Pressure-sensitive adhesive paper

Abstract

To provide a pressure-sensitive adhesive paper excellent in print quality and pseudo adhesive strength of an adhesive layer, and less susceptible to a decrease in adhesive strength due to temperature changes over time and during production.SOLUTION: A pseudo-bondable pressure-sensitive adhesive paper having a pressure-sensitive adhesive layer formed on at least one side of a substrate sheet, wherein the pressure-sensitive adhesive layer contains silica particles and a natural rubber-based emulsion, and does not contain an ink-fixing agent or latex.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive paper suitable for use in adhesive postcards, delivery slips, etc., and in particular to a pressure-sensitive adhesive paper having a pressure-sensitive adhesive layer on at least one side of a base sheet, which is pseudo-adhesive and suitable for use in inkjet recording and other recording applications. [Background technology]

[0002] So-called pre-glued inkjet adhesive paper is used for adhesive postcards, delivery slips, and the like. This inkjet adhesive paper has a pressure-sensitive adhesive layer on at least one side of a base sheet, and an image can be recorded on the pressure-sensitive adhesive layer using an inkjet printer. For example, the confidential sides of two sheets of paper, each with a confidential side (pressure-sensitive adhesive layer) on one side, can be pressed together using a press or the like, and then peeled off as needed, allowing the information printed on the confidential side to be viewed. Other types of adhesive paper exist, such as a double-sided type, where the paper is folded in half with the pressure-sensitive adhesive layer on one side facing inward, or a two-sided type, where the paper has pressure-sensitive adhesive layers on both sides and is folded in three in a Z-shape. When the surfaces of the pressure-sensitive adhesive layers are overlapped and pressed together, they adhere (pseudo-adhesion) to such an extent that they can be easily peeled off. The adhesive strength between the surfaces of the pressure-sensitive adhesive layers is appropriately referred to as "pseudo-adhesion."

[0003] A technology has been developed for such pressure-sensitive adhesive layers that, in addition to natural rubber emulsion, also contains lubricants, surfactants, and particulate fillers (silica) of a specified particle size to prevent uneven printing and set-off after pressure bonding (Patent Document 1). Furthermore, a technology has been developed in which latex is added to a natural rubber emulsion as a pressure-sensitive adhesive layer to suppress changes in pseudo-adhesion strength over time (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-025299 [Patent Document 2] Japanese Patent Publication No. 2022-023402 Summary of the Invention [Problem to be solved by the invention]

[0005] However, it has been found that the addition of latex to the pressure-sensitive adhesive layer reduces the print quality on the surface of the pressure-sensitive adhesive layer. Furthermore, it was found that when an ink fixing agent consisting of a cationic polymer or a polyvalent metal salt is added to the pressure-sensitive adhesive layer, the pseudo-adhesive strength fluctuates greatly due to temperature changes during production, such as between summer and winter, and the pseudo-adhesive strength decreases significantly over time.

[0006] In other words, the present invention has been made to solve the above-mentioned problems, and aims to provide pressure-sensitive adhesive paper that has excellent printing quality and pseudo-adhesive strength of the adhesive layer, and that is less susceptible to deterioration in adhesive strength due to temperature changes over time or during manufacturing. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the pressure-sensitive adhesive paper of the present invention is a pseudo-adhesive pressure-sensitive adhesive paper having a pressure-sensitive adhesive layer on at least one side of a base sheet, wherein the pressure-sensitive adhesive layer contains silica particles and a natural rubber emulsion, but does not contain an ink fixative or latex.

[0008] In the pressure-sensitive adhesive paper of the present invention, the silica particles preferably have a pH of more than 7 and 9 or less. In the pressure-bonded paper of the present invention, the oil absorption of the silica particles is preferably 150 to 250 ml / 100 g. [Effects of the Invention]

[0009] According to the present invention, a pressure-sensitive adhesive paper can be obtained which has an adhesive layer with excellent print quality and pseudo-adhesive strength, and which is less susceptible to deterioration in adhesive strength due to temperature changes over time or during production. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a configuration of a pressure-sensitive adhesive paper according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention is not limited to inkjet pressure-sensitive adhesive paper, but is hereinafter described by way of example only. The pressure-sensitive adhesive paper is formed by providing a pressure-sensitive adhesive layer on at least one side of a base sheet.

