The appearance quality of printing elastic white glue is the external expression of its quality and quality, which includes the appearance state, fineness and fluidity of printing elastic white glue. The appearance of good-quality printing elastic white glue should be uniform liquid, white viscous semi-paste, delicate and balanced, good fluidity, and shiny surface. However, poor quality printing elastic white glue often has layered solidification, poor fluidity, flocculation and water separation, excessive viscosity, and paste-like body during storage, which directly affects its quality, color, covering power, water resistance, leveling, Opacity, gloss, color yield and other properties.
There are many factors that affect the appearance quality of printing elastic white glue: raw materials such as resin (adhesive) wetting and dispersing agent, thickener, filler and its formula and production process will affect it.
Reasons Affecting the Appearance Quality of Printing Elastic White Mucilage
1. Grease is the film-forming substance of printing elastic white glue. During the chemical polymerization reaction of resin, temperature, time, reaction speed, heat preservation, stirring speed and addition of additives will cause incomplete chemical reaction and residual Too many monomers will cause poor chemical and physical stability, and the resin will also coagulate and coalesce, resulting in delamination of printing elastic white glue, strong odor, poor adhesion, network blocking and other unstable factors. Therefore, the resin must have good chemical stability, storage stability, good elasticity, strong adhesion, softness and non-stick characteristics.
2. Judging from the sedimentation velocity (Stokes’ law)
V=218r2(P-P1)/η
In the formula: V-falling speed, ㎝/s; r-particle radius, ㎝;
P-pigment particle density, g/cm3; P1-liquid density, g/cm3
η-liquid particle size, 0.1pa.s
The sedimentation velocity of the filler has a multiple relationship with the grinding fineness, that is, the greater the grinding fineness, the sedimentation velocity of the filler will be multiplied. Printing elastic white glue will separate water and flocculate in layers in a short time. So the general fineness is within 15-20μm. However, finer pigment particles only delay settling and do not prevent settling. Printing elastic white glue is a viscous liquid with non-Newtonian fluidity, and its viscosity must be measured with a rotational viscometer.
3. The influence of printing elastic white glue additives
The wetting and dispersing agent in the printing elastic white mucilage can evenly disperse various fillers. The loose network is introduced into its composition to make the filler particles suspend without sedimentation, effectively reduce the viscosity of the slurry, and prevent the printing elastic white mucilage from flocculating. and precipitation layering; the addition of leveling reduces the mutual restraint between macromolecular chains, reduces the friction of substances and reduces viscosity. The thickener plays a more important role in adjusting the appearance quality of printing elastic white glue.
4. The influence of printing elastic white glue production process
Excessive speed of the agitator will cause the resin to be demulsified by high shear, and the incorrect addition of additives such as dispersants, flow agents, and thickeners will also lead to the demulsification of the printing elastic white glue and the formation of gel particles. Control the time, temperature and product fineness of the production process.
Appearance Quality Control Method of Printing Elastic White Glue
1. Select the resin suitable for formula design requirements
Resin is the most important part of the printing elastic white glue formula. Different resins have different particle size distribution, chemical ion stability, mechanical stability, water-in-oil, oil-in-water and hydrophilicity, which have a great influence on the appearance. Therefore, when choosing a resin, it is necessary to fully consider the characteristics of the resin itself, especially the compatibility of the resin, so as to coordinate the selection of fillers and additives in the process formula.
2. Match well with dispersant and leveling agent
Leveling agents and dispersants produced by different manufacturers have different HLB values. Generally, dispersants and leveling agents (water-based) with larger HLB values will reduce the viscosity of the system more; with the increase of HLB values, different types of dispersing and leveling agents will reduce the viscosity of the system and affect the resin Also bigger. The hydrophilic dispersing and leveling agent will improve the storage stability of the printing elastic white glue, and the hydrophobic dispersing and leveling agent will improve the scrub resistance of the printing elastic white glue after film formation. Therefore, the combination of hydrophilic and hydrophobic dispersing and leveling agents can effectively improve the storage of printing elastic white glue. If more dispersing and leveling agent is added, its hydrophilicity and fluidity will be improved, but its washing fastness will be reduced and its water resistance will be deteriorated. If too little dispersing and leveling agent is added, it will directly affect the quality of its appearance, so generally it should be controlled between 3%-5%.
3. Reasonable selection of thickeners to improve the performance of printing elastic white glue
At present, thickeners commonly used in printing elastic white glue include: polyacrylic acid, cellulose ether, alkali-soluble acrylic, and non-ionic associative polyurethane.
Cellulosic thickeners (mainly including hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose) have high thickening efficiency and good stability, but poor leveling and easy to cause web marks in screen printing , and have a certain effect on the gloss of the slurry. Polyurethane thickeners are more expensive and are rarely used in printing elastic white glue. Polyacrylic acid thickeners have good leveling properties, are not easy to produce network marks, do not affect the gloss of the slurry, have good water resistance and biological stability, and have good compatibility, so that molecular links are formed between particles, resulting in Resin-filler-resin forms a network structure, providing high medium and high shear speeds, making the printing elastic white glue have better rheology, and making the appearance of milky white fluid semi-paste.
4. Use the correct production process
The thickener should be diluted with water before adding. The resin should be added first, and the agitator must be kept at a medium-low speed to avoid resin demulsification caused by excessive shearing. During the production process, the viscosity of the slurry should be observed at any time, and the stirring speed and temperature of the slurry during production should be well controlled. And before adjusting the slurry, add an appropriate amount of surfactant to protect the resin particles from demulsification.
Post time: Mar-04-2023