Manufacturing methods for polypropylene resin foamed granules, polypropylene resin foamed molded bodies, and polypropylene resin foamed granules.

Abstract

One embodiment of the present invention aims to provide polypropylene resin foam particles with excellent production yield for polypropylene resin foam molding, and polypropylene resin foam molding articles formed from the polypropylene resin foam particles. This is achieved by forming a matrix resin with a peak strength ratio of I... 720 / I 810 The above-mentioned problems are solved by producing polypropylene resin foam particles with a shrinkage rate of 0.45 to 0.67 and a shrinkage rate of less than 20%, wherein the base resin contains propylene random copolymers and propylene block copolymers.

Description

Technical Field

[0001] This invention relates to polypropylene resin foamed granules, polypropylene resin foamed molded articles, and methods for manufacturing polypropylene resin foamed granules. Background Technology

[0002] Polypropylene resin foamed molded parts are used in various applications such as thermal insulation materials, cushioning packaging materials, and turnover boxes, primarily for automotive interior components and core materials for automotive bumpers (Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-173012 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, from a productivity point of view, the existing technology described above is insufficient and there is room for further improvement.

[0008] One embodiment of the present invention was made in view of the aforementioned problems, and its object is to provide polypropylene resin foam particles with excellent productivity for polypropylene resin foam molding, and polypropylene resin foam molding body formed by molding the polypropylene resin foam particles.

[0009] Solution for solving the problem

[0010] The inventors conducted in-depth research to solve the aforementioned problems, and as a result, completed this invention.

[0011] That is, the polypropylene resin foamed particles of one embodiment of the present invention comprise the following composition.

[0012] A polypropylene resin foaming granule comprises a base resin, wherein the base resin contains a propylene random copolymer and a propylene block copolymer. When the content ratio of the aforementioned block copolymer is set as X (%) and the foaming pressure during manufacturing is set as Y (MPa), the aforementioned X and Y satisfy the following formula (1): Y < -0.07X + 3.6… (1).

[0013] In addition, the polypropylene resin foamed particles of another embodiment of the present invention comprise the following composition.

[0014] A polypropylene resin foam granule comprises a base resin, wherein the base resin contains a propylene random copolymer and a propylene block copolymer, and the peak intensity ratio of the polypropylene resin foam granule is I. 720 / I 810The shrinkage rate is 0.45–0.67, and the shrinkage rate is below 20%.

[0015] Among them, the aforementioned peak intensity ratio I 720 / I 810 The wavelength 720cm was obtained from the spectrum obtained through infrared spectroscopy analysis. -1 The peak intensity I 720 Relative to wavelength 810cm -1 The peak intensity I 810 The ratio,

[0016] The aforementioned shrinkage rate (%) is a value obtained by formula (2) below;

[0017] The aforementioned shrinkage rate (%) = (BD - VBD) × 100 / VBD…(2)

[0018] In formula (2), the aforementioned BD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23℃ and a pressure of 0.1MPa, and the aforementioned VBD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23℃ and a pressure of -0.09MPa.

[0019] In addition, a method for manufacturing polypropylene resin foamed particles according to one embodiment of the present invention includes the following composition.

[0020] A method for manufacturing polypropylene resin foamed granules includes a foaming step in which polypropylene resin granules containing a base resin are depressurized and foamed at a foaming temperature below 163.5°C and a foaming pressure below 2.80 MPa. The base resin contains propylene random copolymers and propylene block copolymers. When the total amount of propylene random copolymers and propylene block copolymers is set to 100% by weight, the base resin contains 73% to 95% by weight of the aforementioned propylene random copolymers and 5% to 27% by weight of the aforementioned propylene block copolymers.

[0021] In addition, another embodiment of the present invention provides a method for manufacturing polypropylene resin foamed particles, comprising the following components.

[0022] A method for manufacturing polypropylene resin foamed granules includes a foaming step, wherein the foaming step involves depressurizing and foaming polypropylene resin granules containing a base resin at a foaming temperature below 163.5°C and a foaming pressure below 2.80 MPa, wherein the base resin contains propylene random copolymers and propylene block copolymers.

[0023] The effects of the invention

[0024] According to one aspect of the present invention, the following effects are achieved: polypropylene resin foam particles with excellent productivity are provided, as well as polypropylene resin foamed articles formed from the polypropylene resin foam particles. Detailed Implementation

[0025] The following describes one embodiment of the present invention, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope shown in the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included within the technical scope of the present invention. Moreover, by combining the technical means disclosed in each embodiment, new technical features can be formed. It should be noted that all academic and patent documents described in this specification are cited as references in this specification. Additionally, unless otherwise specified in this specification, "A~B" representing a numerical range means "A or more (inclusive of A and greater than A) and B or less (inclusive of B and less than B)".

[0026] In this specification, the structural unit derived from monomer X contained in a polymer, copolymer or resin is sometimes referred to as "unit X".

[0027] Unless otherwise specified in this specification, X will also be included. 1 Unit, X 2 Unit, ... and X n A copolymer in which units (n is an integer greater than 2) serve as structural units is called "X". 1 / X 2 / … / X n "Copolymer". As X 1 / X 2 / … / X n Unless otherwise specified, copolymers are not particularly limited by polymerization method and can be random copolymers, alternating copolymers, block copolymers, or graft copolymers.

[0028] [1. Technical concept of one embodiment of the present invention]

[0029] Propylene-based random copolymers are commonly used as raw materials for polypropylene resin foams. On the other hand, propylene-based block copolymers are sometimes used as raw materials for polypropylene resin foams. For example, in cases where the impact resistance of polypropylene resin foams is improved, or when recycled resin is used from the viewpoint of reducing environmental impact.

[0030] As a recycled resin of polypropylene resins, propylene block copolymers have a much higher throughput compared to propylene random copolymers.

[0031] Driven by the aforementioned motivation, the inventors conducted in-depth research on polypropylene resin foam particles that combine propylene random copolymers and propylene block copolymers to provide raw materials for polypropylene resin foamed molding articles.

[0032] During in-depth research, the inventors independently obtained the following new insights: When using a combination of propylene-based random copolymers and propylene-based block copolymers to manufacture polypropylene-based resin foam particles, and then using the resulting polypropylene-based resin foam particles to manufacture polypropylene-based resin foam molded articles, the productivity of the polypropylene-based resin foam molded articles sometimes becomes unsatisfactory. For example, in the manufacture of polypropylene-based resin foam molded articles using molds, sometimes cooling is performed before removing the obtained polypropylene-based resin foam molded article from the mold to reduce expansion after removal. This cooling time is significantly related to the productivity of the polypropylene-based resin foam molded article. The aforementioned "unsatisfactory productivity of polypropylene-based resin foam molded articles" refers to the situation where the cooling time of the polypropylene-based resin foam molded article becomes longer.

[0033] Therefore, the inventors have conducted further in-depth research in order to provide polypropylene resin foam particles that exhibit excellent productivity even when using a combination of propylene random copolymers and propylene block copolymers.

[0034] As a result, the inventors independently discovered the following new insights, thereby completing the present invention: by using propylene-based random copolymers and propylene-based block copolymers in a specific ratio to foam the polypropylene-based resin foam particles in a manner that the shrinkage rate of the resulting polypropylene-based resin foam particles is within a specific range, it is surprisingly possible to provide polypropylene-based resin foam particles with excellent productivity of polypropylene-based resin foamed molded articles.

[0035] [1. Polypropylene resin foamed granules]

[0036] In one embodiment of the present invention, polypropylene resin foamed particles comprise a base resin, wherein the base resin contains propylene random copolymers and propylene block copolymers. When the content ratio of the aforementioned block copolymers is set as X (%) and the foaming pressure during manufacturing is set as Y (MPa), the aforementioned X and Y satisfy the following formula (1).

[0037] Y<-0.07X+3.6…(1).

