JPH0219240B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a paper coating liquid that improves the whiteness, smoothness, hiding power, gloss, ink receptivity, etc. of paper such as thin paper, cardboard, and paperboard. More specifically, the present invention relates to a method of producing a paper coating liquid that has a low viscosity despite a high solids concentration. Conventional paper coating liquids are mainly prepared through the following steps: (1) About 30% by weight of starch such as oxidized starch, aminophosphate starch, hydroxyethyl starch, etc. and about water.
A starch slurry containing 70% by weight is gelatinized by heating in a starch gelatinization tank at a temperature of 70°C or higher for about 20 to 30 minutes to obtain gelatinized starch with a concentration of about 20 to 30% by weight, or Alternatively, starch slurry can be gelatinized with an enzyme to obtain enzyme-modified starch with a concentration of about 10 to 35%; (2) As a pigment, for example, 70 parts by weight of clay and 30 parts by weight of water can be mixed in a pigment dispersion tank to form an aqueous pigment. preparing a dispersion; and (3) mixing the gelatinized starch slurry with the pigment dispersion in a coating liquid preparation tank. In such conventional methods, a large amount of water is required to gelatinize the starch. For that water
The solid content concentration of the coating liquid becomes low. Removal of excess water during the manufacturing process of coated paper consumes a large amount of thermal energy for drying. Moreover, since drying equipment and space for its installation are required, the cost is extremely high.
The heating performed to gelatinize the starch also consumes significant energy. In an attempt to reduce the amount of water required for gelatinizing starch, gelatinizing starch in the presence of pigments or denaturing it with enzymes has been proposed, for example, by James P. Casey, “Pulp and
Paper, Chemistry & Chemical Technology”
Disclosed in vol.2, P.1020-1025 (1952).
The above-mentioned document also discloses that starch is modified with an enzyme in the total amount of water used in the coating liquid and a pigment is added to the modified starch. Both methods have the significant disadvantage that large amounts of water must be heated and the entire tank must be cooled to reduce the temperature of the starch and pigment before use. The purpose of the present invention is to directly add powdered or granular dry starch to an aqueous pigment dispersion.
An object of the present invention is to provide a method for producing a coating liquid having a high solids concentration and a low viscosity. Still another object of the present invention is to provide a method for producing a coating liquid containing cold water soluble starch, in which the starch used is soluble in a cold water dispersion of pigment and gelatinization is performed, so that neither gelatinization equipment nor gelatinization heating is required. It is about providing. Still another object of the present invention is to provide a method for producing a coating liquid that requires less heat energy for drying when applied to paper due to its high solids concentration. Yet another object of the present invention is to provide a method for producing a coating fluid that requires significantly less preparation time. The present invention will be explained below. The coating liquid of the present invention is prepared by directly adding the cold water soluble starch to the pigment dispersion in the form of powder or granules. Since starch is soluble in cold water, the water in the pigment dispersion can be used and it can be dissolved without heating. Due to the direct addition of powder, the resulting coating liquid is highly concentrated. Despite its high concentration, this coating liquid has high fluidity and low viscosity. Due to its high concentration and low viscosity, it produces the following effects in the paper coating process: (a) normal coating liquid flow is maintained at the blade edge of the coating equipment; (b) at the blade edge. (c) Since selective absorption into the base paper layer is prevented, streak troubles and roll patterns do not occur on the coated paper; (d) The resulting coated paper has excellent properties. smoothness, hiding power,
It has good gloss, ink receptivity, etc.; and (e) along with improved fluidity, mottles (uneven coating) that commonly occur with air knife coaters are improved. What is the cold water soluble starch used in the present invention?D.
E.20% by weight or less of enzyme-modified starch, pregelatinized starch, roasted dextrin, starch derivatives, etc. that have been treated to be soluble in cold water. Enzyme-modified starch is
Starch slurry derived from corn, waxy corn, potatoes, sweet potatoes, wheat, rice, tapioca, sago and its starch derivatives is adjusted to a specified concentration and pH, and then liquefied using α-amylase and other enzymes. It is obtained by carrying out a reaction, then inactivating the enzyme by heating (for example, 110 to 150°C) or using an acid, and then drying this. This enzyme-modified starch is in powder or granule form and has a moisture content of 20%
