A flame retardant for EVA materials and its preparation method

Abstract

This application relates to the field of flame retardants, and specifically discloses a flame retardant for EVA materials and a preparation method thereof. A flame retardant for EVA materials is prepared from the following raw materials in percentage by weight: 30-40% of organic nitrogen-based flame retardant, 45-55% of phosphorus-based flame retardant, 10-15% of intumescent flame retardant, and the balance is modified montmorillonite; the modified montmorillonite is prepared from montmorillonite, methacryloyloxyethyl trimethyl ammonium chloride, polyvinyl methyl ether / maleic anhydride copolymer, silane coupling agent, dispersant and activator; Preparation method: Grind the organic nitrogen-based flame retardant, phosphorus-based flame retardant and intumescent flame retardant and stir and disperse them with the modified montmorillonite. The preparation process of this application is simple, the amount of the prepared flame retardant used in EVA materials is small, and it has good flame retardant stability without affecting the mechanical properties of EVA materials.

Description

Technical Field

[0001] The present application relates to the field of flame retardants, and more specifically, it relates to a flame retardant for EVA materials and a preparation method thereof. Background Art

[0002] EVA material, whose full name is Ethylene-Vinyl Acetate Copolymer, is a thermoplastic plastic copolymerized from ethylene monomer and vinyl acetate monomer. EVA material has advantages such as good elasticity, softness, tear resistance, and corrosion resistance, and is widely used in fields such as sealing materials and cable materials.

[0003] However, the flame retardant performance of EVA material is poor, and generally, flame retardants are added to improve the flame retardant performance of EVA material. Commonly used environmentally friendly flame retardants include inorganic flame retardants, phosphorus-based flame retardants, organic nitrogen-based flame retardants, and phosphorus-nitrogen flame retardants. However, inorganic flame retardants generally include magnesium hydroxide, etc., and the usage amount generally reaches 40-60%, and the addition amount of phosphorus-based flame retardants is generally 20-30%. The addition amount of flame retardants is relatively large, which easily affects the mechanical properties of EVA material; while organic nitrogen-based flame retardants and phosphorus-nitrogen flame retardants generally have hygroscopicity. When added to EVA material, as the EVA material is used, the organic nitrogen-based flame retardant will migrate or precipitate from the EVA material, reducing the flame retardancy of the EVA material. Summary of the Invention

[0004] In order to solve the problem that conventional flame retardants are applied to EVA materials, with a large addition amount and easy precipitation, reducing the flame retardancy and mechanical properties of EVA materials, the present application provides a flame retardant for EVA materials and a preparation method thereof.

[0005] In the first aspect, the present application provides a flame retardant for EVA materials, adopting the following technical solution:

[0006] A flame retardant for EVA materials is prepared from raw materials in the following weight percentages:

[0007] Organic nitrogen-based flame retardant 30-40%

[0008] Phosphorus-based flame retardant 45-55%

[0009] Intumescent flame retardant 10-15%

[0010] Modified montmorillonite the balance;

[0011] The modified montmorillonite is prepared from montmorillonite, methacryloyloxyethyl trimethyl ammonium chloride, poly(methyl vinyl ether / maleic anhydride) copolymer, silane coupling agent, dispersant, and activator.

[0012] By adopting the above technical solutions, the organic nitrogen-based flame retardant can generate non-combustible gases to dilute the concentration of combustible gases. Meanwhile, the formed carbon layer has the functions of heat insulation and oxygen isolation. The phosphorus-based flame retardant decomposes at high temperatures to produce phosphoric acid, which further promotes the formation of the carbon layer and enhances the stability and integrity of the carbon layer. The intumescent flame retardant expands rapidly when heated to form a dense foamy carbonaceous layer, which can not only isolate oxygen and heat but also effectively prevent the spread of flames. The organic nitrogen-based flame retardant, phosphorus-based flame retardant, and intumescent flame retardant have good synergistic effects, achieving good flame retardant effects with less dosage. The modified montmorillonite can be evenly dispersed into the flame retardant system and form a uniform hydrophobic protective layer on the surface of the flame retardant. While improving the stability of the flame retardant, it plays a good role in enhancing flame retardancy, further reducing the dosage of the flame retardant, and thus avoiding the impact on the mechanical properties of the EVA material while maintaining good flame retardant effects.

