JPH044942B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing a polyolefin foam molded product useful as a heat insulating material for walls, floors, etc., a core material for car bumpers, and a cushion material for containers. It is something. [Prior Art] Polyolefin foams such as cross-linked polyethylene, non-cross-linked polypropylene, and cross-linked polypropylene have superior mechanical strength and oil resistance compared to polystyrene foam, so they are used as core materials for bumpers, televisions, electric refrigerators, etc. It is used as a packaging cushioning material for packaging. The following method is known as a method for producing such a polyolefin foam. (1) Cross-linked polyethylene foam particles are pressurized with an inorganic gas, then depressurized and foamed to form non-shrinkable particles with a built-in gas pressure of 1.18 atmospheres or more, which are then molded into a mold with steam holes. The foamed particles are filled under normal pressure or reduced pressure, and heated with steam while the particles contain a built-in pressure of 1.18 atmospheres or more to foam the foamed particles, and the particles are fused together to produce molded foam products. Pressure ripening molding method (Special Publication No. 51-22951). (2) Polypropylene foam particles are pressurized with an inorganic gas or a mixed gas of an inorganic gas and a volatile organic expansion agent, so that the partial pressure of the inorganic gas is 0.4 to 1.1 Kg/cm ²
G, partial pressure of volatile organic swelling agent is 0.8 to 1.6 Kg/cm ²
G and a total pressure of 1.4 to 2.5 Kg/cm ² G, the particles are filled into a mold with steam holes at normal pressure, and then heated with steam to make the particles mutually Pressure ripening molding method for manufacturing molded foam products by fusing with
No. 12035). (3) Cross-linked polyethylene foam particles are compressed to 40 to 80% of their original apparent bulk volume using gas pressure of an inorganic gas or volatile organic expansion agent and filled into a mold with steam holes, and then steamed. A compression-filling molding method (Japanese Patent Publication No. 33996/1983) that produces molded foam products by heating and fusing particles together. The pressure aging molding methods (1) and (2) have the advantage of producing products with a better appearance without gaps between foam particles than the molded products obtained by the compression filling molding method (3). However, it has the disadvantage that the pressure treatment of the foam particles with inorganic gas, the foaming by removing pressure, and the pressure aging time to form foam particles without shrinkage are long, ranging from 20 to 40 hours.
Poor productivity. The compression filling molding method (3) is superior to the above-mentioned pressure aging molding method in terms of the molding cycle, but the foam particles are compressed to 40 to 80% of their original apparent volume and filled into a mold. Since this method requires bulky foam particles with low density, the transportation cost of the foam particles from the foam particle manufacturer to the mold product processing manufacturer is high, and the storage cost is also high. It has the disadvantage of being expensive. [Problems to be Solved by the Invention] The present invention solves the disadvantage of the long molding cycle in the pressure aging molding method by combining both the pressure aging molding method and the compression filling molding method, and improves the appearance. The present invention provides a method for manufacturing a foam product with good quality. In other words, in the method of manufacturing a molded foam product by filling foam particles into the mold cavities of a mold having steam holes and heating and fusing them, the foam particles filled in the mold cavities are A void is created. In order to fill these voids, in the pressure aging molding methods (1) and (2), an inorganic gas or volatile organic expansion agent is infiltrated into the foam particles to give them expandability, and then heated. The foam particles are expanded to fill the voids between the particles. In the latter compression filling molding method, the compressed foam particles are decompressed and multiple forces are used to fill the voids between the particles. [Specific means for solving the problem] In the present invention, by using both methods in combination, the molding cycle and pressure aging time in the pressure aging molding method are shortened, and at the same time, the molding cycle and the pressure aging time can be shortened, and the This makes it possible to obtain a foam product with a good appearance. That is, in the method of the present invention, the expansion force of the inorganic gas and/or volatile organic expansion agent that penetrates the voids between the foam particles in the mold cavity and the restoration of the compressed foam particles are combined. Since force is used in combination, the gas pressure for infiltration can be lowered than in the case of the pressure aging molding method alone, and therefore the molding cycle can be shortened. That is, the present invention provides polyolefin foam particles having closed cells with a pressurized gas of 0.3 to 1 Kg/cm ² G.
