Molded body, automotive member, and production method for molded body

Abstract

A molded body having a foam region that includes a skin layer A, a foam layer, and a skin layer B in this order in the thickness direction, wherein the average diameter of cells included in the foam layer is 0.40 mm or more.

Description

Molded body, automotive component, and method for manufacturing molded body

[0001] The present disclosure relates to a molded article, an automotive component, and a method for manufacturing a molded article.

[0002] In recent years, in order to reduce the weight of automobiles, metal components have been increasingly replaced with resin components for interior and exterior use. In particular, molded articles containing bubbles (also called cells) obtained by foaming resin are lighter than metals and are expected to further improve automobile fuel efficiency.

[0003] A foam molded article used as an automobile part is known to be obtained by the method described in Patent Document 1. In this method, a molten resin is injected into a cavity formed in a pair of molding dies, and the resin is foamed to produce a molded article.

[0004] Japanese Patent Application Laid-Open No. 2005-238726

[0005] As mentioned above, the use of foamed molded articles makes it possible to reduce the weight of automotive components and the like. However, foamed molded articles tend to have lower mechanical properties, such as tensile modulus, than unfoamed molded articles. Therefore, foamed molded articles that can achieve both weight reduction and good mechanical properties are desirable.

[0006] In view of the above circumstances, an object of the present disclosure is to provide a molded body that can achieve both weight reduction and mechanical properties, an automobile component including this molded body, and a method for manufacturing the molded body.

[0007] Specific means for solving the above problems include the following aspects. <1> A molded article having a foamed portion including a skin layer A, a foam layer, and a skin layer B in this order in the thickness direction, wherein the average diameter of cells contained in the foamed layer is 0.40 mm or more. <2> The molded article according to <1>, wherein the maximum diameter of cells contained in the foamed layer is 0.85 mm or more. <3> The molded article according to <1> or <2>, wherein the ratio of the maximum diameter of cells contained in the foamed layer to the average diameter of cells contained in the foamed layer is 2.90 or less. <4> The number of cells per unit cross-sectional area of ​​the foamed layer is 10 cells / mm ２The molded article according to any one of <1> to <3>, which is as follows: <5> An automotive component, comprising the molded article according to any one of <1> to <4>. <6> A method for producing the molded article according to any one of <1> to <4>, comprising the steps of: supplying a composition containing a resin and a foaming agent into a molding device having a movable portion; and moving a portion of the molding device to increase the volume of the interior of the molding device.

[0008] According to the present disclosure, there are provided a molded article that can achieve both weight reduction and mechanical properties, an automobile component including this molded article, and a method for manufacturing the molded article.

[0009] Fig. 1 is a schematic cross-sectional view of an example of the configuration of a molding apparatus used to produce a molded body. Fig. 2 is a schematic cross-sectional view of an example of the configuration of an injection apparatus used to produce a molded body. Fig. 3 is an X-ray CT scan image of a cross section of a molded body produced in Example 1. Fig. 4 is an X-ray CT scan image of a cross section of a molded body produced in Example 2. Fig. 5 is an X-ray CT scan image of a cross section of a molded body produced in Comparative Example 1.

[0010] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present invention.

[0011] In the present disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved.

[0012] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the present disclosure, numerical ranges described in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, the upper or lower limit value of a numerical range described in the present disclosure may be replaced with a value shown in the Examples. In the present disclosure, when multiple substances corresponding to each component are present in the composition, the content of each component refers to the total content of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where the layer is formed over the entire region when the region where the layer is present is observed, as well as cases where the layer is formed only in a portion of the region. When embodiments are described in the present disclosure with reference to drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. The sizes of the components in each figure are conceptual, and the relative size relationships between the components are not limited thereto.

[0013] <Molded Article> The molded article of the present disclosure has a foamed portion including a skin layer A, a foamed layer, and a skin layer B in this order in the thickness direction, and the foamed layer contains cells with an average diameter of 0.40 mm or more.

