JP7487448B2 - Foam molded product and method for producing foam molded product - Google Patents

Description

Applicable under Article 30, Paragraph 2 of the Patent Act. Announced at the 56th Hitachi Chemical Research Presentation Session (2018) on June 1, 2018.

The present invention relates to a foam molded product and a method for producing a foam molded product.

2. Description of the Related Art Injection foam molded articles made of thermoplastic resins such as polypropylene resins and acrylonitrile-butadiene-styrene copolymer resins are used as automobile components because of their light weight and excellent rigidity.
One of the injection foam molding methods 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. When this molding method is used, the surface layer of the molded body becomes a skin layer with a lower foaming rate than the foam layer, and the inside of the molded body becomes a uniform, high-expansion foam layer (for example, see Patent Document 1).

JP 2014-121793 A

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

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

The present invention was made in consideration of the above-mentioned conventional circumstances, and aims to provide a foamed molded product in which the occurrence of pockmarks is suppressed, and a method for producing the same.

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

<7> A method for producing a foamed molded product according to any one of <1> to <6>, the method including a step of foaming the resin material.

The present invention provides a foamed molded product in which the occurrence of pockmarks is suppressed, and a method for producing the same.

FIG. 2 is a diagram for explaining an outline of a molding device equipped with a mold. 1 is a graph showing the results of measuring the storage modulus in Examples 1 and 2 and Comparative Example 1.

Hereinafter, the embodiment for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiment. In the following embodiment, the components (including element steps, etc.) are not essential unless specifically stated. The same applies to the numerical values and their ranges, and they do not limit the present invention.
In the present disclosure, the term "step" includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.
In the present disclosure, the numerical range indicated using "to" includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present disclosure, in which numerical ranges are 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 numerical range described in stages.
In the present disclosure, each component may contain multiple types of the corresponding substance. 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 an embodiment of the present disclosure is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the size of the members in each drawing is conceptual, and the relative relationship between the sizes of the members is not limited to this.
In the present disclosure, the thicknesses of the foam molded product, the foam layer, and the skin layer refer to the portions where the thickness is greatest when the cross section of the foam molded product is observed using a stereomicroscope, a SEM (scanning electron microscope), or a polarizing microscope.

<Foam Molded Article>
The foamed molded article of the present disclosure is formed by foaming a resin material containing a resin and a foaming agent, and has a storage modulus of 1.00 MPa or more at 137 ° C. In the foamed molded article of the present disclosure, the occurrence of pits is suppressed, and the reason is presumed to be as follows. Since the storage modulus at 137 ° C. measured as described below is 1.00 MPa or more, when the surface part in contact with the mold cools in the process of the molten resin material flowing into the mold, crystallization proceeds quickly and solidifies, forming a skin layer with high rigidity. In the process of the molten resin material flowing into the mold, the foaming agent is decomposed due to a sudden reduction in pressure at the end of the flow, generating bubbles, which are generated inside the resin material when the position of the movable side mold is slid, and the expanding bubbles are cooled, causing volumetric shrinkage, and the negative stress that tries to draw the resin material inside is suppressed, so that the rigidity of the skin layer is superior to the negative stress that tries to draw the resin material inside.

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 pockmarks. 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 a method described later in the Examples section 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.

The crystallization peak temperature in the foam molded product 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 pockmarks. In addition, the crystallization peak temperature in the foam molded product of the present disclosure may be 130° C. or lower, or may be 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 that is the raw material of the foamed molded body of the present disclosure, except that it does not contain a foaming 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 foamed molded body, using the method described in the Examples.

In the foamed 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 by having a melt tension at 180 ° C. of 5.0 mN or more, bubbles generated by reduced pressure inside the resin material when the resin material flows inside the mold are less likely to break, and when the position of the movable side mold is slid, the resin is stretched as the bubbles expand, suppressing bubble breakage. It is presumed that this reduces the opportunity for bubbles to move to the surface portion in contact with the mold, thereby more suitably suppressing the occurrence of pitting.

