Polypropylene resin foamed particles, method for producing the same, and polypropylene resin foamed particle molded body

Abstract

Polypropylene resin foamed particles (1) have a core layer (2) and a coating layer (3) covering the core layer (2). The base resin (II) of the coating layer (3) is a composition (X) consisting of a polypropylene resin (B) with a melting point of 125-150°C, carbon nanotubes (C), and a polypropylene resin (D) with a melting point of 70-100°C. The amount of carbon nanotubes (C) relative to 100 parts by mass of polypropylene resin (B) is 3-20 parts by mass, and the amount of polypropylene resin (D) is 6-120 parts by mass. The mass ratio (D) / (C) of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) is 2-10.

Description

Technical Field

[0001] This invention relates to polypropylene resin foamed granules, their manufacturing method, and molded polypropylene resin foamed granules. Background Technology

[0002] Foamed granules are effectively used as packaging materials for spacers, boxes, etc., taking advantage of their excellent impact absorption properties. The objects protected by these packaging materials include, for example, precision equipment, electronic devices, and electronic components.

[0003] For bundling materials used, for example, in packaging electronic devices and components, properties such as electrostatic diffusion, or other electrical characteristics that allow for the slow discharge of static electricity, are sometimes sought in addition to shock absorption. Furthermore, in this specification, "electrostatic diffusion" specifically refers to a surface resistivity of 1×10⁻⁶. 5 Ω or above 1×10 9 Electrical properties in the range below Ω. The foamed particles used to make this packaging material contain conductive materials such as conductive carbon black and carbon nanotubes.

[0004] For example, Patent Document 1 describes a foamed molding material formed by adding an aqueous gel, which is prepared by dispersing multilayer carbon nanotubes in water, to pre-foamed polystyrene beads and then heating and mixing them. Patent Document 2 describes conductive foamed beads composed of a resin composition containing multiple pores with an average diameter of 10 to 200 μm. The resin composition includes a polyolefin resin, a carbon nanotube aggregate composed of multiple carbon nanotubes with an average outer diameter of 8 to 50 nm and an average inner diameter of at least 40% of the average outer diameter, and a foaming agent.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2012-87041

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-108540 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, when a conductive material is applied to the foamed particles as in Patent Document 1, the process of applying the conductive material to the foamed particles after the foamed resin particles have been foamed becomes cumbersome. Furthermore, if a large amount of conductive material is applied to the surface of the foamed particles in this manner, it may detach from the surface of the foamed particles during processes such as in-mold forming.

[0011] On the other hand, as in Patent Document 2, when a conductive material is incorporated into the foamed particles, a larger amount of the conductive material is required to achieve the desired electrical properties. However, if the amount of conductive material incorporated into the resin increases, the foaming properties of the resin particles tend to deteriorate, the bubble diameter of the foamed particles becomes smaller, or the deviation in bubble diameter increases. Furthermore, if the secondary foaming properties of the foamed particles deteriorate, there may be situations where, for example, the bubbles in the foamed particles are prone to rupture during in-mold molding or it becomes difficult to reduce the apparent density of the molded foamed particle body.

[0012] The present invention was made in view of the above background, and is capable of imparting desired electrical properties to foamed granule molded articles and suppressing the shedding of carbon nanotubes, and is intended to provide polypropylene resin foamed granules with excellent foaming properties, a method for manufacturing the same, and polypropylene resin foamed granule molded articles.

[0013] means for solving problems

[0014] One aspect of the present invention is the method for manufacturing polypropylene resin foamed particles as described below [1] to [6].

[0015] [1] A method for manufacturing polypropylene resin foamed particles, comprising foaming polypropylene resin particles having a core layer and a coating layer covering the core layer, wherein...

[0016] The substrate resin (I) of the core layer is a polypropylene resin (A).

[0017] The base resin (II) of the coating layer is made from resin with a melting point Tm. (B) Polypropylene resin (B) with a temperature range of 125℃ to 150℃, carbon nanotubes (C), and a melting point Tm (D) Composition (X) is made of polypropylene resin (D) that is heated to a temperature between 70°C and 100°C.

[0018] The amount of carbon nanotubes (C) incorporated is between 3 and 20 parts by weight relative to 100 parts by weight of the polypropylene resin (B).

[0019] The amount of the polypropylene resin (D) is between 6 and 120 parts by weight relative to 100 parts by weight of the polypropylene resin (B).

[0020] The mass ratio (D) / (C) of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) is more than 2 and less than 10.

[0021] [2][1] The method for manufacturing polypropylene resin foamed particles, wherein the heat of fusion Q of the polypropylene resin (B) is... (B)[J / g] Heat of fusion of the base resin (II) with Q (II) The ratio of [J / g] to Q (B) / Q (II) It is between 1.2 and 3.5.

[0022] The method for manufacturing polypropylene resin foamed particles as described in [3][1] or [2], wherein the weight-average molecular weight of the polypropylene resin (D) is more than 40,000 and less than 100,000.

[0023] The method for manufacturing polypropylene resin foamed granules according to any one of [4][1] to [3], wherein the heat of fusion of the polypropylene resin (D) Q (D) The value is between 0 J / g and 50 J / g.

[0024] The method for manufacturing polypropylene resin foamed particles according to any one of [5][1] to [4], wherein the melting point Tm of the base resin (II) is... (II) The temperature is between 120°C and 140°C, and the heat of fusion is Q. (II) The value is between 5 J / g and 50 J / g.

[0025] The method for manufacturing polypropylene resin foamed granules according to any one of [6][1] to [5], wherein the melt flow rate (MFR) of the base resin (II) at a temperature of 230°C and a load of 2.16 kg is... (II) The melt flow rate (MFR) of the base resin (II) is 1 g / 10 min or more and 30 g / 10 min or less. (II) Melt Flow Rate (MFR) of the Substrate Resin (I) (I) The ratio of MFR (II) / MFR (I) It is between 0.2 and 4.5.

[0026] Another aspect of the present invention is the polypropylene resin foamed particles described in [7] to

[12] below.

[0027] [7] A polypropylene resin foamed particle, which is a foamed particle having a foamed core layer and a coating layer covering the core layer, wherein,

[0028] The substrate resin (I) of the core layer is a polypropylene resin (A).

[0029] The base resin (II) of the coating layer is made from resin with a melting point Tm. (B) Polypropylene resin (B) with a temperature range of 125℃ to 150℃, carbon nanotubes (C), and a melting point Tm (D) Composition (X) is made of polypropylene resin (D) that is heated to a temperature between 70°C and 100°C.

[0030] The amount of carbon nanotubes (C) incorporated is between 3 and 20 parts by weight relative to 100 parts by weight of the polypropylene resin (B).

[0031] The amount of the polypropylene resin (D) is between 6 and 120 parts by weight relative to 100 parts by weight of the polypropylene resin (B).

[0032] The mass ratio (D) / (C) of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) is more than 2 and less than 10.

[0033] [8][7] The polypropylene resin foamed particles, wherein the heat of fusion of the polypropylene resin (B) is Q (B) [J / g] Heat of fusion of the base resin (II) with Q (II) The ratio of [J / g] to Q (B) / Q (II) It is between 1.2 and 3.5.

[0034] The polypropylene resin foamed particles described in [9][7] or [8], wherein the weight-average molecular weight of the polypropylene resin (D) is more than 40,000 and less than 100,000.

[0035] The polypropylene resin foamed particles described in any one of

[10] [7] to [9], wherein the heat of fusion of the polypropylene resin (D) is Q (D) The value is between 0 J / g and 50 J / g.

[0036] The polypropylene resin foamed particles described in any one of

[11] [7] to

[10] , wherein the melting point Tm of the base resin (II) is... (II) The temperature is between 120°C and 140°C, and the heat of fusion is Q. (II) The value is between 5 J / g and 50 J / g.

[0037] The polypropylene resin foamed particles described in any one of

[12] [7] to

[11] , wherein the melt flow rate (MFR) of the base resin (II) at a temperature of 230°C and a load of 2.16 kg is... (II) The melt flow rate (MFR) of the base resin (II) is 1 g / 10 min or more and 30 g / 10 min or less. (II) Melt Flow Rate (MFR) of the Substrate Resin (I) (I) The ratio of MFR (II) / MFR (I) It is between 0.2 and 4.5.

[0038] Another aspect of the present invention is the polypropylene resin foamed granule molded body as described in

[13] below.

[0039]

[13] A polypropylene resin foamed granule molded body, which is a polypropylene resin foamed granule molded by in-mold forming of polypropylene resin foamed granules as described in any one of [7] to

[12] , wherein...

