JPH0794530B2 - Method of curing epoxy resin - Google Patents

Description

The present invention relates to a method for curing an epoxy resin.

Epoxy resins are compounds having highly reactive epoxy groups in the molecule, and many compounds having different chemical structures are known. Of these, bisphenol A type epoxy resin accounts for 75% of the market and is most widely used.
This resin is a mixture of oligomers of relatively low molecular weight, and various grades with different molecular weights, from liquid or semi-solid resin with a molecular weight of 500 or less at room temperature to solid resin with a molecular weight of about 6000. Is obtained.

The bisphenol A type epoxy resin is used as a cured product by adding various curing agents to cause a curing reaction. Since a cured product of an epoxy resin is excellent in toughness, adhesiveness, chemical resistance, strength properties and high temperature characteristics, it is widely used as an adhesive, a binder for laminated plates, a coating material and the like.

(Prior Art) The curing of an epoxy resin is usually performed by adding a curing agent such as amines and heating. Recently, its application is expanding as a sealant and protective coating material for electronic parts such as printed wiring boards and chips. However, since it is not preferable to expose such a product to a high temperature, the method of adding a curing agent and curing by heating cannot be adopted. Therefore,
A method has been developed in which an onium salt such as triphenylsulfonium hexaphosphate is added to an epoxy resin as a photocation initiator to irradiate ultraviolet rays. This is because, in this method, the curing reaction can be performed by irradiation at room temperature without particularly heating. Further, there is an advantage that the curing reaction can be performed by irradiation of ultraviolet rays for a shorter time than the curing reaction by heating.

In such a process, an epoxy resin is applied to a target material prior to curing, and then ultraviolet rays are irradiated. However, the liquid bisphenol A type epoxy resin is a fairly viscous liquid having a viscosity of 100 to 200 poise at room temperature, even if it is the most widely used resin having an average molecular weight of about 300 to 400, and is applied as it is. Is difficult. Therefore, it must be heated to 50-80 ℃ during coating. Alternatively, in order to carry out the coating smoothly at room temperature, it is necessary to dilute it with a solvent such as acetone or methyl ethyl ketone. In this case, it is necessary to remove and recover the solvent after coating or curing. The third method is a method using a reactive diluent, for example, a method using an alkyl monoglycidyl ether or the like for dilution. In this case, the diluent reacts at the time of curing to form a resin component, but there is a drawback that the curing rate generally decreases.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for curing an epoxy resin that does not have such problems.

(Means for Solving Problems) In order to achieve this object, the inventor of the present invention has conducted a thorough search for a reactive diluent effective for an epoxy resin, and as a result, tetrahydrofuran, which is an excellent solvent for the epoxy resin, is At room temperature under the addition of a cationic reaction initiator, curing at a high rate by irradiation with radiation in the presence of air, tetrahydrofuran was copolymerized with an epoxy oligomer, it was found that a cured product having excellent hardness is obtained, the present invention Arrived

In a method for producing a cured product by irradiating an epoxy resin with radiation in the presence of a photocationic initiator, a photocation such as triphenylsulfonium hexafluorophosphate is added to a bisphenol A diglycidyl ether type epoxy resin which is liquid at room temperature. When producing a cured product of epoxy resin by adding a reaction initiator and irradiating with radiation, add up to 50 parts of commercially available tetrahydrofuran without purification to 100 parts (weight standard) of the epoxy resin. And a method for curing an epoxy resin.

In the method of the present invention, tetrahydrofuran is used in a maximum amount of 50 parts per 100 parts by weight of the epoxy resin. At this time, if the amount of tetrahydrofuran is too large, the viscosity of the resin solution will be too low at the time of application, and the volatility of tetrahydrofuran will increase, making handling difficult. Furthermore, the hardness of the cured product decreases, which is not preferable. The blending amount of tetrahydrofuran is the molecular weight of the epoxy resin,
It can be adjusted depending on the desired properties of the cured product.

The epoxy resin used in the method of the present invention is not particularly limited, but is preferably a liquid bisphenol A diglycidyl ether type epoxy resin. Is used.

