Method for manufacturing foamed particles

Abstract

To provide a production method of foam particles, capable of producing foam particles suppressed in unevenness of an expansion ratio and reduction of a closed cell ratio, and improving the external appearance of a foam particle molded body molded by using the foam particles, with respect to a method for producing foam particles by using as a base resin, a mixture obtained by mixing a polypropylene resin A as a non-recovery material, and a polypropylene resin B as a recovery of a post consumer material.SOLUTION: A production method of foam particles, including using as a base resin, a mixture obtained by mixing a polypropylene resin A having a melting point of 130°C or more and 155°C or less, and a polypropylene resin B as a recovery of a post consumer material is such that: a mixing ratio of the polypropylene resin A in the mixture is 40 wt.% or more and 97 wt.% or less, and a mixing ratio of the polypropylene resin B is 3 wt.% or more and 60 wt.% or less (the total amount of the polypropylene resin A and the polypropylene resin B is 100 wt.%); a melting point difference (the polypropylene resin B-the polypropylene resin A) between the polypropylene resin A and the polypropylene resin B is 10°C or more and 30°C or less; an ash content of the polypropylene resin B is 5 wt.% or less based on 100 wt.% of the polypropylene resin B; and a difference (Tme-Tms) between an extrapolation melting initiation temperature (Tms) of a melting peak, and an extrapolation melting finishing temperature (Tme) in a melting peak shown in a DSC curve in a heat flux differential scanning calorimetry of the polypropylene resin B is 30°C or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing foamed polypropylene resin particles, and more specifically, to a method for producing foamed particles using polypropylene resin A, which is a non-recoverable material, and polypropylene resin B, which is a recovered post-consumer material, as the polypropylene resin. [Background technology]

[0002] In recent years, amidst the movement to promote a circular economy, the utilization of recycled materials recovered from used products has become a social issue. In the field of plastic product technology, there is a growing social demand to utilize waste materials that end users have discarded as recycled materials, and in particular, the use of recycled polypropylene obtained from waste materials such as disposable containers made of polypropylene resin is being considered.

[0003] In response to this, technologies for utilizing used polyolefin resin foam molded products have been proposed. For example, Patent Document 1 proposes a technology for producing polyolefin resin foam molded products by crushing a waste polyolefin resin molded product, mixing the crushed product with virgin polyolefin resin to produce pellets, and then impregnating the pellets with a foaming agent. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-283576 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, Patent Document 1 had the following problems and there was room for improvement. Specifically, when foamed particles were manufactured using recovered post-consumer material made from waste polyolefin resin molded articles and non-recovered polyolefin resin material, variations occurred in the foaming ratio of the resulting foamed particles, and there was a risk that the percentage of closed cells in the foamed particles would decrease. Furthermore, when a foamed particle molded article was formed using the foamed particles obtained in this way, there was a risk that defects in appearance would be observed.

[0006] The present invention has been made in view of the above problems. Specifically, the present invention relates to a method for producing foamed particles using a mixture of polypropylene resin A, which is a non-recoverable material, and polypropylene resin B, which is a recovered post-consumer material, as a base resin, and provides a method for producing foamed particles that can produce foamed particles in which variations in foaming ratio and a decrease in the closed-cell ratio are suppressed, and that can produce a foamed particle molded article with a good appearance when molded using the foamed particles. [Means for solving the problem]

[0007] The present invention provides a method for producing foamed particles, in which polypropylene resin particles dispersed in an aqueous medium in a sealed container are impregnated with a foaming agent, and the polypropylene resin particles containing the foaming agent are released from the sealed container together with the aqueous medium under a pressure lower than that inside the sealed container, causing foaming to occur at a pressure of 10 kg / m³. 3 More than 200kg / m 3 A method for producing polypropylene resin foam particles having the following bulk density, The above polypropylene resin particles use a base resin that is a mixture of polypropylene resin A, which has a melting point of 130°C or higher and 155°C or lower, and polypropylene resin B. The blending ratio of polypropylene resin A in the above mixture is 40% by weight or more and 97% by weight or less, and the blending ratio of polypropylene resin B is 3% by weight or more and 60% by weight or less (however, the total of polypropylene resin A and polypropylene resin B is 100% by weight), The melting point difference between the above polypropylene resin A and the above polypropylene resin B (polypropylene resin B - polypropylene resin A) is 10°C or more and 30°C or less, the above polypropylene resin B is a recovered material of post-consumer materials, the ash content contained in 100% by weight of the above polypropylene resin B is 5% by weight or less, in the melting peak shown in the DSC curve in the measurement of the heat flux differential scanning calorimetry of the above polypropylene resin B, the difference (Tme - Tms) between the extrapolated melting start temperature (Tms) and the extrapolated melting end temperature (Tme) of the above melting peak is 30°C or more.

Advantages of the Invention

[0008] According to the production method of the present invention, even though a recovered material of post-consumer materials is blended, it is possible to produce foamed particles in which the variation in the expansion ratio and the decrease in the closed cell ratio are suppressed. Further, the foamed molded body molded using the foamed particles produced by the production method of the present invention has a good appearance. According to the present invention that exhibits the above-described excellent effects, it is possible to effectively utilize the recovered materials of plastic products and provide practical foamed particles and foamed particle molded bodies. Therefore, the present invention greatly contributes to the solution of environmental problems such as material recycling required in a recycling-based society and reduction of carbon dioxide emissions by using waste products.

Brief Description of the Drawings

[0009] [Figure 1] It is an example of the second DSC curve of the recovered resin and the differential curve of the second DSC curve. [Figure 2] It 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 heat quantity of the foamed particles.

Modes for Carrying Out the Invention

[0010] The method for producing the foamed particles of the present invention will be described below. In the following, the method for producing the polypropylene-based resin foamed particles of the present invention may be simply referred to as the "method of the present invention." In relation to the present invention, post-consumer materials refer to materials that have been used by consumers as products. More specifically, as defined in JIS Q14021:2000, post-consumer materials refer to materials discharged from households, or materials generated from commercial facilities, industrial facilities, and various other facilities that are end-users of products and can no longer be used for their original purpose, and this includes materials returned from distribution channels. Furthermore, recovered post-consumer materials (recovered materials) refer to these used materials that have been collected. On the other hand, resins newly prepared as resin materials are sometimes called virgin resins or non-recoverable resins.

[0011] The manufacturing method of the present invention involves impregnating polypropylene resin particles dispersed in an aqueous medium in a sealed container with a foaming agent, releasing the polypropylene resin particles containing the foaming agent together with the aqueous medium from the sealed container under a pressure lower than that inside the sealed container, and foaming up to 10 kg / m³. 3 More than 200kg / m 3 This is a method for producing polypropylene resin foam particles having the following bulk density. This foaming method makes it easy to obtain polypropylene resin foam particles exhibiting the desired bulk density. The manufacturing method of the present invention uses a mixture of polypropylene resin A, which has a melting point of 130°C to 155°C, and polypropylene resin B, which is a recovered post-consumer material, as the base resin. The blending ratio of polypropylene resin A in the above mixture is 40% to 97% by weight, and the blending ratio of polypropylene resin B is 3% to 60% by weight (however, the total of polypropylene resin A and polypropylene resin B is 100% by weight). Furthermore, these resins are selected such that the difference in melting points between polypropylene resin A and polypropylene resin B (melting point of polypropylene resin B - melting point of polypropylene resin A) is 10°C to 30°C. In the manufacturing method of the present invention, a resin material is selected as the polypropylene resin B having an ash content of 5% by weight or less and a difference between the extracellular melting start temperature (Tms) and the extracellular melting end temperature (Tme) (Tme-Tms) of 30°C or more.

[0012] The manufacturing method of the present invention, having the above-described configuration, achieves good foaming properties, thereby avoiding the effects of variations in the melting point of polypropylene resin B, which is a post-consumer material recovery, and suppressing variations in the foaming ratio of the manufactured foam particles, while also enabling a high closed-cell ratio. Furthermore, the foam particle molded article formed using the foam particles manufactured in this way has a good appearance. Further details of the present invention are described below.

[0013] [Base resin] In the manufacturing 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 containing these mixtures is not particularly limited, but it is preferable that it be pelletized so that it can be easily used in the foaming method described above. Furthermore, the term "base resin" as used herein refers to the main resin material constituting the polypropylene resin foam particles produced by the present invention. Other resins other than polypropylene resin A and polypropylene resin B may be further blended into the base resin, to the extent that they do not hinder the intended effects of the present invention. It is preferable that the mixture of polypropylene resin A and polypropylene resin B constitutes 90% by weight or more, more preferably 95% by weight or more, and even more preferably 98% by weight or more, based on 100% by weight of the base resin.

[0014] [Polypropylene resin A] Polypropylene resin A is a non-recoverable resin. Polypropylene resin A may consist only of polypropylene resin that is substantially virgin resin, or it may also contain other resins other than polypropylene resin, polymer materials such as thermoplastic elastomers, and optional additives, to the extent that they do not hinder the intended effects of the present invention. Preferably, any polymer materials other than polypropylene resin included in polypropylene resin A are non-recoverable materials. The polypropylene resin contained in polypropylene resin A is a resin in which the propylene component units in the resin amount to 50% by weight or more, and examples include propylene homopolymers or copolymers of propylene with other olefins copolymerizable with other olefins. Examples of other olefins copolymerizable with propylene include ethylene and α-olefins with 4 or more carbon atoms, such as 1-butene. Furthermore, the copolymer may be a polypropylene random copolymer or a block copolymer, and may be a binary copolymer or a ternary copolymer. In addition, these polypropylene resins may be used individually or in combination of two or more types.

[0015] Examples of polymer materials that may be appropriately included in polypropylene resin A include, for example, other resins other than polypropylene resin as shown below. Examples of other resins include ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid copolymer, and ethylene-methacrylic acid ester copolymer; polystyrene resins such as polystyrene, high-impact polystyrene, and styrene-acrylonitrile copolymer; acrylic resins such as polymethyl methacrylate; and polyester resins such as polylactic acid and polyethylene terephthalate. These resins may be used individually or in combination of two or more. Furthermore, as the polymer material mentioned above, thermoplastic elastomers such as olefin-based elastomers like ethylene-hexene copolymers and ethylene-propylene-diene copolymers, or styrene-based elastomers such as styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, and their hydrogenated derivatives can also be used. These thermoplastic elastomers can be used individually or in combination of two or more types.

[0016] The manufacturing method of the present invention can use any one of the above-mentioned polymer materials, other resins, and the above-mentioned thermoplastic elastomers, or a combination thereof, as the polymer material. The blending ratio of the above polymer material in polypropylene resin A is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less.

[0017] Melting point of polypropylene resin A: The melting point of polypropylene resin A is 130°C or higher and 155°C or lower. If the melting point is below 130°C, the rigidity of the foamed particle molded article formed using the foamed particles according to the present invention may be low. From the viewpoint of being able to exhibit compressive stress equivalent to or greater than that of a foamed particle molded article formed using foamed particles manufactured using only polypropylene resin A, which is a non-recoverable material, the melting point is preferably 135°C or higher, and more preferably above 140°C. On the other hand, if the melting point exceeds 155°C, the amount of steam required for molding when performing in-mold molding using the foamed particles according to the present invention becomes very large, which increases manufacturing costs and makes it uneconomical. From this viewpoint, the melting point is preferably 150°C or lower.

