Polypropylene resin foam particles, polypropylene resin foam molded body, and method for manufacturing polypropylene resin foam particles

Abstract

The purpose of one embodiment of the present invention is to provide: polypropylene resin foam particles excellent in productivity of a polypropylene resin foam molded body; and a polypropylene resin foam molded body obtained by molding the polypropylene resin foam particles. The present invention solves the abovementioned problem by means of polypropylene resin foam particles including a base resin that contains a polypropylene random copolymer and a polypropylene block copolymer, said polypropylene resin foam particles having a peak strength ratio I720 / I810 of 0.45 to 0.67 and a shrinkage rate of 20% or less.

Description

Polypropylene-based resin expanded beads, polypropylene-based resin expanded molded article, and method for producing polypropylene-based resin expanded beads

[0001] The present invention relates to expanded polypropylene resin beads, expanded molded polypropylene resin articles, and a method for producing expanded polypropylene resin beads.

[0002] Polypropylene resin foam molded articles are used in a variety of applications, including automobile interior components, core materials for automobile bumpers, heat insulating materials, cushioning packaging materials, and returnable boxes (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2014-173012

[0004] However, the above-mentioned conventional techniques are not sufficient from the viewpoint of productivity, and there is room for further improvement.

[0005] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide expanded polypropylene resin beads that are excellent in productivity for producing expanded polypropylene resin articles, and expanded polypropylene resin articles obtained by molding the expanded polypropylene resin beads.

[0006] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0007] That is, the expanded polypropylene resin beads according to one embodiment of the present invention have the following structure: Expanded polypropylene resin beads include a base resin containing a propylene random copolymer and a propylene block copolymer, and when the content ratio of the block copolymer is X (%) and the expansion pressure during production is Y (MPa), X and Y satisfy the following formula (1): Y<-0.07X+3.6... (1).

[0008] Further, the expanded polypropylene resin beads according to another embodiment of the present invention have the following constitution: A base resin containing a propylene random copolymer and a propylene block copolymer, and a peak intensity ratio I ７２０ / I ８１０Expanded polypropylene resin particles having a peak intensity ratio I of 0.45 to 0.67 and a shrinkage rate of 20% or less. ７２０ / I ８１０ is the wavelength of 810 cm obtained in the spectrum obtained by infrared spectroscopy. －１ is the intensity of the peak I ８１０ for a wavelength of 720 cm －１ is the intensity of the peak I ７２０ The shrinkage ratio (%) is a value calculated by the following formula (2): shrinkage ratio (%)=(BD-VBD)×100 / VBD (2) In formula (2), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a range where the temperature is 23°C and the pressure is 0.1 MPa, and VBD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a range where the temperature is 23°C and the pressure is -0.09 MPa.

[0009] A method for producing expanded polypropylene-based resin beads according to one embodiment of the present invention comprises the following steps: A method for producing expanded polypropylene-based resin beads comprises an expansion step of depressurizing and expanding polypropylene-based resin particles comprising a base resin containing a propylene-based random copolymer and a propylene-based block copolymer at an expansion temperature of 163.5°C or lower and an expansion pressure of 2.80 MPa or lower, wherein the base resin contains 73 to 95% by weight of the propylene-based random copolymer and 5 to 27% by weight of the propylene-based block copolymer, when the total amount of the propylene-based random copolymer and the propylene-based block copolymer is taken as 100% by weight.

[0010] Another embodiment of the present invention provides a method for producing expanded polypropylene-based resin beads, which comprises the steps of: (1) depressurizing and expanding polypropylene-based resin beads, the polypropylene-based resin beads including a base resin containing a propylene-based random copolymer and a propylene-based block copolymer, at an expansion temperature of 163.5°C or lower and an expansion pressure of 2.80 MPa or lower.

[0011] According to one aspect of the present invention, it is possible to provide expanded polypropylene-based resin beads that are excellent in productivity for use in expanding polypropylene-based resin molded articles, and a expanded polypropylene-based resin molded article obtained by molding the expanded polypropylene-based resin beads.

[0012] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0013] In this specification, a constitutional unit derived from an X monomer contained in a polymer, copolymer, or resin may be referred to as an "X unit."

[0014] Unless otherwise specified in this specification, the structural unit is X １ Units and X ２ Units, ... and X ｎ A copolymer containing units (n is an integer of 2 or more) is referred to as "X １ / X ２ / ・・・ / X ｎ Also referred to as "copolymer". X １ / X ２ / ・・・ / X ｎ Unless otherwise specified, the polymerization mode of the copolymer is not particularly limited, and the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0015] [1. Technical Concept of One Embodiment of the Present Invention] Propylene-based random copolymers are generally used as raw materials for polypropylene-based resin foam molded articles. On the other hand, propylene-based block copolymers may also be used as raw materials for polypropylene-based resin foam molded articles. For example, when the impact resistance of polypropylene-based resin foam molded articles is to be improved or recycled resins are used to reduce environmental impact.

[0016] As a recycled polypropylene resin, propylene block copolymers are distributed in much larger quantities than propylene random copolymers.

[0017] Based on the above-mentioned motivation, the present inventors have conducted extensive research into providing expanded polypropylene resin particles, which are a raw material for polypropylene resin foam moldings, by using a combination of a propylene-based random copolymer and a propylene-based block copolymer.

[0018] Through extensive research, the present inventors independently discovered that when polypropylene resin foam beads are produced using a combination of a propylene-based random copolymer and a propylene-based block copolymer, and the resulting polypropylene resin foam beads are used to produce a polypropylene resin foam molded article, the productivity of the polypropylene resin foam molded article may be poor. For example, when producing a polypropylene resin foam molded article using a mold, the resulting polypropylene resin foam molded article may be cooled before being removed from the mold in order to reduce swelling of the polypropylene resin foam molded article after removal from the mold. This cooling time significantly contributes to the productivity of the polypropylene resin foam molded article. The above-mentioned "poor productivity of the polypropylene resin foam molded article" refers to a case where the cooling time of the polypropylene resin foam molded article is long.

[0019] Therefore, the present inventors have conducted further intensive studies in order to provide expanded polypropylene resin particles that are excellent in productivity for polypropylene resin expansion moldings, even when a propylene random copolymer and a propylene block copolymer are used in combination.

[0020] As a result, the present inventors independently discovered the following novel finding, which led to the completion of the present invention: by using a propylene-based random copolymer and a propylene-based block copolymer in a specific ratio and expanding the polypropylene-based resin particles so that the shrinkage rate of the resulting expanded polypropylene-based resin particles falls within a specific range, it is surprisingly possible to provide expanded polypropylene-based resin particles that are excellent in productivity for producing expanded polypropylene-based resin articles.

[0021] [1. Expanded Polypropylene Resin Beads] The expanded polypropylene resin beads according to one embodiment of the present invention comprise a base resin containing a propylene random copolymer and a propylene block copolymer, and when the content ratio of the block copolymer is X (%) and the expansion pressure during production is Y (MPa), X and Y satisfy the following formula (1):

[0022] Y<-0.07X+3.6...(1).

[0023] Another embodiment of the expanded polypropylene resin beads of the present invention includes a base resin containing a propylene random copolymer and a propylene block copolymer, and has a peak intensity ratio I ７２０ / I ８１０ is 0.45 to 0.67, and the shrinkage rate is 20% or less. ７２０ / I ８１０ is the wavelength of 810 cm obtained in the spectrum obtained by infrared spectroscopy. －１ is the intensity of the peak I ８１０ for a wavelength of 720 cm －１ is the intensity of the peak I ７２０ The shrinkage ratio (%) is a ratio calculated by the following formula (2): Shrinkage ratio (%) = (BD - VBD) x 100 / VBD (2). In formula (2), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement at a temperature of 23°C and a pressure of 0.1 MPa. In formula (2), VBD is the bulk density of the expanded polypropylene resin beads obtained by measurement at a temperature of 23°C and a pressure of -0.09 MPa.

[0024] In this specification, "expanded polypropylene resin beads" may be referred to as "expanded beads," "expanded polypropylene resin beads according to one embodiment of the present invention" may be referred to as "the present expanded beads," and "expanded polypropylene resin molded body" may be referred to as "expanded molded body."

[0025] The present expanded beads have the above-described structure, which is advantageous in that they provide excellent productivity for foamed molded articles. For example, when the expanded beads are used in in-mold foam molding using a mold, the present expanded beads have the advantage of being able to shorten the cooling time of the foamed molded article in the mold. The present expanded beads also have the above-described structure, which is advantageous in that they can provide foamed molded articles with excellent strength.

