Re-wettable adhesive sheet

Abstract

To provide a re-wettable adhesive sheet that does not use release paper and has superior adhesion compared to conventional sheets. [Solution] The above problem is solved by a re-wettable adhesive sheet X1 having an adhesive layer on one side of a paper substrate 1, wherein a re-wettable adhesive 2 containing 90% by mass or more of polyvinyl alcohol with a saponification degree of 70% to 90% and starch is applied, and the mixing ratio of the polyvinyl alcohol to the starch in the re-wettable adhesive 2 is 100:10 to 100:50.

Description

[Technical Field]

[0001] This invention relates to a re-moisturizing adhesive sheet, such as a re-moisturizing adhesive sheet that does not require release paper, which is affixed to the outside of a storage box containing products or goods. [Background technology]

[0002] In the logistics process, such as when manufacturers deliver goods to retailers or when shipping goods to customers in mail order or online sales, labels containing a list of the various items stored inside and the recipient's address are printed on them using a printer and attached to the outside of cardboard boxes or other packaging boxes.

[0003] These labels primarily consist of a paper base with one side for displaying the product name, etc., and the other side for applying adhesive, and a release liner covering the adhesive side. The reason for this is that the adhesive side is protected, making it easier to handle.

[0004] However, because the application of labels generates a large amount of release paper, creating a significant environmental burden, labels that do not use release paper have been proposed (Patent Documents 1-3). However, these labels required the use of thermal reactions or dissolution with organic solvents to achieve adhesive properties.

[0005] Therefore, as disclosed in Patent Document 4, for example, an adhesive paper has been proposed that does not require a release liner, by applying a surface treatment agent to one side of a paper substrate and laminating a re-wetting adhesive layer that is activated by moisture to the other side.

[0006] In Patent Document 4, as described in claim 4, "the surface treatment agent is one of polyvinyl alcohol as a fully saponified product, oxidized starch, acrylic copolymer resin, or acrylic composite resin, and the re-wetting adhesive is selected from one of vinyl acetate polymer, a compound of polyvinyl alcohol and dextrin as a partially saponified product, wheat starch, acrylic copolymer resin, or acrylic composite resin." [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-63616 [Patent Document 2] Japanese Patent Publication No. 2013-45036 [Patent Document 3] Japanese Patent Publication No. 2015-141399 [Patent Document 4] Patent No. 5758840 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, it has been found that the re-wetting adhesive layer described in Patent Document 4 does not provide sufficient adhesive strength.

[0009] Therefore, the main objective of the present invention is to provide a re-wetting adhesive sheet with excellent adhesion properties. [Means for solving the problem]

[0010] The re-wetting adhesive sheet that solves the above problems is as follows: <First aspect> One side of the paper substrate has a re-wetting adhesive layer containing 90% or more by mass of polyvinyl alcohol with a saponification degree of 70% to 90% and starch. In the aforementioned re-wetting adhesive, the composition ratio of polyvinyl alcohol to starch is 100:10 to 100:50. A rewettable adhesive sheet characterized by the following.

[0011] (Function and effect) The rewettable adhesive sheet of this embodiment has a rewettable adhesive containing polyvinyl alcohol and starch applied to one side of a paper substrate. This rewettable adhesive has no adhesiveness when solidified to form a layer, but becomes adhesive again by reacting with moisture. When the saponification degree of polyvinyl alcohol is within the above range and the composition ratio of polyvinyl alcohol and starch is within the above range, the compatibility of polyvinyl alcohol and starch is good, and a rewettable adhesive sheet with more excellent adhesive strength can be obtained.

[0012] <Second embodiment> It has a pseudo-adhesive layer on the other side of the paper substrate, and the paper substrate and the second sheet are detachably adhered via the pseudo-adhesive layer. The rewettable adhesive sheet of the first embodiment.

[0013] (Function and effect) In the rewettable adhesive sheet of this embodiment, for example, a second sheet on which information such as a name or a product name is described is adhered to a paper substrate coated with a rewettable adhesive via a pseudo-adhesive layer, and the second sheet can be peeled off from the paper substrate. In this way, it can be used as a pseudo-adhesive sheet.

