Molded component

Abstract

To provide a molded component of uneven thickness that is lightweight yet has excellent strength and appearance.　A molded component 1 is made of a thermoplastic resin and comprises a base 2 and first ribs 6. The base 2 has a thin part 3, a thick part 4, and a step part 5 formed between the thin part 3 and the thick part 4. The first ribs 6 protrude from one surface 3a of the thin part 3 in the thickness direction of the thin part 3 and contact the step part 5. The ratio of foam cells in the thin part 3 is 0-5%. The ratio of foam cells in the thick part 4 is 5-50%. A width W of the base of the first ribs 6 is 1.0 times or more the average thickness t1 of the thin part 3. The ratio of the foam cells in the first ribs 6 is from more than 0% to 90%.

Description

Formed part

[0001] The present invention relates to a formed part with uneven wall thickness having a thin-walled part and a thick-walled part, more specifically, a formed part made of a thermoplastic resin.

[0002] As a means for increasing the strength of a resin molded body, a method of forming ribs on the back surface of a base material for reinforcement is widely adopted. On the other hand, during injection molding, it is difficult for molten resin to flow into the rib portion, and it is difficult for the filling pressure to reach the tip of the rib. Due to this, sink marks (depressions) along the rib shape may occur on the surface on the opposite side of the rib. This problem becomes more prominent as the area of the formed part increases or as the wall thickness of the formed part decreases. Although the sink marks can be made less noticeable by reducing the height or width of the ribs, the reinforcement effect decreases.

[0003] As a method for suppressing such sink marks, there is foam molding. Patent Document 1 (PCT / JP2023 / 39703) proposes a formed part that is lightweight while being excellent in strength and appearance. The formed part of Patent Document 1 includes a base and a plurality of ribs formed so as to project from one surface of the base in the thickness direction of the base. In the formed part of Patent Document 1, the flatness of the surface opposite to the surface on which the plurality of ribs of the base are formed is 15 μm or less, the width of the root portion of each of the plurality of ribs is 1.0 to 4.0 times the average thickness t of the base, the ratio of foam cells in the base is 0 to 5%, and the ratio of foam cells in each of the plurality of ribs is 0 to 90%. At least one of the plurality of ribs has foam cells. The difference between the maximum value and the minimum value of the ratio of foam cells in the plurality of ribs is 35% or less.

[0004] PCT / JP2023 / 39703

[0005] However, the formed part of Patent Document 1 has a constant thickness of the base, and no proposal has been made regarding the reinforcement effect in a formed part with uneven wall thickness having a thin-walled part and a thick-walled part. That is, regarding the reinforcement of the thin-walled part where the strength can be more easily reduced in a formed part with uneven wall thickness, no proposal has been made.

[0006] An object of the present disclosure is to provide a formed part that is lightweight while being excellent in strength and appearance in a formed part with uneven wall thickness.

[0007] To solve the above-mentioned problems, the molded part of the present disclosure employs the following solutions. Specifically, the molded part according to the present disclosure is a molded part made of thermoplastic resin and comprises a base having a thin-walled portion, a thick-walled portion, and a stepped portion formed between the thin-walled portion and the thick-walled portion, and a first rib that protrudes from one surface of the thin-walled portion in the thickness direction of the thin-walled portion and is in contact with the stepped portion. The proportion of foamed cells in the thin-walled portion is 0 to 5%. The proportion of foamed cells in the thick-walled portion is 5 to 50%. The width W of the base portion of the first rib is 1.0 times or more the average thickness t1 of the thin-walled portion. The proportion of foamed cells in the first rib is greater than 0% and 90% or less.

[0008] According to this disclosure, a molded part with uneven thickness is provided that is lightweight while having excellent strength and appearance.

[0009] Figure 1 is a schematic perspective view showing the configuration of a molded part according to the first embodiment of this disclosure. Figure 2 is a schematic perspective view showing the configuration of a molded part according to the second embodiment of this disclosure. Figure 3 is a schematic perspective view showing the configuration of a molded part according to the third embodiment of this disclosure. Figure 4 is a schematic diagram showing a bending test performed in the example.

