Sheet, and method for producing sheet

Abstract

To provide a sheet which allows easy manual cutting in a specific direction at any position.SOLUTION: A sheet comprises a substrate made of resin. The substrate has a first tensile strength of 85 MPa or less and a puncture strength of 14.0 N or less. The first tensile strength is a tensile strength along at least one of multiple directions parallel to the surface of the substrate.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a sheet and a method for manufacturing the sheet.

Background Art

[0002] Patent Document 1 discloses a method for manufacturing an easily unsealable packaging material in which a perforation line or a half-cut line is provided in a conductive ink portion by forming a free-form line with a conductive ink on a base material made of a plastic film and then performing an electron beam or an electric discharge treatment. The perforation line or the half-cut line is formed by melting the base material due to the heat generation of the conductive ink accompanying the electron beam or the electric discharge treatment.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique of Patent Document 1, the electron beam or the electric discharge treatment is performed to generate heat in the conductive ink, and substantially does not affect the mechanical properties of the base material in the portion where there is no conductive ink. Therefore, with the above technique, the packaging material including the base material can be cut only at the position of the perforation line or the half-cut line formed by the free-form line of the conductive ink.

[0005] One object of the present invention is to provide a sheet that can be easily cut by hand in a specific direction at an arbitrary position.

Means for Solving the Problems

[0006] (1) A sheet according to one aspect of the present invention includes a base material made of resin. The first tensile strength of the base material is 85 MPa or less. The piercing strength of the base material is 14.0 N or less. The first tensile strength is the tensile strength along at least one of a plurality of directions parallel to the surface of the base material.

[0007] The direction indicating the first tensile strength may be one or a plurality. For example, the first tensile strength may be the tensile strength along any one of the plurality of directions. In this case, the first tensile strength is the tensile strength with the smallest value among the tensile strengths in the plurality of directions. The first tensile strength may be the tensile strength along each of two or more of the plurality of directions. In this case, the plurality of first tensile strengths may have the same value or different values.

[0008] The sheet in the above (1) can be easily cut by hand in a specific direction at any position. The specific direction is a second direction orthogonal to the first direction indicating the first tensile strength. This second direction is the direction in which the break of the sheet progresses when the sheet is cut by hand. If there is one first direction indicating the first tensile strength, there is one pair of the first direction and the second direction. If there are a plurality of first directions indicating the first tensile strength, there are a plurality of pairs of the first direction and the second direction. If there are a plurality of pairs of the first direction and the second direction, there are a plurality of directions that can be easily cut by hand.

[0009] When the piercing strength is 14.0 N or less, when a force is applied to the base material to cut the base material by hand, a starting point of breakage is formed in the base material. When the first tensile strength is 85 MPa or less, the base material is divided in the first direction while the breakage progresses along the second direction from the starting point of the breakage. By satisfying the specific tensile strength and piercing strength, the base material can be easily cut by hand in the second direction even without a perforation line or a half-cut line. Cutting in the second direction includes not only being able to cut substantially along the second direction but also cutting obliquely with a slight inclination with respect to the second direction.

[0010] (2) In the sheet of (1) above, the first tensile strength may be 30 MPa or more.

[0011] When the first tensile strength is 30 MPa or more, it is difficult for unintentional breakage to occur during the use of the sheet, and it is easy to handle.

[0012] (3) In the sheet of (1) or (2) above, the second tensile strength of the base material may be greater than the first tensile strength. The second tensile strength is the tensile strength along a second direction that is parallel to the surface of the base material and orthogonal to the first direction indicating the first tensile strength.

[0013] When the second tensile strength is greater than the first tensile strength, the sheet including the base material can be easily cut by hand substantially along the second direction. A base material with a second tensile strength greater than the first tensile strength is manufactured, for example, by stretching in two directions, the flow direction of the raw material and the width direction orthogonal to the flow direction, during the manufacture of the base material. Such a biaxially stretched base material is superior in rigidity, transparency, and impact resistance compared to an unstretched base material.

[0014] (4) The sheet of (3) above may be provided with a marker that specifies at least one of the first direction and the second direction.

[0015] In a biaxially stretched base material, it may not be possible to specify the first direction and the second direction just by looking at the base material. For example, when the shape of the base material is long, just by looking at the base material, it can be specified that the direction along the length longer than the width is the first direction. For example, when the shape of the base material is circular, just by looking at the base material, it is not possible to specify which direction is the first direction or the second direction. If a marker is provided, the first direction and the second direction can be specified regardless of the shape of the base material. If the second direction can be specified by the marker, the base material can be easily cut by hand in that second direction.

[0016] (5) In the sheet of (3) or (4) above, the second tensile strength may be 200 MPa or less.

[0017] In a biaxially stretched substrate, when the second tensile strength is 200 MPa or less, the tensile strength of the entire substrate is low, and the substrate can be easily cut by hand in the second direction.

[0018] (6) In the sheet of (5) above, the second tensile strength may be 30 MPa or more.

[0019] When the second tensile strength is 30 MPa or more, unintentional breakage is less likely to occur during the manufacture and use of the sheet, and it is easy to handle.

[0020] (7) In the sheet of any one of (1) to (6) above, the substrate may be made of polypropylene.

[0021] A substrate made of polypropylene is easily available and has excellent durability.

[0022] (8) The sheet of any one of (1) to (7) above may further include a separator and an adhesive layer provided between the separator and the substrate.

[0023] If the sheet has an adhesive layer and a separator, the sheet can be cut by hand to a desired size and the separator can be peeled off, so that the sheet can be pasted at a desired location.

[0024] (9) In the sheet of any one of (1) to (7) above, the substrate may be a long member having a length longer than the width. In this case, the first direction indicating the first tensile strength is the direction along the length of the long member.

[0025] When the shape of the substrate is long, just by looking at the substrate, the direction along the length longer than the width can be specified as the first direction. When the shape of the substrate is long, the substrate is usually cut by hand in the direction along the width of the long member. Since the first tensile strength of the substrate is 85 MPa or less, the long member can be easily cut by hand in the direction along the width from any position on the side edge of the substrate, that is, the long member. Therefore, the long member can be cut by hand to a desired length.

[0026] (10) The sheet of (9) above may further include an adhesive layer provided on the first surface of the long material and a release layer provided on the second surface of the long material.

