CN116981723A

CN116981723A - Resin foam and foam member

Info

Publication number: CN116981723A
Application number: CN202280020186.XA
Authority: CN
Inventors: 儿玉清明; 伊关亮; 佐佐木彰吾
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-03-31
Filing date: 2022-03-30
Publication date: 2023-10-31
Also published as: JPWO2022210957A1; JPWO2022210956A1; WO2022210957A1; KR20230164049A; CN117062861A; KR20230164050A; WO2022210956A1

Abstract

The invention provides a resin foam with low dielectric property and excellent punching processability. The resin foam of the present invention has a bubble structure, and the apparent density of the resin foam is less than 0.4g/cm ³ In applying 1000g/cm to the resin foam ² The thickness recovery rate after 120 seconds is 80% or more in the loaded state. In one embodiment, the resin foam has a bubble count density of 30 bubbles/mm ² The above. In one embodiment, the resin foam has an average cell diameter of 10 μm to 200. Mu.m.

Description

Resin foam and foam member

Technical Field

The present invention relates to a resin foam and a foam member.

Background

For the purpose of protecting the screen of an electronic device, protecting a substrate, protecting an electronic component, and the like, a foam is often used as a buffer material. In recent years, in response to the trend toward thinning of electronic devices, there is a demand for narrowing the gap of a portion where a buffer material is disposed. Further, with miniaturization and multifunction of electronic devices, there is a trend toward miniaturization of electronic components to be used, and there is a need for smaller cushioning materials (foams). In addition, the above-mentioned cushioning material (foam) is sometimes required to have low dielectric properties in order to prevent communication failure in communication equipment, prevent electrical failure in electronic equipment, and the like.

In general, when a foam of a desired shape is obtained, a foam roll is punched. In the blanking process, a high pressure is applied to the foam by using a die, thereby obtaining a foam having a desired shape. In the conventional foam, the thickness reduced by punching is not sufficiently recovered after the above-described processing, and as a result, there is a case where the thickness is changed. This phenomenon is particularly problematic when applied to a portion having a narrow gap, and when punched out in a shape having a narrow width (for example, a width of 1 mm) such as a rim.

Patent document 1 discloses a resin foam having excellent impact absorbability. However, there is no disclosure or teaching in this document regarding workability at the time of blanking (blanking workability). Patent document 2 discloses a resin foam having a thin layer and excellent impact absorbability. However, this document does not disclose recovery and crushing after punching. Further, a resin foam having both low dielectric properties and punching workability is not realized.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open publication No. 2017-186504

Patent document 2: japanese patent laid-open No. 2015-034299

Patent document 3: japanese patent laid-open publication 2016-69493

Disclosure of Invention

Problems to be solved by the invention

The problem of the present invention is to provide a resin foam having excellent low dielectric properties and excellent punching workability.

Solution for solving the problem

The resin foam of the present invention has a bubble structure, and the apparent density of the resin foam is less than 0.4g/cm ³ In applying 1000g/cm to the resin foam ² The thickness recovery rate after 120 seconds is 80% or more in the loaded state.

In one embodiment, the resin foam has a bubble count density of 30 bubbles/mm ² The above.

In one embodiment, the resin foam has an average cell diameter of 10 μm to 200. Mu.m.

In one embodiment, the coefficient of variation of the cell diameter of the resin foam is 0.5 or less.

In one embodiment, the resin foam has a bubble ratio of 30% or more.

In one embodiment, the resin foam has a tensile modulus of 1.5MPa or more at 25 ℃.

In one embodiment, the resin foam has a 50% compression load of 20N/cm ² The following is given.

In one embodiment, the resin foam includes a polyolefin resin.

In one embodiment, the polyolefin-based resin is a mixture of polyolefin and polyolefin-based elastomer other than polyolefin-based elastomer.

In one embodiment, the resin foam has a heat-fusible layer on one or both surfaces.

According to another aspect of the present invention, there is provided a foaming member. The foam member has a resin foam layer and an adhesive layer disposed on at least one side of the resin foam layer, and the resin foam layer is the resin foam.

Effects of the invention

According to the present invention, there can be provided a resin foam which has little thickness change before and after the punching process and which is excellent in punching workability. The resin foam of the present invention is also excellent in having low dielectric properties.

Drawings

Fig. 1 is a schematic cross-sectional view of a foam member according to an embodiment of the present invention.

Detailed Description

A. Resin foam

The resin foam of the present invention has a bubble structure (cell structure). As the bubble structure (cell structure), there can be mentioned: an independent bubble structure, an open bubble structure, a semi-continuous semi-independent bubble structure (a bubble structure in which an independent bubble structure and an open bubble structure are mixed) and the like. Preferably, the foam structure of the resin foam is a semi-continuous semi-independent foam structure. Typically, the resin foam of the present invention can be obtained by foaming a resin composition. The resin composition contains at least a resin constituting the resin foam.

The apparent density of the resin foam is less than 0.4g/cm ³ . In addition, 1000g/cm of the resin foam was applied ² The thickness recovery rate (hereinafter also referred to as the instantaneous recovery rate) after 120 seconds of maintenance in the loaded state is 80% or more. According to the present invention, a resin foam excellent in punching workability can be obtained without inhibiting low dielectric properties by providing a proper void and having excellent low dielectric properties and setting the instantaneous recovery rate to a specific range. More specifically, the resin foam has a small shape change such as a thickness change even in punching, and exhibits a preferable behavior of recovering in a short time even when the thickness is temporarily reduced by punching, and is excellent in punching property.

The apparent density of the resin foam is preferably 0.4g/cm ³ Hereinafter, more preferably 0.01g/cm ³ ～0.3g/cm ³ More preferably 0.02g/cm ³ ～0.2g/cm ³ Further preferably 0.03g/cm ³ ～0.1g/cm ³ Particularly preferably 0.03g/cm ³ ～0.05g/cm ³ . In such a range, the above-described effects become remarkable. Further, when the apparent density is within the above range, a resin foam excellent in flexibility and stress dispersibility can be obtained. On the other hand, a resin foam having an excessively high apparent density may deform the applied portion by pressing. Such a problem becomes remarkable particularly in the case of being applied to a place where the gap is narrow. The foamability can be judged from the apparent density. The method for measuring the apparent density will be described later.

Applying 1000g/cm to the resin foam ² The thickness recovery rate (hereinafter also referred to as instantaneous recovery rate) after 120 seconds of maintenance in a loaded state is preferably 80% or more, more preferably 85% or more, still more preferably 87% or more, and particularly preferably 90% or more. In such a range, the above effect becomes remarkable. The higher the thickness recovery ratio, the better, and the upper limit thereof is, for example, 99% (preferably 100%). The method for measuring the thickness recovery rate will be described later.

In one embodiment, the resin foam as described above can be formed by using, as the resin constituting the resin foam, a resin having a melting point (melting point of the resin constituting the resin foam) +a die swell ratio at 20 ℃ of 1.4 or less. That is, in one embodiment, the die swell ratio of the resin forming the resin foam is 1.4 or less at the melting point +20 ℃ before foaming. When a resin having a die swell ratio in the above range is used, shrinkage at the time of forming a resin foam body, which may contain cells having a small cell size, can be prevented to form a resin foam body having a relatively large thickness. The die swell ratio of the resin forming the resin foam at the melting point +20 ℃ before foaming is preferably 1.2 or less, more preferably 1.1 or less. The lower limit of the die swell ratio of the resin (before foaming) is, for example, 1.05 (preferably 1.02, more preferably 1.01). The die swell ratio at the melting point +20℃ofthe resin constituting the resin foam (i.e., the resin after foaming) is preferably 1.4 or less, more preferably 1.2 or less, and still more preferably 1.1 or less. The lower limit of the die swell ratio of the resin (after foaming) is, for example, 1.05 (preferably 1.02, more preferably 1.01). In the present specification, the die swell ratio is a value obtained by dividing the diameter of the resin discharged from the die when the resin in a molten state is discharged from the die by the diameter of the die. The die swell ratio was calculated from the equation of the diameter (mm) of the molded article/die diameter (mm) by extruding a resin in a molten state at a melting point of +20℃, at a shear rate of 20mm/s, using a die having a length of 10mm and a diameter of 1mm phi. The melting point of the resin was measured by Differential Scanning Calorimetry (DSC) to obtain the peak top temperature of the endothermic peak. Differential Scanning Calorimetry (DSC) measurements were performed using a differential scanning calorimeter (e.g., trade name "Q-2000", TA Instruments) at a sample weight of 3mg and a heating rate of 10℃per minute. When two or more peaks are present, the peak top temperature on the high temperature side is set to the melting point.

