Crosslinked polyolefin resin foam, and cushioning material including the crosslinked polyolefin resin foam, and transport container

Abstract

To provide a technique for imparting moderate conductivity to a crosslinked polyolefin resin foam while retaining its physical properties.SOLUTION: The present technology provides a crosslinked polyolefin resin foam comprising a polyolefin resin and a donor-acceptor type antistatic agent. The density of the crosslinked polyolefin resin foam of the present technology may be 250 kg / m3 or less. The crosslinked foam of the present technology can be used for cushioning materials and transport containers.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present technology relates to a crosslinked polyolefin-based resin foam. More specifically, the present technology relates to a crosslinked polyolefin-based resin foam, and a cushioning material and a transport container using the crosslinked polyolefin-based resin foam. [Background technology]

[0002] The transport containers used to transport various products use cushioning materials that are tailored to the shape of the product to protect it from collisions between products and external shocks and vibrations. Cushioning materials must have a moderate flexibility so as not to damage the product, and a moderate strength to ensure support and workability. In addition, from the standpoint of reducing the load during transport and reducing costs, the lower the density of the cushioning materials used in transport containers, the more advantageous it is.

[0003] Resin foam is suitable as a material that satisfies these conditions, but resin foam is usually an insulator and is easily charged by friction, etc. In particular, when transporting electronic parts and electronic devices, it is necessary to consider damage caused by static electricity. Therefore, when using resin foam as a transport container or cushioning material, it is necessary to eliminate static electricity, and a method of selecting a special material or using an additional member is used. As a method of eliminating static electricity, it is possible to eliminate static electricity from the outside using an ionizer or humidity control, but applying these methods during transportation is often expensive and impractical.

[0004] As a method for preventing the resin foam from being charged, it is generally known to impart a suitable electrical conductivity to the resin foam itself. In order to prevent charging, a suitable electrical conductivity is necessary, but if the electrical resistance is too low, i.e., if the electrical conductivity is too high, a problem occurs in that discharge from the outside is induced to the resin foam. In order to solve such a problem, a method of imparting a suitable electrical conductivity to the resin foam is used, such as a method of adding a surfactant, a conductive polymer, a conductive filler, etc. to the resin foam, a method of attaching a conductive film to the surface of the resin foam, or a method of coating the surface of the resin foam with a conductive paint.

[0005] For example, Patent Document 1 describes a method for extruding and foaming a polypropylene resin composition having a melt flow rate (MFR) of 1 to 5 g / 10 min and a melting point of 150° C. or higher, to which 10 to 25 parts by weight of a polymer-type antistatic agent having a melt flow rate (MFR) of 1 to 15 g / 10 min and a melting point of 150° C. or higher has been added, to obtain a polypropylene resin composition having a density of 0.05 to 0.1 g / cm. 3 , thickness is 0.5 to 2 mm, the number of bubbles in the thickness direction is 1 to 3 / mm, and the surface resistivity is 1×10 13 A technology has been disclosed for obtaining a polypropylene-based resin foam sheet having an antistatic coefficient of less than (Ω / □), which has excellent antistatic properties, is thin, and is rigid, making it suitable for use in automatic packaging lines. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-191195 A [Patent Document 2] JP 2023-33251 A [Patent Document 3] JP 2020-158557 A Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, in order to contribute to the formation of a sustainable society, there has been a demand for a technology that can increase the number of times that transport containers and cushioning materials can be used. From the viewpoint of extending the product life, a crosslinked polyolefin resin foam obtained by crosslinking and foaming a polyolefin resin composition is suitable, but a technology for imparting electrical conductivity to a crosslinked polyolefin resin has not yet been developed.

[0008] Therefore, a main object of the present technology is to provide a technology for imparting appropriate and durable electrical conductivity to a crosslinked polyolefin resin foam while maintaining the physical properties of the crosslinked polyolefin resin foam. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present inventors tried various methods for preventing static electricity buildup in crosslinked polyolefin resin foams, but found that it was extremely difficult to impart appropriate conductivity while maintaining the physical properties of crosslinked polyolefin resin foams, for example, it was not possible to obtain appropriate conductivity, or even when conductivity was obtained, the physical properties required of the crosslinked polyolefin resin foams were reduced.

[0010] Specifically, for example, as shown in the examples described later, when a surfactant or a conductive polymer is used as an antistatic agent, it is difficult to impart conductivity to a crosslinked polyolefin resin foam in a general amount. Since the surfactant bleeds onto the surface of the crosslinked polyolefin resin foam and exerts conductivity by attracting moisture in the air, moisture in the air is essential for the development of conductivity, and there is a problem that it is highly environmentally dependent and stable conductivity cannot be obtained depending on the amount of moisture in the air. Although it was possible to impart conductivity to the crosslinked polyolefin resin foam by increasing the amount of surfactant added, when a surfactant is used, the surfactant migrates (bleeds out) to the surface of the product and escapes depending on the usage environment (especially high temperature conditions or conditions with drastic temperature changes, etc.), so it was not possible to obtain sustained conductivity.

