Paper and manufacturing method thereof, and paper modifier and manufacturing method thereof

Abstract

To provide a paper and a manufacturing method thereof, using filamentous algae as a new raw material of paper pulps not depending on lumber resources.SOLUTION: A paper includes fibers derived from filamentous algae, wherein the aspect ratio of the fibers is 10-130. A manufacturing method of a paper includes: removing starch and protein components from fibers derived from filamentous algae; bleaching the fibers derived from filamentous algae from which starch and protein component have been removed; neutralizing the fibers derived from filamentous algae having been bleached; and paper-making by using the fibers derived from filamentous algae having been neutralized.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to paper and its manufacturing method, and to paper modifiers and its manufacturing method. [Background technology]

[0002] Approximately 180 million tons of paper pulp are produced worldwide each year, and approximately 90% of this is derived from wood. Research into the planned use of forest resources has been ongoing for a long time, and biodegradable paper is expected to be an alternative to plastics. The processing of forest resources requires a highly alkaline and high-temperature cooking process, which places a large burden on the environment. Therefore, new raw materials for paper pulp that do not depend on wood resources are needed. An example of a new raw material for paper pulp is algae material (see, for example, Patent Document 1). Patent Document 1 discloses a method for producing paper from seaweed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3165282 Summary of the Invention [Problem to be solved by the invention]

[0004] One of the features of Patent Document 1 is that the algae material is pulverized into particles with diameters of 500 μm or less. However, paper made using pulverized particles does not exhibit the necessary strength, making it difficult to use it as a raw material for regular paper. The present disclosure has been made in consideration of the above-mentioned conventional circumstances, and an object of one aspect of the present disclosure is to provide paper using filamentous algae as a new raw material for paper pulp that does not rely on wood resources, and a method for producing the same. Another object of the present disclosure is to provide a paper modifier using filamentous algae, and a method for producing the same. [Means for solving the problem]

[0005] Specific means for achieving the above object are as follows. <1> Contains fibers derived from filamentous algae, The paper, wherein the aspect ratio of the fibers is 10 to 130. <2> The filamentous algae includes at least one species selected from the group consisting of Oedogonium borisianum, Cladophora fracta, and Cladophora pusilla. <1> The paper described in. <3> Also contains wood-derived pulp <1> or <2> The paper described in. <4> Contains fibers derived from filamentous algae, The paper modifier, wherein the fiber has an aspect ratio of 10 to 130. <5> removing starch and protein components from filamentous algae-derived fibers; bleaching the filamentous algae-derived fiber from which the starch and protein components have been removed; neutralizing the bleached filamentous algae-derived fibers; and making paper using the neutralized filamentous algae-derived fibers. <6> Removing the starch and protein components comprises soaking the filamentous algae-derived fibers in an alkaline aqueous solution. <5> A method for producing paper according to claim 1. <7> The bleaching agent used in the bleaching process contains at least one of hypochlorite and hydrogen peroxide. <5> or <6> A method for producing paper according to claim 1. <8> The amount of bleaching agent used in the bleaching is 1 g or less per 100 g of the fiber derived from the filamentous algae. <5> ~ <7> 13. A method for producing paper according to any one of claims 1 to 12. <9> The bleaching is carried out in a state where the concentration of the filamentous algae-derived fibers is 15% by mass or more. <8> A method for producing paper according to claim 1. <10> The method further comprises beating the neutralized filamentous algae-derived fibers, The aspect ratio of the filamentous algae-derived fibers used in the papermaking process is 10 to 130. <5> ~ <9> 13. A method for producing paper according to any one of claims 1 to 12. <11> removing starch and protein components from filamentous algae-derived fibers; bleaching the filamentous algae-derived fiber from which the starch and protein components have been removed; and neutralizing the bleached filamentous algae-derived fibers. Effect of the Invention

[0006] According to one aspect of the present disclosure, it is possible to provide paper using filamentous algae as a new raw material for paper pulp that does not depend on wood resources, and a method for producing the same. Also, according to another aspect of the present disclosure, it is possible to provide a paper modifier using filamentous algae and a method for producing the same. [Brief description of the drawings]

[0007] [Figure 1] 1 is an electron microscope photograph of the surface of the paper obtained in Example 1. [Diagram 2] 1 is an electron microscope photograph of the surface of the paper obtained in Example 2. [Diagram 3] 1 is an electron microscope photograph of the surface of the paper obtained in Comparative Example 1. [Figure 4] 1 is an optical microscope photograph of the fracture surface of the paper obtained in Example 1. [Diagram 5] 1 is an optical microscope photograph of a fracture surface of the paper obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless specifically stated. The same applies to the numerical values ​​and their ranges, and do not limit the present disclosure.

[0009] In the present disclosure, the term "step" includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the present disclosure, a numerical range indicated using "~" includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple types of corresponding substances. When multiple types of substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.

[0010] <Paper and its manufacturing method> The paper of the present disclosure contains fibers derived from filamentous algae, and the fiber aspect ratio is 10-130. The paper of the present disclosure uses fibers derived from filamentous algae as a new raw material for paper pulp that does not depend on wood resources. Since the aspect ratio of the fibers derived from filamentous algae is 10 to 130, it is possible to obtain paper with higher strength than paper made from pulverized particulate material derived from algae material. In addition, filamentous algae grow naturally in small rivers, irrigation canals, and shallow seas in both saltwater and freshwater environments from spring to summer when temperatures are relatively warm, and can grow four times larger in a week, reaching 25 t / ha per year, or 1 kg / m2 in dry weight. 3 In recent years, water purification systems using filamentous algae have been proposed, and large amounts of filamentous algae can be obtained by operating these systems. Due to their reproductive ability, filamentous algae can clog irrigation channels and inhibit the growth of aquatic animals such as sweetfish. This makes it laborious to remove the filamentous algae. Furthermore, the removed filamentous algae must be disposed of. If these filamentous algae could be used as a raw material for papermaking, it would be advantageous in terms of the supply volume and price of the raw material. In addition, because filamentous algae do not contain lignin, their yield as a cellulose fiber raw material is as high as that of wood. Because filamentous algae can be made into paper pulp without the strong alkaline, high-temperature cooking process required for wood, the cost of making paper pulp from filamentous algae is estimated to be less than half that of wood. By using filamentous algae that do not contain lignin, it is possible for them to be used as much or more than wood. As a result, by reducing the consumption of forest resources, forest depletion can be curbed, contributing to the solution of environmental problems. Because filamentous algae are produced in the aquatic environment, they do not compete with terrestrial crops, leading to the use of blue carbon. Furthermore, the fiber length of the fibers derived from filamentous algae can be adjusted by mechanical treatment or the like. Furthermore, fibers derived from filamentous algae have thinner cell walls than wood fibers, making them highly flexible. When drying fibers derived from filamentous algae, bonds are more likely to form between the fibers, improving their elastic modulus and making them more transparent. Thus, paper containing fibers derived from filamentous algae has various advantages over paper containing fibers derived from wood resources.

