Flame-retardant material and flame-retardant sheet

Abstract

To provide a novel flame-retardant material and a flame-retardant sheet including anionically modified pulp.SOLUTION: A flame-retardant material and a flame-retardant sheet according to embodiments include anionically modified pulp in which the counter ions of anionic groups include metal ions, wherein the anionically modified pulp contains anionic groups in an amount of 1.1-3.0 mmol / g as measured after converting all anionic groups into an acid type.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a flame-retardant material and a flame-retardant sheet containing anionic modified pulp.

Background Art

[0002] Pulp inherently has no flame retardancy, and paper made of pulp also has no flame retardancy. To impart flame retardancy, flame retardants such as inorganic compounds are added, but it is necessary to add a large amount, and it is not easy to disperse them uniformly.

[0003] Patent Document 1 discloses a flame-retardant molded article containing composite fibers in which the surface of fibers such as cellulose fibers is coated with inorganic particles and a water-insoluble flame retardant, and that the molded article has a sheet shape, and that the composite fibers are prepared by synthesizing inorganic particles in a liquid containing fibers. Patent Document 1 also discloses anionic modified cellulose fibers such as TEMPO-oxidized CNF as the above fibers, but does not disclose that the metal salt of anionic modified pulp has flame retardancy.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An embodiment of the present invention aims to provide a novel flame-retardant material and a flame-retardant sheet containing anionic modified pulp.

Means for Solving the Problems

[0006] The inventors have found that by introducing an anionic group into pulp and using the metal salt of the anionic group, the pulp can be made flame-retardant, and have devised a flame-retardant material and a flame-retardant sheet using the metal salt of such an anion-modified pulp. The present invention includes the embodiments shown below.

[0007] [1] A flame-retardant material containing an anion-modified pulp in which the counter ion of the anionic group contains a metal ion, wherein the amount of the anionic group measured with all the anionic groups in the acid form is 1.1 to 3.0 mmol / g. [2] The flame-retardant material according to [1], wherein the metal ion contains a polyvalent metal ion. [3] The flame-retardant material according to [1] or [2], wherein the anionic group is a carboxy group.

[0008] [4] A flame-retardant sheet containing an anion-modified pulp in which the counter ion of the anionic group contains a metal ion, wherein the amount of the anionic group measured with all the anionic groups in the acid form is 1.1 to 3.0 mmol / g. [5] The flame-retardant sheet according to [4], wherein the metal ion contains a polyvalent metal ion. [6] The flame-retardant sheet according to [4] or [5], wherein the anionic group is a carboxy group. [7] The flame-retardant sheet according to any one of [4] to [6], further containing unmodified pulp. [Advantages of the Invention]

[0009] According to the embodiment of the present invention, a novel flame-retardant material and a flame-retardant sheet containing an anion-modified pulp can be provided. [Embodiments for Carrying Out the Invention]

[0010] [Flame-Retardant Material] The flame-retardant material according to this embodiment contains an anion-modified pulp in which the counter ion of the anionic group contains a metal ion. If it is an anion-modified pulp, metal ions can be efficiently introduced into the anionic group, and the pulp can be made flame-retardant. Therefore, it can be used as a material for imparting flame retardancy. Further, by introducing metal ions, for example, when the pulp is formed into a sheet, the strength such as tensile strength can be increased, and thus both strength and flame retardancy can be achieved.

[0011] An anion-modified pulp is a pulp into which an anionic group has been introduced, and is obtained by chemically modifying an unmodified pulp. "Pulp" refers to cellulose fibers extracted by mechanically and / or chemically treating plant bodies such as wood. The anionic group is preferably introduced at least on the fiber surface of the pulp.

[0012] Examples of plant-derived pulps include softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, wastepaper pulp, and the like. Any one of these may be used, or two or more of them may be used in combination.

[0013] Examples of the anionic group include at least one selected from the group consisting of a carboxy group, a phosphoric acid group, a sulfuric acid group, a sulfonic acid group, a nitric acid group, and a boric acid group. Among these, at least one selected from the group consisting of a carboxy group, a phosphoric acid group, and a sulfuric acid group is preferable. These anionic groups may be directly bonded to the glucose unit, which is a constituent unit of the cellulose molecule, or may be indirectly bonded. When indirectly bonded, an alkylene group having 1 to 4 carbon atoms may be present between the glucose unit and the anionic group. The anionic group may be bonded to one or more of all the glucose units constituting the cellulose molecule, or may be bonded to one or more of some of the glucose units constituting the cellulose molecule.

