JP7716864B2 - Water-degradable tack paper - Google Patents

Description

The present invention relates to water-disintegrable tack paper.

With a view to promoting the creation of a sustainable, recycling-oriented society, efforts have long been made to recycle various types of paper as waste paper. Regarding paper recycling, the Waste Paper Recycling Promotion Center, a public interest incorporated foundation, has established waste paper quality standards, which state that waste paper destined for recycling must not contain any prohibited items. An example of a prohibited item is adhesive sheets (Patent Document 1). These adhesive sheets are classified as prohibited items because they contain adhesive elements (adhesive). However, if the adhesive elements are removed from the paper, the paper can be recycled as waste paper.

Among adhesive sheets, tack paper, which is used for coated printing paper (pigment coated paper, cast coated paper, etc.) classified as high-quality recycled paper, is of high quality and highly useful as its main raw material is high-brightness bleached kraft pulp. Establishing technology to recycle tack paper into deinked pulp, WP, etc. would enable advanced utilization of recycled paper and would also be desirable from the perspective of promoting the creation of a sustainable, recycling-oriented society.

As one technique for removing adhesive elements from paper, Patent Document 2 proposes a technology related to a water-dissociable adhesive composition. This water-dissociable adhesive composition has excellent adhesive properties, and changes in adhesive properties and redispersibility over time are minimal even in humid and hot environments. It also claims that the adhesive layer redisperses in water at an appropriate size, does not pollute water quality, and does not adversely affect the performance of recycled paper.

Patent Document 3 proposes an invention related to a warm-water peelable label as a technology for peeling off paper attached to containers. The warm-water peelable label has strong adhesive strength to various containers, and does not peel off due to impacts or abrasions during transportation, nor does it peel off when wet with rain. Furthermore, when collecting the label, it can be easily peeled off by washing it with warm water at approximately 60-80°C for several tens of seconds.

Patent Document 4 proposes technology related to an alkali-soluble adhesive composition. The alkali-soluble adhesive composition can be used for tack paper, adhesive tape, etc., and can be easily disintegrated in alkaline water when repulped for the purpose of resource conservation.

Japanese Patent Application Laid-Open No. 2002-338909 Japanese Patent Application Publication No. 11-140407 Japanese Patent Application Laid-Open No. 2002-140008 Japanese Patent Application Publication No. 5-156222

However, the technology of Patent Document 2 uses high-quality paper or kraft paper as the base paper, which contains as little inorganic papermaking particles as possible, such as calcium carbonate or clay (also known as kaolin), in order to change the balance between the adhesive strength and cohesive strength of the adhesive over time. Considering that calcium carbonate and clay promote the hydrolysis of the adhesive, the adhesive layer does not easily hydrolyze during disintegration. The technology of Patent Document 3 disintegrates the adhesive with warm water, and it cannot be disintegrated with unheated water, such as that used in paper mill wastepaper recycling processes. From a recycling perspective, the cost of preparing warm water is high, making it uneconomical. The technology of Patent Document 4 disintegrates the adhesive with pH-adjusted alkaline water, and the used alkaline water must be neutralized and discharged into the environment, resulting in cumbersome wastewater treatment.

The problem to be solved by this invention is to provide a tack paper in which the adhesive layer is easily hydrolyzed even in water that has not been heated or pH adjusted, and a method for producing the same.

The inventors conducted extensive research, taking into consideration the properties of the adhesive layer, such as its dispersibility and water-disintegrability, and selected a base paper suitable for the easy water-disintegrability of the adhesive layer, thereby solving the above-mentioned problems. As a result, the following aspects of the invention were completed.

[First Aspect]
a composite paper having an inorganic pigment layer provided on one side of a base paper;
The composite paper has an adhesive layer provided on one side thereof,
The base paper contains calcium carbonate in addition to pulp,
The pulp is contained in an amount of 50 to 90 parts by mass per 100 parts by mass of the base paper,
the pressure-sensitive adhesive layer has a composition containing a copolymer of an acrylic acid ester monomer and a functional group-containing monomer, a nonionic surfactant, a neutralizing agent, and a fatty acid soap;
The composite paper contains 10 to 30% by mass of calcium carbonate.
A water-dissolvable tack paper characterized by:

The acrylic ester monomer, which is the adhesive component, has a carboxyl group in its composition. If this carboxyl group chemically reacts with calcium carbonate or clay, the adhesive strength of the acrylic ester monomer may decrease. For this reason, efforts have been made to develop technologies for adhesive sheets with a relatively low calcium content, as disclosed in Patent Document 1.

