JPH07195436A - Method and apparatus for injection molding - Google Patents

Abstract

PURPOSE:To obtain a gate-cut surface with precision and fine appearance without sink marks having no core exposed thereon and, moreover, obtain a mold item with no sinks having high dimensional accuracy in a sandwich injection molding method. CONSTITUTION:A resin reservoir 19 is provided between a cavity or core 6 and a resin flow path 4 and, after injection, the resin reservoir 19 and flow path 4 are cut while imparting vibration to a punch member 7 before a core layer 17 is solidified during or after the completion of a dwelling process, and the skin layer 16 in the resin reservoir is permitted to thrust and come into contact with the cavity or core 6 so that the core layer 17 is coated with the skin layer 16, followed by effecting a compression molding process thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method in which product compression and gate cutting are performed in a mold during injection molding, and more particularly to a sandwich molding method in which two kinds of resins are filled.

[0002]

2. Description of the Related Art In sandwich molding in which two kinds of resins are injected, generally, a skin material, which is a material called a skin layer for forming a surface of an injection-molded article, is first injected, and then a time is spent. A core material, which is an injection material of a portion called a core layer forming the inside of the injection-molded article, is injected. Next, the skin material and the core material are simultaneously injected, and finally, the skin material is injected for the purpose of cleaning the nozzle tip of the injection molding machine for the next molding, and one step is completed. However, the tip of the nozzle is cleaned by the injection of the skin material in the last step, but in order to save the material and shorten the process, the skin material and the core material are solidified in the state of being injected at the same time. And the core material are mixed. Therefore, when the molded product is taken out of the mold after cooling and solidification and the gate is cut in a later step,
The cut surface of the gate has a mixture of skin material and core material, which is inferior in appearance and strength. Therefore, there is a problem that surface treatment such as painting is required after cutting the gate, resulting in high cost. Further, since the gate cutting and the coating are performed after the injection molding, the defect occurrence rate such as scratches of the product is increased, which is not a preferable means.

Further, in the sandwich molding, since the shrinkage rates of the two kinds of materials after molding are different from each other, there is a problem that sink marks are generated in the molded product and the dimensional stability may be insufficient.
Therefore, for the purpose of reducing sink marks, a method of taking a wide range of molding conditions such as a pressure-holding step, and a partial pressure method of partially pushing in a portion that is prone to sink marks are used. Since the cost increases due to the elongation, the latter method cannot be said to be a preferable means such as causing crack distortion.

Therefore, in Japanese Patent Laid-Open No. 261778/1993, a resin inflow path (runner, gate, etc.) is formed on the abutting surface, in which the gate cutting and the compression molding are performed simultaneously.
And a fixed mold and a movable mold that form a cavity or a core forming a product part, and a resin reservoir is provided between the inflow passage of the resin and the cavity or the core. A punch member that can be pushed in and that can cut the inflow path and the resin reservoir is slidably arranged in a movable mold, and resin is injected and filled from a sprue, and micro vibration is applied to the punch member after injection and filling. Meanwhile, there is disclosed an injection molding method in which the punch member is forcibly displaced to perform so-called gate cutting for cutting the resin inflow path and the resin reservoir portion, and at the same time, the punch member is pressed into the cavity or the core material to perform compression molding. .

[0005]

According to this method, since the gate cutting and the compression molding can be performed during the injection molding process, the molding time is short, and no scratches are generated due to the cutting of the gate in the subsequent process. In addition, since it is compression molded while applying vibration, there is no shrinkage and no cracking or distortion. However, on the sprue side of the so-called gate cut surface, the skin layer and the core layer are exposed in layers, while on the product side compression surface, the skin layer and the core layer may be mixed or exposed in layers, which may be inferior in appearance and strength. was there. In view of the above-mentioned problems, an object of the present invention is to obtain a so-called gate cut surface in which a core material is not exposed on the surface, which is precise and beautiful in a mold, and has a high dimensional accuracy without sink marks. At the same time,
An object is to provide an injection molding method and apparatus.

[0006]

In order to achieve the above object, in the present invention, a cavity or core into which a molten resin flows to form a molded article and a resin filled from a sprue into the cavity or core are injected and flowed in. Has an inflow path to
In a sandwich molding apparatus in which two types of resins are injected into the cavity or core to form a skin layer and a core layer, a resin reservoir is provided between the cavity or core and the inflow path. A punch member is provided which is capable of cutting the resin reservoir portion and the inflow path and in which the resin reservoir portion can be inserted into the cavity or the core. The punch member is provided with a molded product contact surface so that a molded product can be formed by the punch member and the cavity or core after the resin pool has entered the cavity or core.

