Resin molded product and its manufacturing method

Abstract

To increase a strength of an entire molded product by causing long fibers to flow evenly and reliably to tips of ribs, even if a surface of the molded product has the ribs extending in a band shape with a width of several millimeters, when forming the resin molded products by press molding using fiber-reinforced resin containing the long fibers.SOLUTION: A base material sheet made of fiber-reinforced resin with a fiber orientation tensor oriented at 0.7 or more and 0.9 or less is placed around ribs so that a longitudinal direction of the ribs and a main direction of fiber orientation of the base material sheet are aligned, which is then press molded to form a resin molded product with the ribs.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a resin molded article formed using a fiber-blended resin and a method for producing the same. [Background technology]

[0002] BACKGROUND ART Resin molded products (hereinafter simply referred to as "molded products") made of fiber-reinforced resin, in which reinforcing fibers are compounded with resin, are used in a wide range of industrial fields because of their high strength and light weight.

[0003] When a base material made of fiber-reinforced resin is press-molded to form a resin molded product having protruding portions such as walls, ribs, and bosses on its surface (hereinafter simply referred to as "ribs"), the ribs may not be filled with enough fiber, and the molded product may not have the strength expected from the fiber blend. To address this issue, a technique is known that aims to increase the strength of the molded product by placing raw materials with short fiber lengths around the ribs of the molded product, thereby ensuring the fiber content of the ribs (see Patent Document 1). Furthermore, there is a known technology that aims to ensure rigidity through fiber blending even against loads in unintended directions throughout the molded product by preventing areas of low fiber orientation from occurring throughout the molded product, even when the molded product has a thickness distribution (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-148443 [Patent Document 2] Japanese Patent Publication No. 2021-104626 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, when a raw material containing short fibers is placed around the ribs, the filling of the fibers into the ribs is promoted, but the reinforcing effect is reduced because the fibers are short. Furthermore, as mentioned above, if the fiber orientation tensor is within a specified range, it is possible to ensure strength for the entire molded product. However, depending on the initial orientation and length of the fibers mixed into the raw fiber-reinforced resin and the size of the ribs provided on the molded product, the fiber orientation tensor may not be within the target range or the fiber content may be lower than expected, making it impossible to ensure the expected strength.

[0006] Specifically, the fiber-reinforced resins used in press molding contain long fibers of 10 mm or more for CF (carbon fiber) and GF (glass fiber), generally 25 mm long fibers for SMC molding, and continuous fibers for GMT molding and the like. Resins containing such long fibers lack fluidity, making it difficult to mold thin-walled molded products intended for weight reduction or molded products with complex shapes having a thickness distribution of several millimeters. When press molding is used to form a molded product with thin ribs on the surface that are several millimeters wide and thick, the long fibers of several tens of millimeters have difficulty flowing into the ribs, which are several millimeters wide, and the fiber content at the tips of the ribs is low, inevitably resulting in low strength.

[0007] In addition, ribs on molded products are generally designed to increase bending rigidity and strength in the rib direction, but in the unlikely event of a tensile mode in the direction perpendicular to the rib, defects may occur around the rib, so care must be taken in the design. Furthermore, since ribs on molded products are generally placed on the side that is least visible when the product is completed, the appearance of the back side where the ribs are placed is important. The inclusion of ribs can cause differences in the thickness of the molded product, which can lead to problems with poor appearance, such as warping or sink marks on the back side of the ribs.