In one embodiment, the resin foam described above can be formed by using a resin having a melting point (melting point of resin constituting the resin foam) +a shear viscosity of 3000pa·s or less at 20 ℃. That is, in one embodiment, the resin forming the resin foam has a shear viscosity of 3000pa·s or less at a melting point +20 ℃ before foaming. When a resin having a shear viscosity in the above range is used, the gas used for forming the bubble structure can be preferably dispersed in the formation of the resin foam, and as a result, a resin foam having a small bubble size can be obtained. The shear viscosity of the resin forming the resin foam is preferably 2500pa·s or less, more preferably 2100pa·s or less, further preferably 2000pa·s or less, particularly preferably 1900pa·s or less at the melting point +20 ℃ before foaming. The lower limit of the shear viscosity of the resin (before foaming) is, for example, 500pa·s (preferably 700pa·s, more preferably 1000pa·s). The shear viscosity at the melting point +20℃ofthe resin constituting the resin foam (i.e., the resin after foaming) is preferably 3000pa·s or less, more preferably 2500pa·s or less, still more preferably 2100pa·s or less, particularly preferably 2000pa·s or less, and most preferably 1900pa·s or less. The lower limit of the shear viscosity of the resin (after foaming) is, for example, 500pa·s (preferably 700pa·s, more preferably 1000pa·s). In the present specification, the shear viscosity can be measured by extruding a resin in a molten state at a melting point of +20℃, using a die having a length of 10mm and a bore of 1mm phi at a shear rate of 20 mm/s.

The thickness of the resin foam is preferably 100 μm to 8000. Mu.m, more preferably 200 μm to 5000. Mu.m, still more preferably 300 μm to 4000. Mu.m, still more preferably 400 μm to 3000. Mu.m, still more preferably 500 μm to 2000. Mu.m. When the amount is within this range, a fine and uniform bubble structure can be formed, which is advantageous in that excellent punching workability and impact absorbability can be exhibited.

The average cell diameter (average cell diameter) of the resin foam is preferably 10 μm to 200. Mu.m, more preferably 20 μm to 180. Mu.m, still more preferably 40 μm to 150. Mu.m, particularly preferably 40 μm to 80. Mu.m. When the amount is in this range, a resin foam having more excellent flexibility and stress dispersibility can be obtained. Further, a resin foam excellent in compression recovery, punching workability and resistance to repeated impact can be obtained. In one embodiment, the average cell diameter (average cell diameter) of the resin foam is 90 μm or less (preferably 80 μm or less). When the amount is within this range, a resin foam having a low dielectric constant and excellent punching workability can be obtained. The method for measuring the average bubble diameter will be described later.

The coefficient of variation of the cell diameter (cell diameter) of the resin foam is preferably 0.5 or less, more preferably 0.4 or less, further preferably 0.3 or less, further preferably 0.25 or less, and particularly preferably 0.2 or less. If the air bubbles are deformed in such a range, the variation in deformation of the air bubbles is small when the compression force is applied by punching or the like. In such a resin foam, for example, when punching is performed, a processed product (cut product) having excellent thickness accuracy can be obtained. When the coefficient of variation in the bubble diameter is within the above range, deformation due to impact becomes uniform, local stress load can be prevented, and a resin foam excellent in stress dispersibility and particularly excellent in impact resistance can be obtained. The smaller the coefficient of variation, the more preferable the lower limit thereof is, for example, 0.15 (preferably 0.1, more preferably 0.01). The method for measuring the coefficient of variation in the bubble diameter will be described later.

The bubble ratio (cell ratio) of the resin foam is preferably 30% or more, more preferably 50% or more, and further preferably 80% or more. In such a range, a resin foam having appropriate flexibility can be obtained. Such a resin foam is excellent in punching workability, and can prevent cutting residues during punching. The upper limit of the bubble rate is, for example, 99% or less. The method for measuring the bubble fraction will be described later.

The thickness of the cell walls (cell walls) of the resin foam is preferably 0.1 μm to 10. Mu.m, more preferably 0.3 μm to 8. Mu.m, still more preferably 0.5 μm to 5. Mu.m, particularly preferably 0.7 μm to 4. Mu.m, and most preferably 1 μm to 3. Mu.m. In such a range, a resin foam having appropriate strength can be obtained. Such a resin foam is excellent in punching workability, and can prevent breakage, dust generation, cutting residue, and the like during punching. Further, when the thickness of the cell wall is within the above range, a resin foam having more excellent flexibility and stress dispersibility can be obtained. In one embodiment, the thickness of the cell walls (cell walls) of the resin foam is 5 μm or less. In such a range, the above-described effects become remarkable. The thickness of the cell wall can be measured by introducing an enlarged image of the cell portion of the resin foam and analyzing the image using analysis software of the same meter.

In the case where the foam structure of the resin foam is a semi-continuous semi-independent foam structure, the proportion of independent foam structure therein is preferably 40% or less, more preferably 30% or less. In the present specification, the proportion of the independent cell structure of the resin foam can be determined, for example, as follows: the object to be measured was immersed in water at a temperature of 23℃and a humidity of 50%, the subsequent mass was measured, and the object was dried sufficiently in an oven at 80℃to measure the mass again. Further, since water is retained in the form of continuous bubbles, the mass of the continuous bubbles can be measured and obtained. The proportion of open cells in the resin foam is preferably more than 60%, more preferably more than 70%. In such a range, a resin foam having a low dielectric constant can be obtained. The proportion of open cells can also be determined as follows: the object to be measured was immersed in water at a temperature of 23℃and a humidity of 50%, the subsequent mass was measured, and the object was dried sufficiently in an oven at 80℃to measure the mass again.

The number density of bubbles of the resin foam is preferably 30 per mm ² The above is more preferably 50 pieces/mm ² The above is more preferably 65 pieces/mm ² The above is more preferably 80 pieces/mm ² The above is more preferably 90 pieces/mm ² The above is more preferably 100 pieces/mm ² The above is particularly preferably 110 pieces/mm ² The above. When the amount is within this range, a resin foam having a preferable flexibility, a low dielectric constant and excellent punching workability can be obtained. Further, the higher the cell number density is, the more energy is easily accumulated during compression, and a resin foam excellent in compression recovery force can be obtained. The upper limit of the cell number density of the resin foam is preferably 400 cells/mm ² More preferably 200 pieces/mm ² More preferably 150 pieces/mm ² . The number density of cells in the resin foam is the number density in the cross section of cells observed in a randomly selected cross section of the resin foam, and can be obtained by analyzing the image of the cross section of the resin foam.

The resin foam preferably has a 50% compression load of 20N/cm ² Hereinafter, more preferably 10N/cm ² Hereinafter, it is more preferably 8N/cm ² Hereinafter, it is more preferably 5N/cm ² Hereinafter, 3N/cm is particularly preferred ² The following is given. When the amount is within this range, a resin foam having preferable flexibility and excellent punching workability can be obtained. The lower limit of the 50% compression load of the resin foam is, for example, 0.5N/cm ² . The 50% compression load of the resin foam means that the stress (N) when compressed to a compression ratio of 50% is converted into a value of the compression ratio per unit area (1 cm ² ) Is a value of (2).

The tensile modulus of the resin foam at 25℃is preferably 1.5MPa or more, more preferably 1.6MPa to 2.5MPa, and still more preferably 1.8MPa to 2.0MPa. In such a range, the shape can be maintained even after punching by having a predetermined strength. The tensile modulus was obtained from a tensile strain-tensile strength curve obtained by fixing a sample (size: 10 mm. Times.80 mm) at a chuck pitch of 40mm and performing a tensile test at a tensile speed of 500mm/min, and from the slope of a straight line connecting the origin of the curve and the tensile strength at a tensile strain of 10%.

The resin foam preferably has a relative dielectric constant of 3 or less, more preferably 2 or less, still more preferably 1.5 or less, and particularly preferably 1.2 or less. According to the present invention, a resin foam having a low relative dielectric constant and suitable for communication equipment, electronic equipment, and the like can be obtained. The lower limit of the relative dielectric constant of the resin foam is, for example, 1.01. The method for measuring the relative permittivity will be described later.

The impact absorbability of the resin foam is preferably 20% or more, more preferably 27% or more, further preferably 30% or more, particularly preferably 35% or more, and most preferably 40% or more. Impact absorbency can be measured as follows.

