JP2023034629A - Resin composition for foam molding, and foamed article - Google Patents

Abstract

To provide a resin composition for foam molding which enables molding of a foamed article that can be made lighter and is excellent in surface formation property.SOLUTION: A resin composition for foam molding contains polypropylene having a melt flow rate at 230°C of 45 g/10 min or more, and a foaming agent.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present disclosure relates to a resin composition for foam molding and a foam molded article.

2. Description of the Related Art In recent years, with the aim of reducing the weight of automobiles, the replacement of metal members with resin members for interior and exterior parts is progressing. Among them, a foam molded product containing cells obtained by foaming a resin is lighter than metal, and is expected to further improve the fuel efficiency of automobiles.

As a foam molded article used as an automobile part, for example, one obtained by the method described in Patent Document 1 is known. In this method, after injecting a molten resin composition into a molding cavity formed by a movable mold and a fixed mold, the movable mold is slightly opened (core-backed). A foam molded article is formed by performing a foaming process.

JP-A-2005-238726

In order to further reduce the weight of automobiles, it is desired to further reduce the weight of foam molded articles. That is, it is desired to reduce the mass per unit volume of the foam molded article.
In order to further reduce the weight of the foam-molded article, there is a method of increasing the expansion ratio of the resin when producing the foam-molded article. However, if the foaming ratio of the resin is increased, it may not be possible to ensure surface tension, which is one of the appearance characteristics required for the foam molded article.
The present disclosure has been made in view of the above-described conventional circumstances, and one aspect of the present disclosure provides a resin composition for foam molding that enables molding of a foam molded product that can be reduced in weight and has excellent surface tension. for the purpose. Another object of the present disclosure is to provide a foam molded article having excellent surface tension.

Specific means for achieving the above object are as follows.
<1> A resin composition for foam molding containing polypropylene having a melt flow rate of 45 g/10 minutes or more at 230°C and a foaming agent.
<2> A resin composition for foam molding, containing polypropylene and a foaming agent, wherein the melt flow rate at 230°C after foaming of the foaming agent is 45 g/10 minutes or more.
<3> The resin composition for foam molding according to <1> or <2>, which is used for producing a foam molded article having an expansion ratio of 2 or more.
<4> A foam molded article containing polypropylene and having a melt flow rate of 45 g/10 minutes or more at 230°C.
<5> The foam molded article according to <4>, which has an expansion ratio of 2 or more.

According to one aspect of the present disclosure, it is possible to provide a resin composition for foam molding that enables molding of a foam molded product that is lightweight and has excellent surface tension. In addition, according to another aspect of the present disclosure, it is possible to provide a foam molded article having excellent surface covering properties.

1 is a schematic cross-sectional view of an example of the configuration of a molding apparatus used for manufacturing a foam molded article; FIG. 1 is a schematic cross-sectional view of an example of the configuration of an injection device used for manufacturing a foam molded article; FIG.

Hereinafter, embodiments for implementing the resin composition for foam molding and the foam molded article of the present disclosure will be described in detail. However, the present disclosure 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 disclosure.

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 of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step. . Moreover, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
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.
In the present disclosure, the term "layer" includes not only the case where the layer is formed in the entire region when observing the region where the layer exists, but also the case where it is formed only in part of the region. included.
In the present disclosure, the melt flow rate at 230 ° C. is JIS K7210-1: 2014 (Plastics - Determination of melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics - Part 1: Standard test Method) refers to the value measured by

