JP2955798B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for injection molding of a thermoplastic resin, an injection molding method and an injection molded product. More specifically, the strength of the weld portion around the weld line of the molded product, which originally produces a weld line and obtains only extremely low weld strength, is significantly improved.
The present invention also relates to an injection molding die, an injection molding method, and an injection molded article having improved weld strength for improving the appearance of a weld portion.

[0002]

2. Description of the Related Art In molding a molded product using a mold shown in FIG.
When the molten resin is injected and filled from below, a plurality of resin flows A ₁ and A ₂ are generated in the cavity immediately below the sprue 3 and a weld line or a weld is formed at a fusion point B where the resin flows merge. Marks occur. Even when the cavity is filled with the molten resin from a single gate, the core 7 provided in the cavity as shown in FIG.
In the case where the resin flows are divided into the resin flows A ₁ and A ₂ due to the above, a weld line is generated at a fusion point B where the separated resin flows are merged and integrated. Furthermore, even when the molded product has an uneven thickness portion, the molten resin to be injected and filled causes the resin to flow divergently due to a difference in the resin filling speed between the thick portion and the thin portion. Weld lines often occur at the part where they are merged and integrated. Such a weld line of a molded product is often caused by a combination of various factors as described above, and it is extremely difficult to obtain a molded product having no weld line in a molded product of an actual complicated shape. . Such a weld line not only causes a linear pattern on the surface and impairs the appearance of the molded product, but also causes the flow tip of the molten resin to simply join and fuse, and is uniform at the flow tip where the viscosity of the resin is high. In some cases, mixing is not performed, and the resin or the filler contained in the resin is oriented in parallel across the weld line, and in the weld portion, strength much lower than the original strength of the resin is obtained. A very serious problem arises.

[0003] As a technique for improving the problem of the strength reduction at the weld portion by a molding method, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 71459 discloses that after a resin is filled using a mold provided with a resin reservoir at a position where a weld line is generated,
There is disclosed a molding method for improving the strength of a weld portion by pushing resin inside a resin reservoir back into a mold.
Japanese Patent Application Laid-Open No. Hei 2-202414 discloses that a plurality of resin flows generated by injection-filling a resin from a plurality of gates having an opening / closing valve are merged and fused to form a gate after a weld line is formed. A molding method is disclosed in which the opening / closing valve is operated to make the filling pressure of the resin flow different so as to disturb the weld portion and improve the strength of the weld portion.

[0004]

However, in the former method (JP-A-48-71459),
It is difficult to generate a sufficient resin flow in the weld portion after the formation of the weld line to disturb the orientation of the resin or filler in the weld portion, and the strength in the weld portion has not been sufficiently improved. Further, the method described in the latter (Japanese Patent Application Laid-Open No. 2-202414) has disadvantages in that not only the structure of the mold and the device becomes complicated, the production cost becomes high, but also it is difficult to control the on-off valve during molding. is there.

[0005]

The inventor of the present invention has conducted intensive studies with the aim of solving the above problems and obtaining a molded article having improved weld strength by using a mold having less structural restrictions. Before the weld line is solidified after the formation of the resin, the resin moves in the weld portion while the resin still maintains fluidity inside, and disturbs the orientation of the resin or filler in the weld portion. Thus, the present inventors have found a method for efficiently improving the weld strength and the like and a mold therefor, and have reached the present invention.

That is, according to the present invention, a molded product cavity or runner is provided on at least one side of the cavity or runner from the point where the molten thermoplastic resin to be injected and filled flows to the point where the resin joins and a weld line is formed. A resin reservoir protruding from the product gate is provided, the gate sealing time of the product gate is longer than the time from when the molten thermoplastic resin passes through the product gate until the weld line is formed, and the weld line is passed after the resin reservoir gate passes. After the step of forming a weld line after the resin has passed through the product gate, using an injection molding mold having a product gate and a resin reservoir gate in which the gate sealing time of the resin reservoir gate is longer than the time required to form the resin gate, Performs the process of sealing the product gate and forms a weld line after passing through the resin sump gate After extent, an injection molding method of performing the step of sealing the resin reservoir gates. Here, the gate sealing time refers to a time from when the injection molding resin passes through the product gate or the resin reservoir gate until the resin is cooled and solidified in the product gate or the resin reservoir gate and the resin flow stops.

[0007]

According to the above-mentioned means, in molding using an injection mold and a molding method in which a resin reservoir is provided at a predetermined position according to the above-described means, the time required for the resin to pass through the product gate until a weld line is formed can be reduced. As long as the gate sealing time of the gate is long and the gate sealing time of the resin reservoir gate is longer than the time from the passage of the resin reservoir gate to the formation of the weld line, the resin is melted by the injection pressure or holding pressure applied to the resin. A pressure difference is generated on both sides of the weld by pouring the resin into the resin reservoir, and the resin on the side where the resin reservoir is not provided is pressed into the resin on the side where the resin reservoir is provided, and the resin or the filler in the weld portion is formed. By disturbing the orientation or the like, the strength of the weld portion is improved, and the weld line becomes less noticeable.

