JP5771033B2 - Multilayer paper manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a multilayer paper having a multiple structure of two or more layers. More particularly, the present invention relates to a method for producing a multilayer paper using cellulose nanofibers as an interlayer adhesive.

  In recent years, due to the increasing awareness of environmental protection, paper and paperboard using forest resources are required to save resources, and the weight reduction (low basis weight) of paper and paperboard has become an unavoidable trend. However, there is a problem that the weight reduction causes a decrease in strength such as tensile strength and tear strength, and the decrease in strength causes paper breakage during manufacturing and printing, and processing defects during box making. In particular, in multi-layer papers made by combining multiple paper layers such as paperboard and postcard paper, the interlaminar strength between paper layers is also important. There was a problem that the adhesive strength was lowered.

  Conventionally, a method for improving interlayer adhesive strength has been proposed for multilayer paper such as paperboard. For example, Patent Document 1 discloses a method of spraying dried fine fibers or filler on both sides or one side of a wet paper layer. Patent Documents 2 to 5 disclose a method of applying or spraying a starch-based interlayer adhesive on one wet paper layer before making two wet paper layers together. Furthermore, Patent Documents 6 and 7 disclose polyacrylamide-based interlayer strength improvers.

JP-A-5-186998 JP 2009-249785 A JP 2005-264356 A JP 2000-080598 A Japanese Patent Laid-Open No. 5-230792 JP 2002-317393 A JP 2002-138388 A

  The inventors preliminarily studied the methods described in Patent Documents 1 to 7, and found that these methods cannot sufficiently improve the interlayer adhesive strength. In particular, it has been clarified that when a large amount of chemicals is used to improve the interlayer adhesive strength, the density increases and the formation deteriorates. In view of such circumstances, an object of the present invention is to provide a method for producing a multilayer paper having excellent interlayer adhesive strength.

The inventors have found that interlayer adhesive strength can be improved by supplying cellulose nanofibers between paper layers, and have completed the present invention.
That is, the above-mentioned subject is the following present invention:
Step A: forming a wet paper layer by making a paper stock containing pulp and water; applying an aqueous dispersion containing cellulose nanofibers having a fiber diameter of 50 nm or less on the wet paper layer obtained in Step A; Solved by a method for producing a multilayer paper comprising at least a step B of spraying; and a step C of newly forming a wet paper layer on the surface of the wet paper layer to which the aqueous dispersion has been applied or sprayed. .

  According to the present invention, a method for producing a multilayer paper having excellent interlayer adhesion strength can be provided.

It is a schematic diagram which shows the measuring method of interlayer adhesive strength.

Hereinafter, the present invention will be described in detail. In the present specification, “to” includes both ends thereof.
1. Multilayer paper manufacturing method The multilayer paper manufacturing method of the present invention is a process A in which a paper stock containing pulp and water is made to form a wet paper layer, and the fiber diameter is 50 nm or less on the wet paper layer. A step B of applying or spraying an aqueous dispersion containing cellulose nanofibers and a step C of further forming a wet paper layer on the surface of the wet paper layer on which the aqueous dispersion has been applied or sprayed are provided.

1-2. Process A
(1) Paper stock In step A, the paper stock is made to form a wet paper layer. Paper stock is an aqueous suspension containing pulp. Pulp is an aggregate of cellulose fibers derived from wood or plants. In the present invention, known pulp may be used, and examples thereof include chemical pulp (CP), groundwood pulp (GP), chemiground pulp (CGP), refiner ground pulp (RGP), thermomechanical pulp (TMP), chemi Thermomechanical pulp (CTMP), semi-chemical pulp (SCP), and bleached or unbleached pulp, deinked pulp (DIP), and corrugated cardboard disaggregated pulp (RPD) using corrugated cardboard as raw paper materials are included.

  The paper stock used in the present invention may contain a filler. Filler is a powdery additive added to paper. In the present invention, known fillers may be used, but preferred examples include calcium carbonate, white carbon, kaolin, clay, silica-calcium carbonate complex, and regenerated filler. Of these, calcium carbonate is preferred because it is easily available and has the effect of improving formation as described below, and is suitable for neutral papermaking.

