Process for producing thermoplastic resin foam

In producing a foam by foaming a melt-plasticized styrene/maleic anhydride copolymer resin, a process for producing a highly foamed styrene/maleic anhydride copolymer resin foam characterized by using as the blowing agent at least one compound selected from the group consisting of a carboxylate of a metal of group Ia of the periodic table of elements, a carbonate of a metal of group Ia, a carboxylate of a metal of group IIa and a carbonate of a metal of group IIa; or by first blending with said copolymer resin at least one compound selected from the group consisting of a carboxylate of a metal of group Ia of the periodic table of elements, a carbonate of a metal of group Ia, a carboxylate of a metal of group IIa and a carbonate of a metal of group IIa, then melt-blending the mixture, followed by extruding and granulating the blend to form a pre-expanded granular product, and thereafter foaming the granular product thus obtained.

This invention relates to a process for producing a highly foamed 
styrene/maleic anhydride copolymer resin foam. 
In producing a thermoplastic resin foam say by the extrusion molding 
technique, the usual process for obtaining the desired shaped article 
comprises extruding a blowing agent-containing melt-plasticized resinous 
composition from a pressurized state into an atmosphere of normal pressure 
thereby effecting the expansion of the resinous composition by its change 
in pressure. 
Polystyrene and polyethylene are well known as being typical all-purpose 
thermoplastic resins for use in the foregoing process. Especially in the 
case of polystyrene, since the dependence on temperature of its melt 
viscosity is small and thus low-temperature extrusion is possible, not 
only the choice of the blowing agent is simplified, but also a viscosity 
suitable for foaming can be readily obtained. It is hence possible to form 
highly foamed products relatively easily by the use of a low-boiling 
blowing agent. Usable as this blowing agent are the inert gases such as 
carbon dioxide, nitrogen and helium, saturated aliphatic hydrocarbons of 
up to 8 carbon atoms such as methane, ethane, propane, butane and pentane, 
the halogenated hydrocarbons such as methylene chloride and Freon, 
saturated alicyclic hydrocarbons such as cyclohexane ethylcyclopentane, 
aromatic hydrocarbons such as benzene and xylene, ketones such as acetone 
and methyl ethyl ketone, and petroleum ethers, etc. 
In using a low-boiling blowing agent, a costly apparatus for metering the 
high-pressure gas to be introduced into the extruder from a cylinder is 
required. Further, care must be exercised to ensure against such hazards 
as explosions and poisoning resulting from the leakage of the blowing 
agent gas. 
On the other hand, there are available inorganic and organic chemical 
blowing agents, which do not require the use of costly apparatuses and in 
which there is practically no need to consider such hazards as explosions 
and poisoning. Inorganic chemical b-owing agents that are usually used 
include, for example, sodium hydrogencarbonate, ammonium carbonate, 
ammonium hydrogencarbonate, sodium borohydride and light metals (e.g. Mg, 
Zn and Al). On the other hand, the usually used organic chemical blowing 
agents include, for example, azodicarbonamide, azobisformamide, 
azobisisobutyronitrile, diazoaminobenzene, 
N,N'-dinitrosopentamethylenetetramine, 
N,N'-dimethyl-N,N'-dinitroterephthalamide, benzenesulfonyl hydrazide, 
p-toluenesulfonyl hydrazide and p,p'-oxybisbenzenesulfonyl hydrazide. 
However, in the method which uses these chemical blowing agents the 
blowing agent forms cells by the separation and association of the gas in 
solution in the resin, with the consequence that there is no quenching and 
hardening of the membranes of the cells. Hence, the permeability of the 
gas evolved is great, and thus a highly foamed product cannot be readily 
obtained. 
Our extensive styrene/maleic with the view of obtaining a highly foamed 
product free of the aforementioned drawbacks of the prior art led to the 
discovery that by using a dry blended resinous composition consisting of a 
styrele/maleic anhydride copolymer resin and as a blowing agent at least 
one compound selected from the group consisting of a carboxylate of a 
metal of group Ia of the periodic table of elements, a carbonate of a 
metal of group Ia, a carboxylate of a metal of group IIa and a carbonate 
of a metal of group IIa and foaming this composition by say extrusion 
molding, it was possible to obtain a highly foamed product having an 
expansion ratio of at least 8 times, an expansion ratio impossible of 
attainment by the use of conventional chemical blowing agents. 
