GB2099000A - Inorganic filler-containing vinyl monomer compositions and process for the production therefrom of polymer particles - Google Patents

Abstract

A polymerizable composition contains by weight 20 to 90% of a vinyl monomer (e.g. styrene), 80 to 10% of an inorganic filler (e.g. a metal hydroxide), and, by weight of the filler, 0.1 to 5% of a silane coupling agent and 0.01 to 2% of an accelerator for the silane, e.g. dibutyltin dilaurate. Optionally, the composition contains 5 to 50% by weight of the monomer of a vinyl polymer, e.g. polystyrene, which is soluble, at least at polymerization temperature, in the vinyl monomer. To produce polymer particles, an initiator is added and the composition is subjected (i) to preliminary partial bulk polymerization until the 20 DEG C viscosity is 100 to 10,000 cp and then (ii) to either aqueous suspension or further bulk polymerization to complete the vinyl monomer polymerization.

Description

SPECIFICATION Inorganic filler-containing vinyl monomer compositions and process for the production therefrom of polymer particles The present invention relates to inorganic filler-containing polymerizable compositions and a process for the production of polymer particles using the compositions. More particularly, it is concerned with inorganic filler-containing polymerizable compositions having a low viscosity (e.g., 100--10,000 cps at 200 C) which are prepared by uniformly dispersing inorganic fillers in radicalpolymerizable vinyl monomers and a process for the production of polymer particles having a narrow grain size distribution (e.g., 0.1-100 a) by the use of such compositions.

It is known that the stiffness, dimensional stability, electrical properties, ease of incineration, etc., of polymers can be improved by the addition of large amounts of inorganic fillers to the polymers. The addition of such inorganic fillers is generally performed by mixing the inorganic fillers with molten polymers by the use of rolls, kneaders, extruders, etc.

In accordance with such methods, however, it is difficult to prepare a uniform mixture as the amount of the inorganic filler increases. If kneading is performed for a long period of time in order to improve the dispersion of the inorganic filler in the polymer, polymer deterioration occurs.

In order to remove the above described defect, there has been proposed a method in which inorganic fillers are added to radical-polymerizable vinyl monomer, such as styrene, and then the monomer is polymerized to prepare a polymer composition in which the inorganic fillers are uniformly dispersed. This method, however, suffers from various defects. For example, in the case that the inorganic filler content is more than 10% by weight, it is difficult to prepare a uniform dispersion for the reason that the inorganic filler tends to precipitate, and, in general, the composition obtained is greasy or clay-like. Further, it is substantially impossible to transfer the composition to a polymerization reactor and to polymerize the composition.

Styrene-based polymer particles, for example, are produced by suspension polymerizing styrene monomer in the presence of polymerization initiators and suspension stabilizers. The grain size distribution of polymer particles prepared by the suspension polymerization is broad even if the degree of stirring, polymerization temperature and time, and the method of adding styrene monomer and polymerization initiators are appropriately chosen. Polymer particles having such a broad grain size distributions have the following disadvantages: (1) When the polymer particles are extruded, polymer particles having a small grain size quite often separate from polymer particles having a large grain size in a feed hopper, a feed section of an extruder or a screw section of an extruder. This results in an undesired substantial variation in the quantity of molten extruded polymer per hour.

(2) When expandable beads which are prepared by impregnating a blowing agent into polymer particles during or after the suspension polymerization are expanded in a mold, differences in the degree of expansion among the polymer beads leads to the resulting molded articles having uneven weight, or cause the polymer beads to show uneven cooling periods during molding.

In general, expandable beads having a small grain size are poor in expansion force but can be heated and cooled in a short period of time; however, as grain size increases, the expansion force increases and the time required for heating and cooling increases.

The optimum grain size of expandable beads influences the cooling time, the degree of expansion, the thickness of the molded article and so on. Molded articles are broadly divided into general purpose articles having a thickness of 5 to 50 mm and block articles having a thickness of 100 mm or more. In the production of block articles, it is necessary to use expandable beads having a greater grain size. It has been the practice, however, to sieve expandable beads into several grades having different grain sizes, even in the above two major application fields, according to the purpose for which the ultimate molded article is used.

Expandable beads prepared by suspension polymerizing styrene monomer containing an inorganic filler have a broader grain size distribution than such beads containing no inorganic fillers, which is due to the aggregation of fillers in the styrene.

One object of the invention is to solve the problems encountered in dispersing inorganic fillers in vinyl monomers in a proportion of 10 to 80% by weight based on the weight of vinyl monomer and inorganic filler.

Another object of the invention is to provide a process for producing polymer particles having a narrow grain size distribution in a stable manner in order to solve the problems due to a broad grain size distribution during molding.

As a result of extensive investigations to solve the problems encountered in compounding 10% or more of one or more inorganic fillers into one or more vinyl monomers, it has been found that a silane coupling treatment of the inorganic filler(s) in a vinyl monomer (containing substantially no water) makes dispersion of the inorganic filler(s) in vinyl monomer(s) easy, and, at the same time, lowers the viscosity of the resulting dispersion.

Furthermore, it has been found that the introduction of one or more vinyl polymers soluble in the one or more vinyl monomers further increases the dispersion stability of inorganic fillers in the resulting mixture.

The present invention, therefore, provides: (1) An inorganic filler-containing polymerizable composition comprising 90 to 20% by weight of one or more vinyl monomers and 10 to 80% by weight of one or more inorganic fillers dispersed in the vinyl monomer(s), which further contains one or more silane coupling agents and one or more silane coupling accelerators in an amount of 0.1 to 5% by weight and 0.01 to 2% by weight, respectively, based on the weight of the inorganic filler(s). Hereafter, for brevity, the singular is generally used to refer to such "one or more" components.

