EP0020460A1

EP0020460A1 - Polycarbonate compositions having improved color stability and melt flow

Info

Publication number: EP0020460A1
Application number: EP79901271A
Authority: EP
Inventors: Joseph Blair Williams; Steven William Scott
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1978-09-25
Filing date: 1980-04-22
Publication date: 1981-01-07
Also published as: JPS55500732A; EP0020460A4; WO1980000708A1

Abstract

Des compositions de polycarbonate pigmentees ayant une stabilite de couleur et une stabilite d'ecoulement en fusion amelioree sont obtenues par melange d'une resine de polycarbonate aromatique d'un poids moleculaire eleve contenant un pigment avec un fluide de silicone hydrogene methyle. Alternativement, le pigment peut etre enrobe avec le fluide de silicone hydrogene methyle et une fois enrobe il peut etre melange avec la resine de polycarbonate aromatique.Pigmented polycarbonate compositions having improved color stability and melt flow stability are obtained by mixing a high molecular weight aromatic polycarbonate resin containing a pigment with a hydrogenated hydrogen silicone fluid. Alternatively, the pigment can be coated with methyl hydrogenated silicone fluid and once coated it can be mixed with the aromatic polycarbonate resin.

Description

Polycarbonate compositions Having Improved Color Stability and Melt Flow

This invention relates to polycarbonate compositions having improved color stability and melt flow, said compositions comprising an admixture of an aromatic polycarbonate, pigment and a methyl hydrogen silicone fluid. BACKGROUND OF THE INVENTION

In the past, much effort has been expended in preparing thermally stable polycarbonate compositions which would be color stable at elevated temperatures and particularly at the high molding temperatures generally employed to prepare molded polycarbonate articles. Many different additives have been found that are quite suitable for rendering polycarbonates heat and color stable. Most recently, various phosphite and phosphonite compounds have been found particularly useful, including those containing epoxies and oxetanes, such as are disclosed in U.S. Patents 3,305,520; 3,729,440; 3,953,388; 3,794,629.

DESCRIPTION OF THE INVENTION It has now been discovered that when a pigmented aromatic polycarbonate is admixed with a methyl hydrogen silicone fluid, the resulting polycarbonate composition has improved thermal stability, as exemplified by its resistance to yellowing when subjected to high molding temperatures, as well as improved melt flow stability. More pronounced thermal stability and melt flow are realized when the pigment is coated with the methyl hydrogen silicone fluid prior to being mixed with the aromatic polycarbonate. Pigments are typically included in polycarbonate compositions in amounts up to about 5.0 parts per hundred (pph) of the aromatic polycarbonate, preferably about 0.1-2.0 pph. Polycarbonate compositions containing a white pigment such as titanium dioxide (TiO₂) are most subject to revealing thermal degradation and are generally

used as the standard to determine the degree of thermal stability.

The methyl hydrogen silicone fluids (MHSF) that can be employed in the practice of this invention are those which are commercially available such as those obtainable from Rhodia, Inc. under their trademark Rhodorsil hydrofugeant 68 fluid. When used as an additive, MHSF can be employed in amounts of about 0.01-1.0 pph, preferably 0.02-0.20 pph, of said aromatic polycarbonate. When used to pre-coat the pigment prior to adding the coated pigment to the aromatic polycarbonate, MHSF is employed in amounts sufficient to provide about the same level of MHSF in the polycarbonate composition. Typically, the amount of MHSF employed to coat a pigment is about 0.05-10.0 pph, preferably 1.0-5.0 pph, of the pigment.

The aromatic polycarbonates that can be employed in the practice of this invention are homopolymers and copolymers and mixtures thereof that are prepared by reacting a dihydric phenol with a carbonate precursor.

