JPH11291275A - Foam molding of thermoplastic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a foamed molded product capable of being recycled to its raw material and having a soft feeling almost same to that of a urethane foamed molded product and a free shape within a mold by using a thermoplastic resin as a raw material. SOLUTION: A mixture of a thermoplastic resin powder 3, a lipophilic liquid substance 4 capable of being absorbed by the thermoplastic resin powder 3 and a foaming agent is injected into a mold and heated and foamed to form the foam filling the mold. The foaming agent is foamed by heating and the thermoplastic resin powder absorbs the lipophilic substance to swell and the mutual bonding of the adjacent particles of the thermoplastic resin powder is generated. Since fluidizing, foaming and the absorption of the lipophilic liquid substance by the thermoplastic resin powder are generated almost at the same time, a homogenous foamed molded product is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a molding method for forming a foam from a thermoplastic resin and a lipophilic liquid substance.
The foam molded article obtained by the present invention has a soft feeling and is excellent in recyclability.

[0002]

2. Description of the Related Art A urethane foam molding method has been widely known as a foam molding method. In this urethane foam molding method, a main agent composed of a polyether polyol or the like and a curing agent composed of an isocyanate are simultaneously injected into a molding die, and the main agent and the curing agent react with each other to form a urethane bond and, for example, coexist. This is a method of foaming with carbon dioxide gas generated by the reaction between water and isocyanate. This urethane foam molding method is widely used in various fields because it can produce a wide range of foam molded articles from hard to soft.

[0003] On the other hand, various molding methods for forming a foam molded article from a thermoplastic resin are known. For example, in order to form an expanded polystyrene molded product, expandable beads in which a polystyrene bead is impregnated with a foaming agent such as pentane are charged into a mold, heated by blowing steam, foamed, and filled in the mold. A bead foam molding method is used.

There is also known a method in which a foaming agent is mixed with a polyvinyl chloride paste to form a foam, and the foamed leather is coated to form a foamed leather.

[0005]

SUMMARY OF THE INVENTION In order to make effective use of resources on the earth, in the case of products manufactured from materials that can be melted and reused, such as thermoplastic resin products and glass products, the products are recovered from waste products, then melted and re-used. Recycling is used for raw materials. Also in automobile parts, the names of raw materials are described in various resin members, and it is easy to sort the collected various resin members into the same material, which is helpful in promoting recycling.

[0006] However, the urethane foam molded article has a stable chemical bond because it is cured by a cross-linking reaction, and although it can be scientifically recycled to the original raw material, its cost is extremely high. . Therefore, at present, waste materials of urethane foam molded articles are used for heat recycling or landfill utilizing heat from incineration. Therefore, in consideration of recyclability, it is conceivable to manufacture a foam molded article using a thermoplastic resin. However, in the case of the polyvinyl chloride foam molding method and the like, the shape of the molded article is limited, and it is difficult to form a molded article having a free shape like the urethane foam molding method.

[0007] In addition, according to the bead foam molding method, a molded article having a relatively free shape can be formed. However, the formed polystyrene foam molded article or the like does not provide a soft feeling as much as a urethane foam molded article. The surface quality of the molded product is inferior to that of the urethane foam molded product. In addition, the filling accuracy in the mold is low, and it has been difficult to form a foamed molded article having a complicated shape.

[0008] In other words, in the conventional foaming method of thermoplastic resin, a foamed molded article having a softness and a good surface quality comparable to that of a urethane foamed molded article and having a free shape using a molding die is formed. It was difficult to do. The present invention has been made in view of such circumstances, and enables recycling of a foamed molded product from a thermoplastic resin as a raw material, and free-form foaming having a soft feeling similar to a urethane foamed molded product. An object is to enable a molded article to be formed in a mold.

[0009]

The thermoplastic resin foam molding method of the present invention which solves the above-mentioned problems is characterized by comprising a thermoplastic resin powder, a lipophilic liquid substance which can be absorbed by the thermoplastic resin powder, and a foaming agent. An object of the present invention is to form a foam filled in a mold by injecting the mixture into a mold and subjecting the mixture to foaming by heating.

[0010]

DETAILED DESCRIPTION OF THE INVENTION In the foam molding method of the present invention, a thermoplastic resin powder and a lipophilic liquid substance that can be absorbed by the thermoplastic resin powder are injected into a mold together with a foaming agent.
The thermoplastic resin powder flows using a lipophilic liquid substance as a carrier, and is filled into every corner even in a complicated mold.

