JPH069837B2 - Injection molding method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plastic injection molding method and apparatus suitable for obtaining a warp-free precision molded product.

[Prior Art and its Problems] When a plastic material, particularly a crystalline plastic material, is injection-molded, warpage is likely to occur in a molded product, which is a major problem in obtaining a molded product. In order to solve this problem, various studies have been conventionally performed in terms of resin materials and molding methods. For example, there is a method of fixing a molded product taken out of a mold to a jig and forcibly improving warpage. But,
This method can be applied only to a molded product having a simple shape that can be fixed to a jig, and has a drawback of increasing the number of steps. Further, a method of adding a nucleating agent to crystalline plastic has been proposed.
However, this method also has a problem that it is effective for a molded product having a simple shape, but is not effective for a molded product having a box shape having a corner.

[Means for Solving the Problem] As a result of various studies on the method of reducing warpage in an injection-molded product having a corner, the inventors of the present invention have found that the resin on the opposing surfaces of the fixed side and the moving side of the mold is Maximum temperature,
That is, it was found that a warp-free molded product can be obtained by an extremely simple operation of substantially matching only the maximum temperature of the respective surfaces of the resins at positions facing each other in the mold, thereby completing the present invention. Came to do.

That is, the present invention, when the resin molded body having a corner portion is obtained by injection molding, the maximum temperature of the resin surface at the positions where the fixed side and the moving side of the mold face each other is substantially the same at the corner portion of the mold. An injection molding method characterized in that the fixed side and the moving side of the mold are temperature-controlled separately so that they coincide with each other.

In the injection molding method of the present invention, it is extremely important to prevent warpage of the obtained molded product in which the maximum temperatures of the resin on the surfaces of the mold on the fixed side and on the moving side that are opposed to each other are substantially matched. Generally, the warp is substantially improved by maintaining the difference between the maximum temperatures of the resin on both surfaces of the fixed side and the moving side of the mold facing each other within 5 ° C, preferably within 3 ° C. can do. It is desirable that the maximum temperature of the resin in the mold is substantially the same at each point from the gate for injecting the resin to the end of the mold in the molding by the injection molding machine, but in the present invention, It is important to match at the corners of the mold.

Further, in the present invention, by substantially matching the maximum temperature of each surface of the resin at the positions facing each other on the fixed side and the moving side of the mold together with the cooling rate of the resin temperature, the molded product The sled can be improved further. That is, the cooling rate of the resin temperature on the other surface of the mold may be controlled so as to substantially match the cooling rate of the resin temperature on the one surface facing the fixed side and the moving side.

The method of matching the maximum temperature and the cooling temperature of the resin is not particularly limited, but in particular, the method of controlling the mold temperature controller by the signals of the temperature detection sensors respectively installed on the opposite surfaces of the fixed side and the moving side of the mold. Is preferably adopted. For example, the signal for each shot from the temperature detection sensor described above is input to a microcomputer or the like, the maximum temperature of the resin on the fixed side and the moving side of the mold, or the maximum temperature and cooling rate of the resin is calculated, and the calculation result Based on the above, the mold temperature controller may be controlled so that the maximum temperature of both surface portions of the resin on the fixed side and the moving side of the mold, or the maximum temperature of the resin and the cooling rate are equal. Therefore, in the present invention, in order to achieve a good injection molding method, a mold of a resin molded body having a corner portion, in which the fixed side and the moving side of the mold in the corner portion of the mold face each other. There is also provided an injection molding apparatus in which a temperature detection sensor for detecting the maximum temperature temperature of the resin surface is installed near the surface of the mold, and a mold temperature controller for controlling the temperature of the resin by the signal is installed.

As the temperature detection sensor used in the present invention, known ones can be used without particular limitation, but in general, a thermocouple or an infrared sensor is preferably used. There is no particular limitation on the method of installing this temperature detection sensor in the mold, but it is necessary to install it as close to the mold surface as possible on the fixed and moving surfaces of the mold so that temperature control can be performed accurately. , Is necessary to achieve the object of the present invention. Further, in the case of a box-shaped molded product, it is preferable to install the temperature detecting sensors on the surfaces facing each other at the corners, and in some cases, a plurality of pairs of temperature detecting sensors can be installed. The mold temperature controller may use the heating mechanism and the cooling mechanism generally attached to the injection molding apparatus as they are, or may be separately installed. That is, generally, the maximum temperature of the resin at the position where the fixed side and the moving side face each other in the mold is substantially matched by the signal of the temperature detection sensor described above, or the maximum temperature and cooling rate of the resin are controlled. A mold temperature controller may be connected so that it can be done.

