MATTE CERAMIC TILE AND PREPARATION METHOD THEREOF
20230382804 · 2023-11-30
Inventors
- Zhanwen Gu (Dongguan, CN)
- Yanjun Wang (Dongguan, CN)
- Jiangwen Deng (Dongguan, CN)
- Huiyin Xiao (Dongguan, CN)
- Quan Yang (Dongguan, CN)
- Chaoxian Pan (Dongguan, CN)
- Yongqiang Wang (Dongguan, CN)
- Xuebin Liu (Dongguan, CN)
- Junjun Jiang (Dongguan, CN)
- Jun WANG (Dongguan, CN)
Cpc classification
C04B2235/349
CHEMISTRY; METALLURGY
C03C3/087
CHEMISTRY; METALLURGY
C04B41/4578
CHEMISTRY; METALLURGY
C03C2209/00
CHEMISTRY; METALLURGY
C03C8/02
CHEMISTRY; METALLURGY
C03C8/20
CHEMISTRY; METALLURGY
C04B2235/3472
CHEMISTRY; METALLURGY
C04B33/1324
CHEMISTRY; METALLURGY
C04B2235/40
CHEMISTRY; METALLURGY
International classification
C04B41/45
CHEMISTRY; METALLURGY
C04B41/00
CHEMISTRY; METALLURGY
C03C8/20
CHEMISTRY; METALLURGY
C03C1/00
CHEMISTRY; METALLURGY
C03C8/02
CHEMISTRY; METALLURGY
Abstract
A blank material for a ceramic tile consists of the following components in percentage by weight: nepheline powder: 10%-15%; clay with a carbon content of ≥3.0 wt %: 10%-15%; clay with a carbon content of ≤0.5 wt %: 15%-22%; clay with a carbon content between 0.5 wt % and 3.0 wt %: 10%-15%; recycled waste blank: 5%-10%; sodium potassium powder: 5%-10%; sodium feldspar powder: 12%-20%; desulfurization residue: 0%-7%; waste from edging and polishing: 15%-26%; waste porcelain powder: 5%-10%; liquid gel remover: 0.3%-1.0%; liquid reinforcing agent: 0.2%-0.8%. Its preparation method comprises the following steps: preparing raw materials for a blank body and ball milling, powder spray granulation, aging, pressing and molding of the blank body, drying, polishing the blank body, spraying water, glazing, applying a decorative pattern, firing.
Claims
1. A matte ceramic tile, wherein a blank material for the ceramic tile consists of the following components in percentage by weight: nepheline powder: 10%-15%; clay with a carbon content of ≥3.0 wt %: 10%-15%; clay with a carbon content of ≤0.5 wt %: 15%-22%; clay with a carbon content between 0.5 wt % and 3.0 wt %: 10%-15%; recycled waste blank: 5%-10%; sodium potassium powder: 5%-10%; sodium feldspar powder: 12%-20%; desulfurization residue: 0%-7%; waste from edging and polishing: 15%-26%; waste porcelain powder: 5%-10%; liquid gel remover: 0.3%-1.0%; liquid reinforcing agent: 0.2%-0.8%; wherein the desulfurization residue is a desulfurized gypsum produced by treating a kiln flue gas with a wet desulfurization method; the desulfurized gypsum comprises calcium sulfate dihydrate (CaSO.sub.4.Math.2H.sub.2O) crystal and water, with a mass proportion of water ranging from 25-35%.
2. The matte ceramic tile according to claim 1, wherein the waste from edging and polishing consists of water and a solid waste gathered from edging and polishing of a semi-finished ceramic product, the solid waste comprises SiO.sub.2, Al.sub.2O.sub.3, CaO, K.sub.2O, Na.sub.2O, MgO, MgCl.sub.2, and SiC, wherein a total content of SiO.sub.2, Al.sub.2O.sub.3 is greater than 83%; the waste from edging and polishing has a water content of 32 wt % to 36 wt %.
3. The matte ceramic tile according to claim 1, wherein the liquid gel remover is one or more selected from the group consisting of methacrylic acid, sodium methallylsulfonate, sodium persulfate, hydroquinone, polyimide, sodium hydroxide, sodium chloride, and sodium carbonate; the liquid gel remover has a pH of 7.0 to 9.0.