[0010] (Configuration 1) The molded part according to the embodiment of the present disclosure is a molded part made of thermoplastic resin and comprises a base having a thin-walled portion, a thick-walled portion, and a stepped portion formed between the thin-walled portion and the thick-walled portion, and a first rib that protrudes from one surface of the thin-walled portion in the thickness direction of the thin-walled portion and is in contact with the stepped portion. The proportion of foamed cells in the thin-walled portion is 0 to 5%. The proportion of foamed cells in the thick-walled portion is 5 to 50%. The width W of the base portion of the first rib is 1.0 times or more the average thickness t1 of the thin-walled portion. The proportion of foamed cells in the first rib is greater than 0% and 90% or less.

[0011] This makes it possible to obtain molded parts with uneven thickness that are lightweight yet have excellent strength and appearance.

[0012] (Configuration 2) In the molded part of Configuration 1, when the average thickness of the thin-walled portion is t1, the average thickness of the thick-walled portion is t2, and the average height of the first rib is t3, the equation (t2-t1) ≤ t3 ≤ 5.0(t2-t1) may be satisfied. This makes it possible to achieve a good balance between weight reduction and strength.

[0013] (Configuration 3) A molded part according to Configuration 1 or 2, which may further include a second rib that protrudes from one side of the thickened portion in the thickness direction of the thickened portion and extends from the first rib. This can further improve strength.

[0014] (Configuration 4) A molded part made from any one of Configurations 1 to 3, wherein a plating film may be formed on the surface of the molded part. This improves the aesthetic appearance of the molded part and also improves the strength of the molded part, such as its flexural modulus.

[0015] (Configuration 5) A molded part made from any one of Configurations 1 to 4, wherein the thermoplastic resin may be an amorphous resin or a crystalline resin. By using an amorphous resin for the thermoplastic resin, a glossy and high-quality appearance similar to that of a solid product can be obtained even when foam molding is performed. Furthermore, by using a crystalline resin for the thermoplastic resin, the ratio of foam cells in the ribs can be increased by combining it with a filler, etc.

[0016] The embodiments of this disclosure will be described in detail below with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0017] [First Embodiment] As shown in Figure 1, the molded part 1 is a molded part made of thermoplastic resin and comprises a base 2 and a plurality of ribs 6.

[0018] The base 2 has a thin-walled portion 3 and a thick-walled portion 4. The thin-walled portion 3 and the thick-walled portion 4 each have a shape that extends in a direction perpendicular to the thickness direction. That is, the thin-walled portion 3 and the thick-walled portion 4 each have a flat plate shape. However, the thin-walled portion 3 and the thick-walled portion 4 may each have a three-dimensional shape with irregularities in the in-plane direction, or they may have a curved shape.

[0019] The thin-walled section 3 and the thick-walled section 4 have different thicknesses. That is, the average thickness t1 of the thin-walled section 3 is smaller than the average thickness t2 of the thick-walled section 4. Therefore, a step 5 is formed between the thin-walled section 3 and the thick-walled section 4.

[0020] The average thickness t1 of the thin-walled portion 3 may be 0.5 to 3.0 mm. If the average thickness t1 is too small, it becomes difficult to ensure strength and to fill the mold with molten resin during molding. On the other hand, if the average thickness t1 is too large, it becomes difficult to reduce the proportion of foamed cells, which will be described later. The lower limit of the average thickness t1 is preferably 1.0 mm, and the upper limit of the average thickness t1 is preferably 2.0 mm. In other words, the average thickness t1 of the thin-walled portion 3 is preferably 1.0 mm to 2.0 mm. To put it another way, the average thickness t1 is preferably 0.5 mm or more, preferably 1.0 mm or more, and preferably 3.0 mm or less, preferably 2.0 mm or less.

[0021] The average thickness t2 of the thick-walled portion 4 is greater than the average thickness t1 of the thin-walled portion 3, and may be limited to 20 times the average thickness t1 of the thin-walled portion 3. For example, the average thickness t2 of the thick-walled portion 4 can be 3 mm to 60 mm or less. If the average thickness t2 is too small, it may be difficult to ensure strength. On the other hand, if the average thickness t2 is too large, the weight of the molded part may increase, and the reinforcing effect of the ribs 6 may become relatively small. From this viewpoint, the average thickness t2 of the thick-walled portion 4 should be 3 mm to 60 mm, preferably 10 mm to 50 mm, and more preferably 20 mm to 40 mm. In other words, the average thickness t2 should be 3 mm or more, preferably 10 mm or more, and more preferably 20 mm or more, and 60 mm or less, preferably 50 mm or less, and more preferably 40 mm or less.

