Uncoated paper and method for producing uncoated paper

Abstract

To provide an uncoated paper with excellent burst strength without using petroleum-derived materials.SOLUTION: The uncoated paper comprises base paper and chitosan with a weight-average molecular weight of 500,000 to 3,000,000 kDa. When divided into four layers in the thickness direction, the ratio of "chitosan content of each layer" to "total chitosan content of all layers" is 0.1 or greater in every layer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an uncoated paper containing chitosan and a method for manufacturing the uncoated paper.

Background Art

[0002] For packaging materials of foods such as confectionery, high burst strength and tensile strength are required. Conventionally, it has been common to use plastic films. In recent years, due to the increasing environmental awareness, a shift from plastic products to paper products for packaging materials has been demanded, and the number of packaging materials that shift from plastic products to paper products has been increasing. However, it has been difficult for thin papers such as general printing papers to achieve strength characteristics such as burst strength and tensile strength required for uncoated papers for packaging.

[0003] As a packaging material using paper, a technique of laminating a plastic film to a thin paper (such as Patent Document 1) is known. As a technique related to the burst strength of paper itself, generally, a method of adding a paper strengthening material such as cationized starch or polyacrylamide in the papermaking process is used. In addition, methods of applying an externally added paper strengthening material (such as Patent Document 2) and techniques for uniformizing the distribution of fine fibers while improving the yield of paper stock (such as Patent Document 3) have been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technology of Patent Document 1, petroleum-derived materials are partially used, and it cannot be said to be petroleum-free. Further, Patent Document 2 proposed using specific materials, but the usage conditions and the like were not specified. Furthermore, the technology of Patent Document 3 could only be implemented in a paper mill having a specific paper-making machine.

[0006] Generally, by applying polysaccharides such as starch and chitosan with high viscosity to the surface of paper, the strength of the paper such as stiffness is improved, but the burst strength characteristics cannot be improved.

[0007] Therefore, an object of the present invention is to provide an uncoated paper having excellent burst strength without using petroleum-derived materials. Another object of the present invention is to provide a method for manufacturing an uncoated paper capable of manufacturing an uncoated paper having excellent burst strength without using a special device.

Means for Solving the Problems

[0008] As a result of intensive studies to achieve such an object, the present inventor has found that it is effective to uniformly distribute a specific chitosan in the paper, and has completed the present invention.

[0009] The present invention provides the following. (1) An uncoated paper containing a base paper and chitosan having a weight average molecular weight of 50 to 3,000,000 kDa, wherein when divided into 4 layers in the thickness direction, the value of (chitosan content in each layer) / (total chitosan content in all layers) is all 0.1 or more. (2) The uncoated paper according to (1), further containing an acid, wherein the blending ratio of the chitosan and the acid is 10:1 to 1:10. (3) The uncoated paper according to (2), wherein the acid is at least one selected from the group consisting of lactic acid, citric acid, and malic acid. (4) The uncoated paper according to (1), wherein the Schopper-Riegler degree of the base paper is 50 seconds or less. (5) A coating step of coating a coating liquid containing chitosan with a weight average molecular weight of 50 to 3 million kDa on a base paper is included. The coating liquid has a total solid content concentration of 3.5% or less, and the B-type viscosity measured under the conditions of 40 °C and 60 rpm of the coating liquid is 500 mPa·s or less. The sizing degree of the base paper is 50 seconds or less. A method for manufacturing uncoated paper, characterized in that. (6) The method for manufacturing uncoated paper according to (5), wherein the coating liquid is a clear coating liquid further containing an acid.

Effects of the Invention

[0010] According to the present invention, it is possible to provide uncoated paper having excellent bursting strength without using petroleum-derived materials. Further, according to the present invention, it is possible to provide a method for manufacturing uncoated paper capable of manufacturing uncoated paper having excellent bursting strength without using a special device. Since the uncoated paper of the present invention also has excellent surface strength, it can be suitably used for offset printing.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. In the present invention, "~" includes the end values. That is, "X~Y" includes the values X and Y at both ends.