[0014] In the present disclosure, "foam layer" refers to a portion containing cells in the resin (for example, a portion containing cells with a diameter of 0.2 mm or more), and "skin layer" refers to a portion containing no cells in the resin (for example, a portion containing no cells with a diameter of 0.2 mm or more). In the present disclosure, the portion of the molded body in which skin layer A, foam layer, and skin layer B are located in this order in the thickness direction may be referred to as the "foam portion." The ratio of the thickness of the foam layer to the total thickness of skin layer A, foam layer, and skin layer B may be referred to as the "foam layer ratio." Skin layer A and skin layer B may each be referred to as the "skin layer."

[0015] The molded article of the present disclosure can be made lighter by including a foam layer. Furthermore, the molded article of the present disclosure has a foam layer with an average cell diameter of 0.40 mm or more, which tends to be larger than the average cell diameter of molded articles with foam layers conventionally used as automotive parts. In this case, the mechanical strength (e.g., high tensile modulus) of the molded article can be ensured.

[0016] From the viewpoint of weight reduction, the foam layer ratio is preferably 75.0% or more, more preferably 77.0% or more, and even more preferably 80.0% or more. The upper limit of the foam layer ratio is not limited, and may be 84.0% or less.

[0017] When the thickness of the foamed portion of the molded body is not constant, the ratio of the thickness of the foamed layer to the total thickness of the skin layer and foamed layer measured at the portion where the foamed layer thickness is greatest is defined as the "foamed layer ratio" of the molded body.

[0018] In the present disclosure, the thicknesses of the skin layer and the foam layer are measured by observing a cross-sectional image of the foamed portion of the molded article. The type of cross-sectional image is not particularly limited, and X-ray CT scan images, electron microscope photographs, etc. can be used. The observation area is set to a width of at least 1.5 mm. Specifically, in the cross-sectional image of the foamed portion of the molded article, the thickness of the region where cells are not observed is measured as the thickness of the skin layer, and the thickness of the region where cells are observed is measured as the thickness of the foamed layer. In the above measurement, the boundary between the skin layer and the foamed layer is determined as follows: In the cross-sectional image of the foamed portion, a straight line perpendicular to the thickness direction of the foamed portion is drawn and moved from the outermost part to the center of the foamed portion. The movement of this line is stopped at the position where it first comes into contact with a cell whose horizontal or vertical diameter is 0.03 mm or more, and this is the boundary between the skin layer and the foamed layer. In the present disclosure, the horizontal diameter of the cell means the maximum width of the cell in the direction perpendicular to the thickness direction of the foamed portion, and the vertical diameter of the cell means the maximum width of the cell in the thickness direction of the foamed portion.

[0019] From the viewpoint of the mechanical strength of the molded article, the average diameter of the cells contained in the foam layer is preferably 0.42 mm or more, more preferably 0.45 mm or more, and even more preferably 0.48 mm or more. From the viewpoint of the mechanical strength of the molded article, the average diameter of the cells contained in the foam layer may be 0.70 mm or less, 0.65 mm or less, 0.60 mm or less, or 0.55 mm or less.

[0020] From the viewpoint of the mechanical strength of the molded article, the maximum diameter of the cells contained in the foam layer is preferably 0.85 mm or more, more preferably 0.90 mm or more, and even more preferably 1.00 mm or more. From the viewpoint of the mechanical strength of the molded article, the maximum diameter of the cells contained in the foam layer is preferably 2.00 mm or less, more preferably 1.80 mm or less, and even more preferably 1.50 mm or less.

[0021] From the viewpoint of the mechanical strength of the molded article, the ratio of the maximum diameter of the cells contained in the foam layer to the average diameter of the cells contained in the foam layer is preferably 2.95 or less, more preferably 2.90 or less, and even more preferably 2.50 or less. The lower limit of this ratio is not particularly limited, and may be, for example, 1.50 or more.

