JPWO2019189776A1 - Paper containing carboxymethylated cellulose nanofibers - Google Patents

Abstract

Provided is a paper containing pulp and carboxymethylated cellulose nanofibers, wherein the degree of carboxymethyl substitution of the glucose unit of the carboxymethylated cellulose nanofibers is 0.01 to 0.60.

Description

The present invention relates to paper containing carboxymethylated cellulose nanofibers.

Cellulose nanofibers have been studied for use in various applications, but their addition to paper has also been studied (Patent Documents 1 and 2). In addition, one of the uses of paper is food use. Paper for food use is widely used in daily life, such as fast food containers, take-out paper bags, paper cups, and cardboard for packing fruits and vegetables. There is a shift from packaging with paper to packaging with paper. The paper often comes into direct contact with food, and not only strength but also food safety may be required. Anion-modified cellulose nanofibers are known as cellulose nanofibers used for food additives (Patent Document 3).

As a method for producing cellulose nanofibers, which is a kind of anion-modified cellulose nanofibers, it is known to make carboxymethylated cellulose finer (Patent Document 4). Carboxymethylated cellulose has a structure in which hydrogen atoms of some hydroxyl groups in glucose residues constituting the skeleton of cellulose are substituted with carboxymethyl groups. As the amount of carboxymethyl groups increases (ie, as the degree of carboxymethyl substitution increases), the carboxymethylated cellulose becomes soluble in water. On the other hand, if the degree of carboxymethyl substitution is adjusted to an appropriate range, the fiber shape can be maintained even in water. Carboxymethylated cellulose having a fibrous shape can be converted into nanofibers having a nanoscale fiber diameter by mechanically defibrating (Patent Document 5).

As a method for producing carboxymethylated cellulose, a method is known in which cellulose is treated with an alkali (mercerization) and then treated with an etherifying agent (also referred to as carboxymethylating agent) (also referred to as carboxymethylation or etherification). Has been done. A method in which both mercerization and carboxymethylation are carried out in water and a method in which both mercerization and carboxymethylation are carried out in an organic solvent or a mixed solvent of an organic solvent and water are known (Patent Document 6). Is called the "water medium method" and the latter is called the "solvent method".

JP-A-2009-263849 JP-A-2010-242286 International Publication No. 2017/199924 Japanese Unexamined Patent Publication No. 2008-1728 International Publication No. 2014/088072 JP-A-2017-149901

An object of the present invention is to provide a paper having excellent strength and which can be used for food applications.

The present inventors have found that paper containing specific carboxymethylated cellulose nanofibers can solve the above-mentioned problems. That is, the above-mentioned problem is solved by the following invention.
(1) Paper containing pulp and carboxymethylated cellulose nanofibers.
Paper having a degree of carboxymethyl substitution in glucose units of the carboxymethylated cellulose nanofibers of 0.01 to 0.60.
(2) The paper according to (1), wherein the degree of carboxymethyl substitution is 0.1 to 0.40.
(3) The paper according to (1), which is a paper provided with a base paper and a coating layer, wherein the base paper layer contains carboxymethylated cellulose nanofibers.
(4) The paper according to any one of (1) to (3), which contains 5% by weight or less of the carboxymethylated cellulose nanofibers with respect to the pulp.
(5) The paper according to any one of (1) to (4), which is a paper provided with a base paper and a coating layer, wherein the coating layer contains carboxymethylated cellulose nanofibers.
(6) The paper according to any one of (1) to (5), wherein the average fiber diameter of the carboxymethylated cellulose nanofibers is 2 nm or more and less than 500 nm.
(7) The paper according to any one of (1) to (6), wherein the base paper layer of the paper contains a salt of a metal selected from the group consisting of sodium, calcium, magnesium, aluminum, and a combination thereof.
(8) When the carboxymethylated cellulose nanofiber is used as an aqueous dispersion having a solid content of 1% (W / v), the light transmittance of light having a wavelength of 660 nm and an optical path length of 10 mm is 70% or more (1) to (1). The paper according to any one of 7).

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a paper having excellent strength and usable for food applications.

Hereinafter, the present invention will be described in detail. In the present invention, "X to Y" includes the fractional values X and Y. Cellulose nanofibers are also referred to as "CNF", and carboxymethylated cellulose nanofibers are also referred to as "CMized CNF".

The present invention relates to paper containing CMized CNF. Carboxymethylated cellulose has a structure in which hydrogen of some hydroxyl groups in glucose residues constituting cellulose is substituted with a carboxymethyl group.

CNF is a cellulosic single microfibril obtained by defibrating a cellulosic raw material, and CM-ized CNF is a cellulose single microfibril obtained by defibrating a cellulosic raw material obtained by CM. Is. The carboxymethylated cellulose raw material is called carboxymethyl cellulose (CMC) and is used as a thickener, a shape-retaining agent, etc. for foods, cosmetics, and water-based paints. Therefore, the CM-ized CNF made from CMC can be used as an additive to paper that is added to food or comes into contact with food. The carboxymethylated cellulose may take the form of a salt such as a metal salt such as a sodium salt of the carboxymethylated cellulose, and the nanofibers of the carboxymethylated cellulose may also take the form of a salt.

The CMized CNF of the present invention maintains at least a part of its fibrous shape even when dispersed in water. That is, when the aqueous dispersion of CM-ized CNF is observed with an electron microscope, a fibrous substance can be observed. Moreover, when the CM-ized CNF is measured by X-ray diffraction, the peak of the cellulose type I crystal can be observed.

The paper of the present invention has different characteristics depending on the degree of carboxymethyl substitution per anhydrous glucose unit (hereinafter, also simply referred to as “DS”) of the CM-formed CNF used. Therefore, the present invention will be described below in each case.

