JP2001162640A - Method for manufacturing thermoplastic resin foamed molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thermoplastic resin foamed molding excellent in shape stability and high in the mutual fusion strength of foamed resin particles. SOLUTION: A thermoplastic resin foamed molding consists of a core layer 11 comprising a crystalline thermoplastic resin in a foamed state and a coating layer 12 substantially coating the core layer 11 in a non-foamed state and the coating layer contains an ethylenic polymer having a melting point lower than that of the thermoplastic resin or not substantially showing a melting point. A method for manufacturing this foamed molded object consists of a process for preparing foamed resin particles with an L/D ratio of the long diameter L and short diameter D of each of the particle of 0.5-3 and a process introducing the foamed resin particles into a mold 211 to heat and mold them by hot air 5 to obtain a foamed molding 3 wherein the foamed resin particles comprising the termoplastic resin are mutually fused. As the hot air, dry air with steam pressure of 5-50 kPa is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic resin foam used for a heat insulating material, a cushioning material, a packaging container, a sound absorbing material, a floating material, and the like.

[0002]

2. Description of the Related Art A foamed molded article made of a thermoplastic resin such as polystyrene, polyethylene, or polypropylene is used for a heat insulating material, a cushioning material, a packaging container, a sound absorbing material, and a floating material. Such a foamed molded article has a closed cell structure, is lightweight, and has good heat insulating properties and cushioning properties. Due to this heat insulating property, these foamed resin particles are difficult to be uniformly heated at the time of heat molding, and the common point is that foamed molded articles are produced using pressurized steam having a large heat capacity as a heating medium. The foam molded article is formed by placing foamed resin particles in a mold, heating and fusing the particle surfaces. Conventionally, in order to fuse resin particles to each other, the vapor pressure of the pressurized steam is 0.1 MPa or less for polystyrene, 0.2 MPa or less for polyethylene, and 0.5 MPa for polypropylene.
a or less pressurized steam (steam gauge pressure) was used.

[0003]

However, in the above-mentioned conventional fusion method using pressurized steam heating, moisture infiltrates into the voids or particles of the foamed resin particles in a gaseous state at the time of heat fusion. Therefore, when cooling is performed in this state, water condenses from a gas to a liquid state, and the foamed resin particles undergo volume contraction.
As a result, the pressure in the voids or inside the particles of the foamed resin particles is reduced, and the foamed molded article formed by such particles contracts and deforms. As a result, there is a problem that the shape stability is poor, and it is difficult to obtain a molded article according to the mold. Further, in the foam molded article, it is required that the foamed resin particles are sufficiently fused and have high mechanical strength.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for producing a foamed thermoplastic resin article having excellent shape stability and high fusion strength between foamed resin particles.

[0005]

The present invention comprises a foamed core layer made of a crystalline thermoplastic resin, and a substantially non-foamed coating layer covering the core layer. It contains an ethylene polymer having a melting point lower than or substantially not showing a melting point than that of the thermoplastic resin, and has a major axis L of the particles.
Preparing foamed resin particles having an L / D ratio of 0.5 to 3 with respect to the diameter of the foamed resin, placing the foamed resin particles in a mold, and heat-molding with hot air to form the foamed resin particles. Obtaining a thermoplastic resin foam molded article obtained by fusing together with each other, and using a dry gas having a steam pressure of more than 5 kPa and 50 kPa or less as the hot air. It is.

Next, the operation and effect of the present invention will be described.
In the present invention, the foamed resin particles are placed in a mold, and are heated and formed into a desired shape using hot air made of a dry gas having the above-mentioned specific steam pressure. Therefore, the amount of water vapor in the dry gas is small, and almost no water vapor penetrates into the voids or particles of the foamed resin particles during heat molding. Therefore, the foamed resin particles are strongly fused to each other, and the fusion strength between the foamed resin particles is increased. Further, the conventional compact has no water content due to the condensation of pressurized steam, and the volume shrinkage of the compact does not occur. Therefore, the foamed resin molded article of the present invention has excellent shape stability.