[0011] In addition, as for the conductive polymer, by increasing the amount added, it was possible to impart conductivity to the crosslinked polyolefin resin foam. However, when the amount of the conductive polymer was increased, the crosslinked polyolefin resin foam became too soft or had an effect on the compression set, making it difficult to obtain the required hardness while maintaining the lightweight properties achieved by foaming, and the crosslinked polyolefin resin foam ended up being heavy in weight relative to its hardness.

[0012] In addition, in the method using conductive filler, the conductivity of the crosslinked polyolefin resin foam becomes too high, which induces discharge from the outside to the product, making it difficult to control the conductivity. There is also a risk of short circuit due to detachment of the filler, and depending on the filler used (e.g. carbon), the color is limited to black, etc., which affects visibility. Furthermore, in the method using film or paint, problems arise such as the need for post-processing, which increases costs, and the risk of malfunction due to damage such as peeling of the film or paint.

[0013] Under such circumstances, the present inventors have further conducted intensive research and have succeeded in imparting appropriate and durable electrical conductivity to a crosslinked polyolefin resin foam while maintaining its physical properties by using a donor-acceptor type antistatic agent as an antistatic agent. Note that Patent Documents 2 and 3 disclose techniques for using a donor-acceptor type antistatic agent in a polyolefin resin foam, but in reality, neither of these foams is a crosslinked foam and does not have the physical properties required for a crosslinked polyolefin resin foam.

[0014] That is, in the present technology, first, a polyolefin resin and and a donor-acceptor type antistatic agent. The density of the crosslinked polyolefin resin foam of this technology is 250 kg / m 3 It can be as follows: The crosslinked polyolefin resin foam according to the present technology can have a compression set of 10% or less in a compression set test according to JIS K6767.

[0015] Next, the present technology provides a cushioning material and a transport container using the crosslinked polyolefin resin foam according to the present technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A preferred embodiment for carrying out the present technology will be described below. The embodiments described below are examples of typical embodiments of the present technology, and any of the embodiments can be combined. In addition, the scope of the present technology is not narrowly interpreted by these.

[0017] 1. Cross-linked polyolefin resin foam The crosslinked polyolefin resin foam according to the present technology contains a polyolefin resin and a donor-acceptor type antistatic agent. That is, the crosslinked polyolefin resin foam according to the present technology is a crosslinked foam of a resin composition containing a polyolefin resin and a donor-acceptor type antistatic agent. In addition, the resin composition for producing the crosslinked polyolefin resin foam according to the present technology (hereinafter also referred to as "the resin composition") can contain a foaming agent, a crosslinking agent, a foaming assistant, a lubricant, a crosslinking accelerator, and various other components that can be used in the production of the crosslinked polyolefin resin foam depending on the purpose. Each component will be described in detail below.

[0018] (1) Polyolefin resin The polyolefin resin that can be used in the polyolefin resin foam of the present technology is a resin mainly composed of an olefin component unit. A resin mainly composed of an olefin component unit is a resin containing 50% by mass or more of an olefin component unit. In the present technology, the content of the olefin component unit in the resin is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and it is particularly preferable that the resin component is composed only of a polyolefin resin.

[0019] Examples of polyolefin-based resins that can be used in the present technology include polyethylene-based resins, polypropylene-based resins, polybutene, polypentene, and copolymers of olefin-based monomers and monomers that can be copolymerized with the olefin-based monomers. These can be used alone or in combination of two or more kinds.

[0020] Examples of polyethylene resins include ethylene homopolymers such as high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and very low density polyethylene (VLDPE); ethylene-propylene random copolymers, ethylene-propylene block copolymers, ethylene-butene block copolymers, ethylene-butene random copolymers, ethylene-vinyl acetate copolymers, and ethylene-methyl methacrylate copolymers.

[0021] Examples of polypropylene-based resins include propylene homopolymers such as isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene; propylene-ethylene random copolymers, propylene-ethylene block copolymers, propylene-butene random copolymers, propylene-butene block copolymers, propylene-ethylene-butene terpolymers, propylene-acrylic acid copolymers, and propylene-maleic anhydride copolymers.

[0022] Among these, in the present technology, it is preferable to use a polyethylene-based resin, and among the polyethylene-based resins, it is preferable to use low-density polyethylene (LDPE). In the present technology, the content of the polyethylene-based resin in the resin component is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more.

