JP2584575B2 - Molding method and molding die for synthetic resin hollow molded article - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow molded article made of synthetic resin, for example, a double-panel panel, a double-wall lighting dome, and a relatively large-sized double-walled panel which is used for a large-sized internally illuminated signboard. And a molding die for a synthetic resin hollow molded article.

[0002]

2. Description of the Related Art Conventionally, as a method for forming a relatively large double-walled hollow plate-like molded body as described above, the following molding method called a double sheet molding method is known.

That is, as shown in FIG. 8, two thermoplastic synthetic resin sheets (31) and (32) are used as molding materials.
The peripheral parts are sandwiched between the upper and lower clampers (34) and (35) via spacers (33), and both sheets (31)
(32) are supported in parallel and horizontally at a predetermined interval. Then, both sheets (31) and (32) are heated from above and below by an infrared heater (not shown) to soften them.
At the same time, the air nozzle (3
From 8), the two sheets (31) and (32) are placed inside the peripheral clamping position while a pair of upper and lower molding dies (36) ) (37).

[0004] By bringing the two dies closer to a predetermined closed position in this way, the sheet clamping surfaces (36a
9) The two sheets (31) and (32) are sandwiched between (37a) and their peripheral edges are joined and integrated, and a molding air nozzle (39) provided on at least one mold as shown in FIG. Through the sheet (31), and introduce compressed air at a predetermined pressure into a closed space between the two sheets (31).
(32) is brought into close contact with the inner surface of the cavity of both molds (36) and (37). At this time, a vacuum is sometimes drawn from the inner surface side of the molding die to assist the sheet in intimate contact with the die.

Next, after cooling while maintaining the internal pressure between the two sheets, the two blades (31) are cut by the cutting blade (40).
(32) is cut at the outer peripheral edge of the joint (41),
The mold is opened to take out a hollow molded body (B) as shown in FIG.

The above-mentioned molding method is advantageous in that a plate-shaped hollow body having an arbitrary shape having a double wall can be formed relatively easily, even if it is quite large.

However, as described above, both dies (36) (3
7) Sheet (31) between sheet clamping surfaces (36a) and (37a)
Since the (32) is pressed and joined, a joint (41) projecting outward remains at the peripheral edge of the hollow molded body (B), and this may hinder the hollow molded article depending on its use. For this reason, there is often a need for a hollow molded body that does not have the above-mentioned lug-like joints.

In response to such a request, a sheet clamping surface (FIG. 11) of a molding die (36) (37) is used in accordance with a conventional method often used in the blow molding method. 36
a) On the inner peripheral edge of (37a), ridges (42) and (43) for bite-off, that is, pinch-off are provided to face each other, and the ridges provide a thickness of 0.2 to 1 to the peripheral edge of the molded body. Attempts have been made to produce a hollow molded body having no overhang-shaped joint at the periphery by forming a thin cut portion (44) having a thickness of about 0.0 mm and cutting the formed cut portion.

[0009]

However, it has been found that a new problem arises in the above-mentioned molding method.

That is, in the hollow molded body from which the peripheral joint is cut off as described above, both peripheral sheets (31) and (32)
Is weak at the joint (45) and easily breaks there. This is due to the fact that the joint (44) of the two sheets (31) and (32) at the time of molding has a weld portion that is inherently inferior in strength, and that the portion becomes thin. .

Accordingly, the present invention solves the above problems and provides a method of forming a hollow molded body capable of maintaining sufficient strength even at a peripheral joint, and a molding die used for the method. The purpose is to provide a structure.

[0012]

SUMMARY OF THE INVENTION One object of the present invention is to form two thermoplastic synthetic resin sheets on a peripheral edge thereof in such a manner that a predetermined closed space is provided therebetween. After the two sheets are heated and softened, the sheet is sandwiched between a pair of upper and lower dies inside the clamp position on the periphery, and compressed air is introduced into a closed space between the two sheets. In a method of forming a hollow molded body in which both sheets are closely contacted with the inner surfaces of upper and lower molds, an inner ridge and an outer ridge for pinch-off are provided on a sheet sandwiching surface of a peripheral edge of the upper and lower dies. The resin recess is formed in two rows with
When the upper and lower molds are closed, the sheet portion sandwiched between the sheet sandwiching surfaces and crushed overflows from the resin reservoir concave portion, and is pressed and flows in the cavity direction of the mold, so that both sides of the molded body are pressed. The gist of the present invention is a method of forming a synthetic resin hollow molded body, characterized in that a reinforcement portion having a built-up shape is formed on an inner surface of a joint portion of a sheet.

Another aspect of the present invention is a molding die used in the method of molding a hollow molded body, wherein an inner ridge and an outer ridge for pinch-off are formed on a peripheral surface of the sheet sandwiching surface. It is formed in two rows with a recess for resin pool between them, and the volume of the resin pool space formed by the recess when the mold is closed is smaller than the volume of the sheet portion sandwiched between both protruding edges. The present invention provides a mold for molding a synthetic resin hollow molded body, which is set.

