JP6978843B2 - Manufacturing method of cellulose nanofiber film and cellulose nanofiber film - Google Patents

Description

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

Currently, cellulose nanofibers (hereinafter also referred to as CNF) whose fiber diameter of wood pulp has been miniaturized to the nano-order are used for papermaking, cosmetics, daily necessities, resin reinforcing materials, power storage element separators, functional filters, and low CTE groups. Applications to applications such as material films and base materials for bio-medical materials are being studied.

On the other hand, CNF can be made into a film by applying it to a paper base material 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 the desired film from CNF.

For example, Patent Document 1 states that "a suspension of nanofibrillated cellulose is directly applied and diffused on the surface of the material of a plastic support, whereby the nanofibrillated cellulose is filmed on the material of the support. A method for producing a CNF film (film) is proposed. However, the proposal does not examine the point of peeling the obtained film from the support (easiness of peeling). In addition, the proposal does not consider the point of improving the appearance of the obtained film, for example, the point of making the obtained film free from wrinkles and cracks.

Further, for example, in Patent Document 2, as shown in paragraph 0042 and after, "(1) Cellulose microfibrils 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. or more. An aqueous dispersion containing 0.5% by weight or more and 10% by weight or less of the following oily compound and 85% by weight or more and 99.5% by weight or less of water, which is an emulsion in which the oily compound is dispersed in an aqueous phase. A step of preparing an aqueous dispersion to prepare a liquid, (2) a papermaking step of controlling the concentration of cellulose microfibrils (solid content concentration) and the concentration of an oily compound to a specific range to obtain a concentrated composition, and (3) a concentrated composition. A method for producing a cellulose sheet, which comprises three steps of a drying step of evaporating and removing an oily compound and water from the concentrated composition by heating the concentrated composition. However, the manufacturing process of this proposal is complicated and the manufacturing cost is high.

Japanese Patent Publication No. 2015-502835 Japanese Unexamined Patent Publication No. 2012-036529

The main problem to be solved by the present invention is a method for producing a cellulose nanofiber film and a cellulose nanofiber film, which can be easily peeled off from the substrate and have an excellent appearance, but the manufacturing process is not complicated. To make a suggestion.

The means to solve the above problems are
Additives containing glycerin, sorbitol, and polyvinylacetamide compounds are added to the dispersion of cellulose nanofibers to obtain a coating solution.
This coating liquid is defoamed, applied to a resin substrate, and dried to form a film.
This is a method for producing a cellulose nanofiber film.
Preferably, it is contained in the dispersion liquid of the cellulose nanofibers.
The addition ratio of glycerin is 1.0 to 10.0% by mass, and the addition ratio of sorbitol is 1.0 to 10.0% by mass.
The addition ratio of the polyvinylacetamide-based compound is 1.0 to 10.0% by mass.

According to the present invention, the method for producing a cellulose nanofiber film and the cellulose nanofiber film are not complicated in the production process, although they can be easily peeled off from the substrate and have an excellent appearance.

Next, a mode for carrying out the present invention will be described. 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, one or more , preferably all additives selected from glycerin, sorbitol, and a polyvinylacetamide-based compound are added to an aqueous solution of CNF. A coating liquid is obtained, this coating liquid is defoamed, coated on a resin substrate, and dried to form a film. More preferably, alginate and a polyamide epichlorohydrin-based compound are further added to the aqueous solution of CNF. Hereinafter, they will be described in order.

(CNF)
CNF (cellulose fine fiber) is obtained by defibrating (miniaturizing) the cellulose fiber (raw material 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 desired. However, as the raw material fiber, it is preferable to use a plant-derived fiber (plant fiber), and it is more preferable to use a pulp fiber which is a kind of plant fiber. When the raw material fiber is pulp fiber, it is easy to adjust the physical characteristics of CNF.

