Polypropylene resin foam particles, their production method, and polypropylene resin foam molded article

Abstract

The present invention relates to polypropylene resin foam particles, the base resin of which has polypropylene resin as the main component, wherein the polypropylene resin foam particles are characterized in that: the polypropylene resin foam particles have only one melting peak in the temperature range of 130-170°C inclusive in the first temperature rise in differential scanning calorimetry and the melting energy in the temperature range 130-170°C inclusive is 90% or more of the total melting energy; the melting point Tm represented by the value of the melting peak obtained by the second temperature rise in differential scanning calorimetry is 159-170°C inclusive; the fusion fracture rate at a temperature of 200°C is 5-45 m / min; and the open cell ratio is 15% or lower. Provided thereby are polypropylene resin foam particles with which it is possible to obtain a polypropylene resin foam molded article having high heat resistance as well as good moldability, a method for producing the same, and a polypropylene resin molded article.

Description

[Technical field]

[0001] The present invention relates to expanded polypropylene resin particles, a production method thereof, and expanded molded polypropylene resin articles. [Background technology]

[0002] An in-mold foam molded article obtained by filling a mold with expanded polypropylene resin particles and heat-molding with water vapor has the advantages of an in-mold foam molded article, such as the freedom in shape, light weight, heat insulation, etc. Due to these characteristics, the in-mold foam molded article obtained using the expanded polypropylene resin particles is used for various purposes such as heat insulation materials, cushioning packaging materials, automobile interior parts, and core materials for automobile bumpers. For example, Patent Document 1 describes polypropylene resin pre-expanded particles that use a polypropylene resin having a melt flow rate (also referred to as melt index) of 3 g / 10 min or more and 20 g / 10 min or less as a base resin, have an expansion ratio of 5 times or more and 45 times or less, and have two melting points, with a higher melting point of 150° C. or more and a lower melting point of less than 137° C., as measured by a differential scanning calorimeter. Patent Document 2 describes polypropylene resin pre-expanded particles containing a hydrophilic compound and a polypropylene resin base resin containing 85 to 99 mass% of a polypropylene resin having a melt flow rate of 3 g / 10 min to 20 g / 10 min and a melting point of 145° C. to 165° C. In addition, it describes that the polypropylene resin pre-expanded particles have multiple heat of fusion peaks. Patent Document 3 describes pre-expanded polypropylene resin particles using a modified polypropylene resin, in which the loss tangent tanδ at an angular frequency of 0.1 rad / s in dynamic viscoelasticity measurement at 200°C and the melt fracture take-up speed at 200°C satisfy a predetermined relationship.

[0003] In order to improve the heat resistance of polypropylene-based resin foamed moldings, a propylene homopolymer is preferably used as the base resin. For example, Patent Document 4 proposes polypropylene-based resin foamed particles using a polypropylene-based resin as the base resin having a melting point of 155°C or more, a tensile yield strength of 31 MPa or more, a tensile breaking elongation of 20% or more, and a molecular weight distribution (Mw / Mn) of 4.4 or more. Patent Document 5 proposes expanded polypropylene resin particles obtained by expanding a resin composition having a melt tension of 5 to 30 g at 230°C and containing a linear polypropylene resin as a main component by 10 times or more using a blowing agent containing at least carbon dioxide in a supercritical state, and cutting the resulting strands into particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2009 / 051035 [Patent Document 2] International Publication No. 2017 / 030124 [Patent Document 3] International Publication No. 2018 / 016399 [Patent Document 4] JP 2003-313353 A [Patent Document 5] JP 2007-308560 A Summary of the Invention [Problem to be solved by the invention]

[0005] Particularly in automotive applications, polypropylene resin foam molded articles are being widely adopted with the main objective of reducing the weight of vehicles. However, when polypropylene resin foam molded articles using the polypropylene resin foam particles described in the cited documents 1 to 3 are exposed to high temperatures around the engine, etc., they suffer from thermal shrinkage and cannot withstand repeated use. Therefore, there is a demand for foam molded articles with higher heat resistance, specifically, foam molded articles that hardly undergo thermal shrinkage even in the temperature range of 130 to 140°C. In addition, expanded beads using polypropylene resins with high melting points such as propylene homopolymers as the base resin require too high a molding pressure to be molded using a normal molding machine, but in Reference 4, the molding pressure is reduced by treating with an organic peroxide in an autoclave. However, the foaming temperature is high, and if the foaming temperature is increased by steam, the foaming temperature may not be reached, making mass production difficult, and if the foaming temperature is increased by oil, the production cycle becomes very long because it takes time to increase the temperature and cool, resulting in a problem of poor productivity. As proposed in Reference 5, when polypropylene resin expanded beads are produced by the extrusion foaming method, the expanded beads may become open cells (the open cell ratio increases), and moldability may be poor.

[0006] In order to solve the above-mentioned problems in the conventional art, the present invention provides polypropylene-based resin foamed beads capable of giving polypropylene-based resin foamed molded articles having high heat resistance and good moldability, a method for producing the same, and polypropylene-based resin foamed molded articles. [Means for solving the problem]

[0007] In one or more embodiments, the present invention relates to expanded polypropylene-based resin beads, the main component of which is a base resin, characterized in that the expanded polypropylene-based resin beads have only one melting peak in a temperature range of 130°C to 170°C in a first heating run in differential scanning calorimetry, and the heat of fusion in the temperature range of 130°C to 170°C is 90% or more of the total heat of fusion, the expanded polypropylene-based resin beads have a melting point Tm2 indicated by the melting peak value obtained in a second heating run in differential scanning calorimetry of the expanded polypropylene-based resin beads is 159°C to 170°C, the expanded polypropylene-based resin beads have a melt rupture speed at a temperature of 200°C of 5 m / min to 45 m / min, and the expanded polypropylene-based resin beads have an open cell ratio of 15% or less.

[0008] In one or more embodiments, the present invention relates to a method for producing expanded polypropylene-based resin beads, which comprises melt-kneading a base resin mainly composed of a polypropylene-based resin and a blowing agent, extruding the mixture, and cutting the extruded molten mixture to obtain expanded polypropylene-based resin beads, and the melt-kneading is performed in two stages, with the temperature in the second stage being lower than the temperature in the first stage.

[0009] In one or more embodiments, the present invention relates to a polypropylene-based resin foamed molded article comprising the above-mentioned polypropylene-based resin foamed particles. Effect of the Invention

[0010] The present invention provides expanded polypropylene resin particles that can give expanded polypropylene resin articles having high heat resistance and good moldability. According to the method for producing expanded polypropylene resin beads of the present invention, expanded polypropylene resin beads capable of giving expanded polypropylene resin molded articles having high heat resistance and good moldability can be produced simply and with good productivity. The present invention can also provide a polypropylene resin foam molded article having good heat resistance. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram illustrating the ratio of the heat of fusion in a temperature range of 130° C. or more and 170° C. or less to the total heat of fusion (heat of fusion ratio) in a differential scanning calorimetry curve (DSC curve) obtained during the first heating in differential scanning calorimetry measurement for the expanded polypropylene resin beads according to one or more embodiments of the present invention. [Diagram 2] FIG. 2 is a DSC curve obtained during the first temperature rise in differential scanning calorimetry of the expanded polypropylene resin beads obtained in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present inventors have conducted extensive research to solve the above problems. As a result, it has been found that in expanded polypropylene resin particles (hereinafter also simply referred to as "expanded particles") whose base resin is mainly composed of a polypropylene resin, there is only one melting peak in the temperature range of 130°C to 170°C in the first heating in differential scanning calorimetry (hereinafter, the value of the melting peak may be referred to as Tm1), and the heat of fusion in the temperature range of 130°C to 170°C is the total heat of fusion (hereinafter, also simply referred to as "heat of fusion ratio"). the melting point Tm2, ​​which is indicated by the melting peak value during the second heating in differential scanning calorimetry, is 159°C or higher and 170°C or lower; the melt rupture speed at a temperature of 200°C is 5 m / min or higher and 45 m / min or lower; and the open cell rate is 15% or lower, the polypropylene resin foamed molded article (hereinafter also simply referred to as "foamed molded article") using the polypropylene resin foamed particles has high heat resistance and good moldability.