[0026] <Components> (Base Resin) The base resin contains at least a propylene-based random copolymer and a propylene-based block copolymer as resin components. The base resin may optionally contain additives such as a foam nucleating agent in addition to the resin components. The base resin can also be considered to be the component that essentially constitutes the expanded beads. Therefore, the types and amounts of each component contained in the base resin can also be considered to be the types and amounts of each component contained in the expanded beads.

[0027] Both the propylene random copolymer and the propylene block copolymer are polypropylene resins.

[0028] In this specification, the term "polypropylene resin" refers to a resin containing 50 mol % or more of propylene units out of 100 mol % of all structural units constituting the resin.

[0029] (Propylene-based random copolymer) The propylene-based random copolymer contains at least propylene units and structural units other than the propylene units. In this specification, the "structural units other than the propylene units" contained in the polypropylene-based resin may also be referred to as "comonomer units." In other words, the propylene-based random copolymer contains at least propylene units and comonomer units.

[0030] Comonomers 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.

[0031] From the viewpoint of lowering the molding temperature during in-mold foam molding of the expanded beads, the comonomer unit contained in the propylene-based random copolymer is preferably an ethylene unit, in other words, the propylene-based random copolymer is preferably a propylene / ethylene random copolymer containing a propylene unit and an ethylene unit.

[0032] The propylene-based random copolymer is not limited to a propylene / ethylene random copolymer. Examples of propylene-based random copolymers other than a propylene / ethylene random copolymer include a propylene / 1-butene random copolymer, a propylene / ethylene / 1-butene random copolymer, a propylene / vinyl chloride random copolymer, and a propylene / maleic anhydride random copolymer.

[0033] The propylene-based random copolymer may be a combination of a propylene / ethylene random copolymer and one or more propylene-based random copolymers other than the propylene / ethylene random copolymer.

[0034] The melting point of the propylene random copolymer is not particularly limited, but is preferably 130° C. or higher, more preferably 130° C. to 160° C., more preferably 135° C. to 155° C., and even more preferably 140° C. to 150° C. When the propylene random copolymer has a melting point of (i) 130° C. or higher, the expanded molded article obtained from the expanded beads has excellent heat resistance, and (ii) when the melting point is 160° C. or lower, it is advantageous in that it becomes easy to increase the expansion ratio of the expanded beads in the production of the expanded beads.

[0035] In this specification, the melting points of the propylene-based random copolymer and the propylene-based block copolymer described below are values ​​determined by measurement using a differential scanning calorimeter (hereinafter referred to as the "DSC method"). Specific operating procedures are as described in the examples described below. As the differential scanning calorimeter, for example, a DSC7020 model manufactured by Seiko Instruments Inc. can be used.

[0036] The melt flow rate (MFR) of the propylene random copolymer is not particularly limited. In this specification, "MFR of the propylene random copolymer" refers to the MFR of the propylene random copolymer at 230°C. The MFR of the propylene random copolymer is preferably 3 g / 10 min to 30 g / 10 min, more preferably 4 g / 10 min to 20 g / 10 min, and even more preferably 5 g / 10 min to 18 g / 10 min. When the MFR of the propylene random copolymer at 230°C is within the above range, there is an advantage that expanded beads having a relatively high expansion ratio can be easily obtained. Furthermore, in this case, there are also advantages that the surface aesthetics of the expanded molded article are excellent and the shrinkage rate of the expanded molded article is low.

[0037] In this specification, the MFR at 230°C of the propylene-based random copolymer and the propylene-based block copolymer described below is a value determined by measurement using a melt mass-flow rate (hereinafter, referred to as MFR) measuring device described in JIS-K7210 under the following conditions: orifice diameter 2.0959±0.005 mm, orifice length 8.000±0.025 mm, load 2160 g, and temperature 230±0.2°C.

[0038] The propylene random copolymer may be one obtained by a known method, or a recycled resin may be used. It is preferable to use a non-recycled resin because the quality of the foamed molded article is stable.

[0039] (Propylene-Based Block Copolymer) The propylene-based block copolymer contains at least propylene units and comonomer units.

[0040] The comonomer unit contained in the propylene-based block copolymer is not particularly limited. Specific examples of the comonomer are the same as those described above in the (propylene-based random copolymer) section, and therefore the description therein is incorporated by reference and will not be repeated here.

[0041] From the viewpoint of availability, the comonomer unit contained in the propylene-based block copolymer is preferably an ethylene unit. In other words, the propylene-based block copolymer is preferably a propylene / ethylene block copolymer containing a propylene unit and an ethylene unit. Furthermore, the propylene-based block copolymer is preferably a copolymer containing at least an ethylene block (e.g., a propylene / ethylene block copolymer). The propylene-based block copolymer includes substances that are considered to be propylene-based block copolymers in the technical field of polypropylene-based resins. For example, the propylene / ethylene block copolymer contains a homopolypropylene matrix and a polyethylene layer covered with an ethylene / propylene elastic copolymer as a domain, and is sometimes referred to as an impact copolymer.

[0042] The propylene-based block copolymer is not limited to a propylene / ethylene block copolymer. Examples of propylene-based block copolymers other than the propylene / ethylene block copolymer include a propylene / 1-butene block copolymer, a propylene / ethylene / 1-butene block copolymer, a propylene / vinyl chloride block copolymer, and a propylene / maleic anhydride block copolymer.

[0043] The propylene-based block copolymer may be a combination of a propylene / ethylene block copolymer and one or more propylene-based block copolymers other than the propylene / ethylene block copolymer.

[0044] The melting point of the propylene-based block copolymer is not particularly limited, but is preferably 160° C. or higher, more preferably 162° C. or higher, and even more preferably 165° C. or higher. The upper limit of the melting point of the propylene-based block copolymer is not particularly limited, but is, for example, preferably 180° C. or lower, more preferably 175° C. or lower, and even more preferably 170° C. or lower. When the propylene-based block copolymer has a melting point of (i) 160° C. or higher, it has the effect of providing excellent heat resistance, and when it has a melting point of (ii) 180° C. or lower, it has the effect of providing excellent moldability.

[0045] In one embodiment of the present invention, the difference between the melting point of the propylene-based block copolymer and the melting point of the propylene-based random copolymer (i.e., the value (°C) obtained by subtracting the melting point of the propylene-based random copolymer from the melting point of the propylene-based block copolymer) is not particularly limited, but is preferably not more than 30°C, and more preferably not more than 21°C. This configuration has the advantage that the minimum molding pressure during in-mold molding can be equivalent to that of expanded beads obtained using only a propylene-based random copolymer as the base resin.

[0046] The MFR of the propylene-based block copolymer is not particularly limited. In this specification, "MFR of the propylene-based block copolymer" refers to the MFR of the propylene-based block copolymer at 230°C. The MFR of the propylene-based block copolymer is preferably 3 g / 10 min to 30 g / 10 min, more preferably 4 g / 10 min to 20 g / 10 min, and even more preferably 5 g / 10 min to 18 g / 10 min. When the MFR of the propylene-based block copolymer at 230°C is within the above range, expanded beads having a relatively large expansion ratio are easily obtained, and the resulting expanded molded article has the advantage of excellent surface aesthetics.

[0047] The propylene-based block copolymer may be one obtained by a known method, but is preferably a recycled resin. As described above, the amount of propylene-based block copolymers in circulation as recycled polypropylene-based resins is greater than the amount of propylene-based random copolymers in circulation. Recycled propylene-based block copolymer resins are relatively easy to obtain. Using recycled resin as all or part of the propylene-based block copolymer not only reduces environmental pollution, but also significantly reduces the amount of plastic waste generated and the amount of plastic used in production. Therefore, an embodiment in which recycled resin is used as all or part of the propylene-based block copolymer has the advantage of contributing to the achievement of the Sustainable Development Goals (SDGs).

[0048] In this specification, the term "recycled resin" refers to a resin that has been in the form of a resin product (for example, foam beads, foam molded articles, films, packaging containers such as food trays and bags, bottles, miscellaneous goods such as clothing cases and clear files) more than once, and then has been re-formed into the form of a resin (or resin particles) by means of melting or the like.

[0049] The propylene-based block copolymer may be a mixture of recycled resin and non-recycled resin (a resin that has never been in the form of a resin product). From the viewpoint of reducing the environmental load, the proportion of recycled resin in 100% by weight of the propylene-based block copolymer is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 100% (i.e., composed only of recycled resin).

