JPH0723223Y2 - Gas press-fitting mold - Google Patents

Description

[Detailed Description of the Invention] (Industrial field of application) The present invention is a back part of a part which is required to prevent sink marks on the surface of an uneven thickness part or a thick part of a molded product made of a synthetic resin. The present invention relates to a mold for molding a molded product having no sink mark by pressurizing gas.

(Prior Art) Various injection-molded products made of synthetic resin having an uneven thickness portion or a thick portion are generally susceptible to sink marks on the surface of the uneven thickness portion or the thick portion, resulting in poor appearance in many cases. .

It is known that sink marks are generated in a portion that is difficult to cool due to a difference in shrinkage amount during cooling.

Conventionally, in order to compensate for this defect, for example, as described in Japanese Patent Publication No. 57-14968, a sufficient amount of molten resin is injected to fill the mold cavity, and then the gas body alone or the molten resin and the gas body are injected. It has been proposed to press and fill the mold cavity to bring the molten resin into close contact with the wall surface of the mold to form a hollow mold without sink marks.

However, in this method, the inside of the wall of the molded product to be molded is made hollow so as to prevent sinking of the surface corresponding to that part, and the peripheral edge of the molded product at a position far from the gas injection gate. It is impossible to press gas into a portion such as an uneven thickness portion or a thick portion of the portion, and it is impossible to prevent sink marks from being generated in this portion.

Further, the molten resin is injected and injected into the mold cavity of the mold to be filled with the resin, and then the pressurized gas body is injected from the gate for gas injection, and the gas body is kept in a pressurized state, A method of cooling the mold and waiting for the solidification of the resin has also been proposed, but this method also cannot prevent the occurrence of sink marks such as an uneven thickness portion and a thick portion at the peripheral portion of the molded product located at a position far from the gate.

(Problems to be Solved by the Invention) The present invention has been made for the purpose of solving the above-mentioned conventional problems, in which a molded product surface having an uneven thickness portion or a thick portion is formed. In order to prevent sink marks from being generated, gas is pressed into the back of parts that need to prevent sink marks, such as uneven thickness parts and thick parts, to form molded products without sink marks. The purpose is to provide a molding die.

(Means for Solving Problems) A gas press-fitting mold of the present invention is a mold for molding a thin-walled molded product, and a cavity for forming a wall of the molded product to be molded. And, there is provided a gas passage part for press-fitting gas into the back part of the molded product which requires prevention of sink mark, and the gas passage part is located below the wall part of the molded product. When the mold is placed in the mold, the center position of the gas injection gate should be at or below the center in the height direction of the thick part consisting of the gas flow path part and the wall part of the molded product. The above-mentioned object is achieved by this.

In the present invention, the molded product having the uneven thickness portion or the thick wall portion, etc., has a sink mark generated on the surface of the molded product at that portion by pressing gas into the back portion of the uneven thickness portion or the thick wall portion. It can be lost.

The present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing a mold of the present invention, which is composed of a fixed mold A and a movable mold B. The mold has a cavity portion 1 forming a wall portion of a molded product to be molded and rib formation. Part 4 and
A gas flow path 3 for pressurizing the gas is provided in the back portion of the rib forming portion via the gas injection gate 2.

FIG. 2 is a partially cutaway perspective view of the movable die B, in which 1 is a cavity for forming a wall, 3 is a gas flow path, 4,
Reference numerals 4'and 4 "are rib forming portions, and 5 is a boss forming portion.

The gas flow path 3 includes a T-shaped main flow path 3 and tributary flow paths 31, 32, 33, 34 branching from the main flow path 3.

The tributaries 31 and 32 extend to the peripheral edge of the cavity 1.

Rib forming portions 4 and 4'are provided in parallel to the backs of the tributary channels 31 and 32, respectively.

Further, FIG. 3 is a view showing the positional relationship of the gas injection gate 2 of the movable mold B. As for the position of the gas injection gate 2, the gas flow path is located below the wall of the molded product. When the mold is placed as described above, the center position of the gas injection gate is located at or below the center in the height direction of the thick portion formed by the gas flow passage portion and the wall portion of the molded product.

FIG. 4 is a perspective view of a molded product molded according to the present invention.

A gas passage b, ribs c, c ′, c ″, and a boss d are provided on the side of the wall portion a.

Next, the usage of the mold of the present invention will be described.

As shown in FIG. 1, by closing the fixed mold A and the movable mold B,
The synthetic resin is injected into the mold from the nozzle, and the gas is pressed into the gas flow path 3 through the gas injection gate 2.

Gas is pressure-input from the gas injection gate 2 through the gas flow path 3 to a back portion such as an uneven thickness portion or a thick portion where it is necessary to prevent the occurrence of sink marks at the peripheral edge of the molded product.

At this time, as shown in FIG. 3, the center of the gas injection gate is located at the center of the gas flow path 3 in the height direction or lower, so that the gas is at least at the center of the gas flow path cross section or lower. Will flow through.

Therefore, the gas does not flow into the molded product wall portion forming portion 1 of the cavity, and it is possible to prevent the strength of the molded product from being lowered due to the formation of the hollow portion in the molded product wall portion a shown in FIG.

As a structure of a mold having such a mechanism, a method such as providing a protrusion on the cavity side of the mold to change the parting line, providing a slide core, or adopting a tunnel gate method is considered. .

By limiting the gas injection gate position in this way, it is possible to prevent gas from flowing into the wall of the molded product during gas injection molding from the nozzle, and to effectively feed it to uneven thickness parts and thick parts. , It is possible to prevent sink marks that occur in that part.

