JP3415349B2 - Epoxy resin composition for composite materials - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an epoxy resin composition for composite materials, which is very stable at room temperature and hardens at a relatively low temperature (80 ° C.).

[0002]

2. Description of the Related Art Epoxy resins are used in a wide range of fields because they have excellent mechanical and electrical properties after curing.
For example, it is widely used as a sealant for electronic materials, paints / paving materials, and adhesives. In recent years, it has been used as a matrix resin for fiber-reinforced composite materials because of its excellent mechanical properties and heat resistance.

The properties required of such an epoxy resin are not only excellent in mechanical properties after curing, but also long-term stability at room temperature and handleability (low flow (flowability),
It is required to have appropriate tack and excellent drape property (flexibility) when formed into a sheet. In recent years, there has been an increasing demand for low temperature curing or short time curing in order to shorten the molding cycle and reduce the energy cost during molding.

In response to such demands, the temperature is from room temperature to 80 to 90
There are already some resins that cure at low temperatures of ° C. However, most of these are two-component resin compositions in which the main agent and the curing agent are mixed immediately before curing, the stability at room temperature after mixing the two components is poor, and their pot life is long and is on the order of several hours. is there. Moreover, the resin viscosity immediately after mixing is low, and the handling and working environment are poor. Further, as a one-component epoxy resin composition, JP-A-61-43616 discloses a combination of an epoxy resin with a dibasic acid dihydrazide compound, a urea compound and an alcohol-based or phenol-based compound having a melting point of 50 ° C. or higher. It is disclosed. Stability of these epoxy resin compositions at room temperature is 14 days or more,
Curing conditions of a relatively high temperature and a long time of 2 hours at 00 ° C. are required, and at a temperature of 90 ° C. or lower, it cannot be practically used because of insufficient curing.

Further, Japanese Patent Laid-Open No. 1-129084 discloses an epoxy resin, bisphenol A and bisphenol A.
There is disclosed a resin adhesive comprising a reaction product of the above-mentioned monoglycidyl ether and an imidazole compound which is a curing agent and a curing accelerator. 2 at 96 ° C of this resin composition
In addition to requiring high temperature and long time, the CFRP characteristics of this resin composition as a matrix resin are as follows: bending strength in fiber direction 130 kg / mm ² , elastic modulus 12 ton / m
m ² , interlayer shear strength of 7.6 kg / mm ² and current 120
It is lower than the CFRP properties that are generally used for general-purpose applications of ℃ curing. Further, this resin composition has a large viscosity increase during resin preparation, and it is difficult to form a hot melt film.

Recently, amine-adduct type and microcapsule type latent curing agents for epoxy resins are commercially available. If these latent curing agents are used, they are excellent in stability at room temperature and It is possible to prepare a one-part epoxy resin composition that cures at 80 ° C. However, when it is used as a matrix resin for prepreg (intermediate for composite materials), it is not only necessary to use one liquid, but it is important that it is easy to handle (tack and drape) as a prepreg. As a method of optimizing, a method of introducing a high molecular weight epoxy resin and adjusting the viscosity of the resin is generally used.

However, in the case of a material which cures at a relatively low temperature around 80 ° C., the introduction of a high molecular epoxy resin causes a decrease in the mobility of epoxy molecules at the curing temperature, resulting in a decrease in reactivity. This phenomenon is more remarkable when the curing agent is a catalyst type curing agent that accelerates the ring-opening polymerization reaction of the epoxy resin. That is, a composition comprising a relatively low-molecular-weight, for example, a bisphenol A type epoxy resin which is liquid at room temperature and a commercially available latent curing agent can be prepreg adjusted even if it is sufficiently cured at 80 ° C. for 1 hour. A composition in which a high molecular weight bisphenol A type epoxy resin that is solid at room temperature is introduced to a degree and the viscosity is adjusted does not cure at 80 ° C. for 1 hour, and in severe cases, it no longer cures at 80 ° C. It was

[0008]

DISCLOSURE OF THE INVENTION The present invention is keen on an epoxy resin composition for a composite material, which retains its handleability for 30 days or longer at room temperature and is cured at 80 ° C. for a short time until it has practically sufficient properties. As a result of examination, the present invention has been reached.