In this embodiment, the inventors focused on the reactivity between acrylic ester monomers and calcium carbonate and discovered that adjusting the calcium carbonate content can produce tack paper with the desired adhesive strength and water-disintegrability. In this embodiment, an adhesive layer having a composition containing acrylic ester monomers is provided on one side of composite paper containing a specific amount of calcium carbonate, so the adhesive strength of the adhesive layer to the composite paper weakens over time compared to the inherent adhesive strength of the acrylic ester monomers. Therefore, when the tack paper of this embodiment is disintegrated in water, the adhesive layer easily separates from the composite paper.

The adhesive layer of this tack paper is easily hydrolyzed even when the water used for disintegration is not heated. This is presumably because the fatty acid soap that makes up the adhesive layer has low hydrolysis resistance and therefore is hydrolyzed in water.

The tack paper of this embodiment is easily disintegrated even in water that has not been pH-adjusted. This is because the neutralizing agent that is a component of the adhesive layer has high redispersibility, making it easily hydrolyzable in water.

[Second Aspect]
a composite paper having inorganic pigment layers provided on both sides of a base paper;
an adhesive layer provided on one surface of the composite paper;
The base paper contains calcium carbonate in addition to pulp,
The pulp is contained in an amount of 50 to 90 parts by mass per 100 parts by mass of the base paper,
the pressure-sensitive adhesive layer has a composition containing a copolymer of an acrylic acid ester monomer and a functional group-containing monomer, a nonionic surfactant, a neutralizing agent, and a fatty acid soap;
The composite paper contains 10 to 30% by mass of calcium carbonate.
A water-dissolvable tack paper characterized by:

In this embodiment, the adhesive layer is provided on one side of the composite paper, and the calcium carbonate reduces the adhesiveness of the adhesive layer over time, allowing the adhesive layer to be easily separated from the composite paper during disintegration.

[Third Aspect]
The thickness of the pressure-sensitive adhesive layer is 10 to 30 μm.
The water-decomposable tack paper according to the first or second embodiment.

When the thickness of the adhesive layer is within the above range, the adhesive strength of the side of the adhesive layer opposite the side facing the base paper, i.e., the side that is attached to the object to be attached, will be relatively strong. The reason for this is not clear, but it is thought that this is probably because the part of the adhesive layer facing the base paper is more likely to react with the calcium carbonate contained in the base paper, while the part facing the object to be attached is further away from the base paper in the thickness direction and is less likely to react with calcium carbonate.

[Fourth Aspect]
The adhesive strength of the pressure-sensitive adhesive layer is 8 to 25 N/25 mm.
The water-decomposable tack paper according to any one of the first to third aspects.

With this type of water-degradable tack paper, the tack paper will not naturally roll up or peel off once it has been attached to an object, and when you try to peel it off by pinching the edge of the tack paper, part of the tack paper will remain on the object and will not tear.

[Fifth Aspect]
The content of each component in 100 parts by mass of the composition is 35 to 65 parts by mass of the acrylic acid ester monomer, 10 to 35 parts by mass of the functional group-containing monomer, 25 to 40 parts by mass of the nonionic surfactant, 1 to 4 parts by mass of the neutralizing agent, and 1 to 5 parts by mass of the fatty acid soap.
The water-decomposable tack paper according to any one of the first to fourth aspects.

When the acrylic acid ester monomer content of the water-dissolvable tack paper is within the above-mentioned range, and the functional group-containing monomer content and nonionic surfactant content are within the above-mentioned ranges, the adhesive layer is significantly more hydrolyzable in water. Furthermore, when the acrylic acid ester monomer, functional group-containing monomer, and nonionic surfactant content of the water-dissolvable tack paper are within the above-mentioned ranges, and the neutralizer content and fatty acid soap content are within the above-mentioned ranges, the adhesive layer is extremely easily hydrolyzed in water that has not been heated or pH adjusted.

[Sixth Aspect]
The composite paper has a basis weight of 70 to 100 g/m ² and a paper thickness of 75 to 120 μm.
The water-decomposable tack paper according to any one of the first to fifth aspects.

The water-disintegrable tack paper of this embodiment is less likely to tear when applied or removed, is easy to grasp at the edges, and is easy to handle. It also disperses easily into particles of an appropriate size when disintegrated in water, making it easy to disintegrate in water.