[0013] Preferably, the modified montmorillonite is prepared from the following raw materials in parts by weight:

[0014] 100 - 120 parts of montmorillonite

[0015] 100 - 200 parts of 55 - 85wt% ethanol aqueous solution

[0016] 5 - 10 parts of silane coupling agent

[0017] 2 - 4 parts of activator

[0018] 2 - 4 parts of dispersant, 5 - 10 parts of methacryloyloxyethyl trimethyl ammonium chloride

[0019] 4 - 6 parts of polymethyl vinyl ether / maleic anhydride copolymer.

[0020] By adopting the above technical solutions, the dispersant and activator can improve the surface modification efficiency of montmorillonite, silane coupling agent, methacryloyloxyethyl trimethyl ammonium chloride, and polymethyl vinyl ether / maleic anhydride copolymer. The silane coupling agent, methacryloyloxyethyl trimethyl ammonium chloride, and polymethyl vinyl ether / maleic anhydride copolymer can form a cross-linked network structure on the surface of montmorillonite, which can increase the layer spacing of montmorillonite, improve the dispersion performance of montmorillonite in the flame retardant system, and at the same time improve the compatibility of montmorillonite in organic substances, forming a uniform hydrophobic layer on the surface of the flame retardant. While making the flame retardant have good flame retardant stability, it reduces the impact of the addition of the flame retardant on the mechanical properties of the EVA material.

[0021] Preferably, the activator is composed of ammonium persulfate and ethylenediamine with a weight ratio of 1:(0.2 - 0.4).

[0022] By adopting the above technical solution, ammonium persulfate and ethylenediamine with a relatively optimal weight ratio as activators can improve the modification efficiency of montmorillonite, and further improve the flame retardant stability of the prepared flame retardant.

[0023] Preferably, the dispersant is any one or a combination of alkyl aryl phosphates, alkyl benzene sulfonates, and dialkyl sulfosuccinates.

[0024] By adopting the above technical solution, the above-mentioned dispersant can synergistically improve the dispersibility of montmorillonite with the activator, and further improve the modification efficiency of the modified montmorillonite.

[0025] Preferably, the silane coupling agent is composed of tetramethyldivinyldisilazane and dodecyltriethoxysilane with a weight ratio of 1:(1 - 3).

[0026] By adopting the above technical solution, the silane coupling agent composed of tetramethyldivinyldisilazane and dodecyltriethoxysilane can form an intertwined system of silanes, thereby improving the dispersibility and hydrophobicity of the prepared modified montmorillonite, improving the compatibility between montmorillonite and EVA materials, so that when the flame retardant is applied to EVA materials, it can have good flame retardancy with a relatively small addition amount.

[0027] Preferably, the modified montmorillonite is prepared by the following steps:

[0028] Add the dispersant and the activator into an ethanol aqueous solution, stir and dissolve, then add montmorillonite, silane coupling agent, methacryloyloxyethyltrimethylammonium chloride, and polymethyl vinyl ether / maleic anhydride copolymer, heat up to 60 - 70 °C, react for 2 - 3 h, filter, and dry to obtain the modified montmorillonite.

[0029] By adopting the above technical solution, during the preparation process of the modified montmorillonite, the addition of the dispersant and the activator can effectively improve the dispersibility of montmorillonite in the ethanol aqueous solution, ensuring the full mixing of each component. Then add the silane coupling agent, methacryloyloxyethyltrimethylammonium chloride, and polymethyl vinyl ether / maleic anhydride copolymer to form a crosslinked hydrophobic protective layer on the surface of montmorillonite. The modified montmorillonite prepared by this process can significantly reduce the addition amount of the flame retardant, and improve the flame retardant performance of the EVA material without affecting the mechanical properties of the EVA material.

[0030] Preferably, the organic nitrogen-based flame retardant is melamine cyanurate and / or melamine phosphate.

[0031] Preferably, the phosphorus-based flame retardant is one or a combination of aluminum diethylphosphinate, boron phosphate, ammonium polyphosphate, and ammonium phosphate.

[0032] Preferably, the intumescent flame retardant is piperazine pyrophosphate.

