GB1592485A - Preparation of coloured pigments of improved dispersibility - Google Patents

Abstract

Pulverulent coloured pigments are prepared by coagulating the polymer latex of an intimate mixture of a dispersant-free pigment suspension and an aqueous polymer latex by addition of an electrolyte with vigorous mixing. The resultant pigments can subsequently be separated off, dried and ground. The pigments obtained in this way can be used for pigmenting organic plastics, printing inks, lacquers, paints and coating materials.

Description

(54) PREPARATION OF COLOURED PIGMENTS OF IMPROVED DISPERSIBILITY (71) We, BAYER AKTIENGESELLSCHAFT, a body corporate organised and existing under the laws of Germany, of Leverkusen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The invention relates to a process for the preparation of pulverulent coloured pigments of improved dispersibility and the use of the coloured pigments prepared according to the invention for pigmenting plastics, printing inks, lacquers, paints and coating agents.

When pigmenting materials such as thermoplastic resins, thermosetting resins and printing inks, as fine and uniform a distribution of the pigment as possible is aimed at which, however, is impeded by the relatively poor wettability and dispersibility of dry powdered pigments in these media.

There is frequently a changeover to employing, for the coloration of plastics and printing inks, pigment formulations which are obtained by dispersing a powdered pigment in a suitable medium by means of kneaders, mixing mills and similar apparatuses. In these pigment formulations, which in general contain 15 to 705t0 of pigment, the pigment is present in a well-dispersed state. Suitable media are, for example, resins, plastics, solvents, plasticisers, dispersing agents or combinations of these substances.

However, the applicability of these formulations is often limited to the coloration of those plastics, printing inks and the like which are identical to, or at least compatible with, the medium present in the formulations. This applies, in particular, to pigment formulations which are used for pigmenting polyolefines, polystyrene and other plastics and which contain high proportions of thermoplastic resins.

In addition, because of the high energy and apparatus costs, the preparation of pigment formulations is troublesome and expensive. A further disadvantage is that the physical properties of the pigmented end product, for example the notched impact strength, can be adversely influenced by the foreign substances automatically incorporated with the formulations.

In addition to the customary method for the preparation of pigment formulations, for example by kneading a powdered pigment with a thermoplastic composition at elevated temperature, other processes have also been disclosed.

A process for the preparation of pulverulent pigment dispersions by mixing an aqueous pigment composition, containing an organic dispersing agent (surface-active agent), with a stabilised aqueous polyolefine dispersion, coagulating, separating off the aqueous phase, drying the product and pulverising is described in DT-AS (German Published Specification) 1,156,761. The aqueous pigment composition is treated with the surface-active agent, for example in a ball mill, before the mixing.

British Patent Specification 954, 938 describes a process for the preparation of pigment dispersions by mixing highly disperse aqueous pigment pastes, which are obtained by grinding a pigment in water in the presence of a surfaceactive compound, with a stable aqueous polyvinyl chloride or vinyl chloride/acetate copolymer latex and subsequently coagulating the mixture.

A process for the preparation of pigment formulations, for the coloration of polyolefines, in which an aqueous alkali metal silicate solution and a polyethylene dispersion are added to a pigment and the mixture is subsequently coagulated by acidifying is known from DT-OS (German Published Specification) 2,204,223.

A process for the preparation of pigment formulations, which are free from dispersing agents, by mixing an aqueous dispersion of an emulsion polymer in, for example, methyl ethyl ketone with an aqueous pigment suspension and subsequently removing the mixture of organic solvent and water and by further kneading of the mixture above the softening point of the polymer used is described in DT-OS (German Published Specification) 2,019,230.

The disadvantages of these processes are that they necessitate the addition of dispersing agents or other substances, such as alkali metal silicates, to the pigment dispersions, which makes the general applicability of the formulations impossible, or that additional mechanical working in the presence of organic solvents is necessary when formulations which are free from dispersing agents are to be prepared.