[0014] In one embodiment, the anionic group of the anion-modified pulp is preferably a carboxy group. When it is a carboxy group, the strength improvement effect when forming a sheet using the pulp is more excellent than that of other anionic groups.

[0015] In one embodiment, examples of the anion-modified pulp having a carboxy group include oxidized cellulose fibers obtained by oxidizing the hydroxyl group of the glucose unit in the cellulose molecule, and carboxymethylated cellulose fibers obtained by carboxymethylating the hydroxyl group of the glucose unit in the cellulose molecule. Examples of the oxidized cellulose fibers include those in which the hydroxyl group at the C6 position of the glucose unit in the cellulose molecule is selectively oxidized and modified to a carboxy group. The oxidized cellulose fibers can be obtained by oxidizing natural cellulose such as wood pulp using a co-oxidizing agent in the presence of an N-oxyl compound. As the N-oxyl compound, a compound having a nitroxyl radical generally used as an oxidation catalyst is used, for example, a piperidine nitroxyl radical, and particularly 2,2,6,6-tetramethylpiperidinooxyl radical (TEMPO) or 4-acetamido-TEMPO is preferable. The anion-modified cellulose fibers according to a preferred embodiment are TEMPO-oxidized cellulose fibers oxidized using TEMPO.

[0016] In this embodiment, the anionic modified pulp has an amount of anionic groups measured with all anionic groups in the acid form of 1.1 to 3.0 mmol / g. By having the amount of anionic groups of 1.1 mmol / g or more, flame retardancy can be imparted. The amount of anionic groups is preferably 1.3 to 2.8 mmol / g, more preferably 1.5 to 2.6 mmol / g, and still more preferably 1.7 to 2.5 mmol / g. Since the anionic modified pulp according to this embodiment is a metal salt type anionic modified pulp, when measuring the amount of anionic groups, all anionic groups are converted to the acid form and then measured. The amount of anionic groups is the amount of substance (mmol) of anionic groups per dry mass of the acid form of the anionic modified pulp, and can be measured by a known method. Specifically, it can be measured by the method described in the Examples section. In this specification, the "dry mass" refers to the mass after drying at 140°C until the mass change rate per minute becomes 0.05% or less.

[0017] In this embodiment, as the anionic modified pulp, those having metal ions as counter ions of the anionic groups are used. That is, metal ions are bonded to the anionic groups to form metal salts. In that case, it is preferable that the counter ions of all anionic groups are metal ions, but it may have counter ions other than metal ions. For example, the anionic groups may contain an onium salt together with the metal salt, and not all may be in the salt form. It may contain an acid form (the counter ion is H + and is also referred to as the H form. For example, in the case of a carboxy group, it is -COOH). As the introduction amount of the metal salt, for example, it is preferably 50 mol% or more of the anionic groups, more preferably 80 mol% or more, still more preferably 90 mol% or more, and even more preferably 100 mol%. Here, the introduction amount of the metal salt is the ratio of the anionic groups forming the metal salt to 100 mol% of the anionic groups, and is calculated from the above-mentioned amount of anionic groups and the metal content measured by an ICP emission spectroscopic analyzer.

[0018] Examples of the metal ions include monovalent metal ions such as sodium ion, lithium ion, and potassium ion; divalent metal ions such as magnesium ion and calcium ion; and trivalent metal ions such as aluminum ion. Any one of these may be used, or two or more of them may be used in combination.

[0019] The metal ions may be monovalent metal ions only, polyvalent metal ions such as magnesium ion, calcium ion, and aluminum ion only, or a combination of monovalent metal ions and polyvalent metal ions. The combined use means that among the anionic groups of the anion-modified pulp, there are an anionic group bonded to a monovalent metal ion and an anionic group bonded to a polyvalent metal ion.

[0020] In one embodiment, from the viewpoints of flame retardancy and strength, the metal ions preferably contain polyvalent metal ions. That is, the metal ions as counterions may be polyvalent metal ions only, or a combination of polyvalent metal ions and monovalent metal ions. The ratio of polyvalent metal ions to 100 mol% of the metal ions is not particularly limited, but for example, 30 mol% or more is preferable, more preferably 50 mol% or more, still more preferably 70 mol% or more, still more preferably 90 mol% or more, and particularly preferably 100 mol%. Here, the ratio of polyvalent metal ions is determined by measuring various metal contents using an ICP emission spectroscopic analyzer, and specifically, it can be measured by the method described in the Examples section.

