CA1315035C - Pigmented, flame resistant polycarbonate compositions - Google Patents

Abstract

Mo-2728 PIGMENTED, FLAME RESISTANT POLYCARBONATE COMPOSITIONS
ABSTRACT OF THE DISCLOSURE
The present invention is directed to flame retardant, pigmented polycarbonate molding compositions which properties include both good flame resistance properties and virtual freedom from streaking. The compositions are particularly suitable for use in molding machines using hot runner tools. The composi-tion of the invention comprise a thermoplastic aromatic polycarbonate resin, a flame retarding agent, pigments, polytetrafluoroethylene - ASTM Type 3 - and an amount of finely divided hydrophobic silicon dioxide sufficient for providing streaking-free molded articles.
Mo-2728

Description

Mo~2728 PIGMENTED, FLAME RESISTANT POLYCARBONATE COMPOSITIONS
Field of the Invention The invention concerns polycarbonate molding compositions and articles molded therefrom. More particularly, the compositions are pigmented and flame resistant.
Backqround of the Invention Streaking is a term of art used to describe a particular surface cosmetic defect in a molded part~ It lo is believed that this defect which appears as striations in molded pigmented resins results from poor dispersion of the pigment. Moldings prepared from flame retardant, pigmented polycarbonates were noticed to exhibit a particularly ob~ectionable degree of streaking if PTFE was used as a drip suppressant in the composition. As is described below, the art sought the means to alle~iate the defect yet no solutions proposed hitherto were completely satisfactory.
U.S. Patent 4,049,614 discloses polycarbonate molded articles containing pigments where silica was used to improve the surface appearance, i.e., to provide color homogeneity throughout the surface. U.S. Patent 3,360,498 discloses polycarbonate compositions containing silica powder having a treated surface. The compositions are said to exhibit an improved level of hydrolytic and thermal stability as well as abrasive and solvent resistance. Thermally stable translucent polycarbonate compositions containing a mixture of poly(dimethyl-siloxane) gum and finely divided silica have been disclosed in U.S. Patent 3,933,730.
SUMMARY OF THE INVENTION
The present invention is directed to a flame retardant, pigmented polycarbonate molding composition which properties include both good flame resistant ., .

ri

-2-properties and virtual freedom from streaking. The composition is particularly suitable for use in molding machines using hot runner tools. The composition of the invention comprises a thermoplastic aromatic polycarbonate 5 resin, a pigmenting agent, about 0.1 to 0.4~ of a complex ion metal ~salt, about .15 to .3% of ASTM Type 3 polytetra-fluoroethylene and finely divided hydrophobic silica in an amount sufficient to provide streaking free molded articles having a rating of UL 94 5V at .125".
DETAILED DESCRIPTION OF THE INVENTION
The Polycarbonate Resin The polycarbonate resins useful in the practice of the invention are homopolycarbonates, copolycarbonates and terpolycarbonates or mixtures thereof. The poly-carbonates generally have a molecul~r weight of10,000-200,000 (weight average molecular weight), preferably 20,000-80,000 and their melt flow rate, per ASTM D-1238 at 300C, is about 1 to about 24 gm/10 min., preferably about 2-15 gm/10 min. They may be prepared, for example, by the known diphasic interface process from a carbonic acid derivative such as phosgene and dihydroxy compounds by polycondensation (see German Offenlegungs-schriften 2,063,050; 2,063,052; 1,570,703; 2,211,956, 2,211,957 and 2,248,817; French Patent 1,561,518; and the monograph H. Schnell, "Chemistry and Physics of Polycarbonates", Interscience Publishers, New York, 1964.
In the present context, dihydroxy compounds suitable for the preparation of the copolycarbonates of the invention conform to the structural formulae (1) or (2) 110--2728 ~(A) ~ 03 3~ (2) tZ) d (z) f (Z) f ~ .
. .

