JP6577891B2 - Thermoplastic elastomer foam and method for producing thermoplastic elastomer foam - Google Patents

Description

  The present invention relates to a thermoplastic elastomer foam obtained by foaming a resin composition containing a thermoplastic elastomer. Moreover, this invention relates to the manufacturing method of the thermoplastic elastomer foam which obtains the said thermoplastic elastomer foam.

  Conventionally, a thermoplastic resin foam obtained by foam-molding a thermoplastic resin has been used in various applications. The thermoplastic resin foam is often used, for example, as a cushioning material and an automobile structural member.

  Patent Document 1 listed below discloses a resin foam obtained by foam molding a resin composition containing polytetrafluoroethylene and a resin other than polytetrafluoroethylene using an injection foam molding machine. ing.

  In Patent Document 2 below, extrusion foam molding is performed with an annular die using a polyolefin resin composition containing a polyolefin resin as a thermoplastic resin and carbon dioxide (carbon dioxide) as a foaming agent. The polyolefin resin foam obtained by the above is disclosed. The polyolefin resin composition includes (a) a polyolefin resin, (b) (b1) an elastomer, and (b2) a plastomer. The blending ratio of the above (a) and (b) is in the range of 90/10 to 10/90 by weight ratio. The blending ratio of the above (b1) and (b2) is in the range of 90/10 to 10/90 by weight ratio.

Japanese Patent Laying-Open No. 2015-224266 JP, 2014-084341, A

  Conventional foams such as those described in Patent Documents 1 and 2 may not have sufficiently high cushioning properties. In addition, as described in Patent Document 1, the cushioning property may not be sufficiently increased by simply using polytetrafluoroethylene.

  Moreover, in patent document 1, since the resin composition containing polytetrafluoroethylene and resin other than polytetrafluoroethylene is injection-foam-molded, it is difficult to make a foam small.

  An object of the present invention is to provide a thermoplastic elastomer foam excellent in cushioning properties. Another object of the present invention is to provide a method for producing a thermoplastic elastomer foam, which can obtain a thermoplastic elastomer foam excellent in cushioning properties.

  According to a wide aspect of the present invention, there is provided a foam of a resin composition containing a thermoplastic elastomer and polytetrafluoroethylene, and the polytetrafluoroethylene is contained in a fibrous form in the continuous phase of the thermoplastic elastomer. A thermoplastic elastomer foam (abbreviated as a foam) having a foaming ratio of 2 to 20 times and an average cell diameter of 10 to 200 μm in the center. Is provided).

  In a specific aspect of the foam according to the present invention, an average minor axis of the polytetrafluoroethylene in the foam is 5 μm or less, and in another specific aspect, the polytetrafluoroethylene in the foam. All the minor axes are 10 μm or less.

  In a specific aspect of the foam according to the present invention, the foam has air bubbles in a surface portion, and an average cell diameter in a central portion of the foam and an average cell diameter in a surface portion of the foam The absolute value of the difference is 100 μm or less.

  In a specific aspect of the foam according to the present invention, a ratio of a content of the thermoplastic elastomer in the foam to a content of the polytetrafluoroethylene in the foam is 9 or more and 999 or less. .

  In a specific aspect of the foam according to the present invention, the foam has an open cell ratio of 50% or more and 95% or less.

  In a specific aspect of the foam according to the present invention, the foam is a particle having an aspect ratio of 10 or less.

  In a specific aspect of the foam according to the present invention, the thermoplastic elastomer is an amide elastomer or an olefin elastomer.

  In a specific aspect of the foam according to the present invention, the foam is a non-crosslinked foam.

  On the specific situation with the foam which concerns on this invention, the melt flow rate of the said resin composition is 0.5 g / 10min or more and 4.0 g / 10min or less.

  On the specific situation with the foam which concerns on this invention, the said resin composition contains polyolefin resin.

  In a specific aspect of the foam according to the present invention, a ratio of a content of the thermoplastic elastomer in the foam to a content of the polyolefin resin in the foam is 1.5 or more and 19 or less. is there.

  According to a wide aspect of the present invention, there is provided a method for producing the thermoplastic elastomer foam described above, a melting step for melting the resin composition, and foaming the melted resin composition to obtain a thermoplastic elastomer foam. And a foaming step for obtaining a thermoplastic elastomer foam.

  On the specific situation with the manufacturing method of the foam which concerns on this invention, the said polytetrafluoroethylene in the said resin composition currently melt | dissolved is sheared in the said fusion | melting process.

  The thermoplastic elastomer foam according to the present invention is a foam of a resin composition containing a thermoplastic elastomer and polytetrafluoroethylene, and the polytetrafluoroethylene is fibrous in the continuous phase of the thermoplastic elastomer. In addition, it has a foaming ratio of 2 times or more and 20 times or less, and has air bubbles with an average bubble diameter of 10 μm or more and 200 μm or less in the center portion, so that it has excellent cushioning properties.