[0008] In view of the above-mentioned problems, the present invention aims to, when forming a resin molded product by press molding using a fiber-reinforced resin containing long fibers, ensure that even if a strip-like rib with a width of about several millimeters is arranged on the surface of the molded product, the long fibers flow evenly and reliably to the tip of the rib, increasing the fiber content within the rib, and ensuring the strength of the entire molded product, including the rib, due to the fiber blend. [Means for solving the problem]

[0009] A resin molded product formed by press molding is basically in the form of a flat plate because the resin material is pressed, and ribs are partially arranged on the surface to impart strength to the product. As shown in Figure 1(A), a resin molded product is formed by placing a base sheet BMS, a resin material containing fiber F, in the cavity CV of a molding die M and pressing it with a core. The base sheet BMS is formed by scattering fiber F on a resin film transported at a constant speed and then sandwiching it between other resin films to form a single integrated unit. The fiber F is randomly oriented within the base sheet BMS. Therefore, in molded products with thin ribs on the surface, when the base sheet BMS is pressed, the randomly oriented fiber F bends over the ribs, forming bridges and preventing it from flowing into the ribs. This is particularly true for long fibers, as shown in Figure 1(B). In Figure 1(A) and the cross-sectional views shown below, the open circles in the base sheet BMS and molded product MLD indicate the end and cross-section of fiber F, and the long open lines indicate the side and cross-section of fiber F.

[0010] In response to this phenomenon, the present inventors have discovered that, as a means for increasing the fiber content at the tips of the ribs of a molded product, it is possible to use a base sheet BMS in which fibers F are oriented in a predetermined direction, as shown in Figure 2(A), place the base sheet BMS on the cavity CV so that the orientation of the fibers F aligns with the longitudinal direction of the ribs arranged in the molded product, and press it with a core, thereby filling the fibers F up to the tips of the ribs R of the molded product MLD, as shown in Figure 2(B). However, even if the fiber content within the ribs R can be increased by using a base sheet BMS in which fibers F are oriented in a predetermined direction, there is a risk that the physical properties of the molded product as a whole, such as its strength and mechanical properties, may decrease. Therefore, the inventors have discovered conditions for the ratio of the fiber content of the ribs and the molded product and the fiber orientation state that will ensure the strength of the entire molded product, including the ribs, and have completed the present invention.

[0011] That is, the present invention is a fiber-containing resin molded product having band-like ribs on its surface, wherein the fiber content at the tip of the rib is 60% or more of the fiber content of the entire molded product, and the fiber orientation tensor at the tip of the rib is 0.7 or more and 0.9 or less. The rib tip portion refers to the portion extending from the middle portion (half the length portion) of the protruding length of the rib to the tip side of the rib.

[0012] The present invention also provides a method for manufacturing a resin molded product having strip-shaped ribs on its surface, characterized in that a press material made of fiber-reinforced resin with a fiber orientation tensor of 0.7 to 0.9 is placed around the rib so that the longitudinal direction of the rib is aligned with the main direction of the fiber orientation of the press material, and then press-molded.

[0013] The resin molded product and its manufacturing method having the above configuration are characterized in that the ratio (L / D) of the length L of the fibers contained in the resin molded product or the press material to the width D of the rib is 3 or more. [Effects of the Invention]

[0014] According to the present invention, by disposing a base sheet made of a fiber-containing resin material with a high fiber orientation in the rib direction, it becomes easier for fibers to flow into the rib, preventing the rib from having a low fiber content. From the viewpoints of fiber content and fiber orientation, it is possible to further increase the bending rigidity and strength in the rib direction, which is the original purpose of providing the rib. If the initial fiber orientation of the base sheet is too high, it will be extremely weak in the load mode perpendicular to the rib. Therefore, it is preferable to use a base sheet with a fiber orientation tensor in the range of 0.7 to 0.9. By placing this on the surface of the molded product in the direction of the rib extension, it is possible to increase the rigidity and strength in the rib longitudinal direction and obtain a molded product without a significant decrease in strength in the rib perpendicular direction. The higher the fiber orientation in the rib direction, the higher the rigidity in the longitudinal direction of the rib, which is expected to have the effect of suppressing warpage in the longitudinal direction of the rib.In addition, in the width direction of the rib, when the fiber orientation tensor is in the range of 0.7 to 0.9, warpage is offset by sink marks on the end faces of the rib, resulting in a molded product with a flat back side, especially where the rib is installed. [Brief explanation of the drawings]