[0011] Then, the foaming agent is foamed by heating, and the lipophilic liquid substance is absorbed by the thermoplastic resin powder, whereby the thermoplastic resin powder swells and bonds between adjacent thermoplastic resin powders occur. Since the above-mentioned flow, foaming, and absorption of the lipophilic liquid substance into the thermoplastic resin powder occur almost simultaneously, a homogeneous foam molded article is formed.

In the obtained foam molded article, the molding material is reliably filled in the molding die by foaming and flowing before and during absorption of the lipophilic liquid substance into the thermoplastic resin powder.
Even a complicated mold surface shape is reliably transferred, and the accuracy of the shape is high. Further, the lipophilic liquid substance is absorbed in the thermoplastic resin and does not remain as a liquid, and the absorption of the lipophilic liquid substance provides a very good soft feeling as compared with a foamed molded article made of only the thermoplastic resin. Since the thermoplastic resin and the lipophilic liquid substance are both present in the foamed molded product in an unreacted state, it is possible to recycle them as raw materials.

As the thermoplastic resin powder, powders of olefin resins such as polypropylene and polyethylene, powders of olefin elastomers such as ethylene propylene rubber (EPR) and EPDM, a mixture thereof, and copolymers thereof are used. it can. The particle size of the thermoplastic resin powder is not particularly limited, but is preferably 500 μm or less. If the thermoplastic resin powder exceeds 500 μm, the fluidity during molding will be low and it will be difficult to apply it to molded products with complicated shapes, or the absorption of lipophilic liquid substances will be insufficient in short molding cycles Soft feeling and appearance quality may be reduced.

The lipophilic liquid substance is desirably liquid at room temperature, but any substance which becomes liquid by heating can be used, and a substance which can be absorbed by the thermoplastic resin powder used is used. For example, when an olefin resin is used as the thermoplastic resin powder, a paraffin hydrocarbon such as liquid paraffin, beeswax, and squalane can be used. In this case, a paraffinic hydrocarbon having about 8 to 20 carbon atoms in the molecule can be used, and
About 35 is preferred, and liquid paraffin which is liquid at room temperature is particularly preferred.

Any foaming agent can be used without particular limitation as long as it generates a gas upon heating. For example, azodicarbonamide (ADCA) is a typical example.
In addition, azobisisobutyronitrile, N, N'-dinitrosopentamethylenetetramine, P, P'-oxybisbenzenesulfonylhydrazide, barium azodicarboxylate,
Trihydrazinotriazine and the like can be used.

The amount of the lipophilic liquid substance is desirably mixed with the thermoplastic resin powder in an amount smaller than the amount at which absorption into the thermoplastic resin powder is saturated. If the mixing amount of the lipophilic liquid substance exceeds this saturation amount, stickiness may remain in the obtained foam molded article. Also, as the mixing amount of the lipophilic liquid substance becomes smaller than the saturation amount, the softness of the obtained foamed molded article becomes lower. Therefore, the mixing amount of the lipophilic liquid substance is determined according to the intended softness.

The thermoplastic resin powder has a saturation weight change rate of 80% or more with respect to the lipophilic liquid substance (absorbs at least 80 parts by weight of the lipophilic liquid substance with respect to 100 parts by weight of the thermoplastic resin powder). It is desirable to use As a result, a foam molded article having a good soft feeling is surely obtained. If the saturated weight change rate is less than 80%, the softness of the foam molded product obtained depending on the type of the thermoplastic resin powder or the like may be insufficient.

[0018] The thermoplastic resin powder and the lipophilic liquid substance
It is desirable that the specific gravities are close to each other. By doing so, the thermoplastic resin powder can be uniformly dispersed in the lipophilic liquid substance, so that a problem such as separation of the two in the mold can be prevented, and a foam molded article having a more uniform composition can be formed. Can be. It is preferable to keep the expansion ratio in the mold within a range of 2 to 3 times. That is, the injection amount of the molding material composed of the thermoplastic resin powder, the lipophilic liquid substance, and the foaming agent may be set to １ ／ to ３ of the volume of the target foam molded article. If the injection amount is less than this and the foaming ratio is more than 3 times, foam breakage may occur and the soft feeling and appearance quality may be impaired.