[Seventh Aspect]
The composite paper contains 7 to 15% by mass of kaolin.
The water-decomposable tack paper according to any one of the first to sixth aspects.

In the case of the water-decomposable tack paper of this embodiment, even if the adhesive dissolves during water decomposition in a pulper facility in a paper factory and residual components remain, since the paper contains a specific amount of kaolin, which has high oil absorption properties,
The kaolin has the effect of adsorbing the remaining components of the adhesive and discharging them outside the system, thereby enabling the water-decomposable tack paper to be more efficiently recycled as waste paper.

[Eighth Aspect]
The inorganic pigment layer contains kaolin and calcium carbonate.
The water-decomposable tack paper according to any one of the first to seventh embodiments.

Because the inorganic pigment layer contains kaolin and calcium carbonate, the adhesive strength of this water-disintegrable tack paper decreases over time, and when the water-disintegrable tack paper is disintegrated, the adhesive layer is easily separated from the base paper due to the action of kaolin, which has excellent oil absorption properties.

The present invention provides a water-disintegrable tack paper in which the adhesive layer is easily hydrolyzed when disintegrated in water that has not been heated or pH adjusted, and a method for producing the same.

FIG. 1 is a cross-sectional view of a water-disintegrable tack paper. FIG. 1 is a cross-sectional view of a water-disintegrable tack paper.

Next, a description will be given of an embodiment of the invention. Note that this embodiment is merely an example of the present invention. The scope of the present invention is not limited to the scope of this embodiment.

One embodiment of the present invention is a water-decomposable tack paper 1 that includes a composite paper 11 having an inorganic pigment layer 20 provided on one or both sides of a base paper 10, and an adhesive layer 12 provided on one side of the composite paper 11, the adhesive layer 12 having a composition including a copolymer of an acrylic acid ester monomer and a functional group-containing monomer, a nonionic surfactant, a neutralizing agent, and a fatty acid soap, and the composite paper contains 10 to 20% by mass of calcium carbonate. Each component will be described in detail below.

(composite paper)
The composite paper 11 is made up of a base paper 10 and an inorganic pigment layer 20 .

(Inorganic pigment layer)
The inorganic pigment layer 20 is a layer containing an inorganic pigment. Examples of inorganic pigments include calcium hydroxide, silica, talc, aluminum hydroxide, titanium oxide, calcium carbonate, and kaolin. In particular, calcium carbonate and kaolin are preferred because they are hydrolyzable and oil-absorbent.

(Base paper)
The base paper 10 is mainly composed of pulp, and contains calcium carbonate in addition to pulp, and may also contain kaolin.

The pulp content can be 50 to 90 parts by weight, preferably 70 to 80 parts by weight, per 100 parts by weight of the base paper. Examples of pulp include natural pulp and synthetic pulp. Natural pulp is not particularly limited, and examples include pulp fibers obtained from recycled paper pulp (DIP), chemical pulp, mechanical pulp, and non-wood pulps such as kenaf, bagasse, hemp, and cotton. Examples of chemical pulp include bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), sulfite hardwood pulp, and sulfite softwood pulp. Examples of mechanical pulp include thermomechanical pulp (TMP), pressurized kraft pulp, refiner ground pulp, and ground pulp (GP). Examples of waste paper pulp include disintegrated waste paper pulp, disintegrated and deinked waste paper pulp (DIP), and disintegrated, deinked, and bleached waste paper pulp, which are produced from brown waste paper, kraft envelope paper, magazine paper, newspaper paper, flyer paper, office paper, corrugated cardboard, white waste paper, Kent paper, imitation paper, and land tax paper. Among these, bleached kraft pulp, such as hardwood bleached kraft pulp and softwood bleached kraft pulp, is used as coated paper for printing, such as pigment-coated paper and cast-coated paper, and is suitable for use as the base paper 10 of the water-decomposable tack paper 1. These pulps can be used alone or in combination.

The base paper 10 contains calcium carbonate. The adhesive strength of the adhesive layer 12 upon dissolution in water, and over time, can be adjusted by the calcium carbonate content. The exact mechanism is unclear, but it is thought to be roughly as follows: The adhesive layer 12, which is provided on one side of the composite paper 11, contains acrylic ester monomers. The carboxyl groups that make up this acrylic ester monomer react chemically with calcium ions to form crosslinks with other acrylic ester monomers. This crosslinking reduces the adhesive strength of the adhesive layer 12 over time, making it suitable for dissolution in water. Therefore, for example, if the water-dissolvable tack paper 1 has a high calcium carbonate content, dissolution of the adhesive layer 12 is accelerated when the water-dissolvable tack paper 1 is disintegrated in water, and the adhesive layer 12 is more easily separated from the composite paper 11.