<Resin composition for foam molding>
A first resin composition for foam molding of the present disclosure contains polypropylene having a melt flow rate (hereinafter sometimes referred to as MFR) at 230° C. of 45 g/10 minutes or more and a foaming agent.
According to the first resin composition for foam molding of the present disclosure, it is possible to mold a foam molded article that can be lightened and has excellent surface tension. Although the reason is not clear, it is presumed as follows. In the present disclosure, "excellent surface tension" means that appearance defects such as dents and shrinkage are less likely to occur on the surface of the foamed molded product. Uneven foaming of the resin composition for foam molding is one of the causes of appearance defects such as depressions and shrinkage appearing on the surface of foam moldings.
Here, since the first resin composition for foam molding of the present disclosure contains polypropylene having an MFR of 45 g/10 minutes or more at 230 ° C., the resin composition for foam molding flows in the temperature range where the foam molded article is molded. improve sexuality. As the fluidity of the foam molding resin composition is improved, the foam molding resin composition can easily follow the movement of the movable mold when core-backing the movable mold. Since the resin composition for foam molding can easily follow the movement of the movable mold, the occurrence of uneven foaming of the resin composition for foam molding in the foam molded body can be easily suppressed. As a result, according to the first resin composition for foam molding of the present disclosure, it is presumed that molding of a molded article having excellent surface tension is possible.
It should be noted that uneven foaming of the resin composition for foam molding tends to occur more easily when the foaming ratio of the resin is increased. Since the first resin composition for foam molding of the present disclosure is excellent in fluidity, uneven foaming hardly occurs even when the foaming ratio is increased. Therefore, according to the first resin composition for foam molding of the present disclosure, it is possible to improve the expansion ratio without causing deterioration of the surface tension, and as a result, the weight of the foam molded product can be reduced. It is assumed that it will be easier.

The second resin composition for foam molding of the present disclosure contains polypropylene and a foaming agent, and has an MFR at 230° C. of 45 g/10 minutes or more after foaming the foaming agent. The MFR at 230°C after foaming of the foaming agent refers to the MFR at 230°C of the resin composition after foaming of the foaming agent, which is obtained by heating the second resin composition for foam molding.
According to the second resin composition for foam molding of the present disclosure, it is possible to mold a molded body that can be lightened and has excellent surface tension. Although the reason is not clear, it is presumed as follows.
The MFR at 230° C. of the resin composition for foam molding after foaming the foaming agent shows approximately the same value as the MFR at 230° C. of the polypropylene contained in the resin composition for foam molding. If the MFR at 230° C. of the resin composition for foam molding after foaming the foaming agent is 45 g/10 min or more, for the same reason as in the case of the first resin composition for foam molding of the present disclosure, It is presumed that it becomes possible to mold a molded article having excellent surface tension, and that it becomes easier to achieve weight reduction of the foamed molded article.
In the second resin composition for foam molding, the MFR at 230° C. after foaming the foaming agent is preferably 46 g/10 min or more, more preferably 47 g/10 min or more, and even more preferably 48 g/10 min or more. .
In the second resin composition for foam molding, the MFR at 230° C. after foaming the foaming agent is preferably 150 g/10 min or less, more preferably 120 g/10 min or less, from the viewpoint of ensuring the strength of the foam molded product. More preferably, 100 g/10 minutes or less is even more preferable.

In the following description, the first resin composition for foam molding of the present disclosure and the second resin composition for foam molding of the present disclosure may be collectively referred to as the resin composition of the present disclosure.
The first resin composition for foam molding of the present disclosure contains a polypropylene having a melt flow rate of 45 g/10 minutes or more at 230° C. and a foaming agent, and optionally contains a colorant and other components. good. In addition, the second resin composition for foam molding of the present disclosure contains polypropylene and a foaming agent, and may contain a colorant and other components as necessary.
Each component contained in the resin composition of the present disclosure will be described below. In the following description, a polypropylene having an MFR of 45 g/10 minutes or more at 230°C may be referred to as a specific polypropylene. Further, the specific polypropylene will be described together with other thermoplastic resins other than the specific polypropylene in the section (Thermoplastic resin).