A resin foam, a double-sided tape (model No.5603W, manufactured by Nitto electric Co., ltd.), and a PET film (model DIAFOIL MRF75, manufactured by Mitsubishi resin) were sequentially disposed on the impact sensor to form a test body. 66g of iron balls were dropped from a height of 50cm above the PET film to the test piece, and the impact force F1 was measured.

The iron ball was directly dropped onto the impact force sensor as described above, and the blank impact force F0 was measured.

Impact absorbability (%) was calculated from F1 and F0 by the formula (F0-F1)/F0X 100.

The resin foam may be of any suitable shape according to the purpose. As such a shape, a sheet shape is typical.

The resin foam may have a heat-fusible layer on one or both surfaces. The resin foam having the heat-melted layer can be obtained, for example, by rolling a resin foam (or a precursor (foam structure) of the resin foam) using a pair of heated rolls heated to a temperature equal to or higher than the melting temperature of the resin composition constituting the resin foam.

The resin foam may be formed by any suitable method within a range that does not impair the effects of the present invention. As such a method, a method of foaming a resin composition containing a resin material (polymer) is typically mentioned.

A-1. Resin composition

The resin foam of the present invention can be typically obtained by foaming a resin composition. The resin composition comprises any suitable resin material (polymer). In one embodiment, a non-crosslinkable resin composition is used. The non-crosslinkable resin composition can be suitably used in a method for forming a resin foam described later.

Examples of the polymer include: acrylic resins, silicone resins, urethane resins, polyolefin resins, ester resins, rubber resins, and the like. The above polymers may be used alone or in combination of two or more.

The content of the polymer is preferably 30 to 95 parts by weight, more preferably 35 to 90 parts by weight, still more preferably 40 to 80 parts by weight, particularly preferably 40 to 60 parts by weight, based on 100 parts by weight of the resin composition. When the amount is in this range, a resin foam having more excellent flexibility and stress dispersibility can be obtained.

In one embodiment, a polyolefin resin is used as the polymer. When such a resin is used, a resin foam with a preferably adjusted dielectric constant can be obtained.

The content of the polyolefin resin is preferably 50 to 100 parts by weight, more preferably 70 to 100 parts by weight, even more preferably 90 to 100 parts by weight, particularly preferably 95 to 100 parts by weight, and most preferably 100 parts by weight, based on 100 parts by weight of the polymer.

The polyolefin-based resin is preferably at least one selected from the group consisting of polyolefin and polyolefin-based elastomer, and more preferably polyolefin and polyolefin-based elastomer are used in combination. The polyolefin and the polyolefin-based elastomer may be used alone or in combination of two or more. In the present specification, the term "polyolefin" does not include "polyolefin elastomer".

When the polyolefin and the polyolefin-based elastomer are used in combination as the polyolefin-based resin, the weight ratio of the polyolefin to the polyolefin-based elastomer (polyolefin/polyolefin-based elastomer) is preferably 1/99 to 99/1, more preferably 10/90 to 90/10, still more preferably 20/80 to 80/20, and particularly preferably 30/70 to 70/30. In one embodiment, the weight ratio of polyolefin to polyolefin-based elastomer (polyolefin/polyolefin-based elastomer) is preferably 25/75 to 75/25, more preferably 35/65 to 65/35. When the amount is within this range, the compression recovery property is excellent, and a resin foam having appropriate strength and excellent punching workability can be obtained while suppressing shape changes (particularly thickness changes) before and after punching.

As the polyolefin, any suitable polyolefin may be used within a range that does not impair the effects of the present invention. Examples of such polyolefin include: linear polyolefin, branched (branched) polyolefin, and the like. In one embodiment, a branched polyolefin is used as the polyolefin resin. In this embodiment, as the polyolefin, only a branched polyolefin may be used, or a combination of a branched polyolefin and a linear polyolefin may be used. By using a branched polyolefin, a resin foam having a small average cell diameter and excellent impact resistance can be obtained. The content ratio of the branched polyolefin is preferably 30 to 100 parts by weight, more preferably 50 to 80 parts by weight, based on 100 parts by weight of the polyolefin.

Examples of the polyolefin include: a polymer comprising structural units derived from an alpha-olefin. The polyolefin may be constituted of only structural units derived from an α -olefin, or may be constituted of structural units derived from an α -olefin and structural units derived from a monomer other than an α -olefin. In the case where the polyolefin is a copolymer, any suitable copolymerization system may be employed as the copolymerization system. Examples include: random copolymers, block copolymers, and the like.

The α -olefin which can constitute the polyolefin is preferably, for example, an α -olefin having 2 to 8 carbon atoms (preferably 2 to 6, more preferably 2 to 4) such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, or the like. The α -olefin may be one kind only, or two or more kinds.

Examples of the monomer other than α -olefin constituting polyolefin include: ethylenically unsaturated monomers such as vinyl acetate, acrylic acid esters, methacrylic acid esters, vinyl alcohol, and the like. The monomers other than the α -olefin may be one kind only or two or more kinds.

Specific examples of the polyolefin include: low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene (propylene homopolymer), copolymers of ethylene and propylene, copolymers of ethylene and an alpha-olefin other than ethylene, copolymers of propylene and an alpha-olefin other than propylene, copolymers of ethylene, propylene and an alpha-olefin other than ethylene and propylene, copolymers of propylene and an ethylenically unsaturated monomer, and the like.

In one embodiment, as the polyolefin, a polypropylene-based polymer having a structural unit derived from propylene is used. Examples of the polypropylene polymer include: polypropylene (propylene homopolymer), a copolymer of ethylene and propylene, a copolymer of propylene and an α -olefin other than propylene, and the like are preferable. The polypropylene polymer may be used alone or in combination of two or more.

From the viewpoint of further exhibiting the effects of the present invention, the Melt Flow Rate (MFR) of the polyolefin at a temperature of 230℃is preferably from 0.25g/10 min to 10g/10 min, more preferably from 0.3g/10 min to 6g/10 min, still more preferably from 0.35g/10 min to 5g/10 min, particularly preferably from 0.35g/10 min to 1g/10 min, and most preferably from 0.35g/10 min to 0.6g/10 min. In the present specification, the Melt Flow Rate (MFR) refers to an MFR measured at a temperature of 230℃under a load of 2.16kgf (21.2N) based on ISO1133 (JIS-K-7210). In one embodiment, the die swell ratio and shear viscosity of the resin are controlled by the melt flow rate of the polyolefin comprising the resin foam.

The weight average molecular weight of the polyolefin is preferably 50000 to 120000, more preferably 55000 to 110000, still more preferably 60000 to 100000. If the ratio is within such a range, the die swell ratio and the shear viscosity of the resin can be preferably adjusted. The polyolefin has a molecular weight distribution (weight average molecular weight/number average molecular weight) of preferably 7 to 10, more preferably 6 to 9. If the ratio is within such a range, the die swell ratio and the shear viscosity of the resin can be preferably adjusted.

The weight average molecular weight and the number average molecular weight can be determined by gel permeation chromatography (solvent: tetrahydrofuran, polystyrene conversion).

As the polyolefin, commercially available products can be used, and examples thereof include: "E110G" (manufactured by Premann polymers, inc.), "EA9" (manufactured by Japanese polypropylene Co., ltd.), "EA9FT" (manufactured by Japanese polypropylene Co., ltd.), "E-185G" (manufactured by Premann polymers, inc.), "WB140HMS" (manufactured by Borealis Co., ltd.), and "WB135HMS" (manufactured by Borealis Co., ltd.).

Any suitable polyolefin elastomer can be used as the polyolefin elastomer within a range that does not impair the effects of the present invention. Examples of such polyolefin elastomers include: so-called non-crosslinked thermoplastic olefin-based elastomers (TPOs) such as ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-vinyl acetate copolymers, polybutenes, polyisobutenes, chlorinated polyethylenes, elastomers obtained by physically dispersing a polyolefin component and a rubber component, and elastomers having a structure in which a polyolefin component and a rubber component are microphase separated; a dynamic cross-linked thermoplastic olefin elastomer (TPV) obtained by dynamically heat-treating a mixture containing a resin component a (olefinic resin component a) forming a matrix and a rubber component B forming domains (domains) in the presence of a cross-linking agent, and the like, the dynamic cross-linked thermoplastic olefin elastomer being a polymer having a heterogeneous system in which cross-linked rubber particles are finely dispersed as islands-in-sea structures in the resin component a as a matrix (sea phase).

