GB2278114A

GB2278114A - Pigmenting fillers for polymeric compositions

Info

Publication number: GB2278114A
Application number: GB9410115A
Authority: GB
Inventors: David George Jeffs
Original assignee: ECC International Ltd
Current assignee: Imerys Minerals Ltd
Priority date: 1993-05-20
Filing date: 1994-05-20
Publication date: 1994-11-23
Anticipated expiration: 2014-05-20
Also published as: DE4417833A1; GB9310438D0; ITTO940416A0; FR2705353A1; KR100254404B1; JPH073184A; GB2278114B; AU6303694A; ITTO940416A1; IT1265969B1; FR2705353B1; GB9410115D0; AU672891B2

Description

1 2278114 PIGMENTING FILLERS FOR POLYMERIC COMPOSITIONS This invention

concerns low-profile fillers or additives for polymeric compositions which have the additional property of imparting colour to the compositions.

The invention is especially concerned with thermosetting polymeric compositions which are specially adapted for forming shaped articles by sheet moulding or by bulk, or dough, moulding processes.

Sheet moulding compounds (SMC) and bulk moulding compounds (BMC) generally contain a thermosetting polymeric material which may be, for example, an unsaturated polyester resin, an epoxy resin, a vinyl ester resin or a phenolic resin. In the case of the unsaturated polyester resins, the compound contains, in addition to the polyester, which is generally formed by the reaction between one or more dibasic acids and a dihydric alcohol, an unsaturated alkylbenzene crosslinking agent, for example styrene, a peroxide catalyst, a filler and a fibrous reinforcing material such as glass fibre. The moulding compounds are generally formed into shaped articles, either threedimensional bodies or sheets, by heating the composition to a temperature in the range from 120 to 1800C and moulding the shaped article in a press at a pressure of about 4MPa.

As these moulding compounds cure, or cross-link, in the mould they tend to contract, with the result that warpage of the shaped article can occur. There is also a tendency for the compound to withdraw slightly from the walls of the mould with the result that the surface finish of the shaped article is impaired. The reinforcing glass fibres may become partially exposed at the surfaces of the shaped article, giving the surface a rough feel and an unattractive appearance.

In order to overcome this problem an additive A known as a "low profile additive" is often included in the moulding compound. In the case of unsaturated polyester resins, this is usually an elastomeric or thermoplastic polymeric material which is soluble in the cross-linking agent for the unsaturated polyester resin, but does not itself cross-link. The elastomeric or thermoplastic polymeric material may be, for example, a natural rubber, a natural rubber which has been substituted with functional groups, a synthetic rubber, an acrylic copolymer, a poly(vinyl acetate) or a copolymer of vinyl acetate. If an appropriate amount of a low profile additive of one of the above types is included in the moulding compound it is found that the low profile additive expands in the mould, and that this expansion can compensate for the contraction of the unsaturated polyester resin, with the result that the compound as a whole exhibits no shrinkage, and can even be caused to show a small net expansion. As a result, warpage of the shaped articles is largely eliminated and the appearance and feel of the surfaces of the shaped articles are greatly enhanced.

It is often required that the shaped article produced from the moulding compound should have a definite colour which is different from the natural colour of the moulding compound. In order to produce the desired colour, an appropriate pigment is added, generally in the form of a colour paste or a suspension of the pigment in a liquid vehicle. This liquid vehicle is usually a low molecular weight polyester material, and polyesters of this type tend to have poor resistance to weathering and strength properties when compared with the polyesters which are used as the principal components in the moulding compounds. The depth of colour which can be produced with colour pastes is therefore limited by the level of the liquid vehicle which can be tolerated in the compound. The -3 result is generally that the intensity of the colour produced is poor and that the surface of the shaped article produced from the moulding compound has a mottled or marbled effect. This mottled or marbled effect is heightened by the presence of low profile additives, which are generally added separately to the compound, and which form a separate phase during the cross linking reaction, since the low profile additives do not readily take up the added pigment.

GB-A-2179665 describes unsaturated polyester compositions which contain a filler which has been prepared by mixing an aqueous suspension of the filler with a latex, and drying the mixture to form surfacetreated filler particles.

