JP2001081686A - Cellulose fiber sheet and molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cellulosic fiber sheet that shows excellent resistance to water and high wet strength, is biodegradable and can be reprocessed together with used paper after being used. SOLUTION: One hundred parts by weight of cellulose fiber, for example, pulp or the like are formulated to 10-250 pts.wt. of a powder with an average particle size of 5-300 μm comprising at least one selected from the group consisting of casein, alginic acid and hemicellulose that is biodegradable, thermoplastic, soluble in organic solvent and is soluble in a weak alkali or a fibrous substance with an average particle of 5-100 μm and a fiber length of 1-20 mm whereby the objective fiber sheet is obtained. In addition, the sheet is hot-pressed to produce the objective formed body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention has excellent water resistance and wet strength when used in a natural environment, and has, in addition to biodegradability, dispersibility in a weak alkaline aqueous solution which can be reprocessed together with used paper after use. The present invention relates to a molded article and a cellulose fiber sheet as a raw material thereof.

[0002]

2. Description of the Related Art In recent years, as awareness of environmental protection has increased, recycling campaigns regarding containers and packaging materials have been spreading as a national effort involving not only administrative organizations but also manufacturers and citizen groups. Also, as for the recycling of paper products, the collection rate has reached over 50% as a symbol of the recycling campaign. Further improvement in the recovery rate is desired in the future, but there are paper products such as synthetic resin laminated paper and adhesive paper that are not suitable for recycling, which hinders reuse.

[0003] With regard to these paper products that are not suitable for recycling, there have been attempts to enable recycling by selecting materials that can be dissolved or dispersed in a weakly alkaline aqueous solution used in the process of recycling used paper. Has not been obtained. In particular, synthetic resin-laminated paper is often manufactured by melt-extruding a synthetic resin having melt moldability, and when using existing facilities, the selection of materials is greatly restricted and development is delayed.

[0004] As a material for producing and recycling a laminated paper using existing equipment, it is necessary to have a melt-forming processability and to have solubility or dispersibility in a weak alkaline aqueous solution. One that may be satisfactory is polyvinyl alcohol, which is marketed by Kuraray Co., Ltd. However, polyvinyl alcohol does not have water resistance and cannot be said to be a suitable material for widely used in household goods, industrial materials and the like.

On the other hand, polymer materials obtained by chemically modifying cellulose with dicarboxylic acid are widely known as having water resistance and being soluble in a weak alkaline aqueous solution. It is known that some cellulose derivatives having an acidic carboxyl group do not dissolve in an acidic or neutral aqueous solution such as tap water, but dissolve in an alkaline aqueous solution, for example, acetic anhydride and phthalic anhydride. Cellulose acetate phthalate obtained by esterifying cellulose with acid (C.
J. Malm et al., Ind. Eng. Chem., 32, 405 (1940)),
Those obtained by chemically modifying phthalic anhydride to hydroxyalkylalkylcellulose or hydroxyalkylcellulose (JP-B-47-6436, JP-B-51-4851)
No. 5) or those obtained by chemically modifying succinic anhydride to cellulose ether (Japanese Patent Publication No. 48-19552).
Many compounds have been used as photosensitive resin binders, enteric coating agents for pharmaceuticals, and the like. However, it is expensive and there is no example in which it is blended with cellulose fibers as a powder.

[0006] Biodegradable resins have been spotlighted in recent years as being suitable for environmental protection as well as recycling, and are expected to be applied to films, sheets, containers and the like for agriculture, horticulture or compost. I have. However, none of them has solubility or dispersibility in a weak alkaline aqueous solution in a used paper recycling process. As a substitute for a synthetic resin film or laminated paper, a biodegradable composite paper comprising a biodegradable resin powder having high water resistance and wet strength and cellulose fibers has been proposed (Japanese Patent Application Laid-Open No. 6-345944). And JP-A-8-269888), which do not have solubility or dispersibility in a weak alkaline aqueous solution. Therefore, a material that exhibits excellent water resistance and wet strength, has high rigidity, and can be reprocessed together with used paper after use has not yet been realized.

[0007]

DISCLOSURE OF THE INVENTION The present invention has excellent water resistance and wet strength when used in a natural environment, and, in addition to biodegradability, disperses in a weak alkaline aqueous solution that can be reprocessed together with used paper after use. An object of the present invention is to provide a molded article having:

[0008]

[Means for Solving the Problems]

In order to solve the above problems, the present invention employs the following configuration. That is, the present invention is a "cellulose fiber sheet formed from powder or fibers of cellulose fibers and a weak alkali-soluble resin".