[0027] If the long material has an adhesive layer and a release layer, the long material can be manually cut to a desired length and attached to a desired location. Since the adhesive layer is provided on the first surface of the long material and the release layer is provided on the second surface of the long material, adjacent turns do not stick to each other even when the long material is wound up.

[0028] (11) In any of the sheets of (1) to (10) above, the thickness of the base material may be 30 μm or more and 60 μm or less.

[0029] A base material with a thickness of 30 μm or more is less likely to break unintentionally during sheet manufacturing and use and is easy to handle. A base material with a thickness of 60 μm or less is easy to cut.

[0030] (12) The method for manufacturing a sheet according to one aspect of the present invention includes an irradiation step of irradiating an electron beam onto a base material made of resin. In the irradiation step, when the thickness of the base material is 40 μm or less, if the dose of the electron beam is 100 kGy or more and less than 200 kGy, the electron beam is irradiated at an acceleration voltage of 200 kV or more. If the dose of the electron beam is 200 kGy or more, the electron beam is irradiated at an acceleration voltage of 80 kV or more. When the thickness of the base material exceeds 40 μm, the electron beam is irradiated at a dose of 600 kGy or more and an acceleration voltage of 80 kV or more.

[0031] With the method for manufacturing a sheet of (12) above, by controlling the dose and acceleration voltage of the electron beam according to the thickness of the base material, a sheet that can be easily cut by hand in a specific direction at an arbitrary position can be manufactured.

[0032] (13) The method for manufacturing a sheet of (12) above may further include a step of providing an adhesive layer on the first surface of the base material and a release layer on the second surface of the base material after the irradiation step.

[0033] By providing an adhesive layer and a release layer on the base material, a sheet that can be manually cut to a desired size and attached to a desired location can be manufactured. By providing an adhesive layer on the first surface of the base material and a release layer on the second surface of the base material, adjacent turns will not stick to each other even when the sheet is wound.

[0034] (14) The method for manufacturing the sheet of (12) may further include a step of preparing a laminate in which an adhesive layer is provided on the first surface of the base material and a release layer is provided on the second surface of the base material, with respect to the base material before irradiating the electron beam. In this case, in the irradiation step, the laminate is irradiated with the electron beam.

[0035] Even in the method for manufacturing the sheet of (14) above, the same effects as those of the method for manufacturing the sheet of (13) are achieved. Furthermore, in the method for manufacturing the sheet of (14), since the electron beam is irradiated with the adhesive layer and the release layer provided on the base material, unintentional breakage of the base material is less likely to occur during the manufacturing process compared to the case where the adhesive layer and the release layer are provided on the base material after irradiating the electron beam. The formation of the base material into a desired shape and dimensions is often performed after providing the adhesive layer and the release layer on the base material. When the electron beam is irradiated with the adhesive layer and the release layer provided on the base material, the electron beam is irradiated onto a laminate having a desired shape and dimensions, and it is easy to miniaturize the electron beam irradiation device.

[0036] (15) The method for manufacturing the sheet of (12) may further include a step of preparing a laminate in which an adhesive layer is laminated on the first surface of the separator, and a step of bonding the laminate to the base material such that the adhesive layer faces the first surface of the base material that has undergone the irradiation step.

[0037] By providing an adhesive layer and a separator on the sheet, a sheet that can be manually cut to a desired size and attached to a desired location can be manufactured by peeling off the separator after cutting the base material to the desired size.

[0038] (16) The method for manufacturing the sheet of (12) may further include a step of preparing a laminate provided with an adhesive layer and a separator on the first surface of the base material before irradiating the electron beam. In this case, in the irradiation step, the laminate is irradiated with the electron beam.

[0039] Also in the method for manufacturing the sheet of (16) above, the same effects as those of the method for manufacturing the sheet of (15) above are achieved. Further, in the method for manufacturing the sheet of (16) above, since the electron beam is irradiated in a state where the adhesive layer and the separator are provided on the base material, it is less likely that the base material will be accidentally broken during the manufacturing process compared to the case where the adhesive layer and the separator are provided on the base material after irradiating the electron beam. The formation of the base material into a desired shape and dimensions is often performed after providing the adhesive layer and the separator on the base material. When the electron beam is irradiated in a state where the adhesive layer and the separator are provided on the base material, the electron beam is irradiated onto a laminate having a desired shape and dimensions, and it is easy to miniaturize the electron beam irradiation device.

[0040] (17) The method for manufacturing the sheet according to any one of (12) to (16) above may further include a display step of providing a marker that specifies at least one of a first direction indicating the smallest tensile strength among the tensile strengths in a plurality of directions parallel to the surface of the base material and a second direction parallel to the surface of the base material and orthogonal to the first direction in the base material that has undergone the irradiation step.

[0041] As described above, depending on the shape of the base material, it may not be possible to specify the first direction and the second direction just by looking at the base material. By providing a marker, it is possible to manufacture a sheet in which the first direction and the second direction can be specified regardless of the shape of the base material.

[0042] (18) In the method for manufacturing the sheet according to any one of (12) to (17) above, the base material may be made of polypropylene.

[0043] A base material made of polypropylene is easily available and has excellent durability.

[0044] (19) In the method for manufacturing any one of the sheets (12) to (18) above, the thickness of the base material may be 30 μm or more and 60 μm or less.

[0045] A base material with a thickness of 30 μm or more is difficult to break unintentionally during the manufacturing process and is easy to handle. If the thickness is 60 μm or less, a sheet that is easy to cut can be manufactured without excessively increasing at least one of the values of the electron beam dose or the acceleration voltage.

Brief Description of the Drawings

[0046]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0047] Hereinafter, specific examples of the sheet of the present invention and the method for manufacturing the sheet will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. The sizes of the members shown in each drawing are represented for the purpose of clarifying the description and do not necessarily represent actual dimensions. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0048] [Embodiment 1] <Sheet> With reference to FIGS. 1 to 3, the sheet 1 of Embodiment 1 will be described. As shown in FIG. 2, the sheet 1 includes a base material 2 made of resin. The sheet 1 of Embodiment 1 further includes an adhesive layer 3 and a release layer 4. One of the features of the sheet 1 of Embodiment 1 is that the base material 2 has a specific tensile strength and puncture strength.

