JP2021161598A - Paper comprising chemically-modified and fibrillated cellulose fiber-containing clear coating layer - Google Patents

Abstract

To provide paper having high print surface strength.SOLUTION: Paper comprises base paper and a clear coating layer, the clear coating layer including starch, chemically-modified and fibrillated cellulose fiber, and metal salt. The starch is preferably oxidized starch.SELECTED DRAWING: None

Description

The present invention relates to a paper comprising a fibrillated, chemically modified cellulose fiber-containing clear coating layer.

Cellulose nanofibers (hereinafter, also referred to as "CNF") are expected as new materials, and various studies have been conducted. Further, as disclosed in Patent Document 1, fibrillated chemically modified cellulose fibers (hereinafter, also referred to as “MFC”), which have a lower degree of defibration than cellulose nanofibers, are also expected as new materials. Various studies have been made.

International Publication No. 2019/189588

Paper is required to have high print surface strength, but Patent Document 1 does not describe this characteristic. In view of such circumstances, it is an object of the present invention to provide a paper having high printing surface strength.

The problem is solved by the following invention.
(1) Paper having a base paper and a clear coating layer.
The clear coating layer contains starch, fibrillated chemically modified cellulose fibers and metal salts.
Paper having a degree of crystallinity of cellulose type I of the fibrillated chemically modified cellulose fiber of 50% or more, a degree of anionization of 0.10 to 2.00 meq / g, and an average fiber diameter of more than 500 nm. ..
(2) The paper according to (1), wherein the starch is oxidized starch.
(3) The paper according to (1) or (2), wherein the metal salt contains a metal element having a divalent value or higher.
(4) The paper according to any one of (1) to (3), further comprising a pigment coating layer.
(5) The paper according to any one of (1) to (4), wherein the fibrillated chemically modified cellulose fiber is anion-modified.
(6) The fibrillated chemically modified cellulose fibers have a carboxyl group of 0.1 to 3.0 mmol / g with respect to the absolute dry weight of the fibrillated chemically modified cellulose fibers (1) to (1). The paper according to any one of 5).
(7) The chemically modified cellulose in the fibrillated chemically modified cellulose fiber is a carboxyalkylated cellulose having a degree of carboxyalkyl substitution per glucose unit of the chemically modified cellulose of 0.01 to 0.50 (1). The paper according to any one of (5).

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a paper having a high printing surface strength.

Hereinafter, the present invention will be described in detail. The paper of the present invention comprises a clear coating layer containing starch, fibrillated chemically modified cellulose fibers (MFC) and a metal salt on one or both sides of the base paper. Further, in the present invention, "X to Y" includes X and Y which are the fractional values thereof.

1. 1. Paper with a clear coating layer containing starch, MFC and metal salts (1) Fibrilized chemically modified cellulose fibers (MFC)
The MFC of the present invention is obtained by defibrating chemically modified cellulose. In chemically modified cellulose, the cellulose chains constituting the fibers are chemically modified. The type of chemically modified cellulose is not limited to these, for example, carboxylated cellulose having a carboxyl group introduced, carboxyalkylated cellulose having an ether bond of a carboxyalkyl group such as a carboxymethyl group, and phosphorus having a phosphate group introduced. Examples thereof include acid esterified cellulose. These manufacturing methods will be described later.

The chemically modified cellulose may take the form of a salt, and in the present invention, the chemically modified cellulose also includes a salt-type chemically modified cellulose. Examples of the salt-type chemically modified cellulose include those forming a metal salt such as a sodium salt.

The chemically modified cellulose retains at least a portion of its fibrous shape when dispersed in water. That is, when the aqueous dispersion of MFC is observed with an electron microscope or the like, a fibrous substance can be observed, and when measured by X-ray diffraction, a peak of cellulose type I crystal can be observed.

MFC is obtained by appropriately beating or defibrating (fibrillating) a chemically modified cellulose raw material using a refiner or the like. MFCs show fluffing of cellulose microfibrils on the fiber surface compared to chemically modified cellulose fibers that have not been beaten or defibrated. Further, as compared with the chemically modified cellulose nanofibers, the fiber diameter is large, and the fiber surface is efficiently fluffed (external fibrillation) while suppressing the miniaturization (internal fibrillation) of the fiber itself.

MFC has features such as high water retention and thixotropy due to chemical modification as compared with non-chemically modified fibrillated cellulose fiber. Further, the MFC obtained by fibrillating the chemically modified cellulose raw material has the cellulose fibers chemically modified at the time of fibrillation as compared with the one obtained by beating the non-chemically modified cellulose raw material and then chemically modifying it. The strong hydrogen bonds existing between the fibers are weakened, and the fibers are easily loosened during fibrillation, and the fibers are less damaged.

The average fiber diameter (average fiber width) of MFC is more than 500 nm, preferably 1 μm or more, and more preferably 10 μm or more. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, still more preferably 20 μm or less. By appropriately fibrillating to the extent that the average fiber diameter falls within this range, it exhibits higher water retention than undefibrated cellulose fibers, and even in a small amount compared to finely defibrated cellulose nanofibers. A high strength-imparting effect and a yield-improving effect can be obtained.

The average fiber length of MFC is preferably 10 μm or more, more preferably 30 μm or more, further preferably 50 μm or more, and may be 100 μm or more, 200 μm or more, or 300 μm or more. The upper limit of the average fiber length is not particularly limited, but is preferably 3000 μm or less, more preferably 1500 μm or less, further preferably 900 μm or less, and even more preferably 500 μm or less. Since the chemically modified cellulose raw material is used for beating or defibration, fibrillation can be promoted without making the fibers extremely short. In addition, since the affinity with water is improved by chemical denaturation, water retention can be increased even when the fiber length is long.

The average fiber diameter and average fiber length can be determined by an image analysis type fiber analyzer such as L & W Fiber Tester Plus manufactured by ABB Ltd. or a fractionator manufactured by Valmet Co., Ltd. Specifically, when a fractionator is used, it can be obtained as length-weighted fiber width and length-weighted average fiber length, respectively.

