JPH078900B2 - Improved epoxy resin curing method - 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 relatively low molecular weight oligomers,
Various grades having different molecular weights can be obtained from a liquid or semi-solid resin having a molecular weight of 500 or less at room temperature to a solid resin having a molecular weight of about 600. The bisphenol A type epoxy resin is used as a cured product by adding various curing agents to cause a curing reaction. A cured product of an epoxy resin is excellent in toughness, adhesiveness, chemical resistance, strength properties, and high-temperature characteristics, and therefore an adhesive, a binder for laminated plates,
It is also widely used for coating materials.

(Prior Art) A conventional method for curing an epoxy resin is performed by adding a curing agent such as amines and then heating.

In recent years, epoxy resins are being increasingly applied as sealants and protective coating materials for electronic components such as printed wiring boards and chips. However, since it is not preferable to expose such a product to a high temperature, a method of adding a curing agent and heat curing cannot be adopted. Therefore, a method has been developed in which an onium salt such as triphenylsulfonium hexafluorophosphate is added to an epoxy resin as a photocation reaction initiator to irradiate with ultraviolet rays. According to 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.

(Problems to be Solved by the Invention) In this curing method by irradiation with ultraviolet rays, an epoxy resin is applied to an object prior to curing and then ultraviolet rays are irradiated. However, the liquid bisphenol A type epoxy resin has the most widely used average molecular weight of 30.
Even a resin of about 0 to 400 is a fairly viscous liquid having a viscosity of 100 to 200 poise at room temperature, and it is difficult to apply it as it is. Therefore, it is necessary to heat at 50 to 80 ° C. at the time of coating, or to dilute it with a solvent such as acetone or methyl ethyl ketone in order to smoothly perform coating at room temperature. In the case of dilution with a solvent, it is necessary to remove and recover the solvent after coating or curing.
Furthermore, there is a method using a reactive diluent, and this method is
For example, it is a method of diluting with alkyl monoglycidyl ether or the like. 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.

As a method for improving such drawbacks, we have found that when tetrahydrofuran is used as a diluent, tetrahydrofuran reacts during curing to form a resin component, and a patent has already been applied for. However, the drawback of this method is that it has a relatively low boiling point of 64 ° C. and is liable to volatilize.

Therefore, an object of the present invention is to provide a method for curing an epoxy resin that solves such problems.

(Means for Solving Problems) As a result of earnest search for a reactive diluent effective for an epoxy resin in order to achieve the above object, the present inventor has found that it is an excellent solvent for an epoxy resin. 1,4-dioxane was cured at a high rate by irradiation with radiation in the presence of air at room temperature under the addition of a photocationic initiator,
It was found that dioxane was copolymerized with an epoxy oligomer, and as a result, a cured product having excellent hardness was obtained, and the present invention was accomplished.

The boiling point of 1,4-dioxane is 101 ° C. under 1 atm, and virtually no volatility is observed at room temperature.

That is, the method of the present invention is a method for producing a cured product by irradiating an epoxy resin with radiation in the presence of a photocationic reaction initiator, in which 1,4-dioxane is added and radiation is performed, Is a method for producing a cured product of an epoxy resin by adding a photocationic reaction initiator such as triphenylsulfonium hexafluorophosphate to a bisphenol A type epoxy resin which is liquid at room temperature and then irradiating the cured product with the radiation. This is a method for curing an epoxy resin, characterized in that a maximum amount of 50 parts by weight of 1,4-dioxane is added to 100 parts (by weight) to perform curing.

In the method of the present invention, 1,4-dioxane is used in a maximum amount of 50 parts by weight based on 100 parts by weight of the epoxy resin. At this time, if the amount of 1,4-dioxane is too large, the viscosity of the resin liquid will be too low at the time of application, the curing speed will be low, and the hardness of the cured product will be low, which is not preferable. The loading of 1,4-dioxane can be adjusted depending on the molecular weight of the epoxy resin and 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 (the structural formula is shown below).
Is used.

The 1,4-dioxane used in the present invention does not need to be strictly purified. It is known that a polymerization and curing reaction initiated by an onium salt such as a triarylsulfonium salt of an epoxy resin occurs by a cation mechanism, and the cation reaction is inhibited by a trace amount of water and other impurities. Sufficient purification is required for smooth polymerization and curing reaction. However, according to the method of the present invention, commercially available 1,
4-dioxane can be used as it is without any particular purification. This is a great advantage of the present invention.

