Flame-retardant materials and flame-retardant sheets, and methods for manufacturing the same.

Abstract

The present invention provides novel flame-retardant materials and flame-retardant sheets containing anion-modified pulp. [Solution] The flame-retardant material and flame-retardant sheet according to the embodiment include anion-modified pulp, wherein the counterions of the anionic groups of the anion-modified pulp include aluminum ions, and further, aluminum compound fine particles are compounded on the surface of the pulp and / or inside the pulp.

Description

[Technical Field]

[0001] The present invention relates to a flame-retardant material and a flame-retardant sheet containing anion-modified pulp, and methods for producing the same. [Background Art]

[0002] Pulp inherently does not have flame retardancy, and paper made from pulp also does not have flame retardancy. To impart flame retardancy, flame retardants such as inorganic compounds are added, but it is necessary to add a large amount thereof, and it is not easy to uniformly disperse the flame retardant.

[0003] Patent Document 1 discloses a flame-retardant molded article containing a composite fiber in which the surface of a fiber such as cellulose fiber is coated with inorganic particles, and a water-insoluble flame retardant. It is disclosed that the molded article has a sheet shape, and that the composite fiber is prepared by synthesizing inorganic particles in a liquid containing the fibers. Patent Document 1 also discloses an anion-modified cellulose fiber such as TEMPO-oxidized CNF as the above fiber. However, Patent Document 1 does not disclose compositing aluminum compound fine particles with an aluminum salt-type anion-modified pulp. [Prior Art Literature] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2021-25003 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] An object of an embodiment of the present invention is to provide a novel flame-retardant material and a novel flame-retardant sheet containing anion-modified pulp. [Means for Solving the Problem]

[0006] The present invention includes the embodiments shown below. [1] A flame-retardant material comprising anion-modified pulp, wherein the counterions of the anionic groups of the anion-modified pulp contain aluminum ions, and further comprising aluminum compound fine particles composited on the surface of the pulp and / or inside the pulp. [2] The flame retardant material according to [1], wherein the anionic modified pulp is such that the amount of anionic groups measured by converting all of the anionic groups to the acid type is 0.8 to 3.0 mmol / g. [3] The flame retardant material according to [1] or [2], wherein the anionic group is a carboxyl group.

[0007] [4] A flame-retardant sheet comprising anion-modified pulp, wherein the counterions of the anionic groups of the anion-modified pulp contain aluminum ions, and further, aluminum compound fine particles are compounded on the surface of the pulp and / or inside the pulp. [5] The flame retardant sheet according to [4], wherein the anionic modified pulp has an amount of anionic groups measured by converting all of the anionic groups to the acid form of 0.8 to 3.0 mmol / g. [6] The flame retardant sheet according to [4] or [5], wherein the anionic group is a carboxyl group. [7] A flame-retardant sheet according to any one of items [4] to [6], further comprising unmodified pulp.

[0008] A method for producing a flame-retardant material described in any one of items [1] to [3] or a flame-retardant sheet described in any one of items [4] to [7], comprising the steps of: neutralizing an acid-type anionic modified pulp; exchanging the counterions of the anionic groups of the neutralized anionic modified pulp for aluminum ions using aluminum chloride; and adjusting the pH to 4.0 or higher using a weak base in the presence of aluminum chloride after ion exchange. [Effects of the Invention]

[0009] According to embodiments of the present invention, novel flame-retardant materials and flame-retardant sheets containing anion-modified pulp can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This is an electron microscope image of the cross-section of the pulp sheet from Example 3. [Figure 2] This is an electron microscope image of the cross-section of the pulp sheet of Comparative Example 1. [Modes for carrying out the invention]

[0011] The inventors have discovered that by introducing anionic groups into pulp, converting these anionic groups into aluminum salts, and further compounding them with aluminum compound fine particles, excellent flame retardancy can be imparted to the pulp. They have devised a method for using this to create flame-retardant materials and flame-retardant sheets.

[0012] [Flame-retardant materials] The flame-retardant material according to this embodiment includes anion-modified pulp, wherein the counterions of the anionic groups of the anion-modified pulp contain aluminum ions, and aluminum compound fine particles are compounded on the surface and / or inside the pulp. In this way, anion-modified pulp containing aluminum ions as counterions and further compounded with aluminum compound fine particles on the surface and / or inside the pulp (hereinafter sometimes referred to as Al-compounded pulp) can improve flame retardancy while suppressing mass increase.

[0013] Anionically modified pulp is pulp into which anionic groups have been introduced, and is obtained by chemically modifying unmodified pulp. "Pulp" refers to cellulose fibers extracted by mechanically and / or chemically processing plant materials such as wood. The anionic groups are introduced on the surface of the pulp and / or inside the pulp (i.e., on the surface of the pulp fibers and / or inside the fibers), and it is preferable that they are introduced at least on the surface of the pulp.

[0014] Examples of plant-derived pulps include unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, and waste paper pulp. Any one of these may be used, or two or more may be used in combination.