The invention relates to a process for the preparation of pigments of improved dispersibility which avoids additional process steps, such as wet grinding of the pigment with a surface-active agent, the addition of auxiliaries having a diluting action (alkali metal silicates) and energy-intensive process steps, such as kneading the pigment and polymer at high temperatures.

The process, according to the invention, for the preparation of pulverulent coloured pigments of improved dispersibility is characterised in that an intimate mixture of an aqueous pigment suspension, which is free from dispersing agents and which contains one or more pigments selected from organic pigments, cadmium pigments, zinc sulphide or mixed phase pigments of the nitrile or spinel type, and an aqueous polymer latex, or a mixture of polymer latexes, the polymer being selected from polyethylene, polystyrene, polyvinyl acetate, a polymethacrycate, or a polyacrylate, is coagulated whilst mixing thoroughly, by adding an electrolyte and optionally, the pigment is subsequently separated off, dried and optionally ground in a known manner.

The pigments thus prepared are suitable for pigmenting organic plastics, printing inks, lacquers, paints and coating agents.

Suitable organic pigments can belong to all known pigment classes; they can be, for example, copper phthalocyanine pigments, quinacridone pigments, diaryl yellow pigments, dioxazine pigments, anthanthrone pigments, thioindigo pigments, naphthalenetetracarboxylic acid pigments and azo pigments of the monoazo and disazo series, especially those of the acetoacetic acid arylamide series, the Phydroxynaphthoic acid arylamide series or the P-hydroxynaphthoic acid lake series.For the purpose of the invention, cadmium pigments, such as cadmium sulphide or cadmium sulphides having a varying content of cadmium selenide, or zinc sulphide, mixed phase pigments of the rutile or spinel type, such as nickel titanium yellow (Ti, Ni, Sb) 2, chromium titanium yellow (Ti, Cr, Sb) 02, cobalt green (Co, Ni, Zn)2 (Ti, Awl)04, cobalt blue, Co(AI, Cr)2 04, cobalt blue, CoAl2 04, phthalocyanine pigments and quinacridone and azo pigments are preferred.

All blue and green phthalocyanine pigments as well as all cadmium pigments assume a particularly preferred position for the purpose of the invention.

Polyethylene, polystyrene, polyvinyl acetate and polyacrylate dispersions are obtained by the generally known processes for the preparation of latices by emulsion polymerisation (H.

Logemann et al. in Houben-Weyl, Methoden der organ. Chemie (Methods of Organic Chemistry), Volume 14, part 1, page 133 et seq., G. Thieme Verlag, Stuttgart 1961). They can be prepared by discontinuous or continuous processes and with or without the use of emulsifiers. The solids content of the latices can vary within wide limits; in general, it is between about 10 and 70%. The latex particle size is, as a rule, non-uniform and is between about 0.1 and 0.35 um. However, dispersions having particle sizes below 0.1 um can also be employed. The average molecular weights of suitable latices can also vary within wide limits and, in general, are in the range between 10,000 and several million. The range from about 10,000 to about 500,000 is preferred.

The thorough mixing is effected by means of customary stirrers or, preferably, with mixing units having a more intensive action.

Examples of these which may be mentioned are: types operating according to the rotorstator principle (for example "Ultra-Turrax" (Trade Mark)), high-speed stirrers (dissolver or disperser), sand or bead mills and the like.

Dry powdered pigments can be used as the starting materials for the preparation of the aqueous pigment suspensions. However, it is in general more advantageous to employ watercontaining pigment pastes or pigment press cakes. The suitable pigment concentrations of these aqueous suspensions can vary within wide limits. Concentrations between about 35 and 5% by weight of pigment have proved to be suitable in practice. If dissolvers are employed, it is advantageous initially to choose higher pigment concentrations of about 60 to 35% by weight, to form pasty consistencies, in order to achieve a better mixing effect.

When the aqueous pigment suspension and the aqueous polymer dispersion are mixed, the sequence is not critical; however, it has proved advantageous initially to introduce the pigment suspension and to allow the latex to run in.

Electrolytes which can be used for the coagulation are preferably inorganic salts and acids.