GB-A-2220666 describes a filler prepared by a process in which an aqueous suspension of carbon black is mixed with an aqueous suspension of a particulate inorganic material and a latex, and thereafter drying the mixture to form filler particles containing the carbon black. This filler may be incorporated into a.glass mat reinforced polypropylene composition.

According to a first aspect of the present invention, there is provided a coated particulate inorganic material, the coating on the particles of the inorganic material comprising a combination of a natural or synthetic polymeric material and a first pigment or dye other than carbon black alone, the polymeric material being present in the coating in an amount of from 1% to 10% by weight, based on the weight of dry inorganic material.

The coated inorganic filler may be made, in accordance with a second aspect of the present invention, by a process which comprises combining, in aqueous suspension, the particulate inorganic material, a natural or synthetic latex composition in an amount such as to provide a coating on the particles of the inorganic material of from 1% to 10% by weight of latex solids, based on the weight of dry inorganic material, and the pigment or dye, and dewatering and drying the resultant mixture to form a particulate filler product. Drying may be performed using a spray drier which may result in hollow microspheres having diameters up to 0.5mm in size, and preferably no smaller than 0.02mm. The spray dried product may be pulverized, if desired.

The invention also provides a process for preparing an improved coated inorganic filler for a thermosetting composition, which comprises combining, in aqueous suspension, a particulate inorganic material, a natural or synthetic latex composition in an amount such as to provide a coating on the particles of the inorganic material of from 1% to 10% by weight of latex solids, based on the weight of dry inorganic material, and a first pigment or dye other than carbon black alone.

The improved coated inorganic filler is particularly suitable for incorporation in a thermosetting moulding composition.

The particulate inorganic material may be chosen from a kaolinitic clay, e.g. kaolin or ball clay, a calcined kaolinitic clay, calcium carbonates, aluminium.

silicates, such as feldspar and nepheline syenite, calcium silicates, e.g. the natural calcium silicate known as wollastonite, bauxite, talc, mica, alumina trihydrate, silica, carbonates and hydroxides of magnesium, e.g. natural hydrotalcite, dolomite, i.e.

the natural double carbonate of calcium and magnesium, calcium sulphate, e.g. gypsum and anhydrite, titanium dioxide and mixtures of any two or more of these. Feldspar is an especially preferred inorganic material. The inorganic material may be natural or synthetic, and, in particular, both natural and synthetic forms of calcium carbonate, silicates of aluminium and calcium, silica, carbonates and hydroxides of magnesium, calcium sulphate and titanium dioxide are within the scope of this invention. Where the inorganic material is synthetic it may be precipitated as in the case of calcium carbonate, silica and titanium dioxide. The inorganic materials specified above are commonly regarded as "white" inorganic materials; but the term "white" does not necessarily mean that the mineral has a pure white colour, but that the colour is substantially free of any strong non-white hue. Many of the inorganic materials which may be employed in the present invention are crystalline.

Preferably the particles of the inorganic material are no larger than about 100pm, more preferably no larger than 50pm, and most preferably no larger than 20pm. The specific surface area of the inorganic material as measured by the BET nitrogen absorption method is preferably at least at least 1m2 g-' and preferably no more than about 300m2 g- 1. Most preferably the specific surface area of the inorganic material is in the range from 2 to 10m2 g- 1.

The natural or synthetic polymeric material forming the coating on the particles is desirably one derived from a natural or synthetic latex, and may be elastomeric or non-elastomeric. Preferably, although not essentially, it is poly(vinyl acetate), which is non-elastomeric.

In the process of the present invention, the particulate inorganic material is preferably provided in the form of an aqueous suspension containing up to 65% by weight of the dry inorganic material and preferably at least 50% by weight, although it should be appreciated that suspensions having as little as 20% by weight of the dry inorganic material can be used and these may not require a dispersing agent. This suspension may be dispersed with the aid of a dispersing agent, for example from about 0.05% to about 0.5% by weight, based on the weight of the dry inorganic material, of a dispersing agent for the inorganic material. The dispersing agent for the inorganic material is preferably a water soluble salt of a poly(acrylic acid) or of a poly(methacrylic acid) having a number average molecular weight of not more than 10,000.

