JPH0755531B2 - Method for producing thermoplastic polyester resin foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a thermoplastic polyester resin foam. More specifically, the present invention relates to a method for producing a thermoplastic polyester resin foam by extrusion foaming using a multi-nozzle die in which a large number of small holes are formed in one die.

(Prior art) Thermoplastic polyester resin (hereinafter referred to as PAT)
Has excellent properties not found in polystyrene or polyethylene. For example, PAT has high rigidity and good formation stability, and has excellent heat resistance to withstand 200 ° C. Therefore, it was planned to foam PAT to make a tough heat insulating material with good heat resistance, a cushioning material, and a structural material.

PAT is a type of thermoplastic resin. When a thermoplastic resin is used as the material, it is known to make a foam using a multi-nozzle die. It is, for example, Japanese Patent Publication Sho 35-10.
518, Japanese Patent Publication No. 53-30744, Japanese Patent Publication No. 56-12499
And Japanese Patent Publication No. 61-17646.

In these publicly known, if it is a thermoplastic resin, it is explained that all can be extruded and foamed by the multi-nozzle die, but it is possible to extrude from the multi-nozzle die to actually make a satisfactory foam. It is limited to the case of using styrene-based, methacrylic-based, olefin-based, polyamide-based, and vinyl chloride-based resins as the resin. In other words, when PAT was used as the thermoplastic resin, it was impossible to form a foam by extruding from the multi-nozzle die to foam and then extruding each of them to fuse with each other. This is because unlike styrene resins, PAT is a resin that is difficult to foam. It is well known that PAT is difficult to foam. This is because PAT is a crystalline resin and rapidly changes into a liquid with low viscosity when heated. That is, in general, in order to extrude foam from a die and foam it, the extruded resin has a viscosity suitable for foaming, and it is necessary to vaporize the foaming agent in the resin to generate bubbles. However, PAT does not exhibit such a viscosity and rapidly decreases with increasing temperature, so it is difficult to maintain a viscosity suitable for foaming, and when the viscosity decreases, the foaming agent This is because the gas that works as is immediately released.

Therefore, it is possible to make some improvements to the PAT, change the extrusion operation, extrude the PAT from the multi-nozzle die to foam, and fuse the extruded foams to each other to form an integral foam. Was requested.

(Problems to be Solved by the Invention) The present invention has been made to meet the above-mentioned demand. That is, the present invention is a PAT extruded and foamed using a multi-nozzle base, and the PAT extruded from each nozzle.
This was done in order to obtain an integrated PAT foam by foaming the string-like bodies and fusing them together.

(Means for Solving the Problems) The present inventor uses a multi-nozzle die to extrude and foam PAT to produce a good foam, and to arrange the nozzles in the multi-nozzle die and the die swell ratio in the PAT. It has been found that appropriate adjustment is necessary. That is, it is necessary that the nozzles are provided with a certain size and close to each other as the die, and as the PAT, the die swell ratio has a certain value under the extrusion condition. It has been found that the above is necessary. The present invention was made based on such knowledge.

The die swell ratio generally means a ratio of the extruded resin swelling in a direction perpendicular to the extruding direction immediately after exiting the die when the resin is extruded into the atmosphere in a molten state.
The standard for expressing the die swell ratio is not defined. Therefore, in the present invention, a method for defining this is defined for convenience. This method heats and melts PAT to a temperature 30 ° C higher than the crystal melting point of PAT, and extrudes it into the atmosphere at a rate of 5.0 kg / hr from a circular hole with a diameter of 5 mm and a length of 40 mm,
The ratio of the extruded resin to swell in the direction perpendicular to the extrusion direction was defined as the die swell ratio.

The multi-nozzle ferrule requires certain conditions for the nozzle arrangement. The conditions are the nozzle opening area ratio and the nozzle dispersion state. Among them, the nozzle opening area ratio is the ratio of the total nozzle cross-sectional area in front of the die to the nozzle dispersion area. Here, the nozzle dispersed area will be described with reference to FIG. This multi-nozzle base is constructed by fitting a base plate 3 having a large number of nozzles 32 formed therein to the outer peripheral portion 2 of the base. In this case, the nozzle dispersion area is defined by the alternate long and short dash line A that surrounds and surrounds the nozzle 32.
The area of When the nozzle dispersion area is defined in this manner, the present invention requires that the ratio of the total nozzle cross-sectional area to the nozzle dispersion area is within the range of 1/6 to 1/36.

