JP7183728B2 - Foamed molded article and method for producing foamed molded article - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies June 1, 2018 Released at the 56th (2018) Hitachi Chemical Research Presentation Meeting

TECHNICAL FIELD The present invention relates to a foam molded article and a method for producing a foam molded article.

BACKGROUND ART Injection foam moldings of thermoplastic resins such as polypropylene resins and acrylonitrile/butadiene/styrene copolymer resins are used as automobile members from the viewpoint of being lightweight and having 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, a movable mold is slid, and then foam-molding is performed. By using this molding method, the surface layer of the molded article becomes a skin layer with a lower foaming rate than the foam layer, and the inside of the molded article becomes a uniform high-ratio foam layer (see, for example, Patent Document 1).

JP 2014-121793 A

When the injection foamed product is used as automotive interior parts such as console boxes, door trims, deck side trims, back door trims and instrument panels, and automotive exterior parts such as fenders, side sills, bumpers and back door outers, etc. The compact is required to be lightweight, thin, and have a good appearance.

However, small circular or elliptical depressions (hereinafter sometimes referred to as "avatars") are likely to occur on the surface of the injection foam molded product, which may pose a problem in terms of appearance. For this reason, it is desired to suppress the generation of avatars in foam molded articles.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a foam molded article in which the generation of avatars is suppressed, and a method for producing the same.

Specific means for achieving the above object are as follows.
<1> A foam-molded product obtained by foaming a resin material containing a resin and a foaming agent and having a crystallization peak temperature of 125° C. or higher.
<2> The foam molded article according to <1>, which has a melt tension of 5.0 mN or more at 180°C.
<3> The foam molded article according to <1> or <2>, wherein the product of the crystallization peak temperature and the melt tension at 180°C is 700 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 polypropylene resin having a branched chain in the resin material is 4% by mass or more.
<6> The foam molded article according to <4> or <5>, wherein the branched polypropylene resin has an MFR at 230° C. of 35 g/10 minutes or more.

<7> A method for producing a foam-molded article according to any one of <1> to <6>, comprising a step of foaming the resin material.

ADVANTAGE OF THE INVENTION According to this invention, the foaming molded object which generation|occurrence|production of the avatar was suppressed, and its manufacturing method can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure for demonstrating the outline of a molding apparatus provided with a metal mold|die.

DETAILED DESCRIPTION OF THE INVENTION Embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present invention.
In the present disclosure, the term "process" includes a process that is independent of other processes, and even if the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .
In the present disclosure, the numerical range indicated using "-" includes the numerical values before and after "-" as the minimum and maximum values, respectively.
In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of another numerical range described step by step. .
In the present disclosure, each component may contain multiple types of applicable substances. When there are multiple types of substances corresponding to each component in the composition, the content rate or content of each component is the total content rate or content of the multiple types of substances present in the composition unless otherwise specified. means quantity.
When embodiments are described in the present disclosure with reference to drawings, the configurations of the embodiments are not limited to the configurations shown in the drawings. Also, the sizes of the members in each drawing are conceptual, and the relative size relationship between the members is not limited to this.
In the present disclosure, the thicknesses of the foamed molded article, the foamed layer and the skin layer are determined by observing the cross section of the foamed molded article using a stereomicroscope, SEM (scanning electron microscope) or a polarizing microscope. refers to the part that becomes

<Foam molding>
The foam molded article of the present disclosure is formed by foaming a resin material containing a resin and a foaming agent, and has a crystallization peak temperature of 125° C. or higher. In the foamed molded article of the present disclosure, the generation of avatars is suppressed, and the reason for this is presumed as follows. Since the crystallization peak temperature measured as described below is a high temperature of 125° C. or higher, the surface portion in contact with the mold is deformed during the process in which the molten resin material flows into the mold. As it cools, crystallization progresses quickly and solidifies, forming a highly rigid skin layer. Bubbles of the foaming agent are generated by decompression when the resin material flows in the mold. When the position of the movable side mold is slid, the negative stress that occurs inside the resin material and expands and shrinks when the air bubbles are cooled and tries to pull the resin material into the skin layer. It is considered that the occurrence of avatars can be suppressed because the rigidity of the

The crystallization peak temperature in the foamed molded article of the present disclosure is preferably 125.5° C. or higher, more preferably 126° C. or higher, from the viewpoint of more suitably suppressing the generation of avatars. In addition, the crystallization peak temperature of the foamed molded article of the present disclosure may be 130° C. or lower or 129° C. or lower in terms of expansion ratio.
The crystallization peak temperature is a value measured by the method described in Examples below. For example, the crystallization peak temperature is a value measured using the same resin material as the raw material of the foam molded article of the present disclosure, except that it does not contain a foaming agent as shown in the examples below. good too. Also, the crystallization peak temperature may be a value measured by the method shown in Examples using a molten resin material obtained by melting a foam molded article.

