JPH05293856A - Injection molding method with improved weld strength, injection molding die and injection molded product - Google Patents

Abstract

PURPOSE:To provide the injection molding method in which a weld section is strengthened extremely effectively and also the outer appearance of the weld section is improved. CONSTITUTION:A mold with a cavity 1 constituted in a manner of forming a rib 4 of wall thickness thinner than any other wall thickness of a molded product on its periphery or a boss of small diameter in the vicinity of a weld section formed by joining molten resin introduced from a nozzle of a molding machine and branched therefrom in the mold cavity 1 is used. The weld section is formed by feeding molten resin into the cavity 1, and then the movement at the weld section is generated by flowing and filling the resin in the rib 4 or the boss of the cavity 1, and the resin on one side of the weld section is fed forcibly into the resin on the other side across the weld section to strengthen the weld section.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art When a single cavity 1 is injected and filled with molten resin from a plurality of gates 2 as in the mold shown in FIG. 1, a plurality of resin flows in the cavity. Occurs, and a weld occurs at the portion B where the resin flows merge and are fused. Further, even when the molten resin is filled into the cavity from a single gate, if the resin is split by the core or the like provided in the cavity, the split resin flows merge and are integrated. Weld occurs in the part. Further, even when the molded product has an uneven thickness portion, in the molten resin to be injected and filled, a resin shunt occurs due to the difference in the resin filling speed between the thick wall portion and the thin wall portion. In many cases, welds are generated in the part where the two merge and are integrated. The weld of such 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 in the actual molded product having a complicated shape. In such a welded portion, not only a linear pattern called a weld mark is formed and the appearance is impaired, but also the molten resin may not simply be mixed and fused and integrated so that the resin is not uniformly mixed. Therefore, a very serious problem arises in that the strength obtained is far lower than the original strength of the resin. As a method of improving such a problem of strength reduction in the weld portion by a molding method, Japanese Patent Application Laid-Open No. Sho 48-71459 discloses resin filling using a mold in which a resin reservoir is formed at a position where the weld portion is generated. After that, there is a molding method for improving the strength of the weld portion by pushing the resin in the resin reservoir portion back into the mold, and in JP-A-2-202414, the resin is injected from a plurality of gates equipped with open / close valves. After a plurality of resin flows generated by filling are merged and integrated to form a weld, the gate opening / closing valve is operated to disturb the weld portion by making a difference in the filling pressure of the resin flow, A molding method for improving the strength of the weld portion is disclosed. However, these methods have drawbacks that the mold structure is complicated and the mold becomes expensive, and that fairly strict molding control is required.

[0003]

Means for Solving the Problems The inventors of the present invention have made extensive studies for the purpose of solving the above problems and obtaining a molded article having improved weld strength. As a result, once the weld is formed, the resin is still formed inside. The present invention found that the weld strength and the like can be efficiently improved by causing the resin to move in the weld while maintaining the fluidity and disturbing the orientation of the resin or the filler in the weld. Reached That is, the present invention is characterized in that a cavity is formed in the vicinity of a weld portion so that a rib having a wall thickness smaller than any wall thickness of a molded product in the peripheral portion or a boss having a small diameter is formed. In injection-molding the mold and the thermoplastic resin, the molten resin introduced from the molding machine nozzle and diverted is joined in the mold cavity in the vicinity of the welded part, where the molded product thickness of the peripheral part is After using a mold in which a cavity is formed so as to provide ribs having a wall thickness smaller than either or bosses having a small diameter, after the weld portion is formed by supplying molten resin to the cavity,
The rib or boss cavity is filled with resin to cause movement in the weld portion, and the resin on one side sandwiching the weld portion is pressed into the resin on the other side to strengthen the weld portion. Injection molding method,
It also relates to injection molded products.

The mold, molding method and molded product of the present invention will be described below with reference to the drawings. 2 and 3
Taking as an example the mold (molded product) of FIG. 4, which is a typical mold (molded product) in which welds respectively occur, in order to improve the weld strength, according to the present invention, a predetermined position, that is, the joining of the molten resin, is performed. One mode of a mold (molded product) configured such that a rib having a wall thickness smaller than any of the wall thickness of the molded product or a boss having a small diameter is provided near the welded part formed by It is shown. Of course, in many actual molds (molded products), such a simple shape is rare, and the method of filling molten resin into the cavity,
Although the process of forming the weld is more complicated, it may be basically performed according to the mold configuration and the molding method shown here and described below. Now, in molding a molded product using such a mold, in the case where ribs or bosses are not provided, that is, in the mold of FIG. 4 including the metal insert 3, the molten resin to be injected and filled is introduced from the gate portion 2. Shortly after
The resin flows A ₁ and A ₂ are divided into _two flows, and a weld is generated at a point B where the divided resins join. In such a welded portion, the tips of the two shunting resins are in contact with each other only to be apparently adhered to each other. Further, the resin or the filler contained in the resin is oriented so as to sandwich the weld, and the two are uniformly mixed. However, there is a problem that the strength is lowered because it is not present, or there is a problem that a crack is generated from the weld portion when a heat shock is applied, and a line called a weld line is generated, which impairs the appearance.

