JPH1034753A - Manufacture of molding having high density skin layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce contraction even for a body of complex shape and to improve its appearance by a method in which when the surface pressure of foamed resin particles packed in a cavity has reached a specified pressure range, air among the particles is discharged, and the steam of a temperature below the melting point of the resin is introduced among the particles from a steam chamber. SOLUTION: When the surface pressure of foamed resin particles packed in a cavity 3 has reached 0.01-1.5kg/cm<2> G, a vacuum conduit 7 valve is opened, a drain conduit 9 valve is closed, a steam chamber 1a and the cavity 3 are evacuated to discharge air among the particles. After that, the vacuum conduit 7 valve is closed, and steam of a temperature necessary for the fusion bonding of the particles in a mold is introduced from a steam conduit 6 to heat the particles. The steam passes through the chamber 1a from the conduit 6, flows into the cavity 3 through a steam hole 1a, and heats the particles. In this process, the steam also behaves as a heating medium for heating a molding mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a molded article having a high-density skin layer, and more particularly, to a molded article having a uniform, high-density, hard skin layer on the surface of the molded article and having a small shrinkage. And a method for producing the same.

[0002]

2. Description of the Related Art Molded articles produced by filling foamed resin particles (hereinafter referred to as "foamed particles") in a cavity of a foaming mold composed of a mold cavity and a core mold each having a steam chamber and heat-sealing them. Is characterized by having a closed-cell structure, being rich in heat insulation and buffering properties, and light in weight, and is used for cushioning materials, heat insulating materials, heat insulating containers, functional members, and the like.

[0003] However, since a small gap between the particles remains on the surface of the molded article, when used repeatedly in applications such as a container, the gap between the particles becomes dirty and easily cracks. There is a problem that the part is soft and easily scratched. Therefore, in the conventional manufacturing method, a method of coating the inner surface of the container or a method of integrally molding with a resin sheet or the like has to be adopted, and there is a problem that the cost of the obtained molded body is high.

[0004] In order to solve these problems, for example, JP-A-48-28060 and JP-A-52-47866.
Japanese Patent Application Laid-Open Publication No. H11-15064 proposes a method of forming a skin layer on the surface of a molded body by melting during molding. In these molding methods, a cavity mold and a core mold each having a steam chamber are used, and a foam molding mold having a large number of steam holes formed on a wall surface facing a cavity of each steam chamber is used. Is filled with foamed particles, steam having a temperature lower than the melting temperature of the foamed particles is introduced into a steam chamber, and the foamed particles are heated and fused together to form a molded body. It is introduced into a chamber, and the surface of the molded body is melt-hardened to form a skin layer on the surface of the molded body.

However, in the case of this method, when the foamed particles are heated with steam at a temperature higher than the melting temperature, the vicinity of the steam holes is excessively melted, and as a result, the thickness of the skin layer near the steam holes and other portions is reduced. And the like, and an uneven skin layer is formed as a whole. In addition, since the fusion of the foamed particles is performed first, the individual foamed particles are bonded to each other, and further free foaming is hindered, and the voids between the foamed particles cannot be sufficiently filled. In addition, the molded article has a problem that a gap is partially generated as the thickness of the skin layer increases,
A molded article having a uniform skin layer with few voids was not obtained.

Japanese Patent Application Laid-Open No. 5-124126 discloses that raw material particles are contact-melted on a molding surface of a mold heated to a melting point of foamed particles or higher, and a molten resin layer is formed on that portion. There has been proposed a foamable resin molded article in which a continuous hardened surface layer is formed in an in-mold foam molding process.

However, the method described in the above-mentioned publication is a method of forming a skin layer by excessive cracking filling, and therefore cannot cope with a molded article having a complicated shape. There is a problem that the ratio becomes low and the compact shrinks.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has as its object to reduce shrinkage by providing a uniform, high-density and hard skin layer on the surface even in a complicated shape. An object of the present invention is to provide a method for producing a molded article having a small appearance and good appearance.

[0009]

That is, the gist of the present invention is to provide a method of manufacturing a molded article by a foaming mold comprising a mold having a steam chamber and a core having a steam chamber. The foamed resin particles are compressed and filled, steam is introduced into one of the above-mentioned steam chambers to heat the mold to a temperature equal to or higher than the melting point of the foamed resin particles, and to melt the foamed resin particles that are in contact with the mold. A skin layer is formed on the surface, and the surface pressure of the foamed resin particles filled in the cavity is 0.01
When the pressure reaches the range of 1.5 kg / cm ² G, the air between the foamed resin particles is exhausted, and steam having a melting point lower than the melting point of the foamed resin is introduced between the foamed resin particles from the other steam chamber to form the foamed resin particles. And a method for producing a molded article having a high-density skin layer, characterized by heating and fusing.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically illustrating an example of a mold for foam molding (hereinafter simply referred to as a mold) used in the method of the present invention. In the present invention, molds each including a mold having a steam chamber and a mold having a core are used.