[0049] In Embodiment 1, a form in which the base material 2 is a long member will be described. The long member has a thin thickness and a length longer than the width. A specific example of the long member is a strip-shaped material. As shown in FIG. 1, in the long base material 2, the direction along the length of the base material 2 is the first direction D1, and the direction along the width of the base material 2 is the second direction D2. The first direction D1 shown in FIG. 1 is the direction along the length of the base material 2 in the portion pulled out from the state of being wound in a spiral shape. Although the first direction D1 and the second direction D2 shown in FIG. 1 are indicated by single arrows, the opposite directions of each of the first direction D1 and the second direction D2 are also similarly referred to as the first direction D1 and the second direction D2.

[0050] <<Base Material>> The base material 2 is a resin film. The base material 2 is a resin film irradiated with an electron beam 8 (Fig. 4) as described later. As shown in Fig. 2, the base material 2 has a first surface 21 and a second surface 22. In this example, as described later, an adhesive layer 3 is provided on the first surface 21, and a release layer 4 is provided on the second surface 22. The sheet 1 includes those that consist only of the base material 2 made of a resin film and do not have the adhesive layer 3, the release layer 4, and the separator 5 described later. The sheet 1 also includes those in which the adhesive layer 3 is provided on the base material 2 but does not have the release layer 4, those in which the adhesive layer 3 and the release layer 4 are provided on the base material 2, and those in which the adhesive layer 3 and the separator 5 are provided on the base material 2.

[0051] The base material 2 is composed of polypropylene. The base material 2 made of polypropylene is excellent in durability. Specifically, the polypropylene is biaxially stretched polypropylene. The base material 2 made of biaxially stretched polypropylene is manufactured by taking polypropylene as a raw material and stretching it in two directions: the flow direction of the raw material and the width direction perpendicular to the flow direction. The flow direction is generally the direction in which the base material 2 is conveyed during the manufacture of the base material 2. The width direction is the direction perpendicular to the above flow direction. The above flow direction is the first direction D1, and the above width direction is the second direction D2. The base material 2 made of biaxially stretched polypropylene is excellent in durability and transparency. The base material 2 made of biaxially stretched polypropylene is also excellent in printability. The base material 2 in this example is colorless and transparent.

[0052] The thickness 2T of the base material 2 is, for example, 30 μm or more and 60 μm or less. If the thickness 2T is 30 μm or more, unintentional breakage is less likely to occur during the manufacture and use of the sheet 1 including the base material 2. The sheet 1 that is less likely to have unintentional breakage is easy to handle. If the thickness 2T is 60 μm or less, it is easy to cut the sheet 1 including the base material 2. The thickness 2T of the base material 2 may be 40 μm or more and 50 μm or less. The thickness 2T is the distance between the first surface 21 and the second surface 22.

[0053] The size of the base material 2, specifically the length and width of the base material 2, is not particularly limited. The base material 2 in this example has a length sufficient to be wound around a core (not shown) in a plurality of turns. The width of the base material 2 is, for example, 10 mm or more and 300 mm or less, or 15 mm or more and 150 mm or less.

[0054] The first tensile strength of the base material 2 is 85 MPa or less. The first tensile strength is the tensile strength along at least one of a plurality of directions parallel to the surface of the base material 2. The surface of the base material 2 is the first surface 21 and the second surface 22. When the base material 2 is a tape as in this example, the first tensile strength is the tensile strength along the length of the tape, along the first direction D1 shown in FIG. 3. When the first tensile strength is 85 MPa or less, if a break starting point is formed in the base material 2, the base material 2 is cut so that the base material 2 is divided in the first direction D1 from the break starting point. The first tensile strength may be 80 MPa or less, 75 MPa or less, 70 MPa or less, 65 MPa or less, or 60 MPa or less.

[0055] The first tensile strength is, for example, 30 MPa or more. When the first tensile strength is 30 MPa or more, unintentional breakage is less likely to occur during the manufacture and use of the sheet 1 including the base material 2. In the case of the long base material 2, when the first tensile strength is 30 MPa or more, breakage is less likely to occur when winding the sheet 1 including the base material 2. The first tensile strength may be 35 MPa or more, or 40 MPa or more.

[0056] The first tensile strength is, for example, 30 MPa or more and 85 MPa or less, 30 MPa or more and 80 MPa or less, 30 MPa or more and 75 MPa or less, 30 MPa or more and 70 MPa or less, 35 MPa or more and 65 MPa or less, or 40 MPa or more and 60 MPa or less.

[0057] The second tensile strength of the base material 2 is, for example, greater than the first tensile strength. The second tensile strength is the tensile strength along a second direction D2 that is parallel to the surface of the base material 2 and orthogonal to a first direction D1 indicating the first tensile strength. When the base material 2 is a long material as in this example, the second tensile strength is the tensile strength along the direction along the width of the long base material 2, i.e., along the second direction D2 shown in FIG. 3. When the second tensile strength is greater than the first tensile strength, the sheet 1 including the base material 2 can be easily cut by hand substantially along the second direction D2. The base material 2 with the second tensile strength greater than the first tensile strength is manufactured, for example, by stretching in two directions, i.e., the flow direction of the raw material and the width direction orthogonal to the flow direction, during the manufacture of the base material 2. Such a biaxially stretched base material 2 is superior in rigidity, transparency, and impact resistance compared to an unstretched base material. The base material 2 may be an unstretched film or a uniaxially stretched film.

[0058] In the biaxially stretched base material 2, the second tensile strength is, for example, 200 MPa or less. When the second tensile strength is 200 MPa or less, the overall tensile strength of the base material 2 is low, and it is easy to cut the base material 2 by hand in the second direction D2. The second tensile strength may be 195 MPa or less, 190 MPa or less, 185 MPa or less, 180 MPa or less, or 160 MPa or less.

[0059] The second tensile strength is, for example, 30 MPa or more. When the second tensile strength is 30 MPa or more, unintentional breakage is less likely to occur during the manufacture and use of the sheet 1 including the base material 2. The second tensile strength may be 35 MPa or more, or 40 MPa or more.

[0060] The second tensile strength is, for example, 30 MPa or more and 200 MPa or less, 30 MPa or more and 195 MPa or less, 30 MPa or more and 190 MPa or less, 30 MPa or more and 185 MPa or less, 35 MPa or more and 180 MPa or less, or 40 MPa or more and 160 MPa or less.

[0061] The first tensile strength and the second tensile strength are obtained by sampling a test piece from the base material 2, setting the test piece in a commercially available tensile testing machine, and conducting a tensile test at a tensile speed of 300 mm / min. The size of the test piece is 15 mm in width and 220 mm in length.