In the present invention, the weak alkali-soluble resin preferably has thermoplastic or organic solvent solubility, and the weak alkali-soluble resin preferably has biodegradability.

When the weak alkali-soluble resin is a powder, the average particle diameter is preferably 5 to 300 μm.

In each of the above-mentioned inventions, it is particularly preferable that the weak alkali-soluble resin is selected from casein, alginic acid and hemicellulose.

The present invention includes a molded article obtained by heating and pressing the above-mentioned cellulose fiber sheet of the present invention. Here, the compact may be a sheet-like compact such as paper or a compact having a three-dimensional shape.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The term "weak alkali-soluble resin" as used in the present invention refers to a resin having a thickness of 50 .mu.m, formed into a sheet of 5 cm square, and heated to 50.degree.
It dissolves when stirred in 100 cc of H aqueous solution for 1 hour. The term “resin” means a synthetic or natural polymer substance.

The cellulose fiber sheet of the present invention is heated and pressurized to soften the weak alkali-soluble resin contained therein, and powder or fibers of the resin are fluidized and bonded to fill the voids between the cellulose fibers. , Rigidity, water resistance,
This is for forming a molded article having high strength and the like (the molded article of the present invention). Therefore, the weak alkali-soluble resin is preferably thermoplastic. However, even if it does not have thermoplasticity itself, any material may be used as long as it becomes thermoplastic by swelling with an organic solvent or water and the above-mentioned effect is obtained. Further, from the gist of the present invention, it is preferable that the weak alkali-soluble resin is also biodegradable.

Specific examples of the weak alkali-soluble resin having the above properties and usable in the present invention include those obtained by chemically modifying celluloses or starches with a carboxylic acid or an inorganic acid. As the celluloses, cellulose and cellulose derivatives can be used. As the cellulose derivative, acetyl group, propionyl group, acyl cellulose such as butyl group, methyl cellulose, alkyl cellulose such as ethyl group, hydroxyethyl group,
Examples thereof include cellulose derivatives such as hydroxyalkyl cellulose such as hydroxypropyl group and hydroxyalkylalkyl cellulose such as hydroxyethylmethyl group and hydroxyethylethyl group. It is desirable that these derivatives have a degree of substitution within a range having biodegradability.

As the starches, starch or starch derivatives can be used. Examples of the starch derivatives include acyl starch such as acetyl group, propionyl group and butyl group, alkyl starch such as methyl group and ethyl group, hydroxyalkyl starch such as hydroxyethyl group and hydroxypropyl group, hydroxyethylmethyl group and hydroxyethylethyl group. And the like. It is desirable that these derivatives have a degree of substitution within a range having biodegradability.

Examples of the above-mentioned celluloses or starches chemically modified with a carboxylic acid include those obtained by bonding a substituent such as a carboxymethyl group and a carboxyethyl group to form a carboxyether, succinic anhydride, and maleic anhydride. And carboxyacylated with a dibasic acid such as trimellitic anhydride, phthalic anhydride, and tetrahydrophthalic anhydride. Among them, in the case of acyl cellulose, the surface layer of powder or fiber can be partially saponified and used.

Another example of the weak alkali-soluble resin that can be used in the present invention is a polyvinyl alcohol-based copolymer. Specifically, maleic anhydride,
Mono- or dialkyl maleic acid ester, itaconic acid or its alkyl ester, acrylic acid, acrylic acid ester and the like are copolymerized and then saponified. Further, similarly to the above-mentioned celluloses, polyvinyl alcohol chemically modified with carboxy ether, dibasic acid or inorganic acid can also be used.

Other resins usable as the weak alkali-soluble resin of the present invention include poly (α-malic acid),
Examples include polylactides such as poly (β-malic acid) and poly (α, β-malic acid). Further, for example, natural materials which are neither thermoplastic nor organic solvent-soluble, such as casein, soybean protein, alginic acid, and hemicellulose, and which exhibit thermoplasticity by water, may be used in the same manner.

