WO2019189770A1

WO2019189770A1 - Paper containing cellulose nanofibers

Info

Publication number: WO2019189770A1
Application number: PCT/JP2019/014024
Authority: WO
Inventors: 遼外岡; 吉松　丈博; 悠生久永; 宗信神代; 敬介田上
Original assignee: 日本製紙株式会社
Priority date: 2018-03-30
Filing date: 2019-03-29
Publication date: 2019-10-03
Also published as: JP2021105224A

Abstract

Provided is a paper having excellent strength and stiffness. This paper is provided with a raw paper layer that contains raw material pulp and cellulose nanofibers, wherein the cellulose nanofibers are mechanically disintegrated, chemically modified cellulose nanofibers, and the moisture content of the paper is 10 wt% or less when the paper is humidity-controlled under the conditions of 23°C and 50±2% according to JIS P 8111.

Description

Paper containing cellulose nanofibers

The present invention relates to paper containing cellulose nanofibers.

Cellulose nanofibers are expected as a new material and various studies have been made. For example, Patent Documents 1 and 2 propose that cellulose nanofibers are used as an additive at the time of paper making to improve the glossiness of the paper or improve the yield in the paper making process.

On the other hand, paper is used in various fields such as information recording medium applications such as printing paper and recording paper and packaging applications, and in any application, it is required to have sufficient strength during use or processing. Yes. Factors that particularly affect the stiffness of paper include paper thickness, pulp type, ash content in paper, moisture in paper, and the like. The higher the paper thickness, the higher the stiffness. When a rigid mechanical pulp or the like is used as the pulp type, the stiffness of the paper is increased. Further, the lower the ash content in the paper, the higher the stiffness, and the lower the moisture content in the paper, the higher the stiffness. When the moisture in the paper increases, water molecules enter between the cellulose fibers in the paper and weaken the hydrogen bonds, resulting in a reduction in paper stiffness.

Japanese Patent Application Laid-Open No. 2018-3215 JP 2011-74528 A

The inventors have conceived that the strength and stiffness of paper can be improved by using cellulose nanofibers. However, since the paper described in Patent Document 1 is a cellulose nanofiber that has not been chemically modified, it cannot be said that the strength and the like are at a sufficient level, and the paper described in Reference 2 is not a technique that focuses on strength. In view of such circumstances, an object of the present invention is to provide a paper having excellent strength and stiffness.

The said subject is solved by the following this invention.
(1) A paper having a base paper layer containing raw pulp and cellulose nanofibers,
The cellulose nanofiber is mechanically defibrated chemically modified cellulose nanofiber,
paper.
(2) Paper as described in (1) provided with a pigment coating layer.
(3) The paper according to any one of (1) to (2), wherein the moisture content of the paper conditioned at 23 ° C. and 50 ± 2% in accordance with JIS P 8111 is 10% by weight or less.
(4) The method according to any one of (1) to (3), comprising: chemically modifying the cellulose raw material and then mechanically defibrating to prepare cellulose nanofibers; and incorporating the cellulose nanofibers into a base paper layer The manufacturing method of the paper of description.

The present invention can provide paper having excellent strength and stiffness.

[Mode for Carrying Out the Invention]

Hereinafter, the present invention will be described in detail. In the present invention, “X to Y” includes X and Y which are their end values.

1. Paper containing cellulose nanofibers The paper of the present invention only needs to contain cellulose nanofibers in the base paper layer. For example, the cellulose nanofiber may be contained in the pigment coating layer in addition to the base paper layer. These layers will be described later.

(1) Cellulose nanofiber Cellulose nanofiber (hereinafter also referred to as “CNF”) is a single microfibril of cellulose obtained by defibrating a cellulose-based raw material, and has an average fiber diameter of less than 500 nm. Mechanically defibrated chemically modified cellulose nanofiber (hereinafter also referred to as "mechanically defibrated chemically modified CNF") is a single microfibril of cellulose obtained by mechanically defibrating a chemically modified cellulose-based raw material.

In the present invention, a B-type viscosity (100 to 10,000 mPa · s) when an aqueous dispersion having a concentration of 1% (w / v) (that is, an aqueous dispersion containing 1 g of CNF (dry weight) in 100 mL of water) is used. It is preferable to use mechanically defibrated chemically modified CNF that gives 60 rpm, 20 ° C. The B-type viscosity is an index for specifying properties such as the functional group amount, the average fiber length, and the average fiber diameter of the mechanically defibrated chemically modified CNF, and is appropriately adjusted according to the application.