The natural or synthetic latex composition may advantageously comprise a latex of a thermoplastic, non-elastomeric material such as poly(vinyl acetate) or a copolymer of vinyl acetate. Alternatively the latex composition may comprise a latex of an elastomer, for example a natural rubber or a natural rubber which has been substituted with functional groups or a synthetic rubber such as a styrene butadiene rubber (SBR). Other suitable latices include those formed from elastomeric or non-elastomeric acrylic copolymers and homopolymers, the non-elastomeric homopolymers and the elastomeric copolymers being preferred. Advantageously the acrylic copolymer comprises a lower alkyl (Cl-4) ester of acrylic acid and a lower alkyl (Cl-4) ester of methacrylic acid; especially preferred is a copolymer of ethyl acrylate and methyl methacrylate. Also especially preferred are the non-elastomeric acrylic homopolymers such as polystyrene and poly(methyl methacrylate). Also suitable are copolymers of lower alkyl (Cl-4) acrylic esters with vinyl acetate, styrene or acrylonitrile. The latex composition is a stabilised suspension of polymer particles in water and will generally contain about 40% to 60% by weight of solids. The latex may be stabilised with the aid of a surfactant or a water-soluble colloid.

The first pigment or dye is preferably introduced into the composition in the form of an aqueous suspension or solution containing from 5% to 40% by weight of the pigment or dye. A dispersing agent for the pigment may be added to the aqueous suspension. An anionic dispersing agent is generally preferred. If the desired colour is red or yellow the pigment or dye may be an appropriate azo dye. If the desired colour is blue the pigment or dye may be, for example, ultramarine blue, phthalocyanine blue or a mixture of these dyes. If the desired colour is grey, the pigment or dye is advantageously prepared by mixing a white pigment or dye, for example titanium dioxide or zinc sulphide, with another pigment or dye, normally a black pigment or dye, for example carbon black in the proportion required to give the desired shade of grey. Generally the proportion of the black pigment or dye in the mixture will be not greater than about 2% by weight of the total weight of black and white pigments or dyes. The amount of the colour pigment or dye included in the coated filler depends on the desired colour but will generally be in the range of from about 0.5% by weight to about 5 by weight, based on the weight of the dry inorganic material.

The filler of the invention is especially suitable for inclusion in an unsaturated polyester moulding compound, but may also be used in compounds containing epoxy resins, vinyl ester resins or phenolic resins.

When the filler of the invention is incorporated in an unsaturated polyester moulding composition, particularly advantageous results have been obtained with the following combinations:

inorganic material polymer feldspar poly(methyl methacrylate) alumina trihydrate poly(methyl methacrylate) alumina trihydrate polystyrene.

In the process aspect of the present invention, the order in which the suspension of the inorganic material, the suspension or solution of the pigment or dye and the latex are added together is unimportant. For example the suspension of the inorganic material can be mixed with the suspension or solution of the pigment or dye and the latex added to the suspension thus formed. Alternatively the suspension of the inorganic material may be mixed with the latex and the suspension or dye of the pigment or dye added to the mixture thus formed. However, it is generally preferred to add the latex to the composition last, as the latex is the least stable component and the most likely to cause rheological problems. The present invention also provides a polymeric (preferably thermosetting) moulding composition incorporating the coated inorganic material of the present invention. Furthermore, the present invention relates to moulded components, for example components for automobiles, made from the polymeric moulding composition of the present invention. 20 The mineral low profile additive of the present invention makes it possible to achieve a more even and more intense coloration of shaped articles prepared from polymeric compositions. The invention will now be illustrated by reference to the following examples.

EXAMPLE 1

A ground natural chalk having a particle size distribution such that 60% by weight consisted of particles having an equivalent spherical diameter smaller than 2pm was suspended in water containing 0.1% by weight, based on the weight of dry chalk, of a sodium polyacrylate dispersing agent having a number average molecular weight of about 4,000, the chalk being in a quantity sufficient to give a suspension containing 60% by weight of dry chalk. The suspension was divided into four portions, to which were added, -g- respectively:- A. Sufficient of an aqueous suspension containing 20 by weight of a yellow azo dye to provide 1% by weight of the dye, based on the weight of dry 5 chalk; or B. Sufficient of an aqueous suspension containing 20% by weight of a red azo dye to provide 2% by weight of the dye, based on the weight of dry chalk; or C. Sufficient of an aqueous suspension containing 20% by weight of a mixture of blue dyes to provide 3% by weight of the mixed dyes, based on the weight of dry chalk, the mixture of blue dyes consisting of 50% by weight of ultramarine blue and 50% by weight of phthalocyanine blue; or D. Sufficient of an aqueous suspension containing 20% by weight of a mixed grey pigment to provide 2% by weight of the mixed pigment, based on the weight of dry chalk, the mixed pigment consisting of 99 by weight of zinc sulphide and 1% by weight of carbon black.

