Polypropylene resin foam particles, polypropylene resin foam molded articles, and methods for producing polypropylene resin foam particles

Abstract

The present invention provides polypropylene resin foam particles that offer excellent productivity for polypropylene resin foam molded articles, and polypropylene resin foam molded articles obtained by molding these polypropylene resin foam particles. [Solution] The base resin contains a propylene-based random copolymer and a propylene-based block copolymer, with a peak intensity ratio of I 720 / I 810 The above problem is solved by using polypropylene resin foam particles with a coefficient of 0.45 to 0.67 and a shrinkage rate of 20% or less.

Description

Technical Field

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

Background Art

[0002] Polypropylene-based resin foamed molded bodies are used in various applications such as automotive interior members, core materials for automotive bumpers, heat insulating materials, cushioning packaging materials, and passing boxes (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conventional technologies as described above 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 view of the above problems, and an object thereof is to provide polypropylene-based resin foamed particles excellent in productivity of a polypropylene-based resin foamed molded body, and a polypropylene-based resin foamed molded body formed by molding the polypropylene-based resin foamed particles.

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.

[0007] That is, the polypropylene-based resin foamed particles according to one embodiment of the present invention include the following configuration. Polypropylene resin foam particles: Y < -0.07X + 3.6···(1), where the base resin contains a propylene random copolymer and a propylene block copolymer, and the content ratio of the block copolymer is X (%) and the foaming pressure during manufacturing is Y (MPa), such that X and Y satisfy the following formula (1).

[0008] Furthermore, a polypropylene-based resin foam particle according to another embodiment of the present invention includes the following configuration. The base resin contains a propylene-based random copolymer and a propylene-based block copolymer, with a peak intensity ratio of I 720 / I 810 Polypropylene resin foam particles with a coefficient of 0.45-0.67 and a shrinkage rate of 20% or less: Here, the peak intensity ratio I 720 / I 810 This is obtained in the spectrum acquired by infrared spectroscopy at a wavelength of 810 cm². -1 I is the peak intensity of 810 For a wavelength of 720 cm -1 I is the peak intensity of 720 It is the ratio of, The aforementioned shrinkage rate (%) is the value obtained by the following formula (2); The aforementioned shrinkage rate (%) = (BD - VBD) × 100 / VBD ... (2) In equation (2), BD is the bulk density of polypropylene resin foam particles 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 polypropylene resin foam particles obtained by measurement in a region where the temperature is 23°C and the pressure is -0.09 MPa.

[0009] Furthermore, a method for producing polypropylene resin foam particles according to one embodiment of the present invention includes the following configuration. A method for producing polypropylene resin foam particles, comprising a foaming step of depressurizing and foaming polypropylene resin particles containing a base resin containing a propylene random copolymer and a propylene block copolymer under conditions of 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 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 100% by weight.

[0010] Furthermore, a method for producing polypropylene resin foam particles according to another embodiment of the present invention includes the following configuration. A method for producing polypropylene resin foam particles, comprising a foaming step of depressurizing and foaming polypropylene resin particles containing a base resin containing a propylene random copolymer and a propylene block copolymer under conditions of a foaming temperature of 163.5°C or lower and a foaming pressure of 2.80 MPa or lower. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to provide polypropylene resin foam particles that exhibit excellent productivity in producing polypropylene resin foam molded articles, and polypropylene resin foam molded articles obtained by molding said polypropylene resin foam particles. [Modes for carrying out the invention]

[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 each configuration described below, and various modifications are possible within the scope indicated in the claims. Further, embodiments or examples obtained by combining technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, by combining the technical means disclosed in each embodiment, new technical features can be formed. All academic documents and patent documents described in this specification are incorporated herein by reference. Also, unless otherwise specified in this specification, "A to B" representing a numerical range is intended to mean "A or more (including A and greater than A) and B or less (including B and less than B)".

[0013] In this specification, a structural 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, as a structural unit, X 1 unit, X 2 unit, ··· and X n unit (n is an integer of 2 or more), a copolymer containing them is also referred to as an "X 1 / X 2 / ··· / X n copolymer". X 1 / X 2 / ··· / X n As the X

[0015] [1. Technical Idea of an Embodiment of the Present Invention] Generally, propylene random copolymers can be used as raw materials for polypropylene foam molded articles. On the other hand, propylene block copolymers can also be used as raw materials for polypropylene foam molded articles. For example, this may be done to improve the impact resistance of the polypropylene foam molded article, or to use recycled resin from the perspective of reducing environmental impact.

[0016] Compared to propylene random copolymers, propylene block copolymers are much more widely used as recycled polypropylene resins.

[0017] For the reasons stated above, the inventors diligently investigated the use of a combination of a propylene-based random copolymer and a propylene-based block copolymer to provide polypropylene-based resin foam particles, which are raw materials for polypropylene-based resin foam molded articles.

[0018] During the course of diligent research, the inventors independently discovered a novel finding: when polypropylene resin foam particles are produced using a combination of propylene random copolymer and propylene block copolymer, and when polypropylene resin foam molded articles are produced using the obtained polypropylene resin foam particles, the productivity of the polypropylene resin foam molded articles may be poor. For example, in the production of polypropylene resin foam molded articles using molds, the obtained polypropylene resin foam molded articles may be cooled before being removed from the mold in order to reduce swelling of the polypropylene resin foam molded articles after removal from the mold. This cooling time greatly contributes to the productivity of the polypropylene resin foam molded articles. The above-mentioned "cases where the productivity of polypropylene resin foam molded articles is poor" refers to cases where the cooling time of the polypropylene resin foam molded articles is long.

[0019] Therefore, the inventors conducted further intensive studies to provide polypropylene resin foam particles that exhibit excellent productivity of polypropylene resin foam molded articles, even when using a combination of propylene-based random copolymer and propylene-based block copolymer.

[0020] As a result, the inventors have independently discovered the following novel findings and completed the present invention: By using a propylene-based random copolymer and a propylene-based block copolymer in a specific ratio, and foaming the polypropylene-based resin particles so that the shrinkage rate of the resulting polypropylene-based resin foam particles falls within a specific range, it is possible to provide polypropylene-based resin foam particles that exhibit excellent productivity for polypropylene-based resin foam molded articles.

[0021] [1. Polypropylene resin foam particles] Polypropylene resin foam particles according to one embodiment of the present invention include a base resin containing a propylene random copolymer and a propylene block copolymer, where X (%) is the content ratio of the block copolymer and Y (MPa) is the foaming pressure during manufacturing, then X and Y satisfy the following formula (1).

