阅读说明：本技术 发泡体片及粘合带 (Foam sheet and adhesive tape ) 是由 松井梨绘 于 2020-02-28 设计创作，主要内容包括：发泡体片为包含生物质系聚烯烃树脂(A)的发泡体片,发泡体片中的生物质率为40质量％以上,厚度为0.05～1.5mm,发泡倍率为1.5～20倍。(The foam sheet is a foam sheet comprising a biomass-based polyolefin resin (A), wherein the biomass fraction in the foam sheet is 40 mass% or more, the thickness is 0.05 to 1.5mm, and the expansion ratio is 1.5 to 20 times.)

1. A foam sheet comprising a biomass-based polyolefin resin (A), wherein the biomass content of the foam sheet is 40 mass% or more, the thickness is 0.05 to 1.5mm, and the expansion ratio is 1.5 to 20 times.

2. The foam sheet according to claim 1, further comprising a polyolefin resin (B) other than the biomass-based polyolefin resin (A).

3. The foam sheet according to claim 2, the polyolefin resin (B) being 1 selected from a polyethylene resin and an ethylene-vinyl acetate copolymer.

4. The foam sheet according to claim 3, wherein the polyethylene resin comprises a polyethylene resin polymerized by a metallocene compound polymerization catalyst.

5. The foam sheet according to claim 3 or 4, wherein the polyethylene resin has a melt index MI of 1.0 to 12g/10 min or more.

6. The foam sheet according to any one of claims 1 to 5, wherein the biomass-based polyolefin resin (A) has a melt index of 1.5 to 12g/10 min or more.

7. The foam sheet according to any one of claims 1 to 6, wherein the average cell diameter in the MD direction and the average cell diameter in the TD direction are both 20 to 350 μm or less.

8. The foam sheet according to any one of claims 1 to 7, wherein the ratio of the average cell diameter in the MD direction and the TD direction to the average cell diameter in the ZD direction is 1.8 to 9.

9. The foam sheet according to any one of claims 1 to 8, wherein the maximum cell diameter in the foam sheet is 500 μm or less.

10. The foam sheet according to any one of claims 1 to 9, which has a 25% compressive strength of 200kPa or less.

11. The foam sheet according to any one of claims 1 to 10, which is used for an electronic device.

12. A pressure-sensitive adhesive tape comprising the foam sheet according to any one of claims 1 to 11 and a pressure-sensitive adhesive material provided on one or both surfaces of the foam sheet.

Technical Field

The present invention relates to a foam sheet containing a biomass-based polyolefin resin, and an adhesive tape provided with the foam sheet.

Background

Foam sheets obtained by foaming a resin are widely used in various fields such as buildings, electronic equipment, and vehicles. The resin used for the foam sheet is generally a resin derived from petroleum, but a large amount of carbon dioxide is discharged in the production process, disposal process, and the like, and thus the load on the environment becomes a problem. Therefore, in order to solve such problems, studies have been made on the use of natural resins.

For example, patent document 1 describes a foam having a biomass degree of 25% or more as measured by ASTM D6866 (made in 2004) using polyethylene (biomass-based polyethylene) containing a component derived from natural ethylene. Patent document 2 discloses a foam containing 20 to 100 mass% of a low-density polyethylene resin containing a natural ethylene component, having a biomass content of 25% or more and a gel fraction of 5 to 60% or less.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-155225

Patent document 2: japanese patent laid-open publication No. 2018-65898

Disclosure of Invention

Problems to be solved by the invention

In recent years, downsizing of electronic devices and high functionality of various parts have been advanced, and accompanying this, there has been a demand for a foam sheet for use in electronic devices to be thin and to improve various performances such as impact resistance and flexibility. On the other hand, there is a demand for a reduction in environmental load, and a foam sheet used for electronic equipment uses a biomass resin to reduce environmental load and to improve various performances such as impact resistance.

The present invention addresses the problem of providing a foam sheet that contains a biomass-based resin and has low environmental impact resistance and other various properties even when the thickness is reduced.

Means for solving the problems

As a result of intensive studies, the present inventors have found that the above problems can be solved by adjusting the biomass ratio in the foam sheet to 40 mass% or more, adjusting the thickness to 0.05 to 1.5mm, and adjusting the expansion ratio to 1.5 to 20 times, and have completed the following invention.

That is, the present invention relates to the following [1] to [12 ].

[1] A foam sheet comprising a biomass-based polyolefin resin (A), wherein the biomass content of the foam sheet is 40 mass% or more, the thickness is 0.05 to 1.5mm, and the expansion ratio is 1.5 to 20 times.