[0021] As described above, the anion-modified pulp is obtained by chemically modifying the unmodified pulp and is not defibrated. In this regard, it is distinguished from cellulose nanofibers obtained by defibrating the pulp to make it finer. The fiber diameter of the anion-modified pulp is equivalent to that of the untreated pulp and varies depending on the raw material pulp, but is usually several tens of μm. Specifically, the number average fiber width of the anion-modified pulp is preferably 5 to 100 μm, more preferably 10 to 60 μm, and may also be 20 to 40 μm.

[0022] The number average fiber width of the anionic modified pulp is measured as follows. For an aqueous suspension of anionic modified pulp diluted to 0.01% by mass, 10 images are taken using an optical microscope, 25 fibers are selected therefrom, the width (diameter) of the fibers is measured, and the arithmetic mean thereof is calculated to obtain the value.

[0023] The flame retardant material according to this embodiment may consist only of the above anionic modified pulp, or may contain an additive as an optional component together with the above anionic modified pulp. The amount of the anionic modified pulp in the flame retardant material is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more, and may be 100% by mass. Examples of the additive include colorants such as pigments and dyes, water resistance agents, flame retardants, plasticizers, antioxidants, light stabilizers, fillers, antistatic agents, and the like. Note that since the anionic modified pulp in the flame retardant material according to this embodiment has flame retardancy, other flame retardants are not necessary. Therefore, in one embodiment, the flame retardant material does not contain other flame retardants.

[0024] The form of the flame retardant material is not particularly limited, and for example, it may be fibrous. "Fibrous" means having a fiber form, and may be, for example, a collection of fibers such as cotton-like, or a fiber sheet such as paper or non-woven fabric.

[0025] The flame retardant material according to this embodiment is used to impart flame retardancy. For example, by adding or blending it to a combustible material, the material can be made less flammable or the flame can be prevented from spreading, and the material can be imparted with flame retardancy.

[0026] For example, when manufacturing paper products such as paper, a flame-retardant material containing the anionic modified pulp is added to the unmodified pulp and mixed, and then a paper product is produced according to a normal method, whereby a flame-retardant paper product can be obtained. Alternatively, the flame-retardant material can be added to a resin and mixed, and then a resin product is produced according to a normal method, whereby a flame-retardant resin product can be obtained. The paper products are not particularly limited, and examples include building interior materials such as wallpaper, filters, honeycomb materials, packaging materials, and the like.

[0027] [Flame-retardant sheet] The flame-retardant sheet according to this embodiment is a sheet containing an anionic modified pulp in which the counter ion of the anionic group contains a metal ion, and is a flame-retardant sheet in which the amount of the anionic group of the anionic modified pulp measured with all the anionic groups in the acid form is 1.1 to 3.0 mmol / g. The details of the anionic modified pulp are as described above for the flame-retardant material, and the description thereof is omitted.

[0028] The flame-retardant sheet is a sheet used for imparting flame retardancy, and can impart flame retardancy to an object (i.e., the target object) by being overlaid on the surface or inside of the object to be flame-retarded. For example, the flame-retardant sheet can be used by being pasted on the surface of the object or sandwiched inside the laminate that is the object. More specific uses include, for example, building interior sheets such as wallpaper, filters, honeycomb materials, packaging materials, and the like. In this specification, "sheet" is a concept that includes "film".

[0029] The flame-retardant sheet may be a single-layer structure sheet composed of a layer containing the above anionic modified pulp, or may be a laminated structure sheet containing a layer containing the above anionic modified pulp and other layers. The thickness of the flame-retardant sheet is not particularly limited, and for example, it may be 0.001 to 50 mm, or may be 0.01 to 5 mm.

[0030] The flame-retardant sheet may consist only of the above anionic modified pulp, or may contain an additive as an optional component together with the above anionic modified pulp. Examples of the additive include colorants such as pigments and dyes, water resistance agents, flame retardants, plasticizers, antioxidants, light stabilizers, fillers, antistatic agents, and the like. Note that since the anionic modified pulp in the present embodiment has flame retardancy, other flame retardants are unnecessary. Therefore, in one embodiment, the flame-retardant sheet does not contain other flame retardants.

