Polypropylene-based resin foam particles and polypropylene-based resin foam particle molded articles

Abstract

To provide polypropylene-based resin foam particles which enable production of a foam particle molding that is excellent in weather resistance over a long period and is excellent in mechanical physical properties, and a polypropylene-based resin foam particle molding.SOLUTION: Polypropylene-based resin foam particles contain a hindered amine-based compound, wherein the hindered amine-based compound has a repeating unit represented by the following general formula (I), the number average molecular weight in terms of polystyrene of the hindered amine-based compound is 1,000 or more and 2,000 or less, and the content of the hindered amine-based compound in the polypropylene-based resin foam particles is 0.01 mass% or more and 2 mass% or less. In the general formula (I), X is an alkylene group having 5 to 10 carbon atoms, Y is an amino group, and Z1 and Z2 are independently a hydrocarbon group, a hydrocarbon group bonded through an oxygen atom, or a hydrogen atom.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polypropylene resin foam particles and polypropylene resin foam particle molded articles. [Background technology]

[0002] Polypropylene-based foam particle molded articles, produced by in-mold molding of polypropylene-based resin foam particles, exhibit superior chemical resistance, impact resistance, and compression strain recovery compared to polystyrene-based resin foam particle molded articles. For this reason, polypropylene-based resin foam particle molded articles are used in a wide range of fields, including as shock absorbers, heat insulating materials, and various packaging materials, such as food transport containers, packaging and cushioning materials for electrical and electronic components, vehicle components such as automobile bumpers, building components such as housing insulation materials, and general merchandise. Although polypropylene resin foam particle molded articles possess the excellent properties described above, under certain usage conditions, such as prolonged exposure to sunlight, the resin may degrade excessively, potentially leading to a decrease in physical properties. Therefore, attempts are being made to enhance the weather resistance of the molded articles by adding weather-resistant agents to suppress this degradation. For example, Patent Document 1 discloses polypropylene resin foam particles containing a hindered amine compound for the purpose of improving weather resistance in addition to fusion properties and heat resistance, wherein the amount of heat of fusion of the endothermic peak on the high-temperature side of the surface layer and the amount of heat of fusion of the endothermic peak on the high-temperature side of the internal foam layer satisfy a specific relationship in the DSC curves of the surface layer and the internal foam layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2003-321567 [Overview of the project] [Problems that the invention aims to solve]

[0004] In recent years, polypropylene-based resin foam particles may be used as a material for molded articles that are exposed to the outside, such as automotive parts, building materials, containers, etc., taking advantage of the above characteristics. Therefore, there is a demand for molded articles that can be used for a long period of several years to several decades even under harsh conditions. On the other hand, in order to improve the weather resistance of the molded article, there are cases where weathering agents cannot impart long-term weather resistance even when added, or where the mechanical properties such as the tensile strength of the molded article deteriorate when a weathering agent is added. There was room for improvement in obtaining a molded article that has high weather resistance and excellent physical properties. Therefore, there is a need for polypropylene-based resin foam particles that can obtain a molded article having higher weather resistance and excellent physical properties than conventional ones. An object of the present invention is to provide polypropylene-based resin foam particles capable of producing a foam particle molded article excellent in long-term weather resistance and excellent in mechanical properties, and a polypropylene-based resin foam particle molded article excellent in long-term weather resistance and excellent in mechanical properties.

Means for Solving the Problems

[0005] As a result of intensive studies, the present inventors have found that the above problems can be solved by containing a specific amount of a hindered amine compound having a specific structure and molecular weight in polypropylene-based resin foam particles and molded articles. One aspect of the present invention is polypropylene-based resin foam particles according to the following [1] to [6] and polypropylene-based resin foam particle molded articles according to the following [7] to [9]. [1] Polypropylene-based resin foam particles containing a hindered amine compound, wherein the hindered amine compound has a repeating unit represented by the following general formula (I), and the polystyrene-reduced number average molecular weight of the hindered amine compound is 1000 or more and 2000 or less, and the content of the hindered amine compound in the polypropylene-based resin foam particles is 0.01% by mass or more and 2% by mass or less. Polypropylene-based resin foam particles.

Chemical formula

[0006] According to the present invention, it is possible to provide polypropylene-based resin foam particles that can be used to produce foam particle molded articles with excellent long-term weather resistance and mechanical properties, and polypropylene-based resin foam particle molded articles with excellent long-term weather resistance and mechanical properties. [Modes for carrying out the invention]

[0007] [Polypropylene resin foam particles] The polypropylene resin foam particles of the present invention are polypropylene resin foam particles containing a hindered amine compound, wherein the hindered amine compound has repeating units represented by the following general formula (I), and the polystyrene-equivalent number average molecular weight of the hindered amine compound is 1000 or more and 2000 or less, and the content of the hindered amine compound in the polypropylene resin foam particles is 0.01% by mass or more and 2% by mass or less. [ka] (However, in the above general formula (I), X represents an alkylene group having 5 to 10 carbon atoms, Y represents an amino group, and Z 1 and Z 2 Each of these independently represents a hydrocarbon group, a hydrocarbon group bonded via an oxygen atom, or a hydrogen atom.

[0008] (Polypropylene resin) The polypropylene resin foam particles are composed of a base resin mainly composed of polypropylene resin. In this specification, "mainly composed of polypropylene resin" means that the polypropylene resin content in the base resin is 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. There is no particular upper limit, and it is 100% by mass or less. In the present invention, polypropylene resins include propylene homopolymers, propylene copolymers, or mixtures thereof, preferably propylene copolymers or mixtures of propylene homopolymers and propylene copolymers, and more preferably propylene copolymers. When the polypropylene resin is a propylene copolymer or a mixture of a propylene homopolymer and a propylene copolymer, the content of structural units derived from propylene in the polypropylene resin is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The content of structural units derived from propylene in the polypropylene resin is preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 97% by mass or less, and even more preferably 96% by mass or less. Examples of propylene copolymers include copolymers of propylene with ethylene and / or α-olefins having 4 to 20 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene. Preferably, the copolymer is of propylene and ethylene or of propylene, ethylene, and 1-butene.

[0009] From the viewpoint of improving the mechanical properties of the resulting molded article, the melting point of the polypropylene resin is preferably 130°C or higher, more preferably 132°C or higher, and even more preferably 135°C or higher. On the other hand, from the viewpoint of improving the in-moldability of foamed particles under low molding pressure conditions, the melting point of the polypropylene resin is preferably 155°C or lower, more preferably 150°C or lower, and even more preferably 146°C or lower. The melting point of polypropylene resins is measured using propylene resin or foamed particles as test specimens, in accordance with JIS K 7121:2012. Specifically, for conditioning the test specimen, "(2) When the melting temperature is measured after a certain heat treatment" is adopted. The test specimen is heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow of 30 mL / min, then held at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve after the second heating). Next, the peak temperature of the melting peak in the DSC curve is determined, and this value can be taken as the melting point of the polypropylene resin. If multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest melting peak height relative to the baseline will be adopted as the melting point.

[0010] The melt flow rate (MFR: JIS K 7210-1:2014, 230°C, load 2.16 kg) of the polypropylene resin is preferably 2 to 10 g / 10 min, and more preferably 5 to 9 g / 10 min.

[0011] (Hindered amine compounds) The hindered amine compound contained in the polypropylene resin foam particles of the present invention has repeating units represented by the following general formula (I), and the polystyrene-equivalent number-average molecular weight of the hindered amine compound is 1000 or more and 2000 or less. [ka] (However, in the above general formula (I), X represents an alkylene group having 5 to 10 carbon atoms, Y represents an amino group, and Z 1 and Z 2 Each of these independently represents a hydrocarbon, a hydrocarbon group bonded via an oxygen atom, or a hydrogen atom.

[0012] The polypropylene resin foam particles of the present invention, by containing a specific amount of the hindered amine compound, result in a foam particle molded article that exhibits excellent long-term weather resistance and superior mechanical properties. The reason for this is not entirely clear, but it is thought to be as follows. The aforementioned hindered amine compound is thought to be able to suppress molecular chain severation (low molecular weight reduction) of the resin due to oxidation, particularly by consuming radicals generated by light, due to the presence of a 2,2,6,6-tetramethyl-4-piperidineamine moiety in its structure, as shown by general formula (II). Furthermore, it is thought that the presence of a triazine moiety shown by general formula (III) and a relatively long-carbon alkylene moiety shown as X in general formula (I), along with a relatively large molecular weight, suppresses bleed-out from the resin. These factors are thought to contribute to providing long-term weather resistance. Furthermore, since inorganic dispersants and the like are less likely to coordinate with the nitrogen atoms located at both ends of the triazine and alkylene portions, it is possible to suppress the adhesion of inorganic dispersants and the like in the dispersion medium to the surface of the foamed particles when the resin particles are foamed, and as a result, the fusion properties of the foamed particles are improved. This is thought to result in a molded article with excellent mechanical properties.

