JP2774814B2 - Method for producing highly elastic thermoplastic resin foam molded article - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Object of the Invention) The present invention relates to highly elastic polystyrene, polyethylene, polypropylene, and the like having excellent rebound resilience, cushioning properties, and secondary workability.
An object of the present invention is to provide a method for producing a foamed molded article of a thermoplastic resin such as polyamide.

(Industrial Application Field) The highly elastic foam molded product obtained by the production method of the present invention is useful as a floor covering material, a heat insulating material for a storage tank, a heat insulating material for a building wall, a bumper core material, and a packaging cushioning material. .

(Prior art) Conventionally, foamed styrenic resin molded articles have been widely used for cushioning packaging materials, containers and the like because of their excellent lightness and heat insulating properties. However, there are drawbacks such as a large compressive strain, a defect of poor rebound resilience, and a difficulty in performing complicated mechanical processing such as grooving, bell-shaped or cylindrical punching because of easy cracking.

As a method for improving the poor elasticity of the styrene resin molded article, pre-expanded particles of styrene resin are filled in a mold, and the pre-expanded particles are expanded by heating with steam and fused together. To form a foamed styrene-based resin molded product, remove the foamed styrene-based resin molded product from the mold, ripen, and then put the foamed styrene-based resin molded product in a mold frame.
A method for producing a highly elastic foamed styrenic resin molded article characterized by being compressed to 50% or less has been proposed (JP-B-61-34378).

(Problems to be Solved by the Invention) The molded article obtained by this method is excellent in elasticity and excellent in return dimensions after compression release, but has the following disadvantages.

(I). The work of compressing the bead in-mold foamed product, releasing the compression, compressing again, and releasing the compression again is performed in three steps.
Unless it is repeated up to 6 times, a highly elastic foam molded article cannot be obtained in a short time.

(Ii). The density of bead foam molded products in the mold is 11.6g / or 16.8
g / like foaming ratio of 60 to 100 times and high foaming,
It can be compressed until the thickness of the foamed bead in the mold is reduced by 80%, but the density of the foamed bead in the mold is 30 ~
When the foaming ratio is as low as 10 to 33 times with 100 g /, the wall thickness is 80
When the in-mold bead foam molded product is compressed so as to reduce the percentage, the styrene resin foam molded product is cracked.

Therefore, unless the degree of compression is gradually and gradually increased from low to high, a highly elastic foam molded article cannot be obtained.

The present invention is not limited to the in-mold bead foam molded product having a high expansion ratio, the in-mold bead foam molded product having a low expansion ratio, and the extruded foam molded product can be cracked in a very short time by high compression. Provided is a method for producing a resin foam molded article having high elasticity.

(Specific Means for Solving the Problems) In the present invention, a thermoplastic resin foam molded article having a closed cell structure (50% or more of the cells only need to be closed cells) is subjected to a reduced pressure treatment and then compressed to be extremely short. A foamed article having high elasticity can be obtained in a short time.

(Resin foam molded products) Foam molded products have a closed cell ratio of 50% or more, regardless of the molding method, such as in-mold bead foam molded products, compression-filled bead fusion molded products, extruded foam products, injection foamed products, etc. Preferably 65-98% or more polystyrene, ABS, styrene-based resin such as styrene-α-methylstyrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer; polypropylene, polyethylene, ethylene-vinyl acetate copolymer, A foam of a thermoplastic resin such as polyamide, polyvinyl chloride, and urea resin can be used. These may be obtained by cutting a block-shaped foam molded product with a heating wire. Further, it may be crosslinked.

The density of the foam molded article is 5 to 100 g /, preferably 8 to 3 g.
0 g /. As the density is smaller, a molded product having higher elasticity can be obtained.

(Decompression treatment) In the decompression treatment of the foam molding machine, the foam molded article 1 is placed in the decompression chamber 2 shown in FIG. And reduce the degree of decompression of the cells inside the foamed molded article to −
759 mmHg to -250 mmHg.

