JP2011074529A - Method for pretreating filler and paper containing the filler pretreated - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide paper having a high filler retention and excellent paper strength. <P>SOLUTION: The paper having a high filler retention and excellent paper strength can be obtained by making paper from a paper material containing a filler pretreated by being mixed with cellulose nanofibers. Preferably, the cellulose nanofibers have a B type viscosity (at 60 rpm and 20°C) of 500 to 7,000 mPa-s in an aqueous dispersion of 2% (w/v) concentration. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pretreatment method for a filler and a paper containing the pretreated filler.

  In recent years, in the production of paper, there is a tendency to increase the ratio of used paper to paper, increase the speed and neutralization of paper production, make the wire part twin wire, and differentiate the paper from high ash. In particular, neutral papermaking changes the papermaking pH from the conventional acidity to neutrality, and the use of calcium carbonate as a filler is expanding accordingly. However, these technical trends are not preferable from the viewpoint of the yield of pulp and filler (or ash), which are papermaking raw materials.

  Papermaking materials that are small compared to long fibers such as fine fibers and fillers are discharged together with water by dehydration at the wire part of the paper machine and squeezing at the press part, so these papermaking materials are put on the wire. It is important to stay. In particular, improving the yield of fillers can be achieved by reducing the drainage load, reducing manufacturing costs by reducing lost materials, improving quality such as improving the two-sidedness of paper, and improving productivity. It has an important meaning in the production of

  Therefore, for the purpose of efficiently retaining the filler in the paper, the filler is pretreated with cationized starch (flocculating agent) or diallyldimethylammonium polymer (coagulant) and added to the paper to make paper. The technique which performs is proposed (patent documents 1, 2). However, the pretreatment method in which the polymer is mixed with the filler has a problem in that the amount of chemicals used is increased and the density of the paper is increased, and there is room for improvement in the formation of the paper.

  In addition, many studies have been made on cellulose modification as described below. In recent years, from the viewpoint of imparting functionality using polysaccharides, the use of water-soluble polymers obtained by chemically modifying cellulose such as carboxymethyl cellulose or carboxyethyl cellulose has been studied, for example, in Patent Document 3 and Patent Document 4 Thus, the improvement effect of size property, water resistance, and filler yield has been reported. Patent Document 5 reports the simultaneous addition of cationized starch and carboxymethylcellulose as an anionic polysaccharide. However, these methods mainly focus on the fixing effect of the sizing agent, and are insufficient as a method for improving the filler yield in a paper having a relatively high ash content such that the ash content in the paper exceeds 10%. Met.

  Further, in terms of modification of another type of cellulose, there is utilization of fine fibrillated cellulose as described in Patent Documents 6 to 8. This is used after fibrillation is promoted by grinding cellulose fibers with an abrasive plate or the like, but when used as a filler fixing agent, a relatively large amount of fine fibrillated cellulose must be blended. For example, it was not sufficient as a yield improvement method in promoting high ash differentiation.

  On the other hand, high ash differentiation of paper is effective for preventing “back-through” and improving ink fillability, for example, in printing paper, where printing can be seen from the opposite side. However, increasing the amount of filler added yields And the pulp content is reduced as compared with conventional paper, and thus there is a problem of reducing paper strength such as strength and stiffness (rigidity) of paper such as tensile strength. The decrease in paper strength causes paper breaks during paper manufacture and printing, resulting in poor operational efficiency and workability such as generation of paper dust during printing. Increasing (increase) raw materials such as pulp to increase paper strength will lead to resource consumption. Also, increasing the amount of chemicals used, such as paper strength agents, will promote deterioration of the formation and soiling of the paper machine.

Japanese Patent No. 4179167 Patent No. 4324073 JP-A-9-291490 Japanese Patent No. 3852470 JP 2005-65887 A JP-A-7-3691 Patent No. 4009423 Patent No. 2967804

  In the prior art, it has been difficult to achieve both good yield of the filler and good paper strength at the same time. Also, with water-soluble polymers such as carboxymethylcellulose, the yield effect on high ash paper is insufficient, and with fine fibrillated cellulose, a relatively large amount should be blended in order to bind the filler effectively. It was necessary to proceed with high ash differentiation.

  Therefore, an object of the present invention is to provide a paper having a high filler yield, a high ash content, and a good paper strength.

  As a means for improving the yield while maintaining good paper strength, the present inventors diligently studied the pretreatment method of the filler, and by mixing cellulose nanofibers, which are very tough ultrafine fibers, It has been found that the yield of the filler can be particularly improved without deteriorating the paper strength by pretreating the filler and adding the pretreated filler to the paper to produce paper.

