JP7779153B2 - Manufacturing method for fiber reinforced plastic molded products - Google Patents

Description

The present invention relates to a method for manufacturing fiber-reinforced plastic molded products, and more specifically to a method for manufacturing fiber-reinforced plastic molded products that can improve productivity while reducing the amount of carbon fiber waste and ensuring the mechanical strength of the molded product.

A molding method for fiber-reinforced plastic has been proposed that is lightweight, has high mechanical strength, maintains a good appearance, allows for easy trimming, and ensures that the strength of the outer periphery is equivalent to that of the central part of the product (see Patent Document 1). This fiber-reinforced plastic molding method involves constructing a preform by placing a second substrate, in which the reinforcing fibers have been pre-impregnated with resin, on at least a portion of the outer periphery of a first substrate made solely of reinforcing fibers such as a woven fabric; the preform is then placed in the cavity of a mold, and resin is then injected and cured. This molding method utilizes the RTM (Resin Transfer Molding) molding method.

JP 2010-76356 A

However, when attempting to further thicken fiber-reinforced plastics such as those described in Patent Document 1, the reinforcing fibers, i.e., the woven carbon fiber portion, become even thicker, which poses the problem of taking longer to impregnate with resin, potentially resulting in poor resin impregnation and reduced mechanical strength. Furthermore, taking longer to impregnate with resin in order to prevent poor resin impregnation reduces productivity. Furthermore, using layers of woven carbon fiber fabrics tends to increase the amount of trimming required when constructing a preform, resulting in a large amount of wasted carbon fiber.

The present invention was made in consideration of these problems with the prior art, and aims to provide a method for manufacturing fiber-reinforced plastic molded products that reduces the amount of carbon fiber waste, ensures the mechanical strength of the molded product, and improves productivity.

After extensive research to achieve the above objective, the inventors discovered that the above objective could be achieved by using a preform made by arranging tape substrates made of carbon fiber bundles in the width direction, stacking them in the thickness direction, and then shaping them, and by arranging the tape substrates with gaps between them when producing this preform, which led to the completion of the present invention.

That is, the method for producing a fiber-reinforced plastic molded product of the present invention is a method for producing a fiber-reinforced plastic molded product that is produced by arranging tape substrates made of carbon fiber bundles in the cavity of a molding die, arranging them in the width direction, stacking them in the thickness direction, and shaping them, and then impregnating and curing the preform with a thermosetting resin material, and that has a fiber volume content ( _Vf ) of 45% to 52%. In this method for producing a fiber-reinforced plastic molded product, when producing the preform, the tape substrates are arranged with gaps between them.
Furthermore, the molding die comprises a fixed die and a movable die, the movable die has a resin injection inlet, and when the tape substrates constituting the surface of the preform located on the resin injection inlet side are arranged, no gaps are provided between the tape substrates within the area from the position of the resin injection inlet to its vicinity in a direction perpendicular to the moving direction of the movable die.

This invention uses a preform made by arranging tape substrates made of carbon fiber bundles in the width direction, stacking them in the thickness direction, and then shaping them. When producing this preform, the tape substrates are arranged with gaps between them. This reduces the amount of carbon fiber waste, ensures the mechanical strength of the molded product, and provides a method for manufacturing fiber-reinforced plastic molded products that can improve productivity.

1 is a flow diagram showing one embodiment of a method for producing a fiber-reinforced resin molded product of the present invention. 2(A) to 2(F) are plan views schematically showing some examples of sheet-like substrates. 3A and 3B are exploded perspective views schematically showing an example and another example of the laminated base material. 4A and 4B are a plan view and a cross-sectional view schematically showing an example of a preform. 1A to 1C are explanatory diagrams schematically illustrating a process for producing a molded product. 1 is a graph showing the relationship between the gap between tape substrates and the fiber volume fraction (V _f ). 1 is a graph showing the relationship between the gap between tape substrates and compressive strength. 1 is a graph showing the relationship between the gap between tape substrates and the tensile strength.