[0014] <Third embodiment> The rewettable adhesive is applied at 5.0 g / m 2 or more and 15.0 g / m 2 or less. The rewettable adhesive sheet of the second embodiment.

[0015] (Function and effect) In the rewettable adhesive sheet of this embodiment, the rewettable adhesive is applied in the range of 5.0 g / m 2 or more and 15.0 g / m 2 or less, thereby exhibiting excellent adhesive strength to an adherend such as cardboard.

[0016] <Fourth embodiment> The tensile strength of the aforementioned re-wettable adhesive sheet in a tensile test against liner paper is 1.8 N / 50 mm to 3.0 N / 50 mm. A re-wettable adhesive sheet according to the first or third embodiment.

[0017] (Effects and Benefits) With the re-wettable adhesive sheet of this embodiment, the re-wettable adhesive sheet attached to a substrate such as cardboard will have an appropriate tensile strength in a tensile test and will not peel off or detach from the substrate.

[0018] <Fifth aspect> A sealing layer is provided between the paper substrate and the pseudo-adhesive layer, and the sealing layer comprises a pigment, an adhesive, and starch. A re-wettable adhesive sheet in a second embodiment.

[0019] (Effects and Benefits) In this embodiment, the re-wettable adhesive sheet has good pseudo-adhesion properties by providing a sealing layer containing pigment, adhesive, and starch between the paper substrate and the pseudo-adhesive layer.

[0020] <Sixth aspect> The degree of polymerization of the polyvinyl alcohol is 400 to 2000 or less, and the starch is esterified tapioca starch. A re-wettable adhesive sheet in a second embodiment.

[0021] (Effects and Benefits) The polyvinyl alcohol with the above degree of polymerization has excellent compatibility with esterified tapioca starch, which has excellent thixotropy, making it easier to obtain a homogeneous coating. Therefore, the re-wettable adhesive sheet in this embodiment has excellent adhesive strength. [Effects of the Invention]

[0022] According to the present invention, it becomes possible to provide a re-wetting adhesive sheet with excellent adhesion properties. [Brief explanation of the drawing]

[0023] [Figure 1] This is a cross-sectional view of a re-wettable adhesive sheet relating to the first layer structure. [Figure 2] This is a cross-sectional view of a re-wettable adhesive sheet relating to the second layer structure. [Figure 3] This is a cross-sectional view of a re-wettable adhesive sheet relating to a third layer structure. [Figure 4] This is a cross-sectional view of a re-wettable adhesive sheet relating to a fourth layer structure. [Modes for carrying out the invention]

[0024] An example of the present invention will be described below. However, the following description and drawings are merely examples, and the content of the present invention should not be interpreted as being limited to the following description and drawings.

[0025] In this embodiment, the re-wettable adhesive sheet X1 has a second sheet 3 having a printing surface on one side of the paper substrate 1 for writing addresses, product information, and designs, which is peelably bonded to the paper substrate 1 via a pseudo-adhesive layer 4, and a re-wettable adhesive 2 is applied to the other side.

[0026] The present invention will be explained using the re-wetting adhesive sheet X1 shown in Figure 1 as a basis, but the present invention is not limited to this form. For example, as shown in Figure 2, a re-wetting adhesive sheet X2 can also be used, in which a sealing layer 5 is provided between the pseudo-adhesive layer 4 and the paper substrate 1.

[0027] (Paper substrate, second sheet) The paper substrate can be (double-sided) kraft paper, fine paper, glassine paper, parchment paper, rayon paper, coated paper, synthetic paper, paper laminated with resin film, thermal paper, etc. The type of paper substrate 1 and the second sheet 3 do not need to be the same, nor do their thicknesses need to be the same. However, it is desirable to select the thickness of the second sheet 3 and paper substrate 1 to be within the range of 50 to 300 μm overall in order to ensure smoothness and printability. Furthermore, considering the possibility of contact with moisture such as rain, the water resistance of the second sheet 3 may be improved by adding a wet-strength enhancer internally or externally.

[0028] Examples of wet strength enhancers include starch-based strength enhancers such as cationic starch, polyacrylamide-based strength enhancers, polyvinyl alcohol-based strength enhancers, and polyamide-based strength enhancers.

