JPH1086214A - Blow molding of hollow double wall structure made of plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve rigidity and strength by thoroughly connecting and integrating double walls with each other by a weld rib without generating weld mark on the surface. SOLUTION: In a molding, a hollow double wall structure of a panel 3 having the hollow double wall structure is formed by blowing of a thermoplastic plastic material. At the blowing, a part of a plasticized melted parison is compressed so as to form a weld rib 4 which integrally connects the double walls on an inngr wall 1. The weld rib 4 forms a recess 5 having a large inner diameter and a protrusion 6 having a narrow inner diameter formed by contracting the inner diameter stepwise. The tip of the protrusion 6 has a spherical surface. The tip of the spherical surface of the protrusion 6 is welded to an outer wall 2 in an embedded state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a housing panel for various electronic devices, a housing panel for furniture, a housing panel for architecture, a panel member for an automobile, a case,
The present invention relates to a blow-molded product having a plastic hollow double-wall structure constituting a molded product such as a container.

[0002]

2. Description of the Related Art Conventionally, a housing case for a machine tool or the like, which is a blow molded product formed by blow molding a thermoplastic material into a hollow double wall structure, is disclosed in Japanese Utility Model Application Laid-Open No. 59-14307.
In this case, a weld rib is formed on the inner wall side at the time of blow molding, and reinforcement is achieved as a structure in which the inner wall and the outer wall are integrally connected.

[0003]

In a blow molded article having a hollow double-walled structure such as the above-mentioned conventional storage case having a hollow middle wall structure, the compressed state of the weld ribs is required to improve the bonding strength of the weld ribs. It may be set high, but on the other hand, welding marks due to the weld ribs appear prominently on the surface.

[0004] In order to prevent the appearance from being impaired by the marks formed when welding the weld ribs, the inventor of the present invention, as shown in FIG. An experiment was conducted to form a thin weld rib c by making it concave, but it is difficult to extend the tip of the weld rib c with a uniform thickness until it is joined to the parison d on the outer wall side at the time of blow molding. There is a problem that molding defects are apt to occur, such as generation of pinholes. Even if the molding is performed well, as shown in FIG. 10, the base end e of the inner wall of the weld rib c becomes particularly thin, and the strength of the weld rib c itself becomes low. It has also been found that the problem of reinforcement is incomplete and that the rigidity and strength of the molded article are reduced.

An object of the present invention is to solve the problem in forming such a thin weld rib at the time of blow molding, and at the time of blow molding, a trapezoidal stepped portion is formed on a part of one of the split molds. And a cavity having a protrusion having a spherical outer end with a spherical outer end at the approximate center position of the step and the other split mold to compress the parison to reduce the inner diameter of the weld rib in a stepwise manner. By forming the protruding part, the entire weld rib is formed to a uniform thickness without generating pinholes and thin parts,
This makes it possible to complete the integration between the double walls by the weld ribs to improve the strength of the molded product, and to make the tip of the protrusion of the weld rib spherical, and to make the spherical tip face the opposite wall. By welding in a buried state, the tip of the protrusion welded to the opposing wall of the weld rib is made a smooth surface so that no welding mark is formed on the surface of the opposing wall, and the tip of the protrusion of the weld rib is made spherical. Accordingly, it is an object of the present invention to provide a blow molded product having a plastic double hollow wall structure having high rigidity and strength, by increasing the surface area of the portion to further improve the welding strength.

[0006]

Means for Solving the Problems The present invention has the following configuration to achieve the object. That is, the plastic is formed by blow-molding a thermoplastic material and forming a weld rib on one of the walls by compressing a part of the plasticized and melted parison at the time of the blow-molding to integrally connect the double walls. This is a blow-molded product with a hollow double-walled structure. The weld rib has a trapezoidal step on a part of one of the split molds and a tip with a spherical outer end with a spherical tip at almost the center of the step. The parison is compressed by the cavity having the projection composed of the part and the other split mold, and a flat concave portion having a large inner diameter toward the opposing wall and a spherical protrusion with a small inner diameter toward the opposing wall side are formed at the tip. A blow molded product having a hollow double-walled structure made of plastic, characterized in that it is formed and the spherical tip of the protruding portion is buried and welded to the opposing wall.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a blow-molded article having a plastic hollow double-wall structure according to the present invention, wherein 1 is an inner wall thereof, 2 is an outer wall, and an inner wall 1 and an outer wall are shown. 2
Are joined at the peripheral surface to form a hollow double-walled panel 3. The panel 3 has a plurality of weld ribs 4 formed on an inner wall 1, and the inner wall 1 and the outer wall 2 are integrally connected by the weld ribs 4. In addition, outer wall 2
The surface has a fine uneven surface for decoration.

