GB1603300A

GB1603300A - Fillers

Info

Publication number: GB1603300A
Application number: GB22277/77A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1977-05-26
Filing date: 1977-05-26
Publication date: 1981-11-25
Also published as: BE867333A; JPS53147743A; FR2392068A1; AT371134B; NL185726B; NZ187318A; IT1158721B; CA1110504A; DE2823156A1; FR2392068B1; ATA384678A; ZA782861B; NL7805676A; IT7823804A0; ES478665A1; DE2823156C2; NL185726C; AU522211B2; ES470237A1; AU3631578A

Description

(54) FILLERS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITE, Imperial Chemical House, Millbank, London SWIP 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to novel fillers and to a process for producing the fillers, and in particular to fillers which are useful in organic polymer compositions.

It is well known to modify the properties of a wide variety of organic polymers by incorporating into such polymers one or more inorganic materials in finely divided form. These inorganic materials, commonly known as fillers, are generally less expensive than organic polymers and they may serve to increase the bulk of the resultant polymer and so permit a polymer to be used more economically, and they may also serve to enhance at least some of the physical properties of the polymer, for example the hardness, tensile modulus, tensile strength, or resistance to wear of the polymer.

Not only is it desirable to make such fillers as compatible as possible with organic polymers but it is also desirable to be able to make compositions containing high proportions of filler so as to confer the physical and cost advantages of the filler on the resulting composition to the maximum practicable extent. It is especially desirable, when considering possible shortages of hydrocarbon raw materials, to be able to use cheap and readily available fillers as much as possible.

We have now found that it is possible to modify a wide variety of basic fillers in such a way that the modified fillers are more readily incorporated into an organic polymer and in such a way that the resultant polymer composition containing the modified filler has properties superior to those of a polymer composition containing an unmodified filler.

According to the present invention we provide a process for the production of a coated particulate filler which process comprises binding to the surface of a basic particulate filler an acidic group-containing organic polymer, which polymer contains at least one unsaturated group and which has a molecular weight of not greater than 100,000.

Within the scope of the term"polymer"in the expression"acidic groupcontaining organic polymer"we include oligomers, indeed the molecular weight of the polymer may be as low as 200 and the number of the repeat units may be sufficiently low that the polymer (or oligomer) is a liquid.

Within the scope of the term"acidic group"in the expression"acidic groupcontaining organic polymer"we include not only organic polymers containing acidic groups in the form of the free acid but also salts of acidic groups and groups convertible to free acid groups under the process conditions, for example anhydride groups.

The invention also provides a basic particulate filler to the surface of which there is bound an organic polymer which contains at least one unsaturated group and which has a molecular weight of not greater than 100, 000.

These products of our invention contain the unsaturated organic polymer bound to the surface of the particulate filler.

It is believed that the organic polymer reacts with the basic particulate filler and is chemically-bound to the surface of the particulate filler. Indeed the organic polymer is not removed from the filler when the filler is washed in a solvent for the polymer, even in a boiling solvent.

The Fillers of the present invention have some of the properties of the filler particles from which they are derived, and in addition have high compatibility with organic polymers and impart a valuable strengthening of the ultimate association of the fillers with an organic polymer composition in which they are incorporated.

The products also have the valable property of being very much more readily mixed with an organic polymer than does the unmodified filler.

According to a further embodiment of the invention we provide a polymer composition comprising a matrix of an organic polymer having incorporated therein a basic particulate filler to the surface of which there is bound an organic polymer which contains at least one unsaturated group and which has a molecular weight of not greater than 100,000.

Any particulate filler may be used in the process of our invention provided that the filler is basic and is thus capable of binding to the acidic group-containing organic polymer. The filler may be for example an oxide, a hydroxide, a carbonate or a basic carbonate. The filler should of course be insoluble in water. Suitable fillers include oxides, hydroxides, carbonates and basic carbonates of alkaline earth metals and of aluminium and zinc, and especially carbonates. Preferred carbonates are the carbonates of calcium and magnesium, especially calcium carbonate. A suitable hydroxide is magnesium hydroxide. The filler particles may be of natural or synthetic origin. For example, calcium carbonate may be in the form of ground chalk or in the form of a precipitated calcium carbonate, for example calcium carbonate prepared by carbonation of milk of time. Mixtures of basic particulate fillers may be used.

The filler particles for use in our invention may have any form suitable for a filler, and may have a wide variety of particle shapes and sizes. For example, they may be of substantially spherical shape, though they may if desired be of fibrillar or laminar form.

Most commonly the filler particles will have a size in the range 40 Angstrom to 1 mm, though we prefer, on account of the superior reinforcing effect, that the particle size is in the range 40 Angstrom to 1000 Angstrom, for example about 200 Angstrom.

Most conveniently the basic particulate filler is in the form of a f. nely divided free flowing powder, and this is the form in which such fillers are usually available in commerce.