In the foam molded article of the present disclosure, from the viewpoint of the 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 that is the raw material of the foamed molded body of the present disclosure, except that it does not contain a foaming agent, as shown 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 foamed molded body, using the method shown in the Examples.

In the foamed molded article of the present disclosure, in order to more effectively suppress the occurrence of pockmarks, 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, in terms of the expansion ratio, the product of the crystallization peak temperature and the melt tension at 180°C may be 1,250 or less, or may be 1,000 or less.

(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.

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

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

The resin material may contain components other than the resin described above and the foaming agent described below. For example, the resin material may contain filler, glass fiber, carbon fiber, etc.

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.

Organic foaming agents include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4'-oxybisbenzenesulfonylhydrazide (OBSH), hydrazodicarbonamide (HDCA), etc., 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.

The content of azodicarbonamide (ADCA) in the total amount of foaming agents 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.

The decomposition temperature of the foaming agent is preferably 50°C to 250°C, and more preferably 100°C to 220°C. Depending on the form of use, the decomposition temperature of the foaming agent may be 130°C to 250°C.

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, from the viewpoint of foamability and moldability, the content of azodicarbonamide (ADCA) in the resin material is preferably within the range of 0.05% by mass to 0.5% by mass, and more preferably within the range of 0.1% by mass to 0.4% by mass. The content of ADCA refers to the proportion in the mixture (composition) before being put into the cylinder of the injection machine described later.

The resin material preferably contains a polypropylene resin having a branched chain in order to increase the crystallization peak temperature and melt tension of the foamed molded body, and more preferably contains a polypropylene resin having a branched chain in addition to the polypropylene-based resin as the resin.

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.

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.

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.

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. and a load of 2.16 kg (load of 21.18 N) in accordance with JIS K7210-1 (2014).

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.

The porosity of the foam layer is preferably 2% or more, more preferably 20% or more. The porosity of the foam layer is 10% or more, which is advantageous in terms of reducing the weight of the foamed molded body, but tends to make the surface of the skin layer more susceptible to pockmarks. However, in the foamed molded body 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 pockmarks even when the porosity of the foam 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 bubble / cross-sectional area of foamed molded body) × 100 (1)

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.

<Method of manufacturing foamed molded article>
The method for producing a foamed molded article according to the present disclosure is a method for producing the foamed molded article according to the present disclosure, and includes a step of foaming the resin material in a mold. The method for producing a foamed molded article according to the present disclosure can provide a foamed molded article in which the generation of pitting is suppressed.

In the manufacturing method of the foam molded body disclosed herein, for example, a foam molded body can be molded by a method that includes a process 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 the fixed side mold and the movable side mold, and a process of filling the cavity with the resin material and then moving the movable side mold in the opening direction from the fixed side mold that constitutes the mold to expand the volume of the cavity.

Figure 1 shows a schematic diagram of a molding device that can be used to manufacture foamed molded bodies. The molding device 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.

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 resin, a foaming agent, and additives used as necessary is supplied from the hopper (supply unit) to the cylinder, and is stirred in the cylinder with a screw or the like to prepare the resin material R. The resin material R is then injected and filled into the cavity 18 through the gate 21 at a predetermined pressure. Note that the injector 22 is not limited to the above configuration as long as it can inject and fill the cavity 18 with molten resin material R through the gate 21.

When the resin material R contains a thermoplastic resin, the resin material R is heated and fluidized before being supplied into the cavity 18.

Furthermore, the fixed side mold 17 and the movable side mold 19 are usually at a lower temperature than 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 parts in contact with the fixed side mold 17 and the movable side mold 19, forming a skin layer.

Next, the movable mold 19 is opened (cored back) a predetermined amount 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. After that, the fixed mold 17 and the movable mold 19 are opened, and the foam molded body is removed from the movable mold 19, obtaining the foam molded body.

