GB2034322A

GB2034322A - Expandable compositions for polyvinyl chloride resin foams

Info

Publication number: GB2034322A
Application number: GB7938892A
Authority: GB
Original assignee: Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd
Priority date: 1978-11-10
Filing date: 1979-11-09
Publication date: 1980-06-04
Also published as: HU184678B; NL7908221A; PT70435A; AR221908A1; MX150950A; BE879945A; BR7907291A; DE2944068A1; FR2440965A1; PL219511A1; AU5257279A; CH642985A5; IT7927170A0; CA1122350A; IT1127209B; SE7909171L; ES8101096A1; GB2034322B; DK475079A; ES485792A0

Abstract

A resin composition of a polyvinyl chloride-based resin expandable into foamed bodies by heating comprises a polyvinyl chloride-based resin having an average degree of polymerization not exceeding 2000 and a pore volume not exceeding 0.20 ml/g and impregnated with a volatilizable foaming agent which is a hydrocarbon compound or a halogenated hydrocarbon compound having a boiling point not exceeding 90 DEG C. The resin composition may further comprise a foam-conditioning agent selected from acrylic resins and styrene-based resins having a reduced viscosity of at least 3.0 dl/g and, optionally, a nucleating agent and a decomposable foaming agent. The resin composition of the invention can give a foamed body of high expansion with very fine and uniform cell structure and also free from undesirable coloration due to the absence or limited use of a decomposable foaming agent which produced colored products by decomposition.

Description

SPECIFICATION Compositions for polyvinyl chloride resin foams The present invention relates to a composition suitable for manufacturing foams of a polyvinyl chloride-based resin.

In the prior art, foams of polyvinyl chloride-based resins (hereinafter abbreviated as PVC resins) are manufactured according to several different principles. For example, (1 ) the resin is blended or impregnated with a decomposable foaming agent which is a compound decomposable at an elevated temperature with evolution of a gas and the resin blend is fabricated with heating by the techniques of extrusion molding, injection molding or other conventional molding means whereby the resin is expanded into foams by the gras produced by the decomposition of the foaming agent, (2) a so-called plastisol of pasty consistency is first prepared by admixing the resin with a plasticizer and the plastisol is processed into foams with entrainment of air by a suitable mechanical means or, alternatively, the plastisol is further admixed with a decomposable foaming agent and the blend is subjected to heating whereby the foaming agent is decomposed to produce a gas simultaneously with the gelation of the plastisol, (3) a resin blend containing a decomposable foaming agent is first fabricated into shaped articles such as plates, slabs, rods, tubes and the like by rolling or other suitable mechanical means at a temperature lower than the decomposition temperature of the foaming agent and then the shaped article is heated to effect expansion into foams by the decomposition of the foaming agent, or (4) a metal mold is filled with a resin blend containing a decomposable foaming agent, optionally with admixture of a volatilizable foaming agent, an organic solvent with which the resin is swellable and a softening agent, and the resin blend is heated under pressure in the metal mold to be molten and gelled followed by cooling to room temperature while still in the metal mold under pressure to give a shaped article, which is subsequently heated again at a temperature higher than the softening temperature of the resin to effect expansion of the resin blend into foams with the gas produced by the decomposition or vaporization of the foaming agents.

As will be understood from the above description, the gas as the entity which effects expansion of the resin blend and is confined in the foams of the PVC resin is mostly either the atmospheric air entrained by a mechanical means or a gas which is a decomposition product of the decomposable foaming agent. The mechanical entrainment of the atmospheric air is, however, unsatisfactory because foams of fine and uniform cell structure and high expansion can hardly be obtained even by the use of a very elaborate mixing apparatus, while the use of a decomposable foaming agent is undesirable when foams of a PVC resin with high whiteness are desired because most of the practically employed decomposable foaming agents are azo compounds which form colored decomposition products leading necessarily to yellowish or brownish coloring of the resin foams manufactured therewith.Furthermore, the cell structure of the resin foams obtained with a decomposable foaming agent is not always satisfactory in its fineness and uniformity, especially when resin foams of high expansion are desired.

In addition to the above drawbacks, the above described methods ( 1 ) to (3) are not suitable for the preparation of rigid or semi-rigid foams of high expansion, i.e. the methods are limited to the manufacture of soft or flexible resin foams, and the method (4) is disadvantageous from the standpoint of efficiency and cost in the production because the process must be carried out batch-wise and the time taken for a batch of the foam preparation is necessarily considerably long due to the complexity of the process.

Another source of the gas in the resin foams is a volatilizable foaming agent which is a compound having a relatively low boiling point and readily converted to a gas when the resin blend containing it is heated so that, if the heating temperature is above the softening point of the resin, resin foams are obtained. This class of foaming agents is desirable owing to the absence of colored decomposition products leading to the coloration of the resin foams since the formation of the gas is effected not by the decomposition but merely by the vaporization of the foaming agent.

The use of a volatilizable foaming agent is successful in the manufacture of several kinds of plastic foams such as foams of polystyrene resins but no successful process has been developed hitherto for the preparation of foams of PVC resins although the reason for the difficulty has not yet been analyzed to a full extent.

Thus, it was found to be desirable to provide a novei composition suitable for manufacturing foams of a PVC resin containing a foaming agent of the volatilizable type with which resin foams of high expansion having a fine and uniform cell structure can readily be obtained without noticeable coloration.

The resin composition of the present invention expandable into foams comprises a PVC resin and a volatilizable foaming agent which is a hydrocarbon or a halogenated hydrocarbon compound having a boiling point not exceeding 900C and impregnated in the above mentioned PVC resin.

The above described resin composition can be expanded into foams of high expansion with satisfactorily fine and uniform cell structure in most cases. However, the cell structure is not always so fine and uniform when the ratio of expansion is extremely high to give resin foams having a bulk density of, for example, 0.10 g/cm3 or smaller.

The inventors of the present invention have further conducted extensive investigations in order to obtain a resin composition which can be expanded into resin foams of extremely high expansion and yet having a very fine and uniform cell structure and arrived at an improvement according to which the above described composition of the PVC resin impregnated with a volatilizable foaming agent is further admixed with from 0.5 to 30 parts by weight of a foam-conditioning resin per 100 parts by weight of the PVC resin composition impregnated with the foaming agent. The foam-conditioning resin here proposed is either an acrylic resin or a styrene-based resin having, in particular, a reduced viscosity of at least 3.0 dl/g.The effect of the above mentioned foam-conditioning resin can better be exhibited when small amounts of nucleating agent are formulated in the resin composition which is a finely divided inorganic powdery material or a combination of solid reactants which can produce carbon dioxide gas upon reaction in the resin composition.

The main ingredient in the composition is a PVC resin which may be a homopolymer or a copolymer mainly composed of vinyl chloride. When the PVC resin is a copolymer, it is recommended that the content of the monomer or monomers copolymerized with vinyl chloride does not exceed 40% by weight or, in other words, at least 60% by weight of the resin constituent is vinyl chloride from the standpoint that the resultant resin foams may have excellent flame retardancy, high mechanical strengths and other desirable properties inherent to vinyl chloride resins.

The ethylenically unsaturated monomers copolymerizable with vinyl chloride are well known in the art as exemplified by vinyl esters such as vinyl acetate and vinyl propionate, vinylidene halides such as vinylidene chloride and vinylidene fluoride, vinyl halides other than vinyl chloride such as vinyl fluoride, acrylic acid and esters thereof such as ethyl acrylate, methacrylic acid and esters thereof such as methyl methacrylate, acrylonitrile, methacryionitrile, maleic acid and esters and anhydride thereof, fumaric acid and esters thereof and olefins such as ethylene and propylene.

Among the above named comonomers, vinyl acetate is particularly advantageous since a copolymer of vinyl chloride and vinyl acetate not only is susceptible to impregnation with a foaming agent but also has a markedly reduced melt viscosity so that smoothness in foaming is ensured leading to the formation of resin foams with a further improved fine and uniform cell structure. In order that such an advantageous effect can be expected by the use of the copolymer, the content of vinyl acetate in the copolymer resin is desirably at least 3% by weight with the upper limit, of course, of 40% by weight as set forth above, arising from the consideration of the flame retardancy and mechanical properties of the resultant resin foams.

The parameters essential for the PVC resins used in the resin composition are the average degree of polymerization and the pore volume. The average degree of polymerization, which is readily determined by the measurement of the solution viscosity of the resin, preferably does not exceed 2000 since a PVC resin having an average degree of polymerization larger than 2000 has an extremely high melt viscosity and poor gelation so that resin foams of high expansion can hardly be obtained even with a large amount of the foaming agent impregnated in the resin. On the other hand, the lower limit of the average degree of polymerization is determined in consideration of the mechanical properties of the resin foams prepared with the resin. For example, a PVC resin having an average degree of polymerization smaller than 300 can only give fragile and mechanically inferior resin foams.

