JP2001018270A - Injection molding method for thermosetting resin and mold unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a molded article of good quality by pressurizing a thermosetting resin under a predetermined pressure. SOLUTION: When an injection screw 9 reaches an advance limit and a predetermined amt. of a resin J is injected in the molding cavity 4c of a mold 4 from an injection nozzle 8a through a sprue 4a and a runner 4b, a pressure plunger 5 is pushed in a resin sump part 4d by a pressure drive device 6 and th injected resin J in the molding cavity 4c is pressurized by the resin in the resin sump part 4d and the runner 4b. The pressure plunger 5 does not come into contact with the inner wall surface 4e of the resin sump part 4d at a time of movement. Even if there is irregularity in the injection amt. of the resin, the pressure of the resin in the molding cavity 4c becomes predetermined pressure by the pressure operation of the pressure plunger 5 and molding is normally performed. Therefore, no flush or sink is generated and a molded article having good dimensional accuracy and a predetermined shape is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosetting resin injection molding method for molding a product using a thermosetting resin such as a phenol resin or a urea resin, and an injection molding method capable of performing the injection molding method. It relates to the mold unit of the machine.

[0002]

2. Description of the Related Art Injection molding of a thermosetting resin product is basically the same as injection molding of a thermoplastic resin, and a thermosetting resin is injected from an injection nozzle into a mold through a resin passage constituted by a sprue and a runner. The resin is injected into a molding cavity, and the injection resin is cured in the molding cavity to obtain a molded product.

[0003]

The injection molding of a thermosetting resin has the following problems to be solved which are different from the molding of a thermoplastic resin due to the special properties of the thermosetting resin.
That is, the reactivity of the thermosetting resin, the material density at the time of measurement,
If even one or more of the material grain size or the like slightly changes, the mold cavity pressure of the mold fluctuates for each shot. For this reason, the appearance and dimensions of the molded product tend to vary.

[0004] Further, since the thermosetting resin is difficult to form a cushion, the supply amount of the resin varies, and as a result, molding tends to be defective. In the case of insert and outsert molding, even if the resin supply amount is uniform, the quality of the molded product changes due to variations in the volume of the insert product.

By the way, in ordinary injection molding, in order to prevent the generation of bubbles and sink marks due to the thermal shrinkage of the injection resin, it is particularly necessary to press the injection resin by sliding the ejector pins along the shaft hole. It is well-known in Japanese Patent Publication No. 3-71254 and Japanese Patent No. 2587575.

However, in this method, since the tip of the ejector pin slides in the shaft hole to press the injection resin, there is a possibility that the pressing force may fluctuate for each shot due to galling, and good molding cannot be performed. Sometimes. This point is remarkable when a material having high hardness, such as glass fiber, is mixed in the thermosetting resin.

The above-mentioned method is structurally simple because the ejector pin is also used for pressurizing the injection resin. However, the ejector speed and pressure for taking out the molded product from the mold, the air bubbles and sink marks, etc. There is also a problem that the control system of the ejector pin becomes complicated because there is a large difference between the pressurizing speed and the pressure for preventing the pressure.

[0008] The present invention has been made in view of the above,
It is an object of the present invention to provide a thermosetting resin injection molding method capable of obtaining a high quality molded product and a mold unit capable of performing the injection molding method. Another object of the present invention is to provide a thermosetting resin injection molding method capable of absorbing a variation in a resin supply amount or a volume of an insert product and accurately molding the resin into a predetermined shape and size. And a mold unit capable of performing the injection molding method. Another object of the present invention is to provide an injection molding method of a thermosetting resin capable of smoothly operating a pressure plunger and a mold unit capable of performing the injection molding method.

[0009]

In order to achieve at least one of the above-mentioned objects, according to the present invention, a thermosetting resin is injected from an injection nozzle through a resin passage into a molding cavity of a mold. In the method of injection molding a thermosetting resin by curing an injection resin in a molding cavity to form a molded product, after the injection of the thermosetting resin into the molding cavity is completed, a pressure plunger is provided in the resin reservoir of the resin passage. The configuration is such that the molten thermosetting resin in the molding cavity is pressed by being pushed in by the operation of the pressure driving device.

In this means, even if the amount of the injected resin into the molding cavity or the volume of the insert product varies and the molding pressure changes as it is, resulting in molding failure, the molding pressure is increased by the pressure of the pressure plunger. Be kept constant. The pressurized plunger is used exclusively for pressurizing the injection resin, and retracts from the push-in position to the original position at an appropriate time until the injection resin cures and the next thermosetting resin is injected into the molding cavity. Then, prepare for the next molding. Since the pressurizing plunger acts only on pressurizing the injection resin, the control system is simplified unlike the case where the pressurizing plunger also serves as the ejector pin.

