JPH11179758A - Synthetic resin hollow molded product and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synthetic resin hollow molded product not generating the leak of a resin toward a hollow part at a bonding part and excellent in the breaking strength of the bonding part and a method for efficiently producing the same. SOLUTION: A plurality of divided pieces 10, 20 formed by the injection molding of a synthetic resin are integrated through a bonding part 30 to form a primary hollow molded product and, after this primary hollow molded product is housed in a mold, the synthetic resin is injected into the mold to form a secondary molded part 40 and the bonding part 30 is fused by this secondary molded part 40 to produce a synthetic resin hollow molded product. In this hollow molded product, the bonding part is formed by insert fitting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin hollow molded article obtained by fusing and integrating a plurality of divided pieces via a joint, and a method of manufacturing the same. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin hollow molded article having no resin leakage to the joint and excellent in breaking strength of a joint, and a method for efficiently producing the synthetic resin hollow molded article.

[0002]

2. Description of the Related Art For example, a synthetic resin hollow molded article having a complicated shape such as an intake manifold for an automobile is difficult to be manufactured by a general injection molding method or a blow molding method. It has been manufactured by a method such as an injection molding method, a molten core injection molding method, a two-shell injection molding method and an injection / blow combination molding method.

[0003] That is, the blow insert injection molding method is a method in which a hollow molded article is molded in advance by a blow molding method, and the molded article is mounted in an injection molding die to further perform injection molding. It is a molding method with a high degree of design. However, in this blow insert injection molding method,
The high pressure applied during the injection molding easily deforms the blow-molded product, so that the dimensional accuracy of the molded product is poor.

[0004] The above-mentioned molten core injection molding method is to set a core made of a tin-bismuth alloy or the like in a molding die, injection-mold a synthetic resin into the molding die, and then heat and melt and remove the core. This is a method for obtaining a synthetic resin hollow molded article, which has the advantage that the degree of freedom of the shape of the molded article is high and the smoothness of the inner surface of the molded article is excellent. However, in this molten core injection molding method, there is a problem that the efficiency is inferior because the weight of the core is large and the equipment including the melting equipment is large-scale.

[0005] The above-mentioned two-shell injection molding method means that a hollow body is made of two
This is a method of obtaining a synthetic resin hollow molded product by injection molding divided pieces of divided shape and bonding these divided pieces by vibration welding or hot plate welding, which has the advantage of excellent dimensional accuracy of the molded product. It is a method to have. However, this 2
In the shell injection molding method, when a high-strength reinforcing material-filled synthetic resin is used, there is a problem that the welding strength of the joint is low and the molded product is easily damaged.

[0006] The injection / blow combination molding method is a method in which a hollow molded body molded by blow molding is combined with a split piece of the above-mentioned two-shell injection molding method, and then bonded and welded. This is a method having both the advantages of the shell injection molding method and the advantages of the blow molding method. However, in this injection / blow combination molding method, the dimensions of the injection-molded product and the blow-molded product are difficult to match, so that it is difficult to obtain a welding margin, and the gap formed in the welded portion is too large. However, there is a problem that the uniformity of the film is lacking.

Therefore, recently, as a method of improving the drawbacks of the above-mentioned conventional methods, a two-stage injection molding method, that is, a plurality of divided pieces formed by injection molding is integrated through a joint to form a primary hollow molded article. None, a method of fusing the joints in a secondary molded part formed by mounting this in a molding die and further injecting synthetic resin was developed, and this method has excellent dimensional accuracy of molded products. In addition, since it is more efficient than the above-mentioned conventional method, it is being widely used.

The synthetic resin hollow molded article obtained by the two-stage injection molding method will be described more specifically with reference to the drawings.

FIGS. 4 to 6 are perspective views of a joint portion of a synthetic resin hollow molded product obtained by a conventional two-stage injection molding method. In each case, the joint portion of the two injection molded products 1a and 1b is protruded. The joining portion 2 is formed by joining, and the secondary forming portion 3 is formed along the joining portion 2, so that the joining portion 2 is fused.

