JP2686509B2 - Method for producing composite foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a composite foam.

[Problems to be solved by conventional technology and invention]

2. Description of the Related Art In recent years, synthetic resin foam molded articles have been widely used as heat insulating materials, cushioning materials, floating materials, and the like. As a method for producing this type of foam molded article, synthetic resin pre-expanded particles are molded into a mold having a desired shape. A so-called bead molding method is known in which the pre-expanded particles are heated after being filled in the inside thereof to form a molded product according to a mold. The bead molding method is preferable as a method for easily obtaining a foamed molded product having a high closed cell ratio and excellent heat insulation and water resistance, but on the other hand, a foamed molded product having a high expansion ratio is foamed molded. The body tends to shrink, and a high degree of technology is required to obtain a molded body with high dimensional accuracy, and if it is not the case, the surface smoothness tends to be difficult.
In addition, since the process of heating the pre-expanded particles in the molding die and then cooling is repeated during molding, the heat energy required for heating the molding die is lost each time molding is performed, and moreover, once molding is performed. It takes a long time to complete the molding process, resulting in a long molding cycle, resulting in low thermal efficiency and low molding efficiency. On the other hand, in the injection molding method, since it is not necessary to heat the molding die to a temperature close to or above the melting point of the resin, the injection molding method can generally improve the thermal efficiency and molding efficiency. Development of a method to obtain a molded product with a higher expansion ratio (low density), because only a molded product with an expansion ratio of about 1.5 times can be obtained with the conventional injection molding method in which foamed molding is performed from synthetic resin pellets) Was required.

In order to solve the above problems, the present inventor has proposed a method of heating and softening synthetic resin foamed particles, and then pressurizing and injecting them into a mold for molding (JP-A-60-96419). According to this method, a foamed product having high foaming can be easily obtained as compared with the conventional injection foaming method. However, according to this method, the expansion ratio of the obtained molded product changes depending on the degree of melting of the foamed particles, and thus the desired value is obtained. There is a problem that it is difficult to obtain a molded product having the expansion ratio of This is due to the fact that the degree of melting of the foamed particles greatly changes with a slight temperature change, and such a tendency becomes more remarkable in the foamed particles made of a highly crystalline resin such as a polyolefin resin, and the mutual expansion of the foamed particles in the molded body is caused. However, there is a problem in that the fusion strength of the resin is likely to be lowered, and the fusion may not be performed depending on the resin. Therefore, there is room for improvement.

[Means for solving the problem]

The present invention has been made to solve the above problems,
An object of the present invention is to provide a method for producing a composite foam which can solve the disadvantages of the prior art.

That is, the present invention provides (1) loading thermoplastic foam particles or a plurality of combinations thereof into an injection molding mold, and then injecting a thermoplastic resin into the mold to obtain a thermoplastic resin and thermoplastic resin foam particles. A method for producing a composite foam, which comprises obtaining an integrated composite.

(2) Thermoplastic resin expanded particles have a density of 0.3 to 0.015 g / cm
^{3. The} method for producing a composite foam according to claim 1, wherein the number is ³ .

(3) The method for producing a composite foam according to claim 1 or 2, wherein the expanded thermoplastic resin particles are expanded polyolefin resin particles.

(4) The polyolefin resin foam particles are any of a non-crosslinked polypropylene resin foam, a non-crosslinked linear low-density polyethylene resin foam, a crosslinked polyethylene resin foam, and a crosslinked polypropylene resin foam. The method for producing a composite foam according to claim 3, which is characterized in that.

It is the gist.

According to the method of the present invention, as shown in FIG. 1, the thermoplastic resin foam particles 3 are supplied from the filling port 2 into the injection molding die 1 to fill the inside of the die, and then, as shown in FIG. The filling port 2 is closed, and then the thermoplastic resin 6 is injected from the injection machine 5 to integrate the expanded particles 3 and the injected thermoplastic resin 6, and the expanded particles 3 have a closed-cell structure of thermoplasticity. It is preferable to use resin expanded particles. The foamed particles 3 preferably have a closed cell ratio of 80% or more. When the closed cell ratio of the foamed particles 3 is low, the surface of the foamed particles is heated by the injected molten resin, and secondary foaming, breakage, shrinkage, etc. occur. It tends to occur. As the foamed particles 3, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene,
Polyolefin resin such as polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer,
Polystyrene resin such as polystyrene, poly-α-styrene, styrene-maleic anhydride copolymer, polyvinyl chloride resin, polyvinylidene chloride resin, nylon, polyamide resin such as aromatic nylon, polyethylene terephthalate, polybutylene Polyethylene resin such as terephthalate, foamed particles made of thermoplastic resin such as polycarbonate resin can be used, but in particular crosslinked foamed particles, crystalline resin foamed particles are melt-flowing high temperature resin injected from an injection molding machine. Is preferable in that the expanded particles are less likely to undergo changes such as melting under the influence of, among others, non-crosslinked polypropylene resin expanded particles, non-crosslinked linear low-density polyethylene resin expanded particles, crosslinked polyethylene resin expanded particles, crosslinked Polypropylene resin foamed particles are preferred, but particularly preferred The crosslinked polyethylene resin foamed beads, cross-linked polypropylene resin foam particles. As the foamed particles 3, those having a density of 0.3 to 0.015 g / cm ³ are preferable because they have appropriate elasticity and heat resistance.