[0009]

The present invention relates to (A) oxa
An epoxy resin having a zolidone ring , (B) a bisphenol F type solid epoxy resin, (C) a urea curing agent, and (D) a latent curing catalyst that is stable at 40 ° C. and activates at a temperature of 80 ° C. or less are essential. As a component, weight ratio (A) /
The gist of the invention is an epoxy resin composition for composite materials, in which (B) is 2/8 to 7/3.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The constitution of the present invention will be described in detail below. The epoxy resin having an oxazolidone ring, which is the component (A) of the present invention, means an epoxy resin having a structure represented by the formula (1).

[0011]

[Chemical 1]

[0012]

[Chemical 2]

[0013]

[Chemical 3]

The epoxy resin having an oxazolidone ring as the component (A) is prepared by reacting an epoxy resin with an isocyanate compound in the presence of a catalyst for forming an oxazolidone group, as disclosed in JP-A-5-43655. A resin in which a stoichiometric amount of the oxazolidone ring, which is considered from the amount of the compound added, is introduced into the epoxy resin can be easily obtained. It is also possible to obtain the component (A) by introducing a glycidyl group after a compound having an oxazolidone ring is obtained by reacting a glycidyl compound with an isocyanate compound in the presence of a catalyst for forming an oxazolidone ring. is there.

Among the epoxy resins or glycidyl compounds that can be used here, the epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin,
Any commercially available epoxy resin such as bisphenol S type epoxy resin, phenol novolac type epoxy resin, and glycidyl amine type epoxy resin can be used, and can be appropriately used depending on the purpose. As the glycidyl compound,
Bisphenol A, bisphenol F, bisphenol S, bisphenol AD, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol S, glycidyl ethers obtained by glycidylating dihydric phenols such as dihydroxynaphthalene, and tris (glycidyloxy) such as bisphenol. Phenyl) alkanes, compounds obtained by glycidylating aminophenols, compounds obtained by glycidylating novolaks such as phenol novolac and cresol novolac, and edited by Hiroshi Kakiuchi [epoxy resin-recent progress-] published by Shodo, 1990.
Years) glycidyl compounds described in 21-46 and the like. These raw material glycidyl compounds may be used alone or in combination of two or more.

Further, in order to impart flame retardancy to the resin composition, at least one hydrogen of the above compounds may be halogenated.

Examples of raw material isocyanate compounds necessary for obtaining the component (A) include methane diisocyanate, butane-1,1-diisocyanate , and ethane.
Bifunctional organic isocyanate such as 1,2-diisocyanate, butane-1,2-diisocyanate, transvinylene diisocyanate, propane-1,3-diisocyanate, butane-1,4-diisocyanate Compounds, dimethyldiisocyanate, phenylmethyldiisocyanate, diphenyldiisocyanate, and other cyanide- based bifunctional isocyanate compounds, polymethylene polyphenyl isocyanate, triphenylmethane triisocyanate, tris (4-phenylisocyanate) Nato thiophosphate) -3,3 ′, 4,4′-diphenylmethane tetraisocyanate and other polyfunctional diisocyanate compounds, and dimers and 3 of the above isocyanate compounds.
Examples thereof include, but are not limited to, multimers such as polymers, block isocyanates masked with alcohol or phenol, and bisurethane compounds. Further, two or more kinds of isocyanate compounds may be used in combination.

The reaction for obtaining the component (A) can be carried out in the presence of an oxazolidone forming catalyst. This catalyst is preferably a catalyst that selectively forms an oxazolidone ring in the reaction between an epoxy group and an isocyanate.

As a catalyst for forming an oxazolidone ring, a lithium compound such as lithium chloride or butoxy lithium,
There are quaternary ammonium salts such as complex salts of boron trifluoride, tetramethylammonium chloride, tetraammonium bromide and tetraammonium iodide, and tertiary such as dimethylaminoethanol, triethylamine, tributylamine, benzylmethylamine and N-methylmorpholine. There are combinations of amines, phosphines such as triphenylphosphine, imidazoles, phosphonium compounds, triphenylantimony and iodine, and these may be used alone or in combination of two or more.