[0050] When the total amount of the propylene-based random copolymer and the propylene-based block copolymer is taken as 100% by weight, the base resin preferably contains (a) 73% to 95% by weight of the propylene-based random copolymer and 5% to 27% by weight of the propylene-based block copolymer, more preferably (b) 74% to 95% by weight of the propylene-based random copolymer and 5% to 26% by weight of the propylene-based block copolymer, or even more preferably (c) 75% to 93% by weight of the propylene-based random copolymer and 7% to 25% by weight of the propylene-based block copolymer. When the contents of the propylene-based random copolymer and the propylene-based block copolymer contained in the base resin are within the above-mentioned ranges, the expanded beads have the advantage of being more productive for producing polypropylene resin expansion molded articles.

[0051] (Other Resins, etc.) The base resin may further contain, as a resin component, a resin other than a propylene-based random copolymer and a propylene-based block copolymer (sometimes referred to as "other resins, etc."), provided that the effect of one embodiment of the present invention is not impaired. Examples of the other resins, etc. include: (a) polypropylene-based resins other than a propylene-based random copolymer and a propylene-based block copolymer; (b) ethylene-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; (c) styrene-based resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer; (d) polyolefin-based waxes such as a propylene-α-olefin-based wax; and (e) olefin-based rubbers such as an ethylene / propylene rubber, an ethylene / butene rubber, an ethylene / hexene rubber, and an ethylene / octene rubber. The content of the other resin in the present expanded beads is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of the base resin.

[0052] (Additives) The base resin may further contain optional additives in addition to the above-mentioned propylene-based random copolymer and propylene-based block copolymer. Examples of additives include colorants, water-absorbing substances, foam nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, crystal nucleating agents, conductive agents, lubricants, etc. Such additives may be added directly to the blend or polypropylene-based resin composition described below in the production of polypropylene-based resin particles.

[0053] <Physical Properties> The physical properties of the present expanded beads will be described below.

[0054] (Peak Intensity Ratio) The present expanded beads have a peak intensity ratio I ７２０ / I ８１０ is preferably 0.45 to 0.67. ７２０ / I ８１０ is a spectrum obtained by infrared spectroscopy at a wavelength of 720 cm －１ The intensity of the peak is called "I ７２０ " and the wavelength is 810 cm －１ The intensity of the peak is called "I ８１０ " When I ８１０ I against ７２０ The infrared spectroscopic analysis can be performed by the method described in the Examples below. －１ The peak at a wavelength of 810 cm may be a peak mainly derived from an ethylene block. －１ The peak at 720 nm in the expanded particles is likely to be a peak derived mainly from propylene. －１ It is intended that the larger the peak, the more ethylene blocks the expanded beads contain.

[0055] Therefore, the peak intensity ratio I obtained by infrared spectroscopic analysis ７２０ / I ８１０ can relatively accurately reflect the ratio of propylene to ethylene blocks contained in the base resin contained in the expanded beads. Specifically, in a preferred embodiment, when the propylene-based block copolymer contains an ethylene block, the peak intensity ratio I ７２０ / I ８１０It is intended that the larger the value of , the greater the amount of the propylene-based block copolymer in the total amount of the propylene-based random copolymer and the propylene-based block copolymer. In one embodiment, the ratio of the propylene-based random copolymer to the propylene-based block copolymer contained in the base resin can be determined by measuring in advance the peak intensity ratio of the propylene-based block copolymer used in producing the base resin.

[0056] The peak intensity ratio is 0.45 to 0.67, preferably 0.45 to 0.65, more preferably 0.47 to 0.63, even more preferably 0.49 to 0.61, and even more preferably 0.50 to 0.60. According to this configuration, the expanded beads have the advantage of being superior in productivity for polypropylene resin expansion molded articles.

[0057] The peak intensity ratio can be controlled by the content of each block copolymer contained in the present expanded beads.

[0058] (Shrinkage Ratio) The shrinkage ratio of the present expanded beads is calculated by the following formula (2): Shrinkage ratio = (BD - VBD) x 100 / VBD (2) In formula (2), BD is the bulk density of the expanded polypropylene resin beads at 23°C and 0.1 MPa (absolute pressure). In other words, BD can also be said to be the bulk density of the expanded polypropylene resin beads under standard atmospheric pressure. VBD is the bulk density of the expanded polypropylene resin beads at 23°C and -0.09 MPa (gauge pressure) or less. In other words, VBD can be said to be the bulk density of the expanded polypropylene resin beads under reduced pressure.

[0059] The shrinkage rate is 20% or less, preferably 18% or less, and more preferably 16% or less. The lower limit of the shrinkage rate is not particularly limited, but may be, for example, 0% or more. When the shrinkage rate is within the above range, the expanded beads have the advantage of being more efficient in the productivity of polypropylene resin expansion molded articles.

[0060] The shrinkage rate can be controlled by adjusting the conditions (for example, the expansion temperature and the expansion pressure) during the production of the expanded beads.

[0061] (DSC ratio of expanded beads) The expanded beads preferably have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry, which will be described later. Of the melting peaks, the heat of fusion determined from the melting peak on the higher temperature side is referred to as the "higher temperature side heat of fusion," and the heat of fusion determined from the melting peak on the lower temperature side is referred to as the "lower temperature side heat of fusion." When there are three or more melting peaks, the heat of fusion determined from the highest temperature melting peak is referred to as the "higher temperature side heat of fusion," and the heat of fusion determined from the other melting peaks is referred to as the "lower temperature side heat of fusion."

[0062] The DSC ratio of the expanded beads is not particularly limited, but is preferably 10.0% to 50.0%, more preferably 15.0% to 40.0%, and even more preferably 18.0% to 30.0%. When the DSC ratio of the expanded beads is 10.0% or more, the expanded beads have the advantage of being able to provide a foamed molded article with sufficient strength. On the other hand, when the DSC ratio of the expanded beads is 50.0% or less, the expanded beads have the advantage of being able to be molded at a relatively low temperature (molding temperature) to provide a foamed molded article.

[0063] In this specification, the DSC ratio refers to the ratio of the heat of fusion at a higher temperature to the total heat of fusion calculated from the DSC curve of the expanded beads. In this specification, the DSC curve is obtained using a differential scanning calorimeter (e.g., DSC7020 manufactured by Hitachi High-Tech Science Corporation). More specifically, the DSC ratio can be measured by the method described in the Examples.

[0064] The DSC ratio of the expanded beads is also a measure of the amount of high-melting-point crystals contained in the expanded beads. That is, a DSC ratio of 10.0% to 50.0% indicates that the expanded beads contain a relatively large amount of high-melting-point crystals. Furthermore, the DSC ratio of the expanded beads is significantly related to the viscoelasticity of the resin beads and the expanded beads when they are foamed and expanded. That is, when the DSC ratio of the expanded beads is 10.0% to 50.0%, the resin beads and the expanded beads can exhibit excellent foamability and expansion properties, respectively, when they are foamed and when they are molded. As a result, the expanded beads have the advantage that they can produce foamed molded articles with excellent internal fusion properties and excellent mechanical strength, such as compressive strength, even at low molding pressures.

[0065] In the present expanded beads, examples of a method for controlling the DSC ratio within a predetermined range include a method for adjusting the conditions during production of the present expanded beads (particularly, the foaming temperature, foaming pressure, holding time, and the temperature of the region (space) from which the dispersion is released, etc.) In terms of ease of adjustment, a method for controlling the DSC ratio within a predetermined range by adjusting the foaming temperature, foaming pressure, and / or holding time is preferred.

[0066] For example, increasing the foaming temperature tends to decrease the DSC ratio, while decreasing the foaming temperature tends to increase the DSC ratio. This is because the amount of unmelted crystals varies depending on the foaming temperature. Increasing the foaming pressure also tends to decrease the DSC ratio, while decreasing the foaming pressure also tends to increase the DSC ratio. This is because the degree of plasticization varies depending on the foaming pressure, thereby changing the amount of unmelted crystals. In addition, the DSC ratio tends to increase as the holding time increases. This is because the amount of growth of unmelted crystals varies depending on the holding time.

[0067] (Expansion Ratio of Expanded Beads) The expanded beads preferably have an expansion ratio of 15 to 50, more preferably 18 to 40, and even more preferably 20 to 25. If the expansion ratio of the expanded beads is (i) 15 or more, a lightweight expanded molded article can be obtained efficiently, and (ii) if it is 50 or less, there is no risk of the strength of the resulting expanded molded article being insufficient. The expansion ratio can be measured by the method described in the examples below.

