JPH0331323B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a rod-shaped body made of thermoplastic synthetic resin.

(Prior Art) In thermoplastic synthetic resin molded products obtained by molding methods such as injection molding, voids occur inside the product or surface shrinkage occurs due to volumetric shrinkage due to temperature changes when the synthetic resin solidifies. These cavities and shrinkage cause a decrease in the strength and dimensional accuracy of the molded product. These cavities and shrinkage can be alleviated by adding a filler to the resin to minimize volumetric shrinkage when the resin solidifies, but they cannot be reduced to zero.

In order to solve these problems, the special public
17679, as shown in FIG. 6, a molten material 200 is injected into a cavity 101 for molding a rod-shaped body having a constant cross section while being pressurized by a piston 102, and this molten material 200 is sequentially cooled from its tip. A method for doing so is disclosed. However, this method only produces rod-shaped bodies with a constant cross section. Moreover, in order to take out the rod-shaped product from the mold cavity 101, the mold 10
0 from the molding machine 103, the work is complicated and productivity is poor.

On the other hand, the flow molding method is known as a molding method for thick-walled molded products, but it is also necessary to remove the nozzle from the mold or open the mold in order to take out the molded product. , poor productivity.

In order to solve the above problems, the molten resin material is injected into the mold while being pressurized, the resin is cooled and solidified, and then the resulting molded product is removed from the mold while being pressurized with the subsequent molten resin material. A method of discharging it outside has been proposed. However, in this method, when the cooled and solidified molded product is discharged, the molded product is pressurized and compressed by the subsequent molten resin, so that it is pressed against the wall surface of the mold cavity. Therefore, the molded product is not easily ejected.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the prior art, and its purpose is to minimize the occurrence of cavities or shrinkage inside or on the surface of a molded product, and to provide excellent strength and dimensional accuracy. An object of the present invention is to provide a method for manufacturing a rod-shaped body made of thermoplastic synthetic resin. Another object of the present invention is to provide a method for manufacturing a rod-shaped body made of thermoplastic synthetic resin, in which the molded article can be easily demolded and has excellent productivity.

(Means for Solving the Problems) The method for producing a rod-shaped body made of thermoplastic synthetic resin of the present invention includes (1) heating and melting a molded resin material to obtain a molten resin material; (2) obtaining a molten resin material; (3) A process of maintaining the temperature at a temperature higher than the melting point, (3) provided in the rod-shaped body forming mold, and having a cross-sectional area of 30% or more of the minimum cross-sectional area of the rod-shaped body forming part.
(4) injecting and filling the molten resin material under pressure into a cavity section consisting of a resin injection section and a rod-shaped body molding section at a temperature within the range of 99%; a step of solidifying the resin material by cooling and maintaining the resin material at a temperature; (5) discharging the rod-shaped product formed in the cavity part into the desired shape from the cavity part while pressurizing it with the subsequent molten resin material; The above object is thereby achieved.

(Example) The present invention will be described below with reference to examples.

An example of a molding apparatus embodying the manufacturing method of the present invention is shown in FIG. The molding device 1 includes an extruder 11,
A joint part 12 is engaged with the tip of the extruder 11 in an air-liquid tight manner, and the joint part 12 has a mold 13 for molding a rod-shaped body that is engaged in an air-liquid tight manner. The joint portion 12 is provided with heating means 121 such as a heater. The mold 13 is provided with a heating means 131 and a cooling means 132. These heating means 131 and cooling means 132
is composed of a plurality of pairs of independent heaters and cooling water circulation pipes provided around and/or inside the mold 13.

As the extruder 11, an extruder normally used for resin molding, such as a single screw extruder or a twin screw extruder, is used. The cylinder portion 111 of the extruder 11 is heated to a temperature higher than the melting point of the molded resin material 2 by a heating means. Therefore, the resin material 2 is kneaded and melted by the screw 112 within the cylinder portion 111. The extrusion pressure of the extruder 11 is
It is determined as appropriate based on the properties of the resin material 2 used and the shape of the rod-shaped molded product 20 to be manufactured.

