JP3142443B2 - Molding method and molded article of thermoplastic resin foam sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed thermoplastic resin sheet, for example, expanded polystyrene, expanded polyvinyl chloride,
The present invention relates to a molding method and a molded article of a thermoplastic resin foam sheet such as foamed polypropylene.

[0002]

2. Description of the Related Art Conventionally, the formation of a foamed sheet of a thermoplastic resin such as expanded polystyrene is performed by thermoplasticization in a heating furnace of a molding machine and a maximum secondary foam thickness, that is, by simple radiation heating in a heating furnace in air. In general, a method is used in which a molded product having a predetermined thickness is obtained by foaming the foam to an obtained foam thickness, transferring the molded product to a molding die, and performing vacuum molding, match molding, or the like.

In conventional molded products, it has been considered that a thicker foam thickness is advantageous in terms of strength as long as the foam thickness is not destroyed, and on the premise that a sufficient foam thickness is obtained by heating in a heating furnace. Studies have been made on molding conditions including heating conditions or physical properties of molded articles.

[0004]

Among molded articles made of thermoplastic resin foam sheets, molding of molded articles such as trays has a great demand for strength, and therefore various improvements have been made. Initially, the strength was controlled by the thickness and weight of the molded product, but when the molded products were piled up, the bulk increased and the problem of transportation cost occurred, so the shape was examined and the thickness of the side wall was reduced. There is a method of increasing the strength by reducing the thickness and increasing the angle, and increasing the thickness of the bottom portion. That is, when the thermoplastic resin foam sheet is heated in a heating furnace of a molding machine to form a molded product between the molding dies, the clearance between the molding dies is increased, and the side wall portion is formed by the secondary foam thickness of the thermoplastic resin foam sheet. A method has been proposed in which the bottom portion is made narrower, the bottom is made thicker, and after the molds are matched, the bottom portion is made thicker by vacuum suction on both sides (Japanese Patent Publication No. 63-65491). However, in this method, a thermoplastic resin foam sheet is formed by foaming to a thickness close to the maximum secondary foam thickness, and in the case of vacuum suction on both sides, bubbles may be broken, the bubbles may be connected, and strength may be reduced. In addition, it is difficult to control the secondary foam thickness of the foamed thermoplastic resin sheet within the required range until it is molded from the heating furnace, and the shape of the molded product will be deformed and the thickness of the bottom will vary. There was something to do.

When a molded article is molded from a thermoplastic resin composite foamed sheet or a thermoplastic resin low-density foamed sheet having a thermoplastic film laminated on at least one surface, a high degree of vacuum is required in a molding die. Therefore, the laminated thermoplastic film peels off, or, in the case of a thermoplastic resin low-density foam sheet,
There has been a problem that the bubbles of the molded article are communicated and the strength is reduced. For this reason, vacuum forming by double-sided vacuum suction, in which the foamed sheet is refoamed in a molding apparatus, is hardly performed for the thermoplastic resin composite foamed sheet or thermoplastic resin low-density foamed sheet laminated with a thermoplastic film. .

On the other hand, many experiments and researches have been conducted on the change of the thermal characteristics of the thermoplastic resin foam sheet with the foaming conditions of the thermoplastic resin foam sheet in the heating furnace and the subsequent molding conditions of the molding apparatus. . That is, 1. The heating characteristics of thermoplastic resin foam sheet are up to 2
The secondary foam thickness is 2.2 to 2.5 times the foam sheet thickness, and although it varies depending on the concentration of the foaming gas remaining in the foam sheet, it is difficult to exceed this value.

[0007] 2. In the case of refoaming by vacuum suction in a molding die, the limit of refoaming without causing cell destruction is a maximum of about 15% increase in the secondary foam thickness, and forced foaming is performed further. In this case, air bubbles are destroyed from the central portion of the sheet cross section, and cavitation is caused. Therefore, it is necessary to mold the foam with a high foam thickness that does not cause cell destruction.

[0008] 3. If the thickness of the foamed foam is regulated by the external pressure of a molding die or the like, the foam tends to be buckled and collapsed. Such facts are known. Against this background,
A molding method has been proposed in which a thermoplastic resin foam sheet in a state before reaching a maximum secondary foam thickness is further foamed between male and female molding dies by vacuum suction to increase the thickness (Japanese Patent Laid-Open No. 4-332623). ), Where 75 to 85% of the maximum secondary foam thickness of the thermoplastic resin foam sheet
It has been shown that when a foamed product to a certain extent is formed by vacuum suction in a molding die, the so-called rib compression strength, which most clearly represents the strength required as a final product, is greatly improved.