The adhesive layer 12 is provided on one side of the composite paper 11, but it can be provided on either the side that has the inorganic pigment layer 20 or the side that does not have the inorganic pigment layer 20.

The calcium carbonate content of the composite paper 11 should be 10 to 30% by mass, preferably 11 to 20% by mass, and more preferably 12 to 18% by mass. If the calcium carbonate content is less than 10% by mass, the adhesive layer 12 will be difficult to separate from the composite paper 11 when the water-disintegrable tack paper 1 is disintegrated with water, and there is a risk that it will become an adhesive foreign body when recycled. If the content is more than 30% by mass, there is a risk that the adhesive strength of the water-disintegrable tack paper 1 will be excessively reduced if stored for a long period of time. For example, the calcium carbonate content can be calculated by calculating the composition ratio of the composite paper. Alternatively, the calcium carbonate content can be calculated based on the calcium ratio when the composite paper is subjected to elemental analysis using an X-ray microanalyzer.

Kaolin is a clay mineral used for internal and external additives (surface coating). Kaolin can be classified based on particle size and shape into fine kaolin, grade 1 kaolin, grade 2 kaolin, delaminated kaolin, etc. In this embodiment, any of these kaolins can be used without any particular restrictions, with fine kaolin being particularly preferred. For example, the kaolin content can be calculated by calculating the composition ratio of the composite paper. Alternatively, the kaolin content can be calculated based on the silica and aluminum ratios in elemental analysis of the composite paper using an X-ray microanalyzer.

Due to the oil-absorbing properties of kaolin, oily adhesives are partially adsorbed by the kaolin. When kaolin is contained in the base paper 10 of the water-disintegrable tack paper 1, for example, the kaolin near the surface of the base paper on which the adhesive layer 12 is formed directly or indirectly adsorbs the adhesive that forms the adhesive layer 12. When this water-disintegrable tack paper 1 is disintegrated with water, the kaolin separates from the base paper 10 while still adsorbing the adhesive, and the adhesive also easily separates from the base paper 10.

Kaolin may be contained in the base paper 10 or composite paper 11, and the content in the composite paper 11 should be greater than 0.1% by mass, but preferably 7 to 15% by mass, more preferably 8 to 15% by mass, and particularly preferably 10 to 15% by mass. If the content exceeds 15% by mass, the oil absorption performance of kaolin will plateau and no further effect can be expected.

While the basis weight and thickness of the composite paper 11 are not particularly limited, a basis weight of 70 to 100 g/m ² and a thickness of 75 to 120 μm are preferred, and a basis weight of 75 to 95 g/m ² and a thickness of 80 to 110 μm are even more preferred. If the basis weight is less than 70 g/m ² or the thickness is less than 75 μm, the strength of the water-disintegrable tack paper 1 is weak and there is a risk of tearing. If the basis weight is more than 100 g/m ² or the thickness is more than 120 μm, the water-disintegrable tack paper 1 may not maintain its adherence to curved surfaces, and parts of the water-disintegrable tack paper 1 may be easily peeled off. Furthermore, the composite paper 11 may not be able to disintegrate into appropriate sizes during water dissolution, which may result in poor dispersibility. The basis weight of the composite paper 11 is a value measured in accordance with JIS P8124 (2011). The thickness of the composite paper 11 is a value measured in accordance with JIS P8118 (2014).

The base paper 10 can be manufactured by papermaking using the above-mentioned raw materials. Papermaking can be carried out using a papermaking machine such as a Fourdrinier papermaking machine, twin-wire papermaking machine, on-top papermaking machine, hybrid papermaking machine, or cylinder papermaking machine. Additives can be added to the pulp during papermaking. Examples of additives include paper strength agents such as polyvinyl alcohol polymer compounds, urea resins, melamine resins, and starch; chemical fixatives such as aluminum sulfate; sizing agents such as cationized starch, polyethyleneimine, polyethylene oxide, rosin size, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA); water-resistant agents such as polyamides, polyamines, and epichlorohydrin; antifoaming agents; fillers such as talc; dyes, color pigments, antibacterial agents, UV absorbers, and pH adjusters. Photographic paper or film can also be used for the base paper 10.

