Non-bleeding transparent silicone additives for plastics

Phenyl containing siloxane fluids are added to transparent thermoplastic polymers to give transparent thermoplastics having improved internal lubrication. For example, PhSi(OMe).sub.3 is equilibrated with (Me.sub.2 SiO).sub.x to give a fluid containing 28 percent by weight phenyl radicals, a PhSiO.sub.3 /2 to Me.sub.2 SiO ratio of 0.72 and an OMe to Si ratio of 0.78. This fluid was added to polystyrene in amount of 1 percent by weight to give a transparent plastic which exhibits no bleed and had excellent surface lubricity.

BACKGROUND OF THE INVENTION 
This invention relates to transparent thermoplastic compositions having 
improved processability, improved mar resistance and reduced friction. 
More particularly, it relates to such compositions containing a 
transparent thermoplastic selected from polystyrene, polyvinyl chloride, 
polyethylene terephthalate, polybutylene terephthalate, acrylate polymers 
or polycarbonate, the compositions being modified by the addition of a 
fluid organosiloxane copolymer. 
Minor amounts of polydimethylsiloxane fluids are often admixed with 
thermoplastics to provide the thermoplastic with beneficial properties 
such as reduced friction and wear, improved mar resistance and improved 
processability. Many such internally lubricated thermoplastic compositions 
have achieved considerable commercial success due to the improved 
properties obtained with minimal cost. 
However, admixtures of polydimethylsiloxane fluids and thermoplastic 
polymers are not useful when transparent thermoplastic objects are desired 
because of the incompatibility of the polydimethylsiloxane with 
thermoplastic polymers. This incompatibility results in admixtures that 
are opaque or milky white in appearance even at very low levels of 
polydimethylsiloxane. For example, U.S. Pat. No. 3,087,908 discloses that 
polydimethylsiloxane gives detectable haze in polycarbonate films at 
concentrations as low as 200 parts per million with significant haze 
occurring at siloxane concentrations above 400 parts per million. While 
these low concentrations may provide some enhancement of film forming 
properties, they are not sufficient to provide the major processing and 
wear benefits of internal lubrication. As disclosed by U.S. Pat. No. 
2,999,835 such benefits are obtained in polycarbonates at siloxane 
concentrations above 0.1 weight percent or even preferably at 1 weight 
percent or above. Similar results have been observed with other 
thermoplastic polymers. 
It is a purpose of the present invention to provide internally lubricated 
transparent thermoplastic compositions. Further, it is a purpose of the 
present invention to provide an organosiloxane that is compatible with 
thermoplastic polymers at concentrations appropriate for effective 
internal lubrication. Still another purpose of the invention is to provide 
a compatible organosiloxane that can provide internal lubrication in 
thermoplastic polymers comparable to that obtained with 
polydimethylsiloxanes. 
SUMMARY OF THE INVENTION 
A transparent thermoplastic composition comprising in admixture a 
transparent thermoplastic resin selected from the group consisting of 
polystyrene, polyvinyl chloride, polyethylene terephthalate, polybutylene 
terephthalate, acrylic polymers, and polycarbonate and a minor amount of a 
fluid siloxane copolymer composed essentially of phenylsiloxane units of 
the general formula (RO).sub.x C.sub.6 H.sub.5 SiO.sub.(3-x)/2 and 
dimethylsiloxane units of the general formula (RO).sub.y (CH.sub.3).sub.2 
SiO.sub.(2-y)/2 wherein R represents an alkyl radical having 1 to 6 carbon 
atoms, x is 2, 1 or 0 and y is 1 or 0, the siloxane copolymer having a 
ratio of phenylsiloxane units to dimethylsiloxane units in the range of 
0.6 to 2, a phenyl radical content above 22 weight percent based on the 
total weight of the copolymer, and a ratio of alkoxy groups to silicon 
atoms above 0.3. 
DETAILED DESCRIPTION OF THE INVENTION 
The siloxane fluids used herein can be prepared by any of the methods known 
in the art such as by the partial cohydrolysis of phenyltrialkoxysilane 
and dimethyldialkoxysilane or partial cohydrolysis of the corresponding 
chlorosilanes followed by alkoxylation. The best way known to applicants 
at this time is the equilibration of phenyltrialkoxysilane with cyclic 
dimethylsiloxanes in the presence of an acid catalyst such as sulfonic 
acids followed by removal of volatile by-products. 
