Water-resistant adhesive for fibrous substrate

Abstract

To provide a water-resistant adhesive for fibrous substrate which offers water resistance and is recyclable with consideration for the environment.SOLUTION: A water-resistant adhesive for fibrous substrate comprising: (A) a polysaccharide derivative represented by either or both of formula (1) and a starch derivative. In formula (1), R1 is independently a hydrogen atom, an alkyl group having 1-6 carbon atoms, or a group represented by -CH2COOX [X is a hydrogen atom or a monovalent cation], n is an integer of 100-10,000, and n' is an integer of 300-10,000); and (B) an organosilicon compound selected from tetraalkoxysilane and a partial hydrolysis product thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-resistant adhesive for fibrous substrates. [Background technology]

[0002] In recent years, environmental pollution caused by organic resin products, such as waste plastics, has become a growing concern. The United Nations Summit adopted the Sustainable Development Goals (SDGs) and is promoting them globally. This has led to a global trend toward reducing organic resin products, which contribute to forest and ocean pollution, as much as possible. To address this issue, paper products have once again attracted attention. This is because paper products are easily recyclable and are considered to have a smaller environmental impact than plastics. However, paper products have significant issues with water resistance, making them unsuitable for wet applications. This is one reason why the shift from plastic to paper has not progressed. To address this issue, water-repellent cardboard, which is made water-repellent to prevent water-induced strength loss in cardboard products, is widely used. One method for imparting water repellency involves coating a water-repellent composition containing a mixed emulsion of paraffin wax, a tackifier, and an emulsifier, and a synthetic resin emulsion with a glass transition temperature ranging from -10°C to 60°C (Patent Document 1). Another method of water-repellent treatment is to apply a mixture of a cationic copolymer quaternary compound and a polyamidepolyamine-epihalohydrin resin as an undercoat, followed by a water-repellent agent (Patent Document 2). A polysiloxane resin-based water-repellent agent has also been developed, using a tetraalkoxysilane in combination with a silane coupling agent that provides water repellency (Patent Document 3). This method has the drawback of using a large amount of the silane coupling agent that provides water repellency, which can easily cause uneven reactions and significantly reduce the strength of the fibrous substrate.

[0003] However, corrugated cardboard, widely used for transporting goods, is not made up of just a single sheet of paper; instead, it is bonded to a surface liner and a central core, thereby achieving its three-dimensional shape and strength. However, even if only the liner or core is treated with a water-repellent coating, if the adhesive is not water-resistant, its strength will be significantly reduced when exposed to water, and it may not be able to maintain its shape. To solve this problem, a water-resistant adhesive has been proposed in which a water-resistant organic resin is added to a standard starch glue (Patent Document 4). This water-resistant adhesive has improved water resistance compared to conventional water-soluble starch glue, and it is also possible to separate the liner and core inside the cardboard by stirring in water. However, even if it is separable, the organic resin itself does not dissolve in water and may disperse in the water in a microplastic-like state. Therefore, if not handled properly, there is a risk of marine pollution. Furthermore, adhesives containing organic resins are undesirable because they may contain formaldehyde. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-183165 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-336663 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-1873 [Patent Document 4] Japanese Patent Application Publication No. 2020-33459 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a water-resistant adhesive for fibrous substrates that is water-resistant and environmentally friendly and recyclable. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides: (A) a polysaccharide derivative represented by either or both of the following formulas (1) and (2): [ka] [ka] (In the formula, R 1 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a group selected from the group represented by -CH2COOX (X is a hydrogen atom or a monovalent cation), n is an integer of 100 to 10,000, and n' is an integer of 300 to 10,000. (B) an organosilicon compound selected from tetraalkoxysilanes represented by the following formula (3) and partial hydrolysates thereof; [ka] (In the formula, R 2 are independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. The present invention provides a water-resistant adhesive for fibrous substrates comprising:

[0007] Such water-resistant adhesives are water-resistant, formaldehyde-free, and allow for easy recycling of fibrous substrates.

[0008] The water-resistant adhesive for fibrous substrates of the present invention preferably contains water as component (C), and the above components (A) and (B) are dissolved in component (C).

[0009] Such a water-resistant adhesive is preferable from the viewpoint of environmental load and safety for the human body.

[0010] Furthermore, the water-resistant adhesive of the present invention is a water-resistant adhesive having R 1 Preferably, one or more of the above has a sodium salt of a carboxymethyl group.

[0011] Such water-resistant adhesives are non-toxic and generally do not cause allergic reactions, making them highly safe for the human body.