[0068] The present expanded beads have the advantage that they can be used to obtain a foamed molded article having an excellent fusion rate (for example, a fusion rate of 80% or more) at a low molding pressure. In other words, the present expanded beads have the advantage that they can provide a foamed molded article having an excellent fusion rate at a molding pressure equivalent to that of foamed beads obtained using only a propylene-based random copolymer as the base resin.

[0069] In this specification, the minimum molding pressure that can provide a foamed molded article having an excellent fusion rate (e.g., a fusion rate of 80% or more) in the production of a foamed molded article using expanded beads is also referred to as the "minimum molding pressure." The minimum molding pressure can be measured by the method described in the Examples below. The present expanded beads also have the advantage of a low minimum molding pressure. In other words, the minimum molding pressure of the present expanded beads can be equivalent to that of expanded beads obtained using only a propylene-based random copolymer as the base resin.

[0070] The minimum molding pressure of the present expanded beads is not particularly limited, but is preferably 0.30 MPa or less, more preferably 0.28 MPa or less, and even more preferably 0.26 MPa or less. The lower limit of the minimum molding pressure is not particularly limited, but may be, for example, 0.15 MPa or more. When the minimum molding pressure is within the above range, there is an advantage that a foamed molded article can be provided with a small economic burden.

[0071] 2. Method for Producing Expanded Polypropylene Resin Beads A method for producing expanded polypropylene resin beads according to one embodiment of the present invention includes an expansion step of depressurizing and expanding polypropylene resin beads, which include a base resin containing a propylene random copolymer and a propylene block copolymer, at an expansion temperature of 163.5°C or lower and an expansion pressure of 2.80 MPa or lower.

[0072]

[0013] Another embodiment of the present invention relates to a method for producing expanded polypropylene-based resin beads, which comprises a foaming step of depressurizing and foaming polypropylene-based resin beads comprising a base resin containing a propylene-based random copolymer and a propylene-based block copolymer at a foaming temperature of 163.5°C or lower and a foaming pressure of 2.80 MPa or lower, wherein the base resin contains 73 to 95% by weight of the propylene-based random copolymer and 5 to 27% by weight of the propylene-based block copolymer, where the total amount of the propylene-based random copolymer and the propylene-based block copolymer is taken as 100% by weight (granulation step). This production method may further comprise a step of producing polypropylene-based resin particles comprising a base resin containing a propylene-based random copolymer and a propylene-based block copolymer (granulation step). In this specification, "polypropylene-based resin particles" may also be referred to as "resin particles."

[0073] Examples of methods for producing resin particles include methods using an extruder. Specifically, resin particles can be produced by, for example, the following methods (1) to (5): (1) blending a block copolymer, a random copolymer, and, if necessary, one or more selected from the group consisting of other resins and additives to produce a blend; (2) feeding the blend into an extruder and melt-kneading the blend to prepare a polypropylene-based resin composition; (3) extruding the polypropylene-based resin composition through a die provided in the extruder; (4) solidifying the extruded polypropylene-based resin composition by cooling it, for example by passing it through water; (5) then cutting the solidified polypropylene-based resin composition into a desired shape, such as a cylindrical, elliptical, spherical, cubic, rectangular, hollow cylinder, or polygonal prism, using a cutter. Alternatively, the melt-kneaded polypropylene-based resin composition in (3) may be directly extruded into water through a die provided in the extruder, and immediately after extrusion, the polypropylene-based resin composition may be cut into particles, cooled, and solidified. By melt-kneading the blend in this manner, more uniform resin particles can be obtained.

[0074] The weight per particle of the resin particles obtained as described above is preferably 0.2 mg / particle to 10.0 mg / particle, and more preferably 0.5 mg / particle to 6.0 mg / particle. When the weight per particle of the resin particles is (A) 0.2 mg / particle or more, the handleability of the resin particles tends to be improved, and the shrinkage rate of the foamed molded article obtained by molding the obtained foamed beads tends to be small. When the weight per particle of the resin particles is (B) 10.0 mg / particle or less, the mold filling property tends to be improved in the in-mold foam molding process.

[0075] (Dispersion Step) The present production method may further include a dispersion step, prior to the foaming step, of dispersing a base resin containing a propylene-based random copolymer and a propylene-based block copolymer, an aqueous dispersion medium, a blowing agent, and, if necessary, a dispersant and / or a dispersion aid, in a container. The dispersion step can also be said to be a step of preparing a dispersion in which the base resin, the blowing agent, and, if necessary, the dispersant and / or a dispersion aid are dispersed in an aqueous dispersion medium. The base resin in the dispersion step may be the resin particles obtained in the above-mentioned granulation step.

[0076] The container is not particularly limited, but is preferably one that can withstand the foaming temperature and foaming pressure described below. The container is preferably, for example, a pressure-resistant container, more preferably an autoclave-type pressure-resistant container. The container may be equipped with a stirrer inside.

[0077] The aqueous dispersion medium is not particularly limited as long as it can uniformly disperse the resin particles, the foaming agent, etc.

[0078] Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, glycerin, or the like to water, (b) water such as ultrapure water, pure water, tap water, and industrial water, and (c) solutions containing salts such as sodium chloride or sodium sulfate (aqueous solutions).

[0079] In terms of enabling stable production of expanded beads, it is preferable to use, as the aqueous dispersion medium, pure water such as RO water (water purified by a reverse osmosis membrane method), distilled water, deionized water (water purified by an ion exchange resin), or ultrapure water.

[0080] Examples of the blowing agent include (a) (a-1) inorganic blowing agents such as nitrogen, carbon dioxide, air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) organic blowing agents such as (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane, (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and (b-3) halogenated hydrocarbons such as monochloromethane, chloroethane, and hydrofluoroolefins.

[0081] As the foaming agent, at least one selected from the group consisting of the inorganic foaming agents and organic foaming agents described above can be used. When two or more foaming agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose. From the viewpoints of environmental impact and foaming power, inorganic foaming agents are preferred as the foaming agent among the above-mentioned foaming agents. Furthermore, carbon dioxide is preferred among inorganic foaming agents because it has a moderately high plasticizing effect and is easy to improve the expandability of the expanded beads in the production of the present expanded beads.

[0082] The aqueous dispersion medium and the blowing agent may each be used alone or in combination of two or more.

[0083] In the present method for producing expanded beads, it is preferable to use a dispersant (e.g., an inorganic substance such as tricalcium phosphate, kaolin, or talc) and a dispersing aid (e.g., an anionic surfactant such as sodium alkanesulfonate or sodium dodecylbenzenesulfonate). This configuration can reduce adhesion of resin particles (sometimes called blocking) and improve the stability of the dispersion in the container. As a result, it has the advantage of enabling stable production of expanded beads.

[0084] (Expansion Step) The specific embodiment of the expansion step is not particularly limited. The expansion step may include, for example, (a) a temperature-pressure increase step of increasing the temperature inside the container to a constant temperature and increasing the pressure inside the container to a constant pressure to depressurize and expand the resin particles, (b) a holding step of maintaining the temperature and pressure inside the container at a constant temperature and constant pressure, and (c) a release step of opening one end of the container and releasing the dispersion inside the container into a region (space) with a pressure lower than the expansion pressure (i.e., the pressure inside the container).

[0085] (Temperature-Pressure Increase Step and Holding Step) The temperature-pressure increase step is preferably carried out after the dispersion step, and the holding step is preferably carried out after the temperature-pressure increase step.

[0086] The foaming temperature is 163.5° C. or lower, preferably 163.3° C. or lower, and more preferably 163.2° C. or lower. The lower limit of the foaming temperature is not particularly limited as long as the resin particles can be depressurized and foamed, but may be, for example, 150° C. or higher.

[0087] The foaming pressure is 2.80 MPa or less, preferably 2.75 MPa or less, more preferably 2.70 MPa or less, and even more preferably 2.60 MPa or less. The lower limit of the foaming pressure is not particularly limited as long as the resin particles can be depressurized and foamed, but may be, for example, 1.5 MPa or more.

