Hollow FRP molded product and its manufacturing method

Abstract

To provide a hollow FRP molded product and its manufacturing method, which can suppress molding defects including a generation of voids between prepregs.SOLUTION: A manufacturing method for a hollow FRP molded product includes: a first process S1 for laminating a plurality of prepregs to form a laminate with a hollow part inside; a second process S2 for setting the laminate in a cavity of a mold; and a third process S3 in which the laminate is heated and molded by pressing it against a cavity surface while expanding the laminate in the cavity by applying pressure to the hollow part. In the first process S1, the laminate is formed to contain at least one low-tack prepreg pair where the tack of adjacent prepreg pairs is 10 N or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hollow FRP molded product and a method for producing the same. [Background technology]

[0002] In recent years, various methods for manufacturing hollow FRP (Fiber Reinforced Plastic) molded products by internal pressure molding have been proposed. For example, Patent Document 1 listed below describes a method for manufacturing a golf club shaft, including the steps of winding and laminating prepregs around a mandrel, de-coreing the wound prepreg laminate from the mandrel, inserting an elastomer tube into the hollow portion of the de-cored wound prepreg laminate and setting them in a molding die, and hot-molding the wound prepreg laminate in the molding die while introducing a fluid into the elastomer tube to expand the tube. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3165060 Summary of the Invention [Problem to be solved by the invention]

[0004] However, hollow FRP molded products obtained using the internal pressure molding method have the problem of being prone to molding defects such as voids (voids caused by residual air between prepregs) and wrinkles.

[0005] As a result of extensive research, the inventors discovered that reducing the tack between stacked sheet-like prepregs to a specific value allows for appropriate slippage between adjacent prepregs during expansion and deformation, thereby solving the above-mentioned problems.

[0006] As described above, a main object of the present invention is to provide a hollow FRP molded product obtained by internal pressure molding that can suppress molding defects, and a method for producing the same. [Means for solving the problem]

[0007] One aspect of the present invention is a method for manufacturing a hollow FRP molded product, comprising: a first step of stacking a plurality of sheet-like prepregs to form a laminate having a hollow portion therein; a second step of setting the laminate in a cavity of a mold; and a third step of applying pressure to the hollow portion within the cavity to expand the laminate while pressing it against the surface of the cavity to heat-form it, wherein in the first step, the laminate is molded to include at least one low-tack prepreg pair, in which the tack between adjacent prepreg pairs is 10 N or less.

[0008] In another aspect of the present invention, the first step may include a step of performing a tack reduction treatment on at least one prepreg of the pair of adjacent prepregs so that the tack is 10 N or less.

[0009] In another aspect of the present invention, the tack reduction treatment may be performed on both of the prepregs constituting the pair.

[0010] In another aspect of the present invention, the first step may produce the laminate so as to include a plurality of the low tack prepreg pairs.

[0011] In another aspect of the present invention, in the first step, the laminate may be manufactured so that all prepreg pairs constitute the low-tack prepreg pairs.

[0012] One aspect of the second invention is a hollow FRP molded product, in which a laminate in which a plurality of prepregs are stacked is molded by an internal pressure molding method, and the hollow FRP molded product includes at least one low-tack prepreg pair among the plurality of prepregs, in which the tack between adjacent prepreg pairs is 10 N or less.

[0013] In another embodiment of the second invention, all of the prepreg pairs may constitute the low-tack prepreg pairs.

[0014] In another embodiment of the second invention, the hollow FRP molded product may be a shaft for a golf club. [Effects of the Invention]

[0015] The hollow FRP molded product and its manufacturing method of the present invention can suppress molding defects in hollow FRP molded products obtained by internal pressure molding. [Brief explanation of the drawings]

[0016] [Figure 1] 2 is a flowchart showing each step of the manufacturing method of the present embodiment. [Figure 2] 2 is a flowchart showing a detailed example of the first step in FIG. 1. [Figure 3] FIG. 2 is a side view of a mandrel used in the manufacturing method of the present embodiment. [Figure 4] FIG. 2 is a side view of a mandrel and a laminate for explaining a first step of the present embodiment. [Figure 5] 5 is a cross-sectional view taken along line VV in FIG. 4. [Figure 6] FIG. 10 is a cross-sectional view of a mold for explaining a second step of the present embodiment. [Figure 7] FIG. 10 is a cross-sectional view of a mold for explaining a third step of the present embodiment. [Figure 8] FIG. 2 is a development view of the prepregs of the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0017] Several embodiments of the present invention are described below. The exemplary embodiments disclosed below are not intended to be limiting in any way. Furthermore, the embodiments of the present invention can be used alone or in various combinations.

