Re-peelable adhesive sheet

Abstract

To provide a re-peelable adhesive sheet which can be easily re-peeled off without an adhesive residue after being securely attached to an object for a certain period of time.SOLUTION: There is provided a re-peelable adhesive sheet 10 in which an adhesive area is formed on at least a part of one surface 11 of a base material sheet, wherein the adhesive area is formed by a plurality of dot-like adhesive parts 12,...,12 made of a hot-melt type adhesive, the surface of the adhesive parts has an arithmetic mean roughness Ra of 4.0 to 5.0 μm and an average spacing Sm of unevenness of 200 to 300 μm, the average diameter Da of the adhesive parts is 1.5 to 3 mm and the average shortest distance La between the adhesive parts is 1 to 3 mm.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a re-peelable adhesive sheet.

Background Art

[0002] A re-peelable adhesive sheet is known as an adhesive sheet that can be easily peeled from an object after being pasted on the object for a certain period of time. The re-peelable adhesive sheet is used, for example, for pasting on personal information written on a postcard so that the recipient can peel it off to read the personal information. Also, it is used for applications such as printing necessary information as a management label between manufacturing processes of a product or a logistics management label in the distribution process of a product and peeling off the label when the purpose of information transmission is no longer required. The re-peelable adhesive sheet is required to have good re-peelability, i.e., it adheres well to the object when pasted, while it can be easily peeled off without adhesive residue or breakage of the base material during re-peeling.

[0003] As a re-peelable adhesive sheet, an adhesive sheet in which an adhesive layer is formed on a base material using an adhesive coating liquid containing adhesive fine particles is known (see, for example, Patent Document 1). The adhesive layer thus formed has an uneven surface due to the inclusion of adhesive fine particles. Therefore, when the re-peelable adhesive sheet is pasted on an object, the contact area between the adhesive layer and the object decreases, and the re-peelability is improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since such a re-peelable adhesive sheet suppresses the adhesive force by blending adhesive fine particles, although it is excellent in re-peelability, its adhesiveness is insufficient. Therefore, although it can be used for applications where it is affixed for a short period of time, it is not suitable for applications such as logistics management labels that need to be securely affixed to an object for a certain period of time.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a re-peelable adhesive sheet that can be easily re-peeled after being securely affixed to an object for a certain period of time.

Means for Solving the Problems

[0007] The present invention has the following configuration. [1] A re-peelable adhesive sheet having an adhesive region formed on at least a part of one surface of a base sheet, The adhesive region is formed by providing a large number of dot-shaped adhesive portions made of a hot-melt adhesive, The surface of the adhesive portion has an arithmetic mean roughness Ra of 4.0 to 5.0 μm and an average spacing Sm of irregularities of 200 to 300 μm, The average diameter Da of the adhesive portions is 1.5 to 3 mm, and the average shortest distance La between the adhesive portions is 1 to 3 mm, a re-peelable adhesive sheet. [2] The hot-melt adhesive has a 180-degree peel strength (JIS Z 0237) of the following test piece having an adhesive layer made of the hot-melt adhesive with respect to the following test plate of 1.6 N / 25 mm or more, the re-peelable adhesive sheet according to [1]. Test plate: A test plate obtained by mirror-finishing a SUS304 steel plate defined in JIS G 4305. Test piece: A test piece having a thickness of 200 μm and an arithmetic mean roughness Ra of 0.25 μm, and having a 20-μm-thick adhesive layer made of the hot-melt adhesive formed on the entire surface of a polyethylene terephthalate base material. [3] The re-peelable adhesive sheet according to [1] or [2], having a release agent layer on the other surface of the base sheet. [4] The releasable pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the hot-melt pressure-sensitive adhesive is a rubber-based hot-melt pressure-sensitive adhesive.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a releasable pressure-sensitive adhesive sheet that can be reliably attached to an object for a certain period of time and then easily peeled off again.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail. [Releasable Pressure-Sensitive Adhesive Sheet] FIG. 1 is a longitudinal sectional view showing the layer structure of a releasable pressure-sensitive adhesive sheet as an example of the present invention, FIG. 2 is a plan view of the releasable pressure-sensitive adhesive sheet of FIG. 1 as viewed from the direction of the arrow indicated by A in FIG. 1, and FIG. 3 is an enlarged plan view showing a part of the plan view of FIG. 2 enlarged.

[0011] The releasable pressure-sensitive adhesive sheet 10 of this example has a rectangular base material sheet 11, a large number of dot-shaped adhesive portions 12,..., 12 regularly arranged on one surface 11a of the base material sheet 11, and a release agent layer 13 formed on the other surface 11b of the base material sheet 11. In the releasable pressure-sensitive adhesive sheet 10 of this example, as shown in FIG. 2, a large number of pressure-sensitive adhesive portions 12,..., 12 are dispersedly arranged in a regular pattern over the entire surface 11a of one surface of the base sheet 11. As a result, the entire surface 11a of one surface of the base sheet 11 becomes an adhesive region that adheres to an object. Each of the pressure-sensitive adhesive portions 12,..., 12 is formed by pattern coating of a hot-melt type pressure-sensitive adhesive by a letterpress printing method, as will be described in detail later.

[0012] As shown in FIG. 1, the releasable pressure-sensitive adhesive sheet 10 of this example has a release agent layer 13 on the surface opposite to the surface on which the pressure-sensitive adhesive portions 12,..., 12 are formed. Therefore, it can be commercialized in a form that does not require release paper, such as a laminated label in which a plurality of releasable pressure-sensitive adhesive sheets 10 are stacked so that the pressure-sensitive adhesive portions 12,..., 12 and the release agent layer 13 are in contact with each other, or a roll-type pressure-sensitive adhesive tape in which a tape-shaped releasable pressure-sensitive adhesive sheet 10 is wound.

