JP7239561B2 - Paper containing microfibril cellulose fibers - Google Patents

Description

The present invention relates to paper containing microfibrillar cellulose fibers.

Paper is used in various fields such as information recording medium applications such as printing paper and recording paper, and packaging applications, and in all applications, it is required to have sufficient strength during use and processing. For the purpose of improving the strength and stiffness of paper, for example, Patent Document 1 discloses a paper base material to which oxidized pulp is added, and Patent Document 2 discloses a paper product containing a co-processed microfibril cellulose and an inorganic particle composition. is disclosed.

WO2014/097929 JP 2017-203243 A

Although oxidized pulp is used in Patent Document 1, the oxidized pulp is not sufficiently dispersible in paper stock, and the reinforcing effect and air resistance of paper are not at a sufficient level. Patent Document 2 uses microfibril cellulose obtained by mechanically treating undenatured pulp together with inorganic particles. However, the microfibril cellulose is also not sufficiently dispersible in the paper material, and the reinforcing effect and air resistance of the paper cannot be said to be at a sufficient level. In view of such circumstances, an object of the present invention is to provide paper having excellent strength and air resistance.

Chemically modified cellulose can loosen cellulose fibers more efficiently than untreated cellulose due to electrostatic repulsion of the introduced functional groups. Therefore, when chemically modified cellulose is beaten, microfibril cellulose is obtained which is more fibrillated and shortened than when chemically modified cellulose is beaten. The inventors have found that the microfibril cellulose has good dispersibility when added to the stock, and the paper obtained from the stock has excellent mechanical strength and high air resistance. I found out. That is, the above problems are solved by the present invention described below.
(1) Paper containing mechanically treated chemically modified microfibril cellulose fibers having an average fiber diameter of 500 nm or more.
(2) The paper according to (1), wherein the microfibril cellulose fibers have an average fine fiber rate of 4.0 or more as measured by a fiber analyzer.
(3) The paper according to (1) or (2), wherein the microfibril cellulose fibers have a cellulose type I crystallinity of 50% or more.
(4) The paper according to any one of (1) to (3), wherein the chemical modification is anion modification.
(5) The paper according to any one of (1) to (4) provided with a pigment coating layer.
(6) The paper according to any one of (1) to (5) provided with a clear coating layer.
(7) The paper according to any one of (1) to (6), which has a moisture content of 10% by weight or less when conditioned under conditions of 23° C. and 50±2% according to JIS P 8111.
(8) a step of wet pulverizing a cellulose raw material to prepare the microfibril cellulose fibers, and a step of preparing a paper stock containing the microfibril cellulose fibers;
The method for producing paper according to any one of (1) to (7), comprising:
(9) The production method according to (8), comprising a step of chemically modifying the cellulose raw material before the wet pulverization.

The present invention can provide paper with excellent strength and air resistance.

Fig. 1 shows a pulp (COOH amount 0.3 mmol/g, c.s.f. 573 ml) that has undergone chemical modification only. A diagram showing MFC (COOH amount 0.3 mmol/g, c.s.f. 67 ml) obtained by SDR beating treatment after chemical modification

Modes for carrying out the invention

The present invention will be described in detail below. In the present invention, "X to Y" includes X and Y which are the end values.

1. Paper Containing Microfibril Cellulose Fibers The paper of the present invention has a base paper layer and may have one or more coating layers. The coating layer may be a pigment coating layer containing an inorganic pigment and an adhesive, or a clear coating layer mainly composed of an adhesive without containing an inorganic pigment. The paper of the present invention may contain microfibril cellulose fibers in any layer constituting the paper. For example, microfibril cellulose fibers are contained in the base paper layer or the pigment coating layer or the clear coating layer. These layers will be described later.

(1) Microfibril cellulose fiber Microfibril cellulose fiber (hereinafter also referred to as "MFC") is a fiber having an average fiber diameter of 500 nm or more obtained by fibrillating a cellulosic raw material such as pulp. The microfibril cellulose of the present invention is different from cellulose nanofibers in which the fibers are refined to a fiber diameter of less than 500 nm, because the fibrillation of the fiber surface is efficiently promoted while maintaining the shape of the pulp fibers to some extent. , the average fiber diameter is 500 nm or more. The average fiber diameter is preferably greater than 1 μm, more preferably 2 μm or more, and even more preferably 10 μm or more. Its upper limit is preferably 60 μm or less. In the present invention, the average fiber diameter is a length-weighted average fiber diameter, and the fiber diameter can be measured with a fiber tester manufactured by ABB Corporation. MFC is obtained by subjecting a chemically modified cellulosic raw material to relatively weak mechanical treatment such as fibrillation or beating using a beater, disperser, refiner, or the like. Therefore, MFC has a larger fiber diameter than cellulose nanofibers having an average fiber diameter of about less than 500 nm, which is obtained by strongly defibrating a cellulose-based raw material, and the fibers themselves are finer (internal fibrillation ) while efficiently fluffing the fiber surface (external fibrillation).