[0015] [Figure 1] 1A is a diagram for explaining an embodiment of conventional press molding, and FIG. 1B is a diagram showing a schematic cross section of a molded product. [Figure 2] 1A is a diagram illustrating an embodiment of press molding according to the present invention, and FIG. 1B is a diagram showing a schematic cross section of a molded product. [Figure 3] 1 is a cross-sectional view showing the configuration of a mold used to manufacture a molded product of the present invention. FIG. [Figure 4] 1A is a diagram illustrating one embodiment of press molding according to the present invention, and FIG. 1B is a diagram showing a schematic cross section of a molded product. [Figure 5] 1A is a diagram illustrating another embodiment of press molding according to the present invention, and FIG. 1B is a diagram showing a schematic cross section of a molded product. [Figure 6] 1A is a diagram illustrating still another embodiment of press molding according to the present invention, and FIG. 1B is a diagram showing a schematic cross section of a molded product. [Figure 7] 1A to 1D are diagrams for explaining a method for evaluating the performance of a molded article of the present invention by simulation. [Figure 8] 1 is a graph showing the correlation between the fiber orientation tensor of the raw materials and the fiber content on the tip side of the rib in the examples and comparative examples. [Figure 9] 1 is a graph showing the correlation between the fiber orientation tensor of the raw materials and the mechanical properties of the molded articles of the examples and comparative examples. [Figure 10] 1 is a graph showing the correlation between the fiber orientation tensor of the raw materials and the warpage appearing in the molded articles of the examples and comparative examples. [Figure 11] 1 is a graph showing the correlation between the ratio of fiber length to rib width, the fiber content at the tip of the rib, and the fiber orientation tensor in the rib direction. DETAILED DESCRIPTION OF THE INVENTION

[0016] A preferred embodiment of the resin molded article of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment.

[0017] (Resin molded product) One embodiment of the present invention Resin molded products MLD For example, as shown in Figure 2(B) above, the surface of the relatively flat main body portion MB is formed with at least one rib R that protrudes from the main body portion MB and extends in a strip-like shape along the main body portion MB. The ribs are provided to increase the strength of the molded product, and their width and protruding height from the surface of the main body are set appropriately depending on the required strength. However, as will be described later, the present invention makes it possible to achieve a good fiber content even when the rib is thin, with a width of only a few millimeters.

[0018] (resin) The molded product is made of a fiber-reinforced resin material. The resin material can be appropriately selected from resins that flow during molding of the molded product, and may be a thermoplastic resin or a thermosetting resin. The resin may be one type or more types.

[0019] Examples of thermoplastic resins include PEEK, polyolefin resin, polyamide resin, polycarbonate resin, ABS resin, and a mixture of two or more of these. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, and mixtures of two or more of these.

[0020] (fiber) The fibers to be blended into the fiber-reinforced resin material can be appropriately selected from fibers that have the property of increasing the strength of the resin material in the resin material. The fibers may be of one type or more.

[0021] Examples of the fiber include glass fiber, aramid fiber, carbon fiber, polyethylene fiber, and a mixture thereof. From the viewpoint of achieving the desired strength of the resin molded article, it is preferable that the fiber is one or more types of fiber selected from the group consisting of glass fiber, aramid fiber, and carbon fiber.

[0022] The length of the fibers can be appropriately determined in consideration of the type of fiber and the strength required for the molded article. If the fiber length is too short, the strength of the molded product may be insufficient, so the fiber length is preferably 1 mm or more, more preferably 5 mm or more, and even more preferably 10 mm or more. On the other hand, if the fiber length is too long, the fiber may break during molding, making it impossible to achieve the intended function, so the fiber length is preferably 100 mm or less, more preferably 50 mm or less, and even more preferably 30 mm or less. As will be described later, in the molded product of this embodiment, a base sheet with fibers oriented in approximately one direction is placed in a mold from the portion where the ribs of the molded product are arranged to the surrounding area, with the fibers oriented along the extension direction of the ribs, and then pressed to form the product. The length of the fibers arranged in the portion from the portion where the ribs are arranged to the surrounding area is not particularly limited, and they may be continuous fibers. The thickness of the fibers can be determined appropriately within the range that allows the molded article to exhibit the desired strength, and for example, fibers with a thickness of 3 μm to 150 μm can be used.