[0022] The average thickness t1 and average thickness t2 can be calculated as follows. The average thickness t1 can be calculated by measuring the thickness at five locations in a plan view: the geometric center position and four arbitrary locations at the outer edge of the thin-walled portion 3, using calipers, and taking the arithmetic mean of these five thicknesses as the average thickness t1. The average thickness t2 can be calculated by measuring the thickness at five locations in a plan view: the geometric center position and four arbitrary locations at the outer edge of the thick-walled portion 4, and taking the arithmetic mean of these five thicknesses as the average thickness t2.

[0023] Each of the multiple ribs 6 is formed to protrude from one surface 3a of the thin-walled portion 3 in the thickness direction of the thin-walled portion 3. Preferably, the direction of protrusion of the ribs 6 is perpendicular to one surface 3a of the thin-walled portion 3. Furthermore, each of the multiple ribs 6 is in contact with the stepped portion 5. Here, "the ribs 6 are in contact with the stepped portion 5" includes not only the case where the base 2 and the ribs 6 are molded separately and the ribs 6 are bonded so as to be in contact with the stepped portion 5, but also the case where the base 2 and the ribs 6 are integrally molded so that the ribs 6 extend from the stepped portion 5. Note that the molded part 1 may have two or more ribs 6, or it may have one rib 6.

[0024] Furthermore, although Figure 1 shows that each of the multiple ribs 6 has a rectangular cross-sectional shape, other cross-sectional shapes are also possible. For example, the cross-sectional shape of the rib 6 may be trapezoidal or semicircular. Alternatively, the cross-sectional shape of the rib 6 may be circular. That is, the rib 6 may be cylindrical in shape, extending from the stepped portion 5 along one surface 3a of the thin-walled portion 3. The cross-sectional shape of the rib 6 may be other shapes than rectangle or trapezoid, but from the viewpoint of ease of filling with molten resin, it is preferable to be rectangular or trapezoidal. Note that the cross-section referred to here is the cross-section obtained by cutting the rib 6 in a direction perpendicular to the direction in which the rib extends in one direction, in a plan view (when the molded part 1 is viewed from the thickness direction of the thin-walled portion 3; the same applies hereinafter).

[0025] In the illustration, the multiple ribs 6 are formed to extend parallel to each other in a plan view, but they may also be formed to intersect each other, or they may be formed in a grid pattern.

[0026] Each of the widths W of the base portion of the rib 6 may be 1.0 times or more the average thickness t1 of the thin-walled portion 3. Also, each of the widths W of the base portion of the rib 6 may be 4.0 times or less the average thickness t1 of the thin-walled portion 3. Here, the "width of the base portion" of the rib refers to the dimension of the portion adjacent to the thin-walled portion 3, and if the rib has a shape that extends in one direction in a plan view (i.e., if the rib has a short side and a long side in a plan view), it refers to the dimension in the direction perpendicular to the direction in which the rib extends in a plan view. In other words, the "width of the base portion" of the rib refers to the dimension of the portion adjacent to the thin-walled portion 3, and is the dimension in the direction of the short side of the rib in a plan view. Furthermore, if the rib has a semicircular or cylindrical shape that extends along one surface 3a of the thin-walled portion 3, the diameter in a cross-sectional view may be used as the "width of the base portion" of the rib.

[0027] The rib 6 may have a cylindrical, conical, or frustoconical shape that protrudes in the thickness direction of the thin-walled portion 3 from one surface 3a of the thin-walled portion 3. In this case, the rib 6 has a circular plan view shape and a rectangular, triangular, or trapezoidal cross-sectional shape. The protrusion height of the rib 6 from one surface 3a of the thin-walled portion 3 can be approximately the same as the average height t3 of the rib 6 shown in Figure 1 and the average height t3 of the rib 6 shown in the second embodiment described later (see Figure 2). Multiple ribs 6 that protrude in a cylindrical shape, etc., may be arranged in parallel along one surface 3a of the thin-walled portion 3, multiple ribs may be scattered on one surface 3a of the thin-walled portion 3, they may be arranged individually, or they may be formed in combination with the long rib 6 shown in Figure 1. The width W of the base portion of the rib 6 that protrudes in a cylindrical shape, etc., can be the diameter in plan view of the location adjacent to the thin-walled portion 3. In this disclosure, even when protruding in a cylindrical shape, etc., it is included in the definition of "rib".

