Foam molded product and method for producing foam molded product

Abstract

To provide a foam molding that prevents the occurrence of a crater.SOLUTION: A foam molding is made by foaming a resin material containing a resin and a foaming agent, and features a storage elastic modulus of 1.00 MPa or more at 137°C and a melt tension of 5.0 mN or more at 180°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a foam molded article and a method for producing a foam molded article. [Background technology]

[0002] Injection foam molded products made from thermoplastic resins such as polypropylene resins and acrylonitrile-butadiene-styrene copolymer resins are used as automotive components due to their light weight and excellent rigidity. One type of injection foam molding method is the core-back method. The core-back method is a molding method in which a thermoplastic resin composition containing a foaming agent is injection-molded, the position of the movable mold is slid, and then foam molding is performed again. When this molding method is used, the surface layer of the molded product becomes a skin layer with a lower expansion rate than the foam layer, and the interior of the molded product becomes a uniform, high-expansion foam layer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-121793 Summary of the Invention [Problem to be solved by the invention]

[0004] When injection foam molded articles are used as automobile interior parts such as console boxes, door trims, deck side trims, back door trims, and instrument panels, or automobile exterior parts such as fenders, side sills, bumpers, and back door outers, the injection foam molded articles are required to be lightweight, thin-walled, and have good appearance.

[0005] However, small circular or elliptical depressions (hereinafter sometimes referred to as "pits") tend to appear on the surface of injection-molded foams, which can cause problems in appearance. For this reason, it is desirable to suppress the occurrence of pits on foam-molded products.

[0006] The present invention has been made in view of the above-mentioned conventional circumstances, and has an object to provide a foamed molded article in which the occurrence of pitting is suppressed, and a method for producing the same. [Means for solving the problem]

[0007] Specific means for achieving the above object are as follows. <1> A foamed molded article which is produced by foaming a resin material containing a resin and a foaming agent, and has a storage modulus at 137°C of 1.00 MPa or more. <2> The crystallization peak temperature is 125°C or higher <1> The foam molded article according to claim 1. <3> Melt tension at 180°C is 5.0mN or more <1> or <2> The foam molded article according to claim 1. <4> The resin material contains a branched polypropylene resin. <1> ~ <3> 10. The foamed molded article according to any one of the above. <5> The content of the branched polypropylene resin in the resin material is 2% by mass or more. <4> The foam molded article according to claim 1. <6> The branched polypropylene resin has an MFR of 35 g / 10 min or more at 230°C. <4> or <5> The foam molded article according to claim 1.

[0008] <7> <1> ~ <6> 10. A method for producing the foam molded article according to any one of claims 1 to 9, comprising a step of foaming the resin material. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a foamed molded article in which the occurrence of pitting is suppressed, and a method for producing the same. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram for explaining an outline of a molding device equipped with a mold. [Figure 2] 1 is a graph showing the results of measuring the storage modulus in Examples 1 and 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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. 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. 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 numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these. In the present disclosure, the thicknesses of the foamed molded article, foam layer, and skin layer refer to the portions where the thickness is greatest when the cross section of the foamed molded article is observed using a stereomicroscope, SEM (scanning electron microscope), or polarized microscope.

[0012] <Foam molded body> The foam molded article of the present disclosure is formed by foaming a resin material containing a resin and a blowing agent, and has a storage modulus at 137°C of 1.00 MPa or more. The foam molded article of the present disclosure suppresses the occurrence of pitting, and the reason for this is presumed to be as follows: Because the storage modulus at 137°C, measured as described below, is 1.00 MPa or more, as the molten resin material flows into the mold, the surface portion in contact with the mold cools and crystallizes rapidly, solidifying, forming a highly rigid skin layer. As the molten resin material flows into the mold, the blowing agent decomposes due to a sudden decrease in pressure at the end of the flow, generating bubbles. These bubbles are generated inside the resin material when the position of the movable mold is slid, and the expanding bubbles cool, causing volumetric shrinkage and negative stress that draws the resin material inward. This is thought to suppress the occurrence of pitting because the rigidity of the skin layer exceeds the negative stress.

[0013] The storage modulus of the foam molded article of the present disclosure at 137°C is preferably 1.00 MPa or more, more preferably 1.50 MPa or more, from the viewpoint of more suitably suppressing the occurrence of pitting. The storage modulus of the foam molded article of the present disclosure at 137°C may be 10.0 MPa or less, or may be 5.00 MPa or less. The storage modulus at 137°C is a value measured by the method described in the Examples below after obtaining a foamed molded article having a thickness of 2.5 mm, which is obtained by foaming a resin material containing a resin and a foaming agent.