When a vacuum chamber having a large volume is used, many foam molded articles can be subjected to vacuum treatment at one time. Of course, a press mold provided with a decompression chamber may be used to perform the decompression process and the subsequent compression. However, in this case, the decompression process is the rate-determining step in the molding process, and the productivity of the foam molded article is not improved.

(Compression treatment) The foam molded product subjected to the decompression treatment is taken out of the decompression chamber, and is immediately or left for 0.5 to 10 hours under the atmospheric pressure, and the internal pressure of the foam molded product is from -150 mmHg to -750 mmHg, preferably -700mmHg~-230mmHg and the summer was that the press molding machine (3, 3 ') the wall thickness of the molded article before compression by using the (t ₀₎ 40~9
0% (thickness t ₁ of the molded article after compression 0.6t ₀ ~0.1t ₀₎ compresses. The compression speed is not particularly limited, but is preferably 50 to 60.
About 0mm / min is good. The temperature at the time of compression may be room temperature or may be heated to a temperature lower by 20 ° C. than the softening point of the resin. The number of compressions may be one or several.

At this time, the mold 4 may be provided (FIG. 3) or not (FIG. 2).

Is compressed, 50-90% of the wall thickness t ₀ of the previous thickness t ₂ of the released molded foam from the press to be compressed (0.5 t ₀ to 0.9
t ₀ ).

Further, when the foamed molded product 1 is compressed into a foamed molded product by compressing the compression load in only one direction by a press machine, although the distortion on both surfaces in the direction in which the compression load is applied is not, the distortion on the surface not subjected to the compression load is reduced. Due to slight occurrence, third
As shown in the figure, if a compressive load is applied in three directions of the foam molded product block, the distortion is eliminated, high elasticity is exhibited in all three directions, cutting becomes easy, and a cardboard box and a refrigerator or TV as a cushioning material are used. When filling in the gaps of stored items,
Since it can be deformed in a three-dimensional direction, there is an advantage that it becomes easy to insert the cushioning material.

(Effects) According to the present invention, since the foam molded article is compressed after being subjected to a reduced pressure treatment, a foam molded article having a low expansion ratio can be made into a highly elastic foam molded article by only one compression.

(Examples, etc.) Examples 1 to 6 A block of a bead foam molded product in a polystyrene mold having a closed cell ratio of 90% and a density of 12 g / (length 1840 mm × width 930 mm × height 4
25mm) was cut with a nichrome wire to form a rectangular parallelepiped block measuring 300 mm x 300 mm x 150 mm.

After placing five blocks of this size in a decompression chamber with an internal volume of 100, and then depressurizing the decompression chamber to -750 mmHg,
Stored in a vacuum chamber for 0.5-20 hours.

Then, the block subjected to the decompression treatment is taken out of the decompression chamber, and immediately or after being left under the atmospheric pressure, the thickness is reduced to 30 mm (compression rate 80%) at a speed of 500 mm / min in a height direction by a 10-ton press. And then the press was raised to obtain a highly elastic foam.

The presence or absence of cracks in this highly elastic foam, the compression modulus (JIS
K-7220) are shown in Table 1.

Example 7 An elastic foam having the physical properties shown in Table 1 was obtained in the same manner as in Example 1 except that the pressure during the depressurizing treatment was -759 mmHg.

Comparative Example 1 Except not performing the decompression treatment, the foamed molded product was broken when pressed in the same manner as in Example 1. Further, the compression modulus was more than twice as high as that obtained by performing the decompression treatment.

Examples 8 to 12 Blocks of foamed beads in a polystyrene mold having a closed cell ratio of 95% and a density of 17 g / (length 1840 mm × width 930 mm × height 4
25mm) was cut with a nichrome wire to form a rectangular parallelepiped block measuring 300 mm x 300 mm x 150 mm.

