WO2021002361A1

WO2021002361A1 - Paper containing cellulose nanofibers

Info

Publication number: WO2021002361A1
Application number: PCT/JP2020/025681
Authority: WO
Inventors: 眞松本; 遼外岡; 吉松　丈博
Original assignee: 日本製紙株式会社
Priority date: 2019-07-01
Filing date: 2020-06-30
Publication date: 2021-01-07
Also published as: JPWO2021002361A1; JP2022101622A; JP7080404B2

Abstract

A paper containing cellulose nanofibers and pulp, the paper being such that: the cellulose nanofibers have carboxyl groups in an amount of 0.9-3.0 mmol/g in relation to the bone-dry weight; and when placed in an aqueous dispersion having a concentration of 1% (w/v), the cellulose nanofibers impart a Brookfield viscosity (60 rpm, 20°C) greater than 2500 mPa∙s and no more than 7000 mPa∙s.

Description

Paper containing cellulose nanofibers

The present invention is a paper containing cellulose nanofibers and pulp, wherein the cellulose nanofibers have a carboxyl group of 0.9 to 3.0 mmol / g based on absolute dry weight and have a concentration of 1%. The present invention relates to paper, which is a cellulose nanofiber that gives a B-type viscosity (60 rpm, 20 ° C.) of more than 2500 mPa · s and 7000 mPa · s or less when made into an aqueous dispersion of (w / v).

Generally, paper is delivered to the user through printing, various processing, etc., but in the process, the paper is often required to have strength. It has been proposed to produce paper from pulp slurries to which cellulose nanofibers have been added in order to improve the strength (Patent Documents 1 and 2).
Further, Patent Document 3 proposes to apply a cellulose nanofiber dispersion liquid to a base paper as a coating liquid.

Japanese Unexamined Patent Publication No. 2012-214943 Japanese Unexamined Patent Publication No. 2016-166444 Japanese Unexamined Patent Publication No. 2016-056460

The inventors conducted a preliminary study and found that the strength of the paper disclosed in the patent document was not at a sufficient level. It is presumed that the reason for this is that the cellulose nanofibers do not have a functional group in Patent Documents 1 and 2, and that the cellulose nanofibers that give a low viscosity when used as an aqueous dispersion are used in Patent Document 3. .. In view of such circumstances, it is an object of the present invention to provide a paper having higher strength.

The present inventors have a specific amount of carboxyl groups (hereinafter, also referred to as "carboxyl group amount") of CNF, and B is relatively high when a dispersion having a concentration of 1% (w / v) is used. It has been found that cellulose nanofibers that give mold viscosity can solve the above problems. That is, the above problem is solved by the following invention.
[1] Paper containing cellulose nanofibers and pulp.
The cellulose nanofibers have a carboxyl group of 0.9 to 3.0 mmol / g with respect to the absolute dry weight, and when made into an aqueous dispersion having a concentration of 1% (w / v), it exceeds 2500 mPa · s and 7000 mPa. -Paper, which is a cellulose nanofiber that gives a B-type viscosity (60 rpm, 20 ° C.) of s or less.
[2] The paper according to [1], wherein the paper includes a single-layer or multi-layer base paper layer, and at least one layer thereof contains the cellulose nanofibers.
[3] The paper according to [1] or [2], which has a layer containing the cellulose nanofibers on one side or both sides of the base paper layer.
[4] The paper according to [1], wherein the paper includes a base paper layer and a layer containing a binder component, and the layer containing the binder component contains the cellulose nanofibers.
[5] The paper according to [4], wherein the layer containing the binder component further contains a white pigment.
[6] The paper according to any one of [1] to [5], wherein the cellulose nanofibers have a carboxyl group of 1.2 mmol / g or more with respect to an absolute dry weight.
[7] The paper according to any one of [1] to [5], wherein the cellulose nanofibers have a carboxyl group of 1.35 mmol / g or more based on an absolute dry weight.
[8] The paper according to any one of [1] to [5], wherein the cellulose nanofibers have a carboxyl group of 2.5 mmol / g or less based on an absolute dry weight.
[9] The paper according to any one of [1] to [5], wherein the cellulose nanofibers have a carboxyl group of 1.6 mmol / g or less based on an absolute dry weight.
[10] The paper according to any one of [1] to [5], wherein the B-type viscosity (60 rpm, 20 ° C.) of the 1% aqueous dispersion has a viscosity of 3000 mPa · s or more.
[11] The paper according to any one of [1] to [5], wherein the B-type viscosity (60 rpm, 20 ° C.) of the 1% aqueous dispersion has a viscosity of 6000 mPa · s or less.
[12] The paper according to any one of [1] to [11], wherein the cellulose nanofibers have an average fiber diameter of 2 to 30 nm.
[13] The method for producing paper according to the above [1].
Cellulose oxidized by oxidizing a cellulosic raw material with an oxidizing agent in the presence of a compound selected from the group consisting of (1) N-oxyl compound and (2) bromide, iodide and a mixture thereof. The process of preparing,
A step of preparing cellulose nanofibers by wet atomizing the oxidized cellulose,
A method for producing paper, comprising a step of preparing a liquid containing the cellulose nanofibers and a step of coating, impregnating or spraying the base paper with the liquid.
[14] The method for producing paper according to the above [1].
Cellulose oxidized by oxidizing a cellulosic raw material with an oxidizing agent in the presence of a compound selected from the group consisting of (1) N-oxyl compound and (2) bromide, iodide and a mixture thereof. The process of preparing,
A step of preparing cellulose nanofibers by wet atomizing the oxidized cellulose,
A method for producing paper, comprising a step of preparing a pulp slurry containing pulp and the cellulose nanofibers, and a step of making the pulp slurry.
[15] The production method according to [13] or [14], wherein the cellulosic raw material is selected from the group consisting of bleached kraft pulp, bleached sulfite pulp, and cellulosic powder.
[16] The production method according to any one of [13] to [15], wherein the N-oxyl compound is selected from 4-hydroxy TEMPO derivatives represented by the following formulas 2 to 4 described later.
[17] The production method according to any one of [13] to [16], wherein the wet atomization treatment comprises defibrating the oxidized cellulose at a pressure of 100 MPa or more using an ultra-high pressure homogenizer.

