JP4806866B2 - Vacuum RTM molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a vacuum RTM (Vacuum Resin Transfer Molding) molding method, and in particular, a vacuum RTM molding method capable of obtaining an excellent quality FRP (fiber reinforced plastic) molded product without occurrence of defective resin impregnation. About.
[0002]
[Prior art]
FRP, especially CFRP (carbon fiber reinforced plastic) is a composite material that is lightweight and can exhibit high mechanical properties, and is used in various fields. A vacuum RTM molding method is known as one of typical FRP molding methods. In the vacuum RTM molding method, a reinforcing fiber substrate is placed in a mold, the inside of the mold cavity is decompressed, and the resin is injected into the cavity using the pressure difference between the decompressed cavity pressure and external pressure. Then, the impregnated resin is impregnated into the reinforcing fiber base, the resin is cured, and the mold is removed after curing to obtain an FRP molded product.
[0003]
In such a vacuum RTM molding method, the inside of the cavity is decompressed, the resin is injected with a pressure difference between the inside and outside of the cavity (maximum, 1 kg / cm ² ), and the reinforcing fiber substrate is impregnated. Since the resin is not sufficiently impregnated, the flow resistance is low, and the resin flows vigorously at a high flow rate. However, the flow resistance varies depending on the location of the base material, and the flow resistance varies. For example, the difference in flow resistance between the overlapping part of the base material and the other part may be double or more. In such a case, the resin impregnation takes a relatively long time due to the large flow resistance in the overlap portion, but the impregnation proceeds promptly in the non-overlap portion because the flow resistance is low. Therefore, there is a time difference in resin flow and impregnation between these parts, the resin is advanced to the part with low flow resistance, and the vacuum from the part with high flow resistance that has not been sufficiently impregnated with resin. The suction path may be blocked. When such a state occurs, vacuum suction from the unimpregnated portion of the resin is hindered, and the flow rate of the resin in the portion is rapidly reduced, and the resin gels before the resin can be sufficiently impregnated. , This causes a problem that the part remains in the unimpregnated state.
[0004]
[Problems to be solved by the invention]
Therefore, the object of the present invention is to focus on the problems in the vacuum RTM molding method as described above, so that the injected resin does not flow too much locally in the cavity, and particularly flows locally at the initial stage of injection. It is an object of the present invention to provide a vacuum RTM molding method capable of preventing the occurrence of unimpregnated portions throughout the reinforcing fiber base material to be impregnated.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the vacuum RTM molding method according to the present invention reduces the pressure in the cavity of the mold in which the reinforcing fiber base material is disposed, and the resin has a differential pressure between the reduced pressure in the cavity and the external pressure. In the vacuum RTM molding method of injecting into the cavity and impregnating the reinforcing fiber base by utilizing the resin injection speed, the resin injection speed is reduced at least at the initial stage of the injection while the pressure in the cavity is reduced. This is a method characterized in that the resin is injected by decelerating to a flow rate lower than the natural flow rate without any control.
[0006]
The vacuum RTM molding method according to the present invention is configured so that the resin flow and impregnation to the portion with low flow resistance do not proceed excessively until the portion with high flow resistance as described above is sufficiently impregnated with resin. In particular, the resin injection speed is controlled to be lower than the natural flow speed without any control so as to suppress the flow speed at the initial stage of flow start (initial injection start). .
[0007]
As control of the resin injection rate, it is preferable to control the initial injection flow rate Vc of the resin to 2/3 or less of the initial injection flow rate Vn at the natural flow rate. By such control, it is possible to prevent the resin flow and impregnation in the part with low flow resistance from proceeding excessively, especially in the initial stage after the start of injection, and prevent the vacuum suction path from being blocked locally. Thus, good resin impregnation of the entire base material can be achieved, and generation of unimpregnated portions can be prevented.
[0008]
However, if the resin injection speed is kept low, the time required for the resin injection process becomes longer, and the cycle time of the entire molding process including the resin injection process becomes longer, which may reduce productivity. Therefore, in order not to make the resin injection process time too long, the viscosity of the resin is lowered, and the flow rate of the resin and the ease of impregnation are kept at a relatively high level. It is preferable that no unimpregnated part is generated. For this purpose, it is preferable to raise the resin injection temperature to such an extent that no problem occurs, thereby lowering the viscosity of the resin. For example, it is preferable to inject the resin at a mold temperature of 50 ° C. or higher. Similarly, from the viewpoint of shortening the molding cycle, it is preferable to cure the resin impregnated in the reinforcing fiber base at a mold temperature of 70 ° C. or higher.