[0013] In this example, as shown in FIGS. 2 and 3, the dot-shaped pressure-sensitive adhesive portions 12,..., 12 arranged on one surface 11a of the base sheet 11 are all perfect circles in plan view. Further, the pressure-sensitive adhesive portions 12,..., 12 are regularly arranged such that, with any one of the pressure-sensitive adhesive portions 12 as the center, six surrounding pressure-sensitive adhesive portions 12 adjacent to the pressure-sensitive adhesive portion 12 form a regular hexagon. Hereinafter, such an arrangement pattern of the pressure-sensitive adhesive portions is also referred to as a "regular hexagon type arrangement". In the case of the regular hexagon type arrangement, the angle α in FIG. 2 is 60°.

[0014] The surface of the pressure-sensitive adhesive portions 12,..., 12 has an arithmetic mean roughness Ra defined by JIS B 0601 (1994) of 4.0 to 5.0 μm and an average interval Sm of unevenness defined by JIS B 0601 (1994) of 200 to 300 μm. When the arithmetic mean roughness Ra and the average spacing Sm of unevenness of the surfaces of the adhesion portions 12, …, 12 are both within the above ranges, the surfaces of the adhesion portions 12, …, 12 become moderately rough. Therefore, the adhesive force exhibited by the hot-melt adhesive in the adhesive region formed by these adhesion portions 12, …, 12 is moderately suppressed, and the balance between adhesiveness and re-peelability becomes excellent. When such a re-peelable adhesive sheet 10 is attached to an object, it adheres firmly to the object for a certain period of time. On the other hand, at the time of re-peeling, it can be easily re-peeled without causing a large peeling resistance, breakage of the base sheet, adhesive residue, etc.

[0015] The arithmetic mean roughness Ra is preferably 4.2 to 4.9 μm, more preferably 4.5 to 4.9 μm. The average spacing Sm of unevenness is preferably 210 to 280 μm, more preferably 220 to 250 μm. If either the arithmetic mean roughness Ra or the average spacing Sm of unevenness of the surfaces of the adhesion portions 12, …, 12 is outside the above ranges, the re-peelability decreases, and when re-peeling, the base sheet may break or a large peeling resistance may occur even if it can be peeled off.

[0016] The average diameter Da of the adhesion portions 12, …, 12 is 1.5 to 3 mm, preferably 1.6 to 2.7 mm, more preferably 1.8 to 2.2 mm. The average shortest distance La between the adhesion portions 12, …, 12 is 1 to 3 mm, preferably 1.6 to 2.7 mm, more preferably 1.8 to 2.2 mm. When the average diameter Da and the average shortest distance La of the adhesion portions 12, …, 12 are within the above ranges, the balance between the adhesiveness and re-peelability of the adhesive region formed by these adhesion portions 12, …, 12 is excellent. Therefore, when the re-peelable adhesive sheet 10 is attached to an object, it adheres firmly to the object for a certain period of time. On the other hand, at the time of re-peeling, it can be easily re-peeled without causing a large peeling resistance, breakage of the base sheet, adhesive residue, etc.

[0017] In this specification, both the arithmetic mean roughness Ra and the average spacing Sm of unevenness are values measured in accordance with JIS B 0601 (1994). Specifically, arbitrarily select 10 adhesive parts from the adhesive area, and measure the arithmetic mean roughness Ra for each adhesive part. Further average the measured values to obtain the arithmetic mean roughness Ra in this specification. Similarly, arbitrarily select 10 adhesive parts, and measure the average interval Sm of unevenness for each adhesive part. Further average the measured values to obtain the average interval Sm of unevenness in this specification. For the measurement of the arithmetic mean roughness Ra, a high-precision shape measurement system "KS-1000" manufactured by Keyence Corporation was used, and a 50 mm square area was measured at intervals of a measurement pitch of 6.4 μm. For the measurement of the average interval Sm of unevenness, analysis software manufactured by Keyence Corporation was used to perform the calculation according to the defined calculation formula.

[0018] From the viewpoint of easily obtaining uniform adhesiveness and re-peelability over the entire adhesive area, among the values of the arithmetic mean roughness Ra measured for the 10 adhesive parts, the minimum value is preferably 4.0 μm or more, and the maximum value is preferably 5.0 μm or less. Among the values of the average interval Sm of unevenness measured for the 10 adhesive parts, the minimum value is preferably 200 μm or more, and the maximum value is preferably 300 μm or less.

[0019] In this specification, the average diameter Da is the average value of the measured values when arbitrarily selecting 10 adhesive parts from the adhesive area and measuring the diameter D (diameter in the case of a perfect circle) for each adhesive part. Note that the shape of the adhesive part may be other than a perfect circle. In that case, as the diameter of each adhesive part, the maximum length in the radial direction (for example, the major axis in the case of an ellipse and the longest diagonal length in the case of a polygon) is adopted. Also, the average shortest interval La is the average value of the measured values when arbitrarily selecting 10 adhesive parts from the adhesive area and measuring the shortest interval L with the other closest adhesive part for each adhesive part.

[0020] Over the entire adhesive area, since it is easy to obtain uniform adhesiveness and re-peelability, among the values of the diameter D measured for 30 adhesive parts, the minimum value is preferably 1.5 mm or more, and the maximum value is preferably 3.0 mm or less. Among the values of the shortest interval L measured for 10 adhesive parts, the minimum value is preferably 1.5 mm or more, and the maximum value is preferably 3.0 mm or less.

[0021] In addition, when the re-peelable adhesive sheet is a small label and the number of adhesive parts is less than 30, for all adhesive parts, the above-mentioned respective measurements are performed, and the average value is adopted. Also, when there are adhesive parts without a complete shape at the peripheral edge of the re-peelable adhesive sheet, those adhesive parts are not selected as the adhesive parts to be measured.