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

[0023] Another embodiment of the present invention provides polypropylene resin foam particles comprising a base resin containing a propylene random copolymer and a propylene block copolymer, with a peak intensity ratio of I 720 / I 810 The peak intensity ratio I is 0.45 to 0.67, and the contraction rate is 20% or less. 720 / I 810 This is obtained in the spectrum acquired by infrared spectroscopy at a wavelength of 810 cm². -1 I is the peak intensity of 810 For a wavelength of 720 cm -1 I is the peak intensity of 720 This is the ratio. The aforementioned shrinkage rate (%) is the value obtained by the following formula (2); Shrinkage rate (%) = (BD - VBD) × 100 / VBD ... (2). In equation (2), BD is the bulk density of polypropylene resin foam particles obtained by measurement in the region where the temperature is 23°C and the pressure is 0.1 MPa. In equation (2), VBD is the bulk density of polypropylene resin foam particles obtained by measurement in the region where the temperature is 23°C and the pressure is -0.09 MPa.

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

[0025] Because these foam particles have the above-described structure, they have the advantage of excellent productivity in foam molded products. For example, when these foam particles are used for in-mold foam molding using a mold, they have the advantage of shortening the cooling time of the foam molded product in the mold. Because these foam particles have the above-described structure, they also have the advantage of providing foam molded products with excellent strength.

[0026] <Ingredients> (Base resin) The aforementioned base resin includes, as resin components, at least a propylene-based random copolymer and a propylene-based block copolymer. In addition to the resin components, the base resin may optionally contain additives such as foaming nucleating agents. The base resin can also be said to be a component that substantially constitutes the foam particles. Therefore, the types and amounts of each component contained in the base resin can also be said to be the types and amounts of each component contained in the foam particles.

[0027] Both propylene-based random copolymers and propylene-based block copolymers are polypropylene-based resins.

[0028] In this specification, "polypropylene resin" refers to a resin that contains 50 mol% or more of propylene units out of 100 mol% of all constituent units of the resin.

[0029] (Propylene-based random copolymer) A propylene-based random copolymer contains at least propylene units and structural units other than propylene units. In this specification, "structural units other than propylene units" contained in polypropylene resins may also be referred to as "comomomeral units." In other words, a propylene-based random copolymer contains at least propylene units and comonomeral units.

[0030] Examples of 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 being able to lower the molding temperature when foaming the foamed particles in a mold, it is preferable that the comonomer units contained in the propylene-based random copolymer are ethylene units. In other words, it is preferable that the propylene-based random copolymer is a propylene / ethylene random copolymer containing both propylene units and ethylene units.

[0032] Propylene-based random copolymers are not limited to propylene / ethylene random copolymers. Examples of propylene-based random copolymers other than propylene / ethylene random copolymers include propylene / 1-butene random copolymers, propylene / ethylene / 1-butene random copolymers, propylene / chlorinated vinyl random copolymers, and propylene / maleic anhydride random copolymers.

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

[0034] The melting point of the propylene-based random copolymer is not particularly limited, but is preferably 130°C or higher, more preferably 130°C to 160°C, even more preferably 135°C to 155°C, and still more preferably 140°C to 150°C. The melting point of the propylene-based random copolymer has the advantages of (i) having excellent heat resistance when it is 130°C or higher, and (ii) being easy to increase the foaming ratio of the foam particles in the production of these foam particles when it is 160°C or lower.

[0035] In this specification, the melting points of propylene-based random copolymers and propylene-based block copolymers described later are values ​​obtained by measurement using differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific operating procedure is as described in the examples below. As a differential scanning calorimetry, 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 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. If the MFR of the propylene random copolymer at 230°C is within the above range, it has the advantage that foamed particles with a relatively large foaming ratio are easily obtained. Furthermore, in this case, it also has the advantages that the surface beauty of the foamed molded article is excellent and the shrinkage rate of the foamed molded article is small.

[0037] In this specification, the MFR at 230°C for propylene random copolymers and propylene block copolymers described later is the value obtained by measuring using a melt mass flow rate (hereinafter, MFR) measuring instrument described in JIS-K7210 under the following conditions: orifice diameter of 2.0959±0.005 mmφ, orifice length of 8.000±0.025 mm, load of 2160 g, and temperature of 230±0.2°C.

[0038] The propylene-based random copolymer may be obtained by known methods or recycled resin may be used. It is preferable to use non-recycled resin because it ensures stable quality of the foamed molded product.

[0039] (Propylene-based block copolymer) A propylene-based block copolymer comprises at least propylene units and comonomer units.

[0040] The comonomer units contained in the propylene-based block copolymer are not particularly limited. Specific examples of comonomers are the same as those described in the section on (propylene-based random copolymers) above, so we will refer to that description and omit further explanation here.

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

[0042] Propylene-based block copolymers are not limited to propylene / ethylene block copolymers. Examples of propylene-based block copolymers other than propylene / ethylene block copolymers include propylene / 1-butene block copolymers, propylene / ethylene / 1-butene block copolymers, propylene / chlorinated vinyl block copolymers, and propylene / maleic anhydride block copolymers.

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

[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 preferably, for example, 180°C or lower, more preferably 175°C or lower, and even more preferably 170°C or lower. When the melting point of the propylene-based block copolymer is (i) 160°C or higher, it has the effect of excellent heat resistance, and when it is 180°C or lower, it has the effect of excellent moldability.

[0045] In one embodiment of the present invention, the difference between the melting point of the propylene block copolymer and the melting point of the propylene random copolymer (i.e., the value obtained by subtracting the melting point of the propylene random copolymer from the melting point of the propylene block copolymer (in °C)) 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 the same as that of foamed particles obtained using only a propylene random copolymer as the base resin.

[0046] The MFR of a propylene-based block copolymer is not particularly limited. In this specification, "MFR of a propylene-based block copolymer" refers to the MFR of a propylene-based block copolymer at 230°C. The MFR of a 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 a propylene-based block copolymer at 230°C is within the above range, foamed particles with a relatively large foaming ratio are easily obtained, which has the advantage of excellent surface beauty of the foamed molded article.

[0047] While propylene block copolymers obtained by known methods may be used, recycled resins are preferred. As mentioned above, the amount of propylene block copolymers in circulation as recycled polypropylene resins is greater than that of propylene random copolymers. Recycled propylene block copolymers are relatively easy to obtain. When recycled resin is used as all or part of a propylene block copolymer, it not only reduces environmental pollution but also significantly reduces the amount of plastic waste generated and the amount of plastic used in manufacturing. Therefore, embodiments that use recycled resin as all or part of a propylene block copolymer have the advantage of contributing to the achievement of the Sustainable Development Goals (SDGs).

[0048] In this specification, "recycled resin" means resin that has gone through the form of a resin product at least once (for example, foamed particles, foamed molded products, films, packaging containers such as food trays and bags and bottles, miscellaneous goods such as clothing cases and clear files, etc.) and then returned to the form of resin (or resin particles) again by means of melting or other means.

[0049] The propylene-based block copolymer may be a mixture of recycled resin and non-recycled resin (resin that has never been in the form of a resin product). From the viewpoint of reducing environmental impact, 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 solely of recycled resin).