However, in the conventional two-stage injection molding method, the joining portion 2 is fitted with a step portion that is alternately tapered (FIG. 4), and a fitting portion with a convex portion and a concave portion that are alternately curved (see FIG. 4). 5) and the fitting of convex portions and concave portions that are alternately inclined (FIG. 6). In general, in such a joint portion 2, it is easy to form the joint itself, but in particular, the joint portion 2 is easily formed. If the injection pressure at the time of the next injection molding is high, there is a problem that resin leaks from the joint to the inside of the hollow portion, and the fracture strength of the joint decreases due to this.

As a method for solving such a problem,
By improving the fluidity of the synthetic resin used for secondary injection molding or increasing the resin temperature during molding, measures have been taken to prevent the synthetic resin for secondary injection molding from leaking from the joint to the hollow part. However, if the fluidity of the secondary injection molding synthetic resin is improved, the material strength is reduced.If the resin temperature is too high, the material is deteriorated and the strength is reduced. For this reason, all of them have a trade-off relationship, and the desired improvement effect cannot be obtained.

[0012]

SUMMARY OF THE INVENTION The present invention has been achieved as a result of studying to solve the problems in the prior art described above.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a synthetic resin hollow molded article which has no resin leakage to the hollow portion side of the joint and has excellent joint breaking strength, and efficiently manufactures the synthetic resin hollow molded article. It is to provide a way to do it.

[0014]

Means for Solving the Problems In order to achieve the above object, a synthetic resin hollow molded article of the present invention is obtained by integrating a plurality of divided pieces formed by injection molding of a synthetic resin via a joint. A synthetic resin hollow molded product obtained by attaching the primary hollow molded product to a molding die and further molding the synthetic resin by injection molding to form a secondary hollow molded product. Wherein the joint is formed by forcible fitting.

In the synthetic resin hollow molded article of the present invention,
That the joint was formed by a spherical forced fit, a tunnel-shaped cavity formed along the edge of one of the divided pieces,
The joining part was formed by forcible fitting with the semi-cylindrical protrusion formed along the edge of the other divided piece, and the plurality of divided pieces and the secondary molded part were made of the same synthetic resin. Are desirable conditions, and by applying these conditions, it is possible to expect to obtain a better effect.

The method for producing a synthetic resin hollow molded article according to the present invention comprises a first step of forming a plurality of divided pieces having joints which can be forcibly fitted to each other by injection molding synthetic resin. A second step of forcibly fitting and integrating the plurality of divided pieces with each other via a joint to form a primary hollow molded article, mounting the primary hollow molded article in a molding die, and injection molding a synthetic resin A secondary forming portion is formed on the peripheral edge of the joining portion on the side opposite to the hollow portion, a third step of fusing the joining portion by the secondary forming portion, and a step of taking out a molded product from the molding die. It is characterized in that each of the four steps is performed sequentially.

In the method for producing a synthetic resin hollow molded article according to the present invention, in the first step, a spherical joint is formed at the edge of each of the divided pieces by forced fitting. A tunnel-shaped cavity is formed along the edge of the divided piece, and a semi-cylindrical projection is formed along the edge of the other divided piece, and a joint is formed by forcibly fitting the cavity and the projection. In addition, in the third step, it is desirable to use, as the resin for forming the secondary molding, a synthetic resin of the same type as the resin for forming the divided pieces in the first step. You can expect to get the effect.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a perspective view showing an example of the synthetic resin hollow molded article of the present invention, and FIGS. 2 and 3 are perspective views of a joint portion of the synthetic resin hollow molded article of the present invention.

As shown in FIG. 1, the synthetic resin hollow molded article of the present invention (in this example, an intake manifold for an automobile) has a plurality of divided pieces, specifically, two divided pieces 10 obtained by injection molding. And 20 are integrated through a joint 30.

Then, as shown in FIG. 2, the joining portion 30 is squeezed by forcibly fitting the edges of the two divided pieces 10 and 20 into a spherical shape. It is fused by a secondary molding part 40 formed by injection molding along the joining part 30.

