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Abstract

The present invention provides a sheet having an adhesive layer containing a self-adhesive adhesive, which can be easily peeled off even if the adhesive layer adheres to a substrate other than the self-adhesive adhesive, and which offers excellent productivity. [Solution] A sheet comprising a first base material layer and an adhesive layer disposed on the first surface of the first base material layer, wherein the adhesive layer comprises a self-adhesive adhesive and a plurality of fine particles dispersed in the self-adhesive adhesive, and the surface of the adhesive layer includes a plurality of protrusions formed by the plurality of fine particles.

Description

Technical Field

[0001] The present invention relates to a sheet.

Background Art

[0002] Patent Document 1 discloses a label continuum in which an adhesive layer is provided on the back surface of a long label base material. An auto-adhesive having a high adhesive force between the adhesive layers is used for the adhesive layer. A blocking layer using a release agent is formed on the surface of the label base material. The label continuum is wound in a roll shape. In the roll body around which the label continuum is wound, the adhesive layer contacts the blocking layer. In the technique of Patent Document 1, by using a release agent for the blocking layer, it is possible to suppress the strong adhesion of the adhesive layer to the surface of the label base material and facilitate the pulling out of the label continuum from the roll body. Hereinafter, the label base material will be referred to as a base material layer, and the label continuum will be referred to as a sheet.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Auto-adhesives are difficult to adhere to adherends other than auto-adhesives. However, under specific conditions, auto-adhesives can adhere to adherends unintentionally. The specific conditions are those in which the auto-adhesive is strongly pressed against the adherend or stored in a harsh environment while in contact with the adherend. A harsh environment is, for example, a high-temperature environment or a high-humidity environment. In a roll body around which a sheet is wound, the adhesive layer contacts the surface of the sheet opposite to the adhesive layer. If the roll body is stored under specific conditions, the adhesive layer can adhere to the above surface unintentionally. In the technique of Patent Document 1, it is necessary to form a blocking layer that is difficult to adhere to the adhesive layer on the surface of the base material layer, and the manufacturing process is complicated.

[0005] One of the objectives of the present invention is to provide a sheet having an adhesive layer containing a self-adhesive adhesive, which can be easily peeled off even if the adhesive layer adheres to a substrate other than the self-adhesive adhesive, and which also offers excellent productivity. [Means for solving the problem]

[0006] (1) A sheet according to one aspect of the present invention comprises a first base layer and an adhesive layer disposed on the first surface of the first base layer. The adhesive layer comprises a self-adhesive adhesive and a plurality of fine particles dispersed in the self-adhesive adhesive. The surface of the adhesive layer includes a plurality of protrusions formed by the plurality of fine particles.

[0007] The adhesive layer's surface includes multiple protrusions, which prevents the adhesive layer from making full contact with the substrate other than the self-adhesive adhesive, thus easily forming areas where the adhesive layer and the substrate are in contact. Because these areas are in contact, even if the adhesive layer adheres to a substrate other than the self-adhesive adhesive, it can be easily peeled off the substrate. For example, in a roll of sheet material, the adhesive layer contacts the surface of the sheet opposite to the adhesive layer. In this case, the surface of the sheet opposite to the adhesive layer is the substrate. Even in a roll of sheet material, the adhesive layer can be easily peeled off the substrate, and the sheet can be easily pulled out of the roll. Since the base of the adhesive layer is made of a self-adhesive adhesive, the adhesive strength between the adhesive layers, i.e., the self-adhesion strength of the adhesive layer, is maintained. The sheet only requires the formation of a self-adhesive adhesive with multiple dispersed fine particles on a substrate, and since this does not increase the manufacturing process, it offers excellent productivity.

[0008] (2) The sheet of (1) above may further include a heat-sensitive layer disposed on the second surface of the first base material layer.

[0009] If a sheet has a heat-sensitive layer, printing can be done on the sheet using heat. The surface of the heat-sensitive layer is generally smooth. In addition, the heat-sensitive layer generally contains components that reduce wear on the thermal head. These components are compatible with self-adhesive adhesives. Therefore, self-adhesive adhesives adhere easily to the heat-sensitive layer. In the case of a roll of sheet material, the adhesive layer can adhere to the heat-sensitive layer. If the surface of the adhesive layer contains multiple protrusions, even if the adhesive layer adheres to the heat-sensitive layer, it can be easily peeled off from the heat-sensitive layer.

[0010] (3) The sheet described in (1) above may further include a release layer disposed on the second surface of the first substrate layer and a label body disposed on the release layer. The label body comprises an adhesive layer, a second substrate layer, and a heat-sensitive layer in this order. The release layer and the adhesive layer are in contact.

[0011] If a sheet has a label, the label and the sheet from which the label has been separated can be used separately by separating the label from the release layer. A sheet with a label is called, for example, a double label. The sheet from which the label has been separated is folded so that different parts of the adhesive layer face each other, and the adhesive layers that are facing each other are bonded together. In other words, the sheet from which the label has been separated is used by wrapping it around the object to which it will be attached. The separated label can be bonded to, for example, an object other than the object to which it will be attached.

[0012] (4) In the sheet described in (3) above, the label body may be provided with a cut line for separating a part of the label body from the release layer.

[0013] The label has a perforated line, making it easy to separate a portion of the label from the release layer along the line.

[0014] (5) In any of the sheets described in (1) to (4) above, the content ratio of the plurality of fine particles to 100 parts by weight of the self-adhesive adhesive may be 4 parts by weight or more and 33 parts by weight or less.

[0015] If the above content ratio is 4 parts by weight or more, multiple protrusions are likely to form on the surface of the adhesive layer. If the above content ratio is 33 parts by weight or less, the number of protrusions will not become too large, and the self-adhesion strength of the adhesive layer will be easily maintained.

[0016] (6) In any of the sheets described in (1) to (5) above, the average particle size of the plurality of fine particles may be greater than the average thickness of the adhesive layer.

[0017] If the average particle size of multiple microparticles is larger than the average thickness of the adhesive layer, multiple protrusions are likely to form on the surface of the adhesive layer.

[0018] (7) In any of the sheets described in (1) to (6) above, the protruding length of the projection may be 0.1 μm or more and 10.0 μm or less.

[0019] If the protruding length of the protrusion is 0.1 μm or more, the adhesive layer is easily peeled off from substrates other than self-adhesive adhesives. If the protruding length of the protrusion is 10.0 μm or less, the self-adhesion strength of the adhesive layer is easily maintained.

