Method for coloring polyvinylchloride

Coloring composition for colouring polyvinylchloride comprising at least 40% by weight of coloring pigment and at most 60% by weight of glycerolmonostearate. The composition may be added directly to extruder for extruding polyvinylchloride, the amount of glycerolmonostearate in the moulded article as obtained being restricted to at most 5%.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a colouring composition for colouring 
polyvinylchloride. The term polyvinylchloride also includes copolymers of 
vinylchloride and otherwise modified polyvinylchloride. 
For colouring polymers, colouring pigments are used on a large scale. 
2. Description of the Prior Art 
It is known e.g. in the art to manufacture by injection moulding plastics 
articles in various different colours, as required by the customers. 
Examples of such articles are pipe fittings, covers, boxes etc. 
It is also known in the art to extrude thermoplastics pipes which have to 
meet different demands, with very particular colours, in order to avoid 
any risk of exchanging plastics pipes, to be used for a certain aim, with 
other pipes, which would be absolutely unsuitable for that aim. So, for 
instance, a plastics pipe for transporting water is given a colour 
differing from the colours used for pipes being employed for transport of 
gases. 
Said colouring compositions present the disadvantage, that the great 
fineness of the colouring particles may be a nuisance, whilst furthermore, 
handling the empty packages of such colouring pigments requires much 
labour, so that transporting said empty packages and preventing the 
hindrance by fine dye particles, should be restricted to a minimum. It is 
not always possible to choose pigments without toxic character, so that 
there is always danger of contamination by handling such pigments. 
Efforts have been made to obviate these disadvantages by providing the 
mixers, in which plastics are mixed with colouring pigments, with metering 
devices, metering the material on a volume- or on a weightbasis, thus 
allowing the use of containers with colouring pigments. 
Metering devices allowing an accurate control of the quantity of colouring 
pigments to be dispensed are, however, extremely expensive; also measures 
have to be taken to avoid dusting. 
Efforts have also been made to admix the colouring pigments with additives 
in the form of molten fatty acid amides and to cast the liquid composition 
into moulds, whereupon the moulded articles obtained after solidification 
may be used for forming a mixture with plastics, or to grind the moulded 
articles and to use the granulate particles as an additive for the 
thermoplastics to be coloured. The latter method is very inconvenient in 
that fatty acid amides melt at rather high temperatures, thus causing the 
risk of impairing the properties of organic colouring pigments. Moreover, 
the high melting points of the additives complicate proper dispersion of 
colouring pigments in the thermoplastics. 
SUMMARY OF THE INVENTION 
In view of the foregoing factors and conditions of the prior art it is a 
primary object of the present invention to provide a colouring composition 
of the aforementioned type, avoiding all the disadvantages mentioned 
hereinbefore and the risk of impairing colouring pigments during mixing as 
well as avoiding contamination of the plant. 
This object is attained in accordance with the invention in that a 
colouring composition for colouring polyvinylchloride to be extruded or 
injection moulded, contains at least 40% by weight of colouring pigments 
and at most 60% by weight of a glycerolmonostearate. 
A colouring composition of this type allows the colouring pigments to be 
admixed with the inexpensive glycerolmonostearate at much lower 
temperatures, so that the properties of the colouring pigments are not 
impaired due to high temperatures. Furthermore a monoglycerolstearate is a 
very good lubricating agent in polyvinylchloride so that according to the 
invention a lubricating agent is added to the plastics composition 
simultaneously with the colouring pigment. Moreover, glycerolmonostearate 
has strong surface active properties so that the colouring pigments are 
excellently coated by the glycerolmonostearate. At least glycerol 
monostearate is very compatible with other additives added to 
polyvinylchloride. 
The aforementioned colouring composition may be added to the thermoplastics 
to be extruded, during the admixture, but also directly to the extruder. 
Of course, the composition is also well suited for adding same to 
polyvinylchloride compositions to be used for injection moulding. 
It should be noted that the expression glycerolmonostearate does not only 
comprise pure glycerolmonostearate, but also impure glycerolmonostearate, 
containing different amounts of glyceroldi- and -tristearate, depending on 
the purity of the glycerolmonostearate. Typical values are: 40-50% 
monostearate, 40-43% distearate and 8-10% tristearate. It has been proved 
in actual practice, that an admixture of a colouring composition 
comprising glycerolmonostearate and a colouring pigment, in accordance 
with the invention, allows better results to be obtained than a separate 
admixture of the two substances of the colouring composition in accordance 
with the invention. 