[0031] The flame-retardant sheet may be a fiber sheet such as paper or non-woven fabric. When forming the fiber sheet, for example, paper may be produced by using a suspension containing anionic modified pulp as a paper stock and performing papermaking. Papermaking is a process of dehydrating the paper stock by filtration to form a sheet, and then pressing and drying to produce paper. For papermaking, known papermaking machines such as a Fourdrinier wet papermaking machine, a twin-wire papermaking machine, a Yankee papermaking machine, a cylinder papermaking machine, and a cylinder Fourdrinier combination papermaking machine may be used. Further, for example, a suspension containing anionic modified pulp may be filtered under reduced pressure to form a sheet, dried, and then pressed to produce a fiber sheet.

[0032] When the metal ion contains a polyvalent metal ion, the method for preparing the anionic modified pulp is not particularly limited. For example, after forming a sheet using a monovalent metal salt of the anionic modified pulp, the sheet may be immersed in an aqueous solution of a polyvalent metal salt to replace the monovalent metal ion with a polyvalent metal ion for preparation.

[0033] In one embodiment, the flame-retardant sheet may contain an unmodified pulp together with the above anionic modified pulp, or may be a composite sheet in which the anionic modified pulp and the unmodified pulp are composite. Such a composite sheet may use, for example, a suspension containing both the anionic modified pulp and the unmodified pulp as a paper stock in the above papermaking, or may filter a suspension containing both the anionic modified pulp and the unmodified pulp under reduced pressure in the production of the above fiber sheet.

[0034] In the above composite sheet, the ratio of the anionic modified pulp to the unmodified pulp is not particularly limited. For example, the mass ratio of anionic modified pulp / unmodified pulp may be 10 / 90 to 90 / 10, may be 20 / 80 to 80 / 20, or may be 30 / 70 to 70 / 30.

Example

[0035] The examples will be described in detail below together with comparative examples. However, the present invention is not limited to these examples.

[0036] The measurement methods of each physical property in the examples and comparative examples are as follows.

[0037] [Amount of anionic groups (amount of carboxyl groups)] Prepare 50 mL of an aqueous suspension of acid-type anionic modified pulp with a pulp concentration of 0.1% by mass, and adjust the pH to about 2.5 with a 0.1 mol / L hydrochloric acid aqueous solution. Then, a 0.05 mol / L aqueous sodium hydroxide solution was dropped into the aqueous suspension, and conductivity measurement was performed until the pH reached about 11. From the amount of sodium hydroxide (V) consumed in the stage of neutralization of the weak acid where the change in conductivity was gentle, the amount of carboxyl groups was calculated according to the following formula. Amount of carboxyl groups (mmol / g) = V (mL) × [0.05 / mass of acid-type anionic modified pulp (g)]

[0038] [Amount of anionic groups (amount of phosphate groups)] The water suspension prepared by diluting anionic modified pulp with ion-exchanged water to a content of 0.2% by mass was treated with an ion-exchange resin to obtain an acid-type anionic modified pulp, and then measured by titration using an alkali. The treatment with the ion-exchange resin was carried out by adding a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) having a volume of 1 / 10 to the water suspension, performing a shaking treatment for 1 hour, and then pouring it onto a mesh with an opening of 90 μm to separate the ion-exchange resin from the water suspension. Further, the titration using an alkali was carried out by measuring the change in the value of the electrical conductivity exhibited by the water suspension while adding 50 μL of a 0.1 mol / L aqueous sodium hydroxide solution to the water suspension treated with the ion-exchange resin once every 30 seconds. The amount of phosphate groups (mmol / g) was calculated by dividing the amount of alkali (mmol) required in the region corresponding to the first region in the measurement results by the solid content (g) in the water suspension to be titrated.

[0039] [Amount of anionic groups (amount of sulfate groups)] A predetermined amount of the acid-type anionic modified pulp was burned, and the sulfur content contained in the combustion product was measured by a combustion ion chromatograph using a method compliant with IEC 62321, and calculated by converting it to the amount of sulfate groups.