[0040] The surface resistivity is 1×10 5 Ω or above 1×10 9 Below Ω.

[0041] Invention Effects

[0042] In the method for manufacturing polypropylene resin foamed particles (hereinafter referred to as "foamed particles"), the core layer of the resin particles is formed by using polypropylene resin (A) as a base resin (I), and the coating layer covering the core layer is formed by using a composition (X) composed of polypropylene resin (B), carbon nanotubes (C), and polypropylene resin (D) as a base resin (II). Thus, by forming the coating layer with a specific base resin (II), the coating layer can be easily coated onto the core layer of the resin particles, and the carbon nanotubes can be uniformly dispersed in the coating layer. Furthermore, in the foamed particles obtained by foaming the resin particles, the coating layer coats the core layer of the foamed particles, and the carbon nanotubes are uniformly dispersed in the coating layer.

[0043] Furthermore, since the foamed core layer is coated by the coating layer, the surface resistance of the foamed particles can be reduced. Moreover, since carbon nanotubes (C) are contained in the substrate resin (II) constituting the coating layer, the shedding of carbon nanotubes (C) from the foamed particles can be suppressed, and the desired electrical properties can be achieved.

[0044] Then, by in-mold molding the aforementioned foamed particles, the desired electrical properties can be easily imparted to the polypropylene resin foamed particle molded body (hereinafter referred to as "foamed particle molded body").

[0045] As described above, the desired electrical properties of the foamed granules can be imparted and the shedding of carbon nanotubes can be suppressed, thus providing polypropylene resin foamed granules with excellent foaming properties, a method for manufacturing the same, and a polypropylene resin foamed granule molded body. Attached Figure Description

[0046] Figure 1 This is an explanatory diagram illustrating the calculation method for the area of ​​a high-temperature peak.

[0047] Figure 2 This is a cross-sectional view of the polypropylene resin foam particles in the examples. Detailed Implementation

[0048] In this specification, when an upper limit and a lower limit of the numerical range are specified for a physical property or property, the values ​​of the upper limit and the lower limit can be arbitrarily combined to create a numerical range that defines both the upper and lower limits.

[0049] (Manufacturing method of polypropylene resin foamed granules)

[0050] In the method for manufacturing the foamed particles, resin particles having a core layer and a coating layer covering the core layer are used. The base resin (I) of the core layer of the resin particles is a polypropylene resin (A), and the base resin (II) of the coating layer is a composition (X) composed of a polypropylene resin (B), carbon nanotubes (C), and a polypropylene resin (D). Hereinafter, the base resin (I) for the core layer and the base resin (II) for the coating layer will be described in detail.

[0051] Furthermore, by foaming the resin particles, foamed particles are obtained having a foamed core layer and a coating layer covering the core layer. It is considered that the resin composition constituting the core layer of the resin particles and the resin composition constituting the core layer of the foamed particles do not change before and after foaming. Therefore, the core layer of the foamed particles and the core layer of the resin particles have the same resin composition. Similarly, the coating layer of the foamed particles and the coating layer of the resin particles have the same resin composition.

[0052] [Core Layer]

[0053] The substrate resin (I) of the core layer is a polypropylene resin (A). In this invention, "the substrate resin (I) of the core layer is the polypropylene resin (A)" means that the polypropylene resin (A) is the basic resin component constituting the core layer. More specifically, the proportion of the polypropylene resin (A) as the substrate resin (I) relative to the total mass of the core layer is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and most preferably 95% by mass or more.

[0054] • Polypropylene resin (A)

[0055] As the polypropylene resin (A), one or more polypropylene resins selected from the group consisting of homopolymers of propylene monomers and propylene copolymers can be used. Furthermore, in this specification, polypropylene resin refers to homopolymers of propylene monomers and propylene copolymers containing 50% by mass or more structural units derived from propylene.

[0056] As homopolymers of propylene monomers, isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, etc., can be used.

[0057] Examples of propylene-based copolymers include copolymers of propylene with 4 to 10 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, and 3-methyl-1-hexene; propylene-acrylic acid copolymers; and propylene-maleic anhydride copolymers. These copolymers can be random copolymers or block copolymers. Furthermore, the copolymers can be binary copolymers, ternary copolymers, or multi-component copolymers (three or more components). The content of structural units other than those derived from propylene in the copolymer is preferably 25% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. Additionally, the lower limit of the content of structural units other than those derived from propylene in the copolymer is approximately 1% by mass.

[0058] Other ingredients

[0059] In addition to the base resin (I), additives such as bubble conditioners, catalyst neutralizers, lubricants, and crystallizing nucleating agents may be added to the core layer. The amount of additives added to the core layer is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, further preferably 5 parts by weight or less, and particularly preferably 1 part by weight or less, relative to 100 parts by weight of the base resin (I) of the core layer. Furthermore, a colorant can be added to the core layer to adjust the color intensity of the coating layer. In this case, the amount of colorant added is preferably 1 to 5 parts by weight, more preferably 1.5 to 3 parts by weight or less, relative to 100 parts by weight of the base resin (I) of the core layer.

[0060] Alternatively, resins other than polypropylene resin (A) used as the base resin (I), elastomers, etc., may be added to the core layer without impairing the purpose and effect of the present invention. Examples of resins other than polypropylene resin (A) include thermoplastic resins such as polyethylene resins, polystyrene resins, polybutene resins, polyamide resins, and polyester resins, as well as olefin thermoplastic elastomers and styrene thermoplastic elastomers. The amount of resins other than polypropylene resin (A) and elastomers added to the core layer is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, relative to 100 parts by weight of the base resin (I) of the core layer. Furthermore, the core layer may consist solely of polypropylene resin (A) used as the base resin (I), but when resins other than polypropylene resin (A) and / or elastomers are added to the core layer, the lower limit of the total amount of resins other than polypropylene resin (A) and elastomers added can be set to approximately 1 part by weight.

[0061] [Covering layer]

[0062] The substrate resin (II) of the coating layer is a composition (X) composed of polypropylene resin (B), carbon nanotubes (C), and polypropylene resin (D). In this invention, the substrate resin (II) of the coating layer is the composition (X) meaning that the composition (X) is the basic resin component constituting the coating layer. More specifically, the proportion of the composition (X) as the substrate resin (II) relative to the total mass of the coating layer is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and most preferably 95% by mass or more. Furthermore, in this invention, the substrate resin (II) is defined as a concept that includes carbon nanotubes that are not resins.

[0063] The composition (X) has a melting point Tm (B) Polypropylene resin (B) with a temperature range of 125℃ to 150℃, carbon nanotubes (C), and a melting point Tm (D) The resin (II) is composed of a polypropylene resin (D) with a temperature range of 70°C to 100°C. The amount of carbon nanotubes (C) in the base resin (II) is 3 to 20 parts by mass relative to 100 parts by mass of the polypropylene resin (B). The amount of polypropylene resin (D) in the base resin (II) is 6 to 120 parts by mass relative to 100 parts by mass of the polypropylene resin (B). The mass ratio (D) / (C) of the amount of polypropylene resin (D) in the base resin (II) is 2 to 10. Furthermore, the contents of polypropylene resin (B), carbon nanotubes (C), and polypropylene resin (D) in the base resin (II) are almost identical to the amounts of polypropylene resin (B), carbon nanotubes (C), and polypropylene resin (D) in the base resin (II).

[0064] • Polypropylene resin (B)

[0065] The base resin (II) contains a melting point Tm (B) The polypropylene resin (B) has a temperature range of 125°C to 150°C. The base resin (II) may contain one or more polypropylene resins (B). The melting point Tm of the polypropylene resin (B) is determined by... (B) Setting it to the specific range can improve the adhesion between the core layer and the covering layer.

[0066] Melting point Tm of polypropylene resin (B) (B)The heat flux can be determined using the differential scanning calorimetry method described in JIS K7121:1987. Specifically, first, a test piece composed of polypropylene resin (B) is conditioned. Then, the temperature is increased from 23°C to 200°C at a heating rate of 10°C / min, followed by a cooling rate of 10°C / min to 23°C. The melting point Tm of the polypropylene resin (B) can then be determined by the peak temperature of the endothermic peak obtained from the DSC curve obtained by again heating from 23°C to 200°C at a heating rate of 10°C / min. (B) Furthermore, when multiple endothermic peaks appear in the DSC curve, the temperature at the vertex of the endothermic peak with the largest area is taken as the melting point.