% by weight or less, crude protein 2.0% by weight or less, crude fat 1.0% by weight or less, crude fiber 1.0% by weight or less, crude ash content 1.0% by weight or less, DE 20% by weight or less, and the viscosity of a 30% dispersion is 3000 cp or less. has value.
In particular, it is desirable that the DE content be 8 to 12% by weight. When the DE content is less than 8% by weight, the viscosity increases, and even if no powder is added, the viscosity of the entire coating liquid increases, making it difficult to coat paper. When the DE content exceeds 12% by weight, the starch particles have a low molecular weight, resulting in a low viscosity and improved fluidity of the coating liquid, but a decrease in adhesive strength. Pregelatinized starch refers to starch obtained by heating, gelatinizing, and drying a slurry of the starch or its starch derivative. Among these, pregelatinized starch from waxy corn is particularly desirable because it is less retrograded and easily soluble in water. Roasted dextrin refers to something obtained by roasting the starch or its starch derivative as it is or with the addition of an acid at a high temperature. Starch derivatives are those that have been etherified, esterified, or reacted with other chemicals to form a functional group, making them soluble in cold water. The coating liquid obtained according to the invention contains 100 parts by weight of pigment, 1 to 50 parts by weight of cold water-soluble starch, and water. If necessary, use a waterproofing agent in an amount of 10 parts by weight or less. Examples of pigments include kaolin, clay, talc, commonly used in the manufacture of coated papers,
Examples include barium sulfate, calcium sulfate, calcium carbonate, satin white, aluminum hydroxide, titanium dioxide, calcium sulfite, zinc oxide, etc., and one or more of these are used as a mixture in an appropriate ratio. Dispersants may be used in preparing pigment dispersions. Examples include sodium polyacrylate, sodium lignin sulfonate, phosphate, commonly used as a pigment dispersant,
Examples include olefin maleic anhydride copolymer, sodium citrate, and sodium succinate, and one or more of these may be used as necessary. Examples of the waterproofing agent include dialdehyde compounds, polyalkylene urea or polyamide urea, formaldehyde or N-methylol compounds or their initial condensates, and epoxy compounds. Dialdehydes are, for example, glyoxal and glutaraldehyde. Examples of polyalkylene urea include diethylenetriamine, triethylenetetramine, tetraethylenepentamine,
It is produced by the deammoniation reaction of a polyalkylene polyamine such as iminobispropylamine and urea. Polyamide urea is produced, for example, by reacting a polyamide obtained by condensing a dicarboxylic acid such as adipic acid or phthalic acid with a polyalkylene polyamine and urea. N
-Methylol compounds include, for example, methylolated melamines such as trimethylolmelamine, dimethyl ether of trimethylolmelamine; partially alkylated methylolmelamines; methylolated ureas; methylolated cyclic ureas such as dimethylolethylene urea and dimethylolglyoxymonourea; be. The initial condensate is obtained by condensing the above N-methylol compound to the extent that water solubility is not lost. Examples of the epoxy compound include glycerol polyglycidyl ether, trimethylpropanol polyglycidyl ether, diglycerol polyglycidyl ether, and sorbitol polyglycidyl ether. The coating liquid obtained according to the present invention may further contain a synthetic resin latex. Synthetic resin latex improves pigment binding ability, adhesion to paper, water resistance and gloss of coated paper, and examples include styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer. diene polymer latex such as; acrylic polymer latex such as a polymer or copolymer of acrylic acid ester and/or methacrylic acid ester; vinyl acetate polymer latex such as ethylene/vinyl acetate copolymer; There are functional group-modified polymer latexes of various polymers. These may be used alone or in combination of two or more. This coating liquid may further contain various commonly used auxiliary agents such as dispersants, flow modifiers, antifoaming agents, dyes, lubricants, waterproofing agents, and water retention agents. The present invention will be further explained in detail based on examples. Example 1 A starch emulsion in almost the final step of the corn starch manufacturing process was adjusted to a concentration of 20 degrees Baumé. Then, slaked lime was added to adjust the pH to 6-7. Add α-amylase (Daiwa Kasei, 10,000 units/g) to this at approximately 0.3% by weight based on starch (converted to anhydrous).
The mixture was added and gelatinized by heating at about 90°C to perform an enzyme liquefaction reaction. The enzyme liquefaction reaction was carried out at about 90°C for 2 hours. After the specified enzyme liquefaction reaction was completed, the enzyme was inactivated by pressurizing and heating to 125°C. The resulting paste containing enzyme-modified starch was spray-dried. The spray dried powder was then passed through a 20 mesh sieve to remove a small amount of coagulum. Table 1 shows the quality and physical properties of the produced enzyme-modified starch.

