NZ200473A - Making expandable vinyl aromatic polymer or copolymer beads - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £00473 200473 Priority Date^s). . ^ complete Specification Filed: Class: .<■*$*? 24 AUu 1384 Publication P.O. Journal Mo: . »■ ^ ~~ " NEW ZEALAND No.: Date: COMPLETE SPECIFICATION "EXPANDABLE VINYL AROMATIC POLYMER OR COPOLYMER BEADS" X/We, MONSANTO AUSTRALIA LIMITED, a Company registered under the laws of the State of Victoria, Commonwealth i of Australia, having its registered office at 151 Flinders Street, Melbourne, in the State of Victoria, Australia, hereby declare the invention for which X / we pray that a patent may be granted toXKSC/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 2 0 0473 BACKGROUND OF THE INVENTION This invention relates to the production of expandable vinyl aromatic polymer or copolymer beads containing a hydrocarbon or other blowing agent and optionally containing a flammability-inhibiting additive, which beads are characterized in having a significantly faster than usual "prefoaming" rate.

Expandable vinyl aromatic polymer and copolymer beads are manufactured by aqueous suspension polymerization of vinyl aromatic monomers or comonomers. The blowing agent is incorporated either during the polymerization or in a subsequent steeping process.

Bead surface water or occluded water within the beads, resulting from the aqueous suspension polymerization process, needs to be removed by some drying process. The conditions under which the drying process is carried out has a material effect on the cell structure of the expanded vinyl aromatic polymer or copolymer bead. A fine uniform cell structure with a cell size of 0.1-0.2 mm is generally regarded as desirable.

Manufacturing foamed articles from expandable vinyl aromatic polymer beads involves several stages. Thus, firstly, the expandable beads are expanded by the action of heat to produce a "prefoam" of expanded beads; secondly, the prefoam is allowed to age for a suitable period; thirdly, the expanded beads are placed in a suitable mould and heated by steam in a moulding operation, wherein further expansion of the beads takes place and an article conforming to the shape of the mould is produced.

In studying the economics of production in manufacturing foamed articles from expandable vinyl aromatic polymer beads," it has been appreciated that the rate at which "prefoam" beads can be produced at a desired expanded bulk-density, has a substantial effect on the cost of producing the foamed articles. Thus, a faster than usual "prefoaming" rate of the expandable beads is economically desirable. 2 004 7.3 The "prefoaming" rate of expandable beads is affected by the level of blowing agents incorporated in them. For any given blowing agent or combination of blowing agents, there is an upper limit to the level of blowing agent, above which the desirable uniform fine cell structure cannot be maintained in the expanded beads, the expanded beads then tending to shrivel and collapse on continued exposure to heat.

The use of additives to improve the cell structure of expandable vinyl aromatic polymer beads has been proposed. For example, Australian Patent 517754 teaches the addition of a Fischer-Tropsch wax to give improved uniform cell structure. U.S. Patent 3,398,105 teaches a similar result by the addition of incompatible resins or polymers selected from divinyl benzene-styrene copolymers and polyolefins. Australian Patent 474637 teaches the addition of fatty acid bis amides to produce a fine uniform cell structure which is tolerant to processing conditions.

Other such additives have been previously proposed for a similar purpose, however, so far as we are aware, there has been no prior proposal to use an additive specifically for increasing the usual "prefoaming" rate of expandable vinyl aromatic polymer or copolymer beads containing a hydrocarbon or other blowing agent.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a method for the production of expandable vinyl aromatic polymer or copolymer beads having significantly increased "prefoaming" rate, which comprises incorporating into the polymer or copolymer matrix of the beads, an effective amount in the range of 0.025% to 1% by weight of the polymer or copolymer of at least one prefoam expanded bead-bulk density accelerator compound which will significantly lessen the relative time taken for the beads to reach a selected expanded bulk density in the prefoam stage, said compound being an organic liquid (excluding aliphatic hydrocarbons) which has a molecular weight of at least 150 and a boiling point of at least 200°C and is compatible with the polymer or copolymer and soluble in the polymer or copolymer to an extent 200473 of at least 1% by weight but not soluble in water beyond 0.1% by weight at 25°C and does not materially interfere with the monomer or comonomer polymerization and does not materially interfere with the incorporation of the blowing agent into the monomer or comonomer beads during the polymerization or in a subsequent steeping process and does not materially cause loss of the foaming agent in the bead drying stage and does not adversely affect the polymer or copolymer of the beads in the production of foamed articles from said beads.