[0013] In one or more embodiments of the present invention, the differential scanning calorimeter curve (DSC curve) of the polypropylene-based resin expanded particles means all of the DSC curves (first heating → cooling → second heating) obtained by using a differential scanning calorimeter to heat the polypropylene-based resin expanded particles from 40 ° C. to 300 ° C. at a heating rate of 10 ° C. / min to melt them, then cooling them from 300 ° C. to 40 ° C. at a heating rate of 10 ° C. / min to crystallize them, and then heating them from 40 ° C. to 300 ° C. at a heating rate of 10 ° C. / min. As the differential scanning calorimeter, for example, DSC6200 type manufactured by Seiko Instruments Inc. can be used. In addition, for measuring the differential scanning calorimeter curve, a foamed molded product may be used as a sample instead of the foamed particles.

[0014] The polypropylene-based resin expanded particles in one or more embodiments of the present invention have only one melting peak in the temperature range of 130° C. or more and 170° C. or less in the DSC curve obtained in the first heating, and the melting peak temperature is the melting point Tm1. Usually, when the polypropylene-based resin expanded particles are produced by the extrusion foaming method, the DSC curve in the first heating has only one melting peak in the temperature range of 130° C. or more and 170° C. or less, except in the case where resins having low compatibility are blended.

[0015] In one or more embodiments of the present invention, the heat of fusion in the temperature range of 130°C to 170°C in the DSC curve obtained by the first heating of the polypropylene-based resin expanded beads is 90% or more of the total heat of fusion, preferably 92% or more, more preferably 92.5% or more, even more preferably 93% or more, and particularly preferably 93.5% or more. When the heat of fusion ratio in the temperature range of 130°C to 170°C is within the above-mentioned range, a foamed molded product with good heat resistance and moldability can be obtained. In addition, if the heat of fusion ratio in the temperature range of less than 130°C increases, the heat resistance may be deteriorated, and if the heat of fusion ratio in the temperature range of more than 170°C increases, the moldability may be deteriorated. In addition, although not particularly limited, for example, from the viewpoint of improving heat resistance, the heat of fusion in the temperature range of 130°C to 170°C in the DSC curve obtained by the first heating of the polypropylene-based resin expanded beads may be 100% or less of the total heat of fusion, or may be 97% or less.

[0016] In one or more embodiments of the present invention, the ratio of heat of fusion in the temperature range of 130° C. or more and 170° C. or less of the DSC curve obtained in the first heating can be calculated as follows. <Heat ratio of fusion> As shown in FIG. 1, a line segment AB is drawn from a point (point A) corresponding to 100°C on the DSC curve obtained in the first heating to the melting end point (point B), and the heat of fusion of the part surrounded by the line segment AB and the DSC curve is calculated and defined as the total heat of fusion Q1. A straight line parallel to the Y axis is drawn on the DSC curve from a point (point C) corresponding to 130°C on the line segment AB, and the intersection point of the line and the DSC curve is defined as point D. Similarly, a straight line parallel to the Y axis is drawn on the DSC curve from a point (point E) corresponding to 170°C on the line segment AB, and the intersection point of the line and the DSC curve is defined as point F. The heat of fusion of the part surrounded by the line segments CD, CE, EF, and the DSC curve is calculated and defined as the heat of fusion Q2 in the temperature range of 130°C to 170°C. Note that when the melting end temperature is less than 170°C, the heat of fusion of the part surrounded by the line segments CD, CB, and the DSC curve is calculated and defined as Q2. Using Q1 and Q2, calculate the heat of fusion ratio using the following formula. If a peak derived from a resin other than the polypropylene resin exists within the range of Q1, the heat of fusion of that resin is also included in Q1. Melting heat ratio (%) = Q2 x 100 / Q1 In addition, when a melting peak from a resin other than the polypropylene resin exists independently outside the range of Q1 on the DSC curve, the heat of fusion of only that melting peak is calculated as the heat of fusion Q3. Using Q1, Q2, and Q3, calculate the heat of fusion ratio using the following formula. Melting heat ratio (%) = Q2 x 100 / (Q1 + Q3)

[0017] In one or more embodiments of the present invention, the melting peak temperature of the DSC curve in the second heating of the polypropylene-based resin expanded beads is the melting point Tm2, ​​and Tm2 is 159°C or higher and 170°C or lower. When the Tm2 of the polypropylene-based resin expanded beads is 159°C or higher, a foamed molded product having high heat resistance, for example, a small dimensional change rate at 140°C, can be obtained. The Tm2 of the polypropylene-based resin expanded beads is preferably 160°C or higher, more preferably 161°C or higher. When the Tm2 of the polypropylene-based resin expanded beads is 170°C or lower, the water vapor pressure during in-mold foaming can be reduced. The melting point Tm2 of the polypropylene-based resin expanded beads is preferably 165°C or lower. When the melting point Tm2 of the polypropylene-based resin expanded beads is too high, the water vapor pressure required to obtain a good molded product in in-mold foaming becomes too high, making it difficult to mold using a molding machine usually used for molding polypropylene-based resin expanded beads.

[0018] In one or more embodiments of the present invention, the open cell ratio of the expanded polypropylene resin particles is 15% or less, preferably 13% or less, more preferably 11% or less, and even more preferably 10% or less. When the open cell ratio of the expanded particles is within the above-mentioned range, the moldability is good, shrinkage is difficult, and the static compressive strength of the foamed molded product can be increased. In addition, although not particularly limited, the open cell ratio of the expanded polypropylene resin particles may be, for example, 0% or more, or 3% or more.

[0019] In one or more embodiments of the present invention, the melt rupture speed of the expanded polypropylene resin beads at a temperature of 200°C (hereinafter, also simply referred to as "melt rupture speed") is 5 m / min or more and 45 m / min or less. When the melt rupture speed of the expanded beads is within the above-mentioned range, the open cell ratio is reduced and moldability is improved. The melt rupture speed of the expanded beads is preferably 43.5 m / min or less, more preferably 42 m / min or less, and even more preferably 40.5 m / min or less. In addition, the melt rupture speed of the expanded beads is preferably 10 m / min or more, and more preferably 20 m / min or more.

[0020] In one or more embodiments of the present invention, the melt rupture rate of the expanded polypropylene resin beads at a temperature of 200° C. can be measured using a sample prepared by returning the expanded beads or the expanded molded product to a resin mass. Since the resin physical properties do not change between the expanded beads and the expanded molded product, either one may be used for the measurement. <Preparation of sample (resin block)> The expanded beads are placed in a dryer whose temperature has been adjusted to Tm2+10°C based on the melting point Tm2 of the expanded beads, and the pressure inside the dryer is reduced to -0.05MPa (cage pressure) to -0.10MPa (cage pressure) over 5 to 10 minutes using a vacuum pump, after which the beads are left in the dryer for 30 minutes to remove the air from inside the expanded beads and form a resin mass. If the resin particles stick together and the mass is large, the resin mass may be cut into small pieces with scissors or crushed with a mixer. In the case of foamed molded bodies, the molded bodies were cut into small pieces with scissors or a slicer, etc., and then crushed in a mixer, etc. The crushed pieces of foamed molded bodies 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 pressure inside the dryer was reduced to -0.05MPa (cage pressure) to -0.10MPa (cage pressure) using a vacuum pump over 5 to 10 minutes, and the dryer was left for 30 minutes to remove the air from the foamed molded bodies and form a resin mass. If the resins are stuck together and the mass is large, the resin mass may be cut into small pieces with scissors, etc., or crushed in a mixer, etc.

[0021] In one or more embodiments of the present invention, the polypropylene-based resin expanded particles preferably have a melt flow rate (MFR) of 1 g / 10 min to 10 g / 10 min, more preferably 2 g / 10 min to 9 g / 10 min, even more preferably 3 g / 10 min to 8 g / 10 min, and particularly preferably 4 g / 10 min to 7 g / 10 min. When the MFR of the polypropylene-based resin expanded particles is within the above-mentioned range, the surface beauty of the foamed molded article is improved and the productivity is also improved.

