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

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

[Technical Field]

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

[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). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-173012 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 include the following components. The expanded polypropylene resin particles comprise a base resin containing a propylene-based random copolymer and a propylene-based 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, expanded polypropylene resin beads according to another embodiment of the present invention include the following components. The base resin contains a propylene-based random copolymer and a propylene-based block copolymer, and the peak intensity ratio I 720 / I 810 Polypropylene resin expanded particles having a modulus of 0.45 to 0.67 and a shrinkage rate of 20% or less: Here, the peak intensity ratio I 720 / I 810 is the wavelength 810 cm obtained in the spectrum obtained by infrared spectroscopy. -1 is the intensity of the peak in 810 For wavelength 720cm -1 is the intensity of the peak in 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), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a region 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 region where the temperature is 23°C and the pressure is -0.09 MPa.

[0009] The method for producing expanded polypropylene resin beads according to one embodiment of the present invention includes the following steps. 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.

[0010] Further, a method for producing expanded polypropylene resin beads according to another embodiment of the present invention includes the following steps. A method for producing expanded polypropylene resin beads, comprising an expansion step of depressurizing and expanding polypropylene resin beads, the 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. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[0012] One 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 X units (n is an integer of 2 or more) is referred to as "X 1 / X 2 / ··· / X n Also called "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 are sometimes 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 molded articles.

[0021] [1. Polypropylene resin foam particles] 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 810 cm obtained in the spectrum obtained by infrared spectroscopy. -1 is the intensity of the peak in 810 For wavelength 720cm -1 is the intensity of the peak in 720 The shrinkage rate (%) is a value calculated by the following formula (2): Shrinkage rate (%) = (BD − VBD) × 100 / VBD (2). In formula (2), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a region where the temperature is 23°C and the pressure is 0.1 MPa. In formula (2), VBD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a region where the temperature is 23°C and the pressure is -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] <Ingredients> (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 random copolymer) A propylene-based random copolymer contains at least a propylene unit and a structural unit other than the propylene unit. In this specification, the "structural unit other than the propylene unit" contained in the polypropylene-based resin may be referred to as a "comonomer unit." In other words, a propylene-based random copolymer contains at least a propylene unit and a comonomer unit.

[0030] Examples of the comonomer 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 when the expanded beads are foamed in a mold, 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 the 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 during 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, it is advantageous in that expanded beads having a relatively high expansion ratio can be easily obtained. Furthermore, in this case, there are also advantages in that the surface beauty of the expanded molded article is 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 specified 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 block copolymer) The propylene-based block copolymer contains at least a propylene unit and a comonomer unit.

[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 in the above (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 (for example, 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 / chlorinated vinyl 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 30°C or less, and more preferably 21°C or less. 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 high expansion ratio are easily obtained, and the advantageous result is that the surface beauty of the expanded molded article is excellent.

[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 resin (or resin particles) by means of melting or other means.

[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 in the base resin are within the above-mentioned ranges, the expanded beads have the advantage of being more productive for polypropylene resin expansion moldings.

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

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

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

[0054] (peak intensity ratio) The expanded particles have a peak intensity ratio of I 720 / I 810 is preferably 0.45 to 0.67. 720 / I810 is the wavelength of 720 cm in the spectrum obtained by infrared spectroscopy. -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 ", I 810 I against 720 The infrared spectroscopic analysis can be performed by the method described in the Examples below. -1 The peak at 810 cm is likely due to the ethylene block. -1 The peak at 720 nm in the expanded particles is likely due to 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 spectroscopy 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 810 It 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. This configuration has the advantage that the expanded beads have excellent 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 rate) The shrinkage rate of the present expanded beads is calculated by the following formula (2). Shrinkage rate = (BD - VBD) × 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 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 particles) The expanded beads preferably have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry (DSC) as described below. The heat of fusion determined from the higher-temperature melting peak is referred to as the "higher-temperature heat of fusion," and the heat of fusion determined from the lower-temperature melting peak is referred to as the "lower-temperature 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 heat of fusion," and the heats of fusion determined from the remaining melting peaks are referred to as the "lower-temperature 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, it 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. A DSC ratio of 10.0% to 50.0% indicates that the expanded beads contain a relatively large amount of high-melting-point crystals. The DSC ratio of the expanded beads also plays a significant role in the viscoelasticity of the resin beads and the expanded beads during foaming and expansion. When the DSC ratio of the expanded beads is 10.0% to 50.0%, the resin beads and the expanded beads exhibit excellent foamability and expansion properties during foaming and molding, respectively. As a result, the expanded beads have the advantage of being able to produce foamed molded articles with excellent internal fusion and mechanical strength, such as compressive strength, even at low molding pressures.

