JPH11138575A - Manufacture of molding with high density skin layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a qualitatively uniform and hard skin layer which is almost free from shrinkage by filling a mold with foamable resin particles under compression so that the particles show a specific compressibility, then heating the particles to a temperature higher than a melt point to form the skin layer on the surface of a molding which comes into contact with the mold, and removing an air from between the particles when the area pressure of the particles is within a specific range to thermally fuse the textures of the resin mutually. SOLUTION: Foaming particles contained in a compression charging tank 4 are charged into the cavity 3 of a mold which is preheated and hermetically sealed within the range of 3-70% of the compressibility C shown by formula C=(1-ρ1/((ρ2×2t2+ρ3×t3)/(t1))×100 (wherein, C is compressibility %; ρ1 is the density kg/m<3> of foamable resin particles before charging; ρ2 is the density kg/m<3> of a skin layer part; ρ3 is the density kg/m<3> of a part other than the skin layer part; t1 is the wall thickness mm of a molding; t2 is the thickness mm of the skin layer part; and t3 is the thickness mm of part other than the skin layer). The halves of the mold are heated at a temperature level above the melts point of the foamable particles. When the area pressure of the foamable particles in the cavity 3 is down to 0.01-1.5 kg/cm<2> G, the foamable particles are mutually fused together after exhausting the air. Thus it is possible to form a qualitatively uniform and high density hard skin layer over the entire face of a molding and consequently, obtain the molding almost free from shrinkage.

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 molded article having a high-density skin layer, and more particularly, to a method for producing a molded article having a uniform, high-density and hard skin layer over substantially the entire surface of the molded article. The present invention relates to a method for manufacturing a molded article.

[0002]

2. Description of the Related Art Molded articles produced by filling foamed resin particles (hereinafter referred to as "foamed particles") in a foaming mold composed of a mold cavity and a core mold each having a steam chamber and heat-sealing the molded articles are independent. It has a bubble structure and is rich in heat insulation and cushioning,
Moreover, it has the feature of being light, and is used for cushioning materials, heat insulating materials, heat insulating containers, and functional members. However,
Since there is a slight gap between particles on the surface of the compact,
When used repeatedly in applications such as containers, there is a problem that dirt enters the gaps between the particles and is easily broken, and the surface of the molded product is soft and easily scratched. For this reason, in the conventional manufacturing method, a method of coating the inside and outside of the container and a method of integrally molding with the resin sheet have to be adopted, and the molded body obtained by increasing the number of manufacturing steps and extending the molding cycle is required. There is a problem that the cost is high.

[0003] In order to solve these problems, a method of forming a skin layer on the surface of a molded article by melting during molding is disclosed in, for example, JP-A-48-28060 and JP-A-52-47866. It has been proposed in gazettes and the like. In these molding methods, a mold for foam molding is used which comprises a mold cavity and a core mold each having a steam chamber, and has a large number of steam holes formed on a wall surface facing a cavity of each steam chamber. After filling the foamed particles in the mold, introducing steam having a melting point lower than the melting point of the foamed particles into the steam chamber and performing heat fusion, further introducing steam having a melting temperature equal to or higher than the melting point of the foamed particles into the steam chamber, The surface is melt-hardened to form a skin layer on the surface of the molded body.

However, in the case of this method, the vicinity of the steam hole is excessively melted, and as a result, the thickness of the skin layer in the vicinity of the steam hole and other portions is different, and a non-uniform skin layer is formed as a whole. You. Further, since the fusion of the foamed particles is performed first, the individual foamed particles are combined to inhibit further free foaming, so that the space cannot be sufficiently filled. Further, the molded article has a problem that voids are partially generated as the thickness of the skin layer increases, and a molded article having a uniform skin layer with few voids has not been 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 foamed 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 publication is a method in which a skin layer is formed by excessive cracking filling, and therefore cannot be applied to a molded article having a complicated shape, and the filling rate is low in a box-shaped rising portion or the like. As a result, the molded article shrinks.

[0006] In general, foamed particles compressed and filled in a mold are:
Although it has a surface pressure (repulsive force) higher than the atmospheric pressure, the volume of the foamed particles decreases with the formation of the skin layer, and the surface pressure decreases with the formation of the skin layer. When the surface pressure is less than the specified value, when heated and fused with water vapor, the foamed particles are excessively foamed and become less than the density before filling, the foaming power is reduced, and defective fusion or shrinkage of the molded body occurs. Good molded products cannot be obtained. On the other hand, when the surface pressure exceeds a specific value, the steam introduced for melting and heating the foamed particles does not penetrate into the interior of the foamed particles, resulting in poor fusion due to insufficient heating, and a good molded body cannot be obtained. .

