JP7290976B2 - Paper or paperboard manufacturing method - Google Patents

Description

The present invention relates to a method of making paper or paperboard.

BACKGROUND ART Paper is used in various fields such as printing paper, packaging paper, paper containers, paperboard, etc. In all applications, it is required to have sufficient strength during use and processing. For the purpose of improving the strength of the paper, Patent Documents 1 and 2, for example, disclose paper in which fine cellulose is added to deinked pulp. In addition, paper used for processing applications is required to have a moderately low specific bending resistance from the viewpoint of workability. From the viewpoint of box-making properties such as crease cracks and folding cracks, it is required to moderately lower the specific bending resistance while maintaining the strength.

JP-A-2002-173884 JP-A-2002-173888

As mentioned above, paper is required to have a moderately low specific bending resistance while maintaining strength, but in general, the higher the strength, the higher the specific bending resistance, so it is easy to meet the above requirements. it wasn't In view of such circumstances, an object of the present invention is to provide paper having high strength and moderately low specific bending resistance.

Means to achieve the task

The inventors have found that paper having high strength and moderately low specific bending resistance can be obtained by adding fine cellulose to raw material pulp and subjecting it to beating treatment. That is, the above problems are solved by the present invention described below.
[1] A step of adding fine cellulose to the raw material pulp to form a mixed pulp,
a step of beating the mixed pulp;
A method for producing paper or paperboard, comprising: preparing a stock containing the beaten mixed pulp; and making paper from the stock.
[2] The production method according to [1] or [2], wherein the mixed pulp after beating has a Canadian standard freeness (c.s.f.) of 50 ml or more and 600 ml or less.
[3] The production method according to [1] or [2], wherein the fine cellulose is chemically modified fine cellulose.
[4] The production method according to [3], wherein the chemically modified fine cellulose is cellulose nanofibers having an average fiber diameter of less than 500 nm.

The present invention can provide paper or paperboard with high strength and reasonably low specific bending resistance.

Diagram showing the relationship between freeness and specific burst strength Diagram showing the relationship between freeness and specific bending resistance

Paperboard generally refers to particularly thick paper among papers, but in the present invention, for example, base paper for corrugated board such as liner and core base paper, paperboard base paper, white paperboard, chipboard, yellow board, carrier tape, paper container base paper, etc. The multi-layered paper is called "paperboard", and the single-layered paper is called "paper".

1. Production method The production method of the present invention comprises a step of adding fine cellulose to a raw material pulp to form a mixed pulp, a beating step of beating the mixed pulp, a step of preparing a paper stock containing the mixed pulp after the beating, and It has a papermaking process for making paper stock.

1-1. Mixed pulp preparation step and beating step (1) Fine cellulose Fine cellulose is a fiber obtained by defibrating a cellulosic raw material such as pulp. The fine cellulose of the present invention preferably has an average fiber diameter of 60 μm or less and an average fiber length of 3 mm or less. In the present invention, the average fiber diameter is the length-weighted average fiber diameter, and the average fiber length is the length-weighted average fiber length, which can be measured by, for example, a Valmet Co., Ltd. fractionator. The fine cellulose of the present invention may be fine cellulose made from unmodified cellulose or fine cellulose made from chemically modified cellulose. Preferably. Chemically modified fine cellulose is obtained by fibrillating a cellulosic raw material such as pulp after chemically modifying it.

In the present invention, fine cellulose refers to cellulose fibers having a fine structure obtained by defibrating (loosening the fibers) or beating (fibrillating the fibers) a cellulose material such as pulp. Fine cellulose having a fiber diameter is referred to as microfibril cellulose fiber (hereinafter also referred to as "MFC"), and fine cellulose having an average fiber diameter of less than 500 nm is referred to as cellulose nanofiber (hereinafter also referred to as "CNF"). Since MFC is obtained by fibrillating the surface of the fiber while maintaining the shape of the pulp fiber used as the raw material, ultrafine cellulose fibers are present. For example, the MFC has a roll-brush shape. On the other hand, in CNF, the microfine cellulose fibers exist independently. It is considered that the ultrafine cellulose fibers of CNF and MFC contribute to the above effects of the present invention. The reason for this is not clear, but compared to ordinary pulp fibers, ultrafine cellulose fibers have a large specific surface area, so there are many bonding points that form hydrogen bonds, and many bonds with the pulp fibers that make up paper. This is thought to be due to the formation of dots and the formation of a dense network structure in the paper.