The joint portion 12 has, for example, a conical hollow portion 120 inside thereof. Joint part 1
One end opening 122 of 2 is connected to the cylinder part 111 of the extruder 11, and the other end opening 123 constitutes an outlet and is connected to the mold cavity part 130. The joint portion 12 is maintained at a temperature equal to or higher than the melting point of the resin material 2 by a heating means 121. Therefore, the molten resin material 2 does not solidify in the hollow part 120 and is always replenished into the mold cavity part 130 by the extrusion pressure of the extruder 11, so that the resin material injected into the cavity part 130 is 2. It becomes difficult for nests and shrinkage to occur inside and on the surface.

The mold cavity part 130 consists of a resin injection part 133 and a rod-shaped body forming part 134. Resin injection part 133
The cross-sectional area of the rod-shaped body forming portion 134 is set smaller than that of the rod-shaped body forming portion 134, for example, as shown in FIGS. 2a to 2c. Specifically, the resin injection part 133
The cross-sectional area of is relative to that of the rod-shaped body forming portion 134.
Set within the range of 30% to 99%. Since the contact surface or contact portion 137 between the cooled and solidified molded product 20 and the subsequent molten resin material 2 has not yet been cooled and solidified, it is pushed against the wall surface of the cavity portion 130 by the pressing force of the subsequent molten resin material and comes into press contact. However, this pressure contact phenomenon occurs because the end portion (that is, the contact portion 137) of the molded product 20 has a sufficiently small cross-sectional area compared to the rod-shaped body forming portion 134 of the resin injection portion 133.
It simply occurs while passing through. As a result, the molded product 20 can be discharged from the cavity portion 130 very easily. If the cross-sectional area of the resin injection section 133 is less than 30% of that of the rod-shaped object forming section, the molten resin material 2 from the extruder 11 will not be refilled sufficiently, resulting in cavities inside or on the surface of the rod-shaped object molded product 20. There is a risk of a decline in sales. If it exceeds 99%, it becomes difficult to demold the molded product.

Moreover, the shape of the resin injection part 133 is the shape of the molded resin material 2.
It is determined as appropriate based on the properties of the molded rod 20 and the shape of the rod-shaped molded product 20 to be manufactured. For example, as shown in FIG. 3a, the cross-sectional area is the same in the axial direction, or as shown in FIG. A shape may be adopted. Thereby, the molded product 20 can be demolded more effectively. The axial length of the resin injection part 133 can be set to the minimum value within a range that allows the molded product 20 to be easily demolded.
For example, it is set to several mm.

The other end opening 135 of the mold cavity portion 130 constitutes a demolding port for the molded product. This demolding port 13
5 is provided with, for example, a lid 136 that can be opened and closed, and by opening this lid 136, the desired rod-shaped molded product 20 in the cavity part 130 is pressurized by the subsequent molten resin material 2 and exits the system. taken out. This lid 136 is continuously opened and closed by an appropriate power means (not shown). Cavity part 130
The air inside is discharged to the outside of the system through a small mounting gap of the lid 136.

The temperature of the mold cavity portion 130 is controlled by heating means 131 and cooling means 132. After the molten resin material 2 is injected into the cavity 130 or in advance by the cooling means 132,
The cavity portion 130 is maintained at a temperature below the melting point of the resin material 2. As a result, the cavity part 130
The molten resin material 2 inside is cooled and solidified. The heating means 131 and the cooling means 132 operate independently. Therefore, the cavity portion 130 can be controlled with any temperature distribution. Cavity part 130
If a temperature gradient is provided so that the temperature gradually decreases from the extruder 11 side toward the demolding port 135, it is possible to effectively prevent cavities and shrinkage from occurring inside and on the surface of the molded rod 20. . More preferably, if the temperature is controlled so that the molten resin material 2 in the rod-shaped body molding part 134 of the cavity part 130 is cooled and solidified, then the molten resin material 2 in the resin injection part 133 is cooled and solidified. The occurrence of cavities and shrinkage on the surface is minimal. The cooling means 132 may also use oil instead of cooling water. The temperature adjustment is appropriately determined by the properties of the resin material 2 used and the shape and dimensions of the rod-shaped molded product 20 to be manufactured.