The foam molded article of the present disclosure preferably has a melt tension at 180° C. of 5.0 mN or more, more preferably 5.5 mN or more, and even more preferably 6.0 mN or more. When the melt tension at 180 ° C. is 5.0 mN or more, the air bubbles generated by the pressure reduction inside the resin material are less likely to break when the resin material flows in the mold, and the movable side mold. It is thought that when the position is slid, the bubbles are expanded and the resin is stretched, thereby suppressing the breakage of the bubbles. It is presumed that this reduces the chances of air bubbles moving to the surface portion that is in contact with the mold, thereby more preferably suppressing the generation of avatars.

In the foam molded article of the present disclosure, the melt tension at 180° C. may be 10 mN or less, or may be 8.0 mN or less, in terms of expansion ratio.
The melt tension at 180°C is a value measured by the method described in Examples below. For example, the melt tension at 180 ° C. is a value measured using the same resin material as the raw material of the foam molded article of the present disclosure, except that it does not contain a foaming agent as shown in the examples below. There may be. Also, the melt tension at 180° C. may be a value measured by the method shown in Examples using a molten resin material obtained by melting a foam molded article.

In the foam molded article of the present disclosure, the product of the crystallization peak temperature and the melt tension at 180° C. is preferably 625 or more, more preferably 700 or more, from the viewpoint of more suitably suppressing the generation of puffs. More preferably, it is 750 or more.
In the foam molded product 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.

(Foam layer and skin layer)
The foam molded article of the present disclosure is obtained by foaming a resin material containing a resin and a foaming agent. For example, the foam molded article of the present disclosure includes 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 obtained by cooling and solidifying the resin material. There may be.

The foam layer may be a layer formed by foam-molding a resin material filled in a mold, and the skin layer is formed by cooling and solidifying a resin material, and is more foamed than the foam layer. It may be a layer with a low modulus.

Examples of resins used as resin materials include polyethylene-based resins, polypropylene-based resins (PP), composite polypropylene-based resins (PPC), polystyrene-based resins, polyethylene terephthalate-based resins, polyvinyl alcohol-based resins, vinyl chloride-based resins, ionomer-based resins, At least one selected from the group consisting of polyamide-based resins, acrylonitrile-butadiene-styrene copolymer resins (ABS), polycarbonate-based 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 preferable.

The resin material may contain components other than the resin described above and the foaming agent described later. For example, the resin material may include filler fillers, glass fibers, carbon fibers, and the like.

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, sodium bicarbonate). In the foam molding of automobile exterior parts, it is preferable to use an organic foaming agent as the foaming agent because of its excellent environmental test performance.

Organic blowing agents include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4'-oxybisbenzenesulfonylhydrazide (OBSH), hydrazodicarbonamide (HDCA) and the like. and azodicarbonamide (ADCA) is preferred. In particular, when manufacturing an exterior product, it is preferable to use azodicarbonamide (ADCA) whose decomposition product contains almost no water.

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, further preferably 90% by mass or more, and 95% by mass or more. % by mass or more is particularly preferred.

The decomposition temperature of the foaming agent is preferably 50°C to 250°C, more preferably 100°C to 220°C. The decomposition temperature of the blowing agent may range from 130°C to 250°C, depending on the mode of use.

It is preferable to appropriately set the content of the foaming agent in the resin material according to the type of the foaming agent. For example, when azodicarbonamide (ADCA) is used as a foaming agent, from the viewpoint of foamability and moldability, the content of azodicarbonamide (ADCA) in the resin material is 0.05% by mass to 0.5% by mass. is preferably within the range of , and more preferably within the range of 0.1% by mass to 0.4% by mass. The content of ADCA means the ratio in the mixture (composition) before injection into the cylinder of the injection machine, which will be described later.

The resin material preferably contains a polypropylene resin having a branched chain from the viewpoint of increasing the crystallization peak temperature, melt tension, etc. of the foam molded product. is more preferred.