[0088] Through extensive research, the present inventors independently discovered the novel finding that, in order to obtain expanded beads with a low shrinkage rate, it is preferable to appropriately set the expansion pressure depending on the amount of propylene-based block copolymer. Specifically, the present inventors independently discovered the novel finding that, in order to obtain expanded beads with a low shrinkage rate, it is preferable to set a lower expansion pressure as the amount of propylene-based block copolymer increases. More specifically, the present inventors independently discovered the novel finding that, when the content ratio of the block copolymer in the polypropylene-based resin beads is X (wt %) relative to the total weight of the propylene-based random copolymer and the propylene-based block copolymer in the polypropylene-based resin beads (100 wt %), the expansion pressure Y (MPa) during the production of the expanded beads preferably satisfies the following formula (1): Y<−0.07X+3.6 (1). The reason why formula (1) is preferably satisfied is unclear, but it is speculated that this is because the propylene-based block copolymer is softer and more extensible than the propylene-based random copolymer. However, one embodiment of the present invention is in no way limited by this speculation.

[0089] It is more preferable that X and Y satisfy the following formula (3), further preferably the following formula (4), and particularly preferably the following formula (5): Y<-0.07X+3.55 (3) Y<-0.07X+3.5 (4) Y<-0.07X+3.45 (5).

[0090] In the holding step, the time (holding time) for holding the dispersion in the container at near the foaming temperature and foaming pressure is not particularly limited. The holding time is preferably 10 to 60 minutes, more preferably 12 to 55 minutes, and even more preferably 15 to 50 minutes. When the holding time is 10 minutes or longer, the amount of unmelted crystals (crystals of polypropylene-based resin) in the resin particles can be made sufficient during the expansion process from the resin particles to the expanded beads. As a result, expanded beads with a low open cell ratio can be obtained, and shrinkage of the resulting expanded beads can be reduced. On the other hand, when the holding time is 60 minutes or shorter, the amount of unmelted crystals in the resin particles does not become excessive during the expansion process from the resin particles to the expanded beads. Therefore, the resulting expanded beads can be molded at a relatively low temperature (molding temperature) to provide a foamed molded article.

[0091] (Releasing Step) The releasing step is preferably carried out after the temperature-pressure increasing step (a) when the holding step is not carried out, or after the holding step (b) when the holding step is carried out. The releasing step allows the resin particles to expand, resulting in expanded particles.

[0092] In the releasing step, the "region under a pressure lower than the foaming pressure" refers to a "region under a pressure lower than the foaming pressure" or a "space under a pressure lower than the foaming pressure", and can also be referred to as "an atmosphere under a pressure lower than the foaming pressure". The region under a pressure lower than the foaming pressure is not particularly limited as long as it is lower than the foaming pressure, and may be, for example, a region under atmospheric pressure.

[0093] In the discharging step, when the dispersion is discharged into a region with a pressure lower than the expansion pressure, the dispersion may be discharged through an orifice having a diameter of 1 mm to 5 mm for the purposes of adjusting the flow rate of the dispersion, reducing variations in the expansion ratio of the resulting expanded beads, etc. Furthermore, for the purpose of improving the expandability, the low-pressure region (space) may be filled with saturated water vapor.

[0094] The process of producing expanded beads from resin beads in this manner is called the "first-stage expansion process," and the resulting expanded beads are called "first-stage expanded beads."

[0095] (Second-stage expansion process) In order to obtain expanded beads with a high expansion ratio, the first-stage expanded beads obtained in the first-stage expansion process may be expanded again. The process of increasing the expansion ratio of the first-stage expanded beads is called the "second-stage expansion process", and the expanded polyolefin resin beads obtained by the second-stage expansion process are called "second-stage expanded beads". The specific method for the second-stage expansion process is not particularly limited, and known methods can be used.

[0096] [3. Polypropylene-based resin foam molded article] A polypropylene-based resin foam molded article according to one embodiment of the present invention is a foam molded article obtained by foam molding the polypropylene-based resin foam beads described in the section [1. Polypropylene-based resin foam beads]. The polypropylene-based resin foam molded article according to one embodiment of the present invention may be a foam molded article obtained by foam molding the polypropylene-based resin foam beads obtained by the production method described in the section [2. Production method of polypropylene-based resin foam beads]. It can also be said that the polypropylene-based resin foam molded article according to one embodiment of the present invention comprises the polypropylene-based resin foam beads described in the section [1. Polypropylene-based resin foam beads] or the polypropylene-based resin foam beads obtained by the production method described in the section [2. Production method of polypropylene-based resin foam beads].

[0097] In this specification, the "polypropylene resin foam molded article according to one embodiment of the present invention" may be referred to as the "present foam molded article."

[0098] The foamed molded article of the present invention has the above-mentioned configuration, and therefore has the advantages of being excellent in productivity and strength.

[0099] (Productivity) In this specification, the productivity of the present foamed molded article is evaluated by the time (seconds) from the start of molding of the present foamed beads to the completion of molding (molding cycle). As described in the Examples below, the start of molding was the time when the present foamed beads were filled into the mold. The completion of molding was the time when the molded article was cooled (water-cooled) and the mold was opened when the surface pressure measured by a surface pressure gauge attached to the surface of the Planck mold decreased to 0.01 MPa, and the mold was released. It is intended that the shorter the molding cycle, the more productive the foamed molded article will be.

[0100] (Surface aesthetics) In this specification, the surface aesthetics of the present foamed molded article is evaluated based on the degree of gaps between the foam particles (hereinafter sometimes referred to as "intergranular gaps") on the surface of the foamed molded article and the wrinkles on the surface of the foamed molded article. The smaller the size and number of intergranular gaps on the surface of the foamed molded article, the better the surface aesthetics of the foamed molded article. Furthermore, the fewer wrinkles on the surface of the foamed molded article, the better the surface aesthetics of the foamed molded article.

[0101] (Static Compressive Strength) The present foam molded article also has the advantage of being excellent in strength. In this specification, the strength of the foam molded article is evaluated by static compressive strength. The method for measuring the static compressive strength of the foam molded article will be described in detail in the Examples below.

[0102] The static compressive strength of the foamed molded article is preferably 0.212 MPa or more, more preferably 0.217 MPa or more, and even more preferably 0.229 MPa or more. The upper limit of the static compressive strength is not particularly limited, but may be, for example, 0.300 MPa or less. This configuration has the advantage of being durable when used in applications such as automotive interior components, core materials for automotive bumpers, heat insulating materials, cushioning packaging materials, and returnable boxes.

[0103] An embodiment of the present invention may include the following features.

[0104] [1] A method for producing expanded polypropylene resin beads, comprising: an expansion step of depressurizing and expanding polypropylene resin particles comprising a base resin containing a propylene-based random copolymer and a propylene-based block copolymer at an expansion temperature of 163.5°C or lower and an expansion pressure of 2.80 MPa or lower, wherein the base resin contains 73% by weight to 95% by weight of the propylene-based random copolymer and 5% by weight to 27% by weight of the propylene-based block copolymer, when the total amount of the propylene-based random copolymer and the propylene-based block copolymer is taken as 100% by weight.

[0105] [2] The method for producing expanded polypropylene resin beads according to [1], which satisfies the following formula (1): Y<-0.07X+3.6 (1); wherein X is the content (wt%) of the propylene block copolymer in the base resin when the total amount of the propylene random copolymer and the propylene block copolymer in the base resin is taken as 100 wt%, and Y is the foaming pressure (MPa) in the foaming step.

[0106] [3] The method for producing expanded polypropylene resin beads according to [1] or [2], wherein the expansion step is a two-stage expansion step.

[0107] [4] The method for producing expanded polypropylene resin beads according to any one of [1] to [3], wherein the expansion temperature is 150°C or higher.

[0108] [5] The method for producing expanded polypropylene beads according to any one of [1] to [4], wherein the expansion pressure is 1.5 MPa or more.

[0109] [6] The method for producing expanded polypropylene beads according to any one of [1] to [5], wherein the melting point of the propylene block copolymer is 160°C or higher and 180°C or lower.

[0110] [7] The method for producing expanded polypropylene beads according to any one of [1] to [6], wherein the propylene block copolymer is a recycled resin.

[0111] [8] The method for producing expanded polypropylene beads according to any one of [1] to [7], wherein the propylene random copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units, and the propylene block copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units.

[0112] [9] The method for producing expanded polypropylene-based beads according to any one of [1] to [8], wherein the propylene-based random copolymer comprises a propylene / ethylene random copolymer containing a propylene unit and an ethylene unit.

[0113]

[10] The method for producing expanded polypropylene beads according to any one of [1] to [9], wherein the melt flow rate of the propylene random copolymer at 230°C is 3 g / 10 min to 30 g / 10 min.

[0114]

[11] The method for producing expanded polypropylene beads according to any one of [1] to

[10] , wherein the difference between the melting point of the propylene block copolymer and the melting point of the propylene random copolymer is 30°C or less.

