JPH0446743B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for in-mold molding of expanded thermoplastic resin particles. More specifically, the present invention relates to an in-mold molding method suitable for obtaining an in-mold foam molded product having greater structural strength with a smaller amount of resin used.

[Prior art] As an in-mold molding method for foamed thermoplastic resin particles,
A method of heating and compressing foamed particles, filling them into a mold, and then reducing the pressure to about atmospheric pressure. A method of heating and compressing foamed particles, filling them into a mold, and then compressing them, reducing the pressure to about atmospheric pressure while reducing the volume of the mold. A method of filling compressed foamed particles into a mold and then heating the foamed particles is known.

[Problems to be Solved by the Invention] However, in molded products obtained by any of the above conventional methods, each part has the same material strength regardless of the strength required for that part. In the case of thick molded products, there is a problem in that the amount of resin used to obtain a molded product of a certain strength is greater than necessary.

The present invention has been made to solve the above problem, and provides a method for molding an in-mold foam molded product with greater structural strength using a smaller amount of resin using expanded thermoplastic resin particles. The purpose is to provide.

[Means for Solving the Problems] The present invention performs in-mold foam molding by filling thermoplastic resin foam particles into a mold while compressing them using pressurized gas, and then heating and fusing the foam particles with steam. The method is characterized in that molded products with partially different densities can be obtained in the same mold by changing the pressure of pressurized gas for compressing the foamed particles during filling. Regarding the in-mold molding method.

[Function] In the in-mold molding method of the present invention, by changing the pressure of pressurized gas for compressing expanded particles during filling, parts with different material strengths are formed within one molded product, and Therefore, the portion having excessive material strength can be reduced, and an in-mold foam molded product having greater structural strength can be obtained with a smaller amount of resin.

[Example] The foamed thermoplastic resin particles used in the present invention are foamed thermoplastic resin particles that are filled into a mold in a compressed state and then heated to form an in-mold foam molded product. If so, it can be used without any particular restrictions. Specific examples include polystyrene, poly-α-methylstyrene, styrene-
Maleic anhydride copolymer, polyphenylene oxide-polystyrene blend or graft polymer, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene terpolymer, styrene-butadiene copolymer,
Styrenic polymers such as ethylene-styrene copolymer and high-impact polystyrene; low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, Polyolefin polymers such as polypropylene, ethylene-propylene-butene random terpolymer, propylene-vinyl chloride copolymer, propylene-butene copolymer, propylene maleic anhydride copolymer; polyvinyl chloride polymer; and polymethyl methacrylate polymer, etc. Examples include foamed resin particles.

These may be used alone or in a blend of two or more. Polyolefin polymers are
It may be used after crosslinking with peroxide or radiation, but it can also be used without crosslinking.

There are no particular restrictions on the manufacturing method, density, or particle size of the foamed thermoplastic resin particles, and foamed particles manufactured by a conventional method may be used, but depending on the foaming power of the foamed particles during heat fusion and the pressurized gas. In terms of the compression amount of the foamed particles during compression, it is preferable to have a density in the range of 16 to 60 g/, and in terms of the fluidity of the foamed particles during filling, it is preferable to have a density in the range of 1 to 15 mm, particularly 3 to 7 mm. It is preferable that the particles have an average particle size.

The foamed thermoplastic resin particles are compressed using pressurized gas, and the compressed foamed particles are filled into a mold in a compressed state and then heated and fused with steam.

The pressurized gas pressure at the time of filling is set to be low when filling parts of the in-mold molded product to be manufactured that may require low material strength, and high when filling parts that require high material strength. be adjusted. The pressure cannot be determined unconditionally because it varies depending on the type, density, particle size, etc. of the foamed particles, but for example, in the case of polypropylene foamed particles, a pressure of 1.0 to 5.0 Kg/cm ² G is used. It is preferable to do so within a range. In the case of polypropylene foam particles, if the pressure is less than 1.0 Kg/cm ² G, the foaming ability is not sufficiently imparted, and voids are formed at the fused interface of the foam particles, resulting in poor surface properties of the molded product. If it exceeds 5.0 Kg/cm ² G, the steam flow tends to deteriorate due to excessive compression and the internal fusion of the molded product tends to deteriorate, both of which are not preferable.

As the pressurized gas, an airless gas such as nitrogen gas or carbon dioxide gas can be used, but air is preferably used in terms of safety and cost.

The steam conditions for heat fusion are generally a temperature of 120 to 150°C and a pressure of 1.0 to 4.0 kg/cm ² G.