However, since the secondary foaming of the thermoplastic resin foam sheet continues even after passing through the heating furnace in the ordinary thermoplastic resin foam sheet, a wide molding range (2 It is necessary to prepare a special foam sheet having a small increase rate of the next foam thickness) or to change the specification of the foam sheet according to a molding die and its clearance.

In view of the above facts, the present invention takes advantage of the above-mentioned thermal properties of a thermoplastic resin foam sheet to maximize the use of the thermoplastic resin foam to obtain a molded product having high strength and low stackability. An object of the present invention is to obtain a sheet forming method and a formed product.

[0011]

Means for Solving the Problems The present inventors have continued molding experiments in order to further pursue the thermal characteristics of the foamed thermoplastic resin sheet. As a result, up to 2
When re-foaming the thermoplastic resin foam sheet foamed to near the next foam thickness by double-sided vacuum suction in the molding die,
It is possible to increase the thickness without causing a decrease in strength up to about 5 to 6% of the maximum secondary foam thickness. If the thickness is further increased, the communication of air bubbles is caused and the strength is reduced. As the clearance of the molding die is made smaller than the thickness of the secondary foam sheet, the bubbles are crushed and the strength is reduced. Therefore, a certain limit is imposed on the clearance of the molding die in relation to the thickness of the secondary foam sheet. It was found that the strength of the foamed sheet which was foamed to a value close to the maximum secondary foaming thickness decreased when the bubbles were crushed.

Based on the findings, the inventors further examined whether there is a more efficient method for forming a foamed thermoplastic resin sheet, and as a result,
Using a foamed thermoplastic resin sheet that has been secondary foamed by heating in a heating furnace to 75 to 90% of the maximum secondary foam thickness, and molding it between molding dies. Cooling the surface of the sheet quickly to stop the operation, first contacting a part of the mold surface with one side of the sheet, and then closing the mold, a molded product with less deformation and good shape is obtained. Obtaining the shape, observing the shape of the bubbles by cutting the molded article after molding, it was found that the strength was increased in the case of a collection of substantially spherical bubbles. Then, by satisfying these conditions, they perceived that a molded article having higher strength can be formed from a foamed sheet or a laminated foamed sheet.

The present invention is based on the above perception,
Basically, a thermoplastic resin foam sheet or a thermoplastic resin composite foam sheet obtained by laminating one or more thermoplastic films on at least one surface of a thermoplastic resin foam sheet is heated in a heating furnace to 75 to 90% of the maximum secondary foam thickness. After heating and secondary foaming, the surface of the secondary foamed sheet is cooled while vacuum-suctioning from one of the male or female molds, and the surface of one of the male or female molds is preceded by the secondary foamed sheet. The method is characterized in that the mold is brought into close contact with the surface of the foam sheet, then the two molds are matched, and both sides are vacuum-sucked.

The present invention further relates to a thermoplastic resin foam sheet or a thermoplastic foam composite foam sheet obtained by laminating at least one layer of a thermoplastic film on at least one surface of a thermoplastic resin foam sheet with heat, and then forming a mold. A molded article obtained by vacuum suction on both sides between the molded articles, wherein the molded article has at least a side wall and a bottom part, and the shape of the air bubbles is almost flat in the side wall in the thickness direction. Also disclosed is a shaped article characterized in that it is substantially spherical in shape at the bottom and mostly at the bottom.

In the present invention, the foamed thermoplastic resin sheet includes polystyrene resin, polyethylene terephthalate resin, polybutylene terephthalate resin,
Materials such as polypropylene resin, polycarbonate resin, and acrylic resin can be used. As polystyrene resins, styrene, methyl styrene, ethyl styrene,
Isopropyl styrene, dimethyl styrene, paramethyl styrene, chlorostyrene, bromostyrene, vinyl toluene, vinyl xylene homopolymer or copolymer,
For example, as the resin, styrene-maleic anhydride copolymer, styrene-acrylic copolymer, impact-resistant polystyrene, styrene-acrylonitrile resin, acrylonitrile-butadiene-styrene resin and other heat-resistant and impact-resistant resins are also used. Can be used. Generally, polystyrene resins are widely used.

