JPH0373578B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solid phase curing method for solidified epoxy resin molded products. Conventionally, as a method of curing epoxy resins, a method of crosslinking and curing at a temperature equal to or higher than the melting point of the resin has generally been adopted. That is, in order to shape it into a certain mold, it needs to be in a molten state, and in order to crosslink and harden it as quickly as possible, it is customary to cure it at a high temperature, that is, in a molten state. In addition, when the crosslinking reaction has progressed to a certain extent and it no longer shows a molten state,
It is also known to cure in a solid state by so-called after-cure. However, in this type of curing method, (1) curing is performed at a temperature above the melting point (liquid phase), so in the case of casting, transfer molding, injection molding, etc., the mold must be removed until crosslinking progresses and the solid state is reached. Can not do it. Usually, it takes a long time to remove the mold, ranging from 10 minutes to 24 hours, and the efficiency of mold utilization is extremely low. (2) From this point of view, there is a method of rapidly curing at a high temperature, but in this case, the curing reaction becomes non-uniform, leaving internal distortion in the molded product, and the cured product becomes brittle. An object of the present invention is to provide an industrially advantageous method for curing epoxy resin molded articles that can be demolded in an extremely short time. Another object of the present invention is to provide a method for curing an epoxy resin molded product that can produce a molded product with excellent strength without causing internal distortion through a uniform curing reaction. A further object of the present invention is to provide a method for curing an epoxy resin molded product which provides a molded product with extremely low curing shrinkage. In the present invention, after demolding a solidified molded product of a cross-linkable epoxy resin with a glass transition temperature (Tg) of 40 to 200°C, heat curing is performed at an ambient temperature not exceeding 20°C above the Tg of the molded product. An epoxy system characterized in that the curing reaction is completed by raising the atmospheric temperature while maintaining the temperature within 20°C above the Tg of the molded material in response to the Tg of the molded material which increases with the progress of curing. This invention relates to a solid phase curing method for resin solidified molded products. Further, the present invention adjusts the above atmospheric temperature to the Tg of the molded product.
The temperature is maintained within a range not exceeding 20°C to allow the curing reaction to proceed, and the Tg of the molded product is determined by the Tg that can be reached upon completion of curing and the initial Tg.
This relates to a solid phase curing method for solidified epoxy resin molded products, which is characterized in that after the temperature rises by at least 60% or more of the difference between Incidentally, Tg in the present invention was measured by the TMA penetration method, in which a sample was heated by a temperature raising method. What is the solidified molded product of epoxy resin mentioned here?
By exposing the molded product to the so-called after-cure temperature (the temperature around the Tg that the molded product ultimately reaches is generally used), with virtually no crosslinking reaction taking place,
It is completely deformed, and is completely different from conventional hardened molded products before after-curing. As an indication that the crosslinking reaction of the solidified molded product has not substantially progressed, stickiness is observed when the surface of the molded product is wetted with acetone at room temperature and rubbed with a fingertip. In the conventional cured molded product before after-cure, most of the crosslinking reaction has proceeded, and this level of acetone does not cause it to become sticky. Since the present invention cures in a solid state, there is no need to maintain the shape in the mold, making the mold extremely efficient to use.Also, the curing reaction can be carried out uniformly at a specific ambient temperature, resulting in curing. The unexpected effect of this method is that the physical properties of the product are excellent, and in particular, the curing shrinkage is much smaller than that of conventional methods. The epoxy resin used in the present invention includes:
For example, in addition to bisphenol type epoxy resin, novolak type epoxy resin, halogenated epoxy resin, hydrogenated epoxy resin, alicyclic epoxy resin, or hydantoin type epoxy resin, silicone epoxy resin, epoxy furan resin, epoxy ester resin, phenoxy Modified epoxy resins such as resins, epoxy urethane resins, or liquid rubbers whose end groups are modified with epoxy, and resins such as those obtained by curing phenols such as polyvinylphenol with epoxy resins can also be used. Examples of compounding agents for these epoxy resins include known reinforcing agents, curing agents, fillers, plasticizers, diluents, flame retardants, photopolymerization initiators, pigments, and the like. Of course, other known thermoplastic or thermosetting resins that are compatible with the above epoxy resin can also be blended. Specifically, as the curing agent, in addition to amines, acid anhydrides, imidazoles, organic peroxides, etc., alcohols, isocyanates, etc. can be used depending on the polymer structure. As reinforcing agents, glass fibers, carbonate fibers, inorganic fibers such as asbestos, aramid fibers, nylon,
In addition to fibrous reinforcing agents such as organic fibers such as polyester, whiskers such as aluminum oxide, silicon carbide, and graphite can also be used. Other additives include fillers and pigments such as glass flakes, glass powder, mica, carbon black, talc, clay, silica, calcium carbonate, aluminum hydroxide, titanium white, or dioctyl phthalate and tricresyl phosphate. Plasticizers such as butyl glycidyl ether, reactive or non-reactive diluents such as xylene, flame retardants such as antimony trioxide and chlorinated paraffin, photoinitiators such as isopropyl benzoin ether, etc. are selected accordingly. It can be used as In the present invention, the above-mentioned epoxy resin blended composition is molded by an appropriate method to obtain a crosslinkable and hardenable solidified molded product having a Tg of 40 to 200°C. like above
As a specific method for obtaining a solidified molded product having a Tg, for example: (1) The Tg of the epoxy resin itself used is approximately 35-35.
Choose one in the 195℃ range. This is because when reinforcing agents and fillers are mixed with epoxy resins, Tg generally tends to increase. (2) When using an epoxy resin with a Tg of 195°C or higher, it is necessary to use other epoxy resins with a lower Tg, or to add compounding agents that lower the Tg, such as heat treatment. 200 by using plastic resins, plasticizers, etc.