This heat fusion results in an in-mold molded product having a low density in the areas filled with low pressure and a high density in the areas filled with high pressure.

Next, an example of the in-mold molding method of the present invention will be explained with reference to the drawings.

FIG. 1 is an explanatory diagram showing an example of an apparatus used in the in-mold molding method of the present invention. In Fig. 1, 1 is a foamed particle supply port, 2 is a pressurized gas inlet, 3 is a foamed particle compression tank, 4 is a pressurized gas inlet for filling the foamed particles, and 5 is a pressurized gas inlet for filling the foamed particles.
is a mold gas pressure adjustment valve, 6 is an exhaust port, 7 is a mold, 11 is a concave mold, 12 is a convex mold, 13 is a mold frame, 14 is a mold back plate, 15 is a filling gun, 16 is a steam chamber, 17 is a pressure equalization line, 18 is a steam line, and 19 is an exhaust valve.

In the apparatus shown in FIG. 1, foamed thermoplastic resin particles are supplied to a foamed particle compression tank 3 from a foamed particle supply port 1, and pressurized gas is supplied to a pressurized gas inlet 2.
Supplied from. At this time, pressurized gas is also supplied to the inside of the mold, which can be closed by the pressure equalization line 17 but cannot be sealed. The pressure in the foamed particle compression tank 3 and the mold 7 is adjusted by a mold gas pressure adjustment valve 5 and raised to a predetermined pressure. At this time, the exhaust valve 19 is closed. The compressed foam particles are then filled between the concave mold 11 and the convex mold 12 by a filling gun 15. Note that filling is performed in the same manner as in normal bead method in-mold molding, and pressurized gas is supplied from the pressurized gas inlet 4 for filling expanded particles. At this time, the mold gas pressure adjustment valve 5 is opened to maintain a predetermined mold gas pressure. When moving from a part that should have a constant material strength to a part that should have a different material strength, the setting of the mold pressure adjustment valve 5 is changed, its opening degree is changed, and the mold gas pressure is changed. Filling continues with the value maintained at .

After filling is completed, excess air in the foamed particle compression tank and the mold is released through an exhaust valve, and then steam is discharged from the steam line 17 to the mold in the same manner as is normally done in bead in-mold foam molding. The thermoplastic foam particles supplied into the mold 7 and filled between the concave mold 11 and the convex mold 12 are heated and fused.

Next, the in-mold molding method of the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 and Comparative Example 1 Figure 2 is a perspective view showing the molded product of Example 1;
The figure is a sectional view showing the same molded product. In Figure 2, dimension a is 50 cm, dimension b is 30 cm, and dimension c is 15 cm.
cm, and the dimension d in FIG. 3 is 2 cm.

A mold for producing the molded product shown in FIGS. 2 and 3 was used, and an apparatus as shown in FIG. 1 was used.

Polystyrene resin with a bulk density of 16 g/, and an average particle size of approximately 5 mm (manufactured by Kanebuchi Chemical Co., Ltd., "Kanepal")
of expanded particles were fed into a compression tank. After that, the mold gas pressure adjustment valve is controlled by dividing the filling time into two stages using a timer, and for the first 5 seconds, the mold pressure is increased and adjusted to 1.4 Kg/cm ² G, and the upper part of the side wall of the molded product is heated. Fill the mold, then increase the mold pressure.
The bottom and lower side walls of the molded product were filled for 3 seconds under a reduced pressure of 0.7 Kg/cm ² G. Air was used as the pressurized gas. After that, 133℃,
Heating and fusing was performed using steam at 2.0 kg/cm ² G for 6 seconds, and after cooling, the mold was removed to obtain a molded product as shown in FIGS. 2 and 3.

The resulting molded product has a density of 25 g/
The density of the bottom and lower side walls was 18 g/1, and the total weight was 145 g.

For comparison, the mold pressure was always 0.85Kg/cm ² during filling.
A molded article of Comparative Example 1 was obtained in the same manner as in Example 1, except that the pressure was increased and adjusted to G and filling was performed for 10 seconds.

The resulting molded product has a density of 23 g/part,
It weighed 160g.

The structural strength of the molded product of Example 1 as a box body sufficiently meets the requirements, and Comparative Example 1, which is heavy,
The structural strength of the molded product was approximately the same as that of the box body.

Example 2 and Comparative Example 2 Figure 4 is a perspective view showing the molded product of Example 2;
The figure is a sectional view showing the same molded product. In Figure 4, dimension e is 30 cm, dimension f is 25 cm, and dimension g is 40 cm.
cm, the dimension h is 32 cm, the dimension i is 40 cm, and the dimension j in FIG. 5 is 1.5 cm.

