• Prevention of shrinkage cavity in water-based paint film
    Prevention of shrinkage cavity in water-based paint film


    Abstract: Reducing the shrinkage of water-based paint film is focused on prevention,designing a rational paint formulation,controlling the paint manufacturing process, and strictly controlling the detection of paint materials, which can reduce the chance of shrinkage. Shrinkage holes have been caused, and it is usually difficult to completely solve them. It is necessary to control the degree of shrinkage holes by internal and external factors. Prevention of shrinkage cavity in water-based paint film 1) Choose a good compatibility defoamer to reduce the chance of shrinkage The prevention and solution of the problem of shrinkage of coatings focuses on controlling the raw materials, production formula and production process of the coatings to ensure the normal production and construction of the coatings. The defoaming agent is used to remove bubbles during the production process of the coatings. The construction process suppresses the generation of bubbles and breaks the bubbles. Release the bubble content air. This is the positive effect of the defoaming agent. The negative effect is to reduce the gloss of the coating film and the poor dispersion of the defoaming agent to form shrinkage cavities. The defoaming agent is a low surface tension material which is insoluble in the system. The dispersing agent with good dispersibility and compatibility can be used to minimize the damage of the shrinkage cavity, and the defoaming agent with good dispersibility and compatibility is in the coating system. It is easy to disperse, the size of the dispersed droplets is suitable, and the defoaming agent in the system is not easy to aggregate into large defoamer droplets. 2) Hydrophobic surface active dispersant used in formula production In the production of paints, raw materials and fillers are often contaminated. The ordinary hydrophilic dispersant is used to grind the surface of the paint slurry to suspend fine oil beads. In severe cases, the flocculent oil powder hybrids will float. The oil powder mixture with fine low surface tension exists inside the paint produced by using such polluted powder, and the construction shrinkage hole is difficult to control. The use of a hydrophobic surfactant-dispersing dispersant and a molecular-grade or non-mineral oil-based defoaming agent ensures the emulsification and dispersion of the oil-contaminated powder. The system has strong tolerance to raw materials and has the potential to prevent shrinkage. Reduce the occurrence of shrinkage cavities.

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  • Factors Affecting Shrinkage of Waterborne Coating Films
    Factors Affecting Shrinkage of Waterborne Coating Films


    Factors Affecting Shrinkage of Waterborne Coating Films In practice, the main causes of shrinkage are as follows: 1. The substrate is contaminated by oil or impurities 2. Apply a paint to the old paint or finish without sanding 3. The interval between constructions of the two paints is too long 4. Too much defoamer in the paint The following focuses on two factors: defoamer and impurity contamination. The effect of defoaming agent Emulsions, wetting agents, dispersants, defoamers, thickeners, etc. are used in latex paints. The main principles of using defoamers are as follows: The raw material contains a surface active material or a surfactant, and bubbles are easily formed. The foam hinders the dispersion of the pigment and filler, reduces the utilization rate of the equipment, prolongs the production cycle, and seriously brings about coating defects, pinholes and shrinkage cavities. After the second coating is used, the construction tool is brought into the air, and the coating wets the substrate to displace the air in the gap of the substrate. The air becomes a bubble under the action of the surface active material, so the antifoaming agent is used to eliminate these bubble. The surface tension of the defoaming agent should be less than the surface tension of the defoaming liquid. The solubility in the defoaming system is as small as possible and has good dispersibility. Can not react with other substances in the system, does not affect the stability of pigments and emulsions, has a strong diffusion capacity, and can not affect the performance of the coating. The most important choice for defoamer selection is the performance of the dry film. To protect the normal production and construction of the coating, defoamers are often used in coating formulations. From the analysis of the relationship between coating composition and properties, although the defoaming agent has little effect on the properties of coatings and coatings, it is a surfactant. The surface tension of the defoamer is lower than that of the coating system, and its HLB value is usually around 3. The defoamer is not dissolved in the coating system, but can be dispersed in the coating system in the form of tiny droplets. The optimal droplet size is the wall thickness of the bubble wall. If the droplets of the defoamer are too large or too small, the performance of the coating will be affected. The droplets of the defoamer will be too small (the excessive dispersion of the defoaming agent) will weaken the defoaming performance; if it is too large, the surface tension in the coating system will be lower than that. The presence of droplets of the bulk coating results in shrinkage of the coating film. Therefore, the shrinkage cavities caused by the defoaming agent are mainly due to the poor compatibility of the defoaming agent itself, or the poor dispersibility, the particles of the defoaming agent dispersed in the coating system are too large, or the defoaming active substances are e...

