JP2022171489A - Pulp fiber-containing presheet - Google Patents

Abstract

To provide a presheet for appropriately producing a fiber-reinforced thermoplastic excellent in mechanical physical properties, and also to provide a fiber-reinforced thermoplastic excellent in mechanical physical properties.SOLUTION: A pulp fiber-containing presheet at least includes a fine fibrous cellulose-containing layer formed on a pulp fiber-containing layer. In the pulp fiber-containing presheet, the pulp fiber-containing layer contains pulp fibers and a thermoplastic resin, the fine fibrous cellulose-containing layer is an outermost surface layer, a content ratio of a fine fibrous cellulose in a molding thereof is 0.5 mass% or more, and a content ratio of a fine fibrous cellulose in the fine fibrous cellulose-containing layer is 10 mass% or more.SELECTED DRAWING: None

Description

The present invention relates to a pulp fiber-containing pre-sheet.

BACKGROUND ART Fiber-reinforced composite materials composed of reinforcing fibers such as glass fibers and pulp fibers and matrix resins are used for general industrial members, sports and leisure goods, aircraft bodies, automobile bodies, construction materials, and the like.
Fiber-reinforced composite materials include fiber-reinforced plastic (FRP), which is obtained by impregnating a cloth of long fibers of reinforcing fibers with a thermosetting resin and curing, and fibers in which short fibers of chopped reinforcing fibers are dispersed in a thermoplastic resin. Reinforced thermoplastics (FRTP) are known.
As a method for producing a fiber-reinforced thermoplastic, a method is known in which a pre-sheet for producing a fiber-reinforced thermoplastic containing reinforcing fibers and thermoplastic fibers is produced in advance, and the pre-sheet for producing a fiber-reinforced thermoplastic is molded ( See Patent Document 1).

JP 2014-047244 A

However, with the method described in Patent Document 1, the mechanical properties of the obtained fiber-reinforced thermoplastic are insufficient, and the environmental consideration is also insufficient. Accordingly, an object of the present invention is to provide a pre-sheet for suitably producing a fiber-reinforced thermoplastic that is environmentally friendly and has excellent mechanical properties. Another object of the present invention is to provide a fiber-reinforced thermoplastic that is environmentally friendly and has excellent mechanical properties.

As a result of extensive studies, the present inventors have found that, while using pulp fibers as reinforcing fibers, a layer containing fine fibrous cellulose is provided, and the content ratio of the fine fibrous cellulose is set to a specific range. We have found that the problem can be solved, and have completed the present invention.
The present invention includes the following aspects.
[1] A pulp fiber-containing pre-sheet in which a fine fibrous cellulose-containing layer is formed on at least a pulp fiber-containing layer,
The pulp fiber-containing layer contains pulp fibers and a thermoplastic resin,
The fine fibrous cellulose-containing layer is the outermost layer,
The content ratio of fine fibrous cellulose in the pulp fiber-containing pre-sheet is 0.5% by mass or more,
The content ratio of fine fibrous cellulose in the fine fibrous cellulose-containing layer is 10% by mass or more,
A pre-sheet containing pulp fibers.
[2] The pre-sheet according to [1], wherein the pulp fiber content in the pulp fiber-containing pre-sheet is 40 to 50% by mass.
[3] The pre-sheet according to [1] or [2], wherein the content of fine fibrous cellulose in the pre-sheet is 1.0 to 5.0% by mass.
[4] The pre-sheet according to any one of [1] to [3], wherein the resin content in the fine fibrous cellulose-containing layer is 70% by mass or less with respect to 100% by mass of the entire cellulose.
[5] The pre-sheet according to any one of [1] to [4], wherein the content of fine fibrous cellulose in the layer containing fine fibrous cellulose is 10 to 95% by mass.
[6] The pre-sheet according to any one of [1] to [5], wherein the pulp fiber-containing layer comprises a pulp fiber layer and a thermoplastic resin layer.
[7] A molded product containing pulp fibers obtained by molding the single or laminated pre-sheet according to any one of [1] to [6].
[8] The pulp fiber-containing molded article according to [7], which is for automobile parts, electrical equipment parts, electronic equipment parts, or precision equipment parts.

The pre-sheet of the present embodiment is environmentally friendly and can suitably provide a fiber-reinforced thermoplastic having excellent mechanical properties. In addition, the molded article of the present embodiment is environmentally friendly and has excellent mechanical properties.

FIG. 2 is a schematic diagram showing a web forming apparatus used in the production method for producing the pulp fiber-containing pre-sheet of the present embodiment. FIG. 2 is a graph showing the relationship between the amount of dropped NaOH and the pH for a fibrous cellulose-containing slurry having a phosphorous acid group. FIG. 3 is a graph showing the relationship between the dropping amount of NaOH and the pH for a fibrous cellulose-containing slurry having carboxyl groups.

≪1. Pre-sheet of this embodiment>>
The pre-sheet of the present embodiment is a pulp fiber-containing pre-sheet in which a fine fibrous cellulose-containing layer is formed on at least a pulp fiber-containing layer, wherein the pulp fiber-containing layer contains pulp fibers and a thermoplastic resin. , the fine fibrous cellulose-containing layer is the outermost layer, the content ratio of fine fibrous cellulose in the pulp fiber-containing pre-sheet is 0.5% by mass or more, and the fine fibrous cellulose-containing layer in the fine fibrous cellulose-containing layer The pulp fiber-containing pre-sheet has a fibrous cellulose content of 10% by mass or more. According to the pre-sheet of the present embodiment, it is possible to provide a molded article having excellent mechanical properties by subjecting it to a molding process.

<1-1. Layer structure of pre-sheet>
The layer structure of the pre-sheet of the present embodiment includes a structure in which a pulp fiber-containing layer and a fine fibrous cellulose-containing layer are laminated. The layer configuration of the pulp fiber-containing layer includes a configuration in which a thermoplastic resin layer is laminated on at least one surface of a laminate of a plurality of pulp fiber layers. A thermoplastic resin layer may be arranged between the plurality of pulp fiber layers. Further, the layer configuration of the pulp fiber-containing layer of the present embodiment includes a configuration in which a pulp fiber layer is laminated on at least one surface of a laminate of a plurality of thermoplastic resin layers. A pulp fiber layer may be arranged between the plurality of thermoplastic resin layers.

As described above, the pulp fiber-containing layer in the pre-sheet of the present embodiment is a laminate composed of a single layer or a plurality of layers of two or more layers. The number of layers contained in the pulp fiber-containing layer and the composition of the layers are determined according to the thickness of each layer constituting the pulp fiber-containing layer with respect to the target thickness of the pulp fiber-containing layer, the desired physical properties of the pre-sheet and the molded product, etc. It can be set differently accordingly. The number of layers included in the pulp fiber-containing layer of this embodiment can be, for example, 1, 2, 3, 4, 5, or more.

For example, the following pulp fiber-containing layer configurations, shown for purposes of illustration and not limitation, are within the scope of the present invention.
(1) A structure consisting only of a pulp fiber layer.
(2) A configuration in which a thermoplastic resin layer and a pulp fiber layer are laminated.
(3) A configuration in which a thermoplastic resin layer, a pulp fiber layer, and a thermoplastic resin layer are laminated in this order.
(4) A configuration in which a thermoplastic resin layer, a pulp fiber layer, and a pulp fiber layer are laminated in this order.
(5) A configuration in which a thermoplastic resin layer, a thermoplastic resin layer, and a pulp fiber layer are laminated in this order.
(6) A configuration in which a pulp fiber layer, a thermoplastic resin layer, and a pulp fiber layer are laminated in this order.
(7) Any combination of the configurations shown in (2) to (6) above.
(8) A configuration in which one or more thermoplastic resin layers or pulp fiber layers are laminated on the surface or between the configurations, in contrast to the configurations shown in (2) to (7) above.

A possible configuration of (7) among these will be described with an example. For example, when the configuration (7) is a combination of (2) and (2), such a configuration includes a thermoplastic resin layer, a pulp fiber layer, a thermoplastic resin layer, and a pulp fiber layer. A structure in which a thermoplastic resin layer, a pulp fiber layer, a pulp fiber layer, and a thermoplastic resin layer are laminated in this order, and a structure in which a pulp fiber layer, a thermoplastic resin layer, and a thermoplastic resin layer are laminated in this order. and the pulp fiber layer are laminated in this order. In this way, when several structures are combined, a structure in which the laminated body is laminated in the same direction (back and front together), and in which the front and back sides are adjacent to each other is included.

In addition, a possible configuration of (8) will be described with an example. For example, when the configuration of (8) is a configuration based on a combination of (3) and (4), such a configuration includes, for example, a thermoplastic resin layer, a pulp fiber layer, a thermoplastic resin layer, and a thermoplastic There is a structure in which a resin layer, a thermoplastic resin layer, a pulp fiber layer, and a pulp fiber layer are laminated in this order. This is an example in which a thermoplastic resin layer is further added between (3) and (4). That is, for example, when one thermoplastic resin layer is thin, by stacking a plurality of thermoplastic resin layers in this manner, the thickness and strength of the resulting pre-sheet can be improved.

When a plurality of pulp fiber layers are included in one pre-sheet and pulp fiber-containing layer, each pulp fiber layer may be the same or different. Moreover, when a plurality of thermoplastic resin layers are included in one pre-sheet and pulp fiber-containing layer, each thermoplastic resin layer may be the same or different.

It is preferable that the outermost layer of the pulp fiber-containing layer is a thermoplastic resin layer. When the outermost layer of the pulp fiber-containing layer is a thermoplastic resin layer, the adhesion with the fine fibrous cellulose-containing layer described below is excellent, and as a result, the pre-sheet and molded article of the present embodiment have excellent mechanical properties.

Other layers may be placed between the layers for the purpose of reinforcing the structure.

<1-2. Pulp fiber-containing layer>
The pre-sheet of this embodiment has a pulp fiber-containing layer. The pulp fiber-containing layer may be a single layer or multiple layers.
When the pulp fiber-containing layer of the present embodiment is composed of a pulp fiber layer, the pulp fiber-containing layer of the present embodiment is formed by hot pressing a single or multiple pulp fiber sheets, or by heat-pressing a single or multiple pulp fiber sheets. It is preferably formed by hot-pressing the sheet and one or more thermoplastic resin sheets.
The pulp fiber-containing layer of this embodiment contains pulp fibers and a thermoplastic resin. The pulp fibers are contained in the pulp fiber layer, and the thermoplastic resin is contained in the pulp fiber layer and/or the thermoplastic resin layer.
In this specification, the terms pulp fiber-containing layer and pulp fiber layer have different meanings. A pulp fiber-containing layer is a broader concept that includes one or more pulp fiber layers and/or thermoplastic resin layers.

<1-3. Pulp fiber sheet and pulp fiber layer>
The pulp fiber sheet becomes a pulp fiber layer by being subjected to a molding process for producing a molded body. The pulp fiber layer can be part or all of the pulp fiber containing layer. The pulp fiber layer is a fine fibrous cellulose-free layer that does not intentionally contain fine fibrous cellulose, unlike the fine fibrous cellulose-containing layer.
A pulp fiber sheet is a sheet-like material containing pulp fibers and, if necessary, a thermoplastic resin. The pulp fiber sheet can be, for example, a nonwoven fabric, and can be formed by, for example, an airlaid method, a wet papermaking method, a spunlace method, a needlepunch method, or the like.
The pulp fiber applicable to the pulp fiber sheet of the present embodiment is not particularly limited in its manufacturing method, type, and the like. For example, chemical pulps such as hardwood and/or softwood kraft pulps, mechanical pulps such as SGP, RGP, BCTMP and CTMP, waste paper pulps such as deinked pulps, and kenaf, jute, bagasse, bamboo, straw, hemp, etc. of non-wood pulp. Chlorine-free pulp such as ECF pulp and TCF pulp can also be used.

Among the above pulp fibers, kraft pulp fibers, particularly softwood kraft pulp fibers (NBKP) are preferably used because they can improve the mechanical properties of molded articles obtained from pre-sheets.

Pulp fibers can be in the form of chopped fibers, for example. In particular, when the pulp fiber sheet of the present embodiment is formed by the airlaid method, the pulp fibers may be in the form of defibrated chopped fibers, for example.
The average fiber length (Lm) of the pulp fibers used in the pulp fiber sheet of the present embodiment is preferably 1 mm or more and 100 mm or less, more preferably 2 mm or more and 80 mm or less, and 2 mm or more and 60 m or less. More preferred. When the average fiber length is within the above range, the web can be easily produced, and a molded product with high strength can be obtained.
Here, the chopped fiber is a short fiber obtained by cutting the fiber bundle. A fiber bundle is a bundle of several hundred to several thousand reinforcing fibers bundled together with a binding agent such as water or resin. Further, the defibrated chopped fiber is a large number of fibers obtained by defibrating the chopped fiber.

