JP2018154699A - Method for producing cellulose nanofiber film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a cellulose nanofiber film that can be easily peeled from a base material and is excellent in appearance, but in which a production process is not complicated.SOLUTION: A method for producing a cellulose nanofiber film includes: adding one or more additives selected from glycerol, sorbitol and a polyvinylacetamide-based compound to a dispersion of a cellulose nanofiber to obtain a coating liquid; defoaming the coating liquid; applying the coating liquid to a resin base material; and drying the resin base material to be formed into a film shape.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a cellulose nanofiber film.

  Currently, cellulose nanofibers (hereinafter also referred to as CNF), which have been refined to a nano-order fiber diameter, are used for papermaking, cosmetics, daily necessities, resin reinforcing materials, power storage element separators, functional filters, low CTE groups Application to materials films, bio-medical base materials, etc. is being studied.

  On the other hand, CNF can be formed into a film by coating on a paper substrate or the like. However, CNF has a gel-like structure even at a low solid content concentration and exhibits a very high viscosity. Therefore, it is difficult to obtain a desired film from CNF.

  For example, Patent Document 1 states that “a nanofibrillated cellulose suspension is directly applied to and diffused on the surface of a plastic support material, whereby the nanofibrillated cellulose is deposited on the support material. A method for producing a CNF film (membrane) characterized in that is formed. However, this proposal does not examine the point (easy peeling) of peeling the obtained film from the support. The proposal also does not consider the point of making the appearance of the obtained film excellent, for example, the point that wrinkles or cracks do not exist.

  Further, for example, as shown in paragraph 0042 and subsequent paragraphs, Patent Document 2 discloses that “(1) cellulose microfibrils are 0.05% by weight or more and 0.5% by weight or less, and the boiling point range under atmospheric pressure is 50 ° C. or more and 200 ° C. An aqueous dispersion containing 0.5 to 10% by weight of the following oily compound and 85 to 99.5% by weight of water, wherein the oily compound is an emulsion dispersed in an aqueous phase A water-based dispersion preparation step for preparing a liquid, (2) a papermaking step for controlling the concentration of the cellulose microfibrils (solid content concentration) and the concentration of the oily compound to a specific range to obtain a concentrated composition, (3) the concentrated composition A method for producing a cellulose sheet comprising three steps of drying the oily compound and water by evaporating and removing the oily compound and water from the concentrated composition is proposed. However, the proposed manufacturing process is complicated and increases the manufacturing cost.

Special table 2015-502835 JP 2012-036529 A

  The main problem to be solved by the present invention is to propose a method for producing a cellulose nanofiber film that can be easily peeled off from a substrate and has an excellent appearance, but does not complicate the production process. .

Means for solving the above problems are as follows:
One or more additives selected from glycerin, sorbitol, and polyvinylacetamide compounds are added to the dispersion of cellulose nanofibers to obtain a coating solution,
Defoam this coating solution, apply it to a resin substrate, dry it into a film,
This is a method for producing a cellulose nanofiber film.

  According to the present invention, the cellulose nanofiber film can be easily peeled from the base material and has an excellent appearance, but the manufacturing process is not complicated.

  Next, the form for implementing this invention is demonstrated. The following embodiment is an example of the present invention. Various modifications can be made to the following embodiments without departing from the spirit of the present invention.

  In the method for producing a cellulose nanofiber (CNF) film of this embodiment, a coating liquid is obtained by adding one or more additives selected from glycerin, sorbitol, and polyvinylacetamide-based compound to an aqueous solution of CNF. The coating solution is defoamed, applied to a resin substrate, and dried to form a film. Preferably, an alginate and a polyamide epichlorohydrin compound are further added to an aqueous solution of CNF. Hereinafter, it demonstrates in order.

(CNF)
CNF (cellulose fine fiber) can be obtained by defibrating (miniaturizing) cellulose fiber (raw fiber).

  As the raw material fiber, for example, a plant-derived fiber, an animal-derived fiber, a microorganism-derived fiber, or the like can be used. These fibers can be used alone or in combination, if necessary. However, it is preferable to use plant-derived fibers (plant fibers) as raw material fibers, and it is more preferable to use pulp fibers which are a kind of plant fibers. When the raw fiber is a pulp fiber, it is easy to adjust the physical properties of CNF.