[0038] Another embodiment of the polypropylene resin foamed particles of the present invention comprises a base resin, said base resin containing propylene random copolymers and propylene block copolymers, with a peak intensity ratio of I. 720 / I 810The value is 0.45–0.67, and the shrinkage rate is below 20%. Among these, the aforementioned peak intensity ratio I... 720 / I 810 The wavelength 720cm was obtained from the spectrum obtained through infrared spectroscopy analysis. -1 The peak intensity I 720 Relative to wavelength 810cm -1 The peak intensity I 810 The ratio. The aforementioned shrinkage rate (%) is a value obtained by the following formula (2);

[0039] Shrinkage rate (%) = (BD-VBD)×100 / VBD…(2).

[0040] In equation (2), BD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23°C and a pressure of 0.1 MPa. In the aforementioned equation (2), VBD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23°C and a pressure of -0.09 MPa.

[0041] In this specification, "polypropylene resin foamed particles" are sometimes referred to as "foamed particles", "polypropylene resin foamed particles of one embodiment of the present invention" are sometimes referred to as "the foamed particles", and "polypropylene resin foamed molded body" is sometimes referred to as "foamed molded body".

[0042] This foamed granule has the above-described structure, and therefore has the advantage of excellent productivity in foamed molding. For example, this foamed granule has the advantage that when using this foamed granule and performing in-mold foaming molding with a mold, the cooling time of the foamed molded body in the mold can be shortened. This foamed granule also has the advantage of providing foamed molded bodies with excellent strength.

[0043] <ingredients>

[0044] (Base material resin)

[0045] The aforementioned base resin includes at least propylene-based random copolymers and propylene-based block copolymers as resin components. In addition to resin components, the base resin may also contain additives such as foaming nucleating agents. The base resin can also be considered a component that substantially constitutes the foamed particles. Therefore, the types and amounts of each component contained in the base resin can also be considered the types and amounts of each component contained in the foamed particles.

[0046] Both propylene-based random copolymers and propylene-based block copolymers are polypropylene-based resins.

[0047] In this specification, "polypropylene resin" refers to a resin in which 50 mol% or more of propylene units are contained in 100 mol% of all structural units constituting the resin.

[0048] (propylene-based random copolymer)

[0049] Propylene-based random copolymers contain at least propylene units and structural units other than propylene units. In this specification, the "structural units other than propylene units" contained in polypropylene resins are sometimes referred to as "comonomer units." In other words, propylene-based random copolymers contain at least propylene units and comonomer units.

[0050] Examples of comonomers include α-olefins with 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.

[0051] From the viewpoint of reducing the molding temperature when in-mold foaming of foamed particles, the comonomer units included in propylene-based random copolymers are preferably ethylene units. In other words, propylene-based random copolymers are preferably propylene / ethylene random copolymers containing both propylene and ethylene units.

[0052] 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 / vinyl chloride random copolymers, and propylene / maleic anhydride random copolymers.

[0053] A propylene-based random copolymer can be a combination of a propylene / ethylene random copolymer and one or more propylene-based random copolymers other than a propylene / ethylene random copolymer.

[0054] 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 even more preferably 140°C to 150°C. When the melting point of the propylene-based random copolymer is (i) 130°C or higher, the foamed molded body obtained from the foamed particles has excellent heat resistance, and (ii) when it is 160°C or lower, it has the advantage of easily increasing the foaming ratio of the foamed particles in the manufacture of the foamed particles.

[0055] In this specification, the melting points of propylene-based random copolymers and propylene-based block copolymers described later are determined by differential scanning calorimetry (hereinafter referred to as "DSC"). Specific operating procedures are described in the examples described later. For example, a Seiko Instruments Inc. DSC 7020 model differential scanning calorimeter can be used.

[0056] The melt flow rate (MFR) of the propylene-based random copolymer is not particularly limited. In this specification, "MFR of the propylene-based random copolymer" refers to the MFR of the propylene-based random copolymer at 230°C. The MFR of the propylene-based 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-based random copolymer at 230°C is within the above range, it has the advantage of easily obtaining foamed particles with a large expansion ratio. Furthermore, in this case, it also has the advantages of excellent surface aesthetics and reduced shrinkage of the foamed molded article.

[0057] In this specification, the MFR of propylene random copolymers and propylene block copolymers described later at 230°C is a value determined by measuring the melt mass flow rate (hereinafter referred to as MFR) using a melt mass flow rate (MFR) tester as described in JIS-K 7210 under the following conditions: orifice... The orifice length is 8.000±0.025mm, the load is 2160g, and the temperature is 230±0.2℃.

[0058] Propylene-based random copolymers can be copolymers obtained by known methods or recycled resins. From the perspective of maintaining the quality of the foamed molded articles, non-recycled resins are preferred.

[0059] (propylene block copolymer)

[0060] Propylene block copolymers contain at least propylene units and comonomer units.

[0061] There are no particular limitations on the comonomer units included in propylene block copolymers. Specific examples of comonomers are the same as those described in the preceding section on (propylene random copolymers), and therefore, their descriptions are omitted here.

[0062] From the viewpoint of ease of acquisition, the comonomer units included in propylene block copolymers are preferably ethylene units. In other words, propylene block copolymers are preferably propylene / ethylene block copolymers containing both propylene and ethylene units. Furthermore, propylene block copolymers are preferably copolymers containing at least ethylene blocks (e.g., propylene / ethylene block copolymers). As for the aforementioned propylene block copolymers, substances included in the technical field of polypropylene resins are considered propylene block copolymers. For example, the aforementioned propylene / ethylene block copolymers contain homopolymer polypropylene as a matrix and a polyethylene layer covered by an ethylene / propylene elastic copolymer as a domain; they are sometimes also referred to as impact copolymers.

[0063] Propylene block copolymers are not limited to propylene / ethylene block copolymers. Examples of propylene block copolymers other than propylene / ethylene block copolymers include propylene / 1-butene block copolymers, propylene / ethylene / 1-butene block copolymers, propylene / vinyl chloride block copolymers, and propylene / maleic anhydride block copolymers.

[0064] A propylene block copolymer can be a combination of a propylene / ethylene block copolymer and one or more propylene block copolymers other than a propylene / ethylene block copolymer.

[0065] The melting point of the propylene 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 block copolymer is not particularly limited, but for example, it is preferably 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 block copolymer is (i) 160°C or higher, it exhibits excellent heat resistance; and (ii) when it is 180°C or lower, it exhibits excellent molding and processability.

[0066] In one embodiment of the 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 (°C)) is not particularly limited, but is preferably 30°C or less, more preferably 21°C or less. According to this configuration, it has the advantage that the minimum molding pressure during in-mold molding can be the same as that obtained using only the propylene random copolymer as the base resin for foamed granules.

[0067] The molecular weight ratio (MFR) of the propylene block copolymer is not particularly limited. In this specification, "MFR of the propylene block copolymer" refers to the MFR of the propylene block copolymer at 230°C. The preferred MFR of the propylene block copolymer is 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 block copolymer at 230°C is within the above range, it has the advantages of easily obtaining foamed particles with a relatively large expansion ratio and excellent surface aesthetics of the foamed molded article.

[0068] Propylene block copolymers can be made from substances obtained by known methods, preferably recycled resins. As mentioned above, as recycled resins of polypropylene resins, propylene block copolymers have a higher throughput than propylene random copolymers. Recycled resins for propylene block copolymers are relatively easy to obtain. When using recycled resins as all or part of the propylene block copolymer, not only can environmental pollution be reduced, but the amount of plastic waste generated and the amount of plastic used in manufacturing can also be significantly reduced. Therefore, embodiments using recycled resins as all or part of the propylene block copolymer have the advantage of contributing to the achievement of Sustainable Development Goals (SDGs).

[0069] In this specification, "recycled resin" refers to resin that has been transformed into resin (or resin particles) again through melting or other methods after being processed into resin products (e.g., foamed granules, foamed molded bodies, films, food trays, bags, bottles and other packaging containers, clothing boxes, transparent folders and other miscellaneous goods) more than once.

[0070] The propylene block copolymer can be a mixture of recycled resin and non-recycled resin (resin that has never been processed into resin products). From the viewpoint of reducing environmental impact, the proportion of recycled resin in 100% by weight of the propylene block copolymer is preferably 50% or more, more preferably 70% or more, further preferably 80% or more, and particularly preferably 100% (i.e., composed solely of recycled resin).