[2] The foam sheet according to the above [1], which further contains a polyolefin resin (B) other than the biomass-based polyolefin resin (A).

[3] The foam sheet according to the above [2], wherein the polyolefin resin (B) is 1 selected from the group consisting of a polyethylene resin and an ethylene-vinyl acetate copolymer.

[4] The foam sheet according to the above [2] or [3], wherein the polyethylene resin comprises a polyethylene resin polymerized by a metallocene compound polymerization catalyst.

[5] The foam sheet according to the above [3] or [4], wherein the polyethylene resin has a Melt Index (MI) of 1.0 to 12g/10 min or more.

[6] The foam sheet according to any one of the above [1] to [5], wherein the melt index of the biomass-based polyolefin resin (A) is 1.5 to 12g/10 min or more.

[7] The foam sheet according to any one of the above [1] to [6], wherein the average cell diameter in the MD direction and the average cell diameter in the TD direction are both 20 to 350 μm or less.

[8] The foam sheet according to any one of the above [1] to [7], wherein the ratio of the average cell diameter in the MD direction and the TD direction to the average cell diameter in the ZD direction is 1.8 to 9.

[9] The foam sheet according to any one of the above [1] to [8], wherein the maximum cell diameter in the foam sheet is 500 μm or less.

[10] The foam sheet according to any one of the above [1] to [9], which has a 25% compressive strength of 200kPa or less.

[11] The foam sheet according to any one of [1] to [10] above, which is used for an electronic device.

[12] An adhesive tape comprising the foam sheet according to any one of [1] to [11] and an adhesive material provided on one or both surfaces of the foam sheet.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, in a foam sheet containing a biomass resin and having a low environmental load, various performances such as impact resistance can be improved even when the thickness is made thin.

Detailed Description

[ foam sheet ]

The foam sheet of the present invention is a foam comprising at least a biomass-based polyolefin resin (A), wherein the biomass fraction in the foam sheet is 40 mass% or more, the thickness is 0.05 to 1.5mm, and the expansion ratio is 1.5 to 20 times.

In the present invention, the biomass fraction of the foam sheet is set to 40 mass% or more and the expansion ratio is adjusted to a specific range, whereby the environmental load is low and the maximum cell diameter can be made small while the cell ratio is set to a constant value or more even in a thin foam sheet. As a result, various performances required for the foam sheet such as impact resistance can be provided even in a thin foam sheet.

The present invention will be described in detail below.

[ Biomass-based polyolefin resin (A) ]

The foam sheet of the present invention is a foam containing at least a biomass-based polyolefin resin (a). The biomass-based polyolefin resin (a) used in the present invention is a polyolefin resin containing a naturally derived component, and specifically, a polyethylene-based resin containing naturally derived ethylene as a structural unit can be exemplified. More specifically, homopolymers of ethylene derived from natural sources and copolymers of ethylene derived from natural sources and olefins derived from petroleum are mentioned, and among these, copolymers of ethylene derived from natural sources and olefins derived from petroleum are preferable from the viewpoint of availability and the like. The petroleum-derived olefin is preferably 1 or more selected from the group consisting of ethylene, propylene, 1-butene and 1-hexene, and among these, ethylene is preferred. Further, the biomass-based polyolefin resin (a) may be an ethylene-vinyl acetate copolymer containing ethylene of natural origin as a structural unit.

The biomass-based polyolefin resin (A) may be used alone in 1 kind or in combination with 2 or more kinds.

The content of the structural unit derived from natural ethylene in the biomass-based polyolefin resin (a) is preferably 40 to 98 mass%, more preferably 75 to 97 mass%, and still more preferably 85 to 96 mass%. That is, the biomass ratio of the biomass-based polyolefin resin (a) is preferably 40 to 98% by mass, more preferably 75 to 97% by mass, and still more preferably 85 to 96% by mass.

When the content of the structural unit derived from natural ethylene is not less than the lower limit, the environmental load is reduced, and the effect of reducing carbon dioxide, for example, is also improved. On the other hand, if the content of the structural unit derived from natural ethylene is not more than the upper limit, the crystallization rate becomes small when a foamable resin sheet described later is obtained, and therefore, a foamable resin sheet having a uniform thickness in the width direction is easily obtained, and various physical properties are easily improved even if the foamable resin sheet is thinned.

The Melt Index (MI) of the biomass-based polyolefin resin (A) is preferably 1.5 to 12g/10 min or more. If the melt index is in the above range, the resin is soft and foaming proceeds appropriately. Therefore, the foam sheet has improved flexibility, and the maximum cell diameter can be reduced to improve the impact resistance, flexibility, and the like of the foam sheet. From these viewpoints, the melt index of the biomass-based polyolefin resin (A) is more preferably 2.0 to 10g/10 min, still more preferably 2.2 to 7.0g/10 min, and yet more preferably 2.4 to 5.0g/10 min.