Another important parameter required in the PVC resin in the composition is the pore volume which desirably does not exceed 0.20 ml/g or, more preferably, 0.10 ml/g of the resin, which value of the pore volume is rather extraordinarily small in comparison with ordinary PVC resins having about 0.25 ml/g or more of the pore volume when the resin is a homopolymer of vinyl chloride. The pore volume is a value determined with a mercury-pressurizing porosimeter where the mercury pressure is increased from 1 to 100 kg/cm2 so that the mercury is forced into pores of the resin particles having a pore diameter of about 30 ym or smaller.

The above limitation of the pore volume is very important because a PVC resin having a larger pore volume is poor in retention of the foaming agent and permits dissipation of the foaming agent not only in storage of the resin composition impregnated with the foaming agent but also in the molding process of the resin composition into a shaped article of the resin foams so that foamed bodies of high expansion can hardly be obtained.

PVC resins which can meet the above requirements may be obtained by the suspension polymerization of vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride monomer in an aqueous medium containing a suspending agent in the presence of a free radical polymerization initiator soluble in the monomer phase.

The volatilizable foaming agent to be impregnated in the above described PVC resin is, as mentioned above, a hydrocarbon or a halogenated hydrocarbon compound having a boiling point not exceeding 900C or, preferably, not exceeding 700C because, when a foaming agent having a boiling point higher than 900C is employed, the resin foams once expanded exhibit remarkable shrinkage upon standing so that the resultant foamed body has a cell structure which is not satisfactory in respect of fineness and uniformity.

The hydrocarbon or halogenated hydrocarbon compounds suitable for use as a foaming agent in the composition are exemplified by propane, butane, isobutane, pentane, neopentane, n-hexane, isohexane, n-heptane, methyl chloride, methylene chloride, chloroform, carbon tetrachloride, ethylidene chloride, ethylidene fluoride, trichloroethylene, 1 ,2-dichloroethane, trichlorofluoromethane, dichlorodifluoromethane, chlorotrifluoromethane, bromotrifluoromethane, tetrafluoromethane, di chlorofluoromethane, chlorodifluorometha ne, trifluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, dibromotetrafluoroethane, chloropentafluoroethane, hexafluoroethane, 1-chloro-1,1 -difluoroethane and the like.It is optional, of course, that two or more of these volatilizable foaming agents may be used as a combination.

The amount of impregnation of the PVC resin with the above mentioned volatilizable foaming agent depends on the desired degree of expansion into resin foams. It may be too much to say that the amount of impregnation must be increased when a foamed body of high expansion ratio is desired and, when a foamed body of low expansion is desired, as small as 3% by weight or smaller of impregnation with the foaming agent may be sometimes sufficient. The amount of the foaming agent is, however, in the range from 1 to 30% by weight or more in most cases where foamed bodies of adequate expansion are to be obtained.

The impregnation of the PVC resin with the volatilizable foaming agent is carried out in principle by bringing these components into contact with each other. Particularly, the PVC resin in a powder form may be merely blended with the foaming agent so that the foaming agent is absorbed in the resin particles. When the foaming agent is gaseous at room temperature under atmospheric pressure, a convenient method for impregnation is to introduce the PVC resin, water and dispersing agent into a pressurizable vessel, e.g. an autoclave, equipped with a stirrer to form a suspension of the resin powder in the aqueous medium and then the foaming agent is introduced into the suspension with pressurization followed by agitation of the mixture with temperature elevation to 30 to 900C for 3 to 20 hours.After absorption equilibrium has been established inside the vessel and the mixture is cooled to room temperature, the resin having absorbed the foaming agent is taken out of the vessel, dehydrated by a suitable means such as centrifugal separation and dried under air flow at a relatively low temperature of, say, 500C or below to give the desired PVC resin impregnated with the foaming agent.

The thus prepared resin composition impregnated with the volatilizable agent can be as such fabricated into shaped articles of resin foams by a known technique such as injection molding and extrusion molding as well as compression molding in a metal mold in which gelation of the resin and expansion of the gelled resin by the gas produced by the vaporization of the foaming agent take place simultaneously. It is optional that the resin composition is, prior to fabrication, admixed with certain kinds of additives conventionally used in the molding of PVC resins such as plasticizers, flame retardants, anti-oxidants, anti-static agents and the like at a relatively low temperature to prevent premature vaporization of the foaming agent.

As is mentioned earlier, one of the difficult problems in obtaining a foamed body of PVC resins is to ensure fineness and uniformity of the cell structure of the resin foams, especially when the ratio of expansion of the foam is extremely high or when the said foams have a bulk density of, for example, 0.10 g/cm3 or smaller. Of course, depending on the manufacturing conditions, the foams could have a bulk density of about 0.30 g/cm3. The inventors of the present invention have conducted investigations to discover a means for conditioning the cell structure by adding a foam-conditioning agent into the resin composition and arrived at a conclusion that addition of certain kinds of thermoplastic resins is particularly effective for the purpose.

The foam-conditioning resins of the present invention include acrylic resins and styrene-based resins and these resins are particularly effective when they have a reduced viscosity of at least 3.0 dl/g as measured in a chloroform solution of 0.1 g/100 ml concentration at250C. These foam-conditioning resins may be blended with the PVC resin impregnated with the volatilizable foaming agent in an amount of from 0.5 to 30 parts by weight per 100 parts by weight of the PVC resin impregnated with the foaming agent before the resin composition is molded into shaped articles of resin foams.

The acrylic resin suitable as the foam-conditioning resin may be either a polymethyl methacrylate or a copolymeric resin mainly composed of methyl methacrylate and one or more of acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate and n-butyl methacrylate, 2-ethylhexyl methacrylate and the like provided that their contents are limited. In any case, the content of methyl methacrylate in the acrylic resin is preferably in the range from 60 to 95% by weight.

It is desirable that the acrylic resin as the foam-conditioning resin have a reduced viscosity of at least 3.0 dl/g, or, preferably, at least 5.0 dl/g as measured in a chloroform solution of 0.1 g/1 00 ml concentration at 250C as mentioned above.

It is recommended to use an acrylic resin with a higher reduced viscosity or, in other words, having a higher average degree of polymerization when the average degree of polymerization of the PVC resin is very large-approximating the upper limit of 2000. Further, it is preferable to use an acrylic resin prepared by the emulsion polymerization of the acrylic monomers because additional improvements are obtained by the use of such a resin in the smoothness of feeding into the molding machines with reduced danger of blockage of the inlet of the resin composition fed to the machine in addition to the acceleration of uniform gelation of the resin composition and increased expandibility of the gelled and molten resin composition.

The amount of the acrylic resin to be admixed as the foam-conditioning agent may be from 0.5 to 30 parts by weight or preferably, from 3 to 20 parts by weight per 1 00 parts by weight of the PVC resin impregnated with the foaming agent because larger amounts of the acrylic resin than above cannot give any further improvement and, instead, undesirable effects are produced in the properties inherent to PVC resins such as flame retardancy.

Styrene-based resins belong to another class of the foam-conditioning resins. The styrene-based resin may be a homopolymer of styrene but it is preferable that the styrene-based resin is a copolymer mainly composed of styrene with a minor amount of acrylonitrile as the comonomer. It is of course optional that the copolymer includes one or more of other comonomers copolymerizable with styrene and acrylonitrile. In any case, the styrene-based resin has a reduced viscosity of at least 3.0 dl/g as measured in a chloroform solution of 0.10 g/100 ml concentration at250C. It is recommended that the styrene-based resin has a reduced viscosity as high as possible when the vinyl chloride-based resin has a large average degree of polymerization approximating the upper limit of about 2000.

The above mentioned comonomers copolymerizable with styrene and acrylonitrile are exemplified by esters of acrylic acid such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2ethylhexyl acrylate and the like, esters of methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate and the like, maleic and fumaric acids and esters thereof and maleic anhydride.

The above described styrene-based resins may be obtained by a known polymerization method and it is recommended that the resin is prepared by emulsion polymerization in an aqueous medium.

The amount of the styrene-based resin to be used as the foam-conditioning agent may be the same as in the acrylic resins, i.e. in the range from 0.5 to 30 parts or, preferably from 3 to 20 parts by weight per 100 parts by weight of the PVC resin impregnated with the volatilizable foaming agent.

The mechanism by which the marked improvement is obtained in the cell structure of the resin foams by the addition of the foam-conditioning resin is presumably that the gelation of the PVC resin is accelerated by the foam-conditioning resin and the melt viscosity of the PVC resin in the molding step is adequately controlled or increased so that the expandability of the foams is enhanced and the cell walls of the foams are strengthened to have a higher resistance against coalescence or collapse of the foams as well as that the shrinkage of the once formed foams at an elevated temperature is prevented with improved retention of the gas produced by the vaporization of the foaming agent.