Specifically, a tunnel-like cavity 11 formed along the edge of one of the divided pieces 10 and the other divided piece 2
The joint 30 is formed by forcible fitting with the projection 21 formed along the edge 21 of the joint 0
Numeral 0 is further fused and fixed firmly by the secondary forming section 40.

The embodiment shown in FIG. 3 shows an embodiment in which the strength of the joining portion 30 is increased by further increasing the thickness of the secondary forming portion 40 as compared with FIG.

In FIG. 2 and FIG.
The portions indicated by and 22 are flange portions for guiding the secondary forming portion 40 formed outside the joint portion 30 along the edges of the divided pieces 10 and 20.

As described above, by forming the joining portions 30 so as to be hard to come out of each other by forcibly fitting, the contact area of the joining portions 30 is increased, and the joining pressure of the joining portions 30 is increased by the molding pressure during the secondary injection molding. Even if the fitting portion is deformed, a gap is formed, and the resin does not leak from the gap into the hollow portion of the molded product. As a result, the secondary injection molding pressure can be sufficiently increased.

Therefore, the synthetic resin hollow molded article of the present invention has a high adhesion at the joint and a remarkably improved fracture strength at the joint surface.

Next, a method for producing the synthetic resin hollow molded article of the present invention will be described.

First, in the first step, a plurality of divided pieces having joints that can be forcibly fitted to each other are formed by injection molding synthetic resin. Here, as a joint formed at the edge of each divided piece, a structure formed by a spherical forcible fitting, preferably a tunnel-shaped cavity formed along the edge of one divided piece, and the other divided It is desirable to have a forcible fitting structure with a semi-cylindrical projection formed along the edge of the piece.

The plurality of divided pieces formed in the first step can be separately injection-molded using a plurality of injection molds, and can be simultaneously injection-molded using one injection mold. You can also.

Next, in the second step, the edges of the plurality of divided pieces are aligned, and the edges are forcibly fitted and fitted together by a pressing force, whereby the plurality of divided pieces are integrated with each other to form the primary hollow molding. Goods.

Next, in the third step, the primary hollow molded article obtained above is mounted in a molding die, and synthetic resin is injection-molded along the joint to thereby form a peripheral edge of the joint opposite to the hollow. A secondary molded part is formed on the base member, and a joint part is fused by the secondary molded part.

In the fourth step, the injection molding die is opened, and the molded product is taken out from the molding die, whereby the synthetic resin hollow molded product of the present invention can be obtained efficiently.

According to the manufacturing method of the present invention described above, since the molding pressure of the secondary injection molding can be set high without increasing the size of the apparatus, it is extremely efficient, the design of the hollow portion is high, and A synthetic resin hollow molded article having excellent dimensional accuracy can be obtained.

In the present invention, there is no particular limitation on the synthetic resin used for the primary injection molding of the above-mentioned split piece.
Polyamides such as nylon 66 and nylon 66, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyolefins such as polyethylene and polypropylene, polyvinyl halides such as polyvinyl chloride and polyvinylidene fluoride, and thermoplastic resins such as polycarbonate and polyphenylene sulfide. Can be used.

These synthetic resins can contain, if necessary, known additives such as dyes, pigments, heat stabilizers, weathering agents, lubricants, plasticizers, fillers and reinforcing materials. , Glass flakes, glass beads, carbon fiber, potassium titanate whiskers, silica, diatomaceous earth,
Fillers or reinforcements such as alumina, titanium oxide, magnesium oxide, talc, clay, mica, asbestos, walastenite, calcium silicate, calcium carbonate, montmorillonite, bentonite, boron fiber, silicon carbide fiber, polyester fiber and polyamide fiber When it is contained in an appropriate amount, a synthetic resin hollow molded article having more excellent strength can be obtained.

The synthetic resin used in the secondary injection molding for forming the secondary molded portion is not particularly limited as long as it is a synthetic resin of the same type as the synthetic resin used in the primary injection molding. It may be the same as the synthetic resin used, or may be different in the same field.

