Injection molding apparatus and method for manufacturing preforms

Abstract

In the process of manufacturing a preform by filling the cavity of a mold through a valve gate via a hot runner unit with molten resin injected from an injection unit, the system suppresses resin dripping that may occur immediately after the valve gate opens, thereby reducing the occurrence of flow marks. [Solution] When filling the cavity 35 of the mold 30 with molten resin injected from the injection unit 10 through the valve gate 25 via the hot runner unit 20, the valve gate 25 is opened with a delay from the timing of the injection of molten resin from the injection unit 10.

Description

Technical Field

[0001] The present invention relates to an injection molding apparatus and a method for manufacturing a preform, and more particularly to an injection molding apparatus suitable for manufacturing a preform for blow molding a synthetic resin container used for various applications, and a method for manufacturing a preform using such an injection molding apparatus.

Background Art

[0002] Conventionally, a bottomed cylindrical preform made of a thermoplastic resin such as polyethylene terephthalate is prepared, and a synthetic resin container formed into a bottle shape by biaxially stretching blow molding or the like is known. In recent years, it has been widely used not only for beverages but also for various applications

[0003] Also, in manufacturing a preform for blow molding this type of synthetic resin container, a valve gate is arranged at a portion on the bottom side, and the molten resin filled into the cavity from the valve gate is injection molded by a mold installed so as to fill the cavity toward the mouth side along the axial direction of the preform (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The inventors of this invention have conducted extensive research on the background technology and have found that if resin dripping occurs immediately after the valve gate opens, and this dripping solidifies and mixes with the molten resin filling the cavity, there is a risk of flow marks occurring on the molded preform. They have also found that synthetic resin containers made by blow molding preforms with flow marks may suffer from defects such as poor appearance and insufficient strength. As a result of further diligent research to suppress such defects, the inventors have completed the present invention. [Means for solving the problem]

[0006] The injection molding apparatus according to the present invention is an injection molding apparatus in which molten resin injected from an injection unit is filled into the cavity of a mold through a valve gate via a hot runner unit, and is configured to be controllable based on a control mode set to delay the timing of opening the valve gate relative to the timing of injection of molten resin from the injection unit.

[0007] Furthermore, the present invention relates to a method for manufacturing a preform, which involves using the above-described injection molding apparatus to manufacture a preform having a mouth portion opening at one end and a body portion including a bottom portion that closes at the other end, wherein the valve gate is positioned at the bottom portion of the preform, the mold is set up so that the molten resin filled into the cavity from the valve gate fills the cavity toward the mouth portion along the axial direction of the preform, the valve gate is opened with a delay from the timing of the injection of the molten resin from the injection unit, and the molten resin injected from the injection unit is filled into the cavity of the mold from the valve gate. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress resin dripping that may occur immediately after the valve gate opens, thereby reducing the occurrence of flow marks. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram illustrating the outline of an injection molding apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0010] Preferred embodiments of the present invention will be described below with reference to the drawings.

[0011] [Injection molding equipment] First, the injection molding apparatus according to this embodiment will be described. Figure 1 is a schematic diagram illustrating the outline of the injection molding apparatus according to this embodiment. The injection molding apparatus 1 shown in Figure 1 is equipped with a valve gate type hot runner system, and is configured so that molten resin injected from the injection unit 10 is filled into the cavity 35 of the mold 30 through the valve gate 25 via the hot runner unit 20.

[0012] The injection unit 10 is not particularly limited in its specific configuration, as long as it can plasticize the thermoplastic resin that will be used as the molding material, and measure and inject the plasticized molten resin. The injection unit 10 may be of any of the following types: in-line screw type, screw pre-plunger type, or plunger type.

[0013] The injection unit 10 is connected to the hot runner unit 20 via a sprue bush 11. The hot runner unit 20 includes a manifold section 21 on which a hot runner 23 is provided to heat the molten resin injected from the injection unit 10 and keep it flowing while maintaining its molten state, and a nozzle section 22 on which a valve gate 25 is provided.