[0013] [ka] (In the above general formula (II), Z represents a hydrocarbon, a hydrocarbon group bonded via an oxygen atom, or a hydrogen atom. In the above general formula (III), Y represents an amino group.)

[0014] In the general formula (I) above, X represents an alkylene group having 5 to 10 carbon atoms. Preferably, X is an alkylene group having 5 to 8 carbon atoms, and more preferably an alkylene group having 6 carbon atoms (hexamethylene group). In the general formula (I) above, Y represents an amino group. Y is preferably a secondary amino group or a tertiary amino group, and more preferably a tertiary amino group. When Y is a tertiary amino group, Y is preferably a dialkylamino group and a morpholinyl group, and more preferably a morpholinyl group. By Y being a morpholinyl group, the resulting foamed particle molded article can be given stable, long-term weather resistance. In the above general formula (I), Z 1 and Z 2Each of these independently represents a hydrocarbon group, a hydrocarbon group bonded via an oxygen atom, or a hydrogen atom. Examples of hydrocarbon groups include alkyl groups and cycloalkyl groups. Examples of hydrocarbon groups bonded via an oxygen atom include alkoxy groups. 1 is preferably an alkyl group or a hydrogen atom, more preferably an alkyl group, even more preferably an alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group. Also, Z 2 is preferably an alkyl group or a hydrogen atom, more preferably an alkyl group, even more preferably an alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group. 1 and Z 2 They may be the same or different, but it is preferable that they be the same. That is, Z 1 and Z 2 Preferably, each is a hydrocarbon group or a hydrogen atom, more preferably each is an alkyl group or a hydrogen atom, even more preferably each is an alkyl group, even more preferably each is an alkyl group having 1 to 4 carbon atoms, and even more preferably each is a methyl group. That is, preferably Z in the general formula (I) above 1 and Z 2 is an alkyl group, more preferably all alkyl groups having 1 to 4 carbon atoms, and even more preferably Z in the general formula (I) 1 and Z 2 This is a methyl group.

[0015] In the hindered amine compounds having the structure shown in the general formula (II), hindered amine compounds in which Z is an alkyl group are called NR-type hindered amines. However, conventionally, when NR-type hindered amines were used, molded articles with superior weather resistance could not be obtained compared to NH-type hindered amines or NOR-type hindered amines. An NH-type hindered amine is a hindered amine compound having a structure in which Z in the general formula (II) is a hydrogen atom (>NH), and a NOR-type hindered amine is, for example, a hindered amine compound having a structure in which Z in the general formula (II) is an alkoxy group (>NOR). On the other hand, the hindered amine compound used in the polypropylene resin foam particles of the present invention has the structure shown in the general formula (I), which is thought to result in a foam particle molded article that has good fusion properties between foam particles, excellent mechanical properties, and excellent weather resistance over a long period of time. In the hindered amine compound used in the polypropylene resin foam particles of the present invention, Z in the general formula (I) 1 and Z 2 However, the hindered amine compounds that are alkyl groups are NR-type hindered amines. An NH-type hindered amine is a compound in the general formula (I) above where Z 1 and Z 2 A hindered amine compound having a structure (>NH) in which Z is a hydrogen atom, and a NOR-type hindered amine is a compound having a structure (>NH) in the general formula (I) above. 1 and Z 2 It is a hindered amine compound having a structure (>NOR) in which a hydrocarbon group is bonded via an oxygen atom.

[0016] The polystyrene-equivalent number-average molecular weight of the hindered amine compound is between 1000 and 2000. Having the polystyrene-equivalent number-average molecular weight within this range ensures good dispersion of the hindered amine compound in the resin, reduces the likelihood of the hindered amine compound bleeding out of the molded article, and allows the molded article to stably exhibit long-term weather resistance. From the viewpoint of suppressing bleed-out from the molded article, the polystyrene-equivalent number-average molecular weight of the hindered amine compound is preferably 1200 or more, and more preferably 1500 or more. Furthermore, from the viewpoint of improving the dispersion state of the hindered amine compound in the resin and ensuring uniform bubble diameter, the polystyrene-equivalent number-average molecular weight of the hindered amine compound is preferably 1900 or less, and more preferably 1800 or less. The polystyrene-equivalent number-average molecular weight of the hindered amine compound is the number-average molecular weight calculated using monodisperse polystyrene as the standard substance, measured by gel permeation chromatography (GPC). The polystyrene-equivalent number-average molecular weight of hindered amine compounds can be determined, for example, by the following method. A hindered amine compound solution is obtained by dissolving 10 mg of a hindered amine compound in 10 mL of tetrahydrofuran. The solution is measured using a Shimadzu LC3A high-performance liquid chromatograph, a Shimadzu RID-4 differential refractometer detector, and a Shimadzu Shim-pack GPC-802 column under measurement conditions of column temperature 23°C and flow rate 1 mL / min to obtain a chromatogram. The retention time in the chromatogram obtained from the measurement is converted to molecular weight using a calibration curve prepared with standard polystyrene to obtain a differential molecular weight distribution curve. The number average molecular weight of the hindered amine compound can be calculated from this differential molecular weight distribution curve. The hindered amine compound may have at least one repeating unit represented by the general formula (I), and may have two or more. It may also be a mixture of compounds having different numbers of repeating units represented by the general formula (I). Furthermore, it is preferable that the number of repeating units represented by the general formula (I) in the hindered amine compound is 2 or more and 5 or less. Also, it is preferable that the terminal group on the triazine portion side of the hindered amine compound is a hydroxyl group or Y in the general formula (I). Furthermore, it is preferable that the terminal group on the alkylene portion side of the hindered amine compound is a hydrogen atom or the triazine portion represented by the general formula (III) in the general formula (I) (wherein the triazine portion, the substituent of the carbon that is not bonded to a nitrogen atom is a hydroxyl group or Y in the general formula (I)).

[0017] The hindered amine compound may be a single compound or a mixture of multiple compounds, provided that it has repeating units represented by the general formula (I) and its polystyrene-equivalent number-average molecular weight is 1000 or more and 2000 or less. When multiple compounds are used in mixture form, the polystyrene-equivalent number-average molecular weight of the hindered amine compound shall be the arithmetic mean of the molecular weights calculated based on the molecular weight of each compound and the mass ratio of each compound.

[0018] The content of the hindered amine compound in the polypropylene resin foam particles of the present invention is 0.01% by mass or more and 2% by mass or less. Preferably, the content of the hindered amine compound in the polypropylene resin foam particles is 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more. Furthermore, preferably, the content of the hindered amine compound in the polypropylene resin foam particles is 2% by mass or less, and more preferably 1.5% by mass or less. By having the content of the hindered amine compound within the above range, a foam particle molded article can be obtained that has excellent long-term weather resistance and excellent mechanical properties such as tensile strength. In particular, if the content is too low, there is a risk that the long-term weather resistance will decrease, and if the content is too high, there is a risk that mechanical properties such as tensile strength will decrease. Furthermore, the content of hindered amine compounds in the foamed particles is determined, for example, by proton nuclear magnetic resonance ( 1 It can be calculated by performing a 1H-NMR measurement. Specifically, the following method can be employed. First, the foam particles are cryopreserved and weighed out to approximately 2 g. Next, the cryopreserved foam particles are subjected to Soxhlet extraction using chloroform as the solvent to remove polymer components and other parts that are insoluble in chloroform. Then, the chloroform-soluble part obtained from the Soxhlet extraction is mixed with acetone to remove the acetone-insoluble part. The solid obtained by removing the solvent from the acetone-soluble part is used as the measurement sample, and proton nuclear magnetic resonance ( 1 The content is calculated from the integral ratio relative to a standard of known concentration (internal standard sample) by measuring using 1H-NMR. Proton nuclear magnetic resonance ( 1 For 1H-NMR, for example, the AL-400 model manufactured by JEOL Ltd. can be used. Furthermore, measurement conditions such as solvent: CDCl3 and internal standard sample: tetrachloroethane (TCE) can be employed.

[0019] (Properties and composition of polypropylene resin foam particles) The polypropylene resin foam particles of the present invention, as described above, contain a specific hindered amine compound, and preferably have the following characteristics.