[0008]

EXAMPLES Hereinafter, the mold and the molding method of the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. FIGS. 1 and 2 show a typical mold (molded product) in which a weld is generated, respectively, and in order to improve the weld strength, etc., according to the present invention, a predetermined position, that is, a molten resin to be injected and filled is used. One aspect of a mold improved by providing a resin reservoir protruding from a molded product cavity or a runner on at least one side of a resin flow path from a branch point to a weld portion formed by merging of the resins. is there. Of course, in many actual molds (molded products), such a simple shape is rare, and the method of filling the cavity with the molten resin, the process of forming a weld, and the like are more complicated. Basically, it is possible to follow the mold configuration and molding method described here and described below.

Example 1 Using a mold having a structure as shown in FIG.
A pellet-shaped resin composition having a length of 12 mm, in which P) was mixed with 40% by weight of glass long fiber (GF), was injection-molded. In such a resin composition, the glass fiber length is substantially the same as that of the pellet (the average fiber length is about 12 mm), and is arranged substantially parallel to the length direction of the pellet. The configuration and molding conditions of the main parts of the mold used here are as follows. Resin reservoir dimensions 18mm x 40mm x 4mm thickness Inlet shape 6mm x 2mm Product wall thickness 4mm Inlet dimensions 6mm x 3mm thickness Runner dimensions 6mm x 8mm Molding conditions Cylinder temperature 220 ° C Mold temperature 50 ° C Injection Speed 1.0 m / min On the other hand, for comparison, a similar molded product was molded as Comparative Example 1 without using the resin reservoir of FIG.

In the first embodiment, the resin is filled as shown in FIG. Multiple gates 5 in a single cavity 6
When the molten resin is injected and filled from 5, the molten resin is divided just below the sprue 3, and a plurality of resin flows A ₁ and A ₂ are generated in the cavity as shown in FIG. A weld line or a weld mark is formed at the joining point B where the welding is performed, as shown in FIG. Next, before the weld portion is solidified, filling of the resin from the resin reservoir gate 2 to the resin reservoir 1 starts. At this time, the resin in contact with the mold in the cavity 6 has already started to solidify.
Start moving as (c), when filled fully resin in the resin reservoir 1 is completed, at the time of weld line formation is welded surface B of the resin flow A ₁ and A ₂ has a flat Figure 3 (d) It has a conical shape.

Embodiment 2 FIG. 4 shows a mold provided with a resin reservoir protruding from a runner according to the present invention. Using this mold, polyamide 66 resin (PA) blended with 40% by weight of glass long fiber (GF), length 12mm
Was injection molded. In such a resin composition, the glass fiber length is substantially the same as that of the pellet (average fiber length is about 12 mm), and is arranged substantially parallel to the length direction of the pellet. The configuration and molding conditions of the main parts of the mold used here are as follows. The thickness of the molded product is 4 mm, the thickness of the resin reservoir is 2 mm, and the resin flows into the resin reservoir when filling the molten resin. Is suppressed as much as possible, and the resin flows into the resin reservoir efficiently after the weld line is formed. Resin reservoir dimensions 90mm x 30mm x 2mm thickness Inlet dimensions 6mm x 2mm thickness Product thickness 4mm Inlet dimensions 6mm x 8mm thick Molding conditions Cylinder temperature 290 ℃ Mold temperature 80 ℃ Injection speed 1m / min Therefore, a similar molded article was molded as Comparative Example 2 without using the resin reservoir of FIG. Examples 1 and 2
The tensile strength and elongation of the molded products of Comparative Examples 1 and 2 were measured.

[0012]

[Table 1]

As shown in Table 1, the gate sealing time of the product gate is longer than the time from when the resin passes through the product gate until the weld line is formed, and the weld line is formed after the resin passes through the resin reservoir gate. In the first and second embodiments, in which the gate sealing time of the resin reservoir gate is longer than the time required to perform the process, a great effect can be obtained in both tensile strength and elongation.

The procedure for actually designing a mold is as follows. When the molding conditions such as the resin used, the product gate size, the cylinder temperature, the mold temperature, the injection speed, etc. are determined for a certain product, the injection amount is calculated. Is determined through the product gate and when the weld is formed. For example, the graph shows the correlation between the gate size and the sealing time of the product gate.

[0015]

[Table 2]

If the relationship between the gate size and the gate sealing time under a certain display condition as shown in Table 2 is grasped, the resin can be used to make the gate sealing time and the resin pass through the resin storing gate. It may be attached at a position and size that is greater than the time from the formation of the weld to the weld. In practice, it is necessary to consider the restrictions on the mounting position of the resin reservoir on the mold structure. Further, the flow amount occurring in the weld portion has a relationship with the size of the resin reservoir, and it is preferable to design the size based on the product capacity from the resin reservoir to the weld portion.