According to the present invention, it is possible to provide paper with further improved strength.

Hereinafter, the present invention will be described in detail. In the present invention, "X to Y" includes X and Y which are fractional values thereof. In addition, cellulose nanofibers are also simply referred to as "CNF".

1. 1. Paper Containing Cellulose Nanofibers (CNF) (1) Paper In the present invention, paper includes a base paper layer obtained by papermaking a raw material slurry containing pulp. The paper of the present invention may have a single-layer base paper layer or may have a multi-layer base paper layer, but if the paper has a single-layer base paper layer, the CNF of the present invention may be used as paper. When internally added (when contained in the base paper layer), the effect of the present invention is likely to be exhibited, which is preferable.

Examples of the pulp used for the paper of the present invention include chemical pulp (coniferous bleached kraft pulp (NBKP), unbleached kraft pulp (NUKP), broadleaf bleached kraft pulp (LBKP), unbleached kraft pulp (LUKP), etc.). Recycled pulp such as mechanical pulp (grand pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc.), deinked pulp (DIP), undeinked pulp, magazine waste paper pulp, cardboard waste paper pulp, etc. These may be used alone or in admixture in any proportion.

The paper of the present invention may contain a filler. Examples of the filler include known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, and synthetic resin filler. Above all, it is preferable to use heavy calcium carbonate or light calcium carbonate from the viewpoint of environment and paper storage stability.

The paper of the present invention has a sulfate band, various anionic, cationic, nonionic or amphoteric yield improvers, drainage improvers, various paper strength improvers, internal sizing agents, bulking agents, dyes, and optical brighteners. If necessary, a known papermaking additive such as an agent, a pH adjuster, an antifoaming agent, a pitch control agent, or a slime control agent may be contained.

Examples of the dry paper strength improving agent include polyacrylamide and starches. Examples of starches include oxidized starch, cationized starch, urea phosphate esterified starch, etherified starch such as hydroxyethyl etherified starch, dextrin and the like. Further, as the wet paper strength improving agent, polyamide amine epichlorohydrin and the like can be exemplified.

As the paper machine used for paper making, a known paper machine such as a long net paper machine, a twin wire paper machine, or a circular net type paper machine can be used. The pH at the time of papermaking may be acidic, neutral or alkaline, but when heavy calcium carbonate or light calcium carbonate is used as the filler, the pH at the time of papermaking is pseudo-neutral or pseudo-neutral so that the pH at the time of papermaking is 6-9. It is preferable to make paper with neutrality.

(2) CNF
CNF is a cellulosic single microfibril obtained by defibrating a cellulosic raw material, and preferably has an average fiber diameter of 2 to 30 nm and an average fiber length of about 0.1 to 5 μm. The average fiber diameter and average fiber length of CNF shall be the average of the fiber diameter and fiber length obtained from the results of observing each fiber using an atomic force microscope (AFM) or a transmission electron microscope (TEM). Obtained by.

In the present invention, it has a carboxyl group of 0.9 to 3.0 mmol / g with respect to the absolute dry weight, and when it is made into an aqueous dispersion having a concentration of 1% (w / v), it exceeds 2500 mPa · s and 7000 mPa · s. A CNF that gives the following B-type viscosity (60 rpm, 20 ° C.) is used.

The CNF used in the present invention having a carboxyl group of 0.9 to 3.0 mmol / g with respect to the absolute dry weight (hereinafter, also referred to as “CNF of the present invention”) is less than 0.9 mmol / g with respect to the absolute dry weight. Compared with CNF having a carboxyl group of, the water retention is good.

The amount of carboxyl groups of CNF in the present invention is preferably 1.2 mmol / g or more, more preferably 1.35 mmol / g or more, based on the absolute dry weight. The amount of carboxyl groups in the CNF of the present invention is preferably 2.5 mmol / g or less, more preferably 1.6 mmol / g or less.

For the amount of carboxyl groups of CNF of the present invention, 60 mL of a 0.5 wt% CNF slurry was prepared, a 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.5, and then a 0.05 N sodium hydroxide aqueous solution was added dropwise. The electrical conductivity is measured until the pH reaches 11, and 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.
Carboxylic acid group amount (mmol / g) = a (ml) x 0.05 / CNF weight (g)

The CNF of the present invention provides an aqueous dispersion having a concentration of 1% (w / v) and a B-type viscosity (60 rpm, 20 ° C.) of more than 2500 mPa · s and 7000 mPa · s or less. 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 the CNF of the present invention is replaced with a hydrophilic substituent in which a part of glucose units is charged. Since it contains a large number of fibers having a long fiber length or many branches, the substituents in the molecular chain spread in a state of being electrostatically repelled in the dispersion liquid, and have a high B-type viscosity. Then it is inferred.

As described above, the CNF of the present invention may contain more fibers having a long fiber length or fibers having many branches as compared with a CNF that gives an aqueous dispersion having a viscosity of 2500 mPa · s or less. .. The CNF of the present invention, which contains a large amount of fibers having a long fiber length, can enter between pulp fibers and form a strong hydrogen bond. Further, since the CNF of the present invention containing many fibers having many branches has many bond points between the pulp fibers or between the CNFs, more hydrogen bonds can be formed and the yield of the CNF itself can be obtained. Becomes good. Further, since the CNF of the present invention that gives the aqueous dispersion having the viscosity has good water retention, the presence of the CNF of the present invention in the raw material slurry of paper improves the yield of the fine fibers to the base paper layer. As a result of the combined action of these elements, it is presumed that by using the CNF of the present invention, the hydrogen bonds between the pulp fibers and the fine fibers are strengthened, and a paper having higher strength can be obtained.