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a uniform, high-density, hard skin layer on almost the entire surface of a molded body even if it has a complicated shape, and has a shrinkage of shrinkage. An object of the present invention is to provide a method for producing a molded article having a high-density skin layer, which can obtain a molded article with a small appearance and good appearance.

[0008]

That is, the gist of the present invention is to provide a method for producing a molded article in which foamed resin particles are filled into a mold for foaming molding comprising a mold cavity and a core mold each having a steam chamber and heated and fused. In this case, foamed resin particles are compressed and filled in a mold, steam is introduced into both of the steam chambers to heat the mold to a temperature higher than the melting point of the foamed resin particles, and the foamed resin in contact with the mold. A skin layer is formed on the surface of the molded body by melting the particles, and the surface pressure of the foamed resin particles filled in the mold is detected. When the surface pressure is in the range of 0.01 to 1.5 kg / cm ² G Discharging air between the foamed resin particles remaining in the mold, introducing steam between the foamed resin particles having a melting point lower than the melting point of the foamed resin, and heating and fusing the foamed resins to each other. The present invention relates to a method for producing a molded article having a skin layer.

[0009]

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 sectional view schematically showing 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, a mold including a mold having a steam chamber and a mold having a core is used.

The mold shown in FIG. 1 comprises a cavity mold (1) having a concave section and a core mold (2) having a convex section, and has a cavity (3) having a box-shaped section. The mold (1) and the core (2) are fitted together with a gap (20) through which the foamed particles cannot pass but a gas can pass. Further, 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 (1) has a first steam chamber (1) inside.
a) and a second steam chamber (1b). The second steam chamber (1b) is located on the cavity (3) side, and the first steam chamber (1a) is located outside the second steam chamber (1b). Each steam chamber has a completely independent structure without communication with each other. The first steam chamber (1a) communicates with a steam pipe (8), a cooling water pipe (6), a vacuum pipe (7), and a drain pipe (19) each having an on-off valve.

The first steam chamber (1a) is provided with a gap (2
Small chamber (22) communicating with cavity (3) via 0)
With the steam hole (1c). Second steam chamber (1
b) has a steam line (1
0), the cooling water pipe (9) and the drain pipe (18) communicate with each other.

On the other hand, the core type (2) has a first steam chamber (2a) and a second steam chamber (2b) inside. The second steam chamber (2b) is located on the cavity (3) side, and the first steam chamber (2a) is located outside the second steam chamber (2b). Each steam chamber has a completely independent structure without communication with each other. The first steam chamber (2a) communicates with a steam pipe (13), a cooling water pipe (11), a vacuum pipe (12), and a drain pipe (17) each having an on-off valve. The first steam chamber (2a) is provided with a gap (2
Small chamber (21) communicating with cavity (3) via 0)
And a vapor hole (2c). Second steam chamber (2
b) has a steam line (1
5), the cooling water pipe (14) and the drain pipe (16) communicate with each other.

In this embodiment, first, the steam line (1)
0), (15) valve and drain line (16), (18)
Is opened, high-temperature steam is introduced into the second steam chambers (1b) and (2b) of the mold mold (1) and the core mold (2), respectively, and the mold is sealed while preheating. Next, the expanded particles stored in the compression filling tank (4) are filled with a filling nozzle (5).
To compress and fill the cavity (3). At this time, the compressed air flowing into the cavity (3) together with the foamed particles from the filling nozzle (5) passes through the small chambers (21) and (22) and the steam holes (1c) and (2c) from the gap (20). After passing through the first steam chambers (1a) and (2a) of the mold, they are discharged from the drain valves (19) and (17) in the open state. The amount of compression of the expanded particles is determined from the compression ratio.

Next, when the mold temperatures of the second steam chambers (1b) and (2b) of both molds reach a certain temperature or higher, the valves of the drain pipes (16) and (18) are closed, and both molds are further closed. The molds of the second steam chambers (1b) and (2b) of the mold are heated to a temperature equal to or higher than the melting point of the foamed particles in the cavity (3).

