label

Abstract

To provide a linerless label with high adhesion to resin substrates. [Solution] A label having a base material and a re-moistened adhesive layer, wherein the water contact angle of the re-moistened adhesive layer surface is 65° or more and less than 85°.

Description

Technical Field

[0001] The present invention relates to a label including a rewet adhesive layer.

Background Art

[0002] An adhesive label is a label having a base material and an adhesive layer, and the adhesive layer surface is attached to an adherend. In order to ensure the adhesiveness of the adhesive layer before attaching it to the adherend, usually, a release liner is laminated on the adhesive layer surface to protect the adhesive layer. When attaching the adhesive label to the adherend, after peeling off the release liner to expose the adhesive layer, it is attached to the adherend. However, in most cases, the peeled release liner is discarded, and a linerless label that does not use a release liner has been proposed from the viewpoints of effective utilization of resources and waste reduction.

[0003] For example, as disclosed in Patent Document 1, a linerless label in which a rewet paste layer (rewet adhesive layer) containing a polyvinyl alcohol-based adhesive is laminated on the surface of a paper base material has been proposed. When attaching this linerless label to an adherend, water is applied to the rewet paste layer to develop tackiness in the rewet paste layer, so that the label can be attached to the adherend.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, the linerless label is used as a delivery label or a sealing label, and mainly aims at paper adherends such as cardboard.

[0006] On the other hand, many of the substrates to which the labels are applied are made of resin, such as resin containers and resin packaging. Therefore, we focused on providing linerless labels that exhibit high adhesion to such resin substrates.

[0007] Therefore, the present invention aims to provide a linerless label with high adhesive strength to a resin substrate. [Means for solving the problem]

[0008] The present invention provides the following:

[0009] (1) A label having a base material and a re-moistened adhesive layer, wherein the water contact angle of the re-moistened adhesive layer surface is 65° or more and less than 85°.

[0010] (2) The label according to (1), wherein the re-wet adhesive layer contains polyvinyl alcohol with a saponification degree of 85 mol% or less.

[0011] (3) The label described in (2), wherein the degree of polymerization of the polyvinyl alcohol is 250 or more and 1000 or less.

[0012] (4) The label according to (2) or (3), wherein the polyvinyl alcohol content is 70% by mass or more relative to the solid content of the re-wetted adhesive layer.

[0013] (5) The label according to any one of (1) to (4), wherein the re-wet adhesive layer comprises a polymer containing vinyl acetate as a monomer component.

[0014] (6) The label according to (5), wherein the polymer content is 5% by mass or more and 30% by mass or less relative to the solid content of the re-wetted adhesive layer.

[0015] (7) A label according to any of (1) to (6), wherein the thickness of the re-wet adhesive layer is 6 μm or more and 15 μm or less. [Effects of the Invention]

[0016] According to the label of the present invention, the adhesive force to the resin adherend is high.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view of a label according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios.

[0019] In this specification, "X to Y" indicating a range means "X or more and Y or less". Also, unless otherwise specified, operations and physical properties are measured under the conditions of room temperature (20 to 25°C) / relative humidity 45 to 55%RH.

[0020] Hereinafter, the configuration of the adhesive label will be described with reference to FIG. 1.

[0021] FIG. 1 is a schematic cross-sectional view of a label 10 according to an embodiment. As shown in FIG. 1, the label 10 according to the embodiment of the present invention has, in order from above, a base material 11 and a rewet adhesive layer (hereinafter, also simply referred to as an adhesive layer) 12. The rewet adhesive layer 12 has a function of bonding to the adherend and exhibits tackiness when water (aqueous medium) is applied. Therefore, it does not have tackiness in a state where water is not applied. As a result, in the case of an adhesive layer having permanent adhesiveness, a release liner is required until use, but the rewet adhesive layer does not require a release liner (linerless). For this reason, the environmental load is small. Thus, the label of one aspect of the present invention does not include a release liner. Furthermore, the rewet adhesive layer does not require a release liner and is usually disposed on the outermost layer of the label.

[0022] The label of FIG. 1 is composed of a base material and an adhesive layer, but may also have other functional layers (for example, a primer layer, a surface protection layer, etc.) on the surface and between each layer. On the other hand, a form in which the rewet adhesive layer is disposed adjacent to the base material is also a preferred form.