The present invention can be applied to a known injection molding apparatus, but is particularly suitable for each type of injection molding apparatus for thermoplastic resin such as polyolefin. FIG. 1 shows a schematic view of a mold part of a typical injection molding apparatus of the present invention. That is, FIG. 1 is composed of a fixed side 1 and a moving side 2 of the mold, and thermocouples 3 and 3'are attached to respective corners of the inner surfaces facing each other, and the ends of the thermocouples are A / D converted. It is connected to the microcomputer 5 via the container 4, and further connected to the temperature controller 6 of the mold temperature controller.

[Operation and Effect] According to the present invention, the warp of the obtained molded article can be improved by making the maximum temperatures of the resin on the surfaces of the mold on the fixed side and on the moving side that are opposite to each other as close as possible. .

According to the present invention, the mechanism of warping of a molded article is improved by making the maximum temperature of the resin in the mold or the maximum temperature and cooling rate of the resin uniform so that the internal structure of the resin in the thickness direction is Is considered to be uniform at the same time.

The injection-molded article having the corner portion obtained by the method of the present invention is compared with the injection-molded article obtained by the conventional method,
The sled is greatly improved. In particular, a remarkable effect can be recognized even for a box-shaped molded product which has been difficult in the past.

[Examples] Hereinafter, the present invention will be described based on examples, but these examples do not limit the present invention in any way.

Example 1 As shown in FIG. 2, a thermoelectric wire having a wire diameter of 1 mm was formed on opposing surfaces of a mold on which a box-shaped molded product having dimensions of 150 mm × 100 mm × 30 mm × thickness of 2 mm was obtained. I attached a pair. Then, each end of the thermocouple is connected to a microcomputer via an A / D converter, and the difference in the maximum temperature of the resin is calculated according to a pre-installed program, and the mold on the moving side is calculated based on the calculation result. A circuit was constructed to output the corrected temperature value to the mold temperature controller.
Using this equipment, polypropylene resin of M19 is resin temperature 230 ℃, injection pressure 500 kg / cm ² , mold temperature (first
Shot setting) Injection molding was performed at 40 ° C. to prepare a box-formed product. The dimensions of this box-formed product were read with a microscope, and the value obtained by dividing the amount of indentation on the inside of the side by the length of the side was displayed as a percentage, and this value was taken as the warp value.

Comparative Example 1 Using the same mold, injection molding machine and resin as in Example 1, the signal from the thermocouple was directly connected to the mold temperature controller, and the normal mold was used without control by the microcomputer. Table 2 shows the maximum temperature and warp value of the resin when molded by controlling the mold temperature.

[Brief description of drawings]

FIG. 1 is a schematic view of a typical injection molding apparatus of the present invention. In FIG. 1, 1 and 2 are fixed and moving sides of the mold, 3 and 3'are thermocouples, 4 is an A / D converter, 5 is a microcomputer, and 6 is a mold temperature controller. Further, FIG. 2 is a diagram showing a mounting state of the thermocouple on the mold. In FIG. 2, 7 and 8 are fixed and moving sides of the mold, and 9 and 9'are thermocouples.

Claims (5)

[Claims] 1. When obtaining a resin molded body having a corner portion by injection molding, the maximum temperature of the resin surface at positions where the fixed side and the moving side of the mold face each other substantially coincides with each other at the corner portion of the mold. The injection molding method is characterized by separately controlling the temperature of the fixed side and the moving side of the mold. 2. The injection molding method according to claim 1, wherein the difference between the maximum temperatures of the resin surfaces at the opposite positions is within 5 ° C. 3. The injection molding according to claim 1, wherein the mold temperature controller is controlled by the signals of temperature detection sensors respectively installed on the mold surfaces at positions where the fixed side and the moving side of the mold face each other. Method. 4. A mold of a resin molded body having a corner portion, wherein the maximum temperature temperature of the resin surface is provided near the mold surface at the position where the fixed side and the moving side of the corner part of the mold face each other. An injection molding machine equipped with a temperature detection sensor that detects the temperature, and a mold temperature controller that controls the temperature of each resin according to the signal. 5. The injection molding apparatus according to claim 4, wherein the temperature detection sensor is a thermocouple or an infrared sensor.