FIG. 1 is a cross-sectional SEM image showing a thermoplastic elastomer foam according to an embodiment of the present invention.

  Hereinafter, the present invention will be described in detail.

  The thermoplastic elastomer foam according to the present invention (sometimes abbreviated as foam) is obtained by foaming a resin composition. The foam according to the present invention is a foam of a resin composition. The foam according to the present invention has a plurality of bubbles. The resin composition contains a thermoplastic elastomer and polytetrafluoroethylene (sometimes referred to as PTFE).

  In the foam according to the present invention, the thermoplastic elastomer constitutes the continuous phase. The foam according to the present invention has a structure in which PTFE is contained in a fibrous form in the continuous phase of the thermoplastic elastomer. The foam according to the present invention has an expansion ratio of 2 times or more and 20 times or less. The foam according to the present invention has bubbles having an average cell diameter of 10 μm or more and 200 μm or less at the center.

  Since the foam according to the present invention has the above-described configuration, it has excellent cushioning properties. Therefore, the foam according to the present invention can be used for applications requiring high cushioning properties. The foam according to the present invention can be used as a cushioning material, for example.

  In the foam, PTFE is fibrous. From the viewpoint of effectively enhancing the cushioning property, the average minor axis of the fibrous PTFE is preferably 5 μm or less, more preferably 4.5 μm or less, and further preferably 4 μm or less. From the viewpoint of effectively increasing the cushioning property, the average minor axis of the fibrous PTFE is preferably 0.01 μm or more, more preferably 0.02 μm or more. The minor axis is the smallest dimension in the radial direction of one fibrous PTFE. An average minor axis is calculated | required by averaging the minor axis of several fibrous PTFE.

  The foam has an expansion ratio of 2 times or more and 20 times or less. From the viewpoint of effectively increasing the cushioning property, the foaming ratio of the foam is preferably 3 times or more. From the viewpoint of effectively increasing the strength of the foam, the foaming ratio of the foam is preferably 15 times or less.

  The foam has bubbles with an average bubble diameter of 10 μm or more and 200 μm or less in the center. The foam preferably has a plurality of bubbles at the center. From the viewpoint of effectively enhancing the cushioning property, the average cell diameter in the center of the foam is preferably 20 μm or more, more preferably 25 μm or more, still more preferably 30 μm or more, preferably 150 μm or less, more preferably 120 μm or less. .

  The average cell diameter at the center can be evaluated by observing a cross section of a 100 μm × 100 μm (square) region centered on the center of the foam.

  The foam preferably has bubbles on the surface portion. The foam preferably has a plurality of bubbles on the surface portion. From the viewpoint of effectively increasing the cushioning property, the average cell diameter in the surface portion of the foam is preferably 10 μm or more, more preferably 20 μm or more, still more preferably 30 μm or more, preferably 200 μm or less, more preferably 180 μm or less, and further Preferably it is 160 micrometers or less.

  The average bubble diameter in the surface portion can be evaluated by cross-sectional observation at a portion where the cross-section of a region of 100 μm × 100 μm (square) can be observed at the position farthest from the central portion.

  From the viewpoint of enhancing the cushioning property uniformly and effectively, the absolute value of the difference between the average cell diameter in the center of the foam and the average cell diameter in the surface of the foam is preferably 0 μm or more, preferably 100 μm or less. More preferably, it is 90 micrometers or less, More preferably, it is 85 micrometers or less.

  From the viewpoint of effectively increasing the cushioning property, the open cell ratio of the foam is preferably 50% or more, more preferably 55% or more, still more preferably 60% or more, preferably 95% or less, more preferably 90%. Hereinafter, it is more preferably 85% or less. A specific method for measuring the open cell ratio is described in the evaluation column of Examples and the like.

  The shape of the foam is not particularly limited. The foam may be a sheet or a particle. The foam can be obtained, for example, by extrusion foaming. For this reason, a foam can be made into a particulate form.

  Examples of the shape of the particles include a true sphere, an elliptical sphere (egg), a columnar shape, a prismatic shape, a pellet shape, and a granular shape.

  From the viewpoint of effectively increasing the cushioning property, the aspect ratio of the particles is preferably 10 or less, more preferably 9 or less, and still more preferably 8 or less. The aspect ratio of the particles is preferably 1 or more. The aspect ratio indicates the major axis / minor axis.

  Since the cushioning property can be sufficiently enhanced even if it is small, the major axis of the particle is preferably 10 mm or less, more preferably 9.5 mm or less, and further preferably 9 mm or less. From the viewpoint of effectively increasing the cushioning property, the major axis of the particles is preferably 1.5 mm or more, more preferably 2 mm or more. When the particles are spherical, the major axis of the particles means the diameter.