[0040] [Ratio of polyvalent metal salts] Regarding Sheets C1 to C9 of Examples 1 to 9 and Sheet C15 of Comparative Example 5, 2.0 g of each sheet was sampled, subjected to Kjeldahl decomposition, and then made up to 100 mL with ultrapure water (50-fold dilution). The contents of various metals were measured by an ICP emission spectroscopic analyzer. From the contents of various metals (ppm) thus obtained, the ratio of polyvalent metals was calculated using the following formula. Ratio of polyvalent metals (mol%) = amount of polyvalent metals (ppm) ÷ [amount of polyvalent metals (ppm) + amount of monovalent metals (ppm)] × 100

[0041] [Flame retardancy of sheet] The sheets C1 to C9 of Examples 1 to 9 and the sheets C11 to C13, C15 of Comparative Examples 1 to 3, 5 were cut into pieces with a length of 5 cm and a width of 1 cm to prepare test pieces. The test pieces were fixed horizontally with a clamp, and the tip of the test piece was brought into contact with a gas burner flame. The flame retardancy was evaluated according to the following criteria. A: Those that self-extinguished within less than 60 seconds after the gas burner flame came into contact with the test piece B: Those that self-extinguished over 60 seconds after the gas burner flame came into contact with the test piece C: Those in which the entire test piece burned

[0042] [Flame Retardancy of Composite Sheet] The composite sheets D1 to D9 of Examples 1 to 9 and the composite sheets D11 to D15 of Comparative Examples 1 to 5 were cut into pieces with a length of 5 cm and a width of 1 cm to prepare test pieces. The test pieces were fixed horizontally with a clamp, and the tip of the test piece was brought into contact with a gas burner flame. The flame retardancy was evaluated according to the following criteria. A: Those that self-extinguished within 60 seconds after the gas burner flame came into contact with the test piece B: Those that self-extinguished over 61 seconds after the gas burner flame came into contact with the test piece C: Those in which the entire test piece burned

[0043] [Tensile Strength of Sheet] The sheets C1 to C9 of Examples 1 to 9 and the sheets C11 to C13, C15 of Comparative Examples 1 to 3, 5 were cut into pieces with a length of 6 cm and a width of 0.5 cm to prepare test pieces. Using a tensile testing machine (EZ-SX, manufactured by Shimadzu Corporation), the test pieces were subjected to a tensile test under the conditions of a grip distance of 3 cm, a tensile speed of 3 mm / min, 23 °C, and 50% RH to obtain the tensile strength (MPa). The tensile strength is the value obtained by dividing the maximum tensile force recorded when the test piece was pulled until it broke by the cross-sectional area of the test piece before the test.

[0044] [Preparation of Anion-Modified Pulps A1 to A5] Prior to the preparation of the sheets of the examples and comparative examples, the acid-type anion-modified pulps A1 to A5 used therein were prepared according to the following Production Examples 1 to 5.

[0045] [Production Example 1: Preparation of Anionic Modified Pulp A1 (TEMPO-Oxidized Cellulose Fiber)] To 2 g of softwood pulp, 150 mL of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO were added, and after thoroughly stirring and dispersing, an aqueous solution of sodium hypochlorite (co-oxidizing agent) at 13% by mass was added such that the amount of sodium hypochlorite was 8.0 mmol / g with respect to 1.0 g of the above pulp, and the reaction was started. Since the pH decreased as the reaction proceeded, a 0.5 mol / L aqueous sodium hydroxide solution was added dropwise to maintain the pH at 10 - 11, and the reaction was carried out until no change in pH was observed (reaction time: 120 minutes). After completion of the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, and then filtration and washing with water were repeated for purification to obtain cellulose fibers with oxidized fiber surfaces. Pure water was added thereto and diluted to a cellulose fiber concentration of 4% by mass to prepare a TEMPO-oxidized cellulose fiber suspension. Thereafter, after adjusting the pH of the slurry to 10 with a 24% by mass aqueous sodium hydroxide solution, sodium borohydride was added at 0.2 mmol / g with respect to the cellulose fiber, and the reaction was started. The reaction was carried out for 2 hours for reduction treatment. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, and then filtration and washing with water were repeated for purification to obtain anionic modified pulp A1 in which the carboxyl group was in the acid form.

[0046] [Production Example 2: Preparation of Anionic Modified Pulp A2 (TEMPO-Oxidized Cellulose Fiber)] An anionic modified pulp A2 in which the carboxyl group was in the acid form was obtained in the same manner as the preparation method of anionic modified pulp A1, except that the addition amount of the aqueous sodium hypochlorite solution was 6.0 mmol / g with respect to 1.0 g of softwood pulp.