The acidic group-containing organic polymer to which the basic particulate filler is bound in the process of our invention should contain at least one acidic group per molecule. Suitable acidic groups include carboxylic acid groups. The acidic group-containing organic polymer may contain on average more than one Ncidic group per molecule and indeed it is preferred that the polymer does contain more than one such group per molecule as in general the greater is the number of such groups per molecule the more likely is the polymer to be water-soluble or at least readily water-dispersible thus permitting the process of our invention to be effected in an aqueous medium.

Water-solubility or dispersibility of the acidic group-containing polymer may be increased by forming a salt of the acidic group, for example, an alkali metal salt, an ammonium salt, or a trialkyl ammonium salt of a carboxylic acid group. An example of a group convertible to a free acid group under the process conditions is a carboxylic acid anhydride group which may be hydrolyse to a free acid in the process, particularly where the process is effected in an aqueous medium.

The acidic group-containing organic polymer also contains at least one unsaturated group per molecule, e. g. an ethylenically unsaturated group. The group preferably should be capable of participating in a cross-linking reaction. The polymer preferably contains a plurality of unsaturated groups. The unsaturated group capable of participating in cross-linking is preferably part of a polydiene structure, that is a polymer derived from a diene, but may be part of a polymer structure of other derivation if desired. Examples of polydiene structures are polymers or copolymers derived by polymerisation or copolymerisation of one or more dienes, of which the most conveniently available is butadiene, though others may be used if desired, for example isoprene, chloroprene (chlorobutadiene) or mixtures thereof. Examples of other compounds which may be copolymerised with the diene or dienes include a wide range of vinyl monomers, for example styrene, acrylonitrile, and mixtures thereof.

Suitable acidic group-containing organic polymers include polydiene carboxylic acids and polydiene polycarboxylic acids, especially dicarboxylic acid polydienes e. g. polybutadienes dicarboxylic acid. Such polydiene carboxylic acids may be prepared by reacting a polydiene e. g. polybutadiene, polyisoprene, or natural rubber, with mercaptoacetic acid, by oxidising unsaturated groups in a polydiene, or by copolymerising a diene with an unsaturated monomer containing a carboxylic acid group or a group which is capable of being converted into such a group. An acidic group-containing organic polymer may also be prepared by reacting an unsaturated polymer, for example a polydiene, e. g. polybutadiene, with maleic anhydride. The thus formed adduct of a polydiene and maleic anhydride may if desired be converted to a salt before use in the process of the invention, or it may be used as such in the process.

The acidic group-containing organic polymer is preferably one which has a molecular weight in the range 200-50, 000, and especially in the range 1000 to 5000. It is also preferred that the acidic group-containing organic polymer is liquid at the temperature at which the process is effected, e. g. at ambient temperature.

Thus, where the acidic group-containing organic polymer is liquid it may conveniently be bound to the particulate filler without the acid of a solvent or dispersant for the polymer. Such liquid polymers will of course have a relatively low molecular weight, for example a molecular weight in the range 1000 to 5000.

Where the acidic group-containing organic polymer is not a liquid the process of the invention should be effected in the presence of a solvent or dispersant for the polymer. Once again relatively low molecular weight polymers are preferred as such polymers may be more readily dissolved or disperse in a solvent or dispersant, and may be dissolved or dispersed at a much higher concentration, than may high molecular weight polymers.

The ability of the acidic group-containing organic polymer to bind to the particulate filler depends to some extent upon such factors as the molecular weight and the number of acid groups in the polymer. In general the greater the number of acidic groups per molecule the greater will be the ability of the polymer to bind to the filler.

The process of our invention is carried out by forming a mixture of the basic particulate filler and the acidic group-containing organic polymer. The mixture may be heated although heating may not be necessary especially where a solvent or dispersant for the polymer is used and/or the acidic group is particularly reactive.

Thus, the binding may be carried out at a temperature over a wide range, depending upon the materials used. The rate at which the binding of the basic particulate filler and the acidic group-containing organic polymer takes place usually increases as higher temperatures are used, but at high temperatures the risk of the decomposition of the organic polymer tends to increase. Thus the binding is preferably effected at a temperature in the range 0 C to 200 C, though other temperatures may be used if desired. The optimum conditions may be determined by simple trial. The time required also depends upon the materials and the conditions employed, but commonly is in the range I minute to 6 hours. The binding may be carried out most conveniently at ambient pressure, though high or lower pressures may be used if desired.

The binding of the components may be further assisted in several ways. For example, the mixture may be stirred or it may be milled, e. g. in a ball mill. Also a solvent or dispersant for the acidic group-containing organic polymer may be used, and is necessary where the polymer is a solid. The solvent or dispersant may serve several useful functions. Thus, it may reduce the viscosity of the acidic group containing organic polymer, improve the ease and evenness of the spreading of the polymer over the basic filler particles, promote the intimate contact and interaction between the components, assist in controlling the temperature of the mixture, or assist in preventing degradation of the polymer by excluding oxygen from it.