[0015] Examples of anionic groups include at least one selected from the group consisting of carboxyl groups, phosphate groups, sulfate groups, sulfonic acid groups, nitrate groups, and boric acid groups. Among these, at least one selected from the group consisting of carboxyl groups, phosphate groups, and sulfate groups is preferred. These anionic groups may be directly bonded to glucose units, which are the constituent units of the cellulose molecule, or they may be bonded indirectly. In the case of indirect bonding, for example, an alkylene group having 1 to 4 carbon atoms may be present between the glucose unit and the anionic group. One or more anionic groups may be bonded to all glucose units constituting the cellulose molecule, or one or more anionic groups may be bonded to some of the glucose units constituting the cellulose molecule.

[0016] In one embodiment, the anionic group of the anionically modified pulp is preferably a carboxyl group. Examples of anionically modified pulp having a carboxyl group include oxidized pulp (oxidized cellulose fiber) obtained by oxidizing the hydroxyl group of the glucose unit in the cellulose molecule, and carboxymethylated pulp (carboxymethylated cellulose fiber) obtained by carboxymethylating the hydroxyl group of the glucose unit in the cellulose molecule. Examples of oxidized pulp include pulp in which the hydroxyl group at the C6 position of the glucose unit in the cellulose molecule is selectively oxidized and modified to a carboxyl group. Oxidized pulp is obtained by oxidizing natural pulp such as wood pulp in the presence of an N-oxyl compound using a co-oxidizing agent. As the N-oxyl compound, compounds having a nitroxyl radical, which are generally used as oxidation catalysts, are used, for example, piperidine nitroxyoxyl radicals, and 2,2,6,6-tetramethylpiperidinooxyl radical (TEMPO) or 4-acetamide-TEMPO are particularly preferred. An anionically modified pulp according to a preferred embodiment is TEMPO-oxidized pulp (TEMPO-oxidized cellulose fiber) obtained by oxidizing with TEMPO.

[0017] In the present embodiment, the anion-modified pulp preferably has an anionic group amount of 0.8 to 3.0 mmol / g as measured when all anionic groups are converted to the acid form. When the amount of anionic groups is 0.8 mmol / g or more, flame retardancy is easily improved. The amount of anionic groups is preferably 1.1 to 2.8 mmol / g, more preferably 1.3 to 2.6 mmol / g, still more preferably 1.5 to 2.5 mmol / g, and even more preferably 1.7 to 2.4 mmol / g. The anion-modified pulp according to the present embodiment is an aluminum salt-type anion-modified pulp, and when measuring the amount of anionic groups, the measurement is performed after converting all anionic groups to the acid form. The amount of anionic groups refers to the amount (mmol) of anionic groups per dry mass of acid-form anion-modified pulp, and can be measured by a known method, specifically, 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.

[0018] In the present embodiment, as the anion-modified pulp, one having aluminum ions as counterions for the anionic groups thereof is used. That is, aluminum ions are ionically bonded to the anionic groups to form an aluminum salt. In this case, it is preferable that the counterions of all anionic groups are aluminum ions, but the anion-modified pulp may have counterions other than aluminum ions. For example, the anionic groups may include other metal salts such as sodium ions and onium salts together with the aluminum salt. Furthermore, not all anionic groups need to be in salt form, and may be in acid form (the counterion is H +, which is also referred to as H-type. For example, in the case of a carboxy group, it may contain -COOH). The introduction amount of the aluminum salt is, for example, preferably 50 mol% or more of the anionic groups, more preferably 80 mol% or more, still more preferably 90 mol% or more, and may be 100 mol%. Here, the introduction amount of the aluminum salt is the ratio of anionic groups forming aluminum salt to 100 mol% of anionic groups, and is calculated from the amount of the aforementioned anionic groups and the aluminum content measured by an ICP emission spectrometer.

[0019] Since aluminum ions are trivalent, anionic modified pulp may have a structure crosslinked by aluminum ions when aluminum ions are ionically bonded as counter ions to the anionic groups of the anion-modified pulp.

[0020] As described above, the anion-modified pulp is obtained by chemically modifying unmodified pulp, and is preferably not defibrated. The fiber diameter of the anion-modified pulp is equivalent to that of untreated pulp, and is usually several tens of micrometers, although it varies depending on the raw material pulp. Specifically, the number average fiber width of the anion-modified pulp is not particularly limited, and may be, for example, 5 to 100 µm, 10 to 60 µm, or 20 to 40 µm.

[0021] The number average fiber width of the anion-modified pulp is measured as follows. For an aqueous suspension of anion-modified pulp diluted to 0.01 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 average is calculated to obtain the value.

[0022] In the present embodiment, aluminum compound fine particles are composited with the anion-modified pulp. The aluminum compound fine particles are fine particles of an inorganic aluminum compound such as an oxide and / or hydroxide of aluminum.

[0023] In one embodiment, aluminum compound fine particles may be produced by reacting aluminum chloride with a weak base. The aluminum compound fine particles obtained in this manner are presumed to contain an aluminum oxide cluster structure, and may be fine particles composed of multiple such oxide clusters, but are not limited to these. For example, the aluminum oxide cluster structure may be Keggin-type Al 13 Cluster structure, Al 26 Cluster structure, Al 30 Examples include cluster structures and aluminum oligomers containing 4 to 5 aluminum atoms.

