Change the performance of the resin

Polyurethane , a versatile tool for re-engineering coating formulations
it is known that polyurethane technology offers many technical advantages over competitive coating systems. In particular, two-group polyurethane (2K PUR) coatings are widely used in applications such as automobiles, windplanes, aircraft, transportation, etc. Although it is a proven technology, it continues to be under pressure to improve or fine-tune technical performance, such as wear resistance, scratch resistance and outdoor durability
China
. The regulations also require formulating designers to further reduce VOCs for high solids (HS) formulations or to turn them into water-based (WB) solutions. Very low viscosity hexaesters can be a tool that can affect VOC and technical performance by reducing emissions and extending the life cycle of coating systems, an important standard for sustainability improvements.
Polyurethane
Has been producing polyurethanes for 40 years and offers a range of polyols suitable for modifiing or fine-tuning the performance of cross-linked coating formulations such as two-part (2K) and single-group (1K) polyurethane systems. Formula properties based on traditional acrylic and polyester can also be adjusted by adding polythylate polyols.
By utilizing a controlled open-loop structure with hydroxyl polymerization to obtain very low acid values (<0.25 mgKOH /g), the chemical structure of hexaesters offers unique possibilities for meeting the specific requirements of different coating systems. Semicrystalline polyols with accurate official energy and narrow molecular weight distribution can be prepared in repeated ways. By selecting the triggers for different hydroxyl hydroxyl groups, a variety of adipose family, low Tg (approximately -60 degrees C), and solvent-free low viscosity polyols are available when preparation of high-performance cross-linked coatings for a variety of applications.
has a series of Capa™ polyols, of which the official energy range is 2 to 4, hydroxyl content between 4.1% to 17%, molecular weight between 300 to 2000 g / molar, it is possible to make technical fine-tuning of the coating formulation. Hethyl esters are usually replaced with standard polyols (acrylic or polyester) in the range of 5% to 20% (mass ratio) for a significant increase in performance.
polyhetides can be added to the solvent-based (SB) systems of acrylics or polyesters and various crosslinkers as resin modifiers because they are compatible and the number of combinations is almost unlimited. They are solvent-free and liquid at room temperature and are ideal as refringing thinners for solvent-free systems. Grades with very low viscosity are also suitable for use in formulations of water-based dispersions, where low viscosity and relatively high water acceptance caused by high hydroxy values allow polyols to migrate into emulsion droplets.
study showed the effects of adding different amounts of 3 and 4 errations to a high solid double-component (HS 2K) polyurethane system (Figure 1). The paper also describes the principle of using them in water-based emulsion systems.
solvent-based
polyester can be easily added to solvent-based formulations at any stage of coating preparation. Due to its excellent pigment wetting properties, it is preferred to add it during the grinding phase when using a pigmented formula. In general, normal formulation principles can be used when using hemase, and conventional tools such as additives, solvents and crosslinkers are available during development work. Their accurate molecular weight and ability contribute greatly to ensuring the final performance of the coating. Even if polyhetides have a lower Tg due to the fat family structure itself - so because physical drying contributes little to the hardness of the final coating - maintaining hardness and mechanical properties, even improved formulations can be easily formulated. This can be explained by increasing the crosslink density - as a result of increasing the hydroxy value - by creating a strong hydrogen bond between the amino acid bonds to achieve higher mechanical strength. Gloss and fog can also be maintained and in many cases improved due to its low viscosity for perfect compatibility and improved fluidity. There is a relatively high reactivity between polyester and isocyanate in general due to its suspension of burkini at one end of the flexible fat chain. By controlling the amount of catalyst added, the curing speed and application period can be adjusted, so that the ideal balance between the two can be achieved.
in this study, all formulations were based on high-solid acrylic formulations (Table 1). In the formula Capa A-C, conventional polyester polyols are replaced with different 3-dpheric hetamines. In Capa A, it is replaced by a mass base, in Capa B, by hydroxyl content, and in Capa C, the amount is doubled to further understand the impact on performance. In the formula Capa D, based on hydroxyl content, conventional polyester is replaced by polythyroids from 4-0 groups. The ratio of NCO/OH remains unchanged at 1.05.
the low
of VOC and polyhexyl esters effectively reduces the VOC of the formula and is still considered a high solid formula. This makes them suitable for what is known as reactive thinners. The reduction in the amount added to Capa C further demonstrates its effect, but also emphasizes the importance of using a low viscosity HDI trimer to achieve a low VOC content (Figure 2).
Wear Resistance
In different applications of polyurethane, wear improvements are a reproducible performance, such as polyurethane dispersions and polyurethane acrylics, which have a significant impact compared to conventional polyester. The semicrystalline structure of the adipose curing film results in lower Tg, but the coating film has a high mechanical strength. The coating film obtained by combining high cross-link density with low Tg has rubber elasticity and good wear resistance. The results of the Taber wear test are shown in Figure 3.
impact resistance
the lipid family structure of polypolycerides can significantly improve impact resistance. To emphasize this, further tests were carried out on the metal plate, which was heated for 24 hours at 80 degrees C to ensure full curing, then cooled to -25 degrees C and placed for 3 hours to check the mechanical properties in cold climates. The results show that the low Tg of heteroester can also reduce the Tg of the curing coating, which can also improve the resistance of automotive coatings to stone and wind truck blades in harsh climate conditions (Figure 4).
