JPH04164617A - Mold for injection molding - Google Patents

Abstract

PURPOSE:To prevent generation of defective molding even under a long-term use of a mold, by a method wherein a plurality of fine grooves extending in the direction of ejection of a molding are provided in an outer circumferential surface of a core. CONSTITUTION:Mold register of a stationary mold 1a and movable mold 1b is performed at a PL in an injection mold, through which a cavity 3 of a cuppy bottomed cylindrical injection molding 2 is constituted. The movable mold 1b is obtained by fitting a core bushing 9 forming forms of the inside of the bottom and an inner circumferential surface of a cylindrical part over an annular stripper bushing 10 forming a form of an end surface of an opening of the molding 2. A plurality of fine grooves 21 extending in an ejecting direction of the molding 2 are formed in an outer circumferential surface 9a of the core bushing 9 extending over the whole circumference, grooves, 21 each have a difference in heights of 0.1-0.7mum and a pitch between the grooves 21 each is 40-400mum. After formation of the molding 2 by injecting molten resin within the cavity 3 and solidifying the same, at the time when the stripper bushing 10 is ejected, air is introduced swiftly into an inner space 22 of the molding 2 from the outside through those grooves 21 and generation of negative pressure in the inner space 22 is prevented.

Description

[Detailed description of the invention] (Industrial application field).

The present invention relates to an injection mold for injection molding a bottomed cylindrical shaped article such as a container for photographic film (prior art). If the inside of the molded product becomes negative pressure during ejection, molding defects such as sink marks and scratches will occur.

For this reason, conventionally, as disclosed in JP-A No. 62-62721, an air hole is provided inside the core using a nest, and air is supplied into the molded product from the gap between the nest at the tip of the core. Efforts have been made to prevent the generation of negative pressure.

(Problem to be solved by the invention) However, when such a negative pressure prevention structure is adopted, if the mold is used for a long period of time, resin gas and dust will block the gap and air will not be able to flow in, resulting in the molded product being damaged. Negative pressure may develop inside the product, resulting in molding defects.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide an injection mold that can prevent molding defects even when the mold is used for a long period of time. It is.

(Means for Solving the Problems) The injection mold according to the present invention has a plurality of fine grooves extending in the direction of ejecting the molded product on the outer peripheral surface of the core, thereby preventing the inside of the molded product from entering the molded product when ejecting the molded product. This is designed to ensure that air can be introduced reliably, thereby achieving the above objective.

That is, a gate bush in which a gate is formed at a position facing the outer surface of the bottom of the bottomed cylindrical injection molded product, a cavity bush that forms the outer peripheral surface of the cylindrical part of the molded product, and a cavity bush that forms one inner surface of the molded product. In an injection mold, the core has a height difference of 0.1 to 0.7 μm and a pitch of 40 to 400 μm in a portion of the core that forms the inner circumferential surface of the cylindrical portion of the molded product.
The molded article is characterized in that a plurality of grooves are formed extending in the direction in which the molded article is ejected.

(Operations and Effects of the Invention) As shown in the above configuration, the injection mold according to the present invention has a height difference of 0.1 to 067 μm, a pitch of 0.1 to 067 μm, and Since multiple grooves of 40 to 400 μm extending in the molded product ejection direction are formed, air can be reliably introduced into the molded product during molded product ejection without clogging caused by resin gas or dust. I can do it.

Therefore, occurrence of molding defects can be prevented even when the mold is used for a long period of time.

Furthermore, according to the present invention, since there is no need to nest the tip of the core as in the conventional case, the cooling water hole can be brought close to the core tip surface, thereby improving the cooling efficiency of the bottom of the molded product. Therefore, bottom sinkage can be reduced and the molding cycle can be shortened.

The height difference and pitch of the grooves were set within the above ranges because while it is preferable to have many large grooves in order to prevent molding defects, if too large grooves are formed, the groove shape may become convex. If a photographic film cartridge or the like is stored in a molded product that has been transferred, the convex parts may be scraped by the stored product and powder may be generated, and if the molded product is transparent, the grooves may If the size is too large or there are too many, transparency will be lost, so these are balanced.