[0062] The piercing strength of the base material 2 is 14.0 N or less. When the piercing strength is 14.0 N or less, when a force is applied to cut the base material 2 by hand, a fracture initiation point is likely to be formed in the base material 2. The piercing strength is an index indicating the ease of occurrence of a fracture initiation point in the base material 2. When a fracture initiation point is formed in the base material 2, since the base material 2 has the first tensile strength described above, the base material 2 is divided in the first direction D1 while the fracture progresses along the second direction D2 from the fracture initiation point. The piercing strength of the base material 2 may be 13.0 N or less, 12.0 N or less, 11.0 N or less, or 10.0 N or less.

[0063] Cutting the base material 2 in the second direction D2 includes not only being able to cut substantially along the second direction D2, but also cutting obliquely with a slight inclination with respect to the second direction D2. As described above, when the second tensile strength is greater than the first tensile strength, the sheet 1 including the base material 2 can be easily cut by hand substantially along the second direction D2.

[0064] The piercing strength of the base material 2 is obtained by sampling a test piece from the base material 2, setting the test piece in a commercially available tensile testing machine, and measuring the strength when a needle penetrates the test piece at a speed of 50 mm / min with the entire test piece in a state of being stretched in both the width direction and the length direction. The size of the test piece is 50 mm in both width and length. The piercing strength in this example is a value measured using a testing machine of model J-CP1-1KN-U manufactured by A&D Company, Limited.

[0065] The base material 2 does not have an auxiliary part for cutting the base material 2 by hand. The auxiliary part is, for example, a perforation line, a half-cut line, and a notch provided on the side of the base material 2.

[0066] The base material 2 may have a printing layer (not shown). The printing layer may contain the marker 6 described in Embodiment 2.

[0067] ≪Adhesive layer and release layer≫ In this example, the adhesive layer 3 is provided on the first surface 21 of the base material 2. The adhesive layer 3 is provided over the entire surface of the first surface 21. The adhesive layer 3 includes a main layer made of, for example, an adhesive based on natural rubber. The adhesive layer 3 may include an underlayer on the upper surface of the main layer. The underlayer is made of a material that enhances the adhesion between the first surface 21 and the main layer. In this example, the release layer 4 is provided on the second surface 22 of the base material 2. The release layer 4 is made of a material having a property of repelling the adhesive layer 3. The material of the release layer 4 is, for example, silicone. In the long base material 2, by providing the adhesive layer 3 on the first surface 21 and the release layer 4 on the second surface 22, adjacent turns do not stick to each other even when the base material 2 is wound up. If the long base material 2 is provided with the adhesive layer 3 and the release layer 4, the base material 2 can be cut by hand to a desired length and attached to a desired location. The sheet 1 in this example is a so-called OPP (Oriented Poly Propylene) tape.

[0068] Since the adhesive layer 3 and the release layer 4 are thinner and have lower strength than the base material 2, they hardly affect the cuttability for cutting the sheet 1 by hand. Therefore, as shown in the test examples described later, the adhesive layer 3 and the release layer 4 can be ignored in the evaluation of the cuttability.

[0069] <Method for manufacturing a sheet> With reference to FIGS. 4 and 5, the method for manufacturing the sheet of Embodiment 1 will be described. The method for manufacturing the sheet includes an irradiation step of irradiating the base material 2 made of resin with an electron beam 8 as shown in FIG. 4. The method for manufacturing the sheet of Embodiment 1 further includes a lamination step of providing the adhesive layer 3 and the release layer 4 on the base material 2 that has undergone the irradiation step as shown in FIG. 5. One of the features of the method for manufacturing the sheet of Embodiment 1 is that in the irradiation step, the dose and acceleration voltage of the electron beam 8 are adjusted according to the thickness 2T of the base material 2, and the adjusted electron beam 8 is irradiated onto the base material 2.

[0070] <<Irradiation Process>> In the irradiation process, the base material 2 made of resin is irradiated with an electron beam 8. The base material 2 is embrittled by the irradiation of the electron beam 8. In FIG. 4, for the sake of convenience of explanation, a cross-section obtained by cutting the base material 2 along the thickness direction is shown. In FIG. 4, the irradiation direction of the electron beam 8 is indicated by a white arrow for easy understanding.

[0071] 〔Base Material〕 The material, size, and planar shape of the base material 2 are the same as those of the base material 2 described in the above item <Sheet>. The base material 2 in this example is a long material having a length longer than the width.

[0072] The first tensile strength of the base material 2 before the electron beam 8 is irradiated is, for example, 100 MPa or more. If the first tensile strength of the base material 2 before the electron beam 8 is irradiated is 100 MPa or more, the base material 2 is difficult to break in the manufacturing stage. The first tensile strength of the base material 2 before the electron beam 8 is irradiated may be 120 MPa or more, or 125 MPa or more.

[0073] The second tensile strength of the base material 2 before the electron beam 8 is irradiated is, for example, 250 MPa or more. If the second tensile strength of the base material 2 before the electron beam 8 is irradiated is 250 MPa or more, the base material 2 is difficult to break in the manufacturing stage. The second tensile strength of the base material 2 before the electron beam 8 is irradiated may be 260 MPa or more, or 265 MPa or more.

[0074] 〔Irradiation Conditions of Electron Beam〕 In the irradiation process, the irradiation conditions of the electron beam 8 vary greatly depending on whether the thickness 2T of the base material 2 is 40 μm or less. The irradiation conditions of the electron beam 8 also vary depending on whether the dose of the electron beam 8 is 200 kGy or more when the thickness 2T of the base material 2 is 40 μm or less.

[0075] When the thickness 2T of the base material 2 is 40 μm or less, if the dose of the electron beam 8 is 100 kGy or more and less than 200 kGy, the electron beam 8 is irradiated with an acceleration voltage of 200 kV or more. When the dose of the electron beam 8 is less than 200 kGy, the energy imparted to the base material 2 is relatively small. Therefore, by setting the acceleration voltage to 200 kV or more, even if the dose of the electron beam 8 is relatively small, the electron beam 8 can be transmitted in the thickness direction of the base material 2. Depending on the thickness 2T of the base material 2, if the dose of the electron beam 8 is 100 kGy or more, the base material 2 is liable to be embrittled without excessively increasing the acceleration voltage. When the thickness 2T of the base material 2 is 40 μm or less and the dose of the electron beam 8 is 100 kGy or more and less than 200 kGy, the acceleration voltage may be 300 kV or less, or 250 kV or less.