[0020] (8) In any of the sheets described in (1) to (7) above, each of the plurality of fine particles may be covered with the self-adhesive adhesive.

[0021] When each of multiple microparticles is covered with a self-adhesive adhesive, the adhesive layers bond to each other through the self-adhesive adhesive, which tends to increase the adhesive strength between the adhesive layers.

[0022] (9) In any of the sheets described in (1) to (8) above, each of the plurality of fine particles may be made of resin.

[0023] Fine particles made of resin are lighter than, for example, fine particles made of metal. Therefore, if resin fine particles are included in large quantities, the weight of the adhesive layer tends to be lighter, and consequently, the weight of the sheet tends to be lighter.

[0024] (10) In the sheet of (9) above, the resin may be an acrylic copolymer.

[0025] Particles made of an acrylic copolymer are excellent in weather resistance and water resistance.

[0026] (11) In any of the sheets from (1) to (10) above, the average particle size of the plurality of fine particles may be 1 μm or more and 20 μm or less.

[0027] If the average particle size of the plurality of fine particles is 1 μm or more, a plurality of protrusions are likely to be formed on the surface of the adhesive layer. If the average particle size of the plurality of fine particles is 20 μm or less, although it depends on the thickness of the adhesive layer, the protruding amount of the protrusions does not become too large, and the self - adhesion of the adhesive layer is likely to be maintained.

[0028] (12) In any of the sheets from (1) to (11) above, the average thickness of the adhesive layer may be 1 μm or more and 15 μm or less.

[0029] If the average thickness of the adhesive layer is 1 μm or more, the self - adhesion of the adhesive layer is likely to be high. If the average thickness of the adhesive layer is 15 μm or less, while maintaining the self - adhesion of the adhesive layer, protrusions are likely to be formed depending on the particle size of the fine particles.

[0030] (13) In any of the sheets from (1) to (12) above, the self - adhesion of the adhesive layer may be 1.5 N / 10 mm or more.

[0031] If the self - adhesion of the adhesive layer is 1.5 N / 10 mm or more, the adhesive force between the adhesive layers is high, and the adhesive layers are difficult to peel off.

Advantages of the Invention

[0032] According to the present invention, in a sheet provided with an adhesive layer containing a self - adhesive adhesive, even when the adhesive layer adheres to an adherend other than the self - adhesive adhesive, it can be easily peeled off and is excellent in productivity.

Brief Description of the Drawings

[0033] [Figure 1] Figure 1 is a schematic diagram of the sheet according to Embodiment 1. [Figure 2] Figure 2 is a schematic diagram of the II-II section of Figure 1. [Figure 3] Figure 3 is a schematic diagram of the sheet according to Embodiment 2. [Figure 4] Figure 4 is a schematic diagram of the section IV-IV in Figure 3. [Figure 5] Figure 5 is a magnified photograph of the surface of the adhesive layer of sample No. 1 in Test Example 1. [Figure 6] Figure 6 is a magnified photograph of the surface of the adhesive layer of sample No. 3 in Test Example 1. [Figure 7] Figure 7 is a magnified photograph of the surface of the adhesive layer of sample No. 8 in Test Example 1. [Figure 8] Figure 8 is a magnified photograph of the cross-section of the adhesive layer of sample No. 8 in Test Example 1. [Modes for carrying out the invention]

[0034] Specific examples of the sheet of the present invention will be described with reference to the drawings. The dimensions of the components shown in the drawings are represented for illustrative purposes only and do not necessarily represent actual dimensions and proportions. The present invention is not limited to these examples and is as defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0035] [Embodiment 1] <Sheet> Sheet 1A of Embodiment 1 will be described with reference to Figures 1 and 2. Sheet 1A comprises a first base layer 2 and an adhesive layer 3, as shown in Figure 2. Sheet 1A of this example further comprises a heat-sensitive layer 7. The adhesive layer 3 contains a self-adhesive adhesive 4.

[0036] The sheet 1A in this example is a long material, as shown in Figure 1. The sheet 1A is wound into a roll, for example, as shown on the left side of Figure 1. When using the sheet 1A, the sheet 1A is pulled out from the roll and cut to the desired length in the direction along the width. The cut sheet 1A is used by wrapping it around the attachment target 100, for example, as shown on the right side of Figure 1. The use of the sheet 1A is not particularly limited. In this example, the sheet 1A is a bag tag. The bag tag may be an RFID (radio frequency identification) tag. The attachment target 100 is not particularly limited. The attachment target 100 is, for example, the handle of a suitcase. When attaching the sheet 1A to the attachment target 100, the sheet 1A is folded so that different parts of the adhesive layer 3 face each other. Since the adhesive layer 3 contains a self-adhesive adhesive 4, the adhesive layers 3 that are positioned facing each other are firmly bonded together.

[0037] One of the features of the sheet 1A in this embodiment is that the adhesive layer 3 contains a plurality of fine particles 5, as shown in Figure 2. The plurality of fine particles 5 are dispersed in the self-adhesive adhesive 4. The surface of the adhesive layer 3 includes a plurality of protrusions 6 formed by the plurality of fine particles 5. The surface of the adhesive layer 3 is the first surface 31 shown in Figure 2. The plurality of protrusions 6 have the function of making it easier to peel the adhesive layer 3 from the adherend, even when the adhesive layer 3 is adhered to an adherend other than the self-adhesive adhesive 4. In this example, the plurality of protrusions 6 have the function of making it easier to pull out the sheet 1A from the roll body, even when the adhesive layer 3 is adhered to the heat-sensitive layer 7 in the roll body around which the sheet 1A is wound.

[0038] ≪First base layer≫ The first base layer 2 is the base portion of sheet 1A. The first base layer 2 is in the form of a sheet. In this example, the first base layer 2 is a long material. A long material is thin in thickness and has a length longer than its width. A specific example of a long material is a strip-shaped material. The first base layer 2 has a first surface 21 and a second surface 22. The first surface 21 and the second surface 22 are surfaces that face opposite directions to each other in the direction along the thickness of the first base layer 2. The thickness of the first base layer 2 is not particularly limited and can be, for example, a known thickness.