The B-type viscosity of the aqueous dispersion of mechanically defibrated chemically modified CNF of the present invention can be measured by a known method. For example, it can be measured using a VISCOMETER TV-10 viscometer manufactured by Toki Sangyo Co., Ltd. The temperature at the time of measurement is 20 ° C., and the rotational speed of the rotor is 60 rpm. The aqueous dispersion of CNF of the present invention has thixotropic properties, has a characteristic that the viscosity is lowered by applying a shearing stress by stirring, and the viscosity increases and gelates in a stationary state, so that it is sufficiently stirred. It is preferable to measure the B-type viscosity in the state.

Mechanically defibrated chemically modified CNF can be produced by chemically modifying cellulosic raw materials to prepare chemically modified cellulose and mechanically defibrating it.
1) Cellulose-based material The cellulose-based material is not particularly limited, and examples thereof include those derived from plants, animals (for example, ascidians), algae, microorganisms (for example, acetic acid bacteria (Acetobacter)), and microorganism products. Examples of plant-derived materials include wood, bamboo, hemp, jute, kenaf, farmland waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleach kraft pulp (NBKP), hardwood unbleached kraft pulp ( LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.). The cellulose raw material used in the present invention may be any one or a combination thereof, but is preferably a plant or microorganism-derived cellulose fiber, more preferably a plant-derived cellulose fiber.

The average fiber diameter of the cellulose fibers is not particularly limited, but is about 30 to 60 μm in the case of softwood kraft pulp, which is a general pulp, and about 10 to 30 μm in the case of hardwood kraft pulp. In the case of other pulps, the average fiber diameter of those having undergone general refining is about 50 μm. For example, when a raw material obtained by purifying a chip such as a chip of several centimeters is used, it is preferable to perform mechanical treatment with a disintegrator such as a refiner or beater to adjust the average fiber diameter to about 50 μm or less, and to about 30 μm or less. It is more preferable.

2) Chemical modification Chemical modification means introducing a functional group into a cellulosic raw material. In the present invention, it is preferable to introduce an anionic group. Examples of the anionic group include acid groups such as a carboxyl group, a carboxyl group-containing group, a phosphate group, and a phosphate group-containing group. Examples of the carboxyl group-containing group include —COOH group, —R—COOH (R is an alkylene group having 1 to 3 carbon atoms), and —O—R—COOH (R is an alkylene group having 1 to 3 carbon atoms). It is done. Examples of the phosphoric acid group-containing group include a polyphosphoric acid group, a phosphorous acid group, a phosphonic acid group, and a polyphosphonic acid group. Depending on the reaction conditions, these acid groups may be introduced in the form of a salt (for example, a carboxylate group (—COOM, M is a metal atom)). In the present invention, the chemical modification is preferably oxidation or etherification. Hereinafter, these will be described in detail.

[Oxidation]
Oxidized cellulose is obtained by oxidizing the cellulose raw material. Although the oxidation method is not particularly limited, for example, the cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a substance selected from the group consisting of bromide, iodide, and a mixture thereof. The method of doing is mentioned. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized to produce a group selected from the group consisting of an aldehyde group, a carboxyl group, and a carboxylate group. Although the density | concentration of the cellulose raw material at the time of reaction is not specifically limited, 5 weight% or less is preferable.

The N-oxyl compound is a compound capable of generating a nitroxy radical. Examples of the nitroxyl radical include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction. The amount of the N-oxyl compound used is not particularly limited as long as it is a catalyst amount that can oxidize cellulose as a raw material. For example, 0.01 mmol or more is preferable and 0.02 mmol or more is more preferable with respect to 1 g of absolutely dry cellulose. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, and even more preferably 0.5 mmol or less. Therefore, the amount of the N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and still more preferably 0.02 to 0.5 mmol with respect to 1 g of absolutely dry cellulose.

Bromide is a compound containing bromine, and examples thereof include alkali metal bromide that can be dissociated and ionized in water, such as sodium bromide. Further, the iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is preferably 0.1 mmol or more, more preferably 0.5 mmol or more, based on 1 g of absolutely dry cellulose. The upper limit of the amount is preferably 100 mmol or less, more preferably 10 mmol or less, and even more preferably 5 mmol or less. Accordingly, the total amount of bromide and iodide is preferably from 0.1 to 100 mmol, more preferably from 0.1 to 10 mmol, and even more preferably from 0.5 to 5 mmol, based on 1 g of absolutely dry cellulose.