  From the viewpoint of suppressing a decrease in cushioning properties, a non-crosslinked foam is preferable. However, from the viewpoint of increasing the strength, a crosslinked foam is preferable.

  From the viewpoint of effectively increasing the cushioning property, the melt flow rate (MFR) of the resin composition is preferably 0.5 g / 10 min or more, more preferably 0 under the conditions of a test temperature of 230 ° C. and a load of 21.18 N. 0.8 g / 10 min or more, preferably 10 g / 10 min or less, more preferably 8 g / 10 min or less, still more preferably 6 g / 10 min or less, particularly preferably 4 g / 10 min or less.

  From the viewpoint of effectively improving the cushioning property, the melt tension of the resin composition is preferably 0.3 cN or more, more preferably 0.5 cN or more, still more preferably 1 cN or more, particularly preferably 5 cN or more, preferably 40 cN or less. More preferably, it is 35 cN or less, More preferably, it is 30 cN or less. Moreover, a bubble can be made still finer as melt tension is more than the said minimum and below the said upper limit.

  In the present invention, regarding the determination of whether or not sufficient cushioning properties are provided, in the measurement of resilience described later in the examples, resilience is preferably 30% or more, more preferably 40% or more, and still more preferably. It can be judged by 50% or more, preferably 80% or less, more preferably 75% or less, and still more preferably 70% or less.

  Hereinafter, other details of the present invention will be described.

(Resin composition)
The resin composition includes a thermoplastic elastomer and PTFE. From the viewpoint of effectively increasing the foaming characteristics (higher magnification, proper foaming temperature, etc.), the resin composition and the foam preferably contain a polyolefin resin. The polyolefin resin is not a thermoplastic elastomer.

Thermoplastic elastomer:
Thermoplastic elastomers exhibit rubber elasticity at room temperature (25 ° C.) and have the property that they can be molded and molded at high temperatures in the same manner as thermoplastic resins.

  Examples of the thermoplastic elastomer include amide elastomers, olefin elastomers, styrene elastomers, polyester elastomers, polyurethane elastomers, and the like.

  From the viewpoint of effectively increasing the cushioning property, the thermoplastic elastomer is preferably an amide elastomer or an olefin elastomer. In this case, the thermoplastic elastomer may be either an amide elastomer or an olefin elastomer, or both. The thermoplastic elastomer is preferably an amide elastomer, and is preferably an olefin elastomer.

  The olefin elastomer is generally a polyolefin resin such as polypropylene or polyethylene whose hard segment is a rubber component such as ethylene-propylene-diene copolymer or ethylene-propylene copolymer or non-crystalline. Polyethylene.

  Olefin-based elastomers are polymerization type elastomers that are produced directly in a polymerization reaction vessel by polymerizing hard segment monomers and soft segment monomers; kneading such as a Banbury mixer or twin screw extruder Blend type elastomer produced by physically dispersing polyolefin resin to be hard segment and rubber component to be soft segment using a machine; using a kneader such as a Banbury mixer or a twin screw extruder When the polyolefin resin that becomes the hard segment and the rubber component that becomes the soft segment are physically dispersed, the rubber component is completely or partially crosslinked in the polyolefin resin matrix by adding a crosslinking agent. , Dynamic rack obtained by micro-dispersion Elastomer, and the like.

  As the thermoplastic elastomer, any of a non-crosslinked elastomer and a crosslinked elastomer can be used. From the viewpoint of effectively increasing the cushioning property, a non-crosslinked elastomer is preferable.

  From the viewpoint of enhancing the recyclability of the foam, the olefin elastomer is preferably a non-crosslinked elastomer produced by physically dispersing a polyolefin resin serving as a hard segment and a rubber component serving as a soft segment. . Moreover, such a non-crosslinked elastomer can be suitably used for extrusion foam molding with an annular die. Further, by using such a non-crosslinked elastomer, foaming failure due to the crosslinked rubber can be suppressed even when the foam is recycled and supplied to the extruder again for extrusion foam molding.

  Specific examples of the olefin elastomer include olefin elastomers such as ethylene-propylene-diene copolymer, ethylene-vinyl acetate copolymer, polybutene, and chlorinated polyethylene; styrene elastomer; polyester elastomer; polyurethane elastomer, etc. Is mentioned.

  When the olefin-based elastomer is an ethylene-propylene-diene copolymer elastomer, examples of the diene component include ethylidene norbornene, 1,4-hexadiene, and dicyclopentadiene. Such an ethylene-propylene-diene copolymer elastomer can be suitably used for extrusion foam molding with an annular die. Only one type of ethylene-propylene-diene copolymer elastomer may be used, or two or more types may be used in combination.

