JPH06262648A - Method and apparatus for injection molding of synthetic resin - Google Patents

Abstract

PURPOSE:To eliminate the weld line of a molded product by sending out ultrasonic waves to a mold so as to generate acoustic streams in the flow of the molten resin within a mold cavity. CONSTITUTION:A molten nozzle is injected from the nozzle of an injection molding machine to fill the cavity of a mold 1 through the sprue and multipoint gate of the mold 1. The horn (transmission part) constituting a part of the mold 1 is provided so as to come into contact with the molten resin in the cavity and an ultrasonic transmitter 21 is attached to the horn through a booster 20. The ultrasonic waves generated in the ultrasonic transmitter 21 pass through the booster 20 to be emitted to the confluent part A of the molten resin in the cavity. When the frequency of ultrasonic waves becomes high, the flow velocity of the molten resin becomes high. When ultrasonic waves with various frequencies are emitted, the ultrasonic waves become the driving force of acoustic streaming and, even when the cavity is filled with the molten resin high in viscosity, secondary flow agitating a weldline is generated before the weldline is solidified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin injection molding method and an injection molding apparatus used therefor.

[0002]

2. Description of the Related Art In principle, an injection molding method suitable for accurately and mass-producing a molded article having a complicated shape is to heat and melt a resin in a melting cylinder to fluidize the resin, Is a method of injecting into a mold by casting, and then cooling and solidifying or hardening in the mold, and then opening the mold and taking out a molded product.

The resin molded product obtained by the injection molding method is not preferable from the viewpoint of the aesthetics of the molded product, which is called a weld line, and the molded product has a thin line which is a serious problem from the mechanical strength of the molded product. It is well known to occur.

The weld line is a thin line formed in a portion where two or more flows of the molten resin join, and the main causes thereof are as follows.

(1) When it is generated due to the flow of resin based on the shape (structure) of the product (2) When the pressure applied from the injection molding machine is insufficient (3) Mold release agent, foreign matter such as air, gas Due to the complicated shape of the molded product, it is unavoidable that the resin merges around the window or the hole, so the weld line could not be erased.

Therefore, the shape and position of the gate, which greatly affects the flow pattern of the molten resin in the cavity of the molding die,
Measures such as moving the position where the weld line exits to another position that is not important for the molded product by selecting the number etc. are taken, but this does not erase the weld line by any means and the purpose of deleting the weld line. Not effective against

[0007]

When a molded product having a complicated shape as described above is injection-molded, the weld line generated at the portion where the molten resin as the molding material merges is eliminated, and the entire molded product is covered. It is required to provide a molding method and apparatus capable of maintaining the mechanical strength as a characteristic of a resin used as a uniform material and improving the appearance of a molded product.

[0008]

As a result of earnest research to solve the above-mentioned problems, the present inventor installed an ultrasonic wave transmission device for transmitting an ultrasonic wave toward the cavity of a molding die,
The present invention has been completed by finding that it is possible to eliminate the weld line in the molded product by generating acoustic streaming across the weld line by the ultrasonic waves from this ultrasonic transmitter and disturbing the resin orientation structure in the weld line. is there.

That is, the present invention is a method for molding a resin molded product using a molding die having a cavity by an injection molding apparatus, wherein ultrasonic waves are applied to the die so as to generate acoustic streaming in the molten resin in the cavity. The present invention relates to an injection molding method which is characterized in that the material is delivered.

In the above-described method of the present invention, when ultrasonic waves are sent to the mold so as to generate acoustic streaming in the flow of molten resin in the cavity, the ultrasonic wave is superposed at the confluence of the flow of molten resin in the cavity. When the structure is such that a sound wave acts, the weld line in the molded product can be eliminated, the molded product is excellent in strength and the appearance is improved.

The present invention also provides an injection molding apparatus for molding a resin molded product using a molding die having a cavity,
The present invention also relates to an injection molding apparatus provided with an ultrasonic wave transmission device for transmitting ultrasonic waves to the mold so as to generate acoustic streaming in the flow of molten resin in the cavity.

