JP2003266453A - Manufacturing method for epoxy cast article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for an epoxy cast article not having a fine flaw such as voids, a crack, a sink, peeling or the like and excellent in reliability. <P>SOLUTION: An epoxy casting resin is injected in a mold as a matrix resin under vacuum and subsequently cured under heating to manufacture the epoxy cast article. In this manufacturing method, a curing condition is set so that the shrink quantity of the matrix resin due to curing reaction is set off by the volumetric expansion of the matrix resin itself due to a temperature rise. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an epoxy which is suitable as an insulating structural material for high-voltage equipment and a structural material for aerospace equipment, and which is free of minute defects such as voids, cracks, sink marks, and peeling and has excellent reliability. The present invention relates to a method for manufacturing a cast product.

[0002]

2. Description of the Related Art Epoxy cast products are prepared by premixing a reinforcing base material such as an inorganic filler, an organic filler, or a metal filler with an epoxy resin and injecting it into a preheated mold under a vacuum. Alternatively, it is common to cure while applying pressure. Above all, a pressure curing method is used in order to eliminate minute defects such as voids, cracks, sink marks, and peeling of cast products.

However, the conventional manufacturing method as described above requires large-scale pressurizing dies, a vacuum and pressurizing line, and large-scale equipment including a resin measuring, mixing, and casting apparatus.

Further, the large mold as described above has a drawback that it is difficult to control the temperature of the cast product. That is, in order to ideally cure the casting resin in the mold, while hardening the part farthest from the casting port, the shrinkage that occurs during gelation is sequentially compensated, and the casting port is finally set. It is essential to solidify. However, in a large-sized casting mold, convection of the casting resin itself and heat generated by hardening of the resin thick portion hinder the ordering of hardening, and are liable to cause sink marks, cracks, dimensional defects, and the like.

[0005]

In order to solve the above problems, as a method for producing a cast product, a method in which the curing shrinkage of the matrix resin is basically compensated by an impregnating resin existing outside the molded product. However, as the size and thickness of the cast product increase, it becomes basically difficult to compensate the curing shrinkage with an external resin. As a result, there has been a problem that the number of internal defects increases as the cast product becomes large and becomes thick, and the mechanical properties and electrical properties of the cast product deteriorate. Therefore, it has been earnestly desired to develop a method for completely completing the cure shrinkage compensation of the casting resin regardless of the size of the casting product, without requiring a large-scale manufacturing device, and easily manufacturing the voidless casting product. Was there.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and its purpose is to have no microdefects such as voids, cracks, sink marks, and peeling, and to be excellent in reliability. Another object of the present invention is to provide a method for manufacturing an epoxy cast product.

[0007]

As a result of intensive studies to achieve the above-mentioned object, the present inventor has used resin compensation for curing shrinkage of a casting resin and volume expansion due to temperature rise of the resin itself. It has been found that the above-mentioned object can be achieved by compensating and offsetting by the above-mentioned method, and the present invention has been completed.

(Production Method of Epoxy Casting Product) In the production method of the epoxy casting product according to the present invention, the epoxy casting product is vacuum-injected as a matrix resin into the mold and then cured by heating to obtain the epoxy casting product. In the production, the curing conditions are set so that the shrinkage amount of the matrix resin due to the curing reaction is offset by the volume expansion of the matrix resin itself due to the temperature rise. Next, the curing conditions in the manufacturing method of the present invention will be described.

(Curing conditions until gelation of matrix resin) In general, when the matrix resin is heated at a constant rate to be cured, the change in volume shrinkage due to the curing reaction increases almost linearly with the curing time, The change in volumetric shrinkage until the matrix resin gels corresponds to about 60% of the volumetric shrinkage rate that is reached until the matrix resin is completely cured.

Here, the volumetric shrinkage rate until the matrix resin gels is the specific volumetric shrinkage rate V1, the curing time until the matrix resin gelates is T1, and the volume expansion rate of the matrix resin in the liquid phase is α ( 1 / ° C.), if the temperature increase value from the curing start temperature to the gelation of the matrix resin at a constant rate is A ° C., the curing shrinkage of the matrix resin is caused by the volume expansion based on the temperature increase of the matrix resin. In order to cancel, it is necessary to satisfy A × α = V1.

In other words, the matrix resin is gelated when the temperature rise width reaches V1 / α (° C.) at a constant temperature increase from the curing start temperature, so that [V1 / (T1 ×
[alpha])] ([deg.] C./minute) or more at a constant heating rate, the curing shrinkage can be offset by the volume expansion due to the temperature rise of the matrix resin.

(Curing conditions from gelling to complete curing of matrix resin) Generally, when the matrix resin after gelling is cured by heating at a constant rate, the change in volume shrinkage due to the curing reaction is relative to the curing time. It rises almost linearly.
When the glass transition temperature of the matrix resin becomes equal to the curing temperature, the curing reaction becomes diffusion-controlled, and as a result, the change in the specific volume contraction rate V2 of the matrix resin becomes saturated.

