JPH09262899A - Molding of blow molded body made of synthetic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the draw down of sheets at heating by a method wherein an air permeable heat-resistant supporting member is spanned between both the sheets parallel to each other so as to carry out the subsequent forming operation under the condition that the above-mentioned spanned state is retained. SOLUTION: When thermoplastic synthetic resin sheets 1 and 2 are pinched by clampers 4a and 4b and supported parallel and horizontally, one layer of air permeable heat-resistant supporting member 6 parallel to both the sheets 1 and 2 is simultaneously spanned. The spanned position of the air permeable heat-resistant supporting member 6 is normally between an upside sheet 1 and a spacer 3. Next, both the sheets 1 and 2 are softened by heating from above and below with heaters 7a and 7b. At this time, though both the sheets 1 and 2 tend to sag with the rise of temperature, the drawdown of the upside sheet 1 is suppressed, since the upside sheet 1 is supported by the air permeable heat-resistant supporting member 6. Further, the sagging of the downside sheet 2 is suppressed together with that of the upside sheet 1 by balancing the pressure in a closed space 5 with the atmospheric pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a hollow molded body made of synthetic resin, and more particularly to a molding method suitable for molding a large-sized, wide-area, flat-plate-shaped hollow molded body.

[0002]

2. Description of the Related Art Conventionally, as a typical molding method for a synthetic resin hollow molded article, two thermoplastic synthetic resin sheets in a heated state are sandwiched between a pair of molds, and compressed air is applied between the two sheets. There is a so-called double sheet forming method of blowing.

In this molding method, as shown in FIG. 5 (a), two thermoplastic synthetic resin sheets (2
1) (22) is clamped from the top and bottom by spacers (23) from above and below by clampers (24a) and (24b) to form a closed space (25), and then both sheets (21) and (22) Is heated by the heaters (27a) and (27b) from above and below to be softened, and compressed air is appropriately blown into the closed space (25) from the air nozzle (28) provided in a part of the spacer (23) to both sheets. (21) (22) is pretensioned in the direction of mutual separation. Then, as shown in FIG. 5B, the two sheets (21) (22) in the heat-softened state are sandwiched between a pair of upper and lower dies inside the peripheral clamp position, and the two dies (29). The (30) is brought close to a predetermined closed position, and is sandwiched between the sheet sandwiching surfaces (29a) (30a) of the peripheral edge thereof, and the sheets (21) (22) are joined and integrated at the peripheral edge portions. Further, as shown in FIG. 5 (c), the compressed air introduction nozzle (31) provided in the upper mold (29) is operated to advance, and this is inserted into the upper sheet (21) and penetrated. Then, after inserting into the closed space (25) between the seats (21) and (22), compressed air having a predetermined pressure is introduced into the closed space (25) through the nozzle (31), and thus the seats (21). The nozzle (22) for compressed air is brought into close contact with the inner surfaces (29b), (30b) of the cavities of both molds (29), (30), and cooled while maintaining the internal pressure between both sheets (21) (22). Retract (31) to move both dies (29) (3
0) is opened and the hollow molded body is taken out to complete the molding operation.

[0004]

In the conventional molding method described above, as shown by the broken line in FIG. 5 (a), the two thermoplastic synthetic resin sheets (21) (22) are the spacers (23).
When heated from above and below with the closed space (25) being sandwiched between the sheets (21) and (22), the sheets (21) and (22) are usually softened to a drooping state. At this time, when the target shape of the hollow molded article is thin and has a small area, both sheets (21) and (22) to be applied may be relatively thin and have a small area, and therefore the weight is small, Since the degree of drooping is small, the mutual distance between the two sheets is kept almost equal to the width of the spacer (23) and the sheets do not come into contact with each other, so that the forming operation can be performed well. However, when the target hollow molded product is a large-sized, large-area hollow molded product, both sheets (21)
If (22) is inevitably required to have a large area, and a relatively large expansion ratio is required, then an even thicker one is required, so the overall weight increases and the degree of drooping Also increases. As a result, there are problems that the lower sheet (22) contacts the heater (27b), and the upper sheet (21) contacts the lower sheet (22) to cause a fusion phenomenon. For such a problem, it was necessary to adjust the positions of the heaters (27a) and (27b) each time. Furthermore, the tip of the compressed air introduction nozzle (31) shown in FIG. 5 (b) cannot penetrate the upper sheet (21) well and penetrate into the closed space (25) between both sheets (21) (22). Even if problems such as inability to introduce compressed air occur, or even if compressed air can be introduced, both sheets (21) and (22) will extend excessively, causing wrinkles on the surface of the molded product as shown in Fig. 5 (c). There is a problem that (e) occurs. To solve such a problem, conventionally, the temperature of the heaters (27a) and (27b) is set low, or the heating time is set to be short, or the distance between the seats and the heaters is set to a large value. ) The temperature is adjusted to a low level so that the degree of droop of (22) becomes small, but on the other hand, as shown in FIG.
Reproducibility of the inner surface of the cavity of (30) is low, so-called a finished state (f), or both sheets (21) (22)
Since there arises a problem that the mutual bonding strength becomes insufficient at the peripheral portions of the, the adjustment by temperature is naturally limited.
That is, the conventional method for forming a hollow molded body made of synthetic resin by the double sheet molding method has a drawback that it is not suitable when the target hollow molded body has a large shape and a large area.