I. Paper containing CM-ized CNF with 0.01 ≦ DS ≦ 0.2 (1) First CM-ized CNF
The CM-ized CNF having the DS is also referred to as "first CM-ized CNF".
[DS]
The DS of the first CM-ized CNF is 0.01 to 0.2. Such CM-ized CNF is easy to manufacture and can provide paper having excellent strength at low cost. The lower limit of DS is preferably 0.05 or more, more preferably 0.10 or more. The upper limit of DS is preferably 0.18 or less.

The DS is measured by, for example, 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 weight (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

[viscosity]
The first CMized CNF has a concentration of 100 to 10,000 mPa · s when made into 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). It is preferable to give a B-type viscosity (60 rpm, 20 ° C.). The viscosity is more preferably 200 to 8000 mPa · s, still more preferably 2000 to 6000 mPa · s, and particularly preferably 300 to 1000 mPa · s. The B-type viscosity is an index for specifying characteristics such as the amount of functional groups, average fiber length, and average fiber diameter of CNF, and is appropriately adjusted according to the intended use. Since the first CM-formed CNF is added to the papermaking raw material dispersion liquid such as pulp slurry and coating liquid in the papermaking process, the viscosity is appropriately adjusted according to the required viscosity and water retention of the pulp slurry and coating liquid. However, within the above range, the viscosity and water retention of the papermaking raw material dispersion can be improved with a small amount.

The B-type viscosity 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 has thixotropic properties, and its viscosity decreases when it is stirred and shear stress is applied, and the viscosity increases and gels when it is left to stand. Therefore, it is B in a sufficiently stirred state. It is preferable to measure the mold viscosity.

[Crystallinity of Cellulose Type I]
Regarding the crystallinity of cellulose in the first CM-formed CNF, it is preferable that the crystallinity of cellulose type I is 60% or more. The degree of crystallinity can be controlled by the concentration of the mercerizing agent, the temperature at the time of treatment, and the degree of carboxymethylation. Since a high concentration of alkali is used in mercerization and carboxymethylation, type I crystals of cellulose are easily converted to type II, but they are modified by adjusting the amount of alkali (mercerizing agent) used. By adjusting the degree, the desired crystallinity can be maintained. The upper limit of the crystallinity of cellulose type I is not particularly limited, but in reality, it is considered that the upper limit is about 90%.

The method for measuring the crystallinity of cellulose type I of carboxymethylated cellulose nanofibers is as follows:
The sample is placed on a glass cell and measured using an X-ray diffraction measuring device (LabX XRD-6000, manufactured by Shimadzu Corporation). The crystallinity is calculated using a method such as Segal, and the diffraction intensity of the 002 surface at 2θ = 22.6 ° and 2θ = are based on the diffraction intensity of 2θ = 10 ° to 30 ° in the X-ray diffraction diagram. It is calculated by the following formula from the diffraction intensity of the amorphous portion of 18.5 °.

Xc = (I _002c ―I _a ) / I _002c × 100
Xc = Cellulose type I crystallinity (%)
I _002c : 2θ = 22.6 °, diffraction intensity of 002 surface _Ia : 2θ = 18.5 °, diffraction intensity of amorphous part.

When the crystallinity of cellulose type I is as high as 60% or more, the proportion of cellulose that does not dissolve in a solvent such as water and maintains the crystal structure becomes high, and the thixotropy property becomes high. As a result, the CM-ized CNF is suitable for viscosity adjusting applications such as thickeners. Further, when the CM-ized CNF is added to a gel-like substance (for example, but not limited to foods and cosmetics), there is an advantage that excellent shape retention can be imparted.

The proportion of type I crystals in the first CMized CNF is usually the same as the proportion in carboxymethylated cellulose before making it into nanofibers.

[Transparency in aqueous dispersion]
The first CM-ized CNF exhibits low transparency when water is used as a dispersion medium to form an aqueous dispersion. In the present invention, the transparency is defined as the transmittance of light having a wavelength of 660 nm and an optical path length of 10 mm when the CM-formed CNF is an aqueous dispersion having a solid content of 1% (w / v). Also called "transparency". The upper limit of the transparency of the first CMized CNF is preferably 10% or less, and the lower limit thereof is not particularly limited, but is 1% or more. When the transparency of the first CM-ized CNF is in this range, there is an advantage that the opacity of the paper is not lowered when it is added to the paper.

[Preparation]
The first CMized CNF can be produced by preparing carboxymethylated cellulose and defibrating it.
Carboxymethylated cellulose can be prepared by a known method. For example, there is a method in which a cellulose raw material as a bottoming raw material is converted into a marcel 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 mixing ratio of the lower alcohol in the mixed solvent is usually 60% by weight or more, 95% by weight or less, and 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>
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 or more, more preferably 1.0 or more, and even more preferably 1.5 times 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 or less, 1.0. 10-fold molars are more preferred, and 1.5-5-fold molars 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 more, preferably 30 minutes or more. The upper limit of the time is usually 8 hours or less, preferably 7 hours or less. Therefore, the reaction time is usually preferably 15 minutes to 8 hours and 30 minutes to 7 hours.

<Carboxymethylation (etherification)>
The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of the carboxymethylating agent include monochloroacetic acid, methyl monochloroacetate, ethyl monochloroacetate, isopropyl monochloroacetate, and sodium monochloroacetate. The amount of the carboxymethylating agent added is preferably 0.05 times or more, more preferably 0.5 times or more, and even more preferably 0.8 times 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, 0.5. ~ 5 is more preferable, and 0.8 to 3 times the molar amount is further preferable. 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. The upper limit 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.

<Defibration>
The carboxymethylated cellulose is defibrated to give the first CMized CNF. The defibration treatment may be performed once or a plurality of times. It is preferable to subject a mixture containing carboxymethylated cellulose and a dispersion medium 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, and a high pressure or ultrahigh pressure homogenizer is preferable, and a wet high pressure type is preferable. Alternatively, an ultrahigh pressure homogenizer is more preferable. The device preferably can apply a strong shear force to the carboxymethylated 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. Further, prior to the defibration and dispersion treatment with a high-pressure homogenizer, the dispersion may be pretreated, if necessary, using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer. ..