The dihydric phenols that can be employed are bisphenols such as bis (4-hydroxyphenyl)methane, 2,2-bis (4-hydroxyphenyl)propane (bisphenol-A) , 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4-bis (4-hydroxyphenyl) heptane, 2,2-bis (4-hydroxy-3 ,5-dichlorophenyl) propane, 2,2-bis (4-hydroxy-3 , 5-dibromophenyl)propane, etc.; dihydric phenol ethers such as bis (4-hydroxyphenyl) ether, bis (3,5-dichloro-4-hydroxyphenyl) ether, etc.; dihydroxydiphenylε such as p,p'-dihydroxydiphenyl, 3 ,3'-dichloro-4,4-dihydroxydiphenyl, etc.; dihydroxyaryl sulfones such as bis(4-hydroxyphenyl) sulfone, bis (3,5-dimethyl-4-hydroxyphenyl) sulfone, etc.; dihydroxy benzenes, resorcinol, hydroguinone, halo- and alkyl-substituted dihydroxy benzenes such as 1,4-dihydroxy-2,5-dichlorobenzene, l,4-dihydroxy-3-methylbenzene, etc.; and dihydroxy diphenyl sulfoxides such as bis (4-hydroxyphenyl) sulfoxide, bis(3,5-dibromo- 4-hydroxyphenyl) sulfoxide, etc. A variety of additional dihydric phenols are also available to provide carbonate polymers such as are disclosed in U.S. Patents 2,999,835, 3,028,365 and 3,153,008. Also suitable for preparing the aromatic carbonate polymers are copolymers prepared from the above dihydric phenols copolymerized with halogen-containing dihydric phenols such as 2,2-bis (3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis (3,5-dibromo-4-hydroxyphenyl) propane, etc. It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with hydroxy or acid terminated polyester, or with a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired for use in the preparation of the aromatic polycarbonates of this invention as well as blends of any of the above materials.

The carbonate precursor can be either a carbonyl halide, a carbonate ester or a haloformate. The carbonyl halides which can be employed are carbonyl bromide, carbonyl chloride and mixtures thereof. Typical of the carbonate esters that can be employed are diphenyl carbonate, di-(halophenyl) carbonates such as di- (chlorophenyl) carbonate, di-(bromophenyl) carbonate, di-(trichlorophenyl) carbonate, di-(tribromophenyl) carbonate, etc., di-(alkylphenyl) carbonates such as di-(tolyl) carbonate, etc., di-(naphthyl) carbonate, di-(chloronaphthyl) carbonate, phenyl tolyl carbonate, chlorophenyl chloronaphthyl carbonate, etc., or mixtures thereof. The haloformates suitable for use herein include bishaloformates of dihydric phenols (bischloroformates of hydroquinone, etc.) or glycols (bishaloformates of ethylene glycol, neopentyl glycol, polyethylene glycol, etc.). While other carbonate precursors will occur to those skilled in the art, carbonyl chloride, also known as phosgene, is preferred.

Also included are the polymeric derivatives of a dihydric phenol, a dicarboxylic acid and carbonic acid. These are disclosed in U.S. Patent 3,169,121 which is incorporated herein by reference.

The aromatic polycarbonates of this invention are prepared by employing a molecular weight regulator, an acid acceptor and a catalyst. The molecular weight regulators which can be employed include monohydric phenols such as phenol, chroman-I, paratertiarybutylphenol, parabromophenol, primary and secondary amines, etc. Preferably, phenol is employed as the molecular weight regulator. A suitable acid acceptor can be either an organic or an inorganic acid acceptor. A suitable organic acid acceptor is a tertiary amine and includes such materials as pyridine, triethylamine, dimethylaniline, tributylamine, etc. The inorganic acid acceptor can be one which can be either a hydroxide, a carbonate, a bicarbonate, or a phosphate of an alkali or alkaline earth metal. The catalysts which can be employed can be any of the suitable catalysts that aid the polymerization of bisphenol-A with phosgene. Suitable catalysts include tertiary amines such as triethylamine, tripropylamine, n,n-dimethylaniline, quaternary ammonium compounds such as tetraethylammonium bromide, cetyl triethylammonium bromide, tetra-n-heptylammonium iodide, tetra-n-propylammonium bromide, tetramethylammonium chloride, tetramethylammonium hydroxide, tetra-n-butylammonium iodide, benzyltrimethylammonium chloride and quaternary phoεphonium compounds such as n-butyl-triphenyl phosphonium bromide and methyltriphenyl phosphonium bromide.