As described above, the synthetic resin hollow molded article of the present invention has a high degree of design in the hollow portion, excellent dimensional accuracy, and does not cause resin leakage from the bonded portion to the hollow portion. Has high adhesion and remarkably improved fracture strength at the joint, so that it can be widely applied to various industrial uses.

Further, according to the method for producing a synthetic resin hollow molded article of the present invention, the molding pressure of the secondary injection molding can be set high without increasing the size of the apparatus. A resin hollow molded article can be produced very efficiently.

[0039]

EXAMPLES The structure and effects of the present invention will be further described below with reference to examples.

Example 1 Nylon 6 containing 30% by weight of glass fiber was used as a reinforcing material, and this was injection molded to have a thickness of 3 mm and a spherical force fit shown in FIG. Two divided pieces having a combined structure were produced.

Next, the two divided piece edges were joined together and forcibly fitted to obtain a primary hollow molded article having an inner volume of 500 cc and having the shape shown in FIG. The thickness of the flange portion of the joint in this primary hollow molded product is 5 m.
m.

Next, the primary hollow molded article is mounted in an injection mold, and the same glass fiber-containing nylon 6 as described above is injection-molded along the flange portion of the joint to form a secondary molded part. Then, the joint was fused at the secondary molded portion to obtain a synthetic resin hollow molded product.

In this case, when the injection pressure during the secondary injection molding was gradually increased, the pressure was 655 kgf / c.
Under the high pressure condition of m ² , a tendency of resin leakage from the joint to the hollow portion of the molded product was observed.

Further, the injection pressure during the secondary injection molding is set to 450
The fusion-bonded portion of the synthetic resin hollow molded product obtained as Kgf / cm ² was cut out and subjected to a destruction test according to ASTM D638. The destruction load was 350 Kgf / cm ^2.
cm ² , and the molded product had excellent dimensional accuracy.

Example 2 A synthetic resin hollow molded article was manufactured in the same manner as in Example 1, except that the thickness of the flange portion of the joint portion in the primary hollow molded article was increased to 8 mm as shown in FIG.

In this case, the pressure is 660 kgf / cm ²
Under the high pressure condition described above, a tendency of resin leakage from the joint to the hollow portion of the molded product was observed.

Further, the injection pressure during the secondary injection molding is set to 500
When a fracture test was performed on the fusion-bonded portion of the synthetic resin hollow molded product obtained as Kgf / cm ^{2 in the same} manner as in Example 1, the fracture load was as high as 400 kgf / cm ² .
The dimensional accuracy of the molded product was also excellent.

Comparative Example 1 In Example 1, the shape of the edge of the two divided pieces was changed as shown in FIG.
As shown in (1), a synthetic resin hollow molded article was manufactured in the same manner except that the stepped portion was alternately tapered.

In this case, the pressure is 210 kgf / cm ²
Under the conditions of low pressure, a tendency of resin leakage from the joint to the hollow portion of the molded product was observed.

The injection pressure during the secondary injection molding is set to 190
When a fracture test was performed on the fusion-bonded portion of the synthetic resin hollow molded product obtained at Kgf / cm ^{2 in the same} manner as in Example 1, the fracture load was inferior to 150 Kgff / cm ² .

Comparative Example 2 In Example 1, the shape of the edge of the two divided pieces was changed as shown in FIG.
As shown in (1), a synthetic resin hollow molded article was manufactured in the same manner, except that the convex and concave portions were alternately fitted.

In this case, the pressure is 255 kgf / cm ²
Under the conditions of low pressure, a tendency of resin leakage from the joint to the hollow portion of the molded product was observed.

The injection pressure during the secondary injection molding is set to 230
When a fracture test was performed on the joint-fused portion of the synthetic resin hollow molded product obtained at Kgf / cm ^{2 in the same} manner as in Example 1, the fracture load was inferior to 200 kgf / cm ² .

Comparative Example 3 In Example 1, the shape of the edge of the two divided pieces was changed as shown in FIG.
As described above, a synthetic resin hollow molded article was manufactured in the same manner, except that the convex and concave portions were alternately fitted.