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

[Raw 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°C, SunAllomer Co., Ltd.)
PP-B (polypropylene, product name "TSOP-GP6", MFR 41g/10min at 230°C, Prime Polymer Co., Ltd.)
(Foaming Agent)
Azodicarbonamide (ADCA)
(Additive)
Branched chain polypropylene (product name "039N", MFR 60g/10min at 230°C, Kaneka Corporation)

[Example 1]
(Preparation of foamed molded body)
A resin material containing PP-A, a foaming agent, and additives was supplied 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 under the condition of a cooling time of 10 seconds. Then, the movable mold was 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. After that, the fixed mold and the movable mold were opened, and a foam molded body of 8 cm x 15 cm x 2.5 mm was taken out.

(Avatar evaluation)
The evaluation of the avatars was carried out by observing the surface of the foamed molded article using a 3D shape measuring instrument (Keyence Corporation, VR-3200), and determining the area of the avatars that was 3 μm or more lower than the surrounding area in the observed area, and evaluating the ratio (area ratio) of the area of the avatars to the entire area of the observed area. The evaluation criteria are as follows:
Grade A: The ratio of the avatar area to the entire observation area is 3% or less.
Grade B: The ratio of the area of the avatar to the total area of the observation region is more than 3%.
The results are shown in Table 1.

(Preparation of Sample for Measuring Storage Modulus)
A measurement sample of 15 mm x 15 mm was prepared by cutting out the foamed molded article prepared as described above.

(Measurement of storage modulus)
The storage modulus was measured using the above-mentioned measurement sample and a viscoelasticity measuring device (product name: MCR302, manufactured by Anton Paar) under the following conditions: measurement temperature: 200° C. to 20° C., temperature drop rate: 5° C./min, frequency: 1 Hz, cone used: diameter 12 mm, strain: 1% to 0.01%, 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 1.00x10 ³ to 1.00x10 ⁹ .

(Preparation of samples for measuring crystallization peak temperature and melt tension)
A molding machine (PLASTER Si-130 II, Toyo Machinery & Metals Co., Ltd.) was used to manufacture the resin molded body.
First, a resin material containing PP-A and additives, with the additives being 4% by mass relative to the total amount, 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. 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 under a cooling time of 10 seconds, thereby obtaining a resin molded body of 9 cm x 9 cm x 1 mm.
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.

(Measurement of Crystallization Peak Temperature)
Using 5 mg of the above-mentioned measurement sample and 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.

(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.

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

[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.

As shown in FIG. 2, in the vicinity of 130° C. to 140° C., Examples 1 and 2 had higher storage modulus than Comparative Examples 1 and 2.
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 less pitting than the foamed molded articles of Example 1.

When the cross sections of the foamed molded bodies of Examples 1 and 2 and Comparative Examples 1 and 2 were visually inspected, 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 shows that in Examples 1 and 2, the stiffness of the skin layer was improved without increasing the thickness of the skin layer, and as a result, the occurrence of pockmarks was suppressed.

16 Molding device 17 Fixed mold 18 Cavity 19 Movable mold 21 Gate 22 Injection machine

Claims (4)

A resin material including a resin, an additive, and a foaming agent is foamed,
The storage modulus at 137°C is 1.50 MPa or more,
The resin is a polypropylene-based resin (excluding branched polypropylene resins),
the additive is a polypropylene resin having a branched chain, and the content of the polypropylene resin having a branched chain is 4 % by mass to 8 % by mass with respect to the resin material;
The content of the foaming agent is 0.05% by mass to 1% by mass with respect to the resin material,
A foamed molded article having a crystallization peak temperature of 125°C or higher and 130°C or lower. The foamed molded article according to claim 1, which has a melt tension of 5.0 mN or more at 180°C. The foamed molded article according to claim 1 or 2, wherein the branched polypropylene resin has an MFR of 35 g/10 min or more at 230°C. A method for producing a foamed molded article according to any one of claims 1 to 3, comprising the steps of:
A method for producing a foamed molded article, comprising the step of foaming the resin material.