  The amide elastomer may be a non-crosslinked amide elastomer. Examples of the amide elastomer include a copolymer having a polyamide block (hard segment) and a polyether block (soft segment).

  Polyamide blocks include, for example, polyε capramide (nylon 6), polytetraethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebamide (nylon 610), polyhexa Methylene dodecamide (nylon 612), polyundecane methylene adipamide (nylon 116), polyundecanamide (nylon 11), polylauramide (nylon 12), polyhexamethylene isophthalamide (nylon 6I), polyhexamethylene terephthalamide ( Polyamide structures derived from nylon 6T), polynanomethylene terephthalamide (nylon 9T), polymetaxylylene adipamide (nylon MXD6), and the like. The polyamide block may be a combination of units constituting these polyamide structures.

  Examples of the polyether block include polyether structures derived from polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), polytetrahydrofuran (PTHF), and the like. The polyether block may be a combination of units constituting these polyether structures.

  The polyamide block and the polyether block may be randomly dispersed.

  The number average molecular weight Mn of the polyamide block is preferably 300 or more, more preferably 600 or more, preferably 15000 or less, more preferably 5000 or less. The number average molecular weight Mn of the polyether block is preferably 100 or more, more preferably 200 or more, preferably 6000 or less, more preferably 3000 or less.

  The melting point of the non-crosslinked amide elastomer is preferably 120 ° C. or higher, more preferably 125 ° C. or higher, preferably 180 ° C. or lower, more preferably 175 ° C. or lower. When the melting point is not less than the above lower limit, the foam is more unlikely to shrink when exposed to room temperature after foaming. When the melting point is not more than the above upper limit, foaming at a desired foaming ratio is further facilitated.

  The melting point of the non-crosslinked amide elastomer is measured with a differential thermal analyzer (DSC) according to JIS K7121. The melting point is the endothermic peak value temperature in the reheating process.

  The crystallization temperature of the non-crosslinked amide elastomer is preferably 90 ° C or higher, more preferably 100 ° C or higher, preferably 140 ° C or lower, more preferably 130 ° C or lower. When the crystallization temperature is equal to or higher than the lower limit, the foam is more unlikely to shrink when exposed to room temperature after foaming. When the crystallization temperature is not more than the above upper limit, foaming at a desired foaming ratio is further facilitated.

  The crystallization temperature of the non-crosslinked amide elastomer is measured with a differential thermal analyzer (DSC) according to JIS K7121. The crystallization temperature is an exothermic peak value temperature in the temperature lowering process at a temperature lowering rate of 2 ° C./min.

  As non-crosslinked amide-based elastomers, U.S. Pat. No. 4,331,786, U.S. Pat. No. 4,115,475, U.S. Pat. No. 4,195,015, U.S. Pat. No. 4,839. 441, U.S. Pat. No. 4,864,014, U.S. Pat. No. 4,230,838 and U.S. Pat. No. 4,332,920 are also used. it can.

  The non-crosslinked amide-based elastomer is preferably a copolycondensate of a polyamide block having a reactive end and a polyether block having a reactive end. Specific examples of this copolycondensate include the following copolycondensates.

1) Copolycondensation product of polyamide block having diamine chain end and polyoxyalkylene block having dicarboxylic acid chain end 2) Cyanoethylation of aliphatic dihydroxylated α, ω-polyoxyalkylene unit called polyether diol And polycondensation product of polyamide unit having dicarboxylic acid chain end obtained by hydrogenation and polyoxyalkylene unit having diamine chain end 3) Copolycondensation of polyamide unit having dicarboxylic acid chain end and polyether diol Product (the copolycondensate obtained in this case is particularly called polyetheresteramide)

  Examples of the compound giving a polyamide block having a dicarboxylic acid chain end include a compound obtained by condensation of a dicarboxylic acid and a diamine in the presence of an α, ω-aminocarboxylic acid, lactam or dicarboxylic acid chain regulator. .

  In the case of the copolycondensate of 1), the non-crosslinked amide-based elastomer includes, for example, polyether diol, lactam (or α, ω-amino acid), and chain limiter diacid in the presence of a small amount of water. It can be obtained by reaction. The non-crosslinked amide-based elastomer may have polyether blocks and polyamide blocks of various lengths, and may be dispersed in the polymer chain by causing each component to react randomly.

  At the time of the above copolycondensation, the polyether diol block may be used as it is, or may be used by copolymerizing a hydroxyl group of the polyether diol block and a polyamide block having a carboxy terminal group. It may be used by condensing with a polyamide block having a carboxy end group after a hydroxyl group of the block is aminated and converted to polyether diamine. It is also possible to obtain a polymer including randomly dispersed polyamide blocks and polyether blocks by mixing polyether diol blocks with a polyamide precursor and a chain limiter and copolycondensation.