An inorganic filler such as talc, calcium carbonate, barium sulfate or the like can be further added to the mixture comprising the thermoplastic resin powder, the lipophilic liquid substance and the foaming agent. It can also be colored with an organic or inorganic coloring pigment or dye, and various additives may be added. The order of injecting the thermoplastic resin powder, the lipophilic liquid substance, and the foaming agent into the molding die may be, for example, stirring and mixing all in advance to form a slurry, which can be injected into the molding die. However, since the lipophilic liquid substance is gradually absorbed by the thermoplastic resin powder even at about room temperature, and is accelerated by heating, if the thermoplastic resin powder and the lipophilic liquid substance are mixed in advance, the viscosity gradually increases. As a result, the fluidity in the mold decreases. Therefore, it is desirable that the thermoplastic resin powder and the lipophilic liquid substance are mixed immediately before being injected into the mold. The blowing agent may be mixed with either the thermoplastic resin powder or the lipophilic liquid substance.

The heating temperature after the injection of the molding material is not particularly limited as long as it is equal to or higher than the temperature at which the foaming agent foams and lower than the melting temperature of the thermoplastic resin powder.

[0021]

The present invention will be described below in detail with reference to examples. In this embodiment, the present invention is used for manufacturing an instrument panel of an automobile. 1 to 3 show process explanatory diagrams. First, a skin 2 formed into a mold surface shape by vacuum forming from a thermoplastic elastomer or the like was arranged on the surface of a lower mold 1 formed of a divided upper mold and a lower mold.

Next, as shown in FIG.
The polypropylene powder 3 obtained by mixing 100 parts by weight of the above polypropylene powder with 10 parts by weight of azodicarbonamide (ADCA) as a foaming agent, and the liquid paraffin 4 having about 20 carbon atoms in the molecule are supplied to the nozzle 5. Then, the mixture was mixed well in the nozzle 5 and injected into the lower mold 1. The mixing ratio between the polypropylene powder and ADCA is 90:10 by weight.

The saturated weight change rate (weight of liquid paraffin absorbed by 100 parts by weight of resin) of the polypropylene powder at 80 ° C. is 150%. The injection amount was adjusted to be 1/3 of the cavity volume of the foaming mold. Next, as shown in FIG. 2, the upper mold 7 on which the base material 6 made of polypropylene is arranged on the mold surface is clamped to the lower mold 1, and the whole foaming mold is heated to 140 ° C. or more and held for 3 minutes. . As a result, ADCA is decomposed to generate nitrogen gas, and the polypropylene powder swells by absorbing liquid paraffin,
Adjacent polypropylene powders join together and the resulting foam fills the foam mold. At this time, the liquid paraffin, which is a liquid, flows in the mold, so that the polypropylene powder is carried to every corner in the mold using the liquid paraffin as a carrier. Further, the skin 2 is pressed against the mold surface of the lower mold 1 by the foaming pressure, and the shaping shape is securely fixed along the mold surface shape.

After holding at 140 ° C. or higher for 3 minutes, the upper mold 7 is opened, and the instrument panel 8 as a foam molded product is taken out as shown in FIG. In the obtained instrument panel 8, the skin 2 is integrally joined to one surface of a foam 9 made of polypropylene and liquid paraffin, and the base material 6 is integrally joined to the other surface. The foam 9 had a soft feeling as good as that of the urethane foam molded article, had no stickiness due to liquid paraffin, and was extremely excellent in shape accuracy.

Further, in the obtained instrument panel, since the foam is composed of polypropylene and liquid paraffin, it can be recycled as a raw material even after being discarded, thereby saving global resources.

[0026]

According to the thermoplastic resin foam molding method of the present invention, since the thermoplastic resin is used as a raw material, it is possible to recycle the foam molded product to the raw material and to have a soft feeling comparable to that of the urethane foam molded product. Free-form foam molded articles can be accurately molded in a mold.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an injection step of a thermoplastic resin foam molding method according to one embodiment of the present invention.

FIG. 2 is an explanatory view showing a mold clamping step of a thermoplastic resin foam molding method according to one embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a mold release step of the thermoplastic resin foam molding method according to one embodiment of the present invention.

[Explanation of symbols]

1: Lower mold 2: Epidermis
3: Polypropylene powder 4: Liquid paraffin 5: Nozzle
6: Base material 7: Upper die 8: Instrument panel
9: Foam

Claims (1)

[Claims] A mixture comprising a thermoplastic resin powder, a lipophilic liquid substance capable of being absorbed by the thermoplastic resin powder, and a foaming agent is injected into a mold, and the mold is filled by heating and foaming. A thermoplastic resin foam molding method, which comprises forming a foam.