[0029] Furthermore, a primer coating layer may be provided on one or both sides of the paper substrate 1. For example, natural polymers, synthetic polymers, etc., can be used as raw materials for the primer coating layer.

[0030] As natural polymer systems, for example, one or more can be selected and used from among those obtained by modifying raw starches such as corn, wheat, tapioca, and potato using various manufacturing methods, such as enzymatically hydrolyzed starch, oxidized starch, hydroxyethylated starch, cationized starch, urea phosphorylated starch, modified oxidized starch, carboxymethylated cellulose (CMC), and carboxyethylated cellulose (CEC).

[0031] As for the synthetic polymer system, one or more can be selected and used from, for example, polyacrylamide (PAM), polyethylene glycol (PEG), etc.

[0032] The undercoat layer may contain additives such as defoamers, fluorescent whitening agents, water-resistant agents, and sizing agents.

[0033] The amount of the undercoat coating layer (solid content) is preferably 0.5 to 10 g / m² per side. 2 , more preferably 0.7~8 g / m 2 Particularly preferred is 1.0 to 2.0 g / m² 2 That is the case.

[0034] The undercoat layer may be colored by incorporating pigments or dyes. However, coloring the undercoat layer will reduce the whiteness and brightness of the paper substrate 1, so it is preferable not to color the undercoat layer.

[0035] On the other hand, the printing surface of the second sheet 3 (the top surface of the drawing) may have pre-printed fields and frames for entering individual product information and addresses, as well as designation information indicating the information to be entered in each field and frame. The printing of this designation information specifying the information to be entered in these fields and frames can be done using various known pigment-based and dye-based inks and various known printing methods such as letterpress printing, gravure printing, and stencil printing. Of course, printing can be done not only with printing inks, but also with inkjet inks, laser printer toners, or thermal printing.

[0036] (Simulated adhesive) Furthermore, in the re-wettable adhesive sheet X1 according to the present invention, the second sheet 3 and the paper substrate 1 are peelably bonded via a pseudo-adhesive layer 4. The pseudo-adhesive layer 4 can be formed from a known pseudo-adhesive. Pseudo-adhesion means that the bonding is such that it can be peeled off by cohesive failure or interlayer delamination of the adhesive, and does not exhibit re-adhesion or adhesive properties after peeling.

[0037] As pseudo-adhesives, hot-melt adhesives with reduced re-adhesion properties, such as those obtained by compounding silicone into a hot-melt adhesive; microparticle-filled adhesives obtained by adjusting the adhesive strength of natural or synthetic rubber-based, acrylic-based, silicone-based, polyurethane-based, polyester-based, organic solvent-based, or emulsion-based non-peelable adhesives by compounding them with known microparticle fillers such as zinc oxide, titanium dioxide, silica, or calcium carbonate; water-soluble emulsion adhesives; vinyl acetate-based adhesives; and starch-based water-soluble adhesives can be used. Particularly preferred are pseudo-adhesives mainly composed of aqueous emulsions such as polypropylene vinyl acetate copolymer, also known as temporary fixing adhesives, which have weak penetration into the paper layer, extremely low adhesion after drying, and can construct a suitable peeling mechanism by cohesive breakdown of the pseudo-adhesive layer.

[0038] In the re-wettable adhesive sheet X1 according to the present invention, when the second sheet 3 is peeled off, the pseudo-adhesive layer 4 is exposed. Therefore, as shown in Figures 3 and 4, by pre-applying some kind of printed layer 6 on the paper substrate or sealing layer, the printed layer 6 becomes visible through the highly transparent pseudo-adhesive layer 4. The type of information that is pre-printed is not particularly limited.

[0039] When the printing layer 6 is printed in advance in this manner, it may also be done by printing directly onto the pseudo-adhesive layer 4, as shown in Figure 3.

[0040] (Re-wetting adhesive) In the re-wettable adhesive sheet X1 according to the present invention, a re-wettable adhesive 2 is applied to a paper substrate 1. The re-wettable adhesive 2 does not have adhesive properties in the absence of moisture, but exhibits adhesive properties upon reaction with moisture.

