JP7789609B2 - Foamed molded article of non-crosslinked olefinic elastomer and method for producing same - Google Patents

Description

The present invention relates to a foam-molded article of a non-crosslinked olefin-based elastomer and a method for producing the same. The foam-molded article of the present invention has excellent flexibility and recovery properties and can be used as seat core materials for railway vehicles, airplanes, and automobiles, as well as beds, cushions, etc.

Elastomers have excellent resilience and mechanical strength, making them classified as engineering elastomers, and their use in a variety of applications, including household goods, electrical appliance parts, sporting goods, automobile parts, and building and civil engineering materials, is being considered. Molded products made from foamed elastomers are expected to be lightweight and have the high resilience inherent to elastomers, so they are molded, for example, by heating foamed beads made from elastomer resins in a mold, causing them to fuse and expand.

Olefin-based elastomers include crosslinked products that have been crosslinked with a crosslinking agent. However, foam molded products made from crosslinked olefin-based elastomers are difficult to recycle, and their high density reduces the lightweight properties of the foam molded products. For this reason, in response to the growing need for recycling in recent years, there has been a demand for alternatives to crosslinked olefin-based elastomer foam molded products, and non-crosslinked olefin-based elastomer foam molded products are being considered (Patent Document 1).

International Publication No. 2016/052112

An object of the present invention is to provide a foam-molded article of a non-crosslinked olefinic elastomer which has a high fusion rate, few voids and a good appearance, and a method for producing the same.
An object of the present invention is to provide a foam-molded article of a non-crosslinked olefinic elastomer which has a high fusion rate, a good appearance with few voids, and a high rebound resilience and high durability against bending, which are characteristic of elastomers.

The present inventors have found that when producing foamed molded articles from non-crosslinked olefinic elastomers, using a non-crosslinked olefinic elastomer with a relatively low melting point as a base resin from the viewpoint of reducing the energy required for foam molding (typically, reducing the temperature of the steam used in foam molding) has drawbacks such as the difficulty in obtaining a low-density foam and the tendency for the foam particles to adhere to each other, resulting in reduced foam moldability.
Furthermore, the present inventors have found that the foam molded article of Patent Document 1 has room for improvement in terms of durability against bending.
The present inventors have also found that when a non-crosslinked olefin-based elastomer with a relatively high melting point is used as the base resin, high-temperature steam is required for foam molding, and foam molded articles obtained under high-temperature conditions tend to shrink easily, causing wrinkles or voids (gaps) to form on the surface of the foam, which tends to have an adverse effect on the appearance.

Based on these findings, the present inventors have investigated solutions and discovered a foam molded article that contains a non-crosslinked propylene-α-olefin copolymer as a non-crosslinked olefin elastomer as a main component and further contains a polyethylene-based resin, and that has two or more specific melting peak temperatures. Specifically, when a non-crosslinked propylene-α-olefin copolymer with a low melting peak temperature (e.g., below 140°C) is used as the base resin, foamability is poor, making it difficult to obtain foamed beads with low bulk density. On the other hand, when a non-crosslinked propylene-α-olefin copolymer with a high melting peak temperature (e.g., 140°C or higher) is used as the base resin, foamed beads tend to coalesce, resulting in uneven foaming and poor moldability. Furthermore, the high temperatures required for foam molding make it prone to thermal shrinkage, resulting in wrinkles or voids (gaps) on the foam surface. Here, the present inventors have discovered that by combining a non-crosslinked propylene-α-olefin copolymer with a polyethylene-based resin and setting the melting peak temperature of the resin within a specific range, these shortcomings can be improved, resulting in a foam molded article with a high rebound resilience and good flexibility.
Furthermore, the present inventors have found that the foamed molded article of the present invention can be produced by using a base resin (a non-crosslinked propylene-α-olefin copolymer and a polyethylene-based resin) mixed with a chemical foaming agent.

The present invention typically includes the following aspects.
Item 1.
A foamed molded article of a non-crosslinked olefin-based elastomer composed of a fused body of foamed beads,
Contains a non-crosslinked propylene-α-olefin copolymer as a main component,
Further containing a polyethylene resin,
the total content of the non-crosslinked propylene-α-olefin copolymer and the polyethylene resin is 80% by mass or more relative to the mass of the foamed molded article,
The foamed molded product has two or more melting peak temperatures (Tm) measured by a differential scanning calorimeter (DSC),
One of the melting peak temperatures (Tm1) is in the range of 90 to 130°C,
Another one of the melting peak temperatures (Tm2) is in the range of 130 to 180°C,
the temperature difference between the melting peak temperature (Tm2) and the melting peak temperature (Tm1) is 20°C or more;
Foam molding.
Item 2.
the mass ratio of the content of the non-crosslinked propylene-α-olefin copolymer to the content of the polyethylene resin is 55:45 to 90:10;
Item 1. A foam-molded article of the non-crosslinked olefin-based elastomer according to item 1.
Item 3.
Item 3. The foam-molded product of a non-crosslinked olefin-based elastomer according to Item 1 or 2, wherein the temperature difference between the melting peak temperature (Tm2) and the melting peak temperature (Tm1) is 20 to 80°C.
Item 4.
Item 4. The non-crosslinked olefin elastomer foam molded article according to any one of Items 1 to 3, wherein the polyethylene resin is one or more resins selected from the group consisting of high-density polyethylene and low-density polyethylene.
Item 5.
Item 5. A foam-molded product of a non-crosslinked olefin-based elastomer according to any one of Items 1 to 4, wherein the proportion of xylene-insoluble matter measured by hot xylene extraction is 3% or less.
Item 6.
Item ^6. A foam-molded article of a non-crosslinked olefin-based elastomer according to any one of Items 1 to 5, having at least one property selected from the group consisting of a density of 0.05 to 0.3 g/cm3, a rebound resilience of 35% or more, and an Asker C hardness of 60 or less.
Section 7.
Item 7. A foam-molded article of a non-crosslinked olefin-based elastomer according to any one of Items 1 to 6, which has flexural durability such that no cracks with a depth of 50% or more and a length of 10 mm or more occur between the foamed particles in a 90° flex test of 10,000 times (test piece size: 150 mm x 24 mm x 11 mm thick) in accordance with ASTM D1052.
Section 8.
Item 8. A method for producing a foamed molded article of a non-crosslinked olefin-based elastomer according to any one of Items 1 to 7, comprising: a step of mixing a non-crosslinked propylene-α-olefin copolymer, a polyethylene-based resin, and a chemical foaming agent to obtain resin particles containing the non-crosslinked propylene-α-olefin copolymer as a main component; a step of impregnating the resin particles with a physical foaming agent and then pre-foaming the resin particles to obtain foamed particles; and a step of foaming the foamed particles in a mold to obtain a foamed molded article.
Item 9.
Item 9. The method for producing a foamed molded article of a non-crosslinked olefin-based elastomer according to Item 8, wherein the chemical foaming agent is a sodium bicarbonate-citric acid-based chemical foaming agent, and the amount of the chemical foaming agent mixed in the step of obtaining resin particles is 0.1 to 2 parts by mass per 100 parts by mass of the total amount of the non-crosslinked propylene-α-olefin copolymer and the polyethylene-based resin.
Item 10.
Item 10. The method for producing a foamed molded article of a non-crosslinked olefin elastomer according to Item 8 or 9, wherein the mass ratio of the non-crosslinked propylene-α-olefin copolymer to the polyethylene resin in the step of obtaining resin particles is 55:45 to 90:10.