[0011] In this disclosure, "filamentous algae" is a general term for algae that have a fibrous structure and are formed by connecting cells to form filaments. "Filamentous algae" includes both those with an unbranched structure and those with a branched structure. Filamentous algae that can be used in the present disclosure are not particularly limited, and include Spirogyra (Zygomorphaceae), Cladophora (Cladophoraceae), Azoglossa (Azoglossaceae), Azoglossa (Zygomorphaceae), and Azoglossa (Azoglossaceae). The filamentous algae may be those belonging to the family Azomorphaceae, Zygomorphaceae, Cladophoraceae, etc. For example, some algae belonging to the family Azomorphaceae have a non-branched structure, while some algae belonging to the family Cladophoraceae have a branched structure. A specific example of the filamentous algae is preferably at least one selected from the group consisting of Oedogonium borisianum, Cladophora fracta, and Cladophora pusilla. The genus Cladophora may be used as the filamentous algae because it is widely distributed and advantageous in terms of biomass.

[0012] The aspect ratio of the filamentous algae-derived fibers contained in the paper of the present disclosure is 10 to 130. Strength tends to be improved when the aspect ratio of the fibers is 10 or more. The aspect ratio of the fibers may be 20 or more, 30 or more, or 50 or more. Furthermore, there is a tendency for the formation to be improved if the aspect ratio of the fibers is 130 or less. The aspect ratio of the fibers may be 110 or less, 100 or less, or 90 or less. The aspect ratio of the fibers may be 20-110, or may be 30-100. The aspect ratio of a fiber is a value measured by the following method. The aspect ratio can be determined by measuring the fiber length and width of each fiber using a device called a Fiber Tester (manufactured by ABB Corporation), calculating the aspect ratio of each fiber, and then taking the arithmetic average of the aspect ratios for a total of 10,000 fibers. Before the aspect ratio is measured, the filamentous algae may be subjected to the following treatment. Since filamentous algae naturally live in water, the fibers are basically in a dispersed state. Therefore, the fiber length and width can be measured in their original state. When the fibers are dried, they condense due to hydrogen bonding between the fibers, so they need to be dispersed in water. In that case, the fibers can be sufficiently dispersed in water by immersing them in water sufficiently and stirring them for 10 minutes at about 120 rpm using a magnetic stirrer, for example. Instead of the measurement using a fiber tester, the fiber may be thoroughly immersed in water and observed under a microscope or the like to measure the fiber width and fiber length, and the ratio between the width and length may be taken as the aspect ratio.

[0013] The Runkel ratio of the filamentous algae-derived fiber contained in the paper of the present disclosure is preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0.15 or more, from the viewpoint of improving the utilization rate. The Runkel ratio of the filamentous algae-derived fiber contained in the paper of the present disclosure is preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.35 or less, and particularly preferably 0.3 or less, from the viewpoint of improving the paper strength and transparency. The Runkel ratio of the filamentous algae-derived fiber contained in the paper of the present disclosure is preferably 0.05 to 0.5, more preferably 0.1 to 0.35, and even more preferably 0.15 to 0.3. The Runkel ratio is calculated by calculating the lumen diameter b = (L-2a) of a fiber based on the cell wall thickness a and fiber diameter L in the fiber cross section, and then calculating the Runkel ratio R = 2a / b.

[0014] Generally speaking, fibers with a Runkel ratio of 1 or less are suitable for papermaking. If the Runkel ratio exceeds 1, the fibers are less likely to be crushed by beating, and interfiber bonds are less likely to form. On the other hand, if the Runkel ratio of fibers is 1 or less, the fibers are more likely to be crushed by beating, and the increased surface area of ​​the fibers makes it easier for interfiber bonds to form. Fibers derived from filamentous algae tend to have a smaller Runkel ratio than fibers derived from wood. Based on the Runkel ratio of the fibers contained in paper, it may be possible to determine whether the fibers are derived from filamentous algae or wood.

[0015] The Runkel ratio of a fiber can be calculated based on the cell wall thickness a and fiber diameter L or lumen diameter b obtained by observing pulp fibers fibrous in water by the above-mentioned method under an optical microscope. The Runkel ratio of a fiber is calculated by determining the Runkel ratio at four points per fiber for 100 fibers, and taking the arithmetic mean of the values ​​obtained.

[0016] The basis weight of the paper of this disclosure is 5 g / m 2 More than 10 g / m is preferable. 2 More preferably, 15 g / m 2More preferably, the basis weight of the paper of the present disclosure is 100 g / m 2 or less, 60 g / m 2 From the viewpoint of transparency, it is preferable that the thickness is 30 g / m or less. 2 Less than 25 g / m is preferred. 2 Less than 20 g / m is more preferable. 2 More preferably, the paper of the present disclosure has a basis weight of 5 g / m 2 ~100g / m 2 is preferred, and 10 g / m 2 ~60g / m 2 More preferably, 15 g / m 2 ~30g / m 2 is more preferred. The basis weight of paper refers to a value obtained by the following method. The basis weight of paper is calculated by dividing the mass (g) of the paper measured on a balance by the area (m 2 ) to find the answer.

[0017] The density of the paper disclosed herein is 0.85 g / cm from the viewpoint of transparency. 3 More than 1.0 g / cm is preferable. 3 More preferably, 1.1 g / cm 3 The density of the paper of the present disclosure is more preferably 1.4 g / cm from the viewpoint of flexibility. 3 Less than 1.3 g / cm is preferred. 3 Less than 1.2 g / cm is more preferable. 3 More preferably, the density of the paper of the present disclosure is 0.85 g / cm 3 ~1.4g / cm 3 is preferred, and 1.0 g / cm 3 ~1.3g / cm 3 More preferably, 1.1 g / cm 3 ~1.2g / cm 3 is more preferred. The density of paper refers to a value obtained by the following method. The density of paper is calculated by multiplying the mass (g) of the paper measured on a balance by the area (m 2 ) and divide by the basis weight (g / m 2 ) and then divide it by the paper thickness (μm).

[0018] The smoothness of the paper of the present disclosure (Oken smoothness) is preferably 25 seconds or more from the viewpoint of printability, more preferably 28 seconds or more, and even more preferably 30 seconds or more. The smoothness of the paper of the present disclosure is preferably 60 seconds or less from the viewpoint of texture, more preferably 55 seconds or less, and even more preferably 50 seconds or less. The smoothness of the paper of the present disclosure is preferably 25 to 60 seconds, more preferably 28 to 55 seconds, and even more preferably 30 to 50 seconds. Oken smoothness (seconds) is measured according to JIS P 8155:2010 Paper and paperboard - Smoothness test method - Oken method.