[0023] The fiber reinforced resin material may contain other components in addition to the resin and the fibers, such as a filler, a polymerization initiator, a lubricant, and the like.

[0024] The fiber content in the molded article can be determined appropriately from the viewpoint of fully achieving the intended strength and other desired physical properties of the molded article. From this viewpoint, the fiber content in the molded article is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more. Also from the above viewpoint, the fiber content in the molded article is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0025] Furthermore, the relationship between the fiber content of the entire molded product and the fiber content of the rib is such that the fiber content at the tip side of the rib, preferably from the middle part (half the length part) of the protruding length of the rib to the tip side of the rib, is 60% or more compared to the fiber content of the entire molded product. If the fiber content at the tip of the rib is 60% or more of the fiber content of the entire molded product, the strength of the molded product including the rib can be sufficiently ensured. On the other hand, if it is less than 60%, the strength of the molded product will be adversely affected.

[0026] The fiber orientation tensor is an index that represents the orientation of the fiber with the fiber at the center. Considering three mutually orthogonal coordinates (1, 2, 3 directions) as the basis, the fiber orientation tensor is expressed as a 3x3 matrix, and its diagonal components represent the magnitude of the fiber orientation in each direction. For example, if the 11 component is large, it means that the fibers are oriented in one direction. In addition, the sum of the diagonal components (11, 22, 33 components) is "1". The fiber orientation tensor in this invention is the value of 11 components when the extension direction of the rib is defined as one direction. It is effective to arrange ribs in the direction in which the strength and rigidity of the molded product are required, and this is often the general design practice. In this invention, a large fiber orientation tensor in the rib direction can increase the strength and rigidity in the direction required by the molded product. However, if the fibers are oriented too much in one direction, the fiber orientation in the other two directions will be small, and the effect of the fibers in improving the strength of the resin molded product in those other two directions may be insufficient. From this perspective, strength can be ensured by setting the fiber orientation tensor at the tip of the rib of the molded product to 0.7 or more and 0.9 or less. The fiber orientation tensor can be measured by a known method. For example, the fiber orientation tensor in a resin composition can be determined using an industrial X-ray CT scanner and software capable of analyzing three-dimensional images of the fibers in the resin composition obtained by the scanner.

[0027] Furthermore, the ratio (L / D) of the length L of the fibers contained in the molded product or fiber reinforced resin material to the width D of the rib is preferably 3 or more. If the ratio (L / D) is 3 or more, the long fibers flowing into the ribs can sufficiently increase the strength of the narrow ribs. On the other hand, if the ratio is less than 3, the fibers flowing into the ribs will be short, making it difficult to obtain the reinforcing effect of the fiber blending on the molded product.

[0028] (Manufacturing method) The molded article of this embodiment having strip-like ribs on its surface is formed by placing a base sheet made of a fiber-reinforced resin material in a press molding die and pressing it. 3 shows the configuration of an example of a press-molding die M. The die M is composed of a cavity CV having a recessed portion shaped to correspond to the outer shapes of the main body MB and ribs R of the molded product MLD, and a core CO having a protruding portion that extends toward the recessed portion, and with a base sheet BMS disposed between the cavity CV and the core CO, the protruding portion of the core CO is advanced into the recessed portion of the cavity CV to press the base sheet BMS, causing the resin in the base sheet BMS to flow through the internal space of the die M and form the molded product MLD.

