Molded component and method for producing molded component

Abstract

Provided is a molded component that has excellent strength and appearance despite being lightweight. A molded component (10) is made of a thermoplastic resin and comprises a base (11) having an average thickness t of 0.5-3.0 mm, and a plurality of ribs (121-123) formed so as to protrude from one surface (11a) of the base (11) in a thickness direction of the base (11). A surface (11b) of the base (11) has a flatness of 15 μm or less. Each of the plurality of ribs (121-123) has a root portion having a width 1.0-4.0 times the average thickness t of the base (11). In the base (11), the proportion of foam cells is 0-5%. The proportion of foam cells in each of the plurality of ribs (121-123) is 0-90%, at least one of the plurality of ribs (121-123) has the foam cells, and the difference between maximum and minimum values of the proportion of the foam cells in the plurality of ribs (121-123) is 35% or less.

Description

Molded parts and methods for manufacturing molded parts

[0001] The present invention relates to a molded part and a method for manufacturing the molded part, and more particularly to a molded part made of a thermoplastic resin and a method for manufacturing the same.

[0002] Forming ribs on the backside of the substrate to reinforce molded parts is a widely used method for increasing their strength. However, during injection molding, molten resin has difficulty flowing into the rib area, making it difficult for the filling pressure to reach the tip of the rib. This can result in sink marks (depressions) along the rib shape on the surface opposite the rib. This problem becomes more pronounced the larger the area of ​​the molded part or the thinner its wall. Reducing the height or width of the rib can make the sink marks less noticeable, but it also reduces the reinforcing effect.

[0003] One method for suppressing such sink marks is foam molding. JP 2013-6396 A discloses a molding method for a resin molded product in which a cavity formed between a movable mold and a fixed mold is filled with a resin material to form a resin molded product having ribs on the back surface of a substrate portion. This molding method is characterized in that the cavity is filled with a molten resin material to which a foaming agent has been added, and then, while the position of the movable mold is maintained and the inside of the cavity is kept at approximately atmospheric pressure, the molten resin is cooled to form a resin molded product.

[0004] Japanese Patent Application Laid-Open No. 2001-322145 discloses a panel-shaped thermoplastic resin foam-molded product having a substrate and protrusions standing on the substrate, characterized in that the protrusions have an average expansion ratio of 1.1 times or less and the substrate has an average expansion ratio of 1.3 times or more.

[0005] Japanese Patent Application Laid-Open Publication No. 2010-36494 discloses a resin molded product that constitutes at least a part of a housing. The resin molded product is made of a thermoplastic resin foam molded product molded to have an expansion ratio of 1.05 to 2.0, and has a plate thickness of 0.5 to 2.0 mm, and on one surface of the substrate, the plate thickness is 0.5 to 2.0 mm, and the height from the base portion located on the surface is 2.0 to 10.0 mm, and the total projected area of ​​the ribs on the surface is 2.5 to 20.0% of the total area of ​​the surface.

[0006] Counterpressure is a method for improving the surface quality of foam-molded parts. The counterpressure method involves filling the mold with pressurized gas before filling it with molten resin, thereby suppressing appearance defects known as swirl marks.

[0007] Japanese Patent Laid-Open Publication No. 8-336852 discloses a method for producing a synthetic resin foam-molded product having an unfoamed portion. This method is characterized by the gas counterpressure molding method in which a portion of a foamable synthetic resin composition cast into a mold cavity is cured to an extent that it will not foam even when the mold cavity is depressurized, and then the remaining portion of the foamable synthetic resin composition is foamed by depressurizing the mold cavity.

[0008] Japanese Patent Application Laid-Open Publication No. 2004-34381 discloses a foam injection molding method for producing a molded product with uneven thickness, having both thin and thick portions. This foam injection molding method uses a mold having a first mold cavity corresponding to the molded product with uneven thickness and a second mold cavity connected to the first mold cavity. A foamable molten resin containing a dissolved physical foaming agent is injected into the first mold cavity. At least the first mold cavity is pressurized with gas to a pressure higher than that at which foaming does not occur at the flow front of the molten resin. During or after injection of the molten resin into the first mold cavity, a portion of the molten resin is ejected into the second mold cavity, thereby foaming only the thick portion of the molded product with uneven thickness produced in the first mold cavity.

[0009] JP 2013-6396 A JP 2001-322145 A JP 2010-36494 A JP 8-336852 A JP 2004-34381 A

[0010] An object of the present invention is to provide a molded part that is lightweight yet has excellent strength and appearance.

[0011] A molded part according to one embodiment of the present invention is a molded part made of a thermoplastic resin, comprising: a base having an average thickness t of 0.5 to 3.0 mm; and a plurality of ribs formed so as to protrude from one side of the base in the thickness direction of the base, wherein the flatness of the side of the base opposite to the side on which the plurality of ribs are formed is 15 μm or less; the width of the base base at its base is 1.0 to 4.0 times the average thickness t of the base; the base has a foam cell ratio of 0 to 5%; each of the plurality of ribs has a foam cell ratio of 0 to 90%; at least one of the plurality of ribs has foam cells; and the difference between the maximum and minimum foam cell ratios of the plurality of ribs is 35% or less.

[0012] A method for manufacturing a molded part according to one embodiment of the present invention is a method for manufacturing the above-mentioned molded part using a mold that includes a fixed mold and a movable mold, and that includes a cavity corresponding to the base and a plurality of rib forming portions corresponding to the plurality of ribs, and includes the steps of: introducing counter-pressure gas into the mold; injecting and filling molten resin containing a foaming agent into the mold; starting to discharge the counter-pressure gas before completion of pressure retention; moving the movable mold in a direction that increases the distance from the fixed mold; and, after moving the movable mold in a direction that increases the distance from the fixed mold, moving the movable mold in a direction that decreases the distance from the fixed mold.

[0013] A method for manufacturing a molded part according to one embodiment of the present invention is a method for manufacturing the above-mentioned molded part using a mold that includes a fixed mold and a movable mold, and that includes a cavity corresponding to the base and a plurality of rib forming portions corresponding to the plurality of ribs, and includes the steps of introducing counter-pressure gas into the mold, injecting and filling molten resin containing a foaming agent into the mold, and starting to discharge the counter-pressure gas before completion of pressure retention.

[0014] According to the present invention, a molded part that is lightweight yet has excellent strength and appearance can be obtained.