It may be adjusted to below ℃. (3) If it is necessary to use an epoxy resin with a Tg of less than 35°C, use other epoxy resins with a higher Tg or other thermosetting resins, or use reinforcing agents that increase the Tg. The Tg may be adjusted within the range of 40 to 200°C by increasing the amount of filler, such as a fibrous reinforcing agent. In the present invention, by setting Tg in the above range of 40 to 200°C, it is possible to increase the atmospheric temperature during curing and shorten the curing time in the solid phase, and also to prevent the curing reaction from proceeding too much during kneading. can be prevented. Furthermore, decomposition of the epoxy resin due to an increase in curing temperature due to too high Tg is suppressed, and the allowable range of molding temperature is widened. In the present invention, after demolding a solidified molded product having the above-mentioned Tg, heat curing is performed at an ambient temperature not exceeding 20°C below the Tg of the molded product, and in response to the Tg of the molded product which increases as the curing progresses, The curing reaction is completed by raising the ambient temperature while maintaining it within a range of 20° C. above the Tg of the molded article. The atmospheric temperature may be raised continuously following the rise in Tg of the molded product, or may be raised stepwise. The preferred ambient temperature is around the Tg of the molded product or about 15°C lower than the Tg,
And its upper limit is 20°C higher than Tg. However, it is generally difficult to control the temperature within this range at all times, and in some cases it is acceptable to temporarily deviate from this range. A solidified molded product of an epoxy resin in a state where the crosslinking reaction has not substantially progressed (hereinafter referred to as an uncured molded product) deforms when exposed to an ambient temperature higher than the Tg of the molded product. However, epoxy resins usually have a wide range of molecular weights, and the Tg of the uncured molded material here is
This means that the average Tg of the entire resin is measured. Therefore, even if the ambient temperature becomes higher than Tg, deformation does not occur immediately, but in practice, deformation does not occur as long as the temperature does not exceed Tg by 20°C, so this range was selected. In a preferred embodiment of the present invention, the Tg of the molded product is
After that temperature is increased by at least 60% of the difference between the initial Tg and the Tg that can be reached upon completion of its curing, the molding is no longer at risk of melting or deforming, and the ambient temperature is then lowered. Tg
The temperature can be set at a temperature exceeding 20° C., thereby further promoting the crosslinking reaction in a solid phase state without causing dimensional changes. In the present invention, in order to effectively carry out the solid phase curing method described above, it is desirable that the initial Tg increase rate of the solidified molded product is in the range of about 0.01 to 10° C./min. The initial Tg increase rate of the solidified molded product referred to here refers to the initial Tg increase rate of the solidified molded product that has not undergone substantial thermal history.
This is the rate of increase in Tg of the solidified molded product at time 0 when the solidified molded product is exposed to the same ambient temperature as Tg. Specifically, the initial Tg ₀ of the solidified molded product is measured in advance, the solidified molded product is exposed to the same ambient temperature as this Tg ₀ , the change in Tg is tracked, and the time 0 of the Tg increase curve is measured.
It is obtained from the slope at . In the above initial Tg increase rate range, the crosslinking reaction progresses quickly and curing can be completed within a relatively short time, and the resulting molded product does not suffer from internal distortion, shrinkage, or warping. preferable.
On the other hand, the atmospheric temperature is adjusted at the initial stage of the solidified molded product.
Approximately 0.2 to 5 times the Tg increase rate, preferably approximately 0.5 to 2
This can easily be achieved by increasing the speed in the double range. In the present invention, various known molding methods can be used as the molding method, including, of course, the casting method, injection molding method, transfer molding method, extrusion molding method, blow molding method, normal pressure injection method, etc. can. In addition to heating gas (e.g. air), heat sources for solid phase curing of the present invention include liquids (e.g. heat medium such as high-boiling oil), powder (e.g. sand), etc.
etc. can be mentioned. Further, electron beam irradiation, microwave irradiation, etc. can also be used. A detailed explanation will be given below with reference to examples. Note that parts simply indicate parts by weight. Note that Tg below was measured using a differential scanning calorimeter manufactured by Rigaku Denki Co., Ltd. Example 1 100 parts of epoxy resin [precondensate, number average molecular weight (Mn) 5200, epoxy equivalent (EE) 1400],
A pelletized mixture of 50 parts of silica (350 mesh) and 0.7 part of BF ₃ monoethylamine complex salt was injection molded at a mold temperature of 65°C, and the Tg of the molded product was measured and found to be 71°C. The initial Tg increase rate at an ambient temperature of 71°C was 0.21°C/min, so when this molded product was raised linearly from 65°C to 150°C at a rate of 0.5°C/min, no deformation occurred. I was able to harden it. The Tg after curing was 144°C. Incidentally, FIG. 1 shows the relationship between the ambient temperature and the Tg of the molded product over time. The diagram shows the atmospheric temperature.
It can be seen that the temperature did not exceed Tg+20℃. Comparative Example 1 The molded product molded in Example 1 was heated to an ambient temperature of 65°C.
When the molded product was raised linearly at a rate of 1.5°C/min from It became a vine. Example 2 Epoxy resin (precondensate, Mn8000,
EE1000) 100 parts, glass fiber (chopped strand CS-03) 30 parts, diaminodiphenylmethane
Mix 5.4 parts and pelletize the mold temperature.
Transfer molding was performed at 75°C, and the Tg of the molded product was measured to be 82°C. When this molded product was placed in a thermostat adjusted to an ambient temperature of 80℃ and heated for 2 hours, the molded product
Tg was 98℃. Here, set the temperature of the thermostat
When heated at 95℃ for 1 hour, the Tg of the molded product was
It was 110 degrees Celsius. Here, further adjust the temperature of the thermostat.
The molded product was heated for 0.5 hours at 110℃.
Tg was 130℃. The highest Tg of the same compound as this molded product is 154℃
(Curing conditions were 150°C x 3 hours, 180°C x 3 hours), and the Tg of the above molded product had reached 67% of the highest achieved Tg, so even if heated to a temperature 20°C higher than Tg. It was determined that there would be no deformation, and it was heated at 160°C for 1 hour. The final molded product had a Tg of 153°C and was not deformed during curing. Further, the shrinkage rate of the cured product was usually 0.8 to 1.0%, but according to this curing method, the shrinkage rate was 0.2% or less. Example 3 Epoxy resin (precondensate, Mn4500,
EE1100) 100 parts, silica (350 mesh) 50 parts,
A mixture of 4.9 parts of diaminodiphenylmethane and pelletized mixture was injection molded at a mold temperature of 60°C, and the Tg of the molded product was measured to be 68°C. When this molded article was cured under the heating conditions shown in Table 1, it did not deform and reached its final Tg of 148°C. The maximum Tg reached was 150°C.