[0041] The re-wetting adhesive 2 of the present invention is formulated with polyvinyl alcohol and starch. Starch, in particular, exhibits excellent adhesion to corrugated cardboard used as the substrate. Other components may be included, as long as the polyvinyl alcohol and starch together constitute 90% or more by mass. If the polyvinyl alcohol and starch together constitute less than 90% by mass, good adhesion to the substrate cannot be achieved.

[0042] The type of polyvinyl alcohol is not particularly limited. In addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, modified polyvinyl alcohols such as polyvinyl alcohol with cation-modified ends and anionic modified polyvinyl alcohol having anionic groups are also included. Modified polyvinyl alcohols into which various functional groups have been introduced are also included.

[0043] As for polyvinyl alcohol, a polyvinyl alcohol with an average degree of polymerization of 400 to 2000 is preferably used, and more preferably in the range of 500 to 1800, because it has excellent compatibility with starch and makes it easier to obtain a homogeneous film. Polyvinyl alcohol exhibits properties where the resulting film strength is strong and it becomes less soluble in water as the degree of polymerization increases, and where the resulting film strength is strong and it becomes less soluble in cold water as the degree of saponification increases. If the degree of polymerization is less than 400, the film strength will be low, and re-wetting water will easily penetrate the coating layer, potentially resulting in excessively strong adhesion. On the other hand, if the degree of polymerization exceeds 2000, the film strength will be high, and re-wetting water will not easily penetrate the coating layer, potentially resulting in excessively weak adhesion. Therefore, polyvinyl alcohol with a degree of saponification of 70% to 90% is preferable, preferably 73% to 90% or less, and more preferably in the range of 80% to 90% or less. If the degree of saponification is less than 70%, the initial adhesive strength (tackiness) upon re-wetting may improve, but the bonded adhesive strength may decrease. On the other hand, if the degree of saponification exceeds 90%, the water solubility is poor, which may lead to poor dispersibility of the coating solution and an inability to obtain uniform adhesive strength.

[0044] Furthermore, using such polyvinyl alcohol allows for good affinity with starch, enabling quick blending of starch and polyvinyl alcohol, improving operability, and reducing mist generation in coating equipment. It is also preferable because it prevents ink transfer to the reverse side after printing on the paper.

[0045] While there are no specific restrictions on the type of starch used, common industrial starches such as tapioca, potato, and waxy maize can be used, with tapioca being particularly preferred.

[0046] Tapioca starch has excellent film-forming and thixotropic properties. Thixotropy is the property that when no external force is applied, viscosity is relatively high and fluidity is low, but when pressure or external force is applied, viscosity decreases and fluidity improves. This means that at the moment the coating composition is applied to paper with an applicator (coating machine), a high shear is applied, increasing the fluidity of the coating composition and making it easier to form a film. However, immediately after application, the force applied to the coating composition disappears, and its viscosity changes to a high level. After application, in the thickness direction of the paper, the coating composition penetrates into the interior of the paper due to capillary action. However, this force is weaker than the force applied during application, and is not strong enough to significantly change the fluidity of the coating composition, so it is thought to remain on the paper substrate.

[0047] Furthermore, it is more preferable that the tapioca starch is esterified tapioca starch. Esterified tapioca starch is preferable because it is superior to other cereal starches in terms of viscosity, film-forming properties, elasticity, and extensibility. In esterified starch, the degree of esterification is not particularly restricted, but the average number of ester bonds introduced is 1 to 3, preferably 1 to 2, per glucose unit. Among esterified starches, hydroxyesterified starch is preferred. This can be easily and inexpensively obtained by oxidizing the raw starch and reducing the carboxymethyl group to a hydroxyethyl group. Most preferably, hydrophobic group-containing esterified tapioca starch can be used, in which a hydrophobic group is introduced to the terminal group of the esterified starch. Furthermore, as an esterified starch that can be preferably used, it has a carboxylic acid (-COOH) structure at the terminal group and in the neutral region, -COO - Ester-modified starch that exhibits thixotropical behavior due to its repulsive properties, as it cannot secure hydrogen bonding through ionization, is preferred because, while it exhibits fluidity during coating, it does not easily penetrate into the base paper after being applied to the base paper surface, and it exhibits high film-forming properties on the base paper surface. Among these esterified starches, 1-octenyl succinate esterified starch, which is obtained by esterifying and modifying tapioca starch as the main raw material, is particularly preferred.