scratch resistance
scratch resistance is the application of a gradual increase in the pressure on the head, while the pressure head on the coating for sliding evaluation. As long as no scratches are observed, only an elastic deformation is formed on the surface, which can be recovered quickly by reflow, the experiment continues. As long as the temperature is higher than Tg, the scratches will eventually regenerate when the load increases further in the plastic deformation area. Finally, the load is increased to form irreversible scratches and the coating is permanently damaged (this needs to be monitored).
results show that adding hetesters has an effect on Tg, which reduces brittleness and the risk of permanent scratches (Table 2). Semicrystalline introduced by polyester also reduces internal stress and increases viscosity elasticity, which also improves reflow performance.
flexibility
polyester increases elongity and softness, especially compared to pure acrylic systems. When the amount of polyhithyl esters is further increased, the effect is more obvious and the pull is increased. Changing the amount and functionality of hetesters does not affect strength and toughness (Figure 5).
anti-ultraviolet properties
will be made without the addition of ultraviolet absorbent and blocked amine light stabilizer transparent varnish coated on the white base coating, and the standard cycle of the plate exposed to QUV-B experimental machine 2000 hours. The adipose structure and very low acid value (<0.25mg KOH/g) provide good UV resistance and excellent hydrolytic stability. Resistance is better than pure acrylic systems, and when the amount of hexaesters in the formula is doubled, the effect is more significant (Capa C) (Figure 6).
water-based
polyester can be easily used in solvent-based and solvent-free formulations. However, they are actually hydrophobic, so they cannot be diluted and dissolved directly into water. And because they have very low acid values, it is not possible to make them water-dilutable by meso-acid base. However, when they are able to migrate into emulsion droplets without adding additional emulsions, they can be used as resin modifiers for acrylic emulsions. Due to the hydrophobicity and viscosity of hexaesters controlled by molecular weight, it is preferred to use low molecular weight and high hydroxyl content of hexyl esters. Both properties make it easier for them to migrate into the emulsion droplets during the required dispersion process. In this system they achieve a complex equilibrium state in which the molecular weight and viscosity of acrylics, but more importantly, the type and quantity of emulsifying agents have a critical impact on success. The amount of different polyhetides added to an acrylic emulsion will vary and may not succeed, depending on the circumstances. The example in Figure 7 shows that up to 16% (mass ratio) of 3 functions can be added to this particular commercially available emulsion, which can be shown through a complete granular distribution map. However, when a 32% (mass ratio) is added, the peak moves to a higher emulsion droplet, adding 40% (mass ratio) to form a clear twin-peak particle size distribution, indicating rapid phase separation.
general advantages of polythyl esters in water-based systems are similar to solvent-based systems. Even VOC can be reduced because the need for cosolts for rapid evaporation is reduced. In these cases, the effect on scratch resistance and impact resistance is more pronounced, as in many cases the molecular weight of water-based acrylic resins exceeds the adhesion of conventional solvent-based acrylates. In this case, the effect of adding low Tg and semicrystalline polythyl esters was more significant.
a well-known disadvantage of using a water-based two-part polyurethane system is that it is more difficult to achieve high gloss and low fog shadow, due to the pattern left by emulsion droplets in the shape of the cured surface. This effect can be reduced by adding organic cosolts, which reduce Tg and minimum film-forming temperatures, which promotes the fusion process and leveling during physical drying. Polyheides have the same function and function in water-based two-component formulations due to their low viscosity and perfect compatibility with acrylic resins. Since hetesters remain in the membrane, unlike fast volatile organic solvents, physical drying and leveling are prolonged and even allow for better leveling. This can be expressed by increasing the gloss, but it is more obvious that the fog shadow is reduced (Figure 8).
In solvent-based and solvent-free systems, due to their low viscosity, hexaesters can naturally be referred to as reactive thinners, but in water-based emulsion-based systems, they are more accurately identified as reactive polysorbants.
conclusion
is a liquid, solvent-free adipose family polyol, suitable as a reactive thinner. They are prepared by open-loop polymerization, which results in low acid values and precise functional groups, making them versatile tools for mating coatings. When partially replacing conventional hydroxyl-containing hydroxyl group resins, they should be considered common raw materials, but the formulation should be balanced in order to take advantage of the unique properties of polyethylene. Even if they are low Tg, semi-crystalline adipose polyols, the balance is easy to achieve, with flexibility, impact resistance and wear resistance significantly improved without affecting hardness or chemical resistance. This makes them suitable for demanding applications requiring good mechanical properties, and stone resistance, wear resistance and rain erosion resistance are important in order to perform well in certain situations.
polyhetide polyols are preferred as resin modifiers in formulations that require higher performance levels. They can be used in formulations that need to circle in the right direction to meet VOC regulations and difficult technical requirements.
results
provide a versatile tool to fine-tune and optimize existing coating formulations.
fatty hexaesters and semi-crystalline properties can have a significant impact on the mechanical properties of coatings.
- Their good structure guarantees repeatable and ultimately excellent performance.
and low viscosity properties of esther are ideal for reactive thinners in solvent-based formulations and as reactive polylytic agents in water-based formulations.
reference
Hill, L.W. Mechanical Properties of Coatings – Waterborne, High Solid & Powder Coatings Symposium March 2000.
Ma, Z. et al. Biodegradable Polyurethane Ureas with Variable Polyester or Polycarbonate Soft Segment: Effect of Crystallinity, Molecular Weight and Composition on Mechanical Properties – Biomacromolecules 2011, 12, 2365-3274.
Ardaud, P. et al. Waterborne and Solvent-Based Surface Resins and Their Applications, Vol III Polyurethanes, John Wiley & Sons, 1998.
Film Formation in Waterborne Polyurethanes: Surface and Bulk Morphology Development.
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