Label paper

Abstract

Provided is a label paper that has printability and includes a re-moistening active glue layer that can suppress blocking and that can suppress occurrence of wrinkles or recesses in the paper when being pasted to an adherend. The present invention provides a label paper comprising: a paper base that has a first surface and a second surface and that is obtained by including, by means of a size press on both surfaces of a source paper containing kraft pulp as a pulp, a water soluble polymer selected from the group consisting of starches and polyvinyl alcohols; and a re-moistening active glue layer that is provided on the second surface of the paper base and that contains a re-moistening active glue. The Bekk smoothness of the first surface of the paper base is 100-300 sec. The oil resistance of the first surface of the paper base exhibits a kit value of 2 or less. The Cobb sizing degree of the first surface of the paper base at a contact time of 30 sec is 10-30 g / m2 <sp / >. The Bekk smoothness of the surface of the re-moistening active glue layer is 150 sec or less.

Description

Label paper

[0001] The present invention relates to a label paper. More specifically, the present invention relates to a label paper having a paper base material containing a water-soluble polymer and a rewettable adhesive layer, and having printability for various printing methods.

[0002] A rewettable adhesive is an adhesive that exhibits no tackiness under normal conditions but becomes tacky and adhesive when moistened with water. Rewettable adhesives are used as adhesives for stamps, stickers, packaging tape, labels, etc. Label paper having a rewettable adhesive layer containing a rewettable adhesive is known. For example, Patent Document 1 discloses a label having a base sheet, an adhesive layer made of a rewettable adhesive laminated over the entire surface of one side of the base sheet, and an adhesion-suppressing layer laminated over at least a portion of the adhesive layer to suppress the adhesive force of the adhesive layer.

[0003] Japanese Patent Application Laid-Open No. 2019-197148

[0004] In the adhesive layer of Patent Document 1, an adhesion-preventing layer is laminated on at least a portion of the adhesive layer to prevent other items from adhering to the remoistened adhesive-coated surface before use. Therefore, the label sheets of Patent Document 1 avoid adhesion to each other even when, for example, they are stored in a rolled state under high ambient humidity conditions that make the remoistened adhesive-coated surface prone to adhesion. Meanwhile, in recent years, label paper has been required to have printability compatible with various printing methods, such as thermal transfer printing, electrophotographic printing, and inkjet printing. Patent Document 1 discloses a base sheet made of high-quality paper intended essentially for use as a slip label, but does not address the printing surface on which delivery information is recorded. Because high-quality paper typically has poor print quality, improving print quality requires coating layers suitable for each printing method, such as a thermal transfer image-receiving layer for thermal transfer printing, a toner-receiving layer for electrophotographic printing, and an ink-receiving layer for inkjet printing. Forming such a coating layer requires an increase in the number of manufacturing steps or the amount of materials used, which is disadvantageous in terms of the manufacturing cost of label paper.

[0005] Furthermore, as described in Patent Document 1, when label paper having a rewettable adhesive layer is stored in a state where the front and back surfaces are in contact due to being wound or stacked, blocking may occur due to the influence of moisture in the air or the paper, etc. Furthermore, when water is applied to the rewettable adhesive layer of the label paper to activate the adhesive and then the label is stuck to an adherend, wrinkles or dents may occur in the label, and a solution to these problems is desired.

[0006] The object of the present invention is to provide label paper having a rewetting active adhesive layer that has printability for various printing methods, particularly for thermal transfer printing, electrophotographic printing, and inkjet printing, even without having a conventionally known coating layer that is compatible with various printing methods, and that can suppress blocking even when the front and back surfaces of the paper come into contact with each other due to winding or lamination, and that can suppress wrinkling or denting of the paper when attached to an adherend.

[0007] The present invention encompasses the following label paper: [1] A label paper comprising a paper base having a first side and a second side, on both sides of which one or more water-soluble polymers selected from the group consisting of starches and polyvinyl alcohols are added by a size press using a base paper containing kraft pulp, and a rewet active adhesive layer containing a rewet active adhesive on the second side of the paper base, wherein the Beck smoothness of the first side of the paper base measured in accordance with ISO 5627:1995 is 85 seconds or more and 300 seconds or less, the oil resistance of the first side of the paper base measured in accordance with TAPPI test method T-559cm-02 is a Kit value of 2 or less, and the Cobb sizing degree of the first side of the paper base measured in accordance with ISO 535:1991 after a contact time of 30 seconds is 10 g / m ２ 30g / m or more ２ [2] A label paper, wherein the content of the water-soluble polymer by the size press is 1 g / m2 or less in terms of dry solid content per side of the paper base material, and the Beck smoothness of the rewettable active adhesive layer surface measured in accordance with ISO 5627: 1995 is 150 seconds or less. ２ 8g / m or more ２ The label paper [1] is as follows.