In the apparatus of the present invention described above, the ultrasonic waves sent to the mold so as to generate the acoustic streaming in the flow of the molten resin in the cavity act on the confluence portion of the flow of the molten resin in the cavity. It is possible to adopt a configuration including an ultrasonic wave transmission device configured as described above.

The present inventor examined the flow behavior of the molten resin in the molding die by changing the intensity, the amplitude and the frequency of the ultrasonic wave delivered to the die and the delivery timing with respect to the molding cycle, and also the weld behavior. The correlation between the presence or absence of lines and the quality of molded products was examined in detail. As a result,
The relationship between the mechanism of generating acoustic streaming, which is the effect of applying ultrasonic waves to the molten resin in the molding die, and the improvement of the fluidity of the molten resin and the appearance or disappearance of the weld line depending on the mechanism was clarified.

Based on these, the ultrasonic wave transmitting device is attached to an appropriate position of the mold attached to the injection molding machine, and the injection start point-plasticization step-molten resin filling step-pressure holding step for each molding cycle is carried out. The ultrasonic waves are sent according to the cycle time to generate the acoustic streaming in the molten resin during the molding process most effectively, and by disturbing the resin orientation, the formation of weld lines in the molded product is prevented and the shape is The inventors have invented a method and an apparatus capable of obtaining a molded product which is uniform, has excellent strength, and has an improved appearance.

When ultrasonic waves are sent to the mold attached to the injection molding machine of the present invention in order to measure the disappearance of the weld line, the ultrasonic transmitter is a molten resin of the mold attached to the injection molding machine. It is preferable that the resin is attached at a position corresponding to the merging portion so that the resin is subjected to the action of ultrasonic waves at the merging portion of the resin.

In the case where the mold for molding the resin has a plurality of confluent portions of the molten resin, ultrasonic waves can be sent to the mold at a plurality of corresponding positions in order to eliminate the weld line.

The ultrasonic wave used in the present invention is an elastic wave whose frequency (frequency) exceeds the audible frequency range, and its frequency is in the range of 20 kHz to 20 MHz. This ultrasonic wave is used with a horn output of 1 W or more and 700 W, although it depends on the size of the mold and the size of the cavity in the mold.

In the present invention, the injection-molded resin is a thermoplastic resin that can be molded by injection molding,
And any of thermosetting resins, such as polyethylene, polypropylene, polybutene-1 and other polyolefins, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polymethacrylate, polymethylmethacrylate, polybutadiene, etc. Polymerization of polymers, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, butadiene-styrene copolymer, etc. Resin, 6-nylon, 6,6-nylon, 4,6-nylon, 11-nylon, 12-nylon, 11,12-na Ron, polycarbonate, polyacetal, polyurethane resins, polyphenylene sulfide, polyester, epoxy resin, phenol - any such polycondensation resin aldehyde resins, etc. may be injection molded by the method of the present invention.

The injection molding machine used in the present invention may be an injection molding machine of various known types, for example, a plunger type or a screw type. Further, it may be a transfer molding machine applied especially in the case of a thermosetting resin.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The injection molding control method and apparatus according to the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of an apparatus for carrying out the present invention.

In the figure, reference numeral 1 is a molding die comprising a cavity block and a core block, and 2 is an injection molding machine nozzle, which is joined to a sprue (not shown). The end of the sprue is connected to the runner, which is the main passage for guiding the molding material to the cavity as shown in Fig. 2.
The molten resin passes through this sprue and is filled between the cavity and the core through a gate, for example, a multi-point gate for feeding the molten resin from two or more places into the cavity to manufacture a molded article having a complicated shape. The molding material dropped from the popper 3 is measured by the measuring device connected to the injection plunger 4 by utilizing its backward movement, and at the same time, the molding material is melted in the heating cylinder 5. When the injection plunger 4 moves forward after the measurement is completed, it is injected into the mold 1 from the nozzle 2 through a narrow passage formed by the topidu 6. Heat is applied to the resin from the heater 11 on the outer periphery of the heating cylinder so that the temperature of the resin does not decrease when the molten resin passes through the topido 6 and the nozzle 2. Reference numeral 7 denotes a molten resin injection part, which is composed of an injection plunger 4, an injection cylinder 8 and a hydraulic oil pressure source including a hydraulic motor 9 and a speed reducer 10.