4. The matte ceramic tile according to claim 1, wherein the liquid reinforcing agent is one or more selected from the group consisting of modified lignin, polyvinyl alcohol, polyacrylate, sodium polyacrylate, water glass, and a phosphate salt.
5. A method for preparing a matte ceramic tile, comprising the following steps: (1) preparing raw materials for a blank body: preparing the raw materials according to a predetermined ratio, feeding the raw materials directly into a three-stage continuous ball mill, adding water to obtain a mixture with a water content of 32 wt % to 35 wt %, and ball milling continuously for 2 to 5 hours to obtain a slurry; wherein the raw materials comprise waste from edging and polishing, desulfurization residue, waste porcelain powder, nepheline powder, sodium potassium powder, potassium feldspar powder, and a carbon-containing clay; (2) powder spray granulation: storing the slurry produced by the continuous ball mill in an underground slurry tank; transferring the slurry into a drying tower by a plunger pump after aging and homogenization for powder spray granulation; a powder obtained by powder spray granulation has a volumetric weight of 1.0 to 1.1 g/cm.sup.3 and a water content of 6.0 wt % to 6.5 wt %; (3) aging: conveying the powder obtained by powder spray granulation to a powder silo directly with a belt, aging the powder in the powder silo for more than 48 hours before pressing and molding; water content of the powder after aging is 5.0 wt % to 6.0 wt %; (4) pressing and molding of the blank body: transporting the powder after aging to a hopper provided at the top of a press; pushing the powder into a mold frame of the press by a grid distributor; applying pressure to the powder by the press to partially release gas trapped in voids of the powder, causing powder particles to shift and combine through internal frictional forces to take on a desired shape, forming a blank body; the shape of the blank body formed has a cross-section identical to that of a mold, and shapes of an upper surface and a lower surface of the blank body are determined by shapes of an upper press mold and a lower press mold in the mold frame; (5) drying: drying the blank body in a roller hearth furnace having 3 to 5 layers; a maximum drying temperature is 160° C. to 200° C., drying time is 30 min to 60 min; strength of the blank body after drying is 1.2 Mpa to 1.8 Mpa, a water content of a dried blank body is <0.1 wt %; (6) polishing the blank body: polishing a surface of the blank body coming out from the roller hearth furnace by a blank body polishing machine; (7) spraying water: spraying water onto the upper surface of the blank body by a high-pressure water-spraying cabinet equipped with a spray gun; the spray gun has a nozzle size of 0.36 mm; water pressure during spraying is 12 bar to 18 bar, water is sprayed in an amount of 55 g/m.sup.2 to 100 g/m.sup.2; (8) glazing: glazing is performed using a linear glazing machine with the following process parameters: specific gravity of a glaze slurry: 1.45 to 1.80; time taken for a glaze slurry to flow out of a viscometer, determined according to Chinese national standard GB/T1723 Paint Viscosity Determination Method: 18 s to 30 s; and a thickness of a glaze layer: 0.03 mm to 0.1 mm; (9) applying a decorative pattern: applying a decorative pattern to a glazed surface of the blank body via any one of screen printing, rubber roller printing, and inkjet printing; and (10) firing: transferring a decorated blank body from the previous step to a firing kiln for firing at a firing temperature of 1050° C. to 1170° C. and a firing time of 50 min to 80 min, wherein a firing time for a stage of between 1150° C. to 1170° C. is 6 min to 10 min.
6. The method for preparing the matte ceramic tile according to claim 5, wherein the desulfurization residue in step (1) is a desulfurized gypsum produced by treating a kiln flue gas with a wet desulfurization method; a main component of the desulfurized gypsum is calcium sulfate dihydrate (CaSO.sub.4.Math.2H.sub.2O) crystal, a major impurity of the desulfurized gypsum is calcium carbonate; the desulfurized gypsum has a purity of 90% to 95%, a water content of 10 wt % to 15 wt %, and a particle size of 30 nm to 50 nm.
7. The method for preparing the matte ceramic tile according to claim 5, wherein the carbon-containing clay in step (1) is selected from one of the following: (1) clay with a carbon content of ≥3.0 wt % and clay with a carbon content of ≤0.5 wt %; (2) clay with a carbon content of ≤0.5 wt %; and (3) clay with a carbon content of ≤0.5 wt % and clay with a carbon content between 0.5 wt % and 3.0 wt %.
