The present invention essentially relates to a process for preparing a coloured thermoplastic material, coloured thermoplastic material grains obtained thereby, a process of manufacture of coloured thermoplastic composite material and coloured thermoplastic composite material obtained thereby.

In the art of manufacturing thermoplastic composite materials, there is a need to colour same by using corresponding dyes or pigments. To introduce these pigments in the composite material during its manufacture through a wet method, it is usually necessary to disperse it within the mixture of components with the aid of dispersant containing reactive functional groups.

On the other hand, for the manufacture of reinforced thermoplastic composite materials with good interfacial adhesion between the reinforcing components, for example glass fibers, and the thermoplastic matrix, it is usually required to add a coupling agent, which is very sensitive to the reactive functional groups attached to the dispersant necessary for dispersing the pigment. This is particularly true in the manufacture of thermoplastic composite materials according to a wet method like that industrially used according to the paper technology.

In the prior art, a first attempt has been performed in document EP-A-0,281,475 ⁽ ARJ0MARI-PRI0UX ⁾ , where an intimate mixture of the thermoplastic resin under powder form and at least one adjuvant is performed before adding the thermoplastic material under powder form in the aqueous suspension of the components of the thermoplastic material. This adjuvant can be carbon black, a pigment (see page 2, lines 41-43 and page 3, lines 17-21). This intimate mixture is performed by melt extrusion of the mixture of the thermoplastic resin and of the adjuvant, preparation of granules while cooling the melting mixture according to a

granulation technology.

Accordingly, this prior art method for preparing an intimate mixture of the thermoplastic material and of the adjuvant, notably a pigment, is complicated, costly and therefore not usable at industrial level.

The purpose of the present invention is to solve the technical problem of providing a coloured thermoplastic material according to a simple process, at a low cost.

Another purpose of the present invention is to solve the technical problem of providing a coloured thermoplastic material, which constitutes a masterbatch usable in the manufacture of reinforced thermoplastic composite materials by a wet method while maintaining good interfacial adhesion, thereby achieving high mechanical properties. A further object of the present invention is to solve the technical problem of preparing coloured thermoplastic materials of wide utility in colouring of a diversity of thermoplastic resins, while further effectively colouring thermoplastic resin compositions having high contents in fiber reinforcements and/or in organic fillers, and notably for the colouring of polyolefines and particularly polypropylene or polyethylene or mixture thereof.

All these technical problems are solved simultaneously for the first time by the present invention in a simple, efficient manner, usuable at industrial level. Therefore, according to a first aspect, the invention provides a process for preparing a coloured thermoplastic material, comprising using pigment particles to colour said thermoplastic material, wherein said pigment particles are surface-coated onto the surface of said thermoplastic material under powder form, thereby providing thermoplastic grains individually pigment surface-coated.

According to a first embodiment of this process, said surface coating is performed in the presence of a coating agent under processing conditions which provide embedding the pigment particles in the coating agent, and physically binding the pigment

particles to said individual thermoplastic grains.

According to a specific invention embodiment, said coating agent comprises a polyolefinic wax having a Low melting point, i.e. lower than that of the thermoplastic material, preferably lower than 130°C, more preferably ranging between 50 and 100°C, said coating is performed under heating at a temperature higher than the melting point of the polyolefinic wax and lower than that of the thermoplastic material. Preferably, the polyolefinic wax is selected from the group consisting of a polyethylene wax, a polypropylene wax and derivatives thereof, such as acid modified products and metal salts of the acid modified products, said polyolefinic wax having a weight average molecular weight ranging between 1,000-40,000.

According to a second embodiment, the coating agent can comprise an aqueous c-ganic binder, which is advantageously curable, such as a latex.

According to another specific invention embodiment, the weight ratio of the coating agent ranges from 1 to 8 X with regard to the thermoplastic material. According to another specific embodiment, the weight ratio of the pigment ranges between 0.25 and 2.5 '/. with respect to the thermoplastic material.