FIG. 2 is a view for explaining the structure of the cavity in the mold. A cavity 14 formed by a split mold of the cavity block 12 and the core block 13 is configured, and a runner 15 that guides a molten resin to the cavity 14 is provided so as to be connected to the injection molding machine nozzle 2.

Next, regarding the transmission of ultrasonic waves to the cavity in the mold, a horn (transmission part) which constitutes a part of the mold 1 and is provided so as to be in direct contact with the molten resin is connected to this. The booster (amplifier) 20 and the ultrasonic wave transmitter 21 that sends out the ultrasonic wave propagating in the booster 20.
As an example, a disk type piezoelectric ceramic vibrator having a diameter of 10 mm is embedded in a case having a diameter of 30 mm, and silicone rubber is embedded in the case. A voltage is supplied from a power source 22 to an ultrasonic oscillator 21, and ultrasonic waves generated by piezoelectric conversion by the piezoelectric ceramic are generated. The generated and generated ultrasonic waves are radiated through the booster 20 toward the portion A where the filled molten resin merges in the cavity.

In this embodiment, a frequency of 700 W and a frequency of 40 kHz is used. It has been found that the higher the frequency of ultrasonic waves, the higher the flow velocity of the molten resin.This is because when ultrasonic waves of high frequency are emitted, the absorption of ultrasonic waves by the molten resin increases, which drives acoustic streaming. Even if the molten resin is filled with force due to poor fluidity and high viscosity, it is possible to generate a secondary flow that disturbs the weld line before it solidifies. FIG. 3 shows the results of measurement of the dependence of the frequency of the radiated ultrasonic wave and the flow rate of the melt when the viscosity of the melted epoxy resin is changed.

FIG. 4 shows the change over time in the mold pressure. The pressure in the mold rises after the start of injection, and 2.
It can be understood that the filling step enters the final stage from the time when 7 seconds have elapsed, and the filling step starts from the pressure holding step where the pressure in the mold drops. Here, as a result of examining the time relationship between the ultrasonic radiation timing and the molding cycle, when ultrasonic waves are radiated to the cavity for 1 second, the ultrasonic radiation effect is the largest and the weld line of the molded product can be eliminated. It has been found that the above is the case when the filling is performed near the completion of the filling, that is, the start of the pressure holding process.

At the same time, as a result of observing the surface of the molded product with a stereoscopic microscope, it was confirmed that the weld line was completely disappeared in the molded product irradiated with ultrasonic waves.

[0027]

As described above, according to the present invention,
The mechanical strength of the injection-molded product is deteriorated, and the aesthetically unwelcome weld line of the molded product can be eliminated by irradiating ultrasonic waves from the mold surface toward the cavity during the molding process. As a result, even in the case of a molded product requiring a complicated shape, the defective molding rate could be significantly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus for carrying out the present invention.

FIG. 2 is a diagram for explaining a structure of a cavity portion in a mold.

FIG. 3 is a diagram showing a relationship between a resin flow velocity and viscosity obtained by changing a frequency of radiated ultrasonic waves.

FIG. 4 is a diagram showing a change over time in the mold pressure.

Claims (4)

[Claims] 1. A method of molding a resin molded article using a molding die having a cavity by an injection molding device,
An injection molding method characterized in that ultrasonic waves are sent to the mold so as to generate acoustic streaming in the flow of the molten resin in the cavity. 2. When ultrasonic waves are sent to the mold so as to generate acoustic streaming in the flow of the molten resin in the cavity, the ultrasonic waves act on the confluence of the flows of the molten resin in the cavity. The injection molding method according to claim 1. 3. In an injection molding apparatus for molding a resin molded product using a molding die having a cavity, ultrasonic waves are sent to the die so as to generate acoustic streaming in the flow of the molten resin in the cavity. Injection molding device equipped with an ultrasonic wave transmission device. 4. An ultrasonic wave transmission in which ultrasonic waves sent to a mold so as to generate acoustic streaming in the flow of molten resin in the cavity act on the confluence of the flow of molten resin in the cavity. The injection molding apparatus according to claim 3, further comprising a device.