  Specifically, it was found that a paper having a high ash content and good paper strength can be obtained by pretreating the filler by mixing cellulose nanofibers with the filler.

  By adding the filler pretreated with the cellulose nanofiber of the present invention and making paper, a high yield of filler, high ash content, and good paper strength can be obtained.

(Cellulose nanofiber)
In the present invention, cellulose nanofibers are mixed in the filler. The cellulose nanofiber is a single microfibril of cellulose having a width of about 2 to 5 nm and a length of about 1 to 5 μm obtained by defibrating a cellulose-based raw material. In the present invention, in particular, the B-type viscosity (60 rpm, 20 ° C.) at a concentration of 2% (w / v) (that is, 2 g of cellulose nanofiber (dry mass) is contained in a 100 ml dispersion) is 500 to 7000 mPa It is preferable to use an aqueous dispersion of cellulose nanofibers that is s, preferably 500 to 2000 mPa · s. Such cellulose nanofibers have moderate viscosity and can be adjusted to a desired concentration. The B type viscosity in a 2% (w / v) aqueous dispersion of cellulose nanofibers is preferably relatively low because it is easy to handle. Specifically, the viscosity is preferably about 500 to 2000 mPa · s, and preferably 500 to 1500 mPa -About s is more preferable and about 500-1000 mPa-s is further more preferable.

  The B-type viscosity of the aqueous dispersion of cellulose nanofibers of the present invention can be measured by a known method. For example, it can be measured using a VICOMETER TV-10 viscometer manufactured by Toki Sangyo.

  Cellulose nanofibers having a B-type viscosity (60 rpm, 20 ° C.) of 500 to 7000 mPa · s, preferably 500 to 2000 mPa · s in an aqueous dispersion having a concentration of 2% (w / v) used in the present invention include, for example, (1) N-oxyl compound, and (2) oxidation using an oxidizing agent in the presence of bromide, iodide or a mixture thereof, and further defibrated by wet atomization treatment of the oxidized cellulose, It can be manufactured by forming into nanofibers.

  Cellulosic raw materials used as raw materials for the cellulose nanofibers of the present invention are not particularly limited, and kraft pulp or sulfite pulp derived from various woods, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer or a mill, or the like. Microcrystalline cellulose powder purified by chemical treatment such as acid hydrolysis can be used. In addition, plants such as kenaf, hemp, rice, bagasse and bamboo can also be used. Among these, when bleached kraft pulp, bleached sulfite pulp, powdered cellulose, and microcrystalline cellulose powder are used, a relatively low viscosity (B-type viscosity of 2% (w / v) aqueous dispersion is 500 to 2000 mPa · s) cellulose nanofibers can be efficiently produced, and it is more preferable to use powdered cellulose or microcrystalline cellulose powder.

  Powdered cellulose is a rod-like particle made of microcrystalline cellulose obtained by removing a non-crystalline portion of wood pulp having a high cellulose purity by acid hydrolysis, and then pulverizing and sieving. The degree of polymerization of cellulose is about 100 to 500, the degree of crystallinity of powdered cellulose by X-ray diffractometry is 70 to 90%, and the average particle size by a laser diffraction type particle size distribution measuring device is 100 μm or less.

  As the N-oxyl compound used for oxidizing the cellulosic raw material, any compound can be used as long as it promotes the target oxidation reaction. For example, the N-oxyl compound used in the present invention includes a substance represented by the following general formula (Formula 1).

(In Formula 1, R ^{1 to} R ⁴ represent the same or different alkyl groups having about 1 to 4 carbon atoms.)
Among the compounds represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO), and 4-hydroxy-2,2,6,6- A compound that generates a tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as 4-hydroxy TEMPO) is preferable. Moreover, the derivative | guide_body obtained from TEMPO or 4-hydroxy TEMPO can also be used preferably, and the derivative | guide_body of 4-hydroxy TEMPO can be used most preferably especially. The 4-hydroxy TEMPO derivative is a derivative obtained by etherifying the hydroxyl group of 4-hydroxy TEMPO with an alcohol having a linear or branched carbon chain having 4 or less carbon atoms, or esterified with carboxylic acid or sulfonic acid. The derivatives obtained are preferred. When 4-hydroxy TEMPO is etherified, if an alcohol having 4 or less carbon atoms is used, the resulting derivative becomes water-soluble regardless of the presence or absence of saturated or unsaturated bonds in the alcohol, making it an excellent oxidation catalyst. A functional 4-hydroxy TEMPO derivative can be obtained.

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

(In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms.)
Furthermore, a radical of an N-oxyl compound represented by the following formula 5, that is, an azaadamantane type nitroxy radical, is particularly preferred because it can produce uniform cellulose nanofibers in a short time.

