JP4566477B2 - Injection molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pressurized fluid introducing device, a mold assembly, and an injection molding method, and more specifically, applied to the inside of a molten thermoplastic resin injected into a mold cavity provided in the injection molding device. Pressurized fluid introduction apparatus for forming an injection molded product having a hollow portion by introducing a pressurized fluid, a mold assembly incorporating such a pressurized fluid introduction apparatus, and injection molding using such a mold assembly Regarding the method.
[0002]
[Prior art]
In order to mold an injection molded article having excellent appearance characteristics free from sink marks and warpage, an injection molding apparatus for injection molding a molten thermoplastic resin is disclosed in, for example, Japanese Patent Laid-Open Nos. 64-14012 and 6-91684. It is disclosed in the gazette. In the injection molding apparatus disclosed in these patent publications, the gas injection nozzle is configured to reciprocate. For example, in an injection molding method using an injection molding apparatus disclosed in Japanese Patent Application Laid-Open No. 64-14012, as shown in FIG. 1 of this patent publication, molten plastic material 19 is placed in a mold cavity. 13 injects.
Next, a pressurized gas is injected into the plastic material 19 injected into the mold cavity 13 to form a gas-containing hollow portion 25 in the plastic material 19. Thereafter, the pressurized gas in the gas-containing hollow portion 25 is released to the atmosphere before the mold is opened.
[0003]
In the configurations disclosed in these patent publications, the gas injection nozzle is positioned at the forward end, and further, a movement for maintaining the position of the forward end against the pressure of the molten resin injected into the cavity. Means are provided. Further, in order to completely release the pressurized gas in the hollow portion formed inside the thermoplastic resin in the cavity to the atmosphere before opening the mold, the gas injection nozzle is moved to the reverse end by the operation of the moving means, The seal between the molded product in the cavity and the tip of the gas injection nozzle is broken.
[0004]
A nozzle device comprising a cylindrical nozzle body having a nozzle opening and an axial core provided so as to be able to advance and retract in the nozzle body in the axial direction leaving a gap serving as a gas passage between the inner surface of the nozzle body For example, it is known from JP-A-9-131747. In the injection molding technique disclosed in this patent publication, pressurization of pressurized gas into a molten resin in a mold and discharge of the pressurized pressurized gas are performed through a nozzle port and a gas passage.
Then, after pressurizing the pressurized gas to form the hollow portion, the shaft core is advanced from the position at the time of the press-fitting, and the through hole leading to the hollow portion is formed to be expanded. Discharge the pressurized gas.
[0005]
Furthermore, a gas injection device comprising a gas injection nozzle, and a gas injection nozzle moving means capable of reciprocating a tip portion of the gas injection nozzle in a guide portion provided in the mold and communicating with the cavity and the outside, Japanese Patent Laid-Open No. 7-47572 discloses a gas injection device in which the reciprocating stroke of the tip portion of the gas injection nozzle in the guide portion is a rotational movement in one direction or forward and reverse directions around the axis of the gas injection nozzle. It is.
[0006]
[Problems to be solved by the invention]
By the way, the moving means described above is configured to require an external high pressure source, for example, a high pressure oil pressure. Accordingly, even when the above-described injection molding is performed using an electric injection molding apparatus, it is necessary to prepare a high-pressure fluid pressure generation source, for example, a high-pressure hydraulic pressure generation apparatus, as the moving means. There is a problem that the manufacturing cost of the product increases. Further, in order to counter the high pressure of the molten thermoplastic resin injected into the cavity, the moving means is required to have a large axial force, and there is a problem that the moving means becomes large.
[0007]
Further, in the nozzle device disclosed in Japanese Patent Application Laid-Open No. 9-131747, there is a problem in that the structure of the nozzle device becomes complicated because it has a shaft core provided in the nozzle body so as to be able to advance and retract in the axial direction. Have
[0008]
Furthermore, in the gas injection device disclosed in Japanese Patent Application Laid-Open No. 7-47572, the pressure received by the tip portion of the gas injection nozzle from the molten resin injected into the mold cavity is substantially the same as the axis of the gas injection nozzle. There is a problem that it is a right angle and the tip of the gas injection nozzle is likely to be deformed.
[0009]
Accordingly, an object of the present invention is to provide a pressurization having a simple structure or having a structure that is not easily deformed by the pressure applied to the tip portion of the gas injection nozzle from the molten resin injected into the mold cavity. An object of the present invention is to provide a fluid introduction device, a mold assembly incorporating such a pressurized fluid introduction device, and an injection molding method using such a mold assembly.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a pressurized fluid introduction apparatus according to the first aspect of the present invention comprises:
(A) a pressurized fluid introduction nozzle having an opening at the tip, and
(B) a moving device for reciprocating the pressurized fluid introduction nozzle;
Consisting of
A pressurized fluid introducing device for molding an injection molded product having a hollow portion by introducing a pressurized fluid into a molten thermoplastic resin injected into a cavity provided in a mold,
When the pressurized fluid is introduced into the molten thermoplastic resin injected into the cavity via the pressurized fluid introduction nozzle, the pressurized fluid introduction nozzle is positioned at the backward end, and the pressurized fluid in the hollow portion is moved to the atmosphere. Upon release, the pressurized fluid introduction nozzle is advanced and retracted at least once by the operation of the moving device.
