WO1994006611A1

WO1994006611A1 - Thermoplastic coating compositions

Info

Publication number: WO1994006611A1
Application number: PCT/GB1993/001996
Authority: WO
Inventors: Keith Herbert Dodd; Peter John Stephenson; Nicholas Jason Welton
Original assignee: H.B. Fuller Company
Priority date: 1992-09-24
Filing date: 1993-09-23
Publication date: 1994-03-31
Also published as: EP0662032A1; AU4828193A; IL107094A0; GB2286795B; WO1994006612A1; AU4828293A; IL107095A0; GB2286795A; GB9505974D0

Abstract

Coating compositions suitable for use in an in-mould coating method in which a thermoplastic coating material and a thermoplastic substrate material are moulded in the same mould to produce a coated substrate, for example, a vehicle component having a high quality paint coating. Polymeric materials for use in the coating compositions include reversibly crosslinkable materials and thermoplastic alloys. A polypropylene-based coating composition can be used to produce a paint layer on a polypropylene vehicle component.

Description

THERMOPLASTIC COATING COMPOSITIONS.

The invention relates to coating compositions suitable for use in manufacturing articles comprising coated substrates, more especially polymeric substrates having a coating, for example, a decorative and/or protective coating, thereon. The invention has particular, but not exclusive, relevance to coating compositions suitable for manufacturing coated plastics parts for use in the automotive industry.

Traditionally, the production of coated, especially painted, polymeric substrates has almost exclusively involved the application of solvent-based coating materials to preformed substrates. Many methods can be used for applying coatings from solution, for example, spraying or dipping of substrates, and solvent-based coating materials can be used with many different types of substrate.

Where a solvent-based coating is applied to a product such as a moulded plastic article, coating is carried out as a separate step after the article has been moulded, usually in a special area dedicated to that purpose. In such an area it is possible to obtain good control over coating quality, and to control, for example, levels of dust and solvents. The last-mentioned point is particularly important in view of recent environmental legislation in relation to the control of emissions and disposal of organic solvents. The use of separate coating steps in special coating areas can, however, add significantly to production costs by, among other things, reducing production rates.

Proposals have been made for the production of coated polymeric articles by applying the coating in sheet or powder form to the preformed substrate, .and there has recently also been interest in in-mould powder coating methods in which a coating and a substrate are shaped in the same mould. In such in-mould powder coating methods, the coating material in powdered form is typically used to cover the inside of the mould before the substrate is moulded. Coating of the mould is normally effected by electrostatic spraying.

There have also been proposals for forming a coated product by the injection of a coating material and a substrate material into the same mould, or by coextrusion.

The previously proposed coatings and coating methods are satisfactory in some situations, but not all. Thus, for example, in many industries, it would be desirable to be able to make articles from tough, durable thermoplastic materials such as polypropylene. For instance, polypropylene would be very useful for making articles such as car bumpers and other components of vehicles if it could be painted simply and at a reasonable cost, and there are many other circumstances where it would be desirable to provide a thermoplastic material with a surface coating which differs in appearance and/or properties from the bulk of the material. Previous proposals for making coated substrates comprising thermoplastic materials such as polypropylene did not, however, give products obtainable at reasonable cost with a high quality durable surface finish. A coating composition suitable for giving high quality coatings on a thermoplastic substrate would represent a significant advance.

The present invention provides a coating composition suitable for use in an in-mould coating method and comprising a first thermoplastic polymeric material, a second, reversibly crosslinkable, thermoplastic polymeric material, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants. In one advantageous embodiment of the invention, the first thermoplastic polymeric material comprises a propylene homo- or copolymer.

The invention also provides a coating composition suitable for use in an in-mould coating method and comprising a thermoplastic alloy, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants.

The invention further provides a thermoplastic paint composition comprising a propylene homo- or copolymer, a colouring material, and at least one substance selected from finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants, the composition being suitable for use in an in-mould coating method for producing an article comprising a polypropylene substrate having thereon a coating formed from the composition.

The invention also provides a thermoplastic paint composition comprising a propylene homo- or copolymer, a UV stabilizer, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials and antioxidants, the composition being suitable for use in an in-mould coating method to produce an article comprising a polypropylene substrate having thereon a coating formed from the composition, the UV stabilizer and the said substance(s) being present in the composition in such a proportion that, after exposure for 200 hours in a QUV test as defined herein, the gloss of the coating, measured in accordance with ASTM D523-67, does not decrease by more than 50 % from the original level, and the coating shows no cracking, chalking or crazing.

The invention further provides a thermoplastic paint composition comprising a propylene homo- or copolymer, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants, the composition being suitable for use in an in-mould coating method to produce an article comprising a polypropylene substrate having thereon a coating formed from the composition, the coating having an abrasion resistance such that it passes a Taber test as specified in ASTM D1044, carried out using 250 cycles.

The invention also provides a thermoplastic paint composition comprising a propylene homo- or copolymer, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants, the composition being suitable for use in an in-mould coating method to produce an article comprising a polypropylene substrate having thereon a coating formed from the composition, the article having an impact resistance which is at least 2J measured as specified in BS 3900, 1973, Part E3 , and is not more than 10 % less than that of the polypropylene substrate.

Colouring materials, for example, pigments, are discussed in greater detail later in this specification.

The invention further provides the use of a composition according to the invention in an in-mould coating method for producing an article comprising a substantially thermoplastic substrate having thereon a coating formed from the composition.

The invention also provides the use of a composition comprising a major proportion of a propylene homo- or copolymer and a minor proportion of an ionomer for producing an article comprising a polymeric substrate having thereon a coating formed from the composition. The polymeric substrate advantageously comprises a propylene homo- or copolymer.

Compositions of the invention may, if desired, be suitable for application by thermal spraying, for example, flame spraying. Alternatively, or in addition, the compositions may be suitable for use in injection moulding apparatus. The compositions may also be suitable for use in coextrusion apparatus. The compositions may be in powder or granular form, but may alternatively be in any other form that is appropriate for the coating method in which they are to be used.

The compositions in accordance with the invention are suitable for use in in-mould coating methods, in which a coating material and a substrate material are shaped in the same mould to produce an article. Compositions according to the invention may also, of course, be used in other methods for manufacturing coated substrates, for example, coextrusion methods. The compositions are particularly suitable for use with substrates comprising thermoplastic polymeric materials.

Articles comprising coatings made from compositions according to the invention may have any desired form. For example, such an article may be a vehicle component. In another possibility the article is made by a coextrusion method and may be, for example, in the form of a frame, for example, a window frame, a cable comprising at least two layers comprising thermoplastic material, or a fibre.

Compositions in accordance with the invention are preferably suitable for use in forming the coating layer in an article comprising a substantially thermoplastic substrate having a thermoplastic coating on at least one surface thereof, the article having been made by a process in which the coating composition and a polymeric material for forming the substrate are introduced into a mould and shaped in the mould to produce the article, if necessary with the application of heat, the coating composition being brought into contact in softened, preferably fluid, or molten form with a surface of the mould or with the substrate material. The compositions of the invention may be used, for example, to form coatings having a thickness of at most 1 mm, for example, at most 500 μm.

