Polypropylene-based resin foam particles, method for producing the same, and polypropylene-based resin foam molded article

Abstract

The present invention pertains to polypropylene-based resin foamed particles in which a base resin contains a polypropylene-based resin, wherein: the polypropylene-based resin contains 40-85 mass of a propylene homopolymer having a branched structure, and 15-60 mass of an α-olefin-propylene random copolymer having a melting point of 135-155°C; the polypropylene-based resin foamed particles have only one melting peak in a temperature range of 130-170°C at the first temperature rise of differential scanning calorimetry; a calorific value of melting in the temperature range of 130-170°C is at least 90.0% of a total calorific value of melting; a melting point Tm2 is 155.0-160.0°C; a melting breaking rate is 30.0-70.0 m / min; and an open cell ratio is at most 30%. Thus, provided are: polypropylene-based resin foamed particles from which a molded body having good moldability and high flexibility can be obtained; a method for producing the same; and a polypropylene-based resin foam molded body.

Description

Technical Field

[0001] The present invention relates to polypropylene-based resin foam particles, a method for producing the same, and a polypropylene-based resin foam molded article.

Background Art

[0002] An in-mold foam molded article obtained by filling polypropylene-based resin foam particles into a mold and heating and molding them with steam has characteristics such as arbitrary shape, light weight, and heat insulation, which are advantages of in-mold foam molded articles. Due to these characteristics, in-mold foam molded articles composed of polypropylene-based resin foam particles are used in various applications such as heat insulation materials, cushioning packaging materials, automotive interior members, and core materials for automotive bumpers.

[0003] The polypropylene-based resin foam particles used in polypropylene-based resin foam molded articles are generally prepared by a so-called "pressure-relief foaming method" in which polypropylene-based resin particles are dispersed in water in a pressure-resistant container together with a volatile foaming agent, heated to a temperature near the melting point of the polypropylene-based resin to impregnate the foaming agent into the polypropylene-based resin particles, and while maintaining the temperature and pressure in the container constant under a pressure equal to or higher than the vapor pressure exhibited by the foaming agent, discharging the dispersion of the polypropylene-based resin particles and water into an atmosphere at a lower pressure than inside the container. However, the manufacturing process of resin foam particles by the pressure-relief foaming method requires a two-step process to obtain foam particles because it once goes through a pelletizing process to make the size suitable for foaming with an extruder and then transfers to the foaming process in a pressure-resistant container, which tends to result in large equipment investment, and also has problems such as the need for wastewater treatment equipment because a dispersion medium such as water is used.

[0004] Therefore, in recent years, in order to overcome the problems in the pressure-relief foaming method, it has been proposed to produce polypropylene-based resin foam particles by an extrusion foaming method.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2015-108033 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] However, when producing polypropylene-based resin foamed particles by the extrusion foaming method, the closed cell ratio of the obtained polypropylene-based resin foamed particles tends to be high, and it is difficult to obtain a molded article with good moldability. Further, when producing polypropylene-based resin foamed particles using a polypropylene-based resin having a branched structure in order to reduce the closed cell ratio, the polypropylene-based resin foamed molded article obtained by in-mold molding of the polypropylene-based resin foamed particles is inferior in flexibility, and there is a problem that it cracks even with a slight deformation when subjected to an impact or the like.

[0007] The present invention provides polypropylene-based resin foamed particles, a method for producing the same, and a polypropylene-based resin foamed molded article capable of obtaining a molded article having good moldability and high flexibility in order to solve the above-mentioned conventional problems. MEANS FOR SOLVING THE PROBLEMS

[0008] In one or more embodiments, the present invention relates to polypropylene-based resin foamed particles in which the base resin contains a polypropylene-based resin. The polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure, and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer having a melting point of 135°C or more and 155°C or less. The polypropylene-based resin foamed particles have only one melting peak in the temperature range of 130°C or more and 170°C or less in the first heating by differential scanning calorimetry, and the heat of fusion in the temperature range of 130°C or more and 170°C or less is 90.0% or more of the total heat of fusion. The melting point Tm2 indicated by the value of the melting peak obtained in the second heating by differential scanning calorimetry of the polypropylene-based resin foamed particles is 155.0°C or more and 160.0°C or less. The melt fracture rate at a temperature of 200°C of the polypropylene-based resin foamed particles is 30.0 m / min or more and 70.0 m / min or less. The polypropylene-based resin foamed particles have a closed cell ratio of 30% or less.

[0009] In one or more embodiments, the present invention relates to a method for producing polypropylene-based resin foamed particles. A base resin containing a polypropylene-based resin is melt-kneaded together with a nucleating agent and a foaming agent and then extruded. The extruded melt-kneaded product is cut to obtain polypropylene-based resin foamed particles. The polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure, and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer. The propylene homopolymer having a branched structure has a melt tension of 10 cN or more and 50 cN or less. The α-olefin-propylene random copolymer has a melting point of 135°C or more and 155°C or less and a melt flow rate of 5 g / 10 min or more and 50 g / 10 min or less.

[0010] In one or more embodiments, the present invention relates to a polypropylene-based resin foam molded article composed of polypropylene-based resin foam particles, wherein the polypropylene-based resin foam particles are extrusion foam particles containing a base resin containing 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure, and have a closed cell ratio of 30% or less. The polypropylene-based resin foam molded article has a density D (g / L) of 60 to 300 g / L, a compressive strength St (kPa) at 50% strain and a density D (g / L) satisfy the following relational expression (1), and a tensile fracture elongation of 10% or more.

Number

Advantages of the Invention

[0011] The present invention can provide polypropylene-based resin foam particles that can obtain a polypropylene-based resin foam molded article with good moldability and high flexibility. According to the method for producing polypropylene-based resin foam particles of the present invention, polypropylene-based resin foam particles that can obtain a polypropylene-based resin foam molded article with good moldability and high flexibility can be easily and highly productively produced. The present invention can also provide a polypropylene-based resin foam molded article with high flexibility.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0013] The present inventors have conducted intensive studies to solve the above problems. As a result, in polypropylene-based resin foam particles in which the base resin contains a polypropylene-based resin (hereinafter, also simply referred to as "foam particles"), the polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure, and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer having a melting point of 135°C or higher and 155°C or lower; in the first heating of differential scanning calorimetry, there is only one melting peak in the temperature range of 130°C or higher and 170°C or lower (hereinafter, the value of the melting peak may also be referred to as Tm1), and the heat of fusion in the temperature range of 130°C or higher and 170°C or lower is 90.0% or more of the total heat of fusion (hereinafter, also simply referred to as "heat of fusion ratio"); the melting point Tm2 indicated by the value of the melting peak during the second heating of differential scanning calorimetry is 155.0°C or higher and 160.0°C or lower; the melt fracture rate at a temperature of 200°C is 30.0 m / min or more and 70.0 m / min or less; and the closed cell ratio is 30% or less. By these, the moldability of a polypropylene-based resin foam molded body (hereinafter, also simply referred to as "foam molded body") using the polypropylene-based resin foam particles is good, the flexibility is also high, and it is less likely to crack even when deformed upon receiving an impact or the like. In particular, in foam particles in which the base resin contains a polypropylene-based resin, the propylene homopolymer having a branched structure has a melt tension of 10 cN or more and 50 cN or less, the α-olefin-propylene random copolymer has a melting point of 135°C or higher and 155°C or lower, and a melt flow rate (hereinafter, also simply referred to as "MFR") of 5 g / 10 min or more and 50 g / 10 min or less, the flexibility of a foam molded body using the foam particles is improved, and it is less likely to crack even when deformed to some extent upon receiving an impact or the like.

[0014] In one or more embodiments of the present invention, the differential scanning calorimetry curve (DSC curve) of the polypropylene-based resin foamed particles is obtained by heating the polypropylene-based resin foamed particles from 40°C to 300°C at a heating rate of 10°C / min using a differential scanning calorimeter to melt them, and then crystallizing them by cooling from 300°C to 40°C at a cooling rate of 10°C / min, and then further heating from 40°C to 300°C at a heating rate of 10°C / min. It means all of the DSC curves (first heating → cooling → second heating). As the differential scanning calorimeter, for example, the DSC6200 type manufactured by Seiko Instruments Inc. can be used. In addition, for this measurement, a foamed molded body may be used instead of the foamed particles.