[0024] Aluminum compound fine particles are compounded into the pulp surface and / or interior of the anionic modified pulp. Preferably, the aluminum compound fine particles are compounded at least on the pulp surface, similar to the anionic groups.

[0025] Composite formation refers to a process where anionic modified pulp and aluminum compound microparticles are not simply mixed together, but are bonded or integrated so that the aluminum compound microparticles do not easily fall off during washing or other processes. As one embodiment of such composite formation, the aluminum compound microparticles are not particularly limited, but for example, they may be produced by reacting aluminum chloride with a weak base in an aqueous dispersion of the aluminum salt of the anionic modified pulp. It is thought that such aluminum compound microparticles are formed when the aluminum compound produced by reacting aluminum chloride with a weak base precipitates around aluminum ions, which are counterions to the anionic groups in the anionic modified pulp, and grows from there. Therefore, composite formation can be achieved so that the microparticles do not easily fall off.

[0026] The size of the aluminum compound nanoparticles is not particularly limited; for example, the average particle diameter may be 50-1000 nm or 100-700 nm. Here, the average particle diameter of the aluminum compound nanoparticles is determined by selecting 25 aluminum compound nanoparticles arbitrarily from an electron microscope image at a magnification of 5500x, measuring their particle diameters, and calculating their arithmetic mean. In reality, small aluminum compound nanoparticles that cannot be observed in the electron microscope image may be formed, but the average particle diameter is determined excluding these.

[0027] The content of aluminum compound fine particles is not particularly limited. For example, it is preferable that the mass increase rate relative to the acid-type anion-modified pulp, corresponding to the total amount of aluminum ions (counterions) and aluminum compound fine particles, is as follows: That is, with 100% by mass of acid-type anion-modified pulp, the mass increase rate relative to this may be 5 to 25% by mass or 7 to 20% by mass.

[0028] The flame-retardant material according to this embodiment may consist solely of anion-modified pulp (Al-compounded pulp) compounded with aluminum compound fine particles, or it may contain additives as optional components along with the Al-compounded pulp. The amount of Al-compounded 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, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 100% by mass. Examples of additives include colorants such as pigments and dyes, water-resistant agents, flame retardants, plasticizers, antioxidants, light stabilizers, fillers, and antistatic agents. In this embodiment, since the Al-compounded pulp is flame-retardant, other flame retardants are not necessary, and therefore, in one embodiment, the flame-retardant material does not contain other flame retardants.

[0029] The form of the flame-retardant material is not particularly limited; for example, it may be fibrous. "Fibrous" refers to something that has the form of fibers, such as a collection of fibers, or it may be cotton-like, or a fibrous sheet such as paper or nonwoven fabric.

[0030] The flame-retardant material according to this embodiment is used to impart flame retardancy. For example, by adding or blending it with a flammable material, it is possible to make the material less flammable or prevent flames from spreading, thereby imparting flame retardancy to the material.

[0031] For example, when manufacturing paper products such as paper, flame-retardant paper products can be obtained by adding and mixing a flame-retardant material containing Al-compounded pulp to unmodified pulp and producing paper products according to conventional methods. Alternatively, flame-retardant resin products can be obtained by adding and mixing the flame-retardant material to a resin and producing resin products according to conventional methods. Paper products are not particularly limited and include, for example, interior building materials such as wallpaper, filters, honeycomb materials, and packaging materials.

[0032] The method for producing flame-retardant materials is not particularly limited, but it is preferable to include the following steps, for example. A process to neutralize acid-type anion-modified pulp (neutralization process), A process of ion-exchanging the counterions of the anionic groups of the neutralized anion-modified pulp with aluminum ions using aluminum chloride (ion exchange process), and After ion exchange, the pH is adjusted to 4.0 or higher using a weak base in the presence of aluminum chloride (microparticle generation process).

[0033] In the neutralization step, an aqueous suspension of acid-type anionic pulp is neutralized with an alkali. The concentration of anionic pulp in the aqueous suspension is not particularly limited and may be, for example, 0.1 to 5% by mass. Alkali metal hydroxides are preferably used as the alkali, such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. These aqueous solutions are added to the aqueous suspension of acid-type anionic pulp to neutralize it. This yields the alkali metal salt of the anionic pulp.

[0034] In the ion exchange step, for example, an aqueous solution of aluminum chloride is added to the aqueous suspension of the alkali metal salt of the anionically modified pulp obtained in the neutralization step. As a result, aluminum ions ionically bond to the anionic groups instead of alkali metal ions, i.e., ion exchange from alkali metal ions to aluminum ions occurs, and an aqueous dispersion of the aluminum salt of the anionically modified pulp is obtained. The pH (at 25°C) of the aqueous suspension after ion exchange is preferably 2.0 to 3.5.