The oxidizing agent is not particularly limited, and examples thereof include halogen, hypohalous acid, halous acid, perhalogen acid, salts thereof, halogen oxide, and peroxide. Among them, hypohalous acid or a salt thereof is preferable because it is inexpensive and has a low environmental burden, hypochlorous acid or a salt thereof is more preferable, and sodium hypochlorite is more preferable. The amount of the oxidizing agent used is preferably 0.5 mmol or more, more preferably 1 mmol or more, and further preferably 3 mmol or more with respect to 1 g of absolutely dry cellulose. The upper limit of the amount is preferably 500 mmol or less, more preferably 50 mmol or less, and even more preferably 25 mmol or less. Therefore, the amount of the oxidizing agent used is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and particularly preferably 3 to 10 mmol with respect to 1 g of absolutely dry cellulose. When an N-oxyl compound is used, the amount of the oxidizing agent used is preferably 1 mol or more with respect to 1 mol of the N-oxyl compound, and the upper limit is preferably 40 mol. Accordingly, the amount of the oxidizing agent used is preferably 1 to 40 mol with respect to 1 mol of the N-oxyl compound.

The conditions such as pH and temperature during the oxidation reaction are not particularly limited, and generally the oxidation reaction proceeds efficiently even under relatively mild conditions. The reaction temperature is preferably 4 ° C or higher, more preferably 15 ° C or higher. The upper limit of the temperature is preferably 40 ° C. or lower, and more preferably 30 ° C. or lower. Accordingly, the reaction temperature is preferably 4 to 40 ° C., and may be about 15 to 30 ° C., that is, room temperature. The pH of the reaction solution is preferably 8 or more, and more preferably 10 or more. The upper limit of pH is preferably 12 or less, and more preferably 11 or less. Accordingly, the pH of the reaction solution is preferably about 8 to 12, more preferably about 10 to 11. Usually, a carboxyl group is generated in cellulose as the oxidation reaction proceeds, and therefore the pH of the reaction solution tends to decrease. Therefore, in order to advance the oxidation reaction efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution in the above range. The reaction medium for the oxidation is preferably water for reasons such as ease of handling and the difficulty of side reactions.

The reaction time in the oxidation can be appropriately set according to the progress of the oxidation, and is usually 0.5 hours or more, and the upper limit is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time in the oxidation is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours. Oxidation may be carried out in two or more stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt generated as a by-product in the first-stage reaction. Can be oxidized well.

Another example of the carboxylation (oxidation) method is ozone oxidation. By this oxidation reaction, at least the 2- and 6-position hydroxyl groups of the glucopyranose ring constituting the cellulose are oxidized and the cellulose chain is decomposed. The ozone treatment is usually performed by bringing a gas containing ozone and a cellulose raw material into contact with each other. The ozone concentration in the gas is preferably 50 g / m ³ or more. The upper limit is preferably 250 g / m ³ or less, and more preferably 220 g / m ³ or less. Accordingly, the ozone concentration in the gas is preferably 50 to 250 g / m ³ , and more preferably 50 to 220 g / m ³ . The amount of ozone added is preferably 0.1% by weight or more, and more preferably 5% by weight or more, based on 100% by weight of the solid content of the cellulose raw material. The upper limit of the amount of ozone added is usually 30% by weight or less. Therefore, the amount of ozone added is preferably 0.1 to 30% by weight and more preferably 5 to 30% by weight with respect to 100% by weight of the solid content of the cellulose raw material. The ozone treatment temperature is usually 0 ° C. or higher, preferably 20 ° C. or higher, and the upper limit is usually 50 ° C. or lower. Accordingly, the ozone treatment temperature is preferably 0 to 50 ° C., and more preferably 20 to 50 ° C. The ozone treatment time is usually 1 minute or longer, preferably 30 minutes or longer, and the upper limit is usually 360 minutes or shorter. Accordingly, the ozone treatment time is usually about 1 to 360 minutes, and preferably about 30 to 360 minutes. When the condition of the ozone treatment is within the above range, the cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved.

Further, the ozone-treated cellulose may be further oxidized using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. Examples of the method for the additional oxidation treatment include a method in which these oxidizing agents are dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the cellulose raw material is immersed in the oxidizing agent solution. The amount of the carboxyl group, carboxylate group, and aldehyde group contained in the oxidized cellulose nanofiber can be adjusted by controlling the oxidizing conditions such as the addition amount of the oxidizing agent and the reaction time.