[0018] The melting point of polypropylene resin A is measured in accordance with JIS K7121-1987. In this case, the condition of the test specimen is as described in "(2) When measuring the melting temperature after performing a certain heat treatment" in the above standard. More specifically, approximately 5 mg of polypropylene resin A is accurately weighed and used as a sample, and based on the differential scanning calorimetry method described in JIS K7121-1987, the temperature is raised from 30°C to 30°C higher than the end of the melting peak at a heating rate of 10°C / min, then maintained at that temperature for 10 minutes, then cooled down to 30°C at a cooling rate of 10°C / min, and then raised again from 30°C to 30°C higher than the end of the melting peak at a heating rate of 10°C / min. The peak temperature of the melting peak determined by the DSC curve obtained (second DSC curve) is defined as the melting point of polypropylene resin A. If two or more melting peaks appear in the DSC curve, the melting point is defined as the temperature at the peak of the melting peak with the largest area. Examples of measurement devices include differential scanning calorimetry (DSC7020, manufactured by SII Nanotechnology Co., Ltd.).

[0019] Melt flow rate of polypropylene resin A: The melt flow rate (MFR) of polypropylene resin A used in the present invention is not particularly limited, but is preferably 4 g / 10 min or more and 12 g / 10 min or less. The above MFR is measured in accordance with JIS K7210-1:2014 under conditions of a test temperature of 230°C and a nominal load of 2.16 kg.

[0020] Furthermore, when measuring the MFR and melting point as described above, if polypropylene resin A is composed of two or more types of polypropylene resin A, the sample shall be a mixture of these two types of resins. The melting and mixing conditions should be the same temperature conditions as those used for melt kneading during the production of polypropylene resin particles.

[0021] [Polypropylene resin B] Polypropylene resin B, which is a recovered post-consumer material, contains polypropylene resin, similar to polypropylene resin A, and may also contain other resins and polymer materials such as thermoplastic elastomers, or any additives, as long as they do not hinder the intended effects of the present invention. The types of polypropylene resin, polymer materials, and additives that may be contained in polypropylene resin B are the same as those described above for polypropylene resin A, so a detailed explanation is omitted here. It is preferable that the polymer materials, etc., contained in polypropylene resin B are recovered materials. Furthermore, it is preferable that the content of the above polymer material in polypropylene resin B is in the range of approximately 10% by weight or less.

[0022] Polypropylene resin B, which is a recovered post-consumer material, is generally prepared by recovering used polypropylene resin molded articles, etc., and crushing and / or melting them. Polypropylene resin B may be prepared from foamed molded articles such as foamed particle molded articles, or it may be prepared from non-foamed resin molded articles. From the viewpoint of reducing impurities and mass production of the material, it is preferable that polypropylene resin B is prepared from non-foamed resin molded articles, and in particular it is preferable that it contains specific materials derived from plastic bottles, food containers, and packaging films, or a combination thereof, and it is preferable that it contains 70% by weight or more of the above specific materials. It is even more preferable that polypropylene resin B is substantially 100% by weight of the above specific materials.

[0023] Method for preparing polypropylene resin B: The method for preparing polypropylene resin B is not particularly limited, but it is preferable to minimize the number of thermal cycles in the recovery and recycling processes of the recovered material. It is also preferable to ensure that the heating temperature in the recovery and recycling processes does not become excessively high. More specifically, the following methods can be used to prepare recovered post-consumer materials made from polypropylene resins. (Collection, crushing, and molten ingot production of used polypropylene resin molded products) There are no particular limitations on the method of collecting used polypropylene resin molded products. Polypropylene resin molded products such as food containers and beverage bottles are marked with a recycling symbol, and it is common practice to separate, dispose of, and collect them based on this symbol. (Selection) Since collected used polypropylene resin molded products may contain items other than the polypropylene resin foam particle molded products themselves, such as packaging bags and labels, it is preferable to sort for foreign objects. Sorting for foreign objects may be done by visual inspection by an operator, or by using a sorting machine. (Manufacturing of crushed materials and molten ingots) For crushing collected used polypropylene resin molded articles, it is preferable to use a crusher. Crushers include compression crushers, shear crushers, and impact crushers. The crushing method can be, for example, to coarsely crush the material once using an impact crusher and then finely crush it again using a shear crusher, or to crush it all at once using a shear crusher. In particular, it is economical and preferable to use a shear crusher with a perforated metal or screen installed at the outlet to crush the material in one step while ensuring uniform particle size. There is no particular limit to the size of the crushed material, but it is preferable that it be between 1 mm and 30 mm in size. The resulting pulverized material is preferably heated and reduced in volume to form a molten ingot. Heating and volume reduction machines include extruders and presses. There are no particular limitations on the processing temperature during volume reduction, but it is preferable to perform the process at the lowest possible temperature to avoid thermal degradation of the polypropylene resin, preferably at 220°C or lower and above the resin's melting point. (Manufacturing of recovered polypropylene resin) It is preferable to crush the molten ingot again using the aforementioned crusher, then melt it using an extruder and pelletize it to obtain polypropylene resin recovery pellets. The pulverizer described above can be the same type of pulverizer as described above. The extruder can be a single-screw extruder, a twin-screw extruder, etc., but a single-screw extruder is preferred from the viewpoint of preventing resin degradation. There are no particular restrictions on the extruder temperature, but it is preferable to use the lowest possible temperature to avoid thermal degradation of the polypropylene resin, preferably 220°C or lower and above the resin melting point. As mentioned above, it is preferable to filter the polypropylene resin melted in the extruder to remove impurities. While woven wire mesh or sintered metal can be used as filters, woven wire mesh is preferred because it is more economical. (Pelletization) As mentioned above, pelletization of molten polypropylene resin can be done using methods such as the underwater cutting method, in which the molten resin is extruded from the die into water or mist and continuously cut and solidified with a rotating blade attached to the front of the die, or the strand cutting method, in which the resin is continuously extruded from the die in strand form, cooled and solidified in a water tank, and then cut with a cutting machine. The strand cutting method is more economical and preferable. There are no particular restrictions on the size of the pellets, but it is preferable that the pellet weight be between 1 and 30 mg. The above describes a method for preparing recovered polypropylene resin post-consumer materials. However, the polypropylene resin B used in the manufacturing method of the present invention may be recovered material produced by a different manufacturing method than described above, or a commercially available product sold as a post-consumer recycled material may be used.

[0024] Melting point of polypropylene resin B: Post-consumer materials for resin products are often mixtures of various plastic products, including those manufactured at different times. Therefore, recovered post-consumer materials are prone to variations in raw material properties, particularly in melting points. Polypropylene resins, in particular, are prone to changes in physical properties due to fluctuations in thermal history. Therefore, when mixing recovered polypropylene resin and non-recovered polypropylene resin, which are both susceptible to melting point fluctuations, it was hypothesized that if the relationship between the melting points of the recovered resin and the non-recovered resin is not within an appropriate range, it would be difficult to set an appropriate foaming temperature and achieve good foaming. From this perspective, the foam particle manufacturing method of the present invention appropriately adjusts temperature conditions such as the foaming temperature. Specifically, in the present invention, the value obtained by subtracting the melting point of polypropylene resin A from the melting point of polypropylene resin B is adjusted to be between 10°C and 30°C. In this predetermined range, if the melting point of polypropylene resin B is higher than that of polypropylene resin A, it is possible to set temperature conditions such as the foaming temperature based on the melting point of polypropylene resin A and achieve good foaming properties. For example, even though the manufacturing method of the present invention uses recovered post-consumer materials, it is possible to set temperature conditions such as the foaming temperature and carry out the foaming process in a manner similar to a foaming process using only polypropylene resin A, which is a non-recovered resin.

[0025] If the melting point difference is less than 10°C, the variation in the foaming ratio of the resulting foamed particles will be significant, and the appearance of the foamed particle molded product made using these particles may also be poor. On the other hand, if the melting point difference exceeds 30°C, the difference between the appropriate foaming temperature of polyamide resin A and the appropriate foaming temperature of polyamide resin B becomes too large, which may lead to a decrease in the closed-cell ratio. Furthermore, when molding a foamed particle molded article using foamed particles containing polypropylene resins A and B with such a large melting point difference, it is necessary to take into account the melting point of polypropylene resin B and increase the molding pressure sufficiently. However, under such high molding pressure, the melting of polypropylene resin A may proceed excessively, and as a result, the foamed particle molded article may not be able to be substantially molded. From the viewpoint of better suppressing variations in the foaming ratio of the manufactured foamed particles, it is preferable that the melting point difference is between 10°C and 20°C.

[0026] Within the range where the melting point difference described above is achievable, polypropylene resin B is preferably selected from recovered post-consumer materials exhibiting a melting point of, for example, 150°C to 170°C. The melting point of polypropylene resin B is measured in the same manner as the method for measuring the melting point of polypropylene resin A described above. However, the arithmetic mean obtained from measurements of 10 or more different test pieces is adopted for the melting point of polypropylene resin B.

[0027] Heat of fusion of polypropylene resin B: The heat of fusion of polypropylene resin B is preferably 70 J / g or more and 120 J / g or less, and more preferably 80 J / g or more and 110 J / g or less. The heat of fusion of polypropylene resin B is measured using a differential scanning calorimeter (DSC) based on JIS K7122-1987. First, the test specimen is conditioned by setting the heating and cooling temperatures to 10°C / min, in accordance with the procedure for "measuring the heat of fusion after a certain heat treatment." Then, a DSC (DSC measurement) is performed with the heating temperature set to 10°C / min, and a second DSC curve is obtained. Based on the obtained DSC curve, the value of the heat of fusion can be determined by calculating the area of ​​the fusion peak. If multiple fusion peaks appear in the DSC curve, the sum of the areas of the multiple fusion peaks is taken as the heat of fusion.

[0028] Melt flow rate of polypropylene resin B: The melt flow rate (MFR) of 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 above MFR is measured in accordance with JIS K7210-1:2014 under conditions of a test temperature of 230°C and a nominal load of 2.16 kg.

[0029] The difference between the MFR of polypropylene resin B and the MFR of polypropylene resin A is preferably 5 or less, and more preferably 3 or less.

[0030] Ash content of polypropylene resin B: The manufacturing method of the present invention uses polypropylene resin B having an ash content of 5% by weight or less. Post-consumer materials may contain ash as an impurity during use or collection. According to the inventors' findings, ash impurities mixed into polypropylene resin B act as nuclei for bubbles during the foaming process, inducing the miniaturization of bubbles in the foamed particles produced. As a result, the bubbles constituting the foamed particles become more prone to bursting, reducing the percentage of closed cells in the produced foamed particles and causing variations in the foaming ratio. Therefore, based on the above findings, the present invention uses post-consumer materials as polypropylene resin B, where the ash content per 100% by weight of polypropylene resin B is 5% by weight or less.

[0031] From the viewpoint of better suppressing the refinement of bubbles and variations in the foaming ratio, the ash content of polypropylene resin B is preferably 1% by weight or less, more preferably 0.5% by weight or less, even more preferably 0.2% by weight or less, and particularly preferably 0.1% by weight or less. On the other hand, it is thought that the presence of ash in polypropylene resin B can suppress the generation of excessively large bubbles when producing foamed particles. From the above viewpoint, the lower limit of the ash content is approximately 0.01% by weight.