In the present specification, the melt index can be measured at 190 ℃ under a 2.16kg load in accordance with ASTM D1238.

The density of the biomass-based polyolefin resin (A) is, for example, 0.900 to 0.940g/cm³Preferably 0.910 to 0.930g/cm³. When the density of the biomass-based polyolefin resin (A) is within the above range, various performances required as a foam, such as impact resistance and flexibility, can be easily improved.

The biomass-based polyolefin resin (a) can be produced by a known method using natural-source ethylene and, if necessary, petroleum-source olefin. Ethylene, which is a natural source of the biomass-based polyolefin resin (a), is obtained by, for example, fermenting sugar obtained from sugar cane, which is a natural raw material, with saccharomyces cerevisiae, which is a fermentation agent, to produce ethanol, and converting the ethanol into ethylene by a contact reaction at a temperature exceeding 300 ℃ using a catalyst such as γ -alumina.

[ resins other than the Biomass-based polyolefin resin (A) ]

The foam sheet may contain a resin other than the biomass-based polyolefin resin (a), and for example, preferably contains a polyolefin resin (B). The polyolefin resin (B) is generally a petroleum-based polyolefin resin produced from a petroleum-derived polyolefin. By using the polyolefin resin (B), the foam sheet can be made thin. Further, the compression strength, the maximum cell diameter, and the average cell diameter of the foam sheet can be easily adjusted to be within the ranges described below.

Examples of the polyolefin resin (B) include polyethylene resins, polypropylene resins, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and the like, and among them, at least 1 selected from polyethylene resins and ethylene-vinyl acetate copolymers is preferable, and polyethylene resins are more preferable. The polyolefin resin (B) may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

Polyethylene resin

Examples of the polyethylene resin include those obtained by polymerization using a polymerization catalyst such as a ziegler-natta compound, a metallocene compound, or a chromium oxide compound, and those obtained by polymerization using a polymerization catalyst of a metallocene compound are preferably used. By using a polyethylene resin obtained by polymerization using a polymerization catalyst of a metallocene compound, crosslinking and the like described later can be made uniform, and various properties as a foam such as flexibility can be easily improved even when the foam is made thin. Further, it is easy to make the maximum bubble diameter small.

Further, the polyethylene resin preferably has a density of 0.930g/cm³The Low Density Polyethylene (LDPE) described below is more preferably a Linear Low Density Polyethylene (LLDPE). By using the linear low-density polyethylene, flexibility can be imparted to the foam sheet, and the foam sheet can be made thin. The linear low-density polyethylene is more preferably a linear low-density polyethylene obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more based on the total monomer amount) with a small amount of an α -olefin as required.

Examples of the α -olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Among them, preferred is an alpha-olefin having 4 to 10 carbon atoms.

The polyethylene resin obtained by polymerization in the polymerization catalyst of the metallocene compound is preferably a linear low-density polyethylene, from the viewpoint of making the foam sheet thin and further improving flexibility.

The density of the polyethylene resin is preferably 0.870-0.930 g/cm³More preferably 0.890 to 0.925g/cm³More preferably 0.900 to 0.923g/cm³. As the polyethylene resin, a plurality of polyethylene resins may be used, and further, polyethylene resins other than the above density range may be added.

The polyethylene resin preferably has a melt index of 1.0 to 12g/10 min, more preferably 1.5 to 8g/10 min, and still more preferably 1.8 to 4.5g/10 min. If the melt index of the polyethylene resin is within the above range, foaming proceeds appropriately, the maximum cell diameter of the foam sheet is easily made small, and the processability and moldability of the foam sheet become good.

(metallocene compound)

Examples of the metallocene compound include compounds such as bis (cyclopentadienyl) metal complexes having a structure in which a transition metal is sandwiched between pi-electron-based unsaturated compounds. More specifically, there may be mentioned compounds in which 1 or 2 or more cyclopentadienyl rings or the like are present as ligands (ligands) in a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, platinum and the like.

Such metallocene compounds have uniform properties of active sites, and each active site has the same degree of activity. Since the polymer synthesized using the metallocene compound has high uniformity in molecular weight, molecular weight distribution, composition distribution, and the like, when a sheet containing the polymer synthesized using the metallocene compound is crosslinked, the crosslinking proceeds uniformly. As a result, the foam sheet can be uniformly stretched, and therefore, the thickness of the foam sheet can be easily made uniform, and the foam sheet can be easily made thin.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted with hydrocarbyl, substituted hydrocarbyl or hydrocarbon-substituted metalloid radicals. Examples of the hydrocarbon group include methyl, ethyl, various propyl groups, various butyl groups, various pentyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various cetyl groups, and phenyl groups. The term "various" means various isomers including normal-, secondary-, tertiary-, and iso-isomers.

