Performance indicators of water-based polyurethane resin-adhesion,water resistance-pubinderchem.com

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Performance indicators of water-based polyurethane resin-adhesion, water resistance

May 13, 2024

Performance indicators of water-based polyurethane resin-adhesion

Water-based polyurethane resin has a relatively large number of polar groups, such as hydrogen bonds, pulse bonds, ionic bonds, etc. There are Coulomb force, van der Waals attraction and hydrogen bonding between it and the surface of the substrate. Some polyurethane adhesives are end-capped with NCO, which can react with surface H2O to establish chemical adhesion. The ideal bonding state is that the bonding force at the interface of the adhered material exceeds the cohesion of the adhered material, but is lower than the cohesion of the adhesive material. When the surface attraction between the adhesive and the adherend is equal and the polarity is the same, the interfacial tension is small and the bonding strength is high. Water-based polyurethane has good adhesion to many kinds of substrates, especially polar substrates and porous substrates. Similar to the solvent type, there are differences in bonding strength for different substrates. The following table shows the bonding strength data of a water-based polyurethane adhesive to various substrates. It can be seen from the table that water-based polyurethane adhesive has good adhesion to soft polyvinyl chloride containing relatively large amounts of plasticizers.

Film gloss:

In some application fields, water-based polyurethane products are required to have better coating gloss. Among the various factors that affect the gloss of a paint film, they mainly include the glossiness of the paint film and the molecular structure of the paint film. The reflection effect of light on a flat surface is obvious. The larger the reflection angle, the stronger the reflected light and the higher the glossiness of the surface. Conversely, if the surface is uneven, diffuse reflection will occur, resulting in a weakening of the light intensity at the reflection angle. For polyurethane emulsion, if the emulsification effect is not good, there are coarse particles that cannot be dispersed in the emulsion, or the paint film is uneven during the construction process, the gloss of the paint film will decrease. When the paint film surface has the same gloss, the gloss is related to the molar refractive index R of the film-forming material. The larger R, the higher the gloss. In general, water-based polyurethane has good leveling properties and good compatibility with various components, which is an important condition for obtaining high gloss.

Performance indicators of water-based polyurethane-water resistance

Normally, the moisture absorption rate and volume expansion rate of the film-forming material increase with the increase in the amount of ionic hydrophilic monomer used. In order to overcome the inherent defects of polyurethane and improve the water resistance of the emulsion coating, cross-linking methods can also be used. Single-component self-crosslinking systems can also adopt two approaches, namely methyl imine cross-linking and auto-oxidative cross-linking. The principle of methylimine cross-linking is based on the reaction between polyamines.

The source of the base is acetoacetate, aldehydes or ketones, which are catalyzed by acid to produce methimine. As the neutralizer and water evaporate, the pH value of the system decreases, and a rapid cross-linking reaction occurs. The resulting The coating film has strong chemical resistance, high hardness and low price, and has been widely used in the coating industry. Auto-oxidative cross-linked polyurethane generally adds polyunsaturated fatty acids or oils. When this emulsion is applied to the substrate, it will react with oxygen in the air under the influence of driers such as cobalt, manganese and metal soaps such as cobalt. The reaction produces cross-linking, and the polyurethane emulsion coating film prepared by this method has relatively good chemical resistance, excellent appearance, and good wettability to wood, and is especially suitable for indoor floor coating. Using the external linking method, aziridine, carbimide, metal salt compounds and hydrophilic polyisocyanate are used for cross-linking at room temperature. The cross-linking reaction occurs on the antelope group of the polyurethane molecule.

This cross-linking agent is usually added when applying polyurethane emulsion because its cross-linking reaction rate is rapid and it produces gel in a short period of time to break the emulsion. The coating film obtained by the external contact method has superior performance and wide adaptability. However, the additional cross-linking agent is more expensive, and the resulting two-component system has a relatively short application period, causing inconvenience to its application. Heat-activated cross-linking and UV cross-linking can also be used, which require baking equipment and UV light sources during use. The development trend of new cross-linking systems is to develop water-dispersed polyurethane systems with normal temperature cross-linking systems, high cross-linking density, relatively stable storage, low cost, and good coating physical and mechanical properties.

aqueous polyurethane dispersion containing reactive groups is mixed with a cross-linking agent containing polyaldehyde groups to prepare a single-component polyurethane. This multi-aldehyde-based cross-linking agent does not react with polyurethane in water. The mixed water dispersion is relatively stable for storage. During the film formation process, with the evaporation of water, the cross-linking reaction can occur at room temperature and can generate stable chemical bonds. , improve the water resistance of the coating film.

Tags : water-based polyurethane Water-based polyurethane resin aqueous polyurethane dispersion

Performance indicators of water-based polyurethane resin-adhesion, water resistance

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