  In addition to non-crosslinked amide elastomer, amide resin, polyether resin, crosslinked amide elastomer, styrene elastomer, olefin elastomer, ester elastomer, etc., as long as the effect of the present invention is not impaired. Other resins may be included. The other resin may be a known thermoplastic resin or thermosetting resin.

PTFE:
The PTFE blended in the resin composition is preferably fibrous. However, in PTFE, the fibers are in close contact with each other. In the foam, it is preferable that the inter-fiber distance of PTFE before blending with the resin composition is widened.

  It is preferable that PTFE is not included in the foam in the foam. The lower the content of the massive PTFE, the higher the cushioning property can be uniformly exhibited throughout the foam. From the viewpoint of effectively increasing the cushioning property, the short diameter of all fibrous PTFE (the short diameter of PTFE having the largest short diameter among all PTFE contained in the foam) is preferably 10 μm or less, more preferably 9 μm. Hereinafter, it is more preferably 8 μm or less.

  The contents of the thermoplastic elastomer and PTFE in the resin composition are substantially equal to the contents of the thermoplastic elastomer and PTFE in the foam. From the viewpoint of effectively increasing the cushioning property, the ratio of the thermoplastic elastomer content in the resin composition to the PTFE content in the resin composition (thermoplastic elastomer content / PTFE content) is preferably Is 9 or more, more preferably 15 or more, preferably 999 or less, more preferably 500 or less. From the viewpoint of effectively increasing the cushioning property, the ratio of the content of the thermoplastic elastomer in the foam to the content of PTFE in the foam (thermoplastic elastomer content / PTFE content) is preferably 9 As mentioned above, More preferably, it is 15 or more, Preferably it is 999 or less, More preferably, it is 500 or less.

Polyolefin resin:
The polyolefin resin is not particularly limited, and examples thereof include a polyethylene resin and a polypropylene resin. From the viewpoint of effectively increasing breakage prevention and flexibility, a polyethylene resin, a polypropylene resin, or a polystyrene resin is preferable.

  The polypropylene resin is obtained by polymerizing a propylene monomer. (A) The polypropylene resin is a polymer. The polymer includes a copolymer. Examples of the polypropylene-based resin include a homopolymer of a propylene monomer and a copolymer of polymerization components mainly composed of the propylene monomer. In a copolymer of a polymerization component mainly composed of a propylene monomer, the content of the propylene monomer is 50% by weight or more, preferably 80% by weight or more, more preferably 90% by weight in 100% by weight of the polymerizable polymerization component. % Or more. The form of copolymerization may be random or block.

  Specific examples of the polypropylene resin include a propylene homopolymer, a propylene random polymer, and a propylene block polymer. The polypropylene resin is preferably a homopolymer of a propylene monomer, and is preferably a propylene homopolymer.

  The polyethylene resin is obtained by polymerizing an ethylene monomer. The polyethylene resin is a polymer. The polymer includes a copolymer. Examples of the polyethylene resin include a homopolymer of ethylene monomer and a copolymer of polymerization components mainly composed of ethylene monomer. In the copolymer of the polymerization component mainly composed of ethylene monomer, the content of ethylene monomer is 50% by weight or more, preferably 80% by weight or more, more preferably 90% by weight in 100% by weight of the polymerizable polymerization component. % Or more. The form of copolymerization may be random or block.

  Specific examples of the polyethylene resin include ethylene homopolymer, ethylene random polymer, and ethylene block polymer. The polyethylene resin is preferably a homopolymer of ethylene monomer, and is preferably an ethylene homopolymer.

  From the viewpoint of effectively increasing the cushioning property, the melt flow rate (MFR) of the polyolefin resin in the foam is preferably 0.1 g / 10 min or more under the conditions of a test temperature of 230 ° C. and a load of 21.18 N. More preferably, it is 0.2 g / 10 min or more, preferably 7 g / 10 min or less, more preferably 5 g / 10 min or less.

  The contents of the thermoplastic elastomer and the polyolefin resin in the resin composition are substantially equal to the contents of the thermoplastic elastomer and the polyolefin resin in the foam. From the viewpoint of effectively increasing the cushioning property, the ratio of the thermoplastic elastomer content in the resin composition to the polyolefin resin content in the resin composition (thermoplastic elastomer content / polyolefin resin content) ) Is preferably 1.5 or more, more preferably 2 or more, preferably 19 or less, more preferably 15 or less. From the viewpoint of effectively increasing the cushioning property, the ratio of the thermoplastic elastomer content in the foam to the polyolefin resin content in the foam (thermoplastic elastomer content / polyolefin resin content) is , Preferably 1.5 or more, more preferably 2 or more, preferably 19 or less, more preferably 15 or less.