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  • Formation of shrinkage cavity problems in waterborne coatings
    Formation of shrinkage cavity problems in waterborne coatings


    Formation of shrinkage cavity problems in waterborne coatings The surface defects of the coating film are mainly depressions, pinholes, and the edges or thick edges of the corners. There are two kinds of cases on the surface of the coating film, one is a circular depression, and a hexagonal polygonal depression. The depression on the surface of the coating film is caused by the surface tension gradient. The surface tension is uneven due to the change of the composition of the coating and the temperature change. The fluid flows from the low surface tension to the high surface tension, and as a result, a depression is formed on the surface of the fluid, which is also called The Maragoni effect eventually leads to edge bulges, shrinkage cavities that are centered in a circle, or Benaldo vortices with edge ridges and central depressions into hexagonal grooves. The material with low surface tension in the center of the shrinkage cavity exists, and the surface tension of the surrounding paint is poor. This difference is the power of the shrinkage hole formation, which causes the surrounding liquid fluid to flow away from it (the shrinkage source) and flow away. And flow into a depression - shrinkage cavity. The coating forms shrinkage holes during the construction drying process, which has problems with the coating itself and the problem of cleaning the substrate. The surface tension is caused by the presence of low surface tension droplets in the coating itself or due to contamination of the coated surface due to contamination. Uneven, the coating flows from a low surface tension to a high surface tension under the effect of surface tension, resulting in a centrally depressed hole-shrinkage. We classify the unevenness of surface tension as the internal cause of shrinkage formation. In fact, some properties of the coating itself, such as paint viscosity, thixotropy, paint drying speed and film thickness, can aggravate or reduce the flow ability of the coating fluid, which will aggravate or weaken the degree of shrinkage. We classify these factors as shrinking. The external cause of the hole. The internal cause is an inevitable condition for shrinkage, and the external cause can appropriately control or aggravate the degree of shrinkage. After coating application, during the dry film forming process, the surface solvent volatilizes, the concentration of the surface polymer increases, and the viscosity of the coating increases, which causes the surface tension and surface density to exceed the bulk and form a depression. In general, thicker coatings (> 4 mm) of liquid coatings, mainly density gradients drive the flow, and thinner liquid coatings are surface tension gradients that control the flow to form individual shrinkage cavities.

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  • Wood closed primer formula solves the outstanding problem of wood grain
    Wood closed primer formula solves the outstanding problem of wood grain


    Wood closed primer formula solves the outstanding problem of wood grain Wood bulges and deforms or wood grain protuberant,It is a common problem in wood painting. We discussed the causes and solutions of this problem in this year's topic.In the article on wood grain protrusions - water-based paints, we recommend three technical solutions: 1. Use a saturated coating of 3-4% binder solids. 2. Use a quick-drying coating such as sinograce's SPECIAL RESIN POLYMER PF-136 waterborne acrylic primer primer transparent primer formulation 3. Use a hybrid system, water-based coating and solvent-based coating. After the article was published, some readers wanted to know the formulation of solvent-based coatings for water-based paints. Special offers are as follows: materials weight notes 1. YP3170D alkyd resin 43.00 2. Xylene mixture of isomer 42.00 3. n-butyl acetate 0.10 4. PMA 0.05 total protein 100.00 Solvent - based closed primer formula for wood Formula manufacturing method 1. Curing agent: 40% TDI 2. Paint: curing agent: 5:1 product performance technical indicator Technical index Fineness/cleanliness ≤15 microns Density (kg/l) 1.00±0.001 colour transparent Solid content (W/W) 30.0±1% Viscosity (25 ℃) 13±1s application property good adhesive force 0-1 class transparency Transparent film without blue light The construction scale direct use

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