[0033] By adopting the above technical solution, melamine cyanurate and / or melamine phosphate is selected as the organic nitrogen-based flame retardant, and one or a combination of aluminum diethyl phosphinate, boron phosphate, ammonium polyphosphate and ammonium phosphate is used as the phosphorus-based flame retardant, and piperazine pyrophosphate is used as the intumescent flame retardant. The three have good synergistic effects. When combustion occurs, the phosphorus-based flame retardant and the organic nitrogen-based flame retardant can form a carbon layer, and under the action of the expanded carbon layer of the intumescent flame retardant, the contact between the material and air is blocked, playing a role in quickly extinguishing the fire; at the same time, a large amount of inert gas is released during the combustion process, diluting the concentration of combustible gas and inhibiting the spread of the flame. The combined use of the three can greatly reduce the dosage of the flame retardant.

[0034] In a second aspect, the present application provides a preparation method of a flame retardant for EVA materials, adopting the following technical solution:

[0035] A preparation method of a flame retardant for EVA materials includes the following steps:

[0036] S1. First, the phosphorus-based flame retardant, the organic nitrogen-based flame retardant and the intumescent flame retardant are respectively pulverized to a particle size less than 5 μm;

[0037] S2. The phosphorus-based flame retardant, the organic nitrogen-based flame retardant, the intumescent flame retardant and the modified montmorillonite are dispersed and stirred evenly to prepare a flame retardant for EVA materials.

[0038] By adopting the above technical solution, by respectively pulverizing the phosphorus-based flame retardant, the organic nitrogen-based flame retardant and the intumescent flame retardant to a particle size less than 5 μm and then fully mixing them with the modified montmorillonite, it is ensured that each component is evenly dispersed, improving the dispersion uniformity performance of the flame retardant.

[0039] In summary, the present application has the following beneficial effects:

[0040] 1. The flame retardant for EVA materials of the present application is prepared by compounding an organic nitrogen-based flame retardant, a phosphorus-based flame retardant and an intumescent flame retardant in an optimal weight ratio. The modified montmorillonite is prepared from montmorillonite, methacryloyloxyethyl trimethyl ammonium chloride, polyvinyl methyl ether / maleic anhydride copolymer, silane coupling agent, dispersant and activator. The modified montmorillonite can be evenly dispersed into the flame retardant system and form a uniform hydrophobic protective layer on the surface of the flame retardant. Under the synergistic effect of the modified montmorillonite, while improving the flame retardancy and flame retardant stability of the flame retardant, it plays a good role in enhancing the flame retardant effect, further reducing the dosage of the flame retardant, so that while maintaining a good flame retardant effect, it will not affect the mechanical properties of EVA materials.

[0041] 2. By using ammonium persulfate and ethylenediamine with an optimal weight ratio as activators, and tetramethyldivinyldisilazane and dodecyltriethoxysilane as silane coupling agents, the compatibility between montmorillonite and EVA materials is improved. When the flame retardant is applied to EVA materials, it can have good flame retardancy with a relatively small addition amount.

[0042] 3. When the flame retardant of this application is applied to EVA materials, it can have good flame retardancy and flame retardant stability with a relatively small dosage, and at the same time, it will not affect the mechanical properties of EVA materials. Detailed implementation manners

[0043] The following further elaborates on this application with reference to examples.

[0044] The following are the sources and specifications of some raw materials of this application. The raw materials used in the preparation examples and implementation examples of this application can all be obtained commercially, including but not limited to the raw materials of the following models and manufacturers, and raw materials with the same performance can all be used:

[0045] 1. Montmorillonite: LingShou, 325 mesh, whiteness 90%, content 92%, density 2.63 g / cm 3 ;

[0046] 2. Poly(methyl vinyl ether / maleic anhydride) copolymer: ChengFeng, CAS No. 9011-16-9, content 98%;

[0047] 3. Melamine cyanurate: Taixing HT-211, content 99.8%;

[0048] 4. Ammonium polyphosphate: CAS No. 68333-79-9;

[0049] 5. Piperazine pyrophosphate: CAS No. 66034-17-1, phosphorus content 20-22%, nitrogen content 23-25%;

[0050] 6. Aluminum diethylphosphinate: CAS 225789-38-8, content 99%;

[0051] 7. EVA material: Formosa Plastics 7470M.