[0023] In addition, the crosslinked polyolefin resin foam according to the present technology may contain other resins, thermoplastic elastomers, thermosetting elastomers, etc., in addition to the polyolefin resin, as long as the purpose and effect of the present technology are not impaired. Examples of resins other than polyolefin resins include thermoplastic resins such as polystyrene resins, polyamide resins, and polyester resins. Examples of thermoplastic elastomers include olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers. Examples of thermosetting elastomers include synthetic rubbers such as ethylene propylene rubber (EPDM) and natural rubber.

[0024] (2) Donor-acceptor type antistatic agents The crosslinked polyolefin resin foam according to the present technology is characterized by the use of a donor-acceptor type antistatic agent. The donor-acceptor type antistatic agent can impart electrical conductivity to the crosslinked polyolefin resin foam even in a relatively small amount, and therefore has little effect on the resin melt viscosity, crosslinking reaction, and foaming reaction during the production of the crosslinked polyolefin resin foam. As a result, the physical properties required for the crosslinked polyolefin resin foam can be well maintained. In addition, since the donor-acceptor type antistatic agent has a relatively low dependency on the amount of addition, the electrical conductivity of the crosslinked polyolefin resin foam does not become too high, and induction of external discharge to the crosslinked polyolefin resin foam can be prevented.

[0025] Furthermore, the donor-acceptor type antistatic agent has the effect of removing the charged charge on the surface and inside of the resin by charge transfer transition when a (+) component or a (-) charge is present. Therefore, a transition reaction occurs in which protons move from the donor compound to the acceptor compound. As a result, the surface of the resin foam is neutralized and eliminated to remove the charged charge, and in parts other than the surface, the donor component transports holes and the acceptor component diffuses electrons, making it possible to remove the charged charge. Therefore, the donor-acceptor type antistatic agent is not affected by the moisture concentration in the air in terms of the development of conductivity, i.e., it is not dependent on the environment, and is not consumed in the development of conductivity like a surfactant, so that the conductivity is continuously developed.

[0026] The donor component may be, for example, an organic boron compound. The acceptor component may be, for example, an organic nitrogen compound. More specific examples of donor-acceptor type antistatic agents include compounds represented by the following chemical formula (1) and chemical formula (2).

[0027] [ka] (R 1 , and R 2R each independently represents an alkyl group having 1 to 24 carbon atoms. 3 , and R 4 R each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. 5 R represents an alkylene group having 1 to 12 carbon atoms. 6 represents an alkyl group having 1 to 24 carbon atoms.

[0028] [ka] (R 1 , and R 2 R each independently represents an alkyl group having 1 to 24 carbon atoms. 3 , and R 4 R each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. 5 R represents an alkylene group having 1 to 12 carbon atoms. 6 represents an alkyl group having 1 to 24 carbon atoms.

[0029] The amount of the donor-acceptor type antistatic agent used in the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the upper limit of the content of the donor-acceptor type antistatic agent relative to 100 parts by mass of the resin component in the resin composition is, for example, 15 parts by mass or less, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. By setting the donor-acceptor type antistatic agent in the resin composition within this range, it is possible to prevent the conductivity of the crosslinked polyolefin resin foam from being excessively improved, and also to prevent the density of the crosslinked polyolefin resin foam from being excessively increased and the hardness of the crosslinked polyolefin resin foam from being excessively decreased.

[0030] In the present technology, the lower limit of the content of the donor-acceptor type antistatic agent relative to 100 parts by mass of the resin component in the resin composition is, for example, 0.005 parts by mass or more, preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and even more preferably 0.05 parts by mass or more. By setting the content of the donor-acceptor type antistatic agent in the resin composition within this range, it is possible to impart appropriate electrical conductivity to the crosslinked polyolefin resin foam, and to improve the antistatic performance of the crosslinked polyolefin resin foam.

[0031] In the present technology, the donor-acceptor type antistatic agent is preferably used as a master batch in which the donor-acceptor type antistatic agent is dispersed in the above-mentioned resin component. By using the master batch, the dispersibility in the resin component can be improved.

[0032] (3) Foaming agent The resin composition for producing the crosslinked polyolefin resin foam according to the present technology may contain a foaming agent. As the foaming agent that can be used in the present technology, one or more foaming agents that can be used in polyolefin resin foams may be freely selected and used as long as the purpose and effect of the present technology are not impaired.

[0033] Examples of the blowing agent that can be used in the present technology include organic or inorganic thermal decomposition type chemical blowing agents. Examples of organic blowing agents include azo compounds such as azodicarbonamide (ADCA), azodicarboxylate metal salts (e.g., barium azodicarboxylate), azobisisobutyronitrile (AIBN), etc.; nitroso compounds such as N,N'-dinitrosopentamethylenetetramine (DPT), etc.; hydrazine derivatives such as hydrazodicarbonamide, 4,4'-oxybis(benzenesulfonylhydrazide), toluenesulfonylhydrazide (TSH), etc.; and semicarbazide compounds such as toluenesulfonylsemicarbazide, etc. Examples of inorganic blowing agents include ammonium carbonate, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate, etc.