[0023] In the label of the present invention, the rewet adhesive layer is exposed on the surface side (linerless). The water contact angle of the rewet adhesive layer surface of the present invention is 65° or more and less than 85°. When the water contact angle is less than 65° or 85° or more, when the adherend is paper, although the adhesive force may be ensured, the adhesive force to the resin adherend is significantly reduced (Comparative Examples 1 to 3 described later). When the water contact angle is less than 65°, it is considered that the wettability to the resin adherend is not sufficient, so that the adhesive force to the resin adherend is significantly reduced. Further, when the water contact angle is 85° or more, the solubility in water applied at the time of adhesion is reduced, and it is considered that the adhesive force is difficult to be developed. The water contact angle may be 68° or more, 70° or more, or 72° or more. The upper limit of the water contact angle may be 80° or less. The water contact angle may be 65° or more and less than 85°, 68° or more and 80° or less, 70° or more and 80° or less, 72° or more and 80° or less, or 75° or more and 80° or less. The method for measuring the water contact angle is, for example, by the method described in the examples.

[0024] The label according to the present invention is attached to the adherend by the adhesive layer after imparting tackiness to the adhesive layer by applying water to the adhesive layer. The water applied to the adhesive layer is not particularly limited, and for example, tap water, ion-exchanged water, etc. can be used, and liquids containing water can also be used.

[0025] The method for applying water to the adhesive layer is not particularly limited, and examples thereof include methods using spraying, a brush, a sponge, a sponge roller, etc. The amount of water applied to the adhesive layer is not particularly limited, and for example, it can be 0.3 g / m 2 or more and 0.6 g / m 2 or less.

[0026] The following describes the individual components that make up each label. Unless otherwise specified, operations and measurements of physical properties are performed under room temperature (20-25°C) / relative humidity of 45-55%RH. In the following description, the labels of the present invention may be simply referred to as "labels." The concept of "labels" includes films, sheets, tapes, etc.

[0027] <Base material> The substrate is not particularly limited and includes resin substrates; so-called synthetic paper made of resin; metal foils such as copper, aluminum, and stainless steel; composite sheet substrates made by laminating metal foil and plastic film; vapor-deposited substrates with aluminum, silica, etc.; nonwoven fabric substrates; or paper substrates. As resin substrates, for example, films made of at least one resin selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyvinyl chloride, polystyrene, polyurethane, polycarbonate, polyamide, polyimide, polyetherimide, poly(meth)acrylic acid ester, polybutene, polybutadiene, polymethylpentene, acrylic urethane, ethylene vinyl acetate copolymer, ethylene(meth)acrylic acid copolymer, ethylene(meth)acrylic acid ester copolymer, ABS resin, ionomer resin, and various thermoplastic elastomers, or single or multiple laminated films selected from these can be used.

[0028] The paper substrate is not particularly limited and includes, for example, fine paper, kraft paper, glassine paper, coated paper, art paper, cast coated paper, impregnated paper, foamed paper, synthetic paper, thermal paper, dust-free paper, parchment paper, rayon paper, recycled paper, etc. The paper substrate may also be a laminate formed by laminating two or more of these materials. When the label is a shipping label, the paper substrate is preferably thermal paper, kraft paper, fine paper, art paper, coated paper, or cast coated paper, and more preferably thermal paper. When the paper substrate is thermal paper, it has a thermal color-developing layer (not shown) on its surface (the side opposite the re-wet adhesive layer). This allows recording on the surface of the thermal paper using a thermal printer, etc. Examples of the thermal color-developing layer include one containing a leuco dye and a developer that reacts with the leuco dye. The heat-sensitive color-developing layer is suitably formed by, for example, applying a coating solution containing, in addition to the above-mentioned leuco dye and developer, a binder, wax, solvent, etc., to the surface of a paper substrate.

[0029] Since it can be used for invoice labels, shipping labels, etc., it is preferable that the base material be paper-based.

[0030] The thickness of the substrate is not particularly limited, but is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm, and even more preferably 30 μm to 120 μm. Such a thickness provides good handling during application.

[0031] Information or displays may be applied to the surface of the substrate (the side facing the re-wet adhesive layer) by printing or other means. Such information or displays may be various types of information or displays, such as combinations of letters, numbers, symbols, and figures (for example, a company logo). Specifically, for example, it may be information about the adherend. For example, if the adherend is a delivery item and the label is used as a delivery slip label, the information about the adherend may include the sender, recipient, the name or company name, address, telephone number of the delivery company, and the contents of the delivery item. This information may be displayed using letters, symbols, figures, or any combination thereof. It may also include displays using two-dimensional codes such as barcodes and QR codes (registered trademarks).

