JP2001113578A - Method for injection molding cylindrical molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for injection molding a cylindrical molding capable of reducing a post contraction and having a uniform density, few warp, deformation, residual strain or the like, no contraction unevenness, accurate dimensions and high appearance. SOLUTION: The method for injection molding a cylindrical molding comprises the steps of filling a resin in a mold A in a state in which a peripheral wall surface temperature of a cavity K is a high temperature of a melting temperature or higher of the filling resin, holding its temperature for a while after filling, then rolling a core die 5 while decentering the die 5 in the cavity mold 1, and cooling to solidify the filled resin while compressing the resin between the die 5 and the mold 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection-molding a tube-shaped article.

[0002]

2. Description of the Related Art In a conventional injection molding method, when a molten resin injected into a mold is cooled and solidified in the mold, the temperature and density distribution of each part of the molded article become non-uniform. In particular, when a cylinder-shaped product is molded by a single point gate, the packing pressure effect is not evenly distributed over the entire product part. I was

[0003] In order to solve this problem, there are a molding method in which a resin is injected through a multipoint gate or a disk gate, and an injection compression molding method. Further, as a method of compressing from the inside of the cylindrical portion, a molding method using a pressure fluid as disclosed in JP-A-63-27226 or a method disclosed in JP-A-5-154896 is used. An injection blow method has been proposed. That is, JP-A-63-2722
In the method described in Japanese Patent Application Publication No. 6 (1994), the mold surface (cavity side surface) of the cavity mold is swelled into the cavity by the action of the working liquid, and the molding resin is compressed in the radial direction and stretched in the axial direction to form the cylinder-formed article. It is designed to be molded.

On the other hand, in the method described in Japanese Patent Application Laid-Open No. 5-154896, a parison having a through-hole is formed by an injection mold, and then the parison is mounted in another hollow mold and heated and blown to form a cylinder. The product is shaped. However, the above methods have the following problems.

[Molding Method Using Multi-Point Gate and Disk Gate] (1) Although the balance of the shrinkage can be designed to some extent, the shrinkage itself cannot be reduced. (2) It takes time to cut the gate of the formed cylinder (particularly disk gate).

[In the case of the injection compression molding method] (1) When molding a cylindrical molded product, a mechanism for compressing the entire circumference is difficult, resulting in partial compression. (2) When compressing the cylindrical end face, mold release (peeling),
Buckling may occur.

[In the case of the method described in JP-A-63-27226] (1) Since a working liquid (hydraulic oil) is used in a mold, liquid leakage (oil leakage) occurs due to deformation of the mold itself during molding. Likely to happen. (2) The working liquid circuit in the mold becomes complicated, which tends to cause a failure.

(3) The core portion comes into sliding contact with the filled resin, and the contact portion is liable to be scratched or the like, which tends to cause poor appearance. (4) The temperature distribution of the filling resin tends to be non-uniform due to heat generated due to contact resistance or the like with the filling resin due to sliding contact.

(5) Particularly when forming a thick tubular body or a cylindrical body, a large force is required, which is not suitable.

[In the case of the method described in Japanese Patent Application Laid-Open No. 5-154896] (1) Since two-stage molding is performed, the amount of investment in manufacturing equipment is large. Also, the manufacturing space becomes large. (2) Since it is a two-stage molding, transferability is poor.

(3) Due to the heat blow, the dimensional accuracy on the inner surface side of the molded product is inferior. (4) Since the parison is formed and then blow-molded, the dimension in the longitudinal direction is not determined, and a device for determining the dimension in the longitudinal direction again after blow molding is required.

(5) Particularly, when molding a cylinder-shaped product having a large thickness, a large force is required, which is not suitable.

In view of the above, the above-mentioned problems of the conventional molding method are solved, a cylinder having a uniform density, a small amount of warpage, deformation, and residual strain, and having high precision dimensions and high appearance without unevenness in shrinkage. In order to obtain a molded article, the inventors of the present invention have already carried out a filling step of injection filling a molten thermoplastic resin into a cavity provided between a cavity mold and a core mold, A cooling and solidifying step of cooling and solidifying the filling resin filled in the core, and between the end of the filling step and the end of the cooling and solidifying step, the core mold is formed into a cylindrical shape whose central axis is molded in the cavity. A cylinder forming product that rolls the core mold in the cavity while compressing the filling resin between the cavity mold and the core mold while keeping it eccentric while maintaining parallel to the center axis of the cylinder part of the product Of injection molding method That (Japanese Patent Application No. 11-211124
issue).

However, according to this method, the temperature distribution and the compression distribution can be made uniform by compressing the filling resin between the core mold and the cavity mold by rolling of the core mold or the like instead of holding pressure. Also, by controlling the amount of eccentricity according to the resin shrinkage situation, shape shaping becomes possible without excessive overcompression, suppressing the occurrence of thermal stress due to shrinkage,
In addition, it became possible to obtain molded products with a small shrinkage distribution. However, by injecting a resin having a temperature of 200 ° C. or more into a mold at a temperature close to room temperature at the time of filling, the shear stress becomes close to the cavity peripheral wall surface. And residual stress is left. Therefore, there remains a problem that the molded product shrinkage after molding (hereinafter referred to as “post-shrinkage”) which occurs for a long time after release cannot be eliminated.

More specifically, in an olefin-based resin pipe joint such as a polyethylene pipe joint for gas distribution and water distribution, as shown in FIG. Because of this, the dimensions of the fittings change during storage of the fittings, often making fitting with the pipe impossible. A problem may occur when the stock is taken out three months or six months later.

[0016]

Accordingly, in view of such circumstances, the present invention has a uniform density, a small amount of warpage, deformation, and residual strain, and a high-precision size and high appearance without shrinkage unevenness. It is an object of the present invention to provide an injection molding method of a cylinder-shaped article which can have and reduce post-shrinkage.

[0017]

In order to achieve such an object, an injection molding method for a tube-shaped article according to the first aspect of the present invention (hereinafter referred to as "the molding method of the first aspect").
The following describes a filling step of injecting and filling a molten thermoplastic resin into a cavity provided between a cavity mold and a core mold, and a cooling and solidifying step of cooling and solidifying the filling resin filled in the cavity. The core mold is provided between the filling step and the cooling and solidifying step while the center axis of the core mold is kept parallel to the center axis of the cylindrical portion of the cylindrical molded article formed in the cavity. A method of injection molding of a cylinder-shaped product, which corrects the thickness of a molded product while compressing a filling resin between a cavity mold and a core mold by moving the molding resin in a cavity, and wherein a cavity peripheral wall surface of a mold is used during a filling process. In addition to heating to a temperature near or above the melting temperature of the resin, after the filling step and before the cooling and solidifying step, the shear stress and molecular or crystal orientation due to the resin flow during resin filling are alleviated in the mold. And the configuration includes a temperature holding step of holding the temperature or a higher temperature for some time near the melting temperature of the resin temperature of the cavity wall surface so as to reduce the molded article shrinkage after molding.

According to a second aspect of the present invention, there is provided an injection molding method of a tube-shaped article (hereinafter referred to as a “method of the second aspect”). The core axis was eccentric from the center axis of the cavity mold, and the core mold was rolled in the cavity to compress the filling resin between the cavity mold and the core mold.

According to a third aspect of the present invention, there is provided a method for injection-molding a tube-shaped article (hereinafter referred to as a "third molding method") according to the first aspect of the present invention. A hitting mechanism of a core mold is provided, and the hitting mechanism hits the core mold in the radial direction, moves the core mold in the hitting direction in the cavity mold, and compresses the filling resin between the cavity mold and the core mold. I did it.

According to a fourth aspect of the present invention, there is provided a method for injection-molding a cylinder-shaped article (hereinafter referred to as a "method of the fourth aspect") provided between a cavity mold and a core mold. A filling step of injecting and filling a molten thermoplastic resin into the cavity, and a cooling and solidifying step of cooling and solidifying the filling resin filled in the cavity, between the end of the filling step and the end of the cooling and solidifying step. A method of injection molding a cylindrical molded product in which a peripheral wall of a core mold is radially expanded in a cavity and a filling resin is compressed between the cavity mold and the core mold. While heating the temperature of the wall surface to a temperature close to or higher than the melting temperature of the resin, and after the filling step and before the cooling and solidifying step, the shear stress and molecular or crystal orientation due to the resin flow at the time of filling the resin in the mold. Relaxation And the configuration includes a temperature holding step of holding the temperature or a higher temperature for some time near the melting temperature of the resin temperature of the cavity wall surface so as to reduce the molded article shrinkage after molding.

According to a fifth aspect of the present invention, there is provided a method for injection-molding a tube-shaped article (hereinafter referred to as a "method of the fifth aspect") according to the first to fourth aspects of the present invention. At the time of compression, the cavity mold and / or the core mold are subjected to vibration in the radial direction of the core mold.