The thermoplastic film used for the thermoplastic foam composite foam sheet includes linear low-density polyethylene, high-density polyethylene, low-density polyethylene, propylene homopolymer, ethylene-propylene random copolymer,
Ethylene / propylene block copolymer, ethylene / propylene
Propylene-butene-terpolymer, ethylene-vinyl acetate copolymer, ethylene-unsaturated carboxylic acid ester copolymer (for example, ethylene-methyl methacrylate copolymer), ethylene-unsaturated carboxylic acid metal salt copolymer (for example, , Ethylene-magnesium acrylate (or zinc) copolymer), propylene-vinyl chloride copolymer, propylene-butene copolymer, propylene-maleic anhydride copolymer, propylene-olefin copolymer (propylene-ethylene copolymer, propylene-butene) -1 copolymer) Modified product of polyethylene or polypropylene with unsaturated carboxylic acid (for example, maleic anhydride),
Examples include ethylene-propylene rubber and atactic polypropylene, and films such as polyethylene, ethylene-propylene copolymer, propylene-butene-1 copolymer, and a mixture of two or more thereof.

As the crystalline polypropylene resin, a crystalline propylene homopolymer is preferable, but other than the above, polypropylene such as a crystalline propylene-ethylene copolymer and a crystalline ethylene-propylene-diene terpolymer are mainly used. And a polymer represented by the formula: Further, resins exemplified by the thermoplastic resin foam, such as a polystyrene resin and a polyester resin, can also be used as appropriate.

Further, in order to prolong the retention of the freshness of the contents, it is preferable to laminate a film or a gas barrier film in which an antibacterial agent such as silver ion or wasabi extract has been mixed in advance on the thermoplastic resin foam sheet. These gas barrier films include ethylene vinyl acetate copolymers, polyvinyl alcohol, polyvinylidene chloride,
Polyamide, polyester, polyacrylonitrile, vinylidene chloride-based acrylonitrile copolymer, acrylonitrile-based methyl methacrylate-butadiene copolymer, nylon 6, biaxially oriented nylon, biaxially oriented polyethylene terephthalate, biaxially oriented polypropylene, high-density polyethylene, An ionomer resin (for example, Surlyn®), a metal-deposited film alone, or a laminate of a plurality of these films is used.

It is also possible to laminate an aluminum foil or a thermoplastic resin film laminated with an aluminum foil. In the present invention, the lamination of the thermoplastic resin foam sheet and the thermoplastic resin film may be performed by lamination using an adhesive, lamination using a hot roll, coextrusion, or a molten state extruded from a T-die in the middle of the foam sheet and the film. And a method of laminating by pressure bonding via an adhesive resin film. As the adhesive that can be used, any of a thermoplastic resin-based adhesive, a thermoplastic elastomer-based adhesive, a pressure-sensitive adhesive, a hot-melt adhesive, a rubber-based adhesive, and the like may be used. For example, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer and mixtures thereof, styrene block butadiene block copolymer elastomer, styrene butadiene copolymer elastomer, and the like can be used.

In the case of thermocompression bonding, the film is heated and pressed from the side opposite to the joining surface by a heat roll. In this case, the surface of the roll to be heated and pressed is coated with chrome or Teflon to prevent adhesion or stickiness with the heated film. In the present invention, it is preferable that the joint surface is heated by a heating device together with the heat compression by the hot roll.

As the molding die used in the present invention, a conventionally known molding die used in a molding method in which a male mold and a female mold are combined and vacuum suction is performed on both surfaces can be used. However, while the surface of the secondary foam sheet is cooled by vacuum suction of one of the male or female mold, one surface of the male or female mold is brought into close contact with the surface of the secondary foam sheet in advance.
Thereby, sufficient cooling for stopping the secondary foaming after passing through the heating furnace can be performed in a wide range and uniformly, and a secondary foam of the secondary foam sheet can be obtained with good shape with less deformation. The thickness can be maintained.