When the resin material contains a polypropylene resin having a branched chain, the content of the polypropylene resin having a branched chain is preferably 4% by mass or more, more preferably 6% by mass or more, relative to the total amount of the resin material. It is preferably 8% by mass or more, and more preferably 8% by mass or more.

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 50 g/10 min or more. is more preferred.

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

The thickness of the foam layer is not particularly limited, and is preferably 0.01 mm to 5.9 mm, more preferably 1.0 mm to 5.0 mm, and 1.7 mm to 2.9 mm. More preferred.

The porosity of the foam layer is preferably 2% or more, more preferably 20% or more. When the porosity of the foam layer is 10% or more, it is advantageous from the point of view of weight reduction of the foam molded article, but tends to tend to cause burrs 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 higher, it is possible to achieve both weight reduction and suppression of puffiness even when the porosity of the foamed layer is increased. it is conceivable that.
In addition, the porosity means the ratio of the total area of each cell existing in a cross section to the cross-sectional area of a certain cross section of the foam molded article, as shown in the following formula (1).
Porosity = (total area of each cell/cross-sectional area of foamed molded body) x 100 (1)

The thickness of the skin layer is not particularly limited, and is preferably 0.05 mm to 2.995 mm, more preferably 0.1 mm to 1.0 mm, and 0.3 mm to 0.5 mm. More preferred.

<Method for producing foam molded product>
A method for producing a foam molded article of the present disclosure is a method for producing the aforementioned foam molded article of the present disclosure, and includes a step of foaming the resin material in a mold. According to the method for producing a foamed molded article of the present disclosure, it is possible to obtain a foamed molded article in which the generation of avatars is suppressed.

In the method for manufacturing a foamed molded product of the present disclosure, for example, a fixed mold and a movable mold that is movable in the opening and closing direction with respect to the fixed mold and forms a cavity that is a gap between the fixed mold and the fixed mold A step of injecting a resin material containing a resin and a foaming agent into a cavity in a set of molds composed of a side mold and a fixed side mold that constitutes the mold after filling the cavity with the resin material and expanding the volume of the cavity by moving the movable side mold from the mold in the opening direction.

FIG. 1 shows a schematic configuration diagram of a molding apparatus that can be applied to manufacture foam molded articles. The molding device 16 shown in FIG. 1 is movable in an opening/closing direction with respect to a stationary mold 17 and the stationary mold 17, and forms a cavity 18 between the stationary mold 17 and the stationary mold 17. A movable mold 19 is provided.

The molding device 16 also includes a gate 21 that passes through the stationary mold 17 to the cavity 18 , and an injector 22 that injects and fills the cavity 18 with the molten resin material R through the gate 21 . The injection machine 22 includes a hopper (supply unit) (not shown) and a cylinder (not shown). In the injection machine 22, a mixture containing a resin, a foaming agent, and optional additives is supplied from a hopper (supply unit) to a cylinder, and stirred by a screw or the like in the cylinder to form a resin material R. The cavities 18 are injected and filled with the resin material R through the gates 21 at a predetermined pressure. The injection machine 22 is not limited to the above configuration as long as it can inject and fill the molten resin material R into the cavity 18 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 .

Also, the fixed side mold 17 and the movable side mold 19 are normally at a temperature lower than that of the resin material R in the molten state. Therefore, when the cavity 18 is filled with the resin material R, the resin material R begins to cool and solidify from the portion 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 (core-backed) by a predetermined amount in the opening direction (mold opening direction) with respect to the fixed mold 17, and the unsolidified resin material R is foamed to form a foam layer. Thereafter, the stationary mold 17 and the movable mold 19 are opened, and the foam molded product is removed from the movable mold 19 to obtain a foam molded product.

EXAMPLES The present invention will be specifically described below by way of examples, but the present invention is not limited to these examples.