Specifically, in accordance with the present invention, 0.1-10% by weight, 
preferably 0.5-5% by weight, of the aforesaid blowing agent that has been 
rendered into a powdered state in advance and 99.9-90% by weight, 
preferably 99.5-95% by weight, of a styrene/maleic anhydride copolymer 
resin optionally added a small quantity of a mineral oil are dry blended, 
after which the blend is heat-melted and foamed say by extrusion molding 
or injection molding to give a foamed product. It is thus possible to 
obtain a highly foamed product by the blowing gas that evolves as a result 
of the reaction between the styrene/maleic anhydride copolymer resin and 
the blowing agent. 
Now, as regards the processes for producing the foams of the aforementioned 
thermoplastic resins inclusive of the styrene/maleic anhydride copolymer 
resin, in the case of say the usually employed extrusion molding method, 
there is (1) the so-called two-stage method which comprises first 
preparing a foamable resin by impregnating the resin with a low-boiling 
blowing agent such as the aforementioned freon, butane or pentane and 
thereafter feeding the so prepared foamable resin to the extruder where it 
is foamed to yield the intended foamed product or (2) the so-called 
one-stage method in which the foamed product is obtained either by 
introducing a low-boiling blowing agent such as described above into a 
melt-plasticized resin and extruding the blend while kneading it under 
pressure or by blending with the resin a chemical blowing agent that 
evolves either nitrogen or carbon dioxide, such as the aforementioned 
azodicarbonamide or sodium hydrogencarbonate, and feeding this blend to 
the extruder for extrusion therefrom. 
In the case of the two-stage method described above, it is necessary that 
the foamable resin be prepared into foamable particles of uniform particle 
size before feeding it to the extruder. It is hence a disadvantage from 
the standpoint of the total cost involved because of the additional 
investment in the required equipment. On the other hand, in the case of 
the direct blowing agent injection system such as the one-stage method 
described hereinabove, this also has is shortcomings. Not only is there 
required a costly equipment such as an apparatus for injecting the blowing 
agent, but also there is the need to exercise special care to ensure 
against the hazards of explosion or poisoning due to leakage of the gas 
that is to become the blowing agent. Above all, in the case where the 
method that uses the aforementioned chemical blowing gents is adopted, the 
expansion ratio is at most about 3 times. There was thus the drawback that 
highly foamed products could not be obtained. 
After having discovered the basic method of obtaining a highly foamed 
product by thc use of a specified compound as the blowing agent, as 
hereinbefore described, we furthered our research concerning embodiments 
thereof. As a result thereof, we found a much more advantageous process, a 
process by which all of the shortcomings of the conventional methods could 
be eliminated. 
There is thus provided in accordance with this invention a process that is 
operated in the following manner. The aforesaid blowing agent is blended 
with a styrene/maleic anhydride copolymer resin in a 
hereinbefore-indicated proportion. The blend thus obtained is fed to an 
extruder where it is uniformly melt-blended and extruded from a pellet die 
of the extruder at such a temperature as to obtain an expansion ratio of 
not greater than 2.0 times, and preferably not greater than 1.5 times. The 
resulting preexpanded pellets are then fed to a usual foaming apparatus to 
yield the intended highly foamed product. 
The term "styrene/maleic anhydride copolymer resin", as used herein, 
denotes a copolymer resin that is obtained by heat-polymerizing monomeric 
styrene with maleic anhydride in the presence of a chain transfer agent 
and a radical generator. Such a styrene/maleic anhydride copolymer resin 
(SMA resin) can be specifically produced by say a procedure comprising 
adding to a ketonic solvent such as acetone or methyl isobutyl ketone a 
monomeric mixture of styrene and maleic anhydride in a mole ratio of 
1.4-49, preferably 4.6-17.0, with a known radical generator and a chain 
transfer agent, followed by carrying out the heat-polymerization reaction 
at 60.degree.-180.degree. C., preferably 75.degree.-140.degree. C., and 
thereafter precipitating the resulting polymer using say a poor solvent 
such as petroleum benzene or methanol. The SMA resin may be one that has 
been granulated by means of an extruder after having been added an 
antioxidant, as required. 
