JPH08197599A - Production of thin-walled molded product - Google Patents

Abstract

PURPOSE: To simplify a mold structure and to produce a thin-walled molded product excellent in strength such as rigidity or the like by providing a thick- walled part for promoting the flow of the resin of a thin-walled part to obtain the resin flow led by the thick-walled part having effect in the lowering of the filling pressure of the resin. CONSTITUTION: Compressed gas is injected from a gas gate 6 in succession to the injection of a resin. A hollow part is formed to a thick-walled part by the injection of the compressed gas. After dwelling is performed for a definite time by the compressed gas, the compressed gas is discharged to take out a molded product from a mold. By allowing the resin to flow in the order of first, second and third thick-walled parts 3, 4, 5 so as to lead resin flow by the thick-walled parts, the third thick-walled part 5 becomes the filling position of the resin and, therefore, the filling of the resin can be performed under low pressure. By effectively providing the thick-walled parts promoting the flow of the molten resin to a thin-walled molded product and obtaining the resin flow led by the thick-walled parts having effect for lowering the filling pressure of the resin, a mold structure becomes simple and the filling of the resin can be performed under low 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 producing a thin wall molded product.

[0002]

2. Description of the Related Art Conventionally, in injection molding of thin-walled molded products,
Since the thin portion has extremely high filling pressure, it is difficult to form the thin portion, and in order to solve this problem, for example, JP-A-3-
In Japanese Patent No. 87217, there is described a method for producing a product having a changed wall thickness in which a thin portion is formed by partially or entirely compressing a resin after injection. Further, Japanese Patent Application Laid-Open No. 6-64002 discloses an injection molding method in which a resin product having a relatively large size and a thin wall is provided with a plurality of resin injecting portions to reduce the resin filling pressure to form the thin wall portion. Has been described. Further, as another method, there is an injection molding method in which a thin portion is formed by using a resin having extremely excellent fluidity.

[0003]

However, as described in JP-A-3-87217, it is necessary to separately incorporate a compression mechanism in the mold in order to compress the resin. There are problems that the cost for molds and equipment increases, and that injection molding becomes complicated and productivity decreases. Further, the latter Japanese Patent Laid-Open No. 6-640 mentioned above.
In Japanese Patent Laid-Open No. 02-202, since a plurality of resin injection parts are provided, the structure of the mold becomes complicated, and the cycle is lengthened due to successive resin filling, resulting in poor productivity.
There are problems that the mold structure becomes complicated and the manufacturing cost increases, and strength such as rigidity is insufficient because the molded product is composed of only a thin portion.

The present invention has been made in view of the above problems, and an object thereof is to solve these problems and to promote the flow of resin in the thin portion. A method for manufacturing a thin-walled molded product that simplifies the mold structure and provides excellent strength such as rigidity by providing a thick-walled portion and making the resin flow led by the thick-walled portion that is effective in reducing the resin filling pressure. Is provided.

[0005]

A method for manufacturing a thin-walled molded article according to the present invention is a method for manufacturing a thin-walled molded article by injection molding in which a thick wall portion is partially provided, and mold shape data,
Using the physical properties of the resin and molding conditions as the initial conditions, the pressure loss of the resin flowing through the thin and thick parts is calculated using the difference method or the finite element method, and this pressure loss is the hydraulic equivalent diameter of the thick part and the thin wall. The thin and thick parts are set to be inversely proportional to the product of the wall thickness of the part, and for the shape composed of only the thin part, the thick part is moved from the gate to the final filling position obtained by resin flow analysis. If the resin flow front reaches the tip of the thick part, the thick part is provided from the vicinity of the resin flow front,
The resin flow analysis is repeated until the resin completely fills the cavity, and the thick portion is provided.

In the above, the proportional region is determined by plotting the pressure loss and the reciprocal of the product of the hydraulic equivalent diameter of the thick portion and the thin portion, as in the pressure loss correlation graph shown in FIG. This region can be a region of the size of the thick portion that has the effect of reducing the pressure.