As an example of chopped fibers applicable to the present invention, chopped pulp fibers having an average fiber diameter of 4 to 10 μm and an average fiber length of 3 to 13 mm manufactured by Toho Tenax Co., Ltd. are known. .

(Thermoplastic resin)
The pulp fiber sheet may contain a thermoplastic resin. Thermoplastic resins have the property of softening and becoming plastic when heated to an appropriate temperature, and of solidifying when cooled. In this embodiment, the thermoplastic resin serves as a matrix resin in the molded article (fiber-reinforced thermoplastic).

The pulp fiber sheet of the present embodiment preferably contains a thermoplastic resin as a constituent component. The thermoplastic resin applicable to the pulp fiber sheet of this embodiment may be fibrous or particulate. The thermoplastic resin is preferably fibrous from the viewpoint of increasing the strength of the molded article obtained from the pre-sheet.

Thermoplastic resins include polypropylene (PP), polyethylene terephthalate (PET), polyamides such as nylon 6, nylon 11, nylon 12, nylon 66, nylon 610, nylon 612, nylon 6T, nylon 9T, and nylon M5T, polycarbonate, poly Examples include lactic acid, polyetherimide (PEI), and the like. Two or more thermoplastic resins may be used in combination.

The thermoplastic resin of the pulp fiber layer and the thermoplastic resin layer that constitute each layer in one pre-sheet may be the same or different. It is preferable that they are the same from the viewpoint of interlayer adhesiveness of the press-formed body. Further, by blending different thermoplastic resins into the thermoplastic resin layer and the pulp fiber layer, the physical properties of each layer of the pre-sheet can be arbitrarily changed. As a result, functions can be imparted to the molded product by, for example, making the physical properties of the surface and the interior different.

When the thermoplastic resin is fibrous, the fineness of the thermoplastic fibers is preferably 1 dtex to 120 dtex, more preferably 1 dtex to 85 dtex. The average fiber length of the thermoplastic fibers is preferably 1 to 50 mm, more preferably 1 to 40 mm, even more preferably 2 to 30 mm. When the fineness and average fiber length of the thermoplastic fibers are within the above ranges, the formation of the pulp fiber layer is facilitated, and uniform binding force and dispersed state are easily obtained.

When the thermoplastic resin is particulate, the average particle size of the thermoplastic particles is preferably 1 to 1,000 μm, more preferably 10 to 800 μm.

When the thermoplastic resin is in the form of pellets, one side is preferably 0.1 to 5 mm, more preferably 0.5 to 5 mm.

(Heat-fusible resin)
The pulp fiber sheet may contain a heat-fusible resin. For example, when the pulp fiber sheet is formed by the airlaid method without using any water, that is, when the pulp fiber sheet is produced by the so-called TDS method (Totally Dry System), the constituent components of the pulp fiber sheet are separated by heat. It is preferable that a heat-sealable resin is included for thermal bonding that binds. Since the TDS method does not use water at all, the pulp fiber sheet can be formed without impairing the functions of the constituent components.
Depending on the relationship between the melting point and the heat treatment temperature in the pre-sheet production process, the heat-fusible resin in the present invention, which may be blended as necessary, melts during the production of the pre-sheet to bind the pulp fibers and the thermoplastic resin together. It is a binder resin that can be adhered. Also, the heat-fusible resin can function as a matrix resin in a molded article (fiber-reinforced thermoplastic). As described above, in the present embodiment, both the thermoplastic resin and the heat-fusible resin can be the matrix resin in the fiber-reinforced thermoplastic. , shall refer to thermoplastic resins.

The heat-fusible resin may be fibrous or particulate. Moreover, when the pre-sheet is produced by a wet method, the heat-fusible resin may be in the form of particles dispersed in a liquid.

Heat-sealable resins include polyethylene (PE), polypropylene, low melting point polyethylene terephthalate, low melting point polyamide, low melting point polylactic acid, polybutylene succinate, acrylic, urethane, styrene-butadiene copolymer, polyvinyl alcohol (PVA), etc. is mentioned. Two or more kinds of heat-fusible resins may be used in combination.

When the heat-fusible resin is fibrous, the fineness of the heat-fusible fiber is preferably 1 dtex to 120 dtex, more preferably 1 dtex to 85 dtex. The average fiber length of the heat-fusible fibers is preferably 1 to 100 mm, more preferably 1 to 60 mm, even more preferably 2 to 30 mm. When the fineness and average fiber length of the heat-fusible fibers are within the above ranges, it is easy to form a pulp fiber layer, and it is easy to obtain a uniform binding force and dispersion state.

When the heat-fusible resin is particulate, the mean particle size of the heat-fusible particles is preferably 10 to 1,000 μm, more preferably 20 to 800 μm. When dispersed in an aqueous solution, the heat-fusible particles preferably have an average particle size of 10 nm to 100 μm.

(Composite of heat-fusible resin and thermoplastic resin)
The thermoplastic resin and heat-sealable resin described above may be combined to form a composite.

As a composite of a thermoplastic resin and a heat-fusible resin, a core-sheath fiber having a core portion made of a thermoplastic resin and a sheath portion made of a heat-fusible resin, half of one side in a cross section perpendicular to the longitudinal direction side-by-side fibers made of a heat-fusible resin and the other half made of a thermoplastic resin, and core-shell particles having a core made of a thermoplastic resin and a shell made of a heat-fusible resin. Among these, core-sheath fibers are preferably used because different types of resins can be easily combined.

The core-sheath fiber is, for example, a PP/PE composite core comprising a core made of polypropylene fiber (melting point 160°C) and a sheath made of polyethylene (melting point 130°C) formed around the core. Sheath fibers may be mentioned.

Other core-sheath fibers include, for example, PET/low-melting-point PET composite core-sheath fiber, high-density polyethylene/low-density polyethylene composite core-sheath fiber, polyethylene/low-melting-point PET composite core-sheath fiber, polyamide/low-melting-point polyamide composite Core-sheath fibers, polylactic acid/low-melting-point polylactic acid composite core-sheath fibers, polylactic acid/polybutylene succinate composite core-sheath fibers, and the like can be mentioned.

Due to the presence of the heat-fusible resin exposed to the outside, these composites can provide heat-fusibility and function as a binder. Therefore, these composites can be blended as the heat-fusible resin in this embodiment. In addition, since these composites contain a thermoplastic resin, they can impart strength to a molded article obtained from a pre-sheet produced by containing the composite.

In this embodiment, it is preferable to use a combination of pulp fibers and core-sheath fibers in the pulp fiber sheet. In this case, the pulp fiber layer includes a composite of pulp fibers, heat-fusible resin and thermoplastic resin. The content mass ratio of pulp fibers and core-sheath fibers is preferably 50:50 to 90:10, more preferably 60:40 to 80:20.

The basis weight of the pulp fiber sheet in the present embodiment is preferably 50-300 g/m ² , more preferably 150-200 g/m ² .

(Pre-sheet manufacturing method using airlaid method)
Next, in the pulp fiber sheet of the present embodiment, a manufacturing method using a suitable air-laid method will be described in detail. A preferred method for producing a pulp fiber sheet includes defibration, mixing, and web forming steps. Each step will be described below.

(Fibrillation process)
The defibration step is a step of defibrating chopped fibers by air flow and/or mechanical shear to obtain defibrillated chopped fibers.

In the method of defibrating chopped fibers by an air flow, an air flow is formed by a blower or the like, chopped fibers are supplied to the air flow, and the chopped fibers are defibrated by the stirring effect of the air flow. Disentanglement by air flow can prevent the pulp fibers from being broken and shortened. In particular, pulp fibers are fragile and easily broken by mechanical shearing force, but breakage can be prevented by defibrating with an air flow.

As the defibration method, it is preferable to defibrate with a swirling air flow. Chopped fibers can be sufficiently defibrated by the fibrillation method using swirling airflow. Therefore, when forming an air-laid web by the air-laid method, the dispersibility of the defibrated chopped fibers can be further enhanced.

Examples of the defibration method using a swirling air flow include a method in which chopped fibers are put into a blower and defibrated by the blower. In addition, there is a method in which air is sent along the circumferential direction into a cylindrical container by a blower to form a swirling flow, and chopped fibers are supplied into the swirling flow, stirred, and defibrated. A method using both air flow and mechanical shear includes a method in which a baffle plate is provided in a blower so that chopped fibers hit the baffle plate and are defibrated by air flow and mechanical shear. Examples of the method of defibrating by mechanical shearing include a method of compressing and expanding a fiber bundle with a roll and a method of carding with a roller with a needle.

The flow velocity of the air stream is appropriately selected according to the amount of chopped fibers, but is usually within the range of 10 to 150 m/sec.

(Mixing process)
The mixing step is a step of mixing the defibrated chopped fibers with a heat-fusible resin, a thermoplastic resin, or the like to obtain a web raw material. Auxiliaries such as flame retardants, which are added as necessary, can be added in this mixing step.

During mixing, it is preferable to stir the defibrated chopped fibers, the thermoplastic resin, and the heat-fusible resin in order to improve the dispersibility of the defibrated chopped fibers. However, in order to prevent breakage of the defibrated chopped fibers, it is preferable to apply stirring using an air flow instead of stirring using a mechanical shearing force.

The mixing step may be performed after the defibration step, or may be performed simultaneously with the fibrillation step. When the mixing step is carried out at the same time as the defibrating step, the defibrated chopped fibers and the heat-fusible resin or the like are mixed using the air flow in the fibrillation step.

(Web forming process)
A web forming step is a step of forming a web from a web raw material. In this embodiment, an air-laid method is employed to obtain an air-laid web. Here, the airlaid method is a method of forming a web by three-dimensionally randomly depositing fibers using an air flow.

In the web forming process in this embodiment, for example, a web forming apparatus 1 shown in FIG. 1 is used. This web forming apparatus 1 comprises a conveyor 10 , an air permeable endless belt 20 , a fiber mixture supply means 30 , a first carrier sheet supply means 40 , a second carrier sheet supply means 50 and a suction box 60 .

Here, the conveyor 10 is composed of a plurality of rollers 11. As shown in FIG. The permeable endless belt 20 is mounted on the conveyor 10 and rotated. The fiber mixture supplying means 30 supplies the air-permeable endless belt 20 with the fiber mixture together with the air flow. The first carrier sheet supply means 40 supplies the first carrier sheet 41 toward the permeable endless belt 20 . The second carrier sheet supply means 50 supplies the second carrier sheet 51 toward the first carrier sheet 41 that has passed through the permeable endless belt 20 . The suction box 60 sucks the permeable endless belt 20 from the inside.

In the web forming apparatus 1, the fiber mixture supply means 30 is installed above the permeable endless belt 20, the first carrier sheet supply means 40 is installed upstream of the permeable endless belt 20, and the second carrier sheet The supply means 50 is installed downstream of the permeable endless belt 20 .

In the web forming process using the web forming apparatus 1 , the rollers 11 are rotated in the same direction to drive the conveyor 10 and rotate the permeable endless belt 20 . Also, the first carrier sheet 41 is let out from the first carrier sheet supply means 40 so as to come into contact with the air-permeable endless belt 20 .

Next, while sucking the air permeable endless belt 20 by the suction box 60, the fiber mixture is lowered together with the air flow from the fiber mixture supply means 30, and the fiber mixture is dropped onto the first carrier sheet 41 on the air permeable endless belt 20. , to deposit. Thus, an airlaid web A is formed.

Next, a second carrier sheet 51 is supplied onto the air-laid web A from a second carrier sheet supplying means 50 to obtain an air-laid web-containing laminate sheet.

The first carrier sheet 41 and the second carrier sheet 51 function as conveying means for conveying the air-laid web in the air-laid method.

(Binding process)
When the bonding process is further included, the bonding method is selected from a chemical bond method, a thermal bond method, and a multi-bond method. Either method may be selected, but the thermal bond method is often used from the viewpoint of binding to reinforcing fibers. The binding step by the thermal bond method is a step of heat-treating the air-laid web to bind the defibrated chopped fibers with a heat-fusible resin.

Examples of the heat treatment of the air-laid web include hot air treatment and infrared irradiation treatment, and hot air treatment is preferred in terms of the low cost of the apparatus.