We have found that the prefoam expanded bead-bulk density accelerator compound must be incorporated into the polymer or copolymer matrix of the expandable vinyl aromatic polymer or copolymer beads in order to achieve the desired increase in "prefoaming" rate. A simple surface coating of the expandable vinyl aromatic polymer or copolymer beads with such a compound does not provide the desired increase in "prefoaming" rate and has undesirable consequences.

The prefoam expanded bead-bulk density accelerator compound may be incorporated into the polymer or copolymer matrix of the expandable vinyl aromatic polymer or copolymer beads either by addition to the vinyl aromatic monomer-prior to or during polymerization, or, in the case of expandable vinyl aromatic polymer or copolymer beads produced by the "steeping" process, the prefoam expanded bead-bulk density accelerator compound may be added to the steeping vessel at the commencement of the process. The practical examples hereinafter demonstrate that the method of addition of the prefoam expanded bead-bulk density accelerator compound does not influence the benefits provided by the present invention.

We have also found that many types of organic liquids (excluding aliphatic hydrocarbons) having a relatively high molecular weight and relatively high boiling point as specified above and possessing the properties specified above, may be utilized for the purpose of the present invention. For example, the esters of phosphorus or phosphoric or phthalic or phthalyl-glycollic or adipic or stearic or abietic or benzoic or citric 200473 or sebacic or isosebacic or acetic or isobutyric or succinic acids, and sulphonamides, provided they are compatible with vinyl aromatic polymers or copolymers and possess the other properties specified above, may be so utilized.

The amount of the prefoam expanded bead-bulk density accelerator compound incorporated into the polymer or copolymer matrix of the beads is in the range of 0.025% to 1.0% by weight of polymer or copolymer, more preferably, 0.025% to 0.5% by weight of the polymer or copolymer, with best results being obtained by having 0.05 to 0.25% by weight of said prefoam expanded bead-bulk density accelerator compound present in beads having from 5 to 10% by weight of a blowing agent. An amount of prefoam expanded bead-bulk density accelerator compound less than 0.025% by weight of polymer or copolymer, provides no benefit, whilst an amount of expanded bulk density accelerator compound in excess of 1.0% by weight of polymer or copolymer, causes the prefoamed beads to shrivel and collapse under the continued action of steam or heat, such as would be experiencedin commercial prefoaming equipment.

PREFERRED EMBODIMENTS OF THE INVENTION The present invention is applicable to expandable vinyl aromatic polymer or copolymer beads which can be manufactured by aqueous suspension polymerization, for instance, homopolymers of vinyl aromatic compounds, and copolymers of such compounds with other olefinically unsaturated monomers. The invention is particularly applicable to expandable polystyrene beads and has been so described in the practical examples set out below, however, other vinyl aromatic compounds apart from styrene are alpha methyl styrene, the vinyl toluenes, and the halogen substituted styrenes. Examples of olefinically unsaturated monomers which may be used to form copolymers are acrylonitrile, methacrylonitrile, methyl methacrylate, butadiene, and unsaturated cyclic anhydrides such as maleic anhydride. Homopolystyrene is the preferred polymer for economic reasons. The weight average molecular weight of the preferred polystyrene as determined by gel permeation chroma- 2 004 73. tography can lie between 150,000 and 350,000 but preferably lies between 230,000 and 300,000.

Polymer/Copolymer Expandable Beads: Expandable vinyl aromatic polymer or copolymer beads, such as expandable polystyrene beads, contain a vapourizable blowing agent which causes the beads to expand or foam when heat or steam is applied to them. The blowing agent may be any material which has a boiling point or boiling range at atmospheric pressure below 100°C, and which has substantially no solvent effect on the polymer or copolymer. Examples of blowing agents are saturated aliphatic or cycloaliphatic hydrocarbons having three to seven carbon atoms, for example, propane, butane, pentane and cyclohexane, or halogenated hydrocarbons having C^ to C^, for example, fluorinated hydrocarbons, or other materials such as petroleum ether, or mixtures thereof. The amount of expanding agent in the beads should be sufficient to produce a cellular mass, which, in general, amounts to about 2-20% by weight based upon the polymer or copolymer. The preferred blowing agents are n-pentane or iso-pentane/n-pentane mixtures containing up to 70% by weight of iso-pentane.