[0020] The average bubble diameter of the polypropylene resin foam particles of the present invention is preferably 50 μm or more and 250 μm or less. More preferably, the average bubble diameter of the polypropylene resin foam particles of the present invention is 60 μm or more, and even more preferably, 65 μm or more. Furthermore, the average bubble diameter of the polypropylene resin foam particles of the present invention is more preferably 200 μm or less, even more preferably 150 μm or less, and even more preferably 120 μm or less. By having the average bubble diameter of the foam particles within the above range, foam particles with excellent in-mold moldability are obtained, and foam particle molded articles with excellent mechanical properties and excellent weather resistance over a long period of time can be stably obtained. In addition, by having the average bubble diameter of the foam particles within the above range, the time required for cooling when removing the molded article from the mold during in-mold molding can be shortened, and foam particles with excellent molding cycles can be obtained. The average bubble diameter can be measured by drawing multiple line segments from the outermost surface of a divided foam particle through its center to the outermost surface of the opposite side in a magnified photograph of the cross-section of the foam particle, and dividing the number of bubbles intersecting each line segment by the total length of the line segments. Specifically, it can be measured by the method described in the examples. The average bubble diameter of the foamed particles can be adjusted to a desired range by controlling the type and amount of foam modifier added to the resin particles, adjusting the amount of hindered amine compounds added, and adjusting the foaming pressure during foaming of the resin particles.

[0021] The average surface thickness of the polypropylene resin foam particles of the present invention is preferably 5 μm or more and 20 μm or less. More preferably, the average surface thickness of the polypropylene resin foam particles of the present invention is 7 μm or more, even more preferably 8 μm or more, and even more preferably 9 μm or more. Furthermore, the average surface thickness of the polypropylene resin foam particles of the present invention is more preferably 18 μm or less, even more preferably 15 μm or less, and even more preferably 13 μm or less. By having the average surface thickness of the foam particles within the above range, foam particles with excellent in-moldability are obtained, and foam particle molded articles with excellent mechanical properties and excellent weather resistance over a long period of time can be stably obtained. In addition, by having the average surface thickness of the foam particles within the above range, the time required for cooling when removing the molded article from the mold during in-mold molding can be shortened, and foam particles with excellent molding cycles can be obtained. The average surface thickness can be calculated by taking an enlarged photograph of the cross-section of the two divided foam particles, drawing multiple line segments from the outermost surface of the foam particle through the center to the outermost surface of the opposite side, measuring the length from the outermost surface of the foam particle to the outermost edge of the bubble located on the outermost surface side of the foam particle at each line segment, and taking the arithmetic mean of these lengths. Specifically, it can be measured by the method described in the examples. The average surface thickness of the foamed particles can be adjusted to a desired range by controlling the type and amount of foam regulator added to the resin particles, adjusting the amount of hindered amine compounds added, and adjusting the pressure inside the sealed container during foaming of the resin particles.

[0022] The bulk density of the polypropylene resin foam particles of the present invention is preferably 10 kg / m³. 3 More than 500kg / m 3 The following applies: The bulk density of the polypropylene resin foam particles of the present invention is more preferably 12 kg / m³. 3 The above is preferable, and more preferably 15 kg / m 3 That concludes the explanation. Furthermore, the bulk density of the polypropylene resin foam particles of the present invention is more preferably 200 kg / m³. 3 The following, and more preferably 100 kg / m3 The following, and more preferably 50 kg / m 3 The following is preferable: Since the bulk density of the foamed particles is within the aforementioned range, a foamed particle molded article that is lightweight and has excellent mechanical properties can be obtained. The bulk density can be measured by the method described in the examples.

[0023] The polypropylene resin foam particles of the present invention preferably have one or more melting peaks (high-temperature peaks) on the high-temperature side of the resin-specific melting peak (resin-specific peak) of the polypropylene resin in the DSC curve obtained by differential scanning calorimetry (DSC) in accordance with JIS K7122-1987. These melting peaks can be obtained by the following method. Specifically, a differential scanning calorimeter can be used to obtain a DSC curve by heating 1-3 mg of foamed particles from 23°C to 200°C at a heating rate of 10°C / min, and the melting peak (high-temperature peak) can be identified from the DSC curve. The peak with the maximum melting heat is defined as the melting peak (resin-specific peak) intrinsically to polypropylene resins, and any melting peaks appearing at higher temperatures are defined as high-temperature peaks. In this case, the DSC curve refers to the DSC curve obtained by heating the foamed particles using the measurement method described above (the DSC curve for the first heating). Furthermore, the resin-specific endothermic peak (resin-specific peak) refers to the endothermic peak due to the melting of the crystals inherent to the polypropylene resin that constitutes the foamed particles. It is considered that the resin-specific peak is an endothermic peak that appears due to the endothermic heat generated by the melting of the crystals that normally exist in the polypropylene resin that constitutes the foamed particles. On the other hand, the endothermic peak on the high-temperature side of the resin-specific peak (high-temperature peak) is the endothermic peak that appears at a higher temperature than the resin-specific peak in the first DSC curve. When this high-temperature peak appears, it is presumed that secondary crystals are present in the resin. Note that when foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / min (first heating), then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min (second heating), the DSC curve obtained (DSC curve for the second heating) shows only the endothermic peak due to the melting of crystals specific to the polypropylene resin constituting the foamed particles. This resin-specific peak appears in both the DSC curve for the first heating and the DSC curve for the second heating, and although the temperature of the peak peak may differ slightly between the first and second heatings, the difference is usually less than 5°C. This allows us to confirm which peak is the resin-specific peak. Furthermore, the foamed particles are preferably foamed particles in which only the melting peak (intrinsic peak) characteristic of polypropylene resin appears in the DSC curve obtained during the second heating, which is obtained when the foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C at a heating rate of 10°C / min.

[0024] The heat of fusion of the high-temperature peak of the polypropylene resin foam particles of the present invention is preferably 5 to 40 J / g, more preferably 7 to 30 J / g, and even more preferably 10 to 20 J / g. When the heat of fusion of the high-temperature peak of the foamed particles falls within the aforementioned range, the range of molding conditions over which a good foamed particle molded article can be obtained is wider, which is preferable. The heat of fusion at the high-temperature peak is measured by the method described above, but more specifically, it can be measured by the method described in the examples.

[0025] The total heat of fusion of the polypropylene resin foam particles of the present invention is the sum of the heats of fusion of all melting peaks (endothermic peaks) appearing in the first DSC curve. The total heat of fusion of the polypropylene resin foam particles of the present invention is preferably 25 to 200 J / g, more preferably 35 to 150 J / g, and even more preferably 50 to 100 J / g. It is preferable that the total heat of fusion of the foamed particles falls within the aforementioned range, as this allows for the stable production of foamed particles that offer an excellent balance between in-moldability and the physical properties of the resulting molded article. The total heat of fusion can be measured by the method described in the examples.

[0026] The polypropylene resin foam particles of the present invention are preferably foam particles obtained by foaming resin particles that have not undergone surface modification with organic peroxides. In this case, foam particles that can be molded in a mold at a relatively low molding pressure can be produced with high productivity. From this viewpoint, it is preferable that the polypropylene resin foam particles of the present invention have one or more melting peaks (high-temperature peaks) on the high-temperature side of the resin-specific melting peak (resin-specific peak) of the polypropylene resin, and satisfy the following relationship of formula (1). ΔHs≧ΔHi×0.86···(1) (In equation (1), ΔHs is the heat of fusion of the high-temperature peak on the surface of the foamed particle, and ΔHi is the heat of fusion of the high-temperature peak inside the foamed particle.) Furthermore, from the viewpoint of enabling in-mold molding at relatively low molding pressure and stably obtaining molded articles with good physical properties, it is preferable that the melting point of the polypropylene resin constituting the foam particles is 155°C or lower, and that the foam particles satisfy formula (1) and the following formula (2). ΔHi × 1.2 ≥ ΔHs···(2) ΔHs can be measured using the same method as the method for measuring the heat of fusion of the high-temperature peak of the polypropylene resin foam particles, except that a sample cut from the surface layer of the foam particle is used. Similarly, ΔHi can be measured using the same method as the method for measuring the heat of fusion of the high-temperature peak of the polypropylene resin foam particle, except that a sample cut from the inside of the foam particle without including the surface layer is used. The surface layer of a foamed particle refers to the area within 200 μm from the surface of the foamed particle toward its center of gravity. When preparing a sample, a predetermined amount of sample may be prepared by cutting out the surface or internal portion from multiple foamed particles, and this sample may be used for measurement.

[0027] The polypropylene resin foam particles of the present invention have an average mass per particle (arithmetic mean of the masses of 200 randomly selected particles) which is preferably 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and even more preferably 0.4 to 2 mg.

