JP2021105224A - Paper containing cellulose nanofiber - Google Patents

Abstract

To provide paper with excellent strength and stiffness.SOLUTION: Paper comprises a base paper layer containing raw material pulp and cellulose nanofibers, wherein the cellulose nanofibers are mechanically defibrated and chemically modified cellulose nanofibers and the moisture content of the paper is 10 wt.% or less, when its humidity adjustment is performed under the condition of 23°C, 50±2% according to JIS P 8111.SELECTED DRAWING: None

Description

The present invention relates to paper containing cellulose nanofibers.

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

On the other hand, paper is used in various fields such as information recording media such as printing paper and recording paper and packaging, and it is required to have sufficient strength at the time of use and processing in any of the applications. There is. Among the strengths of paper, factors that particularly affect the stiffness include paper thickness, pulp type, ash content in paper, moisture in paper, and the like. The thicker the paper, the higher the stiffness, and when rigid mechanical pulp or the like is used as the pulp type, the stiffness of the paper increases. Further, the lower the ash content in the paper, the higher the stiffness, and the lower the water content in the paper, the higher the stiffness. When the water content in the paper becomes high, water molecules enter between the cellulose fibers in the paper and weaken the hydrogen bonds, resulting in a decrease in the stiffness of the paper.

JP-A-2018-3215 Japanese Unexamined Patent Publication No. 2011-74528

The inventors have come up with the idea that the strength and stiffness of paper can be improved by using cellulose nanofibers. However, since the paper described in Patent Document 1 is cellulose nanofibers that have not been chemically modified, the strength and the like cannot be said to be at a sufficient level, and the paper described in Cited Document 2 has an unknown moisture content in the paper and is not strong. It was not the technology of interest. In view of such circumstances, it is an object of the present invention to provide a paper having excellent strength and stiffness.

The problem is solved by the following invention.
[1] A paper provided with a base paper layer containing raw material pulp and cellulose nanofibers.
The cellulose nanofibers are mechanically defibrated and chemically modified cellulose nanofibers.
Paper having a moisture content of 10% by weight or less, which has been conditioned according to JIS P 8111 under the conditions of 23 ° C. and 50 ± 2%.
[2] The paper according to [1], which comprises a pigment coating layer.
[3] The paper according to [1] or [2], which comprises a clear coating layer.
[4] A step of preparing cellulose nanofibers by chemically defibrating a cellulose raw material and then mechanically defibrating it, and a step of preparing a paper material containing the cellulose nanofibers.
The method for producing paper according to any one of [1] to [3].

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a paper having excellent strength and stiffness.

Aspects for carrying out the invention

Hereinafter, the present invention will be described in detail. In the present invention, "X to Y" includes the fractional values X and Y.

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

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

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

The B-type viscosity of the aqueous dispersion of the mechanically defibrated and 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 rotation speed of the rotor is 60 rpm. The aqueous dispersion of CNF of the present invention has thixotropy property, and has the property that the viscosity decreases by stirring and applying shear stress, and the viscosity increases and gels in the stationary state, so that the mixture is sufficiently stirred. It is preferable to measure the B-type viscosity in this state.

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

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 after undergoing general purification is about 50 μm. For example, when a raw material obtained by purifying a chip or the like having a size of several cm is used, it is preferable to perform mechanical treatment with a dissociator such as a refiner or a beater to adjust the average fiber diameter to about 50 μm or less, preferably about 30 μm or less. Is more preferable.

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

[Oxidation]
Oxidized cellulose can be obtained by oxidizing the cellulose raw material. The oxidation method is not particularly limited, but as an 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. There is a way to do it. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of cellulose is selectively oxidized to generate a group selected from the group consisting of an aldehyde group, a carboxyl group, and a carboxylate group. The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by weight or less.

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 is a compound that promotes the desired oxidation reaction. The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing 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 cellulose that has been completely dried. 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 even more preferably 0.02 to 0.5 mmol with respect to 1 g of the dry cellulose.

The bromide is a compound containing bromine, and examples thereof include alkali metals 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 an alkali metal iodide. The amount of bromide or iodide used can be selected within the range in which 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 dry cellulose. The upper limit of the amount is preferably 100 mmol or less, more preferably 10 mmol or less, still more preferably 5 mmol or less. Therefore, the total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5 to 5 mmol, relative to 1 g of dry cellulose.