[0014] The peak crystallization temperature of the foam molded article of the present disclosure is preferably 125° C. or higher, more preferably 125.5° C. or higher, and even more preferably 126° C. or higher, from the viewpoint of more suitably suppressing the occurrence of pitting. Furthermore, the peak crystallization temperature of the foam molded article of the present disclosure may be 130° C. or lower, or 129° C. or lower, from the viewpoint of expansion ratio. The crystallization peak temperature is a value measured by the method described in the Examples below. For example, the crystallization peak temperature may be a value measured using the same resin material as the resin material used as the raw material for the foam-molded article of the present disclosure, except that it does not contain a blowing agent, as shown in the Examples below. The crystallization peak temperature may also be a value measured using a molten resin material obtained by melting the foam-molded article, using the method described in the Examples.

[0015] In the foam molded article of the present disclosure, the melt tension at 180°C is preferably 5.0 mN or more, more preferably 5.5 mN or more, even more preferably 5.6 mN or more, and particularly preferably 6.0 mN or more. It is believed that a melt tension of 5.0 mN or more at 180°C makes it difficult for bubbles generated inside the resin material by reduced pressure when the resin material flows inside the mold to break, and that when the position of the movable mold is slid, the resin is stretched as the bubbles expand, thereby suppressing bubble breakage. It is presumed that this reduces the opportunity for bubbles to migrate to the surface portion in contact with the mold, thereby more effectively suppressing the occurrence of pitting.

[0016] In the foam molded article of the present disclosure, from the viewpoint of expansion ratio, the melt tension at 180°C may be 10 mN or less, or may be 8.0 mN or less. The melt tension at 180°C is a value measured by the method described in the Examples below. For example, the melt tension at 180°C may be a value measured using the same resin material as the resin material used as the raw material for the foam-molded article of the present disclosure, except that it does not contain a blowing agent, as described in the Examples below. The melt tension at 180°C may also be a value measured using a molten resin material obtained by melting the foam-molded article, by the method described in the Examples.

[0017] In the foamed molded article of the present disclosure, in order to more effectively suppress the occurrence of blemishes, the product of the crystallization peak temperature and the melt tension at 180°C is preferably 700 or more, and more preferably 750 or more. In the foam molded article of the present disclosure, the product of the crystallization peak temperature and the melt tension at 180°C may be 1250 or less, or 1000 or less, in terms of expansion ratio.

[0018] (Foam layer and skin layer) The foam molded article of the present disclosure is formed by foaming a resin material containing a resin and a foaming agent. For example, the foam molded article of the present disclosure may include a foam layer and a skin layer covering the foam layer, the foam layer being a layer formed by foaming a resin material, and the skin layer being a layer formed by cooling and solidifying the resin material.

[0019] The foam layer may be a layer formed by foam molding a resin material filled in a mold, and the skin layer may be a layer formed by cooling and solidifying a resin material and having a lower foaming rate than the foam layer.

[0020] Examples of resins used for the resin material include at least one selected from the group consisting of polyethylene resins, polypropylene resins (PP), composite polypropylene resins (PPC), polystyrene resins, polyethylene terephthalate resins, polyvinyl alcohol resins, vinyl chloride resins, ionomer resins, polyamide resins, acrylonitrile-butadiene-styrene copolymer resins (ABS), polycarbonate resins, and polyphenylene sulfide resins (PPS). Among these, at least one selected from the group consisting of polypropylene resins (PP), composite polypropylene resins (PPC), and acrylonitrile-butadiene-styrene copolymer resins (ABS) is preferred.

[0021] The resin material may contain components other than the resin described above and the foaming agent described below, such as filler, glass fiber, or carbon fiber.

[0022] Examples of foaming agents include organic foaming agents such as azodicarbonamide, and inorganic foaming agents such as sodium hydrogen carbonate (also known as sodium bicarbonate or baking soda). In foam molding of automotive exterior parts, it is preferable to use an organic foaming agent as the foaming agent because of its excellent environmental test performance.

[0023] Examples of organic foaming agents include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4'-oxybisbenzenesulfonylhydrazide (OBSH), and hydrazodicarbonamide (HDCA), with azodicarbonamide (ADCA) being preferred. In particular, when manufacturing exterior components, it is preferable to use azodicarbonamide (ADCA), whose decomposition products contain almost no water.