[0047] [Production Example 3: Preparation of Anionic Modified Pulp A3 (TEMPO-Oxidized Cellulose Fiber)] An anionic modified pulp A3 in which the carboxyl group was in the acid form was obtained in the same manner as the preparation method of anionic modified pulp A1, except that the addition amount of the aqueous sodium hypochlorite solution was 10.0 mmol / g with respect to 1.0 g of softwood pulp.

[0048] [Production Example 4: Preparation of Anionic Modified Pulp A4 (TEMPO-Oxidized Cellulose Fibers)] An anionic modified pulp A4 in which the carboxy group is in the acid form was obtained in the same manner as the preparation method of anionic modified pulp A1, except that the addition amount of the aqueous sodium hypochlorite solution was 4.0 mmol / g with respect to 1.0 g of softwood pulp.

[0049] [Production Example 5: Preparation of Anionic Modified Pulp A5 (Phosphate-Esterified Cellulose Fibers)] To 100 parts by mass (dry mass) of softwood kraft pulp, an aqueous mixed solution of ammonium dihydrogen phosphate and urea was added and adjusted to contain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165 °C for 200 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining phosphate-esterified cellulose fibers. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 1.0, and then filtration and washing with water were repeated for purification to obtain an anionic modified pulp A5 in which the fiber surface was phosphate-esterified and the phosphate group was in the acid form.

[0050] [Production Example 6: Preparation of Anionic Modified Pulp A6 (Sulfate-Esterified Cellulose Fibers)] 2 g of softwood kraft pulp, 20 g of sulfamic acid, 50 g of urea, and 100 g of ion-exchanged water were mixed and stirred using a stirrer for 10 minutes. After stirring, the slurry was suction-filtered using filter paper (No. 2). The suction filtration was carried out until the solution stopped dripping. After suction filtration, the pulp was peeled off from the filter paper, and the pulp was placed in a dryer with the temperature of the constant temperature bath set at 50 °C and reacted for 6 hours. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 1.0, and then filtration and washing with water were repeated for purification to obtain an anionic modified pulp A6 in which the fiber surface was sulfated and the sulfate group was in the acid form.

[0051] [Example 1] (Neutralization Step) After diluting anionic modified pulp A2 to 0.2% by mass with ion-exchanged water, it was neutralized with a 0.5 mol / L aqueous sodium hydroxide solution to adjust the pH (25 °C) to 7.0, thereby obtaining a suspension B1 of anionic modified pulp having Na salt-type carboxyl groups.

[0052] (Preparation of sheet) The suspension B1 was subjected to vacuum filtration through a nylon mesh filter with an aperture of 59 μm to obtain a sheet-like wet deposit. After air-drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes under 0.4 MPa using a hot press apparatus to obtain a sheet having Na salt-type carboxyl groups. The sheet having Na salt-type carboxyl groups was immersed in a 0.1 M aluminum chloride aqueous solution for 24 hours and then washed 5 times with purified water. After air-drying this, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes under 0.4 MPa using a hot press apparatus to obtain a 100-μm-thick sheet C1 of Example 1 composed of anionic modified pulp having Al salt-type carboxyl groups.

[0053] (Preparation of composite sheet) Softwood pulp was diluted to 0.2% by mass with ion-exchanged water without modification, and a pulp suspension was prepared by using a pulper to disintegrate it at 3000 rpm for 10 minutes. The pulp suspension and the suspension B1 of anionic modified pulp having Na salt-type carboxyl groups obtained in the above neutralization step were mixed at a mass ratio of 50 to 50. This was subjected to vacuum filtration through a nylon mesh filter with an aperture of 59 μm to obtain a sheet-like wet deposit. After air-drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes under 0.4 MPa using a hot press apparatus to obtain a composite sheet of anionic modified pulp having Na salt-type carboxyl groups and unmodified pulp. This composite sheet was immersed in a 0.1 M aluminum chloride aqueous solution for 24 hours and then washed 5 times with purified water. After air-drying this, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes under 0.4 MPa using a hot press apparatus to obtain a composite sheet D1 of anionic modified pulp having Al salt-type carboxyl groups and unmodified pulp.

[0054] [Example 2] The neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 1, except that anionic modified pulp A1 was used, to obtain sheet C2 and composite sheet D2 of Example 2.

[0055] [Example 3] The neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 1, except that anionic modified pulp A3 was used, to obtain sheet C3 and composite sheet D3 of Example 3.