According to one embodiment of the present invention, it is possible to provide a foamed molded article of a non-crosslinked olefinic elastomer having few voids and a good appearance, and a method for producing the same.
According to one embodiment of the present invention, it is possible to provide a foamed molded article of a non-crosslinked olefin-based elastomer in which the foamed particles have strong fusion with each other during foam molding, and a method for producing the same.
According to one embodiment of the present invention, it is possible to provide a foam-molded article of a non-crosslinked olefin-based elastomer that can be foam-molded at a low temperature, and a method for producing the same.
According to one embodiment of the present invention, it is possible to provide a foam molded article of a non-crosslinked olefin-based elastomer having a high impact resilience and a method for producing the same.
According to one embodiment of the present invention, it is possible to provide a foam molded article of a non-crosslinked olefin-based elastomer having good flexibility, and a method for producing the same.

As used herein, the phrase "comprising" is intended to encompass the phrases "consisting essentially of" and "consisting of."
In this specification, the term "major component" is used to mean that the component is contained in an amount of more than 50% in the target substance, and unless otherwise specified, is used to mean that the component is contained in an amount of more than 50% by mass relative to the mass of the target substance. In this specification, when the specifying method is described in the examples, the numerical values of the physical properties, contents, etc. of materials, intermediate products, final products, etc. are the numerical values determined by the specifying method described in the examples.

In-mold foam molded articles are typically produced using the following steps. These steps can be applied to the present invention as is, or with appropriate modifications. The base resin is cut to an appropriate size to form base resin particles, which are then impregnated with a blowing agent to form expandable particles. The expandable particles are then pre-expanded to prepare expanded particles. These expanded particles are then subjected to the in-mold foam molding process and heated, whereby the expanded particles are expanded and fused to form a fused body, thereby producing the foam molded article. The present invention uses a base resin containing at least a non-crosslinked propylene-α-olefin copolymer and a polyethylene-based resin.

In this specification, "non-crosslinked" means that when a sample is dissolved in an organic solvent, such as xylene, that can dissolve elastomers, the insoluble gel fraction is 3.0% by mass or less. The gel fraction is measured as follows:

The mass W1 of a sample (e.g., base resin, resin particles, expandable particles, expanded particles, foamed molded article, etc.) is measured. Next, the sample is refluxed in 80 milliliters of boiling xylene for 3 hours. Next, the residue in the xylene is filtered using an 80-mesh wire netting, and the residue remaining on the wire netting is dried at 130°C for 1 hour. The mass W2 of the residue remaining on the wire netting is measured, and the gel fraction of the sample can be calculated using the following formula:
Gel fraction (mass%) = 100 × W2 / W1

In the present invention, the base resin, resin particles, expandable particles, expanded particles, and foamed molded articles contain a non-crosslinked propylene-α-olefin copolymer as a main component and further contain a polyethylene-based resin.

(Non-crosslinked olefinic elastomer)
As the non-crosslinked olefin elastomer, at least a non-crosslinked propylene-α-olefin copolymer is used. The non-crosslinked propylene-α-olefin copolymer may be used alone or in combination of two or more. It is preferable to combine two, three, or four (preferably two or three, more preferably two) non-crosslinked propylene-α-olefin copolymers having different melting peak temperatures.
The non-crosslinked propylene-α-olefin copolymer may or may not be used in combination with another non-crosslinked olefin-based elastomer. When the other non-crosslinked olefin-based elastomer is used in combination, the amount of the elastomer used may be 0.01 to 20 parts by mass, 0.01 to 10 parts by mass, or 0.01 to 5 parts by mass per 100 parts by mass of the non-crosslinked propylene-α-olefin copolymer.
Non-crosslinked olefinic elastomers include, for example, those having a structure combining hard and soft segments, which exhibits rubber elasticity at room temperature and plasticizes and becomes moldable at elevated temperatures.
The former polypropylene-based resin may be a resin containing polypropylene as a main component, and may have a stereoregularity selected from isotactic, syndiotactic, atactic, etc.
The latter polyethylene resin may be a resin containing polyethylene as the main component, and examples of components other than polyethylene include polyolefins such as polypropylene and polybutylene, and vinyl acetate.

