JPH07186151A - Mold for dielectric heating resin molding - Google Patents

Abstract

(57) [Summary] [Purpose] Design can be performed almost independently of the wall thickness of the molded product,
A molding die capable of uniformly heating a molded body by dielectric heating. A mold used for dielectric heating resin molding, in which a cavity 4 is filled with a resin material and the resin material is heated and cured by dielectric heating, the molding dies 1 and 2 being epoxy resin and epoxy. It is characterized by comprising talc contained in a resin. The molding die is heated almost without being affected by the wall thickness during dielectric heating and has a high temperature rising rate. Therefore, even if the molding body has a thin portion, the heat radiation is reduced and the molding body is uniformly heated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding die for dielectric heating resin molding, in which a resin material in a molding die is heated and hardened by dielectric heating at a high frequency to form a molded body.

[0002]

2. Description of the Related Art A so-called high-frequency heating resin molding method includes
A dielectric heating method that directly heats the material from the inside by using the dielectric loss of the alternating electromagnetic field, and a resistance loss or hysteresis loss of the eddy current or skin current generated in the mold by the electromagnetic induction of the alternating electromagnetic field Two types of induction heating methods are known, in which a mold is heated to indirectly heat a resin material. Since the former dielectric heating method is advantageous in terms of heating time and thermal efficiency, the dielectric heating method is generally adopted.

Many of the molds used in the dielectric heating molding method are manufactured from silicone rubber, polyester, or the like, which does not block high frequency waves and is hard to heat more than necessary. Some of them are equipped with a high-frequency generator, but due to their low cost and ease of mold renewal, they do not have a high-frequency generator and are generally heat-molded by radiating a high frequency from the outside. is there.

By the way, in the dielectric heating resin molding method, the resin material filled in the molding die is heated by dielectric heating by high frequency, but at the beginning of heat generation, the molding die loses heat and the molding die has a large wall thickness and a large heat capacity. The amount of heat taken away also increases. Also, the thicker the molded body, the larger the amount of heat generation, and the thinner the thickness, the smaller the amount of heat generation.However, the wall thickness of the mold is almost independent of the wall thickness of the molded body, and the amount of heat lost in the thinner part of the molded body In many cases (heat dissipation amount) becomes large.

Therefore, the amount of heat generation / heat radiation varies depending on the difference in the wall thickness of the molded body, and the portion with a small thickness has insufficient heating, and the portion with a large thickness has excessive heating, resulting in carbonization. There was a problem that uniform heating was difficult. Therefore, Japanese Patent Laid-Open No. 4-284207 discloses a molding die in which a part or all of the surface of a molding die for molding a thin portion of a molded body that is difficult to be heated is formed from a molding material containing particles that generate heat at high frequencies. Has been done. By using such a mold, the mold containing heat-generating particles generates heat, which reduces the amount of heat radiated from the thin part, etc. Therefore, the molded body can be heated uniformly.

[0006] For example, as shown in FIG.
In the case of a mold for forming a molded body having a thin portion 101 and
A molding die portion corresponding to the thin portion 101 is composed of a heating die 200 made of silicone rubber containing carbon. When irradiated with a high frequency, the resin material of the thin portion 101 also generates heat and the heating die 200 also generates heat due to the presence of carbon. Therefore, the amount of heat generated by subtracting the amount of heat radiation should be approximately equal in the thick portion 100 and the thin portion 101. It becomes possible to heat uniformly.

[0007]

In the mold having the heat generating mold 200, the heat generating mold 200 also generates heat. Therefore, the molded body receives heat from the heat generating mold 200 in addition to its own heat generation, and the temperature is raised by both heats. To do. For example, if the heating rate of the heating die 200 is the same as the heating rate of the resin material, the total thickness of the thin portion 101 and the heating die 200 should be the same as the thickness of the thick portion 100. As a result, the heating rate of the thin portion 101 becomes the same as that of the thick portion 100, and uniform heating of the whole is possible.

However, when the shape of the molded body is complicated, for example, when the molded body has ribs or bosses, the thickness of the molded body locally increases at that portion, and the thickness of the heating die 200 is reduced. There is a need. However, because of problems with strength,
It is often difficult to change the thickness of the mold according to the shape of the cavity. Therefore, it is not always easy to form the thickness of the heating die 200 to match the shape of the thin portion 101.

Furthermore, the carbon-containing silicone rubber used in the conventional heat-generating type has a large coefficient of thermal expansion. For example, in order to keep the dimensional error within a length of 1 m within ± 0.5 mm, the temperature range with respect to the set temperature is set. Is required to be controlled within a range of ± 1.5 ° C., and since such fine control is difficult, there is a problem that the dimensional accuracy of the molded body is low.