[0052] Preparation examples of modified montmorillonite

[0053] Preparation example 1

[0054] Preparation Example 1 discloses a modified montmorillonite, which is prepared by the following steps: 0.2 kg of sodium dodecylbenzenesulfonate as a dispersant and 0.2 kg of ammonium persulfate as an activator are added to 10 kg of an ethanol aqueous solution with a concentration of 55 wt%, and after stirring and dissolving, 10 kg of montmorillonite, 1 kg of a silane coupling agent (composed of 0.5 kg of vinyltrimethoxysilane and 0.5 kg of dodecyltriethoxysilane), 0.5 kg of methacryloyloxyethyltrimethylammonium chloride and 0.6 kg of a polymethyl vinyl ether / maleic anhydride copolymer are added. The temperature is raised to 60 °C and the reaction is carried out for 2 h, followed by filtration and drying and dispersion to obtain the modified montmorillonite.

[0055] Preparation Examples 2 - 3

[0056] The differences between Preparation Examples 2 - 3 and Preparation Example 1 lie in the raw material dosages and preparation conditions. For details, see Table 1 below.

[0057] Table 1 Parameter Table of Preparation Examples 1 - 3

[0058]

[0059] Preparation Example 4

[0060] The difference between Preparation Example 4 and Preparation Example 1 is that the activator is different. The activator in Preparation Example 4 is composed of ammonium persulfate and ethylenediamine with a weight ratio of 1:0.2, and the others are the same as in Preparation Example 1.

[0061] Preparation Example 5

[0062] The difference between Preparation Example 5 and Preparation Example 1 is that the activator in Preparation Example 5 is composed of ammonium persulfate and ethylenediamine with a weight ratio of 1:0.4, and the others are the same as in Preparation Example 1.

[0063] Preparation Example 6

[0064] The difference between Preparation Example 6 and Preparation Example 4 is that the silane coupling agent is different. The silane coupling agent in Preparation Example 6 is composed of tetramethyldivinyldisilazane and dodecyltriethoxysilane with a weight ratio of 1:1, and the others are the same as in Preparation Example 4.

[0065] Preparation Example 7

[0066] The difference between Preparation Example 7 and Preparation Example 4 is that the silane coupling agent in Preparation Example 7 is composed of tetramethyldivinyldisilazane and dodecyltriethoxysilane with a weight ratio of 1:3, and the others are the same as in Preparation Example 4.

[0067] Preparation Comparative Example 1

[0068] The difference between Preparation Comparative Example 1 and Preparation Example 6 is that methacryloyloxyethyltrimethylammonium chloride is replaced with an equal amount of polydimethyldiallylammonium chloride, and the others are the same as in Preparation Example 6.

[0069] Preparation of Comparative Example 2

[0070] The difference between the preparation of Comparative Example 2 and Preparation Example 6 is that the polymethyl vinyl ether / maleic anhydride copolymer is replaced with methylacryloyloxyethyl trimethyl ammonium chloride in equal amount, and the others are the same as Preparation Example 6.

[0071] Example

[0072] Example 1

[0073] Example 1 discloses a flame retardant for EVA materials, which is prepared by the following steps:

[0074] S1. First, a phosphorus-based flame retardant (composed of aluminum diethyl phosphinate and ammonium phosphate with a weight ratio of 2:1), melamine cyanurate as an organic nitrogen-based flame retardant, and piperazine pyrophosphate as an intumescent flame retardant are respectively pulverized to a particle size of less than 5 μm;

[0075] S2. 4.5 kg of the pulverized phosphorus-based flame retardant, 4 kg of the organic nitrogen-based flame retardant, 1.2 kg of the intumescent flame retardant, and 0.3 kg of the modified montmorillonite prepared in Preparation Example 1 are dispersed for 60 min under the condition of a mixing rate of 2500 r / min to obtain a flame retardant for EVA materials.

[0076] Examples 2 - 3

[0077] The difference between Examples 2 - 3 and Example 1 lies in the different raw material dosages and preparation conditions. For details, see Table 2 below.

[0078] Table 2 Parameter Table of Examples 1 - 3

[0079]

[0080]

[0081] Examples 4 - 7

[0082] The difference between Examples 4 - 7 and Example 1 lies in the different sources of the modified montmorillonite. For details, see Table 3 below.

