JPH06155535A - Molding method of thermoplastic resin - Google Patents

Abstract

PURPOSE:To mold thermoplastic resin having few void and anisotropy and high strength, by a method wherein a flow or a vibration is allowed to generate at fixed frequency on the resin within a mold cavity during a cooling process of the molten resin after injection and casting of the same. CONSTITUTION:Shearing force is allowed to generate in molten resin within a mold cavity by applying pressurizing force and decompressing force alternately to the molten resin by two pistons 5, 6 which are arranged between a cylinder 1 and mold 9 of an injection molding machine and as devices streaming and vibrating the molten resin. At this time, it is preferable that capacity of the resin is made at least 10% of inside capacity of the cavity. Then the molten resin infected through a nozzle 3 is passed through flow paths 7, 8 and filled within the mold cavity 10. The resin within the cavity is moved during solidification by awing the piston 5, 6 alternately after completion of filling. During this cooling process, the shearing force by a flow or an oscillation is allowed to generate in a part or the whole of the resin within the cavity at frequency of 1-5 times per 1-60sec. through which a resinous reinforcing material is oriented in a flowing direction of the resin.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for molding a thermoplastic resin. More specifically, the present invention relates to a method for molding a high-strength thermoplastic resin with few voids.

[0002]

2. Description of the Related Art Thermoplastic resin molded products, unlike metallic molded products, have the advantages that they do not rust, are lightweight, do not necessarily require painting, and have a low total cost, and are widely used for brake levers and bolts. May be available. Brake levers and bolts made of thermoplastic resin are usually manufactured by injection molding using an engineering plastic material containing a fiber-reinforced material such as glass fiber or carbon fiber. It can be molded. However,
When the above-mentioned molded product or the like is molded by an ordinary injection molding method, voids are likely to occur in the center of the molded product, and the orientation of the reinforcing fibers blended in the resin composition becomes insufficient in the center.
There is a problem that anisotropy occurs in the strength, and a molded product having the expected strength cannot be obtained. In particular, bolts, brake levers, etc. are usually required to have high strength, and especially motorcycle brake levers must be able to withstand the impact of a fall,
High mechanical strength is required. Although metal insert moldings are also used for bicycles, they are not always satisfactory in terms of weight reduction and process complexity.

In order to overcome the above-mentioned problems due to voids, anisotropy, etc., Japanese Patent Laid-Open No. 61-179715 discloses that a molten thermoplastic resin is supplied to a mold and a shearing force is applied to the molten resin in the mold. A method of solidifying the resin while adding is disclosed. Although the method of this disclosure is effective in solving the above problems, there are problems that the molding cycle is lengthened or the shearing force is insufficiently generated by selecting the cycle in which the shearing force is generated.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a method for molding a high strength thermoplastic resin having few voids and anisotropy.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies as to a molding method for obtaining a high-strength thermoplastic resin, and as a result, have determined that the molten resin filled in the mold cavity has a certain content of the molten resin. It was found that the above problems can be solved by applying a shearing force by flow or vibration under the cycle of (1) to reduce voids and orient the fiber reinforcing material inside the molded product in a preferred direction, and completed the present invention.

That is, the present invention relates to a method for molding a thermoplastic resin, in which a molten resin is injected into a mold cavity and then cooled in a process of cooling, in which 1 to 1 part or all of the resin in the mold cavity is cooled. The present invention relates to a method for molding a thermoplastic resin, wherein a shearing force is generated by flow or vibration at a frequency of 1 degree or more every 60 seconds.

The thermoplastic resin which can be used in the present invention may be a commercially available thermoplastic resin, but when strength is required for the molded product, glass fiber or a card is used.
Engineering plastics containing bon fibers and the like, and polymer alloys thereof are preferably used. Moldability among the engineering plastics,
From the viewpoint of strength, polyamide resins such as poly (meta-xylylene adipamide), polyphenylene ether, and mixtures thereof are particularly desirable. Examples of reinforcing fibers to be blended in the thermoplastic resin include glass fibers, carbon fibers, potassium titanate whiskers, and combinations of these reinforcing fibers, but the reinforcing fibers are not particularly limited.
Further, although the fiber length and the fiber diameter are not particularly limited, the effect is particularly large when a molding material pellet containing reinforcing fibers having a fiber length of 5 mm or more is used.

