Flame retardant treatment liquid and flame retardant treatment method

Abstract

To provide a flame retardant liquid and a flame retardant method that can impart flame retardancy and water resistance to a target material including an OH group, such as wood, at relatively low temperatures.SOLUTION: A flame retardant liquid includes polyphosphoric acid alkyl amine salt, urea, and water. A flame retardant method includes an impregnation step for impregnating a target material including an OH group with the flame retardant liquid, and a heating step for heating the target material impregnated with the flame retardant liquid within the temperature range of 110°C or higher but lower than 140°C .SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a flame retardant treatment liquid and a flame retardant treatment method.

Background Art

[0002] Conventionally, flame retardancy has been imparted by applying a flame retardant to wood, fibers, etc. For example, as a flame retardant for wood, water-soluble flame retardants such as guanidine phosphate, ammonium phosphate, and ammonium polyphosphate are known. By impregnating wood with a flame retardant treatment liquid obtained by dissolving these flame retardants in water and drying it, flame retardancy can be imparted.

[0003] Among the flame retardants for wood, exterior flame retardants used for wood facing the outdoors, etc., are required to have high water resistance as well as flame retardancy. This is to suppress the leakage of the chemical due to exposure to rain and wind when using wood impregnated with the flame retardant treatment liquid for exterior use.

[0004] However, when a water-soluble flame retardant such as guanidine phosphate is used alone, although it can impart flame retardancy to wood, it cannot sufficiently impart water resistance.

[0005] Also, a method of imparting flame retardancy to wood by fixing phosphoric acid or polyphosphoric acid to wood has been proposed (see, for example, Patent Documents 1, 2, and Non-Patent Document 1). In this method, urea is used as a reaction accelerator, and phosphoric acid or polyphosphoric acid and cellulose in wood are reacted (phosphorylation of cellulose) to fix the chemical to the wood.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007] [Non-Patent Document 1] Journal of Engineering Chemistry, Vol. 69, No. 4, pp. 681-685, 1969. [Overview of the project] [Problems that the invention aims to solve]

[0008] However, while the aforementioned method of fixing phosphoric acid or polyphosphate to wood can impart flame retardancy to the wood, it cannot adequately impart water resistance. When cellulose is phosphate-esterified using ammonium phosphate and urea, the water resistance is poor, which is a problem. Furthermore, while phosphate-esterifying cellulose with polyammonium phosphate and urea allows for both flame retardancy and water resistance, high temperatures (above 140°C) are required for fixation (reaction) to wood. Heating wood above 140°C easily causes thermal damage.

[0009] This disclosure has been made in view of these circumstances, and one embodiment of this disclosure aims to solve the problem of providing a flame-retardant treatment liquid that can impart both flame retardancy and water resistance to a workpiece containing OH groups, such as wood, at a relatively low temperature. Furthermore, other embodiments of this disclosure aim to solve the problem of providing a flame-retardant treatment method that can impart both flame retardancy and water resistance to a workpiece containing OH groups, such as wood, at a relatively low temperature. [Means for solving the problem]

[0010] Specific means for solving the above problems include the following embodiments. <1> A flame-retardant treatment solution containing an alkylamine polyphosphate salt, urea, and water. <2> The alkylamine in the aforementioned alkylamine polyphosphate salt has 1 to 6 carbon atoms. <1> The flame retardant treatment liquid described above. <3> The alkylamine in the alkylamine polyphosphate salt is at least one selected from the group consisting of methylamine, ethylamine, propylamine, isopropylamine, n-butylamine, dimethylamine, methylethylamine, diethylamine, methylpropylamine, ethylpropylamine, trimethylamine, dimethylethylamine, dimethylpropylamine, methyldiethylamine, and triethylamine. <1> or <2> The flame retardant treatment liquid described above. <4> For materials containing OH groups, <1> ~ <3> An impregnation step in which the flame retardant treatment liquid described in any one of the following is impregnated, A heating step of heating the object to be treated, which is impregnated with the flame-retardant treatment liquid, to a temperature of 110°C or higher and less than 140°C, A flame-retardant treatment method including the following. <5> The treated material contains a cellulose structure <4> The flame-retardant treatment method described above. <6> The object to be treated is wood. <4> or <5> The flame-retardant treatment method described above. [Effects of the Invention]

