JP2003071856A - Rtm method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the condition of an RTM (resin transfer molding) method suitable for manufacturing a fiber reinforced composite material excellent in heat resistance and mechanical physical properties with good productivity. SOLUTION: In the RTM method, a thermosetting resin is injected in a mold having a reinforcing fiber substrate arranged therein and held to a temperature Tm of 60-90 deg.C from a container of which the temperature is held to a range of (Tm-20) to (Tm+10) deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for producing a fiber-reinforced composite material which is preferably used for aircraft members, spacecraft members, automobile members, ship members and the like.

[0002]

2. Description of the Related Art Fiber-reinforced composite materials composed of reinforcing fibers such as glass fibers, carbon fibers and aramid fibers and matrix resins such as unsaturated polyester resins, vinyl ester resins, epoxy resins, phenol resins, cyanate resins and bismaleimide resins are known as Although it is lightweight, it has excellent mechanical properties such as strength, rigidity and impact resistance,
It has been applied to numerous fields such as spacecraft components, artificial satellite components, automobile components, railway vehicle components, ship components, and sports equipment components.

For the production of these fiber-reinforced composite materials, a method has been widely used in which a prepreg, which is an intermediate body composed of carbon fibers and an uncured epoxy resin, is prepared, laminated and heat-cured.

However, this method is not necessarily excellent in productivity because an intermediate called prepreg must be produced.

On the other hand, a liquid thermosetting resin is injected into a mold in which a reinforcing fiber base material is installed and heat-cured to obtain a fiber-reinforced composite material.
(Molding) has recently been attracting attention as a method for producing a fiber-reinforced composite material having higher productivity.

In the basic RTM method, a thermosetting resin at a temperature A is injected into a mold at a temperature B, the temperature of the mold is raised to a temperature C, and the temperature is maintained at this temperature for a certain period of time. The temperature is lowered and the mold is removed to obtain a fiber reinforced composite material (FIG. 1). The obtained fiber reinforced composite material is heated again after demolding,
It may be accompanied by a post-curing step of holding for a certain time (Fig. 2). Further, it is also possible to carry out curing in the mold in multiple stages (so-called step cure). As an example of step cure, after the injection is completed, the temperature of the mold is raised to a temperature C1, kept at this temperature for a certain period of time, further raised to a temperature C2, kept at this temperature for a certain period of time, and kept at a temperature D. A method of lowering the temperature to remove the mold can be mentioned (FIG. 3).

Many of the fiber-reinforced composite materials used for aircraft members and spacecraft members are required to have heat resistance. The cured product of the thermosetting resin is amorphous and has a glass transition temperature. Above the glass transition temperature, the rigidity of the cured product of the thermosetting resin is significantly reduced, and along with this, the mechanical properties of the fiber-reinforced composite material are also significantly reduced. Therefore, the glass transition temperature of the thermosetting resin cured product is used as an index of the heat resistance of the fiber-reinforced composite material. The glass transition temperature of the cured product of the thermosetting resin correlates to the maximum temperature received during curing. In the example given above, C in FIG. 1, E in FIG. 2, and C2 in FIG. 3 correspond to the maximum temperature. Specifically, the higher the curing temperature is, the higher the glass transition temperature is likely to be. Therefore, in applications where heat resistance is required, the curing temperature is often set to a temperature selected from the range of 150 to 250 ° C. as the maximum temperature. In particular, in the case of the epoxy resin most often used as the matrix resin, the curing is often carried out with the highest temperature selected from the range of 150 ° C to 180 ° C.

In the method without post-curing (FIGS. 1 and 3), it is necessary to heat the mold to a high temperature. For example, according to the technical data of 3M, as a recommended manufacturing condition for the epoxy resin composition PR500, a resin preheated to 66 ° C., 160 ° C.
The procedure is as follows: pour into a heated mold, raise the mold to 177 ° C., hold at this temperature for 4 hours to cure, and then demold. In such cases, molds, auxiliary materials (used in the manufacturing process but not the raw materials that make up the product, and many are disposable. For example, sealants, tubes, valves, bag films, peel plies,
A release film, an adhesive tape, etc. can be illustrated. ), There is a problem that the cost of the heat source becomes high.