Further, other examples of the weak alkali-soluble resin that can be used in the present invention include a polymer electrolyte and a polymer electrolyte, a polymer electrolyte and a low molecular weight electrolyte, and an ionic complex composed of a polymer electrolyte and a metal ion. . This compound has high water resistance in a neutral aqueous solution, but dissolves when an ion pair is dissociated under acidic or alkaline conditions.
Many of them have thermoplasticity. As the polymer electrolyte, those having biodegradability are preferable, and carboxylic acid,
Polysaccharides, proteins, aliphatic polyesters, polyvinyl alcohols and the like having in their structure at least one of sulfonic acid, sulfate, phosphate, amine and their organic and inorganic salts can be used. Although not biodegradable, polyacrylic acid, carboxy-modified styrene (meth) acrylate copolymer, styrene butadiene (meth) acrylic acid copolymer, isobutylene maleic anhydride copolymer, polyallylamine, polyvinylamine , Polyacrylamide and the like, and at least one of their organic and inorganic salts can be used as necessary. As the low molecular weight electrolyte, an aliphatic electrolyte having at least one kind of a carboxylic acid, a sulfonic acid, a sulfate, a phosphate, an amine and a salt thereof in a structure can be used. As the metal ions, those which do not adversely affect the environment, such as calcium ions, are preferable.

In the present invention, the weak alkali-soluble resin is made into a powdery or fibrous form and is present in a cellulose fiber sheet. In the case of powder, the average particle size is 5 to 300
μm is preferred, and more preferably 10 to 150 μm. If it exceeds 300 μm, it will be difficult to sufficiently penetrate between the cellulose fibers, and if it is less than 5 μm, the yield in the papermaking process will be poor. In the case of a fibrous form, the average fiber diameter is preferably 5 to 100 μm. The fiber length is 1mm ~
20 mm is preferred.

In addition, in the case of powder or fiber, components other than the weak alkali-soluble resin may be contained therein as long as the weak alkali solubility is not impaired. Hereinafter, the powder or fiber of the weak alkali-soluble resin may be referred to as powder or the like. In addition, a weak organic acid, a phenol compound, an epoxy compound, a phosphite compound, a thiophosphite compound, etc. may be used alone or as a mixture of two or more as stabilizers for preventing thermal deterioration and preventing thermal coloring for the purpose of improving specific physical properties. It may be added. In addition, inorganic photodegradation accelerators such as titanium oxide, organic acid-based biodegradation accelerators, lubricants, antistatic agents, lubricants, additives such as conductive compounds, calcium carbonate, clay, talc, colloidal silica, etc. Inorganic pigments, wood flour, pulp, microfibrillated pulp,
Mixing of functional compounds such as an organic filler such as linters, an antibacterial agent, and a deodorant can be used at all. These components other than the weak alkali-soluble resin are contained in the powder or fiber in 5 parts.
0% by weight or less, more preferably,
20% by weight or less.

The cellulose fibers used in the fiber sheet of the present invention include mechanical pulp (MP), thermomechanical pulp (TMP), softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), and softwood unbleached kraft. Pulp (NUKP), unbleached kraft pulp (L
At least one kind can be selected from wood pulp such as UKP) and waste paper pulp, and non-wood pulp such as kenaf, linter and straw.

The amount of the powder or the like made of the weak alkali-soluble resin is 10 to 2 parts by weight based on 100 parts by weight of the cellulose fiber.
50 parts by weight are preferred. When the amount exceeds 250 parts by weight, the productivity of the fiber sheet decreases, and when the amount is less than 10 parts by weight, desired water resistance and wet strength cannot be obtained, which is not preferable.

It is possible to add a third component other than the cellulose fiber, the powder of the weak alkali-soluble resin, and the like. For example, a powdery or fibrous substance exhibiting thermoplastic or organic solvent solubility and acting as a binder can be mixed and used. In this case, those having biodegradability are particularly preferable, and biodegradable resins and starch are preferable. Examples of the biodegradable resin include polyalkylene alkanoates, poly α-hydroxy acids, poly β-hydroxy alkanoates, aliphatic polyesters such as poly ω-hydroxy alkanoates, cellulose acetate, cellulose propionate, cellulose acetate. Cellulose-based ones such as propionate, cellulose butyrate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose are exemplified. Examples of the starch include acetyl starch, propionyl starch, butyryl starch, methyl starch, ethyl starch, hydroxyethyl starch, hydroxypropyl starch and the like.