The present invention has been made in view of such circumstances, and an object thereof is to provide a molding die which can be designed almost irrespective of the wall thickness of a molded body and which can uniformly heat the molded body by dielectric heating. To do.

[0011]

A molding die for dielectric heating resin molding of the present invention which solves the above problems is formed by filling a cavity with a resin material and heating the resin material by dielectric heating to cure the resin material. A molding die used for dielectric heating resin molding, characterized in that the molding die comprises an epoxy resin and talc contained in the epoxy resin.

The mold for dielectric heating resin molding according to the second invention is a mold used for dielectric heating resin molding in which a cavity is filled with a resin material and the resin material is heated and cured by dielectric heating. The mold is capable of being heated by dielectric heating, and is characterized by having a high-frequency shielding member in a thick-walled portion that is overheated.

[0013]

The heat dissipation rate by heat conduction increases as the temperature difference between the heat dissipation side and the heat receiving side increases. Since the molding die of the first aspect of the present invention is made of epoxy resin and talc, it has a high temperature rising rate when irradiated with a high frequency, and shows a temperature rising rate substantially equal to that of the molding resin material. Therefore, molded body (heat radiation side)
Since the temperature difference between the mold and the mold (heat receiving side) is smaller than before, heat radiation from the molded body to the mold is less likely to occur, and even if there is a difference in the wall thickness of the molded body, the thick and thin parts can be released. The difference in the amount of heat is small and uniform heating is possible.

The mold of the first aspect of the invention has a characteristic that the variation in dielectric heating characteristics due to its wall thickness is small. That is, since there is no great difference in the temperature rising rate regardless of whether the thickness is thick or thin, the amount of heat applied from the molding die to the molding is uniform throughout. Further, in the molding die of the first aspect of the present invention formed of epoxy resin and talc, when the temperature reaches a predetermined temperature, the temperature does not rise so much even if high frequency irradiation is continued, which causes a capping phenomenon. Therefore, even if there is a difference in wall thickness of the molding die, the temperature of the molding die is prevented from locally increasing.

Since the mold of the first invention has a smaller coefficient of thermal expansion than the conventional silicone rubber mold containing carbon, the heating temperature range can be easily controlled. The cause of this is not clear, but it is presumed that at high temperatures, the molecular structure of talc changes and it becomes difficult for high frequencies to be absorbed. It is also presumed that one of the causes is that the thermal conductivity of talc increases at high temperatures and heat is easily released to the outside.

The content of talc is 10 to 10 in the resin material.
About 80% by weight is preferable. If the amount is less than this, the amount of heat generated by dielectric heating becomes small, and if the amount is too large, the mechanical strength of the molding die may decrease. The mold of the first invention may be combined with other fillers such as alumina, glass and calcium carbonate depending on workability and use conditions.

The mold of the second invention can be heated by dielectric heating, and has a high-frequency shielding member in a thick and overheated portion. Therefore, since the high frequency is shielded by the presence of the high frequency shielding member in the portion which is overheated when there is no high frequency shielding member, the excessive heating is prevented and the entire mold is uniformly heated. As the high-frequency shielding member, a material such as a metal plate or a wire net that reflects high frequencies, a material such as fluororesin or polyester that has a small absorption of high frequencies, or a material such as an epoxy resin or urethane resin that easily absorbs high frequencies is glass. It is possible to use a material which is difficult to absorb high frequencies as a result of mixing materials such as balloons and quartz which are difficult to absorb high frequencies.

Further, the high frequency shield member may be built in the molding die or may be provided so as to cover the molding die from the outside.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples. (Embodiment 1) FIG. 1 shows a molding die for molding a dielectric heating resin according to an embodiment of the present invention. This molding die is composed of an upper die 1 and a lower die 2, and the upper die 1 and the lower die 2 are closed with a bolt 3 to form a cavity 4 inside.

The upper mold 1 is made of an epoxy resin, which will be described later, and has an upward opening 10 communicating with the cavity 4. A silicone rubber 11 for connecting a hose is fitted into the rising port 10. A frame 12 is fixed to the outer surface of the upper mold 1 to reinforce the upper mold 1. Like the upper mold 1, the lower mold 2 is also made of an epoxy resin described later. A frame 20 is fixed to the outer surface of the lower mold 2 to reinforce the lower mold 2.