[0028] If the width W of the base portion of the rib 6 is too small, it becomes difficult to foam the rib 6, and it may become difficult to increase the ratio of foam cells, as described later. On the other hand, if the width W of the base portion of the rib 6 is too large, the weight of the molded part 1 may increase. The lower limit of the width W of the base portion may preferably be 1.2 times the average thickness t1 of the thin-walled portion 3. The upper limit of the width W of the base portion is preferably 3.0 times the average thickness t1 of the thin-walled portion 3. In other words, the width W of the base portion of the rib 6 should be between 1.0 and 4.0 times the average thickness t1 of the thin-walled portion 3, preferably between 1.2 and 3.0 times.

[0029] In the base 2, the flatness of the surface opposite to the surface on which the multiple ribs 6 are formed may be 15 μm or less. Even when a large number of ribs 6 are arranged on a thin-walled, large-area thin-walled portion 3, it is preferable that no sink marks (recesses) visible to the naked eye occur on the opposite surface. "Surface flatness" refers to the maximum depth of the recess from a virtual surface (reference surface) extended from the base 2. "Surface flatness" can be measured by a stylus-type step meter, an optical shape measuring instrument, a microscope, etc. The surface flatness may preferably be 10 μm or less, and more preferably 5 μm or less. However, a smaller value for surface flatness is preferable.

[0030] In this embodiment, the molded part 1 has a foam cell ratio of 0 to 5% in the thin-walled portion 3, a foam cell ratio of 5 to 50% in the thick-walled portion 4, and a foam cell ratio of 0% to 90% in each of the multiple ribs 6. However, if there are multiple ribs 6, at least one rib 6 has foam cells. That is, the foam cell ratio of at least one rib 6 is greater than 0% and 90% or less.

[0031] The "foam cell ratio" refers to the area percentage occupied by foam cells in a two-dimensional image of the cross-section of molded part 1 (a cross-section parallel to the thickness direction of base 2). The foam cell ratio can be determined by observing the cross-section with a scanning electron microscope (SEM) or optical microscope and performing image analysis.

[0032] In this embodiment, it is preferable to lower the proportion of foamed cells in the thin-walled section 3 and increase the proportion of foamed cells in the rib 6. This improves the strength, appearance, and productivity of the molded part 1. Specifically, lowering the proportion of foamed cells in the thin-walled section 3 ensures the necessary strength and resin filling during molding. Increasing the proportion of foamed cells in the rib 6 reduces the weight of the rib and suppresses sink marks directly beneath the rib, improving the appearance of the molded part 1.

[0033] The ratio of foam cells in the thin-walled section 3 shall be measured using a 500 μm × 500 μm field of view image in a two-dimensional image of the cross-section of the molded part 1 (a cross-section parallel to the thickness direction of the base 2), centered on the center of the area directly below the rib (the center in the thickness direction of the thin-walled section 3 and the center in the width direction of the rib 6).

[0034] The upper limit of the proportion of foamed cells in the thin-walled portion 3 is preferably 4%, and more preferably 3%.

[0035] On the other hand, the ratio of foam cells in rib 6 is measured using a 500 μm × 500 μm field of view image at three locations in the width direction of the rib: near the base of rib 6, near the height direction of rib 6, and near the tip of rib (excluding the skin layer), excluding the area directly beneath the rib as described above, and the average is calculated. Furthermore, the "ratio of foam cells in rib" is determined for each of the multiple ribs. In this embodiment, the ratio of foam cells in each of the multiple ribs 6 is set to 0 to 90%. However, at least one of the multiple ribs 6 has foam cells. That is, at least one of the foam cell ratios of the multiple ribs 6 is not 0. At least one of the foam cell ratios of the multiple ribs 6 is preferably 5% or more, and more preferably 10% or more.