[0009]
As an injection resin that satisfies such requirements, a resin composition comprising a polyamine curing agent and a liquid epoxy resin can be used.
[0010]
Further, in the vacuum RTM molding method according to the present invention, in order to further promote the diffusion of the resin and the impregnation into the base material and more reliably prevent the occurrence of the local non-impregnated part, the surface of the reinforcing fiber base material is used. A resin diffusion medium that lowers the flow resistance of the resin can be disposed thereon. Moreover, the core material which has the groove | channel as a resin flow path on the surface can also be arrange | positioned between reinforcement fiber base materials.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail together with preferred embodiments.
FIG. 1 shows the basic process of the vacuum RTM molding method of the present invention. The basic process shown in FIG. 1 includes a material preparation step 101, a material placement step 102, a vacuum suction step 103, a resin injection impregnation step 104, a resin curing step 105, and a demolding step 106. Each of these steps will be described below.
[0012]
(1) Material preparation step (1) Reinforcing fiber substrate: It is preferable to use a woven fabric of carbon fiber or glass fiber, which is cut into a predetermined dimension. If necessary, it is shaped into a product shape and held in shape with an adhesive. Further, a predetermined number of sheets are stacked.
(2) Resin: It is preferable to use a thermosetting resin, and to vacuum (heat) defoaming the main agent and the curing agent separately. Among these, it is preferable to use a resin composition comprising a polyamine curing agent and a liquid epoxy resin.
(3) Core material: Used for forming a sandwich structure in which a core material and reinforcing fiber bases are arranged on both sides thereof. As the core material, it is mainly desirable to use a foam core (foam core material) from the viewpoint of weight reduction and the like. In some cases, balsacore or wood can also be used. On the surface of the core material, a groove for a resin flow path is processed as necessary.
(4) Auxiliary materials: Prepare a resin injection tube or vacuum suction tube, and a resin diffusion medium, a release woven fabric, a pressing plate, etc. as necessary.
[0013]
(2) Material placement (layup) step (1) The material is placed at a predetermined position on the mold surface to which the release agent is applied.
{Circle around (2)} When arranging, it is preferable to set the fiber orientation of the woven base material, the orientation of the core material, etc. with reference to the reference line marked on the non-molded surface.
[0014]
(3) Vacuum suction step (1) The lower mold cavity in which the reinforcing fiber base material is disposed is closed with the upper mold and the inside of the cavity is sealed, or the lower mold cavity is made of a bag material made of a flexible material ( For example, bagging is performed with a bag material made of a film or rubber material, and the inside is sealed from the outside. Moreover, a pressing plate may be disposed between the bag material made of the flexible material and the reinforcing fiber base material.
(2) The inside of the cavity closed with the upper mold or bagged with the bag material is sucked into a reduced pressure state.
(3) Vacuum suction is at least 20 torr or less, preferably 10 torr or less.
{Circle around (4)} Vacuum suction may be performed when the suction is continued or when the suction port reaches 20 torr or less.
[0015]
(4) Resin injection impregnation step (1) The mold is heated and the resin is injected into the cavity. The mold may be in a heated state in advance from the material placement step.
(2) Resin is injected slowly at a speed slower than the natural flow rate due to atmospheric pressure. Desirably, the speed is controlled to 2/3 or less than the natural flow rate during natural injection. This is because when the initial flow rate is injected without being controlled like natural inflow, the resin that flows into the cavity first flows mainly in the part where the resin flow resistance is low. In a part with high flow resistance such as a part, the flow becomes worse (the difference from the part that tends to flow easily becomes larger), the flow becomes uneven in the direction of the flow, an unimpregnated part is generated, and remains as a void in many cases. Since such a phenomenon is likely to occur at the beginning of injection with a high flow rate, it is necessary to suppress the resin flow rate (injection rate) immediately after the start of resin injection.
(3) Determination of whether or not the resin has been injected and impregnated has been made based on whether or not the resin has been discharged from the vacuum suction port.