The non-crosslinked propylene-α-olefin copolymer may have a melting peak temperature of, for example, 130 to 180°C, 130 to 170°C, 130 to 165°C, greater than 130°C but not greater than 180°C, greater than 130°C but not greater than 170°C, greater than 130°C but not greater than 165°C, 131 to 180°C, 131 to 170°C, 131 to 165°C, or 140 to 180°C. A melting peak temperature of 140 to 170°C is preferred, and a melting peak temperature of 140 to 165°C is more preferred. When the melting peak temperature of the non-crosslinked propylene-α-olefin copolymer is within this range, low-density expanded beads are easily obtained.

Preferably, the non-crosslinked propylene-α-olefin copolymer has a structure that combines a polypropylene resin as the hard segment and an ethylene-vinyl acetate copolymer as the soft segment. Commercially available non-crosslinked propylene-α-olefin copolymers can be used, such as the TAFMER series manufactured by Mitsui Chemicals, Inc., the ESPOLEX series manufactured by Sumitomo Chemical Co., Ltd., and the TPO series manufactured by Prime Polymer Co., Ltd., which have a melting peak temperature of 130 to 180°C.

Non-crosslinked olefin-based elastomers also have the effect of improving the recyclability of the foamed molded articles produced. Furthermore, they can be easily manufactured using the same foaming machines used to foam mold ordinary polyolefin-based resins. Therefore, even when the foamed molded articles are recycled and fed back into the foaming machine for foam molding, poor foaming due to the generation of rubber components can be suppressed.

The content of non-crosslinked olefin-based elastomer in resin particles, expandable particles, expanded particles, and foamed molded articles can be, for example, greater than 50% by mass to 90% by mass, 60 to 90% by mass, 70 to 90% by mass, 60 to 80% by mass, etc.

(Polyethylene resin)
The polyethylene resin may have a peak melting temperature of, for example, 90 to 130°C, 95 to 130°C, 100 to 130°C, 90°C or more but less than 130°C, 95°C or more but less than 130°C, 100°C or more but less than 130°C, 90 to 129°C, 95 to 129°C, or 100 to 129°C, and preferably has a peak melting temperature of 100 to 120°C, and more preferably has a peak melting temperature of 105 to 115°C. When the peak melting temperature of the polyethylene resin is within this range and the temperature difference between Tm2 and Tm1 is within the range described below, coalescence of the foamed particles is unlikely to occur, thereby improving moldability and fusion properties, and further, heat shrinkage is unlikely to occur even when high temperatures are required for expansion molding, and the occurrence of wrinkles and voids (gaps) on the surface of the foam is suppressed.

Examples of polyethylene resins include low-density polyethylene (branched low-density polyethylene, linear low-density polyethylene), high-density polyethylene, etc., with low-density polyethylene and high-density polyethylene being preferred.
The polyethylene resins may be used alone or in combination.
As the polyethylene-based resin, commercially available products may be used, such as the Green Polyethylene series from Braskem, the Novatec series from Japan Polyethylene, the Suntech series from Asahi Kasei, and the UBE Polyethylene series from Ube Maruzen Polyethylene. Of these, those having a melting peak temperature of 90 to 130°C are preferred.

The polyethylene resin content in resin particles, expandable particles, expanded particles, and foamed molded articles can be, for example, 10 to less than 50% by mass, 10 to 40% by mass, 10 to 30% by mass, or 20 to 40% by mass.

The resin particles, expandable particles, expanded particles and foamed molded article each contain a non-crosslinked propylene-α-olefin copolymer as a main component and further contain a polyethylene resin.
In each of the resin particles, expandable particles, expanded particles, and expanded molded article, the total content of the non-crosslinked propylene-α-olefin copolymer and the polyethylene resin may be 80% by mass or more relative to the mass of the resin particles, expandable particles, expanded particles, and expanded molded article. Here, the total content of the non-crosslinked propylene-α-olefin copolymer and the polyethylene resin may be, for example, 80 to 100% by mass, 80 to 99% by mass, 80 to 95% by mass, 85 to 100% by mass, 85 to 99% by mass, 85 to 95% by mass, 90 to 100% by mass, 90 to 99% by mass, 90 to 95% by mass, etc.

The mass ratio of the non-crosslinked propylene-α-olefin copolymer content to the polyethylene resin content in the resin particles, expandable particles, expanded particles, and foamed molded articles is preferably 55:45 to 90:10, and more preferably 60:40 to 90:10.

The resin particles, expandable particles, expanded particles, and foamed molded articles may each have two or more melting peak temperatures (Tm) measured by differential scanning calorimetry (DSC), preferably two or three, and more preferably two.
One of the melting peak temperatures (Tm1) may be in the range of 90 to 130°C, and the other of the melting peak temperatures (Tm2) may be in the range of 130 to 180°C.

Tm1 may be within the range of, for example, 90 to 130°C, 95 to 130°C, 100 to 130°C, 90°C or higher but less than 130°C, 95°C or higher but less than 130°C, 100°C or higher but less than 130°C, 90 to 129°C, 95 to 129°C, or 100 to 129°C. It preferably has a peak melting temperature of 100 to 120°C, and more preferably has a peak melting temperature of 105 to 115°C.

Tm2 may be within the range of, for example, 130 to 180°C, 130 to 170°C, 130 to 165°C, greater than 130°C and not greater than 180°C, greater than 130°C and not greater than 170°C, greater than 130°C and not greater than 165°C, 131 to 180°C, 131 to 170°C, 131 to 165°C, or 140 to 180°C, and preferably has a peak melting temperature of 135 to 170°C, more preferably 135 to 165°C.

The temperature difference between the melting peak temperature (Tm2) and the melting peak temperature (Tm1) is preferably 20°C or more, more preferably 20 to 80°C, even more preferably 20 to 60°C, and particularly preferably 20 to 55°C. When the temperature difference is within this range, the foam particles are less likely to coalesce, improving moldability and fusion properties. Furthermore, even if high temperatures are required for foam molding, thermal shrinkage is less likely to occur, suppressing the occurrence of wrinkles and voids (gaps) on the foam surface. Furthermore, the resulting foamed molded product possesses the high rebound resilience and good flexibility inherent to elastomers.

(Resin particles)
The resin particles contain a non-crosslinked propylene-α-olefin copolymer as a main component, and further contain a polyethylene resin.