The present invention solves the above-mentioned conventional drawbacks, suppresses drooping of the thermoplastic synthetic resin sheet during heating, has a high reproducibility of the molded shape, and has a high strength of the joint portion. It is an object of the present invention to provide a method for forming a hollow molded body made of synthetic resin, capable of obtaining a flat molded hollow molded body having a large area.

[0006]

According to the present invention, for the above object, two thermoplastic synthetic resin sheets are clamped at their peripheral edges via spacers so as to form a closed space therebetween, After heating and softening the sheet, it is sandwiched between a pair of upper and lower molds inside the clamp position on the peripheral edge, and in the method for molding a synthetic resin hollow molded article in which compressed air is introduced between the two sheets, between the two sheets. A gist of a method for molding a hollow molded body made of synthetic resin is characterized in that a breathable heat-resistant support member is stretched in parallel with this and a subsequent molding operation is performed while maintaining the stretched state.

The present invention will be described below with reference to the drawings.

First, as shown in FIG. 1 (a), two thermoplastic synthetic resin sheets (1) used as molding materials.
(2) is clamped by the clampers (4a) and (4b) at their peripheral portions via the spacers (3) to form a closed space (5) between the two sheets (1) and (2). , Parallel to both sheets over the entire area between both sheets when supporting them in parallel and horizontally at a predetermined interval 1
The breathable heat-resistant support member (6) of the layer is stretched at the same time. The stretching position of the breathable heat resistant support member (6) is usually between the upper sheet (1) and the spacer (3). Then, attach both sheets (1) and (2) to heaters (7a) and (7b).
Heat from above and below to soften. At this time, both the sheets (1) and (2) try to hang down as the temperature rises, but the upper sheet (1) is supported by the breathable heat-resistant support member (6) to suppress the hanging down, and the lower sheet. (2) suppresses drooping together with the upper sheet (1) by balancing the pressure in the closed space (5) with the atmospheric pressure. In this case, compressed air can be blown into the closed space (5) from the air nozzle (8) provided in a part of the spacer (3) to pre-stretch the sheets (1) and (2) in the mutually separated direction. .

When both sheets (1) and (2) reach a predetermined softening temperature, as shown in FIG. 1 (b), both sheets (1)
(2) together with the breathable heat-resistant support member (6), a pair of upper and lower molding dies (9) and (10) are brought close to a predetermined closed position inside the peripheral edge clamping position to sandwich the peripheral edge sheet. The attachment surfaces (9a) and (10a) are sandwiched and joined together.

Further, the nozzle (11) for introducing compressed air provided in the upper die (9) is advanced to cause it to penetrate the upper sheet (1) and penetrate therethrough, thereby After being inserted in 5), compressed air having a predetermined pressure is introduced into the closed space (5) through the compressed air introducing nozzle (11) as shown in FIG. Is closely attached to the inner surfaces (9b) and (10b) of the cavity. Next, after cooling while maintaining the internal pressure between both sheets (1) and (2), a nozzle (11) for introducing compressed air
And the molds (9) and (10) are opened to take out the hollow molded body to complete the molding operation.

The breathable heat-resistant support member (6) used in the present invention is in the form of a net or a string, and has a shape that presents a flat surface when it is stretched and expanded with its periphery, and is partially slackened. Something that is not desirable. Further, the heating temperature at the time of molding the thermoplastic synthetic resin sheet, that is, 100 to 22
At a temperature of about 0 ° C., any sheet may be used as long as it can support the sheet when it softens by heating and hangs down, and does not soften or deform itself. Furthermore, in the case of a mesh, the size of the mesh, and in the case of a string, the interval between parallel or crossed strings is preferably large enough to support the thermoplastic synthetic resin sheet in the heat-softened state. , Its size is the shape and size of the intended hollow molded body, the type of thermoplastic synthetic resin sheet used,
It is determined by molding conditions such as thickness and molding temperature. Furthermore, it is desirable that the thickness and the number of the nets and the strings be such that the nets and the strings are embedded in the joints of the hollow molded body and the joint strength of the joints is not deteriorated. As the material, for example, a natural organic material such as cotton thread, silk thread, or hemp thread, a synthetic organic material such as thermosetting resin or heat-resistant rubber, or an inorganic material having a relatively low specific gravity such as glass fiber is applied. To be done.