,~ . ", . , ~

wherein A denotes an alkylene group with 1 to 8 carbon atoms, an alkylidene ~roup with 2 to 8 carbon atoms, a cyclo-alkylene group with 5 to 15 carbon atoms, a cycloalkyli-dene group with 5 to 15 carbon atoms, a carbonyl group,an oxygen atom, a sulfur atom, -SO- or -SO2- or a radical conforming to CH3 CH3~ CH3 or CH3 ~CH3 CH3 C~13 CH3 e and g both denote the number 0 to 1;
Z denotes F, Cl, Br or Cl-C4-alkyl and if several Z
radicals are substituents in one aryl radical, they may be identical or different;
d denotes 0 or an integer of from 1 to 4; and f denotes 0 or an integer of from 1 to 3.
Among the useful bisphenols in the practice of the invention are hydroquinone, resorcinol, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulfoxides, bis-(hydroxyphenyl)-sulfides, bis-(hydroxy-phenyl)-sulfones and ~,~'-bis-(hydroxyphenyl)-diiso-propyl-benzenes, as well as their nuclear-alkylated compounds. These and further suitable aromatic dihydroxy compounds are described, for example, in U.S.
Patents 3,028,356; 2,999,835; 3,148,172; 2,991,273;

3,271,367; and 2,999,846. Further examples of suitable bisphenols are 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A), 2,4-bis-(4-hydroxyphenyl)-2-methyl-butane, l,l-bis-(4-hydroxyphenyl)-cyclohexane, ~,~'-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, 2,2-bis-(3-methyl-4-hydroxyphenyl)-propane, 2,2-bis-Mo-2728 ,~, ~3~ ~3~

(3-chloro-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-

4-hydroxyphenyl)-methane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-4-hydroxy-pnenyl)-sulfide, bis-(3,5-dimethyl-4-hydroxyphenyl)-

5 sulfoxide, bis-(3,5~dimethyl-4-hydroxyphenyl)-sulfone, hydroxybenzophenone, 2,4-bis-(3,5-dimethyl-4-hydroxy-phenyl)-2-methylbutane, l,l-bis-(3,5-dimethyl-4-hydroxy-phenyl)-cyclohexane, ~,~'-bis-(3,5-dimethyl-4-hydroxy-phenyl)-p-diisopropylbenzene and 4,4'-sulfonyl diphenyl.
Examples of particularly preferred aromatic bisphenols are 2,2-bis-(4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane and 1,1-bis-(4-hydroxyphenyl)-cyclohexane.
The most preferred bisphenol is 2,2-bis-15 (4-hydroxyphenyl)-propane (bisphenol A).
The polycarbonates of the invention may entail in their structure units derived from one or more of the suitable bisphenols.
Among the resins suitable in the practice of 20 the invention are included phenolphthalein-based polycarbonate, copolycarbonates and terpolycarbonates such as are described in U.S. Patents 3,036,036 and 4,210,741.
The polycarbonates of the invention may also be 25 branched by condensing therein small quantities, e.g., 0.05-2.0 mol Z (based on the quantity of bisphenols used) of polyhydroxyl compounds. Polycarbonates of this type have been described, for example, in German Offenlegungsschriften 1,570,533; 2,116,974 and 30 2,113,347; British Patents 885,442 and 1,079,821 and U.S. Patent 3,544,514. The following are some examples of polyhydroxyl compounds which may be used for this purpose: phloroglucinol; 4,6-dimethyl-2,4,6-tri-(4-Mo-2728 ~, ` ``` ~ 31~J~