[0015] In one or more embodiments of the present invention, the polypropylene-based resin foamed particles have only one melting peak in the temperature range of 130°C or higher and 170°C or lower in the DSC curve during the first heating, and the melting peak temperature becomes the melting point Tm1. The polypropylene-based resin foamed particles are preferably extrusion foamed particles. Usually, when producing polypropylene-based resin foamed particles by the extrusion foaming method, except when blending resins with low compatibility, there is only one melting peak in the temperature range of 130°C or higher and 170°C or lower in the DSC curve during the first heating.

[0016] In one or more embodiments of the present invention, the heat of fusion in the temperature range of 130°C or higher and 170°C or lower in the DSC curve during the first heating of the polypropylene-based resin foamed particles is 90.0% or more of the total heat of fusion, preferably 92.0% or more, more preferably 92.5% or more, still more preferably 93.0% or more, and particularly preferably 93.5% or more. When the ratio of the heat of fusion in the temperature range of 130°C or higher and 170°C or lower is within the above-described range, a foamed molded article with good moldability can be obtained. Note that if the ratio of the heat of fusion in the temperature range below 130°C increases, there is a risk that the closed cell ratio of the foamed particles will be high and there is a risk that the closed cell ratio will be high during molding. If the ratio of the heat of fusion in the temperature range exceeding 170°C increases, there is a risk that the moldability will deteriorate. Also, although not particularly limited, for example, from the viewpoint of enhancing heat resistance, the heat of fusion in the temperature range of 130°C or higher and 170°C or lower in the DSC curve obtained by the first heating of the polypropylene-based resin foamed particles may be 100% or less, or 97.0% or less, of the total heat of fusion.

[0017] In one or more embodiments of the present invention, the ratio of the heat of fusion in the temperature range of 130°C or higher and 170°C or lower can be calculated as follows. <Ratio of heat of fusion> As shown in Fig. 1, a line segment AB connecting the point corresponding to 100 °C (point A) on the DSC curve obtained during the first temperature increase to the melting end point (point B) is drawn, and the heat of fusion of the portion surrounded by the line segment AB and the DSC curve is calculated to obtain the total heat of fusion Q1. A straight line parallel to the Y-axis is drawn from the point corresponding to 130 °C (point C) on the line segment AB to the DSC curve, and the intersection point of this straight line and the DSC curve is defined as point D. Similarly, a straight line parallel to the Y-axis is drawn from the point corresponding to 170 °C (point E) on the line segment AB to the DSC curve, and the intersection point of this straight line and the DSC curve is defined as point F. The heat of fusion of the portion surrounded by the line segments CD, CE, EF, and the DSC curve is calculated to obtain the heat of fusion Q2 in the temperature range of 130 °C or higher and 170 °C or lower. When the melting end temperature is less than 170 °C, the heat of fusion of the portion surrounded by the line segments CD, CB, and the DSC curve is calculated as Q2. Using Q1 and Q2, the heat of fusion ratio is calculated by the following formula. When there is a peak derived from another resin within the range of Q1, the heat of fusion of that peak is also included in Q1 for calculation. Heat of fusion ratio (%) = Q2 × 100 / Q1 In addition, on the DSC curve, when a melting peak derived from another resin different from the polypropylene-based resin exists independently outside the range of Q1, only the corresponding melting peak is determined as the heat of fusion Q3. Using Q1, Q2, and Q3, the heat of fusion ratio is calculated by the following formula. Heat of fusion ratio (%) = Q2 × 100 / (Q1 + Q3)

[0018] In one or more embodiments of the present invention, the melting peak temperature of the DSC curve during the second temperature increase of the polypropylene-based resin foamed particles is the melting point Tm2, and Tm2 is 155.0 °C or higher and 160.0 °C or lower. When Tm2 of the polypropylene-based resin foamed particles is 155.0 °C or higher, a foamed molded article with good moldability can be obtained. Tm2 of the polypropylene-based resin foamed particles is preferably 156.0 °C or higher. When Tm2 of the polypropylene-based resin foamed particles is 160.0 °C or lower, a foamed molded article with high flexibility can be obtained.

[0019] In one or more embodiments of the present invention, the open cell ratio of the polypropylene-based resin foamed particles is 30% or less, preferably 25% or less, more preferably 20% or less, and still more preferably 15% or less. When the open cell ratio of the foamed particles is within the above-described range, a foamed molded article having good moldability and flexibility can be obtained. Further, although not particularly limited, the open cell ratio of the polypropylene-based resin foamed particles may be, for example, 0% or more, or may be 3% or more.

[0020] In one or more embodiments of the present invention, the melt fracture rate (hereinafter also simply referred to as "melt fracture rate") of the polypropylene-based resin foamed particles at a temperature of 200 °C is 30.0 m / min or more and 70.0 m / min or less. When the melt fracture rate of the foamed particles is within the above-described range, the flexibility of the foamed molded article is likely to be high. The melt fracture rate of the foamed particles is preferably 35.0 m / min or more, and more preferably 46.0 m / min or more.

[0021] In one or more embodiments of the present invention, the melt fracture rate of the polypropylene-based resin foamed particles at a temperature of 200 °C can be measured using a sample obtained by returning the foamed particles or the foamed molded article to a resin mass. Since the resin physical properties do not change between the foamed particles and the foamed molded article, either can be used for the measurement. <Preparation of Sample> The foamed particles are placed in a dryer whose temperature is adjusted to Tm2 + 10 °C based on the melting point Tm2 of the foamed particles, and the inside of the dryer is depressurized with a vacuum pump to -0.05 MPa (gage pressure) to -0.10 MPa (gage pressure) over 5 to 10 minutes, and then left in the dryer for 30 minutes to form a resin mass while removing the air inside the foamed particles. If the resins stick together and the mass is large, the resin mass may be finely cut with scissors or the like, or may be pulverized with a mixer or the like. In the case of the foamed molded article, the molded article was finely cut with scissors, a slicer, or the like and then pulverized with a mixer or the like. The fragments of the foamed molded article were placed in a dryer whose temperature was adjusted to Tm2 + 10°C based on the melting point Tm2 of the foamed particles, and the inside of the dryer was depressurized with a vacuum pump to -0.05 MPa (gage pressure) to -0.10 MPa (gage pressure) over 5 to 10 minutes, and then left in the dryer for 30 minutes to form a resin mass while removing the air inside the foamed molded article. When the resins adhered to each other and the mass was large, the resin mass may be finely cut with scissors or the like, or may be pulverized with a mixer or the like.

[0022] In the polypropylene-based resin foamed particles of one or more embodiments of the present invention, the base resin contains a polypropylene-based resin, and preferably contains the polypropylene-based resin as a main component. In one or more embodiments of the present invention, "containing the polypropylene-based resin as a main component" means containing 90% by mass or more of the polypropylene-based resin, preferably 95% by mass or more, more preferably 97% by mass or more, still more preferably 99% by mass or more, and particularly preferably consisting of 100% by mass of the polypropylene-based resin. Since the base resin contains the polypropylene-based resin as a main component, the melting peak in the temperature range of 130°C or higher and 170°C or lower in the DSC curve during the first heating of the foamed particles tends to be only one, and the heat of fusion in the temperature range of 130°C or higher and 170°C or lower tends to be 90.0% or more of the total heat of fusion.

[0023] In the base resin of one or more embodiments of the present invention, the polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure (hereinafter also referred to as branched polypropylene), and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer having a melting point of 135°C or more and 155°C or less. Preferably, it contains 50% by mass or more and 80% by mass or less of branched polypropylene and 20% by mass or more and 50% by mass or less of an α-olefin-propylene random copolymer. More preferably, it contains 60% by mass or more and 80% by mass or less of branched polypropylene and 20% by mass or more and 40% by mass or less of an α-olefin-propylene random copolymer. Even more preferably, it contains 65% by mass or more and 80% by mass or less of branched polypropylene and 20% by mass or more and 35% by mass or less of an α-olefin-propylene random copolymer. The foamed particles are likely to satisfy the above-mentioned melting point Tm2, melt fracture rate, and closed cell ratio.

