JPH0547579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyolefin resin foam particles. A foam product obtained by filling the mold cavity of a mold having steam holes with the foam particles produced by the method of the present invention, and heating the foam particles with steam to fuse the foam particles together. It is strong and has excellent mechanical strength, making it useful as a heat insulating material for hot spring piping, a heat insulating material for solar water heaters, and a packaging material for refrigerators and televisions.

Polyolefin foams are excellent as insulation materials and packaging cushioning materials, and are used in a wide range of fields. However, this polystyrene foam has a low compression strain recovery rate and a heat resistance of 70 to 80°C at most.

These drawbacks can be solved by using polypropylene foam or cross-linked polyethylene foam, but in order to produce the foam particles that are the raw materials for forming these polyolefin foams, polyolefin resins have a high rate of expansion agent dissipation. Therefore, it has the disadvantage that it is difficult to obtain, and even if it is obtained, the bulk density is at most 0.1 ~
The disadvantage was that only a low foaming product of 0.5 g/cm ³ could be obtained.

As a method to solve this drawback, polyolefin resin particles containing 10 to 70% by weight of an inorganic filler are dispersed in water, which is a dispersion medium, in a sealed container, and the dispersion is heated to a pressure higher than the saturated vapor pressure of the dispersion and Water, which is a dispersion medium, is infiltrated into the polyolefin resin particles by maintaining high pressure under a temperature condition heated above the softening point of A method for producing polyolefin foam particles with a high foaming rate of 0.05 to 0.07 g/ ^cm3 was proposed (Tokuko Sho
49-2183).

This method uses water as a dispersion medium as a blowing agent, and has the advantage of being able to produce foam particles at a lower cost than methods that use foaming agents such as dichlorocyfluoromethane, butane, hexane, etc. . However, the presence of an inorganic filler is not preferable because it inhibits the fusion of the foam particles during molding.

When we repeated the invention without a filler, we found that when using a polyolefin resin that does not contain an inorganic filler that absorbs water, resin foam particles with an expansion ratio of about 18 times can be obtained. It was revealed that the particles contained 2 to 8% of particles with an expansion ratio of 2 to 3 times (small particle size). Irregular shapes of foam particles cause uneven filling rates during molding, making it impossible to obtain molded products with consistent mechanical properties.

The present invention was made in order to solve the problem of irregular shapes of foam particles, in other words, the foaming of resin particles is not uniformly performed. Polyolefin resin particles containing 0.4 to 10% by weight of metal salts of higher fatty acids are dispersed in water, heated to a temperature above the softening temperature of the resin particles and below 25°C higher than the melting point, and water is poured into the particles. The polyolefin resin particles containing the swelling agent and water as a dispersion medium are simultaneously discharged into an atmosphere at a lower pressure than the inside of the container by opening the discharge port provided below the water surface in the sealed container. The present invention provides a method for producing resin foam particles.

A second invention is a method for obtaining foam resin particles with a uniform shape according to the first invention, in which (a) 0.4 to 5% by weight of a metal salt of a higher fatty acid is added to (b) glycerin, sorbitan, polyglycerin, etc. An ester of a selected alcohol and a higher fatty acid with 12 to 22 carbon atoms.
The object of the present invention is to provide a method for producing foam particles having a higher expansion ratio using polyolefin particles containing 0.05 to 2% by weight.

In the present invention, the resin of the polyolefin resin particles includes low density polyethylene, linear low density polyethylene, high density polyethylene, ethylene/vinyl acetate copolymer, polypropylene, ethylene/propylene block copolymer, ethylene/propylene random copolymer, ethylene·
Butene/propylene random terpolymer, silane crosslinked polypropylene, crosslinked polyethylene, etc. are used. These may be mixed. especially,
Propylene resins such as ethylene (4 to 10% by weight)/propylene random copolymer, ethylene/butene/propylene random terpolymer, and silane-crosslinked polypropylene are preferred because they provide foamed particles with excellent heat resistance and excellent moldability.

Next, (a) metal salts of higher fatty acids include metal salts (Zn, Al, K , Na, Ca), particularly aluminum stearate and zinc stearate. This higher fatty acid metal salt is blended into the resin particles at a ratio of 0.4 to 10% by weight, preferably 0.5 to 2% by weight.