In addition, a substance obtained by polymerizing a cyclic compound into an oligomer can be used as a ligand.

Further, in addition to the pi-electron-based unsaturated compound, monovalent anion ligands such as chlorine and bromine, divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryl oxides, amides, arylamides, phosphides, arylphosphides, and the like can be used.

Examples of the metallocene compound containing a tetravalent transition metal and a ligand include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, and dimethylsilyl tetramethylcyclopentadienyl-tert-butylamido zirconium dichloride.

The metallocene compound functions as a catalyst in the polymerization of various olefins by being combined with a specific cocatalyst (co-catalyst). Specific examples of the cocatalyst include Methylaluminoxane (MAO) and boron compounds. The proportion of the cocatalyst to the metallocene compound is preferably 10 to 100 ten thousand mol times, and more preferably 50 to 5,000 mol times.

Polypropylene resin

Examples of the polypropylene resin used as the polyolefin resin (B) include polypropylene, a propylene-ethylene copolymer containing 50 mass% or more of propylene, a propylene- α -olefin copolymer containing 50 mass% or more of propylene, and the like. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

Specific examples of the α -olefin constituting the propylene- α -olefin copolymer include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene, and among them, α -olefins having 6 to 12 carbon atoms are preferable.

The density of the polypropylene resin is preferably 0.870-0.930 g/cm³More preferably 0.890 to 0.925g/cm³More preferably 0.900 to 0.923g/cm³. As the polypropylene resin, a plurality of polypropylene resins may also be used, and further, polypropylene resins other than the above density range may be added.

Ethylene-vinyl acetate copolymer

The ethylene-vinyl acetate copolymer used as the polyolefin resin (B) includes, for example, an ethylene-vinyl acetate copolymer having a vinyl acetate content (VA amount) of preferably 5 to 40 mass%, more preferably 12 to 35 mass%, and still more preferably 15 to 30 mass%. When the vinyl acetate content in the ethylene-vinyl acetate copolymer is in the above range, the maximum cell diameter can be reduced, and a foam sheet having excellent flexibility can be obtained.

In the present invention, for example, 2 or more species different in molecular weight, amount of vinyl acetate in the copolymer component, melting point, and the like may be used in combination.

The ethylene-vinyl acetate copolymer used in the present invention may contain, in addition to ethylene and vinyl acetate, vinyl alcohol obtained by hydrolyzing a part of vinyl acetate.

Examples of the ethylene-vinyl acetate copolymer include "ウルトラセン" manufactured by imperial ソー, "エバフレックス" manufactured by mitsui デュポンポリケミカル, "UBE ポリエチレン" manufactured by yu pill ポリエチレン, and "サンテック" manufactured by asahi ケミカルズ.

The density of the ethylene-vinyl acetate copolymer is preferably 0.900 to 0.980g/cm³More preferably 0.910 to 0.975g/cm³More preferably 0.920 to 0.960g/cm³. As the ethylene-vinyl acetate copolymer, a plurality of ethylene-vinyl acetate copolymers may be used, and further, a copolymer of ethylene and vinyl acetate may be usedEthylene-vinyl acetate copolymers other than the density range described above are added.

The ethylene-vinyl acetate copolymer preferably has a melt index of 1.5 to 15g/10 min, more preferably 2.0 to 10g/10 min, and still more preferably 2.5 to 5g/10 min. When the melt index of the ethylene-vinyl acetate copolymer is within the above range, the maximum cell diameter of the foam sheet is easily made small, and the processability and moldability of the foam sheet become good.

[ contents of respective resins ]

From the viewpoint of reducing the load on the environment and improving the biomass ratio of the foam sheet, the content of the biomass-based polyolefin resin (a) in the foam sheet is preferably 42 mass% or more, more preferably 50 mass% or more, and even more preferably 60 mass% or more, based on the total amount of the resin components. In addition, in order to make the foam sheet thin and to facilitate the performance as a foam good, it is preferable to include a resin other than the biomass-based polyolefin resin (a). From such a viewpoint, the content of the biomass-based polyolefin resin (a) is preferably 95% by mass or less, more preferably 85% by mass or less, and still more preferably 75% by mass or less.