  As plant fibers, for example, wood pulp made from hardwood, conifers, etc., non-wood pulp made from straw, bagasse, etc., recovered paper, waste paper pulp made from waste paper, etc. (DIP), etc. should be used. Can do. These plant fibers can be used alone or in combination.

  As the wood pulp, for example, chemical pulp such as hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), mechanical pulp (TMP), waste paper pulp (DIP) and the like can be used. These wood pulps can be used alone or in combination.

  Hardwood kraft pulp (LKP) may be hardwood bleached kraft pulp, hardwood unbleached kraft pulp, or hardwood semi-bleached kraft pulp. The softwood kraft pulp (NKP) may be softwood bleached kraft pulp, softwood unbleached kraft pulp, or softwood semi-bleached kraft pulp. The waste paper pulp (DIP) may be magazine waste paper pulp (MDIP), newspaper waste paper pulp (NDIP), corrugated waste paper pulp (WP), or other waste paper pulp.

  Prior to defibration, the raw fiber can be subjected to pretreatment such as beating if necessary. This pretreatment can be performed by a physical method or a chemical method, preferably by a physical method or a chemical method. Pretreatment by physical or chemical methods prior to defibration can greatly reduce the number of defibrations and can greatly reduce the energy required for defibration.

  It is preferable to employ beating as pre-processing by a physical method. When the raw material fibers are beaten in advance, the raw material fibers are cut out, so that the problem that the fibers are entangled and aggregated is solved. From such a viewpoint, the beating is preferably performed until the freeness of the raw fiber is 120 ml or less, more preferably 110 ml or less, and particularly preferably 100 ml or less. The freeness is a value measured according to JIS P8121-2 (2012).

  The beating can be performed using, for example, a refiner or a beater.

  Examples of the pretreatment using a chemical method include hydrolysis of a polysaccharide with an acid (acid treatment), hydrolysis of a polysaccharide with an enzyme (enzyme treatment), swelling of the polysaccharide with an alkali (alkali treatment), and oxidation of the polysaccharide with an oxidizing agent ( Oxidation treatment), polysaccharide reduction with a reducing agent (reduction treatment), and the like can be employed.

  The physical method and chemical method as the pretreatment can be performed simultaneously or separately.

  As the pretreatment, in addition to the above, for example, chemical treatment such as phosphate esterification treatment, acetylation treatment, cyanoethylation treatment, and the like can be performed.

  The raw fiber is subjected to pretreatment such as beating and then defibrated (miniaturized). By this defibration, the raw fiber is microfibrillated to become CNF (cellulose nanofiber).

  For example, high-pressure homogenizers, high-pressure homogenizers, etc., stone mill-type friction machines such as grinders, grinders, conical refiners, disc refiners, etc., various devices, etc. More than one means can be selected and used. However, it is preferable that the raw fiber is defibrated using an apparatus / method for defibrating with a water stream, particularly a high-pressure water stream. According to this apparatus and method, the obtained CNF has very high dimensional uniformity and dispersion uniformity. On the other hand, for example, when a grinder that grinds between rotating grindstones is used, it is difficult to defibrate the fibers uniformly, and a fiber lump that cannot be partially broken remains, and the intended effect cannot be obtained. There is a fear. In this regard, the present inventors conducted a test in which pulp fibers were defibrated and each obtained fiber was observed with a microscope by a method of defibrating with a high-pressure water flow and a method of grinding between rotating grindstones. It was. As a result, it was found that the fiber width obtained by the method of defibration with a high-pressure water stream had a uniform fiber width.

  As an apparatus for defibrating with a high-pressure water stream, for example, Starburst (registered trademark) of Sugino Machine Co., Ltd., Nanovaita \ Nanovater (registered trademark) of Yoshida Kikai Kogyo Co., Ltd., and the like exist. In addition, as a grinder, for example, Masukoloyder (registered trademark) of Masuko Sangyo Co., Ltd. exists.

Next, a method for defibration with a high-pressure water stream will be described in detail.
For defibration with a high-pressure water stream, the raw fiber dispersion is pressurized to 30 MPa or more, preferably 100 MPa or more, more preferably 150 MPa or more, particularly preferably 220 MPa or more (high pressure condition) with a pressure intensifier, and the pore diameter is 50 μm or more. It is preferable to carry out by a method of reducing pressure (pressure reduction condition) so that the pressure difference is, for example, 30 MPa or more, preferably 80 MPa or more, more preferably 90 MPa or more. The raw fiber is defibrated by the cleavage phenomenon caused by this pressure difference. When the pressure under the high pressure condition is low or when the pressure difference from the high pressure condition to the reduced pressure condition is small, the defibrating efficiency may be lowered, and it may be necessary to repeat the ejection to obtain a desired fiber diameter.