1) CNFs
CNF is a single microfibril of cellulose and has an average fiber diameter of less than 500 nm, preferably 2 nm or more and 100 nm or less, more preferably 2 nm or more and 30 nm or less. The average fiber length is preferably about 1 μm or more and 5 μm or less. In the present invention, when an aqueous dispersion with a concentration of 1% (w / v) (i.e., an aqueous dispersion containing 1 g of CNF (dry weight) in 100 mL of water) is 100 mPa s or more and 10000 mPa s or less. It is preferred to use CNFs that give a B-type viscosity (60 rpm, 20° C.). The viscosity is more preferably 200 mPa·s or more and 7000 mPa·s. The average fiber diameter and average fiber length of CNF can also be measured using atomic force microscopy (AFM) or transmission electron microscopy (TEM).

The B-type viscosity of the CNF aqueous dispersion can be measured by a known method. For example, it can be measured using a VISCOMETER TV-10 viscometer manufactured by Toki Sangyo Co., Ltd. The temperature at the time of measurement is 20° C., and the rotation speed of the rotor is 60 rpm. The aqueous dispersion of CNF of the present invention has thixotropic properties, the viscosity is reduced by applying shear stress by stirring, and the viscosity increases and gels in a static state. Therefore, it was sufficiently stirred. It is preferable to measure the B-type viscosity in the state.

2) MFCs
The average fiber diameter of MFC is preferably 1 μm or more, more preferably 10 μm or more. Its upper limit is preferably 60 μm or less. The average fiber length of MFC is preferably 300 μm or longer, more preferably 500 μm or longer, and even more preferably 800 μm or longer. 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. The average aspect ratio of 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

MFC is obtained by defibrating or beating a cellulosic raw material relatively weakly with a beater, disperser, or the like. Therefore, MFC has a larger fiber diameter than CNF, and has a shape in which the fiber surface is efficiently fluffed (externally fibrillated) while suppressing the miniaturization of the fiber itself (internal fibrillation). In the present invention, when an aqueous dispersion with a concentration of 1% (w / v) (that is, an aqueous dispersion containing 1 g of MFC (dry weight) in 100 mL of water) is used, B of 10 mPa s or more and 1000 mPa s or less It is preferred to use an MFC that gives a mold viscosity (60 rpm, 20° C.). The viscosity is more preferably 50 mPa·s or more and 800 mPa·s or less.

The MFC used in the present invention is preferably mechanically fibrillated chemically modified MFC obtained by mechanically defibrating the pulp after chemically modifying the pulp. As described above, MFC differs in the degree of fibrillation from cellulosic raw materials. It is generally not easy to quantify the degree of defibration, but in the present invention, it is possible to quantify the degree of defibration by the amount of change in freeness and water retention before and after mechanical fibrillation of MFC. I found out. The mechanically defibrated chemically modified MFC of the present invention is preferably obtained by mechanically defibrating or beating to such an extent that the freeness (F0) of the chemically modified pulp before defibration is reduced by 10 ml or more. That is, if the freeness after treatment is F, the freeness difference ΔF=F0−F is preferably 10 ml or more, more preferably 20 ml or more, and even more preferably 30 ml or more. The freeness of chemically denatured pulp varies depending on the degree of denaturation, but since the freeness of the chemically denatured pulp used as the raw material is used as the standard, by defining in this way, the degree of defibration can be determined regardless of the degree of chemical denaturation. can be identified. As described above, since F0 varies depending on the degree of denaturation of chemically denatured pulp, 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 fibrillation rate of MFC determined by a fractionator manufactured by Valmet Corporation is preferably 3.5% or more, more preferably 4% or more.

3) Amount to be added The amount of fine cellulose to be added is adjusted so that the amount of fine cellulose to be added is the desired amount relative to the raw material pulp in the paper after papermaking. The amount to the raw material pulp is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less. As described above, some CNFs and MFCs have high water retention, and if the amount added exceeds the upper limit, the water retention of the pulp slurry increases, and there is a risk that the drainage during papermaking will deteriorate. If the water is not completely drained during papermaking, it takes a long time for dewatering, resulting in a decrease in productivity. Furthermore, a good texture cannot be formed on the papermaking wire, and there is a possibility that the paper quality such as paper strength is deteriorated. The lower limit of the amount of fine cellulose added is not limited as long as the effect of the present invention can be obtained, but it is preferably about 1 ppm by weight or more, more preferably 3 ppm by weight or more, relative to the raw pulp, and the effect of the present invention can be obtained at a high level. 500 ppm by weight or more is more preferable, and 5000 ppm by weight or more is more preferable.

3) Production of fine cellulose 3-1) Cellulose-based raw material Fine cellulose can be produced by chemically modifying a cellulose-based raw material, if necessary, and then defibrating or beating it. The cellulosic raw material is 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.