In general, it is preferred to use a solvent in which the polymer is substantially completely dissolved rather than disperse, and the process will be described hereafter with reference to use of such a solvent. The solvent should be chemically inert towards the polymer and the basic filler and it is especially desirable that it should be inert towards the basic filler so that it is not preferentially adsorbed thereon to an extent which appreciably diminishes the affinity of the organic polymer for the surface of the basic filler particles.

Examples of organic solvents include hydrocarbons, for example aliphatic, aromatic, araliphatic or cycloaliphatic hydrocarbons, e. g. toluene, xylene and petroleum fractions; halogenated and especially chlorinated hydrocarbons, for example methylene chloride, chloroform, carbon tetrachloride, 1, 2 dichloroethane, trichloroethylene and tetrachloroethylene ; ethers, for example diethyl ether ; and mixtures thereof. The choice of solvent will be guided by such factors as low flammability, low toxicitv, and boiling point, which may be significant both in use and in the removal of the solvent from the treated particulate filler.

A preferred solvent for the acidic group-containing organic polymer is water on account of its ease of handling, its low cost, and the absence of toxicity problems. Furthermore, the basic particulate filler, especially where it is a small particle size svnthetically prepared filler, e. g. calcium carbonate prepared by carbonation of milk of lime, may be available as an aqueous dispersion, and use of water as a solvent for the acidic group-containing organic polymer obviates the need to separate the filler from the aqueous dispersion.

The nature of the solvent which is used will have a bearing on the number of acidic groups in the acidic group-containing organic polymer and on the molecular weight of the polymer. Thus, as organic polymers are generally readily soluble in organic solvents the desired concentration of the acidic group-containing organic polymer in an organic solvent may be achieved even where the molecular weight of the polymer varies over a wide range up to the limit of 100, 000. Also, as the acidic groups in the polymer may in general have little effect on the solubility in organic solvents the number of such groups per mclecule is generally not critical. On the other hand, where water is used as a solvent the molecular weight and the number of acidic groups per molecule is much more critical. As organic polymers are generally at most only sparingly soluble in water, and as the solubility generally decreases as the molecular weight of the polymer increases, low molecular weight acidic group-containing organic polymers are preferred where water is used as a solvent. A molecular weight in the range 200-50, 000 is preferred. Especially preferred is a molecular weight of 100W5000. As the water-solubility of the polymer will tend to increase with an increase in the number of acidic groups per molecule a plurality of acidic groups is preferred where water is used as a solvent.

For a polymer of given molecular weight the number of acidic groups needed to achieve the desired water solubility may be determined experimentally. The precise number will depend on the particular polymer and the molecular weight chosen, and on the concentration of acidic group-containing organic polymer which is desired on the aqueous solution. Acidic groups in the form of salts may also serve to improve the water solubility of the polymer.

The proportion of solvent should be sufficient to dissolve the acidic groupcontaining organic polymer, as incomplete solution may result in undesirable local concentration of unbound polymer, and be sufficient to produce a solution which can readily flow and mix with the basic filler particles. Suitable proportions can be determined by simple trial and are not necessarilv critical.

It is also important that the amount of solution containing the acidic groupcontaining organic polymer which is used should be sufficient to cover the surface of the basic filler particles as thoroughly as possible if the best products, that is the most useful fillers are to result. Conveniently an excess of solution sufficient to produce a thoroughly wetted mixture may be used. The coated particulate filler may be separated from the solution and dried.

The binding may be carried out in the presence of protecting agents, e. g. antioxidants, and/or in an inert atmosphere, e. g. nitrogen, argon or solvent vapour, if it is desired to guard against deterioration of the polymer during any heating that may be necessary.

The proportion of the acidic group-containing organic polymer and the basic filler particles may be varied within wide limits according to the particular materials employed and the properties desired in the product and in the polymer composition in which the coated filler particles may ultimately be incorporated.

Commonly, our coated filler particles contain in the range 0.2% to 40 by weight of the organic polymer and correspondingly 99. 8 to 60 O by weight of the particulate filler, though products having proportions outside this range may be made if desired. Preferred proportions are in the range 1 , to 20 by weight of the organic polymer bound to the basic particulate filler, more preferably 1 i to 10s by weight.

When the acidic group-containing organic polymer has been applied to and bound to the surface of the basic filler particles, the resulting product may be in a form in which it can be used directly as a filler or it may need to be treated mechanically, e. g. by grinding, to break up agglomerates and reduce the filler to a suitably small particle size. This is not essential in all cases, however, as any necessary breakdown of the agglomerates may take place satisfactorily while the filler is being incorporated into a polymer composition, for example by milling.