The mechanically treated chemically modified cellulose fiber (hereinafter also referred to as "mechanically treated chemically modified MFC") used in the present invention is subjected to mechanical treatment after chemically denaturing pulp, or chemically denaturing the mechanically treated pulp. However, from the viewpoint of fibrillation efficiency, the former is preferable. That is, mechanical treatment chemically modified MFC is obtained by subjecting a chemically modified cellulose-based raw material to a relatively weak mechanical treatment such as fibrillation or beating. Compared to MFC that was weakened and merely mechanically defibrated or beaten without chemical modification, the fibers were easily loosened, the fibers were less damaged, and moderate internal and external fibrillation occurred. It has a shape (see FIG. 2). Furthermore, an aqueous dispersion obtained by dispersing the mechanically treated chemically modified MFC in water has high hydrophilicity, water retention and viscosity.

As described above, MFC differs in the degree of fibrillation from cellulosic raw materials. It is generally not easy to quantify the degree of fibrillation, but in the present invention, it is possible to quantify the degree of fibrillation by the amount of change in freeness and water retention before and after mechanical treatment of MFC. I found out. The MFC of the present invention is preferably obtained by mechanical fibrillation or beating to such an extent that the freeness (F ₀ ) of the pulp before mechanical treatment is reduced by 10 ml or more. That is, if the freeness after treatment is F, the freeness difference ΔF=F ₀ −F is preferably 10 ml or more, more preferably 20 ml or more, and even more preferably 30 ml or more. . Although the degree of freeness of pulp varies depending on the degree of denaturation, the degree of fibrillation can be specified regardless of the degree of chemical denaturation, since the degree of freeness of the raw material pulp is used as a reference. As described above, since F ₀ varies depending on the degree of pulp denaturation, it is difficult to unambiguously determine the upper limit of ΔF, but the freeness F after treatment is preferably greater than 0 ml. In order to obtain an MFC with an F of 0 ml, strong mechanical fibrillation is required, so the MFC obtained in this way may have an average fiber diameter of less than 500 nm (cellulose nanofibers). In addition, when a large amount of MFC with a freeness of 0 ml is added to the papermaking process, there is a possibility that drainage of the pulp slurry to be used for papermaking may deteriorate. The average fine fiber rate of the mechanically treated chemically modified MFC of the present invention is preferably 4.0 or higher, more preferably 4.5 or higher, still more preferably 5.0 or higher, and most preferably 8.0 or higher. The average fine fiber rate is a value calculated as items such as "(mean) fibrillation rate (Mean fibril area)", "average fine fiber rate", and "fibril area" when fibers are measured with a fiber analyzer. It is one of the indicators of the degree of fibrillation of the main fiber. For example, it can be measured with an ABB fiber tester or fiber tester plus, and in the present application, the average fine fiber rate is preferably defined as "Mean fibril area" measured with the fiber tester plus.

Although the lower limit of the Canadian standard freeness of the mechanically treated chemically modified MFC of the present invention is not limited, it is preferably higher than 0 ml. The upper limit of the freeness is preferably 500 ml or less, more preferably 350 ml or less, more preferably 150 ml or less, and particularly preferably 100 ml or less. In general, the Canadian standard freeness of cellulose nanofibers that have been defibrated to the single nano level is 0 ml.

The degree of fibrillation of the mechanically treated chemically modified MFC of the present invention can also be quantified by the increase in water retention (H) of the pulp, as described above. The mechanically treated chemically modified MFC of the present invention has a water retention difference (ΔH = H0 - H) defined as the difference between the water retention of the pulp before treatment (HO) and the water retention of the pulp after treatment (H) of 10. % or more, preferably mechanical fibrillation or beating, more preferably mechanical fibrillation or beating to an extent of 50% or more. In chemically modified MFC, the ratio of H-type and Na-type changes depending on the pH, and the degree of water retention changes. Therefore, it is preferable to measure the water retention under the same pH condition before and after defibration. The mechanically treated chemically modified MFC of the present invention preferably has a water retention of 210% or more, more preferably 250% or more, and still more preferably 500% or more. When the water retention is within the above range, the mechanically treated chemically modified MFC is sufficiently fibrillated, and the effects of the present invention can be obtained at a high level.

In the mechanically treated chemically modified MFC of the present invention, when the degree of fibrillation is weak, the degree of fibrillation can be evaluated by the degree of freeness. As the decomposition progresses, the fibers may come off from the mesh and the freeness may appear to increase. In such a case, since the degree of fibrillation cannot be correctly evaluated by the freeness, it is preferable to evaluate by the rate of change of the water retention. That is, the mechanically treated chemically modified MFC of the present invention is preferably chemically modified cellulose that has been mechanically treated so that ΔF is 10 ml or more or ΔH is 10% or more.

A high degree of cellulose type I crystallinity in the mechanically treated chemically modified MFC of the present invention increases the strength of the MFC, which in turn improves the strength of the paper containing it. From this point of view, the cellulose type I crystallinity is preferably 40% or more, more preferably 50 or more. Although the upper limit of the cellulose type I crystallinity is not limited, it is preferably 90 or less. Cellulose type I crystallinity can be measured by X-ray diffraction. For example, mechanically treated chemically modified MFC is lyophilized using liquid nitrogen and compressed to form tablet-shaped pellets. After that, the sample was measured with an X-ray diffractometer (XPert PRO MPD, manufactured by PANalytical), and the obtained graph was peak-separated by graph analysis software PeakFIt (manufactured by Hulinks), and the crystals were separated based on the following diffraction angles. Type I crystallinity can be determined.
Crystal type I: 2θ = 14.8°, 16.8°, 22.6°
Crystal type II: 2θ = 12.1°, 19.8°, 22.0°

1) Cellulosic Raw Materials Cellulosic raw materials are not particularly limited, but examples thereof include those derived from plants, animals (eg, sea squirts), algae, microorganisms (eg, Acetobacter), and microbial products. Plant-derived materials include, for example, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp ( LUKP), bleached hardwood kraft pulp (LBKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.). The cellulose raw material used in the present invention may be any one or a combination thereof, but is preferably plant- or microorganism-derived cellulose fiber, more preferably plant-derived cellulose fiber.