The content of the polyolefin resin (B) is preferably 5% by mass or more, more preferably 15% by mass or more, and further preferably 25% by mass or more, and is preferably 58% by mass or less, more preferably 50% by mass or less, and further preferably 40% by mass or less, based on the total amount of the resin components. When the content of the polyolefin resin (B) is not less than the lower limit, the sheet can be easily made thin, and various physical properties required for the foam sheet such as impact resistance, flexibility, and mechanical strength can be easily improved. Further, by setting the upper limit value to be equal to or less than the above, the environmental load is reduced, and the biomass ratio of the foam sheet is easily increased.

When the polyolefin resin (B) contains a polyethylene resin obtained by polymerization with a polymerization catalyst of a metallocene compound, the polyethylene resin is preferably used alone as the polyolefin resin (B), but may be used in combination with another polyolefin resin (B).

The content of the polyethylene resin obtained by polymerization with the metallocene compound polymerization catalyst is preferably 40 to 100% by mass, more preferably 50 to 100% by mass, and still more preferably 85 to 100% by mass, based on the total amount of the polyolefin resin (B). By increasing the content of the polyethylene resin obtained by polymerization in the metallocene compound polymerization catalyst, the foam sheet can be easily made good in flexibility and the like, and can be made uniform in crosslinking and the like, the sheet can be made thin, and the maximum cell diameter can be easily made small.

< biomass ratio in foam sheet >

The biomass fraction in the foam sheet of the present invention is 40 mass% or more. If the biomass ratio is made less than 40 mass%, the load on the environment cannot be reduced. From this viewpoint, the biomass ratio is preferably 50% by mass or more, and more preferably 60% by mass or more. The upper limit is not particularly limited, but is preferably 90 mass% or less, more preferably 82 mass% or less, further preferably 75 mass% or less, and further preferably 68 mass% or less, from the viewpoint of the strength, flexibility, production cost, and the like of the foam sheet.

The biomass ratio of the foam sheet can be obtained by multiplying the biomass ratio of the biomass-based polyolefin resin (a) by the content ratio of the biomass-based polyolefin resin (a) to the total foam sheet amount. The total foam sheet amount can be calculated by removing the amount of the blowing agent and the amount of the volatile component during production from the total resin composition. The biomass percentage of the biomass-based polyolefin resin (a) is a biomass degree measured by a measurement method defined in ASTM D6866.

< thickness of foam sheet >

The foam sheet of the present invention has a thickness of 0.05 to 1.5 mm. If the thickness is less than 0.05mm, the properties of the foam sheet, such as mechanical strength and impact resistance, cannot be sufficiently improved. Further, if the thickness is made larger than 1.5mm, the thickness becomes difficult to be reduced, and it is not suitable for use in miniaturized electronic equipment. From the viewpoint of reducing the thickness and sufficiently exhibiting the performance of the foam sheet, the thickness of the foam sheet is preferably 1.2mm or less, more preferably 0.9mm or less, further preferably 0.6mm or less, and further preferably 0.08mm or more, further preferably 0.10mm or more.

< expansion ratio >

The foam sheet of the present invention has a foaming ratio of 1.5 to 20 times. If the expansion ratio of the foam sheet is less than 1.5 times, the ratio of cells decreases, and the properties as a foam such as flexibility become insufficient. On the other hand, if the expansion ratio exceeds 20 times, the maximum cell diameter becomes large, and as a result, it becomes difficult to improve various performances of the foam sheet such as impact resistance. From these viewpoints, the expansion ratio of the foam sheet is preferably 1.8 to 15 times, and more preferably 2.5 to 10 times. The expansion ratio is a value calculated by measuring the specific volume (unit: cc/g) before and after expansion and calculating the specific volume after expansion/the specific volume before expansion.

< maximum bubble diameter and average bubble diameter >

The maximum cell diameter of the foam sheet of the present invention is preferably 500 μm or less. If the maximum cell diameter is not more than the upper limit, various properties of the foam sheet such as impact resistance can be improved even if the sheet is made thin. The maximum cell diameter of the foam sheet is more preferably 380 μm or less, and still more preferably 300 μm or less, from the viewpoint of sufficiently ensuring the impact resistance of the foam sheet. The maximum cell diameter of the foam sheet is preferably 50 μm or more, more preferably 80 μm or more, and still more preferably 100 μm or more.

The foam sheet of the present invention preferably has an average cell diameter of 20 to 350 μm or less in both the MD and TD directions. When the average cell diameter is in the above range, the maximum cell diameter is also decreased, and the 25% compressive strength can be brought into a desired range, and the impact resistance, impact absorbability and other properties can be improved. From these viewpoints, the average cell diameter in both the MD direction and the TD direction is preferably 30 to 250 μm, more preferably 50 to 200 μm, and still more preferably 60 to 140 μm.