(2) A process for producing polymer particles containing 10 to 80% by weight of an inorganic filler, comprising mixing the aforesaid inorganic filler, silane coupling agent, and silane coupling accelerator in vinyl monomer to prepare a mixed solution, subjected the mixed solution to a preliminary bulk polymerization in the presence of a polymerization initiator until 5 to 45% by weight of the vinyl monomer is polymerized to adjust the viscosity (at 200C) of the reaction system to 100 to 10,000 centiposes, and introducing the preliminary bulk polymerization solution either (a) into water containing a suspension stabilizer, followed by heating the mixture to perform suspension polymerization of the unreacted vinyl monomer; or (b) into a bulk polymerization reactor, followed by completing the bulk polymerization of the unreacted vinyl monomer in the bulk polymerization reactor.

(3) A polymerizable composition as in (1) above, which contains a vinyl polymer soluble (at least on heating) in the vinyl monomer in an amount of 5 to 50% by weight based on the weight of the vinyl monomer.

(4) A process for producing said polymer particles as in (3) comprising mixing the inorganic filler, silane coupling agent and silane coupling accelerator in a vinyl monomer to prepare a mixed solution, adding a vinyl polymer which is soluble in the vinyl monomer (at least on heating) to the mixed solution to prepare a solution having a viscosity at 200C of 10 to 10,000 centipoises, introducing the solution into water containing a suspension stabilizer, and then heating the resulting solution to perform bulk polymerization of the vinyl monomer.

The term "vinyl monomer" is used herein to refer to vinyl monomers which are liquid at ordinary temperature and can be radical-polymerized. Suitable examples of the vinyl monomers are a compound having a CH=CH2 group. Specific examples of such vinyl monomers include styrene-based monomers, such as styrene, a-methylstyrene, and chiorostyrene, esters of acrylic acid and an alcohol containing 1 to 8 carbon atoms, such as methyl acrylate and n-butyl acrylate, methyl methacrylate, acrylonitrile, vinyl acetate, maleic anhydride or vinyl chloride. These monomers can be used alone or in combination with each other.

The term "inorganic filler" is used herein to refer to fine inorganic compound powders having an average grain size of 0.1 to 100 y. Suitable examples of such inorganic compounds include metal oxides, such as silica, alumina, iron oxide, zinc oxide, and magnesium oxide, metal hydroxides, such as aluminum hydroxide, magnesium hydroxide, and iron hydroxide, metals, such as aluminum and iron, asbestos, glass, calcium carbonate, magnesium carbonate, sodium sulfate, kieselguhr, and glass fibers.

Of these inorganic compounds, metal hydroxides are particularly preferred since they greatly lower the viscosity of the resulting dispersion. They can be used alone or in combination with each other.

Any silane coupling agent which is generally used can be used in the invention. Examples thereof are compounds represented by the general formula: RnSiX3~n (I) (wherein R indicates a monovalent hydrocarbon or halogenated hydrocarbon group having preferably 1 to 12 carbon atoms, such as an alkyl group, e.g., a methyl, ethyl, propyl, octyl or decyl group; an alkenyl group; a vinyl group; an aryl group, e.g., a phenyl, benzyl, or tolyl group; and a haloalkyl group, e.g., a chioropropyl, 3,3,3-trifluoropropane or bromophenyl group; X indicates a hydrolyzable group, such as a formyioxy group, an acetoxy group, a propioxy group, an oxime group or an alkoxy group having preferably 1 to 6 carbon atoms, e.g., a methoxy, ethoxy or propoxy group; and n is 0, 1 or 2); and alkoxy group-containing silane compounds represented by the general formulae (II) to (V):

wherein P1 is H or CH3, R2 is a straight or branched alkyl group containing 4 or less carbon atoms, R3 is OR2 where R2 is as above defined, a straight or branched alkyl group containing 4 or less carbon atoms, or phenyl, and A is a straight or branched alkylene group containing 6 or less carbon atoms.

Suitable examples are ("List A") silane compounds containing no double bond, such as tetra methoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyitributoxysilane, ethyltriethoxysilane, ethyltributoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diphenyldimethoxysilane, phenyltrimethoxysilane, diphenyldiethoxysilane, trimethylmethoxysilane, trimethylethoxysiiane, trimethylpropoxysilane, trimethylbutoxysilane, and tripropoxymonochloropropylsilane; vinyl silane compounds, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, methacryloxymethyltripropoxysilane, methacryloxyethyltrimethoxysilane, methacryloxyethyltriethoxysilane, methacryloxyethyltripropoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropyltripropoxysilane, acryloxymethyltrimethoxysilane, acryloxymethyltriethoxysilane, acryloxymethyltripropoxysilane, acryloxyethyltrimethoxysilane, acryloxyethyltriethoxysilane, acryloxyethyltripropoxysilane, acryloxypropyltrimethoxysila ne, acryloxypropyltri methoxysilane, acryloxypropyltriethoxysilane, and acryloxypropyltripropoxysilane; N-aminomethylaminomethyltrimethoxysilane; y-glycidopropylmethyldipropoxysilane; and p-glycidoxyethylethyidiethoxysilane.

These silane compounds can be used alone or in combination with each other.

Silane coupling accelerators which can be used in the invention include carboxylic acid salts, such as dibutyltindilaurate, dioctyltindilaurate, stannous acetate, stannous octenate, lead naphthenate, zinc octenate, iron 2-ethylhexanate and cobalt naphthenate; titanic acid esters, such as tetrabutyl titanate, tetranonyl titanate and bis(acetylacetonitrile)di-isopropyl titanate; organometallic compounds, such as chelating compounds; and organic bases, such as ethylamine, hexylamine and dibutylamine.

