Method for producing foamed particles

Abstract

The present invention relates to a method for producing foamed particles using, as a base resin, a mixture in which a polypropylene resin A, which is a non-recycled material, and a polypropylene resin B, which is a recycled material of a post-consumer material, are mixed. Provided is a method for producing foamed particles, which is capable of producing foamed particles in which variations in the expansion ratio and a decrease in the percentage of closed area are suppressed, and which is capable of providing a foamed particle molded article molded using the foamed particles with a good appearance. The method for producing foamed particles uses, as a base resin, a mixture in which a polypropylene resin A having a melting point of 130-155 DEG C and a polypropylene resin B, which is a recycled material of post-consumer materials, the blending ratio of the polypropylene resin A in the mixture being 40-97 wt%. The blending ratio of the polypropylene resin B is 3-60 wt% (the total of the polypropylene resin A and the polypropylene resin B is 100 wt%), and the difference between the melting points of the polypropylene resin A and the polypropylene resin B (the melting point of the polypropylene resin B-the melting point of the polypropylene resin A) is 10-30 DEG C (inclusive). The ash content of the polypropylene resin B is 5% by weight or less, and the difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of a melting peak shown in a DSC curve in heat flux differential scanning calorimetry of the polypropylene resin B is 30 DEG C or more.

Description

Technical Field

[0001] The present invention relates to a method for producing polypropylene resin foamed particles, and more particularly to a method for producing foamed particles using a polypropylene resin A which is a non-recycled material and a polypropylene resin B which is a recycled product of a post-consumer material as polypropylene resins. Background Art

[0002] In recent years, in the process of promoting a recycling-oriented society, the use of recycled materials recovered from used products has become a social and technical issue. In the field of plastic product technology, social demand for the use of waste materials used by end users as recycled materials is increasing. In particular, research has been conducted on recycled polypropylene using waste materials such as recycled disposable containers made of polypropylene resin.

[0003] In response to this, a technology related to the utilization of used polyolefin resin foamed molded products has been proposed. For example, Patent Document 1 proposes the following technology: a pulverized product obtained by pulverizing a waste polyolefin resin molded product and a virgin polyolefin resin are mixed to prepare pellets, and a foaming agent is impregnated into the pellets to produce a polyolefin resin foamed molded product.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-283576 Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] However, Patent Document 1 has the following technical problems, which can be improved. That is, when the foamed beads are produced using the recycled post-consumer material made from the waste polyolefin resin molded body and the polyolefin resin material as the non-recycled material, the expansion ratio of the obtained foamed beads may deviate, and the closed cell ratio of the foamed beads may decrease. Furthermore, when the foamed beads obtained in this way are used to mold the foamed bead molded body, the appearance may be poor.

[0009] The present invention has been made in view of the above technical problems. That is, the present invention relates to a method for producing foamed beads using a mixture of a polypropylene resin A as a non-recycled material and a polypropylene resin B as a recycled material of a post-consumer material as a base resin, and to a method for producing foamed beads in which the variation of the expansion ratio and the decrease of the closed cell ratio are suppressed, and the appearance of a foamed bead molded body molded using the foamed beads is good.

[0010] (II) Technical solution

[0011] The method for producing foamed beads of the present invention comprises the steps of impregnating polypropylene resin particles dispersed in an aqueous medium with a foaming agent in a sealed container, releasing the polypropylene resin particles containing the foaming agent together with the aqueous medium from the sealed container to a pressure lower than the pressure in the sealed container to foam the polypropylene resin particles containing the foaming agent, thereby producing a foamed bead having a foaming capacity of 10 kg / m 3 Above 200kg / m 3 The method for producing polypropylene resin foamed particles having a bulk density as follows is characterized in that:

[0012] The polypropylene resin particles are prepared by mixing a polypropylene resin A and a polypropylene resin B having a melting point of 130° C. to 155° C. as a base resin.

[0013] The blending ratio of the polypropylene resin A in the mixture is 40% by weight or more and 97% by weight or less, and the blending ratio of the polypropylene resin B is 3% by weight or more and 60% by weight or less (the total of the polypropylene resin A and the polypropylene resin B is 100% by weight),

[0014] The difference in melting points between the polypropylene resin A and the polypropylene resin B (melting point of the polypropylene resin B - melting point of the polypropylene resin A) is 10° C. or more and 30° C. or less,

[0015] The polypropylene resin B is a recycled product of post-consumer materials.

[0016] The ash content contained in 100% by weight of the polypropylene resin B is 5% by weight or less,

[0017] The difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak shown in the DSC curve in heat flux differential scanning calorimetry of the polypropylene resin B is 30° C. or more.

[0018] (III) Beneficial effects

[0019] The manufacturing method of the present invention can produce foamed particles with suppressed variations in expansion ratio and reduction in closed cell ratio even when recycled post-consumer materials are blended. In addition, the appearance of a foamed molded article molded using the foamed particles manufactured by the manufacturing method of the present invention is good.

[0020] According to the present invention which has the above-mentioned excellent effects, recycled materials of plastic products can be effectively utilized to provide foamed beads and foamed bead molded bodies which are sufficiently practical. Therefore, the present invention has a great contribution to solving environmental problems such as reducing carbon dioxide emissions by recycling raw materials or utilizing waste products required by a recycling-oriented society. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an example of the second DSC curve of the recovered resin and the differential curve of the second DSC curve.

[0022] Figure 2 This is an example of a DSC curve obtained based on the heat flux differential scanning calorimetry method described in JIS K7122-1987 for obtaining the high-temperature peak calorific value of expanded beads. DETAILED DESCRIPTION

[0023] Hereinafter, the method for producing the foamed beads of the present invention will be described. Hereinafter, the method for producing the foamed polypropylene resin beads of the present invention may be simply referred to as the production method of the present invention.

[0024] In addition, for the present invention, post-consumer materials refer to materials after consumers use them as products. Specifically, as defined in JIS Q14021:2000, post-consumer materials refer to materials discharged from households, or materials generated in the form of products that cannot be used for their original purpose from commercial facilities, industrial facilities, and various facilities that are end users of products. The above-mentioned post-consumer materials include materials returned from the circulation path. In addition, recyclates of post-consumer materials (recycled materials) refer to items obtained by recycling the above-mentioned used materials.

[0025] On the other hand, a resin newly prepared as a resin material is sometimes referred to as virgin resin or non-recycled resin.

[0026] In addition, in the following description, the preferred numerical range of the present invention is sometimes appropriately shown. In this case, the preferred range, more preferred range, and particularly preferred range involving the upper and lower limits of the numerical range can be determined by all combinations of the upper and lower limits.

[0027] The production method of the present invention comprises the steps of impregnating polypropylene resin particles dispersed in an aqueous medium with a blowing agent in a sealed container, releasing the polypropylene resin particles containing the blowing agent together with the aqueous medium from the sealed container to a pressure lower than the pressure in the sealed container to foam the polypropylene resin particles containing the blowing agent, thereby producing a polypropylene resin having a strength of 10 kg / m 3 Above 200kg / m 3 The following method is used to prepare polypropylene resin foamed particles having a desired bulk density. According to this foaming method, polypropylene resin foamed particles having a desired bulk density can be easily obtained.

[0028] The manufacturing method of the present invention uses a mixture of a polypropylene resin A having a melting point of 130°C to 155°C and a polypropylene resin B which is a recycled material of a post-consumer material as a base resin. The blending ratio of the polypropylene resin A in the above mixture is 40% by weight to 97% by weight, and the blending ratio of the polypropylene resin B is 3% by weight to 60% by weight. The total of the polypropylene resin A and the polypropylene resin B is 100% by weight. In addition, the above resin is selected so that the melting point difference between the polypropylene resin A and the polypropylene resin B (melting point of the polypropylene resin B - melting point of the polypropylene resin A) is 10°C to 30°C.

[0029] In the production method of the present invention, a resin material having an ash content of 5 wt % or less and a difference (Tme-Tms) between an extrapolated melting start temperature (Tms) and an extrapolated melting end temperature (Tme) of 30° C. or more is selected as the polypropylene resin B.

[0030] The manufacturing method of the present invention having the above-mentioned structure can achieve good foaming properties. Therefore, the manufacturing method of the present invention can avoid the influence caused by the generation of the melting point deviation of the polypropylene resin B which is a post-consumer material, and suppress the deviation of the expansion ratio of the manufactured foamed particles, and at the same time can make the closed cell ratio higher. In addition, the appearance of the foamed molded body formed by using the foamed particles manufactured in this way is good.

[0031] Hereinafter, the present invention will be described in further detail.

[0032] [Base resin]

[0033] In the production method of the present invention, a mixture of polypropylene resin A and polypropylene resin B is used as the base resin. The shape of the base resin including the mixture is not particularly limited, but it is preferably granulated so as to be easily used in the above-mentioned foaming method.

[0034] In addition, the base resin referred to herein refers to the main resin material constituting the polypropylene resin foamed particles produced by the present invention, and other resins other than the polypropylene resin A and the polypropylene resin B may be further blended into the base resin within the range not impairing the intended effect of the present invention. In 100 wt % of the base resin, the mixture of the polypropylene resin A and the polypropylene resin B is preferably 90 wt % or more, more preferably 95 wt % or more, and even more preferably 98 wt % or more.

[0035] [Polypropylene resin A]

[0036] The polypropylene resin A is a non-recycled resin. The polypropylene resin A may basically contain only polypropylene resin which is a virgin resin. In addition, it may contain one or more other resins other than the polypropylene resin and polymer materials such as thermoplastic elastomers and arbitrary additives within the scope that does not hinder the objective effect of the present invention. It is preferred that the polymer materials other than the polypropylene resin contained in the polypropylene resin A are all non-recycled materials.

[0037] The polypropylene resin included in the polypropylene resin A is a resin having a propylene component unit of 50% by weight or more in the resin, and copolymers of propylene homopolymers or propylene and other olefins that can be copolymerized with propylene, etc. can be listed. As other olefins that can be copolymerized with propylene, for example, alpha-olefins with carbon atoms of more than 4 such as ethylene or 1-butene can be illustrated. In addition, the above-mentioned copolymer can be a polypropylene random copolymer, or a block copolymer, and further, can be not only a binary copolymer, but also a ternary copolymer. In addition, these polypropylene resins can use one or more combinations of two or more.

[0038] As the polymer material that can be appropriately included in the polypropylene resin A, for example, other resins other than the polypropylene resin shown below can be exemplified. Examples of other resins include: high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylate copolymers, ethylene-methacrylic acid copolymers, ethylene-methacrylate copolymers and other ethylene resins; polystyrene resins such as polystyrene, high-impact polystyrene, styrene-acrylonitrile copolymers; acrylic resins such as polymethyl methacrylate; polyester resins such as polylactic acid and polyethylene terephthalate, etc. These resins can be used alone or in combination of two or more.

[0039] In addition, as the polymer material, olefin elastomers such as ethylene-hexene copolymers and ethylene-propylene-diene copolymers, and thermoplastic elastomers such as styrene elastomers such as styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof can also be used. These thermoplastic elastomers can be used alone or in combination of two or more.

[0040] The manufacturing method of the present invention can use any one of other resins and the above-mentioned thermoplastic elastomer or a combination of other resins and the above-mentioned thermoplastic elastomer as the above-mentioned polymer material. The blending ratio of the above-mentioned polymer material in the polypropylene resin A is preferably 20% by weight or less, more preferably 10% by weight or less, and further preferably 5% by weight or less.

[0041] Melting point of polypropylene resin A:

[0042] The melting point of the polypropylene resin A is 130°C to 155°C. If the melting point is less than 130°C, the rigidity of the foamed bead molded body molded using the foamed beads of the present invention may be reduced. From the perspective of being able to show a compressive stress equal to or greater than that of a foamed bead molded body molded by using only the polypropylene resin A as a non-recycled material, the melting point is preferably 135°C or more, and more preferably greater than 140°C. On the other hand, when the melting point is greater than 155°C, when the foamed beads of the present invention are used for in-mold molding, the amount of steam required for molding is very large, so the manufacturing cost increases, which is not economical. From this perspective, the melting point is preferably 150°C or less.