Processes for manufacturing expandable vinyl aromatic polymer or copolymer beads by aqueous suspension polymerization are well known. The preferred process is the so-called "steeping" process, in which the vinyl aromatic monomer or comonomer is polymerised in aqueous suspension according to usual practice to produce beads of diameter ranging between about 0.1 to 4.0 mm, more usually between about 0.1 and 2.0 mm. Peroxide initiators and reaction temperatures are chosen to produce a polymer or copolymer of the desired molecular weight range. The beads are dried and sieved into desired size fractions. For example, in the case of polystyrene beads to be used for moulding large blocks for thermal insulation purposes, it is desirable to use beads with a size range from 0.8 to 2.0 mm, whereas for products which are to be used for moulding packaging articles, a smaller bead size range of 0.5 to 0.8 mm is desirable, in order to give finer definition in the moulded article. 200473 In the "steeping" process, beads of a desired size fraction are resuspended in water in a pressure vessel which is heated to a temperature above the glass transition temperature of the vinyl aromatic polymer or copolymer, then 5 the blowing agent is added. The vessel is held at this temperature for a sufficient time for the blowing agent to be substantially absorbed into the vinyl aromatic polymer or copolymer and to be distributed uniformly within the polymer or copolymer beads. The vessel is then cooled and the beads 10 are separated by centifuging or other means and then dried.

In other practices widely used, the expandable vinyl aromatic polymer or copolymer beads are manufactured by a single aqueous suspension polymerization, in which the blowing agent is added either at the beginning or during the polymeri-15 zation of the monomer or comonomer. As in the "steeping" process, expandable beads produced by these, practices are separated from the aqueous suspension medium by centrifuging or other means, then subjected to a drying process. The type of process used for the manufacture of expandable vinyl aromatic 20 polymer or copolymer beads is in no way limiting on the subject matter of the present invention.

After the final drying process in the production of the expandable beads, it is usual practice to coat the expandable beads with a material which functions to prevent clumping 25 or sticking of the expandable beads as they are pre-expanded in prefoaming equipment. Materials which are particularly suitable for this purpose are fatty acid amides or bis amides, fatty acid esters, and water-insoluble metal salts of fatty acids such as zinc stearate.

Also, for many applications, in particular, "ceiling tiles or for thermal insulation in buildings, it is essential to modify the flammability characteristics of foamed products produced from expanded vinyl aromatic polymer or copolymer beads in order to reduce flammability hazards. As is well 35 known, the addition or incorporation of halogenated compounds, in particular, brominated compounds, either alone or in combination with certain peroxides, will achieve the desired Z 0 04 73 modification of the flammability characteristics of foamed articles produced from expanded vinyl aromatic polymer or copolymer beads.

Examples of brominated compounds which are particularly 5 suitable are pentabromochlorocyclohexane, hexabromocyclododecane, pentabromophenyl allyl ether and dibromoethyldibromocyclohexane. Example of peroxides which have a synergistic effect on flammability characteristics when used in combination with brominated compounds are dicumyl peroxide and di-tertiary butyl peroxide. 10 The amounts of brominated compounds which are required to give the desired effects are usually in the range of 0.5 to 2% by weight of the vinyl aromatic polymer or copolymer. The levels of peroxides which may be used are preferred to be in the range of 0.05 to 0.5% by weight of the vinyl aromatic polymer 15 or copolymer. ! ' ■ Use of additives to modify the flammability characteristics of foamed products produced from the expanded vinyl aromatic polymer or copolymer is in no way limiting on the subject matter of the invention. Thus, the benefits derived 2 0 by incorporation of prefoam expanded bead-bulk density accelerator compound into the polymer or copolymer matrix of the expandable beads are obtained whether flammability modifying additives are present or not.

Prefoam Expanded Bead-Bulk Density Accelerator Compound: 2 5 We have found that those organic liquids having a relatively high molecular weight and relatively high boiling point as specified above, collectively known as resin-plasticizers, which are compatible with vinyl aromatic polymers or copolymers and have the other properties specified above,. 30 are ideally suitable for use as prefoam expanded bead-bulk density accelerator compounds in accordance with the present invention. The molecular weight of the said resin-plasticizers generally is within the range of 150-500, and the boiling point generally is within the range of 250-500°C. Said resin-35 plasticizers usually have a viscosity within the range of about 3 to about 5000 centistokes at 25°C but more usually within the range of about 10 to about 2000 centistokes at 25°C. 200473 Suitable resin-plasticizers are the alkyl or aryl or alkaryl or aralkyl esters of inorganic or organic acids, more particularly, phosphoric or phthalic or phthalylglycollic acids, the alkyl or aryl or alkaryl or aralkyl moieties having from 1 to 30 carbon atoms. Specific examples of esters which are highly compatible with vinyl aromatic polymers or copolymers and therefore particularly suitable for use in accordance with the present invention are butyl benzyl phtha-late ("Santicizer 160" resin plasticizer); butyl phthalyl butyl glycollate ("Santicizer B16" resin plasticizer); dimethyl phthalate; diiso-octyl phthalate; dibutyl phthalate; triethyl phosphate; tributyl phosphate/ ethyl phthalyl ethyl glycollate ("Santicizer E15" resin plasticizer).