As for the dispersed state of the nozzles, the center distance between the nozzles needs to be within a range of 2 to 15 times the average diameter of the nozzles. The reason is as follows. First, if the center distance between the nozzles is smaller than twice the average diameter of the nozzles, not only a product with a large cross-sectional area cannot be obtained, but also a product with a large expansion ratio is difficult to obtain. When the distance in one direction is twice or less and the distance in the other direction is increased in order to increase the expansion ratio, the foam discharged from the nozzle becomes a flatly fused product, and the strength difference depending on the direction increases. Also, the center distance between the nozzles is 15 of the average diameter of the nozzles.
If it is more than double, large voids are generated in the product, resulting in a product with low strength.

(Summary of the Invention) The present invention relates to a method of melting PAT containing a foaming agent and extruding it from a multi-nozzle die, concentrating the string-like foam extruded from each nozzle and fusing them together to form an integral foam. , PAT with foaming agent and cross-linking agent added to resin
Increase the die swell ratio of the
It is heated to a high temperature and melted, the diameter is 5 mm and the length is 40 m
Using a resin with a die swell ratio of 3 or more when extruded at a rate of 5.0 kg / hr from a circular hole of m, the total nozzle cross-sectional area in front of the die as a multi-nozzle die is 6 minutes of the nozzle dispersion area. Use a die that occupies 1 to 1/36 and the center distance between the nozzles is in the range of 2 to 15 times the average diameter of the nozzles. From this die, the foamable resin is 5 ° C to 30 ° C above the crystalline melting point. The present invention provides a method for producing a PAT foam, which comprises extruding at a temperature as high as possible to foam and fuse together.

(Explanation of Requirements) PAT which can be used in the present invention is a high molecular weight chain polyester obtained by reacting an aromatic dicarboxylic acid with a dihydric alcohol. As the dicarboxylic acid,
Although terephthalic acid is most often used, isophthalic acid, 2,6-naphthalenedicarboxylic acid can also be used. Others, diphenyl ether dicarboxylic acid,
Diphenyl sulfone dicarboxylic acid and diphenoxy dicarboxylic acid can also be used. Further, ethylene glycol is mainly used as the dihydric alcohol,
Trimethylene glycol, tetramethylene glycol,
Neopentylene glycol, hexamethylene glycol, cyclohexane dimethylol, tricyclodecane dimethylol, 2,2-bis- (4-β-hydroxyethoxyphenyl) propane, 4,4′-bis- (β-hydroxyethoxy) diphenyl Sulfone and diethylene glycol can also be used. Such PAT is commercially available. In the present invention, commercially available PAT can be used.

Of the above PATs, those suitable for use in this invention are:
Examples thereof include polyethylene terephthalate, polybutylene terephthalate, polybutylene terephthalate elastomer, non-crystalline polyester and polycyclohexane terephthalate. The above PATs can be used alone or in combination. The above-mentioned PAT can be used by mixing it with another resin. When other resins are mixed and used, the amount of the other resins needs to be less than that of PAT.

Since PAT is a crystalline resin, it has a crystalline melting point. The crystal melting point differs depending on the kind of the aromatic dicarboxylic acid that constitutes PAT and the dihydric alcohol. But,
The crystalline melting point of PAT is in the range of approximately 220 to 300 ° C.

In the present invention, it is necessary to select and use a PAT having a large die swell ratio. In that case, the one with a large die swell ratio means that the expandable PAT obtained by adding a foaming agent and a cross-linking agent to PAT is heated to a temperature higher by 30 ° C. than its crystal melting point and melted, and has a long diameter of 5 mm. The diameter is 3 times or more when extruded from a 40 mm circular hole at a rate of 5.0 kg / hr. Extrusion conditions consisting of PAT heating temperature, circular hole size and extrusion ratio defined above are
As described above, this is arbitrarily set by the inventor. This is because, as described above, a general condition suitable as a standard for determining the die swell ratio was not found.

To describe this easily, the die swell ratio is the rate at which when the PAT is extruded into the atmosphere under the conditions described above, the extruded PAT is released from the pressure and swells. For example, if the nozzle is a circular hole, its diameter is d, and the maximum diameter of the extruded string-shaped PAT that it has cooled is D, the die swell ratio is the quotient of D divided by d.