The oxazolidone group forming catalyst is 2
0 to 1000 ppm is preferable, but it can be appropriately used depending on the situation.

The number of epoxy groups per molecule of the component (A) is preferably 1.2 to 5 functional groups, more preferably 1.2 to 3 functional groups on average, and the epoxy equivalent is 180 to 5000 g / e.
It is preferably q. This is because when the epoxy equivalent is smaller than the predetermined value, the heat resistance and storage stability of the epoxy resin composition are inferior, and when the epoxy equivalent is larger than the predetermined value, mechanical properties and low temperature curability are deteriorated.

As the resin generally available as such resin, LSAC4016, 4023 manufactured by Asahi Ciba Co. can be exemplified.

By using an epoxy resin having an oxazolidone ring, which is the component (A), as the resin component, both excellent heat resistance and toughness of the matrix resin of the carbon fiber composite material can be achieved.

One of the important components of the present invention is to optimize the handling property (tack and drape property) (B).
A bisphenol F type solid epoxy resin is used as a component.

As described above, there is a method of adding a high molecular weight epoxy resin in order to optimize the handleability as a prepreg, but the reactivity decreases due to the decrease in mobility near the curing temperature of the resin composition. To do. However, as a result of diligent studies by the present inventor, it was found that the high molecular weight bisphenol F type solid epoxy resin can optimize the handleability of the prepreg without lowering the curing reactivity.

The bisphenol F type solid epoxy resin as the component (B) preferably has a softening point of 50 to 120 ° C. When the softening point is less than 50 ° C, the effective addition effect for optimizing the handleability of the prepreg is low. Softening point is 1
If the temperature exceeds 30 ° C, the drapability of the prepreg tends to be lost.

The bisphenol F type solid epoxy resin as the component (B) may be a commercially available product or may be prepared. As an adjusting method, a commercially available low-viscosity bisphenol F type epoxy resin is mixed with an appropriate amount of a curing agent such as dimethyldiphenylmethane or dimethyldiphenylsulfone, and the mixture is reacted. The softening point of the obtained bisphenol F type solid epoxy resin is adjusted by controlling the addition amount of the curing agent and the reaction.

Generally, commercially available products include the E4001p series manufactured by Yuka Shell Epoxy Co., Ltd. However, the component (B) is not limited to these.

The epoxy resin composition of the present invention is (A) /
It is necessary that the weight ratio of (B) is in the range of 2/8 to 7/3. Outside of this range, it is difficult to cure under the curing conditions of 80 ° C. for 1 hour, and even if cured, the heat resistance and CF
As a result, the balance of the adhesiveness with and becomes poor, and the strength in the non-fiber direction becomes low.

Further, other epoxy resins and the like can be added to the epoxy resin composition of the present invention within the range where the components (A) and (B) satisfy the above conditions.
Epoxy resins that can be added include glycidyl ether-based epoxy resins, bisphenol A-type, bisphenol F-type epoxy resins, cycloaliphatic epoxy resins, glycidyl ester-based epoxy resins, glycidylamine-based epoxy resins, and heterocyclic epoxy resins, Examples thereof include, but are not limited to, epoxy resins having a saturated or unsaturated alkyl skeleton and epoxy resins modified with these.

In addition to the epoxy resin, a thermoplastic polymer, silica, a pigment, a rubber-like substance or the like may be added if necessary.

The third important component of the present invention is the combined use of a urea curing agent as a curing component and a latent curing catalyst which is stable at 40 ° C. and activates at a temperature of 80 ° C. or lower. As the urea resin curing agent, the following structural formula (4),
The curing agent for the epoxy resin as shown in (5) can be exemplified.

[0033]

[Chemical 4]

[0034]

[Chemical 5]

As the latent curing agent which is stable at 40 ° C. and is activated at a temperature of 80 ° C. or less, 40 of the latent curing agents such as microcapsule type and amine adduct type are used.
A material that is stable at 0 ° C and that activates at a temperature of 80 ° C or lower is used. Among these, it is particularly preferable that the curing catalyst is a latent curing agent for microcapsules.

