Waterproofed fibrous substrate and method for producing the same

Abstract

To provide a fibrous substrate that achieves significantly improved water resistance with no change in tactile feel, and maintains sufficient strength even when wet with water.SOLUTION: The present invention provides a waterproofed fibrous substrate that has been waterproofed with a treatment agent containing a silazane compound, wherein the ratio (s2 / s1) of the vertical compressive strength (s2) after 3-hour water immersion to the vertical compressive strength (s1) before immersion, as measured by the method described in JIS Z0403-2:1999 (Method A), is 0.15 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a water-resistant fibrous substrate and a method for producing the same.

Background Art

[0002] Fibrous materials typified by paper and cloth are formed from fibrous raw materials, so they have excellent processability and can be used in various applications depending on the manufacturing method. Therefore, they are an indispensable part of our lives as very versatile materials. In particular, paper has a wide range of uses, such as for writing and printing like notebooks and newspapers, for daily necessities like tissue paper and toilet paper, for building materials like shoji, and for food packaging. There are many products on the market with the necessary characteristics for each application, but generally they have the weakness of being vulnerable to water.

[0003] In particular, cardboard is a packaging material used for storing and transporting goods. When used for transporting fresh fruits and seafood, etc., water-repellent cardboard with water repellency applied is widely used to prevent a decrease in strength due to moisture. As a method for imparting water repellency, a method of coating a water repellent composition containing a mixed emulsion containing paraffin wax, tackifier, and emulsifier, and a synthetic resin emulsion having a glass transition temperature in the range of -10°C to 60°C (Patent Document 1), or a method of applying a water repellent after undercoating with a mixed solution composed of a quaternary compound of a cationic copolymer and a polyamide polyamine-epihalohydrin resin (Patent Document 2), etc. are adopted for the water repellency treatment.

[0004] In addition, a polysiloxane resin-based water repellent by the combined use of tetraalkoxysilane and a silane coupling agent for imparting water repellency has also been developed (Patent Document 3). This method has a drawback that since a large amount of a silane coupling agent for imparting water repellency is used, a non-uniform reaction easily occurs and the strength of the fibrous substrate is significantly reduced.

[0005] On the one hand, in applications where being wetted by water is a prerequisite, organic resin (plastic) products such as expanded polystyrene are often used instead of cardboard. However, since organic resins such as expanded polystyrene are not naturally decomposed, if they are not recovered by a prescribed method, it will directly lead to pollution of mountains, forests and the ocean. Especially in recent years, at the United Nations Summit, "Sustainable Development Goals", commonly known as "SDGs", have been adopted and promoted globally. From this, it has become a global trend to reduce organic resin products that lead to pollution of mountains, forests and the ocean as much as possible. In response to this issue, paper products have once again attracted attention. However, most of the paper products that claim water resistance are those with the paper surface and fibers coated with organic resins, etc. (Patent Document 4).

[0006] These coatings are somewhat effective in terms of waterproofing, but they will exhibit a gloss and a smooth touch that are not inherent in the original paper, so the texture will change significantly, and the workability will deteriorate, such as the ink bouncing off or the gum tape not adhering. Also, since it is fibrous, the advantages such as breathability and printability with ink that were originally present will also be lost due to the coating, so such modification is not preferred depending on the application. Furthermore, since it contains an organic resin component at the time of disposal, it is also bad for the environment and does not provide a fundamental solution. In addition to this method, a method of alternately laminating paper and an organic resin sheet to exhibit water resistance has also been proposed, but for the same reason as above, it is not an alternative technology in the true sense (Patent Documents 5 and 6).

[0007] For the above reasons, there is a demand for providing a fibrous substrate that does not impair the functions of the fibrous substrate, improves water resistance by an environmentally considerate method, can maintain sufficient strength even when wetted by water, and is excellent in productivity.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a fibrous substrate that has significantly improved water resistance without changing the texture and can maintain sufficient strength even when wetted with water. [Means for Solving the Problems]

[0010] In order to solve the above problems, in the present invention, a fibrous substrate made water-resistant with a treating agent containing a silazane compound, a water-resistant fibrous substrate is provided in which the ratio (s2 / s1) of the vertical compressive strength (s1) before immersion to the vertical compressive strength (s2) after 3 hours of immersion in water is 0.15 or more in the vertical compressive strength measured by the method described in JIS Z0403-2:1999 (Method A).