[0071] When the total amount of propylene random copolymer and propylene block copolymer is set to 100% by weight, the aforementioned base resin preferably (a) contains 73% to 95% by weight of propylene random copolymer and 5% to 27% by weight of propylene block copolymer, more preferably (b) contains 74% to 95% by weight of propylene random copolymer and 5% to 26% by weight of propylene block copolymer, and even more preferably (c) contains 75% to 93% by weight of propylene random copolymer and 7% to 25% by weight of propylene block copolymer. When the content of propylene random copolymer and propylene block copolymer in the base resin is within the above range, the foamed particles have the advantage of better productivity of polypropylene resin foamed molded articles.

[0072] (Other resins, etc.)

[0073] The base resin may also include resins other than propylene random copolymers and propylene block copolymers (sometimes referred to as other resins, etc.) as resin components, without impairing the effects of one embodiment of the present invention. Examples of such other resins 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 waxes; 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 the foamed particles is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, relative to 100 parts by weight of the base resin.

[0074] (additive)

[0075] In addition to the aforementioned propylene-based random copolymers and propylene-based block copolymers, the base resin may also 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, lubricants, etc. Such additives can be directly added to the blends or polypropylene-based resin compositions described later during the manufacture of polypropylene resin particles.

[0076] <Physical properties>

[0077] The physical properties of these foamed granules are described below.

[0078] (Peak intensity ratio)

[0079] The peak intensity ratio of this foamed particle is I 720 / I 810 Preferably, it is 0.45 to 0.67. Peak intensity ratio I 720 / I 810 In the spectrum obtained through infrared spectroscopy analysis, the wavelength 720cm -1 The peak intensity is set to "I". 720 ", with a wavelength of 810cm -1 The peak intensity is set to "I". 810 "At that time, I 720 Compared to I 810 The ratio. Infrared spectroscopy analysis can be performed using the methods described in the examples below. Wavelength 720cm. -1 The peak can be primarily derived from the ethylene block, with a wavelength of 810 cm⁻¹. -1The peaks could be primarily derived from propylene. The wavelength of the foamed particles is 720 nm. -1 The larger the peak, the more ethylene blocks the foamed particles contain.

[0080] Therefore, the peak intensity obtained by infrared spectroscopy analysis is I 720 / I 810 It can accurately reflect the ratio of propylene to ethylene blocks in the base resin contained in the foamed particles. Specifically, as a preferred embodiment, when the propylene-based block copolymer contains ethylene blocks, the peak intensity ratio I... 720 / I 810 A higher value indicates a greater amount of propylene block copolymer in the total amount of propylene random copolymer and propylene block copolymer. In one embodiment, the ratio of propylene random copolymer to propylene block copolymer contained in the base resin can be determined by pre-measuring the peak intensity ratio of the propylene block copolymer used in the manufacture of the base resin.

[0081] The aforementioned peak intensity ratio is 0.45–0.67, preferably 0.45–0.65, more preferably 0.47–0.63, even more preferably 0.49–0.61, and still more preferably 0.50–0.60. According to this configuration, the foamed particles have the advantage of higher productivity in polypropylene resin foamed molding.

[0082] The aforementioned peak intensity ratio can be controlled by the content of each block copolymer contained in the foamed particles.

[0083] (Shrinkage rate)

[0084] The shrinkage rate of this foamed particle is calculated by the following formula (2).

[0085] Shrinkage rate = (BD - VBD) × 100 / VBD…(2)

[0086] In equation (2), BD is the bulk density of polypropylene resin foam particles at 23℃ and 0.1MPa (absolute pressure). In other words, BD can also be said to be the bulk density of polypropylene resin foam particles under standard atmospheric pressure. VBD is the bulk density of polypropylene resin foam particles at 23℃ and below -0.09MPa (gauge pressure). In other words, VBD can be said to be the bulk density of polypropylene resin foam particles under reduced pressure.

[0087] The aforementioned 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, for example, be 0% or more. When the shrinkage rate is within the above range, the foamed granules have the advantage of superior productivity in polypropylene resin foamed moldings.

[0088] The aforementioned shrinkage rate can be controlled by adjusting the conditions during the manufacturing of foamed particles (such as foaming temperature and foaming pressure).

[0089] (DSC ratio of foamed granules)

[0090] The foamed particles preferably have at least two melting peaks in the DSC curve obtained by differential scanning calorimetry (DSC) as described later. In each melting peak, the heat of fusion determined from the high-temperature melting peak is used as the "high-temperature melting heat," and the heat of fusion determined from the low-temperature melting peak is used as the "low-temperature melting heat." Furthermore, when there are three or more melting peaks, the heat of fusion determined from the highest-temperature melting peak is used as the "high-temperature melting heat," and the heat of fusion determined from the remaining melting peaks is used as the "low-temperature melting heat."

[0091] The DSC ratio of the foamed granules 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 granules is 10.0% or more, the foamed granules have the advantage of being able to provide a foamed molded body with sufficient strength. On the other hand, when the DSC ratio of the foamed granules is 50.0% or less, it has the advantage of being able to mold the foamed granules at a lower temperature (molding temperature) to provide a foamed molded body.

[0092] In this specification, the DSC ratio refers to the ratio of the heat of fusion on the high-temperature side to the total heat of fusion, calculated based on the DSC curve of the foamed particles. In this specification, the DSC curve is obtained using a differential scanning calorimeter (e.g., a Hitachi High-Tech Science Corporation DSC 7020). More specifically, it can be determined using the methods described in the examples.

[0093] The DSC ratio of these foamed particles is also a standard value for the amount of high-melting-point crystals contained in the foamed particles. That is, 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 is closely related to the viscoelasticity of both the resin particles and the foamed particles during foaming and expansion. In other words, when the DSC ratio of the foamed particles is between 10.0% and 50.0%, both the resin particles and the foamed particles exhibit excellent foaming and expansion properties, respectively, during both foaming and molding. As a result, the foamed particles have the advantage of producing foamed molded bodies with excellent internal weldability and superior mechanical strength, such as compressive strength, even under low molding pressure.

[0094] In this foamed granule, methods for controlling the DSC ratio within a specified range include adjusting the manufacturing conditions of the foamed granule (particularly foaming temperature, foaming pressure, holding time, and the temperature of the area (space) where the dispersion is released). From the viewpoint of ease of adjustment, adjusting the foaming temperature, foaming pressure, and / or holding time is preferred as a method for controlling the DSC ratio within a specified range.

[0095] 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 with the foaming temperature. Similarly, increasing the foaming pressure tends to decrease the DSC ratio, while decreasing it tends to increase it. This is because the degree of plasticization changes with the foaming pressure, thus affecting the amount of unmelted crystals. Furthermore, there is a tendency for a longer holding time to result in a larger DSC ratio. This is because the amount of unmelted crystal growth changes with the holding time.

[0096] (Expansion ratio of foamed granules)

[0097] The foaming ratio of the foamed granules is preferably 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 granules is (i) 15 times or more, lightweight foamed molded articles can be obtained with good production efficiency; (ii) if it is 50 times or less, there is no concern about insufficient strength of the obtained foamed molded articles. The aforementioned foaming ratio can be measured by the method described in the examples below.

[0098] (Minimum molding pressure)

[0099] This foamed granule has the following advantages: using this foamed granule, foamed molded articles with excellent weldability (e.g., weldability of 80% or more) can be obtained under low molding pressure. In other words, this foamed granule has the following advantages: it can provide foamed molded articles with excellent weldability under the same molding pressure as foamed granules obtained using only propylene-based random copolymers as the base resin.

[0100] In this specification, the lowest value of the molding pressure that provides a foamed molded article with excellent weldability (e.g., a weldability of 80% or more) in the manufacture of foamed molded articles using foamed particles is also referred to as the "minimum molding pressure". The minimum molding pressure can be measured by the method described in the examples below. This foamed particle also has the advantage of a low minimum molding pressure. In other words, the minimum molding pressure of this foamed particle can be equivalent to that of foamed particles obtained using only propylene-based random copolymers as the base resin.