[0015] FIG. 1 is a cross-sectional view schematically showing the configuration of a molded part according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the configuration of an example of a mold used to produce the molded part of FIG. 1. FIG. 3 is a view schematically showing injection molding using the mold of FIG. 2. FIG. 4 is a view schematically showing injection molding using the mold of FIG. 2. FIG. 5 is a view schematically showing injection molding using the mold of FIG. 2. FIG. 6 is a cross-sectional view schematically showing the foaming process when the core-back process (FIG. 4) is not performed. FIG. 7 is a cross-sectional view schematically showing the configuration of a molded part according to a second embodiment of the present invention. FIG. 8 is a cross-sectional view schematically showing the configuration of an example of a mold used to produce the molded part of FIG. 7. FIG. 9 is a cross-sectional view schematically showing the configuration of a molded part according to a third embodiment of the present invention. FIG. 10 is a cross-sectional view schematically showing the configuration of an example of a mold used to produce the molded part of FIG. 9. FIG. 11 is a cross-sectional view schematically showing the configuration of a molded part according to a third embodiment of the present invention. FIG. 12 is a perspective view of the molded part of FIG. 11. Fig. 13 is a cross-sectional view schematically showing the configuration of an example of a mold used to manufacture the molded part of Fig. 11 . Fig. 14 is a view schematically showing injection molding using the mold of Fig. 13 . Fig. 15 is a cross-sectional view schematically showing the configuration of another example of a mold used to manufacture the molded part of Fig. 11 . Fig. 16 is a view schematically showing injection molding using the mold of Fig. 15 . Fig. 17 is a view schematically showing injection molding using the mold of Fig. 15 . Fig. 18 is a view schematically showing injection molding using the mold of Fig. 15 . Fig. 19 is a perspective view schematically showing the configuration of a molded part manufactured in an example. Fig. 20 is a view schematically showing a bending test performed in an example.

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0017] 1 is a cross-sectional view schematically illustrating the configuration of a molded part 10 according to a first embodiment of the present invention. The molded part 10 is made of a thermoplastic resin and includes a base 11 and ribs 121, 122, and 123.

[0018] The base 11 has a shape that extends in a direction perpendicular to the thickness direction. While Fig. 1 illustrates the case where the base 11 has a flat plate shape, the base 11 may have any shape as long as the average thickness t is within a predetermined range. For example, the base 11 may have a three-dimensional shape with steps or the like in the in-plane direction, or may have a shape with a curved surface.

[0019] The average thickness t of the base 11 is 0.5 to 3.0 mm. If the average thickness t 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 t is too large, it becomes difficult to reduce the foam cell ratio, which will be described later. The lower limit of the average thickness t is preferably 1.0 mm, and the upper limit of the average thickness t is preferably 2.0 mm.

[0020] Each of the ribs 121, 122, and 123 is formed to protrude from one surface 11a of the base 11 in the thickness direction of the base 11. While Fig. 1 illustrates a case in which the molded part 10 includes three ribs (ribs 121, 122, and 123), the number of ribs may be any number as long as it is two or more. In the following description of this embodiment, expressions such as "ribs 121, 122, and 123" can be generalized to "multiple ribs."

[0021] 1, each of the ribs 121, 122, and 123 has a rectangular cross-sectional shape, but the cross-sectional shape of the rib may be a shape other than a rectangle. For example, the cross-sectional shape of the ribs 121, 122, and 123 may be a shape other than a rectangle or a trapezoid. However, from the viewpoint of ease of filling with molten resin, the cross-sectional shape of the rib is preferably a rectangle or a trapezoid.

[0022] Each of the widths W1, W2, and W3 of the root portions of the ribs 121, 122, and 123 is 1.0 to 4.0 times the average thickness t of the base 11. Here, the "root width" of the rib refers to the dimension of the portion adjacent to the base 11 in a plan view (when the molded part 10 is viewed from the thickness direction of the base 11; the same applies below). If the rib has a shape that extends in one direction (i.e., if the rib has a short side and a long side in a plan view), this refers to the dimension in the direction perpendicular to the extension direction of the rib in a plan view. In other words, the "root width" of the rib refers to the dimension of the portion adjacent to the base 11 in the direction of the short side of the rib in a plan view. Furthermore, if the rib is cylindrical, the "root width" of the rib refers to its diameter.

[0023] If the width of the root portion of the rib (the width of the root portion of each of ribs 121, 122, and 123; the same applies below) is too small, it becomes difficult to foam the rib and to increase the foam cell ratio described below. On the other hand, if the width of the root portion of the rib is too large, the weight of the molded part 10 becomes large. The lower limit of each of the root portion widths W1, W2, and W3 is preferably 1.2 times the average thickness t of the base 11. The upper limit of each of the root portion widths W1, W2, and W3 is preferably 3.0 times the average thickness t of the base 11.

[0024] The height of each of the ribs 121, 122, and 123 is preferably 1.0 to 4.0 times its width (width of the base portion; the same applies below) and 2.0 to 10.0 mm. That is, the height H1 of the rib 121 is preferably 1.0 to 4.0 times its width W1 and 2.0 to 10.0 mm. Similarly, the height H2 of the rib 122 is preferably 1.0 to 4.0 times its width W2 and 2.0 to 10.0 mm. The height H3 of the rib 123 is preferably 1.0 to 4.0 times its width W3 and 2.0 to 10.0 mm. Here, the "height" of the rib refers to the distance from the surface 11a of the base 11 to the apex of the rib in the thickness direction of the base 11.

[0025] If the rib height (the height of each of ribs 121, 122, and 123; the same applies below) is too small, the strength-enhancing effect of the rib is reduced. On the other hand, if the rib height is too large, the time required for cooling during molding is extended, reducing productivity. The lower limit of the rib height is more preferably 1.5 times the width. The upper limit of the rib height is more preferably 3.5 times the width.

[0026] The flatness of surface 11b of base 11 (the surface opposite to the surface (surface 11a) on which multiple ribs are formed) is 15 μm or less. Even when a large number of ribs are arranged on thin-walled, large-area base 11, molded part 10 preferably does not have visually noticeable sink marks (depressions) on surface 11b. "Flatness of surface 11b" refers to the maximum depth of the depression from a virtual plane (reference plane) extending from base 11. "Flatness of surface 11b" can be measured using a stylus step gauge, optical shape measuring instrument, microscope, etc. The flatness of surface 11b is preferably 10 μm or less, and more preferably 5 μm or less.

[0027] (Foam Cell Ratio) In the molded part 10 according to this embodiment, the foam cell ratio X in the base 11 is 0 to 5%, and the foam cell ratios Y1, Y2, and Y3 in the ribs 121, 122, and 123 are each 0 to 90%, provided that at least one of the ribs 121, 122, and 123 has foam cells.

[0028] The "foam cell ratio" refers to the area ratio of foam cells in a two-dimensional image of a cross section (a cross section parallel to the thickness direction of the base 11) of the molded part 10. The foam cell ratio can be determined by observing the cross section with a SEM or optical microscope and performing image analysis.