(Thermoplastic resin)
The first resin composition for foam molding of the present disclosure contains specific polypropylene.
The MFR of the specific polypropylene is preferably 46 g/10 minutes or more, more preferably 47 g/10 minutes or more, and even more preferably 48 g/10 minutes or more. From the viewpoint of ensuring the strength of the foam molded article, the MFR of the specific polypropylene is preferably 150 g/10 minutes or less, more preferably 120 g/10 minutes or less, and even more preferably 100 g/10 minutes or less.

The first resin composition for foam molding of the present disclosure may contain thermoplastic resins other than the specific polypropylene.
Other thermoplastic resins include polyethylene-based resins, polystyrene-based resins, polyethylene terephthalate-based resins, polyvinyl alcohol-based resins, vinyl chloride-based resins, ionomer-based resins, polyamide-based resins, acrylonitrile-butadiene-styrene copolymer resins (ABS). and at least one selected from the group consisting of polycarbonate-based resins.

The second resin composition for foam molding of the present disclosure contains polypropylene. The MFR at 230° C. of the polypropylene contained in the second resin composition for foam molding may be 45 g/10 minutes or more, or may be less than 45 g/10 minutes.
The MFR at 230° C. of the polypropylene contained in the second resin composition for foam molding is preferably 46 g/10 minutes or more, more preferably 47 g/10 minutes or more, and even more preferably 48 g/10 minutes or more.
The MFR at 230° C. of the polypropylene contained in the second resin composition for foam molding is preferably 150 g/10 min or less, more preferably 120 g/10 min or less, from the viewpoint of ensuring the strength of the foam molded product. /10 minutes or less is more preferable.
The second resin composition for foam molding of the present disclosure may contain thermoplastic resins other than polypropylene. Specific examples of other thermoplastic resins are as described above.

(foaming agent)
The resin composition of the present disclosure contains a foaming agent.
The type of foaming agent contained in the resin composition of the present disclosure is not particularly limited, and both organic foaming agents and inorganic foaming agents can be used.
Specific examples of organic blowing agents include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4-oxybisbenzenesulfonylhydrazide (OBSH), hydrazodicarbonamide (HDCA), and the like. is mentioned. Specific examples of the inorganic foaming agent include sodium hydrogen carbonate.

Among the organic foaming agents, azodicarbonamide (ADCA) is preferably used when the foam molded article is an exterior member.
The use of azodicarbonamide (ADCA) tends to improve resistance to hot water and suppress the formation of blisters in hot water tests. Blistering refers to a state in which the skin layer is pushed up by the gas generated by the reaction between the unreacted foaming agent remaining in the skin layer on the surface of the foam molded product and water.

The decomposition temperature of the foaming agent is preferably 50°C to 200°C, more preferably 80°C to 200°C. The decomposition temperature of the blowing agent may be between 130°C and 200°C.

It is preferable to appropriately set the content of the foaming agent in the resin composition according to the type of the foaming agent. For example, when an organic foaming agent (preferably azodicarbonamide) is used as the foaming agent, the content of the organic foaming agent in the resin composition is 0.05% by mass to 1.0% by mass from the viewpoint of foamability. is preferably within the range of , and more preferably within the range of 0.1% by mass to 0.5% by mass.
The foaming agent may be added to the resin composition in the form of a masterbatch.
The content rate of the foaming agent is the content rate in the resin composition before being supplied to the molding apparatus.

(coloring agent)
The resin composition of the present disclosure may contain a colorant.
The type of colorant optionally contained in the resin composition of the present disclosure is not particularly limited, and considering the appearance, durability, etc. of a foamed molded product formed using the resin composition, a known colorant is appropriately selected from.
As the colorant, an inorganic pigment, an organic pigment, or the like can be used. Specific examples of inorganic pigments include carbon black, titanium oxide, iron oxide such as red iron oxide, and chromic acid such as yellow lead. Specific examples of organic pigments include azo pigments, phthalocyanine pigments, and threne pigments.