The compositions may be used in the production of an article comprising a recyclable vehicle component, the article comprising a substantially thermoplastic substrate comprising recycled material, the substrate having a substantially thermoplastic coating, for example, thermoplastic paint coating, formed from a composition of the invention thereon. In one embodiment of the invention, both the coating material and the substrate material comprise a propylene homo- or copolymer.

Compositions of the invention have particular utility in the production of vehicle components, for example, recyclable vehicle components, but have many other uses. Examples of articles which may be made using the compositions of the invention, and processes in which the compositions may be used, are given in the copending application (No ) entitled "Coated Substrates" filed by Laporte pic and Rover Group Limited on the same day as the present application.

Certain compositions of the invention are suitable for producing a a transparent or translucent layer which preferably contains a UV stabilizer and which protects the underlying substrate and/or enhances the appearance and/or properties of the article of which the layer forms a part. Thus, for example, the compositions may be suitable for forming a colourless or coloured clearcoat layer. In an advantageous embodiment of the invention, however, the compositions are suitable for forming an opaque coating and comprise a polymeric material and a finely divided relatively infusible material which may be, and in many cases is, a pigment. The finely divided material may impart desired properties and/or a desired appearance to the coating. When the coating is opaque, it may if desired be such that a further layer, for' example, a clearcoat layer, can be applied over it.

In an especially advantageous embodiment of the invention, the compositions comprise one or more substances selected from pigments, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers, and antioxidants and are capable of forming a thermoplastic paint layer on a substrate. Such a paint layer has, inter alia, the advantage of being applied by a process which does not require the use of solvents for the paint. In particular, compositions of the invention, which may be solvent-free paints which are solid at room temperature, may be suitable for producing abrasion- and weather-resistant coatings with a desired appearance, for example, a metallic and/or pearlescent appearance. Further, a high gloss finish may be obtained, if desired. The compositions can thus be such that they can be used to produce articles which do not require a finishing paint coating applied, for example, outside the mould in which they are shaped, although the compositions may be such as to permit the provision of a further coating on the articles, in particular a clear coating.

In another advantageous embodiment of the invention, the compositions contain electrically conductive particles which impart electromagnetic shielding characteristics to coatings produced using the compositions. Alternatively, or in addition, electromagnetic shielding characteristics may be imparted by the use for the compositions of an electrically conductive polymeric material, for example, a polyaniline.

Preferred materials for use in compositions according to the present invention are discussed in greater detail later in this specification. It will be appreciated that coatings produced using compositions of the invention are not necessarily, and in many cases are not layers applied to a previously formed substrate. Thus, articles containing coating layers produced from the compositions may be made by a process in which heat-softened or molten material for forming the substrate is introduced into a mould before, after, or substantially simultaneously with, introduction of the softened or molten coating composition. In the case of coextrusion processes, the coating and substrate are formed at substantially the same time using one or more dies rather than a mould. The coating may be on one or more surfaces of the substrate.

For the purposes of this specification, the coating is the outermost layer on the substrate. Thus, if there is an additional layer between the coating and the bulk of the substrate, that additional layer is regarded for the purposes of this specification as part of the substrate. Such an additional layer, which may readily be produced using, for example, a multiple barrel injection moulding machine or by coextrusion followed by blow moulding, may, for example, be a polymeric paint layer with a metallic appearance on which the coating layer forms a clear coating, or a polymeric primer layer for a coating layer which is a paint layer. There may, however, be circumstances where it is advantageous for the coating layer to be in direct contact with the bulk substrate material, without the intervention of an additional layer between the two.

Where a moulding method is used for producing the article, the thermoplastic coating material is preferably in molten or in a flowable softened form when it is applied to the mould or substrate surface, that is, the coating layer is preferably built up on the mould or substrate surface from a stream of molten or softened thermoplastic material, which may be in particulate form. Preferably, the coating is not, or does not form part of, a previously produced sheet of material which is subsequently brought into contact with the substrate or the substrate material.

The applicants have surprisingly found that the compositions of the invention can be used to produce coating layers which in many cases are suitable for use without additional treatment. Thus, for example, no curing step is necessary after moulding, and the appearance and properties of the coating may be such that it is not necessary to apply a further layer, for example, a paint layer or other protective layer, to the articles before use. Thus, for example, as indicated above, the coating may form a "paint" layer having desired properties and appearance. For such purpose, the coating advantageously has a thickness of at most 500 μm, preferably less than 200 μm, and in some cases coatings having a thickness of less than 100 μm are preferred, and coatings with these thicknesses may also be advantageous for other purposes, for example, when the coating is to provide an EMI shielding layer. Advantageously, coatings prepared from compositions in accordance with the invention have a thickness of at least 5 μm. (When a coating is said to have a particular maximum thickness, local areas of the coating may in some cases have a thickness greater than that maximum, although in other cases substantially the whole of the coating will not exceed the specified maximum.) Compositions of the invention may be used to produce coatings having thicknesses as specified above. In general, thinner paint films will require proportionally more additives such as pigments to give the desired hiding power.

Desired properties may be imparted to coatings produced from the compositions by, for example, the choice of appropriate pigments and/or other finely divided relatively infusible materials, for example, metallic materials, pearlescent materials and fillers, and appropriate levels of such materials, and/or by the inclusion in the compositions of one or more additional substances, for example, UV stabilizers, thermal stabilizers, flow aids, pigment dispersing agents, impact modifiers, compatibilizers, haze controlling agents, stress cracking reducers, and antioxidants. (As discussed in greater detail later in the specification, the properties of coatings can also be modified by the choice of appropriate thermoplastic polymeric materials.) By a finely divided relatively infusible material is meant a finely divided material which is substantially infusible at the temperature at which the compositions are applied and used, so that the finely divided material remains in particulate form in the polymeric material used for the compositions and does not, for example, dissolve in that material. In many cases the finely divided relatively infusible material will be inorganic, but it may be organic, especially in the case of pigments. Advantageously, the finely divided material consists of or comprises one or more substances selected from pigments, metallic materials and pearlescent materials. A mixture of one or more different finely divided relatively infusible materials may be used. A substance which acts as a pigment may also, if appropriate, impart other desired properties to the coating. The finely divided substantially infusible material may if desired be electrically conductive, and, as discussed in more detail below, in some cases it may be desirable that the composition be suitable for producing electrically conductive coatings. For the purposes of this invention a material is said to be finely divided if it does not interfere with the processing steps used in the manufacture of an article which includes a coating produced from the composition. The person skilled in the art will be familiar with particle sizes appropriate for infusible materials to be included in paint compositions.

Suitable pigments for inclusion in the compositions in accordance with the invention include, for example, ferric oxide, titanium dioxide, zinc oxide, quinacridones, phthalocyanines, for example, copper phthalocyanine complexes, anthraquinoids, thioindigo pigments, and carbon black. Pigments are advantageously used in a proportion of 0.5 to 35 wt %, based on the weight of the composition. The proportion of pigment to be used in a particular case will depend on the colour of the pigment, and can be determined by routine experiment.

