JP3611701B2 - Secondary molding method for cross-linked polyethylene foam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of molding a mold from a crosslinked polyethylene foam. More specifically, the present invention relates to a method of forming a mold by inserting a cross-linked polyethylene foam sheet into a pair of male and female molds, and applying heat and pressure.
[0002]
[Prior art]
Polyethylene foams are excellent in heat insulation, elasticity and the like, and are used for a wide range of applications due to their light weight. However, since the polyethylene foam can be obtained only as a simple plate or sheet in the production process, the use of the foam has been expanded by variously forming it.
[0003]
As a method for molding polyethylene foam, vacuum molding, embossing or laminating is generally used. Of these, vacuum molding is a molding method using a thin foam, embossing is molding of the surface portion only, and laminating It is merely a surface treatment.
[0004]
Then, the method of shape | molding a mold from a crosslinked polyethylene-type foam is examined, and the following methods are proposed.
[0005]
1. Compress a polyolefin or a cross-linked foam of a polyolefin and a mixture of rubber and plastic with this in a mold while compressing it at a temperature above the softening point of the polyolefin, compressing it by 20% or more in one direction, and then applying pressure. A method of cooling while standing (Japanese Patent Publication No. 52-49022).
[0006]
2. A method in which a crosslinked foamed ethylene polymer sheet having a gel fraction of 60 to 98% is inserted between a pair of male and female dies and heated under pressure to form a mold (Japanese Patent Laid-Open No. 55-55834).
Such a conventional hot pressing method relates to molding of a simple-shaped mold, and a male and female mold as shown in FIG. 3 is fixed to a hot platen of the press, and the cavity side surface of the female mold is suspended from the opening. Or inclined toward the center of the cavity. The resulting molded product (FIG. 4) had burr 11 on the outside, poor appearance, and limited use.
[0007]
[Problems to be solved by the invention]
Therefore, the object of the present invention is to eliminate the above-mentioned problems of the conventional hot press molding method, and can be molded even in a shape in which the burr is inside the molded product and the side wall wraps around the hollow part, and foams to the back of the cavity An object of the present invention is to provide a secondary molding method of a cross-linked polyethylene-based foam capable of filling the body.
[0008]
[Means for Solving the Problems]
The method for secondary molding of the crosslinked polyethylene foam of the present invention is a method in which a crosslinked polyethylene foam is inserted between a pair of male and female molds and heated under pressure to mold a mold. The tee has a structure with a portion extending to the bottom of the flange surface, the male mold is fixed on the upper side, and the lowermost corner of the tapered section of the male mold that closely contacts the tapered section of the female mold is the female mold. Place the female mold on the iron plate so that it is located directly above the boundary between the flange surface of the corresponding corner of the mold and the cavity, insert the specified polyethylene foam, insert the male and female gold The female mold is slid along the taper portion of the mold to close the mold.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The mold used in the present invention has a cavity that extends to the bottom of the flange. With such a mold, the material can be filled to the back of the cavity, and a mold having a complicated shape can be molded. It's amazing.
[0010]
As the base material of the cross-linked polyethylene foam used in the present invention, high pressure method low density polyethylene, low pressure method low density polyethylene, medium density polyethylene, low pressure method high density polyethylene, metallocene polyethylene, ethylene-vinyl acetate copolymer, Examples thereof include an ethylene-acrylic acid ester copolymer and an ethylene-propyl copolymer. Of these, low density polyethylene and ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% or less are particularly useful. Ordinary lubricants, inorganic fillers, pigments and the like can be appropriately added to these base materials.
[0011]
A method for producing a crosslinked polyethylene foam from these substrates is a pressurized one-stage foaming method in which a foam is obtained by heating in a closed mold under pressure to decompose the foaming agent and the crosslinking agent and then depressurizing. Heat in a pressure-sealing mold to partially decompose the foaming agent and the crosslinking agent to release the pressure to obtain an intermediate foam, and then decompose the remaining foaming agent and the crosslinking agent under normal pressure to obtain the final crosslinking. A conventionally known method such as a two-stage foaming method for obtaining a polyethylene foam can be applied.
[0012]
The expansion ratio of the cross-linked polyethylene foam used in the present invention is 5 to 50 times, preferably 10 to 40 times. If the expansion ratio is too low, it is too hard to be molded and the expansion ratio is too low. If it is too high, the hardness of the molded product will be insufficient.
The metal mold | die used by this invention is demonstrated based on drawing.
[0013]