(In Formula 5, R ₅ and R ₆ represent the same or different hydrogen or a C _{1 to} C ₆ linear or branched alkyl group.)
The amount of the N-oxyl compound such as TEMPO or 4-hydroxyl TEMPO derivative used for oxidizing the cellulosic raw material is not particularly limited as long as it is a catalyst amount capable of converting the cellulosic raw material into nanofibers. For example, it is about 0.01 to 10 mmol, preferably about 0.01 to 1 mmol, and more preferably about 0.05 to 5 mmol with respect to 1 g of an absolutely dry cellulosic material.

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

  As the oxidizing agent used for oxidizing the cellulosic raw material, the target oxidation reaction such as halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide can be promoted. Any oxidizing agent can be used as long as it is an oxidizing agent. Among these, from the viewpoint of production cost, sodium hypochlorite, which is the most widely used in industrial processes and has a low environmental load, is particularly suitable. The amount of the oxidizing agent used can be selected within a range that can promote the oxidation reaction. For example, it is about 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol with respect to 1 g of cellulosic raw material.

  As described above, the oxidation of the cellulose-based raw material in the present invention is the presence of a compound selected from the group consisting of (1) N-oxyl compounds such as 4-hydroxy TEMPO derivatives and (2) bromides, iodides and mixtures thereof. Below, it is characterized by oxidizing a cellulosic raw material in water using an oxidizing agent such as sodium hypochlorite. This method has a feature that the oxidation reaction of the cellulosic raw material can proceed smoothly and efficiently even under mild conditions. Therefore, the reaction temperature may be about 15 to 30 ° C. In addition, since a carboxyl group produces | generates in a cellulose with progress of reaction, the fall of pH of a reaction liquid is recognized. In order to advance the oxidation reaction efficiently, it is desirable to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11, by adding an alkaline solution such as an aqueous sodium hydroxide solution.

  As described above, in the presence of (1) N-oxyl compound and (2) bromide, iodide, or a mixture thereof, an oxidized cellulose material obtained using an oxidizing agent is treated with wet fine particles. Cellulose nanofibers can be produced by fibrillation and defibration. As the wet atomization treatment, for example, a mixing / stirring and emulsifying / dispersing device such as a high-speed shear mixer or a high-pressure homogenizer can be used alone or in combination of two or more. In particular, when wet atomization is performed using an ultrahigh pressure homogenizer that enables a pressure of 100 MPa or more, preferably 120 MPa or more, more preferably 140 MPa or more, a relatively low viscosity (2% (w / v) aqueous dispersion Cellulose nanofibers having a B-type viscosity of about 500 to 2000 mPa · s) can be efficiently produced, which is preferable.

The cellulose nanofiber of the present invention is 0.5 mmol / g or more, preferably 0.9 mmol / g or more, more preferably 1.2 mmol / g or more, as the amount of carboxyl groups in 1 g of completely dried cellulose nanofiber. This is desirable because it results in a uniform dispersion. The amount of carboxyl groups in cellulose nanofibers was prepared by adding 60 ml of a 0.5% by weight slurry of cellulose nanofibers, adding 0.1M hydrochloric acid aqueous solution to pH 2.5, and then dropping 0.05N sodium hydroxide aqueous solution dropwise. Then, the electrical conductivity is measured until the pH reaches 11, and can be calculated from the amount of sodium hydroxide (a) consumed in the weak acid neutralization stage where the change in electrical conductivity is gradual, using the following equation. .
Carboxyl group amount [mmol / g pulp] = a [ml] × 0.05 / oxidized pulp mass [g]
The anion charge density that can be titrated by colloidal titration using 1/1000 N pDADMAC is 0.1 meq./g or more per absolute dry mass of cellulose nanofiber, and 0.5 meq. / G or more is preferable.

(Filler)
Fillers of the present invention include light calcium carbonate, heavy calcium carbonate, clay, calcined kaolin, deramikaolin, white carbon, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, calcium carbonate / Inorganic fillers such as silica composites, aluminum hydroxide, calcium hydroxide, magnesium hydroxide and zinc hydroxide, organic fillers such as urea-formalin resin, polystyrene resin, phenol resin and fine hollow fine particles, a step of recycling used paper, Recycled filler obtained by incinerating sludge generated in the paper manufacturing process, and known fillers such as fillers whose surfaces are coated with calcium carbonate, silica, aluminum hydroxide, etc., alone or in combination of two or more. Can be used. Of these, inorganic particles and organic-inorganic composites containing calcium are preferable.