It was further discovered that the above described foam-conditioning effect obtained by the addition of a foam-conditioning resin is further enhanced when certain kinds of nucleating agent are present in combination with the foam-conditioning resin. A class of nucleating agents suitable for the present invention is an inorganic fine powdery material such as calcium carbonate, talc, barium sulfate, fumed silica, titanium dioxide, clay, aluminum oxide, bentonite, diatomaceous earth and the like having an average particle diameter of 30 ,um or smaller or, preferably, 10 ,um or smaller since coarser particles of these inorganic powders affect the fluidity of the molten resin in the molding step adversely so that the surface condition of the foamed bodies obtained with admixture of such coarser powder is deficient in lustre, sometimes with striation and inferior uniformity of the cell structure.

Another class of the nucleating agents is a combination in about equivalent amounts of an acid such as boric acid and organic acids, e.g. citric acid, tartaric acid and oxalic acid and a carbonate or hydrogen carbonate of sodium, potassium or ammoiiium such as sodium carbonate, sodium hydrogen carbonate, potassium carbonate, ammonium hydrogen carbonate and the like.

The amount of the nucleating agent to be added in combination with the foam-conditioning resin may be in the range from 0.01 to 20 parts by weight per 100 parts by weight of the PVC resin impregnated with the foaming agent. When the amount of the nucleating agent is in excess of 20 parts by weight, the ratio of expansion of the foamed resin is decreased and the resultant foamed body has inferior properties including less smooth surfaces.

The resin composition of the present invention may optionally be admixed with a known decomposable foaming agent provided that the amount thereof is limited to, say, 5 parts by weight or smaller per 100 parts by weight of the PVC resin impregnated with the volatilizable foaming agent. The decomposable foaming agents suitable for this use are exemplified by azo compounds such as azodicarbonamide, azobisisobutyronitrile, diazoa minobenzene, diethylazodicarboxylate, diisopropylazodicarboxylate and the like, nitroso compounds such as N,N'-dinitrosopentamethylene tetramine, N,N'dimethyl-N,N'-dinitroso terephthalamide and the like and sulfonylhydrazide compounds such as benzenesu Ifonylhydrazide, toluenesu Ifonylhydrazide, 4,4'-oxy-bis(benzenesu Ifonylhydrazide), 3,3'di(su Ifonehydrazidephenyl )sulfone, toluenedisulfonylhydrazone, thio-bis(benzenesulfonylhydrazide), toluenesu Ifonylazide, toluenesulfonyl semicarbazide, 4,4'-oxy-bis(benze nesu Ifonylhydrazide) and the like as well as sodium hydrogen carbonate.

The use of these decomposable foaming agents is desirable in order to further improve the fineness and uniformity of the cell structure of the resin foams and to reduce the shrinkage of the foamed body so that the shape of the foamed body is better retained although too much decomposable foaming agent is undesirable due to the coloration of the foamed body by the colored decomposition products thereof and the roughened surface condition of the foamed body, without additional advantages. It is also recommendable to add a decomposition promotor known in the art such as certain kinds of zinc compounds, copper compounds and the like to accelerate the decomposition of the decomposable foaming agent and gas evolution at a temperature lower than the temperature used in the molding of the resin composition.

The above described expandable resin composition with admixture of the foam-conditioning resin is very advantageous in manufacturing shaped bodies of PVC resin foams because the composition can give resin foams of high expansjon with fine and uniform cell structure regardless of the rigidity of the desired foamed products (ranging from soft and flexible to hard and rigid) of the conventional continuous fabrication procedures including extrusion molding, injection molding, compression molding and the like without the necessity of particular cost consideration.

Examples of the present invention are given below to illustrate the invention in further detail. In the Examples parts are all given as parts by weight. The methods for the determination of the amount of the impregnated volatilizable foaming agent in the PVC resin and the pore volume of the resin are as follows.

Amount of impregnation of the volatilizable foaming agent: the PVC resin impregnated with the volatilizable foaming agent is heated in an air oven at 1 300C for 2 hours and the amount of impregnation was calculated by the equation (W1-W2)/W2 x 100 (%), taking the weights before and after heating as W, and W2, respectively.

Pore volume of the PVC resin: the pore volume was determined with a mercury-pressurizing porosimeter (Model 70H) made by CARL ERBA Co., where the pressure of mercury was increased from 1 to 100 kg/cm2 and expressed in ml per gram of the resin.

EXAMPLE 1 (Experiments No. 1 to No. 13) Into an autoclave of 5 liter capacity equipped with a stirrer were introduced 1000 g of a vinyl chloride homopolymer or a copolymer resin composed of vinyl chloride and vinyl acetate as indicated in Table 1 below, in which P and Vp stand for the average degree of polymerization and the pore volume of the resin, respectively, 2000 g of purified water and 1 50 g of trichlorofluoromethane, and 200 g of butane was introduced with pressurization followed by temperature elevation with agitation up to 700C and continued agitation at the same temperature for 8 hours to impregnate the resin with trichlorofluoromethane and butane as the volatilizable foaming agents.

After cooling to room temperature and discharging the excess foaming agents from the autoclave, the thus impregnated resin was taken out of the autoclave dehydrated and dried under air flow at 40 to 500C for about 8 hours.

The amount of impregnation with the foaming agents was determined just after preparation and after storage at 200C for 1 week to give the results set out in Table 1.

The above obtained resin impregnated with the foaming agents, in an-amount of 100 parts, was blended with 2 parts of a tin-containing stabilizing agent and 1 part of calcium stearate and the resin blend was fabricated with a foamed body of cylindrical rod form by extrusion molding with an extruder machine operated under the conditions given below.

The bulk density of the foamed body obtained in each of the experiments was as given in the table.

Operating conditions qf the extruder machine: Diameter of the screw 20 mm Length of the screw 400 mm Compression ratio of the screw 3.0 Die 5 mm diameter of the opening and 70 mm land length Screens one with 80 mesh opening and one with 100 mesh opening Temperature of the cylinder C, = 60 to 1200C C2 = 100 to 1600C C, = 120 to 1800C Temperature of the die about 1 300C Velocity of revolution 50 r.p.m.

The foamed body obtained in Experiment No. 9 was very fragile. Although the foamed body obtained in Experiment No. 11 had a high ratio of expansion, it was inferior in flame retardancy. TABLE 1

Experiment No. 1 2 3 4 5 6 7 8 9 10 11 12 13 Content of vinyl acetate. 5 10 12 0 20 30 40 40 10 5 45 3 0 PVC % by resin weight P 350 400 520 700 800 1.000 1.300 1.800 270 2.500 810 700 1.000 Vp,ml/g 0.009 0.010 0.009 0.035 0.015 0.020 0.080 0.12 0.010 0.20 0.020 0.25 0.35 Impreg- As nation prepared 8.0 10.1 11.0 9.4 9.5 7.5 7.0 7.5 9.0 7.4 9.5 2.5 1.9 with foaming After 1 agemt, week at 7.5 9.4 10.4 8.5 8.8 7.0 6.5 6.0 8.0 5.6 8.5 0.8 0.3 % by 20 C weight Bulk density of foamed 0.073 0.065 0.060 0.19 0.11 0.21 0.23 0.26 0.14 1.35 0.10 1.2 1.35 body, g/ml EXAMPLE 2 (Experiments No. 14 to No. 26) Into the same autoclave as used in Example 1 w'ere introduced 1000 g of a copolymer resin composed of 88% by weight of vinyl chloride and 12% by weight of vinyl acetate having a pore volume Vp of 0.010 ml/g and an average degree of polymerization P of about 650. 2000 g of purified water and 1.0 g of a partially saponified polyvinyl alcohol and one or two kinds of volatilizable foaming agents as indicated in Table 2 below in amounts also indicated in the table were introduced into the autoclave, if necessary with pressurization followed by agitation for 8 hours at 700C to impregnate the resin with the foaming agents.

The notations for the volatilizable foaming agents used in this Example are as follows and will hereafter be used in other examples.

PR: propane PE: pentane HE: n-hexane TCFM: trichiorofluoromethane MC: methyl chloride BU: butane MEC: methylene chloride DCTFE: dichlorotetrafluoroethane DCDFM: dichlorodifluoromethane DCFM: dichlorofluoromethane TCE: 1 ,1 2-trichloroethane TCDFE: tetrachlorodifluoroethane ISO: isooctane The amount of impregnation with the foaming agents and the bulk density of the foamed body of cylindrical rod form fabricated in the same manner as in Example 1 were as set out in Table 2. The foamed bodies in Experiments No. 24 to No. 26 exhibited large shrinkage after molding.