[0008] According to the present invention, it is possible to provide a label paper having a rewettable adhesive layer that has printability for various printing methods, particularly thermal transfer printing, electrophotographic printing, and inkjet printing, even without having a conventionally known coating layer for such printing methods. The label paper of the present invention can suppress blocking when its front and back surfaces come into contact with each other due to winding or lamination, and can suppress the occurrence of wrinkles or dents when the rewettable adhesive layer is activated by applying water to the rewettable adhesive layer and then attached to an adherend.

[0009] The label paper of the present invention comprises a paper base having a first side and a second side, on both sides of which one or more water-soluble polymers selected from the group consisting of starches and polyvinyl alcohols are added by a size press using a base paper containing kraft pulp as the pulp, and a rewettable adhesive layer containing a rewettable adhesive on the second side of the paper base, wherein the first side of the paper base has a Beck smoothness of 85 seconds or more and 300 seconds or less as measured in accordance with ISO 5627:1995, the first side of the paper base has an oil resistance of 2 or less as a Kit value as measured in accordance with TAPPI test method T-559cm-02, and the first side of the paper base has a Cobb sizing degree of 10 g / m2 at a contact time of 30 seconds as measured in accordance with ISO 535:1991. ２ 30g / m or more ２ and the Beck smoothness of the rewettable adhesive layer surface is 150 seconds or less as determined in accordance with ISO 5627: 1995. In this specification, the terms "first side" and "second side" of the paper substrate are used for convenience in distinguishing the sides of the paper substrate, and are not intended to represent the first side and second side of the paper substrate by any chemical or physical specificity.

[0010] The label paper of the present invention comprises a paper substrate having a first side and a second side, and a rewettable adhesive layer on the second side. The first side of the label paper has printability for various printing methods. The paper substrate contains base paper and one or more water-soluble polymers selected from the group consisting of starches and polyvinyl alcohols, which are applied to both sides of the base paper by a size press.

[0011] The base paper contains at least kraft pulp as pulp. The kraft pulp content in the base paper is preferably 80% by mass or more, and more preferably 100% by mass, of the total pulp content of the base paper. When the kraft pulp content in the base paper is within this range, the strength of the label paper of the present invention is likely to be improved.

[0012] Kraft pulp is a type of chemical pulp produced by the kraft method conventionally known in the papermaking field, and includes bleached kraft pulp, which has been bleached, and unbleached kraft pulp, which has not been bleached. Pulp sources include, for example, softwoods, hardwoods, hemp, linters, straw, bamboo, sugarcane, reeds, fruit, paper mulberry, Mitsumata, and gampi. For example, when the pulp source is softwood, the kraft pulp contained in the base paper of the paper substrate constituting the label paper of the present invention may be softwood bleached kraft pulp (NBKP) or softwood unbleached kraft pulp (NUKP). The CSF filtration rate of the kraft pulp contained in the base paper is preferably 250 ml or more and 680 ml or less, from the viewpoint of easily improving the strength of the label paper of the present invention. The CSF freeness is a value determined in accordance with ISO 5267-2:2001 "Pulps - Determination of drainability - Part 2: Canadian Standard Freeness method." The CSF freeness can be adjusted by beating the pulp.

[0013] Base paper can be obtained by preparing a stock by mixing additives known in the papermaking field, such as fillers, internal sizing agents, paper strength agents, binders, fixing agents, retention aids, water-resistant agents, dispersants, thickeners, flow improvers, antifoaming agents, foam suppressors, release agents, foaming agents, penetrating agents, colorants, fluorescent brighteners, UV absorbers, antioxidants, preservatives, and mildew inhibitors, into a slurry containing at least kraft pulp as pulp, and then papermaking the stock using a papermaking machine conventionally known in the papermaking field, such as a Fourdrinier machine, a cylinder machine, or a twin-wire machine. In some embodiments, the base paper does not contain a filler. This is because the strength of the base paper is increased, and as a result, the strength of the level paper is also increased.

[0014] A paper substrate is obtained by subjecting the base paper to a size press using a size press solution containing at least one or more water-soluble polymers selected from the group consisting of starches and polyvinyl alcohols. The water-soluble polymers added to the stock, for example as paper strength agents, and the water-soluble polymers added to the base paper by size pressing can be distinguished from each other by the difference in their state in the paper substrate, since the water-soluble polymers added by size pressing are present in large amounts near the surface of the paper substrate. The content of the water-soluble polymer added by size pressing is set to 1 g / m2 in terms of dry solid content per side of the paper substrate, from the viewpoint of easily improving printability for various printing methods. ２ 8g / m or more ２ It is preferably 1 g / m or less. ２ 4g / m or more ２ More preferably, it is:

[0015] Starches are polysaccharides in which glucose is polymerized via glycosidic bonds, and polysaccharides in which the hydroxyl groups of glucose in polysaccharides in which glucose is polymerized via glycosidic bonds are modified with various substituents, and are conventionally known in the papermaking field. Examples of starches include starch, oxidized starch, enzyme-modified starch, etherified starch, cationic starch, amphoteric starch, dialdehyde starch, esterified starch such as phosphate-esterified starch and urea-phosphate-esterified starch, hydroxyethylated starch, and hydroxybutylated starch.