An example of a method for measuring the amount of carboxyl groups will be described below. Prepare 60 mL of 0.5 wt% slurry (aqueous dispersion) of oxidized cellulose, add 0.1 M hydrochloric acid aqueous solution to pH 2.5, then add 0.05 N sodium hydroxide aqueous solution dropwise to adjust pH to 11. Measure the electrical conductivity until The amount can be calculated from the amount of sodium hydroxide consumed (a) in the neutralization step of the weak acid, whose change in electrical conductivity is gradual, using the following equation.
Amount of carboxyl group [mmol / g oxidized cellulose] = a [mL] × 0.05 / oxidized cellulose weight [g]

The amount of carboxyl groups in the oxidized cellulose thus measured is preferably 0.1 mmol / g or more, more preferably 0.5 mmol / g or more, and further 0.8 mmol / g or more based on the absolute dry weight. preferable. The upper limit of the amount is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and further preferably 2.0 mmol / g or less. Therefore, the amount is preferably 0.1 to 3.0 mmol / g, more preferably 0.5 to 2.5 mmol / g, and still more preferably 0.8 to 2.0 mmol / g.

[Etherification]
As etherification, carboxymethyl (ether), methyl (ether), ethyl (ether), cyanoethyl (ether), hydroxyethyl (ether), hydroxypropyl (ether), ethyl hydroxyethyl (ether) And hydroxypropylmethyl (ether). As an example, a carboxymethylation method will be described below.

The degree of carboxymethyl substitution per anhydroglucose unit in carboxymethylated cellulose or CNF obtained by carboxymethylation is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.10 or more. The upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.40 or less, and still more preferably 0.35 or less. Accordingly, the degree of carboxymethyl group substitution is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and even more preferably 0.10 to 0.30.

The carboxymethylation method is not particularly limited, and examples thereof include a method in which a cellulose raw material as a bottoming raw material is mercerized and then etherified. In the reaction, a solvent is usually used. Examples of the solvent include water, alcohol (for example, lower alcohol), and a mixed solvent thereof. Examples of the lower alcohol include methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, and tertiary butanol. As for the mixing ratio of the lower alcohol in the mixed solvent, the lower limit is usually 60% by weight or more, and the upper limit is 95% by weight or less, preferably 60 to 95% by weight. The amount of the solvent is usually 3 times the weight of the cellulose raw material. Although the upper limit of the amount is not particularly limited, it is 20 times by weight. Therefore, the amount of the solvent is preferably 3 to 20 times by weight.

Mercerization is usually performed by mixing the bottoming material and mercerizing agent. Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of mercerizing agent used is preferably 0.5 moles or more, more preferably 1.0 moles or more, and even more preferably 1.5 moles or more per anhydroglucose residue of the starting material. The upper limit of the amount is usually 20 times mol or less, preferably 10 times mol or less, more preferably 5 times mol or less, and hence the amount of mercerizing agent used is preferably 0.5 to 20 times mol, and 1.0 More preferably, it is ˜10 times mole, and more preferably 1.5 to 5 times mole.

The reaction temperature for mercerization is usually 0 ° C. or higher, preferably 10 ° C. or higher, and the upper limit is usually 70 ° C. or lower, preferably 60 ° C. or lower. Accordingly, the reaction temperature is usually 0 to 70 ° C., preferably 10 to 60 ° C. The reaction time is usually 15 minutes or longer, preferably 30 minutes or longer. The upper limit of the time is usually 8 hours or less, preferably 7 hours or less. Accordingly, the reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

The etherification reaction is usually performed by adding a carboxymethylating agent to the reaction system after mercerization. Examples of the carboxymethylating agent include sodium monochloroacetate. The addition amount of the carboxymethylating agent is usually preferably 0.05 times mol or more, more preferably 0.5 times mol or more, further preferably 0.8 times mol or more per glucose residue of the cellulose raw material. The upper limit of the amount is usually 10.0 times mole or less, preferably 5 moles or less, more preferably 3 times mole or less, and therefore the amount is preferably 0.05 to 10.0 times mole, more The amount is preferably 0.5 to 5, more preferably 0.8 to 3 moles. The reaction temperature is usually 30 ° C. or higher, preferably 40 ° C. or higher, and the upper limit is usually 90 ° C. or lower, preferably 80 ° C. or lower. Accordingly, the reaction temperature is usually 30 to 90 ° C., preferably 40 to 80 ° C. The reaction time is usually 30 minutes or longer, preferably 1 hour or longer, and the upper limit is usually 10 hours or shorter, preferably 4 hours or shorter. Therefore, the reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours. The reaction solution may be stirred as necessary during the carboxymethylation reaction.