Suitably used as this SMA resin is one having a weight average molecular 
weight (Mw) of preferably 100,000-40O,OOO, and more preferably 
150,000-300,000 as measured by gel permeation chromatography, i.e. GPC 
based on a polystyrene standard method. 
The metals of group Ia are typically lithyium, sodium and potassium, while 
the metals of group IIa are magnesium, calcium and strontium. Typical 
examples of the carboxylic acids are aliphatic monocarboxylic acids such 
as formic acid, acetic acid, propionic acid, butyric acid, caprylic acid, 
capric acid, lauric acid, stearic acid and myristic acid; aliphatic 
saturated or unsaturated dicarboxylic acids such as oxalic acid, malonic 
acid, succinic acid, glutaric acid, maleic acid, fumaric acid and 
glutaconic acid; hydroxymonocarboxylic acids such as glycollic acid, 
lactic acid, ethylenelactic acid and glyceric acid; hydroxypolycarboxylic 
acids such as malic acid, tartaric acid and citric acid; and aromatic 
carboxylic acids such as benzoic acid and terephthalic acid. Typical 
carbonates are say sodium carbonate potassium carbonate and sodium 
hydrogencarbonate. 
While this sodium hydrogencarbonate strictly speaking is a 
hydrogencarbonate, it forms as a result of thermal decomposition sodium 
carbonate in the following manner. 
EQU 2NaHCO.sub.3 .fwdarw.Na.sub.2 CO.sub.3 +CO.sub.2 +H.sub.2 O 
Hence, in the process of this invention it is considered to be a substance 
having effects equal to a carbonate of an alkali metal. 
Further, since sodium hydrogencarbonate evolves carbon dioxide on thermal 
decomposition, it is possible to consider it to be one of the so-called 
chemical blowing agents. However, this carbon dioxide does not possess any 
substantial effect in obtaining the highly foamed product of aforesaid SMA 
resin. 
The carboxylates and carbonates are used as blowing agents in this 
invention either independently of each other or in combination. Of these 
blowing agents, those containing water of crystallization are especially 
preferred. 
Further, it is preferred to add to the SMA resin as a wetting agent a 
mineral oil such as CARNATION (a product of Witco Chemical Corp. U.S.A.) 
or as a lubricant a metallic soap such as zinc stearate in practicing the 
process of this invention. Such nucleating agents as talc, calcium 
silicate and kaolin can also be added, as required. These nucleating 
agents should preferably be of the finest possible particle size for 
achieving a uniform mixture with the blowing agent. Usually preferred is a 
powder having particles of diameter of the order of 0.1-10 microns. These 
additives should be added to the SMA resin prior to the addition of the 
blowing agent. 
In practicing the process of this invention, it is preferred that an 
auxiliary foaming agent be added. As such an auxiliary foaming agent, 
mention can be made of the inorganic salts having water of crystallization 
whose dehydration temperature is relatively close to the extrusion die 
temperature, such as CaSO.sub.4.2H.sub.2 O (dehydration temperature 
163.degree. C.), Na.sub.2 SO.sub.4.9 1OH.sub.2 O (dehydration temperature 
100.degree. C.), and CaHPO.sub.4.2H.sub.2 O. 
These auxiliary foaming agent serve to slow down the reaction between the 
blowing agent and the SMA resin to a still greater degree and thus cause 
the reaction-evolved carbon dioxide to remain in the resin for a maximum 
period of time. 
In carrying out the process of this invention, the setting of the expansion 
ratio of the pre-expanded pellets and the choice of the extrusion die to 
be used in the secondary foaming operation are important factors, since 
these factors greatly influence the expansion of the final foamed product. 