[0035] In the fine particle generation process, for example, a weak base is added to an aqueous dispersion of the aluminum salt of the anion-modified pulp to adjust the pH (at 25°C) to 4.0 or higher. The aqueous dispersion of the aluminum salt of the anion-modified pulp contains residual aluminum chloride that was added in excess during the ion exchange process. By adding a weak base to adjust the pH to 4.0 or higher in the presence of this aluminum chloride, the aluminum chloride and the weak base react to form aluminum compound fine particles that are compounded on the pulp surface and / or inside the pulp. As a result, the above-mentioned Al-compounded pulp is obtained. Here, a weak base is a compound that, when dissolved in water, partially dissociates into hydroxide ions and cations and is in equilibrium, and has a degree of ionization significantly less than 1. Specifically, it refers to a base whose degree of ionization in a 0.1 mol / L aqueous solution is 0.1 or less.

[0036] The weak base used in the fine particle production process is not particularly limited, and examples include ammonia, sodium carbonate, and sodium bicarbonate, and aqueous solutions of these are usually used. In the fine particle production process, the pH (at 25°C) after adding the weak base is more preferably 4.3 to 7.0, more preferably 4.5 to 6.0, and even more preferably 4.7 to 5.5.

[0037] After the fine particle generation process, for example, purification and drying may be performed to obtain the flame-retardant material according to the embodiment.

[0038] [Flame-retardant sheet] The flame-retardant sheet according to this embodiment is a sheet containing anion-modified pulp, wherein the counterions of the anionic groups of the anion-modified pulp contain aluminum ions, and aluminum compound fine particles are compounded on the surface and / or inside the pulp. Details of the anion-modified pulp compounded with such aluminum compound fine particles, i.e., Al-compounded pulp, are as described above for flame-retardant materials, and will not be explained further.

[0039] The flame-retardant sheet is a sheet used to impart flame retardancy to an object (i.e., a target object) by layering it on the surface or inside the object to be made flame-retardant. For example, the flame-retardant sheet can be used by attaching it to the surface of the target object or by sandwiching it inside a laminate that is the target object. More specific applications include, for example, building interior sheets such as wallpaper, filters, honeycomb materials, and packaging materials. In this specification, "sheet" is a concept that includes "film".

[0040] The flame-retardant sheet may be a single-layer sheet consisting of a layer containing the above-mentioned Al-composite pulp, or a laminated sheet consisting of a layer containing the above-mentioned Al-composite pulp and other layers. The thickness of the flame-retardant sheet is not particularly limited and may be, for example, 0.001 to 50 mm or 0.01 to 5 mm.

[0041] The flame-retardant sheet may consist solely of the above-mentioned Al-compound pulp, or it may contain additives as optional components along with the Al-compound pulp. Examples of additives include colorants such as pigments and dyes, water-resistant agents, flame retardants, plasticizers, antioxidants, light stabilizers, fillers, and antistatic agents. In this embodiment, since the Al-compound pulp is flame-retardant, other flame retardants are unnecessary, and therefore, in one embodiment, the flame-retardant sheet does not contain other flame retardants.

[0042] The flame-retardant sheet may be a fibrous sheet such as paper or nonwoven fabric. The pulp constituting the flame-retardant sheet may consist solely of the above-mentioned Al-compounded pulp, or it may contain unmodified pulp along with the Al-compounded pulp. In a composite sheet formed by compounding Al-compounded pulp and unmodified pulp, the ratio of Al-compounded pulp to unmodified pulp is not particularly limited. For example, the mass ratio of Al-compounded pulp to unmodified pulp may be 10 / 90 to 90 / 10, 20 / 80 to 80 / 20, or 30 / 70 to 70 / 30.

[0043] The method for manufacturing the flame-retardant sheet is not particularly limited, but it is preferable to include a neutralization step, an ion exchange step, and a fine particle generation step, similar to those for the flame-retardant material described above. The method for forming the Al-compounded pulp into a sheet using the Al-compounded pulp obtained in these steps is not particularly limited.

[0044] For example, paper as a flame-retardant sheet may be produced by papermaking using a suspension containing Al-compounded pulp as the pulp stock. Papermaking is a process in which the pulp stock is dewatered by filtration to form a sheet, and then pressed and dried to produce paper. For papermaking, known papermaking machines such as a long-wire wet papermaking machine, a twin-wire papermaking machine, a Yankee papermaking machine, a cylinder-wire papermaking machine, and a cylinder-wire short-wire combination papermaking machine may be used. Alternatively, for example, a fibrous sheet as a flame-retardant sheet may be produced by vacuum filtration of a suspension containing Al-compounded pulp to form a sheet, drying it, and then pressing it.

[0045] When producing a composite sheet, for example, in the papermaking process described above, a suspension containing both Al-composite pulp and unmodified pulp may be used as the paper stock. Alternatively, a suspension containing both Al-composite pulp and unmodified pulp may be filtered under reduced pressure to form a sheet, dried, and then pressed to produce a fiber sheet.