On the other hand, in the method shown in FIG. 2, in which the thermosetting resin is cured in the mold at a relatively low temperature, and after the mold is removed, the resin is post-cured at a relatively high temperature. It is possible to obtain a fiber-reinforced composite material having high heat resistance without increasing the cost of a heat source, and it is excellent in economic efficiency. For example, SAMPE Journal 3rd
Volume 4, No. 4, page 17, Articles in the collection, Cytec-Fiberite
As a recommended manufacturing condition for the epoxy resin composition Cycom 875RTM of the company, the resin is poured into a mold heated to 60 ° C., the mold is heated to 121 ° C., held at this temperature for 1 hour to cure, and then demolded, An additional post-curing procedure at 177 ° C. for 1 hour is shown.

However, the conventionally proposed conditions have not always been optimum in terms of achieving both productivity and performance.

For example, if the preheating temperature of the resin and the mold temperature at the time of injection are low, only a thermosetting resin having a low viscosity can be used. Generally, the lower the viscosity of a thermosetting resin, the more difficult it is to simultaneously improve various properties of fiber-reinforced composite materials, especially heat resistance and main mechanical properties (tensile strength, compression strength, impact resistance, etc.). This is a disadvantage because (For example, SAMPE
Journal Vol. 34, No. 4, Page 17
As the recommended production conditions for the epoxy resin composition Cycom 823RTM of tec-Fiberite, the conditions are shown in which the resin is poured into a mold at 24 ° C. and is cured in the mold at 121 ° C. for 1 hour. Under such conditions, only a thermosetting resin having an extremely low viscosity can be used. ) Further, if the difference between the mold temperature at the time of injection and the maximum curing temperature in the mold is large, the time required to raise the temperature becomes long, so the mold occupying time becomes long and the productivity is not good.

When the curing temperature in the mold is high, the cost of the mold, auxiliary materials, and heat source becomes high, and the advantage of performing post-curing is lost (for example, according to the technical data of Hexcel, epoxy resin composition RTM 6 In-mold curing is 160 ° C. for 75 minutes, and post-curing is 180 ° C. for 2 hours). On the contrary, if the curing temperature in the mold is too low, it takes a long time to cure and the mold occupy time becomes long, resulting in poor productivity (for example, Ciba Special
According to the technical data of May 1998 by ty Chemicals, the curing condition of the epoxy resin composition RESINFUSION 8605 in a mold is 25 ° C. for 24 hours. ).

[0013]

An object of the present invention is to provide conditions for an RTM method suitable for producing a fiber-reinforced composite material having excellent heat resistance and mechanical properties with high productivity.

[0014]

The RTM method of the present invention comprises:
A reinforcing fiber base material is installed inside, and Tm-20 to Tm + is placed in a mold kept at a temperature Tm selected from the range of 60 to 90 ° C.
It is characterized in that the thermosetting resin is injected from a container kept at a temperature selected from the range of 10 ° C.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the RTM method is
This means a method of injecting a liquid thermosetting resin into a reinforcing fiber base material placed in a mold and curing the resin to obtain a fiber-reinforced composite material.

As the reinforcing fiber, carbon fiber, glass fiber, aramid fiber, metal fiber, or the like, or a combination thereof is used. Carbon fibers are particularly preferably used for aircraft and spacecraft members. The reinforcing fiber base material may be a reinforced fiber woven fabric, a braid, a mat or the like as it is, and these are laminated and shaped, and the form is fixed by a means such as a binder or a stitch to form a preform. Is also good.

The mold may be a closed mold made of a rigid body, or a method using a rigid open mold and a flexible film (bag) is also possible. In the latter case, the reinforcing fiber substrate is placed between the rigid open mold and the flexible film.

As the rigid material, metal (steel,
Various existing materials such as aluminum), FRP, wood, plaster are used. A flexible film material, nylon, fluororesin, silicone resin, or the like is used.

When a rigid closed mold is used, the liquid epoxy resin composition is usually injected by applying pressure and clamping. At this time, a suction port may be provided separately from the injection port and connected to a vacuum pump for suction. It is also possible to inject the liquid epoxy resin only by the atmospheric pressure without performing a suction and using a special pressurizing means.

