JPS62162520A - Manufacture of plastic foam - Google Patents

Abstract

PURPOSE:To obtain a plastic foam having the beautiful external surface, by a method wherein a material for an outer shell composed of vinyl chloride resin and a material for a foamed core member composed of crosslinking vinyl chloride resin are mounted respectively on a surface side of a molding tool and inward side of the molding tool to which dielectric heating is applied. CONSTITUTION:A material 14 for an outer shell composed of vinyl chloride resin is mounted within a cavity 22 of a bottom force 21 which turns outside a molded article. Then a material 15 for a foamed core member composed of crosslinking vinyl chloride resin is mounted so that the same turns inside. A top force 23 is clamped to the bottom force 21 and high frequency voltage is applied to them from electrodes 27, 28. As the melt viscosity of the crosslinking vinyl chloride resin for the foamed core member is improved through crosslinking, high foam having uniform cell structure densely is formed. Along with cubical expansion following to foaming of the material 15 for a foamed core member the material 14 for the outer shell positioned to a tool surface side is bonded to the tool surface with pressure and a plastic foam, whose core member part is high-foaming and an outer shell part is comparatively hard, is molded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method of manufacturing a plastic foam, and in particular, a plastic foam having a high-density outer shell on the front side and a highly foamed core on the inside. The present invention relates to a method for obtaining a foam molded article having the following properties.

(Prior Art) Foam molded products having a relatively hard outer shell on the front side and a foamed core on the inside, such as protective and decorative moldings attached to side panels and door panels of automobiles, etc. has significant advantages over conventional solid moldings in terms of light weight and cushioning properties.

As a conventional method for obtaining this type of foamed plastic molding, a piece of material made of polyvinyl chloride resin mixed with a foaming agent is introduced into a mold equipped with a high-frequency electrode, and the material piece is plasticized and melted by dielectric heating. It is then molded into a predetermined product.

However, in the above manufacturing method, as the expansion ratio increases, the melt viscosity of the resin decreases, so "
There are serious problems with the appearance of the product, such as the formation of a series of air bubbles called "nests" that can damage the surface of the molded product, or the "nests" can become soaked as the product cools and cause the surface to cave in. are doing.

Moldings made of plastic foam with a high expansion ratio are lightweight, have high cushioning properties, and are highly economical, making them extremely useful in practice. These shortcomings are inherent in moldings that are also decorative objects, and can greatly reduce their usefulness.

(Problems to be Solved by the Invention) Therefore, the main purpose of this invention is to prevent the surface of the molded product from being affected by the internal air bubbles, even if it is a plastic foam with a high expansion ratio, so that it can be beautiful. The object of the present invention is to provide a new method for producing a plastic foam that can obtain an outer surface.

Another object of the present invention is to propose a novel method for producing a plastic foam, in which a material is heated to plasticize and melt by applying a high-frequency voltage, and a molded article of a predetermined shape is obtained by decomposing a foaming agent.

Furthermore, the present invention particularly proposes a novel method for producing a plastic foam that uses a crosslinked vinyl chloride resin as a core material to obtain a desired molded product with a highly foamed interior.

The present invention also proposes a method for producing a plastic molding comprising a desired highly foamed core and outer shell.

(Means for Solving the Problems) That is, the method for producing a plastic foam according to the present invention provides a foamed molded product having a high-density outer shell on the front side and a highly foamed core on the inside. To obtain the above, in a mold equipped with a high-frequency electrode, an outer shell material made of vinyl chloride resin is placed on the mold surface side, which is the front side of the molded product, and a foamed core material made of crosslinked vinyl chloride resin is placed in a mold equipped with a high-frequency electrode. They are located on the inside of the mold, and after the mold is clamped, a high frequency voltage is applied to the electrodes to plasticize and melt the material by dielectric heating within the mold, and decompose the foaming agent contained therein to form a predetermined shape. It is characterized by being molded into a shape.

(Function) In the present invention, a crosslinked vinyl chloride resin is used as the material for the foam core, and a highly foamed core is formed inside.

That is, in a mold equipped with a high-frequency electrode, an outer shell material made of vinyl chloride resin is placed on the mold surface side, which is the front side of the molded product, and one foamed core material made of the crosslinked vinyl chloride resin is placed on the mold surface side, which is the front side of the molded product. Each material is placed on the inside of a mold, and after the mold is clamped, a high frequency voltage is applied to the mold to dielectrically heat each of the materials within the mold. The above materials are plasticized and melted by high frequency dielectric heating, but the melt viscosity of the crosslinked vinyl chloride resin material for the foam core located inside the mold is increased due to crosslinking. As the foaming agent contained therein decomposes, a highly foamed material having a dense uniform cell structure can be formed. As the core material expands in volume, the outer shell material located on the side of the mold surface is pressed against the mold surface by the volumetrically expanded core material. In this way, a product having a predetermined outer shell and a foam core integrally is molded.

(Example) The following will be explained along with an example according to the attached drawings.
Fig. 1 is a partial perspective view showing an example of a plastic molding for automobiles obtained by this invention together with a schematic cross section, Fig. 2 is a sectional view showing a molded state according to this invention, and Fig. 3 shows an outer shell material and foaming. FIG. 3 is a cross-sectional view showing a preformed state of the core material.

