Ceramic water-permeable brick with surface coating and preparation process thereof

Abstract

The application discloses a ceramic water-permeable brick with a surface coating and a preparation process thereof, and the preparation process comprises the following steps: pressing all raw materials of a base body to obtain the base body; mixing raw materials of a surface layer and grinding the raw materials by adding water to obtain surface layer slurry, and the solid content of the surface layer slurry is 60%-70%; spraying the surface layer slurry on the base body, drying and sintering to obtain the water-permeable brick; wherein the raw materials of the surface layer comprise 6-17% of an alkaline metal precursor and 6-17% of a fluoride in mass percentage. The preparation process disclosed by the application adds the alkaline metal precursor and the fluoride in the raw materials of the surface layer, increases the expansion coefficient of the glaze, and makes the filled water-permeable brick particles restore the voids in the sintering and cooling steps of the water-permeable brick.

Description

Technical Field

[0001] This invention belongs to the field of permeable bricks, and particularly relates to a ceramic permeable brick with a surface coating and its preparation process. Background Technology

[0002] Permeable ceramic bricks are made by using recycled construction waste as a framework, combined with appropriate amounts of binders / pore-forming agents, and then pressing and sintering at high temperatures. Using permeable ceramic bricks can effectively allow some urban rainwater to flow into the ground, which reduces the pressure on urban sewer systems and pollution of rivers and lakes, as well as the cost of sewage treatment. On the other hand, it can replenish groundwater, overcome the drawbacks of impermeable urban roads, and thus slow down the trend of ground subsidence caused by the decline of groundwater level.

[0003] Many manufacturers apply a coating to the surface of permeable bricks to give them a good decorative function. However, since conventional glazes fill the gaps between the permeable brick particles after being applied to the surface of the permeable bricks, the permeability coefficient of the permeable bricks is reduced, and the permeability performance is decreased. Summary of the Invention

[0004] This invention provides a ceramic permeable brick with a surface coating and its preparation process, aiming to solve the problem in the prior art that applying glaze to the permeable brick substrate leads to a decrease in the permeability coefficient and a decline in the permeability performance of the permeable brick.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a process for preparing a permeable ceramic brick with a surface coating, comprising:

[0007] All raw materials for the matrix are pressed together to obtain the matrix.

[0008] The raw materials for the surface layer are mixed and ground with water to obtain a surface layer slurry with a solid content of 60%-75%.

[0009] The surface layer slurry is sprayed onto the substrate, dried, and sintered to obtain permeable bricks.

[0010] The raw materials of the surface layer include 6-17% by mass of an alkaline metal precursor and 6-17% by mass of a fluoride.

[0011] Because conventional glazes fill the gaps between permeable brick particles after being applied to the surface of the permeable brick substrate, the permeability coefficient of the permeable brick decreases and its permeability performance declines. Therefore, when formulating the surface layer, this invention adds an appropriate amount of alkaline metal precursors and fluorides. Alkaline metal precursors and fluorides can increase the expansion coefficient of the glaze, and the glaze can shrink significantly when the permeable brick cools after firing, so that the gaps between the filled permeable brick particles can be restored to their original open state.

[0012] The addition of barium carbonate and fluorite can increase the whiteness of the surface glaze after firing, reduce the firing temperature of the surface glaze, and improve the solar reflectivity of the radiation-cooled glaze.

[0013] Furthermore, the alkaline metal precursor is selected from at least one of barium carbonate, barium oxide, barium hydroxide, sodium carbonate, potassium carbonate, potassium hydroxide, calcium oxide, and calcium hydroxide.

[0014] At high temperatures, barium carbonate decomposes into barium oxide (BaO). As an alkali metal oxide, BaO disrupts the silicon-oxygen network in the glass structure, reducing the degree of polymerization. Since a looser silicon-oxygen network typically has a higher coefficient of thermal expansion, BaO can increase the coefficient of thermal expansion of permeable bricks by reducing the degree of polymerization. Similarly, alkali metal oxides such as Na₂O, K₂O, CaO, and BaO have a similar effect when introduced into glazes.