The photo cationic initiator used in the present invention, aryl diazonium salts ArN≡N ⁺ X ^-, (Ar: aryl group, X ^-: P
_{^{F 6 -, AsF 6 -,}} SbF 6 -, BF 4 -), such as methoxyphenyl diazonium hexafluorophosphate, diaryliodonium salts Ar ₂ I ⁺ X ^-, for example, diphenyliodonium hexafluorophosphate and bis (4-methyl Phenyl) iodonium hexafluoroantimonate and other triarylsulfonium salts Ar ₃ S ⁺ X ⁻ , such as triphenylsulfonium hexafluorophosphate, tris (4-methylphenyl) -sulfonium hexafluoroarsenate, and further bis [(4 There are well-known onium salts such as disulfonium salts such as -diphenylsulfonio) phenyl] sulfide-bis-hexafluorophosphate. The photocationic initiator is 0.05 to 8%, preferably 0.2 to 8% with respect to the amount of the epoxy resin.
An amount of 4% 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 as the thickness of the order of 1 cm,
For van de Graaf accelerator, Cockcroft-Walton accelerator with energy of 0.5 to 2 MeV, and for thickness of 1 mm or less, transformer type accelerator, 0.
As a thin film having an energy of 1 to 0.7 MeV and a film thickness of the order of 1 μm or less, a linear filament type accelerator of 0.1 to 0.3 MeV, 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.

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

Example 1 Epicoat 828 as a liquid epoxy resin (n = 0.1 in the above formula, molecular weight 380, manufactured by Yuka Shell Epoxy Co., Ltd.)
100 g, 1,4-dioxane (commercial grade, including stabilizer) 5
0 g and 2 g of triphenylsulfonium hexafluorophosphate as a photocation reaction initiator were mixed. Approximately 1 g of this resin mixture is approximately 1 mm thick in an aluminum frame measuring 7 cm x 1.5 cm
Casted on. At this time, the epoxy resin alone was viscous and poor in fluidity and could not be easily cast on an aluminum frame at room temperature of 25 ° C, but the resin solution having the above composition could be easily cast. Speed this
It was placed on a belt conveyor of 0.48 m / min and irradiated with an electron beam of 1.5 MeV, 50 μA from a van der Graaf accelerator for 18 Mrad. 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 110 ° C. The gel content calculated by gravimetric measurement was 90.9%.

The infrared spectrum of this cured product was measured by the KBr tablet method, and the absorption intensity corresponding to the methyl group at 2966 cm ^-1 and 2932 were measured.
Relative ratio to absorption intensity corresponding to methylene group at cm ^-1 D ₂₉₆₆ /
I asked for D ₂₉₃₂ . The cured product from the epoxy oligomer alone had a D ₂₉₆₆ / D ₂₉₃₂ of 1.13, whereas that of the cured product obtained in this example was 1.08, a decrease. That is, the relative amount of methylene groups in the cured product increased with respect to the methyl groups contained in the epoxy oligomer.

From the results of the infrared absorption spectrum and the gel content of the cured product, it can be seen that the epoxy oligomer and 1,4-dioxane are copolymerized. 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 ℃ is 1.1 × 10 ¹⁰ dyne /
It was cm ² .

Further, the thermal decomposition characteristics of this cured product were examined. 11 mg of the cured product was taken and heated at a temperature rising rate of 5 ° C./min in a nitrogen atmosphere to examine the weight change. The results in the following table were obtained by comparing the weight loss at each temperature with the cured product of epoxy oligomer alone.

As can be seen from Table 1, the stability of the cured product containing 1,4-dioxane to thermal decomposition was hardly impaired. The temperature at which the thermal decomposition rate becomes maximum is 409 ° C.
Met. It is clear that this is almost unchanged compared to 411 ° C. of the cured product from the epoxy oligomer alone.

For comparison, a liquid epoxy resin containing no 1,4-dioxane was subjected to an experiment of curing by electron beam irradiation by 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 the cured product of the epoxy resin containing 1,4-dioxane also showed almost the same hardness.