8. The method for preparing the matte ceramic tile according to claim 5, wherein the glaze in step (8) is a matte glaze slurry consisting of a leveling agent and a matte glaze slurry; the leveling agent is one or more selected from the group consisting of a polyacrylic acid leveling agent, a phosphate ester modified acrylic acid leveling agent, a fluorine modified acrylic acid leveling agent, a butyl acrylate leveling agent, a silicone leveling agent, a polyether polyester modified silicone leveling agent, a polyether-modified silicone, a polymethylalkylsiloxane, an alkyl-modified organosiloxane, an end-group modified silicone, and a fluorocarbon leveling agent; the matt glaze slurry consists of 20 wt %-30 wt % of the levelling agent and 70 wt %-80 wt % of the matte slurry; the matte glaze slurry is made from ball-milling 64 wt %-74 wt % of a matte glaze powder, 0.2 wt %-1.2 wt % of an additive, and 25 wt %-35 wt % of water for 5 to 8 hours; fineness of the matte glaze slurry is to an extent that 0.8 wt %-1.2 wt % of the matte glaze slurry is unable to pass a 325 mesh sieve.
9. The method for preparing the matte ceramic tile according to claim 8, wherein the matte glaze powder consists of the following components: nepheline: 8 wt %-13 wt %; albite: 5 wt %-10 wt %; FMC633 frit: 10 wt %-15 wt %; FMC689 frit: 28 wt %-35 wt %; FMC053 frit: 8 wt %-12 wt %; zinc phosphate: 2 wt %-10 wt %; zinc oxide: 2 wt %-6 wt %; wollastonite: 2 wt %-5 wt %; aluminium oxide: 1 wt %-7 wt %; bentonite: 0 wt %-1 wt %; ultrafine zirconia (ZrO.sub.2): 0 wt %-10 wt %; recycled material from scrapping: 5 wt %-15 wt %; ball clay: 7 wt %-10 wt %; carboxymethyl cellulose: 0.2 wt %-0.3 wt %; sodium tripolyphosphate: 0.3 wt %-0.5 wt %; the ultrafine zirconia has D.sub.50 of below 0.47 μm, D.sub.90 of below 1.0 μm; ZrO.sub.2 has a purity of ≥93.27, a refractive index of 1.93-2.01, a melting point of 2370° C. to 2700° C.
10. The method for preparing the matte ceramic tile according to claim 9, wherein calcium and magnesium are introduced into a formulation of the FMC633 frit; the FMC633 frit comprises the following main chemical components in percentage by weight: Ignition lost (I.L)≤0.05%; SiO.sub.2: 51.35%; Al.sub.2O.sub.3: 11.97%; Fe.sub.2O.sub.3: 0.05%; CaO: 17.92%; MgO: 8.25%; K.sub.2O: 2.86%; Na.sub.2O: 2.39%; ZrO.sub.2: 5.16%; the FMC633 frit has a maturation temperature of lower than 1050° C.; aluminium and calcium are introduced into a formulation of the FMC689 frit; the FMC689 frit comprises the following main chemical components in percentage by weight: I.L≤0.05%; SiO.sub.2: 54.52%; Al.sub.2O.sub.3: 21.73%; Fe.sub.2O.sub.3: 0.07%; CaO: 15.11%; MgO: 0.23%; K.sub.2O: 3.49%; Na.sub.2O: 2.43%; B.sub.2O.sub.3: 1.89%; ZnO: 0.48%; the FMC689 frit has a maturation temperature of above 1050° C.; zinc and zirconium are introduced into a formulation of the FMC053 frit; the FMC053 frit comprises the following main chemical components in percentage by weight: I.L≤0.05%; SiO.sub.2: 44.67%; Al.sub.2O.sub.3: 16.36%; Fe.sub.2O.sub.3: 0.05%; CaO: 4.1%; MgO: 0.30%; K.sub.2O: 1.76%; Na.sub.2O: 2.72%; B.sub.2O.sub.3: 2.59%; ZnO: 15.03%; ZrO.sub.2: 11.20%; P.sub.2O.sub.5: 1.17%; the FMC053 frit has a maturation temperature of 1100° C. to 1170° C.; the recycled material from scrapping consists of a blank material and a glaze material, wherein the glaze material comprises a base glaze and a transparent glaze, the recycled material from scrapping has a water content of 9 wt % to 13 wt % and fineness of <1%; the recycled material from scrapping comprises the following chemical components in percentage by weight: IL.: 5%-6%; SiO.sub.2: 59%-61%; Al.sub.2O.sub.3: 20%-21%; Fe.sub.2O.sub.3: 0.1%-0.2%; CaO: 4.5%-5%; MgO: 3%-3.8%; K.sub.2O: 1%-1.5%; Na.sub.2O: 2.5%-3%; and ZrO.sub.2: 0.2%-0.8%.