[Table] Example (a) Preparation of 70% by weight pigment dispersion No. 1 kaolin (manufactured by EMC, UW
-90) 100 parts by weight and 0.2 parts by weight of sodium polyacrylate as a dispersant were dispersed in water using a Coles disperser to prepare a pigment dispersion with a solid content concentration of 70% by weight. (b) Preparation of coating liquid 20 parts by weight of the granulated starch prepared in the example was added.
It was added directly to a 70% by weight kaolin dispersion at room temperature with stirring. The resulting mixture was heated at 550 rpm for 20
The mixture was stirred for a minute to gelatinize. Next, calcium stearate, which is a calendering lubricant, was added and further aged for 30 minutes to prepare a coating liquid.
Its composition is shown below. Kaolin (UW-90) 100 parts by weight Sodium polyacrylate 0.2 parts by weight Starch (solid content) 20 parts by weight Calcium stearate 1.5 parts by weight (c) Manufacture of coated paper ^The above coating liquid was applied to On the original paper, RD
One side was coated using S.Laboratory Coating Rod. Immediately after coating, heat in a hot air dryer at 105℃.
Dry for 3 minutes. Calendar treatment was performed three times using a super calender manufactured by Yuri Roll at a temperature of 55° C. and a linear pressure of 100 kg/cm. The resulting single-sided coated paper was conditioned for 24 hours at a temperature of 20°C and a humidity of 65%, and was used to measure the properties of the coated paper. The results are shown in Table 2. (d) Preparation of control coating solution Add water to commercially available aminophosphoric acid ester starch,
The mixture was heated at 95° C. for 20 minutes to dissolve and prepare a paste solution with a concentration of 30% by weight. After cooling this to 30° C., it was added to a 70% by weight kaolin dispersion and the same procedure as in (b) above was carried out to obtain a control coating liquid. Using this, a control coated paper was obtained through the same procedure as in (c) above. The results are shown in Table 2 as a comparative example. Example The enzyme-modified starch granules obtained in the example were heated at 50°C.
A paste solution with a concentration of 30% by weight was prepared by dissolving it in warm water. This was added to the 70% by weight kaolin dispersion obtained in the example to obtain a coating liquid in the same manner as in the example. A coated paper was obtained using this coating liquid in the same manner as in the example. The results are shown in Table 2. Example The enzyme-modified starch granules obtained in the example were directly added to the 70% by weight kaolin dispersion of the example, which had been preheated to 50°C, with stirring, and then the coating liquid was prepared in the same manner as in the example. Obtained. A coated paper was obtained using this coating liquid in the same manner as in the example. Second result
Shown in the table. As is clear from Table 2, Examples,
Although the solid content concentration is higher than that of the comparative example, the viscosity is lower, and the high shear fluidity is improved. Water retention is equivalent to the comparative example. The surface strength of the coated paper is lower than that of the comparative example. It can be seen that among the methods of adding enzyme-modified starch to the pigment dispersion according to Examples, the method of Examples, in which starch is directly added to the pigment dispersion at room temperature, is the most rational and simple.