[0067] Carbon nanotubes (C)

[0068] Carbon nanotubes (C) are incorporated into the base resin (II) in an amount of 3 to 20 parts by mass relative to 100 parts by mass of the polypropylene resin (B). By setting the amount of carbon nanotubes (C) in the base resin (II) within the aforementioned specific range, foamed particles with desired electrical properties can be easily obtained. Then, by in-mold molding the above-mentioned foamed particles, the desired electrical properties can be easily imparted to the foamed particle molded body. From the viewpoint of more reliably imparting the desired electrical properties to the foamed particle molded body, the lower limit of the amount of carbon nanotubes (C) relative to 100 parts by mass of the polypropylene resin (B) is preferably 3 parts by mass, more preferably 4 parts by mass, and even more preferably 6 parts by mass. On the other hand, the upper limit of the amount of carbon nanotubes (C) relative to 100 parts by mass of the polypropylene resin (B) is preferably 18 parts by mass, more preferably 16 parts by mass, and even more preferably 14 parts by mass. From the same point of view, the amount of carbon nanotubes (C) is preferably 3 parts by mass or more and 18 parts by mass or less, more preferably 4 parts by mass or more and 16 parts by mass or less, and even more preferably 6 parts by mass or more and 14 parts by mass or less.

[0069] If the amount of carbon nanotubes (C) is too small, it is difficult to form a conductive network within the coating layer, potentially failing to impart the desired electrical properties to the foamed particles. On the other hand, if the amount of carbon nanotubes (C) is too large, the melt viscosity of the substrate resin (II) containing carbon nanotubes (C) is easily increased during the manufacturing of resin particles in the foamed particle production process. As a result, it is difficult to use the coating layer forming resin melt for forming the coating layer layer on top of the core layer forming resin melt for forming the core layer, potentially preventing the acquisition of multilayered foamed particles.

[0070] The carbon nanotube (C) can be a single-layer carbon nanotube or a multilayer carbon nanotube. Furthermore, the base resin (II) may contain both single-layer and multilayer carbon nanotubes as the carbon nanotube (C). For example, carbon nanotubes with an aspect ratio of 80 to 1000 and an outer diameter of 9.5 nm to 25 nm are preferred as carbon nanotube (C), and carbon nanotubes with an aspect ratio of 100 to 200 and an outer diameter of 9.5 nm to 12 nm are more preferred.

[0071] • Polypropylene resin (D)

[0072] The base resin (II) contains a melting point Tm (D) This refers to polypropylene resin (D) with a temperature range of 70°C to 100°C. Furthermore, the melting point Tm of polypropylene resin (D) is... (D) The determination method, except that it uses a test piece made of polypropylene resin (D) instead of a test piece made of polypropylene resin (B), is the same as the aforementioned melting point Tm of polypropylene resin (B). (B) The determination method is the same.

[0073] One type of polypropylene resin (D) or two or more types of polypropylene resin (D) may be incorporated into the base resin (II). Furthermore, the amount of polypropylene resin (D) incorporated is 6 to 120 parts by mass relative to 100 parts by mass of polypropylene resin (B). Additionally, the mass ratio (D) / (C) of the amount of polypropylene resin (D) incorporated to the amount of carbon nanotubes (C) is 2 to 10.

[0074] Polypropylene resin (D) has the property of softening more easily than polypropylene resin (B). By incorporating polypropylene resin (D) into the base resin (II), the crystallization of polypropylene resin (B) caused by the addition of carbon nanotubes (C) can be suppressed. Therefore, the sharp increase in viscosity of base resin (II) caused by the crystallization of polypropylene resin (B) can be suppressed, and the coating layer can be easily laminated to the core layer without exposing the core layer. In addition, since the dispersibility of carbon nanotubes (C) in the coating layer is improved by incorporating polypropylene resin (D) into the base resin (II), the desired electrical properties can be easily imparted to the foamed particles and the foamed particle molded articles.

[0075] From the viewpoint of more easily obtaining foamed particles with a multilayer structure, the amount of polypropylene resin (D) relative to 100 parts by mass of polypropylene resin (B) is preferably 10 parts by mass to 100 parts by mass, more preferably 15 parts by mass to 90 parts by mass, further preferably 20 parts by mass to 80 parts by mass, and even more preferably 30 parts by mass to 60 parts by mass. From the same viewpoint, the mass ratio (D) / (C) of the amount of polypropylene resin (D) to carbon nanotubes (C) is preferably 3 to 8.

[0076] If the amount of polypropylene resin (D) is too small relative to the amount of polypropylene resin (B), or if the ratio of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) (D) / (C) is too low, there is a risk that the fluidity of the base resin (II) will be drastically reduced and the coating layer may not be able to be uniformly formed on the core layer.

[0077] On the other hand, even if the amount of polypropylene resin (D) is too high relative to the amount of polypropylene resin (B), or if the ratio of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) (D) / (C) is too high, it may be difficult to uniformly form a coating layer on the core layer and make it difficult to produce foamed particles with the desired layered structure.

[0078] The weight-average molecular weight of polypropylene resin (D) is preferably between 40,000 and 100,000. At its melting point Tm... (D) Based on this, a polypropylene resin (D) with a weight-average molecular weight within the specified range has the effect of reducing the interaction between the polypropylene resin (B) and the carbon nanotubes (C), and can more effectively suppress the crystallization of the polypropylene resin (B) associated with the addition of carbon nanotubes (C). Therefore, by forming a coating layer using a base resin (II) with such a low molecular weight polypropylene resin (D), the change in flowability caused by the crystallization of the polypropylene resin (B) can be suppressed, and the coating layer can be uniformly laminated onto the core layer. As a result, it is possible to produce well-foamed particles in which carbon nanotubes are uniformly dispersed in the coating layer. From the viewpoint of more reliably obtaining the above-mentioned effects, the weight-average molecular weight of the polypropylene resin (D) is more preferably 42,000 to 80,000, and even more preferably 43,000 to 60,000.

[0079] In addition, the weight-average molecular weight of polypropylene resin (D) is the equivalent molecular weight of polystyrene determined by gel permeation chromatography (GPC) using polystyrene as a standard.

[0080] Heat of fusion Q of polypropylene resin (D) (D) Preferably, the concentration is 0 J / g or higher and 50 J / g or lower. This is achieved by incorporating the base resin (II) at a melting point Tm.(D) Based on the heat of fusion Q (D) For polypropylene resins (D) within the specified range, a coating layer can be formed more easily on the core layer. From the viewpoint of more reliably obtaining the above-mentioned effects, the heat of fusion Q of the polypropylene resin (D) (D) More preferably, it is 1 J / g or more and 20 J / g or less; even more preferably, it is 2 J / g or more and 10 J / g or less; and even more preferably, it is 2.5 J / g or more and 7 J / g or less.

[0081] Heat of fusion Q of polypropylene resin (D) (D) The following method can be used to determine this. First, by comparing the melting point Tm of the aforementioned polypropylene resin (D). (D) The same method was used to condition the test specimens. The temperature was then increased from 23°C to 200°C at a rate of 10°C / min, followed by a cooling rate of 10°C / min back to 23°C. This was repeated to obtain the DSC curve. The heat of fusion Q of the polypropylene resin (D) was obtained by dividing the area of ​​the endothermic peak (in J) on the DSC curve by the mass of the test specimen (in g). (D) (Unit: J / g)

[0082] Other ingredients

[0083] In addition to the base resin (II), additives such as catalytic neutralizers, lubricants, crystallizing nucleating agents, and antistatic agents can be added to the coating layer. Furthermore, conductive carbon black can also be added to the coating layer, provided it does not impair the aforementioned effects. The amount of additives in the coating layer is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, relative to 100 parts by weight of the base resin (II).

[0084] In addition to the polypropylene resin (B) and polypropylene resin (D) that are combined with the base resin (II), other resins, elastomers, and other materials may be included in the coating layer without impairing the aforementioned effects. The amount of resins, elastomers, etc., other than the polypropylene resin (B) and polypropylene resin (D) added to the coating layer is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, relative to 100 parts by weight of the base resin (II). Furthermore, the coating layer may be composed solely of the composition (X), or, if resins and / or elastomers other than the polypropylene resin (B) and polypropylene resin (D) included in the composition (X) are added to the coating layer, the lower limit of the total amount of resins and elastomers other than the polypropylene resin (B) and polypropylene resin (D) added can be set to approximately 1 part by weight.

[0085] • Properties of the base resin (II)

[0086] The aforementioned substrate resin (II) preferably has the following properties. Substrate resin (II) having the properties shown below is particularly suitable for the formation of multilayer structures of foamed particles.

