Resin foam and foam member

Abstract

Provided is a resin foam that is excellent in terms of flexibility and low dustiness. [1] A resin foam according to an embodiment of the present invention has a cell structure and satisfies formula (1).　Formula (1): Interlayer strength (N / 20 mm)>apparent density (g / cm3)×40+3 [2] The resin foam described in [1] may have an apparent density of at most 0.4 g / cm3. [3] The resin foam described in [1] or [2] may have an interlayer strength of at least 3 N / 20 mm.

Description

Resin foam and foamed material

[0001] The present invention relates to a resin foam and a foam member.

[0002] Foams are often used as cushioning materials for protecting the screens, substrates, and electronic components of electronic devices. Such foams are required to have excellent flexibility so that they can exhibit desirable cushioning properties. However, increasing the flexibility of foams can lead to the problem of increased dust generation. In other words, conventional techniques have not yet achieved foams that are highly compatible in terms of flexibility and low dust generation.

[0003] JP 2017-186504 A JP 2015-034299 A JP 2006-225571 A

[0004] An object of the present invention is to provide a resin foam that is excellent in flexibility and low in dust generation.

[0005] [1] A resin foam according to an embodiment of the present invention has a cellular structure and satisfies the following formula (1): interlaminar strength (N / 20 mm)>apparent density (g / cm ３ ) × 40 + 3 ... (1) [2] The resin foam described in [1] above has an apparent density of 0.4 g / cm ３ [3] The resin foam according to the above [1] or [2] may have an interlaminar strength of 3 N / 20 mm or more. [4] The resin foam according to any one of the above [1] to [3] may have an average cell diameter of 50 μm or more. [5] The resin foam according to any one of the above [1] to [4] may have a 50% compression load of 40 N / cm ２ [6] In the resin foam according to any one of [1] to [5] above, the resin foam may have a viscosity of 1000 g / cm or less. ２[7] The resin foam according to any one of [1] to [6] above may have a coefficient of variation of cell diameter of 0.6 or less. [8] The resin foam according to any one of [1] to [7] above may contain recycled resin, and the recycled resin ratio in the resin foam may be 0.2 or more, and may satisfy the following formula (2): apparent density (g / cm ３ ) < 0.046 × recycled resin ratio + 0.0121 ... (2) [9] The resin foam according to [8] above may contain a polyolefin as the recycled resin.

[10] The resin foam according to [9] above may have a melt flow rate (MFR) of less than 10 g / 10 min at a temperature of 230°C of the polyolefin as the recycled resin.

[11] The resin foam according to [9] or

[10] above may have a melt tension of 10 cN or more of the polyolefin as the recycled resin.

[12] The resin foam according to any one of [9] to

[11] above may have a die swelling ratio of 1.5 or less at a melting point of the polyolefin as the recycled resin + 20°C.

[13] The resin foam according to any one of [9] to

[12] above may have a polyolefin as the recycled resin.

[14] In the resin foam according to any one of [9] to

[13] above, the polyolefin may be a mixture of a polyolefin other than a polyolefin-based elastomer and a polyolefin-based elastomer.

[15] In the resin foam according to any one of [1] to

[14] above, the die swelling ratio at a melting point of the resin composition forming the resin foam + 20°C may be 1.5 or less.

[16] In the resin foam according to any one of [1] to

[15] above, a heat-melting layer may be formed on one or both sides.

[17] A foam member according to an embodiment of the present invention may have a resin foam layer and a pressure-sensitive adhesive layer disposed on at least one side of the resin foam layer, and the resin foam layer may be the resin foam according to any one of [1] to

[16] above.

[0006] According to the present invention, a resin foam having excellent flexibility and low dust generation properties can be provided.

[0007] 1 is a schematic cross-sectional view of a foam member according to one embodiment of the present invention.

[0008] A. Resin Foam The resin foam according to an embodiment of the present invention satisfies the following formula (1): interlaminar strength (N / 20 mm)>apparent density (g / cm ３ ) × 40 + 3 ... (1)

[0009] In this specification, the interlaminar strength refers to the interlaminar strength at 23° C., and is the maximum load when the resin foam is pulled in the thickness direction and breaks (peels off). The method for measuring the interlaminar strength will be described later.

[0010] In an embodiment of the present invention, the resin foam has a cell structure. Examples of the cell structure include a closed cell structure, an open cell structure, and a semi-open, semi-closed cell structure (a cell structure in which a closed cell structure and an open cell structure are mixed). Preferably, the cell structure of the resin foam is a semi-open, semi-closed cell structure. Typically, the resin foam is obtained by foaming a resin composition containing recycled resin. The resin composition is a composition containing at least the resin that constitutes the resin foam.

[0011] In an embodiment of the present invention, by satisfying formula (1), a resin foam may be provided that exhibits excellent flexibility while exhibiting sufficient interlayer strength. The resin foam with excellent interlayer strength has low dust generation and is suitable as a cushioning material that requires cleanliness and is used for protecting the screen, substrate, and electronic components of electronic devices. In addition, a resin foam with excellent punching processability can be obtained. More specifically, according to the above embodiment, a resin foam with excellent punching processability can be obtained, which exhibits favorable behavior in that shape changes such as thickness change are small even when punched, and recovers in a short time even if the thickness is temporarily reduced by punching. According to the embodiment of the present invention, the above effects can be obtained even in a thin layer.

[0012] {Interlaminar strength (N / 20 mm)} - {Apparent density (g / cm ３ ) × 40 + 3} is preferably 5 or less, more preferably 4 or less, and even more preferably 2.6 or less.

[0013] The interlaminar strength of the resin foam is preferably 3 N / 20 mm or more, more preferably 4 N / 20 mm or more, even more preferably 5 N / 20 mm or more, and particularly preferably 6 N / 20 mm or more. Within such a range, a resin foam with reduced dust generation can be obtained. The higher the interlaminar strength of the resin foam, the more preferable it is, and the upper limit thereof is, for example, 500 N / 20 mm. The upper limit of the interlaminar strength of the resin foam may be 100 N / 20 mm, 50 N / 20 mm, 25 N / 20 mm, 15 N / 20 mm, or 10 N / 20 mm.

[0014] The apparent density of the resin foam is preferably 0.01 g / cm ３ More preferably, 0.02 g / cm ３ The apparent density of the resin foam is preferably 0.4 g / cm ３ or less, more preferably 0.2 g / cm ３ or less, more preferably 0.1 g / cm ３ More preferably, it is 0.08 g / cm or less. ３ More preferably, it is 0.05 g / cm or less. ３ or less, and particularly preferably 0.04 g / cm ３ When the apparent density is within the above range, a resin foam having excellent punching processability, flexibility, and stress dispersibility can be obtained. The foamability can be determined by the apparent density. The method for measuring the apparent density will be described later.

[0015] In one embodiment, the resin foam can be obtained by, for example, adding recycled resin. In one embodiment, the resin foam has a recycled resin ratio of 0.2 or more, more preferably 0.4 or more, even more preferably 0.5 or more, particularly preferably 0.6 or more, and most preferably 0.7 or more. By adding recycled resin at such a ratio, the above-mentioned effects become significant. Furthermore, a resin foam having an excellent effect of suppressing carbon dioxide emissions can be provided. The upper limit of the recycled resin ratio in the resin foam can be 0.9, 0.85, or 0.75. Within such a range, a resin foam having excellent foamability and excellent punching processability can be obtained.

[0016] In this specification, "recycled resin" refers to a resin that has been reused through foam molding. In one embodiment, the "recycled resin" may be a resin that has undergone a temperature history of (melting point + 10°C) or more. The "recycled resin" may also be a resin that has undergone a temperature history of (melting point + 5°C) or more. By using a resin that has undergone a predetermined temperature history, a resin foam that is excellent in flexibility and suppresses dust generation can be obtained. Furthermore, the "recycled resin ratio" refers to the weight ratio of recycled resin to resin foam.

[0017] In one embodiment, the resin foam satisfies the following formula (2): apparent density (g / cm ３ ) < 0.046 × recycled resin ratio + 0.0121 (2) When formula (2) is satisfied, it is possible to provide a resin foam that is excellent in punching processability while suppressing carbon dioxide emissions.

[0018] In one embodiment, the value calculated by [{0.046 × recycled resin ratio} + 0.0121] may be preferably 0.025 or more, 0.030 or more, or 0.040 or more, and may be 0.070 or less, 0.060 or less, or 0.050 or less.

[0019] In one embodiment, [{0.046 × recycled resin ratio} + 0.0121 − apparent density (g / cm ３The value calculated by the formula {0.046 × recycled resin ratio} + 0.0121 − apparent density (g / cm ３ ) may be 0.0001 or more, 0.0005 or more, 0.0008 or more, or 0.001 or more. Within the above ranges, a resin foam that is excellent in punching processability while suppressing carbon dioxide emissions can be provided.

[0020] The resin foam is applied with 1000 g / cm ２ The thickness recovery rate (instantaneous recovery rate) after maintaining the applied load for 120 seconds is preferably 80% or more, more preferably 82% or more, even more preferably 84% or more, even more preferably 86% or more, and particularly preferably 90% or more. Within such a range, a resin foam having excellent punching processability can be provided. The higher the instantaneous recovery rate, the more preferable it is, and the upper limit is, for example, 99% (preferably 100%). The method for measuring the instantaneous recovery rate will be described later.