[0043] The melting point of the polypropylene resin A can be measured based on JIS K7121-1987. At this time, as the state adjustment of the test piece, "(2) After a certain heat treatment, the melting temperature is measured" in the above standard is adopted. More specifically, approximately 5 mg of the polypropylene resin A is accurately weighed and used as a sample. Based on the heat flux differential scanning calorimetry method described in JIS K7121-1987, the temperature is increased from 30°C at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak, and then maintained at this temperature for 10 minutes, and then cooled to 30°C at a cooling rate of 10°C / min, and then the temperature is increased from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min. The top temperature of the melting peak determined from the DSC curve obtained at this time (the second DSC curve) is taken as the melting point of the polypropylene resin A. In addition, when two or more melting peaks appear in the DSC curve, the temperature of the top of the melting peak with the largest area is taken as the melting point. Examples of the measuring apparatus include a heat flux differential scanning calorimeter (manufactured by SII NanoTechnology Inc., model: DSC7020) and the like.

[0044] Melt flow rate of polypropylene resin A:

[0045] The melt flow rate (MFR) of the polypropylene resin A used in the present invention is not particularly limited, but is preferably 4 g / 10 min to 12 g / 10 min. The MFR is measured at a test temperature of 230° C. and a nominal load of 2.16 kg in accordance with JIS K7210-1:2014.

[0046] In addition, for the measurement of the above-mentioned MFR and melting point, when the polypropylene resin A is composed of two or more polypropylene resins A, the product obtained by melt-mixing them is used as a sample. In addition, as the melt-mixing conditions, the melt-mixing can be carried out under the same temperature conditions as the melt-kneading when producing the polypropylene resin pellets.

[0047] [Polypropylene resin B]

[0048] Like the polypropylene resin A, the polypropylene resin B, which is a recycled product of post-consumer materials, contains a polypropylene resin and may contain one or more other resins other than the polypropylene resin and polymer materials such as thermoplastic elastomers, or any additives within the range that does not impair the objective effect of the present invention. Since the types of polypropylene resins, polymer materials, additives, etc. that may be contained in the polypropylene resin B are the same as those of the polypropylene resin A described above, detailed descriptions are omitted here. The polymer materials, etc. contained in the polypropylene resin B are preferably recycled materials.

[0049] The content of the polymer material in the polypropylene resin B is preferably in the range of about 10% by weight or less.

[0050] The polypropylene resin B as a recyclate of post-consumer materials is usually prepared by recycling used polypropylene resin molded bodies and crushing and / or melting them. Polypropylene resin B can be prepared from foamed molded bodies such as foamed particle molded bodies, or from non-foamed resin molded products. From the perspectives of reducing pollutants and mass production of materials, polypropylene resin B is preferably prepared from non-foamed resin molded products, wherein it is preferred to include specific materials derived from any one of plastic bottles, food containers and packaging films or their combinations. Polypropylene resin B preferably includes more than 70% by weight of the above-mentioned specific materials, and it is further preferred that the above-mentioned specific materials are substantially 100% by weight.

[0051] Preparation method of polypropylene resin B:

[0052] The method for preparing the polypropylene resin B is not particularly limited, but it is preferred to reduce the number of heat history in the recovery process and the regeneration process of the recovered product. In addition, the above-mentioned preparation method is preferably considered not to excessively increase the heating temperature in the recovery process and the regeneration process.

[0053] More specifically, as a method for producing a recyclate of post-consumer materials of polypropylene-based resins, the following method can be cited.

[0054] (Collection, pulverization and production of molten ingots of used polypropylene resin molded products)

[0055] There is no particular limitation on the method for collecting used polypropylene resin molded bodies. Polypropylene resin molded bodies such as food containers and beverage bottles are marked with recycling marks and are usually classified, discarded, and recycled according to the marks.

[0056] (filter)

[0057] Since the collected used polypropylene resin molded bodies may contain items other than the polypropylene resin molded bodies, such as packaging bags and labels, it is preferable to perform foreign matter screening. The foreign matter screening can be performed by the naked eye of the operator or by using a screening machine or the like.

[0058] (Manufacturing of pulverized product and molten ingot)

[0059] In the crushing of the collected used polypropylene resin moldings, a pulverizer is preferably used. The pulverizers include compression pulverizers, shearing pulverizers, impact pulverizers, and the like. Regarding the crushing method, for example, an impact pulverizer or the like can be used to first perform coarse crushing, and then a shearing pulverizer or the like can be used again for fine crushing, or a shearing pulverizer or the like can be used for crushing at one time. In particular, a method in which a pulverizer having a punching metal or a screen is provided at the outlet of a shearing pulverizer or the like to make the particle size of the crushed material uniform and to crush the material in one process is more economical and therefore preferred. The size of the crushed material is not particularly limited, and is preferably made into a size of more than 1 mm and less than 30 mm.

[0060] The obtained pulverized product is preferably heated and reduced in volume to form a molten ingot. The heating and volume reduction machine includes an extruder type or an extrusion type. The treatment temperature during volume reduction is not particularly limited. In order to avoid thermal degradation of the polypropylene resin, the volume reduction treatment is preferably performed at the lowest possible temperature, more preferably at a temperature below 220°C and above the melting point of the resin.

[0061] (Manufacturing of recycled polypropylene resin)

[0062] It is preferred that the molten ingot is pulverized again using the above-mentioned pulverizer or the like, then melted using an extruder, and then granulated to obtain polypropylene resin recycled material pellets.

[0063] The pulverizer can be the same as that described above. The extruder can be a single-shaft extruder, a double-shaft extruder, etc., and a single-shaft extruder is preferably used from the perspective of preventing resin degradation. The extruder temperature is not particularly limited. In order to avoid thermal degradation of the polypropylene resin, the melting by the extruder is preferably performed at the lowest possible temperature, more preferably at a temperature below 220°C and above the melting point of the resin.

[0064] As described above, the polypropylene resin melted by the extruder is preferably first passed through a filter to remove foreign matter. The filter can be made of a metal mesh or sintered metal, and the metal mesh is more economical and therefore preferred.

[0065] (Granulation)

[0066] As described above, the granulation of the melted polypropylene resin includes: an underwater cutting method in which the molten resin is extruded from a die into water or mist while being continuously cut and solidified by a rotating blade installed in front of the die; a wire cutting method in which the molten resin is continuously extruded from a die in the form of a wire bundle, cooled and solidified in a water tank, and then cut using a cutter, etc. The wire cutting method is more economical and therefore preferred.

[0067] The size of the pellets is not particularly limited, but the pellet weight is preferably 1 mg to 30 mg.

[0068] The above describes the method for producing a recycled product of post-consumer polypropylene resin. However, the polypropylene resin B used in the production method of the present invention may be a recycled material produced by a production method different from the above, or a commercially available product sold as a post-consumer recycled material may be used.

[0069] Melting point of polypropylene resin B:

[0070] Post-consumer materials of resin products are often mixed with various plastic products or plastic products manufactured at different times, etc. Therefore, the recycled post-consumer materials are prone to fluctuations in raw material properties, especially fluctuations in melting points.

[0071] In particular, the physical properties of polypropylene resins are easily changed due to changes in thermal history. Therefore, when a polypropylene recycled resin that is prone to melting point changes is mixed with a polypropylene non-recycled resin, it is speculated as follows. That is, it is speculated that if the relationship between the melting point of the recycled resin and the melting point of the non-recycled resin is not in an appropriate range, it is difficult to set a suitable foaming temperature and it is difficult to perform good foaming. From the above perspective, the method for manufacturing the foamed particles of the present invention appropriately adjusts the temperature conditions such as the foaming temperature. Specifically, in the present invention, it can be adjusted so that the value of the melting point of the polypropylene resin B minus the melting point of the polypropylene resin A is above 10°C and below 30°C. In this way, within the specified range, when the melting point of the polypropylene resin B is higher than the melting point of the polypropylene resin A, the temperature conditions such as the foaming temperature can be set based on the melting point of the polypropylene resin A, and good foaming properties can be achieved. For example, even if recycled post-consumer materials are used, the manufacturing method of the present invention can also imitate the foaming process performed using only the polypropylene resin A as a non-recycled resin to set the temperature conditions such as the foaming temperature, and implement the foaming process.

[0072] If the melting point difference between the polypropylene resin B and the polypropylene resin A is less than 10° C., the expansion ratio of the obtained foamed beads may vary significantly, and the appearance of a foamed bead molded article molded using the foamed beads may be poor.

[0073] On the other hand, when the above-mentioned melting point difference is greater than 30°C, the difference between the appropriate foaming temperature of the polyamide resin A and the appropriate foaming temperature of the polyamide resin B is too large, so the closed cell ratio may decrease. In addition, when the foamed particle molded body is molded using the foamed particles containing the polypropylene resin A and the polypropylene resin B having such a large melting point difference, it is necessary to sufficiently increase the molding pressure in consideration of the melting point of the polypropylene resin B. However, under such a high molding pressure, the melting of the polypropylene resin A will proceed excessively, and as a result, the foamed particle molded body may be basically unable to be molded.

[0074] From the viewpoint of more satisfactorily suppressing the variation in the expansion ratio of the produced foamed beads, the melting point difference is preferably 10° C. or more and 20° C. or less.

[0075] In the range where the above melting point difference can be achieved, the polypropylene resin B can be appropriately selected from recycled post-consumer materials showing a melting point of 150° C. to 170° C. The melting point of the polypropylene resin B can be measured in the same manner as the method for measuring the melting point of the polypropylene resin A. The melting point of the polypropylene resin B is the arithmetic mean value of measurements of 10 or more different test pieces.

[0076] Heat of fusion of polypropylene resin B:

[0077] The heat of fusion of the polypropylene resin B is preferably from 70 J / g to 120 J / g, more preferably from 80 J / g to 110 J / g.

[0078] The heat of fusion of the polypropylene resin B is measured using a heat flux differential scanning calorimeter based on JIS K7122-1987. First, according to "After a certain heat treatment, the heat of fusion is measured", the heating temperature increase rate and the cooling temperature drop rate are set to 10°C / minute to adjust the state of the test piece. Then, the heating temperature increase rate is set to 10°C / minute and a heat flux DSC (i.e., differential scanning calorimetry) is performed to obtain a second DSC curve. Based on the obtained DSC curve, the area of ​​the melting peak is calculated, thereby determining the value of the heat of fusion. In addition, when multiple melting peaks appear in the DSC curve, the total area of ​​the multiple melting peaks is set as the heat of fusion.

[0079] Melt flow rate of polypropylene resin B:

[0080] The melt flow rate (MFR) of the polypropylene resin B used in the present invention is not particularly limited, but is preferably 3 g / 10 min or more and 15 g / 10 min or less. The MFR is measured based on JIS K7210-1:2014 at a test temperature of 230°C and a nominal load of 2.16 kg. In addition, the melt flow rate is sometimes abbreviated as MFR in the specification.

[0081] The difference between the MFR of the polypropylene resin B and the MFR of the polypropylene resin A is preferably 5 or less, more preferably 3 or less. The MFR of the polypropylene resin B is preferably larger than the MFR of the polypropylene resin A.

[0082] Ash content of polypropylene resin B:

[0083] The production method of the present invention uses a polypropylene resin B having an ash content of 5% by weight or less.

[0084] When using or recycling recyclables of post-consumer materials, ash is sometimes mixed in as a pollutant. According to the view of the inventors of the present application, it is speculated that the ash as a pollutant mixed into the polypropylene resin B becomes the nucleus of the bubble in the foaming process, resulting in the miniaturization of the bubbles of the manufactured foamed particles. And, it is speculated that as a result, the bubbles constituting the foamed particles are easy to break, the closed cell rate of the manufactured foamed particles is reduced, and the foaming ratio is biased. Therefore, based on the above view, the present invention uses a recyclable of post-consumer materials having an ash content of 5% by weight or less in 100% by weight of the polypropylene resin B as the polypropylene resin B.

[0085] From the perspective of better suppressing the miniaturization of bubbles and the deviation of the expansion ratio, the ash content of the polypropylene resin B is preferably 1% by weight or less, more preferably 0.5% by weight or less, further preferably 0.2% by weight or less, and particularly preferably 0.1% by weight or less. On the other hand, it is believed that by including ash in the polypropylene resin B, it is possible to suppress the generation of excessively large bubbles when making foamed particles. From the above perspective, the lower limit of the ash content is about 0.01% by weight.

[0086] Ash content determination method:

[0087] Examples of the ash content of the polypropylene-based resin B include inorganic substances containing elements such as calcium, sodium, and silicon.

