Method for producing polypropylene-based resin foam particle, and polypropylene-based resin foam particle

Abstract

Provided is a method for producing a polypropylene-based resin foam particle, with which it is possible to form a molded body having excellent in-mold moldability and excellent compression properties. In this method for producing a polypropylene-based resin foam particle, in which a foam particle is obtained by foaming a polypropylene-based resin particle, the polypropylene-based resin particle is constituted from a mixed resin obtained by kneading an impact polypropylene having a melt flow rate, as measured at a temperature of 230°C under a load of 2.16 kg, of more than 10 g / 10 min and not more than 80 g / 10 min and a polypropylene-based resin A having a melt flow rate, as measured at a temperature of 230°C under a load of 2.16 kg, of less than 3 g / 10 min. In the polypropylene-based resin particle, the mass ratio of the impact polypropylene and the polypropylene-based resin A is such that impact polypropylene : polypropylene-based resin A =97:3 to 40:60.

Description

Method for producing polypropylene resin foam particles, and polypropylene resin foam particles

[0001] This invention relates to a method for producing polypropylene resin foam particles, and to polypropylene resin foam particles.

[0002] Polypropylene-based foam particle molded articles, which are formed by in-mold molding of polypropylene-based resin foam particles, are used in a variety of applications, such as shock absorbers, heat insulating materials, and various packaging materials. For example, polypropylene-based foam particle molded articles are used as packaging and cushioning materials for electrical and electronic components, and for automotive parts, and are also used as packaging materials in a wide range of industries, from precision parts to food products. Thus, polypropylene-based foam particle molded articles are used in a variety of industrial fields. As will be described later, in this specification, polypropylene-based foam particle molded articles may be abbreviated as "molded articles."

[0003] Patent Document 1 discloses a method for producing polypropylene resin foam particles, in which polypropylene resin particles containing a base resin containing a propylene random copolymer and a propylene block copolymer are foamed under specific conditions to obtain polypropylene resin foam particles containing specific amounts of the propylene random copolymer and the propylene block copolymer, respectively.

[0004] International Publication No. 2023 / 190441

[0005] From the perspective of reducing environmental impact, attention is being drawn to the use and utilization of resins derived from recycled materials such as post-consumer materials. Examples of resins derived from recycled materials include polypropylene resins recovered from used home appliances and automobiles, and polypropylene resins recovered from automobile shredder residue (ASR) generated during the automobile disposal process.

[0006] Polypropylene resin products that use impact polypropylene as a resin raw material are widely used in various industrial fields and applications. Therefore, a large quantity of recycled materials containing impact polypropylene are circulating in the market. From the perspective of manufacturing polypropylene resin foam products that effectively utilize recycled materials, the development of polypropylene resin foam particles containing impact polypropylene is desired.

[0007] However, there was room for further improvement in polypropylene-based foamed resin particles containing a large amount of impact polypropylene, specifically regarding their tendency to have poor in-moldability and the tendency for molded articles obtained by in-molding polypropylene-based foamed resin particles to have poor compressibility.

[0008] One of the objectives of the present invention is to provide a method for producing polypropylene resin foam particles capable of forming molded articles with excellent in-moldability and compressibility, and to provide polypropylene resin foam particles.

[0009] The following technologies are shown in [1] to

[10] regarding aspects of the present invention. [1] A method for producing foamed polypropylene resin particles by foaming polypropylene resin particles, wherein the polypropylene resin particles are composed of a mixed resin obtained by kneading impact polypropylene, which has a melt flow rate of more than 10 g / 10 min and 80 g / 10 min or less as measured at a temperature of 230°C and a load of 2.16 kg, and polypropylene resin A, which has a melt flow rate of less than 3 g / 10 min as measured at a temperature of 230°C and a load of 2.16 kg, and the mass ratio of the impact polypropylene to the polypropylene resin A in the polypropylene resin particles is the impact polypropylene:the polypropylene resin A = 97:3 to 40:60. [2] The melt flow rate MFR of the impact polypropylene Ｉ and the melt flow rate MFR of the polypropylene resin A Ａ The difference (MFR) Ｉ- MFR Ａ A method for producing polypropylene resin foam particles according to [1] above, wherein the melt flow rate of the polypropylene resin particles measured under the conditions of a temperature of 230°C and a load of 2.16 kg is 5 g / 10 min or more and 50 g / 10 min or less. A method for producing polypropylene resin foam particles according to [1] or [2] above, wherein the melt flow rate of the polypropylene resin particles measured under the conditions of a temperature of 230°C and a load of 2.16 kg is 5 g / 10 min or more and 50 g / 10 min or less. A method for producing polypropylene resin foam particles according to any one of [1] to [3] above, wherein the melting point of the polypropylene resin particles is 150°C or more and 165°C or less. A method for producing polypropylene resin foam particles according to any one of [1] to [4] above, wherein the amount of acetone-insoluble matter contained in the n-decane extract of the polypropylene resin particles is 0.05 g or more and 0.3 g or less per gram of the polypropylene resin particles. [6] A method for producing polypropylene resin foam particles according to any one of [1] to [5] above, wherein the melt tension of the polypropylene resin particles at 170°C is 8 mN or more and 40 mN or less. [7] Polypropylene resin foam particles comprising a polypropylene resin composition containing impact polypropylene, wherein the melt flow rate of the polypropylene resin composition measured under conditions of a temperature of 230°C and a load of 2.16 kg is 5 g / 10 min or more and 50 g / 10 min or less, and the melt tension of the polypropylene resin composition at 170°C is 8 mN or more and 40 mN or less. [8] Polypropylene resin foam particles according to [7] above, wherein the melt elongation of the polypropylene resin composition at 170°C is 8 m / min or more and 100 m / min or less. [9] Polypropylene resin foam particles according to [7] or [8] above, wherein the melt point of the polypropylene resin composition is 150°C or more and 165°C or less.

[10] Polypropylene resin foam particles according to any one of [7] to [9] above, wherein the amount of acetone-insoluble matter contained in the n-decane extract of the polypropylene resin composition is 0.05 g or more and 0.3 g or less per gram of the polypropylene resin composition.

[0010] According to the present invention, polypropylene-based resin foam particles capable of forming molded articles with excellent in-moldability and compressibility, and polypropylene-based resin foam particles can be manufactured.

[0011] Figure 1 is a cross-sectional photograph (TEM photograph) illustrating the morphology of the impact polypropylene used in the example.

[0012] An example of an embodiment of the present invention will be described in detail below. The present invention is not limited to the embodiments described below.

[0013] In this specification, matters defined using numerical values, such as numerical values ​​or amounts of additives corresponding to specific attributes, are referred to as numerical specifications (NM). Examples of numerical specifications (NM) include the density and blending amount of specific compounds described later. For example, examples of numerical specifications (NM) include melt flow rate, difference in melt flow rates, melting point, amount of acetone-insoluble matter, melt tension, melt elongation, and the mass ratio of impact polypropylene and polypropylene resin A described later. When multiple numerical ranges are defined for numerical specifications (NM), the upper and lower limits in the combination defining each numerical range for each numerical specification (NM) may be arbitrarily and independently combined. In this specification, the combination defining a numerical range refers to the combination of the upper and lower limits. The numerical range determined by arbitrarily combining the upper and lower limits includes the upper limit, the lower limit, and the value between the upper and lower limits. That is, the numerical range is greater than or equal to the lower limit and less than or equal to the upper limit. For example, consider a case where the numerical value for the target numerical specification (NM) is preferably between MA1 and MB1, preferably between MA2 and MB2, and more preferably between MA3 and MB3. In this case, the lower limit of the target numerical specification (NM) may be any value selected from the group consisting of MA1, MA2, and MA3 (the selected lower limit). The upper limit of the target numerical specification (NM) may be any value selected from the group consisting of MB1, MB2, and MB3 (the selected upper limit). Furthermore, the numerical range of the target numerical specification (NM) may be a numerical range that is greater than or equal to the selected lower limit and less than or equal to the selected upper limit (the selected numerical range). Note that MA1, MA2, MA3, MB1, MB2, and MB3 represent numerical values.

[0014] Furthermore, unless otherwise specified, when combining different numerical specifications (NMs), the upper limit of each numerical specification (NM) may be individually selected as the upper limit. The same applies to the lower limit and numerical range of the numerical specifications (NMs).

[0015] Furthermore, in this specification, the expression MA1 to MB1, which uses the symbol ~ to represent a numerical range, is synonymous with MA1 or greater and MB1 or less, and represents a numerical range that includes MA1 and MB1, which are the endpoints of the numerical range.

[0016] In this specification, polypropylene resin foam particles may be referred to as foam particles. Polypropylene resin particles may also be referred to as resin particles. In this specification, a molded article of polypropylene resin foam particles formed by in-mold molding of foam particles may be referred to as a molded article or an in-molded article. In this specification, polypropylene may be referred to as PP. Impact polypropylene may also be referred to as impact PP. Furthermore, polypropylene resin A may be referred to as resin A.

[0017] [1. Method for manufacturing polypropylene resin foam particles] Polypropylene resin foam particles (foamed particles) are manufactured by foaming polypropylene resin particles (resin particles) as described below.

[0018] [1-1 Polypropylene Resin Particles] To obtain polypropylene resin foam particles, polypropylene resin particles are prepared. The resin particles are composed of the mixed resin described below.

[0019] [Mixed Resin] The resin particles are composed of a mixed resin. The mixed resin is obtained by kneading impact polypropylene that meets predetermined conditions with polypropylene-based resin A.

[0020] [Impact Polypropylene] Impact polypropylene (Impact PP) is a resin with a morphology in which a polypropylene resin matrix is ​​composed of rubber-like materials containing ethylene propylene rubber as domains. The matrix can be described as a continuous phase, and the domains can be described as a dispersed phase.

[0021] The morphology of impact PP can be observed, for example, by the following method: Prepare an observation sample made of impact PP. Embed the observation sample in epoxy resin and stain it with ruthenium tetroxide. Next, sections are prepared from the observation sample using ultramicrotol or the like. Place the sections on the grid of a transmission electron microscope. The sections are then observed at a magnification of approximately 1000x to 5000x, and photographs are taken of the sections. The resulting photographs (TEM images) are cross-sectional images of impact PP. By visually observing the cross-sectional images, the morphology of the polypropylene phase and the rubbery phase containing ethylene propylene rubber that constitute impact PP can be recognized.

[0022] Ethylene-propylene rubber is a rubbery substance containing components derived from ethylene and components derived from propylene. Furthermore, ethylene-propylene rubber may also contain components derived from monomers other than ethylene and propylene, such as dienes.

[0023] Examples of transmission electron microscopes include the JEM-1040Flash manufactured by JEOL Ltd. The observation of the morphology of impact PP will be further explained using Figure 1 in the examples described later.

[0024] (Average diameter of the rubbery phase (domain)) The average diameter of the rubbery phase (domain) in impact PP is preferably 0.5 μm or more and 10 μm or less, and more preferably 0.6 μm or more and 5 μm or less. The average diameter of the domains can be calculated using the TEM photograph described above. 30 domains are randomly selected from the many domains visible in the TEM photograph. The area of ​​each selected domain is measured. The arithmetic mean of the measured area values ​​is calculated. The equivalent circle diameter corresponding to the arithmetic mean (i.e., the average value of the equivalent circle diameter) is calculated. The average value of the equivalent circle diameter is determined as the average diameter of the rubbery phase (domain). The average value of the equivalent circle diameter specified here is the diameter of a perfect circle having the same area as the arithmetic mean of the area values ​​of the rubbery material.

[0025] (Melt Flow Rate) The impact PP used to form the mixed resin has a melt flow rate (MFR) measured under the conditions of a temperature of 230°C and a load of 2.16 kg that exceeds 10 g / 10 min and is 80 g / 10 min or less. When the MFR of the impact PP is a value that satisfies the above numerical range, the in-mold formability of the foamed particles can be improved, and the range of molding pressure in which a good foamed particle molded body can be obtained can be made wider. The melt flow rate (MFR) of the impact PP is sometimes referred to as MFR Ｉ From the viewpoints of the effect of in-mold formability and the effect of the range of molding pressure, MFR Ｉ is preferably 15 g / 10 min or more and 70 g / 10 min or less, and more preferably 20 g / 10 min or more and 60 g / 10 min or less. Note that MFR Ｉ is the value of the melt flow rate of the impact PP measured under the conditions of a temperature of 230°C and a load of 2.16 kg based on JIS K7210-1:2014. The terms MFR Ｉ and melt flow rate MFR Ｉ both indicate the melt flow rate of the impact PP.

[0026] (Melting Point) The melting point Tm of the impact PP Ｉ is preferably 158°C or more and 170°C or less. When the melting point Tm of the impact PP Ｉ is a value that satisfies this numerical range, it becomes easier to obtain a molded body with excellent compression physical properties. From the viewpoint of this effect, the melting point Tm of the impact PP Ｉ is preferably 160°C or more and 169°C or less, and more preferably 162°C or more and 168°C or less.

[0027] The melting point Tm of the impact PP ＩThe transition temperature of plastics can be measured, for example, as follows, according to the method for measuring the transition temperature of plastics specified in JIS K7121:2012. A test specimen made of impact PP is prepared. The test specimen is conditioned according to "(2) When measuring the melting temperature after a certain heat treatment" in "3. Conditioning of test specimens" of JIS K7121:2012. The temperature range for conditioning is 30°C to 230°C, and both the heating rate and cooling rate are 10°C / min. A DSC curve is obtained by heating the conditioned test specimen from 30°C to 230°C at a heating rate of 10°C / min. The temperature at the peak of the melting peak that appears in the DSC curve is adopted as the melting point. The flow rate of nitrogen gas in the measurement environment is 30 mL / min. If multiple melting peaks appear in the DSC curve, the temperature at the peak of the melting peak with the highest height relative to the baseline is adopted as the melting point Tm of impact PP. Ｉ Let's assume that.