As the organic polymer which is bound to the surface of the particulate filler contains at least one unsaturated group the filler, when incorporated in a matrix organic polymer, may be caused to react with the latter polymer through the unsaturated group, especially where the latter organic polymer itself contains such a group, e. g. where the matrix organic polymer is a curable, that is a vulcanisable, rubber. As a result of this reaction the filler may be caused to be bound to the matrix organic polymer in which it is incorporated with the result that the resultant polymer composition will have properties superior to those of a polymer composition containing a filler which has been bound to an acidic group-containing organic polymer which does not contain unsaturation.

Where the matrix organic polymer with which the filler is mixed and into which it is incorporated does not itself contain unsaturation reaction of this organic polymer with the unsaturated organic polymer bound to the surface of the filler particles may be caused to take place by generating free radials during the mixing operation, for example by shearing the mixture or by including a free radial generator in the mixture.

The matrix organic polymer into which the products of our invention may be incorporated may be in any convenient form and incorporation may be carried out by conventional mixing means. This polymer may be a thermosetting resin, e. g. a polyester resin, but is preferably thermoplastic and may be any homopolymer or copolymer having physical properties permitting incorporation of our new products as filles. It is more preferably one containing unsaturation and which is thus curable (vulcanisable).

The polymer may be a massive or particulate plastic or rubbery material, into which our aller may be incorporated by mechanical action, for example milling.

Chemically, the polymer may be of widely varying constitution and may be for example any natural or synthetic rubber or resin known in the art to be usable in conjunction with a filler. The products of our invention are especially useful as fillers in natural or synthetic rubbers, for example butadiene-based rubbers, e. g. butadiene-styrene and butadiene-acrylonitrile rubbers, polybutadiene, polyisoprene, and natural rubber.

The polymer composition may also be produced by mixing a matrix organic polymer with a basic particulate filler and with an acidic group-containing organic polymer which also contains at least one unsaturated group and which has a molecular weight of not greater than 100,000.

It is believed that during the mixing process the basic filler particles bind to the acidic group-containing organic polymer. It is not necessary for all of the acidic group-containing polymer to bind to the basic particulate filler during the mixing operation. Indeed binding may not take place as readily as in the case where basic particulate filler is bound to the acidic group-containing organic polymer in the absence of a matrix polymer, for example when mixed in the presence of a solvent for the acidic group-containing organic polymer, and it may be desirable to use in this process an amount of acidic group-containing organic polymer by weight of basic particulate filler which is greater than would normally be used.

The optimum proportion of filer to the surface of which an organic polymer is bound to matrix organic polymer in which it is incorporated will be determined by the use to which the filled polymer is to be put. In general 5 o to 300 o of fitter by weight of matrix organic polymer into which it is incorporated will suffice, preferably 10% to 200% boy weight.

The polymer composition may also contain conventional additives, for example antioxidants, plasticisers, vulcanisation accelerators, pigments, antiozonants, and fillers other than those of the present invention.

The invention is illustrated by the following Examples.

EXAMPLES I and 2 Carbon dioxide (300 litres/hour) and air (450 litres/hour) were passed through 7 litres of milk of lime (containing 38 g Ca (OH) per litre) until the pH of the suspension had reached 7.0. The suspension was then aged by stopping the carbon dioxide flow and maintaining the air flow and heating the suspension until a temperature of 85 C was reached after 15 minutes. The temperature of the suspension was then maintained at 85 C and carbon dioxide (30 litres/hour) and air (45 litres/hour) were passed through the suspension until the pH of the resultant calcium carbonate suspension had reached 8.0.

A polybutadiene-maleic anhydride adduct was prepared by reacting 100 parts by weight of polybutadiene (Mn 1300) with 25 parts by weight of maleic anhydride under an atmosphere of nitrogen and in the presence of a small amount of xylene and antioxidant at a temperature of 190 C until little or no free maleic anhydride remained. The triethyl ammonium salt of the methyl half ester of the resultant polybutadiene-maleic anhydride adduct was then prepared by reacting the adduct with methanol and triethylamine at a temperature of 80 C for I hour.

Finally, a suspension of calcium carbonate (particle size approximately 70 millimicrons) prepared as described above and containing 100 parts by weight of calcium carbonate was mixed with 3 parts by weight of the above described triethyl ammonium salt (in the form of an aqueous solution containing 60 g of the salt per litre) at a temperature of 85 C for 15 minutes and the thus treated calcium carbonate suspension was filtered and the separated product was dried by heating in an oven at 110 C. The product was then lightly milled. The product is referred to hereafter as Filler A.

By way of comparison a calcium carbonate suspension prepared as described above, containing 100 parts by weight of calcium carbonate, was reacted with 2.5 parts by weight of ammonium stearate (in the form of an aqueous solution containing 75 g of ammonium stearate per litre) at a temperature of 85 C for 15 minutes and the thus treated calcium carbonate was separated, dried and lightly milled following the above-described procedure. The treated calcium carbonate is referred to hereafter as Filler B.