[0034] Among these, in the present technology, it is preferable to use an organic foaming agent as the foaming agent, and among the organic foaming agents, it is preferable to use azodicarbonamide (ADCA).

[0035] The amount of the foaming agent used in the production of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the content of the foaming agent relative to 100 parts by mass of the resin component in the resin composition is, for example, 0.7 parts by mass or more, preferably 2.0 parts by mass or more, and more preferably 4.0 parts by mass or more. By setting the content of the foaming agent in the resin composition within this range, the foamability during foam production can be improved, and the physical properties of the produced foam can be improved.

[0036] In the present technology, the content of the foaming agent relative to 100 parts by mass of the resin component in the resin composition is, for example, 25 parts by mass or less, preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. By setting the content of the foaming agent in the resin composition within this range, formation defects due to excessive foaming can be suppressed, and also contribute to cost reduction.

[0037] In the present technology, the foaming agent can be used as a master batch in which the foaming agent is dispersed in the resin component. By using the foaming agent master batch, the dispersibility in the resin component can be improved.

[0038] (4) Crosslinking agent The polyolefin resin foam according to the present technology is a crosslinked foam. By performing crosslinking during the production of the polyolefin resin foam according to the present technology, the viscosity of the composition (kneaded product) before foaming can be increased, and the foamability can be improved. In addition, the physical properties of the produced foam can be improved.

[0039] The crosslinked polyolefin resin foam according to the present technology can be crosslinked by irradiation with ionizing radiation, but can also be crosslinked chemically using a crosslinking agent. As the crosslinking agent that can be used in the present technology, one or more crosslinking agents that can be used for polyolefin resin foam can be freely selected and used as long as they do not impair the purpose and effect of the present technology.

[0040] Examples of crosslinking agents that can be used in the present technology include crosslinking agents having chemical structures such as silane groups, peroxides, hydroxyl groups, amide groups, ester groups, etc. Among these, in the present technology, it is preferable to use an organic peroxide as the crosslinking agent.

[0041] Examples of organic peroxides include dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, di-t-butylperoxide, di-t-butylperoxy-3,3,5-trimethylcyclohexane, and t-dibutylhydroperoxide. Among these, in the present technology, it is preferable to use dicumyl peroxide as a crosslinking agent.

[0042] The amount of the crosslinking agent used in the production of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the content of the crosslinking agent relative to 100 parts by mass of the resin component in the resin composition is, for example, 0.2 parts by mass or more, preferably 0.4 parts by mass or more, and more preferably 0.6 parts by mass or more. By setting the content of the crosslinking agent in the resin composition within this range, the viscosity can be improved and the foamability can be improved. In addition, the mechanical properties such as heat resistance and durability of the produced foam can be improved.

[0043] In the present technology, the content of the crosslinking agent relative to 100 parts by mass of the resin component in the resin composition is, for example, 4.0 parts by mass or less, preferably 3.0 parts by mass or less, and more preferably 2.0 parts by mass or less. By setting the content of the crosslinking agent in the resin composition within this range, it is possible to prevent cracks and the like from occurring during foaming and improve moldability.

[0044] (5) Foaming assistant The resin composition for producing the crosslinked polyolefin resin foam according to the present technology may contain a foaming aid. As the foaming aid that can be used in the present technology, one or more foaming aids that can be used in polyolefin resin foams may be freely selected and used as long as they do not impair the purpose and effect of the present technology.

[0045] Examples of foaming assistants that can be used in the present technology include urea-based assistants such as urea, metal oxides, and fatty acid metal salts. Examples of metal oxides include zinc oxide, zinc chloride, zinc acetate, zinc nitrate, lead oxide, dibasic lead phosphite, and tribasic lead sulfate. Examples of fatty acid metal salts include zinc stearate, lead stearate, magnesium stearate, and calcium stearate. Among these, in the present technology, it is preferable to use urea and / or zinc oxide as the foaming assistant.

[0046] The amount of foaming aid used in the production of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the content of the foaming aid relative to 100 parts by mass of the resin component in the resin composition is, for example, 0.01 parts by mass or more, preferably 0.02 parts by mass or more, and more preferably 0.03 parts by mass or more. By setting the content of the foaming aid in the resin composition within this range, the foamability during foam production can be improved and the density of the produced foam can be reduced.