Other resin-plasticizers which may be utilized in accordance with the present invention are: triphenyl phosphite; tricresyl phosphate; octyl diphenyl phosphate ("Santicizer 141" resin plasticizer); diethyl phthalate; di(tridecyl)phthalate; butyl octyl phthalate; butyl decyl phthalate;•dioctyl adipate; diiso-decyl adipate; methyl phthalyl ethyl glycollate ("Santicizer M17" resin plasticizer). 'Santicizer' is a registered trademark used by Monsanto Company, St. Louis, United States of America, in marketing the indicated organic compounds.

Still other resin-plasticizers which may be utilized in accordance with the invention are: di-2-ethylhexyl iso-phthalate; n-butyl palmitate; tri-2-ethylhexyl phosphate; tributoxyethyl phosphate; 2-ethylhexyl diphenyl phosphate; di-2-ethylhexyl adipate; octyl decyl adipate; di-2-ethylbutyl azelate; di-n-hexyl azelate; tri-n-butyl citrate; acetyl tri-n-butyl citrate; glycerol, triacetate; dibutyl succinate; N-ethyl-o,p-toluenesulphonamide.

Prefoaming Moulding Cycle: In practice, the expandable vinyl aromatic polymer or copolymer beads are expanded to bulk densities within the 3 range of about 10-30 kg/m , in a commercial steam prefoamer. This apparatus comprises a cylindrical vessel equipped with ^n agitator, into the base of which is fed unprefoamed beads 200473 and steam at predetermined rates. It is common practice to use a screw or similar device to feed the unprefoamed beads.

Upon contact with the steam, the unprefoamed beads expand and overflow into storage containers.

The bulk density of the expanded beads may be varied by either changing the amount of steam, or by varying the rate at which the unprefoamed beads are fed to the vessel. This is conveniently done by varying the speed of the screw feeder.

For a given bulk density of expanded beads being produced by the prefoamer for a given amount of steam, the prefoaming rate is conveniently related to speed of the screw feeder.

After expansion, the expanded beads are aged for 12-48 hours in order to regain resiliency before being moulded into various foamed articles.

! In a typical moulding cycle, the prefoamed or pre-expanded beads are either blown into a closed mould or transferred into an open mould which is then closed; steam is passed through the mould to remove interstitial air which would reduce fusion of the beads; the pressure is raised in the mould, causing the beads to fuse together; the steam is closed off and cooling water is circulated around the mould to reduce the temperature and pressure to ambient; the mould is opened and the foamed moulding removed; and the cycle is repeated.

PRACTICAL EXAMPLES The following practical examples are merely illustrative of the invention and are not to be construed as limitative.

Example 1 Polystyrene beads were prepared by aqueous suspension polymerization in the following manner 100 parts of de-ionized water and 100 parts of styrene were charged to a pressure vessel equipped with a heating and cooling jacket, agitator and baffle. The vessel was sealed, purged with nitrogen and heating commenced. When the temperature reached 90°C, 0.13 parts of tertiary butyl perbenzoate was added, and heating was continued to 118°C. 2 004 73 When the degree of conversion of styrene to polymer was calculated to be 17%, 0.07 parts of a suspending agent consisting of a copolymer of acrylic acid with 2-ethylhexylacrylate as a 3% solution in water, was added. After 90 minutes at 118°C, 5 the batch was heated to 140°C and held for a further 45 minutes. Jacket cooling was then commenced and when the temperature was less than 35°C the vessel was emptied, the polystyrene beads were separated by means of a centrifuge, and dried in a rotary drier. The beads were sieved and a fraction having diameters 10 ranging between 0.96 and 1.8 mm was separated from the remainder. The weight average molecular weight of the polystyrene was 280,000 as determined by gel permeation chromatography. 100 parts of de-ionized water were charged to a pressure vessel equipped with a heating and cooling jacket, agitator and baffle. 15 0.2 part of a partially hydrolysed polyvinyl acetate, 0.8 part of pentabromochlorocyclohexane and 0.5 part of butyl benzyl phthalate was added. With the agitator running, 100 parts of the sieved polystyrene beads having diameters between 0.96 and 1.8 mm were added. The vessel was sealed, heating 20 commenced, and 8.0 parts of a commercial mixture of isopentane and normal pentane of essentially equal parts of each, together with minor amounts of butane and hexanes, was pumped into the vessel over 2.5 hours. The vessel was heated to an operating temperature of 117°C and maintained at that temperature for a 25 total of 5 hours from the commencement of pentane addition.

Jacket cooling was then commenced and continued until the temperature of the suspension was less than 35°C when the vessel was emptied and the expandable polystyrene beads were separated by means of a centrifuge.

