JP4859081B2 - Manufacturing method of composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an epoxy resin composition which is stable at room temperature, can be primarily cured at a relatively low temperature, e.g. at 70-100 deg.C, in a short time, e.g. within 10 h, exhibits a glass transition temperature of 150 deg.C or higher when secondarily cured at 130 deg.C or higher, and gives a cured item excellent in high-temperature mechanical properties, especially an epoxy resin composition which can be suitably used as a matrix resin for a fiber- reinforced composite material. SOLUTION: This composition mainly comprises (a) 100 pts.wt. epoxy resin containing a trifunctional or higher epoxy resin and (b) 3-40 pts.wt. heat-curing- type latent curing agent activated at 70-100 deg.C and satisfies the requirements (1) to (3): (1) the viscosity increase when left standing at 25 deg.C for 3 weeks after the preparation is not higher than 2 times the viscosity just after the preparation; (2) after the primary curing at 100 deg.C or lower for 10 h or shorter, the degree of curing is 70% or higher or the tensile shear strength (adhesive strength) according to JIS K 6848 and 6850 is 10 MPa or higher; and (3) the glass transition temperature of a cured item obtained by the secondary curing at 130 deg.C or higher is 150 deg.C or higher.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an epoxy resin composition that can be primary-cured in a short time at a temperature of 100 ° C. or lower, and then secondarily cured at a temperature higher than the primary curing temperature to obtain a cured product having high heat resistance.
[0002]
[Prior art]
Fiber reinforced composite materials (hereinafter referred to as FRP) have been widely used from sports leisure to aircraft and industrial applications. As a general FRP molding method, there is a method of molding using a molding die. For example, a reinforcing fiber material such as cloth is attached to the mold while impregnating the resin, and this is repeated, then cured, and removed from the mold to obtain a molded product, or the resin is applied to the reinforcing fiber material in advance. A so-called impregnated prepreg is affixed to the mold, and then repeatedly cured, and then a hand lay-up method in which the molded product is obtained by demolding from the mold, and a reinforcing fiber material such as cloth is set in the mold, Resin molding (RTM) method, in which a resin is injected into a mold and cured, and then demolded to obtain a molded product, or a molding compound mixed with a resin is cut into reinforcing fibers, and the molding compound is mixed with the resin and cured. Thus, a method for obtaining a molded product is known.
[0003]
Molds of various materials are used. Metal molds are excellent in heat resistance and durability, but are expensive because they require labor and labor to produce the mold. On the other hand, a resin mold is inferior in heat resistance and durability, but is inexpensive. In order to respond to various needs in recent years, the production of a small variety of products has been increasing, and there are many cases in which a resin mold is used. However, when a resin mold is used, the heat resistance of the mold itself is not sufficient, so it is difficult to mold FRP at a high temperature using this mold, and it cannot be applied to molding a molded product with high heat resistance. There is a problem.
[0004]
In the case of manufacturing a mold made of FRP, a master mold is made from the actual product, and a prepreg or the like is laminated on the master mold and cured to prepare an FRP mold. In order to obtain a molded product having high heat resistance. Needs to be molded at a high temperature, and requires an FRP mold having high heat resistance. In order to mold an FRP mold having high heat resistance, the master mold is also required to have heat resistance. As a result, the production of the master mold has so far required a great deal of cost and labor.
[0005]
Therefore, as a method of obtaining an FRP molded product having high heat resistance using a resin mold or the like having low heat resistance, primary molding is performed at a relatively low temperature (100 ° C. or less) using a resin mold or the like having low heat resistance. Cured and can be removed from the mold, and cured enough to retain the shape, then removed from the mold and left to heat at a higher temperature for secondary curing to produce a highly heat-resistant FRP molded product. Attention has been focused on how to obtain. The same applies when an FRP mold having a high heat resistance is produced using a master mold having a low heat resistance.
[0006]
In recent years, a technique of a resin that is relatively stable at room temperature and is cured at a relatively low temperature of 70 to 100 ° C. has been disclosed in, for example, Japanese Patent Application Laid-Open No. 11-302212. Although mechanical properties can be obtained, sufficient heat resistance cannot be obtained even after secondary curing at a high temperature.