Measurement of the degree of carboxymethyl substitution per glucose unit of carboxymethylated cellulose is, for example, by the following method. That is, 1) About 2.0 g of carboxymethylated cellulose (absolutely dry) is precisely weighed and put into a 300 mL conical stoppered Erlenmeyer flask. 2) Add 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of nitric acid methanol and shake for 3 hours to convert the carboxymethylcellulose salt (carboxymethylated cellulose) to hydrogen-type carboxymethylated cellulose. 3) Weigh accurately 1.5 to 2.0 g of hydrogen-type carboxymethylated cellulose (absolutely dry) and put into a 300 mL Erlenmeyer flask with a stopper. 4) Wet the hydrogen-type carboxymethylated cellulose with 15 mL of 80% methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. 5) Back titrate excess NaOH with 0.1N H ₂ SO ₄ using phenolphthalein as indicator. 6) The degree of carboxymethyl substitution (DS) is calculated by the following formula:
A = [(100 × F ′ − (0.1 N H ₂ SO ₄ ) (mL) × F) × 0.1] / (absolute dry mass of hydrogenated carboxymethylated cellulose (g))
DS = 0.162 × A / (1-0.058 × A)
A: 1N NaOH amount (mL) required for neutralizing 1 g of hydrogen-type carboxymethylated cellulose
F: Factor of 0.1N H ₂ SO ₄ F ′: Factor of 0.1N NaOH

3) Mechanical defibration Chemically modified cellulose is mechanically defibrated to obtain mechanically defibrated chemically modified CNF. The defibrating process may be performed once or a plurality of times. It is preferable to subject the mixture containing chemically modified cellulose and a dispersion medium to a defibrating treatment. As the dispersion medium, water is preferable. The apparatus used for defibration is not particularly limited, and examples thereof include high-speed rotation type, colloid mill type, high-pressure type, roll mill type, ultrasonic type, etc., high-pressure or ultra-high-pressure homogenizers are preferable, and wet high pressure Or an ultra-high pressure homogenizer is more preferable. It is preferable that the apparatus can apply a strong shearing force to the chemically modified cellulose. The pressure that can be applied by the apparatus is preferably 50 MPa or more, more preferably 100 MPa or more, and still more preferably 140 MPa or more. The apparatus is preferably a wet high pressure or ultra high pressure homogenizer. Thereby, defibration can be performed efficiently.

When defibration is performed on a dispersion of chemically modified pulp, the solid content concentration of the modified cellulose in the dispersion is usually preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and 0 More preferably 3% by weight or more. Thereby, the liquid amount with respect to the amount of the modified cellulose becomes an appropriate amount and becomes efficient. The upper limit of the concentration is usually preferably 20% by weight or less, more preferably 15% by weight or less, and still more preferably 10% by weight or less. Thereby, fluidity can be maintained.

4) Form Mechanically defibrated chemically modified CNF is in the form of a dry solid (eg, pellets, particles, powder), a liquid or gel in combination with a liquid medium, or a wet state in between Although it is good also as a solid substance, a powder form is preferable. In the present invention, the dry solid of cellulose nanofibers means a dispersion obtained by dehydrating or drying a dispersion containing cellulose nanofibers to a moisture content of 12% or less. Examples of dry solids of cellulose nanofibers include those obtained by drying a dispersion of cellulose nanofibers, or those obtained by drying a mixed liquid of cellulose nanofibers and a water-soluble polymer. From the viewpoint of the latter, the latter is preferable. Examples of the water-soluble polymer include cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, pullulan, starch, hard starch, Scrap flour, positive starch, phosphorylated starch, corn starch, gum arabic, locust bean gum, gellan gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein lysate, peptone, polyvinyl alcohol, Polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acid, polylactic acid, polymalic acid, polyglycerin Latex, rosin sizing agent, petroleum resin sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide / polyamine resin, polyethyleneimine, polyamine, vegetable gum, polyethylene oxide, hydrophilic cross-linked polymer, polyacrylate , Starch polyacrylic acid copolymer, tamarind gum, gellan gum, pectin, guar gum, colloidal silica, and combinations thereof. Among these, carboxymethylcellulose and its salt are preferable from the viewpoint of compatibility. When adding CNF of this invention to a pulp slurry, although it may be the said powdery form, liquid form, or a gel form, it is preferable that it is liquid form. In this case, a liquid composition in which a dry solid obtained by once drying mechanically denatured chemically modified CNF is dispersed again in a liquid medium such as water may be used, or a liquid composition prepared in the defibrating step. May be used.