  The paper stock used in the present invention contains additives such as a synthetic sizing agent such as sulfate band, AKD, ASA, various starches, dry paper strength agent, wet strength paper strength agent, coagulant, and pH adjuster. Also good. The blending ratio of these components may be as known.

(2) Papermaking Papermaking means that a wet paper layer is obtained by supplying paper material to a member that can transmit water, such as a papermaking net, and filtering it. The wet paper layer is a paper sheet containing pulp as a main component and contains moisture. The solid content concentration of the wet paper layer is 5 to 60% by mass, more preferably 5 to 30% by mass, and further preferably 10 to 25% by mass.

  Paper making may be performed by means of hand-making or machine-making, and as machine-making, a long net paper machine, a twin wire paper machine, a Yankee paper machine, a circular net paper machine, a short net network combination paper machine. A known paper machine such as a machine can be appropriately selected and used. In the present invention, it is preferable to use a multilayer paper machine from the viewpoint of work efficiency and the like. In particular, a papermaking net, an upstream headbox provided upstream of the papermaking net, one or more downstream headboxes provided downstream of the upstream headbox, and between the upstream headbox and the downstream headbox. In addition, using a paper machine equipped with a supply device for supplying an aqueous dispersion containing cellulose nanofibers having a fiber diameter of 50 nm or less, a paper stock is supplied from the upstream head box to the paper making network to form a wet paper layer. It is preferable to do. The papermaking net is a net for supplying paper, and is usually a metal net or a synthetic resin. A head box is an apparatus for storing paper stock and supplying the stock to a papermaking net.

1-2. Process B
In Step B, an aqueous dispersion containing cellulose nanofibers having a fiber diameter of 50 nm or less is applied or sprayed on the wet paper layer obtained in Step A.

(1) Aqueous dispersion containing cellulose nanofibers An aqueous dispersion containing cellulose nanofibers is a liquid in which cellulose nanofibers as a main component are dispersed in water as a dispersion medium. The term “main component” as used herein means that 50% by mass or more of cellulose nanofibers are contained with respect to the total solid content in the aqueous dispersion. In order to efficiently apply or spray an aqueous dispersion containing cellulose nanofibers, the concentration of cellulose nanofibers in the aqueous dispersion is preferably 0.01 to 10% (w / v), 0.05 to 2% ( w / v) is more preferable, and 0.1 to 1% (w / v) is more preferable. If the concentration is too high, the fluidity will deteriorate and the operation efficiency will decrease, and if the concentration is too low, the amount of moisture contained in the resulting multilayer paper will increase, which may lead to poor squeezing and deterioration of the basis weight profile. There is. The aqueous dispersion containing cellulose nanofibers can be prepared by dispersing cellulose nanofibers in water using a high-speed shear mixer or a high-pressure homogenizer.

  In the present invention, the aqueous dispersion may contain additives in addition to cellulose nanofibers. One or more additives may be used in combination. Examples of such additives include, but are not limited to, general papermaking starches, coagulants, retention agents, PVA, CMC, alginic acid, and fine fibers. Hereinafter, the cellulose nanofiber will be described in detail.

1) Cellulose nanofibers Cellulose nanofibers are single microfibrils of cellulose having a diameter of 1 to 100 nm, which are obtained by defibrating a cellulose-based raw material. Different from fine fibers. Cellulose-based raw materials are kraft pulp or sulfite pulp derived from various woods, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer, a mill, or the like, or microcrystalline cellulose powder purified by chemical treatment such as acid hydrolysis .

  The fiber diameter of the cellulose nanofiber used in the present invention is 50 nm or less. The fiber diameter is related to the amount of hydrogen bonding groups present on the surface of the cellulose nanofiber. The hydrogen bonding group is a hydroxyl group, a carboxyl group, or a carboxylate group. The smaller the fiber diameter, the larger the surface area of the cellulose nanofibers. Therefore, when compared with the same mass, the amount of hydrogen bonding groups present on the surface is larger than that of cellulose nanofibers with a large fiber diameter. The greater the amount of hydrogen bonding groups, the easier it is to form hydrogen bonds with the pulp in the wet paper layer, so that the interlayer adhesion strength can be increased. Therefore, the upper limit of the fiber diameter may be 50 nm, but in order to further increase the interlayer adhesion strength, 40 nm or less is preferable, and 30 nm or less is more preferable. On the other hand, if the fiber diameter is excessively small, the cellulose nanofibers may easily aggregate in the dispersion when the cellulose nanofibers are dispersed in water. Therefore, the lower limit of the fiber diameter is preferably 2 nm, and more preferably 10 nm.