(Pretreatment of filler by mixing filler and cellulose nanofiber)
In the present invention, the filler is pretreated by adding and mixing the cellulose nanofibers to the aqueous dispersion of the filler. The “pretreatment” in the present invention refers to a treatment performed before the filler is added to the paper stock.

  The solid content concentration of the aqueous dispersion of the filler during the pretreatment is not particularly limited as long as it can be sufficiently mixed, and is about 1 to 50%, preferably 5 to 30%, more preferably 10 ~ 25%. When the concentration is lower than 1%, the mixing efficiency tends to deteriorate, and when the concentration is higher than 50%, the dispersibility tends to deteriorate. The amount of cellulose nanofiber added is 0.01 to 100 parts by weight, preferably 1 to 20 parts by weight, more preferably 5 to 20 parts by weight, based on the solids content of the cellulose nanofibers. More preferably, it is 5-15 mass parts. If there are too many cellulose nanofibers relative to the filler, the optical suitability decreases because large aggregates are formed, or the excess cellulose nanofibers tend to inhibit the performance of cationic chemicals added in the system, If the amount is too small, the paper strength tends to decrease when the filler yield decreases or when the ash content is high.

  The apparatus used for mixing is not particularly limited as long as the apparatus can sufficiently perform mixing. For example, a general agitator having a propeller blade, a turbine blade, a paddle blade, etc., a high-speed rotating centrifugal radiation such as a disperser. Examples thereof include high-speed rotary shear type stirrers such as a mold stirrer, homogenizer, homomixer and ultramixer, and emulsifiers such as a colloid mill and a planetary mixer. The dispersion liquid obtained by mixing the filler and cellulose nanofiber may be added to the paper stock after being temporarily stored in a tank or the like, but it is preferable to add it to the paper stock immediately after mixing.

  By mixing cellulose nanofibers with the filler, the filler and cellulose nanofibers are selectively brought into contact with each other, and the cellulose nanofibers are entangled with the filler, or the fillers are gradually aggregated. The average particle size of the filler thus pretreated is 1 to 2 times the average particle size of the untreated filler, and preferably 1 to 1.5 times. If it is too large, there will be no problem with the effect of improving the filler yield, but the filler becomes a large aggregate and exists in the paper layer, so that the opacity and whiteness are likely to decrease.

Moreover, the yield improvement effect by the pre-processing filler of this invention becomes large especially by presence of calcium. As a method for adjusting the calcium ion concentration of the filler dispersion liquid, an acidic substance is added to inorganic particles containing calcium, preferably inorganic particles containing calcium carbonate, to dissociate calcium and increase the calcium ion concentration. It is effective. As the acidic substance, sulfuric acid, hydrochloric acid, nitric acid or the like can be used, but it is economically preferable to use a sulfuric acid band generally used in the paper pulp field. The method for adding the acid is not particularly limited, but the addition of cellulose nanofibers after increasing the calcium ion concentration by adding acid increases the effect of promoting aggregation via calcium ions. A part of the acid may be divided and added after adding the cellulose nanofibers. The amount of acid added is not particularly limited. For example, when a sulfuric acid band is used, the amount of sulfuric acid band added is 0.1 to 5% with respect to the filler solid content in terms of aluminum oxide (Al ₂ O ₃ ). preferable.

(Paper containing pretreatment filler)
By adding the filler pretreated with the cellulose nanofibers of the present invention to the paper, it is possible to obtain paper with good paper strength and uniformly distributed ash. Pulp components that can be used for paper production include chemical pulp (conifer bleached kraft pulp (NBKP) or unbleached kraft pulp (NUKP), hardwood bleached kraft pulp (LBKP), unbleached kraft pulp (LUKP), etc. ), Mechanical pulp (grand pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc.), deinked pulp (DIP), etc. May be. In particular, the present invention is suitable in the case where recycled pulp containing a portion of raw material of magazine waste paper containing a large amount of calcium-containing inorganic substances such as calcium carbonate is blended.

  The addition amount of the filler pretreated with cellulose nanofibers may be added so as to be a desired ash content, and is not particularly limited, but is 1 to 50 parts by mass, preferably 10 to 30 parts by mass with respect to the pulp solid content. is there. Although it does not restrict | limit especially as ash content of paper, 5-30 mass% is preferable and it is preferable that it is 10-25 mass%. In the present invention, the ash content is measured by a method in which the combustion temperature is set to 525 ± 25 ° C. in accordance with the ash test method for paper and paperboard specified in JIS P 8251. In addition, when the coating material containing the pigment and binder mentioned later is applied, the ash content is measured including the coating layer.