When a rigid open mold and a flexible film are used, suction and injection at atmospheric pressure are usually used. In order to achieve good impregnation by injection at atmospheric pressure, as shown in US Pat. No. 4,902,215,
It is effective to use a resin diffusion medium.

It is also possible to install a foam core, a honeycomb core, a metal part, etc. in the mold in addition to the reinforcing fiber base material to obtain a composite material integrated with these. In particular, a sandwich structure obtained by arranging reinforcing fiber substrates on both sides of a foam core and molding the same is useful as an outer plate material because it is lightweight and has large bending rigidity.

Further, prior to the installation of the reinforcing fiber base material,
It is also preferable to apply a gel coat to the rigid body type surface.

The thermosetting resin used in the present invention is preferably a thermosetting resin which has high heat resistance and produces almost no volatile matter during curing. Specifically, epoxy resins, cyanate resins, bismaleimide resins, and benzoxazine resins are preferably used. Of these, the epoxy resin is the most preferable in terms of the balance of price and performance, the abundance of commercially available raw materials, and the high degree of freedom in design.

In injecting the thermosetting resin into the mold, the container of the thermosetting resin and the mold are each kept at a predetermined temperature. In the RTM method of the present invention, the mold temperature at this time is set to a temperature selected from the range of 60 to 90 ° C. The mold temperature during pouring is preferably 65 to 80 ° C. A temperature in this range is economically advantageous because a relatively inexpensive heat source, specifically, hot water or hot air can be used, and it is possible to use a thermosetting resin having a relatively high viscosity that easily exhibits high performance. Therefore, it is advantageous to obtain a high performance fiber reinforced composite material.

It is important that the temperature of the thermosetting resin container is close to the temperature of the mold so that the thermosetting resin having a relatively high viscosity flows sufficiently. That is, in the RTM method of the present invention, when the temperature of the mold is Tm, the temperature of the thermosetting resin container is in the range of Tm-20 to Tm + 10 ° C.
It is preferably Tm-10 to Tm + 10 ° C. Below the lower limit of the above numerical range, the viscosity of the thermosetting resin in the container becomes high, which is disadvantageous for liquid transfer. Further, since the thermosetting resin injected into the mold has a high viscosity until the temperature rises to the temperature of the mold, impregnation into the reinforcing fiber is disadvantageous. on the other hand,
If the upper limit is exceeded, the pot life will be shortened, which is not preferable. The thermosetting resin may be injected with a single liquid, or may be injected with two or three containers holding different liquids and mixing them at a constant ratio. When different liquids are held in a plurality of containers, it is preferable that the temperature of all the containers be within the above range.

For the pipe connecting the thermosetting resin container and the mold,
A heat insulating material or a heater can be provided to prevent a decrease in temperature during liquid transfer. However, this is not required if the piping is short.

To enable such injection, it is preferable to use a thermosetting resin having an initial viscosity of 400 mPa · s or less at the temperature Tm. The initial viscosity is 200 mPa · s
The following is more preferable. When the initial viscosity is higher than the above range, impregnation property becomes insufficient. Furthermore, it has a sufficient pot life at the temperature Tm, specifically, 3 after preparation.
It is preferable to use a thermosetting resin whose viscosity when kept at the temperature Tm for 0 minutes is not more than twice the initial viscosity at Tm. It is more preferable to use a thermosetting resin whose viscosity when kept at the temperature Tm for 60 minutes after compounding is not more than twice the initial viscosity at Tm. In the above, the initial viscosity is the viscosity of the thermosetting resin immediately after being mixed, and the mixing is such that the thermosetting resin (or its precursor) can exhibit practical thermosetting properties. First, it is to prepare chemical or physical conditions, for example, to add a curing agent to the thermoplastic resin (or its precursor) in a temperature environment of room temperature or higher. If the pot life is insufficient, molding of a fiber-reinforced composite material with a high reinforcing fiber volume content (specifically 50% or more) or a large fiber-reinforced composite material (specifically, the longest dimension is 2 m or more) You will be at a disadvantage if you do.