  The fiber diameter can be determined from an electron microscope image or an atomic force microscope image of cellulose nanofibers. As will be described later, the fiber diameter can be adjusted mainly by the atomization step in the production of cellulose nanofibers.

  In the cellulose nanofiber used in the present invention, the primary hydroxyl group at the 6-position in the pyranose ring of cellulose is oxidized to a carboxyl group or a salt thereof. A pyranose ring is a six-membered ring carbohydrate consisting of five carbons and one oxygen. The 6-position primary hydroxyl group is an OH group bonded to a 6-membered ring via a methylene group. When the cellulose raw material is oxidized using the N-oxyl compound, the primary hydroxyl group is selectively oxidized. This mechanism can be explained as follows. Natural cellulose is a nanofiber when it is biosynthesized, but it is not a nanofiber because hydrogen bonds are mainly formed on the surface of the nanofiber when they converge to form large units. However, when the cellulose raw material is oxidized using an N-oxyl compound, the primary hydroxyl group at the C6 position of the pyranose ring is selectively oxidized, and this oxidation reaction remains on the surface of the microfibril. Carboxyl groups are introduced at a high concentration. Since the carboxyl groups are negatively charged, they repel each other, and when dispersed in water, the aggregation of microfibrils is hindered, resulting in cellulose nanofibers.

  The carboxyl group may form a salt with an alkali metal or the like. The amount of the carboxyl group and its salt (hereinafter collectively referred to as “carboxyl group and the like”) is preferably 1.10 mmol / g or more based on the dry mass of the cellulose nanofiber. As described above, the carboxyl group and the like can hydrogen bond with the pulp in the wet paper layer, so if this amount is large, the interlayer adhesion strength is improved. Therefore, the lower limit of this amount is more preferably 1.20 mmol / g or more, and further preferably 1.40 mmol / g or more. However, when there are many carboxyl groups etc., when a cellulose nanofiber is disperse | distributed to water, a cellulose nanofiber may become easy to aggregate in water. For this reason, the upper limit of the amount of carboxyl groups and the like is preferably 1.70 mmol / g or less, and more preferably 1.60 mmol / g or less. The amount of a carboxyl group or the like can be measured by the method described in Japanese Patent Application No. 2010-217280, for example. Moreover, as will be described later, the amount of carboxyl groups and the like in cellulose nanofibers can be adjusted by an oxidation step in cellulose nanofiber production.

  Properties such as fiber diameter, fiber length, and degree of polymerization of cellulose nanofibers are reflected in the viscosity of the aqueous dispersion. In the present invention, the viscosity of the aqueous dispersion having a concentration of 2% (w / v) is 500 to 7000 mPa · s from the viewpoints of increasing the interlayer adhesive strength and handling properties as an interlayer adhesive. preferable. Viscosity was measured at 25 ° C. using a B-type viscometer. 64. The concentration w / v is the number of g of cellulose nanofibers per 100 mL of water.

2) Method for Producing Cellulose Nanofiber The cellulose nanofiber used in the present invention is in the presence of (a) an N-oxyl compound and (b) a compound selected from the group consisting of bromide, iodide and a mixture thereof. (C) It is manufactured by a method including an oxidation step of oxidizing a cellulosic raw material using an oxidizing agent, and a wet atomization step in which the oxidized cellulose obtained in the previous step is subjected to wet atomization treatment to form nanofibers. preferable.

i) Oxidation step The N-oxyl compound refers to a compound capable of generating a nitroxy radical. Examples of the N-oxyl compound used in the present invention include substances 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-tetra A compound that generates a methyl-1-piperidine-N-oxy radical (hereinafter referred to as 4-hydroxy TEMPO) is preferable. As the N-oxyl compound, a derivative obtained from TEMPO or 4-hydroxy TEMPO can also be used. Of these, 4-hydroxy TEMPO derivatives are most preferred from the viewpoint of activity. Examples thereof include derivatives 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, and derivatives obtained by esterifying with carboxylic acid or sulfonic acid. It is.