  The paper of the present invention may further contain an aluminum compound such as sulfuric acid band, aluminum chloride, sodium aluminate, basic aluminum chloride, basic polyaluminum hydroxide alumina sol; ferrous sulfate, ferric sulfate, if necessary. And other internal sizing agents such as silica sol, AKD (alkyl ketene dimer), ASA (alkenyl succinic anhydride), petroleum sizing agent, neutral rosin sizing agent, paper strength Enhancer, Yield improver, Drainage improver, Ultraviolet ray inhibitor, Antifading agent, Various starches, Colorant, Dye, Defoamer, Bulking agent, Polyacrylamide, Urea / formalin resin, Melamine / formalin resin, Epoxy Resin, polyamide resin, polyamide polyamine resin, polyamine, polyethyleneimine, vegetable gum, polyvinyl alcohol, Box, polyethylene oxide, hydrophilic crosslinked polymer particle dispersion, and may contain various compounds such as derivatives thereof or modified product. Moreover, a fluorescent whitening agent, an antifoamer, a pH adjuster, a pitch control agent, a slime control agent, etc. can also be added suitably as needed.

  The pH during papermaking is preferably 5 to 10, and more preferably 6 to 9. As a method for adjusting pH, mineral acid such as sulfuric acid, sulfuric acid band, carbon dioxide blowing, or the like can be used. Moreover, alkalis, such as sodium hydroxide and sodium hydrogencarbonate, can be added as needed so that it may become said pH range.

  The paper of the present invention is produced by a known paper machine, but the paper making conditions are not particularly defined. Examples of the paper machine include a long net type, an on-top twin wire type, a gap former type, a circular net type, and a multilayer type.

(surface treatment)
A surface treatment agent may be applied to the paper containing the filler pretreated with the cellulose nanofiber of the present invention. As the surface treatment agent, a surface treatment agent containing a water-soluble polymer as a main component is desirable from the viewpoint of improving surface strength and size. As the water-soluble polymer, starches such as starch, oxidized starch and processed starch, carboxymethyl cellulose, polyacrylamide, polyvinyl alcohol and the like which are usually used as surface treatment agents may be used alone or in combination. it can. Further, as the surface treatment agent, in addition to the water-soluble polymer, a paper strength enhancer for the purpose of improving water resistance and surface strength and an externally added sizing agent for the purpose of imparting sizing properties may be used. When a water-soluble polymer is used, the water-soluble polymer and cellulose nanofiber can be mixed and applied. Cellulose nanofibers can also be applied alone. In this case, the coating amount per one side is preferably 0.01 to 10 g / m ² as the solid content mass of the cellulose nanofiber. In the present invention, a paint containing a pigment such as calcium carbonate, kaolin, or titanium dioxide and a binder may be applied on paper to which the surface treatment agent is applied or not.

(Use)
There are no restrictions on the type, basis weight, etc. of the paper containing the filler pretreated with the cellulose nanofibers of the present invention, and various uses such as fine paper, printing paper, newsprint, information paper, wrapping paper, paperboard, and various base papers In particular, the yield of fillers such as ash and calcium carbonate derived from recycled pulp can be improved.

(Function)
The reason why the filler pretreated with the cellulose nanofibers of the present invention can achieve both improvement in filler yield and good paper strength is not clear, but may be considered as follows, for example.

  Cellulose nanofibers have a large amount of carboxyl groups and are dispersed in water with low electrical conductivity, but are ion-bonded and fixed in the presence of calcium ions or weakly ionized calcium on the surface of inorganic particles. Cellulose nanofibers have a very long fiber length compared to conventional water-soluble polymers such as carboxymethylcellulose, and are considered to have a strong ability to bind particles. Such an effect exhibits the same effect even under conditions with high electrical conductivity and in the presence of polyvalent metal ions such as aluminum other than calcium. In addition, cellulose nanofibers are stiffer fibers than other water-soluble organic polymers such as polyacrylamide, so they have high resistance to shearing forces, so they can achieve high yields even with paper machine shearing forces. It is considered possible. Then, rather than adding cellulose nanofibers directly to the stock, it is presumed that the frequency of contact between the cellulose nanofibers and the filler increases by mixing with the filler in advance, so that the filler can be efficiently retained.