[0076] When the thickness 2T of the base material 2 is 40 μm or less, if the dose of the electron beam 8 is 200 kGy or more, the electron beam 8 is irradiated with an acceleration voltage of 80 kV or more. When the dose of the electron beam 8 is 200 kGy or more, the energy imparted to the base material 2 is relatively large, and by setting the acceleration voltage to 80 kV or more, the base material 2 can be embrittled. When the thickness 2T of the base material 2 is 40 μm or less, the dose of the electron beam 8 may be less than 600 kGy. When the thickness 2T of the base material 2 is 40 μm or less, if the dose of the electron beam 8 is less than 600 kGy, the tensile strength of the base material 2 can be made to be a certain level or more, and a base material 2 in which unintentional breakage is unlikely to occur can be obtained. When the thickness 2T of the base material 2 is 40 μm or less, if the dose is less than 600 kGy, the base material 2 can be embrittled without excessively increasing the dose, and the productivity is excellent. When the thickness 2T of the base material 2 is 40 μm or less and the dose of the electron beam 8 is 200 kGy or more, the acceleration voltage may be 300 kV or less, or 250 kV or less.

[0077] When the thickness 2T of the base material 2 exceeds 40 μm, the electron beam 8 is irradiated at an acceleration voltage of 80 kV or higher with a dose of 600 kGy or higher. The thicker the thickness 2T of the base material 2, the more difficult it is for the electron beam 8 to penetrate in the thickness direction of the base material 2. If the dose of the electron beam 8 is 600 kGy or higher, the energy imparted to the base material 2 can be increased. When the thickness 2T of the base material 2 exceeds 40 μm, by setting the dose of the electron beam 8 to 600 kGy or higher and the acceleration voltage to 80 kV or higher, the electron beam 8 can be made to penetrate in the thickness direction of the base material 2. Depending on the thickness 2T of the base material 2, the dose of the electron beam 8 may be 1500 kGy or less. If the dose of the electron beam 8 is 1500 kGy or less, the tensile strength of the base material 2 can be made to be a certain level or higher, and a base material 2 in which unintentional breakage is less likely to occur can be obtained. The dose of the electron beam 8 may further be 1000 kGy or less. Depending on the thickness 2T of the base material 2, the acceleration voltage may be 400 kV or less, or 300 kV or less.

[0078] In the irradiation step, as described above, the dose and acceleration voltage of the electron beam 8 are adjusted according to the thickness 2T of the base material 2, and the adjusted electron beam 8 is irradiated onto the base material 2. By this irradiation of the electron beam 8, the first tensile strength of the base material 2 after irradiation becomes 85 MPa or less. In other words, in the irradiation step, the dose and acceleration voltage of the electron beam 8 may be adjusted so that the first tensile strength of the base material 2 after irradiation becomes 85 MPa or less.

[0079] ≪Lamination step≫ In the lamination step, for the base material 2 that has undergone the irradiation step, an adhesive layer 3 is provided on the first surface 21 of the base material 2, and a release layer 4 is provided on the second surface 22 of the base material 2. The base material 2 shown in FIG. 5 is a resin film irradiated with the electron beam 8. In FIG. 5, for clarity, the lamination directions of the adhesive layer 3 and the release layer 4 are indicated by arrows. The sheet 1 shown on the right side of FIG. 5 is the same as the sheet 1 shown in FIG. 2. As the lamination method of the adhesive layer 3 and the release layer 4, a known method can be used.

[0080] [Modification Example 1] As shown in FIG. 6, the method for manufacturing the sheet may irradiate the laminate 9 with an electron beam 8. The laminate 9 includes a base material 2, an adhesive layer 3, and a release layer 4 before being irradiated with the electron beam 8. The method for manufacturing the sheet according to Modification 1 further includes a step of preparing a laminate 9 in which the adhesive layer 3 is provided on the first surface 21 of the base material 2 and the release layer 4 is provided on the second surface 22 of the base material 2, with respect to the base material 2 before being irradiated with the electron beam 8. In the irradiation step, the prepared laminate 9 is irradiated with the electron beam 8. In this example, as shown in FIG. 6, the electron beam 8 is irradiated in a direction from the release layer 4 toward the adhesive layer 3. The laminate 9 formed in a long strip shape is often wound up with the adhesive layer 3 on the inside and the release layer 4 on the outside. In that case, the laminate 9 supplied to the irradiation device of the electron beam 8 is fed out with the adhesive layer 3 as the lower surface and the release layer 4 as the upper surface from the wound state. If the electron beam 8 is irradiated from the release layer 4 of the laminate 9, it is easy to arrange the irradiation device, and since the adhesive layer 3 is directed downward, fine foreign matter in the air hardly adheres to the adhesive layer 3. As another method, the electron beam 8 may be irradiated in a direction from the adhesive layer 3 toward the release layer 4.

[0081] In Modification 1, since the electron beam 8 is irradiated with the adhesive layer 3 and the release layer 4 provided on the base material 2, unintentional breakage of the base material 2 is less likely to occur in the manufacturing process compared to the case where the adhesive layer 3 and the release layer 4 are provided on the base material 2 after irradiating the base material 2 with the electron beam 8. The formation of the base material 2 into a desired shape and dimensions is often performed after the adhesive layer 3 and the release layer 4 are provided on the base material 2. In Modification 1, since the laminate 9 having the desired shape and dimensions is irradiated with the electron beam 8, it is easy to miniaturize the irradiation device for the electron beam 8.

[0082] [Embodiment 2] Referring to FIGS. 7 and 8, the sheet 1 according to Embodiment 2 will be described. The sheet 1 according to Embodiment 2 is different from the sheet 1 according to Embodiment 1 in that the planar shape of the base material 2 is different as shown in FIG. 7. Further, the sheet 1 according to Embodiment 2 is different from the sheet 1 according to Embodiment 1 in that an adhesive layer 3 and a separator 5 are provided on the first surface 21 of the base material 2 as shown on the right side of FIG. 8. The following description will focus on the differences from Embodiment 1. The description of the same configurations and the same effects as those of Embodiment 1 may be omitted.