In addition, (b) esters of higher fatty acids having 12 to 22 carbon atoms and glycerin, polyglycerin, and sorbitan include glycerin monostearate, glycerin distearate, glycerin tristearate, sorbitan oleate, sorbitan laurate, Examples include glycerin monooleate, polyglycerin oleate, glyceryl triricinolate, glyceryl acetyl ricinoleate, and glycerin monopalmitylate.

This ester is 0.05 to 5% by weight in the resin particles,
It is preferably used in a proportion of 0.5 to 2% by weight.

When the amount of these higher fatty acid metal salts (a) and esters (b) is large, the resulting polyolefin foam particles are filled into a mold cavity with steam holes, and the foam particles are fused together by steam heating. If a foam product is molded by adhesion, the degree of fusion between the foam particles is low and only a product with low strength can be obtained.

The weight of one polyolefin resin particle is 0.01~
It is 20mg. These resin particles include, in addition to the metal salts and esters of higher fatty acids mentioned above, inorganic fillers such as talc, clay, silica, calcium carbonate, titanium oxide, barium sulfate, and zeolite, stabilizers, ultraviolet absorbers, and volatile expansion agents. It may contain agents etc.

Volatile blowing agents are used to increase expansion ratio. Examples of such expanding agents include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; halogens such as trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride; An organic compound having a boiling point of 80° C. or lower, such as carbonized hydrocarbon, can be used.

It is also possible to impregnate the polyolefin resin particles with this volatile swelling agent in advance and then disperse the resin particles in water, but from the viewpoint of the manufacturing process, the polyolefin resin particles are dispersed in water in a closed container, and then the container is sealed. After supplying an expanding agent into a container and heating it to a temperature equal to or higher than the softening temperature of the propylene copolymer resin particles while maintaining the pressure inside the sealed container at the vapor pressure of the expanding agent or higher, tail,
The pressure is maintained for a certain period of time, and then the discharge port provided below the water surface in the sealed container is opened, and the polyolefin resin particles containing the expanding agent and water are simultaneously discharged into an atmosphere at a lower pressure than the inside of the container, thereby producing the polyolefin resin. Method for producing foam particles (Japanese Unexamined Patent Publication No. 12035/1983,
No. 57-25336, No. 57-90027, No. 57-195131
No. 58-1732, No. 58-23834, No. 58-25334
No. 58-33435, No. 58-55231, No. 58-
No. 76229, No. 58-76231, No. 58-76232, No. 58
-76233, No. 58-76234, and No. 58-87027) are more preferable.

Dispersants for dispersing polyolefin resin particles in water include titanium oxide, aluminum oxide,
A sparingly water-soluble inorganic dispersant such as calcium carbonate, basic magnesium carbonate, zinc carbonate, or tribasic calcium phosphate is used. Dispersants play a role in preventing polyolefin resin particles dispersed in water from fusing together when heated above their softening point. Inorganic dispersants are stable at high temperatures, so polyvinyl alcohol, It is more commonly used than water-soluble polymeric protective colloid agents with poor thermal stability such as methylcarboxycellulose and N-polyvinylpyrrolidone.

When tricalcium phosphate is used as a dispersant, a suspension aid may be used in combination. Such suspension aids include anionic surfactants such as sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkyl sulfate, sodium olefin sulfate, acylmethyltaurine, sodium dialkylsulfosuccinate; polyoxyethylene alkyl; ether,
Examples include nonionic surfactants such as polyoxyethylene fatty acid ester, polyoxyethylene alkyl phenol ether, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid ester; amphoteric surfactants such as alkyl betaine and alkyl diethylene triaminoacetic acid.

Particularly preferred is a solution in which an aqueous solution of calcium hydroxide and an aqueous phosphoric acid solution are mixed to form a slightly water-soluble salt as the suspending agent (A), and sodium dodecylbenzenesulfonate is used as the suspending aid. It is.