After the injection of the thermosetting resin is completed, curing is performed in the mold. As for the curing temperature at this time, the smaller the difference from the mold temperature Tm at the time of injection, the shorter the time required to raise the temperature, which is preferable. Specifically, the temperature is preferably selected from the range of Tm to Tm + 50 ° C., more preferably the temperature selected from the range of Tm to Tm + 30 ° C. The time for maintaining this temperature, that is, the curing time is 0.5 to 1
The time is preferably selected from the range of 2 hours,
It is more preferable that the time is selected from the range of 0.5 to 4 hours because the mold occupancy time becomes short. When the curing temperature is higher than the mold temperature at the time of injection, it is preferable to monotonically increase the temperature to the curing temperature without including the process of temporarily holding the intermediate temperature during the temperature increase (that is, without performing step cure).

In order to satisfy the above conditions, the temperature is preferably 60 to 140 ° C. (more preferably 100 to 135).
C.) is performed in the mold at a temperature selected from the range, and a reactive thermosetting resin suitable for it may be selected. However, in order to achieve both the preferable pot life and the reactivity described above, the temperature of the in-mold curing and the temperature Tm of the mold at the time of injection are required.
Are relatively close, so it is not always easy. In order to achieve both of these, a thermosetting resin having a relatively slow reaction that satisfies the above-mentioned pot life requirement in Tm, and a latent inactive at Tm and active at the in-mold curing temperature are used. A method of blending a curing accelerator is effective. Specifically, an epoxy resin composition in which a latent curing accelerator such as a tertiary sulfonium salt, a sulfonate ester, or a boron halide complex is added to an epoxy resin composition containing an aromatic amine that reacts relatively slowly with the epoxy resin. The composition can be exemplified.

After the curing in the mold is completed, the mold is removed and the fiber reinforced composite material is taken out. The demolding temperature may be any temperature from the curing temperature to room temperature.

The demolded fiber-reinforced composite material can be made into a product without further heat treatment.
It is preferable to post-cure at a temperature selected from the range of to 250 ° C. Unless high heat resistance is required,
Post-curing at a temperature selected from the range of 150 to 190 ° C. is more preferable because it is economical. The time for maintaining the post-curing temperature is preferably a time selected from the range of 0.5 to 4 hours.

The RTM method of the present invention is extremely effective for economically producing a fiber-reinforced composite material which is lightweight, has high strength, high rigidity and is excellent in heat resistance. Specifically, fuselage, main wing, tail, rotor blade, fairing, cowl, door, seat,
Aircraft components such as interior materials, motor cases, spacecraft components such as main wings, structures, artificial satellite components such as antennas, skins, chassis, aerodynamic components, automobile components such as seats, structures, railway vehicle components such as seats, hulls It can be preferably used for manufacturing many members such as ship members such as seats.

[0033]

The present invention will be described in more detail with reference to the following examples. Example 1 (Evaluation of Viscosity of Thermosetting Resin) As the thermosetting resin,
An epoxy resin composition TR-A31 manufactured by Toray Industries, Inc. was used. TR
-A31 is a two-pack type epoxy resin composition which is prepared by mixing a base material mainly composed of an epoxy resin and a curing agent before use. The viscosity of the epoxy resin composition obtained by blending the main agent of TR-A31 and the curing agent at a weight ratio of 100: 38 was measured by measuring the temperature of the measuring part at 70 ° C. A total of TVE-30H was used. Initial viscosity is 54 mP
and the viscosity after 30 minutes was 88 mPa · s. (Manufacture of fiber reinforced composite material) As a mold, length 300mm,
It has a rectangular parallelepiped cavity with a width of 300 mm and a height of 2.2 mm, and the cavity is composed of an upper mold and a lower mold, and a resin injection port is provided in the center of the lower mold.
A steel mold with a resin outlet at each corner and a built-in heater was prepared. A mold release agent was applied to the inner surface of the cavity of the mold.

The mold was attached to a pressing machine, and a carbon fiber plain weave cloth CF6273H (using T700GC-12K, 190 g / m ² basis weight, manufactured by Toray Industries, Inc.) was placed 280 m on each side so that one side was in the warp direction.
Ten pieces cut out in a square of m were stacked in the cavity. The press was closed and the mold was clamped, and the mold temperature was raised to 70 ° C.