[0022] The thickness of each of the adhesive parts 12,…,12 is preferably 5 to 40 μm, more preferably 10 to 25 μm. If the thickness is within the above range, the balance between adhesiveness and re-peelability is excellent, and since the thickness is not larger than necessary, it is also excellent in terms of cost.

[0023] (Base material sheet) As the base material sheet 11, known base materials used for re-peelable adhesive sheets such as logistics management labels can be used. For example, paper base materials, resin films, metal foils, laminates obtained by appropriately combining these, etc. can be mentioned, and they can be appropriately used according to the application. Among them, the paper base material is a preferable base material sheet because when the article to be adhered is paper, it is highly likely to be recovered in the state of being adhered as waste paper. Hereinafter, the paper base material will be described in detail as a representative example.

[0024] Examples of the paper base material include those composed mainly of wood pulp and containing additives such as pigments and various auxiliaries as required. As the wood pulp, either hardwood (L wood) or softwood (N wood) can be used, and various chemical pulps, semi-chemical pulps, mechanical pulps, recycled pulps, etc. may also be used. Examples of chemical pulp include kraft pulp (KP), sulfite pulp (SP), and soda pulp (AP). Examples of semi-chemical pulp include semi-chemical pulp (SCP) and chemigroundwood pulp (CGP). Examples of mechanical pulp include groundwood pulp (GP), thermomechanical pulp (TMP), bleached chemithermomechanical pulp (BCTMP), and refiner groundwood pulp (RGP). Examples of recycled pulp include deinked pulp (DIP) made from waste paper. Moreover, non-wood pulp made from materials such as kozo, mitsumata, hemp, and kenaf may be used.

[0025] When using a paper base material with high whiteness, pulp bleached by combining various bleaching methods using chlorine, chlorine dioxide, oxygen, ozone, hydrogen peroxide, hypochlorous acid, etc. can be used. Among them, pulp obtained by elemental chlorine-free bleaching (ECF) or totally chlorine-free bleaching (TCF) produced in a process without using chlorine is preferably used because it is less likely to cause yellowing. The pulp forming the paper base material may be one type or two or more types.

[0026] Based on the Canadian standard freeness (drainage degree; CSF) defined in JIS P 8121 for the pulp used in the paper base material, the freeness after disintegration is preferably 80 to 650 mL, more preferably 200 to 600 mL. If the freeness is below the upper limit value, the surface of the paper base material is likely to be smooth, and the paper strength of the paper base material can be easily obtained sufficiently. If the freeness is above the lower limit value, good papermaking suitability such as good drainage property and sufficient papermaking speed can be obtained. Also, when printing patterns, characters, etc. on the paper base material, the printing is likely to be clear and excellent in printability. Further, when a layer where writing, stamping, etc. can be performed is provided as the release agent layer 13, good writing property and stamping property can be easily obtained.

[0027] A pigment may be added to the paper base material. By adding a pigment to the paper base material, writing property, stamping property, printability, etc. can be imparted to the surface of the paper base material. Also, opacity can be imparted to the paper base material. Examples of the pigment include light calcium carbonate, calcined kaolin, white carbon, talc, titanium oxide, etc. Among them, talc, light calcium carbonate, and white carbon are preferred, and talc and light calcium carbonate are particularly preferred because they are excellent in papermaking suitability (wire abrasion suitability) and tend to stay during papermaking. When the pigment is blended into the paper base material, the content rate (ash content) of the pigment in the paper base material is preferably 0.1 to 30% by mass, more preferably 10 to 20% by mass. If the content rate of the pigment is at least the lower limit value of the above range, the above-described printability, writability, and stamping property will be good. If the content rate of the pigment is at most the upper limit value of the above range, sufficient paper strength can be easily obtained.

[0028] An auxiliary agent may be blended into the paper base material. Examples of the auxiliary agent include internal sizing agents (such as higher fatty acids, alkyl ketene dimers, etc.), fixing agents (such as sulfuric acid bands, cationic polyelectrolytes, etc.), paper strength enhancers (such as starches, polyacrylamides, polyvinyl alcohols, etc.), cationizing agents, yield improvers, dyes, fluorescent brighteners, fungicides, etc.

[0029] The paper base material can be obtained by papermaking using a known papermaking machine such as a Fourdrinier papermaking machine, a cylinder papermaking machine, a Yankee papermaking machine, a twin-wire former, an inclined wire former, a dryer (such as a Yankee dryer, a multi-cylinder dryer, etc.). The paper base material may be subjected to a known treatment such as calendering.

[0030] The paper base material may be size-treated by a size press or a gate roll for the purpose of adjusting surface strength, sizing property, etc. Examples of the sizing liquid used for sizing treatment include treatment liquids prepared by blending starches, polyvinyl alcohols, polyacrylamides, surface sizing agents, cation resins, etc. in a solvent. Examples of the surface sizing agent include styrene maleic acid copolymer, olefin copolymer, alkyl ketene dimer compound, alkenyl succinic anhydride compound, styrene-acrylic copolymer, higher fatty acid compound, petroleum resin sizing agent, rosin sizing agent, etc.

[0031] When sizing treatment is carried out, the coating amount of the sizing liquid is preferably 0.3 to 5.0 g / m in terms of dry mass 2 and more preferably 0.5 to 3.0 g / m. 2 If the coating amount is equal to or more than the lower limit value of the above range, the effect of sizing treatment can be easily obtained. Also, if the coating amount exceeds the upper limit value, the effect of sizing treatment levels off. Therefore, if the coating amount is equal to or less than the upper limit value, it is advantageous in terms of cost. When sizing treatment is carried out on both sides, the coating amount of the sizing liquid is preferably within the above range in total for both sides.