The suspension agent (A) above is obtained by reacting phosphoric acid in an aqueous solution at a ratio of 0.60 to 0.67 mol to 1 mol of calcium hydroxide, and the pH of the aqueous solution containing the poorly water-soluble salt is 8.5. ~11.5. The aqueous solution of the poorly water-soluble salt is mainly composed of tricalcium phosphate {Ca ₃ (PO ₄ ) ₂ } with an average particle size of 0.01 to 0.8 microns, and contains hydroxyapartite {[Ca ₃
(PO ₄ ) ₂ ] ₃・Ca(OH) ₂ } may also be included.

The aqueous solution containing the poorly water-soluble salt (A) can be used as a dispersion medium for polyolefin resin particles by adjusting the content of the poorly water-soluble salt to 0.01 to 0.3% by weight. If it is less than 0.01% by weight, blocking between the polyolefin resin particles tends to occur.
Moreover, if it exceeds 0.3% by weight, the fusion properties of the resulting foam particles will be inhibited. A water-soluble medium such as methanol, ethanol, glycerin, or ethylene glycol can also be blended with water as a dispersion medium.

The surfactant, which is a suspension aid, is used in an amount of 0.0001 to 0.005% by weight of water, which is a dispersion medium. If it is less than 0.0001% by weight, there is a problem that blocking of the polyolefin resin particles tends to occur under heat and pressure. On the other hand, even if it exceeds 0.005% by weight, it is economically disadvantageous because no further improvement in the anti-blocking effect is required.

The amount of water as a dispersion medium is 200 to 1000 parts by weight, preferably 100 parts by weight of polyolefin resin particles.
It is 250-500 parts by weight. If it is less than 200 parts by weight, heating,
Polyolefins tend to block together when pressurized. If it exceeds 1000 parts by weight, the productivity of the polyolefin resin foam particles decreases and is not economical.

If necessary, a gas is added to an aqueous dispersion of polyolefin resin particles dispersed in water using a fine, slightly water-soluble salt of tricalcium phosphate with an average particle size of 0.01 to 0.8 microns as a suspending agent and a surfactant as a dispersion aid. This dispersion is heated in a closed container to a temperature above the softening point of the polyolefin resin and below 25°C higher than the melting point, and a dispersion medium is supplied. The vapor pressure of the water reaches a certain level, and then the polyolefin resin particles are released from the closed container into a low pressure region, generally atmospheric pressure, along with water as a dispersion medium through the discharge port of a slit, nozzle, etc. provided at the bottom of the closed container. As a result, polyolefin resin foam particles having a bulk density of 0.026 to 0.2 g/cm ³ can be produced.

As the dispersion is heated, the pressure increases, water (if an expanding agent is used, water and a volatile expanding agent) impregnates the polyolefin resin particles, and the resin particles become expandable resin particles. Although the pressure inside the sealed container increases due to heating, nitrogen is added to the sealed container in order to facilitate the impregnation of water into the polyolefin resin particles and to facilitate the subsequent spouting of the acid separating solution from the discharge port. It is preferable to pressurize by supplying an inorganic gas such as air, helium, or argon. The pressurization of the inorganic gas is 1 to 50 Kg/cm ² G, preferably 5 to 25 Kg/cm ²
G, more preferably 5 to 10 kg/cm ² G. Pressurization by this inorganic gas can prevent the polyolefin resin particles from remaining in the closed container after discharging the dispersion liquid, and is significant in obtaining polyolefin resin foam particles having fine and uniform cells. .

The heating temperature was determined by differential thermal analysis (DSC) of the polyolefin resin particles, and the peak of the crystal melting temperature (so-called melting point) of the DSC chart shown in Figure 1 was determined.
Find a) and set the temperature approximately 10℃ lower than this peak temperature.
From (b), it is sufficient to select a temperature that is approximately 10°C higher than the temperature (c) at which this peak descends and reaches the bottom of the DSC chart. Preferably, temperature (c) is preferred. For example, in the case of a propylene homopolymer with a melting point of 164°C, the heating temperature is set at 154 to 193°C.
In addition, in the case of a propylene-ethylene-butene-1 copolymer with a melting point of 135℃, the melting point is 125 to 160℃.
100-135℃ for ethylene homopolymer at 110℃
Set the temperature to However, the heating temperature specifically shown here was selected based on the melting point measured for resin particles containing no expanding agent or organic solvent.