By the way, when the breathable heat-resistant support member (6) is stretched, as shown in FIG.
The space between the upper sheet (1) and the spacer (3) is used, but in the case of this mode, there is an advantage that the hanging of the upper sheet (1) can be suppressed almost completely. However, in the general double sheet molding method, the molding material is placed in the order of the lower clamper (4b), the lower sheet (2), the spacer (3), the upper sheet (1), and the upper clamper (4a). In order to stretch the breathable heat-resistant support member (6) at the same time, the breathable heat-resistant support member (6) is placed on the lower sheet (2) and then clamped in the same manner. If the hanging of the upper sheet is allowed up to the thickness of the spacer, the breathable heat-resistant support member (6) is attached to the lower sheet (2) as shown in FIG.
It may be arranged such that it is stretched between the spacer and the spacer (3). Further, as another aspect, as shown in FIG. 2C, the breathable heat-resistant support member (6) is fitted to the spacer (3) at the peripheral portion thereof, for example, the pressing member (3).
It can also be sandwiched and stretched by p). In this case, in order to prevent the permeable heat-resistant support member (6) from being excessively loosened or damaged, in any of the above modes, the permeable heat-resistant support member (6) located inside the spacer (3). The tensioned state of the two sheets (1) and (2) is maintained so that the two sheets (1) and (2) hanging in the subsequent molding process are supported in a flat state except when supporting the two sheets (1) and (2). It is desirable to adjust the positions of the molding dies (9) and (10) so that the positions coincide with the stretched surface of the breathable heat resistant support member (6).

As shown in FIG. 3, the obtained hollow molded article (F) is trimmed at the joint (d) and then used for the intended purpose. The member (6) is left in the hollow molded body (F).

[0014]

EXAMPLES Next, examples of the present invention will be described together with comparative examples.

Example 1 The dimensional specifications of the intended hollow molded article are 1000 mm in width,
A thin, wide-area, flat-plate-shaped hollow molded body having a length of 1200 mm and a thickness of 25 mm was prepared.

First, a pair of molding dies and other molding equipment members corresponding to the above-mentioned desired dimensional specifications are prepared, and a thermoplastic synthetic resin sheet as a molding material for a hollow molded body has a width of 1200 mm and a length of 1400 mm. , Thickness 2.0m
m ABS resin sheets were prepared.

Further, as a breathable heat resistant support member, a width of 1
A 3-mesh glass fiber net having a size of 100 mm and a length of 1300 mm was prepared.

Next, in the order shown in FIG. 1 (a), the lower clamper (4b), the lower ABS resin sheet (2), the spacer (3), the breathable heat resistant support member (6), Each member of the upper ABS resin sheet (1) and the upper clamper (4a) is placed one after another, and the whole is clamped by the clampers (4a) and (4b), and the temperature of the sheet surface is heated to 180 ° C. It was molded according to the molding operation of the usual double sheet molding method. The hanging amount of the ABS resin sheets (1) and (2) at the time of heating was 2 cm at maximum, supported by the breathable heat-resistant support member (6), and there was no problem in the molding operation. In the obtained hollow molded body, the shapes of the inner surfaces (9b) and (10b) of the mold cavity are accurately reproduced,
It had no defects such as wrinkles. In addition, the peripheral portion of the breathable heat-resistant support member is embedded and the cut end surface is exposed in the joint portion of the hollow molded body after trimming of the periphery, but this does not affect the joint strength of the hollow molded body, which is a practical problem. It was kept high in a range that did not exist.

Example 2 As the breathable heat-resistant supporting member, seven cotton strings (6a) having a thickness of 1 mm were used. As shown in FIG. Molding was performed in the same manner as in Example 1 except that the end portion of the string (6a) was sandwiched between 3) and the pressing member (3p) fitted thereto and stretched in the front, rear, left and right directions. The hanging amount of the ABS resin sheet during heating was 4 cm at maximum, and there was no problem in the molding operation. The shape of the inner surface of the mold cavity was accurately reproduced in the obtained hollow molded article, and there were no defects such as wrinkles. In addition, the peripheral part of the breathable heat-resistant support member is embedded in the joint part of the hollow molded body after trimming of the periphery and the cut end surface is exposed a few, but the joint strength of the hollow molded body is kept high. Met.