[0022] In one or more embodiments of the present invention, the MFR can be measured in accordance with the provisions of JIS K 7210, Method B, with an orifice diameter of 2.0959±0.005 mm, an orifice length of 8.000±0.025 mm, at 230° C., and under a load of 2.16 kg. The MFR of polypropylene-based resin foamed beads is measured using a sample obtained by returning the foamed beads or foamed molded article to a resin mass.

[0023] In one or more embodiments of the present invention, the melt tension of the expanded polypropylene resin beads is preferably 4.5 cN or more, more preferably 5.0 cN or more, even more preferably 5.5 cN or more, and particularly preferably 6.0 cN or more. When the melt tension of the expanded beads is within the above-mentioned range, the open cell ratio is easily reduced and the moldability is also good. On the other hand, from the viewpoint of the workability of extrusion foaming, the melt tension of the expanded polypropylene resin beads is preferably 30 cN or less, more preferably 25 cN or less. The melt tension of the expanded polypropylene resin beads can be measured by the method described in the Examples using a sample obtained by returning the expanded beads or the foamed molded product to a resin mass.

[0024] In one or more embodiments of the present invention, the loss tangent tan δ (hereinafter, also simply referred to as "tan δ") at an angular frequency of 0.1 rad / s in dynamic viscoelasticity measurement of the expanded polypropylene resin beads at 200°C is preferably 2.0 or more and less than 6.0, more preferably 2.0 or more and 5.5 or less, and even more preferably 2.0 or more and 5.0 or less. When the tan δ of the expanded beads is in the above-mentioned range, the open cell ratio tends to be low and the moldability is also good. In one or more embodiments of the present invention, tan δ can be measured, for example, using a viscoelasticity measuring device ARES manufactured by TA Instruments. Specifically, it can be measured by the method described in the examples.

[0025] In the polypropylene resin expanded beads according to one or more embodiments of the present invention, the base resin is mainly composed of a polypropylene resin. In one or more embodiments of the present invention, "mainly composed of a polypropylene resin" means that the polypropylene resin is contained in an amount of 90% by mass or more, preferably 95% by mass or more, more preferably 97% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass of polypropylene resin. Since the base resin is mainly composed of a polypropylene resin, the DSC curve of the expanded beads during the first heating is likely to have only one melting peak in the temperature range of 130°C to 170°C, and the heat of fusion in the temperature range of 130°C to 170°C is likely to be 90% or more of the total heat of fusion.

[0026] In the base resin of one or more embodiments of the present invention, the polypropylene resin preferably contains 60% by mass or more and 100% by mass or less of a polypropylene resin having a branched structure (hereinafter also referred to as a branched polypropylene resin X), more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The expanded beads are likely to satisfy the above-mentioned melting point Tm2, ​​melt rupture rate, and open cell rate.

[0027] In the base resin of one or more embodiments of the present invention, the polypropylene resin may contain a linear polypropylene resin in addition to the branched polypropylene resin X. For example, the polypropylene resin may contain 40% by mass or less, 35% by mass or less, or 30% by mass or less of the linear polypropylene resin. More specifically, in the base resin of one or more embodiments of the present invention, the polypropylene resin preferably contains 60% by mass or more and 100% by mass or less of the branched polypropylene resin X and 0% by mass or more and 40% by mass or less of the linear polypropylene resin, more preferably 65% ​​by mass or more and 100% by mass or less of the branched polypropylene resin X and 0% by mass or more and 35% by mass or less of the linear polypropylene resin, and even more preferably 70% by mass or more and 100% by mass or less of the branched polypropylene resin X and 0% by mass or more and 30% by mass or less of the linear polypropylene resin.

[0028] The linear polypropylene resin may be a crystalline propylene homopolymer, block copolymer, or random copolymer. As the propylene copolymer, a polymer containing 75% by mass or more of propylene is preferable because it maintains the crystallinity, rigidity, chemical resistance, and other characteristics of polypropylene resins. Monomers 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; cyclic olefins such as cyclopentene, norbornene, and tetracyclo[6,2,11,8,13,6]-4-dodecene; 5-methylene 2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, and other dienes; vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methylstyrene, vinyltoluene, divinylbenzene, and other vinyl monomers. In particular, ethylene and 1-butene are preferred from the viewpoints of improving cold brittleness resistance and being inexpensive. These may be used alone or in combination of two or more. From the viewpoint of increasing the heat resistance of the expanded beads and the expanded molded article, propylene homopolymers and / or propylene block copolymers are preferred. As the propylene block copolymer, for example, a propylene / ethylene block polymer is preferred.

[0029] The linear polypropylene resin has a melting point of preferably 145° C. or higher, more preferably 155° C. or higher, and even more preferably 160° C. or higher. The heat resistance of the expanded beads and the expanded molded article is easily improved. On the other hand, although not particularly limited, from the viewpoint of the water vapor pressure during in-mold expansion molding, for example, the melting point Tm of the linear polypropylene resin is preferably 170° C. or lower, and more preferably 166° C. or lower.

[0030] The linear polypropylene resin preferably has an MFR of 1 g / 10 min to 10 g / 10 min, more preferably 1.5 g / 10 min to 9 g / 10 min, and even more preferably 2 g / 10 min to 8 g / 10 min. When the MFR of the linear polypropylene resin is within the above range, the MFR of the expanded beads is likely to be within the above range, improving the surface aesthetics of the expanded molded article and improving productivity.

[0031] The linear polypropylene resin preferably has a tan δ of 2.0 to 7.0, more preferably 2.5 to 6.0, and even more preferably 3.0 to 5.0. When the linear polypropylene resin has a tan δ in the above-mentioned range, the expanded beads are likely to have a tan δ in the above-mentioned range, the open cell ratio is likely to be low, and moldability is also good.

[0032] The branched polypropylene resin X may be any resin having a branched structure, and is not particularly limited. For example, a modified polypropylene resin obtained by treating a linear polypropylene resin with radiation and / or reacting a linear polypropylene resin with a radical polymerization initiator can be used. In either case, a reaction with a functional unsaturated compound may be added or followed. From the viewpoint of ease of production and economical advantage, it is preferable to use a modified polypropylene resin in which a branched structure is introduced by reacting a linear polypropylene resin with a radical polymerization initiator.

[0033] Examples of the radical polymerization initiator generally include peroxides and azo compounds. Preferred are initiators capable of abstracting hydrogen from functional unsaturated compounds such as polypropylene resins and conjugated diene compounds described below. Generally, examples of the radical polymerization initiator include organic peroxides such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters. Among these, initiators having particularly high hydrogen abstraction ability are preferred, and examples thereof include 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; dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, t-butylcumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl- Examples of the peroxyester include dialkyl peroxides such as 2,5-di(t-butylperoxy)-3-hexyne, diacyl peroxides such as benzoyl peroxide, and peroxyesters such as t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy3,5,5-trimethylhexanoate, t-butylperoxyisopropylcarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. These may be used alone or in combination of two or more.

[0034] The amount of the radical polymerization initiator added is preferably 0.01 parts by mass or more and 10 parts by mass or less, and more preferably 0.05 parts by mass or more and 4 parts by mass or less, relative to 100 parts by mass of the linear polypropylene resin. If the amount of the radical polymerization initiator added is within the above range, efficient resin modification is possible.

[0035] As the functional unsaturated compound, for example, a bifunctional unsaturated compound or a polyfunctional unsaturated compound having a functionality of two or more can be used. A bifunctional unsaturated compound that can be polymerized with the aid of a free radical is preferable. As the bifunctional unsaturated compound, for example, a divinyl compound, an allyl compound, a conjugated diene compound, an aromatic and / or aliphatic bis(maleimide)bis(citraconimide), etc. can be mentioned. As the divinyl compound, for example, divinylaniline, m-divinylbenzene, p-divinylbenzene, divinylpentane, and divinylpropane can be mentioned. As the allyl compound, for example, allyl acrylate, allyl methacrylate, allyl methyl maleate, and allyl vinyl ether can be mentioned. As the conjugated diene compound, for example, butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4-hexadiene can be mentioned. 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 tends to proceed uniformly.

[0036] The conjugated diene compound may be used in combination with a copolymerizable monomer, for example, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal acrylates, metal methacrylates, acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate.