[0011]
To achieve the above object, a mold assembly according to the first aspect of the present invention comprises:
(A) A mold having a cavity and a molten resin injection part for injecting a molten thermoplastic resin into the cavity,
(B) a pressurized fluid introduction nozzle having an opening at the tip, and
(C) a moving device for reciprocating the pressurized fluid introduction nozzle;
With
A mold assembly for forming an injection molded product having a hollow portion by introducing a pressurized fluid into the molten thermoplastic resin injected into the cavity,
When the pressurized fluid is introduced into the molten thermoplastic resin injected into the cavity via the pressurized fluid introduction nozzle, the pressurized fluid introduction nozzle is positioned at the reverse end,
When the pressurized fluid in the hollow portion is released into the atmosphere, the pressurized fluid introduction nozzle is advanced and retracted at least once by the operation of the moving device.
[0012]
In order to achieve the above object, an injection molding method according to the first aspect of the present invention comprises:
(A) A mold having a cavity and a molten resin injection part for injecting a molten thermoplastic resin into the cavity,
(B) a pressurized fluid introduction nozzle having an opening at the tip, and
(C) a moving device for reciprocating the pressurized fluid introduction nozzle;
With
An injection molding method for molding an injection-molded product using a mold assembly for molding an injection-molded product having a hollow portion by introducing a pressurized fluid into the molten thermoplastic resin injected into the cavity. There,
(A) With the pressurized fluid introduction nozzle positioned at the reverse end, the molten thermoplastic resin is injected into the cavity,
(B) Pressurized fluid introduction nozzle inside the melted thermoplastic resin injected into the cavity during injection of the molten thermoplastic resin, or after completion of injection, with the pressurized fluid introduction nozzle positioned at the backward end Through which a pressurized fluid is introduced, thereby forming a hollow portion inside the molten thermoplastic resin injected into the cavity,
(C) After a certain time has elapsed, the operation of the moving device causes the pressurized fluid introduction nozzle to move forward and backward at least once to create a gap between the tip of the pressurized fluid introduction nozzle and the thermoplastic resin in the cavity. Generating and releasing the pressurized fluid in the hollow through the gap,
It consists of each process.
[0013]
In the pressurized fluid introduction device, the mold assembly or the injection molding method according to the first aspect of the present invention (hereinafter, these may be collectively referred to as the first aspect of the present invention), The period of advance and retreat of the pressurized fluid introduction nozzle is 0.01 Hz or more (time required for one advance and retreat is 100 seconds or less), preferably 0.1 Hz or more (time required for one advance and retreat is 10). Or less).
[0014]
In the first aspect of the present invention, the advance amount from the backward end to the forward end of the pressurized fluid introduction nozzle and the reverse amount from the forward end to the backward end are 0.01 mm to 2 mm, preferably 0.05 mm to 1 mm. It is desirable to be. If the advance amount and the reverse amount are too large, there is a possibility that a defect may occur in the injection molded product near the pressurized fluid introduction nozzle. The forward and backward movements of the pressurized fluid introduction nozzle may be at least once and may be twice or more.
[0015]
In the first aspect of the present invention, the moving device can be composed of a hydraulic cylinder or a pneumatic cylinder, or an electric motor (more specifically, a combination of an electric motor and a rack and pinion, or (Eccentric motor) or a piezoelectric element. When the pressurized fluid is introduced into the melted thermoplastic resin injected into the cavity via the pressurized fluid introduction nozzle, the pressurized fluid introduction nozzle is positioned at the reverse end, so that it is injected into the cavity. There is no need to provide a moving device that counters the high pressure of the molten thermoplastic resin, and the moving device does not require a large axial force, and a moving device having a small capacity may be provided.
[0016]
In the pressurized fluid introduction device or the die assembly according to the first aspect of the present invention, the tip of the pressurized fluid introduction nozzle generated by at least one advancement and retraction of the pressurized fluid introduction nozzle and the thermoplasticity in the cavity The pressurized fluid in the hollow portion is released through a gap between the resin and the resin.
[0017]
In order to achieve the above object, a pressurized fluid introduction apparatus according to a second aspect of the present invention comprises:
(A) a pressurized fluid introduction nozzle having an opening at the tip, and
(B) a rotating device for rotating the pressurized fluid introduction nozzle about its axis (referred to as a rotation axis);
Consisting of
A pressurized fluid introducing device for molding an injection molded product having a hollow portion by introducing a pressurized fluid into a molten thermoplastic resin injected into a cavity provided in a mold,
The tip portion of the pressurized fluid introduction nozzle that should protrude into the cavity is thinner than the portion of the pressurized fluid introduction nozzle that does not protrude into the cavity,
When releasing the pressurized fluid in the hollow portion into the atmosphere, the pressurized fluid introduction nozzle is rotated by the operation of the rotating device.
[0018]
In order to achieve the above object, a mold assembly according to a second aspect of the present invention comprises:
(A) A mold having a cavity and a molten resin injection part for injecting a molten thermoplastic resin into the cavity,
(B) a pressurized fluid introduction nozzle having an opening at the tip, and
(C) a rotating device for rotating the pressurized fluid introduction nozzle about its axis (rotation axis);
With
A mold assembly for forming an injection molded product having a hollow portion by introducing a pressurized fluid into the molten thermoplastic resin injected into the cavity,
The tip portion of the pressurized fluid introduction nozzle protruding into the cavity is thinner than the portion of the pressurized fluid introduction nozzle not protruding into the cavity,
When releasing the pressurized fluid in the hollow portion into the atmosphere, the pressurized fluid introduction nozzle is rotated by the operation of the rotating device.