Description
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0054] The present invention will be described in further detail below with embodiments.
[0055] The blank material for the ceramic tile consists of the following components in percentage by weight: nepheline powder: 10%-15%; clay with a carbon content of ≥3.0 wt %: 10%-15%; clay with a carbon content of ≤0.5 wt %: 15%-22%; clay with a carbon content of >0.5 wt % and <3.0 wt %: 10%-15%; recycled waste blank: 5%-10%; sodium potassium powder: 5%-10%; sodium feldspar powder: 12%-20%; desulfurization residue: 0%-7%; waste from edging and polishing: 15%-26%; waste porcelain powder: 5%-10%; liquid gel remover: 0.3%-1.0%; liquid reinforcing agent: 0.2%-0.8%.
[0056] In the present embodiment, the waste from edging and polishing consists of water and a solid waste gathered from edging and polishing of a semi-finished ceramic product. The main chemical components of the solid waste comprise SiO.sub.2, Al.sub.2O.sub.3, CaO, K.sub.2O, Na.sub.2O, MgO, MgCl.sub.2, and SiC, wherein a total content of SiO.sub.2 and Al.sub.2O.sub.3 is greater than 83%; the waste from edging and polishing has a water content of 32 wt % to 36 wt %. Water content refers to the ratio of the mass of water to the mass of waste residue.
[0057] The waste from edging and polishing is mainly the solid waste produced during cold working at a later stage of ceramic tile production, that is, after grinding, polishing, edging, chamfering, and other procedures, the solid waste produced during flocculation, sedimentation, pressure filtration, and other processes. This solid waste includes fine particles that are produced during polishing or grinding, that is, fine particles from the grinding of the blank material, the glaze material, and mounted points. The recycled waste blank is from missing corners and clay blanks (not fired) produced during the manufacturing process; these materials are partially dissolved in water to form a slurry or are directly ball-milled to be reused in a clay slurry for the blank. The waste porcelain powder is a material having a desirable particle size obtained after a series of crushing treatments on defective tile products, followed by sieving.
[0058] In the present embodiment, the liquid gel remover is one or more selected from the group consisting of methacrylic acid, sodium methallylsulfonate, sodium persulfate, hydroquinone, polyimide, sodium hydroxide, sodium chloride, and sodium carbonate; the pH of the liquid gel remover is 7.0 to 9.0.
[0059] In the present embodiment, the liquid reinforcing agent is one or more selected from the group consisting of modified lignin, polyvinyl alcohol, polyacrylate, sodium polyacrylate, water glass, and a phosphate salt.
[0060] The liquid reinforcing agent increases the dry strength of the blank body, ensures that the tile is not prone to cracking before entering the kiln. In addition, the liquid reinforcing agent is able to completely evaporate at medium and high temperatures without affecting the quality of the ceramic tile product, i.e., the formation of molten holes, bubbles, color differences, deformation, among others, is prevented.
[0061] The method for preparing a matte ceramic tile comprises the following steps: [0062] (1) preparing raw materials for a blank body: preparing the raw materials according to a predetermined ratio, feeding the raw materials directly into a three-stage continuous ball mill, adding water to obtain a mixture with a water content of 32 wt % to 35 wt %, and ball milling continuously for 2 to 5 hours to obtain a slurry; the raw materials include waste from edging and polishing, desulfurization residue, waste porcelain powder, nepheline powder, sodium potassium powder, potassium feldspar powder, and a carbon-containing clay; the desulfurization residue in step (1) is a desulfurized gypsum produced by treating a kiln flue gas with a wet desulfurization method; a main component of the desulfurized gypsum is calcium sulfate dihydrate (CaSO.sub.4.Math.2H.sub.2O) crystal, a major impurity of the desulfurized gypsum is calcium carbonate; the desulfurized gypsum has a purity of 90% to 95%, a water content of 10 wt % to 15 wt %, and a particle size of 30 nm to 50 nm.