The B-type viscosity at the concentration of 1% (w / v) is preferably 3000 mPa · s or more. Further, it is preferably 6000 mPa · s or less. When the concentration of the CNF is 2% (w / v), the B-type viscosity (60 rpm, 20 ° C.) preferably exceeds 7,000 mPa · s and is preferably 50,000 mPa · s or less.

The B-type viscosity of the aqueous dispersion of 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 a property that the viscosity decreases by agitating and applying shear stress, and the viscosity increases and gels in a stationary state, so that the mixture is sufficiently agitated. It is preferable to measure the B-type viscosity in this state.

The CNF-containing paper of the present invention having the above characteristics has the following characteristics.
First, a case where the CNF of the present invention is internally added to paper (when it is contained in the base paper layer) will be described. As described above, when the CNF of the present invention is contained in the base paper layer, the above-mentioned elements act in a complex manner, and as a result, the hydrogen bonds between the pulp fibers and the fine fibers in the base paper layer are strengthened. It is presumed that the paper with CNF inlaid has higher strength. However, the mechanism of expression of these effects is not limited to the above.

Next, a case where the CNF of the present invention is externally attached to paper (when it is contained in a layer provided on the base paper layer) will be described. Usually, when a second layer is provided on the base paper layer, the layer is formed by coating, impregnating, spraying, or the like with a raw material liquid such as a coating liquid. At this time, since the CNF of the present invention has high water retention, it is suppressed that the component containing CNF together with water penetrates into the base paper layer from the second layer in the undried state. Further, since the CNF of the present invention containing many fibers having many branches has many bonding points between the CNFs, the strength of the second layer itself is improved. Therefore, it is presumed that the paper externally attached with CNF of the present invention has higher strength. Further, since the second layer also has high air permeation resistance and smoothness, the paper externally attached with CNF of the present invention also has excellent barrier properties and printability. However, the mechanism of expression of these effects is not limited to the above.

The CNF used in the present invention, for example, oxidizes a cellulosic raw material with an oxidizing agent in the presence of (1) an N-oxyl compound and (2) a bromide, an iodide or a mixture thereof, and further, the same. It can be produced by wet atomizing the oxidized cellulose, defibrating it, and forming it into nanofibers.

Cellulose-based raw materials are not particularly limited, such as kraft pulp or sulfite pulp derived from various woods, and cellulosic powder obtained by purifying them by chemical treatment such as acid hydrolysis as necessary and further crushing them with a high-pressure homogenizer or a mill. Can be used. In addition, plants such as kenaf, hemp, rice, bagasse, and bamboo can also be used. Among these, bleached kraft pulp (BKP), bleached sulfite pulp (BSP), and cellulose powder are preferable, and cellulose powder is more preferable.

Cellulose powder is obtained by removing the non-crystalline part of wood pulp by acid hydrolysis treatment, crushing it with a high-pressure homogenizer, a mill, etc., and then sieving it. The degree of polymerization of cellulose in the cellulose powder is preferably about 100 to 500, the crystallinity of the cellulose powder by the X-ray diffraction method is preferably 70 to 90%, and the volume average particle diameter by the laser diffraction type particle size distribution measuring device. Is preferably 100 μm or less, and more preferably 50 μm or less. When the volume average particle diameter is 100 μm or less, a CNF dispersion having excellent fluidity can be obtained.

As the cellulose powder used in the present invention, the above-mentioned cellulose powder may be used, or commercially available products such as KC Flock (manufactured by Nippon Paper Industries Co., Ltd.), Theoras TM (manufactured by Asahi Kasei Chemicals Co., Ltd.), and Abyssel R (manufactured by FMC) are used. You may.

As the N-oxyl compound used when oxidizing the cellulosic raw material, any compound can be used as long as it is a compound that promotes the desired oxidation reaction. For example, examples of the N-oxyl compound used in the present invention include substances represented by the following formula 1.

In Formula 1, R1 to R4 are independently alkyl groups having about 1 to 4 carbon atoms. Among the compounds represented by the formula 1, 2,2,6,6-tetramethyl-1-piperidin-N-oxy radical (hereinafter, also referred to as "TEMPO"), 4-hydroxy-2,2,6,6 A compound that generates a-tetramethyl-1-piperidin-N-oxy radical (hereinafter, also referred to as "4-hydroxy TEMPO") is preferable. Derivatives obtained from TEMPO or 4-hydroxy TEMPO can also be used, with 4-hydroxy TEMPO derivatives being most preferred.

The 4-hydroxy TEMPO derivative is obtained by etherifying the hydroxyl group of 4-hydroxy TEMPO with an alcohol having a linear or branched carbon chain having 4 or less carbon atoms, or esterifying it with a carboxylic acid or a sulfonic acid. Derivatives are preferred. When 4-hydroxy TEMPO is etherified, if an alcohol having 4 or less carbon atoms is used, the obtained derivative becomes water-soluble regardless of the presence or absence of saturated or unsaturated bonds in the alcohol, which is good as an oxidation catalyst. A functional 4-hydroxy TEMPO derivative can be obtained.

Examples of the 4-hydroxy TEMPO derivative include compounds of the following formulas 2 to 4.

In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms. Further, the radical of the N-oxyl compound represented by the following formula 5, that is, the azaadamantane type nitroxy radical is also particularly preferable because it can produce a uniform CNF in a short time.

In Formula 5, R5 and R6 are independently hydrogen or linear or branched alkyl groups of C1 to C6.

The amount of N-oxyl compound such as TEMPO or 4-hydroxy TEMPO derivative used when oxidizing the cellulosic raw material is not particularly limited as long as it is a catalytic amount capable of converting the cellulosic raw material into nanofibers. For example, it is about 0.01 to 10 mmol, preferably about 0.05 to 5 mmol, based on 1 g of an absolutely dry cellulosic raw material.

