JPH10278073A - Injection mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding die for gas injection injection molding capable of molding a molded product without sink marks, warpage, distortion, etc., and having a simple structure and not requiring a high gas injection pressure. I will provide a. SOLUTION: A lower mold main body 21 and a nesting portion 22 having a concave portion 23 for forming a thick portion (rib) R on a molded product P are formed on the surface. In the depth direction of the concave portion 23, the thermal conductivity is 0.1 to 0.5 cal / (cmsec.
C), and a first layer portion 221 having a thickness smaller than the thickness of the molded article main body portion P, and a second layer made of a material having a thermal conductivity of less than 0.1 cal / (cm · sec ·) ° C. A mold for injection molding, comprising a layer part 222.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin molded product having less sink marks and warpage by injecting a pressurized gas into a molten resin material injected into an injection mold to form a hollow portion. The present invention relates to an injection mold used for so-called gas injection molding, which is used to mold a molded article (hereinafter simply referred to as a "molded article").

[0002]

2. Description of the Related Art A so-called gas injection molding method has been conventionally known as a technique for molding a molded article having less sink marks and warpage. In the gas injection molding method, the molten resin is injected into the cavity using a mold that has a cavity for molding a thick part such as a rib and a boss attached to the molded product main body and the main body. Pressurized gas is injected into the thick part of the resin, and the resin is pressed against the mold surface to form a hollow part. Is avoided.

In such a gas injection molding method, when a hollow portion is formed near the surface of the main body of a molded product, the thickness of this portion becomes too small, the strength is reduced, and defects in appearance are reduced. There is a problem that it easily occurs. for that reason,
It is most preferable that a hollow portion is formed in a portion where the thickness is the largest.

[0004] However, the conventional techniques are as follows.
The device for injecting gas into the molten resin is fixed at a certain point in the mold, and the parts forming the cavity of the mold are all made of the same material, so the cooling rate of the injected molten resin is partially reduced. Difficult to adjust, rib R
The vicinity of the root of the (thick portion) is rapidly cooled and solidified, and the cooling and solidification of the molded article P at the portion near the surface of the main body M is relatively slow. Therefore, the injected gas is easily dispersed through the portion of the molded product P near the surface of the main body M, and the hollow portion V is easily formed in the portion of the main body M near the surface. Conversely, it is difficult for the hollow portion V to be formed at the intersection of the main body portion M and the rib R where the thickness is maximized. As a result, there has been a problem that the strength of the portion near the surface of the main body portion M is reduced, and the appearance is likely to be poor. (See Fig. 4)

[0005] In addition, the vicinity of the root of the thick portion R is rapidly cooled.
In order to be solidified, the pressure of the injected gas must be increased, and expensive equipment such as a high-pressure gas production device is required. Further, there is also a problem that distortion is left in the molded product due to high pressure of the gas to be injected, which causes deformation and breakage.

Therefore, as a technique for solving such a problem, Japanese Patent Laid-Open Publication No. Hei 5-245867 discloses a technique in which a fluid injection device inserted into a portion where a thick portion is formed is provided with a fluid in a thick portion of a molten resin. Before or / and while injecting
A hollow injection molding method and apparatus are disclosed, wherein the method and apparatus are configured to retreat a controlled distance.

[0007]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 5-245.
The technique described in 867 can easily and effectively inject the fluid into the molten resin even when the fluid pressure is low,
Thereby, a molded product with less sink marks, warpage, distortion and the like is formed. However, since the fluid injection device is provided with a movable mechanism that moves forward and backward in the mold and mechanically operates them, the mold structure is complicated and expensive, and the shape of the protruding pin, cooling circuit, product, etc. is restricted. There is a problem that is easy to receive.

The present invention has been made in view of the above-mentioned problems of the prior art, and a hollow portion can be formed at an optimum position where sink, warpage, distortion, etc. do not occur in a molded product. An object of the present invention is to provide a mold for gas injection injection molding, which has a simple structure and can use a low-pressure gas, and in which the structure of the mold and the shape of the product are hardly restricted.