Further, for comparison, 1,4-dioxane containing only 2% by weight of a photocationic reaction initiator containing no epoxy resin was irradiated with an electron beam. In this case, in order to prevent the evaporation of 1,4-dioxane, a 1,4-dioxane liquid contained in an aluminum frame was coated with a 25 μm-thick polyester film. Since the electron beam energy is 1.5 MeV and the transparency is high, the effect of this coating on the irradiation dose is negligible. 18
No polymerization of 1,4-dioxane occurred after irradiation of Mrad. That is, it can be seen that 1,4-dioxane copolymerizes with the epoxy resin and solidifies only upon irradiation with radiation while mixing the epoxy resin and 1,4-dioxane.

Example 2 Curing reaction was carried out by irradiating under the same conditions as in Example 1 except that 12 g of 1,4-dioxane was added to 100 g of epoxy resin. The gel content of the irradiated product was 96.1%. The dynamic elastic modulus of the irradiated product was 1.2 × 10 ¹⁰ dyne / cm ² .

Example 3 The epoxy resin / 1,4-dioxane mixture was irradiated with an electron beam under exactly the same conditions as in Example 2 except that the irradiation dose was 6 Mrad. The gel content of the irradiated product was 91.6% and the dynamic elastic modulus of the irradiated product was 1.3 × 10 ¹⁰ dyne / cm ² .

Comparative Example 1 70 g of 1,4-dioxane to be added to 100 g of epoxy resin
Epoxy resin under exactly the same conditions as in Example 1 except that
The 1,4-dioxane mixture was irradiated with an electron beam. The gel content of the irradiation product is 88.7% and it is clear that 1,4-dioxane is copolymerized with the epoxy resin. However, this composition has a slower cure rate,
This composition is not preferred because the surface remains tacky and does not dry after irradiation with d.

Example 4 100 g of Epicoat 828, 30 g of 1,4-dioxane and 1 g of triphenylsulfonium hexafluorophosphate
Were mixed in the ratio. Put 20 g of this resin solution in a 50 ml Erlenmeyer flask, put a glass stopper in the presence of air and dose rate
Irradiation with γ rays of 1.5 × 10 ⁵ rad / h was performed for 20 hours, that is, 3 Mrad. The resin mixture solidified completely, so the flask was broken to remove the product. The gel fraction determined by acetone extraction of this irradiated product was 96.1%. The epoxy resin / 1,4-dioxane cured product did not melt at all even when heated to 300 ° C.

For comparison, a 1,4-dioxane solution containing 1% by weight of triphenylsulfonium hexafluorophosphate was irradiated with γ-rays under exactly the same conditions as above.
No polymerization of dioxane occurred. It is clear that polymerization of 1,4-dioxane does not occur at all even in the case of γ-ray irradiation when the epoxy resin does not coexist.

Example 5 100% Epicoat 834 [n = 1.0 in the above formula, manufactured by Yuka Shell Epoxy Co.] as a semi-solid liquid epoxy resin
A resin solution was prepared by mixing 50 g of 1,4, -dioxane and 2 g of diphenyliodonium hexafluoroantimonate. Thereafter, the aluminum frame was cast in the same manner as in Example 1, and the electron beam was irradiated with 18 Mrad under the same irradiation conditions as in Example 1. The gel fraction determined by the acetone extraction test was 95.2%. That is, it is understood that 1,4-dioxane is copolymerized with the cured product.

(Effects of the Invention) As described above, in the epoxy resin curing method according to the present invention, 1,4
-Up to 50 parts (by weight) of dioxane is added, and the epoxy resin is cured by irradiating it with radiation in the presence of a photocationic initiator, so that the epoxy resin can be easily removed at room temperature without removing the solvent. Can be cured.

Claims (3)

[Claims] 1. A method comprising adding up to 50 parts (weight basis) of 1,4-dioxane to 100 parts (weight basis) of a liquid epoxy resin, and irradiating with radiation in the presence of a photocationic reaction initiator. Method of curing epoxy resin. 2. The method for curing an epoxy resin according to claim 1, wherein the liquid epoxy resin is a bisphenol A type epoxy resin which is liquid at room temperature. 3. The method for curing an epoxy resin according to claim 1, wherein the photocationic reaction initiator is triphenylsulfonium hexafluorophosphate.