[0032] Method for measuring ash content: The ash content of polypropylene resin B includes inorganic substances containing elements such as calcium, sodium, and silicon. Such ash content measurements can be performed in accordance with JIS K6226-2:2003. For the measuring device, for example, a thermogravimetric analyzer TGA701 manufactured by LECO can be used. Specifically, 5 g of polypropylene resin B, which is the sample to be measured, is accurately weighed and placed in a crucible, a nitrogen atmosphere is created inside the heating furnace, (1) the temperature of the heating furnace is increased from room temperature to 105°C at a heating rate of 10°C / min under a nitrogen atmosphere, then (2) it is held at 105°C until the measured weight is in equilibrium, (3) it is heated from 105°C to 550°C at a heating rate of 10°C / min, (4) it is held at 550°C until the measured weight is in equilibrium, (5) the heating furnace airflow is changed 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 holding at 950°C for 10 minutes is determined, and (7) it is cooled to room temperature. The ash content of the polypropylene resin is determined by multiplying the weight W1 of the combustion residue by the weight of the sample placed in the crucible (5g), and then multiplying the result by 100 (weight %). The ash content is measured on two or more different test pieces, and the arithmetic mean of these measurements is adopted.

[0033] Melting temperature difference of polypropylene resin B: In the manufacturing method of the present invention, the melting temperature difference of the polypropylene resin B is 30°C or more. Here, the melting temperature difference refers to the difference (Tme-Tms) between the extrapolation melting start temperature (Tms) and the extrapolation melting end temperature (Tme) of the melting peak shown in the second DSC curve of differential scanning calorimetry of the polypropylene resin B.

[0034] By using the polypropylene resin B described above, the foamed particle molded article produced using the foamed particles manufactured by the manufacturing method of the present invention has a good appearance. Although the mechanism of this improvement in appearance is not clear, it is presumed that by including the polypropylene resin B, which has a melting temperature difference of 30°C or more, the melting of the polypropylene resin B becomes slower when the foamed particle molded article is formed, and the air bubbles within the foamed particles tend to be less likely to burst. As a result, it is presumed that a foamed molded article with a high closed-cell ratio and a good appearance is formed.

[0035] From the viewpoint of improving the appearance of the foamed particle molded article, the melting temperature difference of polypropylene resin B is preferably 30°C or higher, more preferably 35°C or higher, and even more preferably 40°C or higher. On the other hand, the upper limit of the melting point difference of polypropylene resin B is not particularly limited, but it is preferably 100°C or less, more preferably 90°C or less, even more preferably 85°C or less, and particularly preferably 80°C or less. For example, the melting temperature difference of the polypropylene resin B used in the present invention is preferably 30°C or more and 100°C or less, more preferably 30°C or more and 90°C or less, even more preferably 35°C or more and 85°C or less, and particularly preferably 35°C or more and 80°C or less.

[0036] The novel finding of using polypropylene resin B, which has a melting temperature difference of 30°C or more, must be implemented only after satisfying the requirements that the blending ratio of polypropylene resin A and polypropylene resin B is adjusted to a predetermined range, and the melting point difference between polypropylene resin A and polypropylene resin B is also adjusted to a predetermined range, as described above.

[0037] In the present invention, the difference in melting temperatures of polypropylene resin A is not particularly limited, but from the viewpoint of making it easier to maintain temperature conditions during the foaming process, it is preferable that it be less than 30°C. The measurement of the difference in melting temperatures of polypropylene resin A is carried out in the same manner as the measurement of the difference in melting temperatures of polypropylene resin B, which will be described later.

[0038] Method for measuring the difference in melting temperature: The method for measuring the difference (Tme-Tms) between the extrapolation melting start temperature (Tms) and the extrapolation melting end temperature (Tme) of the melting peak will be explained using Figure 1. Figure 1 is a graph showing the second DSC curve 100 and the DDSC curve 200, which is the differential curve of DSC curve 100, for polypropylene resin B, a post-consumer material recovery product. The DSC curve 100 can be obtained as follows. Based on the differential scanning calorimetry method of heat flux specified in JIS K7121-1987, approximately 5 mg of resin particles made of polypropylene resin B are accurately weighed to form a test specimen. The DSC curve measured when the specimen is heated and melted from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min is defined as the first DSC curve. Then, after maintaining this temperature for 10 minutes, the specimen is cooled to 30°C at a cooling rate of 10°C / min, and the DSC curve measured when the specimen is heated and melted again to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min is defined as the second DSC curve 100. However, the difference (Tme-Tms) between the extrapolational melting start temperature (Tms) and the extrapolational melting end temperature (Tme) of the melting peak of polypropylene resin B is the arithmetic mean measured for 10 or more different test specimens. The second DSC curve 100, shown as an example in Figure 1, reveals two melting peaks: a small melting peak on the low-temperature side and a large melting peak on the high-temperature side.

[0039] The extracellular melting onset temperature (Tms) is the temperature at the intersection point 30 of the straight line 10, which extends the low-temperature baseline toward the high-temperature side in the second DSC curve 100, and the tangent line 20 drawn at the point where the slope is maximum on the lowest-temperature curve of the melting peak. The extracellular melting termination temperature (Tme) is the temperature at the intersection point 70 of the straight line 50, which is an extension of the high-temperature baseline to the low-temperature side in the second DSC curve 100, and the tangent line 60, which is drawn at the point where the slope is maximum on the hottest side of the melting peak curve. By subtracting the extracellular melting start temperature (Tms) from the obtained extracellular melting end temperature (Tme), the difference between the extracellular melting start temperature (Tms) and the extracellular melting end temperature (Tme) of the melting peak (Tme-Tms) can be determined. The method for determining the extracellular melting start temperature (Tms) and extracellular melting end temperature (Tme) described above conforms to the method for determining the "extracellular melting start temperature" and "extracellular melting end temperature" described in "Method for determining melting temperature" of JIS K7121-1987. Furthermore, polypropylene resin B, which is a recovered post-consumer material, often undergoes processes such as pelletization after melt extrusion during manufacturing. The thermal history during these processes may affect the generation of the melting peak. Therefore, in this invention, in order to eliminate this effect, the extrapolation melting start temperature (Tms) and extrapolation melting end temperature (Tme) are determined using a second DSC curve 100. The melting temperature difference of polypropylene resin B is measured using 10 or more different test pieces, and the arithmetic mean of these measurements is adopted.

[0040] The melting temperature difference described above serves as an indicator for confirming the melting temperature range of polypropylene resin B. The number of peaks shown in the second DSC curve varies depending on the resin material used, and may be one or two or more. In either case, the temperature at the intersection of the straight line extending the low-temperature baseline to the high-temperature side and the tangent line drawn at the point where the slope is maximum on the low-temperature side of the melting peak curve is defined as the extrapolation melting start temperature (Tms). Similarly, in the second DSC curve, the temperature at the intersection of the straight line extending the high-temperature baseline to the low-temperature side and the tangent line drawn at the point where the slope is maximum on the high-temperature side of the melting peak curve is defined as the extrapolation melting end temperature (Tme).

[0041] Furthermore, regarding the extracellular melting initiation temperature (Tms) in this invention, even if the change in melting temperature that appears on the lowest temperature side cannot be confirmed as a peak, it is treated as a change indicating the extracellular melting initiation temperature (Tms) (melting peak). In this case, as shown in Figure 1, the DDSC curve 200 is determined in accordance with the DSC curve 100. Then, the temperature of the inflection point (first inflection point 40) confirmed on the lowest temperature side in the DDSC curve 200 is treated as the extracellular melting initiation temperature (Tms) in the DSC curve 100. That is, when determining the melting temperature difference in this invention, the change in the DSC curve confirmed as an inflection point in the differential curve of the second DSC curve (DDSC curve) is treated as a melting peak. 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 / °C. The peak height of the first inflection point of the DDSC curve can be determined from the difference between the first inflection point in the DDSC curve and the baseline on the lower temperature side of the first inflection point of the DDSC curve.

[0042] Furthermore, regarding the extracellular melting termination temperature (Tme), similar to the extracellular melting initiation temperature (Tms), even if the change in melting temperature appearing on the highest temperature side cannot be confirmed as a peak, it is treated as a change indicating the extracellular melting termination temperature (Tme) (melting peak). In this case, the temperature of the inflection point (high-temperature side inflection point 80) confirmed on the highest temperature side of the DDSC curve is treated as the extracellular melting termination temperature in the DSC curve. 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 determined from the difference between the high-temperature side inflection point in the DDSC curve and the baseline on the higher side of the high-temperature side inflection point of the DDSC curve.

[0043] The extracellular melting initiation temperature of polypropylene resin B is preferably lower than or equal to the extracellular melting initiation temperature of polypropylene resin A. When the polypropylene resin A and 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, making it easier to fill the voids between foam particles, and it is thought that this will improve the appearance of the foam particle molded article and improve the closed-cell ratio. From the above viewpoint, it is more preferable that the heat of fusion of polypropylene resin B, which is lower than or equal to the extracellular melting initiation temperature of polypropylene resin A, is 15 J / g or more, even more preferable that it is 20 J / g or more, and particularly preferable that it is 25 J / g or more. The extracellular melting initiation temperature of polypropylene resin A can be determined using the same method as for polypropylene resin B. Furthermore, the heat of fusion of polypropylene resin B that is below the extracellular melting initiation temperature of polypropylene resin A can be determined as follows. First, in the second DSC curve of polypropylene resin B, a straight line parallel to the vertical axis of the graph is drawn at the extracellular melting initiation temperature of polypropylene resin A. Next, the area enclosed by the straight line extending the low-temperature baseline of the second DSC curve of polypropylene resin B towards the high-temperature side, the straight line parallel to the vertical axis of the graph drawn at the extracellular melting initiation temperature of polypropylene resin A, and the DSC curve is calculated. The amount of heat absorbed corresponding to the above area is the heat of fusion of polypropylene resin B that is below the extracellular melting initiation temperature of polypropylene resin A.

[0044] In the second DSC curve of polypropylene resin B, if polypropylene resin B has two or more melting peaks, it is preferable that the peaks are not completely separated. "Not completely separated" means that in the second DSC curve, the valleys between the peaks do not intersect either the straight line extending the low-temperature baseline towards the high-temperature side or the straight line extending the high-temperature baseline towards the low-temperature side.