Preferably, the clearance between the female mold and the male mold is 90 to 1% of the thickness of the sheet after secondary foaming at the bottom.
10%, and the bottom part has a clearance of 45 to 45%
Use the one with 95%. As a result, in the present invention, the secondary foam thickness in the heating furnace is suppressed to 90% or less of the maximum secondary foam thickness, and rapid cooling allows the secondary foam thickness to be reduced to 2%.
In combination with the fact that the secondary foam thickness is maintained, the bubbles do not break at the bottom portion, the shape of the bubbles can be maintained almost as it is at the time of the secondary foaming, and the buckling of the bubbles at the side wall portion, Collapse hardly occurs, and the bubble shape can be maintained as a spherical shape flattened toward the bottom in thickness. Thereby, a molded product having high strength and low stackability can be easily obtained.

In the molded article according to the present invention, the cell shape C of the molded article, that is, the average value C of the ratio of the cell diameter in the cutting direction to the cell diameter in the cell thickness direction is substantially equal to the center of the side wall in the thickness direction. In the range of 1 ≦ C ≦ 2,
0.9 ≦ C ≦ at almost the center in the thickness direction of the bottom part
A range of 1.1 is a particularly preferred embodiment. Further, in a preferred embodiment of the present invention, at least one of the male mold and the female mold is provided with 0.5 to 2 at the time of molding.
mm, preferably a hole for vacuum suction having a diameter of 0.7 to 1.5 mm is formed in an opening area of 0.15 to 2.5%, and
The mold side can be suitably used by vacuum suction at 250 to 550 mmHg, and a low-density foam sheet can be used without any trouble.

According to experiments performed by the present inventors, the degree of vacuum in the molding die during vacuum suction was 250 mmH.
In the case of less than about g, no particular increase in the effect of deformation, appearance of the molded product, and compressive strength of the molded product is observed. Rather, a thermoplastic foam composite sheet in which at least one thermoplastic film is laminated is used. In the case of molding, there is a problem that the laminated film is peeled off, and when the opening for vacuum suction is relatively large (1.1 mm or more), the hole of the opening for vacuum suction or a trace of a slit is left on the molded product. Further, when the degree of vacuum exceeds 550 mmHg, the vacuum drawing force is insufficient, the cooling is insufficient due to poor contact of the foam sheet with the mold, and the shape of the molded product is not stable. For example, a molded product (molded product) It was found that the bottom of the swelled and became unstable.

Therefore, in the method for molding a foamed thermoplastic resin sheet according to the present invention, the degree of vacuum in the molding die at the time of vacuum suction is preferably from 250 mmHg to 550 mmHg.

[0026]

[Operation] In the present invention, the thermoplastic resin foam sheet is heated in a heating furnace by 75% to 9% of the maximum secondary foam thickness.
Bubble to 0%. As a result, the cell shape at the center of the secondary foam sheet becomes substantially spherical. It is guided into a molding die, close to the secondary foam sheet while vacuum sucking the female mold or male mold, and cooling the surface of the secondary foam sheet to one side of the female mold or male mold. Make contact. Thereafter, by continuing the vacuum suction while moving the secondary foam sheet along the mold, one side of the sheet can be brought into contact with the mold over a wide area while suppressing foaming while cooling one surface of the sheet.

Subsequently, the molds are aligned, and the other surface of the secondary foam sheet is preferably brought into close contact with the mold surface by vacuum suction on both sides to improve the smoothness and at the same time to obtain a shape with less deformation. A molded article is obtained. At the time of molding, since the clearance of the mold is within the predetermined range as described above, the shape of the foam at the bottom can be substantially spherical, and the foam is molded with a high foam thickness as long as the foam does not break. It is possible to do. Further, since the side wall portion is made thinner in a range that does not cause buckling or collapse of bubbles, it is possible to satisfy the requirement of low stackability while maintaining the required rib compressive strength.

[0028]

The present invention will be described below with reference to examples. Example 1 An experiment was conducted using a foamed polystyrene sheet having the following characteristics. Thickness Basis weight Maximum secondary foam thickness (X) Sheet A 2.3 mm 195 g / m ² 5.3 mm Sheet B 1.6 mm 225 g / m ² 3.5 mm A and B sheets are foamed secondarily in a heating furnace. , Introduced into the molding die. 1 before the secondary foam sheet contacts the male mold
Vacuum suction was performed at 50 mmHg, and the female mold was mated about 0.5 second after one surface of the secondary foam sheet had contacted the male mold. Vacuum suction of the female mold was performed slightly before mold matching at 270 mmHg. After matching, the male mold was turned off. After the mold combination, vacuum suction was performed for 0.4 seconds.