After applying a gas pressure of
The apparent bulk volume of this pressurized inorganic gas is 60~
Fill the mold cavity while compressing the foam particles to 90%, then remove gas from the mold cavity while the foam particles are compressed, and then introduce steam into the mold cavity to compress the compressed foam particles. The present invention provides a method for producing a polyolefin foam, characterized by fusing the polyolefin foam. (Foam particles) The foam particles of the present invention have a bulk density of 12 g/~50
g/, polyolefin foam particles having a particle size of 2 to 5 mm, and the polyolefin foam particles may be crosslinked or non-crosslinked. Polyolefins include polyethylene, polypropylene,
Ethylene/propylene random copolymer (ethylene content 1-12% by weight), ethylene/propylene/
Butene-1 random copolymer (ethylene content 1~
10% by weight, butene-1 content 2~10% by weight), ethylene/vinyl acetate copolymer (vinyl acetate content 3~10% by weight),
28% by weight), silane-modified polypropylene, and crosslinked products thereof. The foam particles can be produced by extruding a mixture of polyolefin and a pyrolyzable blowing agent into a strand using an extruder, foaming it, and crosslinking it into pellets, or by adding volatile substances such as dichlorodifluoromethane or butane to the polyolefin particles. Products that have been impregnated with a foaming agent to give them foaming power and then heated and foamed, and products that have been crushed from polyolefin foam products.
Examples include foamed particles obtained by infiltrating polyolefin particles containing an inorganic filler dispersed in water, heating and pressurizing the particles, and then releasing the polyolefin particles together with water into atmospheric pressure from an autoclave. -38716, 49-2183, 51-
No. 22951, No. 56-1344, No. 57-17890, JP-A-Sho
No. 47-34458, No. 57-90027, No. 58-55231,
No. 58-197027, etc.). These foam particles contain stabilizers such as 2,6-t-butylphenol, ultraviolet absorbers, dyes, pigments such as titanium oxide and carbon black, lubricants such as higher fatty acid metal salts, and surface modifications such as triglycerides of higher fatty acids. It may contain a quality agent and the like. These foam particles usually have a closed cell ratio of 70% or more. (Pressure treatment) In order to impart expandability to the polyolefin foam particles, the foam particles are held in a pressurized gas atmosphere and the internal pressure of the cells of the foam particles is adjusted to 0.3 to 1 Kg/cm ² G.
increase to The pressurization treatment is carried out by placing the foam particles in a pressurized container and supplying pressurized gas of 0.1 to 4 kg/cm ² G into the pressurized container for 5 to 20 hours. The temperature during pressure treatment is usually room temperature, but heating may be used.
The above temperature is determined in consideration of the material of the particles, the particle size, the pressure treatment time, etc. The pressurized gas may be an inorganic gas or a volatile organic expansion agent, or both may be used in combination. Examples of the inorganic gas include air, nitrogen, argon, neon, carbon dioxide, etc., and examples of the volatile expansion agent include propane, butane, pentane, cyclobutane, trichlorofluoromethane, dichlorodifluoromethane, methyl chloride, etc. Among these, air is economically preferable. The method of pressure treatment is described in Japanese Patent Publication No. 51-22951 and No. 52.
30304, Japanese Patent Laid-open No. 57-12035, Japanese Patent Application Laid-Open No. 58-101025, etc., detailed explanation will be omitted here. The pressure treatment infiltrates gas into the foam particles and provides a constant gas pressure within the foam particles. This particle internal pressure is 0.3 to 1 Kg/cm ² G.