Further, in order to adjust the thermophysical properties, the solubility in organic solvents, the biodegradability, and the like of the biodegradable resin, a plasticizer may be blended with the resin. In this case, as the plasticizer that can be used, compounds that are commonly used in this field can be used.Examples include polyhydric alcohols such as ethylene glycol and glycerin, diethyl adipate, diethyl succinate, glycerin diacetate, and glycerin triacetate. Polyalkylene alkanoate polyol having an average molecular weight in the range of 300 to 3000, polycaprolactone diol, polycaprolactone triol, polycaprolactone tetraol, etc. Polycaprolactone polyol having an average molecular weight of 300 to 3000, and an average molecular weight of 300 to 300
0 polyethylene glycol and the like.

However, when the amount of the plasticizer is large, it is preferable to use a plasticizer that is soluble in water or an aqueous solution of a weak alkali in order to maintain the weak alkali solubility of the composition. Polyhydric alcohols such as glycerin monoacetate, glycerin diacetate, glycerin triacetate (triacetin)
And the like, polyethylene glycol having an average molecular weight in the range of 300 to 3,000, and the like are preferably used.
The amount of the plasticizer is preferably in a range that does not impair the weak alkalinity of the composite sheet. Further, the plasticizer may be blended in the powder so as to be uniform, or may be absorbed by a porous powder in an appropriate amount.

As the third component other than the biodegradable resin, cellulose fine powder, synthetic resin fiber, synthetic resin emulsion and the like can be used. The cellulose fine powder can be mixed with a biodegradable resin to be used in the form of powder or fiber.

The above-mentioned third component may be used alone or as a mixture, or may be used as a powder or fiber composed of a plurality of compounds. The third component is preferably 20% by weight or less based on the weak alkali-soluble resin. If it exceeds 20% by weight, the dispersibility of the molded article of the present invention in a weak alkaline aqueous solution is undesirably reduced.

When the weak alkali-soluble resin of the present invention, or a plasticizer and various additives are mixed, or the third component is produced, a dry method may be used if a kneader, a twin-screw kneader, a roll mill, a Banbury mixer or the like is usually used. There are no particular restrictions on the use of a wet type or a heated type. In some cases, it is preferable that the kneaded material is formed into a strand by using a strand die or the like, and then pelletized by a pelletizer.

The uniformly mixed weak alkali-soluble resin is
Manufacture pellets or coarse particles by methods widely used in this field such as mechanical pulverization method, freeze pulverization method, solvent method (dissolve in good solvent, precipitate with poor solvent, recover and dry) I do. Furthermore, crush and average particle size 300μ
m or less, or melt-spun to use as fibers.

The fiber sheet of the present invention comprising a powder or the like made of a weak alkali-soluble resin and cellulose fibers can be obtained by forming into a paper sheet by using papermaking techniques usually used in this field, It may be a wet nonwoven fabric. Further, it can also be obtained by applying a liquid in which powder of a weak alkali-soluble resin or the like is dispersed to paper made of cellulose fibers. Among them, when the sheet is formed by using the papermaking technique, the sheet can be formed by wet papermaking using a fourdrinier paper machine or a circular net paper machine, but fillers such as clay, calcium carbonate, and titanium dioxide can be used. It is preferable to appropriately mix a pigment, a dispersant, a sizing agent, a retention agent, a fixing agent, a wet paper strength enhancer, a dry paper strength enhancer, a biodegradable aliphatic polyester binder fiber, a wax emulsion and the like. The basis weight of the sheet thus obtained is preferably 30 to 500 g / m ² , more preferably 50 g / m ² .
３００300 g / m ² .

Regarding the use of the coating technique, at least one surface of a sheet made of cellulose fibers prepared in advance is applied to at least one side of the sheet.
It can be carried out by applying a liquid in which a powder or the like made of a weak alkali-soluble resin is dispersed. In this case, since a large amount of powder and the like can be present near the surface, water resistance can be efficiently realized. Examples of the coater used for coating include a bar coater, a blade coater, a gravure coater, a micro gravure coater, an offset gravure coater and the like usually used in this field.