[0011] If it is such a thing, it will become a fibrous substrate that has significantly improved water resistance without changing the texture and can maintain sufficient strength even when wetted with water.

[0012] Further, the silazane compound is represented by the following formula (1): [Chemical Formula] (In the formula, R 1 is independently a group selected from a hydrogen atom, an aliphatic hydrocarbon group having 1 to 6 carbon atoms, an aromatic hydrocarbon group having 6 to 12 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms. However, R 1Of these, 90% or more are hydrogen atoms. It is preferably a silazane compound having a structure represented by .

[0013] Such a silazane compound has many Si-H bonds in the molecule, so it can be cured to form a hard film, improving water resistance and strength.

[0014] Also, the silazane compound is preferably perhydropolysilazane.

[0015] R in the above formula (1) 1 Perhydropolysilazane in which all are hydrogen atoms is more preferable because it has excellent curability and forms a uniform cured film, so it has excellent water resistance and strength.

[0016] Also, it is preferable that the treatment agent contains a curing catalyst.

[0017] By adding a curing catalyst, short-time curing and low-temperature curing become possible.

[0018] Also, it is preferable that the fibrous substrate is cardboard.

[0019] The present invention can be particularly preferably applied to paper or paperboard whose strength is significantly reduced when wetted with water despite being required to have strength, and among them, to cardboard base paper mainly used for transporting packages.

[0020] Also in the present invention, A method for producing a water-resistant fibrous substrate, comprising: (1) A step of impregnating a fibrous substrate with a treatment agent containing a silazane compound, and (2) A step of heat-treating the fibrous substrate impregnated with the treatment agent at 120°C or higher. A method for producing a water-resistant fibrous substrate is provided.

[0021] In this way, a fibrous substrate with significantly improved water resistance without changing the texture and capable of maintaining sufficient strength even when wetted with water can be obtained.

Advantages of the Invention

[0022] As described above, since the present invention enables easy uniform impregnation and formation of a high-strength ultra-thin glass film by heat curing, it is possible to provide a fibrous substrate that improves water resistance and water repellency without changing the texture and can maintain sufficient strength even when wetted with water.

Embodiments for Carrying Out the Invention

[0023] As described above, there has been a demand for the development of a fibrous substrate that significantly improves water resistance without changing the texture and can maintain sufficient strength even when wetted with water.

[0024] As a result of intensive studies on the above problems, the present inventors have found that by impregnating a fibrous substrate with a silazane compound and then performing heat treatment at a high temperature of 120°C or higher, the water resistance of the fibrous substrate can be significantly improved, and the present invention has been completed.

[0025] That is, the present invention is a fibrous substrate made water-resistant with a treating agent containing a silazane compound, and in terms of the vertical compression strength measured by the method described in JIS Z0403-2:1999 (Method A), it is a water-resistant fibrous substrate in which the ratio (s2 / s1) of the vertical compression strength (s1) before immersion and the vertical compression strength (s2) after 3 hours of immersion is 0.15 or more.

[0026] The present invention is also a method for producing a water-resistant fibrous substrate, which includes (1) a step of impregnating a fibrous substrate with a treating agent containing a silazane compound, and (2) a step of heat-treating the fibrous substrate impregnated with the treating agent at 120°C or higher.

[0027] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0028] [Water-resistant fibrous substrate] The water-resistant fibrous substrate of the present invention is a fibrous substrate water-resistant with a treating agent containing a silazane compound, and in terms of the vertical compression strength measured by the method described in JIS Z0403-2:1999 (Method A), the ratio (s2 / s1) of the vertical compression strength (s1) before immersion and the vertical compression strength (s2) after 3-hour immersion in water is 0.15 or more.

[0029] [Treating agent] The treating agent in the present invention contains a silazane compound, and may further contain a curing catalyst, a solvent, and other additives as necessary.