In some cases a desired colour may be imparted to a thermoplastic paint layer produced from a composition of the invention by a dye which is soluble in the thermoplastic polymeric material rather than by the use of a pigment which remains in particulate form in the thermoplastic material. Such a dye may be used, for example, where a tinted transparent layer is required, although a dye may also be used where, for example, a finely divided substantially infusible filler material imparts opacity to the layer produced using the composition.

Finely divided metallic materials for inclusion in compositions according to the invention include finely divided metals, finely divided metal derivatives, and metal-coated particulate materials. The metallic material may impart a metallic finish to articles containing a coating produced from a composition of the invention. The metallic material may be in any suitable form, for example, in the form of particles, flakes, platelets, or fibres which may, if desired, be coated with an organic substance to aid dispersion in the thermoplastic material. Examples of suitable metals for use in coating compositions are nickel, aluminium, stainless steel and silver, and alloys containing one or more of these metallic materials. Examples of metal derivatives for use as the finely divided relatively infusible material are oxides, carbonyl compounds or salts. Materials in which a metal coating is applied to a particulate material include, for example, nickel- coated graphite and silver-coated graphite. Metallic materials, if used, are advantageously present in a proportion of 5 to 25 wt , preferably 10 to 20 wt %, based on the weight on the composition.

Where the finely divided relatively infusible material is electrically conductive it may, if desired, be used in such a proportion and/or in such a manner as to impart antistatic, semiconductive, or electrically conductive properties to coatings produced from the composition of the invention. An electrically conductive material for use in this way may be, but is not necessarily, metallic. Thus, for example, carbon black may be used to provide an antistatic coating, while finely divided silver may be used to provide a semiconductive coating. An electrically conductive coating may be particularly advantageous where EMI shielding of electrical components is desirable. Stainless steel fibres (for example fibres having a diameter of up to 300 μm and a length of up to 3 mm) are particularly advantageous for giving a coating layer capable of providing EMI shielding, although other metals, for example, nickel or aluminium may be used. A polymeric article in which the coating forms an EMI shielding layer may be used, for example, as an inexpensive, lightweight, housing for electrical equipment requiring shielding.

A coating composition according to the invention comprising a finely divided metallic material may be used to give a metallic finish on, for example, car body parts, without the need for further painting. Both aesthetic appeal and improved durability may be imparted by such a metallic finish. It may also be possible to give a metallic finish to transparent materials, for example, sunglasses or windows, by using a fine dispersion of metal particles in a colourless or tinted clear coating composition.

Pearlescent pigments include, for example, micaceous or ultrafine titanium dioxide, bismuth oxychloride; bismuth oxychloride or mica coated with titanium dioxide; an iron oxide; and chromium oxide or hydroxide. Pearlescent materials, that is, materials which can impart a pearlescent effect to coatings containing them, may, if desired, be used together with finely divided metallic materials to enhance the decorative effect provided by the metals. Some pearlescent materials, for example, mica coated with titanium dioxide, also give a "sparkle" appearance. When pearlescent materials are used, they are . advantageously present in a proportion of 5 to 25 wt %, preferably 10 to 20 wt %, based on the weight of the composition.

UV stabilizers include, for example, hindered amines.

The coating properties indicated below are especially advantageous when articles produced using the compositions of the invention are to be used as vehicle components, but may also be advantageous in other circumstances.

The compositions advantageously contain a UV stabilizer and, preferably, a pigment, in such a proportion that, after exposure for 200 hours in a QUV test as described below, the gloss of the coating produced, measured in accordance with ASTM D523-67, does not decrease by more than 50 % from the original level, and the coating shows no cracking, chalking or crazing. In the QUV test, the coated article, or a flat portion thereof, is exposed in a QUV accelerated weathering tester fitted with 8 QUV 313nm-B lamps for 200 hours using the following cycle:

4 hours light with a black panel temperature of 60°C

4 hours dark with a black panel temperature of 50°C. Condensation forms on the article during exposure. Periodically throughout the test the gloss is measured in accordance with ASTM D523-67, and a visual inspection is carried out.

Preferably, coatings produced from the compositions have an abrasion resistance such that they pass a Taber test as specified in ASTM D1044, carried out using 250 cycles. The abrasion resistance can be varied, if desired, by choosing different fillers, polymeric materials and/or pigments, and/or different proportions of such materials.

Where impact resistance of a coated substrate is required, the impact resistance is preferably not more than 10 % less than that of the substrate material, and may be at least 2J measured as specified in BS 3900, 1973, Part E3. The coated substrate preferably exhibits ductile rather than brittle failure. Impact performance may be enhanced by the use of, for example, a thermoplastic (melt-processable) elastomeric material, for example a material as described later in this specification.

Preferably, coatings produced from the compositions have a class A automotive finish comparable to that obtainable using a solvent-based paint. There should be no evidence of an orange peel effect. In accordance with the invention, a good finish can be obtained because articles can be made by a method in which the coating material is applied to a mould surface, which can be highly polished, in softened or molten form, especially good results being obtained when the coating material is applied in molten form.

Advantageously, the composition has a softening point of at least 155°C, measured by the Vicat softening method (ISO 306 Method A) , for a coating on polypropylene. Advantageous coatings may be obtained by using thermoplastic polymeric coating materials which begin to soften at a relatively high temperature.

The applicants have found that the invention makes it possible to produce articles which pass, for example, Rover Engineering Standard RES.30. EE.102 (June 1990) .

In general terms, the present invention makes it possible to obtain high quality finishes, for example, high quality paint finishes, which are superior to those previously obtainable using solvent-free coating materials. In some cases, a highly polished mould surface may be desirable to produce a surface with high gloss, and it may also be desirable to heat the mould surface. If a matt appearance is required, a grained mould surface can be used, and it may be desirable to maintain the mould surface at a relatively low temperature.

Compositions in accordance with the invention can be used to produce a substantially thermoplastic coating. The coating is substantially thermoplastic in the sense that it has a continuous phase or matrix of one or more thermoplastic materials. Coatings formed from compositions in accordance with the invention normally comprise one or more additional materials within the continuous phase provided by the thermoplastic polymeric material. Thus, for example, the thermoplastic continuous phase of the coating may have one or more finely divided materials uniformly or non-uniformly dispersed therein. The compositions are preferably such that articles made from them are melt-processable, to permit, for example, recycling. In this case, any additional materials included in the article as, for example, reinforcing materials or intermediate layers, should be such that they do not interfere with the melt- processing steps. Where it is desirable that the article be recyclable, the article preferably does not contain any intermediate layers, for example, bonding layers, which are infusible at the temperature at which melt- processing is carried out. The fact that the articles can be such as to be recyclable as a whole is a particular advantage of the invention.

As indicated above, the compositions are such that coatings formed from them are substantially thermoplastic in the sense that they have a continuous phase or matrix of one or more thermoplastic materials. Coatings in which the continuous phase is a thermosetting polymer would not have all the advantages obtainable in accordance with the invention. Thus, for example, articles containing such coatings would not be melt- processable and thus could not readily be recycled. On the other hand, ionomeric materials, in which crosslinks in the form of ionic bonds between polymer chains are broken by heating of the material, but reform when the material is cooled again, can be melt-processed, and are thus included within the term "thermoplastic material" used in this specification, as are thermoplastic elastomers in which crosslinks are reversibly broken down on heating.