The rod-shaped molded product 20 manufactured according to the present invention is
Any shape can be adopted as long as the shape is at least a cylindrical shape and can be removed from the mold cavity part 130 in one direction. For example, a rod-shaped body may be molded in which the rear of the molded body has a larger diameter than the front. In addition, the manufactured rod-shaped body molded product 20
is discharged together with the molded product solidified within the cavity resin injection section 133. After discharge, the desired rod-shaped molded product 20 is obtained by cutting the resin-injected portion of the molded product.

The molded resin material 2 used in the present invention is made of thermoplastic synthetic resin. As a thermoplastic synthetic resin,
Examples include polyamide resin, thermoplastic polyester resin, polyacetal resin, polycarbonate resin, polypropylene resin, polyethylene resin, vinyl chloride resin, polyphenylene resin, and polyphenylene sulfide resin. These synthetic resins may be used singly or in the form of a mixture of two or more. In addition, thermoplastic synthetic resins are usually filled with fillers such as glass fibers, carbon fibers, aramid fibers, potassium titanate fibers, alumina fibers, boron fibers, silicon carbide fibers, and various metal fibers. Known fibers used for reinforcement may be incorporated. These fillers may be used singly or in the form of a mixture of two or more. Furthermore, various molding aids or resin modifiers may be added to the thermoplastic synthetic resin as appropriate.

The molding apparatus 1 functions as follows. First, the extruder 11, the joint portion 12, and the rod-shaped object molding die 13 are each engaged in an air-liquid tight manner through a sealing material such as a gasket or packing. At this time, the demolding port 13 of the mold 13
5 is closed with a lid 136. The resin material 2 is supplied to an extruder 11 and kneaded by a screw 112 in a cylinder section 111. When using a filler, the filler and thermoplastic synthetic resin are separately supplied to the extruder 11 and kneaded by the screw 112 in the cylinder section 111, or the filler and the synthetic resin are kneaded in advance. The pellets may be formed into pellets and fed to the extruder 11. This resin material 2 is uniformly kneaded in the extruder cylinder section 111, heated and melted, and is sequentially pressurized and filled into the mold cavity section 130 from the joint section 12. Since the molten resin material 2 is maintained at a temperature above the melting point by the heating means 121 of the joint part 12 and the heating means 113 of the mold 13, it solidifies within the mold resin injection part 133 and blocks the injection part 133, for example. This is not the case, and the metal is constantly and smoothly supplied to the mold cavity section 130. Therefore, the molten resin material 2 in the cavity 130 is always kept under pressure until it is cooled and solidified by the cooling means 132 of the mold 13. After the molten resin material 2 is injected and filled into the mold cavity 130, it is maintained at a temperature below the melting point by the cooling means 132 of the mold 13 and solidified. Next, the lid 136 provided on the mold removal port 135 is opened, and the desired rod-shaped molded product 20 is discharged from the mold 13 to the outside of the system by the subsequent extrusion pressure of the molten resin material 2. At this time, the cavity part 130
Since the cross-sectional area of the resin injection part 133 is set in the range of 30% to 99% of that of the rod-shaped body molding part 134, the contact area 137 between the molded product 20 and the subsequent molten resin material 2 is the same as that of the rod-shaped body molding part 134. The phenomenon in which the molded product 20 is pressed against the wall surface of the cavity portion 130 is minimized. Therefore, the rod-shaped molded product is easily discharged from the mold cavity portion 130. After demolding is completed, the lid 136 of the demolding port 135 is closed to prepare for the next injection of molten resin material 2 into the cavity 130. In this way, the demolding of the molded product from the mold 13 and the injection and filling of the resin material 2 into the cavity portion 130 are performed continuously, resulting in high productivity.