[0014] The valve gate 25 comprises a gate tip 26 attached to the tip of the nozzle portion 22, and a valve pin 27 configured to reciprocate along the axial direction, for example, by an air cylinder. The opening and closing of the valve gate 25 is controlled by a valve controller such that the valve pin 27 retracts to release the opening of the gate tip 26, thereby opening the valve gate 25, and the valve pin 27 advances to close the opening of the gate tip 26, thereby closing the valve gate 25.

[0015] Molten resin, injected from the injection unit 10 and reaching the nozzle section 22 via the hot runner 23 located in the manifold section 21, is filled into the cavity 35 of the mold 30 through a valve gate 25 that opens and closes as needed. Figure 1 shows a single-cavity mold 30 comprising a cavity mold 31 including a mouth mold 33 and a body mold 34 for molding the outer circumferential surface of the preform 40, and a core mold 32 for molding the inner circumferential surface of the preform 40. However, the mold 30 can have a multi-cavity cavity arrangement. In this case, the hot runner 23 can be branched to each cavity 35, and molten resin can be filled into each cavity 35 through a valve gate 25 located corresponding to each cavity 35.

[0016] In this embodiment, the injection molding apparatus 1 is controllable based on a control mode set such that the timing of opening the valve gate 25 is delayed relative to the timing of injection of molten resin from the injection unit 10. To enable such control, the injection molding apparatus 1 includes, in addition to the valve controller that controls the opening and closing of the valve gate 25 as described above, an injection controller that controls the injection unit 10, input / output devices such as an operation panel that displays setting items and operating status and allows input of various setting values ​​to switch control modes, a storage device that stores control programs and information data, and a processing unit that controls the injection molding apparatus 1 based on the set control mode by executing the control program stored in the storage device.

[0017] Regarding the operation of the injection molding apparatus 1 controlled based on a control mode set such that the timing of opening of the valve gate 25 is delayed with respect to the timing of injecting molten resin from the injection unit 10, an example of manufacturing a preform 40 using the injection molding apparatus 1 will be described below.

[0018] [Method for manufacturing preform] The preform 40 is used for blow molding various synthetic resin containers and is formed into a bottomed cylindrical shape including a mouth portion 41 that opens at one end side and a body portion 42 that includes a bottom portion 43 that closes the other end side. The mouth portion 41 of the preform 40 is a portion that becomes the container mouth portion while generally maintaining its appearance without being stretched by blow molding, and the body portion 42 including the bottom portion 43 is stretched and formed into a predetermined container shape.

[0019] As the molding material of the preform 40, any thermoplastic resin can be used. For example, thermoplastic polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, amorphous polyarylate, polylactic acid, polyethylene furanoate, or copolymers thereof are used, and in particular, ethylene terephthalate-based thermoplastic polyesters such as polyethylene terephthalate are preferably used. Two or more thermoplastic resins used for the molding material may be blended, and various additives may be added as necessary.

[0020] In the injection molding apparatus 1 shown in FIG. 1, the mold 30 for molding the preform 40 is provided with a valve gate 25 at a portion on the bottom portion 43 side of the preform 40, and the molten resin filled into the cavity 35 from the valve gate 25 fills the cavity 35 along the axial direction of the preform 40 toward the mouth portion 41 side.

[0021] To manufacture a preform 40 using the injection molding apparatus 1, first, the mold clamping operation of the mold 30 is started, and when the mold clamping pressure of the mold 30 reaches a predetermined pressure, molten resin is injected from the injection unit 10. At this time, if the injection unit 10 is an in-line screw type, the injection unit 10 is controlled so that the screw advances when the mold clamping pressure of the mold 30 reaches a predetermined pressure. If the injection unit 10 is a screw pre-plunger type or a plunger type, the injection unit 10 is controlled so that the plunger advances when the mold clamping pressure of the mold 30 reaches a predetermined pressure.