[0056] [Example 4] The neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 2, except that in the preparation of the sheet and the composite sheet, it was immersed in a 0.05 M aluminum chloride aqueous solution instead of a 0.1 M aluminum chloride aqueous solution, to obtain sheet C4 and composite sheet D4 of Example 4.

[0057] [Example 5] The neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 2, except that in the preparation of the sheet and the composite sheet, it was not immersed in a 0.1 M aluminum chloride aqueous solution, to obtain sheet C5 and composite sheet D5 of Example 5.

[0058] [Example 6] The neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 2, except that in the preparation of the sheet and the composite sheet, it was immersed in a 0.1 M magnesium chloride aqueous solution instead of a 0.1 M aluminum chloride aqueous solution, to obtain sheet C6 and composite sheet D6 of Example 6.

[0059] [Example 7] The neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 2, except that in the preparation of the sheet and the composite sheet, it was immersed in a 0.1 M calcium chloride aqueous solution instead of a 0.1 M aluminum chloride aqueous solution, to obtain sheet C7 and composite sheet D7 of Example 7.

[0060] [Example 8] Except for using anionic modified pulp A5, the neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 1 to obtain sheet C8 and composite sheet D8 of Example 8.

[0061] [Example 9] Except for using anionic modified pulp A6, the neutralization step, sheet preparation, and composite sheet preparation were carried out in the same manner as in Example 1 to obtain sheet C9 and composite sheet D9 of Example 9.

[0062] [Comparative Example 1] After diluting softwood pulp to 0.2% by mass with deionized water without modification and then dissociating it at 3000 rpm for 10 minutes using a pulper, a pulp suspension was prepared. The obtained suspension was vacuum filtered through a nylon mesh filter with an aperture of 59 μm to obtain a sheet-like wet deposit. After air drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes and 0.4 MPa using a hot press device to obtain sheet C11 of Comparative Example 1 with a thickness of 100 μm.

[0063] [Comparative Example 2] (Preparation of acid-type anionic modified pulp suspension) After diluting anionic modified pulp A1 to 0.2% by mass with deionized water and then dissociating it at 3000 rpm for 10 minutes using a pulper, a suspension B12 of anionic modified pulp having acid-type carboxyl groups was obtained.

[0064] (Sheet preparation) Suspension B12 was vacuum filtered through a nylon mesh filter with an aperture of 59 μm to obtain a sheet-like wet deposit. After air drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes and 0.4 MPa using a hot press device to obtain sheet C12 of Comparative Example 2 made of anionic modified pulp having acid-type carboxyl groups with a thickness of 100 μm.

[0065] (Preparation of Composite Sheet) The softwood pulp was diluted to 0.2% by mass with deionized water without modification, and pulped at 3000 rpm for 10 minutes using a pulper to prepare a pulp suspension. The pulp suspension and suspension B12 of anionic modified pulp having the acid-type carboxy group described above were mixed at a mass ratio of 50 to 50. This was subjected to vacuum filtration through a nylon mesh filter with an opening of 59 μm to obtain a sheet-like wet deposit. After air-drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes at 0.4 MPa using a hot press apparatus to obtain a composite sheet D12 of anionic modified pulp having an acid-type carboxy group and unmodified pulp.

[0066] [Comparative Example 3] (Neutralization Step) After diluting anionic modified pulp A1 to 0.2% by mass with deionized water, it was neutralized with a 0.5 mol / L aqueous solution of tetrabutylammonium hydroxide (TBA) to adjust the pH (25 °C) to 7.0. Thereby, a suspension B13 of anionic modified pulp having a carboxy group of the TBA salt type was obtained.

[0067] (Sheet Preparation) Suspension B13 was subjected to vacuum filtration through a nylon mesh filter with an opening of 59 μm to obtain a sheet-like wet deposit. After air-drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes at 0.4 MPa using a hot press apparatus to obtain a 100-μm-thick sheet C13 of Comparative Example 3 composed of anionic modified pulp having a carboxy group of the TBA salt type.

[0068] (Preparation of Composite Sheet) The softwood pulp was diluted to 0.2% by mass with ion-exchanged water without modification, and then defibrated at 3000 rpm for 10 minutes using a pulper to prepare a pulp suspension. The pulp suspension was mixed with suspension B13 of the anion-modified pulp having carboxy groups in the TBA salt form obtained in the neutralization step above at a mass ratio of 50 to 50. This was subjected to vacuum filtration through a nylon mesh filter with an opening of 59 μm to obtain a sheet-like wet deposit. After air-drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes under 0.4 MPa using a hot press apparatus to obtain a composite sheet D13 of the anion-modified pulp having carboxy groups in the TBA (tetrabutylammonium) salt form and the unmodified pulp.