Examples of vinyl polymers which are soluble in the above described vinyl monomers at least on heating include polystyrene, polymethyl methacrylate, polymethyl acrylate, polyacrylonitrile, an acrylonitrile-styrene copolymer, a styrene-butadiene copolymer, and a styrene-acrylonitrile-butadiene copolymer. The description "being soluble in the vinyl monomer at least on heating" is used herein to mean that the vinyl polymer is always soluble in the vinyl monomer at the temperature at which the bulk polymerization is performed, and, of course, it includes the case where the vinyl polymer is soluble in the vinyl monomer at ordinary temperature.

To make the inorganic filler-containing polymerizable composition of the invention, the inorganic filler is dispersed in the vinyl monomer or a mixture of the vinyl monomers and the vinyl polymer in a proportion of 10 to 80% by weight of the resulting composition. Furthermore, the inorganic fillercontaining polymerizable composition contains the silane coupling agent and the silane coupling accelerator in a proportion of 0.1 to 5% by weight and 0.01 to 2% by weight, respectively, based on the weight of the inorganic filler, and at the same time, it contains the vinyl polymer soluble in the vinyl monomer (at least on heating) in a proportion of 5 to 50% by weight based on the weight of the vinyl monomer.

In preparing the inorganic filler-containing polymerizable composition of the invention by preliminary bulk polymerization of the vinyl monomer, the inorganic filler is added so that it constitutes 10 to 80% by weight, preferably 20 to 70% by weight, of the cdmposition, the silane coupling agent is added so that it constitutes 0.1 to 5% by weight, preferably 0.5 to 3% by weight, of the inorganic filler, and the siiane coupling accelerator is added so that it constitutes 0.01 to 2% by weight of the inorganic filler.

When the proportion of the inorganic filler in the composition is less than 10% by weight, the mechanical strength and dimensional stability of the polymer is insufficiently improved. When the proportion of the inorganic filler in the composition exceeds 80% by weight, it is difficult to uniformly disperse the inorganic filler in the vinyl monomer, and, furthermore, the viscosity of the resulting composition increases and the handling thereof becomes difficult.

The silane coupling agent is added in an amount of 0.1 to 5% by weight, preferably 0.5 to 3% by weight, based on the weight of the inorganic filler. When the amount of the silane coupling agent added is less than 0.1% by weight, it is difficult to disperse the inorganic filler uniformly, and, furthermore, a reduction in the viscosity of the resulting composition cannot be expected. Even if the silane coupling agent is added in greater amounts than 5% by weight, the effect of improving dispersibility or lowering the viscosity cannot be increased. Furthermore, it is disadvantageous from an economic standpoint to use such expensive silane coupling agents in a large amount.

The silane coupling accelerator is used in an amount of 0.01 to 2% by weight based on the weight of the inorganic filler. When the amount of the silane coupling accelerator added is less than 0.01% by weight, the silane coupling reaction proceeds slowly, which is not suitable from a practical standpoint. Even if the silane coupling accelerator is added in greater amounts than 2% by weight, a greater accelerating effect on the silane coupling reaction cannot be expected, and the addition of such large amounts of silane coupling accelerator is disadvantageous from an economic standpoint.

In preparing the composition of the invention, the vinyl monomer and the inorganic filler are firstly mixed together, the silane coupling agent and the silane coupling accelerator are added thereto, and the resulting mixture is uniformly stirred.

Although the exact reason why the composition of the invention with the silane coupling agent compounded thereinto has a low viscosity compared with a composition comprising the inorganic filler and the vinyl monomer, and containing no silane coupling agent is not clear, it is assumed as follows: When the inorganic filler is merely dispersed in the vinyl monomer, since the inorganic filler has poor affinity to the vinyl monomer, particles of the inorganic filler aggregate together, apparently increasing the volume occupied by the inorganic filler in the composition. On the other hand, when the silane coupling agent is added to the composition, it combines with the inorganic filler, providing the inorganic filler with the affinity to the vinyl monomer.Furthermore, the aggregation of filler particles is controlled, the filler is uniformly dispersed in the vinyl monomer, and the apparent increase in the volume occupied by the inorganic filler in the composition is decreased. Therefore, when the same amount of inorganic filler is added to a composition not containing the silane coupling agent, such has a viscosity higher than that of the same composition containing the silane coupling agent.

Furthermore, as the average grain size of the inorganic filler is decreased, aggregation easily occurs and the viscosity of the resulting composition increases.

Although the mechanism of modification of the inorganic filler by the silane coupling agent is not clear, it is assumed that when an alkoxy group-containing silane compound is used as a silane coupling agent, and a metal hydroxide as an inorganic filler, a dealcoholization reaction occurs, chemically bonding the coupling agent and the inorganic filler. In order to accelerate the coupling reaction and to prepare a uniform dispersion in a short period of time, the silane coupling accelerator is added.

To the inorganic filler-containing polymerizable composition which is subjected to the subsequent preliminary bulk polymerization, a radical polymerization initiator is added to the composition at the stage of preparation of the composition or after preparation thereof.

Radical polymerization initiators which can be used include organic peroxides, such as benzoyl peroxide, lauryl peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, 2,5di(peroxybenzoate)hexine-3, and tert-butyl peroxybenzoate, and azo compounds, such as azobisisobutyronitrile, and dimethylazo diisobutylate. The amount of the polymerization initiator used is 0.1 to 5% by weight, preferably 0.5 to 1% by weight, based on the weight of the vinyl monomer.

Additionally, if desired, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, and a rubber material soluble in the vinyl monomer can be added to the composition.