If it is less than 0.3 Kg/cm ² G, it is insufficient to fill the gaps between the foam particles when heating with steam to fuse the foam particles together to produce a molded foam product. On the other hand, if the pressure exceeds 1 kg/cm ² G, there is a drawback that the pressure treatment takes time. (Compression filling) The pressurized foam particles are stored in a pressurized cylindrical container (hopper) and pressurized with pressurized gas to 60 to 90% of the original apparent bulk volume. Compressed with gas (therefore the compression ratio is 10-40%),
The foam particles are then filled into a mold cavity pressurized to 1 to 10 kg/cm ² G formed by a mold consisting of a pair of female and male molds, and then the filling gun is closed and the foam particles are compressed. The pressure inside the mold cavity is adjusted to near or atmospheric pressure, and the restoring force of the compressed foam particles is used to fill the voids between the particles. As the pressurized gas, the above-mentioned inorganic gases and volatile organic expansion agents can be used, but in terms of economy and safety, inorganic gases such as air and nitrogen gas are used. The pressure of the inorganic gas that compresses the foam particles is higher than atmospheric pressure, and is determined by taking into consideration the degree of compression, the time required for compression, and the like. The pressure is 1
~10Kg/ ^cm2G , preferably 3-5Kg/ ^cm2G . The temperature at which the foam particles are compressed is lower than the softening temperature of the polyolefin. Preheating the mold before filling it with foam particles can shorten the molding cycle. (Molding) The foam particles filled in the mold are heated and fused together by introducing water vapor into the mold cavity, and then cooled to form a foam product that is faithful to the mold cavity. During heating, the pressurized gas within the foam particles expands, and the foaming of the resin completely fills the gaps between the particles that could not be filled by the restoring force alone. The pressure of water vapor is 0.2 to 6 Kg/cm ² G. The mold used for molding may be a steam mold having steam holes (or slits) for both the female mold and the male mold, or the male mold or the female mold as disclosed in FIGS. 1 and 4 of West German Published Patent No. 2928119. A mold may be used in which one of the molds has steam holes and the other mold does not have steam holes. It is a good idea to exhaust the inorganic gas present between the foam particles in the mold cavity to the outside of the mold to prevent the formation of cavities in the resulting foam product. As disclosed in the drawings of the above-mentioned West German patent specification, the method for exhausting such inorganic gas is as follows: After introducing steam into a fractionated steam chamber, the steam chamber is of a fractionated type. Stop the supply of steam, and then introduce steam to other fractionated steam chambers,
Next, the steam is introduced into both planned steam chambers for full-scale heating.The steam hole is introduced into the female steam chamber in advance, and then the steam is supplied into the female chamber. One method is to stop the heating, then introduce steam into the male steam chamber, and then introduce steam into both steam chambers to perform full-scale heating. Cooling is performed by introducing cooling water (5 to 60°C) into the mold. The molded foam product thus obtained has a bulk density of 18 to 70 g/, has a good appearance, and has almost no cavities or gaps inside the foam. 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 of manufacturing foam particles: In an autoclave, 250 parts of water, ethylene (4 parts)
%) Propylene copolymer particles (melting point 140℃) 100
parts, 0.7 parts of tricalcium phosphate with a particle size of 0.3-0.5 microns, sodium dodecylbenzenesulfonate
After charging 0.007 parts, nitrogen gas was applied under stirring until the internal pressure of the autoclave reached 5 kg/cm ² G, and the supply of nitrogen gas was stopped. Next, 24 parts of isobutane was supplied into the sealed container and the mixture was heated for 1 hour.
When the autoclave was heated to 135° C. and maintained at the same temperature for 30 minutes, the autoclave internal pressure was 23 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 about 2 seconds to cause foaming. The bulk density of the polypropylene foam particles thus obtained having a particle size of 2.5 to 4 mm was about 21.8 g/. Further, no blocking between foam particles was observed. Example 1 (Pressure treatment) The polypropylene foam particles having a bulk density of 21.8 g/cm2 obtained in the above example were placed in a pressure-resistant container and heated to 3 kg/ ^cm2 .
G air is supplied into a pressure-resistant container, held at the same pressure for 10 hours, and then removed to atmospheric pressure until the internal pressure is
Foam particles of 0.75 Kg/cm ² G were obtained. (Compression filling) The foam particles 10 were placed in a pressure-resistant cylindrical container (hopper) and compressed with compressed air of 3 kg/cm ² G to compress the foam particles to 66% (6.6) of the original bulk volume. Later, the internal volume under pressure of 2.5Kg/cm ² G was 5.8
The compressed foam particles were filled into the mold cavity of a packaging container mold consisting of a pair of female and male molds for 10 seconds, and then the filling gun was closed, and the pressure inside the mold cavity was increased to 0.5 kg/cm ² G.