The polyolefin elastomer preferably contains a rubber component. Examples of such rubber components include those described in JP-A-08-302111, JP-A-2010-241934, JP-A-2008-024838, JP-A-2000-007858, JP-A-2006-052277, JP-A-2012-072306, JP-A-2012-057068, JP-A-2010-241897, JP-A-2009-067969, and JP-A-03/002654.

The elastomer having a structure in which the polyolefin component and the olefinic rubber component are microphase separated is specifically: an elastomer formed of a polypropylene resin (PP) and an ethylene propylene rubber (EPM), an elastomer formed of a polypropylene resin (PP) and an ethylene-propylene-diene rubber (EPDM), and the like. The weight ratio of the polyolefin component to the olefin rubber component (polyolefin component/olefin rubber) is preferably 90/10 to 10/90, more preferably 80/20 to 20/80.

In general, a dynamic cross-linked thermoplastic olefin elastomer (TPV) has a higher modulus of elasticity and a lower compression set than a non-cross-linked thermoplastic olefin elastomer (TPO). This gives a resin foam having good recovery properties, and can exhibit excellent recovery properties when produced.

The dynamic cross-linked thermoplastic olefin-based elastomer (TPV) is a polymer having a heterogeneous system of sea-island structure in which cross-linked rubber particles are finely dispersed as domains (island phases) in a resin component a as a matrix (sea phase) obtained by dynamically heat-treating a mixture comprising a matrix-forming resin component a (olefinic resin component a) and a domain-forming rubber component B in the presence of a cross-linking agent as described above.

Examples of the dynamically crosslinked thermoplastic olefin-based elastomer (TPV) include: the dynamic crosslinking thermoplastic olefin-based elastomer described in Japanese patent application laid-open No. 2000-007858, japanese patent application laid-open No. 2006-052277, japanese patent application laid-open No. 2012-072306, japanese patent application laid-open No. 2012-057068, japanese patent application laid-open No. 2010-241897, japanese patent application laid-open No. 2009-067969, japanese re-Table 03/002654 and the like.

As the dynamic cross-linked thermoplastic olefin-based elastomer (TPV), commercially available products can be used, and examples thereof include: "Zeotherm" (manufactured by Japanese rayleigh Co., ltd.), "THERMORUN" (manufactured by Mitsubishi chemical Co., ltd.), "Sarlink3245D" (manufactured by Toyo Kagaku Co., ltd.).

The Melt Flow Rate (MFR) of the polyolefin elastomer at a temperature of 230℃is preferably 1.5g/10 min to 25g/10 min, more preferably 2g/10 min to 20g/10 min, still more preferably 2g/10 min to 15g/10 min. In one embodiment, the die swell ratio and shear viscosity of the resin are controlled in accordance with the melt flow rate of the polyolefin-based elastomer constituting the resin foam.

In one embodiment, two or more different polyolefin-based elastomers having a Melt Flow Rate (MFR) at a temperature of 230℃in the above-described range are used in combination. In this case, it is possible to use a polyolefin elastomer (low MFR polyolefin elastomer) having a Melt Flow Rate (MFR) at a temperature of 230℃of preferably 1.5g/10 min or more and less than 8g/10 min (more preferably 2g/10 min to 5g/10 min) and a polyolefin elastomer (high MFR polyolefin elastomer) having a Melt Flow Rate (MFR) at a temperature of 230℃of preferably 8g/10 min to 25g/10 min (more preferably 9g/10 min to 20g/10 min, still more preferably 10g/10 min to 20g/10 min). As a result, the effect of the present invention is remarkable, preferably by adjusting the melt tension of the polyolefin elastomer.

The blending ratio of the low MFR polyolefin elastomer to the high MFR polyolefin elastomer (low MFR polyolefin elastomer/high MFR polyolefin elastomer; weight ratio) is preferably 1.5 to 5, more preferably 1.8 to 3.5, particularly preferably 2 to 3. When the amount is within this range, the melt tension of the polyolefin elastomer is preferably adjusted, and as a result, the effect of the present invention becomes remarkable.

The polyolefin elastomer preferably has a melt tension (at 190 ℃ C., at break) of less than 10cN, more preferably from 5cN to 9.5cN. In one embodiment, the die swell ratio and shear viscosity of the resin are controlled by the melt tension of the polyolefin-based elastomer constituting the resin foam.

The JIS A hardness of the polyolefin elastomer is preferably 30 to 95 °, more preferably 35 to 90 °, even more preferably 40 to 88 °, particularly preferably 45 to 85 °, and most preferably 50 to 83 °. The JIS A hardness was measured based on ISO7619 (JIS K6253).

In one embodiment, the above resin foam (i.e., resin composition) may further comprise a filler. By containing the filler, a resin foam which requires a large amount of energy to deform the cell walls (cell walls) can be formed and exhibits excellent impact absorbability. Further, the inclusion of the filler is advantageous in that a fine and uniform bubble structure can be formed and excellent impact absorbability can be exhibited. The filler may be used alone or in combination of two or more.

The content of the filler is preferably 10 to 150 parts by weight, more preferably 30 to 130 parts by weight, and even more preferably 50 to 100 parts by weight, based on 100 parts by weight of the polymer constituting the resin foam. In such a range, the above-described effects become remarkable.

In one embodiment, the filler is an inorganic material. Examples of the material constituting the filler as an inorganic substance include: aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum nitride, aluminum borate whisker, silicon nitride, boron nitride, crystalline silica, amorphous silica, metals (e.g., gold, silver, copper, aluminum, nickel), carbon, graphite, and the like.

In one embodiment, the filler is an organic material. Examples of the material constituting the filler as the organic substance include: polymethyl methacrylate (PMMA), polyimide, polyamideimide, polyetheretherketone, polyetherimide, polyesterimide, and the like.

As the filler, a flame retardant may be used. Examples of the flame retardant include: bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, antimony-based flame retardants, and the like. From the viewpoint of safety, a halogen-free and antimony-free flame retardant is preferably used.

Examples of the halogen-free and antimony-free flame retardant include: compounds comprising aluminum, magnesium, calcium, nickel, cobalt, tin, zinc, copper, iron, titanium, boron, and the like. Examples of such a compound (inorganic compound) include: hydrated metal compounds such as aluminum hydroxide, magnesium oxide/nickel oxide hydrate, and magnesium oxide/zinc oxide hydrate.

Any suitable surface treatment may be applied to the filler. Examples of such a surface treatment include: silane coupling treatment, stearic acid treatment, and the like.

The bulk density of the filler is preferably 0.8g/cm ³ Hereinafter, more preferably 0.6g/cm ³ Hereinafter, it is more preferably 0.4g/cm ³ Hereinafter, it is particularly preferably 0.3g/cm ³ The following is given. When the content is within this range, the filler can be contained with good dispersibility, and the filler addition effect can be sufficiently exhibited even when the content of the filler is reduced. The resin foam having a small content of the filler is advantageous in terms of high foaming, softness, and excellent stress dispersibility and appearance. The lower limit of the bulk density of the filler is, for example, 0.01g/cm ³ Preferably 0.05g/cm ³ More preferably 0.1g/cm ³ 。

The number average particle diameter (primary particle diameter) of the filler is preferably 5 μm or less, more preferably 3 μm or less, and still more preferably 1 μm or less. When the amount is within this range, the filler can be contained with good dispersibility, and a uniform bubble structure can be formed. As a result, a resin foam excellent in stress dispersibility and appearance can be obtained. The lower limit of the number average particle diameter of the filler is, for example, 0.1. Mu.m. The number average particle diameter of the filler was measured by using a particle size distribution meter (MicrtracII, MICROTRAC BEL Co., ltd.) with a suspension prepared by mixing 1g of the filler with 100g of water at 25 ℃.

The specific surface area of the filler is preferably 2m ² Preferably at least/g, more preferably at least 4m ² Preferably at least/g, more preferably at least 6m ² And/g. When the amount is within this range, the filler can be contained with good dispersibility, and a uniform bubble structure can be formed. As a result, a resin foam excellent in stress dispersibility and appearance can be obtained. The upper limit of the specific surface area of the filler is, for example, 20m ² And/g. The specific surface area of the filler can be measured by the BET method, that is, by adsorbing molecules having a known adsorption occupied area to the surface of the filler at a low temperature using liquid nitrogen, and measuring the adsorption amount.