[0015] Furthermore, the fluoride is selected from at least one of fluorite and barium fluoride.

[0016] Fluorite, whose main component is CaF2, can have its silica content reduced by the fluoride ions. Fluoride ions can replace oxygen ions at high temperatures or react with the silicon-oxygen network to form volatile substances such as SiF4. Silica is a network-forming material; its reduction makes the permeable brick structure looser and increases its coefficient of thermal expansion. Furthermore, fluorides may promote crystallization, and if the precipitated crystals have a high coefficient of thermal expansion, they will also affect the overall expansion. Similarly, introducing fluorides such as barium fluoride into the glaze will have a similar effect.

[0017] Furthermore, the raw materials for the surface layer also include, by weight: 10-15 parts feldspar, 10-15 parts quartz, 6-10 parts kaolin, 0.3-0.5 parts sodium tripolyphosphate, and 0.2-0.4 parts sodium methylcellulose.

[0018] That is, the raw materials for the surface layer of the ceramic permeable brick with surface coating disclosed in this invention include, by mass parts: 10-15 parts feldspar, 10-15 parts quartz, 6-10 parts kaolin, 6-10 parts alkaline metal precursor, 6-10 parts fluoride, 0.3-0.5 parts sodium tripolyphosphate, and 0.2-0.4 parts sodium methylcellulose. Further, the alkaline metal precursor and fluoride each account for 6-17% of the total mass percentage of the raw materials in the surface layer.

[0019] Furthermore, in the step of mixing the raw materials of the surface layer and adding water, the water content is 35-40 parts, which leads to the conclusion that the solid content of the surface layer slurry is 60%-75%.

[0020] Furthermore, the surface layer slurry is sprayed onto the substrate to form a spray layer, the thickness of which is 1-2 mm.

[0021] Furthermore, the spraying process includes applying a surface layer slurry to the substrate, with a slurry application rate of 1500-2500 g / m³. 2 .

[0022] Furthermore, the raw materials of the surface layer also include a refrigerant, and the raw materials of the refrigerant include, by mass parts: 50-70 parts Al2O3, 5-15 parts SiO2, 5-15 parts CaO, 5-10 parts ZnO2, and 2-5 parts ZrO2.

[0023] Furthermore, the drying conditions are 100-200℃ for 2-4 hours; the sintering conditions are 1150-1300℃ for 1-2 hours.

[0024] Furthermore, the raw materials of the matrix include, by mass parts: 40-60 parts ceramic fragments, 10-20 parts granite fragments, 10-20 parts inorganic binder, and 2-5 parts pore-forming agent; the inorganic binder includes one or more combinations of bentonite, kaolin, and ball clay, and the pore-forming agent includes one or more combinations of straw, sawdust, starch, and fly ash.

[0025] Since the glaze can fill some of the voids in the upper layer of the permeable brick substrate, it is equivalent to applying a layer of particles with a certain thickness and slightly smaller voids on the upper layer of the permeable brick substrate. Therefore, there is no need to apply finer particles to the substrate surface for secondary pressing, which can achieve the effect of a beautiful and delicate surface and increased strength of the permeable brick. At the same time, it greatly simplifies the production process, reduces energy consumption, and lowers production costs.

[0026] In a second aspect, the present invention provides a permeable ceramic brick with a surface coating, which is prepared by the preparation process of a permeable ceramic brick with a surface coating as described in any one of the first aspects.