[0039] The material of the first base layer 2 is not particularly limited. The first base layer 2 is made of paper, resin, or a composite of paper and resin. Examples of paper include thermal paper, fine paper, recycled paper, glossy paper, oil-resistant paper, coated paper, art paper, kraft paper, glassine paper, or Cascoat paper. Examples of resin include polyester resin, polyimide resin, polypropylene resin, polyamide resin, polycarbonate resin, polyacetate resin, polyethylene resin, or polyphenylene sulfide resin. The paper forming the composite material is one of the above-mentioned papers, and the resin forming the composite material is one of the above-mentioned resins. The composite material may be a laminate of paper and a resin film, or paper coated with resin. In this example, the first base layer 2 is thermal paper.

[0040] ≪Adhesive layer≫ The adhesive layer 3 is positioned facing the first surface 21 of the first substrate layer 2. In this example, the adhesive layer 3 is positioned on the first surface 21. In this example, the adhesive layer 3 is positioned over the entire surface of the first surface 21. The adhesive layer 3 may also be positioned over a portion of the first surface 21.

[0041] The adhesive layer 3 has a first surface 31 and a second surface 32. The first surface 31 and the second surface 32 are surfaces facing opposite directions in the direction along the thickness of the adhesive layer 3. The first surface 31 is the surface that faces different parts of the adhesive layer 3 when the sheet 1A is attached to the mounting object 100. When the sheet 1A is wound in a roll, the first surface 31 is the surface that contacts the surface of the sheet 1A opposite to the adhesive layer 3. In this example, the first surface 31 is the surface that contacts the heat-sensitive layer 7 when the sheet 1A is wound in a roll. The second surface 32 is the surface that faces the first surface 21 of the first base material layer 2.

[0042] The adhesive layer 3 contains a self-adhesive adhesive 4 and a plurality of fine particles 5. The self-adhesive adhesive 4 is the base portion of the adhesive layer 3. The self-adhesive adhesive 4 adheres strongly to other self-adhesive adhesives 4, but does not adhere well to other materials or does not adhere well to other materials. Therefore, when attaching sheet 1A to the mounting target 100, as shown on the right side of Figure 1, sheet 1A is formed into a loop shape and the adhesive layers 3 are brought into contact with each other. Because the adhesive layers 3 adhere strongly to each other, sheet 1A is difficult to detach from the mounting target 100. The adhesive layer 3 at the location where the loop is formed, that is, the adhesive layer 3 other than the location where the adhesive layers 3 are bonded to each other, does not adhere well to the mounting target 100.

[0043] The self-adhesive adhesive 4 has low adhesive strength to substrates other than the self-adhesive adhesive 4. However, the self-adhesive adhesive 4 may unintentionally adhere to a substrate under certain conditions. These specific conditions are when the self-adhesive adhesive 4 is pressed firmly against the substrate or stored in a harsh environment while in contact with the substrate. A harsh environment is, for example, a high-temperature or high-humidity environment. The substrate is, for example, the mounting target 100 shown in Figure 1, or the layer forming the opposite side of the adhesive layer 3 in sheet 1A. In this example, the layer forming the opposite side of the adhesive layer 3 in sheet 1A is the heat-sensitive layer 7.

[0044] As shown in Figure 2, multiple fine particles 5 are dispersed in the self-adhesive adhesive 4, forming multiple protrusions 6 on the first surface 31 of the adhesive layer 3, making it easier to peel the adhesive layer 3 from the adherend even when the adhesive layer 3 is adhered to an adherend other than the self-adhesive adhesive 4. The formation of multiple protrusions 6 on the first surface 31 of the adhesive layer 3 makes it easier for the adhesive layer 3 not to come into contact with the adherend over its entire surface, and for areas where the adhesive layer 3 and the adherend are not in contact to be formed. The formation of areas where the adhesive layer 3 and the adherend are not in contact makes it easier to peel the adhesive layer 3 from the adherend. For example, as shown on the left side of Figure 1, in a roll on which a sheet 1A is wound, the adhesive layer 3 comes into contact with the surface 70 of the heat-sensitive layer 7. If the roll is stored under specific conditions, the adhesive layer 3 and the heat-sensitive layer 7 may adhere to each other unintentionally. When the adhesive layer 3 adheres to the heat-sensitive layer 7, it becomes difficult to pull the sheet 1A out of the roll. Multiple fine particles 5 are dispersed in the self-adhesive adhesive 4 to form multiple protrusions 6, thereby making it easier to pull out the sheet 1A from the roll body.

[0045] The statement that multiple fine particles 5 are dispersed in the self-adhesive adhesive 4 means that the multiple fine particles 5 do not aggregate in the self-adhesive adhesive 4 and exist with a certain amount of space between adjacent fine particles 5. At least some of the multiple fine particles 5 form multiple protrusions 6 on the first surface 31 of the adhesive layer 3, as shown in Figure 2. The multiple protrusions 6 are dispersed on the first surface 31, as shown in Figures 6 and 7 in Test Example 1, which will be described later. The statement that the multiple protrusions 6 are dispersed on the first surface 31 means that the multiple protrusions 6 do not tend to be concentrated on the first surface 31 and exist with a certain amount of space between adjacent protrusions 6.

[0046] The self-adhesive adhesive 4 comprises, for example, a natural rubber latex and a styrene-acrylonitrile copolymer aqueous emulsion, or an elastomer comprising natural rubber and a styrene-isoprene-styrene block copolymer.

[0047] Each of the multiple fine particles 5 is made of, for example, a resin. Fine particles 5 made of resin are lighter than fine particles 5 made of, for example, metal. Therefore, if fine particles 5 made of resin are included in large quantities, the weight of the adhesive layer 3 tends to be lighter, and consequently, the weight of the sheet 1A tends to be lighter. The resin is, for example, an acrylic copolymer. Fine particles 5 made of acrylic copolymer have excellent weather resistance and water resistance. The fine particles 5 may be made of metal or ceramics. Two or more types of fine particles 5 selected from fine particles 5 made of resin, fine particles 5 made of metal, and fine particles 5 made of ceramics may be mixed.

[0048] The content ratio of multiple fine particles 5 when the self-adhesive adhesive 4 is 100 parts by weight is, for example, 4 parts by weight or more and 33 parts by weight or less. If the above content ratio is 4 parts by weight or more, multiple protrusions 6 are easily formed on the first surface 31 of the adhesive layer 3. If the above content ratio is 33 parts by weight or less, the number of protrusions 6 does not become too large, and the self-adhesion strength of the adhesive layer 3 is easily maintained. The above content ratio may also be 4 parts by weight or more and 21 parts by weight or 4 parts by weight or more and 13 parts by weight or less.