[0101] The minimum molding pressure for this foamed granule 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 can be, for example, 0.15 MPa or more. When the minimum molding pressure is within the above range, it has the advantage of being able to provide foamed molded articles with a low economic burden.

[0102] [2. Manufacturing method of polypropylene resin foamed granules]

[0103] One embodiment of the present invention provides a method for manufacturing polypropylene resin foamed particles, which includes a foaming step in which polypropylene resin particles containing a base resin are depressurized and foamed at a foaming temperature of 163.5°C or below and a foaming pressure of 2.80 MPa or below. The base resin contains propylene random copolymers and propylene block copolymers.

[0104] Another embodiment of the present invention provides a method for manufacturing polypropylene resin foamed particles, comprising a foaming step, wherein the foaming step involves depressurizing and foaming polypropylene resin particles containing a base resin under conditions of a foaming temperature of 163.5°C or below and a foaming pressure of 2.80 MPa or below. The base resin contains propylene random copolymers and propylene block copolymers. When the total amount of propylene random copolymers and propylene block copolymers is set to 100% by weight, the aforementioned base resin contains 73% to 95% by weight of the aforementioned propylene random copolymers and 5% to 27% by weight of the aforementioned propylene block copolymers.

[0105] (Granulation process)

[0106] This manufacturing method may further include a step (granulation step) of manufacturing polypropylene resin particles comprising a base resin, wherein the base resin contains propylene random copolymers and propylene block copolymers. In this specification, "polypropylene resin particles" are sometimes referred to as "resin particles".

[0107] One method for manufacturing resin granules is the use of an extruder. Specifically, resin granules can be produced by the following methods (1) to (5): (1) blending block copolymers, random copolymers, and one or more of the group consisting of other resins and additives as needed to prepare a blend; (2) feeding the blend into an extruder and melting and kneading the blend to prepare a polypropylene resin composition; (3) extruding the polypropylene resin composition from a die provided by an extruder; (4) cooling the extruded polypropylene resin composition in water or the like to cure it; (5) then cutting the cured polypropylene resin composition into desired shapes such as cylinders, ellipses, spheres, cubes, cuboids, hollow cylinders, and polygonal prisms using a cutter. Alternatively, in (3), the melt-kneaded polypropylene resin composition can be directly extruded into water using a die provided by an extruder, and immediately after extrusion, the polypropylene resin composition can be cut into granular shapes, cooled, and cured. In this way, more uniform resin particles can be obtained by melt-mixing the blend.

[0108] The weight of each resin particle 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 of each resin particle is (A) 0.2 mg / particle or more, there is a tendency to improve the workability of the resin particles, and in addition, there is a tendency to reduce the shrinkage rate of the foamed molded body formed from the obtained foamed particles. When (B) is 10.0 mg / particle or less, there is a tendency to improve mold filling performance in the in-mold foaming molding process.

[0109] (Dispersed processes)

[0110] This manufacturing method may further include a dispersion step prior to the foaming step, wherein the dispersion step disperses a base resin containing propylene random copolymers and propylene block copolymers, an aqueous dispersion medium, a foaming agent, and, if necessary, a dispersant and / or dispersing aid in a container. The dispersion step can also be described as a step of preparing a dispersion in an aqueous dispersion medium containing the base resin, the foaming agent, and, if necessary, a dispersant and / or dispersing aid. The base resin in the dispersion step may be the resin particles obtained in the granulation step described above.

[0111] The container is not particularly limited, but it is preferably a container capable of withstanding the foaming temperature and foaming pressure described later. For example, a pressure-resistant container is preferred, and a pressure-resistant container of the autoclave type is more preferred. The container may include a stirrer.

[0112] As an aqueous dispersion medium, it is only necessary to uniformly disperse resin particles, foaming agents, etc., without any particular limitations.

[0113] Examples of aqueous dispersion media include: (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol and glycerol 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.

[0114] From the perspective of being able to stably produce foamed granules, the preferred aqueous dispersion medium is pure water such as RO water (water purified by reverse osmosis membrane method), distilled water, deionized water (water purified by ion exchange resin) and ultrapure water.

[0115] Examples of foaming agents include: (a) inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a) inorganic foaming agents such as water; and (b) organic foaming agents such as saturated hydrocarbons with 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane, ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and halogenated hydrocarbons such as monochloromethane, chloroethane, and hydrofluoroolefins.

[0116] As a foaming agent, at least one selected from the group consisting of inorganic and organic foaming agents can be used. When two or more foaming agents are mixed, the mixing ratio can be adjusted appropriately according to the purpose. From the viewpoint of environmental impact and foaming power, inorganic foaming agents are preferred among the above-mentioned foaming agents. Furthermore, from the viewpoint of moderately high plasticizing effect and easy improvement of the foaming properties of the foamed particles in the manufacture of these foamed particles, carbon dioxide is preferred among inorganic foaming agents.

[0117] For the above-mentioned aqueous dispersion media and foaming agents, one type can be used alone, or two or more types can be used in combination.

[0118] In this method for manufacturing foamed granules, a dispersant (e.g., inorganic substances such as tricalcium phosphate, kaolin, and talc) and a dispersing aid (e.g., anionic surfactants such as sodium alkyl sulfonate and sodium dodecylbenzene sulfonate) are preferably used. This composition reduces the aggregation (sometimes referred to as adhesion) of resin particles and improves the stability of the dispersion within the container. As a result, it has the advantage of being able to stably manufacture foamed granules.

[0119] (Foaming process)

[0120] There are no particular limitations on the specific method of the foaming process. For example, the foaming process may include: (a) a temperature-pressure increase process, where the temperature inside the container is increased to a certain temperature, and the pressure inside the container is increased to a certain pressure, causing the resin particles to depressurize and foam.

[0121] (b) The holding process maintains the temperature and pressure inside the container at a constant temperature and pressure.

[0122] (c) Release process: Open one end of the container and release the dispersion in the container into a region (space) where the pressure is lower than the foaming pressure (i.e., the pressure inside the container).

[0123] (Heating-pressurization process and holding process)

[0124] The heating-pressurization process is preferably performed after the dispersion process, and the holding process is preferably performed after the heating-pressurization process.

[0125] The aforementioned foaming temperature is below 163.5°C, preferably below 163.3°C, and more preferably below 163.2°C. There is no particular limitation on the lower limit of the aforementioned foaming temperature, as long as it allows for depressurization and foaming of the resin particles; for example, it can be above 150°C.

[0126] Furthermore, the aforementioned 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. There is no particular limitation on the lower limit of the aforementioned foaming pressure, as long as it allows for depressurization and foaming of the resin particles; for example, it can be 1.5 MPa or more.

[0127] During in-depth research, the inventors independently obtained the following new insights: In order to obtain foamed granules with low shrinkage, it is preferable to appropriately set the foaming pressure based on the amount of propylene block copolymer. Specifically, the inventors independently obtained the following new insights: In order to obtain foamed granules with low shrinkage, it is preferable to set the foaming pressure lower when the amount of propylene block copolymer is greater. More specifically, the inventors independently obtained the following new insights: When the content ratio of block copolymer in 100% by weight of the total amount of propylene random copolymer and propylene block copolymer in polypropylene resin granules is set as X (wt%), the foaming pressure Y (MPa) during the manufacture of foamed granules preferably satisfies the following formula (1):

[0128] Y<-0.07X+3.6…(1).

[0129] The reason for preferably satisfying the aforementioned formula (1) is uncertain, but it is speculated that propylene block copolymers have softer and more easily elongated properties compared to propylene random copolymers. It should be noted that one embodiment of the present invention is not limited by this speculation.

[0130] The aforementioned X and Y more preferably satisfy the following equation (3), further preferably satisfy the following equation (4), and particularly preferably satisfy the following equation (5):

[0131] Y<-0.07X+3.55…(3)

[0132] Y<-0.07X+3.5…(4)

[0133] Y<-0.07X+3.45…(5).