The mold shown in FIG. 1 comprises a cavity mold (1) having a concave cross section and a core mold (2) having a convex cross section, and has a cavity (3) having a box cross section. The tip of a filling nozzle (5) extending from the compressed filling tank (4) for the foamed particles communicates with the cavity (3) through the mold (1).

The mold mold (1) has a steam chamber (1a) inside, and a large number of steam holes (1b) are formed in a wall surface of the steam chamber (1a) facing the cavity (3). And
A steam pipe (6), a vacuum pipe (7), a cooling water pipe (8), and a drain pipe (9) each having an on-off valve are connected to the steam chamber (1a).

On the other hand, the core type (2) has a first steam chamber (2a) and a second steam chamber (2b) inside. The first steam chamber (2a) is located on the cavity (3) side, and the second steam chamber (2b) is located outside the first steam chamber (2a). Each steam chamber has a completely independent structure without communication with each other. The first steam chamber (2a) has a steam pipe (10) and a cooling water pipe (1) each having an on-off valve.
1) and the drain line (12) are in communication. The second steam chamber (2b) has a steam pipe (13), a cooling water pipe (14), and a drain pipe (1) each having an on-off valve.
5) is in communication.

In the above-described mold, after forming a skin layer on the surface of the foamed resin particles filled in the cavity (3), water vapor having a melting point lower than the melting point of the foamed resin is introduced between the foamed resin particles. Since the steam holes (1b) used to heat and fuse the foamed resins to each other are formed on the wall surface facing the cavity (3) of the steam chamber (1a),
The steam for forming the skin layer is introduced into the first steam chamber (2a) and the second steam chamber (2b) of the core mold (2), and is used to heat and fuse the foamed resins to each other. When using a mold in which the steam holes to be formed are formed in positions opposite to the above, the steam for forming the skin layer is introduced into the steam chamber (1a) of the mold type (1). You. In the present invention, any of the molds described above can be used.

The expanded particles used in the present invention include polystyrene resin particles, polyethylene resin particles, and polypropylene resin particles. These foamed particles are compressed and filled into the compression filling tank (4) with compressed air, and then uniformly compressed into the mold cavity (3).

First, in the present invention, foamed resin particles are compression-filled into a cavity (3) of a mold, and steam is introduced into one of the above-mentioned steam chambers to heat the mold to a temperature equal to or higher than the melting point of the foamed resin particles. At the same time, the foamed resin particles in contact with the mold are melted to form a skin layer on the surface.

Specifically, the steam lines (10), (1)
The valve of 3) and the valves of the drain lines (12) and (15) are opened, and high-temperature steam is introduced into the first steam chamber (2a) and the second steam chamber (2b) while preheating the mold. The hermetically sealed foamed particles contained in the compression filling tank (4) are compressed and filled into the cavity (3) by the filling nozzle (5). When the mold temperature of the first steam chamber (2a) and the second steam chamber (2b) reaches a certain temperature or higher, the drain pipe (1
The valves of 2) and (15) are closed, and the mold temperature on the side of the first steam chamber (2a) in contact with the foamed particles in the cavity (3) is raised to the melting point of the foamed particles or more.

In a preferred embodiment of the present invention, the thickness of the skin layer, the density of the skin layer, and the molding other than the skin layer are performed at the time of the above-mentioned filling of the foamed particles in order to ensure the strength and quality of the target molded body. The density of the body is set in advance, and the compression ratio of the foamed particles obtained by the following mathematical expression (I) is used. Here, the density of the solid state of the foamed particles to be used is used as the density of the skin layer. Incidentally, the density of the solid state of the expanded polystyrene particles is 950 to 100.
0 kg / m ^3, the density of the solid state of the polypropylene expanded particles are 850~900kg / m ^3.

In the present invention, the compression ratio of the expanded particles is
Usually, it is 3 to 70%, preferably 10 to 65%. If the compression ratio is less than 3%, the filling amount of the expanded particles is insufficient,
It is difficult to form a skin layer and the molded product shrinks. Also,
When the compression ratio exceeds 70%, the skin layer can be made thicker, but the heating and melting time becomes longer, and the amount of compressed air used during compression filling increases, resulting in higher production costs.