[0050] The base resin preferably contains, when the total amount of propylene-based random copolymer and propylene-based block copolymer is 100% by weight, (a) 73% to 95% by weight of propylene-based random copolymer and 5% to 27% by weight of propylene-based block copolymer; (b) 74% to 95% by weight of propylene-based random copolymer and 5% to 26% by weight of propylene-based block copolymer; and (c) 75% to 93% by weight of propylene-based random copolymer and 7% to 25% by weight of propylene-based block copolymer. When the content of propylene-based random copolymer and propylene-based block copolymer in the base resin is within the above range, the foamed particles have the advantage of being more productive in producing polypropylene-based foamed molded articles.

[0051] (Other resins, etc.) The base resin may further contain resins other than propylene random copolymers and propylene block copolymers (sometimes referred to as "other resins, etc.") as resin components, to the extent that the effects of one embodiment of the present invention are not impaired. Examples of such other resins, etc. include (a) polypropylene resins other than propylene random copolymers and propylene block copolymers, (b) ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer, (c) styrene resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer, (d) polyolefin waxes such as propylene-α-olefin wax, and (e) olefin rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber. The content of other resins in these foamed particles 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) In addition to the propylene-based random copolymer and propylene-based block copolymer described above, the base resin may optionally contain additives. Examples of additives include colorants, water-absorbing substances, foaming 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 later in the production of polypropylene-based resin particles.

[0053] <Physical properties> The following describes the physical properties of these foamed particles.

[0054] (Peak intensity ratio) These foamed particles have a peak intensity ratio of I 720 / I 810 However, it is preferable that it be between 0.45 and 0.67. Peak intensity ratio I 720 / I810 In the spectrum obtained by infrared spectroscopy, at a wavelength of 720 cm⁻¹, -1 The peak intensity is "I 720 " and wavelength 810 cm -1 The peak intensity is "I 810 When "I 810 I 720 This is the ratio. Infrared spectroscopy can be measured by the method described in the examples below. Wavelength 720 cm -1 The peak is likely to be mainly derived from the ethylene block, at a wavelength of 810 cm. -1 The peak may be mainly due to propylene. Wavelength 720nm in foamed particles. -1 The larger the peak, the more ethylene blocks the foamed particles are intended to contain.

[0055] Therefore, the peak intensity ratio I obtained by infrared spectroscopy 720 / I 810 This can relatively accurately reflect the ratio of propylene to ethylene blocks contained in the base resin contained in the foamed particles. Specifically, in a preferred embodiment, when the propylene-based block copolymer contains ethylene blocks, the peak intensity ratio I 720 / I 810 A larger value indicates a higher amount of propylene-based block copolymer in the total amount of propylene-based random copolymer and propylene-based block copolymer. In one embodiment, the ratio of propylene-based random copolymer to propylene-based block copolymer contained in the base resin can be determined by pre-measuring the peak intensity ratio of the propylene-based block copolymer used in the production of 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 still more preferably 0.50 to 0.60. This configuration has the advantage that the foamed particles are more efficient in producing polypropylene-based foamed molded articles.

[0057] The aforementioned peak intensity ratio can be controlled by the content of each block copolymer contained in the foamed particles.

[0058] (Shrinkage rate) The shrinkage rate of these foamed particles can be calculated using the following formula (2). Contraction rate = (BD - VBD) × 100 / VBD ... (2) In equation (2), BD is the bulk density of polypropylene foam particles at 23°C and 0.1 MPa (absolute pressure). In other words, BD can also be said to be the bulk density of polypropylene foam particles under standard atmospheric pressure. VBD is the bulk density of polypropylene foam particles at 23°C and below -0.09 MPa (gauge pressure). In other words, VBD can be said to be the bulk density of polypropylene foam particles 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 0% or more, for example. When the shrinkage rate is within the above range, the foamed particles have the advantage of being more productive in producing polypropylene-based resin foam molded articles.

[0060] The shrinkage rate can be controlled by adjusting the conditions during the production of the foamed particles (e.g., foaming temperature and foaming pressure).

[0061] (DSC ratio of foamed particles) Preferably, these foamed particles have at least two melting peaks in the DSC curve obtained by differential scanning calorimetry, as described below. Of these melting peaks, the heat of fusion obtained from the higher temperature melting peak is defined as the "high-temperature side heat of fusion," and the heat of fusion obtained from the lower temperature melting peak is defined as the "low-temperature side heat of fusion." If there are three or more melting peaks, the heat of fusion obtained from the highest temperature melting peak is defined as the "high-temperature side heat of fusion," and the heat of fusion obtained from the other melting peaks is defined as the "low-temperature side heat of fusion."

[0062] The DSC ratio of the foamed particles 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 foamed particles is 10.0% or higher, the foamed particles 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 foamed particles is 50.0% or lower, the foamed particles 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 the high temperature to the total heat of fusion, calculated from the DSC curve of the foamed particles. In this specification, the DSC curve is obtained using a differential scanning calorimeter (e.g., Hitachi High-Tech Science Corporation DSC7020). More specifically, it can be measured by the method described in the examples.

[0064] The DSC ratio of these foamed particles is also an indicator of the amount of high-melting-point crystals contained in the foamed particles. In other words, a DSC ratio of 10.0% to 50.0% indicates that the foamed particles contain a relatively large amount of high-melting-point crystals. Furthermore, the DSC ratio of the foamed particles greatly influences the viscoelasticity of the resin particles and the foamed particles during foaming and expansion. Specifically, when the DSC ratio of the foamed particles is 10.0% to 50.0%, the resin particles and the foamed particles can exhibit excellent foaming and expansion properties, respectively, during foaming and molding. As a result, the foamed particles have the advantage of producing foamed molded articles with excellent internal bonding properties at low molding pressure and excellent mechanical strength, such as compressive strength.

[0065] Methods for controlling the DSC ratio within a predetermined range in these foamed particles include adjusting the manufacturing conditions of the foamed particles (particularly the foaming temperature, foaming pressure, holding time, and the temperature of the region (space) where the dispersion is released). Because adjustments are easy, adjusting the foaming temperature, foaming pressure, and / or holding time is preferred as a method for controlling the DSC ratio within a predetermined range.

[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. Similarly, increasing the foaming pressure 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. Furthermore, increasing the holding time tends to increase the DSC ratio. This is because the amount of unmelted crystal growth changes depending on the holding time.

[0067] (Foaming ratio of foaming particles) The foamed particles preferably have a foaming ratio of 15 to 50 times, more preferably 18 to 40 times, and even more preferably 20 to 25 times. If the foaming ratio of the foamed particles is (i) 15 times or more, a lightweight foamed molded article can be obtained with production efficiency, and (ii) if it is 50 times or less, there is no risk of insufficient strength in the resulting foamed molded article. The foaming ratio can be measured by the method described in the examples below.