[0032] The basis weight of the paper base material is preferably 40 to 210 g / m 2 and more preferably 60 to 120 g / m. 2 If the basis weight is equal to or more than the lower limit value of the above range, sufficient paper strength can be easily obtained. If the basis weight is equal to or less than the upper limit value of the above range, it is easy to reduce the paper thickness. The density of the paper base material is preferably 0.55 to 1.00 g / m 3 If the density is equal to or more than the lower limit value of the above range, sufficient paper strength can be easily obtained. If the density is equal to or less than the upper limit value of the above range, the above-mentioned printability, writing property, and stamping property will be good.

[0033] The paper base material is preferably uncoated paper or single-sided coated paper provided with a coating layer on one side. The coating layer can be provided, for example, by a blade coater, knife coater, bar coater, air knife coater, die coater, slot die coater, gravure coater, etc.

[0034] (Release agent layer) As the release agent for forming the release agent layer 13, a silicone-based release agent is preferred. Examples of silicone-based release agents include thermosetting release agents (such as addition-curing silicone-based release agents and condensation-curing silicone-based release agents), electron beam-curing silicone-based release agents, and ultraviolet-curing silicone-based release agents (such as radical-curing silicone-based release agents, cationic-curing silicone-based release agents, and mercapto-curing silicone-based release agents). Among them, from the viewpoints of fast curing speed, difficulty in penetrating into the base material sheet 11, and thus lighter peeling, an electron beam-curing silicone-based release agent or an ultraviolet-curing silicone-based release agent is preferred. Also, from the viewpoint of less equipment investment, an ultraviolet-curing silicone-based release agent is more preferred, and a cationic-curing silicone-based release agent using an onium salt-based photoinitiator or the like is particularly preferred. If necessary, various auxiliary agents such as other ultraviolet-curing resins, electron beam-curing resins, photoinitiators, crosslinking agents, dyes, pigments, wetting agents, defoaming agents, dispersants, antistatic agents, leveling agents, and lubricants may be blended into the release agent.

[0035] The dry mass of the release agent layer 13 is preferably 0.2 to 2.0 g / m 2 and more preferably 0.5 to 1.5 g / m 2 If the dry mass of the release agent layer 13 is at least the lower limit value of the above range, peeling becomes lighter, and if the dry mass of the release agent layer 13 is at most the upper limit value of the above range, the above-described printability, writability, and stamping properties become good.

[0036] From the point that peeling becomes lighter, the smoothness of the surface of the release agent layer 13 is preferably 30 seconds or more, and more preferably 50 seconds or more. Also, from the viewpoints of the above-described printability, writability, and stamping properties, the smoothness of the surface of the release agent layer 13 is preferably 200 seconds or less, and more preferably 150 seconds or less. The smoothness is a value defined by the "Ono-type smoothness based on JAPAN TAPPI Paper Pulp Test Method No. 5-2".

[0037] (Adhesive part) Examples of the hot-melt type adhesive that forms dot-shaped adhesive portions 12, …, 12 include those using a thermoplastic polymer such as ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, styrene copolymer, and acrylic copolymer as an adhesive component. Among them, a hot-melt type adhesive using a styrene copolymer as an adhesive component is preferable in terms of adhesion stability, bleed resistance suitability, and cost.

[0038] Examples of the styrene copolymer include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and styrene-ethylene-propylene-styrene block copolymer (SEPS). A hot-melt type adhesive using a styrene copolymer as an adhesive component is preferable because it is easy to adjust the adhesion of a test piece having an adhesive layer made of the hot-melt type adhesive to a SUS plate within the above range, and the balance between the adhesiveness and re-peelability of the formed adhesive region is more excellent. In particular, SIS is particularly preferable.

[0039] The styrene copolymer preferably contains at least a styrene copolymer (I) having a weight average molecular weight (Mw) of 1,000 or more and less than 100,000 and a styrene copolymer (II) having a weight average molecular weight (Mw) of 100,000 or more and 10,000,000 or less. More preferably, it is a pressure-sensitive adhesive containing at least a styrene copolymer (I) having a weight average molecular weight (Mw) of 1,000 or more and less than 100,000 and a dispersity (Mw / Mn) of 1.0 to 1.2, and a styrene copolymer (II) having a weight average molecular weight (Mw) of 100,000 or more and 10,000,000 or less and a dispersity (Mw / Mn) of 1.0 to 1.2. The weight average molecular weight (Mw) and the dispersity (Mw / Mn) are measured by gel chromatography.

[0040] The hot-melt type adhesive may contain a tackifier, a softening agent, a wax, an antioxidant, etc. The tackifier improves the adhesiveness of the adhesive part. The softening agent adjusts the viscosity of the hot-melt type adhesive to an appropriate range described later. The wax reduces the instantaneous adhesiveness of the adhesive part and enhances the peelability when it is necessary to peel off the object immediately after sticking, etc.

[0041] Examples of the tackifier include aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, copolymer (C5 / C9) petroleum resins, dicyclopentadiene (DCPD) petroleum resins, coumarone-indene resins, acrylic resins, styrene resins, rosin, rosin ester resins, terpene resins, aromatic-modified terpene resins, terpene phenol resins, and hydrogenated resins thereof. Among them, it is easy to adjust the adhesive force of the test piece formed with an adhesive layer made of a hot-melt type adhesive to the range described later, and by forming an adhesive part having a surface with an arithmetic mean roughness Ra and an average interval Sm of unevenness, it is easy to obtain an adhesive region with a better balance between adhesiveness and re-peelability. From such points, rosin ester resins are preferred.

[0042] Examples of the softening agent include various plasticizers, polybutene, liquid tackifier resins, polyisobutylene low polymers, polyvinyl isobutyl ether low polymers, lanolin, block copolymer rubbers, process oils, naphthenic oils, paraffinic oils, vulcanized oils, etc. From the point of view of easily adjusting the viscosity of the hot-melt type adhesive to an appropriate range described later, paraffinic oils are preferred.