[0049] The average particle size of the multiple fine particles 5 is, for example, between 1 μm and 20 μm. If the average particle size of the multiple fine particles 5 is 1 μm or more, multiple protrusions 6 are easily formed on the first surface 31 of the adhesive layer 3. If the average particle size of the multiple fine particles 5 is 20 μm or less, although this depends on the thickness of the adhesive layer 3, the amount of protrusion 6 does not become too large, and the self-adhesion strength of the adhesive layer 3 is easily maintained. The average particle size of the multiple fine particles 5 is the particle size that takes the mode value when the mass-based particle size distribution is measured. The particle size distribution can be measured by laser diffraction / scattering using a commercially available particle size distribution analyzer. A commercially available particle size distribution analyzer is, for example, the MT3300EX II particle size distribution analyzer manufactured by Microtrac Bell Co., Ltd. The average particle size of the multiple fine particles 5 may also be between 1 μm and 16 μm, or between 1 μm and 9 μm.

[0050] The average particle size of the multiple fine particles 5 may be larger than the average thickness of the adhesive layer 3. If the average particle size of the multiple fine particles 5 is larger than the average thickness of the adhesive layer 3, multiple protrusions 6 are more likely to form on the first surface 31 of the adhesive layer 3. The average particle size of the multiple fine particles 5 may be smaller than or the same as the average thickness of the adhesive layer 3. If the average particle size of the multiple fine particles 5 is equal to or less than the average thickness of the adhesive layer 3, the higher the proportion of multiple fine particles 5 in the self-adhesive adhesive 4 (100 parts by weight), the more likely multiple protrusions 6 are to form on the first surface 31 of the adhesive layer 3.

[0051] The protruding length 6H of each of the multiple protrusions is, for example, 0.1 μm or more and 10.0 μm or less. If the protruding length 6H of each protrusion 6 is 0.1 μm or more, the adhesive layer 3 is easy to peel off from substrates other than the self-adhesive adhesive 4. If the protruding length 6H of each protrusion 6 is 10.0 μm or less, the self-adhesion strength of the adhesive layer 3 is easily maintained. The protruding length 6H of each protrusion 6 may also be 0.1 μm or more and 5.0 μm or less, or 0.1 μm or more and 2.0 μm or less.

[0052] The projection length 6H of each protrusion 6 can be determined by observing a cross-section of sheet 1A with a scanning electron microscope (SEM) and obtaining the SEM image. The projection length 6H of each protrusion 6 is the distance from the reference line L to the point of maximum protrusion in the SEM cross-section. The reference line L is a straight line connecting the midpoints of each adjacent protrusion 6 when viewing one protrusion 6. In Figure 2, the reference line L is shown as a dashed line. The midpoints are the points that bisect the distance between the boundary point of the arc line that constitutes the surface of each protrusion 6 and the straight line that constitutes the surface of the adhesive layer 3.

[0053] For example, suppose a protrusion 6A formed by fine particles 5A, a protrusion 6B formed by fine particles 5B, and a protrusion 6C formed by fine particles 5C are arranged in that order. Let protrusion 6B be considered as a single protrusion 6, and let the straight line connecting the midpoint α between protrusion 6B and protrusion 6A and the midpoint β between protrusion 6B and protrusion 6C be the reference line L for protrusion 6B. Midpoint α is the point that bisects the distance D1 between the boundary point of the arc line forming the surface of protrusion 6B and the straight line forming the surface of the adhesive layer 3, and the boundary point of the arc line forming the surface of protrusion 6A and the straight line forming the surface of the adhesive layer 3. Midpoint β is the point that bisects the distance D2 between the boundary point of the arc line forming the surface of protrusion 6B and the straight line forming the surface of the adhesive layer 3, and the boundary point of the arc line forming the surface of protrusion 6C and the straight line forming the surface of the adhesive layer 3. The distance from the reference line L to the most protruding part of protrusion 6B is the protrusion length 6H of protrusion 6B. The method for determining the projection length 6H for each of the other individual protrusions 6 is the same.

[0054] The reference line L may be a line connecting points that are separated from the first surface 21 of the first base material layer 2 by the average thickness of the adhesive layer 3. The average thickness of the adhesive layer 3 will be described later. The protruding length 6H of each protrusion 6 is such that the distance from at least one of the reference line L using the intermediate points α and β, and the reference line using the average thickness of the adhesive layer 3, to the most protruding part of the protrusion 6B satisfies the specified length.

[0055] The size of each of the multiple protrusions 6 can be adjusted by the average particle size of the multiple fine particles 5 and the above-mentioned content ratio. The size of each protrusion 6 is the area of ​​each protrusion 6 when viewed from a direction along the thickness of the adhesive layer 3.

[0056] Almost all of the multiple fine particles 5 are covered with the self-adhesive adhesive 4. Almost all of the multiple fine particles 5 means 90% or more of the multiple fine particles 5. This ratio can be determined, for example, by observing the exposure state of the fine particles 5 for 50 or more protrusions 6 in one or more observation fields and calculating the percentage of the number of fine particles 5 covered with the self-adhesive adhesive 4 relative to the total number of protrusions 6. Not all of the multiple fine particles 5 are covered with the self-adhesive adhesive 4. If each fine particle 5 is covered with the self-adhesive adhesive 4, the entire surface of the first surface 31 is made of the self-adhesive adhesive 4. If the entire surface of the first surface 31 is made of the self-adhesive adhesive 4, the adhesive layers 3 are bonded to each other by the self-adhesive adhesive 4, and the adhesive strength between the adhesive layers 3 tends to be high. Some of the multiple fine particles 5 are exposed from the self-adhesive adhesive 4.

[0057] The average thickness of the adhesive layer 3 is, for example, 1 μm to 15 μm. If the average thickness of the adhesive layer 3 is 1 μm or more, the self-adhesion strength of the adhesive layer 3 tends to be high. If the average thickness of the adhesive layer 3 is 15 μm or less, the self-adhesion strength of the adhesive layer 3 is maintained without the thickness of the adhesive layer 3 becoming too thick. The average thickness of the adhesive layer 3 can be determined from the SEM image. The thickness of the adhesive layer 3 is measured at five or more different locations in the SEM image, and the average value is taken as the average thickness of the adhesive layer 3. The thickness of the adhesive layer 3 is the distance between the first surface 31 and the second surface 32 at the midpoint between adjacent protrusions 6. In other words, the thickness of the adhesive layer 3 is the shortest distance from the second surface 32 to a location on the first surface 31 where no protrusions 6 exist. The average thickness of the adhesive layer 3 may be 1 μm to 11 μm, or 1 μm to 8 μm.