[0016] Examples of polyvinyl alcohols include those conventionally known in the papermaking field, such as various polyvinyl alcohols with different degrees of saponification and average degrees of polymerization; modified polyvinyl alcohols into which various functional groups such as silyl groups, carboxyl groups, amino groups, and acetoacetyl groups have been introduced; and vinyl alcohol copolymers having vinyl alcohol units and units based on other monomers such as ethylene.

[0017] The size press can be performed using a size press device known in the papermaking field, such as a film transfer type such as a rod metering size press, a roll metering size press, or a blade metering size press, an inclined size press, a horizontal size press, a shim sizer, an Optisizer, a speed sizer, or a film press as the rod metering size press, or a gate roll coater as the roll metering size press. Other examples of the size press device include a bill blade coater, a twin blade coater, a Belbapa coater, a tab size press, and a calendar size press.

[0018] In addition to the water-soluble polymer selected from the group consisting of starches and polyvinyl alcohols, the size press liquid may further contain other surface sizing agents conventionally known in the papermaking field, provided that the effects of the present invention are not impaired. Examples of such other surface sizing agents include styrene-acrylic acid resins, styrene-methacrylic acid resins, and olefin-maleic acid resins. The size press liquid may further contain various additives, such as cationic resins such as dimethylamine epichlorohydrin polycondensates and diethylenetriamine epichlorohydrin polycondensates; water-soluble polyvalent cation salts such as calcium chloride and calcium nitrate; fixing agents such as aluminum sulfate; celluloses such as carboxymethyl cellulose; paper strength agents such as polyacrylamides; fluorescent dyes, coloring dyes, coloring pigments, thickeners, desiccant agents, preservatives, antioxidants, and scale inhibitors, provided that the effects of the present invention are not impaired.

[0019] The rewetting active adhesive layer of the label paper of the present invention is a layer containing a rewetting active adhesive. Examples of rewetting active adhesives include those conventionally known in the adhesive field, such as chloroprene rubbers, polyvinyl alcohols, starches, vinyl acetate copolymers such as vinyl acetate acrylate copolymers or vinyl acetate methacrylate copolymers, dextrin, gum arabic, glue, and polyacrylamide. These rewetting active adhesives may be used alone or in combination of two or more.

[0020] The rewetting active adhesive layer can be formed by applying a coating composition containing a rewetting active adhesive to the second surface of the paper substrate and drying it. The method of applying a coating composition containing a rewetting active adhesive and drying it to form a rewetting active adhesive layer can be a method using known coating and drying equipment used in the coated paper field, where a coating solution is applied and dried to form a coating layer. Examples of coating equipment include air knife coaters, various blade coaters, various bar coaters, various curtain coaters, and various roll coaters such as the Comma Coater (registered trademark). Examples of coating equipment include coating by various printing methods such as lithography, relief printing, intaglio printing, flexography, gravure printing, and screen printing. Examples of drying equipment include hot air dryers such as linear tunnel dryers, arch dryers, air loop dryers, and sine-curve air float dryers, infrared heating dryers, and dryers using microwaves and ultraviolet rays.

[0021] The rewetting active adhesive layer may contain various auxiliaries such as preservatives, antioxidants, antifoaming agents, surfactants, antifreeze agents, scale inhibitors, colorants, and fragrances in addition to the rewetting active adhesive agent, in order to more easily improve its weather resistance, etc. Furthermore, when a coating composition containing a rewetting active adhesive layer further contains such various auxiliaries, the operability during coating and drying is likely to be improved.

[0022] The label paper of the present invention may further have an intermediate layer between the paper substrate and the rewettable adhesive layer. Such an intermediate layer is a layer conventionally known in the field of recording materials, containing, for example, a resin and, if necessary, a pigment, etc., and can be provided from the viewpoint of improving the adhesion of the rewettable adhesive layer to the paper substrate or supporting the activity of the rewettable adhesive layer.