[0048] By using it in combination with this highly film-forming polyvinyl alcohol and esterified tapioca starch with excellent thixotropy, the fluidity is high at the time of coating on the paper substrate 1, and the fluidity is suppressed after coating. Therefore, polyvinyl alcohol and starch remain on the surface of the paper substrate 1, and a rewettable adhesive layer having high covering properties is formed on the surface of the paper substrate 1. As a result, when reacted with moisture, the reactivity with moisture becomes high, and a rewettable adhesive sheet X1 having excellent adhesiveness is obtained.

[0049] The coating amount (solid content) of the rewettable adhesive is 5.0 g / m 2 ~15.0 g / m 2 It is preferably applied to the paper substrate, and 6.0 g / m 2 ~12.0 g / m 2 is more preferable, and 6.5 g / m 2 ~11.0 g / m 2 is particularly preferable. By being the above coating amount, the adhesiveness to the adherend becomes excellent. If the coating amount is less than 5.0 g / m 2 , the adhesion and retention to the adherend may be insufficient. On the other hand, if the coating amount exceeds 15.0 g / m 2 , the rewettable adhesive sheet does not peel off when recycling the cardboard, and there may be a difficulty in recyclability.

[0050] (Blocking layer) The rewettable adhesive sheet according to the present invention can also be in a form in which a blocking layer 5 is provided between the pseudo-adhesive layer 4 and the paper substrate 1, like the rewettable adhesive sheet X2 shown in FIG. 2. By providing the blocking layer 5, the effect of further preventing the wetting of the rewettable adhesive 2 and the fact that the second sheet 3 is provided combine to obtain the effect of suppressing the curl of the paper substrate 1.

[0051] As components of the blocking layer 5, in addition to starch, pigments, adhesives, etc. can be used, and the blocking layer 5 of the present invention can preferably use a mixture of a pigment, an adhesive, and starch.

[0052] The pigments used are preferably selected from those commonly used as pigments for papermaking, such as calcium carbonate, talc, white carbon, clay, calcined clay, titanium dioxide, aluminum hydroxide, and recycled fillers. Using calcium carbonate, talc, or clay has the advantage of being a general-purpose inorganic material, thus offering fewer limitations on its application. From the viewpoint of sealing properties, it is preferable to use clay, which has high oil absorption.

[0053] Adhesives can include, for example, styrene-butadiene latex, acrylic emulsion, acrylic-styrene emulsion, vinyl acetate emulsion, ethylene-vinyl acetate emulsion, urethane emulsion, starch, modified starch, polyvinyl alcohol (PVA), and other latexes, emulsions, and water-soluble binders.

[0054] The type of starch is not particularly limited, but common industrial starches such as tapioca, corn, potato, and waxy maize can be used, with tapioca being particularly preferred. Among these, esterified tapioca starch is preferred because it is superior to other cereal starches in terms of viscosity, film-forming properties, elasticity, and extensibility. In esterified starch, the degree of esterification is not particularly restricted, but the average number of ester bonds introduced is 1 to 3, preferably 1 to 2, per glucose unit.

[0055] The amount of adhesive added is preferably 5 to 45 parts by mass, more preferably 20 to 40 parts by mass, and particularly preferably 25 to 35 parts by mass, based on solids, per 100 parts by mass of the aforementioned pigment. The amount of starch added is preferably 1 to 15 parts by mass, more preferably 3 to 14 parts by mass, and particularly preferably 5 to 10 parts by mass, based on solids, per 100 parts by mass of the aforementioned pigment.

[0056] (Examples) Next, examples and comparative examples of the present invention will be described. However, the present invention is not limited in any way by the following examples. Various modifications can be made without departing from the spirit of the invention.

[0057] On one side of a paper substrate 1 (manufactured by Daio Paper Corporation: double-sided newsprint), a re-wetting adhesive 2 was applied, which consisted of various starches, including polyvinyl alcohol with different degrees of saponification and polymerization, and esterified tapioca starch. The mixing ratios and coating amounts of these various materials are shown in Table 1 below.