Also included herein are branched polycarbonates wherein a polyfunctional aromatic compound is reacted with the dihydric phenol and carbonate precursor to provide a thermoplastic randomly branched polycarbonate.

These polyfunctional aromatic compounds contain at least three functional groups which are carboxyl, carboxylic anhydride, haloformyl or mixtures thereof. Examples of these polyfunctional aromatic compounds include trimellitic anhydride, trimellitic acid, trimellityl trichloride, 4-chloroformyl phthalic anhydride, pyromellitic acid, pyromellitic dianhydride, mellitic acid, mellitic anhydride, trimesic acid, benzophenonetetracarboxylic acid, benzophenonetetracarboxylic anhydride, and the like. The preferred polyfunctional aromatic compounds are trimellitic anhydride or trimellitic acid, or their haloformyl derivatives.

Also included herein are blends of a linear polycarbonate and a branched polycarbonate.

Obviously, other materials can also be employed with the aromatic polycarbonates of this invention and include such materials as antistatic agents, mold release agents, ultraviolet light stabilizers, reinforcing fillers such as glass and other inert fillers, foaming agents and the like.

DESCRIPTION OF THE PREFERRED EMBODIMENT The following examples are set forth to more clearly illustrate the invention. Unless otherwise specified, parts or percents are by weight.

The following tests were used in the examples:

Yellowness index was determined in accordance with ASTM Yellowness Index (YI) Test D-1925 on samples molded at 316ºC, 343°C. and 360°C. The Streak Test YI included a visual examination of samples for surface degradation typically manifested by increased darkening or marbling; i.e., "streaking", of the surface color. The test samples for this test were obtain by beginning with a mold temperature of 349°C for each five shot run and increasing the mold temperature 11°C for each successive shot beginning with each third shot of each five shot run, the third shot molded at 371°C being subject to the YI test.

Melt flow (MF) was determined in accordance with ASTM D-1238, Condition 0.

S-tensile impact results were determined in accordance with ASTM D-1882.

Gottfert stability was determined by placing a test sample weighing about 15 grams in a rheometer, heating the sample to 149°C and maintaining this temperature for a period of 7 minutes following which the sample was pressed through a capillary at a constant speed of 0.28 cm/sec. The pressure needed to maintain this rate of flow is related to the melt viscosity (MV) of the test sample in the cylinder from which the melt stability (MS) is determined. Melt viscosity (MV) of the test sample is determined according to the following equation: wherein: T = shear stress (g/cm) D = shear rate (cm/sec) P = pressure on the sample (g) R = capillary radius (cm) L = capillary length (cm) V = rate of flow of sample (cc/sec) ∏ = 3.14 Melt stability (MS) is then determined by measuring the melt viscosity after 40 minutes residence time of the sample at 149°C and is calculated by using the following equation. The percent change in melt stability after the 40 minute residence time is shown as the % Δ.

EXAMPLE 1 A polycarbonate composition of a homopolymer of 2,2-bis (4-hydroxyphenyl)propane (bisphenol-A) was prepared by reacting essentially equimolar amounts of bisphenol-A and phosgene in an organic medium with triethylamine, sodium hydroxide and phenol under standard conditions and was mixed with the stabilizers shown in Table I by tumbling the ingredients in a laboratory tumbler. This mixture was then fed to an extruder, which extruder was operated at about 500°F, and the extruded strands chopped into pellets. The pellets were then injected molded at 316°C and 360°C into test samples of about 7.6cm x 5.lcm x 0.3cm. thick.

EXAMPLE 2 The aromatic polycarbonate of Example 1 was blended with commercially obtained phosphites, TiO₂ and MHSF and test samples obtained, following extrusion and molding, all as described in Example 1. The commercially obtained phosphites employed were a phosphite-epoxide mixture (PE), diphenyldecyl phosphite (DDP) and trinonylphenyl phosphite (TNPP) .