[0029] As shown in Figure 3, the base sheet BMS used in the press molding is placed in a mold M, one or more sheets stacked, and pressed.In order to make it easier for the fibers to flow into the ribs during press molding, it is preferable to use a resin in which the fibers are blended with the resin and oriented so that their orientation tensor is 0.7 or more and 0.9 or less. Then, the base sheet BMS is placed in the mold M so that the direction in which the groove portion for forming the rib provided in the mold M extends is aligned with the main direction of the fiber orientation of the base sheet BMS, and the core CO is advanced toward the cavity CV to press the base sheet BMS, which makes it easier for the fibers to enter the rib and enables the fiber content rate at the tip of the rib to be increased.

[0030] The base sheet BMS does not necessarily have to have all fibers aligned in the same direction. For example, as shown in Figure 4(A), by arranging the portion of the base sheet BMS with the highly oriented fibers in and near the grooves for forming the ribs in the mold M and aligning the fiber orientation along the extension direction of the grooves, press molding can be performed. This makes it easier for the fibers to flow into the ribs R, as shown in Figure 4(B), and it is possible to obtain a molded product MLD with a high fiber content near the tip of the rib. In this case, the fibers in the peripheral portion of the base sheet BMS, away from and near the grooves for forming the ribs in the mold M, may be randomly oriented or oriented perpendicular to the extension direction of the grooves.

[0031] Furthermore, as shown in Figure 5(A), by forming a portion of the base sheet BMS where the fibers are highly oriented on the groove side of the cavity CV for forming the rib, and a portion above this portion where the fibers are randomly oriented or oriented in a direction perpendicular to the extension direction of the groove, and then press-molding this, the fibers can easily flow into the rib R, as shown in Figure 5(B), and it is possible to obtain a molded product MLD with a high fiber content at the tip side of the rib. Furthermore, as shown in Figure 6(A), by laying out the fiber orientation in multiple stages in the thickness direction of the sheet, so that from the groove side of the cavity CV for forming the rib, there is a section where the fibers are highly oriented, above which the fibers are randomly oriented or oriented in a direction perpendicular to the extension direction of the groove, and above that a section where the fibers are highly oriented, and then press-molding this, it is possible to easily flow the fibers into the rib R, as shown in Figure 6(B), and to obtain a molded product MLD with a high fiber content at the tip side of the rib. These base sheet BMS can be composed of a single sheet or multiple overlapping sheets.

[0032] (Verification of molded product characteristics) The results of computer simulation of the mechanical properties of a molded product formed by the above-described configuration and manufacturing method will be described below.

[0033] For the verification, as shown in Figure 7, a molded product MLD was used, which had a shape in which a rib R was protruding from the center of the underside of a flat, rectangular main body MB in a plan view, extending between both longitudinal ends of the main body MB. The molded product MLD was formed by press-molding a base sheet made of fiber-reinforced resin, which was unsaturated polyester resin blended with carbon fiber having a fiber length L of 25 mm. The dimensions of each part of the molded product MLD are: length V of the main body MB is 50 mm, width W is 15 mm, width D of the rib R is 2 mm, and protrusion height H is 8 mm. The ratio of fiber length L to width D of rib R (L / D) is 12.5, and the ratio to protrusion height H (L / H) is 3.125.

[0034] The computer simulation used resin flow analysis software 3D TIOMN CompositePRESS to set the initial fiber orientation of the base sheet, which is the raw material, and then analyzed and evaluated the state of fiber flow into the tip of the rib R of the molded product MLD and warpage in relation to the initial fiber orientation.In addition, structural analysis software LS-DYNA was used to carry out a structural analysis that took into account the fiber state of the molded product and evaluate its strength.

[0035] Example 1 The fiber orientation tensor in the rib direction of the raw material was set to 0.875, and the fiber orientation tensor in the direction perpendicular to the ribs within the raw material sheet plane was set to 0.125, and this was press-molded to form the molded product MLD.

[0036] Example 2 The fiber orientation tensor in the rib direction of the raw material was set to 0.75, and the fiber orientation tensor in the direction perpendicular to the ribs within the raw material sheet plane was set to 0.25, and this was press-molded to form the molded product MLD.