  It is preferable to use a high-pressure homogenizer as an apparatus for defibrating with a high-pressure water stream. The high-pressure homogenizer is a homogenizer capable of discharging a dispersion of raw fiber at a pressure of, for example, 10 MPa or more, preferably 100 MPa or more. When the raw material fibers are treated with a high-pressure homogenizer, collisions between the raw material fibers, a pressure difference, microcavitation, and the like act, and defibration occurs effectively. Therefore, the number of times of fibrillation can be reduced, and the production efficiency of CNF can be increased. In addition, when the raw material fiber is sufficiently softened by the pretreatment, it can be effectively defibrated by a high-pressure homogenizer. Therefore, the number of times of defibration can be reduced and productivity can be increased.

  As the high-pressure homogenizer, it is preferable to use a high-pressure homogenizer that makes the raw fiber dispersion collide in a straight line. As such an apparatus, for example, there is an opposed collision type high-pressure homogenizer (microfluidizer / MICROFLUIDIZER (registered trademark), wet jet mill). In this apparatus, two upstream flow paths are formed so that a pressurized dispersion of raw material fibers collides oppositely at the junction. Further, the raw material fiber dispersion collides at the junction, and the collided raw material fiber dispersion flows out of the downstream channel. The downstream flow path is provided perpendicular to the upstream flow path, and a T-shaped flow path is formed by the upstream flow path and the downstream flow path. When this apparatus is used, the energy of the apparatus is converted to collision energy to the maximum, so that the raw fiber can be defibrated more efficiently.

  The fibrillation of the raw fiber is such that the average fiber diameter, average fiber length, water retention, crystallinity, peak value of pseudo particle size distribution, and pulp viscosity of the obtained CNF are the desired values or evaluation as shown below. It is preferable to carry out. However, it is more preferable to defibrate until the raw fiber reaches a predetermined fiber diameter (average fiber diameter). By defibrating until the raw fiber reaches a predetermined fiber diameter, the water retention of CNF can be kept low. As a result, the coating property of the coating liquid can be improved.

(Average fiber diameter)
The average fiber diameter (average diameter of single fibers) of CNF is, for example, 4 to 500 nm, preferably 6 to 300 nm, and more preferably 10 to 100 nm. The average fiber diameter of CNF can be adjusted by, for example, selection of raw fiber, pretreatment, crushing, and the like.

The measurement method of the average fiber diameter of CNF is as follows.
First, 100 ml of an aqueous dispersion of CNF having a solid concentration of 0.01 to 0.1% by mass is filtered through a Teflon (registered trademark) membrane filter, and the solvent is substituted once with 100 ml of ethanol and three times with 20 ml of t-butanol. . Next, the sample is freeze-dried and coated with osmium. This sample is observed with an electron microscope SEM image at a magnification of 5,000, 10,000, or 30,000 depending on the width of the constituent fibers. Specifically, two diagonal lines are drawn on the observation image, and three straight lines passing through the intersections of the diagonal lines are arbitrarily drawn. Further, the total width of 100 fibers intersecting with the three straight lines is visually measured. And let the median diameter of a measured value be an average fiber diameter.

(Average fiber length)
The average fiber length (length of single fiber) of CNF is, for example, 1 to 5000 μm, preferably 10 to 3000 μm, and more preferably 100 to 1000 μm. The average fiber length of CNF can be adjusted by, for example, selection of raw fiber, pretreatment, defibration and the like. The method for measuring the average fiber length is the same as in the case of the average fiber diameter, and the length of each fiber is visually measured. The median length of the measured value is the average fiber length.

(Water retention)
The water retention of CNF is, for example, 300 to 500%, preferably 350 to 480%, more preferably 380 to 450%. The water retention of CNF can be adjusted by, for example, selection of raw fiber, pretreatment, defibration and the like. The water retention is determined by JAPAN TAPPI No. 26 (2000).