[0088] The ash content can be measured in accordance with JIS K6226-2: 2003. The measuring device can be, for example, a thermogravimetric analyzer TGA701 manufactured by LECO Corporation. Specifically, 5 g of a polypropylene resin B as a measurement sample is accurately weighed and placed in a crucible, and the heating furnace is set to a nitrogen flow to perform the following steps. That is, (1) in a nitrogen atmosphere, the temperature of the heating furnace is heated from room temperature to 105°C at a heating rate of 10°C / min, then (2) maintained at 105°C until the weight reaches equilibrium, (3) heated from 105°C to 550°C at a heating rate of 10°C / min, (4) maintained at 550°C until the weight reaches equilibrium, (5) the heating furnace gas flow is replaced from nitrogen to air, and heated from 550°C to 950°C at a heating rate of 10°C / min, (6) the weight W1 of the combustion residue after being maintained at 950°C for 10 minutes is calculated, and (7) cooled to room temperature. The weight W1 of the combustion residue is divided by the weight (5 g) of the measurement sample placed in the crucible and the value (weight %) obtained is multiplied by 100, and the value obtained is taken as the ash content of the polypropylene resin B. In addition, the above ash content is measured for two or more different measurement samples, and the arithmetic average value is adopted.

[0089] Melting temperature difference of polypropylene resin B:

[0090] In the production method of the present invention, the melting temperature difference of the polypropylene resin B is 30° C. or more. Here, the melting temperature difference is related to the melting peak shown in the second DSC curve in the heat flux differential scanning calorimetry of the polypropylene resin B, and refers to the difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak.

[0091] By using the polypropylene resin B, the appearance of the foamed bead molded body molded using the foamed beads manufactured by the manufacturing method of the present invention is good. The mechanism of the improved appearance is not clear, but it is speculated that by including the polypropylene resin B with a melting temperature difference of 30°C or more, when the foamed bead molded body is molded, the melting of the polypropylene resin B becomes slow and the bubbles in the foamed beads tend to be difficult to break. And it is speculated that as a result, a foamed molded body with a high closed cell ratio and good appearance can be molded.

[0092] From the viewpoint of improving the appearance of the foamed bead molded article, the melting temperature difference of the polypropylene resin B is preferably 30° C. or more, more preferably 35° C. or more, and even more preferably 40° C. or more.

[0093] On the other hand, the upper limit of the melting point difference of the polypropylene resin B is not particularly limited, but is preferably 100°C or lower, more preferably 90°C or lower, further preferably 85°C or lower, and particularly preferably 80°C or lower.

[0094] For example, the melting temperature difference of the polypropylene resin B used in the present invention is preferably 30°C to 100°C, more preferably 30°C to 90°C, further preferably 35°C to 85°C, particularly preferably 35°C to 80°C.

[0095] As described above, the key to the new idea of ​​using a polypropylene resin B with a melting temperature difference of 30°C or more is to implement it on the basis of satisfying the following requirements: the blending ratio of the polypropylene resin A and the polypropylene resin B is adjusted to a prescribed range, and at the same time, the melting point difference between the polypropylene resin A and the polypropylene resin B is adjusted to a prescribed range.

[0096] In the present invention, the melting temperature difference of the polypropylene resin A is not particularly limited, but is preferably less than 30° C. from the viewpoint of facilitating the maintenance of the temperature conditions during the foaming process. The melting temperature difference of the polypropylene resin A can be measured in the same manner as the melting temperature difference of the polypropylene resin B described below.

[0097] Determination method of melting temperature difference:

[0098] use Figure 1 The method for measuring the difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak is described below.

[0099] Figure 1 1 is a diagram showing a second DSC curve 100 of a polypropylene-based resin B which is a recyclate of a post-consumer material and a DDSC curve 200 which is a differential curve of the DSC curve 100 .

[0100] The DSC curve 100 can be obtained as follows. According to the heat flux differential scanning calorimetry method of JIS K7121-1987, about 5 mg of resin pellets formed of polypropylene resin B are accurately weighed and made into test pieces, and heated and melted at a heating rate of 10°C / min from 30°C to a temperature 30°C higher than the end of the melting peak. The DSC curve measured at this time is the first DSC curve. Then, after being kept at a temperature 30°C higher than the end of the melting peak for 10 minutes, it is cooled to 30°C at a cooling rate of 10°C / min, and heated and melted again at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak. The DSC curve measured at this time is the second DSC curve 100. The difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak of the polypropylene resin B is the arithmetic average value measured on 10 or more different test pieces.

[0101] For as Figure 1In the second DSC curve 100 shown as an example, two peaks are confirmed: a small melting peak shown on the low temperature side and a large melting peak shown on the high temperature side.

[0102] The extrapolated melting start temperature (Tms) is the temperature of the intersection 30 of the straight line 10 and the tangent line 20 in the second DSC curve 100, wherein the straight line 10 is a straight line obtained by extending the baseline on the low temperature side to the high temperature side, and the tangent line 20 is a tangent drawn from the point with the largest slope in the curve on the lowest temperature side of the melting peak.

[0103] The extrapolated melting end temperature (Tme) is the temperature of the intersection 70 of the straight line 50 and the tangent line 60 in the second DSC curve 100, wherein the straight line 50 is a straight line obtained by extending the baseline on the high temperature side toward the low temperature side, and the tangent line 60 is a tangent drawn from the point with the largest slope in the curve on the highest temperature side of the melting peak.

[0104] The extrapolated melting start temperature (Tms) was subtracted from the obtained extrapolated melting end temperature (Tme), thereby determining the difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak.

[0105] The extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) are obtained in accordance with the method for obtaining the "extrapolated melting start temperature" and "extrapolated melting end temperature" described in "Method for obtaining melting temperature" of JIS K7121-1987.

[0106] In addition, in many cases, the polypropylene resin B, which is a recycled material of post-consumer materials, is melt-extruded during production and then subjected to treatments such as granulation. The thermal history in this treatment may affect the formation of the melting peak. Therefore, in order to eliminate this influence, the second DSC curve 100 is used to obtain the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme).

[0107] The above-mentioned melting temperature difference is an index for confirming the range of the melting temperature of the polypropylene resin B. The number of peaks shown in the second DSC curve varies depending on the resin material used, and there are cases where there is one peak and there are cases where there are more than two peaks. In either case, the temperature of the intersection of the straight line obtained by extending the baseline of the low temperature side to the high temperature side and the tangent line drawn from the point with the largest slope in the curve on the lowest temperature side of the melting peak is taken as the extrapolated melting start temperature (Tms). In addition, similarly, in the second DSC curve, the temperature of the intersection of the straight line obtained by extending the baseline of the high temperature side to the low temperature side and the tangent line drawn from the point with the largest slope in the curve on the highest temperature side of the melting peak is taken as the extrapolated melting end temperature (Tme).

[0108] In addition, even if the change in the melting temperature on the lowest temperature side cannot be confirmed as a peak, the extrapolated melting start temperature (Tms) of the present invention can be captured in the form of a change (melting peak) indicating the extrapolated melting start temperature (Tms). Figure 1 As shown, while obtaining the DSC curve 100, the DDSC curve 200 is obtained. Here, the DDSC curve is a differential curve of the second DSC curve. And, the temperature of the inflection point (first inflection point 40) confirmed on the lowest temperature side in the DDSC curve 200 is regarded as the extrapolated melting start temperature (Tms) in the DSC curve 100. That is, when the melting temperature difference is obtained in the present invention, the change of the DSC curve confirmed as an inflection point in the differential curve (DDSC curve) of the second DSC curve is regarded as the melting peak. In addition, the lower limit of the peak height with the first inflection point of the DDSC curve as the peak top is approximately 0.01 mW / ℃. The peak height of the first inflection point of the DDSC curve can be obtained by the difference between the first inflection point in the above-mentioned DDSC curve and the baseline closer to the low temperature side than the first inflection point of the DDSC curve.

[0109] In addition, regarding the above-mentioned extrapolated melting end temperature (Tme), similar to the extrapolated melting start temperature (Tms), even if the change in the melting temperature appearing on the highest temperature side cannot be confirmed in the form of a peak, it can be captured in the form of a change (melting peak) representing the extrapolated melting end temperature (Tme). At this time, the temperature of the inflection point (high temperature side inflection point 80) confirmed on the highest temperature side in the DDSC curve is regarded as the extrapolated melting end temperature in the DSC curve. In addition, the lower limit of the peak height with the high temperature side inflection point of the DDSC curve as the peak top is approximately 0.01 mW / °C. The peak height of the high temperature side inflection point of the DDSC curve can be calculated by the difference between the high temperature side inflection point in the above-mentioned DDSC curve and the baseline closer to the high temperature side than the high temperature side inflection point of the DDSC curve.

[0110] The extrapolated melting start temperature of the polypropylene resin B is preferably lower than the extrapolated melting start temperature of the polypropylene resin A. It is believed that if the polypropylene resin A and the polypropylene resin B used in the manufacturing method of the present invention satisfy the above relationship, the elongation of the resin during in-mold molding is improved, the gaps between the foamed particles are easily buried, and the appearance and closed cell ratio of the foamed particle molded body can be improved. From the above perspective, the melting heat of the polypropylene resin B below the extrapolated melting start temperature of the polypropylene resin A is more preferably 15 J / g or more, further preferably 20 J / g or more, and particularly preferably 25 J / g or more.

[0111] In addition, the extrapolated melting start temperature of the polypropylene resin A can be obtained by the same method as the extrapolated melting start temperature of the polypropylene resin B. In addition, the melting heat of the polypropylene resin B below the extrapolated melting start temperature of the polypropylene resin A can be obtained as follows. First, in the second DSC curve of the polypropylene resin B, a straight line parallel to the vertical axis of the graph is drawn at the extrapolated melting start temperature of the polypropylene resin A. Next, the area of ​​the portion surrounded by the straight line obtained by extending the baseline on the low temperature side of the second DSC curve of the polypropylene resin B to the high temperature side, the straight line parallel to the vertical axis of the graph drawn at the extrapolated melting start temperature of the polypropylene resin A, and the DSC curve is obtained. The amount of heat absorbed corresponding to the above area is taken as the melting heat of the polypropylene resin B below the extrapolated melting start temperature of the polypropylene resin A.

[0112] When the polypropylene resin B has two or more melting peaks in the second DSC curve of the polypropylene resin B, it is preferred that the peaks are not completely separated. The peaks are not completely separated means that, in the second DSC curve, the valley between the peaks does not intersect with a straight line extending the baseline on the low temperature side toward the high temperature side, nor does it intersect with a straight line extending the baseline on the high temperature side toward the low temperature side.

[0113] Content of ethylene component in polypropylene resin B:

[0114] As mentioned above, polypropylene resin B can include one or more polymer materials such as resins and thermoplastic elastomers other than polypropylene resin, for example, ethylene component and butene component can be included. When the foamed particles contain more ethylene components, there is a tendency that the compressive stress of the foamed particle molded body formed by using the foamed particles is reduced. It is speculated that this is because, by containing ethylene components, the regularity of the crystal structure of the resin is reduced and the melting point is lowered, and the physical properties of the resin will be reduced at the same time. From this perspective, the ethylene component included in 100% by weight of the polypropylene resin B is preferably less than 3% by weight, more preferably less than 2% by weight. In addition, the lower limit of the ethylene component included in 100% by weight of the polypropylene resin B is most preferably 0% by weight, because the polypropylene resin B is a recycled resin, it is approximately more than 0.05% by weight. In addition, with respect to the present invention, ethylene component refers to a structural unit consisting of ethylene. The determination of the content of the ethylene component in the polypropylene resin B can be implemented using a known method obtained by IR spectrum. The ethylene content of the polypropylene resin B can be obtained, for example, by the method described in the Handbook of Polymer Analysis (edited by the Polymer Analysis Research Symposium of the Japanese Society of Analytical Chemistry, published in January 1995, published by Kinokuniya Bookstore, pages and item names: 608-609 "II.2.3 2.3.2 Qualitative method" and 615-618 "II.2.3 2.3.4 Propylene / ethylene copolymer"). That is, the ethylene content can be obtained by a method of quantitatively determining the relationship between the value obtained by correcting the absorbance of ethylene by a predetermined coefficient and the thickness of the film-like test piece. The butene content of the polypropylene resin B can be obtained, for example, by the method described in the Handbook of Polymer Analysis (edited by the Polymer Analysis Research Symposium of the Japanese Society of Analytical Chemistry, published in January 1995, published by Kinokuniya Bookstore, pages and item names: 608-609 "II.2.3 2.3.2 Qualitative method" and 618-619 "II.2.3 2.3.5 Propylene / butene copolymer"). That is, the butene content can be obtained by a method of quantitatively determining the relationship between the value obtained by correcting the absorbance of butene by a predetermined coefficient and the thickness of the film test piece.