With the device for generating the shearing force, a shearing force is generated by flowing or vibrating a part or all of the molten resin in the mold cavity in the process of cooling and solidifying the molten resin after the molten resin is injected. The device for generating the shearing force is not particularly limited, but for example, it is arranged between the injection molding machine cylinder and the mold as shown in FIG. 1 or 2, and at least one means for flowing or vibrating the molten resin is provided. It may be a device having a cylinder and a piston. In the case of FIGS. 1 and 2, the shearing force can be generated by alternately applying a pressing force and a depressurizing force to at least two pistons. The generation cycle of the shearing force is 1 to 60
The frequency is 1 or more times per second, preferably 1 to 5 times. If the cycle of the shearing force is out of the above range, there are disadvantages that the molding cycle is prolonged and the shearing force is insufficiently generated.

It is desirable that the volume of the resin that flows or vibrates by generating a shearing force in the molten resin in the mold cavity in the cooling step is 10% or more of the volume of the mold cavity. If the resin volume that flows or vibrates is less than 10%, the shearing force may be insufficiently generated.

The shape of the molded product molded by the molding method of the present invention is not particularly limited, but the cross-sectional area perpendicular to the longitudinal direction is 1 cm ² or more, and the longitudinal length is the shortest of the cross-sectional portion. In the case of a shape having at least one portion having a length three times or more, the remarkable effect of the present invention can be obtained.

An example of the molding method of the present invention is shown in FIGS. Symbols in the figure are 1: cylinder of injection molding machine, 2:
Screw, 3: Nozzle, 4: Sprue, 5: Piston, 6: Piston, 7: Hot runner, 8: Hot runner, 9: Mold, 10: Mold cavity for bolt, 1
1: mold cavity for brake lever, 12: brake lever, 13: gate position, 14: mounting hole, respectively. Incidentally, the above 5 and 6 are devices for applying shearing force by flowing or vibrating the molten resin in the mold attached to the injection molding machine. The molten resin injected from the nozzle of the injection molding machine passes through the flow paths 7 and 8 and the runner.
And into the mold cavity. After the filling is completed, the pistons 5 and 6 are alternately moved to move the resin in the cavity during the solidification. By flowing or vibrating the molten resin, the fibrous reinforcing material is oriented in the flowing direction of the resin.

Therefore, when molding by the method of the present invention, it is necessary to select a gate structure suitable for the shape of the molded product. In the case of forming a bolt, the gate structure is such that by providing a gate at two points, the head of the bolt and the tip of the screw, the molten resin is made to flow in the longitudinal direction of the bolt by allowing the molten resin to flow during solidification. Can be oriented, and the void in the central portion can be eliminated.

Even when the brake lever is molded by the molding method of the present invention, it is necessary to select a gate structure suitable for the molding shape. By providing gates at both ends of the brake lever as shown in FIG. By flowing the molten resin during solidification, the reinforcing fibers can be oriented in the longitudinal direction of the brake lever, the strength of the weld portion can be improved, and voids can be eliminated.

[0014]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Example 1 A polyamide resin (manufactured by Mitsubishi Gas Chemical Co., Inc., trade name: Reny-1022F) dried at 80 ° C. for 12 hours was used, and the size was M3, M6 and M8 using the molding apparatus shown in FIG. 3 types of hexagon bolts were injection molded. Injection conditions are cylinder temperature of 255 ° C and injection pressure of 1000 kg / cm.
² , mold temperature 130 ℃, M3 (length: 20mm),
Respective mold cavities for M6 (length: 40 cm) and M8 (length: 50 cm) hexagon bolts were used.
Immediately after the molten resin was filled, the pistons 5 and 6 were alternately compressed and decompressed at a pressure of 800 kg / cm ² to flow the molten resin. The period of moving the piston was 40 seconds at a rate of once every 10 seconds. After that, the pistons were simultaneously compressed and held for 20 seconds. After cooling and solidifying, the mold was opened and the product was taken out. There were no voids inside the resulting product, and the glass fibers were oriented in the longitudinal direction of the bolt. The tensile strength of the obtained hexagon bolt molded product was 120 kgf for M3, 470 kgf for M6, and 790 kgf for M8.