[0045] Ethylene content in polypropylene resin B: As described above, polypropylene resin B may contain resins other than polypropylene resin and polymer materials such as thermoplastic elastomers, and may contain, for example, ethylene and butene components. When foamed particles contain a large amount of ethylene, the compressive stress of the foamed particle molded article formed using these foamed particles tends to decrease. This is presumed to be because the inclusion of ethylene reduces the regularity of the crystal structure of the resin, lowers the melting point, and causes a decrease in the physical properties of the resin. From this viewpoint, the amount of ethylene component contained in 100% by weight of polypropylene resin B is preferably 3% by weight or less, and more preferably 2% by weight or less. Furthermore, the lower limit of the ethylene component contained in 100% by weight of polypropylene resin B is most preferably 0% by weight, but since polypropylene resin B is a recycled resin, it is generally 0.05% by weight or more. In this invention, ethylene component refers to structural units made of ethylene. The content of ethylene component in polypropylene resin B can be measured by a known method obtained from an IR spectrum. The ethylene content of polypropylene resin B can be determined, for example, by the method described in the Polymer Analysis Handbook (edited by the Polymer Analysis Research Group of the Japan Society for Analytical Chemistry, published January 1995, published by Kinokuniya Shoten, pages 608-609 "II.2.3 2.3.2 Qualitative Method" and pages 615-618 "II.2.3 2.3.4 Propylene / Ethylene Copolymer"), that is, by a method of quantification based on the relationship between the absorbance of ethylene corrected by a predetermined coefficient and the thickness of a film-like test piece. The butene content of polypropylene resin B can be determined, for example, by the method described in the Polymer Analysis Handbook (edited by the Polymer Analysis Research Group of the Japan Society for Analytical Chemistry, published January 1995, published by Kinokuniya Shoten, pages 608-609 "II.2.3 2.3.2 Qualitative Method" and pages 618-619 "II.2.3 It can be determined by the method described in "2.3.5 Propylene / Butene Copolymer," that is, by a method of quantitative analysis based on the relationship between the absorbance of butene corrected by a predetermined coefficient and the thickness of a film-like test piece.

[0046] Furthermore, when measuring polypropylene resin B as described above, if polypropylene resin B is composed of recovered post-consumer materials of two or more types of polypropylene resins, a sample obtained by melting and mixing them shall be used. The melting and mixing conditions should be the same temperature conditions as those used during the melting and kneading process when manufacturing polypropylene resin particles.

[0047] [Mixing ratio of polypropylene resin A and polypropylene resin B] In the manufacturing method of the present invention, the blending ratio of polypropylene resin A and polypropylene resin B in a mixture is adjusted to be within a predetermined range. Specifically, in a total of 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 40% by weight or more and 97% by weight or less, and the blending ratio of polypropylene resin B is adjusted to be 3% by weight or more and 60% by weight or less. If the blending ratio of polypropylene resin A in a 100% by weight mixture is too low, the variation in the foaming ratio and the closed-cell ratio of the resulting foamed particles tend to decrease. From this viewpoint, in a 100% by weight mixture, the blending ratio of polypropylene resin A is preferably 50% by weight or more, more preferably exceeding 50% by weight, even more preferably 60% by weight or more, and particularly preferably 70% by weight or more. On the other hand, from the viewpoint of suppressing variations in the foaming ratio of the resulting foamed particles and a decrease in the closed-cell ratio, while using a large amount of post-consumer material, the blending ratio of polypropylene resin A in 100% by weight of the mixture is preferably 93% by weight or less, more preferably 90% by weight or less, and even more preferably 80% by weight or less.

[0048] For example, from the viewpoint of using a large amount of post-consumer material while suppressing variations in the foaming ratio of foamed particles and a decrease in the closed-cell ratio, it is preferable to adjust the mixture so that, in 100% by weight, the blending ratio of polypropylene resin A is greater than 50% by weight and 80% by weight or less, and the blending ratio of polypropylene resin B is 20% by weight or more and less than 50% by weight (however, the total of polypropylene resin A and polypropylene resin B is 100% by weight).

[0049] [Ethylene content in foamed particles] The base resin, which is a mixture of polypropylene resin A and polypropylene resin B used in the manufacturing method of the present invention, may contain resins other than polypropylene resin and polymer materials such as thermoplastic elastomers, as described above. For example, the base resin may contain ethylene components and butene components. When the foamed particles contain a large amount of ethylene components, the compressive stress of the foamed particle molded article formed using the foamed particles tends to decrease. This is presumed to be because the inclusion of ethylene components reduces the regularity of the crystal structure of the resin, lowers the melting point, and causes a decrease in the physical properties of the resin. From this viewpoint, it is preferable that the amount of ethylene components contained in the foamed particles be less than 4% by weight, more preferably 3% by weight or less, and even more preferably 2% by weight or less. The ethylene component referred to here is defined in the same way as the ethylene component contained in polypropylene resin B described above. The ethylene content in the foamed particles can be calculated using the same method as the method for calculating the ethylene content in polypropylene resin B, except that the foamed particles produced by the manufacturing method of the present invention are used as the sample.

[0050] [Additives] The foamed particles used in the present invention may contain, in addition to the polypropylene resin A and polypropylene resin B described above, one or more additives, provided that they do not hinder the desired effects of the present invention. Examples of such additives include, but are not limited to, colorants, nucleating agents such as boric acid, antioxidants, UV inhibitors, lubricants, or foam regulators. The blending ratio of the above additives may be determined appropriately by referring to conventionally known methods for producing foamed polypropylene resin particles.

[0051] [Composition of foamed particles] The foamed particles produced by the manufacturing method of the present invention may be single-layer particles or multilayer resin foamed particles having a coating layer made of a polyolefin resin on the surface of the particles. The coating layer may have the same structure as the coating layer in conventionally known multilayer resin foamed particles. For example, when a polyolefin resin is used as the resin constituting the coating layer, the polyolefin resin may consist solely of polyolefin resin, or it may contain, in addition to polyolefin resin, other resins, polymer materials such as elastomer resins, and / or any additives. Examples of the above polyolefin resin include, but are not limited to, polypropylene resin or copolymers of polypropylene resin and other resins, polyethylene resin or copolymers of polyethylene resin and other resins. The resin constituting the coating layer may contain recovered post-consumer materials of polypropylene resin, or it may be entirely non-recovered resin. From the viewpoint of making it easier to obtain a foamed particle molded article with excellent fusion properties between foamed particles, secondary foaming properties, and compressive stress, it is preferable that the resin constituting the coating layer does not contain recovered post-consumer materials.

[0052] The melting point of the polyolefin resin constituting the coating layer is not particularly limited, but it is preferable that it be below the melting or softening point of the resin material constituting the core layer. As a result, when foamed particles manufactured by the manufacturing method of the present invention are used and the core layer of the foamed particles is heated to a temperature at which secondary foaming is possible for in-molding, the coating layer melts before the core layer, resulting in good fusion between adjacent foamed particles. The melting point and softening point of the resin material constituting the core layer, as described above, refer to the melting point or softening point of the base resin composed of polypropylene resin A and polypropylene resin B that make up the core layer.

[0053] The coating layer described above may contain one or more additives, as long as they do not hinder the intended effects of the present invention. The same additives used to add to the foamed particles constituting the core layer can be used. The blending ratio of the additives may be determined appropriately by referring to conventionally known methods for producing polypropylene-based foamed particles.

[0054] The weight ratio of the core layer to the coating layer is not particularly limited, but from the viewpoint of improving the fusion properties of the foamed particles and increasing the consumption of post-consumer materials, it is preferable that the coating layer be 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 8 parts by weight or less, per 100 parts by weight of the core layer. The lower limit of the coating layer per 100 parts by weight of the core layer is approximately 1 part by weight.

[0055] The coating layer may be foamed or non-foamed, but in order for the resulting foamed particle molded article to have excellent mechanical strength, it is preferable that the resin layer be substantially non-foamed. Here, "substantially non-foamed" includes not only those with absolutely no bubbles (including those where bubbles that were initially formed during foaming of the resin particles have melted and been destroyed, causing them to disappear), but also those with a small number of extremely small bubbles, as long as they do not affect the mechanical strength of the resulting foamed particle molded article.

[0056] Furthermore, in multilayer resin foam particles, the core layer may be completely covered by the coating layer, or some of the core layer may be exposed. An example of a structure in which the core layer is exposed is one in which only the sides of a cylindrical core layer are covered by the coating layer, and the core layer is exposed on the top or bottom surface of the cylinder.

[0057] [Each step in the manufacturing method of the present invention] The following describes one embodiment of the manufacturing method of the present invention, divided into several steps. Specifically, the manufacturing method of the present invention will be described in terms of a mixing step, an extrusion step, and a foaming step. In addition, the manufacturing method of the present invention may be modified in part or by adding different steps, as long as it does not hinder the intended effect of the present invention. Furthermore, each step may be carried out independently of the others, or some or all of them may overlap.

[0058] [Mixing process] In the manufacturing method of the present invention, a mixing step is performed first. The mixing step is a step of obtaining a base resin containing a mixture of polypropylene resin A and polypropylene resin B. Specifically, the mixing step is a step of supplying, for example, polypropylene resin A, polypropylene resin B, and appropriately used additives to an extruder, melting and kneading the supplied materials to obtain a molten resin mixture. At this time, the mixing ratio of polypropylene resin A and polypropylene resin B in the molten resin mixture is adjusted to the mixing ratio described above.

[0059] When producing multilayer resin foam particles by the manufacturing method of the present invention, it is preferable to perform the above-mentioned mixing step for preparing the core layer constituent material and the coating layer mixing step for preparing the coating layer constituent material, which is different from the mixing step, independently. The above-mentioned core layer constituent material includes at least polypropylene resin A and polypropylene resin B.

[0060] [Extrusion Process] Next, an extrusion process is carried out in which the mixture obtained in the mixing process described above is extruded and cut from an extruder to obtain polypropylene resin particles. Specifically, for example, a mixture is extruded from an extrusion die located downstream of an extruder to form strands. Then, polypropylene resin particles (hereinafter also simply referred to as resin particles) are obtained by cutting the strands to desired dimensions using a pelletizer or the like. The strands have a circular or similar cross-sectional shape perpendicular to the extrusion direction. The resin particles obtained in this way exhibit a columnar shape, such as a cylindrical shape.

[0061] Furthermore, when manufacturing multilayer foamed resin particles with a multilayer structure including a coating layer, it is preferable to use an extruder for co-extrusion. Specifically, the core layer component material and the coating layer component material are combined in a co-extrusion die located downstream of the extruder, and the coating layer component material is laminated onto the outer circumference of the core layer component material and co-extruded to form a multilayer strand. Then, as described above, the strand is cut to the desired dimensions to obtain multilayer resin particles having a core layer and a coating layer covering the core layer.

[0062] [Foaming process] Next, a foaming process is carried out. Specifically, the resin particles obtained in the extrusion process are dispersed in an aqueous medium in a sealed container and impregnated with a foaming agent. The resin particles containing the foaming agent are then released from the sealed container along with the aqueous medium under a pressure lower than that inside the sealed container, causing foaming to occur at a pressure of 10 kg / m³. 3 More than 200kg / m 3 We manufacture polypropylene resin foam particles having the following bulk density. The foaming process described below will be explained in detail, divided into the dispersion process, the foaming agent impregnation process, and the release process.

[0063] (Dispersion process) The dispersion step involves dispersing the resin particles obtained in the extrusion step into an aqueous medium placed in a container. The aqueous medium contains an inorganic dispersant. The aqueous medium may also contain any other additives as appropriate.

[0064] Aqueous medium: The aqueous medium is a medium for dispersing resin particles within a container. Examples of aqueous mediums include water, alcohols, glycols, and glycerin, with water being preferred from the viewpoint of ease of wastewater treatment. From the viewpoint of improving the dispersibility of resin particles and the productivity of foamed particles, the amount of resin particles added to the aqueous medium is preferably 10 to 100 parts by weight, and more preferably 20 to 80 parts by weight, per 100 parts by weight of the aqueous medium.