[0027] The beneficial effects of this invention compared to the prior art are:

[0028] This invention discloses a permeable ceramic brick with a surface coating and its preparation process, including pressing all the raw materials of the matrix to obtain the matrix; mixing the raw materials of the surface layer and grinding them with water to obtain a surface layer slurry, the solid content of the surface layer slurry being 60%-70%; spraying the surface layer slurry onto the matrix, drying, and sintering to obtain the permeable brick; wherein, the raw materials of the surface layer include 6-17% by mass of an alkaline metal precursor and 6-17% by mass of fluoride, by increasing the expansion coefficient of the glaze by adding alkaline metal precursor and fluoride to the raw materials of the surface layer, the glaze can shrink significantly during the firing and cooling step of the permeable brick, thereby restoring the porosity of the filled permeable brick particles, and achieving the ability to apply glaze to the permeable brick matrix while maintaining the permeability of the permeable brick;

[0029] Since the glaze can fill some of the voids in the upper layer of the permeable brick substrate, it is equivalent to applying a layer of slightly smaller particles of a certain thickness to the upper layer of the permeable brick substrate. Therefore, there is no need to apply finer particles or perform secondary pressing on the substrate surface to achieve the effect of a beautiful and delicate surface and increased strength of the permeable brick. This simplifies the production process, reduces energy consumption, and lowers production costs. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure of a permeable ceramic brick with a surface coating prepared in Example 1 of the present invention. The white part in the figure is the surface coating.

[0032] Figure 2 This is a schematic diagram of the permeable ceramic brick with a surface coating prepared in Example 1 of the present invention from another direction.

[0033] Figure 3 This is a schematic diagram of the permeable brick preparation process disclosed in Example 1. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0036] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0037] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are illustrative of the invention and not limiting. Unless otherwise specified, the present invention does not have special limitations on the source of the components, and commercially available or conventional products well known to those skilled in the art can be used.

[0038] It should be noted that in this invention, all raw material parts are expressed in parts by mass. It should be understood that parts by mass refers to the proportional measurement relationship of the masses of each component. In specific implementation, the parts by mass can be converted into specific units of mass such as grams, kilograms, or tons according to actual production needs. The amount of all raw materials added in this invention is based on absolute dry weight or pure substance mass. If the raw material itself contains water of crystallization or carrier components, its effective component content must be calculated based on 100% purity. When multi-component systems are involved, the sum of the mass parts of each component constitutes a 100% mass reference system, and the mass ratio of each component should strictly maintain the proportional relationship stated in the instruction manual. Furthermore, the mass part system in this invention has a scale-up characteristic; in actual production, while maintaining the same mass ratio of each component, the total amount of raw materials can be increased or decreased proportionally.

[0039] Example 1

[0040] A preparation process for permeable ceramic bricks with surface coating, such as Figure 3 As shown, it includes the following steps:

[0041] Preparation of matrix;

[0042] S1. Weigh 50 parts of ceramic crushed material, 10 parts of granite crushed material, 1 part of inorganic binder, 2 parts of pore-forming agent, and 25 parts of water. After mixing evenly, press and mold to obtain the matrix. The average particle size of the ceramic crushed material and the granite crushed material is 4mm.

[0043] Preparation of surface layer slurry

[0044] S2. Mix and grind 25 parts refrigerant, 13 parts feldspar, 13 parts quartz, 8 parts kaolin, 8 parts barium carbonate, 8 parts fluorite, 0.3 parts sodium tripolyphosphate, 0.3 parts sodium methyl cellulose, and 38 parts water to obtain a surface layer slurry. The refrigerant raw materials consist of 60 parts Al₂O₃, 10 parts SiO₂, 10 parts CaO, 8 parts ZnO₂, and 4 parts ZrO₂. The solid content of the surface layer slurry is approximately 63%, and the mass ratio of barium carbonate and fluorite in the surface layer raw materials is approximately 12% each.

[0045] Preparation of permeable bricks

[0046] S3. Spray the surface layer slurry onto the substrate, dry at 150℃ for 3 hours, and sinter at 1200℃ for 2 hours to obtain permeable bricks. Figure 1 and Figure 2 As shown in the diagram. Spraying involves applying a surface layer of glaze using a linear glazing machine. The glaze thickness is 1 mm, and the application rate is 1500 g / m². 2 .