Any suitable other component may be contained in the resin composition within a range that does not impair the effects of the present invention. Such other components may be one or two or more. Examples of such other components include: rubber, resins other than polymers blended as resin materials, softeners, aliphatic compounds, antioxidants, light stabilizers, weather-proofing agents, ultraviolet absorbers, dispersants, plasticizers, carbons, antistatic agents, surfactants, crosslinking agents, thickeners, rust inhibitors, silicone compounds, tension modifiers, shrinkage-preventing agents, fluidity modifiers, gelation agents, curing agents, reinforcing agents, foaming nucleating agents, colorants (pigments, dyes, etc.), pH adjusting agents, solvents (organic solvents), thermal polymerization initiators, photopolymerization initiators, lubricants, crystallization nucleating agents, crystallization accelerators, vulcanizing agents, surface treating agents, dispersing aids, and the like. In one embodiment, a resin composition that does not contain a crosslinking agent is used.

A-2. Formation of resin foam

The resin foam of the present invention is typically obtained by foaming a resin composition. As a method of foaming (a method of forming bubbles), a method generally used in foam molding such as a physical method and a chemical method can be used. That is, the resin foam may be typically a foam (physical foam) obtained by foaming by a physical method, or may be a foam (chemical foam) obtained by foaming by a chemical method. The physical method is generally a method (mechanical foam) in which gas components such as air and nitrogen are dispersed in a polymer solution and mechanically mixed to form bubbles. Chemical methods are generally methods for obtaining a foam by forming cells using a gas generated by thermal decomposition of a foaming agent added to a polymer matrix.

The resin composition to be used for foam molding can be prepared by mixing the constituent components by any suitable mechanism such as any suitable melt-kneading apparatus, for example, an open type mixing roll, a non-open type Banbury mixer, a single-screw extruder, a twin-screw extruder, a continuous kneader, or a pressure kneader.

Embodiment 1 for forming a resin foam

As one embodiment 1 for forming a resin foam, for example, the following modes can be mentioned: the resin foam is formed through a step (step a) of mechanically foaming and foaming an emulsion resin composition (emulsion containing a resin material (polymer) or the like). Examples of the foaming device include: a high-speed shearing system device, a vibration system device, a pressurized gas discharge system device, and the like. Among these bubbling devices, a high-speed shearing type device is preferable from the viewpoints of miniaturization of bubble diameters and mass production. This embodiment 1 for forming a resin foam can be applied to any resin composition.

From the viewpoint of film forming property, the emulsion is preferably high in solid content concentration. The solid content concentration of the emulsion is preferably 30% by weight or more, more preferably 40% by weight or more, and still more preferably 50% by weight or more.

The bubbles when foaming is carried out by mechanical stirring are formed by the entry of gas (gas) into the emulsion. As the gas, any suitable gas may be used as long as it is inactive to the emulsion within a range that does not impair the effect of the present invention. Examples of such a gas include: air, nitrogen, carbon dioxide, and the like.

The resin foam of the present invention can be obtained by a step (step B) of applying the emulsion resin composition (emulsion resin composition containing air bubbles) foamed by the above method to a substrate and drying the same. Examples of the substrate include: a plastic film subjected to a peeling treatment (a polyethylene terephthalate film or the like subjected to a peeling treatment), a plastic film (a polyethylene terephthalate film or the like), and the like.

In step B, any suitable method may be used as the coating method and the drying method within a range that does not impair the effect of the present invention. The step B preferably includes: a pre-drying step (B1) of drying the bubble-containing emulsion resin composition applied to the substrate at 50 ℃ or higher and lower than 125 ℃; and a main drying step B2 of further drying at 125 ℃ to 200 ℃.

By providing the pre-drying step B1 and the main drying step B2, the air bubbles can be prevented from being integrated and broken due to a rapid temperature rise. In particular, in the case of a foam sheet having a small thickness, the bubbles are integrated and ruptured due to a rapid temperature rise, and therefore, the meaning of providing the pre-drying step B1 is great. The temperature in the pre-drying step B1 is preferably 50℃to 100 ℃. The time of the pre-drying step B1 is preferably 0.5 to 30 minutes, more preferably 1 to 15 minutes. The temperature in the main drying step B2 is preferably 130 to 180℃and more preferably 130 to 160 ℃. The time of the main drying step B2 is preferably 0.5 to 30 minutes, more preferably 1 to 15 minutes.

Embodiment 2 for forming a resin foam

As one embodiment 2 for forming a resin foam, a method of forming a foam by foaming a resin composition with a foaming agent is exemplified. As the foaming agent, a foaming agent generally used in foam molding can be used, and from the viewpoints of environmental protection and low contamination to the object to be foamed, a high-pressure inert gas is preferably used.

As the inert gas, any suitable inert gas may be used as long as it is inactive to the resin composition and can impregnate. Examples of such inert gases include: carbon dioxide, nitrogen, air, etc. These gases may also be used in combination. Among these, carbon dioxide is preferable from the viewpoints of a large impregnation amount into the resin material (polymer) and a high impregnation speed.

The inert gas is preferably in a supercritical state. That is, carbon dioxide in a supercritical state is particularly preferably used. In the supercritical state, the solubility of the inert gas in the resin composition is further increased, and when the inert gas can be mixed in at a high concentration and the pressure is rapidly reduced, the inert gas becomes at a high concentration, and therefore, the generation of the bubble nuclei becomes large, and even if the porosity is the same, the density of the bubbles that can be formed by the growth of the bubble nuclei becomes larger than in the case of other states, and therefore, fine bubbles can be obtained. The critical temperature of carbon dioxide was 31℃and the critical pressure was 7.4MPa.

Examples of the method for forming the foam by impregnating the resin composition with the high-pressure inert gas include a method comprising the following steps: a gas impregnation step of impregnating a resin composition containing a resin material (polymer) with an inert gas under high pressure; a pressure reducing step of reducing the pressure after the step to foam the resin material (polymer); and a heating step of growing bubbles by heating, if necessary. In this case, the pre-molded, unfoamed molded article may be immersed in an inert gas, or the molded article may be obtained by immersing the molten resin composition in an inert gas under pressure and then subjecting the molded article to molding under reduced pressure. These steps may be performed in any of a batch type and a continuous type. That is, the resin composition may be molded into a suitable shape such as a sheet shape in advance to form an unfoamed resin molded article, and then the unfoamed resin molded article may be impregnated with a high-pressure gas to release the pressure, thereby foaming the resin composition in a batch manner. The resin composition may be kneaded and molded under pressure together with a high-pressure gas, and the resin composition may be molded and foamed simultaneously by releasing the pressure.

An example of producing a foam in a batch manner is shown below. For example, a resin sheet for foam molding is produced by extruding a resin composition using an extruder such as a single screw extruder or a twin screw extruder. Alternatively, the resin composition is uniformly kneaded in advance using a roll, a cam, a kneader, a Banbury type kneader or the like provided with blades, and then is press-processed to a predetermined thickness by pressing on a hot plate or the like to produce an unfoamed resin molded article. The unfoamed resin molded article thus obtained is placed in a high-pressure vessel, and a high-pressure inert gas (supercritical carbon dioxide or the like) is injected to impregnate the unfoamed resin molded article with the inert gas. At the time of sufficiently impregnating with the inert gas, the pressure (usually to atmospheric pressure) is released, and a bubble nucleus is generated in the resin. The bubble nuclei may be grown directly at room temperature, but may be grown by heating as the case may be. As the heating method, a known and conventional method such as water bath, oil bath, hot roll, hot air oven, far infrared ray, near infrared ray, microwave and the like can be used. After the cells are grown in this manner, the foam can be obtained by rapidly cooling with cold water or the like and fixing the shape. The unfoamed resin molded article to be foamed is not limited to a sheet, and unfoamed resin molded articles of various shapes may be used depending on the application. The unfoamed resin molded article to be foamed may be produced by other molding methods such as injection molding, in addition to extrusion molding and compression molding.

An example of producing a foam in a continuous manner is shown below. For example, foam molding is performed by a kneading and impregnating step of sufficiently impregnating the resin composition with a high-pressure gas (particularly, an inert gas, and further, carbon dioxide) while kneading the resin composition by using an extruder such as a single screw extruder or a twin screw extruder; in this molding decompression step, the resin composition is extruded through a die or the like provided at the front end of an extruder, whereby the pressure (usually to atmospheric pressure) is released and molding and foaming are performed simultaneously. In addition, when foam molding is performed in a continuous manner, a heating step for growing bubbles by heating may be provided as needed. After the bubbles are grown in this way, the shape can be fixed by rapid cooling with cold water or the like as needed. The introduction of the high-pressure gas may be performed continuously or discontinuously. In the kneading impregnation step and the molding decompression step, an extruder or an injection molding machine may be used, for example. The heating method for growing the bubble nuclei may be any suitable method such as a water bath, an oil bath, a heat roller, a hot air oven, far infrared rays, near infrared rays, or microwaves. Any suitable shape may be used as the shape of the foam. Examples of such a shape include: sheet, prismatic, cylindrical, profiled, etc.