[0037] The amount of the conjugated diene compound added is preferably 0.01 parts by mass or more and 20 parts by mass or less, more preferably 0.05 parts by mass or more and 5 parts by mass or less, and even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, relative to 100 parts by mass of the linear polypropylene resin. When the amount of the conjugated diene compound added is within the above-mentioned range, the effect of modification can be exerted and the cost can be reduced.

[0038] Examples of devices for reacting the linear polypropylene resin, the functional unsaturated compound (e.g., a conjugated diene compound) and the radical polymerization initiator include kneaders such as rolls, co-kneaders, 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.

[0039] There is no particular restriction on the order or method of mixing and kneading (stirring) the linear polypropylene resin, the functional unsaturated compound (e.g., conjugated diene compound) and the radical polymerization initiator. After mixing the linear polypropylene resin, the functional unsaturated compound (e.g., conjugated diene compound) and the radical polymerization initiator, the mixture may be melt-kneaded (stirred), or after melt-kneading (stirring) the linear polypropylene resin, the functional unsaturated compound (e.g., conjugated diene compound) or the radical initiator may be mixed simultaneously or separately, all at once or in portions. The temperature of the kneader (stirrer) is preferably 130°C or higher and 300°C or lower, in that the linear polypropylene resin melts and does not thermally decompose. The time for melt-kneading is generally preferably 1 minute or higher and 60 minutes or lower.

[0040] The branched polypropylene resin X preferably has a melt tension of more than 13.8 cN, more preferably 14.0 cN or more, and even more preferably 14.2 cN or more. The open cell ratio and melt rupture rate of the expanded beads are likely to satisfy the above-mentioned ranges, and the moldability is good. On the other hand, from the viewpoint of workability of extrusion foaming, the branched polypropylene resin X preferably has a melt tension of 50 cN or less, and more preferably 30 cN or less.

[0041] The branched polypropylene resin X preferably has a tan δ of less than 3.3, more preferably 3.0 or less, even more preferably 2.5 or less, even more preferably 2.0 or less, and particularly preferably 1.5 or less. When the tan δ of the branched polypropylene resin X is in the above-mentioned range, the open cell ratio and melt rupture rate of the expanded beads are likely to satisfy the above-mentioned ranges, and the moldability is good. On the other hand, from the viewpoint of workability of extrusion foaming, the tan δ of the branched polypropylene resin X is preferably 0.5 or more, more preferably 0.6 or more.

[0042] The branched polypropylene resin X preferably has a melt rupture speed of more than 3.6 m / min, more preferably 3.7 m / min or more, and even more preferably 3.9 m / min or more. When the branched polypropylene resin X has a melt rupture speed within the above-mentioned range, the open cell ratio and melt rupture speed of the expanded beads are likely to satisfy the above-mentioned ranges, and the moldability is good. On the other hand, from the viewpoint of workability of extrusion foaming, the branched polypropylene resin X preferably has a melt rupture speed of 20 m / min or less, and more preferably 15 m / min or less.

[0043] The branched polypropylene resin X preferably has an MFR of 0.5 g / 10 min to 5 g / 10 min, more preferably 1.0 g / 10 min to 4 g / 10 min, and even more preferably 1.5 g / 10 min to 3 g / 10 min. When the MFR of the branched polypropylene resin X is within the above-mentioned range, the surface beauty of the foamed molded article is improved and the productivity is also improved.

[0044] The branched polypropylene resin X has a melting point of preferably 150° C. or more, more preferably 155° C. or more, and even more preferably 160° C. or more. The heat resistance of the expanded beads and the expanded molded article is easily improved. On the other hand, although not particularly limited, from the viewpoint of the water vapor pressure during in-mold expansion molding, for example, the melting point Tm of the branched polypropylene resin X is preferably 170° C. or less, and more preferably 166° C. or less.

[0045] The branched polypropylene resin X is, for example, Deploy TM Commercially available products such as WB140HMS may also be used.

[0046] 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 a polypropylene-based resin in addition to the polypropylene-based resin, within a range that does not impair the effects of the present invention. 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 resins include polyethylene-based resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer; styrene-based resins such as polystyrene and styrene-maleic anhydride copolymer; polyamide, etc.

[0047] In one or more embodiments of the present invention, the expanded beads may contain additives such as cell nucleating agents (also called bubble nucleating agents) in addition to the base resin, as necessary; colorants; antistatic agents; flame retardants; stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents; crosslinking agents; chain transfer agents; lubricants; plasticizers; fillers; and reinforcing materials. Such additives may be incorporated in a resin at a high concentration in advance to form a master batch, and the master batch resin may be added to the polypropylene-based resin mixture. The resin used in such a master batch resin is preferably a polyolefin-based resin, more preferably a polypropylene-based resin, and more preferably the same polypropylene-based resin as the polypropylene-based resin used in the base resin of the expanded beads is used to form a master batch.

[0048] In one or more embodiments of the present invention, for example, the base resin, the foaming agent, and, if necessary, the additives are melt-kneaded, then extruded, and the extruded molten mixture is cut to obtain polypropylene-based resin expanded beads. The melt-kneading is preferably performed in two stages, with the temperature of the second stage being lower than that of the first stage. Specifically, the base resin, the foaming agent, and, if necessary, the additives are fed to a first stage extruder and melt-kneaded, and then the molten mixture is fed to a second stage extruder having a lower temperature than the first stage extruder and cooled, and then the molten mixture (molten resin containing the foaming agent) is extruded through a die attached to the tip of the second stage extruder, and the extruded molten mixture is cut, which is a so-called extrusion foaming method. Since the temperature of the second stage extruder is lower than that of the first stage extruder, the open cell ratio of the expanded beads is easily reduced, and the moldability is improved. In addition, since the main purpose of the second stage extruder is cooling, it does not have to be an extruder as long as it can achieve that purpose. For example, it can be substituted with a static mixer, a melt cooler, or the like.

[0049] In one or more embodiments of the present invention, from the viewpoint of reducing the open cell ratio of the expanded beads and enhancing 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. Furthermore, although not particularly limited, for example, from the viewpoint of easily lowering the temperature of the second stage to a 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.

[0050] In one or more embodiments of the present invention, the temperature of the first stage is not particularly limited and can be appropriately determined depending on the melting point of the base resin used, the type and / or 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 melting and kneading the base resin and the foaming agent, and, if necessary, the additive. 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.

[0051] In one or more embodiments of the present invention, the temperature of the second stage can be appropriately determined depending on the melting point of the base resin used, the type and / or amount of foaming agent, the type and / or melting point of the additive, the allowable torque of the extruder, etc., and is not particularly limited. The temperature of the second stage is, for example, preferably (Tm2+40°C) or less, more preferably (Tm2+30°C) or less, and even more preferably (Tm2+20°C) or less, from the viewpoint of reducing the open cell ratio and melt extrusion speed of the expanded beads and improving moldability. In addition, the temperature of the second stage extruder is, for example, preferably (Tm2-5°C) or more, and more preferably Tm2 or more, from the viewpoint of improving the workability of extrusion foaming.

[0052] The shredding method for obtaining foamed particles in the extrusion foaming method is generally broadly divided into a cold cut method and a die face cut method. The cold cut method includes a method (strand cut method) in which a molten resin containing a foaming agent extruded from a fine hole die is foamed, and a strand-shaped foam is taken while being cooled by passing through a water tank, and then shredded. The die face cut method is a method in which the molten resin extruded from a fine hole die is cut with a rotating cutter while in contact with the die face or while leaving a small gap. The die face cut method is divided into an underwater cut method, a watering cut method, and a hot cut method based on the difference in the cooling method.

[0053] In one or more embodiments of the present invention, examples of the blowing agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; aliphatic cyclic hydrogens such as cyclopentane and cyclobutane; inorganic gases such as air, nitrogen, and carbon dioxide; and water. These blowing agents may be used alone or in combination of two or more. Among them, inorganic gases and / or water are preferred from the viewpoint of safety during handling and simplification of required equipment specifications, and inorganic gases, particularly carbon dioxide, are preferred from the viewpoint of easiness of obtaining a foam with a high expansion ratio. The amount of the blowing agent to be added varies depending on the type of blowing agent and the expansion ratio of the targeted polypropylene resin expanded particles, so it may be appropriately adjusted, but is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 15 parts by mass or less, relative to 100 parts by mass of the base resin.