The size of the male and female molds is 195 (length) x 12
0 (width) × 25 (height), and the number of the holes for vacuum suction was 120 having a diameter of 0.8 mm and an opening area of 0.18%. For each sheet, a different secondary foam thickness S was obtained by changing the conditions in the heating furnace, and a plurality of types of molding dies having different clearances at the bottom and side portions were used. Vacuum forming was performed. The bottom thickness and the side thickness of each molded product were measured, and the cell shape C of the bottom and side walls, that is, the average value C of the ratio of the cell diameter in the cutting direction to the cell diameter in the cell thickness direction was determined by a method described later. Was. Furthermore, the molded article is left for 5 days,
The rib strength was measured by the repulsive force when the molded product was compressed by 10 mm (400 mm / min) using a load measuring device (manufactured by AIKOH ENGINEERING).

The bubble shape C was determined as follows. The molded product was cut to take enlarged photographs of the bottom part a and the side wall part b (FIG. 1). As shown in FIG. 2 in a partially enlarged manner, the number of bubbles in each of the four layers (distance L) excluding the uppermost and lowermost ones is divided into approximately six equal parts in the thickness direction y. , B, and c, and the total number M was obtained.
Next, the length l was taken in the cutting direction x, the number of bubbles was counted at three places of p, q, and r, and the total N was obtained. And l / L
The value of × M / N was taken as the value of the bubble shape C. Therefore, if C is approximately 1, it is indicated that the bubble is approximately spherical, and 1
As the value deviates from the value, it is shown that the bubble shape is a flat shape. Table 1 shows the results.

[0031]

[Table 1]

As is clear from Table 1, the ratio of the secondary foam thickness S to the maximum secondary foam thickness X is about 70% or less (5) and about 90% or more (6, 9, 11).
Indicates that the shape of the bottom bubble is largely flat and the rib strength is 6
If it is less than 00, sufficient strength cannot be obtained. The ratio of the secondary foam thickness S to the maximum secondary foam thickness X is 75
Even if it is 90%, the ratio of the side clearance to the bottom clearance of the molding die is about 40% or less (1, 7). 600 or less, and sufficient strength cannot be obtained.

Example 2 83 g of sheets A and B
/ M ² using a thermoplastic resin foam composite sheet laminated with an impact-resistant polystyrene film by extrusion.
The same molding as in Example 1 was performed. As a result, no peeling of the laminate film was observed in any case.

[Embodiment 3] The clearance is 4.0 m at the bottom.
Example 1 for sheet A, using a mould, 2.7 mm side mold, and changing the vacuum suction opening of the mold.
Molding was performed under the same conditions. The rib strength of the obtained molded product was measured in the same manner. Table 2 shows the results.

[0035]

[Table 2]

As a result, those having a rib strength of 600 or more were obtained. However, when the diameter was less than 0.5 mm, a lot of clogging occurred due to powder generated from the foamed sheet during molding. Also, when it exceeds 2 mm, traces of the holes for vacuum suction remain on the molded product even if the degree of vacuum is increased. Further, when the opening area of the opening for vacuum suction was less than 0.1%, even if the degree of vacuum was reduced during molding, the contact between the foamed sheet and the inner surface of the molding die was poor, resulting in insufficient cooling and deformation. . Further, the heated secondary foamed sheet moved into the molding die, and the sheet was insufficiently cooled by vacuum suction air before coming into contact with the inner surface of the molding die, resulting in deformation. If it exceeds 2.5%, the opening area becomes more than necessary for lowering the degree of vacuum, which is meaningless.

[Comparative Example 1] The sheet A was secondarily foamed in a heating furnace, and introduced into a molding die, and at the same time, the sheet A was put together.
Vacuum suction was performed at 0 mmHg. The other conditions were the same as in Example 1, and the same items were measured for the molded product. Table 3 shows the results.

[0038]

[Table 3]

As a result, in the case of the manufacturing method of Example 1, the rib strength was 600 or more, but the bubble in the center of the side portion was crushed and became flat. It has dropped to 500 or less. Further, even when the rib strength was 600 or less in Example 1, the rib strength was further reduced.

[Comparative Example 2] Vacuum suction of a female mold was performed for 200 mm.
Hg, 300mmHg, 500mmHg, 600mmH
The molding was performed under the same conditions as in Example 1 except for g. As a result, the degree of vacuum is 500 mmHg to 600 mmHg.
With g, in-mold foaming was insufficient, cooling was insufficient, and many molded articles were deformed. At 200 mmHg, bubble breakage occurred in many molded products, and the rib strength was reduced.