Comparative Example 1 An attempt was made by the usual double sheet molding method in exactly the same manner as in Example 1 except that the breathable heat resistant support member was not used. However, during heating, the ABS resin sheets on either the upper side or the lower side drastically drooped down, and the molding operation became impossible thereafter, and a hollow molded body could not be obtained.

Comparative Example 2 A heating temperature at the time of molding was set to 15 without using a breathable heat resistant support member.
The same as in the example except that the temperature was lowered to 0 ° C.
Attempts were made to form by the heavy sheet forming method. The hanging amount of the ABS resin sheet during heating was 6 cm at the maximum, but there was no problem in the molding operation. However, the obtained hollow molded article has a poor finished state particularly at the corners, and not only the inner surface of the mold is not accurately reproduced, but also the degree of bonding at the joint between two sheets is insufficient. It was a thing.

[0022]

As described above, according to the present invention, by using the breathable heat-resistant support member, it is possible to suppress the drooping of the thermoplastic synthetic resin sheet during heating, and to provide a large-sized, wide-area, flat-plate-shaped member. Even with a hollow molded article, it is possible to easily obtain a hollow molded article with high reproducibility of the molded shape and high strength of the joint portion, and it is possible to remarkably expand the range of application of this type of double sheet molding method. effective.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a molding step in a method for molding a synthetic resin hollow molded article according to the present invention, FIG. 1 (a) is a state when a molding material is heated, and FIG. 1 (b) is a molding die. FIG. 1C shows a state in which the peripheral edges of the materials are joined and integrated, and a state in which compressed air is introduced to perform molding.

FIG. 2 shows a stretched state of a breathable heat-resistant support member used in the present invention, and FIGS. 2A to 2C show deformed stretched states.

FIG. 3 is a partially omitted cross-sectional view of a hollow molded body obtained by the present invention.

FIG. 4 is a partially cutaway perspective view showing an attached state of a breathable heat-resistant support member according to Embodiment 2 of the present invention.

FIG. 5 is a cross-sectional view showing a molding step in a conventional method for molding a synthetic resin hollow molded body, FIG. 5 (a) is a state when the molding material is heated, and FIG. 5 (b) is a molding material by a molding die. FIG. 5 (C) shows a state in which the peripheral edges of are joined and integrated, and a state in which compressed air is introduced for molding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Thermoplastic synthetic resin sheet 2 ... Thermoplastic synthetic resin sheet 3 ... Spacer 3p ... Holding member 4a ... Upper clamper 4b ... Lower clamper 5 ... Closed space 6 ... Breathable heat-resistant support member 7a ... Heater (upper) 7b ... Heater (Lower side) 8 ... Air nozzle 9 ... Mold (upper side) 10 ... Mold (lower side) 11 ... Compressed air introduction nozzle F ... Hollow molded body d ... Joined portion

Claims (7)

[Claims] 1. Two thermoplastic synthetic resin sheets are clamped at their peripheral edges via a spacer so as to form a closed space between them, and both the sheets are heated and softened, and then the clamp positions at the peripheral edges. In a method of molding a synthetic resin hollow molded article in which a compressed air is introduced between a pair of upper and lower molds inside the sheet, a breathable heat-resistant support member is stretched between the two sheets in parallel with the sheet. Then, a molding method of a synthetic resin hollow molded article, characterized in that a subsequent molding operation is performed while maintaining this stretched state. 2. The synthetic resin hollow molded article according to claim 1, wherein the breathable heat-resistant support member is stretched by sandwiching the upper or lower sheet of the two thermoplastic synthetic resin sheets with a spacer. Molding method. 3. The method for molding a synthetic resin hollow molded article according to claim 1, wherein the breathable heat-resistant support member is stretched by attaching it to a spacer. 4. The method for molding a synthetic resin hollow molded article according to claim 1, wherein the breathable heat-resistant support member has a net-like form. 5. The method for molding a synthetic resin hollow molded article according to claim 1, wherein the breathable heat-resistant support member has a string-like form. 6. The method for molding a synthetic resin hollow molded article according to claim 1, wherein the breathable heat-resistant support member is made of an inorganic material. 7. The method of molding a synthetic resin hollow molded article according to claim 1, wherein the breathable heat-resistant support member is made of a natural or synthetic organic material.