A high-pressure homogenizer pressurizes (high pressure) a fluid with a pump and ejects it from a very delicate gap provided in the flow path, so that it is emulsified and dispersed by the total energy such as collision between particles and shearing force due to pressure difference. , A device for crushing, crushing, and ultra-fine particles.

By the above method, cellulose nanofibers can be obtained in an economical way. The reason is not clear, but according to the above method, a relatively high crystallinity of cellulose type I can be maintained, and therefore, even if the carboxymethyl substitution degree is relatively high, the fibers of the carboxymethylated cellulose can be maintained. The present inventors have confirmed that the shape can be maintained. Being able to increase the degree of carboxymethyl substitution while maintaining the fibrous shape (that is, introducing a large number of carboxymethyl groups) is a function imparted by improving the fibrillation property of carboxymethylated cellulose and introducing substituents. It is thought that this will lead to the production of CM-ized CNF that can demonstrate the above level.

[form]
The first CMized CNF is in the form of a dry solid (for example, pellet, particulate, powder), in a liquid or gel form in combination with a liquid medium, or as a wet solid in an intermediate state thereof. Although it may be used, a powdery form is preferable. In the present invention, the dry solid of cellulose nanofibers means a dispersion containing cellulose nanofibers dehydrated or dried to a water content of 12% or less. Examples of the dry solid substance of the cellulose nanofibers include a dried dispersion of cellulose nanofibers and a dried mixture of cellulose nanofibers and a water-soluble polymer, but from the viewpoint of redispersibility. The latter is preferable. 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, polyaronic 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 CMized CNF 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 in which the dry solid of CM-ized CNF is dispersed again in a liquid medium such as water may be used, or the liquid composition prepared in the defibration step may be used.

The average fiber diameter of the first CM-formed CNF is usually about 2 nm or more and less than 500 nm in terms of length-weighted average fiber diameter, but the lower limit is preferably 3 nm or more, and the upper limit is preferably 50 nm or less. 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 degree of substitution per glucose unit in the first CMized CNF is preferably the same as the degree of substitution of carboxymethyl cellulose.

(2) Paper Containing First CM-ized CNF The first CM-ized CNF may be added internally or externally to the paper. In the case of external addition, a clear coating liquid in which an adhesive component and nanofibers are mixed may be applied, or a pigment coating liquid in which a pigment component is further added may be applied. When the clear coating layer contains the first CM-modified CNF, a pigment coating layer not containing the first CM-modified CNF may be provided on the clear coating layer. The paper of the present invention may contain the first CMized CNF in any layer, and the content thereof is preferably 1 ppm by weight to 20% by weight, more preferably 3 ppm by weight to 10% by weight, based on the weight of the pulp. It is by weight%, more preferably 0.1% by weight to 5% by weight. When the first CM-ized CNF is contained in any layer of the paper, the strength of the paper can be effectively improved with a small amount.
1) 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 contains the first CM-ized CNF. The content of the first CMized CNF is preferably 10% by weight or less, more preferably 5% by weight or less, still more preferably 1% by weight or less, based on the pulp. If the effect of the present invention is obtained, the lower limit of the amount of the first CMized CNF is not limited, but it is preferably about 1 ppm by weight or more, more preferably 3 ppm by weight or more, still more preferably 10 ppm by weight or more, and 20 ppm by weight with respect to the pulp. The above is particularly preferable.

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

A known filler can be added to the base paper. As fillers, heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica complex, kaolin, calcined kaolin, deramikaolin, magnesium carbonate, barium carbonate, barium sulfate, aluminum hydroxide, calcium hydroxide, Inorganic fillers such as amorphous silica produced by neutralizing magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, and sodium silicate with mineral acid, urea-formalin resin, melamine resin, polystyrene resin, phenol Examples include organic fillers such as resin. 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 and whiteness, are preferable. The content of the filler in the base paper is preferably 0 to 20% by weight with respect to the weight of the base paper, and the filler may not be added in the paperboard application where whiteness and opacity are not required. 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, a retention agent, a bulking agent, a dry paper strength improver, a wet paper strength improver, a drainage improver, a water retention agent, a dye, a sizing agent, various salts and the like may be used as needed. ..

In the paper of the present invention, various metal salts can be used in order to fix the first CM-formed CNF to the pulp fibers of the base paper and improve the yield of the first CM-formed CNF. Two or more kinds of metal salts may be used in combination. Examples of the metal forming the salt include sodium, calcium, magnesium and aluminum, and examples of the metal salt include aluminum sulfate (sulfate band), calcium chloride, calcium hydroxide, calcium oxide, sodium aluminate and sodium carbonate. Examples thereof include polyaluminum chloride, ferric chloride, and polyferrous sulfate. In the present invention, it is preferable to use aluminum sulfate or calcium chloride alone or in combination.

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 paper machine, a hybrid former paper machine, an on-top former paper machine, a round net paper machine, etc., but the base paper is not limited thereto. The layers may be single or multi-layered,

When the first CM-formed CNF 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 first CM-formed CNF, a pulp refiner step or mixing is performed. It is preferable to add it in the process. When the first CM-formed CNF is added in the mixing step, a mixture of other auxiliary agents such as a filler and a retention agent and the first CM-formed CNF in advance may be added to the pulp slurry. When the base paper has multiple layers, it may be added to any layer of the paper layer, and the content can be set with respect to the pulp of each layer.

The first CMized CNF is preferably added to the base paper layer because it can effectively improve the strength of the base paper.

2) 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. However, calcium carbonate is preferable because it can effectively improve the whiteness and opacity.

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. CMized CNF may be contained in the pigment coating layer. When the first CMized CNF is contained in the pigment coating layer, the amount thereof ^{is preferably 1 × 10 -4} to 4 parts by weight, preferably 3 × 10 ^-4 to 1 part by weight, based on 100 parts by weight of the pigment. Is more preferable. 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 CMized CNF may be present in any of the pigment coating layers. 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.