The hot air treatment includes a method of heat-treating the air-laid web by contacting it with a through-air dryer equipped with a rotating drum having air permeability on its peripheral surface (hot air circulation rotary drum method),
A method of heat-treating the air-laid web by passing it through a box-type dryer and passing hot air through the air-laid web (hot-air circulation conveyor oven method), and the like.

<1-4. Thermoplastic resin sheet and thermoplastic resin layer>
The thermoplastic sheet becomes a thermoplastic resin layer by being subjected to a molding process for producing a molded body. The thermoplastic layer can be part of the pulp fiber-containing layer.

The thermoplastic resin sheet can be a non-woven fabric, and can be formed, for example, by an airlaid method, a wet papermaking method, a spunlace method, a needlepunch method, or the like. Specifically, for example, a thermoplastic resin sheet may be formed by forming reinforcing fibers into a sheet with a carding machine and then entangling them with a needle punch. The thermoplastic resin sheet is preferably a spunbond nonwoven fabric.

The thermoplastic resin sheet may be used as a carrier sheet for an air-laid web when the pulp fiber sheet is formed by an air-laid method. According to this method, a pre-sheet can be produced in one step (one pass). In addition, a pre-sheet (and a pulp fiber-containing layer) having high interlaminar strength between the pulp fiber sheet and the thermoplastic resin sheet can be produced.
By performing the heat treatment at a temperature equal to or higher than the melting point of the heat-fusible resin, it is possible to promote inter-layer adhesion between the layers in the pulp fiber-containing layer and bonding between constituent components within the layer.

When fibers are used in the thermoplastic resin sheet of the present embodiment, the average fiber length (Ls) of the fibers is preferably 5 mm or more and 100 mm or less, more preferably 5 mm or more and 80 mm or less, and 5 mm or more and 60 m. More preferably: When the average fiber length is within the above range, the web can be easily produced, and a molded product with high strength can be obtained.

In the thermoplastic resin sheet of the present embodiment, uniform distribution of the thermoplastic resin in each layer of the pre-sheet makes it possible to uniformize strength in the thickness direction of the pre-sheet.

The thermoplastic resin that can be applied to the thermoplastic resin sheet of the present embodiment may be fibrous, particulate, or pelletized. The thermoplastic resin is preferably fibrous from the viewpoint of increasing the strength of the molded article obtained from the pre-sheet.

As the thermoplastic resin for the thermoplastic resin sheet, the same resin as the thermoplastic resin that can be used for the pulp fiber sheet of the present embodiment can be used. As the thermoplastic resin for the thermoplastic resin sheet, polyolefin is preferred, and polypropylene is more preferred. As the thermoplastic resin sheet, a polyolefin nonwoven fabric is preferable, a polypropylene nonwoven fabric is more preferable, and a polypropylene spunbond nonwoven fabric is even more preferable. Commercially available polyolefin nonwoven fabrics can be used.

The basis weight of the thermoplastic resin sheet in the present embodiment is preferably 10-100 g/m ^{2 , more preferably 20-50 g/m 2 .}

<1-5. Fine fibrous cellulose sheet and fine fibrous cellulose-containing layer>
The pre-sheet of this embodiment has a fine fibrous cellulose-containing layer. The fine fibrous cellulose-containing layer may be a single layer or multiple layers.
The fine fibrous cellulose-containing layer of the present embodiment exists at least as the outermost layer of the pre-sheet of the present embodiment. The fine fibrous cellulose-containing layer of the present embodiment may be present not only in the outermost layer of the pre-sheet of the present embodiment but also in the innermost layer of the pre-sheet of the present embodiment. In the pre-sheet of the present embodiment, both the outermost layer and the innermost layer are preferably fine fibrous cellulose-containing layers. In addition, the fine fibrous cellulose-containing layers of the outermost layer and the innermost layer may be the same or different.

The fine fibrous cellulose-containing layer of the present embodiment is preferably formed by hot-pressing a fine fibrous cellulose sheet. Hereinafter, the fine fibrous cellulose sheet is also simply referred to as the sheet of the present embodiment.

The sheet of the present embodiment is preferably a sheet containing first cellulose fibers with a fiber width of 10 μm or more and second cellulose fibers with a fiber width of 1000 nm or less. In this specification, cellulose fibers having a fiber width of 1000 nm or less are sometimes referred to as fine fibrous cellulose.

The sheet of the present embodiment has good adhesion to resin. Specifically, after laminating a resin layer on the sheet of the present embodiment and heat-pressing (for example, a press pressure of 0.5 MPa or more), the adhesion between the resin layer and the sheet is good, and there is no peeling between the layers. does not occur and the laminated structure is maintained.

The basis weight of the sheet of the present embodiment is preferably 100/m ² or more, more preferably 120 g/m ² or more, and even more preferably 150 g/m ² or more. Further, the basis weight of the sheet of the present embodiment is preferably 300 g/m ² or less, more preferably 250 g/m ² or less, and even more preferably 200 g/m ² or less. The basis weight of the sheet can be calculated according to, for example, JIS P 8124:2011. The basis weight of the sheet of the present embodiment can be appropriately adjusted according to the performance required of the molded article. may be less than 100/m ² and may be 40 g/m ² or less.

The thickness of the sheet of the present embodiment is preferably 5 μm or more, more preferably 10 μm or more, still more preferably 20 μm or more, and particularly preferably 30 μm or more. The upper limit of the thickness of the sheet is not particularly limited, but can be set to 1000 μm, for example. The thickness of the sheet is measured according to, for example, JIS P 8118:2014.

The density of the sheet of the present embodiment is preferably 0.1 g/cm ³ or more, more preferably 0.2 g/cm ³ or more, further preferably 0.3 g/cm ³ or more, It is more preferably 0.50 g/cm ³ or more, even more preferably 0.60 g/cm ³ or more, and particularly preferably 0.65 g/cm ³ or more. Also, the upper limit of the density of the sheet is not particularly limited, but is preferably 5.0 g/cm ³ or less, for example. Here, the density of the sheet is calculated from the basis weight measured in accordance with JIS P 8124:2011, the thickness of the sheet measured in accordance with JIS P 8118:2014, and these values. The density of the sheet may be appropriately adjusted by, for example, calendering, depending on the performance required for the molded article or sheet.

The sheet of this embodiment may be a single-layer sheet or a multi-layer sheet. The sheet of this embodiment is preferably a single-layer sheet. Specifically, it is preferable that both the first cellulose fibers having a fiber width of 10 μm or more and the second cellulose fibers having a fiber width of 1000 nm or less randomly exist in the single-layer sheet. Note that the sheet of the present embodiment is a multi-layer laminate in which two or more single-layer sheets containing both the first cellulose fibers having a fiber width of 10 μm or more and the second cellulose fibers having a fiber width of 1000 nm or less are laminated. It may be a layered sheet. For example, the sheet of the present embodiment includes a first layer containing both first cellulose fibers having a fiber width of 10 μm or more and second cellulose fibers having a fiber width of 1000 nm or less, and a second layer having a fiber width of 10 μm or more. It may be a multilayer sheet having a second layer containing both one cellulose fiber and a second cellulose fiber having a fiber width of 1000 nm or less. In this case, the first layer and the second layer may be the same layer or different layers. Moreover, the thickness and basis weight of the first layer and the second layer may be the same or different. That is, it can be said that the sheet of the present embodiment relates to a multi-layer sheet (for example, a two-layer sheet) in which two or more single-layer sheets are laminated.

(First cellulose fiber)
The sheet of the present embodiment may not contain the first cellulose fibers, but preferably the sheet of the present embodiment contains the first cellulose fibers. Here, the first cellulose fibers are preferably cellulose fibers having a fiber width of 10 μm or more. The fiber width of the first cellulose fibers may be 10 µm or more, preferably 15 µm or more, more preferably 20 µm or more, and even more preferably 25 µm or more. The width of the first cellulose fibers is preferably 100 μm or less, more preferably 80 μm or less, still more preferably 60 μm or less, and particularly preferably 40 μm or less. The first cellulose fibers are also referred to herein as coarse cellulose fibers or pulp.

Details regarding the first cellulose when the sheet of the present embodiment contains the first cellulose are described below.

The fiber width of the first cellulose fiber can be measured using a Kajaani fiber length measuring instrument (FS-200 type) manufactured by Kajaani Automation. Here, the fiber width of the first cellulose fiber is the fiber width of the stem fiber of the cellulose fiber. For example, when the cellulose fibers are fibrillated cellulose fibers, the fiber width of the trunk fibers constituting the main axis is referred to as the fiber width of the first cellulose fibers, not the fiber width of the fibrillated and branched fibers. .

Pulp is preferably used as the fiber raw material for the first cellulose fibers. Pulp includes, for example, wood pulp, non-wood pulp and deinked pulp. Examples of wood pulp include, but are not limited to, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP). ) and chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemigroundwood pulp (CGP), groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP) A mechanical pulp etc. are mentioned. Non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lints, and non-wood-based pulps such as hemp, straw, and bagasse. The deinked pulp is not particularly limited, but includes, for example, deinked pulp made from waste paper. As the first cellulose fiber, one of the above cellulose fibers may be used alone, or two or more of them may be mixed and used.

The first cellulose fibers preferably have ionic substituents. The ionic substituents can include, for example, either one or both of an anionic group and a cationic group. Examples of the anionic group include a phosphate group or a substituent derived from a phosphate group (sometimes simply referred to as a phosphate group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), and a sulfone group or a substituent derived from a sulfone group (sometimes referred to simply as a sulfone group), and at least one selected from a phosphorous acid group and a carboxy group. It is more preferred, and a phosphorous acid group is particularly preferred. When the first cellulose fibers have the above-described ionic substituents, for example, it is possible to suppress twisting of the sheet in the sheet manufacturing process.

A phosphorous acid group or a substituent derived from a phosphorous acid group is, for example, a substituent represented by the following formula (1). Phosphorus oxoacid group is a divalent functional group corresponding to, for example, phosphoric acid from which a hydroxy group has been removed. Specifically, it is a group represented by —PO ₃ H ₂ . Substituents derived from a phosphorous acid group include substituents such as a salt of a phosphorous acid group and a phosphorous acid ester group. In addition, the substituent derived from the phosphorous oxoacid group may be contained in the cellulose fiber as a group in which a phosphoric acid group is condensed (for example, a pyrophosphate group). Further, the phosphorous acid group may be, for example, a phosphorous acid group (phosphonic acid group), and the substituent derived from the phosphorous acid group may be a salt of a phosphorous acid group, a phosphite ester group, or the like. good too.

式（１）中、ａ、ｂおよびｎは自然数である（ただし、ａ＝ｂ×ｍである）。α^１，α^２，・・・，α^ｎおよびα’のうちａ個がＯ^－であり、残りはＲ，ＯＲのいずれかである。なお、各α^ｎおよびα’の全てがＯ^－であっても構わない。Ｒは、各々、水素原子、飽和－直鎖状炭化水素基、飽和－分岐鎖状炭化水素基、飽和－環状炭化水素基、不飽和－直鎖状炭化水素基、不飽和－分岐鎖状炭化水素基、不飽和－環状炭化水素基、芳香族基、またはこれらの誘導基である。また、ｎは１であることが好ましい。

In formula (1), a, b and n are natural numbers (where a=b×m). a of α ^{1 , α 2} , . All of α ⁿ and α′ may be O ⁻ . 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 A hydrogen group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. Moreover, it is preferable that n is 1.

Examples of the saturated straight-chain hydrocarbon group include, but are not limited to, methyl group, ethyl group, n-propyl group, n-butyl group, and the like. The saturated-branched hydrocarbon group includes i-propyl group, t-butyl group and the like, but is not particularly limited. The saturated cyclic hydrocarbon group includes, but is not particularly limited to, a cyclopentyl group, a cyclohexyl group, and the like. The unsaturated straight-chain hydrocarbon group includes, but is not particularly limited to, a vinyl group, an allyl group, and the like. The unsaturated-branched hydrocarbon group includes i-propenyl group, 3-butenyl group and the like, but is not particularly limited. The unsaturated-cyclic hydrocarbon group includes, but is not limited to, a cyclopentenyl group, a cyclohexenyl group, and the like. The aromatic group includes, but is not particularly limited to, a phenyl group, a naphthyl group, or the like.