FIG. 1 is a cross-sectional view of an example of a mold used in the present invention. A male mold 1 is fixed to the lower surface of a press hot platen, and a female die 2 moves on the press hot platen. It is placed in a free state. The cavity 3 of the female mold 2 extends below the flange surface 4. At the stage where the male and female molds 1 and 2 are opened and molding is started, the male mold corresponds to the corner flange surface where the cavity of the female mold 2 is narrower than the diameter and the boundary 5 between the cavities. It is placed so that the lowermost portion 7 of the tapered portion of the corner is positioned, and a crosslinked polyethylene foam 8 is inserted to close the male and female molds together. The taper portion 6 of the male mold slides on the corresponding taper portion 9 of the female mold and enters the depth of the cavity. At that time, the female mold slides and moves on the heating plate.
[0014]
FIG. 2 shows the resulting molded product 10 and the burr 11 is attached to the inside, so that, for example, even if it is used as a cover under a television of a sightseeing bus, the burr surface cannot be seen from the outside, and the appearance is beautiful. It is.
[0015]
The mold temperature may be kept at a normal temperature until the foam is sandwiched and closed, and then heated to the molding temperature, or may be heated to the molding temperature from the time when the foam is sandwiched.
[0016]
Molding is performed by sandwiching the foam between the molds and heating and pressurizing, and the foam is thicker than the gap between the male and female molds in the closed state.
[0017]
In the present invention, as a method for heating the mold, a sealed mold is immersed in a heating medium bath such as hot water or molten salt, or a heating medium flow path such as a steam jacket is provided on the mold surface. In the case where a heating medium flow path such as steam or heating oil is provided in a press for pressurizing and sealing the mold, a heating medium such as steam or heating oil is passed through the flow path, thereby causing 90 to 200 After heating at a temperature of 10 seconds to 40 minutes, the product is cooled and the molded product is removed from the mold. When the heating temperature is 90 ° C. or lower, it is difficult to fix the compressed state, and when the heating temperature is 200 ° C. or higher, it is not preferable from the viewpoint of the surface appearance and economics of the molded product.
[0018]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
[0019]
Example 1
Foam (trade name: Sanperca C-1202 gray, apparent density 0.071 g / cm ³ ) thickness produced by a pressurized one-stage foaming method using an ethylene-vinyl acetate copolymer (vinyl acetate content 15% by weight) as a base material A foam manufactured by two-stage foaming with 5 mm on the bottom and low density polyethylene as the base material (trade name: Sanperca L-2500, apparent density 0.027 g / cm ³ , manufactured by Sanwa Chemical Co., Ltd.) A polyethylene film thickness of 30 μm is inserted between the two foam sheets, and a knitted fabric jersey is applied to the top and bottom of the foam to form a molding mold for a TV stand of a tourist bus as shown in FIG. Inserted in between, closed and pressurized, heated steam was passed through a hot platen of the press, heated at 150 ° C. for 10 minutes and then cooled to obtain a molded product.
The resulting molded product was a two-layer foam heat-sealed with a polyethylene film, the appearance was formed with jersey eyes, no air accumulation, burrs were inside, and the appearance was beautiful and good. .
[0020]
【The invention's effect】
As described above, according to the molding method of the present invention, the burr does not come out, the appearance is beautiful, a complicated shape can be easily molded, the protective cover under the television of the sightseeing bus, the bicycle saddle, A relatively complicated mold such as a protective case of a precision machine (such as an optical machine) can be easily formed.
[Brief description of the drawings]
FIG. 1 is a sectional view of a mold used in the molding method of the present invention in an open state.
FIG. 2 is a perspective view of an example of a molded product obtained by the molding method of the present invention.
FIG. 3 is a cross-sectional view of a mold used in a conventional hot pressing method.
FIG. 4 is a perspective view of an example of a molded product obtained by a conventional hot press molding method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Male mold 2 Female mold 3 Cavity 4 Flange 5 Corner flange surface and cavity boundary 6 Male mold taper part 7 Lowermost part of male mold taper part 8 Cross-linked polyethylene foam 9 Female mold Taper part 10 molded product 11 burr

Claims (1)

In a method in which a cross-linked polyethylene foam is inserted between a pair of male and female molds and heated under pressure to form a mold, the cavity of the female mold has a portion extending to the bottom of the flange surface. The bottom of the corner of the male mold taper that is fixed to the upper side of the male mold and closely contacts the taper of the female mold is the boundary between the flange surface of the corresponding corner of the female mold and the cavity. Place the female mold so that it can move freely in the form of an iron plate so that it is positioned almost directly above, insert a predetermined cross-linked polyethylene foam with jersey applied up and down , along the taper part of the male and female mold A secondary molding method for a cross-linked polyethylene foam, characterized by sliding a female mold, closing the mold, pressurizing and sealing, and heating .

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