3) 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} in terms of solid content per side, and more preferably 0.2 to 0.8 g / m ^2. In the present invention, clear coating refers to various types of starch such as starch and oxidized starch using 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).

In particular, when the first CMized CNF with a high crystallinity (70% or more) and a relatively low degree of substitution (0.10 to 0.20) is used, it is compared with the one having a higher degree of substitution. , It is possible to obtain a paper having a silky texture with relatively little stickiness when applied to paper. is this. It is considered that the first CM-ized CNF has a low degree of substitution and has a relatively low affinity for water. Therefore, when the paper of the present invention is used for a paper container such as a paper cup, it is possible to obtain a paper having a relatively non-sticky surface even if a food or drink having a high water content is added. The same effect can be obtained when the pigment coating layer contains the first CMized CNF or when the base paper layer contains a relatively large amount of the first CMized CNF.

4) Characteristics The paper of the present invention has excellent strength because it contains the first CM-ized CNF having a high aspect ratio. Further, since the CM-formed CNF is made from highly safe carboxymethylated cellulose, the paper of the present invention can be used for food applications.

2. Method for Producing Paper The paper of the present invention is preferably produced through a step of preparing a paper material containing the first CM-ized CNF. The first CMized CNF can be prepared as described above. The paper material can be prepared according to a known method. For example, the slurry obtained by dissociating the pulp may be prepared by adding a first CM-modified CNF filler and, if necessary, an additive, or CM-modified CNF may be added in the pulp dissociation step.

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.

II. Paper containing CM-ized CNF with 0.2 <DS ≦ 0.60 (1) Second CM-ized CNF
The CM-ized CNF having the DS is also referred to as a "second CM-ized CNF".
[DS]
The upper limit of the DS of the second CM-ized CNF is preferably less than 0.50. If the DS exceeds 0.60, it dissolves in water and the fiber shape cannot be maintained. Considering operability, the upper limit of DS is more preferably 0.40 or less. By introducing a carboxymethyl group into cellulose, the celluloses electrically repel each other, so that they can be defibrated into nanofibers. When the DS is higher than 0.20, it becomes easy to defibrate into nanofibers, the dispersibility is improved, and a highly transparent CM-ized CNF dispersion can be obtained. Further, when the DS is higher than 0.20, the polarity of the CMized CNF becomes high, and the compatibility with compounds having other polarities becomes high when added to foods, cosmetics, etc., although not limited to these uses. .. Further, generally, when the DS is higher than 0.20, the stickiness becomes high when the CMized CNF is powdered, but the second CMized CNF of the present invention becomes less sticky for the reason described later. Such characteristics can be adjusted by controlling the DS, the amount of the carboxymethylating agent to be reacted, the amount of the mercerizing agent, the composition ratio of water and the organic solvent, and the like.

[viscosity]
The second CM-formed CNF has a concentration of 100 to 10,000 mPa · s when made into 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). It is preferable to give a B-type viscosity (60 rpm, 20 ° C.). The viscosity is more preferably 1000 to 8000 mPa · s, further preferably 2000 to 7000 mPa · s, and most preferably 3000 to 5000 mPa · s. The B-type viscosity is measured as described above.

[Crystallinity of Cellulose Type I]
Regarding the crystallinity of cellulose in the second CM-formed CNF, it is preferable that the crystallinity of cellulose type I is 60% or more. Generally, it is known that when the DS is increased, the solubility of the fiber is increased and the crystallinity is decreased, but the second CM-formed CNF is higher than 0.2 and has a DS of 0.6 or less. , 60% or more of the crystallinity is maintained. Such a CM-ized CNF can be produced by a method described later. Further, the crystallinity can be controlled by the concentration of the mercerizing agent, the temperature at the time of treatment, and the degree of carboxymethylation. Since a high concentration of alkali is used in mercerization and carboxymethylation, type I crystals of cellulose are easily converted to type II, but they are modified by adjusting the amount of alkali (mercerizing agent) used. By adjusting the degree, the desired crystallinity can be maintained. The upper limit of the crystallinity of cellulose type I is not particularly limited, but in reality, it is considered that the upper limit is about 90%.

The method for measuring the crystallinity of cellulose type I of carboxymethylated cellulose nanofibers is as described above. When the crystallinity of cellulose type I is as high as 60% or more, the proportion of cellulose that does not dissolve in a solvent such as water and maintains the crystal structure becomes high, and the thixotropy property becomes high. As a result, the CM-ized CNF is suitable for viscosity adjusting applications such as thickeners. Further, when the CM-ized CNF is added to a gel-like substance (for example, but not limited to foods and cosmetics), there is an advantage that excellent shape retention can be imparted.

The proportion of type I crystals in the second CMized CNF is usually the same as the proportion in carboxymethylated cellulose before making it into nanofibers.

[Transparency in aqueous dispersion]
The second CM-ized CNF has a feature of exhibiting high transparency when water is used as a dispersion medium to form an aqueous dispersion. Transparency is defined as described above. The lower limit of the transparency of the second CMized CNF is preferably 60% or more, more preferably 70% or more, still more preferably 80% or more, particularly preferably 90% or more, and the upper limit thereof is 100% or less. .. Such cellulose nanofibers are suitable for applications where transparency is required.

[Fiber diameter, aspect ratio]
The average fiber diameter of the second CM-formed CNF is preferably 2 nm or more and less than 500 nm, and the aspect ratio is preferably 10 or more. The average fiber diameter is further preferably 3 nm to 150 nm, more preferably 3 nm to 50 nm, still more preferably 5 nm to 20 nm, and particularly preferably 5 nm to 15 nm. The aspect ratio is more preferably 50 or more. The upper limit of the aspect ratio is not particularly limited, but is usually 1000 or less, preferably 500 or less, and more preferably less than 400. When the aspect ratio is 50 or more, the fibrous shape provides an effect of improving thixotropy. Further, when the aspect ratio is less than 400, the fibers are not excessively long and the entanglement between the fibers is reduced, so that the occurrence of lumps (lumps) of cellulose nanofibers can be reduced.