(Crystallinity)
The crystallinity of CNF is, for example, 50 to 90%, preferably 55 to 88%, more preferably 60 to 85%. The crystallinity of CNF can be adjusted by, for example, selection of raw fiber, pretreatment, defibration, and the like. The crystallinity is a value measured by an X-ray diffraction method in accordance with “General Rules for X-ray Diffraction Analysis” of JIS-K0131 (1996). In this respect, CNF has an amorphous part and a crystalline part, and the crystallinity means the ratio of the crystalline part in the entire CNF.

(Peak value)
The peak value in the pseudo particle size distribution curve of CNF is preferably one peak. When it is one peak, CNF has high uniformity of fiber length and fiber diameter, and is excellent in drying properties.

  The peak value of CNF is, for example, 5 to 25 μm, preferably 7 to 23 μm, and more preferably 10 to 20 μm. The peak value of CNF can be adjusted by, for example, selection of raw fiber, pretreatment, defibration and the like. The peak value is a value measured according to ISO-13320 (2009). More specifically, first, the volume-based particle size distribution of the CNF aqueous dispersion is examined using a particle size distribution measuring device (laser diffraction / scattering type particle size distribution measuring instrument manufactured by Seishin Corporation). Next, the median diameter of CNF is measured from this distribution. This median diameter is the peak value.

(Pulp viscosity)
The pulp viscosity of CNF is, for example, 1.5 to 7.0 cps, preferably 1.8 to 6.8 cps, more preferably 2.0 to 6.5 cps. The pulp viscosity of CNF can be adjusted by, for example, selection of raw fiber, pretreatment, defibration and the like. Pulp viscosity is a value measured according to JIS-P8215 (1998). A higher pulp viscosity means a higher degree of cellulose polymerization.

(CNF dispersion)
CNF obtained by defibration is dispersed in an aqueous medium to form a dispersion. The total amount of the aqueous medium is particularly preferably water (aqueous solution). However, the aqueous medium may be another liquid partly compatible with water. As other liquids, for example, lower alcohols having 3 or less carbon atoms can be used.

  The dispersion is preferably adjusted so that the main component, preferably 1.0% by mass or more, is CNF. The solid content concentration of the dispersion is preferably 1.0% by mass or more because it is easy to handle.

  The B-type viscosity of the dispersion when the CNF concentration is 2% by mass (w / w) is preferably 3500 cps or less from the viewpoint of coatability. The B type viscosity is a value measured according to JIS-Z8803 (2011) “Method for measuring viscosity of liquid” for a dispersion of CNF having a solid content concentration of 2.0 mass%. The B-type viscosity is a resistance torque when the dispersion is stirred, and the higher the viscosity, the more energy required for stirring.

  The following additives are added to the CNF aqueous solution obtained as described above. In this embodiment, it is possible to obtain a CNF film that can be easily peeled off from the base material and has an excellent appearance only by adding an additive. . Hereinafter, the additives will be described in order.

(Glycerin)
Glycerin (glycerol) is a trivalent alcohol. Glycerin is obtained with a fatty acid by hydrolysis of fats and oils, for example. In the present specification, glycerol includes derivatives of glycerol.

  When glycerin is added as an additive, flexibility can be imparted to the CNF film, so that shrinkage wrinkles and cracks during drying can be reduced. (Good appearance can be obtained.)

  As glycerin, it is preferable to use glycerin which is not chemically modified. When glycerin that is not chemically modified is used, the dispersibility of CNF is improved. Moreover, when the glycerin which is not chemically modified is used, a softness | flexibility is provided to the CNF film obtained. This is because glycerin not chemically modified is difficult to crystallize.

  The addition ratio of glycerin is preferably 1.0 to 10.0% by mass, more preferably 2.0 to 10.0% by mass with respect to the total amount of the coating liquid, and 3.0 to 10%. It is particularly preferable that the content be 0.0 mass%. If the addition ratio is less than 1.0% by mass, the CNF film is not flexible, and shrinkage wrinkles and cracks may occur during drying. On the other hand, when the addition ratio exceeds 10.0% by mass, the CNF film may not be peeled from the resin base material. The above phenomenon is presumed to be affected by the wettability of the CNF film and the hydroxyl value of the CNF aqueous solution. On the other hand, if the addition ratio exceeds 10.0% by mass, there is a possibility that fines are generated in the CNF film obtained due to aggregation of glycerin.

(Sorbitol)
Sorbitol is a kind of sugar alcohol of glucose. In this specification, sorbitol includes derivatives of sorbitol.