[0028] (Tensile Modulus) The tensile modulus of impact PP is preferably 800 MPa or more and 2000 MPa or less. When the tensile modulus of impact PP is within this range, foam particles can be stably molded in the mold, making it easier to stably obtain a molded article with good compressible properties. From the viewpoint of this effect, the tensile modulus of impact PP is preferably 900 MPa or more and 1800 MPa or less, and more preferably 1000 MPa or more and 1600 MPa or less.

[0029] The tensile modulus of impact PP can be measured by the method specified in JIS K 7161-2:2014.

[0030] (Density) The density of Impact PP is 0.9 g / cm³. ３ 1.0g / cm or more ３ The following is preferable. Furthermore, regarding the lower limit of the density of impact PP, the density of impact PP is 0.91 g / cm³. ３ It may be greater than or equal to 0.92 g / cm³. ３The above is also acceptable. When using impact PP derived from recycled materials as described later, the density of the impact PP tends to be higher, and the moldability tends to decrease. According to the manufacturing method of the present invention, even when using such impact PP, foamed particles with good in-moldability can be stably obtained.

[0031] The density of impact PP can be measured by the method specified in Method A (water displacement method) described in JIS K 7112:1999.

[0032] (Heat of Melting) The heat of melt of impact PP is preferably 70 J / g or more and 120 J / g or less. When the heat of melt of impact PP is within this range, it becomes easier to stably mold the foamed particles in the mold. It also becomes easier to stably obtain a molded article with good compressible properties. From the viewpoint of stably improving in-moldability, the heat of melt of impact PP is more preferably 75 J / g or more and 110 J / g or less, and even more preferably 80 J / g or more and 105 J / g or less.

[0033] The heat of fusion of impact PP can be measured according to the method for measuring the transition heat of plastics specified in JIS K7122:2012. That is, it can be determined based on the DSC curve. The DSC curve is obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K7122:2012. Specifically, first, a test specimen made of impact PP is prepared. The test specimen is conditioned according to "3. Conditioning of test specimens" "(2) When measuring the melting temperature after performing a certain heat treatment" in JIS K7122:2012. The heating rate and cooling rate in conditioning are both set to 10°C / min, and the temperature range is from 23°C to 230°C. After that, the conditioned test specimen is heated again from 23°C to 230°C at a rate of 10°C / min to obtain the DSC curve (DSC curve for the second heating). The flow rate of nitrogen gas in the measurement environment is set to 30 mL / min. In this DSC curve, a straight line is drawn connecting the point corresponding to 80°C and the high-temperature endpoint of the melting peak with the highest peak temperature. The heat of fusion of impact PP can be calculated based on the area of ​​the region enclosed by the straight line determined in this way and the melting peak of the DSC curve.

[0034] (Acetone-insoluble content in n-decane extract) The amount of acetone-insoluble content in the n-decane extract of Impact PP is preferably 0.1 g or more and 0.3 g or less per gram of Impact PP. In this specification, the acetone-insoluble content in the n-decane extract of the subject may be referred to as A (insol). When Impact PP is the subject, the amount of acetone-insoluble content in the n-decane extract of Impact PP may be referred to as the amount of A (insol) of Impact PP. Also, the amount of A (insol) of Impact PP per gram of Impact PP is A (insol) Ｉ It is sometimes referred to as A (insol). Ｉ (A(insol)) Ｉ It may also be referred to as A (insol). ＩHowever, if the values ​​are within the aforementioned numerical range, it becomes easy to set the state of impact polypropylene such that the ethylene propylene rubber component satisfies a specific range. Furthermore, it becomes easy to impart properties such as impact resistance derived from impact polypropylene to the molded article formed by in-mold molding of the resulting foamed particles.

[0035] (A(insol)) Ｉ The amount of insols in impact PP is obtained by the following method. An n-decane extract is prepared by heating impact PP in n-decane at 145°C and then cooling it to 23°C. Specifically, impact PP is added to n-decane and heated to a temperature of 145°C to dissolve the n-decane-soluble components in impact PP into n-decane. This yields an n-decane solution. The obtained n-decane solution is cooled to 23°C. Then, by removing the components precipitated in the n-decane solution that are insoluble in n-decane at 23°C, an n-decane extract containing n-decane-soluble components is obtained. The n-decane extract is added to acetone. At this time, acetone-insoluble components in the n-decane extract precipitate. Based on the mass of the obtained precipitate (acetone-insoluble components) and the mass of impact PP used for measurement, the amount of insols in impact PP per gram of impact PP is calculated as A(insol). Ｉ It is possible to calculate this.

[0036] Impact PP is the MFR mentioned above. Ｉ Any Impact PP that satisfies the conditions may consist of one type of Impact PP, or a combination of multiple types of Impact PP.

[0037] Furthermore, the impact PP included in the mixed resin is the MFR mentioned above. Ｉ When multiple types of impact PP that satisfy the numerical range conditions are used, MFR ＩFor physical properties other than those mentioned above, the various physical properties measured on the measurement mixture are adopted as the various physical properties of impact PP. The measurement mixture is produced by melt-mixing each impact PP etc. using an extruder or the like. The mixing ratio of each impact PP etc. that constitutes the measurement mixture is the mixing ratio of impact PP during the production of resin particles. As mentioned above, MFR Ｉ Other physical properties besides those mentioned above include, for example, the melting point, the heat of fusion, and the acetone-insoluble content in the n-decane extract.

[0038] [Polypropylene Resin A] Polypropylene resin A (Resin A) refers to a polypropylene resin in which the melt flow rate measured under conditions of a temperature of 230°C and a load of 2.16 kg is less than 3 g / 10 min. In the present invention, polypropylene resin refers to a resin having 50% by mass or more of structural units derived from propylene.

[0039] (Melt Flow Rate) The melt flow rate (MFR) of resin A is a value measured under the conditions of a temperature of 230°C and a load of 2.16 kg, based on JIS K7210-1:2014. When the MFR of resin A constituting the mixed resin is less than 3 g / 10 min, the following effects are enhanced. That is, even when the amount of impact PP contained in the resin particles is large, it is possible to ensure foaming properties when producing foamed particles from the resin particles, while also ensuring a wide molding range as the moldable range of the molded article when molding the foamed particles in a mold. Furthermore, the foamed particles can be made to have excellent in-moldability. Also, from the viewpoint of easily achieving a good kneading state between impact polypropylene and resin A in the mixed resin, the melt flow rate of resin A is preferably 0.1 g / 10 min or more, and more preferably 0.2 g / 10 min or more. The melt flow rate of resin A is MFR Ａ It is sometimes written as MFR. Ａ or meltflow rate MFR Ａ The terms all refer to the melt flow rate of resin A.

[0040] (Material) Resin A is the MFR mentioned above. ＡThe polypropylene resin is not particularly limited as long as it satisfies the conditions. Examples of resin A include homopolypropylene and propylene copolymers. Resin A may consist of one type of resin or a combination of multiple types of resins. Note that the above-mentioned MFR may be used as resin A included in the mixed resin. Ａ When using multiple types of resin A that satisfy the conditions, MFR Ａ Other physical properties, excluding those specified above, are adopted as follows: A measuring compound is prepared by melt-kneading each resin A using an extruder or the like, at the mixing ratio of each resin A used during the production of resin particles. Various physical properties are measured for this measuring compound. The measured various physical properties are adopted as the various physical properties of resin A. Ａ Other physical properties besides those mentioned above include, for example, the melting point and the heat of fusion.

[0041] Examples of polypropylene copolymers include copolymers of propylene with ethylene and / or α-olefins having 4 or more carbon atoms, such as ethylene-propylene copolymer, propylene-butene copolymer, and ethylene-propylene-butene copolymer. These copolymers are preferably random copolymers. From the viewpoint of improving the in-moldability of foamed particles, the proportion of propylene-based random copolymer in resin A is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. Note that the proportion of propylene-based random copolymer in resin A refers to the proportion of propylene-based random copolymer when the total amount of resin A is 100% by mass.

[0042] (Melting point) Melting point Tm of resin A Ａ The melting point Tm of resin A is preferably between 130°C and 165°C. Ａ If the value satisfies this numerical range, the in-moldability of the foamed particles can be stably improved. From the viewpoint of making it easier to improve the in-moldability of the foamed particles, the melting point Tm of resin A is Ａ The temperature is preferably between 135°C and 150°C, and more preferably between 138°C and 148°C.

[0043] Melting point Tm of resin A Ａ The melting point Tm of impact PP is Ｉ Similar to the method used to measure the transition temperature of plastics, it can be measured using the method specified in JIS K7121:2012.

[0044] (Tensile Modulus) The tensile modulus of resin A is preferably 800 MPa or more and 2000 MPa or less. When the tensile modulus of resin A is within this range, the foamed particles can be stably molded in the mold, making it easier to stably obtain a molded article with good compressible properties. From the viewpoint of further improving the in-moldability of the foamed particles, the tensile modulus of impact PP is preferably 900 MPa or more and 1400 MPa or less, and more preferably 950 MPa or more and 1200 MPa or less.

[0045] The tensile modulus of resin A can be measured by the method specified in JIS K 7161-2:2014.

[0046] (Density) The density of resin A is 0.9 g / cm³. ３ 1.0g / cm or more ３ It is preferable that this is the case. Furthermore, the density of resin A may be lower than the density of impact PP. When impact PP derived from recycled materials, as described later, is used as the impact PP, the density of the impact PP tends to be higher, and the moldability tends to decrease. By using resin A, which has a lower density than impact PP, foamed particles with good in-moldability can be stably obtained even in such cases.

[0047] The density of resin A can be measured by the method specified in Method A (water displacement method) described in JIS K7112:1999.

[0048] (Heat of fusion) The heat of fusion of resin A is preferably 60 J / g or more and 120 J / g or less. When the heat of fusion of resin A is within this range, foamed particles can be stably molded in the mold, and a molded article with good compressible properties can be stably obtained. From the viewpoint of easily improving stably moldable properties, the heat of fusion of resin A is more preferably 65 J / g or more and 100 J / g or less, and even more preferably 70 J / g or more and 95 J / g or less.

[0049] The heat of fusion of resin A can be determined based on the DSC curve obtained during the second heating by performing differential scanning calorimetry (DSC) in accordance with JIS K7122:2012, similar to the heat of fusion of impact PP.

[0050] [Difference in MFR between Impact PP and Resin A] The melt flow rate (MFR) of impact polypropylene (impact PP) used to form the mixed resin Ｉ ) and the melt flow rate (MFR) of polypropylene resin A (resin A) Ａ ) difference (MFR Ｉ - MFR Ａ ) is preferably 23 g / 10 min or more and 60 g / 10 min or less. (MFR) Ｉ - MFR Ａ ) If the value satisfies the above range, it becomes easier to obtain foamed particles that can form a molded body with excellent in-moldability and compressibility. From the viewpoint of this effect, (MFR Ｉ - MFR Ａ The amount is preferably 24 g / 10 min or more and 50 g / 10 min or less, and more preferably 25 g / 10 min or more and 40 g / 10 min or less.

[0051] [Difference in melting points between Impact PP and resin A] Regarding Impact PP and resin A used to form a mixed resin, the melting point (Tm) of Impact Polypropylene Ｉ ) (°C) and the melting point (Tm) of polypropylene resin A. Ａ The difference (Tm) from (℃) Ｉ -Tm Ａ ) Preferably, the temperature is between -5°C and 30°C. (TmＩ -Tm Ａ When (Tm) is within the above range, it becomes easier to stably obtain foamed particles with good in-moldability. From the viewpoint of this effect, Ｉ -Tm Ａ The temperature is preferably 0°C to 28°C, more preferably 5°C to 26°C, and even more preferably 10°C to 25°C.

[0052] [Mixing ratio of impact PP and resin A in resin particles] The mixing ratio of impact PP and resin A used to form resin particles is preferably such that the mass ratio (ratio of parts by mass) of impact polypropylene and polypropylene resin A is impact polypropylene:polypropylene resin A = 97:3 to 40:60. More preferably, the above mixing ratio of impact polypropylene to polypropylene resin A is 96:4 to 45:55, and more preferably 95:5 to 50:50. However, the total (parts by mass) of impact polypropylene and polypropylene resin A is set to 100. By setting the mixing ratio within the above range, foamed particles with good in-moldability can be obtained while containing a large amount of components derived from impact polypropylene in the foamed particles. When multiple types of impact polypropylene are used, their total amount is considered the mass of impact polypropylene. When multiple types of polypropylene resin A are used, their total amount is considered the mass of polypropylene resin A.

[0053] [Resins other than Impact PP and Resin A] The resin particles may contain other resins other than Impact PP and Resin A, as long as they can achieve the intended purpose of the present invention. Other resins include those with a melt flow rate (MFR) that is higher than that of Resin A. Ａ ) and Impact PP melt flow rate (MFR Ｉ Examples of polypropylene resins that fall between the above categories can be cited. Other examples of resins include polyethylene resins and polystyrene resins.

[0054] [Origin of the resins constituting the mixed resin] The resins used to form the mixed resin may be virgin polypropylene resins or recycled polypropylene resins. Virgin polypropylene resin refers to resin in an unused and / or unprocessed state. Therefore, virgin polypropylene resin refers to resin that has not undergone the thermal history of molding processes for forming molded products. From the viewpoint that virgin polypropylene resin is different from resin obtained by recycling recovered molded products, etc., it may be called non-recycled polypropylene resin. Recycled polypropylene resin refers to resin that has undergone the thermal history of molding processes for forming molded products. The mixed resin may be composed of virgin resins, recycled resins such as recycled polypropylene resins, or a combination of virgin resins and recycled resins.

