A low-temperature flame-retardant polyurethane material for coal mines, a preparation method and application thereof

Abstract

The present application belongs to the technical field of mine materials, and particularly relates to a low-temperature flame-retardant polyurethane material for coal mines, a preparation method and application thereof. The low-temperature flame-retardant polyurethane material for coal mines comprises the following raw material components in parts by weight: polyether polyol 30-40 parts, isocyanate 35-45 parts, modifier 1-3 parts, catalyst 1-3 parts, flame retardant 5-10 parts, foaming agent 5-10 parts, and stabilizer 10-15 parts. The low-temperature flame-retardant polyurethane material for coal mines has the characteristics of low-temperature synthesis, strong flame-retardant performance, good fluidity, high strength, etc., can be tightly combined with the bonding part of coal blocks without gaps, has good sealing effect, and plays a plugging effect. Meanwhile, the material has high strength and good flame-retardant performance, and has the advantages of low temperature, flame retardancy, high strength, etc. in the use in coal mines.

Description

Technical Field

[0001] The invention belongs to the technical field of mine materials, and particularly relates to a low-temperature flame-retardant polyurethane material for coal mines, a preparation method thereof, and an application thereof. Background Art

[0002] Spontaneous coal combustion is a major disaster in coal mines, primarily occurring in goaf areas. Spontaneous coal combustion continues to pose a global threat to coal mine safety. Areas of high risk for spontaneous coal combustion include geological anomalies, isolated coal pillars, air leaks in goaf areas, and caving in tunnels. In my country, goaf areas created by underground mining can become unstable, leading to large-scale caving and compromising the structural safety of mines.

[0003] Polyurethane polymers, commonly used underground plugging materials, are inherently flammable and can easily cause fires. While polyurethane's various properties are currently under extensive research, the long-term use of polyurethane as a reinforcement for coal seams, which are prone to spontaneous combustion, can increase the internal temperature of the coal seams. This heat builds up, exacerbating spontaneous combustion and causing fires and economic losses. Fires caused by polyurethane reinforcement have been increasing in recent years. Therefore, it is crucial to develop a low-temperature synthesized, flame-retardant polyurethane material for coal mines to address this issue.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-temperature flame-retardant polyurethane material for coal mines, a preparation method and application thereof; the low-temperature flame-retardant polyurethane material for coal mines has the characteristics of low-temperature synthesis, strong flame retardant performance, good fluidity, high strength, etc., can be tightly bonded to coal blocks without gaps, has a good sealing effect, and plays a role in plugging leaks.

[0006] In order to overcome the deficiencies of the prior art, the present invention provides the following technical solutions:

[0007] A low-temperature flame-retardant polyurethane material for coal mines comprises the following raw material components, measured by weight: 30-40 parts of polyether polyol, 35-45 parts of isocyanate, 1-3 parts of modifier, 1-3 parts of catalyst, 5-10 parts of flame retardant, 5-10 parts of foaming agent, and 10-15 parts of stabilizer.

[0008] Furthermore, the following raw material components are included in parts by weight: 34 parts of polyether polyol, 38 parts of isocyanate, 1 part of modifier, 1 part of catalyst, 7 parts of flame retardant, 6 parts of foaming agent, and 13 parts of stabilizer.

[0009] Furthermore, the isocyanate includes one or both of hexamethylene diisocyanate and isophorone diisocyanate.

[0010] Furthermore, the isocyanate is a mixture of hexamethylene diisocyanate and isophorone diisocyanate; the weight ratio of the hexamethylene diisocyanate to isophorone diisocyanate is 1:1.

[0011] Furthermore, the polyether polyol includes one or both of polyether polyol N330 and polyether polyol N303.

[0012] Furthermore, the polyether polyol is a mixture of polyether polyol N330 and polyether polyol N303; the weight ratio of the polyether polyol N330 to the polyether polyol N303 is 1:1.

[0013] Furthermore, the catalyst includes one or both of a tertiary amine catalyst and a tin catalyst;

[0014] And / or, the flame retardant includes one or both of a nano flame retardant and diethyl aluminum hypophosphite.

[0015] and / or, the blowing agent is HCFC-141b;

[0016] And / or, the stabilizer is dimethyl silicone oil.

[0017] In addition, the present invention also provides a method for preparing the above-mentioned low-temperature flame-retardant polyurethane material for coal mines, comprising the following steps:

[0018] The polyether polyol, catalyst, stabilizer, modifier and flame retardant are sequentially added into a reaction vessel, mixed evenly, and then a foaming agent is added. After further stirring, isocyanate is added and mixed evenly to obtain the low-temperature flame-retardant polyurethane material for coal mines.