TABLE 2

Experiment No. 14 15 16 17 18 19 20 21 22 23 24 25 26 Foaming agent PR PE HE TCFM MC BU BU TCFM DCTFE DCDFM TCE TCDFE ISO (g) (300) (300) (300) (300) (200) (300) (200) (200) (100) (150) (200) (200) (200) + + + + + + PE MEC PE TCFM DCFM (200) (100) (200) (200) (150) Impregnatlon with foaming agent, 8.1 8.5 10.2 19.0 20.1 10.5 14.7 18.3 20.4 18.1 11.0 10.2 7.9 % by weight Bulk density of foamed body 0.13 0.13 0.24 0.09 0.13 0.10 0.07 0.08 0.09 0.09 0.75 0.80 0.87 g/ml EXAMPLE 3 (Experiments No. 27 to No. 33) Into a 100 liter capacity autoclave made of stainless steel and equipped with a stirrer were introduced 30 kg of the same copolymer resin of vinyl chloride and vinyl acetate as used in Example 2, 50 kg of purified water and 1 5 g of a partially saponified polyvinyl alcohol and a mixed foaming agent composed of butane and trichlorofluoromethane in 2::1 ratio was introduced with pressurization into the autoclave in an amount indicated in Table 3 below followed by agitation for 8 hours at a temperature also indicated in the table to impregnate the resin with the foaming agent. The dehydration and drying of the resin impregnated with the foaming agent were undertaken in the same manner as in Example 1.

The amount of impregnation with the foaming agent was as set out in Table 3.

Resin blends were prepared each with 100 parts of the above obtained resin impregnated with the foaming agent, 2 parts of a tin-containing stabilizing agent and 1 part of calcium stearate and the resin blend was fabricated into a foamed body in the form of a slab by extrusion molding with an extruder machine operated with the conditions as given below.

The foamed bodies thus obtained were subjected to determination of the bulk density, heat conductivity as measured at 200C according to the method specified in JIS A 1413 and compression strength as measured at 200C according to the method specified in ASTM D 1621 to give the results set out in Table 3.

Operating conditions of the extruder machine: Diameter of the screw 65 mm Length of the screw 1 300 mm Compression ratio of the screw 2.0 Die 100 mm width and 8 mm height Screens one with 80 mesh opening and one with 100 mesh opening Temperature of the cylinder C, = 800C C2= 120 C CO = 1500C Temperature of the die 1200C Velocity of revolution 30 r.p.m.

TABLE 3

Experiment No. 27 28 29 30 31 32 33 Amount of mixed foaming 3 6 8 11 6 6 0.6 agent, kg Temperature, C 70 70 70 70 35 85 70 Impregnation with foaming agent, 5.0 8.2 12.1 13.3 9.1 10.9 0.8 % by weight Bulk density, 0.18 0.080 0.059 0.058 0.070 0.061 0.95 g/mi Properties Heat of foamed conductivity, 0.043 0.037 0.035 0.031 0.035 0.034 0.10 body kcal/m.hr. C Compression strength, 39.0 11.2 6.0 6.3 9,3 7.8 450.0 kg/cm2 EXAMPLE 4 (Experiments No. 34 to No. 43) The procedure for the preparation of the copolymer resin of vinyl chloride and vinyl acetate impregnated with a mixed foaming agent of trichlorofluoromethane and butane was just the same as in Example 1 where the resin used had a content of vinyl acetate, average degree of polymerization P and pore volume Vp as indicated in Table 4 below. The amount of impregnation with the foaming agent as determined just after the preparation and after storage for 1 week at 200C were as set out in the table.

Expandable resin compositions were prepared each by blending 1 00 parts of the above prepared copolymer resin impregnated with the mixed foaming agent, 2 parts of a tin-containing stabilizing agent and 1 part of calcium stearate along with or without the addition of 1 part of talc as the nucleating agent, 1 part of a decomposable foaming agent of an azodicarbonamide compound available by the name of Celmic 133 from Sankyo Kasei Co., Japan and either one of the acrylic resins E-1 and E-2 below in an amount given in Table 4.

The acrylic resin used as the foam-conditioning agent in the experiments and designated as E-1 or E-2 in the table were following products, respectively.

E-1: : a copolymeric resin composed of 90% by weight of methyl methacrylate and 10% by weight of ethyl acrylate having a reduced viscosity of 10 dI/g at 250C in 0.1 g/1 00 ml chloroform solution E-2: a commercial acrylic resin available by the tradename of Paraloid K-1 20 from Rohm 8 Haas Co.

The expandable resin compositions were fabricated into foamed bodies by extrusion molding by use of the same extruder machine and with the same operating conditions of the machine as in Example 1 and the foamed bodies were examined for bulk density and cell structure to give the results as set out in Table 4. The evaluation of the cell structure given in the table was determined according to the following standards.

Cell structure A: diameter of the cells not exceeding 500 jum Cell structure B: diameter of the cells from 500 ,um to 2000 ,um The foamed body obtained in Experiment No. 40 was remarkably fragile. In Experiment No. 43 premature expansion of the resin compositions took place while still in the die leading to the appearance of flow marks on the surface of the foamed body.

TABLE 4

Experlment No. 34 35 36 37 38 39 40 41 42 43 Content of vinyl acelate, % by 12 12 5 20 30 40 10 30 2 45 welght PVC resin P 520 520 350 700 1000 1300 270 1600 800 810 Vp,ml/g 0.010 0.010 0.009 0.012 0.020 0.023 0.010 0.050 0.060 0.020 lmpregnation As with mixed prepred 11.0 11.0 8.0 10.3 7.5 7.0 9.0 6.0 6.9 9.5 toaming agent, % by After weight 1 week 10.3 10.3 7.4 9.7 7.9 6.6 8.0 4.0 5.4 8.5 at 20 C Nucleating agent Yes Yes Yes Yes Yes Yes No No No Yes Decomposable foaming agent No Yes Yes Yes Yes Yes No No No No Acrylic resin E-1 E-1 E-2 E-2 E-2 E-2 None None None None (parts) (10.0) (10.0) (6.0) (6.0) (6.0) (6.0) Bulk density, Foamed g/ml 0.050 0.045 0.050 0.051 0.10 0.20 0.14 0.30 0.23 0.11 body Celi structure A A A A A A B B B B EXAMPLE 5 (Experiments No. 46 to No. 56) Into the same autoclave as used in Example 4 were introduced 1000 g of the same copolymer resin composed of vinyl chloride and vinyl acetate as used in Example 2, 2000 g of purified water and 1.0 g of a partially saponified polyvinyl alcohol, and one or a combination of two kinds of the volatilizable foaming agents as indicated in Table 5 below in amounts also indicated in the table was introduced thereinto with pressurization followed by agitation at 700C for 8 hours to impregnate the resin with the foaming agent or agents. The amounts of impregnation with the foaming agents were as set out in Table 5.

Expandable resin compositions were prepared each by blending 100 parts of the copolymer resin impregnated with the volatilizable foaming agent, 1 part (Experiments No. 46 to No. 48) or 3 parts (Experiments No. 49 to No. 56) of a nucleating agent as indicated in Table 5 along with or without the addition of 6 parts of an acrylic resin (Metablen P551, a product name by Mitsubishi Rayon Co., Japan) as the foam-conditioning agent.

The nucleating agents used in the experiments were as follows.

Orben: an organic complex of a colloidal hydrated aluminum silicate having an average particle diameter of about 0.5 ym, a product of Shiraishi Calcium Co., Japan Hakuenka 0: a calcium carbonate filler having an average particle diameter of 0.02 to 0.03 ,um, a product of Shiraishi Calcium Co., Japan Titanium Dioxide A-1 00: a filler grade titanium dioxide having an average particle diameter of about 0.15 to 0.25 ym, a product of Ishihara Sangyo Co., Japan Aerosil 200: a fumed silica filler having a specific surface area of about 200 m2/g and an average particle diameter of about 0.012 ym, a product of Nippon Aerosil Co., Japan Aerosil 380: a fumed silica filler having a specific surface area of about 380 m2/g and an average particle diameter of about 0.002 ym, a product of Nippon Aerosil Co., Japan Al2O3C: an alumina filler having an average particle diameter of about 0.005 to 0.02 ,um, a product of Nippon Aerosil Co., Japan Barium Sulfate &num;100: a product by Sakai Chemical Co., Japan, having an average particle diameter of about 0.6 ,um Satenton No. 5: a clay product of Tsuchiya Kaolin Co., Japan 3S Talc: a talc product of Nitto Funka Kogyo Co., Japan The expandable resin compositions thus prepared were fabricated into foamed bodies in the form of a cylindrical rod by extrusion molding with the same extruder machine and with the same operating conditions as in Example 4 and the foamed bodies were examined for bulk density to give the results as set out in Table 5.