The composition with the polymerization initiator compounded therein is subjected to a preliminary bulk polymerization in which 5 to 45% by weight, preferably 20 to 35% by weight, of the vinyl monomer is polymerized, to prepare a preliminary bulk polymerization solution of the vinyl monomer whose viscosity at 200C is adjusted to 100 to 10,000 centipoises, preferably 200 to 5,000 centipoises. The preliminary bulk polymerization is generally conducted at temperatures of 60 to 1 300C and pressures of 1 to 2 kg/cm2 in a closed reactor.

The preliminary bulk polymerization solution is then introduced into water containing therein a suspension stabilizer, and the resulting mixture is heated to suspension polymerize the unreacted vinyl monomer, or, alternatively, the preliminary bulk polymerization solution with its viscosity adjusted to 100 to 10,000 centipoises is continuously introduced into a larger bulk polymerization reactor (e.g., 2-10 times larger) where the bulk polymerization is completed. The thus prepared polymer is pulverized to produce the desired polymer particles.

The preliminary bulk polymerization performed prior to the suspension polymerization or the subsequent bulk polymerization further prevents precipitation of the inorganic filler in the reaction system, and renders transportation of the preliminary bulk polymerization solution to the suspension or bulk polymerization reactor and the suspension polymerization or fuli scale bulk polymerization easy.

The preliminary bulk polymerization, when the vinyl monomer is styrene, acrylonitrile or methyl methacrylate, is performed under the following conditions: polymerization temperature of 70 to 11 00C and polymerization time of 1.5 to 10 hours, preferably 2 to 5 hours. In this preliminary bulk polymerization, 5 to 45% by weight, preferably 20 to 35% by weight, of the styrene is preliminarily polym erized.

When the viscosity of the preliminary bulk polymerization solution at 200C reaches 100 to 10,000 centipoises, the preliminary bulk polymerization solution can be transferred continuously to a large scale bulk polymerization reactor where it is bulk-polymerized at 1 50 to 2000C for 5 to 10 hours (see Japanese Patent Publication No. 50961/80); alternatively the preliminary bulk polymerization solution can be introduced into an aqueous medium containing a suspension stabilizer with stirring to prepare a suspension, and suspension polymerization is performed for 2 to 10 hours at 60 to 1 400C, preferably for 4 to 6 hours at 80 to 1300 C, to complete the polymerization of the unreacted styrene.

The polymerizable solution having a viscosity of 100 to 10,000 centipoises at 200C can also be prepared by adding a vinyl polymer as described hereinabove without the preliminary bulk polymerization. In accordance with this method, the polymerizable composition is prepared so that the amount of the inorganic filler is 10 to 80% by weight, preferably 20 to 70% by weight, of the polymerizable composition, the amount of the silane coupling agent is 0.1 to 5% by weight, preferably 1 to 3% by weight, of the inorganic filler, the amount of the silane coupling accelerator is 0.01 to 2% by weight of the inorganic filler, the amount of the vinyl monomer is 10 to 85% by weight, preferably 1 5 to 60% by weight, of the polymerizable composition and the amount of the vinyl polymer is 5 to 50% by weight, preferably 10 to 30% by weight, of the vinyl monomer.It is preferred that the polymerizable composition be prepared so as to have a viscosity of 100 to 10,000 centipoises and preferably 200 to 5,000 centipoises.

When the amount of the vinyl polymer added is less than 5% by weight, the effect of improving the storage stability of the dispersion is poor. On the other hand, when it is more than 50% by weight, the viscosity of the composition undesirably increases to too high a level, making transportation to the polymerization reactor and polymerization difficult.

In preparing the above polymerizable composition, the vinyl monomer and the inorganic filler are firstly mixed, the silane coupling agent and the silane coupling accelerator are added thereto and the system stirred uniformly, and, furthermore, the vinyl polymer is added thereto and the system further uniformly stirred, if necessary while heating at 60 to 1 300C.

Alternatively, the polymerizable composition may be prepared by previously dissolving the vinyl polymer in the vinyl monomer, adding the inorganic filler thereto and mixing, and then adding the silane coupling agent and silane coupling accelerator thereto and mixing.

In the case of a polymerizable composition as prepared above, the radical polymerization initiator necessary for the polymerization can be added during or after the preparation of the composition. If desired or necessary, the polymerizable composition may contain an antioxidant, a heat stabilizer, an ultraviolet absorbant, a plasticizer, and a rubber material soluble in the vinyl monomer.

The polymerizable composition is also particularly useful for the production of polymer particles having a narrow grain size distribution by suspension polymerization.This suspension polymerization is performed by introducing the polymerizable composition with the above polymerization initiator compounded therein into an aqueous medium containing a suspension stabilizer with stirring to prepare a suspension, and heating the suspension to a temperature higher than the decomposition temperature of the polymerization initiator. When the vinyl monomer is styrene, acrylonitrile, methyl methacrylate or the like, the suspension polymerization is performed for 2 to 10 hours at 60 to 1400 C, preferably for 4 to 6 hours at 80 to 1300C, to complete the polymerization of the unreacted vinyl monomer.

In the polymer particles prepared by preliminary bulk suspension polymerization or suspension polymerization of the composition of the invention, the inorganic filler is uniformly dispersed therein.

Suspension stabilizers which can be used in the suspension polymerization include organic suspension stabilizers, e.g., polyvinyl alcohol, polyvinyl pyrrolidone, gelatin, carboxymethyl cellulose, and hydroxyalkyl cellulose, and inorganic suspension stabilizers, e.g., calcium or magnesium salts of phosphoric acid and carbonic acid. When an inorganic suspension stabilizer, for example, calcium tertiary phosphate, is used, it is preferred to use sodium dodecylbenzenesulfonate, an anionic surface active agent, in combination as an auxiliary stabilizer.