[0016]
The deceleration of the resin injection flow rate can be controlled by, for example, restricting the valve where the resin injection line is arranged, and can be controlled to a flow rate pattern as shown in FIG. 2, for example. In FIG. 2, the flow rate pattern A shows the flow rate when the resin is injected with the natural flow rate without being decelerated. On the other hand, for example, the valve in which the resin injection line is arranged is throttled by a certain amount. If it is left as it is, flow velocity characteristics such as a flow velocity pattern B1 are obtained. Flow rate characteristics such as this pattern B1 may be used. However, at a stage where the injection has progressed to some extent, the resin already flows sufficiently well in the cavity even if the flow rate is not lowered so much. From the viewpoint of shortening the molding cycle as much as possible, the flow velocity characteristic can be brought close to the flow velocity pattern A on the way, and the flow velocity characteristic such as the flow velocity pattern B2 can be obtained.
[0017]
(5) Resin curing step (1) After impregnation with resin injection, the resin injection port is closed (preventing inflow of air).
(2) The vacuum suction side may be closed or closed. In particular, when the resin contains a solvent, the suction is continued and the generated gas is discharged from the cavity as much as possible.
[0018]
(6) Demolding step {circle around (1)} Basically, it is preferable to remove the molded product from the mold almost without lowering the mold temperature.
(2) When it is difficult to remove the mold, the mold temperature is intentionally lowered to use the contraction force of the mold to help the mold removal.
[0019]
【Example】
Hereinafter, the present invention will be described based on examples, including more specific examples of molding methods.
Example 1
FIG. 3 shows a vacuum RTM molding method according to Embodiment 1 of the present invention. In FIG. 3, a cavity 3 is formed inside by a double-sided mold of a metal upper mold 1 and a lower mold 2. In the upper mold 1 and the lower mold 2, heating medium channels 4 and 5 like mold heating are built in, respectively.
[0020]
A mold release agent is applied onto the mold surface, and a reinforcing fiber base 6 (manufactured by Toray Industries, Inc., carbon fiber fabric: "Torayca" T300 × 200 g / m ² × 8 ply) was laid up. On top of that, a release woven fabric 7 (nylon taffeta) and a resin diffusion medium 8 (# 200 mesh polyethylene mesh) were placed.
[0021]
Similarly to the lower mold 2, the upper mold 1 heated in advance to about 40 ° C. was pressed onto the lower mold 2 along the guide pins to maintain the fixed state, and the mold was clamped.
[0022]
Via a valve 10 and a vacuum trap 11 (a trap for preventing the resin from flowing into the vacuum pump) from a suction port communicating with the vacuum suction unit 9 which is a trapezoidal groove formed in the width direction of the cavity 3. Vacuum suction was performed by the vacuum pump 12.
[0023]
After the inside of the cavity 3 reaches 10 torr or less, the vacuum suction part 9 that is a vacuum suction groove and the molding part where the base material 6 is disposed are placed in a contrasting position in the same manner as the vacuum suction part 9. The valve 14 of the resin injection line communicating with the resin injection part 13 which is a trapezoidal groove formed in the width direction was opened, and the resin 16 stored in the tank 15 was allowed to flow into the cavity 3 at atmospheric pressure. Vacuum suction was continued with the valve 10 on the vacuum suction line open. Resin and vacuum sealing were performed with an O-ring 17 arranged over the entire circumference on the mold surface. At this time, the opening degree of the valve 14 of the resin injection line was adjusted, and the injection flow rate was lowered to a flow rate of about ½ of the natural flow rate that was normally injected fully open. As the thermosetting resin 16, polyamine curable epoxy resin: TR-C32 (resin composition comprising a polyamine curing agent and an epoxy resin) manufactured by Toray Industries, Inc. was used.