[0115] In addition, for the measurement of the polypropylene resin B, when the polypropylene resin B is composed of recycled materials of two or more types of post-consumer polypropylene resins, the melt-mixed materials are used as a sample. In addition, as the melt-mixing conditions, the melt-mixing can be carried out under the same temperature conditions as the melt-kneading when producing the polypropylene resin pellets.

[0116] [Blending ratio of polypropylene resin A and polypropylene resin B]

[0117] In the manufacturing method of the present invention, in the mixture of polypropylene resin A and polypropylene resin B, the blending ratio of these resin materials is adjusted to be within a specified range. Specifically, in the total 100% by weight of polypropylene resin A and polypropylene resin B, the blending ratio of polypropylene resin A in the mixture is adjusted to be more than 40% by weight and less than 97% by weight, and the blending ratio of polypropylene resin B is made to be more than 3% by weight and less than 60% by weight. If the blending ratio of polypropylene resin A in the mixture of 100% by weight is too low, there is a tendency that the deviation of the expansion ratio of the obtained foamed particles and the closed cell ratio are reduced. From this perspective, in the mixture of 100% by weight, the blending ratio of polypropylene resin A is preferably more than 50% by weight, more preferably greater than 50% by weight, further preferably more than 60% by weight, and particularly preferably more than 70% by weight.

[0118] On the other hand, from the viewpoint of suppressing the variation in the expansion ratio of the obtained foamed beads and the decrease in the closed cell ratio while using a large amount of post-consumer materials, the blending ratio of the polypropylene resin A in 100 wt % of the mixture is preferably 93 wt % or less, more preferably 90 wt % or less, and further preferably 80 wt % or less.

[0119] For example, from the perspective of suppressing the variation in the expansion ratio of the foamed beads and the decrease in the closed cell ratio, and using a large amount of post-consumer materials, it is preferred to adjust so that the blending ratio of the polypropylene resin A is greater than 50% by weight and less than 80% by weight, and the blending ratio of the polypropylene resin B is greater than 20% by weight and less than 50% by weight in the 100% by weight mixture, wherein the total of the polypropylene resin A and the polypropylene resin B is 100% by weight.

[0120] [Ethylene content in foamed particles]

[0121] As mentioned above, the base resin as a mixture of polypropylene resin A and polypropylene resin B used for manufacture method of the present invention can include one or more resins other than polypropylene resin and polymer materials such as thermoplastic elastomers, for example, can include ethylene component and / or butene component in the base resin. When foamed particles contain more ethylene components, there is a tendency that the compressive stress of the foamed particle molded body molded using the foamed particles is reduced. It is inferred that this is because, by containing olefinic components, the regularity of the crystal structure of the resin is reduced and the melting point is lowered, which can cause the physical property of the resin to reduce. From this perspective, the ethylene component included in the foamed particles is preferably less than 4 % by weight, more preferably below 3 % by weight, and further preferably below 2 % by weight. The definition of so-called ethylene component here is the same as the ethylene component included in the above-mentioned polypropylene resin B.

[0122] The content of the ethylene component in the foamed beads can be calculated by the same method as the method for calculating the ethylene component contained in the polypropylene resin B, except that the foamed beads produced by the production method of the present invention are used as samples.

[0123] [additive]

[0124] The foamed particles used in the present invention use the above-mentioned polypropylene resin A and polypropylene resin B, and one or more additives can be further used within the scope that does not hinder the target effect of the present invention. As the above-mentioned additives, for example, colorants, nucleating agents such as boric acid, antioxidants, anti-ultraviolet agents, lubricants or foaming regulators can be exemplified, but are not limited to these. The blending ratio of the above-mentioned additives can be appropriately determined with reference to the manufacturing method of the polypropylene resin foamed particles known in the past.

[0125] [Composition of foamed particles]

[0126] The foamed particles produced by the production method of the present invention may be single-layer particles or multi-layer resin foamed particles having a covering layer composed of a polyolefin resin on the surface of the particles (core layer). The covering layer may have the same structure as the covering layer in the conventionally known multi-layer resin foamed particles.

[0127] For example, when a polyolefin resin is used as the resin constituting the covering layer, the polyolefin resin may be composed only of polyolefin resin, and in addition to the polyolefin resin, it may also contain one or more other resins and polymer materials such as elastomeric resins and / or arbitrary additives. As the above-mentioned polyolefin resin, polypropylene resin or copolymers of polypropylene resin and other resins, polyethylene resin or copolymers of polyethylene resin and other resins, etc. can be exemplified, but are not limited to this. The resin constituting the covering layer may contain recycled materials of post-consumer materials of polypropylene resin, or all non-recycled resins. From the perspective of easily obtaining a foamed particle molded body with excellent fusion-bonding properties, secondary foaming properties and compressive stress between foamed particles, it is preferred that the resin constituting the covering layer does not contain recycled materials of post-consumer materials.

[0128] The melting point of the polyolefin resin constituting the covering layer is not particularly limited, but is preferably a temperature lower than the melting point or softening point of the resin material constituting the core layer. Thus, when the multilayer resin foamed particles produced by the production method of the present invention are used, the core layer of the foamed particles is heated to a temperature at which secondary foaming can be performed and in-mold molding is performed, since the covering layer melts before the core layer, the adjacent foamed particles have good fusion properties.

[0129] The melting point and softening point of the resin material constituting the core layer mentioned above refer to the melting point or softening point of the base resin composed of the polypropylene resin A and the polypropylene resin B constituting the core layer.

[0130] One or more additives may be used in the cover layer within the range that does not hinder the objective effect of the present invention. As the additive, the same additive as that added to the foamed particles constituting the core layer may be used. The blending ratio of the additive may be appropriately determined with reference to the conventionally known method for producing polypropylene resin foamed particles.

[0131] The weight ratio of the core layer to the cover layer is not particularly limited. From the perspective of improving the weldability of the foamed particles and increasing the consumption of post-consumer materials, the cover layer is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and further preferably 8 parts by weight or less relative to 100 parts by weight of the core layer. The lower limit of the cover layer relative to 100 parts by weight of the core layer is about 1 part by weight.

[0132] The covering layer may be in a foamed state or in an unfoamed state. In order to make the obtained foamed particle molded body excellent in physical strength, the resin layer in a substantially unfoamed state is preferably used. In addition, the so-called substantially unfoamed state here includes not only the situation where there are no bubbles at all, but also the situation where there are very small bubbles in a very small amount within the range that does not affect the mechanical strength of the obtained foamed particle molded body. In addition, the above-mentioned covering layer without bubbles at all also includes the situation where the bubbles temporarily formed when the resin particles are foamed are destroyed by melting and the bubbles disappear.

[0133] In addition, the core layer of the multilayer resin foamed particles may be completely covered by the covering layer, or a portion of the core layer may be exposed. As a structure in which the core layer is exposed, for example, only the side of the cylindrical core layer is covered by the covering layer, and the core layer is exposed on the upper surface and bottom surface of the cylinder.

[0134] [Each step of the production method of the present invention]

[0135] Hereinafter, an embodiment of the manufacturing method of the present invention is described in several steps. Specifically, the manufacturing method of the present invention is described in a mixing step, an extrusion step, and a foaming step. In addition, for the manufacturing method of the present invention, within the scope of not impairing the objective effect of the present invention, a part of these steps may be changed, or different steps may be further added, or each step may be implemented independently of each other, or a part or all of the steps may be repeated.

[0136] [Mixing process]

[0137] In the production method of the present invention, a mixing step is first performed. The mixing step is a step of obtaining a base resin comprising a mixture of a polypropylene resin A and a polypropylene resin B. Specifically, the mixing step is a step of supplying, for example, a polypropylene resin A, a polypropylene resin B, and an appropriately used additive to an extruder, melting the supplied materials and kneading them simultaneously to obtain a molten resin kneaded product.

[0138] At this time, the blending ratio of the polypropylene-based resin A and the polypropylene-based resin B in the molten resin kneaded product is adjusted to the above-mentioned blending ratio.

[0139] When the multilayered resin foamed particles are manufactured by the manufacturing method of the present invention, the above-mentioned mixing step for preparing the core layer constituent material constituting the core layer and the covering layer mixing step for preparing the covering layer constituent material constituting the covering layer, which is different from the above-mentioned mixing step, can be independently performed. The above-mentioned core layer constituent material contains at least a polypropylene resin A and a polypropylene resin B.

[0140] [Extrusion process]

[0141] Next, an extrusion step is performed in which the mixture obtained in the mixing step is extruded from an extruder and cut to obtain polypropylene resin pellets.

[0142] Specifically, for example, the mixture is extruded from an extrusion die disposed on the downstream side of the extruder to form a wire bundle. Then, the wire bundle is cut into a desired size using a granulator or the like to obtain polypropylene resin particles (hereinafter, also simply referred to as resin particles). The shape of the cross section of the wire bundle perpendicular to the extrusion direction is circular or the like. The resin particles obtained as described above are, for example, cylindrical or the like.

[0143] In addition, when manufacturing multilayer resin foam particles having a multilayer structure with a covering layer, an extrusion device for coextrusion can be used. Specifically, the core layer constituent material and the covering layer constituent material are combined in a coextrusion die arranged on the downstream side of the extruder, and the covering layer constituent material is stacked on the periphery of the core layer constituent material and coextruded to form a multilayer structure wire bundle. Then, the wire bundle is cut into a desired size in the same manner as above, thereby obtaining a multilayer structure resin particle having a core layer and a covering layer covering the core layer.

[0144] [Foaming process]

[0145] Next, a foaming step is performed. Specifically, the resin particles obtained in the extrusion step are dispersed in an aqueous medium in a sealed container and impregnated with a foaming agent, and the resin particles containing the foaming agent and the aqueous medium are released from the sealed container to a pressure lower than the pressure in the sealed container and foamed, thereby producing a foaming agent having a foaming capacity of 10 kg / m 3 Above 200kg / m3 The following is a detailed description of the foaming process, which is divided into a dispersion process, a foaming agent impregnation process, and a release process.

[0146] (Dispersion process)

[0147] The dispersing step is a step of dispersing the resin particles obtained in the extrusion step in an aqueous medium that has been added to a container. The aqueous medium contains an inorganic dispersant. In addition, the aqueous medium may appropriately contain any additive other than the inorganic dispersant.

[0148] Aqueous media:

[0149] The aqueous medium is a medium for dispersing the resin particles in the container. Examples of the aqueous medium include water, alcohols, glycols, glycerol, etc., and water is preferred from the perspective of ease of drainage treatment. From the perspective of improving the dispersibility of the resin particles and the productivity of the foamed particles, the amount of the resin particles added to the aqueous medium is preferably 10 parts by weight or more and 100 parts by weight or less, and more preferably 20 parts by weight or more and 80 parts by weight or less, relative to 100 parts by weight of the aqueous medium.

[0150] Inorganic dispersants:

[0151] The inorganic dispersant is used to disperse the resin particles well in the aqueous medium and to suppress adhesion of the foamed particles during the foaming step.

[0152] From the perspective of maintaining the in-mold formability of the foamed particles and easily inhibiting the welding between the foamed particles in the release process described later, the amount of the inorganic dispersant added is preferably from 0.01 parts by weight to 2 parts by weight, more preferably from 0.02 parts by weight to 1 part by weight, and further preferably from 0.03 parts by weight to 0.8 parts by weight, relative to 100 parts by weight of the resin particles.

[0153] As the inorganic dispersant, for example, inorganic fine particles such as alumina, hydroxyapatite, magnesium pyrophosphate, zinc oxide, kaolin, and mica can be used. These inorganic fine particles may be used alone or in combination of two or more.

[0154] Optional additives:

[0155] In addition to the inorganic dispersant, the aqueous medium may further include any additives such as one or more dispersing aids and surfactants. As dispersing aids, for example, aluminum sulfate and the like may be cited. In addition, as surfactants, for example, anionic surfactants such as sodium alkylbenzene sulfonate, sodium dodecylbenzene sulfonate, and sodium alkyl sulfonates may be cited. The surfactant may be used alone or in combination of two or more. Typically, the additives are added in an amount of 0.01 to 1 part by weight relative to 100 parts by weight of the resin particles.