[0012] (Uncoated paper) The uncoated paper of the present invention includes a base paper and chitosan with a weight average molecular weight of 50 to 3 million kDa. When divided into 4 layers in the thickness direction, the value of (chitosan content in each layer) / (total chitosan content in all layers) is 0.1 or more for all. In this specification, "uncoated paper" refers to paper that does not have a distinct layer distinguishable from the base paper when the cross-section of the paper is observed with an electron microscope. For example, when a resin component or a polymer component is coated and the amount of the coated component is small and absorbed by the base paper, and as a result, there is no distinct layer distinguishable from the base paper when the cross-section of the paper is observed with an electron microscope, it corresponds to "uncoated paper".

[0013] From the perspective of imparting printability and writability, the non-coated paper of the present invention preferably has a water contact angle on the surface of the non-coated paper of 40 to 110 degrees, more preferably 50 to 100 degrees, under the condition 0.1 second after water droplet deposition. Further, the water contact angle is preferably 20 to 100 degrees, more preferably 30 to 90 degrees, under the condition 1 second after water droplet deposition. If the value of the contact angle is too small compared to the above lower limit value, there is a risk of ink bleeding and blurring. If it is too large compared to the above upper limit value, when used for offset printing, the dampening water is not absorbed by the paper, the balance between the ink and the dampening water on the printing plate is disrupted, and there is a risk of over-emulsification of the ink. The water contact angle can be adjusted, for example, by applying a sizing agent using a size press.

[0014] (Base paper) The pulp used for the base paper is appropriately selected. For fine paper, bleached chemical pulp such as kraft pulp or sulfite pulp is used. For medium paper, bleached or unbleached chemical pulp such as kraft pulp or sulfite pulp, groundwood pulp, mechanical pulp, thermomechanical pulp, etc., bleached or unbleached high-yield pulp, waste paper pulp such as deinked waste paper, etc. can be mentioned. For kraft paper, unbleached or bleached kraft pulp can be used.

[0015] The base paper can be manufactured by either an acidic papermaking method or a neutral papermaking method. However, since the paper manufactured by the neutral papermaking method is more likely to have a lower density than that manufactured by the acidic papermaking method, applying the present invention to the base paper manufactured by the neutral papermaking method can obtain a greater effect. Therefore, neutral papermaking is preferred.

[0016] In the case of acid papermaking, known internal sizing agents for acid papermaking such as rosin sizing agents, reinforced rosin sizing agents, and synthetic sizing agents can be used. The addition amount of the internal sizing agent for acid papermaking is preferably 0.05 to 5% by weight, more preferably 0.05 to 1% by weight, based on the pulp. Also, fillers that are stable even in the acidic region of the papermaking pH can be used. Specifically, inorganic fillers such as clay, calcined kaolin, delaminated kaolin, titanium dioxide, zinc oxide, silicon oxide, and amorphous silica, and organic fillers such as urea-formalin resin, polystyrene resin, phenol resin, and micro-hollow particles can be used alone or in combination of two or more as appropriate. There is no particular limitation on the filler ratio in the paper, but generally 5 to 40% by weight is preferred.

[0017] In the case of neutral papermaking, one sizing agent selected from known internal neutral sizing agents, namely alkyl ketene dimer (AKD)-based sizing agents, alkenyl succinic anhydride (ASA)-based sizing agents, and neutral rosin sizing agents, is used. AKD and ASA are more suitable than neutral rosin sizing agents because they tend to increase the bulk of the paper. The addition amount of the sizing agent is preferably 0.05 to 5% by weight, particularly preferably 0.1 to 1% by weight, based on the pulp. It is necessary to contain at least calcium carbonate as a filler, and one or more selected from other inorganic fillers such as magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay, calcined kaolin, delaminated kaolin, titanium dioxide, zinc oxide, silicon oxide, and amorphous silica, and organic fillers such as urea-formalin resin, polystyrene resin, phenol resin, and micro-hollow particles can be used in combination. There is no particular limitation on the filler ratio in the paper, but it is 5 to 40% by weight.