[0028] Furthermore, the polypropylene resin foam particles of the present invention may contain additives as appropriate, provided that they do not hinder the effects of the present invention. Examples of additives include antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, and foam regulators. These additives can be incorporated into the foam particles, for example, by adding them during the resin particle manufacturing process.

[0029] As a foam regulator, for example, inorganic powders or organic powders can be used. Examples of inorganic powders include metal borate salts such as zinc borate and magnesium borate, while examples of organic powders include fluororesin powders such as polytetrafluoroethylene (PTFE). From the viewpoint of stably obtaining foamed particles that have the desired bulk density and have little variation in bubble diameter, the amount of bubble regulator blended in the resin particles is preferably 50 ppm by mass or more and 5000 ppm by mass or less, more preferably 100 ppm by mass or more and 2000 ppm by mass or less, and even more preferably 150 ppm by mass or more and 1500 ppm by mass or less. Furthermore, from the viewpoint of easily adjusting the average bubble diameter and average surface thickness of the foamed particles to a desired range, it is preferable to use a metal borate salt as a bubble regulator, and more preferable to use zinc borate. When zinc borate is used, the arithmetic mean particle diameter based on the number of particles is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 8 μm or less. The arithmetic mean particle diameter of zinc borate, based on the number of particles, can be determined by first obtaining a particle size distribution based on the number of particles, which is obtained by converting the volume-based particle size distribution measured by laser diffraction scattering by assuming the particle shape to be spherical, and then taking the arithmetic mean of the particle diameters based on this number-based particle size distribution. Note that the above particle diameter refers to the diameter of a hypothetical sphere having the same volume as the particles.

[0030] From the viewpoint of imparting a good appearance to the molded article, the polypropylene resin foam particles of the present invention preferably contain a pigment. In particular, from the viewpoint of imparting a good black appearance, carbon black is preferred as the pigment. When the foamed particles contain carbon black, the carbon black content in the foamed particles is preferably 0.1% by mass or more and 5% by mass or less in the polypropylene resin foamed particles. More preferably 0.5% by mass or more, even more preferably 1% by mass or more, and even more preferably 2% by mass or more. Furthermore, more preferably 4% by mass or less, and even more preferably 3% by mass or less. In general, foamed particle molded articles containing carbon black, obtained using foamed particles containing carbon black, tend to have reduced fusion properties between the foamed particles. Furthermore, due to factors such as increased heat retention from sunlight, the effects of hindered amine compounds decrease, and long-term weather resistance tends to decline. However, the polypropylene resin foamed particles of the present invention, by containing carbon black within the aforementioned range, provide a good black appearance, excellent mechanical properties, and allow for the stable production of foamed particle molded articles exhibiting excellent weather resistance over a long period. Examples of carbon blacks that can be used include channel black, roller black, furnace black, thermal black, and acetylene black.

[0031] From the viewpoint of stably obtaining a foamed particle molded article that has a good black appearance, excellent mechanical properties, and excellent weather resistance over a long period of time, when the foamed particles contain carbon black, the mass ratio of the hindered amine compound to the carbon black in the foamed particles is preferably 0.002 to 2, more preferably 0.05 to 1, and even more preferably 0.1 to 0.6. Furthermore, from the viewpoint of stably obtaining a foamed particle molded article that has a good black appearance, excellent mechanical properties, and excellent weather resistance over a long period of time, the primary particle size of the carbon black is preferably 10 to 100 nm. In addition, the carbon black is preferably furnace black obtained by the furnace method.

[0032] The polypropylene resin foam particles of the present invention may contain the ultraviolet absorber. Examples of the ultraviolet absorber include benzophenone compounds and benzotriazole compounds. Examples of benzophenone compounds include 2-hydroxy-4-octyloxybenzophenone, and examples of benzotriazole compounds include 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzylphenyl)]-2H-benzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzotriazole, and 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole. From the viewpoint of stably obtaining foamed particle molded articles that exhibit excellent weather resistance over a long period of time, the content of ultraviolet absorber in the foamed particles is preferably 0.01% by mass or more and 2% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.8% by mass or less. Furthermore, from the viewpoint of being able to stably obtain a foam particle molded article that exhibits excellent weather resistance over a long period of time without significantly impairing the in-moldability of the foam particles, the mass ratio of the ultraviolet absorber to the hindered amine compound in the foam particles is preferably 0.6 or more and 5 or less, more preferably 0.7 or more and 3 or less, and even more preferably 0.8 or more and 2 or less. The aforementioned ultraviolet absorber is a compound that has the property of absorbing ultraviolet light, and is a compound that can mainly absorb light with a wavelength of 300 to 400 μm. The amount of ultraviolet absorber in the foamed particles can be determined by, for example, proton nuclear magnetic resonance (M / A) testing on the foamed particles, similar to the measurement of the amount of hindered amine compounds in the foamed particles. 1 It can be calculated by performing a 1H-NMR measurement.

[0033] The polypropylene resin foam particles of the present invention may contain resins or elastomers other than the polypropylene resin, to the extent that they do not hinder the desired effects of the present invention. Specifically, they may contain resins or elastomers other than the propylene homopolymer or the propylene copolymer. The content of resins or elastomers other than the polypropylene resin in the polypropylene resin foam particles is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the polypropylene resin.

[0034] The polypropylene resin foam particles of the present invention may have a fusion layer on their surface to enhance the fusion properties between the foam particles during in-mold molding. The fusion layer may be present on the entire surface of the foam particles or on only a part of the surface. Examples of resins constituting the fusion layer include crystalline polyolefin resins having a melting point lower than the melting point of the polypropylene resin constituting the foam particles, amorphous polyolefin resins having a softening point lower than the melting point of the polypropylene resin constituting the foam particles, or adhesive resins such as urethane resins. The method for forming a fusion layer on the surface of foamed particles is not particularly limited. Examples include foaming resin particles having a fusion layer, or obtaining foamed particles and then attaching the fusion layer to them. When obtaining foamed particles by foaming resin particles having a fusion layer, it is preferable to employ a method of laminating the fusion layer on the surface of the resin particles by co-extrusion during the manufacturing of the resin particles.

[0035] [Method for manufacturing polypropylene resin foam particles] As described above, the polypropylene resin foam particles of the present invention contain a hindered amine compound, the hindered amine compound has repeating units represented by the general formula (I), the polystyrene-equivalent number-average molecular weight of the hindered amine compound is 1000 or more and 2000 or less, and the content of the hindered amine compound in the polypropylene resin foam particles is 0.01% by mass or more and 2% by mass or less. There are no particular restrictions on the manufacturing method. Such foam particles can be manufactured, for example, by dispersing polypropylene resin particles containing a foaming agent and a hindered amine compound in an aqueous medium in a container, and then releasing the resin particles together with the aqueous medium from the container into an atmosphere of pressure lower than the pressure inside the container to foam the resin particles. An example of a suitable manufacturing method is shown below.

[0036] A preferred method for producing polypropylene resin foam particles of the present invention includes a dispersion step of dispersing polypropylene resin particles containing a hindered amine compound in an aqueous medium containing an inorganic dispersant in a container; a foaming agent impregnation step of impregnating the polypropylene resin particles with a foaming agent in the container; and a foaming step of releasing the polypropylene resin particles containing the foaming agent together with the aqueous medium from the container to cause foaming. In other words, the preferred method for producing polypropylene resin foam particles of the present invention is a method for producing polypropylene resin foam particles comprising: a dispersion step of dispersing polypropylene resin particles containing a hindered amine compound in an aqueous medium containing an inorganic dispersant in a container; a foaming agent impregnation step of impregnating the polypropylene resin particles with a foaming agent in the container; and a foaming step of releasing the polypropylene resin particles containing the foaming agent together with the aqueous medium from the container to foam, wherein the hindered amine compound has a structure represented by the following general formula (I), the polystyrene-equivalent number average molecular weight of the hindered amine compound is 1000 or more and 2000 or less, and the content of the hindered amine compound in the polypropylene resin particles is 0.01% by mass or more and 2% by mass or less.

[0037] (Manufacturing of polypropylene resin particles) The resin particles used in the production of polypropylene resin foam particles of the present invention can be obtained by supplying the polypropylene resin, the hindered amine compound, and other additives such as foam regulators, pigments, and ultraviolet absorbers as needed into an extruder, heating and kneading them to form a resin molten product, and then extruding the resin molten product from the extruder while pelletizing it using methods such as strand cutting, hot cutting, or underwater cutting.