Example In the above molding apparatus 1, as shown in FIG. 4, D ₁ = φ8 mm, D ₂ = 9 mm, D ₃ = φ10 mm, D ₄ =
A rod-shaped body 20 as shown in FIG. 5 was molded by the method of the present invention using a rod-shaped body mold 13 having a diameter of 14 mm _, L ₁ =5 mm, L ₂ =100 mm, and L 3 =10 mm. As the extruder 11, a twin screw extruder is used,
The extrusion pressure was set at 130 Kg/cm ² . As the resin material 2, glass fiber was added to 100 parts by weight of polyamide resin (manufactured by Ube Industries, Ltd.; Nylon 6 1030B).
100 parts by weight of the mixture was used. The melting point of resin material 2 was 225°C. The temperature of the joint part 12 is 250
℃, and the temperature of the mold cavity portion 130 was set to gradually decrease from 150°C to 120°C from the extruder 11 side toward the tip.

When the longitudinal section and surface of the obtained rod-shaped body 20 were observed under a microscope or visually, no cavities or shrinkage were observed. In addition, 100 molds were continuously molded, and all molded products were easily demolded.

Comparative Example A rod-shaped molded product was obtained in the same manner as in the mold used in the above experimental example, except that the diameter of the resin injection part 133 was made the same as that of the rod-shaped body forming part 134.

No cavities or shrinkage were observed inside or on the surface of the molded product obtained. Also, 100 in a row
The book was molded, but during the process it often became difficult to remove the molded product.

(Effects of the Invention) According to the manufacturing method of the present invention, the molten resin material is supplied to the mold cavity in a constantly pressurized state, so there are no cavities inside or on the surface of the resulting molded product. There is no occurrence of withdrawal etc. Therefore, the molded product has excellent strength and dimensional accuracy. Moreover, the unique shape of the cavity allows the molded product to be easily demolded, resulting in excellent productivity. By replacing the mold, molded products of any shape can be supplied.

[Brief explanation of drawings]

FIG. 1 is a sectional view of essential parts showing an example of a molding apparatus embodying the manufacturing method of the present invention, and FIGS. 2a to 2c
3A and 3B are cross-sectional views of main parts, respectively, showing examples of the resin injection part of the mold cavity of the mold cavity, and FIG. The figure is a sectional view of the main part of the mold used in the experimental example of the present invention, FIG. 5 is a side view showing the rod-shaped molded product obtained in the above experimental example, and
The figure is a sectional view of a main part of an example of a conventional molding device. DESCRIPTION OF SYMBOLS 1... Molding device, 2... Molding resin material, 11... Extruder, 12... Joint part, 13... Mold for rod-shaped body,
DESCRIPTION OF SYMBOLS 20... Rod-shaped body molded product, 121, 131... Heating means, 130... Mold cavity part, 132... Cooling means, 133... Resin injection part, 134... Rod-shaped body forming part.

Claims (1)

[Claims] 1 (1) A step of heating and melting a molded resin material to obtain a molten resin material, (2) A step of maintaining the molten resin material at a temperature equal to or higher than its melting point, (3) A mold for molding a rod-shaped object. The cross-sectional area is 30% to 99% of the minimum cross-sectional area of the rod-shaped body forming part.
a step of injecting and filling the molten resin material under pressure into a cavity portion comprising a resin injection portion and a rod-shaped body forming portion within the range of (4) heating the cavity portion to a temperature below the melting point of the resin material; (5) The rod-shaped molded product of the desired shape formed in the cavity is discharged from the cavity to the outside of the system while being pressurized with the subsequent molten resin material. A method for producing a rod-shaped body made of thermoplastic synthetic resin, including the steps. 2. The manufacturing method according to claim 1, wherein a plurality of pairs of independent heating means and cooling means are arranged in the mold. 3. The manufacturing method according to claim 1, wherein the cavity portion has a temperature gradient. 4. The molten resin material in the resin injection part of the cavity part is cooled and individualized after the molten resin material in the rod-shaped body forming part is cooled and individualized.
The manufacturing method according to item 1 or 3.