In addition, as the derivative group in R, at least one functional group such as a carboxy group, a hydroxy group, or an amino group is added or substituted with respect to the main chain or side chain of the above various hydrocarbon groups. Examples include, but are not limited to, groups. Although the number of carbon atoms constituting the main chain of R is not particularly limited, it is preferably 20 or less, 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 phosphorous acid group can be set within an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of fine cellulose fibers. can also

β ^b+ is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of monovalent or higher-valent cations composed of organic substances include aliphatic ammonium and aromatic ammonium. Examples include cations of divalent metals such as calcium and magnesium, hydrogen ions, and the like, but are not particularly limited. These may be applied singly or in combination of two or more. As the cation having a valence of 1 or more composed of an organic substance or an inorganic substance, sodium or potassium ions are preferable, but not particularly limited, because they are less likely to turn yellow when fiber raw materials containing β are heated and are easily industrially available. β ^b+ may be an organic onium ion, in which case it is particularly preferably an organic ammonium ion.

The amount of the ionic substituent introduced into the first cellulose fiber is preferably 0.3 mmol/g or more, more preferably 0.4 mmol/g or more, more preferably 0.5 mmol/g (mass) of cellulose fiber. /g or more, more preferably 0.7 mmol/g or more, and particularly preferably 1.0 mmol/g or more. In addition, the amount of the ionic substituent introduced into the first cellulose fiber is preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less per 1 g (mass) of cellulose fiber. It is more preferably 0.00 mmol/g or less. Here, the unit mmol/g indicates the amount of substituents per 1 g of mass of the first cellulose fiber when the counter ion of the anionic group is hydrogen ion (H+), for example. By setting the amount of the ionic substituent to be introduced within the above range, it is possible to more effectively suppress the occurrence of twisting in the sheet in the manufacturing process of the sheet.

The introduction amount of the ionic substituents into the first cellulose fibers can be measured, for example, by a neutralization titration method. In the measurement by the neutralization titration method, the introduced amount is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing the first cellulose fibers.

FIG. 2 is a graph showing the relationship between the amount of dropped NaOH and the pH of the cellulose fiber-containing slurry having a phosphorous acid group. The amount of phosphorus oxoacid groups introduced into cellulose fibers is measured, for example, as follows.

First, a slurry containing cellulose fibers is treated with a strongly acidic ion exchange resin. Regarding the first cellulose fibers, before the treatment with the strongly acidic ion exchange resin, the fibrillation treatment similar to the fibrillation treatment step described below is performed on the object to be measured.
Next, while adding sodium hydroxide aqueous solution, the change in pH is observed to obtain a titration curve as shown in the upper part of FIG. The titration curve shown in the upper part of FIG. 2 plots the measured pH against the amount of alkali added, and the titration curve shown in the lower part of FIG. 2 plots the pH against the amount of alkali added. The increment (differential value) (1/mmol) is plotted. In this neutralization titration, two points where the increment (the differential value of the pH with respect to the amount of alkali dropped) are maximized are confirmed in the curve obtained by plotting the measured pH against the amount of alkali added. Among these, the maximum point of the increment obtained first when the alkali is first added is called the first end point, and the maximum point of the increment obtained next is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the first dissociated acid amount of the cellulose fibers contained in the slurry used for titration, and the amount of alkali required from the first end point to the second end point is equal to the second dissociation acid amount of cellulose fibers contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is the total dissociation of cellulose fibers contained in the slurry used for titration. equal to the acid content. A 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 oxoacid group introduced (mmol/g). In addition, when simply referring to the amount of phosphorus oxoacid groups introduced (or the amount of phosphorus oxoacid groups), it means the amount of the first dissociated acid.

In FIG. 2, 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 phosphoric acid group is a phosphoric acid group, and the phosphoric acid group causes condensation, it appears that the amount of weakly acidic groups in the phosphoric acid group (also referred to herein as the second dissociated acid amount) is The amount of alkali required in the second region is less than that required in the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the amount of first dissociated acid) matches the amount of phosphorus atoms regardless of the presence or absence of condensation. In addition, when the phosphorous acid group is a phosphorous acid group, the weakly acidic group does not exist in the phosphorous acid group, so the amount of alkali required for the second region is reduced, or the amount of alkali required for the second region is may be zero. In this case, the titration curve has one point at which the pH increment is maximum.

In addition, since the denominator of the above-described phosphorus oxoacid group introduction amount (mmol/g) indicates the mass of acid-type cellulose fibers, the amount of phosphorus oxoacid groups possessed by acid-type cellulose fibers (hereinafter referred to as the amount of phosphorus oxoacid groups (acid type)). On the other hand, when the counterion of the phosphate group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of the cellulose fiber when the cation C is the counterion. , the amount of phosphorous acid groups (hereinafter referred to as the amount of phosphorous acid groups (C type)) possessed by the cellulose fiber having the cation C as a counter ion can be obtained.

That is, it is calculated by the following formula.
Phosphorus oxo acid group amount (C type) = Phosphorus oxo acid group amount (acid type) / {1 + (W-1) × A / 1000}
・A [mmol/g]: total amount of anions derived from phosphate groups possessed by cellulose fibers (total dissociated acid amount of phosphate groups)
• W: Formula weight per valence of cation C (eg, 23 for Na and 9 for Al).

FIG. 3 is a graph showing the relationship between the amount of dropped NaOH and pH for a dispersion containing cellulose fibers having a carboxyl group as an ionic substituent. The amount of carboxyl groups introduced into cellulose fibers is measured, for example, as follows.

First, a dispersion containing cellulose fibers is treated with a strongly acidic ion exchange resin. Regarding the first cellulose fibers, before the treatment with the strongly acidic ion exchange resin, the fibrillation treatment similar to the fibrillation treatment step described below is performed on the object to be measured.

Next, while adding sodium hydroxide aqueous solution, the change in pH is observed to obtain a titration curve as shown in the upper part of FIG. The titration curve shown in the upper part of FIG. 3 plots the measured pH against the amount of added alkali, and the titration curve shown in the lower part of FIG. 3 plots the pH against the amount of added alkali. The increment (differential value) (1/mmol) is plotted. In this neutralization titration, in the curve plotting the measured pH against the amount of alkali added, one point where the increment (the differential value of pH with respect to the amount of alkali dropped) is maximum was confirmed. 1 end point. Here, the region from the start of titration to the first end point in FIG. 3 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, by dividing the alkali amount (mmol) required in the first region of the titration curve by the solid content (g) in the dispersion containing the cellulose fiber to be titrated, the amount of carboxyl groups introduced (mmol/ g) is calculated.

In addition, since the denominator of the above-mentioned carboxy group introduction amount (mmol/g) is the mass of the acid-type cellulose fiber, the amount of carboxy groups possessed by the acid-type cellulose fiber (hereinafter referred to as the amount of carboxy groups (acid type) call). On the other hand, when the counter ion of the carboxy group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of the cellulose fiber when the cation C is the counter ion. , the amount of carboxy groups (hereinafter referred to as the amount of carboxy groups (C-type)) possessed by cellulose fibers whose counterions are cations C. 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 form))/1000}
W: Formula weight per valence of cation C (for example, 23 for Na and 9 for Al)

When measuring the amount of ionic substituents by the titration method, if the amount of 1 drop of aqueous sodium hydroxide solution is too large, or if the titration interval is too short, the amount of ionic substituents will be lower than the original value. may not be obtained. As a suitable drop amount and titration interval, for example, it is desirable to titrate 10 to 50 μL of 0.1N sodium hydroxide aqueous solution every 5 to 30 seconds. In addition, in order to eliminate the influence of carbon dioxide dissolved in the cellulose fiber-containing slurry, for example, it is desirable to measure while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration to the end of titration.

When the first cellulose fibers and the second cellulose fibers are mixed, they are separated and collected by centrifugal separation, and the amount of phosphate group introduced is measured by the method described above. Centrifugation is performed by adjusting the cellulose dispersion in which the first cellulose fiber and the second cellulose fiber are mixed to a solid content concentration of 0.2% by mass, using a cooling high-speed centrifuge (Kokusan Co., H-2000B), It is carried out under the conditions of 12000 G and 10 minutes. After that, the sedimented solid content obtained is recovered as the first cellulose fibers, and the supernatant liquid is recovered as the second cellulose fibers.

The water retention of the first cellulose fibers is preferably 220% or more, more preferably 230% or more, still more preferably 240% or more, even more preferably 250% or more, and 280%. % or more is particularly preferable. The water retention of the first cellulose fibers is preferably 600% or less, more preferably 500% or less, and even more preferably 400% or less. The water retention of the first cellulose fiber is described in J. Am. It is a value measured according to TAPPI-26. The water retention degree of the first cellulose fiber is the water retention degree of the first cellulose fiber before sheeting, and the water retention degree of the first cellulose fiber after sheeting satisfies the above range. good too.

The content of the first cellulose fibers is preferably 10% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass, relative to the total mass of the cellulose fibers contained in the sheet of the present embodiment. % or more, more preferably more than 40% by mass, 41% by mass or more, 45% by mass or more, 50% by mass or more, more than 50% by mass, or 55% by mass or more, and 60% by mass or more It is more preferable that the content is 70% by mass or more, and it is particularly preferable that the content is 70% by mass or more. In addition, the content of the first cellulose fibers is preferably 99% by mass or less, more preferably 95% by mass or less, and 90% by mass or less with respect to the total mass of the cellulose fibers contained in the sheet. is more preferably 85% by mass or less, and particularly preferably 80% by mass or less. The content of the first cellulose fibers may be 0% by mass with respect to the total mass of the cellulose fibers contained in the sheet of the present embodiment.

<Manufacturing process of the first cellulose fiber>
<Phosphorus oxoacid group introduction step>
When the first cellulose fiber has a phosphorus oxoacid group as an ionic substituent, the manufacturing process of the first cellulose fiber includes a phosphorus oxoacid group introduction step. In the phosphorus oxoacid group-introducing step, at least one compound selected from compounds capable of introducing a phosphorus oxoacid group (hereinafter also referred to as "compound A") is added to cellulose by reacting with a hydroxyl group possessed by a fiber raw material containing cellulose. It is a step of acting on a fiber raw material containing. Through this step, the phosphate group-introduced fiber is obtained.

In the phosphorus oxoacid group-introducing step according to the present embodiment, the reaction between the fiber material containing cellulose and compound A is performed in the presence of at least one selected from urea and derivatives thereof (hereinafter also referred to as "compound B"). may On the other hand, the reaction between the cellulose-containing fiber raw material and the compound A may be carried out in the absence of the compound B.

An example of the method of allowing the compound A to act on the fiber raw material in the presence of the compound B includes a method of mixing the compound A and the compound B with the fiber raw material in a dry state, a wet state, or a slurry state. Among these, it is preferable to use a fiber raw material in a dry state or a wet state, and it is particularly preferable to use a fiber raw material in a dry state, because the uniformity of the reaction is high. Although the form of the fiber material is not particularly limited, it is preferably in the form of cotton or a thin sheet, for example. The compound A and the compound B can be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state by heating to a melting point or higher. Among these, it is preferable to add in the form of a solution dissolved in a solvent, particularly in the form of an aqueous solution, since the uniformity of the reaction is high. Moreover, the compound A and the compound B may be added simultaneously to the fiber raw material, may be added separately, or may be added as a mixture. The method for adding the compound A and the compound B is not particularly limited, but when the compound A and the compound B are in the form of a solution, the fiber raw material may be immersed in the solution to absorb the liquid and then taken out, or the fiber raw material may be taken out. The solution may be added dropwise to the Further, the necessary amount of compound A and compound B may be added to the fiber raw material, or after adding excessive amounts of compound A and compound B to the fiber raw material, the excess compound A and compound B are removed by pressing or filtering. may be removed.

The compound A used in the present embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose. Salts, phosphoric anhydride (diphosphorus pentoxide) and the like can be mentioned, but are not particularly limited. Phosphoric acid of various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. Phosphorous acid includes 99% phosphorous acid (phosphonic acid). Dehydration-condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid by dehydration reaction, and examples thereof 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 acids. It can be a degree of harmony. Among these, the introduction efficiency of the phosphate group is high, the fibrillation efficiency is easily improved in the fibrillation step described later, the cost is low, and it is easy to apply industrially. salt, potassium phosphate, ammonium phosphate or phosphorous acid, sodium phosphite, potassium phosphite, ammonium phosphite, phosphoric acid, sodium dihydrogen phosphate, More preferred are disodium hydrogen phosphate, ammonium dihydrogen phosphate, phosphorous acid, and sodium phosphite.

The amount of compound A added to the fiber raw material is not particularly limited. For example, when the amount of compound A added is converted to the phosphorus atomic weight, the amount of phosphorus atoms added to the fiber raw material (absolute dry mass) is 0.5% by mass or more. It is preferably 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 the first cellulose fibers can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to be equal to or less than the above upper limit, it is possible to balance the effect of improving the yield and the cost.