  Specific 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.)
In the present invention, a radical of an N-oxyl compound represented by the following formula 5, that is, an azaadamantane type nitroxy radical may be used. This compound can produce uniform cellulose nanofibers in a short time.

(In Formula 5, R ₅ and R ₆ are the same or different and represent hydrogen or a linear or branched alkyl group having 1 to 6 carbon atoms.)
The amount of the N-oxyl compound is not particularly limited as long as it is a catalytic amount capable of converting the cellulose-based raw material into nanofibers. The amount of the N-oxyl compound is, for example, 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 the absolutely dry cellulosic raw material.

  Bromide is a compound containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Further, an iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, 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 an absolutely dry cellulosic raw material.

  As the oxidant, known oxidants such as halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide and the like can be used. From the viewpoint of production cost, sodium hypochlorite, which is currently most widely used in industrial processes and has low environmental impact, is particularly preferred. The amount of the oxidizing agent used can be selected within a range that can promote the oxidation reaction. The amount thereof is, for example, about 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol with respect to 1 g of an absolutely dry cellulosic raw material.

Cellulosic materials are as described above.
This oxidation step allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature may be a room temperature of about 15 to 30 ° C. As the reaction proceeds, a carboxyl group is generated in the cellulose, so that the pH of the reaction solution is reduced. In order to advance the oxidation reaction efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11. The reaction medium is preferably water because it is easy to handle and hardly causes side reactions.

ii) Wet atomization step In this step, cellulose nanofibers are produced from the oxidized cellulose-based material obtained in the above step. The wet atomization treatment refers to a treatment for reducing the size of the oxidized cellulose-based raw material performed in a dispersion medium such as water. That is, the oxidized cellulose raw material is defibrated by this wet atomization treatment to be nanofibers. In this step, for example, a mixing / stirring or 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 ultra-high pressure homogenizer that enables a pressure of 100 MPa or more, preferably 120 MPa or more, and more preferably 140 MPa or more, the resulting dispersion has a viscosity in the above range. Cellulose nanofibers can be produced efficiently.

iii) Ultraviolet irradiation treatment In the present invention, before the wet atomization step, the oxidized cellulose raw material obtained in the oxidation step is irradiated with ultraviolet rays to reduce the viscosity of the cellulose nanofiber dispersion and increase the fluidity. It is preferable to carry out the treatment. By the ultraviolet irradiation, the degree of polymerization of the cellulose nanofibers decreases, and the viscosity of the cellulose nanofiber dispersion decreases. The temperature of the oxidized cellulose-based raw material when irradiated with ultraviolet rays is preferably 20 ° C. or higher because the efficiency of the photo-oxidation reaction is increased. It is preferable because it does not reach. Moreover, although the pH at the time of irradiating an ultraviolet-ray is not specifically limited, For example, it is preferable from the point of process simplification to process in the neutral region of about pH 6.0-8.0. The wavelength of the ultraviolet light is preferably 100 to 400 nm. The ultraviolet treatment can be repeated a plurality of times, and the number of repetitions can be appropriately set according to the target quality and the relationship with the post-treatment.

(2) Application or spraying A known device such as a dispenser can be used for application. For spraying, a known device such as a spray nozzle can be used. From the viewpoint of increasing the interlayer adhesion strength, the amount (solid content) of cellulose nanofibers to be applied or sprayed is 0.001 to 30% by mass with respect to the solid content of the wet paper layer formed in Step A, 0.01 -30 mass% is preferable, 0.05-10 mass% is more preferable, 0.1-5 mass% is further more preferable. The solid content of the wet paper layer is a solid content obtained by drying the wet paper layer.

  As described in the step A, it is preferable to use the above-mentioned paper machine in the present invention. In this case, the aqueous dispersion containing cellulose nanofibers is applied or sprayed onto the wet paper layer obtained in step A via a supply device. The supply device is specifically a dispenser or a spray nozzle. The aqueous dispersion containing cellulose nanofibers may be applied or sprayed over the entire width of the wet paper layer in the paper machine width direction or partially. When an aqueous dispersion containing cellulose nanofibers is applied or sprayed over the entire width in the paper machine width direction, the cellulose nanofibers are formed in a very thin layer and are present on the entire surface between the paper layers, resulting in higher interlayer adhesion strength.