[0065] In the present expanded beads, the DSC ratio can be controlled within a predetermined range by adjusting the conditions during production of the present expanded beads (particularly, the expansion temperature, expansion pressure, holding time, and the temperature of the region (space) where the dispersion is released, etc.) In terms of ease of adjustment, the method of controlling the DSC ratio within a predetermined range by adjusting the expansion temperature, expansion 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 it. This is because the amount of unmelted crystals changes depending on the foaming temperature. Increasing the foaming pressure also tends to decrease the DSC ratio, while decreasing the foaming pressure tends to increase it. This is because the degree of plasticization changes depending on the foaming pressure, which in turn changes the amount of unmelted crystals. In addition, the DSC ratio tends to increase as the holding time is longer. This is because the amount of unmelted crystals that grow changes depending on the holding time.

[0067] (Expansion ratio of expanded beads) The expansion ratio of the expanded beads is preferably 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] (Minimum molding pressure) The present expanded beads have the advantage that they can be used to obtain a foamed molded article with 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 with 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 for 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-based resin beads according to one embodiment of the present invention includes an expansion step of depressurizing and expanding polypropylene-based resin beads, which include 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.

[0072] Another embodiment of the present invention relates to a method for producing expanded polypropylene-based resin beads, which comprises an expansion step of depressurizing and expanding polypropylene-based resin beads containing 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. (granulation process) The present production method may further include a step of producing polypropylene-based resin particles (a granulation step) containing a base resin containing a propylene-based random copolymer and a propylene-based block copolymer. 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 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) subsequently 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, 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 process) This production method may further include a dispersion step, prior to the foaming step, in which a base resin containing a propylene-based random copolymer and a propylene-based block copolymer, an aqueous dispersion medium, a blowing agent, and optionally a dispersant and / or a dispersion aid are dispersed in a container. The dispersion step can also be considered a step of preparing a dispersion in which the base resin, the blowing agent, and optionally a 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 (aqueous solutions) containing salts such as sodium chloride or sodium sulfate.

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

[0080] Examples of blowing agents 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 blowing agent, at least one selected from the group consisting of the inorganic blowing agents and organic blowing agents described above can be used. When two or more blowing 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 blowing agents are preferred as the blowing agent among the above-mentioned blowing agents. Furthermore, carbon dioxide is preferred among inorganic blowing 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 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] (Foaming process) The specific embodiment of the expansion step is not particularly limited. The expansion step may include, for example, (a) a temperature-pressure increase step in which the temperature inside the container is increased to a certain temperature and the pressure inside the container is increased to a certain pressure to depressurize and expand the resin particles; (b) a holding step of maintaining the temperature and pressure in the container at a constant temperature and constant pressure; (c) A discharging step of opening one end of the container and discharging the dispersion liquid in the container into a region (space) having a pressure lower than the foaming pressure (i.e., the pressure inside the container).

[0085] (Temperature-pressure increase process and holding process) 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 intensive 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 the expansion pressure lower 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 amount of the propylene-based random copolymer and the propylene-based block copolymer (100 wt%), it is preferable that the expansion pressure Y (MPa) during the production of expanded beads satisfies the following formula (1): Y<-0.07X+3.6···(1). The reason why it is preferable to satisfy the formula (1) is unclear, but it is speculated that this is because propylene-based block copolymers are softer and more extensible than propylene-based random copolymers, although one embodiment of the present invention is not limited to this speculation.

[0089] X and Y more preferably satisfy the following formula (3), further preferably satisfy the following formula (4), and particularly preferably satisfy 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 the 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] (Release process) 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 can be discharged through an orifice with 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) can 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] (2-stage foaming process) In order to obtain expanded beads with a high expansion ratio, the first-stage expanded beads obtained in the first-stage expansion step may be expanded again. The step of increasing the expansion ratio of the first-stage expanded beads is called the "second-stage expansion step," and the expanded polyolefin resin beads obtained by the second-stage expansion step are called "second-stage expanded beads." The specific method for the second-stage expansion step is not particularly limited, and any known method can be used.