To each of the above four mixed suspensions of chalk and pigment or dye there was added sufficient of a latex containing 50 by weight of poly(vinyl acetate) in water to provide 6.5% by weight of poly(vinyl acetate) solids, based on the wight of dry chalk. The components of the mixture were thoroughly mixed together, and in each case the mixed suspension was spray dried in a spray drier to form hollow microspheres having diameters in the range from 0.02 to O.lmm. These products are referred to below as the treated fillers.

An unsaturated polyester moulding compound containing each of the treated fillers, A, B, C and D, was prepared according to the formulation given in Table 1 below. As a comparison, an unsaturated polyester moulding compound was prepared containing each of the four pigments or dyes, but with the pigment or dye, the particulate chalk material and the poly(vinyl acetate) low profile additive being added separately, rather than all three of these ingredients being added together as composite granules. The formulation of these comparative unsaturated polyester moulding compounds is also given in Table 1 below.

Table 1

Ingredient Parts by Weight Comparative A B c D 60.0 40.5 5.0 1.5 248.8 78.0 Invention Unsaturated Polyester Resin Low Profile Additive Pigment Catalyst Treated filler Untreated filler Chopped glass fibre 60.0 40.8 60.0 40.5 2.5 5.0 1.5 1.5 251.2 78.0 60.0 40.0 248.8 78.0 7.4 1.5 246.6 78.0 60.0 1.5 270.0 78.0 The unsaturated polystyrene resin comprised a mixture of polyester monomers consisting essentially of about 50% by weight of propylene glycol, about 25% by weight of maleic anhydride and about 25 % by weight of phthalic anhydride. The low profile additive was a solution containing 40t by weight of poly(vinyl Acetate in styrene. The pigment or dye in Comparative compounds A,B,C and D was added as a paste with low molecular weight polyester material. The untreated filler was the same ground natural chalk as was used for preparing the treated filler. The total amount of styrene was approximately the same in all of the compounds, and the amounts of pigment or dye and poly(vinyl acetate) present in each of the Comparative compounds were the same as the amounts which were included in the treated filler in each of the corresponding Invention compounds.

Each unsaturated polyester compound was formed by injection moulding into discs of diameter 100mm and thickness 3mm.

The colour of each of the compounds was measured, using the disc as a test piece, by a system which is based on the formula known as the C.I.E. 1976 L a b formula which was developed by the Commission Internationale d'Eclairage. Three measurements of the intensity of light reflected from the surface of the sample were made using Tristimulus X, Y and Z filters, which each embrace a broad band of wavelengths in the visible spectrum but are generally red, green and blue in colour, respectively. The measurements were made by means of an Elrepho photometer and L a and b values were calculated from the reflectance values for the X, Y and Z filters according to the formulae:

L = 10-Y, a = 17---S(1. 02XY), VT- b = 70 (Y-0.8467.Z) vfy- The a and b values can be said to be co-ordinates representing chromaticity (i.e. "redness", "yellowness" etc.) and the L value can be said to represent the lightness or darkness of the shade.

The results obtained are set forth in Table 2 below:

Table 2

Compound Colour L a b A (Invention) Yellow 82.0 -4.6 74.5 A (Comparative) Yellow 87.3 -12.2 65.0 B (Invention) Red 45.6 50.5 40.0 B (Comparative) Red 53.4 42.3 19.7 C (Invention) Blue 35.6 29.9 -60.6 C (Comparative) Blue 55.1 1.6 -28.0 D (Invention) Grey 61.0 -1.7 1.4 D (Comparative) Grey 70.8 0.4 0.6 These results show that, in each case, the compound according to the invention gives a lower L value than the comparative compound. The scale of the L value extends from 100 for pure white to 0 for intense black, and a lower L value therefore indicates a deeper or more intense coloration. It can be seen that the difference in the L value is especially pronounced in the case of the blue pigment.