[0087] The melting point Tm of the substrate resin (II) used for the coating layer (II) Preferably, the temperature is between 120°C and 140°C. This is achieved by using the melting point Tm. (II) By forming a coating layer on the substrate resin (II) within the specified range, it is easier to fabricate multilayer foamed particles. Furthermore, the melting point Tm of the substrate resin (II)... (II) Preferably, the melting point Tm of the base resin (I) is higher. (I) Low. Under such circumstances, the weldability of the foamed particles can be further improved. From the viewpoint of further improving the above-mentioned effects, the melting point Tm of the base resin (II) is low. (II) More preferably, the temperature is above 135°C and below 138°C.

[0088] In addition, the melting point Tm of the base resin (I) (I) and the melting point Tm of the base resin (II) (II) The determination method, except that it uses a test piece made of base resin (I) or base resin (II) instead of a test piece made of polypropylene resin (B), is similar to the melting point Tm of the aforementioned polypropylene resin (B). (B) The determination method is the same.

[0089] Heat of fusion of base resin (II) Q (II) Preferably, the heat of fusion is 5 J / g or higher and 50 J / g or lower. This is achieved by using the heat of fusion Q... (II) By forming a coating layer on the substrate resin (II) within the specified range, the change in fluidity caused by the crystallization of the polypropylene resin (B) in the substrate resin (II) can be further reduced, and the coating layer can be more uniformly coated on the core layer. From the viewpoint of further improving the above-mentioned effects, the heat of fusion Q of the substrate resin (II) (II) More preferably, the concentration is 15 J / g or more and 45 J / g or less; even more preferably, the concentration is 20 J / g or more and 40 J / g or less; and even more preferably, the concentration is 25 J / g or more and 39 J / g or less.

[0090] In addition, the heat of fusion Q of the base resin (II) (II) The determination method, except that it uses a test piece made of base resin (II) instead of a test piece made of polypropylene resin (D), is the same as the aforementioned heat of fusion Q of polypropylene resin (D). (D) The determination method is the same.

[0091] The heat of fusion Q of the substrate resin (I) used for the core layer (I) The heat of fusion Q of the substrate resin (II) used for the coating layer (II) The difference Q (II) -Q (I) The absolute value is preferably 10 J / g or higher. This is achieved by measuring the difference in heat of fusion, Q. (II) -Q (I) Setting the absolute value within the specified range can further improve the foaming properties of the foamed particles. From the viewpoint of further improving the above-mentioned effects, the heat of fusion Q of the base resin (I) (I) Heat of fusion of the base resin (II) Q (II) The difference Q (II) -Q (I) The absolute value is more preferably 40 J / g or higher.

[0092] In addition, the heat of fusion Q of the base resin (I) (I) The determination method, except that it uses a test piece made of base resin (I) instead of a test piece made of polypropylene resin (D), is similar to the aforementioned heat of fusion Q of polypropylene resin (D). (D) The determination method is the same.

[0093] Melt Flow Rate (MFR) of Base Resin (II) at 230°C and 2.16 kg Load (II) Preferably, the melt flow rate (MFR) of the base resin (II) is 1 g / 10 min or more and 30 g / 10 min or less. (II) Melt Flow Rate (MFR) of Base Resin (I) (I) The ratio (MFR) (II) / MFR (I) The preferred value is 0.2 or higher and 4.5 or lower. This allows the melt flow rate (MFR) of the base resin (II) to be controlled. (II) Within the specified range and to make the melt flow rate (MFR) of the base resin (II) (II) Melt Flow Rate (MFR) of Base Resin (I) (I) The ratio of MFR (II) / MFR (I) Within the specified range, the coating layer can be more uniformly coated onto the core layer during the manufacturing process of the foamed particles.

[0094] From the viewpoint of further enhancing the above-mentioned effects, the melt flow rate (MFR) of the base resin (II) (II) More preferably, the melt flow rate is 3 g / min or more and 30 g / min or less, and even more preferably, 5 g / 10 min or more and 15 g / 10 min or less. Additionally, the melt flow rate (MFR) of the base resin (II) is... (II) Melt Flow Rate (MFR) of Base Resin (I)(I) The ratio of MFR (II) / MFR (I) Further preferred is 0.2 to 4.0, particularly preferred is 0.4 to 3.8, and most preferred is 0.5 to 3.

[0095] In addition, the melt flow rate (MFR) of the base resin (II) (II) and the melt flow rate (MFR) of the base resin (I) (I) These values ​​were determined based on JIS K7210-1:2014 under test conditions of 230℃ and 2.16kg load.

[0096] Heat of fusion Q of polypropylene resin (B) (B) Heat of fusion of the base resin (II) Q (II) The ratio of Q (B) / Q (II) Preferably, the ratio of heat of fusion is 1.2 to 3.5, more preferably 1.3 to 3.2, and even more preferably 1.5 to 3. This is achieved by adjusting the ratio of heat of fusion Q... (B) / Q (II) Within the specified range, the coating layer can be more uniformly coated onto the core layer during the manufacturing process of the foamed particles.

[0097] In addition, the heat of fusion Q of polypropylene resin (B) (B) The determination method, except that it uses a test piece made of polypropylene resin (B) instead of a test piece made of polypropylene resin (D), is the same as the aforementioned heat of fusion Q of polypropylene resin (D). (D) The determination method is the same.

[0098] [Manufacturing Process]

[0099] The method for manufacturing the foamed granules includes, for example, the following steps:

[0100] In the granulation process, polypropylene resin granules (hereinafter referred to as "resin granules") are produced. The polypropylene resin granules have a core layer and a coating layer. The core layer is produced by co-extruding a core layer containing a molten base resin (I) and a coating layer containing a molten base resin (II) using a resin melt. The extrudate is then cut to obtain an unfoamed state with the polypropylene resin (A) as the base resin (I). The coating layer uses the composition (X) as the base resin (II) and coats the core layer.

[0101] The foaming process involves foaming the core layer of the polypropylene resin particles.

[0102] Granulation process

[0103] In the granulation process, firstly, a core-forming resin melt and a coating-forming resin melt are co-extruded such that the coating-forming resin melt coats the core-forming resin melt, and an extrusion is obtained. By cutting the extrusion, unfoamed resin granules can be obtained. For the production of the extrusion, for example, a core-forming extruder for extruding the core-forming resin melt, a coating-forming extruder for extruding the coating-forming resin melt, and a co-extrusion apparatus having an extrusion die connected to the extrusion port of these extruders can be used.

[0104] The extrudate can be cut immediately after co-extrusion or after the filamentous extrudate from the extrusion die has cooled. More specifically, various methods can be used to cut the extrudate, such as slitting, cutting the extrudate after cooling, thermal cutting, and underwater cutting.

[0105] The core layer of the resin particles obtained after cutting is covered by a coating layer. For example, when resin particles are formed as described above, cylindrical resin particles with a coating layer covering the sides of a cylindrical core layer can be formed. The mass ratio of the core layer to the coating layer in the resin particles can be appropriately set, for example, from a core layer: coating layer ratio of 70:30 to 99:1, and preferably from a core layer: coating layer ratio of 80:20 to 98:2.

[0106] Foaming process

[0107] In the foaming process, the resin particles are foamed to obtain foamed particles. When foaming the resin particles, the desired bulk density can be achieved through a single foaming process or through multiple foaming processes. Hereinafter, the first foaming process will be referred to as the "first-level foaming process," and the second foaming process will be referred to as the "second-level foaming process."

[0108] • First-stage foaming process

[0109] In the primary foaming process, the resin particles are first placed in a sealed container and dispersed in an aqueous dispersion medium such as water. At this point, a dispersant for dispersing the resin particles can be added to the dispersion medium in the sealed container as needed.

[0110] As dispersants, inorganic particles such as alumina, aluminum sulfate, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica, as well as surfactants such as sodium alkylbenzene sulfonate, sodium dodecylbenzene sulfonate, and sodium alkane sulfonate can be used. One of these inorganic particles and surfactants can be used alone, or in combination of two or more.

[0111] After sealing the container, an inorganic physical foaming agent is added to the container, allowing it to impregnate the resin particles. At this point, pressurizing and heating the sealed container simultaneously promotes the impregnation of the inorganic physical foaming agent into the resin particles. Then, after the foaming agent has fully impregnated the resin particles, the contents of the sealed container are released at a pressure lower than the internal pressure of the container, causing the resin particles to foam and become foamed particles.

[0112] Inorganic physical foaming agents can be used, for example, inorganic gases such as carbon dioxide, nitrogen, and air, as well as water. These substances can be used alone or in combination. From the viewpoint of more easily obtaining foamed particles with a higher expansion ratio and narrower particle size distribution, carbon dioxide is preferred as the inorganic physical foaming agent in the primary foaming process.