Further, a high-temperature curing treatment for correcting size and shrinkage deformation is not required. And because there is no water content,
It is not necessary to perform a drying treatment after molding, and the obtained foamed molded article has excellent heat insulating properties and does not cause rust. In addition, in the above-described heat molding using a dry gas, the heat molding used in the conventional heat molding of foamed resin particles, for example, as described above,
A heavy mold that can withstand a high vapor pressure of 0.1 to 0.5 MPa becomes unnecessary, and the heat energy consumption is small.

In the case where a skin made of a thermoplastic resin and the foamed resin particles are integrally molded in a mold to produce a foamed molded body having a skin, the influence of water vapor is almost eliminated. The skin made of the plastic resin and the foamed resin particles are firmly fused. Therefore, the obtained foamed molded article has high fusion strength and excellent mechanical strength. In addition, when a woven or non-woven fabric made of thermoplastic resin is used as the skin, the hair on the surface of the skin which occurs during steam ironing does not fall off, and the appearance such as color and touch is good. This is unnecessary and is industrially advantageous. As the skin, a film, a sheet, a vacuum molded product, an injection molded product, or the like may be used, and these may be integrally formed with the foamed resin particles.

The foamed resin particles are composed of a foamed core layer made of a crystalline thermoplastic resin and a substantially film-like coating layer containing an ethylene polymer. Therefore, by passing hot air with a small heat capacity through the gaps between the foamed resin particles filled in the mold, it is necessary to suppress the softening of the core layer, which has a higher melting point than the coating layer, and to fuse the coating layer. Can heat foamed resin particles up to
Thereafter, the foamed resin particles are fused by effectively utilizing the compression reaction force possessed by the core layer, and a foamed molded article having a high fusion strength can be manufactured.

Next, the details of the present invention will be described. (Preparation of Expanded Resin Particles) The expanded resin particles of the present invention have a composite structure composed of a foamed core layer and a substantially non-foamed covering layer. The foamed core layer has, for example, a closed cell structure or an open cell structure. In this case, it is preferable to have a closed cell structure. The reason is that the closed cell structure has a high compressive reaction force of the core layer at the time of heat molding and a high compressive strength even at a low density. The closed cell rate of the core layer is preferably 50% or more, and more preferably 70% or more. Thereby, the compression reaction force of the core layer at the time of heat molding is further increased, and a foam molded article having high compression strength even at a low density can be obtained. The coating layer is in a non-foamed state. The coating layer is preferably a film-like thermoplastic resin layer having a thickness of 1 to 150 μm.

The core layer is made of a crystalline thermoplastic resin. Such crystalline thermoplastic resins include, for example,
Examples include polypropylene resin, polybutene resin, polymethylpentene resin, polyester resin, polyamide resin, fluorine resin, and crystalline styrene resin. Among these, a propylene homopolymer, a random copolymer of propylene and an α-olefin other than propylene, and a block copolymer are preferable. As a result, it is possible to obtain a foamed molded article that is inexpensive, has excellent recyclability, is lightweight, and has excellent heat insulating properties and cushioning properties.

The coating layer is substantially in a non-foamed state.
The “substantially non-foamed state” refers to, for example, a thickness of 1 to 150 μm.
m means a thin film state without a bubble structure. The film may be perforated, for example, in a mesh state. Further, the coating layer contains an ethylene-based polymer having a lower melting point than the thermoplastic resin used for the expanded resin particles or having substantially no melting point. Such low-melting ethylene polymers include high-pressure low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, vinyl acetate,
Copolymers of ethylene with unsaturated carboxylic acid esters, unsaturated carboxylic acids, vinyl alcohol, and the like can be given.

The above-mentioned "substantially no melting point" means, for example, a resin having no crystallinity that does not show a melting peak when heated by a differential scanning calorimeter. Examples of such an ethylene polymer having substantially no melting point include, for example, ethylene.
Propylene rubber, ethylene propylene diene rubber,
Rubber / elastomer such as ethylene / acryl rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, and the like. These ethylene polymers can be used alone or in combination of two or more.