The oxidizing agent is not particularly limited, and examples thereof include halogens, hypochlorous acids, hypochlorous acids, perhalogenic acids, salts thereof, halogen oxides, and peroxides. Among them, hypochlorous acid or a salt thereof is preferable, hypochlorous acid or a salt thereof is more preferable, and sodium hypochlorite is further preferable because it is inexpensive and has a small environmental load. The amount of the oxidizing agent used is preferably 0.5 mmol or more, more preferably 1 mmol or more, still more preferably 3 mmol or more, based on 1 g of the dry cellulose. The upper limit of the amount is preferably 500 mmol or less, more preferably 50 mmol or less, still 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 the 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. Therefore, the amount of the oxidizing agent used is preferably 1 to 40 mol with respect to 1 mol of the N-oxyl compound.

Conditions such as pH and temperature during the oxidation reaction are not particularly limited, and in general, 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, more preferably 30 ° C. or lower. Therefore, 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, more preferably 10 or more. The upper limit of pH is preferably 12 or less, more preferably 11 or less. Therefore, the pH of the reaction solution is preferably about 8 to 12, more preferably about 10 to 11. Usually, the pH of the reaction solution tends to decrease because a carboxyl group is generated in the cellulose as the oxidation reaction progresses. Therefore, in order to allow the oxidation reaction to proceed 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. Water is preferable as the reaction medium for oxidation because it is easy to handle and side reactions are unlikely to occur.

The reaction time in oxidation can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 hours or more, and the upper limit thereof is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time in oxidation is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours. Oxidation may be carried out in two or more steps. 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 produced as a by-product in the first-stage reaction. Can be oxidized well.

Another example of the carboxylation (oxidation) method is ozonolysis. By this oxidation reaction, the hydroxyl groups at at least the 2nd and 6th positions of the glucopyranose ring constituting the cellulose are oxidized, and the cellulose chain is decomposed. Ozone treatment is usually carried out by bringing a gas containing ozone into contact with a cellulose raw material. 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. Therefore, the ozone concentration in the gas is preferably 50 to 250 g / ^{m 3,} more preferably 50~220g / ^{m 3.} The amount of ozone added is preferably 0.1% by weight or more, 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, more preferably 5 to 30% by weight, based on 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. Therefore, the ozone treatment temperature is preferably 0 to 50 ° C, more preferably 20 to 50 ° C. The ozone treatment time is usually 1 minute or more, preferably 30 minutes or more, and the upper limit is usually 360 minutes or less. Therefore, the ozone treatment time is usually about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within the above ranges, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of the oxidized cellulose becomes good.

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

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

The amount of carboxyl groups in the cellulose oxide measured in this way is preferably 0.1 mmol / g or more, more preferably 0.5 mmol / g or more, and further preferably 0.8 mmol / g or more with respect to 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 even more 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 even more preferably 0.8 to 2.0 mmol / g.

[Aetherization]
As etherification, carboxymethyl (ether), methyl (ether), ethyl (ether), cyanoethyl (ether), hydroxyethyl (ether), hydroxypropyl (ether), ethylhydroxyethyl (ether) And hydroxypropylmethyl (ether) conversion. The method of carboxymethylation will be described below as an example.

The degree of carboxymethyl substitution per anhydrous glucose unit in the carboxymethylated cellulose or CNF obtained by carboxymethylation is preferably 0.01 or more, more preferably 0.05 or more, still 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 even more preferably 0.35 or less. Therefore, 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 marcelled and then etherified. A solvent is usually used for the reaction. 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. The lower limit of the mixing ratio of the lower alcohol in the mixed solvent is usually 60% by weight or more, and the upper limit thereof is 95% by weight or less, preferably 60 to 95% by weight. The amount of solvent is usually 3 times by weight with respect to the cellulose raw material. The upper limit of the amount is not particularly limited, but is 20 times by weight. Therefore, the amount of the solvent is preferably 3 to 20 times by weight.

Mercerization is usually carried out by mixing a bottoming material and a mercerizing agent. Examples of the mercerizing agent include alkali metals hydroxide such as sodium hydroxide and potassium hydroxide. The amount of the mercerizing agent used is preferably 0.5 times mol or more, more preferably 1.0 mol or more, and even more preferably 1.5 times mol or more per anhydrous glucose residue of the bottoming material. The upper limit of the amount is usually 20 times or less, preferably 10 times or less, more preferably 5 times or less, and therefore, the amount of the mercerizing agent used is preferably 0.5 to 20 times by mole, 1.0. 10-fold molars are more preferred, and 1.5-5-fold moles are even more preferred.