[0032] In one embodiment, the substrate may be a substrate that does not display information (i.e., does not have printing on it).

[0033] Furthermore, the substrate may have a printable coating layer on its surface.

[0034] <Rewetting adhesive layer> While any known adhesive can be used for the re-wetted adhesive layer, polyvinyl alcohol is preferred because it is easier to control the contact angle within the above-mentioned range.

[0035] Suitable polyvinyl alcohols for use in the re-wetted adhesive layer include, for example, unmodified polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, and modified polyvinyl alcohol obtained by modifying unmodified polyvinyl alcohol.

[0036] Examples of modified polyvinyl alcohols include α-olefin-modified polyvinyl alcohol, cation-modified polyvinyl alcohol with cation-modified ends, anionic-modified polyvinyl alcohol having anionic groups, silanol-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, and mercapto-modified polyvinyl alcohol. From the viewpoint of adhesion, unmodified polyvinyl alcohol is preferred.

[0037] The degree of saponification of polyvinyl alcohol is preferably 85 mol% or less. A degree of saponification of 85 mol% or less of polyvinyl alcohol is preferable because it improves the wettability to the resin substrate and improves adhesion to the resin substrate. Furthermore, from the viewpoint of adhesion to the substrate and the solubility of polyvinyl alcohol in water, the degree of saponification of polyvinyl alcohol is preferably 60 mol% or more. The degree of saponification of polyvinyl alcohol is preferably 60 to 85 mol%, more preferably 65 to 82 mol%, even more preferably 70 to 80 mol%, and particularly preferably 70 to 75 mol%.

[0038] Here, the degree of saponification refers to the ratio of hydroxyl groups to the total number of acetyloxy groups (derived from the raw material vinyl acetate) and hydroxyl groups in the polyvinyl alcohol resin. In this specification, "degree of saponification of polyvinyl alcohol" refers to the value measured by a method conforming to "degree of saponification" as described in JIS K 6726:1994.

[0039] The degree of polymerization of polyvinyl alcohol is preferably 250 to 1000, more preferably 300 to 800, and even more preferably 400 to 700. Having the degree of polymerization of polyvinyl alcohol within this range allows for more favorable solubility of the polyvinyl alcohol in water, enabling the formation of a more favorable re-wettable adhesive layer and improving adhesive strength when water is applied.

[0040] In this specification, "degree of polymerization of polyvinyl alcohol" refers to the value measured by a method conforming to the "average degree of polymerization" described in JIS K 6726:1994.

[0041] The polyvinyl alcohol content in the re-wetted adhesive layer (solids) may be 50% by mass or more, more than 50%, 60% by mass or more, 70% by mass or more, or 75% by mass or more (up to 100% by mass). Adhesion to the resin substrate is further ensured when the polyvinyl alcohol content is above the lower limit mentioned above.

[0042] The re-wet adhesive layer preferably contains a polymer (vinyl acetate-based polymer) that includes vinyl acetate as a monomer component, as this further improves the adhesive strength to the resin substrate (particularly to polyethylene terephthalate). Here, the vinyl acetate-based polymer does not contain the polyvinyl alcohol mentioned above. In this specification, the above group of resins is referred to as a resin additive.

[0043] Examples of vinyl acetate polymers include polyvinyl acetate, ethylene-vinyl acetate copolymers, vinyl acetate-vinyl chloride copolymers, acrylic acid ester-vinyl acetate copolymers, and mixtures thereof.

[0044] Furthermore, the vinyl acetate polymer is preferably an emulsion resin from the viewpoint of dispersibility in water used during coating. The emulsion resin is, for example, obtained by emulsion polymerization with a polymeric dispersant containing hydroxyl groups.

[0045] The vinyl acetate polymer emulsion resin may be a commercially available product, such as vinyl acetate emulsions like Vinibran manufactured by Nisshin Chemical Industry Co., Ltd., or vinyl acetate-ethylene emulsions like Sumikaflex manufactured by Sumitomo Chemical Co., Ltd.

[0046] The content of resin additives in the re-moistened adhesive layer (solids) is set appropriately, taking into consideration the properties of the materials contained in the re-moistened adhesive layer, for example, the degree of saponification of polyvinyl alcohol. Specifically, as the degree of saponification of polyvinyl alcohol increases, the amount of resin additives required to improve adhesion tends to increase. In one aspect of the present invention, the content of resin additives in the re-moistened adhesive layer (solids) is preferably 5% by mass or more, and more preferably 10% by mass or more. Furthermore, taking into consideration the solubility in water, the content of resin additives in the re-moistened adhesive layer (solids) is preferably 45% by mass or less, and more preferably 40% by mass or less. The content of resin additives in the re-moistened adhesive layer (solids) may be 5% by mass or more and 45% by mass or less, or 10% by mass or more and 40% by mass or less.