[0012] 1 shows the structure of pressure-sensitive adhesive paper (inkjet pressure-sensitive adhesive paper) 10 according to an embodiment of the present invention. Pressure-sensitive adhesive paper 10 has a pseudo-adhesive pressure-sensitive adhesive layer 4 provided on at least one surface of a base sheet 2. After inkjet recording is appropriately performed on pressure-sensitive adhesive layer 4, the paper is folded in half with pressure-sensitive adhesive layer 4 on the inside so that the recording on pressure-sensitive adhesive layer 4 is not visible.

[0013] <Pressure-sensitive adhesive layer> The pressure-sensitive adhesive layer contains silica particles and a natural rubber-based emulsion, and does not contain latex.

[0014] <Natural rubber emulsion> The natural rubber emulsion provides pseudo-adhesion to the pressure-sensitive adhesive layer. As the natural rubber emulsion, one or more types can be appropriately selected from natural rubber graft-polymerized with, for example, styrene, styrene-butadiene copolymer, acrylic, acrylonitrile-butadiene copolymer, alkyl (meth)acrylate, etc.

[0015] <Silica particles> The pressure-sensitive adhesive layer contains silica particles as a particulate filler, which improves the color development (density) of inkjet-recorded images and the drying properties of the ink, making it less susceptible to set-off.

[0016] However, if silica is acidic (pH of 7 or less), it may cause the natural rubber emulsion in the pressure-sensitive adhesive layer to deteriorate over time, which may in turn cause the pseudo-adhesion of the pressure-sensitive adhesive layer to change over time (reduction in adhesive strength). Therefore, it is preferable that the pH of the silica particles is greater than 7 and not greater than 9, since the silica becomes neutral or alkaline and deterioration of the natural rubber emulsion over time can be suppressed. The pH of the silica particles is measured by using a pH meter to measure the pH of the liquid (water, etc.) in which the silica particles are dispersed. The silica concentration in the dispersion is set to 20% by weight.

[0017] As the silica, it is particularly preferable to use synthetic amorphous silica, and as the synthetic amorphous silica, gel-process silica is desirable. "Gel-process silica" refers to amorphous silica fine particles synthesized by a wet process, which are obtained by agglomerating primary particles while suppressing their growth by carrying out a neutralization reaction between sodium silicate and a mineral acid (usually sulfuric acid) in the pH range of 7 to 9. Compared to precipitated silica (manufactured by neutralizing sodium silicate and mineral acid in an alkaline pH range), gel silica has a longer reaction time after aggregation, stronger bonds between primary particles, and tends to have a larger pore volume, which results in better ink absorption and abrasion resistance in printed areas.

[0018] The amount of silica particles blended is, for example, 50 to 200 parts by mass, and more preferably 80 to 150 parts by mass, per 100 parts by mass of the natural rubber emulsion in the pressure-sensitive adhesive layer.

[0019] The silica particles preferably have a 90% volume average particle size (D90) of 20 to 60 μm. If the D90 of the silica particles is less than 20 μm, the adhesive strength may decrease. If the D90 of the silica particles is more than 50 μm, the surface strength may decrease. The D90 of the silica particles is more preferably 25 to 55 μm, and even more preferably 30 to 50 μm. The D90 of the silica particles can be measured using a MASTER SIZER S manufactured by MALVERN using a laser diffraction method, and is measured in a state where the silica particles are dispersed in water.

[0020] The oil absorption of the silica particles is preferably 150 to 250 ml / 100 g, and more preferably 170 to 240 ml / 100 g. If the oil absorption is less than 150 ml / 100 g, the ink-receiving layer may not be able to retain ink sufficiently, and the abrasion resistance and ink absorbency of the printed area may be poor.

[0021] On the other hand, if the oil absorption exceeds 250 ml / 100 g, the viscosity of the paint increases when dispersing the pigment, which can lead to poor paint dispersibility. Also, after coating, the adhesive tends to remain near the surface, making it susceptible to the effects of external factors (light, temperature, humidity, etc.), which can lead to a decrease in pseudo-adhesion strength over time. The oil absorption can be measured by the method specified in JIS-K5101.

[0022] The pore volume of the silica particles is preferably 0.8 to 1.5 ml / g, and more preferably 1.0 to 1.4 ml / g. If the pore volume is less than 0.8 ml / g, the ink-receiving layer may not be able to retain ink sufficiently, and the abrasion resistance and ink absorbency of the printed area may be poor.