  On the other hand, the filler pretreated with the cellulose nanofibers of the present invention is easier to bond with the fibers in the stock than the conventional pretreated with starch, polymer, etc., and paper with excellent paper strength is obtained. It is estimated that. Cellulose nanofibers, unlike starch and polymer water-soluble polymers, are similar in structure to pulp fibers and are likely to form hydrogen bonds with the fibers, so they are thought to increase the bond between fibers. It is done.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to such examples.
<Production Example 1 of Cellulose Nanofiber>
15 g of powdered cellulose (manufactured by Nippon Paper Chemical Co., Ltd., particle size: 24 μm) was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (Sigma Aldrich) and 755 mg (7 mmol) of sodium bromide were dissolved, Stir until the powdered cellulose is uniformly dispersed. After adding 50 ml of a sodium hypochlorite aqueous solution (effective chlorine 5%) to the reaction system, the pH was adjusted to 10.3 with a 0.5N hydrochloric acid aqueous solution to start the oxidation reaction. During the reaction, the pH in the system was lowered, but a 0.5N aqueous sodium hydroxide solution was successively added to adjust the pH to 10. After reacting for 2 hours, oxidized powdered cellulose was separated by centrifugal operation (6000 rpm, 30 minutes, 20 ° C.) and sufficiently washed with water to obtain oxidized powdered cellulose. A 2% (w / v) slurry of oxidized powdered cellulose was treated with a mixer at 12,000 rpm for 15 minutes, and the powdered cellulose slurry was further treated with an ultra-high pressure homogenizer five times at a pressure of 140 MPa to obtain a transparent gel dispersion. A liquid was obtained.

<Production Example 2 of Cellulose Nanofiber>
A cellulose nanofiber dispersion was obtained in the same manner as in Production Example 1, except that the powdered cellulose slurry was treated 5 times with an ultrahigh pressure homogenizer at a pressure of 120 MPa.

<Production Example 3 of Cellulose Nanofiber>
A cellulose nanofiber dispersion was obtained in the same manner as in Production Example 1, except that the powdered cellulose slurry was treated 5 times with an ultrahigh pressure homogenizer at a pressure of 100 MPa.

<Production Example 4 of Cellulose Nanofiber>
Dispersion of cellulose nanofibers in the same manner as in Production Example 1 except that a rotary blade mixer (peripheral speed: 37 m / s, Nippon Seiki Seisakusho Co., Ltd., treatment time: 30 minutes) was used in the wet atomization treatment instead of the ultrahigh pressure homogenizer. A liquid was obtained.

<Production Example 5 of Cellulose Nanofiber>
A cellulose nanofiber dispersion was obtained in the same manner as in Production Example 1 except that 4-methoxy TEMPO was used instead of TEMPO.

<Production Example 6 of Cellulose Nanofiber>
A cellulose nanofiber dispersion was prepared in the same manner as in Production Example 1, except that bleached unbeaten sulfite pulp (manufactured by Nippon Paper Chemicals Co., Ltd.) was used instead of powdered cellulose, and treatment was performed 40 times with a 140 MPa ultrahigh pressure homogenizer. Obtained.

<Production Example 7 of Cellulose Nanofiber>
Production Example 1 except that bleached unbeaten sulfite pulp (manufactured by Nippon Paper Chemicals Co., Ltd.) was used instead of powdered cellulose, and treatment was carried out with a rotary blade mixer (circumferential speed 37 m / s, Nippon Seiki Seisakusho Co., Ltd.) for 5 hours. In the same manner, a cellulose nanofiber dispersion was obtained.

  The B-type viscosity (60 rpm, 20 ° C.) of the cellulose nanofibers obtained in Production Example 1 to Production Example 7 was measured using a VISCOMETER TV-100 viscometer (Toki Sangyo Co., Ltd.). The results are shown in Table 1.

  By the methods of Production Examples 1 to 7, cellulose nanofibers having a B-type viscosity (60 rpm, 20 ° C.) of 500 to 7000 mPa · s in an aqueous dispersion having a concentration of 2% (w / v) could be obtained. Among these, the cellulose nanofibers obtained in Production Examples 1 to 3 and Production Example 5 have a B-type viscosity (60 rpm, 20 ° C.) in an aqueous dispersion having a concentration of 2% (w / v) of 500 to 2000 mPa · s. It was within the range, and the fluidity was very good.

<Example of paper manufacture>
Next, an example in which a filler is pretreated using the cellulose nanofiber obtained by the above-described method and added to a paper material to make a paper is shown. The evaluation measurement in each example was performed by the following method, and the results are shown in Tables 2-7. In addition, a result is represented by the average value of a measured value. Unless otherwise specified, parts and% indicate parts by mass and% by mass.
[Evaluation measurement method]
Ash content: According to JIS P 8251: 2003.
-Breaking length: According to JIS P 8113: 1998.
-Bending stiffness: According to ISO-2493, the bending stiffness with a bending angle of 15 ° was measured using L & W Bending Tester Code 160 (manufactured by Lorentzen & Wettre).