The aspect ratio of the MFC is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more. The upper limit of the aspect ratio is not particularly limited, but is preferably 1000 or less, more preferably 100 or less, and even more preferably 80 or less. The aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter.

The fibrillation rate of MFC measured using a fractionator manufactured by Valmet Co., Ltd. is preferably 1.0% or more, more preferably 2.5% or more, and more preferably 3.5%. The above is more preferable. The fibrillation rate differs depending on the type of cellulose raw material used, but if it is within the above range, it is considered that fibrillation has been performed. Further, in the present invention, it is preferable to carry out fibrillation so that the fibrillation _{rate (f 0} ) of the chemically modified cellulose raw material before fibrillation is improved. Assuming that the fibrillation rate of MFC is f, the difference Δf = ff ₀ of the fibrillation rate may be more than 0, preferably 0.2% or more, and more preferably 1% or more. More preferably, it is 2.5% or more.

The amount of carboxyl groups in the MFC is preferably 0.1 mmol / g or more, more preferably 0.6 mmol / g or more, still more preferably 1.0 mmol / g or more, based on the absolute dry weight of the MFC. The upper limit of the amount is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and even more preferably 2.0 mmol / g or less. Therefore, the amount is preferably 0.1 to 3.0 mmol / g, more preferably 0.6 to 2.5 mmol / g, and even more preferably 1.0 to 2.0 mmol / g.

The chemically modified cellulose in MFC is preferably carboxyalkylated cellulose having a degree of carboxyalkyl substitution per glucose unit of the chemically modified cellulose of 0.01 to 0.50. The upper limit of the degree of substitution is preferably 0.40 or less. If the degree of carboxyalkyl substitution exceeds 0.50, dissolution in water tends to occur, and the fiber morphology may not be maintained in water. Further, in order to obtain the effect of carboxyalkylation, it is necessary to have a certain degree of substitution. For example, if the degree of substitution is less than 0.02, it is due to the introduction of a carboxyalkyl group depending on the application. You may not get the benefit. Therefore, the degree of carboxyalkyl substitution is preferably 0.02 or more, more preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.15 or more. , 0.20 or more, more preferably 0.25 or more. The carboxyalkyl substitution is preferably a carboxymethyl substitution.

<Crystallinity of cellulose type I>
The crystallinity of cellulose in MFC is 50% or more, preferably 60% or more for crystal type I. The crystallinity of cellulose can be controlled by the degree of chemical denaturation. 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 MFC 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 = (I002c-Ia) / I002c × 100
Xc = Cellulose type I crystallinity (%)
I002c: 2θ = 22.6 °, diffraction intensity of 002 surface Ia: 2θ = 18.5 °, diffraction intensity of amorphous part.

<Degree of anionization>
The degree of anionization of MFC (also referred to as "anion charge density") is 0.10 to 2.00 meq / g. The method for measuring the degree of anionization is as follows:
The MFC is dispersed in water to prepare an aqueous dispersion having a solid content of 10 g / L, and the mixture is stirred with a magnetic stirrer at 1000 rpm for 10 minutes or more. After diluting the obtained slurry to 0.1 g / L, 10 mL was collected, titrated with 1/1000 normal diallyldimethylammonium chloride (DADMAC) using a flow current detector (Mutek Particle Charge Detector 03), and flowed. Using the amount of DADMAC added until the current becomes zero, calculate the degree of anionization by the following formula:
q = (V × c) / m
q: Degree of anionization (meq / g)
V: Addition amount (L) of DADMAC until the flow current becomes zero
c: DADMAC concentration (meq / L)
m: Weight (g) of MFC in the measurement sample.

In the present invention, as can be seen from the above measurement method, the "degree of anionization" corresponds to the equivalent amount of DADMAC required to neutralize an anionic group in a unit weight of MFC, and per unit weight of MFC. Corresponds to the equivalent of the anion of.

The degree of anionization of MFC is preferably 1.50 meq / g or less, more preferably 1.30 meq / g or less, further preferably 1.00 meq / g or less, still more preferably 0.80 meq / g or less. It is considered that the chemical denaturation of the MFC having such a range of anionization degree is not local but uniform throughout the cellulose as compared with the MFC having a higher anionization degree, and the effect peculiar to MFC is achieved. For example, it is considered that water retention and the like can be obtained more stably.

<Water retention capacity>
The water retention capacity of MFC measured by the following method is preferably 15 or more. The method for measuring water retention capacity is as follows:
Prepare 40 mL of a slurry (medium: water) having a solid content of 0.3% by weight of MFC. Let A be the weight of the slurry at this time. Then, the entire amount of the slurry is centrifuged at 25,000 G for 30 minutes at 30 ° C. using a high-speed cooling centrifuge to separate the aqueous phase and the sediment. Let B be the weight of the sediment at this time. Further, the aqueous phase is placed in an aluminum cup and dried at 105 ° C. for 24 hours to remove water, and the weight of the solid content in the aqueous phase is measured. Let C be the weight of the solid content in this aqueous phase. The water retention capacity is calculated using the following formula.
Water retention capacity = (B + C-0.003 × A) / (0.003 × AC).

As described in the above formula, the water retention capacity corresponds to the weight of water in the sediment with respect to the weight of the solid content of the fibers in the sediment. The higher the value, the higher the ability of the fiber to retain water. The water retention capacity of the MFC of the present invention is preferably 15 or more, more preferably 20 or more, and further preferably 30 or more. The upper limit is not particularly limited, but in reality, it is considered to be about 200 or less.

The above method for measuring water retention capacity is applied to fibrillated fibers, and is not usually applicable to fibers that have not been fibrillated or defibrated, or cellulose nanofibers that have been defibrated to single microfibrils. When the water retention capacity of unfibrillated or defibrated cellulose fibers is measured by the above-mentioned method, a dense sediment cannot be formed under the above-mentioned centrifugation conditions, and the sediment and the aqueous phase may be separated. Have difficulty. In addition, the cellulose nanofibers hardly settle under the above-mentioned centrifugation conditions.