[0019]
The injection molding method according to the second aspect of the present invention for achieving the above object is as follows:
(A) A mold having a cavity and a molten resin injection part for injecting a molten thermoplastic resin into the cavity,
(B) a pressurized fluid introduction nozzle having an opening at the tip, and
(C) a rotating device for rotating the pressurized fluid introduction nozzle about its axis (rotation axis);
With
The tip portion of the pressurized fluid introduction nozzle protruding into the cavity is thinner than the portion of the pressurized fluid introduction nozzle not protruding into the cavity,
An injection molding method for molding an injection-molded product using a mold assembly for molding an injection-molded product having a hollow portion by introducing a pressurized fluid into the molten thermoplastic resin injected into the cavity. There,
(A) injecting a molten thermoplastic resin into the cavity;
(B) A pressurized fluid is introduced through a pressurized fluid introduction nozzle into the molten thermoplastic resin injected into the cavity during or after the injection of the molten thermoplastic resin, Forming a hollow portion inside the molten thermoplastic resin injected into
(C) After a certain period of time, the pressurized fluid introduction nozzle is rotated by the operation of the rotating device to create a gap between the tip portion of the pressurized fluid introduction nozzle and the thermoplastic resin in the cavity. Release the pressurized fluid in the hollow part,
It consists of each process.
[0020]
In a pressurized fluid introduction device, a mold assembly or an injection molding method according to the second aspect of the present invention (hereinafter, these may be collectively referred to as the second aspect of the present invention). The axis of the tip portion of the pressurized fluid introduction nozzle may be configured not to coincide with the axis (rotation axis) of the pressurized fluid introduction nozzle. The second aspect of the present invention described below includes this configuration.
[0021]
In the second aspect of the present invention, it is possible to simplify the structure of the pressurized fluid introduction nozzle by discharging the pressurized fluid from the opening in a direction substantially parallel to the axis of the pressurized fluid introduction nozzle. From the viewpoint of, it is preferable.
[0022]
In the second aspect of the present invention, the rotational speed of the pressurized fluid introduction nozzle is preferably 1 rpm or more, but is not limited thereto. The distance from the axis of the pressurized fluid introduction nozzle (rotation axis) to the axis of the tip of the pressurized fluid introduction nozzle (sometimes referred to as eccentricity) is 0 mm or more and 1 mm or less, preferably 0.01 mm or more and 0. 0.5 mm or less, more preferably 0.03 mm or more and 0.3 mm or less is desirable from the viewpoint of reliably releasing the pressurized fluid in the hollow portion into the atmosphere and from the viewpoint of the load on the pressurized fluid nozzle.
[0023]
In the second aspect of the present invention, the rotation angle of the pressurized fluid introduction nozzle is 180 degrees or more, preferably 360 degrees or more, so that the pressurized fluid in the hollow portion is reliably released into the atmosphere. From such a viewpoint, it is desirable. The direction of rotation of the pressurized fluid introduction nozzle can be one direction around the axis of rotation or the forward / reverse direction.
[0024]
In the second aspect of the present invention, the rotating device can be composed of a hydraulic cylinder or a pneumatic cylinder, or alternatively can be composed of an electric motor. The pressurized fluid introduction nozzle does not move or displace in a direction parallel to the rotation axis. Therefore, when a pressurized fluid is introduced into the molten thermoplastic resin injected into the cavity via the pressurized fluid introduction nozzle, a moving device that counters the high pressure of the molten thermoplastic resin injected into the cavity is provided. do not need.
[0025]
In the pressurized fluid introduction apparatus or the mold assembly according to the second aspect of the present invention, the gap between the tip portion of the pressurized fluid introduction nozzle generated by the rotation of the pressurized fluid introduction nozzle and the thermoplastic resin in the cavity. The pressurized fluid in the hollow part is released through the gap.
[0026]
In the first aspect of the present invention or the second aspect of the present invention, a check valve for preventing intrusion of the molten thermoplastic resin injected into the cavity is disposed at the tip of the pressurized fluid introduction nozzle. However, if the opening diameter is such that the molten thermoplastic resin injected into the cavity does not enter, the check valve can be dispensed with. In addition, heating the pressurized fluid introduction nozzle by a heating device disclosed in Japanese Patent Laid-Open No. 4-31015 also prevents the pressurized fluid introduction nozzle from being blocked by the thermoplastic resin, It is effective to ensure the introduction. Specifically, a ring heater may be attached to the outer wall of the pressurized fluid introduction nozzle.
[0027]
In the first aspect of the present invention, the pressurized fluid introduction nozzle mounting position in the mold assembly may be in the vicinity of a surface constituting the cavity of the mold (referred to as a cavity surface of the mold), or a molten resin It may be in an injection part, and may be in a sprue part or a runner part. When the pressurized fluid introduction nozzle is attached in the vicinity of the cavity surface of the mold, the tip of the pressurized fluid introduction nozzle when the pressurized fluid introduction nozzle is located at the backward end may be located in the cavity, It may be located in substantially the same plane as the cavity surface of the mold. Further, in this case, the clearance between the tip portion of the pressurized fluid introduction nozzle and the mold is preferably as small as possible, specifically, about 10 μm to 20 μm.
[0028]
In the first aspect of the present invention, the cross-sectional shape of the tip portion of the pressurized fluid introduction nozzle when cut in a direction perpendicular to the axis of the pressurized fluid introduction nozzle (sometimes referred to as a moving direction axis) is circular, An arbitrary shape such as an oval shape, an oval shape, a polygonal shape, or a polygonal shape having a rounded apex portion can be used. Among them, a circular shape or a polygonal shape is preferable. The reciprocating stroke of the pressurized fluid introduction nozzle is a linear motion parallel to the axis of the pressurized fluid introduction nozzle.