Further, the foam sheet preferably has an average cell diameter in the ZD direction of 5 to 250 μm, more preferably 10 to 140 μm, even more preferably 15 to 100 μm, and even more preferably 20 to 60 μm, from the viewpoint of ensuring impact resistance, impact absorbability, and the like.

The average bubble diameter is a value measured by the following method.

A sample obtained by cutting a foam sheet into 50mm squares was prepared as a foam sheet sample for measurement. After being immersed in liquid nitrogen for 1 minute, the film was cut in the thickness direction by razor blades in the MD direction and the TD direction, respectively. A200-fold magnified photograph of the cross section thereof was taken using a digital microscope ("VHX-900" manufactured by キーエンス Co., Ltd.), the bubble diameters of all the bubbles present in the cross section at a length of 2mm in each of the MD direction and the TD direction were measured, and the operation was repeated 5 times. Further, the average value of all the cells is defined as the average cell diameter in the MD direction and the TD direction. The bubble diameters in the ZD direction were also measured for all the measured bubbles, and the average value thereof was set as the average bubble diameter in the ZD direction. Further, the maximum value among all the measured bubble diameters was defined as the maximum bubble diameter.

In the present invention, "MD" means a Machine Direction (Machine Direction) and means a Direction corresponding to the extrusion Direction of the foam sheet or the like. "TD" refers to a Transverse Direction (Transverse Direction) and to a Direction perpendicular to the MD and parallel to the foam sheet. Further, "ZD" means the Thickness Direction (Thickness Direction), which is a Direction perpendicular to both MD and TD.

< ratio of bubble diameter >

The ratio of the average bubble diameter in the MD direction and the TD direction to the average bubble diameter in the ZD direction (hereinafter, also referred to as "(MD + TD)/2 ZD") is preferably 1.3 to 10, more preferably 1.8 to 9, even more preferably 2 to 8, and even more preferably 2.5 to 6. The average cell diameter in the MD and TD is an average of the average cell diameter in the MD and the average cell diameter in the TD.

When (MD + TD)/2ZD is within the above range, bubbles having a shape extending in the MD direction and the TD direction are formed, and therefore, even if the sheet is thin, a foam sheet having excellent impact resistance, flexibility, impact absorbability and the like can be easily obtained. Further, (MD + TD)/2ZD can be adjusted by stretching at the time of production of the foam sheet while adjusting the expansion ratio to the above range.

(iii) compressive Strength of < 25 >

The 25% compressive strength of the foam sheet is, for example, 350kPa or less, but from the viewpoint of flexibility, is preferably 200kPa or less, more preferably 160kPa or less, and still more preferably 100kPa or less. In addition, from the viewpoint of satisfactory flexibility and satisfactory impact resistance, mechanical strength, and the like, the 25% compressive strength of the foam sheet is preferably 20kPa or more, more preferably 35kPa or more, and still more preferably 40kPa or more.

The 25% compressive strength can be adjusted by the type of resin, the cell diameter, the expansion ratio, and the like, and for example, if the expansion ratio is made high, the value of the 25% compressive strength can be made low.

The 25% compression strength is a value measured in accordance with JIS K6767 for the foam sheet.

< degree of crosslinking >

The foam sheet is preferably crosslinked. The degree of crosslinking of the foam sheet is preferably 15% by mass or more. When the crosslinking degree is not less than the lower limit, the average cell diameter can be easily adjusted to the above range, and the cells of the foam sheet can be easily miniaturized. Further, since variations in the size of each bubble are reduced, the maximum bubble diameter is reduced, and the impact resistance and the mechanical strength are easily improved. From such a viewpoint, the degree of crosslinking of the foam sheet is more preferably 25% by mass or more, and still more preferably 30% by mass or more. In addition, the crosslinking degree is preferably 65 mass% or less, more preferably 60 mass% or less, and even more preferably 55 mass% or less, from the viewpoint of improving the flexibility, impact resistance, impact absorbability, and the like of the foam sheet.

The foam sheet is obtained by foaming a resin composition containing the resin and a foaming agent. In addition, since an additive may be further compounded in the foam sheet, the foam sheet may be formed by foaming a resin composition containing the additive in addition to the resin and the foaming agent.

[ foaming agent ]

The foaming agent is preferably a thermal decomposition type foaming agent. Specific examples of the thermal decomposition type foaming agent include organic or inorganic chemical foaming agents having a decomposition temperature of about 140 to 270 ℃.

Examples of the organic foaming agent include azodicarbonamide, metal salts of azodicarboxylic acid (e.g., barium azodicarboxylate), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N '-dinitrosopentamethylenetetramine, hydrazine derivatives such as biurea, 4' -oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonylsemicarbazide.