The average fiber diameter of the cellulose fibers is not particularly limited, but is about 30 to 60 μm for softwood kraft pulp and about 10 to 30 μm for hardwood kraft pulp, which are common pulps. In the case of other pulps, the average fiber diameter is about 50 μm after general refining. For example, when using a refined raw material such as chips with a size of several cm, it is preferable to perform mechanical processing with a refiner, beater, or other disaggregator to adjust the average fiber diameter to about 50 μm or less, preferably about 30 μm or less. is more preferable. A method for producing the mechanically treated chemically modified MFC will be described below.

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

[Oxidation]
Oxidized cellulose is obtained by oxidizing a cellulose raw material. Although the oxidation method is not particularly limited, as an example, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a substance selected from the group consisting of bromides, iodides and mixtures thereof. method. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized to generate a group selected from the group consisting of an aldehyde group, a carboxyl group and a carboxylate group. The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by weight or less.

An N-oxyl compound is a compound capable of generating a nitroxy radical. Nitroxyl radicals include, for example, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction. The amount of the N-oxyl compound to be used is not particularly limited as long as it is a catalyst amount capable of oxidizing the raw material cellulose. For example, it is preferably 0.01 mmol or more, more preferably 0.02 mmol or more, relative to 1 g of absolutely dry cellulose. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, and even more preferably 0.5 mmol or less. Therefore, the amount of the N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.02 to 0.5 mmol, relative to 1 g of absolute dry cellulose.

Bromide is a compound containing bromine, and examples thereof include alkali metal bromides that can be dissociated and ionized in water, such as sodium bromide. Also, iodides are compounds containing iodine, and examples thereof include alkali metal iodides. The amount of bromide or iodide to be used can be selected within a range capable of promoting the oxidation reaction. The total amount of bromide and iodide is preferably 0.1 mmol or more, more preferably 0.5 mmol or more, relative to 1 g of absolute dry cellulose. The upper limit of the amount is preferably 100 mmol or less, more preferably 10 mmol or less, and even more preferably 5 mmol or less. Therefore, the total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, even more preferably 0.5 to 5 mmol, per 1 g of absolute dry cellulose.

Examples of the oxidizing agent include, but are not particularly limited to, halogens, hypohalous acids, halogenous acids, perhalogenates, salts thereof, halogen oxides, and peroxides. Among them, hypohalous acid or a salt thereof is preferred, hypochlorous acid or a salt thereof is more preferred, and sodium hypochlorite is even more preferred, because it is inexpensive and has a low environmental load. The amount of the oxidizing agent to be used is preferably 0.5 mmol or more, more preferably 1 mmol or more, and even more preferably 3 mmol or more, relative to 1 g of absolute dry cellulose. The upper limit of the amount is preferably 500 mmol or less, more preferably 50 mmol or less, and even more preferably 25 mmol or less. Therefore, the amount of the oxidizing agent to be used is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, particularly preferably 3 to 10 mmol, per 1 g of absolute dry cellulose. When an N-oxyl compound is used, the amount of the oxidizing agent to be used is preferably 1 mol or more per 1 mol of the N-oxyl compound, and the upper limit is preferably 40 mol. Therefore, the amount of the oxidizing agent to be used is preferably 1 to 40 mol per 1 mol of the N-oxyl compound.

Conditions such as pH and temperature during the oxidation reaction are not particularly limited, and in general, the oxidation reaction proceeds efficiently even under relatively mild conditions. The reaction temperature is preferably 4°C or higher, more preferably 15°C or higher. The upper limit of the temperature is preferably 40°C or lower, more preferably 30°C or lower. Therefore, the reaction temperature is preferably 4 to 40°C, and may be about 15 to 30°C, that is, room temperature. The pH of the reaction solution is preferably 8 or higher, more preferably 10 or higher. The upper limit of pH is preferably 12 or less, more preferably 11 or less. Therefore, the pH of the reaction solution is preferably about 8-12, more preferably about 10-11. Normally, carboxyl groups are generated in cellulose as the oxidation reaction progresses, so the pH of the reaction solution tends to decrease. Therefore, in order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution within the above range. The reaction medium for oxidation is preferably water because of its ease of handling and the fact that side reactions are less likely to occur.

The reaction time in the oxidation can be appropriately set according to the degree of progress of the oxidation, and is usually 0.5 hours or longer, and its upper limit is usually 6 hours or shorter, preferably 4 hours or shorter. Therefore, the reaction time for oxidation is usually 0.5 to 6 hours, for example about 0.5 to 4 hours. Oxidation may be carried out in two or more steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the reaction in the first step, again under the same or different reaction conditions, the reaction can be efficiently It can be oxidized well.