As the bromide or iodide used for the oxidation of the cellulosic raw material, a compound that can be dissociated and ionized in water, for example, an alkali metal bromide or an alkali metal iodide can be used. The amount of bromide or iodide used can be selected within the range in which the oxidation reaction can be promoted. For example, it is about 0.1 to 100 mmol, preferably 0.1 to 10 mmol, and more preferably about 0.5 to 5 mmol with respect to 1 g of an absolutely dry cellulosic raw material.

Oxidizing agents used for the oxidation of cellulose-based raw materials include halogen, hypohalogenic acid, subhalic acid, perhalogenic acid or salts thereof, halogen oxides, peroxides, and the like, which can promote the desired oxidation reaction. If so, any oxidizing agent can be used. Of these, sodium hypochlorite, which is currently the most widely used in industrial processes and has a low environmental load, is particularly preferable from the viewpoint of production cost. The amount of the oxidizing agent used can be selected within a range in which the oxidation reaction can be promoted. For example, it is about 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol with respect to 1 g of an absolutely dry cellulosic raw material.

As described above, the oxidation of the cellulosic raw material in the present invention comprises (1) an N-oxyl compound such as a 4-hydroxy TEMPO derivative, and (2) a compound selected from the group consisting of bromide, iodide and a mixture thereof. In the presence, it is preferably carried out in water with an oxidizing agent such as sodium hypochlorite. In this method, the oxidation reaction of the cellulosic raw material can proceed smoothly and efficiently even under mild conditions, so that the reaction temperature may be room temperature of about 15 to 30 ° C.

Since a carboxyl group is generated in cellulose as the reaction progresses, the pH of the reaction solution is lowered, but in order to proceed the oxidation reaction efficiently, an alkaline solution such as an aqueous sodium hydroxide solution is added to the reaction. It is desirable to maintain the pH of the solution at 9 to 12, preferably about 10 to 11.

CNF can be produced by defibrating the oxidized cellulosic raw material thus obtained by wet atomization treatment or the like. As the wet atomization treatment, for example, a mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer or a high-pressure homogenizer can be used alone or in combination of two or more, if necessary. In particular, CNF can be efficiently produced by performing a wet atomization treatment using an ultra-high pressure homogenizer capable of applying a pressure of 100 MPa or more, preferably 120 MPa or more, more preferably 140 MPa or more.

The B-type viscosity of the above-mentioned aqueous dispersion can be achieved mainly by optimizing the wet atomization treatment. For example, in the case of the oxidized cellulose prepared as described above, the B-type viscosity of the aqueous dispersion can be set within a desired range by performing a treatment of about 2 to 4 passes at 150 MPa using an ultrahigh pressure homogenizer. If the number of passes is small, defibration becomes insufficient, and it may be difficult to keep the B-type viscosity within the above range. On the other hand, if the number of passes is large, the crystallinity is lowered and the fiber length is shortened, so that it may be difficult to keep the B-type viscosity within the above range. Further, since the B-type viscosity of the aqueous dispersion tends to improve as the amount of carboxyl groups increases, the treatment conditions are appropriately adjusted depending on the amount of carboxyl groups.

(3) Paper Containing CNF As described above, by incorporating the CNF of the present invention into the paper, a paper having improved strength can be obtained. Further, by improving the air permeability resistance and smoothness of the paper, it is possible to obtain a paper having improved barrier properties and printability.

As described above, the CNF of the present invention may be internally added to the paper (contained in the base paper layer), externally attached to the paper (contained in the layer provided in the base paper layer), or both. There may be. In the case of internal addition, the paper contains CNF in the base paper layer, and in the case of external addition, the paper has a CNF-containing layer on the base paper layer.

Paper containing CNF in the base paper layer is suitable for applications such as printing paper, information paper, industrial paper, and household paper. Further, a paper having a CNF-containing layer on the base paper layer is suitable for applications such as printing paper and wrapping paper. The paper of the present invention may further include a layer provided on the base paper layer containing no CNF of the present invention. A detailed description of these papers will be given later.

When the CNF of the present invention is internally added to paper, the dry weight of the CNF is preferably 10% by weight or less, more preferably 5% by weight or less, and 2% by weight or less, based on the dry weight of the entire base paper layer. Is more preferable. The lower limit is not limited as long as the effect of the present invention can be obtained, but it is preferably 1 × ^10-6 % by weight or more.

When the CNF of the present invention is externally added, a layer containing CNF can be formed by applying, impregnating, spraying, or the like a liquid containing CNF, CNF and a binder component, or CNF and a binder component and a white pigment. .. In the present invention, a liquid containing CNF or a liquid containing CNF and a binder component is also referred to as a "clear liquid", and a liquid containing CNF, a binder component and a white pigment is also referred to as a "pigment liquid".

The amount of CNF in the layer containing the CNF is preferably 10 g / m ² or less as dry coating amount per surface, more preferably not more than 5 g / ^{m 2,} more preferably 2 g / ^{m 2} or less. The lower limit is not limited as long as the effect of the present invention can be obtained, but it is preferably 1 × 10 ^-6 g / m ² or more.
The amount of dry coating per side of the layer containing CNF is preferably 0.05 to 3 g / m ² , more preferably 0.1 to 3 g / m ^{2 in} the case of the layer containing CNF and the binder component. Is. Further, in the case of a layer containing CNF, a binder component and a white pigment, it is preferably 1 to 30 g / m ² , more preferably 3 to 25 g / m ² , and even more preferably 8 to 20 g / m ² .

The binder component is a styrene / butadiene copolymer, a styrene / acrylic copolymer, an ethylene / vinyl acetate copolymer, a butadiene / methyl methacrylate copolymer, a vinyl acetate / butyl acrylate copolymer, and a male anhydride. Acid copolymers, various copolymers such as acrylic acid / methyl methacrylate copolymers, proteins such as polyvinyl alcohols, casein, soybean protein, and synthetic proteins, oxidized starch, positive starch, urea phosphate esterified starch, hydroxy Etherealized starch such as ethyl etherified starch, starches such as dextrin, and cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose can be used alone or in combination, if necessary.