On the other hand, a resin that gives a cured product having good heat resistance has a problem that it takes a long time to be cured before it can be demolded by curing at a relatively low temperature of 100 ° C. or lower.
[0007]
[Problems to be solved by the invention]
A cured product that is stable at room temperature and can be primary-cured in a relatively short time (within 10 hours) at a relatively low temperature (less than 100 ° C) and highly heat-resistant by secondary curing at a high temperature (over 130 ° C) (Tg of 150 ° C) The above is to provide an epoxy resin composition having excellent mechanical properties at high temperatures, and particularly to provide an epoxy resin composition that can be used as a matrix resin for fiber-reinforced composite materials.
[0008]
[Means for Solving the Problems]
That is, the gist of the present invention is as follows.
(A) An epoxy resin composition comprising as a main component 100 parts by weight of an epoxy resin containing a tri- or higher functional epoxy resin and (b) 3 to 40 parts by weight of a thermosetting latent curing agent activated at 70 to 100 ° C. The prepreg obtained by impregnating the reinforcing fiber material with the epoxy resin composition satisfying the following (1) to (3) is first cured in a vacuum bag at a temperature of 100 ° C. or lower, and then 130 to 180 ° C. This is a method of forming a composite material that is secondarily cured in a free-standing state in a hot air oven.
(1) After the preparation, the viscosity increase after standing at 25 ° C. for 3 weeks is 2 times or less immediately after the preparation.
(2) The primary curing at 100 ° C. for 5 hours has a curing degree of 70% or more or a tensile shear strength (adhesion strength) in accordance with JIS-K-6848 and 6850 of 10 MPa or more.
(3) The glass transition temperature of the cured product by secondary curing at 130 ° C. or higher is 150 ° C. or higher.
[0009]
In particular, the epoxy resin containing a trifunctional or higher functional epoxy resin of component (a) is an epoxy resin containing a novolac type epoxy resin of structural formula (1) and / or tetraglycidyldiaminodiphenylmethane, and 70 to 70 of component (b) It is preferable to use an epoxy resin composition which is an amine adduct type or microcapsule type latent curing agent as a heat curing type latent curing agent activated at 100 ° C.
[0010]
The epoxy resin composition of the present invention is excellent in stability at room temperature and is cured to such an extent that it can be demolded by primary curing within 10 hours at a temperature of 100 ° C. or lower. If it is within 5 hours at a temperature of 100 ° C. or lower, the molding cycle can be shortened, which is more preferable.
[0011]
“Stable at room temperature” means that the viscosity increase after leaving the resin at 25 ° C. for 3 weeks is not more than twice that immediately after preparation. When the increase in viscosity after standing at 25 ° C. for 3 weeks is 1.5 times or less, the working life is further increased, which is more preferable. The viscosity increase rate is derived by the following method. The viscosity ηi of the resin immediately after preparation at 40 ° C. is measured with a parallel plate using a DSR-200 manufactured by Rheometric Co. or an apparatus having equivalent performance at a frequency of 10 radians / second. Next, the resin is allowed to stand in a thermostat at 25 ° C. for 3 weeks, and thereafter the viscosity η at 40 ° C. is measured in the same manner, and the viscosity increase ratio is determined by η / ηi.
[0012]
Curing to the extent that it can be demolded by primary curing means that the curing heat value (Ei) of the resin immediately after resin preparation and the curing heat value (E1) of the first cured resin are measured with a differential scanning calorimeter (DSC), respectively. And
Curing degree (%) = (Ei−E1) / Ei × 100
The degree of cure can be obtained by the above, and one indication can be that this degree of cure is 70% or more.
[0013]
Alternatively, it can be used as an index that the tensile shear strength (adhesive strength) obtained by the method defined in JIS-K-6848, 6850 of the primary cured resin is 10 MPa or more.
[0014]
As a measurement sample, first, a 12.5 mm lap portion of a 25 × 100 × 1.5 mm aluminum plate (A2024P defined in JIS H4000) is polished with sandpaper (# 240) and degreased with acetone. Next, the resin is uniformly applied to the lap portion, and the lap portions of the aluminum plate processed in the same manner are overlapped. Finally, it is fixed at a pressure of 1 kgf / cm ² and first hardened, and then slowly cooled to room temperature.