[0036] The higher the proportion of foam cells in the rib 6, the lighter the rib 6 can be and the more sink marks can be suppressed. (Note that when molding the molded part 1 by injection molding, sink marks are less likely to occur near the gate, so sink marks can be suppressed even if the proportion of foam cells is low for ribs located near the gate. It is preferable to increase the proportion of foam cells for ribs located far from the gate.) On the other hand, if the proportion of foam cells in the rib 6 is too high, it may become difficult to stably control the proportion of foam cells throughout the entire molded part 1. Also, it may be necessary to complicate the structure of the mold in injection molding. The lower limit of the proportion of foam cells in the rib is preferably 10%, more preferably 20%, and even more preferably 30%. The upper limit of the proportion of foam cells in the rib is preferably 80%, and even more preferably 70%. That is, the range of the proportion of foam cells in the rib 6 is preferably greater than 0% and 90% or less, more preferably 10% or more and 80% or less, and even more preferably 30% or more and 70% or less.

[0037] The finer each foam cell is, the better. The average diameter of the foam cells in rib 6 is preferably 1000 μm or less. More preferably, the average diameter of the foam cells in rib 6 is 500 μm or less, and even more preferably 300 μm or less. However, a smaller average diameter value for the foam cells in rib 6 is preferable.

[0038] In molded part 1, the difference between the maximum and minimum values ​​of the foam cell ratio in each of the multiple ribs 6 may be set to 35% or less. That is, referring to Figure 1, the difference between the ratio of the rib 6 with the largest foam cell ratio and the ratio of the rib 6 with the smallest foam cell ratio among the three ribs 6 may be set to 35% or less. Here, "35% or less" does not mean "35% or less relative to some standard value," but rather means that the difference (in %) between the maximum value of the ratio (in %) and the minimum value of the ratio (in %) is 35 or less. For example, if the maximum value of the ratio is 50% and the minimum value of the ratio is 40%, then the "difference between the maximum and minimum values ​​of the foam cell ratio in the multiple ribs" is 50% - 40% = 10%.

[0039] If the difference between the maximum and minimum values ​​of the foam cell ratio in the multiple ribs 6 is too large, the weight balance of the molded part 1 will deteriorate. The upper limit of the difference between the maximum and minimum values ​​of the foam cell ratio in the multiple ribs 6 is preferably 25%, more preferably 20%, still preferably 15%, still preferably 12%, and still preferably 10%. However, it is preferable that the difference between the maximum and minimum values ​​of the foam cell ratio in the multiple ribs 6 be small.

[0040] The base 2 (thin-walled portion 3 and thick-walled portion 4) and the rib 6 are made of the same thermoplastic resin. The thermoplastic resin that makes up the base 2 and the rib 6 may be amorphous resin or crystalline resin. These resins may contain fillers such as talc and glass fibers, or pigments.

[0041] Examples of amorphous resins include polycarbonate (PC), acrylonitrile-butadiene-styrene copolymer (ABS), and polymer alloys of PC and ABS. Amorphous resins offer a high degree of appearance improvement through the counterpressure method, and even when foam molding is performed, they can achieve a glossy and high-quality appearance similar to that of solid products. On the other hand, because amorphous resins have a low melt tension, the proportion of foam cells in rib 6 tends to be lower compared to when crystalline resins are used.

[0042] Crystalline resins include, for example, polypropylene (PP), polyethylene (PE), high-density polyethylene (HDPE), polyamide (PA), polybutylene terephthalate (PBT), or polyphenylene sulfide (PPS). Crystalline resins have high melt tension, and by combining them with fillers, the proportion of foamed cells in the ribs can be increased. In addition, their high fluidity makes it easy to enlarge and thin the molded parts 1.

[0043] In base 2, the surface opposite to the surface on which the rib 6 is formed may be a mirror finish. Specifically, the surface roughness Ra of the opposite surface may be 10 to 500 nm. Preferably, the surface roughness Ra is 10 to 200 nm. The surface roughness Ra can be measured using a laser microscope, atomic force microscope, or contact-type step diameter tester.

[0044] Although not shown in FIG. 1, the molded part 1 may further include a plating film formed on the surface. By forming a plating film on the surface, the design property can be improved, and the strength such as the bending elastic modulus of the molded part 1 can also be improved. The surface roughness Ra of the plating film may be, for example, 10 to 500 nm.

[0045] The plating film may be formed on a surface roughened by chemical etching, blasting, or the like. By forming a plating film on the roughened surface, the adhesion of the plating film is improved.