In order to compare the reinforcing effects of Filler A and Filler B the fillers were separately compounded on a twin-roll mill with an uncured rubber formulation containing either styrene-butadiene rubber (SBR 1502) (Example I and comparison example respectively) or natural rubber (SMR5) (Example 2 and comparison example respectively), the compounded compositions were cured by heating at a temperature of 153 C, and the properties of the cured rubber compositions were determined.

Details of the components of the rubber compositions in parts by weight, the cure times, and the properties of the cured rubber compositions are given in Table I.

TABLE I Example Comparison Example Comparison Example 2 Example Styrene-butadiene rubber (SBR 1502) 200 200-- Natural rubber (SMR 5)--200 200 Zinc oxide 10 10 10 10 Stearicacid2222 Vulcafor F ("Vulcafor"is a Registered Trade Mark) 4 4 4 4 Sulphur 5 5 5 5 Filler A 200-200 Filler B-200-200 Cure time (minutes) 8.5 10 7 7 Tensile strength (Kg/sq cm) 56 43 161 147 Elongation at bteak % 419 505 531 538 300% Tensile Modulus (Kg/sq cm) 43 23 80 64 Tear Strength (angle) (Kg F/mm) 33 23 68 55 Resilience 52 42 67 73 Heat Build up vT C (Goodrich, ASTM D623-67) 34 40- EXAMPLE 3 A suspension of calcium carbonate prepared by carbonation of milk of lime following the procedure of Example I was filtered, the resultant filter cake was suspended in a mixture of acetone and water and filtered again, the filter cake which was produced was allowed to dry by standing in air at room temperature and thereafter by heating at tOO C, and the calcium carbonate was finally lightly milled (particle size 70 millimicrons).

250 parts by weight of the particulate calcium carbonate was then mixed with 12. 5 parts by weight of a polybutadiene dicarboxylic acid (Mn 4000) and 730 parts by weight of trichloroethylene and the mixture was ball-milled at room temperature for 2 hours. The mixture was then filtered and the separated filler cake was dried in air at room temperature followed by heating at 40 C and was finally lightly milled to produce a particulate calcium carbonate having bound thereto 2. 5'/,/, by weight of polybutadiene. The calcium carbonate is referred hereafter as Filler C.

By way of comparison the above described procedure was repeated in two separate experiments except that the polybutadiene dicarboxylic acid was replace in one experiment by stearic acid and in the other experiment it was omitted.

The calcium carbonate fillers produced are hereafter referred to as fillers D and E respectively.

The reinforcing effects of the Fillers C, D and E in styrene-butadiene rubber were determined following the procedure described in Examples I and 2. Details of the components of the rubber compositions in parts by weight, the cure times, and the properties of the cured rubber compositions are given in Table 2.

TABLE 2 Example Comparison Comparison 3 Example Example Styrene-butadiene rubber (SBR) 1502 100 100 100 Zinc oxide 5 5 5 Stearic acid I-I Vulcafor F 2 2 2 Sulphur 2.5 2.5 2.5 Filler C 100-- Filler D-100- Filler E--100 Cure time (minutes) 8 7 7 Tensile Strength (Kg/sq cm) 53 46 45 Elongation at break % 500 556 535 300% Tensile Modulus (Kg/sq cm) 37 20 21 EXAMPLE 4 Particulate calcium carbonate having a particle size of 70 millimicrons was prepared following the procedure described in Example 3 (subsequent reaction with polybutadiene dicarboxylic acid was not carried out) and the calcium carbonate thus produced was milled on a twin roll mill with styrene-butadiene rubber, zinc oxide, stearic acid, Vulcafor F, and polybutadiene dicarboxylic acid (Mn 4000) as used in Example 3. The compounded composition was then cured at t53 C and the properties of the cured rubber composition were determined.

By way of comparison the above compounding procedure was repeated except that the polybutadiene dicarboxylic acid was replaced by polybutadiene (Mn 4000).

Details of theomponents of the rubber compositions in parts by weight, the cure times, and the properties of the cured rubber compositions are given in Table 3.

TABLE 3 Example Comparison 4 Example Styrene-butadiene rubber (SB R 1502) 100 100 Zinc oxide 5 5 Stearic I I Vulcafor F 2 2 Sulphur 2.5 2.5 Calcium carbonate 100 100 Polybutadiene dicarboxylic acid 6- Polybutadiene-6 Cure time (minutes) 11 8 Tensile Strength (Kg/sq cm) 53 42 Elongation at break XÓ 492 578 300% Tensile Modulus (Kg/sq cm) 38 19 EXAMPLE 5 Particulate calcium carbonate having a particle size of 70 millimicrons was prepared following the procedure described in Example 3 (subsequent reaction with polybutadiene dicarboxylic acid was not carried out) and the calcium carbonate thus produced was milled on a twin roll mil with styrene-butadiene rubber, zinc oxide, stearic acid, Vulcafor F and the polybutadiene mateic anhydride adduct prepared as described in Example 1.