[0083] The planar shape of the base material 2 in this example is rectangular. Rectangular shapes include square shapes and rectangular shapes. Here, the rectangular shape means that the shape surrounded by four sides is substantially rectangular. The rectangular shape in this example does not have to be a rectangle in the geometric sense, and includes a range that can be regarded as substantially rectangular, including shapes with chamfered or rounded corners.

[0084] When the planar shape of the base material 2 is rectangular, the first direction D1 is a direction along either the vertical side or the horizontal side. In the rectangular base material 2, if the vertical side is the first direction D1, the horizontal side is the second direction D2. If the vertical side is the second direction D2, the horizontal side is the first direction D1. In FIG. 5, for clarity, the direction along the vertical side and the direction along the horizontal side are each indicated by a two-dot chain line.

[0085] The sheet 1 in which the planar shape of the base material 2 is rectangular may be provided with a marker 6 that specifies at least one of the first direction D1 and the second direction D2. The shape of the marker 6 is not particularly limited as long as it can specify at least one of the first direction D1 and the second direction D2. The marker 6 shown in FIG. 7 is an arrow that specifies the second direction D2. When the planar shape of the base material 2 is square, it is not possible to specify which direction is the first direction D1 and the second direction D2 just by looking at the base material 2. If the marker 6 is provided, the first direction D1 and the second direction D2 can be specified regardless of the planar shape of the base material 2. If the second direction D2 can be specified by the marker 6, the base material 2 can be easily cut by hand in the second direction D2. The marker 6 may be provided so as to specify the first direction D1. In that case, the base material 2 is cut in a direction perpendicular to the first direction D1.

[0086] The location of the marker 6 is not particularly limited. The marker 6 shown in FIG. 7 is provided so as to be visible from the second surface 22 of the base material 2 on which the adhesive layer 3 and the separator 5 are not provided. The marker 6 may be provided on the first surface 21 or the second surface 22. Even if the marker 6 is provided on the first surface 21, if the base material 2 is transparent, the marker 6 can be visually recognized from the second surface 22. The marker 6 provided on the base material 2 is, for example, a printed matter.

[0087] As shown on the right side of FIG. 8, in the sheet 1 of this example, an adhesive layer 3 is provided on the first surface 21 of the base material 2, and a separator 5 is provided on the adhesive layer 3. That is, in this example, an adhesive layer 3 is provided between the separator 5 and the base material 2. The base material of the separator 5 may be any material generally used for a separator, for example, paper, synthetic paper, or a polyolefin-based resin film. The base material of the separator 5 may be a laminate of a layer made of polyethylene and a paper layer. The separator 5 contains a release agent. The release agent is provided so as to face at least the adhesive layer 3. The separator 5 is removed when the base material 2 is attached to a desired location. The sheet 1 of this example can function as a label.

[0088] The marker 6 may be provided on the separator 5. When the size of the separator 5 is larger than that of the base material 2, the marker 6 may be provided at a location on the separator 5 that does not overlap with the base material 2 when the sheet 1 is viewed from the second surface 22 side. In this case, the marker 6 can be visually recognized before the base material 2 is peeled off from the separator 5. If the marker 6 can be visually recognized before the base material 2 is peeled off from the separator 5, the sheet 1 can be manually cut in a specific direction even in a state with the separator 5 attached.

[0089] In the method for manufacturing the sheet according to Embodiment 2, the irradiation step is the same as the irradiation step described in Embodiment 1. The lamination step is different from the lamination step described in Embodiment 1. In the lamination step, as shown in FIG. 8, an adhesive layer 3 and a separator 5 are provided on the first surface 21 of the substrate 2 that has undergone the irradiation step. The lamination step of this example includes a step of preparing a laminate 9 in which the adhesive layer 3 is laminated on the first surface of the separator 5, and a step of bonding the laminate 9 to the substrate 2 such that the adhesive layer 3 faces the first surface 21 of the substrate 2 that has undergone the irradiation step. The substrate 2 shown in FIG. 8 is a resin film irradiated with an electron beam 8. In FIG. 8, for easy understanding, the lamination direction of the laminate 9 is indicated by an arrow. By preparing the laminate 9 in which the adhesive layer 3 and the separator 5 are integrated and bonding this laminate 9 to the substrate 2, it is difficult for an external force that would break the substrate 2 to be applied to the substrate 2 during the manufacturing stage. In the lamination step, the adhesive layer 3 and the separator 5 may be sequentially formed on the first surface 21 of the substrate 2 that has undergone the irradiation step.

[0090] The method for manufacturing the sheet according to Embodiment 2 further includes a display step of providing a marker 6 that specifies at least one of a first direction D1 and a second direction D2 on the substrate 2 that has undergone the irradiation step. The marker 6 may be provided by printing on the substrate 2 as described above, or may be provided on the release layer 4.

[0091] [Modification Example 2] As shown in FIG. 9, in the method for manufacturing the sheet, the laminate 9 including the substrate 2, the adhesive layer 3, and the separator 5 may be irradiated with an electron beam 8. The substrate 2 in the laminate 9 is a resin film before being irradiated with the electron beam 8. The method for manufacturing the sheet according to Modification Example 2 further includes a step of preparing a laminate 9 in which the adhesive layer 3 and the separator 5 are provided on the first surface 21 of the substrate 2 before being irradiated with the electron beam 8. In the irradiation step, the prepared laminate 9 is irradiated with the electron beam 8. The electron beam 8 is irradiated in a direction from the second surface 22 to the first surface 21 of the substrate 2 as shown in FIG. 9.

[0092] In Modification 2, since the electron beam 8 is irradiated with the adhesive layer 3 and the separator 5 provided on the base material 2, unintentional breakage of the base material 2 is less likely to occur in the manufacturing process compared to the case where the adhesive layer 3 and the separator 5 are provided on the base material 2 after irradiating the electron beam 8. The formation of the base material 2 into a desired shape and dimensions is often performed after providing the adhesive layer 3 and the separator 5 on the base material 2. In Modification 2, since the laminate 9 having the desired shape and dimensions is irradiated with the electron beam 8, it is easy to miniaturize the electron beam 8 irradiation device.

[0093] [Embodiment 3] Referring to FIG. 10, the sheet 1 of Embodiment 3 will be described. The planar shape of the base material 2 of Embodiment 3 is different from that of the sheet 1 of Embodiment 2. The following description will focus on the differences from Embodiment 2. The description of the same configuration and the same effects as those of Embodiment 2 may be omitted.