[0019] Furthermore, the method further comprises the following steps: mixing hexamethylene diisocyanate and isophorone diisocyanate in a weight ratio of 1:1 and stirring uniformly;

[0020] And / or, polyether polyol N330 and polyether polyol N303 are mixed and stirred uniformly in a weight ratio of 1:1.

[0021] In addition, the present invention also provides the above-mentioned low-temperature flame-retardant polyurethane material for coal mines and the use of the low-temperature flame-retardant polyurethane material for coal mines prepared by the above-mentioned preparation method as a plugging material in coal mines.

[0022] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0023] The low-temperature flame-retardant polyurethane material for coal mines of the present invention features low-temperature synthesis, strong flame retardancy, good fluidity, and high strength. It adheres tightly to coal blocks without gaps, providing a good sealing effect and plugging leaks. Furthermore, its high strength and flame retardancy make it safe for use in coal mines, characterized by its low-temperature, flame-retardant, and high-strength properties.

[0024] 2. In the preparation method of the present invention, the temperature of synthesizing polyurethane is low, which has little effect on the spontaneous combustion of coal. The excellent adhesion between polyurethane and coal blocks enables polyurethane to fill and seal, enhance the stability of goaf, and avoid the occurrence of roof collapse accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0026] Figure 1 Schematic diagram of the comparison of thermogravimetric curves of polyurethane (PU-CNTS-ADP) with two flame retardants added and polyurethane without flame retardant added (PU-0) in a nitrogen atmosphere.

[0027] Figure 2 This is the TG-DTG curve of polyurethane with two flame retardants added in nitrogen atmosphere.

[0028] Figure 3 This is a schematic diagram comparing the thermogravimetric curves of polyurethane (PU-CNTS-ADP) with two flame retardants added and polyurethane without flame retardant (PU-0) in an oxygen atmosphere. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0030] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0031] According to a first aspect of the present invention, a low-temperature flame-retardant polyurethane material for coal mines is provided, which comprises the following raw material components in parts by weight: 30 to 40 parts (for example, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, and 40 parts) of polyether polyol, 35 to 45 parts (for example, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, and 40 parts) of isocyanate, and 35 to 45 parts (for example, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, and 40 parts) of isocyanate. 3 parts, 44 parts, 45 parts), modifier 1-3 parts (for example 1 part, 2 parts, 3 parts), catalyst 1-3 parts (for example 1 part, 2 parts, 3 parts), flame retardant 5-10 parts (for example 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts), foaming agent 5-10 parts (for example 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts), stabilizer 10-15 parts (for example 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts).

[0032] The parts by weight described in the present invention primarily include the disclosed numerical ranges, any numerical value (including integers and decimals) or any interval between two numerical values ​​within the disclosed ranges, or multiple discontinuous intervals, and also include numerical values ​​or numerical ranges close to the end values ​​of the numerical ranges where similar effects can be expected. For example, 5-10 parts does not only include 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, and any interval between two parts. Other numerical ranges are not listed one by one, but are all included in the present invention. Therefore, the present invention also includes subranges of any numerical range that has been directly disclosed or any specific numerical value therein.

[0033] The low-temperature flame-retardant polyurethane material of the present invention, through the synergistic effect of its components, exhibits low-temperature synthesis, strong flame retardancy, good fluidity, and high strength. It adheres tightly to coal blocks without gaps, providing a good sealing effect and plugging leaks. Furthermore, its high strength and flame retardancy make it safe for use in coal mines, characterized by its low temperature, flame retardancy, and high strength.

[0034] In particular, the effect of modifiers on polyurethane synthesis is mainly reflected in the role of adhesion and chain extension in the polyurethane synthesis process. This role can enhance the mechanical properties of the synthesized polyurethane and improve the bonding force between the matrix and the filler.

[0035] The addition of stabilizers stabilizes the properties of the synthesized polyurethane. After adding stabilizers, the synthesized polyurethane foam is uniform and the flame retardant is evenly distributed. However, during the synthesis process of polyurethane without stabilizers, other reagents will agglomerate during the stirring process, and the foam will become uneven. During the curing process of polyurethane, if stabilizers are not added, cracks of varying degrees will appear during the curing process. This shows that stabilizers not only play a stabilizing role in the polyurethane synthesis process, but also have a certain effect on stabilizing the overall properties of polyurethane.