A commercially available latent curing agent that meets these conditions alone is PN of Ajinomoto Co., Inc.
-23, HX-3721, HX-372 of Asahi Kasei Corporation
2, H3615,4003,4070 of ACR company can be illustrated. These may be used alone or in combination of two or more.

As long as it is simply cured at 80 ° C., the latent curing catalyst can be used alone as long as it is used in an amount compatible with the epoxy equivalent. Does not provide sufficient strength. On the other hand, when a urea curing agent is used in combination, sufficient physical properties of the composite material, particularly excellent bending strength in the non-fiber direction, can be obtained with a smaller amount of the curing agent. The mechanism of this combined use effect has not been fully clarified yet, but it is presumed that the crosslinked structure formed by the combined use of the curing agent is different from the case of using the latent catalyst alone.

The compounding ratio of these curing agents is as follows.
(C) / based on the total weight of components (A) and (B)
((A) + (B)) is 2/98 to 15/85, (D) /
((A) + (B)) is preferably 3/97 to 20/80. If the amount used is less than this range, the curing reaction does not proceed sufficiently when it is cured at 80 ° C., and the adhesive strength tends not to be obtained. , Storage stability, adhesive strength is reduced,
Not preferable.

A more preferable amount of the curing agent system is
(C) / based on the total weight of components (A) and (B)
((A) + (B)) is 5/95 to 10/90, (D) /
((A) + (B)) is 5/95 to 15/85.

Further, a promoter may be added to the above epoxy resin curing agent system. Particularly, the bisphenol type amine compound can accelerate the curing reaction when used in combination with the latent curing agent. Examples of amine compounds that can be used as a cocatalyst include aromatic diamines such as metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and diaminodiethyldiphenylmethane, but are not limited thereto.

The present invention will be described in more detail with reference to the following examples. Abbreviations and test methods shown in Examples and Comparative Examples are as follows. The curing molding conditions for the resin and the composite material were 80 ° C. for 1 hour in all of the examples and comparative examples.

LSAC-4016: epoxy resin having oxazolidone ring, epoxy equivalent = 338 g / eq,
Softening point = 76 ° C. (Asahi Chiba) Ep828: Epicoat 828 bisphenol A type epoxy resin, 120 poise (Oilized Shell Epoxy Co., Ltd.) Ep807: Epicoat 807 bisphenol F type epoxy resin, 30 poise (Oilized Shell Epoxy Co., Ltd.) Ep1001 : Epikote 1001 Bisphenol A
Type solid epoxy resin, softening point = 64 ° C., epoxy equivalent =
450 g / eq (Okaka Shell Epoxy Co., Ltd.) E4001p: Epicoat 4001 Bisphenol F
Type solid epoxy resin, softening point = 60 ° C., epoxy equivalent =
450 g / eq (Okaka Shell Epoxy Co., Ltd.) E4005p: Epicoat 4005 Bisphenol F
Type solid epoxy resin, softening point = 90 ° C., epoxy equivalent =
1100 g / eq (Okaka Shell Epoxy Co., Ltd.) PN23: Amine adduct type latent hardener (Ajinomoto Co., Inc.) HX-3722: Microcapsule type latent hardener (Novacure, Asahi Kasei Corp.) DCMU: Dichlorophenyl -N, N-dimethylurea PDMU: phenyl-N, N-dimethylurea

(Bending Test and Interlaminar Shear Test of Composite Material) A test piece having the following shape was cut out from the molded composite material, and each test was performed using Tensilon manufactured by Orientec at the following L / D. Sample shape and L / D (distance between supporting points / thickness): Composite material fiber direction bending test: 120 mm length × 10 mm width × 2 mm thickness L / D = 4
0 Composite material non-fiber direction bending test: 60 mm length × 10 mm width × 2 mm thickness L / D = 16 Interlaminar shear strength: 30 mm length × 10 mm width × 4 mm thickness L / D = 4 Indenter tip radius: 3.2 mm CROSS HEAD SPEED: 2 mm / min

(Tg (glass transition temperature)) 60 mm long
A dynamic viscoelasticity measuring device RDA-700 manufactured by Rheometrics Co., Ltd. was used as a test piece composed only of a resin of 12 mm width and 2 mm thickness.
10 rad / s while heating at 5 ° C / SETP
The storage modulus G'was measured by ec. Obtained temperature-G '
Draw a tangent line to G'in the glass state region of the curve of
A tangent line was drawn in the transition region in which the value of Tg changed greatly, and the intersection of both tangent lines was taken as Tg.