The foam particles thus obtained are dried in a room at 30 to 65°C to remove water adhering to the surface, and then used to mold cushioning materials, containers, etc.

As the molding method, various conventionally known methods can be used. An example is shown below.

After filling polyolefin resin foam particles into a mold, the foam particles are compressed to reduce their volume by 15 to 50%, and then steam of 1 to 5 kg/cm ² G is introduced to fuse the foam particles together. ,after that,
Cool the mold and obtain the product.

The foam particles are pre-impregnated with a volatile swelling agent to impart secondary foamability to the foam particles, which are then filled into a mold and steam-molded.

The foam particles are placed in a closed chamber, then air,
By injecting an inorganic gas such as nitrogen gas into the chamber, the pressure inside the cells of the foam particles is increased to give them secondary foaming properties, and the foam particles with secondary foaming properties are filled into a mold and steamed. Shape.

A combination of two or more of the above.

The polyolefin resin foam product molded in this manner has excellent fusion between foam particles and high mechanical strength.

Hereinafter, the present invention will be explained in further detail with reference to Examples. Note that parts and percentages in the examples are based on weight.

Example 1 When an aqueous solution of 0.0716 parts of calcium hydroxide dissolved in 100 parts of water and 0.372 parts of an aqueous solution of 17% phosphoric acid were mixed, 0.1% of salt with a particle size of 0.05 to 0.3 microns was precipitated (PH9. 2). Sodium dodecylbenzenesulfonate was added to this to prepare the following dispersion.

Concentration of poorly soluble salts: 0.1% PH of dispersion: 9.2 Concentration of dodecylbenzenesulfonic acid: 0.003% After transferring 100 parts by weight of this dispersion into an autoclave equipped with a discharge nozzle at the bottom, each particle weighs approximately 1 mg, stearic acid Ethylene (4%) containing 0.5% aluminum and 0.5% stabilizer by weight
%) and propylene (96%) random copolymer particles (melting point 137°C) were added into the autoclave.
Nitrogen gas was supplied into the autoclave until the internal pressure within the autoclave reached 10 Kg/cm ² G.

Then autoclave at 135℃ for about 60 minutes.
The dispersion was heated to a temperature of 100.degree. C. and then kept at the same temperature for 20 minutes. The pressure inside the autoclave at this time is approximately 30Kg/
It was cm ² G.

Thereafter, the dispersion was further heated to 150° C. and maintained at the same temperature for 2 hours, and then the valve of the discharge nozzle at the bottom of the autoclave was opened to discharge the dispersion into atmospheric pressure for 2 seconds to effect foaming. (According to differential thermal analysis,
The expandable polypropylene particles before release are about 4
% of water contained within the particles). The internal pressure of the autoclave was approximately 9 kg/cm ² G at the moment when the dispersion liquid was discharged from the autoclave and the gas phase began to be discharged. Additionally, the temperature of the autoclave was 150° C. during dispersion discharge.

The bulk density of the polypropylene foam particles thus obtained was approximately 0.13 g/cm ³ . Further, the granularity of the foam particles was almost the same, and no blocking between the foam particles was observed.

The foam particles were left in a room at 40°C for 2 days to dry the moisture, then placed in a sealed room for 3 days.
Kg/cm ² G of air was injected for 48 hours to impart secondary foamability to the particles (pressure ripening).

The foam particles imparted with secondary foamability are filled into a mold cavity with steam holes, and then placed into the mold cavity.
Steam of 4.5Kg/cm ² G was introduced to perform secondary foaming, fuse the foam particles together, and then cool the foam to a shape with a bulk density of approximately 0.11g/cm ³ , length 200mm, and width.
A polypropylene foam product of 300 mm and 50 mm height was obtained.

When this product was broken in half by hand and the degree of fusion of the foam particles was examined, it was found to be 70%.

The degree of fusion is defined as 0 when all foam particles are separated at the interface when the product is broken.
%, and the degree of fusion when the foam particles were 100% cohesive failure and peeled off was defined as 100%.