hydro~yphenyl)-heptane; 1,3,5-tri-(4-hydroxyphenyl)-benzene; l,l,l-tri-(4-hydroxyphenyl)-ethane; tri-(4-hydroxyphenyl)-phenylmethane; 2,2-bis-[4,4-(4,4'-dihydroxydiphenyl)-cyclohexyl]-propane; 2,4-bis-(4-5 hydroxy-l-isopropylidine)-phenol; 2,6-bis-(2'-dihydroxy-5'-methylbenzyl)-4-methylphenol;
2,4-dihydroxy-benzoic acid; 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane and 1,4-bis-(4',4"-dihydroxy-triphenylmethyl)-benzene. Some of the other polyfunc-10 tional compounds are 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3,3-bis-(4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.
In addition to the polycondensation process mentioned above, other processes for the preparation of 15 the polycarbonates of the invention are polycondensation in a homogeneous phase and transesterification. The suitable processes are disclosed in U.S. Patents 3,028,365; 2,999,846; 3,153,008; and 2,991,273.
The preferred process for the preparation of 20 polycarbonates is the interfacial polycondensation process.
Other methods of synthesis in forming the polycarbonates of the invention such as disclosed in U.S. Patent 3,912,688, may be used.
Suitable polycarbonate resins are available in commerce, for instance, as Makrolon* 2500, Makrolon 2800 and Makrolon 3200, all of which are bisphenol A based homopolycarbonate resins differing in terms of their respective molecular weights and characterized in that 30 their melt indices per ASTM D-1238 are 12-24, 6-11.9 and 3.0-5.9 gm/10 min.., respectively, all available from Mobay Corporation of Pittsburgh, Pennsylvania.
*Trademark Mo-2728 '' ,çgl A~

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Flame retardant agents ~or polycarbonate resins are known in the art. These agents have been widely reported in the patent literature and include halogenated compounds, especially brominated compounds and most particularly aromatic brominated compounds.
Also included are sulfonate salts of alkali ~etals or alkaline earth metals. Also included are the complex ion metal salts, such as sodium aluminum fluoride, and phosphorus compounds. The relevant literature includes U.S. Patent 3,146,254, which discloses tri-bisphenol A
ester of phosphoric acid, U.S. Patent 3,823,175 relating to halogenated neopentyl chloroformates, U.S. Patent 4,195,156 entailing disulfonic acid salts and U.S.
Patent 4,269,762 relating to tetrahydrocarbylborate salts. Also relevant are U.S. Patents 3,027,349 (phosphate polymers), 3,475,372 (metal salts of mercaptobenzotriazoles), 3,509,090 (halogenated organo-silicones), 3,535,300 (organo metal salts), 3,557,053 (tris-halophenyl phosphates),3,597,390 (tris-halophenyl phosphites), 3,775,367 (perfluorosulfonate salts), 3,836,490 (alkali metal salts), 3,875,107 (alkali metal salts), 4,017,457 (ferrocene), 4,098,754 (alkali metal organic salts), 4,100,130 (sulfur), 4,174,359 (oligo-meric tetrabromo polycarbonate and sulfonate salts), 4,223,100 (alkali metal salts, PTFE and an aromatically bound bromine) as well as U.S. Patents 3,382,207 (decabromodiphenyl carbonate), 3,647,747 (barium carbonate), 3,651,174 (BaCO3, organosiloxane and PTFE), 3,796,772 (titanates), 3,867,336 (an aryloxy substituted polyhalogenated aromatic compound); U.S. Patents 3,931,100, 3,940,366, 3,951,910, 3,953,396, 3,978,024, 4,001,175, 4,007,155, 4,032,506, 4,033,930, 4,039,509, 4,064,101, 4,067,846, 4,073,768, 4,075,164, 4,093,590, 4,093,589, 4,104,245, 4,104,246, 4,115,354, 4,153,595, Mo-2728 .,. ~, . . .
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~ 3 ~ 3 ~

4,201,~32, ~,263,201, 4,268,429, 3,909,490, 3,917,559, 3,919,167 (sulfonic acid salts), 3,933,734 (sulfonates), 3,948,851, 4,092,291 (sulfone-sulfonic salts), 3,953,399 (carboxylic acid esters), 3,971,756 (alkali metal salts 5 and siloxanes), ~,028,297 (salts of inorganic sulfur oxyacids), 4,066,618 (metal salts of halogenated nonaromatic carboxylic acid), 4,069,201, 4,111,977 (unsubstituted or halogenated oxycarbon acids), 4,104,253, 4,113,695 (halogenated organic metal salts), 10 4,209,427 (formaldehydes), ~,220,583 (partially fluorinated olefins), 4,235,978 (organopolysiloxanes), 4,241,434 (alkali or alkaline earth metal salts), 4,254,252 (cyclic polyformates). Preferably the flame retarding agents are sulfonate salts or halogenated 15 aromatic compounds.
The compositions of the invention contain an amount of the flame retarding agent and PTFE Type 3 sufficient to render the composition a flammability rating of UL-94, 5V - 1/8" specimens. Preferably the 20 amount of flame retarding agent is about 0.05 to about 1.0%, more preferably 0.3-0.8Z.
Polytetrafluoroethylene (PTFE) is well known in the art and its utility as a drip suppressant in flame retarding formulations of polycarbonate resins has long 25 been recognized. In the context of the present invention PTFE is used at a level of 0.05% to about 1.0%, preferably 0.15-0.6Z relative to the weight of the polycarbonate resin. The preferred PTFE in the present context is of the type that forms fibrils upon the 30 application of shear, known in the art as ASTM - Type 3.
The pigments used to opacify and color the polycarbonate are those conventionally known to skilled artisans for use in high molecular weight thermoplastic Mo-2728 d ~2~