[0054] As the additive, a bubble nucleating agent may be added for the purpose of controlling the bubble shape. Examples of the bubble nucleating agent include sodium bicarbonate, a mixture of sodium bicarbonate and citric acid, monosodium citrate, talc, and calcium carbonate, and these may be used alone or in combination of two or more. The amount of the bubble nucleating agent to be added is not particularly limited, but is usually preferably 0.01 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the base resin.

[0055] The extrusion output of the second-stage extruder, static mixer, or melt cooler is not particularly limited, and may be, for example, 1 kg / hour to 1000 kg / hour. In a laboratory type, it may be approximately 1 kg / hour to 50 kg / hour, and in a commercial production type, it is preferably 20 kg / hour to 1000 kg / hour.

[0056] The shape of the die used in the second-stage extruder, static mixer or melt cooler is not critical, but from the viewpoint of the appearance of the expanded beads and 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, and more preferably 0.3 mm or more and 1.0 mm or less.

[0057] In one embodiment of the present invention, the mass per particle of the expanded beads 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 particle of the expanded beads is the average resin particle mass calculated based on the mass of 100 randomly selected polypropylene resin expanded beads. When the mass per particle of the polypropylene resin expanded beads is 0.2 mg or more, the dimensional change rate of the foamed molded article does not increase, and when it is 10 mg or less, it tends to be easy to fill the mold.

[0058] In one or more embodiments of the present invention, the expansion ratio of the expanded beads is not particularly limited and may be adjusted as necessary. In one embodiment of the present invention, the expansion ratio of the expanded beads is, for example, preferably 3 times or more and 40 times or less, more preferably 3 times or more and 25 times or less.

[0059] In one or more embodiments of the present invention, the expansion ratio of the expanded polypropylene resin particles is determined by measuring the mass w (g) of the expanded polypropylene resin particles, then immersing them in a measuring cylinder containing ethanol, and measuring the volume v (cm) based on the amount of rise in the water level in the measuring cylinder (submersion method). 3) is measured, the true specific gravity ρb=w / v of the expanded polypropylene resin particles is calculated, and the ratio to the density ρr of the polypropylene resin before expansion (ρr / ρb) can be calculated.

[0060] In one or more embodiments of the present invention, the average bubble diameter (also referred to as the average cell diameter) of the expanded polypropylene resin 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. If the average bubble diameter of the expanded polypropylene resin particles is 100 μm or more, the shrinkage of the expanded molded product tends to be small, and if 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 bubble diameter of the expanded polypropylene resin particles can be measured by the method described in the Examples.

[0061] In one or more embodiments of the present invention, the bulk density of the expanded polypropylene resin beads is not particularly limited, but is preferably 15 g / L or more and 300 g / L or less, and more preferably 30 g / L or more and 300 g / L or less. When the bulk density of the expanded beads is within the above-mentioned range, it is easy to obtain a foamed molded product with high density. In one or more embodiments of the present invention, the bulk density of the expanded polypropylene resin beads can be measured by the method described in the examples.

[0062] In one or more embodiments of the present invention, the expanded polypropylene resin particles constitute an expanded molded article, which has excellent heat resistance and moldability.

[0063] In one or more embodiments of the present invention, a polypropylene-based resin foamed molded article can be obtained by filling the polypropylene-based resin foamed particles into a mold that can be closed but not sealed, and heating the molded article with water vapor or the like to form the molded article.

[0064] To mold a polypropylene resin foamed molded article from the polypropylene resin foamed particles, for example, there can be used: (a) a method in which the foamed particles are pressurized with an inorganic gas to impregnate the particles with the inorganic gas and impart a predetermined internal particle pressure, and then the particles are filled into a mold and heat-fused with steam or the like (e.g., JP-B-51-22951); (b) a method in which the foamed particles are compressed by gas pressure, filled into a mold, and heat-fused with steam or the like by utilizing the recovery force of the particles (e.g., JP-B-53-33996); or (c) a method in which the foamed particles are filled into a mold with an expanded gap, the mold is closed to a predetermined gap, the filled foamed particles are compressed, and then heat-fused with steam or the like.

[0065] In one or more embodiments of the present invention, from the viewpoint of enduring repeated use in a portion exposed to heat, the dimensional change rate of the polypropylene-based resin foam molded article at 140° C. is preferably −2.0% or more and 1.0% or less, more preferably −1.0% or more and 1.0% or less, and particularly preferably −0.5% or more and 0.5% or less. In one or more embodiments of the present invention, the dimensional change rate of the polypropylene-based resin foam molded article at 140° C. can be measured by the method described in the Examples.

[0066] In one or more embodiments of the present invention, the density of the polypropylene resin foam molded body may be appropriately determined depending on the application, and is not particularly limited, but is preferably 80 g / L or more and 300 g / L or less, and more preferably 100 g / L or more and 300 g / L or less. When the density of the foam molded body is within the above-mentioned range, the molded body is unlikely to shrink or deform when heat is applied, and is suitable for repeated use. In one or more embodiments of the present invention, the density of the polypropylene resin foam molded body can be measured by the method described in the examples.

[0067] In one or more embodiments, the present invention may be configured as follows.

[0068] [1] A polypropylene-based resin foamed particle whose base resin is a polypropylene-based resin as a main component, the expanded polypropylene resin particles have only one melting peak in a temperature range of 130° C. or more and 170° C. or less in a first temperature rise in differential scanning calorimetry, and the heat of fusion in the temperature range of 130° C. or more and 170° C. or less is 90% or more of the total heat of fusion; The polypropylene-based resin expanded beads have a melting point Tm2 of 159° C. or more and 170° C. or less, the melting point Tm2 being represented by a melting peak value during a second heating run in differential scanning calorimetry; The polypropylene resin foamed beads have a melt rupture speed of 5 m / min or more and 45 m / min or less at a temperature of 200° C., The expanded polypropylene resin particles have an open cell ratio of 15% or less. [2] The expanded polypropylene resin particles according to [1], wherein the expanded polypropylene resin particles have a melt flow rate of 1 g / 10 min or more and 10 g / 10 min or less. [3] The expanded polypropylene resin particles according to [1] or [2], wherein the polypropylene resin contains 60% by mass or more and 100% by mass or less of a polypropylene resin having a branched structure. [4] The expanded polypropylene resin particles according to [3], wherein the polypropylene resin having a branched structure has a melt tension of more than 13.8 cN and a tan δ of less than 3.3. [5] A method for producing the expanded polypropylene resin particles according to any one of [1] to [4], A base resin mainly composed of a polypropylene-based resin and a foaming agent are melt-kneaded and then extruded, and the extruded molten mixture is cut to obtain expanded polypropylene-based resin particles. The method for producing expanded polypropylene resin beads, wherein the melt kneading is carried out in two stages, and the temperature in the second stage is lower than that in the first stage. [6] The method for producing expanded polypropylene resin particles according to [5], wherein the temperature in the first stage is from (Tm2+20°C) to (Tm2+70°C), and the temperature in the second stage is from (Tm2-5°C) to (Tm2+40°C). [7] The method for producing expanded polypropylene resin particles according to [5] or [6], wherein the foaming agent is at least one selected from the group consisting of inorganic gases and water. [8] A polypropylene-based resin foamed molded article, comprising the polypropylene-based resin foamed particles according to any one of [1] to [4]. [9] The polypropylene-based resin foam molded article according to [8], wherein the polypropylene-based resin foam molded article has a dimensional change rate at 140°C of -2.0% or more and 1.0% or less. EXAMPLES

[0069] One or more embodiments of the present invention will be described in detail below with reference to examples, although the present invention is not limited to these examples.

[0070] The following polypropylene resins were used in the examples and comparative examples. Table 1 below shows the melt tension, melt rupture rate, melting point, MFR and tan δ of the polypropylene resins. (1) B-PP-1: A homopolymer of propylene having a branched structure (Daploy, manufactured by Borealis) TM WB140HMS) (2) B-PP-2: A homopolymer of propylene having a branched structure (Amppleo, manufactured by Braskem) TM 1025MA) (3) B-PP-3: Propylene homopolymer having a branched structure (Sabic® PP-UMS HEX17112 manufactured by Sabic) (4) PP-4: Ethylene / propylene block copolymer (BC250MO manufactured by Borealis), 99.5% by mass of propylene (5) PP-5: Propylene homopolymer (F113G manufactured by Prime Polymer Co., Ltd.) (6) PP-6: Ethylene / propylene random polymer (RD234CF manufactured by Borealis), 98% by mass of propylene

[0071] [Table 1]

[0072] The evaluation and measurement methods carried out in the examples and comparative examples are as follows.