[0012] In the water-resistant adhesive of the present invention, the component (B) preferably has three or more alkoxy groups in one molecule.

[0013] Such a water-resistant adhesive has reinforced adhesive properties due to component (A), and is endowed with water resistance.

[0014] In the water-resistant adhesive of the present invention, it is preferable that all of the alkoxy groups in component (B) are methoxy groups.

[0015] Such water-resistant adhesives provide faster adhesion. [Effects of the Invention]

[0016] As described above, the present invention can provide an environmentally friendly water-resistant adhesive for fibrous substrates that is water-resistant, formaldehyde-free, and highly recyclable. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a top view of a test piece used to evaluate water resistance and recyclability in the examples. [Figure 2] FIG. 2 is a side view of a test piece used to evaluate water resistance and recyclability in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0018] As mentioned above, there was a need for the development of a water-resistant adhesive that was both water-resistant and recyclable, while also being environmentally friendly.

[0019] As a result of extensive research into the above-mentioned problems, the inventors have discovered that a water-resistant adhesive for fibrous substrates containing the above-mentioned components (A) and (B) is water-resistant and an environmentally friendly water-resistant adhesive that can be recycled for fibrous substrates, and have thus completed the present invention.

[0020] That is, the present invention provides: (A) a polysaccharide derivative represented by either or both of the following formulas (1) and (2): [ka] [ka] (In the formula, R 1 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a group selected from the group represented by -CH2COOX (X is a hydrogen atom or a monovalent cation), n is an integer of 100 to 10,000, and n' is an integer of 300 to 10,000. (B) An organosilicon compound selected from tetraalkoxysilanes represented by the following formula (3) and their partial hydrolysates: [ka] (In the formula, R 2 are independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A water-resistant adhesive for fibrous substrates comprising:

[0021] The present invention will be described in detail below, but the present invention is not limited thereto.

[0022] [(A) Polysaccharide derivative] The component (A) in the present invention is a polysaccharide derivative represented by either or both of the following formulas (1) and (2). [ka] [ka] (In the formula, R 1 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a group selected from the group represented by -CH2COOX (X is a hydrogen atom or a monovalent cation), n is an integer of 100 to 10,000, and n' is an integer of 300 to 10,000.

[0023] R in the above formulas (1) and (2) 1 Examples of the carboxyl group include a hydrogen atom, an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or a cyclohexyl group, a carboxymethyl group represented by the above-mentioned -CHCOOX, or a carboxylate in which the hydrogen atom of the carboxyl group is replaced with a monovalent cation such as a sodium ion or an ammonium ion.

[0024] R in one molecule 1 At least one of the groups is preferably an alkyl group or a group represented by -CH2COOX (X is a hydrogen atom or a monovalent cation), more preferably a group represented by -CH2COOX (X is the same as above), and even more preferably -CH2COONa.

[0025] The water-resistant adhesive of the present invention is particularly 1 Preferably, one or more of the above has a sodium salt of a carboxymethyl group.

[0026] Above R 1 Carboxymethylcellulose, which has a carboxymethyl group, and its sodium salt, sodium carboxymethylcellulose, are known as thickeners and emulsion stabilizers for food. Therefore, they are non-toxic and generally unlikely to cause allergic reactions, making them highly safe for the human body and desirable.

[0027] Above R 1 When R is a sodium salt of a carboxymethyl group, the preferred substitution ratio is 1 When the total number is taken as 1, the range is preferably 0.3 to 0.8, and more preferably 0.5 to 0.8. Within this range, the balance between water solubility and viscosity is good, and workability during coating is improved, which is preferable.

[0028] In the above formula (1), n is an integer of 100 to 10,000, and preferably an integer of 1,000 to 5,000. If n is less than 100, the viscosity is low and the composition tends to flow from the substrate during coating, resulting in poor workability, which is undesirable, while if n exceeds 10,000, the viscosity is high and the composition tends to stick in the coater regardless of the coating method, which is undesirable.

[0029] In the above formula (2), n' is an integer of 300 to 10,000, and preferably an integer of 1,000 to 5,000. If n' is less than 300, the viscosity is low and the composition tends to flow from the substrate during coating, resulting in poor workability, which is undesirable, while if n' is more than 10,000, the viscosity is high and the composition tends to stick in the coating machine regardless of the coating method, which is undesirable.