According to a sixth aspect of the present invention, there is provided a method for injection-molding a tube-shaped article (hereinafter referred to as a “method of the sixth aspect”) according to the first to fifth aspects of the present invention. , While using a crystalline resin as the thermoplastic resin,
The temperature of the cavity wall surface of the mold in the filling step and the temperature of the cavity wall surface of the mold in the temperature holding step were equal to or higher than the crystallization temperature of the resin.

According to a seventh aspect of the present invention, there is provided an injection molding method (hereinafter, referred to as a “method of the seventh aspect”) of a tube-shaped article according to the invention of the first to sixth aspects. The cooling and solidifying step comprises a first stage having a high cooling rate, a second stage having a cooling speed lower than the first stage cooling speed, and a third stage having a cooling speed higher than the second stage cooling speed. .

An injection molding method for a tube-shaped article according to the invention of claim 8 of the present invention (hereinafter referred to as “the molding method of claim 6”) is the same as the molding method of claims 1 to 6. , While using a crystalline resin as the thermoplastic resin,
A first step of cooling to a crystallization start temperature at a cooling rate of a predetermined temperature gradient, and after the first step,
It comprises a second stage of maintaining the temperature at the crystallization start temperature, and a third stage of cooling at a cooling rate with a predetermined temperature gradient after the completion of the second stage.

In the present invention, the cylindrical shape of the cylindrical molded product is
The shape may be an oval or an ellipse as well as a cylindrical shape having a perfect circular cross section. In the injection molding method and the injection molding die of the present invention, high crystallinity such as high-density polyethylene can be suitably used for molding using a resin having a large shrinkage. Is also possible.

The material of the core mold is not particularly limited, but at least the portion forming the mold surface of the core mold is made of aluminum, aluminum alloy, zinc alloy,
It is preferably formed of a copper alloy or the like, and among these, aluminum or an aluminum alloy is more preferable from the viewpoint of weight reduction. As the material of the cavity mold,
Although not particularly limited, examples include carbon steel and stainless steel.

In the injection molding method of the second aspect, the amount of eccentricity of the core mold is not particularly limited because the molding conditions and the amount of shrinkage vary depending on the size and shape of the molded product and the type of resin used. When forming a tubular material having a nominal diameter of 50 using the above, the diameter is preferably about 0.5 mm to 6 mm, and more preferably about 2 to 3 mm.

When the core mold rolls, it is preferable that the contact between the core mold and the filling resin be point contact when viewed on a cut surface perpendicular to the axis of the core mold, since the stretching and the rolling are promoted. . The injection mold used in the present invention may be either a vertical type or a horizontal type.

In the present invention, the molded article to be molded is not particularly limited. For example, as shown in FIG. 1 (a), D1 = D2, the roundness of the inner circumference is high, and D3 ≦ D4, the outer circumference Is a circular or elliptical molded product, as shown in FIG. 1 (b), D1 = D2, D3 = D4, and a molded product having high roundness on both the inner and outer circumferences, as shown in FIG. 1 (c), D1 = D2, a molded article having a high roundness on the inner periphery and having plate-shaped protrusions on the outer peripheral surface, as shown in FIG. 1 (d), D1 = D2, a high circularity on the inner periphery, and an outer peripheral surface And molded articles having cylindrical projections.

In injection molding, molecular orientation or crystal orientation occurs due to resin filling in the cavity of the mold and resin flow during the pressure-holding process, which results in dimensional accuracy, shape stability, and the like.
This leads to defects in optical characteristics and the like. The mechanism of shrinkage due to orientation relaxation in the case of high-density polyethylene which is a crystalline resin is as follows.

That is, as shown in FIG.
It has a cross-sectional structure consisting of a spherulite layer, a microcrystal layer, and a skin layer from the center toward the cavity peripheral wall surface. Among them, a layer called a microcrystal layer is shown by enlarging the X part in FIG. 2 in FIG. As shown, crystal lamella (also referred to as a lamella structure or lamella crystal) portion which forms a spherulite and an amorphous portion are alternately arranged in the flow direction of the resin. Therefore, it is considered that when the orientation generated in the amorphous portion of the microcrystalline layer is relaxed over time, contraction occurs.

In particular, in the case of high-density polyethylene, when the temperature of the molded article at the time of mold release is cooled to room temperature, shrinkage by the above mechanism is a main factor of post-shrinkage. this is,
This is because, in a temperature range around room temperature, it is difficult for the crystal part to grow, change the structure, or recrystallize, and the object of contraction is almost the amorphous part orientation relaxation.

Therefore, in order to reduce post-shrinkage,
(1) The orientation should not be generated, (2) the generated orientation should be relaxed during molding, and then released. (3) The amount of the skin layer and microcrystal layer in which the orientation occurs (the amount of each layer in the cross-sectional structure of the molded product) It is important to reduce the thickness).

In the present invention, the above (2)
Regarding (3), it relates to means for achieving at least one of them. The technical points will be described below.

That is, in the case of the above (2), when polyethylene is used as the resin, the orientation relaxation proceeds even at room temperature, as the problem of post-shrinkage actually occurs. However, since the relaxation rate increases as the resin temperature increases,
It is effective to maintain the resin temperature at a high temperature to promote relaxation.

In the above (3), the skin layer and the microcrystalline layer are formed in a portion where the resin is rapidly cooled and solidified by the contact between the resin and the peripheral wall surface of the mold when the resin is filled in the cavity. Also, the thickness of these layers, the mold temperature, especially if the temperature of the cavity peripheral wall surface is equal to or less than the solidification temperature of the resin, the greater the cooling rate, that is, the greater the difference between the cavity peripheral wall surface temperature and the filling resin temperature It is thought that it develops. Therefore, the smaller the difference between the resin temperature and the temperature of the cavity peripheral wall surface, the more effective.

For the relaxation temperature and the heat retention time, it is desirable to measure the stress relaxation characteristics of the molding resin in advance, and to calculate the relaxation temperature and the heat retention time from the results. As shown in FIG. 4, the relationship between the stress relaxation and the required time shows a linear tendency in the log-logarithmic representation. Therefore,
In real time, a great relaxation effect can be expected at the start of relaxation, and thereafter, the effect of relaxation on the relaxation time becomes low. By knowing the stress relaxation characteristics, the relaxation temperature and time are determined in consideration of the relaxation effect (degree of post-shrinkage) and productivity, and by maintaining the resin temperature during this time at or above the crystallization temperature, efficient relaxation is achieved. Process can be established.

The degree of crystallinity of the resin changes depending on the environment in which the resin solidifies. In particular, it is known that it depends on the cooling rate when solidifying from a molten state. In the case of slow cooling, more crystals are produced by slow cooling over time, and the crystals grow larger and the crystallinity increases. Conversely, in the case of rapid cooling, the supercooling phenomenon becomes remarkable, and the crystallization start temperature shifts to a lower temperature side, so that there is no time for crystal generation and growth, and the degree of crystallinity decreases.

More specifically, it is known that a crystalline resin has a temperature range in which crystals are formed and grown (a crystallization temperature range). Therefore, when controlling the degree of crystallinity, it is almost determined by what cooling rate this crystallization temperature region is cooled. Therefore, even in the case of rapid cooling, by performing slow cooling in an appropriate temperature range, crystallization is promoted, and the degree of crystallinity can be increased.In the entire cooling process, by performing in an appropriate temperature range, Originally, when increasing the degree of crystallinity by supercooling, it is not necessary to gradually cool at a constant rate in the entire cooling process, and only in the crystallization temperature range, the molding cycle is efficiently performed without wasting and prolonging the molding cycle. Thus, the degree of crystallinity can be improved.

Although the crystallization temperature range and the crystallization start temperature vary depending on the environment in which the resin solidifies (especially the cooling rate) as described above, it is determined by a PvT (pressure-specific volume-temperature) measuring device as described later. It can be known by performing PvT characteristics, calorimetric analysis using a differential scanning calorimeter (hereinafter abbreviated as “DSC”), or the like.

When the molten resin is solidified in the cavity,
The resin in contact with the cavity peripheral wall is cooled most. Therefore, the resin temperature has a temperature distribution in the thickness direction of the molded product. This indicates that the cooling rates are different in the thickness direction at the same time. That is, the cooling rate of the molded product surface is the fastest, and the core is the slowest. Therefore, this difference in cooling rate directly leads to a difference in crystallinity.

Therefore, as in the molding method of the present invention, the cooling step of the resin is composed of three stages, the cooling speed is high in the first stage, the cooling speed is low in the second stage, and the cooling speed is in the third stage. It is preferable to increase the speed, but specific examples thereof include the modes shown in FIGS. 5 (a) to 5 (d). That is, as shown in (a), (c), and (d) of FIG. 5, the gradient of the temperature with respect to time is changed in a curve, and as shown in (b) of FIG. A mode in which the change is performed linearly, or a mode in which these are appropriately combined to combine a curved change and a linear change can be adopted.

Further, in a special mode such as the molding method of the eighth aspect shown in FIGS. 5E and 5F, that is, in the second stage of the cooling step, the temperature is once set to be constant, and the temperature is set for a while. It is preferable to maintain the temperature, and it is more effective to set the starting temperature of the second stage near the crystallization starting temperature.