Example 2 0.5% by weight of zinc stearate as resin particles,
Calcium stearate 0.05% by weight, stabilizer
Example 1 except that ethylene (4% by weight)/propylan lindum copolymer particles containing 0.5% by weight were used.
Foam particles were obtained in the same manner as described above.

The bulk density of the obtained polypropylene foam particles was about 0.11 g/cm ³ and the particle sizes were uniform. Also,
No blocking between the foam particles was observed (the foam particles had absorbed approximately 3.8% water before release).

These foam particles were heated and aged in the same manner as in Example 1 to impart secondary foaming power, and then steam-molded to obtain a foam product having a bulk density of about 0.10 g/cm ³ .

The degree of adhesion of the foam particles of this product was approximately 65%.

Example 3 Aluminum stearate was used as resin particles
Ethylene (4%) containing 1.0% by weight, 1.0% by weight of glycerin monostearate and 0.5% by weight of stabilizers
Foam particles were obtained in the same manner as in Example 1, except that propylene random copolymer particles (% by weight) were used.

The bulk density of the obtained polypropylene foam particles was about 0.061 g/cm ³ and the particle sizes were uniform. Also,
No blocking between foam particles was observed (the foam particles had absorbed approximately 3.6% water before release).

These foam particles were aged under pressure in the same manner as in Example 1 to impart secondary foaming power, and then steam-molded to obtain a foam product having a bulk density of about 0.06 g/cm ³ .

The degree of fusion of the foam particles of this product was approximately 60%.

Comparative Example 1 Ethylene (4% by weight)/propylene random copolymer particles containing 0.5% by weight of stabilizer were used as resin particles, and the release temperature of the dispersion was set to 155%.
Foam particles were obtained in the same manner as in Example 1 except that the temperature was changed to .degree.

The average bulk density of the obtained polypropylene foam particles is about 0.05 g/cm ³ , about 5% for foam particles with an expansion ratio of 2 to 3 times, and about 2% for those with an expansion ratio of 20 to 25 times. (The expandable particles before release had absorbed approximately 4.4% water).

These foam particles were aged under pressure in the same manner as in Example 1 to impart secondary foaming power, and then steam-molded to obtain a foam product having a bulk density of approximately 0.047 g/cm ³ .

The degree of fusion of the foam particles of this product was about 70%.

Example 4 The same procedure as in Example 1 was used except that an ethylene (9% by weight)/propylene random copolymer was used as the ethylene/propylene random copolymer, and the dispersion temperature was set at 155°C. Polypropylene foam particles were obtained.

The bulk density of the foam particles was approximately 0.045 g/cm ³ .

Example 5 Aluminum stearate as resin particles
Polypropylene foam particles with uniform granularity were obtained in the same manner as in Example 1, except that an ethylene (4% by weight)/propylene random copolymer containing 1.0% by weight and 1.0% by weight of glycerin monooleate was used.

The bulk density of the foam particles was approximately 0.056 g/cm ³ .

Example 6 Aluminum stearate as resin particles
Polypropylene with uniform granules was prepared in the same manner as in Example 1, except that ethylene (4% by weight)/propylene random copolymer particles containing 1.0% by weight, 0.5% by weight of sorbitan monooleate, and 0.2% by weight of stabilizer were used. Foam particles were obtained.

The bulk density of the foam particles was approximately 0.052 g/cm ³ .

Example 7 Polypropylene foam particles with uniform granularity were obtained in the same manner as in Example 6, except that polyglycerol monooleate was used instead of sorbitan senooleate.

The bulk density of the foam particles was approximately 0.050 g/cm ³ .

Example 8 When an aqueous solution of 0.0716 parts of calcium hydroxide dissolved in 100 parts of water and 0.372 parts of an aqueous solution of 17% phosphoric acid were mixed, 0.1% of salt with a particle size of 0.05 to 0.3 microns was precipitated (PH9. 2). Sodium dodecylbenzenesulfonate was added to this to prepare the following dispersion.

