JPS5922661B2 - Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a thermoplastic resin foam, and more particularly to a method for producing a thermoplastic resin foam having a defective portion suitable for mulch films, packaging materials, and the like.

Conventionally, to produce this type of thermoplastic resin foam, first, a thermoplastic resin such as polyethylene is mixed with a pyrolytic foaming agent and a chemical crosslinking agent, and then molded using an extruder or the like to form a foamable sheet. After that, you can heat it to cross-link and foam it, or
Alternatively, a pyrolyzable foaming agent is mixed with polyethylene, molded using an extruder or the like to form a foamable sheet, then irradiated with ionizing radiation to crosslink it, and further heated and foamed to produce a sheet-like foam. .

Thereafter, this sheet-like foam is punched to provide a desired-shaped cutout to produce a thermoplastic resin foam for use in mulch films, packaging materials, and the like. However, in the above method, a sheet-like foam having a large area is punched after foaming, which makes the processing complicated and also generates a large amount of foam waste that cannot be reused.

Furthermore, since the cut air bubbles are exposed at the defective portion of the obtained foam, that is, the peripheral side wall of the punched hole, the tensile strength and water resistance of the defective portion are significantly reduced. The present invention was made as a result of intensive research to eliminate the above-mentioned drawbacks.

That is, the present invention is a thermoplastic resin that is characterized in that a thermoplastic resin foamed sheet is provided with a defective portion of a desired shape at a desired location in advance and is heated to cause the thermoplastic resin to foam without suppressing expansion in a direction parallel to the sheet surface. This is a method for producing a foam. below,
The present invention will be explained in detail. First, the thermoplastic resin used in the present invention includes, for example, high-density and low-density polyethylene,
Olefin polymers such as polypropylene and polybutene,
Or olefin copolymers such as ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, vinyl chloride-vinyl acetate copolymer, polyester, etc. It is a mixture of one or more selected from acrylic acid, polymethacrylic acid, etc., or a mixture of various rubbers with other polyolefins.

Next, a pyrolytic foaming agent and a chemical crosslinking agent are added to the thermoplastic resin to produce a foamable composition.

Examples of the thermally decomposable blowing agent used in the furnace include azodicarbonamide, dinitrosopentamethylenetetramine, P,P'-oxybispentylsulfonyl hydrazide, and azobisisobutyronitrile. Examples of the chemical crosslinking agent include ditertiarybutyl peroxide, 113bis(tertiarybutylperoxyisopropyl)benzene, dicumyl peroxide, and the like. After kneading the above foamable composition using a mixing roll, pressure kneader, bumper mixer, press machine, etc., a foamable sheet is continuously molded using a press molding machine or a press molding machine.
The foamable sheet is punched out, a desired number of cutouts are formed in a desired shape, such as a circular shape, a cross shape, or a horseshoe shape, and then heat treatment is performed using an infrared heater, a hot air heating furnace, a salt bath, a metal bath, etc. to cause crosslinking and foaming. Make a thermoplastic resin foam.

However, when crosslinking a foamable sheet using method IIC of the present invention, the above-mentioned chemical crosslinking agent is not used, and a thermoplastic resin and a pyrolytic foaming agent are mixed into a foamable sheet before punching. It may be crosslinked by irradiating it with ionizing radiation.

According to the method of the present invention, a foam sheet is punched in advance to form a defect in a desired shape, and then heated and foamed to expand the defect to a desired size. The punching operation is significantly simpler than the method of punching a foamed sheet made of a foamed sheet.

Furthermore, since the foamable sheet has a large specific surface area, foaming efficiency is high and foaming occurs in a short time. Further, the foam sheet waste generated during the punching operation of the foam sheet can be reused as a foam sheet, and raw materials can be used effectively. Furthermore, a skin layer similar to the skin layer is formed on the exposed surface of the defective part of the obtained thermoplastic resin foam, that is, the peripheral wall of the punched hole during heat foaming, so the tear strength and water resistance of the defective part are significantly improved. As a result, the durability of the foam itself is improved. Embodiments of the present invention will be described below with reference to the drawings.