In the cooling step of the injection molding, the cooling rate pattern used depends on the crystalline resin used and the desired degree of crystallinity. Regarding the crystalline resin to be used, it is necessary to grasp the relationship between the cooling rate and the crystallinity in advance. In order to grasp the relationship between the cooling rate and the crystallinity, the crystallinity of the resin sample solidified at various cooling rates is measured by DSC or the like, and the relationship between the cooling rate and the crystallinity is grasped. Also, DSC or PvT that can change the cooling rate
The use of the measuring device makes it possible to grasp the crystallization start temperature and the crystallization temperature range that change depending on the cooling rate. In particular, in the case of a DSC in which a wide range of cooling rates can be set, the resin sample is cooled in a cooling pattern to be actually molded, and the crystallinity in various cooling patterns is measured by measuring the crystallinity of the sample given its temperature history. The degree of change can be grasped.

Here, the crystallization start temperature or the crystallization temperature range is determined by DSC or Pv in the conventional cooling step.
Judgment is made from the results obtained by the T measurement. That is, DSC
In the case of use, as shown in FIG. 6, from the temperature-caloric curve, the temperature range where the curve greatly deviates from the baseline is the crystallization temperature range, and the maximum value in the temperature range is the crystallization start temperature. Become. In the case of PvT measurement, as shown in FIG. 7, in the temperature-specific volume curve, the temperature range where the rate of change of the specific volume is the highest is the crystallization temperature range, and the maximum value is the crystallization start temperature. Temperature.

The means for heating and maintaining the cavity peripheral wall surface at a temperature near or above the crystallization temperature of the resin is not particularly limited. For example, an electric heater is provided in a mold, and the electric heater is turned on. Thus, a high temperature may be maintained, or a heating means using high-frequency vibration or near-infrared rays may be employed.

Alternatively, instead of providing a heater in the mold,
A heating medium circulation pipe may be provided in the mold, and the heating oil may be supplied to the heating medium circulation pipe of the mold by a mold temperature controller through a conduit provided with an electromagnetic valve.

In the method of the present invention, the means for changing the cooling rate is not particularly limited.
A method can be adopted. (1) A method of changing the flow rate of the refrigerant. (2) Switching between refrigerants having different temperatures. (3) Switching the passage position of the refrigerant. (4) A method using a combination of cooling by a refrigerant and heating by a heater.

In the method (1) for changing the flow rate of the refrigerant, the cooling rate can be changed by changing the flow rate of the refrigerant flowing through the cooling pipe in the mold. That is, the heat transfer efficiency increases and the cooling rate increases as the flow rate of the refrigerant increases. The flow rate is controlled in a wide range, for example, from 0 to 20 liters / minute by using a refrigerant pumping device. During the cooling process, the cooling rate can be changed at a preset timing by controlling the opening amount of the flow control valve provided on the cooling pipe manually or according to a signal from a control device.

In the method (2) for switching refrigerants having different temperatures, a plurality of mold temperature controllers (temperature controllers) are used, and a plurality of refrigerants having different temperatures are used. The cooling rate is changed by utilizing the fact that the cooling rate changes due to the temperature difference between the mold and the refrigerant. In this case, the cooling rate increases as the temperature difference increases. During the cooling process, the solenoid valve provided in the conduit from the mold temperature controller is appropriately switched according to a signal from a manual or control device to supply the coolant to the mold refrigerant flow pipe, and by switching these refrigerants, The cooling rate can be changed at the set timing.

In some cases, it is possible to set the temperature over a wider range (for example, 5 to 180 ° C.) by changing the type of the refrigerant, that is, chiller, water, oil, or the like. In this method, it is possible to maintain the temperature of the peripheral wall of the cavities at a constant temperature (cooling rate = 0) and, if necessary, to reheat the refrigerant within the temperature range of the refrigerant. Using a plurality of mold temperature control devices for different types of refrigerant, appropriately switching solenoid valves provided in the conduits from each mold temperature control device to supply to the mold refrigerant flow pipes, these different Switching the type of refrigerant makes it possible to set the temperature of the mold.

In the method (3) for switching the passage position of the refrigerant, the distance between the cavity and the refrigerant is changed by selectively flowing the refrigerant through the cooling pipe arranged in the mold so that the distance to the cavity is different. The cooling rate can be changed by utilizing the fact that the heat transfer efficiency is affected. In this case, the shorter the distance between the cavity and the cooling pipe, the higher the cooling rate. During the cooling process, by manually or according to a signal from the control device, by switching the flow path of the refrigerant,
The cooling rate can be changed at a preset timing.

In the method (4) in which the cooling by the refrigerant and the heating by the heater are used in combination, the mold is provided with a cooling pipe for passing the refrigerant and a heater, and the cooling rate by the refrigerant is adjusted by the heater. ,
The cooling rate can be varied.

Alternatively, a plurality of mold temperature control devices are used, one of the mold temperature control devices supplies a refrigerant to the refrigerant flow pipe of the mold, and the other mold temperature control device controls the heating medium of the mold. You may make it supply to a heating medium distribution pipe.

During the cooling step, the cooling rate can be changed at a preset timing by turning on / off the heating heater manually or according to a signal from a control device. In this method, the temperature of the cavity peripheral wall surface is kept constant (cooling rate = 0),
If necessary, reheating can be performed within the temperature range of the refrigerant.

Each of the above four methods may be used alone, or a combination of these methods may be used.
According to the combined method, the control range or control pattern can be further expanded. The heating heater is not particularly limited. For example, a sheath heater or a heating means such as infrared rays can be used.

The cooling rate control means may be determined and controlled based on the cavity peripheral wall surface or the temperature of the resin in contact with the cavity peripheral wall surface or the elapsed time during the molding cycle.

As the simplest control means, for the required cooling rate, the set values of the above-mentioned four cooling rate variable methods are checked in advance, and the elapsed time during the molding cycle (for example, from the start of resin filling and the start of cooling). (Elapsed time), the setting value may be switched manually or by timer control. In this method, if a set value is derived in advance, it is not always necessary to measure the cavity peripheral wall temperature or the resin temperature in actual molding. However, it should be noted that the actual cooling pattern may slightly deviate from the target pattern due to disturbances such as changes in the ambient temperature and molding conditions.

In order to more accurately control the cooling rate, it is necessary to control the cooling rate by installing a sensor for measuring the temperature of the cavity peripheral wall or the resin in contact with the cavity peripheral wall as needed in the mold. is there. The measurement data from the sensor is sent to the control unit, and the cooling rate is calculated every moment from the temperature gradient with respect to the measurement interval, and the cooling rate is controlled so as to be a preset cooling rate.

In the second stage, when maintaining a constant temperature, it is preferable to control so as to maintain the set temperature for a time set as a cooling pattern.

[0061]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings.

[First Embodiment (Embodiment 2)] The first embodiment of the injection molding method for a tube-shaped article according to the present invention.
In this embodiment, first, a precision injection mold A as shown in a cross section in FIG. 8 is prepared.

That is, as shown in FIG.
A cavity mold (mold body) 1 and a cylindrical core mold 5 that forms a cavity K between the cavity mold 1 are provided. That is, the cavity mold 1 includes the fixed mold part 2, the movable mold part 3, and the slide mold parts 4, 4, and when the mold is closed, the upper end surface of the core mold 5 comes into close contact with the inner wall surface of the fixed mold part 2. ,
The lower end surface of the core die 5 is in close contact with the inner wall surface of the movable die portion 3, and a cylindrical cavity K is formed between the inner wall surfaces of the slide die portions 4, 4 and the peripheral wall surface of the core die 5. ing.

As shown in FIGS. 8 and 9, the fixed mold portion 2 includes a sprue 21, a gate 22, a cooling air inflow passage 23 of the core mold 5, a cooling air discharge passage 24 of the core mold 5, and a An upper recess 25 into which the upper bearing 51 of the core mold 5 is loosely fitted, and two hydraulic cylinders 26, 26 are provided. As shown in FIG. 10, a ring-shaped cooling air inflow groove 27 communicating with the cooling air inflow passage 23 of the upper bearing 51 and a ring-shaped cooling airflow communicating with the cooling air discharge passage 24 are formed on the bottom surface of the upper concave portion 25. An air discharge groove 28 is provided.

The hydraulic cylinders 26, 26
The cylinder rod 261 advances and retreats into the upper concave portion 25 to fix and open the upper bearing 51 as described later.
That is, the hydraulic cylinders 26, 26 are
Together with the hydraulic cylinder 32 provided on the side, it serves as support means for the core mold 5. Each of the slide-type portions 4 has a cooling channel 41 for cooling water therein, and a heater wire as heating means (not shown) is embedded therein.

The movable mold part 3 has a lower recess 31 into which a lower bearing 52 of the core mold 5 described later is loosely fitted, and a hydraulic cylinder 3
2 is provided. The hydraulic cylinder 32 is mounted on the outer wall surface of the movable mold part 3 so as to be located immediately below one hydraulic cylinder 26 on the fixed mold part 2 side.
1 faces the inside of the lower concave portion 31, and the tip is the lower bearing 5.
It is fixed to 2.