[0019] The average fiber length of the filamentous algae-derived fibers contained in the paper of the present disclosure is preferably 0.5 mm or more, more preferably 0.7 mm or more, and even more preferably 0.8 mm or more, from the viewpoint of improving strength. The average fiber length of the filamentous algae-derived fibers contained in the paper of the present disclosure is preferably 2.0 mm or less, more preferably 1.5 mm or less, and even more preferably 1.1 mm or less, from the viewpoint of formation. The average fiber length of the filamentous algae-derived fibers contained in the paper of the present disclosure is preferably 0.5 mm to 2.0 mm, more preferably 0.7 mm to 1.5 mm, and even more preferably 0.8 mm to 1.1 mm. The average fiber length of the fibers is measured according to the fiber length measurement method specified in the method for measuring aspect ratio, and is the value obtained by calculating the arithmetic mean of the fiber lengths of 10,000 fibers.

[0020] The average fiber width of the filamentous algae-derived fibers contained in the paper of the present disclosure is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more, from the viewpoint of strength. The average fiber width of the filamentous algae-derived fibers contained in the paper of the present disclosure is preferably 60 μm or less, more preferably 55 μm or less, and even more preferably 50 μm or less, from the viewpoint of paper flexibility. The average fiber width of the filamentous algae-derived fibers contained in the paper of the present disclosure is preferably 15 μm to 60 μm, more preferably 20 μm to 55 μm, and even more preferably 25 μm to 50 μm. The average fiber width of the fibers is measured according to the fiber width measurement method specified in the method for measuring aspect ratio, and is the value obtained by calculating the arithmetic mean of the fiber widths of 10,000 fibers.

[0021] The single fiber tensile strength of the filamentous algae-derived fiber contained in the paper of the present disclosure is preferably 0.5 g / fiber or more, more preferably 0.75 g / fiber or more, and even more preferably 1 g / fiber or more, from the viewpoint of the tensile strength of the paper. The upper limit of the single fiber tensile strength of the filamentous algae-derived fiber contained in the paper of the present disclosure is not particularly limited, and may be 5 g / fiber or less, 4 g / fiber or less, or 3 g / fiber or less. The single fiber tensile strength of the filamentous algae-derived fiber contained in the paper of the present disclosure may be 0.5 g / fiber to 5 g / fiber, 0.75 g / fiber to 4 g / fiber, or 1 g / fiber to 3 g / fiber. The single fiber tensile strength of the fiber is a value obtained by the following method. The fibers are removed from the fully disintegrated pulp suspension and attached to a slit-lined backing using an acetic acid-based adhesive. The backing is attached to the clamps of a tensile tester and then cut away. A tensile test is performed in a temperature and humidity controlled room at an air temperature of 23°C ± 1°C and a relative humidity of 50% ± 2%, and the stress at break found at a tensile speed of 10 mm / min is taken as the single fiber tensile strength of each fiber. The single fiber tensile strength is measured for 50 fibers, and the arithmetic average is taken as the single fiber tensile strength of the fiber. As the tensile tester, a tabletop tensile / compression tester MCT series manufactured by A&D Co., Ltd. can be used.

[0022] From the viewpoint of durability, the tensile index of the paper of the present disclosure is preferably 15 N·m / g or more, more preferably 18 N·m / g or more, and even more preferably 20 N·m / g or more. The upper limit of the tensile index of the paper of the present disclosure is not particularly limited, and may be 100 N·m / g or less, 80 N·m / g or less, or 60 N·m / g or less. The tensile index of the paper of the present disclosure may be 15 N·m / g to 100 N·m / g, 18 N·m / g to 80 N·m / g, or 20 N·m / g to 60 N·m / g. The tensile strength index of paper is calculated by dividing the breaking load of the paper by the product of the paper basis weight and the width of the test piece (15 mm in the example below). The breaking load of the paper is determined as the arithmetic average of the values ​​obtained by preparing 30 test pieces of 15 mm width and conducting a tensile test in a constant temperature and humidity room under environmental conditions of 23°C temperature and 23%RH to 28%RH, with the tensile tester's gripping distance of 10 cm and a tensile speed of 10 mm / min. As the tensile tester, a tabletop tensile / compression tester MCT series manufactured by A&D Co., Ltd. can be used.

[0023] The tensile modulus of the paper of the present disclosure is preferably 5 GPa or more from the viewpoint of stiffness, more preferably 6 GPa or more, and even more preferably 7 GPa or more. The upper limit of the tensile modulus of the paper of the present disclosure is not particularly limited, and may be 10 GPa or less, 9 GPa or less, or 8 GPa or less. The tensile modulus of the paper of the present disclosure may be 5 GPa to 10 GPa, 6 GPa to 9 GPa, or 7 GPa to 8 GPa. The tensile modulus of paper is calculated as the ratio of the tensile load per unit area to the elongation per unit length in the elastic region for the paper.

[0024] The tensile breaking elongation of the paper of the present disclosure is preferably 0.5% or more from the viewpoint of durability, more preferably 1% or more, and even more preferably 1.5% or more. The tensile breaking elongation of the paper of the present disclosure is preferably 3% or less from the viewpoint of processability, more preferably 2.5% or less, and even more preferably 2% or less. The tensile breaking elongation of the paper of the present disclosure is preferably 0.5% to 3%, more preferably 1% to 2.5%, and even more preferably 1.5% to 2%. The tensile elongation at break of paper is calculated from data obtained under the same conditions as those for measuring the breaking load of paper.

[0025] In one embodiment, the freeness of the pulp used as the raw material for the paper of the present disclosure is preferably 400 mL or less, more preferably 300 mL or less, and even more preferably 200 mL or less, from the viewpoint of increasing the strength of the paper. In this case, the freeness may be 50 mL or more. In one embodiment, the freeness of the pulp is preferably 50 mL to 400 mL, more preferably 50 mL to 300 mL, and even more preferably 50 mL to 200 mL. In another embodiment, the freeness of the pulp that is the raw material of the paper of the present disclosure is preferably 300 mL or more, more preferably 400 mL or more, and even more preferably 500 mL or more, from the viewpoint of processability. In this case, the freeness may be 700 mL or less. In another embodiment, the freeness of the pulp is preferably 200 mL to 700 mL, more preferably 300 mL to 700 mL, and even more preferably 400 mL to 700 mL. The freeness of paper refers to a value obtained by the following method. Put 3.0g of pulp (absolute dry mass) into 1L of water and disintegrate thoroughly to prepare a pulp suspension with a concentration of 0.03%. Pour 1L of this pulp suspension into the filter bottle and measure the amount of filtrate discharged from the side tube. Record the water temperature at that time. Correct the freeness according to JIS P 8121-2:2012 Pulp - Freeness test method - Part 2: Canadian standard freeness method to obtain the Canadian standard freeness. The absolute dry mass is the value measured when the material is dried at 105°C until there is no change in mass. As the Canadian standard freeness tester, a Canadian Freeness Tester manufactured by Kumagai Riki Kogyo Co., Ltd. can be used. "Freeness" in this disclosure means Canadian Standard Freeness.