In this molding method, the position and volume of the resin reservoir are determined by the solidification speed of the resin, the volume of the molded product, the distance or the volume from the resin branch point to the weld, the molding conditions such as the resin temperature and the injection speed, and the filling. Molten resin is related to the amount that a part of it flows into the resin reservoir before weld formation, and it is difficult to define uniquely, but after the weld line is formed, there is room for the resin to flow by cavity internal pressure, There is basically no problem as long as the liquidity is maintained. Therefore, under arbitrary molding conditions, the thickness of the resin reservoir inlet, the thickness of the resin reservoir, and the like may be manipulated so that the resin flows into the resin reservoir after the formation of the weld line. Generally, in order to minimize the resin inflow into the resin reservoir when filling the molten resin, and to make the resin inflow into the resin reservoir efficiently after forming the weld line, the thickness of the resin reservoir inlet should be the thickness of the molded product around the inlet. It is preferable to make the film thinner, particularly preferably 0.2 to 0.7 times. Further, it is preferable that the capacity of the resin reservoir be equal to or larger than the molded product volume from the resin reservoir inlet to the weld portion.

The injection molding method and mold of the present invention can be applied to injection molding of any known thermoplastic resin. However, in the conventional molding method, the method is applied to a case where the strength is significantly reduced at a weld portion. It is particularly effective to do so. For example, in the conventional molding of a thermoplastic resin mixed with an inorganic filler, particularly a fibrous filler, the inorganic filler, particularly the fibrous filler, extends along the weld line on both sides of the weld. In order to orient in parallel, only a significantly lower strength can be obtained in the weld portion than in other portions, but according to the molding method and the mold of the present invention, such orientation in the weld portion is efficiently disturbed. Sufficient strength improvement is possible. Above all, in the molding of a mixture containing a fibrous filler having an average fiber length of 3 mm or more, the orientation of the fibers along the weld was strong, and the decrease in the weld strength was liable to be particularly problematic. The molding method and the mold are particularly effective for molding such a resin composition. In the molding of a resin composition mainly composed of a crystalline thermoplastic resin, particularly a liquid crystalline resin, the same problem is likely to occur due to the orientation of the crystalline resin along the weld. The method and the mold are extremely effective for molding such a resin composition.

[0019]

As is clear from the above description and the examples, when injection molding a thermoplastic resin molded article which originally produces a weld portion and which can obtain only a very low weld strength, the present invention is applied to a case where a predetermined position is obtained according to the present invention. After a weld is formed by supplying molten resin to the molded product cavity using a mold provided with a resin reservoir, the gate of the product gate is determined by the time from when the resin passes through the product gate until the weld line is formed. While the sealing time is long and the gate sealing time of the resin sump gate is longer than the time between the passage of the resin sump gate and the formation of the weld line, the resin in the weld sump is formed by flowing the resin into the resin sump. According to the injection molding method of the present invention, the resin on one side sandwiching the weld portion is press-fitted into the resin on the other side. The weld portion is very efficiently reinforced by disturbing the orientation of the resin or the filler in the weld portion, and has the excellent feature that a molded article with an improved appearance of the weld portion can be obtained, It is of high practical value.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view in which a resin reservoir is provided in a mold having two gates for a single cavity according to Embodiment 1 of the present invention.

FIG. 2 is a schematic explanatory view in which a resin reservoir is provided in a mold having one gate for a single cavity having a core.

FIG. 3 is an explanatory view showing movement of a resin in a weld portion in the mold of FIG. 1;

FIG. 4 is an explanatory view of injection-molding a combination mold according to a second embodiment.

FIG. 5 is an explanatory view of a conventional mold having two gates for a single cavity.

FIG. 6 is an explanatory view of a conventional mold having one gate for a single cavity having a core.

[Explanation of symbols]

Reservoir 1 ... resin, 2 ... resin reservoir gate, 3 ... sprue 4 ... runner 5 ... gate, 6 ... cavity 7 ... core, A _1, A ₂ ... resin flow, B · -Fusion point.

Claims (1)

(57) [Claims] 1. A resin projecting from a molded product cavity or a runner on at least one side of a cavity or a runner from a point at which a molten thermoplastic resin to be injected and filled flows to a point where the resin joins and a weld line is formed. Providing a reservoir, the gate sealing time of the product gate is longer than the time from when the molten thermoplastic resin passes through the product gate until the weld line is formed, and the time between the passage of the resin reservoir gate and the formation of the weld line. Use an injection mold with a product gate and a resin sump gate where the gate sealing time of the resin sump gate is longer than the time, and seal the product gate after the process of forming the weld line after the resin passes through the product gate. After the step of forming a weld line after passing through the resin reservoir gate, An injection molding method that performs a step of sealing a reservoir gate.