  When sorbitol is added as an additive, the fluidity of the CNF aqueous solution is improved and the compatibility with other additives is improved. (Agglomerates are reduced and a good appearance can be obtained.) In addition, when sorbitol is added as an additive, the strength of the CNF film can be improved, and the CNF film can be prevented from being broken when peeled from the resin substrate. improves.

  As sorbitol, it is preferable to use sorbitol which is not chemically modified. When sorbitol which is not chemically modified is used, compatibility with other additives having a hydroxyl group is improved.

  The addition ratio of sorbitol is preferably 1.0 to 10.0% by mass, more preferably 2.0 to 10.0% by mass, and preferably 3.0 to 10% with respect to the total amount of the coating liquid. It is particularly preferable that the content be 0.0 mass%. If the addition ratio is less than 1.0% by mass, the fluidity of the CNF aqueous solution may be deteriorated, resulting in difficulty in coating properties. (Poor appearance)

  On the other hand, when the addition ratio exceeds 10.0% by mass, the wettability (hydroxyl value) of the CNF aqueous solution increases, and the CNF film may not be peeled from the resin substrate. (Making peeling difficult)

(Polyvinylacetamide compound)
When a polyvinyl acetamide compound is added as an additive, compatibility with other additives is improved. (Agglomerates are reduced and a good appearance is obtained.) Moreover, when a polyvinyl acetamide-based compound is added as an additive, the shear stress of the CNF aqueous solution can be reduced, and the film formation of the CNF film can be made uniform. Is possible. (Good appearance can be obtained.)

  As the polyvinyl acetamide compound, it is preferable to use poly-N-vinylacetamide having a weight average molecular weight of 5,000 to 2,000,000. Poly-N-vinylacetamide is a hydrophilic / alcoholic polymer having N-vinylacetamide as the main monomer. The above weight average molecular weight is a value measured by gel permeation chromatography (GPC method).

  The addition ratio of the polyvinyl acetamide compound is preferably 1.0 to 10.0% by mass, more preferably 2.0 to 10.0% by mass with respect to the total amount of the coating liquid. It is especially preferable to set it as 0-10.0 mass%. When the addition ratio is less than 1.0% by mass, the compatibility with other additives is poor, and aggregates may be generated. (Poor appearance of CNF film) On the other hand, when the addition ratio exceeds 10.0% by mass, the shear stress of the CNF aqueous solution is excessively lowered, and there is a possibility that the film formation cannot be made uniform. (Appearance defect of CNF film)

  The total addition ratio of glycerin, sorbitol, and polyvinylacetamide compound is preferably 8.0 to 12.0 mass%, more preferably 8.5 to 11.5 mass%, and 8. It is particularly preferably 8 to 11.3% by mass. If the total addition ratio is less than 8.0% by mass, the appearance of the CNF film may be impaired. On the other hand, when the addition ratio exceeds 12.0% by mass, the CNF film may not be peeled from the resin base material.

(Alginate)
Alginic acid is a sticky acidic polysaccharide obtained from brown algae. Alginate is its salt. When an alginate is added as an additive, the strength of the CNF film can be improved.

As the alginate, at least sodium alginate and potassium alginate,
Either one is preferably used. When these alginates are used, the strength is easily improved due to the film property of the alginate itself.

  The addition ratio of the alginate is preferably 1.0 to 6.0% by mass, more preferably 2.0 to 6.0% by mass, with respect to the total amount of the coating solution, and 3.0 to The content is particularly preferably 6.0% by mass. When the addition ratio is less than 1.0% by mass, there is a possibility that the intended strength of the CNF film cannot be obtained. (Making peeling difficult) On the other hand, if the addition ratio exceeds 6.0% by mass, the CNF film becomes strong, and shrinkage wrinkles during drying may occur. (Poor appearance)

(Polyamide epichlorohydrin compound)
When a polyamide epichlorohydrin compound is added as an additive, the wet strength of the CNF film can be improved.

  The addition ratio of the polyamide epichlorohydrin compound is preferably 0.1 to 2.0% by mass, more preferably 0.3 to 2.0% by mass, based on the total amount of the coating liquid. 0.5 to 2.0% by mass is particularly preferable. If the addition ratio is less than 0.1% by mass, the intended wet strength of the CNF film may not be obtained. (Reduction of application and difficulty in peeling) On the other hand, when the addition ratio exceeds 2.0 mass%, the additive may be aggregated. (Poor appearance)

(Other additives)
In the CNF dispersion, for example, an antioxidant, a corrosion inhibitor, a light stabilizer, an ultraviolet absorber, a heat stabilizer, a polymerization inhibitor, an inorganic or organic filler, a metal powder, a pigment, a dye, An antistatic agent, a plasticizer, a flame retardant, etc. can be added.