The shape of the particulate resin is not particularly limited, and examples thereof include a spherical shape, an oval spherical shape (egg-shaped), a cylindrical shape, a prismatic shape, a pellet shape, and a granular shape.
The size of the resin particles is not particularly limited as long as the desired expandability and moldability are obtained, and from the viewpoint of expandability and moldability, it is preferable that the resin particles have an average particle diameter of, for example, 0.5 mm to 8.0 mm, preferably 0.5 mm to 6.0 mm, and more preferably 0.5 mm to 3.0 mm.

The resin particles, expandable particles, expanded particles, and expanded molded products may each contain other components such as flame retardants, colorants, antibonding agents, antistatic agents, spreading agents, plasticizers, flame retardant aids, fillers, lubricants, and cell control agents. The content of other components may be 10% by mass or less, preferably 5% by mass or less, and particularly preferably 2% by mass or less, based on the mass of the resin particles, expandable particles, expanded particles, and expanded molded products. When the resin particles, expandable particles, expanded particles, and expanded molded products contain other components, the lower limit of the content can be, for example, 0.01% by mass, 0.05% by mass, 0.1% by mass, 0.5% by mass, 1% by mass, 2% by mass, etc. These lower limits can be appropriately combined with the upper limits, i.e., 10%, 5%, and 2% by mass, to form the range of the content of the other components.

Examples of the flame retardant include hexabromocyclododecane and triallyl isocyanurate hexabromide.
Examples of colorants include carbon black, iron oxide, graphite, and the like.
Examples of the anti-binding agent (anti-coalescence agent) include talc, calcium carbonate, and aluminum hydroxide.
Examples of the antistatic agent include polyoxyethylene alkylphenol ether and stearic acid monoglyceride.
Examples of the spreading agent include polybutene, polyethylene glycol, and silicone oil.
Examples of the foam control agent include higher fatty acid amides, higher fatty acid bisamides, higher fatty acid salts, and inorganic foam nucleating agents.

The resin particles can be obtained using known production methods and production equipment. For example, they can be produced by feeding a non-crosslinked propylene-α-olefin copolymer, a polyethylene resin, and a chemical foaming agent into an extruder, melt-kneading the mixture, extruding the mixture from the extruder, and cutting it into a desired size and shape. The temperature, time, pressure, etc. during melt-kneading can be appropriately set depending on the raw materials used and the production equipment.
The melt-kneading temperature in the extruder during melt-kneading is a temperature at which the resin is sufficiently softened. Therefore, it can be set appropriately depending on the resin used. It is preferably 160 to 260°C, more preferably 200 to 250°C. The melt-kneading temperature means the temperature of the molten mixture inside the extruder, measured by a thermocouple thermometer at the center of the flow path of the molten mixture near the extruder head.

(chemical foaming agent)
Chemical foaming agents include sodium bicarbonate-citric acid-based chemical foaming agents, bicarbonate-based foaming agents, carbonate-based foaming agents, etc., and can be used alone or in combination of two or more. Sodium bicarbonate-citric acid-based chemical foaming agents decompose at the melt-kneading temperature to generate water (and CO ₂ ), so their use is generally avoided. However, in the present invention, sodium bicarbonate-citric acid-based chemical foaming agents are more preferred.

A baking soda-citric acid-based chemical blowing agent is an inorganic chemical blowing agent that uses baking soda and citric acid or a citrate salt. This chemical blowing agent generates carbon dioxide gas through a chemical reaction between an acid (citric acid) and a base (baking soda), and is used to foam a thermoplastic resin with the generated gas. While baking soda and citric acid can each be used in a powdered state, from the standpoint of ease of handling, it is common to combine baking soda and citric acid into a single masterbatch, which is then kneaded with a base resin.
As the sodium bicarbonate-citric acid based chemical foaming agent, commercially available products can be used, such as the Fine Cell Master series (eg, PO412K) manufactured by Dainichi Seika Chemicals Co., Ltd.

Bicarbonate-based and carbonate-based blowing agents are thermally decomposed to generate carbon dioxide gas, which is used to foam thermoplastic resins. Examples of bicarbonate-based blowing agents that can be used include sodium bicarbonate. Examples of carbonate-based blowing agents that can be used include sodium carbonate, calcium carbonate, and magnesium carbonate.

The amount of chemical foaming agent mixed in the process for obtaining resin particles is preferably 0.1 to 2 parts by mass, and more preferably 0.3 to 1.8 parts by mass, per 100 parts by mass of the combined content of the non-crosslinked propylene-α-olefin copolymer and polyethylene resin.

(expanded particles)
The expanded beads contain a non-crosslinked propylene-α-olefin copolymer as a main component, and further contain a polyethylene resin.
The expanded particles are particles obtained by pre-expanding resin particles impregnated with a physical blowing agent, and can be obtained using known manufacturing methods and manufacturing equipment. For example, the expanded particles can be obtained by impregnating resin particles with a physical blowing agent to form expandable particles, and then pre-expanding the expandable particles.
The resin particles can be impregnated with the physical foaming agent by a known method, for example, by injecting the physical foaming agent under pressure into a sealed container containing the resin particles.
The pre-expansion conditions, such as the type and amount of the physical foaming agent and the pre-expansion temperature, may be adjusted so that the bulk density of the resulting expanded beads is at a desired value.

Physical blowing agents that can be used include organic gases such as propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane, n-hexane, and isohexane, as well as inorganic gases such as carbon dioxide, nitrogen, helium, argon, and air. These physical blowing agents can be used alone or in combination. Suitable organic gases are n-butane, isobutane, n-pentane, and isopentane, or a combination of these.

