JPH04284207A - Mold for molding resin under dielectric heating - Google Patents

Abstract

PURPOSE:To prevent the delay of dielectric heating at the thin-wall part of a molded article. CONSTITUTION:A mold for molding resin under dielectric heating, in which a portion of said mold where the hardly heatable part of a molded article is molded is formed of a mold material containing particles which generate heat by high frequency. For example, a top force 1 and a bottom force body 4 are made of a polyester resin, while a portion of the mold where a thin-wall part 11 of a molded article is molded is made of a carbon-containing silicone rubber 3. The mold into which a resin material is injected is put into a microwave heating furnace, and when high frequency is applied to said mold for several minutes, the resin material and the carbon-containing silicone rubber 3 generate heat. As a result, heat generated at the thin-wall part 11 of the molded article is not absorbed to the mold, or the thin-wall part 11 is heated by the carbon-containing silicone rubber 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for dielectric heating resin molding which heats a resin material within the mold using high frequency waves.

0002

[Prior Art] The so-called high-frequency resin molding method includes a dielectric heating method that directly heats the material from the inside using dielectric loss of an alternating electromagnetic field, and a dielectric heating method that directly heats the material from the inside using the dielectric loss of an alternating electromagnetic field. There is an induction heating method (see Japanese Unexamined Patent Publication No. 78708/1983) in which a mold is heated using resistance loss or hysteresis loss of the skin current to indirectly heat the resin material. The former dielectric heating method is advantageous in terms of heating time and thermal efficiency, and uses a high frequency of 1 to 300 MHz. A so-called microwave oven is a heater using this dielectric heating method.

[0003] Molding molds for dielectric heating resin molding are broadly classified into those equipped with high frequency generation means and those without high frequency generation means. The latter is more common when considering mold renewal, and in this case, the molded product is manufactured by filling the mold with a resin material that generates heat when exposed to high frequency waves, and then heating it with a high frequency generator (microwave heating furnace). This is done by heating and hardening the resin material inside the mold using high frequency waves.

[0004] The mold is made of silicone rubber or epoxy resin, which is a material that does not block high frequencies and is itself not easily heated by high frequencies. FIG. 10 shows an example of a mold consisting of an upper mold 21 and a lower mold 22 made of epoxy resin, and FIG. 11 shows a lower mold 2.
3 and the upper mold body 24 are made of epoxy resin, and the parts with poor demoldability such as the undercut molding part 25 and the rib molding part 26 are made of silicone rubber 6. Since the silicone rubber 6 can be deformed as shown in FIG. 8 (the molded product 19 is also deformed), demolding becomes easy. A large mold is reinforced by attaching frames 27 and 28 to an upper mold 21 and a lower mold 22, as shown in FIG. Sometimes small molds are made entirely of silicone rubber.

[0005]

The resin material filled in the mold is heated by high frequency waves, but at the beginning of the heat generation, the temperature is taken away by the mold. Therefore, it is good for dielectric heating resin molding when the molded product to be molded has a uniform thickness, but if the thickness is not uniform, the difference in heat generation and heat dissipation may result in partial under- or overheating. There is a problem in that it is difficult to obtain a perfectly shaped molded product.

[0006] To explain with a specific example, when molding using a silicone rubber integrated type that does not generate any heat at high frequency, if high frequency heating is applied until the thin part is fully cured, the thick part will be heated too much and become carbonized. become. This is because heat dissipation from the thin wall portion is large and heat storage is small, that is, the temperature of the thin wall portion is difficult to rise. On the other hand, if high-frequency heating is performed using an epoxy resin mold that generates some heat with high frequency, thin-walled parts can be cured before carbonization occurs in thick-walled parts, but the epoxy resin mold partially This will result in burning and significantly reduce the durability of the mold.

[0007] In order to avoid under- or over-heating, thin parts that are difficult to be heated with high frequency waves are sometimes heated from outside the mold using a constant temperature oven, hot air blowing, etc.; however, in this case, the heating time is 45 to 24 minutes. It often takes a long time, about hours. Therefore, dielectric heating resin molding is currently only being used for the production of prototypes, and cannot be said to be a molding method suitable for mass production.

[0008] The present invention was made to solve the above problem, and the problem to be solved is to provide a dielectric heating method that can heat and harden thin-walled parts of molded products in the same way as thick-walled parts in a short time. An object of the present invention is to provide a mold for resin molding.