[0156] (Blowing agent impregnation step)

[0157] The blowing agent impregnation step is performed after the above-mentioned dispersion step is performed, or at a timing overlapping with a part or all of the dispersion step.

[0158] The blowing agent impregnation step is a step performed in a conventional foaming particle production method in which the blowing agent is impregnated into the resin particles dispersed in the aqueous medium. For example, a sealed container containing the resin particles is sealed, and a physical blowing agent is added into the sealed container. In this way, the physical blowing agent can be impregnated into the resin particles to obtain expandable resin particles.

[0159] The physical foaming agent may be added to the sealed container at any time before the resin particles are foamed. The foaming agent in a solid or liquid state may be added to the aqueous medium together with the resin particles during the dispersion process, and then the foaming agent in a gaseous state may be impregnated into the resin particles by heating or the like. In addition, the foaming agent in a gaseous state may be pressed into the sealed container simultaneously with the dispersion process or after the dispersion process is completed, so that the foaming agent is impregnated into the resin particles.

[0160] Foaming agent:

[0161] The foaming agent used in the present invention can be appropriately selected from foaming agents generally used to obtain foamed particles, but a physical foaming agent is preferred.

[0162] As a physical foaming agent, specifically, an inorganic physical foaming agent and / or an organic physical foaming agent can be used. Examples of the inorganic physical foaming agent include carbon dioxide, air, nitrogen, helium, argon, water, and the like. Examples of the organic physical foaming agent include: aliphatic hydrocarbons such as propane, butane, and hexane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; and halogenated hydrocarbons such as methyl chloride, ethyl chloride, dichloromethane, 2,3,3,3-tetrafluoropropylene, 1,3,3,3-tetrafluoropropylene, 1-chloro-3,3,3-trifluoropropylene, 1-chloro-2,3,3,3-tetrafluoropropylene, and 1,1,1,4,4,4-hexafluoro-2-butene.

[0163] These physical foaming agents can be used alone or in combination of two or more. Among these foaming agents, it is preferred to use a foaming agent with an inorganic physical foaming agent such as carbon dioxide, nitrogen, air, etc. as the main component, and carbon dioxide is more preferred. In the present invention, the above-mentioned inorganic physical foaming agent as the main component means that the physical foaming agent contains 50 mol% or more of the inorganic physical foaming agent. Preferably, the physical foaming agent contains 70 mol% or more of the inorganic physical foaming agent, more preferably 90 mol% or more, and further preferably, the physical foaming agent is composed only of an inorganic physical foaming agent.

[0164] The amount of the physical foaming agent added can be appropriately determined according to the type of base resin constituting the resin particles, the type of the foaming agent, the target bulk density of the foamed particles, etc. For example, when carbon dioxide is used as the physical foaming agent, the amount of carbon dioxide added is preferably 0.1 parts by weight or more and 30 parts by weight or less, more preferably 0.5 parts by weight or more and 15 parts by weight or less, and further preferably 1 part by weight or more and 10 parts by weight or less, relative to 100 parts by weight of the resin particles.

[0165] High temperature peak:

[0166] Furthermore, in order to adjust the crystal state of the obtained foamed beads, the temperature increase rate of the sealed container may be adjusted in the above-mentioned dispersion step and / or blowing agent impregnation step and / or the sealed container may be kept at a predetermined temperature for a predetermined time. For example, the adjustment may be made so that, in the first DSC curve obtained by the heat flux differential scanning calorimetry method described in JIS K7121-1987, the melting peak (high temperature peak) appears on the high temperature side compared to the melting peak inherent to the resin constituting the obtained foamed beads.

[0167] From the perspective of being able to obtain a wider range of molding conditions for good foamed particle molded bodies, foamed particles that have a high temperature peak are preferred. The adjustment for obtaining the above-mentioned high temperature peak can be carried out, for example, in the following manner. In the above-mentioned dispersion process and / or foaming agent impregnation process, a primary holding process is carried out at a temperature of (resin melting point of resin particles - 20°C) or more and less than (resin melting point of resin particles + 20°C) for about 10 minutes to 60 minutes. Then, adjust to a temperature of (resin melting point of resin particles - 15°C) or more and less than (resin melting point of resin particles + 15°C). Then, a secondary holding process is carried out as needed to further maintain the temperature for about 10 minutes to 60 minutes. Next, by implementing the foaming process described later, foamed particles having a high temperature peak can be manufactured. Regarding the maintenance in the range of above (resin melting point of resin particles - 15°C) and less than (resin melting point of resin particles + 15°C) for forming a high temperature peak, it is possible to set it in multiple stages within this temperature range, and it is also possible to form the high temperature peak by slowly raising the temperature within this temperature range for a sufficient time.

[0168] In addition, regarding the resin melting point of the resin pellets, the resin pellets were made into test pieces and used, and based on the heat flux differential scanning calorimetry method described in JIS K7121-1987, the temperature was raised from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min, and then the temperature was maintained for 10 minutes, and then the temperature was lowered to 30°C at a cooling rate of 10°C / min, and the temperature was again raised from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min, and the top temperature of the melting peak determined from the second DSC curve obtained at this time was taken as the resin melting point of the resin pellets. In addition, when two or more melting peaks appear in the second DSC curve, the temperature of the top of the melting peak with the largest area is taken as the resin melting point.

[0169] (Release process)

[0170] After the expandable resin particles are obtained in the above-mentioned blowing agent impregnation step, a releasing step is performed.

[0171] The release step is a step of releasing resin particles containing a blowing agent (foamable resin particles) from a container simultaneously with an aqueous medium to foam the particles, thereby obtaining foamable particles. More specifically, the foamable resin particles are released together with the aqueous medium to a pressure lower than the internal pressure of the sealed container, thereby foaming the foamable resin particles.

[0172] According to the foaming process described above, it is easy to obtain a bulk density of 10kg / m 3 Above 200kg / m 3 The following foamed particles are preferred.

[0173] (Secondary Foaming Process)

[0174] The bulk density of the expanded beads produced as described above can be adjusted by, for example, appropriately changing the foaming conditions such as the temperature and pressure in the sealed container when releasing the contents of the sealed container in the releasing step.

[0175] When the bulk density of the expanded beads produced by the above-mentioned production method is higher than the desired bulk density, or when it is desired to provide expanded beads having a further lower bulk density, the secondary expansion step described below may be appropriately performed.

[0176] For the secondary foaming process, the following operation is first performed: the foamed particles obtained in the manner described above are stored in a pressurized sealed container, and a gas such as air is pressed into the sealed container to perform a pressurization treatment to increase the internal pressure in the bubbles of the foamed particles. Then, the foamed particles are taken out of the sealed container, and the foamed particles are heated with steam or hot air to further foam the foamed particles, thereby implementing the secondary foaming process. By implementing the secondary foaming process, foamed particles (secondary foamed particles) with a lower bulk density can be obtained.

[0177] (Variation of the method for producing multi-layered resin foamed beads)

[0178] In the above, the method of performing coextrusion in the extrusion step for producing multi-layered resin foamed beads has been described, but in the present invention, the method of producing multi-layered resin foamed beads is not limited thereto.

[0179] For example, as a different method for manufacturing multi-layer resin foam particles, a mixture as a core layer constituent material is obtained through a mixing process, and the mixture is supplied to an extrusion process to prepare core layer particles that are pre-formed into a granular single layer. Then, it is put into a mixing device with a mixing function and a heating function to heat the surface layer of the core layer particles. Next, the covering layer constituent material used to constitute the covering layer is put into the above-mentioned mixing device, etc., and the heated core layer particles are mixed with the covering layer constituent material. Thus, multi-layer resin particles having a covering layer formed by covering the surface of the core layer particles with the above-mentioned covering layer constituent material are obtained. By supplying the multi-layer resin particles to a foaming process to foam them, multi-layer resin foam particles can be obtained.

[0180] [Polypropylene resin foam particles]

[0181] The polypropylene resin foamed particles manufactured in the above manner contain a polypropylene resin B which is a recycled material of a post-consumer material of a polypropylene resin molded body, and contribute greatly to solving environmental problems such as reducing carbon dioxide emissions based on raw material recycling or waste utilization required by a recycling-oriented society. In addition, the foamed particles manufactured using the present invention can show good moldability equal to or better than that of existing foamed particles manufactured using only the polypropylene resin A as a non-recycled material, and can provide a foamed particle molded body with excellent appearance and rigidity. Hereinafter, the foamed particles manufactured using the manufacturing method of the present invention will be described.

[0182] (Bulk density)

[0183] The bulk density of the foamed particles produced by the production method of the present invention is 10 kg / m 3 Above and 200kg / m 3From the perspective of providing a foamed particle molded body with excellent mechanical strength, the above-mentioned bulk density is preferably 15 kg / m 3 More than 20 kg / m 3 More preferably, 25 kg / m 3 On the other hand, from the perspective of providing a foamed particle molded body with light weight and excellent cushioning properties, 150 kg / m 3 Below, more preferably 100kg / m 3 Below, more preferably 80kg / m 3 the following.

[0184] The bulk density of the foamed particles can be measured by the following method. First, place the foamed particles to be measured in an environment with a temperature of 23°C, a relative humidity of 50%, and 1 atm for more than 24 hours. Fill the foamed particle group with a weight W (g) obtained in the above manner into a measuring cylinder, and tap the bottom of the measuring cylinder on the ground several times to stabilize the filling height of the foamed particle group in the measuring cylinder. Read the bulk volume V (L) of the foamed particle group pointed to by the scale of the measuring cylinder, and divide the weight W of the foamed particle group by the bulk volume V (W / V) of the foamed particle group. Convert the unit of the value thus obtained into kg / m 3 , from which the bulk density of the foamed particles (kg / m 3 ).

[0185] (Ash content)

[0186] The expanded particles produced by the production method of the present invention may contain inorganic substances containing elements such as calcium, sodium, and silicon as ash.

[0187] The measurement of the ash content is carried out in the same manner as the above-mentioned method for measuring the ash content in the polypropylene resin B, except that 5 g of the expanded beads are used as the measurement sample.

[0188] (Foaming ratio)

[0189] The expansion ratio of the foamed particles is determined by the resin density of the polypropylene resin (900 kg / m 3 ) divided by the bulk density of the aforementioned foamed particles.

[0190] (Measurement of the Deviation Rate of Foaming Ratio)

[0191] Accurately weigh 300mL~500mL of polypropylene resin foam particles and sieve them with 8 standard sieves specified in JIS Z8801. The mesh sizes of the 8 standard sieves are 5 mesh, 6 mesh, 7 mesh, 8 mesh, 9 mesh, 12 mesh, 14 mesh, and 16 mesh. Then, measure the weight of the foam particles (residual foam particles) remaining on each sieve, and calculate the weight fraction Wi of the weight of the residual foam particles relative to the weight of the foam particles used for screening. In addition, according to the above method, calculate the foaming ratio Ki of the foam particles.

[0192] Then, first, the average expansion ratio Kav is calculated from the following formula (1).

[0193] [Mathematical formula 1]

[0194]

[0195] Next, the standard deviation σm is calculated using the following formula (2).

[0196] [Mathematical formula 2]

[0197]

[0198] Then, the deviation rate (%) of the foaming ratio can be calculated using the following formula (3).

[0199] [Mathematical formula 3]

[0200]

[0201] In order to confirm that the variation in the expanded bead diameter confirmed by the above-mentioned sieving is not caused by the weight of the expanded beads but is caused by the variation in the expansion ratio, the following confirmation can be performed.

[0202] Specifically, 500 foamed particles are randomly selected from the manufactured foamed particles, and the weight of each foamed particle is measured with a precision balance to the second decimal place, and the measured values ​​are arithmetic averaged to obtain the average weight. Then, the foamed particles whose measured values ​​of the weight of the foamed particles fall within the range of ±10% relative to the above average weight are counted. As described above, as long as the number of foamed particles counted is more than 95% of the 500 foamed particles, it can be judged that the deviation of the foamed particle diameter confirmed by screening is derived from the deviation of the foaming ratio.

[0203] (High temperature peak)

[0204] The foamed particles manufactured using the manufacturing method of the present invention are preferably foamed particles in which the inherent melting peak of the resin and the melting peak on the high temperature side (high temperature peak) can be measured by heat flux differential scanning calorimetry, and the melting peak (high temperature peak) on the high temperature side is caused by the secondary crystals of the resin formed by the thermal history of foaming the resin particles until the foamed particles are obtained.