[0046] Alternatively, the molded part 1 may have a mixed layer, which is a region where the resin of the base material and the metal of the plating film are mixed, at the interface between the base material (such as the base 2 and the rib 6; the same applies hereinafter) and the plating layer. By providing the mixed layer, the adhesion of the plating film is also improved. Such a mixed layer can be manufactured, for example, by swelling the resin with an acid or the like and then performing electroless plating.

[0047] The plating film may be formed only on a part of the surface of the base material. However, by covering the entire surface of the base material with the plating film, effects such as shielding the intrusion of moisture into the base material, suppressing the thermal expansion of the base material, and an electromagnetic wave shielding effect can be obtained. When attempting to obtain these effects, it is preferable that the plating film covers 90% or more of the surface area of the base material, and more preferably 95% or more.

[0048] The plating film may include, for example, an electroless plating film formed directly on the base material and an electrolytic plating film formed on the electroless plating film. The electroless plating film is not limited to these, and examples include an electroless copper plating film, an electroless nickel plating film, an electroless nickel-phosphorus plating film, etc., and an electroless nickel-phosphorus plating film is particularly preferable. The electrolytic plating film is not limited to these, and examples include an electrolytic copper plating film, an electrolytic nickel plating film, an electrolytic chromium plating film, etc.

[0049] The plating film may be a laminate of an electroless plating film and multiple electrolytic plating films. For example, the plating film may include a structure in which an electroless nickel-phosphorus plating film or an electroless nickel plating film, an electrolytic copper plating film, and an electrolytic nickel plating film are laminated in this order from the substrate side. In this case, the electrolytic copper plating film mainly functions as an interference layer that absorbs stress, and the electrolytic nickel plating film mainly functions as a hard layer to ensure mechanical strength. To provide corrosion resistance and aesthetic appeal, an electrolytic chromium plating film may be further formed on top of the electrolytic nickel plating film. Also, when forming an electrolytic chromium plating film on top of an electrolytic nickel plating film, the electrolytic nickel plating film may be laminated in multiple layers such as a semi-gloss layer, a glossy layer, and a microporous layer.

[0050] [Second Embodiment] Next, the molded part 1 of the second embodiment will be described in detail with reference to Figure 2. Here, only the configurations that differ from the molded part 1 of the first embodiment will be described.

[0051] As shown in Figure 2, the average height t3 of each of the multiple ribs 6 preferably satisfies the following equation: (t2 - t1) ≤ t3 ≤ 5.0(t2 - t1). In other words, the average height t3 of the ribs 6 is 1.0 to 5.0 times the difference (t2 - t1) between the average thickness t1 of the thin-walled portion 3 and the average thickness t2 of the thick-walled portion 4. That is, the average height t3 of the ribs 6 may be 1.0 times or more, and 5.0 times or less, the difference (t2 - t1) between the average thickness t1 of the thin-walled portion 3 and the average thickness t2 of the thick-walled portion 4. This makes it possible to balance weight reduction and strength of the molded part 1.

[0052] If the average height t3 of the rib 6 is too small, it will be difficult to obtain a reinforcing effect. On the other hand, if the average height t3 is too large, the weight may increase. The lower limit of the average height t3 may preferably be 1.5 times the difference (t2-t1) between the average thickness t1 of the thin-walled portion 3 and the average thickness t2 of the thick-walled portion 4. The upper limit of the average height t3 may preferably be 3.5 times the difference (t2-t1) between the average thickness t1 of the thin-walled portion 3 and the average thickness t2 of the thick-walled portion 4. In other words, the average height t3 of the rib 6 should be 1.0 to 5.0 times, preferably 1.5 to 5.0 times, and more preferably 1.5 to 3.5 times, the difference (t2-t1) between the average thickness t1 of the thin-walled portion 3 and the average thickness t2 of the thick-walled portion 4. Here, the "average height t3" of the rib 6 is the distance along the thickness direction of the thin-walled portion 3 from the surface 3a of the thin-walled portion 3 to the upper surface of the rib 6, and can be calculated as follows. First, in the thin-walled section 3, the heights of the rib 6 at three points—both ends and the center—along the longitudinal direction in which the rib 6 extends are measured using calipers. The arithmetic mean of these three points can be taken as the average height t3 of the rib 6.

[0053] [Third Embodiment] Next, the molded part 1 of the second embodiment will be described in detail with reference to Figure 3. Here, only the configurations that differ from the molded part 1 of the first and second embodiments will be described.