The amount of the suspension stabilizer used is 0.1 to 3% by weight of the reaction solution, and the amount of the auxiliary stabilizer used is 0.002 to 0.05% by weight of the water.

The volume ratio (phase ratio) of the reaction solution to the water in the suspension polymerization is 0.5 to 2.0, preferably 1.0 to 1.5. When the phase ratio is increased to not less than 0.5, the batch size of the reactor can be reduced, which is economical and leads to a reduction in the water content of the polymer particles obtained, facilitating the drying thereof. On the other hand, when the phase ratio is more than 2.0, stirring becomes difficult as the polymerization proceeds.

Molded articles obtained by injection molding, extrusion molding or roll molding of the inorganic filler-containing polymer particles according to the invention are excellent in stiffness and dimensional stability. The molding conditions are described, for example, in Injection Extrusion and Blowing of Expandable Polystyrene, Brit. Plastics, p. 172, Apr. (1962).

Although the invention has been explained hereinbefore with reference to a process for the production of polymer particles containing no blowing agent, polymer particles containing a blowing agent can be prepared by performing the above suspension polymerization and then impregnating the polymer particles thus obtained with a blowing agent, or, alternatively, by introducing the blowing agent into the reaction system during the bulk polymerization or suspension polymerization and then performing the polymerization. In general, introduction of the blowing agent into the reaction system during the suspension polymerization is convenient from a standpoint of polymerization steps.

However, when the expandable particles obtained have a small grain size, it is preferred to impregnate the particles with the blowing agent after the suspension polymerization, taking into the consideration the fact that the blowing agent may be scattered during screening and storage of the particles.

Blowing agents which can be used include aliphatic hydrocarbons, such as propane, n-butane, isobutane, n-pentane, neopentane and hexane, alicyclic hydrocarbons, such as cyclobutane and cyclopentane, and halogenated hydrocarbons, such as methyl chloride and dichlorodifluoromethane.

These can be used alone or in combination with each other. The blowing agent is usually introduced so that the blowing agent content of the particles formed be about 5 to 20% by weight of the vinyl polymer.

Styrene-based polymer particles obtained by the practice of the invention contain 45% or more of particles falling within one grade on the market, and the grain size distribution of the particles is narrow (e.g. 0.1-100 ) and the screening is easy.

The following examples are given to illustrate the invention in greater detail. All parts and percents (%) are by weight unless otherwise indicated.

The viscosity of the dispersion, and the precipitation time of the inorganic filler were measured as follows: Viscosity: The viscosity of the dispersion at 200C as determined with a viscometer (Model B produced by Tokyo Keiki Co., Ltd.); Precipitation time: One liter of a dispersion prepared by mixing and stirring was transferred to a cylindrical measuring cylinder promptly after the stirring was stopped, and then was allowed to stand.

The time required for 20% by volume of a supernatant liquid to be formed by the precipitation of the inorganic filler was determined as the precipitation time.

Example 1 To 100 parts of styrene was added 40 parts of aluminum hydroxide having an average grain size of 1 7 y (sold under the trade name of "Higilite" by Showa Keikinzoku Co., Ltd.) at 200C with stirring.

Then, phenyltrimethoxysilane (sold under the trade name of "KBM-103" by Shin-Etsu Kagaku Co., Ltd.) and dibutyltindilaurate were added thereto in an amount of 1.0% and 0.2%, respectively, based on the weight of the aluminum hydroxide, and the resulting mixture was stirred at 200C for 1 5 minutes to prepare a uniform dispersion.

The viscosity of the dispersion at 200C was 5 centipoises (as determined with a viscometer (Model B produced by Tokyo Keiki Co., Ltd.).

Examples 2 and 3 Dispersions were prepared in the same manner as in Example 1 except that the amount of aluminum hydroxide added was changed to 150 parts and 300 parts.

The viscosities of the dispersions were 23 centipoises and 1,075 centipoises.

Comparative Examples 1 to 3 Comparative dispersions were prepared in the same manner as in Examples 1 to 3 except that phenyltrimethoxysilane and dibutyltin dilaurate were not added. The appearance and physical properties of each comparative dispersion are given in Table I below.

Table 1 Comparative Example Appearance Viscosity (centipoises) 1 Dispersion 12 2 Dispersion 1,370 3 Greasy More than 1 x105 Examples 4 and 5 Dispersions were prepared in the same manner as in Example 1 except that the average grain size of aluminum hydroxide was changed to 1 y and 60 y.

The viscosities of the dispersions were 120 centipoises and 3.5 centipoises, respectively.

Comparative Examples 4 and 5 Comparative dispersions were prepared in the same manner as in Comparative Example 1 except that the average grain size of the aluminum hydroxide was changed to 1 F and 60 u.

The viscosities of the comparative dispersions are given in Table 2 below.

Table 2 Comparative Example Viscosity (centipoises) 4 No uniform dispersion was obtained 5 7 Example 6 In the same manner as in Example 2 except that y-methacryloxypropyltrimethoxysilane (sold under the trade name of "KBM-503" by Shin-Etsu Kagaku Co., Ltd.) was used in place of phenyltrimethoxysilane, a stable dispersion having a viscosity of 22 centipoises was prepared.

Examples 7 to 12 and Comparative Examples 6 to 11 Compositions composed of the ingredients shown in Table 3 were prepared in the same manner as in Example 1, and the appearance and physical properties of each composition were examined. The results are shown in Table 3.