[0011] According to one embodiment of the present disclosure, a flame-retardant treatment liquid is provided that can impart both flame retardancy and water resistance to a workpiece containing OH groups, such as wood, at a relatively low temperature. According to other embodiments of this disclosure, a flame retardant treatment method is provided that can impart both flame retardancy and water resistance to a workpiece containing OH groups, such as wood, at a relatively low temperature. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the presumed mechanism by which cellulose is phosphate-esterified by the flame-retardant treatment solution relating to this disclosure. [Figure 2] This is a schematic diagram showing an example of a procedure for flame-retardant treatment of wood using the flame-retardant treatment method described herein. [Modes for carrying out the invention]

[0013] Hereinafter, the flame retardant treatment liquid and the flame retardant treatment method according to the present disclosure will be described in detail with reference to the drawings.

[0014] In this specification, the numerical range indicated by using "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in this specification, the upper limit value described in a certain numerical range may be replaced with the upper limit value of the numerical range described in other step-by-step descriptions, and the lower limit value described in a certain numerical range may be replaced with the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0015] In this specification, the amount of each component in the flame retardant treatment liquid means the total amount of a plurality of substances present in the flame retardant treatment liquid when there are a plurality of substances corresponding to each component in the flame retardant treatment liquid, unless otherwise specified. In this specification, the combination of two or more preferred embodiments is a more preferred embodiment. In this specification, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.

[0016] [Flame Retardant Treatment Liquid] The flame retardant treatment liquid according to the present disclosure contains an alkylamine polyphosphate salt, urea, and water. By impregnating the flame retardant treatment liquid according to the present disclosure into a workpiece containing an OH group such as wood (which may be simply referred to as "workpiece" in this specification) and performing heat treatment at a relatively low temperature below 140°C, it is possible to impart both flame retardancy and water resistance. The reason why such flame retardancy and water resistance can be achieved simultaneously is not clear, but it is presumed as follows.

[0017] It is believed that using the flame-retardant treatment solution described herein, even when heat-treated at relatively low temperatures, the treated material containing OH groups will be phosphate-esterified, thereby imparting both flame retardancy and water resistance. Figure 1 shows the hypothesized mechanism by which cellulose is phosphate-esterified when the treated material contains a cellulose structure, using the flame-retardant treatment solution described herein. Heating to a temperature between 110°C and below 140°C decomposes urea, generating isocyanic acid. Then, isocyanic acid adds to polyphosphate, which has been dissociated from the alkylamine polyphosphate salt by alkylammonium ions, improving its reactivity. Note that the dissociated alkylammonium ions are omitted in Figure 1. The reaction between the polyphosphate, whose reactivity has been improved by the addition of isocyanic acid, and cellulose is thought to proceed via either pathway A or B. In pathway A, the polyphosphate, whose reactivity has been improved by the addition of isocyanic acid, further polymerizes with polyphosphate and then reacts with cellulose to produce phosphate esterification. In pathway B, the polyphosphate, whose reactivity has been improved by the addition of isocyanic acid, reacts with cellulose to produce phosphate esterification.

[0018] It is presumed that the phosphate esterification of cellulose using a flame-retardant treatment solution containing ammonium polyphosphate proceeds through a similar mechanism. However, because ammonium polyphosphate has stronger ionic bonds than alkylamine polyphosphate salts, the ammonium ions are less likely to dissociate. Therefore, the reaction with isocyanic acid also proceeds less smoothly, and it is presumed that the reaction rate of phosphate esterification decreases.

[0019] It should be noted that the mechanism described above is speculative, and the flame-retardant treatment liquid and flame-retardant treatment method relating to this disclosure are not limited in any way to the speculative mechanism shown in Figure 1.

[0020] The following describes each component contained in the flame-retardant treatment liquid related to this disclosure.

[0021] <Alkylamine polyphosphate salt> Alkylamine polyphosphate salts can be obtained, for example, by reacting ammonium polyphosphate with an alkylamine in an aqueous solution (salt exchange). Water-soluble alkylamine polyphosphate salts are preferred. Examples of alkylamines in alkylamine polyphosphate salts include monoalkylamines such as methylamine, ethylamine, propylamine, isopropylamine, and n-butylamine; dialkylamines such as dimethylamine, methylethylamine, diethylamine, methylpropylamine, and ethylpropylamine; and trialkylamines such as trimethylamine, dimethylethylamine, dimethylpropylamine, methyldiethylamine, and triethylamine.