[0115]

[12] The method for producing expanded polypropylene beads according to any one of [1] to

[11] , wherein the melt flow rate of the propylene block copolymer at 230°C is 3 g / 10 min to 30 g / 10 min.

[0116]

[13] The method for producing expanded polypropylene resin beads according to any one of [1] to

[12] , wherein the expanded polypropylene resin beads have a DSC ratio of 10.0% to 50.0%.

[0117]

[14] The method for producing expanded polypropylene resin beads according to any one of [1] to

[13] , wherein the expanded polypropylene resin beads have an expansion ratio of 15 to 50 times.

[0118]

[15] A method for producing a polypropylene-based resin foamed molded article, comprising a step of molding the expanded polypropylene-based resin beads obtained by the method for producing expanded polypropylene-based resin beads according to any one of [1] to

[14] at a molding pressure of 0.30 MPa or less.

[0119]

[16] A substrate resin containing a propylene-based random copolymer and a propylene-based block copolymer, wherein the peak intensity ratio I ７２０ / I ８１０ Expanded polypropylene resin particles having a peak intensity ratio I of 0.45 to 0.67 and a shrinkage rate of 20% or less. ７２０ / I ８１０ is the wavelength of 810 cm obtained in the spectrum obtained by infrared spectroscopy. －１ is the intensity of the peak ８１０ for a wavelength of 720 cm －１ is the intensity of the peak ７２０The shrinkage ratio (%) is a value calculated by the following formula (2): shrinkage ratio (%)=(BD-VBD)×100 / VBD (2) In formula (2), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a range where the temperature is 23°C and the pressure is 0.1 MPa, and VBD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a range where the temperature is 23°C and the pressure is -0.09 MPa.

[0120]

[17] The expanded polypropylene resin particles according to

[16] , wherein the base resin contains 73 to 95% by weight of the propylene random copolymer and 5 to 27% by weight of the propylene block copolymer, when the total amount of the propylene random copolymer and the propylene block copolymer is taken as 100% by weight.

[0121]

[18] The expanded polypropylene resin particles according to either

[16] or

[17] , wherein the melting point of the propylene block copolymer is 160°C or higher and 180°C or lower.

[0122]

[19] The expanded polypropylene resin particles according to any one of

[16] to

[18] , wherein the propylene block copolymer is a recycled resin.

[0123]

[20] The expanded polypropylene resin particles according to any one of

[16] to

[19] , wherein the propylene random copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units, and the propylene block copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units.

[0124]

[21] The expanded polypropylene resin particles according to any one of

[16] to

[20] , wherein the propylene random copolymer comprises a propylene / ethylene random copolymer containing a propylene unit and an ethylene unit.

[0125]

[22] The expanded polypropylene resin particles according to any one of

[16] to

[21] , wherein the melt flow rate of the propylene random copolymer at 230°C is 3 g / 10 min to 30 g / 10 min.

[0126]

[23] The expanded polypropylene resin particles according to any one of

[16] to

[22] , wherein the difference between the melting point of the propylene block copolymer and the melting point of the propylene random copolymer is 30°C or less.

[0127]

[24] The expanded polypropylene resin particles according to any one of

[16] to

[23] , wherein the propylene block copolymer has a melt flow rate at 230°C of 3 g / 10 min to 30 g / 10 min.

[0128]

[25] Expanded polypropylene resin particles according to any one of

[16] to

[24] , having a DSC ratio of 10.0% to 50.0%.

[0129]

[26] Expanded polypropylene resin particles according to any one of

[16] to

[25] , having an expansion ratio of 15 to 50 times.

[0130]

[27] The expanded polypropylene resin beads according to any one of

[16] to

[26] , wherein when the expanded polypropylene resin beads are molded, the minimum molding pressure required to provide a polypropylene resin expansion molded article having a fusion rate of 80% or more is 0.30 MPa or less.

[0131]

[28] A polypropylene resin foam molded article obtained by foam molding the expanded polypropylene resin beads according to any one of

[16] to

[27] .

[0132]

[29] The propylene-based resin foam molded article according to

[28] , having a static compressive strength of 0.212 MPa or more.

[0133] Another embodiment of the present invention includes the following configuration.

[0134] [1] A polymer film comprising a base resin containing a propylene-based random copolymer and a propylene-based block copolymer, and having a peak intensity ratio I ７２０ / I ８１０ Expanded polypropylene resin particles having a peak intensity ratio I of 0.45 to 0.65 and a shrinkage rate of 20% or less. ７２０ / I ８１０is the wavelength of 810 cm obtained in the spectrum obtained by infrared spectroscopy. －１ is the intensity of the peak ８１０ for a wavelength of 720 cm －１ is the intensity of the peak ７２０ The shrinkage ratio (%) is a ratio of the temperature and pressure of the expanded polypropylene resin beads to the bulk density of the expanded polypropylene resin beads, and the shrinkage ratio (%) is a value calculated by the following formula (1): Shrinkage ratio (%)=(BD-VBD)×100 / VBD (1) In formula (1), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a range where the temperature is 23°C and the pressure is 0.1 MPa, and VBD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a range where the temperature is 23°C and the pressure is -0.09 MPa.

[0135] [2] The expanded polypropylene resin particles according to [1], wherein the base resin contains 75% by weight to 95% by weight of the propylene random copolymer and 5% by weight to 25% by weight of the propylene block copolymer, when the total amount of the propylene random copolymer and the propylene block copolymer is taken as 100% by weight.

[0136] [3] The expanded polypropylene resin particles according to [1] or [2], wherein the melting point of the propylene block copolymer is 160°C or higher.

[0137] [4] The expanded polypropylene resin particles according to any one of [1] to [3], wherein the propylene block copolymer is a recycled resin.

[0138] [5] A polypropylene resin foam molded article obtained by foam molding the expanded polypropylene resin beads according to any one of [1] to [4].

[0139] [6] A method for producing expanded polypropylene resin beads, comprising an expansion step of depressurizing and expanding polypropylene resin beads comprising a base resin containing a propylene random copolymer and a propylene block copolymer at an expansion temperature of 163.5°C or less and an expansion pressure of 2.80 MPa or less.

[0140] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0141] [Materials] In the examples and comparative examples, the following materials were used, but no particular purification or the like was carried out.

[0142] <Polypropylene Resins> Propylene / Ethylene Block Copolymer 1 [MFR=12 g / 10 min, melting point 166°C, recycled resin containing 5 wt% carbon black] Propylene / Ethylene Block Copolymer 2 [J715M manufactured by Prime Polymer Co., Ltd., MFR=9 g / 10 min, melting point 165°C, recycled resin] Propylene / Ethylene Block Copolymer 3 [MFR=29 g / 10 min, melting point 165°C, recycled resin] Propylene / Ethylene Random Copolymer [MFR=7 g / 10 min, melting point 145°C, non-recycled resin] <Resin Particle Additives> Talc [Talc Powder PK-S manufactured by Hayashi Kasei Co., Ltd.] Glycerin [Purified Glycerin D manufactured by Lion Corporation] [Measurement Methods] The evaluation methods used in the examples and comparative examples are described below.

[0143] <Measurement of Melting Point of Polypropylene-Based Resin> The melting point of the polypropylene-based resin particles was measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). The specific measurement method is as follows: (1) 5 to 6 mg of the sample to be measured was heated from 40°C to 220°C at a heating rate of 10°C / min to melt it; (2) Thereafter, the temperature was lowered from 220°C to 40°C at a heating rate of 10°C / min to crystallize it; (3) The temperature was further increased from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (melting peak) of the DSC curve obtained during the second heating (i.e., during (3)) was taken as the melting point of the polypropylene-based resin particles.

[0144] <Measurement of MFR of Polypropylene-Based Resin> The MFR of a polypropylene-based resin was measured using a melt mass-flow rate (hereinafter, referred to as MFR) measuring device described in JIS K7210 under the following conditions: orifice diameter: 2.0959±0.005 mm, orifice length: 8.000±0.025 mm, load: 2160 g, and temperature: 230±0.2°C.

[0145] <Measurement of DSC Ratio of Expanded Polypropylene Resin Beads> The DSC ratio was measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). Specifically, the area of ​​the melting peak on the low-temperature side of the DSC curve obtained during the first temperature rise when 5 to 6 mg of expanded polypropylene resin beads was heated from 40°C to 220°C at a heating rate of 10°C / min was determined as Q ｌ The melting peak area on the high temperature side is Q ｈ The DSC ratio (%) was calculated using the following formula: ｈ / (Q ｌ +Q ｈ ) × 100 Strictly speaking, the area enclosed by the melting peak on the low temperature side and the tangent to the melting initiation baseline from the maximum point between the melting peak on the low temperature side and the melting peak on the high temperature side is defined as Q ｌ The heat quantity of the melting peak on the high temperature side, which is the heat quantity enclosed by the melting peak on the high temperature side and the tangent line from the maximum point between the melting peak on the low temperature side and the melting peak on the high temperature side to the melting end baseline, is defined as Q ｈ It was decided.