[0094] The planar shape of the base material 2 in this example is circular. The circular shape includes a perfect circle and an ellipse. When the planar shape of the base material 2 is circular, the first direction D1 is a direction along any one of eight different directions shifted by 22.5° in sequence. In FIG. 10, for easy understanding, eight different directions shifted by 22.5° in sequence are indicated by a two-dot chain line. The direction indicating the smallest tensile strength among the tensile strengths in these eight directions is regarded as the first direction D1.

[0095] When the planar shape of the base material 2 is circular, similar to Embodiment 2, it may be provided with a marker 6 for specifying at least one of the first direction D1 and the second direction D2. The marker 6 shown in FIG. 10 is an arrow for specifying the second direction D2.

[0096] [Embodiment 4] Although not shown, the planar shape of the base material may be a polygon other than a rectangular shape. When the planar shape of the base material is a polygon, similar to Embodiment 3, the first direction is regarded as a direction along any one of eight different directions shifted by 22.5° in sequence. When the planar shape of the base material 2 is a polygon, similar to Embodiment 3, it may be provided with a marker 6 for specifying at least one of the first direction D1 and the second direction D2.

[0097] [Embodiment 5] Although not shown, depending on the shape of the base material, there may be a plurality of first directions indicating the first tensile strength. If there are a plurality of first directions, there are a plurality of pairs of the first direction and the second direction. If there are a plurality of pairs of the first direction and the second direction, there are a plurality of directions that can be easily cut by hand. For example, if there are a direction showing a tensile strength of 80 MPa and a direction showing 70 MPa, either the direction showing 80 MPa may be adopted as the first direction, or the direction showing 70 MPa may be adopted as the first direction. However, it is easier to cut the sheet 1 including the base material 2 along the second direction D2 when the direction showing the smaller value of 70 MPa is used as the first direction. Each direction of the pair may or may not be orthogonal to each other.

[0098] [Embodiment 6] Although not shown, the sheet may be composed only of a base material made of a resin film. A long sheet composed only of the base material can be used, for example, as a band for binding a container and a lid such as a lunch box. In the case of a long sheet composed only of the base material, the ends of the sheet are connected, for example, by fusion. Each end of the sheet may be connected to the container. When opening the lid from the container, it can be easily cut by hand in the width direction at an arbitrary position of the long sheet.

[0099] [Test Example 1] In Test Example 1, an electron beam was irradiated to a base material made of resin, and the tensile strength and puncture strength of the base material after irradiation were measured. In addition, a sensory test was conducted to examine the cutability of the base material, that is, whether the sheet using the base material can be cut by hand.

[0100] <Sample> A long base material made of biaxially stretched polypropylene was prepared. The width of the base material is 15 mm. The length of the base material 2 has a length sufficient to be wound around a core in a plurality of turns. The thickness of the base material is 40 μm. The conditions of the prepared base material are the same for all of Sample No. 1-1 to Sample No. 1-9. In all samples, the direction along the length of the base material is the first direction, and the direction along the width of the base material is the second direction.

[0101] From Specimen No. 1-2 to Specimen No. 1-9, the prepared substrates were irradiated with electron beams. The irradiation conditions of the electron beams are as shown in Table 1. Specimen No. 1-1 was not irradiated with electron beams on the prepared substrate.

[0102] <Tensile Strength> Test pieces were taken from each specimen, and the test pieces were set on a commercially available tensile testing machine, and a tensile test was conducted at a tensile speed of 300 mm / min. The size of the test piece was 15 mm in width and 220 mm in length. For the test pieces of each specimen, the first tensile strength along the first direction and the second tensile strength along the second direction were measured respectively. The results are shown in Table 1. Table 1 shows two values, one indicated in units of mN / 15 mm (millinewton / 15 millimeters) and the other indicated in units of MPa. The value indicated in units of MPa is a value obtained by unit conversion using the value indicated in units of mN / 15 mm, the width, and the thickness of the substrate. Specifically, the value indicated in units of MPa is obtained by calculating the area using the width of the substrate of 15 mm and the thickness of 40 μm, and dividing the value indicated in units of mN / 15 mm by the above area.

[0103] <Puncture Strength> Square test pieces with a side length of 15 mm were taken from each specimen, and the test pieces were set on a commercially available tensile testing machine. With the entire test piece in a state of being stretched in both the width direction and the length direction, the strength when the needle penetrated the test piece was measured when the needle was punctured into the test piece at a speed of 50 mm / min. The tensile testing machine used was a testing machine of model J-CP1-1KN-U manufactured by A&D Company, Limited. The results are shown in Table 1.

[0104] <Sensory Test> In Specimens No. 1-1 to No. 1-9, an adhesive layer was provided on the first surface of the substrate irradiated with electron beams, and a release layer was provided on the second surface of the substrate. Specimens No. 1-1 to No. 1-9 having the substrate, the adhesive layer, and the release layer are so-called OPP tapes.

[0105] Strip-shaped test pieces were taken from each sample, and 20 subjects cut the test pieces by hand in the second direction. The cutting was performed according to the following procedure. First, using Nichiban's cellophane tape (registered trademark), get a feel for the force required to cut the cellophane tape by hand. The width of the cellophane tape is the same as that of each sample, 15 mm. After getting a feel for the above-mentioned force, cut each test piece by hand in the second direction with that force. The cutting was done by holding each test piece or the cellophane tape with both hands and twisting the test piece or the cellophane tape in a direction where both hands move away from each other. The cellophane tape was cut each time a sample was cut. The 20 subjects tested each sample 5 times. For each sample, it was determined whether it could be cut or not, and the cuttability was calculated. For example, if a subject cut a certain sample and was able to cut it 3 times out of 5 and unable to cut it 2 times, the cuttability is 60%. The cuttability of each sample is the average value of the cuttability by 20 subjects. The results are shown in Table 1.

[0106]

Table 1

[0107] As shown in Table 1, from Sample No. 1-4 to Sample No. 1-9, the first tensile strength is 85 MPa or less, the puncture strength is 14.0 N or less, and the cuttability is 80% or more. The puncture strength being 14.0 N or less forms a starting point of fracture in the substrate, and the first tensile strength being 85 MPa or less causes the substrate to be divided in the first direction while the fracture progresses along the second direction from the starting point of the fracture, and it is considered that the substrate could be easily cut by hand in the second direction.