The core mold 5 is shown in FIGS. 8, 9, 11, and 12.
As shown in FIG. 13, in a state where the center axis of the cavity mold 1 and the center axis of the core mold coincide with each other, heat shrinkage generated from filling to resin solidification or shrinkage due to crystallization is taken into consideration. The outer diameter is designed so that a thicker gap is formed between the core mold 5 and the cavity mold 1 depending on the thickness of the molded product to be obtained, and the upper bearing 51, the lower bearing 52, and the transmission Geared motor with mechanism
53, an arm 55 rotatably supported by a drive shaft 54 directly connected to the motor 53, a first sprocket 571 fixed to the drive shaft 54, and a shaft at the tip of the arm 55. A second sprocket 572 supported,
An internal gear 581 provided coaxially with the second sprocket 572 and an external gear 582 integrally provided on the inner peripheral surface of the core mold 5 and engaged with the internal gear 571.
, A first sprocket 571 and a second sprocket 572
And a chain 59 that is hung on the chain.

The external gear 582 and the internal gear 581 are not particularly limited, but are preferably in the range of modules 3 to 8, more preferably in the range of 8 to 10, and allow smoother rolling. Therefore, it is preferable to use a trochoidal curve gear or an involute curve gear.

The arm 55 has a length such that the distance from the center of the drive shaft 54 to the outer peripheral surface of the core mold 5 in the direction of the arm 55 is slightly longer than the radius of the core mold 5. As shown in FIG. 9, the upper bearing 51 is provided with a cooling air inflow hole 51.
1 and a cooling air discharge hole 512, which are slidably adhered to the bottom surface (the ceiling surface in the figure) of the upper concave portion 25 when the mold is closed.

The lower bearing 52 is, as shown in FIG.
A thrust receiving portion 521 and a fixing portion 522 fixed to the core die 5 rotatably received by the thrust receiving portion 521 are provided, and the lower end surface of the thrust receiving portion 521 slides on the bottom surface of the lower concave portion 31. Adhering freely. Motor 5
Reference numeral 3 is provided with a speed change mechanism capable of freely changing the speed in the range of 5 to 500 rpm, and is suspended from the lower end surface of the fixed mold portion 2 so as to be slidable in the direction in which the cylinder rod 321 of the hydraulic cylinder 32 moves forward and backward. And the drive shaft 5
4 is inserted into the fixing portion 522 of the lower bearing 52 so as to be shifted from the center of the core mold 5. That is, the fixed portion 522 serves as a bearing for the drive shaft 54.

The motor 53 has an encoder, and the arm 55 always faces the hydraulic cylinder 32 when the motor 53 is stopped.

The mold A is as described above.
The tubular molded article can be formed as follows.

As shown in FIG. 8, the cavity mold 1 and the core mold 5 are closed, and at the same time, the cavity which is the central axis of the molded product for which the hydraulic cylinder 32 is operated to obtain the core mold 5 as the central axis. After being arranged so that the central axis of K coincides with the center axis, the hydraulic cylinders 26, 26 are actuated so that the upper bearing 51 of the core mold 5 is connected to both thin rods 261, 261.
To fix the core mold 5. At the same time, the heater wire is energized so that the peripheral wall of the cavity K is heated to the melting temperature of the thermoplastic resin used or higher.

A molten resin is injected into the cavity K from an injection molding machine (not shown) through the sprue 21 and the gate 22, and the amount of the filled resin corresponding to the volume of the cavity K is increased as shown in FIG. P is filled for a time corresponding to the volume of the cavity K.

When the filling is completed, as shown in FIG. 15, the cavity K is heated to a melting temperature or higher for a while so as to relax the shear stress and the molecular or crystal orientation due to the resin flow at the time of filling the resin in the mold. The temperature of the peripheral wall surface is maintained. After the completion of the temperature holding step, as shown in FIG.
The cooling and solidifying step and the compressing step are performed simultaneously. That is, in the first stage of the cooling and solidifying step, first, the resin is rapidly cooled to near the crystallization start temperature of the resin.

Then, simultaneously with the start of the first stage of the cooling and solidifying process, the cylinder rods 261,
261 is retracted to release the holding of the upper bearing 51, and the motor 53 is driven to rotate at a preset rotation speed to roll the core mold 5 along the inner wall surface of the filling resin. Activate the core mold 5
With the motor 53 in the direction of the hydraulic cylinder 32 to keep the center axis of the core mold 5 eccentric from the center axis of the cavity K while maintaining a state parallel to the center axis of the cavity K in response to the heat shrinkage of the resin accompanying cooling. Let it.

That is, by the rotation of the motor 53, the rotational force of the motor is transmitted to the internal gear 571 via the drive shaft 54, the first sprocket 571, the chain 59, and the second sprocket 572, and the internal gear 581 is connected to the external gear. Rotate while engaging with 582. And this inscribed gear 581
The arm 55 rotates around the drive shaft 54 with the rotation of the inscribed gear 581 due to the rotation of the core mold 5, and the core die 5 rolls along the inner wall surface of the filling resin accordingly. Also, the arm 55
Since the distance from the center of the drive shaft 54 to the outer peripheral surface of the core mold 5 in the direction of the arm 55 is formed to have a length slightly longer than the radius of the core mold 5, as shown in FIG. With the rotation of 55, the inner wall surface of the core mold 5 is
1 and rolls while compressing the filling resin in the direction of the cavity mold 1 while maintaining the eccentric state, so that the filling resin P moves between the core mold 5 and the cavity mold 1 on the extension of the arm 55. Rolling and stretching are repeated over the entire circumference.

The resin P on the eccentric side is compressed between the core mold 5 and the cavity mold 1, and the eccentric space S between the core mold 5 and the resin P on the other surface side. Occurs.
Further, the core mold 5 itself has an eccentric space S between the core mold 5 and the filling resin P, and the inner peripheral length of the filling resin portion is longer than the outer peripheral length of the core mold 5. 571 rotates in the opposite direction to the rotation direction. Further, since the cylinder rods 261 and 261 are retracted, the core type 5
Although the upper bearing 51 is in a free state when rolling, the eccentric shaft shifts because the upper bearing 51 and the lower bearing 52 are firmly supported at two points vertically by the cavity mold 1. Rolls smoothly without any.

As shown in FIG. 15, the core mold 5 is rolled while the eccentric amount of the core mold 5 is further increased in accordance with the shrinkage accompanying the crystallization shrinkage. The temperature is maintained for a while near the crystallization start temperature of the resin. As shown in FIG. 15, after the second stage of the cooling and solidifying step, the core mold 5 is rolled while the eccentric amount of the core mold 5 is further increased in accordance with shrinkage, and the temperature is changed from around the crystallization start temperature to room temperature. The resin P is rapidly cooled until the resin P is cooled and solidified.

Until the mold A is opened, the core mold 5 continues rolling, and the motor 53 is stopped at an arbitrary timing.
The mold is opened and the molded product W is taken out. The filling resin P is
Cooling water is supplied to the cooling channel 41 to cool the cavity mold 1, and the cooling air is sent to the core mold 5 through the cooling air inflow path 23, the cooling air inflow groove 27, and the cooling air inflow hole 511. The core mold 5 is cooled and solidified by cooling from the inside.

The cooling air entering the core mold 5 is
After the core mold 5 is cooled, the core die 5 is discharged through the cooling air discharge hole 512, the cooling air discharge groove 28, and the cooling air discharge passage 24. As the core die 5 rolls in an eccentric state, the cooling air inflow hole 511 and the cooling air discharge hole 512 also rotate eccentrically. The cooling air inflow holes 511 and the cooling air discharge holes 512 are always formed in the shape of the cooling air and the cooling air inflow grooves 27 and the cooling air Discharge groove 2
8, a cooling air inlet 23 and a cooling air outlet 24
Is kept in communication. That is, the core 5 of the cooling air
The supply to the inside is continuously performed without interruption.

The injection molding method of the first embodiment is as described above, and has the following excellent effects.

(1) When filling the mold A with the resin, the peripheral wall surface of the cavity K is maintained at or above the melting temperature of the resin.
After the resin filling is completed, the peripheral wall temperature of the cavity K is kept at or above the melting temperature until the shear stress and molecular or crystal orientation at the time of filling are sufficiently relaxed. Because it was switched to three stages, increasing the crystallinity, molding a molded product with a uniform crystallinity distribution, eliminating heat shrinkage after mold release, reducing the shrinkage of the molded product after molding, A prolonged molding cycle can be prevented.

(2) The compression step by rolling of the core mold is provided by eliminating the pressure-holding step, and the resin shrinks without generating the shear stress, temperature distribution and pressure distribution which cause post-shrinkage and crystal shrinkage unevenness. Since the core mold is decentered in accordance with the behavior and is shaped into the thickness of the molded product, the molding dimension at the time of release from the mold dimension is improved, and subsequent shrinkage can be prevented. (3) By making the wall thickness at the time of filling larger than the wall thickness of the molded product, the generation of shear stress is smaller than in the case where the resin is filled into the cavity having the larger wall thickness of the molded product. In addition to exerting the effect, the production of a thin molded product is also facilitated.