Compound B used in this embodiment is at least one selected from urea and derivatives thereof as described above. Compound B includes, for example, urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. 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 to the fiber raw material (absolute dry mass) is not particularly limited, but is preferably 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, More preferably, it is 100% by mass or more and 350% by mass or less.

In the reaction between the fiber raw material containing cellulose and 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, dimethylacetamide and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine and hexamethylenediamine. Among these, triethylamine in particular is known to work as a good reaction catalyst.

In the phosphorus oxoacid group-introducing step, it is preferable to heat-treat the fiber raw material after adding or mixing the compound A or the like to the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature that can efficiently introduce phosphorus oxoacid groups while suppressing thermal decomposition and hydrolysis reaction of the fiber. The heat treatment temperature is, for example, preferably 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. In addition, for the heat treatment, equipment having various heat media can be used, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll heater, a plate heater, a fluidized bed dryer, and a band dryer. A mold drying device, a filter drying device, a vibrating fluidized drying device, a flash drying device, a vacuum drying device, an infrared heating device, a far infrared heating device, a microwave heating device, and a high frequency drying device can be used.

In the heat treatment according to the present embodiment, for example, the compound A is added to a thin sheet-like fiber raw material by a method such as impregnation, and then heated, or the fiber raw material and the compound A are heated while kneading or stirring with a kneader or the like. method can be adopted. This makes it possible to suppress unevenness in the concentration of the compound A in the fiber raw material, and to more uniformly introduce the phosphorous acid groups to the surface of the cellulose fibers contained in the fiber raw material. This is because when water molecules move to the surface of the fiber material during drying, the dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the fiber material (that is, the concentration unevenness of the compound A is It is thought that this is due to the fact that it is possible to suppress the occurrence of

In addition, the heating device used for the heat treatment always removes the moisture retained by the slurry and the moisture generated due to the dehydration condensation (phosphorylation) reaction between the compound A and the hydroxyl groups contained in the cellulose etc. in the fiber raw material. It is preferable that the device can be discharged to the outside of the device system. As such a heating device, for example, an air-blowing oven can be used. By constantly draining the water in the device system, it is possible to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of phosphorylation, and to suppress the acid hydrolysis of the sugar chains in the fiber. can. Therefore, it is possible to obtain the first cellulose fibers having a high axial ratio.

The heat treatment time is, for example, preferably 1 second or more and 300 minutes or less, more preferably 1 second or more and 1000 seconds or less, and 10 seconds or more and 800 seconds or less, after water is substantially removed from the fiber raw material. is more preferable. In the present embodiment, the amount of phosphorus oxoacid groups to be introduced can be set within a preferable range by setting the heating temperature and the heating time within appropriate ranges.

The phosphorus oxoacid group-introducing step may be performed at least once, but may be performed repeatedly two or more times. By performing the phosphorus oxoacid group-introducing step two or more times, many phosphorus oxoacid groups can be introduced into the fiber raw material.

<Carboxy Group Introduction Step>
When the first cellulose fiber has a carboxy group as an ionic substituent, the manufacturing process of the first cellulose fiber includes a carboxy group introduction step. In the step of introducing a carboxy group, the fiber raw material containing cellulose is subjected to oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, a compound having a carboxylic acid-derived group or a derivative thereof, or a carboxylic acid-derived group. This is done by treating the compound with an acid anhydride or a derivative thereof.

The compound having a carboxylic acid-derived group is not particularly limited. Examples include tricarboxylic acid compounds. Derivatives of compounds having a carboxylic acid-derived group are not particularly limited, but include, for example, imidized acid anhydrides of compounds having a carboxy group and derivatives of acid anhydrides of compounds having a carboxy group. Examples of imidized acid anhydrides of compounds having a carboxy group include, but are not particularly limited to, imidized dicarboxylic acid compounds such as maleimide, succinimide and phthalimide.

The acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited. acid anhydrides; In addition, the acid anhydride derivative of the compound having a group derived from carboxylic acid is not particularly limited. Acid anhydrides in which at least some of the hydrogen atoms are substituted with substituents such as alkyl groups and phenyl groups can be mentioned.

In the carboxyl group introduction step, when the TEMPO oxidation treatment is performed, it is preferable to perform the treatment under the condition of pH 6 or more and 8 or less. Such treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment includes, for example, sodium phosphate buffer (pH=6.8), pulp as a fiber raw material, and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst. This can be done by adding sodium hypochlorite as a nitroxy radical, sacrificial reagent. Furthermore, coexistence of sodium chlorite enables efficient oxidation of aldehydes generated in the process of oxidation to carboxyl groups. Moreover, the TEMPO oxidation treatment may be performed under the condition that the pH is 10 or more and 11 or less. Such treatment is also called alkali 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 to be introduced into the first cellulose fiber varies depending on the type of substituent, but for example, in the case of introducing carboxyl groups by TEMPO oxidation, the amount is 0.10 mmol/g or more per 1 g (mass) of cellulose fibers. It is preferably 0.20 mmol/g or more, 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 first cellulose fibers is preferably 3.65 mmol/g or less, more preferably 3.00 mmol/g or less, and 2.50 mmol/g or less. It is 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, it may be 5.8 mmol/g or less per 1 g (mass) of cellulose fibers. By setting the amount of carboxyl groups to be introduced within the above range, the fiber raw material can be easily made finer, and the stability of the first cellulose fiber can be enhanced.

<Washing process>
In the first method for producing cellulose fibers in the present embodiment, the ionic substituent-introduced fibers can be subjected to a washing step, if necessary. The washing step is performed by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. Further, the washing step may be performed after each step described later, and the number of washings performed in each washing step is not particularly limited.

<Alkali treatment process>
In the first method for producing cellulose fibers in the present embodiment, alkali treatment may be performed on the ionic substituent-introduced fibers after washing, if necessary. In this case, it is preferable to adjust the pH to 12 or more and 13 or less by diluting the washed ionic substituent-introduced fiber with 10 L of ion-exchanged water, and then gradually adding a 1N alkaline solution while stirring. . 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 the present embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of its high versatility. Moreover, 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 water or a polar solvent including a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing 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.

Although the temperature of the alkaline solution in the alkaline treatment step is not particularly limited, it is preferably 5° C. or higher and 80° C. or lower, more preferably 10° C. or higher and 60° C. or lower. The immersion time of the ionic substituent-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, more preferably 10 minutes or more and 20 minutes or less. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but for example, it is preferably 100% by mass or more and 100000% by mass or less, and 1000% by mass or more and 10000% by mass with respect to the absolute dry mass of the ionic substituent-introduced fiber. The following are more preferable. In addition, after the alkali treatment step, the cleaning step described above may be further provided.

(Second cellulose fiber)
The sheet of this embodiment contains second cellulose fibers (fine fibrous cellulose) having a fiber width of 1000 nm or less. The fiber width of the second cellulose fibers can be measured, for example, by electron microscopic observation. The second cellulose fiber is, for example, monofilament-like cellulose.

The fiber width of the second cellulose fiber may be 1000 nm or less, preferably 500 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and even more preferably 100 nm or less. It is preferably 50 nm or less, even more preferably 20 nm or less, and particularly preferably 10 nm or less. Since the sheet of the present embodiment contains such fine fibrous cellulose with a small fiber width, the resulting molded product has excellent mechanical properties. By using both the second cellulose fibers and the first cellulose fibers (coarse cellulose fibers), the adhesion to the resin can be effectively improved. In addition, when the fine fibrous cellulose having a small fiber width is used in combination with the first cellulose fibers having an ionic substituent (coarse cellulose fibers), the occurrence of twisting in the sheet is suppressed in the manufacturing process of the sheet. be able to. Further, when the fine fibrous cellulose having a small fiber width is used in combination with the first cellulose fibers having an ionic substituent (coarse cellulose fibers), the transparency of the sheet is improved.

The fiber width of the second cellulose fibers is measured using, for example, an electron microscope as follows. First, an aqueous suspension of the second cellulose fibers having a concentration of 0.05% by mass or more and 0.1% by mass or less was prepared, and this suspension was cast on a hydrophilized carbon film-coated grid and observed by TEM. Use as a sample. SEM images of surfaces cast on glass may be observed if they contain wide fibers. Then, an electron microscope image is observed at a magnification of 1,000, 5,000, 10,000, or 50,000 times depending on the width of the fiber to be observed. However, the sample, observation conditions and magnification are adjusted so as to satisfy the following conditions.
(1) A single straight line X is drawn at an arbitrary point in the observed image, and 20 or more fibers intersect the straight line X.
(2) Draw a straight line Y that intersects the straight line perpendicularly in the same image, and 20 or more fibers intersect the straight line Y.
Widths of fibers intersecting the straight lines X and Y are visually read from the observation image satisfying the above conditions. In this way, at least three sets of observed images of surface portions that do not overlap each other are obtained. Then, for each image, the width of the fiber that crosses straight line X and straight line Y is read.

The fiber length of the second cellulose fiber is not particularly limited, but for example, it 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 0.1 μm or more and 600 μm or less. is more preferred. By setting the fiber length within the above range, it is possible to suppress breakage of the crystal regions of the second cellulose fibers. Also, it is possible to set the slurry viscosity of the second cellulose fibers within an appropriate range. The fiber length of the second cellulose fibers can be determined by image analysis using TEM, SEM, or AFM, for example.

Preferably, the second cellulose fibers have a Type I crystal structure. Here, the fact that the second cellulose fibers have a type I crystal structure can be identified in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by having typical peaks at two positions near 2θ=14° or more and 17° or less and 2θ=22° or more and 23° or less.

The proportion of the I-type crystal structure in the second cellulose fibers is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. As a result, even better performance can be expected in terms of heat resistance and low coefficient of linear thermal expansion. The degree of crystallinity is determined by a conventional method from the pattern of X-ray diffraction profiles (Seagal et al., Textile Research Journal, vol. 29, p. 786, 1959).

Although the axial ratio (fiber length/fiber width) of the second cellulose fibers is not particularly limited, it is preferably 20 or more and 10,000 or less, and more preferably 50 or more and 1,000 or less. A sheet containing the second cellulose fibers can be easily formed by making the axial ratio equal to or higher than the above lower limit. By setting the axial ratio to be equal to or less than the above upper limit, for example, when the second cellulose fiber is treated as an aqueous dispersion, it is preferable in terms of ease of handling such as dilution.

The second cellulose fibers in this embodiment have, for example, both crystalline and amorphous regions. In particular, the second cellulose fibers having both a crystalline region and an amorphous region and having a high axial ratio are realized by the method for producing fine fibrous cellulose described later.

The second cellulose fiber in this embodiment preferably has an ionic substituent. The ionic substituents can include, for example, either one or both of an anionic group and a cationic group. Examples of the anionic group include a phosphate group or a substituent derived from a phosphate group (sometimes simply referred to as a phosphate group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), and a sulfone group or a substituent derived from a sulfone group (sometimes referred to simply as a sulfone group), and at least one selected from a phosphorous acid group and a carboxy group. It is more preferred, and a phosphorous acid group is particularly preferred. The phosphorous acid group is the same as the phosphorous acid group that the first cellulose fiber may have. When both the first cellulose fiber and the second cellulose fiber have an ionic substituent, the ionic substituent of the first cellulose fiber and the ionic substituent of the second cellulose fiber are the same but different. They may be the same, but they are preferably the same.

The amount of the ionic substituent introduced into the second cellulose fibers is, for example, preferably 0.1 mmol/g or more, more preferably 0.3 mmo/g or more per 1 g (mass) of the second cellulose fibers. , is more preferably 0.5 mmol/g or more, still more preferably 0.7 mmol/g or more, and particularly preferably 1.0 mmol/g or more. In addition, the amount of the ionic substituent introduced into the second cellulose fiber is preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less, per 1 g (mass) of cellulose fiber. It is more preferably 0.00 mmol/g or less. Here, the unit mmol/g indicates the amount of substituents per 1 g of mass of the second cellulose fiber when the counter ion of the anionic group is hydrogen ion (H ⁺ ), for example.

The amount of ionic substituents introduced into the second cellulose fiber can be measured, for example, by a neutralization titration method. In the measurement by the neutralization titration method, the introduced amount is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing the second cellulose fibers. A specific method for measuring the amount of introduced ionic substituents is the same as the method for measuring the amount of introduced ionic substituents in the first cellulose fiber. When measuring the introduction amount of the ionic substituents in the first cellulose fibers, fibrillation treatment is performed before the treatment with the strongly acidic ion exchange resin, but the ionic substitution in the second cellulose fibers When measuring the amount of groups to be introduced, the fibrillation treatment does not have to be performed before the treatment with the strongly acidic ion exchange resin.