In the first place, the extrusion temperature for obtaining the 
pre-expanded pellets should preferably be low for restraining the 
pre-expansion as much as possible. A temperature in the neighborhood of 
130.degree.-140.degree. C. is usually used. On the other hand, the 
pre-expansion ratio, as previously indicated, should preferably be not 
greater than 2 times. 
The foaming method by means of an extrusion die for carrying out the 
secondary foaming include such methods as the T-die extrusion molding 
method, the circular die extrusion incision method or circular die 
extrusion press-adhesion method, or the fish tail die extrusion molding 
method. Any of these known methods can be used in carrying out the process 
of this invention. The intended final expansion ratio should preferably 
range from 5 to 20 times. 
The SMA resin foam thus obtained can be utilized for such applications as 
insulating boards, various lagging materials and building materials such 
as panels. Above all, it is expected to find use as a structural material 
possessing superior heat resistance. 
The following examples and comparative examples will serve to illustrate 
the present invention more specifically. Unless otherwise specified, the 
parts and percentages used in the examples are on weight basis.

EXAMPLE 1 
A styrene/maleic anhydride copolymer resin (990 g) having a melt flow rate 
(MFR) of 1.2 g/10 min (JIS Method K7210-1976, load: 5 kg, temperature: 
200.degree. C.) whose surface was coated with a small quantity of a 
mineral oil, and 10 g of powdered sodium acetate (Wako 1st grade, produced 
by Wako Jyunyaku Kogyo Co., Ltd., Japan) were thoroughly blended. The 
resulting blend was molded by extruding it through an extruder having a 
cylinder of 26-mm diameter [manufactured by Sanjo Seiki Co., Ltd., Japan, 
length/diameter ratio (L/D)=14, compression ratio 2.2] under the 
conditions of die temperature: 125.degree. C., C.sub.1 : 225.degree. C., 
C.sub.2 : 180.degree. C., and screw rotation speed: 40 rpm. 
The foam thus molded by extrusion had a satisfactory skin layer at its 
surface and was one whose interior was made up of minute cells 0.1-0.3 mm 
diameter. The expansion ratio of this foam was 9.8 times, this being 
calculated as follows: 
##EQU1## 
(This expansion ratio will apply equally in the following examples.) 
EXAMPLE 2 
Example 1 was repeated but using a styrene/maleic anhydride copolymer resin 
having an MFR of 0.41 g/10 min (maleic anhydride content 15%). The 
extrusion-molding was otherwise carried out as in Example 1. 
The foam thus extrusion molded had a satisfactory skin layer at its surface 
and its interior was made up of minute cells 0.1-0.3 mm diameter. Its 
expansion ratio was 14 times. 
EXAMPLE 3 
The extrusion-molding operation was carried out as in Example 1, except 
that 970 g of a styrene/maleic anhydride copolymer resin having an MFR of 
0.41 g/10 min and as the blowing agent 30 g of sodium oxalate (Wako 1st 
grade, produced by Wako Jyunyaku Kogyo Co., Ltd.) were used. 
The thus extrusion-molded foam had a satisfactory skin layer at its 
surface, while its interior was made up of fine cells 0.2-0.5 mm diameter. 
The expansion ratio was 9.2 times. 
EXAMPES 4 
Example 3 was repeated but changing the amount used of the styrene/maleic 
anhydride copolymer resin to 990 g and using as blowing agent 10 g of 
sodium lactate instead of sodium oxalate. The resulting extrusion-molded 
foam had a good skin layer at its surface, and its interior was made up of 
fine cells 0.2-0.5 mm diameter. Its expansion ratio was 8.5 times. 
EXAMPLE 5 
The extrusion-molding was carried out by operating as in Example 3 but 
using instead of sodium oxalate an equal amount of sodium tartrate (Wako 
1st grade, a product of Wako Jyunyaku Kogyo Co., Ltd.). The resulting foam 
had a good skin layer at its surface, and its interior was made up of 
minute cells 0.2-0.5 mm diameter. The expansion ratio of this foam was 9.0 
times. 