In a preferred embodiment of the molding die, the depth of the resin reservoir recess is gradually increased inward of the die. Furthermore, the height of the inner ridge for pinch-off is set relatively lower than the height of the outer ridge, and the clearance between the inner ridges is reduced between the outer ridges when both molds are closed. It is configured to be larger than the clearance.

[0015]

Next, the present invention will be described more specifically and in detail based on illustrated embodiments.

In FIG. 1, (1) and (2) are two thermoplastic synthetic resin sheets as molding materials, (3) and (4) are a pair of upper and lower molding dies, and (5) is an upper molding. Mold (3)
Table (6) is a bed in which a lower molding die (4) is fixed on the upper surface, (7) is a spacer having a predetermined thickness forming an annular frame, and (8) and (9) are clampers. , (10) and (11) denote die spacing regulating members which are attached to the periphery of the upper table (5) and the bed (6) so as to face each other. And (13) for properly regulating the mutual closing positions of both molding dies (3) and (4) when closing.
(14) and (15) are infrared heaters.

Synthetic resin sheet as molding material (1)
The material of (2) is not particularly limited as long as it is made of a thermoplastic resin. Depending on the application of the hollow molded body, any material is selected and used, but generally a resin sheet having a thickness of about 2 to 10 mm made of, for example, a vinyl chloride resin, an acrylic resin, a polycarbonate resin, or the like is used. . In addition, the two resin sheets (1) and (2)
Different materials or different colors may be used.

When performing double sheet molding of the resin sheets (1) and (2), first, a spacer (7) is interposed between the peripheral portions of the sheets (1) and (2). The parts are clamped from above and below by clampers (8) and (9), and both sheets (1) and (2) are supported in a parallel and horizontal manner in such a manner as to leave a closed space (16) therebetween.

Next, infrared heaters (14) and (15) are introduced above and below the sheets (1) and (2), and the sheets are heated and softened from both upper and lower surfaces to a predetermined molding temperature. On this occasion,
As shown in FIG. 2, at the same time, compressed air is introduced from the air nozzle (7a) provided in a part of the spacer (7) into the closed space (16) between the two sheets (1) and (2), and the free air of both sheets is freed. The sheet is pretensioned while preventing gravitational deformation.

After removing the heaters (14) and (15) while continuing this pre-stretching operation, a pair of upper and lower moldings are formed on both sheets (1) and (2) inside the clamp position on the periphery thereof. The molds (3) and (4) are brought close to each other, and both sheets (1) are sandwiched between the sheet holding portions (3a) and (4a) on the peripheral wall.
As shown in FIG. 3, the molding air nozzle (19) provided on at least one of the molds (3) is connected to a driving means (19) such as a driving cylinder.
By advancing in a), at least one sheet (1) is penetrated. Then this air nozzle (19)
The compressed air is introduced into the closed space (16) between the two sheets (1) and (2) from the outside, so that the two sheets (1) and (2) are formed into the cavity inner surface ( 3b) (4b)
Close to. Next, after performing required cooling while maintaining the internal pressure, the air nozzle (19) is removed, and the molds (3) and (4) are opened to take out a predetermined hollow molded body. The above forming operation is substantially the same as the conventional double sheet forming method.

In the present invention, as shown in detail in FIGS. 4 and 5, the molding die (3)
On both sides of the sheet holding surfaces (17, 18) at the leading end of the sheet holding portions (3a), (4a) in (4), inner ridges (20), (21) for pinch-off and outer ridges (20), (21) are provided. 22) and (23) are provided in two rows with resin reservoir recesses (24) and (25) therebetween. Moreover, the substantial height (h ₁ ) of the inner ridges (20) and (21) is set to be relatively lower than the substantial height (h ₂ ) of the outer ridges (22) and (23). And the clearance (c ₁ ) between the inner ridges (20) and (21) when both the dies (3) and (4) are closed as shown in FIG.
Is larger than the clearance (c ₂ ) between the outer ridges (22) and (23). In addition, the concave portions (24) and (25) of the resin reservoir have a gradually increasing depth toward the inside of the molds (3) and (4) because their bottom surfaces are formed in an inclined shape. I have. Furthermore, when the molds (3) and (4) are closed, the volume of the resin pool space formed by the concave portions (24) and (25) is reduced when the molds (3) and (4) are closed. The volume is set to be smaller than the volume of the sheet portion sandwiched between 20), (21), (22) and (23). In a specific example of the mold design, the width of the sheet clamping surfaces (17) and (18) is, for example, about 30 mm, and the tips of pinch-off ridges (20) (21) (22) (23). The width of the surface is, for example, about 1 mm, and the clearance between the inner and outer ridges (20), (21), (22), and (23) is 0.
The clearance is set in the range of about 2 to 1.0 mm, and the clearance difference (c ₁ -c ₂ ) at the time of closing the mold is set to about 0.1 to 0.5.