Other ingredients:
Various additives may be used as necessary as long as the effects of the present invention are not impaired. Additives include surfactants, dispersants, weathering stabilizers, light stabilizers, pigments, dyes, flame retardants, plasticizers, lubricants, UV absorbers, antioxidants, fillers, reinforcing agents and antistatic agents. Etc. By using the surfactant, the slipperiness and the anti-blocking property are further enhanced. By using the dispersant, the dispersibility of each compounding component is increased. Examples of the dispersant include higher fatty acids, higher fatty acid esters and higher fatty acid amides.

(Method for producing foam)
A method for producing a thermoplastic elastomer foam (foam) according to the present invention comprises a melting step for melting a resin composition, and a foaming step for foaming the melted resin composition to obtain a thermoplastic elastomer foam. . In the molten resin composition, PTFE does not have to be melted. The resin used as a matrix should just melt | dissolve in the molten resin composition.

  As a method for dispersing PTFE in the resin composition, a twin screw extruder or a single screw extruder (including a tandem extruder in which two extruders are connected) can be used. Also, as a method of dispersing PTFE in the resin composition, the resin composition and PTFE are melt-kneaded with a twin screw extruder or a single screw extruder to produce a compound, which is then placed in the extruder and gas is injected. Examples thereof include a method of obtaining a foam, and a method of obtaining a foam by injecting a gas while melting and mixing the resin composition and PTFE with an extruder. Any method of obtaining these foams may be adopted.

(Use of foam)
The foam can be used for various applications that require cushioning. Moreover, when a foam is particle | grains, it can shape | mold and can be used as a molded object.

  The present invention will be described in more detail with reference to the following examples. The present invention is not limited only to the following examples.

  The following materials were prepared.

Thermoplastic Elastomer (Arkema Amide Elastomer, “Pebax5533”, MFR: 7 g / 10 min (235 ° C.))
Thermoplastic elastomer (Akema amide elastomer, “Pebax 7233”, MFR: 4 g / 10 min (235 ° C.))
Thermoplastic elastomer ("Hytrel 5577" manufactured by Toray DuPont, MFR: 1.8 g / 10 min (230 ° C))
Thermoplastic elastomer (“R110E” manufactured by Prime Polymer, MFR: 1.5 g / 10 min (230 ° C.))
Polyolefin resin ("WB140" manufactured by Borealis, MFR: 2.1 g / 10 min (230 ° C))

Example 1
A mixed resin was prepared by adding 5 parts by weight of polytetrafluoroethylene powder to 95 parts by weight of a thermoplastic elastomer (amide-based elastomer “Pebax 5533” manufactured by Arkema Co., Ltd., MFR: 7 g / 10 min).

  The mixed resin was supplied to a twin screw extruder having a diameter of 30 mm manufactured by Plastic Engineering Laboratory Co., Ltd. and melt kneaded. The temperature of the extruder was set to 200 ° C., and extrusion was performed with a strand from the tip of the twin screw extruder under the conditions of a screw rotation speed of 70 rpm, a discharge rate of 2 kg / h, and a molten resin temperature of 200 ° C.

  The extruded strand was passed through an aqueous layer having a water temperature of 30 ° C., sufficiently cooled, and then cut with a pelletizer to produce pellets. In the obtained pellet, there was no cut defect and it was favorable.

  Next, a tandem type extruder in which a second extruder having a diameter of 65 mm was connected to the tip of a first extruder having a diameter of 50 mm was prepared. The obtained mini-pellet was supplied to the first extruder of the tandem type extruder and melt kneaded. After 3.0 parts by weight of butane gas is injected as a foaming agent from the middle of the first extruder, and the molten pellet and butane gas are uniformly mixed and kneaded, the molten resin composition containing the foaming agent is fed into the second extruder. Continuously fed.

  Thereafter, from a die (φ1.0 mm × 20 holes, land length 3 mm) attached to the tip of the second extruder, the discharge amount is 30 kg / hour, the molten resin temperature is 200 ° C., and the tip pressure of the second extruder is 12 MPa. The resin was extruded, and the foamed resin immediately after extrusion was cut under water at a water temperature of 50 ° C., a cutter rotation speed of 3000 rpm, and a cutter pressure of 3 bar to obtain foamed particles (thermoplastic elastomer foam).

  The obtained expanded particles were good with no cut defects, no inclusion or shrinkage.

(Examples 2 to 10 and Comparative Examples 1 to 5)
In the same manner as in Example 1 except that the thermoplastic elastomer, polyolefin resin, polytetrafluoroethylene (PTFE) type and blending amount, and the expansion ratio were set as shown in Table 1 below, expanded particles ( A thermoplastic elastomer foam) was obtained.

