JP7676830B2 - Lens, optical member, and laminate for optical member - Google Patents

Description

The present invention relates to lenses, optical components, and laminates for optical components.

Conventionally, lenses are used in various optical devices such as cameras and vehicle headlights, as well as in concentrating lenses for solar power generation. Lenses are required to have optical properties according to their intended use. For example, when lenses are used as optical components, they are required to have high transparency as well as durability properties such as excellent heat resistance and weather resistance. Furthermore, when lenses are used as optical components, shape properties such as light weight and small size may also be required.

In recent years, in order to meet the wide variety of needs that are placed on lenses, the use of transparent polymeric materials such as acrylic resin, polycarbonate resin, COP (cycloolefin polymer) resin, PET (polyethylene terephthalate) resin, silicone-modified epoxy resin, and silicone resin as lens raw materials has been considered, instead of transparent inorganic materials such as inorganic glass. Lenses made from polycarbonate resin and COP resin in particular are being considered for use in lenses, as they are light and resistant to impact. Development is also underway on composite lenses, in which glass lenses are coated with transparent polymeric materials.

For example, Patent Document 1 discloses a hybrid lens having a first lens molded from a silicone resin and a second lens molded from inorganic glass, acrylic resin, polycarbonate resin, cycloolefin polymer resin, or silicone-modified epoxy resin. Patent Document 2 discloses a compound lens having a first lens and a second lens that are polycarbonate lenses.

JP 2011-095492 A Special Publication No. 2009-506387

As mentioned above, the development of lenses containing transparent polymeric materials is progressing. In particular, polycarbonate resin and COP resin are widely used in lens applications due to their excellent mechanical strength and heat resistance. However, for example, lenses made of polycarbonate resin or COP resin may not have sufficient impact resistance, and improvements have been required.

Therefore, in order to solve these problems of the conventional technology, the inventors have carried out research with the aim of providing a lens that includes a resin layer and can exhibit excellent impact resistance.

As a result of intensive research to solve the above problems, the inventors have found that, in a lens including a resin layer, a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less can be laminated to the resin layer, thereby obtaining a lens that can exhibit excellent impact resistance.
Specifically, the present invention has the following configuration.

[1] A fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less;
A lens comprising a laminate having at least one fiber layer and a resin layer in contact with one surface of the fiber layer.
[2] The lens according to [1], wherein the resin layer contains at least one resin selected from the group consisting of polycarbonate resins and polyolefin resins.
[3] The lens according to [1] or [2], wherein the resin layer contains an adhesion assistant.
[4] The lens according to [3], wherein the adhesion assistant is at least one selected from an isocyanate compound and an organosilicon compound.
[5] A fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less;
and a resin layer in contact with one surface of a fiber layer.
[6] The optical member according to [5], wherein the resin layer contains at least one resin selected from the group consisting of polycarbonate resins and polyolefin resins.
[7] The optical member according to [5] or [6], wherein the resin layer contains an adhesion assistant.
[8] The optical member according to [7], wherein the adhesion assistant is at least one selected from an isocyanate compound and an organosilicon compound.
[9] A fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less;
A laminate for an optical member, comprising at least one fiber layer and a resin layer in contact with one surface of the fiber layer.
[10] The laminate for optical members according to [9], wherein the resin layer contains at least one resin selected from the group consisting of polycarbonate resins and polyolefin resins.
[11] The laminate for optical members according to [9] or [10], wherein the resin layer contains an adhesion assistant.
[12] The laminate for optical members according to [11], wherein the adhesion assistant is at least one selected from an isocyanate compound and an organosilicon compound.
[13] The laminate for an optical member according to any one of [9] to [12], wherein the optical member is a lens, a display, a polarizing plate, a viewing angle correction film, a retardation film, a touch panel, a force sensor, a back sheet, a cover, or a housing.

The present invention may also have the following configuration.
[14] A fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less;
A display comprising a laminate having at least one layer and a resin layer in contact with one surface of a fiber layer.
[15] The display according to [14], wherein the resin layer contains at least one resin selected from the group consisting of polycarbonate resins and polyolefin resins.
[16] The display according to [14] or [15], wherein the resin layer contains an adhesion assistant.
[17] The display according to [16], wherein the adhesion assistant is at least one selected from an isocyanate compound and an organosilicon compound.

According to the present invention, it is possible to obtain a lens that includes a resin layer and is capable of exhibiting excellent impact resistance. According to the present invention, it is also possible to obtain a display or optical component that includes a resin layer and is capable of exhibiting excellent impact resistance.

FIG. 1 is a cross-sectional view illustrating the configuration of a laminate for an optical member of the present invention. FIG. 2 is a cross-sectional view illustrating the configuration of the laminate for optical members of the present invention. FIG. 3 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having phosphorus oxoacid groups and pH. FIG. 4 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and the pH.

The present invention will be described in detail below. The following explanation of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

(Laminate for optical components)
The present invention relates to a laminate for optical components, which has at least one fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less and a resin layer in contact with one side of the fiber layer. In this specification, the fibrous cellulose having a fiber width of 1000 nm or less is also called fine fibrous cellulose or CNF. Since the laminate of the present invention has the above-mentioned structure, it can be an optical component having high transparency and excellent impact resistance.

Figure 1 is a cross-sectional view illustrating the configuration of the laminate for optical components of the present invention. As shown in Figure 1, the laminate for optical components 10 of the present invention has a fiber layer 2 and a resin layer 6. The fiber layer 2 and the resin layer 6 are laminated so that they are in contact with each other on one side.

The laminate for optical components of the present invention may have at least one fiber layer 2 and one resin layer 6, but may have two or more fiber layers 2, or may have two or more resin layers 6. For example, FIG. 2 shows a laminate for optical components 10 having two resin layers 6. As shown in FIG. 2, the two resin layers 6 may be provided on both sides of the fiber layer 2. Also, the fiber layer 2 sandwiched between the resin layers 6 may be a fiber layer having a multi-layer structure.

The total thickness of the laminate for optical components of the present invention is not particularly limited, but is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. In addition, the total thickness of the laminate for optical components is preferably 20 mm or less. It is preferable to adjust the thickness of the laminate for optical components appropriately depending on the application.

The thickness of the fiber layer of the optical component laminate is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. The thickness of the fiber layer is preferably 500 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. Here, the thickness of the fiber layer constituting the optical component laminate is a value measured by cutting out a cross section of the optical component laminate with an ultramicrotome UC-7 (manufactured by JEOL) and observing the cross section with an electron microscope, a magnifying glass, or visually. When the optical component laminate contains multiple fiber layers, it is preferable that the total thickness of the fiber layers is within the above range.

The thickness of each resin layer of the laminate for optical components is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. The thickness of each resin layer is preferably 0.1 μm or more. The thickness of each resin layer provided on both sides of the fiber layer is preferably within the above range. Here, the thickness of the resin layer constituting the sheet is a value measured by cutting out a cross section of the sheet with an ultramicrotome UC-7 (manufactured by JEOL) and observing the cross section with an electron microscope, a magnifying glass, or visually.

The total light transmittance of the laminate for optical components is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. By setting the total light transmittance of the laminate for optical components within the above range, it becomes easier to apply the laminate for optical components of the present invention to applications where transparent glass has traditionally been used. Here, the total light transmittance is a value measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7361-1:1997.

The haze of the laminate for optical components is preferably 5% or less, more preferably 1% or less, and even more preferably 0.5% or less. The lower the haze, the easier it is to apply the laminate for optical components of the present invention to applications where transparent glass has traditionally been used. Here, the haze is a value measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7136:2000. If the haze of the laminate for optical components is within the above range, the visibility of the laminate for optical components can be evaluated as good. Furthermore, if the haze of the laminate for optical components is within the above numerical value, an optical component with good visibility and no cloudiness can be obtained.

The tensile modulus of the optical component laminate at 23°C and a relative humidity of 50% is preferably 2.5 GPa or more, more preferably 5.0 GPa or more, and even more preferably 10 GPa or more. The tensile modulus of the optical component laminate at 23°C and a relative humidity of 50% is preferably 30 GPa or less, more preferably 25 GPa or less, and even more preferably 20 GPa or less. The tensile modulus of the optical component laminate is a value measured in accordance with JIS P 8113:2006.

The optical member laminate of the present invention is also excellent in water resistance. Here, the water resistance of the optical member laminate can be evaluated by the water contact angle of the surface of the optical member laminate. Specifically, the water contact angle of both surfaces of the optical member laminate is preferably 75° or more, more preferably 80° or more. That is, it is preferable that the water contact angles of both the optical member laminate surface on which one resin layer (first resin layer) is provided and the optical member laminate surface on which the other resin layer (second resin layer) is provided are each within the above range. Here, the water contact angle of the surface of the optical member laminate is the water contact angle 30 seconds after 4 μL of distilled water is dropped on the surface of the optical member laminate. A dynamic water contact angle tester is used for the measurement. As the dynamic water contact angle tester, for example, 1100DAT manufactured by Fibro can be used.

(Resin Layer)
The resin layer is a layer mainly composed of natural resin or synthetic resin. Here, the main component refers to a component contained in an amount of 50% by mass or more relative to the total mass of the resin layer. The content of the resin is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more relative to the total mass of the resin layer. The content of the resin may be 100% by mass or may be 95% by mass or less.

Examples of natural resins include rosin-based resins such as rosin, rosin ester, and hydrogenated rosin ester.

Examples of synthetic resins include polycarbonate resins, polyolefin resins (e.g., polyethylene resins and polypropylene resins), polyethylene terephthalate resins, polyethylene naphthalate resins, polyimide resins, polystyrene resins, acrylic resins, etc. Among them, the synthetic resin is preferably an amorphous resin, more preferably at least one selected from polycarbonate resins and polyolefin resins, and particularly preferably a polycarbonate resin.

Examples of the polycarbonate resin constituting the resin layer include aromatic polycarbonate resins and aliphatic polycarbonate resins. Specific examples of these polycarbonate resins are known, and examples of these include the polycarbonate resins described in JP 2010-023275 A.

Examples of polyolefin resins that make up the resin layer include polyethylene resin, polypropylene resin, cycloolefin resin (COP resin), and modified polyolefin resin.

In this embodiment, the resin layer preferably contains an adhesion aid. Examples of the adhesion aid include a compound containing at least one selected from the group consisting of an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group, and a silanol group, and an organosilicon compound. In particular, the adhesion aid is preferably at least one selected from a compound containing an isocyanate group (isocyanate compound) and an organosilicon compound. Examples of the organosilicon compound include a silane coupling agent condensate and a silane coupling agent.

The isocyanate compound may be a polyisocyanate compound or a polyfunctional isocyanate having more than 6 carbon atoms. Specific examples of the polyisocyanate compound include aromatic polyisocyanates having 6 to 20 carbon atoms excluding the carbon in the NCO group, aliphatic polyisocyanates having 2 to 18 carbon atoms, alicyclic polyisocyanates having 6 to 15 carbon atoms, aralkyl polyisocyanates having 8 to 15 carbon atoms, modified products of these polyisocyanates, and mixtures of two or more of these. Among these, alicyclic polyisocyanates having 6 to 15 carbon atoms, i.e., isocyanurates, are preferably used.

Specific examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis(2-isocyanatoethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate.

The organosilicon compound may be a compound having a siloxane structure or a compound that forms a siloxane structure by condensation. For example, a silane coupling agent or a condensate of a silane coupling agent may be mentioned. The silane coupling agent may have a functional group other than an alkoxysilyl group, or may not have any other functional group. Examples of functional groups other than an alkoxysilyl group include a vinyl group, an epoxy group, a styryl group, a methacryloxy group, an acryloxy group, an amino group, a ureido group, a mercapto group, a sulfide group, an isocyanate group, and the like. The silane coupling agent used in the present invention is preferably a silane coupling agent containing a methacryloxy group.

Specific examples of silane coupling agents having methacryloxy groups in the molecule include methacryloxypropylmethyldimethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, methacryloxypropyltriethoxysilane, and 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane. Among these, at least one selected from methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, and 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane is preferably used. The silane coupling agent preferably contains three or more alkoxysilyl groups.

In the case of a silane coupling agent, silanol groups are generated after hydrolysis, and it is preferable that at least some of the silanol groups remain even after laminating the fiber layer. Since silanol groups are hydrophilic groups, the adhesion between the resin layer and the fiber layer can be improved by increasing the hydrophilicity of the surface of the resin layer facing the fiber layer.