As shown in FIG. 2, the weld ribs 4 are gradually reduced in inner diameter from a concave portion 5 having a larger inner diameter toward the outer wall 2 to form a projection 6 having a narrower inner diameter and a spherical end. And the spherical tip is the outer wall 2
And is buried and welded. This weld rib 4
The width H between the inner surface of the concave portion 5 and the outer surface of the outer wall 2 is defined as H = (2.1 to 6.5) × t1, where H1 is an average thickness of the inner wall 1, and preferably H = (2.2). ４4.0) × t1. Further, assuming that the average thickness of the outer wall 2 is t2, the thickness of the most compressed welded portion 7 is t3, and the inner width of a portion rising 0.5 times from the deepest wall surface of the protruding portion 6 is D, D = (0.3-2.5) × t1 t3 = (0.45-0.98) × (t1-t2) Preferably, D = (1.1-2.1) × t1 t3 = (0.58 ０．９0.94) × (t1−t2). The average thickness t1 of the inner wall 1 and the average thickness t2 of the outer wall 2 are both 1.5 to 3.0.
Preferably, it is in the range of 5 mm.

The reason why the width H between the inner surface of the concave portion 5 and the outer surface of the outer wall 2 is specified in the above range is that if the width is less than 2.1t1, the inner surface of the parison around the weld rib 4 is welded during blow molding. When the width exceeds 6.5t1, the corner portion of the weld rib 4 becomes thin and the strength is impaired, but the molding is performed well within the above range.

On the other hand, if the inner width D exceeds 2.5 times t1, the plasticized plastic in contact with the weld rib at the time of molding is cooled and does not expand, so that the compressive force of the welded portion 7 is increased and the outer wall becomes harder. No. 2 shows a marked weld mark on the surface, and if it is less than 0.3 times the average thickness t1 of the inner wall 1, molding defects such as pinholes occur during molding, and the thickness becomes extremely non-uniform, and the connection is made. Strength decreases. On the other hand, if the thickness t3 of the welded portion 7 exceeds 0.98 times of (t1-t2), poor welding will appear remarkably, and if it is less than 0.5 times of (t1-t2), welding marks will appear significantly. However, in the above range, the bonding strength,
The appearance is also good.

The hollow double-walled panel 3 configured as described above is used, for example, as a housing panel 9 of an electronic device (electronic copying machine) 8, as shown in FIG.

As shown in FIG. 4, the hollow double-walled panel 3 is formed by blow molding a thermoplastic material. That is, 10 and 11 are a pair of split molds, 12 and 13 are the cavities,
One of the cavities 13 is provided with a projection 14 for forming the weld rib 4. The projection 14 has a stepped shape including a trapezoidal stepped portion 15 corresponding to the shape of the weld rib 4 and a tip end portion 16 having a spherical and thin outer diameter at a substantially central position of the stepped portion 15. is there. Reference numeral 17 denotes an extrusion head, and reference numeral 18 denotes a molten parison.

In the blow molding of the panel 3 having a hollow double wall structure using the pair of split molds 10 and 11, the Paris 18 extruded from the extrusion head 17 as shown in FIG. When the split molds 10 and 11 are closed, a part of the paris 18 corresponding to the protrusion 14 is moved to the protrusion 1 on one cabty 13 side as shown in FIG.
4 and gradually expands around the tip portion 16, and also contacts the minute uneven surface of the other cavity 12,
As the blow further proceeds, as shown in FIG.
8 are welded together and blow-molded to further expand the paris 18 while being supported and held at the edge of the step 15 of the protrusion 14, and as shown in FIG. And the weld ribs 4 satisfying the above conditions are formed.

In FIG. 6, parison 18 in a plasticized state is shown.
The central portion P which has contacted the projection 14 is cooled and its elongation is reduced to some extent, but the contact area is as narrow as the thickness of the paris 18, and the paris 18 is
The approaching portion P2 of the central portion P contacting with the base portion 4 is sequentially extended toward the base side of the projection 14 so as to be bent at a substantially right angle as it is blow-molded. In addition to the above, the protrusion 6 having a spherical tip is formed, so that the occurrence of welding marks due to compressive force is suppressed, and the welding strength of the welding portion 7 is increased.

As the thermoplastic material constituting the hollow double-walled panel 3, styrene-modified polyphenylene oxide, ABS resin, polycarbonate, polyamide, polybutylene terephthalate, polypropylene, polyethylene and the like are used, but the surface appearance is important. For a housing panel which is viewed as a structural member by itself, the tensile strength (ASTM-D638) is 50.
Styrene-modified polyphenylene oxide of 0 kg / cm ² or more, ABS resin, polycarbonate, polyamide, and polybutylene terephthalate are preferred.