<Viscosity>
The MFC of the present invention preferably exhibits a relatively low viscosity when water is used as a dispersion medium as a dispersion (aqueous dispersion). As a result, the material has good handleability even though it is made into fibril. In the present invention, the method for measuring viscosity is as follows:
The MFC is weighed in a polypropylene container and dispersed in 160 mL of ion-exchanged water to prepare an aqueous dispersion having a solid content of 1% by weight. After adjusting the temperature of the aqueous dispersion to 25 ° C, measure the viscosity after 1 minute at a rotation speed of 60 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) according to the method of JIS-Z-8803. do.

The viscosity (25 ° C., 60 rpm) of the MFC of the present invention is preferably 10000 mPa · s or less. The lower limit is preferably 10 mPa · s or more, more preferably 20 mPa · s or more, further preferably 50 mPa · s or more, and the upper limit value is more preferably 7,000 mPa · s or less.

<Others>
The MFC of the present invention preferably has an electrical conductivity of 500 mS / m or less when made into an aqueous dispersion having a solid content concentration of 1.0% by weight. The electrical conductivity is more preferably 300 mS / m or less, further preferably 200 mS / m or less, even more preferably 100 mS / m or less, and particularly preferably 70 mS / m or less. The lower limit of the electric conductivity is preferably 5 mS / m or more, and more preferably 10 mS / m or more. The method for measuring electrical conductivity is as follows:
Prepare 200 g of an aqueous dispersion having a solid content concentration of MFC of 1.0% by weight, and stir well. Then, the electric conductivity is measured using an electric conductivity meter (ES-71 type manufactured by HORIBA).

The BET specific surface area of the MFC of the present invention is preferably 30 m ² / g or more, more preferably 50 m ² / g or more, and further preferably 100 m ² / g or more. When the BET specific surface area is high, for example, when it is used as an additive for papermaking, it easily binds to pulp, which has advantages such as an improvement in yield and an enhancement in the effect of imparting strength to paper. The BET specific surface area can be measured by the following method with reference to the nitrogen gas adsorption method (JISZ8830).
(1) About 2% slurry of MFC (dispersion medium: water) is separately placed in a centrifuge container so that the solid content becomes about 0.1 g, and 100 mL of ethanol is added.
(2) Add a stirrer and stir at 500 rpm for 30 minutes or more.
(3) The stirrer is taken out, and the MFC is settled in a centrifuge under the conditions of 7000 G, 30 minutes, and 30 ° C.
(4) Remove the supernatant while trying not to remove the MFC as much as possible.
(5) Add 100 mL of ethanol, add a stirrer, stir under the condition of (2), take out the stirrer, centrifuge under the condition of (3), remove the supernatant under the condition of (4), and remove this. Repeat once.
(6) The solvent of (5) is changed from ethanol to t-butanol, and stirring, centrifugation, and removal of the supernatant are repeated three times in the same manner as in (5) at room temperature equal to or higher than the melting point of t-butanol.
(7) After the final removal of the solvent, 30 mL of t-butanol is added, mixed lightly, transferred to an eggplant flask, and frozen using an ice bath.
(8) Cool in the freezer for 30 minutes or more.
(9) Attach to a freeze-dryer and freeze-dry for 3 days.
(10) BET measurement is performed (pretreatment conditions: 105 ° C. for 2 hours under a nitrogen stream, relative pressure 0.01 to 0.30, sample volume of about 30 mg).

The shopper-rigra freeness of the MFC of the present invention is not particularly limited, but is preferably 1 ° SR or higher. The method for measuring the freeness of shopper / leaguer is based on JIS P8211-1: 2012, and specifically, it is as follows:
MFC is dispersed in water to prepare an aqueous dispersion having a solid content of 10 g / L, a stirrer is added, and the mixture is stirred at 1000 rpm for 10 minutes or more. The resulting slurry is diluted to 2 g / L. A 60 mesh screen (wire thickness 0.17 mm) is set on DFR-04 manufactured by Mutec, and the amount of liquid passing through the mesh is measured for 60 seconds from 1000 ml of the test solution, and conforms to JIS P8121-1: 2012. Calculate the Shopper-Regula free water content by the above method.

The shopper-ligler filtrate is an index of the degree of drainage of the fiber suspension, the lower limit is 0 ° SR, the upper limit is 100 ° SR, and the shopper-ligra filtrate approaches 100 ° SR. The more the water runs out (the amount of drainage), the less the water runs out.

The lower limit of the shopper-rigra freeness of the MFC of the present invention is not particularly limited, but is preferably 1 ° SR or higher, more preferably 10 ° SR or higher, more preferably 25 ° SR or higher, and more. It is preferably 40 ° SR or higher, and more preferably 50 ° SR or higher. The upper limit is not particularly limited and is 100 ° SR or less.

The MFC of the present invention preferably has a transparency (transmittance of 660 nm light) of an aqueous dispersion having a solid content concentration of 1.0% by weight of less than 60%, more preferably 40% or less. , 30% or less, more preferably 20% or less, and particularly preferably 10% or less. The lower limit is not particularly limited and may be 0% or more. When the transparency is in such a range, the degree of fibrillation is appropriate, and the effect of the present invention can be easily obtained. Transparency can be measured by the following method.

An aqueous dispersion of MFC (solid content concentration 1.0% (w / v), dispersion medium: water) was prepared, and a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) was used to obtain an optical path length of 10 mm. The transmittance of light having a wavelength of 660 nm is measured using a square cell.

When water is used as a dispersion medium, the MFC of the present invention has a solid content concentration of about 2% by weight or more and becomes a translucent to white gel, cream or paste. The MFC 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 stretching and drying on a glass plate, a fluidized bed drying method, a microwave drying method, etc. , Known methods such as a 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.

<Manufacturing method of MFC>
The MFC of the present invention can be produced by first preparing a chemically modified cellulose raw material and then fibrillating it. As described above, examples of the type of chemical modification include, but are not limited to, carboxylation, carboxyalkylation, and phosphoric acid esterification of cellulose. As the chemically modified cellulose raw material to be subjected to fibrillation, a commercially available one may be used, or for example, it may be produced by chemically modifying cellulose described later.