[Preparation]
The second CM-formed CNF can be produced by performing mercerization under a solvent mainly containing water, and then carrying out carboxylation (also referred to as etherification) under a mixed solvent of water and an organic solvent. The carboxymethylated cellulose thus obtained can be obtained by a conventional water medium method (a method of performing both marcellation and carboxylation using water as a solvent) or a solvent method (under an organic solvent or a mixed solvent of water and an organic solvent). Compared with the carboxymethylated cellulose obtained by the method of performing both marcelation and carboxylation in (1), CM formation that provides a highly transparent cellulose nanofiber aqueous dispersion while having a high effective utilization rate of the carboxymethylating agent. It can be converted to CNF. The raw materials and the like used in this production method are as described in the first CM-ized CNF. Hereinafter, the characteristic parts of the present manufacturing method will be described.

<Mercerization>
The above-mentioned cellulose is used as a raw material, and mercerized cellulose (also referred to as alkaline cellulose) is obtained by adding a mercerizing agent (alkali). The mercerization reaction is carried out under a solvent mainly containing water. The solvent mainly containing water means a solvent containing water in a proportion higher than 50% by weight. The amount of water in the solvent is preferably 55% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more, and particularly preferably 100% by weight. % (Ie water). The higher the proportion of water in the mercerization reaction, the higher the transparency of the cellulose nanofiber aqueous dispersion obtained by defibrating carboxymethylated cellulose. Examples of the solvent other than water in the solvent include an organic solvent used as a solvent for carboxymethylation in the subsequent stage. For example, alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol and tertiary butanol, ketones such as acetone, diethyl ketone and methyl ethyl ketone, ethers such as dioxane and diethyl ether, benzene and the like. Aromatic hydrocarbons of the above, halogenated hydrocarbons such as dichloromethane can be mentioned. These can be used alone or in combination of two or more. The amount of the organic solvent in the solvent is preferably 45% by weight or less, 40% by weight, 30% by weight or less, 20% by weight or less, 10% by weight or less, or 5% by weight or less, and particularly preferably. It is 0% by weight.

Examples of the mercerizing agent include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, and any one or a combination of two or more of these can be used. The mercerizing agent is not limited to this, but these alkali metal hydroxides are used in the reactor as an aqueous solution of, for example, 1 to 60% by weight, preferably 2 to 45% by weight, more preferably 3 to 25% by weight. Can be added. In one embodiment, the amount of the mercerizing agent used is preferably 0.1 to 2.5 mol, more preferably 0.3 to 2.0 mol, based on 100 g (absolutely dry) of cellulose. , 0.4 to 1.5 mol or less, more preferably.

The amount of the solvent is not particularly limited as long as it can be stirred and mixed with the raw materials, but is preferably 1.5 to 20 times by weight, more preferably 2 to 10 times by weight with respect to the cellulose raw material.

In the mercerization treatment, the bottoming material (cellulose) and a solvent mainly composed of water are mixed, and the temperature of the reactor is adjusted to 0 to 70 ° C., preferably 10 to 60 ° C., more preferably 10 to 40 ° C. Then, an aqueous solution of the mercerizing agent is added, and the mixture is stirred for 15 minutes to 8 hours, preferably 30 minutes to 7 hours, and more preferably 30 minutes to 3 hours. As a result, mercerized cellulose (alkaline cellulose) is obtained.

The pH at the time of mercerization is preferably 9 or more, whereby the mercerization reaction can proceed. The pH is more preferably 11 or more, still more preferably 12 or more, and may be 13 or more. The upper limit of pH is not particularly limited.

Mercerization can be carried out using a reactor capable of mixing and stirring each of the above components while controlling the temperature, and various reactors conventionally used for the mercerization reaction can be used. For example, a batch type agitator in which two shafts agitate and each of the above components is mixed is preferable from the viewpoint of both uniform mixing property and productivity.

<Carboxymethylation (etherification)>
Carboxymethylated cellulose is obtained by reacting mercerized cellulose with a carboxymethylating agent (also referred to as an etherifying agent).

Examples of the carboxymethylating agent include monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate, isopropyl monochloroacetate and the like. Of these, monochloroacetic acid or sodium monochloroacetate is preferable in terms of availability of raw materials. The carboxymethylating agent is preferably added in the range of 0.5 to 1.5 mol per anhydrous glucose unit of cellulose. The lower limit of the above range is more preferably 0.6 mol or more, further preferably 0.7 mol or more, and the upper limit is more preferably 1.3 mol or less, still more preferably 1.1 mol or less. The carboxymethylating agent can be added to the reactor as an aqueous solution of, for example, 5 to 80% by weight, more preferably 30 to 60% by weight, without limitation, and is added in a powder state without being dissolved. You can also do it.

The molar ratio of mercerizing agent to carboxymethylating agent (mercerizing agent / carboxymethylating agent) is generally 0.9 to 2.45 when monochloroacetic acid or sodium monochloroacetic acid is used as the carboxymethylating agent. Degree. The reason is that if the ratio is less than 0.9, the carboxymethylation reaction may be insufficient, and unreacted monochloroacetic acid or sodium monochloroacetate may remain, which may be uneconomical. Further, if the ratio exceeds 2.45, a side reaction between the excess marcel agent and monochloroacetic acid or sodium monochloroacetate may proceed to form an alkali metal glycolic acid salt, which may be uneconomical.

In carboxymethylation, the effective utilization rate of the carboxymethylating agent is preferably 15% or more, more preferably 20% or more, still more preferably 25% or more, and particularly preferably 30% or more. The effective utilization rate of the carboxymethylating agent refers to the ratio of the carboxymethyl group introduced into cellulose among the carboxymethyl groups in the carboxymethylating agent. By using a solvent mainly containing water for marcel formation and using a mixed solvent of water and an organic solvent for carboxymethylation, a high effective utilization rate of the carboxymethylating agent (that is, a carboxymethylating agent) It is possible to produce carboxymethylated cellulose capable of obtaining a cellulose nanofiber dispersion having high transparency when defibrated (economically) without significantly increasing the amount of the solvent used. The upper limit of the effective utilization rate of the carboxymethylating agent is not particularly limited, but in reality, the upper limit is about 80%. The effective utilization rate of the carboxymethylating agent may be abbreviated as AM.