[0038] The average mass per resin particle (the arithmetic mean of the masses of 200 randomly selected particles) is preferably adjusted to 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and even more preferably 0.4 to 2 mg. The external shape of the particles is not particularly limited as long as it can achieve the intended purpose of the present invention, but is preferably cylindrical. When the external shape of the resin particles is cylindrical, the particle diameter (length in the extrusion direction) of the resin particles is preferably 0.1 to 3.0 mm, and more preferably 0.3 to 1.5 mm. Furthermore, the ratio (length / diameter ratio) of the length of the resin particles in the extrusion direction to the length in the direction perpendicular to the extrusion direction (diameter of the resin particles) is preferably 0.5 to 5.0, and more preferably 1.0 to 3.0.

[0039] In the strand cutting method, the particle size, length / diameter ratio, and average mass of the resin particles can be adjusted by appropriately changing the extrusion speed, take-up speed, cutter speed, etc., when extruding the molten resin.

[0040] (Manufacturing of polypropylene resin foam particles) A preferred method for producing polypropylene resin foam particles of the present invention includes a dispersion step of dispersing polypropylene resin particles containing a hindered amine compound in an aqueous medium containing an inorganic dispersant in a container, a foaming agent impregnation step of impregnating the polypropylene resin particles with a foaming agent in the container, and a foaming step of releasing the polypropylene resin particles containing the foaming agent together with the aqueous medium from the container to cause foaming, and it is preferable that these steps be performed in this order.

[0041] In a preferred method for producing polypropylene resin foam particles of the present invention, the first step includes a dispersion step in which polypropylene resin particles containing a hindered amine compound are dispersed in an aqueous medium containing an inorganic dispersant in a container. An aqueous dispersion medium is used as the dispersion medium for dispersing the resin particles obtained as described above in a sealed container. The aqueous dispersion medium is a dispersion medium whose main component is water. The proportion of water in the aqueous dispersion medium is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. Examples of dispersion media other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, ethanol, etc. Furthermore, from the viewpoint of being able to produce foamed particles that can be molded in a mold at relatively low molding pressure and stably form molded articles with good physical properties, with high productivity, it is preferable that no organic peroxides are added to the aqueous medium.

[0042] In the dispersion medium discharge foaming method, which is preferably used in the present invention and involves releasing polypropylene resin particles containing a foaming agent from a container together with an aqueous medium to cause foaming, it is preferable to add a dispersant to the dispersion medium so that the heated polypropylene resin particles in the container do not fuse together within the container. Any dispersant that prevents the polypropylene resin particles from fusing together within the container is acceptable, and both organic and inorganic dispersants can be used, but inorganic dispersants are preferred, and fine-grained inorganic dispersants are even more preferred due to their ease of handling. Examples include natural or synthetic clay minerals such as amsnite, kaolin, mica, and clay, as well as aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and iron oxide. One type may be used, or two or more types may be used in combination. Among these, natural or synthetic clay minerals are preferred. The amount of dispersant added is preferably 0.001 to 5 parts by mass per 100 parts by mass of the resin particles. Furthermore, depending on the type of hindered amine compound incorporated into the resin particles, the inorganic dispersant in the dispersion medium may easily adhere to the surface of the resin particles. This can lead to a large amount of inorganic dispersant adhering to the surface of the resulting foamed particles, potentially worsening the fusion of the foamed particles during in-mold molding. However, in the present invention, by using a specific hindered amine compound, it is possible to obtain a molded article with good fusion, excellent mechanical properties, and long-term weather resistance.

[0043] Furthermore, when using a dispersant, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylsulfonate, or sodium oleate as a dispersing aid. It is preferable to add the dispersing aid in an amount of about 0.001 to 1 part by mass per 100 parts by mass of the resin particles.

[0044] A preferred method for producing polypropylene resin foam particles of the present invention includes, after the dispersion step, a foaming agent impregnation step in which a foaming agent is impregnated into the polypropylene resin particles in a container. For foaming polypropylene resin particles, it is preferable to use a physical blowing agent. Examples of physical blowing agents include inorganic physical blowing agents and organic physical blowing agents. Examples of inorganic physical blowing agents include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, and hexane; cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1-chloro-1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride. The physical blowing agent may be used alone or in mixtures of two or more. It is also possible to mix an inorganic physical blowing agent with an organic physical blowing agent. From the viewpoint of environmental impact and ease of handling, the blowing agent used in this manufacturing method is preferably an inorganic physical blowing agent, and more preferably carbon dioxide.

[0045] The amount of foaming agent added per 100 parts by mass of resin particles is preferably 0.1 to 30 parts by mass, and more preferably 0.5 to 15 parts by mass.

[0046] In the foam particle manufacturing process, a preferred method for impregnating resin particles with a foaming agent is to disperse the resin particles in an aqueous dispersion medium in a sealed container, inject the foaming agent into the sealed container under pressure, and maintain the inside of the sealed container at a predetermined temperature and pressure to impregnate the resin particles with the foaming agent.

[0047] A preferred method for producing polypropylene resin foam particles of the present invention includes a foaming step, after the foaming agent impregnation step, in which the polypropylene resin particles containing the foaming agent are released from a container together with an aqueous medium and foamed. The pressure inside the sealed container during foaming (internal pressure) is preferably 0.5 MPa(G) or higher, more preferably 0.8 MPa(G) or higher. The upper limit is preferably 4 MPa(G) or lower, more preferably 3 MPa(G) or lower. Within the above range, the desired foamed particles can be safely manufactured without the risk of damage or explosion of the sealed container. Furthermore, it is preferable to raise the temperature to 100 to 200°C, more preferably 130 to 160°C, hold it at that temperature for about 5 to 30 minutes, and then release the resin particles containing the foaming agent from the sealed container into an atmosphere with a pressure lower than the pressure inside the sealed container (for example, under atmospheric pressure) to cause foaming.

[0048] Furthermore, the polypropylene resin foam particles obtained as described above can be further processed by increasing the pressure inside the bubbles of the foam particles by pressurizing them with air or the like, and then heating them with steam or the like to cause foaming (two-stage foaming), resulting in foam particles with a higher foaming ratio (lower bulk density).

[0049] [Polypropylene-based resin foam particle molded product] The polypropylene resin foam particle molded article of the present invention is an in-mold molded article of foam particles, and is obtained by in-mold molding the foam particles. Specifically, the polypropylene resin foam particles are formed by in-mold molding and containing 0.01% to 2% by mass of a hindered amine compound having repeating units represented by the general formula (I) and having a polystyrene-equivalent number-average molecular weight of 1000 to 2000. In other words, the polypropylene resin foam particles are formed by in-mold molding, wherein the polypropylene resin foam particles contain a hindered amine compound, the hindered amine compound has repeating units represented by the general formula (I), the polystyrene-equivalent number-average molecular weight of the hindered amine compound is 1000 or more and 2000 or less, and the content of the hindered amine compound in the polypropylene resin foam particles is 0.01% by mass or more and 2% by mass or less. Therefore, the polypropylene resin foam particle molded article of the present invention contains 0.01% to 2% by mass of a hindered amine compound having repeating units represented by the general formula (I) and having a polystyrene-equivalent number-average molecular weight of 1000 to 2000.

[0050] The polypropylene resin foam particle molded article of the present invention is preferably obtained by in-mold molding of the foam particles. In-mold molding can be performed by filling a mold with foamed particles and then heating and molding them using a heating medium such as steam. Specifically, after filling the mold with foamed particles, a heating medium such as steam is introduced into the mold to heat and foam the foamed particles, causing them to fuse together and form a molded foamed particle body with the shape of the molded space. Alternatively, in-mold molding in this invention can also be performed by a pressure molding method (for example, Japanese Patent Publication No. 51-22951) in which the foamed particles are pre-pressurized with a pressurized gas such as air to increase the pressure inside the bubbles of the foamed particles, the pressure inside the foamed particles is adjusted to a pressure 0.01 to 0.3 MPa higher than atmospheric pressure, the foamed particles are filled into a mold under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied into the mold to heat and fuse the foamed particles. Furthermore, the product can also be molded using a compression filling molding method (Japanese Patent Publication No. 4-46217), in which foam particles pressurized to a pressure exceeding atmospheric pressure are filled into a mold pressurized to a pressure exceeding atmospheric pressure using compressed gas, and then a heating medium such as steam is supplied into the cavity to heat and fuse the foam particles. In addition, the product can also be molded using an atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795), in which foam particles with high secondary foaming strength obtained under special conditions are filled into the cavity of a mold under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied to heat and fuse the foam particles, or a method combining the above methods (Japanese Patent Publication No. 6-22919).