[0021] The apparent density of the resin foam is preferably 0.01 g / cm ３ More preferably, 0.02 g / cm ３ The apparent density of the resin foam is preferably 0.4 g / cm ３ or less, more preferably 0.2 g / cm ３ or less, more preferably 0.1 g / cm ３ More preferably, it is 0.08 g / cm or less. ３ More preferably, it is 0.05 g / cm or less. ３ or less, and particularly preferably 0.04 g / cm ３ When the apparent density is within the above range, a resin foam having excellent punching processability, flexibility, and stress dispersibility can be obtained. The foamability can be determined by the apparent density. The method for measuring the apparent density will be described later.

[0022] The resin foam has a cell content (cell ratio) of preferably 97% or less, more preferably 96% or less. The resin foam has a cell content (cell ratio) of preferably 30% or more, more preferably 50% or more, and even more preferably 60% or more. Within these ranges, a resin foam having appropriate flexibility can be obtained.

[0023] The cell density of the resin foam is preferably 30 cells / mm ２ More preferably, 50 pieces / mm ２ More preferably, 70 pieces / mm ２ More preferably, 80 pieces / mm ２ More preferably, 90 pieces / mm ２ More preferably, 100 pieces / mm ２ More preferably, it is 110 pieces / mm ２ or more, and most preferably 120 / mm ２ Within this range, a resin foam having favorable flexibility and excellent punching processability can be obtained. Furthermore, the higher the cell number density, the easier it is to store energy when compressed, and a resin foam having excellent compression recovery force can be obtained. The upper limit of the cell number density of the resin foam is preferably 400 cells / mm ２ and more preferably 350 pieces / mm ２ and more preferably 300 pieces / mm ２ and more preferably 250 pieces / mm ２ and particularly preferably 200 pieces / mm ２ The cell number density of a resin foam is the number density of cells in a cross section observed in a randomly selected cross section of the resin foam, and can be determined by image analysis of the cross section of the resin foam.

[0024] The resin foam has an average bubble diameter (average cell diameter) of preferably 300 μm or less, more preferably 270 μm or less, even more preferably 250 μm or less, even more preferably 220 μm or less, even more preferably 200 μm or less, and particularly preferably 180 μm or less. Within these ranges, a resin foam with excellent impact absorption properties can be obtained. In one embodiment, the resin foam has an average bubble diameter (average cell diameter) of 180 μm or less. Furthermore, the resin foam has an average bubble diameter (average cell diameter) of preferably 20 μm or more, even more preferably 50 μm or more, even more preferably 80 μm or more, even more preferably 100 μm or more, even more preferably 110 μm or more, and particularly preferably 120 μm or more. When the average bubble diameter (average cell diameter) is within the above range, a resin foam with high interlayer strength, excellent flexibility and stress dispersibility, and favorable impact absorption properties can be obtained. Furthermore, a resin foam having excellent compression recovery, punching processability, and resistance to repeated impacts can be obtained. In one embodiment, the resin foam has an average cell diameter of 120 μm or more. Within this range, a resin foam having particularly excellent interlayer strength can be obtained. The method for measuring the average cell diameter will be described later.

[0025] The resin foam has a maximum cell diameter of preferably 400 μm or less, more preferably 350 μm or less, even more preferably 300 μm or less, particularly preferably 250 μm or less, and most preferably 220 μm or less. The resin foam also has a maximum cell diameter of preferably 40 μm or more, more preferably 80 μm or more, even more preferably 120 μm or more, and particularly preferably 160 μm or more. Within these ranges, a resin foam with particularly excellent impact absorption properties can be obtained. In one embodiment, the resin foam has a maximum cell diameter of 250 μm or less.

[0026] The coefficient of variation of the cell diameter of the resin foam is preferably 0.6 or less, more preferably 0.55 or less, even more preferably 0.5 or less, even more preferably 0.4 or less, and particularly preferably 0.35 or less. Within this range, deformation due to impact is uniform, local stress load is prevented, and a resin foam having excellent stress dispersion and particularly excellent impact absorption properties can be obtained. The smaller the coefficient of variation, the more preferable it is, and the lower limit is, for example, 0.15 (preferably 0.1, more preferably 0.01). A method for measuring the coefficient of variation of the cell diameter will be described later.

[0027] When the resin foam has a semi-open, semi-closed cell structure, the proportion of closed cell structures therein is preferably 40% or less, more preferably 30% or less. In this specification, the proportion of closed cell structures in a resin foam is determined, for example, by submerging a measurement target in water at a temperature of 23°C and a humidity of 50%, measuring the mass thereafter, and then thoroughly drying the target in an oven at 80°C and measuring the mass again. Furthermore, since open cells can retain moisture, the mass of the open cells is measured and determined.

[0028] The aspect ratio of the cells in the resin foam is preferably 4 or less, more preferably 3 or less, even more preferably 2 or less, still more preferably 1.5 or less, and particularly preferably 1.3 or less. Within such a range, a resin foam having excellent impact absorption properties can be provided. The aspect ratio of the cells in the resin foam is, for example, 1 or more, preferably greater than 1.1. A method for measuring the aspect ratio of the cells in a resin foam will be described later.

[0029] The thickness of the cell walls of the resin foam is preferably 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.5 μm or more, particularly preferably 0.7 μm or more, and most preferably 1 μm or more. The thickness of the cell walls of the resin foam is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 5 μm or less, particularly preferably 4 μm or less, and most preferably 3 μm or less. Resin foams with a thickness within this range can have appropriate strength. Such resin foams have excellent punching processability and are prevented from tearing, dust generation, or remaining cuts during punching. Furthermore, a cell wall thickness within the above range can result in a resin foam with superior flexibility and stress dispersibility. The cell wall thickness can be measured by capturing an enlarged image of the cell portion of the resin foam and analyzing the image using the instrument's analysis software.

[0030] The 50% compression load of the resin foam is preferably 40 N / cm ２ More preferably, it is 20 N / cm or less. ２ and more preferably 10 N / cm or less. ２ More preferably, it is 5 N / cm or less. ２ and particularly preferably 4 N / cm ２ and most preferably 3 N / cm ２ Within this range, a resin foam having favorable flexibility and excellent punching processability can be obtained. The lower limit of the 50% compression load of the resin foam is, for example, 0.5 N / cm ２ The 50% compression load of a resin foam is the stress (N) when compressed to a compression rate of 50% per unit area (1 cm ２ ) converted into

[0031] The 25% compression load of the resin foam is preferably 25 N / cm ２ More preferably, it is 15 N / cm or less. ２ and more preferably 10 N / cm or less. ２ More preferably, it is 6 N / cm or less. ２More preferably, it is 5 N / cm or less. ２ and particularly preferably 3 N / cm ２ and most preferably 2 N / cm ２ Within this range, a resin foam having preferable flexibility and impact absorption properties can be obtained. The lower limit of the 25% compression load of the resin foam is, for example, 0.5 N / cm ２ The 25% compression load of a resin foam is the stress (N) when compressed to a compression rate of 25% per unit area (1 cm ２ ) converted into

[0032] The thickness of the resin foam is preferably 8000 μm or less, more preferably 5000 μm or less, even more preferably 4000 μm or less, and particularly preferably 2000 μm or less. The thickness of the resin foam is preferably 100 μm or more, more preferably 200 μm or more, even more preferably 300 μm or more, and particularly preferably 400 μm or more. A thickness in this range is advantageous in that a fine and uniform cell structure can be formed, and excellent impact absorption properties can be achieved.

[0033] The impact absorption of the resin foam is preferably 40% or more, more preferably 55% or more, even more preferably 60% or more, even more preferably 70% or more, particularly preferably 75% or more, and most preferably 80% or more. The impact absorption of the resin foam is, for example, 97% or less, preferably 99% or less. Impact absorption is measured as follows: A test specimen is formed by placing the resin foam, double-sided tape (product number: No. 5603W, manufactured by Nitto Denko), and PET film (product number: Diafoil MRF75, manufactured by Mitsubishi Plastics) in this order on an impact force sensor. A 66 g iron ball is dropped on the test specimen from a height of 50 cm above the PET film to measure the impact force F1. Furthermore, the iron ball is dropped directly onto the impact force sensor as described above to measure the impact force F0 of the blank. Impact absorption (%) is calculated from F1 and F0 using the formula (F0 - F1) / F0 x 100.

[0034] The stress retention of the resin foam is preferably 60% or more, more preferably 63% or more. Furthermore, the stress retention of the resin foam is preferably 100% or less, more preferably 95% or less. Within these ranges, a resin foam can be obtained that has excellent stress dispersion properties and exhibits excellent impact absorption even when thin. In this specification, the stress retention is defined as the ratio of the tensile strength immediately after stretching to the tensile strength after 120 seconds of holding after stretching (tensile strength after 120 seconds of holding / stress retention immediately after stretching × 100) when a resin foam (width 10 mm × length 100 mm) is stretched 20% in the longitudinal direction at a speed of 300 m / min.

[0035] In one embodiment, the resin foam described above can be formed by using a resin having a die swell ratio of 1.4 or less at a melting point (the melting point of the resin constituting the resin foam) + 20°C as the resin constituting the resin foam. Using a resin with a die swell ratio within the above range prevents shrinkage during resin foam formation, allowing for the formation of a thick resin foam, which may contain small bubbles. The die swell ratio at a melting point + 20°C of the resin constituting the resin foam is preferably 1.2 or less, more preferably 1.1 or less. The lower limit of the die swell ratio of the resin is, for example, 1.05 (preferably 1.02, more preferably 1.01). In this specification, the die swell ratio refers to the value obtained by dividing the diameter of the resin extruded from a die by the diameter of the die. The die swell ratio is calculated by extruding a resin molten at melting point + 20 ° C. using a die with a length of 10 mm and a diameter of 1 mmφ at a shear rate of 20 mm / s, measuring the diameter of the resulting string-like molded product, and calculating the formula: molded product diameter (mm) / die diameter (mm). The melting point of the resin is measured by the peak-top temperature of the endothermic peak obtained by differential scanning calorimetry (DSC) measurement. Differential scanning calorimetry (DSC) is measured using a differential scanning calorimeter (e.g., trade name "Q-2000", TA Instruments) under the conditions of a sample weight of 3 mg and a heating rate of 10 ° C. / min. When there are two or more peaks, the peak-top temperature on the higher temperature side is taken as the melting point.