[Example 1]
(Pretreatment of filler)
With respect to light calcium carbonate (filler; Rosetta type, aqueous dispersion having an average particle size of 3.5 μm and a solid content concentration of 20.0%), the cellulose nanofibers of Production Example 1 are adjusted to a solid mass ratio of 0.1. (CNF: filler = 1: 10, CNF represents cellulose nanofiber) and mixed at a speed of 300 rpm with a three-one motor to obtain a pretreated light calcium carbonate dispersion.

(Manufacture of paper)
10 grams of the above pretreated light calcium carbonate was added to a slurry of hardwood bleached kraft pulp (LBKP, CSF (Canadian Standard Freeness) 410 ml) based on the pulp solid mass while stirring at a speed of 500 rpm with a three-one motor. 0.0% by mass (corresponding to 9% by mass of ash content in paper), 1.0% by mass of sulfuric acid band and 100% of yield improver (trade name: Realizer R300, manufactured by Somar) A paper stock was prepared by adding and mixing as described above. Next, five handsheets were produced based on JIS P 8209.

[Example 2]
The same procedure as in Example 1 was conducted, except that cellulose nanofibers of Production Example 1 were mixed with light calcium carbonate so that the solid mass ratio was 0.07 (CNF: filler = 1: 15).

[Example 3]
The same procedure as in Example 1 was conducted, except that cellulose nanofibers of Production Example 1 were mixed with light calcium carbonate so that the solid mass ratio was 0.03 (CNF: filler = 1: 30).

[Comparative Example 1]
Instead of the pretreated light calcium carbonate, untreated light calcium carbonate (not mixed with cellulose nanofibers) was used, but the same as Example 1.

  From the results of Examples 1 to 3 and Comparative Example 1, by pre-treating the filler with cellulose nanofiber, the filler yield is good even under relatively high ash conditions such as 9% ash in paper, and the paper strength is high. It can be seen that good paper is obtained.

[Example 4]
Example 1 was repeated except that 15.0% by mass of pretreated light calcium carbonate was added (corresponding to 12% by mass of ash content in paper).

[Example 5]
The same procedure as in Example 2 was performed except that 15.0% by mass of pretreated light calcium carbonate was added (corresponding to 12% by mass of ash content in paper).

[Example 6]
Example 3 was repeated except that 15.0% by mass of pretreated light calcium carbonate was added (corresponding to 12% by mass of ash content in paper).

[Comparative Example 2]
Example 4 was repeated except that untreated light calcium carbonate was used instead of the pretreated light calcium carbonate.

[Comparative Example 3]
Comparative Example 2 was carried out except that 0.1% by mass of a paper strength agent (trade name: Hermide EX288, manufactured by Harima Chemicals Co., Ltd.) was added.

  From the results of Examples 4 to 6 and Comparative Examples 2 and 3, by pre-treating the filler with cellulose nanofiber, the filler yield is good and the paper strength is good even under high ash conditions such as ash content in paper of 12%. It can be seen that good paper is obtained. In particular, it can be seen that the papers of the present invention (Examples 4 to 6) using a filler pretreated with cellulose nanofibers are less susceptible to tearing than papers added with a paper strength agent (Comparative Example 3).

[Example 7]
The same procedure as in Example 1 was performed except that 20.0% by mass of pretreated light calcium carbonate was added (corresponding to 15% by mass of ash content in paper).

[Example 8]
The procedure was the same as Example 2 except that 20.0% by mass of pretreated light calcium carbonate was added (corresponding to 15% by mass of ash content in paper).

[Example 9]
The procedure was the same as Example 3 except that 20.0% by mass of pretreated light calcium carbonate was added (corresponding to 15% by mass of ash content in paper).

[Comparative Example 4]
Example 7 was repeated except that untreated light calcium carbonate was used instead of the pretreated light calcium carbonate.

  From the results of Examples 7 to 9 and Comparative Example 4, by pretreating the filler with cellulose nanofiber, the filler yield is good and the paper strength is good even under conditions of high ash content of 15% in paper. It turns out that paper is obtained.

[Example 10]
Light calcium carbonate pretreated in Example 2 based on the pulp solids mass while stirring at a speed of 500 rpm with a slurry of hardwood bleached kraft pulp (LBKP, CSF (Canadian Standard Freeness) 410 ml) 10.0% by mass and untreated light calcium carbonate 5.0% by mass (total amount of filler corresponding to 12% by mass of ash in paper, pretreated filler: untreated filler (solid content mass ratio) = 2: 1) Was further added and mixed so that a sulfuric acid band was 1.0% by mass and a yield improver (trade name: Realizer R300, manufactured by Somar Co., Ltd.) was 100 ppm. Next, five handsheets were produced based on JIS P 8209.