[0051] The density of the polypropylene-based resin foam particle molded article of the present invention is preferably 10 kg / m³. 3 More than 500kg / m 3 The following is more preferable: 12 kg / m 3The above is preferable, and more preferably 15 kg / m 3 That concludes the explanation. Furthermore, a more preferable value is 200 kg / m³. 3 The following, and more preferably 100 kg / m 3 The following, and more preferably 50 kg / m 3 The following is preferable: By having the density of the foamed particle molded body within the aforementioned range, it is possible to stably obtain a foamed particle molded body that is lightweight and has excellent mechanical properties. The density of the foam is calculated by dividing the mass of the foam particle molded body by the volume calculated based on its dimensions, and can be measured by the method described in the examples.

[0052] The ratio of the tensile strength of the polypropylene resin foam particle molded article of the present invention to its density [tensile strength / density] is preferably 0.016 MPa / [kg / m]. 3 ] or more, and more preferably 0.017 MPa / [kg / m 3 The pressure should be 0.018 MPa / kg / m² or higher, and more preferably 0.018 MPa / kg / m². 3 The limit is 0.030 MPa / kg / m². While there is no upper limit, practically speaking, it is 0.030 MPa / kg / m². 3 [ ] or less, preferably 0.025 MPa / [kg / m 3 The following is preferable: When the ratio of the tensile strength of the foamed particle molded article to the density of the foamed particle molded article is within the above range, the fusion state is good, the mechanical properties are excellent, and the molded article exhibits stable weather resistance over a long period of time. Furthermore, the tensile strength of a foam particle molded article is related to the state of fusion between the foam particles constituting the article. For the same article density, a higher tensile strength indicates a higher degree of fusion between the foam particles constituting the article. On the other hand, since the tensile strength of a molded article also depends on the density of the article, the fusion state of the article can be appropriately evaluated by adopting the ratio of the tensile strength of the foam particle molded article to the density. Tensile strength can be measured in accordance with JIS K6767:1999, for example, by the method described in the examples. Tensile strength refers to the maximum tensile stress generated in the test specimen until it breaks during a tensile test. Furthermore, the ratio of tensile strength to density (tensile strength per unit density) can be calculated by dividing the measured tensile strength value by the density value.

[0053] The tensile elongation of the polypropylene resin foam particle molded article of the present invention is preferably 10% or more, more preferably 15% or more, even more preferably 18% or more, and particularly preferably 20% or more. There is no upper limit, but practically it is 40% or less, and preferably 35% or less. When the tensile elongation of the foam particle molded article is within the above range, the fusion state between the foam particles is good, and in particular the foam particles inside the molded article are well fused. This results in a molded article with excellent durability, which is desirable. Tensile elongation can be measured in accordance with JIS K6767:1999, for example, by the method described in the examples. Tensile elongation refers to the elongation rate of the test specimen when the specimen is cut during a tensile test.

[0054] The polypropylene resin foam particle molded articles of the present invention have excellent long-term weather resistance and excellent mechanical properties, and can be used as shock absorbers, heat insulating materials and various packaging materials, etc., in applications such as food transport containers, packaging and cushioning materials for electrical and electronic components, vehicle components such as automobile bumpers, building components such as housing insulation materials, and general merchandise. [Examples]

[0055] Next, the present invention will be described in more detail with reference to examples, but these examples do not limit the present invention in any way.

[0056] [Measurement and Evaluation] The hindered amine compounds, resins, foamed particles, and molded foamed particle articles used in the examples and comparative examples were subjected to the following measurements and evaluations. The evaluation of the foamed particles or molded foamed particle articles was performed after conditioning them for two days under conditions of 50% relative humidity, 23°C, and 1 atm.

[0057] <Number average molecular weight of hindered amine compounds> The number-average molecular weight of hindered amine compounds is measured by gel permeation chromatography (GPC) and is calculated using monodisperse polystyrene as the standard substance.

[0058] <Bulk density of foamed particles> Approximately 500cm 3 The foamed particle group was filled into a graduated cylinder, and the filling height of the foamed particle group inside the cylinder was stabilized by lightly tapping the floor several times with the bottom of the graduated cylinder. The bulk volume of the foamed particle group indicated by the scale on the graduated cylinder was read and designated as V1 (L). Next, the mass of the foamed particle group was measured and designated as W1 [g]. Divide the mass W1 [g] of the foam particles by the volume V1 (W1 / V1) and convert the unit to [kg / m³]. 3 The bulk density of the foamed particles was determined by converting it to [a specific value].

[0059] <Total heat of fusion and high-temperature peak heat of fusion of foamed particles> The total heat of fusion and high-temperature peak heat of fusion of the foamed particles were measured by differential scanning calorimetry in accordance with JIS K7122-1987. Specifically, approximately 2 mg of foamed particles were collected, and temperature measurements were taken from 23°C to 200°C at a rate of 10°C / min using a differential scanning calorimetry meter (DSC7020, Hitachi High-Tech Science Corporation), obtaining a DSC curve with one or more melting peaks. In the following explanation, the resin-specific peak is denoted as A, and the high-temperature peak appearing at a higher temperature is denoted as B. A straight line (α-β) was drawn connecting point α on the DSC curve corresponding to 80°C and point β on the DSC curve corresponding to the melting termination temperature T of the foamed particles. The melting termination temperature T is the high-temperature endpoint of the high-temperature peak B, and is the intersection point of the high-temperature peak and the high-temperature baseline. Next, a straight line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve, which is in the valley between the resin-specific peak A and the high-temperature peak B, and the point where it intersects with the straight line (α-β) was denoted as δ. The area of ​​high-temperature peak B is the area enclosed by the curve of the high-temperature peak B portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ), and this was defined as the heat of fusion of the high-temperature peak. The area of ​​the total melting peak is the area enclosed by the curve of the resin-specific peak A portion of the DSC curve, the curve of the high-temperature peak B portion, and the line segment (α-β), and this was defined as the total heat of fusion.

[0060] <Heat of fusion (ΔHs) of the high-temperature peak at the surface of the foamed particle and heat of fusion (ΔHi) of the high-temperature peak inside the foamed particle> In each example and comparative example, a sample of approximately 2 mg was prepared by cutting out a portion of multiple foamed particles that was contained within a range of 200 μm from the surface of the foamed particle toward the center of gravity of the foamed particle. This sample was designated as the surface layer of the foamed particle. In each example and comparative example, approximately 2 mg of sample was prepared by cutting out the interior of a foamed particle from multiple foamed particles, excluding the surface layer. This sample was used as the interior of the foamed particle. The surface layer and interior of the foamed particles were each subjected to differential scanning calorimetry using the same method as described above for the <total heat of fusion and high-temperature peak heat of fusion of the foamed particles>, and the high-temperature peak heat of fusion was obtained. The heat of fusion of the high-temperature peak on the surface of the foamed particle was denoted as ΔHs, and the heat of fusion of the high-temperature peak inside the foamed particle was denoted as ΔHi. A value 0.86 times ΔHi was calculated and then multiplied by 0.86, resulting in ΔHi × 0.86. The results are shown in Table 1.

[0061] <Average bubble diameter of foamed particles> The average bubble diameter of the foamed particles was measured as follows: Thirty foam particles were randomly selected from the group of foam particles. Each foam particle was cut in half through its center, and magnified photographs of each cross-section were taken. In each cross-sectional photograph, four line segments were drawn from the outermost surface of the foam particle through the center to the outermost surface of the opposite side, such that the angles between adjacent line segments were equal. The number of bubbles intersecting each line segment was measured, and the average bubble diameter of each foam particle was calculated by dividing the total length of the four line segments by the total number of bubbles intersecting the segments. The average bubble diameter of the foam particles was then calculated by taking the arithmetic mean of these values.

[0062] <Average surface thickness of foamed particles> Thirty foam particles were randomly selected from the group of foam particles. Each foam particle was cut in half through its center, and magnified photographs of each cross-section were taken. In each cross-sectional photograph, eight line segments were drawn from the outermost surface of the foam particle through the center to the outermost surface on the opposite side, such that the angles between adjacent line segments were equal. Along these eight line segments, the length from the outermost surface of the foam particle to the outermost edge of the bubble located on the outermost surface side of the foam particle (outermost surface resin thickness) was measured, and the average outermost resin thickness of each foam particle was calculated by arithmetic mean of these values. Then, the average surface thickness of the foam particles was calculated by arithmetic mean of the average outermost thickness of the 30 foam particles.

[0063] <Density of foamed particle molded body> The foamed particle molded body was left for 2 days under conditions of 50% relative humidity, 23°C, and 1 atm. Next, its mass was measured and defined as W [g]. Next, based on the dimensions of the foamed particle molded body, the volume V [cm³] of the foamed particle molded body is calculated. 3 ] was measured. The mass W [g] of the foamed particle molded body is divided by the volume V (W / V), and the unit is [kg / m³]. 3 The density of the foamed particle molded body was determined by converting it to [ ].