(4) A molded article having good appearance can be obtained without sink marks due to post-shrinkage. (5) Since the amount of shrinkage itself from the dimensions of the mold is small and stable, it is suitable for precision molding.

(6) The amount of shrinkage is made uniform over the entire molded product and the amount of shrinkage is small, so that the number of times of correcting the die and the like are reduced, and the die design is facilitated. (7) Since the circumferential distribution of post-shrinkage is suppressed, not only the long-term dimensional stability is improved, but also the accuracy of the roundness of the molded product is improved, and the joining strength when joining by heat fusion is improved. Improves reliability.

(8) When the core die 5 rolls, a gap is formed between the core die 5 and the filling resin P in a portion other than the compression surface, so that stress relaxation is more likely to occur. (9) When moving to the cooling and solidifying step, since the peripheral wall surface of the cavity K is in a molten state in which the filling resin P is kept at a high temperature, that is, the core mold 5 is rolled. Thus, a large force is not required, the capacity of the motor 53 can be reduced, and a molded product having good transferability can be obtained.

(10) Since the core die 5 only rolls, almost no slippage occurs on the contact surface between the core die 5 and the filling resin P, and the rolling of the core die 5 causes the contact with the filling resin P. No heat is generated between them.

[Second Embodiment (Embodiment 3)] In a second embodiment of the injection molding method of the present invention, a mold shown in FIGS. It is the same as the first embodiment except that the mold B is used.

That is, as shown in FIGS. 16 to 19, the mold B includes a cavity mold 6, a core mold 7, and a striking mechanism (vibration mechanism) 8. The cavity mold 6 includes a fixed mold 61 and a movable mold 62.

The core mold 7 has a cylindrical shape made of a lightweight metal material such as aluminum, and has a small-diameter cylindrical portion 71 opened at both ends. Ka is formed. The striking mechanism 8 has a rotating shaft 81 that is rotatable by a driving device (not shown) so as to be able to change the angular velocity and to rotate forward and backward.
And a plate-shaped impactor (vibrator) 82 slidable in a direction orthogonal to the rotation shaft 81 and narrower than the inner diameter of the core mold 7.
And a slide drive means (vibration mechanism) 83 for reciprocating the striker 82 at a frequency set in the slide direction by an electromagnetic force.

The rotating shaft 81 is provided along the center axis of the cavity Ka, and has a stopper 9 slidably mounted as support means for the core mold 7.
As shown in FIG. 17, the stopper 9 slides toward the core mold 7 and fits into the small-diameter cylindrical portion 71, and the core mold 7 is positioned at a position where the center axis of the core mold 7 coincides with the center axis of the cavity mold 6. It can be fixed. Although not shown, the stoppers 9 are provided on both sides of the core mold 7.

The mold B is as described above.
Except for the following compression mechanism, the above mold A
A cylindrical molded article can be manufactured in the same manner as in the method using. That is, first, as shown in FIG. 17, the compression mechanism of the molding method using the mold B
The cavity mold 6 is closed in a state of being fitted to the small-diameter cylindrical portion 71, and the molten resin is injected from the gate 63 provided on the fixed mold 61 side by an injection molding machine (not shown) into the cavity Ka.
Injection-filling is carried out in an amount and time corresponding to the volume of the product. At this time, as shown in FIG.
To a position that does not contact the inner wall surface of the

After the filling is completed, as shown in FIG. 16, the stopper 9 is removed, and the core mold 7 is rotated in the cavity mold 6 by the rotating shaft 81.
To be slidable in a direction orthogonal to. Next, the rotation shaft 81 is rotated forward and reverse at predetermined time intervals, and while changing the angular velocity, the slide driving means 83 is operated to reciprocate the striker 82, and the striker 82 is moved for every forward movement and backward movement.
At both ends, the filling resin Pa is compressed while hitting the inner wall surface of the core mold 7.

That is, as shown in FIG. 19 (a), the filling resin Pa filled in the cavity Ka is hit on the inner wall surface of the core mold 7 by the striker 82 as shown in FIG. 19 (b). The core mold 7 moves in the striking direction while maintaining a state parallel to the center axis of the core mold and the center axis of the cavity mold 6, that is, the center axis of the cylindrical molded product to be obtained. Accordingly, part of the filling resin Pa is radially compressed between the core mold 7 and the cavity mold 6 along the pressure line. On the other side, an eccentric space Sa is generated between the core mold 7 and the filling resin Pa.

Then, as shown in FIG. 19 (c), since the rotating shaft 81 is rotating, the hitting position of the hitting element 82 changes one after another, and the core mold 7 moves in parallel in the cavity mold 6. It starts to vibrate while doing. Therefore, the filling resin Pa
19D, a compact Wa uniformly compressed on the inside can be obtained as shown in FIG. 19D.

This injection molding method is as described above, has the same effects as in the first embodiment, and has the same effect as the first embodiment.
Almost at the contact surface between the resin and the filling resin Pa (shearing force)
Does not occur and the filling motion Pa
No heat is generated between the two. Moreover, since no shearing force is generated in the circumferential direction, there is no residual stress in the circumferential direction.
Therefore, the strength is improved, and cracking by the solvent hardly occurs.

[Third Embodiment (Embodiments of Claims 2 and 5)] A third embodiment of the injection molding method of the present invention is shown in FIG. It is the same as the first embodiment except that the mold C is used.

As shown in FIG. 20, the mold C is a vertical mold, and includes a cavity mold 100, a cylindrical core mold 200 forming a cavity K1 between the cavity mold 100, and a core mold 200. A rolling rotation mechanism 300 for the mold 200;
And a core vibration imparting mechanism 400 of the core mold 200.

That is, the cavity mold 100 includes a cavity mold body 110, a nest mold 120, and a nest mold 12.
0 cavity type vibration imparting mechanism 500.
The cavity mold main body 110 includes a fixed mold part 130, a movable mold part 140, and slide mold parts 150, 150.

As shown in FIGS. 20 and 21, the fixed mold part 130 includes a sprue 131, a gate 132, an upper bearing part 133, a core type hydraulic cylinder 134, and a rotary cylinder hydraulic cylinder 135. Have. The upper bearing portion 133 is fixed at the position facing the cavity K1.
The first concave portion 1331 and the second concave portion 1332 that decrease in diameter in a stepwise manner toward the zero side.
32, a bearing body 136 is provided slidably in the horizontal direction with respect to the parting line.

In the rotary cylinder hydraulic cylinder 135, the tip of the cylinder rod 1351 faces the inside of the second recess 1332, and is fixed to the side surface of the bearing body 136. That is, as the cylinder rod 1351 moves forward and backward, the bearing body 136 slides in the second recess 1332 in the direction in which the cylinder rod 1351 moves.
The bearing main body 136 has, in the center thereof, an upper end 32 of a rotating shaft 320 of a rotating cylinder 310 of a rolling rotation mechanism 300 described later.
1 is a connecting portion 136 of a spline structure into which a sliding fit is made.
1, the end of the rotating shaft 320 is slidably fitted to the connecting portion 1361 to rotatably support the rotating shaft 320.

The core mold hydraulic cylinder 134 has a tip end of a cylinder rod 1341 facing the inside of the first concave portion 1331 and a tip end of a positioning member 137 of a core mold 200 described later.
Is provided. The positioning member 137 has a substantially inverted truncated conical cylindrical shape, the rotating shaft 320 penetrates the inside thereof, and a lower end 1371 which is a small diameter side thereof is provided at an upper end of a core mold 200 described later. It is loosely fitted in the engagement hole 221 of the small diameter portion 220 thus formed.

As shown in FIGS. 20 and 22, the movable mold section 140 includes a lower bearing section 141, a core mold hydraulic cylinder 142, and a rotary cylinder hydraulic cylinder 143. The lower bearing portion 141 has a first diameter decreasing stepwise toward the movable mold portion 140 at a position facing the cavity K1.
The bearing body 144 includes a recess 1411 and a second recess 1412, and the bearing body 144 is slidably provided in the small-diameter second recess 1412 similarly to the bearing body 136 of the upper bearing portion 133.

In the rotary cylinder hydraulic cylinder 143, the tip of the cylinder rod 1431 faces the second recess 1412 and is fixed to the side surface of the bearing main body 144. That is, as the cylinder rod 1431 moves forward and backward, the bearing main body 144 slides in the second recess 1412 in the direction in which the cylinder rod 1431 moves forward and backward.
The bearing body 144 is provided at the center thereof with a rotating cylinder 3 described later.
The lower ends 322 of the ten rotating shafts 320 are rotatably supported.

The core mold hydraulic cylinder 142 has a tip end of a cylinder rod 142a facing the first concave portion 1411 and a tip end of a positioning member 145 of a core mold 200 described later.
Is provided. The positioning member 145 has a substantially frustoconical cylindrical shape, the rotating shaft 320 penetrates the inside, and the upper end 1451 on the smaller diameter side is provided at the lower end of the core mold 200 described later. The engagement hole 231 of the small diameter portion 230 is loosely fitted.

The nesting type 120 is, as shown in FIG.
It is housed in the cavity mold body 110 and has a cylindrical shape, and forms a cavity K1 with the core mold 200. As shown in FIGS. Is provided with a flange portion 122 having a substantially triangular cross-section, which gradually extends while forming a tapered surface 121 toward the fixed side, and a cooling water passage 120a is spirally provided inside. As shown in FIGS. 23 and 24, the slide die 150 is provided with a cutout 152 having a substantially triangular cross section having a tapered surface 151 having a slightly obtuse angle than the tapered surface 121 at a portion corresponding to the flange 122 of the nesting die 120. Have been.

Also, as shown in FIGS. 23 and 24, the portion of the fixed mold portion 130 corresponding to the
2 is provided with a ring-shaped concave groove 138. That is, when vibration is applied to the nesting mold 120 by the cavity-type vibration imparting mechanism 500 described below with the mold C closed, the nesting mold 120 is moved to the cavity mold body 1.
It is slidable in the interior 10 toward the fixed mold part 130 side.

The cavity-type vibration applying mechanism 500 has a 1H
Vibration can be applied variably in the range of z to 100 KHz. As shown in FIG. 20, a vibration generator 510 fixed to the outer wall surface of the movable mold 140 and a movable mold 14
0, the tip of which is movable
A vibrator 520 is provided in contact with the 0-side wall surface, and the vibration generated by the vibration generator 510 is applied to the nesting mold 120 via the vibrator 520.

That is, as shown in FIG. 24A, the upper end surface 125 of the nest type 120 is located at substantially the same level as the upper end surface 155 of the slide die 150 immediately after filling. When the vibration is applied via 520, first, as shown in FIG. 24B, the vibration is temporarily pushed up to the fixed mold part 130 side by the vibrator 520 (0.02
mm). That is, vibration is transmitted in the direction of arrow X1.

Next, the recoil which returns to the original state is shown in FIG.
As shown in FIG.
It is in a state (about 0.02 mm) that is slightly penetrated into the side,
Vibration is transmitted in the direction of the arrow X2 and the tapered surface 121,
151 allows vibration to be transmitted in the direction of arrow Y1. Thereafter, as shown in FIG. 24D, the state returns to the original state again. At this time, the vibration is transmitted in the directions of the arrow Y2 and the arrow X1.

As shown in FIG. 20, the core mold 200 has a large-diameter main body 210 having a cylindrical shape to form a mold surface, and a first concave portion 1331, which protrudes from both ends of the main body 230.
1411 facing small diameter portions 220 and 230,
It is formed of an aluminum alloy. Body 21
0, as shown in FIG. 21, the upper end surface 215 is received on the lower end surface 139 of the fixed mold portion 130, and the lower end surface 216 is received on the upper end surface 149 of the movable mold portion 140, as shown in FIG. It has become.

The small-diameter portions 220 and 230 are provided with trumpet-shaped engagement holes 221 and 231 at their ends, respectively, and as described above, the lower end 137 of the positioning member 137 is formed.
1 and the upper end 1451 of the positioning member 145
21 and 231 are loosely fitted. That is, the core mold 200 is rotatable in the cavity mold 100, and is positioned on the inner wall surfaces of the engagement holes 221 and 231 by moving the cylinder rods 1341 and 1421 of the core mold hydraulic cylinders 134 and 142 forward and backward. Member 13
The peripheral surfaces of the cylinder rods 1341 and 1421 can move in the advancing and retreating directions while the peripheral surfaces of the cylinder rods 7 and 145 are in contact with each other and keep the central axis parallel.

The rolling rotation mechanism 300 includes a rotating cylinder 310
And a motor 350. The rotating cylinder 310 is
The rotating shaft 320 is eccentrically provided so that a part of the outer wall surface always makes a point contact with the inner wall surface of the core type main body.

The outer diameter of the rotating shaft 320 is slightly smaller than the inner diameter of the positioning members 137 and 145 on the smaller diameter side. The rotation speed of the motor 350 is variable in the range of 5 to 500 rpm, and the drive shaft 351 is connected to the rotation shaft 320 of the rotation cylinder 310 through the movable mold part 140 to rotate the rotation cylinder 310. It is designed to rotate about an axis 320.

The core-type vibration imparting mechanism 400 includes the rotary cylinder 3
The electromagnetic generator 41 is provided integrally with the rotating shaft 320 of the
0 and a striker 420. Electromagnetic generator 410
Is fixed to a rotating shaft 320 so as to rotate with the rotating shaft 320, and its output is variable.

The striker 420 has a rotating shaft 3 at a frequency ranging from 1 Hz to 100 Hz according to the output of the electromagnetic generator 420.
20 vibrates in a direction perpendicular to the direction of rotation of the rotary cylinder 3 at its tip.
The vibration is transmitted to the core mold 200 by hitting the inner wall surface of the contact portion with the core mold 200. The motor 350 includes an encoder (not shown).
When 0 is stopped, the contact portion of the rotary cylinder 310 with the core mold 200 always faces the rotary shaft hydraulic cylinders 135 and 143.

This mold C can be used to manufacture a cylindrical molded product in the same manner as the method using the mold A except that the compression mechanism is different. That is, the compression mechanism of the mold C first closes the cavity mold 100 and the core mold 200, as shown in FIGS. 15 and 20 (a), and simultaneously rotates the rotary shaft hydraulic cylinders 135, 143 and the core mold. By operating the hydraulic cylinders 134 and 142 for use, the core mold 200 is arranged so that the central axis thereof coincides with the central axis of the cavity K1 which is the central axis of the molded product to be obtained.

Next, the molten resin is injected into the cavity K1 from the injection molding machine (not shown) through the sprue 131 and the gate 132, and as shown in FIG. The filling resin P1 is filled for a time corresponding to the volume of the cavity K1.

When the filling is completed, the rotary shaft hydraulic cylinder 1
The cylinder rods 135a and 143a of the cylinders 35 and 143 are retracted, and the hydraulic cylinders 134 and 142 for the core mold are retracted.
Of the rotary shaft 320 as shown in FIG. The central axis is aligned with the central axis of the cavity K1. That is, while maintaining the state parallel to the central axis of the cavity K1, the core mold 2
The center axis of 00 is eccentric from the center axis of the cavity K1. Due to this eccentricity, as shown in FIG. 25B, the main body 21 of the core mold 200 is so formed that the eccentric side filling resin P1 has a thickness corresponding to the thickness of the molded product to be obtained.
0 and the nesting mold 120, and the eccentric space S between the other surface of the main body 210 and the filling resin P1.
1 results.

Then, the motor 350 is driven to rotate at a preset rotation speed to rotate the rotary cylinder 310, and the striker 420 is vibrated by the electromagnetic generator 410 to strike the inner wall surface of the rotary cylinder 310. And the rotating cylinder 31
Vibration is applied to the core mold 200 through the zero. Also, at the same time,
By vibrating the vibrator 520 by the vibration generator 510,
Vibration is applied to the nesting mold 120.

That is, since the rotating shaft 320 of the rotating cylinder 310 is provided at a position eccentric from the center axis of the rotating cylinder 310, the rotation of the rotating cylinder 310 causes the core mold 20 to rotate.
0 is urged in a direction in which the rotating cylinder 310 contacts the inner wall surface of the core mold 200, and rolls while maintaining an eccentric state. Then, by this rolling, as shown in FIG.
Rolling / stretching of the filling resin P1 is repeated over the entire circumference between the core mold 200 and the nest mold 120.

In the core mold 200 itself, an eccentric space S1 is generated between the core mold 200 and the filling resin P1, and the inner peripheral length of the filling resin portion is
Since it is longer than the outer peripheral length of the core mold 200, the rotary cylinder 310 rotates in the direction opposite to the rotation direction with the rolling. In the core mold 200, the upper end surface 215 of the main body portion 210 abuts on the lower end surface 139 of the fixed mold portion 130, and the lower end surface 216 of the main body portion 210 corresponds to the upper end surface 14 of the movable mold portion 140.
9 and is supported at two points with certainty, so that the eccentric shaft smoothly rolls without shifting.

Until the filling resin P1 is cooled and solidified or immediately before the mold C is opened, the rolling of the core mold 200, the hitting of the rotary cylinder 310 by the striker 420, and the nesting by the vibrator 520. After continuously applying vibration to 120 and forming the molded body W1 as shown in FIG.
After stopping the motor 350, the core-type vibration applying mechanism 400, and the cavity-type vibration applying means 500 at an arbitrary timing, the rotary cylinder hydraulic cylinders 135 and 143 and the core type hydraulic cylinders 134 and 142 are activated to operate the core. The mold is opened with the center axis of the mold 200 aligned with the center axis of the cavity K1, and the molded product W1 is taken out.