[0068] (Minimum molding pressure) These foamed particles have the advantage of enabling the production of foamed molded articles with excellent fusion rates (for example, fusion rates of 80% or more) at low molding pressures. In other words, these foamed particles have the advantage of providing foamed molded articles with excellent fusion rates at the same molding pressures as foamed particles obtained using only propylene-based random copolymers as the base resin.

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

[0070] The minimum molding pressure for these foam particles 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 the advantage that a foamed molded product can be provided with a small economic burden.

[0071] [2. Method for producing polypropylene resin foam particles] A method for producing polypropylene resin foam particles according to one embodiment of the present invention comprises a foaming step in which polypropylene resin particles, which include a base resin containing a propylene random copolymer and a propylene block copolymer, are depressurized and foamed under conditions of a foaming temperature of 163.5°C or lower and a foaming pressure of 2.80 MPa or lower.

[0072] A method for producing polypropylene resin foam particles according to another embodiment of the present invention comprises a foaming step in which polypropylene resin particles, which include a base resin containing a propylene random copolymer and a propylene block copolymer, are depressurized and foamed under conditions of 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 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 100% by weight. (granulation process) This manufacturing method may further include a step (granulation step) for producing polypropylene resin particles containing a base resin containing a propylene random copolymer and a propylene block copolymer. In this specification, "polypropylene resin particles" may be referred to as "resin particles".

[0073] One method for producing resin particles is to use an extruder. Specifically, for example, resin particles can be produced by the following methods (1) to (5): (1) Blend one or more selected from the group consisting of block copolymers, random copolymers, and other resins and additives as needed to produce a blend; (2) Put the blend into an extruder and melt-knead it to prepare a polypropylene resin composition; (3) Extrude the polypropylene resin composition from a die provided in the extruder; (4) Solidify the extruded polypropylene resin composition by cooling it by passing it through water, etc.; (5) Then, cut the solidified polypropylene resin composition with a cutter into desired shapes such as cylindrical, elliptical, spherical, cubic, rectangular parallelepiped, hollow cylindrical, polygonal prism, etc. Alternatively, in (3), the melt-kneaded polypropylene resin composition may be directly extruded into water from a die provided in the extruder, and immediately after extrusion, the polypropylene resin composition may be cut into particle shapes, cooled, and solidified. In this way, by melting and kneading the blended materials, 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 handling properties of the resin particles tend to improve, and the shrinkage rate of the foamed molded article obtained by molding the resulting foamed particles tends to be smaller. When the weight per particle is (B) 10.0 mg / particle or less, the mold filling properties tend to improve in the in-mold foaming molding process.

[0075] (Dispersion process) This manufacturing 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 foaming agent, and optionally a dispersant and / or dispersion aid are dispersed in a container. The dispersion step can also be described as a step of preparing a dispersion in which the base resin, foaming agent, and optionally a dispersant and / or dispersion aid are dispersed in an aqueous dispersion medium. The base resin in the dispersion step may be resin particles obtained in the granulation step described above.

[0076] The container is not particularly limited, but it is preferable that it be able to withstand the foaming temperature and pressure described later. For example, a pressure-resistant container is preferable, and an autoclave-type pressure-resistant container is more preferable. The container may be equipped with an agitator.

[0077] The aqueous dispersion medium can be any medium capable of uniformly dispersing resin particles, foaming agents, etc., and is not particularly limited.

[0078] Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, and glycerin 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] To enable stable production of foamed particles, it is preferable to use pure water and ultrapure water such as RO water (water purified by reverse osmosis), distilled water, and deionized water (water purified by ion exchange resin) as the aqueous dispersion medium.

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

[0081] As a blowing agent, at least one type selected from the group consisting of the inorganic and organic blowing agents described above can be used. When using a mixture of two or more blowing agents, the mixing ratio may be adjusted as appropriate depending on the purpose. From the viewpoint of environmental impact and blowing power, inorganic blowing agents are preferred among those described above. Furthermore, carbon dioxide is preferred among inorganic blowing agents because it has a moderately high plasticizing effect and easily improves the blowing properties of the foamed particles in the production of these foamed particles.

[0082] The aqueous dispersion medium and foaming agent described above may be used individually or in combination of two or more types.

[0083] In this method for producing foamed particles, it is preferable to use a dispersant (for example, inorganic substances such as tricalcium phosphate, kaolin, and talc) and a dispersion aid (for example, anionic surfactants such as sodium alkanesulfonate and sodium dodecylbenzenesulfonate). This configuration reduces adhesion between resin particles (sometimes referred to as blocking) and improves the stability of the dispersion in the container. As a result, it has the advantage of being able to produce foamed particles stably.

[0084] (Foaming process) The specific form of the foaming process is not particularly limited. The foaming process may include, for example, (a) a heating-pressure step in which the temperature inside the container is raised to a certain temperature and the pressure inside the container is raised to a certain pressure to depressurize and foam the resin particles, (b) A holding step for maintaining the temperature and pressure inside the container at a constant temperature and constant pressure, (c) The method may include a discharge 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 foaming pressure (i.e., the pressure inside the container).

[0085] (Heating-pressure boosting process and holding process) The heating-pressure step is preferably performed after the dispersion step, and the holding step is preferably performed after the heating-pressure 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 it is possible to depressurize and foam the resin particles, but it may be, for example, 150°C or higher.

[0087] Furthermore, 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 it is possible to depressurize and foam the resin particles, but it may be, for example, 1.5 MPa or more.

[0088] In the course of diligent research, the inventors have independently discovered a novel finding that, in order to obtain foamed particles with low shrinkage, it is preferable to appropriately set the foaming pressure depending on the amount of propylene-based block copolymer. Specifically, the inventors have independently discovered a novel finding that, in order to obtain foamed particles with low shrinkage, it is preferable to set the foaming pressure lower as the amount of propylene-based block copolymer increases. More specifically, when the content ratio of block copolymer in the total amount of propylene-based random copolymer and propylene-based block copolymer in polypropylene resin particles is X (weight%), the inventors have independently discovered a novel finding that, when the foaming pressure Y (MPa) during foamed particle production is satisfied by the following formula (1): Y < -0.07X + 3.6 ... (1). The reason why it is preferable to satisfy formula (1) is not clear, but it is presumed that propylene-based block copolymers are softer and more extensible than propylene-based random copolymers. However, the embodiment of the present invention is not limited in any way to this presumption.

[0089] It is more preferable that X and Y satisfy the following formula (3), even more preferable that they satisfy the following formula (4), and particularly preferable that they 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 process, the time for holding the dispersion in the container at or near the foaming temperature and pressure (holding time) 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 more, the amount of unmelted crystals (crystals of polypropylene resin) in the resin particles can be made sufficient during the foaming process from resin particles to foamed particles. As a result, foamed particles with a low open-cell ratio can be obtained, and the shrinkage of the resulting foamed particles can be reduced. On the other hand, when the holding time is 60 minutes or less, the amount of unmelted crystals in the resin particles does not become excessive during the foaming process from resin particles to foamed particles. Therefore, the resulting foamed particles can be molded at a relatively low temperature (molding temperature) to provide a foamed molded article.