[0030] [(B) Organosilicon Compounds] The component (B) in the present invention is an organosilicon compound selected from tetraalkoxysilanes represented by the following formula (3) and their partial hydrolysates. [ka] (In the formula, R 2 are independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0031] R in one molecule of the above formula (3) 2 Preferably, one or more of the groups is an alkyl group.

[0032] In the above formula (3), R 2 Examples of the alkyl group include a hydrogen atom and an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, and a cyclohexyl group.

[0033] In the water-resistant adhesive of the present invention, the component (B) preferably has three or more alkoxy groups in one molecule, and it is also preferable that all of the alkoxy groups in the component (B) are methoxy groups.

[0034] The hydrolysis rate of tetraalkoxysilane varies depending on the type of alkoxy group bonded to it, but generally the more carbon atoms there are, the slower the hydrolysis rate becomes. 2 is most preferably a methyl group.

[0035] The partial hydrolysis product of tetraalkoxysilane is a M unit [(R 2 O)3SiO 1 / 2 ], D unit [(R 2 O)2SiO 2 / 2 ], T unit [R 2 OSiO 3 / 2 ], Q units [SiO 4 / 2 ] can be used.

[0036] Furthermore, since tetraalkoxysilanes can polymerize through hydrolysis to form high molecular weights, a smaller molecular weight is preferable. Therefore, the tetraalkoxysilane is preferably a monomer or a dimer to trioctamer, preferably a trioctamer to 2octamer oligomer. Within this range, the water-resistant adhesive of the present invention can achieve both good storage stability and good curing speed. Furthermore, it has excellent solvent solubility and is easy to handle.

[0037] Furthermore, since the number of alkoxy groups is related to the amount of crosslinking that affects water resistance, it is preferable for one molecule to have three or more alkoxy groups, more preferably within the range of 4 to 62, and even more preferably 6 to 42.

[0038] The (B) component of the present invention serves to reinforce the (A) component used as an adhesive and provide water resistance. The polysaccharide derivative (A) is water-soluble and loses its strength when wetted with water. However, by adding the (B) component, it becomes silica glass after curing, exhibiting a reinforcing effect. Furthermore, the water resistance can be adjusted by the amount of the (B) component added, allowing the balance between water resistance and recyclability to be adjusted as desired. The amount of the (B) component added is preferably 0.1 to 80% by mass, more preferably 10 to 50% by mass, of the amount of the (A) component added. When the amount added is within the range of 0.1 to 80% by mass, the reinforcing effect of the (B) component is easily achieved, and recyclability is also achieved.

[0039] [Curing catalyst] In order to increase the curing rate of the adhesive, any curing catalyst may be added. There are no particular restrictions on the curing catalyst as long as it accelerates the hydrolysis or condensation reaction of the alkoxysilane. Examples of suitable compounds that can be used to adjust the curing rate include inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid; organic acids such as formic acid, acetic acid, propionic acid, citric acid, and oxalic acid; inorganic bases such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; organic bases such as pyridine and triethylamine; triethoxyaluminum, tributoxyaluminum, dibutoxy(2-oxo-5-oxa-3-hepten-4-yloxy)aluminum, di(ethylacetoacetate)monobutoxyaluminum, ethylacetoacetatedi(isopropoxy)aluminum, aluminum trichloride, tetraethoxytitanium, tetraisopropoxytitanium, tetrabutoxytitanium, tetra(2-ethylhexoxide)titanium, titanium tetrachloride, tetrakis(2,4-pentanedionato)titanium, diisopropoxybis(ethylacetoacetate)titanium, zinc chloride, and zinc acetate.

[0040] Although all catalysts allow the curing reaction to proceed satisfactorily at room temperature, metal compounds that are effective at smaller addition amounts are preferred, and among these, aluminum compounds, titanium compounds, and zinc compounds are more preferred from the viewpoint of curing speed. Generally, it is preferable to add the catalyst in an amount of 0.01 to 10 mass% of the component (B), but from the viewpoint of environmental load, it is more preferable to add as little as possible.

[0041] [Additives] The water-resistant adhesive of the present invention may contain additives and fillers as needed.

[0042] Examples of the additives include UV absorbers, UV scattering agents, antioxidants, heavy metal deactivators, flame retardants, and antistatic agents.

[0043] Examples of fillers include reinforcing inorganic fillers such as fumed silica, fumed titanium dioxide, and fumed alumina, and inorganic fillers such as fused silica, alumina, zirconium oxide, calcium carbonate, calcium silicate, titanium dioxide, ferric oxide, and zinc oxide, and these can be added in any desired ratio.