[0024] The content of azodicarbonamide (ADCA) in the total amount of the blowing agent is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0025] The decomposition temperature of the blowing agent is preferably 50° C. to 250° C., more preferably 100° C. to 220° C. The decomposition temperature of the blowing agent may be 130° C. to 250° C. depending on the form of use.

[0026] The content of the foaming agent in the resin material is preferably set appropriately depending on the type of foaming agent, etc. For example, when azodicarbonamide (ADCA) is used as the foaming agent, the content of azodicarbonamide (ADCA) in the resin material is preferably within a range of 0.05% by mass to 0.5% by mass, more preferably within a range of 0.1% by mass to 0.4% by mass, from the viewpoints of foamability and moldability. The content of ADCA refers to the proportion in the mixture (composition) before being charged into the cylinder of the injection machine, which will be described later.

[0027] The resin material preferably contains a branched polypropylene resin in order to increase the crystallization peak temperature, melt tension, etc. of the foamed molded body, and more preferably contains a branched polypropylene resin together with a polypropylene-based resin as the resin.

[0028] When the resin material contains a branched polypropylene resin, the content of the branched polypropylene resin is preferably 4% by mass or more, more preferably 6% by mass or more, and even more preferably 8% by mass or more, based on the total amount of the resin material.

[0029] When the resin material contains a branched polypropylene resin, the content of the branched polypropylene resin may be 20% by mass or less, or 16% by mass or less.

[0030] The MFR (melt flow rate) of the branched polypropylene resin at 230°C is preferably 35 g / 10 min or more, more preferably 40 g / 10 min or more, and even more preferably 50 g / 10 min or more.

[0031] The MFR at 230°C of the branched polypropylene resin may be 100 g / 10 min or less, or may be 80 g / 10 min or less. The MFR is a value measured at 230°C under a load of 2.16 kg (21.18 N) in accordance with JIS K7210-1 (2014).

[0032] The thickness of the foam layer is not particularly limited, but is preferably 0.01 mm to 5.9 mm, more preferably 1.0 mm to 5.0 mm, and even more preferably 1.7 mm to 2.9 mm.

[0033] The porosity of the foam layer is preferably 2% or more, and more preferably 20% or more. A porosity of 10% or more in the foam layer is advantageous in terms of reducing the weight of the foamed molded article, but tends to make pitting more likely to occur on the surface of the skin layer. However, in the foamed molded article of the present disclosure, since the crystallization peak temperature is 125°C or more, it is believed that it is possible to achieve both weight reduction and suppression of pitting even when the porosity of the foamed layer is increased. The void ratio means the ratio of the total area of ​​all the cells present in a certain cross section of a foamed molded article to the cross-sectional area of ​​the cross section, as shown in the following formula (1). Porosity = (total area of ​​each cell / cross-sectional area of ​​foamed molded product) × 100 (1)

[0034] The thickness of the skin layer is not particularly limited, but is preferably 0.05 mm to 2.995 mm, more preferably 0.1 mm to 1.0 mm, and even more preferably 0.3 mm to 0.5 mm.

[0035] <Method of manufacturing foam molded article> The method for producing a foam molded article according to the present disclosure is a method for producing the foam molded article according to the present disclosure, and includes a step of foaming the resin material in a mold. The method for producing a foam molded article according to the present disclosure can produce a foam molded article with reduced pitting.

[0036] In the manufacturing method of the foam molded body disclosed herein, for example, a foam molded body can be molded by a method that involves the steps of injecting a resin material containing a resin and a foaming agent into a cavity in a set of molds that is composed of a fixed side mold and a movable side mold that is movable in the opening and closing direction relative to the fixed side mold and forms a cavity that is a gap between it and the fixed side mold, and then filling the cavity with the resin material and moving the movable side mold in the opening direction from the fixed side mold that constitutes the mold to expand the volume within the cavity.

[0037] A schematic diagram of a molding apparatus applicable to the production of foam molded articles is shown in Figure 1. The molding apparatus 16 shown in Figure 1 includes a fixed mold 17 and a movable mold 19 that is movable in the opening and closing direction relative to the fixed mold 17 and forms a cavity 18, which is a gap between the fixed mold 17 and the movable mold 19.