The fiber sheet of the present invention thus formed is formed into a molded body by a heating and pressing treatment. The heating and pressing treatment may be performed in-line by using a drying or calendering part in the fiber sheet manufacturing process. Alternatively, it may be performed offline after the production of the fiber sheet. The heating and pressurizing treatment is, when the weak alkali-soluble resin has thermoplasticity, a method of passing the sheet through a drying zone that can be heated to a temperature at which flow starts, and after heating by the above method, further applying a suitable temperature and pressure. Or a method of passing between heated rolls that can be heated to about the temperature at which flow starts. In the case where the heating and pressurizing treatment is performed off-line, it is possible to simultaneously perform the heating treatment and the sheet molding in a heated mold by using a heating and compression molding method such as vacuum molding or pressure molding.

When the weak alkali-soluble resin does not have thermoplasticity but has solubility in an organic solvent, it is swollen with an organic solvent, and then formed into a molded article by heating and pressing. The molded body was heated and pressurized in a state where the surface layer of the powder or the like was swollen by the solvent, thereby bonding between the powder and the like and between the powder and the cellulose fiber and adding entanglement of the cellulose fiber. The entire sheet is integrally reinforced. As a method for swelling the powder or the like with an organic solvent, the sheet may be immersed in the solvent, or the solvent may be applied to the sheet. The solvent used for swelling the powder or the like is preferably a good solvent for efficiently swelling the powder or the like. The organic solvent varies depending on the weak alkaline aqueous solution-soluble resin constituting the powder and the like, for example, methanol, ethanol, alcohols such as propanol, ethylene glycol, ethylene glycol monoalkyl ether,
Glycols such as diethylene glycol, diethylene glycol monoalkyl ether, propylene glycol and propylene glycol monoalkyl ether, ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, hydrocarbons such as toluene and xylene, and water Etc. can be used. As a good solvent when cellulose acetate having an acetylation degree of 30 to 56% is used as a main component of the powder, acetone, acetone / water,
Examples include ethanol and ethanol / water. In addition, in order to control the complexation, a weak alkaline aqueous solution-soluble resin, a biodegradable resin, a plasticizer, and the like can be dissolved in a solvent.

When the powder or the like is neither thermoplastic nor organic solvent-soluble, but has a thermoplasticity manifested by water, it should be heated and pressurized in the same manner as in the case of the organic solvent-soluble condition, after containing an appropriate amount of water. Can be.

The thus obtained molded article of the present invention can be dissolved in weakly alkaline water by dissolving the weak alkali solubility, and the cellulose fibers can be easily recovered. In the present invention, the dispersibility of the weak alkali aqueous solution is determined by the evaluation described in <Evaluation method> in Examples described later, but the weak alkali-soluble resin in the molded body is dissolved, and the cellulose fibers and other additives are dispersed. Refers to the state of having done. The molded article of the present invention showing such a weak alkaline aqueous solution dispersibility,
In actual situations, for example, treatment with a weak alkaline aqueous solution such as an aqueous solution of about 0.005 to 0.2N NaOH,
It can be collected, reused and used.

The biodegradability is either buried in soil or
In accordance with IS-K-6950, it is possible to evaluate from weight loss and the like. However, since this test is an easy-degradability test method, when examining essential biodegradability, ASTM
A controlled environment such as soil or activated sludge containing microorganisms adapted to D-5338 or a compound used as a biodegradable resin can also be used. In the present invention, a molded product having dispersibility in a weak alkaline aqueous solution can be obtained by a method with extremely high productivity, and a packaging field such as a functional packaging material in which an olefin-based molded product has been conventionally used, and agriculture such as mulch. It can be applied to a wide range of fields from use in the environment to daily necessities such as the field of materials, the field of construction materials such as anti-condensation films, and the field of printing base materials such as outdoor posters and advertisements.

[0040]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but it should not be construed that the invention is limited thereto. <Example 1> Cellulose acetate phthalate (manufactured by Wako Pure Chemical Industries, Ltd.) was cooled to liquid nitrogen temperature, and then adjusted to a powder having an average particle diameter of 65 µm by a pulverizer.

Next, the Canadian Standard Freeness (hereinafter CSF)
To 150 parts by weight of powder adjusted to an average particle size of 65 μm, based on 100 parts by weight of NBKP beaten to 520 ml according to JIS-P-8209.
A sheet of the invention of 5 g / m ² was produced. Further, the sheet produced above was subjected to a pressure treatment for 30 seconds in a heating press apparatus heated to 150 ° C. while applying a load of 200 kg / cm ² to the molded article of the present invention.
The wet tensile strength, water resistance, dispersibility in weak alkaline aqueous solution and biodegradability of the obtained molded article were evaluated by the following methods, and the results are shown in Table 1 together with other examples and comparative examples.