[0044] [Fiber base material] The water-resistant adhesive of the present invention can bond any fibrous substrates together. Examples of fibrous substrates include newsprint used for newspapers, printing paper used for notebooks and copy paper, wrapping paper used for envelopes, shopping bags, rice bags, etc., sanitary paper used for tissue paper and toilet paper, Japanese paper such as calligraphy paper and shoji screens, paperboard such as cardboard base paper, paper boxes, and plastic wrap cores, fabrics such as cotton and quartz fiber, woods such as cypress, pine, cedar, oak, beech, and zelkova, or plywood thereof, and molded products such as cellulose and carbon nanofiber. From the viewpoints of water resistance, recyclability, and environmental impact, paper products that can be reused or recycled within a short period of time are preferred, and corrugated cardboard, which requires water resistance, is even more preferred.

[0045] [How to use water-resistant adhesive] A preferred method of using the water-resistant adhesive of the present invention is to dissolve the above components (A) and (B) in a solvent in which they are soluble, adjust the viscosity, apply the adhesive as a water-resistant adhesive, and then dry the solvent.

[0046] There are no restrictions on the type or concentration of the solvent, but water is preferred from the viewpoints of environmental impact, safety for the human body, etc. Furthermore, the water-resistant adhesive of the present invention preferably contains water as component (C), and the components (A) and (B) are preferably dissolved in component (C).

[0047] Furthermore, the concentration of the solvent is preferably in the range of 0.01 to 50% by mass relative to the solvent, as this affects workability during coating.Within this range, both adhesion and workability can be achieved.

[0048] There are no particular restrictions on the coating method as long as it can be applied to the desired location. Examples of coating methods include roll coating methods using a chamber doctor coater, single-roll kiss coater, reverse kiss coater, bar coater, reverse roll coater, forward rotation roll coater, blade coater, knife coater, etc., as well as spin coating, dispensing, dipping, spraying, transfer, and slit coating. Coating can be performed by an appropriate method depending on the size and shape of the substrate. Furthermore, if necessary, the fibrous substrate may be subjected to a surface modification treatment before coating. Examples of surface modification treatments include inactive modification treatments such as argon plasma treatment, xenon excimer treatment, and UV treatment, and active modification treatments such as oxygen plasma treatment and ozone treatment.

[0049] After coating using the above method, another fibrous substrate is laminated and bonded. This substrate may be the same or different from the substrate coated with the adhesive. Heat or pressure may also be applied during lamination. After laminating the substrates, the solvent is dried and the tetraalkoxysilane is cured. This drying and curing can be carried out at room temperature, but if bonding is desired in a short time, heating can be used to shorten the processing time. When heating, the upper limit of the heating temperature varies depending on the heat resistance temperature of the fibrous substrate and the adhesive, but is generally within the range of 40 to 180°C for 1 minute to 72 hours.

[0050] [Water resistance evaluation] In the present invention, the "water resistance" is evaluated based on the presence or absence of peeling on a substrate tested under the following conditions. 1. Fill a water tank that is sufficiently larger than the test specimen with tap water to a depth of 10 cm and adjust the temperature to room temperature (20±1°C). 2. Prepare a test specimen as shown in Figure 1 of JIS K 6850:1999. The thickness of the cardboard substrate is 4 mm. Specifically, prepare a test specimen as shown in Figures 1 and 2 below. Figure 1 is a top view of the test specimen used to evaluate water resistance and recyclability in the examples, and Figure 2 is a side view of the test specimen used to evaluate water resistance and recyclability in the examples. 3. Immerse the test piece prepared in step 2 above in the 10cm deep water tank prepared in step 1 above for up to 30 minutes in 10 minute increments. 4. After each immersion time, the test piece is subjected to a tensile test according to the test method described in JIS K 6850:1999. 5. The test is continued until either peeling of the adhesive or rupture of the test specimen substrate is confirmed, and the maximum time at which rupture of the test specimen substrate occurs before peeling of the adhesive is determined as the water resistance evaluation time.

[0051] [Recyclability evaluation] In the present invention, "recyclability" is evaluated based on the presence or absence of adhesive residue on a substrate tested under the following conditions. 1. Prepare a test piece as shown in Figure 1 of JIS K 6850:1999. Specifically, prepare a test piece as shown in Figures 1 and 2 above. 2. Place 1 L of water and the test piece prepared in step 1 above into a 2 L container and stir for 2 minutes at a rotation speed of approximately 15,000 rpm. 3. Recyclability is judged based on the state of the adhesive after stirring. If the adhesive is completely dissolved, it is rated as "recyclable," and if the adhesive remains as a solid on the substrate, it is rated as "not recyclable." [Example]

[0052] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0053] In the following examples and comparative examples, "parts" refers to parts by mass. Furthermore, room temperature refers to a temperature range of 5 to 35°C as described in JIS Z 8703:1993.