[0015]
Furthermore, the epoxy resin composition of the present invention is obtained by secondary curing to obtain a molded product having high heat resistance. The cured product obtained by secondary curing at a curing temperature of 130 ° C. or higher has a glass transition temperature of 150 ° C. or higher. There is something. In particular, when the glass transition temperature is 180 ° C. or higher by secondary curing at 150 ° C. or higher (for example, 180 ° C.), it is preferable because the heat resistance is further improved. The time for secondary curing is not particularly limited, but is preferably within 10 hours, and more preferably within 5 hours.
[0016]
The glass transition temperature of the cured product is measured by the following method.
Using a Rheometric RDA-700 or a viscoelasticity measuring device having equivalent performance, the storage elastic modulus (G ′) when the temperature is increased stepwise is measured at each temperature. The temperature is raised at 5 ° C./step. In each step, the temperature is held for 1 minute after the temperature is stabilized and then measured. The frequency is measured at 10 radians / second. The logarithmic value of G ′ is plotted against the temperature, and the temperature at the intersection of each tangent of the obtained G ′ curve is defined as the glass transition temperature. (See Figure 1)
[0017]
In the epoxy resin composition of the present invention, an epoxy resin containing a trifunctional or higher functional epoxy resin is used as the component (a). Thus, a molded cured product having excellent heat resistance after secondary curing can be obtained. In particular, it is more preferable that the component (a) contains a trifunctional or higher functional epoxy resin in an amount of 40 wt% or more, more preferably 60 wt% or more. Examples of such a tri- or higher functional epoxy resin include tetraglycidyl diaminodiphenylmethane, aminophenol type epoxy resin, aminocresol type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, and an epoxy represented by the following structural formula (1). Resin etc. can be illustrated.
[0018]
[Chemical formula 2]
[0019]
In the structural formula, n is an integer of 0 or more.
[0020]
In particular, a novolac-type epoxy resin represented by the structural formula (1) and / or an epoxy resin containing tetraglycidyldiaminodiphenylmethane can be preferably used.
In addition, a trifunctional epoxy resin may be included, and examples thereof include a bisphenol type epoxy resin, a hydrogenated bisphenol type epoxy resin, a biphenol type epoxy resin, and a naphthalene diol type epoxy resin. If you want to ensure heat resistance as much as possible, even if you use epoxy with a relatively rigid skeleton structure such as biphenol type epoxy resin, naphthalene diol type epoxy resin, etc., even if it is less than trifunctional epoxy resin, it will bring good results it can.
[0021]
The use of, for example, a bisphenol S-type epoxy resin having an SO ₂ structure or a pre-reacted product of an aromatic diamine and a bisphenol-type epoxy resin is preferable because there is a merit that a cured product having relatively high heat resistance and toughness can be obtained.
[0022]
As the thermosetting latent curing agent that is activated at 70 to 100 ° C. as the component (b), a cyano compound such as dicyandiamide, or a combination system of a cyano compound and a urea compound such as dichlorophenyldimethylurea or phenyldimethylurea is used. Other examples include amine adduct type curing agents. Amine adduct-type curing agents are commercially available from Ajinomoto Co., Inc. under the trademark “Amicure”, and examples thereof include Amicure PN-23 and MY-24.
[0023]
Further, a microcapsule type curing agent is mentioned and is commercially available from Asahi Ciba Co., Ltd. under the trademark “Novacure”. For example, NovaCure HX3721 and HX3722 can be mentioned.
[0024]
Further, as those having an active hydrogen part and a catalytic site in the molecule, Fuji Cure FXE-1000, FXR-1030 manufactured by Fuji Kasei Kogyo Co., Ltd., ACR Hardener H-3615 manufactured by AC R Corporation, H-4070, H-3293, H-3366, H-3849, H-3670, Cure Duct P-0505, Curesol 2E4MZ-CNS, C11Z-CNS, C11Z-A, etc. manufactured by Shikoku Kasei Kogyo Co., Ltd. It can be illustrated.