In the method of injection molding a thermosetting resin according to claim 1, the inner diameter of the inner wall surface of the resin reservoir is larger than the outer diameter of the pressure plunger, and the pressure plunger contacts the inner wall surface of the resin reservoir. It is preferable that the resin is pushed into the resin reservoir without causing it to occur (claim 2). With this configuration, there is no galling between the pressure plunger and the inner wall surface of the resin reservoir, and the pressure plunger operates smoothly to accurately apply the resin in the molding cavity at a given pressure. Press. The cross-sectional shape of the inner wall surface of the resin reservoir and the pressure plunger is usually a perfect circle, but is not limited to this. The inner wall surface of the resin reservoir may be a straight line parallel to the pressure plunger.

In the injection molding method for a thermosetting resin according to the first or second aspect, the inner wall surface of the resin reservoir may be gradually widened (claim 3). With this configuration, there is no galling between the pressure plunger and the inner wall surface of the resin reservoir, and the pressure plunger operates smoothly to accurately apply the resin in the molding cavity at a given pressure. In addition to pressing, it is easy to take out the runner from the resin reservoir.

In the injection molding method for a thermosetting resin according to the first, second or third aspect, the pressure plunger is pushed into the resin reservoir with a low pressing force, and the skin layer is formed on the injection resin in the molding cavity. It is preferable to control the pressure of the pressurizing plunger in multiple stages after it is formed (claim 4). In this configuration, since the pressing force of the pressure plunger is increased after the skin layer is formed, burrs are reduced by the skin layer. The number of pressure switching stages of the pressure plunger is not limited to two, but may be three or more.

According to a fifth aspect of the present invention, a resin is injected from an injection nozzle through a resin passage into a molding cavity of a mold.
In an injection molding machine in which the injection resin is cured in a molding cavity to form a molded product, a resin reservoir is formed in the resin passage, and a pressure is applied to a shaft hole of the mold after the injection of the resin into the molding cavity is completed. A pressure plunger, which is pushed into the resin reservoir portion without contacting the inner wall surface of the resin reservoir portion by operation of the driving device and pressurizes the molten resin in the molding cavity, is movably inserted.

According to this means, the injection molding method of the thermosetting resin according to the first to fourth aspects can be suitably carried out.

[0016]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIGS. 1 and 2 show an example of a main part of an injection molding machine for performing an injection molding method of a thermosetting resin according to the present invention. This injection molding machine includes a mold unit 1 and an injection unit 2.

The mold unit 1 includes a mold clamping device (not shown).
A pair of molds 4 (not shown in the figure for convenience) are mainly used. The mold 4 has a sprue 4
a, the runner 4b, and the molding cavity 4c are formed in a known manner, and the molten thermosetting resin J injected into the sprue 4a is filled into the molding cavity 4c through the runner 4b.

A resin reservoir 4d is formed at a resin passage composed of the sprue 4a and the runner 4b, more precisely, at a position facing the sprue 4a at the intersection of the sprue 4a and the runner 4b. The inner wall surface 4e of the resin reservoir 4d is
It has a tapered shape that spreads as it approaches.

The mold 4 is provided with a pressure plunger 5. The pressure plunger 5 is pressed into the resin reservoir 4d by the pressure driving device 6, and presses the resin in the molding cavity 4c through the resin reservoir 4d and the resin in the runner 4b. The center axis is aligned with the center line of the sprue 4a and the resin reservoir 4d, and the tip 5a of the mold 4 is slightly protruded into the resin reservoir 4d (or may be flush with the bottom surface of the resin reservoir 4d). It is inserted through the shaft hole 4f. The outer diameter of the pressure plunger 5 is smaller than the inner diameter of the inner wall surface 4e of the resin reservoir 4d.

For this reason, the pressure plunger 5 is connected to the inner wall surface 4e.
Is not in contact with the inner wall surface 4e when moving forward and backward, and the tip 5a
There is no galling between the shaft hole 4f. In addition,
The cross-sectional shapes of the sprue 4a, the resin reservoir 4d, and the pressure plunger 5 are all round, but may be other shapes.

As the pressure driving device 6, an electric motor such as a hydraulic cylinder for directly moving the pressure plunger 5 with a piston rod or a servomotor for moving the pressure plunger 5 via a screw mechanism for changing a rotary motion to a linear motion. And the like, but in the present invention, the specific structure and type are arbitrary.

The pressure driving device 6 can freely change the pressing force and the speed. After the pressing plunger 5 is pushed into the resin reservoir 4d with a relatively low pressure, the pressing force is increased at an arbitrary timing. You can do it.

The injection unit 2 is of a well-known type, and is constituted by inserting an injection screw 9 into a heating cylinder 8 so as to be rotatable in the circumferential direction and movably in the axial direction. After the injection screw 9 is retracted at a predetermined back pressure while the conductive resin is being melted and the molten resin is measured at the tip of the heating cylinder 8, the injection screw 9 is advanced and the measurement resin is injected from the injection nozzle 8a into the sprue 4a. And the runner 4b can be injected into the molding cavity 4c of the mold 4.