The compounded composition was then cured at 153 C and the properties of the cured rubber composition were determined.

By way of comparison, the above procedure was repeated except that the polybutadiene-maleic anhydride adduct was omitted.

Details of the components of the rubber compositions in parts by weight, cure times, and the properties of the cured rubber compositions are given in Table 4.

TABLE 4 Example Comparison 5 Example Styrene-butadiene rubber (SB R 1502) 100 100 Zinc oxide 5 5 Stearic Acid I I Vulcafor F 2 2 Sulphur 2.5 2.5 Calcium carbonate 100 100 Polybutadiene-maleic anhydride adduct 3- Cure time (minutes) 9 10 Tensile Strength (Kg/sq cm) 82 57 Elongation at break % 606 576 300 Tensile Modulus (Kg/sq cm) 36 22 EXAMPLE 6 To the aqueous solution of the triethylammonium salt prepared by reacting the polybutadiene-maleic anhydride with methanol and triethylamine as described in Example t there was added dilute hydrochloric acid. The resultant precipitated free carboxylic acid was extracted with diethyl ether, the diethyl ether solution was dried over magnesium sulphate, and the solution was distilled and the free carboxylic acid collecte. The acid was then milled into Styrene-butadiene rubber together with zinc oxide, stearic acid, Vulcafor F and calcium carbonate as used in Example 5.

By way of comparison, the above procedure was repeated except that the carboxylated polybutadiene was omitted.

Details of the components of the rubber compositions in parts by weight, cure times, and properties of the cured rubber compositions are given in Table 5.

TABLE 5 Example Comparison 6 Example Styrene-butadiene rubber SB R (1502) 100 100 Zinc Oxide 5 5 Stearic 1 I Vulcafor F 2 2 Sulphur 2.5 2.5 Calcium carbonate 100 100 Carboxylated polybutadiene 3- Cure time (minutes) 10. 5 10 Tensile Strength (Kg/sq cm) 63 57 Elongation at break"/,,, 544 576 300% Tensile Modulus 33 22 EXAMPLES 7 to 11 A polybutadiene-maleic anhydride adduct prepared following the procedure described in Example 1, was reacted with isobutanof at a temperature of 80 C for I hour, and then 4% by weight aqueous ammonium hydroxide solution was added to produce an ammonium salt of an isobutyl half ester of the polybutadiene-maleic anhydride adduct (Mn of polybutadiene 3400).

In five separate experiment samples of calcium carbonate coated with respectively 2,3,4,6 and 8% boy weight of the above ammonium salt were produced following the procedure described in Example I except that the above ammonium salt was used in place of the triethyl ammonium salt of the methyl half ester of the polybutadiene-maleic anhydride adduct used in Example 1. The samples of coated calcium carbonate will be referred to as Fillers F, G, H, I and J respectively.

The samples of coated calcium carbonate were then separately compounded with styrene-butadiene rubber (SBR 1502) and the compounded compositions were cured at a temperature of 153 C following the procedure described in Example l.

Details of the components of the rubber compositions in parts by weight, the cure times, and the properties of the cured rubber compositions are given in Table 6.

For comparison the properties of a rubber containing a stearate (~2 2.7%) coated precipitated calcium carbonate (Filler K) are also given (prepared following the procedure of Example 1).

TABLE 6 Example Example Example Example Example 7 8 9 10 11 Comparison Styrene-butadiene rubber (SBR 1502)) 200 200 200 200 200 200 zinc Oxide 10 10 10 10 10 10 Stearic acid 2 2 2 2 2 2 Vulcafor F 4 4 4 4 4 4 Sulphur 5 5 5 5 5 5 Filler F 200 - - - - Filler G - 200 - - - Filler H - - 200 - - Filler J - - - 200 - Filler I - - - - 200 Filler K - - - - - 200 Cure time (minutes) 13 13.5 13.5 14 13 16 Tensile Strength (Kg/sq cm) 64 66 69 77 84 46 Elongation at break% 478 440 439 472 550 601 300% Tensile Modulus (Kg/sq cm) 40 46 50 52 51 16 Tear Strength (angle) (Kg F/mm) 2.9 3.0 3.5 3.5 3.6 1.7 Resilience% 46 46 43 38 39 37 Hardness IRHD 75 78 75 80 80 73 EXAMPLE 12 80 g of fine particle size magnesium hydroxide was mixed with 450 ml of water and the mixture was stirred and heated to 80 C. Stirring was continued and 90 ml of a solution in 750 ml of water of 40 g of a triethylammonium salt of a methyl half ester of a polybutadiene-maleic anhydride'adduct was added (as prepared in Example I except that the polybutadiene had an Mn of 3400).