[0046] The sheet formation process does not necessarily have to be carried out after the preparation of the Al-compounded pulp. For example, after the neutralization process, a sheet may be formed using a suspension of alkali metal salt-type anionic modified pulp, and then an ion exchange process and a microparticle generation process may be performed on the obtained sheet in that order to produce a flame-retardant sheet containing Al-compounded pulp. In this case, in the ion exchange process, the sheet made of alkali metal salt-type anionic modified pulp is immersed in an aqueous solution of aluminum chloride, and then in the microparticle generation process, the pH is adjusted to 4.0 or higher using a weak base to compound aluminum compound microparticles, which are then purified and dried by pressing to obtain a flame-retardant sheet. [Examples]

[0047] Examples are described in detail below, along with comparative examples. However, the present invention is not limited to these examples.

[0048] The methods for measuring each physical property in the examples and comparative examples are as follows.

[0049] [Amount of anionic groups (amount of carboxyl groups)] A 50 mL aqueous suspension of an acid-type anionic modified pulp with a pulp concentration of 0.1% by mass was prepared, and the pH was adjusted to approximately 2.5 with a 0.1 mol / L hydrochloric acid aqueous solution. Next, a 0.05 mol / L sodium hydroxide aqueous solution was added dropwise to the aqueous suspension, and the electrical conductivity was measured, continuing until the pH reached approximately 11. The amount of carboxyl groups was calculated from the amount of sodium hydroxide (V) consumed during the neutralization stage of the weak acid, where the change in electrical conductivity was gradual, according to the following formula. Carboxylate group content (mmol / g) = V (mL) × [0.05 / mass of acid-type anion-modified pulp (g)]

[0050] [Amount of anionic groups (amount of phosphate groups)] An aqueous suspension was prepared by diluting anionically modified pulp with deionized water to a content of 0.2% by mass. This aqueous suspension was treated with an ion exchange resin to convert it into an acidic type anionically modified pulp, and the amount of phosphate groups was measured by titration with an alkali. The treatment with the ion exchange resin was performed by adding 1 / 10 the volume of strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the aqueous suspension, shaking for 1 hour, and then pouring it onto a 90 μm mesh to separate the ion exchange resin from the aqueous suspension. The titration with alkali was performed by adding 0.1 mol / L sodium hydroxide aqueous solution to the aqueous suspension after treatment with the ion exchange resin in 50 μL increments every 30 seconds, and measuring the change in the electrical conductivity value of the aqueous suspension. 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 of the measurement results by the solid content (g) of the aqueous suspension being titrated.

[0051] [Amount of anionic groups (amount of sulfate groups)] A predetermined amount of acid-type anion-modified pulp was burned, and the sulfur content in the burnt material was measured using a combustion ion chromatograph in accordance with IEC 62321, and then calculated by converting it to the amount of sulfate groups.

[0052] [Presence or absence of fine particles] Pulp sheets were cut with a cutter, and the presence or absence of aluminum compound microparticles was evaluated from electron microscope images of the cut surface at a magnification of 5500x.

[0053] [Average particle size of fine particles] A pulp sheet was cut with a cutter, and 25 aluminum compound microparticles were randomly selected from electron microscope images of the cut surface at a magnification of 5500x. The particle size (equivalent diameter of the projected area circle) was measured, and the average particle size of the aluminum compound microparticles was determined by calculating the arithmetic mean.

[0054] [Mass Increase Rate] The anionically modified pulp with acid-type anionic groups before the neutralization process was dried at 105°C for 3 hours, and its oven-dry mass was measured. Similarly, the pulp after flame-retardant treatment was dried at 105°C for 3 hours, and its oven-dry mass was measured. Subsequently, the mass increase rate was calculated using the following formula. Here, the pulp after flame-retardant treatment refers to the pulp after the fine particle generation process for Examples 1-8 and Comparative Examples 1, 4, and 5, the acid-type anionically modified pulp for Comparative Example 2, and the pulp after the neutralization process for Comparative Example 3. Furthermore, for Comparative Example 4, the denominator in the formula was the oven-dry mass of unmodified softwood kraft pulp instead of the oven-dry mass of the acid-type anionically modified pulp.

number

[0055] [LOI Examination] A 5cm x 7mm test specimen was cut from a pulp sheet or composite sheet, and the Limiting Oxygen Index (LOI) was measured according to JIS K 7201-2. The test specimen was exposed to an indirect flame for 10 seconds, and extinguishing was defined as the complete extinguishing of the flame within 180 seconds of combustion. The minimum oxygen concentration required for the test specimen to maintain combustion for 180 seconds or more was measured, and this value was defined as the LOI. A higher LOI value indicates that the material is less flammable and has superior flame retardancy.