[0025]
Even if the amine adduct type curing agent and the microcapsule type curing agent are mixed with an epoxy resin, they are relatively stable at room temperature to 50 ° C. and hardly react, but are activated at 70 to 100 ° C. and the reaction starts. It can be particularly preferably used.
[0026]
The amount of these latent curing agents added is suitably 3 to 40 parts by weight with respect to 100 parts by weight of the epoxy resin of component (a), and if the amount is less than 3 parts by weight, the primary curing is insufficient. If the amount exceeds 40 parts by weight, the stability of the resin at room temperature decreases, which is not preferable.
[0027]
These latent curing agents may be used alone, or these latent curing agents may be used in combination with a urea compound, a cyano compound, a dihydrazide compound, an acid anhydride, and the like.
In particular, an aromatic urea compound is preferable, and a compound represented by the following structural formula (2) is preferable.
[0028]
[Chemical 3]
[0029]
X1 and X2 represent H or Cl and may be the same or different.
[0030]
Moreover, an additive can be added to the epoxy resin composition of the present invention within a range that does not impair the characteristics of the present invention. For example, it is preferable to add a thermoplastic resin after dissolving it so that the stickiness of the resin can be suppressed, the tack of the prepreg can be adjusted to an appropriate level, or the tack can be prevented from changing over time. Examples of such thermoplastic resins include phenoxy resin, polyvinyl formal, polyethersulfone, and the like.
[0031]
In addition, for the purpose of improving the toughness of the cured product, a particulate or short fiber thermoplastic resin or a rubber component may be added. As an additive, a thermoplastic resin such as polyamide, polyimide, polyurethane, polyethersulfone, etc. Examples thereof include rubber components such as acrylic rubber, butadiene rubber and butyl rubber, and molecular end-modified products thereof. Furthermore, fine particles of inorganic components such as metals such as talc, silica and steel may be added for the purpose of improving the rigidity of the cured product.
[0032]
The use of the epoxy resin composition of the present invention is not particularly limited and can be used anywhere as long as the characteristics of the epoxy resin composition can be utilized, but is suitable as a matrix resin for fiber-reinforced composite materials. Can be used for In this case, the reinforcing fiber is not particularly limited, and any carbon fiber, glass fiber, high-strength organic fiber, metal fiber, inorganic fiber, or the like generally used as a reinforcing fiber for a fiber-reinforced composite material can be used.
[0033]
In particular, when the viscosity at 60 ° C. is 10 Pa · sec or more and 700 Pa · sec or less in the epoxy resin composition of the present invention, a matrix resin for so-called prepreg in which a reinforcing fiber is impregnated with a matrix resin to form a sheet. It can be used suitably.
[0034]
When the viscosity at 60 ° C. is less than 10 Pa · sec, tackiness and stickiness of the prepreg become too strong, which is not preferable. On the other hand, when the viscosity at 60 ° C. exceeds 700 Pa · sec, the prepreg drapability is poor and becomes too hard, which is not preferable. More preferably, the matrix resin for prepreg has a viscosity at 60 ° C. in the range of 30 Pa · sec to 500 Pa · sec. The method for measuring the viscosity is as described above except that the measurement temperature is 60 ° C.
[0035]
Further, if it is made into a film and the resin flow is suppressed and set to the eye, or glass cloth or the like is impregnated with resin, it can be used as a sheet-like adhesive. Furthermore, it is possible to add a microballoon or a foaming agent as an additive and use it as a light weight auxiliary material.
[0036]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
Abbreviations of compounds in Examples and Comparative Examples are as follows.