[0063] The carbon-containing clay in step (1) is selected from one of the following: (1) clay with a carbon content of ≥3.0% and clay with a carbon content of ≤0.5%; (2) clay with a carbon content of ≤0.5%; and (3) clay with a carbon content of ≤0.5% and clay with a carbon content of >0.5% and <3.0%. [0064] (2) powder spray granulation: storing the slurry produced by the continuous ball mill in an underground slurry tank; transferring the slurry into a drying tower by a plunger pump after aging and homogenization for powder spray granulation; a powder obtained by powder spray granulation has a volumetric weight of 1.0 to 1.1 g/cm.sup.3 and a water content of 6.0 wt % to 6.5 wt %. [0065] (3) Aging: conveying the powder obtained by powder spray granulation to a powder silo directly with a belt, aging the powder in the powder silo for more than 48 hours before pressing and molding; water content of the powder after aging is 5.0% to 6.0%. [0066] (4) Pressing and molding of the blank body: transporting the powder after aging to a hopper provided at the top of a press; pushing the powder into a mold frame of the press by a grid distributor; applying pressure to the powder by the press to partially release gas trapped in voids of the powder, causing powder particles to shift and combine through internal frictional forces to take on a desired shape, forming a blank body; the shape of the blank body formed has a cross-section identical to that of a mold, and shapes of an upper surface and a lower surface of the blank body are determined by shapes of an upper press mold and a lower press mold in the mold frame. [0067] (5) Drying: drying the blank body in a roller hearth furnace having 3 to 5 layers; a maximum drying temperature is 160° C. to 200° C., drying time is 30 min to 60 min; strength of the blank body after drying is 1.2 Mpa to 1.8 Mpa, a water content of a dried blank body is <0.1 wt %. [0068] (6) Polishing the blank body: polishing a surface of the blank body coming out from the roller hearth furnace by a blank body polishing machine. [0069] (7) Spraying water: spraying water onto the upper surface of the blank body by a high-pressure water-spraying cabinet equipped with a spray gun; the spray gun has a nozzle size of 0.36 mm; water pressure during spraying is 12 bar to 18 bar, water is sprayed in an amount of 55 g/m.sup.2 to 100 g/m.sup.2. [0070] (8) Glazing: glazing is performed using a linear glazing machine with the following process parameters: specific gravity of a glaze slurry: 1.45 to 1.80; time taken for a glaze slurry to flow out of a viscometer, determined according to Chinese national standard GB/T1723 Paint Viscosity Determination Method: 18 s to 30 s (which means a viscosity of 10˜40 mPa.Math.s); and a thickness of a glaze layer: 0.03 mm to 0.1 mm Specific gravity, also known as relative density, is a measure of the density of a glaze slurry in comparison to the density of water. In the Paint Viscosity Determination Method, a Paint-4 Viscometer is used to measure the viscosity of fluids. The viscosity of fluids is expressed as the elapse time (unit: second) of a sample flowing out from a standard effuse hole after filling the sample in a specific container. Viscosity can be converted into kinematic viscosity by mathematical calculation.
[0071] The glaze is a matte glaze slurry consisting of a leveling agent and a matte glaze slurry.
[0072] The leveling agent is one or more selected from the group consisting of a polyacrylic acid leveling agent, a phosphate ester modified acrylic acid leveling agent, a fluorine modified acrylic acid leveling agent, a butyl acrylate leveling agent, a silicone leveling agent, a polyether polyester modified silicone leveling agent, a polyether-modified silicone, a polymethylalkylsiloxane, an alkyl-modified organosiloxane, an end-group modified silicone, and a fluorocarbon leveling agent.
[0073] The matt glaze slurry consists of 20 wt %-30 wt % of the levelling agent and 70 wt %-80 wt % of the matte slurry.
[0074] The matte glaze slurry is made from ball-milling 64 wt %-74 wt % of a matte glaze powder, 0.2 wt %-1.2 wt % of an additive, and 25 wt %-35 wt % of water for 5 to 8 hours; fineness of the matte glaze slurry is to an extent that 0.8 wt %-1.2 wt % of the matte glaze slurry is unable to pass a 325 mesh sieve.