[0018] 1 shows the steps of a method for manufacturing a hollow FRP molded product according to this embodiment. In this embodiment, the following description will be given using an example in which the hollow FRP molded product is a hollow shaft for a golf club. However, the hollow FRP molded product is not limited to golf club shafts, and can be applied to various hollow FRP molded products such as fishing rods, tennis rackets, and various structural piping.

[0019] 1, the method for manufacturing a hollow FRP molded product of this embodiment includes a first step S1, a second step S2, a third step S3, and a fourth step S4. The manufacturing method of this embodiment is characterized by the first step S1, in which a specific laminate is molded, and the second step S2 and subsequent steps can be carried out as appropriate in accordance with the conventional practice of internal pressure molding.

[0020] In the first step S1 of this embodiment, a plurality of sheet-like prepregs are laminated to form a laminate having a hollow portion therein. In a preferred embodiment, the first step S1 is performed, for example, according to the procedure shown in FIG.

[0021] [Determining shaft performance requirements] 2, in the first step S1 of this embodiment, the required performance of the shaft to be manufactured is determined (step S11). The required performance of the shaft may include, for example, one or more of the length, mass, outer diameter, inner diameter, bending rigidity, torque, etc.

[0022] [Determining the prepreg composition] Next, in the first step S1 of this embodiment, the prepreg configuration is determined based on the required performance (step S12). The prepreg configuration may include information such as prepreg dimensions (axial and circumferential directions of the shaft), type of prepreg, number of prepregs, and winding order. The outer diameter and axial length of the mandrel (FIG. 3), which is a core metal described below, are also determined here.

[0023] Prepregs are composites of fibers and uncured (including semi-cured) matrix resins, and in this embodiment, sheet-like prepregs are used. For example, the prepregs are heated using a mold or the like, causing the matrix resin to cure into a predetermined shape, resulting in an FRP molded product. By determining the type of prepreg, the elastic modulus of the fibers, the basis weight of the prepreg, the specific gravity of the prepreg, and the like can be determined.

[0024] The fibers of the prepreg are, for example, carbon fibers, and are oriented substantially in one direction in this embodiment. A prepreg in which the fibers are oriented substantially in one direction in this manner is also called a unidirectional prepreg. In another embodiment, a prepreg sheet in which the fibers are woven can also be used as the prepreg.

[0025] In addition to carbon fibers, examples of fibers for prepregs include glass fibers, metal fibers (boron, titanium, tungsten, stainless steel, etc.), and aramid fibers, and one or more of these can be used.

[0026] Examples of the matrix resin constituting the prepreg include thermosetting resins such as epoxy resins, unsaturated polyester resins, phenolic resins, and vinyl ester resins, and one or more of these can be used.

[0027] Furthermore, prepregs have tackiness because the uncured matrix resin is exposed on the surface. To prevent the prepreg from wrinkling or becoming dirty during storage or before use, the prepreg is usually covered on both sides with a cover sheet (release paper). When forming a laminate, as described below, the cover sheet is peeled off from the prepreg before use.

[0028] [Measurement of tack of prepreg pairs] Next, in the first step S1 of this embodiment, the tack of a pair of adjacent prepregs is measured when forming a prepreg laminate (step S13). In this specification, "tack" is an index relating to the adhesiveness of a prepreg, and the larger this value, the higher the adhesiveness.

[0029] In this specification, the "tack" of a prepreg pair is measured using a tack tester (PICMA Tack Tester II, manufactured by Toyo Seiki Seisakusho) by compressing one prepreg (the moving side) of the prepreg pair, measuring 10 mm x 10 mm, and the other prepreg (the fixed side) of the prepreg pair, measuring 50 mm x 100 mm (adhesion area: 10 mm x 10 mm), with a load of 1.96 N for 30 seconds, peeling at a rate of 10 mm / min, and measuring the resistance force (N) during peeling five times, and then averaging the results. The measurement is conducted at room temperature (23°C) within 0.5 hours of removing the cover sheet from the prepreg.

[0030] [Application of low tack prepreg pairs] Next, in the first step S1 of this embodiment, it is determined whether or not there is a low-tack prepreg pair in which the tack of adjacent prepreg pairs is 10 N or less (step S14). If the prepreg stack does not include a low-tack prepreg pair (N in step S14), a tack reduction process is performed so that at least one prepreg pair becomes a low-tack prepreg pair (step S15).