[0026] The thickness of the paper of the present disclosure is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more, from the viewpoint of handling. The thickness of the paper of the present disclosure may be 100 μm or less, 90 μm or less, or 85 μm or less. From the viewpoint of transparency, the thickness of the paper of the present disclosure is preferably 60 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less. In one embodiment, the thickness of the paper of the present disclosure is preferably 10 μm to 100 μm, more preferably 20 μm to 90 μm, and even more preferably 30 μm to 85 μm. In another embodiment, the thickness of the paper of the present disclosure is preferably 10 μm to 60 μm, more preferably 20 μm to 50 μm, and even more preferably 30 μm to 40 μm. The thickness of the paper is a value obtained by the following method. According to JIS P8118:2014 Paper and paperboard-Test methods for thickness, density and specific volume, use a micrometer to measure the thickness of each test paper in three places, and the arithmetic mean of the obtained values ​​shall be the thickness of each test paper. Measure the thickness of five test papers, and the arithmetic mean of the thickness of the five test papers shall be the thickness of the paper.

[0027] From the viewpoint of color reproducibility by printing, the whiteness of the paper of the present disclosure is preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 100%. From the viewpoint of reducing the load in the bleaching process, the whiteness of the paper of the present disclosure is preferably 90% or less, more preferably 87% or less, even more preferably 82% or less, and particularly preferably 77% or less. The whiteness of the paper of the present disclosure may be 75% to 87%, 80% to 90%, 85% to 100%, or even 75% to 100%. The whiteness of paper represents the ratio of light reflected when light is applied to the surface of a test piece. The whiteness of paper refers to the ISO whiteness (JIS P 8148:2018 (ISO 2470-1:2016)). The whiteness of paper can be measured using the Spectrophotometer for Paper PF7000 by Nippon Denshoku Industries Co., Ltd.

[0028] The paper of the present disclosure may optionally further comprise wood-derived pulp. Examples of wood-derived pulp include mechanical pulp (broken wood pulp, refiner mechanical pulp, or thermomechanical pulp), semi-chemical pulp (semi-chemical pulp or chemiground pulp), chemical pulp (kraft pulp or sulfite pulp), and waste paper pulp (disintegrated pulp or deinked pulp). More specifically, examples of wood-derived pulp include hardwood bleached kraft pulp (hardwood bleached pulp fiber (LBKP)), softwood bleached kraft pulp (softwood bleached pulp fiber (NBKP)), waste paper pulp, etc. Examples of waste paper that can be used as a raw material for waste paper pulp include newspapers, flyers, rough magazines, coated magazines, pressure-sensitive recording paper, imitation paper, colored wood-free paper, copy paper, computer output paper, and mixed waste paper thereof. Among these, bleached hardwood kraft pulp is preferred from the viewpoint of formation. When the paper of the present disclosure contains wood-derived pulp, the proportion of wood-derived pulp in the entire paper may be 20% by mass to 50% by mass, 10% by mass to 20% by mass, or 10% by mass to 15% by mass.

[0029] When filamentous algae-derived fibers and wood-derived pulp are each made under the same conditions, the paper made using filamentous algae-derived fibers tends to be denser and therefore more elastic than the paper made using wood-derived pulp. The strength of paper is determined by two factors: the strength of the single fiber and the strength of the bonds between fibers. While most papers made from wood tend to break due to the bonds between the fibers, papers made from fibers derived from filamentous algae tend to break due to the strength of the single fiber. Therefore, papers made from both types of fibers can complement each other's weaknesses in breaking, and the physical properties can be changed compared to papers made from each fiber alone.

[0030] The paper of the present disclosure may have an opacity of 20% or less. To achieve an opacity of 20% or less, the paper of the present disclosure may be impregnated with starch, fats and oils, wax, natural resins, synthetic resins, and the like. In recent years, research has been conducted into giving transparency to paper as an alternative to plastics. The cellulose contained in fibers derived from filamentous algae is essentially nearly transparent, but when made into paper, the gaps between the fibers cause light to refract and diffuse, making the paper appear white. However, by filling the gaps between the fibers with oil or other materials that have a refractive index close to that of cellulose, it is possible to give the paper transparency. The fibers derived from filamentous algae tend to be easily crushed due to their shape, and the density of the paper tends to be high, so there are fewer gaps between the fibers, which is advantageous for imparting transparency. Paper containing filamentous algae-derived fibers has a high density, so it is easier to paper thinly compared to paper containing wood-derived fibers. Therefore, it is easier to impart transparency to paper than paper containing wood-derived fibers. According to the findings of the present inventors, in paper made only from fibers derived from filamentous algae and made to a thickness of 0.04 mm, high transparency can be selectively imparted to the paper by, for example, applying a 10% by mass aqueous solution of starch. However, it may be difficult to impart high transparency to paper derived from wood.

[0031] The paper of the present disclosure may contain various additives as necessary, such as dyes, fluorescent whitening agents, pH adjusters, defoamers, sizing agents, etc. The content of the additives is not particularly limited, and each additive may be added in an amount necessary to exert its function.

[0032] The paper of the present disclosure may be manufactured by any process. In the paper making process of the present disclosure, it is preferred to use fibers derived from filamentous algae from which the starch and chlorophyll have been removed. Methods for removing starch and chlorophyll from filamentous algae may include immersing the filamentous algae in a solvent and boiling the algae, and immersing the boiled filamentous algae in an organic solvent. When boiling, a low concentration of acid or alkali may be added to the solvent, or mechanical pressure may be applied to improve the effect of removing starch and chlorophyll. When boiling in an organic solvent, the subsequent step of removing starch and chlorophyll with an organic solvent can be omitted. Examples of the solvent used when boiling the filamentous algae include organic solvents such as ethanol and water. Among these, water or ethanol is preferred from the viewpoint of reducing the burden on the environment. The boiling time is not particularly limited, but from the viewpoint of efficiency, it is preferably 10 to 30 minutes, and more preferably 20 to 30 minutes. Examples of the organic solvent used when immersing the boiled filamentous algae in the organic solvent include alcohol-based solvents such as methanol and ethanol, and ketone-based solvents such as acetone and methyl ethyl ketone. Among these, ethanol is preferred from the viewpoint of productivity. The immersion time when the boiled filamentous algae are immersed in the organic solvent is not particularly limited, but from the viewpoint of processability, it is preferably 5 minutes to 1440 minutes, and more preferably 720 minutes to 1440 minutes. After the boiled filamentous algae are immersed in the organic solvent, the filamentous algae may be taken out of the organic solvent and then immersed in the organic solvent again. The number of times that the filamentous algae are immersed in the organic solvent may be two to five times.