Inorganic salts which are employed are, preferably, salts having polyvalent cations, such as magnesium chloride, magnesium sulphate, calcium chloride, barium chloride, aluminium chloride, aluminium sulphate, iron-II chloride, cobalt chloride, nickel chloride, copper chloride or zinc chloride. Magnesium sulphate, calcium chloride and aluminium sulphate are particularly preferred. Preferred inorganic acids are hydrochloric acid, nitric acid and sulphuric acid. The coagulation by adding an electrolyte can be carried out in the cold or also at elevated temperature. The range between about 20 and 80"C has proved particularly appropriate. An aqueous solution of the inorganic salt or also the solid salt can be used.

In general, 0.5 to 10% by weight of inorganic salt are required, relative to the sum of the weights of pigment employed and latex solid. If an acid is used, exclusively or additionally, for the coagulation, it has proved advantageous to adjust the pH value to between 6 and 1.

The pulverulent coloured pigments which are prepared according to the invention consist, in each case, to an extent of preferably 40 to 10% by weight of polymer.

According to the invention it is also possible, in the preparation of the aqueous pigment suspension, to use more than one pigment or to mix more than one polymer dispersion with the pigment.

Drying of the products can be effected at 10 to 3000C, preferably at 50 to 2000C. It is also possible to spray-dry the aqueous coagulate, if appropriate without prior separation.

The coloured pigments prepared according to the invention exhibit, compared with the corresponding powdered pigments of the starting materials, an improved dispersibility in organic plastics and in printing inks, lacquers, paints and coating agents. Furthermore, they are distinguished by the fact that in their technological properties they are closer to pulverulent pigment formulations, and on the other hand in their coloristic properties they are close to pure, undiluted pigments. In addition, the pigments of the invention dust less and are more free-flowing.

For pigmenting, the products prepared according to the invention are added individually or in mixtures to the plastics, printing inks and the like in the amounts which are customary for the particular plastic, the particular printing ink and the like.

It is also possible to combine several of the coloured pigments prepared according to the invention or to combine one or more of the coloured pigments prepared according to the invention with at least one organic or inorganic pigment which is in the form of a conventional powdered pigment or of a pigment formulation.

The incorporation of the products can be carried out in screw injection moulding machines, which have a good plasticising capacity and a good kneading action, direct during the shaping of the thermoplastic composition. In other cases, the incorporation can be carried out on the machines customary for the particular plastic, for example extruders, kneaders or mixing mills, under the particular customary conditions.

The customary additives, such as propellants, anti-static agents, stabilisers, lubricants or other auxiliaries, can be admixed to the plastics pigmented with the pigments prepared according to the invention. The pigmented plastics can be processed to mouldings, sheets, filaments or fibres on the customary machines by known processes.

EXAMPLES A 17.5% strength aqueous pigment suspension was prepared from 70 g of P-copper phthalocyanine (C.I. Pigment Blue 15, No.

74, 160) and 330 g of water by means of an Ultra-Turrax and was warmed to about 40"C during this procedure. 75 g of a 40% strength aqueous polyethylene dispersion (Hordamer PE 02, average particle size 0.1-0.2 Crm, average molecular weight of the solid 16,00020, 000, data from the manufacturer Hoechst AG) were then allowed to run in, whilst the mixing unit continued to run. Without switching off the Ultra-Turrax, 30 g of a 10% strength aluminium sulphate solution were then added.

The coagulate was filtered off, washed thoroughly with warm water at dried at about 500C in vacuo. This gave about 100 g of a product which consisted to the extent of 70% by weight of copper phthalocyanine and to the extent of 30% by weight of polyethylene.

EXAMPLE 2 70 g of P-copper phthalocyanine (C.I.

Pigment Blue 15, No. 74, 160) and 70 g of water were mixed in a laboratory dissolver in the course of 10 minutes to form a 50% strength paste and the paste was then diluted with 140 g of water to form a 25% strength pigment suspension. 75 g of the polyethylene dispersion in Example 1 were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. Only then was the dissolver switched off and the coagulate was isolated, washed and dried. This gave about 98 g of a product which consisted to the extent of 70% by weight of copper phthalocyanine and to the extent of 30% by weight of polyethylene.