The adhesion aid may be contained in a state of being uniformly dispersed in the resin layer. Here, the state in which the adhesion aid is uniformly dispersed in the resin layer refers to a state in which, when the concentrations of the adhesion aid are measured in the following three regions ((a) to (c)) and the concentrations of any two regions are compared, the difference in concentration is no more than two times.
(a) A region from the surface of the resin layer facing the fiber layer to 10% of the total thickness of the resin layer; (b) A region from the surface of the resin layer opposite to the surface facing the fiber layer to 10% of the total thickness of the resin layer; (c) A region from the center surface in the thickness direction of the resin layer to ±5% of the total thickness (total of 10%)

The adhesion aid may be unevenly distributed in the region of the resin layer on the fiber layer side. For example, when an organosilicon compound is used as the adhesion aid, the organosilicon compound may be unevenly distributed in the region of the resin layer on the fiber layer side.
Here, the state in which the adhesion aid is unevenly distributed in the region of the resin layer on the fiber layer side refers to a state in which, when the concentrations of the two adhesion aids in the following regions ((d) and (e)) are measured, there is a difference of two times or more between these concentrations.
(d) A region from the surface of the resin layer facing the fiber layer to 10% of the total thickness of the resin layer; (e) A region from the center plane in the thickness direction of the resin layer to ±5% (total 10%) of the total thickness. Here, the concentration of the adhesion aid is a numerical value measured by an X-ray electron spectrometer or an infrared spectrophotometer, and is a value obtained by cutting out a cross section of a predetermined region of a laminate for optical components with an ultramicrotome UC-7 (manufactured by JEOL) and measuring the cross section with the same device.

An organosilicon compound-containing layer may be provided on the surface of the resin layer facing the fiber layer, and such a state is also included in the state in which the organosilicon compound is unevenly distributed in the region of the resin layer facing the fiber layer. The organosilicon compound-containing layer may be a coating layer formed by applying an organosilicon compound-containing coating liquid.
In addition, when an organosilicon compound-containing layer is provided on the surface of the resin layer facing the fiber layer, in the above region (d), "the surface of the resin layer facing the fiber layer" shall be read as "the exposed surface of the organosilicon compound-containing layer", and "the thickness of the entire resin layer" shall be read as "the combined thickness of the resin layer and the organosilicon compound-containing layer".

The content of the adhesion assistant is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the resin contained in the resin layer, and is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, relative to 100 parts by mass of the resin contained in the resin layer.
When the adhesion aid is an isocyanate compound, the content of the isocyanate compound is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 18 parts by mass or more, relative to 100 parts by mass of the resin contained in the resin layer. The content of the isocyanate compound is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the resin contained in the resin layer.
When the adhesion assistant is an organosilicon compound, the content of the organosilicon compound is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the resin contained in the resin layer, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the resin contained in the resin layer.
By setting the content of the adhesion assistant within the above range, the adhesion between the fiber layer and the resin layer can be more effectively improved, and thus the impact resistance of the laminate for optical members can be more effectively improved.

When the adhesion aid is an isocyanate compound, the content of isocyanate groups contained in the resin layer is preferably 0.5 mmol/g or more, more preferably 0.6 mmol/g or more, even more preferably 0.8 mmol/g or more, and particularly preferably 0.9 mmol/g or more. The content of isocyanate groups contained in the resin layer is preferably 3.0 mmol/g or less, more preferably 2.5 mmol/g or less, even more preferably 2.0 mmol/g or less, and particularly preferably 1.5 mmol/g or less.

The surface of the resin layer facing the fiber layer may be subjected to a surface treatment. Examples of the surface treatment method include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, and flame treatment. Of these, it is preferable that the surface treatment is at least one type selected from corona treatment and plasma discharge treatment. It is preferable that the plasma discharge treatment is vacuum plasma discharge treatment.

The surface of the resin layer facing the fiber layer may have a fine uneven structure. The surface of the resin layer facing the fiber layer may have a fine uneven structure, which can more effectively increase the adhesion between the fiber layer and the resin layer. When the surface of the resin layer facing the fiber layer has a fine uneven structure, such a structure is preferably formed by a processing step such as blast processing, embossing processing, etching processing, corona processing, plasma discharge processing, etc. In this specification, the fine uneven structure refers to a structure in which the number of recesses present on a line of 1 mm length drawn at any point is 10 or more. When measuring the number of recesses, the optical component laminate is immersed in ion-exchanged water for 24 hours, and then the fiber layer is peeled off from the resin layer. Then, the surface of the resin layer facing the fiber layer can be measured by scanning it with a stylus surface roughness meter (manufactured by Kosaka Laboratory, Surfcorder series). When the pitch of the irregularities is extremely small, on the order of submicrons or nanometers, the number of irregularities can be measured from images observed using a scanning probe microscope (Hitachi High-Tech Science Corporation, AFM5000II and AFM5100N).

The resin layer may contain optional components other than synthetic resins. Examples of optional components include known components used in the field of resin films, such as fillers, pigments, dyes, UV absorbers, antioxidants, antistatic agents, and light diffusing agents.

(Fiber layer)
The fiber layer contains fibrous cellulose (fine fibrous cellulose) having a fiber width of 1000 nm or less. The content of the fine fibrous cellulose contained in the fiber layer is preferably 60 mass% or more, more preferably 70 mass% or more, and even more preferably 80 mass% or more, based on the total mass of the fiber layer.

The density of the fiber layer is preferably 1.0 g/cm ³ or more, more preferably 1.2 g/cm ³ or more, and even more preferably 1.4 g/cm ³ or more. The density of the fiber layer is preferably 1.7 g/cm ³ or less, more preferably 1.65 g/cm ³ or less, and even more preferably 1.6 g/cm ³ or less. When the laminate for optical members contains two or more fiber layers, it is preferable that the density of each fiber layer is within the above range.

The density of the fiber layer is calculated from the basis weight and thickness of the fiber layer in accordance with JIS P 8118:2014. The basis weight of the fiber layer can be calculated in accordance with JIS P 8124:2011 by cutting the fiber layer of the laminate for optical components using an ultramicrotome UC-7 (manufactured by JEOL) so that only the fiber layer remains. Note that if the fiber layer contains any component other than fine fibrous cellulose, the density of the fiber layer is the density including any component other than fine fibrous cellulose.

In the present invention, the fiber layer is also characterized in that it is a non-porous layer. Here, the fiber layer being non-porous means that the density of the entire fiber layer is 1.0 g/cm ³ or more. If the density of the entire fiber layer is 1.0 g/cm ³ or more, it means that the porosity contained in the fiber layer is suppressed to a predetermined value or less, and it is distinguished from a porous sheet or layer.
The non-porous nature of the fibrous layer is also characterized by a porosity of 15 volume % or less. The porosity of the fibrous layer referred to here is calculated simply by the following formula (a):
Formula (a): Porosity (volume%) = {1-B/(M x A x t)} x 100
Here, A is the area of the fiber layer (cm ² ), t is the thickness of the fiber layer (cm), B is the mass of the fiber layer (g), and M is the density of cellulose.

<Fine fibrous cellulose>
The fiber layer contains fibrous cellulose (fine fibrous cellulose) having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is more preferably 100 nm or less, and even more preferably 8 nm or less.

The fiber width of fibrous cellulose can be measured, for example, by observation under an electron microscope. The average fiber width of fibrous cellulose is, for example, 1000 nm or less. The average fiber width of fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By making the average fiber width of fibrous cellulose 2 nm or more, it is possible to suppress dissolution of cellulose molecules in water, and to more easily realize the effect of improving strength, rigidity, and dimensional stability due to fibrous cellulose. The fibrous cellulose is, for example, monofilament cellulose.

The average fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. If the sample contains wide fibers, an SEM image of the surface cast onto glass may be observed. Next, the electron microscope image is observed at a magnification of 1000x, 5000x, 10000x, or 50000x depending on the width of the fiber to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

(1) A straight line X is drawn at an arbitrary location within the observed image, and 20 or more fibers intersect with the straight line X.
(2) Within the same image, a straight line Y is drawn that intersects the straight line perpendicularly, and 20 or more fibers intersect the straight line Y.

For observation images that satisfy the above conditions, the width of the fibers that intersect with lines X and Y is visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the width of the fibers that intersect with lines X and Y is read. In this way, the width of at least 20 fibers x 2 x 3 = 120 fibers is read. The average of the read fiber widths is then determined as the average fiber width of the fibrous cellulose.

The fiber length of the fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the fibrous cellulose can be suppressed. It is also possible to set the slurry viscosity of the fibrous cellulose to an appropriate range. The fiber length of the fibrous cellulose can be determined, for example, by image analysis using a TEM, SEM, or AFM.

It is preferable that the fibrous cellulose has an I-type crystal structure. Here, the fact that the fibrous cellulose has an I-type crystal structure can be identified from the diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromatized with graphite. Specifically, it can be identified from the presence of typical peaks at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°. The proportion of I-type crystal structure in the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

The axial ratio (fiber length/fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, 20 to 10,000, and more preferably 50 to 1,000. By setting the axial ratio to the above lower limit or more, it is easy to form a sheet containing fine fibrous cellulose. In addition, sufficient thickening is easily obtained when a solvent dispersion is produced. By setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when the fibrous cellulose is treated as an aqueous dispersion, handling such as dilution is easier.

The fibrous cellulose in this embodiment has, for example, both crystalline and non-crystalline regions. Fine fibrous cellulose having both crystalline and non-crystalline regions and an axial ratio within the above range is realized by the method for producing fine fibrous cellulose described below.

In this embodiment, the fibrous cellulose preferably has an ionic substituent. The ionic substituent may include, for example, either one or both of an anionic group and a cationic group. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. In addition, the ionic substituent is preferably a group that is linked to the fibrous cellulose via an ester bond. In this case, the ester bond is formed by dehydration condensation between the fibrous cellulose and a compound that becomes the ionic substituent.

Examples of anionic groups as ionic substituents include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfate ester groups or substituents derived from sulfate ester groups (sometimes simply referred to as sulfate ester groups), xanthate groups, phosphonic groups, phosphine groups, sulfone groups, carboxyalkyl groups, etc. Among these, the anionic group is preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, substituents derived from carboxy groups, sulfate ester groups, substituents derived from sulfate ester groups, carboxymethyl groups, and sulfone groups, more preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfate ester groups, and substituents derived from sulfate ester groups, and particularly preferably phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups. By introducing a phosphorus oxoacid group as an anionic group, the dispersibility of the fibrous cellulose can be further increased, even under alkaline or acidic conditions, and as a result, a sheet with high strength and high transparency can be easily obtained. Examples of cationic groups as ionic substituents include ammonium groups, phosphonium groups, and sulfonium groups. Among these, the cationic group is preferably an ammonium group.

The phosphorus oxoacid group or the substituent derived from the phosphorus oxoacid group is, for example, a substituent represented by the following formula (1). A plurality of types of the substituent represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (wherein a=b×m). At least one of the n α and α' is ^O- , and the rest are R or OR. All of the α and α' may be ^O- . The n α may be the same or different. ^{β b+} is a monovalent or higher cation made of an organic or inorganic substance.

Each R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from any of these. In formula (1), n is preferably 1.

Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, or n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl or t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl or cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl or allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl or 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl or cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl or naphthyl groups.

In addition, the derivative group in R includes, but is not limited to, a functional group in which at least one selected from functional groups such as a carboxy group, a carboxylate group ( ^-COO- ), a hydroxy group, an amino group, and an ammonium group is added to or substituted for the main chain or side chain of the above-mentioned various hydrocarbon groups. In addition, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxo acid group can be set to an appropriate range, which facilitates penetration into the fiber raw material and increases the yield of fibrous cellulose. Note that when there are multiple R in formula (1) or when multiple types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the multiple R present may be the same or different.

β ^b+ is a monovalent or higher cation made of an organic or inorganic substance. As the monovalent or higher cation made of an organic substance, an organic onium ion can be mentioned. As the organic onium ion, for example, an organic ammonium ion or an organic phosphonium ion can be mentioned. As the organic ammonium ion, for example, an aliphatic ammonium ion or an aromatic ammonium ion can be mentioned, and as the organic phosphonium ion, for example, an aliphatic phosphonium ion or an aromatic phosphonium ion can be mentioned. As the monovalent or higher cation made of an inorganic substance, an ion of an alkali metal such as sodium, potassium, or lithium, an ion of a divalent metal such as calcium or magnesium, a hydrogen ion, an ammonium ion, etc. can be mentioned. In addition, when there are multiple β ^{b+ in} the formula (1) or when multiple types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the multiple β ^{b+ may be the same or different. As the monovalent or higher cation made of an organic or inorganic substance, sodium or potassium ions are preferable because they are less likely to yellow when a fiber raw material containing β b+} is heated and are easy to use industrially, but are not particularly limited.