The content of the physical blowing agent in the expandable particles is preferably 5 to 25 parts by mass relative to 100 parts by mass of the expandable particles. The content (impregnation amount) of the physical blowing agent relative to 100 parts by mass of the resin particles is measured as follows.
The mass of resin particles is measured in Xg before they are placed in a pressure vessel. After the resin particles are impregnated with the physical blowing agent in the pressure vessel, the mass of the impregnated material is measured in Yg after it is removed from the pressure vessel. The content of the physical blowing agent impregnated per 100 parts by mass of resin particles (impregnation amount) is calculated using the following formula:
Physical foaming agent content (parts by mass) = ((Y - X) / X) x 100

The bulk density of the expanded beads is preferably 0.02 g/cm ³ to 0.45 g/cm ³ , more preferably 0.03 g/cm ³ to 0.4 g/cm ³ , and even more preferably 0.05 g/cm ³ to 0.3 g/cm ^3. A bulk density within this range is advantageous in that wrinkles and voids in the foamed molded article are suppressed and the foamed molded article is lightweight. The bulk density can be determined by the method described in the examples.

The expanded beads preferably have a spherical or nearly spherical shape. Their average particle diameter is preferably 1.0 mm to 9.0 mm, and more preferably 2.0 mm to 6.0 mm. An average particle diameter within this range is advantageous in that it allows for good mold filling.

Expanded particles can be obtained by pre-expanding expandable particles to the desired bulk density using a known method. Pre-expanding can be achieved by expanding the expandable particles using heated steam, preferably at a pressure of 0.005 MPa to 0.05 MPa (gauge pressure), more preferably 0.006 MPa to 0.04 MPa.

(Foam molded article)
The foamed molded article contains a non-crosslinked propylene-α-olefin copolymer as a main component and further contains a polyethylene-based resin. The foamed beads are resistant to adhesion between the foamed beads, resulting in excellent foam moldability. Furthermore, even when foamed at high temperatures, the foamed molded article is resistant to wrinkles and voids on its surface, contributing to a good appearance. Furthermore, foamed molded articles made from the foamed beads have a high rebound resilience and good flexibility.

Foamed molded articles can be obtained by in-mold foaming of foamed beads using known methods. For example, foamed beads are filled into the mold of a foam molding machine, heated to expand the foamed beads, and then thermally fused together. Steam is a suitable heating medium. Heating is carried out at a gauge pressure of, for example, 0.05 MPa to 0.35 MPa, preferably 0.06 MPa to 0.30 MPa.

The density of the foamed molded article is preferably 0.05 g/cm ³ to 0.3 g/cm ³ , more preferably 0.05 g/cm ³ to 0.2 g/cm ³ , and even more preferably 0.10 g/cm ³ to 0.20 g/cm ³ . A density within this range is advantageous in that it is easy to achieve both a high impact resilience, good flexibility, and excellent lightness. The density can be determined by the method described in the examples.

The fusion rate of the foamed molded article may be 80-100%, preferably 90-100%, and more preferably 95-100%. A fusion rate within this range is advantageous in that it can impart sufficient strength and good flexibility to the foamed molded article. The fusion rate can be determined by counting the number of broken foam beads in any range (a range containing 100 foam beads) on the fracture surface of a foamed molded article measuring 400 mm x 300 mm x 20 mm thick, which is divided into two pieces; specifically, it can be determined by the method described in the Examples.

The rebound resilience of the foamed molded article may be 35% or more, 35-60%, 40% or more, 40-60%, 40-55%, 40-50%, etc., with 35-55% being preferred and 35-50% being more preferred. The rebound resilience can be determined by Method A described in JIS K6400-3:2011, and specifically by the method described in the examples.

The surface hardness (Asker C hardness) of the foamed molded product is preferably 60 or less, more preferably 50 or less, and even more preferably 45 or less. The surface hardness may be 30 to 60, 30 to 50, 30 to 45, or 35 to 45, etc. A surface hardness within this range is advantageous in that it prevents bottoming out when used as a shock-absorbing material in sports goods such as shoes. Surface hardness can be determined by the method described in JIS K7312:1996, and specifically, by the method described in the Examples.

The foamed molded article preferably has sufficient flexibility that no cracks occur between the foam particles that make up the foamed molded article in a 90° flex test of 10,000 cycles (test piece size: 150 mm x 24 mm x 11 mm thick) in accordance with ASTM D1052. The cracks may be at least 50% deep and at least 10 mm long. Details of this flex test are described in the Examples. The measuring device used for the flex test is preferably a Rothflexing Tester from Yasuda Seiki Seisakusho.

Foamed molded articles can be used, for example, for midsoles, insoles, and outsoles that make up shoe soles; core materials for hitting implements such as rackets and bats; protective equipment for sports such as pads and protectors; medical, nursing care, welfare, and healthcare products such as pads and protectors; tire core materials for bicycles and wheelchairs; interior materials for transportation vehicles such as automobiles; seat core materials; shock-absorbing and vibration-absorbing materials; shock-absorbing materials such as fenders and floats; toys such as balls, blocks, and building blocks; floor underlayment materials; wall materials; seat core materials for railway vehicles and airplanes; bed mattresses; cushions, etc.

In the production of conventional foamed molded articles, a non-crosslinked olefin-based elastomer with a relatively high melting point is used as the base resin, which requires a foaming process using high-temperature steam. However, the foamed molded article production method of the present invention makes it difficult for voids to occur on the surface of the foamed molded article, resulting in foamed molded articles with good appearance. This is thought to be because the fusion between the foamed particles is promoted and thermal shrinkage during the foaming process is suppressed, thereby improving the expansion of the surface of the foamed molded article.
The foamed molded article has sufficient impact resilience and good flexibility, which is thought to be due to the high fusion rate and good surface expansion.
The foamed molded article is easy to recycle because it is mainly composed of a non-crosslinked olefin-based elastomer.

The following examples further illustrate one embodiment of the present invention, but the present invention is not limited to these examples. The methods for specifying various physical properties, raw materials, etc. used in the examples are described below.