The content of the second cellulose fibers is preferably 1% by mass or more, more preferably 5% by mass or more, and 10% by mass with respect to the total mass of the cellulose fibers contained in the sheet of the present embodiment. % or more, more preferably 15 mass % or more, and particularly preferably 20 mass % or more. In addition, the content of the second cellulose fibers is preferably 90% by mass or less, more preferably 80% by mass or less, and 70% by mass or less with respect to the total mass of the cellulose fibers contained in the sheet. is more preferably 50% by mass or less, even more preferably 40% by mass or less, and particularly preferably 30% by mass or less. The content of the second cellulose fibers may be 100% by mass with respect to the total mass of the cellulose fibers contained in the sheet of this embodiment.

<Manufacturing process of fine fibrous cellulose>
<Textile raw material>
Microfibrous cellulose is produced from fibrous raw materials containing cellulose. The fibrous raw material containing cellulose is not particularly limited, but pulp is preferably used because it is readily available and inexpensive. Pulp includes, for example, wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP). ) and chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemigroundwood pulp (CGP), groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP) A mechanical pulp etc. are mentioned. Non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lints, and non-wood-based pulps such as hemp, straw, and bagasse. The deinked pulp is not particularly limited, but includes, for example, deinked pulp made from waste paper. The pulp 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, for example, from the viewpoint of availability. In addition, among wood pulps, the cellulose ratio is high and the yield of fine fibrous cellulose at the time of defibration is high, and the decomposition of cellulose in the pulp is small, and fine fibrous cellulose of long fibers with a large axial ratio can be obtained. From the point of view, for example, chemical pulp is more preferable, and kraft pulp and sulfite pulp are more preferable.

As the fiber raw material containing cellulose, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria can be used. Fibers formed by straight-chain nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used instead of fiber raw materials containing cellulose.

<Phosphorus oxoacid group introduction step>
When the fine fibrous cellulose has a phosphorous acid group, the process for producing the fine fibrous cellulose includes a phosphorous acid group-introducing step. The phosphorus oxoacid group-introducing step is the same as the phosphorus oxoacid group-introducing step in the first cellulose fiber production step.

<Carboxy Group Introduction Step>
When the fine fibrous cellulose has a carboxy group, the production process of the fine fibrous cellulose includes a carboxy group introduction step. The carboxy group-introducing step is the same as the carboxy group-introducing step in the first cellulose fiber production step.

<Washing process>
In the method for producing fine fibrous cellulose according to the present embodiment, the phosphorous acid group-introduced fiber can be subjected to a washing step, if necessary. The washing step is the same step as the first washing step in the manufacturing process of the cellulose fibers.

<Alkali treatment process>
When producing fine fibrous cellulose, the fiber raw material may be subjected to alkali treatment between the ionic substituent introduction step and the fibrillation treatment step described later. The alkali treatment method is the same as the alkali treatment method in the first manufacturing process of the cellulose fibers. In addition, after the alkali treatment step, the cleaning step described above may be further provided.

<Fibrillation treatment>
Fine fibrous cellulose is obtained by defibrating the fibers in the fibrillation treatment step. In the defibration treatment process, for example, a fibrillation treatment device can be used. The fibrillation treatment device is not particularly limited, but for example, a high-speed fibrillator, a grinder (stone mill type pulverizer), a high pressure homogenizer, an ultra-high pressure homogenizer, a high pressure impact type pulverizer, a ball mill, a bead mill, a disk refiner, a conical refiner, and a biaxial refiner. A kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, or the like can be used. Among the above defibration equipment, it is more preferable to use a high-speed fibrillation machine, a high-pressure homogenizer, and an ultrahigh-pressure homogenizer, which are less affected by the grinding media and less likely to cause contamination.

In the fibrillation treatment step, the fibers are preferably diluted with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from organic solvents such as water and polar organic solvents can be used. The polar organic solvent is not particularly limited, but is preferably alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, and the like. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol and the like. Examples of polyhydric alcohols include ethylene glycol, propylene glycol and glycerin. Ketones include acetone, methyl ethyl ketone (MEK), and the like. 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 and the like. Examples of esters include ethyl acetate and butyl acetate. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP) and the like.

The solid content concentration of the fine fibrous cellulose at the defibration treatment can be appropriately set. In addition, the slurry obtained by dispersing the fibers in the dispersion medium may contain solids other than the ionic substituent-introduced fibers, such as urea having hydrogen bonding properties.

(ratio)
The mass ratio of the first cellulose fiber to the second cellulose fiber (first cellulose fiber: second cellulose fiber) is preferably 30:70 to 90:10, and 40:60 to 90:10. more preferably 60:40 to 90:10, particularly preferably 70:30 to 90:10. The mass ratio of the first cellulose fibers and the second cellulose fibers may be first cellulose fibers:second cellulose fibers=0:100. Here, the first cellulose fibers in the sheet can be observed, for example, with a scanning electron microscope (S-3600N, manufactured by Hitachi High-Technologies Corporation). Also, the second cellulose fibers can be observed, for example, with a high-resolution field emission scanning electron microscope (S-5200, manufactured by Hitachi, Ltd.). Based on such observation, the mass ratio may be calculated from the volume ratio of each fiber. However, the mixing ratio of each cellulose fiber in the sheet manufacturing process, which will be described later, is the same as the ratio of the first cellulose fiber and the second cellulose fiber in the sheet.

(other fibers)
The sheet of this embodiment may contain other cellulose fibers in addition to the first cellulose fibers and the second cellulose fibers. Other cellulose fibers include, for example, highly beaten pulp obtained by beating the first cellulose fibers to a fiber width of more than 1 μm and less than 10 μm. Here, the fiber width of other fibers is the fiber width of trunk fibers of cellulose fibers. For example, when the other fibers are fibrillated cellulose fibers, the fiber width of the other fibers is not the fiber width of the fibrillated and branched fibers but the fiber width of the stem fibers.

Beating of other cellulose fibers can be performed, for example, using a defibration treatment apparatus. The fibrillation treatment device is not particularly limited. Examples thereof include high-speed defibrators, grinders (stone mill-type grinders), high-pressure homogenizers, ultra-high-pressure homogenizers, CLEARMIX, high-pressure collision-type grinders, ball mills, bead mills, disk-type refiners, and conical refiners. In addition, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, or a wet pulverizing device can be used as appropriate.

(Water-soluble polymer/low molecular compound)
The sheet of this embodiment may further contain a water-soluble polymer. Water-soluble polymers include, for example, carboxyvinyl polymer, polyvinyl alcohol (PVA), alkyl methacrylate/acrylic acid copolymer, polyvinylpyrrolidone, sodium polyacrylate, polyethylene glycol, diethylene glycol, triethylene glycol, polyethylene oxide, propylene glycol, di Synthetic water-soluble polymers exemplified by propylene glycol, polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, and polyacrylamide; xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, Polysaccharide thickeners exemplified by alginic acid, pullulan, carrageenan, and pectin; cellulose derivatives exemplified by carboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose; cationic starch, raw starch, oxidized starch, etherified starch, Starches exemplified by esterified starch and amylose; glycerins exemplified by polyglycerin; hyaluronic acid, metal salts of hyaluronic acid, and the like. Among these, the water-soluble polymer is preferably polyvinyl alcohol.

Also, the sheet of the present embodiment may contain a hydrophilic low-molecular-weight compound instead of the water-soluble polymer. Hydrophilic low-molecular-weight compounds include glycerin, diglycerin, erythritol, xylitol, sorbitol, galactitol, and mannitol, but are not particularly limited.

The content of the water-soluble polymer or hydrophilic low-molecular-weight compound in the sheet 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 entire cellulose fibers. It is more preferably 1.0 parts by mass or more, and particularly preferably 5.0 parts by mass or more. In addition, the content of the water-soluble polymer is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and 30 parts by mass or less with respect to 100 parts by mass of the entire cellulose fiber. More preferably, it is particularly preferably 20 parts by mass or less. By setting the content of the water-soluble polymer or hydrophilic low-molecular-weight compound within the above range, the strength of the sheet can be more effectively improved.

(paper strength agent)
The sheet of the present embodiment preferably further contains a paper strength agent. This makes it possible to further improve the strength of the sheet. Paper strength agents include dry strength agents and wet strength agents. Examples of dry paper strength agents include cationized starch, polyacrylamide (PAM), carboxymethyl cellulose (CMC), and acrylic resins. Examples of wet paper strength agents include polyamide epihalohydrin, urea, melamine, and thermally crosslinkable polyacrylamide. Among others, the sheet of the present embodiment preferably contains polyamine polyamide epihalohydrin.

Polyamine polyamide epihalohydrin is a cationic thermosetting resin obtained by subjecting an aliphatic dibasic carboxylic acid or a derivative thereof and a polyalkylene polyamine to thermal condensation to synthesize a polyamide polyamine, and then reacting the polyamide polyamine with epihalohydrin. is. Since the polyamine polyamide epihalohydrin is an aqueous resin, the polyamine polyamide epihalohydrin can be added as an aqueous solution to the sheet-forming slurry.

Examples of polyamine polyamide epihalohydrin include polyamine polyamide epichlorohydrin, polyamine polyamide epibromohydrin, and polyamine polyamide epiiodohydrin.

The content of the paper strength agent in the sheet is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and 0.5 parts by mass with respect to 100 parts by mass of cellulose fibers. It is more preferably 2.0 parts by mass or more, and particularly preferably 2.0 parts by mass or more. In addition, the content of the paper strength agent is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and further preferably 30 parts by mass or less with respect to 100 parts by mass of the cellulose fiber. It is preferably 15 parts by mass or less, more preferably 7.0 parts by mass or less. By setting the content of the paper strength agent within the above range, the strength of the sheet can be improved more effectively.

The sheet of the present embodiment preferably contains both polyvinyl alcohol and polyamine polyamide epihalohydrin. By containing both of them, the adhesion between the fine fibrous cellulose-containing layer and the pulp fiber-containing layer in the pre-sheet of the present embodiment is excellent. Therefore, as a result, the pre-sheet and molded article of the present embodiment are excellent in mechanical properties.

(Optional component)
The sheet of the present embodiment may contain optional components other than the components described above. Optional components include, for example, preservatives, antifoaming agents, lubricants, UV absorbers, dyes, pigments, stabilizers, surfactants, sizing agents, coagulants, retention improvers, bulking agents, drainage improvers, pH adjusters, fluorescent whitening agents, pitch control agents, slime control agents, antifoaming agents, water retention agents, dispersing agents and the like can be mentioned.

The content of the optional component contained in the sheet of the present embodiment is preferably 50% by mass or less, more preferably 40% by mass or less, and 30% by mass or less with respect to the total mass of the sheet. is more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

(resin layer)
A resin layer may be provided on the surface of the sheet of the present embodiment, which is in contact with the pulp fiber-containing layer. The resin layer is preferably a resin layer formed by coating (coated resin layer).

The resin layer is a layer containing a modified polyolefin resin, and preferably a layer containing a modified polyolefin resin as a main component. Here, the main component refers to a component that is contained in an amount of 50% by mass or more with respect to the total mass of the resin layer. The content of the modified polyolefin resin is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and 90% by mass of the total mass of the resin layer. % by mass or more is particularly preferred. In addition, the content of the modified polyolefin resin may be 100% by mass.
A modified polyolefin resin is obtained by modifying a polyolefin resin. Methods for modifying the polyolefin resin include acid modification, chlorination, and acrylic modification. Among them, the modified polyolefin resin is preferably an acid-modified polyolefin resin. At this time, the acid-modified component is preferably an unsaturated carboxylic acid component. The unsaturated carboxylic acid component is a component derived from an unsaturated carboxylic acid or its anhydride. acid, fumaric acid, crotonic acid and the like. Among them, the unsaturated carboxylic acid component is preferably at least one selected from acrylic acid, methacrylic acid, maleic acid and maleic anhydride, and particularly at least one selected from maleic acid and maleic anhydride. preferable.

Examples of the olefin component constituting the modified polyolefin resin include alkenes having 2 to 6 carbon atoms such as ethylene, propylene, isobutylene, 1-butene, 1-pentene and 1-hexene. The modified polyolefin resin may be a copolymer having two or more of the above olefin components. Moreover, the modified polyolefin resin may contain other copolymerization components such as vinyl acetate and norbornenes in addition to the above olefin components.

Among them, the modified polyolefin resin is preferably a modified polypropylene resin, more preferably an acid-modified polypropylene resin, and even more preferably a maleated polypropylene resin or a maleated anhydride polypropylene resin.