[0022] In the present disclosure, the average cell diameter and maximum cell diameter are measured by observing a cross-sectional image of the foamed portion of a molded article obtained in the same manner as the cross-sectional images for measuring the thicknesses of the skin layer and foam layer. Specifically, the horizontal and vertical widths of a cell observed in the cross-section of the foamed portion of a molded article are defined as the horizontal and vertical diameters of that cell, the sum of the arithmetic mean values ​​of the horizontal diameters and the arithmetic mean values ​​of the vertical diameters of 20 randomly selected cells (excluding cells with a horizontal or vertical diameter of less than 0.03 mm) is defined as the "average cell diameter," and the maximum value of the horizontal and vertical diameters of all the selected cells is defined as the "maximum cell diameter."

[0023] The number of cells per unit cross-sectional area of ​​the foam layer is 10 / mm ２ It is preferable that the number of particles is 5 or less per mm. ２ More preferably, the number is 3 or less per mm. ２The lower limit of the number of cells per unit cross-sectional area of ​​the foam layer is not particularly limited, and is, for example, 0 cells / mm ２ or more, and ２ It may be more than that.

[0024] In the present disclosure, the number of cells per unit cross-sectional area of ​​the foam layer is measured by observing a cross-sectional image of the foamed portion of a molded article obtained in the same manner as the cross-sectional image for measuring the thickness of the skin layer and the foam layer. More specifically, 20 randomly selected cells (excluding cells with a horizontal or vertical diameter of less than 0.03 mm) from the cells observed in the cross-section of the foam layer are counted as a function of the cross-sectional area (mm ２ The value obtained by dividing the calculated value by the cross-sectional area of ​​the foam layer is the number of cells per unit cross-sectional area of ​​the foam layer.

[0025] The cells contained in the foam layer may be oriented in the thickness direction of the foam layer. The state in which the cells are oriented in the thickness direction of the foam layer is thought to be formed by cells formed by foaming the resin in the molding process of the molded article, stretching in the direction of movement of the mold. The state in which the cells are oriented in the thickness direction of the foam layer means that the foam layer has reached a sufficient thickness within the limit that can ensure the necessary strength.

[0026] In the present disclosure, "a state in which cells are oriented along the thickness direction of the foam layer" means that the average aspect ratio of the cells contained in the foam layer is 1.01 or more, or 1.10 or more. The average aspect ratio of the cells is the ratio of the arithmetic mean value of the longitudinal diameter of the cells to the arithmetic mean value of the lateral diameter of the cells measured by the above-mentioned method (arithmetic mean value of longitudinal diameter / arithmetic mean value of lateral diameter). From the viewpoint of ensuring the strength of the molded article, the average aspect ratio of the cells contained in the foam layer is preferably 1.80 or less, more preferably 1.70 or less, and even more preferably 1.35 or less.

[0027] The thickness of the foam layer in the foamed portion is not particularly limited as long as it satisfies the above-mentioned condition for the foam layer ratio. For example, the thickness of the foam layer may be 2.00 mm to 4.00 mm. When the foam layer thickness is within the above range, weight reduction tends to be achieved while ensuring sufficient strength when a typical foam molding method is carried out. When the foam layer thickness of the molded article is not constant, the thickness measured at the portion where the foam layer thickness is greatest is taken as the "foam layer thickness."

[0028] The thickness of the skin layer in the foamed portion is not particularly limited as long as it satisfies the above-mentioned condition for the foam layer ratio. For example, the thickness of the skin layer may be 0.26 mm to 0.36 mm, or 0.28 mm to 0.32 mm. When the skin layer thickness is within the above range, weight reduction tends to be achieved while ensuring sufficient strength when a typical foam molding method is carried out. The thickness of the skin layer is the thickness of one of the skin layers A and one of the skin layers B located on both sides of the foam layer. When the thickness of the skin layer varies depending on the location of the molded article, the thickness measured at the location where the foam layer is thickest is taken as the "thickness of the skin layer."