[0037] Comparative Example 1 The fiber orientation tensor in the rib direction of the raw material was set to 1 (the extension direction of the rib), and the fiber orientation tensor in the direction perpendicular to the rib within the raw material sheet plane was set to 0, and this was press-molded to form the molded product MLD.

[0038] Comparative Example 2 The fiber orientation tensor in the rib direction of the raw material was set to 0.625, and the fiber orientation tensor in the direction perpendicular to the ribs within the raw material sheet plane was set to 0.375, and this was press-molded to form the molded product MLD.

[0039] Comparative Example 3 The fiber orientation tensor of the raw material in the rib direction was set to 0.5, and the fiber orientation tensor in the direction perpendicular to the rib within the raw material sheet plane was set to 0.5, and this was press-molded to form the molded product MLD. The fiber orientation tensor setting of the raw material in this example is equivalent to the case where the fibers are randomly oriented in various directions within the base sheet BMS, as shown in Figure 1 above.

[0040] For the molded articles MLD of the above-mentioned examples and comparative examples, the fiber orientation tensor in the rib direction in the range of the tip half of the protruding height H of the rib R and the fiber content in the entire molded article were derived. The results are shown in Table 1 and Figure 8. Figure 8 shows the fiber content and fiber orientation tensor in the rib direction at the tip side of the rib R when the fiber orientation tensors of the raw materials of the above-mentioned Examples and Comparative Examples are used.

[0041] The mechanical properties of the molded articles MLD of the above examples and comparative examples were examined. The verification was carried out by calculating the maximum bending moment when a load was applied to both longitudinal ends of the molded product MLD, as shown in Figure 7(A), and the maximum tensile load when a load was applied to both ends of the main body part MB of the molded product MLD so as to pull them outward toward each other in a direction perpendicular to the rib R, as shown in the same figure (B). The maximum bending moment and maximum tensile load derived in Comparative Example 3, where the fiber orientation of the raw material was random, were set to 1, and the ratios of these to the derived results for each Example and Comparative Example were calculated. The calculation results are shown in Table 1 and Fig. 9. Fig. 9 shows the mechanical properties of molded articles when the fiber orientation tensors of the raw materials of the Example and Comparative Example are used.

[0042] Furthermore, the molded articles MLD of the above-mentioned Examples and Comparative Examples were analyzed to see how much warpage occurred due to the influence of heat and fiber orientation after molding. As shown in Figure 7(C), the analysis was performed by taking the coordinates of the center point A of the main body MB of the molded product MLD and point B, which is at one end of the main body MB in the longitudinal direction and directly above the rib R, up and down, and deriving the warpage between points A and B. Also, as shown in the same figure (D), the analysis was performed by taking the coordinates of the center point A of the main body MB and point B, which is at the end of the main body MB in the lateral direction, up and down, and deriving the warpage between points A and B. As in the above, the warpage derived in Comparative Example 3 was set to 1, and the ratio of this to the results derived for each Example and Comparative Example was calculated. The calculation results are shown in Table 1 and Fig. 10. Fig. 10 shows the correlation of warpage appearing in molded products when the fiber orientation tensors of the raw materials of the Examples and Comparative Examples are used.

[0043] [Table 1]

[0044] According to the results of the simulation, in Example 1, where the fiber orientation tensor in the rib direction of the raw material was set to 0.875, and in Example 2, where it was set to 0.75, the fiber orientation tensor in the rib direction at the tip end of the rib of the molded product was 0.83 and 0.80, respectively, and the fiber content of the entire molded product was 74% and 62%, respectively.It was confirmed that the amount of fiber flowing into the rib could be increased in both cases compared to the molded product of Comparative Example 3, which used a raw material with a random fiber orientation. It was also confirmed that the maximum bending moment of the molded products of Examples 1 and 2 was larger than that of Comparative Example 3. On the other hand, the maximum tensile load in the direction perpendicular to the rib was smaller than that of Comparative Example 3, but this was not an extreme reduction, such as a reduction to half of the maximum tensile load, and is therefore not considered to be a problem in practical use. Furthermore, in the molded products of Examples 1 and 2, because the fiber orientation is along the extension direction of the rib, it was confirmed that warpage in the rib direction after molding is suppressed, and warpage in the direction perpendicular to the rib direction is also suppressed. Warpage perpendicular to the rib direction is offset by sink marks on the end faces of the ribs, making it possible to obtain molded products with a flat backside where the ribs are installed. In the molded products of Examples 1 and 2, the fiber content of the ribs is increased and the maximum bending moment is increased, thereby increasing the strength of the entire molded product including the ribs, and it is possible to ensure the strength of the ribbed molded product expected from the fiber blend.