Then, in sandwich injection molding,
A skin resin for forming a skin layer and a core resin for forming a core layer are injected and filled, and a minute vibration is applied to a punch member during or after pressure holding and before solidification of the core layer. After softening the skin layer between the inlet and the inflow path, or while softening, the punch member is forcibly displaced while applying vibration to disconnect the resin reservoir and the inflow channel, and the resin reservoir. This was solved by pressing the mold into the cavity or the core and bringing the molded product contact surface of the punch member into contact with the molded product to compression mold the molded product.

It is preferable that a skin layer having a thickness equal to or larger than the filling thickness of the core layer is formed in the resin reservoir during injection filling.

When the resin member is pushed into the cavity or core by the punch member and then the punch member is brought into contact with the molded product, the punch member is brought into contact with the molded product while giving a minute vibration or gentle reciprocating motion. The finished surface of the molded product is improved by bringing the surface into contact with the molded product for at least a short time.

Further, a fixed mold and a movable mold for forming a resin inflow path and a cavity or core forming a product portion on the contact surface, and a resin reservoir between the inflow path and the cavity or core are provided. In an injection molding apparatus in which a punch member capable of pushing a puddle into the cavity or the core and slidable a punch member capable of cutting the inflow passage and the resin puddle is arranged in a movable mold, the resin puddle portion is an inflow part punch member. By providing a space between the sliding part and the punch member,
Makes it easier to control the capacity of the skin layer during pressing.

[0011]

In the above-mentioned sandwich molding, the resin for forming the skin layer, which is previously injected, first comes into contact with the surface of the mold and solidifies relatively quickly. On the other hand, since the resin forming the core layer is injected between the skin layers, the solidification speed of the resin is slightly slower than that of the skin layers. Therefore,
After the injection is completed and during or after the pressure holding, before the core layer is solidified, the punch member is vibrated so that the resin reservoir portion is pushed toward the cavity or the core, and the skin layer is softened. Although the deformation starts, the core layer still has fluidity, so that it is pushed by the skin layer due to the thrust of the punch member, and is compressed and moved to the resin inflow path side and the cavity side. At this time, if the core layer is solidified or the fluidity is lowered, the skin layer cannot smoothly extrude the core layer, the core layer breaks through the skin layer, or the skin layer and the core layer are vibrated by the vibration energy of the punch member. Cause problems such as mixing.

At the same time, the side surface of the punch member is brought into contact with the space between the inflow portion and the resin reservoir portion to move the punch member, so that the inflow portion and the resin reservoir portion are cut by shearing.
The cut surface on the inflow side has a skin layer and a core layer which are substantially layered.

On the other hand, on the resin reservoir side, while the punch member vibrates, the skin layer is pushed in and the core layer is pushed into the cavity or core side through the skin layer. Then, when the punch member approaches the cutting completion position of the inflow portion, the skin layer on the punch member side and the skin layer on the cavity or core contact each other. Further, when the punch member is compressed while applying vibration, the skin layers are combined and the core layer is covered with the skin layer. This action is similar to the relationship between bean paste (corresponding to the core layer), which is the contents of Daifuku rice cake, and mochi (corresponding to the skin layer), which is skin.

Further, when so-called vibration compression molding is performed in which the punch member is pushed in while giving a minute vibration, the resin is compressed while the vibration energy is replenished, so that a highly accurate injection molded product without shrinkage or cracking is obtained.

Since the skin layer on the punch member side when the punch member is inserted forms the outer shape of the molded product after compression molding, the core layer cannot be extruded and the core layer is exposed if the thickness is thin. Therefore, by making the thickness of the skin layer on the punch member side of the resin reservoir larger than the thickness of the core layer, the core layer is reliably extruded and the core layer is prevented from being exposed.

When the resin member is pushed into the cavity or core by the punch member and then the punch member is brought into contact with the molded product, the punch member is brought into contact with the molded product while giving a minute vibration or a gentle reciprocating motion. When the surface is brought into contact with the molded product for at least a short time, the contact surface of the punch member is transferred to the molded product to improve the surface accuracy of the molded product.

If a space is provided between the punch member sliding portion and the inflow portion of the resin reservoir portion, the skin resin will be preferentially supplied to this space when the resin is injected, and a large amount of skin will be present. Layers can be easily secured. Therefore, even if the skin layer in the other portion is thinner than the core layer, the amount of the skin layer in the resin reservoir can be secured, so that the skin resin can reliably confine the core layer and prevent the core layer from being exposed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a sectional view of a mold used in the injection molding method of the embodiment in the case of taking one piece, and FIG. FIG. 3 is a gate part molding state diagram of the injection molding method, and FIG. 3 is a gate cutting state diagram. In each figure, FIG.
Indicates the state after processing.