As the plant fiber, for example, wood pulp made from broadleaf trees, coniferous trees, etc., non-wood pulp made from straw, bagasse, etc., recovered waste paper, used paper pulp made from waste paper, etc. (DIP), etc. shall be used. Can be done. These plant fibers can be used alone or in combination of two or more.

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

The 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 used paper pulp (DIP) may be magazine used paper pulp (MDIP), newspaper used paper pulp (NDIP), stepped used paper pulp (WP), or other used paper pulp.

Prior to defibration, the raw material fiber can be subjected to pretreatment such as beating, if necessary. This pretreatment can be performed by physical or chemical methods, preferably by physical and chemical methods. By pretreating by a physical method or a chemical method prior to defibration, the number of defibration can be significantly reduced, and the energy required for defibration can be significantly reduced.

As the pretreatment by the physical method, it is preferable to adopt tapping. When the raw material fibers are beaten, the raw material fibers are trimmed, so that the problem that the fibers are entangled with each other and aggregated is solved. From such a viewpoint, the beating is preferably carried out until the freeness of the raw material 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 in accordance with JIS P8121-2 (2012).

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

Pretreatment by chemical method includes, for example, hydrolysis of polysaccharide with acid (acid treatment), hydrolysis of polysaccharide with enzyme (enzyme treatment), swelling of polysaccharide with alkali (alkali treatment), oxidation of polysaccharide with oxidizing agent (acid treatment). Oxidation treatment), reduction of polysaccharides with a reducing agent (reduction treatment), and the like can be adopted.

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

As the pretreatment, in addition to the above, chemical treatment such as phosphoric acid esterification treatment, acetylation treatment, and cyanoethylation treatment can also be performed.

The raw material fiber is defibrated (miniaturized) after being subjected to pretreatment such as beating. By this defibration, the raw material fiber is microfibrillated into CNF (cellulose nanofiber).

For defibration of raw material fibers, for example, one or two of high-pressure homogenizers, homogenizers such as high-pressure homogenizers, stone mill type friction machines such as grinders and grinders, refiners such as conical refiners and disc refiners, and various devices. It can be done by selectively using more than a kind of means. However, it is preferable to defibrate the raw material fiber by using a device / method for defibrating with a water stream, particularly a high-pressure water stream. According to this device / method, the dimensional uniformity and dispersion uniformity of the obtained CNF are very high. On the other hand, for example, when a grinder that grinds between rotating grindstones is used, it is difficult to uniformly defibrate the fibers, and some undissolved fiber lumps remain, so that the desired effect cannot be obtained. There is a risk. In this regard, the present inventors conducted a test in which pulp fibers were defibrated by a method of defibrating with a high-pressure water flow and a method of grinding between rotating grindstones, and the obtained fibers were observed under a microscope. rice field. As a result, it was found that the fiber width obtained by the method of defibrating with a high-pressure water stream became more uniform.

Examples of the device for defibrating with a high-pressure water stream include Sugino Machine Limited's Starburst (registered trademark) and Yoshida Kikai Kogyo Co., Ltd.'s Nanovater (registered trademark). Further, as a grinder, for example, a mascoroider (registered trademark) of Masuko Sangyo Co., Ltd. exists.

Next, the method of defibrating with a high-pressure water stream will be described in detail.
For defibration by a high-pressure water flow, the dispersion liquid of the raw material fibers is pressurized to, for example, 30 MPa or more, preferably 100 MPa or more, more preferably 150 MPa or more, particularly preferably 220 MPa or more (high pressure conditions), and the pore diameter is 50 μm or more. It is preferable to use a method of ejecting the fiber from the nozzle of No. 1 and reducing the pressure so that the pressure difference is, for example, 30 MPa or more, preferably 80 MPa or more, more preferably 90 MPa or more (decompression condition). The raw material 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 defibration efficiency is lowered, and it may be necessary to repeat the ejection in order to obtain the desired fiber diameter.