Table 3 Composition (parts) Inorganic filler Average grain Viscosity Run No. Vinyl monomer size ( ) Coupling agent accelerator (cps) Appereance Ex. 7 Styrene (100) 4 Mg(OH)2 Phenyltri- Dibutyltin 61 Dispersion methoxysilane (0.4) dilaurate (0.08) Ex. 8 ,, ,, ,, (100) ,, (1.0) ,, (0.2) 3,650 ,, Ex. 9 ,,8 Al(OH)3 (100) ,, (1.0) ,, (0.2) 35 ,, Ex. 10 ,, 4 Talc (50) ,, (0.5) ,, (0.1) 360 ,, Ex. 11 Methyl 17 (Al(OH)3 (100) " (1.0) " (0.2) 20 " methacrylate (10) Comp.Styrene 4 Mg(OH)2 (40) 1,200 Ex. 6 ,, 7 ,, ,, ,, (100) More than Greasy ,, 8 ,, 8 Al(OH)3 (100) 3,500 Dispersion ,, 9 ,, 4 Talc (50) 1,830 ,, ,, 10 Methyl 17 Al(OH)3 (100) 950 ,, methacrylate (100) ,, 11 acrylonitrile (100) 17 ,, (100) 400 ,, Example 13 To 100 parts of styrene were added 0.4 part of phenyltrimethoxysilane and 0.08 part of dibutyltin dilaurate, and the mixture was uniformly stirred at 200C.

Then, 40 parts of aluminum hydroxide having an average grain size of 17 u was added, and the resulting mixture was stirred at 200C to obtain a dispersion having a viscosity at 200C of 6 centipoises.

Example 14 To the dispersion having a viscosity of 5 centipoises as obtained in Example 1 were added 0.3 part of benzoyl peroxide and 0.2 part of tert-butyl peroxybenzoate, and the resulting mixture was introduced into an autoclave where it was heated to 800 C.

Preliminary bulk polymerization was performed at that temperature for 2.5 hours to prepare a styrene bulk polymerization solution (styrene monomer plus styrene polymer). The degree of polymerization of styrene in the solution (ratio of infrared absorptions at 1,632 cm-1 and 1,602 cm-1) was 21.2%.

The viscosity at 200C of the styrene preliminary bulk polymerization solution was 3,070 centipoises. When one liter of the solution was introduced into a cylindrical measuring cylinder and allowed to stand, the precipitation time required until the volume of the supernatant liquid reached 20% was 20 hours.

The preliminary bulk polymerization solution of styrene was introduced into 200 parts of water with 0.6 part of polyvinyl pyrrolidone dissblved therein while stirring at 200 rpm and the temperature of the suspension polymerization reactor was raised from 800C to 1 250C over a period of 7 hours. By continuing the stirring at 1 250C for 1 hour, the suspension polymerization was completed to produce polymer particles.

The thus produced polymer particles contained 53% of particles having grain sizes of 0.59 to 1 mm, and had an average grain size of 0.81 mm. The aluminum hydroxide content of the particles was 24.9% (theoretical value: 25.6%).

Example 15 To the dispersion having a viscosity of 5 centipoises prepared in Example 1 was added 0.3 part of benzoyl peroxide. While introducing the dispersion continuously at a constant rate into a preliminary polymerization reactor which was controlled at 850C, 40% by weight of the styrene was preliminarily bulk polymerized. The thus obtained preliminary bulk polymerization solution was continuously supplied to a reactor equipped with a stirrer, where bulk polymerization was performed at 1 600C until 99.2% of the styrene was polymerized. Finally, polymer particles were obtained by the use of an extruder equipped with a degassing device.

The aluminum hydroxide content of the polymer Iparticles was 25.3% (theoretical value: 25.6%).

Examples 16 to 18 To 100 parts of styrene was added 40 parts of aluminum hydroxide (sold under the trade name of "Higilight" by Showa Keikinzoku Co., Ltd.) having an average grain size of 1 7 . Then, phenyltrimethoxysilane (sold under the trade name of "KBM-103" by Shin-Etsu Kagaku Co., Ltd.) and dibutyltin dilaurate were added thereto in an amount of 1.0% and 0.2%, respectively, based on the weight of the aluminum hydroxide.

Subsequently, polystyrene having a number average molecular weight of 1 50,000 was added to each of three samples prepared as above at 200C in an amount of 10 parts, 25 parts and 50 parts with stirring to prepare corresponding dispersions.

The viscosity and precipitation time of each dispersion were measured, and the results are shown in Table 4.

Examples 19 to 20 and Comparative Examples 12 to 16 Dispersions composed of the ingredients shown in Table 4 were prepared in the same manner as in Example 1 6.

The viscosity and precipitation time of each dispersion were measured, and the results are given in Table 4.

Table 4 Compositons (parts) Phenyltri- Dibutyltin Viscosity Precipitation Rin no. Styrene Al(OH)3 methoxysilane dilaurate Polystyrene (cps) time Example 16 100 40 0.4 0.08 10 120 36 min ,, 17 100 40 0.4 0.08 25 1,307 45 hr ,, 18 100 40 0.4 0.08 40 7,200 120 hr ,, 19 100 150 1.5 0.3 10 760 79 min ,, 20 100 300 3.0 0.6 10 9,500 1,410 min Comparative Example 12 100 40 0.4 0.08 0 5 5 min ,, 13 100 40 0 0 0 12 7 sec ,, 14 100 40 0 0 0 10 249 13 min ,, 15 100 40 0 0 25 3,820 2.5 hr ,, 16 100 40 0 0 50 40,600 16 hr As can be seen from the results shown in Table 4 above, the dispersions of Comparative Examples 1 2-1 4 have poor storage stability, the dispersion of Comparative Example 1 6 has very high viscosity and is difficult to polymerize and the dispersion of Comparative Example 1 5 which should be compared to Example 1 7 has poor storage stability.