[0056] [Flame Retardant Test] Measurements were taken in accordance with JIS Z 2150. After drying each sample of pulp sheet and composite sheet at 50°C for 48 hours, they were left in a desiccator containing silica gel for 24 hours and then subjected to the flammability test described below. The sample was mounted on a support frame (25cm x 16cm) and then placed in the flammability test apparatus, ensuring there was no slack. After igniting the gas burner, the sample was heated for 1 minute, and the carbonization length, afterflame time, and dust time were measured. A Meckel burner (height 160mm, inner diameter 20mm) was used for heating, and combustion was carried out by supplying only gas without mixing in primary air. The fuel used was liquefied petroleum gas No. 5 (mainly butane and butylene, JIS K 2240), and the flame length was adjusted to 65mm without the sample attached. Next, in accordance with the provisions of JIS Z 2150, the flame retardancy (flame resistance) of the heated test specimen was evaluated according to the fire resistance class described below. • Flame retardant class 1: Carbonized length 5cm or less, no afterburn, no dust remaining after 1 minute. • Flame retardant level 2: Carbonization length 10 cm or less, afterburn 5 seconds or less, no dust remaining after 1 minute. • Flame retardant level 3: Carbonization length 15 cm or less, afterburn 5 seconds or less, no dust remaining after 1 minute. • Not applicable: Does not fall under any of the above fire-retardant grades 1-3. Here, the carbonization length, afterflame, and dust are as follows: • Carbonization length: Measure the maximum length in the longitudinal direction of the support frame for the carbonized portion (the part where carbonization has clearly altered the strength) on the heated surface of the test specimen. • Afterflame: Measure the time the test specimen continues to burn with a flame from the end of heating. (No afterflame means the afterflame lasts approximately 1 second or less.) • Residual dust: Refers to the state of flameless combustion from the end of heating.

[0057] <Preparation of anion-modified pulp A1-A6> Prior to the preparation of the sheets for the examples and comparative examples, the acid-type anion-modified pulps A1 to A6 used therein were prepared according to the following production examples 1 to 6.

[0058] [Manufacturing Example 1: Preparation of Anionically Modified Pulp A1 (TEMPO Oxidized Pulp)] To 2 g of coniferous kraft pulp, 150 mL of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO were added and thoroughly stirred to disperse the mixture. Then, a 13% by mass sodium hypochlorite aqueous solution (co-oxidant) was added so that the amount of sodium hypochlorite was 4.0 mmol / g per 1.0 g of pulp, and the reaction was started. As the reaction progressed, the pH decreased, so a 0.5 mol / L sodium hydroxide aqueous solution was added dropwise to maintain the pH at 10-11, and the reaction was continued until no further change in pH was observed (reaction time: 120 minutes). After the reaction was complete, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, and then the mixture was purified by repeated filtration and washing with water to obtain pulp with an oxidized fiber surface. This was diluted with pure water to a pulp concentration of 4% by mass to prepare a TEMPO-oxidized pulp suspension. Subsequently, the pH of the slurry was adjusted to 10 with a 24% by mass sodium hydroxide aqueous solution, and then 0.2 mmol / g of sodium borohydride was added relative to the pulp to initiate the reaction. The reaction was carried out for 2 hours to perform the reduction treatment. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 2.0, and then the mixture was purified by repeated filtration and washing with water to obtain anionic modified pulp A1 in which the carboxyl group was in the acid form.

[0059] [Manufacturing Example 2: Preparation of Anionically Modified Pulp A2 (TEMPO Oxidized Pulp)] Anionic modified pulp A2, in which the carboxyl group is in the acid form, was obtained using the same method as for preparing anionic modified pulp A1, except that the amount of sodium hypochlorite aqueous solution added was 6.0 mmol / g per 1.0 g of coniferous kraft pulp.

[0060] [Manufacturing Example 3: Preparation of Anionically Modified Pulp A3 (TEMPO Oxidized Pulp)] Anionic modified pulp A3, in which the carboxyl group is in the acid form, was obtained using the same method as for preparing anionic modified pulp A1, except that the amount of sodium hypochlorite aqueous solution added was 8.0 mmol / g per 1.0 g of coniferous kraft pulp.

[0061] [Manufacturing Example 4: Preparation of Anionically Modified Pulp A4 (TEMPO Oxidized Pulp)] Anionic modified pulp A4, in which the carboxyl group is in the acid form, was obtained using the same method as for preparing anionic modified pulp A1, except that the amount of sodium hypochlorite aqueous solution added was 10.0 mmol / g per 1.0 g of coniferous kraft pulp.

[0062] [Manufacturing Example 5: Preparation of Anionically Modified Pulp A5 (Phosphate-Esterified Pulp)] To 100 parts by mass (oven-dry mass) of coniferous kraft pulp, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to adjust the mixture to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain chemically impregnated pulp. Next, the obtained chemically 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, obtaining phosphate-esterified pulp. After the reaction, 0.1 mol / L hydrochloric acid was added to adjust the pH to 1.0, and then purification was carried out by repeated filtration and washing with water to obtain anionic modified pulp A5 in which the fiber surface was phosphate-esterified and the phosphate groups were in the acid type.

[0063] [Manufacturing Example 6: Preparation of Anionically Modified Pulp A6 (Sulfate-Esterified Pulp)] 2 g of coniferous kraft pulp, 20 g of sulfamic acid, 50 g of urea, and 100 g of deionized water were mixed and stirred with a stirring bar for 10 minutes. After stirring, the slurry was filtered by suction using filter paper (No. 2). Suction filtration was continued until no more solution dripped out. After suction filtration, the pulp was peeled off the filter paper and the pulp was placed in a drying oven set to a constant temperature of 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 the pulp was purified by repeated filtration and washing with water, resulting in anionically modified pulp A6 in which the fiber surface was sulfated and the sulfate groups were in the acid form.