The possibility of using for the compositions ionomers or thermoplastic elastomers or, in general, materials in which crosslinks are reversibly broken on heating, is a particular advantage of the invention, making it possible to obtain coatings, for example, thermoplastic paint coatings, with properties superior to those of thermoplastic coatings in which the thermoplastic materials do not contain crosslinks between chains at ambient temperatures. Reversibly crosslinkable materials are further discussed later in this specification.

As indicated above, coating compositions according to the invention may be used to produce articles comprising a thermoplastic coating on a thermoplastic substrate. In this case, the compositions advantageously comprise a thermoplastic polymeric material which is compatible with the thermoplastic substrate material at least at the temperature at which the article is shaped in the mould. Compatibility of the coating and substrate materials enhances adhesion of the coating to the substrate, and is particularly desirable when the coating does not completely envelop the substrate.

Compatible polymers for use in preparing articles comprising a thermoplastic coating on a thermoplastic substrate are preferably at least partly miscible at least at the temperature at which the article is shaped in the mould. With some coating/substrate combinations, however, it may be possible, particularly when using, for example, a thermal spraying step when making the article, to achieve some intimate mixing at the interface of the two materials which with controlled cooling may lead to coating material being trapped in the substrate material thereby giving an interpenetrating polymer network. (Such intimate mixing does not normally result when applying a coating material using electrostatic spraying techniques.) For the purposes of the invention, materials mixed in such a way are also regarded as compatible.

The use of thermal spraying and, in particular, flame spraying to apply a coating material may also make it possible to use initially incompatible coating materials which are rendered more compatible by the heat of the spraying system to give a bonded coating.

Adhesion can be improved (that is, compatibility can be enhanced) by the addition of compatibilizing agents to initially incompatible coating compositions. Suitable compatibilizing agents include polymers having portions with ah affinity to each of the polymers to be blended, and agents which produce a low level of crosslinking between the polymers without affecting the thermoplastic nature of the polymers.

In order to obtain good adhesion, it may be desirable for the coating composition to comprise a polymer in which the majority of repeating units are the same as the majority of repeating units in the substrate material, but this is not always essential.

The coating and substrate materials, and conditions of manufacture, are preferably chosen such that the article passes the Crosshatch test (BS 3900 E 6/ISO 2409) , which measures the adhesion of a coating to a substrate.

If the coating is completely to surround and encapsulate the substrate material then it is not always necessary for there to be good adhesion between the two. In such a case incompatible materials may be used without any modification. An incompatible coating encapsulating a substrate could be used to protect the surface of the substrate, the coating, which is not strongly adhered to the substrate, being readily removable to reveal a clean surface.

In some cases, the thermoplastic polymeric material used for the coating composition is chosen solely with a view to obtaining maximum adhesion to the substrate material. In other cases, however, the contribution that the thermoplastic polymeric material makes to the physical properties of the coating will also be of importance. The properties of the coating can be influenced by, for example, the molecular weight of the polymeric coating material, the choice of particular types of polymeric coating materials, and/or the use of mixtures of polymeric coating materials. A polymer with a higher molecular weight than that of the substrate may be preferred for the coating when it is desirable to produce a coating which is tougher and more durable than the substrate surface. It is an advantage of the present invention that the thermoplastic polymer used for the coating material may have a molecular weight higher than that normally usable when applying solvent-based paints and/or when applying coatings electrostatically. Thus, for example, when applying a powdered coating material using electrostatic methods, the molecular weight and the melt flow index of the polymeric material are limited by the flow characteristics required to give a coating with an acceptable appearance. Compositions of the invention may be suitable for use in a method in which the coating material is in a plastic condition when it contacts a mould surface, so that higher molecular weights can be tolerated. The use of polymers of higher molecular weight may make it possible to obtain coatings with superior scratch resistance, hardness and mechanical properties compared with coatings which are applied electrostatically to the mould surface.

In a preferred embodiment of the invention, the coating composition comprises a reversibly crosslinkable thermoplastic polymeric material, for example, an ionomer or a thermoplastic elastomer, in which crosslinks are reversibly broken on heating. Where ionomers or thermoplastic elastomers are included in the coating material, the coating material preferably also comprises a further thermoplastic polymeric material, advantageously in a major proportion, the reversibly crosslinkable material then being present in a minor proportion.

An ionomer is a thermoplastic material provided with a low degree of crosslinking in the solid state by the addition of a metal salt which provides ionic bonds between the polymer chains. The ionic links formed are thermally reversible and so melt processing techniques suitable for typical thermoplastic materials may be used to form products from the ionomers. Ionomers may if desired be blended with other types of polymers, for example, thermoplastic polymers mentioned in this specification. Where ionomer(s) is or are used, they advantageously form 5 % to 80 % by weight of the coating composition, preferably 5 to 15 wt %, especially about 10 wt %.

The ionic crosslinks in ionomers enhance the toughness/stiffness, the hardness, and the heat deflection temperature of coatings produced from coating compositions containing the ionomers. Further, because free radicals (which could undergo unwanted reactions) are not formed when ionic links are broken, the impact resistance of the coatings is enhanced. Ionomers can also act to increase the compatibility of pigments with the polymeric material in the coating composition, and to enhance the paintability of the final coating. The properties of the final coating can be modified by appropriate choice of the proportion of ionomer in a thermoplastic polymer/ionomer blend used for the coating material and/or by appropriate choice of the level of crosslinking in the ionomer: the level of crosslinking will normally be dependent on the proportion of metal salt used in making the ionomer. Where a matt finish is required in the final product it may be desirable to use a relatively large proportion of ionomer: smaller proportions of ionomer may be desirable when a glossier finish is required.

The inclusion in the composition of a reversibly crosslinkable melt-processable elastomeric material may be desirable to impart a desired impact strength to the coating. Such an elastomeric material, if present, preferably comprises from 1 to 70 % of the weight of the coating composition, amounts of up to 10 wt. % being preferred. An example of such a thermoplastic elastomeric material is a styrene- ethylene/butylene- styrene copolymer, which is crosslinked at ambient temperatures. The crosslinks are reversibly broken on the application of heat, thus allowing melt-processing of the material.

In a further advantageous embodiment of the invention, the coating composition comprises a thermoplastic polymeric alloy. A thermoplastic alloy may be obtained by melt-blending two or more thermoplastic polymers in the presence of a compatibilizing agent, the resulting alloy having chemical and/or physical properties superior to those of either of the individual polymers alone and to a simple mixture of the polymers. If desired, the compatibilizing agent may be added after the melt- blending step. An example of a thermoplastic alloy suitable for use in accordance with the invention is a polyamide/polypropylene alloy.

The compositions of the invention may comprise more than one thermoplastic polymeric material in order to impart desired properties to a coating produced from the compositions. Thus, for example, the compositions may comprise a blend of a thermoplastic polymeric material having a good compatibility with a proposed substrate material, and a second thermoplastic polymeric material which enhances the physical properties of the coating (and which may or may not also have good compatibility with the substrate material) . A number of advantageous blends are mentioned in this specification.