[0009]

In order to achieve the above object, the present invention provides an injection molding method for producing a resin molded article having a hollow portion by injecting a molten resin and then injecting a gas into a thick portion thereof. In the molding die, the injection molding die is composed of a main body and a nest having a concave portion for forming a thick part in the molded product on the surface, and the nest portion extends in a depth direction of the concave from the main body side. Toward, thermal conductivity of 0.1 to 0.5 cal / (cmsec.
C), and a first layer having a thickness smaller than the thickness of the molded article main body, and a second layer comprising a material having a thermal conductivity of less than 0.1 cal / (cm · sec · ° C.). Consisting of:

In the present invention, the material constituting the first layer portion has a thermal conductivity of 0.1 to 0.5 cal / (cm · sec).
・ ℃) is important. Thermal conductivity is 0.1ca
If the temperature is less than 1 / (cm · sec · ° C.), the temperature of the molten resin at the center of the cross section of the thick portion is too high due to insufficient heat radiation, and the direction of the flow path after gas injection tends to be unstable. Therefore, the position of the hollow portion tends to be unstable. Also,
If it exceeds 0.5 cal / (cm · sec · ° C.), cooling and solidification of the molten resin starts before gas injection, and the gas pressure must be increased. Materials constituting the first layer include copper, aluminum, nickel, and alloys thereof.

The thickness of the first layer portion varies depending on the size of the nest portion, the area of the opening of the concave portion, the thickness of the molded article main body, and the like, but must be smaller than the thickness of the molded article main body. For example, in the case of a molded product main body having a thickness of 1.6 to 3.0 mm,
It is preferably set to 0.002 to 2.0 mm. If the thickness of the first layer exceeds 2.0 mm, the high-temperature portion of the thick portion in contact with the second layer is biased toward the surface side of the molded article main body, causing sink marks on the surface of the molded article main body. It will be easier.

When the thermal conductivity of the material constituting the second layer portion exceeds 0.1 cal / (cm · sec · ° C.), the heat radiation from the surface of the thick portion becomes excessive and the cooling rate becomes high. In other words, the flow path after gas injection approaches the surface of the molded article main body, the wall thickness is reduced, and the strength of the molded article main body may be reduced. As the material constituting the second layer portion, a material obtained by impregnating a porous metal with a thermosetting resin having excellent heat resistance, such as an epoxy alloy, and curing the material is preferably used.

The thickness of the second layer is preferably 2 to 10 mm when the thickness of the first layer is 0.002 to 2.0 mm, for example. If it is less than 2 mm, the heat insulating effect is small, so that the molten resin solidifies quickly and the gas pressure must be increased. If the thickness exceeds 10 mm, the heat radiation is insufficient, so that the temperature of the molten resin in the central portion of the cross section of the thick portion is too high, and the direction of the flow path after gas injection tends to be unstable. Tends to be unstable.

Further, the nested portion used in the present invention is not limited to the structure of only the first layer portion and the second layer portion. May be provided.

The gases used in the present invention include:
Although air, nitrogen, helium and the like can be used, easily available and inexpensive air is preferably used.

(Function) By bringing a material having a high thermal conductivity of the first layer portion into contact with the back surface side of the molded article main body portion, the resin in that portion is rapidly cooled and hardened, and the thick layer portion has the second layer portion. By contacting a material having a low thermal conductivity, the cooling and hardening of the thick portion can be delayed more than the other portions, and a hollow portion can be formed at the center. Then, by applying a gas pressure (10 to 50 kgf / cm ² ) to the hollow portion and cooling and solidifying the resin while pressing the resin against the surface of the mold, a molded product with less sink marks and warpage can be obtained.

The nest portion is compact, and the material and thickness of the first layer portion and the second layer portion can be selected according to the shape and size of the molded product and the type of resin. It is simple and does not require complicated moving mechanisms.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a part of a molded product molded by using the present invention, and FIG. 2 is an explanatory view of a main part showing an embodiment of an injection mold of the present invention. FIG. 2B is a longitudinal sectional view taken along line XX. In addition, this injection molding die is obtained by modifying a conventional die in which a molded product P shown in FIG.

As shown in FIG. 1, the molded product P has a thickness of 3 m.
The molded product main body M has a thin plate shape m and a plurality of ribs R (thick portions) formed below the molded product main body M. A portion where the molded article main body portion M and the rib R intersect is a maximum thickness portion T, and a hollow portion V is formed substantially at the center of the maximum thickness portion T.