1) Cellulose The cellulose used as a raw material for MFC is not particularly limited, and examples thereof include those derived from plants, animals (for example, ascidians), algae, microorganisms (for example, acetobacter), and microbial products. Be done. Plant-derived materials include, for example, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleached kraft pulp (NBKP), broadleaf unbleached kraft pulp (NBKP). LUKP), hardwood bleached kraft pulp (LBKP), coniferous unbleached sulphite pulp (NUSP), coniferous bleached sulphite pulp (NBSP), thermomechanical pulp (TMP), coniferous melted pulp, broadleaf tree melted pulp, recycled pulp, waste paper pulp Etc.). Moreover, you may use the cellulose powder which pulverized the above-mentioned cellulose. Any one or a combination of these may be used as the cellulose, but it is preferably a cellulose derived from a plant or a microorganism, more preferably a cellulose derived from a plant, and further preferably a pulp derived from a plant.

In the present invention, in order to maintain the crystallinity of cellulose I type in MFC of 50% or more, it is preferable to use cellulose having a high crystallinity of cellulose I type as a raw material. The crystallinity of cellulose type I of cellulose is preferably 70% or more, and more preferably 80% or more. The method for measuring the crystallinity of cellulose type I is as described above.

2) Chemical denaturation Chemical denaturation refers to the introduction of a functional group into cellulose, and it is preferable to introduce an anionic group. Examples of the anionic group include an acid group such as a carboxyl group, a carboxyl group-containing group, a phosphoric acid group, and a phosphoric acid group-containing group. Examples of the carboxyl group-containing group include -R-COOH (R is an alkylene group having 1 to 3 carbon atoms) and -OR-COOH (R is an alkylene group having 1 to 3 carbon atoms). Examples of the phosphoric acid group-containing group include a polyphosphoric acid group, a phosphorous acid group, a phosphonic acid group, and a polyphosphonic acid group. Depending on the reaction conditions, these acid groups may be introduced in the form of salts (for example, carboxylate groups (-COOM, M is a metal atom)). The chemical denaturation is preferably oxidation or etherification. Oxidation or etherification can be carried out according to a known method such as that described in JP-A-2019-104833 and the like. Further, the amount of carboxyl groups of MFC and the degree of carboxymethyl substitution per glucose unit of chemically modified cellulose can also be measured according to a known method as described in, for example, Japanese Patent Application Laid-Open No. 2019-104833.

3) Fibrilization MFC is obtained by defibrating or beating a chemically modified cellulose raw material. For defibration or beating in fibrillation, a refiner such as a disc type, conical type, cylinder type, etc., a high-speed defibrator, a shear type agitator, a colloid mill, a high-pressure injection disperser, a beater, a PFI mill, a kneader, a disperser, etc. are used. It is preferable to carry out the process wet (that is, in the form of a dispersion using water or the like as a dispersion medium), but the device is not particularly limited to these devices, and any device that imparts mechanical defibration force by wet method will be used. It may be.

In the present invention, it is obtained by treating chemically modified cellulose as a raw material into fibrils using a double disc refiner (sometimes abbreviated as "DDR") which is a kind of disc type refiner (disc refiner). It is preferable to use the DDR-treated MFC that is used. Since the DDR-treated MFC is becoming more fibrilized, the paper containing the DDR-treated MFC in the clear coating layer exhibits high print surface strength. The process performed by the apparatus may be a beating process or a defibration process, preferably a beating process.

<Disc refiner>
A disc refiner is a disk with a beating blade (a disc plate (sometimes referred to simply as a "disc") facing each other at a close distance, and only one or both of them face each other at a predetermined number of revolutions in opposite directions. A device that rotates and gives the effect of pressure beating and the effect of continuous delivery by centrifugal force to the slurry passing between them. Of the disc refiners, those having two beating gaps formed by the disc plate are called double disc refiners (sometimes abbreviated as "DDR").

<Double Disc Refiner>
The double disc refiner is provided with two discs DA and DB and a disc DM between them, and one of the DA and DB or DM is fixed and the other is rotated, or the DA, DB and DM are reversed. It has a configuration that rotates in the direction. As a double disc refiner, two discs DA and DB are fixed discs, and DM is a floating disc that rotates freely between them. For example, a double disc refiner manufactured by Aikawa Iron Works, Ltd., Mitsubishi. Examples include double disc refiners made by Heavy Industries / Beloit (Jones), twin hydra discs made by Ishikawajima Sangyo Kikai / Black Clawson, and twin disc refiners made by Hitachi Zosen (Hitachi Zosen Tomioka Machinery) / Escher Wyss.

In this embodiment, the beating process using the double disc refiner may be a cyclic process, or the beating process using a plurality of double disc refiners may be continuously performed as a continuous process. The number of beat processing passes when the beating process using the double disc refiner is a cyclic process or a continuous process is not limited as long as the desired MFC can be obtained, but from the viewpoint of productivity and excessive shortening and processing of fibers. From the viewpoint of suppressing deterioration due to heat generated from time to time, 30 times or less is preferable, 20 times or less is more preferable, 10 times or less is further preferable, and 5 times or less is further preferable.

The number of passes of the beating process in the case where the beating process is a cyclic process and the partial circulation is used is obtained by multiplying the number of times the raw material to be processed passed through one double disc refiner and recovered by the following n. Let it be a number.
n = 1 / (1-a)
Here, a = circulation ratio. (When the circulation rate is 50%, a = 0.5, and when the circulation rate is 75%, a = 0.75)

The number of passes for beating processing in the case of continuous processing using a plurality of double disc refiners that perform partial circulation is calculated by the above method for each refiner and added up.

When the beating process is a circulation process and the batch processing is performed by complete circulation, the number of passes of the beating process is the number of times the raw material to be processed has passed through the double disc refiner before being recovered.