[0065] Inorganic dispersants: Inorganic dispersants are used to effectively disperse resin particles in an aqueous medium and to suppress blocking between foamed particles during the foaming process. From the viewpoint of maintaining the in-moldability of the foamed particles while making it easier to suppress the fusion of foamed particles with each other in the discharge process described later, the amount of inorganic dispersant added is preferably 0.01 parts by weight or more and 2 parts by weight or less, more preferably 0.02 parts by weight or more and 1 part by weight or less, and even more preferably 0.03 parts by weight or more and 0.8 parts by weight or less, per 100 parts by weight of resin particles.

[0066] As inorganic dispersants, for example, inorganic fine particles such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica can be used. These inorganic fine particles may be used individually or in combination of two or more types.

[0067] Optional additives: The aqueous medium may contain, in addition to the inorganic dispersant, one or more optional additives such as a dispersing aid and a surfactant. Examples of dispersing aids include aluminum sulfate. Examples of surfactants include anionic surfactants such as sodium alkylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium alkanesulfonate. Surfactants may be used alone or in combination of two or more. These additives are usually added in an amount of 0.001 parts by weight or more and 1 part by weight or less per 100 parts by weight of resin particles.

[0068] (Foaming agent impregnation process) After the dispersion process described above, or at a time that overlaps with part or all of the dispersion process, the foaming agent impregnation process is carried out. The foaming agent impregnation process is a step performed in general foam particle manufacturing methods in which a foaming agent is impregnated into resin particles dispersed in an aqueous medium. For example, a sealed container containing resin particles is sealed, and a physical foaming agent is added to the sealed container. This impregnates the resin particles with the physical foaming agent, thereby obtaining foamable resin particles. The addition of the physical blowing agent to the sealed container can be done at any time before the resin particles are foamed. The blowing agent may be added to the aqueous medium along with the resin particles during the dispersion process, and then the blowing agent, which has become gaseous by heating or other means, may be impregnated into the resin particles. Alternatively, the blowing agent in gaseous form may be injected into the sealed container under pressure in parallel with or after the dispersion process to impregnate the resin particles.

[0069] Foaming agent: The foaming agent used in the present invention is appropriately selected from among foaming agents used to obtain general foamed particles, but a physical foaming agent is preferred. Specific examples of physical blowing agents include inorganic and / or organic physical blowing agents. Examples of inorganic physical blowing agents include carbon dioxide, air, nitrogen, helium, argon, and water. Examples of organic physical blowing agents 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, methylene chloride, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, 1-chloro-3,3,3-trifluoropropene, 1-chloro-2,3,3,3-tetrafluoropropene, and 1,1,1,4,4,4-hexafluoro-2-butene.

[0070] These physical blowing agents may be used individually or in combination of two or more. Of these blowing agents, preferably, a blowing agent mainly composed of an inorganic physical blowing agent such as carbon dioxide, nitrogen, or air is used, and more preferably, carbon dioxide is used. In the present invention, "mainly composed of an inorganic physical blowing agent" means that the physical blowing agent contains 50 mol% or more of the inorganic physical blowing agent. Preferably, the physical blowing agent contains 70 mol% or more of the inorganic physical blowing agent, more preferably 90 mol% or more, and even more preferably, the physical blowing agent consists solely of the inorganic physical blowing agent.

[0071] The amount of physical blowing agent added is determined appropriately depending on the type of base resin constituting the resin particles, the type of blowing agent, the bulk density of the target foamed particles, etc. For example, when carbon dioxide is used as the physical blowing 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 even more preferably 1 part by weight or more and 10 parts by weight or less, per 100 parts by weight of resin particles.

[0072] High temperature peak: Furthermore, in order to adjust the crystalline state of the resulting foam particles, adjustments may be made in the dispersion step and / or foaming agent impregnation step described above, such as adjusting the heating rate of the sealed container or holding the sealed container at a predetermined temperature for a predetermined time. For example, it is possible to adjust the first DSC curve obtained based on the heat flux differential scanning calorimetry method described in JIS K7121-1987 so that the melting peak (high temperature peak) appears at a higher temperature than the melting peak inherent to the resin constituting the resulting foam particles. Foamed particles exhibiting a high-temperature peak are preferable from the viewpoint that they provide a wider range of molding conditions for obtaining a good foamed particle molded body. The adjustments to obtain the high-temperature peak described above can be carried out, for example, as follows: In the dispersion step and / or foaming agent impregnation step described above, a first-stage holding step is performed in which the mixture is held for about 10 to 60 minutes at a temperature of (resin melting point of the resin particles - 20°C) or higher but less than (resin melting point of the resin particles + 20°C). After that, the temperature is adjusted to (resin melting point of the resin particles - 15°C) or higher but less than (resin melting point of the resin particles + 15°C). Then, if necessary, a second-stage holding step is performed in which the mixture is held for another 10 to 60 minutes at that temperature. Subsequently, foamed particles having a high-temperature peak can be produced by performing the foaming step described later. Holding within the range of (resin melting point of the resin particles - 15°C) or higher but less than (resin melting point of the resin particles + 15°C) to form the high-temperature peak can be set in multiple stages within that temperature range, or the high-temperature peak can be formed by slowly raising the temperature within that temperature range over a sufficient period of time. The resin melting point of the resin particles is determined by using the resin particles as a test specimen and, based on the differential scanning calorimetry method described in JIS K7121-1987, raising the temperature from 30°C to 30°C higher than the end of the melting peak at a heating rate of 10°C / min, holding at that temperature for 10 minutes, then cooling down to 30°C at a cooling rate of 10°C / min, and then raising the temperature again from 30°C to 30°C higher than the end of the melting peak at a heating rate of 10°C / min. The melting point of the resin particles is determined by the peak temperature of the melting peak obtained from the second DSC curve. If two or more melting peaks appear in the DSC curve, the melting point of the resin is determined by the temperature of the peak of the melting peak with the largest area.

[0073] (Release process) After foaming resin particles are obtained in the foaming agent impregnation process described above, a release process is carried out. The release process involves releasing resin particles containing a foaming agent (foaming resin particles) from a container together with an aqueous medium to cause foaming and obtain foamed particles. More specifically, the foaming resin particles are foamed by releasing them together with an aqueous medium under a pressure lower than the internal pressure of a sealed container. According to the foaming process described above, the bulk density is 10 kg / m³. 3 More than 200kg / m 3 The following foamed particles are easily obtainable and therefore preferable.

[0074] (Two-stage foaming process) As described above, the bulk density of the foamed particles produced can be adjusted, for example, by appropriately changing the foaming conditions such as the temperature and pressure inside the sealed container when releasing the contents of the sealed container during the release process. If the bulk density of the foamed particles produced by the manufacturing method described above is higher than desired, or if it is desired to provide foamed particles with an even lower bulk density, the following two-stage foaming process can be carried out as appropriate. The two-stage foaming process first involves storing the foamed particles obtained as described above in a pressurized sealed container and pressurizing the container by injecting air or other gas to increase the internal pressure within the bubbles of the foamed particles. Subsequently, the foamed particles are removed from the sealed container and heated using steam or hot air to further foam them, thereby carrying out the two-stage foaming process. By performing this two-stage foaming process, it is possible to obtain foamed particles (two-stage foamed particles) with a lower bulk density.

[0075] (Variations of the method for manufacturing multilayer resin foam particles) The above describes a method for producing multilayer resin foam particles by performing co-extrusion in the extrusion process. However, the method for producing multilayer resin foam particles in the present invention is not limited to this. For example, as a different manufacturing method of multilayer resin foam particles, a mixture as the core layer constituent material is obtained through a mixing process, and this is subjected to an extrusion process to prepare single-layer core layer particles previously formed into a particulate state. Then, these are put into a mixing device having a mixing function and a heating function to heat the surface layer portion of the core layer particles. Next, a coating layer constituent material for forming the coating layer is put into the mixing device or the like, and the heated core layer particles and the coating layer constituent material are mixed. Thereby, multilayer resin particles provided with a coating layer formed by coating the surface of the core layer particles with the coating layer constituent material are obtained. By subjecting the multilayer resin particles to a foaming process to foam them, multilayer resin foam particles are obtained.

[0076] [Polypropylene-based resin foam particles] The polypropylene-based resin foam particles manufactured as described above contain polypropylene-based resin B, which is a recovered material of the post-consumer material of the polypropylene-based resin molded body, and greatly contribute to solving environmental problems such as material recycling required in a recycling-oriented society and reduction of carbon dioxide emissions through utilization of waste products. In addition, the foam particles manufactured according to the present invention can exhibit good moldability equivalent to or better than that of conventional foam particles manufactured using only polypropylene-based resin A, which is a non-recovered material, and can provide a foam particle molded body excellent in appearance and rigidity. Hereinafter, the foam particles manufactured by the manufacturing method of the present invention will be described.

[0077] (Bulk density) The bulk density of the foam particles manufactured by the manufacturing method of the present invention is 10 kg / m 3 or more and 200 kg / m 3 or less. From the viewpoint of being able to provide a foam particle molded body excellent in mechanical strength, the above bulk density is preferably 15 kg / m 3 or more, more preferably 20 kg / m 3 or more, and still more preferably 25 kg / m 3 or more. On the other hand, from the viewpoint of being able to provide a foam particle molded body excellent in lightness and cushioning properties, it is preferably 150 kg / m 3 or less, more preferably 100 kg / m 3 or less, and 80 kg / m3 The following is even more preferable:

[0078] The bulk density of foamed particles is measured by the following method. First, the foamed particles to be measured are left for at least 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. The resulting group of foamed particles, weighing W (g), is then filled into a graduated cylinder, and the filling height of the foamed particles inside the cylinder is stabilized by lightly tapping the floor several times with the bottom of the graduated cylinder. The bulk volume V (L) of the foamed particles indicated by the scale on the graduated cylinder is read, and the weight W of the foamed particles is divided by the bulk volume V (W / V). The resulting value is obtained in kg / m 3 By converting the units, the bulk density of the foamed particles (kg / m³) can be calculated. 3 ) can be obtained.

[0079] (ash content) The foamed particles produced by the manufacturing method of the present invention may contain inorganic substances such as calcium, sodium, and silicon as ash. This method of measuring ash content is the same as the method for measuring ash content in polypropylene resin B described above, except that 5 g of foamed particles were used as the measurement sample.

[0080] (Expansion ratio) The foaming ratio of the foamed particles is determined by the resin density of the polypropylene resin (900 kg / m³). 3 This can be obtained by dividing ) by the bulk density of the foamed particles mentioned above.