[0033] The filamentous algae are removed from the organic solvent to obtain filamentous algae-derived fibers from which chlorophyll has been removed. In the case of fibers containing water, it is preferable not to dry them, but they may be dried to facilitate long-term storage and transportation.

[0034] The paper manufacturing method of the present disclosure may include removing starch and protein components from fibers derived from filamentous algae, bleaching the filamentous algae-derived fibers from which the starch and protein components have been removed, neutralizing the bleached filamentous algae-derived fibers, and making paper using the neutralized filamentous algae-derived fibers. Through the above steps, protein components are removed from the fibers derived from filamentous algae, and further bleaching is performed.

[0035] In the case of wood-derived fibers, it is necessary to remove lignin and protein components and bleach them in multiple stages. As an example, the bleaching sequence for typical cedar kraft pulp (used for copy paper with a brightness of 80% to 90%) often involves a DEHD or DEHED process, with alkaline extraction (E), hypochlorite treatment (H), and chlorine dioxide treatment (D). In addition, hydrogen peroxide treatment (P) is often used as a finishing step because it has a weak bleaching power. Because filamentous algae-derived fibers do not contain lignin, a coloring substance that must be bleached, a simplified HP process can achieve a whiteness of 85% or more. Using filamentous algae-derived fibers is less environmentally-intensive and less expensive, and is more advantageous than using wood-derived fibers in that it can be bleached with hydrogen peroxide alone, which has a weaker bleaching power, and therefore reduces processing time, the amount of chemicals used, and the environmental impact.

[0036] Methods for removing starch and protein components from filamentous algae-derived fibers include immersing the filamentous algae-derived fibers in an alkaline aqueous solution, immersing the fibers in hydrogen peroxide, etc. Since any of these methods is the same as the process for removing chlorophyll, it is possible to easily remove starch and protein components from the filamentous algae-derived fibers without any special operations. The pH of the alkaline aqueous solution is preferably 9-12, and more preferably 10-12. Examples of the alkaline component include sodium hydroxide, sodium carbonate, calcium hydroxide, etc. Among these, sodium hydroxide is preferred from the viewpoint of convenience in that it can raise the pH with a small amount. The concentration of the alkaline component in the alkaline aqueous solution can be appropriately adjusted so that the pH of the alkaline aqueous solution becomes a desired value. When sodium hydroxide is used as the alkaline component, the concentration of sodium hydroxide is preferably 0.14% by mass to 14% by mass. The immersion time when immersing the filamentous algae-derived fibers in the alkaline aqueous solution is not particularly limited, but from the viewpoint of efficiency, it is preferably 30 to 120 minutes, more preferably 60 to 90 minutes. The temperature of the alkaline aqueous solution is preferably from 20°C to 60°C, and more preferably from 30°C to 60°C. From the viewpoint of efficiency, the concentration (pulp concentration) of the filamentous algae-derived fibers immersed in the alkaline aqueous solution is preferably 1% by mass or more. The pulp concentration may be 2% by mass to 5% by mass, 5% by mass to 10% by mass, or 10% by mass to 25% by mass.

[0037] Methods for bleaching the filamentous algae-derived fibers from which starch and protein components have been removed include a method of immersing the filamentous algae-derived fibers in a bleaching agent solution, a method of exposing the fibers to sunlight, etc. Among these, the method of immersing the filamentous algae-derived fibers in a bleaching agent solution is preferred because it is possible to bleach the filamentous algae-derived fibers easily. When bleaching fibers derived from filamentous algae, each bleaching step may be carried out in a state where the fibers derived from filamentous algae from which starch and protein components have been removed are placed in a nylon mesh bag or the like.

[0038] The pH of the bleach solution is preferably 9-11, and more preferably 10-11. The bleaching agent used for bleaching the fibers derived from filamentous algae is not particularly limited, and bleaching agents generally used in the paper-making industry can be used. Examples of the bleaching agent include hypochlorite, hydrogen peroxide, chlorine dioxide, etc. Among these, from the viewpoint of availability, it is preferable that the bleaching agent contains at least one of hypochlorite and hydrogen peroxide. The concentration of the bleaching agent in the bleaching agent solution can be appropriately set in consideration of the type of bleaching agent, the amount of fibers derived from filamentous algae added to the bleaching agent solution, the reaction efficiency, and the like. When hydrogen peroxide is used as the bleaching agent, the content of hydrogen peroxide in the hydrogen peroxide solution is preferably 0.1% by mass to 10% by mass. When, for example, hypochlorite is used as the bleaching agent, the content of available chlorine in the aqueous hypochlorite solution is preferably 1% by mass to 2% by mass. The immersion time when immersing the filamentous algae-derived fibers in the bleach solution is not particularly limited, but from the viewpoint of efficiency, it is preferably 30 to 120 minutes, and more preferably 60 to 90 minutes. The temperature of the bleach solution is preferably from 20°C to 60°C, and more preferably from 30°C to 60°C. The concentration (pulp concentration) of the fibers derived from filamentous algae immersed in the bleach solution is preferably 2% by mass or more, and may be 5% by mass to 7.5% by mass, 7.5% by mass to 10% by mass, or 10% by mass to 25% by mass. By bleaching filamentous algae-derived fibers at a concentration (pulp concentration) of 5% by mass or more, productivity can be improved. When bleaching wood-derived fibers, the pulp concentration of wood-derived fibers is generally set to 10% by mass or less.

[0039] The amount of bleaching agent used for bleaching may be 1 g or less per 100 g of filamentous algae-derived fiber. In this case, the concentration (pulp concentration) of the filamentous algae-derived fiber may be 15 mass % or more. Unlike wood-derived fiber, filamentous algae-derived fiber does not contain lignin, so it is possible to reduce the amount of bleaching agent when bleaching filamentous algae-derived fiber. When bleaching wood-derived fiber, the amount of bleaching agent is generally about 3 g per 100 g of wood-derived fiber.

[0040] Examples of methods for neutralizing bleached fibers derived from filamentous algae include a method in which an acid component such as hydrochloric acid or citric acid is added to a bleaching agent solution containing the fibers derived from filamentous algae. The pH of the aqueous solution containing the filamentous algae-derived fibers after neutralization is preferably 6 to 7.