EXAMPLE 2

Three suspensions were prepared each containing 60% by weight of a different particulate inorganic material and 0.1% by weight, based on the weight of the particulate inorganic material, of the same sodium polyacrylate dispersing agent as was used in Example 1.

The three particulate inorganic materials were, respectively:

1. Alumina trihydrate 2. Alumina 3. Feldspar To each suspension there was added a suspension of a dark brown pigment which was prepared by mixing together:

sufficient of a suspension of red ferric oxide pigment to provide 2% by weight of the dry pigment, based on the weight of dry particulate inorganic material; sufficient of a suspension of yellow ferric oxide pigment to provide 3% by weight of the dry pigment, based on the weight of dry particulate inorganic material; sufficient of a suspension of ultramarine blue pigment to provide 2% by weight of the dry pigment, based on the weight of dry particulate inorganic material; and sufficient of a suspension of carbon black to provide 0.4% by weight of dry carbon black, based on the weight of dry particulate inorganic material.

The suspension containing the alumina trihydrate was divided into three portions each of which was treated with sufficient of a different latex containing 50% by weight of a non-elastomeric polymer to provide 7% by weight of polymer solids, based on the weight of dry particulate inorganic material.- The polymers con- tained in the three latices were, respectively:- A. poly(vinyl acetate) B. polystyrene C. poly(methyl methacrylate).

The suspension containing the alumina was treated with sufficient of the latex containing 50% by weight of poly(vinyl acetate) to provide 7% by weight of polymer solids, based on the weight of dry alumina.

The suspension containing feldspar was treated with sufficient of the latex containing 50% by weight of the poly(methyl methacrylate) to provide 7% by weight of polymer solids, based on the weight of dry feldspar.

The components of each mixture were thoroughly mixed together, and in each case the mixed suspension was spray dried in a spray drier to form hollow microspheres having diameters in the range from 0.02 to 0. lmm.

An unsaturated polyester bulk moulding compound containing each of the treated fillers prepared as described above was prepared according to the 5 formulation given in Table 3 below. Table 3 JIngredient JParts by weigh I Unsaturated polyester resin Styrene Catalyst Treated filler Zinc stearate mould re ease agent Chopped glass fibre 58.0 23.1 1.5 270.0 6.0 63.0 The unsaturated polyester resin comprised a mixture of maleic anhydride and polyethylene glycol. The catalyst comprised a mixture of 1.25 parts by weight of "TRIGONOX C" and 0.25 parts by weight of "TRIGONOX 21" ("TRIGONOX" is a trade mark).

Each unsaturated polyester bulk moulding compound was formed by injection moulding into discs of diameter 100mm and thickness 3mm. The resistance to scratching shown by each polyester compound was evaluated by measuring scratch depth and scratch whiteness by the methods described below.

Scratch depth was determined by making five parallel scratches on a test disc of diameter 100mm and thickness 3mm by drawing five times across the face of the test disc a scratch head which comprised a lmm diameter steel ball acted upon by a 2kg weight. An area of the marked disc which encompassed part of the five scratches was then scanned by the measuring head of a TALYSTEpTM profilometer, which was linked to a computer which controlled the movement of the test disc beneath the head while recording the deflection of the head from a given reference height. Repeated scanning of the test area provided a three- dimensional graphic representation of the scratched surface. It was possible from this representation to identify the scratches and to measure their depth. An average depth in pm was obtained.

Scratch whiteness, which is a measure of the degree to which individual filler particles have been torn from the polyester composition by the scratching, and thus exposed, was determined by scanning the scratched area of the disc with an optical sensor head which was coupled to an image analyser. The shade of grey of the area beneath the sensor was recorded on a scale which varied from 0 for black to 255 for white and a value was obtained for each of the five scratches and an average value calculated.

The colour of each of the polyester compounds was measured using the disc as a test piece by the system described in Example 1, and the values of L 0, a and b were recorded.