Example 2 A polyamide resin (manufactured by Mitsubishi Gas Chemical Co., Inc., trade name: Reny-1022F) dried at 80 ° C. for 12 hours was used, and the size was the same as that of Example 1 under the same injection conditions as in Example 1. Similar M
Three types of hexagon bolts of 3, M6 and M8 were injection molded. Immediately after the molten resin was filled, the pistons 5 and 6 were alternately compressed and decompressed at a pressure of 800 kg / cm ² to flow the molten resin. The piston was moved for 40 seconds at a rate of once per second. After that, the pistons were simultaneously compressed and held for 20 seconds. After cooling and solidifying, the mold was opened and the product was taken out. There were no voids inside the resulting product, and the glass fibers were oriented in the longitudinal direction of the bolt. The tensile strength of the obtained hexagon bolt molded product is 100 kgf for M3,
M6 was 400 kgf and M8 was 670 kgf.

Comparative Example 1 Polyamide resin (manufactured by Mitsubishi Gas Chemical Co., Inc., trade name Reny-1022) dried under the same conditions as used in Example 1.
M), M6 and M8 as in Example 1 using F)
3 types of hexagon bolts were injection molded. Using the apparatus shown in FIG. 1, the molding was carried out under the condition that the piston was not moved, the molten resin was filled, and then the pressure was kept at 800 kg / cm ² for 20 seconds by a molding machine screw to cool and solidify. Voids were generated inside the obtained molded product. The tensile strength of the obtained hexagon bolt molded product is 90 kgf for M3 and M6.
Was 360 kgf and M8 was 610 kgf.

Example 3 Glass fiber reinforced polyamide resin (Mitsubishi Gas Chemical Co., Inc.)
Manufactured by Reny 1022F), and using an injection molding machine as shown in the conceptual diagram of FIG.
After drying at 0 ° C for 12 hours, a cylinder temperature of 255 ° C, an injection pressure of 1000 kg / cm ² , and a mold temperature of 130 ° C, a brake lever as shown in Fig. 3 (length: 120 cm, outer diameter of the central surface vertical to the longitudinal direction). : 15 mmφ) was filled with the molten resin from the gates on both tip sides. 800 pressure immediately after filling
The pistons 5 and 6 were alternately compressed at a pressure of kg / cm ² and a depressurizing operation was performed to flow the molten resin. The piston was moved for 40 seconds at a frequency of once every 10 seconds. Thereafter, the pistons were simultaneously compressed and held for 20 seconds, the mold was opened and the product was taken out. No void was found inside the obtained product, and the glass fibers were oriented in the longitudinal direction of the brake lever. Using a resin impact tester conforming to ASTM D256, fix the mounting hole (14 in FIG. 3) of the obtained product with a fixing jig, and position 30 cm from the tip opposite to the position with the mounting hole. Impact strength (I ₁ ) of the lever surface and the impact strength (I ₂ ) perpendicular to the lever surface
Was measured 10 times, I ₁ was 180 kgf · cm
(Standard deviation 4.0 kgf · cm), I ₂ is 170 kgf
-Cm (standard deviation 3.5 kgf-cm).