As a device for defibrating with a high-pressure water stream, it is preferable to use a high-pressure homogenizer. The high-pressure homogenizer is a homogenizer capable of discharging a dispersion liquid of raw material fibers 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, pressure difference, microcavitation and the like act to effectively cause defibration. Therefore, the number of times of defibration can be reduced and the production efficiency of CNF can be improved. If the raw material fiber is sufficiently softened by the pretreatment, it can be effectively defibrated by the high-pressure homogenizer. Therefore, the number of defibration can be reduced and the productivity can be increased.

As the high-pressure homogenizer, it is preferable to use a high-pressure homogenizer in which the dispersion liquids of the raw material fibers collide with each other in a straight line. As such an apparatus, for example, there is a counter-collision type high pressure homogenizer (microfluidizer / MICROFLUIDIZER®, wet jet mill). In this device, two upstream flow paths are formed so that the dispersed liquids of the pressurized raw material fibers collide with each other at the confluence. Further, the dispersion liquid of the raw material fibers collides with each other at the confluence, and the dispersion liquid of the colliding raw material fibers flows out from the downstream flow path. The downstream flow path is provided perpendicular to the upstream side flow path, and a T-shaped flow path is formed by the upstream side flow path and the downstream side flow path. When this device is used, the energy of the device is converted to the collision energy to the maximum, so that the raw material fiber can be defibrated more efficiently.

In the defibration of the raw material fiber, the average fiber diameter, average fiber length, water retention degree, crystallinity, peak value of pseudo particle size distribution, and pulp viscosity of the obtained CNF are desired values or evaluations as shown below. It is preferable to do this. However, it is more preferable to defibrate until the raw material fiber has a predetermined fiber diameter (average fiber diameter). By defibrating the raw material fibers until they reach a predetermined fiber diameter, the water retention level of CNF can be suppressed to a low level. As a result, the coatability of the coating liquid can be improved.

(Average fiber diameter)
The average fiber diameter of CNF (average diameter of single fiber) 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 material fibers, pretreatment, crushing and the like.

The method for measuring the average fiber diameter of CNF is as follows.
First, 100 ml of an aqueous dispersion of CNF having a solid content concentration of 0.01 to 0.1% by mass is filtered through a membrane filter made of Teflon (registered trademark), and the solvent is replaced once with 100 ml of ethanol and three times with 20 ml of t-butanol. .. Next, it is freeze-dried and coated with osmium to prepare a sample. This sample is observed with an electron microscope SEM image at a magnification of 5,000 times, 10,000 times, or 30,000 times 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 width of a total of 100 fibers intersecting with these three straight lines is visually measured. Then, the median diameter of the measured value is taken as the average fiber diameter.

(Average fiber length)
The average fiber length (length of a 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 material fibers, 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 average fiber length is the medium length of the measured value.

(Water retention)
The water retention of CNF is, for example, 300 to 500%, preferably 350 to 480%, and more preferably 380 to 450%. The water retention level of CNF can be adjusted by, for example, selection of raw material fibers, pretreatment, defibration and the like. The degree of water retention is as follows: JAPAN TAPPI No. It is a value measured according to 26 (2000).

(Crystallinity)
The crystallinity of CNF is, for example, 50 to 90%, preferably 55 to 88%, and more preferably 60 to 85%. The crystallinity of CNF can be adjusted by, for example, selection of raw material fibers, pretreatment, defibration and the like. The crystallinity is a value measured by an X-ray diffraction method in accordance with the "general rule of X-ray diffraction analysis" of JIS-K0131 (1996). In this respect, CNF has an amorphous portion and a crystalline portion, and the crystallinity means the ratio of the crystalline portion in the entire CNF.

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

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 material 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 aqueous dispersion of CNF is examined using a particle size distribution measuring device (a laser diffraction / scattering type particle size distribution measuring device manufactured by Seishin Enterprise Co., Ltd.). Next, the median diameter of CNF is measured from this distribution. This median diameter is taken as 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, and more preferably 2.0 to 6.5 cps. The pulp viscosity of CNF can be adjusted by, for example, selection of raw material fibers, pretreatment, defibration and the like. The pulp viscosity is a value measured according to JIS-P8215 (1998). The higher the pulp viscosity, the higher the degree of polymerization of cellulose.