More specifically, examples of the phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group include a phosphate group (-PO ₃ H ₂ ), a salt of a phosphate group, a phosphorous acid group (phosphonic acid group) (-PO ₂ H ₂ ), and a salt of a phosphite group (phosphonic acid group). In addition, the phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group may be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methylphosphonic acid group), etc.

The sulfate ester group (sulfate ester group or a substituent derived from a sulfate ester group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is any number (wherein 1=b×m). When n is 2 or more, the multiple p's may be the same number or different numbers. In the above structural formula, β ^b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. In addition, when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β ^b+ present may be the same or different. As the organic or inorganic cation having a valence of one or more, sodium or potassium ions are preferred, which are less likely to yellow when the fiber raw material containing β ^b+ is heated and are easy to use industrially, but are not particularly limited.

The amount of ionic substituent introduced into fibrous cellulose is preferably 0.10 mmol/g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.40 mmol/g or more, and particularly preferably 0.60 mmol/g or more. The amount of ionic substituent introduced into fibrous cellulose is preferably 5.20 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, even more preferably 2.00 mmol/g or less, even more preferably 1.50 mmol/g or less, and particularly preferably 1.00 mmol/g or less. Here, the denominator in the unit mmol/g indicates the mass of fibrous cellulose when the counter ion of the ionic substituent is a hydrogen ion (H ⁺ ). By setting the amount of ionic substituent introduced within the above range, it is possible to easily refine the fiber raw material and increase the stability of the fibrous cellulose.

The amount of ionic substituents introduced into fibrous cellulose can be measured, for example, by neutralization titration. In the measurement by neutralization titration, an alkali such as an aqueous sodium hydroxide solution is added to the obtained slurry containing fibrous cellulose, and the amount introduced is measured by determining the change in pH.

3 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into the fibrous cellulose is measured, for example, as follows.
First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement target may be subjected to a defibration treatment similar to the defibration treatment step described below prior to the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding the aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of Figure 3 is obtained. In the titration curve shown in the upper part of Figure 3, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of Figure 3, the increment (differential value) (1/mmol) of pH against the amount of alkali added is plotted. In this neutralization titration, two points are confirmed in the curve plotting the measured pH against the amount of alkali added, where the increment (differential value of pH against the amount of alkali added) is maximum. Of these, the first maximum point of the increment obtained after starting to add the alkali is called the first endpoint, and the second maximum point of the increment obtained next is called the second endpoint. The amount of alkali required from the start of titration to the first end point is equal to the amount of the first dissociated acid of the fibrous cellulose contained in the slurry used for titration, the amount of alkali required from the first end point to the second end point is equal to the amount of the second dissociated acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol/g). Note that when simply referring to the amount of phosphorus oxo acid group introduced (or the amount of phosphorus oxo acid group), it refers to the amount of the first dissociated acid.
In FIG. 3, the region from the start of titration to the first end point is called the first region, and the region from the first end point to the second end point is called the second region. For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weak acid groups in the phosphorus oxoacid group (also referred to as the second dissociated acid amount in this specification) appears to decrease, and the amount of alkali required in the second region becomes smaller than the amount of alkali required in the first region. On the other hand, the amount of strong acid groups in the phosphorus oxoacid group (also referred to as the first dissociated acid amount in this specification) is equal to the amount of phosphorus atoms regardless of the presence or absence of condensation. In addition, when the phosphorus oxoacid group is a phosphorous acid group, the weak acid groups are no longer present in the phosphorus oxoacid group, so the amount of alkali required in the second region becomes smaller, or the amount of alkali required in the second region may become zero. In this case, there is only one point on the titration curve where the pH increment is maximized.

The above-mentioned amount of phosphorus oxoacid groups introduced (mmol/g) indicates the amount of phosphorus oxoacid groups possessed by the acid-type fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid type)), since the denominator indicates the mass of the acid-type fibrous cellulose. On the other hand, when the counter ion of the phosphorus oxoacid group is replaced with an arbitrary cation C so as to be the charge equivalent, the amount of phosphorus oxoacid groups possessed by the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C type)) can be obtained by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion.
That is, it is calculated according to the following formula.
Amount of phosphorus oxoacid group (C type)=Amount of phosphorus oxoacid group (acid type)/{1+(W−1)×A/1000}
A [mmol/g]: total amount of anions derived from phosphorus oxoacid groups in the fibrous cellulose (total amount of dissociated acids from phosphorus oxoacid groups)
W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

4 is a graph showing the relationship between the amount of NaOH dropped onto a dispersion containing fibrous cellulose having a carboxy group as an ionic substituent and the pH. The amount of carboxy group introduced into the fibrous cellulose is measured, for example, as follows.
First, a dispersion liquid containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment step described below may be performed on the measurement target prior to the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding the aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 4 is obtained. In the titration curve shown in the upper part of FIG. 4, the measured pH is plotted against the amount of added alkali, and in the titration curve shown in the lower part of FIG. 4, the increment (differential value) (1/mmol) of pH against the amount of added alkali is plotted. In this neutralization titration, one point where the increment (differential value of pH against the amount of added alkali) is maximum is confirmed in the curve plotting the measured pH against the amount of added alkali, and this maximum point is called the first end point. Here, the region from the start of titration to the first end point in FIG. 4 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. Then, the amount of alkali required in the first region of the titration curve (mmol) is divided by the solid content (g) in the dispersion containing the fibrous cellulose to be titrated to calculate the amount of carboxyl groups introduced (mmol/g).

The above-mentioned amount of carboxyl groups introduced (mmol/g) indicates the amount of carboxyl groups in the acid-type fibrous cellulose (hereinafter referred to as the amount of carboxyl groups (acid type)) since the denominator is the mass of the acid-type fibrous cellulose. On the other hand, when the counter ion of the carboxyl group is replaced with any cation C so as to be the charge equivalent, the amount of carboxyl groups in the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of carboxyl groups (C type)) can be obtained by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated by the following formula.
Carboxy group amount (C type)=Carboxy group amount (acid type)/{1+(W-1)×(Carboxy group amount (acid type))/1000}
W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

When measuring the amount of ionic substituents by titration, if too much sodium hydroxide solution is added or if the titration interval is too short, the amount of ionic substituents may be lower than it should be, and an accurate value may not be obtained. For example, an appropriate amount of sodium hydroxide and titration interval is preferably 10 to 50 μL of 0.1 N sodium hydroxide solution added every 5 to 30 seconds. In addition, in order to eliminate the effects of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is preferable to measure while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of titration.

The amount of sulfate ester groups introduced into fibrous cellulose can be calculated by freeze-drying a slurry containing fibrous cellulose, pulverizing the slurry, and measuring the amount of sulfur in the resulting pulverized sample. Specifically, a slurry containing fibrous cellulose is freeze-dried, and the resulting pulverized sample is subjected to pressurized heating decomposition using nitric acid in a closed container, and then appropriately diluted and the amount of sulfur is measured using ICP-OES. The value calculated by dividing the value by the bone dry mass of the fibrous cellulose used is taken as the amount of sulfate ester groups in the fibrous cellulose (unit: mmol/g).

<Optional ingredients>
The fiber layer may contain any component other than the fine fibrous cellulose. Examples of the optional component include hydrophilic polymers and organic ions. The hydrophilic polymer is preferably a hydrophilic oxygen-containing organic compound (excluding the above-mentioned cellulose fibers). The oxygen-containing organic compound is preferably non-fibrous, and such non-fibrous oxygen-containing organic compounds do not include fine fibrous cellulose or thermoplastic resin fibers.

The oxygen-containing organic compound is preferably a hydrophilic organic compound. The hydrophilic oxygen-containing organic compound can improve the strength, density, chemical resistance, and the like of the fiber layer. The hydrophilic oxygen-containing organic compound preferably has an SP value of, for example, 9.0 or more. In addition, the hydrophilic oxygen-containing organic compound is preferably one in which, for example, 1 g or more of the oxygen-containing organic compound dissolves in 100 ml of ion-exchanged water.

Examples of oxygen-containing organic compounds include hydrophilic polymers such as polyethylene glycol, polyethylene oxide, casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (such as acetoacetylated polyvinyl alcohol), polyethylene oxide, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, acrylic acid alkyl ester copolymers, urethane copolymers, and cellulose derivatives (such as hydroxyethyl cellulose, carboxyethyl cellulose, and carboxymethyl cellulose); and hydrophilic low-molecular-weight compounds such as glycerin, sorbitol, and ethylene glycol. Among these, from the viewpoint of improving the strength, density, chemical resistance, and the like of the fiber layer, polyethylene glycol, polyethylene oxide, glycerin, and sorbitol are preferred, and at least one selected from polyethylene glycol and polyethylene oxide is more preferred, and polyethylene glycol is even more preferred.

The oxygen-containing organic compound is preferably an organic polymer having a molecular weight of 50,000 to 8,000,000. The molecular weight of the oxygen-containing organic compound is also preferably 100,000 to 5,000,000, but may be a low molecular weight compound having a molecular weight of less than 1,000, for example.

The content of the oxygen-containing organic compound contained in the fiber layer is preferably 1 part by mass or more and 40 parts by mass or less, more preferably 10 parts by mass or more and 30 parts by mass or less, and even more preferably 15 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the fine fibrous cellulose contained in the fiber layer. By setting the content of the oxygen-containing organic compound within the above range, it becomes easy to form a laminate for optical components having high transparency and impact resistance.

Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion, lauryltrimethylammonium ion, cetyltrimethylammonium ion, stearyltrimethylammonium ion, octyldimethylethylammonium ion, lauryldimethylethylammonium ion, didecyldimethylammonium ion, lauryldimethylbenzylammonium ion, and tributylbenzylammonium ion. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Examples of tetrapropylonium ion and tetrabutylonium ion include tetra-n-propylonium ion and tetra-n-butylonium ion, respectively.

<Method of producing fine fibrous cellulose>
<Fiber raw materials>
The fine fibrous cellulose is produced from a fiber raw material containing cellulose. The fiber raw material containing cellulose is not particularly limited, but it is preferable to use pulp because it is easily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not particularly limited to, chemical pulp such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP) and oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. Examples of non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, and bagasse. Examples of deinked pulps include, but are not limited to, deinked pulp made from waste paper. The pulps of this embodiment may be used alone or in combination of two or more. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of availability. Among wood pulps, chemical pulps are more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoint of a high cellulose ratio and a high yield of fine fibrous cellulose during defibration treatment, and of small decomposition of cellulose in the pulp and of obtaining long-fiber fine fibrous cellulose with a large axial ratio. The viscosity tends to increase when long-fiber fine fibrous cellulose with a large axial ratio is used.

As fiber raw materials containing cellulose, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria can be used. Also, instead of fiber raw materials containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can be used.

In order to obtain fibrous cellulose having an ionic substituent introduced therein, it is preferable to have an ionic substituent introduction step for introducing an ionic substituent into the above-mentioned cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and an acid treatment step may be included instead of or in addition to the washing step. Examples of ionic substituent introduction steps include a phosphorus oxoacid group introduction step, a carboxy group introduction step, a sulfate ester group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

<Phosphorus Oxo Acid Group Introduction Step>
The manufacturing process of fine fibrous cellulose preferably includes an ionic substituent introduction step, and an example of the ionic substituent introduction step is a phosphorus oxo acid group introduction step. The phosphorus oxo acid group introduction step is a step of reacting at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups possessed by a fiber raw material containing cellulose with the fiber raw material containing cellulose. This step results in the production of a fiber into which a phosphorus oxo acid group has been introduced.

In the phosphorus oxoacid group introduction process according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). On the other hand, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the absence of compound B.

One example of a method for allowing compound A to act on a fiber raw material in the presence of compound B is to mix compound A and compound B with a fiber raw material in a dry, wet, or slurry state. Of these, it is preferable to use a fiber raw material in a dry or wet state, and it is particularly preferable to use a fiber raw material in a dry state, because the reaction is highly uniform. The form of the fiber raw material is not particularly limited, but it is preferable to use a cotton-like or thin sheet-like form. Compound A and compound B can be added to the fiber raw material in a powder form, a solution form dissolved in a solvent, or a melted state by heating to a melting point or higher. Of these, it is preferable to add them in a solution form dissolved in a solvent, especially in an aqueous solution form, because the reaction is highly uniform. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method of adding compound A and compound B is not particularly limited, but when compound A and compound B are in a solution form, the fiber raw material may be immersed in the solution to absorb the liquid and then removed, or the solution may be dripped onto the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

Compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, and may include, but is not limited to, phosphoric acid or its salt, phosphorous acid or its salt, dehydrated condensed phosphoric acid or its salt, and anhydrous phosphoric acid (diphosphorus pentoxide). Phosphoric acid may be of various purities, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid may be 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is phosphoric acid in which two or more molecules are condensed by a dehydration reaction, and examples of such include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, and these may be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphate groups, easier improvement of defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, and ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid and sodium phosphite are more preferred.