[0024] The branched polypropylene is not particularly limited. For example, a modified polypropylene-based resin obtained by treating a propylene homopolymer with radiation and / or reacting a propylene homopolymer with a radical polymerization initiator can be used. In any case, a reaction with a functional unsaturated compound may be incidental or subsequent. From the viewpoints of easy production and economic advantage, it is preferable to use a modified polypropylene-based resin having a branched structure introduced by reacting a propylene homopolymer with a radical polymerization initiator or the like.

[0025] Examples of the radical polymerization initiator generally include peroxides and azo compounds. However, initiators having the ability to abstract hydrogen from functional unsaturated compounds such as propylene homopolymers and conjugated diene compounds described below are preferred. Examples of the initiator having the ability to abstract hydrogen generally include organic peroxides such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxydicarbonate, and peroxyester. Among these, initiators having particularly high hydrogen abstraction ability are preferred. For example, peroxyketals such as 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl 4,4-bis(t-butylperoxy)valerate, and 2,2-bis(t-butylperoxy)butane; dialkyl peroxides such as dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, t-butyl cumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne; diacyl peroxides such as benzoyl peroxide; peroxydicarbonates such as di-normal propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, di-sec-butyl peroxydicarbonate, and dicetyl peroxydicarbonate; peroxyesters such as t-butyl peroxy octoate, t-butyl peroxy isobutyrate, t-butyl peroxy laurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxy isopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxy acetate, t-butyl peroxy benzoate, and di-t-butyl peroxy isophthalate. These may be used alone or in combination of two or more.

[0026] The addition amount of the radical polymerization initiator is preferably 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 4 parts by mass or less, based on 100 parts by mass of the propylene homopolymer. If the addition amount of the radical polymerization initiator is within the above range, efficient resin modification is possible.

[0027] As the functional unsaturated compound, for example, a bifunctional unsaturated compound or a polyfunctional unsaturated compound having two or more functional groups can be used. A bifunctional unsaturated compound that can be polymerized with the help of free radicals is preferred. Examples of the bifunctional unsaturated compound include divinyl compounds, allyl compounds, conjugated diene compounds, aromatic and / or aliphatic bis(maleimide) bis(citraconimide), etc. Examples of the divinyl compound include divinylaniline, m-divinylbenzene, p-divinylbenzene, divinylpentane, and divinylpropane. Examples of the allyl compound include allyl acrylate, allyl methacrylate, allyl methyl maleate, and allyl vinyl ether. Examples of the conjugated diene compound include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, 2,5-dimethyl-2,4-hexadiene, etc. These may be used alone or in combination of two or more. Among these, conjugated diene compounds are preferred, and butadiene and / or isoprene are particularly preferred because they are inexpensive, easy to handle, and the reaction proceeds uniformly.

[0028] The conjugated diene compound may be used in combination with copolymerizable monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal salts of acrylic acid, metal salts of methacrylic acid, acrylic esters, methacrylic esters, etc. Examples of acrylic esters include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate. Examples of methacrylic esters include ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate.

[0029] The addition amount of the conjugated diene compound is preferably 0.01 part by mass or more and 20 parts by mass or less, more preferably 0.05 part by mass or more and 5 parts by mass or less, and even more preferably 0.2 part by mass or more and 2.5 parts by mass or less, based on 100 parts by mass of the propylene homopolymer. When the addition amount of the conjugated diene compound is within the above-mentioned range, the modification effect can be exerted and the cost can also be reduced.

[0030] Examples of the apparatus for reacting the propylene homopolymer, the functional unsaturated compound (e.g., conjugated diene compound), and the radical polymerization initiator include kneaders such as rolls, coneyders, Banbury mixers, Brabenders, single-screw extruders, and twin-screw extruders; horizontal stirrers such as twin-screw surface renewal machines and twin-screw multi-disk devices; and vertical stirrers such as double helical ribbon stirrers. Among these, it is preferable to use a kneader, and in particular, extruders such as single-screw extruders and twin-screw extruders are preferable from the viewpoint of productivity.

[0031] There are no particular restrictions on the order and method of mixing and kneading (stirring) a propylene homopolymer, a functional unsaturated compound (e.g., a conjugated diene compound), and a radical polymerization initiator. After mixing the propylene homopolymer, the functional unsaturated compound (e.g., a conjugated diene compound), and the radical polymerization initiator, melt kneading (stirring) may be performed, or after melt kneading (stirring) the propylene homopolymer, the functional unsaturated compound (e.g., a conjugated diene compound) or the radical initiator may be mixed simultaneously or separately, either all at once or in portions. The temperature of the kneading (stirring) machine is preferably 130°C or higher and 300°C or lower in terms of the propylene homopolymer melting and not undergoing thermal decomposition. Also, the melt kneading time is generally preferably 1 minute or longer and 60 minutes or shorter.

[0032] The branched polypropylene preferably has a melt tension of 10 cN or more and 50 cN or less, more preferably 11 cN or more and 40 cN or less, still more preferably 12 cN or more and 30 cN or less, and particularly preferably 13 cN or more and 20 cN or less. The foamed particles are likely to satisfy the above-mentioned melting point Tm2, melt fracture rate, and closed cell ratio, and the moldability and flexibility of the molded article are improved.

[0033] The branched polypropylene preferably has an MFR of 0.5 g / 10 min or more and 5 g / 10 min or less, more preferably 1.0 g / 10 min or more and 4 g / 10 min or less, and still more preferably 1.5 g / 10 min or more and 3 g / 10 min or less. When the MFR of the branched polypropylene is within the above-mentioned range, the surface property of the foamed molded article is improved and the productivity is also enhanced.

[0034] The branched polypropylene preferably has a melting point of 150°C or higher, more preferably 155°C or higher. The heat resistance of the foamed particles and the foamed molded article is likely to be improved. On the other hand, although not particularly limited, for example, from the viewpoint of the steam pressure during in-mold foaming, the melting point of the branched polypropylene is preferably 165°C or lower, more preferably 163°C or lower.

[0035] As the branched polypropylene, for example, Deploy manufactured by Borealis may be used. TM Commercially available products such as WB140 HMS may also be used.

[0036] In the α-olefin-propylene random copolymer, examples of the α-olefin copolymerizable with propylene include α-olefins having 2 or 4 to 12 carbon atoms such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene. Particularly, ethylene and 1-butene are preferable in terms of improving cold brittleness and being inexpensive. These may be used alone or in combination of two or more.

[0037] The α-olefin-propylene random copolymer preferably contains 1% by mass or more and 25% by mass or less of the α-olefin and 75% by mass or more and 99% by mass or less of propylene, more preferably contains 1.5% by mass or more and 15% by mass or less of the α-olefin and 85% by mass or more and 98.5% by mass or less of propylene, and even more preferably contains 1.5% by mass or more and 6% by mass or less of the α-olefin and 94% by mass or more and 98.5% by mass or less of propylene. This is preferable in that it imparts flexibility to the foam molded article and retains the crystallinity, rigidity, chemical resistance, etc., which are characteristics of polypropylene-based resins.

[0038] The α-olefin-propylene random copolymer has a melting point of 135°C or higher and 155°C or lower, preferably 137°C or higher and 152°C or lower, and more preferably 138°C or higher and 150°C or lower. When the melting point is 155°C or lower, the flexibility of the foam molded article is improved. Also, when the melting point is 135°C or higher, the moldability of the foam molded article is improved.

[0039] The α-olefin-propylene random copolymer preferably has an MFR of 5 g / 10 min or more and 50 g / 10 min or less, more preferably 6 g / 10 min or more and 45 g / 10 min or less, still more preferably 7 g / 10 min or more and 42 g / 10 min or less, and even more preferably 15 g / 10 min or more and 42 g / 10 min or less. The closed cell ratio of the foam particles tends to be low, and the moldability and flexibility of the foam molded body are improved.