[Table] Example In order to improve the surface strength of coated paper, modified styrene-butadiene copolymer latex was used in addition to starch as an adhesive. 20 parts by weight of an adhesive consisting of starch and the latex was used for 100 parts by weight of a 70% by weight kaolin dispersion. Granular powder of enzyme-modified starch was added directly to the 70% by weight kaolin dispersion in the range of 75-15% by weight based on the total amount of adhesive. Next, the latex was added and mixed in an amount ranging from 25 to 85% by weight based on the total amount of the adhesive. After adding calcium stearate to the resulting mixture, the pH was adjusted to 9 with aqueous ammonia. Dilution water was added to obtain a coating liquid with a solid content concentration of 50% by weight. Its composition is shown below.

[Table] Using the above coating liquid, coated paper was obtained in the same manner as in the examples. The results are shown in Table 3. The control coating liquid was
After adding the 30 wt % aminophosphoric acid starch paste used in the comparative example of the example to the 70 wt % kaolin dispersion, the preparation was carried out in the same manner as in the example. A control coated paper was similarly obtained using this control coating liquid. The results are shown in Table 3 as a comparative example. From Table 3, it can be seen that although the solids concentration of the coating fluids of the Examples is almost the same as that of the Control, the viscosity thereof is significantly lower than that of the Control. High shear fluidity is also improved, and coating properties are also good. The use of latex reduces water retention, and this tendency becomes more pronounced as the blending ratio of latex increases. The white paper gloss, which is one of the properties of coated paper, is 5~5% higher than that of the control.
It is 10 points higher and has been greatly improved. The K&N ink test, which indicates the printability of coated papers and also evaluates ink receptivity, is slightly better than the control. The printing gloss is 50% latex.

[Table] The above are equivalent. IGT surface strength and
The RI printing strength depends on the latex blending ratio.
Equivalent in 50% or more. Example In this example, the effect of a water-resistant agent was investigated in order to improve the water resistance of coated paper. The coating liquid was 70% by weight of enzyme-modified starch granule powder as in the example.
It was prepared by adding it to a kaolin dispersion. In addition to this starch, latex (JSR#0692) was used as an adhesive in the same manner as in the examples. This example differs from the example in that a water resistant agent was used. Melamine resin (Sumitomo Chemical Co., Ltd.: Sumiretsu Resin #613) was used as the water resistant agent. The composition of the resulting coating liquid was as follows: Kaolin (UW-90) 100 parts by weight Sodium polyacrylate 0.2 parts by weight Starch (solid content) 10 parts by weight Latex (JSR#0692) 10 parts by weight Stair Calcium phosphate 1.5 parts by weight Melamine resin (Violet Resin #613) (water resistant agent) 5-15% by weight (based on starch) Ammonia water Appropriate amount Coated paper was obtained using this coating liquid and the quality was evaluated. Ivy. The results are shown in Table 4. The coating liquid for the control was the same as the control for the example except that a melamine-based resin (violet resin #613) was used as a water-resistant agent. The test results for the control coating fluid and coated paper are as follows: Comparative Example Treatment 1
Shown in the table. Example Everything was the same as in Example, except that an epoxy resin (Denacol #PC-1000, manufactured by Nagase Kasei) was used instead of the melamine resin as the water-resistant agent in the coating liquid of Example. The results are shown in Table 4. The test results for the control coating fluid and coated paper are shown in Table 4 as Comparative Example Treatment 2. As is clear from Table 4, the water resistance of the coated paper is almost the same as that of the control when an epoxy resin is used as the water resistance agent. Even when a melamine-based resin is used as a water-resistant agent, sufficient water resistance is exhibited 7 days after coating.

[Table] Examples and Effects of the amount of adhesive in the coating liquid and the dilution water required during preparation were investigated. In the example, 15 parts by weight of an adhesive consisting of 35% by weight of the enzyme-modified starch granule powder of the example and 65% by weight of the latex used in the example was used for 100 parts by weight of kaolin. The coating liquid was prepared by directly adding this starch to a 70% by weight kaolin dispersion in the same manner as in the example, and then in the same manner as in Process 5 of the example. Next, a coating solution was prepared with dilution water added to give a solid content concentration of 62% by weight, and another without using dilution water at all.
A coating liquid having a high solid content concentration of 67.7% by weight was obtained. The compositions of these coating liquids were as follows: Kaolin (UW-90) 100 parts by weight Sodium polyacrylate 0.2 parts by weight Starch Powder latex 15 parts by weight Calcium stearate 1.5 parts by weight Epoxy resin (Denacol #PC- 1000)
5% by weight (based on starch) Aqueous ammonia Appropriate amount Table 5 shows the quality of this coating liquid and the coated paper obtained using it. The control coating liquid was the same as the control (comparative example) of the example except that 15 parts by weight of adhesive was used for 100 parts by weight of kaolin, and a 30% by weight size liquid of commercially available aminophosphoric acid ester starch was mixed with 70% by weight of kaolin. It was added to the dispersion liquid and prepared in the same manner as in the control of the example (comparative example treatment 2). If no dilution water was used, the solids concentration of this control coating solution would be 62.6.
It was in weight%. This control is shown in Table 5 as a comparative treatment. The only difference in this example is that 20 parts by weight of the adhesive was used instead of 15 parts by weight. The coating liquid when dilution water was used had a solid content concentration of 62% by weight, and the coating liquid when dilution water was not used had a solid content concentration of 67.4% by weight. The composition of this coating liquid was as follows: Kaolin (UW-90) 100 parts by weight Sodium polyacrylate 0.2 parts by weight Starch Powder latex 20 parts by weight Calcium stearate 1.5 parts by weight Epoxy resin (Denacol #PC- 1000)
5% by weight (based on starch) Aqueous ammonia Appropriate amount Table 5 shows the quality of the coating liquid and the coated paper obtained using the coating liquid. A control coating solution was prepared in the same manner as Comparative Example 1 above except that 20 parts by weight of the adhesive was used instead of 15 parts by weight. Its solid content concentration was 61.4% by weight. This is shown in Table 5 as Comparative Example Treatment 2. Table 5 shows that the coating fluid of the present invention has a low viscosity despite its high solids concentration. Water retention has also been improved. An improvement in high shear fluidity is observed at the same solid content concentration. Also,
Coatability with a blade coder was also good, with no streaks or scratches occurring during coating. The properties of the coated paper and printability are also approximately the same as those of the comparative example.