[0091] (Release process) The release step is preferably performed (a) after the heating-pressure step if the holding step is not performed, or (b) after the holding step if the holding step is performed. The release step allows the resin particles to foam, resulting in foamed particles.

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

[0093] In the discharge process, when discharging the dispersion into a region with a pressure lower than the foaming pressure, the dispersion can be discharged through an open orifice with a diameter of 1 mm to 5 mm for purposes such as adjusting the flow rate of the dispersion and reducing variations in the foaming ratio of the resulting foamed particles. Furthermore, to improve foaming properties, the low-pressure region (space) may be filled with saturated water vapor.

[0094] The process of manufacturing foamed particles from resin particles in this manner is called the "single-stage foaming process," and the resulting foamed particles are called "single-stage foamed particles."

[0095] (Two-stage foaming process) To obtain foamed particles with a high foaming ratio, the foamed particles obtained in the first foaming step may be foamed again. The step of increasing the foaming ratio of the first foamed particles is called the "second foaming step," and the polyolefin resin foamed particles obtained in the second foaming step are called "second foamed particles." The specific method for the second foaming step is not particularly limited, and known methods can be used.

[0096] [3. Polypropylene-based resin foam molded product] A polypropylene resin foam molded article according to one embodiment of the present invention is a foam molded article obtained by foam molding the polypropylene resin foam particles described in section [1. Polypropylene Resin Foam Particles]. A polypropylene resin foam molded article according to one embodiment of the present invention may also be a foam molded article obtained by foam molding polypropylene resin foam particles obtained by the manufacturing method described in section [2. Method for Producing Polypropylene Resin Foam Particles]. A polypropylene resin foam molded article according to one embodiment of the present invention can also be said to include polypropylene resin foam particles described in section [1. Polypropylene Resin Foam Particles], or polypropylene resin foam particles obtained by the manufacturing method described in section [2. Method for Producing Polypropylene Resin Foam Particles].

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

[0098] Because this foamed molded product has the above-described structure, it has the advantages of excellent productivity and superior strength.

[0099] (productivity) In this specification, the productivity of the foamed molded article is evaluated by the time (seconds) (molding cycle) from the start of molding of the foamed particles to the completion of molding. As described in the examples below, the start of molding is defined as the time when the foamed particles are filled into the mold. The completion of molding is defined as the time when the molded article is cooled (water-cooled), the surface pressure gauge attached to the surface of the plank mold has decreased to 0.01 MPa, the mold is opened, and demolding is completed. A shorter molding cycle is intended to indicate superior productivity of the foamed molded article.

[0100] (Surface beauty) In this specification, the surface aesthetics of the foamed molded article are evaluated by the degree of gaps between foam particles on the surface of the foamed molded article (hereinafter sometimes referred to as "intergranular gaps") and the wrinkles on the surface of the foamed molded article. The smaller the size of the intergranular gaps on the surface of the foamed molded article, and the fewer the number of intergranular gaps, 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) This foamed molded article also has the advantage of excellent strength. In this specification, the strength of the foamed molded article is evaluated by its static compressive strength. The method for measuring the static compressive strength of the foamed molded article will be described in detail in the following examples.

[0102] The static compressive strength of this foamed molded article is preferably 0.212 MPa or higher, more preferably 0.217 MPa or higher, and even more preferably 0.229 MPa or higher. The upper limit of the static compressive strength is not particularly limited, but may be, for example, 0.300 MPa or lower. This configuration has the advantage of being able to withstand use in applications such as automotive interior components, automotive bumper core materials, thermal insulation materials, cushioning packaging materials, and reusable containers.

[0103] One embodiment of the present invention may include the following configuration: [1] A method for producing polypropylene resin foam particles, comprising a foaming step of depressurizing and foaming polypropylene resin particles containing a base resin containing a propylene random copolymer and a propylene 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 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 100% by weight. [2] A method for producing polypropylene resin foam particles as described in [1], satisfying the following formula (1): Y < -0.07X + 3.6 ···(1); Here, X is the content ratio (weight %) of the propylene-based block copolymer in the base resin, where the total amount of propylene-based random copolymer and propylene-based block copolymer is 100% by weight, and Y is the foaming pressure (MPa) in the foaming process. [3] The method for producing polypropylene resin foamed particles according to [1] or [2], wherein the foaming step is a two-stage foaming step. [4] A method for producing polypropylene resin foam particles according to any one of [1] to [3], wherein the foaming temperature is 150°C or higher. [5] A method for producing polypropylene foamed particles according to any one of [1] to [4], wherein the foaming pressure is 1.5 MPa or higher. [6] A method for producing polypropylene foam particles according to any one of [1] to [5], wherein the melting point of the propylene-based block copolymer is 160°C or higher and 180°C or lower. [7] The method for producing polypropylene foamed particles according to any one of [1] to [6], wherein the propylene-based block copolymer is a recycled resin. [8] A method for producing polypropylene foamed particles 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 the total structural units, and the propylene block copolymer contains 50 mol% or more of propylene units in 100 mol% of the total structural units. [9] The method for producing polypropylene foamed particles according to any one of [1] to [8], wherein the propylene random copolymer comprises a propylene / ethylene random copolymer containing propylene units and ethylene units.

[10] The method for producing polypropylene foamed particles 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.

[11] A method for producing polypropylene foamed particles 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.

[12] A method for producing polypropylene foamed particles according to any one of [1] to

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

[13] A method for producing polypropylene resin foam particles according to any one of [1] to

[12] , wherein the DSC ratio of the polypropylene resin foam particles is 10.0% to 50.0%.

[14] A method for producing polypropylene resin foam particles according to any one of [1] to

[13] , wherein the foaming ratio of the polypropylene resin foam particles is 15 to 50 times. A method for producing a polypropylene resin foamed molded article, comprising the step of molding polypropylene resin foamed particles obtained by the method for producing polypropylene resin foamed particles described in any one of [1] to

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

[16] A base resin containing a propylene-based random copolymer and a propylene-based block copolymer, with a peak intensity ratio of I 720 / I 810 Polypropylene resin foam particles with a coefficient of 0.45-0.67 and a shrinkage rate of 20% or less: Here, the peak intensity ratio I 720 / I 810 This is obtained in the spectrum acquired by infrared spectroscopy at a wavelength of 810 cm². -1 I is the peak intensity of 810 For a wavelength of 720 cm -1 I is the peak intensity of 720 It is the ratio of, The aforementioned shrinkage rate (%) is the value obtained by the following formula (2); The aforementioned shrinkage rate (%) = (BD - VBD) × 100 / VBD ... (2) In equation (2), BD is the bulk density of polypropylene resin foam particles 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 polypropylene resin foam particles obtained by measurement in a region where the temperature is 23°C and the pressure is -0.09 MPa.