An injection port 21 communicating with the cavity 4 is formed at a part of the boundary between the upper mold 1 and the lower mold 2.
A silicone rubber 22 for connecting a hose is fitted to the connector 1. Hereinafter, the composition of the mold of this example will be described by explaining the manufacturing method. As the epoxy resin forming the base bodies of the upper mold 1 and the lower mold 2, a resin having high heat resistance is desirable because it can be heated at a high frequency in a short time. In order to cure the urethane resin, an allowable temperature range of 80 ° C. ± 5 ° C. is required, but the molding die must withstand higher temperatures. Therefore, on the premise of heating up to a maximum of 120 ° C., it is necessary to have a heat resistance of 140 ° C. or higher in consideration of safety.

As such an epoxy resin, there are a bisphenol F type and a phenol novolac type, but it is decided to use a bisphenol F type which is liquid at room temperature and can be cured at a low temperature of 80 to 150 ° C. and has good workability. Also, measure the heating rate when dielectric heating various filler powders,
The results are shown in Figure 2. It can be seen from FIG. 2 that talc has a high rate of temperature rise, and when the temperature rises to some extent, the rate of temperature rise slows down to a level.

Next, FIG. 3 shows a graph of temperature rising characteristics when talc and quartz are added to the bisphenol F type epoxy resin in three kinds of contents and dielectric heating is performed. From this, it can be seen that the one to which talc is added has a high rate of temperature rise and maintains the characteristics of talc in which the temperature reaches a peak at high temperatures. Therefore, the respective raw materials were mixed in the following formulation to prepare a resin composition for molded bodies.

Epoxy resin (“Epiclon 830”, manufactured by Dainippon Ink and Chemicals, Inc.) 38% by weight Epoxy curing agent (“H-491”, manufactured by Ace Kaken Co., Ltd.)
11 wt% Talc (“MS Talc” manufactured by Nippon Talc Co., Ltd.)
23% by weight Glass powder ("EGP-200" manufactured by Central Glass Co., Ltd.) 13% by weight Glass balloon ("K-28" manufactured by 3M Co., Ltd.) 6% by weight Glass chop ("ECS-015" Central Glass Co., Ltd. )) 9% by weight The glass powder and the glass balloon are used for adjusting the viscosity of the resin composition to improve workability in producing a mold. Glass chops are also used to improve the strength of the mold.

This resin composition was used as silicone rubber 11 and 2.
2 is placed on a predetermined wooden mold and molded by room temperature or heat curing to form an upper mold 1 and a lower mold 2, and a frame 1
The mold was fixed to 2, 20 to obtain the mold of this example. The obtained molding die was determined to be filled when the upper mold 1 and the lower mold 2 were closed with bolts, the liquid urethane resin was injected from the injection port 21 and the resin was discharged from the rising port 10.
And high frequency output 3-15Kw, heating time 15 minutes or less,
When dielectrically heated under the heating temperature of 80 to 90 ° C,
A molded body was obtained in which the whole was uniformly cured. (Experimental Example) Diameter 100 mm, thickness 1 from the above resin composition
Three types of test pieces of 0, 20, 40 mm were molded, and the dielectric heating characteristics of each test piece were examined. In the test, two test pieces having the same thickness were stacked and placed in a microwave oven, and the temperature of the central portion between the two test pieces was measured with heating time.

Although the output of the microwave oven is 1 Kw, the high frequency output acting on the test piece was reduced by about half by heating the test piece alone and by heating the test piece with 2 liters of water contained in the container. The measurement was performed under the two types of conditions. The respective results are shown in FIGS. 4 and 5. Silicone rubber ("KE-1310ST" manufactured by Shin-Etsu Chemical Co., Ltd.)
Carbon (“Asahi Thermal” manufactured by Asahi Carbon Co., Ltd.)
Regarding the conventional composition containing 30% by weight, the test piece was molded in the same manner as above, and the results of similarly examining the dielectric heating characteristics are shown in FIGS. 6 and 7.

From FIGS. 4 to 7, the difference in temperature rising rate between the epoxy resin and talc due to the thickness of the test piece is smaller, and in particular, the thickness of the test piece is smaller than that of the silicone rubber + carbon in the initial 5 minutes of heating. It is clear that the difference in temperature rise due to is extremely small. That is, as is clear from this experimental example, the mold made of epoxy resin + talc has a higher temperature rising rate in the initial heating stage than the mold made of silicone rubber + carbon, and the temperature rise due to the difference in wall thickness. The speed difference is small. Therefore, in the initial stage of heating, heat is not taken from the molding resin material to prevent temperature rise, and the temperature rising characteristics are almost the same even when the mold thicknesses are partially different. Can be heated uniformly. (Embodiment 2) FIG. 8 shows an embodiment of the second invention. This mold has substantially the same structure as that of the mold of Example 1, but a high-frequency shielding member 50 made of a foam (eg, urethane foam) which is hard to be subjected to high-frequency dielectric heating is provided inside the thick portion 25 of the lower mold 2. It is different from the first embodiment in that it is embedded and that the surface of the upper mold 1 and the surface of the lower mold 2 facing the thick portion 25 are covered with the high frequency shielding member 51 made of a metal plate or a wire mesh. .