[0029]
In the second aspect of the present invention, the pressurized fluid introduction nozzle when cut in the direction perpendicular to the axis of the tip portion of the pressurized fluid introduction nozzle protruding into the cavity (hereinafter sometimes referred to as the tip portion axis) The cross-sectional shape of the tip portion of the pressurized fluid introduction nozzle and the portion of the pressurized fluid introduction nozzle when cut in the direction perpendicular to the axis of the portion of the pressurized fluid introduction nozzle that does not protrude into the cavity (hereinafter referred to as the rotational axis) The cross-sectional shape may be any shape such as a circle, an ellipse, an egg, a polygon, or a polygon with a rounded apex. In particular, when the amount of eccentricity is 0 mm, when the pressurized fluid introduction nozzle is rotated by the operation of the rotating device, a gap is formed between the tip portion of the pressurized fluid introduction nozzle and the injection molded product, and the inside of the hollow portion is increased. From the viewpoint that the pressurized fluid can be reliably released to the atmosphere, the cross-sectional shape of the tip portion of the pressurized fluid introduction nozzle when cut in the direction perpendicular to the tip portion axis is a shape other than a circle, such as an ellipse, egg It is preferable to use a shape, a polygon, a polygon with rounded corners, or the like. On the other hand, when the amount of eccentricity exceeds 0 mm, it is preferably circular or polygonal. The tip part axis is a straight line passing through the center of gravity of the cross-sectional shape of the tip part. When the cross-sectional shape is circular, for example, the tip end portion axis is a straight line passing through the center of the circular cross-sectional shape. The rotation axis is a straight line passing through the center of gravity of the cross-sectional shape of the portion of the pressurized fluid introduction nozzle that does not protrude into the cavity. When the cross-sectional shape is circular, for example, the rotation axis is a straight line passing through the center of the circular cross-sectional shape. It should be noted that the center of the opening and the tip partial axis may coincide or may not coincide.
[0030]
The structure of the molten resin injection part can be any known structure.
[0031]
In the injection molding method according to the first aspect or the second aspect of the present invention, the introduction start time of the pressurized fluid into the molten thermoplastic resin in the cavity is after the start of injection of the molten thermoplastic resin into the cavity. What is necessary is just to complete the injection during the injection of the molten thermoplastic resin into the cavity, or after a certain time has elapsed after the injection is completed. The amount of the molten thermoplastic resin injected into the cavity may be an amount that completely fills the cavity with the molten thermoplastic resin, or an amount that is not completely filled.
[0032]
There is no restriction | limiting in particular in the thermoplastic resin used by this invention, Polyolefin resin, such as a polyethylene resin and a polypropylene resin; Styrenic resin, such as a polystyrene resin, AS resin, ABS resin, and AES resin; Methacrylic type, such as PMMA resin Resin; Polyoxymethylene (polyacetal) resin; Polyamide resin such as polyamide 6, polyamide 66, polyamide MXD; Modified polyphenylene ether (PPE) resin; Polyphenylene sulfide resin; Polyethylene terephthalate (PET) resin, Polybutylene terephthalate (PBT) resin Examples thereof include polyester resins such as: thermoplastic resins such as liquid crystal polymers, or polymer alloys composed of at least two kinds of these thermoplastic resins. For example, glass fibers, glass flakes, carbon fibers, wollastonite, aluminum borate whisker fibers are added to these thermoplastic resins in order to impart mechanical properties typified by rigidity, dimensional stability, etc. to the molded product. Further, inorganic fibers composed of at least one material selected from the group consisting of potassium titanate whisker fibers, basic magnesium sulfate whisker fibers, calcium silicate whisker fibers and calcium sulfate whisker fibers may be contained. Further, for example, an effective expression amount of a stabilizer, a release agent, or an ultraviolet absorber may be blended in the thermoplastic resin.
[0033]
As the pressurized fluid to be introduced, gaseous substances such as nitrogen gas, carbon dioxide gas, air, and helium gas can be used at room temperature, and a liquid such as water or a gas liquefied under high pressure can also be used.
[0034]
When molding a molded product, various conditions such as the amount of molten thermoplastic resin during injection molding, temperature, pressure or injection speed, amount of pressurized fluid to be introduced, pressure or speed, mold cooling time, etc. are used. Depending on the type of resin to be used, the shape of the mold, etc., it is necessary to select and control appropriately, and it cannot be determined uniquely.
[0035]
In the first aspect of the present invention, when the pressurized fluid is introduced into the molten thermoplastic resin injected into the cavity via the pressurized fluid introduction nozzle, the pressurized fluid introduction nozzle is positioned at the reverse end. When the pressurized fluid in the hollow portion is released to the atmosphere, the pressurized fluid introduction nozzle has only to be moved forward and backward by the operation of the moving device, so that the high pressure of the molten thermoplastic resin injected into the cavity is increased. A means for holding the pressurized fluid introduction nozzle against the pressure (for example, a fluid pressure generating source as a moving means having a large axial force in the conventional injection molding apparatus) becomes unnecessary, and the structure of the pressurized fluid introduction apparatus is eliminated. Simplification can be achieved.
[0036]
In the second aspect of the present invention, the pressurized fluid introduction nozzle does not move back and forth, and when releasing the pressurized fluid in the hollow portion into the atmosphere, the pressurized fluid introduction nozzle is rotated by the operation of the rotating device. Therefore, a means for holding the pressurized fluid introduction nozzle against the high pressure of the molten thermoplastic resin injected into the cavity (for example, as a moving means having a large axial force in the conventional injection molding apparatus) The fluid pressure generation source is not required, and the structure of the pressurized fluid introduction device can be simplified.
[0037]
【Example】
Hereinafter, the present invention will be described based on examples with reference to the drawings.
[0038]
Example 1
Example 1 relates to a pressurized fluid introduction device, a mold assembly, and an injection molding method according to the first aspect of the present invention. A conceptual diagram of an injection molding apparatus including the mold assembly of Example 1 is shown in FIG.