Another example of a carboxylation (oxidation) method is ozone oxidation. This oxidation reaction oxidizes at least the hydroxyl groups at the 2nd and 6th positions of the glucopyranose rings that constitute the cellulose, and causes decomposition of the cellulose chain. Ozone treatment is usually carried out by contacting a cellulose raw material with an ozone-containing gas. The ozone concentration in the gas is preferably 50 g/m ³ or more. The upper limit is preferably 250 g/m ³ or less, more preferably 220 g/m ³ or less. Therefore, the ozone concentration in the gas is preferably 50-250 g/m ³ , more preferably 50-220 g/m ³ . The amount of ozone added is preferably 0.1% by weight or more, more preferably 5% by weight or more, relative to 100% by weight of the solid content of the cellulose raw material. The upper limit of the amount of ozone added is usually 30% by weight or less. Therefore, the amount of ozone added is preferably 0.1 to 30% by weight, more preferably 5 to 30% by weight, based on 100% by weight of the solid content of the cellulose raw material. The ozone treatment temperature is usually 0° C. or higher, preferably 20° C. or higher, and the upper limit is usually 50° C. or lower. Therefore, the ozone treatment temperature is preferably 0 to 50.degree. C., more preferably 20 to 50.degree. The ozone treatment time is usually 1 minute or more, preferably 30 minutes or more, and the upper limit is usually 360 minutes or less. Therefore, the ozone treatment time is usually about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within the above range, excessive oxidation and decomposition of cellulose can be prevented, and the yield of oxidized cellulose is improved.

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

An example of the method for measuring the amount of carboxyl groups is described below. Prepare 60 mL of 0.5% by weight slurry (aqueous dispersion) of oxidized cellulose, add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then drop 0.05 N sodium hydroxide aqueous solution to adjust the pH to 11. Measure the electrical conductivity until the It can be calculated using the following formula from the amount (a) of sodium hydroxide consumed in the neutralization stage of the weak acid whose electrical conductivity changes slowly.
Carboxyl group amount [mmol/g oxidized cellulose] = a [mL] x 0.05/oxidized cellulose weight [g]

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

[Etherification]
Etherification includes carboxymethyl (etherification), methyl (etherification), ethyl (etherification), cyanoethyl (etherification), hydroxyethyl (etherification), hydroxypropyl (etherification), ethylhydroxyethyl (ether) conversion, hydroxypropylmethyl (ether) conversion, and the like. The carboxymethylation method will be described below as an example of these methods.

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

Although the carboxymethylation method is not particularly limited, for example, a method of mercerizing a cellulose raw material as a base raw material and then etherifying it can be mentioned. A solvent is usually used for the reaction. Examples of solvents include water, alcohols (eg, lower alcohols), and mixed solvents thereof. Lower alcohols include, for example, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol. The mixing ratio of the lower alcohol in the mixed solvent is usually 60% by weight or more as a lower limit and 95% by weight or less as an upper limit, preferably 60 to 95% by weight. The amount of solvent is usually 3 times the weight of the cellulose raw material. Although the upper limit of the amount is not particularly limited, it is 20 times the weight. Therefore, the amount of solvent is preferably 3 to 20 times the weight.

Mercerization is usually carried out by mixing the base material and the mercerizing agent. Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of the mercerizing agent to be used is preferably 0.5-fold mol or more, more preferably 1.0-fold mol or more, and even more preferably 1.5-fold mol or more per the anhydroglucose residue of the starting raw material. The upper limit of the amount is usually 20-fold mol or less, preferably 10-fold mol or less, more preferably 5-fold mol or less. ~10-fold molar is more preferred, and 1.5 to 5-fold molar is more preferred.

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

The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Carboxymethylating agents include, for example, sodium monochloroacetate. The amount of the carboxymethylating agent to be added is preferably 0.05-fold mol or more, more preferably 0.5-fold mol or more, and even more preferably 0.8-fold mol or more, per the glucose residue in the cellulose raw material. The upper limit of the amount is usually 10.0-fold mol or less, preferably 5-fold mol or less, more preferably 3-fold mol or less. It is preferably 0.5 to 5, more preferably 0.8 to 3 mol. The reaction temperature is generally 30°C or higher, preferably 40°C or higher, and the upper limit is generally 90°C or lower, preferably 80°C or lower. Therefore, the reaction temperature is usually 30-90°C, preferably 40-80°C. The reaction time is generally 30 minutes or longer, preferably 1 hour or longer, and its upper limit is generally 10 hours or shorter, preferably 4 hours or shorter. Accordingly, the reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours. The reaction solution may be stirred if necessary during the carboxymethylation reaction.