[0134] In the holding process, the time (holding time) for maintaining the dispersion in the container 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 more, the amount of unmelted crystals (crystals of polypropylene resin) in the resin particles is sufficient during the foaming process from resin particles to foamed particles. As a result, foamed particles with a low continuous bubble rate can be obtained, and the shrinkage of the obtained 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 is not excessive during the foaming process from resin particles to foamed particles. Therefore, the obtained foamed particles can be molded at a relatively low temperature (molding temperature) to provide a foamed molded article.

[0135] (Release process)

[0136] The release process is preferably performed either (a) after the heating-pressurization process without performing a holding process, or (b) after the holding process if a holding process has been performed. The release process enables the resin particles to foam, resulting in foamed particles.

[0137] In the release process, "the area with pressure lower than the foaming pressure" refers to "the area under pressure lower than the foaming pressure" or "the space under pressure lower than the foaming pressure," or it can be described as "the atmosphere under pressure lower than the foaming pressure." There are no specific limitations on the area with pressure lower than the foaming pressure; for example, it could be an area under atmospheric pressure.

[0138] In the release process, when releasing the dispersion into a region with a pressure lower than the foaming pressure, the dispersion can be released through an opening with a diameter of 1 mm to 5 mm in order to adjust the flow rate of the dispersion and reduce the deviation in the foaming ratio of the obtained foamed particles. Alternatively, to improve foaming properties, the aforementioned low-pressure region (space) can be filled with saturated water vapor.

[0139] It should be noted that the process of manufacturing foamed granules from resin particles is called the "first-stage foaming process", and the resulting foamed granules are called "first-stage foamed granules".

[0140] (2-stage foaming process)

[0141] To obtain foamed granules with a high expansion ratio, the foamed granules obtained in the first foaming process can be foamed again. The process of increasing the expansion ratio of the first-stage foamed granules is called the "second-stage foaming process," and the polyolefin resin foamed granules obtained through the second-stage foaming process are called "second-stage foamed granules." There are no particular limitations on the specific method for the second-stage foaming process; well-known methods can be used.

[0142] [3. Polypropylene Resin Foamed Molded Body]

[0143] One embodiment of the polypropylene resin foamed molded body of the present invention is a foamed molded body formed by foaming polypropylene resin foamed particles described in section [1. Polypropylene Resin Foamed Particles]. Another embodiment of the polypropylene resin foamed molded body of the present invention may be a foamed molded body formed by foaming polypropylene resin foamed particles obtained by the manufacturing method described in section [2. Method for Manufacturing Polypropylene Resin Foamed Particles]. A third embodiment of the polypropylene resin foamed molded body of the present invention may also include polypropylene resin foamed particles described in section [1. Polypropylene Resin Foamed Particles], or polypropylene resin foamed particles obtained by the manufacturing method described in section [2. Method for Manufacturing Polypropylene Resin Foamed Particles].

[0144] In this specification, "a polypropylene resin foamed molded article according to an embodiment of the present invention" is sometimes referred to as "the foamed molded article".

[0145] Because of the above-described structure, this foamed molded body has the advantages of excellent productivity and excellent strength.

[0146] (productivity)

[0147] In this specification, the productivity of the foamed molded body is evaluated by the time (seconds) from the start of molding the foamed particles to the completion of molding (molding cycle). It should be noted that, as described in the embodiments below, the molding start time is the moment when the foamed particles are filled into the mold. Furthermore, the molding completion time is the moment when the molded body is cooled (water-cooled), and the mold is opened and demolded when the surface pressure decreases to 0.01 MPa as indicated by the surface pressure gauge mounted on the plank mold surface. A shorter molding cycle results in a higher productivity of the foamed molded body.

[0148] (Surface aesthetics)

[0149] In this specification, the surface aesthetics of the foamed molded body are evaluated based on the degree of gaps between the foam particles on the surface of the foamed molded body (hereinafter sometimes referred to as "particle gaps") and the wrinkles on the surface of the foamed molded body. The smaller the size or the fewer the number of particle gaps present on the surface of the foamed molded body, the better the surface aesthetics of the foamed molded body. In addition, the fewer the wrinkles present on the surface of the foamed molded body, the better the surface aesthetics of the foamed molded body.

[0150] (Static compressive strength)

[0151] This foamed molded body also has the advantage of excellent strength. In this specification, the strength of the foamed molded body is evaluated by its static compressive strength. The method for determining the static compressive strength of the foamed molded body is described in detail in the following examples.

[0152] The static compressive strength of this 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 can be, for example, 0.300 MPa or less. According to this configuration, it 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 turnover boxes.

[0153] One embodiment of the present invention may include the following configuration.

[0154] [1] A method for manufacturing polypropylene resin foamed particles, comprising a foaming step, wherein the foaming step involves depressurizing and foaming polypropylene resin particles containing a base resin under conditions of a foaming temperature below 163.5°C and a foaming pressure below 2.80 MPa, wherein the base resin contains propylene random copolymers and propylene block copolymers, and when the total amount of propylene random copolymers and propylene block copolymers is set to 100% by weight, the aforementioned base resin contains 73% to 95% by weight of the aforementioned propylene random copolymers and 5% to 27% by weight of the aforementioned propylene block copolymers.

[0155] [2] The method for manufacturing polypropylene resin foamed particles according to [1] satisfies the following formula (1):

[0156] Y<-0.07X+3.6…(1);

[0157] Wherein, X is the content ratio (by weight%) of the aforementioned propylene block copolymer when the total amount of propylene random copolymer and propylene block copolymer in the aforementioned base resin is set to 100% by weight, and Y is the foaming pressure (MPa) in the aforementioned foaming process.

[0158] [3] The method for manufacturing polypropylene resin foamed particles according to [1] or [2], wherein the aforementioned foaming process is a two-stage foaming process.

[0159] [4] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to [3], wherein the aforementioned foaming temperature is 150°C or higher.

[0160] [5] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to [4], wherein the aforementioned foaming pressure is 1.5 MPa or more.

[0161] [6] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to [5], wherein the melting point of the aforementioned propylene block copolymer is above 160°C and below 180°C.

[0162] [7] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to [6], wherein the aforementioned propylene block copolymer is a recycled resin.

[0163] [8] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to [7], wherein the aforementioned propylene random copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units, and the aforementioned propylene block copolymer contains 50 mol% or more of propylene units in 100 mol% of all structural units.

[0164] [9] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to [8], wherein the aforementioned propylene random copolymer comprises a propylene / ethylene random copolymer, and the propylene / ethylene random copolymer comprises propylene units and ethylene units.

[0165]

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

[0166]

[11] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to

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

[0167]

[12] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to

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

[0168]

[13] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to

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

[0169]

[14] The method for manufacturing polypropylene resin foamed particles according to any one of [1] to

[13] , wherein the foaming ratio of the aforementioned polypropylene resin foamed particles is 15 to 50 times.

[0170]

[15] A method for manufacturing a polypropylene resin foamed molded body, comprising a step of molding polypropylene resin foamed particles obtained by the method for manufacturing polypropylene resin foamed particles according to any one of [1] to

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

[0171]

[16] A polypropylene resin foamed particle, comprising a base resin, wherein the base resin contains an propylene random copolymer and an propylene block copolymer, and the peak intensity ratio of the polypropylene resin foamed particle is I. 720 / I 810 The shrinkage rate is 0.45–0.67, and the shrinkage rate is below 20%.

[0172] Among them, the aforementioned peak intensity ratio I 720 / I 810 The wavelength 720cm was obtained from the spectrum obtained through infrared spectroscopy analysis. -1 The peak intensity I 720 Relative to wavelength 810cm -1 The peak intensity I 810 The aforementioned shrinkage rate (%) is a value obtained by the following formula (2);

[0173] The aforementioned shrinkage rate (%) = (BD - VBD) × 100 / VBD…(2)

[0174] In formula (2), the aforementioned BD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23℃ and a pressure of 0.1MPa, and the aforementioned VBD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23℃ and a pressure of -0.09MPa.