White pigments include kaolin, clay, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, satin white, etc. Organic pigments such as inorganic pigments and plastic pigments can be used, and these white pigments can be used alone or in combination as needed. In the present invention, it is preferable to use heavy calcium carbonate and / or light calcium carbonate from the viewpoint of whiteness and printability, and heavy calcium carbonate and / or light calcium carbonate in 100 parts by weight of the pigment. Is more preferably contained in an amount of 50 parts by weight or more in total.

In the paper having a CNF-containing layer on the base paper layer of the present invention, a dispersant, a thickener, a water retaining agent, a defoaming agent, a water resistant agent, and a coloring agent are added to the CNF-containing layer, if necessary. Various auxiliary agents used for papermaking such as, etc. may be appropriately contained.

Hereinafter, specific embodiments of the CNF-containing paper of the present invention will be described.
The CNF-containing paper of the present invention described above is suitable for use as printing paper. Specific examples of printing paper include newspaper paper, high-grade printing paper (high-quality paper), intermediate printing paper (medium-quality paper and high-quality paper), etc. that do not have a layer containing a white pigment, art paper, and coated paper. Examples thereof include those having a layer containing a white pigment such as paper, finely coated paper, and cast-coated paper. The physical characteristics of each printing paper are appropriately set, and for example, the basis weight is about 20 to 300 g / m ² .

Newspaper paper is generally produced using 100% recycled pulp or mechanical pulp produced by loosening recycled pulp and wood as raw material pulp. High-grade printing paper (high-quality paper) is made of 100% chemical pulp from which lignin is removed by chemically treating wood, and intermediate printing paper (medium-quality paper and wood-free paper) is made of 40 to 100% chemical pulp. The base paper layer is composed of pulp other than 60 to 0% of chemical pulp.

Since the newspaper paper containing CNF of the present invention has higher strength, it is possible to prevent paper breakage in the printing process. In particular, newspaper paper having a CNF-containing layer on the base paper layer has a good print density because it suppresses excessive penetration of printing ink into the newspaper paper. In addition, the smoothness of the paper surface is improved, and the print quality is improved. The basis weight of newspaper paper is about 30 to 60 g / m ² .

The CNF-containing paper of the present invention includes wet and dry electrophotographic paper, inkjet recording paper, heat-sensitive recording paper, pressure-sensitive recording paper, information paper such as foam paper, moisture-proof paper, wallpaper backing paper, paper container paper, and molded paper. It is suitable for industrial paper such as base paper for laminated boards provided with a synthetic resin layer, household paper such as sanitary paper, wrapping paper such as kraft paper, and paperboard such as paperboard and white paperboard. In particular, the wallpaper lining paper containing CNF of the present invention has high smoothness and air permeability resistance, so that it suppresses excessive penetration of an adhesive such as water-based starch paste into the base paper layer and fluffs on the base paper surface. It is preferable because it can suppress the occurrence of protrusions on the wallpaper resin.

2. 2. Method for Producing Paper Containing CNF (1) Method by Inner Addition In this method, it is preferable to add the CNF of the present invention to the raw material slurry when the raw material slurry containing the pulp described above is made into paper. When the paper has a multi-layer base paper layer, the base paper layer containing CNF is not limited, and any one or more layers may contain CNF.

(2) Method by external addition In this method, CNF is contained by applying, impregnating, or spraying a liquid containing CNF, CNF and a binder component, or CNF and a binder component and a white pigment on one or both sides of a base paper layer. Layers can be formed. The liquid preferably uses water as a solvent or a dispersion medium. As the binder component and the white pigment, the above-mentioned ones can be used. The concentration of CNF in the liquid is not limited as long as the effect of the present invention can be obtained and the viscosity of the liquid can be coated, impregnated, sprayed, etc., but is not limited, for example, 0.05 to 3% ( w / v) is preferable.

Equipment for coating and impregnation includes film transfer type roll coaters such as 2-roll coaters, gate roll coaters, blade metering coaters, rod metering coaters, and sim sizers, flooded nip / blade coaters, jet fountains / blade coaters. , Short dwell time applicator type coater, rod metering coater using grooved rod, plain rod or the like instead of blade, curtain coater, die coater and other known equipment can be used.

Further, the paper may be surface-treated in order to improve smoothness and print quality. For the surface treatment, a known device such as a super calendar using a cotton roll as the elastic roll and a soft nip calendar using a synthetic resin roll as the elastic roll can be used. The calendar is used at a linear pressure within the normal operating range, but when producing bulky paper, a soft nip calendar capable of surface treatment at a low linear pressure is preferable.

The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to such Examples. In each of the Examples and Comparative Examples, "parts" indicates "parts by weight" and "%" indicates "% by weight" unless otherwise specified.

[Example 1-1]
<CNF>
As the CNF, TEMPO-oxidized CNF (manufactured by Nippon Paper Industries, Ltd.) having a cellulosic raw material of NBKP, a carboxyl group amount of 1.55 mmol / g, and a high-pressure homogenizer treatment of 3 passes was used. The B-type viscosity of the aqueous dispersion of this CNF (hereinafter, “CNF-1”) was as follows.
Water dispersion with a concentration of 1% (w / v): 2530 mPa · s
Water dispersion with a concentration of 2% (w / v): 13119 mPa · s