The cross-sectional shape of the gas flow path 3 may be any of square, rectangle, trapezoid, semicircle, inverted triangle, and the like, but the cross-section of the hollow portion formed inside the gas flow path 3 by pressurizing gas is Since an inverted triangle is usually used, the inverted triangle is preferable from the viewpoint of saving the resin raw material.

As the synthetic resin described in the present invention, a general thermoplastic resin used in general injection molding or extrusion molding is used, but it is not limited to this as long as it can be injection molded.

Further, various additives may be added to the synthetic resin.

The gas described in the present invention is a substance that is gaseous at room temperature, and substances such as air, carbon dioxide, nitrogen, etc. having a boiling point below room temperature are used.

The gas is injected from a nozzle by injecting an insufficient amount or a sufficient amount of the molten resin to fill the mold cavity, and then alone or together with the molten resin after injecting the insufficient amount.

Alternatively, the gas may be directly pressed into the mold.

In this case, after injecting the molten resin from the nozzle in an insufficient amount or a sufficient amount to fill the mold cavity, press it directly into the mold, or inject the molten resin from the nozzle in a sufficient amount, and then inject the molten resin from the nozzle. It is injected into the mold while pouring.

By using a mold in which such a gas flow path portion is provided from the gas injection gate to the back of the uneven thickness portion or thick portion of the molded product, there is no sink mark by molding the gas by press molding, and It is possible to obtain a molded product in which gas does not flow on the wall.

(Function) By providing the gas passage, it is possible to reliably press the gas from the gas passage to the back of the uneven thickness portion or the thick portion of the molded product, so that it is difficult to cool the uneven thickness portion or the thick portion. It is possible to prevent the occurrence of sink marks on the surface by pressing from the back when cooling, and especially when the gas flows into the wall of the molded product due to the balance of resin pressure and gas pressure, the gas injection gate The gas flows at least in the center or below the center of the cross section of the gas flow path because the gas is located at the center or below the flow path height direction.

Therefore, the gas does not flow to the wall of the molded product, and it is possible to prevent a hollow portion from being formed in the wall of the molded product.

(Example) Example 1 Thickness (t) 3 mm of wall of molded product shown in FIG. 1 and FIG.
Then, in a mold provided with a cavity portion 1 for forming a thick portion and a gas flow path 3 having a width (w) of 9 mm and a height (h) of 6 mm, a gas injection gate has a diameter of 2 mm and its center is gas. In the center of the flow path, 240t injection molding machine as the device, polypropylene resin as the resin, nitrogen gas as the press-fit gas,
Gas injection molding was carried out under conditions of a mold temperature of 40 ° C., a resin temperature of 240 ° C., an injection time of 2 seconds, a pressure of gas pressure of 60 kg / cm ² , a gas holding pressure of 30 seconds, and a cooling time of 30 seconds.

The molded product had no sink mark on the surface of the thick part and the wall of the molded product was not hollow (see FIG. 5).

Example 2 Gas injection molding was performed under the same conditions as in Example 1 except that the center of the gas injection gate was located 5 mm from the surface of the molded product.

The molded product had no sink mark on the surface of the thick part and the wall of the molded product was not hollow (see FIG. 5).

Comparative Example 1 Gas injection molding was performed under the same conditions as in Example 1 except that the upper surface of the gas injection gate was at the same position as the surface of the molded product.

The wall of the molded product was hollow near the gas injection gate (see FIG. 6).

(Effects of the Invention) The gas press-fitting mold of the present invention has a gas flow path on the back of the wall of the molded product that sends gas from the gas injection gate to a desired site such as an uneven thickness portion or a thick wall portion of the molded product. It is provided, and when the mold is placed such that the gas flow path portion is located below the wall of the molded product, the center position of the gas injection gate is the gas flow path portion and the molded product. Since the thick portion formed of the wall portion is located at the center or below in the height direction, gas does not flow through the molded product wall portion and the molded product wall portion does not become hollow.

Also, it is possible to reliably press gas into the back of the uneven thickness portion or thick portion of the molded product, to prevent the occurrence of sink marks on the surface of the molded product at that portion, and to prevent the occurrence of sink marks without changing its physical properties. It can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of a gas injection molding die of the present invention, FIG. 2 is a partially cutaway perspective view of a movable die B, FIG. 3 is a sectional view showing a movable die and a gas injection gate position, and FIG. FIG. 5 is a perspective view of a molded product molded according to the present invention, FIG. 5 is a cross-sectional view of a gas channel for explaining Examples 1 and 2, and FIG. 6 is a gas channel for explaining Comparative Example 1. FIG. In the figure, A ... Fixed type B ... Movable type 1 ... Cavity molded part wall forming part 2 ... Gas injection gate 3 ... Gas flow path 4,4 ', 4 "... Rib forming part 5 …… Boss forming part 6 …… Runner 7 …… Hollow part a …… Molded product wall b …… Gas pressure inlet c, c ′, c ″ …… Rib d …… Boss

Claims (1)

[Scope of utility model registration request] 1. A mold for molding a thin-walled molded article, comprising:
A cavity for forming a wall of a molded product to be molded, and a gas flow path for press-fitting a gas to the back of a portion of the molded product that needs to prevent sinking are provided, When the mold is placed such that the flow path is located under the wall of the molded product, the center position of the gas injection gate is a thick part formed by the gas flow path and the wall of the molded product. A mold for gas press-fitting, characterized in that it is located at or below the center in the height direction of.