(Viscosity measurement) Using a dynamic viscoelasticity measuring instrument RDA-700 manufactured by Rheometrics,
Frequency 10 rad using mmφ Disk Plate
The viscosity was measured in / sec.

(Resin Life Measurement) The prepared resin was placed in a constant temperature dryer at 30 ° C. and subjected to heat history, and the viscosity at 30 ° C. of the resin after a lapse of a predetermined number of days was measured by the above-mentioned viscosity measuring method to obtain an initial viscosity of 2 The number of days elapsed when the viscosity doubled was defined as the resin life.

(Examples 1 to 4 and Comparative Examples 1 and 2) As the component (A), an epoxy resin (semi-solid oxazolidone ring) having an epoxy equivalent of 240 g / eq according to the method described in JP-A-5-43655 ( A-1) was obtained. Table 1
The resin components (numerical values are parts by weight) shown in FIG. 2 are melt-mixed at 130 ° C.
The components were mixed at 60 ° C. to obtain a resin composition.

A unidirectional prepreg was produced from the resin composition and carbon fiber (Pyrofil TR-40 manufactured by Mitsubishi Rayon Co., Ltd.) by a hot melt method. The carbon fiber basis weight of the prepreg was 150 g / m ² , and Vf (carbon fiber volume fraction) was 40%. This prepreg is about 2 in one direction
It was laminated to have a thickness of mm and was formed by a vacuum bag forming method. The bending strength and the interlaminar shear strength of the obtained unidirectional composite material in the fiber direction of 0 ° and the non-fiber direction of 90 ° were measured. The results are also shown in Table 2.

(Examples 5 to 10 and Comparative Examples 3 to 6) Asahi Ciba Co., Ltd. LSAC-4016 was used as the component (A), and the resin composition shown in Table 1 was used. A directional prepreg and a composite material were prepared, molded, and similarly tested. The results are shown in Table 1.

[0050]

[Table 1]

[0051]

The epoxy resin composition for composite materials of the present invention retains its handleability for 30 days or longer at room temperature and has practically sufficient properties in a short time even when cured at 80 ° C.

Continuation of front page (56) Reference JP-A-8-59793 (JP, A) JP-A-5-222160 (JP, A) JP-A-5-43655 (JP, A) JP-A-59-135265 (JP , A) JP-A-9-71634 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08G 59/00-59/72 C08G 18/58 C08J 5/24

Claims (6)

(57) [Claims] 1. An epoxy resin having (A) an oxazolidone ring , (B) a bisphenol F type solid epoxy resin,
(C) urea-based curing agent and (D) stable at 40 ° C.,
An epoxy resin composition for a composite material, which contains a latent curing catalyst that is activated at a temperature of 80 ° C. or lower as an essential component and has a weight ratio (A) / (B) of 2/8 to 7/3. 2. The weight ratio (C) / ((A) + (B)) is 2
/ 98 to 15/85, (D) / ((A) + (B)) is 3
It is / 97-20 / 80, The epoxy resin composition for composite materials of Claim 1. 3. An epo having an oxazolidone ring of (A)
Epoxy equivalent of xy resin is 180-5000g / eq
A set of epoxy resin for composite material according to claim 1 or 2.
A product. 4. The temperature of (D) which is stable at 40 ° C. and is not higher than 80 ° C.
The latent curing catalyst that activates with time
Any of claims 1 to 3, characterized in that it is a resident curing agent.
The epoxy resin composition according to item 1. 5. The bisphenol F type solid epoxy of (B)
The softening point of the resin is 50 to 120 ° C.
The resin composition according to any one of claims 1 to 4. 6. The curing agent of (C) is phenyl-N, N-di
Methyl urea according to any one of claims 1 to 5.
Resin composition.