[0030] [Silazane compound] The silazane compound in the present invention has the following formula (1): [Chemical formula] (In the formula, R 1 is independently a group selected from a hydrogen atom, an aliphatic hydrocarbon group having 1 to 6 carbon atoms, an aromatic hydrocarbon group having 6 to 12 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms. However, 90% or more of the whole R 1 is a hydrogen atom.) It is preferably a silazane compound (polysilazane) having a structure represented by this. Since such a silazane compound has many Si-H bonds in the molecule, it can be cured to form a hard film, improving water resistance and strength.

[0031] R 1 Perhydropolysilazane in which all are hydrogen atoms is more preferable because it has excellent curability and forms a uniform cured film, thus having excellent water resistance and strength.

[0032] The curing method requires curing such that the silazane compound forms a strong film on the fibrous substrate. In the present invention, the heating temperature needs to be 120 °C or higher. By setting the temperature above this level, the curing of the silazane compound is promoted, and a strong glass film can be obtained. Further, when sufficient curing cannot be achieved due to restrictions such as the heat resistance temperature of the fibrous substrate to be coated, a curing catalyst described below may be added, and additives such as the solvents and fillers described below may be added as necessary.

[0033] There are no particular restrictions on the molecular weight, but generally, it is preferably in the range of 1,000 to 100,000 in terms of polystyrene-converted weight average molecular weight. If the weight average molecular weight is 1,000 or more, volatilization at normal temperature is less, and a sufficient coating film is formed, which is preferable. Further, when the weight average molecular weight is 100,000 or less, the viscosity does not become too high, so it can enter the gaps between the fibers and enable coating of each fiber, which is preferable. The measurement of the weight average molecular weight can be carried out by the following method using a GPC device.

[0034] [Measurement conditions] Developing solvent: Tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: UV detector Column: TSK Guardcolumn SuperH-L TSKgel SuperMultipore HZ-M (4.6 mm I.D. × 15 cm × 4) (Both are manufactured by Tosoh Corporation) Column temperature: 40 °C Sample injection volume: 20 μL (THF solution with a concentration of 0.5% by weight)

[0035] The blending amount of the silazane compound in the treatment agent is not particularly limited. For example, it can be 0.1 to 20 parts by mass, preferably 0.5 to 10 parts by mass, based on a total of 100 parts by mass of the silazane compound and the solvent.

[0036] [Curing catalyst] A curing catalyst may be added to the treatment agent in the present invention as needed. By adding a curing catalyst, curing in a short time or at a low temperature becomes possible. There are no particular restrictions on the curing catalyst as long as the curing of hydrosilyl groups, alkoxysilyl groups, etc., which are bonding functional groups contained in the silazane compound used, is promoted.

[0037] Examples of the curing catalyst include, in the case of hydrosilyl groups, platinum group compounds such as nickel, palladium, and platinum; aliphatic amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, and tetramethylethylenediamine; aliphatic aminoalcohols such as methylaminoethanol and dimethylaminoethanol; aromatic amines such as aniline, phenylethylamine, and toluidine; heterocyclic amines such as pyrrolidine, piperidine, piperazine, pyrrole, pyrazole, imidazole, pyridine, pyridazine, pyrimidine, and pyrazine; and aminosilanes such as aminopropyltriethoxysilane, aminoethylaminopropyltrimethoxysilane, and aminoethylaminopropylmethyldiethoxysilane.

[0038] In the case of a hydroxysilyl group or an alkoxysilyl group generated by hydrolysis of a silazane compound, examples include metal compounds such as triethoxyaluminum, tributoxyaluminum, dibutoxy(2-oxo-5-oxa-3-hepten-4-yloxy)aluminum, di(ethylacetoacetate)monobutoxyaluminum, ethylacetoacetate di(isopropoxy)aluminum, aluminum trichloride, tetraethoxytitanium, tetraisopropoxytitanium, tetrabutoxytitanium, tetra(2-ethylhexoxide)titanium, titanium tetrachloride, tetrakis(2,4-pentanedionato)titanium, diisopropoxybis(ethylacetoacetate)titanium, zinc chloride, zinc acetate, etc., inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, organic acids such as formic acid, acetic acid, propionic acid, citric acid, oxalic acid, inorganic bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and organic bases such as pyridine, triethylamine, etc. Also, these catalysts may be added in any ratio of two or more kinds.