Concentration of poorly soluble salts: 0.1% PH of dispersion: 9.2 Concentration of dodecylbenzenesulfonic acid: 0.003% After transferring 100 parts by weight of this dispersion into an autoclave equipped with a discharge nozzle at the bottom, each particle weighed approximately 1 mg, aluminum stearate
33 parts of ethylene (4%)/propylene (96%) random copolymer particles (melting point 137°C) containing 0.5% by weight and 0.2% by weight of stabilizer were added into the autoclave, and nitrogen gas was introduced into the autoclave. The supply was continued until the internal pressure within the tank reached 10 kg/cm ² G.

Next, 18 parts of butane gas was added into the autoclave with stirring, and the dispersion was heated to 130° C. over about 60 minutes, and further maintained at the same temperature for 20 minutes. At this time, the pressure inside the autoclave was approximately 30 kg/cm ² G.

Thereafter, the valve of the discharge nozzle at the bottom of the autoclave was opened, and the dispersion was discharged into atmospheric pressure for 2 seconds to effect foaming. The internal pressure of the autoclave was approximately 9 kg/cm ² G at the moment when the dispersion liquid was discharged from the autoclave and the gas phase began to be discharged. Also, during dispersion discharge, the temperature of the autoclave was 130°C.

The bulk density of the polypropylene foam particles thus obtained was approximately 0.027 g/cm ³ . Also,
No blocking between foam particles was observed.

According to differential thermal analysis, the expandable particles before release had absorbed approximately 0.18% by weight of water.

The foam particles were left in a room at 40°C for 2 days to dry the moisture, then placed in a sealed room for 3 days.
Kg/cm ² G of air was injected for 48 hours to impart secondary foamability to the particles.

The foam particles imparted with secondary foamability are filled into a mold cavity with steam holes, and then placed into the mold cavity.
Steam of 4.5Kg/cm ² G was introduced to perform secondary foaming, and the foam particles were fused together, and then cooled to a shape with a bulk density of about 0.025g/cm ³ , length 200mm, and width.
A polypropylene foam product of 300 mm and 50 mm height was obtained.

When this product was broken in half by hand and the degree of fusion of the foam particles was examined, it was found to be 70%.

Example 9 After 100 parts by weight of water containing 0.3% by weight of fine particles of aluminum oxide was transferred into an autoclave equipped with a discharge nozzle at the bottom, each particle weighed approximately 1 mg.
and 1.0% by weight of aluminum stearate,
Ethylene (4%)/propylene (96%) random copolymer particles containing 1.0% by weight of glycerin monostearate and 0.2% by weight of stabilizer (melting point
137°C) was added into the autoclave.

Next, 19 parts of dichlorodifluoromethane was added to the autoclave with stirring, and the mixture was heated for about 60 minutes.
The acid separation solution was heated to 122°C and further maintained at the same temperature for 20 minutes. The pressure inside the autoclave at this time is approximately
It was 33Kg/cm ² G.

After that, it was heated to 130℃ and kept at the same temperature for 2 hours, and then the dispersion was brought into atmospheric pressure by opening the discharge nozzle valve at the bottom of the autoclave while applying back pressure by supplying nitrogen gas into the autoclave. It was released in 2 seconds to complete foaming. The internal pressure of the autoclave was approximately 21 kg/cm ² G at the moment when the dispersion liquid was discharged from the autoclave and the gas phase began to be discharged.

The bulk density of the polypropylene foam thus obtained was approximately 0.068 g/cm ³ . Further, no blocking between foam particles was observed.

The foam particles were left in a room at 40°C for 2 days to dry the moisture, then placed in a sealed room for 3 days.
Kg/cm ² G of air was injected for 48 hours to impart secondary foamability to the particles.

The foam particles imparted with secondary foamability are filled into a mold cavity with steam holes, and then placed into the mold cavity.
Steam of 4.5Kg/cm ² G was introduced to perform secondary foaming, fuse the foam particles together, and then cool the foam to a shape with a bulk density of about 0.067g/cm ³ , length 200mm, width
A polypropylene foam product of 300 mm and 50 mm height was obtained.

When this product was broken in half by hand and the degree of fusion of the foam particles was examined, it was found to be 50%.