The compactness of the composite paper 11 is preferably 0.95 to 1.20 g/ ^cm³ , and more preferably 1.00 to 1.15 g/ ^cm³ . If the compactness of the composite paper 11 is less than 0.95 g/ ^cm³ , the surface of the composite paper 11 will become uneven, potentially making it difficult to uniformly form the adhesive layer 12. If the compactness of the composite paper 11 is greater than 1.20 g/ ^cm³ , the cushioning (elasticity) of the base paper will be insufficient, and the water-disintegrable tack paper 1 will not bend flexibly, potentially making it difficult to adhere neatly to the surface to which it is to be attached. The compactness of the composite paper 11 can be adjusted using known devices, such as a machine calender, super calender, or thermal calender. The compactness of the composite paper 11 is a value measured in accordance with JIS P 8118 (2014).

(Adhesive layer)
The adhesive layer 12 is formed by coating the composite paper 11 with an adhesive, and has adhesive strength that allows it to adhere to an object to which it is attached. The adhesive layer 12 easily separates from the composite paper 11 when the water-dissolvable tack paper 1 is disintegrated in water. The adhesive layer 12 contains the following composition, specifically, an acrylic acid ester monomer, a functional group-containing monomer, a nonionic surfactant, and a fatty acid soap, and also contains a neutralizer.

The acrylic acid ester monomer is the main component of the composition of the adhesive layer 12. Examples of acrylic acid ester monomers include (meth)acrylic acid alkyl esters, such as butyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate. While the number of carbon atoms in the alkyl group of the (meth)acrylic acid alkyl ester is not particularly limited, a carbon number of 4 to 12 is preferred, as this facilitates adjustment to the desired adhesive strength. Adhesive strength is optimally expressed when the acrylic acid ester monomer is contained in an amount of preferably 35 to 65 parts by weight, more preferably 40 to 60 parts by weight, and even more preferably 45 to 55 parts by weight per 100 parts by weight of the composition of the adhesive layer 12.

The functional group-containing monomer has the effect of imparting water dispersibility to the PSA layer 12. When the functional group forming the functional group-containing monomer is, in particular, a carboxyl group or an alkoxy group, the PSA layer 12 has high water dispersibility, which is preferred. The functional group-containing monomer may be one or a combination of two or more selected from acrylic acid, methacrylic acid, acrylic acid dimer, caprolactone adducts of (meth)acrylic acid, alkoxy acrylates such as methoxyacrylate, ethoxyacrylate, and butoxyacrylate, and acrylic esters such as itaconic acid. When the PSA layer 12 contains 35 to 65 parts by mass of the acrylic ester monomer per 100 parts by mass of the composition, the PSA layer 12 has high water dispersibility, which is preferred when the functional group-containing monomer is contained in an amount of preferably 10 to 35 parts by mass, more preferably 20 to 30 parts by mass. When the content of the functional group-containing monomer is less than 10 parts by mass, the ratio of the functional group-containing monomer to the acrylic ester monomer is low, which may result in poor water dispersibility of the PSA layer 12. If the content of the functional group-containing monomer exceeds 35 parts by mass, the content of the functional group-containing monomer relative to the acrylic acid ester monomer is somewhat excessive, which is undesirable as it increases the glass transition temperature (Tg) of the polymer, deteriorates adhesion properties at low temperatures, and the effect of increasing the dispersibility of the adhesive layer 12 in water reaches a plateau.

The nonionic surfactant emulsifies the adhesive layer 12 that separates from the composite paper 11 when the water-dissolvable tack paper 1 is disintegrated in water, turning it into fine particles. The emulsifying action of the nonionic surfactant makes it easier for the adhesive layer 12 to separate from the composite paper 11 during disintegration. Furthermore, the emulsifying action of the nonionic surfactant prevents the fine particles from agglomerating, thereby preventing problems caused by the agglomerated adhesive adhering to the disintegrator or other equipment. Furthermore, it is preferable for lipophilic adhesives as it promotes emulsification.

The nonionic surfactant may be, for example, one or a combination of two or more selected from polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene monolaurate, polyoxyethylene monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, etc.