[0039] Among these, in the case of a hydrosilyl group, aminopropyltriethoxysilane is more preferable from the viewpoints of curing rate and stability. Also, in the case of a hydroxysilyl group or an alkoxysilyl group, although the curing reaction proceeds sufficiently at room temperature with any catalyst, metal compounds that are effective with a smaller addition amount are preferable, and among them, aluminum compounds, titanium compounds, and zinc compounds are more preferable from the viewpoint of curing rate.

[0040] These curing catalysts can be added in any ratio for adjusting the curing rate and curing temperature, but generally, it is preferable that they are in the range of 0.01 to 10% by mass with respect to the silazane compound.

[0041] [Solvent] The treating agent used in the present invention is preferably diluted with a solvent before use.

[0042] Examples of the solvent include aliphatic unsaturated hydrocarbon compounds such as 1-octene, 1-nonene, 1-decene, and 1-dodecene; cyclic saturated hydrocarbon compounds such as cyclohexane and decahydronaphthalene; cyclic unsaturated hydrocarbon compounds such as toluene, xylene, and limonene; ether compounds such as diethyl ether and dibutyl ether; ester compounds such as n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, isoamyl acetate, ethyl acetoacetate, and ethyl caproate; and glycol ether compounds such as bis(2-methoxyethyl) ether, bis(2-ethoxyethyl) ether, and bis(2-butoxyethyl) ether.

[0043] There are no particular restrictions on the solvent that can be used, but it is preferable to select an appropriate solvent in view of the wettability and workability with respect to the substrate, and it is important that the substrate is not dissolved. From the above viewpoints, decahydronaphthalene and dibutyl ether are particularly preferred.

[0044] The blending amount of the solvent in the treatment agent is not particularly limited. For example, with respect to a total of 100 parts by mass of the silazane compound and the solvent, the solvent can be 80 to 99.9 parts by mass, preferably 90 to 99.5 parts by mass.

[0045] [Additive] In the treatment agent of the present invention, additives may be added in addition to the curing catalyst as necessary. Examples of the additives include metal fillers containing metal elements such as magnesium, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, gallium, zirconium, niobium, palladium, and platinum; reinforcing inorganic fillers such as fumed silica, fumed titanium dioxide, and fumed alumina; non-reinforcing inorganic fillers such as fused silica, alumina, zirconium oxide, calcium carbonate, calcium silicate, titanium dioxide, ferric oxide, and zinc oxide; ultraviolet reflectors; ultraviolet absorbers such as benzophenone-based, benzotriazole-based, and triazine-based; organosiloxane oligomers containing at least two, preferably two or three functional groups selected from Si-H group, alkenyl group, alkoxysilyl group, and epoxy group; adhesion aids such as organooxysilyl-modified isocyanurate compounds and their hydrolysis condensates; silicone oils such as dimethyl silicone and phenyl silicone, etc., which can be added in any proportion.

[0046] [Fibrous substrate] In the present invention, the fibrous substrate is not particularly limited in its manufacturing method or the like as long as it is formed from fibrous raw materials.

[0047] Examples of the fibrous substrate include newsprint used for newspapers, printing paper used for notebooks and copy paper, packaging paper used for envelopes, shopping bags, and rice bags, sanitary paper used for tissue paper and toilet paper, papers such as Japanese paper used for calligraphy practice paper and shoji, cardboard papers such as corrugated cardboard base paper (corrugated paper), paper boxes, and cores of wraps, cloths such as cotton and quartz fiber, woods such as cypress, pine, cedar, oak, beech, and zelkova, or their plywoods, and molded products such as cellulose and carbon nanofibers.

[0048] Among them, papers and cardboard papers that are required to have strength but whose strength significantly decreases when wet with water are preferred. Furthermore, among them, corrugated cardboard base paper mainly used for transporting goods is particularly preferred.

[0049] [Evaluation of water resistance] In the present invention, "being water-resistant" is evaluated based on the compressive strength of the base material measured under the following conditions. 1. A test piece for measuring the vertical compressive strength described in JIS Z0403-2:1999 (Method A) is cut out from the fibrous base material of the present invention, and the vertical compressive strength is measured based on the method described in the above standard [s1]. 2. The above test piece is immersed in a water tank with a water depth of 10 cm at room temperature for 3 hours. 3. The vertical compressive strength of the immersed test piece is measured in the same manner as above [s2]. 4. Calculate the ratio of the measured values before and after immersion ([s2] / [s1]). If it is 0.15 or more, it is determined that the material is water-resistant.