1-3. Process C
In step C, a wet paper layer is further formed on the surface of the wet paper layer obtained in step B on which the aqueous dispersion has been applied or sprayed. The wet paper layer provided in this step is referred to as “upper wet paper layer” for convenience.

  The method for forming the upper wet paper layer is not limited. For example, a wet paper layer was prepared in the same manner as in Step A, and the aqueous dispersion of the wet paper layer obtained in Step B was applied or sprayed thereon. An upper wet paper layer can be formed by laminating so as to face the surface. Alternatively, the upper wet paper layer may be formed by supplying the stock on the surface of the wet paper layer obtained in step B on which the aqueous dispersion is applied or sprayed. The stock used in Step C may be the same as or different from the stock used in Step A.

  As already described, since it is preferable to use the paper machine in the present invention, the paper from the downstream head box is placed on the surface of the wet paper layer obtained in step B on which the aqueous dispersion is applied or sprayed. It is preferable to form a top wet paper layer by supplying a material.

  By performing Step B after Step C and further repeating this cycle, a multilayer paper having a desired number of layers can be produced.

1-4. Other Steps The production method of the present invention may further include a step of pressing a wet paper layer including at least the layer obtained in steps A to C and a step of drying. These steps may be performed as known.

1-5. Mechanism of Action Multilayer paper having excellent interlayer adhesion strength can be obtained by the production method of the present invention. Although this mechanism is not limited, it is considered as follows.

  The cellulose nanofiber used in the present invention has a large number of hydrogen bonding groups on the fiber surface. In the present invention, the aqueous dispersion containing the cellulose nanofibers is supplied to the wet paper layer surface. For this reason, the pulp and cellulose nanofiber which exist in a wet paper layer are in the state which can flow, and the pulp and cellulose nanofiber which exist in a wet paper layer couple | bond together through a hydrogen bond. Furthermore, since a new upper wet paper layer is formed on this surface, the pulp existing on the upper wet paper layer surface and cellulose nanofibers are bonded through hydrogen bonds. As a result, a multilayer paper having excellent interlayer adhesive strength can be produced.

2. Multilayer paper The multilayer paper obtained by the production method of the present invention has a plurality of paper layers and cellulose nanofibers existing between the layers. As described above, the pulp on the paper layer surface and the cellulose nanofiber are bonded through hydrogen bonds, and thus have excellent interlayer adhesion strength. For this reason, the multilayer paper obtained by the production method of the present invention can be used for various applications, and is useful as a cardboard liner, white paperboard, paper tube base paper, bag making paper, postcard paper and the like. Basis weight, paper thickness, etc. are not specifically limited, What is necessary is just to set suitably according to a desired use. Further, the multilayer paper of the present invention may be provided with a coating layer containing a pigment on one side or both sides thereof.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited by an Example.
[Production Example 1]
Powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 24 μm) 15 g (absolutely dried) 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 cellulose is uniformly dispersed. After adding 50 ml of sodium hypochlorite aqueous solution (effective chlorine 5%) to the reaction system, the pH was adjusted to 10.3 with 0.5N hydrochloric acid aqueous solution, and the oxidation reaction was started. 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, the oxidized powdered cellulose was separated by centrifugal operation (6000 rpm, 30 minutes, 20 ° C.), and washed sufficiently 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 5 times at a pressure of 140 MPa to obtain a transparent gel dispersion. Got. In addition, about the obtained cellulose nanofiber, the B-type viscosity (60 rpm, 20 degreeC) measured using VISCOMETER TV-10 viscometer (made by Toki Sangyo Co., Ltd.) was 890 mPa * s. Moreover, the maximum fiber diameter of the cellulose nanofiber was 10 nm, and the number average fiber diameter was 6 nm from observation with an atomic force microscope (AFM).

[Production Example 2]
After obtaining powdered cellulose oxidized in the same manner as in Production Example 1, it was treated with a 20 W low-pressure mercury lamp that irradiates ultraviolet rays of 254 nm for 0.5 hours. Next, a 1% (w / v) slurry of oxidized powdered cellulose treated with ultraviolet rays was treated 10 times with an ultra-high pressure homogenizer at a pressure of 140 MPa to obtain a transparent gel dispersion. The cellulose nanofibers obtained had a B-type viscosity of 700 mPa · s, a maximum fiber diameter of 10 nm, and a number average fiber diameter of 6 nm.