Tetrahydrofuran used in the present invention does not need to be strictly purified. It is known that the cationic polymerization of tetrahydrofuran is prohibited by trace amounts of water and other impurities. Although sufficient purification is necessary for smooth polymerization, commercially available tetrahydrofuran can be used as it is without any particular purification in the method of the present invention. This is a great advantage of the present invention.

The photo cationic initiator used in the present invention, aryl diazonium salt ArN NX ^-, Ar: aryl _{^{group, X -: PF 6 -,}} AsF 6 -, SbF 6 -, BF 4 - , etc., e.g., methoxyphenyl diazonium such as hexafluorophosphate, diaryliodonium salts ArI X ^-, for example, diphenyl iodonium hexafluorophosphate, bis (4-methylphenyl) - such as iodonium hexafluoroantimonate, triarylsulfonium salts Ar ₃ SX ^-, for example, triphenyl Sulfonium hexafluorophosphate, tris (4-methylphenyl) -sulfonium hexafluoroarsenate and the like, and further, bis [(4-diphenylsulfonio) phenyl] sulfide-bis-hexafluorophosphate and the like disulfonium salts and the like. Lap There is an onium salt.

The photocationic initiator is 0, based on the amount of epoxy resin.
05-8%, preferably 0.2-3% is used.

As radiation, α rays, β rays, γ from radioactive isotopes
Rays and electron beams from an accelerator are used, but γ rays from Cobalt 60, particularly electron beams from an accelerator are preferably used.

As the electron beam accelerator, various types can be used, but if the thickness is in the order of 1 cm,
0.5 to 2 MeV energy like Van de Graaf accelerator, Cockcroft-Walton type accelerator, 0.1 mm to 0.7 MeV energy like transformer type accelerator if it is 1 mm or less, 1 μm order thin film If,
A 0.1-0.3 MeV linear filament type accelerator, such as an electro curtain, is conveniently used.

Irradiation dose varies mainly depending on the dose rate and is not particularly limited, but usually 0.1 to 50 Mrad is used. The irradiation temperature is also not particularly limited, but room temperature is preferably used.

(Example) Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 100 g of Epicoat 828 [n = 0.1 in the above formula, manufactured by Yuka Shell Epoxy Co., Ltd.] as a liquid epoxy resin, 50 g of tetrahydrofuran [commercially available special grade product, including a stabilizer] 50 g, and triphenylsulfonium hexa as a photocation reaction initiator 2 g of fluorophosphate was mixed. About 1 g of this resin mixed solution was cast to a thickness of about 1 mm in an aluminum frame of internal size 7 cm × 1.5 cm. At this time, the epoxy resin alone could not be easily cast on the aluminum frame at room temperature of 25 ° C., but the resin solution having the above composition could be cast easily. This was placed on a belt conveyer at a speed of 0.48 m / min and irradiated with 18 Mrad of 1.5 McV, 50 μA electron beam from a Bande-Glarke accelerator. The irradiation completely solidified the resin liquid. This solidified cured product was removed from the aluminum frame, weighed, and then immersed in acetone at room temperature.
Acetone was exchanged with fresh one every 24 hours and soaked for 10 days to extract the soluble part from the irradiation product. After the completion of the extraction operation, the irradiation product was vacuum dried at 80 ° C. The gel content calculated by gravimetric measurement was 98.5%.
That is, it was found that the resin liquid containing tetrahydrofuran was almost completely polymerized and crosslinked, and terorahydrofuran was copolymerized with the epoxy resin.

This cured product was measured for dynamic viscoelasticity, and the dynamic elastic modulus was determined as a measure of hardness. The dynamic elastic modulus at 25 ° C was 1.0 × 10 ¹⁰ dyne / cm ² .

For comparison, a liquid epoxy resin containing no tetrahydrofuran was subjected to an experiment of curing by electron beam irradiation in exactly the same operation. The gel content was 98.4%. The dynamic elastic modulus of this cured product was 1.4 × 10 ¹⁰ dyne / cm ² . That is, it was found that a cured product of an epoxy resin containing tetrahydrofuran also showed almost the same hardness.