[0040] In one or more embodiments of the present invention, the base resin may contain 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less of a resin other than the polypropylene-based resin within a range that does not inhibit the effects of the present invention, in addition to the polypropylene-based resin. More specifically, in one or more embodiments of the present invention, the base resin may contain 90% by mass or more and 100% by mass or less of a polypropylene-based resin and 0% by mass or more and 10% by mass or less of another resin, 95% by mass or more and 100% by mass or less of a polypropylene-based resin and 0% by mass or more and 5% by mass or less of another resin, 97% by mass or more and 100% by mass or less of a polypropylene-based resin and 0% by mass or more and 3% by mass or less of another resin, or 99% by mass or more and 100% by mass or less of a polypropylene-based resin and 0% by mass or more and 1% by mass or less of another resin. Examples of the other resin include polyethylene-based resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer; polystyrene-based resins such as polystyrene and styrene-maleic anhydride copolymer; and polyamide.

[0041] In one or more embodiments of the present invention, in addition to the base resin, the foamed particles may contain, as necessary, a nucleating agent (also referred to as a bubble nucleating agent); a colorant; an antistatic agent; a flame retardant; antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent brighteners, metal soaps, acid adsorbing agents, and other stabilizers; a crosslinking agent; a chain transfer agent; a lubricant; a plasticizer; a filler; a reinforcing material, and other additives. Such additives may be previously incorporated into the resin at a high concentration to form a masterbatch, and this masterbatch resin may be added to the polypropylene-based resin mixture. As the resin used for such a masterbatch resin, a polyolefin-based resin is preferable, a polypropylene-based resin is more preferable, and it is even more preferable to form a masterbatch with the same polypropylene-based resin used as the base resin of the foamed particles.

[0042] In one or more embodiments of the present invention, the polypropylene-based resin foamed particles can be produced, for example, by melt-kneading a base resin containing a polypropylene-based resin, preferably a base resin mainly composed of a polypropylene-based resin, together with a nucleating agent and a foaming agent, and then extruding the melt-kneaded product, and cutting the extruded melt-kneaded product, that is, by a so-called extrusion foaming method. In the production method of one or more embodiments of the present invention, the polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer. The propylene homopolymer having a branched structure has a melt tension of 10 cN or more and 50 cN or less, and the α-olefin-propylene random copolymer preferably has a melting point of 135°C or more and 155°C or less and a melt flow rate of 5 g / 10 min or more and 50 g / 10 min or less. Thereby, it is easy to obtain foamed particles in which Tm1, Tm2, the melt fracture rate, and the closed cell ratio satisfy the above-described ranges, and by using such foamed particles, a foamed molded article having good moldability and flexibility can be obtained.

[0043] Examples of the nucleating agent include sodium hydrogen carbonate, a sodium hydrogen carbonate-citric acid mixture, monosodium citrate, talc, calcium carbonate, etc. These may be used alone or in combination of two or more. From the viewpoint of easily obtaining foamed particles in which Tm1, Tm2, the melt fracture rate, and the closed cell ratio satisfy the above-described ranges, the nucleating agent preferably contains at least one selected from the group consisting of talc, sodium hydrogen carbonate, and calcium carbonate, and more preferably contains talc. The addition amount of the nucleating agent is not particularly limited, but is usually preferably 0.01 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base resin.

[0044] Examples of the foaming agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; alicyclic hydrocarbons such as cyclopentane and cyclobutane; inorganic gases such as air, nitrogen, and carbon dioxide gas; and water. These foaming agents may be used alone or in combination of two or more. Among these, from the viewpoints of safety during handling and simplification of the required equipment specifications, inorganic gas and / or water is preferable, and from the viewpoint of easily obtaining a foam with a high expansion ratio, inorganic gas, particularly carbon dioxide gas, is preferable. The addition amount of the foaming agent varies depending on the type of the foaming agent and the expansion ratio of the target polypropylene-based resin foamed particles, and thus may be appropriately adjusted. For example, it is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 2 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the base resin.

[0045] In the manufacturing method of one or more embodiments of the present invention, the melt kneading can be carried out in two stages. The temperature of the second stage may be the same as that of the first stage, but it is preferably lower than the temperature of the first stage. Specifically, after supplying the base resin, the nucleating agent, the foaming agent, and, if necessary, other additives to the first-stage extruder for melt kneading, the melt kneaded product is supplied to the second-stage extruder having a lower temperature than the first-stage extruder for cooling, and then the melt kneaded product (the melt kneaded product containing the foaming agent) is extruded through a die attached to the tip of the second-stage extruder, and the extruded melt kneaded product is cut to produce it. Since the temperature of the second-stage extruder is lower than that of the first-stage extruder, the continuous cell ratio of the foamed particles is likely to be reduced, and the moldability is improved. Further, since the main purpose of the second-stage extruder is cooling, it does not have to be an extruder as long as the purpose can be achieved. For example, it can be substituted with a static mixer, a melt cooler, or the like.

[0046] In one or more embodiments of the present invention, from the viewpoint of reducing the continuous cell ratio of the foamed particles and improving the moldability, the difference between the temperature of the first stage and the temperature of the second stage is preferably 5°C or more, more preferably 8°C or more, and even more preferably 10°C or more. Further, although not particularly limited, for example, from the viewpoint of easily lowering the temperature of the second stage to the target temperature, the difference between the temperature of the first stage and the temperature of the second stage is preferably 50°C or less, and more preferably 40°C or less.

[0047] In one or more embodiments of the present invention, the temperature of the first stage can be appropriately determined according to the melting point of the base resin to be used, the type and / or addition amount of the foaming agent, the type and / or melting point of the additive, the allowable torque of the extruder, etc., from the viewpoint of sufficiently melt kneading the base resin, the nucleating agent, and the foaming agent (and other additives if necessary), and is not particularly limited. For example, the temperature of the first stage is preferably (Tm2 + 20°C) or more and (Tm2 + 70°C) or less, more preferably (Tm2 + 20°C) or more and (Tm2 + 60°C) or less, and even more preferably (Tm2 + 20°C) or more and (Tm2 + 50°C) or less.

[0048] In one or more embodiments of the present invention, the temperature in the second stage can be appropriately determined according to the melting point of the base resin to be used, the type and / or addition amount of the foaming agent, the type and / or melting point of the additive, the allowable torque of the extruder, etc., and is not particularly limited. From the viewpoint of, for example, reducing the closed cell ratio of the foamed particles and improving the moldability, the temperature in the second stage is preferably (Tm2 + 40°C) or lower, more preferably (Tm2 + 30°C) or lower, and even more preferably (Tm2 + 20°C) or lower. Further, from the viewpoint of, for example, enhancing the productivity and stable operation of the extrusion foaming, the temperature of the second-stage extruder is preferably (Tm2 - 5°C) or higher, and more preferably Tm2 or higher.

[0049] The cutting method for obtaining foamed particles by the extrusion foaming method is roughly classified into a cold cut method and a die face cut method. The cold cut method includes a method (strand cut method) in which the molten resin containing the foaming agent extruded from the pore die is foamed, and the strand-like foam is taken out while cooling, such as passing through a water tank, and then cut. The die face cut method is a method of cutting the molten resin extruded from the pore die with a cutter that rotates while contacting the die face or while securing a slight gap. The die face cut method is classified into an under water cut method, a watering cut method, and a hot cut method according to the difference in the cooling method.

[0050] The extrusion discharge amount in the second-stage extruder, static mixer, or melt cooler is not particularly limited, but may be, for example, 1 kg / hour or more and 1000 kg / hour or less. In the laboratory type, it may be generally 1 kg / hour or more and 50 kg / hour or less, and in the actual production machine type, 20 kg / hour or more and 1000 kg / hour or less is preferable.