The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the effect of improving the yield and costs.

As described above, the compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of the compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea.
From the viewpoint of improving the uniformity of the reaction, it is preferable to use an aqueous solution of compound B. Also, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

The amount of compound B added relative to the fiber raw material (bone dry mass) is not particularly limited, but is preferably from 1% by mass to 500% by mass, more preferably from 10% by mass to 400% by mass, and even more preferably from 100% by mass to 350% by mass.

In the reaction of a fiber raw material containing cellulose with compound A, in addition to compound B, for example, amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine in particular is known to act as a good reaction catalyst.

In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material, and then heat-treat the fiber raw material. It is preferable to select a temperature for the heat treatment that can efficiently introduce phosphorus oxo acid groups while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. In addition, for the heat treatment, equipment having various heat media can be used, such as a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

In the heat treatment according to this embodiment, for example, a method of adding compound A to a thin sheet-like fiber raw material by a method such as impregnation and then heating the material, or a method of heating the fiber raw material and compound A while kneading or stirring the fiber raw material with a kneader or the like can be adopted. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and introduce phosphorus oxoacid groups more uniformly onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be due to the fact that when water molecules move to the surface of the fiber raw material as it dries, the dissolved compound A can be prevented from being attracted to the water molecules by surface tension and moving to the surface of the fiber raw material in the same way (i.e., causing unevenness in the concentration of compound A).

The heating device used for the heat treatment is preferably one that can constantly discharge, from the system, moisture held by the slurry and moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. An example of such a heating device is an oven that uses a blowing fan. By constantly discharging moisture from within the system, the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, can be suppressed, and acid hydrolysis of the sugar chains in the fibers can also be suppressed. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.

The heat treatment time is preferably, for example, from 1 second to 300 minutes after the moisture has been substantially removed from the fiber raw material, more preferably from 1 second to 1000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, the amount of phosphorus oxoacid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within an appropriate range.

The phosphorus oxo acid group introduction process needs to be carried out at least once, but can also be repeated two or more times. By carrying out the phosphorus oxo acid group introduction process two or more times, many phosphorus oxo acid groups can be introduced into the fiber raw material.

The amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 0.10 mmol/g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.50 mmol/g or more, and particularly preferably 1.00 mmol/g or more. The amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 5.20 mmol/g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol/g or less, and even more preferably 3.00 mmol/g or less. By setting the amount of phosphorus oxoacid groups introduced within the above range, it is possible to easily fine the fiber raw material and increase the stability of the fine fibrous cellulose.

<Carboxy Group Introduction Step>
The process for producing fine fibrous cellulose may include, for example, a carboxyl group introduction step as an ionic substituent introduction step. The carboxyl group introduction step is carried out by subjecting a fiber raw material containing cellulose to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or treating the raw material with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

Examples of compounds having a group derived from a carboxylic acid include, but are not limited to, dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Examples of derivatives of compounds having a group derived from a carboxylic acid include, but are not limited to, imidized products of acid anhydrides of compounds having a carboxy group, and derivatives of acid anhydrides of compounds having a carboxy group. Examples of imidized products of acid anhydrides of compounds having a carboxy group include, but are not limited to, imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

The acid anhydrides of compounds having a group derived from carboxylic acid include, but are not limited to, acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. In addition, the derivatives of acid anhydrides of compounds having a group derived from carboxylic acid include, but are not limited to, acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, and diphenylmaleic anhydride in which at least some of the hydrogen atoms are substituted with a substituent such as an alkyl group or a phenyl group.

When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of pH 6 or more and 8 or less. Such a treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as a fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by allowing sodium chlorite to coexist, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. In addition, the TEMPO oxidation treatment may be performed under conditions of pH 10 or more and 11 or less. Such a treatment is also called alkaline TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a cocatalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material.

The amount of carboxyl groups introduced into the fibrous cellulose varies depending on the type of the substituent. For example, when the carboxyl groups are introduced by TEMPO oxidation, the amount is preferably 0.10 mmol/g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.40 mmol/g or more, and particularly preferably 0.60 mmol/g or more. The amount of carboxyl groups introduced into the fibrous cellulose is preferably 3.65 mmol/g or less, more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, even more preferably 2.00 mmol/g or less, even more preferably 1.50 mmol/g or less, and particularly preferably 1.00 mmol/g or less. In addition, when the substituent is a carboxymethyl group, the amount of carboxyl groups introduced may be 5.8 mmol/g or less per 1 g (mass) of fine fibrous cellulose. By setting the amount of carboxyl groups introduced within the above range, it is possible to easily refine the fiber raw material and increase the stability of the fibrous cellulose.

<Sulfate ester group introduction step>
The process for producing fine fibrous cellulose may include, for example, a sulfate ester group introduction step as an ionic substituent introduction step, in which a hydroxyl group in a fiber raw material containing cellulose reacts with a sulfur oxoacid to obtain a cellulose fiber having a sulfate ester group (sulfate ester group-introduced fiber).

In the sulfate ester group introduction step, instead of compound A in the above-mentioned <phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfate ester groups by reacting with hydroxyl groups possessed by fiber raw materials containing cellulose is used. Compound C may be any compound that has a sulfur atom and can form an ester bond with cellulose, and examples of the compound include, but are not limited to, sulfuric acid (phosphonic acid) or its salt, sulfurous acid or its salt, and sulfuric acid amide. As the sulfuric acid (phosphonic acid), those of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). As the sulfurous acid, 5% sulfurous acid water can be used. As the sulfate or sulfite, lithium salt, sodium salt, potassium salt, ammonium salt, and the like of sulfate or sulfite can be used, and these can be neutralized to various degrees. As the sulfuric acid amide, sulfamic acid, etc. can be used. In the sulfate ester group introduction step, it is preferable to use compound B in the above-mentioned <phosphorus oxo acid group introduction step> in the same manner.

In the sulfate ester group introduction process, it is preferable to mix the cellulose raw material with an aqueous solution containing sulfur oxoacid and urea and/or a urea derivative, and then heat treat the cellulose raw material. It is preferable to select a heat treatment temperature that can efficiently introduce sulfate ester groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

In the heat treatment step, it is preferable to heat until substantially no moisture is present. For this reason, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of the aqueous solution containing sulfur oxoacid and urea and/or urea derivative added, but is preferably, for example, 10 seconds to 10,000 seconds. For the heat treatment, equipment having various heat media can be used, such as a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

The amount of sulfate ester groups introduced into the cellulose raw material is preferably 0.50 mmol/g or more, more preferably 0.70 mmol/g or more, and even more preferably 1.00 mmol/g or more. The amount of sulfate ester groups introduced into the cellulose raw material is preferably 5.00 mmol/g or less, and more preferably 3.00 mmol/g or less. By setting the amount of sulfate ester introduced within the above range, it is possible to easily refine the fiber raw material and increase the stability of the fibrous cellulose.

<Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)>
The process for producing fine fibrous cellulose may include an oxidation step with a chlorine-based oxidizing agent as an ionic substituent introduction step. In the oxidation step with a chlorine-based oxidizing agent, the chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the standpoint of efficiency of introducing substituents, and therefore defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in an appropriate solvent and added.

The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is, for example, preferably 1% by mass or more and 1,000% by mass or less, more preferably 5% by mass or more and 500% by mass or less, and even more preferably 10% by mass or more and 100% by mass or less, converted into an effective chlorine concentration. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 10 parts by mass or more and 10,000 parts by mass or less, and even more preferably 100 parts by mass or more and 5,000 parts by mass or less.

The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably from 5 to 15, more preferably from 7 to 14, and even more preferably from 9 to 13. At the start of the reaction, it is preferable to maintain the pH during the reaction constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

<Xanthate group introduction step (xanthogen acid esterification step)>
The manufacturing process of fine fibrous cellulose may include a xanthate group introduction step (hereinafter also referred to as a xanthate formation step) as an ionic substituent introduction step. In the xanthate formation step, carbon disulfide and an alkali compound are added to a wet or dry fiber raw material having a hydroxyl group to react with each other, thereby introducing a xanthate group into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

<<Alkaline cellulose>>
When introducing an ionic substituent into a fiber raw material, it is preferable to make the cellulose contained in the fiber raw material into an alkali cellulose by applying an alkali solution to the cellulose. This treatment causes a part of the hydroxyl groups of the cellulose to be ionized, and the nucleophilicity (reactivity) can be increased. The alkali compound contained in the alkali solution is not particularly limited, and may be an inorganic alkali compound or an organic alkali compound. Because of its high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The alkali cellulose may be made into an alkali cellulose simultaneously with the introduction of an ionic substituent, may be made before the introduction, or may be made at both timings.

The solution temperature at the start of alkali cellulose conversion is preferably 0°C or higher and 50°C or lower, more preferably 5°C or higher and 40°C or lower, and even more preferably 10°C or higher and 30°C or lower.

The alkali concentration in the alkaline solution is preferably 0.01 mol/L or more and 4 mol/L or less, more preferably 0.1 mol/L or more and 3 mol/L or less, and even more preferably 1 mol/L or more and 2.5 mol/L or less. In particular, when the treatment temperature in alkali cellulose formation is less than 10°C, the alkali concentration is preferably 1 mol/L or more and 2 mol/L or less.

The processing time for alkali cellulose formation is preferably 1 minute or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more. The alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress the penetration of the alkaline solution into the crystalline regions of the cellulose, making it easier to maintain the crystalline structure of cellulose type I, and increasing the yield of fine fibrous cellulose.

When the introduction of ionic substituents and the conversion to alkali cellulose are not performed simultaneously, the conversion to alkali cellulose is preferably performed prior to the introduction of ionic substituents. In this case, the alkali cellulose obtained by the conversion to alkali cellulose is preferably subjected to solid-liquid separation and water removal by a general deliquation method such as centrifugation or filtration. This improves the reaction efficiency in the subsequent ionic substituent introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% or more and 50% or less, more preferably 10% or more and 40% or less, and even more preferably 15% or more and 35% or less.

<Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)>
The process for producing fine fibrous cellulose may include a phosphonic or phosphine group introduction step (phosphoalkylation step) as an ionic substituent introduction step. In the phosphoalkylation step, a compound having a reactive group and a phosphonic or phosphine group (compound E _A ) as an essential component, an alkali compound as an optional component, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group to carry out a reaction, thereby introducing a phosphonic or phosphine group into the fiber raw material.

Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).
Examples of the compound E _A include vinylphosphonic acid, phenylvinylphosphonic acid, phenylvinylphosphinic acid, etc. From the viewpoints of the efficiency of introducing a substituent, and therefore the defibration efficiency, cost, and ease of handling, it is preferable that the compound E _A is vinylphosphonic acid.
Furthermore, as an optional component, it is also preferable to use compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

When compound E _A is added, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in a suitable solvent and added. It is preferable that the fiber raw material is converted into alkali cellulose in advance or converted into alkali cellulose simultaneously with the reaction. The method of conversion into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _A added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed away with water and removed by filtration, etc.

<Sulfone group introduction step (sulfoalkylation step)>
The process for producing fine fibrous cellulose may include a sulfone group introduction step (sulfoalkylation step) as an ionic substituent introduction step. In the sulfoalkylation, a compound (compound E _B ) having a reactive group and a sulfone group as an essential component, and an optional component, an alkali compound, and a compound B selected from the above-mentioned urea and its derivatives, are added to a wet or dry fiber raw material having a hydroxyl group to carry out a reaction, thereby introducing a sulfone group into the fiber raw material.

Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).
Examples of compound E _B include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, etc. Among these, from the viewpoints of the efficiency of introducing a substituent, and therefore the defibration efficiency, cost, and ease of handling, it is preferable that compound E _B is sodium vinylsulfonate.
Furthermore, as an optional component, it is also preferable to use compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

When compound E _B is added, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in a suitable solvent and added. It is preferable that the fiber raw material is converted into alkali cellulose in advance or simultaneously with the reaction. The method of conversion into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _B added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed away with water by filtration or the like.