[0039]
The mold assembly according to the first embodiment includes a mold 10 and a pressurized fluid introduction device 20 including a pressurized fluid introduction nozzle 21 and a moving device 30. The mold 10 includes a fixed mold part 11 and a movable mold part 12, and a cavity 13 is formed when the mold is clamped. The mold 10 is provided with a molten resin injection portion (gate portion 14) for injecting a molten thermoplastic resin into the cavity 13. The gate part 14 shown in FIG. 1 has a direct structure and communicates with the injection cylinder 16 via a runner part and a sprue part (indicated by reference numeral 15). The structure of the gate portion 14 is not limited to the direct structure.
[0040]
The pressurized fluid introduction nozzle 21 has an opening 23 at the tip 22. Further, a check valve (not shown) is disposed at the tip portion. The mounting position of the pressurized fluid introduction nozzle 21 in the mold assembly is in the vicinity of the cavity surface of the mold in the example shown in FIG. The tip 22 of the pressurized fluid introduction nozzle 21 when the pressurized fluid introduction nozzle 21 is located at the reverse end is located within the cavity 13. The circular pressurized fluid introduction nozzle 21 having a diameter of 7 mm in cross-sectional shape at the tip of the pressurized fluid introduction nozzle 21 when cut in a direction perpendicular to the moving direction axis of the pressurized fluid introduction nozzle 21 was used. The pressurized fluid introduction nozzle 21 is connected to a pressurized fluid source via a pipe. In addition, illustration of piping and a pressurized fluid source was abbreviate | omitted. The moving device 30 for reciprocating the pressurized fluid introduction nozzle 21 is composed of a hydraulic cylinder including a cylinder portion 31 and a piston portion 32. The rear end of the pressurized fluid introduction nozzle 21 is attached to the front end of the piston portion 32. The cylinder part 31 is attached to the movable mold part 12 by an appropriate method. Oil is fed into the cylinder portion 31 from a hydraulic system (not shown), or the oil is discharged from the cylinder portion 31 and the piston portion 32 reciprocates.
The pressure generated by the moving device 30 when the pressurized fluid introduction nozzle 21 is moved forward is about 2 × 10.⁶The moving device 30 is composed of a hydraulic cylinder having a pressure of Pa. Further, when the pressurized fluid introduction nozzle 21 is moved forward and backward at a frequency of 0.5 Hz (the time required for one forward and backward movement is 2 seconds), when the pressurized fluid in the hollow portion is released to the atmosphere, the moving device The pressurized fluid introduction nozzle was set to be advanced and retracted twice by the above operation.
[0041]
2 and 3 which are schematic sectional views of the mold 10 and the like, and FIG. 4 schematically showing a part of the pressurized fluid introduction nozzle 21 and the movable mold portion 12 and the cavity 13 in the vicinity thereof. And with reference to FIG. 5, the injection molding method of Example 1 is demonstrated. 2 and 3, the illustration of the injection cylinder 16 is omitted.
[0042]
[Step-100]
First, as shown in FIG. 1, the fixed mold part 11 and the movable mold part 12 are clamped so that the tip 22 of the pressurized fluid introduction nozzle 21 protrudes into the cavity 13. The piston part 32 and the pressurized fluid introduction nozzle 21 in the cylinder part 31 are located at the backward movement end.
[0043]
[Step-110]
After the thermoplastic resin is plasticized, melted and measured in the injection cylinder 16, the molten thermoplastic resin 40 is injected into the cavity 13 from the injection cylinder 16 through the runner part, the sprue part 15 and the gate part 14. Ejected (see FIG. 2). The injection conditions are illustrated in Table 1 below. The thermoplastic resin used was a polypropylene resin. Further, the volume of the molten thermoplastic resin 40 injected into the cavity 13 was set to a volume that did not completely fill the cavity 13. The pressurized fluid introduction nozzle 21 is located at the reverse end.
[0044]
[Table 1]
Injection amount of molten thermoplastic resin: 25cm^Three
Melt thermoplastic resin temperature: 210 ° C
Mold temperature: 40 ° C
Injection time: 2.5 seconds
[0045]
The position of the pressurized fluid introduction nozzle 21 is not displaced even by the pressure of the molten thermoplastic resin 40 injected into the cavity 13. Further, the molten thermoplastic resin enters from the tip of the pressurized fluid introduction nozzle 21, but the check valve (not shown) prevents the molten thermoplastic resin from entering upstream from the check valve. Furthermore, since the clearance between the tip portion of the pressurized fluid introduction nozzle 21 and the movable mold portion 12 is about 10 μm to 20 μm, there is no possibility that the molten thermoplastic resin leaks outside from this clearance.
[0046]
[Step-120]
Simultaneously with the completion of the injection of the molten thermoplastic resin 40 into the cavity 13, a pressurized fluid (specifically, nitrogen is introduced into the molten thermoplastic resin 40 injected into the cavity 13 through the pressurized fluid introduction nozzle 21. Gas) began to be introduced. As a result, a hollow portion 41 is formed in the molten thermoplastic resin 40 injected into the cavity 13 (see FIGS. 3 and 4A). The conditions for introducing the pressurized fluid are illustrated in Table 2 below. The pressurized fluid introduction nozzle 21 is located at the reverse end.