It is also preferred that the modified polyolefin resin is a chlorinated polyolefin resin. In this case, the chlorine content is preferably 5% by mass or more, more preferably 10% by mass or more, relative to the total mass of the chlorinated polyolefin resin. Also, the chlorine content is preferably 50% by mass or less with respect to the total mass of the chlorinated polyolefin resin.

The modified polyolefin resin is particularly preferably an acid-modified chlorinated polyolefin resin. Among them, the modified polyolefin resin is preferably a maleated anhydride-chlorinated polyolefin resin or a maleated-chlorinated polyolefin resin. By using an acid-modified chlorinated polyolefin resin, it is possible to obtain a laminated sheet with more excellent transparency.

The main chain of the modified polyolefin resin preferably has a graft chain containing a carboxy group at its terminal. As used herein, the graft chain is a linking group that binds to the main chain of the modified polyolefin resin and a group that has a carboxyl group at the end of the linking group. The linking group constituting the graft chain is preferably an alkylene group having 1 to 10 carbon atoms. That is, in a preferred embodiment of the present invention, the modified polyolefin resin has a polyolefin main chain skeleton, and an —R—COOH group (R represents an alkylene group having 1 to 10 carbon atoms) grafted onto the main chain skeleton. It is a graft polymer.

The modified polyolefin resin may be a water-based modified polyolefin resin, but is preferably an organic solvent-based modified polyolefin resin. When the modified polyolefin resin is an organic solvent-based modified polyolefin resin, the resin composition forming the resin layer containing the modified polyolefin resin contains the organic solvent. Examples of organic solvents used in this case include aliphatic organic solvents, alcohol organic solvents, ketone organic solvents, ester organic solvents, ether organic solvents, aromatic organic solvents, and cyclic alkane organic solvents. can. Among them, the organic solvent is preferably an aromatic organic solvent or a cyclic alkane organic solvent. Examples of aromatic organic solvents include benzene, toluene, and xylene. Examples of cyclic alkane-based organic solvents include cyclohexane, cyclopentane, cyclooctane, methylcyclohexane, and the like. In addition, when a resin layer is formed from a resin composition containing an organic solvent as described above, a small amount of the organic solvent remains in the resin layer without being volatilized. Therefore, the resin layer may contain an aromatic organic solvent or a cyclic alkane organic solvent.

A commercially available product may be used as the modified polyolefin resin. Examples of commercially available products include Hardren TD-15B manufactured by Toyobo, Hardren F-2MB manufactured by Toyobo, and Arrowbase SB-1230N manufactured by Unitika. The resin layer may contain an adhesion aid in addition to the modified polyolefin resin.

(Manufacturing method of sheet)
The sheet manufacturing method of the present embodiment includes a step of forming a sheet from a slurry containing second cellulose fibers having a fiber width of 1000 nm or less and optionally further containing first cellulose fibers having a fiber width of 10 μm or more. include. The method for manufacturing the sheet of the present embodiment will be described below on the premise that the first cellulose fibers are used.

The sheet of the present embodiment includes a first layer containing both first cellulose fibers having a fiber width of 10 μm or more and second cellulose fibers having a fiber width of 1000 nm or less, and a first layer having a fiber width of 10 μm or more. In the case of a multilayer sheet having a second layer containing both cellulose fibers and second cellulose fibers having a fiber width of 1000 nm or less, the first cellulose fibers having a fiber width of 10 μm or more and a fiber width of 1000 nm After forming the first layer (or the second layer) from a slurry containing the following second cellulose fibers, on the layer, the first cellulose fibers having a fiber width of 10 μm or more and the second cellulose fibers having a fiber width of 1000 nm or less A step of forming a second layer (or first layer) by applying a slurry containing cellulose fibers of No. 2 may be provided. Also, after forming the first layer and the second layer from a slurry containing the first cellulose fibers having a fiber width of 10 μm or more and the second cellulose fibers having a fiber width of 1000 nm or less, these layers are stacked. The combination may form a multi-layer sheet having a first layer and a second layer.

The solid content concentration in the slurry in which the first cellulose fibers and the second cellulose fibers are dispersed is preferably 10% by mass or less, more preferably 5% by mass or less. Moreover, the solid content concentration contained in the slurry is preferably 0.01% by mass or more.

Here, the water retention of the first cellulose fibers is preferably 220% or more, more preferably 230% or more, and even more preferably 240% or more. Also, the water retention of the first cellulose fibers is preferably 600% or less. Note that the water retention of the first cellulose fiber is described in J. Am. It is a value measured according to TAPPI-26. In the sheet manufacturing process of the present embodiment, by using the first cellulose fibers having a water retention of 220% or more, a slurry in which the fibers are uniformly dispersed can be obtained. Moreover, by using the first cellulose fibers having a water retention of 220% or more, it is possible to suppress aggregation of the cellulose fibers even in a slurry having a high cellulose fiber concentration.

<Papermaking process>
When papermaking the slurry containing the 1st cellulose fiber and the 2nd cellulose fiber, papermaking of the slurry is carried out with a paper machine. The paper machine used in the papermaking process is not particularly limited, but examples thereof include continuous paper machines such as fourdrinier, cylinder, and inclined paper machines, and multi-layer paper machines combining these. In the paper-making process, a known paper-making method such as hand-making may be employed.

The papermaking process is carried out by filtering the slurry with a wire and dehydrating it to obtain a wet paper sheet, which is then pressed and dried. The filter cloth used for filtering and dehydrating the slurry is not particularly limited, but it is more preferable that, for example, fibrous cellulose does not pass through and the filtration rate does not become too slow. Such a filter cloth is not particularly limited, but preferably includes, for example, a sheet, a fabric, or a porous membrane made of an organic polymer. Although the organic polymer is not particularly limited, non-cellulose organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferred. In this embodiment, for example, a polytetrafluoroethylene porous film having a pore size of 0.1 μm or more and 20 μm or less, or a polyethylene terephthalate or polyethylene fabric having a pore size of 0.1 μm or more and 20 μm or less can be used.

In the sheeting process, a method for producing a sheet from a slurry includes, for example, a water squeezing section for discharging a slurry containing cellulose fibers onto the upper surface of an endless belt and squeezing a dispersion medium from the discharged slurry to form a web; A drying section that dries the web to form a sheet. An endless belt is provided from the water squeezing section to the drying section, and the web produced in the water squeezing section is conveyed to the drying section while being placed on the endless belt.

The dehydration method used in the papermaking process is not particularly limited, and includes, for example, dehydration methods commonly used in the manufacture of paper. Among these, the method of dehydrating with a fourdrinier, a circular net, an inclined wire, or the like and then further dehydrating with a roll press is preferable. Moreover, the drying method used in the papermaking process is not particularly limited, but includes, for example, methods used in the manufacture of paper. Among these, a drying method using a cylinder dryer, Yankee dryer, hot air drying, near-infrared heater, infrared heater, or the like is more preferable.

After such a papermaking process, one side of the obtained sheet may be calendered. Alternatively, a rewet casting process may be performed in which one surface is re-wet with a re-wetting liquid and pressed against a casting drum.

<Coating process>
In the step of applying the slurry containing the first cellulose fibers and the second cellulose fibers onto the substrate (coating step), for example, the slurry (coating liquid) containing fibrous cellulose is applied onto the substrate. A sheet can be obtained by peeling the sheet formed by drying this from the substrate. In addition, sheets can be continuously produced by using a coating device and a long base material.

The material of the base material used in the coating process is not particularly limited, but a material with high wettability to the slurry may suppress shrinkage of the sheet during drying, but the sheet formed after drying is easy. It is preferable to select a material that can be easily peeled off. Among them, a resin film or plate or a metal film or plate is preferable, but is not particularly limited. For example, resin films and plates such as polypropylene, acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polycarbonate, and polyvinylidene chloride, metal films and plates such as aluminum, zinc, copper, and iron plates, and those whose surfaces have been oxidized. , a stainless steel film or plate, a brass film or plate, or the like can be used.

In the coating process, when the viscosity of the slurry is low and it spreads on the base material, a dam frame is fixed on the base material in order to obtain a sheet with a predetermined thickness and basis weight. may Although the damming frame is not particularly limited, it is preferable to select a frame that allows easy peeling of the edge of the sheet that adheres after drying, for example. From such a point of view, a molded resin plate or metal plate is more preferable. In this embodiment, for example, resin plates such as polypropylene plates, acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polycarbonate plates, and polyvinylidene chloride plates, and metal plates such as aluminum plates, zinc plates, copper plates, iron plates, etc. , and those whose surfaces have been oxidized, and those obtained by molding a stainless steel plate, a brass plate, or the like can be used.

The coating machine for coating the slurry on the base material is not particularly limited, but for example, a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. can be used. A die coater, a curtain coater, and a spray coater are particularly preferable because they can make the thickness of the sheet more uniform.

The slurry temperature and the ambient temperature when the slurry is applied to the substrate are not particularly limited, but for example, it is preferably 5 ° C. or higher and 80 ° C. or lower, more preferably 10 ° C. or higher and 60 ° C. or lower, and 15 ° C. It is more preferably 50° C. or higher, and particularly preferably 20° C. or higher and 40° C. or lower. If the coating temperature is at least the above lower limit, the slurry can be more easily coated. When the coating temperature is equal to or lower than the above upper limit, volatilization of the dispersion medium during coating can be suppressed.

In the coating step, the slurry is applied to the substrate so that the finished basis weight of the sheet is preferably 5 g/m ² or more and 500 g/m ² or less, more preferably 10 g/m 2 or more and 300 g/m ² or less. It is preferable to apply to The coating process can also produce a thin film sheet having a basis weight of 30 g/m ² or less, for example.

The coating step includes the step of drying the slurry applied onto the substrate, as described above. The step of drying the slurry is not particularly limited, but may be performed by, for example, a non-contact drying method, a method of drying while restraining the sheet, or a combination thereof.

The non-contact drying method is not particularly limited, but for example, a method of drying by heating with hot air, infrared rays, far infrared rays, or near infrared rays (heat drying method), or a method of drying in a vacuum (vacuum drying method) is applied. can do. Although the heat drying method and the vacuum drying method may be combined, the heat drying method is usually applied. Drying with infrared rays, far-infrared rays, or near-infrared rays is not particularly limited, but can be performed using, for example, an infrared device, a far-infrared device, or a near-infrared device.

The heating temperature in the heat drying method is not particularly limited, but is preferably 20° C. or higher and 150° C. or lower, more preferably 25° C. or higher and 105° C. or lower. If the heating temperature is equal to or higher than the above lower limit, the dispersion medium can be rapidly volatilized. Further, if the heating temperature is equal to or lower than the above upper limit, it is possible to suppress the cost required for heating and suppress discoloration of the cellulose fibers due to heat.

<1-6. Pre-sheet>
The outermost layer of the pre-sheet of the present embodiment is a fine fibrous cellulose-containing layer. Therefore, excellent mechanical properties can be obtained when formed into a molded article.

The ratio of the content of fine fibrous cellulose to the pre-sheet of the present embodiment is 0.5% by mass or more. Moreover, the ratio of the content of fine fibrous cellulose to the layer containing fine fibrous cellulose is 10% by mass or more. Therefore, excellent mechanical properties can be obtained when formed into a molded article.

The content ratio of fine fibrous cellulose to the pre-sheet of the present embodiment is preferably 1.0% by mass or more. Also, the content ratio of fine fibrous cellulose to the pre-sheet of the present embodiment is preferably less than 10% by mass, more preferably 8.0% by mass or less, and even more preferably 5.0% by mass or less.

The content ratio of fine fibrous cellulose to the fine fibrous cellulose-containing layer of the present embodiment is preferably 15% by mass or more, more preferably 20% by mass or more. In addition, the content ratio of fine fibrous cellulose to the fine fibrous cellulose-containing layer of the present embodiment is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

The content ratio of pulp fibers to the pre-sheet of the present embodiment is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. In addition, the content ratio of pulp fibers to the pre-sheet of the present embodiment is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

The total ratio of (1) the pulp fiber content in the pulp fiber layer and (2) the cellulose content in the fine fibrous cellulose-containing layer to the pre-sheet of the present embodiment is preferably more than 50% by mass. , 51% by mass or more is more preferable. When the ratio is more than 50% by mass, the pre-sheet and molded article of the present embodiment are more environmentally friendly, and can contribute to biodegradability after disposal and reduction of incinerator load during incineration.

≪2. Molded body≫
The molded article of the present embodiment is obtained by heating and then pressurizing the pre-sheet of the present embodiment. The temperature during heating is preferably a temperature that exceeds the melting point of the thermoplastic resin. The pressurizing condition is preferably 1.5 to 10 MPa.