The average fiber diameter of the mechanically defibrated chemically modified CNF is usually about 2 nm or more and less than 500 nm in terms of length-weighted average fiber diameter, preferably 2 to 50 nm. The average fiber length is preferably 50 to 2000 nm in terms of length-weighted average fiber length. Length-weighted average fiber diameter and length-weighted average fiber length (hereinafter simply referred to as “average fiber diameter” or “average fiber length”) are measured using an atomic force microscope (AFM) or a transmission electron microscope (TEM). It is obtained by observing each fiber. The average aspect ratio of the nanofiber is usually 10 or more. Although an upper limit is not specifically limited, Usually, it is 1000 or less. The average aspect ratio can be calculated by the following formula.
Average aspect ratio = average fiber length / average fiber diameter

The amount of carboxyl groups and the degree of substitution per glucose unit in the mechanically defibrated chemically modified CNF are preferably the same as those of chemically modified cellulose.

(2) Base Paper Layer A base paper layer is a layer that becomes a base of paper and contains pulp as a main component. In the present invention, the base paper may be a single layer or a multilayer. The base paper layer contains mechanically defibrated chemically modified CNF. In the case of a multilayer, it is sufficient that at least one of the base paper layers contains mechanically defibrated chemically modified CNF, and all layers may contain mechanically defibrated chemically modified CNF. In order to make the base paper layer contain the mechanically defibrated chemically modified CNF, the papermaking raw material may contain the mechanically defibrated chemically modified CNF in advance, and a coating solution containing the mechanically defibrated chemically modified CNF is applied after papermaking. The base paper layer may be impregnated. The former is called internal addition, and the latter is also called external addition. In the case of internal addition, the concentration of mechanically defibrated chemically modified CNF in the thickness direction of the base paper layer is relatively uniform. On the other hand, in the case of external addition, a concentration gradient of mechanically defibrated chemically modified CNF is observed in the thickness direction of the base paper layer. The content of mechanically defibrated chemically modified CNF is not limited as long as the effect of the present invention is obtained, but is preferably 0.0001% by weight or more, and 0.0003% by weight or more based on the pulp weight of the entire base paper layer. Is more preferable, and 0.001% by weight or more is more preferable. If the content is less than 0.0001% by weight, the effect of the present invention may not be obtained due to the small amount of addition. Further, the upper limit of the content is preferably 10% by weight or less, more preferably 5% by weight or less, further preferably 4% by weight or less, and most preferably 1% by weight or less.

The pulp raw material of the base paper used in the present invention is not particularly limited. Mechanical pulp such as ground pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), deinked pulp (DIP), conifer kraft pulp ( Chemical pulps such as NKP) and softwood kraft pulp (LKP) can be used. As the deinking (waste paper) pulp, it is possible to use selected waste paper such as high quality paper, medium quality paper, lower grade paper, newspaper, flyers, magazines, etc. or unselected waste paper in which these are mixed. In the present invention, even if chemical pulp such as kraft pulp is used, the effect of improving paper strength can be obtained, so that the content of kraft pulp may be large. The amount is preferably 50 parts by weight or more, more preferably 80 parts by weight or more, and still more preferably 85 parts by weight or more with respect to 100 parts by weight of the pulp. On the other hand, the content of waste paper pulp is preferably less than 20 parts by weight with respect to 100 parts by weight of pulp.

Although known fillers can be added to the base paper, it is not necessary to add fillers for applications such as paperboard where opacity and whiteness are not required, and when raw materials such as waste paper are used. When the filler is added, the fillers include heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, deramikaolin, magnesium carbonate, barium carbonate, barium sulfate, hydroxide Inorganic fillers such as amorphous silica produced by neutralization of aluminum, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, sodium silicate with mineral acid, urea-formalin resin, melamine series Organic fillers such as resin, polystyrene resin and phenol resin are listed. These may be used alone or in combination. Among them, calcium carbonate and light calcium carbonate, which are typical fillers for neutral papermaking and alkaline papermaking, and which can provide high opacity, are preferable. The content of the filler in the base paper is preferably 5 to 25% by weight, more preferably 6 to 20% by weight, based on the weight of the base paper. In the present invention, even if the ash content in the paper is high, a decrease in paper strength is suppressed. Therefore, the filler content in the base paper is more preferably 10% by weight or more.

As the internal additive, a bulking agent, a dry paper strength improver, a wet paper strength improver, a freeness improver, a dye, a neutral sizing agent, and the like may be used as necessary.