【table】

[Table] Example The sixth example was prepared using the same procedure as in the example described above.
A coating liquid having the composition shown in the upper row of the table was obtained. This was applied to a base paper for coating using a test plant bar coater at a coating speed of 70 m/min. The coating weight on each side of the resulting coated paper was 11 g/m ² in solid form. After drying, the coated paper was supercalendered. The properties of the coating liquid, workability, and quality of the coated paper are shown in the lower middle row of Table 6. The control coating liquid was the same as Example X except that aminophosphate starch was used as the starch.
is the same as Using this as a comparative example, the sixth
Shown in the table. Table 6 shows that the viscosity and high shear fluidity of the coating liquid are improved. Regarding coating properties using a test plant bar coater, no streak troubles such as streaks or scratches occurred. In terms of coated paper quality, white paper gloss is particularly excellent. Next, a prototype was produced using a test plant bar coater using the paper coating liquids of Examples and Comparative Examples.

【table】

[Table] Actual printing was performed on coated paper under the following conditions. Table 7 shows workability during printing, picking, paper dust generation, printing quality, and other comprehensive evaluations.

[Table] Table 7 shows that the coated paper prototyped using the paper coating liquid of the present invention was the most excellent in the overall printing evaluation. Printing conditions 1 Printing machine Roland Record RZK3 type 2-color press 2 Test version Fuji Photo Film GAP- 3 Blanket Kinyosha Co., Ltd. S5300W Air blanket semi-hard finish 4 Ink Dainippon Ink Co., Ltd. New Champion Super Apex S type 5 printing Order Indigo → Red 6 Dampening water Factory water + EPA 5% Addition of 0.5% DH-78 from Dainippon Ink Co., Ltd. 7 impressions Linear pressure between plate cylinder and blanket cylinder 15/100
mm Linear pressure between blanket cylinder and impression cylinder 15/100 mm 8 Printing speed 5000 sheets/hour 9 Number of sheets printed 2000 sheets Example XI Commercially available Waxy α was used as the cold water soluble starch. The composition of the coating liquid is shown below. Kaolin (UW-90) 100 parts by weight Sodium polyacrylate 0.2 parts by weight Starch 5.6 parts by weight Latex (JSR#0692) 10.4 parts by weight Calcium stearate 1.5 parts by weight Coated paper was obtained through the same procedure as in the example. The measurement results are shown in Table 8. Regarding the control coating liquid, Example
is the same as The measurement results for the control coating liquid are shown in Table 8 as a comparative example.