[0050] [Method for manufacturing a water-resistant fibrous base material] Further, the present invention provides a method for manufacturing a water-resistant fibrous base material, comprising: (1) a step of impregnating a fibrous base material with a treatment agent containing a silazane compound; and (2) a step of heat-treating the fibrous base material impregnated with the treatment agent at 120°C or higher. The present invention provides a method for manufacturing a water-resistant fibrous base material including the above steps.

[0051] [Step (1)] Step (1) is a step of impregnating a fibrous base material with a treatment agent containing a silazane compound.

[0052] The fibrous base material of the present invention has fibers coated with oxides, oxynitrides, and nitrides formed from a silazane compound. From the viewpoint of maintaining strength when wet with water, it is required that the contact surfaces between fibers are coated. In the present invention, impregnation is required as a method for coating fibers with a silazane compound. By performing impregnation, the space between fibers can be evenly impregnated, and uniform coating on the fibers can be achieved.

[0053] The pressure in the impregnation method is preferably in the range of 0.005 to 0.5 MPa, and the impregnation time is preferably in the range of 10 minutes to 12 hours. If the pressure is in a reduced or increased state with respect to atmospheric pressure, the impregnating liquid can penetrate between the fibers in a short time, which is preferable. Even if the pressure is too high, there is no demerit, but no significant effect corresponding to it can be obtained, and equipment and running costs are unnecessarily incurred, so it is preferably within 0.5 MPa. Also, similarly, if the impregnation time is 10 minutes or more, sufficient effects can be expected, and even if it is 12 hours or more, no greater effect can be obtained, so it is preferably within an appropriate range.

[0054] The coating amount has no particular limitation as long as characteristics such as water resistance and strength improvement are exhibited. Generally, it is preferably in the range of 0.001 to 0.5 g per 1 g of the fibrous substrate. If it is 0.001 g or more, the coating effect on the fiber appears, which is preferable, and if it is within 0.5 g, the texture of the fibrous substrate is not impaired, which is preferable.

[0055] [Step (2)] Step (2) is a step of heat-treating the fibrous substrate impregnated with the treatment agent at 120°C or higher.

[0056] After thus coating the fibrous substrate with the silazane compound, the substrate is heat-treated for drying and curing of the silazane compound. By heating simultaneously during drying and curing, the curing time can be shortened. In this step, the purpose is to remove the solvent contained in the coating film and to promote curing reactions such as dealcoholization condensation, dehydrogenation condensation, and deammoniation condensation by hydrolysis, dehydration condensation of the hydrosilyl group and hydroxy silyl group contained in the silazane compound.

[0057] In the present invention, it is necessary to perform heating at 120°C or higher, and the temperature range is preferably 120 to 180°C. Although the silazane compound reacts with moisture in the air and the like even at room temperature and the curing proceeds, the curing reaction is further promoted by performing heating at 120°C or higher. Generally, when the silazane compound is cured by heating, a denser coating film can be obtained compared to the case where it is reacted with moisture. Therefore, heating is also effective in terms of water resistance. In addition, the time for performing the standing step before heating is appropriately optimized according to conditions such as temperature and humidity, but it is desirable to stand until at least a finger-touch dry state is achieved.

[0058] The "finger-touch dry state" refers to a state where, as described in JIS 5600-1-1:1999, the center of the coated surface is gently touched with a fingertip and the fingertip does not get dirty.

Examples

[0059] Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the following examples.

[0060] In the following examples, "parts" indicate parts by mass. Also, "normal temperature" indicates that the temperature is in the range of 5 to 35°C as described in JIS Z 8703:1993. Also, "normal pressure" indicates an atmosphere under atmospheric pressure without pressurization or depressurization.

[0061] In addition, the following evaluations were performed on each substrate obtained in the following reference examples, examples, and comparative examples. The results are shown in Table 1.

[0062] [Appearance] The appearance of the coating film was evaluated visually.