Among the above ethylene polymers, high-pressure low-density polyethylene, linear low-density polyethylene, and linear ultra-low-density polyethylene are preferred. Among them, linear low-density polyethylene polymerized using a metallocene catalyst,
Linear ultra low density polyethylene is most preferred.

The above-mentioned ethylene polymer constituting the coating layer has substantially no melting point, or even if it has a
The temperature is preferably 25 ° C. or lower. The reason is that the heating temperature for molding the foamed resin particles can be set to a lower temperature.

Further, as the coating layer, it is preferable to select and use an ethylene polymer having a melting point lower by 15 ° C. or more than the thermoplastic resin constituting the core layer. The difference between the melting points of the ethylene polymer and the thermoplastic resin is preferably 20 ° C.
-100 ° C. If the above melting point difference is less than 15 ° C., the coating layer made of the ethylene polymer may foam under the conditions for foaming the thermoplastic resin of the core layer.

Further, the coating layer is preferably a mixture of the ethylene polymer and a crystalline thermoplastic resin of the same type as the core layer. Thereby, the adhesion between the coating layer and the core layer is improved. The mixing ratio of the thermoplastic resin mixed in the coating layer is 1 to 100 parts by weight of the ethylene polymer.
Preferably, it is selected from the range of 100 parts by weight. When the blending ratio of the thermoplastic resin is less than 1 part by weight, the effect of improving the adhesion between the core layer and the coating layer may be reduced. On the other hand, if it exceeds 100 parts by weight, the sea-island morphology of the coating layer changes, and the thermoplastic resin forms a continuous sea phase, so that the heating temperature during molding does not become too low. Further, the mixing ratio of the thermoplastic resin is preferably in the range of 1 to 50 parts by weight based on 100 parts by weight of the ethylene polymer. Thereby, the adhesiveness between the core layer and the coating layer is improved, and the heating temperature during molding can be reduced.

In the above foamed resin particles, the thickness of the coating layer is preferably 1 to 150 μm. When the thickness of the coating layer is less than 1 μm, the effect of sufficiently lowering the heating temperature during molding is small. On the other hand, when the thickness of the coating layer is 150
If it exceeds μm, the heating temperature can be lowered during molding, but the ratio of the substantially non-foamable portion in the coating layer is large, and the mechanical strength of the molded product is low compared to the expansion ratio. There is a tendency. Furthermore, the thickness of the coating layer is 10
It is preferably 100 μm. This makes it possible to lower the heating temperature during molding and increase the mechanical strength of the foam molded article.

As shown in FIG. 1, the L / D ratio between the major axis L and the minor axis D of the foamed resin particles 1 of the present invention is 0.5 to 3.
If it is less than 0.5, the surface area of the coating layer 12 becomes small, resulting in poor fusion. If it exceeds 3,
The particle shape becomes slender, the filling efficiency deteriorates, and molding failure and shape stability decrease. L / D ratio is 1.5-3
When it is relatively large, it is easy to obtain a molded body having many voids, but it is preferably 0.8 to 2 from the viewpoint of moldability.

As shown in FIG. 1, for example, the foamed resin particles 1 are made of a core layer 1 made of a crystalline thermoplastic resin.
1 and a coating layer 1 containing an ethylene polymer having a melting point lower than that of a thermoplastic resin or substantially not showing a melting point.
2 are composite particles. Generally, both ends of the core layer 11 are exposed from the coating layer 12. The foamed resin particles 1 are obtained by impregnating a non-foamed state of the composite particles with a volatile foaming agent, followed by heating and foaming.

The volatile foaming agents include propane,
Lower aliphatic hydrocarbons such as butane, pentane, heptane, cyclopentane, and cyclohexane; halogenated hydrocarbons such as dichlorodifluoromethane and trichloromonofluoromethane; and inorganic gases such as nitrogen, air, and carbon dioxide. These are used alone or in combination of two or more.