compositions. By far the most preferred pigment used to opacify and whiten molded articles is titanium dioxide.
However, other white pigments such as lithopone, zinc sulfide, zinc oxide, antimony trioxide, and the like may be used. To impart color (other than white) to the polycarbonate pigments such as red lead, carbon black, iron black, cuprous oxide, cadmium reds, cinnabar, antimony vermilion (red and brown pigments); zinc yellow, chrome yellows and oranges, cadmium yellow, l~ antimony yellow, (orange and yellow pigments); chrome greens, chrome oxide green (green pigments); cobalt blue, iron blues (blue pigments); lampblacks, vegetable blacks, animal blacks (black pigments) and the like may be used.
In addition to the inorganic pigments, recited above, organic pigments may be used such as pigment chlorine, lithol fast yellow, toluidine red, permanent orange and the like. Dyes may be added to impart color to the polycarbonate such as the phthalocyamines, the anthraquinones and the like.
TiO2 is most frequently used in polycarbonate at a level of about 2 to 8 grams TiO2 per pound of polycarbonate and more preferably 2 to 4 grams per pound of polycarbonate. The above ranges are sufficient to acceptably opacify the polycarbonate article.
The silica used in the practice of the invention is hydrophobic and is characterized in that its incorporation in a polycarbonate resin does not degrade the resin to any significant degree. The silica has an average particle size of up to 10 microns and more preferably between about 1 and 50 nanometers and its purity is 99.8% or greater (as SiO2) and is prefer-ably produced by the flame hydrolysis of SiC14. The silica is incorporated into the polycarbonate at a range Mo-2728 ~3~3!~

g of 0.01 to 3% by weight and more preferably between 0.1 to 0.5% by weight based on the weight of the polycarbon-ate resin.
In ~he preparation of the polycarbonates of the 5 invention, the polycarbonate resin in pellet or powdered form, may be mixed in a tumble drum blender with the pigments PTFE and silica. The mixture may be then extrusion biended and subsequently molded to form the final polycarbonate molded article. In place of drum 10 tumbling the pigment, silica and polycarbonate may be mixed by a high speed, high shear blender or other apparatus which provides intimate mixing of the powders.
Many alternative mixing procedures may be utilized for example, a masterbatch having a high 15 concentration of pigment and silica can be made and subsequently let down with more polycarbonate resin.
This procedure has the advantage of having a large amount of pigmented polycarbonate concentrate which can be added to polycarbonate resin to form any articles 20 with minimal variation in color.
The invention is further illustrated, but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
The procedure for testing flame retardant materials is known in the art. The criteria of UL-94 V-O and 5V are described in the publication "Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances" UL-94, Third Edition as 30 revised September 25, 1981.
Experimental I. A flame retardant formulation of pigmented polycarbonate - based on a linear, bisphenol A based Mo-2728 ~3 ~