When the resin composition of the present disclosure contains a coloring agent, the content of the coloring agent in the resin composition is preferably set appropriately according to the type of the coloring agent. For example, when carbon black is used as the colorant, the content of the colorant in the resin composition is preferably in the range of 0.5% by mass to 10% by mass, from the viewpoint of colorability, and 1% by mass. More preferably, it is in the range of ~5% by mass.
The colorant may be added to the resin composition in the form of a masterbatch.
The content rate of the colorant is the content rate in the resin composition before being supplied to the molding apparatus.

(rubber component)
The resin composition of the present disclosure may contain a rubber component.
The type of rubber component that is optionally contained in the resin composition of the present disclosure is not particularly limited, and is appropriately selected from known rubber components in consideration of the strength of foam molded articles formed using the resin composition. be done.
Examples of rubber components include silicone rubber, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), butadiene rubber (BR), urethane rubber (UR), acrylic rubber (AR), and the like.

When the resin composition of the present disclosure contains a rubber component, it is preferable to appropriately set the content of the rubber component in the resin composition according to the type of the rubber component. The content of the rubber component in the resin composition is preferably within the range of 10% by mass to 40% by mass, more preferably within the range of 15% by mass to 35% by mass.
The content rate of the rubber component is the content rate in the resin composition before being supplied to the molding apparatus.

The second resin composition for foam molding preferably contains a rubber component so that the MFR at 230° C. after foaming the foaming agent is 45 g/10 minutes or more.

(other ingredients)
The resin composition of the present disclosure may contain a thermoplastic resin, a foaming agent, a colorant used as necessary, and components other than the rubber component.
Other components include glass fibers, carbon fibers, inorganic fillers such as talc, and additives such as release agents and antioxidants. When the resin composition contains other components, the total is preferably 40% by mass or less, more preferably 35% by mass or less, and further preferably 30% by mass or less of the entire resin composition. preferable. Moreover, when the resin composition contains other components, the total may be 15% by mass or more of the entire resin composition.

(Expansion ratio)
There is no particular limitation on the expansion ratio when producing a foamed molded article using the resin composition of the present disclosure. By using the resin molded product of the present disclosure, it is possible to obtain a foam molded product having excellent surface tension even when the foam molded product is produced at a high expansion ratio. In addition, by producing a foamed molded article with a high expansion ratio, it is possible to further reduce the weight of the foamed molded article. From the above, the resin composition of the present disclosure is preferably used for producing a foamed molded article having an expansion ratio of 2 times or more, and more preferably used for producing a foamed molded article having an expansion ratio of 2.1 times or more. . The resin composition of the present disclosure may be used for producing a foam molded article having an expansion ratio of 2.5 times or less.
In the present disclosure, the “expansion ratio” refers to the cavity spacing B after moving the movable side mold (after core back) when performing foam molding, before moving the movable side mold (before core back) ) to the cavity spacing A (spacing B/spacing A).

<Foam molding>
The foam molded article of the present disclosure contains polypropylene and has an MFR of 45 g/10 minutes or more at 230°C. The MFR at 230° C. of the foam molded product of the present disclosure is preferably 46 g/10 minutes or more, more preferably 47 g/10 minutes or more, and even more preferably 48 g/10 minutes or more. From the viewpoint of securing the strength of the foam molded article, the MFR of the foam molded article of the present disclosure at 230° C. is preferably 150 g/10 minutes or less, more preferably 120 g/10 minutes or less, and even more preferably 100 g/10 minutes or less.
The foam molded article of the present disclosure may be produced by foam molding the resin composition of the present disclosure. When the foam molded article of the present disclosure is produced by foam molding the resin composition of the present disclosure, the expansion ratio may be 2 times or more, or 2.1 times or more. When the foam molded article of the present disclosure is produced by foam molding the resin composition of the present disclosure, the expansion ratio may be 2.5 times or less.
Applications of the foam molded article of the present disclosure are not particularly limited. Since the foamed molded article of the present disclosure is lightweight and has excellent surface tension, it is suitably used for applications where both weight reduction and appearance are important, such as interior and exterior parts of automobiles. Specific examples of automotive interior and exterior members include sacco moldings, arch moldings, side moldings, rocker moldings, bumpers, back door trims, and the like.