(Coating fluid)
The coating liquid obtained by adding various additives to the CNF dispersion liquid preferably has a solid content concentration of 0.5 to 2.0 mass% from the viewpoint of coating properties. The B-type viscosity of the coating liquid is preferably 500 to 3500 cps for the same reason. As a method of adjusting the solid content concentration and B-type viscosity of the coating liquid to the above ranges, a method of adding water to dilute when adding an additive, a method of adding other additives for adjusting viscosity, etc. Exists.

(Defoaming process)
As a defoaming method of the coating liquid, for example, there is a method of stirring with a bladed stirrer and the like, followed by natural defoaming (standing) or stirring and vacuum defoaming. However, since CNF exhibits thixotropy under conditions of high shearing force, there is a possibility that bubbles are not completely lost by natural defoaming or stirring vacuum defoaming. Therefore, in order to completely eliminate the bubbles, it is preferable to make the coating solution into a thin film and to blow the bubbles. As a method for repelling the bubbles, it is preferable to use a method in which the coating liquid is put into a container and the coating liquid in the container is rotated (planetary rotation) while revolving the container. In this method, a liquid having a high specific gravity in the coating liquid moves outward by centrifugal force, and bubbles mixed in the liquid are pushed inward to be separated from the liquid and defoamed. In addition, since the container into which the coating liquid is charged undergoes a rotating action while undergoing a revolving action, a spiral flow (vortex) is generated in the coating liquid in the container and is stirred by this vortex. In the defoaming step, the number of revolutions and the number of rotations can be appropriately changed according to the properties (particularly viscosity) of the coating liquid. In addition, the rotation direction of the container can be changed forward and backward during the revolution of the container.

(Resin base material)
As the resin base material, for example, an optical resin sheet, an elastic resin sheet, a polymer resin sheet, or the like can be used. As the polymer resin sheet, for example, a plastic sheet made of polyethylene terephthalate, polyvinylidene chloride, polyethylene, polypropylene, polycarbonate, polystyrene or the like can be used. As the polymer resin sheet, a sheet obtained by applying a release agent such as a silicone compound or a fluorine compound to an appropriate sheet can also be used.

  The thickness of the resin base material is preferably 10 to 75 μm, more preferably 15 to 70 μm, and particularly preferably 20 to 60 μm. When the thickness of the resin base material is less than 10 μm, the flexibility becomes too high, and the resin base material is wrinkled or cracked during drying, and the resulting CNF film is wrinkled or cracked (decrease in appearance). There is a fear. On the other hand, if the thickness of the resin substrate exceeds 75 μm, wrinkles and cracks may be formed (decrease in appearance) in the resulting CNF film due to the difference in shrinkage between the resin substrate and the CNF film during drying. is there.

(Coating)
The coating method of the coating liquid on the resin substrate may be a continuous method or a batch method. As the continuous method, for example, the coating liquid is continuously supplied to the coating apparatus, and the coating liquid is extruded thinly (in a thin layer) onto the resin base material by a discharging means such as a die attached to the coating apparatus. Examples thereof include a method and a coating method using a roll coater, knife coater, roll knife coater, reverse coater, gravure coater and the like. Examples of the batch method include a method in which a coating liquid is cast on a resin substrate, and a thin layer is formed using an applicator, a Meyer bar, a knife coater, or the like.

(Dry)
Drying of the coating liquid applied to the resin substrate can be performed, for example, by applying drying air. The coating solution may be dried in a single drying step or a combination of a plurality of drying steps.

(CNF film)
The CNF film obtained by drying the coating solution preferably has a thickness of 10 to 1000 μm, more preferably 12 to 500 μm, and 15 to 100 μm. It is particularly preferable to do this. If the thickness is less than 10 μm, the intended strength may not be obtained. On the other hand, if the thickness exceeds 1000 μm, a large-scale apparatus is required for the drying process, which may complicate the manufacturing process. The thickness of the CNF film is a value measured in accordance with JIS P8118 (2014) “Paper and paperboard—Test method for thickness, density and specific volume”.