[0058] The self-adhesion strength of adhesive layer 3 is, for example, 1.5 N / 10 mm or more. If the self-adhesion strength of adhesive layer 3 is 1.5 N / 10 mm or more, the adhesive strength between adhesive layers 3 is high, and they are difficult to peel off from each other. The self-adhesion strength of adhesive layer 3 can be measured according to JIS Z 0237:2022. The specific measurement method will be explained in the test example below. The self-adhesion strength of adhesive layer 3 may be 2.0 N / 10 mm or more.

[0059] ≪Heat-sensitive layer≫ The heat-sensitive layer 7 is positioned facing the second surface 22 of the first substrate layer 2. In this example, the heat-sensitive layer 7 is positioned on the second surface 22. In this example, the heat-sensitive layer 7 is positioned over the entire surface of the second surface 22. The heat-sensitive layer 7 may also be positioned over a portion of the second surface 22. The second surface 22 may be pre-treated to improve adhesion with the heat-sensitive layer 7. Pre-treatment may include, for example, corona treatment, plasma treatment, or ozone treatment.

[0060] The thermal layer 7 is a layer that changes color when heated. The color it changes to is, for example, black. When the thermal layer 7 is heated by the thermal head of a thermal printer, a portion of the thermal layer 7 changes color, and the desired information is printed on the thermal layer 7.

[0061] The surface 70 of the heat-sensitive layer 7 is generally smooth. The heat-sensitive layer 7 generally contains components to reduce wear on the thermal head. These components are compatible with the self-adhesive adhesive 4. Therefore, the self-adhesive adhesive 4 adheres easily to the heat-sensitive layer 7. In a roll in which the sheet 1A is wound into a roll, the adhesive layer 3 can adhere to the heat-sensitive layer 7. Because the first surface 31 of the adhesive layer 3 includes multiple protrusions 6, even if the adhesive layer 3 adheres to the heat-sensitive layer 7, the adhesive layer 3 can be easily peeled off from the heat-sensitive layer 7. Therefore, the sheet 1A can be easily pulled out from the roll.

[0062] [Embodiment 2] <Sheet> Sheet 1B of Embodiment 2 will be described with reference to Figures 3 and 4. Sheet 1B comprises an adhesive layer 3, a release liner 8, and a label body 9, as shown in Figure 4. The adhesive layer 3 is the same as the adhesive layer 3 in Sheet 1A of Embodiment 1. The release liner 8 comprises a first base layer 81 and a release layer 82. The adhesive layer 3 is located on the first surface 811 of the first base layer 81. The release layer 82 is located on the second surface 812 of the first base layer 81. The first base layer 81 corresponds to the first base layer 2 in Sheet 1A of Embodiment 1. A known release layer can be used for the release layer 82. The label body 9 comprises an adhesive layer 91, a second base layer 92, and a heat-sensitive layer 93 in this order. The release layer 82 and the adhesive layer 91 are in contact. The heat-sensitive layer 93 corresponds to the heat-sensitive layer 7 in Embodiment 1. A known adhesive layer used in a label body can be used for the adhesive layer 91. The second substrate layer 92 can also be a known substrate layer used for label bodies. The label body 9 in this example includes a cut line 95 for separating a portion of the label body 9 from the release layer 82. In Figures 3 and 4, the cut line 95 is shown as a dashed line.

[0063] The sheet 1B in this example is a long material, as shown in Figure 3. The sheet 1B is wound into a roll, for example, as shown on the left side of Figure 3. When using the sheet 1B, the sheet 1B is pulled out from the roll on which it is wound, and the sheet 1B is cut to the desired length in the direction along the width. At this time, a portion of the label body 9 can be separated from the release layer 82 along the cutting line 95. After a portion of the label body 9 has been separated, the sheet 1B has a window portion 96 formed along the cutting line 95. The release layer 82 is exposed through the window portion 96. After a portion of the label body 9 has been separated, the sheet 1B is used by wrapping it around the object to be attached 100, for example, as shown on the right side of Figure 3. When attaching the sheet 1B to the object to be attached 100, the sheet 1B is folded so that different portions of the adhesive layer 3 face each other, and the adhesive layers 3 that are positioned facing each other are firmly bonded together. The separated label body 9, the label piece 98, is then bonded to an object other than the object to be attached 100, for example. For example, the thermal layer 93 of the sheet 1B wrapped around the object to be attached 100 and the thermal layer 93 of the label piece 98 may have marks printed on them to identify each other.

[0064] As shown on the left side of Figure 3, in a roll on which sheet 1B is wound, the adhesive layer 3 comes into contact with the surface 930 (Figure 4) of the heat-sensitive layer 93. When the roll is stored under specific conditions, the adhesive layer 3 and the heat-sensitive layer 93 may unintentionally adhere to each other. In the sheet 1B of Embodiment 2, as with sheet 1A of Embodiment 1, multiple fine particles 5 are dispersed in the self-adhesive adhesive 4 to form multiple protrusions 6, making it easy to pull out the sheet 1B from the roll even when the adhesive layer 3 is adhered to the heat-sensitive layer 93.

[0065] Although not shown in the diagram, an undercoat layer may be placed between the adhesive layer 91 and the second substrate layer 92. At least one of the layers, such as an undercoat layer, an anchor layer, and a printing layer, may be placed between the second substrate layer 92 and the thermal layer 93. A protective layer may be placed on the surface 930 of the thermal layer 93.

[0066] [Test Example 1] In Test Example 1, an adhesive layer was prepared in which multiple fine particles were dispersed in a self-adhesive adhesive, and the self-adhesion strength of the adhesive layer and the peeling force of the adhesive layer from a substrate other than the self-adhesive adhesive were investigated. In Test Example 1, a sample was prepared in which an adhesive layer was formed on one side of the release paper provided on the sheet of Embodiment 2.

