Process for warp-free pigmenting of polyolefins

Details Process for warp-free pigmenting of polyolefins Process for warp-free pigmenting of polyolefins

2000-10-13

2001-09-11

Sanders, Kriellion (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S205000, C428S407000, C524S087000, C524S088000

Reexamination Certificate

active

06288142

ABSTRACT:

The present invention relates to a process for the warp-free pigmenting of polyolefins using organic pigments coated by polar polymers.
In the colouring of polyolefins, in particular polyethylene, using organic pigments, it is frequently observed that a number of mechanical properties of the coloured material changes with time; defects occur which are collectively known as warping phenomena. In large-volume injection-moulded parts, such as bottle crates, made from high density polyethylene, for example, deformation and shrinkage can be observed, sometimes resulting in cracking and usually rendering the articles unusable. Frequently, embrittlement of the material also sets in after a relatively short service life. These disadvantages relate to the majority of organic pigments, while inorganic pigments and a minority of organic pigments have a neutral behaviour. It is assumed that these disadvantages arise because the typical crystallisation behaviour of the polyolefins is disturbed by the presence of the pigments, since the latter can act as centres of nucleation.
Various methods have already been proposed for overcoming these disadvantages. These mostly relate to certain classes of pigments. For example, warp-free colouring of polyolefins is achieved, according to U.S. Pat. No. 4,233,206, by using organic pigments containing methylol groups which have been esterified by carboxylic acids (in particular copper phthalocyanines); according to JP Kokai 53/124 555, U.S. Pat. No. 4,107,133 and JP Kokai 53/143 646 by using an isoindolinone or copper phthalocyanine pigment which has been treated with a silane coupler; according to JP Kokai 53/132 048 by using an isoindolinone pigment with addition of a salicyloyl hydrazide; according to JP Kokai 57/73 029 by using a quinacridone, isoindolinone, azo or phthalocyanine pigment which is adsorbed onto inorganic material (for example silica gel) and then treated with a silane or titanium coupler, according to JP Kokai 57/159 831 by using an isoindolinone pigment which has been treated with a phenylenebistetrachlorobenzamide; and according to JP Kokai 58/23 840 by using a phthalocyanine pigment with addition of a halomethylcopper phthalocyanine which has been treated with an amine.
According to JP Kokai 57/51 733 and 57/155 242, the warp properties of isoindolinone pigments can also be improved by recrystallising the pigment. However, as is generally known amongst those skilled in the art, the increase in mean particle size which this produces is at the cost of other important pigment properties, in particular the colour strength.
U.S. Pat. No. 4,049,615 describes a process for the warp-free colouring of polyolefins using an organic pigment, in particular a perylene, perinone, bisazo or isoindolinone pigment, coated with a melamine-formaldehyde resin.
These methods do not always meet the high demands of modern industry and, depending on the pigment, do not always give the desired result. Thus, for example, no method is known which would allow diketopyrrolopyrrole pigments to be used for the warp-free pigmenting of polyolefins.
The coating of pigments with polar polymers is known per se. Thus, for example, U.S. Pat. No. 3,806,464 discloses pigments for example copper phthalocyanine, quinacridone, azo, thioindigo and flavanthrone pigments, whose particles are coated with a certain acrylic polymer composition which pigments, for compatibility reasons, are particularly suitable for colouring the acrylic finishes which are increasingly employed today in the automotive industry.
DE-A-2 200 322 discloses polyvinyl alcohol pigment compositions which are suitable, for example, as aquarelle colours.
U.S. Pat. No. 3,904,562 describes polyvinylpyrrolidone pigment compositions which have advantages in coating compositions with respect to heat resistance, bleeding and gloss.
Although the coating of pigments with polar polymers has already been disclosed, the effect of such pigments on the warping properties on colouring of polyolefins has hitherto not been recognised.
It has been found that virtually all organic pigments and in particular diketopyrrolopyrrole pigments are surprisingly suitable for the warp-free pigmenting of polyolefins if they are coated directly or indirectly with a film of a polar polymer.
The invention accordingly relates to a process for the warp-free pigmenting of polyolefins wherein an organic pigment is used whose particles are coated on the surface with one or more films of polar polymers.
Polar polymers which are suitable for the coating are selected, for example, from the group comprising linear or branched homopolymers or copolymers from the classes comprising the
acrylic polymers based on acrylic acid, methacrylic acid and/or alkyl esters thereof,
polyvinyl alcohols,
polyvinylpyrrolidones,
cellulose derivatives and
maleic anhydride-styrene copolymers.
The abovementioned polymers are employed, for example, in an amount of from 0.5 to 20% by weight, preferably from 1 to 10% by weight, based on the pigment.
The abovementioned acrylic polymers can, if desired, be modified by generally conventional methods by incorporating derivatives of the acids, for example amides, or by using further comonomers, such as styrene, acrylonitrile, vinyl acetate, vinylphosphonates, vinyl propionate, vinyl chloride, itaconic acid, maleic acid and derivatives thereof or other &agr;,&bgr;-unsaturated compounds (cf., for example, Ullmanns Encyclopädie der technischen Chemie [Ullmann's Encyclopaedia of Industrial Chemistry], Volume 19, pp. 1 ff., in particular p. 7, 4th Edition).
Suitable alkyl esters of acrylic and methacrylic acids to be employed according to the invention are expediently the methyl, ethyl, n-propyl, isopropyl, hydroxymethyl and hydroxyethyl esters, it also being possible, in addition, for smaller amounts of long-chain alkyl esters to be present (long-chain alkyl is, for example, branched or unbranched octyl, nonyl, decyl, dodecyl, hexadecyl or octadecyl). Methyl esters are preferred.
Of the polyvinyl alcohols which are of particular interest as the coating, the generally known polyvinyl alcohols, unmodified or modified by esters, ethers or acetal groups, and polyvinyl alcohol-containing copolymers, for example block copolymers with polyvinyl alcohol segments, are suitable. Preferred polyvinyl alcohols are those having a degree of hydrolysis of greater than 80%, in particular between 85 and 99.8%, and a degree of polymerisation of from 200 to 2500, in particular from 250 to 1800 (MW about 10,000-100,000).
The polyvinylpyrrolidones may also be modified by using copolymers such as styrene, acrylonitrile, vinyl propionate, vinyl chloride and, in particular, vinyl acetate. Preferred polyvinylpyrrolidones are those having a molecular weight between 5000 and 500,000.
Preferred copolymers based on maleic anhydride/styrene are those having a maleic anhydride:styrene ratio of from 1:1 to 1:3.
Preferred cellulose derivatives are sodium carboxymethylcellulose, cellulose acetobutyrate, cellulose acetopropionate, ethylhydroxyethylcellulose and, in particular, hydroxyethylcellulose.
The coating of the pigment can in principle be carried out by two generally known methods: by adsorption of a preformed, soluble polymer or oligomer onto the pigment or by polymerisation of corresponding monomers in the presence of the pigment. The latter method can be employed, in particular, when acrylic polymers are used.
In the former case, the pigment to be treated is post-treated in aqueous suspension with the polar polymer with stirring. The starting material may be the dry pigment powder, a press cake or a suspension as obtained from the synthesis. The polymer may either be predissolved in water or added in solid form to the pigment suspension. If necessary, the suspension can be dispersed by conventional methods using a dispersion unit (for example a high-pressure homogeniser or a high-speed stirrer). This is usually not necessary since the polar polymers generally have very good wetting properties. The pigment content in the suspension can be va

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