[0043] Examples of the wax preferably include plant waxes, animal waxes, mineral waxes, petroleum waxes, and processed / modified waxes thereof in addition to synthetic waxes. As the plant wax, carnauba wax and wood wax are more preferred. As the animal wax, beeswax is more preferred. As the mineral wax, montan wax and ozokerite are more preferred. As the petroleum wax, paraffin wax and microcrystalline wax are preferred. As the synthetic wax, Fischer-Tropsch wax, polyethylene wax, polypropylene wax, oil-based (esters, ketones, amides) synthetic wax, and hydrogenated wax are more preferred. As the processed / modified wax, the processed / modified wax of the more preferred waxes described above is preferred. From the viewpoint of reducing the instantaneous adhesiveness of the adhesive part and facilitating peeling off the object without damaging it immediately after sticking, for example, paraffin wax having a melting point of 42 to 73°C is preferred.

[0044] The polyolefin wax generally has a molecular weight of about 1,000 to 10,000, that is, it is generally known as a polyolefin wax. This polyolefin wax is usually obtained by a high-pressure polymerization method, a low-pressure polymerization method, or thermal decomposition of a high-molecular-weight polyolefin. Specific examples of the processed / modified wax include, for example, those obtained by oxidizing the above-mentioned wax and introducing polar groups such as hydroxyl groups, ester groups, carboxyl groups, aldehyde groups, and peroxide groups into the wax.

[0045] When using a tackifier, the content of the tackifier in the hot-melt adhesive is preferably 10 to 70 parts by mass, more preferably 30 to 60 parts by mass, and particularly preferably 30 to 50 parts by mass with respect to 100 parts by mass of the adhesive component (styrene-based copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, etc.). If the content of the tackifier is within the above range, it is easy to adjust the adhesive strength of the test piece formed of the hot-melt adhesive layer to the SUS plate to be within the range described later, and the formed adhesive region has a better balance between adhesiveness and re-peelability.

[0046] When using a softening agent, the content of the softening agent in the hot melt adhesive is preferably 1 to 50 parts by mass, more preferably 5 to 35 parts by mass, and particularly preferably 10 to 25 parts by mass with respect to 100 parts by mass of the adhesive component (styrene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, etc.). If the content of the softening agent is within the above range, it is easy to maintain the viscosity of the hot melt adhesive within an appropriate range described later, and it is easy to perform pattern coating by the relief printing method described later.

[0047] When using wax, the content of the wax in the hot melt adhesive is preferably 0.1 to 25 parts by mass, more preferably 0.5 to 15 parts by mass, and particularly preferably 1 to 10 parts by mass with respect to 100 parts by mass of the adhesive component (styrene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, etc.). If the content of the wax is within the above range, it is possible to lower the instantaneous adhesiveness of the adhesive parts 12,..., 12, and it is easy to peel off the object immediately after sticking without damaging it, and it also has excellent persistent adhesiveness.

[0048] The hot melt adhesive preferably has a viscosity at 140°C measured by a B-type viscometer of 10,000 to 50,000 mPa·s, more preferably 15,000 to 43,000 mPa·s, and still more preferably 18,000 to 38,000 mPa·s. When the viscosity of the hot melt adhesive is equal to or higher than the lower limit value of the above range, it is easy to form the adhesive parts 12,..., 12 having the surface of the arithmetic mean roughness Ra and the average interval Sm of unevenness described above, and the viscosity of the hot melt adhesive is not too low, and it is difficult for glue residue to occur during the re-peeling of the re-peelable adhesive sheet 10. On the other hand, when the viscosity of the hot melt adhesive is equal to or lower than the upper limit value of the above range, it is easy to form the adhesive parts 12,..., 12 having the surface of the arithmetic mean roughness Ra and the average interval Sm of unevenness described above, and the viscosity of the hot melt adhesive is not too high and has flexibility, so it has excellent adhesiveness to the object. Also, when the viscosity is within the above range, transfer defects are less likely to occur during pattern coating by the relief printing method described later.

[0049] From the perspective of the balance between adhesiveness and re-peelability, it is preferable that the adhesive force of a test piece having an adhesive layer made of a hot melt adhesive to a SUS plate is 1.6 N / 25 mm or more. When using a hot melt adhesive that can obtain such a relatively large adhesive force to the SUS plate, when forming the adhesive portions 12,..., 12 having the surface with the above-mentioned arithmetic mean roughness Ra and the average spacing Sm of unevenness, the adhesive force is appropriately suppressed, and an adhesive region excellent in the balance between adhesiveness and re-peelability can be formed. It is more preferable that the adhesive force to the SUS plate is 2.0 N / 25 mm or more. The preferable upper limit value of the adhesive force to the SUS plate is about 2.6 N / 25 mm.

[0050] In this specification, the "adhesive force to the SUS plate" is the 180-degree peel-off force (JIS Z 0237) of the following test piece having an adhesive layer made of a hot melt adhesive to the following test plate. Test plate: A test plate obtained by mirror-finishing a SUS304 steel plate specified in JIS G 4305. Test piece: A test piece formed with an adhesive layer having a thickness of 20 μm made of the above-mentioned hot melt adhesive on the entire surface of a paper substrate was sampled into 25 mm × 100 mm, the adhesive layer was bonded to the SUS plate surface, and one round trip was made with a 2 kg pressure roller.

[0051] [Method for manufacturing a re-peelable adhesive sheet] The re-peelable adhesive sheet 10 in the illustrated example can be manufactured, for example, by a method having the following steps (1) and (2). Step (1): A step of forming a release agent layer 13 on the other surface 11b of the base material sheet 11 to obtain a laminated sheet of the base material sheet 11 and the release agent layer 13. Step (2): A step of forming an adhesive region by providing a large number of dot-shaped adhesive portions 12,..., 12 on one surface 11a of the base material sheet 11 by pattern coating of a hot melt adhesive by the letterpress printing method. Note that either step (1) or step (2) may be performed first. Also, when manufacturing a re-peelable adhesive sheet having no release agent layer, it is not necessary to perform step (1).