[0051] Regarding the die used in the second extruder, static mixer, or melt cooler, its shape is not limited. However, from the viewpoints of the appearance of the foamed particles and the ease of shaping, the die opening is preferably circular, and the diameter of the opening is preferably 0.1 mm or more and 2.0 mm or less, more preferably 0.3 mm or more and 1.0 mm or less.

[0052] In one or more embodiments of the present invention, the mass per foamed particle of the foamed particles is preferably 0.2 mg or more and 10 mg or less, more preferably 0.5 mg or more and 6.0 mg or less. In one embodiment of the present invention, the mass per foamed particle of the foamed particles is the average resin particle mass calculated based on the mass of 100 randomly selected polypropylene-based resin foamed particles. When the mass per foamed particle of the polypropylene-based resin foamed particles is 0.2 mg or more, the dimensional change rate of the foam molded body does not increase, and when it is 10 mg or less, there is a tendency to be easily filled into the mold.

[0053] In one or more embodiments of the present invention, the expansion ratio of the foamed particles is not particularly limited and may be adjusted as needed. However, even if the expansion ratio is low, it is possible to obtain a molded body with high flexibility. Therefore, in one embodiment of the present invention, the expansion ratio of the foamed particles may be, for example, 3 times or more and 15 times or less, or 4 times or more and 10 times or less.

[0054] In one or more embodiments of the present invention, for the expansion ratio of the polypropylene-based resin foamed particles, after measuring the mass w (g) of the polypropylene-based resin foamed particles, it is submerged in a graduated cylinder containing ethanol, and the volume v (cm 3 ) is measured by the increase in the water level of the graduated cylinder (water immersion method). The true specific gravity ρb = w / v of the polypropylene-based resin foamed particles is calculated, and further, it can be calculated as the ratio (ρr / ρb) with the density ρr of the polypropylene-based resin before foaming.

[0055] In one or more embodiments of the present invention, the bulk density of the polypropylene-based resin foam particles is not particularly limited, but is preferably, for example, 60 g / L or more and 300 g / L or less, and more preferably 80 g / L or more and 300 g / L or less. When the bulk density of the foam particles is within the above-described range, a foam molded article having a high density and good flexibility can be obtained. In one or more embodiments of the present invention, the bulk density of the polypropylene-based resin foam particles can be measured by the method described in the examples.

[0056] In one or more embodiments of the present invention, the average cell diameter (also referred to as the average bubble diameter) of the polypropylene-based resin foam particles is not particularly limited, but is preferably, for example, 100 μm or more and 500 μm or less, and more preferably 120 μm or more and 400 μm or less. When the average bubble diameter of the polypropylene-based resin foam particles is 100 μm or more, the shrinkage of the foam molded article tends to be small, and when it is 500 μm or less, the molding cycle during in-mold foam molding tends to be shortened. In one or more embodiments of the present invention, the average cell diameter of the polypropylene-based resin foam particles can be measured by the method described in the examples.

[0057] In one or more embodiments of the present invention, a foam molded article is obtained by in-mold foam molding of the polypropylene-based resin foam particles. The foam molded article has good moldability and flexibility, specifically, good tensile elongation.

[0058] In one or more embodiments of the present invention, the polypropylene-based resin foam molded article can be obtained by filling the polypropylene-based resin foam particles into a mold that can close but cannot be sealed, and heating and molding with steam or the like.

[0059] To form a polypropylene resin foamed molded article from the polypropylene resin foamed particles, for example, (a) a method in which the foamed particles are pressure-treated with an inorganic gas to impregnate the inorganic gas into the particles to impart a predetermined internal pressure of the particles, then filled into a mold, and heat-sealed with steam or the like (for example, Japanese Patent Publication No. 51-22951), (b) a method in which the foamed particles are compressed with gas pressure, filled into a mold, and heat-sealed with steam or the like by utilizing the restoring force of the particles (for example, Japanese Patent Publication No. 53-33996), (c) a method in which the foamed particles are filled into a mold with an expanded gap, then the mold is closed to a predetermined gap to compress the filled foamed particles, and heat-sealed with steam or the like can be used.

[0060] In one or more embodiments of the present invention, the density of the polypropylene resin foamed molded article may be appropriately determined according to the use and is not particularly limited. For example, it is preferably 60 g / L or more and 300 g / L or less, more preferably 90 g / L or more and 300 g / L or less, and even more preferably 100 g / L or more and 300 g / L or less. When the density of the foamed molded article is within the above-described range, a good molded article is easily obtained, shrinkage and deformation hardly occur when heat is applied to the molded article, and it is suitable for repeated use. In one or more embodiments of the present invention, the density of the polypropylene resin foamed molded article can be measured by the method described in the examples.

[0061] In one or more embodiments of the present invention, from the viewpoint of excellent flexibility, when the density of the foamed molded article is 60 g / L or more (preferably 90 g / L or more), the tensile elongation measured based on ISO1798 is preferably 10.0% or more, more preferably 10.5% or more, and even more preferably 11.0% or more. The tensile elongation is not particularly limited, but for example, from the viewpoint of practicality, it may be 100% or less.

[0062] In one or more embodiments of the present invention, from the viewpoint of achieving both energy absorption performance and flexibility, it is preferable that the compression strength St (kPa) and density D (g / L) at 50% strain of the foamed molded body satisfy the following relational expression (1). More preferably, the compression strength St (kPa) and density D (g / L) at 50% strain of the foamed molded body satisfy the following relational expression (1), and the tensile elongation measured based on ISO1798 is 10% or more. Such a polypropylene-based resin foamed molded body can be suitably used as a cushioning material. [Number] However, in the relational expression (1), St means a numerical value expressed in units of kPa, and D means a numerical value expressed in units of g / L.

[0063] In one or more embodiments of the present invention, it may be configured as follows. [1] Polypropylene-based resin foamed particles in which the base resin contains a polypropylene-based resin, The polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure, and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer having a melting point of 135°C or more and 155°C or less. The polypropylene-based resin foamed particles have only one melting peak in the temperature range of 130°C or more and 170°C or less in the first heating of differential scanning calorimetry, and the heat of fusion in the temperature range of 130°C or more and 170°C or less is 90.0% or more of the total heat of fusion. The melting point Tm2 indicated by the value of the melting peak during the second heating of differential scanning calorimetry of the polypropylene-based resin foamed particles is 155.0°C or more and 160.0°C or less. The melt fracture rate of the polypropylene-based resin foamed particles at a temperature of 200°C is 30.0 m / min or more and 70.0 m / min or less. Polypropylene-based resin foamed particles characterized in that the closed cell ratio of the polypropylene-based resin foamed particles is 30% or less. [2] The polypropylene-based resin foam particles according to [1], wherein the polypropylene-based resin foam particles are extrusion foam particles. [3] The polypropylene-based resin foam particles according to [1] or [2], wherein the bulk density of the polypropylene-based resin foam particles is 60 g / L or more and 300 g / L or less. [4] The polypropylene-based resin foam particles according to any one of [1] to [3], wherein the average cell diameter of the polypropylene-based resin foam particles is 100 μm or more and 500 μm or less. [5] The polypropylene-based resin foam particles according to any one of [1] to [4], wherein the propylene homopolymer having the branched structure has a melt tension of 10 cN or more and 50 cN or less. [6] The polypropylene-based resin foam particles according to any one of [1] to [5], wherein the propylene homopolymer having the branched structure has a melt flow rate of 0.5 g / 10 min or more and 5 g / 10 min or less. [7] The polypropylene-based resin foam particles according to any one of [1] to [6], wherein the propylene homopolymer having the branched structure has a melting point of 150 °C or more and 165 °C or less. [8] The polypropylene-based resin foam particles according to any one of [1] to [7], wherein the α-olefin-propylene random copolymer has a melt flow rate of 5 g / 10 min or more and 50 g / 10 min or less. [9] A method for producing polypropylene-based resin foam particles, A base resin containing a polypropylene-based resin is melt-kneaded together with a nucleating agent and a foaming agent and then extruded, and the extruded melt-kneaded product is cut to obtain polypropylene-based resin foam particles, wherein the polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer, the propylene homopolymer having the branched structure has a melt tension of 10 cN or more and 50 cN or less, The method for producing polypropylene-based resin foamed particles is characterized in that the α-olefin-propylene random copolymer has a melting point of 135°C or higher and 155°C or lower, and a melt flow rate of 5 g / 10 min or higher and 50 g / 10 min or lower.