The method for calculating the effective utilization rate of the carboxymethylating agent is as follows:
AM = (DS x number of moles of cellulose) / number of moles of carboxymethylating agent DS: degree of carboxymethyl substitution (measurement method is as described above)
Number of moles of cellulose: Pulp weight (dry weight when dried at 100 ° C. for 60 minutes) / 162 (162 is the molecular weight of cellulose per glucose unit).

The concentration of the cellulose raw material in the carboxymethylation reaction is not particularly limited, but is preferably 1 to 40% (w / v) from the viewpoint of increasing the effective utilization rate of the carboxymethylating agent.

Simultaneously with, before, or immediately after the addition of the carboxymethylating agent, an organic solvent or an aqueous solution of the organic solvent is appropriately added to the reactor to form a mixed solvent of water and the organic solvent, and carboxymethyl is formed under the mixed solvent. Proceed with the chemical reaction. Alternatively, the reaction mixture after mercerization may be reduced in the amount of the organic solvent or the like used in the mercerization reaction under reduced pressure to form a mixed solvent in the carboxymethylation reaction. The timing of addition or weight loss of the organic solvent may be between the end of the mercerization reaction and immediately after the addition of the carboxymethylating agent, and is not particularly limited, but for example, 30 minutes before and after the addition of the carboxymethylating agent. Within is preferable.

Examples of the organic solvent include alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol and tertiary butanol, ketones such as acetone, diethyl ketone and methyl ethyl ketone, and dioxane and diethyl ether. Examples include aromatic hydrocarbons such as ether and benzene, and halogenated hydrocarbons such as dichloromethane. These can be used alone or in combination of two or more. Of these, monohydric alcohols having 1 to 4 carbon atoms are preferable, and monohydric alcohols having 1 to 3 carbon atoms are more preferable because of their excellent compatibility with water.

The ratio of the organic solvent in the mixed solvent at the time of carboxymethylation is preferably 20 to 99% by weight, more preferably 30 to 99% by weight, based on the total amount of water and the organic solvent. It is more preferably 40 to 99% by weight, even more preferably 45 to 99% by weight.

The proportion of water in the mixed solvent during carboxymethylation is preferably less than the proportion of water in the water-based solvent during mercerization. By using such a combination of solvents, it becomes easy to increase the degree of carboxymethyl substitution while maintaining the crystallinity of the raw material carboxymethylated cellulose, and the cellulose nanofiber aqueous dispersion having high transparency when defibrated. Is given, CM-ized CNF can be produced more efficiently. Further, when such a combination of solvents is used, when shifting from the mercerization reaction to the carboxymethylation reaction, the mixture is mixed by a simple means of adding a desired amount of organic solvent to the reaction system after the completion of the mercerization reaction. A solvent can be formed.

After forming a mixed solvent of water and an organic solvent and adding a carboxymethylating agent to the mercerized cellulose, the temperature is preferably kept constant in the range of 10 to 40 ° C. for 15 minutes to 4 hours, preferably 15 Stir for about 1 minute to 1 hour. The mixing of the liquid containing mercerized cellulose and the carboxymethylating agent is preferably carried out in a plurality of times or by dropping in order to prevent the reaction mixture from becoming hot. After adding the carboxymethylating agent and stirring for a certain period of time, the temperature is raised if necessary, and the reaction temperature is set to 30 to 90 ° C., preferably 40 to 90 ° C., more preferably 60 to 80 ° C. for 30 minutes to The etherification (carboxymethylation) reaction is carried out for 10 hours, preferably 1 to 4 hours to obtain carboxymethylated cellulose.

At the time of carboxymethylation, the reactor used for mercerization may be used as it is, or another reactor capable of mixing and stirring each of the above components while controlling the temperature may be used. ..

After completion of the reaction, the remaining alkali metal salt may be neutralized with a mineral acid or an organic acid so that the pH becomes 6 to 8. Further, if necessary, the by-produced inorganic salts, organic acid salts and the like may be washed with hydrous methanol to remove them, and then dried, pulverized and classified to obtain carboxymethylated cellulose or a salt thereof. When washing for removing by-products, the acid type may be used in advance for washing, and the salt type may be returned after washing. Examples of the device used for dry pulverization include impact mills such as hammer mills and pin mills, medium mills such as ball mills and tower mills, and jet mills. Examples of the apparatus used in the wet pulverization include apparatus such as a homogenizer, a mascoroider, and a pearl mill.

<Defibration>
The defibration is as described for the first CM-ized CNF.

[form]
The second CMized CNF may be in the form of a dispersion obtained after production, but may be dried if necessary, or may be redispersed in water. The drying method is not limited, but for example, a freeze-drying method, a spray-drying method, a shelf-stage drying method, a drum drying method, a belt drying method, a method of thinly spreading and drying on a glass plate, a fluidized bed drying method, a microwave drying method, and a microwave drying method. Known methods such as the method and the heating fan type vacuum drying method can be used. After drying, it may be crushed with a cutter mill, a hammer mill, a pin mill, a jet mill or the like, if necessary. Further, the method of redispersion in water is not particularly limited, and a known disperser can be used.

Furthermore, the second CM-ized CNF is less sticky. The CM-formed CNF has a structure in which any of the hydroxyl groups at the 2, 4 and 6 positions of β-glucose forming cellulose is substituted with a carboxymethyl group. The CMized CNF produced by the conventional method has a portion having a large number of substituents and a portion having a small number of substituents in one fiber, and the substituents are localized, and the said portion is easily dissolved in water. Conceivable. On the other hand, since the substituents are uniformly introduced into the second CM-modified CNF, it is presumed that the DS is less soluble in water than the conventional CM-modified CNF having the same DS, which makes it less sticky.