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 a specific value, the vacuum channels (7) and (12) Open the valve, drain line (17),
(19) After closing the valve and evacuating the steam chambers (1a) and (2a) and the cavity (3), the vacuum lines (7) and (12) are closed and the expanded particles in the cavity (3) are closed. Steam having a temperature necessary for fusion is introduced from the steam line (8) and / or (13) and heated. The steam passes through the first steam chamber (1a) and / or (2a) from the steam line (8) and / or (13), and passes through the steam holes (1c) and / or (2).
After passing through the small chambers (21) and / or (22) via c), it flows into the cavity (3) through the gap (20) and heats the foamed particles.

Next, the steam lines (8), (10),
Close the valves of (13) and (15) and set the drain line (1
6) Open the valves of (17), (18) and (19),
The valves in the cooling water lines (9) and (14) are also opened. After cooling the dies by introducing cooling water into the second steam chambers (1b) and (2b) of both dies, the compacts are taken out.

The mold shown in FIG. 2 is a cross-sectional view schematically showing another example of the foam molding mold used in the present embodiment. The mold shown in FIG. 2 has only the steam chamber (1b) inside the mold (1). Further, it has a nozzle (23) for penetrating the steam chamber (1b) and for introducing steam into the cavity (3).

When the mold shown in FIG. 2 is used, the steam chamber (1b)
While heating (2b), the foamed particles are compression-filled into the cavity (3), and the steam chambers (1b) and (2b)
While heating to a predetermined surface pressure of the foamed particles filled in the cavity (3) while heating the gas to a temperature equal to or higher than the melting point of the foamed particles in the cavity (3), the first steam chamber (2a) is passed through the vacuum line (12). The steps until the inside of the cavity (3) is evacuated are performed according to the above-described molding using the mold shown in FIG.
Subsequently, after closing the vacuum line (12) with steam at a temperature necessary for fusing the foamed particles in the cavity (3),
The foamed particles are introduced into the cavity (3) through the steam line (8) via the nozzle (23) and heated.

Next, the valve of the steam line (8) is closed, the valves of the drain lines (16), (17) and (18) are opened, and the valves of the cooling water lines (9) and (11) are also opened. I do. After cooling the mold by introducing cooling water into the steam chamber (1b) and the second steam chamber (2b), the compact is taken out.

The expanded particles used in the present invention include expanded polystyrene particles, expanded polyethylene particles, expanded polypropylene particles, and the like. As polystyrene-based expanded particles, as a base resin, a styrene monomer is polymerized in a composition containing 50% by weight or more,
Mixed, for example, styrene homopolymer,
It is a styrene-acrylonitrile copolymer, a styrene-acrylonitrile-butadiene copolymer or a modified product thereof with a rubber or the like.

The polyethylene-based foamed particles are polymerized or mixed with a composition containing 50% by weight or more of an ethylene monomer as a base resin. For example, high-pressure low-density polyethylene, medium-high density Polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer and modified products thereof. The polypropylene-based foamed particles are polymerized or mixed with a composition containing 50% by weight or more of a propylene monomer as a base resin. Examples thereof include a propylene homopolymer, an ethylene-propylene copolymer, and butene. -Propylene copolymers and modified products thereof.

These foamed particles are compressed in a compression filling tank (4) by compressed air, and then uniformly compressed in a cavity (3) of a mold. Since the foamed particles filled in the mold cavity (3) are heated to form a skin layer, a part of the foamed particles in contact with the mold cavity (3) are thermally contracted, and the volume is reduced to 1 /. Decrease by 30 to 1/50. In order to fill the space formed by the heat shrinkage, the foam particles filled in the cavity (3) expand. However, when the filling rate is low and the repulsion is small, the space cannot be sufficiently filled. As a result, the obtained molded body shrinks, and a good appearance cannot be secured.

The feature of the foamed particle heating in the present invention is that the surface pressure (repulsive force) of the foamed particles filled in the cavity (3) is controlled as a heating condition for heating the skin layer. That is, although the foamed particles filled in the cavity (3) have a surface pressure higher than the atmospheric pressure, the volume of the foamed particles decreases with the formation of the skin layer.
The surface pressure, which was higher than the atmospheric pressure, decreases with the formation of the skin layer. By controlling the surface pressure in an appropriate range, a molded article having a good skin layer can be obtained.

In the present invention, the above surface pressure is 0.0
The range is 1 to 1.5 kg / cm ² G. If the surface pressure is less than 0.01 kg / cm ² G, when the foamed particles are heated and fused with steam, the foamed particles are excessively foamed.
Insufficient fusion, shrinkage of the molded body, and peeling phenomena between the skin layer and the outside of the skin layer occur, and a good molded body cannot be obtained. On the other hand, when the surface pressure exceeds 1.5 kg / cm ² G, the steam introduced for fusing the foamed particles does not penetrate into the inside of the foamed particles. Good molded products cannot be obtained.