The fine uneven surface formed on the surface of the outer wall 2
The depth is 30 to 200 μm, and especially 30 to 8 μm.
In the case of forming an extremely fine uneven surface of 0 μm, a mark due to welding of the weld rib 4 may appear. Therefore, as described above, the protrusion 6 of the weld rib 4 is made thinner and the tip thereof is formed in a spherical shape. It is effective to keep the compression ratio in such a range in order to maintain good appearance.

The shape of the projecting portion 6 of the weld rib 4 may be a sectional shape or the like as shown in FIG. Further, the weld ribs 4 are not dotted but may be linear weld ribs 4 'as shown in FIG.

According to the hollow double-walled panel 3 configured as described above, the welded portion 7 of the protruding portion 6 is formed thin so that the inner diameter of the weld rib 4 is reduced stepwise during blow molding. Therefore, the weld ribs 4 can be formed with a uniform thickness without generating pinholes or thin portions during blow molding. Therefore, the integral integration between the double walls by the weld ribs 4 can be completed, and the rigidity and strength of the molded product can be improved without deteriorating its appearance. In addition, since the tip of the projection 6 is formed in a spherical shape and the spherical tip surface is welded to the opposing wall in a buried manner, the welding portion 7 is smooth and the surface area of the portion is increased, so that the welding strength is increased. Is further improved, and the rigidity and strength of the molded product are increased.

[0019]

According to the present invention, a thermoplastic resin material is blow-molded, and a part of the parison plasticized and melted at the time of blow molding is compressed to form weld ribs on one of the walls which integrally connect the double walls. A plastic hollow double-walled blow molded product having a trapezoidal step formed on a part of one of the split molds and a narrow outer end having a spherical end at substantially the center of the step. The parison is compressed by the cavity having the projection having the tip end of the diameter and the other split mold, and the flat concave portion having a large inner diameter toward the opposing wall and the tip having a spherical inner end having a small inner diameter toward the opposing wall side. Since the projecting portion is formed and the spherical tip of the projecting portion is buried and welded to the opposing wall, the tip of the projecting portion welded to the opposing wall of the weld rib is formed as a smooth spherical surface. Marks on the surface of In addition, the welding strength is further improved by increasing the surface area of the welded portion of the protrusion of the weld rib so as to further improve the welding strength, and it is possible to obtain a blow molded article having a rigid and strong plastic hollow double wall structure. .

[Brief description of the drawings]

FIG. 1 is an overall perspective view of a panel having a hollow double-wall structure, which is an example of a blow-molded product having a hollow double-wall structure made of plastic according to the present invention.

FIG. 2 is an enlarged vertical sectional perspective view of a part of the panel having the hollow double-wall structure shown in FIG.

FIG. 3 is a perspective view of an electronic apparatus using the panel having the hollow double-wall structure shown in FIG.

FIG. 4 is a cross-sectional view showing a blow molding mode of a panel having a hollow double wall structure, which is an example of a blow molded product having a hollow double wall structure made of plastic according to the present invention.

FIG. 5 is a sectional view showing a step subsequent to that of FIG. 4;

FIG. 6 is a sectional view showing a step subsequent to FIG. 5;

FIG. 7 is a sectional view showing a step subsequent to FIG. 6;

FIG. 8 is an overall perspective view of a hollow double-walled panel which is another example of the blow-molded product of the plastic hollow double-walled structure according to the present invention.

FIG. 9 is a partial cross-sectional view showing a blow-molding mode of a panel having a hollow double-walled structure for explaining the problem of the present invention.

10 is a cross-sectional view of a part of a panel having a hollow double-walled structure formed by the blow molding mode shown in FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inner wall 2 Outer wall 3 Hollow double wall structure panel 4 Weld rib 5 Weld rib recess 6 Weld rib projection 7 Welding part 10, 11 A pair of split molds 12, 13 Cavity 14 Protrusion 15 Protrusion trapezoidal step 16 Tip of projection 17 Extrusion head 18 Parison

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Claims (1)

[Claims] 1. A plastic material obtained by blow molding a thermoplastic material and forming, on one wall, weld ribs for compressing a part of the plasticized and melted parison at the time of blow molding to integrally connect the double walls. A blow molded product having a hollow double-wall structure, in which a weld rib has a trapezoidal step on a part of one of the split molds and a tip with a spherical outer diameter at a substantially central position of the step. The parison is compressed by the cavity having the projection made of and the other split mold, forming a flat concave portion having a large inner diameter toward the opposing wall, and a spherical protruding portion having a small inner diameter toward the opposing wall side. A blow molded article having a hollow double wall structure made of plastic, wherein a spherical tip of the protruding portion is buried and welded to an opposing wall.