[0055] (Recycled Polypropylene Resins) Examples of recycled polypropylene resins include polypropylene resins derived from pre-consumer materials and polypropylene resins derived from post-consumer materials. Polypropylene resins derived from post-consumer materials can also be called post-consumer recycled polypropylene resins (PCR-PP). Resins derived from materials, such as polypropylene resins derived from pre-consumer materials, refer to resins recovered from the target material (pre-consumer material, etc.).

[0056] In this specification, "post-consumer materials" means "materials or products that have been used as products and subsequently discarded" as described in the certification standards document "Plastic Products Version 2.13" issued by the Eco Mark Office of the Japan Environment Association. In this specification, "pre-consumer materials" means "materials such as scraps or defective products generated from the waste route of the product manufacturing process, which have undergone recycling processes such as collection and sorting" as described in the certification standards document "Plastic Products Version 2.13" issued by the Eco Mark Office of the Japan Environment Association.

[0057] Specifically, post-consumer materials include, for example, post-consumer materials derived from automotive components and post-consumer materials derived from home appliances. Examples of post-consumer materials derived from automotive components include exterior materials such as bumpers and interior materials such as instrument panels removed from used automobiles. Other examples include automotive shredder residue (ASR) generated during the automobile disposal process. Polypropylene resins recovered from such materials can be used as recycled polypropylene resins.

[0058] (Automotive Shredder Residue (ASR)) Automotive shredder residue (ASR) refers to "automotive shredder residue" as defined in Article 2-5 of the "Act on Recycling of End-of-Life Vehicles" (Act No. 87 of 2002). Specifically, the following can be cited as examples of materials that qualify as ASR: End-of-life vehicles are dismantled by removing recyclable parts such as engines and batteries. The dismantled vehicles are then shredded. Metals and other useful materials are separated and recovered from the shredded vehicle material. The materials that remain after these materials have been recovered qualify as ASR.

[0059] ASR typically contains polypropylene resins derived from automotive components, as well as other plastics other than polypropylene resins, such as polystyrene (PS) and acrylonitrile-butadiene-styrene resin (ABS), rubber, and various metals.

[0060] (Method for recovering recycled polypropylene resin from ASR) There are no particular limitations on the method for recovering the desired resin from ASR. By combining sorting methods using magnetic force or wind force, or sorting methods using differences in specific gravity or electrostatic charge, it is generally possible to recover the desired resin from ASR. The resin recovered from ASR generally contains polypropylene resin as its main component, which has undergone a thermal history due to molding processes for forming automotive parts.

[0061] Furthermore, impact PP is often used as a resin raw material in polypropylene resin products, including automotive components. For this reason, recycled polypropylene resins derived from post-consumer materials such as automotive components contain a large amount of impact PP as a resin component.

[0062] In the present invention, the properties of foamed particles using recycled resin as impact PP and the properties of foamed particles using virgin resin as impact PP can be substantially the same if the following two conditions are met. The two conditions are, firstly, that the physical properties such as MFR of impact PP as recycled resin and the physical properties such as MFR of impact PP as virgin resin are the same or approximate. Secondly, that the foamed particles are manufactured under the same conditions except for using impact PP of different origins. Therefore, in the present invention, foamed particle molded articles formed from foamed particles using recycled resin as impact PP and foamed particle molded articles formed from foamed particles using virgin resin as impact PP can also have similar properties.

[0063] In the present invention, excellent foamed particles can be produced. These foamed particles can be produced to form molded articles with excellent in-moldability and compressibility, and contain a large amount of impact PP. Furthermore, as described above, according to the present invention, it is possible to suppress the occurrence of differences in properties (e.g., compressibility) between products that use a large amount of recycled resin (referred to as the first product) and products that use a large amount of virgin resin (referred to as the second product). In this way, even polypropylene resin foamed particles containing recycled polypropylene resin can have excellent in-moldability and their properties can be made to be roughly the same between the first product and the second product. This makes it possible to obtain molded articles with excellent compressibility while more effectively utilizing recycled resin mainly composed of impact PP, which is widely available on the market. In this respect as well, the present invention is useful.

[0064] [Various additives other than resin] When manufacturing resin particles, various additives may be added in addition to the mixed resin, as long as the effects of the present invention are not lost. Examples of various additives include crystal nucleating agents, flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, ultraviolet absorbers, light stabilizers, antibacterial agents, and colorants.

[0065] [Composition and Properties of Resin Particles] (Ratio of Resins Constituting Resin Particles) The mass ratio (ratio of parts by mass) of impact polypropylene and polypropylene resin A in the resin particles is preferably 97:3 to 40:60, similar to the explanation given for the mixing ratio of impact PP and resin A. However, the total (parts by mass) of impact polypropylene and polypropylene resin A is set to 100. When the mass ratio of impact PP and resin A in the resin particles satisfies the above numerical range, foamed particles containing a large amount of impact PP can be obtained, and an in-molded article containing a large amount of impact PP can be obtained. From this viewpoint, the mass ratio of impact PP and resin A is more preferably 96:4 to 45:55, and more preferably 95:5 to 50:50, when the total of impact PP and resin A is set to 100 parts by mass.

[0066] (MFR of resin particles) The melt flow rate (MFR) of resin particles is measured under the conditions of a temperature of 230°C and a load of 2.16 kg. Ｐ ) is preferably 5 g / 10 min or more and 50 g / 10 min or less. MFR Ｐ When the above range is achieved, it becomes easier to form a molded article that has good in-moldability and excellent compressibility. From the viewpoint of such effects, MFR Ｐ Regarding the upper limit, MFR Ｐ It is more preferable that the amount is 45 g / 10 min or less, and even more preferable that it is 40 g / 10 min or less.

[0067] Melt flow rate (MFR) of resin particles ＰThis value is measured under the conditions of a temperature of 230°C and a load of 2.16 kg, in accordance with JIS K7210-1:2014.

[0068] (Melting point of resin particles) Melting point Tm of resin particles Ｐ The temperature is preferably between 150°C and 165°C. Ｐ When the value satisfies this numerical range, foamed particles formed using resin particles can be made to have excellent in-moldability. From the viewpoint of this effect, the melting point Tm Ｐ It is preferable that the temperature is between 152°C and 164°C.

[0069] Melting point Tm of resin particles Ｐ The melting point Tm of impact PP is Ｉ Similar to the method used to measure [the other method], it can be identified by performing differential scanning calorimetry (DSC) in accordance with JIS K7121:2012.

[0070] (Heat of fusion of resin particles) The heat of fusion of the resin particles is preferably 70 J / g or more and 110 J / g or less. When the heat of fusion of the resin particles is within this numerical range, foamed particles with good in-moldability can be stably obtained, and molded articles with excellent compressibility can be stably obtained. From this viewpoint, the heat of fusion of the resin particles is more preferably 75 J / g or more and 105 J / g or less, and even more preferably 80 J / g or more and 100 J / g or less.

[0071] The heat of fusion of the resin particles can be determined, similar to the heat of fusion of impact PP, based on the DSC curve obtained by differential scanning calorimetry (DSC) in accordance with JIS K7122:2012 during the second heating.

[0072] (Acetone-insoluble content in n-decane extract of resin particles) It is preferable that the amount of acetone-insoluble content (A(insol)) in the n-decane extract is 0.05 g or more and 0.3 g or less per gram of resin particles. The amount of acetone-insoluble content (A(insol)) in the n-decane extract of resin particles per gram of resin particles is (A(insol)) Ｐ It is sometimes referred to as such.

[0073] The resin particle A (insol) typically contains rubbery components, including ethylene propylene rubber derived from impact PP. Therefore, (A (insol)) Ｐ This can be used as an indicator of the impact PP component content in the resin particles. Furthermore, regarding the content of rubber-like material in the resin particles used to form foamed particles, it is conceivable that this content may affect the compressible properties of the in-molded product formed from the foamed particles. (A(insol)) Ｐ However, if the value satisfies the numerical range described above, the amount of rubbery material contained in the resin particles is (A (insol)) Ｐ The amount is appropriate for the following effects. Specifically, it is possible to maintain the in-moldability when forming an in-molded body from foamed particles while improving the impact resistance of the in-molded body. Furthermore, it is possible to reduce the change in stress of the in-molded body that occurs with increasing compressive strain. That is, (A(insol)) Ｐ However, by satisfying the numerical range described above, it becomes easy to obtain foamed particles that can form molded articles with good in-moldability and exhibit properties derived from impact polypropylene.

[0074] From the perspective of making properties derived from impact polypropylene more likely to manifest, (A (insol)) Ｐ The lower limit is preferably 0.08 g, and more preferably 0.12 g.

[0075] From the perspective of easily obtaining foamed particles with good in-moldability in a stable manner, (A (insol)) Ｐ The upper limit is preferably 0.25 g, and more preferably 0.2 g.

[0076] The acetone-insoluble components (A(insol)) contained in the n-decane extract of resin particles can be obtained using the same method as for A(insol) of impact PP. Specifically, the resin particles are heated in n-decane at 145°C and then cooled to 23°C to obtain the n-decane extract. The n-decane extract is then added to acetone. At this time, the acetone-insoluble components (A(insol)) in the n-decane extract precipitate.

[0077] (A(insol)) Ｐ This is calculated as follows: The mass of precipitate (acetone-insoluble matter) contained in the n-decane extract of the resin particles is obtained using the method described above. Then, based on the mass of precipitate (acetone-insoluble matter) contained in the n-decane extract of the resin particles and the mass of the resin particles used in the measurement, the amount of A (insol) of the resin particles per gram of resin particles is calculated. This calculated value is (A (insol)). Ｐ That is the case.

[0078] [1-2 Manufacturing of Foamed Particles] An example of a method for manufacturing polypropylene resin foamed particles will be described in detail below.

[0079] Polypropylene resin foam particles are manufactured by foaming polypropylene resin particles. This foaming process involves foaming resin particles containing a foaming agent. This allows for the production of foamed particles. Specifically, this can be achieved by performing a step of preparing the polypropylene resin particles (resin particle preparation) and a step of foaming the resin particles, as shown below.

[0080] (1. Preparation of Resin Particles) Resin particles can be manufactured as follows: Prepare an extruder equipped with a die on the downstream side. Supply impact PP and resin A to the extruder, and heat and knead the impact PP and resin A in the extruder. This yields a mixed resin of impact PP and resin A in a molten state. The molten mixed resin is extruded from a die attached to the downstream side of the extruder in a shape such as a strand. The extruded material is taken up by a take-up machine or the like and cut to the desired length. This yields resin particles composed of a mixed resin of impact PP and resin A. The impact PP and resin A supplied to the extruder are the impact PP and resin A described above, respectively, which constitute the resin particles.

[0081] Furthermore, the extruder may be supplied with foam regulators, various additives, and other resins. Examples of other resins include those described above in "[Resins other than the impact PP and resin A that constitute the mixed resin]".

[0082] Impact PP and resin A may be supplied to the extruder separately, or they may be supplied to the extruder as a pre-mixed mixture.

[0083] (2. Foaming of Resin Particles) The method for foaming the resin particles obtained using the above-described process is not particularly limited, and direct foaming methods can be employed. Next, we will continue by explaining an example of a method for foaming resin particles.

[0084] A pressure vessel is prepared. An autoclave or the like can be used as an example of a pressure vessel. The pressure vessel is configured to allow the inside of the pressure vessel to be opened and closed to the outside at a predetermined location. The pressure vessel is also configured to allow the pressure inside the pressure vessel, which has been built up in a sealed state, to be released.

[0085] Resin particles and a dispersion medium are supplied to a pressure vessel, and the resin particles are dispersed in the dispersion medium. Water or other materials can be used as the dispersion medium. Furthermore, a foaming agent is injected under pressure into the sealed pressure vessel, and the pressure vessel is heated so that the temperature inside the pressure vessel is above the softening temperature of the resin particles. In this way, resin particles impregnated with the foaming agent can be obtained. The pressure vessel is configured such that one end below the upper surface of the dispersion medium inside the pressure vessel (or the water surface if the dispersion medium is water) can be opened.

[0086] After impregnating resin particles with a foaming agent, the inside of a pressure vessel is maintained at a predetermined pressure, and one end of the pressure vessel below the upper surface of the dispersion medium is opened. At this time, the resin particles containing the foaming agent, along with the dispersion medium such as water, are released from the pressure vessel into an atmosphere with a pressure lower than the pressure inside the vessel (usually atmospheric pressure), causing the resin particles to foam. In this way, foamed particles are obtained by the foaming of the resin particles.

[0087] To adjust the bubble diameter of the foamed particles to a desired range, it is preferable that a bubble regulator is added to the resin particles. Examples of bubble regulators include inorganic substances such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, and alum. The amount of bubble regulator added is preferably 0.001 to 1 part by mass, and more preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of resin particles.

[0088] A dispersant may be used to prevent the fusion of resin particles within the pressure vessel. Any dispersant, whether inorganic or organic, can be used, as long as it does not dissolve in the dispersion medium and does not melt upon heating. It is preferable to use an inorganic dispersant.

[0089] Suitable inorganic dispersants include powders such as kaolin, talc, mica, aluminum oxide, titanium oxide, and aluminum hydroxide. The average particle size of the dispersant is preferably 0.001 to 100 μm, and particularly preferably 0.001 to 30 μm. Furthermore, the amount of dispersant added is preferably 0.01 to 10 parts by mass per 100 parts by mass of resin particles.

[0090] The average weight per resin particle supplied to the pressure vessel is not particularly limited, but is preferably 0.02 mg or more and 10 mg or less, and more preferably 0.1 mg or more and 5 mg or less.