On the other hand, according to the present invention, in molding using a mold as shown in FIGS. 2 and 3 in which ribs 4 (FIG. 2) or bosses 5 (FIG. 3) of predetermined sizes are provided at predetermined positions, injection is performed. The molten resin to be filled splits into resin streams A ₁ and A ₂ ,
After a weld is formed at the point B where these join, a molten resin is further poured into the rib or boss by the injection pressure or holding pressure applied to the resin to generate a pressure difference in the cavity on both sides of the weld, and the rib or boss is formed. The resin on the side not provided with the ribs or bosses is forced to flow into the resin on the side provided with the ribs or bosses to disturb the orientation or the like of the resin or the filling material in the weld portion, or the ribs or bosses are provided from the side without ribs or bosses Since the cone weld-like minute press-fitting flow to the side where is provided expands the substantial weld contact area, the strength of the weld portion is improved, and the weld line becomes less noticeable. In the mold and the molding method of the present invention, the rib or boss is provided in the vicinity of the weld portion and at a position where the resin can be filled after the weld is formed by the joining of the branched resin. Although the position varies depending on the viscosity of the resin, the solidification rate, the shape and size of the molded product, the number of gates, etc., it is preferably provided at a position approximately 1 to 20 mm from the weld portion. Further, it is essential that the thickness of the rib or the diameter of the boss is thinner than the thickness of the molded product around the weld (for example, t _{1 in} FIGS. 2 and 3). If the thickness of the rib or the diameter of the boss is larger than that, the rib or boss is filled with resin before the weld is formed, and the effect of the present invention does not occur. On the other hand, if the ribs or bosses are extremely thin or have a small diameter, it is difficult to fill the ribs or bosses with resin after the weld is formed, and the resin filling amount is also small. The strength improving effect is also small. Therefore, the thickness of the rib or the diameter of the boss is preferably 0.2 to 0.7 times the minimum thickness of the molded product around the weld. Further, in the mold of the present invention, a plurality of ribs or bosses may be provided. When providing a plurality of ribs or bosses, it is possible to provide the ribs or bosses only on one side sandwiching the weld or on both sides of the weld portion. In particular, using a mold provided with ribs or bosses by the latter method, after the weld is formed by filling the molten resin, the resin is poured into the ribs or bosses on one side that sandwiches the weld, and then the ribs or bosses on the other side are continued. The molding method in which the resin is poured into is particularly preferable as a method for improving the weld strength and the appearance, because the disturbance of the weld portion can be more efficiently caused by the alternating resin movement in the weld portion and the accompanying press-fitting of the resin. Is the way.

The injection molding method and mold of the present invention can be applied to injection molding of any known thermoplastic resin. However, the conventional molding method is applied to those in which the strength decrease at the weld portion was severe. It is especially effective to do so. For example, in molding a thermoplastic resin containing an inorganic filler, particularly a fibrous filler, by a conventional method, the inorganic filler, particularly the fibrous filler, is formed along the weld on both sides of the weld. Since the orientation is oriented, the welded portion has a remarkably lower strength than the other portions. However, according to the molding method and the mold of the present invention, such orientation in the welded portion is efficiently disturbed to obtain sufficient strength. It can be improved. Among them, in the molding of the one in which the fibrous filler having an average fiber length of 3 mm or more is blended, the orientation of the fibers along the weld is strong, and the decrease in the weld strength is apt to cause a particular problem. The molding method and the mold are particularly effective for molding such a resin composition. Further, in the molding of a resin composition mainly composed of a crystalline thermoplastic resin, the same problem is likely to occur due to the orientation of the crystalline resin along the weld, but the molding method and mold of the present invention are It is also extremely effective for molding such a resin composition. Furthermore, the molding method and the mold of the present invention are extremely effective for liquid crystal polymers in which fluid orientation is remarkably exhibited.

[0007]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Comparative Example 1 In molding a pulley having a shape as shown in FIG. 5, a metal bearing 3 was mounted on a mold, and 40% by weight of glass fiber was filled on the outside of the mold, and a polyphenylene sulfide (PPS) resin and a glass fiber. Then, a PPS resin filled with 65% by weight of an inorganic substance is injected and molded. In this case, the gates are 8-point pin gates arranged at equal distances on the circumferential surface A, and welds occur at eight locations between the gates. A test in which these molded products were left alternately in an atmosphere of −40 ° C. and an atmosphere of + 140 ° C. for 1 hour each was repeated up to 100 times, and the number of cracks in the weld was measured. Example 1 The present invention is applied as a countermeasure against this, and the distance from each weld is 3 mm.
Measured ribs (thickness: 1.5 mm) shown in Fig. 6 at the shifted positions
8 pieces of 4 were installed and molded in the same manner. The molded product was evaluated in the same manner as in Comparative Example 1. The results are also shown in Table 1.