[0175]

[17] According to the polypropylene resin foaming particles of

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

[0176]

[18] Polypropylene resin foamed particles according to any one of

[16] or

[17] , wherein the melting point of the aforementioned propylene block copolymer is above 160°C and below 180°C.

[0177]

[19] Polypropylene resin foamed particles according to any one of

[16] to

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

[0178]

[20] Polypropylene resin foamed particles according to any one of

[16] to

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

[0179]

[21] Polypropylene resin foamed particles according to any one of

[16] to

[20] , wherein the aforementioned propylene random copolymer includes a propylene / ethylene random copolymer, and the propylene / ethylene random copolymer includes propylene units and ethylene units.

[0180]

[22] Polypropylene resin foamed particles according to any one of

[16] to

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

[0181]

[23] Polypropylene resin foamed particles according to any one of

[16] to

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

[0182]

[24] Polypropylene resin foamed particles according to any one of

[16] to

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

[0183]

[25] The polypropylene resin foamed particles according to any one of

[16] to

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

[0184]

[26] The polypropylene resin foamed particles according to any one of

[16] to

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

[0185]

[27] Polypropylene resin foamed granules according to any one of

[16] to

[26] , wherein when the aforementioned polypropylene resin foamed granules are molded, the minimum molding pressure required to provide a polypropylene resin foamed molded body with a weld ratio of 80% or more is 0.30 MPa or less.

[0186]

[28] A polypropylene resin foamed molded body, which is formed by foaming polypropylene resin foamed particles as described in any one of

[16] to

[27] .

[0187]

[29] The polypropylene resin foamed molded body according to

[28] has a static compressive strength of 0.212 MPa or higher.

[0188] In addition, another embodiment of the present invention includes the following configuration.

[0189] [1] A polypropylene resin foamed particle, comprising a base resin, wherein the base resin contains a propylene random copolymer and a propylene block copolymer, and the peak intensity ratio of the polypropylene resin foamed particle is I. 720 / I 810 The shrinkage rate is 0.45–0.65, and the shrinkage rate is below 20%.

[0190] Among them, the aforementioned peak intensity ratio I 720 / I 810 The wavelength 720cm was obtained from the spectrum obtained through infrared spectroscopy analysis. -1 The peak intensity I 720 Relative to wavelength 810cm -1 The peak intensity I 810 The aforementioned shrinkage rate (%) is a value obtained by the following formula (1);

[0191] The aforementioned shrinkage rate (%) = (BD - VBD) × 100 / VBD…(1)

[0192] In formula (1), the aforementioned BD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23°C and a pressure of 0.1 MPa, and the aforementioned VBD is the bulk density of polypropylene resin foamed particles measured at a temperature of 23°C and a pressure of -0.09 MPa.

[0193] [2] According to the polypropylene resin foaming particles of [1], when the total amount of propylene random copolymer and propylene block copolymer is set to 100% by weight, the aforementioned base resin contains 75% to 95% by weight of the aforementioned propylene random copolymer and 5% to 25% by weight of the aforementioned propylene block copolymer.

[0194] [3] Polypropylene resin foamed particles according to [1] or [2], wherein the melting point of the aforementioned propylene block copolymer is above 160°C.

[0195] [4] Polypropylene resin foamed particles according to any one of [1] to [3], wherein the aforementioned propylene block copolymer is a recycled resin.

[0196] [5] A polypropylene resin foamed molded body, which is formed by foaming polypropylene resin foamed particles as described in any one of [1] to [4].

[0197] [6] A method for manufacturing polypropylene resin foamed particles, comprising a foaming step, wherein the foaming step involves depressurizing and foaming polypropylene resin particles containing a base resin at a foaming temperature below 163.5°C and a foaming pressure below 2.80 MPa, wherein the base resin contains propylene random copolymers and propylene block copolymers.

[0198] Example

[0199] The following examples and comparative examples further illustrate one embodiment of the present invention. The present invention is not limited to these examples.

[0200] [Material]

[0201] In the examples and comparative examples, the following materials were used, but no special purification was performed.

[0202] <Polypropylene Resins>

[0203] • Propylene / ethylene block copolymer 1 [MFR = 12 g / 10 min, melting point 166 °C, recycled resin, containing 5% by weight carbon black]

[0204] • Propylene / ethylene block copolymer 2 [Prime Polymer Co., Ltd. J715M, MFR = 9 g / 10 min, melting point 165 °C, recycled resin]

[0205] • Propylene / ethylene block copolymer 3 [MFR = 29 g / 10 min, melting point 165 °C, recycled resin]

[0206] • Propylene / ethylene random copolymer [MFR = 7 g / 10 min, melting point 145 °C, non-recycled resin]

[0207] <Resin Particle Additive>

[0208] Talc [Made by Hayashi Kasei Corporation, Talcan Powder PK-S]

[0209] • Glycerin [LION Corporation, purified glycerin D]

[0210] [Determination Method]

[0211] The evaluation methods implemented in the embodiments and comparative examples are described below.

[0212] <Determination of Melting Point of Polypropylene Resins>

[0213] The melting point of polypropylene resin particles was determined using a differential scanning calorimeter (DSC 7020, manufactured by Hitachi High-TechScience Corporation). The specific determination method is as follows: (1) 5-6 mg of the sample was heated from 40°C to 220°C at a heating rate of 10°C / min until it melted; (2) then, it was cooled from 220°C to 40°C at a cooling rate of 10°C / min until it crystallized; (3) then, 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 at the second heating (i.e., at (3)) was taken as the melting point of the polypropylene resin particles.

[0214] <MFR Determination of Polypropylene Resins>

[0215] For polypropylene resins, the melt mass flow rate (MFR) tester as described in JIS K7210 was used to determine the MFR under the following conditions: [Orifice details missing] The orifice length is 8.000±0.025mm, the load is 2160g, and the temperature is 230±0.2℃.

[0216] <Determination of DSC ratio of polypropylene resin foamed particles>

[0217] The DSC ratio was determined using a differential scanning calorimeter (DSC 7020, manufactured by Hitachi High-Tech Science Corporation). Specifically, the melting peak area on the low-temperature side of the DSC curve obtained when 5–6 mg of polypropylene resin foaming particles were heated from 40 °C to 220 °C at a heating rate of 10 °C / min was defined as Q. l The melting peak area on the high-temperature side is set as Q. h The value can be obtained from the following formula.

[0218] DSC ratio (%) = Q h / (Q l +Q h )×100

[0219] It should be noted that, strictly speaking, Q is defined as the area enclosed by the melting peak on the low-temperature side and the tangent drawn from the maximum point between the melting peaks on the low-temperature and high-temperature sides to the melting initiation baseline. l The heat enclosed by the melting peak on the high-temperature side and the tangent drawn 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 termination baseline, i.e., the heat of the melting peak on the high-temperature side, is taken as Q. h .

[0220] Infrared Spectroscopic Analysis of Polypropylene Resin Foamed Particles

[0221] The ratio of peak intensities originating from propylene and block ethylene was determined by infrared spectroscopy analysis of polypropylene resin foam particles. The determination was performed using the attenuated total reflection (ATR) method. The polypropylene resin foam particles were crushed between metal plates and pressed into a crystal within an ATR measuring device (PerkinElmer Japan, Spectrum Two). The resolution was set to 4 cm⁻¹. --1 The cumulative measurement was set to 16 times, and the spectrum was obtained. At this point, the image was taken at 1376 cm⁻¹. -1 The pressure applied during crimping was adjusted so that the peak intensity was 0.15 A. Next, the wavelength at 810 cm⁻¹ was read from the obtained spectrum. -1 Peak intensity (I) 810 ) and wavelength 720cm -1 Peak intensity (I) 720 ), by [(I 720 ) / (I 810 The peak intensity ratio was calculated. It should be noted that in this embodiment, the wavelength is 810cm. -1 The peak intensity is the peak intensity of CH3 derived from propylene, with a wavelength of 720 cm⁻¹. -1 The peak intensity is derived from the ethylene chain. It should be noted that the measurement was performed using five polypropylene resin foam particles of any given quantity, and their arithmetic mean was used. Furthermore, as described below, no foam particles were obtained for Comparative Example 3; therefore, resin particles were used in the same manner for the measurement. It is anticipated that if the measurement conditions are the same, there will be almost no difference in the peak intensity ratio between the cases using foam particles and the cases using resin particles as samples.