[0024]
The resin 16 pressurized at atmospheric pressure once reaches and fills the resin injecting portion 13 having grooves formed in the width direction, and then a film gate formed by an upper and lower mold gap that is a communication path with the cavity 3. It reaches the cavity 3 through 18 (gap = about 0.5 mm). Then, it flows into the resin diffusion medium 8 whose flow resistance is much lower than that of the substrate 6. Then, while the resin flows mainly in the resin diffusion medium 8, the resin is gradually impregnated in the base material 6 in the thickness direction, and eventually reaches the vacuum suction part 9 in which grooves are formed in the width direction. Thereafter, when the resin started to appear on the vacuum suction line, the valve 14 of the resin injection line was closed to stop the resin injection. The time from the start of resin injection until the resin was seen on the vacuum suction line was about 20 minutes, and the mold temperature was raised to 80 ° C. during the 20 minutes. Since the flow rate of the resin injection was suppressed, as a result of checking with a molded product to be described later, the resin wraps around the cavity, that is, the portion to be impregnated with the resin, and no unimpregnated portion was generated.
[0025]
The cavity 3 was filled with the resin, and the base material 6 was impregnated at a mold temperature of 80 ° C. for about 1 hour and 40 minutes. The resin was cured until it could be removed by heating from the mold.
[0026]
After the resin was cured, the mold temperature was lowered, the upper mold 1 was raised and released from the lower mold 2 to release the molded product from the mold.
[0027]
The demolded molded product was a fender as an automobile member, and the molded product was a non-impregnated portion, the surface state was glossy, and no voids or pinholes were found at all.
[0028]
Thus, by appropriately reducing the injection rate of the thermosetting resin, it is possible to ensure good impregnation of the resin throughout the molding site without significantly increasing the molding cycle, and good quality of the FRP product. Could get.
[0029]
Example 2
In this example, the lower mold 21 was used as a single-sided mold, and the upper mold was not used, and the sheet-shaped bag material 22 was used for the covering. The metal lower mold 21 is provided with a heat medium passage 23 for heating the mold. A mold release agent was applied on the mold surface, and the mold temperature was heated to about 40 ° C. by the heat medium passage 23 through which hot water passed.
[0030]
Reinforced fiber base material 24 (manufactured by Toray Industries, Inc., carbon fiber fabric: “Torayca” T700 × 300 g / m ² × ² ply) was laid up on the mold surface. Further, an acrylic foam core material 25 (thickness: 10 mm) is disposed thereon, and then a reinforcing fiber base material 24 (manufactured by Toray Industries, Inc., carbon fiber fabric: “Torayca” T700 × 300 g / m ^2). X2ply). On top of that, an FRP pressing plate 26 having the same outer dimensions as the foam core material 25 and a thickness of 3 mm was placed, and the entire lower mold surface was covered with a nylon bag material 22. The bag material 22 and the lower mold 21 were sealed with an adhesive seal material. Further, a silicon rubber heater 28 incorporating a heater wire was placed on the bag material 22. The foam core material 25 is formed with a narrow groove (width 1.5 mm × depth 3 mm) for the resin inflow path from the resin injection portion 29 toward the decompression suction portion 30 on both the upper and lower surfaces.
[0031]
Vacuum suction was performed by a vacuum pump 34 through a valve 32 and a vacuum trap 33 from a suction port communicating with the vacuum suction unit 30 which is a trapezoidal groove formed in the width direction of the cavity 31. At this time, the temperature of the rubber heater 28 was started to 70 ° C. Then, after the inside of the cavity 31 reaches 6 torr or less, the reduced pressure suction part 30 and the reduced pressure suction part 30 are located at a position in a contrasting relationship via the molding part where the base material 24 is disposed with the reduced pressure suction part 30 serving as a vacuum suction groove. Similarly, the valve 35 of the resin injection line communicating with the resin injection portion 29 which is a trapezoidal groove formed in the width direction was opened, and the resin 37 stored in the tank 36 was allowed to flow into the cavity 31 at atmospheric pressure. At this time, the opening degree of the valve 35 was adjusted, and the injection flow rate was lowered to a flow rate of about ½ of the natural flow rate that was normally injected with the valve fully open. The valve 32 on the vacuum suction line was kept open and vacuum suction was continued. Resin and vacuum sealing were performed with an O-ring 27 communicating with the entire circumference on the mold surface. Further, the thermosetting resin 37 used here is a polyamine curable epoxy resin: TR-C32 manufactured by Toray Industries, Inc., and its viscosity at 70 ° C. is about 50 mPa · s.