The separated beads were dried in a batch drier operating with air at an inlet temperature of 25°C. After drying to a moisture content of less than 0.15%, the beads were coated in a double conical blender with 0.2% of sorbitan monopalmitate.

The incorporation of the butyl benzyl phthalate into the 35 polymer matrix of the expandable polystyrene beads was confirmed by examining the infra red spectrum of a film prepared 2 0 0473 by dissolving the beads in dichloromethane, forming a thin film of the solution, and then evaporating the dichloromethane solvent. Benzyl butyl phthalate has characteristic infra red absorption bands at 1725 cm ^ and 1280 cm \ These bands were 5 present in the infra red spectrum of the film prepared from the expandable polystyrene beads. The relative intensity of these bands indicated that 10-20% of the benzyl butyl phthalate charged had been incorporated into the polymer matrix of expandable polystyrene beads, that is, the concentration of 10 butyl benzyl phthalate in the polymer matrix of the beads was between 0.05 and 0.10%.

Example 2 - Control Example 1 was repeated except that the butyl benzyl phthalate was omitted.

Comparative Tests Prefoam Rate The performance of expandable polystyrene beads with respect to prefoam rate in a commercial prefoamer can be predicted from a simple laboratory batch prefoam experiment. For 20 example, 200 gm of expandable polystyrene beads are spread out on a fine mesh cloth supported above the base of a rectangular container. Steam at a pressure of 28kPa is introduced at the base of the container for a given period of time. The expanded beads are then removed from the steaming container, 25 and should be able to be easily broken up by hand into a free-flowing prefoam of expanded polystyrene beads. The bulk density can then be measured.

The relative prefoam rate in a continuous prefoamer can be inferred from the relative time taken for the beads in the 30 batch prefoam experiment to expand to a given bulk density.

This will be illustrated with the expandable polystyrene beads produced in accordance with Examples 1 and 2.

Expandable polystyrene beads from Example 1 and Example 2 were separately prefoamed in the laboratory batch prefoamer 35 for different times and the bulk density of the prefoamed beads was determined. The results obtained are set out in 200473 in Table 1 below. In all tests, the prefoam beads easily broke into free flowing individual beads.

Table 1 3 Bulk Density (kg/m ) Steaming Time (minutes) Example 1 Example 2 1 18.4 2 14.8 16.4 4 12.5 13.5 3 A bulk density of 16 kg/m is widely used for the production of polymer or copolymer foamed blocks for insulation purposes, It can be inferred from the results in Table 1 that the expandable polystyrene beads of Example 1 will take 1.6 3 minutes to reach an expanded bulk density of 16 kg/m , : whereas those of the control Example 2 will take 2.2 15 minutes. This indicates that the expandable polystyrene beads of Example! 1 containing butyl benzyl phthalate have a faster prefoaming rate than those of the control Example 2.

Expandable polystyrene beads from Example 1 were prefoamed in a continuous prefoamer into which unprefoamed bead was fed 20 by a screw type feeder. The amount of steam and revolution rate of the screw feeder were adjusted such that the bulk density of the prefoamed bead flowing out of the prefoamer 3 was 15.8 kg/m . The required revolution rate of the feed screw was 60 rpm.

With the amount of steam held constant, beads from the control Example 2 were fed to the prefoamer. In order to maintain the bulk density of the expanded beads at 15.8 kg/m , the rate of revolution of the feed screw had to be reduced to 45 rpm. This shows that a significant increase 30 in prefoaming rate, which leads to a material economic benefit, is to be gained by the present invention.

Table 1 also illustrates another feature of this invention, namely, that for a given level of blowing agent, expandable polystyrene beads containing a prefoam expandable bead-bulk 2 00473 density accelerator compound can be expanded to a lower bulk density. This also has obvious economic advantages.

Cell Size Expandable polystyrene beads obtained from both Example 1 5 and Example 2 had desirable uniform, fine cell size. In each case the cell size was within the range of 0.12 to 0.17 mm for beads expanded in either the batch or continuous prefoamer.

Moulded Properties Expandable polystyrene beads obtained from Example 1 and Example 2 were expanded in a continuous prefoamer to a bulk 3 density of 16 kg/m . After ageing in the atmosphere for 24 hours, they were moulded into a foamed block 0.5m x 1.0m x 1.0m using a perforated mould into which steam was injected 15 according to normal practice. Blocks were removed from the mould after cooling for 30 minutes.

Physical properties of the foamed blocks were determined using specimens cut and conditioned according to Australian Standard ASK 156-1965, Expanded Polystyrene for Thermal 20 Insulation.