[0031] Tack reduction treatments include various processes that reduce the tackiness of the prepreg surface. For example, a prepreg with the cover sheet removed may be left at room temperature for several hours. This exposes the resin exposed on the surface of the prepreg to air, reducing the tackiness of the surface.

[0032] Another tack reduction treatment involves heating the surface of the prepreg from which the cover sheet has been removed, for example, at a temperature of 45°C or higher, preferably 50°C or higher, and more preferably 55°C or higher. Such a low-temperature heating step can be performed using an iron, a hairdryer, or an oven. Meanwhile, in the low-temperature heating step, it is desirable to adjust the heating temperature so as not to accelerate curing of the matrix resin of the prepreg. For example, when the matrix resin is an epoxy resin, the low-temperature heating step is performed at a temperature below 80°C, preferably 75°C or lower, and more preferably 70°C or lower.

[0033] In low-tack prepreg pairs, the adhesive strength between adjacent prepregs is relatively low. Therefore, when an external force is applied, adjacent prepregs in a low-tack prepreg pair tend to slide relatively easily against each other. In this embodiment, by including a low-tack prepreg pair in the laminate, the prepreg laminate is appropriately deformed in the third step described below, thereby suppressing molding defects.

[0034] Here, the tack reduction treatment may be performed on only one prepreg of an adjacent pair, as long as the tack of the prepreg pair can be reduced to 10 N or less. If the tack is large, the tack can be more effectively reduced by performing the tack reduction treatment on both prepregs constituting the pair.

[0035] In step S14, if there is a low-tack prepreg pair in which the tack of the adjacent prepreg pair is 10N or less (Y in step S14), the process may proceed to step S16 without going through step S15.

[0036] Furthermore, prior to manufacturing a shaft, the tack of multiple types of prepreg pairs can be measured and the results can be compiled into a database. In this case, by referencing the database, the step of measuring the tack of the prepreg pairs to be used (step S13) can be omitted. Furthermore, since the tack of prepreg pairs often exceeds 10 N, step S15 may be performed without performing the step of measuring the tack (step S13).

[0037] [Prepreg lamination] Next, as described above, a plurality of prepregs are laminated together so as to include at least one low-tack prepreg pair, to form a laminate having a hollow portion therein (step S16).

[0038] Fig. 3 shows a side view of mandrel 10, which is a core metal for forming a laminate for a shaft. Fig. 4 shows a side view of laminate 20 in which prepreg 22 is wound around mandrel 10, and Fig. 5 shows a cross section taken along line VV.

[0039] As shown in Figure 3, the mandrel 10 is, for example, cylindrical and has a desired taper angle in this embodiment. The axial length, outer diameter, taper angle, etc. of the mandrel can be appropriately set in step S12 of the first process S1 depending on the shaft to be manufactured. As an example, the total length of the mandrel 10 is generally about 1200 to 1400 mm, the diameter of the large diameter end 10a is about 10 to 15 mm, and the diameter of the small diameter end 10b is about 3 to 6 mm. In addition, a chuck portion 12, for example, may be provided on the side of the large diameter end 10a of the mandrel 10.

[0040] 5, a laminate 20 of prepregs 22 is obtained by sequentially winding prepregs 22 around a mandrel 10. In this embodiment, the laminate 20 is formed of five prepregs 22a to 22d. Specifically, the prepregs 22 are formed of first, second, third, fourth, and fifth prepregs 22a to 22e that are sequentially wound around the mandrel 10 from the inside.

[0041] In the above embodiment, adjacent pairs of prepregs are a first pair P1 consisting of the first prepreg 22a and the second prepreg 22b, a second pair P2 consisting of the second prepreg 22b and the third prepreg 22c, a third pair P3 consisting of the third prepreg 22c and the fourth prepreg 22d, and a fourth pair P4 consisting of the fourth prepreg 22d and the fifth prepreg 22e, for a total of four pairs. In this embodiment, it is sufficient that at least one of the first to fourth pairs P1 to P4 is a low-tack prepreg pair.

[0042] Next, the laminate 20 is removed from the mandrel 10. This results in a pipe-shaped laminate 20 having a hollow portion i (see FIG. 7) therein. It is desirable to form a thin film of lubricant on the surface of the mandrel 10 before winding and laminating the prepreg 22 around the mandrel 10, as this allows the laminate 20 to be easily removed from the mandrel 10.

[0043] [Second process] 6 shows a cross-sectional view of the mold 30 used in this embodiment. As shown in FIGS. 1 and 6, in the second step S2 of this embodiment, the laminate 20 formed in the first step S1 is set in the cavity 31 of the mold 30.