EXAMPLE 3 An about 15% strength aqueous pigment suspension was prepared from 70 g of P-copper phthalocyanine (C.I. Pigment Blue 15, No.

74, 160) and 400 g of water by means of a laboratory bead mill in the course of a few minutes. The suspension was transferred to an open vessel which was fitted with a blade stirrer. 75 g of the polyethylene dispersion in Example 1 and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in, whilst stirring. After switching off the stirrer, the coagulate was isolated, washed and dried. This gave about 97 g of a product which consisted to the extent of 70% by weight of copper phthalocyanine and to the extent of 30% by weight of polyethylene.

EXAMPLE 4 Preparation of a polyvinyl acetate latex: N2 was passed through 250 ml of water for about 'k hour. 100 g of vinyl acetate and 4 g of a sodium C12-C18-alkyl-sulphonate, as the emulsifier, were then added, whilst stirring vigorously and passing N2 over the mixture. A solution of 0.5 g of K2 S2 8 and 0.25 g of NaHSO3 in 50 ml of water was now slowly added dropwise at 500C and the mixture was stirred for a further 4 hours at this temperature.

This gave a storable, about 25% strength polyvinyl acetate latex.

A 20% strength aqueous pigment suspension was prepared from 80 g of P-copper phthalocyanine (C.I. Pigment Blue 15, No. 74, 160) and 320 g of water by means of an Ultra-Turrax.

80 g of the polyvinyl acetate latex, prepared as described, were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the mixing unit, the coagulate was isolated, washed and dried. This gave about 100 g of a product which consisted to the extent of 80% by weight of copper phthalocyanine and to the extent of 20% by weight of polyvinyl acetate.

EXAMPLE5 A 21% strength aqueous pigment suspension was prepared from 178 g of a 45% strength, water-containing a-copper phthalocynanine press cake (C.I. Pigment Blue 15, No. 74, 160) and 200 g of water by means of an Ultra Turrax. 80 g of a polymethyl methacrylate latex, prepared analogously to Example 4, were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the Ultra-Turrax, the coagulate was isolated, washed and dried. This gave about 100 g of a product which consisted to the extent of 80% by weight of copper phthalocyanine and to the extent of 20% by weight of polymethylmethacrylate.

EXAMPLE 6 An 18% strength aqueous pigment suspension was prepared from 200 g of the blue press cake in Example 5 and 300 g of water by means of an Ultra-Turrax. 40 g of a polybutyl acrylate latex, prepared analogously to Example 4, were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the mixing unit, the coagulate was isolated, washed and dried. This gave about 100 g of a product which consisted to the extent of 90% by weight of copper phthalocyanine and to the extent of 10% by weight of polybutyl acrylate.

EXAMPLE 7 A 15.5% strength aqueous pigment suspension was prepared from 114 g of an about 70% strength, watercontaining press cake of a perchlorinated copper phthalocyanine (C.I.

Pigment Green 7, No. 74, 260) and 400 g of water by means of an Ultra-Turrax. 80 g of a polystyrene latex, prepared analogously to Example 4, were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the mixing unit, the coagulate was isolated, washed and dried. This gave about 99 g of a product which consisted to the extent of 80% by weight of copper phthalocyanine and to the extent of 20% by weight of polystyrene.

EXAMPLE 8 A 16% strength aqueous pigment suspension was prepared from 107 g of an about 75% strength, watercontaining press cake of a perhalogenated (9-10 chlorine atoms and 5-6 bromine atoms in the molecule) copper phthalocyanine (C. I. Pigment Green 38, No.

74, 265) and 400 g of water by means of an Ultra-Turrax. 80 g of the polystyrene latex in Example 7 were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the mixing unit, the coagulate was isolated, washed and dried. This gave about 100 g of a product which consisted to the extent of 80% by weight of copper phthalocyanine and to the extent of 20% by weight of polystyrene.