(Peak melting temperature (melting point) of foamed molded article)
The melting peak temperature was measured by the method described in JIS K7121:2012, except that the sampling method and temperature conditions were as follows.
5.5±0.5 mg of sample was packed into the bottom of an aluminum measurement container so that there were no gaps, and then an aluminum lid was placed on it. Differential scanning calorimetry was then performed using a Hitachi High-Tech Science DSC7000X, AS-3 differential scanning calorimeter. The sample was heated and cooled in the following steps under a nitrogen gas flow rate of 20 mL/min, to obtain a DSC curve.
(Step 1) The temperature is lowered from 30°C to -40°C and then maintained for 10 minutes.
(Step 2) Heat the mixture from -40°C to 220°C (first heating) and hold for 10 minutes.
(Step 3) The temperature is decreased (cooled) from 220°C to -40°C and maintained for 10 minutes.
(Step 4) Heat the mixture from -40°C to 220°C (second heating).
All heating and cooling was performed at a rate of 10°C/min. Alumina was used as the reference material. Using the analysis software provided with the device, the temperature indicated by the top of the melting peak observed during the second heating process was read and determined as the melting peak temperature (melting point). The highest peak top temperature within the range of 90 to 130°C was determined as the melting peak temperature Tm1, and the highest peak top temperature within the range of 130 to 180°C was determined as the melting peak temperature Tm2. When there were two peak tops near 130°C and they were very close to each other, the higher melting peak temperature was determined as Tm2 and the lower melting peak temperature was determined as Tm1.
The melting peak temperatures of the resin and the expanded particles can be measured in the same manner.

(Bulk density of expanded particles)
W g of expanded beads were collected as a measurement sample, and this measurement sample was allowed to fall naturally into a measuring cylinder. The bottom of the measuring cylinder was then struck to make the apparent volume (V) ^cm3 of the sample constant, and the mass of the sample was measured. The mass (W) g of the measurement sample was calculated by subtracting the mass of the empty measuring cylinder. The bulk density of the expanded beads was measured based on the following formula:
Bulk density (g/cm ³ )=mass of measurement sample (W)/apparent volume of measurement sample (V)

(Average particle size of resin particles and expanded particles)
Using a low-tap sieve shaker (manufactured by Iida Seisakusho), approximately 25 g of sample was classified for 10 minutes using JIS standard sieves (JIS Z8801-1:2006) with sieve openings of 4.00 mm, 3.35 mm, 2.80 mm, 2.36 mm, 2.00 mm, 1.70 mm, 1.40 mm, 1.18 mm, 1.00 mm, 0.85 mm, 0.71 mm, 0.60 mm, 0.50 mm, 0.425 mm, 0.355 mm, 0.300 mm, 0.250 mm, 0.212 mm, and 0.180 mm, and the weight of the sample on the sieve was measured. A cumulative weight distribution curve was created from the obtained results, and the particle diameter (median diameter) at which the cumulative weight reached 50% was taken as the average particle diameter.

(Density of foamed molded product)
The density was measured according to the method described in JIS K7222:2005. First, the sample was cut so as not to change the original cell structure, and test pieces with a volume of 100 cm or ^more were prepared, and the test pieces were conditioned as described below. Next, the mass of the conditioned test pieces was measured, and the density was calculated according to the following formula.
Density (g/cm ³ )=mass of test piece (g)/volume of test piece (cm ³ )
Test specimen conditioning Test specimens for measurement were cut from samples 72 hours or more after molding. The test specimens were conditioned for 16 hours or more under the standard atmosphere of JIS K7100:1999, symbol "23/50", grade 2, before measuring the mass and volume.

(Evaluation of Appearance of Foam Molded Article)
The state of gaps (voids) between foam particles on the surface of a 400 mm x 300 mm foam molded article (400 mm x 300 mm x 20 mm thick) was visually observed and evaluated according to the following criteria.
◯: No voids between the foam particles.
△: 10 or less voids between the foam particles.
x: 11 or more voids are present between the expanded particles.
Here, the voids refer to those having a size of 2 mm square or more.

(Fusion rate)
A 400 mm x 300 mm x 20 mm thick foam molded article was cut with a cutter knife into a surface with a depth of approximately 5 mm along a straight line connecting the centers of a pair of long sides, and then the foam molded article was divided into two along the cut line. An arbitrary area containing 100 foam beads that appeared on the fracture surface of the divided foam molded article was set, and the number of foam beads that had broken within the foam beads (a) and the number of foam beads that had broken at the interface between the foam beads (b) were counted within this area, and the fusion rate F (%) was calculated using the following formula.
F (%)=a/(a+b)×100

(Surface hardness of foam molded product (Asker C hardness))
The surface hardness was measured according to the method described in JIS K7312:1996. The samples were conditioned for 88 hours under a standard atmosphere of JIS K 7100:1999, "23/50", grade 2, before being used for measurement. The sample size was 50 x 50 x 10 mm thick. Five samples were used. The surface hardness was measured using an "Asker Rubber Plastic Hardness Tester, Type C" manufactured by Kobunshi Keiki Co., Ltd. A load of 1 kg was applied to the sample using this hardness tester, and the value immediately read was taken as the surface hardness. The surface hardness was calculated by averaging five measured values.

(Rebound resilience of foam molded article)
The rebound resilience was measured according to Method A of JIS K6400-3:2011. A "Rebound Resilience Tester Model FR-1" manufactured by Kobunshi Keiki Co., Ltd. was used for the measurement. The test specimen was 100 mm square and 20 mm thick. A steel ball (diameter 16±0.5 mm, mass 16.8±1.5 g) with a nominal size of 16 mm and a grade of G40, as specified in JIS B1501, was used for the measurement. The rebound resilience was calculated using the following formula. However, the ball falling distance was set to 500 mm.
Rebound elasticity (%) = maximum rebound distance (mm) / drop distance (500 mm) × 100
The test pieces were conditioned for 16 hours in a standard atmosphere of grade 2, symbol "23/50" of JIS K 7100:1999, before being used for the measurements. The measurements were carried out in the same standard atmosphere.