[0064] The amount of anionic groups was measured for the anion-modified pulps A1 to A6 of the production examples 1 to 6 prepared above. The results are shown in Table 1 below.

[0065] [Example 1] (neutralization process) Anion-modified pulp A1 was diluted to 0.2% by mass with deionized water, and then neutralized with a 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH (25°C) to 7.0. This yielded a suspension of anion-modified pulp having a sodium salt type carboxyl group.

[0066] (Ion exchange process) To the neutralized suspension, a 0.1 mol / L aqueous aluminum chloride solution was added in an amount equivalent to the amount of carboxyl groups in the anion-modified pulp, and ion exchange between sodium ions and aluminum ions was performed by immersion for 24 hours.

[0067] (Fine particle generation process) Ammonia water was added to the anion-modified pulp suspension after ion exchange, and the pH (25°C) was adjusted to 5.0. This suspension was filtered under reduced pressure using a nylon mesh filter with a mesh size of 59 μm, and then ion-exchanged water was added to adjust the anion-modified pulp concentration to 0.2% by mass. This procedure was repeated three times to wash the anion-modified pulp with water.

[0068] (Preparation of individual pulp sheets) The anion-modified pulp suspension after the generation of fine particles was filtered under reduced pressure using a nylon mesh filter with a mesh size of 59 μm to obtain a sheet-like wet deposit. After air-drying the wet deposit 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 to obtain sheet B1 of Example 1 with a thickness of 100 μm.

[0069] (Preparation of composite sheets) A pulp suspension was prepared by diluting unmodified coniferous pulp to 0.2% by mass with deionized water and dissociating it using a pulper at 3000 rpm for 10 minutes. This pulp suspension and the 0.2% by mass anion-modified pulp suspension obtained in the above fine particle generation step were mixed in a 50:50 mass ratio. A sheet-like wet deposit was obtained by vacuum filtration through a nylon mesh filter with a mesh size of 59 μm. After air-drying the wet deposit 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 to obtain a composite sheet C1 of anion-modified pulp and unmodified pulp.

[0070] [Example 2] Except for using anion-modified pulp A2, the neutralization step, ion exchange step, fine particle generation step, preparation of single pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 1 to obtain sheet B2 and composite sheet C2 of Example 2.

[0071] [Example 3] Except for using anion-modified pulp A3, the neutralization step, ion exchange step, fine particle generation step, preparation of single pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 1 to obtain sheet B3 and composite sheet C3 of Example 3.

[0072] [Example 4] Except for using anion-modified pulp A4, the neutralization step, ion exchange step, fine particle generation step, preparation of single pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 1 to obtain sheet B4 and composite sheet C4 of Example 4.

[0073] [Example 5] Except for adjusting the pH from 5.0 to 4.5 in the microparticle generation process, the neutralization process, ion exchange process, microparticle generation process, preparation of individual pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 3 to obtain Sheet B5 and composite sheet C5 of Example 5.

[0074] [Example 6] Except for adjusting the pH from 5.0 to 6.0 in the microparticle generation process, the neutralization process, ion exchange process, microparticle generation process, preparation of individual pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 3 to obtain Sheet B6 and composite sheet C6 of Example 6.

[0075] [Example 7] Except for using anion-modified pulp A5, the neutralization step, ion exchange step, fine particle generation step, preparation of individual pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 1 to obtain sheet B7 and composite sheet C7 of Example 7.

[0076] [Example 8] Except for using anion-modified pulp A6, the neutralization step, ion exchange step, fine particle generation step, preparation of single pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 1 to obtain sheet B8 and composite sheet C8 of Example 8.

[0077] [Comparative Example 1] Except for adjusting the pH from 5.0 to 3.4 in the microparticle generation process, the neutralization process, ion exchange process, microparticle generation process, preparation of individual pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 3 to obtain Sheet B11 and Composite Sheet C11 of Comparative Example 1.

[0078] [Comparative Example 2] In Example 3, the neutralization step, ion exchange step, and fine particle generation step were omitted. Instead, the pulp was kept in its acidic state, and the individual pulp sheets and composite sheets were prepared in the same manner as in Example 3 to obtain Sheet B12 and composite sheet C12 of Comparative Example 2.

[0079] [Comparative Example 3] Using anion-modified pulp A3, a neutralization step was carried out in the same manner as in Example 3. Subsequently, without performing the ion exchange step and the fine particle generation step, a single pulp sheet and a composite sheet were prepared in the same manner as in Example 3 to obtain Comparative Example 3's sheet B13 and composite sheet C13.

[0080] [Comparative Example 4] Except for using softwood kraft pulp instead of anion-modified pulp A3, the neutralization process, ion exchange process, fine particle generation process, preparation of single pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 3 to obtain Sheet B14 and composite sheet C14 of Comparative Example 4.

