CA1084193A - Pigmented polycarbonates comprising submicron silica stabilizer - Google Patents

Abstract

TITLE
PIGMENTED POLYCARBONATES

ABSTRACT OF THE DISCLOSURE
Polycarbonates are pigmented with an opaque pigment such as TiO2 and contain, intimately mixed therein, a silica at a level of 0.01 to 3% by weight. The silicas are those produced by the flame hydrolysis of SiCl4 and have a particle size up to about 10 microns. The pigmented polycarbonates can be moulded to form articles having excellent surface appearance and are especially adapted for moulding polycarbonates in moulds having radical contours and fine interstices which constrict the flow path of the polycarbonate during moulding.

Description

~ 8~93 D-1087 BACKGROUND OF THE INVENTION
-Field of the In~ention This invention relates to polycarbonate polymers and more particularly to pigmented polycarbonates which are used to form moulded articles.

Description of the Prior Art Polycarbonates derived from reactions involving organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their 10 excellent physical properties. These thermoplastic polymers are particularly suited for the manufacture of moulded products where impact strength, rigidity, toughness and excellent electrical properties are required.

In many polycarbonate uses, an opaque moulding is 15 required to provide aesthetic qualities to the moulded article and/or to provide protection from light to materials to be stored within containers moulded from polycarbonates.
Because of the high viscosity of the polycarbonate resins and pigmented polycarbonate resins a high degree of force 20 is necessary to mould polycarbonate articles. The rheology of pigmented polycarbonates causes problems in moulding articles which have radical contours and fine interstices in the moulds used to form these articles which restrict the flow path of the thermoplastic resin.

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In many instances pigmented polycarbonate articles, which have been made in moulds having such radical contours and fine interstices, exhibit a striation in surface appear-ance. This striation is not a discernible irregularity in the surface smoothness of the article, but an irregularity in color characterized by definite tonal differences having discrete boundaries on the polycarbonate surface. The striation substantially detracts from the appearance of the moulded polycarbonate article making pigmented polycarbonates somewhat undesirable for moulded articles having radical contours and fine interstices.

The exact mechanism which causes the striation is not known, but it is theorized to be caused by a melt fracture in the moulding which does not reknit.

In accordance with the present invention, a pig-mented polycarbonate is provided which can be moulded into articles from moulds having radical contours and fine inter-stices with constricted flow paths, while producing a moulded article with excellent surface properties.

SUMMARY OF THE INVENTION

The instant invention relates to a process for improving the surface properties of articles moulded from a pigmented polycarbonate in moulds having radical contours and fine interstices, the improvement comprising blending 0.01 to 3~ by weight of silica having a particle size between about 1 and 50 millimicrons into a polycarbonate resin containing sufficient pigment to opacify said polycar-bonate resin when moulded into an article. The instant invention also relates to the moulded pigment polycarbonate articles produced according to this process.

B D-1087 2.

When used herein "polycarbonate resin" means the neat resin without additives; "Polycarbonate" means both the formulated polycarbonate resin with pigments, dyes and other additives.
The polycarbonate resins useful in practice of the invention are produced by reacting di-(monohydroxyaryl)-alkanes or dihydroxybenzenes and substituted dihydroxybenzenes with derivatives of the carbonic acids such as carbonic acid diesters, phosgene, bis-chloro-carbonic acid esters of di-(monohydroxy-10 aryl)-alkanes and the bis-chloro-carbonic acid esters of the dihydroxybenzenes and the substituted dihydroxybenzenes.
The two aryl residues of the di-(monohydroxyaryl)-alkanes applied according to the invention can be alike or different. The aryl residues can also carry substituents 15 which are not capable of reacting in the conversion into polycarbonates, such as halogen atoms or alkyl groups, for example, the methyl, ethyl, propyl or tert-butyl groups. The alkyl residue of the di-(monohydroxyaryl)-alkanes linking the two benzene rings can be an open chain or a cycloaliphatic ;20 ring and may be substituted, if desired, for example by an aryl residue.
Suitable di-(monohydroxyaryl)-alkanes are for example (4,4'-dihydroxy-diphenyl)-methane, 2,2'-(4,4'-di-hydroxy-diphenyl)-propane, l,l-(4,4'-dihydroxy-diphenyl)-25 cyclohexane, 1,1-(4,4'-dihydroxy-3,3'-dimethyl-diphenyl)-cyclohexane, 1,1-(2,2'-dihydroxy-4,4'-dimethyl-diphenyl)-~;butane, 2,2-(2,2'-dihydroxy-4,4'-di-tert.-butyl-diphenyl)-' ~-~ D-1087 3.