[0146] <Infrared Spectroscopic Analysis of Expanded Polypropylene Resin Beads> The ratio of peak intensities derived from propylene and block ethylene was determined by infrared spectroscopic analysis of expanded polypropylene resin beads. The measurement was performed by an attenuated total reflection method (hereinafter referred to as an ATR method). The expanded polypropylene resin beads were sandwiched between metal plates and crushed, and then pressed against the crystal of an ATR measurement device (Spectrum Two, manufactured by PerkinElmer Japan Co., Ltd.) with a resolution of 4 cm. －１ The measurement was carried out with 16 accumulations to obtain a spectrum. －１The pressure applied during compression was adjusted so that the peak intensity at a wavelength of 810 cm was 0.15 A. －１ The peak intensity (I ８１０ ) and wavelength 720 cm －１ The peak intensity (I ７２０ ) and [(I ７２０ ) / (I ８１０ In this example, the peak intensity ratio was calculated from the following: －１ The peak intensity of propylene CH ３ The peak intensity is derived from the wavelength of 720 cm －１ The peak intensity of was the peak intensity derived from ethylene chains. The measurement was performed on five randomly selected polypropylene resin expanded beads, and the arithmetic mean value was used. In Comparative Example 3, since expanded beads were not obtained as described below, the measurement was similarly performed using resin beads. If the measurement conditions are the same, it is expected that there will be almost no difference in the measurement results of the peak intensity ratio between the case where expanded beads are used as a sample and the case where resin beads are used.

[0147] <Measurement of Expansion Ratio of Expanded Polypropylene Resin Beads> Approximately 3 g to 10 g of expanded polypropylene resin beads are taken, dried at 60° C. for 6 hours, and then conditioned in a room at 23° C. and 50% humidity. １ After measuring (g), the sample is submerged in a measuring cylinder containing ethanol, and the volume v (cm) is determined by the amount of water level rise in the measuring cylinder (submersion method). ３ ) and the true specific gravity ρ ｂ =w １ / v is calculated, and the density ρ of the polypropylene resin particles before foaming is calculated. ｒ The ratio of (ρ ｒ / ρ ｂ In the following examples and comparative examples, the density ρ of the polypropylene-based resin particles (polypropylene-based resin particles) before foaming was calculated as ｒ are all 0.9 g / cm ３ It was.

[0148] <Measurement of Shrinkage Ratio of Expanded Polypropylene Resin Beads> The shrinkage ratio of expanded polypropylene resin beads was calculated from the bulk density (hereinafter referred to as BD) and the bulk density of the expanded polypropylene resin beads under reduced pressure (hereinafter referred to as VBD) by the following method. The weight of the expanded polypropylene resin beads to be measured was defined as W １ The volume V was measured using a measuring cylinder at 23°C under atmospheric pressure (standard atmospheric pressure 0.1 MPa). １ The bulk density BD of the expanded polypropylene resin beads at 23°C and 0.1 MPa (standard atmospheric pressure) was calculated according to the following formula: BD (g / L) = W １ ÷V １ The polypropylene resin foam particles were weighed again and their weight was calculated as W ２ The contents were placed in a pressure-resistant container with a scale, and the pressure inside the pressure-resistant container was reduced using a vacuum pump or the like. After confirming with a pressure gauge that the pressure had been reduced to -0.09 MPa (gauge pressure) or less, the pressure-resistant container was vibrated using a vibrator until the scale on the top of the foamed beads stopped changing, and then the scale on the top of the polypropylene resin foamed beads inside the pressure-resistant container was read, and this was used to determine the volume V ２ During decompression, the expanded beads may push against each other, inhibiting volumetric change. Therefore, the pressure vessel was turned sideways to prevent the expanded beads from inhibiting volumetric change, and the pressure was gradually reduced. The bulk density VBD of the expanded polypropylene resin beads at 23°C and a reduced pressure of -0.09 MPa (gauge pressure) or less was calculated according to the following formula: VBD (g / L) = W ２ ÷V ２ The shrinkage rate of the expanded polypropylene resin beads was calculated using the following formula.

[0149] (BD-VBD)÷VBD×100.

[0150] <Minimum molding pressure for polypropylene-based resin in-mold foam molded articles> The steam pressure setting for the main heating step in the "Preparation of polypropylene-based resin in-mold foam molded articles" described below was changed in 0.01 MPa increments within the range of 0.20 to 0.32 MPa (gauge pressure) and molding was performed to obtain foam molded articles for evaluation. A crack approximately 5 mm deep was made in the surface of the obtained foam molded articles with a knife, and the in-mold foam molded article 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 determined to evaluate the fusion rate of the molded article. The minimum molding pressure was determined as the lowest steam pressure at which the fusion rate reached 80% or more.

[0151] <Molding Cycle for Polypropylene-Based Resin In-Mold Foam Molded Articles> The molding cycle in the manufacturing method for polypropylene-based resin in-mold foam molded articles was measured from the start of molding to the end of molding, when the molded article was demolded. The start of molding was the point at which the polypropylene-based resin foam beads began to be filled into the mold. Steam was pumped into the mold to heat the mold, and the molded article was then water-cooled. The mold was opened when the surface pressure measured by a pressure gauge attached to the surface of the Planck mold dropped to 0.01 MPa. The end of molding was the point at which demolding was completed. The steam heating pressure was evaluated as the minimum molding pressure calculated in the above-mentioned <Minimum Molding Pressure for Polypropylene-Based Resin In-Mold Foam Molded Articles>. Productivity was evaluated based on the following criteria: ⊚ (Very Excellent): Molding cycle was 180 seconds or less. ∘ (Excellent): Molding cycle was longer than 180 seconds but not exceeding 210 seconds. × (Poor): Molding cycle was 210 seconds or longer.

[0152] <Surface Beauty of Polypropylene Resin In-Mold Foam Molded Article> A 350 mm long x 450 mm wide surface of the obtained polypropylene resin in-mold foam molded article was visually observed, and the surface beauty was judged according to the following criteria. Interparticle gaps (gaps between polypropylene resin foam particles), which are one of the evaluation indices for surface quality, were judged by visually counting the number of gaps present in a 50 mm square area at the center of the surface of the molded article. ⊚ (Beautiful surface appearance): No wrinkles and 0 to 1 interparticle gap. ◯ (Good surface appearance): No wrinkles and 2 to 3 interparticle gaps. △ (Passable surface appearance): Wrinkles are observed or 4 to 5 interparticle gaps are present. × (Failed surface appearance): Wrinkles are observed or 6 or more interparticle gaps are present.

[0153] <Measurement of static compressive strength of polypropylene-based resin in-mold foam molded article> A test piece measuring 50 mm long x 50 mm wide x 25 mm thick was cut out from a polypropylene-based resin in-mold foam molded article, and the compressive stress at 50% compression was measured when the test piece was compressed at a rate of 10 mm / min using a tension-compression tester (TG series, manufactured by MinebeaMitsumi Inc.) The compressive stress at 50% compression is a measure of the rigidity of the in-mold foam molded article.

[0154] The methods for producing polypropylene resin particles, expanded polypropylene resin particles, and in-mold foamed polypropylene resin articles in Examples and Comparative Examples will be described below.

[0155] Example 1 [Method for producing polypropylene-based resin particles] 89.75 parts by weight of ethylene / propylene random copolymer, 10 parts by weight of ethylene / propylene block copolymer, 0.2 parts by weight of glycerin, and 0.05 parts by weight of talc were weighed and dry-blended using a blender. The dry-blended mixture was melt-kneaded at a resin temperature of 220°C using a twin-screw extruder (TEM26-SX, manufactured by Toshiba Machine Co., Ltd.), and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene-based resin particles (1.2 mg / particle).