[0023] On the other hand, if the pore volume exceeds 1.5 ml / g, the viscosity of the paint increases when dispersing the pigment, which can lead to poor paint dispersibility. Furthermore, although the paint is more likely to adsorb the adhesive, the amount of adhesive adsorbed can vary depending on the temperature and time from preparation to application, making it difficult to ensure stable adhesive strength. Furthermore, after coating, the adhesive tends to remain near the surface and is easily affected by the outside air (light, temperature, humidity, etc.), which may result in a decrease in the pseudo-adhesive strength over time. The pore volume can be measured by a method specified in the nitrogen adsorption method.

[0024] <Latex> The pressure-sensitive adhesive layer does not contain latex, since the addition of latex to the pressure-sensitive adhesive layer reduces the print quality on the pressure-sensitive adhesive layer surface. Generally, the latex functions as a binder. Examples of latex include latexes of various copolymers such as styrene-butadiene copolymers, styrene-acrylic copolymers, ethylene-vinyl acetate copolymers, and butadiene-methyl methacrylate copolymers.

[0025] <Ink fixing agent> The pressure-sensitive adhesive layer does not contain an ink fixative made of a cationic polymer or polyvalent metal salt. If a cationic polymer or polyvalent metal salt (ink fixative) is added to the pressure-sensitive adhesive layer, the pseudo-adhesive strength fluctuates greatly with temperature changes during manufacturing, and the pseudo-adhesive strength decreases significantly over time. Generally, cationic polymers and polyvalent metal salts are added to bind with anionic dyes such as direct dyes or acid dyes contained in the water-soluble ink to firmly immobilize them (ink fixation).

[0026] Examples of cationic polymers include polyamines, polyallylamines, dicyandiamide condensates, polydimethyldiallylammonium, polyethyleneimines, and epichlorohydrin derivatives. Examples of polyvalent metal salts include calcium and magnesium hydrochlorides, nitrates, sulfates, lactates, and the like.

[0027] <Binder> The pressure-sensitive adhesive layer may contain 10 to 50 parts by mass, more preferably 20 to 40 parts by mass, of a binder other than latex per 100 parts by mass of the natural rubber emulsion in the pressure-sensitive adhesive layer. The inclusion of a binder can prevent the coating layer from powder falling off during printing and pressure bonding.

[0028] Specific examples of binders include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, terminal alkyl-modified polyvinyl alcohol, and ethylene vinyl alcohol; cellulose ethers such as hydroxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose, and derivatives thereof; and precipitates. Examples of suitable emulsions include starches such as flour, enzyme-modified starch, thermochemically modified starch, oxidized starch, esterified starch, etherified starch (e.g., hydroxyethylated starch), and cationized starch; water-soluble polymers such as polyvinyl acetal, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid copolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein; and emulsions of hydrophobic polymers such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, and ethylene / vinyl acetate copolymer. In particular, polyvinyl alcohols are excellent in terms of surface strength and suitability for inkjet printing.

[0029] <Stilt agent> The pressure-sensitive adhesive layer may contain 0 to 50 parts by mass of a tilting agent per 100 parts by mass of the natural rubber emulsion in the pressure-sensitive adhesive layer. The tilting agent has the effect of preventing adhesion due to pressure (unintentional pressure) other than that required to make the adhesive layer bondable to the adherend. As the stilt agent, pulp powder, raw starch powder, plastic pigment, etc. can be used.

[0030] <Lubricant (wax)> The pressure-sensitive adhesive layer may contain 0.1 to 0.6 parts by mass of a lubricant per 100 parts by mass of the natural rubber emulsion. If the lubricant content is less than 0.1 parts by mass, when the inkjet pressure-sensitive paper is pressed using a press such as a mail sealer during the pressing process, the pressure-sensitive adhesive layer may be rubbed by the pressing roll of the press and accumulate on the pressing roll, resulting in "roll contamination." The roll contamination causes problems such as the need to clean the roll, which reduces workability, and the pressure-sensitive adhesive layer deposited on the pressure roll is transferred to the pressure-sensitive paper, which then becomes contaminated. On the other hand, if the content of the above-mentioned lubricant exceeds 0.6 parts by mass, set-off may occur. In addition, the adhesive tends to remain near the surface after coating, making it susceptible to the effects of the outside air (light, temperature, humidity, etc.), which may also affect the reduction in pseudo-adhesion strength over time.

[0031] In the case of two-ply (double-page spread) laminated paper with a single-side coating, the surface that comes into contact with the press machine's compression roll is the side of the base sheet opposite the pressure-sensitive adhesive layer, so the problem of roll contamination does not occur. On the other hand, in the case of Z-fold double-page spread laminated paper, the pressure-sensitive adhesive layer is provided on both sides of the base sheet, so the surface that comes into contact with the press machine's compression roll is the coated side (the side with the pressure-sensitive adhesive layer). As a result, the pressure-sensitive adhesive layer is removed and accumulated on the compression roll, causing the problem of roll contamination.