In addition to the above configuration, as shown in claim (2), a concave spherical correction is applied to the portion of the gate bush that forms the bottom outer surface of the molded product, and the core forms the bottom inner surface of the molded product. By adopting a configuration in which the convex portion has approximately the same amount of spherical correction as the gate bushing, even if the molding cycle is further increased and bottom sink occurs, that amount of correction will be made. Therefore, it is possible to improve the molding cycle.

(Examples) Examples of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. M1 is a side sectional view showing one embodiment of an injection mold according to the present invention.

In this injection mold, a fixed mold 1a and a movable mold 1b are fitted together at the PL (parting line) in the figure, and these two molds are used to injection mold a bottomed cylindrical shape. A cavity 3 of a product 2 (specifically, a container for photographic film) is constructed. The fixed mold 1a is made up of a gate bushing 4 that forms the outer shape of the bottom part of the molded product 2, and a cavity bushing 5 that forms the outer peripheral surface shape of the cylindrical part of the molded product 2, which are fixed to each other. A gate 6 and a hot runner 7 formed at a position facing the bottom outer surface of the molded product 2 for filling with molten resin are provided, and the cavity bush 5 is provided with an annular cooling water that surrounds the cylindrical portion of the cavity 3. A hole 8 is formed. On the other hand, the movable mold 1b is made up of a core bushing 9 that forms the bottom inner surface and the inner peripheral surface shape of the cylinder part of the molded product 2, and an annular stripper pusher zlO that forms the shape of the opening end surface of the molded product 2, After molding of the molded product 2 is completed and the fixed mold 1a and the movable mold 1b are opened, the stripper bush 10 moves upward relative to the core bushing 9 to release the molded product 2. It has become.

A circular hole 11 is formed inside the core bush 9, and its tip extends to the vicinity of the tip surface of the core bush 9 facing the bottom inner surface of the molded product 2. This circular hole 1
1 is provided with a partition plate (separator) 12 that divides the hole 11 into left and right halves except for the upper end portion, and this allows the cooling water hole 1 to circulate inside the core bush 9.
3 is formed.

That is, the movable mounting plate 14 fixed to the core bush 9 has a supply hole 15 for supplying and discharging cooling water.
and a pair of communication holes 17a formed to extend left and right at the lower end of the hole 11 of the core bush 9,
The cooling water flowing into the cooling water holes 13 from the supply hole 15 through the communication hole 17a rises inside the cooling water hole 13 along the partition plate 12. Then, it detours above the partition plate 12 and descends inside the cooling water hole 13 along the partition plate 12 again, and flows through the communication hole 17b.
It flows out to the discharge hole 16 of the movable side mounting plate 14 through the. Supply hole 15 at the upper end of the movable side mounting plate 14
An O-ring 18 is provided at the connecting portion between the drain hole I6 and the communicating hole 17a, and at the connecting portion between the discharge hole I6 and the communicating hole 17b, respectively, to prevent cooling water from leaking.

On the inner surface 19 near the tip surface of the core bush 9, that is, on the ceiling surface of the folded part of the cooling water hole 13 at the upper end of the cylindrical hole 11, there is a groove extending approximately parallel to the flow direction of the cooling water flowing inside the cooling water hole 13. A rib 20 that overhangs the cooling water hole I3 is provided.

FIG. 2 is a cross-sectional view of the core bushing 9 shown by the row line in FIG. 1, and FIG. FIG. 3 is an enlarged view of part m in FIG. 2 showing details.

As shown in FIG. 3, the outer peripheral surface 9a of the core bush 9 has a plurality of fine grooves 21 extending in the direction in which the molded product 2 is ejected.
It is formed around the entire circumference. Valley groove 21 has 0 height difference
．． 1 to 0.7 μm, and the pitch between each groove 21 is 40 to 0.7 μm.
It is 400 μm.

The reason why the height difference and pitch of the grooves 21 are set within the above range is that while it is preferable to have large grooves or a large number of grooves in order to prevent molding defects, if too large grooves are formed,
When a photographic film cartridge is stored in a molded product 2 (i.e., a container for photographic film) in which this groove shape is transferred into a convex shape, the convex part may be scraped by the cartridge and powder may be generated, and the molding If the item 2 is a transparent body, transparency will be lost if the grooves are too large or there are too many grooves, so these are balanced.