YI results were obtained for samples molded at 316°C, 343°C and 360°C In addition, the melt flow (MF) and the Gottfert stability at 7 minutes and the differential percentage (%Δ) from 7-40 minutes were also obtained. The data is shown in Table I below. A

* Included 0.3 pph of a silanol containing siloxy copolymers as described in Serial No. 867,534, filed 1-6-78.

The results in Table I above reveal that as little as 0.01 pph MHSF lowers the YI and stabilizes the molded samples. Increasing the MHSF concentration to 0.1 pph does not materially affect melt flow (MF) or Gottfert stability and shows only a small improvement in lowering YI (Compare sample H with sample G and sample L with sample K) . As little as 2.0 pph TiO₂ causes melt flow to drop about 2.5 units (Sample I vs. Sample J) whereas the addition of only 0.05 pph MHSF with TiO₂ at the 2.0 pph level reduces the melt flow drop to about 0.42 units (Sample I vs. Sample K) . The data in Table I also indicates that the MHSF is a better color stabilizer than a phosphite (Sample N vs. Sample 0) , but a combination of both phosphite and MHSF improves both color and melt stability (Sample P) .

EXAMPLE 3 The same procedure was followed as in Example 2 above using two different commercially obtained phosphites and two different commercially obtained methyl hydrogen silicone fluids (MHSF). The phosphites employed were diphenyl decyl phosphite (DDP) and bis-2,4-di-t-butyl-pentaerithrytol diphosphite (PEDP). The samples obtained all contained 2.0 pph TiO₂ and were subjected to the same tests as in Example 2 and the results are set forth in Table II below.

* Samples splayed; i.e., streaked.

** Included 0.3 pph of a silancl containing siloxy copolymers as described in Serial No. 867,534, filed 1-6-78

The results in Table II above reveal that MHSF is a better stabilizer than either of the phosphites (DDP or PEDP), but that

MHSF in combination with either of the phosphites exhibits even more improved stability

EXAMPLE 4

The procedure of Example 3 was followed to obtain the same compositions as in Example 3 except that the extruded pellets were molded into test bars measuring 12.7 cm x 1.3 cm x 0.3 cm thick. These test bars (samples q-w corresponding to Q-W of Example 3) were then subjected to the S-tensile impact test after being heat aged in an oven at 140°C. The results obtained are set forth in Table III below.

The results in Table III indicate that the samples containing only phosphite (q and r) did not age well, those containing phosphite plus MHSF (t-w) aged somewhat better, but the sample containing only MHSF (sample s) aged the best.

EXAMPLE 5 The procedure of Example 2 was followed to prepare additional samples containing 2.0 pph TiO₂ to further compare the effects of employing MHSF and/or a phosphite in combination with TiO₂. The YI, melt flow (MF) and Gottfert stability results obtained are shown in Table IV below wherein the phosphite employed was diphenyl decyl phosphite (DDP) :

* Included 0.3 pph of a εilanol containing siloxy copolymers as described in Serial No. 867,534, filed 1-6-78.

As the results in Table IV above reveal, increasing the concen tration of either the phosphite (DDP) and/or MHSF from 0.05 pph to

0.1 pph only slightly improved color and melt stability, but significantly improved melt flow (MF). However, when the phosphite and MHSF were each added at a concentration of 0.075 pph for a total concentration of 0.15 pph, color, melt stability and melt flow all showed marked improvement. EXAMPLE 6

The procedure of Example 2 was followed except that the aromatic polycarbonate was first mixed with 0.05 pph diphenyl decyl phosphite (DDP) and the TiO₂ was first coated with MHSF before being blended with the polycarbonate. Coating the TiO₂ was accomplished by charging a Patterson-Kelly twin shell blender with 5 Kg TiO₂, turning on the blender, metering 100 g MHSF into the blender over a period of about 2 minutes, and continuing rotation of the blender for an additional time to provide a 2 pph MHSF coating. A 10 pph MHSF coating on the TiO₂ was similarly prepared, all parts being based on the TiO₂. The additional blending time to provide these MHSF coating levels was about 5 minutes and 10 minutes, respectively. The coated TiO₂ was then mixed with the polycarbonate to provide a TiO₂ concentration of 2 pph. The YI and melt flow were determined for the samples obtained and this data is set forth in TABLE V below.

