Views: 2 Author: Site Editor Publish Time: 2022-01-22 Origin: Site
Sodium carboxymethyl cellulose, English abbreviation CMC, ceramic industry is commonly known as "Sodium CMC", is a kind of anionic substance, is made of natural cellulose as raw material, by chemical modification and white or light yellow powder. CMC has good solubility and can be dissolved into transparent and uniform solution in both cold and hot water.
1. Brief introduction of CMC uses in ceramics
1.1 application of CMC in ceramics
1.1.1. Application principle
CMC has a unique linear polymer structure. When CMC is added to water, its hydrophilic group (-Coona) is combined with water to form a solvated layer, which gradually disperses CMC molecules in water. The network structure between CMC polymers is formed by hydrogen bond and van der Waals force, thus showing cohesivity. Body-specific CMC can be used as excipient, plasticizer and reinforcer of billet in ceramic industry. Adding proper amount of CMC to the billet can increase the bonding force of the billet, make the billet easy to form, increase the flexural strength by 2 ~ 3 times, and improve the stability of the billet, so as to improve the quality rate of ceramics, reduce the cost of later processing. At the same time, due to the addition of CMC, the processing speed of green billet can be improved and production energy consumption can be reduced, and the water in the billet can be evenly evaporated to prevent drying and cracking, especially in the large size of floor tile billet and polished brick billet, the effect is more obvious. Compared with other body-strengthening agents, body-specific CMC has the following characteristics:
(1) less dosage: the dosage is generally less than 0.1%, which is 1/5 ~ 1/3 of other body strengthening agent, while the bending strength of green body is obvious and the cost can be reduced.
(2) good burning loss: after burning almost no ash, no residue, does not affect the green color.
(3) with good suspension: to prevent poor raw materials and pulp precipitation, so that the slurry evenly dispersed.
(4) Wear resistance: in the ball grinding process, the molecular chain is less damaged.
1.1.2. Method of addition
The general amount of CMC in the billet is 0.03 ~ 0.3%, which can be adjusted according to the actual needs. For the slurry with a lot of poor raw materials in the formula, CMC can be added to the ball mill and ground together with the mud, pay attention to the uniform dispersion, so as not to be difficult to dissolve after agglomeration, or CMC can be predissolved with water at 1:30 separately and then added to the ball mill for mixing 1 ~ 5 hours before grinding.
1.2. Application of CMC in glaze slurry
1.2.1 Application principle
Glaze paste special TYPE CMC is excellent performance stabilizer and binder, used for ceramic tile bottom glaze and surface glaze, can increase the bonding force of glaze slurry and body, because glaze slurry is easy to precipitation and poor stability, and CMC and all kinds of glaze compatibility is good, has excellent dispersion and protective colloid, so that the glaze body is in a very stable dispersion state. After adding CMC, the surface tension of glaze can be improved, the water can be prevented from diffusing from glaze to the body, the smoothness of glaze can be increased, the cracking and fracture phenomenon caused by the drop in the strength of the body after glaze application can be avoided, and the pinhole phenomenon of glaze can also be reduced after baking.
1.2.2. Adding method
The amount of CMC added to the bottom glaze and surface glaze ranges from 0.08 to 0.30%. It can be adjusted according to actual needs. First, the CMC is prepared into 3% aqueous solution. If it needs to be stored for several days, the solution should be put in an airtight container with appropriate preservatives and kept at a low temperature. Then, the solution is mixed evenly with the glaze.
1.3 application of CMC in printing glaze
1.3.1, printing glaze special CMC has good thickening property and dispersity and stability, the special CMC to adopt new technology, good solubility, high transparency, almost no insolubles, but also has superior shear thinning and lubrication, greatly improve the printing glaze printing adaptability, reduced the screen, screen blocking phenomenon, reduce the network times, when printing smooth operation, Clear pattern, good color consistency.
1.3.2 The general amount of adding printing glaze is 1.5-3%. CMC can be soaked with ethylene glycol and then added with water to make it presoluble, or 1-5% sodium tripolyphosphate and color materials can be dry mixed together, and then dissolved with water, so that various materials can be fully dissolved and evenly.
1.4. Application of CMC in infiltration glaze
1.4.1 Application principle
Penetration glaze contains a lot of soluble salt, acid, and some partial penetration glaze special CMC has superior acid salt resistance stability, make the penetration glaze in the process of use and placement keep stable viscosity, prevent due to the changes of viscosity, color and penetration glaze special CMC water soluble, net permeability and water retention is very good, to maintain the stability of the soluble salt glaze has a lot of help .
1.4.2. Method of addition
Dissolve CMC with ethylene glycol, some water and complexing agent, then mix well with the dissolved color solution.
2.CMC should be paid attention to in ceramic production
2.1 Different types of CMC play different roles in ceramic production. Proper selection can achieve the purpose of economy and efficiency.
2.2. In the glaze and printing glaze, it is not necessary to coopt CMC products with low purity, especially in the printing glaze, high purity CMC with high purity, good acid and salt resistance and high transparency must be selected to prevent ripples and pinholes on the glaze. At the same time, can also prevent the use of plug net, poor leveling and color and other phenomena.
2.3 If the temperature is high or the glaze needs to be placed for a long time, preservatives should be added.
3. Analysis of common problems of CMC in ceramic production
3.1. The fluidity of mud is not good and it is difficult to put glue.
Due to the viscosity of CMC itself, mud viscosity is too high, which leads to the difficulty of pulping. The solution is to adjust the amount and type of coagulant, recommend the following decoagulant formula :(1) sodium tripolyphosphate 0.3%; (2) sodium tripolyphosphate 0.1%+ sodium silicate 0.3%; (3) Sodium humate 0.2%+ sodium tripolyphosphate 0.1%
3.2. Glaze paste and printing oil are thin.
The reasons for selecting glaze paste and printing oil are as follows :(1) glaze paste or printing oil is eroded by microorganisms, so that CMC fails. The solution is to wash the container of glaze paste or printing oil thoroughly, or add preservatives such as formaldehyde and phenol. (2) Under the continuous stirring of shear force, the viscosity decreases. It is recommended to adjust CMC aqueous solution.
3.3. Paste the mesh when using the printing glaze.
The solution is to adjust the amount of CMC, so that the printing glaze viscosity is moderate, if necessary, add a small amount of water to stir evenly.
3.4, blocking network, wipe the number of times.
The solution is to improve the transparency and solubility of CMC. Printing oil preparation after the completion of 120 mesh sieve, printing oil also need to pass 100 ~ 120 mesh sieve; Adjust printing glaze viscosity.
3.5, water retention is not good, after printing the surface flour, affect the next printing.
The solution is to increase the amount of glycerin in the process of printing oil preparation; Switch to a high degree of substitution (replace good uniformity), low viscosity CMC to prepare printing oil.