OF SPOT AND 15-SECOND RINSE WITH WARM
WATER FOLLOWED BY DRYING
After concluding the observations set forth in Table 1,
the panels were rinsed off under warm water and dried with
compressed nitrogen. The surfaces were then ~ ;ned for
staining and spotting.
SAMPLE APPEARANCE OF PANEL SURFACE GRADING SCALE
(0=WORST; 10=BEST)
A POTS ~,~
B POTS ~,~
C OME SPOTS 3,2
D LIGHT SPOTS 5,4
E SLIGHT SPOTS 7,5
F SLIGHT SPOTS 7,5
G POTS 2,2
H LI~HT POTS 6,6
I NO POT 10,10
J ~O OT 10,9
K POT 8,8
L NO OTS (HIGH TEMP) 10,9
Grading Scale: 0 represents significant white residue; 10
represents no observable residue.
It can be seen that the compositions of the invention
offer advantages with respect to staining and spotting
resistance.
CA 02218167 1997-11-04
. The invention has been described in detail with reference
to preferred embodiments thereof. It should be understood,
however, that variations and modifications can be made within
the spirit and scope of the invention and of the following
claims.