[0032] As the lubricant, derivatives of higher fatty acids such as stearic acid, lauric acid, octylic acid, etc. Examples of the derivatives include metal salts of calcium, magnesium, zinc, etc., and amide derivatives. In the present invention, it is preferable to use a lubricant in which the higher fatty acid is stearic acid and the derivative is a calcium salt, zinc salt, or amide derivative, i.e., calcium stearate, zinc stearate, or amide stearic acid, because this makes it possible to effectively suppress the occurrence of roll contamination and set-off.

[0033] <Surfactant> The pressure-sensitive adhesive layer preferably contains 0.3 to 2.5 parts by mass, and more preferably 0.5 to 2.3 parts by mass, of a surfactant per 100 parts by mass of the natural rubber emulsion. If the surfactant content is less than 0.3 parts by mass per 100 parts by mass of the natural rubber emulsion in the pressure-sensitive adhesive layer, the set-off described above may occur, or the ink may dry poorly after inkjet recording on the pressure-sensitive adhesive layer.If the surfactant content is 2.5 parts by mass or more, printing unevenness may occur when inkjet recording is performed on the pressure-sensitive adhesive layer.

[0034] As the surfactant, a nonionic surfactant can be suitably used, and examples thereof include ester-type surfactants such as glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, etc., ether-type surfactants such as fatty alcohol ethoxylates, polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, alkyl glycosides, etc. In the present invention, the use of an ether-type nonionic surfactant is preferred because it makes it possible to effectively suppress the occurrence of set-off and printing unevenness, and polyoxyalkylene alkyl ethers are more preferred.

[0035] If necessary, various auxiliary agents such as pigment dispersants, thickeners, water retention agents, antifoaming agents, foam inhibitors, release agents, preservatives, water-resistant agents, and pH adjusters may be added to the pressure-sensitive adhesive layer in an amount of approximately 0 to 50 parts by mass per 100 parts by mass of the natural rubber emulsion in the pressure-sensitive adhesive layer.

[0036] <Base sheet> The base sheet is not particularly limited as long as it is in sheet form and may be fine paper, coated paper, recycled paper, synthetic paper, or the like.

[0037] When the base sheet is paper, the main components of the paper are pulp and internal fillers. Any commonly known pulp can be used. For example, chemical pulp can be used, such as bleached hardwood kraft pulp, unbleached hardwood kraft pulp, bleached softwood kraft pulp, unbleached softwood kraft pulp, bleached hardwood sulfite pulp, unbleached hardwood sulfite pulp, bleached softwood sulfite pulp, unbleached softwood sulfite pulp, or pulp produced by chemically treating fibrous materials such as wood, cotton, hemp, and bast. Other examples include ground wood pulp, which is mechanically pulped from wood or chips; chemimechanical pulp, which is mechanically pulped after impregnating wood or chips with a chemical solution; and thermomechanical pulp, which is pulped in a refiner after cooking chips until slightly soft. For the bonded paper of the present invention, bleached hardwood kraft pulp, which has high brightness and excellent formation, is preferably used.

[0038] Pulp made from waste paper, i.e., pulp obtained by disintegrating unprinted waste paper such as offcuts, broken sheets, and width-reduced white, extra white, medium white, and white damage generated in bookbinding, printing factories, cutting shops, etc.; high-quality printed waste paper such as fine paper and fine coated paper that has been printed or copied; waste paper written on with water-based ink, oil-based ink, or pencil; waste newspaper including printed flyers on fine paper, fine coated paper, medium paper, medium coated paper, etc.; medium paper, medium coated paper, sawn paper, etc., can also be used.

[0039] As the internal filler, known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers can be used. In the present invention, the inclusion of a filler (internal filler) improves the smoothness, opacity, whiteness, etc. of the base paper, but reduces the interlaminar strength of the resulting base paper. Therefore, in the present invention, the filler is an optional component, and the filler content must be determined taking these properties into consideration; it is preferable that the base paper does not contain a filler. Whether or not the base paper contains a filler (for example, an inorganic substance) can be determined by examining the presence or absence of inorganic substances in the paper layer through SEM analysis or elemental analysis of the cross section of the base paper.