[0064] <Molding cycle evaluation> During the in-mold molding of foamed particle bodies, the time (cooling time) from the end of heating until the pressure (surface pressure) on the inner surface of the mold reached 0.04 MPa(G) was measured and evaluated according to the following criteria. • Evaluation criteria A: Cooling time is 40 seconds or less. B: Cooling time is between 40 and 50 seconds. C: Cooling time is between 50 and 60 seconds. D: Cooling time exceeds 60 seconds When the cooling time is 50 seconds or less, more preferably 40 seconds or less, the time required for cooling is short, and in-mold molding of the foamed particle molded body can be performed efficiently, resulting in a particularly excellent molding cycle. In the molding cycle evaluation, the cooling time was measured and evaluated when molding was performed at the lowest molding pressure that yielded a good molded product with good fusion between foam particles, minimal shrinkage, and few gaps on the surface of the molded product.

[0065] <Weather resistance of foamed particle molded products> The molded body was irradiated with light under the following conditions in accordance with JIS K 7350-2:2008. The weather resistance of the foamed particle molded body was evaluated by measuring the mechanical properties (tensile strength, tensile elongation, tensile strength per unit density) of the molded body after light irradiation by tensile testing and by observing the change in appearance (changes before and after light irradiation). (Light irradiation conditions) Equipment used: i Super Xenon Tester XER-W83, manufactured by Iwasaki Electric Co., Ltd. Light source: Xenon arc lamp Filter: Inner filter: Quartz glass, Outer filter: Borosilicate glass Irradiance: 120W / m 2 Radiation duration: 330 hours (equivalent to 0.5 years of sunlight) or 1320 hours (equivalent to 2 years of sunlight) Black panel temperature: 63℃ Spray cycle: 18 minutes of water spraying out of 120 minutes (102 minutes of spectral irradiation followed by 18 minutes of spectral irradiation and water spraying) Humidity inside the tank: 50% Test specimen size: 150 x 70 x 10 mm

[0066] (Tensile test of foamed particle molded body) Tensile tests of the foamed particle molded articles were conducted in accordance with JIS K6767:1999 under the following conditions. From the foamed particle molded body or the foamed particle molded body after irradiation with light under the above conditions, a cut piece was prepared using a vertical slicer so that all surfaces were cut surfaces (excluding the surface portion). From this cut piece, a dumbbell-shaped test specimen (measurement section length 40 mm, width 10 mm, thickness 10 mm) was prepared using a jigsaw. A tensile test was performed on the test specimen at a tensile speed of 500 mm / min, and the maximum load and the gauge length at break were measured. The maximum tensile stress in the tensile test was defined as the tensile strength, and the elongation at break of the test specimen ([gauge length at break - gauge length before test] ÷ gauge length at break × 100) was defined as the tensile elongation. A Tensilon universal tester (manufactured by Orientec Co., Ltd.) was used as the measuring device. Furthermore, the tensile strength per unit density (ratio of the tensile strength of the foamed particle molded body to the density of the foamed particle molded body [tensile strength / density]) was determined by dividing the maximum tensile strength by the density.

[0067] (Visual evaluation of foamed particle molded products) The appearance of the foamed particle molded product was evaluated using the following criteria, with the appearance of the molded product before light irradiation as the standard. • Appearance evaluation criteria A: No change in appearance B: Chalking (powdering) is observed on the surface.

[0068] [Raw materials] The raw materials used in the examples and comparative examples are as follows. (Polypropylene resin) • FL7540L: Manufactured by TPC, FL7540L, propylene-ethylene-butene copolymer, melting point 141℃, MFR (load 2.16kg, 230℃, JIS K7210) 7g / 10min

[0069] (Hindered amine compounds) • UV-3529: Cyasorb UV-3529, manufactured by Solvay, NR-type hindered amine, poly{[6-morpholinyl-1,3,5-triazine-2,4-diyl][(1,2,2,6,6-pentamethyl-4-piperidyl)imino]hexamethylene[(1,2,2,6,6-pentamethyl-4-piperidyl)imino]}, a compound represented by the following formula (IV), in general formula (I), where X is a hexamethylene group, Y is a morpholinyl group, Z 1 is a methyl group, Z 2 It is a methyl group. Polystyrene equivalent number-average molecular weight: 1700 [ka] • NOR116: Manufactured by BASF, Flame stab NOR116, NOR-type hindered amine, compound represented by the following formula (V), molecular weight 2261 [ka] Tinuvin622: Manufactured by BASF, Tinuvin622, NR-type hindered amine, dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, a compound represented by the following formula (VI), polystyrene-equivalent number-average molecular weight 3550. [ka] • UV70: Sabostab UV70, manufactured by Songwong, is an NH-type hindered amine, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, a compound represented by the following formula (VII), with a molecular weight of 481. [ka]

[0070] [Manufacturing of polypropylene resin foam particles and foam particle molded products] (Example 1) An extruder with an inner diameter of 26 mm was prepared, equipped with a strand-forming die on the outlet side. FL7540L, zinc borate (arithmetic mean particle size based on number: 7 μm) as a foam regulator, and UV-3529 were supplied to the extruder and melt-kneaded to form a resin molten product. UV-3529 was supplied so that the zinc borate content in the foamed particles was 500 ppm by mass and the UV-3529 content in the foamed particles was as shown in Table 1. The obtained molten resin was extruded as strands from a strand-forming die, the extruded strands were water-cooled, and cut with a pelletizer to obtain polypropylene resin particles with an average mass of 1.0 mg per particle.

[0071] 500g of the polypropylene resin particles, 3.5L of water as a dispersion medium, 3g of kaolin as a dispersant, and 0.2g of sodium dodecylbenzenesulfonate (product name: Neogen, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a surfactant were placed in a 5L sealed container. Next, carbon dioxide was injected into a sealed container as a foaming agent, and the container was pressurized to a gauge pressure of 2.5 MPa(G). Then, while stirring the contents of the sealed container, the container was heated to the foaming temperature (146°C) at a heating rate of 2°C / min. The container was then held at the same temperature for 15 minutes. The high-temperature peak heat quantity (obtained from the endothermic curve by DSC measurement) can be adjusted by changing the holding temperature and holding time. After that, the contents of the sealed container were released to atmospheric pressure to obtain polypropylene resin foam particles. The measurement results of the physical properties of the obtained polypropylene resin foam particles are shown in Table 1.

[0072] The aforementioned polypropylene resin foam particles were filled into a flat mold measuring 250 mm in length, 200 mm in width, and 50 mm in thickness. A plate-shaped foam particle molded body was obtained by in-mold molding under pressure using steam heating. The heating method involved preheating (exhaust process) by supplying steam for 5 seconds with the drain valves on both sides of the mold open. Then, steam was supplied from one side of the mold for heating, and then from the other side for further heating. Subsequently, steam was supplied from both sides of the mold at a molding heating steam pressure of 0.24 MPa (G) for heating (main heating). After the main heating was completed, the pressure was released, and the molded body was cooled with water until the pressure generated on the molded surface due to the foaming force of the molded body (surface pressure) reached 0.04 MPa (G). After that, the mold was opened and the molded body was removed from the mold. The molded body removed from the mold was cured in an 80°C oven for 12 hours, and then slowly cooled to room temperature to obtain a foam particle molded body. Table 1 shows the results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded body.

[0073] (Example 2) Polypropylene resin foam particles were obtained in the same manner as in Example 1, except that the amount of UV-3529 was changed so that the UV-3529 content in the foam particles was as shown in Table 1. The measurement results of the physical properties of the obtained polypropylene resin foam particles are shown in Table 1. Using the polypropylene resin foam particles obtained here, a foam particle molded article was obtained in the same manner as in Example 1. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded article are shown in Table 1.

[0074] (Example 3) Polypropylene resin foam particles were obtained in the same manner as in Example 1, except that the amount of UV-3529 was changed so that the UV-3529 content in the foam particles was as shown in Table 1. The measurement results of the physical properties of the obtained polypropylene resin foam particles are shown in Table 1. Using the polypropylene resin foam particles obtained here, a foam particle molded article was obtained in the same manner as in Example 1. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded article are shown in Table 1.