As shown in FIG. 2, the injection mold has a fixed upper die 1 and a movable lower die 2, and the lower die 2 moves upward to close the upper die. Mold 1 and lower mold 2
A cavity 3 is formed between them. Then, the molten resin melted and kneaded by a molding machine (not shown) is injected from a nozzle of the molding machine, and a sprue (not shown)
The cavity 3 is filled through a runner and a gate.

The upper mold 1 is an upper mold body for entirely molding the molded article main body M, and the lower mold 2 is composed of a molded article main body M and a rib R.
Lower body 21 for forming the tip of the lower body 21
And a recess 23 having a width of 6 mm for forming a portion of the rib R connected to the molded article main body M is formed on the surface of the nest 22.

The upper mold 1 and the lower mold body 21 are made of carbon steel (thermal conductivity: 0.17 cal / (cm · sec · ° C.)). On the other hand, the nested portion 22 has a thickness of 0.5 mm from above in the depth direction of the concave portion 23 from the cavity 3 side.
Beryllium copper (thermal conductivity: 0.29 cal / (cm
sec. ° C.)) and a thickness of 7 m.
m epoxy alloy (thermal conductivity: 0.025 cal / (c
m · sec · ° C.)).

The lower mold body 21 at the back of the nesting portion 22
A groove 24 extending from the recess 23 is formed in the groove.

Then, at least one portion of the groove 24,
A gas injection nozzle housing hole 4 is formed, and a gas injection nozzle 5 driven by a hydraulic cylinder is movable in the gas injection nozzle housing hole 4 in the vertical direction.

Next, an example in which a molded article is molded by the above-described injection mold will be described. After the polycarbonate resin melted and kneaded by the injection molding machine is injected into the injection molding die shown in FIG.
A molded product P was obtained by injecting f / cm ² of compressed air.

As a result of examining the position and shape of the hollow portion by cutting the obtained molded product P, as shown in FIG. 3, the intersection (maximum thickness portion T) of the molded product main body M and the rib R was found. In the cross-section position,
It was confirmed that a hollow portion V having a substantially uniform cross section reaching the nest portion 22 was formed. No hollow portion was found on the surface of the molded article main body M. No defects such as sink marks, warpage, and local shortage of the thickness of the main body M were found in the molded product P.

[0027]

As is apparent from the above description, by using the injection mold of the present invention, a hollow portion having a substantially uniform cross section is formed in the maximum thickness portion of the molded product. As a result, it is possible to obtain a molded article P having good appearance and high strength without defects such as sink marks, warpage, and local shortage of the thickness of the main body part, thereby improving the quality and productivity of the molded article. I do.

Also, a low-pressure gas can be used,
In addition, since there is no need to provide a fluid injection device or a movable mold part and operate them mechanically, the structure of the mold is simple, the mold and product shape are not restricted, and the mold cost is low. It is cheap.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a part of a molded product molded using the present invention.

FIG. 2 is an explanatory view of a main part showing an embodiment of the injection molding die of the present invention, wherein (A) is a cross-sectional view, and (B) is (A).
FIG. 3 is a longitudinal sectional view taken along line XX of FIG.

FIG. 3 is a longitudinal sectional view of a molded product molded by the injection mold according to the present invention.

FIG. 4 is a longitudinal sectional view of a molded product formed by a conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 upper die 2 lower die 21 lower die main body part 22 nest part 221 first layer part 222 second layer part 23 concave part 24 groove part 3 cavity 4 gas injection nozzle accommodation hole 5 gas injection nozzle P molded product M molded product main body R rib T Maximum thickness V Hollow

Claims (1)

[Claims] 1. An injection molding die for injecting a gas into a thick portion thereof after injecting a molten resin to produce a resin molded product having a hollow portion, wherein the injection molding die comprises a main body and a molded product. And a nested portion having a concave portion on the surface for forming a thick portion. The nested portion has a thermal conductivity of 0.1 to 0.5 cal / (cm · cm) from the main body portion side in the depth direction of the concave portion. sec ・
C), and a first layer having a thickness smaller than the thickness of the molded article main body, and a second layer comprising a material having a thermal conductivity of less than 0.1 cal / (cm · sec · ° C.). A metal mold for injection molding, comprising: