JP2002301740A - Method for manufacturing injection-molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of precisely molding a plurality of injection-molded products having cylindrical parts, at the same time by one mold. SOLUTION: The method for manufacturing the injection-molded product has a resin filling process for bringing the mold A which is equipped with a plurality of cavities and has core molds 31 and cavity molds 11 so that at least cylindrical cavities K are formed between the core molds 31 and the cavity molds 11 at the time of mold clamping, to a closed state to inject a resin in a molten state to fill the cavities in the respective cavities; and a compression process for setting the core molds 31 of the respective cavities so that the axes of them become an eccentric state parallel to the center axes of the cylindrical cavities K until the filled resin P is solidified, and revolving all of the core molds 31 around the center axes of the cylindrical cavities K in the mold by the driving force of one electromotor 5, while allowing the outer surfaces of the core molds 31 to conform to the inner surfaces of the filled resin P to compress the filled resin P between the cavity molds 11 and the core molds 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing an injection molded article.

[0002]

2. Description of the Related Art Conventionally, in injection molding, 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 uneven, and as a result, the shrinkage rate decreases. In particular, when a cylindrical molded product is molded by a one-point gate, the pressing effect is not uniformly distributed over the entire product part, and the shape of the circumferential portion of the molded product is poorly formed.

[0003] As a method of molding a cylindrical molded product requiring precision such as roundness by injection molding, the inventors of the present invention use at least an eccentric revolving core mold provided on a movable mold. A resin filling step of injecting and filling a molten resin into a cylindrical cavity formed by being inserted into a fixed mold, and at least a part of the eccentric revolving core mold is set at the center thereof until solidification of the filled resin. While revolving around the central axis of the cylindrical cavity portion in the cylindrical cavity portion while keeping the axis parallel to the central axis of the corresponding cylindrical cavity portion, at least the peripheral wall surface of the eccentric revolving core type is filled resin. And a radial compression step of compressing the filling resin in the radial direction of the cylindrical cavity portion while rolling along the cylinder. See No. 77).

That is, in the case of this method, as shown in FIG.
00 indicates that the eccentric revolving core mold 300 is
In order to revolve in an eccentric state within 0, the cylindrical cavity 10
The filling resin in the cylinder 0 is compressed in the radial direction of the cylindrical cavity portion 100. In addition, the resin 200 filled in the cylindrical cavity portion 100 is heated once to relieve the stress, and then uniformly cooled by the cooling water. Therefore, according to this manufacturing method, it is possible to obtain a cylindrical molded article 400 having a uniform density, having a small amount of warpage, deformation, residual strain, and the like, having high-precision dimensions without shrinkage unevenness, and having an excellent appearance. .

[0005] However, in the method previously proposed by the inventors, only one molded product could be obtained by one injection.

[0006]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention provides an injection molded article which can simultaneously and precisely mold an injection molded article having a plurality of cylindrical portions with one mold. The purpose of the present invention is to provide a manufacturing method.

[0007]

In order to achieve the above object, a method for manufacturing an injection-molded article according to the present invention has a core mold part and a cavity mold part, and the core mold part and the cavity mold part are closed when the mold is closed. A resin filling step of injecting molten resin into each cavity by closing a mold having a plurality of cavities in which at least a cylindrical cavity portion is formed between the cavity mold portion and the filled filling; Before the resin is solidified, the core mold portion of each cavity is eccentric with its axis parallel to the central axis of the cylindrical cavity portion, and the outer surface of the core mold portion is aligned with the inner surface of the filled resin. A compression step of revolving all the core mold parts around the central axis of the cylindrical cavity part in the mold with the driving force of one electric motor to compress the filling resin between the cavity mold part and the core mold part And a configuration having:

In the manufacturing method of the present invention, a plurality of cavities having different diameters or shapes may be provided in the mold.

The resin used in the production method of the present invention is not particularly limited. For example, a resin having high crystallinity and high shrinkage such as high-density polyethylene is preferable. And the like can be used.

The material of the mold is not particularly limited, but at least a portion forming the mold surface of the cavity mold portion and the core mold portion is formed of aluminum, aluminum alloy, zinc alloy, copper alloy or the like having high thermal conductivity. Preferably, aluminum or an aluminum alloy is more preferable from the viewpoint of weight reduction, and the other portions are preferably formed of, for example, carbon steel or stainless steel. Also, to improve the transferability,
It is preferable that the portion in contact with the filling resin is mirror-finished.

By appropriately changing the shapes (diameters) of the cavity mold portion and the core mold portion, the compression may be performed in accordance with the type of resin used and the amount of shrinkage of each resin. The amount of eccentricity of the core mold portion varies depending on the size, shape, or type of resin used of the cylindrical portion of the molded product to be obtained, and molding conditions and shrinkage amount are not particularly limited. When molding a cylindrical molded product with a nominal diameter of 50, the maximum undercut amount + 0.5 to 6
mm is preferable, and the maximum undercut amount + about 2 mm is more preferable.

[0012] The contact between the outer surface of the core mold portion and the filler resin during compression by the core mold portion is preferably a point contact in a section perpendicular to the axis in order to promote stretching and rolling.

In the present invention, the term “cylindrical” refers to not only a cylindrical shape having a cross-sectional shape but also an oval shape or an elliptical shape. May be protruded.

In the manufacturing method of the present invention, when filling the resin into the mold, the temperature of the peripheral wall surface of the cavity is heated to a temperature near or higher than the melting temperature of the resin, and after the filling step is completed, it is cooled and solidified. Before the process, the temperature of the peripheral wall of the cavity should be set to a value close to the melting temperature of the resin 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. It is preferable to include a temperature maintaining step of maintaining the temperature at or above.

[0015] In the cooling step, the resin cooling step is composed of three stages, and in the first stage, the cooling rate is increased.
In the second stage, it is preferable to keep the temperature once, maintain the temperature for a while, and in the third stage, increase the cooling rate again. In particular, when the starting temperature in the second stage is set near the crystallization starting temperature, it is more preferable. It is effective.

In the cooling step, 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 understand the relationship between the cooling rate and the crystallinity, the crystallinity of the resin sample solidified at various cooling rates was determined by D
Measure by SC or the like to understand the relationship between cooling rate and crystallinity. If a DSC or PvT measuring device capable of changing the cooling rate is used, the crystallization start temperature and the crystallization temperature range that change according to the cooling rate can also be grasped. In particular, in the case of a DSC in which a wide range of cooling rates can be set, a resin sample is cooled in a cooling pattern to be actually molded, and the crystallinity is measured by a sample given its temperature history.
The crystallinity in various cooling patterns 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, from the temperature-caloric curve, the temperature range where the curve is greatly deviated from the baseline is the crystallization temperature range, and the maximum value in the range is the crystallization start temperature. Also, P
In the case of the vT measurement, in the temperature-specific volume curve, the temperature range where the rate of change of the specific volume is the largest is the crystallization temperature range,
The maximum value among them is the crystallization start temperature.

The means for heating and holding the peripheral wall surface of the cavity 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 provided. A high temperature may be maintained by energizing, 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 flow pipe may be provided in the mold, and the heating oil may be supplied to the heating medium flow pipe of the mold by a mold temperature controller through a pipe provided with an electromagnetic valve.

In the production method of the present invention, the means for changing the cooling rate is not particularly limited.
The following four methods 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 of 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 pipe line from the mold temperature controller is appropriately switched according to a signal from a manual or control device to supply the coolant to the coolant circulation pipe of the mold, and by switching these coolants, The cooling rate can be changed at the set timing.

In some cases, the temperature can be set 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 keep the temperature of the peripheral wall surface of the cylindrical cavity at a constant temperature (cooling rate = 0) and, if necessary, to reheat the refrigerant within the temperature range of the refrigerant. Use multiple mold temperature controllers for different types of refrigerants,
The temperature of the mold can be set by appropriately switching an electromagnetic valve provided in a conduit from each mold temperature control device to supply the coolant to a coolant circulation pipe of the mold, and switching between these different types of coolant.

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

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

Alternatively, a plurality of mold temperature control devices are used, one of the mold temperature control devices supplies a refrigerant to a refrigerant flow pipe of the mold, and the other mold temperature control device controls a 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 peripheral wall surface of the cylindrical cavity is kept constant (cooling rate = 0),
Further, 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 the control pattern can be further expanded. The heating heater is not particularly limited, but for example, a sheathed heater, high-frequency heating, heating means for near-infrared rays, far-infrared rays, etc. can be used.

The cooling rate control means may be determined and controlled based on the cavity peripheral wall surface, 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 to 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 temperature of the peripheral wall surface of the cylindrical cavity 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 fluctuations in the ambient temperature, molding conditions, and the like.

In order to more accurately control the cooling rate, the mold is provided with a sensor for measuring the temperature of the peripheral wall surface of the cylindrical cavity or the resin in contact with the peripheral wall surface of the cylindrical cavity as needed. Need to control speed. 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.

[0033]

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. 1 and 2 show one embodiment of an injection molding die used in the method for producing an injection molded product according to the present invention, and FIG. 3 shows the production of the injection molded product according to the present invention using this die. The method is shown in the order of steps.

As shown in FIGS. 1 and 2, this mold A
Is a horizontal type having a fixed mold 1a and a movable mold 2a, and four cavities including a cylindrical cavity portion K are formed in a closed state and are arranged in a vertical direction. ing. That is, as shown in FIGS. 1 and 3, the fixed mold 1a includes four cylindrical cavity mold portions 11 that are opened on the movable mold 2a side.

The movable mold 2a faces the inside of the cavity mold portion 11 when the mold is closed, and forms a cavity including the cylindrical cavity portion K with the cavity mold portion 11.
And an eccentric rotation mechanism for eccentrically rotating the core mold portion 31 and revolving around the central axis of the cylindrical cavity portion K while maintaining the eccentric state, as will be described in detail later. 4 and 4 sets. That is, the eccentric rotation mechanism 4 includes a rotation case 41, an advance / retreat member 42, a slide block 43, and a connection shaft 44.

The rotating case 41 is supported by a bearing 22 provided in a casing 21 of the movable mold 2a, and a gear 41a is provided on a peripheral surface thereof. Each rotating case 41 is, as shown in FIGS.
a, which extends from the gear 51 of the electric motor 5 fixed to the outer wall surface of the casing 21 of FIG.
The rotational driving force of the electric motor 5 is simultaneously transmitted via the chain 52 so as to rotate at the same time.

Although not shown, the reciprocating member 33 has a substantially oval cross section, is slidably inserted into the rotating case 41 in the direction of the fixed mold 1a, and rotates with the rotation of the rotating case 41. By rotating and moving the mold closing plate 23 of the movable mold 2a toward the fixed mold 1a, the inside of the rotating case 41 is moved in the direction of the fixed mold 1a. In addition, an angular hole 42 of a slide block 43 to be described later is
Angular pin 4 having the same cross-sectional shape as a and having a rectangular cross-section
3a is protruded. The angular pins 43a are provided to be inclined at the same inclination angle so as to intersect the slide axes of the respective reciprocating members 42.

On the other hand, the slide block 43 has an angular hole 42a on the surface on the side of the advance / retreat member 42 at the same inclination angle as that of the angular pin 43a of the advance / retreat member 42, into which the angular pin 43a is slidably inserted. Connecting shaft 4
Numeral 4 is provided on the surface of the slide block 43 on the side of the fixed die 1a so that its central axis coincides with the center of rotation of the slide block 43, and the core type member 3a has its central axis aligned with the central axis. It is supported rotatably around the central axis.

That is, as the slide block 43 advances and retreats in the direction of the fixed mold 1a, the tip of the angular pin 43a is moved into the angular hole 42a.
Move in and out. In addition, since the angular hole 42a and the angular pin 43a are provided to be inclined with respect to the advance / retreat axis of the advance / retreat member 42, the slide block 4 is moved by the advance / retreat of the angular pin 43a into the angular hole 42a.
3 slides in the rotating case 41 in a direction whose central axis is orthogonal to the central axis of the cylindrical cavity portion K. When the reciprocating member 42 rotates with the rotation of the rotating case 41, the rotational force is transmitted to the slide block 43 via the angular pin 43a, and the slide block 43 also rotates with the reciprocating member 42. . The core mold member 3a includes a core mold portion 31 and a connecting shaft 4
4 and a substrate portion 32 rotatably attached to the substrate portion 4.

Therefore, the core block 3a is configured such that the slide block 43 is eccentric while the slide is transmitted through the connection shaft 44 and the center axis of the slide block 43 is kept parallel to the center axis of the cylindrical cavity K. And rotating case 4
By one rotation, the cylindrical cavity K revolves around the central axis. Further, the fixed mold 1a and the movable mold 2a are provided with a heater H along the peripheral wall of the cylindrical cavity K.
And a cooling pipe R through which a refrigerant of a cooling unit (not shown) passes. In FIG. 1, reference numeral 14 denotes a hot runner, and FIG.
Reference numeral 15 denotes a valve gate.

Next, a first embodiment of the method for manufacturing an injection-molded article of the present invention using the mold A will be described in the order of steps with reference to FIG.

(1) As shown in FIG. 3A, the mold A is closed with each core mold 31 inserted into the cavity mold 11 of the fixed mold 1a. A position at which the central axis coincides with the central axis of the cylindrical cavity K;
That is, after the core mold portion 31 is disposed at the neutral position, the temperature of the peripheral wall surface of the cylindrical cavity portion is controlled to be higher than the melting temperature of the resin, and for example, the hot runner is melted with a resin such as high-density polyethylene. 14. Inject into the cylindrical cavity K through the valve gate 15. However, if there is no problem in filling, it is not always necessary to arrange the core mold portion 31 at the neutral position. When the gate is provided at the asymmetric position, the eccentric revolving core mold may be deviated from the neutral position at the time of filling in consideration of the ease of filling.

(2) With the temperature of the molten resin kept at the mold temperature at the time of filling, the electric motor 5 is driven to rotate the rotating case 41.
While rotating the mold, the mold closing plate 23 is gradually moved in the direction of the fixed mold 1a to advance the reciprocating member 33 toward the fixed mold 1a, and as shown in FIG. The molten resin in the cavity K is radially compressed between the outer surface of the core mold 31 and the inner surface of the cavity mold 11.
In other words, since the base member ａ is rotatably supported by the connection shaft 44, the core block 3a is
Even if is rotated, while revolving around the central axis of the cylindrical cavity portion K while maintaining the eccentric state, the outer surface of the core mold portion 31 rotates while rolling along the inner surface of the filling resin △.

(3) When the amount of eccentricity becomes a predetermined amount of eccentricity, the molded product is sufficiently shaped to obtain the filled resin と と も に, and when the resin is almost solidified, the mold closing plate 23 is slightly retracted. After returning the center axis of the core mold part 31 to the position where it is aligned with the center axis of the cylindrical cavity part K, the mold A is opened,
A molded product is taken out from each cylindrical cavity K.

Before the cooling step, the filling resin P in the mold A is first temporarily maintained at a temperature near the melting temperature for a while or higher, and then cooled. In the cooling step, first, the resin is cooled to a temperature near the crystallization temperature at a stretch, and once cooled to a temperature near the crystallization temperature and then solidified.

As described above, the method of manufacturing an injection-molded article is as follows.
Since the core mold portion 31 is compressed in the radial direction while being eccentric within the cylindrical cavity portion K, it has high dimensional accuracy and uniform density, and has little warpage, deformation, residual strain, etc., and has no shrinkage unevenness. The molded article 6 can be molded.
In addition, a precise cylindrical molded product can be obtained simultaneously with the four cylindrical cavities K provided in one mold A.

Further, since all the core-shaped portions 31 can revolve in an eccentric state by the rotational driving force of one electric motor 5, the structure is simple and easy to handle including maintenance. Furthermore, since the mold temperature is maintained at a temperature higher than the melting temperature of the resin at the time of filling the resin, the occurrence of weld at the time of filling is reduced, and the appearance is further improved by adding a compression effect to this. Also, since the resin is compressed at a high temperature, the mold transferability is good and a glossy appearance can be obtained.

Further, in the cooling step, since the temperature is once kept at a constant value near the crystallization temperature of the resin, crystallization proceeds and a molded product excellent in strength can be obtained. Furthermore, after the eccentric compression is completed, the eccentric revolving core mold returns to the initial center axis, so that a gap is formed between the eccentric revolving core mold and the inner surface of the molded product, and there is no sticking and the releasability is improved.

FIG. 4 shows a second embodiment of the method for manufacturing an injection-molded article according to the present invention.

As shown in FIG. 4, in this manufacturing method, by closing the movable mold 2b and the fixed mold 1b, two cylindrical cavities K are formed, and the advancing / retreating member 45 is formed. Is a protruding plate 2 which can be moved back and forth in the direction of the fixed mold 1b by the hydraulic cylinder 25 in a mold closed state.
6, the fixed die 1b is provided with an angular hole 45a at an end thereof, the slide block 46 is provided with an angular pin 46a at an end of the movable die 2b, and the substrate 33 of the core type member 3b is provided. Is fixed to the end of the slide block 46 on the fixed mold 1b side, and the core mold part 34 is connected to a core part 34a integrated with the substrate part 33 and a needle bearing (not shown) on the core part 34a. This embodiment is the same as the above-described embodiment except that two molded products are simultaneously manufactured using a mold B composed of a cylindrical main body 34b rotatably provided.

That is, according to this manufacturing method, FIG.
As shown in (b), the protruding plate 26 is moved toward the fixed mold 1b by moving the hydraulic cylinder 25, and the reciprocating member 45 is advanced toward the fixed mold 1b. 34a
Is eccentric parallel to the central axis of the cylindrical cavity K. Then, the filled resin P filled in the cylindrical cavity portion K is compressed between the outer surface of the core mold portion 34, that is, between the outer surface of the main body 34b and the inner surface of the cavity mold portion, so that a precise molded product can be obtained. . Moreover, the core mold part 3
4 for rotating core 4 with slide block 46
And the core portion 34a is composed of a rotatable cylindrical main body 34b. Therefore, even if the molding surface of the core mold portion 34 is worn or scratched, only the main body 34b needs to be replaced. Excellent in nature.

FIG. 5 shows a third embodiment of the method for producing an injection-molded article according to the present invention. As shown in FIG. 5 (a), this manufacturing method is based on the inclination angle θ1 of the angular pin 46a of the slide block 46 of the eccentric rotation mechanism of the one core mold portion 34 with respect to the advance / retreat axis of the advance / retreat member 45,
The reciprocating member 4 of the angular pin 46a of the slide block 46 'constituting the eccentric rotation mechanism of the other core type part 34'
The second embodiment is the same as the second embodiment, except that a mold C having a different inclination angle θ2 with respect to the advance / retreat axis 5 ′ is used.

In this manufacturing method, when the resin is filled in the cylindrical cavity portion and the protruding plate 26 is moved by the stroke width h in the direction of the fixed mold 1b, as shown in FIG. 34 ′ are eccentric at the same time, but the angle of inclination θ1 of the angular pin 46a of one slide block 46 with respect to the advance / retreat axis of the advance / retreat member 45, and the angle of the angular pin 46 of the slide block 46 ′ of the other core type part 34 ′.
Since the inclination angle θ2 of the a / a reciprocating member 45 ′ with respect to the advancing / retreating axis is different, one of the two core mold portions 34 and 34 ′ has a width Δ1 and the other core mold portion 34 ′ has a width Δ2. Each is eccentric. Therefore. The compression ratio of the obtained molded article can be changed. That is, in the case of molded products having different inner diameters and wall thicknesses, the amount of resin shrinkage also differs for each molded product, and different amounts of eccentricity must be given. By simply moving the same stroke width h at the same time, molded products having different thicknesses and shapes can be precisely manufactured in one mold C. Note that the width Δ1 (Δ2) is ht
can be obtained by an θ1 (θ2).

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the mold is a horizontal type, but may be a vertical type. In the above embodiment, the driving force of the electric motor 5 is transmitted to each rotating case by the chain 52. However, the driving force is transmitted using a crank and a cam, or transmitted by combining gears. It does not matter. Further, in the first embodiment, the four cavities are provided side by side in the vertical direction. However, the four cavities may be arranged in the horizontal direction. Not limited.

In the above embodiment, the cross-sectional shape of the angular pin is rectangular, but the cross-sectional shape having at least one major axis and at least one minor axis such as elliptical cross-section, hexagonal cross-section, and spline If so, any shape may be used. In addition, the cylindrical molded product obtained by the production method of the present invention is not limited to a straight tube, but if the fixed mold can be divided, a shape having both ends expanded, a both ends expanded, Elbow-shaped or cheese-shaped products can also be formed. Also, a cap-shaped product or a molded product having an undercut portion on the inner surface or outer surface can be manufactured.

[0056]

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

(Example 1) A cylindrical molded product having an inner diameter of 62 mm and an outer diameter of 76 mm was obtained by using a mold having the same dimensions as the mold C shown in FIG. A cylindrical molded product having an inner diameter of 70 mm and an outer diameter of 76 mm was simultaneously molded.

<Dimensions of each part of the mold> (for the first cavity) ・ Outer diameter of core mold part ・ ・ ・ 60.00mm ・ Inner diameter of cavity mold part ・ ・ ・ 78.00mm ・ Eccentric width of core mold part ・ ・ ・ 1 0.4mm (for the second cavity) ・ Core mold part outer diameter ・ ・ ・ 68.00mm ・ Cavity mold part inner diameter ・ ・ ・ 78.00mm ・ Core mold part eccentric width ・ ・ ・ 2.2mm

<Molding conditions>-Resin used-high density polyethylene (MFR = 0.4
Injection resin temperature: 220 ° C. Mold temperature: 150 ° C. during filling, 30 ° C. during cooling after starting rotation ・ Revolution speed of core mold: 60 rpm ・ Revolution stop timing ・・ ・ Judgment by cavity setting temperature sensor (90 ℃) ・ Release timing ・ ・ ・ Judgment by cavity setting temperature sensor (80 ℃)

The first cavity (cylindrical cavity) and the second cavity (cylindrical cavity) of the first embodiment.
Each of the molded products obtained in the above, and each of the molded products molded to have the same dimensions only by conventional injection (hereinafter, referred to as “conventional product”), was left in a room at room temperature of 23 ° C. for 2 weeks after molding, Measure the inner diameter of the end of each molded product in eight places in the circumferential direction,
When the difference between the maximum value and the minimum value was determined as the roundness, the roundness was as shown in Table 1.

[0061]

[Table 1]

[0062]

The method of manufacturing an injection-molded article according to the present invention is configured as described above, so that an injection-molded article having a plurality of cylindrical portions can be simultaneously and precisely molded by one mold. be able to. In addition, since all the core mold portions can be revolved in an eccentric state by the rotational driving force of one electric motor, the structure is simple and easy to handle including maintenance. In particular, according to the second aspect, molded products having cylindrical portions having different diameters and shapes can be simultaneously and precisely molded.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a mold used in a method of manufacturing an injection-molded article according to the present invention.

FIG. 2 is a sectional view taken along line ZZ of FIG.

FIG. 3 is a view for explaining a first embodiment of a method of manufacturing an injection-molded article according to the present invention using the mold of FIG. 1, and FIG. 3A shows a state immediately after resin filling. FIG. 3B is a cross-sectional view of a main part showing an eccentric state of the core mold part.

FIG. 4 is a view for explaining a second embodiment of the method for manufacturing an injection-molded article according to the present invention, wherein FIG. 4A is a sectional view of a mold showing a state immediately after resin filling, and FIG. FIG. 2B is a mold sectional view showing an eccentric state of a core mold portion.

5A and 5B are diagrams illustrating a third embodiment of the method of manufacturing an injection-molded article according to the present invention, wherein FIG. 5A is a cross-sectional view of a mold showing a state immediately after resin filling, and FIG. FIG. 2B is a mold sectional view showing an eccentric state of a core mold portion.

FIG. 6 is an explanatory diagram illustrating a molding process of a method of manufacturing an injection-molded article previously proposed by the present inventors.

[Explanation of symbols]

 A, B, C Mold K Cylindrical cavity part (cavity) 31, 34, 34 'Core mold part 11 Cavity mold part 5 Electric motor

Claims (2)

[Claims] 1. A mold having a plurality of cavities having a core mold portion and a cavity mold portion, wherein at least a cylindrical cavity portion is formed between the core mold portion and the cavity mold portion when the mold is closed. A resin filling step of injecting and filling a molten resin into each cavity in a state, and until the filled resin is solidified, the core mold portion of each cavity has its axis of the cylindrical cavity portion. With the eccentric state parallel to the central axis and the outer surface of the core mold portion along the inner surface of the filled resin, all the core mold portions are driven by one electric motor into the center of the cylindrical cavity portion in the mold. A compression step of revolving around a shaft to compress the filling resin between the cavity mold portion and the core mold portion. 2. The method according to claim 1, wherein a plurality of cavities having different diameters or shapes are provided in the mold.