  The foamed particles obtained in Examples 2 to 10 were good with no cut defects.

  In Comparative Examples 4 and 5, the amount of polytetrafluoroethylene (PTEF) added was large, and when melt-kneaded, it was agglomerated and could not be uniformly dispersed, and the resin tension could not be modified. Furthermore, since polytetrafluoroethylene was not uniformly dispersed, variations in MFR and melt tension occurred between the pellets. The pellets produced a product with a large amount of polytetrafluoroethylene and a product with a small amount. Therefore, the resin characteristics were not stabilized in the extruder, and a foam could not be obtained.

(Evaluation)
(1) Average cell diameter in foam (foamed particles) The average cell diameter of the foamed particles was measured by the following test method. The expanded particles are cut so as to be approximately bisected, and the cut surface is photographed with a scanning electron microscope (S-3400N or SU1510, manufactured by Hitachi High-Technologies Corporation) at a magnification of 20 to 100 times. The magnification to enlarge was adjusted suitably according to the bubble size.

  The photographed image was printed on A4 paper, and the average chord length (t) of bubbles was calculated from the number of bubbles on an arbitrary straight line (length 60 mm) in the vertical and horizontal directions by the following formula. When the number of bubbles for 60 mm length could not be counted, the number of bubbles for 30 mm or 20 mm was counted and converted to the number of bubbles for 60 mm. However, as much as possible, any straight line was made so that the bubbles did not touch only at the contact points (included in the number of bubbles if contacted). The measurement was performed at 6 locations in the vertical and horizontal directions.

  Average chord length t (mm) = 60 / (number of bubbles × photo magnification)

  And the bubble diameter in each direction was computed by following Formula.

  D (mm) = t / 0.616

  Furthermore, the square root of the product was taken as the average bubble diameter.

  Average bubble diameter (μm) = 1000 × (D length × D width) 1/2

(2) Average short diameter of PTFE in foam (particles) 500 to 5000 using a scanning electron microscope (S-3400N or SU1510 manufactured by Hitachi High-Technologies Corp.) in the same manner as the average bubble diameter in the foam. The picture was taken at double magnification. The captured image was displayed on a personal computer and measured using the included software.

(3) Open cell ratio in foam (foamed particles) The open cell ratio of the expanded particles was measured by the following method.

A sample cup of an air comparison hydrometer (“Air Comparison Hydrometer 1000” manufactured by Tokyo Science Co., Ltd.) was prepared. The total weight A (g) of the expanded particles in an amount satisfying about 80% of the sample cup was measured. The volume B (cm ³ ) of the whole expanded particle was measured by a 1-1 / 2-1 atmospheric pressure method using an air comparative hydrometer. The air comparison type hydrometer was corrected with a standard sphere (large 28.9 cc, small 8.5 cc). Subsequently, a container made of a wire mesh was prepared in which foamed particles put in a state where the lid was closed did not spill. This wire mesh container was immersed in water, and the weight C (g) of the wire mesh container in the state immersed in water was measured. Next, after all the foamed particles were put in the wire mesh container, the wire mesh container was immersed in water, and the container was shaken several times to remove bubbles adhering to the container and the foam particles. . Then, the weight D (g) which combined the container made from a metal mesh in the state immersed in water and the whole quantity of the foaming particle put into this container made from a metal mesh was measured. As an electronic balance used for measuring the weight in water, “Electronic Balance HB3000” manufactured by Daiwa Seisen Co., Ltd. was used. And the apparent volume E (cm < ³ >) of the expanded particle was computed by the following formula. Based on the apparent volume E and the volume B (cm ³ ) of the entire foamed particle, the open cell ratio of the foamed particle can be calculated by the following formula. The volume of 1 g of water was 1 cm ³ and the number of tests was 5. The sample was adjusted for 16 hours in a JIS K7100-1999 symbol 23/50, second grade environment, and then measured in a JIS K7100-1999 symbol 23/50, second grade environment.

  E = A + (CD)

  Open cell ratio (%) = 100 × (EB) / E

(4) Cushioning property (rebound) of foam
The obtained expanded particles were allowed to stand at room temperature (23 ° C.) for 1 day and then sealed in a pressure vessel. After the inside of the pressure vessel was replaced with nitrogen gas, the nitrogen gas was reduced to an impregnation pressure (gauge pressure) of 1.0 MPa. Press-fitted. It left still in a 20 degreeC environment, and pressure curing was implemented for 8 hours. The obtained foamed particles are filled into a molding die of 23 mm × 300 mm × 400 mm, heated with 0.27 MPa of water vapor for 40 seconds, and then the maximum surface pressure of the foamed molded product is reduced to 0.01 MPa. The foamed molded product was obtained by cooling to 1.