[0041] The neutralized filamentous algae-derived fibers may be subjected to a beating treatment as necessary to improve the interfiber bond strength. Beating is a mechanical process that involves the action of metal or blades on the pulp fibers around a rotating shaft in a refiner, beater, PFI mill, kneader, disperser, etc., or by friction between the pulp fibers themselves. The beating conditions are not particularly limited and may be appropriately adjusted depending on the type of mechanical treatment used. For example, beating may be performed so that the freeness becomes 100 mL to 600 mL.

[0042] The filamentous algae-derived fibers that have been neutralized and, if necessary, beaten can be used to make paper, thereby obtaining paper containing the filamentous algae-derived fibers. The aspect ratio of the filamentous algae-derived fibers used in the papermaking process may be 10 to 130. When the paper of the present disclosure contains wood-derived pulp, the filamentous algae-derived fibers and wood-derived fibers may be mixed after beating is completed. Alternatively, the filamentous algae-derived fibers and wood-derived pulp may be mixed and beaten together.

[0043] The papermaking method is not particularly limited, and can be carried out using a known papermaking machine. Examples of the papermaking machine include a Fourdrinier papermaking machine, a cylinder papermaking machine, a cylinder, and a twin wire papermaking machine. In order to improve the surface smoothness of the paper, surface treatment may be performed by applying heat and pressure during or after the papermaking process. Specific examples of the surface treatment method include calendaring, such as machine calendaring and super calendaring.

[0044] <Paper modifier and its manufacturing method> The paper modifier of the present disclosure contains fibers derived from filamentous algae, and the aspect ratio of the fibers is 10-130. The paper modifier of the present disclosure contains fibers derived from filamentous algae, and as described above, exhibits different properties from fibers derived from wood. Therefore, by adding the paper modifier of the present disclosure to paper containing fibers derived from wood, it is possible to obtain paper exhibiting different properties compared to paper consisting only of fibers derived from wood. For example, it may be possible to strengthen the interfiber bonding strength of the fibers derived from wood and improve the tensile modulus. The amount of paper modifier added is not particularly limited, and can be an amount that allows the paper obtained by adding the paper modifier of the present disclosure to exhibit the desired properties. A method for producing a paper modifier of the present disclosure may include removing starch and protein components from fibers derived from filamentous algae, bleaching the fibers derived from filamentous algae from which the starch and protein components have been removed, and neutralizing the bleached fibers derived from filamentous algae. Details of the method for producing a paper modifier, such as the method for removing starch and protein components from fibers derived from filamentous algae, the method for bleaching the fibers derived from filamentous algae from which the starch and protein components have been removed, and the method for neutralizing the bleached fibers derived from filamentous algae, are the same as those of the paper producing method disclosed herein. EXAMPLES

[0045] The present disclosure will be described in more detail below with reference to examples. The materials, amounts, ratios, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present disclosure. Therefore, the present disclosure should not be interpreted as being limited by the specific examples shown below.

[0046] [Example 1] The paper of Example 1 was produced through the following steps. -Treatment of filamentous algae- The fibers derived from Cladophora fracta were boiled for 10 minutes, then soaked in 99.9% ethanol for 10 minutes to remove the chlorophyll. The fibers were then cut into 5 cm pieces using a food mixer, and the pulp fibers were dried. - Fiber preparation - The dried Cladophora fracta-derived fibers obtained as described above were immersed in water and left to stand for 24 hours to cause the fibers to swell with the water, thereby obtaining swollen fibers. -Alkaline extraction- The fibers were treated in a 5% by mass aqueous solution of sodium hydroxide for 1 hour in an environment with a pulp concentration of 20% by mass, pH of 10 to 12, and 60°C. -bleaching- The fibers were treated for 1 hour in an aqueous sodium hypochlorite solution with 1% available chlorine by mass, 20% pulp by mass, pH: 10-11, and 60° C. The amount of bleaching agent (available chlorine) per 100 g of Cladophora fracta-derived fiber was 1 g. -Neutralization- Hydrochloric acid was added to the aqueous sodium hypochlorite solution to neutralize the pulp suspension to a pH of 6-7. - Beating - The neutralized pulp was filtered out of the suspension, and the obtained pulp was placed in the mill house of a PFI mill (a beater manufactured by Kumagai Riki Kogyo Co., Ltd.). The pulp was pressed evenly against the inner wall and then beaten 5,000 times to obtain beaten pulp. -Papermaking- Basis weight 60g / m 2 The pulp suspension (with an area of ​​200 cm2) 2 A total of 800 mL was collected when the pulp concentration was 0.15% by mass. The pulp suspension was poured into the cylinder of the hand-sheet machine, which had water stored to a height of 20 to 30 cm, and water was poured into the cylinder again. The perforated plate was moved up and down inside the cylinder to thoroughly agitate the pulp, after which the water was drained and paper was made. Two sheets of filter paper of the same size were placed on top of the wet paper formed on the wire net, and a metal plate was placed on top. A couch roll was moved back and forth over the top of the paper to absorb water, and then the filter paper was removed and the prepared test handsheet was attached to the metal plate. -press- A metal plate, paper, thin filter paper, and absorbent filter paper were stacked in that order and pressurized at 410 kPa for 5 minutes. After pressing, the absorbent filter paper was replaced and pressure was applied again for 2 minutes. -Drying- The absorbent filter paper was removed and the paper was dried by clamping it between tension drying rings. The dried paper was then peeled off from the metal plate, and the thin filter paper was then peeled off from the dried paper. Through these steps, the paper of Example 1 containing fibers derived from Cladophora fracta was obtained.

[0047] [Example 2] Paper containing fibers derived from Cladophora fracta was obtained in Example 2 in the same manner as in Example 1, except that instead of bleaching with an aqueous sodium hypochlorite solution, the paper was treated for 1 hour in an aqueous 5% by mass hydrogen peroxide solution with a pulp concentration of 20% by mass, pH: 10 to 11, and an environment of 60° C. The amount of bleaching agent (hydrogen peroxide) per 100 g of fibers derived from Cladophora fracta was 1 g.

[0048] [Example 3] The paper of Example 3 containing fibers derived from Oedogonium borisianum was obtained in the same manner as in Example 1, except that fibers derived from Oedogonium borisianum were used instead of the fibers derived from Cladophora fracta.

[0049] [Example 4] Paper containing fibers derived from Cladophora pusilla of Example 4 was obtained in the same manner as in Example 1, except that fibers derived from Cladophora pusilla were used instead of fibers derived from Cladophora fracta.