[0063] [Water resistance] Test pieces described in JIS Z0403-2:1999 (Method A) were prepared and immersed in tap water with a water depth of 10 cm for 3 hours. Then, the upper and lower ends of the substrate were fixed vertically, and the compressive strength when compressed in the vertical direction was measured [s2]. In addition, a test piece before the immersion treatment was separately prepared and the compressive strength was measured [s1], and a comparison of the compressive strength before and after the immersion treatment was performed ([s2] / [s1]).

[0064] [Paint Test] It was evaluated whether an oil-based marker could be used to write on the corrugated cardboard surface. As the oil-based marker, Mackie (manufactured by Zebra Co., Ltd.) was used. The evaluation criteria are as follows. Writeable: ○ Writeable (partial repulsion, discontinuous): △ Unwriteable: ×

[0065] [Label Peel Test] A peel test of the label seal attached to the corrugated cardboard surface was conducted. For the peel test, referring to JIS Z 0237:2009, the peel angle was 180°, and as the label, Yupo UV PAT1 (manufactured by Lintec Corporation) was used. The evaluation criteria are as follows. No breakage on the corrugated cardboard: ○ Partial breakage on the corrugated cardboard (10% or less of the label area): △ Partial or complete breakage on the corrugated cardboard (more than 10% of the label area): ×

[0066] [Example 1] 2 parts of perhydropolysilazane as a silazane compound, 0.1 part of aminopropyltriethoxysilane as a curing catalyst, and 98 parts of dibutyl ether as a diluting solvent were mixed to prepare a treatment agent. A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with the treatment agent at normal temperature and pressure for 3 hours. Then, the test piece was allowed to stand for 1 hour and cured at 120°C for 24 hours. When the appearance of the cured test piece was visually confirmed, there was no change compared to before impregnation. The results of the water resistance, paint test, and label peel test of the treated test piece are shown in Table 1.

[0067] [Example 2] A treatment agent was prepared by mixing 2 parts of perhydropolysilazane as a silazane compound, 0.1 parts of aminopropyltriethoxysilane as a curing catalyst, and 98 parts of dibutyl ether as a dilution solvent, and a test piece described in JIS Z 0403-2:1999 (A method) was impregnated with the treatment agent at room temperature and normal pressure for 3 hours. The test piece was then left to stand for 1 hour and cured at 150°C for 24 hours. When the appearance after curing was visually confirmed, there was no change from before impregnation. As in Example 1, the various evaluation results are shown in Table 1.

[0068] [Example 3] A treatment agent was prepared by mixing 2 parts of perhydropolysilazane as a silazane compound, 0.1 parts of aminopropyltriethoxysilane as a curing catalyst, and 98 parts of dibutyl ether as a dilution solvent, and a test piece described in JIS Z 0403-2:1999 (A method) was impregnated with the treatment agent at room temperature and normal pressure for 3 hours. The test piece was then left to stand for 1 hour and cured at 150°C for 48 hours. When the appearance after curing was visually confirmed, there was no change from before impregnation. As in Example 1, the various evaluation results are shown in Table 1.

[0069] [Example 4] As the silazane compound, R in the structure of formula (1) 1 A treatment agent was prepared by mixing 2 parts of methyl-modified polysilazane, in which 0.91 is hydrogen atom and 0.09 is methyl group, 0.1 parts of aminopropyltriethoxysilane as a curing catalyst, and 98 parts of dibutyl ether as a diluting solvent, and a test piece described in JIS Z 0403-2:1999 (A method) was impregnated with the treatment agent at room temperature and normal pressure for 3 hours. Then, the test piece was left to stand for 1 hour and cured at 150°C for 24 hours. When the appearance after curing was visually confirmed, there was no change from before impregnation. As in Example 1, various evaluation results are shown in Table 1.

[0070] [Example 5] As a silazane compound, 5 parts of perhydropolysilazane, 0.25 part of aminopropyltriethoxysilane as a curing catalyst, and 95 parts of dibutyl ether as a diluting solvent were mixed to prepare a treating agent. A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with the treating agent at normal temperature and pressure for 3 hours. Then, the test piece was allowed to stand for 1 hour and cured at 150 °C for 24 hours. When the appearance after curing was visually confirmed, there was no change compared to before impregnation. Similar to Example 1, various evaluation results are shown in Table 1.