A mold for producing the molded product shown in FIGS. 4 and 5 was used, and an apparatus as shown in FIG. 1 was used.

Expanded particles of cross-linked polyethylene resin (low-density polyethylene, "Sumikasen" manufactured by Sumitomo Chemical Co., Ltd.) having a bulk density of 25 g/m and an average particle diameter of about 4 mm were supplied to a compression tank. After that, the mold gas pressure adjustment valve is controlled by dividing the filling time into two stages using a timer, and for the first 6 seconds, the mold pressure is increased and adjusted to 1.2 kg/cm ² G, and the upper part of the side wall of the molded product is heated. Then, the mold pressure was reduced and adjusted to 0.6 kg/cm ² G, and the bottom and lower side walls of the molded product were filled for 6 seconds. Air was used as the pressurized gas. After that, heating and fusing was performed for 7 seconds with steam of 2.5 kg/cm ² G at 138°C, and after cooling, the mold was removed and the molded product as a heat insulating container as shown in Figs. 4 and 5 was prepared. I got it.

The resulting molded product has a density of 42g/
The density of the bottom and the lower part of the side wall was 31 g/3, and the total weight was 320 g, and both the fusion between the particles and the stability of the shape were satisfactory as an insulating container.

For comparison, the mold pressure is always 0.9Kg/during filling.
A molded article of Comparative Example 2 was obtained in the same manner as in Example 2, except that the pressure was increased and adjusted to cm ² G and filling was performed for 12 seconds.

The obtained molded article had a density of 37 g/in each part and a weight of 320 g/in the same manner as in Example 2.
However, the shape of the upper end surface of the side wall was unstable and deformation occurred, making it almost impossible to put it to practical use.

Example 3 and Comparative Example 3 The mold used in Example 1 was used, and an apparatus as shown in FIG. 1 was used.

Expanded particles of polypropylene resin ("Noblen", manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 3.3% by weight) having a bulk density of 25 g/m and an average particle diameter of about 3.3 mm were supplied to a compression tank. After that, the mold gas pressure adjustment valve was controlled by dividing the filling time into two stages using a timer, and the mold pressure was kept at 2.0 kg/cm ² for the first 3 seconds.
The upper part of the side wall of the molded product is filled with the pressure increased and adjusted to G (this is equivalent to 50% compression), and then the mold pressure is increased to 0.9Kg/cm ² G (this is equivalent to 20% compression). The bottom and lower side walls of the molded product were filled for 7 seconds under reduced pressure and adjusted conditions. Air was used as the pressurized gas. After that, 140℃, 3.0
Heat and fuse with Kg/cm ² G steam for 10 seconds. After cooling, remove the mold and
A molded product as shown in the figure was obtained.

The resulting molded product has a density of 40g/
The density of the bottom and lower side walls was 25g/2, and the total weight was 200g.

For comparison, the mold pressure was always 1.4Kg/during filling.
A molded article of Comparative Example 3 was obtained in the same manner as in Example 3, except that the pressure was increased and adjusted to cm ² G (this is equivalent to 40% compression) and filling was performed for 10 seconds.

The resulting molded product had a density of 33 g/part and a weight of 230 g.

The structural strength of the molded product of Example 3 as a box body sufficiently meets the requirements, and Comparative Example 3, which is heavy,
The structural strength of the molded product was approximately the same as that of the box body.

[Effects of the Invention] The in-mold molding method of the present invention has the effect that an in-mold foam molded product having greater structural strength can be obtained with a smaller amount of resin by using expanded thermoplastic resin particles.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an apparatus used in the method of the present invention, and FIG. 2 is an example 1 according to the method of the present invention.
3 is a sectional view showing a molded product of Example 1, FIG. 4 is a perspective view of a molded product of Example 2 produced by the method of the present invention, and FIG. 5 is a cross-sectional view of a molded product of Example 2.
FIG. 2 is a sectional view showing a molded product. Main symbols in the drawing: 1... Foamed particle supply port, 2...
... Pressurized gas inlet, 3 ... Foamed particle compression tank, 5
...Mold gas pressure adjustment valve, 7...Mold.

Claims (1)

[Claims] 1. A method for obtaining an in-mold foamed product by filling a mold with foamed thermoplastic resin particles while compressing them using pressurized gas, and then heating and fusing the foamed particles with steam, the method comprising: An in-mold molding method characterized by producing molded products with partially different densities within the same mold by changing the pressure of pressurized gas during filling.