[0037]
Ep604: Tetraglycidyldiaminodiphenylmethane “Epicoat 604” manufactured by Yuka Shell
Tactix 742: manufactured by Dow Chemical Co., solid trifunctional epoxy resin “TACTIX 742”, structural formula (1), n = 0, epoxy resin Ep 1032: Yuka Shell, special novolac type epoxy resin “Epicoat 1032S50” structural formula (1) Epoxy Resin N740: Phenol Novolac Epoxy Resin “Epicron N-740” manufactured by Dainippon Ink
Ep828: Yuka Shell Co., Ltd., liquid bisphenol A type epoxy resin “Epicoat 828”
Ep1001: Semi-solid bisphenol A type epoxy resin “Epicoat 1001” manufactured by Yuka Shell
EXA1514: Dainippon Ink & Chemicals, bisphenol S type epoxy resin “Epiclon EXA-1514”
HX3722: Asahi Ciba Co., Ltd., latent curing agent "Novacure HX3722"
FXE1000: manufactured by Fuji Kasei Co., Ltd., latent curing agent “Fujicure FXE-1000”
PN23: latent curing agent “Amicure PN-23” manufactured by Ajinomoto Co., Inc.
Dicy: Dicyandiamide “Dicy7” manufactured by Yuka Shell
PDMU: PhT dimethylurea “OMICURE 94” manufactured by BTR Japan
PES: manufactured by Sumitomo Chemical Co., Ltd., polyethersulfone "Sumika Excel PES 3600P"
DDS: Diaminodiphenyl sulfone “Seika Cure S” manufactured by Wakayama Seika Co., Ltd.
Aerosil 300: “Aerosil 300” manufactured by Nippon Aerosil Co., Ltd.
BF3MEA: Boron trifluoride monomethylamine manufactured by Hashimoto Kasei Kogyo Co., Ltd.
(Examples 1 to 11)
First, component (a) was uniformly mixed at 150 ° C. with the compositions shown in Tables 1 and 2 (numerical values are parts by weight). When there was an additive such as a thermoplastic resin, it was added at this time and dissolved or mixed. Next, it cooled to 50-60 degreeC, the component (b) was added, and it mixed uniformly, and prepared the epoxy resin composition of this invention. The stability of the resin composition was evaluated by the method described above.
[0039]
The resin composition was heated to 60 ° C., casted onto a glass plate having been subjected to a release treatment with a thickness of 2 mm, sandwiched between glass plates having been subjected to the same treatment, and cured under each primary curing condition. The degree of cure after primary curing was measured by the method described above. On the other hand, the tensile shear strength (adhesion strength) of the resin after primary curing was measured by the method described above.
[0040]
Furthermore, it hardened | cured in the hot stove with the free stand on each secondary hardening condition, and measured the glass transition temperature by the method mentioned above after that. Furthermore, the value of G ′ at high temperatures (150 ° C. and 180 ° C.) was determined as a standard for developing the physical properties of the resin at high temperatures. This is a measure of the physical properties at a high temperature when a composite material is used.
[0041]
(Comparative Example 1)
DDS was dissolved and mixed in Ep604 at 130 ° C. with the composition shown in Table 3, and the temperature was immediately lowered to 70 ° C., and BF3MEA was dissolved and mixed to prepare a resin composition.
The resin composition is stable at room temperature, and has a good heat resistance at a glass transition temperature of 205 ° C. when cured at 180 ° C. for 2 hours. However, in the primary curing at 100 ° C. × 10 hours, The curing was poor.
[0042]
(Comparative Example 2)
Ep828 and Ep1001 having the compositions shown in Table 3 were uniformly mixed at 120 ° C. Thereafter, HX3722 and PDMU were mixed at 60 ° C. to obtain a resin composition.
In the same manner as in Example 1, the resin and the resin plate were evaluated. The evaluation results are shown in Table 3. After secondary curing, it did not have sufficient heat resistance.
[0043]
(Comparative Example 3)
Ep1032, Ep828, and Ep1001 having the compositions shown in Table 3 were uniformly mixed at 120 ° C. Thereafter, PDMU and Dicy were added at 70 ° C. and dispersed and mixed.
In the same manner as in Example 1, the resin and the resin plate were evaluated. The evaluation results are shown in Table 3. After secondary curing, it did not have sufficient heat resistance.
[0044]
(Examples 12 and 13)
Resin compositions were prepared in the same manner as in Examples 2 and 5, respectively. The resin viscosities at 60 ° C. were 80 Pa · sec and 40 Pa · sec, respectively.