[0096] [3. Polypropylene resin foam molding] 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 Section [1. Expanded Polypropylene Resin 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 Section [2. Production Method of Expanded Polypropylene Resin 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 Section [1. Expanded Polypropylene Resin Beads] or the polypropylene-based resin foam beads obtained by the production method described in Section [2. Production Method of Expanded Polypropylene Resin 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 foamed molded article is evaluated by the time (seconds) from the start of molding of the foamed beads to the completion of molding (molding cycle). As described in the Examples below, the start of molding was defined as the time when the foamed beads were filled into the mold. The completion of molding was defined as 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 beauty) In this specification, the surface aesthetics of the present foamed molded article are 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 foamed molded article also has the advantage of being excellent in strength. In this specification, the strength of the foamed molded article is evaluated by static compressive strength. The method for measuring the static compressive strength of the foamed 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 containing 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] A method for producing expanded polypropylene resin beads according to [1], which satisfies the following formula (1): Y<-0.07X+3.6···(1); Here, X is the content (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%, 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 beads according to any one of [1] to [8], wherein the propylene random copolymer includes a propylene / ethylene random copolymer containing propylene units and ethylene units.

[0113]

[10] The method for producing expanded polypropylene beads according to any one of [1] to [9], wherein the propylene random copolymer has a melt flow rate at 230°C of 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 propylene block copolymer has a melt flow rate at 230°C of 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 base resin containing a propylene-based random copolymer and a propylene-based block copolymer, wherein the peak intensity ratio I 720 / I 810Polypropylene resin expanded particles having a modulus of 0.45 to 0.67 and a shrinkage rate of 20% or less: Here, the peak intensity ratio I 720 / I 810 is the wavelength 810 cm obtained in the spectrum obtained by infrared spectroscopy. -1 is the intensity of the peak in 810 For wavelength 720cm -1 is the intensity of the peak in 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), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a region 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 region 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% 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.

[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] Expanded polypropylene resin particles according to any one of

[16] to

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

[0125]

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

[16] to

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

[0126]

[23] 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] 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 an expanded polypropylene resin molded article having a fusion rate of 80% or more is 0.30 MPa or less.

[0131]

[28] A polypropylene resin expansion molded article obtained by expansion 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 base resin containing a propylene-based random copolymer and a propylene-based block copolymer, and a peak intensity ratio I 720 / I 810 Polypropylene resin expanded particles having a modulus of 0.45 to 0.65 and a shrinkage rate of 20% or less: Here, the peak intensity ratio I 720 / I 810 is the wavelength 810 cm obtained in the spectrum obtained by infrared spectroscopy. -1 is the intensity of the peak in 810 For wavelength 720cm -1 is the intensity of the peak in 720 is the ratio of The shrinkage rate (%) is a value calculated by the following formula (1): The shrinkage rate (%)=(BD−VBD)×100 / VBD (1) In formula (1), BD is the bulk density of the expanded polypropylene resin beads obtained by measurement in a region 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 region 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 expansion molded article obtained by expansion 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. [Example]

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

[0142] <Polypropylene resin> Propylene / ethylene block copolymer 1 [MFR=12g / 10min, melting point 166℃, recycled resin, contains 5% by weight of carbon black] Propylene / ethylene block copolymer 2 [Prime Polymer J715M, MFR = 9 g / 10 min, melting point 165°C, recycled resin] Propylene / ethylene block copolymer 3 [MFR=29g / 10min, melting point 165℃, recycled resin] Propylene / ethylene random copolymer [MFR=7g / 10min, melting point 145℃, non-recycled resin] <Resin particle additive> Talc [Hayashi Kasei Co., Ltd., Talc Powder PK-S] Glycerin [Lion Corporation, refined glycerin D] [Measurement method] The evaluation methods used in the examples and comparative examples are described below.