[0054] The water resistance and recyclability were evaluated for each of the test pieces obtained in Examples 1 to 5 and Comparative Examples 1 to 4. The results are shown in Table 1.

[0055] [water resistance] The water resistance of each test piece was evaluated in accordance with the above-mentioned "Evaluation of Water Resistance."

[0056] [Recyclability] According to the above-mentioned "Evaluation of recyclability", the recyclability of each test piece was evaluated.

[0057] [Example 1] An adhesive was prepared by mixing 3 parts of sodium carboxymethylcellulose as component (A), 0.3 parts of methoxysilane oligomer (methyl silicate 53A, manufactured by Colcoat Co., Ltd., a heptamer of tetramethoxysilane) as component (B), and 96.7 parts of water as a dilution solvent. A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When the water resistance of this test piece was evaluated, the substrate broke within 20 minutes of immersion in water. Furthermore, in the recyclability evaluation, all of the adhesive was dissolved.

[0058] [Example 2] An adhesive was prepared by mixing 3 parts of sodium carboxymethylcellulose as component (A), 1 part of methoxysilane oligomer (methyl silicate 53A, manufactured by Colcoat Co., Ltd., a heptamer of tetramethoxysilane) as component (B), and 96 parts of water as a dilution solvent. A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When the water resistance of this test piece was evaluated, the substrate broke within 30 minutes of immersion in water. Furthermore, in the recyclability evaluation, all of the adhesive dissolved.

[0059] [Example 3] An adhesive was prepared by mixing 3 parts of sodium carboxymethylcellulose as component (A), 1.5 parts of methoxysilane oligomer (methyl silicate 53A, manufactured by Colcoat Co., Ltd., a heptamer of tetramethoxysilane) as component (B), and 95.5 parts of water as a dilution solvent. A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When the water resistance of this test piece was evaluated, the substrate broke within 30 minutes of immersion in water. Furthermore, in the recyclability evaluation, all of the adhesive dissolved.

[0060] [Example 4] An adhesive was prepared by mixing 3 parts of methylcellulose as component (A), 1.5 parts of methoxysilane oligomer (methyl silicate 53A, manufactured by Colcoat Co., Ltd., a heptamer of tetramethoxysilane) as component (B), and 95.5 parts of water as a dilution solvent. A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When the water resistance of this test piece was evaluated, the substrate broke within 20 minutes of immersion in water. Furthermore, in the recyclability evaluation, all of the adhesive dissolved.

[0061] [Example 5] An adhesive was prepared by mixing 3 parts of starch as component (A), 1.5 parts of methoxysilane oligomer (methyl silicate 53A, manufactured by Colcoat Co., Ltd., a heptamer of tetramethoxysilane) as component (B), and 95.5 parts of water as a dilution solvent. A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When the water resistance of this test piece was evaluated, the substrate broke within 10 minutes of immersion in water. Furthermore, in the recyclability evaluation, all of the adhesive was dissolved.

[0062] [Comparative Example 1] Starch glue was used instead of component (A), and component (B) was not added to create the adhesive. Using corrugated cardboard as the substrate, test specimens as shown in Figures 1 and 2 were prepared. When the test specimens were evaluated for water resistance, the cardboard substrate peeled off in a water bath 10 minutes after immersion, making evaluation impossible. Furthermore, when evaluating recyclability, all of the adhesive dissolved.

[0063] Comparative Example 2 An adhesive was prepared by mixing 3 parts of methylcellulose as component (A) with 97 parts of water as a dilution solvent without adding component (B). A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When this test piece was evaluated for water resistance, the cardboard substrate peeled off in a water bath within 5 minutes of immersion, making it impossible to evaluate. Furthermore, when evaluating recyclability, all of the adhesive dissolved.

[0064] Comparative Example 3 An adhesive was prepared by mixing 3 parts of sodium carboxymethylcellulose as component (A) with 97 parts of water as a dilution solvent without adding component (B). A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When this test piece was evaluated for water resistance, the cardboard substrate peeled off after 10 minutes of immersion in water, making it impossible to evaluate. Furthermore, when evaluating recyclability, all of the adhesive dissolved.