The filling resin P1 is cooled and solidified by flowing cooling water through the cooling water passage 1201 and cooling the nesting mold 120.

This injection molding method is as described above, has the same effects as in the first embodiment, and applies vibrations to the core mold 200 and the nest mold 120. It is transmitted to the filling resin P1, and the compression effect of the filling resin is further increased, and the residual stress is dispersed,
Make it more uniform.

[Fourth Embodiment (Embodiment 4)] In a fourth embodiment of the injection molding method of the present invention, a mold shown in FIGS. It is the same as the first embodiment except that the mold D is used.

That is, as shown in FIGS. 26 to 29, the die D is made to expand and contract the core mold 5q by the expanding and reducing device 51q, and is expanded by the expanding and reducing device 51q. By doing so, the filling resin is compressed between the core mold 5q and the cavity mold.

The core mold 5q is composed of a plurality of metal plates 50q, 50q.
.. are combined. Diameter expansion / reduction device 51
q is provided with a shaft 52q that can move forward and backward,
Around the bend link 53q, 53q, 53q
Are provided, and the bent portions of the links 53q, 53q, 53q are axially attached to the inner surfaces of the metal plates 50q, 50q,... Of the core mold 5q, and the shaft 52q is advanced in the direction of the arrow in FIG. Is expanded so that the filling resin is compressed between the core mold 5q and the cavity mold.

The shaft 52q is moved forward and backward by the operation of a hydraulic clamp of an injection molding machine (not shown).

[Fifth Embodiment (Embodiment 4)] In a fifth embodiment of the injection molding method of the present invention, a mold shown in FIGS. It is the same as the first embodiment except that the mold E is used.

That is, as shown in FIGS. 30 to 34, the core mold 5r is formed of a spiral tube whose diameter can be increased and decreased, and the core mold 5r and the cavity mold are formed by expanding the diameter of the core mold 5r. The compressed resin is compressed between the steps. In the core die 5r, the helical tube is wound by spirally winding the strip-shaped metal plate, and the protrusion protruding from one of the adjacent strip-shaped metal plates is fitted into the groove recessed from the other. Is formed.

As shown by the arrow in FIG. 32, the end of the band-shaped metal plate of the core mold 5r is rotated clockwise by a motor or the like to thereby reduce the diameter of the core mold 5r from the reduced state as shown in FIGS. Is expanded as shown in FIG. 33 and FIG.

A core member 51r is inserted into the core die 5r in a reduced diameter state shown in FIGS. 31 and 32, and a core member 52r is shown in FIGS.
4 is a core material inserted into the core mold 5r in the expanded state shown in FIG. Assume that the inner diameter of the core mold 5r in the reduced diameter state shown in FIGS. 31 and 32 is D1, the length is L1, and the inner diameter of the core mold 5r in the enlarged diameter state shown in FIGS. 33 and 34 is D2, and the length is L2. D2 / D1 = L1 / L2.

The injection molding method for a tube-shaped article according to the present invention is not limited to the above embodiment. For example, in the above-described mold A, the arm 55 is rotatable with respect to the drive shaft 54, and is connected to the internal gear 581 via the drive shaft 54, the first sprocket 571, the chain 59, and the second sprocket 572. Although the rotational force of the motor is transmitted and the internal gear 581 is rotated while engaging with the external gear 582, the arm is fixed to the drive shaft,
A rotatable roller may be provided at the tip of the arm, and the roller may be pressed against the inner wall surface of the core mold to press the core mold in the cavity mold direction and rotate the arm with the rotation of the drive shaft. .

In the above-described mold C, the striker 82 is a single plate-like body. However, the striker has a plate-like shape if the core can be moved by hitting while keeping the axis parallel. It may not be necessary, and a plurality of strikers may be realized in synchronization. In the above-described mold C, the striker 82 strikes the inner wall surface of the core mold 7 at both ends. However, the striker 82 may strike only one side.

In the mold C, the hydraulic cylinders 134 and 142 for the core mold and the hydraulic cylinders 13 for the rotary cylinder are used.
5 and 143, the core mold 200 and the upper and lower bearing main bodies 136 and 144 are slid.
A rack and a pinion may be used.

[0138]

Embodiments of the present invention will be described below in more detail.

Example 1 A mold A having a cavity mold made of carbon steel and a core mold made of an aluminum alloy as shown in FIG. 1 was used, and a nominal diameter of 50 mm (standard value: 60.5 (0.2 mm) socket (joint) was molded.

[Molding conditions] (Resin): High-density polyethylene resin (resin temperature 160
10000 poise (or MI (melt index) = 20) in terms of viscosity at ° C. (cavity shape): inner diameter 60.2 mm, outer diameter 79.5
mm, length 107 mm, wall thickness 9.65 mm ・ (Molding conditions): 220 ° C. resin temperature, 220 ° C. peripheral wall temperature of cavity at filling ・ (Time required for temperature holding step): 1 minute ・ (Compression by core mold Conditions: core core final eccentric width 2 mm, core mold rotation speed 60 rpm, first stage cooling condition 220 ° C. → 125 ° C., second stage cooling condition 125 ° C. → 1
15 ° C., third stage cooling condition 115 ° C. → normal temperature (at the time of mold release) The eccentric amount (thickness movement amount) in each stage of the core type is shown in Table 1 by feeding back the value of the temperature sensor. . -(Method of raising the temperature of the mold): This was performed with a sheath heater built in the mold. -(Cooling method): As the cooling rate, a cooling rate control method by adjusting the flow rate of the refrigerant and using the heater together was adopted. -(Temperature control of mold): Regarding the temperature control of the mold, the temperature near the peripheral wall surface of the cavity was measured by a temperature sensor and controlled by feedback control. As a control pattern, in addition to the temperature control in accordance with the set cooling rate, the cooling rate can be switched according to the time from the start of filling.

[0141]

[Table 1]

(Comparative Example 1) A socket was formed in the same manner as in Example 1 except that the temperature of the peripheral wall surface of the cavity of the mold was 30 ° C.

(Comparative Example 2) A socket was formed in the same manner as in Example 1 except that compression by the core mold was not performed (no eccentricity).

Comparative Example 3 A socket was mounted in the same manner as in Example 1 except that the temperature of the peripheral wall surface of the cavity of the mold was kept constant at 30 ° C., and compression was not performed by the core mold (no eccentricity). Molded.

After the sockets obtained in Example 1 and Comparative Examples 1 to 3 were taken out of the mold, each was stored in a room at a temperature of 23 ° C., the dimensions were measured one hour after molding, and the molding was performed for one hour. The dimensions were measured periodically up to two weeks (336 hours) after molding, based on the dimensions after the molding, and the shrinkage defined by the following equation was determined. Shrinkage = [Dimension after 1 hour of molding-Measured dimension] / Dimension after 1 hour of molding

Further, the inner diameter of the end of the obtained socket was measured at eight locations one hour after molding and two weeks after molding in the circumferential direction, and the difference between the maximum inner diameter and the minimum inner diameter was measured. Asked. Table 2 shows the shrinkage and roundness of each socket determined as described above.

[0147]

[Table 2]

As shown in Table 2, the present invention not only causes no sink marks but also reduces the effects of in-mold shrinkage up to the initial mold release and thermal shrinkage to room temperature after mold release. As a result, it can be seen that a precision molded product having a close mold size can be obtained. Further, as for the inner diameter, since the inner diameter is enlarged to a predetermined dimension by core rotational molding, the dimension at the time of mold release falls within the predetermined dimension than the dimension of the normal injection molding which is undergoing heat shrinkage. Therefore, as in the case of the normal injection molding as in Comparative Example 3, it is necessary to take into account the heat shrinkage and the crystal shrinkage as the shrinkage, and manufacture the mold with a larger size obtained by multiplying the shrinkage by the desired size. It turns out that there is no.

That is, in the case of Comparative Example 2 in which the temperature holding step was not provided and only the compression step was performed by rolling the core mold, the dimensions after two weeks changed, whereby the dimensions deviated from the desired dimensions. In the case of Comparative Example 1 in which the temperature was controlled in the holding step and the cooling and solidifying step, and the compression step was not performed, the change in the inner diameter from one hour after the dimension to two weeks later could be suppressed. It will be out of the way. Regarding roundness, in the case of normal injection molding, crystallinity distribution due to differences in temperature distribution / pressure distribution and cooling rate in the cylinder cross section,
Furthermore, the shrinkage mechanism differs depending on the distribution of the shear stress at the time of filling and the distribution of the residual stress due to the cooling state, and the shape formed in a perfect circle is distorted into an elliptical shape or an irregular shape. In this case, the difference between the maximum inner diameter and the minimum inner diameter is used as one of the roundness and the dimensional evaluation of the cylindrical body.

As can be seen from the results, in the case of Comparative Example 2, the roundness was greatly improved immediately after molding, but the roundness became poor two weeks later. This is attributable to the occurrence of post-shrinkage, but the subsequent shrinkage is not uniform in the circumferential direction and has a distribution. For example, when the cooling rate is high, the relaxation time is short, and the residual stress is large. Therefore, the post-shrinkage in that part is conversely large. Therefore, only Example 1 resulted in that the roundness was within the desired range even after two weeks.