EXAMPLE 6 
The experiment was operated as in Example 4, except that instead of sodium 
lactate an equal amount of sodium benzoate (Wako 1st grade, a product of 
Wako Jyunyaku Kogyo Co., Ltd.) was used. The resulting foam had a 
satisfactory skin layer at its surface, and its interior was made up of 
0.1-0.4 mm diameter fine cells. The expansion ratio of this foam was 8.3 
times. 
EXAMPLE 7 
Example 4 was repeated but using instead of sodium lactate an equal amount 
of magnesium acetate (Wako 1st grade, Wako Jyunyaku Kogyo Co., Ltd.). The 
resulting foam had a good skin layer at its surface, while its interior 
was made up of minute cells 0.2-0.5 mm diameter. The expansion ratio of 
the foam was 13 times. 
EXAMPLE 8 
The experiment was operated as in Example 3 but using instead of sodium 
oxalate an equal amount of calcium oxalate. The resulting foam had a 
satisfactory skin layer at its surface, and its interior was made up of 
fine cells 0.2-0.5 mm diameter. The expansion ratio of this foam was 9.2 
times. 
COMATIVE EXAMPLE 1 
The extrusion-molding operation was carried out as in Example 1, except 
that the blowing agent used was changed to lead acetate (Wako 1st grade, a 
product of Wako Jyunyaku Kogyo Co., Ltd.). The extrusion-molded foam had a 
satisfactory skin layer at its surface, but its interior was made up of 
relatively large cells, and the expansion ratio was 3.2 times. 
COMATIVE EXAMPLE 2 
The extrusion-molding operation was carried out as in Example 1, except 
that the resin used was changed to DIC STYRENE XC-510 having an MFR of 1.6 
g/10 min (a styrene resin produced by Dainippon Ink & Chemicals, Inc., 
Japan). The extrusion-molded foam had a rough surface, and its interior 
foaming was irregular. Moreover, its expansion ratio was 1.5 times. 
EXAMPLE 9 
The extrusion-molding operation was carried out as in Example 1 but using 
instead of sodium acetate an equal amount of sodium carbonate (Wako 1st 
grade, a product of Wako Jyunyaku Kog yo Co., Ltd.). The resulting foam 
had a good skin layer at its surface, and its interior was made up of 
0.2-0.5 mm diameter fine cells. The expansion ratio of this foam was 10 
times. 
EXAMPLE 10 
Example 2 was repeated but using instead of sodium acetate an equal amount 
of sodium carbonate (the same as that used above). The foam thus obtained 
had a satisfactory skin layer at its surface, and its interior was made up 
of fine cells 0.1-0.3 mm diameter. The expansion ratio was 13 times. 
EXAMPLE 11 
The extrusion-molding operation was carried out as in Example 1, except 
that the styrene/maleic anhydride copolymer resin used was one having an 
MFR of 0.41 g/10 min, which was used in an amount of 970 g, and the 
blowing agent was changed to 30 g magnesium carbonate (Wako 1st grade, a 
product of Wako Jyunyaku Kogyo Co., Ltd.). 
The extrusion-molded foam had a satisfactory skin layer at its surface, and 
its interior was made up of fine cells 0.2-0.5 mm diameter. Its expansion 
ratio was 11 times. 
EXAMPLE 12 
Example 11 was repeated but using instead of magnesium carbonate an equal 
amount of sodium hydrogencarbonate. The foam thus obtained had a 
satisfactory skin layer at its surface, while its interior was made up of 
0.2-0.5 mm diameter cells. The expansion ratio of this foam was 15 times. 
EXAMPLE 13 
The extrusion-molding operation was carried out as in Example 1, except 
that the molding machine used was changed to a 1-ounce in-line screw type 
injection molding machine (manufactured by Sanjo Seiki Co., Ltd., Japan), 
and sodium acetate was changed to an equal amount of sodium carbonate. The 
expansion ratio of the resulting foam was 2.3 times. The molding 
temperature conditions in this case were: C.sub.1 =225.degree. C., C.sub.2 
=200.degree. C., and nozzle=180.degree. C. 