In addition, in FIG. 1, the molded product 2 of the gate bush 4
A concave spherical correction is applied to the portion of the core bushing 9 that forms the bottom outer surface of the molded product 2, and a convex spherical correction of approximately the same amount as the gate bushing 4 is applied to the portion of the core bushing 9 that forms the bottom inner surface of the molded product 2. is applied.

Next, the operation of this embodiment will be explained.

As shown in FIG. 1, after injecting and solidifying the molten resin into the cavity 3 to form the molded product 2, the movable UL is moved to open the mold, and as shown in FIG. By moving the stripper bushing 10 relative to the core bushing 9 in the direction of the arrow shown in the figure, the molded product 2 is ejected from the core bushing 9.

During this ejection, if the internal space 22 of the molded product 2 becomes negative pressure, molding defects such as bottom sink and scratches may occur. A plurality of fine grooves 21 extending in the direction of protrusion of
are formed, so that when the stripper bush 10 is ejected, air is quickly introduced from the outside into the internal space 22 of the molded product 2 through these grooves 21, and thereby,
This will prevent the generation of negative pressure in the internal space 22. Note that in order to introduce air through the groove 21,
It is necessary for the molded product 2 to move away from the core bush 9 to some extent, but in order to make this operation easier, in this embodiment, FIG. As shown, an annular groove 23 is formed near the PL of the stripper bushing 10, and the annular groove 23 and the core bushing 9 are connected to each other.
A communication groove 24 (depth 1/1100
(about a) is formed.

As described in detail above, the injection mold according to this embodiment has a height difference of 0.1 to 0.7 μm and a pitch of 40 to 40 in the portion of the core bushing 9 that forms the inner peripheral surface of the cylindrical part of the molded product 2.
Since a plurality of grooves 21 of 0 μm are formed that extend in the molded product ejection direction, air can be surely introduced into the internal space 22 of the molded product 2 when the molded product is ejected without causing clogging due to resin gas or dust. can be done.

Therefore, occurrence of molding defects can be prevented even when the mold is used for a long period of time.

In addition, according to this embodiment, since there is no need to nest the core tip as in the conventional case, the cooling water hole 13 can be brought close to the core tip surface, thereby improving the cooling efficiency of the bottom of the molded product 2. Therefore, bottom sinkage can be reduced and the molding cycle can be shortened.

Furthermore, according to this embodiment, since spherical correction is applied to the gate bush 4 and the core bush 9, even if the molding cycle is further increased and bottom sink occurs, the corresponding correction will be made. Therefore, it is possible to improve the molding cycle.

In addition, FIG. 6 shows the difference in the degree of bottom sink due to the presence or absence of the above-mentioned spherical correction in relation to the magnitude of the molding cycle.

[Brief explanation of drawings]

Figure M1 is a side sectional view showing one embodiment of the injection mold according to the present invention, Figure 2 is a sectional view taken along the line ■-■ in Figure 1, and Figure 3 is the section m in Figure 2. FIG. 4 is a diagram similar to FIG. 1, showing the effect of this embodiment. FIG. 5 is an enlarged view of the V section in FIG. 1. FIG. It is a graph. 1a...Fixed type 1b...Movable type 2
...Bottomed cylindrical injection molded product 4...Gate bush 5...Cavity bush 6...Gate 9...
・Core bush (core) 21...Groove 2, 6, I A type + 712 ru, 1□ included

Claims (2)

[Claims] (1) A gate bushing in which a gate is formed at a position facing the outer surface of the bottom of a bottomed cylindrical injection molded product, a cavity bushing that forms the outer peripheral surface of the cylindrical portion of the molded product, and an inner surface of the molded product. In an injection mold comprising a core, a portion of the core that forms the inner circumferential surface of the cylindrical part of the molded product has a height difference of 0.1 to 0.7 μm and a pitch of 40 to 400 μm.
An injection mold according to the above, characterized in that a plurality of grooves are formed extending in the direction in which the molded product is ejected. (2) A concave spherical correction is applied to the portion of the gate bush that forms the bottom outer surface of the molded product, and a convex spherical correction is applied to the portion of the core that forms the bottom inner surface of the molded product. 2. The injection mold according to claim 1, wherein the spherical surface correction is substantially the same as that of the gate bush.