In one advantageous embodiment of the invention, the coating composition comprises the main polymer component of the proposed substrate material with the addition, where appropriate, of one or more substances selected from finely divided relatively infusible materials and the additional substances mentioned above as being suitable for imparting desired properties to the coatings. For example, polypropylene paints give very good coatings on polypropylene substrates. The polymeric material, for example, the polypropylene, of the coating may have the same average molecular weight as that of the substrate, or may, if desired, have a different, for example, higher, average molecular weight. One advantageous form of polypropylene for the coating composition of the invention is linear polypropylene having a number average molecular weight of more than 150,000 (measured by gel permeation chromatography) . Particularly advantageous coating compositions comprise a reversibly crosslinkable thermoplastic material as well as polypropylene.

In a further advantageous embodiment of the invention, the coating composition comprises a blend comprising at least one polymer compatible with the proposed substrate material and/or at least one polymer in which the majority of the repeating units are the same as the majority of repeating units in the proposed substrate material, and at least one polymeric material, for example, a reversibly crosslinkable material, which can impart to the coating properties different from those of the substrate. Such a blend can be tailored to provide the properties required of the coating by varying the components and proportions of the blend. Thus, for example, an advantageous blend for use with a polypropylene substrate is a blend comprising a minor proportion of polyethylene, and, if desired, a reversibly crosslinkable material, and a major proportion of polypropylene, while an advantageous blend for use with a polyamide substrate is a polyamide/ polypropylene blend, for example, the polyamide/ polypropylene alloy sold by AtoChem under the trade name Orgalloy R60ES. Examples of thermoplastic materials which may be used for the compositions in an article of the invention include homo- and copolymers of propylene, and thermoplastic alloys containing propylene homo- and/or copolymers (for example, polypropylene/polyamide alloys) , homo- and copolymers of ethylene, polyamides, ABS polymers, polystyrene, poly(meth) acrylates, polycarbonates, thermoplastic polyimides, polyesters, polyurethanes, polyvinylidene fluoride, and polyvinyl chloride. Blends and alloys of two or more of those materials may of course be used.

The thermoplastic polymeric material in the composition is preferably chosen to minimize haze in the final coating layer.

Although compositions in accordance with the invention can be used to produce a paint layer which renders unnecessary the subsequent painting of the article, there may be circumstances in which the application of a further layer, for example, a clearcoat layer, may be desirable. Further, it may be desirable that a coating composition in the form of a paint be such that the paint can be touched up if the coating layer is damaged in use. For these purposes, it may desirable to include in the coating layer a polymer, for example, a functionalized polyolefin, containing a relatively low proportion of polar groups, for example, carboxyl groups, or to include another additive which enhances the adhesion of a subsequently applied paint to the coating. It is however normally important that the proportion of polar groups should not be so high that the coating material readily sticks to metal: coating composition that readily stick to metals will not normally be suitable for use in in-mould coating methods. An appropriate level of polar groups can readily be determined by routine experiment. A coating material in accordance with the invention may be prepared in any suitable manner. In one advantageous process, the thermoplastic polymeric matrix or carrier material is premixed, for example, in a tumble, fountain, or other mixer, with the desired additives, for example, a pigment, filler, metallic particles or UV absorber, and the mixture is melt-mixed, cooled, and converted to particulate form. Melt-mixing, which facilitates thorough dispersal of the additives in the matrix material, may be effected using, for example, an extruder or a two roll mill. The molten mixture may then, for example, be passed through a die head and quenched at the die face or in a water bath to produce strands which are then pelletized by cutting blades. In one case, paint particles having a length of 3 mm and diameter of 2 mm were found to be advantageous when forming the article using a dual injection machine, although any size of particles suitable for the feed system of the injection moulding machine may be used.

In a further possibility certain of the additives, for example, metallic particles and/or pearlescent particles, are not added in the premixing step but are added at a later stage to prevent damage to the particles on processing. One means of achieving this is first to soften in a heated fluid bed dryer granules comprising all the components of the coating composition apart from the metallic or pearlescent materials, and then to add the metallic or pearlescent particles, which stick to the exterior of the softened granules. Alternatively, a concentrate of the metallic or pearlescent particles in a compatible carrier can be introduced into the remainder of the coating material towards the end of an extrusion barrel.

When preparing coating compositions for use in certain methods of manufacturing the articles (for example, flame spray methods) , it may be advantageous to grind the coating material cryogenically to form a ' coating powder. Typically, when the coating material contains more than one component, the components are blended, the blend is extruded and formed into, for example, granules or pellets which are then cryogenically ground, the temperature in the mill being -50°C or lower, typically lower than -80°C. Other methods of preparing thermoplastic powders may be used.

If desired, pigments and other substances to be incorporated in the coating compositions may be blended with a relatively small proportion of the thermoplastic polymeric material to form a masterbatch, which may be blended, when desired, with the remaining thermoplastic material for forming the coating. The preparation of a masterbatch aids dispersion and makes it possible to avoid the use of powdered pigment in large scale manufacture. This is particularly advantageous for preventing pollution of the local environment and/or preventing the build up of potentially explosive dust mixtures.

In principle, any thermoplastic material can be used for producing the substrate in articles comprising coatings produced from compositions in accordance with the invention, although particular materials may have advantages in certain applications because, for example, of the physical properties and/or the cost of those materials. Because high quality coatings can be produced using compositions according to the invention, the substrate material can be chosen without regard to the surface properties and/or the appearance of the article, which in many cases will make it possible to use low-cost and/or recycled material, for example, material containing mixtures of polymeric materials and/or containing pigments and/or other particulate substances derived from the melt-processing of recycled thermoplastics articles. Indeed, the recycled material can contain relatively large contaminants provided that these do not interfere with the processes used in making the articles or the properties of the articles. The substrate material may contain substances, for example, fillers, to impart desired properties to the materials and may, if desired, contain a blowing agent so that a foamed substrate is obtained.

Examples of suitable substrate materials are homo- and copolymers of propylene, homo- and copolymers of ethylene, polyamides, ABS polymers, polystyrene, poly(meth) acrylates, polycarbonates, thermoplastic polyimides, polyesters, polyurethanes, and polyvinyl chloride, and blends and/or alloys of those polymers.

As indicated above, articles comprising coatings formed from compositions of the invention may be made by any suitable method. Preferred methods for forming the article involve shaping the coating and the substrate in the same mould after sequential or simultaneous introduction of the coating material and substrate material into the mould, although coextrusion methods can be used where it is appropriate to do so.

Methods by which the coating material can be introduced into a mould include, for example, thermal spraying, particularly flame spraying, in which coating material is sprayed onto a surface of the mould under conditions such that it is in a softened or molten condition before it contacts the surface, and application of the coating material to the mould surface in powder form, for example, by electrostatic spraying, and then melting the powder to form the coating. Methods in which the coating material is in a softened or molten form (including a mixture of softened and molten material) before it contacts the mould surface are preferred.

In some cases, it may be advantageous to apply the coating material to the substrate material rather than to a surface of the mould. Thus, for example, the coating material may be sprayed onto the substrate material, for example, by thermal spraying, following which the substrate material is positioned in the mould.