[0205] That is, as described below, the foamed beads manufactured by the manufacturing method of the present invention preferably can confirm the high temperature peak. First, the foamed beads are made into a test piece, and based on the heat flux differential scanning calorimetry method described in JIS K7121-1987, the foamed beads are heated and melted from 30°C at a heating rate of 10°C / min to a heating end temperature 30°C higher than the end of the melting peak, and the first DSC curve measured at this time is obtained. In this first DSC curve, more than two melting peaks are confirmed, and it is confirmed that the two or more melting peaks include the inherent melting peak of the resin constituting the foamed beads, and the melting peak (high temperature peak) on the high temperature side having a vertex temperature closer to the high temperature than the vertex temperature of the inherent melting peak of the resin. Then, it is stored at the heating end temperature for 10 minutes, then cooled to 30°C at a cooling rate of 10°C / min, and heated and melted again at a heating rate of 10°C / min to a heating end temperature 30°C higher than the end of the melting peak, and the second DSC curve measured at this time is obtained. In addition, as described above, heating is performed from 23°C to 200°C at a heating rate of 10°C / min (i.e., the first heating), then cooling is performed from 200°C to 23°C at a cooling rate of 10°C / min, and then heating is performed again from 23°C to 200°C at a heating rate of 10°C / min (i.e., the second heating). In the DSC curve obtained at this time, only the endothermic peak based on the inherent melting of the resin constituting the foamed particles is seen, so the inherent melting peak of the resin and the melting peak (high temperature peak) caused by the high temperature side of the secondary crystals of the resin can be distinguished.

[0206] The foamed particles used to make the test piece may be about 1 mg to 3 mg. When the foamed particles are larger than 3 mg, the foamed particles may be divided into two equal parts to make a 1 mg to 3 mg test piece and use it. As described above, the foamed particles that have been confirmed to have a high temperature peak have excellent in-mold moldability and can improve the mechanical properties such as compressive stress of the obtained foamed particle molded body.

[0207] The “resin constituting the foamed beads” mentioned above refers to the polypropylene resin A and the polypropylene resin B contained in the base resin.

[0208] (High temperature peak heat and total heat)

[0209] As described above, the method for measuring the calorific value of the high temperature peak and the total calorific value of the melting peak confirmed can refer to the measuring method implemented in the examples described later.

[0210] (Average bubble diameter)

[0211] The bubble diameter of the foamed particles obtained by the manufacturing method of the present invention is not particularly limited. When molding the foamed particle molded body, from the perspective of easily providing a foamed particle molded body that is not easy to break and has excellent appearance, the average bubble diameter of the foamed particles is preferably 50 μm or more, more preferably 60 μm or more, further preferably 70 μm or more, and particularly preferably 80 μm or more. On the other hand, the average bubble diameter of the foamed particles is preferably 300 μm or less, more preferably 200 μm or less, and further preferably 150 μm or less. For example, the average bubble diameter of the foamed particles is preferably 50 μm or more and 300 μm or less, more preferably 60 μm or more and 200 μm or less, and further preferably 70 μm or more and 150 μm or less.

[0212] The average bubble diameter of the foamed particles can be obtained by taking an enlarged photograph of a cross section of the foamed particles roughly divided into two equal parts using a microscope. First, in the enlarged photograph of the cross section of the foamed particles, draw four line segments extending from one surface of the foamed particles to the other surface and passing through the approximate center of the cross section of the foamed particles. Among them, the line segments are drawn in a manner to form radial straight lines extending from the approximate center of the cross section of the foamed particles toward the cut particle surface in 8 directions at equal intervals. Next, the total number of bubbles N (number) intersecting with the above 4 line segments is calculated. The sum L (μm) of the lengths of each of the 4 line segments is calculated, and the value (L / N) obtained by dividing the sum L by the total number N is taken as the average bubble diameter of one foamed particle. This operation is performed on more than 10 foamed particles, and the value obtained by arithmetic averaging the average bubble diameters of each foamed particle is taken as the average bubble diameter of the foamed particles.

[0213] (Closed Porosity)

[0214] The closed porosity can be determined using an air comparison densitometer based on ASTM-D2856-70.

[0215] [Foamed particle molded body]

[0216] The foamed particles obtained by the manufacturing method of the present invention are used for in-mold molding, thereby obtaining a foamed particle molded body. For example, the foamed particle molded body can be manufactured in the following manner. First, the foamed particles are filled in a molding die having a cavity corresponding to the shape of the desired foamed particle molded body, and the foamed particles filled in the molding die are heated by a heating medium such as steam. The foamed particles in the cavity are further foamed due to the heating and are simultaneously welded to each other. Thus, the foamed particles are integrated with each other to obtain a foamed particle molded body corresponding to the shape of the cavity.

[0217] The expanded bead molded article molded using the expanded beads produced by the production method of the present invention has excellent appearance and excellent physical properties such as compressive stress at 50% deformation.

[0218] (Molding body density)

[0219] The density of the foamed bead molded article is not particularly limited, but is preferably 100 kg / m 3 Below, more preferably 80kg / m 3 On the other hand, from the perspective of producing a molded body with excellent mechanical properties, 10 kg / m 3 More preferably 30kg / m 3 For example, the density of the foamed particle molded body is preferably 10 kg / m 3 Above 100kg / m 3 Below, more preferably 30kg / m 3 Above 80kg / m 3 the following.

[0220] The density of the molded article can be determined by measuring the weight of the expanded bead molded article and dividing the weight by the volume of the expanded bead molded article determined by the water immersion method.

[0221] (Compression stress at 50% deformation)

[0222] The compressive stress at 50% deformation of the foamed bead molded body is not particularly limited, but is preferably 0.50 MPa or more, more preferably 0.52 MPa or more, and further preferably 0.53 MPa or more from the perspective of obtaining a foamed bead molded body with excellent compressive properties. On the other hand, the upper limit of the compressive stress at 50% deformation of the foamed bead molded body is approximately 0.58 MPa or less.

[0223] Ten test pieces of 50 mm in length, 50 mm in width, and 25 mm in thickness with the surface removed are cut out at equal intervals from a foamed particle molded body (250 mm in length, 200 mm in width, and 50 mm in thickness). A compression test is performed at a compression rate of 10 mm / min based on JIS K6767:1999, thereby obtaining the compressive stress of the foamed particle molded body when it is 50% deformed. For example, the arithmetic mean of the values ​​obtained by testing 10 test pieces can be used as the compressive stress when it is 50% deformed. In addition, the compressive stress when it is 50% deformed is an indicator of the rigidity of the foamed particle molded body.

[0224] Example

[0225] Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited thereto. In addition, for each embodiment and each comparative example implemented as described below, the bulk density, ash content, ethylene content, expansion ratio, high temperature peak heat, total heat, average bubble diameter, closed cell ratio, and expansion ratio deviation rate of the obtained foamed particles are measured. In addition, the deviation of the expansion ratio of the obtained foamed particles is evaluated. In addition, the molded body density of the foamed particle molded body formed using the obtained foamed particles and the compressive stress at 50% deformation are measured, and the appearance and rigidity are evaluated at the same time. The above-mentioned measurement results and evaluation results are shown in Tables 2 to 4.

[0226] The following examples, comparative examples, and reference examples used polypropylene resins A and B shown in Table 1. Polypropylene resin A shown in Table 1 is a resin material that is a non-recycled material, and polypropylene resin B is a recycled product of a post-consumer polypropylene resin.

[0227] (Ethylene content of polypropylene resin B)

[0228] The ethylene content of polypropylene resin B is determined by the method described in the Handbook of Polymer Analysis (edited by the Polymer Analysis Research Symposium of the Japanese Society of Analytical Chemistry, published in January 1995, published by Kinokuniya Bookstore, pages and item names: 608-609 "II.2.3 2.3.2 Qualitative method" and 615-618 "II.2.3 2.3.4 Propylene / ethylene copolymer"). That is, the ethylene content is determined by a quantitative method using the relationship between the value obtained by correcting the absorbance of ethylene with a specified coefficient and the thickness of the film test piece. Specifically, first, the polypropylene resin B is heat-pressed and molded into a film at 180°C to prepare a plurality of test pieces of different thicknesses. Next, the IR spectrum of each test piece is measured to read the 722 cm-1 wavelength derived from ethylene. -1 and 733cm -1 The absorbance (A 722 , A 733 ). Next, for each test piece, the ethylene content in the polypropylene resin B was calculated using the following mathematical formula. For each test piece, the value obtained by arithmetic averaging the obtained ethylene content was taken as the ethylene content (wt%) in the polypropylene resin B.

[0229] [Formula 4]

[0230]

[0231] [Formula 5]

[0232]

[0233] [Mathematical formula 6]

[0234]

[0235] Among them, in formulas (4) to (6), K' a : Apparent absorption coefficient at each wavelength (K' a =A / ρt), K' c : Corrected absorption coefficient, A: absorbance, ρ: density of resin (g / cm 3 ), t: thickness of the film test piece (cm).

[0236] (Butene content of polypropylene resin B)

[0237] The butene content of polypropylene resin B is determined by the method described in the Handbook of Polymer Analysis (edited by the Polymer Analysis Research Forum of the Japanese Society of Analytical Chemistry, published in January 1995, published by Kinokuniya Bookstore, pages and item names: 608~609 "II.2.3 2.3.2 Qualitative method" and 618~619 "II.2.3 2.3.5 Propylene / butene copolymer"). That is, the butene content is determined by a quantitative method using the relationship between the value obtained by correcting the absorbance of butene with a specified coefficient and the thickness of the film test piece. In the same manner as the determination of the ethylene content of the polypropylene resin described above, a plurality of test pieces of different thicknesses are prepared from the polypropylene resin. The IR spectrum of each test piece is then measured, thereby reading the 766cm -1 The absorbance (A 766 ). Next, for each test piece, the value obtained by arithmetic averaging the butene component contents obtained using the following mathematical formula (7) was used as the butene component content (wt %) in the polypropylene resin.

[0238] [Formula 7]

[0239]

[0240] Among them, A 766 :766cm -1 Absorbance of absorption, L: thickness of film test piece (mm).

[0241] The melt flow rate of the polypropylene resin was measured under the conditions of a test temperature of 230° C. and a nominal load of 2.16 kg in accordance with JIS K7210-1:2014.

[0242] (Ash content of polypropylene resin B)

[0243] The ash content was measured as follows using a thermogravimetric analyzer TGA701 manufactured by LECO Corporation based on JIS K6226-2:2003.

[0244] 5 g of polypropylene resin B was accurately weighed and placed in a crucible after weighing, and a nitrogen flow was set in the heating furnace to perform the following steps. That is, (1) the temperature of the heating furnace was heated from room temperature to 105°C at a heating rate of 10°C / min in a nitrogen atmosphere, then (2) the temperature was kept at 105°C until the measured weight reached equilibrium, (3) the temperature was heated from 105°C to 550°C at a heating rate of 10°C / min, (4) the temperature was kept at 550°C until the measured weight reached equilibrium, (5) the heating furnace gas flow was replaced from nitrogen to air, and the temperature was heated from 550°C to 950°C at a heating rate of 10°C / min, (6) the weight W1 of the combustion residue after holding at 950°C for 10 minutes was calculated, and (7) the mixture was cooled to room temperature. The weight W1 of the combustion residue was divided by the weight (5 g) of the measurement sample placed in the crucible and the value was multiplied by 100 to calculate the amount (weight %) of ash content of polypropylene resin B. The above operation was performed twice, and the arithmetic mean value was taken as the ash content of the polypropylene resin B.

[0245] The second DSC curve was obtained as described below, and the melting points of the polypropylene resin A and the polypropylene resin B shown in Table 1, as well as the peak temperature of the DSC melting peak and the melting heat were obtained. Using the obtained second DSC curve, the extrapolated melting start temperature (Tms), the extrapolated melting end temperature (Tme) and the melting temperature difference (Tme-Tms) were obtained. In addition, starting from the high temperature side, the melting peaks confirmed in the second DSC curve were set as DSC melting peak 3, DSC melting peak 2, and DSC melting peak 1. That is, when only one melting peak appears, only DSC melting peak 3 is shown in Table 1, and when three melting peaks appear, DSC melting peak 3, DSC melting peak 2, and DSC melting peak 1 are shown in Table 1. For the melting heat, when multiple DSC melting peaks appear, the total of all melting heats is shown in Table 1. In addition, in the second DSC curve of the polypropylene resin B, it was confirmed whether the respective peaks of the polypropylene resin B were not completely separated. For the recovered resins 1 to 5, the respective peaks were not completely separated.