[0036] In one embodiment, the resin foam described above can be formed by using a resin having a shear viscosity of 3000 Pa·s or less at a melting point (the melting point of the resin constituting the resin foam) + 20°C. Using a resin with a shear viscosity within this range allows for favorable dispersion of the gas used to form the cellular structure during resin foam formation, resulting in a resin foam with small cell sizes. The shear viscosity of the resin constituting the resin foam at a melting point + 20°C is preferably 2500 Pa·s or less, more preferably 2100 Pa·s or less, even more preferably 2000 Pa·s or less, and particularly preferably 1900 Pa·s or less. The lower limit of the shear viscosity of the resin is, for example, 500 Pa·s (preferably 700 Pa·s, more preferably 1000 Pa·s). In this specification, the shear viscosity can be measured by extruding a resin in a molten state at a temperature 20°C above the melting point through a die having a length of 10 mm and an opening diameter of 1 mm at a shear rate of 20 mm / s.

[0037] The resin foam may have a heat-melting layer on one or both sides thereof. A resin foam having a heat-melting layer can be obtained, for example, by rolling the resin foam (or a precursor of the resin foam (a foam structure)) 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.

[0038] The resin foam can be formed by any suitable method as long as the effects of the present invention are not impaired. A representative example of such a method is a method of foaming a resin composition containing a resin material (polymer).

[0039] A-1. Resin Composition The resin foam of the present invention can typically be obtained by foaming a resin composition. The resin composition contains any appropriate resin material (polymer). In one embodiment, the resin material in the resin composition contains recycled resin. The resin material may contain a combination of recycled resin and non-recycled resin.

[0040] Examples of the polymer include acrylic resins, silicone resins, urethane resins, polyolefin resins, ester resins, rubber resins, etc. The polymers may be used alone or in combination of two or more.

[0041] The polymer content is preferably 30 to 95 parts by weight, more preferably 35 to 90 parts by weight, even more preferably 40 to 80 parts by weight, and particularly preferably 40 to 60 parts by weight, relative to 100 parts by weight of the resin composition. Within such ranges, a resin foam having superior flexibility and stress dispersibility can be obtained.

[0042] The content of the recycled resin is preferably 30 to 90 parts by weight, more preferably 40 to 85 parts by weight, and even more preferably 50 to 80 parts by weight, per 100 parts by weight of the polymer.

[0043] In one embodiment, a polyolefin resin is used as the polymer. In one embodiment, a polyolefin resin is used as the recycled resin. That is, a polyolefin resin that is a non-recycled resin and a polyolefin resin that is a recycled resin may be used in combination.

[0044] The content of the polyolefin resin (the total content of the polyolefin resin as a recycled resin and the polyolefin resin as a non-recycled 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, relative to 100 parts by weight of the polymer.

[0045] The polyolefin-based resin is preferably at least one selected from the group consisting of polyolefins and polyolefin-based elastomers, and more preferably, a combination of polyolefins and polyolefin-based elastomers is used. The polyolefins and polyolefin-based elastomers may each be used alone or in combination of two or more. In this specification, the terms "polyolefin," "recycled polyolefin," and "non-recycled polyolefin" do not include "polyolefin-based elastomer." In one embodiment, recycled polyolefins are used as polyolefins. Such recycled polyolefins may be used in combination with non-recycled polyolefins. In other words, in one embodiment, recycled polyolefins and / or non-recycled polyolefins are used in combination with polyolefin-based elastomers as polyolefin-based resins.

[0046] When a polyolefin and a polyolefin elastomer are used in combination as the polyolefin resin, the weight ratio of the polyolefin (e.g., the total of recycled polyolefin and non-recycled polyolefin) to the polyolefin elastomer (polyolefin / polyolefin elastomer) is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 90 / 10, even more preferably 20 / 80 to 80 / 20, and particularly preferably 30 / 70 to 70 / 30. In one embodiment, the weight ratio of the polyolefin to the polyolefin elastomer (polyolefin / polyolefin elastomer) is preferably 25 / 75 to 75 / 25, more preferably 35 / 65 to 65 / 35. Within this range, a resin foam can be obtained that exhibits excellent compression recovery, suppresses shape changes (particularly thickness changes) before and after punching, and has appropriate strength and excellent punching processability.

[0047] Any appropriate polyolefin may be used as the polyolefin as long as it does not impair the effects of the present invention. Examples of such polyolefins include linear polyolefins and branched (branched) polyolefins. In one embodiment, a branched polyolefin is used as the polyolefin-based resin. In this embodiment, only a branched polyolefin may be used as the polyolefin, or a branched polyolefin and a linear polyolefin may be used in combination. By using a branched polyolefin, a resin foam having a small average cell diameter and excellent impact resistance can be obtained. Furthermore, by using the branched polyolefin as the non-recycled resin, a resin foam having excellent punching processability can be obtained even when used in combination with a recycled resin. The content of the branched polyolefin is preferably 30 to 100 parts by weight, more preferably 50 to 80 parts by weight, per 100 parts by weight of the polyolefin.

[0048] Examples of the polyolefin include polymers containing structural units derived from α-olefins. The polyolefin may be composed solely of structural units derived from α-olefins, or may be composed of structural units derived from α-olefins and structural units derived from monomers other than α-olefins. When the polyolefin is a copolymer, any appropriate copolymerization form may be adopted. Examples include random copolymers and block copolymers.

[0049] Examples of α-olefins that can constitute polyolefins include α-olefins having 2 to 8 carbon atoms (preferably 2 to 6, more preferably 2 to 4) (e.g., ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, etc.). Only one type of α-olefin may be used, or two or more types may be used.

[0050] Examples of the monomer other than α-olefin constituting the polyolefin include ethylenically unsaturated monomers such as vinyl acetate, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, vinyl alcohol, etc. The monomer other than α-olefin may be one type only, or two or more types may be used.

[0051] Specific examples of polyolefins 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 α-olefin other than ethylene, copolymers of propylene and an α-olefin other than propylene, copolymers of ethylene, propylene and an α-olefin other than ethylene and propylene, and copolymers of propylene and an ethylenically unsaturated monomer.

[0052] In one embodiment, a polypropylene-based polymer having a structural unit derived from propylene is used as the polyolefin. Examples of the polypropylene-based polymer include polypropylene (propylene homopolymer), a copolymer of ethylene and propylene, and a copolymer of propylene and an α-olefin other than propylene, and polypropylene (propylene homopolymer) is preferred. One type of polypropylene-based polymer may be used alone, or two or more types may be used in combination.

[0053] The melt flow rate (MFR) of the polyolefin at a temperature of 230°C is preferably 0.25 g / 10 min to 20 g / 10 min, more preferably 0.3 g / 10 min to 6 g / 10 min, even more preferably 0.35 g / 10 min to 5 g / 10 min, particularly preferably 0.35 g / 10 min to 1 g / 10 min, and most preferably 0.35 g / 10 min to 0.6 g / 10 min, in order to further exhibit the effects of the present invention. Note that, in this specification, the melt flow rate (MFR) refers to the MFR measured at a temperature of 230°C and a load of 2.16 kgf (21.2 N) in accordance with ISO 1133 (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 constituting the resin foam.

[0054] The melt flow rate (MFR) of the polyolefin as the recycled resin at a temperature of 230°C is preferably less than 20 g / 10 min, more preferably less than 10 g / 10 min, even more preferably less than 6 g / 10 min, and even more preferably less than 5 g / 10 min. Furthermore, the melt flow rate (MFR) of the polyolefin as the recycled resin at a temperature of 230°C is preferably 0.25 g / 10 min or more, more preferably 0.3 g / 10 min or more, and even more preferably 0.35 g / 10 min or more. Within such a range, the effects of the present invention are remarkable. This is particularly advantageous in that a resin foam with excellent impact absorption properties can be obtained.

[0055] In one embodiment, the die swell ratio of the polyolefin as the recycled resin at a melting point +20°C is 1.5 or less (preferably 1.25 or less). Within this range, a resin foam containing small-sized bubbles and having a low density can be obtained. Such a resin foam has excellent impact absorption properties. It is also advantageous in that it emits less carbon dioxide. The lower limit of the die swell ratio of the polyolefin as the recycled resin is, for example, 1.05 (preferably 1.02, more preferably 1.01).

[0056] The melt tension of the polyolefin used as the recycled resin is preferably 10 cN or more, more preferably 15 cN or more, and even more preferably 18 cN or more. The melt tension of the polyolefin used as the recycled resin is preferably 50 cN or less, more preferably 45 cN or less. Within this range, a resin foam containing small bubbles and having a low density can be obtained. Such a resin foam has excellent impact absorption properties. It is also advantageous in that it emits less carbon dioxide.

[0057] The weight-average molecular weight of the polyolefin may preferably be 500,000 or more, 550,000 or more, or 600,000 or more. The weight-average molecular weight of the polyolefin may preferably be 1,200,000 or less, 1,100,000 or less, or 1,000,000 or less. Within these ranges, the die swell ratio and shear viscosity of the resin can be preferably adjusted. The molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the polyolefin may preferably be 5.5 or more, 6 or more, or 7 or more. The molecular weight distribution of the polyolefin may preferably be 12 or less, 11 or less, or 10 or less. Within these ranges, the die swell ratio and shear viscosity of the resin can be preferably adjusted. The weight-average molecular weight and number-average molecular weight can be determined by gel permeation chromatography (solvent: tetrahydrofuran, polystyrene equivalent).