[0047] Example 2

[0048] A process for preparing a permeable ceramic brick with a surface coating includes the following steps:

[0049] Preparation of matrix;

[0050] S1. Weigh 60 parts of ceramic crushed material, 20 parts of granite crushed material, 20 parts of kaolin, 5 parts of starch, and 30 parts of water. After mixing evenly, press the mixture into shape to obtain the matrix. The average particle size of the ceramic crushed material and the granite crushed material is 4mm.

[0051] Preparation of surface layer slurry

[0052] S2. Mix and grind 40 parts refrigerant, 15 parts feldspar, 15 parts quartz, 10 parts kaolin, 10 parts barium carbonate, 10 parts fluorite, 0.5 parts sodium tripolyphosphate, 0.4 parts sodium methyl cellulose, and 35 parts water to obtain a surface layer slurry. The refrigerant raw materials are 70 parts Al₂O₃, 15 parts SiO₂, 15 parts CaO, 10 parts ZnO₂, and 5 parts ZrO₂. The solid content of the surface layer slurry is approximately 75%, and the mass ratio of barium carbonate and fluorite in the surface layer raw materials is approximately 9% each.

[0053] Preparation of permeable bricks

[0054] S3. The surface layer slurry is sprayed onto the substrate, dried at 150℃ for 3 hours, and sintered at 1200℃ for 2 hours to obtain permeable bricks. The spraying process involves applying a single layer of surface slurry glaze using a linear glazing machine, with a glaze thickness of 1 mm and a glaze application rate of 1500 g / m². 2 .

[0055] Example 3

[0056] A process for preparing a permeable ceramic brick with a surface coating includes the following steps:

[0057] Preparation of matrix;

[0058] S1. Weigh 40 parts ceramic crushed material, 10 parts granite crushed material, 10 parts ball soil, 2 parts fly ash, and 20 parts water. After mixing evenly, press into shape to obtain the matrix. The average particle size of the ceramic crushed material and granite crushed material is 4mm.

[0059] Preparation of surface layer slurry

[0060] S2. Mix and grind 25 parts refrigerant, 10 parts feldspar, 10 parts quartz, 6 parts kaolin, 6 parts barium carbonate, 6 parts fluorite, 0.3 parts sodium tripolyphosphate, 0.2 parts sodium methyl cellulose, and 35 parts water to obtain a surface layer slurry. The refrigerant raw materials are 50 parts Al₂O₃, 5 parts SiO₂, 5 parts CaO, 25 parts ZnO, and 2 parts ZrO₂. The solid content of the surface layer slurry is approximately 64%, and the mass ratio of barium carbonate and fluorite in the surface layer raw materials is approximately 9% each.

[0061] Preparation of permeable bricks

[0062] S3. The surface layer slurry is sprayed onto the substrate, dried at 150℃ for 3 hours, and sintered at 1200℃ for 2 hours to obtain permeable bricks. The spraying process involves applying a single layer of surface slurry glaze using a linear glazing machine, with a glaze thickness of 1 mm and a glaze application rate of 1500 g / m². 2 .

[0063] Example 4 differs from Example 1 in that barium carbonate is replaced with barium oxide and fluorite is replaced with cryolite. Specifically:

[0064] S2. Mix and grind 25 parts refrigerant, 3 parts feldspar, 13 parts quartz, 8 parts kaolin, 8 parts barium oxide, 8 parts barium fluoride, 0.3 parts sodium tripolyphosphate, 0.3 parts sodium methylcellulose, and 38 parts water to obtain a surface slurry.

[0065] Example 5 differs from Example 1 in that barium carbonate is replaced with barium hydroxide and fluorite is replaced with barium fluoride. Specifically:

[0066] S2. Mix and grind 25 parts refrigerant, 3 parts feldspar, 13 parts quartz, 8 parts kaolin, 8 parts barium hydroxide, 8 parts cryolite, 0.3 parts sodium tripolyphosphate, 0.3 parts sodium methylcellulose, and 38 parts water to obtain a surface slurry.