EXAMPLE 14 
Example 13 was repeated but using instead of sodium carbonate an actual 
amount of sodium hydrogencarbonate. The expansion ratio of the resulting 
foam was 2.6 times. 
EXAMPLE 15 
A styrene/maleic anhydride copolymer resin (970 g) having an MFR of 0.41 
g/10 min whose surface was coated with a small quantity of oil was 
thoroughly blended with 15 g of powdered sodium carbonate and 15 g of 
sodium acetate, after which the blend was extruded through a 26-mm 
diameter extruder. 
The resulting foam had a good skin at its surface, and its interior was 
made up of 0.2-0.5 mm diameter minute cells. The expansion ratio of the 
form was 14 times. 
COMATIVE EXAMPLE 3 
The extrusion molding was carried out by operating as in Example 9, except 
that instead of sodium carbonate an egual amount of an iron carbonate 
(Wako 1st grade, a product of Wako Jyunyaku Kogyo Co., Ltd.) was used. 
The extrusion-molded foam had a satisfactory skin layer at its surface, but 
its interior was made up of relatively large cells, and its expansion 
ratio was 1.7 times. 
COMATIVE EXAMPLE 4 
The extrusion-molding operation was carried out as in Example 9, except 
that the resin used was changed to DIC STYRENE XC-510 whose MFR was 1.6 
g/10 min. 
The surface of the extrusion-molded foam was rough, and its interior 
foaming was irregular. Its expansion ratio was 1.5 times. 
COMATIVE EXAMPLE 5 
The extrusion molding was carried out as in Example 12, except that the 
resin used was changed to DIC STYRENE XC-510. The surface of the resulting 
foam was rough, and its interior foaming was also irregular. Its expansion 
ratio was 3 times. 
COMATIVE EXAMPLE 6 
The extrusion molding was carried out as in Example 13 but using as the 
resin DIC STYRENE XC-510. Scarcely any foaming took place in the product, 
the expansion ratio being only 1.1 times. 
COMATIVE EXAMPLE 7 
The extrusion molding was carried out as in Example 14, except that the 
resin used was changed to DIC STYRENE XC-510. There was scarcely any 
foaming in the resulting product, the expansion ratio being only 1.5 
times. 
EXAMPLES 16-19 AND COMATIVE EXAMPLES 8-10 
One hundred parts each of Dylark #232 and Dylark #332 (SMA resins produced 
by ARCO/Polymers Inc., U.S.A.) and DIC STYRENE CR-4500 (polystyrene 
produced by Dainippon Ink & Chemicals, Inc.), after having coated their 
surface with the spreading agents indicated in Table 1, were mixed with 
the alkali metal salts, lubricants, nucleating agents and auxiliary 
foaming agents indicated in said table in the amounts shown therein. The 
several mixtures were then melt-blended, after which the several blends 
were extruded through a 26 mm diameter extruder (manufactured by Sanjo 
Seiki Co., Ltd., Japan; L/D=14, compression ratio 2.2 and having two 3 mm 
diameter rod dies). The extrudate was pelleted by cutting it at a point 
2-3 mm from the outlet of the die followed by quenching the so formed 
pellets. Pre-expanded pellets whose foaming has been restrained were thus 
obtained. The pelleting conditions were as follows: 
______________________________________ 
C.sub.1 C.sub.2 Die 
______________________________________ 
Temperature 225.degree. C. 
150.degree. C. 
130.degree. C. 
Screw rotation speed 
40 r.p.m. 
Quenching conditions 
Water-cooled 
______________________________________ 
The several pellets thus obtained were then severally foamed using a 
circular die extruder (manufactured by Union Plastics Co., Ltd., Japan, 50 
mm diameter, L/D=24, compression ratio 36; die 23 mm (outside 
diameter/17.9 mm (inside diameter)). There was thus formed tubular foams. 
In this case the distance between the die and sizer was set at 500-1000 
mm, and the following extrusion conditions were employed. 