[0222] <Determination of the expansion ratio of polypropylene resin foamed granules>

[0223] Take 3g to 10g of polypropylene resin foam granules, dry them at 60℃ for 6 hours, then condition them in a room at 23℃ and 50% humidity. After measuring the weight w1 (g), immerse them in a graduated cylinder containing ethanol, and measure the volume v (cm³) by the rise in water level in the graduated cylinder (immersion method). 3 ), calculate the true specific gravity ρ of the polypropylene resin foam particles. b =w1 / v, and then calculate the density ρ of the polypropylene resin particles before foaming. r The ratio (ρ) r / ρ b It should be noted that in the examples and comparative examples shown below, the density ρ of the polypropylene resin particles (polypropylene resin particles) before foaming is... r Both are 0.9 g / cm³3 .

[0224] <Determination of Shrinkage Rate of Polypropylene Resin Foamed Particles>

[0225] The shrinkage rate of polypropylene resin foamed granules is calculated using the following method from the bulk density (hereinafter referred to as BD) and the bulk density of polypropylene resin foamed granules under reduced pressure (hereinafter referred to as VBD). The weight of the measured polypropylene resin foamed granules is set as W1. The volume V1 is determined using a graduated cylinder at 23°C and atmospheric pressure (standard atmospheric pressure 0.1 MPa). The bulk density BD of the polypropylene resin foamed granules at 23°C and 0.1 MPa (standard atmospheric pressure) is then calculated using the following formula.

[0226] BD(g / L)=W1÷V1

[0227] Measure the polypropylene resin foam granules again, denote their weight as W2, and place them in a graduated pressure container. Use a vacuum pump or similar device to reduce the pressure inside the container. After confirming a pressure reduction below -0.09 MPa (gauge pressure) using a pressure gauge, vibrate the pressure container until the scale above the foam granules stops changing. Then, read the scale above the polypropylene resin foam granules in the pressure container and take this as the volume V2. It should be noted that during pressure reduction, the foam granules may sometimes compress against each other, hindering volume change. Therefore, the pressure container should be positioned laterally to prevent the foam granules from hindering volume change, and the pressure should be gradually reduced. Calculate the bulk density VBD of the polypropylene resin foam granules at 23°C and a pressure reduction below -0.09 MPa (gauge pressure) using the following formula.

[0228] VBD(g / L)=W2÷V2

[0229] In addition, the shrinkage rate of polypropylene resin foamed granules is calculated by the following formula.

[0230] (BD-VBD)÷VBD×100.

[0231] Minimum molding pressure for in-mold foamed polypropylene resin articles

[0232] In the [Preparation of In-Mold Foamed Polypropylene Resin Body] section described later, the steam pressure of the main heating process was adjusted by 0.01 MPa each time within the range of 0.20–0.32 MPa (gauge pressure) to obtain foamed bodies for each evaluation object. For the obtained foamed bodies, a crack of approximately 5 mm depth was created on the surface with a knife. The in-mold foamed body was then divided along the crack, and the fracture surface was observed. The ratio of the number of broken particles on the fracture surface to the total number of particles was calculated to evaluate the weldability of the molded body. The lowest steam pressure at which the weldability reached 80% or higher was taken as the minimum molding pressure.

[0233] <Molding cycle of polypropylene resin in-mold foamed articles>

[0234] The molding cycle in the manufacturing method of polypropylene resin in-mold foamed articles is defined as the period from the start of molding to the end of molding, i.e., the demolding of the article. Molding begins when the polypropylene resin foam particles are filled into the mold. The mold is heated by introducing steam, followed by water cooling. Molding ends when the surface pressure drops to 0.01 MPa as indicated by a surface pressure gauge mounted on the mold surface. The steam heating pressure is set to the minimum molding pressure calculated from the aforementioned <minimum molding pressure of polypropylene resin in-mold foamed articles>, and evaluation is performed accordingly. The productivity evaluation criteria are as follows.

[0235] ◎(Excellent): Molding cycle is within 180 seconds.

[0236] ○(Excellent): Molding cycle is longer than 180 seconds and within 210 seconds.

[0237] × (Poor): The molding cycle is more than 210 seconds.

[0238] <Surface Aesthetics of In-Mold Foamed Polypropylene Body>

[0239] The surface aesthetics of the 350mm x 450mm longitudinal and transverse surfaces of the in-mold foamed polypropylene resin body obtained by visual inspection are judged according to the following criteria. For particle gaps (the gaps between polypropylene resin foam particles), which is one of the evaluation indicators of surface quality, the number of such gaps in a 50mm square area on the central surface of the body is counted by visual inspection to make a judgment.

[0240] ◎(Beautiful surface appearance): No wrinkles, and the gap between particles is 0 to 1.

[0241] ○(Good surface appearance): No wrinkles, and 2-3 gaps between particles.

[0242] △(Surface appearance qualified): Wrinkles are observed, or there are 4 to 5 gaps between particles.

[0243] × (Surface appearance is not up to standard): Wrinkles are observed, or there are more than 6 gaps between particles.

[0244] <Determination of Static Compressive Strength of In-Mold Foamed Polypropylene Articles>

[0245] Test pieces measuring 50 mm in length × 50 mm in width × 25 mm in thickness were cut from in-mold foamed polypropylene (IMF) bodies. The compressive stress at 50% compression (manufactured by Minebea Mitsumi Inc., TG series) was measured using a tensile compression testing machine. It should be noted that the compressive stress at 50% compression is a measure of the rigidity of the IMF body.

[0246] The following describes the manufacturing methods of polypropylene resin particles, polypropylene resin foamed particles, and polypropylene resin in-mold foamed articles in the examples and comparative examples.

[0247] (Example 1)

[0248] [Manufacturing method of polypropylene resin particles]

[0249] The following mixture was dry-mixed using a mixer: 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 glycerol, and 0.05 parts by weight of talc. The dry-mixed mixture was then melt-blended using a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26-SX) at a resin temperature of 220°C. The extruded filament was water-cooled in a 2-m long water bath and then cut to produce polypropylene resin granules (1.2 mg / granule).

[0250] [Preparation of polypropylene resin foam granules]

[0251] In a 10L pressure vessel, 100 parts by weight (2.4 kg) of polypropylene resin granules 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, NEOPELEX G-15) as a surfactant were added. Then, 4 parts by weight of carbon dioxide as a foaming agent were added while stirring. The contents of the pressure vessel were heated to a foaming temperature of 158.2°C and held for 10 minutes. Carbon dioxide was then added to increase the pressure inside the pressure vessel to a foaming pressure of 2.60 MPa. After holding at the aforementioned foaming temperature and pressure for 20 minutes, the valve at the bottom of the pressure vessel was opened, releasing the material to atmospheric pressure through a 3.6 mm diameter opening, thus obtaining polypropylene resin foamed granules with a foaming ratio of 24. During this release, carbon dioxide was added and maintained without reducing the pressure inside the container.

[0252] [Preparation of In-Mold Foamed Polypropylene Articles]

[0253] The obtained polypropylene resin foam granules were dried at 75°C. The dried polypropylene resin foam granules were then placed in a pressure-resistant container, impregnated with pressurized air, and filled into a mold measuring 370mm (length) × 320mm (width) × 50mm (thickness) with pre-adjusted internal pressure of 0.20MPa (absolute pressure). The mold cavity was then heated using steam at a specified pressure to fuse the foam granules together. After water cooling of the mold and the surface of the molded body, the molded body was removed, yielding a polypropylene resin in-mold foamed body. This process was performed by varying the steam pressure from 0.20MPa (gauge pressure) to 0.32MPa in increments of 0.01MPa, and the minimum pressure required for complete fusion of the polypropylene resin foam granules was determined as the lower limit molding pressure. The resulting in-mold foamed body was allowed to stand at 23°C for 2 hours, followed by curing at 75°C for 13 hours.