[0246] Based on the heat flux differential scanning calorimetry method of JIS K7121-1987, about 5 mg of resin particles formed by polypropylene resin A or polypropylene resin B are accurately weighed and made into test pieces. The above test piece is heated and melted from 30°C at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak, and the DSC curve measured at this time is taken as the first DSC curve. Then, after keeping at this temperature for 10 minutes, it is cooled to 30°C at a cooling rate of 10°C / min, and heated and melted again at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak. The DSC curve measured at this time is taken as the second DSC curve. The vertex temperature of the peak appearing in the second DSC curve is taken as the DSC melting peak temperature. In addition, the melting point of the resin is the vertex temperature of the peak showing the maximum heat of melting confirmed in the second DSC curve. The above measurement was performed on 10 randomly selected test pieces, and the melting peak temperature, the melting point of the resin, the extrapolated melting start temperature (Tms), and the extrapolated melting end temperature (Tme) were each calculated by taking the arithmetic mean.

[0247] The second DSC curve was obtained as described below, and the heat of fusion of the polypropylene resin A and the polypropylene resin B shown in Table 1 was obtained. In addition, resins 1 to 6 shown in Table 1 use virgin materials formed from polypropylene random copolymers. Recycled resins 1 and 2 use recycled materials of post-consumer materials of polypropylene resin products manufactured by Guolong Plastic Chemical Co., Ltd. Recycled resin 3 uses recycled materials of post-consumer materials of polypropylene resin products manufactured by Dongguan Pengyi Plastic Raw Materials. Recycled resin 4 uses a commercial product (product name: rPPCPP0500RP) manufactured by REEF Technology Co., Ltd. that is commercially available as recycled materials of post-consumer materials of polypropylene resin products. Recycled resin 5 uses recycled materials of post-consumer materials of polypropylene resin products prepared by recycling, crushing, washing, melting and granulating used polypropylene resin molded bodies.

[0248] Based on the heat flux differential scanning calorimetry method of JIS K7122-1987, about 5 mg of resin particles formed by polypropylene resin A or polypropylene resin B are accurately weighed and made into test pieces. The above test piece is heated and melted from 30°C at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak, and the DSC curve measured at this time is taken as the first DSC curve. Then, after keeping at this temperature for 10 minutes, it is cooled to 30°C at a cooling rate of 10°C / min, and heated and melted again at a heating rate of 10°C / min to a temperature 30°C higher than the end of the melting peak. The DSC curve measured at this time is taken as the second DSC curve. The top temperature of the peak appearing in the second DSC curve is taken as the DSC melting peak temperature, and the melting heat (J / g) is calculated using the area of ​​the peak. In addition, the above measurement is performed on 10 randomly selected test pieces, and the melting heat is respectively taken as the value obtained by arithmetic average.

[0249] (Example 1)

[0250] Preparation of resin particles:

[0251] Resin 1 shown in Table 1 was used as polypropylene resin A, and recycled resin 1 shown in Table 1 was used as polypropylene resin B, and the mixture was blended in the ratio shown in Table 2, melt-kneaded in an extruder to make a mixture, and used as a base resin. In addition, during melt-kneading, in addition to the above materials, zinc borate ("FireBreak ZB" manufactured by Borax) was used as a foaming regulator. The zinc borate was added in a manner of 0.05% by weight in 100% by weight of the melt-kneaded product (the total of resin 1, recycled resin 1 and zinc borate). The base resin in a molten state was extruded from a mold already provided in an extruder in a bundle shape and cooled in water, and then cut using a granulator to obtain cylindrical resin particles each having an average weight of 1.0 mg.

[0252] Preparation of foamed particles:

[0253] 100 kg of the obtained resin pellets were supplied together with 220 L of water as an aqueous medium into a sealed container having a content of 400 L. Furthermore, 0.3 parts by weight of kaolin as an inorganic dispersant, 0.004 parts by weight (in terms of effective ingredient) of sodium alkylbenzene sulfonate as a dispersing aid, and 0.001 parts by weight of aluminum sulfate were added to the sealed container, respectively, based on 100 parts by weight of the resin pellets.

[0254] Next, carbon dioxide as a foaming agent is pressed into the sealed container and pressurized to a gauge pressure of 1.8 MPa (G). In addition, the pressure marked with (G) is the gauge pressure, that is, the value of the pressure based on atmospheric pressure. Then, while stirring the sealed container, heat it at a heating rate of 2°C / min to the foaming temperature (150.5°C), and then further pressurize carbon dioxide in a manner to achieve a specified foaming pressure (2.6 MPa (G)), and maintain it at the same temperature for 10 minutes. Thus, adjustment is made so that a high temperature peak appears in the endothermic curve obtained by the first DSC measurement of the obtained foamed particles.

[0255] Then, the contents of the sealed container (resin particles and water) were released to atmospheric pressure to obtain a bulk density of 49.8 kg / m 3 Foamed particles (primary foamed particles).

[0256] (Examples 2, 3, 5 to 9)

[0257] Except that the resin materials and blending ratios used were set as shown in Table 2, and the foaming temperature and foaming pressure were adjusted in a manner to achieve the bulk density and high-temperature peak heat as shown in the table, foamed particles and foamed particle molded bodies were manufactured in the same manner as Example 1, as Examples 2, 3, 5 to 9.

[0258] (Example 4)

[0259] As Example 4, foamed beads and a foamed bead molded body were produced in the same manner as in Example 1, except that multilayered resin particles were produced and used as shown below, and the foaming temperature and foaming pressure were adjusted so as to obtain the bulk density and high-temperature peak heat amount shown in the table.

[0260] Preparation of resin particles:

[0261] A manufacturing device is prepared, which includes a core layer forming extruder with an inner diameter of 50 mm, a multilayer wire bundle forming die set on the downstream side of the core layer forming extruder, and a cover layer forming extruder with an inner diameter of 30 mm. In addition, the downstream side of the cover layer forming extruder of the manufacturing device is connected to the multilayer wire bundle forming die, forming a structure that can stack molten kneaded materials for forming each layer in the die and can be co-extruded.

[0262] As the core layer forming material constituting the core layer, resin 1 and recycled material 1 shown in Table 1 were used in the blending ratio shown in Table 2. The above core layer forming material was supplied to the core layer forming extruder and melt-kneaded. In addition, zinc borate ("Fire Break ZB" manufactured by Borax) as a foaming regulator was added together with the above materials in such a manner that zinc borate as a foaming regulator was 0.05% by weight in 100% by weight of the melt-kneaded product (the total of resin 1, recycled resin 1 and zinc borate).

[0263] As the covering layer forming material constituting the covering layer, the resin 4 shown in Table 1 was used at the blending ratio shown in Table 2, and these components were supplied to an extruder for covering layer formation and melt-kneaded.

[0264] The mixture for forming each layer obtained by melt kneading in the above manner is introduced into a die for forming a multilayer wire harness, and the mixture is merged in the die, and a multilayer wire harness having a two-layer structure (cover layer / core layer structure) is extruded from the fine holes of the die installed on the downstream side of the die. The extruded wire harness is water-cooled and cut using a pelletizer to obtain cylindrical resin pellets each having an average weight of 1.0 mg.

[0265] (Example 10)

[0266] As shown in Table 4, foamed beads were produced in the same manner as in Example 1, and foamed beads and a foamed bead molded body were produced in the same manner as in Example 1, except that the foamed beads (primary foamed beads) were used to perform secondary foaming as described below. This was designated as Example 10.

[0267] Secondary foaming:

[0268] The primary foamed particles obtained in the same manner as in Example 1 are placed in an environment of 23°C, 50% relative humidity, and 1 atm for 24 hours for aging. Then, the aged primary foamed particles are added to a pressurized sealed container, the pressure in the sealed container is increased from normal pressure, and the foamed particles are pressurized. The pressurized state of the foamed particles is maintained for a specified time to allow air to be impregnated into the bubbles of the foamed particles. Then, the primary foamed particles are taken out from the sealed container to obtain primary foamed particles having an internal pressure of 0.7 MPa (G) in the bubbles of the foamed particles. Then, the primary foamed particles are supplied to a secondary foaming device. Steam is supplied to the device to foam the primary foamed particles to obtain a bulk density of 26.6 kg / m 3 of foaming particles.

[0269] (Comparative Examples 1 to 6)

[0270] As Comparative Examples 1 to 6, foamed beads and foamed bead molded bodies were prepared in the same manner as in Example 1, except that the resin materials and blending ratios used were set to those shown in Table 3, and the foaming temperature and foaming pressure were adjusted to obtain the bulk density and high-temperature peak heat amount shown in the table.

[0271] (Reference Example 1)

[0272] Except that a base resin containing only resin 1 without recycled materials was used as a constituent resin, and the foaming temperature and foaming pressure were adjusted so as to obtain the bulk density and high-temperature peak heat amount shown in the table, foamed beads and a foamed bead molded article were produced in the same manner as in Example 1 as Reference Example 1. Reference Example 1 is an example of conventional polypropylene resin foamed beads that do not use recycled resin.

[0273] (Reference Example 2)

[0274] As Reference Example 2, foamed beads and a foamed bead molded article were produced in the same manner as in Example 1 except that a base resin prepared by blending resin 1 and resin 6 as non-recycled resins at the ratio shown in Table 3 was used as a constituent resin and the foaming temperature and foaming pressure were adjusted so as to obtain the bulk density and high-temperature peak heat amount shown in the table. Reference Example 2 is an example of conventional polypropylene resin foamed beads that do not use recycled resin.

[0275] (Reference Example 3)

[0276] Reference Example 3 was obtained by producing foamed beads and a foamed bead molded article in the same manner as in Reference Example 1, except that secondary foaming was carried out in the same manner as in Example 10 as shown in Table 4.

[0277] (Ash content of foamed particles)

[0278] Ash content determination method:

[0279] The ash content was measured as follows using a thermogravimetric analyzer TGA701 manufactured by LECO Corporation based on JIS K6226-2:2003.

[0280] 5 g of the foamed particles obtained as described above were accurately weighed and placed in a crucible after weighing, and a nitrogen flow was set in the heating furnace to perform the following steps. That is, (1) the temperature of the heating furnace was heated from room temperature to 105°C at a heating rate of 10°C / min under a nitrogen atmosphere, then (2) the temperature was maintained at 105°C until the measured weight reached equilibrium, (3) the temperature was heated from 105°C to 550°C at a heating rate of 10°C / min, (4) the temperature was maintained at 550°C until the measured weight reached equilibrium, (5) the heating furnace gas flow was replaced from nitrogen to air, and the temperature was increased from 550°C to 950°C at a heating rate of 10°C / min, (6) the weight W1 of the combustion residue after being maintained at 950°C for 10 minutes was calculated, and (7) the mixture was cooled to room temperature. The weight W1 of the combustion residue was divided by the weight (5 g) of the measurement sample placed in the crucible and the value was multiplied by 100 to calculate the amount (weight %) of the ash content of the foamed particles. The above operation was performed twice, and the arithmetic mean value was taken as the ash content of the expanded beads.

[0281] (Ethylene content of foamed particles)

[0282] The ethylene content of the foamed particles was determined in the same manner as the ethylene content of the polypropylene resin described above, except that the foamed particles were used as test pieces.

[0283] (High temperature peak heat and total heat of foamed particles)

[0284] About 1 mg of foamed particles were accurately weighed and made into a test piece. The test piece was heated and melted based on the heat flux differential scanning calorimetry method described in JIS K7122-1987 to obtain the DSC curve at this time. The measurement temperature range was set from 30°C to a temperature 30°C higher than the temperature at which the melting peak of the test piece ends, and the heating rate during heating was set to 10°C / min to obtain the first DCS curve.

[0285] The first DSC curve obtained in the above manner is shown in Figure 2 In the DSC curve, a straight line is drawn connecting point I corresponding to 80°C and point II corresponding to the melting end temperature of the foamed particles. In addition, the melting end temperature is the end point on the high temperature side of the high temperature peak b, which is the intersection of the high temperature peak b in the DSC curve and the baseline on the high temperature side compared to the high temperature peak b.

[0286] like Figure 2 As shown, after drawing a straight line connecting point I and point II, the intersection of a straight line passing through the maximum point III between the resin's inherent melting peak a and high temperature peak b and parallel to the vertical axis of the graph and the straight line connecting point I and point II is taken as IV.