[0058] For coating, known coating machines such as two-roll size press coaters, gate roll coaters, blade metering coaters, rod metering coaters, blade coaters, air knife coaters, roll coaters, brush coaters, kiss coaters, squeeze coaters, curtain coaters, die coaters, bar coaters, rod coaters, and gravure coaters can be used.

[0059] The adhesive strength of the obtained paper substrate 1 was investigated by sensory evaluation and tensile strength measurement. The results are shown in Table 1 below. The evaluation criteria for sensory evaluation are as follows.

[0060] A certain amount of water was applied to the coated surface of the re-wetting adhesive 2 using a sponge, and the adhesive was then attached to the surface of the liner paper. After 10 seconds, it was peeled off and the adhesive strength was evaluated. "Material failure" means that the material broke. The liner paper used in this test was "JPK" manufactured by Daio Paper Corporation. Liner paper refers to various types of liners used on the surface of cardboard, etc., and the surface refers to the side on which printing is applied. It was determined that only an evaluation value of 3 or higher was acceptable for practical evaluation. 5: Almost the entire liner paper is delaminated. 4: Part of the liner paper has broken (delamination). 3: Almost the entire surface of the liner paper is fuzzy. 2: Part of the liner paper surface is fuzzy. 1: No fuzz on the liner paper surface.

[0061] Furthermore, tensile strength was measured by applying water at a rate of 12 g / m² to the re-wet adhesive coated surface of a paper substrate sample (1) cut to a width of 50 mm using a plain rod. 2After applying the coating and attaching it to the surface of the liner paper, the tensile strength was measured after 60 seconds in a tensile testing machine and peeling it 180 degrees at a tensile strength of 500 mm / min. The liner paper used in this test was "JPK120g / m²" manufactured by Daio Paper Corporation. 2 The following was used. Note that liner paper refers to various types of liners used on the surface of corrugated cardboard, etc., and the surface refers to the side on which printing is applied. The aforementioned tensile strength of 1.8N / 50mm to 3.0N / 50mm provides excellent adhesion and retention to the adherend. If the adhesive strength is less than 1.8N / 50mm, twisting or lifting of the re-wettable adhesive sheet may occur in actual use. On the other hand, if the adhesive strength exceeds 3.0N / 50mm, the re-wettable adhesive sheet may not peel off when recycling corrugated cardboard, potentially causing difficulties in recyclability.

[0062] Furthermore, a sealing layer 5 was provided on the paper substrate 1 on the side opposite to the surface coated with the re-wettable adhesive 2. The sealing layer 5 was prepared by blending pigment (fine clay particles), SB latex, and starch in the proportions shown in the table. Similar to the re-wettable adhesive 2, known coating machines such as 2-roll size press coaters, gate roll coaters, blade metering coaters, rod metering coaters, blade coaters, air knife coaters, roll coaters, brush coaters, kiss coaters, squeeze coaters, curtain coaters, die coaters, bar coaters, rod coaters, and gravure coaters can be used. The coating amount (solid content) of the sealing layer was 1 g / m². 2 ~5g / m 2 It is preferable to do so.

[0063] The sealing properties and curl correction effect of the obtained paper substrate 1 were investigated. The results are shown in Table 2 below. The evaluation criteria for sealing properties are as follows.

[0064] Two mL of a toluene reagent containing dye was dropped onto a re-moistened adhesive coated surface and immediately wiped off, after which the dye bleed-through was evaluated. ○: No dye bleeding through to the back. △: Checked for slight dye bleed-through on the back of the fabric. ×: Dye bleeding through to the back of the fabric.

[0065] Furthermore, after applying the sealing layer 5, the paper substrate 1 was cut into 10 cm squares, and the samples of the paper substrate 1 were suspended under conditions of room temperature 23°C and humidity 50%, and the curl of the four corners of the paper substrate 1 after 10 minutes was evaluated. ○: Has a curl-correcting effect. △: Has a slight curl-correcting effect. ×: No curl-correcting effect

[0066] [Table 1]

[0067] [Table 2]

[0068] The results in Tables 1 and 2 show that the re-wetting adhesive 2 exhibits superior adhesive strength when it is formulated with polyvinyl alcohol with a saponification degree of 88% and a polymerization degree of 500-1800, and esterified tapioca starch (product name: Filmcoat 370, manufactured by Ingredion Japan Co., Ltd.) in a ratio of 100:10 to 100:50, more preferably 100:25 to 100:45.