3-2) 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). is mentioned. 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.

Oxidation can be carried out as known. Examples include a method of oxidizing a cellulose raw material 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. 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. Alternatively, an ozone oxidation method may be mentioned. According to this oxidation reaction, at least the hydroxyl groups at the 2nd and 6th positions of the glucopyranose rings constituting cellulose are oxidized, and the cellulose chain is decomposed.

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 manner is preferably 0.1 mmol/g or more, more preferably 0.5 mmol/g or more, still more preferably 0.8 mmol/g, relative to the absolute dry weight. That's it. The upper limit of the amount is preferably 3.0 mmol/g or less, more preferably 2.5 mmol/g or less, still more preferably 2.0 mmol/g or less. Therefore, the amount is preferably 0.1 mmol/g or more and 3.0 mmol/g or less, more preferably 0.5 mmol/g or more and 2.5 mmol/g or less, and further 0.8 mmol/g or more and 2.0 mmol/g or less. preferable.

Etherification includes carboxymethyl (etherification), methyl (etherification), ethyl (etherification), cyanoethyl (etherification), hydroxyethyl (etherification), hydroxypropyl (etherification), ethylhydroxyethyl (ether) conversion, hydroxypropylmethyl (ether) conversion, and the like. Among these, carboxymethylation is preferred. Carboxymethylation can be carried out, for example, by mercerizing a cellulose raw material as a starting raw material, followed by etherification.

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) About 1.5 g to 2.0 g of hydrogen-form carboxymethylated cellulose (absolute dry) is accurately weighed and placed in a 300 mL conical flask 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) Back _- titrate excess NaOH with 0.1N _H2SO4 using phenolphthalein as indicator. 6) Calculate the degree of carboxymethyl substitution (DS) by the formula:
A = [(100 × F'-(0.1 N 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 _H2SO4 F': Factor of 0.1N _NaOH

The degree of carboxymethyl substitution per anhydroglucose unit in the carboxymethylated cellulose 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 or more and 0.50 or less, more preferably 0.05 or more and 0.40 or less, and still more preferably 0.10 or more and 0.30 or less.

3-3) Defibrillation or beating Fine cellulose can be produced by mechanically defibrating or beating cellulose, and chemically modified fine cellulose can be produced by mechanically defibrating or beating chemically modified cellulose. 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, the timing and place of each defibration or beating are not limited, and the equipment to be 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, a high-speed disaggregator, or the like, in which a metal or a blade acts on a rotating shaft with pulp fibers, or by friction between pulp fibers can be used.

(2) Raw Pulp The raw pulp is the pulp that forms the main component of the paper or paperboard of the present invention. As raw material pulp, commonly used pulp such as mechanical pulp (MP), hardwood kraft pulp (LKP), and softwood kraft pulp (NKP) can be used. Recycled pulp may also be used, and examples of waste paper used as a raw material for recycled pulp include high-quality paper, medium-quality paper, low-grade paper, newspaper, leaflets, magazines, and the like.

(3) Mixed pulp A mixed pulp is obtained by adding fine cellulose to raw material pulp. The method of mixing is not limited, but it is preferable to prepare a slurry consisting of raw material pulp and water and a slurry consisting of fine cellulose and water and mix the two.

In the present invention, raw material pulp and fine cellulose are mixed to form a mixed pulp, which is beaten (refiner treatment). The beating treatment is usually performed for the purpose of softening raw material pulp, which is a raw material for papermaking, and loosening fiber bundles, and the degree of beating is adjusted according to the application. In papermaking pulp (raw material pulp), beating reduces the freeness and increases the density of the resulting paper, improving bursting strength and tensile strength. Drainage is also worsened (improved affinity between pulp and water). This mechanism is presumed to be due to the increase in bonding points between fibers due to fibrillation of the pulp surface. On the other hand, the inventors found that when the mixed pulp of the present invention is beaten, the freeness is more likely to decrease than when the raw material pulp is beaten alone. Unlike the above-mentioned mechanism, a large number of networks are formed between the cellulose fibers of the raw material pulp and the microcellulose fibers of the fine cellulose, and the free fine cellulose that does not contribute to the network traps water. , as a result, water is trapped in the fibers, and it is assumed that the freeness tends to decrease. In addition, since a large number of networks are formed as described above, it is considered that high paper strength is exhibited when the pulp is made into paper and dried.