[0287] Then, the area of ​​the part surrounded by the straight line connecting point I and point IV, the straight line connecting point III and point IV, and the DSC curve connecting point I and point III is used as the area of ​​the melting peak a inherent in the resin. In addition, the area of ​​the part (oblique line part) surrounded by the straight line connecting point IV and point II, the straight line connecting point III and point IV, and the DSC curve connecting point III and point II is used as the area of ​​high temperature peak b, and it is used as the high temperature peak heat (J / g) of the foamed particles. In addition, the sum of the area of ​​the melting peak a inherent in the resin and the area of ​​the high temperature peak b is used as the total heat (J / g).

[0288] After the first DSC curve is obtained in the above manner, the sample is stored at the heating end temperature for 10 minutes, then cooled to 30°C at a cooling rate of 10°C / min, and heated and melted again at a heating rate of 10°C / min to a heating end temperature 30°C higher than the end of the melting peak, thereby obtaining the second DSC curve measured at this time. It was confirmed that no high temperature peak appeared in the second DSC curve.

[0289] (Average bubble diameter of foamed particles)

[0290] Use a microscope to photograph a cross section that roughly divides the foamed particles into two equal parts, and obtain an enlarged cross-sectional photograph. In the above enlarged cross-sectional photograph, draw 4 line segments that extend from one surface of the foamed particles to the other surface and pass through the approximate center of the cross section of the foamed particles. Among them, the line segments are drawn in a manner to form radial straight lines extending from the approximate center of the cross section of the foamed particles toward the surface of the cut particles in 8 directions at equal intervals. Next, find the total number of bubbles N (number) that intersect with the above 4 line segments. Find the sum L (μm) of the lengths of each of the 4 line segments, and divide the sum L by the total number N to obtain the value (L / N) as the average bubble diameter of one foamed particle. Perform this operation on more than 10 foamed particles, and take the value obtained by arithmetic averaging the average bubble diameters of each foamed particle as the average bubble diameter of the foamed particles.

[0291] (Closed cell ratio of foamed particles)

[0292] The closed cell ratio (%) of the foamed particles was determined using an air comparative densitometer based on ASTM-D2856-70.

[0293] (Bulk density of foamed particles)

[0294] The bulk density of the foamed particles is determined as follows. The foamed particle group is placed in an environment with an air temperature of 23°C, a relative humidity of 50%, and 1 atm for 24 hours. The foamed particle group obtained in this way is filled into a measuring cylinder in a natural stacking manner, and the bulk volume (unit: L) of the foamed particle group is read according to the scale of the measuring cylinder. Then, the value obtained by dividing the mass of the foamed particle group in the measuring cylinder (unit: g) by the aforementioned bulk volume (unit: L) is converted into units, thereby obtaining the bulk density of the foamed particles (unit: kg / m 3 ).

[0295] (Expansion ratio of foamed particles)

[0296] The expansion ratio of the foamed particles is determined by the resin density of the polypropylene resin (0.9 kg / m 3 ) divided by the bulk density of the aforementioned foamed particles.

[0297] (Deviation rate of expansion ratio of expanded particles)

[0298] Weigh 300mL~500mL of foamed particles accurately and sieve them with 8 standard sieves specified in JIS Z8801. The mesh sizes of the 8 standard sieves are 5 mesh, 6 mesh, 7 mesh, 8 mesh, 9 mesh, 12 mesh, 14 mesh, and 16 mesh. Next, measure the weight of the foamed particles (residual foamed particles) remaining on each sieve, and calculate the weight fraction Wi of the weight of the residual foamed particles relative to the weight of the foamed particles used for sieving. In addition, calculate the foaming ratio Ki of the foamed particles according to the above method.

[0299] Then, first, the average expansion ratio Kav is calculated from the following formula (1).

[0300] [Mathematical formula 8]

[0301]

[0302] Next, the standard deviation σm is calculated using the following formula (2).

[0303] [Mathematical formula 9]

[0304]

[0305] Then, the deviation rate (%) of the foaming ratio was calculated using the following formula (3).

[0306] [Formula 10]

[0307]

[0308] In addition, the following confirmation was performed to confirm that the variation in the expanded bead diameter confirmed by the above-mentioned sieving is not caused by the weight of the expanded beads but is caused by the variation in the expansion ratio.

[0309] Randomly select 500 foamed particles from the manufactured foamed particles, measure the weight of each foamed particle with a precision balance to the second decimal place, perform arithmetic averaging on the measured values, and calculate the average weight. Then, count the foamed particles whose measured values ​​of the weight of the foamed particles fall within the range of ±10% relative to the above average weight. In the examples, comparative examples, and reference examples, the number of foamed particles counted is 95% or more of the 500 foamed particles.

[0310] (Appearance Evaluation of Foamed Bead Molded Article)

[0311] <Appearance>

[0312] As an evaluation of the surface appearance of the foamed particle molded body, a 100mm×100mm rectangle is drawn in the central part of the foamed particle molded body, and a line is drawn on the diagonal line starting from the corner of the rectangular area. The number of voids (gaps) with a size of 1mm×1mm or more on the line is counted, and the degree of the voids (gaps) between the foamed particles is evaluated as follows.

[0313] A (◎: very good): The number of voids is less than 5.

[0314] B (○: good): The number of voids is 5 or more and less than 10.

[0315] C (△: poor): The number of voids is 10 or more and less than 15.

[0316] D (×: poor): The number of voids is 15 or more.

[0317] (Molding body density of foamed particle molded body)

[0318] The weight of the expanded beads molded article is measured, and the weight is divided by the volume of the expanded beads molded article determined by the water immersion method to determine the molded article density of the expanded beads molded article.

[0319] (Compression stress at 50% deformation of foamed particle molded body)

[0320] Ten test pieces of 50 mm in length, 50 mm in width, and 25 mm in thickness were cut from the foamed particle molded body (250 mm in length, 200 mm in width, and 50 mm in thickness) at equal intervals, with the surface removed, as test pieces. Using the test pieces, a compression test was performed at a compression rate of 10 mm / min based on JIS K6767:1999 to determine the 50% compression stress of the foamed particle molded body. The arithmetic mean of the values ​​of the 10 test pieces was taken as the compression stress at 50% deformation.

[0321] (Evaluation of Rigidity of Foamed Bead Molded Article)

[0322] The compressive stress at the time of 50% deformation was evaluated for each density according to the following criteria.

[0323] Density of molded body: 60kg / m 3 :

[0324] A: The compressive stress at 50% deformation is 0.54MPa or more

[0325] B: The compressive stress at 50% deformation is 0.52 MPa or more and less than 0.54 MPa

[0326] C: The compressive stress at 50% deformation is less than 0.52MPa

[0327] Density of molded body: 30kg / m 3 :

[0328] A: The compressive stress at 50% deformation is 0.25MPa or more

[0329] B: The compressive stress at 50% deformation is 0.23 MPa or more and less than 0.25 MPa

[0330] C: The compressive stress at 50% deformation is less than 0.23MPa

[0331] [Table 1]

[0332]

[0333] [Table 2]

[0334]

[0335] [Table 3]

[0336]

[0337] [Table 4]

[0338]

[0339] The present invention described above includes the following technical concepts.

[0340] (1) A method for producing foamed particles, comprising: impregnating polypropylene resin particles dispersed in an aqueous medium with a foaming agent in a sealed container, releasing the polypropylene resin particles containing the foaming agent together with the aqueous medium from the sealed container to a pressure lower than the pressure in the sealed container, thereby foaming the polypropylene resin particles containing the foaming agent, and producing a foamed particle having a foaming capacity of 10 kg / m 3 Above 200kg / m 3 The method for producing the polypropylene resin foamed particles having the following bulk density is characterized in that:

[0341] The polypropylene resin particles include a mixture of a polypropylene resin A and a polypropylene resin B having a melting point of 130° C. to 155° C. as a base resin.

[0342] The blending ratio of the polypropylene resin A in the mixture is 40 wt % to 97 wt %, and the blending ratio of the polypropylene resin B is 3 wt % to 60 wt % (the total of the polypropylene resin A and the polypropylene resin B is 100 wt %),

[0343] The difference in melting points between the polypropylene resin A and the polypropylene resin B (melting point of the polypropylene resin B minus the melting point of the polypropylene resin A) is 10° C. or more and 30° C. or less,

[0344] The polypropylene resin B is a recyclate of post-consumer materials.

[0345] The ash content of the polypropylene resin B is 5% by weight or less relative to 100% by weight of the polypropylene resin B,

[0346] The difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak shown in the DSC curve in heat flux differential scanning calorimetry of the polypropylene resin B is 30° C. or more.

[0347] (2) The method for producing foamed beads according to the above (1) is characterized in that the blending ratio of the polypropylene resin A in the mixture is greater than 50 weight % and less than 80 weight %, and the blending ratio of the polypropylene resin B is greater than 20 weight % and less than 50 weight % (the total of the polypropylene resin A and the polypropylene resin B is 100 weight %).

[0348] (3) The method for producing foamed beads according to (1) or (2) above, wherein the difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak is 30°C to 100°C.

[0349] (4) The method for producing foamed beads according to any one of (1) to (3) above, characterized in that the difference in melting points between the polypropylene resin A and the polypropylene resin B (melting point of the polypropylene resin B minus the melting point of the polypropylene resin A) is 10°C to 20°C.

[0350] (5) The method for producing foamed beads according to any one of (1) to (4) above, wherein the ash content of the polypropylene resin B is 0.5 wt% or less relative to 100 wt% of the polypropylene resin B.

[0351] Description of Reference Numerals

[0352] 10: straight line obtained by extending the baseline on the low temperature side toward the high temperature side; 20: tangent line drawn from the point with the largest slope in the curve on the lowest temperature side of the melting peak; 30: intersection of straight line 10 and tangent line 20; 40: first inflection point; 50: straight line obtained by extending the baseline on the high temperature side toward the low temperature side; 60: tangent line drawn from the point with the largest slope in the curve on the highest temperature side of the melting peak; 70: intersection of straight line 50 and tangent line 60; 80: inflection point on the high temperature side; 100: second DSC curve of polypropylene resin B; 200: DDSC curve which is a differential curve of DSC curve 100.

Claims

1. A method for producing foamed particles, comprising: impregnating polypropylene resin particles dispersed in an aqueous medium with a foaming agent in a sealed container, releasing the polypropylene resin particles containing the foaming agent together with the aqueous medium from the sealed container to a pressure lower than the pressure in the sealed container, thereby foaming the polypropylene resin particles containing the foaming agent, and producing a foamed particle having a foaming capacity of 10 kg / m 3 Above 200kg / m 3 The method for producing the polypropylene resin foamed particles having the following bulk density is characterized in that: The polypropylene resin particles include a mixture of a polypropylene resin A and a polypropylene resin B having a melting point of 130° C. to 155° C. as a base resin. The blending ratio of the polypropylene resin A in the mixture is 40 wt % to 97 wt %, and the blending ratio of the polypropylene resin B is 3 wt % to 60 wt % (the total of the polypropylene resin A and the polypropylene resin B is 100 wt %), The difference in melting points between the polypropylene resin A and the polypropylene resin B (melting point of the polypropylene resin B minus the melting point of the polypropylene resin A) is 10° C. or more and 30° C. or less, The polypropylene resin B is a recyclate of post-consumer materials. The ash content of the polypropylene resin B is 5% by weight or less relative to 100% by weight of the polypropylene resin B, The difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak shown in the DSC curve in heat flux differential scanning calorimetry of the polypropylene resin B is 30° C. or more.

2. The method for producing foamed particles according to claim 1, characterized in that: The blending ratio of the polypropylene resin A in the mixture is greater than 50 wt % and less than 90 wt %, and the blending ratio of the polypropylene resin B is greater than 10 wt % and less than 50 wt % (the total of the polypropylene resin A and the polypropylene resin B is 100 wt %).

3. The method for producing foamed particles according to claim 1 or 2, characterized in that: The difference (Tme-Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the melting peak is 30° C. or more and 100° C. or less.

4. The method for producing foamed particles according to any one of claims 1 to 3, characterized in that: The difference in melting points between the polypropylene resin A and the polypropylene resin B (melting point of the polypropylene resin B−melting point of the polypropylene resin A) is 10° C. or more and 20° C. or less.

5. The method for producing foamed particles according to any one of claims 1 to 4, characterized in that: The ash content of the polypropylene-based resin B is 0.5% by weight or less relative to 100% by weight of the polypropylene-based resin B.

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