[0073] <Melt point measurement of polypropylene resin> The melting point of the polypropylene resin was measured using a differential scanning calorimeter DSC [Seiko Instruments Inc., DSC6200]. Specifically, 5 to 6 mg of the sample was melted by heating from 40°C to 220°C at a heating rate of 10°C / min, then crystallized by cooling from 220°C to 40°C at a heating rate of 10°C / min, and then further heated from 40°C to 220°C at a heating rate of 10°C / min. The melting peak temperature in the DSC curve during the second heating was taken as the melting point.

[0074] <Differential scanning calorimetry of expanded polypropylene resin particles> Using a differential scanning calorimeter (DSC) (Seiko Instruments Inc., DSC6200 model), 5 to 6 mg of the obtained polypropylene resin foam particles were heated from 40°C to 300°C at a heating rate of 10°C / min to melt them, and then cooled from 300°C to 40°C at a heating rate of 10°C / min to crystallize them. After that, the temperature was further increased from 40°C to 300°C at a heating rate of 10°C / min to obtain DSC curves during the first and second heating periods. 《Heat ratio》 A line segment AB was drawn connecting the point (point A) corresponding to 100 ° C. on the DSC curve during the first heating to the melting end point (point B), and the heat of fusion of the part surrounded by the line segment AB and the DSC curve was calculated and defined 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 point of the line and the DSC curve was defined 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 point of the line and the DSC curve was defined as point F. The heat of fusion of the part surrounded by the line segments CD, CE, EF, and the DSC curve was calculated and defined as the heat of fusion Q2 in the temperature range of 130 ° C. to 170 ° C. In addition, when the melting end temperature is less than 170 ° C., the heat of fusion of the part surrounded by the line segments CD, CB, and the DSC curve was calculated and defined as Q2. Using Q1 and Q2, the heat of fusion ratio was calculated using the following formula. Melting heat ratio (%) = Q2 x 100 / Q1 Melting Point The melting peak temperature obtained during the second heating was taken as the melting point Tm2 of the expanded polypropylene resin particles.

[0075] <Melt flow rate (MFR)> The measurements were taken in accordance with the provisions of JIS K 7210, Method B, with an orifice diameter of 2.0959±0.005mm, an orifice length of 8.000±0.025mm, at 230°C and under a load of 2.16kg. Specifically, in accordance with the provisions of JIS K 7210 B method, the amount of resin extruded from the die at 230°C and 2.16 kg in a certain time was converted to the amount extruded in 10 minutes using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho). The certain time is 120 seconds when the melt flow rate is more than 0.5g / 10 minutes and 1.0g / 10 minutes or less; 60 seconds when the melt flow rate is more than 1.0g / 10 minutes and 3.5g / 10 minutes or less; 30 seconds when the melt flow rate is more than 3.5g / 10 minutes and 10g / 10 minutes or less; 10 seconds when the melt flow rate is more than 10g / 10 minutes and 25g / 10 minutes or less; 5 seconds when the melt flow rate is more than 25g / 10 minutes and 100g / 10 minutes or less; and 3 seconds when the melt flow rate is more than 100g / 10 minutes.

[0076] <Melt tension> A Capillograph (manufactured by Toyo Seiki Seisakusho) equipped with an attachment for measuring melt tension and having a cylinder of 10 mm diameter with an orifice of 1 mm diameter and 10 mm length at the tip was used to measure the melt tension. The strand discharged from the die when the piston was lowered at 200°C with a piston lowering speed of 10 mm / min was hung on a pulley with a load cell 350 mm below and taken up at a speed of 1 m / min. After stabilization, the take-up speed was increased at a rate 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. If the strand did not break, the melt tension was deemed unmeasurable.

[0077] <Melting fracture speed> In the measurement of the melt tension, the take-up speed was increased, and the take-up speed at which the strand broke was measured and recorded as the melt breakage speed. If the strand did not break, the melt breakage speed was deemed unmeasurable. The melt breakage speed is an index of the extensibility of the molten resin during foaming.

[0078] <Preparation of samples for measuring MFR, melt tension and melt fracture speed of polypropylene resin foam beads> The MFR, melt tension and melt rupture speed of polypropylene resin foam beads were measured using samples prepared by returning foam beads or foam molded products to a resin mass. Since the resin properties do not change between foam beads and foam molded products, either one can be used for the measurement. The expanded beads are placed in a dryer whose temperature has been adjusted to (Tm2+10℃) based on the melting point Tm2 of the expanded beads, and the pressure inside the dryer is reduced to -0.05MPa (cage pressure) to -0.10MPa (cage pressure) over 5 to 10 minutes using a vacuum pump, after which the beads are left in the dryer for 30 minutes to remove the air from inside the expanded beads and form a resin mass. If the resin particles stick together and the mass is large, the resin mass may be cut into small pieces with scissors or crushed with a mixer. In the case of foamed molded bodies, the molded bodies were cut into small pieces with scissors or a slicer, etc., and then crushed in a mixer, etc. The crushed pieces of foamed molded bodies were placed in a dryer whose temperature was adjusted to (Tm2+10°C) based on the melting point Tm2 of the foam particles, and the pressure inside the dryer was reduced to -0.05MPa·G to -0.10MPa·G using a vacuum pump over a period of 5 to 10 minutes, after which the dryer was left for 30 minutes, and the foamed molded bodies were made into resin blocks while the air was removed. If the resin pieces stuck together and the blocks were large, the resin blocks may be cut into small pieces with scissors, etc., or crushed in a mixer, etc.

[0079] <Loss tangent tanδ> A polypropylene resin or a polypropylene resin foam particle was hot pressed at 190°C for 5 minutes using a 1.5mm thick spacer to prepare a 1.5mm thick press plate, and a 25mmφ punch was used to punch out the press plate to obtain a 25mmφ test piece. As a measuring device, a TA Instruments viscoelasticity measuring device ARES was used, and a 25mmφ parallel plate type jig was attached. A thermostatic bath was installed to surround the jig, and the jig was preheated at 200°C. Thereafter, the thermostatic bath was opened, a 25mmφ test piece was inserted between the parallel plates, the thermostatic bath was closed, and the parallel plate interval was compressed to 1mm after preheating for 5 minutes. After compression, the thermostatic bath was opened again, the resin protruding from the parallel plates was scraped off with a brass spatula, the thermostatic bath was closed, and the temperature was maintained for 5 minutes again, after which dynamic viscoelasticity measurement was started. The measurement was performed at angular frequencies ranging from 0.1 rad / s to 100 rad / s, and the storage modulus and loss modulus at each angular frequency, as well as the loss tangent tanδ as a calculated value, were obtained. Among these results, the loss tangent tanδ value at an angular frequency of 0.1 rad / s was adopted. The measurement was performed at a strain of 5% in a nitrogen atmosphere.

[0080] <Open cell ratio of polypropylene resin foam particles> The volume of the polypropylene resin foamed particles obtained according to the method described in PROSEDURE C of ASTM D2856-87 is defined as Vc (cm 3 ) and the open cell ratio (%) was calculated according to the following formula: Open cell rate (%) = ((Va-Vc) x 100) / Va Vc was measured using an air comparison specific gravity meter Model 1000 manufactured by Tokyo Science Co., Ltd. The volume Va (cm 3 ) is the apparent volume of the expanded polypropylene resin particles, which is determined by immersing the entire amount of the expanded polypropylene resin particles after measuring Vc with the air comparison type specific gravity meter in a measuring cylinder containing ethanol and measuring the rise in the liquid level of the measuring cylinder (submersion method).

[0081] <Bulk density of polypropylene resin foam particles> The expanded polypropylene resin particles were collected in a 1 L measuring cup, and the mass was measured. The mass (g) was divided by the volume (1 L) to obtain the bulk density.