[0047]
[Table 2]
Pressurized fluid pressure during introduction: 1 × 10⁷Pa
Pressurized fluid metering: 100cm^Three
Pressurized fluid holding period: 20 seconds from start of pressurized fluid introduction
Final pressurized fluid pressure: 2 × 10⁷Pa
[0048]
[Step-130]
After 25 seconds from the start of injection, by operating the moving device 30, specifically, by sending oil from a hydraulic system (not shown) to the cylinder portion 31, the piston portion 32 is advanced, and the pressurized fluid introduction nozzle 21 is moved forward. Was moved forward and positioned at the forward end (see FIG. 4B). Subsequently, by discharging the oil from the cylinder portion 31, the piston portion 32 was retracted, the pressurized fluid introduction nozzle 21 was retracted, and was positioned at the backward end (see FIG. 5). This operation was repeated twice. The advance amount from the reverse end to the forward end of the pressurized fluid introduction nozzle 21 and the reverse amount from the advance end to the reverse end (hereinafter referred to as the movement distance) were set to 0.5 mm. As a result, a gap 42 is formed between the tip 22 of the pressurized fluid introduction nozzle 21 and the thermoplastic resin 40A in the cavity 13, and the pressurized fluid in the hollow portion 41 is released to the atmosphere via the gap 42. did.
[0049]
[Step-140]
After 35 seconds have elapsed from the start of injection, the mold is opened and the molded product is removed from the mold. Thus, an injection molded product having the hollow portion 41 could be formed by introducing the pressurized fluid into the molten thermoplastic resin injected into the cavity 13 provided in the mold 10. No noticeable indentation was observed in the obtained injection molded product. Moreover, the pressurized fluid in the hollow part 41 was able to be reliably released into the atmosphere.
[0050]
The hydraulic cylinder was replaced with a pneumatic cylinder, and injection molding similar to that in Example 1 was performed. However, an injection molding product similar to that in Example 1 was obtained. Furthermore, the hydraulic cylinder is replaced with a moving device composed of a combination of an electric motor and a rack and pinion (the cycle of forward and backward movement of the pressurized fluid introduction nozzle 21: 0.1 Hz, moving distance: 0.1 mm). The same injection molding as in Example 1 was performed, but an injection molded product similar to that in Example 1 was obtained. Moreover, the pressurized fluid in the hollow part could be reliably released into the atmosphere. Further, the hydraulic cylinder was replaced with a piezoelectric element (driving frequency 1 Hz, moving distance 0.1 mm), and injection molding similar to that in Example 1 was performed. However, an injection molding product similar to that in Example 1 was obtained. . Moreover, the pressurized fluid in the hollow part could be reliably released into the atmosphere.
[0051]
(Comparative Example 1)
Except for the point that the moving distance was changed to 5 mm, the same mold assembly as in Example 1 was used, and injection molding was performed under the same conditions as in Example 1. As a result, although the pressurized fluid in the hollow portion could be reliably released into the atmosphere, the surface of the portion near the pressurized fluid introduction nozzle 21 of the obtained injection molded product was whitened and cracked. .
[0052]
(Example 2)
Example 2 relates to a pressurized fluid introduction device, a mold assembly, and an injection molding method according to the second aspect of the present invention. FIG. 6 shows a conceptual diagram of an injection molding apparatus including a mold assembly according to the second embodiment. FIG. 7A schematically shows part of a pressurized fluid introduction nozzle, a movable mold part in the vicinity thereof, and a cavity. FIG. 7B shows a schematic front view of the pressurized fluid introduction nozzle.
[0053]
The mold assembly according to the second embodiment includes a mold 10 and a pressurized fluid introduction device 50 including a pressurized fluid introduction nozzle 51 and a rotating device 60. Since the mold 10 can be configured substantially the same as the mold described in the first embodiment, detailed description thereof is omitted.
[0054]
In the mold assembly in the second embodiment, the attachment position of the pressurized fluid introduction nozzle 51 is in the vicinity of the cavity surface of the mold 10. The pressurized fluid introduction nozzle 51 has an opening 53 at the tip 52. Further, a check valve (not shown) is disposed at the tip portion.
The rotating device 60 is configured so that the pressurized fluid introduction nozzle 51 has its axis line (rotating axis line; in FIG.₀). The tip portion 54 of the pressurized fluid introduction nozzle 51 protruding into the cavity 13 is narrower than the portion 55 of the pressurized fluid introduction nozzle 51 that does not protrude into the cavity 13, and the tip portion 54 of the pressurized fluid introduction nozzle 51. Axis (the tip partial axis, and in FIG.₁Is the rotation axis L₀Does not match. Rotation axis L₀To tip part axis L₁The distance (the amount of eccentricity) L was 0.05 mm. Also, the tip part axis L₁The outer cross-sectional shape of the tip portion 54 of the pressurized fluid introduction nozzle 51 when cut in a direction perpendicular to the vertical direction is a circle having a diameter of 3 mm. Tip partial axis L₁Passes through the center of such a circle. On the other hand, the rotation axis L₀The outer cross-sectional shape of the portion 55 of the pressurized fluid introduction nozzle 51 when cut in a direction perpendicular to the vertical direction is a circle having a diameter of 7 mm. Rotation axis L₀Passes through the center of such a circle. Center of opening 53 and tip portion axis L₁And matched. The front end surface 56 of the portion 55 of the pressurized fluid introduction nozzle 51 is a flat surface and is configured to substantially coincide with the cavity surface of the mold. In this pressurized fluid introduction nozzle 51, the rotation axis L₀A pressurized fluid (specifically, nitrogen gas) is discharged from the opening 53 in a direction substantially parallel to the opening 53.