[0029] In this embodiment, it is preferable to reduce the foam cell ratio X in the base 11 and increase the foam cell ratios Y1, Y2, and Y3 in the ribs 121, 122, and 123. This improves the strength, appearance, and productivity of the molded part 10. That is, reducing the foam cell ratio X in the base 11 ensures the necessary strength and resin filling during molding. Increasing the foam cell ratios Y1, Y2, and Y3 in the ribs 121, 122, and 123 reduces the weight of the ribs and suppresses sink marks directly below the ribs, improving the appearance of the molded part 10.

[0030] The ratio of foam cells in the base 11 is measured in an image of a 500 μm × 500 μm field of view centered at the center (the center in the thickness direction of the base 11 and the center in the width direction of the rib) of the point directly below the rib (the point indicated by the two-dot chain line 11c in Figure 1).

[0031] The upper limit of the foam cell ratio X in the base 11 is preferably 4%, and more preferably 3%.

[0032] On the other hand, the foam cell ratio in the rib is measured using images of a 500 μm × 500 μm field of view at three locations: the center of the rib width, near the base of the rib, near the center of the rib height, and near the tip of the rib (excluding the skin layer), excluding the location directly below the rib (the location indicated by the two-dot chain line 11c in FIG. 1 ), and the average of the measurements is calculated. The "foam cell ratio in the rib" is calculated for each of the multiple ribs (ribs 121, 122, and 123). In this embodiment, the foam cell ratios Y1, Y2, and Y3 of the ribs 121, 122, and 123 are each set to 0 to 90%. However, at least one of the ribs 121, 122, and 123 has foam cells. That is, at least one of the foam cell ratios Y1, Y2, and Y3 of the ribs 121, 122, and 123 is not zero. At least one of the foam cell ratios Y1, Y2 and Y3 of the ribs 121, 122 and 123 is preferably 5% or more, and more preferably 10% or more.

[0033] The greater the foam cell ratio in the rib (the foam cell ratio in each of the ribs 121, 122, and 123; the same applies below), the lighter the rib and the more suppressed the occurrence of sink marks. (Note that, because sink marks are less likely to occur near the gate 532 described below, ribs closer to the gate 532 may be able to suppress sink marks even with a low foam cell ratio. Ribs farther from the gate 532 are preferably made to have a higher foam cell ratio.) On the other hand, if the foam cell ratio in the rib is too high, it may be difficult to stably control the foam cell ratio throughout the molded part 10. Furthermore, the mold structure may need to be more complex. The lower limit of the foam cell ratio in the rib is preferably 10%, more preferably 20%, and even more preferably 30%. The upper limit of the foam cell ratio in the rib is preferably 80%, and even more preferably 70%.

[0034] The smaller the foam cells, the better. The average diameter of the foam cells in the rib is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 300 μm or less.

[0035] In the molded part 10, the difference between the maximum and minimum foam cell ratios in the plurality of ribs is 35% or less. That is, the difference between the maximum of the ratios Y1, Y2, and Y3 and the minimum of the ratios Y1, Y2, and Y3 is 35% or less. Here, "35% or less" does not mean "35% or less with respect to some reference value," but rather means that the difference (unit: %) between the maximum of the ratios Y1, Y2, and Y3 (unit: %) and the minimum of the ratios Y1, Y2, and Y3 (unit: %) is 35 or less. For example, if the ratio Y1 is 40%, the ratio Y2 is 45%, and the ratio Y3 is 50%, then the "difference between the maximum and minimum foam cell ratios in the plurality of ribs" is Y3-Y1=50%-40%=10%.

[0036] If the difference between the maximum and minimum values ​​of the foam cell ratios in the multiple ribs is too large, it will deteriorate the weight balance of the molded part 10. The upper limit of the difference between the maximum and minimum values ​​of the foam cell ratios in the multiple ribs is preferably 25%, more preferably 20%, even more preferably 15%, even more preferably 12%, and even more preferably 10%.

[0037] (Materials of Molded Part 10) The base 11 and the ribs 121, 122, and 123 are made of the same thermoplastic resin. The thermoplastic resin that makes up the base 11 and the ribs 121, 122, and 123 may be an amorphous resin or a crystalline resin. These resins may contain fillers such as talc or glass fiber, pigments, etc.

[0038] Examples of amorphous resins include polycarbonate (PC), acrylonitrile-butadiene-styrene copolymer (ABS), and polymer alloys of PC and ABS. Amorphous resins have a high appearance improvement effect using the counterpressure method described below, and even when foam-molded, they can achieve a glossy, luxurious appearance similar to that of solid products. On the other hand, because amorphous resins have low melt tension, the proportion of foam cells in the ribs tends to be lower than when crystalline resins are used.

[0039] Examples of crystalline resins include polypropylene (PP), polyethylene (PE), high-density polyethylene (HDPE), and polyamide (PA). Crystalline resins have high melt tension, and by combining them with fillers, the ratio of foam cells in the ribs can be increased. Furthermore, their high fluidity makes it easy to increase the size and thickness of the molded part 10.

[0040] The surface 11b of the base 11 (the surface opposite to the surface (surface 11a) on which the ribs 121 and the like are formed) may be a mirror surface. Specifically, the surface roughness Ra of the surface 11b may be 10 to 500 nm. The surface roughness Ra of the surface 11b is preferably 10 to 200 nm. The surface roughness Ra can be measured using a laser microscope, an atomic force microscope, a contact step diameter meter, or the like.

[0041] 1, the molded part 10 may further include a plating film formed on its surface. Forming a plating film on the surface can improve the design and also the strength, such as the flexural modulus, of the molded part 10. The surface roughness Ra of the plating film may be, for example, 10 to 500 nm.

[0042] The plating film may be formed on a surface that has been roughened by chemical etching, blasting, etc. Forming the plating film on a roughened surface improves the adhesion of the plating film.

[0043] Alternatively, the molded part 10 may have a mixed layer at the interface between the substrate (such as the base 11 and the rib 121; the same applies below) and the plating layer, which is a region where the resin of the substrate and the metal of the plating film are mixed. The provision of a mixed layer also improves the adhesion of the plating film. Such a mixed layer can be produced, for example, by swelling the resin with an acid or the like and then performing electroless plating.

[0044] The plating film may be formed on only a portion of the surface of the substrate, but covering the entire surface of the substrate with the plating film provides effects such as blocking moisture penetration into the substrate, suppressing thermal expansion of the substrate, and providing electromagnetic wave shielding. To achieve these effects, the plating film preferably covers 90% or more, and more preferably 95% or more, of the surface area of ​​the substrate.