[0082] <Average cell diameter of polypropylene resin foam particles> Using a double-edged razor [Feather, high stainless double-edged], the polypropylene resin expanded particles were cut almost in the center, with great care not to destroy the bubble membrane (cell membrane), and the cut surface was observed at 100 times magnification using a microscope [Keyence, VHX-100] to obtain an image. In the obtained image, a line segment equivalent to a length of 1000 μm was drawn on the part of the polypropylene resin expanded particle excluding the surface layer, and the number of bubbles (cell number) n through which the line segment passed was measured, and the cell diameter was calculated as "1000 / n" (μm). The same procedure was performed on 10 polypropylene resin expanded particles, and the average value of the calculated cell diameters was taken as the average cell diameter.

[0083] <Moldability of polypropylene resin foam molded products> 《Forming method》 Using a polyolefin foam molding machine manufactured by Teubert Maschinenbau GmbH, a block-shaped mold (length 381 mm x width 381 mm x thickness 60 mm) was used, with a gap between the molds (hereinafter referred to as cracking) of 18 mm (cracking rate 30%), and polypropylene resin foam particles were filled into the mold, and then 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 the mold was heated and molded on both sides for 5 seconds using steam at a specified pressure to obtain a polypropylene resin foam molded body. At this time, the steam pressure was increased from 0.32 MPa (gauge pressure) in increments of 0.01 MPa to produce a molded body. The steam pressure was increased up to a maximum of 0.42 MPa (gauge pressure). Evaluation Method The obtained foam molded products were left in a drying chamber at 75°C for 24 hours, and then left at room temperature for 4 hours to prepare the evaluation objects, and the fusion rate and surface expansion of the foam molded products to be evaluated were evaluated. The lowest steam pressure at which the fusion rate and surface expansion were acceptable was defined as the minimum molding pressure, and the highest steam pressure at which the mold could be released using only air after molding was defined as the maximum molding pressure. The difference between the maximum molding pressure and the minimum molding pressure was defined as the molding processing heating width, and moldability was evaluated based on the magnitude of this value. Good: Heat width for molding process is 0.04MPa or more Defective: Heat width for molding process is less than 0.04MPa (1) Evaluation of fusion rate A crack of about 5 mm depth was made on the surface of the obtained foamed molded product with a knife, the foamed molded product was split along the crack, the fracture surface was observed, and the ratio of the number of broken particles to the total number of particles on the fracture surface was calculated to evaluate the fusion rate of the molded product. A fusion rate of 80% or more was considered to be acceptable. (2) Surface elongation evaluation The obtained foamed molded article was evaluated for the presence of gaps between the foam particles in the center of the largest surface area. If the steam pressure during in-mold foaming is insufficient, the gaps between the foam particles are not filled sufficiently. Those with few gaps between the foam particles and a beautiful surface were rated as passing.

[0084] <Density of polypropylene resin foam molding> The mass W (g) of the polypropylene resin foam molded body was measured, and the length, width, and thickness were measured with a vernier caliper to obtain the volume V (cm 3 ) was calculated to determine the density of the green body in W / V. However, the unit was converted to g / L.

[0085] <Dimensional change rate at 140℃> Measurement was performed according to JIS K 6767. The polypropylene resin foam molded body was cut into a rectangular parallelepiped with a length of 150 mm and a width of 150 mm, and three straight lines with a length of 100 mm were drawn in parallel at 50 mm intervals in the length direction and width direction in the center of the test piece, and the length of each straight line was recorded and the average value L0 was calculated. The test piece was heated in a hot air circulation dryer at a temperature of 140 ± 2 ° C for 22 hours. The test piece taken out of the dryer was left to stand for 1 hour under an environment with a temperature of 23 ± 2 ° C and a humidity of 50 ± 5%, and then the length of each straight line was measured, the average value L1 was calculated, and the dimensional change rate at 140 ° C was calculated using the following formula. Dimensional change rate at 140℃ (%) = (L1-L0) x 100 / L0

[0086] Example 1 [Preparation of polypropylene resin foam particles] 100 parts by mass of the polypropylene resin shown in Table 2 below was blended with 1 part by mass of a bubble nucleating agent master batch (sodium bicarbonate master batch manufactured by Dainichi Seika Chemicals Co., Ltd., sodium bicarbonate content: 20%, base resin: low-density polyethylene resin) in a tumbler, and the blend was fed to an extruder (twin-screw extruder with a diameter of 26 mm) set at 210°C. 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, the molten kneaded product was cooled by passing it through a melt cooler set at 185°C, and then extruded from a die equipped with three 0.8 mm diameter holes attached to the tip of the melt cooler at a discharge rate of 10 kg / hour under atmospheric pressure. A chamber attached to the tip of the die was filled with water so that it was in contact with the die, and the water pressure was 0.40 MPa (gauge pressure). The molten resin containing the foaming agent extruded from the die was cut in 80°C water so that the mass per particle was 1.5 to 2.0 mg, obtaining polypropylene resin foam particles.

[0087] [Preparation of polypropylene resin foam molded body] Using a polyolefin foam molding machine manufactured by Teubert Maschinenbau GmbH, a block-shaped mold (length 381 mm × width 381 mm × thickness 60 mm) was cracked 18 mm (cracking rate 30%), polypropylene resin foam particles were filled into the mold, and the mold was compressed to a thickness of 60 mm. Next, the air in the mold was expelled with steam at 0.15 MPa (gauge pressure), and then the mold was heated and molded for 5 seconds using steam at the minimum molding pressure (gauge pressure) shown in Table 2 to obtain a polypropylene resin foam molded product.

[0088] Example 2 [Preparation of expanded polypropylene resin beads] Except for setting the temperature of the melt cooler to 200°C, the same procedure as in Example 1 was repeated to prepare expanded polypropylene resin beads and expanded polypropylene resin molded articles.

[0089] Example 3 Polypropylene-based resin expanded beads and polypropylene-based resin expanded molded bodies were prepared in the same manner as in Example 1, except that in [Preparation of polypropylene-based resin expanded beads], the mixed resin shown in Table 2 below was used as the polypropylene-based resin, 3.5 parts by mass of carbon dioxide gas was injected into the extruder as a foaming agent, and in [Preparation of polypropylene-based resin expanded molded bodies], water vapor was used at the minimum molding pressure (gauge pressure) shown in Table 2 below.

[0090] (Examples 4 to 5) Polypropylene-based resin expanded beads and polypropylene-based resin expanded molded bodies were prepared in the same manner as in Example 1, except that in [Preparation of polypropylene-based resin expanded beads], a mixed resin shown in Table 2 below was used as the polypropylene-based resin, and in [Preparation of polypropylene-based resin expanded molded bodies], water vapor was used at the minimum molding pressure (gauge pressure) shown in Table 2 below.

[0091] Example 6 Polypropylene-based resin foamed beads and polypropylene-based resin foamed molded bodies were produced in the same manner as in Example 1, except that in [Preparation of polypropylene-based resin foamed beads], the temperature of the melt cooler was set to 170°C, and the water pressure in the chamber attached to the tip of the die was set to 0.10 MPa (gauge pressure), and in [Preparation of polypropylene-based resin foamed molded bodies], water vapor was used at the minimum molding pressure (gauge pressure) shown in Table 2 below.

[0092] Comparative Example 1 Polypropylene-based resin expanded beads and polypropylene-based resin expanded molded bodies were prepared in the same manner as in Example 1, except that in [Preparation of polypropylene-based resin expanded beads], a resin shown in Table 3 below was used as the polypropylene-based resin, and in [Preparation of polypropylene-based resin expanded molded bodies], water vapor was used at the minimum molding pressure (gauge pressure) shown in Table 3 below.

[0093] Comparative Example 2 Expanded polypropylene resin particles were produced in the same manner as in Example 1, except that the resins shown in Table 3 below were used as the polypropylene resin in [Preparation of expanded polypropylene resin particles]. A polypropylene resin foamed molded article was produced in the same manner as in Example 1, except that the obtained polypropylene resin foamed beads were used, but a good molded article could not be obtained even when the steam molding pressure was increased to 0.42 MPa (gauge pressure). The open cell rate of the foamed beads was high, and the obtained molded article was shrunken.

