JP2785076B2 - Method for producing bead-in-mold molded product - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an in-mold bead foam molded article useful for a landfill for soft ground, a corner pad for packaging heavy goods such as electric appliances, and the like.

[0002]

2. Description of the Related Art In-mold bead foam molded products made of polystyrene, polypropylene, polyethylene, etc. are commercially available. These molded products are excellent in light weight, heat insulation properties, cushioning properties, etc., and are therefore used in various types of packaging. It is widely used for materials, containers, architectural heat insulating materials, core materials for automobile bumpers, and the like.

[0003]

In the above applications,
Generally, high lightness and high compressive strength are required. Conventionally, as a method of increasing the compressive strength of a foamed molded article in a mold, there is a method of decreasing the expansion ratio, in other words, increasing the density. According to this method, there are problems that the weight of the product increases, the cost increases, and the cushioning property decreases.

[0004] In particular, a material for reclaiming soft ground (Japanese Utility Model 1)
JP-A-120533 and JP-A-63-194948) are blocks having dimensions of 1000 mm in length, 2000 mm in width, and 500 mm in height (density is 0.02 g / cm ³ ).
The weight of one is 20kg. Light (low density)
If blocks having the same compressive strength are present, it is possible to reduce the weight of each block, and not only handling such as transportation becomes easy, but also material cost can be reduced. The same applies to a core material of an automobile bumper having a length of 1500 mm, a width of 120 mm, and a height of 100 to 150 mm.

[0005] It is said that, in the in-mold bead foam molded article of the same material and density, the smaller the cell diameter, the greater the compressive strength. Although a cell adjusting material is used for adjusting the bubble diameter, it is currently difficult to expect much improvement in compressive strength by adjusting the bubble diameter, and such improvement is known.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to obtain an in-mold bead foam molded article having a higher compressive strength even if the foam is made of the same material and the same density. It is to provide a manufacturing method of.

[0007]

In order to achieve the above-mentioned object, a method for producing an in-mold bead expanded molded product according to the present invention is characterized in that pre-expanded particles are filled into a mold capable of changing the volume of a cavity. While the particles are heated and foamed by steam or the like and fused together, or after fusion to obtain a foam in which a gap between the particles remains, one of the molds or both molds are separated. By moving the split mold, the volume in the cavity of the mold is increased by 1.1 to 2 times, and the foam is heated and expanded in the cavity, so that foam molding faithful to the shape of the cavity is performed. Form the body,
Next, the foam molded article is cooled.

Thus, the pre-expanded particles used in this production method, for example, the pre-expanded particles of a styrene-based resin, are fatty acid hydrocarbons such as propane, butane, pentane and hexane, or halogens such as methyl chloride and tetrachloroethylene. Styrene-based resin particles containing 2 to 15 parts by weight of this expanding agent in particles are heated by steam while stirring to obtain a density of 0.015 to 15.15. It is pre-foamed to a size of 0.15 g / cm ³ and a particle size of 2 to 8 mm. Further, as the styrene resin, a homopolymer of a styrene monomer such as styrene, methylstyrene, chlorostyrene, a copolymer between monomers of this kind, or a monomer of this kind and another And copolymers with butadiene, isoprene, vinyl chloride, methyl methacrylate, and the like.

Further, in the present invention, expansion and compression of the foam are carried out at a temperature higher than the temperature at which the raw material resin of the foam gives plasticity (75 to 80 ° C. for polystyrene).
In practicing the present invention, the foam is at the temperature higher than the heat deformation temperature at the time of expansion and compression only by first steam heating the pre-expanded particles, so that external heating is not necessary, but if necessary, May be externally heated. Further, as the pre-expanded particles, pre-expanded particles of a thermoplastic resin such as polypropylene, low density polyethylene, high density polyethylene, and linear polyethylene can be used.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an example of a mold used for carrying out the method of the present invention will be described with reference to the drawings. In FIG. 1, 1
Is a mold that can change the volume of the cavity 2 and is formed by a split mold 1a and a split mold 1b that can be freely attached and detached. 3 is split type 1
It is a contact surface (parting line) of a and 1b. 4 is a chamber for introducing a heating fluid (steam) or a cooling fluid (water), 5 is a large number of holes formed in the split molds 1a and 1b so as to allow steam to pass therethrough but not pre-expanded particles. Reference numeral 6 denotes a filling port for the molding material perforated on the side of the split mold 1b. Reference numeral 7 denotes a filling gun mounted on the filling port 6, which is capable of filling the pre-expanded particles into the cavity 2 by compressed air supplied by an air supply pipe 8. have. Reference numeral 9 denotes a material supply pipe connected to a hopper (not shown), and reference numeral 10 denotes a piston that opens and closes the filling port 6.

Next, the method of the present invention using the mold 1 will be described. After filling the pre-expanded particles into the cavity 2 of the mold 1 with the contact surface 3 of the split mold 1a and the split mold 1b being 1 mm apart by using the filling gun 7 and closing the filling port 6, the pressure is reduced. Introduces steam of 0.5 to 5 kg / cm ² G into the chamber 4 of the split mold 1b for 5 to 10 seconds, and removes air existing between particles as much as possible.
b, and then steam is introduced into the chamber 4 of the split molds 1a and 1b at the same pressure for about 20 to 100 seconds to heat and expand the particles and to fuse the particles together. At this time, it is necessary to leave 5 to 30% of voids through which steam for heating can pass in the next heating step, not in a completely adhered state in which the particles are fused.