When the beating process is a continuous process using a plurality of double disc refiners, the number of passes of the beating process is added once each time the raw material to be processed passes through one double disc refiner.

The blade widths of the two discs DA and DB are preferably 0.3 to 1.5 mm, more preferably 0.5 to 1.3 mm. The groove widths of DA and DB are preferably 0.5 to 2.0 mm, more preferably 0.8 to 1.7 mm. The blade width and groove width of DA and DB may be the same or different. The blade angle is not particularly limited, but is preferably 0 to 40 °, particularly preferably 5 to 20 °.

Double disc refiners are roughly classified into two types, monoflow type and duoflow type, depending on the raw material flow method. The monoflow method is a method in which the raw material flows from the beating gap near the raw material inflow side to the other beating gap, and the duoflow type is a method in which the raw material is inserted from the center and the beating gap formed on both sides of the DM is formed. It is a method that flows in parallel. In the production method of the present invention, a monoflow method is preferable as a raw material flow method from the viewpoint of efficient defibration.

In one aspect, the double disc refiner has a raw material inlet, a beating chamber for beating the pulp raw material input from the inlet, and a rotating disc DM arranged in the chamber, and predetermined blades are provided on both sides of the rotating disc DM. A blade with width and groove width is attached. On the inner wall of the beating chamber, a fixed disk DA and a fixed disk DB are arranged so as to face the blades attached to both sides of the rotating disk DM. A blade having a predetermined blade width and groove width is attached to the fixed disc DA and the fixed disc DB. The rotary disc DM is attached to a drive shaft, and the drive shaft is connected to a motor and is rotationally driven. The beating chamber is provided with a circulation pipe for circulating the beaten raw material to the beating chamber, a discharge port for discharging the beaten raw material to the outside of the beating chamber, and an outlet pipe for sending the beaten raw material from the discharge port to the collection tank. ing. The flow rate of the circulation pipe and the outlet pipe is adjusted by a manual valve.

When the raw material flow method is a monoflow method, of the two discs DA and DB, the blade width (X1) of DA, which is the first disc, and DB, which is the second disc, counting from the raw material inlet side. There are the following merits depending on the relationship of the blade width (X2).
X1 = X2: The fiber width and fiber length of the obtained MFC can be easily matched.
X1> X2: Since the raw material is beaten on a wide blade to be fibrillated and then beaten by a narrow blade to proceed with cutting, it becomes difficult for the raw material to pass through undefibrated fibers.
X1 <X2: Since the raw material is beaten by a narrow blade to advance cutting, and then beaten on a wide blade to promote fibrillation, it is easy to obtain fine fibers with advanced fibrillation.

When the raw material flow method is a monoflow method, of the two discs DA and DB, the groove width (Y1) of DA, which is the first disc counting from the raw material inlet side, and the second disc are used. Depending on the relationship of the groove width (Y2) of a certain DB, there are the following merits.
Y1 = Y2: The fiber width and fiber length of the obtained MFC can be easily matched.
Y1> Y2: Since the raw material passes through the narrow beating gap after passing through the wide beating gap, it is difficult to apply an excessive load and is suitable for processing a material having a high viscosity.
Y1 <Y2: When first passing through a narrow beating gap, defibration proceeds and the viscosity tends to increase, but the next wide beating gap is passed, and the raw material can pass without delay.

As the operating conditions of the double disc refiner, the clearance between DA and DM and DB and DM is preferably 0.6 mm or less, more preferably 0.4 mm or less, and further preferably 0.2 mm or less. The lower limit is not limited, but 0.02 mm or more is preferable in order to avoid metal touch. The operating temperature is preferably 5 to 120 ° C. The flow rate, treatment time, other conditions, etc. are appropriately adjusted so that chemically modified microfibril cellulose fibers having a desired fiber width can be obtained.

The chemically modified cellulose is subjected to a beating treatment step as an aqueous dispersion, and the solid content concentration at that time is usually 15% by weight or less, preferably 0.3 to 10% by weight, and 0. More preferably, 5 to 6% by weight. If the solid content concentration is too low, it is difficult to come into contact with the blade of the plate during beating, and the beating efficiency is lowered. The solid content concentration may fluctuate during the mechanical treatment including the beating treatment, but in the present invention, the solid content concentration at the start of the beating treatment is referred to as the solid content concentration in the beating treatment step.

Dilution can be mentioned as a method for adjusting the solid content concentration of the chemically modified pulp to 15% by weight or less.

Before and after the beating process using the double disc refiner, one or more mechanical process steps for performing the mechanical process using an apparatus other than the double disc refiner may be provided. Further, before and after the beating treatment step, a mechanical treatment step of mechanically treating the aqueous dispersion of chemically modified cellulose having a solid content concentration of more than 15% by weight may be provided.

The mechanical treatment refers to mixing fibers and further making them finer or fibrillated, and includes beating, defibration, dispersion, kneading and the like. Here, the mechanical treatment under the condition that the solid content concentration is higher than 15% by weight is sometimes referred to as "high-concentration mechanical treatment", and particularly when the mechanical treatment is beating, it is also referred to as "high-concentration beating". Similarly, mechanical treatment under the condition of solid content concentration of 15% by weight or less may be referred to as "low concentration mechanical treatment", and particularly when the mechanical treatment is beating, it is also referred to as "low concentration beating". In the present invention, it is preferable to perform the beating treatment step at a solid content concentration of 15% by weight or less using a double disc refiner at least once, and in that case, the mechanical treatment may be carried out a plurality of times.

The mechanical processing may be a circulation operation (batch processing), a partial circulation operation, or a continuous processing in which mechanical processing using a plurality of devices is continuously performed. High-concentration mechanical treatment and low-concentration mechanical treatment may be performed in combination, and when these mechanical treatments are combined, the order of treatment is not limited, but high-concentration mechanical treatment is performed from the viewpoint of ease of concentration. It is preferable to perform the treatment first. For example, after a high-concentration mechanical treatment of chemically modified cellulose, the chemically modified cellulose obtained by the treatment is diluted to 15% by weight or less and subjected to beating treatment using a double discifier to obtain MFC. May be good.