[0020]

C = (1-ρ)₁/ ((Ρ_Two× t_Two+ Ρ_Three× t_Three) / T₁)) × 100 (I) C: Compression rate (%) ρ₁: Density of expanded resin particles before filling (kg / m^Three ) Ρ_Two: Density of skin layer (kg / m^Three) Ρ_Three: Density other than skin layer (kg / m^Three) T₁: Molded body thickness (mm) t_Two: Thickness of skin layer (mm) t_Three: Thickness other than skin layer (mm)

The foamed particles compressed and filled in the mold have a surface pressure higher than the atmospheric pressure. However, the volume of the foamed particles decreases with the formation of the skin layer. The existing surface pressure decreases with the formation of the skin layer.

Therefore, in the present invention, when the surface pressure of the foamed resin particles filled in the cavity (3) reaches the range of 0.01 to 1.5 kg / cm ² G, the internal In order to obtain a molded body with better fusion of the particles, air between the foamed resin particles is discharged, and steam having a melting point lower than the melting point of the foamed resin is introduced between the foamed resin particles to heat and fuse the foamed resins to each other.

More specifically, when the surface pressure of the foamed particles filled in the cavity (3) decreases from a certain value with the formation of the skin layer and reaches the above-mentioned specific value, the vacuum line (7) ) Open the valve, close the drain line (9) valve, evacuate the steam chamber (1a) and the cavity (3), then close the vacuum line (7) valve, and fuse the expanded particles in the mold. Is introduced through a steam line (6) and heated. The steam passes through the steam chamber (1a) from the steam line (6), flows into the cavity (3) through the steam hole (1b), and heats the foamed particles. At this time, the water vapor also acts as a heat medium for heating the molding die. That is, according to the steam heating, a uniform temperature can be efficiently obtained in a short time by utilizing the large heat capacity.

When the surface pressure is less than 0.01 kg / cm ² G, when the foamed particles are heated and fused with water vapor, the foamed particles are excessively foamed and the packing density is reduced, so that the foaming power is reduced. However, poor fusion occurs, shrinkage of the molded body, and a peeling phenomenon between the skin layer portion and the molded body portion occur, and a good molded body cannot be obtained.
If the surface pressure exceeds 1.5 kg / cm ² G, the steam introduced for fusing and heating the foamed particles does not penetrate into the foamed particles. Good molded products cannot be obtained.

Next, in the present invention, the valves of the steam lines (6), (10) and (13) are closed, the valves of the drain lines (9), (12) and (15) are opened, and cooling is performed. The valves of the water lines (8), (11) and (14) are also opened. Then, after cooling water is introduced into the steam chamber (1a), the first steam chamber (2a), and the second steam chamber (2b) to cool the mold, the molded body is taken out.

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the embodiment, the apparatus shown in FIG.
mm, a height of 250 mm and a wall thickness of 20 mm were used. In each of the following examples, the compression ratio, the degree of fusion of the molded body, and the shrinkage in the production of the molded body were determined as follows.

<Compression Ratio> The compression ratio was determined by the formula (1−expanded particle density / molded product density) × 100%.

<Degree of fusion> The degree of fusion was evaluated by the ratio of the area of the molded article which was broken at the interface other than the interface of the foamed particles to the area of the entire fracture.

<Shrinkage> Shrinkage occurs when the size of the molded article is 5/10.
The case where it decreased by 0 or more was judged as “present”, and the case where it decreased less than 5/100 was judged as “absent”.

Example 1 The thickness of the skin layer was 0.5 mm and the density of the skin layer was 850.
kg / m ^3, density of 50 kg / m ³ other than the skin layer, since the thickness of the entire shaped body to produce a molded body of 20 mm, was calculated about 54% compression rate than formula (1).

The compression-filled tank (4) is filled with expanded polypropylene particles having a density of 32 kg / m ³ , and then the valves of the steam lines (10) and (13) and the drain line (1) are filled.
2) Open the valves of (15) and put 1 in the first steam chamber (2a).
Steam was introduced into the second steam chamber (2b) at 75 ° C., and the mold was sealed while preheating the mold.

The foaming particles were compression-filled into the cavity (3) from the compression-filling tank (4) by the filling nozzle (5). When the mold temperature of the first steam chamber (2a) and the second steam chamber (2b) reaches 100 ° C. or more, the drain pipe (1
The valves of 2) and (15) were closed. As a result, the mold temperature on the side of the first steam chamber (2a) in contact with the foamed particles in the cavity (3) rapidly rose to 170 ° C. and was stabilized.