The design of the thick portion using the resin flow analysis will be described below with reference to the drawings regarding a specific thin molded product having a box shape. 2 to 4 are perspective views for explaining the design process for forming the thick portion of the thin-walled molded product 10, with the bottom as the upper surface. The resin flow analysis is performed on the box shape 1 composed of only the thin portion, and the final filling position 1a of the resin is obtained from the gate 2 as shown in FIG. Next, from the gate 2 toward the final filling position 1a, first thick-walled portions 3 that fill the area of the box shape 1 are provided to intersect along the diagonal direction of the bottom surface, and further extended to the end of the corner portion. Set up.

The resin flow analysis is performed again. When the resin flows under the initiative of the thick portion 3 and the resin flow front 1b reaches the tip of the thick portion 3 and is filled, as shown in FIG. Two second thick portions 4 that fill the area are provided in the vertical direction on each side surface. Further, the resin flow analysis is performed, and when the resin flow led by the thick portion 4 is completed, as shown in FIG.
One strip is provided on each side in the vertical direction.

When the resin flow analysis is performed again, the resin flow is led by the thick wall portion, and is performed in the order of the first thick wall portion 3, the second thick wall portion 4, and the third thick wall portion 5, and the box shape 1 Filling of the resin is completed so as to fill the entire area of.

As described above, the first thick portion 3, the second thick portion 4, and then the third thick portion 5 are made to flow in the order of the thick portion of the resin, whereby the third thick portion 5 is formed. Since is the final resin filling position, the resin can be filled at a low pressure.
Further, at least one of the thick portions needs to communicate with the gate.

When the pressure-holding pressure in the injection process is performed by the resin filled in the cavity, the resin in the thin-walled portion rapidly cools and solidifies to make it difficult to hold the pressure. It is preferable that they are in communication with.

Further, in the case of a molded product having a hollow portion, if the holding pressure is carried out by the pressurized fluid, even if the injection position of the pressurized fluid is one, it must be communicated with all the thick portions. is necessary. It is sufficient that the pressurized fluid can enter the thick portion provided for communication, and it does not have to be a region in which the reciprocal of the product of the pressure loss and the hydraulic equivalent diameter of the thick portion is proportional. Further, the injection location of the pressurized fluid is preferably upstream of the resin gate or inside the cavity near the gate.

Further, when the pressurized fluid is injected from a plurality of places, it is not necessary to communicate with all the thick portions, and it is sufficient to provide an injection portion in each thick portion to inject. or,
When the injection location of the pressurized fluid is restricted due to the structure of the mold, it can be used together with the communication to the thick portion.

When the hydraulic equivalent diameter of the thick portion is D, it can be calculated by the following formula. D = 4S / L Here, S is the cross-sectional area of the thick portion, and L represents the peripheral length that contributes to heat transfer. In this case, the sectional shape of the thick portion is not particularly limited, but a semicircular shape is preferable in consideration of the influence on cooling.

In order to perform injection molding of a thin-walled molded product by using a pressurized gas as a pressurized fluid, in the case of a box-shaped thin-walled molded product as shown in FIG. 4, a gas gate provided at the center of the thick wall portion A method of injecting a pressurized gas from No. 6 is adopted. At this time, the amount of resin to be filled in the cavity may be any amount sufficient to fill the cavity in volume or slightly insufficient amount, but sufficient amount to prevent the generation of hesitation lines. Filling is preferred.

Following the injection of the resin, a pressurized gas is injected from the gas gate 6. The injection of this pressurized gas forms a hollow portion in the thick portion. After holding the pressure for a fixed time with the pressurized gas, the pressurized gas may be discharged and the molded product may be taken out from the mold.

Examples of molding materials used in the method for producing a thin-walled molded article of the present invention are: polyethylene resin, polypropylene resin, polybutene resin, polycarbonate resin, polystyrene resin. -Polyethylene ionomer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, acrylonitrile-butadiene-styrene copolymer. -Vinyl chloride resin, chlorinated vinyl chloride resin, vinylidene fluoride resin, polytetrafluoroethylene, polyphenine ether, polyphenylene sulfide. -Polyamide, polysulfone, polyethersulfone, polyetherimide, polyetheretherketone. ·polyethylene terephthalate. -A thermoplastic resin such as a liquid crystal polymer can be used.