[0058] As the polyolefin, commercially available products may be used, for example, "E110G" (manufactured by Prime Polymer Co., Ltd.), "EA9" (manufactured by Japan Polypropylene Corporation), "EA9FT" (manufactured by Japan Polypropylene Corporation), "E-185G" (manufactured by Prime Polymer Co., Ltd.), "WB140HMS" (manufactured by Borealis), and "WB135HMS" (manufactured by Borealis).

[0059] Any appropriate polyolefin elastomer may be used as the polyolefin elastomer as long as it does not impair the effects of the present invention. Examples of such polyolefin elastomers include so-called non-crosslinked thermoplastic olefin elastomers (TPOs) such as ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-vinyl acetate copolymers, polybutene, polyisobutylene, chlorinated polyethylene, elastomers in which a polyolefin component and a rubber component are physically dispersed, and elastomers in which a polyolefin component and a rubber component are microphase-separated; and dynamically crosslinked thermoplastic olefin elastomers (TPVs) which are multiphase polymers obtained by dynamically heat-treating a mixture containing a resin component A (olefin resin component A) that forms a matrix and a rubber component B that forms domains in the presence of a crosslinking agent, and which have a sea-island structure in which crosslinked rubber particles are finely dispersed as domains (island phases) in the resin component A that forms a matrix (sea phase).

[0060] The polyolefin-based 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-2008-024882, 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.

[0061] Specific examples of elastomers having a microphase-separated structure of a polyolefin component and an olefinic rubber component include elastomers made of polypropylene resin (PP) and ethylene-propylene rubber (EPM), elastomers made of polypropylene resin (PP) and ethylene-propylene-diene rubber (EPDM), etc. The weight ratio of the polyolefin component to the olefinic rubber component (polyolefin component / olefinic rubber) is preferably 90 / 10 to 10 / 90, and more preferably 80 / 20 to 20 / 80.

[0062] Dynamically crosslinked thermoplastic olefin elastomers (TPVs) generally have a higher elastic modulus and a smaller compression set than non-crosslinked thermoplastic olefin elastomers (TPOs), which results in good recovery properties and allows the formation of resin foams with excellent recovery properties.

[0063] As described above, a dynamically crosslinked thermoplastic olefin-based elastomer (TPV) is obtained by dynamically heat-treating a mixture containing a resin component A (olefin-based resin component A) that forms a matrix and a rubber component B that forms domains in the presence of a crosslinking agent, and is a multiphase polymer having a sea-island structure in which crosslinked rubber particles are finely dispersed as domains (island phases) in the resin component A that forms the matrix (sea phase).

[0064] Examples of dynamically crosslinked thermoplastic olefin-based elastomers (TPVs) include those described in 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.

[0065] As the dynamically crosslinked thermoplastic olefin-based elastomer (TPV), commercially available products may be used, such as "Zeotherm" (manufactured by Zeon Corporation), "Thermorun" (manufactured by Mitsubishi Chemical Corporation), and "Sarlink 3245D" (manufactured by Toyobo Co., Ltd.).

[0066] The polyolefin elastomer preferably has a melt flow rate (MFR) of 1.5 g / 10 min to 25 g / 10 min, more preferably 2 g / 10 min to 20 g / 10 min, and even more preferably 2 g / 10 min to 15 g / 10 min at a temperature of 230° C. In one embodiment, the die swell ratio and shear viscosity of the resin constituting the resin foam are controlled by the melt flow rate of the polyolefin elastomer.

[0067] In one embodiment, two or more polyolefin elastomers having different melt flow rates (MFR) at 230°C within the above range are used in combination. In this case, a polyolefin elastomer (low MFR polyolefin elastomer) having a melt flow rate (MFR) at 230°C of preferably 1.5 g / 10 min or more and less than 8 g / 10 min (more preferably 2 g / 10 min to 5 g / 10 min) can be used in combination with a polyolefin elastomer (high MFR polyolefin elastomer) having a melt flow rate (MFR) at 230°C of preferably 8 g / 10 min to 25 g / 10 min (more preferably 9 g / 10 min to 20 g / 10 min, and even more preferably 10 g / 10 min to 20 g / 10 min). In this way, the melt tension of the polyolefin elastomer can be preferably adjusted, resulting in remarkable effects of the present invention.

[0068] 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, and particularly preferably 2 to 3. Within such a range, the melt tension of the polyolefin elastomer can be suitably adjusted, resulting in remarkable effects of the present invention.

[0069] The melt tension of the polyolefin elastomer (at 190°C at break) is preferably less than 10 cN, more preferably 5 cN to 9.5 cN. In one embodiment, the die swelling ratio and shear viscosity of the resin constituting the resin foam are controlled by the melt tension of the polyolefin elastomer.

[0070] 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 is measured in accordance with ISO 7619 (JIS K6253).

[0071] In one embodiment, the resin foam (i.e., the resin composition) may further contain a filler. By incorporating a filler, a resin foam can be formed that requires a large amount of energy to deform the cell walls, and the resin foam exhibits excellent impact absorption properties. Furthermore, by incorporating a filler, a fine and uniform cell structure can be formed, which is advantageous in that excellent impact absorption properties can be exhibited. Only one type of filler may be used alone, or two or more types may be used in combination.

[0072] 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, relative to 100 parts by weight of the polymer constituting the resin foam. Within such a range, the above-mentioned effects become significant.

[0073] In one embodiment, the filler is an inorganic substance. Examples of materials constituting the inorganic filler include aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, aluminum oxide, aluminum nitride, aluminum borate whiskers, silicon nitride, boron nitride, crystalline silica, amorphous silica, metals (e.g., gold, silver, copper, aluminum, nickel), carbon, and graphite.

[0074] In one embodiment, the filler is an organic substance. Examples of materials constituting the organic filler include polymethyl methacrylate (PMMA), polyimide, polyamide-imide, polyether ether ketone, polyether-imide, and polyester-imide.

[0075] A flame retardant may be used as the filler. Examples of the flame retardant include bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, and antimony-based flame retardants. From the viewpoint of safety, a non-halogen, non-antimony-based flame retardant is preferably used.

[0076] Examples of non-halogen-non-antimony flame retardants include compounds containing aluminum, magnesium, calcium, nickel, cobalt, tin, zinc, copper, iron, titanium, boron, etc. Examples of such compounds (inorganic compounds) include hydrated metal compounds such as aluminum hydroxide, magnesium hydroxide, magnesium oxide-nickel oxide hydrate, and magnesium oxide-zinc oxide hydrate.

[0077] The filler may be subjected to any suitable surface treatment, such as silane coupling treatment or stearic acid treatment.

[0078] The bulk density of the filler is preferably 0.8 g / cm ３ or less, more preferably 0.6 g / cm ３ More preferably, it is 0.4 g / cm or less. ３ or less, and particularly preferably 0.3 g / cm ３ Within this range, the filler can be incorporated with good dispersibility, and the effect of adding the filler can be fully exhibited even with a low filler content. A resin foam with a low filler content is advantageous in that it is highly foamed, flexible, and has excellent stress dispersibility and appearance. The lower limit of the bulk density of the filler is, for example, 0.01 g / cm ３ and preferably 0.05 g / cm ３ and more preferably 0.1 g / cm ３ is.

[0079] The number average particle diameter (primary particle diameter) of the filler is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. Within this range, the filler can be incorporated with good dispersibility and a uniform cell structure can be formed. As a result, a resin foam with excellent stress dispersion and appearance can be obtained. The lower limit of the number average particle diameter of the filler is, for example, 0.1 μm. The number average particle diameter of the filler can be measured using a particle size distribution analyzer (Micrtrac II, Microtrac Bell Co., Ltd.) using a suspension prepared by mixing 1 g of filler with 100 g of water as a sample.

[0080] The specific surface area of ​​the filler is preferably 2 m ２ / g or more, more preferably 4m ２ / g or more, and more preferably 6m ２ / g or more. Within this range, the filler can be incorporated with good dispersibility and a uniform cell structure can be formed. As a result, a resin foam with excellent stress dispersion and appearance can be obtained. The upper limit of the specific surface area of ​​the filler is, for example, 20 m ２ The specific surface area of ​​the filler can be measured by the BET method, that is, by adsorbing molecules with known adsorption areas onto the surface of the filler at low temperatures using liquid nitrogen, and measuring the amount of adsorption.

[0081] The resin composition may contain any appropriate other component as long as the effects of the present invention are not impaired. Such other components may be present in a single type or in two or more types. Examples of such other components include rubber, resins other than the polymers blended as the resin material, softeners, aliphatic compounds, antioxidants, antioxidants, light stabilizers, weathering agents, UV absorbers, dispersants, plasticizers, carbon, antistatic agents, surfactants, crosslinking agents, thickeners, rust inhibitors, silicone compounds, tension modifiers, shrinkage inhibitors, flow modifiers, gelling agents, curing agents, reinforcing agents, foaming agents, foam nucleating agents, colorants (pigments, dyes, etc.), pH adjusters, solvents (organic solvents), thermal polymerization initiators, photopolymerization initiators, lubricants, crystal nucleating agents, crystallization accelerators, vulcanizing agents, surface treatment agents, and dispersing aids.