[Example 1]
The cardboard was disaggregated in water to prepare an aqueous dispersion (slurry) of raw pulp (CSF (Canadian Standard Freeness) 420 ml). Using a three-one motor, a paper stock was prepared by adding a sulfuric acid band while stirring the aqueous dispersion at a speed of 600 rpm. The addition amount of the sulfuric acid band was set to 3.5% by mass of the pulp solid content in the stock. Next, a wet paper layer was made based on JIS P 8209, and dehydrated with a couch roll to produce six hand-made wet paper layers having a water content of 75 to 80% by mass. The amount of water was determined according to JIS P 8127: 1998.

  Using a spray nozzle, an aqueous dispersion in which the concentration of the cellulose nanofibers obtained in Production Example 1 was adjusted to 0.25% (w / v) was sprayed on one side of the handmade wet paper layer. At this time, the cellulose nanofiber solid content was 0.1% by mass with respect to the solid content of the handmade wet paper layer.

  Another hand-made wet paper layer (corresponding to the upper wet paper layer) was bonded so as to face the spray surface, and pressing was performed based on JIS P 8209. Then, it was made to dry at 110 degreeC for 5 minute (s) with the cylinder dryer, and the multilayer paper was manufactured. Similarly, a total of three multilayer papers were produced.

The interlayer adhesive strength of the multi-layer paper thus obtained was measured as follows. A method for measuring the interlayer adhesive strength will be described with reference to FIG. In FIG. 1, 1 is a test piece and 2 is a delamination part. In FIG. 1, the vertical tensile testing machine is omitted.
1) A test piece 1 was prepared by cutting a multilayer paper composed of two layers into a length of 30 mm or more and a width of 38 mm.
2) The interlayer peeling part 2 was provided by peeling the interlayer in a part near the end part of the test piece 1.
3) Using a vertical tensile tester (Autograph AGS-100D, manufactured by Shimadzu Corporation), one layer in the delamination part 2 was fixed to the lower base, and the other layer was fixed to the upper clamp.
4) The upper clamp was moved 30 mm upward at a peeling speed of 30 mm / min to delaminate the test piece 1.
5) The measured value was defined as interlayer adhesion strength.

[Example 2]
A multilayer paper was produced and evaluated in the same manner as in Example 1 except that the solid content of the sprayed cellulose nanofibers was changed to 0.8 mass% with respect to the solid content of the handmade wet paper layer.

[Example 3]
A multilayer paper was produced and evaluated in the same manner as in Example 1 except that the solid content of the sprayed cellulose nanofibers was 1.5% by mass with respect to the solid content of the handmade wet paper layer.

[Comparative Example 1]
A multilayer paper was produced and evaluated in the same manner as in Example 1 except that the cellulose nanofiber was not sprayed.

[Comparative Example 2]
A multilayer paper was produced and evaluated in the same manner as in Example 1 except that 5.0% by mass of water was sprayed instead of cellulose nanofibers.

[Comparative Example 3]
Multilayer paper in the same manner as in Example 1 except that 0.4% by mass of a paper strength agent (RB14-004 Harima Co., Ltd.) was sprayed on the solid content of the handmade wet paper layer instead of cellulose nanofibers. Were manufactured and evaluated.

[Comparative Example 4]
A multilayer paper was prepared in the same manner as in Example 1 except that starch (SK-100 manufactured by Nippon Corn Starch Co., Ltd.) was sprayed in an amount of 1.0% by mass with respect to the solid content of the handmade wet paper layer instead of cellulose nanofibers. Manufactured and evaluated.

[Comparative Example 5]
Example 1 except that 0.8% by mass of cellulose nanofibers was added to the paper stock with respect to the solid content of the stock (pulp and sulfate bands), and the aqueous dispersion of cellulose nanofibers was not sprayed. In the same manner, multilayer paper was produced and evaluated.

[Comparative Example 6]
A multilayer paper was produced and evaluated in the same manner as in Comparative Example 5 except that 0.4% by mass of a paper strength agent (RB14-004 manufactured by Harima Co., Ltd.) was added to the paper material instead of cellulose nanofibers.