Example 10 When an aqueous solution of 0.0716 parts of calcium hydroxide dissolved in 100 parts of water was mixed with 0.372 parts of an aqueous solution of 17% phosphoric acid, 0.1% of salt with a particle size of 0.05 to 0.3 microns was precipitated (PH9. 2). Sodium dodecylbenzenesulfonate was added to this to prepare the following acid solution.

Concentration of poorly soluble salts: 0.1% PH of dispersion: 9.2 Concentration of dodecylbenzenesulfonic acid: 0.003% After transferring 100 parts by weight of this dispersion into an autoclave equipped with a discharge nozzle at the bottom, each particle weighed approximately 1 mg, aluminum stearate
33 parts of cross-linked low-density polyethylene particles (melting point 110°C) containing 1.0% by weight, 1.0% by weight of glycerin monostearate, and 0.1% by weight of stabilizer were added into the autoclave, and nitrogen gas was introduced into the autoclave to reduce the internal pressure inside the autoclave. was supplied until it reached 10Kg/cm ² G.

The dispersion was then heated to 103°C over approximately 45 minutes.
After further holding at the same temperature for 20 minutes, it was heated to 120°C and held at the same temperature for 60 minutes. At this time, the pressure inside the autoclave was approximately 25 kg/cm ² G.

Thereafter, the valve of the discharge nozzle at the bottom of the autoclave was opened, and the dispersion was discharged into atmospheric pressure for 2 seconds to effect foaming. At the moment when the dispersion liquid is released from the autoclave, the internal pressure of the autoclave is approximately 7.
It was Kg/cm ² G.

The bulk density of the crosslinked polyethylene foam thus obtained was approximately 0.046 g/cm ³ . Further, no blocking between foam particles was observed.

After leaving the foam particles in a room at 40°C for 2 days to dry the moisture, they were placed in a sealed room for 2 days.
Kg/cm ² G of air was injected for 48 hours to impart secondary foamability to the particles.

The foam particles imparted with secondary foamability are filled into a mold cavity having steam holes, and then
Kg/cm ² G of steam is introduced to perform secondary foaming, fuse the foam particles together, and then cool the foam to a bulk density of approximately 0.043 g/cm ³ , length 200 mm, width 300 mm.
A cross-linked polyethylene foam product with a height of 50 mm and a height of 50 mm was obtained.

When this product was broken in half by hand and the degree of fusion of the foam particles was examined, it was found to be 90%.

[Brief explanation of the drawing]

FIG. 1 is a chart of differential thermal analysis of the resin.

Claims (1)

[Claims] 1. In a closed container, polyolefin resin particles containing 0.4 to 10% by weight of a metal salt of a higher fatty acid having 12 to 22 carbon atoms are dispersed in water, and at a temperature higher than the softening temperature of the resin particles, The particles are heated to a temperature below 25°C higher than the melting point to absorb water, and then the discharge port provided below the water surface in the sealed container is opened to separate the polyolefin resin particles and water as a dispersion medium. A method of producing polyolefin resin foam particles by simultaneously releasing the air into an atmosphere at a lower pressure than the inside of the container. 2 In a sealed container, (a) 0.4 to 10% by weight of a metal salt of a higher fatty acid having 12 to 22 carbon atoms and (b) glycerin,
Sorbitan, an ester of an alcohol selected from polyglycerin and a higher fatty acid with 12 to 22 carbon atoms.
Polyolefin resin particles containing 0.05 to 5% by weight are dispersed in water, and the temperature is higher than the softening temperature of the resin particles.
The particles are heated to a temperature below 25°C higher than the melting point to absorb water, and then the discharge port provided below the water surface in the sealed container is opened to separate the polyolefin resin particles and water as a dispersion medium. A method of producing polyolefin resin foam particles by simultaneously releasing the air into an atmosphere at a lower pressure than the inside of the container. 3. The method for producing polyolefin resin foam particles according to claim 1 or 2, wherein the metal salt of higher fatty acid is aluminum stearate or zinc stearate. 4. The method for producing polyolefin resin foam particles according to claim 2, wherein the ester is glycerin monostearate.