[0113] The amount of inorganic physical foaming agent added can be appropriately set according to the type of polypropylene resin (A) contained in the core layer, the type of foaming agent, and the packing ratio of the foaming particles intended for use. For example, the amount of inorganic physical foaming agent added can be appropriately set from 0.1 parts to 10 parts by weight relative to 100 parts by weight of polypropylene resin (A) contained in the core layer, preferably 1 part to 9 parts by weight, and more preferably 3 parts to 8 parts by weight.

[0114] The primary foaming process may also include a process for generating the high-temperature peak (described later) before foaming the resin particles. As a method for generating the high-temperature peak, for example, heat treatment can be performed by maintaining the resin particles within a specific temperature range in a dispersion medium within a sealed container. There is no particular limitation on the timing of the heat treatment; it can be performed at any point before, during, or after impregnation with the foaming agent, or from any of the aforementioned points to another. Through this heat treatment, foamed particles with a crystalline structure exhibiting a melting peak (intrinsic peak) showing the inherent crystallinity of the polypropylene resin (A) and a melting peak (high-temperature peak) located at a higher temperature than the intrinsic peak can be obtained.

[0115] In the manufacturing method described above, a primary foaming process can foam the resin particles to a desired bulk density, or even to a higher bulk density. In the former case, the resulting foamed particles can be used for in-mold molding as is. In the latter case, a secondary foaming process, etc., can be performed to reduce the bulk density of the foamed particles to the desired value.

[0116] Secondary foaming process

[0117] In the two-stage foaming process, firstly, foamed granules obtained from the first-stage foaming process are filled into a pressure vessel. Next, the pressure vessel is pressurized with an inorganic gas, causing the inorganic gas to impregnate the foamed granules. This impregnation with the inorganic gas increases the pressure within the bubbles of the foamed granules compared to before impregnation. Furthermore, in the case of a two-stage foaming process, the resin granules obtained in the first-stage foaming process are sometimes referred to as "first-stage foamed granules."

[0118] In the secondary foaming process, the primary foaming particles inside the pressure vessel can be heated and pressurized simultaneously. Under such conditions, the impregnation of the inorganic gas into the primary foaming particles can be further promoted. When heating the primary foaming particles in the secondary foaming process, from the viewpoint of suppressing agglomeration, or in other words, suppressing the phenomenon of primary foaming particles fusing together to form lumps, it is preferable that the heating temperature of the primary foaming particles is higher than the melting point Tm of the substrate resin (II) constituting the coating layer. (II) Low.

[0119] Carbon dioxide, nitrogen, air, steam, etc., can be used as the inorganic gas in the secondary foaming process. These inorganic gases can be used alone or in combination. A mixture of steam and air is preferred for the inorganic gas used in the secondary foaming process. In this case, the primary foaming particles can be moderately heated, which further promotes the impregnation of the inorganic gas and more effectively inhibits the agglomeration of the primary foaming particles.

[0120] Furthermore, the pressure inside the bubble (internal pressure) can be measured, for example, by the method described in Japanese Patent Application Publication No. 2003-201361.

[0121] After the inorganic gas impregnation of the primary foamed particles is completed, the primary foamed particles are removed from the pressure vessel. The primary foamed particles can be heated using steam or the like at a pressure lower than the internal pressure of the bubbles, causing each bubble to expand. As a result, the primary foamed particles can be further foamed to obtain foamed particles with the desired bulk density.

[0122] Furthermore, in this specification, the container used in the primary foaming process is referred to as a "closed container," and the container used in the secondary foaming process is referred to as a "pressure-resistant container," but both can be containers that can be sealed and subjected to pressure. Additionally, the closed container in the primary foaming process and the pressure-resistant container in the secondary foaming process can be the same container or different containers.

[0123] (Polypropylene resin foamed granules)

[0124] The foamed particles are multi-layered foamed particles having a foamed core layer and a coating layer covering the core layer. The coating layer can cover the entire core layer or a portion of the core layer, but preferably a portion of the core layer is covered by the coating layer. Particularly preferred is that the foamed core layer is cylindrical, and the coating layer is uniformly formed on the side of the core layer. Furthermore, more preferably, carbon nanotubes (C) are uniformly dispersed within the coating layer. In addition, the side of the core layer is sometimes referred to as the lateral surface.

[0125] The core layer uses polypropylene resin (A) as the base resin (I), and the coating layer uses resin with a melting point Tm. (B) Polypropylene resin (B) with a temperature range of 125℃ to 150℃, carbon nanotubes (C), and a melting point Tm (D) The composition (X) is composed of a polypropylene resin (D) that can withstand temperatures between 70°C and 100°C, serving as the base resin (II). Furthermore, the content of carbon nanotubes (C) is 3 to 20 parts by mass relative to 100 parts by mass of the polypropylene resin (B). The content of polypropylene resin (D) is 6 to 120 parts by mass relative to 100 parts by mass of the polypropylene resin (B). The mass ratio (D) / (C) of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) is 2 to 10.

[0126] The foamed particles with the above-described structure effectively suppress carbon nanotube shedding because the coating layer contains carbon nanotubes. Furthermore, due to the multilayer structure in which the coating layer is uniformly stacked relative to the core layer and the carbon nanotubes are uniformly dispersed in the core layer, stable electrical properties are achieved. In addition, the foamed particles with the above-described structure also exhibit excellent foaming properties, such as secondary foaming during molding.

[0127] [Bulk density]

[0128] The bulk density of the foamed particles is preferably 18 g / L to 180 g / L, more preferably 20 g / L to 150 g / L, even more preferably 25 g / L to 120 g / L, and even more preferably 30 g / L to 100 g / L. Generally, the higher the foaming ratio of the resin particles and the lower the bulk density of the foamed particles, the more difficult it is to uniformly form a coating layer during foaming. In contrast, in the foamed particles, since the composition (X) is used in the base resin (II) of the coating layer, even with a low bulk density, a coating layer can be uniformly formed on the core layer, easily achieving the effects of the present invention.

[0129] The bulk density of the foamed granules is calculated using the following method: First, a granule group consisting of 500 or more foamed granules is placed in an environment with an air temperature of 23°C, a relative humidity of 50%, and a humidity of 1 atm for at least 24 hours. The resulting granule group is then naturally packed into a graduated cylinder to fill it, and the packed volume (in L) is read from the graduated cylinder's scale. Then, the bulk density of the foamed granules (in g / L) is obtained by dividing the mass of the granule group in the graduated cylinder (in g) by the aforementioned packed volume.

[0130] [High Temperature Peak]

[0131] The foamed particles preferably have a crystalline structure in which one or more endothermic peaks (hereinafter referred to as "high-temperature peaks") appear on the high-temperature side of the apex of the endothermic peak (hereinafter referred to as "intrinsic peak") inherent to the polypropylene resin (A) in the DSC curve obtained by differential scanning calorimetry of heat flux. In this case, the independent bubble rate of the foamed particles can be further improved, and the molding conditions for molding the foamed particle molded body can be selected from a wider range. In addition, the rigidity of the obtained foamed particle molded body can be further improved. From the above viewpoint, the heat endothermic at the high-temperature peak (hereinafter referred to as "high-temperature peak heat") is preferably 5 J / g or more, more preferably 8 J / g or more. In addition, the high-temperature peak heat is preferably 50 J / g or less, more preferably 40 J / g or less. From the same viewpoint, the high-temperature peak heat is preferably 5 J / g or more and 50 J / g or less, more preferably 8 J / g or more and 40 J / g or less.

[0132] The high-temperature peak heat of foamed granules can be calculated using the following method. First, using approximately 1–3 mg of foamed granules as a test piece, obtain the DSC curve when the test piece is heated to melt, according to the method for determining the heat transfer of plastics specified in JIS K7122-1987. The temperature range of the DSC curve is from 30°C to a temperature 30°C higher than the temperature at the end of the melting peak, with a heating rate of 10°C / min. In cases where the foamed granules exhibit a high-temperature peak, such as… Figure 1As shown, the DSC curve shows an inherent peak ΔH1 and a high-temperature peak ΔH2 with a peak closer to the high-temperature side than the inherent peak ΔH1.

[0133] Next, draw a straight line L1 connecting point α, which corresponds to 80°C on the DSC curve, and point β, which corresponds to the melting end temperature T of the foamed particles. Furthermore, the melting end temperature T is the endpoint of the high-temperature side of the high-temperature peak ΔH2; in other words, it is the intersection of the high-temperature peak ΔH2 and the baseline on the high-temperature side of the DSC curve.