<Carboxyalkylation step (third carboxy group introduction step)>
The process for producing fine fibrous cellulose may include a carboxyalkylation step as an ionic substituent introduction step. A compound having a reactive group and a carboxy group (compound E _C ) as an essential component, an alkali compound as an optional component, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxy group into the fiber raw material.

Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).
As the compound E _C , monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the standpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling.
Furthermore, as an optional component, it is also preferable to use compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

When compound E _C is added, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in a suitable solvent and added. It is preferable that the fiber raw material is converted into alkali cellulose in advance or simultaneously with the reaction. The method of conversion into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _C added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed away with water and removed by filtration, etc.

<Cationic group introduction step (cationization step)>
The process for producing fine fibrous cellulose may include a cationic group introduction step as an ionic substituent introduction step. A compound having a reactive group and a cationic group (compound E _D ) as an essential component, and an alkali compound and a compound B selected from the above-mentioned urea and its derivatives as optional components are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce the cationic group into the fiber raw material.

Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).
Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among these, the cationic group is preferably an ammonium group.
As the compound E _D , glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling.
Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner. The amount of addition is also preferably as described above.

When compound E _D is added, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in a suitable solvent and added. It is preferable that the fiber raw material is converted into alkali cellulose in advance or simultaneously with the reaction. The method of conversion into alkali cellulose is as described above.

The reaction temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

The amount of compound E _D added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed away with water and removed by filtration, etc.

<Cleaning process>
In the method for producing fine fibrous cellulose in this embodiment, a washing step can be carried out on the ionic substituent-introduced fiber as necessary. The washing step is carried out, for example, by washing the ionic substituent-introduced fiber with water or an organic solvent. The washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

<Alkaline treatment step>
When producing fine fibrous cellulose, an alkali treatment may be carried out on the fiber raw material between the step of introducing an ionic substituent and the step of defibrating the fiber, which will be described later. The method of the alkali treatment is not particularly limited, but may be, for example, a method of immersing the fiber having an ionic substituent introduced therein in an alkali solution.

The alkaline compound contained in the alkaline solution is not particularly limited, and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among them, the solvent contained in the alkaline solution is preferably a polar solvent including water or a polar organic solvent such as alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of its high versatility.

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic substituent-introduced fiber.

In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated ionic substituent-introduced fiber with water or an organic solvent after the alkaline treatment step and before the defibration treatment step.

<Acid treatment step>
When producing fine fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing an ionic substituent and the defibration treatment step described later. For example, the step of introducing an ionic substituent, the acid treatment, the alkali treatment, and the defibration treatment may be performed in this order.

The method of acid treatment is not particularly limited, but for example, a method of immersing the fiber raw material in an acidic solution containing an acid can be mentioned. The concentration of the acidic solution used is not particularly limited, but for example, it is preferably 10% by mass or less, more preferably 5% by mass or less. The pH of the acidic solution used is not particularly limited, but for example, it is preferably 0 to 4, more preferably 1 to 3. The acid contained in the acidic solution can be, for example, an inorganic acid, a sulfonic acid, a carboxylic acid, etc. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid, etc. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, etc. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid, etc. Among these, it is particularly preferable to use hydrochloric acid or sulfuric acid.

The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably from 5°C to 100°C, and more preferably from 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably from 5 minutes to 120 minutes, and more preferably from 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably from 100% to 100,000% by mass, and more preferably from 1,000% to 10,000% by mass, based on the absolute dry mass of the fiber raw material.

<Defibrillation treatment>
The ionic substituent-introduced fibers are defibrated in a defibration process to obtain fine fibrous cellulose. In the defibration process, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, and for example, a high-speed defibrator, a grinder (stone mill type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision type grinder, a ball mill, a bead mill, a disk type refiner, a conical refiner, a biaxial kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater can be used. Among the above defibration treatment devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

In the fiber defibration process, for example, it is preferable to dilute the ionic substituent-introduced fiber with a dispersion medium to make it into a slurry state. As the dispersion medium, one or more types selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but for example, alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, etc. are preferable. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol, etc. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, glycerin, etc. Examples of ketones include acetone, methyl ethyl ketone (MEK), etc. Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-butyl ether, propylene glycol monomethyl ether, etc. Examples of esters include ethyl acetate, butyl acetate, etc. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), etc.

The solids concentration of the fine fibrous cellulose during the defibration process can be set as appropriate. In addition, the slurry obtained by dispersing the ionic substituent-introduced fibers in a dispersion medium may contain solids other than the ionic substituent-introduced fibers, such as urea with hydrogen bonding properties.

(Method for producing laminate for optical member)
The present invention also relates to a method for producing a laminate for an optical member, the method comprising either the following step (a) or (b):
(a) A step of forming a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less, followed by applying a resin composition onto the fiber layer.
(b) A step of applying a fine fibrous cellulose dispersion containing fibrous cellulose having a fiber width of 1000 nm or less onto the resin layer after the step of forming the resin layer.

In the above steps (a) and (b), an adhesion aid may be included in the resin composition forming the resin layer. For example, in the above step (a), the adhesion aid is preferably at least one selected from an isocyanate compound and an organosilicon compound, and more preferably an isocyanate compound. In the above step (b), the adhesion aid is preferably at least one selected from an isocyanate compound and an organosilicon compound, and more preferably an organosilicon compound.

The above step (a) includes a step of forming a fiber layer containing fine fibrous cellulose (hereinafter also referred to as a fine fibrous cellulose-containing sheet). The manufacturing process of the fine fibrous cellulose-containing sheet includes a step of applying a fine fibrous cellulose dispersion (a fine fibrous cellulose-containing slurry) onto a substrate, or a step of making paper from the fine fibrous cellulose dispersion. In particular, the manufacturing process of the fine fibrous cellulose-containing sheet preferably includes a step of applying a fine fibrous cellulose dispersion onto a substrate.

<Coating process>
The coating process is a process in which a fine fibrous cellulose dispersion is coated on a substrate, the substrate is dried, and the resulting fine fibrous cellulose-containing sheet is peeled off from the substrate to obtain a sheet. By using a coating device and a long substrate, the sheet can be produced continuously. The concentration of the fine fibrous cellulose dispersion to be coated is not particularly limited, but is preferably 0.05% by mass or more and 5% by mass or less.

The quality of the substrate used in the coating process is not particularly limited, but a substrate with high wettability with respect to the fine fibrous cellulose dispersion liquid is better in that it can suppress the shrinkage of the sheet during drying, but it is preferable to select a substrate from which the sheet formed after drying can be easily peeled off. Among these, a resin plate or a metal plate is preferable, but there is no particular limit. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, polyvinyl chloride plates, polystyrene plates, polyvinylidene chloride plates, etc., metal plates such as aluminum plates, zinc plates, copper plates, iron plates, etc., and those with their surfaces oxidized, stainless steel plates, brass plates, etc. can be used.

In the coating process, if the viscosity of the fine fibrous cellulose dispersion is low and it spreads on the substrate, a blocking frame may be fixed on the substrate to obtain a fine fibrous cellulose-containing sheet of a specified thickness and basis weight. The quality of the blocking frame is not particularly limited, but it is preferable to select one that allows the edge of the sheet to be easily peeled off after drying. Among them, molded resin plates or metal plates are preferable, but are not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, polyvinyl chloride plates, polystyrene plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and metal plates with their surfaces oxidized, stainless steel plates, brass plates, etc. can be used.

As a coating machine for applying the fine fibrous cellulose dispersion, for example, a bar coater, roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. can be used. Bar coaters, die coaters, curtain coaters, and spray coaters are preferred because they can achieve a more uniform thickness.

The coating temperature is not particularly limited, but is preferably 20°C or higher and 45°C or lower. If the coating temperature is equal to or higher than the lower limit, the fine fibrous cellulose dispersion can be easily coated, and if the coating temperature is equal to or lower than the upper limit, evaporation of the dispersion medium during coating can be suppressed.

In the coating step, it is preferable to coat the fine fibrous cellulose dispersion so that the finished sheet has a basis weight of 10 g/ ^m2 or more and 100 g/m2 or ^less . By coating so that the basis weight is within the above range, a fiber layer having excellent strength can be obtained.

The manufacturing process of the fine fibrous cellulose-containing sheet preferably includes a step of drying the fine fibrous cellulose dispersion applied to the substrate. The drying method is not particularly limited, but may be either a non-contact drying method or a method in which the sheet is dried while being restrained, or a combination of these methods.

As a non-contact drying method, there is no particular limitation, but a method of drying by heating with hot air, infrared rays, far-infrared rays or near-infrared rays (heat drying method) and a method of drying by vacuum (vacuum drying method) can be applied. Although the heat drying method and the vacuum drying method can be combined, the heat drying method is usually applied. Drying with infrared rays, far-infrared rays or near-infrared rays can be performed using an infrared device, a far-infrared device or a near-infrared device, but there is no particular limitation. The heating temperature in the heat drying method is not particularly limited, but is preferably 20°C or higher and 150°C or lower, and more preferably 25°C or higher and 105°C or lower. If the heating temperature is set to the lower limit value or higher, the dispersion medium can be quickly volatilized, and if the heating temperature is set to the upper limit value or lower, the cost required for heating can be suppressed and discoloration of the fine fibrous cellulose due to heat can be suppressed.

After drying, the resulting fine fibrous cellulose-containing sheet is peeled off from the substrate. If the substrate is a sheet, the fine fibrous cellulose-containing sheet and the substrate may be rolled up while still stacked, and the fine fibrous cellulose-containing sheet may be peeled off from the substrate immediately before use.

<Paper making process>
The manufacturing process of the fine fibrous cellulose-containing sheet may include a process of making a paper from the fine fibrous cellulose dispersion. Examples of the papermaking machine in the papermaking process include continuous papermaking machines such as Fourdrinier, cylinder, and tilting machines, and multi-layer papermaking machines that combine these machines. In the papermaking process, known papermaking methods such as handmaking may be used.

In the papermaking process, the fine fibrous cellulose dispersion is filtered and dehydrated on a wire to obtain a wet sheet, which is then pressed and dried to obtain a sheet. The concentration of the fine fibrous cellulose dispersion is not particularly limited, but is preferably 0.05% by mass or more and 5% by mass or less. When the fine fibrous cellulose dispersion is filtered and dehydrated, the filter cloth used during filtration is not particularly limited, but it is important that the fine fibrous cellulose does not pass through and that the filtration speed does not become too slow. Such filter cloth is not particularly limited, but is preferably a sheet, fabric, or porous membrane made of an organic polymer. The organic polymer is not particularly limited, but is preferably a non-cellulose organic polymer such as polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), etc. Specific examples include, but are not limited to, a polytetrafluoroethylene porous membrane with a pore size of 0.1 μm to 20 μm, for example, 1 μm, polyethylene terephthalate or polyethylene woven fabric with a pore size of 0.1 μm to 20 μm, for example, 1 μm.

Methods for producing a sheet from a fine fibrous cellulose dispersion include, but are not limited to, a method using a production apparatus described in WO2011/013567. This production apparatus includes a water squeezing section that discharges the fine fibrous cellulose dispersion onto the top surface of an endless belt and squeezes the dispersion medium out of the discharged fine fibrous cellulose dispersion to produce a web, and a drying section that dries the web to produce a fiber sheet. An endless belt is disposed between the water squeezing section and the drying section, and the web produced in the water squeezing section is transported to the drying section while still placed on the endless belt.

The dehydration method that can be used in the present invention is not particularly limited, but includes dehydration methods that are commonly used in paper manufacturing, and a method in which dehydration is performed using a fourdrinier, cylinder, or inclined wire, followed by dehydration using a roll press, is preferred. In addition, the drying method is not particularly limited, but includes methods that are used in paper manufacturing, and for example, methods such as a cylinder dryer, Yankee dryer, hot air drying, near-infrared heater, and infrared heater are preferred.

The above step (a) includes a step of applying a resin composition containing an adhesion aid after the step of forming a fiber layer. The resin composition may contain a resin, and preferably further contains an adhesion aid and a solvent. Examples of the coater that can be used to apply the resin composition include a bar coater, a roll coater, a gravure coater, a die coater, a curtain coater, and an air doctor coater.

After coating, it is preferable to provide a process for curing the resin. In the curing process, it is preferable to heat the resin to a temperature of 20°C or higher and 150°C or lower.