[0108] As shown in Table 1, when the thickness of the base material is 40 μm, if the electron beam dose is 100 kGy or more and less than 200 kGy, it can be seen that by irradiating the electron beam at an acceleration voltage of 200 kV or more, the first tensile strength can be made 85 MPa or less and the piercing strength can be made 14.0 N or less. Also, when the thickness of the base material is 40 μm, if the electron beam dose is 200 kGy or more, it can be seen that by irradiating the electron beam at an acceleration voltage of 80 kV or more, the first tensile strength can be made 85 MPa or less and the piercing strength can be made 14.0 N or less. That is, it can be seen that by adjusting the electron beam dose and acceleration voltage according to the thickness of the base material and irradiating the adjusted electron beam to the base material, the first tensile strength can be made 85 MPa or less and the piercing strength can be made 14.0 N or less.

[0109] [Test Example 2] In Test Example 2, a base material with a thickness of 60 μm was used, and the base material was irradiated with an electron beam, and a sensory test was conducted to examine the cuttability of the base material after irradiation.

[0110] The conditions of the prepared base material are the same as those in Test Example 1 except for the thickness. The conditions of the prepared base material are all the same from Sample No. 2-1 to Sample No. 2-10. All the base materials from Sample No. 2-1 to Sample No. 2-10 were irradiated with an electron beam. The irradiation conditions of the electron beam are as shown in Table 2. In Samples No. 2-1 to No. 2-10, an adhesive layer was provided on the first surface of the base material irradiated with the electron beam, and a release layer was provided on the second surface of the base material. Then, a sensory test was conducted in the same manner as in Test Example 1, and the cuttability of each sample was calculated. The results are shown in Table 2.

[0111]

Table 2

[0112] As shown in Table 2, when the thickness of the base material is 60 μm, it can be seen that if the electron beam is irradiated at a dose of 600 kGy or more and an acceleration voltage of 80 kV or more, the cuttability can be made 80% or more. That is, by adjusting the dose and acceleration voltage of the electron beam according to the thickness of the base material and irradiating the adjusted electron beam to the base material, it can be seen that the first tensile strength can be made 85 MPa or less and the piercing strength can be made 14.0 N or less. Although it becomes more difficult for the electron beam to penetrate in the thickness direction of the base material as the thickness of the base material increases, it can be seen that the base material can be made fragile enough to be cut by hand by setting the dose of the electron beam to 600 kGy or more and the acceleration voltage to 80 kV or more.

Explanation of Signs

[0113] 1 Sheet 2 Base material, 21 First surface, 22 Second surface, 2T Thickness 3 Adhesive layer 4 Release layer 5 Separator 6 Marker 8 Electron beam 9 Laminate D1 First direction, D2 Second direction

Claims

1. A sheet comprising a base material made of resin, wherein a first tensile strength of the base material is 85 MPa or less, a piercing strength of the base material is 14.0 N or less, and the first tensile strength is a tensile strength along at least one of a plurality of directions parallel to the surface of the base material.

2. The sheet according to claim 1, wherein the first tensile strength is 30 MPa or more.

3. A second tensile strength of the base material is greater than the first tensile strength, and the second tensile strength is a tensile strength along a second direction parallel to the surface of the base material and orthogonal to a first direction indicating the first tensile strength. The sheet according to claim 1 or claim 2.

4. The sheet according to claim 3, further comprising a marker specifying at least one of the first direction and the second direction.

5. The sheet according to claim 3, wherein the second tensile strength is 200 MPa or less.

6. The sheet according to claim 5, wherein the second tensile strength is 30 MPa or more.

7. The sheet according to claim 1 or claim 2, wherein the base material is made of polypropylene.

8. A separator, and an adhesive layer provided between the separator and the base material. The sheet according to claim 1 or claim 2.

9. The base material is a long member having a length longer than a width, and a first direction indicating the first tensile strength is a direction along the length of the long member. The sheet according to claim 1 or claim 2.

10. An adhesive layer provided on a first surface of the long member, and a release layer provided on a second surface of the long member. The sheet according to claim 9.

11. The sheet according to claim 1 or claim 2, wherein a thickness of the base material is 30 μm or more and 60 μm or less.

12. An irradiation step of irradiating an electron beam to a base material made of resin, wherein in the irradiation step, when a thickness of the base material is 40 μm or less, if a dose of the electron beam is 100 kGy or more and less than 200 kGy, the electron beam is irradiated at an acceleration voltage of 200 kV or more, if the dose of the electron beam is 200 kGy or more, the electron beam is irradiated at an acceleration voltage of 80 kV or more, when the thickness of the base material exceeds 40 μm, the electron beam is irradiated at a dose of 600 kGy or more and an acceleration voltage of 80 kV or more. A method for manufacturing a sheet.

13. ​ The method for manufacturing a sheet according to claim 12, further comprising a step of providing an adhesive layer on a first surface of the substrate and a release layer on a second surface of the substrate, after the irradiation step has been performed on the substrate.

14. The method for manufacturing a sheet according to claim 12, further comprising a step of preparing a laminate in which an adhesive layer is provided on a first surface of the substrate and a release layer is provided on a second surface of the substrate, with respect to the substrate before the electron beam is irradiated. In the irradiation step, the laminate is irradiated with the electron beam, the method for manufacturing a sheet according to claim 12.

15. A step of preparing a laminate in which an adhesive layer is laminated on a first surface of a separator; The method for manufacturing a sheet according to claim 12, further comprising a step of bonding the laminate to the substrate such that the adhesive layer faces a first surface of the substrate that has undergone the irradiation step.

16. The method for manufacturing a sheet according to claim 12, further comprising a step of preparing a laminate in which an adhesive layer and a separator are provided on a first surface of the substrate before the electron beam is irradiated. In the irradiation step, the laminate is irradiated with the electron beam, the method for manufacturing a sheet according to claim 12.

17. The method for manufacturing a sheet according to claim 12, further comprising a marking step of providing a marker for specifying at least one of a first direction indicating the lowest tensile strength among tensile strengths in a plurality of directions parallel to the surface of the substrate and a second direction parallel to the surface of the substrate and perpendicular to the first direction, in the substrate that has undergone the irradiation step.

18. The method for manufacturing a sheet according to claim 12, wherein the substrate is made of polypropylene.

19. The method for manufacturing a sheet according to claim 12, wherein the thickness of the substrate is 30 μm or more and 60 μm or less.

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