[0038] The molding device 16 also includes a gate 21 that penetrates the fixed mold 17 to the cavity 18, and an injector 22 that injects and fills the cavity 18 with molten resin material R through the gate 21. The injector 22 includes a hopper (supply unit) (not shown) and a cylinder (not shown). In the injector 22, a mixture containing a resin, a foaming agent, and additives used as needed is supplied from the hopper (supply unit) to the cylinder, where it is stirred with a screw or the like to prepare the resin material R, and the resin material R is injected and filled into the cavity 18 through the gate 21 at a predetermined pressure. Note that the configuration of the injector 22 is not limited to the above, as long as it can inject and fill the molten resin material R into the cavity 18 through the gate 21.

[0039] When the resin material R contains a thermoplastic resin, the resin material R is heated to be fluidized and then supplied into the cavity 18 .

[0040] Furthermore, the fixed-side mold 17 and the movable-side mold 19 are usually at a temperature lower than that of the molten resin material R. Therefore, when the resin material R is filled into the cavity 18, the resin material R starts to cool and solidify from the portions in contact with the fixed-side mold 17 and the movable-side mold 19, forming a skin layer.

[0041] Next, the movable mold 19 is opened (cored back) a predetermined distance in the opening direction (mold opening direction) relative to the fixed mold 17, and the unsolidified resin material R is foamed to form a foam layer. Thereafter, the fixed mold 17 and the movable mold 19 are opened, and the foam molded body is removed from the movable mold 19, thereby obtaining the foam molded body. [Example]

[0042] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0043] [Raw materials for resin materials] The resin materials used in producing the foamed molded article are as follows. (resin) PP-A (polypropylene, product name "MX01HX", MFR 41g / 10min at 230℃, SunAllomer Co., Ltd.) PP-B (polypropylene, product name "TSOP-GP6", MFR 41g / 10min at 230℃, Prime Polymer Co., Ltd.) (foaming agent) Azodicarbonamide (ADCA) (additives) Branched-chain polypropylene (product name "039N", MFR 60g / 10min at 230℃, Kaneka Corporation)

[0044] [Example 1] (Production of foam molded body) A resin material containing PP-A, a foaming agent, and additives was fed from a hopper to a cylinder, and the resin material was stirred in the cylinder at 100 rpm using a screw at 200° C. The foaming agent content of the total resin material was 1% by mass, and the additive content was 4% by mass. Next, the molten resin material was injected into a mold adjusted to 60°C at a resin pressure of 10 MPa and an injection speed of 90 mm / s. After injection, the resin material was cooled and solidified over a 10-second cooling period. The movable mold was then opened 2.5 mm in the opening direction (mold opening direction) relative to the fixed mold, and the unsolidified resin material was foamed to form a foam layer. The fixed mold and movable mold were then opened, and an 8 cm x 15 cm x 2.5 mm foam molded object was removed.

[0045] (Avatar rating) To evaluate the avatars, the surface of the foamed molded product was observed using a 3D shape measuring device (Keyence Corporation, VR-3200), and areas in the observed area that were 3 μm or more lower in height than the surrounding area were defined as avatars. The ratio of the avatar area to the total area of ​​the observed area (area ratio) was calculated and evaluated. The evaluation criteria are as follows: Grade A: The ratio of the avatar's area to the total area of ​​the observation area is 3% or less. Grade B: The ratio of the avatar's area to the total area of ​​the observation area is more than 3%. The results are shown in Table 1.

[0046] (Preparation of sample for measuring storage modulus) A measurement sample was prepared by cutting a piece of 15 mm x 15 mm from the foam molded article prepared as described above.

[0047] (Measurement of storage modulus) Using the above-mentioned measurement sample and a viscoelasticity measuring device (product name MCR302, Anton Paar), the storage modulus was measured at a measurement temperature of 200°C to 20°C, a temperature drop rate of 5°C / min, a frequency of 1Hz, a cone diameter of 12mm, a strain of 1% to 0.01%, and in a liquid nitrogen atmosphere. The results are shown in Table 1 and Figure 2. In Figure 2, 1.00E+03 to 1.00E+09 means 1.00 x 10 3 ~1.00×10 9 This means:

[0048] (Preparation of samples for measuring crystallization peak temperature and melt tension) A molding machine (PLASTER Si-130 II, Toyo Machinery & Metal Co., Ltd.) was used to manufacture the resin molded body. First, a resin material containing PP-A and additives, with 4% additives by mass, was fed from a hopper into a cylinder, and the resin material was stirred at 100 rpm using a screw inside the cylinder at 200°C. Next, the molten resin material was injected into a mold adjusted to 60°C at a resin pressure of 10 MPa and an injection speed of 90 mm / s. After injection, the resin material injected into the mold was solidified after a 10-second cooling period, yielding a 9 cm x 9 cm x 1 mm resin molded body. The obtained resin molded body was pulverized using a pulverizer (TH-1328, HORAI Co., Ltd.) to prepare samples for measuring the crystallization peak temperature and melt tension.