In view of obtaining a highly foamed resin foam, the mixing amount of the gas at the time of foam molding of the resin composition is preferably 2 to 10% by weight, more preferably 2.5 to 8% by weight, and even more preferably 3 to 6% by weight, relative to the total amount of the resin composition.

The pressure at which the inert gas is impregnated into the resin composition can be appropriately selected in consideration of operability and the like. Such a pressure is, for example, preferably 6MPa or more (for example, 6MPa to 100 MPa), more preferably 8MPa or more (for example, 8MPa to 50 MPa). In the case of using carbon dioxide in a supercritical state, the pressure is preferably 7.4MPa or more from the viewpoint of maintaining the supercritical state of carbon dioxide. When the pressure is lower than 6MPa, the bubble growth during foaming is remarkable, and the bubble diameter becomes too large, and a preferable average cell diameter (average bubble diameter) may not be obtained. This is because, when the pressure is low, the gas infiltration amount is relatively small compared to that at a high pressure, the bubble nucleus formation rate is low, and the number of bubble nuclei formed becomes small, so that the gas amount per 1 bubble on average increases instead, and the bubble diameter becomes extremely large. In addition, in the pressure region below 6MPa, only a slight change in the impregnation pressure causes a large change in the bubble diameter and the bubble density, and therefore, control of the bubble diameter and the bubble density is liable to become difficult.

The temperature in the gas impregnation step varies depending on the inert gas used, the kind of the components in the resin composition, and the like, and can be selected from a wide range. In consideration of operability and the like, it is preferably 10 to 350 ℃. The impregnation temperature at the time of impregnating the unfoamed molded article with the inert gas is preferably 10 to 250 ℃, more preferably 40 to 230 ℃ in the case of batch. In addition, the impregnation temperature in the case of extruding the molten polymer impregnated with the gas and simultaneously foaming and molding is preferably 60 to 350 ℃ in the case of continuous type. In the case of using carbon dioxide as the inert gas, the temperature at the time of impregnation is preferably 32 ℃ or higher, more preferably 40 ℃ or higher, in order to maintain the supercritical state.

In the depressurizing step, the depressurizing rate is preferably 5 MPa/sec to 300 MPa/sec in order to obtain uniform fine bubbles.

The heating temperature in the heating step is preferably 40 to 250 ℃, more preferably 60 to 250 ℃.

In one embodiment, after a foamed structure is obtained through a predetermined process (for example, after a resin foam is obtained by the method of < embodiment 1 > or < embodiment 2 "), the foamed structure is thinned, and then roll-rolled, whereby a resin foam can be obtained. By performing such a step, a resin foam having an appropriately adjusted aspect ratio can be obtained. In addition, a resin foam having a small thickness (for example, 0.2mm or less) can be obtained. The hot melt layer may be formed by the roll forming.

The foaming structure can be thinned by using any suitable slicer. The thickness of the foamed structure after the film formation is preferably 0.01 to 3mm, more preferably 0.05 to 2mm, still more preferably 0.1 to 1mm, particularly preferably 0.1 to 0.5mm.

Preferably, the roll used for the rolling of the rolls is a heated roll. The temperature of the roll is preferably 150 to 250 ℃, more preferably 160 to 230 ℃.

The rolling reduction (thickness after rolling/thickness before rolling×100) of the foam structure is preferably 80% or less, more preferably 10% to 80%, further preferably 20% to 75%, and particularly preferably 30% to 75%. In such a range, a resin foam having an appropriately adjusted aspect ratio can be obtained.

B. Foaming member

Fig. 1 is a schematic cross-sectional view of a foam member according to an embodiment. The foam member 100 has a resin foam layer 10 and an adhesive layer 20 disposed on at least one side of the resin foam layer 10. The resin foam layer 10 is composed of the above resin foam.

The thickness of the pressure-sensitive adhesive layer is preferably 5 μm to 300. Mu.m, more preferably 6 μm to 200. Mu.m, still more preferably 7 μm to 100. Mu.m, particularly preferably 8 μm to 50. Mu.m. By setting the thickness of the pressure-sensitive adhesive layer within the above range, the foamed member of the present invention can exhibit excellent impact absorbability.

As the adhesive layer, a layer formed of any suitable adhesive may be used. Examples of the binder constituting the binder layer include: rubber-based adhesives (synthetic rubber-based adhesives, natural rubber-based adhesives, etc.), urethane-based adhesives, acrylic adhesives, silicone-based adhesives, polyester-based adhesives, polyamide-based adhesives, epoxy-based adhesives, vinyl alkyl ether-based adhesives, fluorine-based adhesives, rubber-based adhesives, etc. The adhesive constituting the adhesive layer is preferably at least one selected from the group consisting of an acrylic adhesive, a silicone adhesive, and a rubber adhesive. Such binders may be used alone or in combination of two or more. The pressure-sensitive adhesive layer may be one layer or two or more layers.

As the binder, if classified by adhesion, for example, there are: emulsion adhesives, solvent adhesives, ultraviolet-crosslinking (UV-crosslinking) adhesives, electron beam crosslinking (EB-crosslinking) adhesives, hot-melt adhesives (hot-melt adhesives), and the like. Such binders may be used alone or in combination of two or more.

The water vapor permeability of the adhesive layer is preferably 50 (g/(m) ² 24 hours)) toHereinafter, it is more preferably 30 (g/(m) ² 24 hours), more preferably 20 (g/(m) ² 24 hours), particularly preferably 10 (g/(m) ² 24 hours)) or less. If the water vapor permeability of the adhesive layer is within the above range, the foam sheet can stabilize the impact absorbability without being affected by moisture. The water vapor permeability can be measured, for example, by a method according to JIS Z0208 under test conditions of 40 ℃ and a relative humidity of 92%.

Any suitable other component may be contained in the adhesive constituting the adhesive layer within a range that does not impair the effect of the present invention. Examples of the other components include: other polymer components, softeners, antioxidants, curing agents, plasticizers, fillers, antioxidants, thermal polymerization initiators, photopolymerization initiators, ultraviolet absorbers, light stabilizers, colorants (pigments, dyes, etc.), solvents (organic solvents), surfactants (e.g., ionic surfactants, silicone surfactants, fluorine surfactants, etc.), crosslinking agents (e.g., polyisocyanate-based crosslinking agents, silicone-based crosslinking agents, epoxy-based crosslinking agents, alkyl etherified melamine-based crosslinking agents, etc.), and the like. The thermal polymerization initiator and the photopolymerization initiator may be contained in a material for forming the polymer component.

The foaming member described above may be manufactured by any suitable method. Examples of the method for producing the foaming member include: a method of producing a laminate of a resin foam layer and an adhesive layer; and a method in which the pressure-sensitive adhesive layer is formed by laminating a pressure-sensitive adhesive layer-forming material and a resin foam layer and then forming the pressure-sensitive adhesive layer by a curing reaction or the like.

Examples

The present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The test and evaluation methods in examples and the like are as follows. Note that "part by weight" refers to "part by weight" unless otherwise specified, and "%" refers to "% by weight" unless otherwise specified.

< evaluation method >)

(1) Apparent density of

The density (apparent density) of the resin foam was calculated as follows. The resin foam obtained in the example/comparative example was punched out into a 20mm×20mm size to obtain a test piece, and the size of the test piece was measured with a caliper. Next, the weight of the test piece was measured by an electronic balance. And calculated according to the following formula.

Apparent Density (g/cm) ³ ) Weight of test piece/volume of test piece.