According to another specific embodiment, the coating agent, notably the polyolefinic wax, can initially contain the pigments dispersed and/or disolved therein. Examples of polyolefinic waxes already containing pigments are Holcobatch C

Black 93909^sold by Holland Color, the Netherlands.

According to a second aspect, the present invention also relates to coloured thermoplastic material grains, having pigment particles coated _<nto the surface of said grains, preferably said pigment particles being embedded in a coating agent.

Preferred embodiments of the coloured thermoplastic material grains result from the above description with regard to the process.

According to a third aspect, the present invention provides a process of manufacture of coloured reinforced thermoplastic composite material by a wet method, generally used in the paper industry, comprising use of a powdery thermoplastic material having grains individually surface-coated with pigments, said pigments being preferably embedded within an inert coating agent or a material which contains the same chemical functional groups as the coupling agent.

Specific embodiments of this process result from the above description observing that the coating agent is an inert material or a material which contains the same chemical functional groups as the coupling agent.

For the manufacture of coloured reinforced thermoplastic composite materials, any type of thermoplastic resin can be used, such as polypropylene, polyethylene, and copolymers of same, polyvynyl chloride, polystyrene and copolymers, polyamides, saturated polyesters, polyphenylene ethers, polycarbonates and plastic alloy . As reinforcing components, can be advantageously used inorganic and organic reinforcing fibers, which are physically unchanged after heat transformation of the composite material, these reinforcing fibers are preferably selected from the group consisting of glass fibers, carbon fibers, ceramic fibers, boron fibers, glass wool, rock wool, metallic fibers, high melt organic synthetic fibers, such as aromatic polyamides, polyesters.

According to a specific embodiment, the reinforcing fibers have a length ranging between 5 and 50 mm and a diameter ranging between 10 and 20 micrometres.

According to another specific embodiment, the thermoplastic material under powder form has a mean particle size higher than 500 microns, preferably about 700 microns or greater.

Preferably the thermoplastic material is supplemented by a coupling agent which in the final product improves contact between the thermoplastic and the reinforcing material. Preferred coupling agents are acid or anhydride functional thermoplastic such as alpha, beta unsaturated carboxylic acid functionalized

thermoplastics. One such example is maleic or itaconic anhydride grafted polypropylene.

According to a further embodiment of the process of manufacture of a reinforced thermoplasti composite material, said composite material can comprise cellulosic fibers in a weight ratio ranging between 12 and 55 '/., if it is so desired. Also, said composite material can comprise an inorganic filler such as a talc, a carbonate, mica.

According to another specific embodiment, said composite material can comprise a polyolefinic pulp in a weight ratio from 2 to 20 '/..

Further, the reinforcing fibers can be sized, notably with a organosilane or organosi licon.

The coloured reinforced thermoplastic composite materials prepared according to the invention are useful in particular for the manufacture of car parts, notably instrument panels and knee bolsters.

A general process for preparing the coloured thermoplastic material is as follows :

A) With a dry inert binder, such as a polyolefinic wax

In a high intensity mixer able to reach a tool peripheral speed ranging between 10 and 50 metres per second, preferably about

30 metres per second, and equipped with heating means to reach a temperature within the mixture of 50 to 100 C, preferably about

75°C, it is introduced 98 to 92 weight % of thermoplastic granules, such as polypropylene, polyethylene, polyphenylene ether, etc, 2 to

8 % of a polyolefinic wax containing pigments, said polyolefinic wax having a melting point ranging between 50 and 100°C, preferably about 75 C.

In the mixture, the temperature is raised up to at least the melting temperature of the polyolefinic wax but lower than that of the thermoplastic material and the mixture of the components is mixed during a mixing time from 5 to 20 minutes depending on mixer power.

B) With an aqueous inert binder, such as a latex

It is used here a high or medium intensity mixer with heated walls and a vacuum system permitting a vacuum of 5 millibars capable of working at a tool peripheral speed of 4 to 50 metres per second, preferably 20 to 30 metres per second, and at a temperature ranging from 80 to 120°C, preferably about 100"C.