The degree of carboxymethyl substitution per glucose unit of carboxymethylated cellulose is measured, for example, by the following method. That is, 1) About 2.0 g of carboxymethylated cellulose (absolute dry) is precisely weighed and placed in a 300 mL Erlenmeyer flask with a common stopper. 2) Add 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of nitric acid methanol, and shake for 3 hours to convert carboxymethylcellulose salt (carboxymethylated cellulose) into hydrogen-type carboxymethylated cellulose. 3) Accurately weigh 1.5 to 2.0 g of hydrogen-type carboxymethylated cellulose (absolutely dry) and put it in a 300 mL Erlenmeyer flask equipped with a common stopper. 4) Wet hydrogen carboxymethyl cellulose with 15 mL of 80% methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. 5) Backtitrate excess NaOH with 0.1N _H2SO4 using phenolphthalein as indicator _. 6) Calculate the degree of carboxymethyl substitution (DS) by the formula:
A=[(100×F′−(0.1N H ₂ SO ₄ ) (mL)×F)×0.1]/(absolute dry weight of hydrogen-form carboxymethylated cellulose (g))
DS = 0.162 x A/(1 - 0.058 x A)
A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogen-type carboxymethylated cellulose
F: Factor of 0.1N H ₂ SO ₄ F': Factor of 0.1N NaOH

3) Mechanical fibrillation or beating In this step, the chemically modified cellulose is mechanically fibrillated or beaten to have an average fiber diameter of 500 nm or more. In the present invention, mechanical defibration or beating is referred to as "mechanical treatment", and mechanical treatment of the raw material cellulose aqueous dispersion is referred to as "wet pulverization". The defibration or beating treatment may be performed once, or may be performed multiple times singly or in combination. In the case of multiple times, each defibration or beating may be performed at any time, and the equipment used may be the same or different.

The equipment used for fibrillation or beating treatment is not particularly limited, but examples thereof include equipment of types such as high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type. A beater, a PFI mill, a kneader, a disperser, or the like, in which a metal or blade acts on a rotating shaft with pulp fibers, or by friction between pulp fibers can be used.

When fibrillation or beating is performed on an aqueous dispersion of chemically modified pulp, that is, when wet pulverization is performed, the concentration (solid content concentration) of chemically modified pulp in the aqueous dispersion is usually 0.1% by weight. The above is preferable, 0.2% by weight or more is more preferable, and 0.3% by weight or more is even more preferable. As a result, the amount of liquid relative to the amount of chemically modified cellulose becomes appropriate and efficient. The upper limit of the concentration is not particularly limited as long as fibrillation or beating can be performed, but it is usually preferably 90% by weight or less, more preferably 50% by weight or less, and even more preferably 40% by weight or less.

This step yields a mechanically treated chemically modified MFC. The mechanically treated chemically modified MFC has an average fiber diameter of 500 nm or more, preferably 1 μm or more, more preferably 10 μm or more, in terms of length-weighted average fiber diameter. The upper limit of the average fiber diameter is preferably 60 µm or less, more preferably 40 µm or less. The average fiber length is preferably 300 μm or more, more preferably 500 μm or more, and even more preferably 800 μm or more in terms of length-weighted average fiber length. The upper limit of the average fiber length is preferably 3000 µm or less, preferably 1500 µm or less, and more preferably 1100 µm or less. According to the present invention, since the raw material pulp is chemically denatured in advance, fibrillation and shortening tend to proceed when the pulp is mechanically defibrated or beaten. Also, the mechanically treated chemically modified MFC of the present invention is different from CNF. In general, CNF is subjected to a strong defibration treatment, so it is finely divided and accompanied by a decrease in fiber width. Since a treatment such as weak fibrillation or beating is applied to promote fibrillation, the fibers are fibrillated or shortened while maintaining the fiber width.

The length-weighted average fiber diameter and the length-weighted average fiber length are determined using a fiber tester manufactured by ABB Corporation or a fractionator manufactured by Valmet Corporation. The average aspect ratio of the mechanically treated chemically modified MFC is preferably 10 or more, more preferably 30 or more. Although the upper limit is not particularly limited, it is preferably 1000 or less, more preferably 100 or less, and even more preferably 80 or less. The average aspect ratio can be calculated by the following formula.
Average aspect ratio = average fiber length/average fiber diameter

The amount of carboxyl groups in the mechanically treated oxidized MFC obtained in this step is preferably the same as the amount of carboxyl groups in the aforementioned oxidized cellulose. Similarly, the degree of substitution per glucose unit of the mechanically treated carboxymethylated MFC obtained in this step is preferably the same as the degree of substitution of carboxymethylcellulose.

The mechanically treated chemically modified MFC of the present invention may contain metal ions, preferably in a total amount of 0 or more and less than 10 mg/g. Examples of the metal ion include Ag, Au, Pt, Ni, Mn, Fe, Ti, Al, Zn, Cu, etc., and preferably a metal ion having a valence of 2 or more. The content of the metal ions can be confirmed by a scanning electron microscope image and an ICP emission spectrometry of the liquid extracted with a strong acid. In other words, the presence of metal ions cannot be confirmed by scanning electron microscope images, while the presence of metals can be confirmed by ICP emission spectroscopy. On the other hand, for example, when the metal is reduced and exists as metal particles, the metal particles can be confirmed in the scanning microscope image. The mechanically treated chemically modified MFC of the present invention is used in the process of paper manufacturing (papermaking, coating, etc.) by mixing with other papermaking chemicals. Many chemicals with electrical charges, such as cations and anions, are used in papermaking chemicals. The use of chemically modified MFCs may upset the charge balance in the system. Therefore, the content of metal ions is preferably less than 10 mg/g in order to reduce troubles in the papermaking process.