[0067] Example 6 differs from Example 1 in that barium carbonate is replaced with potassium hydroxide, and fluorite is replaced with a mixture of barium fluoride and fluorite in equal proportions. Specifically:

[0068] S2. Mix and grind 25 parts refrigerant, 3 parts feldspar, 13 parts quartz, 8 parts kaolin, 8 parts potassium hydroxide, 4 parts barium fluoride, 4 parts fluorite, 0.3 parts sodium tripolyphosphate, 0.3 parts sodium methylcellulose, and 38 parts water to obtain a surface slurry.

[0069] Example 7 differs from Example 1 in that barium carbonate is replaced with calcium oxide and fluorite is replaced with barium fluoride. Specifically:

[0070] S2. Mix and grind 25 parts refrigerant, 3 parts feldspar, 13 parts quartz, 8 parts kaolin, 8 parts calcium oxide, 8 parts barium fluoride, 0.3 parts sodium tripolyphosphate, 0.3 parts sodium methylcellulose, and 38 parts water to obtain a surface slurry.

[0071] Example 8 differs from Example 1 only in that all the raw materials used for the surface layer are: 6 parts barium carbonate, 6 parts fluorite, 3 parts kaolin, 5 parts quartz, 20 parts potassium sodium feldspar, 6 parts zinc oxide, 10 parts sodium bicarbonate, 5 parts strontium carbonate and 5 parts lepidolite.

[0072] Example 9 differs from Example 1 only in that the surface layer material uses 11 parts barium carbonate and 11 parts fluorite.

[0073] Comparative Example 1: Ordinary permeable ceramic bricks without glaze.

[0074] Comparative Example 2 uses permeable bricks containing conventional glazes (without barium carbonate / fluorite).

[0075] Comparative Example 3 differs from Example 1 only in that no fluoride is added to the surface layer raw material. Specifically, the surface layer raw material used is 25 parts refrigerant, 10 parts feldspar, 10 parts quartz, 6 parts kaolin, 6 parts barium carbonate, 0.3 parts sodium tripolyphosphate, 0.2 parts sodium methylcellulose, and 35 parts water.

[0076] Comparative Example 4 differs from Example 1 only in that no alkaline metal precursor is added to the surface layer raw material. Specifically, the surface layer raw material used is 25 parts refrigerant, 10 parts feldspar, 10 parts quartz, 6 parts kaolin, 6 parts fluorite, 0.3 parts sodium tripolyphosphate, 0.2 parts sodium methylcellulose, and 35 parts water.

[0077] Comparative Example 5 differs from Example 1 only in that the surface layer material used consists of 5 parts barium carbonate and 5 parts fluorite.

[0078] Comparative Example 6 differs from Example 1 only in that the surface layer raw materials used are 15 parts barium carbonate and 15 parts fluorite.

[0079] To further illustrate the technical effects of the present invention, permeable bricks from Examples 1-8 and Comparative Examples 1-6 were subjected to performance tests, including permeability coefficient, flexural strength, solar reflectance, surface temperature difference, glaze whiteness, and porosity. The permeability coefficient, flexural strength, solar reflectance, glaze whiteness, and porosity were measured after 28 days of standard curing of the permeable bricks, according to standards such as "Permeable Pavement Bricks and Permeable Pavement Panels" (GB / T 25993-2023), "Permeable Concrete" (JC / T 2558-2020), "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019), and "Test Methods for Reflectivity and Emissivity of Materials and Coatings" (GJB 5023.1A-2012). Surface temperature difference was detected using infrared thermal imaging and compared with the surface temperature of Comparative Example 1. The permeable brick samples were 400×800mm in size. The test results are shown in Table 1 below.

[0080] Table 1 Performance test results of each embodiment and comparative example

[0081]

[0082] Based on Examples 1-9 and the data in Table 1, it can be seen that, compared with the comparative example, the permeability coefficient of the ceramic permeable brick prepared by adding an alkaline metal precursor and fluoride to the raw materials of the surface layer is significantly improved. It can achieve the goal of maintaining the permeability of the permeable brick while applying glaze to the permeable brick matrix. Furthermore, the permeable brick prepared by selecting barium carbonate as the alkaline metal precursor and fluorite as the fluoride has better air permeability.