[0022] Next, the valve pin 27 is retracted so that the valve gate 25 opens with a delay from the timing of the injection of molten resin from the injection unit 10. The timing of the valve gate 25 opening can be controlled, for example, as in (1) or (2) below.

[0023] (1) The timing of the valve gate 25 opening is controlled so that it opens simultaneously with a predetermined time (for example, 0.01 to 10.00 seconds) elapsed from the time when the injection of molten resin from the injection unit 10 begins. That is, the timing of the valve gate 25 opening is controlled so that it opens when a predetermined time has elapsed, counting from the time when the screw or plunger of the injection unit 10 begins to move forward.

[0024] (2) The timing of the valve gate 25 opening is controlled so that when the screw or plunger of the injection unit 10 moves forward to a predetermined position from the time the injection of molten resin from the injection unit 10 is started, the valve gate 25 opens at the same time. In other words, the timing of the valve gate 25 opening is controlled so that when the screw or plunger of the injection unit 10 moves forward from the position immediately before the start of injection to a predetermined position, the valve gate 25 opens at the same time.

[0025] The molten resin injected from the injection unit 10 is filled into the cavity 35 of the mold 30 through the valve gate 25, pushing out the molten resin remaining in the hot runner 23 as the valve gate 25 opens. By delaying the opening of the valve gate 25 after the injection of the molten resin from the injection unit 10, the injection pressure immediately before the valve gate 25 opens is increased, thereby accelerating the initial flow velocity of the molten resin as it fills the cavity 35. This improves the response from the opening of the valve gate 25 until the molten resin begins to fill the cavity 35, and as a result, resin dripping that may occur immediately after the valve gate 25 opens can be suppressed, reducing the occurrence of flow marks.

[0026] When delaying the opening of the valve gate 25, if the injection pressure becomes too high, it may overload the device and lead to undesirable situations. For this reason, it is preferable to control the injection pressure so that the rate of increase just before the valve gate 25 opens is within 30% of the rate when the valve gate 25 opening timing is controlled without delay. Depending on the molding material, flow marks may not be observed, in which case it is also possible to control in standard mode without delaying the opening of the valve gate 25.

[0027] After a predetermined amount of molten resin is injected from the injection unit 10 and the cavity 35 of the mold 30 is filled with molten resin, the valve pin 27 is advanced to close the valve gate 25 and block the inflow of molten resin from the hot runner 23 into the cavity 35. Then, after the cooling process, the preform 40 is removed from the mold 30 that has been opened, and the above process is repeated to continuously manufacture preforms 40. [Examples]

[0028] The present invention will be described in more detail below with reference to specific examples.

[0029] [Example 1] In the injection molding apparatus 1 shown in Figure 1, the mold 30 is configured with a multi-cavity arrangement of 96 cavities, and a hot runner 23 is branched to each cavity 35, so that molten resin is filled into each cavity 35 from a valve gate 25 located corresponding to each cavity 35. The injection unit 10 is of the screw pre-plunger type.

[0030] Using the injection molding apparatus configured in this way, polyethylene terephthalate was used as the molding material to continuously produce bottomed cylindrical preforms 40 weighing 38 g. During this process, the timing of the valve gate 25 opening was controlled so that it opened 0.05 seconds after the plunger of the injection unit 10 began to move forward. The injection pressure immediately before the valve gate 25 opened was 93-102 kgf / cm² per shot. 2 There was some variation, but the average was 97 kgf / cm². 2 The increase compared to the case where the timing of opening the valve gate 25 was controlled without delay (see Comparative Example 1) was 10.2%.

[0031] 294 preforms were randomly selected from the manufactured preforms 40 and visually inspected for the presence or absence of flow marks. Flow marks were found in 28 preforms 40, resulting in an occurrence rate of 9.5%.