[0023] The coating amount of the rewetting active adhesive layer is 2 g / m in terms of dry solid content. ２ 25g / m or more ２ It is preferably 5 g / m or less. ２ 15g / m or more ２When the coating amount of the rewetting active adhesive layer is within the above range, the occurrence of curling can be reduced or suppressed when the rewetting active adhesive layer of the label paper of the present invention is moistened. In addition, when an intermediate layer is further provided between the paper substrate and the rewetting active adhesive layer, the coating amount including the rewetting active adhesive layer and the intermediate layer is 2 g / m2 or less in terms of dry solid content. ２ 25g / m or more ２ Preferably, it is 7 g / m or less. ２ 20g / m or more ２ More preferably, it is:

[0024] In the label paper of the present invention, the Beck smoothness of the first surface of the paper substrate is 85 seconds or more and 300 seconds or less. The Beck smoothness of the first surface of the paper substrate is preferably 85 seconds or more and 293 seconds or less. The Beck smoothness is a value determined in accordance with ISO 5627:1995 "Paper and board--Determination of smoothness (Bekk method)." Beck smoothness is a principle that measures the time (seconds) it takes for a certain amount of air to escape, and it can be said that the larger the value, the smoother the surface.

[0025] Furthermore, in the label paper of the present invention, the oil resistance of the first surface of the above-mentioned paper substrate is a Kit value of 2 or less. The oil resistance is a Kit value consisting of 12 levels determined in accordance with TAPPI test method T-559cm-02 "Grease resistance test for paper and paperboard" (KIT method). In the KIT method, the higher the Kit value, the higher the oil resistance. In other words, a Kit value of 2 or less means that the oil resistance of the first surface of the paper substrate is low.

[0026] In addition, in the label paper of the present invention, the Cobb sizing degree of the first surface of the paper base material described above at a contact time of 30 seconds is 10 g / m ２ 30g / m or more ２ The Cobb sizing degree of the first surface of the paper substrate at a contact time of 30 seconds is 11 g / m ２ 28g / m or more ２The following is preferred. The Cobb sizing degree, also known as the Cobb water absorbency, is a value determined in accordance with ISO 535:1991 "Paper and board--Determination of water absorbency-Cobb method" with a contact time of 30 seconds with water. The Cobb sizing degree is a test that measures the amount of water absorbed (mass) when one side of a pulp sheet is in contact with water for a certain period of time, and the smaller the value, the higher the sizing ability. The sizing ability of a paper substrate is basically improved by increasing the hydrophobicity of the surface.

[0027] Furthermore, in the label paper of the present invention, the Beck smoothness of the rewettable adhesive layer surface is 150 seconds or less. The Beck smoothness of the rewettable adhesive layer surface is preferably 20 seconds or more. As described for the Beck smoothness of the first surface of the paper substrate, the Beck smoothness is a value determined in accordance with ISO 5627:1995. When the Beck smoothness of the rewettable adhesive layer surface is within the above-described range, the adhesiveness of the rewettable adhesive layer when the label paper of the present invention is attached to an adherend is good. In some embodiments, the Beck smoothness of the rewettable adhesive layer surface is 20 seconds or more and 150 seconds or less. In at least one embodiment, the Beck smoothness of the rewettable adhesive layer surface is 24 seconds or more and 136 seconds or less.

[0028] The label paper of the present invention has a Beck smoothness of 85 to 300 seconds on the first surface of the paper substrate, which corresponds to the surface suitable for printing using various printing methods, and a Beck smoothness of 20 to 150 seconds on the rewet active adhesive layer surface. The Beck smoothness of the paper substrate can be adjusted by controlling various conditions in methods conventionally known in the papermaking field, such as the press part conditions of the papermaking machine, and calendering and its conditions. The Beck smoothness of the rewet active adhesive layer surface of the label paper can be adjusted by controlling various conditions in methods conventionally known in the coated paper field, such as the type and conditions of the coating device, the drying time after coating, and calendering and its conditions. For example, with a contour coating device such as a curtain coater, the longer the time between applying a coating composition containing a rewet active adhesive and drying to form a rewet active adhesive layer, the smoother the rewet active adhesive layer tends to be. On the other hand, in coating devices using a smooth coating method such as blade coaters and bar coaters, the shorter the time it takes to apply a coating composition containing a rewetting active adhesive and dry it to form a rewetting active adhesive layer, the smoother the rewetting active adhesive layer tends to be.

[0029] Calendering can be carried out using a calendering device conventionally known in the papermaking field, such as a hard nip calender, a soft nip calender, a hard-soft nip calender, a super calender, a multi-stage calender, or a multi-nip calender. The calendering device may be on-machine or off-machine. From the viewpoint of effectively obtaining smoothness by setting the Beck smoothness of the first surface of the paper substrate within the above-mentioned range, calendering can be carried out by adjusting the temperature of the calender rolls using a heat source such as hot water, steam, or electricity.