[0050] [Example 5] Dried softwood bleached pulp fiber (NBKP) was soaked in sufficient water for 24 hours to allow the fiber to swell sufficiently with the water. The pulp was sieved and the water was squeezed by hand to make the pulp concentration 10%. The pulp was then placed in the mill house of a beating mill, and the pulp was pressed evenly against the inner wall by hand. A roll was then lowered into the mill house, the mill house was rotated, and the roll was rotated to beat the pulp 5,000 times. The pulp was then taken out and thoroughly disintegrated using a disintegrator. The basis weight was 60 g / m2. 2 The pulp suspension (with an area of ​​200 cm2) 2 When the pulp concentration was 0.15 mass%, 800 mL was collected. The beaten pulp of fibers derived from Cladophora fracta obtained through a process similar to that of Example 1 and the beaten pulp of softwood bleached pulp fibers obtained as described above were mixed in a 1:1 ratio based on pulp dry mass to form a mixed pulp. The resulting mixed pulp was used for papermaking, pressing and drying in the same manner as in Example 1 to obtain paper of Example 5 containing fibers derived from Cladophora fracta and softwood bleached pulp fibers.

[0051] [Reference example] -Treatment of filamentous algae- Fibers derived from Oedogonium borisianum were boiled for 10 minutes, then soaked in 99.9% ethanol to remove chlorophyll. The fibers were cut into pieces of about 5 cm using a food mixer to obtain a pulp suspension. -Paper making, drying, etc.- Basis weight 60g / m 2 The pulp suspension was then poured into the cylinder of a hand sheet making machine, stirred, the water in the cylinder was drained, and the paper was simply made onto a wire net. Then, the filter paper was placed on the handmade sheet on the net to remove moisture. The handmade sheet was carefully peeled off, and the sheet was attached to a metal plate for drying, and the filter paper and drying ring were placed on top of it, and it was dried. Through these steps, a reference paper containing fibers derived from Oedogonium borisianum was obtained.

[0052] [Comparative Example 1] - Fiber preparation - Dried softwood bleached pulp fiber (NBKP) was soaked in sufficient water for 24 hours to allow the fiber to swell sufficiently with the water. The pulp was sieved and the water was squeezed by hand to make the pulp concentration 10%. The pulp was then placed in the mill house of a beating mill, and the pulp was pressed evenly against the inner wall by hand. A roll was then lowered into the mill house, the mill house was rotated, and the roll was rotated to beat the pulp 5,000 times. The pulp was then taken out and thoroughly disintegrated using a disintegrator. -Papermaking- Basis weight 60g / m 2 The pulp suspension (with an area of ​​200 cm2) 2A total of 800 mL was collected when the pulp concentration was 0.15% by mass. The pulp suspension was poured into the cylinder of the hand-sheet machine, which had water stored to a height of 20 to 30 cm, and water was poured into the cylinder again. The perforated plate was moved up and down inside the cylinder to thoroughly agitate the pulp, after which the water was drained and paper was made. Two sheets of filter paper of the same size were placed on top of the wet paper formed on the wire net, and a metal plate was placed on top. A couch roll was moved back and forth over the top of the paper to absorb water, and then the filter paper was removed and the prepared test handsheet was attached to the metal plate. -press- A metal plate, paper, thin filter paper, and absorbent filter paper were stacked in that order and pressurized at 410 kPa for 5 minutes. After pressing, the absorbent filter paper was replaced and pressure was applied again for 2 minutes. -Drying- The absorbent filter paper was removed and the paper was dried by clamping it between tension drying rings. The dried paper was then peeled off from the metal plate, and the thin filter paper was then peeled off from the dried paper. Through these steps, paper containing softwood bleached pulp fibers of Comparative Example 1 was obtained.

[0053] [Comparative Example 2] - Fiber preparation - Dry bleached hardwood pulp fiber (LBKP) was soaked in sufficient water for 24 hours to allow the fiber to swell sufficiently with the water. The pulp was sieved and the water was squeezed by hand to a pulp concentration of 10%. The pulp was then placed in the mill house of a beating mill, and the pulp was pressed evenly against the inner wall by hand. A roll was then lowered into the mill house, the mill house was rotated, and the roll was rotated to beat the pulp 5,000 times. The pulp was then removed and thoroughly disintegrated using a disintegrator. -Papermaking- Basis weight 60g / m 2 The pulp suspension (with an area of ​​200 cm2) 2A total of 800 mL was collected when the pulp concentration was 0.15% by mass. The pulp suspension was poured into the cylinder of the hand-sheet machine, which had water stored to a height of 20 to 30 cm, and water was poured into the cylinder again. The perforated plate was moved up and down inside the cylinder to thoroughly agitate the pulp, after which the water was drained and paper was made. Two sheets of filter paper of the same size were placed on top of the wet paper formed on the wire net, and a metal plate was placed on top. A couch roll was moved back and forth over the top of the paper to absorb water, and then the filter paper was removed and the prepared test handsheet was attached to the metal plate. -press- A metal plate, paper, thin filter paper, and absorbent filter paper were stacked in that order and pressurized at 410 kPa for 5 minutes. After pressing, the absorbent filter paper was replaced and pressure was applied again for 2 minutes. -Drying- The absorbent filter paper was removed and the paper was dried by clamping it between tension drying rings. The dried paper was then peeled off from the metal plate, and the thin filter paper was then peeled off from the dried paper. Through these steps, a paper of Comparative Example 2 containing hardwood bleached pulp fibers was obtained.

[0054] <Evaluation> The papers of the Examples, Reference Examples, and Comparative Examples were evaluated as follows. The aspect ratio, Runkel ratio, density, smoothness, average fiber length, specific tensile strength, tensile modulus, tensile breaking elongation, average fiber width, freeness, basis weight, thickness and whiteness were measured by the methods described above. The opacity was measured by the method described later. The results are shown in Table 1. In addition, the single fiber tensile strength of each fiber was measured by the above-mentioned method. The single fiber tensile strength of the fiber derived from Cladophora fracta used in Example 1 was 1 g weight / fiber, the single fiber tensile strength of the fiber derived from Cladophora fracta used in Example 2 was 2 g weight / fiber, the single fiber tensile strength of the fiber derived from Oedogonium borisianum used in Example 3 was 0.75 g weight / fiber, the single fiber tensile strength of the fiber derived from Cladophora pusilla used in Example 4 was 1.5 g weight / fiber, the single fiber tensile strength of the fiber derived from Oedogonium borisianum used in the Reference Example was 1.5 g weight / fiber, the single fiber tensile strength of the softwood bleached pulp fiber (NBKP) used in Comparative Example 1 was 6 g weight / fiber, and the single fiber tensile strength of the hardwood bleached pulp fiber (LBKP) used in Comparative Example 2 was 3 g weight / fiber.