<Method for producing foam molded product>
The method for producing the foam molded article of the present disclosure is not particularly limited as long as the resin composition of the present disclosure is used for foam molding.
The method for producing a foamed molded article of the present disclosure comprises the steps of: supplying the resin composition of the present disclosure to the inside of a molding device having a movable part; and increasing the volume.
In the step of increasing the internal volume of the molding apparatus, the expansion ratio may be 2 times or more, or 2.1 times or more. Also, the expansion ratio may be 2.5 times or less.

In the above method, the movable portion of the molding apparatus supplied with the resin composition is moved to increase the internal volume of the molding apparatus. At that time, cells are generated by the action of the foaming agent contained in the resin composition. As a result, it is possible to produce a foamed molded article including a foamed portion having a foamed layer containing cells and skin layers disposed on both sides of the foamed layer.

In the above method, the foam layer ratio and other conditions in the foamed molded article to be produced are, for example, the types and amounts of the thermoplastic resin and foaming agent contained in the resin composition, and the molding conditions (the resin composition and the temperature of the molding apparatus, molding time, etc.) can be adjusted.

In the above method, the temperature of the resin composition when supplied to the molding apparatus is not particularly limited. The temperature is preferably equal to or higher than the softening point of polypropylene contained in the resin composition.

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

FIG. 1 shows an example of a molding apparatus. The molding apparatus shown in FIG. and a gate 4 penetrating the fixed side mold 2 up to. Hereinafter, the movable mold 1 and the fixed mold 2 may be collectively referred to as "molds".

First, as shown in FIG. 1(A), the resin composition 3 is supplied into the cavity 6 from an injection device (not shown) through the gate 4 . The resin composition 3 is supplied into the cavity 6 in a state in which the thermoplastic resin is melted or softened and has fluidity.

The mold is normally at a temperature lower than that of the resin composition 3 to be supplied. Therefore, when the cavity 6 is filled with the resin composition 3 as shown in FIG. 1(B), solidification of the resin composition 3 starts from the part that comes into contact with the mold.

Then, as shown in FIG. 1(C), the movable side mold 1 is moved to widen the distance between the molds (core back), and the non-solidified portion of the resin composition 3 is foamed to form a foam layer 5. to form A skin layer 7 is formed from the solidified resin composition 3 between the foam layer 5 and the mold.

The material of the mold that constitutes the molding device is not particularly limited, and a general material can be used. Examples include stainless steel, pre-hardened steel, alloy tool steel, high speed tool steel and cemented carbide tool steel.

A method of supplying the resin composition to the molding apparatus shown in FIG. 1 is not particularly limited. For example, as shown in FIG. 2, an injection device that continuously prepares a resin composition and supplies it to a molding device may be used.

The injection device 10 shown in FIG. 2 includes a cylinder 11 and a hopper 12 into which the raw material of the resin composition is introduced. The outlet of the cylinder 11 is connected to the mold 13 of the molding device.

The cylinder 11 includes a screw 11A for stirring raw materials to prepare a resin composition and moving the resin composition to the mold 13 side of the molding apparatus, a motor 11B for driving the screw 11A, and the inside of the cylinder 11. and a heater (not shown) for heating. The raw material supplied inside the cylinder 11 becomes molten while moving toward the mold 13 . The molten resin composition is supplied to the mold 13 .

EXAMPLES The present disclosure will be specifically described below with reference to Examples, but the present disclosure is not limited to these Examples.