Examples of the inorganic foaming agent include ammonium carbonate, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, monosodium citrate anhydride, and the like.

Among them, from the viewpoint of obtaining fine bubbles and from the viewpoint of economy and safety, azo compounds and nitroso compounds are preferable, azodicarbonamide, azobisisobutyronitrile, N' -dinitrosopentamethylenetetramine are more preferable, and azodicarbonamide is particularly preferable. These thermal decomposition type foaming agent can be used alone or in combination of 2 or more.

The amount of the thermal decomposition type foaming agent is preferably 1 to 30 parts by mass per 100 parts by mass of the resin component. By using such a blending amount, the sheet can be appropriately foamed without breaking the bubbles. Further, if the amount of the thermal decomposition type foaming agent is increased, the expansion ratio is increased, and the flexibility can be improved. Therefore, the amount of the thermal decomposition type foaming agent is more preferably 3 to 25 parts by mass, and still more preferably 5 to 18 parts by mass.

[ additives ]

In the foam sheet, a cell nucleus regulator is preferably compounded as an additive. Examples of the cell nucleus regulator include zinc compounds such as zinc oxide and zinc stearate, and organic compounds such as citric acid and urea. Among them, zinc oxide and zinc stearate are more preferable, and either one or both of them may be used. By using a cell nucleus modifier in addition to the blowing agent, the average cell diameter and the variation in cell diameter can be easily reduced.

The amount of the cell nucleus modifier is preferably 0.1 to 8 parts by mass, more preferably 0.2 to 5 parts by mass, and still more preferably 0.3 to 2.5 parts by mass, per 100 parts by mass of the resin component.

In the foam sheet, an antioxidant may be compounded as an additive. Examples of the antioxidant include a phosphorus antioxidant, a phenol antioxidant, a sulfur antioxidant, and an amine antioxidant. The antioxidant is blended, for example, in an amount of 0.01 to 5 parts by mass per 100 parts by mass of the resin component.

In addition, in the foam sheet, a coloring agent may be compounded as an additive. The colorant is blended as a substance for adjusting the color of the foam sheet. Specific examples of the colorant include pigments and dyes. The colorant is blended, for example, in an amount of 0.5 to 5 parts by mass per 100 parts by mass of the resin component.

In addition to the above, additives generally used in foam sheet such as a heat stabilizer, a flame retardant, an antistatic agent, and a filler may be added to the foam sheet as required.

< method for producing foam sheet >

The foam sheet is preferably produced by the following method: a resin composition obtained by compounding and kneading a resin, a foaming agent, and, if necessary, other additives is molded into a sheet form to prepare a foamable resin sheet, and then the sheet is crosslinked by ionizing radiation or the like and then heated in a heating device such as a heating furnace or an oven to be foamed.

The resin sheet can be obtained by continuously extruding a resin composition obtained by kneading various components using a kneader such as a banbury mixer or a pressure kneader by an extruder, a calender, a belt casting, or the like.

Examples of the method of crosslinking the foamable resin sheet include crosslinking with ionizing radiation and crosslinking with an organic peroxide, but crosslinking with ionizing radiation is preferred.

When the crosslinking is performed by ionizing radiation, examples of the ionizing radiation include ultraviolet light, γ rays, and electron beams. The dose of ionizing radiation is preferably 0.5 to 10Mrad, more preferably 1.5 to 8 Mrad. When the crosslinking is performed by ionizing radiation, a foam sheet having a small diameter and a uniform bubble diameter can be obtained.

In the case of crosslinking by an organic peroxide, examples of the organic peroxide include diisopropylbenzene hydroperoxide, 2, 4-dichlorobenzoyl peroxide, benzoyl peroxide, t-butyl perbenzoate, cumyl hydroperoxide, t-butyl hydroperoxide, 1-di (t-butylperoxy) -3,3, 5-trimethylhexane, n-butyl-4, 4-di (t-butylperoxy) valerate, α' -bis (t-butylperoxyisopropyl) benzene, 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexyne-3, t-butylperoxycumene and the like.

The amount of the organic peroxide is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 7 parts by mass, per 100 parts by mass of the resin component.

Examples of the method of foaming the foamable resin sheet include a batch method such as an oven, and a continuous foaming method in which a foamable resin sheet is formed into a long sheet and continuously passed through a heating oven. The heating temperature is preferably 200 to 320 ℃, and more preferably 250 to 300 ℃.