Example 1 Example 2 Compressive strength at 10% compression (kPa) 73 69 Cross breaking strength (kPa) 197 191 Density (kg/m^) 16 16 Flammability characteristics of the foamed blocks were compared according to Method A of Australian Standard AS 2122 Part 1 - 1978 (Combustion Propagation Characteristics of Plastics Part 1 - Determination of Flame Propagation 30 following Surface Ignition of Vertically Oriented Specimens of Cellular Plastics). The specimens for this test were preconditioned at 70°C for 7 days prior to testing.

Median volume retained -V (%) m 8 value volume retained -Vg(%) Median flame duration -t (S) in 8th value flame duration -tg(S) 2 004 7 3 Example 1 48 47 0.8 1.4 Example 2 45 46 0.8 1.2 These tests show that there is essentially no difference iri physical properties or flammability characteristics between foamed articles produced from expandable polystyrene beads of Example 1 and Example 2.

Example 3 - Control Expandable polystyrene beads from Example 2 were coated with (a) 0.1% by weight, and (b) 0.2% by weight, of butyl benzyl phthalate. The beads were expanded in the laboratory batch prefoamer and the bulk density of the prefoam was determined.

Coating Prefoam Steaming time bulk^density (minutes) (kg/m ) Comments nil nil 16.4 13.5 Prefoam easily broken into individual free flowing beads. 0.1% butyl benzyl phthalate 17.0 14.0 Difficult to break prefoam into free-flowing beads. 0.2% butyl benzyl 2 17.4 More difficult, phthalate 4 14.5 This example shows that the compatible plasticizer must be incorporated into the polymer matrix of the beads. Use of the plasticizer merely as a surface coating gives no change in prefoam rate, moreover,- the prefoam beads show an undesirable tendency to stick and clump. 2 ? 0 4 7 3 Example 4 Example 1 is followed except that 0.1 part of butyl benzyl phthalate is added to the polymerization vessel prior to the commencement of polymerization. The addition of 0.5 part of butyl benzyl phthalate to the steeping vessel is omitted.

The infra red spectrum of a film of the expandable polystyrene obtained as described for Example 1 showed the absorption bands characteristic of butyl benzyl phthalate. The relative intensities of these bands indicated that the butyl benzyl phthalate concentration in the expandable polystyrene beads was 0.08 to 0.09%.

The properties of the expandable polystyrene beads were similar to those of Example 1, whilst the advantage in prefoaming rate was maintained.

This example shows that the manner in which the prefoam expanded bead-bulk density accelerator compound is incorporated into the polymer matrix of the expandable beads is not critical.

Example 5 - Control Example 1 is repeated except that the amount of butyl benzyl phthalate is reduced to 0.1%. The infra red spectrum of a film of the product was obtained as described for Example 1.

The absorption bands due to the butyl benzyl phthalate were too weak to be measured accurately, indicating that the concentration of butyl benzyl phthalate incorporated into the polymer matrix of the expandable polystyrene beads was less than 0.02%.

In the batch prefoam rate test, no significant difference was observed between this bead and that from Example 2 -control. This example shows that there is a lower limit to the level of plasticizer below which no benefits are to be gained.

Example 6 - Control 00473 Example 1 is repeated except that the level of butyl benzyl phthalate is increased to 2%. In the batch prefoam test, the expanded polystyrene beads shrivelled and collapsed even 5 at short steaming times such as 2 and 4 minutes.

This example shows the undesirable consequences of excessive amounts of prefoam expanded bead-bulk density accelerator compound.

Example 7 Example 1 and the control Example 2 were repeated without the addition of pentabromochlorocyclohexane. The expandable polystyrene beads containing butyl benzyl phthalate had a faster prefoaming rate than had beads without the butyl benzyl phthalate.

This example, shows that the invention is not limited to expandable bead containing additives to modify their flamm^-ability characteristics.

Example 8 Example 1 and the control Example 2 were repeated except 20 that the air inlet temperature to the drier used for drying the expandable polystyrene beads was increased from 25°C to 35°C. The effects on the cell size and structure of the expanded polystyrene beads was observed.

Cell Structure Dry Air . Temperature ( C) Butyl benzyl phthalate added No butyl, benzyl phthalate present °C 95% fine, uniform 5% coarse 95% fine, uniform 5% coarse °C 60% fine, uniform % fine, uniform 40% coarse 80% coarse £30473 Expanded polystyrene beads exhibiting greater than 60% coarse cells, that is, cells with sizes ranging from 0.4 to 1 mm are unacceptable for many applications.

This example shows that the cell structure of expanded poly-5 styrene beads containing a prefoam expanded bead-bulk density accelerator compound is less sensitive to drying conditions.