[0040] Furthermore, whether or not the base paper contains a filler (for example, an inorganic internal filler) is correlated with the interlayer strength of the base paper, as will be described later. The reason for this is that the incorporation of internal fillers physically inhibits the bonding of fibers, thereby reducing the interlayer strength of the paper. If the interlayer strength of the paper is weaker than the pseudo-adhesion force of the pressure-sensitive adhesive layer, the paper surface will be destroyed when peeled off. Therefore, when the base sheet is paper, it is preferable that it does not contain fillers. By increasing the interlayer strength of the base paper by eliminating fillers, the interlayer strength of the paper becomes higher than the pseudo-adhesion force, and peeling of the base paper layer can be suppressed during peeling.

[0041] The basis weight of the base sheet is not particularly limited, but is preferably in the range of 60 to 200 g / m², taking into consideration that it will be processed into laminated paper. When applying this invention to laminated postcards, the specific basis weight is selected so as to satisfy the postcard weight standards in the Postal Act, and is set so that the weight when made into a laminated postcard is in the range of 2 to 6 g.

[0042] In the pressure-sensitive adhesive paper according to an embodiment of the present invention, the adhesive force between the pressure-sensitive adhesive layer and the base sheet is greater than the pseudo-adhesion force. Therefore, the pressure-sensitive adhesive paper according to the embodiment of the present invention can be suitably used as inkjet pressure-sensitive adhesive paper for confidential postcards, delivery slips, etc. Furthermore, confidential postcards manufactured using this inkjet pressure-sensitive adhesive paper are less expensive than confidential postcards that are pseudo-adhesive by laminating an expensive resin film instead of a pressure-sensitive adhesive layer.

[0043] <Production of pressure-sensitive adhesive paper> The pressure-sensitive adhesive paper according to the embodiment of the present invention can be manufactured, for example, as follows. First, a coating material (pressure-sensitive adhesive composition) that will become the pressure-sensitive adhesive layer is prepared by mixing the above-mentioned agents. Then, the coating material is applied to at least one surface of the substrate sheet to form a pressure-sensitive adhesive layer. As a coating method, the coating material may be applied to the substrate sheet by a conventional coating method such as a bar blade coater, bent blade coater, curtain coater, or air knife coater.

[0044] The coating amount of the pressure-sensitive adhesive layer after drying is preferably 3 to 9 g / m per side. 2 , more preferably 4 to 8 g / m 2 is. If the coating weight is too low, the pseudo-adhesion strength is low, and the print quality is poor in set-off and print drying properties. Increasing the coating weight increases the pseudo-adhesive strength, but the print density becomes weaker and the barcode readability deteriorates. Therefore, the coating weight of the pressure-sensitive adhesive layer is set to 3 to 9 g / m per side. 2 By doing so, it is possible to ensure both print quality and pseudo-adhesive strength. After coating, the paper may be dried at a paper surface temperature of about 40°C to 120°C so that the natural rubber does not deteriorate due to heat.

[0045] By applying the paint to the substrate sheet and drying it, the adhesive strength (interlayer strength) between the pressure-sensitive adhesive layer and the substrate sheet after the paint has dried increases. On the other hand, the pseudo-adhesion strength when the surfaces of the pressure-sensitive adhesive layers are overlapped and pressed together after the paint has dried is set to be smaller than the interlayer strength. [Example]

[0046] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the examples, "parts" and "%" represent "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0047] [Example 1] (Preparation of base paper) A mixture of 80 parts by mass of hardwood kraft pulp (LBKP) with a Canadian standard freeness (CSF) of 400 ml and 20 parts by mass of softwood kraft pulp (NBKP) with a Canadian standard freeness (CSF) of 500 ml was used to prepare the raw pulp. A 1.0 part by mass cationic starch strength agent was added to 100 parts by mass of the raw pulp. Subsequently, 1.0 part by mass of aluminum sulfate, 0.5 part by mass of a wet strength agent, and 1.0 part by mass of an acidic sizing agent were added. The resulting paper was then made using a Fourdrinier paper machine to a basis weight of 110 g / m. 2 The base paper was obtained. The coating amount after drying is 6.0 g / m per side on both sides of the base paper. 2 A pressure-sensitive adhesive layer coating material having the following composition was applied using an air knife coater and then dried to prepare inkjet adhesive paper.