Example 21 To 100 parts of styrene was added 40 parts of aluminum hydroxide (sold under the trade name of "Higilite" by Showa Keikinzoku Co., Ltd.) having an average grain size of 1 7 y with stirring, and phenyltrimethoxysilane (sold under the trade name of "KBM-103" by Shin-Etsu Kagaku Co., Ltd.) and dibutyltin dilaurate were added thereto in an amount of 1.0% and 0.2%, respectively, based on the weight of the aluminum hydroxide to apply a silane coupling treatment to the aluminum hydroxide.

To the styrene solution containing the aluminum hydroxide subjected to the silane coupling treatment were added 0.3 part of benzoyl peroxide and 0.2 part of tert-butylperoxy benzoate per 100 parts of styrene, and additionally, 15 parts of polystyrene having a number average molecular weight of 1 50,000 per 100 parts of styrene, and they were dissolved therein. Then, the resulting dispersion was added to 200 parts of an aqueous solution containing 0.6 part of polyvinyl pyrrolidone with stirring at 300 rpm and was suspended therein.

The temperature of the suspension was raised from 800C to 1 250C continuously over a period of 7 hours, and by heating the suspension at 1 250C for 1 hour the polymerization of styrene was completed.

The thus prepared beads were washed with water and dried in air. The 50% average grain size of the beads was 0.85 mm. The aluminum hydroxide content of the polymer beads was 25.3% as calculated from the ash content. This shows that 99.0% of the aluminum hydroxide added was contained in the polymer beads.

Examples 22 and 23 The procedure of Example 21 was repeated with the exception that the amount of aluminum hydroxide was changed to 1 50 parts or 300 parts, and the amount of the 0.3% aqueous solution of polyvinyl pyrrolidone was changed to 250 parts or 400 parts, respectively.

The 50% average grain size of the polymer beads was 1.07 mm in the former case and 1.23 mm in the latter case. The aluminum hydroxide content of the polymer beads was 55.7% (theoretical value: 56.4%) in the former case and 70.8% (theoretical value: 72.1%) in the latter case.

Comparative Examples 17 to 19 The procedures of Examples 21 to 23 were repeated with the exception that phenyltrimethoxysiiane and dibutyltin dilaurate were not added (Comparative Examples 1 7 to 19, respectively).

The 50% average grain size of the polymer beads obtained in Comparative Example 1 7 was 2.5 mm, and the aluminum hydroxide content was 5.1% (theoretical value: 25.6%).

In comparative Examples 1 8 and 19, since the viscosity of each dispersion was high, a uniform dispersion in water could not be obtained, and the suspension polymerization could not be completed.

Comparative Examples 20 to 22 The procedures of Examples 21 to 23 were performed with the exception that the polymerization was performed without the addition of polystyrene (Comparative Examples 20 to 22, respectively).

The 50% average grain size of the polymer beads obtained was 0.47 mm in Comparative Example 20. 0.63 mm in Comparative Example 21, and 0.71 mm in Comparative Example 22. The aluminum hydroxide content was 17.7% (theoretical value: 28.4%) in Comparative Example 20, 44.8% (theoretical value: 59.8%) in Comparative Example 21, and 59.2% (theoretical value: 74.8%) in Comparative Example 22.

Comparative Example 23 Suspension polymerization was performed in the same manner as in Example 1 6 except that phenyltrimethoxysilane and dibutyltin dilaurate were not added; polymer beads having a 50% average grain size of 2.15 mm and an aluminum hydroxide content of 1.6% (theoretical value: 28.9%) were obtained.

Example 24 Suspension polymerization was performed in the same manner as in Example 23 except that aluminum hydroxide having an average grain size of 1 y was used in place of the aluminum hydroxide having an average grain size of 1 7,u; polymer beads having a 50% average grain size of 1.72 mm and an aluminum hydroxide content of 71.9% (theoretical value: 72.1%) were obtained.

Examples 25 and 26 Suspension polymerization was performed in the same manner as in Example 23 except that aluminum hydroxide having an average grain size of 4 u was used in place of the aluminum hydroxide having an average grain size of 1 7 Ae (Example 25), or ferric oxide having an average grain size of 8 y was used in place of the aluminum hydroxide having an average grain size of 1 7 u (Example 26). The polymer beads obtained in each example were as follows: 50% Average grain Filler content* Example size (mm) (o/0) 25 1.63 70.8 26 1.47 69.2 *The theoretical value is 72.1%.

Example 27 In the same manner as in Example 23 except that y-methacryloxypropyltrimethoxysilane was used in place of the phenyltrimethoxysilane, polymer beads having a 50% average grain size of 1.27 mm and an aluminum hydroxide content of 72.0% (theoretical value: 72.1%) were obtained.

Example 28 Polymerization was performed in the same manner as in Example 23 except that methyl methacrylate was used in place of styrene, and polymethyl methacrylate having a number average molecular weight of 150,000 was used in place of polystyrene.

The thus obtained polymer beads had a 50% average grain size of 0.96 mm and an aluminum hydroxide content of 70.9%.

Example 29 In Example 21, the suspension system was heated at 1 250C for 1 hour and then cooled down to 900C and a mixture of isobutane and n-butane (4/6 by volume) was introduced thereinto as blowing agent. The resulting mixture was maintained at that temperature for 5 hours to complete suspension polymerization, and, after cooling, the thus obtained polymer beads were washed with water and airdried to obtain expandable polystyrene beads having blowing agent content of 6.3%.