[0052] (Step (1)) The method for forming the release agent layer 13 is not particularly limited. For example, methods of applying a release agent using a bar coater, a multi-stage roll coater, an air knife coater, a gravure coater, an offset gravure coater, etc. can be mentioned. When the release agent is curable, after application, a hot air dryer, an infrared dryer, an ultraviolet irradiation device, an electron beam irradiation device, etc. can be used to cure it to form the release agent layer 13. The coating amount of the release agent is preferably adjusted so that the dry mass of the release agent layer 13 is within the above-mentioned range. Before forming the release agent layer 13, if necessary, printing such as patterns and characters may be performed on the other surface 11b of the base sheet 11. The printing method is not particularly limited, and for example, it can be performed using a known ink such as an ultraviolet curable ink by a known method such as letterpress printing, offset printing, or flexographic printing.

[0053] (Step (2)) In step (2), a large number of dot-shaped adhesive portions 12,..., 12 are formed on one surface 11a of the base sheet 11 by pattern coating of a hot melt type adhesive by a letterpress printing method. Pattern coating has the merit that it can cope with small lot production compared to, for example, die coating, etc., and it is also easy to form an adhesive portion only on a part of the base sheet. Pattern coating by the letterpress printing method can be continuously performed by a coating device 20 including a plate cylinder 21 having a large number of convex portions 21a provided on the outer peripheral surface corresponding to the arrangement pattern of the adhesive portions 12,..., 12 and a pressure cylinder 22 provided at a position facing the plate cylinder 21, as schematically shown in FIG. 4, for example. The convex portions 21a of the plate cylinder 21 are made of, for example, a silicone resin or the like.

[0054] Specifically, a hot-melt type adhesive S is transferred and supplied from the adhesive supply unit 23 onto the convex portion 21a of the plate cylinder 21, and a laminated sheet 30 of the base material sheet 11 and the release agent layer 13 obtained in step (1) is supplied between the plate cylinder 21 and the impression cylinder 22. Thereby, while the laminated sheet 30 is sandwiched between the plate cylinder 21 and the impression cylinder 22, it is conveyed in the direction of arrow B in FIG. 4. The laminated sheet 30 is supplied such that one surface 11a of the base material sheet 11 is positioned on the side of the plate cylinder 21. Thereby, the hot-melt type adhesive S transferred from the adhesive supply unit 23 onto the convex portion 21a of the plate cylinder 21 is further transferred onto one surface 11a of the base material sheet 11, and the releasable pressure-sensitive adhesive sheet 10 of the illustrated example in which a large number of dot-shaped adhesive portions 12,..., 12 are formed can be manufactured. The thickness of the adhesive portions 12,..., 12 to be formed can be controlled by adjusting the distance between the plate cylinder 21 and the impression cylinder 22.

[0055] When pattern coating in step (2), the temperature of the sheet surface is preferably 40 to 90°C, more preferably 50 to 80°C. By performing the temperature of the sheet surface within the above range, the hot-melt type adhesive S can be transferred from the convex portion 21a of the plate cylinder 21 onto one surface 11a of the base material sheet 11 in a state where the viscosity of the hot-melt type adhesive S is high. As a result, the surface of the adhesive portions 12,..., 12 formed by the transfer becomes appropriately rough, and it is easy to obtain the arithmetic mean roughness Ra and the average spacing Sm of the unevenness described above. When the temperature of the sheet surface is less than the lower limit value of the above range, the hot-melt type adhesive S is not sufficiently melted, and transfer tends to be difficult. On the other hand, when the temperature of the sheet surface exceeds the upper limit value of the above range, the viscosity of the hot-melt type adhesive S when transferring the hot-melt type adhesive S from the convex portion 21a of the plate cylinder 21 onto one surface 11a of the base material sheet 11 becomes low. As a result, transfer may become difficult, or even if transfer is possible, the surface of the adhesive portions 12,..., 12 formed on one surface 11a of the base material sheet 11 becomes smooth, and it is difficult to obtain the arithmetic mean roughness Ra and the average spacing Sm of the unevenness described above. Further, when using an adhesive whose viscosity at 140°C measured by a B-type viscometer is within the above range as the hot-melt type adhesive S, it is easy to form the adhesive portions 12,..., 12 having the surfaces of the arithmetic mean roughness Ra and the average spacing Sm of the unevenness described above.

[0056] Note that the temperature of the sheet surface during pattern coating is the paper surface temperature of the plate cylinder during coating, which can be measured by an infrared surface thermometer.

[0057] In the re-peelable adhesive sheet described above, a plurality of dot-shaped adhesive portions made of a hot-melt adhesive are provided to form an adhesive region. The surface of the adhesive portion has an arithmetic mean roughness Ra of 4.0 to 5.0 μm and an average interval Sm between unevennesses of 200 to 300 μm. Therefore, the surface of the adhesive portion is moderately rough, and the adhesive force of the adhesive region exhibited by the hot-melt adhesive is moderately suppressed, and the balance between adhesiveness and re-peelability is excellent. Such a re-peelable adhesive sheet reliably adheres to an object over a certain period of time. On the other hand, at the time of re-peeling, it can be easily re-peeled without causing a large peeling resistance, breakage of the base sheet, adhesive residue, etc. Therefore, such a re-peelable adhesive sheet is, for example, used for the purpose of being pasted on personal information written on a postcard and the recipient peeling it off to read the personal information; a management label between the processes of manufacturing a product; a logistics management label in the distribution process of a product; etc. It is preferably used for applications that are required to adhere well to an object over a certain period of time and can be easily peeled off without adhesive residue or breakage of the base sheet when peeled off.