The foamable resin sheet can be stretched in at least one of the MD direction and the TD direction, preferably, both directions thereof at the time of foaming. By stretching in the MD direction and the TD direction, the average cell diameter and the ratio of the average cell diameter can be easily adjusted to fall within the above range. Further, the foamable resin sheet may be stretched in at least one of the MD direction and the TD direction, preferably both of them, after foaming. In the case of stretching the foamable resin sheet after foaming, the stretching may be continued without cooling after foaming while maintaining the molten state at the time of foaming, or may be performed after cooling and reheating to form a molten or softened state.

< use >)

The foam sheet of the present invention is suitably used for electronic equipment. That is, the foam sheet of the present invention is suitably used in, for example, a mobile phone such as a smartphone, an electronic device such as a camera, a game device, an electronic account, a tablet terminal, and a notebook personal computer, and preferably in a mobile phone such as a smartphone. The foam sheet is used as, for example, a sealing material or an impact absorbing material in an electronic device.

[ adhesive tape ]

The foam sheet of the present invention can be used for an adhesive tape having the foam sheet as a base material. The pressure-sensitive adhesive tape includes, for example, a foam sheet and a pressure-sensitive adhesive material provided on at least one surface of the foam sheet. The adhesive tape can be adhered to other members via an adhesive material. The pressure-sensitive adhesive tape may have a pressure-sensitive adhesive material on both surfaces of the foam sheet, or may have a pressure-sensitive adhesive material on one surface.

The pressure-sensitive adhesive material may be a single pressure-sensitive adhesive layer laminated on the surface of the foam sheet or a double-sided pressure-sensitive adhesive sheet adhered to the surface of the foam sheet, and is preferably a single pressure-sensitive adhesive layer. The double-sided adhesive sheet further includes a substrate and adhesive layers provided on both sides of the substrate. A double-sided pressure-sensitive adhesive sheet is used to bond one pressure-sensitive adhesive layer to a foam sheet and to bond the other pressure-sensitive adhesive layer to another member.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited, and for example, an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, or the like can be used. Further, a release sheet such as release paper may be further bonded to the adhesive material.

The thickness of the adhesive material is preferably 5 to 200 μm, more preferably 7 to 150 μm, and further preferably 10 to 100 μm.

Examples

The present invention will be described in further detail with reference to examples, but the present invention is not limited to these examples.

[ example 1]

Biomass resin (1) and polyethylene resin (1), azodicarbonamide as a thermal decomposition type foaming agent, zinc stearate and zinc oxide as a cell nucleus regulator, an antioxidant, and a black pigment were supplied to an extruder at compounding amounts shown in table 2, and were melt-kneaded at 130 ℃. The resin composition was extruded to obtain a long foam resin sheet.

Next, both surfaces of the long foam resin sheet were irradiated with 4.5Mrad of electron beam having an acceleration voltage of 500kV to crosslink the resin sheet. The crosslinked foamable resin sheet was continuously fed into a foaming furnace maintained at 250 ℃ by hot air and an infrared heater, and foamed while being stretched in the MD direction and the TD direction, to obtain a foam sheet having a thickness as shown in table 1.

Examples 2 to 17 and comparative examples 1 to 2

Resin compositions were obtained in the same manner as in example 1, except that the components to be supplied to the extruder were adjusted as shown in table 2. Then, the procedure was carried out in the same manner as in example 1, except that the irradiation amount of the electron beam was adjusted so that the degree of crosslinking was as shown in table 2, and the degree of stretching was adjusted so that (MD + TD)/2ZD was as shown in table 2.

The foam sheets obtained in examples and comparative examples were evaluated in the following manner.

< degree of crosslinking >

A test piece of about 100mg was sampled from the foam sheet, and the weight A (mg) of the test piece was precisely measured. Next, the test piece was subjected to 30cm xylene at 120 ℃ C³After being left for 24 hours, the resultant was filtered through a 200-mesh wire gauze to collect insoluble matter on the wire gauze, which was then vacuum-dried, and the weight B (mg) of the insoluble matter was precisely measured. From the obtained values, the degree of crosslinking (% by mass) was calculated by the following formula.

Degree of crosslinking (% by mass) — (B/a) × 100

< expansion ratio >

The specific volumes (unit: cc/g) before and after foaming were measured and calculated from the specific volume after foaming/the specific volume before foaming.

< biomass ratio in foam sheet >

Calculated by the method described in the specification.

< average bubble diameter and maximum bubble diameter >

The average cell diameter and the maximum cell diameter of the foam sheet are measured by the methods described in the specification.

(iii) compressive Strength of < 25 >

The foam sheet was measured for 25% compression strength in accordance with JIS K6767.

[ Table 1]

[ Table 2]

From the results in table 2, it is understood that the foam sheet of each example has a high biomass ratio, and even when the thickness is small, the maximum cell diameter can be made small, and various performances such as impact resistance can be improved.