Next, after the mold 1 is opened to increase the volume of the cavity 2 by 1.1 to 2 times, and steam is introduced into the chamber 4 to expand the foam (see FIG. 2). ), Cooling water is introduced into the chamber 4 for about 30 seconds to cool the foamed molded body, and then the mold 1 is opened to obtain a molded product. As shown in FIG. 3, in the cross section of the molded product f, the bubble diameter in the direction (arrow) in which the mold 1 is opened is larger than the diameter in the perpendicular direction, and the compressive strength in this direction is perpendicular to the perpendicular direction. Greater than compressive strength. In this case, if the volume increase of the cavity 2 due to the mold opening is less than 1.1 times, the obtained foamed molded article does not show an improvement in compressive strength, and if it exceeds 2 times, the molded article having a smooth surface ( A molded product faithful to the cavity shape of the mold cannot be obtained.

Embodiment 1 A mold 1 shown in FIG.
0 mm, 500 mm in width, and 200 mm in height) within the polystyrene pre-expanded particles [JF-151 (trade name) manufactured by Mitsubishi Yuka Birdsie Co., Ltd., bulk density 0.03 g /
cm ³ ], and then 0.6 kg / cm ² G of steam was introduced into the cavity 2 for 5 seconds to be degassed.
Steam at the same pressure was introduced for 20 seconds to obtain a foam having a porosity of about 10% (first step). Then, without cooling the foam, the mold 1 was opened by 30% while the temperature was 80 ° C. or higher (the mold opening speed was 68 m / sec) and 0.6 kg /
cm ² G steam was introduced for 15 seconds to complete foaming and to adhere to the cavity shape.
m, width 500 mm, height 260 mm) (second step). Then, water at 20 ° C. was introduced into the chamber 4 for 15 seconds, and after cooling for 5 minutes, the mold was opened and the density was reduced to about 0. A molded product with a smooth surface of 0.023 g / cm ³ (in-mold bead foam molded product faithful to the cavity shape of the mold) was obtained.
The compressive strength at 5% strain in the height direction of this foamed molded product was 2.04 kg / cm ² , and the compressive strength at 5% strain in a direction perpendicular to this was 1.45 kg / cm ² .

Comparative Example 1 The mold 1 shown in FIG.
(Vertical 500mm, horizontal 500mm, height 200m
m) is filled with polystyrene pre-expanded particles (JF-151 (trade name, manufactured by Mitsubishi Yuka Birdsie Co., Ltd., bulk density: 0.03 g / cm ³ )).
After degassing by introducing steam of cm ² G into the cavity 2 for 5 seconds, steam at the same pressure was introduced for 35 seconds. Next, water at 20 ° C. was introduced into the chamber 4 for 15 seconds, and after cooling for another 5 minutes, the mold was opened and the density was about 0.03 g /
A ³ cm ³ in-mold bead foam molded article (length 500 mm, width 500 mm, height 200 mm) was obtained. The compressive strength of this foam molded article at 5% strain in the height direction is 2.40 kg.
/ Cm ² , and the compressive strength at 5% strain in a direction perpendicular to this direction was 2.37 kg / cm ² .

Examples 2 and 3 and Comparative Examples 2 and 3 Example 1 was repeated except that pre-expanded particles having different bulk densities were used. Production was performed in the same manner as in Comparative Example 1 to obtain a foam molded article as shown in Table 1.

Embodiment 4 In place of opening the mold by 30% in Embodiment 1 above, 60%
A foam molded article (see Table 1) faithful to the shape of the cavity of the mold was obtained in the same manner except for changing the above.

[0017]

[Table 1]

As shown in Table 1 above, the in-mold bead foam molded product obtained by the production method of the present invention has a compressive strength in the direction in which the mold is opened of about 30 to 4 in comparison with a normal product (comparative example).
It can be understood that it is improved by 0%.

[0019]

The present invention is as described above. Even if the same material is used for the same density foam, it is possible to produce an in-mold bead foam molded article having a higher compressive strength, thereby saving material. The economic effect is enormous, coupled with the fact that the cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a mold used for carrying out the production method of the present invention, showing an initial molding stage when pre-expanded particles are filled.

FIG. 2 is a cross-sectional view of a mold in a final molding stage.

FIG. 3 is a partially enlarged sectional view of a molded product.

Claims (1)

(57) [Claims] 1. A pre-expanded particle is filled in a mold capable of changing the volume of a cavity, and the group of particles is heated and foamed to be fused to each other or to be fused to leave a gap between the particles. After obtaining a foam, one or both of the mold halves are moved to reduce the volume in the cavity of the mold to l. Heat-expanding the foam in this cavity, increasing by a factor of 1-2, to form a foam molded article that is faithful to the shape of the cavity,
A method for producing an in-mold bead foam molded article, comprising cooling the foam molded article.