[0036] Catalysts play a crucial role in regulating the reaction rate of polyurethane synthesis. Commonly used polyurethane catalysts include tertiary amine catalysts and organotin catalysts. The important function of catalysts is to catalyze internal reactions. The two types of catalysts have different focuses. Tertiary amine catalysts primarily act on the synthesis reaction between -NCO and -OH, while also promoting CO2 gas, which can promote bubbling and volume expansion during the polyurethane synthesis reaction. During the polyurethane synthesis process, while tertiary amine catalysts have a certain catalytic effect on the NCO-OH reaction, their catalytic effect on the NCO-H2O reaction is stronger. Organotin catalysts can compensate for the shortcomings of tertiary amine catalysts and exhibit a strong catalytic effect on the NCO-OH reaction. Therefore, in this chapter, triethylenediamine (a tertiary amine catalyst) and stannous octoate (an organotin catalyst) are selected as composite catalysts to catalyze the polyurethane synthesis reaction.

[0037] In particular, blowing agents play a crucial role in the synthetic foaming of polyurethane. They introduce gas and promote the foaming reaction, which forms the foam structure. During the reaction, the gas is introduced, forming the pore structure of the foam.

[0038] In order to further improve the effect of low-temperature flame-retardant polyurethane materials for coal mines, the present invention studied the influence of different ratios of various raw material components on their performance, and obtained better raw material component ratios, namely 34 parts of polyether polyol, 38 parts of isocyanate, 1 part of modifier, 1 part of catalyst, 7 parts of flame retardant, 6 parts of foaming agent, and 13 parts of stabilizer.

[0039] In the above-mentioned low-temperature flame-retardant polyurethane material for coal mines, as a preferred embodiment, the isocyanate includes one or both of hexamethylene diisocyanate and isophorone diisocyanate.

[0040] Preferably, the isocyanate is a mixture of hexamethylene diisocyanate and isophorone diisocyanate, with the weight ratio of hexamethylene diisocyanate to isophorone diisocyanate being 1:1. When isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI) are mixed in varying proportions, a higher proportion of isophorone diisocyanate results in a polyurethane with higher strength but at a higher synthesis temperature. A higher proportion of hexamethylene diisocyanate results in a lower hardness and lower synthesis temperature.

[0041] In the above-mentioned low-temperature flame-retardant polyurethane material for coal mines, as a preferred embodiment, the polyether polyol includes one or both of polyether polyol N330 and polyether polyol N303.

[0042] Preferably, the polyether polyol is a mixture of polyether polyol N330 and polyether polyol N303; the weight ratio of the polyether polyol N330 and the polyether polyol N303 is 1:1.

[0043] The hydroxyl values of the two polyols, polyether polyol N330 and N303, are different, and the difference in the hydroxyl value will have different effects on the reaction speed, but the difference in the hydroxyl value will affect the strength of the synthesized polyurethane, the higher the hydroxyl value, the higher the reaction speed, the higher the strength, but the higher the synthesis temperature, and the two polyether polyols are compounded to achieve a balance of strength and temperature. Therefore, the two polyols are compounded, and the synergistic effect of the two polyether polyols is mainly reflected in the coordination of temperature and strength. The temperature of the polyurethane synthesized by polyether polyol N330 and N303 is also different, and the strength of the polyurethane synthesized by polyether polyol N330 is greater than that of the polyurethane synthesized by polyether polyol N303. Compared with polyether polyol N303 and N330, under the same conditions, the strength of the polyurethane synthesized by polyether polyol N330 is greater than that of the polyurethane synthesized by polyether polyol N303. The synthesis process of the polyurethane should consider the problems of temperature and strength, and the economic value should be considered, and the polyether polyol N303 and N330 can be compounded to prepare the low-temperature synthesized polyurethane.

[0044] In the above coal mine low-temperature flame-retardant polyurethane material, as a preferred embodiment, the catalyst includes one or both of tertiary amine catalyst and tin catalyst;

[0045] Optionally, the flame retardant includes one or both of nano flame retardant and aluminum diethyl phosphite.

[0046] Optionally, the modifier is a silane coupling agent;

[0047] Optionally, the foaming agent is HCFC-141b;

[0048] Optionally, the stabilizer is dimethyl silicone oil.

[0049] According to a second aspect of the present application, a preparation method of the coal mine low-temperature flame-retardant polyurethane material is provided, comprising the following steps:

[0050] The polyether polyol, the catalyst, the stabilizer, the modifier, and the flame retardant are sequentially added to the reaction vessel, mixed uniformly, and then the foaming agent is added, and the mixture is continuously stirred uniformly, and then the isocyanate is added, and the mixture is mixed uniformly to obtain the coal mine low-temperature flame-retardant polyurethane material.