In a preferred embodiment of the present invention, the thickness of the skin layer, the density of the skin layer, and the thickness of the molded body other than the skin layer are determined in order to ensure the strength and quality of the molded body at the time of filling the expanded particles. Is set in advance, and the compression ratio C of the expanded particles obtained by the following equation (I) is used. Incidentally, the density of the solid state of the expanded polystyrene particles is 950 to 1000 kg / m ³ , and the density of the expanded polypropylene particles is 850 to 900 kg / m ³ .
m is ^3.

C = (1−ρ 1 / ((ρ 2 × 2t 2 + ρ 3 × t 3) / t 1)) × 100 (I) C; compression ratio (%) ρ 1; density of foamed resin particles before filling (kg / m ³ ) ρ2: Density of skin layer portion (kg / m ³ ) ρ3: Density other than skin layer portion (kg / m ³ ) t1; thickness of molded body (mm) t2; thickness of skin layer portion (mm) t3; skin Thickness other than layer (mm)

In the present invention, the compression ratio of the expanded particles is from 3 to
It is preferably set to 70%. If the compression ratio is less than 3%, the filling amount of the expanded particles is insufficient, a skin layer is hardly formed, and the molded product shrinks. On the other hand, if the compression ratio exceeds 70%, the skin layer can be made thicker, but the heating and melting time will be longer, and the amount of compressed air used for compression filling will increase, thus increasing the production cost.

In the present invention, in order to obtain a molded body having better fusion of the internal particles after the formation of the skin layer, after the air between the foamed particles remaining in the mold is discharged, it is usually lower than the melting point, preferably. In this method, steam having a temperature from a temperature lower than the melting point to a temperature higher than the melting point of −20 ° C. is directly introduced between the foamed particles, and the foamed particles are heated and fused. Water vapor also acts as a heating medium for heating the molding die. That is, according to the steam heating, a large amount of heat can be used to efficiently obtain a uniform temperature in a short time.

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 thereof. In the embodiment, the apparatus shown in FIG.
m, a height of 250 mm, and a wall thickness of 30 mm were used as a box-shaped mold. 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 (1−expanded particle density / molded product density) × 100%. <Fusion Degree> The degree of fusion was evaluated by the ratio of the area of the molded body which was fractured and cracked other than at the interface of the foamed particles to the total fracture area. <Shrinkage> Shrinkage is measured when the size of the molded product is 5/100
The case of the above decrease was defined as “present”, and the case of less than 5/100 was defined as “absent”. <Appearance> The appearance is “good” when the skin layer portion of the molded product is smooth and there is no peeling from the portion other than the skin layer portion, and when the skin layer portion is not smooth or when there is peeling from the portion other than the skin layer portion. Is "poor".

Example 1 As shown in Table 1, the thickness of the skin layer was 0.3 mm, the density of the skin layer was 850 kg / m ³ , the density other than the skin layer was 50 kg / m ³ , and the overall thickness of the molded body. Has a compression ratio of about 50 from the above formula (I) in order to produce a compact having a thickness of 30 mm.
% Was calculated. The foamed polypropylene particles having a density of 33 kg / m ³ are filled into the compression filling tank (4) shown in FIG. 1, and then the valves of the steam lines (10) and (15) and the drain lines (16) and (18) ) Was opened, and steam was introduced at 175 ° C. into the second steam chambers (1b) and (2b) of both molds, and the molds were sealed while preheating.

A compression filling tank (4) is provided in the cavity (3).
The foamed particles were compression-filled with a filling nozzle (5).
The mold temperature of the second steam chambers (1b) and (2b) of both molds is 1
When the temperature reaches 00 ° C or more, the drain pipes (16), (1)
8) Close the valve and set the second steam chambers (1b) and (2
b) was heated. The second steam chambers (1b) and (2
The mold temperature of b) rapidly rose to 170 ° C. and was stabilized.

At this time, the surface pressure of the foamed particles filled in the cavity (3) was 1.6 kg / cm ² G. The surface pressure decreased as shown in FIG. When the surface pressure reaches 0.5 kg / cm ² G, the vacuum lines (7) and (12) are opened and the drain line ((17),
(19) The valves are closed and the first steam chambers (1a) and (2
After evacuation of a) and the cavity (3), the valves of the vacuum lines (7) and (12) are closed, and steam having a melting point lower than the melting point of the foamed particles is introduced from the steam lines (8) and (13) and heated. did. The expanded particles pass through the first steam chambers (1a) and (2a) from the steam lines (8) and (13), and pass through the steam holes (1c).
After passing through (2c) and (2c), they were heated by the steam flowing through the small chambers (21) and (22) and flowing into the cavity (3) through the gap (20). The steam temperature was 150 ° C. and the retention time was 15 seconds.