[Example 11]
Pretreated light calcium carbonate: Same as Example 10 except that untreated light calcium carbonate (solid content mass ratio) was 1: 2.

  From the results of Examples 10 and 11 and Example 5 and Comparative Examples 2 and 3, when a part of the filler pretreated with cellulose nanofiber was replaced with an untreated filler, the filler yield and paper strength were slightly reduced. It can be seen that both are sufficiently maintained in the high ash content region.

[Example 12]
Light calcium carbonate pretreated in Example 2 based on the pulp solids mass while stirring at a speed of 500 rpm with a slurry of hardwood bleached kraft pulp (LBKP, CSF (Canadian Standard Freeness) 410 ml) 7.5% by mass and 7.5% by mass of untreated light calcium carbonate (corresponding to 12% by mass of ash content in the paper in total, pretreated filler: untreated filler (solid content mass ratio) = 1: 1) Further, 0.5% by mass of cellulose nanofibers of Production Example 1, 1.0% by mass of sulfuric acid band, and 100 ppm of yield improver (trade name: Realizer R300, manufactured by Somaru) A paper stock was prepared by adding and mixing as described above. Next, five handsheets were produced based on JIS P 8209.

[Comparative Example 5]
Instead of the pretreated filler, untreated light calcium carbonate was used, and the same procedure as in Example 12 was performed except that the addition amount of cellulose nanofibers in Production Example 1 was 1.0% by mass. .

  From the results of Example 12, Comparative Example 5 and Example 5, a part of the filler pretreated with cellulose nanofiber was replaced with an untreated filler, and cellulose nanofiber was added directly to the paper stock (Example 12). ) Is slightly lower in filler yield and paper strength than when no untreated filler is used (Example 5), but the filler is not pretreated with cellulose nanofibers, and cellulose nanofibers are added directly to the paper stock. Compared to the case (Comparative Example 5), it can be seen that the filler yield at high ash content is good and it is difficult to tear.

[Example 13]
Example 2 Based on the mass of pulp solids, a slurry of recycled pulp (DIP, CSF (Canadian Standard Freeness) 210 ml) made from newspaper waste paper and magazine waste paper was stirred with a three-one motor at a speed of 500 rpm. 15.0% by weight of pretreated light calcium carbonate (corresponding to 13% by weight of ash in paper), 1.0% by weight of sulfuric acid band, yield improver (trade name: Realizer R300) , Manufactured by Somar Co., Ltd.) was added and mixed so as to be 100 ppm to prepare a paper material. Next, five handsheets were produced based on JIS P 8209.

[Example 14]
In place of 15.0% by mass of pretreated light calcium carbonate, 10.0% by mass of pretreated light calcium carbonate and 5.0% by mass of untreated light calcium carbonate (pretreated filler: untreated filler (solid content mass) Ratio), which corresponds to 2: 1).

[Example 15]
Same as Example 14 except that pretreated light calcium carbonate: untreated light calcium carbonate (solid content mass ratio) was 1: 2.

[Comparative Example 6]
The same procedure as in Example 13 was performed except that untreated light calcium carbonate was used instead of the pretreated filler.

  From the results of Examples 13 to 15 and Comparative Example 6, it can be seen that even in paper containing recycled pulp, the filler yield and paper strength at high ash content are good.

Claims (9)

  A pretreatment method for a filler, wherein the filler is pretreated by mixing cellulose nanofibers with a papermaking filler.   The pretreatment method according to claim 1, wherein the cellulose nanofiber has a B-type viscosity (60 rpm, 20 ° C) of 500 to 7000 mPa · s in an aqueous dispersion having a concentration of 2% (w / v).   The pretreatment method according to claim 1 or 2, wherein an addition ratio of the cellulose nanofiber to the filler is 0.01 to 100 parts by mass as the cellulose nanofiber solid content with respect to the filler solid content.   The pretreatment method according to any one of claims 1 to 3, comprising calcium carbonate as the filler.   The pretreatment method according to claim 1, further comprising adding an acid.   The pretreatment method according to claim 5, wherein the acid is a sulfuric acid band. The cellulose nanofiber is
(1) N-oxyl compound, and (2) oxidized cellulose by oxidizing a cellulosic raw material with an oxidizing agent in the presence of a compound selected from the group consisting of bromide, iodide and mixtures thereof. The pretreatment method according to any one of claims 1 to 6, which is obtained by a method comprising a step of preparing, and a step of wet atomizing the oxidized cellulose to form nanofibers.   A method for producing paper, comprising adding the filler treated by the pretreatment method according to any one of claims 1 to 7 to the paper stock to make paper.   A paper obtained by papermaking a stock containing a filler treated by the pretreatment method according to any one of claims 1 to 7.