The manufacturing method for a fiber-reinforced plastic molded product of the present invention will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings cited below have been exaggerated for the sake of explanation and may differ from the actual proportions.

As shown in Figure 1, the method for manufacturing a fiber-reinforced plastic molded product of this embodiment includes a preform manufacturing process S1 and a molded product manufacturing process S2.

<Preform manufacturing process S1>
The preform manufacturing process S1 includes a sheet-like substrate manufacturing process S11, a laminated substrate manufacturing process S12, and a shaping process S13. Each process will be described in more detail below.

(Sheet-like substrate production step S11)
2(A) to 2(E), tape substrates 15 made of carbon fiber bundles are arranged in the width direction to prepare a sheet substrate 13 for forming the pre-shaping laminated substrate 11 (11') (see FIG. 3). When preparing the sheet substrate 13, the tape substrates 15 are arranged with gaps 15A between them.

Examples of the tape substrate 15 made of carbon fiber bundles include a tape-shaped carbon fiber bundle formed by bundling continuous carbon fibers with a thread, and a tape-shaped carbon fiber bundle formed by further bundling and integrating carbon fiber bundles with a thread. The width of the tape substrate 15 is preferably, for example, 5 mm to 50 mm, and more preferably 5 mm to 25 mm. The thickness of the tape substrate 15 is preferably, for example, 0.1 mm to 0.5 mm. Furthermore, the tape substrate 15 preferably contains a binder such as an epoxy resin on the front and back sides thereof that can be used to fix the tape substrate to other tape substrates or a molding die, and the content of the binder is preferably 5 g/ ^m² to ¹⁵ g/m².

The width of the gap 15A is preferably 0.5 mm or more and 3 mm or less, and more preferably 0.5 mm or more and 2 mm or less.

When arranging the tape substrates 15, it is preferable to use sheet substrates 13 in which the orientation of the tape substrate 15 is changed relative to the molded product, such as sheet substrates 131 and 134 in which the longitudinal direction of the tape substrate 15 is 0° (see Figures 2(A) and (D)), sheet substrates 132 and 135 in which the longitudinal direction is 45° (see Figures 2(B) and (E)), and sheet substrate 133 in which the longitudinal direction is -45° (see Figure 2(C)).

Note that, although only narrow-width sheet-like substrates 134 with the longitudinal direction of the tape substrate 15 set to the 0° direction are shown (see Figure 2(D)), tape substrates with the longitudinal direction set to the 45° or -45° direction, similar to the wide-width sheet-like substrates 132 and 133 shown in Figures 2(B) and (C), can also be used as appropriate.

In this embodiment, when producing the sheet-like substrate 13 that is disposed on the resin injection port 33A side of the movable mold 33 used to produce the molded product and that forms the surface of the preform 10, it is preferable that no gaps 15A be provided between the tape substrates 15 in the region from the location of the resin injection port 33A to its vicinity in a direction perpendicular to the direction of movement of the movable mold 33 (see Figures 2(E), 4, and 5). Note that the perpendicular direction is the in-plane direction of the sheet-like substrate in Figure 2(E).

It is preferable that the distance from the location of the resin injection port 33A to the surrounding area be 50 mm or less.

In addition, a woven or non-crimp fabric 136 made of carbon fiber may be provided as a sheet-like substrate 13 on the surface of the preform 10 on the resin injection port 33A side (see Figure 2 (F)).

In addition, trimming may be performed at the end of the sheet-like substrate production process.

(Laminated base material manufacturing process S12)
In the laminated substrate preparation step, for example, 19 sheets of sheet-like substrates 13 are stacked to prepare the laminated substrate 11 (11') before shaping (see FIG. 3). Although not shown, the gaps provided in each sheet-like substrate are preferably provided in a staggered manner between the layers of the laminated substrate from the viewpoint of suppressing disorder of the tape substrate. On the other hand, the gaps provided in each sheet-like substrate are preferably provided uniformly between the layers of the laminated substrate from the viewpoint of improving resin impregnation. A typical example of the gaps being provided in a staggered manner is one in which they are provided with a stagger of half the width of the tape substrate.