[0067] <Sample> Multiple samples were prepared, each with an adhesive layer on the surface of a release liner. In all samples, the release liner used was S7 manufactured by OSP Labelstock Co., Ltd. As shown in Figure 4, the release liner comprises a first base layer and a release layer. The adhesive layer is provided on the first surface of the first base layer. In all samples, the self-adhesive adhesive that forms the base of the adhesive layer was Saibinol Pressure Adhesive E (trade name) manufactured by Saiden Chemical Co., Ltd. In all samples, the average thickness of the adhesive layer was in the range of 1 μm to 8 μm.

[0068] In sample No. 1, the adhesive layer consists solely of a self-adhesive adhesive. Sample No. 1 does not contain any fine particles in the adhesive layer. Samples No. 2 to No. 23 contain multiple fine particles in the adhesive layer. The material, average particle size, and content ratio of the multiple fine particles contained in samples No. 2 to No. 23 are shown in Table 1. The fine particles in samples No. 2 to No. 11 use acrylic copolymer manufactured by Saiden Chemical Co., Ltd. The fine particles in samples No. 12 to No. 17 use methyl methacrylate / ethylene glycol dimethacrylate copolymer manufactured by Sekisui Chemical Co., Ltd. The fine particles in samples No. 18 to No. 22 use n-butyl methacrylate / ethylene glycol dimethacrylate copolymer manufactured by Sekisui Chemical Co., Ltd. The fine particles in sample No. 23 use crosslinked acrylic copolymer manufactured by Sekisui Chemical Co., Ltd. The average particle size of the multiple fine particles is the particle size that takes the mode when the mass-based particle size distribution is measured. The proportion of multiple fine particles is expressed as the proportion per 100 parts by weight of the self-adhesive adhesive.

[0069] <Surface condition of the adhesive layer> The surface of the adhesive layer of each sample was observed using a scanning electron microscope (SEM). The SEM magnification was 4500x. Figure 5 shows the surface of the adhesive layer of sample No. 1. Figure 6 shows the surface of the adhesive layer of sample No. 3. Figure 7 shows the surface of the adhesive layer of sample No. 8. In each figure, the gray areas represent relatively flat parts of the adhesive layer surface, and the whitish areas represent protrusions. In sample No. 1, as shown in Figure 5, the surface of the adhesive layer is almost entirely flat. In sample No. 1, it is thought that no protrusions were formed on the surface of the adhesive layer because the adhesive layer did not contain fine particles. In sample No. 3, as shown in Figure 6, multiple protrusions are dispersed on the surface of the adhesive layer. In sample No. 3, it is thought that multiple protrusions were formed by the multiple fine particles contained in the adhesive layer. In sample No. 8, as shown in Figure 7, multiple protrusions are dispersed on the surface of the adhesive layer. The size of the protrusions in sample No. 8 is larger than the size of the protrusions in sample No. 3. In sample No. 8, a relatively large protrusion was formed because it contained multiple fine particles with a larger average particle size than sample No. 3. Although not shown in the figures, samples No. 2, No. 4 through No. 7, and No. 9 through No. 23 also contained multiple fine particles in the adhesive layer, resulting in multiple protrusions formed by these fine particles being dispersed on the surface of the adhesive layer.

[0070] <Condition of protrusions formed on the surface of the adhesive layer> The cross-section of the adhesive layer of each sample was observed using a scanning electron microscope (SEM). The SEM magnification was 8000x. In this SEM image, the distance from the reference line L, using the midpoints α and β shown in Figure 2, to the most protruding point was measured and defined as the protrusion length of the protrusion. Figure 8 shows the cross-section of the adhesive layer of sample No. 8. In sample No. 8, as shown in Figure 8, a protrusion was formed on the surface of the adhesive layer by fine particles. The protrusion length of this protrusion was 3.1 μm. Although not shown, samples No. 2 to No. 7 and samples No. 9 to No. 23 also had protrusions formed on the surface of the adhesive layer by fine particles, and the protrusion lengths of these protrusions were in the range of 0.1 μm to 10.0 μm. For example, the protrusion length of sample No. 3 was 0.2 μm. The protrusion length of sample No. 10 was 4.1 μm. The protrusion length of sample No. 15 was 2.2 μm. The protrusion length of sample No. 17 was 4.0 μm. The protruding length of the projection in sample No. 23 was 6.6 μm.

[0071] In all of samples No. 2 through No. 23, almost all of the microparticles were not exposed from the self-adhesive adhesive; in other words, they were covered by the self-adhesive adhesive. However, in Figure 8, when the cross-section of the adhesive layer was taken, the self-adhesive adhesive covering the protrusions peeled off, making it appear as if some of the microparticles were exposed from the self-adhesive adhesive.

[0072] <Self-adhesion strength of the adhesive layer> The self-adhesion strength of the adhesive layers of each sample was investigated. The self-adhesion strength was measured according to JIS Z 0237:2022. Specifically, two test pieces measuring 25 mm in width and 150 mm in length were taken from each sample. The first test piece was attached to a stainless steel test plate with the adhesive layer facing upwards, and the adhesive layer of the second test piece was aligned with the adhesive layer of the first test piece and pressed together with a 1 kg roller. Within one minute after pressing, the second test piece was peeled off from the first test piece at a 180° angle. After the start of measurement, the measurement value for the first 25 mm length was ignored, and the average value of the adhesive strength measurement value over the 50 mm length peeled off from the first test piece was calculated. The stainless steel test plate is a steel plate made of SUS304 as specified in JIS G 4305:2021, and its surface has a BA (Bright Anneal) finish. The surface roughness of this steel plate is 50 ± 25 nm in arithmetic mean roughness Ra as specified in JIS B 0601:2013. The results are shown in Table 1. Table 1 shows the results for a test specimen with a width of 25 mm, converted to values ​​equivalent to a specimen with a width of 10 mm. The unit is Newtons per 10 millimeters (N / 10 mm).

[0073] The condition of the adhesive layer after peeling off each sample was visually examined. Specifically, we checked whether the adhesive layer of one test specimen (the first or second specimen) had transferred to the adhesive layer of the other test specimen. The results were evaluated as A, B, or C. A indicates that most of the adhesive layer of one test specimen had transferred to the adhesive layer of the other test specimen. B indicates that less than half of the adhesive layer of one test specimen had transferred to the adhesive layer of the other test specimen. C indicates that the adhesive layers of the first and second test specimens separated at the interface. The results are shown in Table 1.