[0143] <Melt point measurement of polypropylene 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 melted by heating from 40°C to 220°C at a heating rate of 10°C / min; (2) The sample was then crystallized by cooling from 220°C to 40°C at a heating rate of 10°C / min; (3) The sample was further heated 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 resin> For polypropylene-based resins, the melt mass flow rate (hereinafter referred to as MFR) was measured using a melt mass flow rate (MFR) measuring device specified in JIS K7210 under the following conditions: orifice 2.0959±0.005 mmφ, 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 when 5 to 6 mg of expanded polypropylene resin particles was heated from 40 to 220 °C at a heating rate of 10 °C / min during the first heating was defined as Q. l The melting peak area on the high temperature side is Q h It was calculated using the following formula: DSC ratio (%)=Q h / (Q l +Q h ) x 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 called 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 Q h It was decided.

[0146] <Infrared spectroscopic analysis of polypropylene resin foam particles> The ratio of peak intensities derived from propylene and block ethylene was determined by infrared spectroscopic analysis of the expanded polypropylene resin particles. The measurement was carried out by the attenuated total reflection method (hereinafter referred to as the ATR method). The expanded polypropylene resin particles 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.). The resolution was set to 4 cm. -1 The measurement was performed with 16 accumulations to obtain a spectrum. -1 The pressure applied during compression was adjusted so that the peak intensity was 0.15 A. Next, from the obtained spectrum, -1 Peak intensity (I 810 ) and wavelength 720 cm -1 Peak intensity (I 720 ) and [(I 720 ) / (I 810In this example, the peak intensity ratio was calculated from the -1 The peak intensity is the peak intensity derived from propylene CH3, and the wavelength is 720 cm -1 The peak intensity 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 Polypropylene Resin Expanded Beads> Polypropylene resin foam particles weighing 3g or more and 10g or less are taken, dried at 60°C for 6 hours, and then conditioned in a room at 23°C and 50% humidity. After measuring the weight w1 (g), the particles are 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 measure the true specific gravity ρ b = w1 / v, and then calculate the density ρ of the polypropylene resin particles before foaming. r The ratio (ρ r / ρ b In the examples and comparative examples shown below, the density ρ of the polypropylene-based resin particles (polypropylene-based resin particles) before foaming was calculated as r are all 0.9g / cm 3 It was.

[0148] <Measurement of shrinkage rate of expanded polypropylene resin beads> The shrinkage rate of the 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) using the following method. The weight of the expanded polypropylene resin beads to be measured was designated as W1, and the volume V1 was determined using a measuring cylinder at 23°C and atmospheric pressure (standard atmospheric pressure 0.1 MPa). The bulk density BD of the expanded polypropylene resin beads at 23°C and 0.1 MPa (standard atmospheric pressure) was calculated using the following formula: BD(g / L)=W1÷V1 The expanded polypropylene resin beads were weighed again, and their weight was designated as W2. They were then placed in a graduated pressure-resistant container, and the pressure inside the container was reduced in pressure using a vacuum pump or other device. 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 expanded polypropylene resin beads stopped changing. The scale on the top of the expanded polypropylene resin beads inside the container was then read and recorded as the volume, V2. During pressure reduction, the expanded beads may push against each other, inhibiting volume change. Therefore, the pressure container was turned sideways to prevent the expanded beads from inhibiting volume 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 using the following formula: VBD(g / L) = W2 ÷ V2 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 resin in-mold foam molding> The steam pressure setting for the main heating step in the "Preparation of In-Mold Polypropylene Resin Foam Molded Articles" described below was changed in 0.01 MPa increments within the range of 0.20 to 0.32 MPa (gauge pressure) during molding to obtain foam molded articles for evaluation. A crack approximately 5 mm deep was made in the surface of the resulting foam molded article 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 steam pressure at which the fusion rate reached 80% or more was defined as the minimum molding pressure.

[0151] <Molding cycle for polypropylene resin in-mold foam molding> The molding cycle in the manufacturing method for polypropylene 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 when the polypropylene resin foam beads began to be filled into the mold. The mold was heated by pumping steam into it, and then the molded article was cooled with water. The mold was opened when the contact pressure measured by a pressure gauge attached to the surface of the Planck mold dropped to 0.01 MPa. The end of molding was when demolding was complete. The steam heating pressure was evaluated as the minimum molding pressure calculated in the above-mentioned "Minimum molding pressure for polypropylene resin in-mold foam molded articles." The productivity evaluation criteria were as follows: ◎ (Very good): Molding cycle is within 180 seconds. ○ (Excellent): Molding cycle is longer than 180 seconds and within 210 seconds. × (poor): Molding cycle is 210 seconds or more.