To 100% by weight of LBKP, 1.5% by weight (solid content) of sulfuric acid band, 0.025% by weight (solid content) of polyethyleneimine, 4% by weight (solid content) of CNF-1 were sequentially added, and further dried. As a paper strength improver, 0.6% by weight (solid content) of polyacrylamide and 0.2% by weight (solid content) of an internal sizing agent are sequentially added, and the raw material is stirred at a speed of 500 rpm with a three-one motor. A slurry was prepared. Paper was produced by hand using the raw material slurry and evaluated by the method described later. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Example 1-5]
Paper was produced by hand and evaluated in the same manner as in Example 1-1 except that the amount of CNF-1 added was changed to 0.1% by weight (solid content). Table 1 shows the physical characteristics and evaluation results of the manufactured paper.
[Example 1-6]
Paper was produced by hand and evaluated in the same manner as in Example 1-1 except that the amount of CNF-1 added was changed to 1% by weight (solid content). Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Comparative Example 1-1]
Paper was produced by hand and evaluated in the same manner as in Example 1-1 except that CNF-1 was not added. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Example 1-7]
<CNF>
As the CNF, TEMPO-oxidized CNF (manufactured by Nippon Paper Industries, Ltd.) having a cellulosic raw material of NBKP, a carboxyl group amount of 1.03 mmol / g, and a high-pressure homogenizer treatment of 3 passes was used. The B-type viscosity of the aqueous dispersion of this CNF (hereinafter, “CNF-3”) was as follows.
Water dispersion with a concentration of 1% (w / v): 2750 mPa · s

Paper was produced by hand and evaluated in the same manner as in Example 1-1 except that CNF-1 was changed to CNF-3. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Example 1-8]
<CNF>
As the CNF, TEMPO oxidized CNF (manufactured by Nippon Paper Industries, Ltd.) having a cellulosic raw material of NBKP, a carboxyl group amount of 1.29 mmol / g, and a high-pressure homogenizer treatment of 3 passes was used. The B-type viscosity of the aqueous dispersion of this CNF (hereinafter, “CNF-4”) was as follows.
Water dispersion with a concentration of 1% (w / v): 3310 mPa · s

Paper was produced by hand and evaluated in the same manner as in Example 1-1 except that CNF-1 was changed to CNF-4. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Comparative Example 1-4]
<CNF>
As the CNF, TEMPO-oxidized CNF (manufactured by Nippon Paper Industries, Ltd.) having a cellulosic raw material of NBKP, a carboxyl group amount of 0.81 mmol / g, and a high-pressure homogenizer treatment of 3 passes was used. The B-type viscosity of the aqueous dispersion of this CNF (hereinafter, “CNF-6”) was as follows.
Water dispersion with a concentration of 1% (w / v): 2640 mPa · s

Paper was manufactured and evaluated by hand in the same manner as in Example 1-1 except that CNF-1 was changed to CNF-6. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Comparative Example 1-5]
<CNF>
As the CNF, TEMPO-oxidized CNF (manufactured by Nippon Paper Industries, Ltd.) having a cellulosic raw material of NBKP, a carboxyl group amount of 0.96 mmol / g, and a high-pressure homogenizer treatment of 2 passes was used. The B-type viscosity of the aqueous dispersion of this CNF (hereinafter, “CNF-7”) was as follows.
Water dispersion with a concentration of 1% (w / v): 2070 mPa · s

Paper was produced and evaluated by hand in the same manner as in Example 1-1 except that CNF-1 was changed to CNF-7. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Example 1-2]
Paper was produced and evaluated by hand in the same manner as in Example 1-1 except that 100% by weight of LBKP was replaced with 100% by weight of used magazine paper and the amount of CNF-1 added was changed to 0.1% by weight. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Comparative Example 1-2]
Paper was produced by hand and evaluated in the same manner as in Example 1-2 except that CNF-1 was not added. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Example 1-3]
Paper was produced and evaluated by hand in the same manner as in Example 1-2 except that the amount of CNF added was changed to 0.001% by weight (solid content) and the basis weight was changed. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Example 1-4]
Paper was produced by hand and evaluated in the same manner as in Example 1-2 except that the basis weight was changed. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Comparative Example 1-3]
Paper was produced by hand and evaluated in the same manner as in Example 1-3 except that CNF-1 was not added. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Examples 1-9, 1-10, Comparative Examples 1-6, 1-7]
Paper was produced and evaluated by hand in the same manner as in Example 1-4 except that CNF-1 was changed to CNF-3, CNF-4, CNF-6, and CNF-7, respectively. Table 1 shows the physical characteristics and evaluation results of the manufactured paper.

[Example 2-1]
<CNF>
5.00 g (absolutely dry) of bleached unbeaten kraft pulp derived from coniferous tree (whiteness 85%: manufactured by Nippon Paper Industries, Ltd.) with 39 mg (0.05 mmol per 1 g of absolutely dried cellulose) of TEMPO (manufactured by Sigma Aldrich) 514 mg of sodium bromide (1.0 mmol per 1 g of dry cellulose) was added to 500 mL of an aqueous solution, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite content was 5.5 mmol / g, and the oxidation reaction was started at room temperature. Although the pH in the system decreased during the reaction, a 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system did not change.

The reaction mixture was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The yield of pulp was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.52 mmol / g. This was adjusted to 1% (w / v) with water and treated with an ultrahigh pressure homogenizer (20 ° C., 150 MPa) for 3 passes to obtain an aqueous dispersion of CNF.
The obtained CNF (hereinafter, "CNF-2") has an average fiber diameter of 3 nm, an average fiber length of 0.75 μm, a carboxyl group amount of 1.52 mmol / g, and a concentration of 1% (w / v). The B-type viscosity of was 3060 mPa · s.

<Clear liquid>
Oxidized starch (SK20, manufactured by Japan Corn Starch) was added to the aqueous dispersion of CNF-2 produced as described above to produce a clear solution having a starch: CNF-2 weight ratio of 15: 1. Table 2 shows the B-type viscosity of the clear liquid at a solid content concentration of 10% by weight, 30 ° C., and 60 rpm.

<Paper manufacturing>
0.5% by weight (solid content) sulfuric acid band, 0.77% by weight (solid content) cationized starch, and 0.05% by weight (solid content) wet paper strength improver are added to 100% by weight of LBKP. A raw material slurry having a solid content concentration of 0.7% by weight was prepared. A single-layer base paper layer was produced by a paper machine using the obtained raw material slurry.
The clear liquid was applied by hand on the base paper layer and dried by a conventional method to produce paper. The paper was evaluated by the method described later. Table 2 shows the amount of dry coating per side of the clear liquid, the physical characteristics of the paper, and the evaluation results.