The die swell ratio is changed by adding other additives to PAT.

In order to actually measure the die swell ratio of PAT containing no foaming agent, a die C having a circular hole whose cross section is shown in FIG. 2 is used, and this die is extruded as shown in FIG. Attached to the tip of the machine, extruded PAT at a rate of 5.0 kg / hr at a temperature 30 ° C higher than the crystal melting point of PAT, and extruded PAT into a water tank E of 25 ° C from a height of 1000 mm, and extruded PAT.
When the string-shaped body reaches the bottom of the water tank E, the string-shaped body is cut, the maximum cross-sectional area of the obtained string-shaped body is measured, and the diameter thereof is calculated, which is defined as pmm. The quotient obtained by dividing the value of p thus obtained by the value of the nozzle diameter of 5 mm in front of the die is defined as the die swell ratio.

The die swell ratio of PAT containing no foaming agent, that is, PAT itself, is usually a value of 1.5 or less when measured as described above, and never exceeds 2. The addition of a blowing agent seems to increase the die swell ratio somewhat, but none of them exceeds 2. In the present invention, a foaming agent and a cross-linking agent are added to this to make the die swell ratio 3 or more.

Various crosslinking agents can be used. For example, compounds having two or more acid anhydride groups in one molecule such as pyromellitic dianhydride and benzophenonetetracarboxylic dianhydride, and polyfunctional compounds such as diglycidyl terephthalate and diglycidyl hexaphthalate. Epoxy compounds can be added and diisocyanate compounds such as 2,4-tolylene diisocyanate can be used. These compounds react with a carboxylic acid or a hydroxyl group at the end of PAT to cause branching in PAT,
It is considered to increase the die swell ratio.

In order to include the cross-linking agent in the PAT, it is preferable to melt the PAT, mix the cross-linking agent with the PAT, and knead the mixture.

Various foaming agents can be used. Broadly speaking, a foaming agent is a solid compound that decomposes to generate gas at a temperature above the softening point of PAT, a liquid that vaporizes in PAT when heated, an inert gas that can be dissolved in PAT under pressure, etc. However, any of them can be used in the present invention. Solid compounds are, for example, azodicarbonamide, dinitrosopentamethylenetetramine, hydrazocarbonamide, sodium bicarbonate and the like. The liquid to be vaporized is, for example, a saturated aliphatic hydrocarbon such as hexane, pentane or butane, an aromatic hydrocarbon such as benzene or xylene, a halogenated hydrocarbon such as methylene chloride or Freon (registered trademark). The inert gas is, for example, carbon dioxide or nitrogen. In addition, as the blowing agent, as disclosed in JP-A-59-135237, a chain aromatic polycarbonate having a high molecular weight can be used.

Various methods can be used to include the foaming agent in the PAT. When the foaming agent is liquid, it may be sufficient to immerse PAT in the foaming agent under normal pressure, but in order to facilitate impregnation, the PAT is heated and immersed while preventing evaporation of the foaming agent. Therefore, the dipping must be carried out under warm pressure. For impregnation under heating and pressurization, it is preferable to melt PAT in advance and then press the foaming agent in the melt. For this purpose, it is advantageous to melt PAT using an extruder and press the foaming agent from the middle of the extruder. Further, by using an extruder, it is possible to mix the cross-linking agent into PAT and press-in the foaming agent at the same time, and it is possible to perform extrusion molding as it is,
It is also convenient because it can be foamed at the same time.

The die swell ratio of PAT containing a foaming agent cannot be measured in exactly the same manner as the die swell ratio of PAT containing no foaming agent. It is a PAT containing a blowing agent,
This is because it has a low density and floats on water. Therefore, the PAT containing the foaming agent is cooled in the air without being submerged in water to form a string-like body, and its maximum diameter is measured to calculate the die swell ratio. In the present invention, the die swell ratio thus measured is set to 3 or more.

In this invention, the PAT containing the foaming agent having a large die swell ratio as described above is extruded from the multi-isle base. The conditions for extrusion are extrusion at a temperature 5 ° C to 30 ° C higher than the crystal melting point of PAT. Since PAT lowers the die swell ratio at higher temperatures than the crystal melting point, when PAT is extruded at a temperature higher than the crystal melting point by 5 ° C to 30 ° C, the PAT always has a die swell ratio of 3 or more. Is kept. Therefore, in the present invention, the crystal melting point is 5 to 30 ° C.
It will be extruded at a high temperature.