Next, the valves of the steam lines (8) and (13) were closed, and the valves of the drain lines (16), (17), (18) and (19) were also opened. The second steam chamber of both molds (1
After cooling water was introduced into b) and (2b) and the mold was cooled to 40 ° C., the molded body was taken out from the mold. The removed molded article had a uniform, high-density, and hard skin layer over substantially the entire surface. The density and thickness of the skin layer and the fusion, shrinkage, appearance and the like of the molded product were substantially the same in the bottom portion of the box-shaped molded product and the other side rising portions. Table 1 shows the results.

Example 2 The conditions shown in Table 1 were adopted, and 48 k
The molding was performed under the same conditions as in Example 1 except that foamed polypropylene particles of g / m ³ were compression-filled, and when the surface pressure reached 0.4 kg / cm ² G, evacuation was performed. Table 1 shows the results.

Comparative Example 1 Molding was performed under the same conditions as in Example 1 except that when the surface pressure of the foamed particles was 0 kg / cm ² G, vacuum evacuation was performed. Table 1 shows the results.

Comparative Example 2 Molding was performed under the same conditions as in Example 1 except that when the surface pressure of the expanded particles was 1.6 kg / cm ² G, the evacuation was performed.
Table 1 shows the results.

COMPARATIVE EXAMPLE 3 The mold was changed to cracking filling with an opening of 30 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 rising portion on the side was 10.7%. The conditions were adopted. Otherwise, molding was performed under the same conditions as in Example 1. Table 1 shows the results.

[0040]

[Table 1]

[0041]

According to the manufacturing method of the present invention described above, a good molded product having a uniform, high-density and hard skin layer on almost the entire surface of the molded product 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 an explanatory sectional view showing an example of a mold for producing a molded article according to the present invention.

FIG. 2 is an explanatory sectional view showing another example of a mold for producing a molded article according to the present invention.

[Explanation of symbols]

 1. . . Mold type, 2. . . Core type, 1a, 2a. . . First steam chamber, 1b, 2b. . . Second steam chamber, 1c, 2c. . . Steam holes, 3. . . Cavity, 4. . . Compression filling tank, 5. . . Filling nozzles, 6, 9, 11, 14,. . . Cooling water line, 7,12. . . Vacuum line, 8, 10, 13, 15. . . Steam line, 16, 17, 18, 19; . . Drain line, 20. . . Gap, 21, 22,. . . Komuro, 23. . . Steam nozzle,

Claims (3)

[Claims] 1. A method for producing a molded article in which foamed resin particles are filled and heated and fused in a foaming mold having a mold cavity and a core mold each having a steam chamber. The particles are compressed and filled, steam is introduced into both of the above-mentioned steam chambers to heat the mold to a temperature higher than the melting point of the foamed resin particles, and the foamed resin particles in contact with the mold are melted to form a surface of the molded body. When a skin layer is formed and the surface pressure of the foamed resin particles filled in the mold is in the range of 0.01 to 1.5 kg / cm ² G, air between the foamed resin particles remaining in the mold is discharged. A method for producing a molded article having a high-density skin layer, characterized in that steam having a melting point lower than that of the foamed resin is introduced between the foamed resin particles and the foamed resins are heated and fused to each other. 2. The method of manufacturing a molded article according to claim 1, wherein the compression ratio C represented by the following formula (I) is 3-7.
A method for producing a molded article having a high-density skin layer, characterized in that foaming particles are filled so as to be in a range of 0%. C = (1−ρ1 / ((ρ2 × 2t2 + ρ3 × t3) / t1)) × 100 (I) C: Compressibility (%) ρ1; Density of foamed resin particles before filling (kg / m ³ ) ρ2; Density of layer part (kg / m ³ ) ρ3; Density other than skin layer part (kg / m ³ ) t1; Thickness of molded body (mm) t2; Thickness of skin layer part (mm) t3; Thickness (mm) 3. The method for producing a molded article according to claim 1, wherein the expanded resin particles are polystyrene resin particles,
A method for producing a molded article having a high-density skin layer, wherein the molded article is at least one selected from the group consisting of polyethylene resin particles and polypropylene resin particles.