Example 4 Using a device similar to that described in Example 3, a glass fiber reinforced polyamide resin (manufactured by Mitsubishi Gas Chemical Co., Inc., trade name:
Rennie 1022F) was dried at 80 ° C. for 12 hours, and then filled with molten resin from the gates on both ends of the brake lever as shown in FIG. 3 at a cylinder temperature of 255 ° C., an injection pressure of 1000 kg / cm ² , and a mold temperature of 130 ° C. Immediately after filling, the pistons 5 and 6 are simultaneously compressed with a pressure of 800 kg / cm ² ,
A depressurization operation was performed to cause the molten resin to flow. The piston was moved for 20 seconds at a frequency of once every 20 seconds. Thereafter, the pistons were simultaneously compressed and held for 20 seconds, the mold was opened and the product was taken out. No void was found inside the obtained product, and the glass fibers were oriented in the longitudinal direction of the brake lever. The impact strength of the obtained product was measured 10 times by the same evaluation method as described in Example 3. As a result, I ₁ was 155 kgf · cm (standard deviation 4.0 kgf).
· Cm), I ₂ is 130kgf · cm (standard deviation 5.5
It was kgf · cm).

Comparative Example 2 A glass fiber reinforced polyamide resin (trade name: manufactured by Mitsubishi Gas Chemical Co., Inc.) was used, using the same apparatus as described in Example 3.
Rennie 1022F) was dried at 80 ° C. for 12 hours, and then filled with molten resin from the gates on both tip sides of the brake lever as shown in FIG. 2 at a cylinder temperature of 255 ° C., an injection pressure of 1000 kg / cm ² , and a mold temperature of 130 ° C. Immediately after the filling, the pressure was kept at 800 kg / cm ² for 20 seconds, the mold was opened, and the product was taken out. Voids were generated in the center of the obtained product, and glass fibers were not oriented in the longitudinal direction of the brake lever at the center. The impact strength of the obtained product was measured 10 times by the same evaluation method as described in Example 3, and I ₁ was 95 kgf · cm (standard deviation 2).
0 kgf · cm) and I ₂ were 30 kgf · cm (standard deviation 2.5 kgf · cm).

[0020]

By employing the molding method of the present invention, it is possible to obtain a high-strength thermoplastic resin molded product in which voids are not generated inside the molded product.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a bolt forming device provided with a shearing force generator of the present invention.

FIG. 2 is a conceptual diagram of a brake lever molding device provided with the shearing force generator of the present invention.

FIG. 3 is a plan view of a brake lever obtained in a third embodiment.

[Explanation of symbols]

1: Cylinder of injection molding machine 2: Screw 3: Nozzle 4: Sprue 5: Piston 6: Piston 7: Hot runner 8: Hot runner 9: Mold 10: Mold cavity for bolt 11: Mold cavity for brake lever 12 : Brake lever 13: Gate position 14: Mounting hole

Claims (7)

[Claims] 1. A method of molding a thermoplastic resin, wherein 1 to 6 is applied to a part or all of the resin in the mold cavity in the process of cooling after injection and injection of a molten resin into the mold cavity.
A method for molding a thermoplastic resin, wherein shearing force is generated by flow or vibration at a frequency of once or more per 0 seconds. 2. The frequency of generating shearing force on a part or all of the resin in the mold cavity is 1 to 5 per 1 to 60 seconds.
The method for molding a thermoplastic resin according to claim 1, wherein the thermoplastic resin is a resin. 3. The device for generating shearing force is arranged between an injection molding machine cylinder and a mold, and the means for flowing or vibrating the molten resin is a device having at least one cylinder and piston. A method for molding the thermoplastic resin described. 4. The volume of the resin that flows or vibrates by generating shearing force in the molten resin in the mold cavity is 10% or more of the volume of the mold cavity. The method for molding a thermoplastic resin according to 1. 5. A molded article molded by the method for molding a thermoplastic resin according to claim 1 has a cross-sectional area perpendicular to the longitudinal direction of 1 cm ² or more and a longitudinal length of the cross-sectional portion. A molded article having a shape having at least one portion having a length three times or more of the shortest length. 6. A thermoplastic resin bolt molded by the thermoplastic resin injection molding method according to any one of claims 1 to 4. 7. A thermoplastic resin brake lever molded by the thermoplastic resin injection molding method according to any one of claims 1 to 4.