homopolycarbonate resin - exhibits no streaking upon molding. The addition of 0.15-0.35% of PTFE to this composition, for the purpose of improving the flammability rating resulted in severe streaking.
A most dramatic improvement, the virtual elimi-nation of streaking resulted upon the incorporation in the composition of a sma~l amount, i.e., 0.25%, of - silica. The molded parts - using hot runner tools -were completely streak-free.
It was observed that the improvement in accordance with the invention is effective even in hot runner systems which systems are known to be more prone to cause streaking than do sprue gate systems. The hot runner systems are known in the art - see for instance "Advances in the Construction of Hot-Runner Systems" by H.M. Wolff. Grube Messel/Darunstadt, Kunststoff 74 (1984) 12 pp. 710-713. Essentially a hot runner system differs from a conventional sprue gate system in that the heat distribution within the mold is independent of the injection molding machine. System heat is provided via cartridge heaters within the manifold block or torpedo heaters within the melt channels. Temperature controllers control the temperatures of the various zones throughout the hot runner system. Generally, temperatures in a hot runner system are as high or higher than in the injection barrel. In carrying out the Examples in the course of this work, a 13" disc hot runner system comprising one temperature zone for the main manifold and two temperature zones for the gate drops, one zone for each drop was used. Heating was by torpedo type heaters within the manifold channel. The melt temperature was about 650F.
The compositions in accordance with the invention appear additionally to exhibit an improved Mo-2728 ^J ~

level of flame retardance. One formulation containing 0.3% PTFE and 0.25% silica yielded streak-free parts which when tested under UL-94 5V conditions went through more than 6 cycles of burning before dripping occurred (80% went through 9 cycles). By comparison a similar formulation having no silica produced streaked parts which survived only 6 cycles of burning before dripping occurred.
The compositions were compounded in a ZSK twin screw extruder. The extrusion conditions were as follows: production rate 175-200 lbs/min., screw speed 155 rpm, extruder torque 50%, extrusion temperature about 300-330. Vacuum (24 mm Hg) was applied between port zones 4 and 5, during the extrusion. The results are shown in Table 1.

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O o~) O ~ I` ~ e~ ~ ,;~, 00 e~ cn I
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II. In the series of Experiments which are described below, there was evaluated the effect of silica additions on the flame retardant, pigmented poly-carbonate compositions. The mechanical and burning properties were determined on samples which were molded on a sprue gate system; the appearance, i.e., the streaking was evaluated by inspection of parts which were molded using a hot runner system. Extrusion blending on a ZSK was carried out as was described above. The compositions contained in addition to poly-carbonate, 0.30% of PTFE (ASTM Type 3) powder, 0.37%
cryolite and 0.45% of a mold release agent, the latter having no criticality in the present context. In addition, the compositions contained the indicated pigmenting agent and hydrophobic silica where noted.
The results of the testing and evaluations are presented in Table 2.

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Although the invention has been described in detail in the foregoing for the purpose of illus~ration, it is to be understood that such detail is sole.ly for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Mo-2728

Claims (10)

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. A thermoplastic molding composition comprising (i) a polycarbonate resin, (ii) a pigmenting agent, (iii) about 0.1 to 0.4 percent of a complex ion metal salt, (iv) about 0.15 to 0.3 percent of ASTM-Type 3 polytetrafluoroethylene and (v) finely divided hydrophobic silica in an amount sufficient to render the composition a rating of UL-94 5V
(0.125" specimens).

2. The composition of Claim 1 wherein said complex ion metal salt is cryolite.

3. The composition of Claim 1 wherein said silica is present at an amount of about 0.01 to about 3.0%.

4. The composition of Claim 1 wherein said silica has an average particle size of up to 10 microns.

5. The composition of Claim 4 wherein said particle size is between about 1 and about 50 nanometers.

6. The composition of Claim 1 wherein said silica is present in an amount of 0.1 to about 0.5%.

7. In the molding of a pigmented polycarbonate composition which comprises about 0.15 to about 0.3% of polytetrafluoroethylene of ASTM-Type 3 and about 0.1 to about 0.4% of a complex ion metal salt using a hot runner system the improvement comprising incorporating in said composition a finely divided hydrophobic silica in an amount sufficient to render the composition a flammability rating of UL 94-5V (0.125" specimen).
Mo-2728

8. The improvement of Claim 7 wherein said complex ion metal salt is cryolite.

9. The improvement of Claim 7 wherein said silica has an average particle size of up to 10 microns

10. The improvement of Claim 8 wherein said silica has an average particle size of 1 to 50 nanometers.
Mo-2728