(Bending test of foam molded article)
The flex test was performed according to the method described in ASTM D1052. The test specimen size was 150 mm x 24 mm x 11 mm thick. A Ross Flexing Tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) was used as the measuring device. Both ends of the test specimen were fixed to the measuring device, and the specimen was flexed 90° at a frequency of 100 times/minute. After 10,000 times, the occurrence of cracks was visually confirmed and evaluated according to the following criteria.
◯: No cracks on the surface of the test piece.
×: There is one or more cracks on the surface of the test piece that are 50% or more deep and 10 mm or longer.

(A: Non-crosslinked propylene-α-olefin copolymer)
Elastomer A1: Toughmer PN-2060 (Mitsui Chemicals, Inc.); melting peak temperature: 160°C
Elastomer A2: ESPOLEX 901 (Sumitomo Chemical Co., Ltd.); melting peak temperature: 144°C
Elastomer A3: Toughmer PN-2070 (Mitsui Chemicals, Inc.); melting peak temperature: 140°C
Elastomer A4: Toughmer PN-3560 (Mitsui Chemicals, Inc.); melting peak temperature 160°C
Elastomer A5: Prime TPO R110E (Prime Polymer Co., Ltd.); melting peak temperature 156°C
Elastomer A6: Vistamaxx 3980FL (ExxonMobil); melting peak temperature 74.5°C

(B: polyethylene resin)
Resin B1: Braskem Green PE SEB853; melting peak temperature 111°C
Resin B2: Braskem Green SHC7260; peak melting temperature 134°C
Resin B3: Braskem Green SLH218; peak melting temperature 125°C

(acrylic polymer)
Metablen P-1050 (Mitsubishi Chemical Corporation)

(baking soda-citric acid based chemical foaming agent)
Fine Cell Master PO410K (Dainichiseika Color & Chemicals Mfg. Co., Ltd.)

Example 1
(1) Resin Particles: 53 parts by weight of elastomer A1, 24 parts by weight of elastomer A2, 23 parts by weight of polyethylene-based resin B1, 5 parts by weight of an acrylic polymer as a processing aid, and 1 part by weight of a sodium bicarbonate-citric acid-based chemical blowing agent were fed into a single-screw extruder at a rate of 10 kg/h and melt-kneaded. The materials were initially melt-kneaded at 160°C, then heated to 200°C. The molten resin was then cooled and extruded through each nozzle of a multi-nozzle die (with nine 1.0 mm diameter nozzles) attached to the front end of the single-screw extruder. The extruded resin was then cut in water at 20-50°C to obtain resin particles. The average particle diameter D50 of the resin particles was 1.52-1.55 mm.

(2) Expandable Particles 2.0 kg (100 parts by mass) of the resulting resin particles, 1.5 L of distilled water, and 3 g of a surfactant (sodium linear alkylbenzene sulfonate, product name: "Newlex R", manufactured by Yuka Sangyo Co., Ltd.) were placed in a 5 L autoclave equipped with a stirrer and sealed. Then, 10 parts by mass of a blowing agent, butane (normal butane:isobutane = 7:3 (volume ratio)), was added under pressure while stirring. The autoclave was then heated at 30°C for 2 hours and cooled to 25°C. After cooling, the autoclave was depressurized, and the surfactant was immediately washed with distilled water and dehydrated to obtain expandable particles. The amount of gas impregnated in the expandable particles was 7.7% by mass.

(3) Expanded beads 2.0 kg of the obtained expandable beads were charged into a 50 L cylindrical pre-expander equipped with a stirrer, and pre-expanded by heating with steam at a gauge pressure of 0.01 MPa while stirring to obtain expanded beads. The bulk density and average particle size of the obtained expanded beads were measured.

(4) Foamed Molded Article The resulting foamed beads were placed in an autoclave, and air was injected at a gauge pressure of 0.25 MPa. The foamed beads were then allowed to stand at room temperature for 18 hours to impregnate the foamed beads with air (apply internal pressure). The amount of air impregnated was 0.75% by mass.
The foamed beads with internal pressure were removed from the autoclave and immediately filled into a molding cavity (400 mm × 300 mm × 20 mm thick) equipped with a steam vent, followed by heat molding with steam at 0.20 MPa to obtain a foamed molded article. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 1.

Example 2
A foamed molded article was produced in the same manner as in Example 1, except that 64 parts by mass of elastomer A1 and 12 parts by mass of polyethylene resin B1 were used. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 1.

Example 3
A foamed molded article was produced in the same manner as in Example 1, except that 32 parts by mass of Elastomer A1 and 45 parts by mass of Elastomer A2 were used. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 1.

Example 4
A foamed molded article was produced in the same manner as in Example 1, except that 13 parts by mass of elastomer A2 and 34 parts by mass of polyethylene resin B1 were used. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 1.

Example 5
Except for using Elastomer A3 instead of Elastomer A1, a foamed molded article was produced in the same manner as in Example 1. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 1.

Example 6
Except for using Elastomer A4 instead of Elastomer A1, a foamed molded article was produced in the same manner as in Example 1. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 1.

(Comparative Example 1)
Expanded beads were produced in the same manner as in Example 1, except that 100 parts by mass of elastomer A1 was used and elastomer A2 and polyethylene-based resin B1 were not used. However, since the expanded beads remained in a bead-like form even when heated in the expansion molding process, a fused body of the expanded beads was not formed, and an expanded molded product was not obtained.

(Comparative Example 2)
A foamed molded article was produced in the same manner as in Example 1, except that 100 parts by mass of Elastomer A5 was used instead of Elastomer A1, and Elastomer A2 and polyethylene-based resin B1 were not used. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 2.

(Comparative Example 3)
A foamed molded article was produced in the same manner as in Example 1, except that Elastomer A1 was not used and 77 parts by mass of Elastomer A2 was used. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 2.

(Comparative Example 4)
A foamed molded article was produced in the same manner as in Example 1, except that 77 parts by mass of Elastomer A6 was used instead of Elastomers A1 and A2. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 2.

(Comparative Example 5)
A foamed molded article was produced in the same manner as in Example 1, except that polyethylene resin B2 was used instead of polyethylene resin B1. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 2.