The base paper is manufactured by a known paper making method. For example, it can be carried out using a long net paper machine, a gap former type paper machine, a hybrid former type paper machine, an on-top former type paper machine, a round net paper machine, etc., but is not limited thereto.

When the base paper contains the mechanically defibrated chemically modified CNF of the present invention by internal addition, the mechanically defibrated chemically modified CNF may be added at any step in the step of preparing the pulp slurry. In order to improve the mixing efficiency, it is preferable to add in the pulp refiner process or the mixing process. In the case of adding mechanically defibrated chemically modified CNF in the mixing step, in order to improve the yield of CNF, a mixture of CNF and other auxiliary agents such as a filler and a retention agent may be added to the pulp slurry.

(3) Pigment coating layer The pigment coating layer is a layer containing a white pigment as a main component. Commonly used pigments such as calcium carbonate, kaolin, clay, calcined kaolin, amorphous silica, zinc oxide, aluminum oxide, satin white, aluminum silicate, magnesium silicate, magnesium carbonate, titanium oxide, plastic pigment, etc. Is mentioned.

The pigment coating layer contains an adhesive. Examples of the adhesive include oxidized starch, positive starch, urea phosphated starch, etherified starch such as hydroxyethyl etherified starch, various starches such as dextrin, proteins such as casein, soy protein, synthetic protein, polyvinyl Alcohol, cellulose derivatives such as carboxymethyl cellulose and methyl cellulose, styrene-butadiene copolymer, conjugated diene polymer latex of methyl methacrylate-butadiene copolymer, acrylic polymer latex, vinyl-based polymers such as ethylene-vinyl acetate copolymer Polymer latex etc. are mentioned. These can be used alone or in combination of two or more, and it is preferable to use a starch adhesive and a styrene-butadiene copolymer in combination.

The pigment coating layer may contain various auxiliary agents such as dispersants, thickeners, antifoaming agents, colorants, antistatic agents, preservatives and the like used in the general paper manufacturing field. Chemically modified CNF may be contained in the pigment coating layer. When the mechanically defibrated chemically modified CNF is contained in the pigment coating layer, it is preferably 1 × 10 ⁻³ to 1 part by weight based on 100 parts by weight of the pigment. In the case of the said range, the pigment coating liquid with moderate water retention can be obtained, without increasing the viscosity of a coating liquid significantly.

The pigment coating layer can be provided by coating the coating liquid on one side or both sides of the base paper by a known method. The solid content concentration in the coating solution is preferably about 30 to 70% by weight from the viewpoint of coating suitability. The pigment coating layer may be one layer, two layers, or three or more layers. When a plurality of pigment coating layers are present, the mechanically defibrated chemically modified CNF may be present in any pigment coating layer. The coating amount of the pigment coating layer may be appropriately adjusted depending on the use, but in the case of a coated paper for printing, it is 5 g / m ² or more in total per side, and preferably 10 g / m ² or more. . The upper limit is preferably 30 g / m ² or less, and preferably 25 g / m ² or less.

(4) Clear coating layer The paper of the present invention may have a clear (transparent) coating layer on one or both sides of the base paper. By applying clear coating on the base paper, the surface strength and smoothness of the base paper can be improved, and the coating property when applying pigment can be improved. The amount of clear coating is preferably from 0.1 to 1.0 g / m ² , more preferably from 0.2 to 0.8 g / m ² in terms of solid content per side. In the present invention, clear coating means, for example, using a coater (coating machine) such as a size press, a gate roll coater, a pre-metering size press, a curtain coater, a spray coater, starch, oxidized starch, processed starch, Applying a coating solution (surface treatment solution) mainly composed of water-soluble polymers as surface treatment agents such as various starches such as dextrin, carboxymethylcellulose, polyacrylamide, polyvinyl alcohol etc. on the base paper (size press) , Impregnation. In addition to the water-soluble polymer, a water-resistant agent and an external sizing agent may be used as the surface treatment agent.

(5) Characteristics The paper of the present invention preferably has a moisture content of 10% by weight or less after being conditioned under conditions of 23 ° C. and 50 ± 2% according to JIS P8111. Mechanically defibrated chemically modified CNF has a relatively high water retention rate, so that dehydration and drying may be difficult in the papermaking process. However, it is preferable to adjust the amount of mechanically defibrated chemically modified CNF and the amount of the modified group so that the moisture content of the paper is within the above range, since the dehydrating property and drying property can be improved in the paper making process. On the other hand, when the water content is higher than 10% by weight, a large amount of water molecules enter between the celluloses constituting the paper fiber and hydrogen bonds are weakened, which may reduce the stiffness. Although the lower limit of the moisture content is not limited, it is preferably 4% by weight or more. When the dehydration in the process of producing paper is insufficient or when CNF is added in an extremely large amount, the water content may be higher than 10% by weight.