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. Therefore, 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. Therefore, the reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

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

The degree of carboxymethyl substitution per glucose unit of carboxymethylated cellulose is measured, for example, by the following method. That is, 1) Approximately 2.0 g of carboxymethylated cellulose (absolutely dried) is precisely weighed and placed in an Erlenmeyer flask with a 300 mL stopper. 2) Add 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol nitrate, and shake for 3 hours to convert the carboxymethyl cellulose salt (carboxymethylated cellulose) into hydrogen-type carboxymethylated cellulose. 3) Weigh 1.5 to 2.0 g of hydrogen-type carboxymethylated cellulose (absolutely dry) and put it in an Erlenmeyer flask with a 300 mL stopper. 4) Wet hydrogen-type carboxymethylated cellulose with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. 5) Using phenolphthalein as an indicator, back titrate excess NaOH with _{0.1 N H 2} SO _4. 6) Calculate the degree of carboxymethyl substitution (DS) by the following formula:
A = [(100 x F'-(0.1 N H ₂ SO ₄ ) (mL) x F) x 0.1] / (absolute dry mass (g) of hydrogen-type carboxymethylated cellulose)
DS = 0.162 × A / (1-0.058 × A)
A: 1N NaOH amount (mL) required to neutralize 1 g of hydrogen-type carboxymethylated cellulose
F: 0.1N H ₂ SO ₄ factor F': 0.1N NaOH factor

3) Mechanical defibration Chemically modified cellulose is mechanically defibrated to obtain mechanical defibration chemically modified CNF. The defibration treatment may be performed once or a plurality of times. It is preferable that the mixture containing the chemically modified cellulose and the dispersion medium is subjected to the defibration treatment. Water is preferable as the dispersion medium. The device used for defibration is not particularly limited, and examples thereof include high-speed rotary type, colloid mill type, high-pressure type, roll mill type, ultrasonic type, and the like, preferably a high-pressure or ultra-high pressure homogenizer, and a wet high pressure. Alternatively, an ultrahigh pressure homogenizer is more preferable. The device preferably can apply a strong shear force to the chemically modified cellulose. The pressure that can be applied by the device is preferably 50 MPa or more, more preferably 100 MPa or more, and even more preferably 140 MPa or more. The device is preferably a wet high pressure or ultra high pressure homogenizer. As a result, defibration can be performed efficiently.

When defibration is carried out 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. .3% by weight or more is more preferable. As a result, the amount of liquid becomes appropriate with respect to the amount of modified cellulose, which makes it efficient. The upper limit of the concentration is usually preferably 20% by weight or less, more preferably 15% by weight or less, still more preferably 10% by weight or less. This makes it possible to maintain liquidity.

4) Morphology Mechanical defibration chemically modified CNF is in the form of a dry solid (for example, pellet, particulate, powder), in liquid or gel form in combination with a liquid medium, or in an intermediate state, wet. It may be a solid, but a powdery form is preferable. In the present invention, the dry solid substance of cellulose nanofibers means a dispersion liquid containing cellulose nanofibers dehydrated or dried to a water content of 12% or less. Examples of the dry solid matter of cellulose nanofibers include those obtained by drying a dispersion of cellulose nanofibers and those obtained by drying a mixture of cellulose nanofibers, a water-soluble polymer, and redispersibility. The latter is preferable from the viewpoint of. Examples of the water-soluble polymer include cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose), xanthan gum, xyloglucane, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, purulan, starch, and starch. Waste powder, positive starch, phosphorylated starch, corn starch, arabic gum, locust bean gum, gellan gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soybean protein solution, peptone, polyvinyl alcohol, Polyacrylamide, sodium polyacrylic acid, polyvinylpyrrolidone, vinylacetate, polyamino acid, polylactic acid, polyapple acid, polyglycerin, latex, rosin-based sizing agent, petroleum resin-based sizing agent, urea resin, melamine resin, epoxy resin, polyamide Resins, polyamide / polyamine resins, polyethyleneimines, polyamines, vegetable gums, polyethylene oxide, hydrophilic cross-linked polymers, polyacrylates, starch polyacrylic acid copolymers, tamarind gum, gellan gum, pectin, guar gum, colloidal silica, and these. Combination of. Of these, carboxymethyl cellulose and salts thereof are preferable from the viewpoint of compatibility. When the CNF of the present invention is added to the pulp slurry, it may be in the powdery, liquid or gel form, but it is preferably liquid. In this case, a liquid composition obtained by redispersing a dry solid material obtained by drying the mechanically defibrated chemically modified CNF in a liquid medium such as water may be used, or the liquid composition prepared in the defibration step may be used. 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, but is preferably 2 to 50 nm. The average fiber length is preferably 50 to 2000 nm in terms of length-weighted average fiber length. The length-weighted average fiber diameter and the length-weighted average fiber length (hereinafter, also simply referred to as "average fiber diameter" and "average fiber length") are determined by using an atomic force microscope (AFM) or a transmission electron microscope (TEM). It is obtained by observing each fiber. The average aspect ratio of nanofibers is usually 10 or more. The upper limit is not particularly limited, but is usually 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 in the chemically modified cellulose.