[0081] (Measurement of variation rate in foaming ratio) 300 mL to 500 mL of polypropylene resin foam particles are accurately weighed and sieved using eight types of standard sieves specified in JIS Z8801. The mesh sizes of the eight standard sieves are 5 mesh, 6 mesh, 7 mesh, 8 mesh, 9 mesh, 12 mesh, 14 mesh, and 16 mesh. Next, the weight of the foam particles remaining in each sieve (residual foam particles) is measured, and the weight fraction Wi of the weight of the residual foam particles relative to the weight of the foam particles used for sieving is determined. Furthermore, the foaming ratio Ki of the foam particles is determined following the method described above. First, we calculate the average expansion ratio Kav from the following formula (1).

number

number

number

[0082] Furthermore, to confirm that the variation in foam particle size observed through the above-mentioned sieving method is not due to variations in the weight of the foam particles but rather to variations in the foaming ratio, the following checks should be performed. Specifically, 500 foam particles are randomly selected from the manufactured foam particles, and the weight of each foam particle is measured to two decimal places using a precision balance. The average weight is then calculated by taking the arithmetic mean of the measured values. Then, foam particles whose measured weight falls within ±10% of the above average weight are counted. If the number of counted foam particles is 95% or more of the 500 foam particles, it can be concluded that the variation in foam particle size observed through sieving is due to variation in the foaming ratio.

[0083] (High temperature peak) Preferably, the foamed particles produced by the manufacturing method of the present invention are such that, by differential scanning calorimetry, the melting peak inherent to the resin and the high-temperature melting peak (high-temperature peak) caused by the secondary crystals of the resin formed by the thermal history from foaming the resin particles to obtaining the foamed particles can be measured. In other words, it is preferable that the foamed particles produced by the manufacturing method of the present invention exhibit the following high-temperature peaks. First, the foamed particles are used as test pieces, and the first DSC curve is obtained by heating and melting them from 30°C to a heating termination temperature 30°C higher than the end of the melting peak, at a heating rate of 10°C / min, based on the differential scanning calorimetry method described in JIS K7121-1987. In this first DSC curve, two or more melting peaks are confirmed, and it is confirmed that these two or more melting peaks include a melting peak specific to the resin constituting the foamed particles and a high-temperature melting peak (high-temperature peak) whose peak temperature is higher than the peak temperature of the melting peak specific to the resin. Next, after holding at the heating termination temperature for 10 minutes, the particles are cooled to 30°C at a cooling rate of 10°C / min, and a second DSC curve is obtained by heating and melting them again at a heating rate of 10°C / min to a heating termination temperature 30°C higher than the end of the melting peak. It is preferable that the foamed particles do not exhibit the high-temperature melting peak in this second DSC curve. The foamed particles used as test specimens should be approximately 1 to 3 mg in size. If the foamed particles are larger than 3 mg, they can be divided into equal parts to produce 1 to 3 mg test specimens. As mentioned above, foamed particles that exhibit a high-temperature peak have excellent in-moldability and can improve the mechanical properties, such as compressive stress, of the resulting foamed particle molded body. Furthermore, the term "resin constituting the foamed particles" as used above refers to the polypropylene resin contained in polypropylene resin A and polypropylene-based resin B, which are included in the base resin.

[0084] (High-temperature peak heat and total heat) As described above, the measurement methods for the heat quantity of the high-temperature peak and the total heat quantity of the melting peak are the same as those used in the examples described later.

[0085] (Average bubble diameter) The bubble diameter of the foamed particles obtained by the manufacturing method of the present invention is not particularly limited. From the viewpoint of providing a foamed particle molded body that is less prone to bubble bursting and has an excellent appearance when molding the foamed particle molded body, the average bubble diameter of the foamed particles is preferably 50 μm or more, more preferably 60 μm or more, even more 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 even more preferably 150 μm or less.

[0086] The average bubble diameter of a foamed particle can be determined as follows, based on magnified photographs taken under a microscope of a cross-section of a foamed particle that has been roughly divided in half. First, in the magnified photograph of the cross-section of the foamed particle, four line segments are drawn from one surface of the foamed particle to the other, passing through approximately the center of the cross-section. However, these line segments are drawn so as to form eight radial lines extending from approximately the center of the cross-section to the surface of the cut particle at equal intervals. Next, the total number N (bubbles) intersecting the above four line segments is determined. The sum L (μm) of the lengths of the four line segments is determined, and the value obtained by dividing the sum L by the total number N (L / N) is taken as the average bubble diameter of one foamed particle. This process is performed for 10 or more foamed particles, and the arithmetic mean of the average bubble diameters of each foamed particle is taken as the average bubble diameter of the foamed particle.

[0087] (Percentage of closed cells) The closed-cell ratio can be determined using an air-comparison hydrometer based on ASTM-D2856-70.

[0088] [Foam particle molded body] A molded foam particle body can be obtained by in-mold molding using foam particles obtained by the manufacturing method of the present invention. For example, a molded foam particle body can be manufactured as follows: First, foam particles are filled into a mold having a cavity corresponding to the shape of the desired molded foam particle body, and the foam particles filled into the mold are heated with a heating medium such as steam. The foam particles in the cavity foam up further upon heating and fuse together with each other. As a result, the foam particles become integrated, and a molded foam particle body corresponding to the shape of the cavity is obtained. A foam particle molded article produced using foam particles manufactured by the manufacturing method of the present invention has excellent appearance and excellent physical properties, such as compressive stress at 50% strain.

[0089] (Molded body density) The density of the above-mentioned foamed particle molded body is not particularly limited, but from the viewpoint of lightweight properties, 100 kg / m³ is preferred. 3 The following is preferable: 80 kg / m 3 The following is more preferable. On the other hand, from the viewpoint of producing a molded product with excellent mechanical properties, 10 kg / m 3 Preferably, it should be 30 kg / m 3 It is more preferable that the above conditions are met. The density of the molded body described above is determined by measuring the weight of the foamed particle molded body and dividing this weight by the volume of the foamed particle molded body determined by the immersion method.

[0090] (Compressive stress at 50% strain) The compressive stress of a foamed particle molded article at 50% strain is not particularly limited, but from the viewpoint of obtaining a foamed particle molded article with excellent compressibility, it is preferably 0.50 MPa or higher, more preferably 0.52 MPa or higher, and even more preferably 0.53 MPa or higher. On the other hand, the upper limit of the compressive stress of a foamed particle molded article at 50% strain is generally around 0.58 MPa or lower. The compressive stress at 50% strain of a foam particle molded body can be determined by cutting 10 test pieces of 50mm x 50mm x 25mm at equal intervals from a foam particle molded body (250mm x 200mm x 50mm thick), excluding the skin, and performing a compression test at a compression speed of 10mm / min according to JIS K6767:1999. For example, the test can be performed on 10 test pieces, and the arithmetic mean of the obtained values ​​can be taken as the compressive stress at 50% strain. The compressive stress at 50% strain serves as an indicator of the stiffness of the foam particle molded body. [Examples]

[0091] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. For each example and comparative example carried out as described below, the bulk density, ash content, ethylene content, foaming ratio, high-temperature peak heat value, total heat value, average cell diameter, closed cell ratio, and foam particle variation rate of the obtained foam particles were measured. The variation of the obtained foam particles was also evaluated. Furthermore, the molded density and compressive stress at 50% strain of the foam particle molded body molded using the obtained foam particles were measured, and the appearance and rigidity were evaluated. The measurement results and evaluation results described above are shown in Tables 2 to 4.

[0092] The examples, comparative examples, and reference examples described below use polypropylene resin A and polypropylene resin B shown in Table 1. Polypropylene resin A shown in Table 1 is a non-recoverable resin material, and polypropylene resin B is a recovered post-consumer material of polypropylene resin.

[0093] (Ethylene content of polypropylene resin B) The ethylene content of polypropylene resin B was determined using the method described in the Polymer Analysis Handbook (edited by the Polymer Analysis Research Group of the Japan Society for Analytical Chemistry, published January 1995, Kinokuniya Shoten, pages 608-609 "II.2.3 2.3.2 Qualitative Method" and pages 615-618 "II.2.3 2.3.4 Propylene / Ethylene Copolymer"), that is, a quantitative method based on the relationship between the absorbance of ethylene corrected by a predetermined coefficient and the thickness of the film-like test specimen. Specifically, first, polypropylene resin B was hot-pressed at 180°C to form a film, and multiple test specimens of different thicknesses were prepared. Then, the IR spectrum of each test specimen was measured to determine the ethylene-derived 722 cm⁻¹. -1 and 733cm -1 Absorbance at (A 722 , A 733 The following was read. Next, the ethylene content in polypropylene resin B was calculated for each test piece using the following formula. The arithmetic mean of the ethylene content obtained for each test piece was defined as the ethylene content (wt%) in polypropylene resin B.

number

number

number

[0094] (Butene content of polypropylene resin B) The butene content of polypropylene resin B was determined by the method described in the Polymer Analysis Handbook (edited by the Polymer Analysis Research Group of the Japan Society for Analytical Chemistry, published January 1995, published by Kinokuniya Shoten, pages 608-609 "II.2.3 2.3.2 Qualitative Method" and pages 618-619 "II.2.3 2.3.5 Propylene / Butene Copolymer"), that is, by quantifying the butene content from the relationship between the absorbance of butene corrected by a predetermined coefficient and the thickness of the film-like test piece. Multiple test specimens of different thicknesses were prepared from polypropylene resin in the same manner as the measurement of the ethylene content of the polypropylene resin described above. Then, by measuring the IR spectrum of each test specimen, the butene-derived 766 cm⁻¹ was obtained. -1 Absorbance at (A 766 The following values ​​were read. Next, for each test piece, the arithmetic mean of the butene content obtained using the following formula (7) was defined as the amount of butene component in the polypropylene resin (wt%).

number

[0095] The melt flow rate of polypropylene resin was measured according to JIS K7210-1:2014, under conditions of a test temperature of 230°C and a nominal load of 2.16 kg.

[0096] (Ash content of polypropylene resin B) In accordance with JIS K6226-2:2003, the ash content was measured as follows using a LECO TGA701 thermogravimetric analyzer. 5 g of polypropylene resin B was accurately weighed and placed in a crucible. The furnace was heated with a nitrogen atmosphere, (1) the furnace temperature was increased from room temperature to 105°C at a rate of 10°C / min, then (2) it was held at 105°C until the measured weight was in equilibrium, (3) it was heated from 105°C to 550°C at a rate of 10°C / min, (4) it was held at 550°C until the measured weight was in equilibrium, (5) the furnace airflow was changed from nitrogen to air and heated from 550°C to 950°C at a rate of 10°C / min, (6) the weight W1 of the combustion residue after holding at 950°C for 10 minutes was determined, and (7) it was cooled to room temperature. The amount of ash (weight %) of polypropylene resin B was determined by dividing the weight W1 of the combustion residue by the weight of the sample (5 g) placed in the crucible and multiplying the result by 100. The above procedure was performed twice, and the arithmetic mean of these results was taken as the ash content of polypropylene resin B.

[0097] The melting points, peak temperatures of the DSC melting peaks, and heat of fusion for polypropylene resins A and B shown in Table 1 were determined by obtaining a second DSC curve as follows. Using the obtained second DSC curve, the extrapolation melting start temperature (Tms), extrapolation melting end temperature (Tme), and melting temperature difference (Tme-Tms) were determined. The melting peaks observed in the second DSC curve were designated as DSC melting peak 3, DSC peak 2, and DSC peak 1, starting from the high-temperature side. In other words, if only one melting peak appeared, only DSC melting peak 3 was shown in Table 1; if three melting peaks appeared, DSC melting peak 3, DSC peak 2, and DSC peak 1 were shown in Table 1. For heat of fusion, if multiple DSC melting peaks appeared, the sum of all heats of fusion was shown in Table 1. In addition, in the second DSC curve for polypropylene resin B, it was checked whether each peak of polypropylene resin B was completely separated. The peaks in the recovered resins 1-5 were not completely separated.