The above step (b) includes a step of forming a resin layer first. In the step of forming the resin layer, it is preferable to form the resin layer from a resin composition containing a resin. In this case, it is preferable that the resin composition contains an adhesion aid. In addition, after forming the resin layer from the resin composition, a diluted adhesion aid solution may be applied or sprayed onto at least one surface of the resin layer. In the step of applying the diluted adhesion aid solution, the resin layer may be impregnated with the diluted adhesion aid solution. When the resin layer is impregnated with the diluted adhesion aid solution, the concentration of the diluted adhesion aid solution is preferably 0.1% by mass or more, and more preferably 0.2% by mass or more. In addition, the concentration of the diluted adhesion aid solution is preferably 20% by mass or less, and more preferably 10% by mass or less. By setting the concentration of the diluted adhesion aid solution within the above range, the adhesion between the fiber layer and the resin layer can be more effectively increased.

The above step (b) includes, after the step of forming a resin layer, a step of applying a fine fibrous cellulose dispersion (fine fibrous cellulose-containing slurry) containing fibrous cellulose having a fiber width of 1000 nm or less. The fiber layer formed in the above step (b) is a coating layer. In this case, the solid content concentration of the fine fibrous cellulose dispersion is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. In addition, the solid content concentration of the fine fibrous cellulose dispersion is preferably 10% by mass or less.

The fine fibrous cellulose dispersion preferably contains an oxygen-containing organic compound. The content of the oxygen-containing organic compound is preferably 1 part by mass or more and 40 parts by mass or less, more preferably 10 parts by mass or more and 30 parts by mass or less, and even more preferably 15 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the fine fibrous cellulose contained in the fine fibrous cellulose dispersion.

In the process of applying the fine fibrous cellulose dispersion, if the viscosity of the fine fibrous cellulose dispersion is low and it spreads unintentionally on the resin layer, a blocking frame may be fixed on the resin layer to obtain a fiber layer of a specified thickness and basis weight. The quality of the blocking frame is not particularly limited, but it is preferable to select one that allows the end of the fiber layer to be easily peeled off after drying. Among them, molded resin plates or metal plates are preferable, but are not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, polyvinyl chloride plates, polystyrene plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and their surfaces may be oxidized, and molded stainless steel plates, brass plates, etc. may be used.

As a coating machine for applying the fine fibrous cellulose dispersion, for example, a bar coater, roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. can be used. Bar coaters, die coaters, curtain coaters, and spray coaters are preferred because they can achieve a more uniform thickness.

The coating temperature is not particularly limited, but is preferably 20°C or higher and 45°C or lower. If the coating temperature is equal to or higher than the lower limit, the fine fibrous cellulose dispersion can be easily coated, and if the coating temperature is equal to or lower than the upper limit, evaporation of the dispersion medium during coating can be suppressed.

In the coating step, it is preferable to coat the fine fibrous cellulose dispersion so that the finished basis weight of the fiber layer is 10 g/ ^m2 or more and 100 g/m2 or ^less . By coating so that the basis weight is within the above range, a fiber layer having excellent strength can be obtained.

The manufacturing process of the fiber layer preferably includes a step of drying the fine fibrous cellulose dispersion applied onto the resin layer. The drying method is not particularly limited, but may be either a non-contact drying method or a method of drying while restraining the fiber layer, or a combination of these.

As a non-contact drying method, there is no particular limitation, but a method of drying by heating with hot air, infrared rays, far-infrared rays or near-infrared rays (heat drying method) and a method of drying by vacuum (vacuum drying method) can be applied. Although the heat drying method and the vacuum drying method can be combined, the heat drying method is usually applied. Drying with infrared rays, far-infrared rays or near-infrared rays can be performed using an infrared device, a far-infrared device or a near-infrared device, but there is no particular limitation. The heating temperature in the heat drying method is not particularly limited, but is preferably 20°C or higher and 120°C or lower, and more preferably 25°C or higher and 105°C or lower. If the heating temperature is set to the lower limit value or higher, the dispersion medium can be quickly volatilized, and if the heating temperature is set to the upper limit value or lower, the cost required for heating can be suppressed and discoloration of the fine fibrous cellulose due to heat can be suppressed.

In the above step (b), at least one surface of the resin layer may be subjected to a surface treatment such as a corona treatment, a plasma discharge treatment, a UV irradiation treatment, an electron beam irradiation treatment, or a flame treatment.
The step (b) may include a step of forming a fine uneven structure. Examples of the step of forming a fine uneven structure include a blasting treatment, an embossing treatment, an etching treatment, a corona treatment, and a plasma discharge treatment.

In addition to the above-mentioned methods, examples of methods for manufacturing laminates for optical components include a method in which a resin layer is placed on a fiber layer and then heat-pressed. Another example is a method in which a fiber layer is placed in a mold for injection molding, and heated, molten resin is injected into the mold to bond the resin layer to the fiber layer.

(Laminate for optical member having other layers)
The laminate for optical members of the present invention may further include an inorganic film (hereinafter, also referred to as an inorganic layer). The inorganic layer may be laminated on the fiber layer side or on the resin layer side. In addition, the inorganic layer may be laminated on both sides of the laminate for optical members.

The material constituting the inorganic layer is not particularly limited, but examples thereof include aluminum, silicon, magnesium, zinc, tin, nickel, and titanium; their oxides, carbides, nitrides, oxycarbides, oxynitrides, and oxycarbonitrides; and mixtures thereof. From the viewpoint of stably maintaining high moisture resistance, silicon oxide, silicon nitride, silicon oxide carbide, silicon oxynitride, silicon oxycarbonitride, aluminum oxide, aluminum nitride, aluminum oxide carbide, aluminum oxynitride, and mixtures thereof are preferred.

The method for forming the inorganic layer is not particularly limited. Generally, methods for forming thin films can be broadly divided into chemical vapor deposition (CVD) and physical vapor deposition (PVD), and either method may be used. Specific examples of CVD methods include plasma CVD, which uses plasma, and catalytic chemical vapor deposition (Cat-CVD), which uses a heated catalyst to catalytically decompose a material gas. Specific examples of PVD methods include vacuum deposition, ion plating, and sputtering.

Atomic Layer Deposition (ALD) can also be used as a method for forming an inorganic layer. The ALD method is a method for forming a thin film in atomic layers by alternately supplying the raw material gases of each element that constitutes the film to be formed to the surface on which the layer is to be formed. Although it has the disadvantage of a slow film formation speed, it has the advantage of being able to form a thin film with fewer defects and to cover even surfaces with complex shapes more neatly than the plasma CVD method. The ALD method also has the advantage that the film thickness can be controlled to the nano order, and it is relatively easy to cover a large surface. Furthermore, the ALD method is expected to improve the reaction rate, achieve low-temperature processing, and reduce unreacted gas by using plasma.

The thickness of the inorganic layer is not particularly limited, but for example, when the objective is to exhibit moisture-proof performance, it is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. From the viewpoints of transparency and flexibility, the thickness of the inorganic layer is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 600 nm or less.

The optical component laminate of the present invention may further have another resin layer. This can more effectively improve the strength of the optical component laminate. The other resin layer can be provided on one side of the above-mentioned resin layer, on the side opposite to the side on the fiber layer side. The other resin layer and the above-mentioned resin layer are different types of layers. This can improve the interlayer adhesion in the entire optical component laminate while improving the strength of the optical component laminate.

(Application)
The laminate for optical members of the present invention has high transparency, and is therefore preferably used for various optical members. Furthermore, by incorporating the laminate for optical members into an optical member, it is possible to impart excellent impact resistance. Examples of optical members include lenses, displays, polarizing plates, viewing angle correction films, retardation films, touch panels, force sensors, backsheets, covers, or housings.

(Optical components)
The present invention relates to an optical component comprising the above-mentioned laminate for optical components. That is, the present invention also relates to an optical component comprising a laminate having at least one fiber layer containing fibrous cellulose with a fiber width of 1000 nm or less and a resin layer in contact with one side of the fiber layer. Here, the preferred embodiment of the laminate constituting the optical component is the same as the preferred embodiment of the above-mentioned laminate for optical components.

When constructing an optical component, other layers may be laminated on the above-mentioned laminate for optical components. For example, in the resin layer/fiber layer/resin layer configuration of the laminate for optical components, the optical component may be constructed by laminating other layers on the side of the resin layer that is not in contact with the fiber layer. Examples of other layers include a polycarbonate film, a cycloolefin polymer film, and a polyimide film.

(lens)
The present invention relates to a lens having the above-mentioned laminate for optical components. That is, the present invention also relates to a lens having a laminate having at least one fiber layer containing fibrous cellulose with a fiber width of 1000 nm or less and a resin layer in contact with one surface of the fiber layer. Here, the preferred embodiment of the laminate constituting the lens is the same as the preferred embodiment of the above-mentioned laminate for optical components.

The lens in this embodiment has excellent impact resistance because it is provided with the laminate for optical components described above. In addition, the lens in this embodiment has high transparency and excellent visibility.

The haze of the lens is preferably 5% or less, more preferably 1% or less, and even more preferably 0.5% or less. Here, the haze of the lens is a value measured in accordance with JIS K 7136:2000 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory). If the haze of the lens is within the above range, the visibility of the lens can be evaluated as good.

The impact resistance of a lens can be evaluated, for example, by performing a ball drop test in which a 1 kg steel ball is dropped from a height of 50 cm toward the center of the lens. If the lens does not break or crack during the ball drop test, the lens can be evaluated as having excellent impact resistance. The lens used in the ball drop test was obtained by integrating the optical component laminate with molten resin by injection molding, as described in the examples.

The lens in this embodiment also has excellent water resistance. Here, the water resistance of the lens can be evaluated by the water contact angle of the lens surface. Specifically, the water contact angle of both surfaces of the lens is preferably 75° or more, and more preferably 80° or more. In other words, it is preferable that the water contact angles of both the lens surface on which one resin layer (first resin layer) is provided and the lens surface on which the other resin layer (second resin layer) is provided are each within the above range. Here, the water contact angle of the lens surface is the water contact angle 30 seconds after 4 μL of distilled water is dropped on the lens surface. A dynamic water contact angle tester is used for the measurement. For example, 1100DAT manufactured by Fibro can be used as the dynamic water contact angle tester.

(display)
The present invention also relates to a display comprising the above-mentioned laminate for optical components. That is, the present invention also relates to a display comprising a laminate having at least one fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less and at least one resin layer in contact with one surface of the fiber layer. Here, the preferred embodiment of the laminate constituting the display is the same as the preferred embodiment of the above-mentioned laminate for optical components.

The display in this embodiment has excellent impact resistance because it is equipped with the above-mentioned laminate for optical components.

The display of this embodiment also has excellent water resistance. The water resistance of the display can be measured by the method described above, and the water contact angle of both surfaces of the display is preferably 75° or more, and more preferably 80° or more.

The features of the present invention are explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

<Production Example 1>
(Production of phosphorylated pulp)
As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 208 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121-2:2012 after disintegration is 700 mL) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to prepare 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical solution-impregnated pulp. Next, the obtained chemical solution-impregnated pulp was heated in a hot air dryer at 165°C for 200 seconds to introduce phosphoric acid groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

The phosphorylated pulp obtained was then subjected to a washing process. The washing process was carried out by repeatedly pouring 10 L of ion-exchanged water per 100 g (bone dry weight) of phosphorylated pulp to obtain a pulp dispersion, stirring the pulp to uniformly disperse the pulp, and then filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

The washed phosphorylated pulp was then subjected to an alkali treatment (neutralization treatment) as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. The phosphorylated pulp slurry was then dehydrated to obtain phosphorylated pulp that had been subjected to an alkali treatment (neutralization treatment).

Next, the phosphorylated pulp after neutralization was subjected to the above-mentioned washing treatment. The infrared absorption spectrum of the phosphorylated pulp obtained by this was measured using FT-IR. As a result, absorption due to P=O of the phosphoric acid group was observed around 1230 cm ^-1 , and it was confirmed that the phosphoric acid group was added to the pulp. In addition, when the phosphorylated pulp obtained was used as a test sample and analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, and it was confirmed that the cellulose had type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry having a solid content of 2% by mass. This slurry was treated four times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (A) containing fine fibrous cellulose.

X-ray diffraction confirmed that the fine fibrous cellulose maintained cellulose type I crystals. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. The amount of phosphoric acid groups (amount of first dissociated acid) measured using the method for measuring the amount of phosphorus oxoacid groups described below was 1.45 mmol/g. The total amount of dissociated acid was 2.45 mmol/g.