[0054] As shown in Figure 3, the molded part 1 of the third embodiment further includes a plurality of ribs 7.

[0055] Each of the multiple ribs 7 and each of the multiple ribs 6 are formed to protrude from one surface 4a of the thickened portion 4 in the thickness direction of the thickened portion 4. Each of the multiple ribs 7 is integrally formed with each of the multiple ribs 6 described above so as to extend along the longitudinal direction of the rib 6. The molded part 1 may have two or more ribs 7, or it may have only one rib 7, corresponding to the number of ribs 6. The cross-sectional shape, material, and foam cell ratio of the ribs 7 are the same as those of the ribs 6.

[0056] The average height t4 of the rib 7 can be changed in various ways. That is, as shown in Figure 3, the average height t4 of the rib 7 may be the same as the average height t3 of the rib 6 (the rib on the left in the figure), it may be greater than the average height t3 of the rib 6 (the rib in the center in the figure), or it may be less than the average height t3 of the rib 6 (the rib on the right in the figure).

[0057] By providing ribs 7 to the thick-walled portion 4 in this manner, the strength can be further improved. The ribs 7 may protrude from one surface 4a of the thick-walled portion 4 in a cylindrical, conical, or frustoconical shape, similar to the ribs 6 that protrude from one surface 3a of the thin-walled portion 3 in a cylindrical shape as described above.

[0058] Next, the manufacturing method for the molded part 1 will be briefly described. The molded part 1 can be manufactured using a foam injection molding method or the like described in PCT / JP2023 / 39703. For example, the counterpressure method. However, the manufacturing method for the molded part 1 is not limited to this.

[0059] The molded parts according to each of the embodiments described above can reduce the amount of resin used by making the ribs from foamed molded material. As a result, the molded parts according to each of the embodiments described above can improve resource utilization efficiency, reduce transportation burden, reduce energy consumption and CO2 emissions. ２ This can contribute to reducing emissions. By providing molded parts to society, we can contribute to achieving four of the 17 Sustainable Development Goals (SDGs) established by the United Nations: Goal 7 (Affordable and Clean Energy), Goal 9 (Industry, Innovation and Infrastructure), Goal 11 (Sustainable Cities and Communities), and Goal 12 (Responsible Consumption and Production).

[0060] Although embodiments of this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the invention.

[0061] In the following examples 1 to 5 (see Figures 1 to 3) and comparative examples 1 to 3 shown in Table 1, each molded part was manufactured using polycarbonate resin (L1225Y manufactured by Teijin Limited) by foam injection molding. The rate of change in weight, the amount of deformation by a three-point bending test, and the quality of appearance of each molded part were evaluated. In Table 1, "contact" of the rib indicates whether or not there is contact between the rib and the stepped portion. If the base is foam-molded, the rib is also foam-molded in the same way. The size of the base in plan view (width: 40 mm, length: 100 mm) and the average thickness of the thin-walled and thick-walled portions (thin-walled portion: 1 mm, thick-walled portion: 3 mm) were the same for each test piece in Examples 1 to 5 and Comparative Examples 1 to 3. Furthermore, this disclosure is not limited to these examples.

[0062]

[0063] [Weight Change Rate] The weight change rate of each molded part was determined by measuring each test piece of Examples 1 to 5 and Comparative Examples 1 to 3 using a weighing scale (Mettler Toledo "PJ3300"). The weight of the test piece of Comparative Example 3 (a test piece in which the base is formed from a non-foamed thin-walled section and no ribs are formed) was compared with the weight of each test piece of the other examples and comparative examples. For example, the weight change rate of the test piece of Example 1 was calculated using the formula {(Weight of Example 1 - Weight of Comparative Example 3) / Weight of Comparative Example 3 × 100}.

[0064] [Deformation] The amount of deformation was measured by a three-point bending test as shown in Figure 4. Specifically, the molded part 1 was positioned so that the stepped portion 5 was located in the center between the two support points, and the amount of displacement of the central part of the molded part 1 when a load N of 5N was applied from above the center between the two support points was defined as the amount of deformation. The distance between the support points was 100 mm (d1 was 50 mm and d2 was 50 mm), and the width of the molded part 1 (width from the front to the back in the illustration in Figure 4) was 10 mm.