[0091] Examples of blowing agents include organic and inorganic physicoblasting agents. Examples of organic physicoblasting agents include organic compounds such as propane, isobutane, butane, isopentane, pentane, cyclopentane, hexane, cyclobutane, cyclohexane, chlorofluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, and 1-chloro-1,2,2,2-tetrafluoroethane. Examples of inorganic physicoblasting agents include nitrogen, carbon dioxide, argon, and air. From the viewpoint of superior productivity, it is preferable to use an inorganic physicoblasting agent, and in particular, it is preferable to use an inorganic physicoblasting agent selected from nitrogen, air, and carbon dioxide. A mixture of two or more substances selected from the various substances listed above may be used as the blowing agent.

[0092] The amount of foaming agent used is appropriately selected depending on the type of foaming agent and the relationship between the apparent density of the foamed particles to be obtained and the foaming temperature.

[0093] The dispersion medium used to disperse resin particles within a pressure vessel is not particularly limited as long as it does not dissolve the resin particles. Examples of dispersion mediums include water, ethylene glycol, glycerin, methanol, and ethanol. From the viewpoint of ease of handling, water is preferably selected as the dispersion medium.

[0094] In addition to the dispersant, a dispersion aid may be added to the pressure vessel. Suitable dispersion aids include anionic surfactants such as sodium dodecylbenzenesulfonate and sodium oleate, and aluminum sulfate. It is preferable to add the dispersion aid in an amount of 0.001 to 5 parts by mass per 100 parts by mass of resin particles.

[0095] The pressure difference when releasing resin particles containing a foaming agent is preferably approximately 0.5 MPa to 4 MPa, from the viewpoint of obtaining the effect of setting the density of the foamed particles to an appropriate value. The above-mentioned pressure difference refers to the difference between the pressure inside the pressure vessel and the pressure of the pressure atmosphere which is lower than the pressure inside the pressure vessel.

[0096] (3. When manufacturing resin particles using recycled impact PP) Regarding the mixed resin used in (1. Preparation of resin particles) above, we will explain the case where the impact PP constituting the mixed resin is recycled polypropylene resin (recycled impact PP).

[0097] As mentioned above, recycled polypropylene resins can include polypropylene resins derived from pre-consumer materials and polypropylene resins derived from post-consumer materials.

[0098] Impact PP can be produced by using recycled polypropylene resin and appropriately carrying out the steps shown in (1. Preparation of Resin Particles) above. At this time, the recycled polypropylene resin is prepared so as to satisfy at least the following conditions. The following three conditions are: The first condition is the MFR of Impact PP (MFR Ｉ The second condition is that the MFR of resin A is greater than 10 g / 10 min and 80 g / 10 min or less. Ａ The third condition is that the amount is less than 3 g / 10 min. The mass ratio of impact PP to resin A contained in the mixed resin (resin particles) satisfies impact polypropylene: the polypropylene-based resin A = 97:3 to 40:60 (assuming the total of impact PP and resin A is 100 parts by mass).

[0099] Foamed particles can be produced by appropriately carrying out the steps described in (2. Foaming of Resin Particles) above using the obtained resin particles.

[0100] [1-3 Effects of the Method for Manufacturing Foamed Particles] When manufacturing molded articles by in-mold molding using foamed particles containing a large amount of impact PP, the secondary foaming properties of the foamed particles were low, and gaps tended to form between the foamed particles in the resulting molded articles. In addition, the fusion properties between the foamed particles tended to be low, and there was room for improvement in terms of in-moldability. Furthermore, it is conceivable to increase the steam pressure and molding temperature during in-mold molding in order to improve the secondary foaming properties and fusion properties of the foamed particles. However, in this case, there was room for improvement in terms of the tendency for the closed-cell ratio of the molded article to decrease and the tendency for dents to occur in the molded article after molding. Moreover, even when a molded article was obtained, the range of steam pressures in which the molded article could be molded was narrow, and depending on the shape of the molded article, it was difficult to obtain a good product.Therefore, there was room for improvement in terms of obtaining foamed particles that can stably produce good products even when molding various molded articles, such as molded articles with thickness differences in the constituent parts of the molded article.

[0101] The manufacturing method of the present invention (method for manufacturing polypropylene resin foam particles) allows for a wide range of steam pressure conditions that enable the production of good molded articles from the above-mentioned viewpoint. In other words, the manufacturing method of the present invention makes it possible to obtain foam particles that are excellent in mold moldability in terms of the wide range of steam pressure conditions. Furthermore, the molded articles obtained by the manufacturing method of the present invention can contain a large amount of impact PP. For this reason, the manufacturing method of the present invention makes it possible to easily obtain molded articles with excellent compressibility. Furthermore, the manufacturing method of the present invention makes it possible to obtain foam particles that enable the production of good molded articles from the following predetermined viewpoint. The predetermined viewpoint is that the foam particles have good fusion properties with each other and that the spaces between the foam particles are sufficiently filled.

[0102] Furthermore, according to the manufacturing method of the present invention, a good molded article can be obtained using foamed particles containing a certain amount of impact PP or more. Therefore, according to the manufacturing method of the present invention, efficient recycling of post-consumer materials including impact PP can be achieved from the viewpoint of reducing environmental impact. Recycled impact PP tends to have a relatively high MFR, such as an MFR of 20 g / 10 min or more. When such impact PP is used, the in-moldability of the resulting foamed particles tends to decrease. In this respect, the present invention makes it possible to obtain foamed particles with good in-moldability.

[0103] Next, a description of the polypropylene resin foam particles according to the present invention will be provided.

[0104] [2. Foamed Particles] The polypropylene resin foamed particles according to the present invention are polypropylene resin foamed particles that can be obtained by the manufacturing method of the present invention. The polypropylene resin foamed particles according to the present invention may be referred to as foamed particles. Alternatively, the polypropylene resin foamed particles according to the present invention may be referred to as foamed particles of the present invention.

[0105] The foamed particles of the present invention are composed of a polypropylene-based resin composition.

[0106] The polypropylene resin composition includes impact PP. As the polypropylene resin composition, the mixed resin described in the manufacturing method of the present invention described above can be used. Furthermore, the polypropylene resin composition corresponds to the components of the resin particles described in the manufacturing method of the present invention shown in [1. Method for manufacturing foamed polypropylene resin particles] above.

[0107] Impact PP is the same as the impact PP that constitutes the mixed resin described in the manufacturing method of the present invention described above. The properties and other conditions of the impact PP that constitutes the polypropylene resin composition also satisfy the same conditions as the impact PP that constitutes the mixed resin. Therefore, in the description of the foamed particles of the present invention, the descriptions of the polypropylene resin composition and impact PP are omitted.

[0108] (Melt flow rate of polypropylene resin composition) The melt flow rate of the polypropylene resin composition measured under the conditions of a temperature of 230°C and a load of 2.16 kg for the foamed particles of the present invention is 5 g / 10 min or more and 50 g / 10 min or less. The melt flow rate of the polypropylene resin composition is MFR Ｃ It is sometimes referred to as MFR. Ｃ When the above range is achieved, it becomes easier to form a molded article that has good in-moldability and excellent compressibility. From the viewpoint of such effects, MFR Ｃ Regarding the upper limit, MFR Ｃ It is more preferable that the amount is 45 g / 10 min or less, and even more preferable that it is 40 g / 10 min or less. MFR of the polypropylene resin composition Ｃ The numerical range and effect are determined by the MFR of the resin particles (MFR Ｐ The numerical range and effects are the same as for the polypropylene resin composition. Ｃ The same applies to the preferred numerical range.

[0109] Melt flow rate (MFR) of polypropylene resin composition constituting foamed particles Ｃ This value is measured under the conditions of a temperature of 230°C and a load of 2.16 kg, in accordance with JIS K7210-1:2014.

[0110] (Melting Tension of Foamed Particles) In the foamed particles of the present invention, the melting tension of the polypropylene resin composition at 170°C is 8 mN or more and 40 mN or less. Having a melting tension within the above numerical range allows for appropriate secondary foaming properties to be imparted to the foamed particles, resulting in foamed particles with excellent in-mold moldability. From this viewpoint, it is more preferable that the melting tension of the polypropylene resin composition at 170°C is 10 mN or more and 35 mN or less.

[0111] (Measurement of Melt Tension) The melt tension is measured using a measuring instrument such as the Capillograph 1D manufactured by Toyo Seiki Seisakusho Co., Ltd. First, prepare a measuring instrument equipped with a cylinder with a diameter of 9.55 mm and a length of 350 mm, and an orifice with a nozzle diameter of 2.095 mm and a length of 8.0 mm. Perform the following operations using the measuring instrument. Set the temperature of the cylinder and orifice to 170°C, place the foamed particles to be measured into the cylinder, and leave the sample for 4 minutes. Note that foamed particles that have been defoamed by heating and volume reduction may be used as the sample. The sample will be molten resin. Next, extrude the molten resin from the orifice in a string-like manner at a piston speed of 10 mm / min. The extruded string-like material is placed on a tension-sensing pulley with a diameter of 45 mm, and the string-like material is taken up by a take-up roller while increasing the take-up speed at a constant acceleration so that the take-up speed reaches 200 m / min from 6 m / min in 30 seconds, and the tension at the point when the string-like material breaks is obtained. The above operation is performed a total of 10 times using different measurement samples. This results in 10 tension measurements. The first median value is taken as the arithmetic mean of the multiple tension measurements obtained from the 10 tension measurements. From the multiple tension measurements described above, the three largest values ​​and the three smallest values ​​are removed. The remaining four tension values ​​are the first median values. The value obtained by the arithmetic mean of the first median values ​​is defined as the melt tension (mN) in this invention.

[0112] Furthermore, if the string-like material does not break even when the draw speed reaches 200 m / min when measuring the molten tension using the method described above, the tension value (mN) obtained by maintaining a constant draw speed of 200 m / min shall be adopted. That is, in the same manner as described above, the molten resin composed of the sample to be measured is extruded in a string-like form from the orifice. The extruded string-like material is placed on a tension detection pulley, and the draw roller is rotated while increasing the draw speed at a constant acceleration so that the draw speed reaches 200 m / min from 6 m / min to 200 m / min in 30 seconds, and the machine is waited until the rotation speed reaches 200 m / min. After the rotation speed reaches 200 m / min, data collection for molten tension is started and stopped after 30 seconds. The average value (Tave) of the maximum tension (Tmax) and minimum tension (Tmin) obtained from the tension load curve obtained during these 30 seconds shall be taken as the measured tension value. Here, Tmax is the value obtained by dividing the total number of peak values ​​detected in the tension load curve by the number of detected peaks, and Tmin is the value obtained by dividing the total number of dips detected in the tension load curve by the number of detected dips.

[0113] (Melting elongation of foamed particles) In the foamed particles of the present invention, it is preferable that the melting elongation of the polypropylene resin composition at 170°C is 8 m / min or more and 100 m / min or less. When the melt tension is within the above range and the melting elongation of the foamed particles is within a specific range, it becomes easier to impart appropriate secondary foaming properties to the foamed particles, and it becomes easier to obtain foamed particles with excellent in-moldability. From this viewpoint, it is more preferable that the melting elongation of the polypropylene resin composition at 170°C is 10 m / min or more and 80 m / min or less.

[0114] (Measurement of melt elongation) Melt elongation is measured using a method similar to that for melt tension. Specifically, as described in the above explanation of the measurement of melt tension, the measuring instrument is prepared and the above operations are performed. Then, the drawing speed at the time when the string-like material breaks is specified, and this is taken as the value of melt elongation. The measurement of melt elongation is carried out 10 times. Among the plurality of measured values of tension obtained from the 10 measurements of melt elongation, three values in order from the largest value and three values in order from the smallest value are excluded. The value obtained by the arithmetic mean of the melt elongation values for the remaining four tension values is taken as the melt elongation (m / min) in the present invention. In addition, when the string-like material does not break even when the drawing speed reaches 200 m / min, the value of melt elongation in that measurement is taken as 200 m / min.

[0115] (Melting point of polypropylene-based resin composition) The melting point Tm of the polypropylene-based resin composition Ｃ is preferably 150°C or higher and 165°C or lower. When Tm Ｃ is a value within this numerical range, the foamed particles formed using the resin particles can be made to have excellent in-mold formability. From the viewpoint of this effect, the melting point Tm Ｃ is preferably 152°C or higher and 164°C or lower. The numerical range and effect of the melting point of the polypropylene-based resin composition are the same as those for the numerical range and effect of the melting point of the resin particles. This also applies to the preferred numerical range of the melting point of the polypropylene-based resin composition.

[0116] The melting point Tm of the polypropylene-based resin composition Ｃ can be specified by carrying out differential scanning calorimetry (DSC) in accordance with JIS K7121:2012, except that foamed particles are used as the measurement sample, in the same manner as the method for measuring the melting point Tm Ｐ of the resin particles. Incidentally, the melting point of the resin particles and the melting point of the polypropylene-based resin composition constituting the foamed particles obtained by foaming the resin particles generally correspond. Therefore, the melting point of the resin particles can also be regarded as the melting point of the polypropylene-based resin composition.

[0117] (Amount of acetone-insoluble matter contained in n-decane extract) It is preferable that the amount of acetone-insoluble matter (A(insol)) contained in the n-decane extract of the polypropylene-based resin composition is 0.05 g or more and 0.3 g or less per 1 g of the polypropylene-based resin composition. The amount of acetone-insoluble matter (A(insol)) contained in the n-decane extract of the polypropylene-based resin composition per 1 g of the polypropylene-based resin composition is (A(insol)) Ｃ may be referred to as.