[0044] The mold 30 of this embodiment is composed of, for example, an upper mold 30A and a lower mold 30B. The upper mold 30A and the lower mold 30B are separable from each other vertically, and by separating the upper mold 30A and the lower mold 30B, for example, the laminate 20 is set in the cavity of the lower mold 30B. Thereafter, by fitting the upper mold 30A to the lower mold 30B, the laminate 20 is set in the cavity 31 for molding the outer surface of the shaft.

[0045] A heat source (not shown) is connected to the mold 30 (upper mold 30A and lower mold 30B). This heats the surface of the cavity 31 of the mold 30 to a temperature required to promote the curing of the prepreg. Although not shown, in a preferred embodiment, the cavity 31 may be connected to a vacuum device or the like for discharging excess air between the cavity 31 and the laminate 20 to the outside of the mold 30.

[0046] Furthermore, in the second step S2 of this embodiment, the elastomer tube 40 in a contracted state is inserted into the hollow portion i of the laminate 20. One end 40a of the elastomer tube 40 is closed, and the other end 40b is connected to a pressure source (not shown).

[0047] [3rd step] Fig. 7 shows a cross-sectional view of the mold 30 for illustrating the third step S3 of this embodiment. As shown in Fig. 7, in the third step S3, pressure is applied to the hollow portion i of the laminate 20 in the cavity 31, causing the laminate 20 to expand and be pressed against the surface of the cavity 31 to be thermoformed. In this embodiment, the elastomer tube 40 expands when a high-pressure fluid F is supplied into the elastomer tube 40, and the laminate 20 undergoes expansion and deformation via this elastomer tube 40.

[0048] That is, while the laminate 20 expands and deforms into the shape defined by the cavity 31 and the elastomer tube 40, heat is received from the surface of the cavity 31, and the matrix resin hardens. During this process, since the laminate 20 contains at least one low-tack prepreg pair, relative slippage between the prepregs is likely to occur. As a result, the laminate 20 can expand and deform smoothly. This prevents air from being trapped between the prepregs and also suppresses the occurrence of wrinkles on the surface of the molded product. As described above, the laminate 20 of this embodiment can be molded into a hollow FRP molded product with reduced molding defects such as wrinkles and voids.

[0049] In a preferred embodiment, a plurality of low-tack prepreg pairs can be included in the first to fourth pairs P1 to P4 of the laminate 20. In a particularly preferred embodiment, all pairs of prepregs 22 (first to fourth pairs P1 to P4) of the laminate 20 are low-tack prepreg pairs. This allows for well-balanced relative sliding between the prepregs in the third step S3, allowing the laminate 20 to expand and deform more smoothly.

[0050] In addition, when adjacent prepregs 22 are wound while being shifted in the shaft circumferential direction, the first prepreg 22a and the third prepreg 22c may be partially adjacent to each other. In such partial adjacent areas, the impact is small, so tucks here do not need to be considered a problem.

[0051] [4th step] In the fourth step S4, once the heat molding using the mold 30 is completed, the elastomer tube 40 is shrunk. Then, the upper mold 30A and the lower mold 30B are opened, and the shaft 1, which is the hollow FRP molded product formed, is removed from the cavity 31. In this way, the shaft 1 can be manufactured.

[0052] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above specific disclosure, and can be implemented in various modified forms within the scope of the technical idea described in the claims. [Example]

[0053] Based on the specifications in Table 1, several golf club shafts with an axial length of approximately 1000 mm were prototyped and evaluated for appearance and void ratio. Note that Fig. 8 shows the configuration of the prepregs 22a to 22e used, and the angle indication on the right side of the figure indicates the angle with respect to the axial direction of the prepreg fibers.

[0054] For each example, the tack of all prepreg pairs was measured in advance and all were found to exceed 10 N, so all prepregs 22a to 22e were subjected to a tack reduction treatment. The tack reduction treatment was performed by peeling off the release paper from the prepreg and leaving it at room temperature (23°C) for 96 hours. Thereafter, the tack of each prepreg pair was measured and all were found to be 10 N or less. Note that no tack reduction treatment was performed on the comparative examples.

[0055] Next, in Fig. 8, the prepreg 22a was wound around the mandrel 10 in order from the upper prepreg 22a to form a laminate. The following two types of laminate configurations were used. <Configuration example 1> First prepreg 22a: 3 sheets Second prepreg 22b: 3 sheets 3rd prepreg 22c: 3 sheets 4th prepreg 22d: 1 sheet 5th prepreg 22e: 2 sheets <Configuration example 2> First prepreg 22a: 1 sheet Second prepreg 22b: 1 sheet Third prepreg 22c: 2 sheets 4th prepreg 22d: 1 sheet 5th prepreg 22e: 2 sheets

[0056] Thereafter, the laminate was removed from the mandrel 10, and an elastomer tube was inserted into the hollow portion of the laminate. Thereafter, the laminate together with the elastomer tube was set in a mold.