[0049] (Measurement of crystallization peak temperature) Using 5 mg of the above-mentioned measurement sample and a Discovery DSC Q1000 (TA Instruments), the sample was held at 40°C for 3 minutes, heated to 230°C at a rate of 50°C / min, held at 230°C for 3 minutes, and cooled to 60°C at a rate of 30°C / min to measure the crystallization peak temperature. The results are shown in Table 1.

[0050] (Melt tension measurement) Using the above-mentioned measurement sample and Capillograph 1D (Toyo Seiki Seisakusho, Ltd.), the melt tension was measured at a measurement temperature of 180° C., a piston extrusion shear rate of 60 mm / min, and a take-up rate of 200 m / min. The results are shown in Table 1.

[0051] [Example 2] The same evaluation as in Example 1 was carried out, except that the resin was changed to PP-B and the amount of additive was changed from 4% by mass to 8% by mass with respect to the total amount of the resin material. The results are shown in Table 1 and FIG.

[0052] [Comparative Example 1] The same evaluation as in Example 1 was carried out except that no additive was used. The results are shown in Table 1 and FIG. Comparative Example 2 The same evaluation as in Example 2 was carried out except that no additive was used. The results are shown in Table 1 and FIG.

[0053] [Table 1]

[0054] As shown in FIG. 2, Examples 1 and 2 had higher storage moduli than Comparative Examples 1 and 2 at temperatures in the range of 130°C to 140°C. As shown in Table 1, the foamed molded articles of Examples 1 and 2 had less pitting than the foamed molded articles of Comparative Examples 1 and 2. In particular, the foamed molded articles of Example 2 had more pitting than the foamed molded articles of Example 1.

[0055] When the cross sections of the foam molded articles of Examples 1 and 2 and Comparative Examples 1 and 2 were visually inspected, it was found that the thickness of the skin layer was almost the same in Examples 1 and 2 and Comparative Examples 1 and 2, regardless of the presence or absence of additives. This indicates that in Examples 1 and 2, the rigidity of the skin layer was improved without increasing the thickness of the skin layer, and as a result, the occurrence of pockmarks was suppressed. [Explanation of symbols]

[0056] 16 Molding equipment 17 Fixed side mold 18 cavities 19 Movable mold Gate 21 22 Injection machine

Claims

1. A resin material comprising a polypropylene resin (excluding branched polypropylene resins), an organic foaming agent, and a branched polypropylene resin, the resin being foamed, The storage modulus at 137°C is 1.00 MPa or more, The melt tension at 180°C is 5.0 mN or more, The polypropylene resin has an MFR of 41 g / 10 min or more at 230°C, The branched polypropylene resin has an MFR of 50 g / 10 min or more at 230°C, A foamed molded article, wherein the content of the organic foaming agent is 0.05% by mass to 1% by mass relative to the resin material.

2. 2. The foamed molded article according to claim 1, which has a crystallization peak temperature of 125°C or higher.

3. 3. The foam molded article according to claim 1, wherein the content of the branched polypropylene resin in the resin material is 2% by mass or more.

4. A foamed molded body described in any one of claims 1 to 3, wherein the organic foaming agent is azodicarbonamide.

5. A foam molded body as described in Claim 4, wherein the content of azodicarbonamide in the resin material is within the range of 0.05 mass% to 0.5 mass%.

6. A foam layer and a skin layer covering the foam layer, The foam molded article according to any one of claims 1 to 5, wherein the foam layer has a thickness of 0.01 mm to 5.9 mm.

7. A foam layer and a skin layer covering the foam layer, The foam molded article according to any one of claims 1 to 6, wherein the foam layer has a porosity of 2% or more.

8. A method for producing a foamed molded article according to any one of claims 1 to 7, A method for producing a foamed molded article, comprising the step of foaming the resin material.

Images