The multi-noise base has a large number of nozzles dispersed therein. It is desirable that each nozzle has a diameter of 3 mm or less. Further, although it is desirable that the nozzles have the same size, they may have different sizes.
The distance between nozzles refers to the distance from the diameter center of the nozzle to the diameter center, and the distance is 2 to 15 of the average diameter of the nozzle.
It will be within the double range. The distance between the nozzles is preferably 2.5 to 12 times the average diameter of the nozzles.

In the multi-nozzle die, the sum of the nozzle cross-sectional areas occupies 1/6 to 1/36 of the nozzle dispersion area. Since the die swell ratio is 3 or more, the extruded PAT cord-like body indicates the cross-sectional area up to at least the square of the die-swell ratio, so that the adjacent cord-like bodies are in contact with each other on the surface without any gap. Constitutes a foam.

At this time, the string-shaped foam extruded from each nozzle forms a low-foaming skin layer on the surface, and as a result of this being fused, the obtained integrated foam body contains the surface of each string-shaped body. A low foam layer is formed in the fused portion. For this reason, the obtained foam contains a low foam layer penetrating in the longitudinal direction inside, and as a result, it becomes hard to bend in the longitudinal direction and has a high bending strength. Therefore, the foam is suitable for use as a structural material.

In practicing this invention, various additives can be included in PAT. For example, a small amount of talc powder may be added as a bubble control agent, or I, II, II in the periodic table may be added.
A group I metal compound, a colorant, an antistatic agent, a flame retardant and the like can be added.

Further, PAT is generally a resin that is easily hydrolyzed at high temperatures, and therefore, when foaming the PAT, it is desirable to dry it beforehand. For drying, for example, a dehumidifying dryer may be used. In that case, the drying conditions include, for example, a dew point of −30.
It suffices to heat the air at ℃ to 160 ℃ and expose PAT in this air for about 4 hours.

Further, the string-shaped foam extruded from the multi-nozzle mouthpiece, immediately after that, passes through a mold provided in the vicinity of the mouthpiece, where the shape in the circumferential direction is adjusted and then exposed to the atmosphere, It is desirable to continue foaming. Further, it is desirable that the cord-like foams then pass through the forming frame and are pressed from the peripheral direction by the forming frame to further complete the mutual fusion bonding. When the string-like foams thus fused to each other are subsequently entered into the cooling tank, they are further pressed from the circumferential direction to adjust the cross-sectional shape, water-cooled in the cooling tank, and the rolls assembled in a cross beam shape. It is desirable that the cross-sectional shape can be adjusted through.

In this way, the integrated molded body formed by melting and cooling the string-like foam bodies together is pressed against the heating plate by contacting the surface thereof, and the surface is partially melted to reduce the cross section. Then, it is desirable that it is cooled in contact with a cooling plate in that state to give a hard and glossy surface.

(Effect of the Invention) According to the present invention, PAT is mixed with a foaming agent and a cross-linking agent.
It is heated to a temperature 30 ° C higher than the crystalline melting point of AT and melted.
PAT with a die swell ratio of 3 or more when extruded from a circular hole with a diameter of 5 mm and a length of 40 mm at a rate of 5.0 kg / hr is used at a temperature of 30 ° C or higher higher than the melting point of the crystal. When extruded, the PAT, after exiting the die, expands its diameter by at least a factor of three in the direction perpendicular to the extrusion direction. Such PAT is 5-30% higher than the crystal melting point of PAT.
Since it was decided to push it out from the base at a temperature as high as ℃,
The extruded resin has a diameter three times or more larger in the direction perpendicular to the extrusion direction. On the other hand, a multi-nozzle die is used as the die, in which the sum of the nozzle cross-sectional areas in the front of the die occupies 1/6 to 1/36 of the nozzle dispersion area, and the center distance between the nozzles is the average of the nozzles. Since the diameter is in the range of 2 to 15 times, the cord-like foam extruded from each nozzle comes close to each other, and as described above, it greatly expands in the direction perpendicular to the extrusion direction. , Adjacent string-like foams are well fused to each other, and a PAT foam integrated with the same can be obtained. Moreover, the PAT foam thus obtained has a high bending strength because it contains the low foam layer therein as described above. Moreover, since this foam is made of PAT, it has high heat resistance, high rigidity, and good shape stability. Therefore, this foam is particularly suitable as a structural material.