The substrate material may be introduced into the mould in any suitable manner. Thus, for example, the substrate material may be in the form of a coherent mass which is positioned as such in the mould and then submitted to a compression moulding step. In this case the coating material can be applied to a surface of the substrate material, preferably before the substrate material is positioned in the mould, or to a surface of the mould.

In another advantageous method, the substrate material is injected into the mould in molten form. If desired, the substrate material can be introduced into the mould in the form of foamed or foamable material.

In another method for forming articles according to the invention, the coating material and substrate material are simultaneously extruded through an extrusion die in a coextrusion step.

Because articles comprising coatings formed from compositions according to the invention can comprise a thermoplastic coating material and a thermoplastic substrate material, the need for curing of the coating or substrate after moulding can be avoided. The finished article can simply be removed from the mould, if necessary after cooling of the article, or allowing it to cool. If desired the article can be cooled out of the mould.

Additional information about preferred processes for making the articles of the invention is given below.

As indicated above, one advantageous method for forming the coating involves spraying the coating material onto a surface under conditions such that it is in a molten and/or softened condition before it contacts the surface. The coating material can then coalesce on the surface to form a substantially continuous coating layer. This method is very suitable for the production of injection moulded articles and compression moulded articles, and may if desired be used in the production of articles moulded by other methods.

The surface onto which the coating material is sprayed may be a surface of the mould or a surface of the substrate material. Preferably substantially all the coating material is in softened or molten form (or is a mixture of softened material and molten material) before it contacts the surface, although a minor proportion may still be in solid, non-plastic form provided that it melts and flows on contact with the surface or the softened or molten coating material thereon. In the preferred case, where the coating material is molten before it contacts the surface, it does not depend on the heat of the surface to melt it, although additional heat may be supplied by either or both of the mould and the substrate material, if desired, or by the support. Thus, for example, it may be desirable to maintain the mould at a temperature above ambient temperature, but below the. melting temperature of the substrate material, to achieve good cycle times and substrate and coating formation.

The coating material may be, for example, applied to a surface, for example, an interior surface, of an open mould or to a surface of a closed mould.

Heat may be applied to the coating material, before it contacts the surface, by any suitable external energy source. Thus, for example, a hot air gun may be used to heat the air through which a powdered coating material passes as it travels towards the surface. Alternatively, detonation spraying or plasma spraying, in air, or in a vacuum chamber or high pressure chamber, may be used. Preferably, however, the coating material is applied to the surface using a flame spray gun. The coating material, in the form of a powder, may pass down the centre of a flame, or around a flame, and is heated by hot gas, for example, hot air. If the correct conditions, including temperature and particle size, are chosen then the powder is not burnt by the flame, but is heated enough to soften or melt it. The most appropriate particle size for any given powder can be determined by routine experiment. The most suitable range of particle sizes in any particular case is dependent on the gun setting used.

When the coating material is applied by thermal spraying, the material for forming the substrate may be introduced into the mould by any suitable method, for example, by injection of the substrate material at such a temperature that the substrate material is molten, or by the introduction of a self-supporting sheet or preform of substrate material, which may contain, for example, a reinforcing material, for example, glass fibres, and which may, if desired or required, be heated before introduction into the mould. (The use of a self- supporting sheet or preform of substrate material may be useful, for example, for producing floor or ceiling tiles.) In general, the coating material is applied to the mould surface before, or substantially simultaneously with, introduction of the substrate material into the mould. The coating material and substrate material may be shaped to produce an article in accordance with the invention by any desired moulding method, for example, injection moulding or compression moulding. Additional heat may be supplied, if necessary, during the moulding process. When moulding is complete, the moulded article is, if necessary, cooled or allowed to cool, and is then removed from the mould.

The applicants have surprisingly found that, when using the above-described method, durable coatings can be obtained on plastics substrates, even when the substrate material is injected at high velocities. The application of coating material to mould surfaces by, for example, electrostatic spraying, tends to lead to flow lines being formed in the powder when substrate material is injected at high velocity. Thermal spraying makes it possible to obtain uniform coating layers of a desired thickness. The coating thickness may be controlled by appropriate choice of spraying conditions.

As indicated earlier in this specification, the coating material may comprise one or more metallic materials in finely divided form, for example, as particles, fibres or flakes. It has been found that when particles of metallic materials are included in coating materials used in the above-described thermal spraying method to give coated injection moulded products, the particles are forced to the surface of the coating giving an excellent decorative finish. When the same coating material is used for producing compression moulded products it is found that the metal particles are forced towards the interface of the coating and substrate. This would be useful for EMI shielding of electrical components.

The compositions of the invention make it possible to obtain high quality, durable coatings on, for example, thermoplastic substrates, for example, polypropylene or polyethylene substrates, which cannot be satisfactorily coated, at reasonable cost, using previously proposed compositions. Good adhesion of the coating can be obtained without the need to modify the surface of the substrate by prior treatment (for example, flame treatments, corona discharge, chemical etching or plasma treatments) or by modification of the bulk polymer. The production of coated substrates may be achieved with short cycle times and, where coatings of low surface energies are used, without the use of release agents on the mould surface. Further, because the coating material can be in softened or molten form when it comes into contact with the mould, any excess material is normally removed from the mould with the moulded article, so that little or no cleaning of the mould is necessary, even when the mould is to be used for articles of a different colour. The compositions can be used in the production of articles having relatively complex shapes.

A particular advantage of the compositions of the invention is that they make it possible, especially where highly polished moulds are used, to obtain articles, for example, vehicle components, having a paint layer with a sufficiently high gloss for use without further treatment even in circumstances where a high gloss finish is essential. The compositions thus represent a major advance in, for example, the manufacture of vehicle components comprising thermoplastic substrate materials.

The compositions of the invention make it possible to form, for example, articles from a low-cost thermoplastic material, including recycled material, without the need to incorporate large quantities of additives into the material to impart desired properties or a desired appearance to the bulk of the material. Instead, any additional substances can be confined to the coating layer, and it is feasible to use for the coating compositions, if desired, relatively expensive materials, for example, high performance engineering polymers, including polymer blends and alloys. The problems inherent in the use of solvent-based coating methods are also avoided. If desired, the coating composition can be chosen to be such that a further coating layer, for example, a clear lacquer coating, can be applied over a coating produced from it, although the invention will normally make it possible to dispense with such lacquer coatings. The coating composition can be supplied as a solid, solventless, thermoplastic paint in, for example, granulated or powdered form, and does not require curing.

When a metal-containing coating composition is used it may be necessary to coat the mould with a release agent before applying the coating composition. Other coating compositions used to give coatings may not require release agents to be used if, for example, the coating material has a low surface energy so that it has little tendency to adhere to the mould.

In particular the invention makes it possible to provide vehicle components which are formed from a thermoplastic substrate material and which have a high quality coating layer which can be obtained without the application of a sheet of coating material to a preformed substrate. The invention thus represents a major advance in the automobile industry, solving a problem (the manufacture of coated thermoplastic vehicle components) which has been the subject of extensive research in the industry.