[0045] The plating film may include, for example, an electroless plating film formed directly on the substrate and an electrolytic plating film formed on the electroless plating film. Examples of electroless plating films include, but are not limited to, electroless copper plating films, electroless nickel plating films, and electroless nickel-phosphorus plating films, with electroless nickel-phosphorus plating films being particularly preferred. Examples of electrolytic plating films include, but are not limited to, electrolytic copper plating films, electrolytic nickel plating films, and electrolytic chromium plating films.

[0046] The plating film may be a laminate of an electroless plating film and multiple electrolytic plating films. The plating film may include, for example, 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 functions primarily as an interference layer that absorbs stress, and the electrolytic nickel plating film functions primarily as a hard layer that ensures mechanical strength. To impart corrosion resistance and design, an electrolytic chromium plating film may be further formed on the electrolytic nickel plating film. Furthermore, when an electrolytic chromium plating film is formed on the electrolytic nickel plating film, the electrolytic nickel plating film may be laminated in multiple layers, such as a semi-bright layer, a bright layer, and a microporous layer.

[0047] [Method of Manufacturing Molded Part 10] Next, a method of manufacturing the molded part 10 will be described. Fig. 2 is a cross-sectional view schematically showing the configuration of a mold 50, which is an example of a mold used to manufacture the molded part 10. Mold 50 includes a fixed mold 511 and a movable mold 512, and includes a cavity 520, rib forming portions 521 to 523, a spool 531, a gate 532, etc. The interface between the fixed mold 511 and the movable mold 512 is sealed with an O-ring 513.

[0048] The mold 50 also includes a gas flow path 514 for passing a counter-pressure gas, which will be described later. The gas flow path 514 is connected to a valve (not shown), and is configured so that gas can be introduced into the mold 50 or discharged from the mold 50 at any timing.

[0049] Cavity 520 is the region between fixed mold 511 and movable mold 512, and is the portion corresponding to base 11 of molded part 10 (FIG. 1). Similarly, rib forming portions 521-523 are regions between fixed mold 511 and movable mold 512, and are portions corresponding to ribs 121-123 of molded part 10, respectively. Note that although the term "cavity" is sometimes used to refer to the fixed mold, in this specification it refers to the portion corresponding to base 11 of molded part 10, as described above.

[0050] The spool 531 is a portion into which molten resin is injected from an injection unit (not shown). The gate 532 is a portion that connects the spool 531 and the cavity 520.

[0051] 3 to 5 are schematic diagrams illustrating injection molding using a mold 50. First, before filling the mold 50 with molten resin, a counter-pressure gas is introduced into the mold 50. Examples of counter-pressure gas that can be used include air, carbon dioxide, and nitrogen. When manufacturing molded parts with excellent appearance using amorphous resins such as PC and ABS, it is preferable to use carbon dioxide, which is highly effective in improving the transferability of the mold surface. When the quality requirements for appearance are not strict, it is preferable to use air from a cost perspective. The pressure of the counter-pressure gas can be, for example, 1 to 5 MPa.

[0052] After filling the mold 50 with counter-pressure gas, molten resin R containing a foaming agent is injected and filled into the mold 50 (see FIG. 3). It is preferable to use a physical foaming agent, which has a stronger foaming power than chemical foaming, as the foaming agent mixed with the molten resin R. For example, the supercritical foam molding method of MuCell (registered trademark) or the low-pressure foam molding method described in Japanese Patent No. 6139038 can be used.

[0053] After injecting and filling the molten resin R containing a foaming agent, it is preferable to suppress foaming in the base 11 (FIG. 1) and solidify it using a full-shot method including dwelling while reducing the counter-pressure gas pressure. The timing to start discharging the counter-pressure gas is preferably before the completion of dwelling. If the timing to start discharging the counter-pressure gas is later than the completion of dwelling, the counter-pressure gas will act as a reaction force, making it difficult to fill the molten resin R into the rib forming portions 521-523. The timing to start discharging the counter-pressure gas is more preferably between the completion of the primary filling (for example, 5 seconds, preferably 1 second, depending on the shape of the molded part) and the start of dwelling.

[0054] The rate at which the gas is exhausted and the rate at which the foaming pressure is reduced in the mold 50 differ depending on the distance from the gate 532, and the larger the mold 50, the more variation there is in the foaming state. In the rib-forming portion located close to the gate, the pressure is less likely to be reduced by the pressure during dwelling and filling, and foaming is less likely to occur than in the rib-forming portion located farther from the gate.

[0055] In this embodiment, after starting to discharge the counterpressure gas, the movable mold 512 is moved by a distance g in a direction increasing the distance from the fixed mold 511 (see FIG. 4; hereinafter, this process is referred to as the "core-back process"). This rapidly reduces the pressure in the rib-forming portions 521-523, promoting foaming in the rib-forming portions 521-523. This increases the proportion of foamed cells in each of the ribs 121-123 (FIG. 1), and reduces variation in the proportion of foamed cells in the ribs 121-123.

[0056] The distance g over which the movable mold 512 is moved is preferably 0.1 to 2.0 times the average thickness t of the base 11 (FIG. 1). If the distance g is too small, foaming in the rib forming portions 521 to 523 is not sufficiently promoted. On the other hand, if the distance g is too large, burrs or deformation may occur. The lower limit of the distance g is more preferably 0.2 times the average thickness t of the base 11. The upper limit of the distance g is more preferably 1.0 times the average thickness t of the base 11, and even more preferably 0.5 times the average thickness t.

[0057] After the core-back process, the movable mold 512 is again moved in a direction that reduces the distance between it and the fixed mold 511, thereby correcting the thickness of the base 11 (see FIG. 5 ; hereinafter, this process will be referred to as the “re-clamping process”). If this process is not performed, foam cells may occur in the base 11. Furthermore, warping or undulation may occur in the base 11.

[0058] Through the above steps, the molded part 10 is manufactured.

[0059] 6 is a cross-sectional view showing a typical foaming process when the core-back process (FIG. 4) is not performed. As described above, the closer the rib-forming portion is to the gate 532, the higher the filling pressure of the molten resin R becomes, making it more difficult for foaming to occur, and the greater the variation in the foam cell ratio. In contrast, according to this embodiment, the core-back process (FIG. 4) and the re-clamping process (FIG. 5) are performed, thereby making it possible to reduce the variation in the foam cell ratio.

[0060] The molded part 10 according to the first embodiment of the present invention and the method for manufacturing the same have been described above. According to this embodiment, a molded part that is lightweight yet has excellent strength and appearance can be obtained.

[0061] 7 is a cross-sectional view schematically illustrating the configuration of a molded part 20 according to a second embodiment of the present invention. The molded part 20 includes ribs 221 to 223 instead of the ribs 121 to 123 of the molded part 10 (FIG. 1).

[0062] In the molded part 20, the width of the root portion of the rib that is closer to the gate 532 than a predetermined threshold Gth is smaller than the width of the root portion of the rib that is farther from the gate 532 than the threshold Gth.