[0058] [Regarding Other Embodiments] In the releasable adhesive sheet 10 of the illustrated example, the arrangement pattern of a number of adhesive portions 12, …, 12 was a “regular hexagonal arrangement”. That is, with any one of the adhesive portions 12, …, 12 as the center, the six surrounding adhesive portions 12, …, 12 adjacent to the adhesive portion 12, …, 12 were regularly arranged so as to form a regular hexagon. However, the arrangement pattern of the adhesive portions is not limited to the regular hexagonal arrangement. For example, as shown in FIG. 5, with any one of the adhesive portions 12 as the center, the four surrounding adhesive portions 12, …, 12 adjacent to the adhesive portion 12 may be arranged in a “square arrangement” in a regular pattern such that they form a square. The “regular hexagonal arrangement” and the “square arrangement” are preferable because it is easy to obtain uniform adhesiveness and releasability over the entire adhesive area. Also, the number of adhesive portions may be arranged in other regular patterns or may be arranged irregularly (randomly).

[0059] In the releasable adhesive sheet 10 of the illustrated example, a number of adhesive portions 12, …, 12 are regularly and dispersedly arranged over the entire one surface 11a of the base sheet 11, whereby the entire one surface 11a of the base sheet 11 is an adhesive area. However, only a part of one surface of the base sheet may be an adhesive area. For example, as shown in FIG. 6, on one surface 11a of the base sheet 11, no adhesive portion is formed in the area (non-adhesive area) C2 including one of the four corners, and a number of adhesive portions 12, …, 12 are arranged in the portion excluding this area C2 to form an adhesive area C1. In this way, when a part of one surface 11a of the base sheet 11 is the non-adhesive area C2, since the non-adhesive area C2 does not adhere to the object, it serves as a curling margin during releasability. Such a releasable adhesive sheet is easy to release.

[0060] In the releasable adhesive sheet 10 of the illustrated example, each of the adhesive portions 12, …, 12 is a perfect circle, and therefore, it is easier to obtain uniform adhesive force and peeling force over the entire adhesive area. However, the shape of the adhesive portion is not limited to a perfect circle and may be an ellipse, a polygon, etc., as described above.

[0061] Furthermore, the releasable pressure-sensitive adhesive sheet 10 in the illustrated example has a release agent layer 13 on the other surface 11b side of the base material sheet. Therefore, it can be commercialized in a form that does not require release paper, such as a laminated label in which a plurality of releasable pressure-sensitive adhesive sheets 10 are stacked so that the adhesive portions 12,..., 12 are in contact with the release agent layer 13, or a roll-type adhesive tape in which a tape-shaped releasable pressure-sensitive adhesive sheet 10 is wound. However, it may also be in a form that does not include a release agent layer and instead has a known release paper that covers the adhesive portions 12,..., 12.

Example

[0062] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In the examples, "parts" and "%" indicate "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0063] [Example 1] (Manufacture of paper base material (base material sheet)) Hardwood bleached kraft pulp (LBKP) was beaten until it reached a freeness of 440 mL (CSF), and a pulp slurry with a concentration of 0.5% was prepared. To this pulp slurry, 2.0% of cationized starch, 0.4% of alkyl ketene dimer, 0.1% of anionic polyacrylamide resin, 0.7% of polyamide polyamine epichlorohydrin resin, and talc as a pigment were added based on the absolute dry mass of the pulp, and they were sufficiently stirred and dispersed. The addition amount of talc was adjusted to be 2% with respect to the resulting paper base material. Next, water was added to oxidized starch (trade name "Ace A", manufactured by Oji Cornstarch Co., Ltd.) and heated to dissolve it, and the concentration was adjusted to 5% to obtain a size press solution. After the pulp slurry was formed into a base paper using a paper-making machine, the base paper was sized on both sides with the size press solution using a size press attached to the paper-making machine to obtain a paper base material. The absorption amount of the size press solution into the paper base material was 50 mL / m in total for both sides. 2 It was. Finally, calendering treatment was performed using a machine calender at the end of the paper-making machine to obtain a paper base material with a basis weight of 100 g / m 2 , a density of 0.85 g / cm 3 , and a Stoke's sizing degree of 35 seconds.

[0064] (Manufacture of laminated sheet) On one surface of the obtained paper substrate, pictures and letter patterns were printed using amine-free UV ink (trade name: NVR) manufactured by TOKA Co., Ltd. Next, on the entire surface thereof, a release agent coating obtained by mixing 5 parts of an onium salt-based photoinitiator (trade name: Silicone Release CATA211, manufactured by Rhodia Co., Ltd.) with 100 parts of polyorganosiloxane (trade name: Silicone Release POLY201, manufactured by Rhodia Co., Ltd.) was applied using a flexographic printing machine, and ultraviolet irradiation was performed at an ultraviolet irradiation dose of 140 mJ / cm 2 under the condition of 2 to cure and form a release agent layer. The coating amount of the release agent coating used for forming the release agent layer was 1 g / m in terms of solid content mass (dry mass).

[0065] (Manufacture of hot melt adhesive) Next, 20 parts of SIS having a styrene component of 40%, an isoprene component of 60%, a weight average molecular weight (Mw) = 5 × 104, and a dispersity (Mw / Mn) = 1.04, 30 parts of SIS having a styrene component of 10%, an isoprene component of 90%, a weight average molecular weight (Mw) = 5 × 105, and a dispersity (Mw / Mn) = 1.06, 30 parts of rosin ester (Super Ester A-115 manufactured by Arakawa Chemical Co., Ltd.), 20 parts of paraffinic oil (Shellflex 371N manufactured by Shell Chemical Company, USA), 10 parts of hydrogenated castor oil amide wax (Disparon 4110 manufactured by Kusumoto Chemical Co., Ltd.), and 1 part of antioxidant (Sumilizer GM manufactured by Sumitomo Chemical Co., Ltd.) were blended and stirred and mixed under heating at 150°C to obtain a hot melt adhesive. The adhesive force to SUS plate measured by the method described above was 13 N / 25 mm.