[0082] A-2. Formation of Resin Foam The resin foam of the present invention is typically obtained by foaming a resin composition. As the foaming method (cell formation method), methods commonly used in foam molding, such as physical methods and chemical methods, can be used. That is, the resin foam may typically be a foam formed by foaming using a physical method (physical foam) or a foam formed by foaming using a chemical method (chemical foam). The physical method generally involves dispersing a gas component such as air or nitrogen into a polymer solution and forming bubbles by mechanical mixing (mechanical foam). The chemical method generally involves forming cells using gas generated by thermal decomposition of a blowing agent added to a polymer base, thereby obtaining a foam.

[0083] The resin composition to be subjected to foam molding may be prepared, for example, by mixing the constituent components using any suitable melt-kneading device, such as 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.

[0084] <Embodiment 1 for Forming Resin Foam> One embodiment 1 for forming a resin foam includes, for example, forming a resin foam through a step (Step A) of mechanically foaming an emulsion resin composition (an emulsion containing a resin material (polymer), etc.) to form foam. Examples of foaming devices include high-speed shear devices, vibration devices, and pressurized gas discharge devices. Among these foaming devices, high-speed shear devices are preferred from the viewpoints of miniaturizing the bubble diameter and large-volume production. This embodiment 1 for forming a resin foam can be applied to formation from any resin composition.

[0085] From the viewpoint of film-forming properties, the solids concentration of the emulsion is preferably high, and the solids concentration of the emulsion is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more.

[0086] The bubbles generated by mechanical stirring are gases trapped in the emulsion. Any suitable gas can be used as long as it is inert to the emulsion and does not impair the effects of the present invention. Examples of such gases include air, nitrogen, and carbon dioxide.

[0087] The resin foam of the present invention can be obtained by applying the foamed emulsion resin composition (bubble-containing emulsion resin composition) to a substrate and drying it (Step B). Examples of the substrate include a release-treated plastic film (e.g., a release-treated polyethylene terephthalate film) and a plastic film (e.g., a polyethylene terephthalate film).

[0088] Any appropriate method can be used as the coating method and drying method in step B as long as the effects of the present invention are not impaired. Step B preferably includes a preliminary drying step B1 in which the bubble-containing emulsion resin composition applied to the substrate is dried at 50°C or higher and lower than 125°C, and a main drying step B2 in which the bubble-containing emulsion resin composition is further dried at 125°C or higher and 200°C or lower.

[0089] By providing the preliminary drying step B1 and the main drying step B2, it is possible to prevent bubble coalescence and bubble burst due to a sudden rise in temperature. The preliminary drying step B1 is particularly significant in a foamed sheet with a small thickness, since a sudden rise in temperature can cause bubbles to coalesce and burst. The temperature in the preliminary drying step B1 is preferably 50°C to 100°C. The duration of the preliminary 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°C to 180°C or less, more preferably 130°C to 160°C. The duration of the main drying step B2 is preferably 0.5 to 30 minutes, more preferably 1 to 15 minutes.

[0090]

[0032] <Embodiment 2 for Forming a Resin Foam> In embodiment 2 for forming a resin foam, a foam is formed by foaming a resin composition with a foaming agent. As the foaming agent, a foam typically used in foam molding can be used, and from the viewpoints of environmental protection and low contamination of the foamed object, it is preferable to use a high-pressure inert gas.

[0091] Any suitable inert gas can be used as the inert gas as long as it is inert to the resin composition and can be impregnated. Examples of such inert gases include carbon dioxide, nitrogen gas, and air. These gases may be used in combination. Among these, carbon dioxide is preferred from the viewpoints of a large amount of impregnation into the resin material (polymer) and a fast impregnation rate.

[0092] The inert gas is preferably in a supercritical state. That is, it is particularly preferable to use carbon dioxide in a supercritical state. In a supercritical state, the solubility of the inert gas in the resin composition is further increased, allowing for high concentrations of the inert gas to be mixed in. In addition, the inert gas becomes highly concentrated during a sudden pressure drop, resulting in increased generation of bubble nuclei. The density of the bubbles formed by the growth of the bubble nuclei is greater than in other states even if the porosity is the same, so that fine bubbles can be obtained. The critical temperature of carbon dioxide is 31°C and the critical pressure is 7.4 MPa.

[0093] Examples of methods for forming a foam by impregnating a resin composition with a high-pressure inert gas include a gas impregnation step in which a resin composition containing a resin material (polymer) is impregnated with an inert gas under high pressure, a decompression step in which the pressure is reduced to foam the resin material (polymer), and a heating step in which bubbles are grown by heating, if necessary. In this case, a pre-formed unfoamed molded body may be impregnated with the inert gas, or a molten resin composition may be impregnated with the inert gas under pressure and then molded under reduced pressure. These steps may be performed using either a batch process or a continuous process. That is, a batch process may be used in which the resin composition is pre-formed into an appropriate shape, such as a sheet, to form an unfoamed resin molded body, and then the unfoamed resin molded body is impregnated with a high-pressure gas and foamed by releasing the pressure. Alternatively, a continuous process may be used in which the resin composition is kneaded with a high-pressure gas under pressure, molded, and then the pressure is released simultaneously, thereby simultaneously molding and foaming.

[0094] An example of producing a foam using the batch method 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 using a kneader equipped with blades such as a roller, cam, kneader, or Banbury type, and then pressed to a predetermined thickness using a hot plate press or the like to produce an unfoamed resin molded body. The unfoamed resin molded body thus obtained is placed in a high-pressure container and a high-pressure inert gas (such as carbon dioxide in a supercritical state) is injected to impregnate the unfoamed resin molded body with the inert gas. Once the inert gas has sufficiently impregnated the unfoamed resin molded body, the pressure is released (usually to atmospheric pressure) to generate bubble nuclei in the resin. The bubble nuclei may be allowed to grow at room temperature or, in some cases, may be grown by heating. Heating methods that can be used include known and conventional methods such as a water bath, oil bath, heated roll, hot air oven, far infrared rays, near infrared rays, and microwaves. After the bubbles have grown in this way, the product is rapidly cooled with cold water or the like to fix the shape, thereby obtaining a foam. The unfoamed resin molded product to be foamed is not limited to a sheet-like product, and various shapes can be used depending on the application. The unfoamed resin molded product to be foamed can also be produced by other molding methods such as extrusion molding, press molding, and injection molding.

[0095] An example of continuous foam production is shown below. For example, a resin composition is kneaded using an extruder such as a single-screw extruder or a twin-screw extruder while injecting (introducing) a high-pressure gas (particularly an inert gas, or even carbon dioxide) to impregnate the resin composition with the sufficiently high-pressure gas in a kneading / impregnation step. The resin composition is then extruded through a die or the like at the tip of the extruder to release the pressure (usually to atmospheric pressure), and foaming and foaming are simultaneously performed in a molding / decompression step. Furthermore, continuous foam molding may optionally include a heating step in which cells are grown by heating. After the cells are grown in this manner, the cells may be rapidly cooled with cold water or the like to fix the shape, if necessary. The high-pressure gas may be introduced continuously or discontinuously. Furthermore, the kneading / impregnation step and the molding / decompression step may be performed using, for example, an extruder or an injection molding machine. Heating methods for growing cell nuclei include any appropriate method, such as a water bath, an oil bath, a heated roll, a hot air oven, far infrared rays, near infrared rays, or microwaves. The foam may have any suitable shape, such as a sheet, a prism, a cylinder, or an irregular shape.

[0096] The amount of gas mixed when foam-molding 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, in order to obtain a highly foamed resin foam.

[0097] The pressure when impregnating the resin composition with an inert gas can be appropriately selected taking into consideration operability, etc. Such a pressure is, for example, preferably 6 MPa or more (e.g., 6 MPa to 100 MPa), more preferably 8 MPa or more (e.g., 8 MPa to 50 MPa). When using carbon dioxide in a supercritical state, the pressure is preferably 7.4 MPa or more from the viewpoint of maintaining the supercritical state of carbon dioxide. If the pressure is lower than 6 MPa, bubble growth during foaming is significant, the bubble diameter becomes too large, and a desirable average cell diameter (average cell diameter) may not be obtained. This is because, at low pressures, the amount of gas impregnated is relatively small compared to high pressures, the rate of bubble nucleation decreases, and the number of bubble nuclei formed decreases. Consequently, the amount of gas per bubble increases, resulting in an extremely large bubble diameter. Furthermore, in pressure regions lower than 6 MPa, even a small change in impregnation pressure significantly changes the bubble diameter and cell density, making it difficult to control the bubble diameter and cell density.

[0098] The temperature in the gas impregnation step varies depending on the type of inert gas used and the types of components in the resin composition, and can be selected from a wide range. When operability and other factors are taken into consideration, the temperature is preferably 10°C to 350°C. When an unfoamed molded body is impregnated with an inert gas, the impregnation temperature is preferably 10°C to 250°C, and more preferably 40°C to 230°C, in a batch process. When the gas-impregnated molten polymer is extruded to simultaneously foam and mold, the impregnation temperature is preferably 60°C to 350°C in a continuous process. When carbon dioxide is used as the inert gas, the temperature during impregnation is preferably 32°C or higher, and more preferably 40°C or higher, in order to maintain a supercritical state.

[0099] In the depressurizing step, the depressurizing speed is preferably 5 MPa / sec to 300 MPa / sec in order to obtain uniform fine bubbles.

[0100] The heating temperature in the heating step is preferably 40°C to 250°C, more preferably 60°C to 250°C.