[0047] In the present technology, the content of the foaming aid in the resin composition relative to 100 parts by mass of the resin component is, for example, 3.0 parts by mass or less, preferably 2.0 parts by mass or less, and more preferably 1.0 part by mass or less. By setting the content of the foaming aid in the resin composition within this range, formation defects due to excessive foaming can be suppressed, and also contribute to cost reduction.

[0048] (6) Lubricants The resin composition for producing the crosslinked polyolefin resin foam according to the present technology can contain a lubricant. As the lubricant that can be used in the present technology, one or more lubricants that can be used in polyolefin resin foam can be freely selected and used as long as the purpose and effect of the present technology are not impaired. Examples of the foaming assistant that can be used in the present technology include stearic acid, zinc stearate, calcium stearate, polyethylene glycol, silicone oil, sorbitan monostearate, and sorbitan tristearate.

[0049] The amount of lubricant used in the production of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the content of the lubricant relative to 100 parts by mass of the resin component in the resin composition is, for example, 0.01 parts by mass or more, preferably 0.02 parts by mass or more, and more preferably 0.03 parts by mass or more. By setting the content of the lubricant in the resin composition within this range, the workability during the production of the foam can be improved.

[0050] In the present technology, the content of the lubricant in the resin composition relative to 100 parts by mass of the resin component is, for example, 3.0 parts by mass or less, preferably 2.0 parts by mass or less, and more preferably 1.0 part by mass or less. By setting the content of the lubricant in the resin composition within this range, formation defects can be suppressed and also contribute to cost reduction.

[0051] (7)Other In producing the crosslinked polyolefin resin foam according to the present technology, one or more of various components that can be used in the production of polyolefin resin foams can be freely selected and used as other components depending on the purpose, as long as the purpose and effects of the present technology are not impaired.

[0052] Examples of components that can be used in the production of the polyolefin resin foam according to the present technology include crosslinking accelerators, inorganic fillers, foam stabilizers, flame retardants, stabilizers, plasticizers, colorants, antioxidants, dispersants, and ultraviolet absorbers.

[0053] (8) Density The density of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the lower limit of the density of the crosslinked polyolefin resin foam is set to, for example, 10 kg / m 3 More than 20kg / m 3 More preferably, 25 kg / m 3 More preferably, 35 kg / m 3 By setting the lower limit of the density of the crosslinked polyolefin resin foam within this range, it is possible to prevent the foam from becoming too soft and to impart appropriate elasticity to the foam.

[0054] The upper limit of the density of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. For example, it is set to 250 kg / m 3 Less than 200 kg / m 3 Less than or equal to 150 kg / m 3 More preferably, 100 kg / m or less 3 More preferably, 90 kg / m or less 3 Less than 85 kg / m 3 Less than or equal to 80 kg / m 3 By setting the density of the crosslinked polyolefin resin foam within this range, it is possible to impart cushioning properties without impairing flexibility (preventing the foam from becoming too hard).

[0055] In the present technology, the density of the polyolefin resin foam is a value measured in accordance with a method based on JIS K6767.

[0056] (9) Asker C hardness The Asker C hardness of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the lower limit of the Asker C hardness of the crosslinked polyolefin resin foam is, for example, 10 or more, preferably 20 or more, more preferably 25 or more, and even more preferably 35 or more. By setting the lower limit of the Asker C hardness of the crosslinked polyolefin resin foam within this range, the durability of the crosslinked polyolefin resin foam can be improved.

[0057] The upper limit of the Asker C hardness of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology, and is, for example, not more than 80, preferably not more than 75, more preferably not more than 70, and even more preferably not more than 60. By setting the Asker C hardness of the crosslinked polyolefin resin foam within this range, it is possible to prevent the foam from becoming too hard and to impart appropriate flexibility.

[0058] In the present technology, the Asker C hardness of the polyolefin resin foam is a value measured in accordance with a method based on JIS K7312.

[0059] (10)Surface resistivity The surface resistivity of the crosslinked polyolefin resin foam according to the present invention can be freely set as long as it does not impair the purpose and effect of the present invention. In the present invention, the lower limit of the surface resistivity of the crosslinked polyolefin resin foam is set to, for example, 1×10 10 Ω / □ or more, preferably 1×10 11 Ω / □ or more, preferably 1×10 12 By setting the lower limit of the surface resistivity of the crosslinked polyolefin resin foam within this range, the antistatic performance of the crosslinked polyolefin resin foam can be improved.

[0060] The upper limit of the surface resistivity of the crosslinked polyolefin resin foam according to the present invention can be freely set as long as it does not impair the purpose and effect of the present invention. For example, 16 Ω / □ or less, preferably 1×10 15 Ω / □ or less, more preferably 1×10 15 Ω / □ or less, more preferably 1×10 14 By setting the surface resistivity of the crosslinked polyolefin resin foam in this range, it is possible to prevent electrical discharge from the outside from being induced to the crosslinked polyolefin resin foam.