[0152] <Surface beauty of polypropylene resin in-mold foam moldings> The 350mm x 450mm surface of the obtained polypropylene resin in-mold foamed molded article was visually observed, and the surface appearance was judged according to the following criteria: The interparticle gaps (gaps between the polypropylene resin foamed particles), which is one of the evaluation indices for surface appearance, were judged by visually counting the number of gaps present within a 50mm square at the center of the surface of the molded article. ◎ (Beautiful surface appearance): No wrinkles and 0 to 1 gap between grains. ○ (Good surface appearance): No wrinkles and 2 to 3 gaps between grains. △ (Surface appearance is acceptable): Wrinkles are observed or there are 4 to 5 gaps between the grains. × (surface appearance is unacceptable): wrinkles are observed or there are 6 or more intergranular spaces.

[0153] <Static compressive strength measurement of polypropylene resin in-mold foam molded body> Test pieces measuring 50 mm long x 50 mm wide x 25 mm thick were cut out from the polypropylene resin in-mold foam molded article, and the compressive stress at 50% compression was measured when the test pieces were compressed at a rate of 10 mm / min using a tension and compression testing machine (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 of manufacturing polypropylene 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 (Toshiba Machine Co., Ltd., TEM26-SX). 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 polypropylene resin foam particles] 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 (BASF ASP170) as a water-insoluble inorganic compound, and 0.06 parts by weight of sodium dodecylbenzenesulfonate (Kao Corporation Neopelex G-15) as a surfactant. Then, with stirring, 4 parts by weight of carbon dioxide was added as a blowing agent. The contents of the autoclave were heated to a foaming temperature of 158.2°C and maintained for 10 minutes. Then, 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 pressure for 20 minutes, the valve at the bottom of the autoclave was opened, and the contents were released to atmospheric pressure through a 3.6 mm diameter orifice, yielding expanded polypropylene resin particles with an expansion ratio of 24 times. During this process, carbon dioxide was injected to maintain the pressure inside the vessel.

[0157] [Preparation of polypropylene resin in-mold foamed body] The resulting polypropylene-based resin foamed beads were dried at 75°C. The dried polypropylene-based resin foamed beads were placed in a pressure-resistant container and impregnated with pressurized air. The polypropylene-based resin foamed beads, previously adjusted to an internal 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 surface of the molded article were then water-cooled, and the molded article was removed to obtain an in-mold polypropylene-based resin foamed article. This procedure 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 foamed article was left to stand at 23°C for 2 hours and then cured at 75°C for 13 hours.

[0158] (Examples 2 to 7, Comparative Examples 1 to 3, Reference Example 1) Polypropylene-based resin beads, expanded polypropylene-based resin beads, and polypropylene-based resin in-mold foamed articles were prepared in the same manner as in Example 1, except that the resin formulation in [Preparation of Polypropylene-Based Resin Beads] was changed as shown in Table 1, and the foaming conditions in [Preparation of Expanded Polypropylene-Based Resin Beads] 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 required 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 beads and in-mold foamed articles are shown in Table 1.

[0159] [Table 1] When the peak intensity ratio determined by infrared spectroscopy is 0.45 or higher, the propylene-based block copolymer is sufficiently contained, and using a recycled polypropylene-based resin as the propylene-based block copolymer improves recyclability. 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, exhibited 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 at 163.7°C, also exhibited 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. [Industrial Applicability]

[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 resin beads includes an expansion step of depressurizing and expanding polypropylene resin particles containing 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.

2. The method for producing expanded polypropylene resin beads according to claim 1, which satisfies the following formula (1): Y<-0.07X+3.6...(1); where: X represents the content (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%, and 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. The composition includes 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 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 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 beads measured under a temperature of 23°C and a pressure of 0.1 MPa, The VBD is the bulk density of the expanded polypropylene resin beads measured in a region where the temperature is 23° C. and the pressure is −0.09 MPa.

5. 5. The expanded polypropylene resin beads according to claim 4, 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, where 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 expanded polypropylene resin beads according to claim 4, 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.

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 expanded polypropylene resin particles according to claim 4, wherein the propylene 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 expanded polypropylene resin particles according to claim 4, wherein the propylene 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, wherein the DSC ratio is 10.0% to 50.0%.

14. The expanded polypropylene resin particles according to claim 4, wherein the expansion ratio is 15 to 50 times.

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

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