As the thermoplastic resin 6 injected from the injection machine 5, in addition to the resin similar to the resin forming the foamed particles 3, a polyacetal resin, a polyphenylene oxide resin, a polyphenylene sulfide resin, a polyfluphone resin, a polyurethane resin is used. Resins such as ABS resin and the like can also be used. It is preferable that these resins have a low melt viscosity and easily flow between the expanded particles or the expanded particle bonded body. If necessary, a foaming agent may be contained in these resins. If the foaming agent is contained, it is possible to prevent the occurrence of sink marks and prevent an increase in the total weight. Examples of the foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and the like, and when the foaming agent is contained, the addition amount thereof is 100 parts by weight of the resin and 0.1
-10 parts by weight is preferred. The foamed particles 3 need to be filled so as to have a particle gap (space in which the thermoplastic resin 6 is injected) when they are filled in the mold 1, but there is a space in which the thermoplastic resin 6 is injected. If foamed particles 3
May be compressed and filled. However, when compression filling is not carried out, it is preferable to fill it so as to be 60% or more (relative to the apparent volume of expanded particles) of the internal volume of the mold, and if it is less than 60%, the thermoplasticity in the resulting composite foam The proportion of the resin increases, and even if the blowing agent is contained in the injected thermoplastic resin, the weight of the composite foam may increase.

The injection conditions for injecting the above resin are injection pressure 500
~ 1500 kg / cm ² · G, injection speed 0.2 ~ 3 m / sec, temperature of injection resin is 100 ~ 250 ℃, melting point of each resin, melt viscosity of molten resin-temperature characteristic, line breaking stress-melt viscosity characteristic Etc. are taken into consideration when deciding. The mold temperature is preferably 30 to 90 ° C. Cooling is performed after resin injection, and the cooling time is preferably about 60 to 300 seconds.

In the present invention, the filling port 2 for the expanded particles 3 may be provided on the upper surface side of the mold 1 as shown in FIG. Further, the number of the filling port 2 is not limited to one in one mold, and a mold having a plurality of filling ports may be used.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

Examples 1 to 7 The foamed particles shown in Table 1 were used to measure length 100 mm x width 100 mm x height 30
mm in an injection molding die heated to 85 ° C. at a filling rate shown in Table 1, and then a thermoplastic resin is injected under the injection conditions shown in the same table, followed by cooling for 200 seconds. I took it out. Table 2 shows the properties of the obtained composite foam.

* 1 The filling rate is indicated by the apparent volume of foam particles filled in the mold with respect to the internal volume of the mold.

* 2 The amount of foaming agent added is shown in parts by weight per 100 parts by weight of resin.

* 3 The presence or absence of deformation of the foam was observed and evaluated according to the following criteria.

 ○: No deformation is observed.

 X: Deformation is recognized.

* 4 The surface of the foam was observed and evaluated according to the following criteria.

 ○: The surface is smooth.

 X: An uneven pattern of foamed particles remains on the surface.

〔The invention's effect〕

As described above, according to the method of the present invention, a molded article having a lower density can be easily obtained as compared with the conventional injection molding method in which foam molding is performed from unfoamed synthetic resin pellets. Moreover, according to the method of the present invention, the density of the molded product can be easily determined by the volume ratio of the expanded particles and the thermoplastic resin, so that the density of the resulting molded product can be easily controlled, and various physical properties due to the difference in density can be obtained. The molded body can be easily manufactured, and the molded body obtained by the method of the present invention has higher strength than the conventional one. Further, the present invention is based on a combination of expanded particles and a non-expanded resin, and since the type of the resin can be changed, a combination of expanded particles of crosslinked polyethylene and a hard polyester, or a relatively hard ethylene-propylene resin is used. A combination of a resin foam and a soft ethylene-vinyl acetate copolymer can be freely selected as necessary. In addition, in the case of the conventional foaming injection molding method, the surface layer also has a cell structure, so that the surface hardness is low, the surface layer may be easily broken by friction, and the cell structure may be exposed. It was difficult to get. However, according to the method of the present invention, the surface layer can be smoothed or the thickness of the surface layer can be changed.

In the method of the present invention, the density of foamed particles is 0.3 to 0.015 g / cm ^3.
Even if the temperature of the injection resin is high, there is no fear that the bubbles of the foamed particles will be broken and become continuous bubbles, or that the shrinkage and the density increase will occur even if the temperature of the injection resin is high. Further, in the present invention, it is possible to obtain an excellent composite foam when using the polyolefin foamed particles as the foamed particles, but especially among the polyolefin foamed particles, non-crosslinked polypropylene resin foamed particles,
By using non-crosslinked linear low-density polyethylene-based resin foamed particles, crosslinked polyethylene-based resin foamed particles, and crosslinked polypropylene-based resin foamed particles, it is possible to obtain a composite foam having less shrinkage and a good surface condition.

[Brief description of the drawings]

The drawings show one embodiment of the present invention. FIGS. 1 and 2 are schematic vertical sectional views of a molding apparatus showing steps of the method of the present invention, and FIG. 3 is a schematic vertical sectional view showing a different aspect of the molding apparatus. 1 ... Injection mold, 3 ... Expanded particles, 5 ... Injection machine, 6 ... Thermoplastic resin

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29K 105: 24

Claims (4)

(57) [Claims] 1. A thermoplastic resin foamed particle or a plurality of combinations thereof are loaded into an injection molding mold, and then a thermoplastic resin is injected into the mold to integrate the thermoplastic resin and the thermoplastic resin foamed particle. A method for producing a composite foam, which comprises obtaining a composite. 2. The density of expanded thermoplastic resin particles is 0.3 to 0.015.
The method for producing a composite foam according to claim 1, wherein the composite foam is g / cm ³ . 3. The method for producing a composite foam according to claim 1, wherein the expanded thermoplastic resin particles are expanded polyolefin resin particles. 4. A foamed polyolefin resin particle is a non-crosslinked polypropylene resin foam, a non-crosslinked linear low-density polyethylene resin foam, a crosslinked polyethylene resin foam,
The method for producing a composite foam according to claim 3, wherein the composite foam is any one of crosslinked polypropylene resin foams.