The alkoxy group on the silicon can be any such group containing 1 to 6 
carbon atoms such as methoxy, ethoxy, isopropoxy or hexyloxy. In order to 
obtain the desired clarity coupled with the improved internal lubrication 
of the thermoplastic, it is necessary that the critical ratios shown above 
be observed. 
The fluids can be mixed with the thermoplastic polymers by any convenient 
method such as by the use of a common solvent or by mixing the fluid with 
the molten plastic in a screw-type injection molding machine. Any amount 
of fluid which gives the desired results can be used but preferably the 
fluid is used in amount of 0.1 to 5 percent by weight based on the weight 
of the thermoplastic. 
The term "polystyrene" includes not only polystyrene per se but polymers of 
derivatives thereof such as polyalphamethylstyrene, polyvinyltoluene, 
poly-t-butylstyrene and copolymers thereof with styrene as well as 
transparent copolymers of styrene with minor amounts of other monomers 
such as acrylonitrile and butadiene. The term "acrylic polymers" includes 
both acrylates and methacrylates such as methyl methacrylate, ethyl 
methacrylate, ethyl acrylate and copolymers thereof.

The following examples are illustrative only and should not be construed as 
limiting the invention which is properly delineated in the appended 
claims. 
EXAMPLE 1 
A mixture of phenyltrimethoxysilane (965 g, 4.9 moles) and 
dimethylcyclosiloxanes (535 g, 7.2 equivalents) was circulated through a 3 
m.times.1.9 cm column packed with a sulfonic acid cation exchange resin 
(Amberlyst.RTM. 15, a product of Mallinckrodt Chemical Works, of St. 
Louis, Mo.). While the mixture circulated, effluent from the column was 
passed through a 45 cm Vigreau column maintained at 40.degree.-50.degree. 
C. and 1 mm Hg (.about.133 Pa) to remove volatile components. After 30 
hours of circulating, the product was collected and stripped to a 
temperature of 150.degree. C. at 1 mm Hg (.about.133 Pa). The product (940 
g) was treated with fuller's earth and activated carbon to remove a haze. 
The product had a ratio of phenylsiloxane units to dimethylsiloxane units 
of 0.98, a phenyl radical content of 31 weight percent, and a ratio of 
methoxy groups to silicon atoms of 0.90 as determined by nuclear magnetic 
resonance analysis. 
The transparency of the above siloxane product in combination with a 
transparent thermoplastic polymer was evaluated by the following 
procedure. Polyvinylchloride powder (5 g) and the siloxane product (0.25 
g) were dissolved in 100 ml of tetrahydrofuran. The solvent was allowed to 
evaporate from the solution in a 10 cm diameter petri dish. Residual 
solvent was removed in a vacuum oven at 60.degree. C. and 1 mm Hg 
(.about.133 Pa). The cast films were evaluated visually for clarity. Also, 
the films were evaluated for siloxane bleed by applying a strip of 
adhesive tape to the casting and to the petri dish. If the tape adhesion 
to the surfaces was normal and if subsequent adhesion of the tape to 
another surface was not significantly reduced, the composition was rated 
non-bleeding. Films cast with the above siloxane were visually clear and 
non-bleeding. 
EXAMPLE 2 
A mixture of phenyltrimethoxysilane (198 g, 1.0 mole) and 
dimethylcyclosiloxanes (148 g, 2.0 equivalents) was equilibrated in a 
batch process employing a sulfonic acid action exchange resin (34.6 g, 
Amberlyst.RTM. 15). Low boiling equilibration products were removed while 
the mixture was maintained at 65.degree. C. for 18 hours at .about.1 mm Hg 
(.about.133 Pa) pressure. The product was stripped up to 150.degree. C. at 
.about.1 mm Hg to yield 246 g of siloxane copolymer. The copolymer was 
treated with fuller's earth and activated carbon to remove a haze. The 
copolymer had a ratio of phenylsiloxane units to dimethylsiloxane units of 
0.80, a phenyl radical content of 29 weight percent, and a ratio of 
methoxy groups to silicon atoms of 0.88 as determined by nuclear magnetic 
resonance analysis. 