(2) Paper Containing Second CM-ized CNF The second CM-ized CNF may be added internally or externally to the paper. In the case of external addition, a clear coating liquid in which an adhesive component and nanofibers are mixed may be applied, or a pigment coating liquid in which a pigment component is further added may be applied. When the clear coating layer contains the second CMized CNF, a pigment coating layer not containing the second CMized CNF may be provided on the clear coating layer. The paper of the present invention may contain the second CMized CNF in any layer, and the content thereof is preferably 1 ppm by weight to 20% by weight, more preferably 3 ppm by weight to 10% by weight, based on the weight of the pulp. It is by weight%, more preferably 0.1% by weight to 5% by weight. When the second CM-ized CNF is contained in any layer of the paper, the strength of the paper can be effectively improved with a small amount.

The base paper layer is as described in the paper containing the first CM-ized CNF. The second CMized CNF is preferably added to the base paper layer because it can effectively improve the strength of the base paper.

2) Pigment coating layer The pigment coating layer is as described in the first CM-containing CNF-containing paper. However, 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 preferably 3 g / m 2} or more, and 10 g / m ² or more. Is more preferable. The upper limit is ^{preferably 30 g / m 2} or less, and ^{more preferably 25 g / m 2} or less.

3) 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 the clear coating is preferably 0.1~4.0g / m ² in terms of solid per side content, more preferably ^{0.2~2.0g / m 2, 1.0g / m} 2 or less is more preferred. 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 prepolymering size press, a curtain coater, or a spray coater. , Polyacrylamide, polyvinyl alcohol, styrene-butadiene copolymer, etc., which is a coating liquid (surface treatment liquid) containing a water-soluble polymer as a main component, is applied (size pressed) on the base paper.

The clear coating layer may contain various auxiliaries such as dispersants, thickeners, defoamers, colorants, antistatic agents, and preservatives used in the general paper manufacturing field, and is used as a second layer. CMized CNF may be contained in the clear coating layer. The amount can be 1 ppm by weight to 100% by weight, preferably 0.01% by weight to 10% by weight, based on 100% by weight of the adhesive component. In the case of the clear coating liquid, it is not necessary to consider the deterioration of the drainage of the paper as compared with the case of adding it to the base paper, so that the content of the second CMized CNF having a large water retention improving effect should be increased. Can be done. Paper containing the second CMized CNF in the clear coating layer can be used for food applications, and has excellent strength and barrier properties. The reason is not limited, but when the clear coating layer contains the second CM-formed CNF, the second CM-formed CNF and some of the other adhesive components permeate into the paper and some are coated on the paper. To form. As a result, it is presumed that the second CM-formed CNF that has penetrated into the paper contributes to the improvement of paper strength, and the second CM-formed CNF that forms a film on the paper contributes to the improvement of barrier properties and surface strength. To. Even when the pigment coating layer contains the second CMized CNF, the same effect can be obtained when the pigment coating layer is provided in contact with the base paper. In particular, when a second CMized CNF with a high crystallinity (70% or more) and a high degree of substitution (more than 0.2 and 0.5 or less) is used, it is applied to paper as compared with the one with a low degree of substitution. It is possible to obtain a paper with a smooth texture with less stickiness when it is squeezed. The reason for this is not clear, but as described above, it is considered that the second CMized CNF is due to the uniform introduction of the carboxymethyl group. Therefore, when the paper of the present invention is used for a paper container such as a paper cup, it is possible to obtain a paper having a relatively non-sticky surface even if a food or drink having a high water content is added. The same effect can be obtained when the pigment coating layer contains the second CMized CNF or when the base paper layer contains a relatively large amount of the second CMized CNF.

4) Characteristics The paper of the present invention has a high aspect ratio, and further has excellent strength because it contains a second CM-formed CNF having a high degree of crystallinity and substitution. Further, since the second CM-ized CNF forms a dense network in the paper, it is possible to obtain a paper having high paper strength and barrier properties. Further, since the second CM-ized CNF is highly safe, the paper of the present invention can be used for food applications.

2. Method for Producing Paper The paper of the present invention is preferably produced through a step of preparing a paper material containing a second CM-ized CNF, a clear coating liquid or a pigment coating liquid. The second CMized CNF can be prepared as described above. Paper materials, clear coating liquids and pigment coating liquids can be prepared according to known methods. For example, the slurry obtained by dissociating the pulp may be prepared by adding a second CM-formed CNF, a filler, and if necessary, an additive, and carboxymethylated cellulose nanofibers are added in the pulp dissociation step. You can also do it. When the second CM-ized CNF is added to the clear coating liquid, it may be added when the adhesive component such as starch is steamed, and it is added in the step of adding an auxiliary agent such as a sizing agent. May be good. Further, when the second CMized CNF is added to the pigment coating liquid, other adhesives and auxiliaries may be added after being mixed with the pigment in advance, and the pigment, the adhesive and the auxiliaries are mixed. After that, a second CMized CNF may be added.

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 layer or a pigment coating layer on the surface of the paper may be carried out.

The paper obtained in the present invention can be used for various purposes in which strength is required. Applications are not limited to these, but for example, printing papers such as offset, gravure, inkjet, electrophotographic methods, thermal papers, pressure sensitive papers, process papers, release papers, newspapers, wrapping papers, paperboards, cardboards, paper containers, etc. can give.

Hereinafter, the present invention will be described with reference to examples. Parts and% mean parts by weight and% by weight unless otherwise specified.
(1) Evaluation Basis weight, bulk thickness, and bulk density: Measured with reference to JIS P 8223: 2006.
Canadian standard drainage (csf: ml): JIS P 811-2: 2012 was followed.
Specific burst strength: JIS P 8131: 2009 was followed.
Short span ratio Compressive strength: JIS P 8156: 2012.
Air permeability resistance: Measured by a Wangken type smoothness / air permeability tester according to JIS P8117: 2009.