(Examples) Hereinafter, the reason why the method of the present invention is excellent will be specifically described with reference to Examples and Comparative Examples. In the following, simply "parts" means "parts by weight".

Example 1 As PAT, polyethylene terephthalate (PET 9902) manufactured by Eastman Kodak Company was used. The crystalline melting point of this resin was 255 ° C.

The above PAT was placed in a hot air dehumidifying dryer, and air having a dew point of -30 ° C was heated to 160 ° C and circulated, and exposed to this air for 4 hours to be dried. To 100 parts of PAT dried in this way, 0.5 part of pyromellitic dianhydride, 2 parts of talc powder and 0.2 part of brown pigment were added and mixed well, and then this mixture was put into an extruder.
Since this mixture contains pyromellitic acid as a cross-linking agent, the die swell ratio is large, and 5.0 kg from a circular hole with a diameter of 5 mm and a length of 40 mm at a temperature 30 ° C. higher than the crystal melting point of the resin. The die swell ratio when extruded at a ratio of / hr was 2.3.

The extruder has a feed section of 280 ° C, a compression section of 285-3 and a tip section of 27.
While maintaining the temperature at 5 ° C and the die at 275 ° C, butane as a foaming agent was pressed in from the middle of the barrel of the extruder. Butane is 1.
It was pressed in so as to occupy 6% by weight. When the die swell ratio of the foamable resin in which butane was press-fitted was measured under the above conditions, the die swell ratio was 3.6.

The PAT extruded from the extruder was processed as shown in FIG. In FIG. 3, the multi-nozzle mouthpiece is attached to the tip portion 1 of the extruder, but the multi-nozzle mouthpiece is configured by fitting the mouthpiece plate 3 into the outer peripheral portion 2 of the mouthpiece.
The outer peripheral portion 2 of the mouthpiece is provided with a resin passage 22 therein,
22 is connected to a large number of small holes 32 provided in the base plate 3. As shown in FIG. 4, the mouth plate 3 had the small holes 32 arranged in a straight line arranged in two rows.

More specifically, the arrangement of the small holes 32 will be described below. The base plate 3 is a rectangular plate having a length of 22 mm and a width of 152 mm, and a small hole 32 is formed in the center of the rectangular plate at intervals of 4 mm in the vertical direction along two straight lines. The small holes 32 each had a diameter of 1.6 mm, and 20 holes were arranged in a row in the lateral direction at intervals of 4 mm, for a total of 40 small holes 32.

Each of the string-like bodies extruded from the multi-nozzle base was foamed and was brought into contact with the surface thereof. On the way, it passed through the surface processing apparatus 8 consisting of the heating plate 81 kept at 280 ° C. and the cooling plate 82 kept at 30 ° C., and was then taken by the take-up machine 9.

The PET foam produced in this way has a thickness of 4.5 mm and a width of 1.5 mm.
The string-like bodies were arranged in two steps, and were firmly fused together to form a flat plate that was 7.5 times as thick as 9 mm thick and 90 mm wide. This foam had a large bending strength, and no voids were observed on the fused surface inside. Further, this foam had a fusion-bonded surface of a string-like body that appeared linearly on the surface, and had an appearance like the grain of natural wood.

The total cross-sectional area of the nozzle corresponded to 1/10 of the cross-sectional area of the foam.

Example 2 The PAT mixture having the same composition as that used in Example 1 was put into another extruder, and the blowing agent was pressed under the same temperature conditions as in Example 1 to obtain the same blowing agent PAT. However, by changing the multi-nozzle base and the device located in front of the multi-nozzle base,
It carried out as shown in the figure. That is, the deflection plate 4 was attached to the tip of the multi-nozzle die, the molding frame 5 was installed at the tip thereof, and the water tank 7 was further provided at the tip thereof.