It is introduced in the mixer 96 to 99% of thermoplastic granules, such as polypropylene, polyethylene, polyamides, polyphenylene ether; 0.5 to 2 % of latex, 0.5 to 2 % of dry pigment or water dispersed pigments.

The mixing time ranges from 20 to 60 minutes depending on the tool speed, and the temperature is raised at a temperature sufficient under the vacuum condition in the mixer to achieve water evaporation and latex reticulation, so that the pigment is embedded in the latex binder and physically bound to the surface of the thermoplastic granules.

Now, the pigment coated thermoplastic granules can be used for the manufacture of coloured reinforced thermoplastic composite materials according the following general process. The pigment surface coated thermoplastic granules, as above prepared under A) or under B), can be mixed with a suspension of wet chopped reinforcing fibers such as glass fibers, dispersed in water. The proportion of reinforcing fibers in the dry feed can range from 12 to 55 weight %. Total thermoplastic content in the reinforced thermoplastic composite, based upon dry weight of material dispersed in water, is 40 - 78%, preferably 45 -78%, most preferably 50 - 75%. Included within the term thermoplastic content is any amounts of non-coloured thermoplastic granules (otherwise meeting thermoplastic granule requirements described herein) and thermoplastic coupling agents effective to improve adhesion between the thermoplastic components and the reinforcing fibers.

The suspension is then fed on a wire where water is filtrated to form a wet felt according to the usual wet method of the traditional paper technology. Then, the wet felt is dried, surfaced, heated up and pressed, as well known to any body skilled in the art.

Then, the coloured sheet, which is obtained, can be molded into any desired shape as well known in the stamping-molding technology.

Further purposes, advantages and technical results achieved by the invention will appear clearly from the following description made in reference to several illustrative examples, not limiting the scope of the invention.

In these examples, the percentages are given by weight, unless otherwise indicated.

Examples 1 to 4 and 6 relate to the preparation of pigment surface-coated thermoplastic granules, and examples 7 to 10 and 13 relate to use of them in the manufacture of reinforced thermoplastic composite materials and their further use to make a final industrial product, whereas comparative examples 5, 11 and 12 are present to show the superiority of the invention over the prior art.

INVENTION EXAMPLE 1

96 kg of polypropylene granules, of mean particle size of 700 microns was mixed with 4 kg of a polyolefinic wax containing carbon black pigment (reference Holcobatch C Black 93909 ^R supplied by Holland Color; the ratio of carbon black pigment and polyolefinic wax is 1:3) in a Henschel mixer at 75 ^β C and at a speed of 30 metres per second for 10 minutes. After which the originally white polypropylene granules were completely and uniformly surface coated with carbon black pigment.

INVENTION EXAMPLE 2

This example differs in Example 1 in that 2 kg of polyolefinic wax containing carbon black pigment were added into the mixer and the amount of polypropylene is increased to 98 kg.

INVENTION EXAMPLE 3

This example differs in Example 1 in that 8 kg of polyolefinic wax containing carbon black pigment were added into the mixer and the amount of polypropylene is decreased to 92 kg.

INVENTION EXAMPLE 4

96 kg of polypropylene granules, of mean particle size 700 microns were . mixed together with 2 kg of a latex (reference Rhodopas ^R A206 supplied by RHONE-POULENC) and 2 kg of carbon black dispersed already in water (reference Tincolor BS supplied by GMC, the USA) in a high intensity mixer such as the one supplied by Diosna at 100 ^β C and at a speed of 30 metres per second for 40 minutes. After which the originally white polypropylene granules were completely and uniformly coated with carbon black pigment.

COMPARATIVE EXAMPLE 5 (according to EP-A-0,281,475)

23.2 kg of polypropylene granules were dry mixed with 1.7 kg of a carbon black masterbatch (reference P30PPH by Cabot) in a tumbler at room temperature. This mixture was then melt mixed in a conventional single screw extruder at 200°C and followed by grinding to produce black polypropylene granules with a mean particle size of 700 microns.