[0018] In the papermaking of the base paper used in the present invention, various nonionic and cationic retention aids, drainage improvers, paper strength improvers, and other internal additives for papermaking that have been conventionally used are appropriately selected and used as needed. Further, for example, basic aluminum compounds such as sulfuric acid band, aluminum chloride, sodium aluminate, basic aluminum chloride, and basic polyaluminum hydroxide, water-soluble aluminum compounds such as alumina sol that is easily decomposable in water, polyvalent metal compounds such as ferrous sulfate and ferric sulfate, and silica sol may be internally added. As other papermaking aids, various starches, polyacrylamide, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide, polyamine resin, polyamine, polyethyleneimine, plant gum, polyvinyl alcohol, latex, polyethylene oxide, hydrophilic cross-linked polymer particle dispersions, and various compounds such as derivatives or modified products thereof can be used. Furthermore, internal additives for papermaking such as dyes, fluorescent brighteners, pH adjusters, defoamers, pitch control agents, and slime control agents can be appropriately added according to the application.

[0019] Since the base paper used in the present invention needs to sufficiently penetrate the coating liquid containing chitosan, it is preferable that the sizing degree of the base paper is low, and the Stoke's sizing degree measured according to JIS P 8122 is preferably 0 seconds or more and 50 seconds or less, and more preferably 0 seconds or more and 10 seconds or less. By using low molecular weight and low viscosity chitosan, the permeability of the coating liquid to the base paper becomes good. However, by limiting the sizing degree of the base paper to below the above upper limit value, the coating liquid can be uniformly penetrated into the base paper regardless of the coating conditions.

[0020] The basis weight of the base paper used in the present invention is not particularly limited. However, from the viewpoint of the transportability in the printing and processing steps, it is preferably 10~300 g / m 2 and more preferably 30~250 g / m 2 and even more preferably 35~150 g / m 2This is the case. Low basis weight paper is more likely to have a problem with stiffness compared to high basis weight paper, and also has high permeability to the coating liquid, so the effects of the present invention can be enjoyed at a higher level. Also, although the paper thickness of the base paper used in the present invention is not particularly limited, from the viewpoint of the transportability in the printing and processing steps, it is preferably 15 to 120 μm, more preferably 30 to 80 μm. Also, although the density of the base paper used in the present invention is not particularly limited, from the viewpoint of the ease of coating the coating liquid, it is preferably 0.4 to 1.0 g / cm 3 and more preferably 0.6 to 0.8 g / cm 3 .

[0021] (Chitosan) The chitosan used in the present invention has a weight average molecular weight of 50 to 3 million kDa from the viewpoints of strength development and coating suitability, preferably 70 to 2.9 million kDa, and more preferably 90 to 2.8 million kDa. When the weight average molecular weight is less than the above lower limit value, there is a risk of insufficient strength, and when it is greater than the above upper limit value, there is a risk of coating difficulty. The weight average molecular weight of chitosan can be measured by the following method using GPC.

[0022] (Analysis of chitosan molecular weight) The weight average molecular weight of chitosan can be measured under the following analysis conditions. Column: Shodex Ohpak SB-G + SB-805HQ + SB-806HQ Solvent, mobile phase: 0.5 M acetic acid / 0.5 M sodium acetate buffer Flow rate: 1.0 mL / min Temperature: 40 °C Detector: RI (differential refractometer) Sample concentration and injection volume: 0.05%, 200 μL For calculating the molecular weight, standard pullulan standards Shodex Pullulan P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1600 (molecular weights are 5,900, 11,800, 22,800, 47,300, 112,000, 212,000, 404,000, 788,000, 1,600,000 respectively) and chitohexaose (molecular weight 1,203) may be used.

[0023] In addition, in this specification, when referring to low-molecular-weight chitosan, it means that the weight-average molecular weight is 500,000 kDa or more and less than 1,500,000 kDa, and when referring to high-molecular-weight chitosan, it means that the weight-average molecular weight is 1,500,000 kDa or more and 3,000,000 kDa or less.

[0024] The chitosan used in the present invention preferably has a B-type viscosity of 1 to 2,000 mPa·s, more preferably 10 to 1,000 mPa·s, when the chitosan is made into a 3% aqueous acid solution by adding an acid to chitosan and water, from the viewpoint of coating applicability. If the B-type viscosity is less than the above lower limit value, there is a risk of insufficient coating amount, and if it is greater than the upper limit value, there is a risk of difficult liquid feeding.