EXAMPLE 9 A 21% strength aqueous pigment suspension was prepared from 80 g of a cadmium red pigment (C. I. Pigment Red 108, No. 77, 196) and 300 g of water by means of an Ultra Turrax. 80 g of the polystyrene latex in Example 7 were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the mixing unit, the coagulate was isolated, washed and dried. This gave about 100 g of a product which consisted to the extent of 80% by weight of cadmium pigment and to the extent of 20% by weight of polystyrene.

EXAMPLE 10 A 19.5% strength aqueous pigment suspension was prepared from 114 g of an about 70% strength, water-containing cadmium red pigment paste (C. I. Pigment Red 108,'No. 77, 196) and 300 g of water by means of an Ultra Turrax. 80 g of the polystyrene latex in Example 7 were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the mixing unit, the coagulate was isolated, washed and dried. This gave about 98 g of a product which consisted to the extent of 80% by weight of cadmium pigment and to the extent of 20% by weight of polystyrene.

EXAMPLE 11 An 18.5% strength aqueous pigment suspension was prepared from 133 g of an about 60% strength, water-containing cadmium yellow pigment paste (C. I. Pigment Yellow 37, 77, 199) and 300 g of water by means of an Ultra Turrax. 50 g of the polyethylene dispersion in Example 1 were subsequently allowed to run in, and then 30 g of a 10% strength aluminium sulphate solution were allowed to run in. After switching off the mixing unit, the coagulate was isolated, washed and dried. This gave about 100 g of a product which consisted to the extent of 80% by weight of cadmium pigment and to the extent of 20% by weight of polyethylene.

EXAMPLE 12 6 g of the pigment prepared according to Example 4 were added to a printing ink binder consisting of 7.5 g of vinyl chloride/vinyl acetate copolymer (manufacturer Hoechst AG), 5 g of cyclohexanone and 31.5 g of methyl ethyl ketone. This mixture was put into a 250 cm glass bottle which contained 200 g of glass balls (3 mm ). Dispersing was effected in an intensive-shaking machine according to DIN 53, 238 (draft). In parallel thereto, the corresponding starting materials, that is to say the untreated pigment, was examined. After 6 and 60 minutes dispersing time, samples were taken and applied to various printable materials.

Furthermore, the samples taken were mixed with a white printing ink which contained TiO2 and which was of similar composition, and the whitened blends thus obtained were also applied to the printable materials. In comparison with the starting materials, the pigment prepared according to this example already achieved 97% of the final colour strength (60 minutes) after a dispersing period of6 minutes; starting material: 80%. Furthermore, prints based on the treated pigment were advantageous in lustre; transparent print films which are free from specks were already achieved on regenerated cellulose films after a dispersing period of 6 minutes, which was not achieved in the case of the untreated pigment, even after the longer dispersing time.

EXAMPLE 13 In each case, 0.57 g of the pigments prepared according to Example 1 to 3 were mixed with 200 g of white-pigmented low-pressure polyethylene (density 0.96 g/cm3, manufacturer: Chem. Werke Hulls). The coloured granules were directly converted to the moulding by injection in a screw injection-moulding machine at 220"C. Mouldings were thus obtained which exhibited a homogeneous distribution of the pigment. A moulding produced with the starting pigment used in Examples 1 to 3 and with the same pigment concentration was not homogeneously coloured. Pigment specks and streaks were clearly visible.The colour strength of the colorations which were obtained with the pigments prepared according to Examples 1 to 3 were rated at 161, 150 and 165% (coloration with starting pigment = 100%) according to DIN 53, 234.

EXAMPLE 14 In each case, 2.86 g of the pigments prepared according to Example 1 to 3 were mixed with 1 kg of white-pigmented polystyrene (K value 64, density 1.05 g/cm3,manufacturer: Chem.

Werk Hauls). The coloured granules were directly converted to the moulding by injection in a screw injection-moulding machine at 2400C.

Mouldings were thus obtained which exhibited a homogeneous distribution of the pigment. A moulding produced with the starting pigment used in Examples 1 to 3 and with the same pigment concentration was not homogeneously coloured. Pigment specks and streaks were clearly visible. The colour strength of the colorations which were obtained with the pigments prepared according to Examples 1 to 3 were rated at 177, 160 and 180% (coloration with starting pigment = 100 SO) according to DIN 53, 234.