[0061] In the present technology, the surface resistivity of the polyolefin resin foam is a value measured in accordance with a method based on JIS K6911.

[0062] (11) Compression set The compression set of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the upper limit of the compression set of the crosslinked polyolefin resin foam can be freely set as long as it does not impair the purpose and effect of the present technology, and is, for example, 12% or less, preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. By setting the compression set of the crosslinked polyolefin resin foam within this range, the durability of the crosslinked polyolefin resin foam can be improved.

[0063] The lower limit of the compression set of the crosslinked polyolefin resin foam according to the present technology is not particularly limited, but can be set to, for example, 0.5% or more, 1% or more, etc.

[0064] In the present technology, the compression set of the polyolefin resin foam is a value measured in accordance with a method based on JIS K6767.

[0065] (12) Gel fraction The gel fraction of the crosslinked polyolefin resin foam according to the present technology can be freely set as long as it does not impair the purpose and effect of the present technology. In the present technology, the lower limit of the gel fraction of the crosslinked polyolefin resin foam can be freely set as long as it does not impair the purpose and effect of the present technology, and is, for example, 50% or more, preferably 55% or more, more preferably 60% or more, and even more preferably 70% or more. By setting the gel fraction of the crosslinked polyolefin resin foam in this range, the durability of the crosslinked polyolefin resin foam can be improved.

[0066] The upper limit of the gel fraction of the crosslinked polyolefin resin foam according to the present technology is not particularly limited, but can be set to, for example, 95% or less, 90% or less, etc.

[0067] In the present technology, the gel fraction of the polyolefin resin foam is a value measured in accordance with a method based on JIS K 6796 / ISO-15875-2:2003.

[0068] 2. Manufacturing method of crosslinked polyolefin resin foam The crosslinked polyolefin resin foam according to the present technology is characterized by its composition, and its manufacturing method is not particularly limited. For example, a method can be adopted in which a crosslinking agent and a foaming agent are added to a polyolefin resin and a donor-acceptor type antistatic agent, and other additives are added and mixed as necessary, and then foam molding is performed. Preferably, the manufacturing method of the crosslinked polyolefin resin foam may be any of the following one-stage block foaming method, two-stage block foaming method, long-length foaming method using chemical crosslinking, and long-length foaming method using electron beam crosslinking.

[0069] <One-stage block foaming method> The one-stage block foaming method includes, for example, the following steps (1) and (2). (1) Mixing process A polyolefin resin, a donor-acceptor type antistatic agent, a foaming agent, a crosslinking agent, and optionally required foaming assistants, lubricants, and other optional components are melt-kneaded at a temperature equal to or lower than the decomposition temperature of the foaming agent by a kneading device such as an extruder, a Banbury mixer, a kneader, or a roll to prepare a foamable resin composition. (2) Foaming process The foamable resin composition obtained in the kneading step is filled into a mold, sealed, and heated under pressure at a temperature equal to or higher than the decomposition temperature of the foaming agent and the crosslinking agent for a predetermined period of time to promote decomposition of the foaming agent and the crosslinking agent. The mold is then opened to release the pressure, thereby obtaining a crosslinked polyolefin resin foam.

[0070] <Two-stage block foaming method> The two-stage block foaming method includes, for example, the following steps (1) to (3). (1) Mixing process A polyolefin resin, a donor-acceptor type antistatic agent, a foaming agent, a crosslinking agent, and optionally required foaming assistants, lubricants, and other optional components are melt-kneaded at a temperature equal to or lower than the decomposition temperature of the foaming agent by a kneading device such as an extruder, a Banbury mixer, a kneader, or a roll to prepare a foamable resin composition. (2) Primary foaming process The foamable resin composition obtained in the kneading step is filled into the molding space of the primary mold and heated under pressure. This causes a part of the foaming agent and a part or all of the crosslinking agent to decompose. The pressure is then released, and the foamable resin composition intermediate (primary foam) is taken out. The heating temperature is usually 120-150°C, and the heating time is usually determined within the range of 25-70 minutes. (3) Secondary foaming process The foamable resin composition intermediate (primary foam) obtained in the primary foaming step is placed in the molding space of an unsealed secondary mold, heated under normal pressure to cause secondary foaming, and cooled, and then the resin foam is removed from the secondary mold. The heating temperature is usually 140-180°C, and the heating time is usually determined in the range of 25 minutes to 6 hours.