[0047] The re-wet adhesive layer may contain other components. Examples of other components include fillers, softeners, heat and light stabilizers, antioxidants, and crosslinking agents.

[0048] The thickness of the re-wetted adhesive layer is not particularly limited and can be set as appropriate to achieve the desired adhesive strength, but it is preferably 6 μm to 15 μm and more preferably 10 μm to 13 μm.

[0049] <Label manufacturing method> Next, we will explain the label manufacturing method.

[0050] The label can be manufactured, for example, by a method comprising an adhesive layer-forming composition coating step, in which an adhesive layer-forming composition containing an adhesive (preferably polyvinyl alcohol) is coated onto one surface of a substrate, and a drying step, in which the adhesive layer-forming composition is dried to form an adhesive layer.

[0051] [2-1] Coating process for composition for forming adhesive layer In the adhesive layer formation composition coating process, the adhesive layer formation composition is coated onto the substrate.

[0052] As the adhesive layer-forming composition, for example, a composition containing water in addition to the aforementioned adhesive layer components can be used. The concentration of the components is, for example, 5 to 30% by mass. This allows for more favorable coating of the adhesive layer-forming composition, enabling the formation of an adhesive layer of a suitable thickness while more favorably suppressing undesirable variations in thickness. Furthermore, it can improve the productivity of labels.

[0053] Methods for applying the adhesive layer-forming composition include, for example, roll coating, spray coating, bar coating, knife coating, roll-knife coating, blade coating, die coating, and gravure coating.

[0054] [2-2] Drying process In the drying process, the adhesive layer-forming composition is dried to form the adhesive layer. In other words, the adhesive layer is formed by removing the moisture contained in the adhesive layer-forming composition coated onto the substrate.

[0055] This process can be carried out, for example, by natural drying or air drying, but it is preferable to carry it out by heating. The drying temperature, that is, the heating temperature of the adhesive layer-forming composition coated on the substrate, is preferably 60°C to 100°C, and more preferably 70°C to 90°C.

[0056] By the method described above, labels like the one shown in Figure 1 can be suitably manufactured.

[0057] <Label uses> The label is used, for example, as a shipping label. In other words, it is preferable that the label is a shipping label.

[0058] When the label is a shipping label, the object to which it is attached is, for example, the item being shipped. The item being shipped typically consists of the goods being shipped and the packaging materials used to pack those goods. Examples of packaging materials include packing paper, packing film, packing bags, packing boxes, and packing containers. The shipping label is usually affixed to the packaging materials of the item being shipped. Alternatively, the label can also be used as sealing tape for packaging materials.

[0059] Furthermore, since the label of the present invention exhibits high adhesion to resin substrates, a resin substrate is a preferred object to which the label is applied. The resin constituting the resin substrate is not particularly limited, but examples include polyethylene, polypropylene, polyethylene terephthalate, acrylic, polyvinyl chloride, polycarbonate, polyurethane, polystyrene, and ABS (acrylonitrile-butadiene-styrene). [Examples]

[0060] The effects of the present invention will be explained using the following examples and comparative examples. In the examples, the units "parts" or "%" may be used, but unless otherwise specified, they represent "parts by mass" or "mass%". Unless otherwise specified, each operation is performed at room temperature (25°C).

[0061] (Example 1) A polyvinyl alcohol with a saponification degree of 81.5 mol% and a degree of polymerization of 500 was dissolved in water to prepare an adhesive layer-forming composition with a solid content concentration of 15% by mass. The adhesive layer-forming composition was coated onto the side of 80 μm thick thermal paper opposite the thermal layer, dried at 80°C for 1 minute to form a re-wet adhesive layer, and a label was obtained. The thickness of the re-wet adhesive layer was 11 μm.

[0062] (Example 2) A label was obtained in the same manner as in Example 1, except that the polyvinyl alcohol had a saponification degree of 71.5 mol% and a polymerization degree of 500.

[0063] (Example 3) The labels were obtained in the same manner as in Example 2, except that the thickness of the re-wetted adhesive layer was changed to 9 μm.