[0074] <Peel strength of adhesive layers from substrates other than self-adhesive adhesives> The peeling force of the adhesive layer from substrates other than self-adhesive adhesives was investigated for each sample. The substrate used was thermal paper VD manufactured by OSP Label Stock Co., Ltd. The peeling force was measured as follows: First, a test piece measuring 50 mm in width and 100 mm in length was taken from each sample, and the adhesive layer of this test piece was pressed against the substrate with a 1 kg roller. Within 1 minute after pressing, the test piece was clamped in the upper chuck, and the substrate was clamped in the lower chuck, and the test piece was peeled off the substrate by pulling them in the direction away from each other. After the start of measurement, the measurement value for the first 25 mm length was ignored, and the average value of the adhesive strength measurement value for the 50 mm length after it was peeled off the substrate was calculated. The results are shown in Table 2. The unit is millinewtons per 50 mm (mN / 50 mm). The peeling force of the adhesive layer from the substrate was measured in four patterns. In the first pattern, a sample was prepared with an adhesive layer on the surface of release paper, and the measurement was taken 30 minutes later. In the second pattern, the prepared samples were stored for 7 days at a temperature of 40°C and a humidity of 15%. In the third pattern, the prepared samples were stored for 7 days at a temperature of 60°C and a humidity of 15%. In the fourth pattern, the prepared samples were stored for 7 days at a temperature of 40°C and a humidity of 90%. The results are shown in Table 2.

[0075] [Table 1]

[0076] [Table 2]

[0077] As shown in Table 1, when a self-adhesive adhesive contains multiple microparticles, the self-adhesion strength decreases as the proportion of microparticles increases. Looking at samples No. 2 to No. 11, for microparticles made of acrylic copolymer, a self-adhesion strength of 1.5 N / 10 mm or more is satisfied when the proportion of microparticles is 12 parts by weight or less. A self-adhesion strength of 1.5 N / 10 mm or more indicates that the adhesive layers are strongly bonded, to the point that when the bonded layers are separated, a large portion of one adhesive layer transfers to the other. Looking at samples No. 12 to No. 17, for microparticles made of methyl methacrylate / ethylene glycol dimethacrylate copolymer, a self-adhesion strength of 1.5 N / 10 mm or more is satisfied when the proportion of microparticles is 29 parts by weight or less. Methyl methacrylate / ethylene glycol dimethacrylate copolymer has a higher specific gravity than acrylic copolymer. Therefore, it is considered that microparticles made of methyl methacrylate / ethylene glycol dimethacrylate copolymer are less likely to form protrusions compared to microparticles made of acrylic copolymer, and thus require a higher proportion of microparticles. Looking at samples No. 18 to No. 22, for fine particles made of n-butyl methacrylate / ethylene glycol dimethacrylate copolymer, the self-adhesion force is 1.5 N / 10 mm or more if the content of fine particles is 18 parts by weight or less. Although n-butyl methacrylate / ethylene glycol dimethacrylate copolymer has a higher specific gravity than acrylic copolymer, it is lighter than methyl methacrylate / ethylene glycol dimethacrylate copolymer. Therefore, fine particles made of n-butyl methacrylate / ethylene glycol dimethacrylate copolymer are less likely to form protrusions compared to fine particles made of acrylic copolymer, and thus require a higher concentration of fine particles. Furthermore, fine particles made of n-butyl methacrylate / ethylene glycol dimethacrylate copolymer are more likely to form protrusions compared to fine particles made of methyl methacrylate / ethylene glycol dimethacrylate copolymer, allowing for a lower concentration of fine particles. In sample No. 23, where the fine particles are made of cross-linked acrylic copolymer, the average particle size of the fine particles was 20.0 μm, but the self-adhesion force was high at 3.0 N / 10 mm or more.

[0078] As shown in Table 2, when a self-adhesive adhesive contains multiple microparticles, the adhesive strength decreases as the proportion of microparticles increases. In all of the following scenarios—preparing a sample with an adhesive layer on the surface of release paper, storing the sample at 40°C and 15% humidity for 7 days, storing the sample at 60°C and 15% humidity for 7 days, and storing the sample at 40°C and 90% humidity for 7 days—the presence of multiple microparticles in the self-adhesive adhesive reduces the peeling strength compared to when no microparticles are present. For example, when microparticles made of an acrylic copolymer are included, if the proportion is 6 parts by weight or more, the peeling strength decreases to less than half compared to when no microparticles are present. In particular, when the prepared sample is stored for 7 days at a temperature of 40°C and a humidity of 15%, when the prepared sample is stored for 7 days at a temperature of 60°C and a humidity of 15%, and when the prepared sample is stored for 7 days at a temperature of 40°C and a humidity of 90%, if the sample contains fine particles made of acrylic copolymer, and the content is 6 parts by weight or more, the peeling force decreases to 1 / 3 or less compared to when the sample does not contain fine particles.

[0079] As shown in Sample No. 1, the peeling force increases with longer storage time. However, as shown in Samples No. 2 to No. 23, when fine particles are included in a predetermined proportion, the adhesive layer can be easily peeled off even if it adheres to a substrate other than a self-adhesive adhesive, even if the sheet has been stored for more than 7 days before use.

[0080] As shown in Tables 1 and 2, by including multiple fine particles in a self-adhesive adhesive in an amount of 5 to 29 parts by weight, it is possible to reduce the peeling force while maintaining the self-adhesive strength. In particular, if the fine particles are made of acrylic copolymer, the peeling force tends to decrease even at a relatively small content. If the average particle size of the fine particles made of acrylic copolymer is relatively large, the peeling force tends to decrease even more easily.

[0081] [Test Example 2] In Test Example 2, the substrate was changed for samples No. 1 to No. 11 from Test Example 1, and the peeling force of the adhesive layer from the substrate was investigated. The substrate used was thermal paper V9 manufactured by OSP Label Stock Co., Ltd. Thermal paper V9 has more than three times the smoothness of thermal paper VD. The method for measuring the peeling force was the same as the method described in Test Example 1. The results are shown in Table 3.

[0082] [Table 3]

[0083] As shown in Table 3, when a self-adhesive adhesive contains multiple fine particles, the adhesive strength decreases as the proportion of fine particles increases, regardless of the type of substrate. In all of the following scenarios—preparing a sample with an adhesive layer on the surface of release paper, storing the sample at 40°C and 15% humidity for 7 days, storing the sample at 60°C and 15% humidity for 7 days, and storing the sample at 40°C and 90% humidity for 7 days—the presence of multiple fine particles in the self-adhesive adhesive reduces the peeling strength compared to the case without fine particles. If the proportion of fine particles is 6 parts by weight or more, the peeling strength decreases to less than half compared to the case without fine particles.