Stirring was continued for 15 minutes at 80 C, the mixture was filtered, and the filtrate was dried by heating at 110 to 120 C for 10 hours. The resultant magnesium hydroxide contained approximately 5% by weight of coating.

'Following the procedure of Example 1 75 parts by weight of the coated magnesium hydroxide was compounded with 100 parts by weight of SBR 1502, 1 part by weight of stearic acid, 5 parts by weight of zinc oxide, 2 parts by weight of Vulcafor F, and 2.5 parts by weight of sulphur, and the compounded composition was cured following the procedure of Example 1. The properties of the cured composition are given in Table 7 together with those of a composition in which the coated magnesium hydroxide was replace by uncoated magnesium hydroxide (for the purposes of comparison).

TABLE 7 Coated Magnesium magnesium hydroxide hydroxide (comparison) Tensile Strength (Kg/sq cm) 95 75 Elongation at break % 626 655 100% tensile modulus (Kg/sq cm) 24 19 200% tensile modulus (Kg/sq cm) 34 23 300% tensile modulus (Kg/sq cm) 43 27 Tear Strength (angle (KgF/mm) 3.3 2.25 Hardness B. S. 73 ~ EXAMPLES 13 to 15 100 parts by weight of a natural calcium carbonate whiting have a particle size predominantly less than 10 microns was mixed for 10 minutes in a Henschel mixer with 3 parts by weight of a polybutadiene-maleic anhydride adduct as prepared in Example 1 (except that the polybutadiene had an Mn of 3400) and 100 parts by weight of the resultant coated calcium carbonate were compounded with 100 parts by weight of SBR 1502, I part by weight of stearic acid, 5 parts by weight of zinc oxide, 2 parts by weight of Vulcaor F and 2.5 parts by weight of sulphur. The compounded composition was cured following the procedure of Example I (Example 13).

The above procedure of Example 13 was repeated except that the polybutadiene-maleic anhydride adduct was replace by a methyl half ester of the same adduct (Example 14).

The compounding procedure of the above described Example 13 was repeated except that the coated calcium carbonate was replace by 97 parts by weight of the natural calcium carbonate whiting and 3 parts by weight of the polybutadiene maleic anhydride adduct used in Example 13. (Example 15).

The properties of the cured compositions are given in Table 8 together with, and for comparison, those of a composition containing the calcium carbonate but no polybutadiene-maleic anhydride adduct or methyl half ester.

TABLE 8 Example Example Example 13 14 15 Comparison Tensile Strength (Kg/sq cm) 50 34 45.5 28 Elongation at break % 343 324 369 493 100% tensile modulus (Kg/sq cm) 23 20 23 14. 5 200% tensile modulus (Kg/sq cm) 37.6 28 34 16 300% tensile modulus (Kg/sq cm) 46 33 41 18. 5 Tear Strength (angle) (KgF/mm) 2.93 2.66 2.66 1. 84