[0094] (Comparative Examples 3 to 4) [Preparation of polypropylene-based resin expanded particles] In the procedure of Example 1, except that the resin shown in Table 3 below was used as the polypropylene-based resin, 4.0 parts by mass of carbon dioxide gas was injected into the extruder as a foaming agent, and water at a water pressure of 0.35 MPa (gauge pressure) was supplied into the chamber attached to the tip of the die, the polypropylene-based resin expanded particles were prepared in the same manner as in Example 1. When the obtained polypropylene resin foamed beads were used to prepare a polypropylene resin foamed molded article in the same manner as in Example 1, a good molded article could not be obtained even when the steam pressure was increased to 0.42 MPa (gauge pressure). The open cell rate of the foamed beads was high, and the obtained molded article was significantly shrunk.

[0095] Comparative Example 5 [Preparation of polypropylene-based resin expanded particles] In the procedure of Example 1, except that the resin shown in Table 3 below was used as the polypropylene-based resin, 4.0 parts by mass of carbon dioxide gas was injected into the extruder as a foaming agent, the temperature of the melt cooler was set to 170°C, and water at a water pressure of 0.35 MPa (gauge pressure) was supplied into the chamber attached to the tip of the die, the polypropylene-based resin expanded particles were prepared in the same manner as in Example 1. When the obtained polypropylene resin expanded beads were used to produce a polypropylene resin expanded molded article in the same manner as in Example 1, a molded article could not be obtained even when the steam pressure was increased from 0.20 MPa (gauge pressure) to 0.36 MPa (gauge pressure). The open cell rate of the expanded beads was high, and the obtained molded article was significantly shrunk.

[0096] Comparative Example 6 [Preparation of polypropylene-based resin foam particles] In the procedure of Example 1, except that the mixed resin shown in Table 3 below was used as the polypropylene-based resin, 3.5 parts by mass of carbon dioxide gas was injected into the extruder as a foaming agent, and water at a water pressure of 0.35 MPa (gauge pressure) was supplied into the chamber attached to the tip of the die, the polypropylene-based resin foam particles were prepared in the same manner as in Example 1. When the obtained polypropylene resin foamed beads were used to prepare a polypropylene resin foamed molded article in the same manner as in Example 1, a good molded article could not be obtained even when the steam pressure was increased to 0.42 MPa (gauge pressure). The open cell rate of the foamed beads was high, and the obtained molded article was significantly shrunk.

[0097] Comparative Example 7 In [Preparation of polypropylene-based resin foam particles], the mixed resin shown in Table 3 below was used as the polypropylene-based resin, 3.5 parts by mass of carbon dioxide gas was injected into the extruder as a foaming agent, the temperature of the melt cooler was set to 180°C, and water with a water pressure of 0.35 MPa (gauge pressure) was supplied into the chamber attached to the tip of the die, except that in [Preparation of polypropylene-based resin foam molded body], the minimum molding pressure (gauge pressure) shown in Table 3 below was used and the cracking rate was 50%, but the same procedure was followed as in Example 1 to prepare polypropylene-based resin foam molded body.

[0098] Comparative Example 8 Polypropylene-based resin expanded beads and polypropylene-based resin expanded molded bodies were prepared in the same manner as in Example 1, except that in [Preparation of polypropylene-based resin expanded beads], the resin shown in Table 3 below was used as the polypropylene-based resin, the temperature of the melt cooler was set to 210°C, and in [Preparation of polypropylene-based resin expanded molded bodies], the minimum molding pressure (gauge pressure) shown in Table 3 below was used.

[0099] The evaluation results of the polypropylene resin expanded beads and polypropylene resin expanded molded articles obtained in the Examples and Comparative Examples are shown in the following Tables 2 and 3. In the "Extrusion Foaming Conditions" in Tables 2 and 3, the first-stage temperature is the temperature of the extruder, and the second-stage temperature is the temperature of the melt cooler.

[0100] Fig. 2 shows the DSC curve obtained in the first heating in the differential scanning calorimetry of the expanded polypropylene resin particles of Example 1. From Fig. 2, it can be seen that in the first heating, only one melting peak exists in the temperature range of 130°C or more and 170°C or less. Although the DSC curves of the expanded polypropylene resin particles of Examples 2 to 6 are not shown, it was confirmed that in the first heating, only one melting peak exists in the temperature range of 130°C or more and 170°C or less.

[0101] [Table 2]

[0102] [Table 3]

[0103] As can be seen from the data in Table 2, in Examples 1 to 6, in the first heating run in differential scanning calorimetry of the expanded beads, there was only one melting peak in the temperature range of 130°C or higher and 170°C or lower, the heat of fusion in the temperature range of 130°C or higher and 170°C or lower was 90% or more of the total heat of fusion, the melting point Tm2 was 159°C or higher and 170°C or lower, the melt rupture speed was 5 m / min or higher and 45 m / min or lower, and the open cell ratio was 15% or lower, and the expanded beads were used to obtain highly heat-resistant expanded molded articles with good moldability.

[0104] On the other hand, as can be seen from the data in Table 3, Comparative Example 1, in which the melt rupture speed of the expanded beads exceeded 45 m / min, exhibited poor moldability. Comparative Examples 2 to 6, in which the melt rupture speed of the expanded beads exceeded 45 m / min and the open cell ratio exceeded 15%, also exhibited poor moldability. Comparative Example 8, in which the open cell ratio was less than 15%, also exhibited poor moldability. Comparative Example 7, in which the melt rupture speed of the expanded beads was greater than 45 m / min, the open cell ratio was greater than 15%, and the melting point was less than 159°C, exhibited poor moldability and poor heat resistance of the foamed molded article.

[0105] The present invention can be implemented in other forms than those described above without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited thereto. The scope of the present invention is interpreted based on the description of the claims, and all modifications within the scope of the claims are included in the scope of the claims.

Claims

1. The base resin is a polypropylene-based resin expanded particle mainly composed of a polypropylene-based resin, the expanded polypropylene resin particles have only one melting peak in a temperature range of 130° C. or more and 170° C. or less in a first temperature rise in differential scanning calorimetry, and the heat of fusion in the temperature range of 130° C. or more and 170° C. or less is 90% or more of the total heat of fusion; The polypropylene-based resin expanded beads have a melting point Tm2 of 159° C. or more and 170° C. or less, the melting point Tm2 being determined by a melting peak value during a second heating run in a differential scanning calorimetry measurement. The polypropylene-based resin foamed beads have a melt rupture speed of 10 m / min or more and 45 m / min or less at a temperature of 200° C., The polypropylene-based resin foam particles have a melt flow rate of 2 g / 10 min or more and 9 g / 10 min or less, The expanded polypropylene resin particles have an open cell ratio of 15% or less.

2. The expanded polypropylene resin particles according to claim 1 , wherein the polypropylene resin contains 60% by mass or more and 100% by mass or less of a polypropylene resin having a branched structure.

3. 3. The expanded polypropylene resin particles according to claim 2, wherein the branched polypropylene resin has a melt tension of more than 13.8 cN and a tan δ of less than 3.

3.

4. A method for producing the expanded polypropylene resin beads according to any one of claims 1 to 3, comprising the steps of: A base resin mainly composed of a polypropylene-based resin and a foaming agent are melt-kneaded and then extruded, and the extruded molten mixture is cut to obtain expanded polypropylene-based resin particles. The method for producing expanded polypropylene resin beads, wherein the melt kneading is carried out in two stages, and the temperature in the second stage is lower than that in the first stage.

5. The method for producing expanded polypropylene resin beads according to claim 4, wherein the temperature in the first stage is from (Tm2+20°C) to (Tm2+70°C), and the temperature in the second stage is from (Tm2-5°C) to (Tm2+40°C).

6. 6. The method for producing expanded polypropylene resin particles according to claim 4, wherein the foaming agent is at least one selected from the group consisting of inorganic gases and water.

7. A polypropylene resin foamed molded article, comprising the polypropylene resin foamed particles according to any one of claims 1 to 3.

8. The polypropylene resin foam molded article according to claim 7, wherein the polypropylene resin foam molded article has a dimensional change rate at 140° C. of −2.0% or more and 1.0% or less.

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