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

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

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

The additives shown below are added to the aqueous solution of CNF obtained as described above. In the present embodiment, a CNF film that can be easily peeled off from the substrate and has an excellent appearance can be obtained only by adding an additive, so that there is no possibility that the manufacturing process is complicated. .. Hereinafter, the additives will be described in order.

(Glycerin)
Glycerin (glycerol) is a trihydric alcohol. Glycerin is obtained together with fatty acids, for example, by hydrolysis of fats and oils. As used herein, glycerin also includes derivatives of glycerin.

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. (A good appearance can be obtained.)

As the glycerin, it is preferable to use glycerin that has not been chemically modified. The use of unmodified glycerin improves the dispersibility of CNF. Also, the use of unchemically modified glycerin imparts flexibility to the resulting CNF film. This is because glycerin that has not been 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, and 3.0 to 10% with respect to the total amount of the coating liquid. It is particularly preferable to set it to 0.0% by mass. If the addition ratio is less than 1.0% by mass, the CNF film is inflexible, and shrinkage wrinkles and cracks may occur during drying. On the other hand, if the addition ratio exceeds 10.0% by mass, the CNF film may not be able to be peeled off from the resin base material. It is presumed that the above phenomenon is affected by the wettability of the CNF film and the hydroxyl value of the CNF aqueous solution. Further, if the addition ratio exceeds 10.0% by mass, fine substances may be generated in the CNF film obtained due to the aggregation of glycerin.

(Sorbitol)
Sorbitol is a type of glucose sugar alcohol. As used herein, sorbitol also 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. (Agglutination is reduced and a good appearance can be obtained.) Further, when sorbitol is added as an additive, the strength of the CNF film can be improved, the CNF film can be prevented from breaking when peeled from the resin substrate, and the peelability is improved. improves.

As the sorbitol, it is preferable to use sorbitol which has not been chemically modified. The use of unchemically modified sorbitol improves compatibility with other additives that have hydroxyl groups.

The addition ratio of sorbitol is preferably 1.0 to 10.0% by mass, more preferably 2.0 to 10.0% by mass, and 3.0 to 10% by mass with respect to the total amount of the coating liquid. It is particularly preferable to set it to 0.0% by mass. If the addition ratio is less than 1.0% by mass, the fluidity of the CNF aqueous solution may deteriorate and the coatability may be difficult. (Poor appearance)

On the other hand, if the addition ratio exceeds 10.0% by mass, the wettability (hydroxyl value) of the CNF aqueous solution becomes high, and the CNF film may not be peeled off from the resin base material. (Difficulty of peeling)

(Polyvinylacetamide compound)
When a polyvinylacetamide compound is added as an additive, the compatibility with other additives is improved. (Agglutination is reduced and a good appearance can be obtained.) Further, when a polyvinylacetamide-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. It is possible. (A good appearance can be obtained.)

As the polyvinylacetamide-based compound, it is preferable to use poly-N-vinylacetamide having a weight average molecular weight of 5000 to 2000000. Poly-N-vinylacetamide is a hydrophilic / pro-alcoholic polymer containing N-vinylacetamide as a main monomer. The above-mentioned 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, based on the total amount of the coating liquid. It is particularly preferably 0 to 10.0% by mass. If the addition ratio is less than 1.0% by mass, the compatibility with other additives is poor and agglomerates may be generated. (Poor appearance of CNF film) On the other hand, if the addition ratio exceeds 10.0% by mass, the shear stress of the CNF aqueous solution may be too low to make the film uniform. (Poor appearance of CNF film)

The total addition ratio of glycerin, sorbitol, and polyvinylacetamide-based compound is preferably 8.0 to 12.0% by mass, more preferably 8.5 to 11.5% by 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, if the addition ratio exceeds 12.0% by mass, it may not be possible to peel off the CNF film from the resin substrate.