[0057] Thereafter, high-pressure air (0.6 MPa) was supplied to the elastomer tube, and the cavity of the mold was heated to about 130° C., followed by heat molding for 2 hours. The cavity was then placed in a reduced-pressure atmosphere using a vacuum device.

[0058] [Shaft appearance evaluation] After heat molding, the shaft was removed from the mold and its appearance was visually inspected to determine whether there were any wrinkles or dents on the shaft surface, and a score was given out of 10. The higher the score, the better the appearance. A score of 7 or above was deemed usable as a product, and anything below that was deemed unusable.

[0059] [Evaluation of void ratio] The void fraction was measured by taking images of the cross section at a position 90 mm from the small diameter end of the shaft, a position 90 mm from the large diameter end of the shaft, and the center position in the axial direction of the shaft. The void area Sb and shaft cross-sectional area Sm were determined for each image, and the void fraction was calculated using the following formula. Table 1 shows the average void fraction at the above three positions. The smaller the value, the better the result. Rb(%) = (Sb / Sm) × 100 The test results are shown in Table 1.

[0060] [Table 1]

[0061] As a result of the test, it was confirmed that the shafts of the examples had a good appearance and a small void ratio. [Explanation of symbols]

[0062] 20 laminate 22 Prepreg 30 molds 31 Cavity i Hollow part

Claims

1. A method for manufacturing a hollow FRP molded product, A first step of laminating a plurality of sheet-like prepregs to form a laminate having a hollow portion therein; a second step of setting the laminate in a cavity of a mold; a third step of applying pressure to the hollow portion in the cavity to expand the laminate and press the laminate against the surface of the cavity to heat-mold the laminate, In the first step, the laminate is formed to include at least one low-tack prepreg pair in which the tack of adjacent prepreg pairs is 3.2 to 9.8 N; The tack of the pair of adjacent prepregs was measured using a tack tester, with one prepreg of the pair (movable side) being 10 mm x 10 mm in size and the other prepreg of the pair (fixed side) being 50 mm x 100 mm in size, with an adhesive area of ​​10 mm x 10 mm, and the prepreg was pressed together with a load of 1.96 N for 30 seconds, and then peeled off at a rate of 10 mm / min, and the resistance force (N) at the time of peeling was measured five times and calculated as the average value. The measurement is performed at 23°C and within 0.5 hours of removing the cover sheet from the prepreg. Manufacturing method for hollow FRP molded products.

2. 2. The method for producing a hollow FRP molded product according to claim 1, wherein the first step includes a step of performing a tack reduction treatment on at least one prepreg of the pair of adjacent prepregs so that the tack is 9.8 N or less.

3. The method for producing a hollow FRP molded product according to claim 2, wherein the tack reduction treatment is performed on both of the prepregs constituting the pair.

4. 4. The method for producing a hollow FRP molded product according to claim 1, wherein in the first step, the laminate is produced so as to include a plurality of the low-tack prepreg pairs.

5. 5. The method for producing a hollow FRP molded product according to claim 1, wherein in the first step, the laminate is produced so that all prepreg pairs constitute the low-tack prepreg pairs.

6. A hollow FRP molded product, A laminate in which a plurality of prepregs are laminated is formed by an internal pressure molding method, Among the plurality of prepregs, at least one low-tack prepreg pair is included, in which the tack of adjacent prepreg pairs is 3.2 to 9.8 N, The tack of the pair of adjacent prepregs was measured using a tack tester, with one prepreg of the pair (movable side) being 10 mm x 10 mm in size and the other prepreg of the pair (fixed side) being 50 mm x 100 mm in size, with an adhesive area of ​​10 mm x 10 mm, and the prepreg was pressed together with a load of 1.96 N for 30 seconds, and then peeled off at a rate of 10 mm / min, and the resistance force (N) at the time of peeling was measured five times and calculated as the average value. The measurement is performed at 23°C and within 0.5 hours of removing the cover sheet from the prepreg. Hollow FRP molded product.

7. The hollow FRP molded product according to claim 6, wherein all prepreg pairs constitute the low-tack prepreg pairs.

8. 8. The hollow FRP molded product according to claim 6 or 7, which is a shaft for a golf club.

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