(2) Paper As described later, the paper of the present invention may contain the mechanically treated chemically modified MFC in the base paper layer, or may contain the mechanically treated chemically modified MFC in the coating layer. The former is also referred to as "inner attachment" and the latter as "external attachment". The content of mechanically treated chemically modified MFC in the paper of the present invention is preferably less than 20% by weight, more preferably 10% by weight or less in the total pulp (total of mechanically treated chemically modified MFC and pulp other than this). be. If the amount of mechanically treated chemically modified MFC is 20% by weight or more, in the case of internal addition, there is a risk that the pulp will be dehydrated and the runnability will deteriorate. Efficiency may deteriorate. The paper of the present invention can be used for applications such as paper, paperboard, communication paper, industrial paper, and corrugated board.

(3) Base paper layer The base paper layer is a layer that serves as the base of paper and contains pulp as a main component. In the present invention, the base paper may be single-layered or multi-layered. Preferably, the base paper layer comprises mechanically treated chemically modified MFC. In the case of multiple layers, at least one of the base paper layers should contain the MFC, and all the layers may contain the MFC. The MFC content is preferably 1×10 ⁻⁴ to 10 parts by weight, more preferably 3×10 ⁻⁴ to 1 part by weight, based on 100 parts by weight of the pulp in each layer.

The pulp raw material of the base paper used in the present invention is not particularly limited, and mechanical pulp such as ground pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), deinked pulp (DIP), softwood kraft pulp ( NKP), chemical pulp such as softwood kraft pulp (LKP), and the like can be used. As the deinked (waste paper) pulp, it is possible to use those derived from sorted waste paper such as high quality paper, medium quality paper, low grade paper, newspaper, leaflets, and magazines, and unsorted waste paper in which these are mixed.

Although known fillers can be added to the base paper, fillers may not be added in applications where opacity and whiteness are not required, such as paperboard. When adding fillers, fillers include heavy calcium carbonate, light calcium carbonate, clay, silica, light calcium carbonate-silica composite, kaolin, calcined kaolin, delaminated kaolin, magnesium carbonate, barium carbonate, barium sulfate, hydroxide Inorganic fillers such as aluminum, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, amorphous silica produced by neutralizing sodium silicate with mineral acid, urea-formalin resin, melamine type Organic fillers such as resins, polystyrene resins and phenolic resins can be used. These may be used alone or in combination. Among these, calcium carbonate and light calcium carbonate, which are representative fillers in neutral papermaking and alkaline papermaking and can provide high opacity, are preferred. The filler content in the base paper is preferably 5 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 the filler content in the base paper is more preferably 10% by weight or more.

Bulking agents, dry paper strength improvers, wet paper strength improvers, freeness improvers, dyes, neutral sizing agents, and the like may be used as internal additives, if necessary.

The base paper is produced by a known papermaking method. For example, a Fourdrinier paper machine, a gap former paper machine, a hybrid former paper machine, an on-top former paper machine, a cylinder paper machine, or the like can be used, but not limited to these.

When the mechanically treated chemically modified MFC of the present invention is added to the base paper, it may be added at any step in the process of preparing the pulp slurry. Addition in the process is preferred. When the MFC is added in the mixing step, a mixture of the MFC and other auxiliary agents such as fillers and retention agents may be added to the pulp slurry.

The density of the base paper is preferably 0.2 g/cm ³ or more, more preferably 0.4 g/cm ³ or more. The paper of the present invention has numerous fibrils on the mechanically treated chemically modified MFC surface. In the paper of the present invention, the fibrillated mechanically treated chemically modified MFC is present between the pulp fibers constituting the paper, so that the bonding points between the pulp fibers are increased, and as a result, the paper strength is enhanced. Therefore, a higher paper strength increasing effect can be exhibited in relatively high-density paper with a short interfiber distance of pulp. Although the basis weight of the base paper is not particularly limited, it is preferably 20 g/m ² or more, more preferably 30 g/m ² or more, and still more preferably over 40 g/m ² .

(4) 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. is mentioned.

The pigmented coating layer contains an adhesive. Examples of the adhesive include oxidized starch, positive starch, urea phosphate esterified starch, etherified starch such as hydroxyethyl etherified starch, various starches such as dextrin, proteins such as casein, soybean protein, synthetic protein, polyvinyl Alcohol, cellulose derivatives such as carboxymethyl cellulose and methyl cellulose, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer conjugated diene polymer latex, acrylic polymer latex, ethylene-vinyl acetate copolymer, etc. polymer latex and the like. 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 together.

The pigment coating layer may contain various auxiliary agents such as dispersants, thickeners, antifoaming agents, colorants, antistatic agents, and preservatives, which are commonly used in the field of paper manufacturing. A mechanically treated chemically modified MFC may be included in the pigment coating layer. When the pigment coating layer contains the MFC, its amount is preferably 1×10 ^-3 to 1 part by weight per 100 parts by weight of the pigment. In the case of the above range, a pigment coating liquid having moderate water retention 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 or both sides of the base paper by a known method. The solid content concentration in the coating liquid is preferably about 30 to 70% by weight from the viewpoint of coating suitability. The pigment coating layer may be one layer, two layers, or three or more layers. When multiple pigment coating layers are present, the MFC may be present in any of the pigment coating layers. The coating amount of the pigment coating layer may be appropriately adjusted depending on the application, but in the case of coated printing paper, 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, more preferably 25 g/m ² or less.