______________________________________ 
C.sub.1 
C.sub.2 C.sub.3 Flange 
D.sub.1 
D.sub.2 
______________________________________ 
Temperature 
210.degree. C. 
170.degree. C. 
150.degree. C. 
165.degree. C. 
155.degree. C. 
155.degree. C. 
Screw 50 r.p.m. 
rotation speed 
Die pressure 
350-430 kg/cm.sup.2 
______________________________________ 
As is apparent from Table 1, the products of this invention (Examples 
16-19) showed far greater expansion ratios than the product of Comparative 
Example 8 (two-stage extrusion product of polystyrene). The expansion 
ratios of the invention products also exceeded those of the products of 
Comparative Examples 9 and 10 (commercially available foams). 
TABLE 1 
__________________________________________________________________________ 
Foaming compound Expansion 
DIC Sodium 
Sodium Nucle- 
Auxiliary 
ratio 
Expansion 
Dylark Dylark 
Styrene 
Sodium 
car- 
hydrogen- 
Lubri- 
Wetting 
ating 
foaming 
prefoamed 
ratio of 
#232 #332 
CR-4500 
acetate 
bonate 
carbonate 
cant 
agent 
agent 
agent 
pellets 
foam 
__________________________________________________________________________ 
Example 16 
100 1.0 0.5 0.05 1.5 0.3 2.0 15.0 
Example 17 
100 1.0 0.5 0.05 1.5 0.3 2.0 18.0 
Example 18 
100 1.0 0.5 0.05 1.5 0.3 2.0 14.0 
Example 19 
100 1.0 0.5 0.05 1.5 0.3 2.0 16.0 
Compar- 100 1.0 0.5 0.05 1.5 0.3 1.2 1.5 
ative 
example 8 
Compar- 
Commercial product (polystyrene-type closed cellular 
--ticle 
8.5 
ative which used low-boiling foaming agent) 
example 9 
Compar- 
Commercial product (polystyrene-type closed cellular 
--ticle 
10.0 
ative which used low-boiling foaming agent) 
example 10 
__________________________________________________________________________ 
Lubricant: zinc stearate 
Wetting agent: CARNATION 
Nucleating agent: CROWN TALC (P2, particle diameter 8.5 microns, produced 
by Matsumura Sangyo Co., Ltd., Japan) 
Auxiliary foaming agent: CaSO.sub.4.2H.sub.2 O 
EXAMPLES 20-24 
The experiments were carried out by operating as in Examples 16-19 and 
Comparative Examples 8-10, except that the foaming compounds were changed 
as shown in Table 2. As shown in Table 2, products of high expansion 
ratios of the order of 11-15 were obtained in all of the examples. 
TABLE 2 
__________________________________________________________________________ 
Expansion 
Cal- Lub- 
Wet- 
Nucle- 
Auxiliary 
ratio 
Expansion 
Dylark Dylark 
cium 
Sodium 
Sodium 
Sodium 
Magnesium 
ri- 
ting 
ating 
foaming 
prefoamed 
ratio of 
#232 #332 
oxalate 
lactate 
tartrate 
benzoate 
carbonate 
cant 
agent 
agent 
agent 
pellets 
foam 
__________________________________________________________________________ 
Exam- 1.0 1.5 
0.1 3.0 0.3 2.0 14.0 
ple 20 
Exam- 
100 1.0 1.5 
0.1 3.0 0.3 2.0 13.0 
ple 21 
Exam- 100 1.0 1.5 
0.1 3.0 0.3 1.4 11.0 
ple 22 
Exam- 100 1.0 1.5 
0.1 3.0 0.3 1.3 12.0 
ple 23 
Exam- 100 1.0 1.5 
0.1 3.0 0.3 1.5 14.0 
ple 24 
__________________________________________________________________________ 
Nucleating agent: HAKUENKA CCR (particle diameter 0.08 micron, produced b 
Shiraishi Calcium Co., Ltd., Japan) 
Auxiliary foaming agent: CaHPO.sub.4.2H.sub.2 O 
The wetting agent and lubricant were the same as those indicated 
hereinbefore.