[0055]
The pressurized fluid introduction nozzle 51 is connected to a pressurized fluid source via a pipe. In addition, illustration of piping and a pressurized fluid source was abbreviate | omitted. A rotating device 60 for rotating the pressurized fluid introduction nozzle 51 is composed of a pneumatic cylinder including a cylinder portion 61 and a piston portion 62. A rack (not shown) is attached to the front end of the piston part 62, and a pinion (not shown) is attached to the rear end of the pressurized fluid introduction nozzle 51. The cylinder part 61 and the pressurized fluid introduction nozzle 51 are attached to the movable mold part 12 by an appropriate method. Compressed air is fed into the cylinder part 61 from a pneumatic system (not shown), or the compressed air is discharged from the cylinder part 61 and the piston part 62 reciprocates. The reciprocating motion of the piston portion 62 is converted into the rotational motion (or rotational motion) of the pressurized fluid introduction nozzle 51 by the rack and pinion. The pressure generated by the rotating device 60 when the pressurized fluid introduction nozzle 51 is rotated is about 2 × 10.⁶The rotating device 60 is composed of a pneumatic cylinder having Pa. Further, when the number of rotations of the pressurized fluid introduction nozzle 51 is set to 6 rpm and the pressurized fluid in the hollow portion is released into the atmosphere, the pressurized fluid introduction nozzle 51 is rotated twice by the operation of the rotating device 60. It was set.
[0056]
Hereinafter, the injection molding method of Example 2 will be described with reference to FIGS. 8 and 9 schematically showing a part of the pressurized fluid introduction nozzle 51 and the movable mold part 12 and the cavity 13 in the vicinity thereof.
[0057]
[Step-200]
First, as shown in FIG. 6, the fixed mold portion 11 and the movable mold portion 12 are clamped, and the tip portion 54 of the pressurized fluid introduction nozzle 51 is projected into the cavity 13.
[0058]
[Step-210]
After the thermoplastic resin is plasticized, melted and measured in the injection cylinder 16, the molten thermoplastic resin 40 is injected into the cavity 13 from the injection cylinder 16 through the runner part, the sprue part 15 and the gate part 14. Ejected (see FIG. 8A). The same thermoplastic resin as in Example 1 was used, and the injection conditions were the same as those exemplified in Table 1. Further, the volume of the molten thermoplastic resin 40 injected into the cavity 13 was set to a volume that did not completely fill the cavity 13.
[0059]
The position of the pressurized fluid introduction nozzle 51 is not displaced even by the pressure of the molten thermoplastic resin 40 injected into the cavity 13. In addition, the molten thermoplastic resin enters from the tip of the pressurized fluid introduction nozzle 51, but the check valve (not shown) prevents the molten thermoplastic resin from entering upstream from the check valve. Further, since the clearance between the tip portion of the pressurized fluid introduction nozzle 51 and the movable mold portion 12 is about 10 μm to 20 μm, there is no possibility that the molten thermoplastic resin leaks outside from this clearance.
[0060]
[Step-220]
Simultaneously with the completion of the injection of the molten thermoplastic resin 40 into the cavity 13, a pressurized fluid (specifically, nitrogen is introduced into the molten thermoplastic resin 40 injected into the cavity 13 through the pressurized fluid introduction nozzle 51. Gas) began to be introduced. As a result, a hollow portion 41 is formed inside the molten thermoplastic resin 40 injected into the cavity 13 (see FIG. 8B). The conditions for introducing the pressurized fluid were the same as those exemplified in Table 2.
[0061]
[Step-230]
After 40 seconds from the start of injection, by operating the rotating device 60, specifically, by sending compressed air from a pneumatic system (not shown) to the cylinder part 31, the piston part 62 is advanced, and a pressurized fluid introduction nozzle 51 was rotated (see FIG. 9). FIG. 9 shows a state where the pressurized fluid introduction nozzle 51 is rotated 180 degrees. The pressurized fluid introduction nozzle 51 was rotated twice. As a result, a gap 42 is formed between the tip portion 54 of the pressurized fluid introduction nozzle 51 and the thermoplastic resin 40A in the cavity 13, and the pressurized fluid in the hollow portion 41 is introduced into the atmosphere through the gap 42. Released.
[0062]
[Step-240]
After 60 seconds have elapsed from the start of injection, the mold is opened and the molded product is removed from the mold. Thus, an injection molded product having the hollow portion 41 could be formed by introducing the pressurized fluid into the molten thermoplastic resin injected into the cavity 13 provided in the mold 10. No noticeable indentation was observed in the obtained injection molded product. Moreover, the pressurized fluid in the hollow part 41 was able to be reliably released into the atmosphere.
[0063]
The pneumatic cylinder was replaced with a hydraulic cylinder, and injection molding similar to that in Example 2 was performed. However, an injection molded product similar to that in Example 2 was obtained. Furthermore, the combination of the pneumatic cylinder and the rack and pinion is a combination of the electric motor and the rack and pinion (the rotation speed of the pressurized fluid introduction nozzle 51: 60 rpm, the rotation axis L₀To tip part axis L₁Was replaced with a rotating device constituted by a distance (eccentric amount L: 0.05 mm), and injection molding similar to that in Example 2 was performed, but an injection molded product similar to that in Example 2 was obtained. . Moreover, the pressurized fluid in the hollow part could be reliably released into the atmosphere.
[0064]
Also, the tip part axis L₁The outer cross-sectional shape of the tip portion of the pressurized fluid introduction nozzle when cut in a direction perpendicular to the vertical axis is an ellipse having a major axis of 5.0 mm and a minor axis of 4.8 mm, and the rotation axis L₀The pressurized fluid introduction nozzle was replaced with a pressurized fluid introduction nozzle having a circular shape with a diameter of 7 mm. Rotation axis L₀To tip part axis L₁The distance (eccentric amount) L was set to 0 mm. Then, the same injection molding as in Example 2 was performed, but the same injection molded product as in Example 2 was obtained. Moreover, the pressurized fluid in the hollow part could be reliably released into the atmosphere.