The following Examples illustrate the invention. In the Examples, percentages are by weight, unless otherwise indicated.

Example 1

A thermoplastic paint composition comprising:

87.1 % polypropylene (Melt index 25.0 g/10 in as measured by ISO 1133 (2.16 kg at 230°C) )

10.0 % BaS0₄ filler

2.0 % black pigment

0.5 % antioxidant

0.4 % UV stabiliser was used in the manufacture of a coated polypropylene vehicle component (a battery tray) . The components of the paint composition were mixed, and the mixture was extruded to form pellets which were cryogenically ground at a mill temperature of -80°C in an Alpine UPZ 160 mill to give a powder having an average particle size of 120 μ .

The powder was flame sprayed onto the inside of an open injection mould using a hand-held flame spray gun with a right-angled nozzle and a small gravity feed hopper. The mould was preheated to a temperature of 80 to 100°C. Compressed air was supplied to the gun at a pressure of 2.25 bar (0.225 MPa) , giving a powder flow rate of about 25 g/min (about 0.4 g/s) . The fuel gases used were oxygen and acetylene.

When the interior of the mould had a continuous coating thereon, the mould was closed and polypropylene substrate material at a temperature of about 200°C was injected into the mould. After partial cooling, the thermoplastic moulded article was removed from the mould and allowed to cool to room temperature. The coating had an average thickness of 150 μm. The coating passed the Crosshatch adhesion test (BS 3900 E 6/ISO 2409) before and after a 24 hour watersoak with a 0 % loss. The coating also passed an environmental cycling (65/U) test (RES 30EE102 Issue 9, which is part of Rover Engineering Standard RES.22.PL.08) , humidity test (BS 3900 Part F2 - 168hr) , and a power wash (80°C, 80 bar (8 MPa) , 1 min (60 sec) ) test.

Example 2

A thermoplastic paint composition comprising: 79.1 wt. % polypropylene (as in the paint composition of Example 1) 20.0 wt. % white pigment 0.9 wt. % antioxidant

was used to apply a paint layer to a sheet of glass fibre-reinforced polypropylene. The paint, in the form of a powder of average particle size 120 μm, was flame sprayed, using the same gun type and gun setting as in Example 1, onto an inner surface of an open compression mould (Hounsell press) preheated to a temperature in the range of 80 to 100°C. When the said inner surface of the mould had a continuous coating thereon, a preheated preform of the substrate sheet was positioned in the mould on the sprayed surface. The mould was then closed, thereby punching out the desired shape. After partial cooling, the moulded article was removed from the mould and allowed to cool to room temperature. The coating, which had an average thickness of 150 μm, was of a high quality.

A coating of high quality, having a thickness of 150 μm, was also obtained when this Example was repeated spraying the coating material onto the substrate material rather than onto the mould surface.

Example 3

99.25 wt. % polyamide/polypropylene alloy sold under the trade name Orgalloy R60ES

0.50 wt. % of carbon black masterbatch

0.25 wt. % of antioxidant were mixed, extruded and ground as described in Example 1 to give a thermoplastic paint composition having an average particle size of 120 μm. (In the masterbatch, the carbon black was blended with a small amount of polypropylene.) This composition was flame sprayed onto the interior of an injection mould using a flame spray gun as described in Example 1.

When the interior of the mould had a continuous coating thereon, a polyamide-6, 6 substrate material, at a temperature of about 250 to 300°C, was injected into the mould. The coating layer in the final thermoplastic article had an average thickness of 150 μm and was found to adhere well to the substrate material. Examples 4 to 8

A thermoplastic paint composition comprising:

91.6 % polypropylene (as in the paint composition of Example 1)

2.5 % carbon black masterbatch

0.5 % antioxidant

0.4 % UV stabilizer

5.0 % acrylic-modified polyolefinic ionomer was used (Example 4) to produce a thermoplastic article (coated substrate) using the general method described in Example 1, polypropylene being used as the substrate material.

In Examples 5 to 7 , the acrylic-modified polyolefinic ionomer was replaced by 5 % of a reversibly crosslinkable styrene-ethylene/butylene-styrene rubber sold under the trade name Kraton, a low molecular weight ionomer, and a polyolefinic ionomer, respectively. In Example 8, the polypropylene and acrylic-modified polyolefinic ionomer were replaced by 96.6 % of a polypropylene/polyethylene blend. The substrate material in each of Examples 5 to 8 was polypropylene.

In each of Examples 4 to 8 , the article produced included a coating of thickness of not more than 150 μm and having excellent properties. Similar results were obtained when Example 4 was repeated using a mixture of recycled polyolefins as the substrate material.

Example 9

The coating method described in Example 1 was repeated using the same substrate material and the following coating material:

87 % polypropylene (as in the paint composition in

Example 1) 0.5 % antioxidant 0.4 % UV stabilizer 4 % finely divided aluminium (average particle size

75 μm) 2 % finely divided aluminium (average particle size

200 μm) 4.1 % styrene-ethylene/butylene-styrene reversibly crosslinkable rubber. A thermoplastic article including a metallic coating having a thickness of less than 150 μm and excellent appearance and properties, including EMI shielding properties, was obtained. The finely divided aluminium was well below the exposed surface of the coating, and was thus protected from oxidation.

Example 10

A sample of polypropylene homopolymer in pellet form having a weight average molecular weight Mw of between 200,000 and 280,000 (measured by gel permeation chromatography) and a melt flow index of 25 g/10 minutes measured in accordance with IS01133 was premixed in a barrel blender with a εtyrene-ethylene/butylene-styrene cross-linkable rubber, a hindered phenol antioxidant sold under the trade mark Irganox 1010, two UV stabilisers, transparent micaceous titanium dioxide in platelet form, and a mixture of pigments. The proportions of the various components were as fol lows :

Parts by weight Polypropylene 2028

Styrene-ethylene/butylene-styrene cross-linkable rubber 250

Irganox 1010 12.5

Green phthalocyanine (BASF L8730) 25

Blue phthalocyanine (BASF L6920) 25

Special Black 4A (Carbon black) 1.35

Supersparkle mica coated with Ti0₂ 82.5

Sparkle mica coated with Ti0₂ 12.5

Exterior Hi-lite Blue (micaceous Ti0₂ with 50.0 chromium oxide coating) UV stabilizers 13.50

The mixture was extruded using a thermoplastic extruder at 200 rpm with an 1/d ratio of 16 at temperature settings of 160°C at the inlet, 160°C in the barrel and 180°C at the diehead. The strand produced at the diehead was quenched in a water bath and pelletized to produce pellets of paint 5 mm in length and 2 mm in diameter.

The pellets were used in an in-mould coating method to produce a coating (average thickness 300 μm) on a polypropylene substrate, the finished article being a vehicle component.

The surface of the finished part had a gloss measured by ASTM D523-67, of 90 % at a 60 degree head. On comparison with a standard automotive panel the metallic appearance (imparted by the pearlescent material) was bright and of a class A finish.

The finished part was subjected to and passed the following performance tests. Adhesion BS 3900/ISO 2409 - pass GtO at 2 mm.

Saltspray ASTM 117B 1000 hours - no cracking or blistering.