  The cushioning property was measured according to the test method of JIS K6400-3: 2011. Specifically, using a foam rebound resilience tester FR-2 type manufactured by Kobunshi Keiki Co., Ltd., a steel ball having a diameter of 5/8 inch and a mass of 16.3 g is dropped from a height of 500 mm onto a foamed molded product. , Read the height of the rebound maximum. The same operation was repeated 5 times in total, the average value was adopted, and the resilience was calculated from the following formula.

  Rebound (%) = 100 × height when reaching the maximum rebound (mm) / 500 (mm)

(5) Melt flow rate (MFR) of resin composition
The melt mass flow rate (MFR) is a semi-auto melt indexer 2A manufactured by Toyo Seiki Seisakusho Co., Ltd. B) Measured by a method of measuring the time for the piston to move a predetermined distance described in the B method. The measurement conditions were 3 to 8 g of sample, preheating 270 seconds, load hold 30 seconds, test temperature 180 ° C., test load 21.18 N, piston moving distance (interval) 4 mm or 25 mm. The number of test of the sample was three times, and the average of the three times was taken as the value of melt mass flow rate (g / 10 min).

(6) Melt tension (MT) of resin composition
The melt tension of the resin composition was measured using a twin-bore capillary-rheometer-Rheological 5000T manufactured by Chiast, Italy. A measurement sample resin was filled in a 15 mm diameter barrel heated to a test temperature of 200 ° C., and then preheated for 5 minutes. After that, the capillary die (2.095 mm in diameter, length 8 mm, inflow angle 90 degrees (conical)) of the above measuring device is held while the piston descending speed (0.07730 mm / s) is kept constant and extruded into a string shape. The passed string is passed through a tension detecting pulley located 27 cm below the capillary die, and then the winding speed is set at an initial speed of 3.94388 mm / s and an acceleration of 12 mm / s ² using a winding roll. Winding while gradually increasing, the average of the maximum value and the minimum value just before the point where the string-like material was cut was taken as the melt tension of the resin composition.

  Details and results are shown in Table 1 below.

  FIG. 1 shows a cross-sectional SEM (scanning electron microscope) image of the thermoplastic elastomer foam according to an embodiment of the present invention.

Claims (13)

A foam of a resin composition comprising a thermoplastic elastomer and polytetrafluoroethylene,
The continuous phase of the thermoplastic elastomer has a structure in which the polytetrafluoroethylene is contained in a fibrous form,
Has an expansion ratio of 2 times or more and 20 times or less,
The average cell diameter 10μm or more in the center, have a bubble is 200μm or less,
A thermoplastic elastomer foam, which is a particle having an aspect ratio of 10 or less .   The thermoplastic elastomer foam according to claim 1, wherein an average minor axis of the polytetrafluoroethylene in the foam is 5 µm or less.   The thermoplastic elastomer foam according to claim 1 or 2, wherein a short diameter of all of the polytetrafluoroethylene in the foam is 10 µm or less. Have air bubbles on the surface,
The thermoplasticity according to any one of claims 1 to 3, wherein an absolute value of a difference between an average cell diameter at the center of the foam and an average cell diameter at the surface of the foam is 100 µm or less. Elastomer foam.   The ratio of the content of the thermoplastic elastomer in the foam to the content of the polytetrafluoroethylene in the foam is 9 or more and 999 or less, according to any one of claims 1 to 4. Thermoplastic elastomer foam.   The thermoplastic elastomer foam according to any one of claims 1 to 5, which has an open cell ratio of 50% or more and 95% or less. The thermoplastic elastomer foam according to any one of claims 1 to 6 , wherein the thermoplastic elastomer is an amide elastomer or an olefin elastomer. The thermoplastic elastomer foam according to any one of claims 1 to 7 , which is a non-crosslinked foam. The thermoplastic elastomer foam according to any one of claims 1 to 8 , wherein a melt flow rate of the resin composition is 0.5 g / 10 min or more and 4.0 g / 10 min or less. The thermoplastic elastomer foam according to any one of claims 1 to 9 , wherein the resin composition contains a polyolefin resin. The thermoplastic elastomer foam according to claim 10 , wherein a ratio of the content of the thermoplastic elastomer in the foam to the content of the polyolefin resin in the foam is 1.5 or more and 19 or less. . A method according to claim 1 to 11 Thermoplastic elastomer foam according to any one of,
A melting step for melting the resin composition;
A foaming step of foaming the melted resin composition to obtain a thermoplastic elastomer foam. A method for producing a thermoplastic elastomer foam. The method for producing a thermoplastic elastomer foam according to claim 12 , wherein, in the melting step, the polytetrafluoroethylene in the resin composition is sheared in the molten resin composition.