[0025] For the uncoated paper of the present invention, when evenly divided into 4 layers in the thickness direction, the value of (chitosan content of each layer) / (total chitosan content of all layers) is 0.1 or more from the viewpoint of paper strength expression. If this condition is not satisfied, there is a risk of insufficient paper strength. Also, if this condition is not satisfied, since the strength of the layer with a chitosan distribution less than 0.1 becomes locally weak, the obtained uncoated paper may have low interlayer strength and poor bursting strength.

[0026] The uncoated paper of the present invention essentially includes a base paper and chitosan, and may optionally contain an acid and a binder component other than chitosan.

[0027] When the uncoated paper of the present invention contains an acid, the blending ratio of chitosan to the acid (chitosan: acid) is preferably 10:1 to 1:10, and more preferably 5:1 to 1:5. If the blending ratio of the acid is too less than the above lower limit value, there is a risk of poor dissolution of chitosan, and if it is too more than the above upper limit value, there is a risk of a decrease in the concentration of chitosan.

[0028] When the uncoated paper of the present invention contains an acid, the type of acid that can be used is not particularly limited, but from the viewpoint of chitosan solubility, lactic acid, malic acid, and citric acid are preferable, and lactic acid is more preferable. These acids can be used alone or in combination of two or more.

[0029] When the uncoated paper of the present invention contains, in addition to chitosan, other binder components (hereinafter, also simply referred to as "binder"), it is preferable because printing surface strength can be obtained. As the binder that can be used in combination with chitosan, binders generally used in the coating liquid for uncoated paper can be used without particular limitation. For example, various starches such as starch, oxidized starch, modified starch, dextrin, water-soluble polymers such as carboxymethyl cellulose, polyacrylamide, and polyvinyl alcohol can be mentioned. From the viewpoint of achieving both coating suitability and printing surface strength, it is preferable to use starch. Further, the blending ratio of chitosan to the binder (chitosan: binder) is preferably 5:1 to 1:5, and more preferably 3:1 to 1:3, from the viewpoint of achieving both coating suitability and paper strength improvement effect.

[0030] (Method for producing uncoated paper) The method for producing the uncoated paper of the present invention includes a coating step of applying a coating liquid containing chitosan having a weight average molecular weight of 50 to 3,000,000 kDa, preferably 70 to 2,900,000 kDa, more preferably 90 to 2,800,000 kDa onto a base paper having a Scott sizing degree of 50 seconds or less, preferably 0 seconds or more and 20 seconds or less.

[0031] (Coating liquid) The total solid content concentration of the coating liquid used in the manufacturing method of the present invention is 3.5% or less, preferably 1.0% or more and 3.0% or less, from the viewpoints of coating applicability and coating amount adjustment. If the concentration is too high compared to the above upper limit value, the amount of dehydrated water may decrease. Further, the B-type viscosity of the coating liquid measured under the conditions of 40°C and 60 rpm is 500 mPa·s or less, more preferably 10 to 300 mPa·s, from the viewpoint of the pump feeding suitability of the coating liquid. If the B-type viscosity of the coating liquid is too high compared to the above upper limit value, there is a risk that liquid feeding may not be possible.

[0032] The coating liquid used in the present invention contains chitosan as an essential component, and may contain an acid and other binder components other than chitosan as required. Examples of other binder components include various starches such as starch, oxidized starch, processed starch, and dextrin, and water-soluble polymers such as carboxymethyl cellulose, polyacrylamide, and polyvinyl alcohol. Further, the coating liquid used in the present invention may contain various additives such as a water resistance agent, an external sizing agent, a surface paper strength agent, a dye pigment, a fluorescent coloring agent, and a water retention agent.