[0118] (A(insol)) Ｃ By being a value that satisfies the above numerical range, it is possible to easily manufacture a molded body having good in-mold formability and exhibiting characteristics derived from impact PP. From the viewpoint of facilitating the manifestation of characteristics derived from impact PP, (A(insol)) Ｃ preferably has a lower limit of 0.08 g, more preferably 0.12 g. From the viewpoint of easily and stably obtaining foamed particles having good in-mold formability, the upper limit of (A(insol)) Ｃ is preferably 0.25 g, more preferably 0.2 g. The numerical range and effect of (A(insol)) Ｃ are the same as the numerical range and effect of (A(insol)) Ｐ This also applies to the preferable numerical range of (A(insol)) Ｃ

[0119] (A(insol)) Ｃ can be specified by using the same method as (A(insol)) Ｐ except that foamed particles are used as the measurement sample. The amount of acetone-insoluble matter contained in the n-decane extract of the resin particles generally corresponds to the amount of acetone-insoluble matter contained in the n-decane extract of the polypropylene-based resin composition constituting the foamed particles obtained by foaming the resin particles. Therefore, the amount of acetone-insoluble matter contained in the n-decane extract of the resin particles can also be regarded as the amount of acetone-insoluble matter contained in the n-decane extract of the polypropylene-based resin composition.

[0120] The polypropylene resin foam particles according to the present invention, which are composed of a polypropylene resin composition containing impact polypropylene, have a melt flow rate within a specific range and a melt tension within a specific range of the polypropylene resin composition constituting the foam particles. Foam particles having such characteristics exhibit excellent in-moldability in terms of a wide range of steam pressure conditions. Furthermore, the molded article obtained by in-molding the foam particles of the present invention can contain a large amount of impact PP. Therefore, a molded article with excellent compressibility can be easily obtained. Foam particles having such characteristics can preferably be manufactured by the manufacturing method of the present invention.

[0121] Furthermore, the foamed particles of the present invention that can be produced by the manufacturing method of the present invention have the following bulk density, closed cell ratio, and high-temperature peak.

[0122] (Bulk density of foamed particles) According to the manufacturing method of the present invention, the foamed particles have a bulk density of 10 kg / m³. ３ More than 200kg / m ３ The following can be obtained: The bulk density of the foamed particles is 10 kg / m³. ３ More than 200kg / m ３ If the values ​​satisfy the following numerical range, it is possible to easily obtain a molded body that is both lightweight and has good mechanical strength. From the perspective of enhancing this effect, the bulk density of the foam particles should be 12 kg / m³. ３ More than 100kg / m ３ It is more preferable that the following conditions apply: 15 kg / m ３ More than 80kg / m ３ It is even more preferable that the following conditions apply: 20 kg / m ３ More than 70kg / m ３ The following is particularly preferable. However, in the manufacturing method of the present invention, it is not prohibited that the obtained polypropylene resin foam particles do not satisfy the following descriptions (numerical values, etc.) regarding their bulk density, the closed-cell ratio described later, and the high-temperature peak described later.

[0123] (Method for measuring bulk density) The bulk density of foamed particles can be determined, for example, by the following method: Allow the foamed particles to stand for 24 hours or more in an environment of 50% relative humidity, 23°C, and 1 atm pressure to adjust the state of the foamed particles. Fill a graduated cylinder with the foamed particles obtained in this way and stabilize the filling height of the foamed particle group in the graduated cylinder by lightly tapping the floor surface several times with the bottom of the graduated cylinder. Read the bulk volume (unit: L) of the foamed particle group from the scale of the graduated cylinder. Then, convert the value obtained by dividing the mass (unit: g) of the foamed particle group in the graduated cylinder by the bulk volume mentioned above. This gives the bulk density (unit: kg / m³) of the foamed particles. ３ ) can be obtained.

[0124] (Closed-cell ratio of foamed particles) According to the manufacturing method of the present invention, foamed particles having a closed-cell ratio of 70% or more can be obtained. When the closed-cell ratio of the foamed particles is within the above range, the in-moldability of the foamed particles is further improved, and a good molded product can be easily obtained over a wide range of molding pressures. From the viewpoint of enhancing this effect, the closed-cell ratio of the foamed particles is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0125] (Method for measuring the closed-cell ratio) The closed-cell ratio of foamed particles is a value measured using an air-comparison hydrometer based on ASTM-D2856-70 Procedure C. Next, an example of the method for measuring the closed-cell ratio of foamed particles will be explained. A sample with a bulk volume of approximately 20 cm³ will be used for measurement. ３The foamed particles are prepared after conditioning. The sample is placed in a graduated cylinder containing ethanol, and the sample is submerged in the ethanol. The liquid level before the sample is placed in the cylinder is compared with the liquid level after the sample is submerged. The apparent volume Va of the sample is measured based on the rise in the liquid level. The sample, whose apparent volume Va has been measured, is thoroughly dried. Then, in accordance with procedure C described in ASTM-D2856-70, the true volume Vx of the sample is measured using an air-comparison hydrometer (for example, Beckman Model 1000 AirComparison Phycmeter, manufactured by Tokyo Science Co., Ltd.). Using the volume values ​​Va and Vx, the percentage of closed cells (%) of the sample is calculated based on the following formula (1). The above procedure is repeated five times with different samples. This allows the percentage of closed cells in five samples to be calculated. The arithmetic mean of the calculated closed-cell ratios (N=5) is then considered to be the closed-cell ratio of the foamed particles.

[0126]

[0127] However, the values ​​of Vx, Va, W, and ρ in formula (1) above, with respect to the closed-cell ratio of the foamed particles, are as follows: Vx: The true volume of the foamed particles measured by the above method, that is, the sum of the volume of the resin constituting the foamed particles and the total volume of the closed-cell portion within the foamed particles (unit: cm ３ ) Va: The apparent volume of the foaming particles, measured from the rise in the liquid level when the foaming particles are submerged in a graduated cylinder containing ethanol (unit: cm³) ３ ) W: Mass of foamed particles (sample for measurement) (unit: g) ρ: Density of the resin constituting the foamed particles (unit: g / cm³) ３ )

[0128] (High-temperature peak (temperature and thermal melting amount)) According to the manufacturing method of the present invention, foamed particles can be obtained that have a crystalline structure such that a first melting peak and one or more second melting peaks located at a higher temperature than the first melting peak appear on the DSC curve. When foamed particles have such a crystalline structure, the in-moldability of the foamed particles can be improved. The first melting peak is a melting peak due to the melting of components intrinsic to the resin constituting the foamed particles. The first melting peak can also be said to be a melting peak that appears due to the melting of crystals normally present in the resin constituting the foamed particles. The first melting peak is sometimes referred to as an intrinsic peak. The second melting peak that appears at a higher temperature than the first melting peak is referred to as a high-temperature peak. The high-temperature peak (second melting peak) is presumed to appear due to the melting of secondary crystals formed in the resin components during the manufacturing process of the foamed particles. That is, when a high-temperature peak appears on the DSC curve, it is presumed that secondary crystals are formed in the resin components.

[0129] The fact that the foamed particles obtained by the manufacturing method of the present invention have a crystalline structure having the high-temperature peak described above can be determined by obtaining a DSC curve using the foamed particles as the measurement target. That is, a DSC curve is obtained by using the foamed particles obtained by the manufacturing method of the present invention as a sample and performing differential scanning calorimetry (DSC) in accordance with JIS K7122:2012. Then, a judgment can be made based on the obtained DSC curve. Note that when performing DSC, it is sufficient to use 1 to 3 mg of foamed particles as a sample.

[0130] The acquisition of the DSC curve and the determination of intrinsic and high-temperature peaks based on the DSC curve can be carried out as follows. In accordance with JIS K7122:2012, a DSC curve is obtained by heating from 23°C to 230°C at a heating rate of 10°C / min (i.e., the first heating). The obtained DSC curve shows both the intrinsic and high-temperature peaks. After the first heating, the temperature is cooled from 230°C to 23°C at a cooling rate of 10°C / min. Then, when heating again from 23°C to 230°C at a heating rate of 10°C / min (i.e., the second heating), only the intrinsic peak is observed in the obtained DSC curve. Therefore, by comparing the DSC curve obtained during the first heating and the DSC curve obtained during the second heating, the intrinsic and high-temperature peaks can be distinguished.

[0131] According to the manufacturing method of the present invention, it is preferable to obtain foamed particles such that, in the DSC curve of the foamed particles, both an intrinsic peak and a high-temperature peak appear in the first DSC curve, and only an intrinsic peak appears in the second DSC curve.

[0132] (Heat of melt at high temperature peak) The heat of melt at the high temperature peak of the foamed particles is preferably 5 J / g or more and 50 J / g or less. When the heat of melt at the high temperature peak is within this range, the foamed particles exhibit excellent in-moldability, and a molded article with good physical properties can be stably obtained. From the viewpoint of achieving a good balance of these effects, the heat of melt at the high temperature peak of the foamed particles is more preferably 10 J / g or more and 45 J / g or less, and even more preferably 15 J / g or more and 40 J / g or less.

[0133] (Method for measuring the heat quantity of the high-temperature peak) The heat quantity of the high-temperature peak of foamed particles is calculated from the DSC curve of the foamed particles measured according to JIS K7122:2012 as follows. First, a DSC curve is obtained by performing differential scanning calorimetry on a sample of foamed particles (1 mg to 3 mg) heated from 23°C to 230°C at a heating rate of 10°C / min. The flow rate of nitrogen gas in the measurement environment is set to 30 mL per minute. If the foamed particles have a high-temperature peak, the DSC curve will show an intrinsic peak and a high-temperature peak located at a higher temperature than the intrinsic peak.

[0134] On the DSC curve, draw a straight line L1 connecting point α, which corresponds to 80°C, and point β, which corresponds to the melting termination temperature T of the foamed particles. Note that the melting termination temperature T is the high-temperature end point of the high-temperature peak.

[0135] A straight line L2 is drawn parallel to the vertical axis of the graph showing the DSC curve, passing through the pole γ located between the intrinsic peak and the high-temperature peak. This line L2 separates the intrinsic peak from the high-temperature peak. The heat of fusion of the high-temperature peak can be calculated based on the area enclosed by the part of the DSC curve that forms the high-temperature peak, and the lines L1 and L2.

[0136] (Coating Layer) The foamed particles obtained by the manufacturing method of the present invention may have a coating layer formed on them. By producing multilayer foamed particles having a foamed particle body and a coating layer by the manufacturing method of the present invention, it is expected that the fusion properties between the foamed particles during in-mold molding will be made easier to achieve. The coating layer may be present on the entire surface of the foamed particle or on a part of the surface. Examples of resins constituting the coating layer include polyolefin resins. In this case, the polypropylene resin composition constituting the foamed particle body corresponds to the polypropylene resin composition constituting the foamed particles of the present invention.

[0137] The method for forming a coating layer on the surface of foamed particles is not particularly limited. Examples include a method of foaming multilayer resin particles having a coating layer covering the resin particle body, or a method of attaching a coating layer to the surface of foamed particles after obtaining them. When foamed particles are obtained by foaming multilayer resin particles, it is preferable to use an extruder capable of co-extrusion when manufacturing the resin particles. As an example of a method using an extruder capable of co-extrusion, it is preferable to use an extruder to co-extrude a molten mixture for forming the resin particle body and a molten resin for forming the coating layer, thereby coating the surface of the resin particle body with a coating layer. The resin particle body undergoes foaming when the resin particles are foamed. When multilayer foamed particles are manufactured, the resin particle body forms the foamed particle body.

[0138] [3. Molded Article] A polypropylene resin foam particle molded article can be manufactured by performing in-mold molding as follows using the foam particles obtained by the manufacturing method of the present invention. The same applies when manufacturing the multilayer foam particles described above using the manufacturing method of the present invention. Next, an example of in-mold molding will be described.

[0139] A mold is prepared according to the shape of the molded body. Foam particles are filled into the mold. Furthermore, a heating medium such as steam is supplied into the mold to soften the foam particles, induce secondary foaming, and cause the foam particles to fuse together. After that, the mold is cooled and released to obtain the molded body.

[0140] The foamed particles obtained by the manufacturing method of the present invention are excellent in terms of in-moldability. Excellent in-moldability means that the moldable range of conditions is excellent when manufacturing a molded body. In the evaluation of moldability (evaluation of in-moldability) in the present invention, the evaluation of moldability is determined when the shape of the peripheral edge of the test specimen, the state of fusion, and the presence or absence of indentations meet predetermined conditions. The test specimen described above is a molded body obtained by in-mold molding using foamed particles. The predetermined conditions will also be described in the examples below. Excellent in terms of the moldable range of conditions means that there is a wide range of pressure conditions in which moldability is recognized. When there is a wide range of pressure conditions in which moldability is recognized, it becomes easy to manufacture a molded body that is excellent overall, even if the shape of the molded body has differences in wall thickness.

[0141] By using the foamed particles obtained by the manufacturing method of the present invention, it is possible to obtain a molded article having the following density and closed-cell ratio.

[0142] (Density of the molded body) By using the foamed particles obtained by the manufacturing method of the present invention, the density of the molded body is 10 kg / m³. ３ More than 200kg / m ３ It is possible to obtain a product that satisfies the following numerical range. When the density of the molded product satisfies the numerical range described above, the molded product using the foamed particles obtained by the manufacturing method of the present invention tends to be lightweight and have excellent compressibility.

[0143] From the perspective of improving the compressible properties of the molded body, the lower limit of the density of the molded body is set at a density of 12 kg / m³. ３ Preferably, it is 15 kg / m ３ It is more preferable that the amount be greater than or equal to 20 kg / m ３ It is even more preferable that the above conditions are met.

[0144] From the perspective of ensuring the lightweight nature of the molded body, the upper limit of the density of the molded body is set at 100 kg / m³. ３ Preferably, it is 80 kg / m ３It is more preferable that the following conditions are met: 70 kg / m ３ The following is even more preferable:

[0145] The density of a molded body is calculated by dividing its mass by its volume (determined from its external dimensions) and then performing a unit conversion.