As a specific method for producing the above-mentioned composite particles used as a raw material of the expanded resin particles, the following methods are used. For example, Japanese Patent Publication Nos. 41-16125 and 43-125
A sheath-core type composite die described in JP-A-23858, JP-A-44-29522 and JP-A-60-185816 is used. In this case, two extruders were used. One extruder melt-kneaded the thermoplastic resin constituting the core layer, and the other extruder melt-kneaded the ethylene polymer composition constituting the coating layer. After that, a sheath-core, long columnar composite is discharged using a die as a core layer of a thermoplastic resin and a coating layer of an ethylene-based polymer composition.

Next, the composite thus obtained was cut into 0.1%. 1 to 10 mg of composite particles. If the weight of the composite particles is less than 0.1 mg, the ratio of the coating layer that effectively lowers the heating temperature of the molding process increases, so that
The mechanical strength of the obtained foam molded article is reduced. On the other hand, when the weight of the composite particles exceeds 10 mg, the filling property into the mold at the time of molding tends to deteriorate.

The above-mentioned sheath-core type composite particles are impregnated with a volatile foaming agent and then foamed by heating to obtain the foamed resin particles. As such a heating foaming method, specifically,
For example, JP-B-49-2183, 56-134
4, West German Unexamined Patent Publication Nos. 1285722 and 2107683 can be used.

In this case, the sheath-core type composite particles are put together with the volatile foaming agent in a closed container, heated to a temperature higher than the softening temperature of the crystalline resin of the core layer, and the composite particles are impregnated with the volatile foaming agent. Let it. Thereafter, the contents in the closed container are discharged into a low-pressure atmosphere from the closed container, and then subjected to a drying treatment to obtain foamed resin particles.

The heating temperature during foaming of the composite particles is usually
The temperature is set to be equal to or higher than the softening temperature of the thermoplastic resin of the core layer, and is preferably set to a temperature higher than the melting point of the ethylene polymer of the coating layer (in the case of a composition, the melting point of the main component). In the present invention, it is preferable to provide a stirrer in order to prevent the composite particles from fusing with each other in the closed vessel.

At the time of heating and foaming the composite particles, it is preferable to use water, alcohol, or the like as a dispersion medium for the composite particles. In addition, aluminum oxide, tribasic calcium phosphate,
Insoluble inorganic substances such as magnesium pyrophosphate and zinc oxide; water-soluble protective colloids such as polyvinylpyrrolidone, polyvinyl alcohol and methylcellulose; and anionic surfactants such as sodium dodecylbenzenesulfonate and sodium α-olefin sulfonate. It is preferable to use a single compound or a mixture of two or more compounds.

Preferably, the composite particles are released into a low pressure atmosphere. As a result, the thermoplastic resin of the composite particles foams, and foamed resin particles comprising a foamed core layer and a coating layer covering the core layer can be obtained. When the composite particles are released into a low-pressure atmosphere, the same inorganic gas or volatile foaming agent as described above is introduced into the closed container from outside to keep the pressure inside the closed container constant to facilitate the release. Is preferred.

In the foamed resin particles, the thermoplastic resin of the core layer exhibits a foamed state of a closed cell structure from the state of the cut cross section of the particles, while the ethylene polymer of the coating layer has a substantially non-foamed film. State (see FIG. 1).

(Heat molding of foamed resin particles) The foamed resin particles are molded by heating with hot air. Here, the hot air is obtained by heating the air by a heating means such as an electric heater or a steam heater. In addition, when supplied using a blower and compressed air, the foamed resin particles can be efficiently heated. Further, by using a method of collecting and circulating hot air, loss of heat energy can be reduced.

Hot air has a water vapor pressure exceeding 5 kPa and a pressure of 50 kPa.
A dry gas of Pa or less is used. Thereby, it is possible to prevent water vapor from infiltrating into voids or particles of the foamed resin particles at the time of heat molding, and it is possible to sufficiently secure the shape stability of the foamed molded article.