Although the method of beating is not limited, it is preferable to use a commonly used refiner or high-speed deagglomerator. Examples of refiners include single disc refiners and double disc refiners. The raw material pulp to be subjected to the treatment may be already beaten or unbeaten, but the latter is preferable from the viewpoint of production efficiency. The mixed pulp slurry to be beaten preferably has a solid content (total concentration of pulp and fine cellulose) of 0.5% by weight or more and 35% by weight or less. The beating conditions are such that the mixed pulp after beating has a Canadian standard freeness (c.s.f.) of 50 ml or more and 600 ml or less, preferably 300 ml or more and 600 ml or less. Mixed pulp after beating c. s. When f is within the above range, the beating of raw material pulp proceeds appropriately, and paper or paperboard having both paper strength and moderately low specific bending resistance can be obtained. Furthermore, from the viewpoint of obtaining better effects, it is preferable that the mixed pulp does not contain papermaking chemicals such as fillers and retention agents during the beating treatment.

1-2. Paper Making Process (1) Paper Stock To the beaten mixed pulp prepared as described above, if necessary, known papermaking chemicals such as fillers and retention agents are added to prepare paper stock. Stock contains water. The concentration of each component in the stock is adjusted appropriately.

(2) Papermaking Papermaking can be carried out by a known method. That is, a paper stock containing the beaten mixed pulp prepared as described above is prepared, and a fourdrinier wet paper machine, twin wire paper machine, Yankee paper machine, cylinder paper machine, cylinder wire mesh combination paper machine, etc. It can be carried out using a known paper machine. When paperboard (multi-layered paper) is to be made, the material for each layer is prepared separately and can be carried out using a fourdrinier type wet paper machine or the like.

1-3. Other Steps The manufacturing method of the present invention may comprise a coating step of providing a clear coating layer or a pigment coating layer on the base paper, and further comprises a step of surface-treating the resulting paper or paperboard. may be Moreover, fine cellulose may be contained in the clear coating layer or the pigment coating layer. These methods can be performed as known.

2. Paper or Paperboard (1) Basis Weight The basis weight of the paper (single-layer paper) obtained by the present invention as base paper is preferably 10 g/m ² or more, more preferably 20 g/m ^{2 or} more. The upper limit of the basis weight is preferably 500 g/m ² or less. The basis weight of the paperboard (multilayered paper) obtained by the present invention as base paper is preferably 10 g/m ² or more per layer, more preferably 20 g/m ² or more. The upper limit of the basis weight per layer is preferably 500 g/m ² or less, more preferably 200 g/m ² or less.

(2) Properties The paper or paperboard produced according to the present invention has excellent burst strength and low specific bending resistance. The reason for this is not limited, but when unbeaten raw material pulp and fine cellulose are simultaneously beaten, the raw material pulp is beaten to form fibrils, and at the same time, the fine cellulose forms interfiber bonds with the fibrils of the pulp to form dense fibers. It is presumed that this is because a network structure is constructed and the fine cellulose uniformly contributes to the enhancement of interfiber bonding. Furthermore, the paper thus obtained exhibits not only the formation of near-plane fiber bonds between rigid pulp fibers, but also a large number of three-dimensional bonds between the fine cellulose fibers and the pulp fibers that have entered between the pulp fibers. It is presumed that the strength improvement effect is exhibited while simultaneously suppressing the increase in specific bending resistance due to the formation of a strong bond point.

The present invention will be described with reference to the following examples. Unless otherwise specified, the weights of pulp and the like are absolute dry weights.

(1) Evaluation Basis weight: according to JIS P 8223:2006.
Bulk thickness and bulk density: Measured with reference to JIS P 8223:2006.
Canadian standard freeness (c.s.f.: ml): in accordance with JIS P 8121-2:2012.
Specific burst strength: According to JIS P 8131:2009.
Specific bending resistance: According to JIS P 8125-1:2017 (bending length 10 mm, 30°).

(2) Production of chemically modified fine cellulose After subjecting NBKP (manufactured by Nippon Paper Industries Co., Ltd.) to TEMPO oxidation treatment according to a standard method, it is defibrated using a high-pressure homogenizer, and chemically modified cellulose nanofibers having a carboxyl group amount of 1.53 mmol / g ( Hereinafter, simply referred to as “CNF”) was obtained.