TABLE 5

Experiment No. 46 47 48 49 50 51 52 53 54 55 56 Volatizable PR PE TCFM BU BU TCFM TCFM TCFM TCFM TCDFE ISO foaming agent (300) (300) (300) (300) (200) (200) (30) (100) (200) (200) (200) (g) + + + + + MEC PE BU BU BU (100) (100) (30) (100) (400) Imprefgnation with foaming agent, 6.5 7.0 15.4 7.3 11.0 12.4 3.4 8.2 15.0 9.8 7.4 % by weight Nucleating Orben Orten Hakuenka Titanium Aerosll Al2O3 C Barium Talc Clay Aerosil Hakuenka agent O Dioxide 200 Suifate 380 O A-100 &num;;100 Decomposable No No No No No Yes Yes Yes Yes Yes Yes foaming agent Acrylic resin Yes Yes Yes Yes Yes Yes Yes Yes Yes No No Bulk density of 0.089 0.093 0.077 0.080 0.039 0.059 0.15 0.073 0.030 0.70 0.81 foamed bydy, g/ml EXAMPLE 6 (Experiments No. 58 to No. 71) Into a 100 liter capacity autoclave made of stainless steel and equipped with a stirrer were introduced 30 kg of a copolymer resin composed of 88% by weight of vinyl chloride and 12% by weight of vinyl acetate and having an average degree of polymerization P of about 850 and a pore volume Vp of 0.01 5 ml/g, 50 kg of purified water, 1 5 g of a partially saponified polyvinyl alcohol and 6 kg of trichlorofluoromethane, and 3 kg of butane was introduced with pressurization thereinto followed by agitation at 700C for 8 hours to impregnate the resin with trichlorofluoromethane and butane as the volatilizable foaming agents.After completion of impregnation, cooling to room temperature and discharging of excess foaming agents, the resin was dehydrated by centrifugal separation and dried under air flow at 40 to 500 C. The total amount of the foaming agents in the resin impregnated therewith was 11.8% by weight.

Expandable resin compositions were prepared each by blending 100 parts of the above obtained copolymer resin impregnated with the volatilizable foaming agents, 2 parts of a tin-containing stabilizing agent and 1 part of calcium stearate along with or without the addition of talc (Experiments other than No. 62) in an amount indicated in Table 6 below or a combination of 0.5 part of sodium hydrogen carbonate and 0.4 part of citric acid (Experiment No. 62) as a nucleating agent, a decomposable foaming agent and an acrylic resin as a foam-conditioning agent as given in Table 6.

The notations used in Table 6 for the decomposable foaming agents and the acrylic resins are as follows.

AIBN: a,a'-azobisisobutyrnnkdle PTS: p-toluenesulfonyl hydrazide OBS: 4,4'-oxy-bis(benzenesu Ifonyl hyd razide) DNM: dinitrosopentamethylenetetramine Celmic 133: see Example 4.

E-3: a copolymer resin composed of 80% by weight of methyl methacrylate, 10% by weight of butyl acrylate and 10% by weight of ethyl acrylate having a reduced viscosity of 5.5 dl/g at 250C E 4: a copolymer resin composed of 85% by weight of methyl methacrylate and 1 5% by weight of butyl acrylate having a reduced viscosity of 5.0 dl/g at 250C E-5: a commercial acrylic resin available by the tradename of Paraloid K-i 25 from Rohm s Haas Co.

E-6: a commercial acrylic resin available by the tradename of Paraloid K-i 47 from Rohm s Haas Co.

Each of the resin compositions was fabricated into a foamed body in the form of a slab by extrusion molding with the same extruder machine operated with the same operating conditions as in Example 3 and the foamed bodies were examined for bulk density, cell structure, appearance, compression strength and other mechanical properties and heat conductivity. The determination of the compression strength was carried out in accordance with the method specified in ASTM D 1 621 and the heat conductivity was determined in accordance with the method specified in JIS A 1413. The results are set out in Table 6.

In Experiments No. 70 and No. 71, premature expansion of the resin composition took place while still in the die leading to broken foams and appearance of flow marks on the surface of the foamed body.

The appearance of the foamed body obtained in Experiment No. 69 was also less satisfactory. The cell structure of the foamed bodies was satisfactorily good in all of the experiments except that the foamed body in Experiment No. 68 exhibited less uniformity in the cell structure.

TABLE 6 - 1

Experiment No. 58 59 60 61 62 Nucleating agent, 1.0 1.0 1.0 1.0 (See text) (parts) Decomposable AIBN PTS OBS DNM Celmic foaming agent (1.0) (1.0) (1.0) (1.0) 133 (parts) (1.0) Urea (1.0) Acrylic resin E-3 Matablen E-4 E-5 E-5 (parts) (5.0) P 501 (5.0) (1.0) (20) (5.0) Bulk density. 0.034 0.035 0.035 0.030 0.033 compression strength, 3.3 3.5 3.5 3.0 3.4 Properties kg /cm2 of foamed body Flexural strength, 5.1 5.4 5.4 4.8 5.3 kgicm Tensile strength, 5.0 5.2 5.3 4.8 5.1 kg/cm2 Heat conductivity, 0.025 0.026 0.026 0.025 0.028 kcal/m.hr. C TABLE 6 - 2

63 64 65 66 67 68 69 70 71 1.0 0.02 15 1.0 1.0 0.005 30 1.0 1.0 Al BN None None Celmic Celmic None None Celmic Celmic (1.0) 133 133 133 133 (0.5) (4.0) (8.0) (1.0) E-5 E-5 E-5 ES ES E-3 E-3 E-3 E-3 (30) (10) (25) (10) (10) (5.0) (5.0) (5.0) (0.3) 0.035 0.034 0.040 0.033 0.045 0.070 0.059 0.080 0.095 3.6 3.6 4.8 3.3 5.0 7.3 6.0 7.3 12.4 6.7 6.5 7.8 5.5 8.1 10.3 8.8 13.0 20.1 5.5 5.4 7.0 5.3 7.8 10.5 9.0 16.8 21.3 0.028 0.027 0.029 0.028 0.031 0.037 0.035 0.038 0.043 EXAMPLE 7 (Experiments No. 72 to No. 92) Into an autoclave of 5 liter capacity made of stainless steel and equipped with a stirrer were introduced 1000 g of a homopolymeric polyvinyl chloride resin or a copolymer resin composed of vinyl chloride and vinyl acetate as indicated in Table 7 below, 2000 9 of purified water, and one or a combination of two kinds of volatilizable foaming agents as indicated in the table in amounts also given in the table with, if necessary, pressurization, followed by agitation at 700C for 8 hours to impregnate the resin with the volatilizable foaming agent. After completion of impregnation, cooling to room temperature and discharging of excessive foaming agents, the resin was dehydrated by filtration and dried under air flow at 40 to 500C for about 5 hours.The resins thus obtained were examined for the amount of the foaming agent contained therein to give the results as set out in Table 7. Further, the resins were kept at 200C for 1 week to examine the loss by dissipation during storage. The decrease in the amount of the foaming agent ranged from 6 to 9% for each of the resins.

Expandable resin compositions were prepared each by blending 1 00 parts of the above obtained resins impregnated with the volatilizable foaming agent, 2 parts of a tin-containing stabilizing agent and 1 part of calcium stearate along with or without the addition of a nucleating agent, a decomposable foaming agent and an acrylic resin (E-1) as the foam-conditioning agent as indicated in Table 7 below and the resin compositions were each fabricated into a foamed body in the form of a cylindrical rod by extrusion molding. The operating conditions of the extruder machine were as follows.

Operating conditions of the extruder machine: Diameter of the screw 25 mm Length of the screw 750 mm Compression ratio of the screw 3.0 Die 8 mm diameter of the opening and 100 mm land length Screens one with 80 mesh opening and one with 100 mesh opening Temperature of the cylinder C1 = 60 to 1 200C C2 = 100 to 1600C C3=120 to 180 C Temperature of the die 100 to 1 300C Velocity of revolution 50 r.p.m.

The thus obtained foamed bodies were examined for bulk density and the condition of the cell structure to give the results as set out in Table 7.

See preceding Examples for the notations of the volatilizable and decomposable foaming agents.

The criteria for the cell structure A and B are given in Example 4 and the cell structure C indicates that the cells of the foams have a diameter exceeding 1 mm and the structure is coarse and not uniform.

The foamed body obtained in Experiment No. 87 was remarkably fragile and the foamed bodies in Experiments No. 91 and No. 92 exhibited remarkable shrinkage after molding.