(Comparative Example 6)
A foamed molded article was produced in the same manner as in Example 1, except that elastomer A3 was used instead of elastomer A1 and polyethylene-based resin B3 was used instead of polyethylene-based resin B1. The physical properties of the obtained foamed beads and foamed molded article are shown in Table 2.

(Comparative Example 7)
The same procedure as in Example 1 was conducted except that 53 parts by mass of elastomer A1, 13 parts by mass of elastomer A2, and 34 parts by mass of polyethylene-based resin B1 were used and no chemical foaming agent was used. However, the expandable particles were not pre-expanded, and no expanded particles were obtained.

In Examples 1 to 6, foam molding was possible using steam at 0.20 MPa. Furthermore, in Examples 1 to 6, Tm2-Tm1 was 30 to 52° C. In Examples 1 to 6, foam molded articles excellent in appearance, fusion rate, hardness, rebound resilience, and flexibility were obtained.
In Comparative Example 2, a peak top was observed in the temperature range of Tm2 (130 to 180°C) in the measurement of the peak melting temperature of the foamed molded article. However, since no polyethylene resin was used in combination with the non-crosslinked polypropylene-α-olefin copolymer, no other peak tops were observed.
In Comparative Example 3, a polyethylene resin was used in combination with a non-crosslinked polypropylene-α-olefin copolymer, and Tm2-Tm1 was 31°C.
In Comparative Example 4, a polyethylene resin was used in combination with a non-crosslinked polypropylene-α-olefin copolymer, and two peak tops were observed in the measurement of the peak melting temperature of the foamed molded article. A peak top was observed at 106°C within the temperature range of Tm1 (90 to 130°C), but no peak top was observed within the temperature range of Tm2 (130 to 180°C), and a peak top was observed at 75°C.
In Comparative Example 5, two types of non-crosslinked polypropylene-α-olefin copolymer and a polyethylene resin were used in combination, and two peak tops were observed in the measurement of the peak melting temperature of the foamed molded article. Peak tops were observed at 134°C and 159°C within the temperature range of Tm2 (130 to 180°C), but no peak top was observed within the temperature range of Tm1 (90 to 130°C).
In Comparative Example 6, two types of non-crosslinked polypropylene-α-olefin copolymers and a polyethylene resin were used in combination, and two peak tops were observed in the measurement of the peak melting temperature of the foamed molded article. Tm2 - Tm1 was 13°C.

Claims (10)

A foamed molded article of a non-crosslinked olefin-based elastomer composed of a fused body of foamed beads,
Contains two or more non-crosslinked propylene-α-olefin copolymers as main components,
One of the two or more non-crosslinked propylene-α-olefin copolymers has a melting peak temperature of 144°C as measured by differential scanning calorimetry (DSC);
Further containing a polyethylene resin,
the total content of the non-crosslinked propylene-α-olefin copolymer and the polyethylene resin is 80% by mass or more relative to the mass of the foamed molded article,
The foamed molded product has two or more melting peak temperatures (Tm) measured by a differential scanning calorimeter (DSC),
One of the melting peak temperatures (Tm1) of the foamed molded product is in the range of 90 to 130°C,
Another melting peak temperature (Tm2) of the foamed molded product is in the range of 139 to 180°C,
the temperature difference between the melting peak temperature (Tm2) and the melting peak temperature (Tm1) is 20°C or more;
Foam molding. the mass ratio of the content of the non-crosslinked propylene-α-olefin copolymer to the content of the polyethylene resin is 55:45 to 90:10;
A foamed molded article of the non-crosslinked olefinic elastomer according to claim 1. The foamed molded article of a non-crosslinked olefin-based elastomer according to claim 1 or 2, wherein the temperature difference between the melting peak temperature (Tm2) and the melting peak temperature (Tm1) is 20 to 80°C. The non-crosslinked olefin-based elastomer foam molded article according to any one of claims 1 to 3, wherein the polyethylene-based resin is one or more resins selected from the group consisting of high-density polyethylene and low-density polyethylene. A foam-molded product of a non-crosslinked olefin-based elastomer according to any one of claims 1 to 4, having a xylene-insoluble content of 3% or less as measured by hot xylene extraction. 6. The foam-molded article of a non-crosslinked olefin-based elastomer according to any one of claims 1 to 5, which has at least one property selected from the group consisting of ^a density of 0.05 to 0.3 g/cm3, a rebound resilience of 35% or more, and an Asker C hardness of 60 or less. A foam molded article of a non-crosslinked olefin-based elastomer according to any one of claims 1 to 6, which has flexural durability such that no cracks develop between the foam particles to a depth of 50% or more and a length of 10 mm or more in a 90° flex test of 10,000 cycles in accordance with ASTM D1052 (test piece size: 150 mm x 24 mm x 11 mm thick). A method for producing a foamed molded article from a non-crosslinked olefin-based elastomer according to any one of claims 1 to 7, comprising the steps of: mixing a non-crosslinked propylene-α-olefin copolymer, a polyethylene-based resin, and a chemical foaming agent to obtain resin particles containing a non-crosslinked propylene-α-olefin copolymer as a main component; impregnating the resin particles with a physical foaming agent and then pre-expanding them to obtain expanded particles; and foaming the expanded particles in a mold to obtain a foamed molded article. The method for producing a foamed molded article from a non-crosslinked olefin-based elastomer according to claim 8, wherein the chemical foaming agent is a sodium bicarbonate-citric acid-based chemical foaming agent, and the amount of the chemical foaming agent mixed in the step of obtaining resin particles is 0.1 to 2 parts by mass per 100 parts by mass of the total content of the non-crosslinked propylene-α-olefin copolymer and the polyethylene-based resin. The method for producing a foamed molded article from a non-crosslinked olefin-based elastomer according to claim 8 or 9, wherein the mass ratio of the amount of the non-crosslinked propylene-α-olefin copolymer mixed to the amount of the polyethylene-based resin mixed in the step of obtaining resin particles is 55:45 to 90:10.