[0156] [Preparation of Expanded Polypropylene Resin Beads] A 10 L pressure-resistant autoclave was charged with 100 parts by weight (2.4 kg) of the polypropylene resin particles obtained as described above, 200 parts by weight of water, 0.3 parts by weight of kaolin (manufactured by BASF, ASP170) as a water-insoluble inorganic compound, and 0.06 parts by weight of sodium dodecylbenzenesulfonate (manufactured by Kao Corporation, Neopelex G-15) as a surfactant, and then 4 parts by weight of carbon dioxide was added as a blowing agent under stirring. The contents of the autoclave were heated to a foaming temperature of 158.2°C and maintained for 10 minutes. After that, additional carbon dioxide was injected to increase the internal pressure of the autoclave to a foaming pressure of 2.60 MPa. After maintaining the foaming temperature and foaming pressure for 20 minutes, the valve at the bottom of the autoclave was opened, and the contents were released into atmospheric pressure through a 3.6 mm diameter orifice, yielding expanded polypropylene resin beads with an expansion ratio of 24 times. During this release, carbon dioxide was injected to maintain the pressure in the container so that it would not decrease.

[0157] [Preparation of Polypropylene-Based Resin In-Mold Foam Molded Article] The resulting polypropylene-based resin foam beads were dried at 75°C. The dried polypropylene-based resin foam beads were placed in a pressure-resistant container and impregnated with pressurized air. The polypropylene-based resin foam beads, previously adjusted to an internal foam pressure of 0.20 MPa (absolute pressure), were then filled into a mold measuring 370 mm long, 320 mm wide, and 50 mm thick. The mold chamber was then heated with steam at a predetermined pressure to fuse the foamed beads together. The mold interior and the molded article surface were then water-cooled, and the molded article was removed to obtain a polypropylene-based resin in-mold foam molded article. This operation was repeated while varying the steam pressure from 0.20 MPa (gauge pressure) to 0.32 MPa in 0.01 MPa increments. The minimum pressure required for sufficient fusion of the polypropylene-based resin foamed beads was determined and used as the lower limit molding pressure. The resulting in-mold foam molded article was left to stand at 23°C for 2 hours and then aged at 75°C for 13 hours.

[0158] (Examples 2 to 7, Comparative Examples 1 to 3, Reference Example 1) Polypropylene-based resin particles, expanded polypropylene-based resin particles, and in-mold polypropylene-based resin foams were prepared in the same manner as in Example 1, except that in the preparation of polypropylene-based resin particles, the resin formulation was changed as shown in Table 1, and in the preparation of expanded polypropylene-based resin particles, the foaming conditions were changed as shown in Table 1. The foaming step was not performed for Comparative Example 3. Based on the results of the Examples, when the ethylene / propylene block copolymer content was 10 parts by weight per 100 parts by weight of the resin components, a foaming temperature of 158°C was selected to obtain foamed beads of suitable quality, and when it was 20 parts by weight, a foaming temperature of 164°C was selected. Therefore, in the case of Comparative Example 3, in which the ethylene / propylene block copolymer content was 30 parts by weight per 100 parts by weight of the resin components, the foaming temperature to obtain foamed beads of suitable quality was expected to exceed the upper limit of the temperature that could be reached in the pressure-resistant autoclave used in the Examples. The resin formulation conditions, foaming conditions, and evaluation results of the resulting expanded polypropylene-based resin particles and in-mold polypropylene-based resin foams are shown in Table 1.

[0159] When the peak intensity ratio determined by infrared spectroscopy is 0.45 or higher, the propylene-based block copolymer is sufficiently contained, and when recycled polypropylene-based resin is used as the propylene-based block copolymer, recyclability is improved. On the other hand, Table 1 shows that when the peak intensity ratio is 0.7, the molding temperature becomes too high, resulting in failure to obtain expanded beads or reduced productivity. Furthermore, Comparative Example 1, which was foamed at a foaming pressure of 2.90 MPa, almost the same as Reference Example 1, showed a longer molding cycle, reduced productivity, and a significant decrease in the static compressive strength of the foamed molded article. Furthermore, Comparative Example 2, in which the foaming temperature was set to 163.7°C, also showed a similarly longer molding cycle and a significant decrease in the static compressive strength of the foamed molded article.

[0160] On the other hand, when the expansion conditions are adjusted so that the shrinkage rate of the expanded polypropylene resin beads is 20% or less as in Examples 1 to 7, the molding cycle can be sufficiently shortened and the decrease in static compressive strength also tends to be suppressed, although it is longer than in Reference Example 1. Furthermore, expanded polypropylene resin beads containing an ethylene / propylene block copolymer can be molded in a mold at the same molding pressure as expanded polypropylene resin beads consisting only of an ethylene / propylene random copolymer, and the obtained expanded molded article has excellent surface beauty.

[0161] According to one embodiment of the present invention, it is possible to provide expanded polypropylene resin beads with improved productivity due to a short molding time during in-mold molding, and therefore, the expanded polypropylene resin beads can be used in a variety of applications, including automotive interior components, core materials for automotive bumpers, heat insulating materials, cushioning packaging materials, and returnable boxes.

Claims

1. A method for producing expanded polypropylene-based resin particles, comprising: an expansion step of depressurizing and expanding polypropylene-based resin particles comprising a base resin containing a propylene-based random copolymer and a propylene-based block copolymer under conditions of an expansion temperature of 163.5°C or lower and an expansion pressure of 2.80 MPa or lower, wherein the base resin contains 73% by weight to 95% by weight of the propylene-based random copolymer and 5% by weight to 27% by weight of the propylene-based block copolymer, when the total amount of the propylene-based random copolymer and the propylene-based block copolymer is taken as 100% by weight.

2. The method for producing the expanded polypropylene resin beads according to claim 1, which satisfies the following formula (1): Y<-0.07X+3.6...(1); Where: X is a content ratio (wt%) of the propylene-based block copolymer when the total amount of the propylene-based random copolymer and the propylene-based block copolymer in the base resin is taken as 100 wt%, The Y is the foaming pressure (MPa) in the foaming step.

3. The method for producing expanded polypropylene resin beads according to claim 1 or 2, wherein the expansion temperature is 150° C. or higher.

4. A base resin containing a propylene-based random copolymer and a propylene-based block copolymer, Peak intensity ratio I ７２０ / I ８１０ is 0.45 to 0.67, Polypropylene resin expanded particles having a shrinkage rate of 20% or less: Here, the peak intensity ratio I ７２０ / I ８１０ is a wavelength of 810 cm obtained in a spectrum obtained by infrared spectroscopy. －１ is the intensity of the peak I ８１０ For wavelength 720 cm －１ is the intensity of the peak I ７２０ is the ratio of The shrinkage rate (%) is a value calculated by the following formula (2): The shrinkage rate (%)=(BD−VBD)×100 / VBD (2) In formula (2), The BD is a bulk density of the expanded polypropylene resin particles measured in a region where the temperature is 23° C. and the pressure is 0.1 MPa, The VBD is the bulk density of the expanded polypropylene resin particles measured in a region where the temperature is 23° C. and the pressure is −0.09 MPa.

5. The expanded polypropylene resin particles according to claim 4, wherein the base resin contains 73% by weight to 95% by weight of the propylene random copolymer and 5% by weight to 27% by weight of the propylene block copolymer, when the total amount of the propylene random copolymer and the propylene block copolymer is taken as 100% by weight.

6. The expanded polypropylene resin particles according to claim 4, wherein the melting point of the propylene block copolymer is 160°C or higher and 180°C or lower.

7. The expanded polypropylene resin particles according to claim 4, wherein the propylene block copolymer is a recycled resin.

8. The polypropylene-based resin expanded particles according to claim 4, wherein the propylene-based random copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units, and the propylene-based block copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units.

9. The expanded polypropylene resin particles according to claim 4, wherein the propylene random copolymer comprises a propylene / ethylene random copolymer containing propylene units and ethylene units.

10. 5. The polypropylene-based resin expanded particles according to claim 4, wherein the propylene-based random copolymer has a melt flow rate at 230° C. of 3 g / 10 min to 30 g / 10 min.

11. 5. The expanded polypropylene resin particles according to claim 4, wherein the difference between the melting point of the propylene block copolymer and the melting point of the propylene random copolymer is 30° C. or less.

12. 5. The polypropylene-based resin expanded particles according to claim 4, wherein the propylene-based block copolymer has a melt flow rate at 230° C. of 3 g / 10 min to 30 g / 10 min.

13. The expanded polypropylene resin particles according to claim 4, having a DSC ratio of 10.0% to 50.0%.

14. The expanded polypropylene resin particles according to claim 4, having an expansion ratio of 15 to 50 times.

15. A polypropylene resin foamed molded article obtained by foam molding the expanded polypropylene resin beads according to any one of claims 4 to 14.