TABLE 7 - 1

Experiment No. 72 73 74 75 76 77 Content of vinyl acetate, 5 10 0 10 10 10 % by weight PVC resin P 400 750 750 1000 1000 1000 Vp,ml/g 0.11 0.013 0.060 0.025 0.025 0.025 Volatilizsble TCFM TCFM TCFM TCFM TCFM TCFM foaming agent (150) (150) (150) (150) (150) (150) used (g) + + + + + + BU BU BU BU BU BU (100) (100) (100) (100) (100) (100) Impregnation with foaming agent % by 11.0 10.8 7.8 9.7 9.7 9.7 weight Nucleating agent Talc Talc Talc Hakuenks Orben Talc (parts) (1.0) (1.0) (1.0) (1.5) (5) (0.5) Decompossble None Celmic PTS ALEN SHC SHC+ foaming agent 133 (0.03) (0.5) (0.5) (2) (parts) (1.0) Acrylic resin 10 10 10 10 10 10 (E-1),parts Bulk density. 0.065 0.045 0.060 0.054 0.052 0.053 Foamed g/ml boby Cell A A A A A A struclure *) Sodium hydrogencarbonate TABLE 7-2

78 79 80 81 82 83 84 85 86 10 35 10 10 10 10 10 10 10 1000 1700 850 850 850 850 850 850 850 0.025 0.029 0.015 0.015 0.015 0.015 0.015 0.015 0.015 TCFM TCFM PR BU PE TCFM TCFM TCFM TCFM (150) (150) (300) (300) (300) (300) (300) (100) (200) + 4- + BU BU BU BU BU (100) (100) (300) (100) (400) 9.7 9.3 6.5 7.5 8.3 15.6 3.4 8.6 15.0 Talc Talc Talc Talc Talc Talc Talc Talc Talc (0.05) (1.0) (0.5) (0.5) (1.0) (1.0) (1.0) (1.0) (1.0) SHC None None None Celmic Celmic Celmic Celmic Celmic (5) 133 133 133 133 133 (2,0) (0.5) (0.5) (0.5) (0.5) 10 10 10 10 5 5 5 5 5 0.046 0.068 0.080 0.071 0.085 0.058 0.090 0.069 0.045 A A A A A A A A A TABLE 7 - 3

88 88 89 90 - - 91 92 10 10 0 10 10 10 290 800 1700 2100 850 850 0.015 0.030 0.25 0.12 0.015 0.015 TCFM TCFM TCFM TCFM TCDFE ISO (150) (150) (150) (150) (200) (200) + + + BU BU BU BU (200) (200) (200) (200) 9.0 7.8 2.7 3.5 10.3 7.6 Talc Talc None None Talc Talc (0.01) (1.0) (1.0) (1.0) None None AIBN None Celmic Celmic (1.0) 133 133 (0.5) (0.5) 0 0 0 10 0 O 0.15 0.25 1.1 1.1 0.78 0.93 B B C C C C EXAMPLE 8 (Experiments No. 96 to No. 109) Into an autoclave of 100 liter capacity made of stainless steel and equipped with a stirrer were introduced 30 kg of a copolymer resin composed of 90% by weight of vinyl chloride and 1 O% by weight of vinyl acetate and having an average degree of polymerization of 1 050 and a pore volume of 0.023 ml/g, 50 kg of purified water, 1 5 g of a partially saponified polyvinyl alcohol and 6 kg of trichlorofluoromethane, and 3 kg of butane was introduced thereinto with pressurization followed by agitation at 700C for 8 hours to impregnate the resin with trichlorofluoromethane and butane as the volatilizable foaming agents. After completion of impregnation, cooling to room temperature and discharging of excess foaming agents, the resin was dehydrated by centrifugal separation and dried under air flow at 40 to 500C.The total amount of trichiorofluoromethane and butane in the thus impregnated resin was 1 2.0% by weight.

Expandable resin compositions were prepared each by blending 1 00 parts of the above prepared resin impregnated with the volatilizable foaming agents, 2 parts of a tin-containing stabilizing agent and 1 part of calcium stearate along with or without the addition of 1 part of talc as the nucleating agent, 0.5 part of Celmic 133 as the decomposable foaming agent and either one of the acrylic resins E-7 to E-1 3 in an amount as indicated in Table 8 below and the resin compositions were fabricated into foamed bodies in the form of a slab by use of an extruder machine operated with the conditions as given below.

The nucleating agent was omitted in Experiments No. 106 and No. 1 07 and the decomposable foaming agent was omitted in Experiments No. 106 and No. 108.

Acrylic resins: E-7: a copolymer resin composed of 90% by weight of methyl methacrylate and 10% by weight of ethyl acrylate and having a reduced viscosity of 4.5 dl/g at 250C E-8: a copolymer resin composed of 90% by weight of methyl methacrylate and 10% by weight of ethyl acrylate and having a reduced viscosity of 7.0 dl/g at 250C E-9: a copolymer resin composed of 90% by weight of methyl methacrylate and 10% by weight of ethyl acrylate and having a reduced viscosity of 11.0 dl/g at 250C E-1 0: a copolymer resin composed of 90% by weight of methyl methacrylate and 10% by weight of ethyl acrylate and having a reduced viscosity of 1 5.3 dl/g at 250C E-1 1:: a copolymer resin composed of 95% by weight of methyl methacrylate and 5% by weight of butyl acrylate and having a reduced viscosity of 10.7 dl/g at 250C E-1 2: a copolymer resin composed of 80% by weight of methyl methacrylate, 5% by weight of ethyl acrylate, 5% by weight of butyl acrylate and 10% by weight of butyl methacrylate and having a reduced viscosity of 11.0 dl/g at 250C E-1 3: a copolymer resin composed of 80% by weight of methyl methacrylate and 20% by weight of ethyl acrylate and having a reduced viscosity of 2.0 dl/g at 250C Operating conditions of the extruder machine:: Diameter of the screw 65 mm Length of the screw 1950 mm Compression ratio of the screw 3.0 Die 100 mm width and 8 mm height Screens one with 80 mesh opening and one with 100 mesh opening Temperature of the cylinder C, = 950C C2=1300C C3=1500C Temperature of the die 1 200C Velocity of revolution 20 r.p.m.

The thus obtained foamed bodies were examined for the bulk density, cell structure, compression strength as determined by the method specified in ASTM D 1 621 and flexural strength as determined by the method specified in ISO R 1209 to give the results set out in Table 8.

In Experiments No.104 and No.105, premature expansion of the resin composition took place while still in the die leading to a great extent to broken foams and shrinkage of the foamed body after molding with less uniform cell structure. The foamed bodies obtained in Experiments No. 108 and No.

109 were also less uniform in cell structure although no premature expansion of the resin composition took place.

As will be understood from the results given in the table, an acrylic resin with a higher reduced viscosity can give the advantages of a possibility of reducing the amount of the acrylic resin as well as increased retention of the gas to build the foams, stabilization of the foam cells and decrease in shrinkage. On the other hand, when the acrylic resin used has a low reduced viscosity or the amount of the acrylic resin is insufficient, the foams become broken to a large extent leading to substantial shrinkage of the foams after molding and coarser cell structure of the foams.

TABLE 8 - 1

Experiment No. 96 97 98 99 100 101 Acrylic resin E-7 E-8 E-9 E-11 E-12 E-10 (parts) (10) (6) (5) (6) (6) (2) Bulk density, 0.048 0.048 0.043 0.050 0.049 0.067 g/ml Properties Cell of foamed structure A A A A A A body Compression strength, 3.4 3.4 3.0 4.5 4.4 6.3 kg/cm2 Flexural strength, 5.7 5.6 5.0 6.3 6.0 9.3 kg/cm2 TABLE 8 - 2

102 103 104 105 106 107 108 109 E-10 E-10 E-10 E-10 E-7 E-7 None None (5) (25) (0.3) (5) (10) (10) 0.042 0.050 0.23 0.25 0.12 0.095 0.16 0.15 A A B B B B C C 3.0 3.6 21.0 22.3 - - - 5.1 6.5 29.3 30.4 - - - EXAMPLE 9 (Experiments No. 110 to No. 117) Into an autoclave of 1 0 liter capacity made of stainless steel and equipped with a stirrer were introduced 3 kg of a homopolymeric polyvinyl chloride resin or a copolymer resin of vinyl chloride and vinyl acetate, of which the content of vinyl acetate in the resin was given in Table 9 below, having an average degree of polymerization and a pore volume as indicated in the table, 5 kg of purified water, 1.5 g of a partially saponified polyvinyl alcohol and 600 g of trichlorofluoromethane, and 300 g of butane was introduced thereinto with pressurization followed by agitation at 700C for 8 hours to impregnate the resin with trichlorofluoromethane and butane as the volatilizable foaming agents. After completion of impregnation, cooling to room temperature and discharging of excess foaming agents, the resin was dehydrated by filtration and dried under air flow at 500C for 5 hours. The total amount of the foaming agents in the thus impregnated resin was as set out in the table.