[0075] The matte glaze powder consists of the following components: nepheline: 8 wt %-13 wt %; albite: 5 wt %-10 wt %; FMC633 frit: 10 wt %-15 wt %; FMC689 frit: 28 wt %-35 wt %; FMC053 frit: 8 wt %-12 wt %; zinc phosphate: 2 wt %-10 wt %; zinc oxide: 2 wt %-6 wt %; wollastonite: 2 wt %-5 wt %; aluminium oxide: 1 wt %-7 wt %; bentonite: 0 wt %-1 wt %; ultrafine zirconia (ZrO.sub.2): 0 wt %-10 wt %; recycled material from scrapping: 5 wt %-15 wt %; ball clay: 7 wt %-10 wt %; carboxymethyl cellulose: 0.2 wt %-0.3 wt %; sodium tripolyphosphate: 0.3 wt %-0.5 wt %.
[0076] The ultrafine zirconia has D.sub.50 of below 0.47 μm, D.sub.90 of below 1.0 μm; ZrO.sub.2 has a purity of ≥93.27, a refractive index of 1.93-2.01, a melting point of 2370° C. to 2700° C.
[0077] Ultrafine zirconia is defined as having D.sub.50 of below 0.47 μm and D.sub.90 of below 1.0 μm.
[0078] Calcium and magnesium are introduced into a formulation of the FMC633 frit; the FMC633 frit comprises the following main chemical components in percentage by weight: [0079] Ignition lost (I.L)≤0.05%; SiO.sub.2: 51.35%; Al.sub.2O.sub.3: 11.97%; Fe.sub.2O.sub.3: 0.05%; CaO: 17.92%; MgO: 8.25%; K.sub.2O: 2.86%; Na.sub.2O: 2.39%; ZrO.sub.2: 5.16%.
[0080] The FMC633 frit has a maturation temperature of lower than 1050° C.
[0081] Aluminium and calcium are introduced into a formulation of the FMC689 frit; the FMC689 frit comprises the following main chemical components in percentage by weight: [0082] I.L≤0.05%; SiO.sub.2: 54.52%; Al.sub.2O.sub.3: 21.73%; Fe.sub.2O.sub.3: 0.07%; CaO: 15.11%; MgO: 0.23%; K.sub.2O: 3.49%; Na.sub.2O: 2.43%; B.sub.2O.sub.3: 1.89%; ZnO: 0.48%. [0083] the FMC689 frit has a maturation temperature of above 1050° C.
[0084] Zinc and zirconium are introduced into a formulation of the FMC053 frit; the FMC053 frit comprises the following main chemical components in percentage by weight: [0085] I.L≤0.05%; SiO.sub.2: 44.67%; Al.sub.2O.sub.3: 16.36%; Fe.sub.2O.sub.3: 0.05%; CaO: 4.1%; MgO: 0.30%; K.sub.2O: 1.76%; Na.sub.2O: 2.72%; B.sub.2O.sub.3: 2.59%; ZnO: 15.03%; ZrO.sub.2: 11.20%; P.sub.2O.sub.5: 1.17%.
[0086] The FMC053 frit has a maturation temperature of 1100° C. to 1170° C.
[0087] The recycled material from scrapping consists of a blank material and a glaze material, wherein the glaze material comprises a base glaze and a transparent glaze, the recycled material from scrapping has a water content of 9 wt % to 13 wt % and fineness of <1%; the recycled material from scrapping comprises the following chemical components in percentage by weight: [0088] IL.: 5%-6%; SiO.sub.2: 59%-61%; Al.sub.2O.sub.3: 20%-21%; Fe.sub.2O.sub.3: 0.1%-0.2%; CaO: 4.5%-5%; MgO: 3%-3.8%; K.sub.2O: 1%-1.5%; Na.sub.2O: 2.5%-3%; and ZrO.sub.2: 0.2%-0.8%. [0089] (9) Applying a decorative pattern: applying a decorative pattern to a glazed surface of the blank body via any one of screen printing, rubber roller printing, and inkjet printing; and [0090] (10) Firing: transferring a decorated blank body from the previous step to a firing kiln for firing at a firing temperature of 1050° C. to 1170° C. and a firing time of 50 min to 80 min, wherein a firing time for a stage of between 1150° C. to 1170° C. is 6 min to 10 min.
[0091] The description above is only the preferred embodiments of the present invention. Any alterations, modifications, and equivalent substitutions made by a person having ordinary skill in the art all fall within the protection scope of the present invention.