[10] The method for producing polypropylene-based resin foamed particles according to [9], wherein the nucleating agent contains one or more selected from the group consisting of talc, sodium hydrogen carbonate, sodium hydrogen carbonate-citric acid mixture, sodium citrate, and calcium carbonate.

[11] The method for producing polypropylene-based resin foamed particles according to [9] or

[10] , wherein the foaming agent contains one or more selected from the group consisting of propane, butane, pentane, hexane, air, nitrogen, carbon dioxide gas, and water.

[12] A polypropylene-based resin foamed molded article composed of the polypropylene-based resin foamed particles according to any one of [1] to [8], wherein the polypropylene-based resin foamed molded article has a closed cell ratio of 30% or less, and the polypropylene-based resin foamed molded article has a density D (g / L) of 60 to 300 g / L, the compressive strength St (kPa) at 50% strain and the density D (g / L) satisfy the following relational expression (1), and the tensile fracture elongation is 10% or more. A polypropylene-based resin foamed molded article characterized by that.

Number

[13] A polypropylene-based resin foamed molded article composed of polypropylene-based resin foamed particles, wherein the polypropylene-based resin foamed particles are extrusion foamed particles containing a base resin containing 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure, and have a closed cell ratio of 30% or less, and the polypropylene-based resin foamed molded article has a density D (g / L) of 60 to 300 g / L, the compressive strength St (kPa) at 50% strain and the density D (g / L) satisfy the following relational expression (1), and the tensile fracture elongation is 10% or more. A polypropylene-based resin foamed molded article characterized by that.

Number

Example

[0064] Hereinafter, one or more embodiments of the present invention will be described in detail based on examples. Note that the present invention is not limited to these examples.

[0065] The evaluation and measurement methods carried out in the examples and comparative examples are as follows.

[0066] <Measurement of melting point of polypropylene-based resin> For the measurement of the melting point of the polypropylene-based resin, a differential scanning calorimeter DSC [manufactured by Seiko Instruments Inc., model DSC6200] was used. Specifically, 5 to 6 mg of the sample was heated from 40°C to 220°C at a heating rate of 10°C / min to be melted, and then crystallized by cooling from 220°C to 40°C at a cooling rate of 10°C / min. After that, the melting peak temperature in the DSC curve during the second heating obtained when heating from 40°C to 220°C at a heating rate of 10°C / min was taken as the melting point Tm2.

[0067] <Differential scanning calorimetry of polypropylene-based resin foamed particles> 5 to 6 mg of the obtained polypropylene-based resin foamed particles were melted by heating from 40°C to 300°C at a heating rate of 10°C / min using a differential scanning calorimeter DSC [manufactured by Seiko Instruments Inc., model DSC6200], and then crystallized by cooling from 300°C to 40°C at a cooling rate of 10°C / min. After that, DSC curves during the first heating and the second heating were obtained by heating from 40°C to 300°C at a heating rate of 10°C / min. 《Heat quantity ratio》 A line segment AB was drawn connecting the point (point A) corresponding to 100 °C on the DSC curve during the first temperature increase to the melting end point (point B), and the heat of fusion of the portion enclosed by the line segment AB and the DSC curve was calculated as the total heat of fusion Q1. A straight line parallel to the Y-axis was drawn on the DSC curve from the point (point C) corresponding to 130 °C on the line segment AB, and the intersection of this straight line and the DSC curve was designated as point D. Similarly, a straight line parallel to the Y-axis was drawn on the DSC curve from the point (point E) corresponding to 170 °C on the line segment AB, and the intersection of this straight line and the DSC curve was designated as point F. The heat of fusion of the portion enclosed by the line segments CD, CE, EF, and the DSC curve was calculated as the heat of fusion Q2 in the temperature range of 130 °C or higher and 170 °C or lower. When the melting end temperature was less than 170 °C, the heat of fusion of the portion enclosed by the line segments CD, CB, and the DSC curve was calculated as Q2. Using Q1 and Q2, the heat of fusion ratio was calculated by the following formula. Heat of fusion ratio (%) = Q2 × 100 / Q1 《Melting point》 The melting peak temperature obtained during the second temperature increase was taken as the melting point Tm2 of the polypropylene-based resin foamed particles.

[0068] <Melt flow rate (MFR)> It was measured in accordance with the provisions of Method B of JIS K 7210 under an orifice diameter of 2.0959 ± 0.005 mm, an orifice length of 8.000 ± 0.025 mm, at 230 °C, and a load of 2.16 kg. Specifically, in accordance with the provisions of Method B of JIS K 7210, using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho), the value was converted to the amount extruded in 10 minutes from the amount of resin extruded from the die in a certain period of time under 230 °C and 2.16 kg. The aforementioned certain period of time is 120 seconds when the melt flow rate exceeds 0.5 g / 10 min and is 1.0 g / 10 min or less; 60 seconds when it exceeds 1.0 g / 10 min and is 3.5 g / 10 min or less; 30 seconds when it exceeds 3.5 g / 10 min and is 10 g / 10 min or less; 10 seconds when it exceeds 10 g / 10 min and is 25 g / 10 min or less; 5 seconds when it exceeds 25 g / 10 min and is 100 g / 10 min or less; and 3 seconds when it exceeds 100 g / 10 min.

[0069] <Melt tension> A capillary graph (manufactured by Toyo Seiki Seisakusho) equipped with an attachment for measuring melt tension and having a cylinder with a diameter of 10 mm with an orifice with a diameter of 1 mm and a length of 10 mm attached to the tip was used. When lowered at 200 °C and a piston lowering speed of 10 mm / min, the strand discharged from the die was hung on a pulley with a load cell 350 mm below and pulled at a speed of 1 m / min. After stabilization, the pulling speed was increased at a rate that reached a speed of 200 m / min in 4 minutes, and the load (unit: cN) applied to the pulley with the load cell when the strand broke was taken as the melt tension. In the case where the strand did not break, the melt tension was considered unmeasurable.

[0070] <Melt fracture speed> In the measurement of the melt tension, the pulling speed was increased and the pulling speed when the strand broke was measured and taken as the melt fracture speed. In the case where the strand did not break, the melt fracture speed was considered unmeasurable. The melt fracture speed is an index of the ductility of the molten resin during foaming.

[0071] <Preparation of samples for measuring the melt tension and melt fracture speed of polypropylene-based resin foamed particles> The melt tension and melt fracture speed of polypropylene-based resin foamed particles were measured using a sample obtained by returning the foamed particles or the foamed molded article to a resin mass. Since the resin physical properties do not change between the foamed particles and the foamed molded article, either can be used for the measurement. The foamed particles were placed in a dryer adjusted to a temperature of (Tm2 + 10 °C) based on the melting point Tm2 of the foamed particles, and the inside of the dryer was depressurized with a vacuum pump to -0.05 MPa (gage pressure) to -0.10 MPa (gage pressure) over 5 to 10 minutes, and then left in the dryer for 30 minutes to form a resin mass while removing the air inside the foamed particles. If the resins adhered to each other and the mass was large, the resin mass may be finely cut with scissors or the like, or pulverized with a mixer or the like. In the case of the foamed molded article, after cutting the molded article finely with scissors, a slicer, etc., it was pulverized with a mixer, etc. The fragments of the pulverized foamed molded article were put into a dryer whose temperature was adjusted to (Tm2 + 10°C) based on the melting point Tm2 of the foamed particles, and the inside of the dryer was depressurized with a vacuum pump over 5 to 10 minutes until it reached -0.05 MPa (gauge pressure) to -0.10 MPa (gauge pressure), and then left in the dryer for 30 minutes to obtain a resin mass while removing the air from the foamed molded article. When the resins adhered to each other and the mass was large, the resin mass may be finely cut with scissors or pulverized with a mixer, etc.