INVENTION EXAMPLE 6

This example differs in Example 1 in that 4 kg of polyolefinic wax containing maroon pigment was added into the mixer.

INVENTION EXAMPLE 7 (Preparation of a composite sheet through a wet method)

In 7 liters of water containing 3 g of a cationic dispersant based on fatty acid (Cartaspers DSl of Sandoz), 32 g of glass fibers which are sized to have good dispersion in aqueous medium (reference R16 EX25 supplied by OWENS CORNING FIBERGLAS EUROPE) having an average length of 13 mm and 16 microns diameter, are added with strong stirring. 6 g of synthetic pulp were then introduced with moderate stirring. After suitable dispersion, 56 g carbon black coated polypropylene powder as prepared in Example 1 and 6 g of maleic anhydride-grafted polypropylene coupling agent (reference EXXELOR 2011 supplied by EXXON CHEMICAL) was added under stirring. After dilution until the suspension contains about 5 g of solids per liter, the mixture was then admitted on a wire screen, dewatered then dried according to the conventional paper making technique. A sheet of 700 g/m ² was thus obtained which comprised sufficient cohesion to be handled, stored, transported and in which the various components of the formulation have been perfectly retained.

INVENTION EXAMPLE 8

This example differs in Example 7 in that 0.5 weight % of wax coated carbon black was used instead of 1 %.

INVENTION EXAMPLE 9

This example differs in Example 7 in that 2 g of wax coated carbon black was used instead of 1 g.

INVENTION EXAMPLE 10

This example differs in Example 7 in that 2 g of latex coated black was used instead of wax coated carbon black.

COMPARATIVE EXAMPLE 11

This example differs in Example 7 in that 2 g of water dispersed carbon black was added separately in the suspension and the polypropylene powder has not been pigment coated, in accordance with FR-A-2,481,707.

COMPARATIVE EXAMPLE 12

This comparative example differs in Example 7 in that 2 g of melt extruded carbon black, which have been dry mixed, melt mixed and grinded with polypropylene, according to comparative example 5, was used instead of the pigment surface coated.

INVENTION EXAMPLE 13

This example differs in Example 7 in that 1 g of w ax coated maroon pigment surface coated on the polypropylene was used instead of carbon black.

All the mechanical properties, which are obtained for the final industrial product, are set forth in the following table.

In the table, for the invention examples, it has been separately shown the amount of the pigment for comparison purpose with the comparative examples, alth αgh the pigment was coated on the surface of polypropylene granules.

From these datas, it can be concluded as follows : a) Example 7 versus Examples 8 and 9 shows that varying the relative amount of polyolefinic wax containing carbon black pigment do not significantly influence the mechanical properties indicating the polyolefinic wax is a relative inert material. b) Example 10 shows by using an inert latex as a "binder" to physically attach carbon black pigment to the polypropylene granules is also a very feasible route. c) Example 11 is a comparative example. It shows that by using the current method of colouring the composite by a water dispersed carbon black according to FR-A-2,481,707, a lot of mechanical properties is lost due to the interaction of the dispersant needed in the water dispersed carbon black with the coupling agent. d) Example 12 is another comparative example, according to EP-A-0,281,475. It shows that although comparable mechanical properties can be attained, this is a labour intensive and costly method to colour our composite. The pigment is dry mixed, melt mixed and grinded with polypropylene. e) Example 13 shows that color pigment is not restricted to carbon black. The maroon colour is an illustrative example.

Cλl υ. σ

D O EXAMPLES 8 10 11 12 13

Pulpex 1 Coupling agent

Dispersant*

Flocculent*

Wax coated carbon black

Latex coated carbon black

Water dispersed carbon black

(FR-A-2,481,707)

Melt extruded carbon black

Flexural modulus 5248 5088 4858 5177 4200 Flexural strength 158 147 140 149 126 Tensile strength 111 102 105 149 126 Charpy impact 53 48 58 58 40