EXAMPLE 15 2.5 g of the pigment prepared according to Example 8 were processed as described in Example 14. Mouldings were thus obtained which exhibited a homogeneous distribution of the pigment. A moulding produced with the starting pigment used in Example 8 and with the same pigment concentration was not homogeneously coloured. Pigment specks and streaks were clearly visible. The colour strength of the coloration with the pigment according to Example 8 was rated at 170% (coloration with starting pigment = 100%) according to DIN 53, 234.

EXAMPLE 16 2.5 g of the pigment prepared according to Example 9 were processed as described in Example 14. Mouldings were thus obtained which exhibited a homogeneous distribution of the pigment as well as great clarity of shade.

A moulding produced with the starting pigment used in Example 9 and with the same pigment concentration was not homogeneously coloured Clouds of colour and pigment specks were visible.

EXAMPLE 17 2.5 g of the pigment prepared according to Example 10 were processed as described in Example 14. Mouldings were thus obtained which exhibited a homogeneous distribution of the pigment. A moulding produced with the starting pigment used in Example 10 and with the same pigment concentration was not homogeneously coloured. Pigment specks were clearly visible. The colour strength of the coloration with the pigment according to Example 10 was rated at 117% (coloration with starting pigment = 100%) according to DIN 53, 234.

EXAMPLE 18 2.5 g of the pigment prepared according to Example 11 were mixed with 1 kg of the polyethylene in Example 13 and converted to mouldings by injection as described in Example 13. Mouldings were thus obtained which exhibited a homogeneous distribution of the pigment. A moulding produced with the starting pigment used in Example 11 and with the same pigment concentration was not homogeneously coloured. Pigment specks were clearly visible.

The colour strength of the coloration with the pigment according to Example 11 was rated at 197% (coloration with starting pigment = 100%) according to DIN 53, 234.

EXAMPLE 19 An aqueous pigment dispersion was prepared and treated with the polyethylene dispersion according to example 1. The pH was adjusted to 2 by means of 10% by strength sulfuric acid without stopping the Ultra-Turrax. The coagulate was filtered off, washed thoroughly with warm water and dried at about 50"C in vacuo.

This gave about 100 g of a product which consisted to the extent of 70% by weight of copper phthalocyanine and to the extent of 30% by weight of polyethylene.

WHAT WE CLAIM IS: 1. A process for the production of a pulverulent coloured pigment in which an intimate mixture of an aqueous pigment suspension, which is free from dispersing agents and which contains one or more pigments selected from organic pigments, cadmium pigments, zinc sulphide or mixed phase pigments of the nitrile or spinel type, and an aqueous polymer latex, or a mixture of polymer latexes, the polymer being selected from polyethylene, polystyrene, polyvinyl acetate, a polymethacrylate or a polyacrylate, is coagulated whilst mixing thoroughly, by adding an electrolyte.

2. A process according to claim 1 in which the pigment is subsequently separated off and dried.

3. A process according to claim 2, in which the pigment is ground after drying.

4. A process according to any of the foregoing claims, in which the pulverulent coloured pigment prepared consists of 60 to 90% by weight of pigment and 40 to 10% by weight of polymer.

5. A process according to claim 1, when carried out substantially as described in any one of Examples 1 to 11.

6. A pulverulent coloured pigment when produced by the process of any of the fore

Claims (1)

1. going claims.

   7. A process for pigmenting an organic plastics, a printing ink, a lacquer, a paint or a coating agent, comprising incorporating therein a pulverulent coloured pigment as claimed in claim 6.

   8. A process according to claim 7, when carried out substantially as described in any one of Examples 12 to 18.

   9. An organic plastics, printing ink, a lacquer, a paint or a coating agent when pigmented by the process of claim 7 or 8.

   10. A process according to claim 1, when carried out substantially as described in Example 19.

   11. A pulverulent coloured pigment when produced by the process of claim 10.