(2) Preparation of the first CM-ized CNF To a biaxial kneader whose rotation speed was adjusted to 100 rpm, 760 parts of IPA and 13 parts of sodium hydroxide were dissolved in 250 parts of water, and hardwood kraft pulp (Nippon Paper Industries, Ltd.) was added. (Manufactured) was charged in 100 copies by absolute dry weight. Mercerized cellulose was prepared by stirring and mixing at 30 ° C. for 90 minutes. While further stirring, 14 parts of monochloroacetic acid dissolved in 16 parts of an IPA aqueous solution having a concentration of 90% was added, the temperature was raised to 70 ° C., and an etherification reaction was carried out for 90 minutes. The IPA concentration in the reaction medium was 90%. After completion of the reaction, the reaction was neutralized, drained, dried and pulverized to obtain sodium carboxymethyl cellulose having a degree of carboxymethyl substitution (DS) of 0.14 per anhydrous glucose unit and a crystallinity of 73% (CMC1). After adjusting the solid content concentration of the obtained aqueous dispersion of CMC1 to 1.5%, it was treated three times at a pressure of 150 MPa with a high-pressure homogenizer to have a transparency of 8%, an average fiber diameter of 5.2 nm, and a solid content concentration of 1. A first CM-ized CNF aqueous dispersion having a B-type viscosity of 2500 mPa · s at 25 ° C. and 60 rpm was obtained.

[Example A1]
0.001% by weight (solid content) of CM-ized CNF and 1.0% by weight of sulfuric acid so that the total of the recycled paper raw material for corrugated cardboard (manufactured by Nippon Paper Industries Co., Ltd.) and the first CM-made CNF is 100% by weight. A pulp slurry was prepared by adding a band, 0.15% by weight paper strength agent, and 70 ppm of anionic polymer. Using the obtained pulp slurry, a hand-made sheet was produced and evaluated with a target basis weight of 100 g / m ^2. The hand-made sheet was manufactured with reference to JIS P8222.

[Examples A2 and A3]
A hand-made sheet was produced and evaluated by the same method as in Example A1 except that the amount of CM-ized CNF added was changed to 0.1% by weight and 4% by weight, respectively.

[Comparative Example A1]
A hand-made sheet was produced and evaluated by the same method as in Example A1 except that CMized CNF was not used. These results are shown in Table 1.

From Table 1, it is clear that the paper of the present invention is excellent in strength particularly required for packaging containers and corrugated cardboard used by putting luggage and food inside, such as specific burst strength and compressive strength. Furthermore, since the paper of the present invention contains CMized CNF that can also be used as a food additive, it is suitable as a paper used for applications in which it comes into direct contact with food.

(3) Preparation of the second CM-ized CNF A hardwood kraft pulp (Nippon Paper Industries, Ltd.) was added by adding 130 parts of water and 20 parts of sodium hydroxide dissolved in 100 parts of water to a biaxial kneader whose rotation speed was adjusted to 100 rpm. 100 copies of (manufactured by the company) were charged by absolute dry weight. Mercerized cellulose was prepared by stirring and mixing at 30 ° C. for 90 minutes. While further stirring, 100 parts of IPA and 60 parts of monochloroacetic acid were added, the temperature was raised to 70 ° C., and an etherification reaction was carried out for 90 minutes. The IPA concentration in the reaction medium was 30%. After completion of the reaction, the reaction was neutralized, drained, dried and pulverized to obtain sodium carboxymethyl cellulose having a degree of carboxymethyl substitution (DS) of 0.24 per anhydrous glucose unit and a crystallinity of 73% (CMC2). The obtained CMC2 was adjusted to a solid content concentration of 1.5% and treated three times at a pressure of 150 MPa with a high-pressure homogenizer to have a transparency of 84.4%, an average fiber diameter of 3.5 nm, a solid content concentration of 1%, and a solid content concentration of 25 ° C. , A second CMized CNF aqueous dispersion having a B-type viscosity of 5350 mPa · s at 60 rpm was obtained.

[Example B1]
A hand-made sheet was produced and evaluated by the same method as in Example A3, except that different lots of used paper raw materials for corrugated cardboard were used and a second CM-ized CNF was used instead of the first CM-made CNF.

[Comparative Example B1]
A hand-made sheet was produced and evaluated by the same method as in Example B1 except that CMized CNF was not used.

[Comparative Example B2]
A hand-made sheet was produced and evaluated by the same method as in Example B1 except that CMC2 was used instead of CM-ized CNF. These results are shown in Table 1.

It is clear that the paper of the present invention has excellent strength.

Claims (8)

Paper containing pulp and carboxymethylated cellulose nanofibers
Paper having a degree of carboxymethyl substitution in glucose units of the carboxymethylated cellulose nanofibers of 0.01 to 0.60. The paper according to claim 1, wherein the degree of carboxymethyl substitution is 0.1 to 0.40. The paper according to claim 1, which is a paper provided with a base paper and a coating layer, wherein the base paper layer contains carboxymethylated cellulose nanofibers. The paper according to any one of claims 1 to 3, which contains 5% by weight or less of the carboxymethylated cellulose nanofibers with respect to the pulp. The paper according to any one of claims 1 to 4, wherein the paper includes a base paper and a coating layer, and the coating layer contains carboxymethylated cellulose nanofibers. The paper according to any one of claims 1 to 5, wherein the average fiber diameter of the carboxymethylated cellulose nanofibers is 2 nm or more and less than 500 nm. The paper according to any one of claims 1 to 6, wherein the base paper layer of the paper contains a salt of a metal selected from the group consisting of sodium, calcium, magnesium, aluminum, and a combination thereof. Any of claims 1 to 7 in which the wavelength of 660 nm and the optical path length of 10 mm are 70% or more when the carboxymethylated cellulose nanofiber is used as an aqueous dispersion having a solid content of 1% (W / v). The paper described in.