[0146] (Closed-cell ratio of the molded article) By using the foamed particles obtained by the manufacturing method of the present invention, it is possible to obtain a molded article that satisfies a numerical range of 70% or more for the closed-cell ratio. When the closed-cell ratio of the molded article satisfies the numerical range described above, the molded article using the foamed particles obtained by the manufacturing method of the present invention tends to have excellent compressibility.

[0147] From the viewpoint of improving the compressible properties of the molded article, it is preferable that the closed-cell ratio of the molded article be 75% or more, and more preferably 80% or more.

[0148] The closed-cell ratio of the molded body is measured according to ASTM 2865-70 Procedure C, similar to the closed-cell ratio of the foamed particles described above, and is calculated using equation (1) shown for the closed-cell ratio of the foamed particles described above. However, the values ​​of Va, Vx, W, and ρ in equation (1) are those determined by the method described below. A test piece measuring 25 mm in length, 25 mm in width, and 30 mm in height is cut from the center of the molded body, and the product of the length (unit: cm), width (unit: cm), and height (unit: cm) is calculated. The calculated value is the volume of the test piece Va (unit: cm ３ ) Furthermore, the true volume value Vx of the test specimen is measured using an air-comparison hydrometer in accordance with procedure C described in ASTM-D2856-70. When calculating the closed-cell ratio of the molded body, the mass W (unit: g) is the mass of the test specimen made from the molded body, and the density ρ (unit: g / cm³) is used. ３ ρ is the density of the resin constituting the molded body (foamed particles). It is calculated by applying equation (1), which was shown above for the closed-cell ratio of the foamed particles, using the values ​​of volume Va, the true volume Vx of the test specimen, mass W (unit: g), and density ρ.

[0149] The closed-cell ratio of the molded product is calculated for each of the five test specimens, and the arithmetic mean of the closed-cell ratios of the five test specimens is taken as the closed-cell ratio (%) of the molded product.

[0150] (Compression Properties) The compressibility of a molded article can be determined by comparing the values ​​of its 50% compressive stress. The 50% compressive stress of the molded article is measured when the article is molded at the lower limit of the pressure at which it can be molded.

[0151] (50% Compressive Stress) A test specimen of a predetermined shape is taken from the molded body, and the 50% compressive stress of the test specimen is determined by performing a compression test on the test specimen at a compression rate of 10 mm / min according to the method specified in JIS K7220:2006. This value is determined as the 50% compressive strength of the molded body.

[0152] [4. Examples of Application] Molded articles formed using foamed particles obtained by the manufacturing method of the present invention can be used, for example, as packaging and cushioning materials for electrical and electronic components, packaging and cushioning materials for automobile parts, vehicle components such as bumpers and seat core materials, etc.

[0153] The manufacturing method of the present invention will be further explained using examples.

[0154] To carry out Examples 1 to 8 and Comparative Examples 1 to 8, the following resins, bubble regulators, and apparatus were prepared.

[0155] (Resin) Impact polypropylene (Impact PP) and polypropylene-based resins were prepared as resins. Five types of Impact PP resins were prepared, as shown in Table 1. The five types of resins shown in Table 1 are distinguished by the codes X1, X2, X3, X4, and X5, respectively. In Tables 3 and 4, the prepared Impact PP is identified using the codes X1, X2, X3, X4, and X5.

[0156] All prepared impact polypropylenes (IPPs) have a morphology in which rubbery phases (domains) containing ethylene propylene rubber are dispersed in a polypropylene resin phase (matrix). Furthermore, the IPPs corresponding to types X1 to X4 are virgin impact polypropylenes. Type X1 is product name: J707G (manufactured by Prime Polymer Co., Ltd.), Type X2 is product name: J709QG (manufactured by Prime Polymer Co., Ltd.), Type X3 is product name: J704UG (manufactured by Prime Polymer Co., Ltd.), and Type X4 is product name: BC10HFR (manufactured by Nippon Polypropylene Co., Ltd.). The IPP corresponding to type X5 is recycled impact polypropylene, product name: PLC-A02 (manufactured by Planic Co., Ltd.). The average diameter of the rubbery phases (domains) in the IPP corresponding to type X1 was 0.9 μm. The average diameter of the rubbery phases (domains) in the IPP corresponding to type X5 was 1.2 μm. The average diameter of the rubbery phase in impact PP was measured based on the method described above (Average diameter of the rubbery phase (domain)).

[0157] Five types of polypropylene resins were prepared, as shown in Table 2. These five resins are distinguished by the codes Y1, Y2, Y3, Y4, and Y5. In Tables 3 and 4, the prepared polypropylene resins are identified using the codes Y1, Y2, Y3, Y4, and Y5. Polypropylene resins of types Y1 to Y3 correspond to the aforementioned resin A. The polypropylene resin of type Y1 is product name: B221WC (manufactured by Prime Polymer Co., Ltd.), the polypropylene resin of type Y2 is product name: E-330GV (manufactured by Prime Polymer Co., Ltd.), and the polypropylene resin of type Y3 is product name: E-100GV (manufactured by Prime Polymer Co., Ltd.). Polypropylene resins of types Y4 and Y5 are polypropylene resins different from both Impact PP and resin A. The resins corresponding to Y1, Y2, Y4, and Y5 are propylene-based random copolymers (indicated as rPP in the material column in Table 2). The resin corresponding to type Y3 polypropylene resin is homopolypropylene (indicated as hPP in the material column in Table 2).

[0158] The values ​​listed in the melt flow rate column of Tables 1 and 2 are the melt flow rate values ​​(g / 10min) measured under the conditions of a temperature of 230°C and a load of 2.16 kg, based on the method specified in JIS K7210-1:2014. The values ​​listed in the density column of Tables 1 and 2 are the values ​​(g / cm³) measured by the method specified in Method A (water displacement method) described in JIS K7112:1999. ３ The values ​​listed in the melting point column of Tables 1 and 2 are measured in °C according to the method for measuring the transition temperature of plastics specified in JIS K7121:2012, as described in the explanation of the melting point of Impact PP and the melting point of resin A above. The values ​​listed in the heat of fusion column of Tables 1 and 2 are measured according to the method for measuring the transition heat of plastics specified in JIS K7122:2012.

[0159] The values ​​listed in the tensile modulus column of Tables 1 and 2 were measured according to the method specified in JIS K 7161-2:2014. Specifically, the tensile modulus was determined as follows.

[0160] Using a heat press machine, 4 mm thick sheets were produced by heat pressing each resin listed in Tables 1 and 2 (resins corresponding to types X1 to X5 in Table 1 and types Y1 to Y5 in Table 2) at 200°C. The obtained sheets were punched out into dumbbell-shaped 1A-type specimens to produce 1A-type test pieces. After conditioning the 1A-type test pieces, tensile tests were performed using a Shimadzu Autograph AGS-X universal testing machine at a test speed of 1 mm / min and a gauge length of 75 mm. Based on the results of the tensile tests, the tensile modulus (MPa) of each polypropylene resin was determined.

[0161] The values ​​listed in the "Acetone-Insoluble Content per gram of Resin" column in Table 1 represent the amount of acetone-insoluble content (A (insol)) contained in the n-decane extract, as described above. Furthermore, the values ​​listed in the "Acetone-Insoluble Content" column are those measured for each resin in Table 1 (resins corresponding to types X1 to X5 in Table 1) using the method described below.

[0162] (Acetone-insoluble content per gram of resin) Approximately 5 g of resin was accurately weighed as a sample for measurement. The sample (approximately 5 g of resin) was added to 200 ml of n-decane, and the sample and n-decane were heated at 145°C for 30 minutes. At this time, the sample dissolved in the n-decane. The resulting n-decane solution was cooled to 23°C over 2 hours. After further cooling to 23°C, the n-decane solution was left to stand for 30 minutes. At this time, components insoluble in n-decane (components insoluble under 23°C conditions) precipitated from the n-decane solution. The precipitate was removed by filtering the n-decane solution. This yielded an n-decane extract containing n-decane-soluble components (components soluble under 23°C conditions).

[0163] The obtained n-decane extract was added to approximately three times its volume of acetone. The solution containing the n-decane extract was left to stand at 23°C for 18 hours. This allowed the acetone-insoluble components in the n-decane extract to precipitate. The precipitated acetone-insoluble components (precipitate) were collected by filtration. After the collected precipitate was dried, its mass was measured. The measured mass of the precipitate (in grams) was then divided by the mass of the sample (in grams) to calculate the amount of acetone-insoluble components in the n-decane solution per gram of resin (in grams).

[0164]

[0165]

[0166] (Observation of the morphology of impact PP) Using impact PP corresponding to type X1 (impact PP used in Examples 1 to 6 and Comparative Examples 1 to 3), the morphology of impact PP was observed as shown below.

[0167] An observation sample is prepared from type X1 impact PP. The observation sample is embedded in epoxy resin and then stained with ruthenium tetroxide. Next, sections are prepared from the observation sample using ultramicrotol. The sections are placed on the grid of a transmission electron microscope and photographed at a magnification of 5000x. The resulting photographs (TEM images) are shown in Figure 1. Figure 1 is a TEM image, which is a cross-sectional image of impact PP. In Figure 1, a morphology is visually recognized in which the polypropylene phase constituting impact PP is represented as the matrix (in Figure 1, the matrix is ​​indicated by the symbol M), and the rubbery phase containing ethylene propylene rubber is represented as the domain (in Figure 1, the domain is indicated by the symbol D).

[0168] Example 1 (Production of Resin Particles) An extruder was prepared, and impact PP and polypropylene resin as shown in the Example 1 column of Table 3 were supplied to the extruder. Specifically, impact PP corresponding to type X1 and polypropylene resin corresponding to type Y1 (corresponding to resin A) were supplied to the extruder. In addition to the resins mentioned above, a foam regulator was supplied to the extruder.

[0169] The ratio of impact PP to polypropylene resin supplied to the extruder (mixing ratio) is the value (mass ratio) shown in the "Mixing Ratio (%)" column of Table 3. However, the value shown in the "Mixing Ratio (%)" column of Table 3 assumes that the total mass ratio of the resin supplied to the extruder is 100 (%). For example, in Example 1, as shown in Table 3, the mixing ratio of impact PP corresponding to type X1 is 70% (70 mass%), and the mixing ratio of polypropylene resin corresponding to type Y1 is 30% (30 mass%).

[0170] Zinc borate was used as the foam regulator supplied to the extruder. The amount of zinc borate added was 0.05% by mass relative to 100% by mass of the total of Impact PP and polypropylene resin.

[0171] Inside the extruder, the resin was melted and kneaded to form a molten mixed resin of impact PP corresponding to type X1 and polypropylene resin corresponding to type Y1. The mixed resin was extruded through small holes in a die located downstream of the extruder, forming a strand-shaped extruded material. The strand-shaped extruded material was taken up, cooled, and cut to appropriate lengths by a pelletizer. This yielded resin particles.

[0172] (Foaming of Resin Particles) 1 kg of resin particles and 3 L of water as a dispersion medium were supplied into a 5 L pressure vessel (an autoclave was used). Kaolin, sodium alkylbenzenesulfonate, and aluminum sulfate were added to the vessel. Kaolin was used as a dispersant. The amount of kaolin added was 0.3 parts by mass per 100 parts by mass of resin particles. Sodium alkylbenzenesulfonate and aluminum sulfate were both used as dispersion aids. The amount of sodium alkylbenzenesulfonate added was 0.02 parts by mass per 100 parts by mass of resin particles. The amount of aluminum sulfate added was 0.01 parts by mass per 100 parts by mass of resin particles.

[0173] Resin particles were dispersed in a dispersion medium, and carbon dioxide was supplied to the container as a foaming agent. Furthermore, while stirring the contents of the container, such as the dispersion medium and resin particles, the temperature inside the container was gradually raised to 164°C over 80 minutes. The container was then maintained at this temperature for 15 minutes. At this time, the pressure inside the container was 2.1 MPa(G). Subsequently, one end of the bottom of the container was opened, and the contents were released into an atmospheric pressure atmosphere, causing the resin particles to foam. At this time, foamed resin particles were obtained. The obtained particles were dried for 24 hours in an atmosphere at a temperature of 23°C and a relative humidity of 50%. This obtained the foamed particles of Example 1. In the foaming process of resin particles in Examples 2 to 8 and Comparative Examples 1 to 8 described later, various physical properties (for example, bulk density (kg / m³) as shown in Tables 3 and 4) were used. ３ To produce foamed particles having a closed-cell ratio (%), the foaming temperature of the resin particles was adjusted to a range of 160 to 170°C, and / or the pressure of the pressure vessel by injecting carbon dioxide was adjusted to a range of 2 to 3 MPa(G). In Examples 2 to 8 and Comparative Examples 1 to 8, foamed particles were produced under the respective adjusted foaming temperature and pressure conditions.

[0174] The bulk density (kg / m³) of the obtained foamed particles was determined based on the measurement method described below. ３ The closed-cell ratio (%) and the heat energy of the high-temperature peak (J / g) were measured. The results are shown in Table 3.

[0175] (Method for measuring bulk density) The state of the foamed particles was adjusted by leaving them to stand for more than 24 hours in an environment with a relative humidity of 50%, a temperature of 23°C, and a pressure of 1 atm. The adjusted bulk volume was approximately 500 cm³. ３ The foamed particles were filled into a graduated cylinder. Furthermore, by tapping the bottom of the graduated cylinder, the height of the entire group of foamed particles (foamed particle group) filled into the graduated cylinder was stabilized. By reading the scale on the graduated cylinder in this state, the exact bulk volume of the foamed particle group was measured. Then, by converting the value obtained by dividing the mass of the foamed particle group in the graduated cylinder by its bulk volume, the bulk density of the foamed particles (unit: kg / m³) was determined. ３ The following was calculated:

[0176] (Method for measuring the percentage of closed cells) The percentage of closed cells (%) of the foamed particles was measured using the method described in (Method for measuring the percentage of closed cells) in [2 Foamed Particles] above, that is, using the method using an air-comparison hydrometer based on ASTM-D2856-70 Procedure C and the above-mentioned formula (1).