[0101] In one embodiment, after obtaining a foam structure through a predetermined process (e.g., after obtaining a resin foam by the method of <Embodiment 1> or <Embodiment 2>), the foam structure is thinned and then rolled to obtain a resin foam. By undergoing such a process, a resin foam having an appropriately adjusted aspect ratio can be obtained. Furthermore, a resin foam having a small thickness (e.g., 0.2 mm or less) can be obtained. The heat-melting layer may be formed by the roll rolling.

[0102] The foam structure can be thinned using any appropriate slicer. The thickness of the foam structure after thinning is preferably 0.01 mm or more, more preferably 0.05 mm or more, even more preferably 0.1 mm or more, and particularly preferably 0.15 mm or more. The upper limit of the thickness of the foam structure after thinning is preferably 3 mm or less, more preferably 2 mm or less, even more preferably 1.5 mm or less, even more preferably 1 mm or less, even more preferably 0.8 mm or less, and particularly preferably 0.5 mm or less. Within such a range, the number of cells in the resin foam is particularly preferably adjusted, making it difficult for crushing to occur due to punching, and therefore, a resin foam with particularly excellent punching processability can be obtained.

[0103] Preferably, the rolls used for the rolling are heated rolls, and the temperature of the rolls is preferably 150°C to 250°C, more preferably 160°C to 230°C.

[0104] The rolling ratio of the foamed structure (thickness after rolling / thickness before rolling × 100) is preferably 80% or less, more preferably 10% to 80%, even more preferably 20% to 75%, and particularly preferably 30% to 75%. Within such ranges, a resin foam with an appropriately adjusted aspect ratio can be obtained.

[0105] B. Foam Member Fig. 1 is a schematic cross-sectional view of a foam member according to one embodiment. The foam member 100 has a resin foam layer 10 and a pressure-sensitive 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-described resin foam.

[0106] The thickness of the pressure-sensitive adhesive layer is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 7 μm or more, and particularly preferably 8 μm or more. The thickness of the pressure-sensitive adhesive layer is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and most preferably 50 μm or less. When the thickness of the pressure-sensitive adhesive layer is within the above range, the foam material of the present invention can exhibit excellent impact absorption properties.

[0107] The pressure-sensitive adhesive layer may be a layer made of any appropriate pressure-sensitive adhesive. Examples of pressure-sensitive adhesives constituting the pressure-sensitive adhesive layer include rubber-based pressure-sensitive adhesives (synthetic rubber-based pressure-sensitive adhesives, natural rubber-based pressure-sensitive adhesives, etc.), urethane-based pressure-sensitive adhesives, acrylic urethane-based pressure-sensitive adhesives, acrylic-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, polyester-based pressure-sensitive adhesives, polyamide-based pressure-sensitive adhesives, epoxy-based pressure-sensitive adhesives, vinyl alkyl ether-based pressure-sensitive adhesives, fluorine-based pressure-sensitive adhesives, and rubber-based pressure-sensitive adhesives. The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is preferably at least one selected from acrylic-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, and rubber-based pressure-sensitive adhesives. Only one type of such pressure-sensitive adhesive may be used, or two or more types may be used. The pressure-sensitive adhesive layer may be a single layer, or two or more layers.

[0108] Pressure-sensitive adhesives can be classified by adhesive form, for example, emulsion-type pressure-sensitive adhesives, solvent-type pressure-sensitive adhesives, ultraviolet-crosslinking (UV-crosslinking) pressure-sensitive adhesives, electron-beam-crosslinking (EB-crosslinking) pressure-sensitive adhesives, hot-melt pressure-sensitive adhesives, etc. Only one type of such pressure-sensitive adhesive may be used, or two or more types may be used.

[0109] The water vapor permeability of the pressure-sensitive adhesive layer is preferably 50 (g / (m ２ 24 hours)) or less, and more preferably 30 (g / (m ２ 24 hours)) or less, and more preferably 20 (g / (m ２ 24 hours)) or less, and particularly preferably 10 (g / (m ２When the water vapor permeability of the pressure-sensitive adhesive layer is within the above range, the foam sheet can stabilize its impact absorption properties without being affected by moisture. The water vapor permeability can be measured, for example, according to JIS Z 0208 under test conditions of 40°C and a relative humidity of 92%.

[0110] The adhesive constituting the adhesive layer may contain any appropriate other components as long as the effects of the present invention are not impaired. Examples of other components include other polymer components, softeners, antioxidants, curing agents, plasticizers, fillers, antioxidants, thermal polymerization initiators, photopolymerization initiators, UV absorbers, light stabilizers, colorants (pigments, dyes, etc.), solvents (organic solvents), surfactants (e.g., ionic surfactants, silicone surfactants, fluorine-based 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.). The thermal polymerization initiator or photopolymerization initiator may be included in the material for forming the polymer component.

[0111] The foam material can be produced by any appropriate method, such as a method of laminating a resin foam layer and a pressure-sensitive adhesive layer, or a method of laminating a pressure-sensitive adhesive layer-forming material and a resin foam layer, and then forming a pressure-sensitive adhesive layer by a curing reaction or the like.

[0112] The present invention will be specifically described below using examples, but the present invention is not limited to these examples. The test and evaluation methods used in the examples are as follows. The term "parts" means "parts by weight" unless otherwise specified, and the term "%" means "% by weight" unless otherwise specified.

[0113] <Evaluation Method> (1) Apparent Density The density (apparent density) of the resin foam was calculated as follows. The resin foam obtained in each of the Examples and Comparative Examples was punched out to a size of 20 mm x 20 mm to prepare a test piece, and the dimensions of the test piece were measured with a vernier caliper. Next, the weight of the test piece was measured with an electronic balance. Then, the apparent density (g / cm) was calculated using the following formula. ３ ) = weight of test piece / volume of test piece

[0114] (2) 50% Compression Load: This was measured in accordance with the method for measuring the compression hardness of resin foams described in JIS K 6767. Specifically, the resin foams obtained in the Examples and Comparative Examples were cut into test pieces of 30 mm x 30 mm in size, and the stress (N) when compressed to a compression rate of 50% at a compression rate of 10 mm / min was measured per unit area (1 cm). ２ ) and converted to a 50% compression load (N / cm ２ )

[0115] (3) 25% Compression Load: This was measured in accordance with the method for measuring the compression hardness of resin foams described in JIS K 6767. Specifically, the resin foams obtained in the examples and comparative examples were cut into test pieces of 30 mm x 30 mm in size, and the stress (N) when compressed at a compression rate of 10 mm / min until the compression ratio reached 25% was measured per unit area (1 cm). ２ ) and converted to a 25% compression load (N / cm ２ )

[0116] (4) Coefficient of variation of average bubble diameter (average cell diameter), maximum bubble diameter (maximum cell diameter), and bubble diameter (cell diameter) The resin foam was cut using a razor blade in the direction perpendicular to the main surface of the resin foam (thickness direction). A digital microscope (trade name "VHX-500", manufactured by Keyence Corporation) was used as a measuring instrument to capture an image of the cross section of the resin foam. The image was analyzed using the instrument's analysis software to determine the number-average bubble diameter (average cell diameter) and maximum bubble diameter (maximum cell diameter). The number of bubbles in the captured enlarged image was approximately 400. The standard deviation was calculated from all cell diameter data, and the coefficient of variation was calculated using the following formula: Coefficient of variation = standard deviation / average bubble diameter (average cell diameter).

[0117] (5) Cell diameter aspect ratio Using a digital microscope (product name "VHX-2000" manufactured by Keyence Corporation) as a measuring instrument, the aspect ratio of the cells in the resin foams obtained in the Examples and Comparative Examples was measured by the following method. The resin foam was cut with a razor blade in the direction perpendicular to the main surface of the resin foam (thickness direction), and the cut surface was measured with a microscope (for example, "VHX-2000" manufactured by Keyence) to determine the cell diameter aspect ratio of a predetermined area (3 mm ２ The area was observed at 100x magnification, and the length of each bubble in the thickness direction and the length perpendicular to the thickness direction were measured. Similar measurements were performed on all bubbles present within a given area. The aspect ratio of a bubble was calculated by dividing the length perpendicular to the thickness direction by the length in the thickness direction. The same calculation was performed on all bubbles, and the average value was used as the "aspect ratio of bubbles in the resin foam."

[0118] (6) Melt Tension The recycled resin contained in the resin foam was extruded into a molten strand at an extrusion speed of 8.8 mm / min using a twin capillary rheometer "RH7-2" (manufactured by Rosand Precision) at a temperature 20°C higher than the melting point of the recycled resin and an orifice diameter of 1 mm, and the strand was taken up at a take-up speed of 0.5 m / min. The take-up speed was increased in increments of 0.1 m / min, and the melt tension at which the strand-shaped resin broke was taken as the "melt tension."

[0119] (7) Die swell ratio Using an extensional viscometer (trade name "RH-7", Malvern Instruments) as a measuring instrument, a sample (size: 5 mm square) was placed in a cylinder at a temperature 20 ° C higher than the melting point of the resin constituting the resin foam, and the sample was allowed to melt for 7 minutes. Then, the molten material was extruded at a shear rate of 20 mm / s into a die having a length of 10 mm and a diameter of 1 mmφ, and the diameter of the resulting string-like molded product was measured using a digital caliper (trade name "CD67-s PM", Mitutoyo Corporation), and the die swell ratio was calculated using the following formula. Die swell ratio = diameter (mm) / die diameter (mm) The recycled resin contained in the resin foam and the resin composition forming the resin foam were used as the sample, and the die swell ratio was measured for these samples.