[0254] (Examples 2-7, Comparative Examples 1-3, Reference Example 1)

[0255] In the [Preparation of Polypropylene Resin Particles], the resin formulation was changed as shown in Table 1. In the [Preparation of Polypropylene Resin Foamed Particles], the foaming conditions were changed as shown in Table 1. Otherwise, polypropylene resin particles, polypropylene resin foamed particles, and polypropylene resin in-mold foamed articles were prepared by the same operation as in Example 1. It should be noted that the foaming process was not performed for Comparative Example 3. Based on the results of the examples, when the content of ethylene / propylene block copolymer was 10 parts by weight per 100 parts by weight of the resin composition, 158°C was selected as the foaming temperature for obtaining 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, where the content of ethylene / propylene block copolymer was 30 parts by weight per 100 parts by weight of the resin composition, it was anticipated that the foaming temperature would exceed the upper limit of the temperature that could be raised in the pressure vessel used in the examples in order to obtain foamed particles of suitable quality. The evaluation results of the resin formulation conditions, foaming conditions, obtained polypropylene resin foamed particles and polypropylene resin in-mold foamed articles are shown in Table 1.

[0256] [Table 1]

[0257]

[0258] When the peak intensity ratio determined by infrared spectroscopy is 0.45 or higher, the recyclability is improved when using recycled polypropylene resin as the propylene block copolymer, as it fully contains propylene-based block copolymers. On the other hand, as shown in Table 1, when the peak intensity ratio is 0.7, the molding processing temperature becomes high, resulting in no foamed particles or a decrease in productivity. Furthermore, it can be seen that Comparative Example 1, which foams at approximately the same foaming pressure as Reference Example 1 (2.90 MPa), has a longer molding cycle, lower productivity, and a significant decrease in the static compressive strength of the foamed molded body. Similarly, Comparative Example 2, which sets the foaming temperature to 163.7°C, also has a longer molding cycle and a significant decrease in the static compressive strength of the foamed molded body.

[0259] On the other hand, when the foaming conditions are adjusted as in Examples 1 to 7 to make the shrinkage rate of the polypropylene resin foam particles less than 20%, although the molding cycle is longer than that in Reference Example 1, it can still be shortened sufficiently, and the decrease in static compressive strength is also tended to be suppressed. In addition, the polypropylene resin foam particles containing ethylene / propylene block copolymer can be molded in-mold under the same molding pressure as polypropylene resin foam particles formed only from ethylene / propylene random copolymer, and the surface aesthetics of the obtained foamed molded articles are excellent.

[0260] Industrial availability

[0261] According to one embodiment of the present invention, due to the short molding time during in-mold molding, polypropylene resin foam particles with improved productivity can be provided. Therefore, one embodiment of the present invention can be used in various applications such as automotive interior parts, automotive bumper core materials, thermal insulation materials, cushioning packaging materials, and turnover boxes.

Claims

1. A method for manufacturing polypropylene resin foamed granules, comprising a foaming step, wherein the foaming step involves depressurizing and foaming polypropylene resin granules containing a base resin under conditions of a foaming temperature below 163.5°C and a foaming pressure below 2.80 MPa, wherein the base resin contains propylene random copolymers and propylene block copolymers, and when the total amount of the propylene random copolymers and propylene block copolymers is set to 100% by weight, the base resin contains 73% to 95% by weight of the propylene random copolymers and 5% to 27% by weight of the propylene block copolymers. The propylene-based random copolymer comprises one or more copolymers selected from the group consisting of propylene / ethylene random copolymers and propylene / ethylene / 1-butene random copolymers, wherein the propylene / ethylene random copolymer comprises propylene units and ethylene units, and the propylene / ethylene / 1-butene random copolymer comprises propylene units, ethylene units, and 1-butene units. The propylene-based block copolymer comprises a propylene / ethylene block copolymer, wherein the propylene / ethylene block copolymer comprises propylene units and ethylene units.

2. The method for manufacturing polypropylene resin foamed granules according to claim 1, wherein the granules satisfy the following formula (1): Y<-0.07X+3.6 …(1); in, X is the content ratio of the aforementioned propylene block copolymer when the total amount of propylene random copolymer and propylene block copolymer in the base resin is set to 100% by weight. The percentage of the propylene block copolymer is expressed in weight %. Y is the foaming pressure in the foaming process. The unit of the foaming pressure is MPa. The value of Y is below 2.

80.

3. The method for manufacturing polypropylene resin foamed granules according to claim 1 or 2, wherein, The foaming temperature is above 150℃ and below 163.5℃.

4. A polypropylene resin foamed granule, comprising a base resin, wherein the base resin contains a propylene random copolymer and a propylene block copolymer. The peak intensity ratio of the polypropylene resin foam particles is I 720 / I 810 The value is 0.45~0.

67. The propylene-based random copolymer comprises one or more copolymers selected from the group consisting of propylene / ethylene random copolymers and propylene / ethylene / 1-butene random copolymers, wherein the propylene / ethylene random copolymer comprises propylene units and ethylene units, and the propylene / ethylene / 1-butene random copolymer comprises propylene units, ethylene units, and 1-butene units. The propylene-based block copolymer comprises a propylene / ethylene block copolymer, wherein the propylene / ethylene block copolymer comprises propylene units and ethylene units. The polypropylene resin foamed particles are obtained by depressurizing and foaming polypropylene resin particles containing the base resin at a foaming temperature below 163.5°C and a foaming pressure below 2.80 MPa. The shrinkage rate is below 20%. in, The peak intensity ratio I 720 / I 810 The wavelength 720cm was obtained from the spectrum obtained through infrared spectroscopy analysis. -1 The peak intensity I 720 Relative to wavelength 810cm -1 The peak intensity I 810 The ratio, The shrinkage rate (%) is a value obtained by the following formula (2); The shrinkage rate (%) = (BD - VBD) × 100 / VBD …(2) In formula (2), BD is the bulk density of polypropylene resin foam particles measured at a temperature of 23°C and an absolute pressure of 0.1 MPa. The VBD is the bulk density of polypropylene resin foam particles measured in a region with a temperature of 23°C and a gauge pressure of -0.09 MPa.

5. The polypropylene resin foamed granules according to claim 4, wherein, When the total amount of propylene random copolymer and propylene block copolymer is set to 100% by weight, 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.

6. The polypropylene resin foamed granules according to claim 4 or 5, wherein, The propylene-based block copolymer has a melting point above 160°C and below 180°C.

7. The polypropylene resin foamed granules according to claim 4 or 5, wherein, The propylene-based block copolymer is a recycled resin.

8. The polypropylene resin foamed granules according to claim 4 or 5, wherein, The propylene-based random copolymer contains more than 50 mol% propylene units in 100 mol% of all structural units, and the propylene-based block copolymer contains more than 50 mol% propylene units in 100 mol% of all structural units.

9. The polypropylene resin foamed granules according to claim 4 or 5, wherein, The propylene-based random copolymer includes a propylene / ethylene random copolymer, which comprises propylene units and ethylene units.

10. The polypropylene resin foamed granules according to claim 4 or 5, wherein, The melt flow rate of the propylene-based random copolymer at 230°C is 3 g / 10 min to 30 g / 10 min.

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

12. The polypropylene resin foamed granules according to claim 4 or 5, wherein, The melt flow rate of the propylene block copolymer at 230°C is 3 g / 10 min to 30 g / 10 min.

13. The polypropylene resin foamed granules according to claim 4 or 5, wherein the DSC ratio of the polypropylene resin foamed granules is 10.0% to 50.0%.

14. The polypropylene resin foamed granules according to claim 4 or 5, wherein the foaming ratio of the polypropylene resin foamed granules is 15 to 50 times.

15. A polypropylene resin foamed molded body, which is formed by foaming polypropylene resin foamed particles according to any one of claims 4 to 14.

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