[Raw materials for resin materials]
The resin materials used in the production of the foamed moldings 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 41 g / 10 min at 230 ° C., Prime Polymer Co., Ltd.)
PP-C (polypropylene, product name "BXF04G", MFR 37 g / 10 min at 230 ° C., Japan Polypropylene Corporation)
(foaming agent)
Azodicarbonamide (ADCA)
(Additive)
Branched chain polypropylene (product name "039N", MFR 60 g / 10 min at 230 ° C., Kaneka Corporation)

[Example 1]
(Preparation of foam molded article)
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 200° C. at 100 rpm using a screw. The content of the foaming agent in the total amount of the resin material was 1% by mass, and the content of the additive was 4% by mass.
Next, a 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 the injection, the resin material was cooled and solidified under the conditions of a cooling time of 10 seconds. Then, the movable side mold was opened 2.5 mm in the opening direction (mold opening direction) with respect to the fixed side mold, and the unsolidified resin material was foamed to form a foam layer. After that, the stationary side mold and the movable side mold were opened to take out a foamed molding of 8 cm×15 cm×2.5 mm.

(Evaluation of avatar)
For the evaluation of the avatar, the surface of the foamed molded product was observed using a 3D shape measuring machine (VR-3200, Keyence Corporation), and the area in the observation area whose height was 3 μm or more lower than the surrounding area was regarded as the avatar and observed. The ratio (area ratio) of the area of the avatar to the entire area of the region was calculated and evaluated. The evaluation criteria are as follows.
Evaluation A: The ratio of the area of the avatar to the entire area of the observation area is 3% or less.
Evaluation B: The ratio of the area of the avatar to the entire area of the observation area exceeds 3%.
Table 1 shows the results.

(Preparation of sample for measurement of melt tension and crystallization peak temperature)
A molding machine (PLASTER Si-130 II, Toyo Machinery & Metal Co., Ltd.) was used for the production of resin moldings.
First, a resin material containing PP-A and additives and containing 4% by mass of additives with respect to the total amount is supplied from a hopper to a cylinder, and 100% of the resin material is supplied to the cylinder at 200 ° C. using a screw. Stirred at rev/min. Next, a 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 the injection, the resin material injected into the mold was solidified under the conditions of a cooling time of 10 seconds to obtain a resin molding of 9 cm×9 cm×1 mm.
The resulting resin molding was pulverized using a pulverizer (TH-1328, Horai Co., Ltd.) to prepare a sample for measuring melt tension and crystallization peak temperature.

(Measurement of melt tension)
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 using the aforementioned measurement sample and Capillarograph 1D (Toyo Seiki Seisakusho Co., Ltd.).
Table 1 shows the results.

(Measurement of crystallization peak temperature)
Using 5 mg of the above measurement sample and Discovery DSC Q1000 (TA Instruments), held at 40 ° C. for 3 minutes, heated to 230 ° C. at 50 ° C./min, held at 230 ° C. for 3 minutes, The crystallization peak temperature was measured by cooling to 60°C under the condition of 30°C/min.
Table 1 shows the results.

[Examples 2 to 5]
Evaluation was performed in the same manner as in Example 1, except that the type of polypropylene and the amount of additive were changed as shown in Table 1.
Table 1 shows the results.

[Comparative Examples 1 and 2]
Evaluation was performed in the same manner as in Example 1, except that the type of polypropylene was as shown in Table 1 and no additive was used.
Table 1 shows the results.

As shown in Table 1, in the foam molded articles of Examples 1 to 5, the generation of puffiness was suppressed as compared with the foam molded articles of Comparative Examples 1 and 2.

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

Claims (6)

A resin material containing a resin and a foaming agent is foamed,
The crystallization peak temperature is 125° C. or higher,
The resin material includes a polypropylene resin having a branched chain,
MFR at 230 ° C. of the polypropylene resin having a branched chain is 35 g / 10 minutes or more,
The crystallization peak temperature was measured by using the resin material and a differential scanning calorimeter (DSC), holding at 40° C. for 3 minutes, raising the temperature to 230° C. at 50° C./min, and holding at 230° C. for 3 minutes. , a value obtained by cooling to 60°C at a rate of 30°C/min . The foam molded article according to claim 1, which has a melt tension of 5.0 mN or more at 180°C. 3. The foam molded article according to claim 1 or 2, wherein the product of the crystallization peak temperature and the melt tension at 180°C is 700 or more. The foam molded article according to any one of claims 1 to 3 , wherein the content of the branched polypropylene resin in the resin material is 4% by mass or more. The foam molded article according to any one of claims 1 to 4, wherein the content of the polypropylene resin having a branched chain in the resin material is 20% by mass or less. A method for producing a foam molded article for producing the foam molded article according to any one of claims 1 to 5 ,
A method for producing a foam molded article, comprising the step of foaming the resin material.

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