[17] The polypropylene resin foam 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 100% by weight.

[18] Polypropylene resin foam particles according to either

[16] or

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

[19] The polypropylene-based foamed resin particles according to any one of

[16] to

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

[20] The polypropylene resin foam particle 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 the total structural units, and the propylene block copolymer contains 50 mol% or more of propylene units in 100 mol% of the total structural units.

[21] The polypropylene resin foam 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.

[22] The polypropylene resin foam 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.

[23] Polypropylene resin foam 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.

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

[16] to

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

[25] Polypropylene resin foam particles as described in any one of

[16] to

[24] , wherein the DSC ratio is 10.0% to 50.0%.

[26] Polypropylene resin foam particles as described in any one of

[16] to

[25] , having a foaming ratio of 15 to 50 times.

[27] The polypropylene resin foam particles according to any one of

[16] to

[26] , wherein, when the polypropylene resin foam particles are molded, the minimum molding pressure required to provide a polypropylene resin foam molded article with a fusion rate of 80% or more is 0.30 MPa or less. A polypropylene resin foam molded article obtained by foam molding polypropylene resin foam particles described in any one of

[28] ,

[16] , to

[27] .

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

[28] , wherein the static compressive strength is 0.212 MPa or higher.

[0104] Furthermore, another embodiment of the present invention includes the following configuration. [1] A base resin containing a propylene-based random copolymer and a propylene-based block copolymer, with a peak intensity ratio of I 720 / I 810 Polypropylene resin foam particles with a coefficient of 0.45 to 0.65 and a shrinkage rate of 20% or less: Here, the peak intensity ratio I 720 / I 810 This is obtained in the spectrum acquired by infrared spectroscopy at a wavelength of 810 cm². -1 I is the peak intensity of 810 For a wavelength of 720 cm -1 I is the peak intensity of 720 It is the ratio of, The aforementioned shrinkage rate (%) is the value obtained by the following formula (1); The aforementioned shrinkage rate (%) = (BD - VBD) × 100 / VBD ... (1) In formula (1), BD is the bulk density of polypropylene resin foam particles 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 polypropylene resin foam particles obtained by measurement in a region where the temperature is 23°C and the pressure is -0.09 MPa. [2] The polypropylene resin foam particles according to [1], wherein the base resin contains 75% to 95% by weight of the propylene random copolymer and 5% to 25% by weight of the propylene block copolymer, when the total amount of the propylene random copolymer and propylene block copolymer is 100% by weight. [3] Polypropylene resin foam particles according to [1] or [2], wherein the melting point of the propylene-based block copolymer is 160°C or higher. [4] The propylene-based block copolymer is a recycled resin, and the polypropylene resin foam particles are as described in any one of [1] to [3]. A polypropylene resin foam molded article obtained by foam molding polypropylene resin foam particles described in any one of [5], [1], to [4]. [6] A method for producing polypropylene resin foam particles, comprising a foaming step of depressurizing and foaming polypropylene resin particles containing a base resin containing a propylene random copolymer and a propylene block copolymer at a foaming temperature of 163.5°C or lower and a foaming pressure of 2.80 MPa or lower. [Examples]

[0105] The present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited to these examples.

[0106] 〔material〕 In the examples and comparative examples, the following materials were used, but no special purification or other procedures were performed.

[0107] <Polypropylene resin> • Propylene / ethylene block copolymer 1 [MFR = 12g / 10min, melting point 166℃, recycled resin, containing 5% by weight of carbon black] • Propylene / ethylene block copolymer 2 [Prime Polymer J715M, MFR = 9g / 10min, 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-recyclable resin] <Resin particle additive> • Talc [Manufactured by Hayashi Chemical Co., Ltd., Talc Powder PK-S] • Glycerin [Manufactured by Lion Corporation, refined glycerin D] [Measurement method] The evaluation methods used in the examples and comparative examples are described below.

[0108] <Measuring the melting point of polypropylene resins> The melting point of polypropylene resin particles was measured using a differential scanning calorimeter (DSC7020, Hitachi High-Tech Science Corporation). The specific measurement method was as follows: (1) 5-6 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) Then, it was cooled from 220°C to 40°C at a cooling rate of 10°C / min to crystallize it; (3) Furthermore, it was 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., at (3)) was taken as the melting point of the polypropylene resin particles.

[0109] <MFR measurement of polypropylene resins> For polypropylene resin, the melt mass flow rate (MFR) was measured using a melt mass flow rate measuring instrument described in JIS K7210 under the following conditions: orifice diameter of 2.0959 ± 0.005 mm, orifice length of 8.000 ± 0.025 mm, load of 2160 g, and temperature of 230 ± 0.2 °C.

[0110] <Measurement of DSC ratio of polypropylene resin foam particles> The DSC ratio was measured using a differential scanning calorimeter (DSC7020, Hitachi High-Tech Science Corporation). Specifically, when 5-6 mg of polypropylene resin foam particles were heated from 40°C to 220°C at a heating rate of 10°C / min, the melting peak area on the low-temperature side of the DSC curve obtained during the first heating was defined as Q. l Let Q be the melting peak area on the high-temperature side. h The result was obtained using the following formula. DSC ratio (%)=Q h / (Q l +Q h ) × 100 More precisely, Q is the area enclosed by the melting peak on the low-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 onset baseline. l Let Q be the heat quantity of the high-temperature melting peak, 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 low-temperature melting peak and the high-temperature melting peak to the melting end baseline. h That's what I decided.

[0111] <Infrared Spectroscopic Analysis of Polypropylene-Based Resin Foam Particles> Infrared spectroscopy was used to determine the ratio of peak intensities originating from propylene and block ethylene in polypropylene resin foam particles. The measurement was performed using the Attenuated Total Reflection (ATR) method. Polypropylene resin foam particles were compressed between metal plates and then pressed against the crystal of an ATR measuring device (PerkinElmer Japan, Spectrum Two) with a resolution of 4 cm². -1 The measurement was performed with 16 cumulative measurements, and the spectrum was obtained. At this time, the reading was 1376 cm⁻¹. -1 The pressure during crimping was adjusted so that the peak intensity was 0.15A. Next, from the obtained spectrum, the wavelength 810 cm was selected. -1 Peak intensity (I 810 ) and wavelength 720cm -1 Peak intensity (I 720 ) read [(I 720 ) / (I 810The peak intensity ratio was calculated from the following. In this example, the wavelength was 810 cm. -1 The peak intensity is derived from the CH3 group of propylene, at a wavelength of 720 cm. -1 The peak intensity was derived from the ethylene chain. The measurement was performed using five arbitrary polypropylene resin foam particles, and the arithmetic mean was used. In Comparative Example 3, as foam particles could not be obtained as described later, resin particles were used and the measurement was performed similarly. If the measurement conditions are the same, it is expected that there will be almost no difference in the measurement results of the ratio of peak intensities between when foam particles and resin particles are used as samples.

