Note: Descriptions are shown in the official language in which they were submitted.
~ 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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D-1087
.
193
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.
4193
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.
,
4.
D-1087
:`:
84193
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.
3~g~
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.
D-1087
.
93
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.
D-1087
)
93
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
:`
8.
D-1087
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.
'~
, :
9.
D-1087
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.
10 .
D-1087
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D-1087