The CNF film obtained by drying the coating solution preferably has a basis weight of 5.0 to 100.0 g / m ² and preferably 10.0 to 80.0 g / m ^2. More preferably, it is 20.0-60.0 g / m < ² >. If the basis weight is less than 5.0 g / m ² , the intended strength may not be obtained. (Making peeling difficult). On the other hand, if the basis weight exceeds 100.0 g / m ² , a large-scale apparatus is required for the drying process, which may complicate the manufacturing process. The basis weight of the CNF film is a value measured in accordance with JIS P8124 (2011) “Paper and paperboard—basis weight measurement method”.

  Next, examples of the present invention will be described. The following embodiments can be variously modified without departing from the spirit of the present invention.

(Example)
First, hardwood bleached kraft pulp (LBKP) for papermaking was used as a 1.0 mass% aqueous dispersion. This aqueous dispersion was beaten using a refiner until the freeness was 100 ml or less, and further refined using a high-pressure homogenizer. In this way, CNF (average fiber length 1.5 μm, average fiber diameter 39 nm, water retention 280%, crystallinity 78%, peak value 20 μm, pulp viscosity 3.3 cps) was obtained.

  Next, an additive was added to the CNF aqueous solution obtained as described above to obtain a coating solution. The types and amounts of additives are shown in Table 1. Moreover, the obtained coating liquid was stirred and defoamed using a stirring device (product name: KK-400W) manufactured by Kurashiki Boseki Co., Ltd.

  The defoamed coating solution was applied such that the thickness of the CNF film obtained on one surface of a PET resin substrate (product name: E5000, thickness 38 μm) was 10 μm.

The physical properties and evaluation of the obtained CNF film are shown in Table 1. In addition, "mass%" in a table | surface is an absolute dry mass ratio when a CNF film is 100 mass (absolutely dry). Further, “-” indicates that it is not blended. Furthermore, the following were used as various additives.
Alginate: Product name “Argi Deluxe M” (Kimika Co., Ltd.)
Glycerin: Product name “Purified Glycerin” (manufactured by Sakamoto Pharmaceutical Co., Ltd.)
Sorbitol: Product name "Sorbit KK (60%)" (MC Food Specialties Co., Ltd.)
Polyvinylacetamide compound: product name “GE191-053” (manufactured by Showa Denko KK)
Polyamide epichlorohydrin compound: Trade name “WS4024” (manufactured by Seiko PMC Co., Ltd.)

(Comparative Example 1)
First, polysaccharide hydrolase in an amount of 1.0% by mass to dry pulp was added to hardwood bleached kraft pulp (LBKP) for papermaking, and reacted at 50 ° C. for 5 hours. After the reaction, the enzyme was inactivated at 105 ° C. for 5 minutes to obtain a 1.0 mass% aqueous dispersion. This aqueous dispersion was beaten using a refiner until the freeness was 100 ml or less, and refined using a high-pressure homogenizer. In this way, CNF (average fiber length of 1.0 μm, average fiber diameter of 40 nm, water retention of 450%, crystallinity of 70%, peak value of 16 μm, pulp viscosity of 3.0 cps) was obtained.

  The aqueous solution of CNF obtained as described above was stirred and defoamed using a stirring device (product name: KK-400W) manufactured by Kurashiki Boseki Co., Ltd. without adding an additive.

  The defoamed coating solution was applied so that the thickness of the CNF film obtained on one surface of the coating solution was 10 μm.

  The physical properties and evaluation of the obtained CNF film are shown in Table 1.

(Comparative Examples 2 and 3)
The coating liquid obtained by the method similar to the Example was applied to one surface of a PET resin substrate (product name: E5000, thickness: 38 μm). The physical properties and evaluation of the obtained CNF film are shown in Table 1.

(Evaluation method)
The evaluation method was as described below. In the table, “-” indicates that measurement was not possible.

(Appearance: Cracks / wrinkles)
A: The obtained CNF film has no cracks or wrinkles.
◯: Although extremely fine wrinkles are partially seen in the obtained CNF film, there are no cracks.
Δ: Although there are linear cracks and wrinkles, there are some practical difficulties. (Maximum crack length is less than 5mm)
X: There are linear cracks and wrinkles, which cannot be used practically. (Maximum crack length is 5mm or more)

(Appearance: Bubble)
(Double-circle): There is no mixing of a bubble between the 10 cm squares of the obtained CNF film.
○: One or two bubbles of 1 mm in size are observed between 10 cm squares of the obtained CNF film.
Δ: 3 to 5 bubbles of 1 mm in size are observed between 10 cm squares of the obtained CNF film, which is somewhat difficult in practical use.
X: Between the 10 cm square of the obtained CNF film, mixing of a 1 mm-sized bubble exceeded 5 pieces, and it cannot be used practically.