[0084] [Test Example 3] In Test Example 3, the static and dynamic friction coefficients with respect to the adherend were investigated for samples No. 1 to No. 11 from Test Example 1. A stainless steel plate was used as the adherend. The stainless steel plate was made of SUS304 as specified in JIS G 4305:2021, and its surface was BA finished. The surface roughness of this steel plate was 50 ± 25 nm in arithmetic mean roughness Ra as specified in JIS B 0601:2013. The static and dynamic friction coefficients were measured according to JIS P 8147:2010. Specifically, a test piece measuring 120 mm in width and 250 mm in length was taken from each sample and placed on a horizontal plate. The stainless steel plate was placed on the test piece, and a weight was placed on top of the stainless steel plate. The weight was fixed to the upper surface of the stainless steel plate. The weight was slid using a tensile testing machine at a tensile speed of 10 mm / min. The load of the weight was 0.70 N. A commercially available friction measuring device was used to measure the frictional force when a weight was moved 50 mm. The peak observed at the moment the weight began to move was defined as the static friction force, and the frictional force observed while the weight continued to move was defined as the kinetic friction force. The static friction coefficient was calculated from the measured static friction force, and the kinetic friction coefficient was calculated from the measured kinetic friction force. The results are shown in Table 4.

[0085] [Table 4]

[0086] As shown in Table 4, the presence of multiple microparticles in a self-adhesive adhesive reduces the static and dynamic friction coefficients. When multiple microparticles are present in a self-adhesive adhesive, the higher the proportion of microparticles, the greater the reduction in static and dynamic friction coefficients. It is thought that multiple protrusions are formed on the adhesive layer by the multiple microparticles, and these protrusions reduce the static and dynamic friction coefficients. When the static and dynamic friction coefficients of the adhesive layer surface are low, for example, in a roll body where a sheet is wound into a roll, it is thought that the sheet can be easily pulled out from the roll body even when the adhesive layer is in contact with the surface of the sheet opposite to the adhesive layer. Furthermore, when the static and dynamic friction coefficients of the adhesive layer surface are low, it is thought that conveying defects such as sheet deflection due to gripping can be reduced on conveying rolls used in printers or manufacturing processes.

[0087] [Test Example 4] In Test Example 4, the probe tack to the adherend was investigated for samples No. 1 to No. 11 from Test Example 1. A stainless steel rod was used as the adherend. The diameter of the end face of the stainless steel rod was 5 mm. Probe tack was measured according to ASTM D 2979:2016. Specifically, a test piece 20 mm wide and 20 mm long was taken from each sample. The end face of the stainless steel rod was brought into contact with the adhesive layer of the test piece with a load of 200 g for 1 second, and then the stainless steel rod was peeled perpendicularly from the adhesive layer at a speed of 1 cm / second. The maximum load during peeling was measured. This probe tack test was performed five times, and the average value was taken as the probe tack value. The unit is Newtons per square centimeter (N / cm). 2 The results are shown in Table 5.

[0088] [Table 5]

[0089] As shown in Table 5, the presence of multiple microparticles in a self-adhesive adhesive reduces probe tack. It is thought that the multiple microparticles form multiple protrusions in the adhesive layer, and these protrusions reduce probe tack. When probe tack is low, even if the sheet adheres to the substrate, the adhesive layer can be easily peeled off the substrate. [Explanation of Symbols]

[0090] Sheets 1A and 1B 2. First substrate layer 21 first page, 22 second page 3 Adhesive layer 31 first page, 32 second page 4 Self-adhesive adhesive 5 Fine particles 6, 6A, 6B, 6C: Protrusion, 6H: Projection length L reference line, D1, D2 distance, α, β intermediate point 7 heat sensitive layer, 70 surface 8. Release paper 81 First substrate layer, 811 First surface, 812 Second surface, 82 Release layer 9 Label type 91 Adhesive layer, 92 Second substrate layer 93 heat sensitive layer, 930 surface 95 Cutting line, 96 Window section, 98 Label piece 100 Installation Targets

Claims

1. The first substrate layer, The first substrate layer comprises an adhesive layer disposed on the first surface of the first substrate layer, The aforementioned adhesive layer is Self-adhesive adhesive, The self-adhesive adhesive comprises a plurality of fine particles dispersed in the self-adhesive adhesive, The surface of the adhesive layer includes a plurality of protrusions formed by the plurality of fine particles, Seat.

2. The sheet according to claim 1, further comprising a heat-sensitive layer disposed on the second surface of the first substrate layer.

3. A release layer disposed on the second surface of the first substrate layer, The system further comprises a label body disposed on the aforementioned release layer, The label body comprises an adhesive layer, a second substrate layer, and a heat-sensitive layer in this order. The sheet according to claim 1, wherein the release layer and the adhesive layer are in contact.

4. The sheet according to claim 3, wherein the label body is provided with a cut line for separating a portion of the label body from the release layer.

5. The sheet according to claim 1 or claim 2, wherein the content ratio of the plurality of fine particles to 100 parts by weight of the self-adhesive adhesive is 4 parts by weight or more and 33 parts by weight or less.

6. The sheet according to claim 1 or claim 2, wherein the average particle size of the plurality of fine particles is greater than the average thickness of the adhesive layer.

7. The sheet according to claim 1 or claim 2, wherein the protruding length of the projection is 0.1 μm or more and 10.0 μm or less.

8. The sheet according to claim 1 or claim 2, wherein each of the plurality of fine particles is covered with the self-adhesive adhesive.

9. The sheet according to claim 1 or claim 2, wherein each of the plurality of fine particles is made of resin.

10. The sheet according to claim 9, wherein the resin is an acrylic copolymer.

11. The sheet according to claim 1 or claim 2, wherein the average particle size of the plurality of fine particles is 1 μm or more and 20 μm or less.

12. The sheet according to claim 1 or claim 2, wherein the average thickness of the adhesive layer is 1 μm or more and 15 μm or less.

13. The sheet according to claim 1 or claim 2, wherein the self-adhesion strength of the adhesive layer is 1.5 N / 10 mm or more.

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