[0033] The coating liquid used in the present invention preferably has a dehydrated water amount of 100 to 500 g / m 2 and more preferably 150 to 300 g / m 2 from the viewpoint of the penetration of the coating liquid into the paper. If the dehydrated water amount of the coating liquid is too less than the above lower limit value, the coating liquid is difficult to penetrate into the base paper, resulting in a small chitosan content ratio near the center of the paper, and thus the obtained uncoated paper may have low interlayer strength and poor burst strength. Conversely, if the dehydrated water amount of the coating liquid is too more than the above upper limit value, the amount of chitosan remaining on the paper surface may decrease, and the surface strength may become weak. Further, when the coating liquid comes into contact with the paper in the manufacturing process, there is a risk of paper breakage due to a sudden increase in the water content in the paper. The dehydrated water amount of the coating liquid can be adjusted by adjusting the coating liquid concentration.

[0034] From the perspective of ensuring stable solubility of chitosan, the coating liquid used in the present invention is preferably a clear coating liquid. In this specification, the clear coating liquid means a coating liquid that does not contain pigments such as white pigments. Examples of white pigments include calcium carbonate, kaolin, clay, calcined kaolin, amorphous silica, zinc oxide, aluminum oxide, satin white, aluminum silicate, magnesium silicate, magnesium carbonate, titanium oxide, plastic pigment, and the like.

[0035] In the production method of the present invention, the coating amount of the coating liquid can be appropriately adjusted according to the coating liquid concentration and the like, and is not particularly limited. However, on a solids basis, it is usually 0.1 to 4.0 g / m on both sides 2 in the range. It is preferably 0.2 to 3.0 g / m on both sides 2 and more preferably 0.3 to 2.0 g / m on both sides 2 When the coating amount of the coating liquid increases, the weight of the obtained uncoated paper tends to increase. However, especially when the uncoated paper of the present invention is used as packaging paper, problems such as poor transportability during packaging processing may occur.

[0036] The apparatus for applying the coating liquid is not particularly limited, and coating (application) can be performed by known coating machines such as a two-roll size press, a pond size press, a rod metering size press, a gate roll coater, a blade coater, a spray coater, and a curtain coater. In the present invention, from the perspective of coating amount control, it is preferable to use a rod metering size press.

[0037] The uncoated paper of the present invention contains chitosan having a weight average molecular weight in a specific range and has an even distribution of chitosan in the thickness direction. Therefore, in addition to tensile strength, it also has excellent burst strength (interlayer strength), and further has the characteristic of excellent deodorizing property. In addition, even when no sizing agent is added, it can be made to suppress bleeding and blurring of ink. Furthermore, it also has the characteristic of being excellent in strength development compared to starch.

Examples

[0038] Hereinafter, embodiments of the present invention will be described by way of examples, but the present invention is not limited thereto.

[0039] 1. Examination of chitosan solubility (Production Example 1) Water was added to and stirred with high molecular weight chitosan (manufactured by Koyo Chemical Co., Ltd., SK-200) to prepare a chitosan dispersion. Separately, water was added to starch (manufactured by Nippon Corn Starch Co., Ltd., SK-20), and the paste was steamed to a solid content concentration of 17%. The above-mentioned high molecular weight chitosan dispersion and paste were mixed so that the amount of starch was 75 parts by weight with respect to 25 parts by weight of high molecular weight chitosan, and a coating liquid of Production Example 1 with a total solid content concentration of 3% was prepared.

[0040] (Production Examples 2 to 5) Dispersions of high molecular weight chitosan were each prepared by adding the minimum addition amount of acid described in Table 1, and coating liquids of Production Examples 2 to 5 with a total solid content concentration of 3% were prepared in the same manner as in Production Example 1 except that these were mixed with the paste. In addition, acid was added to the dispersion in which chitosan was dispersed in water, and the minimum addition amount of acid was determined when chitosan was sufficiently dissolved.

[0041] Regarding the coating liquids obtained in the production examples, the pH and B-type viscosity (40 °C, 60 rpm) were measured, and the results are shown in Table 1. In the B-type viscosity measurement, the rotor was appropriately selected according to the viscosity. In addition, the following evaluation was performed, and the results are shown in Table 1.

[0042] <Evaluation> (1) Odor The odor when acid was added until chitosan dissolved was sensory evaluated according to the following criteria. 〇: The odor is small and there is no problem in the operation of the actual machine. ×: The odor is strong and there is a risk of hindering the operation of the actual machine.