Comparative Example 3 85 μm HIPS on Sheet A
(Impact-resistant polystyrene) Using a material obtained by extruding and laminating a film, molding was performed in the same manner as in Example 1 while changing the degree of vacuum. Mold clearance is 4.0mm at bottom, 2.7mm at side, 0.8mm in diameter of vacuum hole, 1
Using 20 molds (opening area: 0.18%), the sheet was molded such that the film surface of the sheet was outside the container. As a result, peeling of the film occurred when the degree of vacuum was 210 mmHg or less. Also, at 600 mmHg, the mold is poorly protruded,
The deformation of the molded product was observed.

[Consideration] From the above, after heating in a heating furnace to cause secondary foaming to 75 to 90% of the maximum secondary foam thickness, the vacuum foam suction is performed from at least one of the male and female molds. While cooling the surface of the secondary foam sheet, one surface of the male or female mold is first brought into close contact with the surface of the secondary foam sheet, and then both molds are matched and both sides are vacuum sucked. This shows that a molded product having higher rib strength can be obtained as compared with the conventional rectangular method in which the molds are simultaneously adjusted and vacuum suction is performed (compared with Comparative Example 1).

The clearance between the male and female molds is about 90% to 110% of the thickness of the secondary foam sheet at the bottom, and 45 to 9% of the clearance at the bottom at the side.
By setting it to 5%, the shape of the air bubbles becomes mostly spherical in the thickness direction in the side wall portion, and the majority becomes substantially spherical in the bottom portion. Is also obtained.

Further, according to this method, the degree of vacuum is 20
Since the film does not peel off up to about 0 mmHg, good molding can be performed even on a thermoplastic composite foam sheet in which at least one layer of a thermoplastic film is laminated on at least one surface of a thermoplastic resin foam sheet. It can be seen that it is. Further, when the degree of vacuum is about 600 mmHg, the mold is poorly formed and the molded product is deformed. Therefore, in the present invention, the degree of vacuum is about 250 mmHg to 5 mm.
It turns out that the range of 50 mmHg is effective.

[0045]

As described above, according to the present invention, a molded product having high rib strength and low stackability can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a molded product obtained by a method of the present invention, illustrating a bubble shape.

FIG. 2 is a partially enlarged view of FIG. 1;

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Claims (4)

(57) [Claims] 1. A foamed thermoplastic resin sheet or a thermoplastic composite foamed sheet obtained by laminating at least one layer of a thermoplastic film on at least one surface of a foamed thermoplastic resin sheet is heated in a heating furnace to a maximum secondary foaming thickness of 75 to 100%. After secondary foaming to 90%, the surface of the secondary foam sheet is cooled while vacuum-suctioning from one of the male and female molds, and one surface of the male or female mold is preceded by the secondary foam sheet. A method for forming a foamed thermoplastic resin sheet, comprising: bringing the two molds into close contact with each other and then performing vacuum suction on both sides thereof. 2. The method for molding a foamed thermoplastic resin sheet according to claim 1, wherein the clearance between the male and female molds is 90 to 110% of the thickness of the secondary foamed sheet at the bottom portion and at the side portions. Is the bottom clearance of 45-9
A method for forming a thermoplastic resin foam sheet, the content being 5%. 3. At least one piece of a thermoplastic resin foam sheet
Thermoplastic composite with one or more layers of thermoplastic film laminated on the surface
A molded article obtained by plasticizing the foamed sheet with heat and then vacuum-suctioning between molding dies, the molded article having at least a side wall and a bottom portion, and the shape of a cell. However, most of the side walls have a spherical shape flattened in the thickness direction, and most of the bottom portions have a substantially spherical shape.
Yes, the cell shape C of the molded product, ie, the thickness direction of the cells
The average value C of the ratio of the bubble diameter in the cutting direction to the bubble diameter of
At substantially the center in the thickness direction of the side wall, 1 ≦ C ≦ 2
It is a range, and almost at the center in the thickness direction of the bottom part,
Molding characterized by the range of 0.9 ≦ C ≦ 1.1
Goods. 4. A degree of vacuum of 250 mmHg to 550 mmHg.
4. The method according to claim 3, wherein the vacuum suction is performed on both sides.
Molded products.