[0022] Furthermore, amines with a large number of carbon atoms, such as methyldipropylamine and dibutylamine, are water-insoluble, and therefore salt exchange reactions do not proceed easily in aqueous solutions. From the viewpoint of water solubility, the alkylamine in the alkylamine polyphosphate salt preferably has 1 to 6 carbon atoms, and more specifically, it is preferably at least one selected from dimethylamine, diethylamine, trimethylamine, triethylamine, and n-butylamine.

[0023] In particular, from the viewpoint of water solubility when preparing the flame-retardant treatment solution and imparting flame retardancy and water resistance to the treated object by heating it at the lowest possible temperature, it is preferable that the alkylamine in the alkylamine polyphosphate salt is at least one selected from the group consisting of diethylamine, trimethylamine, triethylamine, and n-butylamine. The flame retardant treatment solution may contain one type of alkylamine polyphosphate salt, or two or more types.

[0024] The molecular weight of the alkylamine polyphosphate salt is not particularly limited, but from the viewpoint of preparing the flame retardant treatment solution, impregnation into the treated object, and flame retardancy, a range of 200 to 4500 is preferred.

[0025] The content of the alkylamine polyphosphate salt in the flame retardant treatment solution is not particularly limited, but from the viewpoint of imparting high flame retardancy to the treated material, it is preferably 10 to 40% by mass, and more preferably 15 to 35% by mass, based on the total mass of the flame retardant treatment solution.

[0026] <Urea> The urea in the flame retardant treatment solution acts as a reaction accelerator. The urea content in the flame retardant treatment solution is not particularly limited, but from the viewpoint of imparting high flame retardancy to the treated material, it is preferably 10 to 40% by mass, and more preferably 15 to 35% by mass, relative to the total mass of the flame retardant treatment solution.

[0027] <Water> Tap water, deionized water, etc., can be used for the water. The water content is not particularly limited as long as it can dissolve the alkylamine polyphosphate salt and urea, but is preferably 15% to 75% by mass, and more preferably 25% to 65% by mass, based on the total mass of the flame retardant treatment solution.

[0028] <Other ingredients> The flame-retardant treatment liquid relating to this disclosure may also contain other components as needed. Other components include, for example, boric acid, phosphoric acid, sulfuric acid, sulfamic acid, sodium borate, guanylurea phosphate, guanidine borate, guanidine sulfate, guanidine sulfamate, and ammonium phosphate.

[0029] <Preparation of flame-retardant treatment solution> The method for preparing the flame-retardant treatment solution relating to this disclosure is not particularly limited, and can be prepared, for example, by the following procedure. After dissolving water-soluble ammonium polyphosphate in water, add ion exchange resin, stir, and filter. Next, alkylamine is added to the obtained filtrate while stirring, and after the addition is complete, stirring is continued to obtain an aqueous solution of alkylamine polyphosphate salt. Furthermore, urea is added to the obtained aqueous solution of alkylamine polyphosphate and stirred at room temperature. This yields the flame-retardant treatment solution according to the present disclosure.

[0030] [Flame retardant treatment method] Next, the flame-retardant treatment method related to this disclosure will be described. The flame retardant treatment method according to this disclosure includes an impregnation step of impregnating a workpiece containing OH groups with the aforementioned flame retardant treatment liquid according to this disclosure, and a heating step of heating the workpiece impregnated with the flame retardant treatment liquid at 110°C or higher and less than 140°C. The following describes each step of the flame-retardant treatment method related to this disclosure.

[0031] <Impregnation process> The object to be treated, which contains OH groups, is impregnated with the flame-retardant treatment solution according to this disclosure. For example, the object to be treated can be impregnated by immersing it in a container containing the flame-retardant treatment solution.

[0032] The material to be treated is not limited as long as it contains OH groups and is impregnated with the flame-retardant treatment solution. Examples include wood, cloth made from plant fibers such as cotton and hemp, paper, and nonwoven fabrics containing a cellulose structure, with wood being particularly preferred. The size and shape of the object to be processed are not particularly limited, and any object of a desired size and shape can be used.