(Alginate)
Alginic acid is a sticky acidic polysaccharide obtained from brown algae. Alginate is the salt thereof. Adding alginate as an additive can improve the strength of the CNF film.

As the alginate, at least sodium alginate and potassium alginate,
It is preferable to use either one. When these alginates are used, the strength tends to be further improved due to the film property of the alginate itself.

The addition ratio of alginate is preferably 1.0 to 6.0% by mass, more preferably 2.0 to 6.0% by mass, and 3.0 to 6.0% by mass with respect to the total amount of the coating liquid. It is particularly preferable to set it to 6.0% by mass. If the addition ratio is less than 1.0% by mass, the strength desired by the CNF film may not be obtained. (Difficulty of peeling) On the other hand, if the addition ratio exceeds 6.0% by mass, the CNF film becomes strong, so that shrinkage wrinkles during drying may occur. (Poor appearance)

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

The addition ratio of the polyamide epichlorohydrin-based 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 desired wet strength of the CNF film may not be obtained. (Reduction of use and difficulty in peeling) On the other hand, if the addition ratio exceeds 2.0% by mass, the additive may aggregate. (Poor appearance)

(Other additives)
CNF dispersions may include, if necessary, antioxidants, corrosion inhibitors, light stabilizers, UV absorbers, heat stabilizers, polymerization inhibitors, inorganic or organic fillers, metal powders, pigments, dyes, etc. Antistatic agents, plasticizers, flame retardants and the like can be added.

(Coating liquid)
From the viewpoint of coatability, the coating liquid obtained by adding various additives to the dispersion liquid of CNF preferably has a solid content concentration of 0.5 to 2.0% by mass. Further, the B-type viscosity of the coating liquid is preferably 500 to 3500 cps for the same reason. As a method for adjusting the solid content concentration and the B-type viscosity of the coating liquid in the above range, a method of diluting by adding water or the like when adding an additive, a method of adding another additive for adjusting the viscosity, etc. Exists.

(Defoaming process)
As a method for defoaming the coating liquid, for example, there is a method of stirring with a stirrer with blades and then spontaneously defoaming (standing) or stirring vacuum defoaming. However, since CNF exhibits thixotropic properties under the condition of high shear force, there is a possibility that bubbles may not completely disappear by natural defoaming or stirring vacuum defoaming. Therefore, in order to completely eliminate the bubbles, it is preferable to make the coating liquid into a thin film and repel 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, the liquid having a heavy specific gravity in the coating liquid is moved to the outside by the centrifugal force, and the bubbles mixed in the liquid are pushed inward to be separated from the liquid and thus defoamed. Further, since the container into which the coating liquid is charged undergoes a rotation action while undergoing a revolution action, a spiral flow (vortex flow) is generated in the coating liquid in the container, and the container is agitated by this vortex flow. 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 in the forward and reverse directions while the container is revolving.

(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. Further, as the polymer resin sheet, a sheet obtained by applying a mold 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. If the thickness of the resin base material is less than 10 μm, the flexibility becomes too high, wrinkles and cracks occur in the resin base material during drying, and wrinkles and cracks are formed in the obtained CNF film (deterioration of appearance). There is a risk. On the other hand, if the thickness of the resin base material exceeds 75 μm, wrinkles and cracks may be formed in the obtained CNF film (deterioration of appearance) due to the shrinkage difference between the resin base material and the CNF film during drying. be.

(Coating)
The coating method of the coating liquid on the resin base material may be a continuous method or a batch method. As a continuous method, for example, the coating liquid is continuously supplied to the coating equipment, and the coating liquid is thinly (thinly layered) extruded onto the resin base material by a discharge means such as a die attached to the coating equipment. Examples thereof include a method and a method of coating using a roll coater, a knife coater, a roll knife coater, a reverse coater, a gravure coater, and the like. As a batch method, for example, a method of casting a coating liquid on a resin base material and forming a thin layer using an applicator, a Meyer bar, a knife coater, or the like can be exemplified.