Here, the laminated substrate 111 is formed by laminating a sheet-like substrate 133 on a sheet-like substrate 132. Furthermore, the laminated substrate 112 is formed by laminating eleven narrow sheet-like substrates. More specifically, six sheet-like substrates 134 are laminated together, and tape substrates with orientations changed in the 45° and -45° directions are laminated on top of these, followed by three sheet-like substrates 134. Furthermore, the laminated substrate 113 is formed by laminating four sheet-like substrates 131 on top of the sheet-like substrate 133. When laminating the sheet-like substrates 13, it is preferable to integrate the tape substrates 15 that make up the sheet-like substrate 13 by changing the orientation as described above.

In the laminated substrate production process, trimming is preferably performed at the end, as this makes it easier to position the sheet-like substrate. Depending on the shape of the laminated substrate, trimming may also be performed midway through.

(Shaping process S13)
In the shaping process, for example, the laminated substrate 11 is placed in a preform mold not shown, and is shaped by applying a pressure of 25 kPa or more and 100 kPa or less using a press, and holding the pressure for 10 seconds or more and 60 seconds or less to produce a preform 10 (see Figure 4).

<Molded product production process S2>
The molded product production process preferably utilizes, for example, a high-pressure RTM molding method. Specifically, as shown in FIG. 5 , a preform (not shown) is placed in a cavity 30A of a mold 30, which includes a fixed mold 31 and a movable mold 33, with the movable mold 33 having a resin column inlet 33A. Next, a thermosetting resin base 21 and a curing agent 23 are supplied under high pressure from a thermosetting resin base container 35 and a curing agent container 37, respectively, and a mixture of these, a thermosetting resin material 20, is supplied into the cavity 30A through a resin injection path 39 and the resin injection inlet 33A. The thermosetting resin material 20 is then impregnated into and cured in a preform (not shown), thereby producing a fiber-reinforced resin molded product 1 having a fiber volume content (V _f ) of 45% to 52%. Such a fiber-reinforced resin molded product can be used, for example, in a center pillar, an example of an automotive part. In FIG. 5, a resin column inlet 33A is provided at approximately the center of the movable mold 33 so that the thermosetting resin material 20 can be uniformly impregnated and hardened.

Here, epoxy resin is a suitable example of the thermosetting resin. The viscosity of the thermosetting resin base is preferably, for example, 5,000 mPa·s or more and 15,000 mPa·s or less at 25°C. The injection pressure of the thermosetting resin base and curing agent is preferably, for example, 8 MPa or more and 20 MPa or less. The injection speed of the thermosetting resin material is preferably 80 cm ³ /s or more and 200 cm ³ /s or less, and the ratio of the thermosetting resin base and curing agent is preferably 2.5 to 4:1 by volume. The injection speeds of the thermosetting resin base and curing agent are particularly preferably, for example, 78 cm ³ /s and 22 cm ³ /s, respectively. The mold clamping force is preferably, for example, 250 tons or more and 300 tons or less. The mold gap is preferably, for example, 2.5 mm or more and 3.5 mm or less. The degree of vacuum inside the mold is preferably, for example, 0.35 kPa or more and 0.55 kPa or less. The mold clamping holding time is preferably 30 seconds or more and 40 seconds or less.

Next, the advantages of this embodiment will be described.
According to the method for producing a fiber-reinforced plastic molded product of this embodiment, by arranging the tape substrates with gaps between them when producing the preform as described above and setting the fiber volume content (V _f ) of the fiber-reinforced plastic molded product to 45% or more and 52% or less, it is possible to reduce the amount of wasted carbon fiber, promote resin flow during resin impregnation, and further improve resin impregnation. This makes it possible to provide a method for producing a fiber-reinforced plastic molded product that can reduce the amount of carbon fiber waste, ensure the mechanical strength of the molded product, and improve productivity. Furthermore, because resin impregnation is improved, there is the secondary advantage that the required mold clamping force can be reduced, allowing the press to be made smaller.