[0069] Comparative Examples 1-4 show data obtained when polyvinyl alcohol with different degrees of polymerization and application amounts was applied. Polyvinyl alcohol alone consistently exhibited adhesive strengths of 1-3, which were lower than the desired level. Furthermore, as shown in Comparative Example 7, polyvinyl alcohol with a 97% saponification degree also exhibited a weak adhesive strength of 1 even when combined with esterified tapioca starch. This suggests that excessively high saponification of the polyvinyl alcohol increased the film strength of the paper substrate 1, preventing water from penetrating the re-wetting adhesive layer and thus resulting in poor adhesive strength.

[0070] Furthermore, regarding the type of starch, Example 11 shows a mixture of polyvinyl alcohol and corn starch in a ratio of 100:35. The adhesive strength was 3, which was not as strong as that of esterified tapioca starch, but it still met the acceptance criteria for the present invention. In addition, Example 13 shows a mixture of polyvinyl alcohol and etherified tapioca starch in a ratio of 100:35. The adhesive strength was also 3, which was not as strong as that of esterified tapioca starch, but it still met the acceptance criteria for the present invention. From these results, it was found that a mixture of polyvinyl alcohol and esterified tapioca starch exhibits superior adhesive strength.

[0071] This is thought to be because the esterified tapioca starch has excellent thixotropy, allowing the polyvinyl alcohol, which has excellent film-forming properties, and the esterified tapioca starch to remain on the surface of the paper substrate 1, resulting in high coating properties on the surface of the paper substrate 1, and thus strong adhesive strength when reacted with moisture.

[0072] Next, we consider the sealing layer 5. Based on the results in Table 2, the sealing layer made of starch alone is 2.0 g / m². 2 When coated, curl correction was observed, but some dye bleeding through to the back of the fabric was detected.

[0073] On the other hand, when 30 parts by mass of SB latex adhesive and 7 parts by mass of starch were mixed with 100 parts by mass of pigment, the desired results were obtained for both sealing and curl correction. From these results, it was found that the sealing layer 5 mixed in the above proportions is effective for sealing and curl correction. [Industrial applicability]

[0074] This invention can be used as a re-wetting adhesive sheet with excellent adhesion that does not require release paper. [Explanation of Symbols]

[0075] 1...Paper substrate, 2...Re-wetting adhesive, 3...Second sheet, 4...Simulated adhesive layer, 5...Sealing layer, 6...Printing layer, X1~X4...Re-wetting adhesive sheets.

Claims

1. One side of the paper substrate has a re-wetting adhesive layer containing 90% or more by mass of polyvinyl alcohol with a saponification degree of 70% to 90% and starch. In the aforementioned re-wetting adhesive, the composition ratio of the polyvinyl alcohol to the starch is 100:10 to 100:

50. A re-wetting adhesive sheet characterized by the following features.

2. The other side of the paper substrate has a pseudo-adhesive layer, The paper substrate and the second sheet are peelably bonded together via the pseudo-adhesive layer. The re-wetting adhesive sheet according to claim 1.

3. The aforementioned re-wetting adhesive is 5.0 g / m² ２ ~15.0 g / m ２ The aforementioned paper substrate is coated with The re-wetting adhesive sheet according to claim 2.

4. The tensile strength of the aforementioned re-wettable adhesive sheet in a tensile test against liner paper is 1.8 N / 50 mm to 3.0 N / 50 mm. The re-wetting adhesive sheet according to claim 1 or 3.

5. A sealing layer is provided between the paper substrate and the pseudo-adhesive layer, and the sealing layer comprises a pigment, an adhesive, and starch. The re-wetting adhesive sheet according to claim 2.

6. The degree of polymerization of the polyvinyl alcohol is 400 to 2000, and the starch is esterified tapioca starch. The re-wetting adhesive sheet according to claim 2.

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