Evaluation of the siloxane copolymer in a polyvinyl chloride casting as 
described in Example 1 indicated no apparent opacity or bleeding. 
EXAMPLE 3 
This example illustrates the effect on the transparency of a composition of 
the invention when the ratio of phenylsiloxane units to dimethylsiloxane 
units in the siloxane copolymer is varied. Cast films of vinyl chloride 
and several siloxane copolymers were prepared and evaluated as described 
in Example 1. The results are set forth in Table 1. 
TABLE 1 
______________________________________ 
Siloxane Composition Cast 
C.sub.6 H.sub.5 
Film Properties 
Weight Trans- 
Dimethylsiloxane Units 
Percent CH.sub.3 O/Si 
parent Bleed 
______________________________________ 
(1) 1.06 33 .72 Yes No 
(2) .72 28 .78 Yes No 
(3) .50* 24 .62 No No 
(4) .30* 19 .32 No No 
______________________________________ 
*For comparison only 
EXAMPLE 4 
This example illustrates the effect on the transparency of a composition of 
the invention when the ratio of alkoxy groups to silicon atoms in the 
siloxane copolymer is varied. 
A siloxane copolymer having a ratio of phenylsiloxane units to 
dimethylsiloxane units of 0.86, a phenyl radical content of 29 weight 
percent and a ratio of alkoxy groups to silicon atoms of 1.0 was prepared 
by the method of Example 1. Portions (150 g) of the siloxane copolymer 
were hydrolyzed with various amounts of water using 3 drops of 
tetrabutyltitanate and 3 drops of tetramethylguanidine trifluoroacetate as 
hydrolysis condensation catalysts. The partially hydrolyzed samples were 
vacuum stripped to 100.degree. C. at about 1 mm Hg (.about.133 Pa) and 
filtered through diatomaceous earth to give a series of siloxane 
copolymers with different alkoxy group contents as shown in Table 2. 
Polyvinyl chloride compositions containing 5 weight percent of the 
siloxane copolymers were prepared and evaluated as described in Example 1. 
TABLE 2 
______________________________________ 
PVC Composition 
Siloxane With 5 Percent Siloxane 
C.sub.6 H.sub.5 Weight 
(CH.sub.3 O)/Si 
Percent Transparent Bleed 
______________________________________ 
1 29 Yes No 
.82 30 Yes No 
.65 32 Yes No 
.53 33 Yes No 
.37* 34 Yes No 
.22 35 No No 
______________________________________ 
*Siloxane contained less than 0.05 weight percent silanol. 
EXAMPLE 5 
This example illustrates the use of a siloxane copolymer containing 
hexyloxy groups to prepare transparent compositions of the invention. 
Portions of the siloxane copolymer employed in Example 4 were mixed with 
various amounts of hexyl alcohol and 3 drops of tetramethylguanidine 
trifluoroacetate per 100 g of siloxane. After mixing for 30 minutes, the 
product was stripped first to 200.degree. C. at atmospheric pressure and 
then to 100.degree. C. at .about.1 mm Hg (.about.133 Pa). The samples were 
analyzed by nuclear magnetic resonance to determine the extent of ester 
interchange. Polyvinyl chloride compositions containing 5 weight percent 
of the siloxanes were prepared and evaluated as described in Example 1. 
The results are set forth in Table 3. 
TABLE 3 
______________________________________ 
Siloxane Composition Cast Film Properties 
C.sub.6 H.sub.5 Weight 
C.sub.6 H.sub.13 O/Si 
CH.sub.3 O/Si 
Percent Transparent 
______________________________________ 
0 .97 30 Yes 
.14 .81 28 Yes 
.20 .76 27 Yes 
.39 .59 24 Yes 
.53 .41 23 Yes 
.60 .28 23 Yes 
.59 .15 23 Yes 
______________________________________ 
EXAMPLE 6 
This example illustrates the relative percent of light transmission with 
polycarbonate and polystyrene compositions containing 1 percent by weight 
of siloxane copolymer. 
The various fluids shown in Table 4 below were mixed with the molten 
polystyrene or polycarbonate in a screw type injection molding machine. 
The transmission of each sample was determined according to ASTM 
D-1003-61. 