When the adhesive layer 12 contains 35 to 65 parts by mass of acrylic ester monomer per 100 parts by mass of the composition, it is preferable to contain 20 to 40 parts by mass of nonionic surfactant, more preferably 25 to 35 parts by mass, because the emulsification action causes the adhesive layer 12 separated from the composite paper 11 to disperse in water as fine particles. If the nonionic surfactant content is less than 35 parts by mass, emulsification may not be sufficient. If the nonionic surfactant content is more than 65 parts by mass, the nonionic surfactant content relative to the acrylic ester monomer is somewhat excessive, and the emulsification effect will plateau, making it uneconomical.

Fatty acid soap can be added to the composition of the adhesive layer 12 to suppress pulp fluffing caused by disintegration and prevent deterioration of pulp quality. The fatty acid soap can be one or a combination of two selected from sodium and potassium salts of palmitic acid, stearic acid, oleic acid, etc. The content of the fatty acid soap per 100 parts by weight of the composition of the adhesive layer 12 is preferably 1 to 10 parts by weight, more preferably 3 to 7 parts by weight.

Neutralizing agents are used to react with some or all of the carboxyl groups of the acrylate ester monomers to impart hydrophilicity or water solubility to the acrylate ester monomers. While basic compounds can be used as neutralizing agents, amines and substituted amines are preferred. Specifically, one or two of the following organic amino compounds can be used in combination: ammonia, alkaline ammonium salts, primary amines such as monoethylamine and monoethanolamine, secondary amines such as diethylamine and diethanolamine, tertiary amines such as triethylamine, triethanolamine, N,N,N'-trimethylethylenediamine, N-methyldiethanolamine, N,N-diethylhydroxylamine, and N,N-dimethylformamide diethylacetal, diamines, amino compounds with multiple N atoms in one molecule such as polyethyleneimine, and cyclic amino compounds such as pyridine.

The neutralizing agent content per 100 parts by mass of the adhesive layer 12 composition is preferably 1 to 10 parts by mass, and more preferably 3 to 7 parts by mass, to maximize the effect of adding the neutralizing agent.

The adhesive layer 12 provided on one side of the composite paper 11 preferably has a thickness of 10 to 30 μm, and more preferably 15 to 25 μm. If the thickness is less than 10 μm, the desired adhesive strength may not be achieved. If the thickness is more than 30 μm, the concentration of the adhesive layer 12 in the disintegrating liquid may be high, and the adhesive layer 12 that has separated from the composite paper 11 due to disintegration may reattach to the composite paper 11.

The adhesive strength of the adhesive layer 12 is preferably 8 to 25 N/25 mm, and more preferably 10 to 15 N/25 mm. If the adhesive strength is less than 8 N/25 mm, the paper may easily peel or unravel when attached to an object. If the adhesive strength exceeds 25 N/25 mm, the water-decomposable tack paper 1 may tear when attempting to remove it.

(Release paper)
In order to protect the surface of the adhesive layer 12 provided on the composite paper 11, a removable release paper 13 can be provided to cover the surface. For example, the release paper 13 can be a sheet having a release agent, a pigment, and a binder provided on one or both sides of the sheet. Here, the surface of the adhesive layer 12 refers to the side of the adhesive layer 12 opposite to the side facing the composite paper 11.

Examples of sheets include fine paper, medium-quality paper, bleached or unbleached kraft paper (acid paper or neutral paper) used for packaging, and pure white roll paper.

The pigment used in the release paper 13 can contain either flat or non-flat pigments. Flat and non-flat pigments can be distinguished by their aspect ratios; for example, flat pigments are those with an aspect ratio of 5 or greater, while non-flat pigments are those with an aspect ratio of less than 5. The aspect ratio is the value obtained by dividing the particle diameter (Ferret diameter) of the pigment by its thickness. It can be obtained by magnifying and observing the particle with an electron microscope and averaging the value of 20 randomly selected particles. When flat pigments are used in the sheet, the release agent applied to the sheet can be prevented from penetrating into the sheet. The release agent can be, for example, one containing a silicone resin diluted with an organic solvent such as toluene.

The flat pigments applied to the release paper 13 can be, for example, one or a combination of two or more selected from clay (clay minerals), mica, brittle mica, pyrophyllite, talc, smectite, vermiculite, chlorite, septe chlorite, serpentine, stilpnomelane, montmorillonite, etc., with clay being preferred. Furthermore, the non-flat pigments can be, for example, one or a combination of two or more selected from calcium carbonate, white carbon, titanium oxide, aluminum hydroxide, etc.