[Comparative Example 2-1]
Paper was produced and evaluated in the same manner as in Example 2-1 except that CNF-2 was not used as the clearing liquid.

[Examples 2-2 to 2-4, Comparative Examples 2-2, 2-3]
<CNF>
As the CNF, TEMPO oxidized CNF (manufactured by Nippon Paper Industries, Ltd.) having a cellulosic raw material of NBKP, a carboxyl group amount of 1.38 mmol / g, and a high-pressure homogenizer treatment of 4 passes was used. The B-type viscosity of the aqueous dispersion of this CNF (hereinafter, “CNF-5”) was as follows.
Water dispersion with a concentration of 1% (w / v): 5500 mPa · s

Paper was produced and evaluated in the same manner as in Example 2-1 except that CNF-2 was changed to CNF-3 to CNF-7, respectively. Table 2 shows the amount of dry coating per side of the clear liquid of the produced paper, its physical properties, and the evaluation results.

[Example 3-1]
<CNF>
An aqueous dispersion of CNF-2 was obtained in the same manner as in Example 2-1.

<Clear liquid>
Oxidized starch (SK20, manufactured by Japan Corn Starch) was added to the aqueous dispersion of CNF-2 to produce a clear liquid having a starch: CNF-2 weight ratio of 15: 1. Table 3 shows the B-type viscosity of the clear liquid at a solid content concentration of 5% by weight, 30 ° C., and 60 rpm.

<Pigment liquid>
A pigment having a solid content of 60% by weight by adding 2 parts by weight (solid content) of a styrene-butadiene copolymer and 6.7 parts by weight (solid content) of starch to 100 parts by weight of heavy calcium carbonate. The liquid was prepared.

<Paper manufacturing>
0.7% by weight (solid content) sulfuric acid band, 0.30% by weight (solid content) cationized starch, and 0.06% by weight (solid content) wet paper strength improver were added to 100% by weight of LBKP. A raw material slurry having a solid content concentration of 0.7% by weight was prepared. A single-layer base paper layer was produced by a paper machine using the obtained raw material slurry.
The clear liquid was applied onto the base paper layer by a gate roll coater and dried by a conventional method, and further, the pigment solution was applied onto the base paper layer by a blade coater and dried by a conventional method to produce paper. The paper was evaluated by the method described later. Table 3 shows the amount of dry coating per side of the clear liquid and pigment liquid, the physical characteristics of the paper, and the evaluation results.

[Comparative Example 3-1]
Paper was produced and evaluated in the same manner as in Example 3-1 except that CNF-2 was not used as the clearing liquid. Table 3 shows the dry coating amount, physical properties, and evaluation results per side of the clear liquid and pigment liquid of the produced paper.

[Examples 3-2 to 3-4, Comparative Examples 3-2, 3-3]
Paper was produced and evaluated in the same manner as in Example 3-1 except that CNF-2 was changed to CNF-3 to CNF-7, respectively. Table 3 shows the dry coating amount, physical properties, and evaluation results per side of the clear liquid and pigment liquid of the produced paper.

[Example 4-1]
<CNF>
CNF-1 was prepared as CNF.
<Clear liquid>
Oxidized starch (manufactured by Japan Corn Starch, SK20) was added to water to produce a clear liquid. Table 4 shows the B-type viscosity of the clear liquid at a solid content concentration of 5% by weight, 30 ° C., and 60 rpm.
<Pigment liquid>
To 100 parts by weight of heavy calcium carbonate, 2 parts by weight (solid content) of a styrene-butadiene copolymer and 6.7 parts by weight (solid content) of starch were added as binder components, and CNF-1 0.2. A part by weight (solid content) was added to prepare a pigment solution having a solid content of 60% by weight.

<Paper manufacturing>
0.7% by weight (solid content) sulfuric acid band, 0.30% by weight (solid content) cationized starch, and 0.06% by weight (solid content) wet paper strength improver were added to 100% by weight of LBKP. A raw material slurry having a solid content concentration of 0.7% by weight was prepared. A single-layer base paper layer was produced by a paper machine using the obtained raw material slurry.

The clear liquid was applied onto the base paper layer by a gate roll coater and dried by a conventional method, and further, the pigment solution was applied on the base paper layer by a blade coater and dried by a conventional method to produce paper. The paper was evaluated by the method described later. Table 4 shows the amount of dry coating per side of the clear liquid and pigment liquid, the physical characteristics of the paper, and the evaluation results.

[Examples 4-2 to 4-4]
Paper was produced and evaluated in the same manner as in Example 4-1 except that CNF-1 was changed to CNF-3 to CNF-5, respectively. Table 4 shows the dry coating amount, physical properties, and evaluation results per side of the clear liquid and pigment liquid of the produced paper.

[Comparative Example 4-1]
Paper was produced and evaluated in the same manner as in Example 4-1 except that CNF-1 was not used as the pigment solution. Table 4 shows the amount of dry coating per side of the clear liquid and pigment liquid, the physical characteristics of the paper, and the evaluation results.

[Comparative Examples 4-2 and 4-3]
Paper was produced and evaluated in the same manner as in Example 4-1 except that CNF-1 was changed to CNF-6 and CNF-7, respectively. Table 4 shows the dry coating amount, physical properties, and evaluation results per side of the clear liquid and pigment liquid of the produced paper.

[Evaluation method]
(1) Basis weight Measured based on JIS P 8124: 1998.
(2) Paper thickness and density Measured based on JIS P 8118: 2014.
(3) Ash content Measured based on JIS P 8251: 2003.
(4) Tensile strength Measured based on JIS P8113.
(5) Tension stiffness The measurement was performed using a tensile strength measuring machine sEO62 / 064 manufactured by Lorentzen & Wetter.