[Comparative Example 7]
A multilayer paper was produced and evaluated in the same manner as in Comparative Example 5 except that 1.0% by mass starch (SK-100, manufactured by Nippon Corn Starch Co., Ltd.) was added to the paper material instead of cellulose nanofibers.

  These results are shown in Table 1.

From this result, it was clarified that the interlayer adhesive strength is greatly improved by supplying cellulose nanofibers between wet paper layers.
Further, from the comparison between Examples and Comparative Examples 2 to 4, by supplying moisture, a paper strength agent, or starch between wet paper layers, the interlayer adhesive strength is slightly improved, but there is no improvement effect as much as cellulose nanofibers. It became clear.

Furthermore, from the comparison between Example and Comparative Example 5, it became clear that even when cellulose nanofibers were internally added to the stock, the interlayer adhesion strength was not improved.
Furthermore, from the comparison between Examples and Comparative Examples 6-7, it was found that when a paper strength agent or starch was added internally to the paper stock, the interlayer adhesive strength was slightly improved, but the improvement effect was not as good as the Examples. . When a paper strength agent or starch is internally added to the stock, the yield of fine fibers in the paper layer is improved. In Comparative Examples 6 to 7, it is considered that the interlayer adhesive strength is slightly improved.

1 Test piece 2 Delamination part

Claims (9)

Step A for forming a wet paper layer by making a paper stock containing pulp and water,
On the wet paper layer obtained in step A, the fiber diameter of Ri der less 50 nm, a step of applying or spraying an aqueous dispersion containing cellulose nanofibers having a Karuboshireto group is a carboxyl group or a salt thereof B, and the A step C of further forming a wet paper layer on the surface of the wet paper layer on which the aqueous dispersion has been applied or sprayed;
A method for producing a multilayer paper comprising at least A papermaking net, an upstream headbox provided upstream of the papermaking net, one or more downstream headboxes provided downstream of the upstream headbox, and provided between the upstream headbox and the downstream headbox, fiber diameter Ri der below 50 nm, the paper machine used with the feeding apparatus for feeding an aqueous dispersion containing cellulose nanofibers having a Karuboshireto group is a carboxyl group or a salt thereof,
In the step A, the wet stock layer is formed by supplying the stock from the upstream headbox to the papermaking net,
In the step B, an aqueous dispersion containing the cellulose nanofibers is applied or sprayed on the wet paper layer obtained in the step A using the supply device, and the wetness obtained in the step B in the step C The method for producing a multilayer paper according to claim 1, wherein a wet paper layer is formed by supplying the stock from the downstream head box on a surface of the paper layer on which the aqueous dispersion has been applied or sprayed. The manufacturing method of Claim 1 or 2 whose total amount of the carboxyl group in the said cellulose nanofiber and the carbosylate group which is its salt is 1.10 mmol / g or more with respect to the absolute dry mass of a cellulose nanofiber. The manufacturing method of Claim 3 whose total amount of the carboxyl group in the said cellulose nanofiber and the carbosylate group which is its salt is 1.70 mmol / g or less with respect to the absolute dry mass of a cellulose nanofiber. The manufacturing method in any one of Claims 1-4 whose density | concentration of the cellulose nanofiber in the said dispersion liquid is 0.05-2% (w / v). A plurality of paper layers state, and are fiber diameter of 50nm or less present in the interlayer, multilayer paper having a cellulose nanofibers having a Karuboshireto group is a carboxyl group or a salt thereof. According obtained by the method of any of claim 1 to 5, a plurality of paper layers state, and are fiber diameter of 50nm or less present in the interlayer, and cellulose nanofibers having a Karuboshireto group is a carboxyl group or a salt thereof Multi-layer paper having. The multilayer paper of Claim 6 or 7 whose total amount of the carboxyl group in the said cellulose nanofiber and the carbosylate group which is its salt is 1.10 mmol / g or more with respect to the absolute dry mass of a cellulose nanofiber. The multilayer paper of Claim 8 whose total amount of the carboxyl group in the said cellulose nanofiber and the carbosylate group which is its salt is 1.70 mmol / g or less with respect to the absolute dry mass of a cellulose nanofiber.

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