[0083] Table 3 Source Table of Modified Montmorillonite in Examples 4 - 7

[0084] Example Source Table of Modified Montmorillonite Example 4 Preparation Example 4 Example 5 Preparation Example 5 Example 6 Preparation Example 6 Example 7 Preparation Example 7

[0085] Comparative Example Comparative Example 1

[0086] The difference between Comparative Example 1 and Example 6 is that the modified montmorillonite is sourced from the preparation of Comparative Example 1, and the others are the same as Example 6.

[0087] Comparative Example 2

[0088] The difference between Comparative Example 2 and Example 6 is that the modified montmorillonite is from the preparation of Comparative Example 2, and the others are the same as Example 6.

[0089] Comparative Example 3

[0090] The difference between Comparative Example 3 and Example 6 is that the modified montmorillonite is replaced with montmorillonite in equal amount, and the others are the same as Example 6.

[0091] Comparative Example 4

[0092] The difference between Comparative Example 4 and Example 6 is that the amount of the intumescent flame retardant is 0.5 kg and the amount of the organic nitrogen-based flame retardant is 4.7 kg, and the others are the same as Example 6.

[0093] Application Example

[0094] Application Example 1

[0095] Application Example 1 discloses an EVA material, and the preparation process is as follows:

[0096] Mix 9 kg of EVA resin and 1 kg of the flame retardant prepared in Example 1 evenly, and carry out melt extrusion to obtain the EVA material.

[0097] Application Examples 2 - 11

[0098] The difference between Application Examples 2 - 11 and Application Example 1 is that the sources of the flame retardants are different, and the specific details are shown in Table 4 below.

[0099] Table 4 Sources of Flame Retardants for Application Examples 2 - 11

[0100] Application Example Source of Flame Retardant Application Example 2 Example 2 Application Example 3 Example 3 Application Example 4 Example 4 Application Example 5 Example 5 Application Example 6 Example 6 Application Example 7 Example 7 Application Example 8 Comparative Example 1 Application Example 9 Comparative Example 2 Application Example 10 Comparative Example 3 Application Example 11 Comparative Example 4

[0101] Performance Detection Test The EVA materials prepared in Application Examples 1 - 11 are subjected to performance tests as follows: The EVA materials prepared in Application Examples 1 - 12 are injection molded, cut into test strips with a thickness of 1.5 mm and a width of 50 mm, and performance tests are carried out;

[0102] 1. Tensile Strength Test:

[0103] Use a tensile testing machine to test the tensile strength (MPa) of the test strips, and test and record the test results;

[0104] 2. Flame Retardancy Test:

[0105] Refer to the test method in GB / T 2406 to carry out the limiting oxygen index test on the test strips, denoted as the first limiting oxygen index (unit: %), and test and record the test results;

[0106] 3. Flame Retardant Stability Test:

[0107] The limiting oxygen index of the test strip was tested and recorded as the second limiting oxygen index (unit: %), and the test results were recorded. The following are the performance test data of the EVA materials prepared in Application Examples 1-11. For details, see Table 5 below.

[0108] Table 5 Performance data table of EVA materials in Application Examples 1-11

[0109]

[0110] Combining Application Examples 1-3 and Application Examples 4-5 and referring to Table 5, it can be concluded that when using ammonium persulfate and ethylenediamine with a relatively optimal weight ratio as activators, the flame retardant prepared and applied to EVA materials has good flame retardancy and mechanical properties. Compared with Application Example 1, the breaking strength in Application Examples 4-5 increased by 12 MPa, the first limiting oxygen index increased by 0.9%, the second limiting oxygen index of Application Example 1 after the flame retardant stability test decreased by 0.9%, while the second limiting oxygen index of Application Example 4 decreased by 0.6%. Compared with Application Example 1, the flame retardant stability of Application Example 4 was improved.

[0111] Combining Application Example 4 and Application Examples 6-7 and referring to Table 5, it can be concluded that when using tetramethyldivinyldisilazane and dodecyltriethoxysilane with a relatively optimal weight ratio as silane coupling agents, the flame retardant prepared and applied to EVA materials has good flame retardancy and mechanical properties. Compared with Application Example 4, the breaking strength in Application Examples 6-7 increased by 10 MPa, the first limiting oxygen index increased by 0.9%, the second limiting oxygen index of Application Example 6 decreased by 0.2%. Compared with Application Example 4, the flame retardant stability of Application Example 6 was improved.