[0030] The oil resistance of the first side of the paper substrate can be adjusted by, for example, the type of pulp, the degree of beating of the pulp, the type and content of additives contained in the paper stock, the density of the base paper, the type and content of water-soluble polymer added in the size press, and the type and content of surface sizing agent added as needed in the size press. For example, base paper tends to exhibit oil resistance as its density increases. Although it depends on the type of water-soluble polymer, paper substrates tend to exhibit oil resistance as the amount of water-soluble polymer added in the size press increases. Therefore, when the content of water-soluble polymer added to both sides of the base paper in the size press is 5 g / m2 in dry solid content per side, ２ Below, especially 3g / m ２ If it is below this, it will be easier to keep the kit value at 2 or less.

[0031] The Cobb sizing degree of a paper base material can be adjusted by, for example, the degree of beating of the pulp, the type and content of internal sizing agents contained in the stock, the type and content of additives other than internal sizing agents contained in the stock, the press part conditions and drying conditions of the paper machine, the density of the base paper, the type and content of water-soluble polymers added in the size press, and the type and content of surface sizing agents added as needed in the size press. For example, the Cobb sizing degree value of a paper base material decreases when the dry strength is reduced, the density of the base paper is increased, or a large amount of water-soluble polymer is added in the size press. In other words, sizing ability is improved. Here, examples of internal sizing agents include those conventionally known in the papermaking field, such as rosin-based sizing agents for acidic paper; and alkenyl succinic anhydride-based sizing agents, alkyl ketene dimer-based sizing agents, neutral rosin-based sizing agents, fatty acid-based sizing agents, and cationic styrene acrylic resin-based sizing agents for neutral paper. These internal sizing agents may be used alone or in combination. In particular, from the viewpoint of facilitating designing the paper base material within the above-mentioned Cobb sizing degree range, it is preferable that the internal sizing agent is a rosin-based sizing agent. In at least one embodiment, the content of the rosin-based sizing agent is 2.5 parts by mass or more and 5.0 parts by mass or less per 1,000 parts by mass of pulp in the paper base material.

[0032] The first side of the label paper of the present invention is printable by various printing methods. Examples of printing methods include thermal transfer printing, electrophotographic printing, and inkjet printing. In other words, the first side of the label paper of the present invention is printable by thermal transfer printing, electrophotographic printing, and inkjet printing. In at least one embodiment, the first side of the label paper of the present invention is printable by thermal transfer printing.

[0033] Thermal transfer printing is a printing method in which dyes and other substances contained in a transfer sheet or ink ribbon are vaporized or melted by heat and transferred to paper. In the thermal transfer printing used for printing on the label paper of the present invention, ink ribbons that can be used can be classified into three types depending on the main binder component: wax-based ink ribbons using wax, semi-resin-based ink ribbons using wax and resin, and resin-based ink ribbons using resin. For thermal transfer printing, paper with a thermal transfer image-receiving layer specifically designed for thermal transfer printing has traditionally been used to ensure high print quality. The thermal transfer image-receiving layer is required to not thermally fuse with the thermal ink ribbon during printing, to have good dye receptivity, and to have good dye fixability. The inventors have discovered that in thermal transfer printing, the smoothness, oil resistance, and sizing of the paper affect its fusion with the ink ribbon, its dye receptivity and fixability, and overall print quality.

[0034] Electrophotographic printing is a method of forming an image by exposing the surface of a charged photosensitive drum, adhering powder toner to the image area, transferring the toner to paper, and then thermally fixing the transferred toner on the paper. Exposure methods include a laser beam method using a semiconductor laser and an electron beam method, which forms an image by discharging from a recording electrode. For electrophotographic printing, paper with a toner-receiving layer specifically designed for electrophotographic printing has traditionally been used to ensure high print quality. The electrophotographic image-receiving layer is required to have good toner receptivity and fixability. The inventors have discovered that in electrophotographic printing, the smoothness, oil resistance, and sizing of the paper affect toner receptivity and fixability, as well as overall print quality.

[0035] Inkjet printing is a printing method in which minute ink droplets are sprayed directly onto paper. Ink is broadly divided into two types: aqueous dye and aqueous pigment. Inkjet printing has traditionally used paper with an ink-receiving layer specialized for inkjet printing to ensure high print quality. The inkjet image-receiving layer is required to have good ink receptivity, fixability, and color development. The inventors have discovered that in inkjet printing, the smoothness, oil resistance, and sizing properties of the paper affect the ink receptivity and fixability, as well as overall print quality.

[0036] The label paper of the present invention does not have a conventional image-receiving layer and is printable using various printing methods. It can suppress blocking when the front and back surfaces come into contact with each other, and it can suppress the occurrence of wrinkles or dents in the label paper when it is attached to an adherend.