In this embodiment, by setting the width of the gap to between 0.5 mm and 3 mm, in addition to the above-mentioned advantages, there is also the advantage that compressive strength can be reliably ensured.

In this embodiment, by setting the gap width to 0.5 mm or more and 2 mm or less, in addition to the above-mentioned advantages, there is also the advantage that compressive strength and tensile strength can be reliably ensured.

According to this embodiment, as described above, no gaps are provided between the tape substrates in the region from the location of the resin injection port to its vicinity. In addition to the advantages described above, this embodiment can also suppress disturbance of the tape substrate near the resin injection port. This in turn can suppress a decrease in mechanical strength.

In this embodiment, by setting the distance from the resin injection port to the surrounding area to 50 mm or less, in addition to the above-mentioned advantages, mechanical strength can be reliably ensured. Another secondary advantage is that a preform can be produced using only the tape substrate, without using woven fabric or non-crimp fabric.

According to this embodiment, by providing a carbon fiber woven fabric or non-crimp fabric on the surface of the preform on the resin injection port side, in addition to the above-mentioned advantages, it is possible to suppress disturbance of the tape substrate. This makes it possible to suppress a decrease in mechanical strength.

The present invention will now be explained in more detail using some test examples.

(Test Examples 1 to 9)
Tape substrates (width: 25 mm, thickness: 0.33 mm) made of carbon fiber bundles were arranged with gaps between the tape substrates of −2.5 mm to 10 mm to obtain sheet-like substrates (see FIG. 2).

Eight of the resulting sheet-like substrates were then stacked to obtain the laminated substrate for each example. The orientation directions of the tape substrates of each sheet-like substrate in each example's laminated substrate were -45°/45°/0°/0°/0°/0°/45°/-45° (see Figure 3). The gaps between sheet-like substrates made of tape substrates with the same orientation direction were aligned.

Furthermore, the resulting laminated substrate for each example was placed on a flat mold, pressed at 50 kPa, and held for 30 seconds to obtain a preform for each example.

The resulting preform was then placed in the cavity of a mold equipped with a fixed and movable die, and the epoxy resin material was impregnated and cured to obtain the fiber-reinforced resin molded product for each example (see Figure 5). Note that a gap of -2.5 mm means that the tape substrate was overlapped by 2.5 mm.

Here, the viscosity of the epoxy resin base is 10,000 mPa·s at 25°C. The injection pressure of the epoxy resin base and the curing agent is 10 MPa. Furthermore, the injection rates of the epoxy resin base and the curing agent are 78 cm ³ /s and 22 cm ³ /s, respectively. The mold clamping force is 275 tons. The mold gap is 3 mm. The degree of vacuum inside the mold is 0.45 kPa. The mold clamping holding time is 35 seconds. The molding mold temperatures of both the fixed mold and the movable mold are 120°C.

In each of the above test examples (except for the case where the gap was -2.5 mm), resin flow during resin impregnation was promoted, further improving resin impregnation. As a result, these manufacturing methods were able to reduce the amount of carbon fiber waste and improve productivity while maintaining the mechanical strength of the fiber-reinforced resin molded product. On the other hand, poor resin impregnation was observed in the test example where the gap was -2.5 mm.

<Measurement of fiber volume content (V _f )>
A sample was cut out from a relatively inner portion of the fiber-reinforced resin molded article of each example, and the fiber volume fraction (V _f ) was measured and calculated by the combustion method.

As shown in Figure 6, there is a correlation between the gap between the tape substrates and the fiber volume content ( _Vf ). In particular, it was found that when the tape substrate width is 25 mm, the experimental value and the calculated value are nearly identical. When the tape substrate width is 25 mm or less, it is preferable to narrow the gap width compared to when the tape substrate width is 25 mm in order to set the fiber volume content ( _Vf ) to 45% or more and 52% or less. Furthermore, when the tape substrate width is greater than 25 mm, the gap width can be slightly wider in order to set the fiber volume content ( _Vf ) to 45% or more and 52% or less. For example, when the tape substrate width is 50 mm, the gap width can be widened to about 7 mm.