The results obtained are set forth in Table 4 below:

ul r 1-1:3 H. (D U) H. j (Q nj F-4 C 3 P. 0 (D l-i 0 z (D (n rt 91 FA c W 0 5.5 6.7 5.4 6.0 8.3 6.1 4.5 8.5 4.8 7.8 otrOE3owt-fb 0 k-l 1-h (D 0 5 (D rt E3 fD_ et:Y " h- 91 r 0) M f--4 W (0 0 P- (D " 9-3 0) 10 0) Or H- ct h (D rt (D 0 (D ID Ch 11 (D E1 0 C X H. 0 -i bi:v:1 m 11. ct < H. 0) ^ 0) f 0) t:r 0 0 F- s-3 H- rt 0 (D M Inorganic Material Latex r_:Y fl. M m rt 9 (D (D M P. 0 1:Y ct X lumina trihydrate PVAc a rt N4 0.i P- (D:v fl:Y ct tlumina trihydrate PS M (D (D h Fi. 0 tr C$ 0) 0 (D 0) M (D M ct (0 (f c+ Alumina trihydrate PMMA (n (D Alumina PVAc ty m 0 H. h (D Ch li. m Feldspar PMMA rt 0 m b-, 0 (D:4 rt to (D M 0 0 rt 0 91 _ rt (D " ty 0 (D 1<:Y - 0 1< 0 (Q (D C.t 0 (D (D 0 m 11 0 (D Ct 0:Y 1 0 0 tr 0 0 #-f) -i 0)-A- E3 0 03 r. 10 0 bl fl 14.

0 0) 1J. 0) 0 0 (D (D:j a 0 P. 0 (0 Table 4

Scratch Depth Whiteness Colour L - 1 a b 33.03 28.59 32.27 32.28 32.241 11.35 12.22 12.10 11.36 12.07 15.56 18.59 18.39 1.

17.421 Note:PVAc = poly(vinyl acetate) PS = polystyrene PMMA = POly(Methyl methacrylate) 1 bi m 1

Claims

1. A coated particulate inorganic material, the coating on the particles of the inorganic material comprising a combination of a natural or synthetic polymeric material and a first pigment or dye other than carbon black alone, the polymeric material being present in the coating in an amount of from 1% to 10% by weight, based on the weight of dry inorganic material.

2. A coated particulate inorganic material according to claim 1, wherein the inorganic material is a kaolinitic clay, a calcined kaolinitic clay, a calcium carbonate, a silicate of aluminium and/or calcium, bauxite, talc, mica, alumina trihydrate, silica, a carbonate or hydroxide of magnesium, a double carbonate of calcium and magnesium, calcium sulphate, or titanium dioxide.

3. A coated particulate inorganic material according to claim 2, wherein the inorganic material is selected from feldspar and alumina trihydrate.

4. A coated particulate inorganic material according to claim 1, 2 or 3, wherein the inorganic material has a particle size no larger than about 100 Pm.

5. A coated particulate inorganic material according to any of claims I to 4, wherein the specific surface area of the inorganic material, as measured by the BET nitrogen absorption method, is from 1 m2 9- 1 to 300 m2 9- 1.

6. A coated particulate inorganic material according to any of claims 1 to 5, wherein the polymeric material is selected from poly(vinyl acetate), poly(methyl methacrylate) and polystyrene.

7. A coated particulate inorganic material according to any of claims 1 to 6, wherein the inorganic material is selected from feldspar and alumina trihydrate and the polymeric material is selected from poly(methyl methacrylate) and polystyrene.

8. A process for preparing a coated particulate inorganic material which comprises combining, in aqueous suspension, a particulate inorganic material, a natural or synthetic latex composition in an amount such as to provide a coating on the particles of the inorganic material of from 1% to 10% by weight of latex solids, based on the weight of dry inorganic material, and a first pigment or dye other than carbon black alone, and dewatering and drying the resultant mixture to form a particulate filler product.

9. A thermosetting moulding composition containing a coated particulate inorganic material according to any of claims 1 to 7.

10. A coated particulate inorganic material, substantially as hereinbefore described, with reference to the accompanying examples. 20

11. A process for preparing a coated particulate inarganic material, substantially as hereinbefore described, with reference to the accompanying examples.

12. A thermosetting moulding composition, substantially as hereinbefore described, with reference to the accompanying examples.