[0069] [Comparative Example 4] (Preparation of sheet) After suspending aluminum hydroxide in ion-exchanged water at 2% by mass, the resulting suspension was subjected to vacuum filtration through a nylon mesh filter with an opening of 59 μm to obtain a wet deposit, but it could not be formed into a sheet. Therefore, the evaluation of the sheet was not carried out.

[0070] (Preparation of composite sheet) The softwood pulp was diluted to 0.2% by mass with ion-exchanged water without modification, and then defibrated at 3000 rpm for 10 minutes using a pulper to prepare a pulp suspension. The pulp suspension was mixed with a 0.2% by mass aluminum hydroxide aqueous suspension at a mass ratio of 50 to 50. This was subjected to vacuum filtration through a nylon mesh filter with an opening of 59 μm to obtain a sheet-like wet deposit. After air-drying at room temperature, it was sandwiched between polyimide films and heated at 105 °C for 5 minutes under 0.4 MPa using a hot press apparatus to obtain a composite sheet D14 of the unmodified pulp and aluminum hydroxide.

[0071] [Comparative Example 5] The neutralization step, the preparation of the sheet, and the preparation of the composite sheet were carried out in the same manner as in Example 1 except that anion-modified pulp A4 was used to obtain sheet C15 and composite sheet D15 of Comparative Example 5.

[0072] For the sheets C1 to C9 of Examples 1 to 9 and the sheet C15 of Comparative Example 5 prepared above, the ratio of the polyvalent metal salt was measured. Further, for these sheets C1 to C9 and C15, and the sheets C11 to C13 of Comparative Examples 1 to 3, the flame retardancy and tensile strength were evaluated. Furthermore, for the composite sheets D1 to D9 of Examples 1 to 9 and the composite sheets D11 to D15 of Comparative Examples 1 to 5, the flame retardancy was evaluated. The results are shown in Table 1.

[0073]

Table 1

[0074] As shown in Table 1, Comparative Example 1, which is a sheet made of unmodified pulp, and Comparative Examples 2 and 3, in which the counter ion of the anionic modified pulp is not a metal ion, had no flame retardancy.

[0075] On the other hand, in Examples 1 to 9, where the counter ion of the anionic modified pulp is a metal ion and the amount of the anionic group is above a specified level, not only the sheet of the anionic modified pulp alone but also the composite sheet with the unmodified pulp was flame-retarded. Also, in Examples 1 to 9, the tensile strength was improved for the sheet made of the anionic modified pulp other than the unmodified pulp and the metal salt. It was recognized that the carboxy group had a higher tendency for the tensile strength than the case where the anionic group was a phosphate group or a sulfate group. Also, regarding the metal ion as the counter ion, the polyvalent metal was superior to the monovalent metal in terms of flame retardancy and tensile strength.

[0076] In addition, the various numerical ranges described in the specification can arbitrarily combine their upper limit values and lower limit values, and all of these combinations are described in the specification as preferred numerical ranges. Also, the description of the numerical range of "X to Y" means X or more and Y or less.

[0077] Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their omissions, replacements, changes, etc. are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Claims

1. A flame-retardant material containing an anion-modified pulp in which the counter ion of the anionic group contains a metal ion, wherein the amount of the anionic group measured with all the anionic groups in the acid form is 1.1 to 3.0 mmol / g in the anion-modified pulp.

2. The flame-retardant material according to Claim 1, wherein the metal ion contains a polyvalent metal ion.

3. The flame-retardant material according to Claim 1 or 2, wherein the anionic group is a carboxy group.

4. A flame-retardant sheet containing an anion-modified pulp in which the counter ion of the anionic group contains a metal ion, wherein the amount of the anionic group measured with all the anionic groups in the acid form is 1.1 to 3.0 mmol / g in the anion-modified pulp.

5. The flame-retardant sheet according to Claim 4, wherein the metal ion contains a polyvalent metal ion.

6. The flame-retardant sheet according to Claim 4 or 5, wherein the anionic group is a carboxy group.

7. The flame-retardant sheet according to Claim 4 or 5, further containing an unmodified pulp.

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