[0112] Further combining Application Example 6 and Application Examples 8-10 and referring to Table 5, it can be concluded that by using the dispersant, activator, silane coupling agent, methacryloyloxyethyltrimethylammonium chloride and poly(methyl vinyl ether / maleic anhydride) copolymer of the present application to prepare modified montmorillonite, the flame retardant prepared and applied to EVA materials has good flame retardancy, flame retardant stability and mechanical properties. In Application Examples 8-9, when changing the components of methacryloyloxyethyltrimethylammonium chloride and poly(methyl vinyl ether / maleic anhydride) copolymer, the breaking strength decreased by 33 MPa, the first limiting oxygen index decreased by 3.5%, and the flame retardant stability also decreased significantly; in Application Example 10, when directly using montmorillonite, the flame retardant prepared and applied to EVA materials had significantly reduced flame retardancy, flame retardant stability and mechanical properties, probably because the dispersion and hydrophobic protection of the modified montmorillonite for the flame retardant system were reduced, thereby reducing the flame retardancy and mechanical properties of the EVA material.

[0113] Combining Application Example 6 and Application Example 11 and referring to Table 5, it can be concluded that optimizing the ratio of organic nitrogen-based flame retardant, phosphorus-based flame retardant and intumescent flame retardant can improve the flame retardancy and flame retardant stability of the prepared flame retardant.

[0114] In summary, the flame retardant of the present application has a small dosage in the EVA material. 10% can achieve a limiting oxygen index of 34%, and it will not affect the mechanical properties of the EVA material.

[0115] This specific embodiment is only an explanation of the present application and is not a limitation thereof. Those skilled in the art can make modifications to this embodiment without creative contributions according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A flame retardant for EVA materials, characterized in that, Prepared from raw materials with the following weight percentages: Organic nitrogen-based flame retardant 30 - 40% Phosphorus-based flame retardant 45 - 55% Intumescent flame retardant 10 - 15% Modified montmorillonite The balance; The modified montmorillonite is prepared from raw materials with the following weight parts: Montmorillonite 100 - 120 parts 55 - 85wt% ethanol aqueous solution 100 - 200 parts Silane coupling agent 5 - 10 parts Activator 2 - 4 parts Dispersant 2 - 4 parts Methacryloyloxyethyl trimethyl ammonium chloride 5 - 10 parts Poly(methyl vinyl ether / maleic anhydride) copolymer 4 - 6 parts; The activator is composed of ammonium persulfate and ethylenediamine with a weight ratio of 1:(0.2 - 0.4); The dispersant is any one or combination of alkyl aryl phosphates, alkyl benzene sulfonates, and dialkyl sulfosuccinates; The silane coupling agent is composed of tetramethyldivinyldisilazane and dodecyltriethoxysilane with a weight ratio of 1:(1 - 3).

2. The flame retardant for EVA materials according to claim 1, wherein: The modified montmorillonite is prepared by the following steps: Add the dispersant and activator to the ethanol aqueous solution, stir and dissolve, then add montmorillonite, silane coupling agent, methacryloyloxyethyl trimethyl ammonium chloride, and poly(methyl vinyl ether / maleic anhydride) copolymer, heat up to 60 - 70°C, react for 2 - 3 h, filter, and dry to obtain the modified montmorillonite.

3. A flame retardant for EVA materials according to claim 1, characterized in that: The organic nitrogen-based flame retardant is melamine cyanurate and / or melamine phosphate.

4. A flame retardant for EVA materials according to claim 1, characterized in that: The phosphorus-based flame retardant is one or combination of aluminum diethyl phosphinate, boron phosphate, ammonium polyphosphate, and ammonium phosphate.

5. A flame retardant for EVA materials according to claim 1, characterized in that: The intumescent flame retardant is piperazine pyrophosphate.

6. A preparation method of a flame retardant for EVA materials as described in any one of claims 1-5, characterized in that, Including the following steps: S1. First, crush the phosphorus-based flame retardant, organic nitrogen-based flame retardant, and intumescent flame retardant to a particle size less than 5 µm respectively; S2. Disperse and stir evenly the phosphorus-based flame retardant, organic nitrogen-based flame retardant, intumescent flame retardant, and modified montmorillonite to obtain the flame retardant for EVA material.

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