When the pressure is 5 kPa or less, static electricity is easily generated, and the charge amount of the foamed molded article may be increased. On the other hand, if it exceeds 50 kPa, the humidity in the dry gas, which is hot air, increases, and the object of the present invention cannot be achieved. The humidity in the dry gas at the above steam pressure is, for example, 5% humidity and 120% at 100 ° C. when the steam pressure is 5 kPa.
The humidity is 3% at 100 ° C., 10% at 100 ° C. at 10 kPa, 5% at 120 ° C., 50% at 100 ° C. at 50 kPa, and 25% at 120 ° C. The temperature of the hot air used for producing the foamed molded product is usually 90 to 90 when the core layer is made of a polypropylene resin.
140 ° C. In addition, as the dry gas of the hot air,
For example, air having a water vapor pressure in the above range is used.

Further, as described in claim 3, the temperature at the time of heat molding is preferably lower than the melting point of the crystalline thermoplastic resin to be the core layer. If the temperature is higher than this, the core layer resin may be softened and melted, and the shrinkage and deformation of the foamed molded article may be increased. Preferably, the melting point of the core layer resin is 10 ° C. or less. Further, when the coating layer has a melting point, heating is performed at a temperature equal to or higher than the melting point of the coating layer.

When a foamed resin particle is obtained by heating and molding a foamed resin particle, the state of compression of the foamed resin particle is appropriately set according to the physical properties required for the molded body. A foamed molded article having a void with a small contact area therebetween is obtained. Either heating or compression may be performed first. The compression may be during heating.

Next, as described in the second aspect, it is preferable that the heat molding is performed in a state where the bulk density of the foamed resin particles is compressed to 50 to 99% to increase the apparent density.
Thereby, at the time of heat molding, the gap amount between the foamed resin particles and the density of the foamed molded article can be adjusted, and the foamed molded article having desired physical properties can be obtained.

If the bulk volume of the foamed resin particles is reduced to less than 50%, a foamed article having almost no voids is obtained, and the density of the foamed article is simply increased. Just makes no sense. When it is higher than 99%, the contact area between the foamed resin particles becomes smaller, and the foamed molded article has low fusion strength.

As a specific method for producing a foamed molded article by heat-molding the foamed resin particles, for example, as shown in FIG. 2, first, the foamed resin particles 1 are filled in a gas-permeable lower mold 211 (a ). Thereafter, while the hot air 5 is passed through the gap between the foamed resin particles 1 filled in the lower mold 211, the surface temperature of the foamed resin particles 1 is adjusted to the temperature required for the coating layer constituting the foamed resin particles to fuse. (B). afterwards,
The bulk volume of the foamed resin particles 1 is reduced to 50 to 95 by the upper mold 212.
% To obtain a foam molded article 3 (c).

As shown in FIG. 3, first, the foamed resin particles are put into a hermetically sealed mold 22 while the bulk volume of the foamed resin particles 1 is compressed to 50 to 95% and held (a). Then, the hot air pressurized gas 51 is press-fitted therein, and the hot air pressurized gas 51 is passed through the gap between the foamed resin particles 1 so that the surface temperature of the foamed resin particles 1 is reduced. Is heated to a temperature required for fusing (b). Next, the compressed gas 51 is discharged to recover the compressed state of the foamed resin particles 1 to obtain the foamed molded article 3 (c).

In the present invention, the molding conditions are selected in consideration of the properties of the expanded resin particles and the shape and density of the expanded molded article.
The use of expanded resin particles having an increased foaming power makes it easier to obtain a foamed molded article having a lower density. In addition, it is also possible to produce a plate-like foamed molded article by using a gas permeable belt instead of a pair of air permeable irregularities.

The foamed thermoplastic resin article obtained by the above-mentioned production method includes foamed resin particles comprising a foamed core layer made of a crystalline thermoplastic resin and a coating layer covering the core layer. Wherein the coating layer contains an ethylene polymer having a melting point lower than that of the thermoplastic resin or substantially no melting point, and is not foamed. It is a thermoplastic resin foam molded article characterized by being in a state.