The binder used in the release paper 13 can be a synthetic resin latex, or the same type used to form coating layers on coated paper. Examples of latex include one or a combination of two or more selected from the group consisting of styrene-butadiene copolymers, acrylic-styrene copolymers, methacrylate-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic copolymers, polyester copolymers, and polyurethane copolymers. These may also contain a water-soluble polymer compound bonded to them. An example of a water-soluble polymer compound is polyvinyl alcohol.

The water-disintegrable tack paper 1 of this embodiment dissolves in water that has not been heated or pH-adjusted. "Water that has not been heated" refers to water that has not been treated to raise its temperature with equipment such as steam or a heater. Also, water that has not been treated to raise its temperature but is already at 40°C or higher is not included in "water that has not been heated." "Water that has not been pH-adjusted" refers to water to which nothing has been added that changes the pH to acidic or alkaline, and can also be defined as water with a pH in the range of 6 to 8.

(Composite paper of Example 1)
Calcium carbonate was added as a filler to raw materials consisting of hardwood kraft pulp and softwood kraft pulp (ash content 5.0%), and paper was made using an on-top paper machine to obtain a base paper of 61.0 g/m ² . Next, a coating composition (50 parts by mass of kaolin, 50 parts by mass of calcium carbonate (100 parts by mass in total), 7 parts by mass of latex, and 1.5 parts by mass of starch) was applied to one side of the obtained base paper to a bone-dry weight of 14.0 g/ ^m² to obtain a composite paper with an inorganic pigment layer. Further, a cast coating composition (55 parts by mass of kaolin and 45 parts by mass of calcium carbonate (100 parts by mass in total), 12 parts by mass of organic pigment, 30 parts by mass of binder such as casein, and 5 parts by mass of release agent and calcium formate) was applied to the outer side of the inorganic pigment layer to a bone-dry weight of 14.0 g/ ^m² to obtain a mirror-finished composite paper (cast-coated paper, 89.0 g/ ^m² ). Here, the composition ratio of the composite paper was pulp and other components: calcium carbonate: kaolin = 74%:14%:12% by mass.

(Composite Papers of Examples 2 and 3, and Comparative Examples 1, 2, 4, and 5)
The composite paper of Examples 2 and 3 and Comparative Examples 1, 2, 4 and 5 was obtained by changing the composition ratio of the composite paper obtained in Example 1.

(Composite paper of Example 4)
Calcium carbonate was added as a filler to hardwood kraft pulp and softwood kraft pulp (ash content 8.0%), and paper was made on an on-top papermaking machine to obtain a base paper weighing 60.0 g/ ^m2 . Next, a coating composition (7 parts by weight of latex and 1.5 parts by weight of starch to a pigment consisting of 30 parts by weight of kaolin and 70 parts by weight (total 100 parts by weight)) was applied to both sides of the obtained base paper to a bone-dry coating weight of 25.0 g/ ^m2 , to prepare a composite paper (coated paper, 89.0 g/ ^m2 ) provided with an inorganic pigment layer. The composition ratio of the composite paper was pulp and other components: calcium carbonate: kaolin = 68% by weight: 25% by weight: 7% by weight.

(Comparative Example 3 and 6 composite papers)
The composite papers of Comparative Examples 3 and 6 were obtained by changing the composition ratio of the composite paper (coated paper) obtained in Example 4.

The physical properties, composition, and disintegration properties of the examples and comparative examples are shown in Table 1.

(Adhesive)
Adhesive A was used as the adhesive in Examples 1 to 4. The composition of Adhesive A was a copolymer of 50% by mass of acrylic acid ester monomer and 15% by mass of functional group-containing monomer, 30% by mass of surfactant, 2% by mass of neutralizer, and 3% by mass of fatty acid soap.
Adhesive B was used as the adhesive for Comparative Examples 1 to 3. The composition of Adhesive B was a copolymer of 30% by mass of an acrylic acid ester monomer and 45% by mass of a functional group-containing monomer, 20% by mass of a surfactant, and 5% by mass of a neutralizing agent.
Adhesive C was used as the adhesive in Comparative Examples 4 to 6. The composition of Adhesive C was a copolymer of 70% by mass of acrylic acid ester monomer and 15% by mass of functional group- containing monomer, and 15% by mass of surfactant.