[0064] (Example 4) In the adhesive layer forming composition, 100 parts by mass of polyvinyl alcohol with a degree of saponification of 71.5 mol% and a degree of polymerization of 500 was dissolved in water, and then 25 parts by mass of polyvinyl acetate emulsion (Vinibran GV-6181, manufactured by Nisshin Chemical Industry Co., Ltd.) was added on a solid content basis to prepare an adhesive layer forming composition with a solid content concentration of 15% by mass, except that the procedure was the same as in Example 2.

[0065] (Comparative Example 1) A label was obtained in the same manner as in Example 1, except that the polyvinyl alcohol had a saponification degree of 88.0 mol% and a degree of polymerization of 500.

[0066] (Comparative Example 2) Labels were obtained in the same manner as in Example 1, except that in the adhesive layer forming composition, 100 parts by mass of polyvinyl alcohol with a degree of saponification of 71.5 mol% and a degree of polymerization of 500 was dissolved in water, and then 100 parts by mass of polyvinyl acetate emulsion (Vinibran GV-6181, manufactured by Nisshin Chemical Industry Co., Ltd.) was added on a solid content basis to prepare an adhesive layer forming composition with a solid content concentration of 15% by mass.

[0067] (Comparative Example 3) A label was obtained in the same manner as in Example 1, except that the polyvinyl alcohol had a saponification degree of 42.0 mol% and a polymerization degree of 500.

[0068] [Measuring contact angle] The water contact angle on the surface of the re-wet adhesive layer of the label was measured using a contact angle meter (KRUSS, product name "DSA100S"). Specifically, 2 μL of distilled water was dropped onto the surface and the static contact angle was calculated using the θ / 2 method.

[0069] [Evaluation Method 1: Measurement of Adhesion] For each example and each comparative example, 0.45 g / m² of deionized water was sprayed onto the adhesive layer surface of the label. 2 The material was sprayed at a specific ratio to induce tackiness. Next, it was applied to each substrate with a 2kg roller under a one-backward load, and the adhesive strength was measured by peeling it off immediately after application and 24 hours later. The peel-off adhesive strength was measured according to the method specified in JIS Z 0237:2022, 10.4.1. The adhesive strength was measured both immediately after application and 24 hours later.

[0070] Four types of substrates were used: polyethylene film (PE), polypropylene film (PP), polyethylene terephthalate film (PET), and K-liner (paper substrate), which is the surface paper of corrugated cardboard.

[0071] The immediate adhesive strength is more preferably 3.0 N / 25 mm or more, and particularly preferably 5.0 N / 25 mm or more. Furthermore, the adhesive strength after 24 hours is more preferably 3.0 N / 25 mm or more, and particularly preferably 5.0 N / 25 mm or more. In addition, the immediate adhesive strength to PET is more preferably greater than 3.0 N / 25 mm, and particularly preferably 5.0 N / 25 mm or more. Furthermore, the adhesive strength to PET after 24 hours is preferably 3.0 N / 25 mm or more, and particularly preferably 5.0 N / 25 mm or more.

[0072] The results are shown in Table 1 below.

[0073] [Table 1]

[0074] From these results, the labels of the examples showed high adhesion not only to paper substrates but also to polyethylene film, polypropylene film, and polyethylene terephthalate film. On the other hand, the labels of Comparative Examples 1 and 2 showed high adhesion to paper substrates but low adhesion to resin substrates. The label of Comparative Example 3 showed low adhesion regardless of the substrate. [Explanation of symbols]

[0075] 10 labels, 11 base material, 12 Re-wetting adhesive layer.

Claims

1. Having a base material and a re-wet adhesive layer, A label having a water contact angle of 65° or more and less than 85° on the re-wet adhesive layer surface.

2. The label according to claim 1, wherein the re-wet adhesive layer contains polyvinyl alcohol with a saponification degree of 85 mol% or less.

3. The label according to claim 2, wherein the degree of polymerization of the polyvinyl alcohol is 250 or more and 1000 or less.

4. The label according to claim 2 or 3, wherein the polyvinyl alcohol content is 60% by mass or more relative to the solid content of the re-wetted adhesive layer.

5. The label according to claim 1 or 2, wherein the re-wet adhesive layer comprises a polymer containing vinyl acetate as a monomer component.

6. The label according to claim 5, wherein the polymer content is 5% by mass or more and 45% by mass or less with respect to the solid content of the re-wetted adhesive layer.

7. The label according to claim 1 or 2, wherein the thickness of the re-wet adhesive layer is 6 μm or more and 15 μm or less.

Images