In this case, the pressure is 360 kgf / cm ²
Under the conditions of low pressure, a tendency of resin leakage from the joint to the hollow portion of the molded product was observed.

Further, the injection pressure during the secondary injection molding is set to 320
When a fracture test was performed on the fusion-bonded portion of the synthetic resin hollow molded product obtained at Kgf / cm ^{2 in the same} manner as in Example 1, the fracture load was inferior to 250 kgf / cm ² .

[0057]

As described above, the synthetic resin hollow molded article of the present invention has a high degree of design in the hollow portion, has excellent dimensional accuracy, and does not cause resin leakage from the joint to the hollow portion. Since the bonding strength of the bonding portion is high and the breaking strength of the bonding surface is significantly improved, it can be widely applied to various industrial uses.

Further, according to the method for producing a synthetic resin hollow molded article of the present invention, the molding pressure of the secondary injection molding can be set high without increasing the size of the apparatus. A resin hollow molded article can be produced very efficiently.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a synthetic resin hollow molded article of the present invention. 2 and 3 are perspective views of a joint portion of the synthetic resin hollow molded article of the present invention.

FIG. 2 is a perspective view showing a joint portion of the synthetic resin hollow molded article of the present invention.

FIG. 3 is a perspective view showing another example of a joint portion of the synthetic resin hollow molded article of the present invention.

FIG. 4 is a perspective view showing a joint portion of a synthetic resin hollow molded product obtained by a conventional two-stage injection molding method.

FIG. 5 is a perspective view showing a joint portion of a synthetic resin hollow molded product obtained by a conventional two-stage injection molding method.

FIG. 6 is a perspective view showing a joint portion of a synthetic resin hollow molded product obtained by a conventional two-stage injection molding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 One divided piece 11 Tunnel-shaped cavity 20 The other divided piece 21 Kamaboko-shaped projection 30 Joining part 40 Secondary forming part

Claims (8)

[Claims] 1. A plurality of divided pieces formed by injection-molding a synthetic resin into a primary hollow molded product through a joining portion to form a primary hollow molded product. A synthetic resin hollow molded product obtained by fusing the joint with a secondary molded portion formed by injection molding, wherein the joint is formed by forcible fitting. Molding. 2. The synthetic resin hollow molded article according to claim 1, wherein the joint portion is formed by a spherical force fit. 3. A joining portion is formed by forcibly fitting a tunnel-shaped cavity formed along the edge of one of the divided pieces and a semicylindrical projection formed along the edge of the other divided piece. The synthetic resin hollow molded article according to claim 1 or 2, wherein: 4. The synthetic resin hollow molded product according to claim 1, wherein the plurality of divided pieces and the secondary molded portion are made of the same synthetic resin. 5. A first step of forming a plurality of divided pieces having joints which can be forcibly fitted to each other by injection-molding a synthetic resin, wherein said plurality of divided pieces are mutually connected via a joint. A second step in which the primary hollow molded article is forcibly fitted and integrated into a primary hollow molded article, and the primary hollow molded article is mounted in a molding die, and a synthetic resin is injection-molded to form a peripheral edge of the joint section opposite to the hollow section. Forming a secondary molded part, and sequentially performing a third step of fusing the joint part by the secondary molded part and a fourth step of removing a molded product from the molding die. A method for producing a synthetic resin hollow molded article. 6. The method for manufacturing a synthetic resin hollow molded article according to claim 5, wherein, in the first step, a joint formed by spherical fitting is formed at an edge of each divided piece. . 7. In the first step, a tunnel-shaped cavity is formed along the edge of one of the divided pieces, and a semi-cylindrical projection is formed along the edge of the other divided piece. The method for manufacturing a synthetic resin hollow molded article according to claim 5, wherein the joining portion is formed by forcible fitting. 8. The method according to claim 5, wherein in the third step, a synthetic resin of the same type as the resin forming the divided pieces in the first step is used as the resin for forming the secondary molding. Item 14. The method for producing a synthetic resin hollow molded article according to the above item.