A block of this size was placed in a decompression chamber, and then the pressure inside the decompression chamber was reduced to -755 mmHg for 3 hours, and the foamed molded product had an internal cell pressure of -230 mmHg. Then, the block subjected to the decompression treatment was taken out of the decompression chamber, and the compression ratio was 40%, 50% in the height direction at a speed of 200 mm / min by a 10-ton press.
%, 60%, 70% and 80% and then the press was raised to obtain a highly elastic foam.

 Table 2 shows the compression elastic modulus and height of this high elastic foam.

Comparative Examples 2 and 3 A foam molded article having the physical properties shown in Table 2 was obtained in the same manner as in Examples 6 to 10, except that the compression ratio was changed to 20% and 30%.

Comparative Example 4 A foam molded article having the physical properties shown in Table 2 was obtained in the same manner as in Example 9 except that the decompression treatment was not performed.

Example 13 In Example 1, the compression elastic modulus and dimensions in each direction of the three-way compression-treated foam obtained by instantaneously compressing 80% each in the horizontal and vertical directions after compression in the height direction are as follows. It was on the street.

Example 14 A nichrome wire cutting block of a foamed bead in a polystyrene mold having a density of 10.8 g / and a closed cell ratio of 82% (length: 300 m)
m × 300 mm × 150 mm) in a vacuum chamber at −755 mmHg for 10 hours, and after 5 minutes 80
% To obtain an elastic foam block having the physical properties shown in Table 3.

Comparative Examples 5 to 6 In Example 13, the procedure was the same except that the decompression treatment was not performed (Comparative Example 5), or the compression was repeated three times without the decompression treatment (Comparative Example 6), except that Thus, an elastic block having the physical properties shown in Table 3 was obtained.

Example 15 In-mold bead foam molding was performed at a density of 15 g / closed cell rate.
A chamber containing 86% polystyrene foam (300 mm x 300 mm x 150 mm) inside the cavity is depressurized to -500 mmHg and maintained at that pressure for 30 minutes to maintain the same pressure inside the cavity that communicates with the chamber via a steam hole. After decompressing the foam and depressurizing the foam, the upper mold is further lowered to reduce the foam to 40
% Compression, then open the mold and have a flexural modulus of 9.8 kg / cm ² ,
A crack-free foam having a height of 98 mm was obtained.

Example 16 The density of beads formed in a mold was 50 g /, and the compression modulus was 70.7.
A polypropylene resin foam having a closed cell ratio of about 86% in kg / cm ² is subjected to a decompression treatment at −500 mmHg for 180 minutes in a decompression chamber, and then taken out of the decompression chamber, and is taken up and down by 80% in a pressing mold. The compression modulus of the product obtained by compressing three times is 15.0 kg / c
Atsuta in m ^2.

Comparative Example 7 A compression-treated molded article obtained in the same manner as in Example 16 except that the depressurization treatment was not performed was 26.0 kg / cm ² .

Example 17 In Example 16, three compression treatments at 80% compression rate were performed in the up-down direction, the front-rear direction, and the left-right direction, but the compression elastic modulus was about 17 to 18 kg / cm ² .

Comparative Example 8 In Example 17, except that the decompression treatment was not performed, the same compression treatment was performed, but the compression elastic modulus was 35 to 38 kg / cm ² .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state where the pressure of a foam molded article is reduced;
2 and 3 are plan views showing a state in which the foam molded article is compressed, and FIG. 4 is a perspective view showing a direction in which the foam molded article is compressed.

Claims (2)

(57) [Claims] 1. A foamed thermoplastic resin article having a closed cell structure is placed in a reduced pressure chamber, exposed to a reduced pressure, and then the foamed article is compressed to 40 to 90% of its thickness. A method for producing an elastic thermoplastic resin foam molded article. 2. A block of a thermoplastic resin foam molded article having a closed cell structure is placed in a reduced pressure chamber and exposed to a reduced pressure. A method for producing a highly elastic thermoplastic resin foam block, wherein the block is compressed to 90%.