In the molding die of this embodiment, since heating of the thick portion 25 is suppressed by the high-frequency shielding members 50 and 51 during dielectric heating resin molding, the temperature rise of the molding die can be made more uniform. In this embodiment, epoxy resin + talc is used as the material of the molding die, but the material is not limited to this and any material capable of dielectric heating can be used. (Embodiment 3) FIG. 9 shows another embodiment of the second invention. This mold is made of an epoxy putty (“A-129”) manufactured by Ace Kaken Co., Ltd.
And a bisphenol A type epoxy resin which is easily dielectrically heated.

Since the lower die 6 portion having the slide core 60 is a thick wall portion, if only the slide core 60 is made of a material that is not easily dielectrically heated, the temperature rise of the entire thick wall portion can be delayed. Since the temperature of the other thin portions can be made substantially the same, the temperature of the mold can be made more uniform. In this example, the molding die was formed from the bisphenol A type epoxy resin, but it goes without saying that the molding die can be formed from the same epoxy resin as in Example 1 + talc.

[0030]

[Effects of the Invention] That is, according to the mold of the present invention, even if there is a partial difference in the wall thickness of the molded body or the wall thickness of the mold, the resin material filled in the cavity is heated uniformly. It is possible to form a molded product of uniform quality. Further, according to the molding die of the first invention, since the temperature control range is wide, it is possible to easily manufacture a molded body having high dimensional accuracy. Since the epoxy resin is not easily attacked by the urethane resin raw material for molding or the solvent, the life of the molding die is improved by about 5 times as compared with the silicone rubber mold. In addition, it is easier to manufacture than a conventional molding die made of silicone rubber and polyester. Further, since polyester has a large amount of heat generated during mold making, it is difficult to make it thick at one time, but since epoxy resin hardly generates heat, it can be made thick at one time, which shortens the mold making time.

According to the mold of the second aspect of the present invention, the heating of the mold is uniform only by providing the high-frequency shielding member in the thick portion of the mold, so that the amount of heat received by the molded body from the mold is uniform. Become. Since the high-frequency shielding member shields high-frequency waves regardless of its thickness, the mold can be easily manufactured. Therefore, according to the molding die in which the first invention and the second invention are combined, the molded body can be heated extremely uniformly regardless of the thickness of the molding die.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a mold according to an embodiment of the present invention.

FIG. 2 is a graph showing a temperature rising rate during dielectric heating of various powders.

FIG. 3 is a graph showing a temperature rising rate during dielectric heating of a material in which various fillers are added to bisphenol F type epoxy resin.

FIG. 4 is a graph showing the rate of temperature rise during dielectric heating of the composition constituting the mold of one example of the present invention.

FIG. 5 is a graph showing the rate of temperature rise during dielectric heating of the composition constituting the mold of one example of the present invention.

FIG. 6 is a graph showing a temperature rising rate during dielectric heating of a composition constituting a conventional molding die.

FIG. 7 is a graph showing a temperature rising rate during dielectric heating of a composition forming a conventional molding die.

FIG. 8 is a sectional view of a molding die according to a second embodiment of the present invention.

FIG. 9 is a cross-sectional view of a molding die according to a third embodiment of the present invention.

FIG. 10 is a cross-sectional view of a conventional molding die.

[Explanation of symbols]

1: Upper mold 2: Lower mold 4: Cavity

Claims (2)

[Claims] 1. A molding die used for dielectric heating resin molding, which comprises molding a resin material into a cavity and heating the resin material by dielectric heating to cure the resin material, wherein the molding die comprises an epoxy resin and A molding die for dielectric heating resin molding, which comprises talc contained in an epoxy resin. 2. A molding die used for dielectric heating resin molding, wherein a cavity is filled with a resin material, and the resin material is heated and cured by dielectric heating to be molded. The molding die is heated by dielectric heating. Mold for dielectric heating resin molding characterized by having a high frequency shielding member in a thick, overheated portion that is possible.