Very conveniently a colouring composition comprises 75% by weight of 
colouring pigments, the remaining percentage of said composition 
consisting of glycerolmonostearate, serving as a lubricating agent. 
The invention also relates to a process of manufacturing polyvinylchloride 
articles comprising extrusion or injection moulding of polyvinylchloride 
mixed with a lubricating agent and a colouring pigment, wherein a 
particulate colouring composition is added to the polyvinylchloride, said 
composition containing at least 40% by weight of colouring pigments and at 
most 60% by weight of a glycerol monostearate. 
Preferably, glycerolmonostearate is present in the polyvinylchloride in a 
total amount of at most 5% by weight. 
The features of the present invention which are believed to be novel are 
set forth with particularity in the appended claims. 
Other claims and many of the attendant advantages will be more readily 
appreciated as the same becomes better understood by reference to the 
following detailed examples.

DESCRIPTION OF PREFERRED EMBODIMENTS 
EXAMPLE I 
5,5 kg of molten glycerolmonostearate is admixed with 4,5 kg of 
cadmiumsulfide-yellow. After mixing the composition is solidified in 
moulds. The moulded compositions as obtained, which may be given a very 
accurate weight, may be supplied as such to the mixers for mixing same 
with polyvinylchloride. 
The moulded articles as produced may also be crushed in order to obtain 
granulate particles, which are suitable for mixing with polyvinylchloride 
to be extruded by means of an extruder. 
EXAMPLE II 
A colouring composition according to the present invention is prepared by 
mixing 50 kg glycerolmonostearate with 50 kg phtalocyanine-green, 
whereupon the molten mixture is solidified in moulds and the moulded 
articles are crushed so that granulate particles are obtained. Said 
granulate particles may be appropriately mixed with polyvinylchloride in 
the mixers. 
In this manner green coloured polyvinylchloride pipes are obtained, the 
colouring properties and composition of which are much better than those 
of pigment particles and lubricating agents being separately added. 
EXAMPLE III 
75 kg phtalocyanine-blue are mixed with 50 kg of molten 
glycerolmonostearate, whereupon said mixture is cast into a mould so that 
the moulded compositions are obtained having a specifically defined 
weight. The products as such are supplied directly to the extruder for 
extruding polyvinylchloride which contains normal additives. The 
glycerolmonostearate acts as a lubricating agent: the total amount of 
glycerolmonostearate in the extruded polyvinylchloride amounts to 3%. 
EXAMPLE IV 
50 kg of black iron oxide is mixed with 50 kg of molten 
glycerolmonostearate. After mixing the molten mixture is cast into a mould 
and the moulded compositions are crushed in order to obtain granulate 
particles. Adding these granulates to an extruder fed with 
polyvinylchloride, provides a very convenient colouring, whilst the 
coloured pipe presents optimum properties. In order to avoid exuding of 
the glycerolmonostearate it is in general recommended to restrict the 
total amount of glycerolmonostearate to 5% based on the polyvinylchloride. 
EXAMPLE V 
75 kg titanium dioxode is admixed with 25 kg molten glycerolmonostearate 
and the molten mixture is cast into a mould. In this manner shaped 
compositions are obtained which are added to an extruder fed with 
polyvinylchloride. The total amount of glycerolmonostearate in the 
extruded pipe is 4%. 
EXAMPLE VI 
75 kg of cadmium-yellow is mixed with 25 kg of molten glycerolmonostearate 
containing 40% of glyceroldistearate and 10% of glyceroltristearate. 
After solidification and moulding of the composition the moulded 
composition is, after crushing, added to an injection moulding device fed 
with polyvinylchloride. The total amount of glycerolmonostearate in the 
finished pipefitting is 4% by weight. The respective pipe will be coloured 
very effectively, whilst said pipe will show very good properties. 
EXAMPLE VII 
Example VI is repeated, but now the colouring composition is added to 
polyvinylchloride to be extruded, which addition will take place while 
mixing said polyvinylchloride with other substances. 
EXAMPLE VIII 
75 kg of a brown colouring pigment are mixed with 25 kg of 
glycerolmonostearate. After solidification a moulded colouring composition 
is obtained which lends itself very appropriately for colouring 
polyvinylchloride.