[0032]
The resin 37 pressurized at atmospheric pressure once reaches and fills the resin injection portion 29 in the same manner as in the first embodiment shown in FIG. 2, and then extends from the cavity 31 to the resin injection portion 29. 24 to reach into the cavity 31. However, in order to lower the resin resistance, the same resin diffusion medium as described in FIG. 3 was disposed on the base material (not shown in FIG. 4) in the extended portion of the base material. After that, it flows into the narrow groove formed in the core material 25 whose flow resistance is much lower than that of the base material 24. Then, the resin 39 gradually impregnates the base material 24 in the thickness direction while flowing mainly in the narrow grooves on the upper and lower surfaces of the core material 25, and eventually reaches the vacuum suction part 30. Thereafter, when the resin began to appear on the vacuum suction line, the mold temperature was raised to 80 ° C., and the valve 35 of the resin injection line was closed to stop the resin injection.
[0033]
The resin was filled in the cavity 31 of the mold that reached 80 ° C., and held in the base material 24 for about 1 hour and 40 minutes. The resin was eventually cured by heating from the mold.
[0034]
After the resin was cured, the rubber heater 28 and the bag material 22 were stripped from the lower mold 21 to remove the molded product from the mold. In this case, the mold temperature was lowered from 80 ° C. to 50 ° C., and the molding cycle was shortened as much as possible.
[0035]
The demolded molded product was a bonnet hood, which is an automobile member, and no unimpregnated portion of resin was observed. The design surface was more glossy due to the gel coat, and the texture of the base fabric woven appeared on the outer surface without painting, thereby increasing the commercial value.
[0036]
【The invention's effect】
As described above, according to the vacuum RTM molding method of the present invention, by suppressing the injection rate of the resin appropriately, undesired flow in the cavity of the injected resin can be prevented and unimpregnated portions and voids can be prevented. Generation | occurrence | production can be prevented effectively and the outstanding quality of a FRP molded product can be ensured.
[Brief description of the drawings]
FIG. 1 is a process flow diagram showing a basic process of a vacuum RTM molding method of the present invention.
FIG. 2 is a characteristic diagram of a resin injection flow rate.
FIG. 3 is a schematic configuration diagram showing a vacuum RTM molding method according to Embodiment 1 of the present invention.
FIG. 4 is a schematic configuration diagram showing a vacuum RTM molding method according to Embodiment 2 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Upper mold | type 2,21 Lower mold | type 3,31 Cavity 4,5,23 Heat-medium flow path 6,24 Reinforcement fiber base material 7 Weaving cloth 8 Resin diffusion medium 9,30 Vacuum suction part 10,14,32, 35 Valve 11, 33 Vacuum trap 12, 34 Vacuum pump 13, 29 Resin injection part 15, 36 Tank 16, 37 Thermosetting resin 17, 27 Sealing O-ring 22 Bag material 25 Core material 26 Press plate 28 Rubber heater

Claims (7)

Vacuum RTM molding in which the inside of the mold cavity where the reinforcing fiber substrate is placed is decompressed, and the resin is injected into the cavity using the pressure difference between the decompressed cavity pressure and the external pressure to impregnate the reinforcing fiber substrate. In the method, the resin injection speed due to the differential pressure is reduced to a flow rate lower than the natural flow rate without any control by narrowing the valve of the resin injection line while reducing the inside of the cavity at least at the initial stage of injection. A vacuum RTM molding method characterized by controlling and injecting resin. The vacuum RTM molding method according to claim 1, wherein the initial injection flow rate Vc of the resin is controlled to be 2/3 or less of the initial injection flow rate Vn at the natural flow rate. The vacuum RTM molding method according to claim 1 or 2, wherein the resin is injected at a mold temperature of 50 ° C or higher. The vacuum RTM molding method according to claim 1, wherein the resin impregnated in the reinforcing fiber base is cured at a mold temperature of 70 ° C. or higher. The vacuum RTM molding method according to any one of claims 1 to 4, wherein a resin composition comprising a polyamine curing agent and a liquid epoxy resin is used as the injection resin. The vacuum RTM shaping | molding method in any one of Claims 1-5 which arrange | positions the resin diffusion medium which lowers the flow resistance of resin on the surface of a reinforced fiber base material. The vacuum RTM shaping | molding method in any one of Claims 1-5 which arrange | positions the core material which has the groove | channel as a resin flow path on the surface between reinforcement fiber base materials.

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