<Example 1>
Polypropylene #1 (MFR at 230 ° C. is 49 g / 10 minutes) 100 parts by mass, blowing agent (azodicarbonamide (ADCA) containing masterbatch) 0.5 parts by mass and black pigment masterbatch (pigment: carbon black, in masterbatch Pigment content of 35 mass% to 45 mass%) 3 parts by mass are put into the hopper of the injection device configured as shown in FIG. 2, polypropylene # 1 is melted and mixed in the heated cylinder, and the resin composition prepared the product. This resin composition was supplied into the cavity of a pair of molds, one of which is movable. After the resin composition was supplied to the cavity, the movable side mold (core) was moved to foam the resin composition and cooled to produce a foam molded product.
A foamed molded article having an expansion ratio of 2.1 times and a foamed molded article having an expansion ratio of 1.6 times were obtained. Weight reduction rates were 46% and 29%, respectively. The "weight reduction rate" refers to the ratio of weight reduction to a non-foamed molded product with a plate thickness of 2.8 mm. The value (%) obtained by subtracting the value of the cavity distance before backing, dividing the obtained value by the plate thickness (2.8 mm) of the unfoamed molded product, and multiplying by 100.
When the foaming ratio was 2.1 times, the interval between the cavities before the core-back was set to 1.5 mm, and the interval between the cavities after the core-back was set to 3.2 mm.
When the foaming ratio was 1.6 times, the interval between the cavities before the core-back was set to 2.0 mm, and the interval between the cavities after the core-back was set to 3.2 mm.
The appearance of the obtained foamed molding was visually observed. A foam-molded product was evaluated as A when no appearance defects such as dents or shrinkage occurred on the surface, and B was evaluated when appearance defects such as dents or shrinkage occurred on the surface of the foam-molded product. Table 1 shows the results obtained.
Also, the MFR at 230° C. was measured for a foamed molded article having an expansion ratio of 2.1. Table 1 shows the results obtained. The MFR at 230° C. of the foam molded product corresponds to the MFR at 230° C. of the resin composition containing polypropylene, the foaming agent, and the black pigment masterbatch and after foaming the foaming agent.

<Examples 2-3 and Comparative Examples 1-3>
Foam moldings having expansion ratios of 2.1 and 1.6 were produced in the same manner as in Example 1 except that polypropylene #1 was changed to polypropylene #2 to #5, and the appearance was evaluated. Table 1 shows the results obtained. The details of Polypropylene #2 to #5 are as follows.
Polypropylene #2: 87 g/10 min melt flow rate at 230°C Polypropylene #3: 70 g/10 min melt flow rate at 230°C Polypropylene #4: 29 g/10 min melt flow rate at 230°C Polypropylene #5: 230 Melt flow rate at ° C. is 38 g/10 minutes

From the evaluation results in Table 1, the resin compositions for foam molding of Examples containing polypropylene having an MFR of 45 g/10 min or more at 230° C. are superior in surface tension to the resin compositions for foam molding of Comparative Examples. It can be seen that it is superior to It is also found that by using the resin composition for foam molding of the example, the surface tension of the foam molded product is excellent even if the expansion ratio is increased.

DESCRIPTION OF SYMBOLS 1... Movable side mold, 2... Fixed side mold, 3... Resin composition, 4... Gate, 5... Foaming layer, 6... Cavity, 7... Skin layer, 10... Injection device, 11... Cylinder, 11A... Screw , 11B... motor, 12... hopper, 13... mold

Claims (5)

A resin composition for foam molding comprising polypropylene having a melt flow rate of 45 g/10 minutes or more at 230°C and a foaming agent. A resin composition for foam molding, comprising polypropylene and a foaming agent, wherein the melt flow rate at 230°C after foaming of the foaming agent is 45 g/10 minutes or more. 3. The resin composition for foam molding according to claim 1 or 2, which is used for producing a foam molded article having an expansion ratio of 2 or more. A foam molded article containing polypropylene and having a melt flow rate at 230°C of 45 g/10 minutes or more. 5. The foamed molding according to claim 4, wherein the foaming ratio is 2 or more.

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