<Compression strength measurement>
A sample was cut out from a relatively inner portion of a fiber reinforced resin molded product produced by the same manufacturing method as the fiber reinforced resin molded product of each of the above-mentioned examples, and the compressive strength in the 0° direction was measured and calculated in accordance with JIS K 7076.

From Figure 7, it can be seen that from the perspective of ensuring a compressive strength of 350 MPa or more, it is preferable that the width of the gap between the tape substrates be 0.5 mm or more and 3 mm or less.

<Measurement of tensile strength>
A sample was cut out from a relatively inner portion of a fiber reinforced resin molded product produced by the same manufacturing method as the fiber reinforced resin molded product of each of the above-mentioned examples, and the tensile strength in the 0° direction was measured and calculated in accordance with JIS K 7073.

From Figures 7 and 8, it can be seen that from the perspective of ensuring a compressive strength of 350 MPa or more and a tensile strength of 750 MPa or more, the width of the gap between the tape substrates is preferably 0.5 mm or more and 3 mm or less. Furthermore, from Figures 7 and 8, it can be seen that from the perspective of ensuring a compressive strength of 350 MPa or more and a tensile strength of 1200 MPa or more, the width of the gap between the tape substrates is preferably 0.5 mm or more and 2 mm or less.

The present invention has been described above using one embodiment and a few test examples, but the present invention is not limited to these and various modifications are possible within the scope of the present invention.

For example, in the above embodiment, an example was given in which tape substrates were first arranged to produce a sheet-like substrate, and then these were stacked to produce a laminated substrate. However, a laminated substrate may also be produced by arranging tape substrates and stacking them at the same time.

In addition, for example, in the above-described embodiment, the molding die includes a fixed die and a movable die, and the movable die has a resin column inlet. However, the shape of the molding die can be changed as appropriate depending on the shape of the fiber-reinforced resin molded product.

1 Fiber reinforced resin molded product 10 Preform 11, 11', 111, 112, 113 Laminated base material 13, 131, 132, 133, 134, 135, 136 Sheet-like base material 15 Tape base material 15A Gap 20 Thermosetting resin material 21 Thermosetting resin base material 23 Hardener 30 Mold 30A Cavity 31 Fixed mold 33 Movable mold 33A Resin injection port 35 Thermosetting resin base material container 37 Hardener container 39 Resin injection path

Claims (5)

A method for producing a fiber-reinforced plastic molded product, the method comprising: impregnating a preform made by arranging tape substrates made of carbon fiber bundles in the width direction, stacking them in the thickness direction, and shaping the preform within a cavity of a mold with a thermosetting resin material and curing the preform; and the fiber volume content ( _Vf ) is 45% or more and 52% or less;
When preparing the preform, the tape substrates are arranged with gaps between them ,
the mold comprises a fixed mold and a movable mold,
the movable mold has a resin injection port,
When arranging the tape substrates constituting the surface of the preform located on the resin injection port side, no gaps are provided between the tape substrates in the region from the position of the resin injection port to its vicinity in the direction perpendicular to the moving direction of the movable mold.
A method for producing a fiber-reinforced resin molded product, comprising: The method for manufacturing a fiber-reinforced resin molded product described in claim 1, characterized in that the width of the gap is 0.5 mm or more and 3 mm or less. The method for manufacturing a fiber-reinforced resin molded product described in claim 1, characterized in that the width of the gap is 0.5 mm or more and 2 mm or less. 2. The method for manufacturing a fiber-reinforced resin molded product according to claim 1, wherein the distance from the position of the resin injection port to the area in its vicinity is 50 mm or less . the mold comprises a fixed mold and a movable mold,
the movable mold has a resin injection port,
A woven fabric or a non-crimp fabric made of carbon fiber is provided on the surface of the preform on the resin injection port side.
4. The method for producing a fiber-reinforced resin molded product according to claim 1.