The thermoplastic resin foam molded article obtained by the present invention may be, for example, a heat insulating material, a cushioning material, a packaging container, a sound absorbing material,
Used for flotation materials, industrial components, etc. Further, the thermoplastic resin foam molded article is also used for a woven fabric, a nonwoven fabric, a film, a sheet, a vacuum molded product, an integrally molded product with an injection molded product, and the like made of a thermoplastic resin.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in comparison with Examples 1 to 4 and Comparative Examples 1 to 4. Example 1 An ethylene / propylene random copolymer having an ethylene content of 1.5% by weight (melting point: 153 ° C.) was kneaded using a single-screw extruder having an inner diameter of 40 mm, and the density was adjusted using a single-screw extruder having an inner diameter of 25 mm. Linear low density polyethylene (melting point 91 ° C.) polymerized with a 0.895 metallocene catalyst was kneaded. Next, a strand was extruded from a die having a die orifice having a diameter of 1.5 mm, using the ethylene / propylene random copolymer as a core layer and a linear low-density polyethylene as a coating layer.

Further, this strand was cooled through a water bath and cut into 1.2 mg. Observation of the cross section of this composite particle with a phase contrast microscope revealed a thickness of 30 μm.
m linear low density polyethylene covered the ethylene / propylene random copolymer.

Next, the composite particles 10 are placed in a closed container.
0 parts by weight, 250 parts by weight of water, 1.0 part by weight of tribasic calcium phosphate having a particle size of 0.3 to 0.5 μm and 0.007 part by weight of sodium dodecylbenzenesulfonate.
Next, 20 parts by weight of butane was supplied into the closed vessel under stirring. After filling the contents at a filling rate of 62%, the temperature was raised to 145 ° C. over one hour and maintained at the same temperature for 30 minutes.

Thereafter, the valve of the discharge hole at the bottom of the closed container is opened, and nitrogen gas is introduced from the outside into the gas phase in the closed container, and the contents are brought to atmospheric pressure while maintaining the pressure in the container. Discharged to obtain foamed resin particles. The foamed resin particles thus obtained had an average bulk density of 17 kg / m ³ and an average cell diameter of 12
0 μm, and there was no blocking between the foamed resin particles.

When the cross section of the expanded resin particles was observed with a phase contrast microscope, the ethylene / propylene random copolymer in the core layer was in a closed-cell expanded state, while the linear low-density polyethylene was substantially expanded. In a non-foamed film state, the foamed core layer of the ethylene / propylene random copolymer was covered. As shown in FIG. 1, the L / D ratio of the major axis L and the minor axis D of the expanded resin particles is 0.9.

The foamed resin particles are completely dried in a drying chamber at 40 ° C., and are filled in a pair of air-permeable concave and convex molds.
Hot air of 20 ° C. (4% humidity) was supplied. Thereby, hot air was passed through the gap between the foamed resin particles, and the surface temperature of the foamed resin particles was heated to 120 ° C. Next, the foamed resin particles were fused while the inner volume of the mold was reduced to 60%.
Then, it cooled with air and took out the foaming molded object from the inside of a type | mold. The foamed molded article had a density of 28 kg / m ³ , a size of 200 mm in length, 300 mm in width, and 40 mm in thickness, had no water content, and had a shape similar to a mold without shrinkage deformation.

From the above foam molded article, a length of 200 mm,
Twenty test pieces having a width of 30 mm and a thickness of 12.5 mm were prepared, wound around a cylinder having a diameter of 50 mm, and bent to a 90 ° angle. As a result, 80% or more of the test pieces did not crack.

Examples 2 to 4 and Comparative Examples 1 to 4 In Examples 2 to 4 and Comparative Examples 1 to 4, as shown in Table 1, the resin and condition of the core layer, the resin and condition of the coating layer, and the average bulk A foam molded article was manufactured by changing the density, the L / D ratio, the heating medium, the heating temperature, and the compression ratio. Others are described in Example 1.
It was manufactured in the same manner as described above.

The physical properties of Examples 1 to 4 and Comparative Examples 1 to 4 were measured by the following methods. <Melting point> Measured by a differential scanning calorimeter (DSC). First, 3-5 mg of the resin was heated to a temperature at which the product melted, and then cooled to room temperature at a rate of 10 ° C./min. Then,
The temperature was raised by heating at a rate of 10 ° C./min, and the peak temperature of the obtained endothermic curve was defined as the melting point.