In FIG. 1, the reference numeral 10 represents a plastic molding for an automobile, 11 represents an outer shell portion made of a relatively hard layer constituting the front side of the molding, 12 represents a highly foamed core portion, and 13 represents the foamed core portion. This is an outer surface layer formed on the outer surface of 13 and consisting of a dense cell structure.

Reference numeral 20 in FIG. 2 is a mold for the automobile plastic molding 10 shown in FIG.
The mold is composed of a lower mold 21 having an upper mold cavity 24 and an upper mold 23 having an upper mold cavity 24. These molds 21 and 23 are made of a material with low dielectric loss such as silicone resin or fluororesin, and are connected to an electrode plate 27 connected to a high frequency generator 29.
, 28 are installed.

Reference numerals 25 and 26 are cooling pipes through which a refrigerant such as water is passed for cooling the mold, and an appropriate number of pipes are provided as necessary.

Reference numeral 14 inside the cavity 21 indicates a material constituting the outer shell of the plastic molding.

This outer shell material 14 is a commonly used vinyl chloride resin, and in addition to non-foamed materials, materials containing a slight foaming agent may also be used. When mixing the foaming agent, it is preferable that the blowing agent has a higher decomposition temperature than the foaming agent mixed into the foamed core material 15 described below, and it is preferable that the amount mixed into the foamed core material is smaller than that of the foaming agent mixed into the foamed core material 15 described below. desirable.

In contrast, the code 15 in the same cavity 22
represents a material for composing the foam core of the molding. As mentioned earlier, this foam core material 15 is made of material by crosslinking in order to form a highly foamed body having a uniform cell structure. The material resin is a crosslinked vinyl chloride resin with increased melt viscosity, and it is composed of a foaming agent and a plasticizer.

Here, to explain the crosslinked vinyl chloride resin, the following are exemplified as the crosslinked vinyl chloride resin used in the present invention.

a. A mixture of vinyl chloride resin and polyethylene, polypropylene, or a copolymer thereof, crosslinked with a crosslinking agent.

b. A product obtained by copolymerizing a vinyl chloride resin with a polyolefin such as polyethylene or polypropylene, or a product obtained by crosslinking a mixture of the copolymer and a vinyl chloride resin with a crosslinking agent.

A product obtained by copolymerizing C8 vinyl chloride resin with ethylene vinyl acetate, acrylic ester, or vinyl ether and crosslinking it with a crosslinking agent.

d. A mixture of vinyl chloride resin without active hydrogen and vinyl chloride resin with active hydrogen, crosslinked with isocyanate.

Note that the material resins a to C above are explained in detail and specifically in Patent Application Publication No. 195133/1982, and the material resin d is described in Patent Application Publication No. 59-23730.

The above material resin is used as a base material, and additives such as a known plasticizer, a stabilizer, a chemical blowing agent to be described later, and other pigments are appropriately kneaded to obtain a foam core material.

Chemical blowing agents used here include azodicarbonamide, azobisformamide, which generates nitrogen gas,
Azo compounds such as azobisisobutylene nitrile, nitroso compounds such as dinitrosopentamethylenethramine, hydrazide compounds such as PP'-oxybisbenzenesulfonyl hydrazide, carbonates that generate carbon dioxide gas, and dicarbonates. is preferably used.

It goes without saying that the amount of foaming agent mixed is determined depending on the desired foaming ratio.

Plasticizers, stabilizers and other additives are retranslated, respectively.
For example, dioctyl phthalate (DOP), barium and zinc stabilizers are used as appropriate.

The method of manufacturing protective and decorative plastic moldings for automobiles using these molding materials will now be described with reference to the diagram of FIG.

First, a predetermined amount of the outer shell material 14 made of ordinary vinyl chloride resin is placed in the cavity 22 of the lower mold 21, which has a mold surface that will be the front side of the molded product. At the same time, a foam core material 15 made of cross-linked vinyl chloride resin is added to the outer shell material 14.
In other words, it is placed on the inside of the cavity.

In this state, the upper mold 23 is closed to the lower mold 21, and the upper and lower electrodes 2
7. Apply high frequency voltage from 28 onwards.

By applying a high frequency voltage, the plastic material inside the cavity is heated, plasticized and melted. Since the melt viscosity of the material resin is dramatically increased by crosslinking, a highly foamed material having a dense uniform cell structure is formed as the foaming agent contained therein decomposes. As the core material expands in volume due to foaming, the outer shell material located on the mold surface side is pressed against the mold surface by the volumetrically expanded core, resulting in a product that integrally has a predetermined outer shell and foam core. molded.

Note that the foam core material 15 is directly pressed against the mold surface of the upper mold cavity 24, which is the back side of the molded product 10, to form an outer surface layer 13 having a dense cell structure there.

In addition, during actual molding according to the method of the present invention, in order to introduce the outer shell material 14 and the foam core material 15 into the mold in a predetermined amount and in a predetermined positional relationship, the remolding material 1 is
4 and 15 are preferably preformed into predetermined shapes as shown by numerals 16 and 17 in FIG. 3 by extrusion molding, calender molding, or the like.