[0037] In some embodiments, the label paper of the present invention comprises a paper substrate having a first surface and a second surface containing a water-soluble polymer selected from the group consisting of starches and polyvinyl alcohols, which are formed by size pressing on both surfaces of a base paper containing kraft pulp as the pulp, and a rewettable adhesive layer containing a rewettable adhesive on the second surface of the paper substrate, wherein the Beck smoothness of the first surface of the paper substrate is 85 seconds or more and 300 seconds or less, the oil resistance of the first surface of the paper substrate is 2 or less, and the Cobb sizing degree of the first surface of the paper substrate after a contact time of 30 seconds is 10 g / m ２ 30g / m or more ２ In at least one embodiment, the label paper of the present invention comprises a paper substrate having a first side and a second side containing a water-soluble polymer selected from the group consisting of starches and polyvinyl alcohols by size pressing on both sides of a base paper containing kraft pulp as the pulp, and a rewet active adhesive layer containing a rewet active adhesive on the second side of the paper substrate, wherein the Beck smoothness of the first side of the paper substrate is 85 seconds to 300 seconds, the oil resistance of the first side of the paper substrate is 2 or less, and the Cobb sizing degree of the first side of the paper substrate after a contact time of 30 seconds is 10 g / m ２ 30g / m or more ２the Beck smoothness of the rewetting active adhesive layer surface is 20 seconds or more and 150 seconds or less, and the paper substrate contains a rosin-based sizing agent as an internal sizing agent.

[0038] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. In the following description, "parts by mass" and "% by mass" represent the dry solid content or the substantial component amount, respectively. The amounts of starches, polyvinyl alcohols, and surface sizing agents applied represent values ​​based on the dry solid content. Label paper in each example and comparative example was prepared as follows.

[0039] 1. Constituent Materials 1-1. Pulp and Stock <Kraft Pulp> Kraft pulp bleached by the hydrogen peroxide method and having an ISO brightness of 83% and having a predetermined CSF freeness was prepared by beating. The hardwood kraft pulp had a CSF freeness of 420 ml, and the softwood kraft pulp had a CSF freeness of 530 ml. <Stock> Stock was prepared using water as a medium with the following composition: Hardwood kraft pulp 600 parts by mass Softwood kraft pulp 400 parts by mass Rosin-based sizing agent 4 parts by mass Aluminum sulfate 10 parts by mass Paper strength agent (cationized starch) 12 parts by mass Retention aid (acrylamide-based resin) 0.1 parts by mass

[0040] 1-2. Preparation of size press liquid Two types of size press liquid were prepared by dissolving and / or dispersing the following materials in water: Size press liquid α: 100 parts by mass of oxidized starch, 0.125 parts by mass of surface sizing agent (styrene acrylic acid resin), Size press liquid β: 100 parts by mass of polyvinyl alcohol with a saponification degree of 97 mol%, 0.125 parts by mass of surface sizing agent (styrene methacrylic acid resin), 50 parts by mass of water-soluble polyvalent cation (calcium chloride).

[0041] 1-3. Preparation of coating composition for rewetting active glue layer The coating composition for rewetting active glue layer was prepared by dissolving and / or dispersing the following materials in water: Partially saponified polyvinyl alcohol 100 parts by weight Antifoaming agent (acetylene glycol) 0.1 parts by weight

[0042] 2. Preparation of Label Paper Examples 1 to 8 and Comparative Examples 1 to 9 The above-mentioned paper stock was made into base paper using a Fourdrinier paper machine, and the size press liquid shown in Table 1 was used on both sides of the base paper to adjust the content of the components by size pressing to 1 to 8 g / m per side. ２ The size press was carried out by adjusting the weight within the range of 0.01g / m², and then, if necessary, on-machine and / or off-machine calendering was carried out to obtain a paper base material. In Comparative Example 9, water not containing dry solids was used as the size press liquid. The basis weight of the paper base material was 80 g / m², excluding the content of components incorporated by the size press. ２ Next, the coating composition for the rewetting active adhesive layer was applied to the second surface of the obtained paper substrate using an air knife coater, and then dried using a hot air dryer to obtain a label paper. The coating amount of the coating composition for the rewetting active adhesive layer was 15 g / m ２ When producing the label paper, the press part conditions and drying conditions of the paper machine, whether or not the base paper was subjected to a calendering treatment and the treatment conditions, the drying conditions after applying the coating composition of the rewetting active adhesive layer, the size press treatment conditions, and the subsequent calendering treatment conditions were adjusted so that the Beck smoothness, oil resistance, and Cobb sizing degree on the first side of the paper substrate, and the Beck smoothness of the rewetting active adhesive layer, were predetermined values.