[0066] (Pattern coating) Using the above hot-melt adhesive, a large number of dot-shaped adhesive portions with a thickness of about 20 μm each were formed on the entire surface of the side of the base sheet where the release agent layer was not formed. The formation of the adhesive portions was carried out by pattern coating using a convex printing method with an apparatus (manufactured by Santsuru Co., Ltd.) equipped with a plate cylinder 21 and a pressure cylinder 22 as shown in FIG. 4. The temperature of the pattern coating was set at 50°C. The thickness of the adhesive portions was measured using a THIKNESS METER B-1 manufactured by Toyo Seiki Co., Ltd. The arrangement pattern of the large number of dot-shaped adhesive portions was set as the "regular hexagonal arrangement" shown in FIGS. 2 and 3. Also, each adhesive portion was a perfect circle with a diameter of 2 mm, and the shortest distance between any adhesive portion and the other adhesive portion closest to it was set at 2 mm. That is, both the average diameter Da and the average shortest distance La were set at 2 mm. In this way, the re-peelable adhesive sheet of Example 1 was obtained. The obtained re-peelable adhesive sheet was cut into rectangles measuring 8 cm in length and 12 cm in width, and 50 labels made of the re-peelable adhesive sheet were obtained. Then, these 50 labels were stacked so that the adhesive portions were in contact with the release agent layer to form a laminated label.

[0067] For one label, the arithmetic mean roughness Ra and the average spacing Sm of the unevenness on the surface of the adhesive portion were measured. The results are shown in Table 1. The measurement was carried out in accordance with JIS B 0601 (1994) as described above, and Table 1 shows the average values of 10 arbitrarily selected adhesive portions. The measurement of the arithmetic mean roughness Ra and the average spacing Sm of the unevenness was carried out using the above-mentioned apparatus under the above-mentioned conditions respectively.

[0068] (Evaluation of re-peelability) Ten re-peelable adhesive sheets were peeled off one by one from the laminated label and attached to a cardboard made of K-liner (kraft liner). After leaving this in an environment of 23°C and 50% RH for one week, the re-peelability when the ten re-peelable adhesive sheets were peeled off from the cardboard by hand was evaluated in the following four levels. The results are shown in Table 1. Note that all 10 releasable adhesive sheets were still well adhered to the cardboard even after being left in an environment of 23°C and 50% RH for one week. ◎: Very good. For all 10 releasable adhesive sheets, they could be re-released without feeling a large resistance during peeling. ○: Good. For all 10 releasable adhesive sheets, a slight resistance was felt during peeling, but they could be re-released without problems. ×: Poor. For all 10 releasable adhesive sheets, a large resistance was felt during peeling, and re-release was difficult.

[0069] [Examples 2 - 3, Comparative Examples 1 - 3] Except for changing the diameter and the shortest interval of the adhesive parts as shown in Table 1, in the same manner as in Example 1, a releasable adhesive sheet with an "equilateral hexagonal pattern" of the adhesive part arrangement pattern was manufactured and evaluated in the same way. The results are shown in Table 1. Note that in the releasable adhesive sheets of each example, a large number of adhesive parts were all perfect circles with the same diameter, and the shortest intervals were also the same (constant).

[0070] [Comparative Example 4] In the same manner as in Example 1, a laminated sheet and a hot-melt type adhesive were manufactured. Then, with a hot-melt die coater, the hot-melt type adhesive was coated on the entire surface of the side of the laminated sheet where the release agent layer was not formed. The thickness was set to 20 μm. The obtained releasable adhesive sheet was evaluated in the same way as in Example 1. The results are shown in Table 1. Note that in Comparative Example 4, the arithmetic mean roughness Ra and the average interval of unevenness Sm were respectively the average values of three measurement values. The cut-off value was set to 0.08 mm, and the evaluation length was set to 15 mm.

[0071]

Table 1

[0072] As shown in Table 1, the releasable pressure-sensitive adhesive sheet of each example had an appropriate adhesive portion with an arithmetic mean roughness Ra and an average spacing Sm of unevenness, and thus had excellent releasability. On the other hand, in Comparative Examples 1 to 3 in which at least one of the arithmetic mean roughness Ra and the average spacing Sm of unevenness was not in a suitable range, and in Comparative Example 4 in which the adhesive portion was not dot-shaped, the releasability was poor in all cases.

Explanation of reference numerals

[0073] 10 Releasable pressure-sensitive adhesive sheet 11 Base material sheet 11a One surface of the base material sheet 12 Adhesive portion 13 Release agent layer

Claims

1. A re-peelable adhesive sheet having an adhesive area formed on at least a part of one surface of a base sheet, wherein the adhesive area is formed by providing a large number of dot-shaped adhesive portions made of a hot-melt adhesive, the surface of the adhesive portion has an arithmetic mean roughness Ra of 4.0 to 5.0 μm and an average interval Sm between irregularities of 200 to 300 μm, and the average diameter Da of the adhesive portions is 1.5 to 3 mm, and the average shortest interval La between the adhesive portions is 1 to 3 mm. The re-peelable adhesive sheet.

2. The re-peelable adhesive sheet according to claim 1, wherein the hot-melt adhesive has a 180-degree peel strength (JIS Z 0237) of the following test piece having an adhesive layer made of the hot-melt adhesive with respect to the following test plate of 1.6 N / 25 mm or more. Test plate: A test plate obtained by mirror-finishing a SUS304 steel plate defined in JIS G 4305. Test piece: A test piece having a thickness of 200 μm and an arithmetic mean roughness Ra of 0.25 μm, and having a 20-μm-thick adhesive layer made of the hot-melt adhesive formed on the entire surface of a polyethylene terephthalate base material.

3. The re-peelable adhesive sheet according to claim 1 or 2, having a release agent layer on the other surface of the base sheet.

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