[0065]
As mentioned above, although this invention was demonstrated based on the preferable Example, this invention is not limited to these. The structure of the mold assembly described in the examples, the thermoplastic resin used in the examples, the injection molding conditions, and the like are examples, and can be changed as appropriate. In the embodiment, the pressurized fluid introduction device is arranged in the movable mold part 12, but it can also be arranged in the fixed mold part 11. Moreover, the attachment position of the pressurized fluid introduction nozzles 21 and 51 in the mold assembly can be in the molten resin injection part (gate part 14), or in the sprue part or the runner part. In the first embodiment, the tip 22 of the pressurized fluid introduction nozzle 21 is positioned in the cavity 13. However, when the tip 22 of the pressurized fluid introduction nozzle 21 is positioned at the backward movement end, the tip 22 of the pressurized fluid introduction nozzle 21 and the cavity surface of the die They may be positioned in substantially the same plane. In the first embodiment, the configuration may further include a biasing means (for example, a spring) that biases the pressurized fluid introduction nozzle 21 in the backward direction.
[0066]
【The invention's effect】
In the present invention, a means for holding the pressurized fluid introduction nozzle against the high pressure of the molten thermoplastic resin injected into the cavity becomes unnecessary, and the structure of the pressurized fluid introduction device is simplified. Can do. As a result, it is possible to solve the problem that the manufacturing cost of the entire injection molding apparatus increases, and finally it is possible to suppress an increase in the manufacturing cost of the injection molded product. In addition, the structure of the pressurized fluid introduction nozzle is extremely simple, it is unlikely to fail, and the pressure of the gas injection nozzle is also affected by the pressure received by the tip of the gas injection nozzle from the molten resin injected into the mold cavity. Deformation is unlikely to occur at the tip.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an injection molding apparatus including a mold assembly according to a first embodiment.
2 is a conceptual diagram of a mold assembly for explaining an injection molding method according to Embodiment 1. FIG.
FIG. 3 is a conceptual diagram of a mold assembly for explaining the injection molding method of Example 1 following FIG. 2;
4 is a view schematically showing a pressurized fluid introduction nozzle, a movable mold part in the vicinity thereof, and a part of a cavity for explaining an injection molding method of Example 1. FIG.
FIG. 5 is a diagram schematically showing a part of a pressurized fluid introduction nozzle, a movable mold part in the vicinity thereof, and a part of a cavity for explaining the injection molding method of Example 1 following FIG. 4;
6 is a conceptual diagram of an injection molding apparatus including a mold assembly of Example 2. FIG.
FIG. 7 is a view schematically showing a pressurized fluid introduction nozzle, a movable mold portion in the vicinity thereof, and a part of a cavity in Example 2, and a schematic front view of the pressurized fluid introduction nozzle.
FIG. 8 is a diagram schematically showing a pressurized fluid introduction device, a movable mold part in the vicinity thereof, and a part of a cavity for explaining an injection molding method of Example 2.
FIG. 9 is a diagram schematically showing part of the pressurized fluid introduction device, the movable mold part in the vicinity thereof, and a part of the cavity for explaining the injection molding method of Example 2 following FIG. 8;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Mold, 11 ... Fixed mold part, 12 ... Movable mold part, 13 ... Cavity, 14 ... Gate part, 15 ... Runner part and sprue part, 16. ..Cylinder for injection, 20, 50 ... pressurized fluid introduction device, 21, 51 ... pressurized fluid introduction nozzle, 22, 52 ... tip, 23, 53 ... opening, 54 ...・ A tip portion of the pressurized fluid introduction nozzle projecting into the cavity, 55... A portion of the pressurized fluid introduction nozzle not projecting into the cavity, 30... Moving device, 60. .... Cylinder part, 32, 62 ... piston part, 40 ... molten thermoplastic resin, 40A ... thermoplastic resin, 41 ... hollow part, 42 ... gap

Claims (4)

(A) A mold having a cavity and a molten resin injection part for injecting a molten thermoplastic resin into the cavity,
(B) a pressurized fluid introduction nozzle having an opening at the tip, and
(C) a moving device for reciprocating the pressurized fluid introduction nozzle;
With
An injection molding method for molding an injection-molded product using a mold assembly for molding an injection-molded product having a hollow portion by introducing a pressurized fluid into the molten thermoplastic resin injected into the cavity. There,
(A) With the pressurized fluid introduction nozzle positioned at the reverse end, the molten thermoplastic resin is injected into the cavity,
(B) Pressurized fluid introduction nozzle inside the melted thermoplastic resin injected into the cavity during injection of the molten thermoplastic resin or after completion of injection, with the pressurized fluid introduction nozzle positioned at the backward end Through which a pressurized fluid is introduced, thus forming a hollow portion inside the molten thermoplastic resin injected into the cavity,
(C) After a certain time has elapsed, the movement of the moving device causes the pressurized fluid introduction nozzle to advance and retreat at least once, so that a gap is formed between the tip of the pressurized fluid introduction nozzle and the thermoplastic resin in the cavity. Generating and releasing the pressurized fluid in the hollow through the gap,
Each process consists of
An injection molding method characterized in that a forward movement amount from a reverse end to a forward end of a pressurized fluid introduction nozzle and a reverse amount from a forward end to a reverse end are 0.01 mm to 2 mm .   The injection molding method according to claim 1, wherein the moving device comprises a hydraulic cylinder or a pneumatic cylinder.   The injection molding method according to claim 1, wherein the moving device comprises an electric motor.   The injection molding method according to claim 1, wherein the moving device includes a piezoelectric element.

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