[0043] 3. Evaluation of Label Paper 3-1. Basic Physical Properties of Label Paper The following physical properties of the label paper obtained in each Example and Comparative Example were measured in accordance with the following ISO standards. Beck smoothness of the first surface of the paper substrate: Determined in accordance with ISO 5627:1995 "Paper and board -- Determination of smoothness (Bekk method)." Oil resistance of the first surface of the paper substrate: Determined as the kit value in accordance with TAPPI test method T-559cm-02 "Grease resistance test for paper and paperboard" (KIT method), and used as the oil resistance. Cobb sizing degree of the first surface of the paper substrate: Measured according to ISO 535:1991 "Paper and board - Determination of water absorbency - Cobb method" with a contact time of 30 seconds. Beck smoothness of the rewettable adhesive layer: Measured according to ISO 5627:1995, as with the first surface of the paper substrate. The results are shown in Table 1.

[0044] 3-2. Printability of Label Paper The label paper obtained in each Example and Comparative Example was evaluated for printability with various printing methods from the following perspectives: (1) Thermal Transfer Printing (1a) Fusing Condition with Ink Ribbon An ink donor sheet was placed on the first side of the label paper as an ink ribbon, and heated from the ink donor sheet side at 180°C for 2 seconds to transfer the ink, and an image of the evaluation pattern was printed on the first side of the label paper. The fusing condition between the label paper and the ink donor sheet was then observed and evaluated according to the following criteria. A rating of A or B was considered to be suitable for printability with thermal transfer printing in terms of fusing with the ink ribbon. A: No fusing was observed (good) B: Fusing was observed but the label could be easily peeled off (generally good) C: Fusing was observed and the label paper could not be easily peeled off (difficult to use in practice)

[0045] (1b) Ink Fixability: An image of an evaluation pattern was printed on the first surface of a label paper in the same manner as in (1a) above, and the label paper was placed with the printed side facing up in a Sutherland-type rub tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.). Next, an unprinted label paper was attached to a 1 kg weight and placed in the rub tester so that the printed side would rub against the first surface of an unprinted label paper that was common to the printed label paper. The printed surface of the label paper with the image of the evaluation pattern and the first surface of the unprinted label paper were automatically rubbed back and forth five times, and then the presence or absence of scratches on the image of the printed evaluation pattern and ink transfer to the first surface of the unprinted label paper was observed and evaluated according to the following criteria. A rating of A, B, or C was determined to be suitable for thermal transfer printing in terms of ink fixability. A: Image scratches and ink transfer are generally not observed (good) B: At least one of image scratches and ink transfer is inferior to A above, and image scratches or ink transfer is very slightly observed (generally good) C: At least one of image scratches and ink transfer is inferior to B above, and image scratches or ink transfer is slightly observed (practically usable) D: Image scratches or ink transfer are more severe than C above (not practical)

[0046] (1c) Printing quality Using a thermal transfer printing printer (Zebra's "Z4M Plus" (product name)), a black monochrome evaluation pattern was printed on the first side of label paper with a wax-based ink ribbon. The printed matter was visually observed in terms of white spots, blurring, definition, etc. and evaluated according to the following criteria. If the print quality was rated A, B, or C, it was determined that the print was suitable for thermal transfer printing. A: Good B: Generally good C: Practically usable D: Not practical

[0047] (2) Electrophotographic Printing (2a) Toner Fixability A full-color evaluation pattern was printed on the first surface of label paper using a dry electrophotographic printer (Canon Inc.'s "Satera (registered trademark) LBP622C" (product name). The label paper was set with the printed side facing up in a Sutherland type rub tester (Toyo Seiki Seisaku-sho, Ltd.), and the toner fixability was evaluated using the same procedures and criteria as in (1b) above. If the evaluation was A, B, or C, it was determined that the toner had printability for electrophotographic printing in terms of toner fixability.

[0048] (2b) Printing quality: A full-color evaluation pattern was printed on the first side of label paper in the same manner as in (2a) above, and the printed matter was visually observed and evaluated in terms of color development, color density, color vividness, uniformity, etc., according to the following criteria. If the evaluation was A, B, or C, it was determined that the print quality was suitable for electrophotographic printing. A: Good B: Generally good C: Practically usable D: Not practically usable

[0049] (3) Inkjet Printing (3a) Ink Fixability A full-color evaluation pattern was printed on the first side of label paper using two models: an inkjet printer using aqueous dye ink (product name "Colorio (registered trademark) EP315" manufactured by Seiko Epson Corporation) and an inkjet printer using aqueous pigment ink (product name "PX-105" manufactured by Seiko Epson Corporation). The label paper was set with the printed side facing up in a Sutherland type love tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.), and the ink fixability of the printed patterns on both models was evaluated using the same procedures and criteria as in (1b) above. The final evaluation was based on the worse of the two models. A rating of A, B, or C was determined to be suitable for inkjet printing in terms of ink fixability.