[0120] (8) CO derived from raw materials ２ Amount generated [kg / m ２ ] CO required to manufacture petroleum-derived resin (non-recycled resin) ２ The amount generated is 1.8 kg / kg-resin, and the CO required to produce recycled resin ２ The generated amount is set to 0 kg / kg-resin, and the foam is 1 m ２ When the weight of the petroleum-derived resin (non-recycled resin) contained in the foam is wp and the weight of the recycled resin is wb, the CO2 derived from the raw materials of the foam is ２ The amount of generated dust can be calculated by 1.8×wp+0×wb.

[0121] (9) Punching Processability The resin foam was punched using a mold (two processing blades (trade name "NCA07", thickness 0.7 mm, blade angle 43°, manufactured by Nakayama Corporation)) to a size of 10 mm x 10 mm in the MD direction (flow direction) and the TD direction (direction perpendicular to the flow direction), respectively. The cross section in the MD direction and the TD direction where the thickness change was greater was observed with a microscope (trade name "VHX-2000", manufactured by Keyence Corporation), and the thickness of the end and center parts was measured from the image. Using the measured thickness, the thickness recovery rate after processing was measured using the following formula. The greater the thickness recovery rate, the smaller the shape change due to punching and the more excellent the punching processability. Thickness recovery rate after processing (%) = 100 x (1 - (center thickness - end thickness) / center thickness)

[0122] (10) Thickness recovery rate (instantaneous recovery rate) ２ The load was applied and maintained for 120 seconds, the compression was released, and the thickness of the resin foam 0.5 seconds after the release (thickness 0.5 seconds after the compressed state was released) was measured. The thickness recovery rate (instantaneous recovery rate) was calculated from the "thickness 0.5 seconds after the compressed state was released" and the thickness of the resin foam before the load was applied (initial thickness) using the following formula: Thickness recovery rate (%) = {(thickness 0.5 seconds after the compressed state was released) / (initial thickness)} × 100

[0123] (11) Presence or absence of damage after carrier tape processing After storing a resin foam (width: 10 mm x length: 120 mm) in an atmosphere of temperature: 23 ± 2 ° C. and humidity: 50 ± 5 RH% for 24 hours or more (pretreatment conditions conforming to JIS Z 0237), it was fixed to a SUS plate using a double-sided adhesive tape (product name "No. 5603" manufactured by Nitto Denko Corporation) with a width: 10 mm x length: 120 mm, and pressed with a 2 kg roller once back and forth so that the opposite side of the resin foam was in contact with the adhesive layer surface of a weak adhesive carrier tape (product name "3165S" manufactured by Kern Co., Ltd.) and left for 24 hours to prepare a measurement sample. The carrier tape was quickly peeled off by hand, and the state of peeling was visually confirmed to evaluate whether the foam was attached to the surface of the carrier tape. In Table 1, if no foam adhered to the surface of the carrier tape, it was marked as "○", if broken pieces of foam were observed, it was marked as "△", and if interlayer destruction of the foam was observed, it was marked as "×".

[0124] (12) Interlaminar Strength A resin foam (width: 20 mm x length: 120 mm) was stored for 24 hours or more under an atmosphere of temperature: 23 ± 2 ° C. and humidity: 50 ± 5 RH% (pretreatment conditions conforming to JIS Z 0237), and then fixed to a SUS plate using a double-sided adhesive tape (trade name "No. 5000NS" manufactured by Nitto Denko Corporation) with a width of 20 mm x length of 120 mm. The opposite side was pressed with a double-sided adhesive tape (trade name "No. 5000NS" manufactured by Nitto Denko Corporation) using a 2 kg roller, with one stroke back and forth. The sample was left for 30 minutes to prepare a measurement sample. The sample was peeled off at a peel angle of 90° at a speed of 300 mm / min using a tensile tester, and the strength at which the resin foam broke was measured.

[0125] (13) Impact Absorption A test specimen was formed by placing a resin foam, double-sided tape (product number: No. 5603W, manufactured by Nitto Denko), and a PET film (product number: Diafoil MRF75, manufactured by Mitsubishi Plastics) in this order on an impact force sensor. A 66 g iron ball was dropped on the test specimen from a height of 50 cm above the PET film to measure the impact force F1. In addition, an iron ball was dropped directly onto the impact force sensor as described above to measure the blank impact force F0. From F1 and F0, the impact absorption (%) was calculated using the formula (F0-F1) / F0×100.

[0126] [Example 1] [Preparation of polyolefin resin foam composition (virgin pellets)] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230°C, load 21.2 N), density: 0.90 g / cm ３50 parts by weight of a polyolefin elastomer (melt tension at 230°C: 16 cN), 50 parts by weight of a polyolefin elastomer (ethylene content: 0 wt%, propylene content: 100 wt%, weight average molecular weight: 645,000, molecular weight distribution: 8.43), 10 parts by weight of magnesium hydroxide (trade name "KISUMA 5P" manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at a cylinder temperature of 200°C in a twin-screw kneader manufactured by The Japan Steel Works, Ltd. to obtain a polyolefin resin foam composition. This composition was extruded into a strand, water-cooled, and formed into cylindrical pellets with a cross-sectional radius of 2 mm and a height of 4 mm to obtain virgin pellets A. [Preparation of Polyolefin Resin Foam] Virgin pellets A were loaded into a JSW single-screw extruder, and carbon dioxide was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere of 220°C. The carbon dioxide was injected at 5% by weight of the polymer components of the polyolefin resin foam composition. After sufficient carbon dioxide saturation, the mixture was extruded through a die to obtain a polyolefin resin foam. [Preparation of Recycled Resin Pellets] The waste foam recovered in the polyolefin resin foam production process (the skin layer of the foam and the unnecessary portion after punching) was recycled into pellets using a Hagiwara Kogyo Co., Ltd. single-screw extruder with an integrated shredder. Specifically, the waste foam was loaded into the hopper of a shredder equipped with a nip-type feed roll equipped with a speed adjustment mechanism, and then crushed by being pressed against the shredder by a slider attached to the hopper. The crushed waste foam was fed into an extruder by a feed flight installed on the extension of the shredder, and melted at a cylinder temperature of 180°C and a screw rotation speed of 130 rpm. The molten waste foam was removed of foreign matter using a screen mesh (#60) installed at the extruder outlet, and then fed into a hot-cut pelletizer through the nozzle holes of a circular die and molded into cylindrical pellets with a cross-sectional radius of 2 mm and a height of 4 mm, thereby obtaining recycled resin pellets B. [Preparation of resin foam containing recycled resin] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230°C, load 21.2 N), density: 0.90 g / cm ３, ethylene content: 0 wt%, propylene content: 100 wt%, weight average molecular weight: 645,000, molecular weight distribution: 8.43) 31 parts by weight, recycled resin pellet B (MFR: 4.0 g / 10 min (230°C, load 21.2 N) 55 parts by weight, polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°) 10 parts by weight, polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°) 4 parts by weight, magnesium hydroxide (trade name "KISUMA Five parts by weight of "Kyowa Chemical Industry Co., Ltd." (product name "5P"), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into strands, cooled with water, and formed into pellets. The pellets were placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere with a foaming temperature of 176°C. Carbon dioxide gas was injected at a ratio of 5.2 parts by weight per 100 parts by weight of resin. After sufficient carbon dioxide gas saturation, the mixture was cooled to a temperature suitable for foaming and extruded through a die to obtain a sheet-like resin foam. The mixture was then thinned using a slicer to obtain Resin Foam A with a thickness of 1.0 mm. The resulting Resin Foam A was subjected to the above-mentioned evaluations. The results are shown in Table 1.

[0127] [Example 2] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３26 parts by weight of recycled resin pellets B (MFR: 4.0 g / 10 min (230°C, load 21.2 N)) 55 parts by weight, polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°) 17 parts by weight, polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°) 7.3 parts by weight, magnesium hydroxide (trade name "KISUMA Five parts by weight of "Kyowa Chemical Industry Co., Ltd." (product name "5P"), 10 parts by weight of carbon (product name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into strands, cooled with water, and formed into pellets. The pellets were placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere with a foaming temperature of 174°C. Carbon dioxide gas was injected at a ratio of 4.8 parts by weight per 100 parts by weight of resin. After sufficient carbon dioxide gas saturation, the mixture was cooled to a temperature suitable for foaming and extruded through a die to obtain a sheet-like resin foam. The mixture was then thinned using a slicer to obtain Resin Foam B with a thickness of 1.0 mm. The resulting Resin Foam B was subjected to the above-mentioned evaluations. The results are shown in Table 1.

[0128] [Example 3] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３18 parts by weight of recycled resin pellets B (MFR: 4.0 g / 10 min (230°C, load 21.2 N)) 55 parts by weight, polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°) 22.5 parts by weight, polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°) 9.6 parts by weight, magnesium hydroxide (trade name "KISUMA Five parts by weight of "Kyowa Chemical Industry Co., Ltd." (product name "5P"), 5 parts by weight of carbon (product name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into strands, cooled with water, and formed into pellets. The pellets were placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere with a foaming temperature of 173°C. Carbon dioxide gas was injected at a ratio of 4.8 parts by weight per 100 parts by weight of resin. After sufficient carbon dioxide gas saturation, the mixture was cooled to a temperature suitable for foaming and extruded through a die to obtain a sheet-like resin foam. The mixture was then thinned using a slicer to obtain Resin Foam C with a thickness of 1.0 mm. The resulting Resin Foam C was subjected to the above-mentioned evaluations. The results are shown in Table 1.