[0081] [Comparative Example 5] Except for using a 0.1 M sodium hydroxide aqueous solution instead of ammonia water in the fine particle generation process, the neutralization process, ion exchange process, fine particle generation process, preparation of individual pulp sheets, and preparation of composite sheets were carried out in the same manner as in Example 3 to obtain Sheet B15 and composite sheet C15 of Comparative Example 5.

[0082] [Comparative Example 6] A 0.1 mol / L aqueous solution of aluminum chloride was mixed with aqueous ammonia to adjust the pH (25°C) to 5.0. This suspension was filtered under reduced pressure using a nylon mesh filter with a mesh size of 59 μm, and then washed with water by repeating the process of adding deionized water three times. The resulting particulate precipitate was filtered under reduced pressure using a nylon mesh filter with a mesh size of 59 μm to obtain fine particles, but sheet formation was not possible.

[0083] For Examples 1-8 and Comparative Examples 1-5, the mass increase rate due to flame retardant treatment was measured. Furthermore, for sheets B1-B8 of Examples 1-8 and sheets B11-B15 of Comparative Examples 1-5, the presence or absence of fine particles and their average particle size were measured, and LOI tests and flame retardant tests were performed. Additionally, for composite sheets C1-C8 of Examples 1-8 and composite sheets C11-C15 of Comparative Examples 1-5, LOI tests and flame retardant tests were performed. The results are shown in Tables 1 and 2 below.

[0084] [Table 1]

[0085] [Table 2]

[0086] As shown in Table 2, Comparative Example 4, which was made into a sheet using unmodified pulp, and Comparative Example 2, which was made into a sheet using acid-type anion-modified pulp, did not exhibit flame retardancy. Furthermore, Comparative Example 3, in which the counterion of the anion-modified pulp was a sodium ion, also showed inferior flame retardancy.

[0087] On the other hand, in Comparative Examples 1 and 5, sheets were formed using anion-modified pulp in which the counterion was an aluminum ion. In Comparative Example 1, the pH after adding a weak base in the microparticle production process was low, and as shown in Figure 2, no aluminum compound microparticles were observed on the surface or inside the pulp in the electron microscope image (magnification 5500x) of the cross-section of the pulp sheet. In Comparative Example 5, the pH was adjusted with a strong base in the microparticle production process, and no aluminum compound microparticles were observed on the surface or inside the pulp in electron microscope observation. Therefore, although Comparative Examples 1 and 5 showed an improvement in flame retardancy compared to Comparative Examples 2 to 4, the effect was insufficient.

[0088] In contrast, in Examples 1 to 8, electron microscopy (magnification 5500x) revealed the formation of aluminum compound fine particles on the surface and inside the pulp. Figure 1 shows an example of this, an electron micrograph of a cross-section of a pulp sheet from Example 3, where the formation of fine particles on the surface and inside the pulp was observed. The presence of these aluminum compound fine particles was confirmed by subsequent electron microscopy observation, even though the pulp was washed after pH adjustment in the fine particle generation process, indicating that they were not simply mixed in but were compounded into the pulp. Examples 1 to 8 showed higher LOI (Liquid Element Indication) and improved flame retardancy compared to Comparative Examples 1 and 5, as well as Comparative Examples 2 to 4. Furthermore, flame retardancy was improved while suppressing the mass increase compared to Comparative Examples 1 and 5.

[0089] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

[0090] Although several 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, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, and modifications are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. A flame-retardant material comprising anion-modified pulp, wherein the counterions of the anionic groups of the anion-modified pulp contain aluminum ions, and further, aluminum compound fine particles are compounded on the surface of the pulp and / or inside the pulp.

2. The flame retardant material according to claim 1, wherein the anion-modified pulp has an amount of anionic groups measured by converting all of the anionic groups to the acid type of 0.8 to 3.0 mmol / g.

3. The flame retardant material according to claim 1, wherein the anionic group is a carboxyl group.

4. A flame-retardant sheet comprising anion-modified pulp, wherein the counterions of the anionic groups of the anion-modified pulp contain aluminum ions, and further, aluminum compound fine particles are compounded on the surface of the pulp and / or inside the pulp.

5. The flame-retardant sheet according to claim 4, wherein the anion-modified pulp has an amount of anionic groups measured by converting all of the anionic groups to the acid form of 0.8 to 3.0 mmol / g.

6. The flame-retardant sheet according to claim 4, wherein the anionic group is a carboxyl group.

7. Furthermore, the flame-retardant sheet according to claim 4, further comprising unmodified pulp.

8. A method for manufacturing a flame-retardant material according to any one of claims 1 to 3 or a flame-retardant sheet according to any one of claims 4 to 7, A process to neutralize acid-type anion-modified pulp, A process of ion-exchanging the counterions of the anionic groups of the neutralized anion-modified pulp with aluminum ions using aluminum chloride, and After ion exchange, the pH is adjusted to 4.0 or higher using a weak base in the presence of aluminum chloride. A manufacturing method that includes this.

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