[0032] [Example 2] The preform 40 was manufactured continuously in the same manner as in Example 1, except that the timing of the valve gate 25 opening was controlled so that it opened 0.10 seconds after the plunger of the injection unit 10 began to move forward. The injection pressure immediately before the valve gate 25 opened was 107-115 kgf / cm² per shot. 2 There was some variation, but the average was 111 kgf / cm². 2 The increase compared to the case where the timing of opening the valve gate 25 was controlled without delay (see Comparative Example 1) was 26.1%.

[0033] 294 preforms were randomly selected from the manufactured preforms 40 and visually inspected for the presence or absence of flow marks. Flow marks were found in 21 preforms 40, resulting in an incidence rate of 7.1%.

[0034] [Example 3] The preform 40 was manufactured continuously in the same manner as in Example 1, except that the timing of the valve gate 25 opening was controlled so that it opened at the same time as the plunger of the injection unit 10 advanced by 0.7 mm. The injection pressure immediately before the valve gate 25 opened was 96-104 kgf / cm² per shot. 2 There was some variation, but the average was 101 kgf / cm². 2 The increase compared to the case where the timing of opening the valve gate 25 was controlled without delay (see Comparative Example 1) was 14.8%.

[0035] 294 preforms were randomly selected from the manufactured preforms 40 and visually inspected for the presence or absence of flow marks. Flow marks were found in 19 preforms 40, resulting in an occurrence rate of 6.5%.

[0036] [Comparative Example 1] Except for controlling the timing of the injection of molten resin from the injection unit 10 and the opening of the valve gate 25 to be simultaneous, the preform 40 was manufactured continuously in the same manner as in Example 1. The injection pressure immediately before the valve gate 25 opened was 87-90 kgf / cm² per shot. 2 There was some variation, but the average was 88 kgf / cm². 2 That was the case.

[0037] 294 preforms were randomly selected from the manufactured preforms 40 and visually inspected for the presence or absence of flow marks. Flow marks were found in 37 preforms 40, representing an incidence rate of 12.6%.

[0038] From these results, it was confirmed that delaying the timing of the valve gate 25 opening relative to the timing of molten resin injection from the injection unit 10 reduces the rate of flow marks.

[0039] Although the present invention has been described above with reference to preferred embodiments, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the present invention. [Explanation of Symbols]

[0040] 1 Injection molding equipment 10 Injection Units 20 Hot Runner Units 25 Valve Gate 30 mold 35 Cavity 40 preforms 41 Mouth 42 Torso 43 Bottom

Claims

1. In an injection molding apparatus in which molten resin injected from an injection unit is filled into the cavity of a mold through a valve gate via a hot runner unit, An injection molding apparatus characterized in that it is controllable based on a control mode set such that the timing of opening the valve gate is delayed relative to the timing of injecting molten resin from the injection unit.

2. The injection molding apparatus according to claim 1, wherein the timing of opening the valve gate is controlled such that the valve gate opens simultaneously with a predetermined time having elapsed from the time when the injection of molten resin from the injection unit is started.

3. The injection molding apparatus according to claim 1, wherein the injection unit is of the inline screw type, and the timing of opening the valve gate is controlled such that when the screw of the injection unit moves forward to a predetermined position from the time when the injection of molten resin from the injection unit is started, the valve gate opens at the same time.

4. The injection molding apparatus according to claim 1, wherein the injection unit is of the screw pre-plunger type or plunger type, and the timing of opening the valve gate is controlled such that when the plunger of the injection unit moves forward to a predetermined position from the time when the injection of molten resin from the injection unit is started, the valve gate opens at the same time.

5. A method for manufacturing a preform, comprising an injection molding apparatus according to any one of claims 1 to 4, wherein the preform has a mouth portion that opens at one end and a body portion that includes a bottom portion that closes at the other end, The valve gate is positioned at the bottom portion of the preform, and the mold is set up so that the molten resin filled into the cavity from the valve gate fills the cavity along the axial direction of the preform toward the opening. A method for manufacturing a preform, characterized by opening the valve gate at a delay before injecting molten resin from the injection unit, thereby filling the cavity of the mold with the molten resin injected from the injection unit through the valve gate.

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