[0065] [Appearance] The appearance was evaluated as follows: if neither warping nor sink marks occurred based on visual inspection, it was evaluated as "A"; if either warping or sink marks occurred, it was evaluated as "B"; and if both warping and sink marks occurred, it was evaluated as "C".

[0066] [Comparison of Examples 1-5 and Comparative Examples 1-8] In Examples 1-5, where the proportion of foamed cells in the thin-walled section was 0-5%, the proportion of foamed cells in the thick-walled section was 5-50%, ribs were present, the ribs abutted against the stepped section, the proportion of foamed cells in the ribs was 0-90%, and furthermore, the width W of the base portion of the ribs was 1.0 times or more the average thickness t1 of the thin-walled section, it was possible to reduce the amount of deformation and ensure an excellent appearance while reducing weight, that is, while making it lighter.

[0067] On the other hand, in Comparative Example 1, although ribs were formed, the ribs did not contact the stepped portion, resulting in a larger deformation compared to Examples 1 to 5, and the strength could not be ensured. In Comparative Example 2, no ribs were formed, resulting in an even larger deformation than in Comparative Example 1. In Comparative Example 3, no ribs were formed, and the thin-walled and thick-walled portions were not foam-molded, so weight reduction could not be achieved, and the deformation was also larger compared to Examples 1 to 5. In Comparative Example 4, the proportion of foam cells in the thin-walled portion exceeded 5%, resulting in reduced strength and a larger deformation compared to Examples 1 to 5. In Comparative Example 5, the proportion of foam cells in the thick-walled portion was less than 5%, resulting in a relatively small weight change rate, as well as both warping and sink marks, and an appearance evaluation of "C". In Comparative Example 6, the proportion of foam cells in the thick-walled portion exceeded 50%, resulting in reduced strength and a larger deformation compared to Examples 1 to 5. In Comparative Example 7, the W / t1 value was less than 1.0, resulting in a larger deformation compared to Examples 1 to 5. Furthermore, in Comparative Example 8, the proportion of foamed cells in the ribs exceeded 90%, resulting in reduced strength and greater deformation compared to Examples 1-5.

[0068] [Comparison of Examples 1-5] In Examples 2-4, by setting the value of "t3 / (t2-t1)" to 1-5, that is, by satisfying the above formula "(t2-t1) ≤ t3 ≤ 5.0(t2-t1)", it was possible to achieve a good balance between weight reduction (lightweighting) and small deformation (ensuring strength) while maintaining an appearance evaluation of "A". In Example 1, the average height t3 of the ribs was relatively small, so the deformation was slightly larger compared to Examples 2-4. In Example 5, the average height t3 of the ribs was relatively large, so although the deformation was reduced, the sink mark suppression effect by foam molding of the ribs was not fully realized, resulting in sink marks, and the weight change rate was also small.

[0069] 1. Molded part, 2. Base, 3. Thin-walled section, 4. Thick-walled section, 5. Stepped section, 6. Rib, 7. Rib, t1. Average thickness of thin-walled section, t2. Average thickness of thick-walled section, t3. Average height of rib, t4. Average height of rib

Claims

1. A molded part made of thermoplastic resin, comprising: a base having a thin-walled portion, a thick-walled portion, and a stepped portion formed between the thin-walled portion and the thick-walled portion; and a first rib projecting from one surface of the thin-walled portion in the thickness direction of the thin-walled portion and in contact with the stepped portion, wherein the proportion of foamed cells in the thin-walled portion is 0 to 5%, the proportion of foamed cells in the thick-walled portion is 5 to 50%, the width W of the base portion of the first rib is 1.0 times or more the average thickness t1 of the thin-walled portion, and the proportion of foamed cells in the first rib is greater than 0% and 90% or less.

2. A molded part according to claim 1, wherein when the average thickness of the thin-walled portion is t1, the average thickness of the thick-walled portion is t2, and the average height of the first rib is t3, the following formula (1) is satisfied: (t2 - t1) ≤ t3 ≤ 5.0(t2 - t1) 3. A molded part according to claim 1 or 2, further comprising a second rib that protrudes from one surface of the thickened portion in the thickness direction of the thickened portion and extends from the first rib.

4. A molded part according to claim 1 or 2, wherein a plating film is formed on the surface of the molded part.

5. A molded part according to claim 1 or 2, wherein the thermoplastic resin is an amorphous resin or a crystalline resin.

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