[0071] [Example 6] As a silazane compound, 2 parts of perhydropolysilazane, 0.02 part of silica filler with an average particle size of 0.1 μm, 0.1 part of aminopropyltriethoxysilane as a curing catalyst, and 98 parts of dibutyl ether as a diluting solvent were mixed to prepare a treating agent. A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with the treating agent at normal temperature and pressure for 3 hours. Then, the test piece was allowed to stand for 1 hour and cured at 150 °C for 24 hours. When the appearance after curing was visually confirmed, there was no change compared to before impregnation. Similar to Example 1, various evaluation results are shown in Table 1.

[0072] [Comparative Example 1] A vertical compression test was performed on a test piece described in JIS Z 0403-2:1999 (Method A) before and after immersion in tap water for 3 hours. The value before the test was 0.995 kN / m, but the test piece decomposed during the test. Also, the paint test and label test results are shown in Table 1. The water resistance, paint test, and label peeling test results of the untreated test piece are shown in Table 1.

[0073] [Comparative Example 2] As a silazane compound, 2 parts of perhydropolysilazane, 0.1 part of aminopropyltriethoxysilane as a curing catalyst, and 98 parts of dibutyl ether as a diluting solvent were mixed to prepare a treating agent. A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with the treating agent at normal temperature and pressure for 3 hours. Then, the test piece was cured at normal temperature for 24 hours. When the appearance after curing was visually confirmed, there was no change compared to before impregnation. Similar to Example 1, various evaluation results are shown in Table 1.

[0074] [Comparative Example 3] As the silazane compound, 5 parts of perhydropolysilazane, 0.25 part of aminopropyltriethoxysilane as a curing catalyst, and 95 parts of dibutyl ether as a diluting solvent were mixed to prepare a treating agent. A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with the treating agent at normal temperature and pressure for 3 hours. Then, the test piece was allowed to stand for 1 hour and cured at 100 °C for 24 hours. When the appearance after curing was visually confirmed, there was no change compared to before impregnation. Similar to Example 1, various evaluation results are shown in Table 1.

[0075] [Comparative Example 4] 5 parts of dimethyl silicone oil and 95 parts of toluene as a diluting solvent were mixed to prepare a treating agent. A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with the treating agent at normal temperature and pressure for 3 hours. Then, the test piece was heated at 120 °C for 1 hour to remove the solvent. When the appearance after solvent removal was visually confirmed, there was no change compared to before impregnation. Similar to Example 1, various evaluation results are shown in Table 1.

[0076] [Comparative Example 5] 5 parts of tetraethoxysilane (TEOS), 0.01 part of tetra-t-butoxytitanium as a curing catalyst, 50 parts of water and 45 parts of methanol as a diluting solvent were mixed to prepare a treating agent. A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with the treating agent at normal temperature and pressure for 3 hours. Then, the test piece was allowed to stand for 1 hour and cured at 150 °C for 24 hours. When the appearance after curing was visually confirmed, it had a wet-like appearance. Similar to Example 1, various evaluation results are shown in Table 1.

[0077] [Comparative Example 6] A test piece described in JIS Z 0403-2:1999 (Method A) was impregnated with Epokwik FC (manufactured by Buehler Co., Ltd.) as an epoxy resin at normal temperature for 3 hours. Then, the test piece was cured at normal temperature and pressure for 24 hours. When the appearance after curing was visually confirmed, the surface had a smooth texture and was shiny. Similar to Example 1, various evaluation results are shown in Table 1.

[0078]

Table 1

[0079] From the results in Table 1, in Comparative Example 1 where the corrugated cardboard test piece was used as it was, and in Comparative Example 4 where non-curable dimethyl silicone oil was used instead of the silazane compound, the corrugated cardboard test piece decomposed when immersed in tap water for 3 hours. On the other hand, in Examples 1 to 6 and Comparative Examples 2, 3, 5, and 6, the corrugated cardboard test piece did not decompose even when immersed in tap water for 3 hours.