[0048] <Coating for pressure-sensitive adhesive layer> Natural rubber-acrylic copolymer emulsion (product name: Saivinol N-900, manufactured by Saiden Chemical Co., Ltd.): 100 parts Synthetic amorphous silica (gel-process silica, trade name: Carplex BS308N, average particle size (D50): 10.0 μm, (D90): 38.7 μm, pH: 8.1, oil absorption: 215 ml / 100 g, manufactured by EVONIK): 100 parts Binder (polyvinyl alcohol, product name: PVA-117, manufactured by Kuraray Co., Ltd.): 30 parts Lubricant (calcium stearate, product name: SN Coat 246, manufactured by San Nopco): 0.2 parts Nonionic surfactant (polyoxyalkylene alkyl ether, product name: LX106, manufactured by Kao Corporation): 2 parts Antifoaming agent (trade name: DF-480, manufactured by San Nopco): 0.5 parts

[0049] [Example 2] Inkjet adhesive paper was prepared in the same manner as in Example 1, except that the synthetic amorphous silica in the coating material for the pressure-sensitive adhesive layer was changed to Mizukasil P-50 (gel-method silica, average particle size: (D50): 10.0 μm, (D90): 35.0 μm, pH: 7.3, oil absorption: 170 ml / 100 g, manufactured by Mizusawa Chemical Industries).

[0050] [Comparative Example 1] Inkjet adhesive paper was prepared in the same manner as in Example 1, except that the synthetic amorphous silica in the coating material for the pressure-sensitive adhesive layer was changed to Syloid ED (gel-process silica, average particle size: (D50): 8.0 μm, (D90): 16.1 μm, pH: 5.3, oil absorption: 215 ml / 300 g, manufactured by Grace).

[0051] Comparative Example 2 Inkjet adhesive paper was prepared in the same manner as in Example 1, except that the synthetic amorphous silica in the coating material for the pressure-sensitive adhesive layer was changed to Syloid C-809 (gel-process silica, average particle size: (D50): 9.0 μm, (D90): 16.9 μm, pH: 3.4, oil absorption: 320 ml / 100 g, manufactured by Grace).

[0052] Comparative Example 3 Inkjet pressure-sensitive adhesive paper was prepared in the same manner as in Example 1, except that the synthetic amorphous silica in the coating material for the pressure-sensitive adhesive layer was changed to Nipgel AY-603 (gel-method silica, average particle size: (D50): 4.2 μm, (D90): 14.7 μm, pH: 7.0, oil absorption: 290 ml / 100 g, manufactured by Tosoh Silica Corporation).

[0053] Comparative Example 4 Inkjet adhesive paper was prepared in the same manner as in Example 1, except that the synthetic amorphous silica in the coating material for the pressure-sensitive adhesive layer was changed to Nipgel CX-200 (gel-method silica, average particle size: (D50): 6.0 μm, (D90): 30.8 μm, pH: 7.0, oil absorption: 115 ml / 100 g, manufactured by Tosoh Silica Corporation).

[0054] Comparative Example 5 An inkjet pressure-sensitive adhesive paper was prepared in the same manner as in Example 1, except that 1.0 part of magnesium sulfate, a polyvalent metal salt, was added to the coating material for the pressure-sensitive adhesive layer.

[0055] Comparative Example 6 An inkjet pressure-sensitive adhesive paper was produced in the same manner as in Example 1, except that the binder in the coating material for the pressure-sensitive adhesive layer was changed to SB latex (product name: PA0330, manufactured by Nippon A&L Co., Ltd.).

[0056] The inkjet pressure-sensitive adhesive papers obtained in the above Examples and Comparative Examples were evaluated by the following methods, and the evaluation results are shown in Table 1.

[0057] <Initial adhesive strength (pseudo adhesive strength)> To measure the pseudo-adhesion strength of the resulting inkjet pressure-sensitive adhesive paper, the pressure-sensitive adhesive paper was left in an environment of 23°C and 50% RH for more than 24 hours, and then three sheets of inkjet pressure-sensitive adhesive paper (100 mm wide, 148 mm long) were stacked and pressed together using a press (Duplo Mail Sealer MS6100). In this evaluation, in order to achieve the target adhesive strength (130 to 200 gf / 25 mm), measurements were taken on samples processed with the above press machine gap set to "sealer gap 33" (pressing roll spacing 280 μm).