[0134] After drawing straight line L1, draw straight line L2 parallel to the vertical axis of the graph, passing through the maximum point γ between the intrinsic peak ΔH1 and the high-temperature peak ΔH2. The intrinsic peak ΔH1 and the high-temperature peak ΔH2 are separated by this straight line L2. The heat absorption of the high-temperature peak ΔH2 can be calculated based on the area enclosed by the portion of the high-temperature peak ΔH2 that constitutes the DSC curve, and the areas enclosed by straight lines L1 and L2.

[0135] Furthermore, after obtaining the DSC curve using the aforementioned method, if the foamed particles are temporarily cooled and the DSC curve is obtained again, only the inherent peak ΔH1 appears in the DSC curve, while the high-temperature peak ΔH2 disappears from the DSC curve.

[0136] [Core Layer]

[0137] The core layer of the foamed granules is formed using a base resin (I). The polypropylene resin (A) used as the base resin (I) is the same as the polypropylene resin (A) used in the aforementioned method for manufacturing foamed granules.

[0138] [Covering layer]

[0139] The core layer of the foamed particles is covered by a coating layer. The coating layer may cover the entire core layer or only a portion of it. Furthermore, the coating layer may be in a foamed or non-foamed state. The mass ratio of the core layer to the coating layer in the foamed particles can be appropriately set, for example, within the range of core layer:coating layer = 70:30 to 99:1.

[0140] The coating layer is formed using a base resin (II). The composition of the base resin (II) is the same as that of the base resin (II) used in the aforementioned method for manufacturing foamed particles.

[0141] In addition, the substrate resin (II) used for the coating layer is made from resin with a melting point Tm. (B) Polypropylene resin (B) with a temperature range of 125℃ to 150℃, carbon nanotubes (C), and a melting point Tm (D)Composition (X) is a composition of polypropylene resin (D) with a temperature of 70°C to 100°C. The content of carbon nanotubes (C) is 3 to 20 parts by mass relative to 100 parts by mass of polypropylene resin (B). The content of polypropylene resin (D) is 6 to 120 parts by mass relative to 100 parts by mass of polypropylene resin (B). The mass ratio (D) / (C) of the amount of polypropylene resin (D) to the content of carbon nanotubes (C) is 2 to 10. That is, it is considered that the contents of polypropylene resin (B), carbon nanotubes (C), and polypropylene resin (D) in the base resin (II) are almost the same as the contents of polypropylene resin (B), carbon nanotubes (C), and polypropylene resin (D) in the base resin (II).

[0142] (Polypropylene resin foamed granules)

[0143] By in-mold forming the foamed granules, a polypropylene resin foamed granule molded body can be obtained. The surface resistivity of the foamed granule molded body formed by in-mold forming of the foamed granules is 1×10⁻⁶. 5 Ω or above 1×10 9 Ω or less. Foamed granules with surface resistivity within the above range are suitable as cushioning materials and packaging materials for electronic components, electronic devices, etc., because they can slowly discharge static electricity charged in the packaged items.

[0144] The surface resistivity of the foamed granule molded body was determined according to the method specified in JIS K6271-1:2015. Specifically, firstly, a test piece with a cuboid shape of 100 mm in length, 100 mm in width, and 20 mm in thickness was collected from the foamed granule molded body. The test piece was then collected with at least one of the two faces having the dimensions of 100 mm x 100 mm as the skin surface, in other words, the face that would contact the mold during in-mold molding. After electrodes were mounted on the skin surface of the test piece, a voltage of 10 V was applied between the electrodes in an atmosphere of 23°C and 50% relative humidity. The surface resistivity (in Ω) at the point 30 seconds after the voltage was applied was then taken as the surface resistivity of the foamed granule molded body.

[0145] Example

[0146] Examples of polypropylene resin foamed particles and molded polypropylene resin foamed particle articles will be described. Furthermore, the specific embodiments of the polypropylene resin foamed particles and molded polypropylene resin foamed particle articles according to the present invention are not limited to those shown in the following embodiments, and the configuration can be appropriately modified without prejudice to the spirit of the present invention. Additionally, in the following embodiments, "polypropylene" is sometimes omitted as "PP", and carbon nanotubes are sometimes omitted as "CNT".

[0147] The polypropylene resin used in this example has the following melting point, melt flow rate, heat of fusion, and weight-average molecular weight.

[0148] PP1; Propylene-1-butene-ethylene copolymer (density: 900 g / cm³) 3 MFR: 6g / 10min, Melting point: 133℃, Heat of fusion: 63J / g, Flexural modulus: 650MPa, Ethylene content: 3.1%

[0149] PP2; Low melting point polypropylene resin (manufactured by Idemitsu Kosan Co., Ltd., "L-MODU (registered trademark) S400", density: 870 g / cm³) 3 MFR: 2600g / 10min, Melting point: 84℃, Heat of fusion: 3J / g, Weight-average molecular weight: 45000

[0150] PP3; ethylene-propylene random copolymer (density: 900 g / cm³) 3 MFR: 8g / 10min, Melting point: 143℃, Heat of fusion: 79J / g, Flexural modulus: 950MPa, Ethylene content: 3.1%

[0151] The physical properties of the aforementioned polypropylene resins were determined as follows.

[0152] Melting point and heat of fusion of polypropylene resins

[0153] The melting point and heat of fusion of polypropylene resins were determined using the differential scanning calorimetry (DSC) method described in JIS K7121:1987. First, test pieces made of polypropylene resin were prepared and conditioned using a DSC apparatus at 23°C and 50% RH for at least one day. The conditioned test pieces were then heated from 23°C to 200°C at a rate of 10°C / min, cooled back to 23°C at a rate of 10°C / min, and then heated again from 23°C to 200°C at a rate of 10°C / min. The melting point of the resin was then determined by the peak temperature of the endothermic peak as determined by the DSC curve obtained during the second heating. Furthermore, in cases where multiple endothermic peaks appeared in the second DSC curve, the peak temperature of the endothermic peak with the largest area was taken as the melting point. The DSC curves were obtained using a differential scanning calorimetry device (DSC7020 manufactured by SII Nano Technology Co., Ltd.).

[0154] In addition, the area (in J) of the endothermic peak corresponding to the melting of the polypropylene resin was calculated from the second DSC curve obtained by the aforementioned method. The value obtained by dividing the area of ​​this endothermic peak by the mass (in g) of the test piece is the heat of melting of the polypropylene resin (in J / g).

[0155] [Mel flow rate of polypropylene resins]

[0156] The melt flow rate of the polypropylene resin was determined according to JIS K7210-1:2014, under conditions of 230°C and 2.16 kg load (unit: g / 10 min).

[0157] [Weight-average molecular weight of polypropylene resins]

[0158] The weight-average molecular weight of polypropylene resins was calculated based on chromatographic data obtained by gel permeation chromatography (GPC) using polystyrene as a standard.

[0159] For obtaining the chromatogram, a 150C column manufactured by Waters was used. A sample solution with a concentration of 2.2 mg / mL was prepared by dissolving the resin used as the analyte in 1,2,4-trichlorobenzene. Using a TSKgel (registered trademark) GMHHR-H(S)HT column as the column, separation conditions were set as follows: eluent: 1,2,4-trichlorobenzene, flow rate: 1.0 mL / min, temperature: 145 °C. The analyte was separated by gel permeation chromatography (GPC) based on the difference in molecular weight, thus obtaining the chromatogram.

[0160] Then, the retention time in the chromatogram obtained using a calibration curve prepared with standard polystyrene was converted into molecular weight, yielding a differential molecular weight distribution curve. The weight-average molecular weight (Mw) of the polypropylene resin was calculated based on this differential molecular weight distribution curve.

[0161] In addition, Table 1 shows the types, average lengths, average outer diameters, and aspect ratios of the carbon nanotubes used in this example.

[0162] Table 1

[0163] CNT symbol CNT1 CNT2 CNT3 CNT4 type Multi-layer CNT Multi-layer CNT Multi-layer CNT Multi-layer CNT Average length (μm) 1.5 1 10 3～12 Average outer diameter (nm) 9.5 12 10～25 12～25 Aspect Ratio 158 83 400～1000 200～1000

[0164] (Example 1)

[0165] like Figure 2 As shown, the foamed particle 1 in this example has a foamed core layer 2 and a coating layer 3 covering the core layer 2. As shown in Table 2, the core layer 2 uses PP3 as the base resin (I), which is a polypropylene-based resin (A). The coating layer 3 uses resin with a melting point Tm. (B) PP1, carbon nanotubes (C), and the melting point Tm of polypropylene resin (B) with a temperature range of 125℃ to 150℃ are used as the references.(D) The composition (X) is composed of PP2 of polypropylene resin (D) with a temperature of 70°C to 100°C, and the base resin (II) is used.