[0177] (Method for measuring the heat content of the high-temperature peak) The heat content of the high-temperature peak was measured using the method described in (Method for measuring the heat content of the high-temperature peak) in [2 Foamed Particles] above. Specifically, the heat content (J / g) of the high-temperature peak was measured from the area of ​​the high-temperature peak identified from the first DSC curve obtained by differential scanning calorimetry in accordance with JIS K7122:2012. The above measurement was performed three times on different sample samples, and the arithmetic mean obtained by averaging the measured values ​​from each measurement was taken as the heat content of the high-temperature peak.

[0178] Table 3 lists the melt flow rate (MFR) and melting point for the impact PP and polypropylene resins mentioned above. These values ​​are based on the information in Tables 1 and 2 (the same applies to Table 4). Table 3 also lists the difference in MFR between impact polypropylene and polypropylene resins (g / 10min) in the "Difference in MFR" column. Furthermore, the difference in melting point between impact polypropylene and polypropylene resins (°C) is listed in the "Difference in Melting Point" column. The MFR difference and melting point difference shown in Table 3 are values ​​specific to the resin used to form the resin particles. The same descriptions regarding the MFR difference and melting point difference shown in Table 3 also apply to the MFR difference and melting point difference shown in Table 4.

[0179] Table 3 also lists the MFR (g / 10min) of the resin particles, the melting point of the resin particles (°C), the heat of fusion of the resin particles (J / g), and the acetone-insoluble content per gram of resin particles (g).

[0180] MFR (g / 10min) value of resin particles (MFR Ｐ The melting point (Tm) of the resin particles was measured according to JIS K7210-1:2014 under conditions of a temperature of 230°C and a load of 2.16 kg. Ｐ The temperature (°C) was determined by performing differential scanning calorimetry (DSC) in accordance with JIS K7121:2012. The heat of fusion (J / g) of the resin particles was determined based on the second DSC curve obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K7122:2012.

[0181] The acetone-insoluble content (g) per gram of resin particles was measured using the same method as described above in (Acetone-Insoluble Content of Resin). However, instead of approximately 5 g of resin, approximately 5 g of resin particles were used as the sample for measurement.

[0182] (In-moldability of foamed particles) The lower limit of the moldable pressure conditions and the number of moldable pressure conditions were adopted as indicators to evaluate the in-moldability of the obtained foamed particles.

[0183] (Lower Limit of Moldable Pressure Conditions) The lower limit of moldable pressure conditions was determined as follows. As a condition for the steam pressure introduced into the cavity when manufacturing a molded body, as described later, conditions were set in the range of 0.45 MPa(G) or less, with 0.01 MPa as one unit and changing it in increments of 1 unit (0.01 MPa), and a flat molded body was manufactured under each steam pressure condition. The obtained flat molded body was used as a test specimen, and a determination was made as to whether three evaluation items met the predetermined conditions. The three evaluation items were defined as the shape of the test specimen, the fusion state of the foam particles constituting the test specimen, and the presence or absence of indentations in the test specimen. The determination was made by evaluating if the predetermined conditions were met as a pass, and if the predetermined conditions were not met as a fail.

[0184] For each test specimen, it was defined that all three evaluation criteria passed if the specimen was moldable. Furthermore, among the defined steam pressure conditions, the steam pressure corresponding to moldability was identified.

[0185] Among the specified steam pressure conditions, the lower limit of the steam pressure corresponding to the case where molding is possible was identified, and this lower limit was set as the lower limit of the moldable pressure condition. The results are shown in Table 3.

[0186] In other words, as shown in Table 3, for Example 1, the lower limit of the steam pressure when moldable was 0.41 MPa(G), so the lower limit of the moldable pressure condition was 0.41 MPa(G).

[0187] (Number of moldable pressure conditions) The number of moldable pressure conditions was determined as follows. Using the same method as when determining the lower limit of the moldable pressure conditions described above, the steam pressures corresponding to the moldable case were identified from among the pressures defined as steam pressure conditions. The number of selectable conditions for steam pressures corresponding to the moldable case was identified from among the pressures defined as steam pressure conditions, and this number was determined to be the number of moldable pressure conditions. The results are shown in Table 3.

[0188] In other words, as shown in Table 3, for Example 1, there were four types of steam pressures corresponding to moldability: 0.41 MPa(G), 0.42 MPa(G), 0.43 MPa(G), and 0.44 MPa(G). Therefore, the number of moldable pressure conditions was four.

[0189] The evaluation methods and criteria for the three evaluation items mentioned above—the shape of the test specimen, the fusion state of the foamed particles constituting the test specimen, and the presence or absence of indentations in the test specimen—are as follows.

[0190] The shape of the test specimen was evaluated by visually observing whether the periphery of the flat test specimen was roughly linearly shaped according to the shape of the mold (presence or absence of irregularities). Based on the results of the visual observation, the shape of the test specimen was evaluated according to the evaluation criteria shown below.

[0191] Pass: The gaps between foam particles are sufficiently filled in the peripheral area of ​​the test specimen, and the test specimen is deemed to have been molded to the shape corresponding to the mold. Fail: The gaps between foam particles are not sufficiently filled in the peripheral area of ​​the test specimen, and there are parts of the test specimen that have not been molded to the shape corresponding to the mold.

[0192] The fusion state of the foam particles constituting the test specimen was evaluated by performing a fracture test. The fracture test was conducted as follows: The flat test specimen was fractured by bending it at its center (the center in the longitudinal direction of the specimen) with the bending axis roughly aligned with the transverse direction of the specimen. At this time, the number of foam particles present on the fracture surface (C1) and the number of destroyed foam particles (C2) were measured. The ratio of destroyed foam particles to foam particles (C2 / C1 × 100) was then calculated. This ratio indicates the strength of the fusion of the foam particles and was defined as the fusion rate (%). Based on this fusion rate (%), the fusion state of the test specimen was evaluated according to the evaluation criteria shown below.

[0193] Pass: Fusion rate (%) is 80% or higher. Fail: Fusion rate (%) is less than 80%.

[0194] The evaluation of whether or not there were dents in the test specimens was carried out based on the results of the thickness ratio measurement, as shown below.

[0195] (Thickness Ratio Measurement) For a flat plate-shaped test specimen, the thickness t1 (cm) at a designated position near the end of the specimen (referred to as the thickness t2 near the end) and the thickness t2 (cm) at a designated position near the center of the specimen (referred to as the thickness t2 in the center) were measured. The thickness t1 at the designated position near the end was determined as follows: The thickness t1(a) at a designated position near one end of the longitudinal ends of the specimen and the thickness t1(b) at a designated position near the other end were measured. The larger of the two values, t1(a) and t1(b), was taken as the thickness t1 at the designated position near the end. Based on the obtained thicknesses t1 and t2, the ratio of the thickness t2 in the center to the thickness t1 near the end (t2 / t1 × 100) (%) was calculated. The value (t2 / t1 × 100) (%) is referred to as the thickness ratio between the edges and the center.

[0196] Specifically, the position designated near the end as described above refers to the intersection of a point 10 mm inward from the end towards the center in the longitudinal direction of the test specimen and a point that divides the test specimen in two in the transverse direction. Specifically, the position designated near the center as described above refers to the intersection of a point that divides the test specimen in two in the longitudinal direction and a point that divides it in two in the transverse direction.

[0197] Based on the thickness ratio measurement results, specifically the thickness ratio between the edges and the center, the presence or absence of dents in the test specimen was evaluated according to the following evaluation criteria.

[0198] Pass: The thickness ratio between the edges and the center is 95% or more. Fail: The thickness ratio between the edges and the center is less than 95%.

[0199] If the evaluation result for the presence or absence of dents based on the evaluation criteria is satisfactory, it can be determined that excessive shrinkage has not occurred in the central part of the test specimen.

[0200] The method used to produce the molded body when determining the lower limit of the moldable pressure conditions and the number of moldable pressure conditions is as described in the following explanation of molded body production.

[0201] (Preparation of molded articles) Using the obtained foamed particles, molded articles were prepared by applying the following method.

[0202] Foam particles were filled into the cavity of the mold. The mold used had a cavity that could accommodate a flat molded body measuring 250 mm in length, 200 mm in width, and 50 mm in thickness.

[0203] In the process of filling the mold with foam particles, an action known as cracking was performed. Specifically, the mold was opened 5 mm in the thickness direction of the molded body to be manufactured (10% cracking) relative to the closed state of the mold, and the foam particles were filled into the mold. After filling the mold with foam particles, the mold was completely closed. Then, a predetermined amount of steam was supplied into the cavity to heat the foam particles, causing secondary foaming and fusion of the foam particles. As a result, the molded body was formed inside the mold. Furthermore, the mold was water-cooled until the surface pressure of the molded body inside the mold reached 0.04 MPa(G). Finally, the mold was opened, and the molded body was removed from inside the mold.

[0204] After being removed from the mold, the molded body underwent a curing process by being left to stand in an 80°C oven for 12 hours. Following the curing process, the molded body was left to stand for 24 hours under conditions of 50% relative humidity, 23°C, and 1 atm. This allowed the molded body to be conditioned.

[0205] The density, closed-cell ratio, and 50% compressive stress were measured using molded articles produced by the method described above. The measurements of density, closed-cell ratio, and 50% compressive stress were performed on molded articles obtained under conditions where the steam pressure was set to a pressure corresponding to the lower limit of the moldable pressure conditions.

[0206] (Density of the molded body) The density of the molded body was calculated by dividing the mass of the molded body by the volume obtained from the external dimensions of the molded body and then converting the units. The results are shown in Table 3.

[0207] (Closed-cell ratio of the molded body) The closed-cell ratio of the molded body is measured in accordance with ASTM 2865-70 Procedure C, similar to the explanation given for the closed-cell ratio of the foamed particles above, and is calculated using equation (1) shown above for the closed-cell ratio of the foamed particles. However, the values ​​of Va, Vx, W, and ρ in equation (1) are those determined by the method described below. A test piece measuring 25 mm in length, 25 mm in width, and 30 mm in height is cut from the center of the molded body, and the product of the length (unit: cm), width (unit: cm), and height (unit: cm) is calculated. The calculated value is the volume of the test piece Va (unit: cm ３ ) is considered to be the case. In addition, the true volume value Vx of the test specimen is measured using an air-comparison hydrometer in accordance with procedure C described in ASTM-D2856-70. When calculating the closed-cell ratio of the molded body, the mass W (unit: g) is the mass of the test specimen made from the molded body, and the density ρ (unit: g / cm³) is considered to be the density ρ (unit: g / cm³). ３ ) is the density of the resin constituting the foamed particles. Using the values ​​of volume Va, the true volume Vx of the test specimen, mass W (unit: g), and density ρ, the closed-cell ratio of the foamed particles described above was calculated using equation (1) shown above.

[0208] (50% Compressive Stress) A rectangular parallelepiped specimen measuring 50 mm in length, 50 mm in width, and 25 mm in thickness was taken from the center of the molded body. A compression test was performed on the specimen at a compression rate of 10 mm / min according to the method specified in JIS K7220:2006. A stress-strain curve was obtained based on the compression test. The compression test was performed in an atmosphere of 23°C. The compressive stress at 50% deformation of the specimen was calculated based on the obtained stress-strain curve. This value was taken as the 50% compressive strength of the molded body.

[0209] Examples 2 to 4 In Examples 2 to 4, the same method as in Example 1 was applied, except that the blending ratio (%) of Impact PP and the blending ratio (%) of polypropylene resin (corresponding to resin A) shown in the respective columns of Examples 2 to 4 in Table 3 were adopted. In Examples 2 to 4, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, as in Example 1. In addition, the bulk density (kg / m³) of the obtained foamed particles was measured, as in Example 1. ３ The following were measured: the pressure (%), the percentage of closed cells (%), and the heat energy of the high-temperature peak (J / g). Furthermore, for molded articles made using foamed particles, the lower limit of the moldable pressure conditions (MPa(G)), the number of moldable pressure conditions, and the density (kg / m³) were measured. ３ The closed-cell ratio (%) and 50% compressive stress (kPa) were measured. The results are shown in Table 3.

[0210] Examples 5 to 6 In Examples 5 to 6, the blending ratio (%) of Impact PP and the blending ratio (%) of polypropylene resin (corresponding to resin A) shown in the respective columns of Examples 5 to 6 in Table 3 were adopted, and the same method as in Example 1 was applied to other aspects, such as the use of the polypropylene resin shown in the respective columns of Examples 5 to 6 in Table 3. In Examples 5 to 6, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, as in Example 1. Furthermore, the bulk density (kg / m³) of the obtained foamed particles was measured, as in Example 1. ３ The following were measured: the pressure (%), the percentage of closed cells (%), and the heat energy of the high-temperature peak (J / g). Furthermore, for molded articles made using foamed particles, the lower limit of the moldable pressure conditions (MPa(G)), the number of moldable pressure conditions, and the density (kg / m³) were measured. ３ The closed-cell ratio (%) and 50% compressive stress (kPa) were measured. The results are shown in Table 3.