[0033] There are no particular limitations on the immersion time, and it depends on the material of the object to be treated. However, in the case of wood, it is preferable to immerse it for 10 minutes or more from the viewpoint of allowing the flame retardant treatment solution to penetrate sufficiently.

[0034] <Heating process> After the impregnation process, the object to be treated, which has been impregnated with the flame-retardant treatment solution, is heated to a temperature between 110°C and 140°C. By heating the material impregnated with the flame-retardant treatment solution at a temperature of 110°C to less than 140°C, the isocyanic acid produced by the decomposition of urea adds to the polyphosphate, improving reactivity. This allows for the esterification of cellulose into polyphosphate at a relatively low temperature, while also suppressing heat-induced damage to the material. From the viewpoint of suppressing urea decomposition and heat-induced damage to the material, a heating temperature of 115°C to 130°C is preferred. The heating time depends on the heating temperature, the material of the material being treated, the content of the alkylamine polyphosphate salt, the content of urea, etc., but from the viewpoint of phosphate esterification and productivity, it is preferably 2 hours to 15 hours, and more preferably 4 hours to 10 hours. When treating wood for flame retardancy using a flame retardant solution containing, for example, triethylamine salt of polyphosphate as an alkylamine polyphosphate, the reaction (phosphate esterification) can be carried out at 120-130°C for 3-10 hours.

[0035] Here, we will describe an example of a preferred procedure for flame-retardant treatment of wood using the flame-retardant treatment method according to this disclosure. Figure 2 is a schematic diagram showing an example of a procedure for flame-retardant treatment of wood using the flame-retardant treatment method according to this disclosure.

[0036] (A) Rough machining First, the wood to be treated is roughly processed to a size that fits into the chemical solution pool. In the case of wood, if the outer surface to which flame retardancy has been imparted by the flame retardant treatment according to this disclosure is shaved down to the desired shape, the flame retardancy will decrease. Therefore, it is preferable to process the wood to the desired shape or a shape close to it in advance.

[0037] (B) Drying treatment After rough processing, a drying treatment is performed. For example, the roughly processed wood is placed in a desiccator or dryer and left at 20-100°C for 1-20 hours to remove moisture. Removing moisture through the drying treatment makes it easier for the flame retardant treatment solution to penetrate the wood.

[0038] (C) Chemical impregnation After drying, the wood is immersed in a pool of flame-retardant treatment solution (chemical solution) to allow it to be impregnated. The wood is left immersed in the chemical solution for, for example, 1 to 30 hours. The impregnation may be accelerated by reducing the pressure inside the container. Alternatively, the chemical solution may be heated to accelerate impregnation.

[0039] (D) Drying treatment After impregnating the wood with the chemical solution, remove the wood from the solution pool and leave it in a desiccator or dryer at 20-100°C for 1-40 hours to remove the moisture from the solution.

[0040] (E) Heat treatment After drying, the wood is placed in a drying oven and heated to a temperature between 110°C and 140°C to allow the chemicals to react. The heating conditions (heating temperature and heating time) should be set for each chemical solution.

[0041] (F) Processing After heat treatment, the material is processed to the desired size and shape as needed.

[0042] Through the above process, wood with both flame retardancy and water resistance can be obtained. The flame-retardant treated wood according to this disclosure not only has flame retardancy but also high water resistance, meaning that the leaching of chemicals due to exposure to rain and wind is suppressed, making it suitable for use as wood for exteriors and other outdoor applications. [Examples]

[0043] The following describes examples of the flame-retardant treatment liquid and flame-retardant treatment method relating to this disclosure, but this disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure.

[0044] <Preparation of flame-retardant treatment solution> A flame retardant treatment solution was prepared using the following flame retardants (1) to (8) to achieve a solid content of 30% by mass.

[0045] (1) Guanidine phosphate type flame retardant 500g of AP-307 [Sanwa Chemical's guanidine phosphate aqueous solution NV50] was mixed with 333g of water and stirred at 25°C for 1 hour to prepare a flame-retardant treatment solution.