These resin compositions were uniformly coated on a release process paper at 60 ° C. to prepare resin films having a basis weight of 80 g / m ² . Next, carbon fiber TR50S-12L manufactured by Mitsubishi Rayon Co., Ltd. is aligned and aligned in one direction so that the carbon fiber basis weight is 150 g / m ² on the resin film. To obtain unidirectional prepregs. These prepregs had good tack and drape properties.
[0045]
These prepregs were allowed to stand at 25 ° C. for 3 weeks, and the prepreg tack and drape properties were evaluated by tactile sensation. Tack even after 3 weeks. There was little change in drapability and the product had a good life.
[0046]
14 plies of these prepregs were laminated in one direction, and were primarily cured by vacuum bag molding. As temperature conditions for primary curing, the temperature was raised from room temperature to 100 ° C. over 1 hour and left at 100 ° C. for 4 hours. After the primary curing, the molded plate was sufficiently cured to such an extent that it could be removed from the mold and not to crack even when cut with a diamond wet cutter. When G ′ was measured and the glass transition temperature was measured, they were 115 ° C. and 102 ° C., respectively. The primary molded plate was further left in a hot air oven (free stand) to perform secondary curing. The temperature condition of the secondary curing was such that the temperature was raised from room temperature to 180 ° C. in 3 hours, maintained at 180 ° C. for 4 hours, and further cooled to room temperature over 3 hours. When ultrasonic flaw detection was performed on the obtained cured molded plate having a thickness of about 2 mm, there were almost no voids in the former and some voids were observed in the latter, but these prepregs had good moldability. I understood. When the test body was cut out from the cured plate and G ′ was measured to measure the glass transition temperature, they were 185 ° C. and 186 ° C., respectively. Interlaminar shear strength was measured at room temperature (23 ° C.), 100 ° C., 160 ° C., and 180 ° C. in accordance with ASTM D 2344. The results are shown in Table 4.
[0047]
[Table 1]
[0048]
[Table 2]
[0049]
[Table 3]
[0050]
[Table 4]
【Effect of the invention】
The epoxy resin composition of the present invention is stable at room temperature, can be primary-cured in a relatively short time (within 10 hours) at a relatively low temperature of 100 ° C. or lower (70 to 100 ° C.), and high temperature higher than the primary curing temperature The cured product obtained by secondary curing at (130 ° C. or higher) has a high glass transition temperature (150 ° C. or higher) and is excellent in mechanical properties at high temperatures. In particular, it can be suitably used as a matrix resin for fiber-reinforced composite materials in applications requiring heat resistance.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the relationship between temperature and storage modulus.
[Explanation of symbols]
G ': storage elastic modulus

Claims (4)

(A) An epoxy resin composition comprising as a main component 100 parts by weight of an epoxy resin containing a tri- or higher functional epoxy resin and (b) 3 to 40 parts by weight of a thermosetting latent curing agent activated at 70 to 100 ° C. The prepreg obtained by impregnating the reinforcing fiber material with the epoxy resin composition satisfying the following (1) to (3) is first cured in a vacuum bag at a temperature of 100 ° C. or lower, and then 130 to 180 ° C. A method of forming a composite material, which is secondarily cured in a free-standing state in a hot air oven.
(1) After the preparation, the viscosity increase after standing at 25 ° C. for 3 weeks is 2 times or less immediately after the preparation.
(2) The primary curing at 100 ° C. for 5 hours has a curing degree of 70% or more or a tensile shear strength (adhesion strength) in accordance with JIS-K-6848 and 6850 of 10 MPa or more.
(3) The glass transition temperature of the cured product by secondary curing at 130 ° C. or higher is 150 ° C. or higher. The molding of the composite material according to claim 1, wherein the epoxy resin containing a trifunctional or higher functional epoxy resin of the component (a) is a novolac type epoxy resin of the following structural formula (1) and / or an epoxy resin containing tetraglycidyldiaminodiphenylmethane. Method.
In the structural formula, n is an integer of 0 or more.   The method for molding a composite material according to claim 1, wherein the latent curing agent of component (b) is an amine adduct type latent curing agent.   The method for molding a composite material according to claim 1, wherein the latent curing agent of component (b) is a microcapsule type latent curing agent.