[0071] <Three-stage block foaming method> The three-stage block foaming method includes, for example, the following steps (1) to (3). (1) Mixing process A polyolefin resin, a donor-acceptor type antistatic agent, a foaming agent, a crosslinking agent, and optionally required foaming assistants, lubricants, and other optional components are melt-kneaded at a temperature equal to or lower than the decomposition temperature of the foaming agent by a kneading device such as an extruder, a Banbury mixer, a kneader, or a roll to prepare a foamable resin composition. (2) Primary foaming process The foamable resin composition obtained in the kneading step is filled into the molding space of the primary mold and heated under pressure. This causes a part of the foaming agent and a part or all of the crosslinking agent to decompose. The pressure is then released, and the foamable resin composition intermediate (primary foam) is taken out. The heating temperature is usually 120-150°C, and the heating time is usually determined within the range of 25-70 minutes. (3) Secondary foaming process The foamable resin composition intermediate (primary foam) obtained in the primary foaming step is filled into the molding space of the secondary mold and heated under pressure. This causes a part of the foaming agent and a part or all of the crosslinking agent to decompose. The pressure is then released, and the foamable resin composition intermediate (secondary foam) is taken out. The heating temperature is usually determined to be 120-150°C, and the heating time is usually determined to be in the range of 25-70 minutes. (4) Tertiary foaming process The foamable resin composition intermediate (secondary foam) obtained in the secondary foaming step is placed in the molding space of an unsealed tertiary mold, heated under normal pressure to cause tertiary foaming, and then the resin foam is removed from the tertiary mold. Alternatively, the foamable resin composition intermediate (secondary foam) obtained in the secondary foaming step is placed in an oven (constant temperature bath) and exposed to low-temperature (about 90°C) hot air for about 24 hours to obtain a resin foam.

[0072] <Long-length foaming method using chemical crosslinking> The long length foaming method includes, for example, the following steps (1) and (2). (1) Mixing process A polyolefin resin, a donor-acceptor type antistatic agent, a foaming agent, a crosslinking agent, and optionally required foaming assistants, lubricants, and other optional components are kneaded and extruded into a sheet using a single-screw extruder, a twin-screw extruder, or the like to extrude a foamable resin composition of a predetermined shape such as a sheet (hereinafter referred to as a mother plate). Kneading and extrusion can be performed all at once using an extruder. (2) Foaming process The mother plate obtained in the kneading step is heated and foamed at 120-250°C (above the decomposition temperature of the foaming agent and crosslinking agent) for 5-20 minutes while being transported into a heating device such as an oven, to obtain a resin foam. Note that it is preferable to use a device in which a heating device such as an oven and a transport device are integrated, since this allows the mother plate to be treated continuously.

[0073] <Long-length foaming method using electron beam crosslinking> The long length foaming method using electron beam crosslinking includes, for example, the following steps (1) to (3). (1) Mixing process A polyolefin resin, a donor-acceptor type antistatic agent, a foaming agent, a crosslinking agent, and optionally required foaming assistants, lubricants, and other optional components are kneaded in a single screw extruder, a twin screw extruder, or the like, and a resin composition having a predetermined shape such as a sheet (hereinafter referred to as a mother plate) is extruded. Kneading and extrusion can be performed all at once using an extruder. (2) Crosslinking process The base plate obtained in the kneading step is crosslinked. As a crosslinking method, a method of irradiating with ionizing radiation such as electron beams or gamma rays can be used, and crosslinking by electron beam irradiation (electron beam crosslinking) is preferred. Electron beam crosslinking can be performed using an electron beam irradiator. If necessary, a crosslinking agent such as the above-mentioned organic peroxide may be used in combination. (3) Foaming process The crosslinked mother plate obtained in the crosslinking step is heated at 120-250°C (above the decomposition temperature of the foaming agent) for 5-20 minutes while being transported into a heating device such as an oven to foam the mother plate, thereby obtaining a resin foam. Note that it is preferable to use a device in which a heating device such as an oven and a transport device are integrated, since this allows the mother plate to be treated continuously.

[0074] In the method for producing a crosslinked polyolefin resin foam according to the present technology described above, other steps can be performed depending on the purpose. For example, after the crosslinking step or the foaming step, a cooling step, an aging step, etc. can be performed. In addition, a molding step such as cutting the edges or slicing the produced foam can also be performed.

[0075] 3. Applications of cross-linked polyolefin resin foam The crosslinked polyolefin resin foam according to the present technology can be used for all kinds of applications in all fields by utilizing its high quality. For example, it can be suitably used for construction cushioning materials, construction seal materials, home appliance seal materials, packaging materials, transport containers, vehicle cushioning materials, construction interior materials, vehicle interior materials, home appliance cushioning materials, pipe insulation materials, various covers, cushioning materials, toys, miscellaneous goods, cleaners, various sponges, toys, kickboards, floats, sporting goods, etc. The crosslinked polyolefin resin foam according to the present technology can be suitably used for transport containers and cushioning materials that require durability for repeated use such as returnable boxes, particularly for transport containers and cushioning materials used for transporting electronic parts, electronic devices, etc. EXAMPLES

[0076] The present technology will be described in more detail below based on examples. Note that the examples described below are representative examples of the present technology, and the scope of the present technology is not to be interpreted narrowly by these examples.