Further, for comparison, the electron beam was irradiated to tetrahydrofuran containing only 2% by weight of the photocationic reaction initiator containing no epoxy resin. In this case, in order to prevent the evaporation of tetrahydrofuran, a 25 μm-thick polyester film was coated with the tetrahydrofuran solution contained in the aluminum frame. Since the electron beam energy is 1.5 MeV and has a high transparency, the effect of this coating on the irradiation dose can be ignored.
After the irradiation of 18 Mrad, polymerization of tetrahydrofuran did not occur at all. That is, it is understood that the tetrahydrofuran is copolymerized with the epoxy resin and solidified only when the mixture is irradiated with the epoxy resin and the tetrahydrofuran.

Example 2 In Example 1, the curing reaction was carried out by irradiating under exactly the same conditions except that 12 g of tetrahydrofuran was added to 100 g of the epoxy resin. Irradiation product gel content is 98.3%
Met. The dynamic elastic modulus of the irradiated object is 1.3 × 10 ¹⁰ dyne / cm.
^{Was 2} .

Example 3 In Example 2, the epoxy resin-tetrahydrofuran mixture was subjected to electron beam irradiation under exactly the same conditions except that the irradiation dose was 10 Mrad. Irradiation product has a gel content of 9
8.8%, the dynamic elastic modulus of the irradiated object is 1.4 × 10 ¹⁰ dyne / cm ²
Met.

Comparative Example 1 The electron beam irradiation of the epoxy resin-tetrahydrofuran mixture was performed under exactly the same conditions as in Example 1, except that the amount of tetrahydrofuran blended with 100 g of the epoxy resin was 70 g. The gel content of the irradiation product is 91.2% and it is clear that tetrahydrofuran is copolymerized with the epoxy resin. However, tetrahydrofuran is often volatilized during handling, and the dynamic elastic modulus of the irradiated object is 5.9.
This composition is not preferable because it is × 10 ⁹ dyne / cm ² and the hardness is slightly lowered.

Example 4 To 100 g of Epicoat 828, 30 g of tetrahydrofuran,
Triphenylsulfonium hexafluorophosphate was mixed in a ratio of 1 g. 50 ml of 20 g from this resin liquid
Put it in an Erlenmeyer flask, put a glass stopper in the presence of air, and give a γ-ray with a dose rate of 1.5 × 10 ⁵ rad / h for 20 hours, that is, 3 Mr
The ad was irradiated. Since the resin mixture has completely solidified,
The product was taken out by breaking the flask. The gel fraction determined by acetone extraction of this irradiated product was 99.2%. Epoxy resin / tetrahydrofuran cured product is 300
It did not melt at all even when heated to ℃.

For comparison, a tetrahydrofuran solution containing 1% by weight of triphenylsulfonium hexafluorophosphate was irradiated with γ-rays under exactly the same conditions as above, but the polymerization of tetrahydrofuran did not occur at all. It is clear that even in the case of γ-ray irradiation, the polymerization of tetrahydrofuran does not occur at all unless the epoxy resin coexists.

Example 5 Epicoat 834 [n = 1.0 in the above formula, manufactured by Yuka Shell Epoxy Co.] as a semi-solid liquid epoxy resin 100
g, tetrahydrofuran 50 g, diphenyliodonium hexafluoroantimonate 2 g resin solution was prepared. Then, the casting was performed on an aluminum frame in the same manner as in Example 1, and
The electron beam was irradiated with 18 Mrad under the same irradiation conditions as in. The gel fraction determined by the acetone extraction test was 97.6%.
That is, it is found that tetrahydrofuran is copolymerized with the cured product.

Claims (3)

[Claims] 1. A cationic photoinitiator is added to 100 parts (weight standard) of a bisphenol A diglycidyl ether type epoxy resin which is liquid at room temperature, up to 50 parts (weight standard) of commercially available tetrahydrofuran without purification. A method for curing an epoxy resin, which comprises irradiating with radiation at room temperature in the presence of. 2. The method for curing an epoxy resin according to claim 1, wherein the photocationic reaction initiator is triphenisulfonium hexafluorophosphate. 3. As the radiation, gamma rays from cobalt 60,
In particular, the method for curing an epoxy resin according to item 1, wherein the electron beam is emitted from an accelerator.