Examples of devices that can be used for low-concentration mechanical processing include high-speed rotary type, colloidal mill type, high-pressure type, roll mill type, ultrasonic type, etc., and include high-pressure or ultra-high pressure homogenizers and conical refiners. Refiners, beaters, PFI mills, kneaders, dispersers, top finers, seven finers, beat finers, twin beat finers, henschel mixers, homomic line mills, etc. Alternatively, those due to friction between pulp fibers, or those in which pulp fibers are dispersed or defibrated by cavitation, water flow or water pressure can be used.

Devices that can be used for high-concentration mechanical processing include, for example, high-speed rotary type, colloidal mill type, high pressure type, roll mill type, ultrasonic type, etc., and include high-pressure or ultra-high pressure homogenizers, refiners, and the like. A beater, a PFI mill, a kneader, a disperser, a top finer, or the like in which a metal or a blade and a pulp fiber act on each other around a rotation axis, or one by friction between pulp fibers can be used.

The preferred average fiber diameter (average fiber width) of the DDR-treated MFC is as described above. The average fiber length of the DDR-treated MFC is preferably 10 μm or more, more preferably 30 μm or more, further preferably 50 μm or more, and may be 100 μm or more, 200 μm or more, or 300 μm or more. The upper limit of the average fiber length is not particularly limited, but is preferably 3000 μm or less, more preferably 1500 μm or less, further preferably 900 μm or less, and even more preferably 500 μm or less. Since the chemically modified cellulose raw material is treated with a double disc refiner, fibrillation can be promoted without extremely shortening the fibers. In addition, since the affinity with water is improved by chemical denaturation, water retention can be increased even when the fiber length is long.

The solid content concentration of the raw material in the dispersion of the chemically modified cellulose raw material to be subjected to fibrillation is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, still more preferably 1.0% by weight or more. 2.0% by weight or more is more preferable. The upper limit of the concentration is preferably 40% by weight or less, more preferably 30% by weight or less.

The chemically modified cellulose raw material obtained by the above method may be pre-dried and pulverized before preparing the dispersion for fibrillation. Next, the dry-pulverized chemically modified cellulose raw material may be dispersed in a dispersion medium and subjected to fibrillation (wet). The apparatus used for dry pulverization of raw materials is not particularly limited, and examples thereof include impact mills such as hammer mills and pin mills, medium mills such as ball mills and tower mills, and jet mills.

As described above, the fibrillation is carried out in a range in which the average fiber diameter is maintained over 500 nm, preferably 1 μm or more, and more preferably 10 μm or more. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, still more preferably 20 μm or less. By appropriately fibrillating to the extent that the average fiber diameter falls within this range, it exhibits higher water retention than undefibrated cellulose fibers, and even in a small amount compared to finely defibrated cellulose nanofibers. A high strength-imparting effect and a yield-improving effect can be obtained.

Further, as described above, it is preferable to carry out fibrillation so that the fibrillation _{rate (f 0} ) of the chemically modified cellulose raw material before fibrillation is improved. Assuming that the fibrillation rate of MFC is f, the difference Δf = ff ₀ of the fibrillation rate may be more than 0, preferably 0.2% or more, and more preferably 1% or more. More preferably, it is 2.5% or more. The fibrillation rate can be measured using a fractionator manufactured by Valmet Co., Ltd.

(2) Starch Starch is a polymer of D-glucose, preferably a mixture of amylose and amylopectin. In this embodiment, the starch also includes a polymer compound derived from starch. Examples of the polymer include those obtained by modifying, modifying, or processing starch. In the present invention, oxidized starch in which an anionic group is introduced by an oxidation reaction is preferable. Examples of the anionic group include a carboxyl group.

Oxidized starch is a white powder or granules that are insoluble in cold water. Unless the oxidation level is very low, the aqueous suspension lowers the gelatinization start temperature as the oxidation level increases, forming a low-viscosity transparent paste liquid. Oxidized starch is usually a wet or dry reaction by oxidizing the starch with an oxidizing agent such as hypochlorite (preferably Na salt), bleaching powder, hydrogen peroxide, potassium permanganate, or ozone. Manufactured. Although it depends on the oxidation conditions, the oxidized starch usually has a carboxy group and a carbonyl group, and has a structure in which the glycosidic bond is cleaved.

(3) Metal salt The metal salt that can be used in this embodiment is not limited, and examples thereof include magnesium salt, calcium salt, aluminum salt, sodium salt, and potassium salt. Among them, metal salts containing divalent or higher metal elements such as magnesium salt, calcium salt, and aluminum salt form a chelate with an anionic group present in CNF or starch, and the strength of the coating film is improved. Therefore, it is preferable. Further, the counter ion is also not limited, but from the viewpoint of easy availability, water solubility, and the metal element ionized in water easily forms the chelate, a sulfate ion other than the organic acid ion is preferable. Examples thereof include inorganic acid ions such as ions, chloride ions, nitrate ions and carbonate ions, and hydroxide ions. Therefore, specific examples of preferable metal salts include aluminum sulfate (sulfate band), magnesium sulfate, calcium chloride, magnesium chloride, aluminum chloride and the like.

(4) Base paper The base paper is a base layer of paper and contains pulp as a main component. The pulp raw material of the base paper is not particularly limited, and mechanical pulp such as ground pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), deinked pulp (DIP), coniferous kraft pulp (NKP), and coniferous tree. Chemical pulp such as kraft pulp (LKP) can be used. As the deinked (waste paper) pulp, selected waste paper such as high-quality paper, medium-quality paper, low-grade paper, newspaper, leaflets, and magazines, and unsorted waste paper obtained by mixing these can be used.