[0009]

[Means for Solving the Problems] In the mold for dielectric heating resin molding of the present invention, the portion of the mold that molds the part of the molded product that is difficult to be heated is formed of a mold material containing particles that generate heat by high frequency waves. It is characterized by

[0010] Portions of the molded product that are difficult to heat (hereinafter referred to as hard-to-heat portions) include, for example, thin-walled portions, burrs, and portions with low high frequency density due to the structure of the heating device. Particles that generate heat due to high frequency waves preferably have a heat generating property comparable to or higher than that of the resin material, and powdered carbon is a typical example. The heating rate of the mold material containing particles that generate heat due to high frequency waves can be adjusted by changing the content of the particles. A wide range of contents, usually from 10 to 60%, is conceivable.

[0011] The mold material is preferably one that transmits high frequency waves and is not easily heated more than necessary. For example, epoxy resins, silicone rubbers, etc. that have been conventionally used in molds for dielectric heating resin molding can be used, but newly discovered polyester resins are also suitable. It is not necessary that the mold material of the portion of the molded product where the hard-to-heat portion is molded be the same as the mold material of the other portions. The molding material filled in the mold is of course a material that heats and hardens upon receiving high frequency waves, such as a polyurethane liquid resin material.

0012

[Operation] When exposed to high frequency, a normal mold hardly generates heat, but a mold material containing particles that generate heat due to high frequency generates a sufficient amount of heat. Therefore, if the part of the mold that molds the difficult-to-heat part of the molded product is formed of a mold material containing the above-mentioned particles, the heat generated in the difficult-to-heat part of the molded product will not be removed from the mold, or it will be difficult to The heating section will be heated by the mold. In this way, the temperature of the difficult-to-heat portion rises in the same way as other parts, and all parts of the molded product are cured at the same time. Furthermore, since there are no areas where heating is delayed, the curing time is also accelerated.

[0013]

[Example] Example 1 An example of the molding die for dielectric heating resin molding of the present invention is shown in FIG.
Explain using. This mold consists of an upper mold 1 and a lower mold main body 4.
is made of polyester resin, but carbon-containing silicone rubber 3 is used for a part of the mold surface. This is made by adding 30% by weight of carbon particles to a silicone rubber raw material liquid and then heating and molding the mixture. The slightly elastic carbon-containing silicone rubber 3 is backed up and held by the lower mold body 4, and a reinforcing frame 10 is attached to the outside of the mold to further increase the rigidity of the entire mold, so that the shape of the cavity 2 is It will not be distorted. The upper die 1 and the lower die main body 4 are fixed with bolts and nuts 9.

Polyester resin (upper mold 1 and lower mold main body 4)
) allows high frequency waves to pass through and generates almost no heat, but carbon-containing silicone rubber 3 generates heat when the carbon therein receives high frequency waves. The silicone rubber is replaced when it deteriorates. The portion where this carbon-containing silicone rubber 3 is used is the portion where the thin wall portion 11 of the molded product is formed. The liquid resin material is injected into the cavity 2 from an injection port 6 provided at a low position on the side of the mold, and the excess resin material that has been injected exits to a rising port 8 provided at a position higher than the cavity. The injection port 5 and the rising port 8 are made of silicone rubber 6. A hose for supplying resin material is inserted into the injection port 5, and a funnel is attached to the rising port 8 to prevent overflow of the resin material.

Since the diameters of the injection port 5 and the rising port are larger than the thickness of the molded product, it is necessary to prevent the resin material accumulated in the injection port 5 and the rising port 8 from being heated and burned by high frequency waves. Therefore, silicone rubber 6 containing no carbon is used as the silicone rubber for the injection port 6 and the rising port 8. The molded product is manufactured by placing the mold into which the resin material has been injected into a microwave heating furnace and exposing it to high frequency waves for about 3 minutes. The resin material and carbon-containing silicone rubber 3 generate heat due to the high frequency. When the mold is removed, a molded product whose entire surface is uniformly heated and hardened is obtained.

Embodiment 2 FIG. 2 shows a mold of another embodiment. The mold is
This is a mold for producing molded products with thin walls throughout. In the figure, components that are considered to have the same function in comparison with FIG. 1 are indicated by the same reference numerals. The feature of the mold of this example is that the mold surface of the lower mold is completely made of carbon-containing silicone rubber 3. As the thickness of the molded product is thin, the amount of heat generated by the resin material is low, and if the entire mold was made of polyester resin as in the past, heat would be absorbed by the mold and it would take a considerable amount of time for the molded product to harden. In the mold of this embodiment, the carbon-containing silicone rubber 3 generates heat and heats the molded product, so that the heat curing time is significantly shortened.