[0072] <Apparent porosity of polypropylene-based resin foamed particles> The volume of the polypropylene-based resin foamed particles obtained according to the method described in Procedure C of ASTM D2856-87 was designated as Vc (cm 3 ), and the apparent porosity (%) was determined according to the following formula. Apparent porosity (%) = ((Va - Vc) × 100) / Va Incidentally, Vc was measured using an air comparison type specific gravity meter model 1000 manufactured by Tokyo Science Co., Ltd. Also, the volume Va (cm 3 ) was the apparent volume of the polypropylene-based resin foamed particles obtained by submerging the total amount of the polypropylene-based resin foamed particles after measuring Vc with the air comparison type specific gravity meter into a graduated cylinder containing ethanol and obtaining it from the increase in the liquid level of the graduated cylinder (water immersion method).

[0073] <Bulk density of polypropylene-based resin foamed particles> The polypropylene-based resin foamed particles were collected with a 1 L measuring cup, and after scraping the powder surface, its mass was measured, and the bulk density was determined by dividing the mass (g) by the volume of 1 L.

[0074] <Average cell diameter of polypropylene-based resin foamed particles> Using a double-edged razor [made of feathers, high stainless steel double-edged], taking sufficient care not to break the bubble film (cell membrane), cut approximately the center of the polypropylene-based resin foam particles, and observe the cut surface at a magnification of 100 times using a microscope [Keyence Corporation, VHX-100] to obtain an image. In the obtained image, draw a line segment corresponding to a length of 1000 μm in the portion excluding the surface layer of the polypropylene-based resin foam particles, measure the number of bubbles (cells) n through which the line segment passes, and calculate the cell diameter as "1000 / n" (μm). The same was done for 10 polypropylene-based resin foam particles, and the average value of the calculated cell diameters was taken as the average cell diameter.

[0075] <Expansion ratio of polypropylene-based resin foam particles> After measuring the mass w (g) of the polypropylene-based resin foam particles, immerse them in a graduated cylinder containing ethanol, and measure the volume v (cm 3 ) by the increase in the water level in the graduated cylinder (water immersion method), calculate the true specific gravity ρb = w / v of the polypropylene-based resin foam particles, and further calculate it as the ratio (ρr / ρb) with the density ρr of the polypropylene-based resin before foaming.

[0076] <Moldability of polypropylene-based resin foam molded body> 《Molding method》 Using a polyolefin foam molding machine manufactured by Teubert Maschinenbau GmbH, in a block-shaped mold (381 mm long × 381 mm wide × 60 mm thick), set the gap between the molds (hereinafter referred to as cracking) to 18 mm (cracking rate 30%), fill the polypropylene-based resin foam particles into the mold, and then compress them so that the mold thickness becomes 60 mm. Next, expel the air in the mold with steam at 0.15 MPa (gauge pressure), and then heat and mold both sides for 5 seconds using steam at a predetermined pressure to obtain a polypropylene-based resin foam molded body. At this time, the molded body was produced by increasing the pressure of the steam by 0.01 MPa from 0.32 MPa (gauge pressure). The pressure of the steam was increased up to a maximum of 0.44 MPa (gauge pressure). 《Evaluation method》 The obtained foamed molded article was left in a drying chamber at 75°C for 24 hours and then left at room temperature for 4 hours to obtain an object to be evaluated. The fusion rate and surface unevenness of the foamed molded article to be evaluated were evaluated. The lowest steam pressure at which the fusion rate and surface unevenness passed was defined as the minimum molding pressure, and after molding, the highest steam pressure within the range where demolding was possible with only air was defined as the maximum molding pressure. The difference between the maximum molding pressure and the minimum molding pressure was defined as the molding process heating range, and the moldability was evaluated based on the magnitude of this value. A: The moldable width is 0.04 MPa or more, and the moldability is good B: The moldable width is 0.02 MPa or more and less than 0.04 MPa, and the moldability is somewhat good C: The moldable width is less than 0.02 MPa, and the moldability is poor (1) Fusion rate evaluation A crack about 5 mm deep was made on the surface of the obtained foamed molded article with a knife, the foamed molded article in the mold was cut along the crack, the fracture surface was observed, the ratio of the number of fractured particles to the total number of particles on the fracture surface was determined, and the fusion rate of the molded article was evaluated. A case where the fusion rate was 80% or more was considered to pass. (2) Surface unevenness evaluation At the center of the largest surface area of the obtained foamed molded article, it was evaluated whether there was a gap between the foamed particles. If the steam pressure during in-mold foaming molding was insufficient, the gap between the foamed particles would not be filled sufficiently. A case where there were few gaps between the foamed particles and the surface was beautiful was considered to pass.

[0077] <Energy absorption performance of polypropylene-based resin foamed molded article> (1) Density of polypropylene-based resin foamed molded article The mass W (g) of the polypropylene-based resin foamed molded article was measured, and the longitudinal, lateral, and thickness dimensions were measured with calipers to calculate the volume V (cm 3 )), and the density of the foamed molded article was determined by W / V. However, it was converted so that the unit became g / L. Based on the following formula 2, the density coefficient was calculated.

Equation

[0078] <Tensile elongation of the polypropylene-based resin foam molded body> Based on ISO1798, the tensile elongation of the polypropylene-based resin foam molded body was measured, and the flexibility was evaluated according to the following criteria. Good: The tensile elongation is 10% or more, and it does not crack even when deformed upon receiving an impact or the like. Poor: The tensile elongation is less than 10%, and it cracks even with a slight deformation upon receiving an impact or the like.

[0079] In the examples and comparative examples, the polypropylene-based resins shown in Table 1 below were used.

[0080]

Table 1

[0081] (Examples 1 to 7) [Production of polypropylene-based resin foam particles] To a total of 100 parts by mass of a raw material resin (polypropylene-based resin) of the type shown in Table 2 below, 0.2 part by mass of a nucleating agent (talc) was blended in a tumbler, and then the blend was fed into an extruder (a twin-screw extruder with a diameter of 26 mm) set at the temperature of the first stage shown in Table 2. 3.0 parts by mass of carbon dioxide gas as a foaming agent was injected into the extruder, and the blend was melt-kneaded. Next, after the melt-kneaded product was passed through a melt cooler set at the temperature of the second stage shown in Table 2 and cooled, the melt-kneaded product was extruded at an atmospheric pressure from a die equipped with three pores each having a diameter of 0.8 mm at the tip of the melt cooler at a discharge rate of 10 kg / hour. Water was filled in a chamber attached to the die tip so as to have the water pressure (gauge pressure) shown in Table 2 in contact with the die, and the melt-kneaded product extruded from the die was cut in water at 80°C so that the mass per particle was 1.5 to 2.0 mg / particle to obtain polypropylene-based resin foamed particles.

[0082] [Production of Polypropylene-Based Resin Foamed Molding] Using a polyolefin foaming molding machine manufactured by Teubert Maschinenbau GmbH, cracking was set to 18 mm (cracking rate: 30%) in a block-shaped mold (length: 381 mm, width: 381 mm, thickness: 60 mm), and after filling the polypropylene-based resin foamed particles into the mold, it was compressed so that the mold thickness became 60 mm. Next, the air in the mold was expelled with steam at 0.15 MPa (gauge pressure), and then, by heating and molding for 5 seconds using steam at the minimum molding pressure (gauge pressure) shown in Table 2, a polypropylene-based resin foamed molding was obtained.

[0083] (Comparative Examples 1 to 14) In [Production of Polypropylene-Based Resin Foamed Particles], the resins shown in Tables 3 and 4 below were used as the raw material resin, the temperature of the second stage was set as shown in Tables 3 and 4, and the water pressure (gauge pressure) in the chamber was made as shown in Tables 3 and 4. Polypropylene-based resin foamed particles and polypropylene-based resin foamed moldings were produced in the same manner as in Example 1, except that steam at the minimum molding pressure (gauge pressure) shown in Tables 3 and 4 below was used in [Production of Polypropylene-Based Resin Foamed Molding].