(2) Base paper layer The base paper layer is a layer that is the base of paper and contains pulp as a main component. In the present invention, the base paper may be a single layer or a multi-layer. The base paper layer contains a mechanically defibrated and chemically modified CNF. In the case of multiple layers, at least one of the base paper layers may contain the mechanically defibrated and chemically modified CNF, and all the layers may contain the mechanically defibrated and chemically modified CNF. The content of the mechanically defibrated chemically modified CNF is not limited as long as the effect of the present invention can be obtained, but is preferably 0.0001% by weight or more, preferably 0.0003% by weight or more, based on the total pulp weight of the base paper layer. Is more preferable, and more preferably 0.001% by weight or more. If the content is less than 0.0001% by weight, the amount added is small and the effect of the present invention may not be obtained. The upper limit of the content is preferably 4% by weight or less, more preferably 1% by weight or less, and further preferably less than 0.01% by weight.

The pulp raw material of the base paper used in the present invention is not particularly limited, and mechanical pulp such as ground pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), deinked pulp (DIP), and coniferous kraft pulp ( NKP), chemical pulp such as coniferous kraft pulp (LKP) and the like can be used. As the deinked (waste paper) pulp, selected waste paper such as high-quality paper, medium-quality paper, low-grade paper, newspaper, leaflets, and magazines, and unsorted waste paper obtained by mixing these can be used.

A known filler can be added to the base paper, but it is not necessary to add the filler when using paperboard or other applications where opacity or whiteness is not required, or when using raw materials with a large amount of brought-in ash such as used paper. When a filler is added, the filler includes heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica complex, kaolin, calcined kaolin, deramikaolin, magnesium carbonate, barium carbonate, barium sulfate, hydroxide. Inorganic fillers such as amorphous silica produced by neutralizing aluminum, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, and sodium silicate with mineral acid, urea-formalin resin, and melamine. Examples include organic fillers such as resins, polystyrene resins, and phenolic resins. These may be used alone or in combination. Among these, calcium carbonate and light calcium carbonate, which are typical fillers for neutral papermaking and alkaline papermaking and can obtain 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, the decrease in paper strength is suppressed, so that the content of the filler in the base paper is more preferably 10% by weight or more.

As the internal chemicals, bulking agents, dry paper strength improvers, wet paper strength improvers, drainage improvers, dyes, neutral sizing agents and the like may be used as necessary.

The base paper is produced by a known papermaking method. For example, it can be performed 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, and the like, but the present invention is not limited thereto.

When the mechanically defibrated and chemically modified CNF of the present invention is added to the base paper, it may be added at any step in the step of preparing the pulp slurry, but in order to improve the mixing efficiency of the mechanically defibrated and chemically modified CNF, the pulp is added. It is preferably added in the refiner step or the mixing step. When mechanically defibrated and chemically modified CNF is added 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 in advance 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. White pigments include 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, and plastic pigments. Can be mentioned.

The pigment coating layer contains an adhesive. Examples of the adhesive include etherified starch such as oxidized starch, positive starch, urea phosphate esterified starch and hydroxyethyl etherified starch, various starches such as dextrin, proteins such as casein, soybean protein and synthetic protein, and 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 such as ethylene-vinyl acetate copolymer Examples include polymer latex. These can be used alone or in combination of two or more, and it is preferable to use a starch-based adhesive and a styrene-butadiene copolymer in combination.

The pigment coating layer may contain various auxiliaries such as dispersants, thickeners, defoamers, colorants, antistatic agents, and preservatives used in the general paper manufacturing field, and may contain various auxiliary agents such as mechanical defibration. 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, 1 × 10 ^-3 to 1 part by weight is preferable with respect to 100 parts by weight of the pigment. In the above range, a pigment coating liquid having an appropriate water retention property can be obtained without significantly increasing the viscosity of the coating liquid.