A known filler can be added to the base paper, but it is not necessary to add the filler when using paperboard or other applications where opacity or whiteness is not required, or when using raw materials with a large amount of brought-in ash such as used paper. When a filler is added, the filler includes heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica complex, kaolin, calcined kaolin, deramikaolin, magnesium carbonate, barium carbonate, barium sulfate, hydroxide. Inorganic fillers such as amorphous silica produced by neutralizing aluminum, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, and sodium silicate with mineral acid, urea-formalin resin, and melamine. Examples include organic fillers such as resins, polystyrene resins, and phenolic resins. These may be used alone or in combination. Among these, calcium carbonate and light calcium carbonate, which are typical fillers for neutral papermaking and alkaline papermaking and can obtain high opacity, are preferable. The content of the filler in the base paper is preferably 5 to 25% by weight, more preferably 6 to 20% by weight, based on the weight of the base paper. In the present invention, even if the ash content in the paper is high, the decrease in paper strength is suppressed, so that the content of the filler in the base paper is more preferably 10% by weight or more.

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

The base paper is produced by a known papermaking method. For example, it can be performed using a long net paper machine, a gap former type paper machine, a hybrid former type paper machine, an on-top former type paper machine, a round net paper machine, and the like, but the present invention is not limited thereto.

The base paper may be single-layer or multi-layer. The base paper may contain the MFC. In the case of the multilayer base paper, some of the plurality of paper layers may contain MFC, or all layers may contain MFC. When the base paper contains MFC, the content thereof is preferably 0.0001% by weight or more, more preferably 0.0003% by weight or more, still more preferably 0.001% by weight or more, based on the total pulp weight of the base paper.

(5) Clear coating layer The starch: MFC (weight ratio) in the clear coating layer is preferably 1000: 1 to 20: 1, more preferably 350: 1 to 30: 1, and even more preferably 300. : 1 to 50: 1. The amount of the metal salt is preferably 0.05 to 1 part by weight, more preferably 0.1 to 0.5 parts by weight, based on 100 parts by weight of starch. When the weight ratio of each component is in this range, the film-forming property of the clear coating layer mainly composed of starch is improved, and as a result, high print surface strength can be achieved.

The coating amount of the clear coating layer is preferably 0.01~3.0g / ^{m 2} in terms of solid per side content, and more preferably 0.1 to 2.0 g / ^{m 2.} For clear coating, for example, a coater (coating machine) such as a size press, a gate roll coater, a pre-metering size press, a curtain coater, or a spray coater is used, and a clear coating liquid containing starch as a main component is used as a base paper. It can be formed by coating on top. As an example, when coating with a gate roll coater, the clear coating liquid has a B-type viscosity (30 ° C., 60 rpm) of 5 to 450 mPa · s when the solid content concentration is 5% by weight from the viewpoint of coating suitability. Is preferable, and 10 to 300 mPa · s is more preferable. When coating with a gate roll coater, if the B-type viscosity of the clear coating liquid is less than 5 mPa · s, the viscosity is too low and it is difficult to secure the coating amount, and if it exceeds 450 mPa · s, boiling occurs. Operability may deteriorate. The solid content concentration of the clear coating liquid is adjusted so as to achieve the above concentration, but is preferably 2 to 14% by weight.

The amount of MFC derived from the clear coating layer is preferably 1.0 × 10 ^{-5 to} 0.1 g / m ² per side, more preferably 1.0 × 10 ^{-4 to} 5.0 × 10 ^-2 g. / M ² .

(6) Pigment coating layer The paper in this embodiment may include a 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. Examples of calcium carbonate include light calcium carbonate and heavy calcium carbonate.

The pigment coating layer contains an adhesive. Examples of the adhesive include proteins such as starch, casein, soybean protein, and synthetic protein, polyvinyl alcohol, cellulose derivatives such as carboxymethyl cellulose and methyl cellulose, styrene-butadiene copolymer, and conjugated diene of methyl methacrylate-butadiene copolymer. Examples thereof include a system polymer latex, an acrylic polymer latex, and a vinyl polymer latex such as an ethylene-vinyl acetate copolymer. These can be used alone or in combination of two or more, and it is preferable to use a starch-based adhesive and a styrene-butadiene copolymer in combination.

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

The pigment coating layer can be provided by applying a coating liquid to one side or both sides of the base paper by a known method. The solid content concentration in the coating liquid is preferably about 30 to 70% by weight from the viewpoint of coating suitability. The pigment coating layer may be one layer, two layers, or three or more layers. 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.

When the paper in this embodiment further has a pigment-coated layer, it is possible to obtain a pigment-coated paper having excellent surface strength and print glossiness in addition to high ink mileage.

(7) Characteristics The paper of this embodiment has high printing surface strength. The reason for this is not limited, but it is presumed that functional groups such as COOH groups in starch and MFC form a crosslinked structure with metal ions to improve the strength of the clear coating layer. The basis weight of the paper of this embodiment measured according to JIS P 8124 is usually ^{about 20} to 500 g / m 2, preferably 30 to 250 g / m ² .

(8) Method for producing paper of this embodiment The paper of this embodiment is produced through a step of applying a clear coating liquid containing starch, MFC and a metal salt on a base paper prepared by a known method. Is preferable. Specifically, the paper of this embodiment is preferably produced by a method including the following steps.
Step 1: A step of preparing a clear coating liquid containing starch, MFC, and a metal salt Step 2: A step of forming a clear coating layer on a base paper using the clear coating liquid.

The starch, MFC, and metal salt used in step 1 are as described above. The method for preparing the coating liquid and its characteristics are also as described above. The coating in step 2 can also be carried out as described above. Step 1 preferably includes the following steps.
Step 1A: Step of preparing a mixed solution containing starch and MFC Step 1B: Step of preparing a clear coating solution containing the mixed solution and a metal salt The starch in Step 1A is preferably steamed starch. Further, step 1A may be prepared by adding starch to the aqueous dispersion of MFC. In this case, starch can be added to the aqueous dispersion of MFC, and the solution can be steamed to prepare a mixed solution. In the clear coating liquid prepared in this way, starch and MFC are uniformly dispersed.

The paper of this embodiment may be produced by a method including the following steps 3 in addition to the above-mentioned steps 1 and 2.
Step 3: A step of forming a pigment coating layer containing a pigment and an adhesive on a clear coating layer containing starch, MFC and a metal salt. Step 3 can be carried out by a known method.