[0043] (2) Coating suitability Using the B-type viscosity (40 °C, 60 rpm) as an index, the coating suitability was evaluated in the following four grades. ◎: The B-type viscosity was low, making it easy to apply (coat). 〇: Although the B-type viscosity was slightly high, it could be applied (coated) without problems. △: The B-type viscosity was high, and problems occurred during application (coating). ×: Due to reasons such as the B-type viscosity being too high or having undissolved substances, it could not be applied (coated).

[0044] (3) Strength development The coating liquids obtained in Production Examples 2 to 4 were applied to high-quality paper (manufactured by Nippon Paper Industries Co., Ltd., basis weight 52 g / m 2 , Stoke sizing degree 0 seconds) on both sides to prepare samples coated to 1.2 g / m 2 . The tensile strength (MD) of the obtained samples was measured and compared with the measurement results of the paper without the coating liquid, and the degree of improvement in tensile strength (strength development) was evaluated in the following four levels. The Stoke sizing degree of the high-quality paper used as the base paper was measured according to JIS P 8122. ◎: The improvement rate of the tensile strength was 70% or more, and the strength improvement effect was fully manifested. 〇: The improvement rate of the tensile strength was 50% or more and less than 70%, and a strength improvement effect was observed. △: The improvement rate of the tensile strength was 1% or more and less than 50%, and a slightly strength improvement effect was observed. ×: The improvement rate of the tensile strength was less than 1%, and no strength improvement effect was observed.

[0045]

Table 1

[0046] Production Example 1 was a condition without adding an acid, but starch and chitosan did not dissolve and it could not be used as a coating liquid. The coating liquid with acetic acid added in Production Example 5 had an odor, and there were also crushed chitosans, making it non-uniform, so it was unsuitable as a coating liquid. The coating liquids with lactic acid, malic acid, and citric acid added in Production Examples 2 to 4 had no odor, were excellent in coating suitability, and the paper obtained by coating this had a higher tensile strength compared to the paper without the coating liquid.

[0047] 2. Uncoated paper (Example 1) 22 parts by weight of high molecular weight chitosan (manufactured by Koyo Chemical Co., Ltd., SK-200), 13 parts by weight of lactic acid, and water were mixed to prepare a chitosan solution. Separately, water was added to 65 parts by weight of starch (manufactured by Nippon Corn Starch Co., Ltd., SK-20), and the paste solution was steamed to a solid content concentration of 20%. The aforementioned high molecular weight chitosan solution and paste solution were mixed so that the amount of starch was 65 parts by weight with respect to 22 parts by weight of high molecular weight chitosan, and the total solid content concentration was 1.9%, the B-type viscosity (40 °C, 60 rpm) was 291 mPa·s, and the water removal amount was 175 g / m 2 A clear coating solution of was prepared. The obtained coating solution was applied to high-quality paper (manufactured by Nippon Paper Industries Co., Ltd., basis weight 52 g / m 2 , paper thickness 71 μm, density 0.73 g / cm 3 , Steki sizing degree 0 seconds) on both sides at 0.69 g / m 2 and then dried with a hot air dryer so that the water content in the paper was in the range of 2 to 10% to produce uncoated paper. The Steki sizing degree of the high-quality paper used as the base paper was measured according to JIS P 8122.

[0048] (Example 2) Uncoated paper was produced in the same manner as in Example 1 except that the coating solution was applied on both sides at 0.39 g / m 2 .

[0049] (Example 3) Low molecular weight chitosan (manufactured by Koyo Chemical Co., Ltd., SK-50) was used instead of high molecular weight chitosan, and a coating solution with a total solid content concentration of 3.1%, a B-type viscosity (40 °C, 60 rpm) of 126 mPa·s, and a water removal amount of 246 g / m 2 was prepared, and the obtained coating solution was applied on both sides at 1.03 g / m 2 and uncoated paper was produced in the same manner as in Example 1.

[0050] (Example 4) The coating solution was applied on both sides at 0.64 g / m 2A non-coated paper was produced in the same manner as in Example 3, except that it was coated so as to achieve [specific conditions].