[0166] In producing the foamed granules 1 in this example, firstly, a base resin (II) for forming the coating layer was prepared by the following method. A masterbatch containing carbon nanotubes (C) dispersed in polypropylene resin PP1 as shown in Table 2 was prepared. Furthermore, the content of carbon nanotubes (C) in the masterbatch was 15% by mass. This masterbatch was then compounded in an extruder with polypropylene resin (B) and polypropylene resin (D) as shown in Table 1 to produce granules of base resin (II) with a mass ratio of polypropylene resin (B), carbon nanotubes (C), and polypropylene resin (D) as shown in Table 2.

[0167] Next, a core-forming extruder with an inner diameter of 26 mm and a coating-forming extruder with an inner diameter of 25 mm were arranged side by side, and a filament was produced using a co-extrusion apparatus equipped with a die on the exit side capable of co-extruding multiple multi-layer filaments. Polypropylene resin (A) as shown in Table 2 and a bubble modifier at a mass of 1000 ppm relative to polypropylene resin (A) were supplied to the core-forming extruder, and the two were mixed within the core-forming extruder. Additionally, particles of a base resin (II) prepared by the aforementioned method, having the composition shown in the "Coating" column of Table 2, were supplied to the coating-forming extruder. Furthermore, zinc borate powder was used as a bubble modifier.

[0168] Subsequently, the core layer forming resin melt and the coating layer forming resin melt were co-extruded from each extruder in a mass ratio of core layer to coating layer as shown in the "Core Layer: Coating Layer" column of Table 2. The molten compound extruded from each extruder merged within the die and was extruded through a fine orifice of a connector mounted at the front end of the extruder as a multi-layered linear material with the sides of the core layer coated by the coating layer. By water cooling this extrudate, a multi-layered linear material was obtained.

[0169] The obtained wire was cut using a fan-shaped cutter to a weight of approximately 1.0 mg. This yielded resin particles having an unfoamed core layer and a coating layer covering the sides of the core layer.

[0170] Next, a primary foaming process is performed to foam the resin particles. 1000g of resin particles, 3L of water as a dispersion medium, 3g of kaolin as a dispersant, 0.2g of surfactant, and 0.1g of aluminum sulfate are sealed in a closed container. Specifically, a 20% aqueous solution of sodium alkylbenzene sulfonate (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., "Neogen (registered trademark) S-20F") is used as the surfactant.

[0171] Subsequently, carbon dioxide, acting as a foaming agent, was supplied into the sealed container to pressurize it at a gauge pressure of 2.1 MPa (G). Under these conditions, the container was heated while being stirred, raising the temperature to 149.8°C. After maintaining this foaming temperature for 10 minutes, the container was opened by pressurizing it with carbon dioxide, maintaining the gauge pressure at 2.6 MPa (G), releasing the contents at atmospheric pressure, thus foaming the resin particles. This yielded primary foamed particles with a multi-layered structure consisting of a foamed core layer and a coating layer covering the core layer. Furthermore, since the primary foamed particles contained moisture immediately after being released from the sealed container, they were cured at 23°C for 24 hours.

[0172] Next, a secondary foaming process is performed to further foam the primary foamed particles. After filling a pressure vessel with the primary foamed particles, air, an inorganic gas, is injected into the vessel, thus impregnating the air bubbles within the primary foamed particles. The pressure within the air bubbles of the primary foamed particles removed from the pressure vessel is 0.45–0.5 MPa(G) at gauge pressure. Then, steam is supplied to the primary foamed particles removed from the pressure vessel, and heating is performed at atmospheric pressure. The pressure of the supplied steam during heating is 0.02–0.12 MPa(G) at gauge pressure, and the heating time is 15 seconds. This further foaming process yields secondary foamed particles.

[0173] Next, in-mold forming was performed to produce the foamed granule molded body. First, the secondary foamed granules were sealed in a closed container, and then compressed air was used to pressurize the container, raising the internal pressure of the bubbles in the secondary foamed granules to 0.09–0.13 MPa(G) under gauge pressure. This secondary foamed granule was then filled into the forming mold of the EPP molding machine, and forming was performed using steam. The steam forming pressure was 0.22–0.36 MPa(G) under gauge pressure.

[0174] (Examples 2 to 6 and Comparative Example 3)

[0175] The foamed particles of Examples 2 to 6 and Comparative Example 3 have the same structure as the foamed particles of Example 1, except that the composition of the coating layer has been changed as shown in Tables 2, 3 or 5.

[0176] (Examples 7 to 9)

[0177] The foamed particles of Examples 7 to 9 have the same composition as the foamed particles of Example 1, except that the carbon nanotubes (C) contained in the coating layer are changed as shown in Table 4.

[0178] (Comparative Example 1, Comparative Example 2)

[0179] As shown in Table 5, the foamed particles of Comparative Example 1 and Comparative Example 2 have the same composition as the foamed particles of Example 1, except that the substrate resin (II) in the coating layer does not contain polypropylene resin (D).

[0180] (Comparative Examples 4 to 6)

[0181] As shown in Table 6, the foamed particles of Comparative Examples 4 to 6 consist only of a core layer made of polypropylene resin (A) as the base resin and do not have a coating layer. Furthermore, the base resin of Comparative Example 4 does not contain any conductive material. The base resin of Comparative Example 5 contains carbon black as a conductive material, and the base resin of Comparative Example 6 contains carbon nanotubes as a conductive material.

[0182] In producing the foamed granules of Comparative Example 4, polypropylene resin (A) was extruded from an extruder to produce a single-layer filament having the composition shown in Table 6. The filament was cut to obtain resin granules. Then, the resin granules were foamed using the same method as the foamed granules of Example 1 to obtain the foamed granules of Comparative Example 4.

[0183] In producing the foamed granules of Comparative Examples 5 and 6, a conductive material was mixed with a polypropylene resin (A) in an extruder, and then extruded from the extruder to produce a single-layer filament having the composition shown in Table 6. The filament was cut to obtain resin granules. Then, the resin granules were foamed using the same method as the foamed granules of Example 1 to obtain the foamed granules of Comparative Examples 5 and 6.

[0184] Next, the evaluation methods for the characteristics shown in Tables 2 to 6 will be explained.

[0185] [Melting point Tm of base resin (II)] (II) And the heat of fusion Q (II) ]

[0186] Melting point Tm of base resin (II) (II) And the heat of fusion Q (II) The determination method is the same as the aforementioned method for determining the melting point and heat of fusion of polypropylene resins, except that a test piece made of base resin (II) is used instead of a test piece made of polypropylene resin for differential scanning calorimetry.

[0187] [Covering properties]

[0188] In Examples 1 to 9 and Comparative Examples 1 to 3, which have multi-layer structures, the coating state of the bar-shaped wire extruded from the co-extrusion apparatus was evaluated by visual observation. In the "Coating Properties" column of Tables 2 to 5, the symbol "A" indicates that the entire side of the wire is uniformly coated by the coating layer; the symbol "B" indicates that the thickness of the coating layer is deviated, but the entire side of the bar-shaped wire is coated by the coating layer; and the symbol "C" indicates that the coating layer is difficult to completely cover the core layer, and a portion of the core layer is exposed on the side of the wire.

[0189] [Extrudability of the coating layer]

[0190] In Examples 1 to 9 and Comparative Examples 1 to 3, which have multilayer structures, the extrudability of the coating layer was evaluated based on the load on the motor of the extrusion molding machine for forming the coating layer during the co-extrusion of the core layer and the coating layer. In the "Extrudability of Coating Layer" column of Tables 2 to 5, the symbol "A" indicates that the coating layer can be extruded without problems, and the symbol "B" indicates adverse conditions such as an increase in the viscosity of the base resin (II) and overload of the motor of the extrusion molding machine for forming the coating layer.

[0191] [Peak heat at high temperature]

[0192] The test sample used for determining the heat of heat at the high-temperature peak can be either primary foamed granules or foamed granules. In this example, differential scanning calorimetry (DSC) was performed using primary foamed granules as the test sample. Specifically, approximately 2 mg of primary foamed granules was used as the test piece, and the test piece was heated and melted according to the method for determining the heat of transfer of plastics as described in JIS K7122-1987, resulting in the DSC curve at this point. The measurement temperature range was from 30°C to a temperature 30°C higher than the end of the melting peak, and the heating rate was 10°C / min.

[0193] Using the aforementioned method, the endothermic peak in the obtained DSC curve is divided into the intrinsic peak ΔH1 and the high-temperature peak ΔH2 (refer to...). Figure 1 Then, the total heat value is the sum of the areas of the inherent peak ΔH1 and the high-temperature peak ΔH2, and the heat value of the high-temperature peak is the area of ​​the high-temperature peak ΔH2.