Next, an embodiment of the injection molding method for a thermosetting resin according to the present invention using the injection molding machine having the above-described configuration will be described. First, the mold 4 is clamped and the pressurizing plunger 5 is retracted by the pressurizing drive device 6 to prepare the thermosetting resin J melted and weighed by the injection unit 2 by moving the injection screw 9 forward. , The molding cavity 4 of the mold 4 from the injection nozzle 8a through the sprue 4a and the runner 4b.
c (see FIG. 1).

Next, when the injection screw 9 reaches the forward limit and a predetermined amount of the resin J is injected into the molding cavity 4c and the filling process is completed, the screw is pressed and held at the forward limit to prevent the resin from flowing back to the cylinder. Then, the pressure driving device 6 is operated at a relatively low pressure, and the pressure plunger 5 is pushed into the resin reservoir 4d as shown in FIG. Pressure is applied via the resin in the portion 4d and the runner 4b.

The above-mentioned pressurization is continued for a predetermined time during which the skin layer is formed on the resin surface in the molding cavity 4c, and when the predetermined time has elapsed, the pressing force of the pressure driving device 6 is increased. When the pressure plunger 5 enters the resin reservoir 4 d, the pressure plunger 5 does not touch the inner wall surface 4 e of the resin reservoir 4 d and does not receive any resistance. Is accurately transmitted to the resin.

If the amount of the injected resin varies, or if the amount of the injected resin is correct, there is an error in the volume of the insert product.
Even when a predetermined pressure cannot be obtained as it is, the pressure of the resin in the molding cavity 4c becomes a predetermined pressure by the pressurizing operation of the pressurizing plunger 5, and the molding is performed normally. Therefore, it is possible to obtain a molded product having a predetermined shape with no burrs or sink marks and high dimensional accuracy.

Further, since the pressure is properly applied and the pressing force is increased to a predetermined pressure after the skin layer is formed, the occurrence of burrs is further reduced.

In the above-mentioned pressurizing operation of the pressurizing plunger 5, if the amount of the injected resin is large or the volume of the insert product is large, the amount of the pressurizing plunger 5 entering the resin reservoir 4d becomes small, It goes without saying that in the reverse case of the above, the amount of approach increases.

Pressurization by the pressure plunger 5 is continued until the resin in the molding cavity 4c is cured, and when the resin is cured, the pressure plunger 5 is retracted to the original state by the pressure driving device 6, and the mold 4 And the molded product is taken out of the mold 4. Hereinafter, the molding cycle is repeated to continue the molding.

FIG. 3 shows an experimental result (cavity pressure diagram) of the injection molding method of the present thermosetting resin when the resin reservoir is subjected to pressure molding, and FIG. 4 shows a pressure plunger. In the case of the normal injection molding method without pressurization, FIG. 5 shows an experimental result in the case where a shaft is opened in the mold cavity and the resin in the mold cavity is directly pressurized by the pressurizing plunger.

As is clear from the comparison between FIG. 3, FIG. 4 and FIG. 5, in FIG. 4, there is a large variation in the cavity pressure line of each shot, but in the present injection molding method of FIG.
It can be seen that the cavity pressure line between shots is beautifully organized with a negligible variation width and rises quickly. This proves the effect of the present invention.

In the case of FIG. 5, when the pressurizing plunger protrudes into the molding cavity, a dent is formed in that part of the molded product, and the depth of the dent is not uniform. In some cases.

When two or more molding cavities 4c are formed in the mold, the resin reservoir 4d is
The resin (c) is provided at a position (usually at the center) of the resin passage where the resin can be uniformly pressed. Alternatively, a plurality of resin reservoirs 4d may be provided, and a pressure plunger 5 may be provided so as to be paired with the resin reservoir 4d. In this case, the resin reservoir 4d may be located anywhere between the sprue 4a and the cavity 4c as long as the pressure can be uniformly transmitted. Sprue 4a, runner 4
b, the shape of the molding cavity 4c, the pressure plunger 5, etc.
The number is not limited to the one shown in the figure, but is arbitrary.

The inner wall surface 4e of the resin reservoir 4d can be formed in a straight line parallel to the pressure plunger 5 if it does not contact the pressure plunger 5. In some cases, only the control system is simplified. In view of the above, a structure that comes into contact with the pressure plunger 5 may be adopted. In order to prevent the pressurized resin from flowing back to the heating cylinder 8 when the pressurized plunger 5 presses the resin, the screw is held at the most advanced position during the pressurized plunger pressurizing operation so that The backflow of the resin can be prevented, and the injection unit does not need to have a special shape, and a conventional one can be used.