[0058] Immediately after pressure bonding, one of the top layers of the three bonded inkjet pressure-sensitive papers was peeled off by hand, and strip-shaped test pieces 25 mm wide and 148 mm long were cut out from the remaining two inkjet pressure-sensitive papers so that their longitudinal direction was perpendicular to the flow direction (i.e., perpendicular to the paper-making direction of the base paper that serves as the support), and a T-peel test was performed at a tensile speed of 300 mm / min. If the adhesive strength is 130 to 200 gf / 25 mm, peeling will not occur unless necessary, and a good pseudo-adhesion state will be obtained in which damage to the paper surface is unlikely to occur upon peeling. In particular, if the adhesive strength is 150 to 180 gf / 25 mm, damage to the paper surface will not occur upon peeling, and good releasability is achieved, which is preferable. The evaluation was based on the following indicators. 〇:150~180gf / 25mm △: 130-200gf / 25mm, other than 150-180gf / 25mm ×: Less than 130gf / 25mm, more than 200gf / 25mm

[0059] The reason three sheets of pressure-sensitive adhesive paper were used is that it is assumed that the package will be opened by folding it in two and opening it in a Z. The reason for measuring the peel test with two sheets is that in the T-peel test, the package is pulled left and right in a T-shape (Y-shape) to peel it off, so by making the number of stacked sheets an even number and making the number of sheets on each side the same, differences in stiffness between the left and right sides are prevented during the test. In addition, when opening a double-sided package, it is assumed that the package is opened by turning it over along the short side of a postcard or the like, and the peel test was carried out in a direction perpendicular to the flow direction.

[0060] <Stability of adhesive strength due to temperature during manufacturing (preparation)> The paints for the pressure-sensitive adhesive layer were prepared while adjusting the paint temperature to 10°C and 30°C, respectively, and the temperature was maintained for 24 hours after preparation before coating. The adhesive strength was measured for inkjet pressure-sensitive adhesive paper under the two temperature conditions mentioned above. Generally, the higher the temperature during production, the more the reaction between the adhesive and cationic substances progresses, forming larger lumps that tend to remain on the surface of the paper after coating, resulting in higher adhesive strength. Therefore, if there are fewer substances that react with the adhesive, there will be less variation due to the production temperature, and therefore there will be less change in adhesive strength and greater stability.

[0061] For this reason, the stability of adhesive strength was evaluated using the following index. The stability of adhesive strength is defined as "{adhesive strength of manufactured product at 10°C (gf / 25mm) / adhesive strength of manufactured product at 30°C (gf / 25mm)} x 100", and if the stability of adhesive strength is 75% or more, there is no problem in practical use. ○: Stability of adhesive strength is over 90% △: Stability of adhesive strength is 90% or less, 75% or more (level that does not cause problems in practical use) ×: Stability of adhesive strength is less than 75% (unusable level)

[0062] <Deterioration of adhesive strength over time> The inkjet pressure-sensitive adhesive paper obtained was left for one month in an environment of 23°C and 50% humidity, and the ratio (%) of the adhesive strength before leaving it (initial adhesive strength) was calculated as the adhesive strength retention rate. If the adhesive strength retention rate is 75% or more, there is no problem in practical use. ○: Retention rate over 90% △: Maintenance rate below 90%, above 75% (no problem in actual use) ×: Maintenance rate less than 75% (unusable level)

[0063] <Print density> The resulting inkjet pressure-sensitive paper was left in an environment of 23°C and 50% RH for at least 24 hours, after which a 2cm square solid image was printed in each of the four colors (black, cyan, magenta, and yellow) on the pressure-sensitive adhesive layer of the inkjet pressure-sensitive paper (10cm wide, 15cm long) using a commercially available pigment inkjet printer (Epson PX-405A, four-color ink, printing mode: plain paper / standard). After 24 hours, the print density was measured using a Macbeth densitometer (RD-914, manufactured by Macbeth Co., Ltd.). If the total of the four colors is 4.4 or higher, the print density is good.

[0064] <Set-off> The resulting inkjet pressure-sensitive paper was left in an environment of 23°C and 50% RH for at least 24 hours, after which a 2 cm square solid image was printed in black on the pressure-sensitive adhesive layer of the inkjet pressure-sensitive paper (10 cm wide, 15 cm long) using a commercially available pigment inkjet printer (EPSON PX-405A, 4-color ink). After one hour, two sheets of unprinted inkjet adhesive paper (10 cm wide, 15 cm long) were placed on top of the printed surface of the inkjet adhesive paper using a press (Duplo Mail Sealer MS6100, gap setting 33 (estimated value above)) and pressed together. The occurrence of set-off (transfer of ink to the unprinted pressure-sensitive adhesive layer) when peeled off after one hour was measured using a color difference meter (L*, a*, b*) and evaluated using ΔE (before and after ink transfer). A ΔE of 8 or less is considered to be acceptable for practical use. ○: ΔE is less than 5 △: ΔE is 5 or more and 8 or less (level that does not cause problems in actual use) ×: ΔE exceeds 8 (unusable level)