Thus, the present invention provides expandable vinyl aromatic polymer or copolymer beads having incorporated into the polymer or copolymer matrix of the beads, an effective 10 amount of a prefoam expanded bead-bulk density accelerator compound, which primarily results in said beads having a faster-than-usual expansion rate, leading to desirable economic advantages in the commercial production of finished articles from the expandable vinyl aromatic polymer or;co-15 polymer. However, the present invention also results in the following further technical benefits and economic advantages: 1: The cell size of the expanded vinyl aromatic polymer or copolymer beads is fine and uniform, this desirable cell structure being less sensitive to the drying conditions than 20 is otherwise the case. 2: The expandable vinyl aromatic polymer or copolymer beads containing the accelerator compound allow a lower level of blowing agent to be utilized for expanding to a given bulk density than would otherwise be required. 3: The expandable vinyl aromatic polymer or copolymer beads containing the accelerator compound can be expanded to a lower bulk density at a commercially acceptable rate, whilst maintaining the desirable uniform fine cell structure. 4: The benefits of the accelerator compound additive are 30 independent of the method of the production of the expandable vinyl aromatic polymer or copolymer beads. The accelerator compound may be added during the steeping process in which blowing agent is incorporated into vinyl aromatic polymer or copolymer beads, or it may be added to the vinyl aromatic 35 monomer or comonomer before or during polymerization.

Claims (19)

200473 5: Moulded foamed articles, in particular foamed blocks, produced from the expandable vinyl aromatic polymer or copolymer beads containing the accelerator compound, exhibit the same desirable mechanical and flammability characteristics 5 as would otherwise be obtained. The matter contained in each of the following claims is to be read as part of the general description of the present invention. - 19 - 200473 What we claim is:

1. A method for the production of expandable vinyl aromatic polymer or copolymer beads having significantly increased prefoaming rate, which comprises incorporating into the polymer or copolymer matrix of the beads, an 5 effective amount in the range of 0.025% to 1% by weight of the polymer or copolymer of at least one prefoam expanded bead-bulk density accelerator compound which will significantly lessen the relative time taken for the beads to reach a selected expanded bulk density in the prefoam stage, 10 said compound being an organic liquid (excluding aliphatic hydrocarbons) which has a molecular weight of at least 150 and a boiling point of at least 200°C and is compatible with the polymer or copolymer and soluble in the polymer or copolymer to an extent of at least 1% by weight but not;; 15 soluble in water beyond 0.1% by weight at 25°C and does not materially interfere with the monomer or comonomer polymerization and does not materially interfere with the incorporation of the blowing agent into the monomer or comonomer beads during the polymerization or in a subsequent 20 steeping process and does not materially cause loss of the foaming agent in the bead drying stage and does not adversely affect the polymer or copolymer of the beads in the production of foamed articles from said beads.

2. A method according to claim 1 wherein the prefoam expanded bead-bulk density accelerator compound is selected from those esters of phosphorus or phosphoric or phthalic or phthalylglycollic or adipic or stearic or abietic or benzoic 5 or citric or sebacic or isosebacic or acetic or isobutyric or succinic acids, and sulphonamides, which are compatible with vinyl aromatic polymers or copolymers and possess the other properties as specified therein.

3. A method according to claim 1 wherein the prefoam expanded bead-bulk density accelerator compound is a resin-plasticizer selected from those alkyl or aryl or alkaryl or aralkyl esters of phosphoric or phthalic or phthalylglycollic - 20 - 200473 acids, the alkyl or aryl or alkaryl or. aralkyl moieties of which have from 1 to 30 carbon atoms, which are compatible with vinyl aromatic polymers or copolymers and possess the other properties as specified therein.

4. A method according to claim 3 wherein the resin-plasticizer is selected from butyl benzyl phthalate; butyl phthalyl butyl glycollate; dimethyl phthalate; diiso-octyl phthalate; dibutyl phthalate; triethyl phosphate;; tributyl phosphate; ethyl phthalyl ethyl glycollate; triphenyl phosphite; tricresyl phosphate; octyl diphenyl phosphate; diethyl phthalate; di(tridecyl)phthalate; butyl octyl phthalate; butyl decyl phthalate; dioctyl adipate; diiso-decyl adipate; ethyl phthalyl ethyl glycollate; methyl phthalyl ethyl glycollate; butyl phthalyl butyl glycollate.