[Example 1]
To a biaxial kneader whose rotation speed was adjusted to 100 rpm, 130 parts by weight of water and 20 parts by weight of sodium hydroxide dissolved in 100 parts by weight of water were added, and hardwood bleached kraft pulp (manufactured by Nippon Paper Industries, Ltd., LBKP) was added. ) Was dried at 100 ° C. for 60 minutes, and 100 parts by weight was charged.

The contents were stirred and mixed at 30 ° C. for 90 minutes to prepare a mercerized cellulose raw material. Further, 100 parts by weight of isopropanol (IPA) and 60 parts by weight of sodium monochloroacetate were added with stirring, and after stirring for 30 minutes, the temperature was raised to 70 ° C. and a carboxymethylation reaction was carried out for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction was 30%.

After completion of the reaction, neutralize with acetic acid to a pH of about 7, and carboxymethylated cellulose raw material (sodium) having a degree of carboxymethyl substitution per glucose unit of chemically modified cellulose of 0.21 and a degree of crystallinity of cellulose type I of 72%. Salt) was obtained. The method for measuring the crystallinity of cellulose type I is as described above. The degree of carboxymethyl substitution per glucose unit of chemically modified cellulose was measured according to the known method described above.

An aqueous dispersion having a solid content concentration of 2% by weight of the obtained carboxymethylated cellulose raw material was prepared and treated with a top finer manufactured by Aikawa Iron Works Co., Ltd. for 10 minutes to make fibrillated carboxymethylated cellulose fibers. (CM-MFC) was prepared.

<Clear coating liquid 1>
Oxidized starch (manufactured by Japan Corn Starch, SK20) and aluminum sulfate (aluminum sulfate band) are added to the aqueous dispersion of CM-MFC produced as described above, and the weight ratio of starch: CM-MFC: metal salt is 100: A clear coating liquid 1 having a ratio of 0.33: 0.33 was produced. Table 1 shows the B-type viscosities at 30 ° C. and 60 rpm when the solid content concentration of the clear coating liquid 1 was 5% by weight.

<Pigment coating liquid>
To 100 parts by weight of heavy calcium carbonate, 2.0 parts by weight of latex and 6.7 parts by weight of oxidized starch were added as adhesives to prepare a pigment coating liquid having a solid content of 60% by weight.

<Paper>
To LBKP (manufactured by Nippon Paper Industries, Ltd., csf 360 ml), 0.5% by weight of sulfuric acid band, 0.77% by weight of cationized starch, and 0.05% by weight of paper strength agent were added. A pulp slurry having a solid content concentration of 0.7% by weight was prepared. Using the obtained pulp slurry, a base paper was produced by a paper machine. On the base paper, the clear coating liquid 1 was applied to both sides of the base paper with a gate roll coater so that the ^{solid content per side was 0.2 g / m 2.} Next, the pigment coating liquid was applied to both sides so that the solid content per side was 7.5 g / m ^2, and dried by a conventional method to obtain a coated paper. The coated paper was evaluated by the method described later.

[Comparative Example 1]
A coated paper was produced and evaluated in the same manner as in Example 1 except that no metal salt was used.

[Example 2]
According to a conventional method, softwood bleached kraft pulp (NBKP, manufactured by Nippon Paper Industries, Ltd.) was oxidized using TEMPO to obtain a carboxylated cellulose raw material having a carboxyl group amount of 1.42 mmol / g. An aqueous dispersion having a solid content concentration of 2% by weight of the obtained carboxylated cellulose raw material was prepared and treated with a top finer manufactured by Aikawa Iron Works Co., Ltd. for 10 minutes to obtain fibrillated carboxylated cellulose fibers (TEMPO). -MFC) was prepared.

<Clear coating liquid 2>
The clear coating liquid 2 was prepared in the same manner as the clear coating liquid 1 except that TEMPO-MFC was used instead of CM-MFC.
<Paper>
A coated paper was produced and evaluated by the same method as in Example 1 except that the clear coating liquid 2 was used instead of the clear coating liquid 1.

[Comparative Example 2]
A coated paper was produced and evaluated in the same manner as in Example 2 except that no metal salt was used.
The results of these evaluations are shown in Table 1.

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

<Evaluation method>
1) Basis weight According to JIS P8124.
2) 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.), printing on solid areas at a printing speed of 8000 sheets / hr. Printing was performed in the order of indigo (CM) so that the meat 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.

3) Picking evaluation Using an offset sheet-fed printing press manufactured by Roland Corporation and Leo Echo Y indigo manufactured by Toyo Ink Co., Ltd. as ink, solid indigo was printed at a speed of 8000 sph. The number of picking on the F side and the W side generated during printing 10 sheets was measured.

Claims (7)

Paper with a base paper and a clear coating layer
The clear coating layer contains starch, fibrillated chemically modified cellulose fibers and metal salts.
Paper having a degree of crystallinity of cellulose type I of the fibrillated chemically modified cellulose fiber of 50% or more, a degree of anionization of 0.10 to 2.00 meq / g, and an average fiber diameter of more than 500 nm. .. The paper according to claim 1, wherein the starch is oxidized starch. The paper according to claim 1 or 2, wherein the metal salt contains a metal element having a divalent value or higher. The paper according to any one of claims 1 to 3, further comprising a pigment coating layer. The paper according to any one of claims 1 to 4, wherein the fibrillated chemically modified cellulose fiber is anion-modified. Any of claims 1 to 5, wherein the fibrillated chemically modified cellulose fiber has a carboxyl group of 0.1 to 3.0 mmol / g with respect to the absolute dry weight of the fibrillated chemically modified cellulose fiber. The paper described in. The chemically modified cellulose in the fibrillated chemically modified cellulose fiber is a carboxyalkylated cellulose having a degree of carboxyalkyl substitution per glucose unit of the chemically modified cellulose of 0.01 to 0.50, according to claims 1 to 5. The paper described in either.