<Bulk Density of Molded Article> This refers to the weight per unit volume (kg / m ³ ) of the foam molded article. <Compression ratio> The compression ratio (%) is represented by (the bulk density of the foamed molded article−the bulk density of the foamed resin particles) × 100 (%) / the bulk density of the foamed molded article. <Porosity> 3 liters of water was placed in a graduated measuring cylinder having an inner diameter of 150 mm and a volume of 5 liters, and the dimensions were 100 ×
A molded body test piece of 100 × 40 mm (volume 0.4 liter) was submerged, and the volume V (liter) indicated by the water surface at this time was measured, and the porosity was determined by equation (1).

{1- (V-3) /0.4} × 100%. . . . . Equation (1)

<Water content> After molding, the molded body weight A was measured within 30 minutes to 1 hour, and the molded body was allowed to stand in an oven at 80 ° C. for 12 hours. The weight B of the compact after being left for a time is measured, and the equation (2)
Was used to determine the moisture content.

{(AB) / B} × 100%. . . . . Equation (2)

<Shrinkage Deformation During Molding> The foamed molded product taken out of the mold was left at a temperature of 20 ° C., and the appearance after 30 minutes was visually judged. None: The shape is kept as it is. Existence: There is shrinkage deformation such as warpage and dent, and the shape is not the same as the type.

<Fusing test> Length 200 mm, width 30 m
A test piece having a thickness of 12.5 mm and a thickness of 12.5 mm was prepared, and the test piece was bent up to 90 degrees along the circumference of a cylinder having a diameter of 50 mm, and evaluated according to the following criteria. ：: 80% or more of the total number of test pieces does not crack. ×: Cracks exceeding 20% of the total number of test pieces were broken. Table 1 shows the above results.

[0057]

[Table 1]

As can be seen from the table, in Examples 1 to 4 of the present invention, there was no water content in the voids or particles of the foamed resin particles, there was no shrinkage deformation during molding, and the fusion strength was high.

[0059]

According to the present invention, it is possible to provide a method for producing a foamed thermoplastic resin article having excellent shape stability and high fusion strength between foamed resin particles.

[Brief description of the drawings]

FIG. 1 is a perspective view of a foamed resin particle according to the present invention.

FIG. 2 is an explanatory view showing a heat molding method using an upper mold and a lower mold in the present invention.

FIG. 3 is an explanatory view showing a heat molding method using hot air pressurized gas in the present invention.

[Explanation of Codes] . . 10. foamed resin particles, . . Core layer, 12. . . 2. a coating layer; . . Foam molding,

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F074 AA25 BA37 CA35 CA38 CA46 CA52 CC03Z CC04Z CC05Z CC46 CD20 DA02 DA03 DA22 DA32 DA33 DA34 DA42 DA57 4F212 AA08 AA09 AB02 AE06 AG03 AG20 UA02 UB01 UF01 UG05 UG07 UG07

Claims (3)

[Claims] 1. A foamed core layer made of a crystalline thermoplastic resin, and a substantially non-foamed coating layer covering the core layer, wherein the coating layer is made of the thermoplastic resin. An L-based polymer containing an ethylene polymer having a low melting point or substantially no melting point, and having a major axis L and a minor axis D,
A step of preparing foamed resin particles having a / D ratio of 0.5 to 3, placing the foamed resin particles in a molding die, and heat-molding the foamed resin particles with hot air to heat the foamed resin particles to each other. A process for obtaining a foamed thermoplastic resin article, wherein the hot air uses a dry gas having a steam pressure of more than 5 kPa and 50 kPa or less. 2. The thermoplastic resin foam molding according to claim 1, wherein the heat molding is performed in a state where the bulk density of the foamed resin particles is reduced to 50 to 99% to increase the apparent density. How to make the body. 3. The method for producing a foamed thermoplastic resin article according to claim 1, wherein the thermoforming is performed at a temperature lower than a melting point of the crystalline thermoplastic resin serving as a core layer. .