[0065] <Barcode reading suitability> Black ink from a commercial inkjet printer (MJP30A, manufactured by Miyakoshi Co., Ltd.) was filled into the ink cartridge of an Epson printer PX-405A, and a barcode (CODE39) was printed using the Epson printer PX-405A. The printed barcode (GS1-128) was then evaluated using a barcode reader (Quick Check PC600, manufactured by Nippon Systex Co., Ltd.). The evaluation was carried out according to the ANSI grade (CEN method, 10 measurements). Evaluations of ◎, ○, and △ indicate that there is no problem in practical use. ◎: 8 or more B or higher grades (A and B grades) ○: 8 or more times of C or higher △: Eight or more times of D or higher judgement (no problem in actual use) ×: Less than 8 times of D or higher rating (unusable level)

[0066] [Table 1]

[0067] As can be seen from Table 1, in each example, the pressure-sensitive adhesive layer had excellent initial adhesive strength, little decrease in adhesive strength over time, and excellent stability of adhesive strength despite temperature changes during production. Furthermore, set-off and uneven printing were prevented, resulting in excellent inkjet suitability.

[0068] In Comparative Examples 1 to 3, where the pH of the silica particles in the pressure-sensitive adhesive layer was 7 or less, the stability of adhesive strength with temperature during manufacturing was poor. This is because the adhesive in the pressure-sensitive adhesive layer is generally a substance with a pH of 11 or higher, and reacts with acidic substances. When the reaction proceeds with silica, which is an acidic substance with a pH of 7 or less, it forms large clumps (aggregates), making it easier for the adhesive to remain on the surface of the paper after coating, increasing adhesive strength. Therefore, it is thought that the degree of reaction changes significantly when the temperature and time during manufacturing change, resulting in poor stability of adhesive strength with temperature during manufacturing. In particular, in Comparative Examples 1 and 2, in which the pH of the silica particles in the pressure-sensitive adhesive layer was less than 7, the adhesive strength of the pressure-sensitive adhesive layer also decreased significantly over time. This is thought to be because the acidity of the silica particles caused the natural rubber emulsion in the pressure-sensitive adhesive layer to deteriorate over time.

[0069] In Comparative Example 4, in which the oil absorption of the silica particles in the pressure-sensitive adhesive layer was 150 to less than 250 ml / 100 g, the initial adhesive strength and print quality (set-off, barcode readability) of the pressure-sensitive adhesive layer were poor. This was because the silica particles did not have sufficient ink-retaining ability in the ink-receiving layer, resulting in poor set-off and barcode readability. Furthermore, the adhesive agent and other ingredients tended to sink into the paper during coating, resulting in less adhesive in the surface layer and possibly lowering the adhesive strength.

[0070] In Comparative Example 5, in which the pressure-sensitive adhesive layer contained an ink fixer made of a polyvalent metal salt, the stability of adhesive strength with temperature during manufacturing was poor. This is because, as mentioned above, the higher the manufacturing temperature, the more the reaction between the adhesive agent and the cationic substance etc. progresses, resulting in higher adhesive strength. As a result, it is thought that the degree of reaction changes significantly when the temperature or time during manufacturing is changed, resulting in poor stability of adhesive strength with temperature during manufacturing.

[0071] In the case of Comparative Example 6, in which latex was contained in the pressure-sensitive adhesive layer, the print quality (set-off, bar code readability) was poor, which is thought to be because the latex inhibited ink absorption. [Explanation of symbols]

[0072] 2 Base sheet 4 Pressure-sensitive adhesive layer 10. Pressure-sensitive adhesive paper (pressure-sensitive adhesive paper for inkjet printers)

Claims

1. A pseudo-adhesive pressure-sensitive adhesive paper having a pressure-sensitive adhesive layer on at least one side of a base sheet, The pressure-sensitive adhesive layer contains silica particles and a natural rubber emulsion, and does not contain an ink fixative or latex.

2. The pressure-sensitive adhesive paper of claim 1 , wherein the silica particles have a pH greater than 7 and not greater than 9.

3. The pressure-sensitive adhesive paper according to claim 1 or 2, wherein the oil absorption of the silica particles is 150 to 250 ml / 100 g.

4. The pressure-sensitive adhesive paper according to claim 1 or 2, wherein the pore volume of the silica particles is 0.8 to 1.5 ml / g.

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