QUV weatherometer 313 nm lamp B 500 hours, no cracking or blistering, and not more than 50 % of original gloss lost.

Spotting tests; Petrol, diesel, brake fluid, acetic acid 0.1M, HC1 0.1M.

No colour change on application.

Example 11

A coating material as in Example 10 having the following formulation was prepared in the manner specif ied in Example 10 :

Parts by weight

Polypropylene 77

Aluminium pigment in protective resin 3

(needle-li_ke particles of 75 μm length)

Pearlescent White 2

Scotchlite ^" CIS/250 glass beads 10

Crosslinkable rubber as in Example 10 8

+ Trade Mark

The coating material was used in an in-mould coating method for the production of a vehicle component. The substrate material was the same as that used in Example 10.

A thermoplastic vehicle component including a very satisfactory coating was obtained. The coating, which had a thickness of 130 to 160 μm on the outer face of the component and a thickness of 20 to 40 μm on the inner face of the component, passed the tests indicated in Example 10, the QUV test for Example 11 being carried out for a period of 300 hours. In the coating the aluminium pigment was close to the surface, but was protected by a layer of polymer. The needles of aluminium were orientated in the coating.

Example 12 (Comparative)

A typical powder coating formulation was prepared by premixing a ther osetting polyester with triglycidyl isocyanurate (TGIC) , a flow aid, and benzoin as a degassing aid. The mixture was then extruded on a Werner Pfleiderer extruder at 120°C.

The resultant extrudate was broken into chips which were then ground to a fine powder having a particle size distribution of:

100 % above 15 microns 55 % above 32 microns 0 % above 100 microns

Aluminium powder was dry blended into the mixture or bonded onto the surface of the powder particles. The powder was then applied through an electrostatic gun onto an aluminium panel and heated for 10 minutes at 200°C.

The resultant paint film was exposed to salt spray and QUV as described in Example 10 and was found to deteriorate rapidly. The sparkle effect achieved was of a low quality and the film did not have a Class A automotive finish.

In general it was found that, although good coatings were produced in all the above Examples of the invention, superior properties were obtained when using coating materials comprising reversibly crosslinkable thermoplastic materials, including thermoplastic alloys. Example 13

This Example illustrates one method of manufacturing of an ionomer suitable for use in compositions of the invention.

A sample of an acid-grafted polypropylene available under the trade name Polybond 2015 was extruded and pelletized, and the pellets were cryogenically ground into a fine powder. The powder was then blended with 10 % sodium hydrogen carbonate by weight, based on the weight of the acid-grafted polypropylene, using a APU extruder (screw speed 250 rpm; torque 55-60 %; barrel temperature 200 °C) and formed into a plaque which was examined, before and after storage at 200°C for 10 minutes, using an infrared spectrometer. Plaques were also obtained using 1 % and 5 % respectively of sodium hydrogen carbonate (extrusion temperatures 148"C and 185°C respectively) . When working on a large scale, blending could be effected in, for example, an extruder, the cryogenic grinding step being omitted.

Infrared measurements showed that the sodium ions neutralised acid groups in the acid-grafted polypropylene to produce ionic crosslinks between the polymer chains. A greater level of crosslinking was obtained when using higher proportions of sodium hydrogen carbonate. The reaction between the salt and the polymer was incomplete after the extrusion step, and the storage step was thus desirable for obtaining complete reaction.

The ionomer produced was particularly suitable for use, in admixture with polypropylene, in a coating material suitable for use with a polypropylene substrate.

Claims

CLAIMS :

1. A coating composition suitable for use in an in-mould coating method and comprising a first thermoplastic polymeric material, a second, reversibly crosslinkable, thermoplastic polymeric material, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants.

2. A composition as claimed in claim 1, wherein the first thermoplastic polymeric material comprises a propylene homo- or copolymer.

3. A coating composition suitable for use in an in-mould coating method and comprising a thermoplastic alloy, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants.

4. A composition as claimed in claim 3, wherein the thermoplastic alloy comprises first and second thermoplastic polymeric materials and a compatibilizer therefor.

5. A composition as claimed in claim 3 or claim 4, wherein the thermoplastic alloy comprises polypropylene and a polyamide.

6. A thermoplastic paint composition comprising a propylene homo- or copolymer, a colouring material, and at least one substance selected from finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants, the composition being suitable for use in an in-mould coating method for producing an article comprising a polypropylene substrate having thereon a coating formed from the composition.

7. A thermoplastic paint composition comprising a propylene homo- or copolymer, a UV stabilizer, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials and antioxidants, the composition being suitable for use in an in-mould coating method to produce an article comprising a polypropylene substrate having thereon a coating formed from the composition, the UV stabilizer and the said substance(s) being present in the composition in such a proportion that, after exposure for 200 hours in a QUV test as defined herein, the gloss of the coating, measured in accordance with ASTM D523-67, does not decrease by more than 50 % from the original level, and the coating shows no cracking, chalking or crazing.

8. A thermoplastic paint composition comprising a propylene homo- or copolymer, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants, the composition being suitable for use in an in-mould coating method to produce an article comprising a polypropylene substrate having thereon a coating formed from the composition, the coating having an abrasion resistance such that it passes a Taber test as specified in ASTM D1044, carried out using 250 cycles.

9. A thermoplastic paint composition comprising a propylene homo- or copolymer, and at least one substance selected from colouring materials, finely divided metallic materials, finely divided pearlescent materials, UV stabilizers and antioxidants, the composition being suitable for use in an in-mould coating method to produce an article comprising a polypropylene substrate having thereon a coating formed from the composition, the article having an impact resistance which is at least 2J measured as specified in BS 3900, 1973, Part E3 , and is not more than 10 % less than that of the polypropylene substrate.

10. A composition as claimed in any one of claims 1 to , which comprises a colouring material which is a pigment.

11. A composition as claimed in any one of claims 1 to 10, which comprises an electrically conductive material and is suitable for producing an EMI shielding layer.

12. A composition as claimed in any one of claims 3 to 11, which also comprises a reversibly crosslinkable material.

13. A composition as claimed in claim 1 or claim 12, wherein the reversibly crosslinkable material is an ionomer.

14. A composition as claimed in claim 1 or claim 12, wherein the reversibly crosslinkable material is a thermoplastic elastomer.

15. A composition as claimed in any one of claims 1 to 14, suitable for application by thermal spraying.

16. A composition as claimed in any one of claims 1 to 15, suitable for application by flame spraying.

17. A composition as claimed in any one of claims 1 to 14, suitable for use in injection moulding apparatus.

18. A composition as claimed in any one of claims 1 to 14, which is also suitable for use in coextrusion apparatus.

19. A composition as claimed in any one of claims 1 to 18, in powder or granular form.

20. A composition as claimed in any one of claims 1 to 19, substantially as described herein.

21. The use of a composition as claimed in any one of claims 1 to 20 in an in-mould coating method for producing an article comprising a substantially thermoplastic substrate having thereon a coating formed from the composition.

22. The use of a composition comprising a major proportion of a propylene homo- or copolymer and a minor proportion of an ionomer for producing an article comprising a polymeric substrate having thereon a coating formed from the composition.