[0063] Gate 532 is a part that connects the part (spool) into which molten resin is injected from the injection unit and molded part 20. In the final product, the resin that filled gate 532 is usually removed, but even in a state where the resin that filled gate 532 has been removed, it is often possible to identify the position of gate 532 from the shape, surface condition, etc. of molded part 20.

[0064] The "distance from the gate 532" refers to the distance along the in-plane direction of the base 11 from the interface between the gate 532 and the base 11 to the side of each rib closer to the gate 532 (the base of the side), as shown in Figure 7, i.e., distances G1, G2, and G3.

[0065] In this embodiment, G1<Gth<G2<G3 holds true. That is, the distance G1 from the gate 532 of the rib 221 is shorter than the threshold value Gth, and the distances G2 and G3 from the gate 532 of the ribs 222 and 223 are longer than the threshold value Gth. Therefore, the width W1 of the base portion of the rib 221 is smaller than the width W2 of the rib 222 and the width W3 of the base portion of the rib 223.

[0066] As described above, in injection molding, the closer to the gate 532 the injection pressure is, the less likely the ribs are to foam. By relatively reducing the width of the base of the ribs that are closer to the gate 532 than the predetermined threshold value Gth, the rate at which the molten resin flows into the rib is slowed, promoting foaming and reducing variation in the proportion of foam cells throughout the molded part 20.

[0067] The magnitude of the threshold Gth and how much to reduce the width of the base part of the rib whose distance from the gate 532 is shorter than the threshold Gth vary depending on the shape of the molded part 10 and the type of resin, but can be determined, for example, by simulation.

[0068] The magnitude of the threshold Gth may be set, for example, to 15 to 30% of the distance Gmax from the gate 532 to the rib located farthest from the gate 532 (in the example of FIG. 7, the distance Gmax = distance G3). The magnitude of the threshold Gth is preferably 20 to 25% of the distance Gmax. Alternatively, the magnitude of the threshold Gth may be set to 10 to 30 mm as an absolute value. The magnitude of the threshold Gth is preferably 15 to 20 mm.

[0069] 8 is a cross-sectional view schematically illustrating the configuration of a mold 60, which is an example of a mold used to manufacture the molded part 20. The mold 60 includes a movable mold 612 instead of the movable mold 512 of the mold 50 (FIG. 2), and includes rib forming portions 621 to 623 instead of the rib forming portions 521 to 523 of the mold 50. The rib forming portions 621 to 623 correspond to the ribs 221 to 223 of the molded part 20 (FIG. 7), respectively.

[0070] In the mold 60 of this embodiment, the width of the root portion of the rib forming portion that is closer to the gate 532 than the predetermined threshold Gth is smaller than the width of the root portion of the rib forming portion that is farther from the gate 532 than the threshold Gth. In the example of Fig. 8, the width W1 of the root portion of the rib forming portion 621 is smaller than the width W2 of the root portion of the rib forming portion 622 and the width W3 of the root portion of the rib forming portion 623. By relatively reducing the width of the root portion of the rib forming portion that is closer to the gate 532 than the predetermined threshold Gth, foaming in the rib forming portion can be promoted, and variation in the proportion of foam cells can be reduced throughout the molded part 20 (Fig. 7).

[0071] When the mold 60 is used, the core-back process (FIG. 4) and the mold re-clamping process (FIG. 5) described in the first embodiment may or may not be performed.

[0072] The molded part 20 according to the second embodiment of the present invention and the method for manufacturing the same have been described above. This embodiment also provides a molded part that is lightweight yet has excellent strength and appearance.

[0073] 9 is a cross-sectional view schematically illustrating the configuration of a molded part 25 according to a third embodiment of the present invention. The molded part 25 includes ribs 271 to 273 instead of the ribs 121 to 123 of the molded part 10 (FIG. 1).

[0074] In molded part 25, the height of the ribs that are closer to gate 532 than a predetermined threshold Gth is greater than the height of the ribs that are farther from gate 532 than threshold Gth. In the example of Fig. 9, height H1 of rib 271 is greater than height H2 of rib 272 and height H3 of rib 273.

[0075] 10 is a cross-sectional view schematically illustrating the configuration of a mold 65, which is an example of a mold used to manufacture the molded part 25. The mold 65 includes a movable mold 662 instead of the movable mold 512 of the mold 50 (FIG. 2), and includes rib forming portions 671 to 673 instead of the rib forming portions 521 to 523 of the mold 50. The rib forming portions 671 to 673 correspond to the ribs 271 to 273 of the molded part 25 (FIG. 9), respectively.

[0076] In the mold 65, among the multiple rib forming portions, the height of the rib forming portions that are closer to the gate 532 than a predetermined threshold Gth is greater than the height of the rib forming portions that are farther from the gate 532 than the threshold Gth. In the example of Fig. 10, the height H1 of the rib forming portion 671 is greater than the height H2 of the rib forming portion 672 and the height H3 of the rib forming portion 673. By relatively increasing the height of the rib forming portions that are closer to the gate 532 than the predetermined threshold Gth, the volume of the rib forming portions is increased, thereby promoting foaming and reducing variation in the proportion of foam cells throughout the molded part 25 (Fig. 9).

[0077] Even when the mold 65 is used, the core-back process (FIG. 4) and the mold re-clamping process (FIG. 5) described in the first embodiment may or may not be performed.

[0078] The molded part 25 according to the third embodiment of the present invention and the method for manufacturing the same have been described above. This embodiment also provides a molded part that is lightweight yet has excellent strength and appearance.

[0079] [Fourth embodiment] Fig. 11 is a cross-sectional view schematically illustrating the configuration of a molded part 30 according to a fourth embodiment of the present invention. Fig. 12 is a perspective view of the molded part 30. The molded part 30 includes ribs 321 to 323 instead of the ribs 121 to 123 of the molded part 10 (Fig. 1).

[0080] A plurality of minute protrusions are formed on each of the upper end faces (end faces located farthest from the base 11) 321a to 323a of the ribs 321 to 323. Specifically, protrusions each having a circle equivalent diameter of 10 to 40 μm when projected onto a plane perpendicular to the thickness direction of the base 11 are formed at a density of 100 / mm. ２ It is formed at a density of more than 10 ...

[0081] [Manufacturing Method 1 for Molded Part 30] Figure 13 is a cross-sectional view schematically showing the configuration of a mold 70, which is an example of a mold used to manufacture the molded part 30. Figure 14 is a diagram schematically showing injection molding using the mold 70. The mold 70 includes a movable mold 712 instead of the movable mold 512 of the mold 50 (Figure 2), and includes rib forming portions 721-723 instead of the rib forming portions 521-523 of the mold 50. The rib forming portions 721-723 correspond to the ribs 321-323 of the molded part 30 (Figure 11), respectively.