[Table] Example 4 The same molded product as in Example 3 was cured without deformation when the ambient temperature was started at 70°C and raised linearly at a rate of 0.16°C/min until it reached 160°C. I was able to do that. Incidentally, Fig. 2 shows the relationship between the ambient temperature and the Tg of the molded product over time. The figure shows that the ambient temperature does not exceed Tg + 20°C.

[Brief explanation of drawings]

1 and 2 are graphs showing the relationship between the ambient temperature and the Tg of the molded product over time in Examples 1 and 4.

Claims (1)

[Claims] 1. After demolding a solidified molded product of a crosslinkable epoxy resin with a glass transition temperature (Tg) of 40 to 200°C, the upper limit of the heating temperature is higher than the Tg of the molded product.
Heat curing is performed at an ambient temperature that does not exceed 20℃, and in response to the Tg of the molded material, which increases as the curing progresses, the ambient temperature is increased while maintaining the Tg of the molded material within a range of no more than 20°C. A method for solid-phase curing of a solidified epoxy resin molded article, characterized in that the curing reaction is completed by curing. 2 After demolding a solidified molded product of a cross-linkable epoxy resin with a glass transition temperature (Tg) of 40 to 200°C, the upper limit of the heating temperature is higher than the Tg of the molded product.
Heat curing is performed at an ambient temperature that does not exceed 20℃, and in response to the Tg of the molded material, which increases as the curing progresses, the ambient temperature is increased while maintaining the Tg of the molded material within a range of no more than 20°C. After the curing reaction has progressed and the difference between the Tg of the molded product and its initial Tg has increased by at least 60%, the ambient temperature should be lowered.
A solid phase curing method for epoxy resin solidified molded products, characterized by curing at a temperature exceeding 20°C above Tg.