[0075] (Example 4) After the foaming process in Example 1, the following two-stage foaming process was performed. In the pressurized sealed container, the polypropylene resin foam particles obtained in the foaming process of Example 1, after being cured at 60°C for 12 hours (hereinafter referred to as "first-stage foam particles"), were filled. The pressure inside the sealed container was increased from normal pressure (atmospheric pressure) to pressurize the foam particles to 0.6 MPa (G). The pressurized state of the foam particles was maintained for 12 hours to increase the pressure inside the bubbles of the foam particles. Subsequently, the first-stage foam particles were removed from the sealed container to obtain first-stage foam particles with an internal bubble pressure of 0.5 MPa (G). These first-stage foam particles were then supplied to a second-stage foaming apparatus. Steam was supplied into the apparatus to foam the first-stage foam particles, resulting in a bulk density of 27 kg / m³. 3 Polypropylene-based foamed particles (two-stage foamed particles) were obtained. The measurement results of the physical properties of the obtained polypropylene-based foamed particles are shown in Table 1. The obtained polypropylene resin foam particles were placed in a pressurized sealed container and pressurized, increasing the pressure inside the bubbles to 0.05 MPa (G). Using these foam particles instead of the foam particles used in Example 1, and changing the molding heating steam pressure to 0.18 MPa (G) during this heating process, in-mold molding was performed in the same manner as in Example 1 to obtain a foam particle molded body. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded body are shown in Table 1.

[0076] (Comparative Example 1) Polypropylene-based foamed resin particles were obtained in the same manner as in Example 1, except that UV-3529 was not used. The measurement results of the physical properties of the obtained polypropylene-based foamed resin particles are shown in Table 1. Using the polypropylene resin foam particles obtained here, a foam particle molded body was obtained in the same manner as in Example 1. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded body are shown in Table 1. In the tensile test after 1320 hours of light irradiation (equivalent to 2 years of sunlight), the molded body collapsed during the preparation of the test specimen, making it impossible to perform the tensile test.

[0077] (Comparative Example 2) Polypropylene-based foamed resin particles were obtained in the same manner as in Example 1, except that UV-3529 was replaced with NOR116. The measurement results of the physical properties of the obtained polypropylene-based foamed resin particles are shown in Table 1. Using the polypropylene resin foam particles obtained here, a foam particle molded article was obtained in the same manner as in Example 1. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded article are shown in Table 1.

[0078] (Comparative Example 3) Polypropylene-based foamed resin particles were obtained in the same manner as in Example 1, except that UV-3529 was replaced with Tinuvin622. The measurement results of the physical properties of the obtained polypropylene-based foamed resin particles are shown in Table 1. Using the polypropylene resin foam particles obtained here, a foam particle molded article was obtained in the same manner as in Example 1. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded article are shown in Table 1.

[0079] (Comparative Example 4) Polypropylene-based foamed resin particles were obtained in the same manner as in Example 1, except that UV-3529 was changed to UV70. The measurement results of the physical properties of the obtained polypropylene-based foamed resin particles are shown in Table 1. Using the polypropylene resin foam particles obtained here, a foam particle molded article was obtained in the same manner as in Example 1. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded article are shown in Table 1.

[0080] (Comparative Example 5) Polypropylene resin foam particles were obtained in the same manner as in Example 1, except that the amount of UV-3529 was changed so that the UV-3529 content in the foam particles was as shown in Table 1. The measurement results of the physical properties of the obtained polypropylene resin foam particles are shown in Table 1. Using the polypropylene resin foam particles obtained here, a foam particle molded article was obtained in the same manner as in Example 1. The results of the molding cycle evaluation and weather resistance evaluation of the obtained foam particle molded article are shown in Table 1.

[0081] [Table 1]

[0082] The results shown in Table 1 indicate that the foamed particle molded articles of the examples exhibit excellent mechanical properties, such as tensile elongation and tensile strength in tensile tests. Furthermore, they maintain their mechanical properties and show no change in appearance even in weathering tests under conditions equivalent to exposure to sunlight for approximately two years. This demonstrates that the polypropylene-based resin foamed particles of the present invention can be used to produce foamed particle molded articles with excellent long-term weather resistance and mechanical properties, and that the polypropylene-based resin foamed particle molded articles of the present invention exhibit excellent long-term weather resistance and mechanical properties.

[0083] (Example 5) Polypropylene resin foam particles were obtained in the same manner as in Example 1, except that, in the production of polypropylene resin particles, carbon black (furnace black, primary particle size: 15 nm) was supplied to the extruder in addition to FL7540L, zinc borate, and UV-3529, and the mixture was melt-kneaded to form a resin molten product. During the production of the polypropylene resin particles described above, UV-3529 was supplied so that the zinc borate content in the foamed particles was 500 ppm by mass, the UV-3529 content in the foamed particles was as shown in Table 2, and carbon black was supplied so that the carbon black content in the foamed particles was 2.6% by mass. Table 2 shows the measurement results of the physical properties of the obtained polypropylene resin foam particles.

[0084] (Example 6) Polypropylene resin foam particles were obtained in the same manner as in Example 1, except that, in the production of polypropylene resin particles, an ultraviolet absorber (Chimassorb81) was supplied to the extruder in addition to FL7540L, zinc borate, and UV-3529, and the mixture was melt-kneaded to form a resin molten product. During the production of the polypropylene resin particles described above, UV-3529 was supplied so that the zinc borate content in the foamed particles was 500 ppm by mass, the UV-3529 content in the foamed particles was as shown in Table 2, and the ultraviolet absorber (Chimassorb81) was supplied so that the ultraviolet absorber (Chimassorb81) content in the foamed particles was 0.2% by mass. The ultraviolet absorber (Chimassorb81) is Chimassorb81 (benzophenone compound: 2-hydroxy-4-(octyloxy)benzophenone, manufactured by BASF). Table 2 shows the measurement results of the physical properties of the obtained polypropylene resin foam particles.

[0085] (Example 7) Polypropylene resin foam particles were obtained in the same manner as in Example 1, except that, in the production of polypropylene resin particles, in addition to FL7540L, zinc borate, and UV-3529, an ultraviolet absorber (Tinuvin326) was supplied to the extruder so that the content of the ultraviolet absorber (Tinuvin326) in the foam particles was 0.2% by mass, and the mixture was melt-kneaded to form a resin molten product. During the production of the polypropylene resin particles described above, UV-3529 was supplied so that the zinc borate content in the foamed particles was 500 ppm by mass, the UV-3529 content in the foamed particles was as shown in Table 2, and the ultraviolet absorber (Tinuvin326) was supplied so that the ultraviolet absorber (Tinuvin326) content in the foamed particles was 0.2% by mass. The ultraviolet absorber (Tinuvin326) is Tinuvin326 (benzotriazole compound: 2-t-butyl-6-(5-chloro-2H-benzotriazole-2-yl)-4-methylphenol, manufactured by BASF). Table 2 shows the measurement results of the physical properties of the obtained polypropylene resin foam particles.

[0086] [Table 2]

[0087] As shown in Table 2, the foamed particle molded articles of the examples exhibit excellent mechanical properties such as tensile elongation and tensile strength in tensile tests. Furthermore, they maintained their mechanical properties and showed no change in appearance even in weathering tests under conditions equivalent to exposure to sunlight for approximately two years.

Claims

1. Polypropylene resin foam particles containing a hindered amine compound, The aforementioned hindered amine compound has repeating units represented by the following general formula (I), and the polystyrene-equivalent number-average molecular weight of the hindered amine compound is 1000 or more and 2000 or less. Polypropylene resin foam particles wherein the content of the hindered amine compound in the polypropylene resin foam particles is 0.01% by mass or more and 2% by mass or less. 【Chemistry 1】 (However, in the above general formula (I), X represents an alkylene group having 5 to 10 carbon atoms, Y represents an amino group, and Z 1 and Z 2 (This represents an alkyl group.)

2. The polypropylene resin foam particle according to claim 1, wherein Y in the general formula (I) is a morpholinyl group.

3. The polypropylene resin foam particles according to claim 1, wherein the average bubble diameter of the polypropylene resin foam particles is 50 μm or more and 250 μm or less.

4. The polypropylene resin foam particles according to claim 1, wherein the average surface thickness of the polypropylene resin foam particles is 5 μm or more and 20 μm or less.

5. The bulk density of the polypropylene resin foam particles is 10 kg / m³ 3 More than 500kg / m 3 The polypropylene resin foam particles according to claim 1, which are as follows:

6. A molded polypropylene resin foam particle body obtained by in-mold molding polypropylene resin foam particles according to any one of claims 1 to 5.

7. The density of the polypropylene-based resin foam particle molded body is 10 kg / m³ 3 More than 100kg / m 3 The ratio of the tensile strength of the polypropylene resin foam particle molded body to its density [tensile strength / density] is 0.016 MPa / [kg / m]. 3 The polypropylene resin foam particle molded article according to claim 6, which is as described above.

8. The polypropylene resin foam particle molded article according to claim 6, wherein the tensile elongation of the polypropylene resin foam particle molded article is 20% or more.

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