<Evaluation method> (1) The wet tensile strength (immersed in water for 5 minutes) was measured according to JIS-K-
The breaking strength was measured according to 7113. (2) Water resistance was evaluated by immersing the molded body sheet in deionized water left at room temperature for 1 hour, and evaluating the water resistance from four levels based on the surface condition. (No change, slight change, partial change, large change) (3) Dispersibility in a weak alkaline aqueous solution is as follows. A molded sheet of 5 cm square is placed in 100 cc of a 0.01 N NaOH aqueous solution heated to 50 ° C. for 1 hour. After stirring, the dispersibility was evaluated on a four-point scale. (Completely dispersed, almost dispersed, partially dispersed, not dispersed) (4) The biodegradability was determined by cutting a molded sheet to a width of 10 cm in length and width, and then outdoors in Koto-ku, Tokyo (Shinonome, Koto-ku, Tokyo) 1-10-6, Oji Paper Co., Ltd. site) 25
buried at a depth of 1 cm, taken out after 1, 3, 6, 9 and 12 months, and evaluated on a three-point scale based on morphological change and weight change.
Weight change is recognized, ×: morphological change and weight change are not recognized).

Example ² A sheet having a basis weight of 76.5 g / m ² was prepared in the same manner as in Example 1 except that casein (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of cellulose acetate phthalate. The prepared sheet was conditioned at 23 ° C. and 50% RH and then heated in a heating press at 120 ° C.
When a load of 200 kg / cm ² is applied to the sample, 30
The molded article of the present invention was subjected to pressure treatment for 2 seconds. The obtained composite sheet was evaluated in the same manner as in Example 1.

Comparative Example 1 C used in Example 1
A sheet having a basis weight of 79.2 g / m ² consisting of only 100% by weight of NBKP beaten to 520 ml with SF was prepared. The obtained molded body was evaluated in the same manner as in Example 1.

Comparative Example 2 A basis weight of 81.2 g / m ² was obtained in the same manner as in Example 1 except that cellulose acetate having no weak alkali solubility (manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of the cellulose acetate phthalate of Example 1. Was prepared. The prepared sheet was immersed in acetone for 1 second,
After drying in an oven heated to 80 ° C. for 1 minute to remove most of the acetone, the sample was subjected to a pressure treatment for 30 seconds in a heating press apparatus heated to 100 ° C. under a load of 200 kg / cm ^2. Into a composite sheet. The obtained molded body was evaluated in the same manner as in Example 1.

The powder and pulp used in the preparation of the molded articles of the examples and comparative examples, the compounding amount of the pulp, the average particle diameter of the powder, the heat treatment temperature, and the wet strength, water resistance and dispersion of the weak alkaline aqueous solution of the obtained molded articles. The properties and biodegradability are shown in Table 1.

[0047]

[Table 1]

[0048]

Industrial Applicability The present invention provides a molded article having excellent water resistance and wet strength when used in a natural environment, and having biodegradability and dispersibility in a weak alkaline aqueous solution which can be reprocessed together with used paper after use. Is provided. Examples 1 and 2 of the present invention have sufficient wet strength, water resistance, good weak alkali dispersibility, and biodegradability that can withstand use in a natural environment. On the other hand, Comparative Example 1 containing no powder has little wet strength, and Comparative Example 2 in which powder that is not weakly alkali-soluble is blended with the powder is preferable because it has no dispersibility and cannot collect cellulose fibers. Absent.

Claims (6)

[Claims] 1. A cellulose fiber sheet formed from a cellulose fiber and a powder or fiber of a weak alkali-soluble resin. 2. The cellulose fiber sheet according to claim 1, wherein the weak alkali-soluble resin has thermoplasticity or organic solvent solubility. 3. The cellulose fiber sheet according to claim 1, wherein the weak alkali-soluble resin has biodegradability. 4. The cellulose fiber sheet according to claim 1, wherein the weak alkali-soluble resin is a powder, and has an average particle size of 5 to 300 μm. 5. The method according to claim 5, wherein the weak alkali-soluble resin is casein,
The cellulose fiber sheet according to any one of claims 1 to 4, which is at least one selected from alginic acid and hemicellulose. 6. A molded product obtained by heating and pressurizing the cellulose fiber sheet according to any one of claims 1 to 5.