As the multi-nozzle mouthpiece, one having a mouthpiece plate 3 as shown in FIG. The base plate 3 is
It is a rectangular plate 22 mm long and 152 mm wide and has a large number of orifices 32. Each orifice 32 has a diameter of 1.6 m.
It was supposed to be m. The orifices 32 were divided into upper and lower two stages, and the orifices in each stage were arranged in a horizontal direction at intervals of 3 mm along a straight line with 33 pieces, and the straight lines were assumed to extend parallel to each other at intervals of 13 mm. . Therefore, on the base plate 3,
A total of 66 orifices were drilled.

The deflecting plate 4 was composed of only plates having a length of 300 mm and a width of 600 mm, which were vertically arranged so as to face each other, and extended in parallel with each other with a space of 13 mm therebetween. The deflection plate 4 was adjusted to 100-110 ° C.

The molding frame 5 has a rectangular opening of 14 mm × 160 mm and has a water tank 7
It was installed near the entrance of the. The aquarium 7 has a plate 6 at the entrance.
And the cooling water is stored inside, and the roll group 71 assembled in the shape of a cross is buried in the cooling water.

The PAT extruded from the multi-nozzle base is formed into a string-like shape and foams, is fused between the deflecting plates 4 and is shaped, and after exiting the deflecting plate 4, it is largely foamed and further melted. Then, it is passed through the forming frame 5 and firmly fused to each other and shaped, and further passes through the plate 6, is cooled by water in the water tank 7, and is shaped by the roll group 71. , Becomes an integral molded body.

The molded body thus obtained then passed through the surface processing device 8 and was then taken up by the take-up roll 9. The surface processing apparatus 8 is composed of the heating and pressing plate 81 and the cooling plate 82 as in the case of the first embodiment, and the heating and pressing plate 81 is heated to 180 ° C. so that the cross-sectional area of the molded body is reduced by 10%. The cooling plate was maintained at 30 ° C. and worked to cool the compact. As a result, it was possible to obtain a PAT foam having a beautiful surface in which the string-like foams were firmly fused to each other.

The obtained PAT foam is a flat plate that is about 7.5 times as thick as 12 mm thick and 110 mm wide, in which 6 mm thick and 3.3 mm wide.
The cord-like foam having a cross section of was firmly fused without any gap. This foam had a high bending strength, and the fused portion of the string-like material on the surface looked like a grain of natural wood, and thus it was lightweight and beautiful, giving a feeling of high-grade wood.

The average crystallinity of this foam was 20% and that of the epidermis was 30%.

The die swell ratio during PAT foaming used at this time was 13.
The total nozzle cross-sectional area was 1/10 of the nozzle dispersion area.

Comparative Example 1 Extruded in exactly the same manner using the same raw materials and equipment as in Example 1 except that the amount of pyromellitic acid was 0.02 parts, but the foam had a density of about 0.72 g / cc. It becomes a high-density one, and each string-shaped foam becomes thin and cut,
No integrated body was obtained. The die swell ratio at this time was 2.8.

[Brief description of drawings]

FIG. 1 is a front view of a multi-nozzle base used in the present invention. FIG. 2 is a vertical sectional view of a PAT die swell ratio measuring device. FIG. 3 is a sectional view showing one embodiment of the method of the present invention. FIG. 4 is a front view of the mouth plate 3 used in FIG. FIG. 5 is a sectional view showing another embodiment of the method of the present invention. FIG. 6 is a front view of the mouth plate 3 used in FIG.

Claims (1)

[Claims] 1. A thermoplastic polyester resin containing a foaming agent is melted and extruded from a multi-nozzle die, and the string-like foam extruded from each nozzle is bundled and fused together to form an integral foam molded body. In the method, a foaming agent and a cross-linking agent are added to the resin to increase the die swell ratio of the foamable resin, and the diameter is 30 ° C. higher than the crystalline melting point of the resin,
Using a resin with a die swell ratio of 3 or more when extruding at a rate of 5.0 kg / hr from a circular hole with a length of 5 mm and a length of 40 mm,
As a multi-nozzle die, the sum of the nozzle cross-sectional areas on the front face of the die occupies 1/6 to 1/36 of the nozzle dispersion area, and the center distance between the nozzles is 2 of the average diameter of the nozzles.
A thermoplastic polyester resin characterized by using a die in the range of 15 to 15 times, and extruding the foamable resin from the die at a temperature higher by 5 ° C. to 30 ° C. than the crystal melting point for foaming and fusing together. Method for producing foam.