The pressure was released to Next, 3 kg/kg was placed in the male steam chamber.
Steam at cm ² G was applied for 4 seconds, then steam was introduced into the female steam chamber for 4 seconds, and then steam at the same pressure was introduced into both chambers for 8 seconds to fuse the foam particles together. Ta. After that, stop the steam supply and heat the mold to 60℃ at 90℃.
After cooling for seconds, the mold was opened, yielding a foam product with a bulk density of approximately 33 g/m. The appearance of this product was smooth and good, and no cavities or gaps were observed in the cross section of the foam. Examples 2 to 4 Molded foam products were obtained in the same manner except that the molding conditions were changed as shown in Table 1. Reference Example 1 (Compression filling method) The polypropylene foam particles with a bulk density of 21.8 g/g obtained in the above example were placed in the hopper used in Example 1, and the foam particles were heated with nitrogen gas of 3 Kg/cm ² G. After compressing to 50% of the original bulk volume, it was fed into a mold cavity under pressure of 2.5 kg/cm ² G, and molded under the conditions shown in Table 1 to produce a molded foam product with the physical properties shown in the table. I got it. Reference Examples 2 to 3 Molded foam products having the physical properties shown in Table 1 were obtained in the same manner as in Reference Example 1, except that the molding conditions were changed as shown in Table 1. Reference Example 4 (Pressure Aging Method) Propylene-ethylene (4% by weight) random copolymer foam particles with a bulk density of approximately 30 g/cm are placed in a pressure-resistant container, and pressurized air of 3 kg/cm ² G is resistant to the pressure. The mixture was supplied into a container, maintained at the same pressure for 40 hours, and then depressurized to atmospheric pressure to obtain foam particles having an internal pressure of 1.8 Kg/cm ² G. These foam particles were filled into the packaging container mold used in Example 1 and molded under the conditions shown in Table 1 to obtain a foam product having a bulk density of about 31 g/. Reference Example 5 A foam product having the physical properties shown in Table 1 was obtained in the same manner as in Reference Example 4, except that the molding conditions were changed as shown in Table 1. The evaluation criteria in the table are as follows. Appearance ◎: The surface has excellent light selection, is smooth, and no deformation is observed. ○: The surface has excellent optical selectivity and is smooth, but some deformation is observed. ×: Surface brightness is normal, but there are some dents on the surface. Also, deformation can be seen. Presence of nests and gaps ◎: There are 5 or less nests and gaps in a cross-sectional area of 100 cm ² (10 x 10). ○: 5 to 10 pieces. △: 10 to 20 pieces. ×: 20 or more. 【table】

Claims (1)

[Claims] 1. A gas pressure of 0.3 to 1 Kg/cm ² G is applied to polyolefin foam particles having closed cells using a pressurized gas, and then this is applied with a pressurized inorganic gas. The foam particles are compressed and filled into the mold cavity so that the apparent bulk volume is 60 to 90%, then gas is removed from the mold cavity while the foam particles are compressed, and then steam is introduced into the mold cavity. A method for producing a polyolefin foam, which comprises fusing compressed foam particles together. 2. The manufacturing method according to claim 1, wherein the polyolefin foam particles are polypropylene foam particles. 3. The manufacturing method according to claim 1, wherein the mold cavity is formed from a pair of female and male molds each having a steam chamber. 4 Steam is introduced into the mold cavity by first introducing the steam into the chamber of one of the male and female molds, passing through the chamber of the other mold and exhausting it outside the mold, and then introducing the steam into the chamber of the other mold. New steam is introduced, this steam passes through the chamber that originally introduced the steam, and is discharged out of the mold.Then, steam is then introduced into both chambers at the same time, and the steam is passed through the chamber and discharged out of the mold. Claim 3, characterized in that the compressed polyolefin foam particles are heated and fused by discharging.
Manufacturing method described in section. 5. The manufacturing method according to claim 1, wherein the polyolefin foam particles are crosslinked polyethylene foam particles.