[0055] [Table 1]

[0056] From the results shown in Table 1, it can be seen that the Runkel ratio of fibers derived from filamentous algae is about 1 / 4 to 1 / 5 of that of wood, and the fibers have the property of being easily crushed when dried. Therefore, the basis weight is 60 g / m 2 It can be seen that the paper containing the filamentous algae-derived fiber has a higher density and smoothness, and a lower freeness and thickness, when compared. It can also be seen that Example 5, which combines the filamentous algae-derived fiber and wood fiber, has intermediate properties. Although the reference example uses fiber derived from filamentous algae, the above-mentioned characteristics are not observed because only the chlorophyll is removed during processing, and the starch and protein contained within the cells remain in the fiber, and the fiber does not go through the stage where it is crushed and flattened during drying.

[0057] -Opacity- The opacity of the papers in each of the Examples, Reference Examples, and Comparative Examples was measured using a Spectrophotometer for Paper manufactured by Nippon Denshoku Industries Co., Ltd. Using a single sample, the luminous reflectance (%) and the intrinsic luminous reflectance (%) measured in a state where the samples were stacked until they became completely opaque were measured, and the quotient obtained by multiplying the former by 100 and dividing the latter was taken as the opacity (%). The results obtained are shown in Table 1.

[0058] -Surface observation- Electron micrographs were taken using a field emission scanning electron microscope (FE-SEM) (SU8020, Hitachi) to observe the surfaces of the papers obtained in Example 1, Example 2, and Comparative Example 1. Prior to observation, the samples were coated with platinum (Pt) by sputtering. The results obtained are shown in FIG. 1 (Example 1), FIG. 2 (Example 2) and FIG. 3 (Comparative Example 1). Comparing Figures 1 or 2 with Figure 3, it can be seen that the fibers of the paper derived from filamentous algae in Figures 1 and 2 were more crushed and flattened than the fibers of the paper derived from coniferous trees. Furthermore, there were almost no gaps between the fibers on the surface of the paper derived from filamentous algae. Therefore, it is believed that the surface of the paper derived from filamentous algae was smoother than that of the paper derived from coniferous trees. This is also evident from the smoothness of both papers shown below. Furthermore, by comparing Figures 1 and 2, it can be seen that the algae fibers treated with sodium hypochlorite tend to be more finely divided than those treated with hydrogen peroxide.

[0059] -Fracture surface observation- The papers obtained in Example 1 and Comparative Example 1 were subjected to a tensile test using a tabletop tensile / compression tester, MCT series, manufactured by A&D Co., Ltd., and the papers obtained in Example 1 and Comparative Example 1 were broken. The fracture surface was observed using an optical microscope (OLYMPUS, SZX10 (product name)). The results are shown in Figure 4 (Example 1) and Figure 5 (Comparative Example 1). Comparing Figures 4 and 5, we can see that the fracture surface of paper made from fibers derived from filamentous algae is linear. This is thought to be because, while wood fibers are broken due to the binding strength between the fibers, algae-derived fibers are broken due to the strength of the individual fibers.

[0060] - Granting transparency 1 - The basis weight during papermaking is 30 g / m 2 Paper to be subjected to the imparting of transparency was made in the same manner as in Example 1 or Comparative Example 1, except that the pulp suspension was collected so that the thickness of the pulp suspension was 100 μm or more. The resulting paper was subjected to the following treatment to obtain starch-coated paper. A 10% starch solution was obtained from starch powder. Basis weight: 30 g / m 2 The paper of Example 1 (filamentous algal fiber paper) adjusted in the above step was thoroughly soaked in a 10% starch aqueous solution, fixed so as not to deform, and then dried. The same procedure was also carried out for the paper of Comparative Example 1. The opacity of the paper coated with the starch obtained as described above was measured as described above. As a result, the opacity of the paper of Example 1 was 18%, and the opacity of the paper of Comparative Example 1 was 75%. Comparing the paper of Example 1 with the paper of Comparative Example 1, it can be seen that it is relatively easy to impart high transparency to paper derived from filamentous algae by using starch.

[0061] - Granting transparency 2 - Polycaprolactone (PCL) was heated at 80°C to obtain a melted PCL liquid. The PCL liquid was thoroughly applied onto the surface of the paper of Example 1 and Comparative Example 1 used in the evaluation of adding transparency 1, and pressed at 30 MP and 75°C for 5 minutes. After pressing, the paper was dried at room temperature. The opacity of the paper coated with PCL obtained as described above was measured as described above. As a result, the opacity of the paper of Example 1 was 15%, and the opacity of the paper of Comparative Example 1 was 50%. Comparing the paper of Example 1 with the paper of Comparative Example 1, it can be seen that it is relatively easy to impart high transparency to paper derived from filamentous algae by using PCL. The lower the opacity, the less light irradiated onto the sample is reflected or absorbed, making the sample appear transparent. Cellulose crystals, the main component of pulp fibers, are inherently transparent, but when processed into paper, the gaps that appear between the fibers cause light to be diffusely reflected, making the paper appear white. By adding starch and PCL, the gaps between the fibers are filled, and it appears that transparency has improved in both Example 1 and Comparative Example 1. On the other hand, as mentioned above, filamentous algal fiber has fewer gaps between the fibers, which is thought to have greatly improved transparency. The density shown above makes it clear that filamentous algal fiber has fewer gaps between the fibers.

Claims

1. Contains fibers derived from filamentous algae, The paper has an aspect ratio of the fibers of 10 to 130.

2. 2. The paper of claim 1, wherein the filamentous algae comprises at least one species selected from the group consisting of Oedogonium borisianum, Cladophora fracta, and Cladophora pusilla.

3. 10. The paper of claim 1 further comprising wood-derived pulp.

4. Contains fibers derived from filamentous algae, The paper modifier, wherein the aspect ratio of the fibers is 10 to 130.

5. removing starch and protein components from filamentous algae-derived fibers; bleaching the filamentous algae-derived fiber from which the starch and protein components have been removed; neutralizing the bleached filamentous algae-derived fibers; and making paper using the neutralized filamentous algae-derived fibers.

6. 6. The method of claim 5, wherein removing the starch and protein components comprises soaking the filamentous algae-derived fibers in an alkaline aqueous solution.

7. The method for producing paper according to claim 5, wherein the bleaching agent used for the bleaching contains at least one of hypochlorite and hydrogen peroxide.

8. 6. The method for producing paper according to claim 5, wherein the amount of bleaching agent used in the bleaching is 1 g or less per 100 g of the fibers derived from the filamentous algae.

9. The method for producing paper according to claim 8 , wherein the bleaching is carried out in a state where the concentration of the filamentous algae-derived fibers is 15% by mass or more.

10. The method further comprises beating the neutralized filamentous algae-derived fibers, The method for producing paper according to claim 5, wherein the aspect ratio of the filamentous algae-derived fibers used in the papermaking process is 10 to 130.

11. removing starch and protein components from filamentous algae-derived fibers; bleaching the filamentous algae-derived fiber from which the starch and protein components have been removed; and neutralizing the bleached filamentous algae-derived fibers.

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