TABLE 4 
______________________________________ 
Percent 
Thermo- Siloxane Compositions 
Light Transmission 
plastic C.sub.6 H.sub.5 Si/ 
C.sub.6 H.sub.5 Wt. 
Relative To The 
Polymer (CH.sub.3).sub.2 Si 
Percent CH.sub.3 O/Si 
Unmodified Polymer 
______________________________________ 
Styrene 1.06 33 .72 97 
Styrene .72 28 .78 95.4 
Poly- 
carbonate 
.98 31 .90 90.8 
______________________________________ 
EXAMPLE 7 
This example illustrates the reduced friction and wear properties 
associated with the transparent compositions of this invention. 
Test bars of polystyrene thermoplastic (Dow Chemical Styron.RTM. GP 686) 
and an aromatic polycarbonate thermoplastic (General Electric Lexan.RTM. 
101) were prepared both with and without 1 percent by weight of a siloxane 
copolymer. The siloxane copolymer had a ratio of phenylsiloxane units to 
dimethylsiloxane units of 0.72, a phenyl radical content of 28 weight 
percent, and a ratio of methoxy groups to silicon atoms of 0.90. The test 
bars (3 mm.times.12.7 cm.times.1.3 cm) were formed by injection molding. 
The test bars were evaluated for friction and mar resistance on a 
crockmeter modified so that the test specimen is attached to a floating 
platform connected to a load cell that monitors and records instantaneous 
frictional forces. Oscillatory motion (60 cpm) across the test bars was 
provided by a 1.3 cm steel ball with a 0.9 Kg load. Tests were continued 
for 1000 cycles with the time of surface failure (scar) recorded. For 
comparison friction values were recorded at several points during the 
test. The test results are set forth in Table 5. 
TABLE 5 
______________________________________ 
Cycles 
to Friction 
Thermoplastic 
Scar Initial 20 Cycles 
1000 Cycles 
______________________________________ 
Polystyrene 
7 .081 .131 .148 
Polystyrene 
85 .056 .118 .138 
with siloxane 
Polycarbonate 
55 .075 .15 .119 
Polycarbonate 
&gt;1000 .038 .048 .063 
with siloxane 
______________________________________ 
EXAMPLE 8 
This example illustrates the improved mold release properties associated 
with the transparent compositions of this invention. 
Fluid composition (2) of Example 3 was mixed with polystyrene (Styron.RTM. 
685 D of Dow Chemical) in amount of 1 percent by weight based on the 
weight of the polystyrene in a screw type injection molding machine. The 
lubricity of the molded article was tested as follows. The plastic mix was 
molded in the form of a cap on a threaded male mold and allowed to cool. A 
wrench was applied to the cap and the foot/pounds of torque required to 
remove the cap was recorded. For comparison the polystyrene blank and the 
same polystyrene containing 1 percent by weight of 30,000 cs (0.03 m.sup.2 
/s) polydimethylsiloxane fluid (200 fluid) were tested. Four samples of 
each were made and tested. The test results are set forth in Table 6. 
TABLE 
__________________________________________________________________________ 
1 2 3 4 Average 
__________________________________________________________________________ 
Styron.RTM. 685 D 
54.6 
(74)* 
54.0 
(73.1) 
52.2 
(70.7) 
53.1 
(71.9) 
53.5 
(72.5) 
Styron.RTM. 685 D + 1% 
38.4 
(52) 
37.8 
(51.2) 
37.0 
(50.1) 
36.2 
(49) 
37.3 
(50.5) 
fluid (2) 
Styron.RTM. 685 D + 
34.2 
(46.3) 
34.2 
(46.3) 
33.8 
(45.8) 
33.4 
(45.2) 
33.9 
(45.9) 
1% 200 fluid 
__________________________________________________________________________ 
This data shows the instant fluids are almost as good as 200 fluid in 
plastic lubricity and in addition the samples were clear while the 200 
fluid samples were cloudy. 
*Figure in parenthesis is the torque converted to newtonmetre (N.cndot.m) 
 
EXAMPLE 9 
Fluid (2) of Example 3 was mixed in amount of 1 percent by weight with the 
acrylic polymer Plexiglas.RTM. V500 (Rhom and Haas Co.) to give a clear, 
lubricated plastic. 
Equivalent results are obtained when the fluid of Example 1 is used in 
polyethylene terephthalate and polybutylene terephthalate.