[0129] [Example 4] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３, ethylene content: 0 wt%, propylene content: 100 wt%, weight average molecular weight: 645,000, molecular weight distribution: 8.43) 31 parts by weight, recycled resin pellets B (MFR: 4.0 g / 10 min (230°C, load 21.2 N) 61 parts by weight, polyolefin elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°) 7 parts by weight, polyolefin elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°) 3 parts by weight, magnesium hydroxide (trade name "KISUMA Five parts by weight of "Kyowa Chemical Industry Co., Ltd." (product name "5P"), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into strands, cooled with water, and formed into pellets. The pellets were placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere with a foaming temperature of 172°C. Carbon dioxide gas was injected at a ratio of 4.7 parts by weight per 100 parts by weight of resin. After sufficient carbon dioxide gas saturation, the mixture was cooled to a temperature suitable for foaming and extruded through a die to obtain a sheet-like resin foam. The mixture was then thinned using a slicer to obtain Resin Foam C with a thickness of 1.0 mm. The resulting Resin Foam C was subjected to the above-mentioned evaluations. The results are shown in Table 1.

[0130] [Example 5] A resin foam containing recycled resin was obtained in the same manner as in Example 4, except that the foaming temperature was 167°C and the amount of carbon dioxide gas injected was 3.5 parts by weight per 100 parts by weight of resin. The foam was then thinned using a slicer to obtain Resin Foam D with a thickness of 1.0 mm. The obtained Resin Foam D was subjected to the above evaluations. The results are shown in Table 1.

[0131] [Example 6] A resin foam containing recycled resin was obtained in the same manner as in Example 4, except that the foaming temperature was 170°C and the amount of carbon dioxide gas injected was 4.5 parts by weight per 100 parts by weight of resin. The foam was then sliced ​​into a thin film using a slicer to obtain Resin Foam E with a thickness of 1.0 mm. The obtained Resin Foam E was subjected to the above evaluations. The results are shown in Table 1.

[0132] [Example 7] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３ , ethylene content: 0 wt%, propylene content: 100 wt%, weight average molecular weight: 645,000, molecular weight distribution: 8.43) 24 parts by weight, recycled resin pellets B (MFR: 4.0 g / 10 min (230°C, load 21.2 N) 73 parts by weight, polyolefin-based elastomer (melt flow rate (MFR): 15 g / 10 min, JIS A hardness: 79°) 6 parts by weight, polyolefin-based elastomer (melt flow rate (MFR): 2.2 g / 10 min, JIS A hardness: 69°) 2 parts by weight, magnesium hydroxide (trade name "KISUMA Five parts by weight of "Kyowa Chemical Industry Co., Ltd." (product name "5P"), 10 parts by weight of carbon (trade name "Asahi #35" manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were kneaded at 200°C in a twin-screw kneader manufactured by Japan Steel Works (JSW), extruded into strands, cooled with water, and formed into pellets. The pellets were placed in a single-screw extruder manufactured by Japan Steel Works, and carbon dioxide gas was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere with a foaming temperature of 171°C. Carbon dioxide gas was injected at a ratio of 4 parts by weight per 100 parts by weight of resin. After sufficient saturation with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming and extruded through a die to obtain a sheet-like resin foam. The mixture was then thinned using a slicer to obtain Resin Foam F with a thickness of 1.0 mm. The resulting Resin Foam F was subjected to the above-mentioned evaluations. The results are shown in Table 1.

[0133] [Example 8] A resin foam containing recycled resin was obtained in the same manner as in Example 7, except that the foaming temperature was 170°C and the amount of carbon dioxide gas injected was 3.9 parts by weight per 100 parts by weight of the resin. The foam was then sliced ​​into a thin film using a slicer, to obtain a resin foam G having a thickness of 1.0 mm.

[0134] Comparative Example 1 Preparation of Polyolefin Resin Foam Composition (Virgin Pellets) 45 parts by weight of polypropylene (melt tension of 25 cN at 230°C), 45 parts by weight of polyolefin elastomer (melt tension of 16 cN at 230°C), 10 parts by weight of polyethylene, 1 part by weight of stearic acid monoglyceride, 10 parts by weight of magnesium hydroxide, and 10 parts by weight of carbon were kneaded in a twin-screw kneader manufactured by The Japan Steel Works, Ltd. at a cylinder temperature of 200°C to obtain a polyolefin resin foam composition. This composition was extruded into a strand, cooled with water, and molded into cylindrical pellets with a cross-sectional radius of 2 mm and a height of 4 mm to obtain virgin pellets C. Preparation of Polyolefin Resin Foam Virgin pellets C were placed in a single-screw extruder manufactured by JSW, and carbon dioxide was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere of 220°C. The carbon dioxide was injected at a ratio of 5 wt% of the polymer components of the polyolefin resin foam composition. After sufficient saturation with carbon dioxide, the mixture was extruded through a die to obtain a polyolefin-based resin foam. [Preparation of Recycled Resin Pellets] Recycled resin pellets D were prepared from the waste foam recovered in the polyolefin-based resin foam production process using the method described in Example 1. [Preparation of Resin Foam Containing Recycled Resin] 23 parts by weight of recycled resin pellets D were blended with 90 parts by weight of virgin pellets C, and the mixture was placed in a short-screw extruder manufactured by The Japan Steel Works, Ltd., and carbon dioxide was injected at a pressure of 13 MPa (12 MPa after injection) in an atmosphere of 220°C. The carbon dioxide was injected at 5% by weight of the polymer component of the resin pellets. After sufficient gas saturation, the mixture was extruded through a die to obtain a recycled resin-containing polyolefin-based resin foam. The mixture was then thinned using a slicer to obtain a resin foam H with a thickness of 1.0 mm.

[0135] [Comparative Example 2] Polypropylene (propylene homopolymer, MFR: 0.4 g / 10 min (230 ° C, load 21.2 N), density: 0.90 g / cm ３50 parts by weight of a resin containing 0% ethylene, 100% propylene, 645,000 weight average molecular weight, and 8.43 molecular weight distribution, 50 parts by weight of a polyolefin elastomer (melt tension of 16 cN at 230°C), 10 parts by weight of magnesium hydroxide (Kisuma 5P, manufactured by Kyowa Chemical Industry Co., Ltd.), 10 parts by weight of carbon (Asahi #35, manufactured by Asahi Carbon Co., Ltd.), and 1 part by weight of stearic acid monoglyceride were mixed in a Japan Steel Works (JSW) twin-screw mixer at 174°C, extruded into strands, cooled with water, and pelletized. The pellets were then placed in a Japan Steel Works single-screw extruder and injected with carbon dioxide gas at a pressure of 13 MPa (12 MPa after injection) under a 220°C atmosphere. The carbon dioxide gas was injected at a ratio of 5.2 parts by weight per 100 parts by weight of resin. After being fully saturated with carbon dioxide gas, the mixture was cooled to a temperature suitable for foaming and extruded through a die to obtain a sheet-like resin foam. The resin foam was then thinned using a slicer to obtain Resin Foam I with a thickness of 1.0 mm. The obtained resin foam was subjected to the above evaluations. The results are shown in Table 1.

[0136] Comparative Example 3 A resin foam was obtained in the same manner as in Example 7, except that the foaming temperature was 169°C and the amount of carbon dioxide gas injected was 3.5 parts by weight per 100 parts by weight of the resin. The resin foam was then sliced ​​into a thin film using a slicer, to obtain Resin Foam J having a thickness of 1.0 mm.

[0137]

[0138] The resin foam of the present invention can be suitably used, for example, as a cushioning material for electronic devices.

[0139] 100 Foam member 10 Resin foam layer (resin foam) 20 Pressure-sensitive adhesive layer

Claims

1. Having a cellular structure, and satisfying the following formula (1), interlaminar strength (N / 20 mm)>apparent density (g / cm ３ ) x 40 + 3 ... (1) Resin foam.

2. Apparent density is 0.4 g / cm ３ The resin foam according to claim 1 , wherein:

3. The resin foam according to claim 1, having an interlaminar strength of 3 N / 20 mm or more.

4. The resin foam according to claim 1, having an average cell diameter of 50 μm or more.

5. 50% compression load is 40N / cm ２ The resin foam according to claim 1 , wherein:

6. The resin foam is applied with a load of 1000 g / cm ２ The resin foam according to claim 1, having a thickness recovery rate of 80% or more after maintaining a load of 1.0 mm for 120 seconds.

7. The resin foam according to claim 1, wherein the coefficient of variation of the cell diameter is 0.6 or less.

8. The resin foam contains recycled resin, and the recycled resin ratio in the resin foam is 0.2 or more, and satisfies the following formula (2), and the apparent density (g / cm ３ ) <0.046 × recycled resin ratio + 0.0121 (2) The resin foam according to claim 1.

9. The resin foam according to claim 8, wherein the recycled resin contains polyolefin.

10. The resin foam according to claim 9, wherein the polyolefin used as the recycled resin has a melt flow rate (MFR) of less than 10 g / 10 min at a temperature of 230° C.

11. The resin foam according to claim 9, wherein the melt tension of the polyolefin as the recycled resin is 10 cN or more.

12. The resin foam according to claim 9, wherein the die swell ratio at a melting point of the polyolefin as the recycled resin + 20°C is 1.5 or less.

13. The resin foam according to claim 9, wherein the polyolefin is polyethylene or polypropylene.

14. The resin foam according to claim 9, wherein the polyolefin is a mixture of a polyolefin other than a polyolefin-based elastomer and a polyolefin-based elastomer.

15. The resin foam according to claim 1, wherein the die swell ratio at the melting point of the resin composition forming the resin foam + 20°C is 1.5 or less.

16. The resin foam according to claim 1, having a heat-fusible layer on one or both sides.

17. A foam member comprising a resin foam layer and a pressure-sensitive adhesive layer disposed on at least one side of the resin foam layer, the resin foam layer being a resin foam according to any one of claims 1 to 16.

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