[0083] Based on Examples 1 and Comparative Examples 3-6, and the data in Table 1, it can be seen that using alkali metal precursors and fluorides alone can also improve the permeability of permeable bricks, but the improvement effect is not as good as the combination of alkali metal precursors and fluorides. Based on Examples 1 and Comparative Examples 5-6, using higher or lower parts of barium carbonate and fluorite significantly affects the performance of the prepared permeable bricks. Although the permeable brick sample prepared with 15 parts of barium carbonate and fluorite has better permeability than the permeable brick samples obtained in Examples 1, this sample experiences significant surface shrinkage and is prone to peeling during firing, failing to meet usage requirements. The permeable brick prepared with 5 parts of barium carbonate and fluorite has poor permeability and cannot meet usage requirements.

[0084] In summary, this invention, by adding alkaline metal precursors and fluorides to the raw materials of the surface layer, breaks the silicon-oxygen network, reduces the degree of glass polymerization, and increases the thermal expansion coefficient of the glaze. This results in permeable bricks that, after glazing and firing, not only do not fill the gaps between the permeable brick particles, but also allow the previously filled gaps to reopen. The permeable ceramic bricks produced using this process can achieve a permeability coefficient of 2.3*10⁻⁶. -2The flexural strength can reach over 55 MPa; at the same time, the refrigerant added to the surface layer material gives the product a solar reflectivity of over 90%, which can effectively reduce ground temperature, promote ecological water circulation, and reduce environmental problems such as heat and humidity during the rainy season in summer.

[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A process for the production of a ceramic water permeable tile having a surface coating, characterized in that, include: All raw materials for the matrix are pressed together to obtain the matrix. The raw materials for the surface layer are mixed and ground with water to obtain a surface layer slurry with a solid content of 60%-75%. The surface layer slurry is sprayed onto the substrate, dried, and sintered to obtain permeable bricks. The raw materials of the surface layer include 6-17% by mass of an alkaline metal precursor and 6-17% by mass of a fluoride. The alkaline metal precursor is selected from at least one of barium carbonate, barium oxide, barium hydroxide, sodium carbonate, potassium carbonate, potassium hydroxide, calcium oxide, and calcium hydroxide. The fluoride is selected from at least one of fluorite and barium fluoride; The raw materials for the surface layer also include, by mass parts: 10-15 parts feldspar, 10-15 parts quartz, 6-10 parts kaolin, 0.3-0.5 parts sodium tripolyphosphate, and 0.2-0.4 parts sodium methylcellulose; The raw materials of the surface layer also include a refrigerant, and the raw materials of the refrigerant include, by mass parts: 50-70 parts Al2O3, 5-15 parts SiO2, 5-15 parts CaO, 5-10 parts ZnO2, and 2-5 parts ZrO2. The raw materials of the matrix, by mass parts, include: 40-60 parts ceramic crushed material, 10-20 parts granite crushed material, 10-20 parts inorganic binder, and 2-5 parts pore-forming agent; the inorganic binder includes one or more combinations of bentonite, kaolin, and ball clay, and the pore-forming agent includes one or more combinations of straw, sawdust, starch, and fly ash.

2. The preparation process of the permeable ceramic brick with a surface coating according to claim 1, characterized in that, The surface layer slurry is sprayed onto the substrate to form a spray layer, the thickness of which is 1-2 mm.

3. The preparation process of the permeable ceramic brick with a surface coating according to claim 2, characterized in that, The spraying process involves applying a surface layer slurry to the substrate, with a slurry application rate of 1500-2500 g / m².

4. The preparation process of the permeable ceramic brick with a surface coating according to claim 1, characterized in that, The drying conditions are 100-200℃ for 2-4 hours; the sintering conditions are 1150-1300℃ for 1-2 hours.

5. A permeable ceramic brick with a surface coating, characterized in that, It is prepared by the preparation process of ceramic permeable brick with surface coating as described in any one of claims 1-4.

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