[0082] The mold 70 further includes a gas flow component 715 disposed in contact with the upper ends of the rib forming portions 521 to 523. The mold 70 also includes a gas flow channel 714 disposed in contact with the gas flow component 715, instead of the gas flow channel 514 of the mold 50 (FIG. 2).

[0083] The gas flow component 715 is a component for passing gas without passing molten resin between the rib forming portions 721 to 723 and the gas flow channel 714. Specifically, the gas flow component 715 has fine through holes that penetrate the gas flow component 715 in the vertical direction (the direction parallel to the thickness direction of the base 11) at a density of 100 holes / mm. ２ It is formed at a number density of more than 1000.

[0084] The cross-sectional shape of the through-holes of the gas flow component 715 (the shape of a cross-section perpendicular to the thickness direction of the base 11) may be any shape, such as circular, elliptical, or rectangular. The size of each through-hole of the gas flow component 715 is preferably 10 to 40 μm in equivalent circle diameter when projected onto a plane perpendicular to the thickness direction of the base 11. If the through-holes are too small, it may not be possible to increase the decompression rate within the rib forming portions 721 to 723. If the through-holes are too large, the molten resin may be sucked into the gas flow path 714.

[0085] When discharging the counterpressure gas, discharging the gas from the gas flow path 714 via the gas flow component 715 increases the decompression rate within the rib-forming regions 721-723, promoting foaming in the rib-forming regions 721-723 (see FIG. 14). This increases the proportion of foam cells in the ribs 321-323 of the molded part 30 (FIG. 11). It also reduces variation in foaming ease depending on the distance from the gate 532. At this time, the through-holes in the gas flow component 715 are transferred to the upper end surfaces 321a-323a (FIG. 12) of the ribs 321-323 of the molded part 30, forming the fine protrusions described above.

[0086] Even when the mold 70 is used, the core-back process (FIG. 4) and the mold re-clamping process (FIG. 5) described in the first embodiment may or may not be performed.

[0087] In the above example, the gas flow component 715 is arranged so as to contact the upper ends of all of the rib forming portions 721 to 723. However, the gas flow component 715 may be arranged so as to contact only the upper ends of some of the rib forming portions 721 to 723. For example, the gas flow component 715 may be arranged so as to contact only the upper end of the rib forming portion 721, which is close to the gate 532 and less likely to cause foaming. Also, in the molded part 30 (FIG. 11), fine protrusions may be formed only on the upper end surfaces of some of the ribs 321 to 323. That is, protrusions having a circle equivalent diameter of 10 to 40 μm when projected onto a plane perpendicular to the thickness direction of the base 11 are formed at a density of 100 / mm on the upper end surfaces of at least some of the ribs. ２ It is sufficient that the particles are formed at a number density equal to or greater than this.

[0088] [Manufacturing Method 2 for Molded Part 30] Figure 15 is a cross-sectional view schematically showing the configuration of a mold 80, which is another example of a mold used to manufacture the molded part 30. Figures 16 to 18 are schematic views showing injection molding using the mold 80. The mold 80 includes a movable mold 812 instead of the movable mold 512 of the mold 50 (Figure 2), and includes rib forming portions 821 to 823 instead of the rib forming portions 521 to 523 of the mold 50. The rib forming portions 821 to 823 correspond to the ribs 321 to 323 of the molded part 30 (Figure 11), respectively.

[0089] As will be described below, the mold 80 is configured so that the volumes of the rib forming portions 821 to 823 can be varied.

[0090] The mold 80 includes a space 816 that is continuous with the rib forming portions 821 to 823. The mold 80 also includes a gas flow path 814 in place of the gas flow path 514 of the mold 50 (FIG. 2), and the gas flow path 814 is arranged so as to be continuous with the space 816.

[0091] The mold 80 further includes a plate 817 disposed within the space 816. The outer peripheral surface of the plate 817 and the inner peripheral surface of the space 816 are sealed by, for example, an O-ring 818. The space 816 is divided by the plate 817 into an area on the gas flow path 814 side and an area on the rib forming portions 821 to 823 side. The plate 817 is configured to be able to slide vertically (in the thickness direction of the base 11) while maintaining airtightness between the area on the gas flow path 814 side and the area on the rib forming portions 821 to 823 side.

[0092] A plurality of gas flow components 815 are fixed to the plate 817. The plurality of gas flow components 815 are configured to move in accordance with the movement of the plate 817 and to fit into the rib forming portions 821 to 823.

[0093] Each of the plurality of gas flow components 815 is a component for allowing gas to pass between the region on the gas flow path 814 side and the region on the rib forming portions 821 to 823 side without allowing molten resin to pass through. Similar to the gas flow component 715 of the mold 70 (FIG. 13), the gas flow component 815 also has fine through-holes that penetrate the gas flow component 815 in the vertical direction (the direction parallel to the thickness direction of the base 11) at a density of 100 holes / mm. ２ It is formed at a number density of more than 1000.

[0094] A method for manufacturing a molded part 30 using a mold 80 will be described below with reference to Figures 16 to 18. First, as shown in Figure 16, counterpressure gas is introduced through the gas flow path 814. At this time, the plate 817 moves toward the rib forming portions 821 to 823 due to the pressure difference between the area on the gas flow path 814 side and the area on the rib forming portions 821 to 823 side. As the plate 817 moves, the gas flow part 815 also moves toward the rib forming portions 821 to 823 side. This reduces the volume of the rib forming portions 821 to 823.

[0095] While maintaining the counter-pressure gas pressure, the molten resin containing the foaming agent is filled (see FIG. 17). After the primary filling is completed (or a few seconds before), the counter-pressure gas is discharged from the gas flow path 814. This causes the plate 817 to move toward the gas flow path 814, and the gas flow component 815 also moves toward the gas flow path 814 (see FIG. 18).

[0096] By moving the gas flow component 815 toward the gas flow path 814, the volume of the rib-forming portions 821-823 increases, promoting foaming in the rib-forming portions 821-823. This increases the ratio of foam cells in the ribs 321-323 of the molded part 30 (FIG. 11). It also reduces the variation in foaming ease depending on the distance from the gate 532. At this time, the through-holes of the gas flow component 815 are transferred to the upper end surfaces 321a-323a (FIG. 12) of the ribs 321-323 of the molded part 30, forming the fine protrusions described above.

[0097] Even when the mold 80 is used, the core-back process (FIG. 4) and the re-clamping process (FIG. 5) described in the first embodiment may or may not be performed.