[0211] Examples 7 to 8 In Examples 7 to 8, the same method as in Example 1 was applied, except that the impact PP shown in each column of Examples 7 to 8 in Table 3 was used. In Examples 7 to 8, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, as in Example 1. In addition, the bulk density (kg / m³) of the obtained foamed particles was measured, as in Example 1. ３ The following were measured: the pressure (%), the percentage of closed cells (%), and the heat energy of the high-temperature peak (J / g). Furthermore, for molded articles made using foamed particles, the lower limit of the moldable pressure conditions (MPa(G)), the number of moldable pressure conditions, and the density (kg / m³) were measured. ３ The closed-cell ratio (%) and 50% compressive stress (kPa) were measured. The results are shown in Table 3.

[0212] Comparative Example 1 In Comparative Example 1, the same method as in Example 1 was applied, except that the polypropylene resin was omitted. In Comparative Example 1, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, as in Example 1. In addition, the bulk density (kg / m³) of the obtained foamed particles was measured, as in Example 1. ３ The percentage of closed cells (%) and the heat energy of the high-temperature peak (J / g) were measured. The results are shown in Table 4.

[0213] In Comparative Example 1, it was not possible to determine steam pressure conditions that could be evaluated as moldable. As shown in Table 4, there were none for both the lower limit of moldable pressure conditions (MPa(G)) and the number of moldable pressure conditions. The density of the molded article (kg / m³) ３ ), the closed-cell ratio (%) and the 50% compressive stress (kPa) were not measured.

[0214] Comparative Examples 2 and 3 In Comparative Examples 2 and 3, the blending ratio (%) of impact PP and the blending ratio (%) of polypropylene resin shown in the Comparative Examples 2 and 3 columns of Table 4 were adopted, and the same method as in Example 1 was applied to all other aspects, except that the polypropylene resin shown in the Comparative Examples 2 and 3 columns of Table 4 was used. In Comparative Examples 2 and 3, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, as in Example 1. Furthermore, the bulk density (kg / m³) of the obtained foamed particles was measured, as in Example 1. ３ The following were measured: the pressure (%), the percentage of closed cells (%), and the heat energy of the high-temperature peak (J / g). Furthermore, for molded articles made using foamed particles, the lower limit of the moldable pressure conditions (MPa(G)), the number of moldable pressure conditions, and the density (kg / m³) were measured. ３ The closed-cell ratio (%) and 50% compressive stress (kPa) were measured. The results are shown in Table 4.

[0215] Comparative Examples 4 and 6 In Comparative Examples 4 and 6, the Impact PP shown in the Comparative Examples 4 and 6 columns of Table 4 was used, and the same method as in Example 1 was applied, except that the polypropylene resin was omitted. In Comparative Examples 4 and 6, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, as in Example 1. In addition, the bulk density (kg / m³) of the obtained foamed particles was measured, as in Example 1. ３ The percentage of closed cells (%) and the heat energy of the high-temperature peak (J / g) were measured. The results are shown in Table 4.

[0216] In Comparative Example 4, it was not possible to determine steam pressure conditions that could be evaluated as moldable. As shown in Table 4, there were no results for either the lower limit of moldable pressure conditions (MPa(G)) or the number of moldable pressure conditions. Note that the density (kg / m³) of the molded body was not determined. ３ ), the closed-cell ratio (%) and the 50% compressive stress (kPa) were not measured.

[0217] For Comparative Example 6, regarding the molded article made using foamed particles, the lower limit of the moldable pressure conditions (MPa(G)), the number of moldable pressure conditions, and the density (kg / m³) are specified. ３ The closed-cell ratio (%) and 50% compressive stress (kPa) were measured. The results are shown in Table 4.

[0218] Comparative Examples 5 and 7: In Comparative Example 5, the same method as in Comparative Example 4 was applied, except that the polypropylene resin (corresponding to resin A) shown in the Comparative Example 5 column of Table 4 was used in the mixing ratio shown in Table 4.

[0219] In Comparative Example 7, the same method as in Comparative Example 6 was applied, except that the polypropylene resin (corresponding to resin A) shown in the column for Comparative Example 7 in Table 4 was used in the mixing ratio shown in Table 4.

[0220] In Comparative Examples 5 and 7, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, similar to Example 1. Furthermore, the bulk density (kg / m³) of the obtained foamed particles was measured, similar to Example 1. ３ The percentage of closed cells (%) and the heat energy of the high-temperature peak (J / g) were measured. The results are shown in Table 4.

[0221] In Comparative Example 5, it was not possible to determine steam pressure conditions that could be evaluated as moldable. As shown in Table 4, there were none for both the lower limit of moldable pressure conditions (MPa(G)) and the number of moldable pressure conditions. Note that the density (kg / m³) of the molded body was not determined. ３ ), the closed-cell ratio (%) and the 50% compressive stress (kPa) were not measured.

[0222] For Comparative Example 7, regarding the molded article made using foamed particles, the lower limit of the moldable pressure conditions (MPa(G)), the number of moldable pressure conditions, and the density (kg / m³) are specified. ３ The closed-cell ratio (%) and 50% compressive stress (kPa) were measured. The results are shown in Table 4.

[0223] Comparative Example 8 In Comparative Example 8, the same method as in Example 7 was applied, except that the polypropylene resin was omitted. In Comparative Example 8, the MFR (g / 10min), heat of fusion (J / g), and acetone-insoluble content (g) per gram of resin particle were measured for the resin particles used to produce the foamed particles, as in Example 7. In addition, the bulk density (kg / m³) of the obtained foamed particles was measured, as in Example 1. ３ The closed-cell ratio (%) and the heat energy of the high-temperature peak (J / g) were measured. The results are shown in Table 4. In Comparative Example 9, it was not possible to determine steam pressure conditions that could be evaluated as moldable. As shown in Table 4, there were none for both the lower limit of moldable pressure conditions (MPa(G)) and the number of moldable pressure conditions. The density (kg / m³) of the molded body was measured. ３ ), the closed-cell ratio (%) and the 50% compressive stress (kPa) were not measured.

[0224] For the foamed particles obtained in Examples 1, 2, and 8, and Comparative Examples 1, 2, 3, 5, and 7, the melt tension (mN) and melt elongation (m / min) of the polypropylene resin composition constituting the foamed particles were measured. The melt tension (mN) and melt elongation (m / min) were measured at 170°C. The melt tension (mN) and melt elongation (m / min) were measured as follows, based on the method described above.

[0225] A Capillograph 1D manufactured by Toyo Seiki Seisakusho Co., Ltd. was prepared as the measuring instrument. This measuring instrument was equipped with a cylinder with a diameter of 9.55 mm and a length of 350 mm, and an orifice with a nozzle diameter of 2.095 mm and a length of 8.0 mm. For the measurement samples, foamed particles obtained in each example were degassed by heat pressing at 200°C and then pelletized, and these were used. First, the temperature of the cylinder and orifice was set to 170°C, and the measurement sample was placed in the cylinder and left for 4 minutes. Next, the molten resin was extruded from the orifice in a string-like shape at a piston speed of 10 mm / min. The extruded string-like material was placed on a tension-detecting pulley with a diameter of 45 mm, and the string-like material was taken up by a take-up roller while increasing the take-up speed at a constant acceleration so that the take-up speed reached 200 m / min from 6 m / min in 30 seconds. The tension and take-up speed (molten elongation) at the point when the string-like material broke were measured. The above procedure was performed a total of 10 times using different measurement samples. Of the multiple tension measurements obtained above, the three largest values ​​and the three smallest values ​​were removed. The melt tension (mN) for each example was obtained by taking the arithmetic mean of the remaining four tension values. In addition, the melt elongation (m / min) for each example was obtained by taking the arithmetic mean of the melt elongation values ​​related to the above four tension values.

[0226] The polypropylene resin composition, as described above, comprises impact PP and polypropylene resin. The polypropylene resin composition constituting the foamed particles is the resin used as a raw material for constituting the resin particles described above. Furthermore, the melt flow rate, melting point, heat of fusion, and amount of acetone-insoluble matter contained in the n-decane extract of the polypropylene resin composition constituting the foamed particles obtained in each example were considered to be the same values ​​as the melt flow rate, melting point, heat of fusion, and amount of acetone-insoluble matter contained in the n-decane extract of the resin particles obtained in the corresponding examples.

[0227] The results of measuring the melt tension (mN) at 170°C for the polypropylene resin compositions are as follows for Examples 1, 2, and 8, and Comparative Examples 1, 2, 3, 5, and 7. For Example 1, the measured melt tension (mN) was 13 (mN), for Example 2 it was 26 (mN), and for Example 8 it was 11 (mN). For Comparative Example 1 it was 6 (mN), for Comparative Example 2 it was 5 (mN), and for Comparative Example 3 it was 4 (mN). For Comparative Example 5 it was 7 (mN), and for Comparative Example 7 it was 3 (mN).

[0228] The measurement results for the melt elongation (m / min) at 170°C for the polypropylene resin compositions are as follows for Examples 1, 2, and 8, and Comparative Examples 1, 2, 3, 5, and 7. For Example 1, the measured melt elongation (m / min) was 10 (m / min), for Example 2 it was 77 (m / min), and for Example 8 it was 10 (m / min). For Comparative Example 1 it was 10 (m / min), for Comparative Example 2 it was 6 (m / min), and for Comparative Example 3 it was 6 (m / min). For Comparative Example 5 it was 6 (m / min), and for Comparative Example 7 it was 6 (m / min).

[0229]

[0230]

[0231] In all of Examples 1 to 8, the lower limit of the moldable pressure conditions was 0.45 MPa or less, and the number of moldable pressure conditions was two or more. In other words, it was confirmed that in Examples 1 to 8, a value lower than 0.45 MPa could be set as the moldable pressure, and a wide range of moldable pressures could be secured. In this respect, it was confirmed that Examples 1 to 8 produced foamed particles with superior in-moldability compared to any of Comparative Examples 1 to 9.

[0232] Furthermore, a comparison between Example 1 and Comparative Example 1 confirmed that foamed particles with excellent in-moldability can be obtained when resin A is included in the polypropylene resin particles such that the mass ratio of impact PP to resin A is within a predetermined range. A comparison between Example 1 and Examples 7 and 8 confirmed that foamed particles with excellent in-moldability can be obtained in each example, not limited to the impact PP of Example 1.

[0233] By comparing Example 1 with Comparative Examples 2, 3, 5, and 7, it was confirmed that foamed particles with excellent in-moldability can be obtained when the MFR of Impact PP and resin A each meet specific conditions.

[0234] A comparison of Examples 1 to 8 with Comparative Examples 2, 3, 5, and 7 revealed that each example performed better than each comparative example in terms of 50% compressive stress, confirming that the foamed particles obtained in each example are superior from the viewpoint of obtaining molded articles with excellent compressibility.

[0235] Furthermore, in the case of the foamed particles of Comparative Examples 1, 4, 5, and 8, the secondary foaming properties were low, making it difficult to fill the gaps between the foamed particles during in-mold molding. This is thought to be the reason why there were no molding conditions that could produce a good molded product. In addition, in the case of the foamed particles of Comparative Examples 2, 3, 6, and 7, heating until the foamed particles were sufficiently fused together during in-mold molding tended to cause shrinkage in the molded product. This is thought to be the reason why there were few molding conditions that could produce a good molded product.

[0236] M: Matrix D: Domain

Claims

1. A method for producing foamed polypropylene resin particles by foaming polypropylene resin particles, wherein the polypropylene resin particles are composed of a mixed resin obtained by kneading impact polypropylene, which has a melt flow rate of more than 10 g / 10 min and 80 g / 10 min or less as measured at a temperature of 230°C and a load of 2.16 kg, and polypropylene resin A, which has a melt flow rate of less than 3 g / 10 min as measured at a temperature of 230°C and a load of 2.16 kg, and the mass ratio of the impact polypropylene to the polypropylene resin A in the polypropylene resin particles is impact polypropylene:polypropylene resin A = 97:3 to 40:

60.

2. Melt flow rate MFR of the impact polypropylene Ｉ and the melt flow rate MFR of the polypropylene resin A Ａ The difference (MFR) Ｉ - MFR Ａ A method for producing polypropylene resin foam particles according to claim 1, wherein the amount is 23 g / 10 min or more and 60 g / 10 min or less.

3. The method for producing polypropylene resin foam particles according to claim 1 or 2, wherein the melt flow rate of the polypropylene resin particles measured under the conditions of a temperature of 230°C and a load of 2.16 kg is 5 g / 10 min or more and 50 g / 10 min or less.

4. A method for producing polypropylene resin foam particles according to any one of claims 1 to 3, wherein the melting point of the polypropylene resin particles is 150°C or higher and 165°C or lower.

5. A method for producing polypropylene resin foam particles according to any one of claims 1 to 4, wherein the amount of acetone-insoluble matter contained in the n-decane extract of the polypropylene resin particles is 0.05 g or more and 0.3 g or less per gram of the polypropylene resin particles.

6. A method for producing polypropylene resin foam particles according to any one of claims 1 to 5, wherein the melt tension of the polypropylene resin particles at 170°C is 8 mN or more and 40 mN or less.

7. Polypropylene resin foam particles comprising a polypropylene resin composition containing impact polypropylene, wherein the melt flow rate of the polypropylene resin composition measured under conditions of a temperature of 230°C and a load of 2.16 kg is 5 g / 10 min or more and 50 g / 10 min or less, and the melt tension of the polypropylene resin composition at 170°C is 8 mN or more and 40 mN or less.

8. The polypropylene resin foam particles according to claim 7, wherein the melt elongation of the polypropylene resin composition at 170°C is 8 m / min or more and 100 m / min or less.

9. The polypropylene resin foam particles according to claim 7 or 8, wherein the melting point of the polypropylene resin composition is 150°C or higher and 165°C or lower.

10. Polypropylene resin foam particles according to any one of claims 7 to 9, wherein the amount of acetone-insoluble matter contained in the n-decane extract of the polypropylene resin composition is 0.05 g or more and 0.3 g or less per gram of the polypropylene resin composition.

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