(Film strength)
It is a measured value measured according to JIS P8113 (2006) “Paper and paperboard—Test method for tensile properties”. When the strength was less than 2.0 N / m, the CNF film was broken at the time of peeling from the resin substrate.

(Peelability)
A: The CNF film can be easily peeled from the resin base material.
○: Some difficulty is required when the CNF film peels from the resin substrate.
(Triangle | delta): When the CNF film peeled from the resin base material, difficulty was required and the CNF film partly fractured.
X: The CNF film could not be peeled from the resin base material.

(Reference example)
A test was performed comparing the substrate A (Reference Example 1) with the one obtained by laminating the CNF film obtained in Example 1 on one side of the substrate A (Reference Example 2). Similarly, the test which contrasted the base material B (reference example 3) and what laminated | stacked the CNF film obtained in Example 1 on the single side | surface of the base material B (reference example 4) was done. The results are shown in Table 2. In addition, the detail of the base material A, the base material B, oil resistance (kit value), and oxygen permeability is as follows.

Base material A: Multi-paper Super White J (manufactured by ASKUL Corporation)
Base material B: Copy paper manufactured by Daio Paper Co., Ltd.
Kit value: It is the oil resistance (kit value according to TAPPI UM-557) of the flat surface measured under the conditions of 23 ° C. and 50% humidity.
Oxygen permeability (cc / m ² · day · atm): JIS-K-7126-1: 2006 “Plastic-film and sheet—Gas permeability test method—Part 1: Differential pressure method” It is a value when measured at 25 ° C. for 2 hours using “GTR-11AET”.

(Discussion)
In the experimental example including glycerin, sorbitol, or polyvinylacetamide-based compound as an additive and subjected to a defoaming step, the effect of the present invention was achieved. On the other hand, in Comparative Example 1 in which no additive was added, the CNF film could not be peeled from the resin base material. This is considered to be related to the wettability of the coating liquid (film layer) with respect to the resin substrate.

  The present invention can be used as a method for producing a cellulose nanofiber film.

Claims (7)

One or more additives selected from glycerin, sorbitol, and polyvinylacetamide compounds are added to the dispersion of cellulose nanofibers to obtain a coating solution,
Defoam this coating solution, apply it to a resin substrate, dry it into a film,
The manufacturing method of the cellulose nanofiber film characterized by the above-mentioned. Included in the dispersion of cellulose nanofibers,
The addition ratio of glycerin is 1.0-10.0 mass%, and the addition ratio of sorbitol is 1.0-10.0 mass%,
The method for producing a cellulose nanofiber film according to claim 1, wherein the addition ratio of the polyvinyl acetamide-based compound is 1.0 to 10.0% by mass. Included in the dispersion of cellulose nanofibers,
The method for producing a cellulose nanofiber film according to claim 2, wherein the total addition ratio of glycerin, sorbitol, and polyvinylacetamide-based compound is 8.0 to 12.0 mass%. The defoaming of the coating liquid is performed by charging the coating liquid in the container while revolving the container, by charging the coating liquid into the container,
The manufacturing method of the cellulose nanofiber film of Claim 1. The cellulose nanofiber dispersion is further added with alginate and polyamide epichlorohydrin compound to obtain the coating solution,
The addition ratio of the alginate is 1.0 to 6.0% by mass,
The method for producing a cellulose nanofiber film according to claim 1, wherein an addition ratio of the polyamide epichlorohydrin compound is 0.5 to 2.0 mass. A cellulose nanofiber film obtained by the method for producing a cellulose nanofiber film according to any one of claims 1 to 5,
The strength according to JIS P8113 (2006) is 2.0 N / m or more,
A method for producing a cellulose nanofiber film. A cellulose nanofiber film obtained by the method for producing a cellulose nanofiber film according to any one of claims 1 to 5,
In the 10 cm square, there are less than 5 bubbles of 1 mm in size,
A method for producing a cellulose nanofiber film.