[0194] [Bulk density of foamed particles]

[0195] More than 500 foamed granules were placed in an environment with an air temperature of 23°C, a relative humidity of 50%, and a humidity of 1 atm for 24 hours. The resulting foamed granule group was then filled into a graduated cylinder by natural stacking, and the stacked volume (in L) of the foamed granule group was read according to the graduated cylinder's scale. Then, the bulk density (in g / L) of the foamed granules was obtained by dividing the mass (in g) of the foamed granule group in the graduated cylinder by the aforementioned stacked volume (in L).

[0196] [Formability of Foamed Particle Molded Articles]

[0197] The formability of the foamed granule molded body was evaluated based on the weld ratio calculated using the following method. First, the foamed granule molded body was bent and broken in a manner that was approximately evenly divided along its length. The exposed fracture surface was then visually observed, and the number of foamed granules that had peeled off from each other's interfaces and the number of foamed granules that had broken internally were counted. Then, the ratio of the number of foamed granules that had broken internally to the total number of foamed granules exposed at the fracture surface—that is, the total number of foamed granules that had peeled off from each other's interfaces and the total number of foamed granules that had broken internally—was calculated. The weld ratio was expressed as a percentage (%).

[0198] In Tables 2-6, the "Formability" column indicates that the weld ratio is over 95%, "A" indicates a weld ratio over 80% but below 95%, and "B" indicates a weld ratio over 70% but below 80%. In the formability evaluation, weld ratios of 80% or higher marked with "A+" or "A" are considered excellent and therefore deemed acceptable.

[0199] [Apparent density of foamed granule molded articles]

[0200] Divide the mass (kg) of the foamed granule molded body by the volume (m³) of the foamed granule molded body calculated based on its external dimensions. 3 The obtained value is used as the apparent density of the foamed granule molded body (unit: kg / m³). 3 ).

[0201] [Surface resistivity of foamed granule molded bodies]

[0202] The surface resistivity of the foamed granule molded body was determined according to the method described in JIS K6271-1:2015. Specifically, firstly, a cuboid-shaped test piece with a length of 100 mm, a width of 100 mm, and a thickness of 20 mm was collected from the foamed granule molded body. The test piece was then collected with at least one of the two faces having a length of 100 mm × a width of 100 mm as the skin surface, in other words, the face that would contact the mold during in-mold molding. After attaching electrodes to the skin surface of the test piece, a voltage of 10 V was applied between the electrodes in an atmosphere of 23°C and 50% relative humidity. The surface resistivity (in Ω) at 30 seconds after the voltage was applied was then taken as the surface resistivity of the foamed granule molded body.

[0203] [Surface resistivity of substrate resin (II)]

[0204] A cuboid-shaped test piece with a length of 100 mm, a width of 100 mm, and a thickness of 20 mm was fabricated using base resin (II). The surface resistivity of the test piece was measured according to the method described in JIS K6271-1:2015. Specifically, electrodes were mounted on the 100 mm x 100 mm surface of the test piece, and a voltage of 10 V was applied between the electrodes in an atmosphere at 23 °C and 50% relative humidity. The surface resistivity (in Ω) at 30 seconds after the voltage was applied was then taken as the surface resistivity of the foamed granule molded body.

[0205] Table 2

[0206]

[0207] Table 3

[0208]

[0209] Table 4

[0210]

[0211] Table 5

[0212]

[0213] Table 6

[0214]

[0215] As shown in Tables 2 to 4, the core layer of the foamed particles in Examples 1 to 9 is formed using a base resin (I), and the coating layer is formed using a base resin (II) having the specific composition described above. Therefore, the foamed particles of Examples 1 to 9 exhibit excellent weldability and formability. Furthermore, by in-mold molding the foamed particles of Examples 1 to 9, foamed particle molded bodies with electrostatic diffusion properties can be easily obtained.

[0216] As shown in Table 5, the coating layer of the resin particles in Comparative Example 1 does not contain polypropylene resin (D). Therefore, it is difficult to form the coating layer and stack the coating layer on the core layer when manufacturing the resin particles of Comparative Example 1.

[0217] In Comparative Example 2, the resin particles had a coating layer containing more carbon nanotubes (C) than those in Comparative Example 1. Therefore, forming the coating layer became more difficult. Furthermore, in Comparative Example 2, the higher amount of carbon nanotubes (C) resulted in reduced formability.

[0218] The amount of carbon nanotubes (C) in the foamed particles of Comparative Example 3 is less than the specified range. Therefore, it is possible to coat the core layer with a coating layer and form foamed particles, but even if the foamed particles of Comparative Example 3 are molded in-mold, it is difficult to impart the desired electrical properties to the foamed particle molded body.

[0219] Comparative Example 4 is an example of foamed particles consisting only of a core layer and not containing any conductive material in the core layer. The foamed particles of Comparative Example 4 have poor formability.

[0220] Comparative Examples 5 and 6 are examples of adding conductive materials to foamed particles consisting only of a core layer. In the above-mentioned foamed particles, a large amount of conductive material needs to be added in order to reduce the resistance of the foamed particles. Therefore, the foamed particles of Comparative Examples 5 and 6 have poor formability.

Claims

1. A method for manufacturing polypropylene resin foamed granules, comprising foaming polypropylene resin granules having a core layer and a coating layer covering the core layer, wherein... The substrate resin (I) of the core layer is a polypropylene resin (A). The base resin (II) of the coating layer is made from resin with a melting point Tm. (B) Polypropylene resin (B) with a temperature range of 125℃ to 150℃, carbon nanotubes (C), and a melting point Tm (D) Composition (X) is made of polypropylene resin (D) that is heated to a temperature between 70°C and 100°C. The amount of carbon nanotubes (C) incorporated is between 3 and 20 parts by weight relative to 100 parts by weight of the polypropylene resin (B). The amount of the polypropylene resin (D) is between 6 and 120 parts by weight relative to 100 parts by weight of the polypropylene resin (B). The mass ratio (D) / (C) of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) is more than 2 and less than 10.

2. The method for manufacturing polypropylene resin foamed granules according to claim 1, wherein, The heat of fusion Q of the polypropylene resin (B) (B) [J / g] Heat of fusion of the base resin (II) with Q (II) The ratio of [J / g] to Q (B) / Q (II) It is between 1.2 and 3.

5.

3. The method for manufacturing polypropylene resin foamed granules according to claim 1 or 2, wherein, The weight-average molecular weight of the polypropylene resin (D) is between 40,000 and 100,000.

4. The method for manufacturing polypropylene resin foamed granules according to any one of claims 1 to 3, wherein, The heat of fusion of the polypropylene resin (D) Q (D) The value is between 0 J / g and 50 J / g.

5. The method for manufacturing polypropylene resin foamed granules according to any one of claims 1 to 4, wherein, The melting point Tm of the base resin (II) (II) The temperature is between 120°C and 140°C, and the heat of fusion is Q. (II) The value is between 5 J / g and 50 J / g.

6. The method for manufacturing polypropylene resin foamed granules according to any one of claims 1 to 5, wherein, The melt flow rate (MFR) of the base resin (II) at a temperature of 230°C and a load of 2.16 kg. (II) The melt flow rate (MFR) of the base resin (II) is 1 g / 10 min or more and 30 g / 10 min or less. (II) Melt Flow Rate (MFR) of the Substrate Resin (I) (I) The ratio of MFR (II) / MFR (I) It is between 0.2 and 4.

5.

7. A polypropylene resin foamed particle, comprising a foamed core layer and a coating layer covering the core layer, wherein, The substrate resin (I) of the core layer is a polypropylene resin (A). The base resin (II) of the coating layer is made from resin with a melting point Tm. (B) Polypropylene resin (B) with a temperature range of 125℃ to 150℃, carbon nanotubes (C), and a melting point Tm (D) Composition (X) is made of polypropylene resin (D) that is heated to a temperature between 70°C and 100°C. The amount of carbon nanotubes (C) incorporated is between 3 and 20 parts by weight relative to 100 parts by weight of the polypropylene resin (B). The amount of the polypropylene resin (D) is between 6 and 120 parts by weight relative to 100 parts by weight of the polypropylene resin (B). The mass ratio (D) / (C) of the amount of polypropylene resin (D) to the amount of carbon nanotubes (C) is more than 2 and less than 10.

8. A polypropylene resin foamed granule molded body, which is a polypropylene resin foamed granule molded by in-mold forming of the polypropylene resin foamed granules according to claim 7, wherein... The surface resistivity is 1×10 5 Ω or above 1×10 9 Below Ω.

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