[0080] However, in Comparative Examples 2, 3, 5, and 6, the strength after immersion decreased significantly. This is because in Comparative Examples 2 and 3 where the silazane compound was cured at a temperature below 120°C, and in Comparative Example 5 where TEOS was used instead of the silazane compound, the curing of the impregnated silazane compound and TEOS was insufficient against water immersion. Also, in Comparative Example 6 where an epoxy resin was used instead of the silazane compound, the fibers of the test piece were not completely coated, and the corn starch, which is the adhesive, was partially dissolved in water and the strength decreased. Although it can be improved by lowering the concentration of the epoxy resin used, corrugated cardboard with an organic resin film is difficult to reuse and has a great impact on recyclability. Furthermore, in Comparative Examples 1 to 6, none of them could sufficiently clear both the paint test and the label peeling test. Especially in the label peeling test, when the label was peeled off, the fibers on the surface of the corrugated cardboard were also torn and peeled off together if the coating and curing between the fibers were not sufficient.

[0081] On the other hand, in Examples 1 to 6, sufficient strength was maintained even after immersion. This is because the silazane compound cured at 120°C or higher strongly bonded the corrugated cardboard fibers and the corn starch of the paste, preventing the fibers from unraveling and the paste from dissolving in water. Also, sufficient performance was exhibited in the paint test and the label peeling test, and there was no case where the fibers on the surface of the corrugated cardboard were torn and peeled off together when the label was peeled off.

[0082] From these results, it can be seen that the fibrous substrate of the present invention does not involve any change in appearance, and is extremely effective in maintaining the structure of the substrate, especially when immersed in water. Moreover, since it does not use an organic resin-based material with a large environmental load, it is possible to provide a substrate that also takes environmental considerations into account.

[0083] This specification encompasses the following inventions.

[0084] [1]: A fibrous substrate made water-resistant with a treatment agent containing a silazane compound, wherein the ratio (s2 / s1) of the vertical compressive strength (s1) before immersion and the vertical compressive strength (s2) after 3 hours of water immersion is 0.15 or more in the vertical compressive strength measured by the method described in JIS Z0403-2:1999 (Method A). A water-resistant fibrous substrate characterized by this.

[0085] [2]: The silazane compound is represented by the following formula (1):

Chemical formula

[0086] [3]: The water-resistant fibrous substrate according to [1] or [2] above, characterized in that the silazane compound is perhydropolysilazane.

[0087] [4]: The water-resistant fibrous substrate according to any one of [1] to [3] above, characterized in that the treatment agent contains a curing catalyst.

[0088] [5]: The water-resistant fibrous substrate according to any one of [1] to [4] above, characterized in that the fibrous substrate is cardboard.

[0089] [6]: A method for manufacturing a water-resistant fibrous substrate, comprising: (1) a step of impregnating a fibrous substrate with a treatment agent containing a silazane compound; and (2) a step of heat-treating the fibrous substrate impregnated with the treatment agent at 120 °C or higher. A method for manufacturing a water-resistant fibrous substrate, characterized by comprising these steps.

[0090] Note that the present invention is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Claims

1. A fibrous substrate hydrophobized with a treating agent containing a silazane compound, wherein the ratio (s2 / s1) of the vertical compressive strength (s1) before immersion to the vertical compressive strength (s2) after 3 hours of water immersion is 0.15 or more in terms of the vertical compressive strength measured by the method described in JIS Z0403-2:1999 (Method A). The hydrophobized fibrous substrate is characterized by this.

2. The hydrophobized fibrous substrate according to Claim 1, wherein the silazane compound is a silazane compound having a structure represented by the following formula (1): 【Chemical 1】 (wherein, R １ is independently a group selected from a hydrogen atom, an aliphatic hydrocarbon group having 1 to 6 carbon atoms, an aromatic hydrocarbon group having 6 to 12 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms. However, among the entire R １ , 90% or more is a hydrogen atom.)

3. The hydrophobized fibrous substrate according to Claim 1, wherein the silazane compound is perhydropolysilazane.

4. The hydrophobized fibrous substrate according to Claim 1, wherein the treating agent contains a curing catalyst.

5. The hydrophobized fibrous substrate according to Claim 1, wherein the fibrous substrate is cardboard.

6. A method for producing a hydrophobized fibrous substrate, comprising: (1) a step of impregnating a fibrous substrate with a treating agent containing a silazane compound; and (2) a step of heat-treating the fibrous substrate impregnated with the treating agent at 120°C or higher. The method for producing a hydrophobized fibrous substrate is characterized by including these steps.