[0065] Comparative Example 4 An adhesive was prepared by mixing 50 parts of methoxysilane oligomer (methyl silicate 53A, manufactured by Colcoat Co., Ltd., a heptamer of tetramethoxysilane) as component (B) with 25 parts of water and 25 parts of ethanol as dilution solvents without adding component (A). A test piece was prepared using corrugated cardboard as the substrate, as shown in Figures 1 and 2. When the water resistance of this test piece was evaluated, the substrate broke within 30 minutes of immersion in water. Furthermore, the adhesive did not dissolve in the recyclability evaluation.

[0066] [Table 1]

[0067] As can be seen from the results in Table 1, in Examples 1 to 5 and Comparative Example 4, the adhesive did not peel off even after immersion in water for 10 minutes or more. However, in Comparative Examples 1 to 3, the adhesive peeled off in less than 10 minutes, losing its adhesive effect. This is because commonly used starch glues and polysaccharide derivatives alone are easily soluble in water and have poor water resistance. Furthermore, when tetraalkoxysilane or its partial hydrolyzate alone was used, water resistance was exhibited, but it solidified strongly to form water-insoluble silicone resins or silica compounds, resulting in poor recyclability. On the other hand, the combination of polysaccharide derivative and tetraalkoxysilane in Examples 1 to 5 was able to impart water resistance of any desired strength without impairing recyclability. This is thought to be because tetraalkoxysilane reinforces the water-soluble polysaccharide derivative, improving water resistance, but physical impacts such as stirring destroy the crosslinks of the tetraalkoxysilane, causing it to dissolve in water.

[0068] These results demonstrate that the water-resistant adhesive of the present invention has significantly improved water resistance compared to conventional water-soluble adhesives, and unlike the organic resin-based adhesives used in conventional water-resistant adhesives, it is possible to provide an adhesive that is easy to recycle from fibrous substrates and does not contain formaldehyde.

[0069] The present specification includes the following aspects. [1]: (A) a polysaccharide derivative represented by either or both of the following formulas (1) and (2): [ka] [ka] (In the formula, R 1 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a group selected from the group represented by -CH2COOX (X is a hydrogen atom or a monovalent cation), n is an integer of 100 to 10,000, and n' is an integer of 300 to 10,000. (B) An organosilicon compound selected from tetraalkoxysilanes represented by the following formula (3) and their partial hydrolysates: [ka] (In the formula, R 2 are independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A water-resistant adhesive for fibrous substrates, comprising: [2]: The water-resistant adhesive for fibrous substrates according to [1], further comprising (C) water, wherein the components (A) and (B) are dissolved in the component (C). [3]: R in the above formula (1) 1 The water-resistant adhesive for fibrous substrates according to [1] or [2] above, wherein one or more of the above has a sodium salt of a carboxymethyl group. [4]: The water-resistant adhesive for fibrous substrates according to [1], [2] or [3] above, wherein component (B) has three or more alkoxy groups in one molecule. [5]: The water-resistant adhesive for fibrous substrates according to any one of [1] to [4] above, wherein all of the alkoxy groups in component (B) are methoxy groups.

[0070] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0071] 1: Grip part of the test piece used to evaluate water resistance and recyclability. 2: Adhesive joint of test specimen used for water resistance and recyclability evaluation. 3: Adhesive layer of test specimen used for water resistance and recyclability evaluation.

Claims

1. (A) a polysaccharide derivative represented by either or both of the following formulas (1) and (2): 【Chemical 1】 【Chemistry 2】 (In the formula, R １ are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and —CH ２ COOX [X is a hydrogen atom or a monovalent cation], n is an integer of 100 to 10,000, and n' is an integer of 300 to 10,000. (B) An organosilicon compound selected from tetraalkoxysilanes represented by the following formula (3) and their partial hydrolysates: 【Chemistry 3】 (In the formula, R ２ are independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A water-resistant adhesive for fibrous substrates, comprising:

2. 2. The water-resistant adhesive for fibrous substrates according to claim 1, further comprising (C) water, wherein the components (A) and (B) are dissolved in the component (C).

3. R in the formula (1) １ 2. The water-resistant adhesive for fibrous substrates according to claim 1, wherein one or more of the following has a sodium salt of a carboxymethyl group.

4. 2. The water-resistant adhesive for fibrous substrates according to claim 1, wherein the component (B) has three or more alkoxy groups in one molecule.

5. 2. The water-resistant adhesive for fibrous substrates according to claim 1, wherein all of the alkoxy groups in component (B) are methoxy groups.

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