Claims

WHAT WE CLAIM IS : 1. A process for the production of a coated particulate filler which comprises binding to the surface of a basic particulate filler an acidic group-containing organic polymer, which polymer contains at least one unsaturated group and which has a molecular weight of not greater than 100,000.
2. A process as claimed in claim I in which the filler is a hydroxide or carbonate of an alkaline earth metal.
3. A process as claimed in claim 2 in which the filler is magnesium hydroxide.
4. A process as claimed in claim 2 in which the filler is calcium carbonate.
5. A process as claimed in any one of claims I to 4 in which the filler has a particle size in the range 40 Angstrom to I mm.
6. A process as claimed in claim 5 in which the filler has a particle size in the range 40 to 1000 Angstrom.
7. A process as claimed in any one of claims 1 to 6 in which the acidic group is a carboxylic acid group.
8. A process as claimed in any one of claims I to 6 in which the acidic group is an anhydride group.
9. A process as claimed in any one of claims I to 6 in which the acidic group is an alkali metal, ammonium, or trialkyl ammonium salt of a carboxylic acid group.
10. A process as claimed in any one of claims I to 9 in which the unsaturated group is an ethylenically unsaturated group.
11. A process as claimed in any one of claims 1 to 10 in which the acidic group containing organic polymer is a polydiene.
12. A process as claimed in claim I I in which the polydiene is polybutadiene.
13. A process as claimed in claim 11 or claim 12 in which the acidic groupcontaining organic polymer is prepared by reacting a polydiene with maleic anhydride.
14. A process as claimed in any one of claims I to 13 in which the molecular weight of the acidic group-containing organic polymer is in the range 200 to 50,000.
15. A process as claimed in claim 14 in which the molecular weight of the acidic group-containing organic polymer is in the range 1000 to 5000.
16. A process as claimed in any one of claims I to 15 in which the acidic groupcontaining organic polymer is liquid at the temperature at which the process is effected.
17. A process as claimed in any one of claims I to 16 in which the process is effected in the presence of a solvent or dispersant for the acidic group-containing organic polymer.
18. A process as claimed in claim 17 in which the solvent or dispersant is water.
19. A process as claimed in any one of claims I to 18, which is effected at a temperature in the range 0 C to 200 C.
20. A process as claimed in any one of claims t to 19 in which the basic particulate filler and acidic group-containing organic polymer are present in proportions which result in the production of a basic particulate filler having an organic polymer bound to the surface thereof in a proportion of 0.2, ó to 40", boy weight of organic polymer to 99.8% to 60% by weight of filler.
21. A process as claimed in claim I substantially as hereinbefore described and as described in any one of Examples t to 6.
22. A process as claimed in claim I substantially as hereinbefore described and as described in any one of Examples 7 to 15.
23. A basic particulate filler having an organic polymer bound to the surface thereof, which polymer contains at least one unsaturated group, produced by a process as claimed in any one of claims I to 22.
24. A basic particulate filler to the surface of which there is bound an organic polymer which contains at least one unsaturated group and which has a molecular weight of not greater than 100,000.
25. A basic particulate filler as claimed in claim 24 in which the filler is a hydroxide or carbonate of an alkaline earth metal.
26. A basic particulate filler as claimed in claim 25 in which the filler is magnesium hydroxide.
27. A basic particulate filler as claimed in claim 25 in which the filler is calcium carbonate.
28. A basic particulate filler as claimed in any one of claims 24 to 27 in which the filler has a particle size in the range 40 Angstrom to I mm.
29. A basic particulate filler as claimed in any one of claims 24 to 28 in which the unsaturated group is an ethylenically unsaturated group.
30. A basic particulate filler as claimed in any one of claims 24 to 29 in which the organic polymer is a polydiene.
31. A basic particulate filler as claimed in claim 30 in which the polydiene is polybutadiene.
32. A basic particulate filler as claimed in any one of claims 24 to 31 in which the molecular weight of the organic polymer is in the range 1000 to 5000.
33. A basic particulate filler as claimed in any one of claims 24 to 32 comprising 0.2 to 40 ; o by weight of organic polymer and 99.8% to 60% boy weight of particulate filler.
34. A basic particulate filler as claimed in claim 24 substantially as hereinbefore described and as described in any one of Examples I to 6.
35. A basic particulate filler as claimed in claim 24 substantially as hereinbefore described and as described in any one of Examples 7 to 15.
36. A polymer composition comprising a matrix of an organic polymer having incorporated therein a basic particulate filler to the surface of which there is bound an organic polymer which contains at least one unsaturated group and which has a molecular weight of not greater than 100, 000.
37. A polymer composition as claimed in claim 36 which comprises 5 Ó to 300% of filler to the surface of which there is bound an organic polymer by weight of the matrix organic polymer.
38. A polymer composition as claimed in claim 37 which comprises 10 Ó to 200% of filler to the surface of which there is bound an organic polymer.
39. A polymer composition as claimed in any one of claims 36 to 38 having incorporated therein a basic particulate filler as claimed in any one of claims 25 to 35.
40. A polymer composition as claimed in any one of claims 36 to 39 in which the matrix organic polymer is a vulcanisable rubber.
41. A polymer composition as claimed in any one of claims 36 to 39 in which the matrix organic polymer is a vulcanised rubber and in which the polymer bound to the surface of the particulate filler is reacted with the vulcanised rubber.
42. A polymer composition as claimed in claim 40 or claim 41 in which the rubber is styrene-butadiene rubber or natural rubber.
43. A polymer composition as claimed in claim 36 substantially as hereinbefore described and as described in any one of Examples I to 6.
44. A polymer composition as claimed in claim 36 substantially as hereinbefore described and as described in any one of Examples 7 to 15.
45. A process for the production of a polymer composition as claimed in any one of claims 36 to 42 which comprises mixing a matrix organic polymer with a basic particulate filler to the surface of which there is bound an organic polymer which contains at least one unsaturated group and which has a molecular weight of not greater than 100, 000.
46. A process for the production of a polymer composition as claimed in any one of claims 36 to 42 which comprises mixing a matrix organic polymer, a basic particulate filler, and an acidic group-containing organic polymer which contains at least one unsaturated group and which has a molecular weight of not greater than 100, 000.
47. A process as claimed in claim 45 substantially as hereinbefore described and as described in any one of Examples I to 3.
48. A process as claimed in claim 45 substantially as hereinbefore described and as described in any one of Examples 7 to 15.
49. A process as claimed in claim 46 substantially as hereinbefore described and as described in any one of Examples 4 to 6.