Example 3 In the mold of this example, both the upper mold 1 and the lower mold 7 are made only of carbon-containing silicone rubber 3, as shown in FIG. This is a mold for manufacturing small parts.
Neither polyester resin nor a reinforcing frame is used because mold strength is not so necessary. It is easy to mold because it is not made from multiple mold materials.

Example 4 If carbon-containing silicone rubber is too thick, it will expand and deform due to heat generation. An example of a mold that does not cause such inconvenience is shown in FIG. Carbon-containing silicone rubber 6 and carbon-free silicone rubber 3 are combined to prevent carbon-containing silicone rubber 3 from becoming thick.

Example 5 The mold of this example has an upper mold 1 and a lower mold 7 as shown in FIG.
, a three-part type insert 12, 13, 14, and a carbon-containing silicone rubber 3 attached to cover the surfaces of the combined inserts 12, 13, 14. When the nest must be constructed of three divided bodies 15, 16, and 17 as shown in FIG. 9, the gap between adjacent divided bodies becomes the burr occurrence site 18. However, the mold of this example (Fig. 5
), since the gap is hidden by the carbon-containing silicone rubber 3, there is no occurrence of burrs caused by the split type insert.

Example 6 Even unnecessary burrs must be completely cured when the molded product is demolded. In conventional molds, very thin burrs have a much slower heating rate than the product part of the molded product and are difficult to harden, but in the mold of this example,
As shown in Fig. 6, since carbon-containing silicone rubber 3, 3 is provided at the burr generation site, the burr is quickly heated and
By the time the product part is cured, the burrs are completely cured. Moreover, since the rubbers 3 and 3 have elasticity, the upper mold 1
A gap is hardly formed between the carbon-containing silicone rubber 3, 3, and almost no burrs can be found.

Example 7 The mold of this example is structurally the same as the mold of Example 1, but differs in material. That is, a carbon-containing polyester resin is used in place of the carbon-containing silicone rubber (see FIG. 1) in the mold of Example 1, and an epoxy resin is used in place of the polyester resin. Similar to the mold of Example 1, this mold can heat-cure the thick and thin parts of the molded product without any difference.

Test Example Test pieces of various mold materials were prepared, and how their temperature was increased by high frequency was investigated. The results are shown in FIG. In the figure, t represents the thickness of the test piece. Carbon content (
%) by weight. As can be seen from FIG. 7, the higher the carbon content, the faster the temperature rises. It can be said that a preferable pattern for the temperature increase curve is one in which the temperature becomes stable (the temperature increase rate becomes slow) after reaching a predetermined temperature at a high temperature increase rate. If temperature rise curves such as those shown in FIG. 7 are obtained for other materials as well, material selection in mold design will be facilitated.

[0022]

[Effects of the Invention] As is clear from the above explanation, according to the mold for dielectric heating resin molding of the present invention, the temperature of the difficult-to-heat parts can be raised in the same way as other parts, and all parts of the molded product can be heated at the same time. Moreover, it can be uniformly heated and cured. Therefore, it is possible to eliminate molding defects due to partial insufficient heating and carbonization due to partial overheating, and improve product yield. Furthermore, since the heating time is shortened, productivity is increased and the usable life of the mold is extended.

[Brief explanation of the drawing]

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

FIG. 2 is a sectional view showing a mold of another example.

FIG. 3 is a sectional view showing a mold of another example.

FIG. 4 is a sectional view showing a mold of still another embodiment.

FIG. 5 is a sectional view showing a mold of still another embodiment.

FIG. 6 is a sectional view showing a mold of still another embodiment.

FIG. 7 is a graph showing mold temperature rise curves (relationship between mold surface temperature and time) for each mold material.

FIG. 8 is an explanatory diagram of the advantages of using silicone rubber.

FIG. 9 is a sectional view showing an example of a conventional mold.

FIG. 10 is a sectional view showing another example of a conventional mold.

FIG. 11 is a sectional view showing another example of a conventional mold.

FIG. 12 is a side view showing still another example of a conventional mold.

[Explanation of symbols]

1 Upper mold 2 Cavity 3 Silicone rubber with carbon 4 Lower mold body 5 Inlet 6 Carbon-free silicone rubber 7 Upper mold 10 Thin wall part

Claims (1)

[Claims] Claim 1: In a mold in which a space constituted by an upper mold and a lower mold is filled with a resin material and then heated and molded, a portion of the molded product that is difficult to be heated is mold material containing particles that generate heat due to a high-frequency electric field. A mold for dielectric heating resin molding, characterized by being formed of.