[0112] <Measurement of foaming ratio of polypropylene resin foam particles> Take approximately 3g to 10g of polypropylene resin foam particles, dry them at 60°C for 6 hours, then allow them to cool in a room at 23°C and 50% humidity. After measuring the weight w1 (g), immerse the particles in a graduated cylinder containing ethanol, and measure the volume v (cm³) by measuring the rise in the water level in the graduated cylinder (submersion method). 3 ) was measured, and the true specific gravity ρ of the polypropylene resin foam particles was measured. b = w1 / v is calculated, and further, the density ρ of the polypropylene resin particles before foaming is calculated. r The ratio (ρ r / ρ b The density ρ of the polypropylene resin particles before foaming was calculated as follows. In the examples and comparative examples shown below, the density ρ of the polypropylene resin particles before foaming was calculated as follows. r Both are 0.9 g / cm³. 3 That was the case.

[0113] <Measurement of shrinkage rate of polypropylene resin foam particles> The shrinkage rate of polypropylene foam particles was calculated from the bulk density (hereinafter referred to as BD) and the bulk density of polypropylene foam particles under reduced pressure (hereinafter referred to as VBD) using the following method. The weight of the polypropylene foam particles to be measured was denoted as W1, and the volume V1 was determined using a graduated cylinder at 23°C under atmospheric pressure (standard atmospheric pressure 0.1 MPa). The bulk density BD of the polypropylene foam particles at 23°C and 0.1 MPa (standard atmospheric pressure) was determined according to the following formula. BD(g / L) = W1 ÷ V1 The polypropylene resin foam particles were weighed again, and their weight was defined as W2. They were placed in a graduated pressure vessel, and the pressure inside the vessel was reduced using a vacuum pump or similar device. After confirming with a pressure gauge that the pressure had been reduced to -0.09 MPa (gauge pressure) or below, the pressure vessel was vibrated using a vibrator until the scale above the foam particles stopped changing. Then, the scale above the polypropylene resin foam particles inside the pressure vessel was read, and this was defined as the volume V2. Note that during depressurization, the foam particles may push against each other, hindering the volume change. Therefore, the pressure vessel was tilted on its side or similar to prevent this from hindering the volume change of the foam particles, and the pressure was reduced gradually. The bulk density VBD of the polypropylene resin foam particles under reduced pressure of -0.09 MPa (gauge pressure) or below at 23°C was determined according to the following formula. VBD(g / L) = W2 ÷ V2 Furthermore, the shrinkage rate of the polypropylene resin foam particles was determined using the following formula.

[0114] (BD - VBD) ÷ VBD × 100.

[0115] <Minimum molding pressure for polypropylene resin-based in-mold foamed molded products> In the [Preparation of Polypropylene Resin In-Mold Foamed Molded Articles] described later, the set steam pressure for this heating step was changed in increments of 0.01 MPa within the range of 0.20 to 0.32 MPa (gauge pressure) to obtain foamed molded articles for each evaluation. For the obtained foamed molded articles, a crack approximately 5 mm deep was made on the surface with a knife, the in-molded foamed molded article was split along the crack, the fracture surface was observed, and the ratio of the number of fractured particles to the total number of particles on the fracture surface was determined to evaluate the molded article fusion rate. The lowest steam pressure at which the fusion rate reached 80% or more was defined as the minimum molding pressure.

[0116] <Molding cycle of polypropylene resin-based in-mold foamed molded products> The molding cycle in the manufacturing method for polypropylene resin in-mold foamed molded articles was defined as the period from the start of molding to the end of molding when the molded article is demolded. The start of molding was defined as the point when the polypropylene resin foam particles began to be filled into the mold, the mold was heated by sending steam into the mold, the molded article was then water-cooled, the mold was opened when the surface pressure, measured by a surface pressure gauge attached to the surface of the plank mold, dropped to 0.01 MPa, and the end of molding was defined as the point when demolding was completed. The steam heating pressure was evaluated as the minimum molding pressure determined in the <Minimum Molding Pressure for Polypropylene Resin In-Mold Foamed Molded Articles> above. The productivity evaluation criteria are as follows. ◎ (Excellent): Molding cycle is within 180 seconds. ○ (Excellent): Molding cycle is longer than 180 seconds but within 210 seconds. × (Inferior): Molding cycle is 210 seconds or longer.

[0117] <Surface aesthetics of polypropylene resin-based in-mold foamed molded products> The surface quality of the obtained polypropylene resin foam molded body was visually observed on a 350 mm x 450 mm surface, and judged according to the following criteria. For intergranular space (gaps between polypropylene resin foam particles), which is one of the evaluation indicators for surface quality, the number of gaps present in a 50 mm square area on the central surface of the molded body was visually counted and judged. ◎(Beautiful surface appearance): No wrinkles, and the spacing between grains is 0-1. ○ (Good surface appearance): No wrinkles, and the spacing between grains is 2-3. △ (Surface appearance is acceptable): Wrinkles are visible, or there are 4-5 spaces between grains. × (Surface appearance is unacceptable): Wrinkles are present, or there are six or more spaces between grains.

[0118] <Static compressive strength measurement of polypropylene resin-based foamed molded articles> A test piece measuring 50 mm (length) x 50 mm (width) x 25 mm (thickness) was cut from a polypropylene resin in-molded foamed body. Using a tensile-compression testing machine (MinebeaMitsumi Inc., TG series), the test piece was compressed at a speed of 10 mm / min, and the compressive stress at 50% compression was measured. The compressive stress at 50% compression is a measure of the rigidity of the in-molded foamed body.

[0119] The following describes the methods for producing polypropylene resin particles, polypropylene resin foam particles, and polypropylene resin molded foam articles in examples and comparative examples.

[0120] (Example 1) [Method for 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). After the extruded strands were water-cooled in a 2m long water tank, they were cut to produce polypropylene resin particles (1.2 mg / particle).

[0121] [Preparation of polypropylene resin foam particles] In a 10L pressure-resistant autoclave, 100 parts by weight (2.4 kg) of polypropylene resin particles obtained as described above, 200 parts by weight of water, 0.3 parts by weight of kaolin (BASF, ASP170) as a poorly water-soluble inorganic compound, and 0.06 parts by weight of sodium dodecylbenzenesulfonate (Kao Corporation, Neoperex G-15) as a surfactant were placed. After stirring, 4 parts by weight of carbon dioxide was added as a foaming agent. The contents of the autoclave were heated to a foaming temperature of 158.2°C and held for 10 minutes. Then, carbon dioxide was added to increase the internal pressure of the autoclave to a foaming pressure of 2.60 MPa. After holding at the foaming temperature and pressure for 20 minutes, the valve at the bottom of the autoclave was opened, and the contents were released through a 3.6 mm diameter open orifice to atmospheric pressure to obtain polypropylene resin foam particles with a foaming ratio of 24 times. During this process, carbon dioxide was added to maintain the pressure inside the container to prevent a drop in pressure.