The pigment coating layer can be provided by applying a coating liquid to one side or both sides of the base paper by a known method. The solid content concentration in the coating liquid 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 mechanical defibration chemically modified CNF may be present in any pigment coating layer. The amount of the pigment coating layer applied may be appropriately adjusted depending on the intended use, but in the case of coated paper for printing, the total amount per side is 5 g / m ² or more, 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 side 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 coatability at the time of pigment coating can be improved. The amount of clear coating is preferably 0.1 to 1.0 g / m ^{2 and} more preferably ^{0.2 to 0.8 g / m 2} in terms of solid content per side. In the present invention, clear coating refers to various types of starch such as starch and oxidized starch using, for example, a coater (coating machine) such as a size press, a gate roll coater, a pre-metering size press, a curtain coater, and a spray coater. , Polyacrylamide, polyvinyl alcohol and other water-soluble polymers as the main component coating liquid (surface treatment liquid) is applied on the base paper (size press).

(5) Characteristics The paper of the present invention has a water content of 10% by weight or less after the humidity is adjusted under the conditions of 23 ° C. and 50 ± 2% according to JIS P8111. Since the mechanically defibrated chemically modified CNF has a relatively high water retention rate, it may be difficult to dehydrate or dry it in the papermaking process. However, by adjusting the amount of mechanically defibrated and chemically modified CNF and the amount of modifying groups to keep the water content of the paper within the above range, dehydration and drying properties can be improved in the papermaking process, which is preferable. On the other hand, if the water content is higher than 10% by weight, a large amount of water molecules enter between the celluloses constituting the paper fibers and the hydrogen bonds are weakened, which may reduce the stiffness. The lower limit of the water content is not limited, but is preferably 4% by weight or more. If dehydration in the process of producing paper is insufficient, or if an extremely large amount of CNF is blended, the water content may be higher than 10% by weight.

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

2. Method for Producing Paper The paper of the present invention is preferably produced through a step of preparing a paper material containing a mechanically defibrated and chemically modified CNF. Mechanical defibration Chemically modified CNF can be prepared by mechanically defibrating a chemically modified cellulose raw material as described above. The paper material can be prepared according to a known method. For example, it can be prepared by adding a mechanically defibrated and chemically modified CNF, a filler, and if necessary, an additive to a slurry obtained by disintegrating pulp.

Paper can be produced by making paper by a known method using the paper material thus obtained. As described above, a coating step of providing a clear coating or a pigment coating layer on the surface of the paper may be carried out.

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 with respect to 100% by weight of the pulp, TEMPO oxide CNF (manufactured by Nippon Paper Industries Co., Ltd.) 100 ppmm, sulfate band 0.9% by weight, yield agent 0 A pulp slurry was obtained by mixing 0.01% by weight and light calcium carbonate. From the obtained pulp slurry, a handmade sheet having a basis weight of 36.2 g / m ² , a paper ash content of 15% by weight, and a water content of 7.4% was produced and evaluated according to JIS P 8222.

[Example 2]
A handmade sheet was produced and evaluated in the same manner as in Examples except that the amount of ash in the paper was 16.5% by weight.
[Comparative Example 1]
A handmade sheet was produced and evaluated in the same manner as in Example 1 except that TEMPO oxide CNF was not added.

The evaluation was performed as follows.
Basis weight: JIS P 8124: 2011 (ISO 536: 1995) was followed.
Density: According to JIS P 8118: 2014.
Ash content: JIS P 8251: 2003 was followed.
ISO bending stiffness: According to ISO 2493.
Opacity: According to JIS P 8149: 2000 (ISO2471).
Moisture content: Humidity was adjusted under the condition of 23 ° C. 50 ± 2% according to JIS P 8111.

Claims (4)

Paper with a base paper layer containing raw material pulp and cellulose nanofibers.
The cellulose nanofibers are mechanically defibrated and chemically modified cellulose nanofibers.
Paper having a moisture content of 10% by weight or less, which has been conditioned according to JIS P 8111 under the conditions of 23 ° C. and 50 ± 2%. The paper according to claim 1, further comprising a pigment coating layer. The paper according to claim 1 or 2, which comprises a clear coating layer. A step of preparing cellulose nanofibers by chemically defibrating a cellulose raw material and then mechanically defibrating it, and a step of preparing a paper material containing the cellulose nanofibers.
The method for producing paper according to any one of claims 1 to 3.