(disintegrability)
The following procedure was carried out to evaluate the disintegrability.
(1) Each of the water-decomposable tack papers of Examples 1 to 4 and Comparative Examples 1 to 6 was cut into a size of 5 x 5 cm, and 100 g of each was collected.
(2) The cut pieces of water-decomposable tack paper were added to 2,400 mL of tap water at 15°C and mixed to adjust the concentration to 4% by weight. The mixture was then decomposed for 50 minutes using a standard decomposition machine specified in Appendix A of JIS P 8220 to obtain a decomposition liquid.
(3) Two 50 g portions of the solid content in the disintegration liquid were collected, diluted with water to a concentration of 4% by weight, and disintegrated for another 10 minutes to obtain two disintegrated raw materials.
(4) The disintegrated raw material was screened with a 6-cut flat screen for 7 minutes (flow rate 10 L/min), and then the screen residue was collected.
(5) The screen residue was dried at 105°C for 1 hour, and then its weight (bone dry weight) was measured, and the disintegration property was evaluated according to the following evaluation criteria. Furthermore, the tap water was replaced with warm water (40-50°C) and a weak alkaline aqueous solution (pH 8), and the disintegration property was evaluated according to the same evaluation criteria. Here, the residue rate is a value calculated by the following formula.
[Equation 1]
Residue rate (%) = [weight (g) of screen residue recovered in the above step (4) / weight (g) of water-decomposable tack paper added in the above step (2)] × 100

The evaluation criteria are as follows:
⊚: Residue rate is less than 1.0%, and disintegration is good.
◯: The residue rate is more than 1.0% and less than 5.0%, and the disintegration property is good, but some sticky foreign matter remains.
x: Residue rate exceeds 5.0%, disintegration is poor, and sticky foreign matter is noticeable.

(adhesive strength)
The adhesive strength of the examples and comparative examples was measured in accordance with the test method specified in JIS Z 0237 (2009). The measurement conditions were as follows:
Peel: 180° peel (peel speed 300 mm/min)
Adherent: SUS304
Test piece width: 25 mm
Pressure bonding: The test piece attached to the adherend was pressed against the adherend under the conditions of 23°C and 50% RH by rolling a 2 kg roller back and forth once.
The tensile test was carried out one day after the test piece was crimped.

This invention can be used as water-dissolvable tack paper.

Claims (8)

a composite paper having an inorganic pigment layer provided on one side of a base paper;
The composite paper has an adhesive layer provided on one side thereof,
The base paper contains calcium carbonate in addition to pulp,
The pulp is contained in an amount of 50 to 90 parts by mass per 100 parts by mass of the base paper,
the pressure-sensitive adhesive layer has a composition containing a copolymer of an acrylic acid ester monomer and a functional group-containing monomer, a nonionic surfactant, a neutralizing agent, and a fatty acid soap;
The composite paper contains 10 to 30% by mass of calcium carbonate.
A water-dissolvable tack paper characterized by: a composite paper having inorganic pigment layers provided on both sides of a base paper;
an adhesive layer provided on one surface of the composite paper;
The base paper contains calcium carbonate in addition to pulp,
The pulp is contained in an amount of 50 to 90 parts by mass per 100 parts by mass of the base paper,
the pressure-sensitive adhesive layer has a composition containing a copolymer of an acrylic acid ester monomer and a functional group-containing monomer, a nonionic surfactant, a neutralizing agent, and a fatty acid soap;
The composite paper contains 10 to 30% by mass of calcium carbonate.
A water-dissolvable tack paper characterized by: The composite paper contains 10 to 15% by mass of kaolin.
The water-disintegrable tack paper according to claim 1 or claim 2. The thickness of the pressure-sensitive adhesive layer is 10 to 30 μm.
The water-decomposable tack paper according to any one of claims 1 to 3. The adhesive strength of the pressure-sensitive adhesive layer is 8 to 25 N/25 mm.
The water-decomposable tack paper according to any one of claims 1 to 4. The composition comprises a copolymer of 35 to 65 parts by mass of an acrylic acid ester monomer and 10 to 35 parts by mass of a functional group-containing monomer , 25 to 40 parts by mass of a nonionic surfactant, 1 to 4 parts by mass of a neutralizing agent, and 1 to 5 parts by mass of a fatty acid soap.
The water-decomposable tack paper according to any one of claims 1 to 5. The composite paper has a basis weight of 70 to 100 g/m ² and a paper thickness of 75 to 120 μm.
The water-decomposable tack paper according to any one of claims 1 to 6. The inorganic pigment layer contains kaolin and calcium carbonate.
The water-decomposable tack paper according to any one of claims 1 to 7.