(2) 50% compression load

The compression hardness of the resin foam was measured according to the method described in JIS K6767. Specifically, the resin foam obtained in example/comparative example was cut out to a size of 30mm×30mm to obtain a test piece, and the test piece was compressed at a compression rate of 10mm/min until the compression rate became 50%, and the stress (N) at this time was converted into a value per unit area (1 cm ² ) Is set to a value of 50% compression load (N/cm ² )。

(3) Average bubble diameter (average cell diameter), coefficient of variation of bubble diameter (cell diameter)

The resin foam was cut in the TD direction (direction perpendicular to the flow direction) and in the perpendicular direction (thickness direction) to the main surface of the resin foam using a razor, an image of the cut surface of the resin foam was introduced using a digital microscope (trade name "VHX-500", manufactured by Keyence corporation) as a tester, and the number average cell diameter (average cell diameter) (μm) was obtained by performing image analysis using analysis software of the same tester. The number of bubbles in the enlarged image to be introduced was about 400. The standard deviation was calculated from all the cell diameter data, and the coefficient of variation was calculated using the following equation.

Coefficient of variation = standard deviation/average bubble diameter (average cell diameter).

(4) Bubble ratio (cell ratio)

The measurement was performed in an environment at a temperature of 23℃and a humidity of 50%. The resin foam obtained in the examples and comparative examples was punched out by a 100mm×100mm blade die (trade name "NCA07", thickness 0.7mm, knife edge angle 43 °, manufactured by NAKAYAMA corporation)), and the size of the punched sample was measured. The thickness was measured by a 1/100 micrometer having a diameter (phi) of the measuring terminal of 20 mm. The volume of the resin foam obtained in the examples/comparative examples was calculated from these values. Next, the weight of the resin foam obtained in example/comparative example was measured by a tray balance having a minimum scale of 0.01g or more. The bubble ratio (cell ratio) of the resin foam obtained in the examples/comparative examples was calculated from these values.

(5) Number density of bubbles

The resin foam was cut with a razor in the TD direction (direction orthogonal to the flow direction) and in the perpendicular direction (thickness direction) to the main surface of the resin foam.

A digital microscope (trade name "VHX-500", manufactured by Keyence Co., ltd.) was used as a measuring instrument, an image of the cut surface of the resin foam was introduced, and analysis software of the same measuring instrument was used to measure [ mm ] per unit area by image analysis ² ]Is a gas bubble number.

(6) Thickness recovery rate (instantaneous recovery rate)

For the resin foam, 1000g/cm of the resin foam was applied ² The resin foam was decompressed for 120 seconds under a load of 120 seconds, and the thickness of the resin foam after 0.5 seconds from the decompression (thickness after 0.5 seconds from the decompressed state) was measured. The thickness recovery rate (instantaneous recovery rate) was determined from the "thickness after 0.5 seconds from the decompressed state" and the thickness of the resin foam before the load was applied (initial thickness) and from the following equation.

Thickness recovery (%) = { (thickness after 0.5 seconds from decompression)/(initial thickness) } ×100.

(7) Relative dielectric constant

The relative dielectric constant was measured at a temperature of 23℃and a humidity of 50% using an E4980A precision LCR meter (Agilent Technologies). The compression ratio was measured by the parallel plate capacitor method (based on JIS C2138) and was set to 0%.

(8) Tensile modulus

The tensile modulus was measured at a tensile speed of 500mm/min by fixing a sample (size: 10 mm. Times.80 mm) at a chuck pitch of 40mm using a tensile tester (RTG-1201, manufactured by Tamsui, co., ltd.) at an ambient temperature of 25℃to obtain a curve composed of tensile strain and tensile strength. The tensile modulus was obtained from the slope of a straight line connecting the origin of the curve and the tensile strength at 10% tensile strain.

(9) Punching workability (10 mm. Times.10 mm)

The resin foam was punched out in the MD direction (flow direction) and the TD direction (direction perpendicular to the flow direction) so as to be 10mm×10mm in size by using a die (2-piece working knife (trade name "NCA07", thickness 0.7mm, knife edge angle 43 °, distance between 2-piece working knives 10mm, manufactured by NAKAYAMA)), and the cross section having the larger thickness variation in the cross section in the MD direction and the TD direction was observed by a microscope (trade name "VHX-2000", manufactured by keyence corporation). The thickness of the end portion measured from the image and the thickness before punching were used, and the thickness recovery rate after the punching was measured according to the following formula. The larger the thickness recovery ratio is, the smaller the shape change by blanking is, and the more excellent the blanking workability is.

Thickness recovery after processing (%) =100× (1- (thickness before punching-thickness of end portion)/thickness before punching).

(10) Punching processability (1 mm wide)

The resin foam was punched out in the MD direction (flow direction) at intervals of 1mm and a length of 50mm by using a die (2-sheet processing knife (trade name "NCA07", thickness 0.7mm, knife edge angle 43 °, manufactured by NAKAYAMA, trade name "VHX-2000", manufactured by keyence corporation)) in a direction perpendicular to the main surface of the resin foam, and the cross section was observed by a microscope (trade name "VHX-2000". The thickness of the end portion measured from the image and the thickness before punching were used, and the thickness recovery rate after the punching was measured according to the following formula. The larger the thickness recovery ratio is, the smaller the shape change by blanking is, and the more excellent the blanking workability is.

(11) Mold release expansion ratio

The die swell ratio of the resin was measured before and after foaming, and it was described that the die swell ratio of the resin was not measured for a foam made of a crosslinking material in comparative example 2.

Die swell ratio = diameter (mm) of the shaped article/die bore (mm).

(12) Shear viscosity

A sample (resin constituting the resin foam (size: 5mm square) was put into a cylinder at a temperature 20℃higher than the melting point of the resin constituting the resin foam using an elongational viscometer (trade name "RH-7", mark company) as a measuring instrument, and the resin foam was put into a molten state for 7 minutes, and then the melt was extruded at a shear rate of 20mm/s using a die having a length of 10mm and a bore of 1mm phi, and the shear viscosity was measured.

[ example 1 ]

Polypropylene (propylene homopolymer, MFR:0.4g/10 min (230 ℃ C., load: 21.2N), density:0.90g/cm ³ ethylene content: 0 wt%, propylene content: 100 wt%, weight average molecular weight: 64500 molecular weight distribution: 8.43 30 parts by weight of a polyolefin-based elastomer (melt flow rate (MFR): 15g/10min, JIS A hardness: 79 DEG) 46 parts by weight of a polyolefin-based elastomer (melt flow rate (MFR): 2.2g/10min, JIS A hardness: 69 °) 19 parts by weight, 10 parts by weight of magnesium hydroxide (trade name "KISUMA 5P", manufactured by the chemical industry Co., ltd.), 10 parts by weight of carbon (trade name "Xu #35" manufactured by Xu carbon Co., ltd.), and 1 part by weight of monoglyceride stearate were kneaded at a temperature of 200 ℃, extruded in the form of strands, water-cooled, and formed into pellets. The pellets were fed into a single screw extruder manufactured by Nippon Steel Co., ltd. And carbon dioxide gas was injected at a pressure of 13MPa (12 MPa after injection) in an atmosphere at 220 ℃. Carbon dioxide gas was injected in a proportion of 4.8 parts by weight with respect to 100 parts by weight of the resin. After sufficiently saturating carbon dioxide gas, the resin foam a was cooled to a temperature suitable for foaming, and then extruded from a die to obtain a sheet-like resin foam a.

Further, the resin foam A was thinned by a microtome to obtain a resin foam A having a thickness of 1.0 mm.

The obtained resin foam a was subjected to the above evaluation. The results are shown in Table 1.

[ example 2 ]

Polypropylene (propylene homopolymer, MFR:0.4g/10 min (230 ℃ C., load 21.2N), density: 0.90 g/cm) was kneaded by using a twin-screw kneader manufactured by Japanese Steel Co., ltd (JSW) ³ Ethylene content: 0 wt%, propylene content: 100 wt%) 35 parts by weight of a polyolefin-based elastomer (melt flow rate (MFR): 15g/10min, JIS A hardness: 79 DEG) 42 parts by weight, a polyolefin-based elastomer (melt flow rate (MFR): 2.2g/10min, JIS A hardness: 69 °) 18 parts by weight of magnesium hydroxide (trade name "KISUMA 5P", co-chemical industry) 10 parts by weight, carbon (trade name "asahi #35" asahi carbon co-product) 10 parts by weight, and monoglyceride stearate 1 part by weight were kneaded at a temperature of 200 ℃, extruded in a strand form, water-cooled, and molded into pellets. The pellets were fed into a single screw extruder manufactured by Nippon Steel Co., ltd.) and fed into a extruder at a temperature of 220℃under an atmosphere of 13MPa (injectionThe latter 12 MPa) of the pressure injected with carbon dioxide gas. Carbon dioxide gas was injected in a proportion of 4.8 parts by weight with respect to 100 parts by weight of the resin. After sufficiently saturating carbon dioxide gas, the resin foam b was cooled to a temperature suitable for foaming, and then extruded from a die to obtain a sheet-like resin foam.