[0122] [Preparation of polypropylene resin in-mold foamed products] The obtained polypropylene resin foam particles were dried at 75°C. The dried polypropylene resin foam particles were placed in a pressure vessel, impregnated with pressurized air, and adjusted to a pre-set internal pressure of 0.20 MPa (absolute pressure). These polypropylene resin foam particles were then filled into a mold measuring 370 mm (length) x 320 mm (width) x 50 mm (thickness). Subsequently, the mold chamber was heated with steam at a predetermined pressure to fuse the foam particles together. After water-cooling the inside of the mold and the surface of the molded body, the molded body was removed to obtain a polypropylene resin in-molded foam molded body. This operation was performed by changing the steam pressure from 0.20 MPa (gauge pressure) to 0.32 MPa in 0.01 MPa increments, and the minimum pressure required for sufficient fusion of the polypropylene resin foam particles was determined and set as the lower limit pressure for molding. The obtained in-molded foam molded body was left to stand at 23°C for 2 hours, and then cured at 75°C for 13 hours.

[0123] (Examples 2-7, Comparative Examples 1-3, Reference Example 1) In the [Preparation of Polypropylene Resin Particles], the resin formulation was changed as shown in Table 1, and in the [Preparation of Polypropylene Resin Foamed Particles], the foaming conditions were changed as shown in Table 1. Except for these changes, polypropylene resin particles, polypropylene resin foamed particles, and polypropylene resin molded articles were prepared using the same procedure as in Example 1. Note that the foaming process 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 resin component, 158°C was selected as the foaming temperature to obtain foamed particles of suitable quality, and when it was 20 parts by weight, 164°C was selected. Therefore, in the case of Comparative Example 3, which contained 30 parts by weight of ethylene / propylene block copolymer per 100 parts by weight of resin component, the foaming temperature to obtain foamed particles of suitable quality was expected to exceed the upper temperature limit that could be raised using the pressure-resistant autoclave used in the Examples. Table 1 shows the resin formulation conditions, foaming conditions, and evaluation results of the obtained polypropylene resin foamed particles and polypropylene resin molded articles.

[0124] [Table 1]

[0125] If the peak intensity ratio determined by infrared spectroscopy is 0.45 or higher, it indicates that the material contains a sufficient amount of propylene-based block copolymer. Therefore, if recycled polypropylene resin is used as the propylene-based block copolymer, the recyclability is improved. On the other hand, Table 1 shows that when the peak intensity ratio is 0.7, the molding temperature is high, resulting in the inability to obtain foamed particles or poor productivity. Furthermore, Comparative Example 1, which was foamed at a foaming pressure of 2.90 MPa, almost the same as Reference Example 1, shows that the molding cycle is longer, productivity is poor, and the static compressive strength of the foamed molded product is significantly reduced. In addition, Comparative Example 2, which was foamed at a foaming temperature of 163.7°C, also shows a similar lengthening of the molding cycle and a significant decrease in the static compressive strength of the foamed molded product.

[0126] On the other hand, by adjusting the foaming conditions so that the shrinkage rate of the polypropylene resin foam particles is 20% or less, as in Examples 1 to 7, the molding cycle can be made sufficiently short, although it is longer than in Reference Example 1, and the decrease in static compressive strength tends to be suppressed. Furthermore, polypropylene resin foam particles containing ethylene / propylene block copolymer can be molded in the same molding pressure as polypropylene resin foam particles consisting only of ethylene / propylene random copolymer, and the resulting foam molded body has excellent surface appearance. [Industrial applicability]

[0127] According to one embodiment of the present invention, polypropylene-based resin foam particles can be provided with improved productivity due to the shorter molding time during in-mold molding. Therefore, one embodiment of the present invention can be used in a variety of applications, including automotive interior components, core materials for automotive bumpers, as well as thermal insulation materials, cushioning packaging materials, and reusable containers.

Claims

1. A method for producing polypropylene resin foam particles, comprising a foaming step of depressurizing and foaming polypropylene resin particles containing a base resin containing a propylene random copolymer and a propylene block copolymer under conditions of 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 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 100% by weight.

2. A method for producing polypropylene resin foam particles according to claim 1, satisfying the following formula (1): Y<-0.07X+3.6...(1); Here, The above X is the content ratio (by weight) of the propylene-based block copolymer in the base resin, when the total amount of propylene-based random copolymer and propylene-based block copolymer in the base resin is set to 100% by weight. Y is the foaming pressure (MPa) in the foaming process.

3. A method for producing polypropylene resin foam particles according to claim 1 or 2, wherein the foaming temperature is 150°C or higher.

4. The base resin contains a propylene-based random copolymer and a propylene-based block copolymer. Peak intensity ratio I ７２０ / I ８１０ The values ​​are 0.45 to 0.

67. Polypropylene resin foam particles with a shrinkage rate of 20% or less: Here, the peak intensity ratio I ７２０ / I ８１０ This is obtained in the spectrum acquired by infrared spectroscopy at a wavelength of 810 cm⁻¹. －１ I is the peak intensity. ８１０ For a wavelength of 720 cm －１ I is the peak intensity. ７２０ It is the ratio of, The aforementioned shrinkage rate (%) is the value obtained by the following formula (2): The aforementioned shrinkage rate (%) = (BD - VBD) × 100 / VBD ... (2) In formula (2), The aforementioned BD is the bulk density of polypropylene resin foam particles obtained by measurement in the region where the temperature is 23°C and the pressure is 0.1 MPa. The aforementioned VBD is the bulk density of polypropylene resin foam particles obtained by measurement in the region where the temperature is 23°C and the pressure is -0.09 MPa.

5. The polypropylene resin foam particles 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, when the total amount of the propylene random copolymer and propylene block copolymer is 100% by weight.

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

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

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

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

10. The polypropylene resin foam particles according to claim 4, wherein the melt flow rate of the propylene random copolymer at 230°C is 3 g / 10 min to 30 g / 10 min.

11. The polypropylene resin foam 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. The polypropylene resin foam particles according to claim 4, wherein the melt flow rate of the propylene-based block copolymer at 230°C is 3 g / 10 min to 30 g / 10 min.

13. Polypropylene resin foam particles according to claim 4, wherein the DSC ratio is 10.0% to 50.0%.

14. Polypropylene resin foam particles according to claim 4, wherein the foaming ratio is 15 to 50 times.

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

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