(Dry)
The coating liquid applied to the resin base material can be dried by, for example, blowing a drying air. The coating liquid may be dried by a single drying step or by combining a plurality of drying steps.

(CNF film)
The CNF film obtained by drying the coating liquid 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 so. If the thickness is less than 10 μm, the desired strength may not be obtained. (Difficulty of peeling) On the other hand, if the thickness exceeds 1000 μm, a large-scale device 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 liquid preferably has a basis weight of 5.0 to 100.0 g / m ² , preferably 10.0 to 80.0 g / m ^2. It is more preferable to use 20.0 to 60.0 g / m ² and it is particularly preferable to use 20.0 to 60.0 g / m 2. If the basis weight is ^{less than 5.0 g / m 2} , the desired strength may not be obtained. (Difficulty of peeling). On the other hand, if the basis weight ^{exceeds 100.0 g / m 2} , a large-scale device 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 Measuring Method".

Next, examples of the present invention will be described. The following examples may be modified in various ways as long as they do not deviate from the gist of the present invention.

( Test Examples 1 to 9 )
First, hardwood bleached kraft pulp (LBKP) for papermaking was used as a 1.0% by mass aqueous dispersion. This aqueous dispersion was beaten using a refiner until the freeness became 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 degree 280%, crystallinity 78%, peak value 20 μm, pulp viscosity 3.3 cps) was obtained.

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

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

Table 1 shows the physical characteristics, evaluation, etc. of the obtained CNF film. In addition, "mass%" in the table is the absolute dry mass ratio when the CNF film is 100 mass (absolute dry). Further, "-" indicates that the mixture is not blended. Further, as various additives, the following were used.
Alginate: Product name "Argi Deluxe M" (manufactured by Kimika Co., Ltd.)
Glycerin: Product name "Purified glycerin" (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.)
Sorbitol: Product name "Sorbit KK (60%)" (manufactured by MC Food Specialties Inc.)
Polyvinylacetamide compound: Product name "GE191-053" (manufactured by Showa Denko KK)
Polyamide epichlorohydrin-based compound: Product name "WS4024" (manufactured by Seiko PMC Corporation)

( Test Example 10 )
First, a polysaccharide hydrolase in an amount of 1.0% by mass based on dry pulp was added to hardwood bleached kraft pulp (LBKP) for papermaking, and the mixture was 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% by mass aqueous dispersion. This aqueous dispersion was beaten using a refiner until the freeness was 100 ml or less, and finely divided using a high-pressure homogenizer. In this way, CNF (average fiber length 1.0 μm, average fiber diameter 40 nm, water retention degree 450%, crystallinity 70%, peak value 16 μm, pulp viscosity 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 Kurabo Industries Ltd. without adding an additive.

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

Table 1 shows the physical characteristics, evaluation, etc. of the obtained CNF film.

( Test Examples 11 and 12 )
The coating liquid obtained by the same method as in the examples was applied to one surface of a PET resin substrate (product name: E5000, thickness 38 μm). Table 1 shows the physical characteristics, evaluation, etc. of the obtained CNF film.

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

(Appearance: cracks / wrinkles)
⊚: The obtained CNF film has no cracks or wrinkles.
◯: Very fine wrinkles are partially seen in the obtained CNF film, but there are no cracks.
Δ: There are linear cracks and wrinkles, but there is some difficulty in practical use. (Maximum crack length is less than 5 mm)
×: There are linear cracks and wrinkles, and it cannot be used practically. (Maximum crack length is 5 mm or more)

(Appearance: bubbles)
⊚: No air bubbles were mixed between the 10 cm squares of the obtained CNF film.
◯: One or two bubbles having a size of 1 mm are observed between the 10 cm squares of the obtained CNF film.
Δ: 3 to 5 bubbles having a size of 1 mm were mixed between the 10 cm squares of the obtained CNF film, which is somewhat difficult in practical use.
X: In the 10 cm square of the obtained CNF film, more than 5 bubbles having a size of 1 mm were mixed, and the film could not be used practically.