TR-A prepared by mixing a main agent and a curing agent in a pressure vessel with a jacket in a weight ratio of 100: 38.
No. 31 was put into the jacket, and the jacket was heated by passing hot water of 70 ° C., and the outlet of the pressure vessel was connected to the inlet of the mold with a polyethylene tube through a valve. A glass cloth was wrapped around the tube as a heat insulating material.

The injection-side valve of the mold was closed, the injection port of the mold was connected to a vacuum pump using a polyethylene tube through the valve and the trap, and the pressure inside the mold was reduced to 0.5 kPa or less. Subsequently, the injection side valve was opened and the pressure vessel was pressurized at 300 kPa to inject the resin. When almost no bubbles are seen in the resin flowing out to the trap, close the pouring side valve,
After pressurization was continued for 10 minutes, the injection side valve was closed. 1 ° C
When the temperature of the mold is raised to 100 ° C./min,
After maintaining this temperature for 4 hours, the heating was terminated, and when the mold temperature dropped to 60 ° C. or lower, the press was opened to remove the mold to obtain a fiber-reinforced composite material.

This fiber-reinforced composite material was placed in an oven set at 50 ° C., heated to 180 ° C. at 1.5 ° C./min, held at this temperature for 2 hours, and then heating was completed. The fiber-reinforced composite material was taken out when the temperature fell to below ℃. (Evaluation of Fiber Reinforced Composite Material) Based on SACMA SRM 1R-94, the compressive strength of the above fiber reinforced composite material in the weft direction was measured using an Instron 4208 type tester (manufactured by Instron). The width of the test piece was 6.355 mm, the length was 25.4 mm, the weft direction was the length direction, the environmental temperature was 23 ° C., and the crosshead speed was 1.0 mm / s. The compressive strength was 604 MPa.

Cut out a small sample of fiber reinforced composite material,
Using a differential scanning calorimeter TA3000 (manufactured by METTLER), temperature rise measurement was performed at a temperature rise rate of 40 ° C / min, and the glass transition temperature was determined from the midpoint of the glass transition region to be 210 ° C.
Met.

[0039]

According to the present invention, it is possible to produce a fiber reinforced composite material having excellent heat resistance and mechanical properties with high productivity.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a temperature history of a thermosetting resin in a basic RTM method.

FIG. 2 is a schematic diagram of a temperature history of a thermosetting resin in an RTM method involving after cure.

FIG. 3 is a schematic diagram of a temperature history of a thermosetting resin in an RTM method performing step cure.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 63:00 C08L 63:00 CF term (reference) 4F072 AA07 AB10 AB28 AD23 AE01 AH12 AH13 AH20 AH21 AJ37 AJ40 AK03 AK20 AL02 4F204 AA39 AD16 AH17 AH28 AH31 AR06 AR11 EB01 EB11 EF01 EF05 EF27 EW02 EW06

Claims (6)

[Claims] 1. A reinforcing fiber base material is installed inside, and 60 to 90
In a mold maintained at a temperature Tm selected from the range of ° C, Tm-
RT characterized by injecting a thermosetting resin from a container kept at a temperature selected from the range of 20 to Tm + 10 ° C
M method. 2. A thermosetting resin having an initial viscosity of 400 mPa · s or less at a temperature Tm is used.
RTM method described in. 3. The RTM method according to claim 1 or 2, wherein a thermosetting resin whose viscosity when kept at the temperature Tm for 30 minutes after preparation is not more than twice the initial viscosity at Tm is used. . 4. The RTM method according to claim 1, wherein the thermosetting resin is an epoxy resin. 5. The RTM according to claim 1, wherein the curing is carried out in the mold at a temperature selected from the range of Tm to Tm + 50 ° C. and a time selected from the range of 0.5 to 12 hours. Method. 6. The RT according to any one of claims 1 to 4, wherein the fiber-reinforced composite material demolded after being cured in the mold is post-cured at a temperature selected from the range of 150 to 250 ° C.
M method.