8~93 propane or 1,1'-(4,4'-dihydroxy-diphenyl)-1-phenyl-ethane, furthermore methane derivatives which carry besides two hydroxyaryl groups an alkyl residue with at least two carbon atoms and a second alkyl residue with one or more 5 carbon atoms, such as 2,2-(4,4'-dihydroxy-diphenyl)-butane,

2,2-(4,4'-dihydroxy-diphenyl)-pentane (melting point 149-150C), 3,3-(4,4'-dihydroxy-diphenyl)-pentane, 2,2-(4,4'-dihydroxy-diphenyl)-hexane, 3,3-54,4'-dihydroxy-diphenyl)-hexane, 2,2-(4,4'-dihydroxy-diphenyl)-4-methyl-10 pentane, 2,2-(4,4'-dihydroxy-diphenyl)-heptane, 4,4-(4,4'-dihydroxy-diphenyl)-heptane (melting point 148-149C.) or 2,2-(4,4'-dihydroxy-diphenyl)-tri-decane. Suitable di-(monohydroxyaryl)-alkanes, the two aryl residues of which are different are, for example, 2,2-(4,4'-dihydroxy-15 3'-methyl-diphenyl)-propane and 2,2-(4,4'-dihydroxy-3-methyl-3'-isopropyl-diphenyl)-butane. Suitable di-(mono-hydroxyaryl)-alkanes, the aryl residues of which carry halogen atoms are for instance 2,2-(3,5,3'5'-tetrachloro-4,4'-dihydroxy-diphenyl)-propane, 2,2-(3,5,3'5'-tetrabromo-. 20 4,4'-dihydroxy-diphenyl)-propane, (3,3'-dichloro-4,4'-dihydroxy-diphenyl)-methane and 2,2'-dihydroxy-5,5'-difluoro-diphenyl-methane. Suitable di-(monohydroxyaryl)-alkanes, the alkyl residue of which, linking the two benzene rings, is substituted by an aryl residue are for instance (4,4'-dihydroxy-diphenyl)-25 phenyl-methane and 1,1-(4,4'-dihydroxy-diphenyl)-1-phenyl-ethane.

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Suitable dihydroxybenzenes and substituted dihydroxybenzenes are hydroquinone, resorcinol, pyrocatecol, methyl hydroquinone and the like. Other suitable dihydroxy-aromatic compounds are 4,4'-dihydroxydiphenylene, 2,2'-dihydroxy-diphenylene, dihydroxynaphthalene, dihydroxy-anthracene and compounds represented by the structural formula:

HO~X~OH

O O O
" " "
wherein X is S, C, S or S.

In order to obtain special properties, mixtures of various di-(monohydroxyaryl)-alkanes can also be used, thus mixed polycarbonate resins are obtained. By far the most useful polycarbonate resins are those based on 4,4'-dihydroxy-diaryl methanes and more particularly bisphenol A ~2,2-(4,4' ?
dihydroxy-diphenyl)-propane]. Thus when flame retardant characteristics are to be imparted to the basic polycarbonate resin, a mixture of bisphenol A and tetrabromobisphenol A
[2,2-(3,5,3'5'-tetrabromo-4,4' dihydroxy-diphenyl)-propane]
is utilized when reacting with phosgene or a like carbonic acid derivative.

The polycarbonate resins are prepared by methods known to those skilled in the art and more particularly by methods disclosed in U. S. Patent 3,028,365.

D-1087 5.

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The pigments used to opacify and color the poly-carbonate are those conventionally known to skilled artisans for use in high molecular weight thermoplastic pigmentation.
By far titanium dioxide is the most preferred pigment to opacify and whiten moulded articles because of its high index of refraction, extreme whiteness and brightness. 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, cuprous oxide, cadmium reds, cinnabar, antimony vermilion (red and brown pigments); zinc yellow, chrome yellows and oranges, cadmium yellow, antimony yellow, (orange and yellow pigments); chrome greens, chrome oxide greens (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 phthalocyanines, the anthraquinones and the like.

This pigment is most frequently TiO2 which is incorporated into the polycarbonate at a level of about 2 to 8 grams TiO2 per pound of polycarbonate and more pre-ferably 2 to 4 grams per pound of polycarbonate. The aboveranges are sufficient to acceptably opacify the polycarbonate article.