[0098] In the above example, a case where multiple gas flow components 815 are connected by the plate 817 has been described, but a sealing mechanism may be provided for each of the multiple gas flow components 815 so that each component can move independently. Also, instead of providing gas flow components 815 on all of the rib forming portions 821 to 823, gas flow components 815 may be provided on only some of the rib forming portions 821 to 823.

[0099] The molded part 30 according to the fourth embodiment of the present invention and the method for manufacturing the same have been described above. According to this embodiment, a molded part that is lightweight yet has excellent strength and appearance can be obtained.

[0100] The molded parts according to the above-described embodiments can reduce the amount of resin used by using a foam molded body for the rib. As a result, the molded parts according to the above-described embodiments can improve resource utilization efficiency, reduce transportation burden, reduce energy consumption, and reduce CO ２ By providing molded parts to society, we can contribute to achieving 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) of the 17 Sustainable Development Goals (SDGs) established by the United Nations.

[0101] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0102] Example 1: Foam injection molding was performed using a mold similar to the mold 50 described in Figure 2. The cavity formed when the fixed mold and movable mold were closed was a 100 mm x 100 mm plate-shaped cavity, with a base having an average thickness of t = 1.5 mm and three ribs of the same shape, each with a width W = 2.0 mm and a height H = 3.0 mm, provided in three locations. The distances from the ends of the gates to the ribs (see Figure 7, etc.) were G1 = 15 mm, G2 = 45 mm, and G3 = 75 mm, respectively.

[0103] The resin used was polycarbonate resin (L1225Y manufactured by Teijin). Nitrogen gas was introduced into the molten resin at a resin temperature of 280°C using a MuCell (registered trademark) injection molding machine at a pressure of 20 MPa and a concentration of 0.2 wt %.

[0104] Carbon dioxide was introduced into the mold as a counter-pressure gas. After pressurizing the cavity to a gas pressure of 4 MPa, injection molding was performed with a filling time of 0.5 seconds. Upon completion of the primary injection filling, the counter-pressure gas was discharged. At the same time, filling was supplemented by dwelling at a pressure of 20 MPa for 2 seconds.

[0105] As a result, when the pressure was released while holding pressure was applied, the rib located 15 mm from the gate did not foam. When the holding pressure was released, the rib also foamed, but swirl marks remained on the surface. Therefore, after the holding pressure was completed, the mold was opened 0.5 mm, the pressure was forcibly reduced, and then the mold was re-clamped to correct the thickness of the base material. Specifically, after reducing the pressure using the core back, the mold was compressed by applying clamping force to flatten the base, which had developed warpage and undulations. Due to the compression, the base became non-foamed, and foaming remained only in the rib.

[0106] The foam cell ratios in the base and ribs were determined by SEM cross-sectional observation and image analysis of the molded parts. The ribs were observed at three locations from the base to the tip, and the base was observed at the center directly below the rib. The foam cell ratios in the ribs were 2%, 25%, and 35% (difference between maximum and minimum = 35% - 2% = 33%) from the side closest to the gate, and no foam cells were observed in the base. No visible sink marks were present throughout the molded parts. The flatness of the surface opposite the ribs was measured using a microscope (Keyence Corporation VHX6000). The maximum depth from the reference plane was 5 to 12 μm on the backside of each rib. The average diameter of the foam cells in this molded part was 200 μm. The surface roughness Ra of the base surface opposite the rib was 50 to 70 nm, and it was glossy.

[0107] In this example, a partially foamed part with ribs was manufactured using the counterpressure method and core-back and re-clamping. It was found that the foaming was insufficient in the ribs close to the gate, resulting in a decrease in uniformity throughout the part. However, because sink marks were less likely to occur near the gate, shape accuracy was maintained. Furthermore, a separate investigation revealed that controlling foaming in the ribs within a distance of 15 to 20 mm from the edge of the gate was particularly difficult.

[0108] Example 2 A molded part was produced in the same manner as in Example 1, except that the width of the rib closest to the gate was set to 1.5 mm, making it smaller than the width of the other ribs. However, unlike Example 1, the core-back and re-clamping were not performed. As a result, the foam cell ratios in the rib were 10%, 25%, and 35% from the side closest to the gate (difference between maximum and minimum values ​​= 35% - 10% = 25%), and foaming variation was reduced compared to Example 1. No sink marks were observed. The flatness of the surface opposite the rib was 5 to 9 μm. The average diameter of the foam cells was 200 μm, the same as in Example 1.

[0109] Example 3 A molded part was produced in the same manner as in Example 1, except that the height of the rib closest to the gate was set to 4.0 mm, which was larger than the height of the other ribs (core-backing and re-clamping were not performed). As a result, the foam cell ratios in the rib were 15%, 25%, and 35% from the side closest to the gate (difference between maximum and minimum values ​​= 35% - 15% = 20%), and foaming variation was reduced compared to Example 1. No sink marks were observed. The flatness of the surface opposite the rib was 5 to 8 μm. The average diameter of the foam cells was 200 μm, the same as in Example 1.

[0110] Example 4 Foam injection molding was performed using a mold similar to the mold 70 equipped with the gas flow part 715 described in Figure 13. Other conditions were the same as in Example 1 to produce a molded part (core-backing and re-clamping were not performed). As a result, the foam cell ratios in the rib were 40%, 45%, and 48% from the side closest to the gate (difference between maximum and minimum = 48% - 40% = 8%), showing less foam variation than in Example 1. No foam cells were observed in the base. No sink marks were observed. The flatness of the surface opposite the rib was 3 to 6 μm.

[0111] The average diameter of the foam cells was 150 μm, which was smaller than that of Example 1. The surface roughness Ra of the base on the side opposite to the rib was 50 to 70 nm, similar to Example 1, and the base had a glossy finish.

[0112] Example 5: Using a mold equipped with the same gas flow components as in Example 4, molded parts with 2.0 mm-high ribs as shown in Figure 19 were produced. Molded parts were produced by changing the average base thickness t to four different values: 0.8 mm, 1.0 mm, 1.2 mm, and 1.5 mm by replacing the mold plates. Using the same resin and molding method as in Example 1, partial foam molding with a smooth surface was performed by adjusting only the filling amount (no core-backing or re-clamping was performed). For moldings with thicknesses of 1.0 mm or less, the mold temperature was increased by 20°C to compensate for the filling.

[0113] Regardless of the base thickness, the foam cell ratio in the rib was 50 to 60%. The difference between the maximum and minimum foam cell ratios in the multiple ribs was 10% or less, and no sink marks were observed. The flatness of the surface opposite the rib was 2 to 10 μm. The average diameter of the foam cells was 150 μm.

[0114] For comparison, solid molded parts (solid products) with a base thickness of 1.5 mm and a rib height of 1.0 mm were produced without using a foaming agent (sink marks occurred when the rib height was set to 2.0 mm). These molded parts were subjected to the bending test shown in Figure 20. The results are shown in Table 1, along with the weight change relative to the solid product.