The paper of the present invention has excellent strength because it contains mechanically defibrated chemically modified CNF having a high aspect ratio.

2. Paper Manufacturing Method The paper of the present invention is preferably manufactured through a process of preparing mechanically defibrated chemically modified CNF and containing the CNF in the base paper layer. Mechanically defibrated chemically modified CNF can be prepared by mechanically defibrating a chemically modified cellulose raw material as described above. The step of incorporating CNF into the base paper layer is preferably carried out by preparing a stock containing the CNF and paper-making it by a known method. The paper stock can be prepared according to a known method. For example, it can be prepared by adding mechanically defibrated chemically modified CNF, filler, and additives as necessary to a slurry obtained by disaggregating pulp. When a base paper layer containing mechanically defibrated chemically modified CNF is prepared by external addition, it is not necessary to add mechanically defibrated chemically modified CNF to the stock.

As described above, a coating process in which a clear coating or a pigment coating layer is provided on the paper surface may be performed.

Hereinafter, the present invention will be described with reference to examples.
[Example 1]
50% by weight of LBKP and 50% by weight of DIP were prepared as pulp, and for 100% by weight of the pulp, 0.9% by weight of sulfate band, 0.3% by weight of cationized starch, TEMPO-oxidized CNF (Japan) Pulp slurry was obtained by mixing 1000 ppmm (manufactured by Paper Industries Co., Ltd.), polyacrylamide 0.06% by weight, yielding agent 250 ppm, and light calcium carbonate. From the obtained pulp slurry, a handsheet having an ash content of 15% by weight and a water content of 9.0% was produced and evaluated in accordance with JIS P 8222.

[Example 2]
A handsheet was produced and evaluated in the same manner as in Example except that the amount of ash in paper was 16.5% by weight.

[Comparative Example 1]
A handsheet was produced and evaluated in the same manner as in Example 1 except that TEMPO-oxidized CNF was not added.

[Example 3]
100% by weight of LBKP was prepared as a pulp. To 100% by weight of the pulp, 0.3% by weight of cationized starch as an auxiliary agent, 1000 ppm of TEMPO-oxidized CNF (manufactured by Nippon Paper Industries Co., Ltd.), 0.06% by weight of polyacrylamide, A pulp slurry was obtained by mixing 250 ppm of a retention agent and light calcium carbonate. From the obtained pulp slurry, handsheets were produced and evaluated according to JIS P 8222 with a basis weight of 38 g / m ² .

[Comparative Example 2]
A handsheet was produced and evaluated in the same manner as in Example 3 except that TEMPO-oxidized CNF was not added.

Evaluation was performed as follows.
Handsheet preparation: JIS P 8222 was used as a reference.
Basis weight: JIS P 8223: 2006 was used as a reference.
Density: According to JIS P 8118: 2014.
Ash content: According to JIS P 8251: 2003.
Tensile strength: Tensile strength (mN / m): Based on JIS P8113, the longitudinal (papermaking flow) direction and the transverse direction (direction perpendicular to the papermaking flow) of the paper were measured.
Breaking length: According to JIS P 8113: 1998.
Tensile stiffness: Measured by the method prescribed in ISO / DIS 1924-3.
Opacity: According to JIS P 8149: 2000 (ISO 2471).
Water content in paper (moisture content): Humidity was adjusted under the conditions of 23 ° C. and 50 ± 2% in accordance with JIS P8111.
Formation index: Measured using a formation tester “FMT-MIII” manufactured by Nomura Corporation. The formation shows that the lower the value, the better.

Claims

A paper having a base paper layer containing raw pulp and cellulose nanofibers,
The cellulose nanofiber is mechanically defibrated chemically modified cellulose nanofiber,
paper.
The paper according to claim 1, further comprising a pigment coating layer.
The paper according to any one of claims 1 to 2, wherein the moisture content of the paper conditioned under conditions of 23 ° C humidity 50 ± 2% according to JIS P 8111 is 10% by weight or less.
The paper production according to any one of claims 1 to 3, comprising a step of preparing cellulose nanofibers by mechanical defibration after chemically modifying the cellulose raw material, and a step of incorporating the cellulose nanofibers into a base paper layer. Method.