[0051] In the preparation method of the low-temperature flame-retardant polyurethane material for coal mines of the present invention, the maximum synthesis temperature of the low-temperature synthesized polyurethane is 51.2°C. The synthesis temperature is an important safety performance that affects its use in mines during the grouting of polyurethane. Specifically, after adding isocyanate and mixing evenly, 200 ml of the test sample is weighed, and after stirring for 15s-30s under a magnetic stirrer, it is poured into a cylindrical glass container with a diameter of 50 mm. The temperature change during the whole process is recorded by a temperature sensor and the maximum reaction temperature is recorded. The temperature sensor used is a KT100 thermocouple, and the temperature change during the whole polyurethane synthesis process is measured by a thermocouple.

[0052] During the preparation process of the present invention, the temperature of the synthesized polyurethane is low, which has little effect on the spontaneous combustion of coal. The excellent adhesion between the polyurethane and the coal block enables the polyurethane to fill and seal, enhance the stability of the goaf, and avoid the occurrence of roof collapse accidents.

[0053] In the above preparation method, as a preferred embodiment, the following steps are further included: mixing hexamethylene diisocyanate and isophorone diisocyanate in a weight ratio of 1:1 and stirring uniformly;

[0054] Optionally, polyether polyol N330 and polyether polyol N303 are mixed and stirred uniformly in a weight ratio of 1:1.

[0055] According to a third aspect of the present invention, there is provided a use of the above-mentioned low-temperature flame-retardant polyurethane material for coal mines as a plugging material in coal mines.

[0056] The present invention will be described in detail below with reference to embodiments of the present invention. Each example is provided by way of explanation of the present invention and is not intended to limit the present invention. In fact, it will be apparent to those skilled in the art that modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is intended that the present invention encompasses such modifications and variations within the scope of the appended claims and their equivalents.

[0057] In the examples of the present invention, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0058] Example 1

[0059] This embodiment provides a low-temperature flame-retardant polyurethane material for coal mines, wherein the components are as follows: 17 parts of polyether polyol N330, 17 parts of polyether polyol N303, 19 parts of hexamethylene diisocyanate, 19 parts of isophorone diisocyanate, 1 part of silane coupling agent, 1 part of stannous octoate, 7 parts of diethylaluminum hypophosphite and carbon nanotubes (the weight ratio of diethylaluminum hypophosphite to carbon nanotubes is 1:1), 6 parts of HCFC-141b, and 13 parts of dimethyl silicone oil.

[0060] The preparation method is as follows:

[0061] (1) Preparation of component A: Mix polyether polyols N303 and N330 in a ratio of 1:1. After mixing, add catalysts stannous octoate and triethylenediamine, flame retardant diethyl aluminum hypophosphite and carbon nanotubes, stabilizer dimethyl silicone oil, and modifier silane coupling agent into a reaction vessel and mix and stir evenly. Finally, add the foaming agent HCFC-141 and stir evenly.

[0062] (2) Preparation of component B: Hexamethylene diisocyanate (HDI) and isophorone isocyanate (IPDI) were mixed in a ratio of 1:1 and stirred to obtain component B;

[0063] (3) Components A and B are mixed and stirred evenly in a mass ratio of 1:1 to obtain the low-temperature flame-retardant polyurethane material for coal mines of this embodiment.

[0064] Example 2

[0065] This embodiment provides a low-temperature flame-retardant polyurethane material for coal mines, wherein the components are as follows: 15 parts of polyether polyol N330, 15 parts of polyether polyol N303, 18 parts of hexamethylene diisocyanate, 18 parts of isophorone diisocyanate, 2 parts of silane coupling agent, 2 parts of stannous octoate, 5 parts of diethylaluminum hypophosphite and carbon nanotubes (the weight ratio of diethylaluminum hypophosphite to carbon nanotubes is 1:1), 5 parts of HCFC-141b, and 10 parts of dimethyl silicone oil;

[0066] The preparation method of this embodiment is the same as that of Example 1.

[0067] Example 3

[0068] This embodiment provides a low-temperature flame-retardant polyurethane material for coal mines, the components of which are as follows: 20 parts of polyether polyol N330, 20 parts of polyether polyol N303, 22 parts of hexamethylene diisocyanate, 22 parts of isophorone diisocyanate, 3 parts of silane coupling agent, 3 parts of stannous octoate, 10 parts of diethylaluminum hypophosphite and carbon nanotubes (the weight ratio of diethylaluminum hypophosphite to carbon nanotubes is 1:1), 10 parts of HCFC-141b, and 15 parts of dimethyl silicone oil;

[0069] The preparation method of this example is the same as that of Example 1.

[0070] Comparative Example 1

[0071] This comparative example provides a low-temperature flame-retardant polyurethane material for coal mines, and the content of each component is the same as that of Example 1, except that the flame retardant is only carbon nanotubes 7 parts, and no aluminum diethyl phosphinate is added.