<Production Example 2>
(Production of Phosphosphite Pulp)
The same procedure as in Production Example 1 was carried out except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate, to obtain a phosphited pulp.

The infrared absorption spectrum of the phosphorous pulp thus obtained was measured using FT-IR. As a result, absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous group, was observed around 1210 cm ^-1 , and it was confirmed that the phosphorous group (phosphonic acid group) was added to the pulp. In addition, when the phosphorous pulp thus obtained was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, and it was confirmed that the cellulose had type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained phosphorous-substituted pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated four times at a pressure of 200 MPa with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (B) containing fine fibrous cellulose. X-ray diffraction confirmed that the fine fibrous cellulose maintained cellulose I type crystals. In addition, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphorous groups (amount of first dissociated acid) measured by the method for measuring the amount of phosphorous oxo acid groups described below was 1.51 mmol/g. The total amount of dissociated acid was 1.54 mmol/g.

<Production Example 3>
(Production of TEMPO oxidized pulp)
As the raw material pulp, softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to an alkaline TEMPO oxidation treatment as follows. First, the raw material pulp equivalent to 100 parts by mass of dry mass, 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, a 13% by mass aqueous solution of sodium hypochlorite was added to 3.8 mmol per 1.0 g of pulp to start the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to keep the pH at 10 to 10.5, and the reaction was deemed to have ended when no change in pH was observed.

Then, the obtained TEMPO oxidized pulp was subjected to a washing process. The washing process was carried out by dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, pouring in 5,000 parts by mass of ion-exchanged water, stirring to disperse uniformly, and then repeatedly filtering and dehydrating the sheet. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

The obtained TEMPO oxidized pulp was also analyzed using an X-ray diffraction device, and typical peaks were confirmed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming that it contains cellulose type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained TEMPO oxidized pulp to prepare a slurry with a solid content concentration of 2% by mass. This slurry was treated four times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (C) containing fine fibrous cellulose. X-ray diffraction confirmed that the fine fibrous cellulose maintained cellulose I type crystals. In addition, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups measured by the method for measuring the amount of carboxyl groups described below was 1.30 mmol/g.

<Production Example 4>
(Production of sulfated pulp)
As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 245 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121-2:2012 after disintegration is 700 ml) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to a sulfate esterification treatment as follows. First, a mixed aqueous solution of amidosulfuric acid and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to prepare 38 parts by mass of amidosulfuric acid, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical solution-impregnated pulp. Next, the obtained chemical solution-impregnated pulp was heated in a hot air dryer at 165°C for 19 minutes to introduce sulfate groups into the cellulose in the pulp, thereby obtaining a sulfate esterified pulp.

The resulting sulfated pulp was then washed. The washing process was carried out by repeatedly pouring 10 L of ion-exchanged water into 100 g (bone dry weight) of sulfated pulp to obtain a pulp dispersion, stirring the resulting solution so that the pulp was uniformly dispersed, and then filtering and dehydrating the solution. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

Next, the washed sulfated pulp was neutralized as follows. First, the washed sulfated pulp was diluted with 10 L of ion-exchanged water, and then 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a sulfated pulp slurry with a pH of 12 to 13. Next, the sulfated pulp slurry was dehydrated to obtain a neutralized sulfated pulp. Next, the neutralized sulfated pulp was subjected to the above-mentioned washing process to obtain a sulfated pulp (neutralized once).

The above neutralization and washing treatments were repeated four more times for the sulfated pulp obtained.
A sulfated pulp (neutralized five times) was obtained.

(Defibrillation process)
Ion-exchanged water was added to the obtained sulfated pulp (neutralized five times), and the mixture was stirred to obtain a slurry with a solid content of 0.5% by mass. This slurry was defibrated for 30 minutes at 21,500 rpm using a defibration treatment device (high-speed rotary defibration treatment device Clearmix 2.2S, manufactured by M-Technique Co., Ltd.) to obtain a fine fibrous cellulose dispersion (D) with a fiber width of 3 to 5 nm. The amount of sulfate ester groups measured by the method for measuring the amount of sulfate ester groups described below was 1.12 mmol/g.

<Production Example 5>
(Production of hypochlorite oxidized pulp)
A sheet (solid content concentration 90% by mass) made from softwood bleached kraft pulp (NBKP) was processed for 15 seconds at a rotation speed of 20,000 rpm using a hand mixer (Osaka Chemical, Labo Millser PLUS) to make a cotton-like fluffing pulp (solid content concentration 90% by mass). Sodium hypochlorite pentahydrate was then added to ion-exchanged water to prepare an aqueous solution with a sodium hypochlorite solid content concentration of 22% by mass. 9000 parts by mass of a 22% by mass aqueous sodium hypochlorite solution was added to 100 parts by mass of the cotton-like fluffing pulp, and the mixture was reacted for 2 hours while adjusting the temperature to 30° C. in a warm bath to obtain a carboxyl group-introduced pulp. During the reaction, a 1N aqueous sodium hydroxide solution was appropriately added to maintain the pH at 11.

Then, the obtained carboxyl group-introduced pulp was subjected to a washing process. The washing process was carried out by pouring ion-exchanged water onto the obtained carboxyl group-introduced pulp to obtain a pulp dispersion, stirring the pulp so that the pulp was uniformly dispersed, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

Furthermore, when the obtained carboxyl group-introduced pulp was analyzed using an X-ray diffraction device, typical peaks were confirmed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming that it contains cellulose type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained carboxyl group-introduced pulp to prepare a slurry having a solid content of 2% by mass. This slurry was treated four times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (E) containing fine fibrous cellulose.

X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. In addition, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups measured using the carboxyl group measurement method described below was 0.70 mmol/g.

<Production Example 6>
(Production of Maleated Pulp)
A sheet (solid content concentration 90% by mass) made from bleached softwood kraft pulp (NBKP) was mixed with a hand mixer (Osaka Chemical, Labo Millser PLUS) at a rotation speed of 20,000 rpm for 15 seconds to produce a cotton-like fluffed pulp (solid content concentration 90% by mass). An autoclave was filled with 100 parts by mass of the cotton-like fluffed pulp and 50 parts by mass of maleic anhydride, and treated at 150° C. for 2 hours to obtain a carboxyl group-introduced pulp.

Then, the obtained carboxyl group-introduced pulp was subjected to a washing process. The washing process was carried out by pouring ion-exchanged water onto the obtained carboxyl group-introduced pulp to obtain a pulp dispersion, stirring the pulp so that the pulp was uniformly dispersed, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

The infrared absorption spectrum of the obtained carboxyl-introduced pulp was measured using FT-IR. As a result, absorption due to carboxyl groups was observed around 1580 and 1720 cm ^-1 , confirming that maleic acid esterification had occurred. In addition, when the carboxyl-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that the cellulose had type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained carboxyl group-introduced pulp to prepare a slurry having a solid content of 2% by mass. This slurry was treated four times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (F) containing fine fibrous cellulose.

X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained cellulose type I crystals. In addition, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups measured using the carboxyl group measurement method described below was 1.22 mmol/g.

<Production Example 7>
(Production of Carboxyethylated Pulp)
As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 245 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured in accordance with JIS P 8121-2:2012 after disintegration is 700 ml) was used.

100 parts by mass (bone dry mass) of this raw pulp was mixed with a chemical solution (total 553 parts by mass) consisting of 250 parts by mass of 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water to obtain a chemical solution-impregnated pulp. The resulting chemical solution-impregnated pulp was then heated for 10 minutes in a hot air dryer at 165°C to introduce carboxyethyl groups (carboxy groups) into the cellulose in the pulp, obtaining a carboxy group-introduced pulp.

Then, the obtained carboxyl group-introduced pulp was subjected to a washing process. The washing process was carried out by pouring ion-exchanged water onto the obtained carboxyl group-introduced pulp to obtain a pulp dispersion, stirring the pulp so that the pulp was uniformly dispersed, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

Next, the washed carboxyl-introduced pulp was neutralized as follows. First, the washed carboxyl-introduced pulp was diluted with 10 L of ion-exchanged water, and then 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a carboxyl-introduced pulp slurry with a pH of 12 to 13. Next, the carboxyl-introduced pulp slurry was dehydrated and washed to obtain a neutralized carboxyl-introduced pulp.

In addition, when the carboxyl-introduced pulp was analyzed using an X-ray diffraction device, typical peaks were confirmed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming that it contains cellulose type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained carboxyl group-introduced pulp to prepare a slurry having a solid content of 2% by mass. This slurry was treated four times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (G) containing fine fibrous cellulose.

X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. The amount of carboxyl groups measured using the carboxyl group measurement method described below was 1.41 mmol/g.

<Production Example 8>
(Production of sulfoethylated pulp)
As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 245 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured in accordance with JIS P 8121-2:2012 after disintegration is 700 ml) was used.

100 parts by mass (absolute dry mass) of this raw pulp was mixed with a chemical solution (total 960 parts by mass) consisting of 180 parts by mass of 2N NaOH aqueous solution and 780 parts by mass of a 25% by mass concentration sodium vinyl sulfonate aqueous solution to obtain a chemical solution-impregnated pulp. The resulting chemical solution-impregnated pulp was then heated for 16 minutes in a hot air dryer at 165°C to introduce sulfoethyl groups (sulfone groups) into the cellulose in the pulp, obtaining a sulfoethyl group-introduced pulp (sulfone group-introduced pulp).

Then, the obtained sulfoethyl group-introduced pulp was subjected to a washing process. The washing process was carried out by pouring ion-exchanged water onto the obtained sulfoethyl group-introduced pulp to obtain a pulp dispersion, stirring the pulp so that the pulp was uniformly dispersed, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

In addition, when sulfoethyl group-introduced pulp was tested and analyzed using an X-ray diffraction device, typical peaks were confirmed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained sulfoethyl group-introduced pulp to prepare a slurry having a solid content of 2% by mass. This slurry was treated four times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (H) containing fine fibrous cellulose.

X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. In addition, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of sulfoethyl groups measured using the sulfoethyl group measurement method described below was 1.48 mmol/g.

<Production Example 9>
(Production of cationic pulp)
As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 245 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured in accordance with JIS P 8121-2:2012 after disintegration is 700 ml) was used.

100 parts by mass (bone dry mass) of this raw pulp was mixed with a chemical solution (505 parts by mass in total) consisting of 180 parts by mass of 1N NaOH aqueous solution and 325 parts by mass of a cationizing agent (Catiomaster G, Yokkaichi Synthetic Co., Ltd., glycidyl trimethylammonium chloride, purity 73.1% by mass, moisture content 20.2% by mass), to obtain a chemical solution-impregnated pulp. The resulting chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 12 minutes to introduce cationic groups into the cellulose in the pulp, and a cationic group-introduced pulp was obtained.

Then, the obtained cationic group-introduced pulp was subjected to a washing process. The washing process was carried out by pouring ion-exchanged water into the obtained cationic group-introduced pulp to obtain a pulp dispersion, stirring the pulp so that the pulp was uniformly dispersed, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

Then, the washed cationic group-introduced pulp was subjected to a neutralization treatment as follows. First, the washed cationic group-introduced pulp was diluted with 10 L of ion-exchanged water, and then 1N hydrochloric acid was added little by little while stirring to obtain a cationic group-introduced pulp slurry with a pH of 1 to 2. The cationic group-introduced pulp slurry was then dehydrated and washed to obtain a cationic group-introduced pulp that had been subjected to a neutralization treatment.

When analyzed using an X-ray diffraction device, typical peaks were confirmed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

(Defibrillation process)
Ion-exchanged water was added to the obtained cationic group-introduced pulp to prepare a slurry having a solid content of 2% by mass. This slurry was treated four times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (I) containing fine fibrous cellulose.

X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. In addition, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of cationic groups measured using the cationic group measurement method described below was 1.45 mmol/g.