(Film strength)
It is a measured value measured in accordance with JIS P8113 (2006) "Paper and Paperboard-Test Method for Tensile Properties". When the strength was less than 2.0 N / m, the CNF film broke when peeled from the resin substrate.

(Removability)
⊚: The CNF film can be easily peeled off from the resin base material.
◯: It takes some difficulty when the CNF film is peeled off from the resin base material.
Δ: When the CNF film was peeled off from the resin base material, it was difficult and the CNF film was partially broken.
X: The CNF film could not be peeled off from the resin base material.

(Reference example)
A test was conducted in which the base material A (Reference Example 1) and the CNF film obtained in Test Example 1 laminated on one side of the base material A (Reference Example 2) were compared. Similarly, a test was conducted in which the base material B (Reference Example 3) and the CNF film obtained in Test Example 1 laminated on one side of the base material B (Reference Example 4) were compared. The results are shown in Table 2. The details of the base material A, the base material B, the oil resistance (kit value), and the oxygen permeability are as follows.

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

(Discussion)
Glysenrin, sorbitol, or a polyvinylacetamide-based compound was contained as an additive, and the effect of the present invention was exhibited in an experimental example that had undergone a defoaming step. On the other hand, in Comparative Example 1 to which no additive was added, the CNF film could not be peeled off from the resin substrate. It is considered that this is related to the wettability of the coating liquid (film layer) with respect to the resin base material.

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

Claims (7)

Additives containing glycerin, sorbitol, and polyvinylacetamide compounds are added to the dispersion of cellulose nanofibers to obtain a coating solution.
This coating liquid is defoamed, applied to a resin substrate, dried to form a film, and then formed into a film.
Included in the dispersion of cellulose nanofibers
The addition ratio of glycerin is 1.0 to 10.0% by mass, and the addition ratio of sorbitol is 1.0 to 10.0% by mass.
A method for producing a cellulose nanofiber film, wherein the addition ratio of the polyvinylacetamide 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 1, wherein the total addition ratio of the glycerin, sorbitol, and polyvinylacetamide-based compound is 8.0 to 12.0% by mass. Defoaming of the coating liquid is performed by putting the coating liquid into a container and rotating the coating liquid in the container while revolving the container.
The method for producing a cellulose nanofiber film according to claim 1. Alginate and a polyamide epichlorohydrin-based compound are further added to the dispersion liquid of the cellulose nanofibers to obtain the coating liquid, and the coating liquid is obtained.
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 the addition ratio of the polyamide epichlorohydrin-based compound is 0.5 to 2.0 mass. The cellulose nanofiber film obtained by the method for producing a cellulose nanofiber film according to any one of claims 1 to 4 is
The strength according to JIS P8113 (2006) is 2.0 N / m or more.
A method for producing a characteristic cellulose nanofiber film. The cellulose nanofiber film obtained by the method for producing a cellulose nanofiber film according to any one of claims 1 to 4 is
The fact that there are less than 5 1 mm-sized bubbles mixed in between 10 cm squares.
A method for producing a characteristic cellulose nanofiber film. A dispersion of cellulose nanofibers and an additive containing glycerin, sorbitol, and a polyvinylacetamide compound are applied to the resin substrate after defoaming.
Included in the dispersion of cellulose nanofibers
The proportion of glycerin is 1.0 to 10.0% by mass, and the proportion of sorbitol is 1.0 to 10.0% by mass.
A cellulose nanofiber film characterized in that the proportion of a polyvinylacetamide-based compound is 1.0 to 10.0% by mass.