[0072] The preparation method of this example is the same as that of Example 1.

[0073] Comparative Example 2

[0074] This comparative example provides a low-temperature flame-retardant polyurethane material for coal mines, and the content of each component is the same as that of Example 1, except that the flame retardant is only aluminum diethyl phosphinate 7 parts, and no carbon nanotubes are added.

[0075] The preparation method of this example is the same as that of Example 1.

[0076] Comparative Example 3

[0077] This comparative example provides a low-temperature flame-retardant polyurethane material for coal mines, and the content of each component is the same as that of Example 1, except that no flame retardant is added.

[0078] The preparation method of this example is the same as that of Example 1.

[0079] The flame-retardant properties of the low-temperature flame-retardant polyurethane materials for coal mines prepared in Examples 1-3 and Comparative Examples 1-3 were tested using a cone calorimeter, and the test results are shown in Table 1:

[0080] Table 1

[0081]

[0082] Figure 1 The comparative diagram of the thermogravimetric curves of the polyurethane with two kinds of flame retardants added (PU-CNTS-ADP) and the polyurethane without adding flame retardants (PU-0) in a nitrogen atmosphere.

[0083] Figure 2 The TG-DTG curves of the polyurethane with two kinds of flame retardants added in a nitrogen atmosphere.

[0084] Figure 3 The comparative diagram of the thermogravimetric curves of the polyurethane with two kinds of flame retardants added (PU-CNTS-ADP) and the polyurethane without adding flame retardants (PU-0) in an oxygen atmosphere.

[0085] The above describes and evaluates some embodiments of the present application, and it is understood that the present application is not limited to the above specific embodiments. Any person skilled in the art can make many possible changes and modifications to the technical solutions of the present application, or modify equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of the present application, which does not affect the essential content of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solutions of the present application,

[0086] still belong to the scope of protection of the technical solutions of the present application.

Claims

1. A low-temperature flame-retardant polyurethane material for coal mines, characterized in that: The invention comprises the following raw material components in parts by weight: 30 to 40 parts of polyether polyol, 35 to 45 parts of isocyanate, 1 to 3 parts of modifier, 1 to 3 parts of catalyst, 5 to 10 parts of flame retardant, 5 to 10 parts of foaming agent, and 10 to 15 parts of stabilizer; the polyether polyol is a mixture of polyether polyol N330 and polyether polyol N303; the flame retardant comprises diethyl aluminum hypophosphite and carbon nanotubes; the modifier is a silane coupling agent; the isocyanate is a mixture of hexamethylene diisocyanate and isophorone diisocyanate; and the stabilizer is dimethyl silicone oil.

2. The low-temperature flame-retardant polyurethane material for coal mines according to claim 1, characterized in that: The raw material components are as follows: 34 parts of polyether polyol, 38 parts of isocyanate, 1 part of modifier, 1 part of catalyst, 7 parts of flame retardant, 6 parts of foaming agent and 13 parts of stabilizer.

3. The low-temperature flame-retardant polyurethane material for coal mines according to claim 1, characterized in that: The weight ratio of the hexamethylene diisocyanate to isophorone diisocyanate is 1:

1.

4. The low-temperature flame-retardant polyurethane material for coal mines according to claim 1, characterized in that: The weight ratio of the polyether polyol N330 to the polyether polyol N303 is 1:

1.

5. The low-temperature flame-retardant polyurethane material for coal mines according to claim 1 or 2, characterized in that: The catalyst includes one or both of a tertiary amine catalyst and a tin catalyst; And / or, the blowing agent is HCFC-141b.

6. A method for preparing a low-temperature flame-retardant polyurethane material for coal mines according to any one of claims 1 to 5, characterized in that: The following steps are involved: The polyether polyol, catalyst, stabilizer, modifier and flame retardant are sequentially added into a reaction vessel, mixed evenly, and then a foaming agent is added. After further stirring, isocyanate is added and mixed evenly to obtain the low-temperature flame-retardant polyurethane material for coal mines.

7. The preparation method according to claim 6, characterized in that The method further comprises the following steps: mixing hexamethylene diisocyanate and isophorone diisocyanate in a weight ratio of 1:1 and stirring uniformly; And / or, polyether polyol N330 and polyether polyol N303 are mixed and stirred uniformly in a weight ratio of 1:

1.

8. Use of the low-temperature flame-retardant polyurethane material for coal mines according to any one of claims 1 to 5 or the low-temperature flame-retardant polyurethane material for coal mines prepared by the preparation method according to claim 6 or 7 as a plugging material in coal mines.

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