[Example A1]
NUKP (manufactured by Nippon Paper Industries Co., Ltd., c.s.f. 671 ml, solid content concentration 9.5% by weight), water and the CNF aqueous dispersion (CNF concentration 0.57% by weight) were mixed to obtain a mixed pulp. A slurry was prepared. However, the amount of CNF added was 1000 ppm with respect to the mixed pulp slurry. Water was added to the mixed pulp slurry to adjust the solid content concentration to 3% by weight, and the mixed pulp slurry was beaten using a single disc refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.). In this example, the treatment was performed only once under the following beating conditions (one-pass treatment) to obtain a mixed pulp having a Canadian standard freeness of 622 ml.
One-pass beating conditions: Clearance 0.20 mm

After adding calcium chloride to the slurry thus obtained so that the calcium ion concentration becomes 1.0% by weight based on the pulp, 2.5% by weight aluminum sulfate, 0.15% by weight polyacrylamide, A stock was prepared with the addition of 0.4% by weight of sizing agent. Hand-made paper was prepared from the stock with reference to JIS P 8222, and paper having a basis weight of 109.2 g/m ² was produced and evaluated.

[Examples A2 to A4]
Paper was produced in the same manner as in Example A1, except that the beating process was changed to 2-pass treatment (clearance 0.10 mm), 3-pass treatment (clearance 0.06 mm), and 4-pass treatment (clearance 0.05 mm). evaluated.

[Comparative Example A1]
Paper was produced and evaluated in the same manner as in Example A1, except that the beating treatment was not performed.

[Comparative Example B1]
After adding calcium chloride to NUKP (manufactured by Nippon Paper Industries Co., Ltd., c.s.f. 475 ml) so that the calcium ion concentration is 1.0% by weight relative to the pulp, 2.5% by weight of sulfuric acid A stock was prepared with the addition of band, 0.15% by weight polyacrylamide, and 0.4% by weight sizing. The stock was hand-made with reference to JIS P 8222 to produce paper having a basis weight of 105.0 g/m ² and evaluated.

[Comparative Example B2]
1000 ppm weight of the CNF was added to NUKP (manufactured by Nippon Paper Industries Co., Ltd., c.s.f. 475 ml) during paper stock preparation, not during beating, and paper was produced and evaluated in the same manner as in Comparative Example B1. bottom.

[Comparative Example C1]
Paper was produced and evaluated in the same manner as in Comparative Example A1, except that CNF was not added.

[Comparative Examples C2 to C4]
Paper was produced and evaluated in the same manner as in Examples A2 to A4, except that CNF was not added.

[Comparative Example C5]
Paper was produced and evaluated in the same manner as in Comparative Example C2, except that the beating process was a 5-pass process (clearance: 0.05 mm).

These results are shown in Tables 1 and 2 and Figures 1 and 2. Table 1 is a table showing changes in freeness and paper quality when raw material pulp and fine cellulose are co-treated (fine cellulose is added before beating). is a table showing changes in paper quality when adding 1 and 2 show the relationship between the freeness of the slurry obtained by mixing and beating the raw material pulp and fine cellulose and the slurry obtained by beating only the raw material pulp, and the specific bursting strength and specific bending resistance of the paper made from them. indicate.

As is clear from Table 1, according to the production method of the present invention, it was possible to efficiently beat the pulp (reduce the freeness). Especially when comparing Comparative Example C4 and Example A4, it is clear that the latter has a lower freeness even though both have the same number of passes. Also, from the comparison between Comparative Example C4 and Example A3, it is clear that Example A3 could achieve a freeness equivalent to that of Comparative Example C4 with a smaller number of passes. Furthermore, as shown in the figure, the specific bursting strength was improved and the specific bending resistance was lowered compared to paper made from the raw material pulp alone (compared with the same C.S.F.).

Regarding the specific bursting strength, compared to the paper obtained by beating only the raw material pulp without adding CNF (Comparative Example C4), the paper obtained by beating a mixture of CNF and raw material pulp (Example A3 ) improved (about 4%). On the other hand, from the comparison of Comparative Example B1 and Comparative Example B2, the specific burst strength of the paper obtained by adding CNF to the pulp slurry after beating (Comparative Example B2) was obtained by beating without adding CNF. Although the specific burst strength was improved by about 2% compared to the paper (Comparative Example B1), the specific bending resistance was also improved and the paper was rigid.

Claims (4)

A step of adding fine cellulose to the raw material pulp to form a mixed pulp;
a step of beating the mixed pulp;
A method for producing paper or paperboard, comprising: preparing a stock containing the beaten mixed pulp; and making paper from the stock. The production method according to claim 1 , wherein the mixed pulp after beating has a Canadian standard freeness (c.s.f.) of 50 ml or more and 600 ml or less. The production method according to claim 1 or 2, wherein the fine cellulose is chemically modified fine cellulose. The production method according to claim 3, wherein the chemically modified fine cellulose is cellulose nanofibers having an average fiber diameter of less than 500 nm.

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