[0036]

As described above, according to the first aspect of the present invention, even if there is a difference in the reactivity of the thermosetting resin, the material density at the time of measurement, the material particle size, the volume of the insert product, etc.
By absorbing this, the resin in the molding cavity can be pressurized at a predetermined pressure and cured. Therefore, it is possible to form a molded product of a thermosetting resin with high quality and high dimensional accuracy without burrs or sink marks.

[0037] In the method of injection molding a thermosetting resin according to claim 1, the inner diameter of the inner wall surface of the resin reservoir is larger than the outer diameter of the pressure plunger, and the pressure plunger is mounted on the inner wall surface of the resin reservoir. If it is configured to be pushed into the resin reservoir without contacting it, operation failure due to galling is prevented, the pressure plunger is smoothly operated, and the resin in the molding cavity can be accurately pressurized with the given pressure. It becomes possible.

In the method of injection molding a thermosetting resin according to the first or second aspect, if the inner wall surface of the resin reservoir is gradually widened, the distance between the pressure plunger and the inner wall surface of the resin reservoir is increased. The pressurizing plunger operates smoothly, presses the resin in the molding cavity accurately at a given predetermined pressure, and facilitates removal of the runner from the resin reservoir.

In the injection molding method for a thermosetting resin according to claim 1, 2, or 3, the pressure plunger is pushed into the resin reservoir with a low pressing force, and the skin layer is formed on the injection resin in the molding cavity. If the pressure of the pressure plunger is controlled in multiple stages after the formation, the occurrence of burrs that impair the appearance of the molded product is further prevented.

According to the fifth aspect of the present invention, the above effects can be obtained by suitably performing the injection molding method of a thermosetting resin according to the first to fourth aspects.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a filling step illustrating an example of a main part of an injection molding machine that performs an injection molding method of a thermosetting resin according to the present invention.

FIG. 2 is a view showing a pressure-holding step in which a pressure plunger is pushed into a resin reservoir.

FIG. 3 is a cavity pressure diagram when molded by the injection molding method of the present invention.

FIG. 4 is a cavity pressure diagram when molded by a normal injection molding method.

FIG. 5 is a cavity pressure diagram when a resin in a molding cavity is directly pressed by a pressing plunger.

[Explanation of symbols]

Reference Signs List 1 mold unit 2 injection unit 4 mold 4a sprue 4b runner 4c molding cavity 4d resin reservoir 4e inner wall surface 4f shaft hole 5 pressure plunger 6 pressure drive device 8 heating cylinder 8a injection nozzle 9 injection screw J resin

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yukio Okada 1-268, Hirosawa-cho, Kiryu-shi, Gunma Prefecture Mitsuba Co., Ltd. (72) Inventor Yasuo Tsuchiya 21110 Nanjo Nanjo, Shirokicho, Hanishina-gun, Nagano Prefecture Nissei Within Resin Industries Co., Ltd. (72) Inventor Toru Ikeda 2110, Nanjo, Nanjo, Hanashi-gun, Nagano Pref. Nissei Resin Industries Co., Ltd. F-term (reference) 4F206 AA36 AR02 JA07 JL02 JM04 JM05 JN14 JN21 JQ81

Claims (5)

[Claims] 1. A thermosetting resin injection molding method comprising: injecting a thermosetting resin from an injection nozzle through a resin passage into a molding cavity of a mold; and curing the injection resin in the molding cavity to form a molded product. After the injection of the thermosetting resin into the molding cavity is completed, a pressure plunger is pushed into the resin reservoir of the resin passage by the operation of the pressure driving device to press the molten thermosetting resin in the molding cavity. An injection molding method for a thermosetting resin. 2. The inner diameter of the inner wall surface of the resin reservoir is larger than the outer diameter of the pressure plunger, and the pressure plunger is pushed into the resin reservoir without contacting the inner wall surface of the resin reservoir. The injection molding method for a thermosetting resin according to claim 1. 3. The method of injection molding a thermosetting resin according to claim 1, wherein an inner wall surface of the resin reservoir gradually widens. 4. The pressurizing plunger is pushed into the resin reservoir with a low pressurizing force, and after the skin layer is formed on the injection resin in the molding cavity, the pressurizing pressure of the pressurizing plunger is controlled in multiple stages. The method of injection molding a thermosetting resin according to claim 1 or claim 2. 5. An injection molding machine for injecting a resin from an injection nozzle through a resin passage into a molding cavity of a mold and curing the injected resin in the molding cavity to form a molded product. Is formed. After the injection of the resin into the molding cavity is completed, the resin is pushed into the resin reservoir without contacting the inner wall surface of the resin reservoir by the operation of the pressure driving device after the injection of the resin into the molding cavity is completed. A mold unit characterized in that a pressurizing plunger for pressurizing a molten resin is movably inserted therethrough.