[0084] The evaluation results of the polypropylene-based resin foamed particles and the polypropylene-based resin foamed molded articles obtained in the examples and comparative examples are shown in Tables 2 to 4 below.

[0085] Figure 2 shows the DSC curve obtained during the first heating in the differential scanning calorimetry measurement of the polypropylene-based resin foamed particles obtained in Example 1. From Figure 2, it can be seen that during the first heating, there is only one melting peak in the temperature range of 130°C or higher and 170°C or lower. Although the DSC curves of the polypropylene-based resin foamed particles of Examples 2 to 7 are not shown, it was similarly confirmed that during the first heating, there is only one melting peak in the temperature range of 130°C or higher and 170°C or lower.

[0086] [Table 2]

[0087] [Table 3]

[0088] [Table 4]

[0089] As can be seen from the data in Table 2, in Examples 1 to 7, by using a polypropylene-based resin in which branched propylene having a predetermined melt tension and an α-olefin-propylene random copolymer having a predetermined melting point and MFR are blended at a specific ratio as the base resin, in the first heating of the differential scanning calorimetry measurement of the obtained foamed particles, there is only one melting peak in the temperature range of 130°C or higher and 170°C or lower, and the heat of fusion in the temperature range of 130°C or higher and 170°C or lower is 90.0% or more of the total heat of fusion, the melting point Tm2 is 155.0°C or higher and 160.0°C or lower, the melt fracture rate is 30.0 m / min or higher and 70.0 m / min or lower, the closed cell ratio is 30% or lower, and by using the foamed particles, a foamed molded article with good energy absorption performance and high flexibility could be obtained with good moldability.

[0090] On the other hand, as can be seen from the data in Table 3, in Comparative Example 1 without blending an α-olefin-propylene random copolymer, and Comparative Examples 2 and 4 with a small blending amount, the melting point Tm2 of the foamed particles was higher than 160.0 °C and the melt fracture rate was less than 30.0 m / min. Therefore, the foamed molded article produced using the foamed particles had low tensile elongation and poor flexibility. In Comparative Examples 3 and 5 with a large blending amount of the α-olefin-propylene random copolymer, the melting point Tm2 of the foamed particles was less than 155.0 °C and the closed cell ratio exceeded 30%. Therefore, even when the pressure of water vapor was increased to 0.44 MPa (gauge pressure), a molded article with a fusion rate and surface unevenness meeting the standards could not be obtained. In Comparative Examples 6 and 7 using an α-olefin-propylene random copolymer with an MFR of less than 5 g / 10 min, since the melt fracture rate was less than 30.0 m / min, the foamed molded article produced using the foamed particles had low tensile elongation and poor flexibility. Further, in Comparative Example 8 using an α-olefin-propylene random copolymer with an MFR of less than 5 g / 10 min, since the closed cell ratio of the foamed particles exceeded 30%, the moldability, energy absorption performance, and flexibility of the foamed molded article were poor. In Comparative Example 9 using an α-olefin-propylene random copolymer with a melting point of less than 135 °C, since the melt fracture rate was less than 30.0 m / min, the flexibility of the foamed molded article was poor. Further, in Comparative Example 10 using an α-olefin-propylene random copolymer with a melting point of less than 135 °C, since the molding temperature greatly exceeded the melting point of the random copolymer, the closed cell ratio deteriorated in the molding process, and the resulting molded article shrank, with poor moldability and energy absorption performance. Further, in Comparative Example 11 using an α-olefin-propylene random copolymer with a melting point of less than 135 °C, the shrinkage of the molded article became even more significant, and even when the pressure of water vapor was increased to 0.44 MPa (gauge pressure), a molded article with a fusion rate and surface unevenness meeting the standards could not be obtained. In Comparative Examples 12 to 13 using an ethylene-propylene block polymer with an MFR of less than 5 g / 10 min, since the melting point Tm2 of the foamed particles was higher than 160.0 °C, the flexibility of the foamed molded body was poor. Further, in Comparative Example 14 using an ethylene-propylene block polymer with an MFR of less than 5 g / 10 min, since the melting point Tm2 of the foamed particles was higher than 160.0 °C and the closed cell ratio exceeded 30%, even when the pressure of steam was increased to 0.44 MPa (gauge pressure), a molded body with a fusion rate and surface gloss that passed the inspection could not be obtained.

Claims

1. A polypropylene-based resin foam particle in which the base resin contains a polypropylene-based resin, wherein the polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer having a melting point of 135°C or more and 155°C or less, the α-olefin-propylene random copolymer has a melt flow rate of 5 g / 10 min or more and 50 g / 10 min or less, in the first heating of differential scanning calorimetry of the polypropylene-based resin foam particles, there is only one melting peak in the temperature range of 130°C or more and 170°C or less, and the heat of fusion in the temperature range of 130°C or more and 170°C or less is 90.0% or more of the total heat of fusion, the melting point Tm2 indicated by the value of the melting peak during the second heating of differential scanning calorimetry of the polypropylene-based resin foam particles is 155.0°C or more and 160.0°C or less, the melt fracture rate of the polypropylene-based resin foam particles at a temperature of 200°C is 30.0 m / min or more and 70.0 m / min or less, and the polypropylene-based resin foam particles have a closed cell ratio of 30% or less. A polypropylene-based resin foam particle characterized by this.

2. The polypropylene-based resin foam particle according to claim 1, wherein the polypropylene-based resin foam particle is an extrusion foam particle.

3. The polypropylene-based resin foam particle according to claim 1 or 2, wherein the bulk density of the polypropylene-based resin foam particle is 60 g / L or more and 300 g / L or less.

4. The polypropylene-based resin foam particle according to any one of claims 1 to 3, wherein the average cell diameter of the polypropylene-based resin foam particle is 100 μm or more and 500 μm or less.

5. The polypropylene-based resin foam particle according to any one of claims 1 to 4, wherein the propylene homopolymer having a branched structure has a melt tension of 10 cN or more and 50 cN or less.

6. The polypropylene-based resin foam particle according to any one of claims 1 to 5, wherein the propylene homopolymer having a branched structure has a melt flow rate of 0.5 g / 10 min or more and 5 g / 10 min or less.

7. The polypropylene-based resin foam particle according to any one of claims 1 to 6, wherein the propylene homopolymer having a branched structure has a melting point of 150°C or more and 165°C or less.

8. A method for producing polypropylene-based resin foam particles, A base resin containing a polypropylene-based resin is melt-kneaded together with a nucleating agent and a foaming agent, and then extruded. The extruded melt-kneaded product is cut to obtain polypropylene-based resin foamed particles. The polypropylene-based resin contains 40% by mass or more and 85% by mass or less of a propylene homopolymer having a branched structure and 15% by mass or more and 60% by mass or less of an α-olefin-propylene random copolymer. The propylene homopolymer having the branched structure has a melt tension of 10 cN or more and 50 cN or less. The α-olefin-propylene random copolymer has a melting point of 135°C or more and 155°C or less and a melt flow rate of 5 g / 10 min or more and 50 g / 10 min or less. A method for producing polypropylene-based resin foamed particles, characterized by the above.

9. The method for producing polypropylene-based resin foamed particles according to claim 8, wherein the nucleating agent contains one or more selected from the group consisting of talc, sodium hydrogen carbonate, a sodium hydrogen carbonate-citric acid mixture, sodium citrate, and calcium carbonate.

10. The method for producing polypropylene-based resin foamed particles according to claim 8 or 9, wherein the foaming agent contains one or more selected from the group consisting of propane, butane, pentane, hexane, air, nitrogen, carbon dioxide gas, and water.

11. A polypropylene-based resin foamed molded body composed of the polypropylene-based resin foamed particles according to any one of claims 1 to 7. The polypropylene-based resin foamed molded body has a density D (g / L) of 60 to 300 g / L, a compressive strength St (kPa) at 50% strain and the density D (g / L) satisfy the following relational expression (1), and a tensile fracture elongation of 10% or more. A polypropylene-based resin foamed molded body, characterized by the above. 【Number 1】

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