(4) Clear coating layer The paper of the present invention may have a clear (transparent) coating layer on one or both sides of the base paper. By applying clear coating to the base paper, the surface strength and smoothness of the base paper can be improved, and the coatability can be improved when pigment coating is applied. The amount of clear coating is preferably 0.1 to 1.0 g/m ² , more preferably 0.2 to 0.8 g/m ² in terms of solid content per side. In the present invention, the clear coating means, for example, using a coater (coating machine) such as a size press, a gate roll coater, a pre-metering size press, a curtain coater, a spray coater, and various starches such as starch and oxidized starch. , polyacrylamide, polyvinyl alcohol, and other water-soluble polymers are applied (size press) onto the base paper. The mechanically treated chemically modified MFC of the present invention may be contained in the clear coat layer.

(5) Properties The paper of the present invention preferably has a moisture content of 10% by weight or less after being conditioned under conditions of 23°C and 50±2% according to JIS P8111. Mechanical treatment The chemically modified MFC has a relatively high water retention rate and can be difficult to dewater and dry in the papermaking process. However, by adjusting the amount of the MFC and the amount of the modifying group to make the water content of the paper within the above range, it is possible to improve the dewatering property and the drying property in the papermaking process, which is preferable. Moreover, paper having a moisture content of 10% by weight or less has sufficient strength. If the water content is higher than 10% by weight, the hydrogen bonds existing between the cellulose fibers of the pulp are disturbed by the water, and the strength, especially the stiffness, of the paper may decrease. From this point of view, although the lower limit of the water content is not limited, it is preferably 4% by weight or more.

Since the paper of the present invention contains a mechanically treated chemically modified MFC having a relatively large fiber diameter and a high fibrillation rate, it has excellent air resistance in addition to excellent strength.

2. Paper Production Method The paper of the present invention may contain the mechanically treated chemically modified MFC in any one of the base paper, the clear coating layer and the pigment coating layer constituting the paper. In order to obtain a high strength improvement effect, it is preferably manufactured through a process of preparing paper stock containing mechanically treated chemically modified MFC, and in order to obtain a high air resistance improvement effect, mechanically treated chemical modification It is preferably manufactured through a step of preparing a coating liquid containing MFC. Mechanical treatment Chemically modified MFC can be prepared by mechanically defibrating or beating a chemically modified cellulose raw material, as described above. The stock can be prepared according to known methods. For example, it can be prepared by adding the above-mentioned MFC, a filler and, if necessary, an additive to a slurry obtained by defibering pulp. In addition, the coating liquid can be prepared according to a known method. For example, the above-mentioned MFC and, if necessary, additives may be added to a binder such as starch, and a white pigment may be added for pigment coating. It may be liquid.

The stock thus obtained can be used to make paper by a known method, or the coating liquid thus obtained can be used to coat a base paper to produce paper. As previously mentioned, the surface of the paper can be provided with a clear coat or a pigmented coating.

The present invention will now be described with reference to examples.
(1) Evaluation Basis weight: JIS P 8223:2006 was used as a reference.
Paper thickness and density: in accordance with JIS P 8118:2014.
Ash content: According to JIS P 8251:2003.
Canadian standard freeness (csf: ml): according to JIS P 8121-2:2012.
Air resistance: Measured with an Oken type smoothness/air permeability tester in accordance with JIS P8117:2009.
Break length: according to JIS P 8113:1998.
Tensile stiffness: Measured by the method specified in ISO/DIS 1924-3.
ISO bending stiffness: in accordance with ISO 2493.
MFC properties: In Examples 1 and 2, the properties of MFC were measured using Fiber Tester Plus manufactured by ABB. The measurement conditions are as follows.

Fiber tester plus measurement conditions: MFC dispersed in water to 0.05% was measured according to a standard method. Measurement items were Mean length, Mean width, Mean fibril area, and Mean fines.

(2) Preparation of MFC [Production Example 1] Preparation 1 of mechanically treated chemically modified MFC from NBKP
NBKP (manufactured by Nippon Paper Industries Co., Ltd.) was subjected to TEMPO oxidation treatment according to a standard method to produce TEMPO oxidized pulps A to C shown in Table 1. The resulting TEMPO oxidized pulp was dispersed in water to form a 3% by weight dispersion and treated with a refiner. goal c. s. f. A mechanically treated chemically modified MFC was obtained by changing treatment conditions such as refiner clearance and the number of treatments according to the average fine fiber ratio. These physical properties are shown in Table 1. Tables 2 and 3 show the properties of the obtained MFC.

[Production Example 2] Preparation 2 of mechanically treated chemically modified MFC from NBKP
NBKP (manufactured by Nippon Paper Industries Co., Ltd.) was subjected to TEMPO oxidation treatment according to a standard method to obtain TEMPO-oxidized pulp D (554 ml of CSF of pH 7.2) having a COOH group content of 1.37. The resulting TEMPO oxidized pulp was dispersed in water to form a 4% by weight dispersion and treated with a refiner. By changing the number of refiner treatments, mechanically treated chemically modified MFC-D was obtained. These MFC properties are shown in Table 4. Mechanical treatment Chemically modified MFC-D was too finely fibrillated, so proper c. s. f. could not be measured.