The expandable polystyrene beads had a 50% average grain size of 0.88 mm and an aluminum hydroxide content of 23.5% (theoretical value: 25.3%).

On soaking the expandable polystyrene beads in boiling water for 2 minutes, preliminary expanded polystyrene beads having a bulk density of 30 g/l were obtained. These preliminary expanded polystyrene beads were placed in a mold (200 mmx200 mmx50 mm), and molded by heating for 90 seconds with 0.8 kg/cm2 G steam. After cooling for 2 minutes, the molded article was removed; it was a good expanded member having a specific gravity of 33 g/l.

Claims (29)

Claims

1. An inorganic filler-containing polymerizable composition comprising 90 to 20% by weight of a vinyl monomer in which is dispersed 10 to 80% by weight of an inorganic filler, which further contains by weight of the filler: 0.1 to 5% of a silane coupling agent and 0.01 to 2% by weight of a silane coupling accelerator.

2. A composition as claimed in Claim 1 , wherein said content of silane coupling agent is 0.5 to 3% by weight.

3. A composition as claimed in Claim 1 or 2, wherein the vinyl monomer is styrene, a:- methylstyrene or chlorostyrene.

4. A composition as claimed in Claim 1 or 2, wherein the vinyl monomer is an ester of acrylic acid and an aicohol containing 1 to 8 carbon atoms.

5. A composition as claimed in any preceding claim, wherein the filler is a powder having an average grain size of 0.1 to 100 microns.

6. A composition as claimed in any preceding claim, wherein the filler is a metal oxide or metal hydroxide or a metal.

7. A composition as claimed in any preceding claim, wherein the silane coupling agent is any of those of the general formula (I) or (II) shown hereinbefore.

8. A composition as claimed in any preceding claim, wherein the silane coupling agent is any of those named hereinbefore in List A.

9. A composition as claimed in any preceding claim, wherein the silane coupling accelerator is a metal salt of a carboxylic acid, a titanic acid ester, an organometallic compound or an organic base.

1 0. A composition as claimed in Claim 9, wherein the accelerator is dibutyl or dioctyl tindilaurate, stannous acetate or octenate, zinc octenate, lead or cobalt naphthenate, iron 2-ethyl hexanate, tetrabutyl ortetranonyl titanate, bis(acetylacetonitrile)diisopropylyl titanate, ethylamine, hexylamine or dibutylamine.

11. A composition as claimed in Claim 1, substantially as hereinbefore described with reference to any of Examples 1 to 13.

12. A composition as claimed in any preceding claim, which also contains 5 to 50%, by weight of the vinyl monomer, of a vinyl polymer which is soluble in the vinyl monomer at least on heating.

1 3. A composition as claimed in Claim 12, wherein the vinyl polymer is polystyrene, polymethyl methacrylate, polymethyl acrylate or polyacrylonitrile.

14. A composition as claimed in Claim 12, wherein the vinyl polymer is a copolymer of styrene with acrylonitrile and/or butadiene.

1 5. A composition as claimed in Claim 12, substantially as hereinbefore described with reference to any of Examples

16 to 23.

1 6. A process of producing a polymerizable composition as claimed in any of Claims 1 to 11, which comprises dispersing the filler, coupling agent and coupling accelerator in the vinyl monomer.

1 7. A process as claimed in Claim 16, wherein a radical polymerization initiator is added to the composition during or after its preparation.

1 8. A process of producing a polymerizable composition as claimed in Claim 1 6, substantially as hereinbefore described with reference to any of Examples 1 to 1 3.

1 9. A process of producing polymer particles, which comprises (i) subjecting a dispersion prepared as claimed in Claim 16, 1 7 or 18 to preliminary bulk polymerization until 5 to 45% by weight of the vinyl monomer is polymerised and the viscosity, at 20% of the reaction system is 100 to 10,000 centipoises and (ii) either (a) introducing the resultant batch of partially polymerized solution into water containing a suspension stabilizer and heating the mixture to perform suspension polymerization of the unreacted vinyl monomer, or (b) introducing the resultant partially polymerized solution continuously into a bulk polymerization reactor wherein the suspension polymerization of the unreacted vinyl monomer is performed.

20. A process as claimed in Claim 19, wherein the preliminary bulk polymerisation is conducted at a temperature of 60 to 1 300C at a pressure of 1 to 2 kg/cm2.

21. A process of producing polymer particles as claimed in Claim 18, substantially as hereinbefore described with reference to Example 1 4 or 1 5.

22. A process of producing a polymerizable composition as claimed in any of Claims 12 to 15, which comprises mixing together the filler, coupling agent and coupling accelerator and monomer and a sufficient amount of vinyl polymer to adjust the viscosity of the mixture at 200C to 100 to 10,000 centipoises.

23. A process as claimed in Claim 22, wherein a radical polymerization initiator is added to the composition during or after its preparation.

24. A process of producing a polymerizable composition as claimed in Claim 22 or 23, substantially as hereinbefore described with reference to any of Examples 1 6 to 20.

25. A process of producing polymer particles, which comprises subjecting a dispersion prepared as in Claim 22, 23 or 24 to batch or continuous suspension polymerization as defined in step (ii) of Claim 19.

26. A process of producing polymer particles as claimed in Claim 25, substantially as hereinbefore described with reference to any of Examples 21 to 28.

27. A process as claimed in any of Claims 19, 20, 21,25 or 26, wherein a blowing agent is added to the mixed solution during or after polymerization.

28. A process as claimed in Claim 27, substantially as hereinbefore described with reference to Example 29.

29. Polymer particles made by the process of any of Claims 19 to 21 or 25 to 28.