[0077] <Experimental Example 1> In Experimental Example 1, the difference in effect due to the difference in antistatic agent was verified when a crosslinked polyolefin resin foam was produced.

[0078] (1) Raw materials Polyolefin resin 1: Low-density polyethylene (LDPE) (MFR: 1.9 g / 10 min, melting point: 110°C) Foaming agent masterbatch: Masterbatch of 65% azodicarbonamide (ADCA) and 35% polyolefin resin 2 (low density polyethylene (LDPE)) Crosslinker: Dicumyl peroxide (DCP) Foaming agent 1: Urea Foaming agent 2: Zinc oxide Lubricant: stearic acid Antistatic agent 1 (antistatic agent master batch 1): "SEIKAEARTH 1120 N" manufactured by Dainichiseika Chemicals Mfg. Co., Ltd. (master batch of 20% donor-acceptor type antistatic agent and 80% polyolefin resin 2 (low-density polyethylene (LDPE))) Antistatic agent 2 (antistatic agent master batch 2): Non-ionic antistatic agent "ELECON SS PE220" manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. (master batch of 20% surfactant and 80% polyolefin resin 2 (low density polyethylene (LDPE))) Antistatic agent 3 (conductive polymer): A block copolymer consisting of a block having a polyoxyethylene chain and a block composed of polyester (ADEKA STAB AS-301E, manufactured by ADEKA Corporation)

[0079] (2) Manufacturing of crosslinked polyolefin resin foam The raw materials shown in Table 1 below were mixed in a kneader, then filled into the molding space of a primary mold, heated under pressure, and then released from the pressure to prepare a primary foam. The primary foam was placed in the molding space of an unsealed secondary mold, heated under normal pressure to cause secondary foaming, and cooled to produce each foam.

[0080] (3) Evaluation The produced crosslinked polyolefin resin foams were evaluated for various physical properties using the following methods.

[0081] [density] Measurements were performed in accordance with JIS K6767.

[0082] [Asker C hardness] Measurements were performed in accordance with JIS K7312.

[0083] [Surface resistivity] Measurement was performed in accordance with JIS K6911 at a measurement voltage of 100 V. The equipment used was a "Digital Ultra-High Resistance / Micro Ammeter 5451 SAMPLE CHAMBER MODEL42" manufactured by ADC Corporation. The surface resistivity after the wet heat cycle is a value measured in accordance with JIS K6911 after a 24-hour wet heat cycle in accordance with JIS C60068-2-38.

[0084] [Compression set] Measurements were performed in accordance with JIS K6767.

[0085] [Gel fraction] Measurements were performed in accordance with JIS K 6796 / ISO-15875-2:2003.

[0086] (4) Results The results are shown in Table 1 below. [Table 1]

[0087] (5) Discussion As shown in Table 1, the crosslinked polyolefin resin foam using the donor-acceptor type antistatic agent has appropriate electrical conductivity, and even when the amount of the donor-acceptor type antistatic agent is increased, the density, hardness, and compression set are not affected, and the physical properties are equivalent to those of conventional crosslinked polyolefin resin foams.

[0088] On the other hand, in Comparative Examples 1 and 2, where a surfactant was used as an antistatic agent, electrical conductivity could not be obtained. As shown in Comparative Examples 3 to 5, by increasing the amount of the surfactant, appropriate electrical conductivity could be obtained, but the electrical conductivity after the wet heat cycle decreased. This is considered to be due to the consumption of the surfactant.

[0089] In addition, in Comparative Examples 6 to 8, where a conductive polymer was used as an antistatic agent, conductivity could not be obtained. As shown in Comparative Examples 9 and 10, the conductivity could be improved by increasing the amount of the conductive polymer, but the hardness tended to decrease, and it was not suitable for applications requiring a certain degree of hardness. Also, as shown in Comparative Example 9, increasing the amount of the conductive polymer affected the compression set.

Claims

1. A polyolefin resin, A crosslinked polyolefin resin foam comprising a donor-acceptor type antistatic agent.

2. Density is 250 kg / m 3 The crosslinked polyolefin resin foam according to claim 1, wherein:

3. 2. The crosslinked polyolefin resin foam according to claim 1, which has a compression set of 10% or less in a compression set test according to JIS K6767.

4. A cushioning material comprising the crosslinked polyolefin resin foam according to any one of claims 1 to 3.

5. A transport container comprising the crosslinked polyolefin resin foam according to any one of claims 1 to 3.

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