[0051] (Comparative Example 1) The base paper (fine paper) without applying the coating liquid was used as the non-coated paper of Comparative Example 1.

[0052] (Comparative Example 2) A coating liquid with a starch solid content concentration of 6.9%, a B-type viscosity (40 °C, 60 rpm) of 10 mPa·s, and a water removal amount of 510 g / m 2 was prepared without adding chitosan and lactic acid. The obtained coating liquid was applied on both sides at 1.84 g / m 2 A non-coated paper was produced in the same manner as in Example 1, except that it was coated so as to achieve [specific conditions].

[0053] (Comparative Example 3) The total solid content concentration of the coating liquid was 3.9%, the B-type viscosity was 1970 mPa·s, and the water removal amount was 89 g / m 2 A non-coated paper was produced in the same manner as in Example 1, except that the double-sided coating amount was 1.09 g / m 2 and [other conditions were the same as in Example 1].

[0054] (Comparative Example 4) A non-coated paper was produced in the same manner as in Comparative Example 3, except that the coating liquid was applied on both sides at 0.55 g / m 2 and [other conditions were the same as in Comparative Example 3].

[0055] (Comparative Example 5) The total solid content concentration of the coating liquid was 6.4%, the B-type viscosity was 862 mPa·s, and the water removal amount was 75 g / m 2 A non-coated paper was produced in the same manner as in Example 3, except that the double-sided coating amount was 1.50 g / m 2 and [other conditions were the same as in Example 3].

[0056] (Comparative Example 6) A non-coated paper was produced in the same manner as in Comparative Example 5, except that the coating liquid was applied on both sides at 0.82 g / m 2 and [other conditions were the same as in Comparative Example 5].

[0057] (Water removal amount) The water loss of the coating liquids used in the examples and comparative examples was measured using an AA-GWR Water Retention Meter manufactured by KALTEC. First, six 5 cm × 5 cm sheets of high-quality paper (manufactured by Nippon Paper Industries Co., Ltd., basis weight 52 g / m 2 , Styx sizing degree 0 seconds) and one membrane filter (manufactured by KALTEC, GWR420 PCTE 5.0 μm 47 mm) were placed on the attached rubber mat, and the attached cup was placed on top of them. Then, 20 mL of the coating liquid was injected from the liquid supply port and the apparatus was set up. After raising the clamp and making it adhere closely to the upper part of the apparatus, the pressure inside the cup was maintained at 50 kPa for 20 seconds using air, then released, and the weight of the high-quality paper was measured. The measurement area was 8 cm 2 . The increased weight of the high-quality paper was the amount of liquid absorbed under pressure, and the water absorption per lm 2 was taken as the water loss in the present invention.

[0058] In the examples and comparative examples, the penetration of the coating liquid into the base paper when applying the coating liquid to the base paper was visually confirmed, and the results are shown in Table 2. Also, for the uncoated papers produced in the examples and comparative examples, the measurement of the distribution of chitosan content, tensile strength, ISO bending strength, interlayer strength, and contact angle, as well as the evaluation of deodorizing properties, were carried out as follows. The results are shown in Table 2.

[0059] (Distribution of chitosan content) (1) Division of uncoated paper A polyester tape (Nitto Denko Corporation No. 31B 35 high) was uniformly attached to the entire surface of the surface layer (the first layer) of the paper (10 mm × 200 mm or more), and the tape was peeled off while being careful to ensure that the whole peeled off uniformly. The weight of the peeled first layer was derived from the weight of the paper before peeling and the weight of the paper after peeling. The above process was repeated several times so that the total weight of the peeled first layer would be 25% of the weight of the paper before peeling. Next, the same type of polyester tape was again uniformly attached to the surface of the paper from which the first layer had been peeled, and the tape was peeled off while being careful to ensure that the entire tape peeled off uniformly. The weight of the peeled second layer was derived from the paper weight before peeling and the paper weight after peeling. The above process was repeated several times so that the total weight of the peeled second layer was 25% of the paper weight before peeling. The third layer was peeled in the same manner as the second layer, and the remaining paper after peeling was designated as the fourth layer.