[0008]

[Table 1]

Comparative Example 2 In the pulley as shown in FIG. 7, the metal bearing 3
Is inserted, and PPS resin filled with 40% by weight of glass fiber or PBT resin filled with 30% by weight of glass fiber or liquid crystalline polyester resin is injected and molded on the outside. In this case, four-point pin gates are arranged at equal distances on the circumferential surface A, and welds occur at four locations between the gates. This molded product is placed in a -30 ° C atmosphere and a + 120 ° C atmosphere each for 2
PPS is obtained by repeating the test in which it is left standing alternately for 300 hours
A crack was generated in the weld portion after 120 times of the resin, 80 times of the PBT resin and 60 times of the liquid crystalline polyester. Embodiment 2 As a countermeasure against this, the present invention is applied and as shown in FIG. 8, a boss 5 having a diameter of 2 mm and a height of 8 mm is placed at a position 4 mm away from each weld portion.
When molded upright, the durability was improved for all materials. The results are shown in Table 2.

[0010]

[Table 2]

[0011]

As is apparent from the above description and the examples, in injection molding a thermoplastic resin molded product that originally has a welded portion and has an extremely low weld strength, the molded product according to the present invention is Using a mold configured to form a thin rib or boss at a predetermined position, a weld portion is formed by supplying molten resin to a molded product cavity, and then a resin is flown into the rib or boss to form a weld. According to the injection molding method of the present invention and its mold, in which the resin on one side sandwiching the weld portion is pressed into the resin on the other side by causing the movement of the resin in the portion,
It has an excellent feature that the weld part is extremely efficiently strengthened by disturbing the orientation of the resin or the filler in the weld part, and the appearance of the weld part is also improved, which is of high practical value. It is a thing.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a typical mold (molded product) and resin flow in which a weld is generated by a multipoint gate, and FIG.
Is a schematic plan view and b is a schematic cross-sectional view.

FIG. 2 is a view showing an example of a mold (molded product) including a typical metal insert in which a weld is generated by a multipoint gate, ribs are provided on the mold according to the present invention, and further, one example of resin flow is shown. 2 is a schematic plan view and b is a schematic cross-sectional view.

FIG. 3 is a diagram showing an example of a mold (molded product) including a typical metal insert in which a weld is generated by a multi-point gate, which is provided with a boss according to the present invention, and further shows an example of resin flow, in which a is a 2 is a schematic plan view and b is a schematic cross-sectional view.

FIG. 4 is a mold (molded product) including a typical metal insert in which a weld is caused by a multipoint gate and a resin flow.
In the figure which shows an example, a is a schematic plan view, and b is a schematic sectional view.

5A and 5B are views showing an example of a metal bearing insert mold (molded product) in which a weld is generated by a multipoint gate, wherein a is a schematic plan view and b is a schematic cross-sectional view.

6 is a diagram showing an example in which a rib is provided by applying the present invention to a metal bearing insert mold (molded product) in which a weld is generated by the multipoint gate shown in FIG. 5, a is a schematic plan view,
b is a schematic cross-sectional view.

7A and 7B are views showing an example of a metal bearing insert mold (molded product) in which a weld is generated by a multipoint gate, wherein a is a schematic plan view and b is a schematic cross-sectional view.

8 is a view showing an example in which the present invention is applied to a metal bearing insert mold (molded product) in which a weld is generated by the multipoint gate shown in FIG. 7 and a boss is provided, and a is a schematic plan view,
b is a schematic cross-sectional view.

[Explanation of symbols]

 1 Cavity 2 Gate 3 Metal Insert 4 Rib 5 Boss

Claims (3)

[Claims] 1. In injection molding a thermoplastic resin,
In the vicinity of the weld formed by the molten resin introduced from the molding machine nozzle and diverted in the mold cavity, a rib with a wall thickness smaller than any of the peripheral wall thickness of the molded product or a small diameter Using a mold having a cavity so as to provide a boss, a weld portion is formed by supplying molten resin to the cavity, and then the rib or boss cavity is filled with the resin so that movement in the weld portion is prevented. An injection molding method characterized in that the resin on one side sandwiching the weld portion is pressed into the resin on the other side to strengthen the weld portion. 2. A metal for injection molding, characterized in that a cavity is formed in the vicinity of the weld portion so that a rib having a wall thickness smaller than any of the wall thickness of a molded product or a boss having a small diameter is formed near the weld portion. Type. 3. An injection-molded article formed by the injection-molding method according to claim 1.