At this time, the surface pressure of the expanded particles filled in the cavity (3) was 1.6 kg / cm ² G. The surface pressure decreased as shown in FIG. Surface pressure is 0.
When the pressure reaches 5 kg / cm ² G, the vacuum line (7) valve is opened, the drain line (9) valve is closed, and the inside of the steam chamber (1a) and the cavity (3) is evacuated. 7) The valve was closed and steam having a melting point lower than the melting point of the foamed particles was introduced from the steam line (6) and heated. The expanded particles pass through the steam chamber (1a) from the steam line (6), and pass through the steam holes (1b).
And heated by the steam flowing into the cavity (3). The steam temperature is 150 ° C. and the holding time is 20
Seconds.

Next, the valves of the steam lines (6), (10) and (13) are closed, the valves of the drain lines (9), (12) and (15) are opened, and the cooling water line (8) is opened. , (11) and (14) were also opened. Introducing cooling water into the steam chamber (1a), the first steam chamber (2a) and the second steam chamber (2b);
The mold was cooled to 40 ° C. The compact was removed from the mold. Table 1 shows the results.

Example 2 In Example 1, the conditions shown in Table 1 were adopted, and 48 kg / m ³ of expanded polypropylene expanded particles were compression-filled into the cavity (3), and the surface pressure was reduced to 0 as shown in FIG. 0.4 kg
/ Cm ² G, molding was performed under the same conditions as in Example 1 except that evacuation was performed. Table 1 shows the results.

Comparative Example 1 In Example 1, the surface pressure of the foamed particles was 0 kg / cm ^2.
Molding was performed under the same conditions as in Example 1 except that the gas was evacuated when the temperature decreased to G. Table 1 shows the results.

Comparative Example 2 In Example 1, the expanded particles had a surface pressure of 1.6 kg / c.
Molding was carried out under the same conditions as in Example 1 except that evacuation was performed at m ² G. Table 1 shows the results.

COMPARATIVE EXAMPLE 3 In Example 1, the mold was changed to cracking filling in which the mold was opened by 20 mm, and the compression ratio of the portion corresponding to the bottom of the box-shaped molded product was 50%, and the average compression ratio of the ridge at the side was 7%. The molding was carried out under the same conditions as in Example 1 except that the condition of 0.4% was adopted. Table 1 shows the results.

[0039]

[Table 1] Left column of Comparative Example 3: Bottom of box-shaped molded product Right column of Comparative Example 3: Upside of side surface other than bottom of box-shaped molded product-: Measurement not possible

The molded articles obtained in Examples 1 and 2 had a uniform skin layer, a good appearance, and no shrinkage.
The molded articles obtained in Comparative Examples 1 to 3 had poor fusion and poor appearance.

[0041]

According to the manufacturing method of the present invention described above, a good molded article having a uniform, high-density and hard skin layer on the surface of the molded article and having a small shrinkage can be obtained. Molding is unnecessary and a molded body can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an example of a mold for producing a molded article according to the present invention.

FIG. 2 is a curve showing a relationship between heating time and surface pressure in Examples 1 and 2.

[Explanation of symbols]

 1: Cabinet type 1a: Steam chamber 1b: Steam hole 2: Core type 2a: First steam chamber 2b: Second steam chamber 3: Cavity 4: Compression filling tank 5: Filling nozzle 6, 10, 13: Steam line 7 : Vacuum lines 8, 11, 14: Cooling water lines 9, 12, 15: Drain lines

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29K 25:00 105: 04

Claims (3)

[Claims] In a method for producing a molded article by a foaming mold comprising a mold and a core each having a steam chamber, foamed resin particles are compression-filled into a cavity of the mold, and the steam is filled. Water vapor is introduced into one of the chambers to heat the mold above the melting point of the foamed resin particles and to melt the foamed resin particles in contact with the mold to form a skin layer on the surface and fill the cavity. When the surface pressure of the foamed resin particles reaches a range of 0.01 to 1.5 kg / cm ² G, the air between the foamed resin particles is discharged, and the foamed resin particles are discharged from the other steam chamber to the space between the foamed resin particles. A method for producing a molded article having a high-density skin layer, comprising introducing steam having a melting point lower than the melting point to heat and fuse the foamed resins to each other. 2. The compression ratio represented by the following equation (I) is 3
The filling of foamed resin particles to be in the range of ~ 70%
The method according to claim 1. C = (1-ρ)₁/ ((Ρ_Two× t_Two+ Ρ_Three× t_Three) / T₁)) × 100 (I) C: Compression rate (%) ρ₁: Density of expanded resin particles before filling (kg / m^Three ) Ρ_Two: Density of skin layer (kg / m^Three) Ρ_Three: Density other than skin layer (kg / m^Three) T₁: Molded body thickness (mm) t_Two: Thickness of skin layer (mm) t_Three: Thickness other than skin layer (mm) 3. The foamed resin particles are at least one selected from the group consisting of polystyrene resin particles, polyethylene resin particles and polypropylene resin particles.
Or the production method according to 2.