[0050] (3b) Printing quality: In the same manner as in (3a) above, the first side of label paper was printed using the two printer models. Each full-color evaluation pattern was visually observed from the viewpoints of color development, color density, color vividness, uniformity, bleeding, etc., and evaluated according to the following criteria. The final evaluation was based on the worse of the two printer models. If the evaluation was A, B, or C, it was determined that the print quality was suitable for inkjet printing. A: Good B: Generally good C: Practically usable D: Not practically usable

[0051] 3-3. Blocking Resistance of Label Paper Two test pieces were prepared by cutting the label paper obtained in each Example and Comparative Example into A4 size with the long side facing vertically. The two test pieces were stacked so that the first surface of one test piece faced the rewetting active adhesive layer of the other test piece, with the other test piece facing upward. An A4 size iron plate weighing 2 kg was placed on the first surface of the other test piece, and the test pieces were left standing at 40°C and a relative humidity of 90% for 24 hours. After standing, the two test pieces were peeled off by hand, and the blocking state was observed and evaluated according to the following criteria. A rating of A, B, or C was considered to have suppressed blocking. A: Can be easily peeled off (good); B: Can be peeled off with slight force (generally good); C: Can be peeled off with force (practically usable); D: Cannot be peeled off without layer peeling or tearing (not practical).

[0052] 3-4. Wrinkling and denting of label paper Twenty 80 mm x 80 mm test pieces were cut from the label paper obtained in each Example and Comparative Example. Using a sponge roller-type stamp moistener, tap water at room temperature (25 ° C.) was applied to the entire surface of the rewettable adhesive layer of the test piece in an amount sufficient to cause the rewettable adhesive layer to develop adhesive properties (roughly 2 to 5 times the coating amount of the rewettable adhesive layer), thereby wetting the rewettable adhesive layer. Next, 20 test pieces were attached to 500 mm x 500 mm corrugated cardboard fixed on a horizontal table, which served as an adherend, while the rewettable adhesive layer was still developing adhesive properties. After application, the state of attachment of each test piece was observed and evaluated according to the following criteria. A rating of A or B was determined to have suppressed the occurrence of wrinkling and denting of the label paper when applied to the adherend. The lowest rating out of 20 test pieces cut out from each label paper was taken as the final rating for wrinkles or dents for each label paper. A: No wrinkles or dents observed (good) B: At least one of wrinkles or dents is inferior to A above, and very slight wrinkles or dents are observed (generally good) C: At least one of wrinkles or dents is inferior to B above, and wrinkles or dents are observed (unsuitable for practical use) The results are also shown in Table 1.

[0053]

[0054] Table 1 shows that the label papers of Examples 1 to 8, which satisfy the requirements of the present invention, are suitable for printing with various printing methods, even without the conventional coating layers used for these methods. They also suppress blocking when the front and back surfaces of the label paper come into contact, and they also suppress wrinkling or denting when the label paper is applied to an adherend after water is applied to the rewettable adhesive layer to activate the adhesive. On the other hand, the label papers of Comparative Examples 1 to 9, which do not satisfy the requirements of the present invention, are unsatisfactory in any of the following areas: printability with various printing methods, suppression of blocking, and suppression of wrinkling or denting when applied to an adherend.

[0055] According to the present invention, it is possible to provide a label paper having a rewettable adhesive layer that is printable for various printing methods, particularly thermal transfer printing, electrophotographic printing, and inkjet printing, even without having a conventional coating layer for these methods. The label paper of the present invention can suppress blocking when its front and back surfaces come into contact after being wound or stacked, and can suppress the occurrence of wrinkles or dents when the rewettable adhesive layer is activated by adding water to the adhesive and then attached to an adherend. Therefore, the present invention has industrial applicability.

Claims

1. A paper substrate having a first side and a second side containing one or more water-soluble polymers selected from the group consisting of starches and polyvinyl alcohols by a size press on both sides of a base paper containing kraft pulp as the pulp, and a rewet active adhesive layer containing a rewet active adhesive on the second side of the paper substrate, wherein the Beck smoothness of the first side of the paper substrate measured in accordance with ISO 5627:1995 is 85 seconds or more and 300 seconds or less, the oil resistance of the first side of the paper substrate measured in accordance with TAPPI test method T-559cm-02 is a Kit value of 2 or less, and the Cobb sizing degree of the first side of the paper substrate measured in accordance with ISO 535:1991 after a contact time of 30 seconds is 10 g / m ２ 30g / m or more ２ and the Beck smoothness of the rewettable active adhesive layer surface measured in accordance with ISO 5627:1995 is 150 seconds or less.

2. The content of the water-soluble polymer by the size press is 1 g / m2 in terms of dry solid content per side of the paper base material. ２ 8g / m or more ２ 2. The label paper according to claim 1, wherein:

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