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The silica used in the practice of the invention provides the improved surface characteristics to the poly-carbonate moulded article. The silica may have a particle size of up to 10 microns and more preferably between about 1 and 50 millimicrons. Preferably the purity of the silica is 99.8% or greater as SiO2 and is produced by the flame hydrolysis of SiC14. Surface areas of the silicas useful in the practice of the invention preferably range from 50 to 380 meter2/gram. The silica is incorporated into the polycarbonate at a range of 0:01 to 3% by weight and more preferably between 0.1 to 0.5% by weight based on the weight of the polycarbonate resin.

In the preparation of the polycarbonates of the invention, the polycarbonate resin in pellet or powdered form, is mixed in a tumble drum blender with the pigments and silica. The pigment/resin mix is then extrusion blended and subsequently moulded to form the final poly-carbonate moulded article. In place of drum 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 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 concentrated which can be added to polycarbonate resin to form many articles with minimal variation in color.

The invention will be further illustrated by the following examples.

Example I

A polycarbonate resin having a melt flow of 6 to 12 grams/10 min. at 300~C. (ASTM D1238) and characterized by the repeating structural formula:

t ~c~r was pigmented with TiO2 and a blue pigment blend to form a polycarbonate masterbatch. The formulation was as follows:

Amount for 9/1 Let Down IngredientGrams/Pound Polycarbonate Powder Blue Dye 2.4 Yellow Pigment 0.1 Green Pigment 0.1 Black Pigment 0.09 ~itanium Dioxide 30.0 :`
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1~8~1~3 The polycarbonate resin was in powdered form and was mixed with the colorant in a Welex ~ labratory high speed mixer for two minutes.

The above masterbatches were extruded on a 1.5 inch Waldron Hartwig single screw extruder using a 3 to 1 compression screw and a 100 mesh screen. The extruded masterbatch was let down at a ratio of 9 parts polycarbonate powder to one part of extruded masterbatch by mixing in the Welex ~ mixer for 2 1/2 minutes at 1500 rpm.

The pigmented polycarbonate was injection moulded into discs having metal inserts therein to constrict the flow path of the polycarbonate. The resultant polycarbonate moulded article had striation on the surface thereof.

Example II

Example I was repeated except the masterbatch was formulated to contain 0.33% based on the weight of the poly-carbonate resin, after let-down of fumed silica (produced by the flame hydrolysis of SiC14) having a surface area of 380 meter2/gram, and an average particle the size of 20 one millimicron. No striation was present on the surface of the polycarbonate moulded article.

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8~193 Example III - VIII

Example I was repeated except that 22.7 grams/pound of polycarbonate of high density microcrystalline polyethylene was added to the masterbatch. Example III was a control having no silica therein with Examples IV through VIII having varying types and levels of silica. The formulations and moulding results of Examples III through VIII are reported on Table 1.

As is demonstrated by the above Examples, the silica containing polycarbonate molded articles demonstrate improved physical properties over the articles which do not contain silica.

The best properties are obtained from the fumed or activated silicas shown in Examples II, IV, V and VI
which are made by the flame hydrolysis of SiC14. Other silicas such as those shown in Examples VII and VIII improve the surface properties of the molded articles.

The foregoing examples illustrate specific materials used to prepare flame retardant compositions. However, the invention is not to be limited only as is set forth in the accompanying claims.

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Claims (8)

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

1. A method for reducing surface striations of articles molded from a pigmented polycarbonate in molds having radical contours and fine interstices, which comprises blending 0.01 to 3% by weight of silica having a particle size between about 1 and 50 millimicrons into a polycarbonate resin containing sufficient pigment to opacify said poly-carbonate resin when molded into an article.

2. The process of Claim 1, wherein said poly-carbonate resin is characterized by the repeating structural formula:

3. The process of Claim 1, wherein said opacifying pigment is TiO2.

4. The process of Claim 3, wherein said TiO2 is present at a level of 2 to 8 g/lb. of polycarbonate.

5. The process of Claim 4, wherein said TiO2 is present at a level of 3 g/lb. of polycarbonate.

6. The process of Claim 1, wherein said silica is present at a level of 0.1 to 0.5% by weight based on the weight of the polycarbonate resin.

7. The process of Claim 1, wherein said silica is produced by the flame hydrolysis of SiC14.

8. A molded pigmented polycarbonate article containing sufficient amounts of silica having a particle size of about 1 to 50 millimicrons to reduce surface striations produced by the process of Claim 1.