Therefore, the volumetric shrinkage ratio from the gelation of the matrix resin to the complete curing is the specific volume contraction ratio V2, the curing time from the gelation of the matrix resin to the complete curing is T2, and the volume of the matrix resin in the solid phase is T2. The expansion rate is β (1
/ ° C), and the temperature rise value until the matrix resin is completely cured by heating at a constant rate from the gelation temperature is B ° C, the curing shrinkage of the matrix resin is caused by volume expansion based on the temperature rise of the matrix resin. To offset
It is necessary to satisfy B × β = V2.

In other words, the matrix resin is completely cured when the temperature rise width reaches V2 / β (° C.) after the gelation temperature is raised at a constant rate, so that [V2 / (T2 ×
[beta]]] ([deg.] C./minute) or more at a constant heating rate, the curing shrinkage can be offset by the volume expansion due to the temperature rise of the matrix resin.

(Filler) The filler used in the present invention is not particularly limited as long as it is an inorganic or organic filler usually used in voidless castings.
For example, alumina, silica, dolomite, etc. can be used. Further, these fillers can be used alone or as a mixture.

(Matrix Resin) As the matrix resin used in the present invention, it is desirable to use an epoxy resin having a low viscosity in consideration of the ease of mixing the filler. This epoxy compound has two carbon atoms and one oxygen atom.
Any curable compound having two or more three-membered rings in one molecule can be appropriately used, and the kind thereof is not particularly limited. For example, bisphenol A
Type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac type epoxy resin, heterocyclic resin such as triglycidyl isocyanate and hydantoin type epoxy resin, and hydantoin type epoxy resin And the like. These compounds are used alone or as a mixture of two or more kinds.

Further, in the present invention, the contraction of the matrix resin due to the curing reaction needs to be offset by the volume expansion of the matrix resin due to the temperature rise. Generally, the smaller the average epoxy equivalent is, the larger the curing shrinkage is, but the volume expansion coefficient of the epoxy resin is not significantly changed.

Therefore, the present inventor examined various epoxy resins having different average epoxy equivalents to determine whether the curing shrinkage can be compensated by the volume expansion of the resins, and the average epoxy equivalent was 185. With the above epoxy resins, it is possible to compensate for the curing shrinkage due to the volume expansion of the resin. However, when the epoxy equivalent is less than 185, the curing shrinkage is large, and the curing shrinkage is obtained only by the volume expansion of the resin. It has proven difficult to compensate.

The matrix resin used in the present invention is not limited to the above-mentioned epoxy resin, and is not particularly limited as long as it has a low viscosity and is capable of compensating the curing shrinkage by the volume expansion of the resin. Alternatively, a thermosetting resin such as a polyester resin, a urethane resin, a vinyl ester resin, a phenol resin, or an imide resin can be used.

(Hardening agent for matrix resin) As described above, in the present invention, it is desirable to use a low-viscosity epoxy resin as the matrix resin in consideration of the ease of mixing the filler. It is desirable to use a liquid acid anhydride, especially methylhexahydrophthalic anhydride, as the curing agent. This methyl hexahydrophthalic anhydride, in combination with epoxy resin,
This is because a low-viscosity impregnated resin system can be constructed. As the other acid anhydride, methyl tetrahydrophthalic anhydride, methyl nadic acid anhydride, hydrogenated methyl nadic acid anhydride, or other acid anhydride liquid at room temperature can be used. Note that these acid anhydride curing agents may be used alone or in combination.

(Curing conditions when epoxy resin is used)
Here, the average epoxy equivalent as the matrix resin is 1
The curing conditions when the 85 epoxy resin is used will be described. That is, the volume expansion coefficient α in the liquid state of the matrix resin composed of an epoxy resin having an average epoxy equivalent of 185 and a liquid acid anhydride curing agent is 0.07% (1 / ° C).
The specific volume shrinkage V1 before the matrix resin gels is 3% regardless of the curing temperature. Therefore, assuming that the time required for the specific volume shrinkage V1 to reach 3% is t (minutes), the above-mentioned [V1 / (T1 × α)] (° C./minute) gives an epoxy resin having an average epoxy equivalent of 185 or more / 3 / (t × 0.07) in case of acid anhydride matrix resin
(° C / min), and the temperature is increased at a constant rate of 43 / t (° C / min) or more on the high temperature side to cure, and the curing shrinkage is offset by the volume expansion due to the temperature rise of the matrix resin. It becomes possible.