Expandable resin composition were prepared each by blending 100 parts of the above obtained resin impregnated with the volatilizable foaming agents,2 parts of a tin-containing stabilizing agent, 1 part of calcium stearate, 1 part of talc as a nucleating agent and 10 parts of either one of the acrylic resins E-7, E-1 0 and E-1 3 (see Example 8) as a foam-conditioning agent and the resin compositions were fabricated into foamed bodies in the form of a cylindrical rod in the same manner as in Example 7. The bulk density and condition of the cell structure of these foamed bodies were as set out in Table 9. The foamed bodies obtained in Experiments No. 1 5 and No. 1 6 exhibited slight shrinkage after molding.

As will be understood from the results given in Table 9, when the vinyl chloride-based resin has a larger degree of polymerization, the use of an acrylic resin with an accordingly larger reduced viscosity is desirable and foamed bodies of high expansion with uniform cell structure can be obtained even with a resin with a small content of vinyl acetate, which otherwise required a relatively high temperature of fabrication, by a suitable selection of the acrylic resin as the foam-conditioning agent.

TABLE 9

Experiment No. 110 112 113 114 115 116 117 Content of vinyl PVC acetate, 5 5 10 0 10 10 0 0 % by resin weight P 700 1050 1500 850 510 1500 850 850 Vp,ml/g 0.021 0.025 0.033 0.038 0.019 0.033 0.038 0.038 Acrylic resin E-10 E-10 E-10 E-10 E-7 E-7 E-7 E-13 (parts) (10) (10) (10) (10) (10) (10) (10) (10) Bulk denslty 0.048 0.051 0.066 0.060 0.040 0.081 0.093 0.25 Foamed g/ml body Cell structure A A A A A A(*1) A B EXAMPLE 10 (Experiments No. 11 8 to No. 1 33) Into an autoclave of 5 liter capacity made of stainless steel and equipped with a stirrer were introduced 1000 g of a homopolymeric polyvinyl chloride resin or a copolymer resin of vinyl chloride and vinyl acetate, of which the content of vinyl acetate was indicated in Table 10 below, having an average degree of polymerization and a pore volume as indicated in the table, 2000 g of purified water, 1.0 g of a partially saponified polyvinyl alcohol and 1 50 g of trichlorofluoromethane, and 100 g of butane was introduced thereinto with pressurization followed by agitation at 700C for 8 hours to impregnate the resin with trichlorofluoromethane and butane as the volatilizable foaming agents.After completion of impregnation, cooling to room temperature and discharging of excess foaming agents, the resin was dehydrated by filtration and dried under air flow at 40 to 500C for about 5 hours.

The total amount of the foaming agents in the resin impregnated therewith was determined to give the results as set out in Table 1 0. The loss of the foaming agents by dissipation during storage at 200C for 1 week ranged from 6 to 9% for each of the resins.

Next expandable resin compositions were prepared each by blending 100 parts of the above obtained resin impregnated with foaming agents, 2 parts of a tin-containing stabilizing agent and 1 part of calcium stearate along with or without the addition of a nucleating agent of the kind indicated in Table 10 in an amount also indicated in the table, a decomposable foaming agent also as given in the table and a copolymer resin S-1 composed of 70% by weight of styrene and 30% by weight of acrylonitrile and having a reduced viscosity of 12.0 dl/g at 250C as a styrene-based foam-conditioning resin in an amount indicated in the table and the resin compositions were fabricated into foamed bodies in the form of a cylindrical rod by extrusion molding. The operating conditions of the extruder machine were substantially the same as in Example 7.

The thus obtained foamed bodies were examined for bulk density and the cell structure to give the results as set out in Table 10.

TABLE 10-1

Experiment No. 118 119 120 121 122 123 Content of vinyl acetate, 5 10 0 10 10 10 % by weight PVC resin P 400 750 750 1000 1000 1000 Vp,ml/g 0.011 0.013 0.060 0.025 0.025 0.025 impregnation with volatilizable foaming 11.0 10.8 7.8 9.7 9.7 9.7 agent, % by weight Nucleating agent Talc Talc Talc Talc Talc Orben (parts) (2.0) (1.0) (1.0) (0.03) (0.5) (5) Decomposable None Celmic None SHC Celmic AlBN foaming agent 133 (4.0) 133 (0.5) (parts) (1.0) (1.5) Styrene-based resin (S-1), 6.0 6.0 10.0 8.0 8.0 8.0 (parts) Bulk density, 0.060 0.044 0.061 0.049 0.050 0.055 Foamed gimi body Cell structure A A A A A A TABLE 10 - 2

124 125 127 128 129 130 131 132 10 35 10 10 10 0 10 45 1000 1700 1000 1000 1000 1700 2100 1800 0.025 0.029 0.030 0.030 0.030 0.25 0.21 0::025 9.7 9.3 9.4 9.4 9.4 2.7 3.5 6.0 Hakuenka Talc Talc None None None None Talc (20) (1.0) (1.0) (1.0) PTS None None Al BN None None None None (0.3) (1.0) 8.0 10.0 None None 8 None 8 None 0.060 0.069 0.20 0.18 0.20 1.1 1.1 0.30 A A C C C C C B EXAMPLE 11 (Experiments No. 134 to No. 143) Into an autoclave of 5 liter capacity made of stainless steel and equipped with a stirrer were introduced 1000 g of a copolymer resin composed of 90% by weight of vinyl chloride and 1 O% by weight of vinyl acetate and having an average degree of polymerization of 850 and a pore volume of 0.01 5 ml/g, 2000 g of purified water and 1.0 g of a partially saponified polyvinyl alcohol and one or a combination of two kinds of volatilizable foaming agents was added or introduced with pressurization thereinto as indicated in Table 11 below followed by agitation at 700C for 8 hours to impregnate the resin with the foaming agent.

After completion of impregnation, cooling to room temperature and discharging of excess foaming agent, the resin was dehydrated by centrifugal separation and dried under air flow. The amount of the foaming agent contained in the resin impregnated therewith was as set out in Table 11.

Expandable resin compositions were prepared each by blending 100 parts of the above obtained resin impregnated with the foaming agent with talc as a nucleating agent, Celmic 133 as a decomposable foaming agent and the styrene-based copolymer resin S-1 as a foam-conditioning agent each in an amount as indicated in Table 11 and the resin compositions were fabricated into foamed bodies in the same manner as in the preceding example. The bulk density of the thus obtained foamed bodies was as set out in Table 1 The foamed bodies in Experiments No. 141 and No. 142 exhibited remarkable shrinkage after molding.

TABLE 11

Experiment No. 134 135 136 137 138 139 140 141 142 143 Volatilizable PR BU PE TCFM TCFM TCFM TCFM TCFE ISO TCFM foaming agent (300) (300) (300) (300) (30) (100) (200) (200) (8.4) (30) (g) + + + BU BU BU (30) (100) (400) Impregnation with foaming agent, 6.5 7.5 8.4 15.6 3.5 8.9 14.0 11.0 8.4 1.5 % by weight Talc,parts 1.0 1.0 2.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 Celmic 133, parts 0 0 1.0 1.0 0.5 0.5 0.5 0.5 0.5 0 Styrene-based resin (S-1), 5 5 5 5 5 5 5 0 0 0 parts Bulk density of foamed body. 0.075 0.064 0.084 0.052 0.088 0.068 0.041 0.79 0.94 0.77 g/ml EXAMPLE 12 (Experiments No. 144 to No. 1 50) Into an autoclave of 1 00 liter capacity made of stainless steel and equipped with a stirrer were introduced 30 kg of a copolymer resin composed of 90% by weight of vinyl chloride and 10% by weight of vinyl acetate and having an average degree of polymerization of 1050 and a pore volume of 0.023 mug, 50 kg of purified water, 1 5 g of a partially saponified polyvinyl alcohol and 6 kg of trichlorofluoromethane, and 3 kg of butane was introduced thereinto with pressurization followed by agitation at 700C for 8 hours to impregnate the resin with trichlorofluoromethane and butane as the volatilizable foaming agents. After completion of impregnation, cooling to room temperature and discharging of excess foaming agents, the resin was dehydrated by centrifugal separation and dried under air flow at 40 to 500C. The total amount of the foaming agents in the resin impregnated therewith was 12.0% by weight.

Expandable compositions were prepared each by blending 100 parts of the above obtained copolymer resin impregnated with the foaming agents, 2 parts of a tin-containing stabilizing agent, 1 part of calcium stearate, 1 part of talc as a nucleating agent, 0.5 part of Celmic 1 33 as a decomposable foaming agent and one of the styrene-based copolymer resins S-2 to S--5 as described below as a foam-conditioning agent in an amount indicated in Table 12 below and the resin compositions were fabricated into foamed bodies in the form of a slab by extrusion molding with an extruder machine operated with the same operating conditions as in Example 8.