[0115]

[0116] From Table 1, it can be seen that the 1.0 mm and 1.2 mm thick foamed parts are lighter and stronger than the solid parts. The foam ribs allow for wall height without significantly increasing weight. It is believed that by increasing the rib height further, a high strength, lightweight part can be achieved without sink marks.

[0117] Example 6 Foam injection molding was performed using a mold similar to mold 80 with a variable volume rib-forming portion, as described in Figure 15. A molded part was produced under the same other conditions as in Example 1 (core-backing and re-clamping were not performed). As a result, the height of each rib was 3.5 mm, 0.5 mm higher than in Example 1. The foam cell ratios in the rib were 50%, 52%, and 55% from the side closest to the gate (difference between maximum and minimum values ​​= 55% - 50% = 5%), resulting in less foam variation than in Example 1. No foam cells were observed in the base. No sink marks were observed. The flatness of the surface opposite the rib was 2 to 10 μm.

[0118] The average diameter of the foam cells was 350 μm, which was larger than that of Example 1. The surface roughness Ra of the base on the side opposite to the rib was 50 to 70 nm, and the base had a glossy appearance.

[0119] Example 7: A molded part made of crystalline resin was manufactured using the same mold as in Example 6, with a variable volume rib-forming portion. Specifically, a polypropylene resin containing 17% by weight of talc was used, with a resin temperature of 190°C, a mold temperature of 40°C, and a counterpressure of 2 MPa. Otherwise, the molded part was manufactured in the same manner as in Example 6. As a result, the height of each rib was 7.0 mm, approximately 4.5 times the base thickness of 1.5 mm. The foam cell ratios in the ribs were 65%, 70%, and 75% (difference between maximum and minimum values ​​= 75% - 65% = 10%) from the side closest to the gate. In the base, the foam cell ratio was approximately 1% in the center directly below the rib, but no foam cells were observed in areas away from the rib. These results demonstrate that the use of a crystalline resin with high melt tension enables the formation of ribs with a high expansion ratio (high foam cell ratio).

[0120] The average diameter of the foamed cells was 600 μm, and the foamed cells were fibrillated. Although no significant cell breakage was observed in this example, if the expansion ratio is too high, there is a concern that fibrillation will progress and the strength of the rib will decrease.

[0121] No sink marks were observed. The flatness of the surface opposite the rib was 2 to 7 μm. In this example, no swirl marks were observed, but the surface roughness Ra was about 0.7 μm, which was about 10% worse than the solid product. This is thought to be because the counter pressure effect was lower compared to the case of amorphous resin, as crystalline resin was used. However, the level was still applicable to exterior parts.

[0122] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0123] 10, 20, 25, 30 Molded parts, 11 Base, 121 to 123, 221 to 223, 271 to 273, 321 to 323 Rib, 50, 60, 65, 70, 80 Mold, 511 Fixed mold, 512, 612, 662, 712, 812 Movable mold, 513 O-ring, 520 Cavity, 521 to 523, 621 to 623, 671 to 673, 721 to 723, 821 to 823 Rib forming portion, 531 Spool, 532 Gate, 514, 714, 814 Gas flow path, 715, 815 Gas flow part, 816 Space, 817 Plate, 818 O-ring

Claims

1. A molded part made of thermoplastic resin, comprising: a base having an average thickness t of 0.5 to 3.0 mm; and a plurality of ribs formed so as to protrude from one side of the base in the thickness direction of the base; the flatness of the side of the base opposite to the side on which the plurality of ribs are formed is 15 μm or less; the width of a 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 foamed cells in the base is 0 to 5%; the ratio of foamed cells in each of the plurality of ribs is 0 to 90%; at least one of the plurality of ribs has foamed cells; and the difference between the maximum and minimum values ​​of the ratio of foamed cells in the plurality of ribs is 35% or less.

2. The molded part according to claim 1, wherein each of the plurality of ribs has a height that is 1.0 to 4.0 times the width of the root portion and is 2.0 to 10.0 mm.

3. The molded part of claim 1, wherein the width of the root portion of the plurality of ribs that are closer to the gate than a predetermined threshold value is smaller than the width of the root portion of the ribs that are farther from the gate than the threshold value.

4. The molded part of claim 1, wherein the height of the plurality of ribs that are closer to the gate than a predetermined threshold value is greater than the height of the ribs that are closer to the gate than the threshold value.

5. The molded part according to claim 1, wherein the surface of the base opposite to the surface on which the plurality of ribs are formed has a surface roughness Ra of 10 to 200 nm.

6. The molded part according to claim 1, wherein the thermoplastic resin is an amorphous resin.

7. The molded part of claim 1, wherein the thermoplastic resin is a crystalline resin.

8. On the upper end surface of at least some of the ribs, there are 100 protrusions / mm2 each having a circle equivalent diameter of 10 to 40 μm when projected onto a plane perpendicular to the thickness direction of the base. ２ The molded part according to claim 1 , which is formed with a number density of at least 100%.

9. The molded part according to claim 3 or 4, wherein the threshold value is between 10 and 30 mm.

10. The molded part of claim 1, wherein the average diameter of foam cells in said plurality of ribs is 500 μm or less.

11. The molded part of claim 1, further comprising a plating layer formed on the surfaces of said base and said ribs.

12. The molded part according to claim 11, further comprising a mixed layer, which is a region where the thermoplastic resin and the metal of the plating film are mixed, at the interfaces between the base and the rib and the plating film.

13. A method for producing a molded part according to any one of claims 1 to 8 and 10 to 12 using a mold comprising a fixed mold and a movable mold, and including a cavity corresponding to the base and a plurality of rib forming portions corresponding to the plurality of ribs, comprising the steps of: introducing a counter-pressure gas into the mold; injecting and filling molten resin containing a foaming agent into the mold; starting to discharge the counter-pressure gas before completion of holding pressure; moving the movable mold in a direction increasing the distance from the fixed mold; and, after moving the movable mold in the direction increasing the distance from the fixed mold, moving the movable mold in a direction decreasing the distance from the fixed mold.

14. A method for producing a molded part according to any one of claims 3, 4 and 8 using a mold comprising a fixed mold and a movable mold, and including a cavity corresponding to the base and a plurality of rib forming portions corresponding to the plurality of ribs, comprising the steps of: introducing a counter-pressure gas into the mold; injecting and filling molten resin containing a foaming agent into the mold; and starting to discharge the counter-pressure gas before completion of holding pressure.

15. The method for manufacturing a molded part according to claim 14, wherein the mold is provided with a gas flow component arranged in contact with at least a portion of the plurality of rib forming portions and which allows the counter pressure gas to pass without allowing the molten resin to pass through.

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