Further, the volume expansion coefficient β of the matrix resin comprising the epoxy resin having an average epoxy equivalent of 185 and the liquid acid anhydride curing agent after gelation is 0.05% (1 / ° C.). When the specific volume contraction rate V2 after gelling reaches 1.5%, the matrix resin has sufficient adhesive strength and mechanical strength with the reinforcing base material, and subsequent curing has the mechanical and electrical characteristics of the molded product. It does not affect. Therefore, assuming that the time required for the specific volume contraction rate V2 after gelation to reach 1.5% is t (minutes), the average epoxy equivalent is determined by the above [V2 / (T2 × β)] (° C./minute). In the epoxy resin / acid anhydride matrix resin of 185 or more, 1.5 / (t ×
0.05) (° C / min), and 30 / t (° C / min) on the high temperature side.
(Min) By raising the temperature at a constant rate and curing, the curing shrinkage can be offset by the volume expansion due to the temperature rise of the matrix resin.

(Operation / Effect) According to the manufacturing method of the present invention as described above, the volumetric shrinkage of the matrix resin is determined by the volume expansion of the matrix resin itself, regardless of the size and thickness of the casting. It will be possible to compensate. As a result, it is possible to significantly reduce the internal defects that occur in the matrix resin, and it is possible to significantly reduce the initial defects that control the mechanical properties of the epoxy casting product. The strength can be greatly improved. Further, in the manufacturing method of the present invention, it is possible to manufacture a large epoxy cast product having excellent mechanical properties and electrical properties without requiring a large device such as a conventional pressure tank. .

[0024]

EXAMPLES The present invention will be specifically described below based on examples. (1) First Example FIG. 1 is a schematic explanatory view showing the structure of a mold used in the first example. This mold also serves as a pressure vessel with a diaphragm for monitoring the curing shrinkage amount in the mold. That is, the mold 1 can be divided and is sealed with the O-ring 11 and fixed with the fixing fitting 12. Epoxy casting resin 3 is the injection port 13 on the upper part of the mold.
Inject from. Further, the diaphragm portion 2 is connected to the bottom portion of the mold 1, and is configured so that the epoxy casting resin 3 and the oil 4 are separated by a partition wall 5 and the pressure of the hydraulic unit 6 is transmitted through the partition wall 5. The partition wall 5 is made of a Teflon (registered trademark) sheet, and the volume of the resin-side space of the diaphragm portion 2 is calculated from the thermal expansion amount and curing shrinkage amount of the epoxy casting resin 3.

Further, the mold temperature is controlled by adjusting the heater 7 embedded in the mold 1 by a predetermined program control by the heating control device 20, whereby the epoxy casting resin 3 is cured. It is like this. As described above, this program control is carried out by [V1 / (T1 ×
[alpha])] ([deg.] C./min) or more at a constant heating rate, and [V2 / (T2 * [beta])] ([deg. C /
It is set so that the temperature is raised at a constant rate at a heating rate equal to or higher than (min).

Further, the length measuring cylinder 8 is connected between the diaphragm portion 2 and the hydraulic unit portion 6 and is displaced in accordance with the curing shrinkage amount of the epoxy casting resin 3. By converting the displacement amount into an electric signal and recording it in the hybrid recorder 9, the curing shrinkage amount can be measured. In this example, turbine oil was used as the pressure medium.

As the epoxy casting resin 3,
Methylhexahydrophthalic anhydride (manufactured by Shin Nippon Rika Co., Ltd., product name: MH700) is (acid anhydride) based on 100 parts by weight of an epoxy resin (produced by Yuka Shell Epoxy Co., Ltd., product name: EP828, epoxy equivalent 185). Matrix resin A was used in such a manner that the product mole / epoxy equivalent) = 0.9. Furthermore, Tris- as a curing accelerator
2,4,6-Dimethylaminomethylphenol (trade name: K-54, manufactured by Yuka Shell Co., Ltd.) was added and mixed so that the gel time at 90 ° C. was 20 hours.

Further, the reaction rate parameter of the matrix resin A was obtained from the data of the time and temperature dependence of the glass transition temperature Tg of the matrix resin A using a differential scanning calorimeter (DSC), and the rate equation of equation (1) was used. The kinetic parameters in the model were calculated.

[Equation 1]

As the filler for the epoxy casting resin, fused silica having an average particle size of about 15 μm was used, and this fused silica was mixed with the matrix resin A at a temperature of 80 ° C. under vacuum at 55% by volume, Epoxy cast resin B was obtained. The mold was preheated at 80 ° C., and the epoxy casting resin B was injected from the injection port under the condition of a vacuum degree of 0.3 to 0.8 Torr.
After the vacuum injection was completed, the injection port was sealed, and pressure was maintained at 1 kg / cm ² from the hydraulic unit via a length measuring cylinder connected to the diaphragm. In addition, by using the cartridge heater embedded in the mold
The temperature was raised at a constant rate so that the temperature reached to 4.3 ° C. in 4.3 hours, and thereafter, the temperature was increased at a constant rate so that the temperature reached from 100 ° C. to 120 ° C. in 2 hours and the resin was cured. Then, the displacement of the length measuring cylinder was converted into an electric signal and recorded in a hybrid recorder. In addition, the constant-velocity temperature raising conditions are in agreement with the curing conditions of the present invention.