The thus obtained foamed bodies were examined for bulk density, cell structure, compression strength and flexural strength to give the results as set out in Table 1 2. In Experiments No. 149 and No.

1 50, premature expansion of the resin composition took place while still in the die leading to broken foams and remarkable shrinkage of the foamed bodies after molding.

Styrene-based copolymer resins: S-2: a copolymer resin composed of 70% by weight of styrene and 30% by weight of acrylonitrile and having a reduced viscosity of 2.0 dl/g at 250C.

S-3: a copolymer resin composed of 70% by weight of styrene and 30% by weight of acrylonitrile and having a reduced viscosity of 4.0 dl/g at 25"C S-4: a copolymer resin composed of 70% by weight of styrene and 30% by weight of acrylonitrile and having a reduced viscosity of 10.0 dl/g at 250C S--5:: a copolymer resin composed of 75% by weight of styrene and 25% by weight of acrylonitrile and having a reduced viscosity of 14.6 dVg at 250C As will be understood from the results given in Table 12, a styrene-based copolymer resin with a larger reduced viscosity as the foam-conditioning agent can give the advantages of improved gas retention or foam building, stabilization of foams and reduced shrinkage even when the amount of the resin admixed is relatively small whereas the use of a resin with a smaller reduced viscosity leads to broken foams and increased shrinkage after molding resulting in coarser cell structure, especially when .the amount of addition is insufficient.

TABLE 12

Experiment No. 144 145 146 147 148 149 150 Styrene-based resin S-3 S-4 S-4 S-4 S-5 S-2 S-4 (parts) (8.0) (2.0) (5.0) (25.0) (5.0) (5.0) (0.3) Bulk density, 0.045 0.059 0.044 0.053 0.042 0.16 0.19 g/ml Cell Properties structure A A A A A C C of foamed body Compression strength. 2.9 3.9 2.9 3.3 2.6 22.4 28.4 kg/cm2 Flexurat strength, 7.4 10.3 7.3 8.6 6.6 31.6 12.4 kg/cm2 EXAMPLE 13 (Experiments No. 1 51 to No. 1 56) Into an autoclave of 10 liter capacity made of stainless steel and equipped with a stirrer were introduced 3 kg of a homopolymeric polyvinyl chloride resin or a copolymer resin of vinyl chloride and vinyl acetate, of which the content of vinyl acetate was as given in Table 1 3 below, having an average degree of polymerization and a pore volume as given in the table, 5 kg of purified water, 1.5 g of a partially saponified polyvinyl alcohol and 600 g of trichlorofluoromethane, and 200 g of butane was introduced therein with pressurization followed by agitation at 700C for 8 hours to impregnate the resin with trichlorofluoromethane and butane as the volatilizable foaming agents. After completion of impregnation, cooling to room temperature and discharging of excess foaming agent, the resin was dehydrated by filtration and dried under air flow at 500C for 5 hours. Total amount of the foaming agents in the resin impregnated therewith was as given in Table 13.

Expandable resin compositions were prepared each by blending 100 parts of the above obtained resin impregnated with the volatilizable foaming agents, 2 parts of a tin-containing stabilizing agent, 1 part of calcium stearate, 1 part of talc as a nucleating agent, 0.5 part of Celmic 133 as a decomposable foaming agent and styrene-based resin of the kind as indicated in the table as a foam-conditioning agent in an amount also given in the table and the resin compositions were fabricated by extrusion molding into foamed bodies in the same manner as in Example 1 0. The bulk density and the condition of cell structure of these foamed bodies were as set out in Table 13.The foamed body in Experiment 1 55 exhibited shrinkage after molding to some extent and remarkable breakage of foams took place in Experiment No. 1 56 resulting in shrinkage of the foamed body after molding to a great extent.

As will be understood from the results given in Table 1 3, the styrene-based resin as the foamconditioning agent should desirably have a larger reduced viscosity when the vinyl chloride-based resin has a relatively large degree of polymerization. A foamed body of high expansion with a uniform cell structure can be obtained even with a vinyl chloride-based resin with no or a relatively small vinyl acetate content, which otherwise requires a relatively high fabricating temperature, by a suitable selection of the foam-conditioning agent.

On the other hand, a copolymer resin having a relatively low degree of polymerization can give a foamed body of high expansion even with a styrene-based resin as the foam-conditioning agent having a relatively low reduced viscosity when the content of vinyl acetate in the copolymer resin is large but a foamed body of high expansion can be obtained with difficulty with a copolymer resin of which the content of vinyl acetate is low.

TABLE 13

Experiment No. 151 152 153 154 155 156 Content of vinyl acetate, 5 10 0 10 10 0 PVC % by weight resin P 700 1500 750 800 1500 850 Vp.ml/g 0.021 0.033 0.037 0.021 0.033 0.038 Impregnation with foaming agent, 11.5 10.5 10.1 11.5 10.5 10.0 % by weight Styrene-based S-5 S-5 S-5 S-3 S-3 S-2 resin (parts) (6) (10) (10) (10) (10) (10) Bulk density, 0.043 0.059 0.055 0.050 0.073 0.15 Foamed g/ml body Cell structure A A A A A C

Claims

1. A resin composition expandable into a foamed body by heating which comprises (all OO parts by weight of a polyvinyl chloride-based resin having an average degree of polymerization not exceeding 2000 and a pore volume not exceeding 0.20 ml/g and (b) at least 1 part by weight of a volatilizable foaming agent selected from aliphatic hydrocarbon compounds and aliphatic halogenated hydrocarbon compounds having a boiling point not exceeding 900C and impregnated in said polyvinyl chloride-based resin.

2. A resin composition expandable into a foamed body by heating which comprises (a) 100 parts by weight of a polyvinyl chloride-based resin having an average degree of polymerization not exceeding 2000 and a pore volume not exceeding 0.20 ml/g, (b) at least 1 part by weight of a volatilizable foaming agent selected from aliphatic hydrocarbon compounds and aliphatic halogenated hydrocarbon compounds having a boiling point not exceeding 900C and impregnated in said polyvinyl chloride-based resin, (c) from 0.5 to 30 parts by weight of a foam-conditioning agent selected from acrylic resins and styrene-based resins, and (d) from 0.01 to 20 parts by weight of a nucleating agent.

3. The resin composition as claimed in claim 1 or claim 2 wherein the polyvinyl chloride-based resin is a copolymer resin composed of from 60 to 97% by weight of vinyl chloride and from 40 to 3% by weight of vinyl acetate.

4. The resin composition as claimed in claim 1, 2 or 3 wherein the polyvinyl chloride-based resin has an average degree of polymerization of at least 300.

5. The resin composition as claimed in claim 2 wherein the foam-conditioning agent has a reduced viscosity of at least 3.0 dl/g as measured in a chloroform solution of 0.1 9/100 ml concentration at 250C.

6. The resin composition as claimed in claim 2 or 5 wherein the nucleating agent is an inorganic powdery material having an average particle diameter not exceeding 30 foam.

7. The resin composition as claimed in claim 2 or 5 wherein the nucleating agent is a combination of an acid which is solid at room temperature and a carbonate or hydrogencarbonate of sodium, potassium orammonium.

8. The resin composition as claimed in claim 7 wherein the acid which is solid at room temperature is boric acid or an organic acid selected from citric acid, tartaric acid and oxalic acid.

9. The resin composition as claimed in claim 2, 5, 6, 7 or 8 wherein the acrylic resin is a polymethyl methacrylate.

1 0. The resin composition as claimed in claim 2, 5, 6, 7 or 8 wherein the acrylic resin is a copolymer resin composed of methyl methacrylate and at least one acrylic ester selected from the group consisting of alkyl acrylates and alkyl methacrylates other than methyl methacrylate.

1

11. The resin composition as claimed in claim 10 wherein the content of methyl methacrylate in the copolymer resin is in the range from 60 to 95% by weight.

12. The resin composition as claimed in claim 2 or any one of claims 5 to 11 wherein the styrene based resin is a copolymer resin composed of from 90 to 40% by weight of styrene and from 10 to 60% by weight of a comonomer copolymerizable with styrene.

13. The resin composition as claimed in claim 12 wherein the comonomer copolymerizable with styrene is acrylonitrile.

14. The resin composition as claimed in any one of claims 2 to 12 which further comprises a decomposable foaming agent in an amount not exceeding 5 parts by weight.

1 5. The resin composition as claimed in claim 1 substantially as described in any of the Experiments.

1 6. A foamed body made from a resin composition as claimed in any preceding claim.