(Reference Example) Immediately after the resin was filled, 200 ° C. /
A molded product was obtained in the same manner as in Example 1 except that the product was cooled to room temperature at a speed of 1 minute. With respect to the molded product obtained in the above reference example and the molded product obtained in Example 1, the crystallinity of the surface of the molded product, about 0.5 mm inside and about 1.0 mm inside from the surface is D
It was measured by SC. The results are shown in Table 3.

[0152]

[Table 3]

[0153]

According to the injection molding method of the present invention, the injection molding method for a cylinder-shaped article has a uniform density, a small amount of warpage, deformation and residual strain, and a high precision without shrinkage unevenness. Dimensions and appearance can be reduced, and post-shrinkage can be reduced. In particular, as in the molding method of claim 2,
If you compress the core while rolling it,

If the vibration is applied at the time of compression as in the molding method of the fifth aspect, the vibration is transmitted to the filling resin, the compression effect of the filling resin is further enhanced, and the residual stress is dispersed, so that more uniformity is obtained. Become According to the molding method of claims 7 and 8, the degree of crystallinity is advanced, and a molded article having more excellent strength can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a molded product that can be molded in the present invention.

FIG. 2 is a cross-sectional view showing a cross-sectional structure of an injection molded product.

FIG. 3 is an enlarged cross-sectional view showing a portion X in FIG. 2;

FIG. 4 is a graph showing the relationship between stress relaxation of resin and time.

FIG. 5 is an explanatory view showing a mode of mold temperature adjustment in the method of the present invention.

FIG. 6 is a graph showing the relationship between the calorific value of resin and temperature.

FIG. 7 is a graph showing the relationship between the specific volume of the resin and the temperature.

FIG. 8 is a cross-sectional view illustrating an example of a mold used in the first embodiment of the injection molding method for a tube-shaped article according to the present invention.

FIG. 9 is an enlarged sectional view of a fixed mold portion of the mold shown in FIG.

FIG. 10 is a transverse sectional view of the fixed mold part shown in FIG. 9;

FIG. 11 is an enlarged sectional view of a movable mold part of the mold shown in FIG. 8;

FIG. 12 is a sectional view taken along line VV of FIG. 11;

FIG. 13 is an enlarged view of a main part of FIG. 12;

FIG. 14 is an explanatory view illustrating a molding method using the mold shown in FIG. 1 in the order of steps.

FIG. 15 is a graph showing an example of a relationship between a mold temperature control pattern and a wall thickness in the method of the present invention.

FIG. 16 is a cross-sectional view illustrating an example of a mold used in a second embodiment of the injection molding method for a tube-shaped article according to the present invention.

FIG. 17 is a sectional view showing a state before injection filling of the mold shown in FIG. 16;

FIG. 18 is a sectional view taken along line XIII-XIII in FIG. 16;

FIG. 19 is an explanatory view illustrating a molding method using the mold shown in FIG. 16 in the order of steps.

FIG. 20 is a cross-sectional view showing an example of a mold used in a third embodiment of the injection molding method for a tube-shaped article according to the present invention.

21 is an enlarged cross-sectional view of the fixed mold side of the mold shown in FIG.

FIG. 22 is an enlarged sectional view of the movable mold side of the mold shown in FIG. 20;

FIG. 23 is an enlarged cross-sectional view of a nest portion of the mold shown in FIG. 20;

FIG. 24 is an explanatory view illustrating the nesting vibration of the mold shown in FIG. 20;

FIG. 25 is an explanatory view illustrating a molding method using the mold shown in FIG. 20 in the order of steps.

FIG. 26 is an explanatory front view showing an example of a mold used in the fourth embodiment of the injection molding method for a tube-shaped article according to the present invention.

FIG. 27 is an explanatory side view of the embodiment shown in FIG. 26;

FIG. 28 is an explanatory front view showing the next step of the embodiment shown in FIGS. 26 and 27;

FIG. 29 is an explanatory side view of the embodiment shown in FIG. 28;

FIG. 30 is an explanatory front view showing an example of a mold used in a fifth embodiment of the injection molding method for a tube-shaped article according to the present invention.

FIG. 31 is an explanatory front view partially cut away of the embodiment shown in FIG. 30;

FIG. 32 is an explanatory side view of the embodiment shown in FIG. 31;

FIG. 33 is a partially cutaway explanatory front view showing the next step of the embodiment shown in FIGS. 31 and 32;

FIG. 34 is an explanatory side view of the embodiment shown in FIG. 34;

FIG. 35 is a graph showing a change in the inner diameter of a pipe joint according to a conventional method.

[Explanation of symbols]

 A, B, C, D, E Mold 1, 6, 100 Cavity mold 5, 7, 200 Core mold 8 Striking mechanism 81 Rotary shaft 82 Striker K, Ka, K1 Cavity P, Pa, P1 Filling resin W, Wa , W1 Molded product

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4F202 AA05 AG08 AJ02 AK02 AP05 AR06 AR11 AR14 CA11 CK06 CK12 CK18 CK52 CK73 CK81 CN12 CN18 CN27 4F206 AA05 AG08 AJ02 AK02 AP054 AR064 AR11 AR14 JA03 JA07 JLJ JN04 J25 JW41

Claims (8)

[Claims] 1. A filling step for injecting and filling a molten thermoplastic resin into a cavity provided between a cavity mold and a core mold, and a cooling and solidifying step for cooling and solidifying the filling resin filled in the cavity. The core mold is provided between the filling step and the cooling and solidifying step while the center axis of the core mold is kept parallel to the center axis of the cylindrical portion of the cylindrical molded article formed in the cavity. A method for injection molding of a cylinder-formed article, in which the filling resin is compressed between a cavity mold and a core mold by moving the molding resin in a cavity, and wherein the thickness of the molded article is corrected. In addition to heating to a temperature near or above the melting temperature of the resin, after the filling step and before the cooling and solidifying step, the shear stress and molecular or crystal orientation due to the resin flow during resin filling are alleviated in the mold. Characterized by comprising a temperature holding step of holding the temperature of the peripheral wall surface of the cavity at a temperature close to or higher than the melting temperature of the resin for a while so as to reduce the shrinkage of the molded product after molding. Injection molding method for products. 2. The method according to claim 1, wherein the core mold is set in a state where the center axis thereof is eccentric from the center axis of the cavity mold, and the core mold is rolled in the cavity to compress the filling resin between the cavity mold and the core mold. Item 1. An injection molding method for a tube-shaped article according to Item 1. 3. A core mold hitting mechanism is provided in a mold, and the core mold is hit in a radial direction by the hitting mechanism, and the core resin is moved in the hitting direction in the cavity mold so that the filling resin is brought into contact with the cavity mold. The injection molding method for a cylinder-shaped article according to claim 1, wherein the molding is performed between a core mold and the core mold. 4. A filling step of injecting and filling a molten thermoplastic resin into a cavity provided between a cavity mold and a core mold, and a cooling and solidifying step of cooling and solidifying the filling resin filled in the cavity. From the end of the filling step to the end of the cooling and solidifying step, the peripheral wall of the core mold is radially expanded in the cavity and the filling resin is compressed between the cavity mold and the core mold to form a molded product. An injection molding method of a cylinder-formed article for correcting a wall thickness, wherein a temperature of a peripheral wall surface of a cavity of a mold is heated to a temperature near or higher than a melting temperature of a resin during a filling process, and after the filling process is completed. Before the cooling and solidification process, the temperature of the cavity wall surface is melted for a while so that the shear stress and molecular or crystal orientation due to the resin flow during resin filling are alleviated in the mold and the shrinkage of the molded product after molding is reduced. Injection molding process of the cylindrical-shaped molded article, characterized in that it comprises a temperature holding step of holding the temperature or higher temperature in the vicinity of degrees. 5. The method according to claim 1, wherein vibrations in the radial direction of the core mold are applied to the cavity mold and / or the core mold during compression. 6. The thermoplastic resin has crystallinity, and the temperature of the cavity wall surface of the mold in the filling step and the temperature of the cavity wall surface of the mold in the temperature holding step are higher than the crystallization temperature of the resin. The injection molding method for a tube-shaped article according to any one of claims 1 to 5. 7. The cooling and solidifying step comprises a first stage having a high cooling rate, a second stage having a cooling speed lower than the first stage cooling speed, and a third stage having a cooling speed higher than the second stage cooling speed. The injection molding method for a cylinder-shaped article according to any one of claims 1 to 6, comprising: 8. The thermoplastic resin has crystallinity, and the cooling and solidifying step includes a first step of cooling to a crystallization start temperature at a cooling rate of a predetermined temperature gradient, and a step of starting crystallization after completion of the first step. The cylinder according to any one of claims 1 to 6, further comprising: a second stage for maintaining the temperature at the temperature; and a third stage for cooling at a cooling rate having a predetermined temperature gradient after completion of the second stage. Injection molding method for molded products.