Next, using each of the above moldings 10 as an example, examples of the composition of each molding material will be shown together with the specific gravity of the product.

[Formulation example 1] (Example with low foaming outer shell) (1) Material for outer shell (Part by weight) Polyvinyl chloride resin without active hydrogen OO Dioctyl phthalate (DOP) 20 Ester plasticizer 10 Epoxy plasticizer agent
10 barium, tin stabilizer
3 Foaming agent 0.5 Pigment
Predetermined amount (2) Foam core material polyvinyl chloride resin without active hydrogen (P=1100
) 100 Polyvinyl chloride resin with active hydrogen 4 Thermoplastic polyurethane resin 3 Blocked isocyanate 1 Blowing agent (azocicabonamide)
8 Barium and zinc stabilizer 3 [Overall specific gravity 0.63] (Outer shell specific gravity 1.04. Core specific gravity 0, 31) [Formulation example 2] (Example with non-foamed outer shell part) (1) Outer shell Material for
(Parts by weight) Polyvinyl chloride resin dioctyl phthalate (DOP) without active hydrogen
60 Ester plasticizer 10 Barium, zinc stabilizer 2 Pigment
Predetermined amount (2) Same composition as the foam core material of foam core material [formulation example 1] [overall specific gravity]
0.68] (Outer shell specific gravity 1.38. Core specific gravity 0, 31) (Effects) As is clear from the above explanation, according to the present invention, vinyl chloride is placed in a mold equipped with a high-frequency electrode. A material for the outer shell made of a polyvinyl chloride resin is placed on the mold surface side, which is the front side of the molded product, and a material for the foam core made of a crosslinked vinyl chloride resin is placed on the inner side of the mold. By plasticizing and melting the material and molding it, the following excellent effects are produced.

That is, according to the above manufacturing method, since a cross-linked vinyl chloride resin is used as the material for the foam core, it is possible to easily obtain a molded product having a core with a dense uniform cell structure and a high expansion ratio. . At the same time, since the outer surface of the molded product is integrally wrapped by a relatively hard outer shell, the surface of the molded product is not affected at all by the highly foamed core; By carefully selecting the material for the outer shell, it is possible to mold a product with the desired surface condition.

According to the present invention, it is possible to easily mold a plastic foam having composite physical properties such that the inner core part is highly foamed and the outer shell part is relatively hard.

In particular, this invention is extremely advantageous for manufacturing moldings for automobiles, etc., because it is lightweight, has high cushioning properties, has a very good surface texture, and can produce economical foam molded products. Large and useful.

[Brief explanation of drawings]

Fig. 1 is a partial perspective view showing an example of a plastic molding for automobiles obtained by this invention together with a schematic cross section, Fig. 2 is a sectional view showing a molded state according to this invention, and Fig. 3 shows an outer shell material and foaming. FIG. 3 is a cross-sectional view showing a preformed state of the core material. 10...Plastic molding for automobiles, 11
... Outer shell part, 12... Core body part, 13... Outer surface layer,
14...Material for outer shell, 15...Material for foam core, 2
0... Molding mold, 22.24... Cavity, 27°28... Electrode plate, 29... High frequency generator.

Claims (1)

[Claims] 1. When obtaining a foam molded product having a high-density outer shell on the front side and a highly foamed core on the inside, vinyl chloride is placed in a mold equipped with a high-frequency electrode. After placing the outer shell material made of polyvinyl chloride resin on the mold side, which is the front side of the molded product, and the foam core material made of crosslinked vinyl chloride resin on the inner side of the mold, the molds are clamped. A method for producing a plastic foam, comprising applying a high frequency voltage to the electrode to plasticize and melt the material by dielectric heating in a mold, and decomposing the foaming agent contained therein to mold it into a predetermined shape. . 2. The method for producing a plastic foam according to claim 1, wherein the crosslinked vinyl chloride resin is a mixture of vinyl chloride resin, polyethylene, polypropylene, or a copolymer thereof, and crosslinked with a crosslinking agent. . 3. A patent claim in which the crosslinked vinyl chloride resin is made by copolymerizing a vinyl chloride resin with a polyolefin such as polyethylene or polypropylene, or by crosslinking a mixture of the copolymer and a vinyl chloride resin with a crosslinking agent. A method for producing a plastic foam according to item 1. 4. The plastic foam according to claim 1, wherein the crosslinked vinyl chloride resin is made by copolymerizing vinyl chloride resin with ethylene vinyl acetate, acrylic ester, or vinyl ether and crosslinking it with a crosslinking agent. Production method. 5. The plastic foam according to claim 1, wherein the crosslinked vinyl chloride resin is made by crosslinking a mixture of a vinyl chloride resin without active hydrogen and a vinyl chloride resin with active hydrogen with isocyanate. Production method. 6. The method for producing a plastic foam according to claim 1, wherein the outer shell material and the foam core material are preformed. 7. A method for producing a plastic foam according to claims 1 to 6, wherein the plastic foam is a protective and decorative molding.