The amount of curing shrinkage is expressed as the amount of displacement of the measuring cylinder. In this embodiment, however, the displacement of the measuring cylinder was hardly detected because the curing contraction was canceled by the volume expansion due to the temperature rise. . The cured epoxy cast product had a good appearance without sink marks, scratches, voids, cracks and the like. Also, usually, in the void-less casting, it is a necessary to pressure curing at ^{2kg / cm 2 ~4kg / cm 2} , in this embodiment, it is sufficient to dwell at most 1 kg / cm ² I understood.

(2) Relationship between Curing Shrinkage and Volume Expansion of Resin Composition in this Example Next, the relationship between curing shrinkage and volume expansion of the resin composition in this example will be described with reference to FIG. To do. The volume shrinkage ratio shown here is a cured volume shrinkage ratio of the epoxy casting resin B when isothermally cured at a predetermined temperature of 88 ° C. to 120 ° C., measured by a dilatometer. In FIG. 2, the cured volume shrinkage of the epoxy casting resin B is indicated by ◯, and the volume expansion coefficient of the epoxy casting resin B due to temperature rise is indicated by ▪.

As shown in FIG. 2, it was shown that the curing volume shrinkage was compensated by the volume expansion due to the rise of the resin temperature. The volume expansion coefficient of the matrix resin A shown in this example was 0.0712% / ° C. in the liquid state and 0.05% / ° C. after gelation.

As described above, according to the present embodiment, the curing shrinkage after gelling, which occurs in the matrix resin composed of the acid anhydride-cured epoxy resin, is caused by the volume expansion of the resin itself generated by increasing the temperature of the resin. Since they cancel each other out, it is possible to greatly reduce the generation of minute defects that occur in the matrix resin itself due to an increase in internal stress due to curing shrinkage and defects that occur at the adhesive interface between the silica filler and the matrix resin. As a result, it has been found that a voidless epoxy cast product can be easily manufactured without requiring a large-scale device unlike the conventional manufacturing method.

[0034]

As described above, according to the present invention, it is possible to provide a method for producing an epoxy cast product which is free from minute defects such as voids, cracks, sink marks and peeling and which is excellent in reliability.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a mold including a heating control device used in a method for manufacturing an epoxy cast product according to the present invention.

FIG. 2 is a graph showing the relationship between curing shrinkage and volume expansion of a resin composition when the production method of the present invention is applied.

[Explanation of symbols]

1 ... Mold 2 ... Diaphragm part 3 ... Resin 4 ... oil 5 ... Partition 6 ... Hydraulic unit 7 ... Heater 8 ... Measuring cylinder 9 ... Hybrid recorder 11 ... O-ring 12 ... Fixing bracket 13 ... Filling port 20 ... Heating control device

Claims (5)

[Claims] 1. A method for producing an epoxy cast product, in which an epoxy cast resin as a matrix resin is vacuum-injected into a mold and then cured by heating, wherein the shrinkage amount of the matrix resin due to a curing reaction is the A method for producing an epoxy cast product, characterized in that curing conditions are set so as to be offset by volume expansion. 2. The curing condition is that until the matrix resin gels, the volume shrinkage rate until the matrix resin gels, the specific volume shrinkage rate V1, and the curing time until the matrix resin gels. Where T1 is the volume expansion coefficient of the matrix resin in the liquid phase is α (1 / ° C.), the matrix resin is started from the curing start temperature, and [V1 / (T1 × α)] ( 2. The method for producing an epoxy cast product according to claim 1, wherein the epoxy cast product is cured by heating at a constant rate at a temperature rising rate of (° C./min) or more. 3. The curing condition is that, after the gelation of the matrix resin until it is completely cured, the volumetric shrinkage ratio from the gelation of the matrix resin to the complete curing is the specific volume shrinkage ratio V2, the gel of the matrix resin. When the curing time from the curing to the complete curing is T2, and the volume expansion coefficient of the matrix resin in the solid phase is β (1 / ° C), the matrix resin starts from the gelation temperature and is heated to the high temperature side [ V2 / (T2
Xβ)] (° C / min) or more and a constant rate of temperature rise to cure the epoxy cast product according to claim 1 or 2. 4. The method for producing an epoxy cast product according to claim 1, wherein the matrix resin is an epoxy resin having an average epoxy equivalent of 185 or more. 5. The method for producing an epoxy cast product according to claim 4, wherein a liquid acid anhydride is used as a curing agent for the matrix resin.