The molded article of the present embodiment can be suitably used for automotive parts, electric equipment parts, electronic equipment parts, or precision equipment parts.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the embodiments.

(Example 1)
<Preparation of sheet containing fine fibrous cellulose containing resin layer>
[Preparation of phosphorylated pulp]
As raw material pulp, softwood kraft pulp manufactured by Oji Paper (solid content 93% by mass, basis weight 208 g / m ² sheet, defibered and measured according to JIS P 8121-2: 2012 Canadian standard freeness (CSF ) used 700 ml). The raw material pulp was subjected to a phosphorylation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea is added to 100 parts by mass (absolute dry mass) of the raw material pulp to obtain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water. A chemical-impregnated pulp was obtained by adjusting as follows. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 200 seconds to introduce phosphoric acid groups into cellulose in the pulp to obtain phosphorylated pulp.

[Washing process]
Then, the obtained phosphorylated pulp was washed. In the washing treatment, a pulp dispersion liquid obtained by pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorylated pulp is stirred so that the pulp is uniformly dispersed, and then filtration and dehydration are repeated. gone. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.

[Neutralization treatment]
Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 or more and 13 or less. . Next, the phosphorylated pulp slurry was dehydrated to obtain neutralized phosphorylated pulp.

[Washing process]
Next, the washing treatment was performed on the phosphorylated pulp after the neutralization treatment. The phosphorylated pulp thus obtained was subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption due to phosphate groups was observed near 1230 cm ⁻¹ , confirming that phosphate groups were added to the pulp. In addition, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffraction device, it was found that the A typical peak was confirmed, confirming that it had cellulose type I crystals. The amount of phosphate groups (first dissociated acid amount) measured by the measurement method described later was 1.45 mmol/g. Moreover, the fiber width measured by the measuring method described later was 30 μm. Ion-exchanged water was added to the obtained phosphorylated pulp to obtain a first cellulose fiber dispersion containing first cellulose fibers having a solid content concentration of 2% by mass.

[Miniaturization]
The first cellulose fiber dispersion obtained by the above method is treated twice with a wet atomization device (manufactured by Sugino Machine Co., Ltd., Starburst) at a pressure of 200 MPa to obtain a second cellulose fiber. A second cellulose fiber dispersion was obtained. X-ray diffraction confirmed that the second cellulose fibers maintained cellulose type I crystals. The amount of phosphate groups (first dissociated acid amount) measured by the measurement method described later was 1.45 mmol/g. Further, the fiber width measured by the measuring method described later was 3 to 5 nm.

[Sheet]
The first cellulose fiber is 75 parts by mass, the second cellulose fiber is 25 parts by mass, polyvinyl alcohol (PVA) is 10 parts by mass, and polyamine polyamide epichlorohydrin (PAE) is 5 parts by mass. 1 cellulose fiber dispersion, 2nd cellulose fiber dispersion, polyvinyl alcohol solution (manufactured by Nippon Synthetic Chemical Industry, Gohsenex Z-200), and polyamine polyamide/epichlorohydrin solution (manufactured by Arakawa Chemical Industries, Arafix 255) were mixed to obtain a coating liquid 1. The solid content concentration of Coating Liquid 1 was adjusted to 0.5% by mass. Next, the coating liquid 1 was measured so that the basis weight of the resulting sheet (layer composed of the solid content of the coating liquid) was 180 g/m ² , coated on a commercially available acrylic plate, and heated at 50 ° C. was dried in a constant temperature dryer. A metal frame for damming (a metal frame with an inner dimension of 180 mm×180 mm and a height of 5 cm) was arranged on the acrylic plate so as to obtain a predetermined basis weight. Next, the dried sheet was separated from the acrylic plate to obtain a sheet containing the first cellulose fibers and the second cellulose fibers. The first cellulose fibers had a fiber width of 29 μm and a water retention rate of 371%, and the second cellulose fibers had a fiber width of 3 to 5 nm.

A maleic anhydride-modified polypropylene resin solution (Hardlen NS-2000, manufactured by Toyobo Co., Ltd.: polypropylene resin component 15% by mass, methylcyclohexane 75% by mass, butyl acetate 10% by mass) was peeled from the acrylic plate of the fine fibrous cellulose-containing sheet. A coating layer was obtained by coating the surface opposite to the side using a bar coater. Thereafter, the fine fibrous cellulose-containing sheet on which the coating layer was formed was heated at 100° C. for 1 hour to cure the coating layer, thereby turning the coating layer into a resin layer. As a result, a fine fibrous cellulose-containing sheet containing a resin layer was obtained. The thickness of the resin layer was 5 μm.

<Preparation of pulp fiber sheet>
NBKP was defibrated using a swirling jet stream defibrator to obtain defibrated chopped fibers. The processing wind speed in the defibrator was 45 m/min, and the flow was turbulent with a baffle provided in the apparatus.

Next, the obtained defibrated chopped fiber and core-sheath type heat-fusible composite fiber (PET/PE composite core-sheath fiber, core melting point 260 ° C., sheath melting point 100 ° C., fineness 2.2 dtex, fiber length 5 mm ) were uniformly mixed with an air flow in a ratio (mass ratio) of 73/27 to obtain a fiber mixture.

Next, using the web forming apparatus 1 shown in FIG. 1, an airlaid web was formed from the fiber mixture. Specifically, the first carrier sheet 41 was let out by the first carrier sheet supplying means 40 onto the air-permeable endless belt 20 mounted on the conveyor 10 and running. In Example 1, as the first carrier sheet 41, a reinforcing fiber sheet (basis weight: 100 g/m ² ) manufactured by forming a sheet of fibrillated chopped fibers with a carding machine and then entangling the sheets with a needle punch was used. The “basis weight” was measured in accordance with “Paper and paperboard—Method for measuring basis weight” described in JIS P8124:2011.

While sucking the permeable endless belt 20 with the suction box 60 , the fiber mixture was dropped and deposited on the first carrier sheet 41 from the fiber mixture supply means 30 together with the air flow. At that time, the fiber mixture was supplied so that the basis weight of the airlaid web portion was 180 g/m ² . Here, the air-laid web portion is the portion of the pre-sheet that is to become the pulp fiber layer.

Next, a second carrier sheet 51 was laminated on the fiber mixture deposit on the first carrier sheet 41 by a second carrier sheet supplying means 50 to obtain an airlaid web-containing laminated sheet. In Example 1, as the second carrier sheet 51, a reinforcing fiber sheet (basis weight: 100 g/m ² ) manufactured by forming a sheet of fibrillated chopped fibers with a carding machine and then entangling the sheets with a needle punch was used. That is, in Example 1, the same reinforcing fiber sheet was used for the first carrier sheet 41 and the second carrier sheet 51 .

The air-laid web-containing laminated sheet thus obtained was passed through a box-type drier of a hot air circulation conveyor oven system and subjected to hot air treatment at a temperature of 140°C. After that, the first carrier sheet and the second carrier sheet were separated to obtain a pulp fiber sheet with a basis weight of 180 g/m ² .

<Preparation of molded body of the present embodiment>
First, a spunbond nonwoven fabric (basis weight: 40 g/m ² ) composed of polypropylene (PP) fibers was prepared. Next, the pulp fiber sheet (PF) was cut into a size of 20 cm x 20 cm, thereby obtaining 5 cut pieces.The SB and the CF were obtained after the hot press treatment described later, They are the thermoplastic resin layer and the pulp fiber layer, respectively.

Then, an 11-layer stack was produced by alternately stacking 6 SBs and 5 PFs so that the SBs were both surface layers (both end surface layers). Furthermore, a fine fibrous cellulose-containing sheet having a resin layer was overlaid on the SB such that the main surface of the SB, which is the outermost layer (outermost layer) of the laminate, and the main surface of the resin layer were in contact with each other. As a result, a laminated structure consisting of sheet A containing fine fibrous cellulose/resin layer A/laminate of 11 layers/resin layer B/sheet B containing fine fibrous cellulose was obtained. The fine fibrous cellulose-containing sheet A constitutes the surface layer, and the fine fibrous cellulose-containing sheet B constitutes the back layer. Next, the laminated structure was placed in a stainless steel mold having an opening of 20 cm x 20 cm and a depth of 2 mm. Next, the mold was set in a hot press, and the laminated structure was treated with hot air at a temperature of 140° C. to obtain a pulp fiber-containing pre-sheet of Example 1. The layer structure of the pulp fiber-containing pre-sheet of Example 1 is fine fibrous cellulose-containing layer A/resin layer A/pulp fiber-containing layer/resin layer B/fine fibrous cellulose-containing layer B. The pulp fiber-containing pre-sheet of Example 1 was preliminarily pressed at a temperature of 180° C. and a pressure of 1.5 MPa for 10 minutes, and further pressurized to 5 MPa for 15 minutes. After that, it was cooled at 5 MPa to obtain a molded body containing pulp fibers of Example 1. The layer structure of the pulp fiber-containing molding of Example 1 is fine fibrous cellulose-containing layer A/resin layer A/pulp fiber-containing layer/resin layer B/fine fibrous cellulose-containing layer B. However, the resin layer A and the resin layer B are thin films that cannot be recognized as layers. The pulp fiber-containing layer is composed of 6 thermoplastic resin layers and 5 pulp fiber layers.

(Example 2, Comparative Example 1)
In the same manner as in Example 1, except that the basis weight of the fine fibrous cellulose-containing sheet, the basis weight of the pulp fiber sheet, the mass ratio of each component, etc. are changed so that the numerical values and types are shown in Table 1. Pre-sheets and pulp fiber-containing compacts of Example 2 and Comparative Example 1 were obtained.

<Evaluation>
The flexural modulus, flexural strength, impact resistance, and impact force of the obtained molded article were measured by the following methods. The measurement results are shown in the table.

(Method for measuring flexural modulus and flexural strength of molded product)
Using a diamond cutter, the obtained molded product was cut into a width of 15 mm and a length of 100 mm to prepare a test piece. After measuring the thickness of the test piece, a three-point bending test was performed at a speed of 5 mm/min and a distance between fulcrums of 80 mm according to JIS K7074 "Bending test method for carbon fiber reinforced plastic". Elastic modulus and bending strength were measured. The values of flexural modulus and flexural strength were used as indices for judging the rigidity of the molded product. It was evaluated that the higher the numerical value, the higher the rigidity and the better the molded product.

(Method for measuring impact resistance of molded product)
Using a diamond cutter, the obtained molded article was cut into a width of 10 mm and a length of 100 mm to prepare a test piece. After measuring the thickness of the test piece, the impact resistance was measured by the "Charpy impact test for plastics" described in JIS K7111-1. The larger the value, the better the impact resistance and the stronger the impact.
(puncture impact force)
The puncture impact force was measured using a puncture impact force tester according to JIS K7211-2.

1 Web Forming Device 30 Fiber Mix Supply Means 41 First Carrier Sheet 51 Second Carrier Sheet A Airlaid Web

Claims (8)

A pulp fiber-containing pre-sheet having a fine fibrous cellulose-containing layer formed on at least a pulp fiber-containing layer,
The pulp fiber-containing layer contains pulp fibers and a thermoplastic resin,
The fine fibrous cellulose-containing layer is the outermost layer,
The content ratio of fine fibrous cellulose in the pulp fiber-containing pre-sheet is 0.5% by mass or more,
The content ratio of fine fibrous cellulose in the fine fibrous cellulose-containing layer is 10% by mass or more,
A pre-sheet containing pulp fibers. 2. The pre-sheet according to claim 1, wherein the content ratio of said pulp fibers in said pulp fiber-containing pre-sheet is 40 to 50% by mass. 3. The pre-sheet according to claim 1, wherein the content of fine fibrous cellulose in said pre-sheet is 1.0 to 5.0% by mass. The pre-sheet according to any one of claims 1 to 3, wherein the content ratio of the resin in the fine fibrous cellulose-containing layer is 70% by mass or less with respect to 100% by mass of the entire cellulose. The pre-sheet according to any one of claims 1 to 4, wherein the content ratio of fine fibrous cellulose in said fine fibrous cellulose-containing layer is 10 to 95% by mass. The pre-sheet according to any one of claims 1 to 5, wherein the pulp fiber-containing layer is composed of a pulp fiber layer and a thermoplastic resin layer. A molded body containing pulp fibers obtained by molding the pre-sheet alone or laminated body according to any one of claims 1 to 6. The pulp fiber-containing molded article according to claim 7, which is used for automobile parts, electrical equipment parts, electronic equipment parts, or precision equipment parts.

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