By using the dies (3) and (4) as described above, the dies (3) and (4) approach the sheets (1) and (2) from above and below as shown in FIG. At the point where the sheets are clamped by the sheet clamping surfaces (17) and (18),
As shown in FIG. 5, the outer ridges (22) and (23) bite deeper into the sheet before the inner ridges (20) and (21). Then, the resin reservoir recesses (24) and (25) correspond to the sheet (1).
When reaching the point of time when the resin is filled in (2), the surplus portion of the resin is pressed from the recesses (24) and (25) by pressure and overflows to the outside. Here, the overflow resin is such that the depth of the concave portions (24) and (25) is formed deeper inward, and the clearance between the inner ridges (20) and (21) at the time of closing the mold ( Together with the fact that c ₁ ) is set to be larger than the clearance (c ₂ ) between the outer ridges (22) and (23), as shown by arrows in FIG. 3) It flows predominantly inward of (4), that is, in the direction of the cavity, and the inner ridges (20) (2)
Flowing from the clearance (c ₂ ) between 1) to the joint (26) of the two sheets (1) and (2) in the cavity,
A build-up reinforcement (27) is formed at the joint. Therefore, as shown in FIG. 6, after the molding operation is completed with both dies (3) and (4) completely closed, the molded product is removed from the dies (3) and (4) and the inner ridges are formed. (20) The hollow molded article (A) obtained by trimming and removing the peripheral portion at the pinch-off portion between (21) does not have a joint protruding like an ear on the outer peripheral edge as shown in FIG. The two sheets (1) and (2) are joined in an abutting manner at the peripheral edge, and have a built-up reinforcement (27) inside the joint (26) to increase the joining strength. Become.

[0023]

According to the first and second aspects of the present invention, a projecting joint is provided on the outer peripheral edge while utilizing a simple molding method similar to the conventional double sheet molding method. Instead, both sheets are joined in abutting manner at the peripheral edge, and furthermore, have a built-up reinforcing portion inside the joined portion,
A hollow molded body having excellent joining strength can be obtained.

Further, according to the third and fourth aspects, the build-up reinforcement can be formed more reliably with a sufficient amount of resin, and the joint strength can be further improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an outline of a molding apparatus according to the present invention.

FIG. 2 is a cross-sectional view of a main part showing a state during a pretensioning step.

FIG. 3 is a sectional view of a main part showing a state at the time of molding.

FIG. 4 is a cross-sectional view of a main part showing a halfway state when the mold is closed.

FIG. 5 is a cross-sectional view of a main part in a state where the mold has been further advanced in the closing direction from the state of FIG. 4;

FIG. 6 is a sectional view of a main part in a state in which a mold is completely closed.

FIG. 7 is a cross-sectional view showing an example of a hollow molded body manufactured according to the present invention.

FIG. 8 is a schematic sectional view of a molding apparatus showing a conventional molding method.

FIG. 9 is a cross-sectional view showing a state at the time of molding by the molding apparatus of FIG. 8;

FIG. 10 is a cross-sectional view showing an example of a hollow molded body manufactured by a conventional molding method.

FIG. 11 is a sectional view of a main part showing another example of a conventional molding method.

[Explanation of symbols]

 (1) (2) resin sheet (3) (4) molding die (7) spacer (8) (9) clamper (14) (15) heater (16) closed space (17) ( 18) Sheet holding surface (19) Air nozzle for molding (20) (21) Inner ridge (22) (23) Outer ridge (24) (25) Resin pool recess (26) Joint (27)… Reinforcing part

Claims (4)

(57) [Claims] 1. A thermoplastic resin sheet is clamped at its peripheral edge via a spacer in such a manner that a predetermined closed space exists between the two thermoplastic synthetic resin sheets, and the two sheets are heated and softened. A hollow molded body sandwiched between a pair of upper and lower molds inside the above-mentioned clamp position, and compressed air is introduced into a closed space between the two sheets to bring both sheets into close contact with the inner surfaces of the upper and lower molds. In the molding method, an inner ridge and an outer ridge for pinch-off are formed in two rows on a sheet holding surface of a peripheral edge of the upper and lower molds with a resin reservoir concave portion interposed therebetween. When the upper and lower molds are closed, the sheet portion sandwiched between the sheet sandwiching surfaces and crushed overflows from the resin reservoir concave portion, and is pressed and flows in the cavity direction of the mold, so that both sides of the molded body are pressed. Form a reinforcement on the inner surface of the joint of the sheet Method of molding a synthetic resin hollow molded body, characterized in Rukoto. 2. A pinch-off inner ridge and an outer ridge are formed in two rows on a peripheral sheet holding surface with a resin reservoir recess therebetween, and the recess is formed when the mold is closed. Wherein the volume of the resin reservoir space formed by the molding is set smaller than the volume of the sheet portion sandwiched between the two projecting edges. 3. The mold for molding a synthetic resin hollow molded article according to claim 2, wherein the depth of said resin reservoir recess is gradually increased inward of the mold. 4. The height of the inner ridge for pinch-off is set relatively lower than the height of the outer ridge, and the clearance between the inner ridges is reduced when both dies are closed. The mold for molding a synthetic resin hollow molded article according to claim 2 or 3, wherein the mold is configured to be larger than the clearance between the strips.