5. A method according to claim 1 wherein the prefoam expanded bead-bulk density accelerator compound is a resin plasticizer selected from di-2-ethylhe*yl isophtha'late; n-butyl palmitate; tri-2-ethylhexyl phosphate; tributoxyethyl phosphate; 2-ethylhexyl diphenyl phosphate; di-2-ethylhexyl adipate; octyl decyl adipate; di-2-ethylbutyl azelate; di-n-hexyl azelate; tri-n-butyl citrate; acetyl tri-n-butyl citrate; glycerol triacetate; dibutyl succinate; N-ethyl-o,p-toluenesulphonamide.;

6. A method according to any one of claims 1 to 5, wherein the amount of the prefoam expanded bead-bulk density accelerator compound incorporated into the polymer or copolymer matrix of the beads is in the range of 0.025% to 0.5% by weight of polymer or copolymer.;

7. A method according to any one of claims 1 to 5, wherein the vinyl aromatic polymer or copolymer beads contain from 5 to 10% by weight of blowing agent and the amount of the prefoam expanded bead-bulk density accelerator compound incorporated into the polymer or copolymer matrix of the beads is in the range of 0.05% to 0.25% by weight of polymer or copolymer .;- 21 -;200473;

8. A method according to any one of claims 1 to 7,;wherein the prefoam expanded bead-bulk density accelerator compound is incorporated into the polymer or copolymer matrix of the expandable vinyl aromatic polymer or copolymer beads;5 by addition to the vinyl aromatic monomer prior to or during polymerization.;

9. A method according to any one of claims 1 to 7,;wherein the prefoam expanded bead-bulk density accelerator compound is incorporated into the polymer or copolymer matrix of the expandable vinyl aromatic polymer or copolymer beads;5 in a steeping process by addition to the steeping vessel at the commencement of the steeping process.;

10. A method according to any one of claims 1 to 9,;wherein the expandable vinyl aromatic polymer or copolymer beads are homopolymers of vinyl aromatic compounds selected from styrene, alpha methyl styrene, the vinyl toluenes, the;5 halogen substituted styrenes, or are copolymers of such compounds with other olefinically unsaturated monomers selected from acrylonitrile, methacrylonitrile, methyl meth-acrylate, butadiene, and maleic anhydride or other such unsaturated cyclic anhydride.;

11. A method according to any one of claims 1 to 9,;wherein the expandable vinyl aromatic polymer beads are homopolystyrene having a weight average molecular weight as determined by gel permeation chromatography of between 150,000;5 and 350,000.;

12. A method according to any one of claims 1 to 11,;wherein the blowing agent is a saturated aliphatic or cyclo-aliphatic hydrocarbon having to C7, or halogenated hydrocarbon having C-^ to Cg, or petroleum ether, or mixtures;5 thereof, in an amount from 2 to 20% by weight based upon the polymer or copolymer, sufficient to produce a cellular mass in use.;

13. A method according to claim 12, wherein the blowing agent is n-pentane or iso-pentane/n-pentane mixtures containing;- 22 -;200473;up to 70% by weight of iso-pentane, in an amount between 5 to 10% by weight based upon the polymer or copolymer.;

14. A method according to any one of claims 1 to 13,;wherein the expandable vinyl aromatic polymer or copolymer beads contain a halogenated flammability-inhibiting additive.;

15. A method according to claim 14, wherein the halogenated flammability-inhibiting additive is a brominated compound selected from pentabromochlorocyclohexane, hexabromocyclo-dodecane, pentabromophenyl allyl ether and dibromoethyldi-bromocyclohexane in an amount in the range of 0.5 to 2% by;^weight of the polymer or copolymer, in combination with dicumyl peroxide or di-tertiary butyl peroxide or other such synergistic peroxide in ah amount in the range of 0.05 to 0.5% by weight of the polymer or copolymer. ,;i- ...;

16. A method according to any one of claims 1 to 15,;wherein the dried polymer or copolymer., beads .are ,coated with a fatty acid amide or bis amide or fatty acid ester or water-insoluble metal salt of a fatty acid or other such bead antidumping or anti-sticking agent.;

17. A method according to any one of claims 1 to 16,;wherein the polymer or copolymer beads have a diameter ranging between 0.8 to 2.0 mm for moulding large blocks for thermal insulation purposes, or a diameter ranging between 0.5 to 0.8 mm for moulding packaging articles.;

18. A method accoi^ing to claim 1 substantially as described in any one of Examples 1-8 but other than each said Control.;

19. Expandable vinyl aromatic polymer or copolymer beads . having significantly increased prefoaming rate, obtained by the method according to any one of claims 1 to 18.;Cellular moulded articles obtained by prefoaming then moulding the expandable vinyl aromatic polymer or copolymer beads according to claim 19.;DATED THIS 30"th DAY OP April;" 23 - A. J. PARK & SON;PER <?/•;*GENfr$ FOR THE APPLICANTS