[0046] (2) Resin-based flame retardants 216 g of guanidine phosphate was mixed with 98 g of 92% paraform and 271 g of water, and heated and stirred at 60°C for 1 hour to obtain a 50% aqueous solution of methylolated guanidine phosphate. 300 g of a 50% aqueous solution of Sanwa Chemical's DMDHEU (dimethylol dihydroxyethylene urea), 300 g of a 50% aqueous solution of methylolated guanidine phosphate, and 400 g of water were added and mixed to prepare a flame-retardant treatment solution. The flame-retardant treatment solution was prepared so that the resin component of Sanwa Chemical's DMDHEU (dimethylol dihydroxyethylene urea) and the flame retardant component were in a 1:1 (weight ratio) solid content.

[0047] (3) Ammonium phosphate type flame retardants A flame-retardant treatment solution was prepared by adding 120 g of urea, 115 g of ammonium phosphate, and 548 g of water, and stirring at 25°C for 1 hour.

[0048] (4) Ammonium polyphosphate type flame retardants A flame-retardant treatment solution was prepared by adding 120 g of urea, 98 g of ammonium polyphosphate [water-soluble ammonium polyphosphate NNA20 manufactured by Amada Co., Ltd.], and 509 g of water, and stirring at 25°C for 1 hour.

[0049] (5) Triethylamine polyphosphate type flame retardants 98 g of ammonium polyphosphate was dissolved in 702 g of deionized water, then 200 cc of ion exchange resin (SK1BH, manufactured by Mitsubishi Chemical Corporation) was added and stirred for 10 minutes, followed by filtration. Next, 101 g of triethylamine was added to the obtained filtrate while stirring, and after the addition was completed, the mixture was stirred for another 5 minutes to obtain an aqueous solution of triethylamine polyphosphate salt. 120 g of urea was added to the obtained aqueous solution and stirred at 25°C for 1 hour to prepare a flame retardant treatment solution.

[0050] (6) Trimethylamine polyphosphate type flame retardants 98 g of ammonium polyphosphate was dissolved in 469 g of deionized water, then 200 cc of ion exchange resin (SK1BH, manufactured by Mitsubishi Chemical Corporation) was added and stirred for 10 minutes, followed by filtration. Next, 197 g of 30% trimethylamine aqueous solution was added to the filtrate while stirring, and after the addition was complete, stirring was continued for another 5 minutes to obtain an aqueous solution of trimethylamine polyphosphate. 120 g of urea was added to the obtained aqueous solution and stirred at 25°C for 1 hour to prepare a flame retardant treatment solution.

[0051] (7) Diethylamine polyphosphate type flame retardants 98 g of ammonium polyphosphate was dissolved in 639 g of deionized water, then 200 cc of ion exchange resin (SK1BH, manufactured by Mitsubishi Chemical Corporation) was added and the mixture was stirred for 10 minutes, followed by filtration. Next, 73 g of diethylamine was added to the filtrate while stirring, and the mixture was stirred for another 5 minutes after the addition was complete to obtain an aqueous solution of diethylamine polyphosphate salt. 120 g of urea was added to the obtained aqueous solution and the mixture was stirred at 25°C for 1 hour to prepare a flame retardant treatment solution.

[0052] (8) n-butylamine polyphosphate type flame retardants 98 g of ammonium polyphosphate was dissolved in 639 g of deionized water, then 200 cc of ion exchange resin (SK1BH, manufactured by Mitsubishi Chemical Corporation) was added and the mixture was stirred for 10 minutes, followed by filtration. Next, 73 g of n-butylamine was added to the filtrate while stirring, and the mixture was stirred for another 5 minutes after the addition was complete to obtain an aqueous solution of n-butylamine polyphosphate. 120 g of urea was added to the obtained aqueous solution and the mixture was stirred at 25°C for 1 hour to prepare a flame-retardant treatment solution.

[0053] <Preparation of wood samples> (Preparation of wood-based materials) A piece of cedar wood measuring 120mm x 30mm x 5mm was prepared and stored in a desiccator containing a desiccant at 25°C for 6 hours. The weight A0 of the wood material after storage was measured using an electronic balance (product name "AP224X", manufactured by Shimadzu Corporation).