[0045] When a raw material with fiber orientation aligned in the extension direction of the rib is used, as in Comparative Example 1, the fiber content in the rib increases, resulting in a high fiber content. However, the maximum tensile load in the direction perpendicular to the rib of the molded product is less than half that of Comparative Example 3, which used a raw material with random fiber orientation, resulting in an extreme decrease in rigidity in the same direction, which creates practical problems. In addition, in Comparative Example 2, in which the fiber orientation tensor in the rib direction of the raw material was set to 0.625, the fiber orientation tensor in the rib direction at the tip of the rib of the molded product was 0.78, and the fiber content of the entire molded product was 49%.The maximum bending moment was not much different from that of Comparative Example 3, and no contribution to increasing the strength of the molded product was observed.

[0046] From the above results, it can be confirmed that it is preferable to press-mold a molded product using a raw material with a fiber orientation tensor in the rib direction of 0.7 to 0.9, which is the range enclosed by the approximately rectangular frame lines in Figures 9 and 10. This allows for a molded product in which the fiber content at the rib tip end is 60% or more compared to the fiber content of the entire molded product, and the fiber orientation tensor at the rib tip end is set in the range of 0.7 to 0.9, making it possible to increase the strength of the entire molded product, including the ribs.

[0047] Next, we will show the analysis results of molded products when the ratio of fiber length L to rib width R (L / D) is changed.

[0048] Example 3 A molded article MLD was formed under the same conditions as in Example 1, except that the ratio (L / D) of the fiber length L to the width D of the rib R was set to 6.25.

[0049] Example 4 A molded article MLD was formed under the same conditions as in Example 1, except that the ratio (L / D) of the fiber length L to the width D of the rib R was set to 3.125.

[0050] Comparative Example 4 A molded article MLD was formed under the same conditions as in Comparative Example 3, except that the ratio (L / D) of the fiber length L to the width D of the rib R was set to 6.25.

[0051] Comparative Example 5 A molded article MLD was formed under the same conditions as in Comparative Example 3, except that the ratio (L / D) of the fiber length L to the width D of the rib R was set to 3.125.

[0052] Comparative Example 6 A molded article MLD was formed under the same conditions as in Example 1, except that the ratio (L / D) of the fiber length L to the width D of the rib R was set to 1.25.

[0053] Comparative Example 7 A molded article MLD was formed under the same conditions as in Comparative Example 3, except that the ratio (L / D) of the fiber length L to the width D of the rib R was set to 1.25.

[0054] For the molded articles MLD of Examples 3 and 4 and Comparative Examples 4 to 7, the fiber orientation tensor in the rib direction in the range of 1 / 2 of the tip side of the rib protrusion height H and the fiber content relative to the entire molded article were derived in the same manner as described above.In addition, the maximum bending moment when a load was applied to both longitudinal ends of the molded article MLD was derived, and the ratio of the fiber length L to the rib R (L / D) to the same Examples or Comparative Examples was calculated. The results derived for Example 3 and Comparative Example 4 are shown in Table 2, the results derived for Example 4 and Comparative Example 5 are shown in Table 3, and the results derived for Comparative Examples 6 and 7 are shown in Table 5.