The die includes a fixed die 2 and a movable die 1, and a runner portion 3, a gate portion 4 which is a resin inflow passage, and a product portion 5 are formed on the contact surfaces of the two die 2, 1. A cavity 7 or a core 6 is formed, and a punch member 7 that forms a part of the gate portion 4 and forms a resin reservoir 19 that can be inserted into the cavity or core 6 is slidable in the movable mold 1. It is movably incorporated. 8 is a sprue, and the runner part 3 connects the gate part 4 and the sprue 8. Punching member 7
With the hydraulic servo cylinder 9, a minute vibration or a gentle reciprocating motion can be selected by program control. A fast response proportional valve may be used in place of the servo valve 12 which gives minute vibration or gentle reciprocating motion. One end of the product discharge pin and the sprue discharge pin are fixed to the ejector plate 15, and the movable mold 1
Penetrate through.

As for the inflowing melted resin 13, a skin material is first injected from a cylinder (not shown) of an injection molding machine, and then a core material is injected after a while. The skin material and the core material are introduced into the cavity or core 6 through the sprue 8, the runner portion 3 and the gate portion 4 to form the product portion 5. As shown in FIG. 2, when the skin material is injected into the mold, the material in the portion in contact with the mold surface is cooled and solidified to form the skin layer 16,
Since the skin layer 16 keeps the internal material in a molten state as a heat insulating function, the core material injected later passes through the skin layer to form the core layer 17. After the resin 13 is injected into the cavity or the core 6, or during the pressure holding process, or during the cooling after the pressure holding is completed, the punch member 7 is compressed by applying no vibration or vibration to the left and right as viewed in FIG. When 7 is forcibly moved, as shown in FIG. 3, the resin in the resin reservoir portion 19 is pushed into the cavity or core 6 while being cut by the cutting portion 21. Since the steps of softening the resin and cutting the gate are completed within just a few seconds, the steps can be completed by the time the cooling of the product portion is completed, which does not impair productivity as compared with conventional molding.

After the gate is cut and the cooling is completed, the movable mold 1 is retracted, the mold is opened, the runner portion 3 and the product portion 5 are taken out, and the molding process is completed, as in normal injection molding. Before the next die clamping, the punch member 7 is returned to its original position by a device (not shown) so as to be ready for the next molding.

Furthermore, while the punch member 7 is slightly vibrated by the servo cylinder 9, the side wall of the punch member 7 is rubbed and rubbed against the cut product surface 18 for a short time to further clean the product surface. You can The vibration of the punch member 7 may give a gentle reciprocating motion for a short time. The shape of the punch member is shown in FIGS.
Although it may have a contact surface 20 parallel to the inflow path as shown in FIG. 2, it may be oblique or curved as will be described next. What is important is that the shape and direction be such that the resin reservoir can be pushed into the product.

(Experimental Example) FIGS. 4 and 5 show a second embodiment of the present invention, which is an experimental example in the case of actually performing sandwich molding. The same parts as those in the first embodiment described above are designated by the same reference numerals and a part of the description is omitted. The product was a lid of a container, and a recycled material of ABS was used as a core resin and an unused material of ABS was used as a skin resin. As injection conditions, resin injection time is 20 seconds, pressure holding time is 5 seconds, and punch member vibration frequency is 20 seconds.
The punch member was plunged with the plunge working time of 3 seconds during the holding frequency of Hz, the punch member amplitude of 0.2 mm, and the pressure holding time. FIG. 4 shows a state during injection molding based on a longitudinal section of a resin which is simply solidified after injection of resin by sandwich molding without cutting compression molding of the present invention. FIG. 5 is a longitudinal section of a product molded according to the present invention. In FIG. 4, the tip 20 of the punch member 7 is made to abut on the product 5 obliquely so as to be part of forming the product shape.
Further, since the product contact surface 18 of the punch member is inclined, a large amount of the skin layer 16 is secured as shown in FIG. Further, by lowering the punch member tip 20 to the position of the chain double-dashed line 27, a larger amount of skin layer can be secured. The punch member 7 is pushed into the product side as shown by the dotted line 22 in FIG. The dotted line 23 is the cutting surface, and the dotted line 22 is the punch contact surface.
Further, the inflow passage 4 is provided in the same shape from the runner 3 so that the resin can flow into the cavity or the core 6 via the resin reservoir 19.

As shown in FIG. 5, according to the present invention, it can be seen that the skin layer 16 is shaped to press the core layer 17 and to confine the skin layer 17.
In particular, the skin layer 24 at the punch member contact surface 18 is pushed toward the core layer 25, and it can be seen that the skin layer formed on the punch member side at the time of resin injection filling pushes the core layer. It can be seen that the amount of skin layer (resin) on the punch member side plays an important role. Further, as shown in the lower right end portion 26 in FIG. 5, the punch member side skin layer and the cavity or core side skin layer are welded by the vibration energy applied from the punch member between the inflow path side and the resin reservoir portion, and the core layer is inflow path. It can be seen that the part and the molded product are separated.