[0098] Based on the differential scanning calorimetry method of JIS K7121-1987, approximately 5 mg of resin particles made of polypropylene resin A or polypropylene resin B were accurately weighed and prepared as test specimens. The DSC curve measured when heating and melting the resin from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min was defined as the first DSC curve. Then, after maintaining that temperature for 10 minutes, the resin was cooled to 30°C at a cooling rate of 10°C / min, and the DSC curve measured when heating and melting the resin again to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min was defined as the second DSC curve. The peak temperature at the top of the peak appearing in the second DSC curve was defined as the DSC melting peak temperature. The melting point of the resin was defined as the peak temperature at the top of the peak showing the largest heat of fusion observed in the second DSC curve. The above measurements were performed on 10 randomly selected test specimens, and the arithmetic mean values ​​were used for the melting peak temperature, resin melting point, extracorporeal melting start temperature (Tms), and extracorporeal melting end temperature (Tme).

[0099] The heat of fusion for polypropylene resins A and B shown in Table 1 was determined by obtaining the second DSC curve as follows. Note that virgin materials consisting of polypropylene random copolymers were used for resins 1-6 shown in Table 1. Recovered resins 1 and 2 were recovered post-consumer materials of polypropylene resin products manufactured by Guolong Plastic Chemical Co., Ltd. Recovered resin 3 was recovered post-consumer materials of polypropylene resin products manufactured by Dongguan Pengyi Plastic Raw Materials. Recovered resin 4 was a commercially available product (product name: rPP CPP0500RP) sold as recovered post-consumer materials of polypropylene resin products manufactured by REEF Technology Co., Ltd. Recovered resin 5 was recovered post-consumer materials of polypropylene resin products prepared by recovering, crushing, washing, melting, and granulating used polypropylene resin molded bodies. Based on the differential scanning calorimetry method of JIS K7122-1987, approximately 5 mg of resin particles made of polypropylene resin A or polypropylene resin B were accurately weighed and prepared as test specimens. The DSC curve measured when heating and melting the material from 30°C to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min was defined as the first DSC curve. Then, after maintaining this temperature for 10 minutes, the material was cooled to 30°C at a cooling rate of 10°C / min, and the DSC curve measured when heating and melting the material again to a temperature 30°C higher than the end of the melting peak at a heating rate of 10°C / min was defined as the second DSC curve. The peak temperature at the top of the peak appearing in the second DSC curve was defined as the DSC melting peak temperature, and the heat of fusion (J / g) was determined from the area of ​​this peak. The above measurement was performed on 10 randomly selected test specimens, and the arithmetic mean value of the heat of fusion was adopted for each specimen.

[0100] (Example 1) Preparation of resin particles: Polypropylene resin A was prepared using resin 1 shown in Table 1, and polypropylene resin B was prepared using recovered resin 1 shown in Table 1. These two materials were blended in the proportions shown in Table 2 and melt-kneaded in an extruder to produce a mixture, which was used as the base resin. In addition to these materials, zinc borate (Borax "Fire Break ZB") was used as a foam regulator during melt-kneading. The zinc borate was added at a concentration of 0.05% by weight per 100% by weight of the melt-kneaded mixture (total of resin 1, recovered resin 1, and zinc borate). The molten base resin was extruded in strand form from a die in the extruder, cooled in water, and then cut with a pelletizer to obtain cylindrical resin particles with an average weight of 1.0 mg per particle.

[0101] Preparation of foamed particles: 100 kg of the obtained resin particles were supplied to a sealed container with a capacity of 400 L along with 220 L of water, which is an aqueous medium. In addition, 0.3 parts by weight of kaolin as an inorganic dispersant, 0.004 parts by weight of sodium alkylbenzenesulfonate (as an active ingredient), and 0.001 parts by weight of aluminum sulfate were added to the sealed container per 100 parts by weight of the resin particles. Next, carbon dioxide was injected into a sealed container as a blowing agent, and the container was pressurized until the gauge pressure reached 1.8 MPa(G). The pressure indicated by (G) is the gauge pressure, i.e., the pressure value relative to atmospheric pressure. After that, the sealed container was heated at a rate of 2°C / min while stirring until the foaming temperature (150.5°C) was reached. Then, carbon dioxide was injected further to reach a predetermined foaming pressure (2.6 MPa(G)), and the container was held at this temperature for 15 minutes. This was done to adjust the endothermic curve obtained from the first DSC measurement of the resulting foamed particles so that a high-temperature peak appeared. Subsequently, the contents of the sealed container (resin particles and water) were released to atmospheric pressure, resulting in a bulk density of 49.8 kg / m³. 3 We obtained foamed particles (single-stage foamed particles).

[0102] (Examples 2, 3, 5-9) Except for using the resin materials and their mixing ratios as shown in Table 2, and adjusting the foaming temperature and pressure to achieve the bulk density and high-temperature peak heat values ​​shown in the table, foamed particles and molded foamed particle articles were manufactured in the same manner as in Example 1, resulting in Examples 2, 3, and 5-9. (Example 4) Example 4 was produced in the same manner as in Example 1, except that multilayer resin particles were manufactured and used as described below, and the foaming temperature and foaming pressure were adjusted to achieve the bulk density and high-temperature peak heat value shown in the table. Preparation of resin particles: A manufacturing apparatus was prepared comprising a core layer forming extruder with an inner diameter of 50 mm, a multi-layer strand forming die attached downstream of the core layer forming extruder, and a coating layer forming extruder with an inner diameter of 30 mm. The manufacturing apparatus is configured such that the downstream side of the coating layer forming extruder is connected to the multi-layer strand forming die, allowing for the stacking of molten kneaded material for forming each layer within the die, as well as enabling co-extrusion. As core-forming materials for the core layer, resin 1 and recovered material 1 shown in Table 1 were used in the mixing ratios shown in Table 2. The above core-forming materials were supplied to a core-forming extruder and melt-kneaded. In addition, zinc borate (Borax "Fire Break ZB") was added as a foam regulator to these materials at a concentration of 0.05% by weight per 100% by weight of the melt-kneaded mixture (total of resin 1, recovered resin 1, and zinc borate). As the coating layer forming material, resin 4 shown in Table 1 was used in the mixing ratio shown in Table 2, and these were supplied to a coating layer forming extruder and melt-kneaded. As described above, the mixtures for each layer, obtained by melt-kneading, were introduced into a die for forming multilayer strands and merged within the die. A multilayer strand having a two-layer structure (coating layer / core layer structure) was then extruded through the pores of a nozzle attached to the downstream side of the die. The extruded strands were water-cooled and cut with a pelletizer to obtain cylindrical resin particles with an average weight of 1.0 mg per particle. (Example 10) As shown in Table 4, foamed particles were manufactured in the same manner as in Example 1, and foamed particles and a molded foamed particle body were manufactured in the same manner as in Example 1, except that a two-stage foaming process was carried out using the foamed particles (single-stage foamed particles) as described below, to form Example 10. Double-stage foaming: The single-stage foamed particles obtained in the same manner as in Example 1 were cured for 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. The cured single-stage foamed particles were then placed in a pressurized sealed container, and the pressure inside the sealed container was increased from atmospheric pressure to pressurize the foamed particles. The pressurized state of the foamed particles was maintained for a predetermined time to impregnate the bubbles of the foamed particles with air. After that, the single-stage foamed particles were removed from the sealed container, and single-stage foamed particles with an internal pressure of 0.7 MPa(G) in the bubbles were obtained. These single-stage foamed particles were then supplied to a two-stage foaming apparatus. Steam was supplied into the apparatus to foam the single-stage foamed particles, resulting in a bulk density of 26.6 kg / m³. 3 We obtained foamed particles.

[0103] (Comparative Examples 1-6) Except for using the resin materials and their mixing ratios as shown in Table 3, and adjusting the foaming temperature and pressure to achieve the bulk density and high-temperature peak heat values ​​shown in the table, foamed particles and molded foamed particle articles were manufactured in the same manner as in Example 1 to produce Comparative Examples 1 to 6.

[0104] (Reference example 1) Except for using a base resin containing only resin 1 without any recovered material as the constituent resin, and adjusting the foaming temperature and foaming pressure to achieve the bulk density and high-temperature peak heat value shown in the table, foamed particles and molded foamed particle articles were manufactured in the same manner as in Example 1 and were presented as Reference Example 1. Reference Example 1 is an example of conventional polypropylene-based resin foamed particles that do not use recovered resin. (Reference example 2) Reference Example 2 was prepared in the same manner as Example 1, except that a base resin prepared by blending non-recovered resins 1 and 6 in the proportions shown in Table 3 was used as the constituent resin, and the foaming temperature and foaming pressure were adjusted to achieve the bulk density and high-temperature peak heat value shown in the table. Reference Example 2 is an example of conventional polypropylene-based resin foamed particles that do not use recovered resin. (Reference example 3) Using the obtained foamed particles, foamed particles and a molded foamed particle body were manufactured in the same manner as in Reference Example 1, except that a two-stage foaming process was carried out in the same manner as in Example 10, as shown in Table 4, and this was designated as Reference Example 3.

[0105] (Ash content of foaming particles) Method for measuring ash content: In accordance with JIS K6226-2:2003, the ash content was measured as follows using a LECO TGA701 thermogravimetric analyzer. As described above, 5 g of the obtained foamed particles were accurately weighed and placed in a crucible. The heating furnace was filled with a nitrogen atmosphere, (1) the temperature of the heating furnace was raised from room temperature to 105°C at a rate of 10°C / min under a nitrogen atmosphere, then (2) it was held at 105°C until the measured weight was in equilibrium, (3) it was raised from 105°C to 550°C at a rate of 10°C / min, (4) it was held at 550°C until the measured weight was in equilibrium, (5) the heating furnace airflow was changed from nitrogen to air and it was raised from 550°C to 950°C at a rate of 10°C / min, (6) the weight W1 of the combustion residue after holding at 950°C for 10 minutes was determined, and (7) it was cooled to room temperature. The amount of ash content (weight %) of the foamed particles was determined by dividing the weight W1 of the combustion residue by the weight of the sample placed in the crucible (5 g) and multiplying the result by 100. The above procedure was performed twice, and the arithmetic mean of these results was taken as the ash content of the foamed particles.

[0106] (Ethylene content of foamed particles) 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 foamed particles were used as test specimens.