(6) Blank paper glossiness The measurement was performed based on JIS P8142.
(7) ISO whiteness Based on JIS P 8148, the measurement was carried out with a color difference meter CMS-35SPX manufactured by Murakami Color Co., Ltd. under conditions including ultraviolet light.
(8) ISO opacity Measured based on JIS P 8149: 2000.
(9) Air permeability resistance Measured with a Wangken air permeability tester based on JIS P8117: 2009.

(10) Printing Gloss Using an offset sheet-fed printing press (4 colors) manufactured by Roland Co., Ltd., using offset sheet-fed ink (NEX-M manufactured by Toyo Ink Co., Ltd.) at a printing speed of 8000 sheets / hour. Printing was performed in the order of indigo red (CM) so that the ink inking density was indigo 1.60 and red 1.50. The glossiness of the indigo red (CM) solid printed portion of the obtained printed matter was measured based on JIS P-8142.

(11) Δ Gloss (difference in print glossiness)
The value obtained by subtracting the white paper gloss from the print gloss is defined as Δ gloss (print gloss difference), and if the Δ gloss is 15% or more, the difference in gloss between the printed part and the blank paper part is sufficiently obtained, and the appearance is good. It can be said that it is a good printed matter.
ΔGloss (%) = Print glossiness (%) -Blank paper glossiness (%)

(12) Picking Evaluation Using an offset sheet-fed printing press manufactured by Roland Corporation and LeoX Y manufactured by Toyo Ink Co., Ltd. as ink, indigo (C) solid was printed at a speed of 8000 sheets / hour. The number of picking on the F side and the W side that occurred during printing 10 sheets was measured, and the average value was calculated.

(13) Ink mileage Ink mileage is the number of sheets that can be printed per unit amount of ink. The amount of ink on the paper surface per unit area required to obtain the same print density was defined as the color development property, and this was evaluated as a simple index of ink mileage.
Good ink mileage means good color development with a small amount of ink on the paper surface. Specifically, solid printing is performed using a proof bow test printing machine (IGT), and the print density of the printed matter is measured with a spectrophotometer overnight after printing assuming sheet-fed printing to determine the total density. I read it. The weight difference between the removable print disc before printing and after printing was taken as the amount of ink on the paper surface. The amount of ink applied to the print disc was changed, the relationship between the amount of ink on the paper surface and the print density was obtained, and the amount of ink on the paper surface required to obtain a predetermined density was calculated from the relational expression. The printing pressure at the time of measurement was 700 N, and the printing speed was 2.0 m / s.

It is clear that the paper containing CNF of the present invention is a paper having higher strength.

Claims

Paper containing cellulose nanofibers and pulp.
The cellulose nanofibers have a carboxyl group of 0.9 to 3.0 mmol / g with respect to the absolute dry weight, and when made into an aqueous dispersion having a concentration of 1% (w / v), it exceeds 2500 mPa · s and 7000 mPa. -Paper, which is a cellulose nanofiber that gives a B-type viscosity (60 rpm, 20 ° C.) of s or less.
The paper according to claim 1, wherein the paper includes a single-layer or multi-layer base paper layer, and at least one layer thereof contains the cellulose nanofibers.
The paper according to claim 1 or 2, which has a layer containing the cellulose nanofibers on one side or both sides of the base paper layer.
The paper according to claim 1, wherein the paper includes a base paper layer and a layer containing a binder component, and the layer containing the binder component contains the cellulose nanofibers.
The paper according to claim 4, wherein the layer containing the binder component further contains a white pigment.
The paper according to any one of claims 1 to 5, wherein the cellulose nanofibers have a carboxyl group of 1.2 mmol / g or more with respect to an absolute dry weight.
The paper according to any one of claims 1 to 5, wherein the cellulose nanofibers have a carboxyl group of 1.35 mmol / g or more with respect to an absolute dry weight.
The paper according to any one of claims 1 to 5, wherein the cellulose nanofibers have a carboxyl group of 2.5 mmol / g or less based on an absolute dry weight.
The paper according to any one of claims 1 to 5, wherein the cellulose nanofibers have a carboxyl group of 1.6 mmol / g or less based on an absolute dry weight.
The paper according to any one of claims 1 to 5, wherein the B-type viscosity (60 rpm, 20 ° C.) of the 1% aqueous dispersion has a viscosity of 3000 mPa · s or more.
The paper according to any one of claims 1 to 5, wherein the B-type viscosity (60 rpm, 20 ° C.) of the 1% aqueous dispersion has a viscosity of 6000 mPa · s or less.
The paper according to any one of claims 1 to 11, wherein the cellulose nanofibers have an average fiber diameter of 2 to 30 nm.
The paper manufacturing method according to claim 1.
Cellulose oxidized by oxidizing a cellulosic raw material with an oxidizing agent in the presence of a compound selected from the group consisting of (1) N-oxyl compound and (2) bromide, iodide and a mixture thereof. The process of preparing,
A step of preparing cellulose nanofibers by wet atomizing the oxidized cellulose,
A method for producing paper, comprising a step of preparing a liquid containing the cellulose nanofibers and a step of coating, impregnating or spraying the base paper with the liquid.
The paper manufacturing method according to claim 1.
Cellulose oxidized by oxidizing a cellulosic raw material with an oxidizing agent in the presence of a compound selected from the group consisting of (1) N-oxyl compound and (2) bromide, iodide and a mixture thereof. The process of preparing,
A step of preparing cellulose nanofibers by wet atomizing the oxidized cellulose,
A method for producing paper, comprising a step of preparing a pulp slurry containing pulp and the cellulose nanofibers, and a step of making the pulp slurry.
The production method according to claim 13 or 14, wherein the cellulosic raw material is selected from the group consisting of bleached kraft pulp, bleached sulfite pulp, and cellulose powder.
The N-oxyl compound has the following formulas 2 to 4:

(In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms)
The production method according to any one of claims 13 to 15, which is selected from the 4-hydroxy TEMPO derivatives represented by.
The production method according to any one of claims 13 to 16, wherein the wet atomization treatment comprises defibrating the oxidized cellulose at a pressure of 100 MPa or more using an ultra-high pressure homogenizer.