[0029] The thickness of the foamed portion of the molded article (i.e., the total thickness of the foamed layer and the skin layers located on both sides thereof) can be set depending on the intended use of the molded article. From the viewpoint of balancing between ensuring rigidity and reducing weight, the thickness of the foamed portion of the molded article is preferably 6 mm or less, more preferably 5 mm or less, and even more preferably 4 mm or less. From the viewpoint of flow resistance when filling a mold with molten resin, the thickness of the foamed portion of the molded article is preferably 1 mm or more, more preferably 1.5 mm or more, and even more preferably 2 mm or more.

[0030] When a molded article has foamed portions and portions that do not fall under the category of foamed portions (for example, bent portions of the molded article), the proportion of the foamed portions in the entire molded article is not particularly limited and can be set depending on the application of the molded article, etc. For example, the proportion of the foamed portions in the entire molded article may be 50% to 100%, 70% to 100%, or 80% to 100% on an area basis when the molded article is viewed from above.

[0031] The type of resin contained in the molded product is not particularly limited. From the viewpoint of ease of molding and the balance between toughness and strength, the resin contained in the molded product is preferably a thermoplastic resin. The resin contained in the molded product may be one type or two or more types.

[0032] Specific examples of the resin include polyethylene resins, polypropylene resins, composite polypropylene resins, polystyrene resins, polyethylene terephthalate resins, polyvinyl alcohol resins, vinyl chloride resins, ionomer resins, polyamide resins, acrylic / methacrylic resins (PMMA), acrylonitrile styrene acrylate copolymer resins (ASA), acrylonitrile butadiene styrene copolymer resins (ABS) and polycarbonate resins. Among these, at least one selected from the group consisting of acrylic / methacrylic resins (PMMA), acrylonitrile styrene acrylate copolymer resins (ASA), polypropylene resins, composite polypropylene resins, acrylonitrile butadiene styrene copolymer resins (ABS) and polycarbonate / ABS resins is preferred, and polypropylene resins, composite polypropylene resins and acrylonitrile butadiene styrene copolymer resins (ABS) are more preferred.

[0033] The molded article may contain components other than resin as needed. Examples of components other than resin include additives such as inorganic fillers, rubbers, and carbon black, and components derived from the foaming agent described below. When the molded article contains components other than resin, the total amount of the components other than resin is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less of the entire molded article.

[0034] When the molded body contains components other than resin, the total amount of resin is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more of the entire molded body. The total amount of resin is not particularly limited as long as it is 100% by mass or less of the entire molded body, and may be 99.5% by mass or less, or may be 99% by mass or less.

[0035] The use of the molded article of the present disclosure is not particularly limited. Because the molded article of the present disclosure is lightweight and has excellent strength, it is suitable for use in applications where both weight reduction and strength are important, such as interior and exterior components of automobiles. Specific examples of interior and exterior components of automobiles include sacco moldings, arch moldings, side moldings, rocker moldings, bumpers, and tailgate trims.

[0036] The type of the automotive component is not particularly limited and can be selected from automotive interior and exterior components such as a sacco molding, an arch molding, a side garnish, a side molding, a rocker molding, a bumper, a back door trim, and a side door trim.

[0037] <Method for manufacturing a molded body> The method for manufacturing a molded body of the present disclosure is the method for manufacturing the molded body described above, and includes the steps of: supplying a composition containing a resin and a foaming agent into a molding device having a movable part; and moving a part of the molding device to increase the volume inside the molding device.

[0038] In the above method, a movable portion of a molding apparatus to which a composition has been supplied is moved to increase the volume inside the molding apparatus. During this process, cells are formed by the action of the blowing agent contained in the composition. As a result, a molded article including a foamed portion having a foamed layer containing cells and skin layers located on both sides of the foamed layer can be produced.

[0039] In the above-mentioned method, the method for controlling the average cell diameter, maximum cell diameter, foam layer ratio, and other conditions of the produced molded article within the above-mentioned ranges is not particularly limited, and examples thereof include a method for adjusting the types and amounts of the resin and foaming agent contained in the composition, molding conditions (temperatures of the composition and molding device, molding time, etc.), etc.