[0055] [Table 2]

[0056] [Table 3]

[0057] [Table 4]

[0058] Furthermore, molding analysis was performed with the ratio of the fiber length L to the width D of the rib R (L / D) set to 12.5, 6.25, 3.125, and 1.25, and the fiber orientation tensor of the raw material in the rib direction set to 1, 0.75, and 0.5, and the ratio of the fiber content at the tip of the rib to the entire molded product was calculated and the results are shown in Figure 11. The condition where the ratio of the fiber length L to the width D of the rib R (L / D) was 12.5 corresponds to Example 2, Comparative Example 1, and Comparative Example 3.

[0059] In press materials containing long fibers, the reinforcing effect of the ribs is expected, but as shown here, there is a tendency for the inflow of fibers into the ribs to be suppressed. However, by setting the fiber orientation tensor to 0.7 or higher, fibers can easily enter the rib tips, making it easier to achieve sufficient reinforcing effect. Also, when the L / D is less than 3, sufficient fibers will flow into the ribs even if the fiber orientation of the raw material is not aligned in the rib direction, but the reinforcing effect expected from the fibers will be reduced.

[0060] Furthermore, as shown in Tables 2 to 4, when the ratio (L / D) of fiber length L to rib width D is small, the molding modes of Examples 3, 4, and Comparative Example 6, which use a raw material with a rib-direction fiber orientation tensor of 0.875, as in Example 1, have shorter fibers in the resin material, resulting in a higher fiber content near the rib tip than Examples 1 and 2. On the other hand, when the fibers are short, the fibers tend to rotate toward the rib tip as the resin flows into the rib, resulting in a smaller fiber orientation tensor in the rib direction than Examples 1 and 2. However, as is clear from the analysis results of Examples 3 and 4 and Comparative Example 5, which have the same ratio (L / D), the maximum bending moment of the molded products of Examples 3 and 4 is greater than that of the molded products of both Comparative Examples, which use a raw material with a random fiber orientation. Furthermore, Comparative Example 6, which has the smallest ratio (L / D), has a molded product with a maximum bending moment not significantly different from that of Comparative Example 7, and the expected fiber inclusion effect is not achieved.

[0061] As in Examples 1 and 2 and Comparative Examples 1 to 3, if the ratio (L / D) of fiber length L to width D of rib R is large, that is, if fiber length L is sufficiently large relative to width D, the flow of long fibers into the rib increases the maximum bending moment of the molded product. Even if a raw material containing shorter fibers is used, as long as the ratio (L / D) of Example 3 is 6.25, the maximum bending moment will be greater than that of the molded products of each of the comparative examples. Also, even if the fibers are shorter than that, and the ratio (L / D) of Example 4 is about 3.125, the maximum bending moment will be greater than that of the molded product of Comparative Example 5, which uses a raw material with the same ratio (L / D) and random fiber orientation. This fully demonstrates the effect of facilitating the flow of fibers into the ribs of the molded product and further increasing the bending rigidity and strength in the rib direction. Although it depends on the shape and placement of the ribs on the molded product, if the ratio of fiber length L to rib width D (L / D) is approximately 3 or more, the fiber content at the tip of the rib will be sufficiently increased, and the strength of the ribbed molded product can be ensured as expected from the fiber blend.

[0062] Although the preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the illustrated forms or molding conditions shown in the examples. The embodiments are merely examples, and various modifications can be made based on design requirements, etc., within the scope of the gist of the present invention. [Explanation of symbols]

[0063] MLD resin molded product (molded product), MB main body, R rib, BMS base sheet, M mold, CO core, CV cavity

Claims

1. A method for producing a resin molded product having band-like ribs on the surface using a resin containing fibers with a fiber length of 5 mm or more, characterized in that a base sheet made of fiber-reinforced resin with a fiber orientation tensor oriented to 0.7 to 0.9 is placed around the ribs so that the longitudinal direction of the ribs and the main direction of the fiber orientation of the base sheet are aligned, and then press-molded.

2. 2. The method for manufacturing a resin molded product according to claim 1, wherein the fibers contained in the base sheet have a ratio (L / D) of their length L to the width D of the rib of the resin molded product of 3 or more.

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