[0025]

According to the present invention, in the sandwich injection molding, the skin resin forming the skin layer and the core resin forming the core layer are injection-filled, during or after the pressure holding and before the solidification of the core layer, After a minute vibration is applied to the punch member, the skin energy between the resin reservoir and the inflow path is softened by this vibration energy, or the punch member is forcibly displaced while being vibrated while being softened, and the resin reservoir The core and the inflow path are cut, the resin reservoir is pushed into the cavity or the core, and the molded product contact surface of the punch member is brought into contact with the molded product so that the molded product is compression molded. The layer can be confined by the skin layer, so that a precise and beautiful so-called gate cut surface with no core material exposed on the surface can be obtained in the mold, and there is no sink mark and the dimensional accuracy is high. Shape article was to provide an injection molding method and apparatus are simultaneously obtained.

Further, if a skin layer having a thickness larger than the filling thickness of the core layer is formed in the resin reservoir during injection filling, the core layer can be more surely prevented from being exposed.

Further, by providing a space between the edge portion of the inflow portion punch member and the punch member in the resin reservoir portion, the capacity of the skin layer at the time of pushing can be easily controlled or ensured, and stable molding can be performed. You can get the goods.

[Brief description of drawings]

FIG. 1 is a mold cross section showing an injection molding method used in an example of the present invention.

FIG. 2 is an explanatory diagram at the time of resin injection according to the injection molding method of the first embodiment of the present invention.

FIG. 3 is an explanatory view showing the injection molding method of the first embodiment of the present invention.

FIG. 4 is an explanatory view showing a state at the time of injection of resin according to the second embodiment of the present invention.

FIG. 5 is a vertical sectional view of a molded product of an experimental example in the second embodiment of the present invention.

[Explanation of symbols]

 1 movable mold 2 fixed mold 3 runner part 4 inflow path (gate part) 5 molded product (product part) 6 cavity or core 7 punch member 8 sprue 9 servo cylinder 10 product discharge pin 11 sprue discharge pin 12 servo valve 13 resin 14 Servo Cylinder Rod 15 Ejector Plate 16, 24, 26 Skin Layer 17, 25 Core Layer 18 Molded Product Contact Surface 19 Resin Reservoir 20, 27 Punch Member Molded Product Contact Surface (Tip) 21, 23 Cut Surface

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Norinaga Yoneoka 4-11-4 Nishikawaguchi, Kawaguchi City, Saitama Prefecture Nissui Kako Co., Ltd.

Claims (4)

[Claims] 1. A cavity or core into which a melted resin flows to form a molded article, and an inflow path into which the resin filled from a sprue is injected and flowed into the cavity or core, and two kinds of resins are provided in the cavity or core. In a sandwich molding apparatus for injecting a resin to form a skin layer and a core layer, a resin reservoir portion is provided between the cavity or core and the inflow passage, and the resin reservoir portion and the inflow passage can be cut and The skin layer is provided with a punch member having a resin contact portion which can be inserted into the cavity or core and has a molded product contact surface for forming a molded product with the cavity or core after the resin pool is projected into the cavity or core. The punch resin is injected and filled with the skin resin forming the core layer and the core resin forming the core layer, and a minute vibration is applied to the punch member during or after the pressure holding and before the core layer is solidified. After the softening of the skin layer between the resin reservoir portion and the inflow path by this vibration energy, or while being softened, the punch member is forcibly displaced while applying vibration, and the resin reservoir portion and An injection molding method, characterized in that the inflow path is cut and the resin reservoir is pushed into the cavity or the core so that the punch contacting surface of the punch member contacts the molded product. 2. The injection molding method according to claim 1, wherein a skin layer having a thickness equal to or larger than the filling thickness of the core layer is formed in the resin reservoir portion during injection filling. 3. The injection molding method according to claim 1, wherein when the resin reservoir is pushed into the cavity or core to bring the punch member into contact with a molded product, a minute vibration is applied to the punch member. An injection molding method, characterized in that the molded product is finished by bringing the molded product contact surface of the punch member into contact with the molded product for at least a short time while giving a gentle reciprocating motion. 4. A fixed mold and a movable mold which form a resin inflow passage and a cavity or core forming a product portion on the abutting surface, and a resin reservoir between the inflow passage and the cavity or core. In an injection molding apparatus in which a punch member capable of pushing a puddle into the cavity or the core and slidably having a punch member capable of cutting the inflow passage and the resin puddle is disposed in a movable mold, the resin puddle portion is the inflow portion. An injection molding apparatus, characterized in that a space is provided between the punch member sliding portion and the punch member.