Further, the resin foam B was thinned by a microtome to obtain a resin foam B having a thickness of 1.0 mm.

The obtained resin foam B was subjected to the above evaluation. The results are shown in Table 1.

[ example 3 ]

A resin foam c was obtained in the same manner as in example 2, except that the injection amount of carbon dioxide gas was set to a ratio of 4.5 parts by weight relative to 100 parts by weight of the resin.

Further, the film was formed by a microtome to obtain a resin foam C having a thickness of 1.0 mm.

The obtained resin foam C was subjected to the above evaluation. The results are shown in Table 1.

[ example 4 ]

A resin foam d was obtained in the same manner as in example 2, except that the injection amount of carbon dioxide gas was set to a ratio of 4.2 parts by weight relative to 100 parts by weight of the resin.

Further, the resin foam D was thinned by a microtome to obtain a resin foam D having a thickness of 1.0 mm.

The obtained resin foam D was subjected to the above evaluation. The results are shown in Table 1.

[ example 5 ]

Polypropylene (propylene homopolymer, MFR:0.4g/10 min (230 ℃ C., load 21.2N), density: 0.90 g/cm) was kneaded by using a twin-screw kneader manufactured by Japanese Steel Co., ltd (JSW) ³ Ethylene content: 0 wt%, propylene content: 100 wt%) 40 parts by weight of a polyolefin-based elastomer (melt flow rate (MFR): 15g/10min, JIS A hardness: 79 DEG) 39 parts by weight, a polyolefin-based elastomer (melt flow rate (MFR): 2.2g/10min, JIS A hardness: 69 DEG) 16 parts by weight, 10 parts by weight of magnesium hydroxide (trade name "KISUMA 5P", manufactured by the chemical industry Co., ltd.), and carbon (trade name "Xu G #) 35 "manufactured by Xu carbon Co., ltd.) 10 parts by weight and 1 part by weight of monoglyceride stearate were kneaded at a temperature of 200℃and extruded in the form of strands, and water-cooled and then molded into pellets. The pellets were fed into a single screw extruder manufactured by Nippon Steel Co., ltd. And carbon dioxide gas was injected at a pressure of 13MPa (12 MPa after injection) in an atmosphere at 220 ℃. Carbon dioxide gas was injected in a proportion of 4.5 parts by weight with respect to 100 parts by weight of the resin. After sufficiently saturating carbon dioxide gas, the resin foam e was cooled to a temperature suitable for foaming, and then extruded from a die to obtain a sheet-like resin foam e.

Further, the resin foam E was thinned by a microtome to obtain a resin foam E having a thickness of 1.0 mm.

The obtained resin foam E was subjected to the above evaluation. The results are shown in Table 1.

[ example 6 ]

Polypropylene (propylene homopolymer, MFR:0.5g/10 min (230 ℃ C., load 21.2N), density: 0.90 g/cm) was kneaded by using a twin-screw kneader manufactured by Japanese Steel Co., ltd (JSW) ³ Ethylene content: 0 wt%, propylene content: 100 wt%, weight average molecular weight: 54500 molecular weight distribution: 9.83 40 parts by weight of a polyolefin-based elastomer (melt flow rate (MFR): 15g/10min, JIS A hardness: 79 DEG) 39 parts by weight, a polyolefin-based elastomer (melt flow rate (MFR): 2.2g/10min, JIS A hardness: 69 °) 16 parts by weight, magnesium hydroxide (trade name "KISUMA5P" manufactured by co-chemical industry) 10 parts by weight, carbon (trade name "asahi #35" asahi carbon co-product) 10 parts by weight, and monoglyceride stearate 1 part by weight were kneaded at a temperature of 200 ℃, extruded in a strand form, water-cooled, and molded into pellets. The pellets were fed into a single screw extruder manufactured by Nippon Steel Co., ltd. And carbon dioxide gas was injected at a pressure of 13MPa (12 MPa after injection) in an atmosphere at 220 ℃. Carbon dioxide gas was injected in a proportion of 4.5 parts by weight with respect to 100 parts by weight of the resin. After sufficiently saturating carbon dioxide gas, the resin foam f is cooled to a temperature suitable for foaming, and then extruded from a die to obtain a sheet-like resin foam f.

Further, the resin foam F was thinned by a microtome to obtain a resin foam F having a thickness of 1.0 mm.

The obtained resin foam F was subjected to the above evaluation. The results are shown in Table 1.

Example 7

A resin foam e was obtained in the same manner as in example 2, except that the injection amount of carbon dioxide gas was set to a ratio of 4.2 parts by weight relative to 100 parts by weight of the resin.

Further, the film was formed by a microtome to obtain a resin foam having a thickness of 0.3 mm. Further, the resin foam E was obtained by passing the resin foam between a pair of rolls (a gap between the rolls) in which one roll was heated to 230 ℃. The gap (clearance) between the rolls was set so that a resin foam E having a thickness of 0.20mm could be obtained.

Comparative example 1

Polypropylene (propylene homopolymer, MFR:0.4g/10 min (230 ℃ C., load 21.2N), density: 0.90 g/cm) was kneaded by using a twin-screw kneader manufactured by Japanese Steel Co., ltd (JSW) ³ Ethylene content: 0 wt%, propylene content: 100 wt%, weight average molecular weight: 108000, molecular weight distribution: 4.93 65 parts by weight of a polyolefin-based elastomer (melt flow rate (MFR): 15g/10min, JIS A hardness: 79 DEG) 35 parts by weight of magnesium hydroxide (trade name "KISUMA 5P", manufactured by the chemical industry Co., ltd.), 5 parts by weight of carbon (trade name "Xu#35" manufactured by Xu carbon Co., ltd.), 10 parts by weight of carbon, and 1 part by weight of monoglyceride stearate were kneaded at a temperature of 200 ℃, extruded in the form of strands, water-cooled, and formed into pellets. The pellets were fed into a single screw extruder manufactured by Nippon Steel Co., ltd. And carbon dioxide gas was injected at a pressure of 13MPa (12 MPa after injection) in an atmosphere at 220 ℃. Carbon dioxide gas was injected in a proportion of 4.5 parts by weight with respect to 100 parts by weight of the resin. After sufficiently saturating carbon dioxide gas, the resin foam f is cooled to a temperature suitable for foaming, and then extruded from a die to obtain a sheet-like resin foam f.

Comparative example 2

Resin foam (apparent density: 0.7 g/cm) ³ ). The resin foam was subjected to the above evaluation. The results are shown in Table 1.

TABLE 1

As is clear from table 1, the resin foam of the present invention has low dielectric properties and excellent punching workability by setting the apparent density and the instantaneous recovery rate to specific ranges.

Industrial applicability

The resin foam of the present invention can be suitably used as a buffer material for electronic devices, for example.

Description of the reference numerals

100: a foaming member; 10: a resin foam layer (resin foam); 20: an adhesive layer.

Claims

1. A resin foam, wherein,

the resin foam has a bubble structure,

the apparent density of the resin foam is less than 0.4g/cm ³ ，

Applying 1000g/cm to the resin foam ² The thickness recovery rate after 120 seconds is 80% or more in the loaded state.

2. The resin foam according to claim 1, wherein,

the number density of bubbles was 30/mm ² The above.

3. The resin foam according to claim 1, wherein,

the average bubble diameter is 10 μm to 200. Mu.m.

4. The resin foam according to claim 1, wherein,

the variation coefficient of the bubble diameter is 0.5 or less.

5. The resin foam according to claim 1, wherein,

the bubble rate is 30% or more.

6. The resin foam according to claim 1, wherein,

the tensile modulus at 25 ℃ is 1.5MPa or more.

7. The resin foam according to claim 1, wherein,

50% compression load of 20N/cm ² The following is given.

8. The resin foam according to claim 1, wherein,

the resin foam contains a polyolefin resin.

9. The resin foam according to claim 8, wherein,

the polyolefin-based resin is a mixture of polyolefin and polyolefin-based elastomer other than polyolefin-based elastomer.

10. The resin foam according to claim 1, wherein,

having a heat-fusible layer on one or both sides.

11. A foaming member, wherein,

the foaming member has a resin foaming layer and an adhesive layer arranged on at least one side of the resin foaming layer,

the resin foam layer is the resin foam according to claim 1.