【table】

[Table] Example XII Roasted dextrin was used as the cold water soluble starch. Diluted 15 times with 61% nitric acid. This was added to corn starch at a ratio of 0.5% as pure nitric acid and mixed to obtain starch with a moisture content of 22%. This starch was pre-dried at 50°C to a moisture content of 5%. Next, add this starch to
By heating at 180°C for 8 hours, a roasted dextrin soluble in cold water was obtained. The composition of the coating liquid obtained by adding this starch powder is shown below. Kaolin (UW-90) 100 parts by weight Sodium polyacrylate 0.2 parts by weight Starch 7 parts by weight Latex (JSR#0692) 13 parts by weight Waterproofing agent (epoxy resin) 0.35 parts by weight Calcium stearate 1.5 parts by weight Aqueous ammonia Appropriate amount Table 9 shows the properties and printability of the coated paper obtained using the above coating liquid. Example A starch derivative was used as the cold water soluble starch. A commercially available emulsion of etherified starch (hydroxypropyl starch) with a degree of substitution of 0.1 (trade name Sunpearl L-1, manufactured by Sanwa Starch Industries Co., Ltd.) was used. A cold water-soluble substance of etherified starch DE2 was obtained by the same procedure as in the example except that the amount of α-amylase added was 0.1% by weight and the liquefaction reaction time was 10 minutes. Next, a coating liquid having the same composition as in Example XII above was prepared using this starch. Table 9 shows the properties of the coating liquid and the properties and printing suitability of the coated paper obtained using the liquid. As a control coating liquid, a commercially available aminophosphoric acid starch paste was used instead of the starch in the example. This is shown in Table 9 as a comparative example.

[Table] The measurement methods in each table above are as follows. The viscosity was measured using a Tokyo Keiki BL type viscometer at 25°C.
Measurement at 60 rpm; "immediately after preparation" indicates the viscosity immediately after preparation of the coating composition; "24 hours later" indicates the value measured 24 hours after preparation. Kumagai Riki Hercules type high shear viscometer
Torque value reading at 8800rpm or 4400rpm. ×10 ⁵ dyne-cm Water retention was determined by the KM _o O ₄ method using No. 6 paper. Measured value using a Murakami gloss meter at an incident angle of 75°C. Measured values with a blue filter using a Murakami Hunter photometer. Measured values with a green filter using a Murakami Hunter photometer. Measured value using Oken type smoothing tester. ′ Value measured by Sumstar smoothness tester. Measured value by Oken style air permeability tester. ′ Value measured by Sumstar air permeability tester. It is expressed as a whiteness reduction rate using K&N ink. Incident angle of solid printing surface using RI print tester
Glossiness at 75°. Reflection density measured using a Dainippon Screen densitometer on a solid printed surface using an RI print tester. Measured value with IGT printing suitability tester. The paper peel resistance during printing was measured and visually evaluated using an RI print tester. (Poor) 1 to 5 (Excellent) Using an RI printing tester, apply water to the coated surface with a water roll, then print, and measure paper peel resistance for visual evaluation. (Poor) 1-5 (Excellent) Using a taper abrasion tester, drop 10ml of distilled water onto the coated surface, rub the wet coated surface 10-20 times with a 250g rubber ring (one ring),
The friction surface was rinsed twice with distilled water and diluted to 100 ml. This is a measured value that indirectly measures the amount of paint removed from the sample by measuring the transmittance using a manual photoelectric colorimeter. Coating was performed at a speed of 600 m/min using a high-speed single-fed blade coater manufactured by Kumagai Riki for testing.
The coated surface was visually evaluated. Continuous coating was performed using a test plant bar coater, and the coated surface was visually evaluated. Note that the relative evaluation was performed in the following five stages. 〓: Extremely excellent. ◎: Excellent. ○: Good. △: Normal. ×: Bad.

Claims (1)

[Scope of Claims] 1. A method for producing a paper coating liquid containing at least a pigment, an adhesive, and water, comprising 1 to 50 parts by weight of powdered or granular cold water-soluble starch having a DE of 8 to 12% by weight as the adhesive. is directly added as a powder or granules to an aqueous pigment dispersion containing 100 parts by weight of the pigment and completely dissolved, thereby obtaining a size liquid without heat treatment. A method for producing paper coating liquid. 2. The method according to claim 1, wherein the cold water soluble starch is at least one selected from the group consisting of enzyme-modified starch, pregelatinized starch, roasted dextrin, and starch derivatives. 3. The method according to claim 1, wherein a synthetic resin latex is used in combination with the cold water soluble starch as the adhesive. 4. The method according to claim 1, further comprising using 10 parts by weight or less of a waterproofing agent. 5. The water resistant agent is at least one selected from the group consisting of dialdehyde compounds, polyalkylene urea, polyamide urea, formaldehyde, N-methylol compounds, initial condensates of N-methylol compounds, and epoxy compounds. The method described in Scope No. 4.