Example 1 17 parts by weight of azodicarbonamide and 1 part by weight of ditertiary butyl peroxide were added to 100 parts by weight of low-density polyethylene, and after kneading well in a pressure kneader, this composition was put into an extruder. While forming a foamable long sheet with a thickness of 1.8 mm and a width of 47011 mm, the foamable long sheet was
．． A large number of holes of 5 m1Lφ are punched out in succession so that the distance between the centers of the holes is approximately 7.5 mm to obtain a foamable long sheet 2 having a circular cutout 1 as shown in FIG. 2 is heat-treated at a temperature of 200° C. while being moved on a wire mesh to crosslink and foam the thermoplastic resin foam 3 having a defective portion 1 expanded to a desired size as shown in FIG. 2.
I got it.

The obtained foam 3 has a thickness of 4.5n1 and a width of 150011 mm, and the diameter of the expanded circular defect portion V is approximately 1511 mm.
The distance between them was 2311.

Further, the specific gravity of this foam 3 was approximately 0.028. When the above-mentioned thermoplastic resin foam was laid in a field as shown in FIG. 3 and seedlings 4 were planted and raised in the circular defect 1' of the foam 3, it was found that the foam 3 had good heat retention and Because of its excellent water absorption resistance, the growth rate of the seedlings 4 was good, and the defective part did not tear when the foam was laid or rolled up.

Example 2 A foamable long sheet similar to that of Example 1 was formed, and a large number of cross-shaped holes were punched out from the foamable long sheet to form a foamable sheet having cross-shaped cutouts 5 as shown in FIG. A long sheet 2 is prepared, and this long sheet 2 is then heat-treated to crosslink and foam to obtain a thermoplastic resin foam 3 having a cross-shaped defect 5' expanded to a desired size as shown in FIG. Ta.

When the thermoplastic resin foam 3 was used for raising seedlings as shown in FIG.
has a good growth rate, and when the foam is laid and rolled up, Vc
Moreover, the cross-shaped cutout 5' was not cut out. Example 3 Only 17 parts by weight of azodicarbonamide was added to 100 parts by weight of low-density polyethylene, and after kneading well in a pressurized kneader, the composition was extruded into a mixture having a thickness of 1.811 mm and a width of 470 mm.
It was formed into a 11 tm foamable elongated sheet, and while being crosslinked by irradiation with ionizing radiation, the crosslinked foamable elongated sheet was punched into a large number of horseshoe shapes to have a horseshoe-shaped cutout 6 as shown in FIG. A foamable elongated sheet 2 is prepared, and this elongated sheet 2 is subsequently heated and foamed to obtain a thermoplastic resin foam 3 having a horseshoe-shaped defect 6' expanded to a desired size as shown in FIG. Ta.

As shown in FIG. 9, the horseshoe-shaped defect 6 of the foam 3
When the holding part 7 formed by ' is opened and the holding part 7 is used to hold down the vibrator 8 and used as a packaging material, the pipe 8 can be held firmly and the horseshoe-shaped missing part 6' can be cut out during transportation. Therefore, pipe 7 did not fall off.

As detailed above, according to the present invention, it is possible to simplify the punching process when creating the defective part, increase the foaming efficiency during foaming, and use raw materials effectively, and improve the tear strength and water absorption resistance of the defective part. It has remarkable effects such as being able to significantly improve sex.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the foamable sheet used in Example 1 of the method of the present invention, Fig. 2 is a perspective view showing the foamable sheet of Fig. 1 in a foamed state, and Fig. 3 is a perspective view of the foamable sheet of Fig. 2. A schematic explanatory diagram showing the state in which the foam is used for raising seedlings, FIG. 4 is a perspective view of the foamable sheet used in Example 2 of the method of the present invention, and FIG. 5 is a diagram showing the state in which the foamable sheet of FIG. 6 is a schematic explanatory view showing the state in which the foam shown in FIG. 5 is used for raising seedlings; FIG. 7 is an example of the method of the present invention;
[Megeki I. ′! 7; = Nakacho = P▼ 2; Fig. 9 is a schematic explanatory view showing the state in which the foam shown in Fig. 8 is used as a packaging material. 1.5, 6... Defect part, 1'. 5', 6'... Defective part after foaming, 2... Foamable long sheet, 3... Thermoplastic resin foam.

Claims (1)

[Claims] 1. Production of a thermoplastic resin foam, characterized in that a thermoplastic resin foam sheet is preliminarily provided with a defective portion of a desired shape at a desired location, heated, and foamed without suppressing expansion in a direction parallel to the sheet surface. Method.