<Measurement>
(Measurement of phosphorus oxoacid group content)
The amount of phosphorus oxo acid groups in the fine fibrous cellulose (equivalent to the amount of phosphorus oxo acid groups in the phosphorus oxo-oxidized pulp) was measured by adding ion exchange water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to adjust the content to 0.2 mass%, treating the dispersion with ion exchange resin, and then titrating the dispersion with an alkali.
The treatment with ion exchange resin was carried out by adding 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose-containing slurry, shaking the mixture for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin and the slurry.
In addition, the titration using alkali was performed by measuring the change in the pH value of the slurry while adding 10 μL of 0.1N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry after the treatment with ion exchange resin every 5 seconds. The titration was performed while blowing nitrogen gas into the slurry 15 minutes before the start of the titration. In this neutralization titration, two points are observed where the increment (differential value of pH with respect to the amount of alkali dropped) is maximum in the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of the increment obtained first after the addition of alkali is called the first end point, and the maximum point of the increment obtained next is called the second end point (FIG. 3). The amount of alkali required from the start of the titration to the first end point is equal to the amount of first dissociated acid in the slurry used for the titration. In addition, the amount of alkali required from the start of the titration to the second end point is equal to the total amount of dissociated acid in the slurry used for the titration. The amount of alkali (mmol) required from the start of titration to the first end point divided by the solid content (g) in the slurry to be titrated was defined as the amount of phosphorus oxoacid group (first dissociated acid amount) (mmol/g). The amount of alkali (mmol) required from the start of titration to the second end point divided by the solid content (g) in the slurry to be titrated was defined as the total dissociated acid amount (mmol/g).

(Measurement of Carboxy Group Amount)
The amount of carboxy groups in the fine fibrous cellulose (equivalent to the amount of carboxy groups in the TEMPO oxidized pulp) was measured by adding ion exchanged water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to adjust the content to 0.2 mass%, treating the dispersion with ion exchange resin, and then titrating the dispersion with an alkali.
The treatment with ion exchange resin was carried out by adding 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a 0.2% by mass slurry containing fine fibrous cellulose, shaking for 1 hour, and then pouring onto a mesh with 90 μm openings to separate the resin and the slurry.
In addition, the titration using an alkali was performed by measuring the change in the pH value of the slurry while adding 0.1N aqueous sodium hydroxide to the fibrous cellulose-containing slurry after the treatment with the ion exchange resin. When the change in pH is observed while adding aqueous sodium hydroxide, a titration curve as shown in FIG. 4 is obtained. As shown in FIG. 4, in this neutralization titration, a point where the increment (differential value of pH with respect to the amount of alkali added) is maximum is observed in the curve plotting the measured pH against the amount of alkali added. This maximum point of the increment is called the first end point. Here, the region from the start of titration to the first end point in FIG. 4 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali required in the first region of the titration curve (mmol) was divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol/g).
The above-mentioned amount of carboxyl groups introduced (mmol/g) indicates the amount of substituents per 1 g of fibrous cellulose mass when the counter ion of the carboxyl group is a hydrogen ion (H ⁺ ) (hereinafter referred to as the amount of carboxyl groups (acid type)).

(Measurement of sulfate ester group amount and sulfone group amount)
The amount of sulfate ester groups or sulfone groups in the fine fibrous cellulose was measured by subjecting a freeze-dried and pulverized sample to pressurized heating decomposition with nitric acid in a closed vessel, appropriately diluting the sample, and measuring the amount of sulfur by ICP-OES. The value calculated by dividing the value by the bone dry mass of the fine fibrous cellulose used was taken as the amount of sulfate ester groups or sulfone groups (mmol/g) in the fine fibrous cellulose.

(Measurement of Amount of Cationic Groups)
The amount of cationic groups in the fine fibrous cellulose was determined by carrying out a nitrogen trace analysis and calculating the value according to the following formula, which was taken as the amount of cationic groups in the fine fibrous cellulose (mmol/g).
(Amount of cationic groups) [mmol/g] = (amount of nitrogen)/14 x 1000/(amount of cationic group-introduced fine fibrous cellulose tested)

Example 1
(Dissolution of polyvinyl alcohol)
Acetoacetyl group-modified polyvinyl alcohol (Poval 105, manufactured by Kuraray Co., Ltd., polymerization degree: 500, saponification degree: 98 to 99 mol%) was added to ion-exchanged water to a concentration of 20 mass%, and the mixture was stirred at 95° C. for 1 hour to dissolve. By the above procedure, an aqueous polyvinyl alcohol solution was obtained.

(Formation of fiber layer)
The fine fibrous cellulose dispersion (A) and the polyvinyl alcohol aqueous solution were each diluted with ion-exchanged water so that the solid content concentration was 0.6% by mass. Next, 70 parts by mass of the diluted fine fibrous cellulose dispersion were mixed with 30 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Furthermore, the mixed solution was weighed so that the finished basis weight of the sheet was 140 g/m ² , and spread on a commercially available acrylic plate. In addition, a damming frame (inner dimensions 250 mm x 250 mm, height 5 cm) was placed on the acrylic plate so that the predetermined basis weight was obtained. After that, it was dried in a dryer at 70 ° C. for 24 hours and peeled off from the acrylic plate to form a fiber layer (fine fibrous cellulose-containing layer). The thickness of the fiber layer was 100 μm.

(Formation of resin layer)
15 parts by mass of modified polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company, Iupizeta FPC-2136), 57 parts by mass of toluene, and 28 parts by mass of methyl ethyl ketone were mixed to obtain a resin coating liquid. Next, 2.25 parts by mass of an isocyanate compound (manufactured by Asahi Kasei Chemicals Corporation, Duranate TPA-100) was added as an adhesion aid to the resin coating liquid and mixed. This resin coating liquid was applied to one side (the side in contact with the acrylic plate) of the fiber layer with a bar coater. Thereafter, the resin coating liquid was cured by heating at 100°C for 1 hour to form a resin layer (first resin layer). Next, a resin layer (second resin layer) was formed on the opposite side of the fiber layer in the same manner. The thickness of the resin layer was 3 μm per side. By the above procedure, a laminate for optical members in which resin layers were laminated on both sides of the fiber layer (fine fibrous cellulose-containing layer) was obtained.

(Lens formation)
A mold having a recess was combined with an injection molding tester (NEX140, manufactured by Nissei Plastics Co., Ltd.) to set a mold for forming a lens shape (size: circle with a diameter of 3 cm, molding thickness of 1 mm). The optical component laminate was arranged parallel to the mold by a clamp mechanism installed at the end of the center surface in the thickness direction of the lens shape obtained by combining the molds. After fixing the optical component laminate, the mold was closed, and molten polycarbonate resin (Iupizeta EP, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was injected into the mold under conditions of a mold temperature of 110°C and a resin temperature of 290°C (at this time, the polycarbonate resin was injected into both sides of the optical component laminate). Furthermore, the mold temperature was lowered to 60°C to solidify the polycarbonate resin. By the above procedure, a lens in which the optical component laminate was encapsulated in a resin component was obtained.

Example 2
A laminate for optical components and a lens in which resin layers were laminated on both sides of a fiber layer were obtained in the same manner as in Example 1 (formation of a fiber layer), except that the mixed amount of the diluted fine fibrous cellulose (A) was 40 parts by mass and the mixed amount of the diluted aqueous polyvinyl alcohol solution was 60 parts by mass.

Example 3
In Example 1 (formation of the fiber layer), the process was repeated except that the finished basis weight of the sheet was changed to 280 g/ ^m2 and a fiber layer with a thickness of 200 μm was obtained, thereby obtaining a laminate for optical members and a lens in which resin layers were laminated on both sides of the fiber layer.

Example 4
In Example 2 (formation of the fiber layer), the same procedure as in Example 2 was conducted except that the finished basis weight of the sheet was changed to 280 g/ ^m2 and the fiber layer had a thickness of 200 μm, thereby obtaining a laminate for optical members and a lens in which resin layers were laminated on both sides of the fiber layer.

Example 5
A laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer were obtained in the same manner as in Example 1 (formation of a fiber layer), except that the fine fibrous cellulose dispersion (B) was used.

Example 6
A laminate for optical members and a lens having resin layers laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (C) was used.

Example 7
A laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (D) was used.

Example 8
A laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that in the (formation of resin layer) of Example 1, methacryloxypropyltrimethoxysilane (SILQUEST A-174 SILANE, manufactured by Momentive Performance Materials Japan, Inc.), which is an organosilicon compound (silane coupling agent), was added as an adhesion assistant in an amount of 1.5 parts by mass per 100 parts by mass of polycarbonate resin and mixed.

<Example 9>
A laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer were obtained in the same manner as in Example 8 (formation of resin layer), except that 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane (TSL9706, manufactured by Momentive Performance Materials Japan, Inc.) was used as the adhesion assistant.

Example 10
In (formation of resin layer) of Example 1, a maleic anhydride modified polypropylene resin solution (Hardlen TD-15B, manufactured by Toyobo Co., Ltd.) was used as the resin solution. In (formation of lens), a cycloolefin resin (Zeonex 480R, manufactured by Zeon Corporation) was used as the molten resin. Except for the above, the same procedures were followed as in Example 1 to obtain a laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer.

Example 11
In the (formation of the resin layer) of Example 2, a maleic anhydride modified polypropylene resin solution (Hardlen TD-15B, manufactured by Toyobo Co., Ltd.) was used as the resin solution. In the (formation of the lens) a cycloolefin resin (Zeonex 480R, manufactured by Zeon Corporation) was used as the molten resin. Except for the above, the same procedures were followed as in Example 2 to obtain a laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer.

Example 12
A laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (E) was used.

<Example 13>
A laminate for optical members and a lens having resin layers laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (F) was used.

<Example 14>
A laminate for optical members and a lens in which resin layers were laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (G) was used.

Example 15
A laminate for optical members and a lens having resin layers laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (H) was used.

<Example 16>
A laminate for optical members and a lens having resin layers laminated on both sides of a fiber layer were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion (I) was used.

<Comparative Example 1>
In Example 1, (the formation of the resin layer) was omitted, and a sheet having only a fiber layer was obtained.

<Comparative Example 2>
In Example 2, the formation of the resin layer was omitted, and a sheet having only a fiber layer was obtained.

<Comparative Example 3>
In Example 1 (formation of lens), injection molding was carried out using only polycarbonate resin to obtain a lens.

<Comparative Example 4>
In Example 10 (lens formation), injection molding was carried out using only the cycloolefin resin to obtain a lens.

<Measurement>
The laminates for optical members obtained in the examples and comparative examples were evaluated by the following methods.

[Thickness of fiber layer (cellulosic fiber-containing layer)]
A cross section of the laminate for an optical member was cut out using an ultramicrotome UC-7 (manufactured by JEOL, UC-7), and the thickness of the fiber layer in the cross section was measured, and the measured value was taken as the thickness of the fiber layer. At this time, observation was performed using an electron microscope, a magnifying glass, or visually.

[Thickness of resin layer]
A cross section of the laminate for an optical member was cut out using an ultramicrotome UC-7 (manufactured by JEOL, UC-7), and the thickness of the resin layer at the cross section was measured, and the measured value was taken as the thickness of the resin layer. At this time, observation was performed using an electron microscope, a magnifying glass, or visually.

<Evaluation>
[Water resistance of laminate for optical members]
In accordance with JIS R 3257:1999, a dynamic water contact angle tester (1100DAT, manufactured by Fibro Corporation) was used to drop 4 μL of ion-exchanged water onto both surfaces of the laminate for optical members, and the water contact angle after 30 seconds was measured.
A: The contact angle on both surfaces of the laminate for optical members is 75° or more. B: The contact angle on at least one surface of the laminate for optical members is less than 75°.

[Total Light Transmittance of Laminate for Optical Members]
The total light transmittance of the laminate for optical members was evaluated using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory) in accordance with JIS K 7361-1:1997.

[Haze of laminate for optical members]
The haze of the laminate for optical members was evaluated in accordance with JIS K 7136 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.).

[Visibility when used as a lens (optical component)]
The haze of the lenses obtained in the examples and comparative examples was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7136: 2000. The visibility of the lenses was evaluated according to the following criteria.
A: Lens haze is less than 0.5%. B: Lens haze is 0.5% or more but less than 1.0%. C: Lens haze is 1.0% or more.

[Impact resistance when used as a lens (optical component)]
A ball drop test was carried out by dropping a 1 kg steel ball from a height of 50 cm toward the center of the lens obtained in the examples and comparative examples. The impact resistance of the lens was evaluated according to the following criteria.
A: No breaks or cracks occur in the lens. B: Breaks or cracks occur in the lens.

In the examples, lenses (optical components) with excellent impact resistance were obtained while maintaining transparency.

2 Fiber layer 6 Resin layer 10 Laminate for optical member

Claims (4)

A fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less;
a resin layer in contact with one surface of the fiber layer ,
A lens, wherein the laminate is encapsulated in a resin component . The lens according to claim 1, wherein the resin layer contains at least one resin selected from the group consisting of polycarbonate resin and polyolefin resin. The lens according to claim 1 or 2, wherein the resin layer contains an adhesion aid. The lens according to claim 3 , wherein the adhesion assistant is at least one selected from the group consisting of an isocyanate compound and an organosilicon compound.