[0107] (High-temperature peak heat and total heat of foamed particles) Approximately 1 mg of foamed particles were accurately weighed to prepare test specimens. The test specimens were heated and melted according to the differential scanning calorimetry method described in JIS K7122-1987, and the DSC curve was obtained. The measurement temperature range was from 30°C to a temperature 30°C higher than the end of the melting peak of the test specimen, and the heating rate was 10°C / min to obtain the first DCS curve. The first DSC curve obtained in this manner is shown in Figure 2. In this DSC curve, a straight line was drawn connecting point I, which corresponds to 80°C on the DSC curve, and point II, which corresponds to the melting termination temperature of the foamed particles. The melting termination temperature is the high-temperature endpoint of the high-temperature peak b, and is the intersection point of the high-temperature peak b and the baseline on the high-temperature side of the DSC curve. As shown in Figure 2, after drawing a straight line connecting point I and point II, point IV was defined as the intersection of a straight line parallel to the vertical axis of the graph and passing through the maximum point III, which lies between the resin-specific melting peak a and high-temperature peak b, and the straight line connecting point I and point II. The area of ​​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 was defined as the area of ​​the resin-specific melting peak a. The area of ​​the region enclosed 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 (shaded area) was defined as the area of ​​the high-temperature peak b, and this was defined as the high-temperature peak heat quantity (J / g) of the foamed particles. The sum of the areas of the resin-specific melting peak a and the high-temperature peak b was defined as the total heat quantity (J / g). As described above, after obtaining the first DSC curve, the material was held at the heating end temperature for 10 minutes, then cooled to 30°C at a cooling rate of 10°C / min. A second DSC curve was then obtained when the material was heated again at a heating rate of 10°C / min to a heating end temperature 30°C higher than the melting peak end temperature. It was confirmed that no high-temperature peak appeared in the second DSC curve.

[0108] (Average bubble diameter of foaming particles) A cross-section of a foam particle, roughly divided in half, was photographed under a microscope to obtain a magnified image of the cross-section. In the magnified image of the cross-section, four line segments were drawn from one surface of the foam particle to the other, passing through approximately the center of the foam particle's cross-section. These line segments were drawn to form eight radial lines extending from approximately the center of the foam particle's cross-section to the surface of the cut particle at equal intervals. Next, the total number of bubbles N intersecting the four line segments was determined. The sum of the lengths of the four line segments, L (μm), was calculated, and the value obtained by dividing the sum L by the total number N (L / N) was taken as the average bubble diameter of one foam particle. This process was performed for 10 or more foam particles, and the arithmetic mean of the average bubble diameters of each foam particle was taken as the average bubble diameter of the foam particle.

[0109] (Percentage of closed cells in foamed particles) The percentage of closed cells (%) in the foamed particles was determined using an air-comparison hydrometer based on ASTM-D2856-70.

[0110] (Bulk density of foamed particles) The bulk density of the foamed particles was measured as follows: The foamed particle group was left for 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. The foamed particle group obtained in this way was filled into a graduated cylinder so that it would naturally accumulate, and the bulk volume (unit: L) of the foamed particle group was read from the scale of the graduated cylinder. Then, the bulk density (unit: kg / m³) of the foamed particle group was obtained by dividing the mass (unit: g) of the foamed particle group in the graduated cylinder by the aforementioned bulk volume (unit: L) and converting the value to units. 3 ) was obtained.

[0111] (Foaming ratio of foaming particles) The foaming ratio of the foamed particles is determined by the resin density of the polypropylene resin (0.9 kg / m³). 3 This was determined by dividing the value by the bulk density of the foamed particles mentioned above.

[0112] (Variation rate of foaming ratio of foaming particles) 300 mL to 500 mL of foamed particles were accurately weighed and sieved using eight types of standard sieves specified in JIS Z8801. The mesh sizes of the eight standard sieves were 5 mesh, 6 mesh, 7 mesh, 8 mesh, 9 mesh, 12 mesh, 14 mesh, and 16 mesh. Next, the weight of the foamed particles remaining in each sieve (residual foamed particles) was measured, and the weight fraction Wi of the weight of the residual foamed particles relative to the weight of the foamed particles used for sieving was determined. Furthermore, following the method described above, the foaming ratio Ki of the foamed particles was determined. First, we calculate the average expansion ratio Kav from the following formula (1).

number

number

number

[0113] Furthermore, in order to confirm that the variation in foam particle size observed through the sieving process described above is not due to variations in the weight of the foam particles, but rather to variations in the foaming ratio, the following checks were performed. 500 foam particles were randomly selected from the manufactured foam particles, and the weight of each foam particle was measured to two decimal places using a precision balance. The average weight was calculated by arithmetic mean of the measured values. Then, foam particles whose measured weight fell within ±10% of the average weight were counted. In all of the examples, comparative examples, and reference examples, the number of counted foam particles was 95% or more of the 500 foam particles.

[0114] (Visual evaluation of foamed particle molded products) <Exterior> To evaluate the surface appearance of the foam particle molded body, a 100mm x 100mm rectangle was drawn in the center of the foam particle molded body, lines were drawn diagonally from the corners of the rectangular area, and the number of voids (gaps) of 1mm x 1mm or larger along these lines was counted. The degree of voids (gaps) between foam particles was then evaluated as follows. A(◎): The number of voids was less than 5. B(〇): The number of voids was 5 or more but less than 10. C(△): The number of voids was between 10 and 15. D(×): The number of voids was 15 or more.

[0115] (Density of molded foam particle molded body) The weight of the foam particle molded body was measured, and the density of the foam particle molded body was determined by dividing this weight by the volume of the foam particle molded body, which was determined by the immersion method.

[0116] (Compressive stress of a foam particle molded body at 50% strain) Ten test specimens measuring 50 mm x 50 mm x 25 mm were cut at equal intervals from a foam particle molded body (250 mm long x 200 mm wide x 50 mm thick), after removing the skin. Using these test specimens, a compression test was performed at a compression speed of 10 mm / min according to JIS K6767:1999 to determine the 50% compressive stress of the foam particle molded body. The arithmetic mean of the values ​​for each of the ten test specimens was taken as the compressive stress at 50% strain.

[0117] (Rigidity evaluation of foamed particle molded bodies) The compressive stress at 50% strain was evaluated for each density according to the following criteria. Molded body density 60kg / m 3 : A: Compressive stress at 50% strain is 0.54 MPa or higher. B: Compressive stress at 50% strain is 0.52 MPa or more and less than 0.54 MPa. C: Compressive stress at 50% strain is less than 0.52 MPa Molded body density 30kg / m 3 : A: Compressive stress at 50% strain is 0.25 MPa or higher. B: Compressive stress at 50% strain is 0.23 MPa or more and less than 0.25 MPa. C: Compressive stress at 50% strain is less than 0.23 MPa.

[0118] [Table 1]

[0119] [Table 2]

[0120] [Table 3]

[0121] [Table 4]

[0122] The present invention described above encompasses the following technical concepts. (1) Polypropylene resin particles dispersed in an aqueous medium in a sealed container are impregnated with a foaming agent, and the polypropylene resin particles containing the foaming agent are released from the sealed container together with the aqueous medium under a pressure lower than that inside the sealed container, causing foaming to occur at a pressure of 10 kg / m³ 3 More than 200kg / m 3 A method for producing polypropylene resin foam particles having the following bulk density, The aforementioned polypropylene resin particles are based on a mixture of polypropylene resin A, which has a melting point of 130°C or higher and 155°C or lower, and polypropylene resin B, with the latter being used as the base resin. The proportion of polypropylene resin A in the mixture is 40% by weight or more and 97% by weight or less, and the proportion of polypropylene resin B is 3% by weight or more and 60% by weight or less (provided that the total of polypropylene resin A and polypropylene resin B is 100% by weight), The difference in melting points between the polypropylene resin A and the polypropylene resin B (polypropylene resin B - polypropylene resin A) is 10°C or more and 30°C or less. The aforementioned polypropylene resin B is a recovered post-consumer material. The ash content of the polypropylene resin B is 5% by weight or less relative to 100% by weight of the polypropylene resin B. A method for producing foamed particles, characterized in that, in the DSC curve of the polypropylene resin B obtained by differential scanning calorimetry, the difference (Tme-Tms) between the extrapolation melting start temperature (Tms) and the extrapolation melting end temperature (Tme) of the melting peak is 30°C or more. (2) The method for producing foamed particles according to (1) above, characterized in that the blending ratio of the polypropylene resin A in the mixture is greater than 50% by weight and 80% by weight or less, and the blending ratio of the polypropylene resin B is 20% by weight or more and less than 50% by weight (provided that the total of polypropylene resin A and polypropylene resin B is 100% by weight). (3) A method for producing foamed particles according to (1) or (2) above, characterized in that the difference (Tme-Tms) between the extrapolation melting start temperature (Tms) and the extrapolation melting end temperature (Tme) of the melting peak is 30°C or more and 100°C or less. (4) A method for producing foamed particles 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 (polypropylene resin B - polypropylene resin A) is 10°C or more and 20°C or less. (5) A method for producing foamed particles according to any one of (1) to (4) above, characterized in that the ash content of the polypropylene resin is 0.5% by weight or less relative to 100% by weight of the polypropylene resin B. [Explanation of symbols]

[0123] 10. A straight line extending the baseline on the low-temperature side towards the high-temperature side. 20. The tangent line drawn at the point where the slope is maximum on the coldest side of the melting peak curve. 30...Intersection of line 10 and tangent line 20 40...First inflection point 50...A straight line extending the baseline on the high-temperature side towards the low-temperature side. 60...Tangent line drawn at the point where the slope is maximum on the hottest side of the melting peak curve. 70...Intersection of straight line 50 and tangent line 60 80...High temperature side inflection point 100...Second DSC curve of polypropylene resin B 200...The DDSC curve is the differential curve of the DSC curve at 100.

Claims

1. Polypropylene resin particles dispersed in an aqueous medium within a sealed container are impregnated with a foaming agent. The polypropylene resin particles containing the foaming agent are then released from the sealed container along with the aqueous medium under a pressure lower than that inside the container, causing foaming to occur at a pressure of 10 kg / m³. ３ More than 200kg / m ３ A method for producing polypropylene resin foam particles having the following bulk density, The aforementioned polypropylene resin particles are a mixture of polypropylene resin A, which is a non-recoverable resin with a melting point of 130°C to 155°C, and polypropylene resin B, with the latter serving as the base resin. The proportion of polypropylene resin A in the mixture is 40% by weight or more and 97% by weight or less, and the proportion of polypropylene resin B is 3% by weight or more and 60% by weight or less (provided that the total of polypropylene resin A and polypropylene resin B is 100% by weight). The difference in melting points between the polypropylene resin A and the polypropylene resin B (polypropylene resin B - polypropylene resin A) is 10°C or more and 30°C or less. The aforementioned polypropylene resin B is a recovered post-consumer material. The ash content of the polypropylene resin B is 5% by weight or less relative to 100% by weight of the polypropylene resin B. A method for producing foamed particles, characterized in that, in the DSC curve of the polypropylene resin B obtained by differential scanning calorimetry, the difference (Tme - Tms) between the extrapolation melting start temperature (Tms) and the extrapolation melting end temperature (Tme) of the melting peak 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% by weight and less than or equal to 90% by weight, and the blending ratio of the polypropylene resin B is 10% by weight or more and less than 50% by weight (provided that the total of polypropylene resin A and polypropylene resin B is 100% by weight).

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

4. A method for producing foamed particles according to claim 1 or 2, characterized in that the difference in melting points between the polypropylene resin A and the polypropylene resin B (polypropylene resin B - polypropylene resin A) is 10°C or more and 20°C or less.

5. A method for producing foamed particles according to claim 1 or 2, characterized in that the ash content of the polypropylene resin B is 0.5% by weight or less relative to 100% by weight of the polypropylene resin B.

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