Further, thermoplastic resins capable of injection molding such as those obtained by filling the above-mentioned thermoplastic resins with glass fiber, talc, etc., and polymer alloys obtained by combining these may be used.

As the pressurized gas injected into the cavity,
In the case of a gas body, generally an inert gas such as nitrogen gas or carbon dioxide gas is suitable, but other dry air, a gas body which has poor reactivity and does not adversely affect the molten resin under the molding temperature condition such as deterioration or the like is used. It is also possible to use.

[0020]

In the method for producing a thin-walled molded product of the present invention, as described in detail in the above section, the thin-walled molded product is effectively provided with a thick wall portion for assisting the flow of the molten resin, and the resin filling pressure is increased. The resin flow is mainly driven by the thick-walled part, which is effective for lowering the pressure of the mold, and the mold structure is simple, and the resin can be filled at a low pressure, making it easy to mold thin-walled products with excellent strength such as rigidity. Now you can do it.

[0021]

Embodiments of the injection mold of the present invention will be described with reference to the drawings. [Example 1] The thin-walled molded product shown in Fig. 4 was molded.
The outer dimensions of this box-shaped thin-walled molded product with a bottom are 300c in the vertical direction.
m × width 320 cm × height 140 cm, the thick portion that assists the flow of the molten resin is semicircular, and the thick portion 5 has a radius of 2.
The thickness of the thick portion 6 was 3 cm, and the radius was 1.0 cm.

Using a 350-ton injection molding machine, a polycarbonate resin and an acrylonitrile-butadiene-styrene copolymer (Cycoloy Japan GE) were used as molding materials. Also, the molding conditions are a cylinder temperature of 250.
℃, mold temperature 50 ℃, injection rate is 500cc / s,
Injection molding was performed. As a result, the gate pressure is 460k.
The resin could be filled at a low pressure of g / cm ₂ . [Comparative Example 1] According to the above-described Example 1, a thin-walled molded product having no thick-walled portion was injection-molded. This result is
When the gate pressure was 700 kg / cm ₂ , the mold was opened and the resin could not be filled up to the end.

[0023]

According to the method for producing a thin-walled molded article of the present invention, the thin-walled molded article is effectively provided with a thick-walled portion for facilitating the flow of the molten resin to effectively reduce the filling pressure of the resin. By using the resin flow led by the section, the mold structure is simplified, and the resin can be filled at a low pressure, so that it is possible to easily form a thin molded product having excellent strength such as rigidity. Therefore, it is preferably used as a method for producing a thin-walled molded product.

[Brief description of drawings]

FIG. 1 is a correlation graph of pressure loss.

FIG. 2 is a perspective view illustrating a design process for forming a thick portion of a thin molded product.

FIG. 3 is a perspective view illustrating a design process for forming a thick portion of a thin molded product.

FIG. 4 is a perspective view illustrating a design process for forming a thick portion of a thin molded product.

[Explanation of symbols]

 1 Box shape 1a Final filling position 1b Flow front 2 Gates 3, 4, 5 Thick wall 6 Gas gate 10 Thin wall molded product

Claims (1)

[Claims] 1. A method of manufacturing a thin-walled molded article by injection molding, in which a thick-walled portion is partially provided, wherein a difference method or a finite element is used, with mold shape data, resin physical properties, and molding conditions as initial conditions. The pressure loss of the resin flowing through the thin and thick parts is calculated using the method, and this pressure loss is inversely proportional to the product of the hydraulic equivalent diameter of the thick part and the thickness of the thin part. Is set, and for the shape composed of only the thin part,
A thick part is provided from the gate to the final filling position determined by resin flow analysis, and the resin flow analysis is performed on the shape with this thick part. When the resin flow front reaches the tip of the thick part, the resin flow A method for producing a thin-walled molded article, characterized in that a thick-walled portion is provided from near the front, and the thick-walled portion is provided by repeating the resin flow analysis until the resin completely fills the cavity.