[0054] (Flame retardant treatment) The dried wood was placed in a container and the pressure was reduced using a vacuum pump (product name "TST-300", manufactured by Sato Vacuum Co., Ltd.). A valved tube was placed in the container, and the valve was opened under reduced pressure, and the prepared flame retardant treatment solution (hereinafter sometimes referred to as chemical solution (1) to (8)) was poured in. After confirming that the wood was completely immersed in the flame retardant treatment solution, the pressure was released and the wood was left at 25°C for 20 hours. The wood impregnated with the flame retardant treatment solution was dried in a dryer (product name "WFO-420", manufactured by Tokyo Rikakikai Co., Ltd.) at 60°C for 20 hours. When chemical solution (1) was used, the samples were then stored in a desiccator with a desiccant at 25°C for 6 hours. When chemical solutions (2) to (8) were used, the samples were heated at 120°C for 9 hours, and then stored in a desiccator with a desiccant at 25°C for 6 hours. The weight A1 of the wood after storage was measured using an electronic balance (product name "AP224X", manufactured by Shimadzu Corporation). The weight obtained by subtracting weight A0 from weight A1 was calculated as the amount of chemical adhering to the wood. Amount of chemical applied = weight A1 - weight A0

[0055] <Evaluation Method> As described above, wood samples impregnated with each flame retardant were evaluated for water resistance and flame retardancy using the following method.

[0056] (water resistance) Wood samples impregnated with each chemical were immersed in 500 mL of 40°C water and left for 8 hours. After 8 hours, the wood samples were removed. The removed wood samples were dried in a drying oven (product name "WFO-420", manufactured by Tokyo Rikakikai Co., Ltd.) at 60°C for 20 hours, and then stored in a desiccator with a desiccant at 25°C for 6 hours. The weight B1 of the wood samples after storage was measured using an electronic balance (product name "AP224X", manufactured by Shimadzu Corporation). The amount of remaining drug was calculated by subtracting weight A0 from weight B1. Drug remaining amount = weight B1 - weight A0 Based on the following formula, the drug retention rate was calculated, and a drug retention rate of 40% or more was evaluated as having excellent water resistance. Drug retention rate (%) = (Amount of drug remaining / Amount of drug adhering) × 100

[0057] (Flame retardant) The oxygen index of wood samples after water resistance evaluation was measured using a candle combustion tester (model "AC-2", manufactured by Toyo Seiki Co., Ltd.). In this specification, the oxygen index refers to the oxygen concentration required for the burning length after ignition to be 8 cm or more, or for the burning time to be 3 minutes or more. Flame retardancy was evaluated based on the measured oxygen index. A material was judged to have excellent flame retardancy if its oxygen index after water resistance evaluation was 40 or higher. The results are shown in Table 1.

[0058] [Table 1]

[0059] <Evaluation Results> It can be seen that using flame retardant solutions (5) to (8) containing alkylamine salts of polyphosphate provides superior water resistance and flame retardancy compared to flame retardant solutions (1) to (4). Similar effects can be expected from amines other than those used in the preparation of the flame-retardant treatment solutions in (5) to (8), as long as they are water-soluble amines.

Claims

1. It contains an alkylamine polyphosphate salt, urea, and water. A flame-retardant treatment liquid that imparts flame retardancy to a treated object, wherein the alkylamine in the alkylamine polyphosphate salt is at least one selected from the group consisting of n-butylamine, diethylamine, trimethylamine, and triethylamine.

2. The content of the alkylamine polyphosphate salt is 10 to 40% by mass relative to the total mass of the flame retardant treatment solution. The urea content is 10 to 40% by mass relative to the total mass of the flame retardant treatment liquid. The flame retardant treatment liquid according to claim 1, wherein the water content is 15 to 75% by mass of the total mass of the flame retardant treatment liquid.

3. An impregnation step of impregnating a workpiece containing OH groups with the flame retardant treatment liquid described in claim 1 or claim 2, A heating step of heating the object to be treated, which is impregnated with the flame-retardant treatment liquid, to a temperature of 110°C or higher and less than 140°C, A flame-retardant treatment method including the following.

4. The flame retardant treatment method according to claim 3, wherein the treated material includes a cellulose structure.

5. The flame retardant treatment method according to claim 3 or 4, wherein the object to be treated is wood.

Images