[0060] (2) Measurement of the amount of starch in paper and calculation of chitosan content Each measurement sample of the first to fourth layers obtained by dividing the uncoated paper was cut into strips with a size of 10 mm × 200 mm. This paper strip was subjected to enzymatic treatment, and the starch content was measured using a biosensor. Specifically, the paper strip was immersed in 2 mL of an amylase solution containing glucoamylase in a test tube and subjected to enzymatic treatment at 50°C for 2 hours or more. The amount of starch was calculated by measuring the glucose concentration in the treatment solution using a biosensor (model: BF-5, manufactured by Oji Scientific Instruments Co., Ltd.). Assuming that the penetration of chitosan into the paper was the same as that of starch, the distribution of the chitosan content in each layer was calculated from the distribution of the starch amount calculated as described above. For Comparative Example 2 in which no chitosan was added in Table 2, the starch content ratio instead of the chitosan content ratio in each layer is described.

[0061] (Tensile strength) It was measured in accordance with JIS P 8113.

[0062] (ISO bending strength) In accordance with ISO-2493, the bending strength at a bending angle of 15 degrees was measured using an L&W Bending Tester (manufactured by Lorentzen & Wettre).

[0063] (Interlayer strength) It was measured using an L&W ZD Tensile Tester (manufactured by Lorentzen & Wettre) in accordance with ISO-15754 / TAPPI T551. Note that the higher the interlayer strength, the better the bursting strength.

[0064] (Contact angle) After dropping 5 μL of distilled water onto the surface of the untreated paper pretreated under the standard conditions specified in JIS-P8111, the contact angles after 0.1 second and 1 second were measured with a contact angle measuring device (manufactured by DAT1100 FIBRO System AB). One side and the other side were each measured, and the average value was taken as the contact angle of the untreated paper of the present invention. The larger the numerical value, the better the sizing property.

[0065] (Deodorizing property) 0.5 g of the test piece (white paper sample) was placed in a gas sampling bag, and 1.5 L of ammonia gas was further introduced thereto so that the initial concentration became 100 ppm. After 1 hour, the ammonia concentration was measured using a detector tube, and the deodorizing property was evaluated according to the following criteria based on the reduction rate from the initial concentration. ○: The reduction rate is 50% or more and 100% or less, and the deodorizing property is excellent. △: The reduction rate is 40% or more and less than 50%, and the deodorizing property is somewhat present. ×: The reduction rate is less than 40%, and the deodorizing property is poor.

[0066]

Table 2

[0067] From Table 2, it was found that the untreated papers of Examples 1 to 4, which contain the base paper and chitosan having a weight average molecular weight of 50 to 3 million kDa and are divided into 4 layers in the thickness direction, and the values of (the chitosan content of each layer) / (the total chitosan content of all layers) are all 0.1 or more, are excellent in tensile strength and interlayer strength (burst strength).

Claims

1. It contains a base paper and chitosan with a weight average molecular weight of 500,000 to 3,000,000 kDa, and is an uncoated paper in which when divided into 4 layers in the thickness direction, the value of (chitosan content of each layer) / (total chitosan content of all layers) is 0.1 or more for each layer.

2. Furthermore, it contains an acid, and the blending ratio of the chitosan and the acid is 10:1 to 1:

10. The uncoated paper according to Claim 1, characterized in that.

3. The uncoated paper according to Claim 2, wherein the acid is at least one selected from the group consisting of lactic acid, citric acid, and malic acid.

4. The uncoated paper according to Claim 1, wherein the Stoke's sizing degree of the base paper is 50 seconds or less.

5. It includes a coating step of coating a coating liquid containing chitosan with a weight average molecular weight of 500,000 to 3,000,000 kDa on a base paper, the coating liquid has a total solid content concentration of 3.5% or less, the Brookfield viscosity of the coating liquid measured under the conditions of 40 °C and 60 rpm is 500 mPa·s or less, and the Stoke's sizing degree of the base paper is 50 seconds or less. A method for manufacturing an uncoated paper, characterized in that.

6. The method for manufacturing an uncoated paper according to Claim 5, wherein the coating liquid is a clear coating liquid further containing an acid.

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