[0040] The type of resin contained in the composition is not particularly limited, and may be selected from the resins that may be contained in the molded article described above.

[0041] The type of foaming agent contained in the composition is not particularly limited, and both organic and inorganic foaming agents can be used. Specific examples of organic foaming agents include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4-oxybisbenzenesulfonylhydrazide (OBSH), and hydrazodicarbonamide (HDCA). Specific examples of inorganic foaming agents include sodium bicarbonate.

[0042] Among organic foaming agents, azodicarbonamide (ADCA) is preferably used when the molded article is an exterior component. The use of azodicarbonamide (ADCA) improves hot water resistance and tends to suppress the occurrence of blisters in hot water tests. Blisters refer to a state in which gas generated by the reaction between unreacted foaming agent remaining in the skin layer and water pushes up the skin layer.

[0043] The decomposition temperature of the blowing agent is preferably 50° C. to 200° C., more preferably 80° C. to 200° C. The decomposition temperature of the blowing agent may be 130° C. to 200° C.

[0044] The content of the blowing agent in the composition is preferably set appropriately depending on the type of blowing agent, etc. For example, when an organic blowing agent (preferably azodicarbonamide) is used as the blowing agent, from the viewpoint of foamability, the content of the organic blowing agent in the composition is preferably within the range of 0.05% by mass to 1.0% by mass, more preferably within the range of 0.1% by mass to 0.5% by mass. The above content of the blowing agent is the content in the composition before being supplied to the molding device.

[0045] In the above method, the temperature of the composition when it is supplied to the molding device is not particularly limited. When the composition contains a thermoplastic resin, the temperature is preferably equal to or higher than the softening point of the thermoplastic resin.

[0046] The molding apparatus used in the method of the present disclosure is not particularly limited as long as at least a portion of the apparatus is movable. From the viewpoint of workability, it is preferable to use a pair of molds, at least one of which is movable.

[0047] An example of a molding apparatus is shown in Figure 1. The molding apparatus shown in Figure 1 includes a movable mold 1, a fixed mold 2, a cavity 6 which is a gap between the movable mold 1 and the fixed mold 2, and a gate 4 which passes through the fixed mold 2 from the outside of the mold to the cavity 6. Hereinafter, the movable mold 1 and the fixed mold 2 may be collectively referred to as the "mold."

[0048] 1A, a composition 3 containing a resin and a foaming agent is supplied from an injection device (not shown) through a gate 4 into a cavity 6. When the composition 3 contains a thermoplastic resin, the composition 3 is supplied into the cavity 6 in a state in which the thermoplastic resin is melted or softened and has fluidity.

[0049] The mold is usually at a temperature lower than that of the supplied composition 3. Therefore, when the composition 3 is filled into the cavity 6 as shown in Fig. 1(B), solidification of the composition 3 begins from the portion that comes into contact with the mold.

[0050] 1(C), the movable mold 1 is moved to increase the distance between the molds (core back), and the unsolidified portion of the composition 3 is foamed to form a foam layer 5. A skin layer 7 is formed between the foam layer 5 and the mold by the solidified composition 3.

[0051] The material of the molding device is not particularly limited, and a common material can be used, such as stainless steel, pre-hardened steel, alloy tool steel, high-speed tool steel, and cemented carbide tool steel.

[0052] There are no particular limitations on the method for supplying the composition to the molding apparatus shown in Fig. 1. For example, an injection apparatus as shown in Fig. 2 may be used, which continuously prepares the composition and supplies it to the molding apparatus.

[0053] 2 includes a cylinder 11 and a hopper 12 for introducing raw materials for the composition into the cylinder 11. The outlet of the cylinder 11 is connected to a mold 13 of a molding device.