* Splayed slightly. As shown in Table V, sample R' containing 2 pph MHSF-coated TiO₂ was roughly equivalent in melt flow and YI to sample Q' containing 0.1 pph added MHSF. However, sample Q' molded at 680°F splayed whereas sample R' molded at 680°F did not. Sample S', containing 10 pph MHSF-coated TiO₂ and a higher level (0.2 pph) of added MHSF, shows no improvement over sample R' .

EXAMPLE 7

The procedure of Example 6 was followed except that the TiO₂ was coated with lower levels of MHSF and was incorporated in the polycarbonate resin in lower concentrations. In addition to obtaining the melt flow results of the samples at 6 and 12 minutes, the samples were also subjected to the YI Streak Test at 700°F.

The results obtained are set forth in TABLE VI below.

The results in Table VI above indicate that sample Y' containing 1.0 pph MHSF coated TiO₂ performed about as well as sample W' containing 2.0 pph MHSF coated TiO₂. Samples Y' and Z' with lower MHSF-coated TiO₂ and lower concentrations of TiO₂ in the resin significantly improve melt flow at both the 6 and 12 minute levels over sample A' ' containing no MHSF and no TiO₂. High temperature color results shown by the streak Test are better for samples containing 1.0 pph and 2.0 pph coated TiO₂ (samples Z' and W' ) than when 0.05 pph MHSF was added (sample U' ) . In general, the results in Table VI indicate that samples containing 1.0 pph MHSF-coated TiO₂ provide significantly better melt flow and color stability than samples containing 0.5 pph MHSF-coated TiO₂.

From the results set forth in the foregoing Examples and Tables it can be seen that the color stability and melt flow of polycarbonate resins containing a white pigment such as TiO₂ is greatly improved when the resins also contain MHSF. Further, where TiO₂ is precoated with MHSF prior to being incorporated in polycarbonate resins, splay is virtually eliminated and melt flow and color stability are obtained with lower concentrations of MHSF than when MHSF is added separately to the polycarbonate resin.

Claims

1. An aromatic polycarbonate composition having improved color stability and melt flow stability, said composition comprising an admixture of a high molecular weight aromatic polycarbonate resin; pigment in an amount of up to about 5.0 pph of said resin; and, from about 0.01-1.0 pph of a methyl hydrogen silicone fluid.

2. The composition of claim 1 wherein said pigment is titanium dioxide.

3. The composition of claim 1 wherein said methyl hydrogen silicone fluid is present in an amount of about 0.05-0.20 pph.

4. An aromatic polycarbonate composition having improved color stability and melt flow stability, said composition comprising a high molecular weight aromatic polycarbonate resin; and, pigment in an amount of up to about 5.0 pph of said resin, said pigment being coated with a methyl hydrogen silicone fluid in an amount of about 0.05-10.0 pph of said pigment.

5. The composition of claim 4 wherein said pigment is titanium dioxide.

6. The composition of claim 4 wherein the amount of coated pigment in said resin is about 0.1 - 2.0 pph of said resin.

7. The composition of claim 6 wherein the methyl hydrogen silicone fluid is coated on said pigment in an amount sufficient to provide about 0.002-0.1 pph of said fluid in said resin.

8. The composition of claim 7 wherein said amount of methyl hydrogen silicone fluid is about 0.01 - 0.05 pph.

9. A particulate pigment coated with a methyl hydrogen silicone fluid in an amount of about 0.05 - 10.0 pph of said pigment.

10. The coated pigment of claim 9 wherein the amount of methyl hydrogen silicone fluid is about 1.0 - 5.0 pph.

11. The coated pigment of claim 9 wherein said pigment is particulate titanium dioxide.