[Example 1-1]
96% by weight of LBKP (manufactured by Nippon Paper Industries Co., Ltd., c.s.f. 400 ml), 4% by weight of mechanically treated chemically modified MFC-A (c.s.f. ) were mixed to form a mixed pulp. 1.5% by weight of aluminum sulfate, 0.025% by weight of polyethyleneimine, 0.6% by weight of polyacrylamide, and 0.2% by weight of sizing agent are added to the total amount of the mixed pulp to reduce the solid content A pulp slurry with a consistency of 0.35% by weight was prepared. Using the obtained pulp slurry, a hand-made sheet having a basis weight of 50 g/m ² was produced and evaluated. Hand-papering was performed according to JIS P 8222.

[Example 1-2]
Same as Example 1-1 except that mechanically treated chemically modified MFC-B (c.s.f. 54 ml, COOH group amount 0.58 mmol / g) was used instead of mechanically treated chemically modified MFC-A. Then, a hand-made sheet was produced and evaluated.

[Comparative Examples 1 and 2]
Mechanically treated TEMPO oxidized pulp A (COOH base content: 0.30 mmol/g, c.s.f. 573 ml) and TEMPO oxidized pulp B (COOH base content: 0.30 mmol/g, c.s.f. 58 mmol/g, c.s.f. 364 ml) was used, but a hand-made sheet was produced and evaluated in the same manner as in Example 1-1.

[Comparative Example 3]
A hand-made sheet was produced and evaluated in the same manner as in Comparative Example 1, except that unmodified MFC (NBKP, COOH group content 0 mmol/g, c.s.f. 450 ml) was used instead of TEMPO oxidized pulp A. .

[Comparative Example 4]
100 wt% LBKP (400 ml c.s.f.) 1.5 wt% aluminum sulfate, 0.025 wt% polyethylenimine, 0.6 wt% polyacrylamide, 0.2 wt% sizing agent was added to prepare a pulp slurry having a solid concentration of 0.35% by weight. Using the obtained pulp slurry, a hand-made sheet having a basis weight of 50 g/m ² was produced and evaluated. These results are shown in Table 2.

[Examples 2-1 to 2-3]
Instead of LBKP, used magazine paper-based undeinked pulp (manufactured by Nippon Paper Industries Co., Ltd., c.s.f. 350 ml) was used, and the amount of mechanically treated chemically modified MFC-A added was 0.01% by weight and 1.0%. A hand-made sheet was produced and evaluated in the same manner as in Example 1-1, except that the weight percentage was changed to 10% by weight.

[Comparative Example 5]
A hand-made sheet was produced and evaluated in the same manner as in Comparative Example 4, except that the basis weight was changed to 43.6 g/m ² . These results are shown in Table 3.

From Tables 2 and 3 it is clear that the papers of the invention have excellent strength and air resistance.

[Examples 3-1 to 3-2, Comparative Example 7]
96% by weight of LBKP (manufactured by Nippon Paper Industries Co., Ltd., c.s.f. 400 ml), 4% by weight of mechanically treated chemically modified MFC-D (COOH group amount 1.37 mmol / g) with different refiner pass times They were each mixed to form a mixed pulp. 1.5% by weight of aluminum sulfate, 0.025% by weight of polyethyleneimine, 0.6% by weight of polyacrylamide, and 0.2% by weight of sizing agent are added to the total amount of the mixed pulp to reduce the solid content A pulp slurry with a consistency of 0.35% by weight was prepared. Using the obtained pulp slurry, a hand-made sheet having a target basis weight of 50 g/m ² was produced and evaluated. Hand-papering was performed according to JIS P 8222. The MFC used in Comparative Example 7 is not mechanically treated chemically modified MFC. These results are shown in Table 4.

From Table 4, the paper containing mechanically treated chemically modified MFC had high tear length and air resistance, and the higher the fibrillation rate of MFC, the higher the tear length and air resistance of the paper. .

[Comparative Example 6]
A hand-made sheet was produced and evaluated in the same manner as in Example 3-1, except that the mechanically treated chemically modified MFC was not used.

Claims (9)

The base paper contains 0.01 to 10% by weight of mechanically treated chemically modified microfibril cellulose fibers having an average fiber diameter of 500 nm or more with respect to 100% by weight of pulp ,
Paper, having a basis weight of more than 40 g/m ² . 2. The paper according to claim 1, wherein the microfibril cellulose fibers have an average fine fiber rate of 4.0 or more as measured by a fiber analyzer. 3. The paper according to 1 or 2, wherein the microfibril cellulose fibers have a cellulose type I crystallinity of 50% or more. The paper according to any one of claims 1 to 3, wherein said chemical modification is anion modification. The paper according to any one of claims 1 to 4, comprising a pigment coating layer. The paper according to any one of claims 1 to 5, comprising a clear coating layer. The paper according to any one of claims 1 to 6, which has a moisture content of 10% by weight or less when conditioned under conditions of 23°C and 50±2% according to JIS P 8111. a step of wet pulverizing a cellulose raw material to prepare the microfibril cellulose fibers, and a step of preparing a paper stock containing the microfibril cellulose fibers;
The method for producing paper according to any one of claims 1 to 7, comprising 9. The production method according to claim 8, comprising a step of chemically modifying the cellulose raw material before the wet pulverization.

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