[0054] Cylinder 11 is equipped with a screw 11A that stirs the raw materials to prepare a composition and moves the composition toward mold 13 of the molding device, a motor 11B that drives screw 11A, and a heater (not shown) that heats the inside of cylinder 11. The raw materials supplied into cylinder 11 become molten while moving toward mold 13.

[0055] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0056] Example 1 A resin (100 parts by mass) and a foaming agent (0.5 parts by mass) were charged into the hopper of an injection device configured as shown in Figure 2, and the resin was melted and mixed in the cylinder to prepare a composition. This composition was supplied into the cavity of a pair of molds, one of which was movable. After the composition was supplied into the cavity, the movable mold (core) was moved to foam the composition, and the composition was cooled to produce a molded product.

[0057] The details of the materials used in preparing the composition are as follows: Resin: Polypropylene Foaming agent: Azodicarbonamide (ADCA)-containing masterbatch

[0058] Example 2 A molded body was produced in the same manner as in Example 1, except that the molding conditions were changed.

[0059] Comparative Example 1 A molded body was produced in the same manner as in Example 1, except that the molding conditions were changed.

[0060] <Cross-section observation and mass measurement of molded article> X-ray CT scan images of cross sections obtained by cutting the molded articles produced in Examples 1 and 2 and Comparative Example 1 along the thickness direction are shown in Figs. 3 to 5. The cross sections of the molded articles produced in Examples and Comparative Example had the skin layer A (cavity side), the foam layer, and the skin layer B (core side) positioned in this order. The thicknesses of the skin layer A, the foam layer, and the skin layer B were measured from the obtained X-ray CT scan images, and the foam layer ratio was calculated. The results are shown in Table 1. The maximum diameter, average diameter, and number per unit cross-sectional area of ​​the cells contained in the foam layer are also shown in Table 1. Furthermore, the maximum diameter, average diameter, and number per unit cross-sectional area of ​​the cells in the foam layer were measured in a 100 cm section of the molded article. ２ The mass per unit is shown in Table 1.

[0061] <Measurement of Tensile Modulus> Test specimens (conforming to JIS K 7139 Multipurpose Test Specimen Type A) with a length of 170 mm were prepared from the molded articles prepared in the Examples and Comparative Examples. Each test specimen was pulled using a tensile tester, and the elongation of the test specimen relative to the load was measured. Next, a graph was prepared from the measured values, with the load on the horizontal axis and the elongation on the vertical axis, and the tensile modulus (MPa) of each test specimen was calculated from the tangent to the rising portion of the load-elongation curve. The results are shown in Table 1.

[0062]

[0063] As shown in Table 1, the molded articles of the Examples, in which the average diameter of the cells contained in the foam layer was 0.40 mm or more, were lighter and had a superior tensile modulus of elasticity than the molded articles of the Comparative Examples, in which the average diameter of the cells contained in the foam layer was less than 0.40 mm. From the above points, molded articles that were both lightweight and had good mechanical properties were obtained in the Examples.

[0064] The disclosure of Japanese Patent Application No. 2023-156503, filed on September 21, 2023, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A molded article having a foamed portion including a skin layer A, a foamed layer, and a skin layer B in that order in the thickness direction, and the average diameter of cells contained in the foamed layer is 0.40 mm or more.

2. The molded article according to claim 1, wherein the maximum diameter of cells contained in the foamed layer is 0.85 mm or more.

3. The molded article according to claim 1, wherein the ratio of the maximum diameter of the cells contained in the foamed layer to the average diameter of the cells contained in the foamed layer is 2.90 or less.

4. The number of cells per unit cross-sectional area of ​​the foam layer is 10 cells / mm ２ The molded body according to claim 1 , wherein:

5. An automobile component comprising the molded article according to any one of claims 1 to 4.

6. A method for producing a molded article according to any one of claims 1 to 4, comprising the steps of: supplying a composition containing a resin and a foaming agent into a molding device having a movable part; and moving a part of the molding device to increase the internal volume of the molding device.

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