this paper discusses the effect of polyester/TGIC, polyurethane/B1530 system and additives on the surface effect of woodprint transfer. By selecting polyester and additives with different acid values (hydroxy) to compare wood-print transfer powder leveling, clarity and transfer tearing paper is difficult, to solve the problem of thermal transfer polyester powder coating production process transfer sticky paper, oil printing and clarity is not enough.
powder coating in the production and coating process, especially solvent release, less pollution, easy to recycle, high utilization advantages, is an environmentally friendly coating
. With the continuous improvement of process conditions and the continuous improvement of market requirements, powder coatings with its own advantages, in recent decades has been rapid development.
transfer, also known as thermal sublimation, is the use of thermal transfer equipment in a short period of time to heat it to a set temperature, so that the pattern on the transfer paper transfer to the substrate on a process. Thermal transfer powder coating can provide colorful, rich layers of transfer patterns, wood grain paper (film) after heating sublimation ink can penetrate into the cured coating 30 to 50 m, after the transfer of the coating durable, will not fall off, crack and fade.
At the same time, thermal transfer powder coating will not change the original coating properties of the coating (such as hardness, anti-scratch, impact resistance, salt spray resistance, acidity and alkali resistance, aging and other properties), in recent years in aluminum profiles have been widely used for building aluminum profiles and furniture decoration provides a wealth of decorative effects.
current thermal transfer polyester powder coating is mainly divided into polyurethane wood powder coating and polyester/ TGIC two kinds. Polyurethane powder coating has a high cross-link density, solidified coating plump, high hardness, leveling and weather resistance, easy to tear paper after transfer, clear pattern, with skin feel and other advantages.
But the disadvantage is that it is expensive, and polyurethane wood grain powder in low-gloss applications more, in high-gloss wood grain powder easy to leave the phenomenon of sticky paper, probably because of the high-gloss polyurethane wood-printed powder after curing a small amount of residual meso-based and ink has a repulsive effect.
polyester/ TGIC curing system of wood-print powder price is low, widely used, but after curing into a film hardness is generally 1H to 2H, such powders for thermal transfer often encounter poor leveling, not easy to tear paper or transfer pattern is not clear. In this paper, through the comparison and screening of polyester resins with different acid values (or hydroxy values), optimized the selection of high reactive curing rate, good leveling polyester, to solve the problem of wood-print powder tearing paper, after transfer coating surface oil printing problems.
2 Experimental part
2.1 resin on the effect of woodprint transfer
The experiment selected three different acid values of polyester resin (resin A, B, C) and a low hydroxy (resin D), a medium hydroxy polyester resin (resin E), a end-to-one-base dual-cell rehydration ester resin (resin F). Their technical indicators are such as table 1.
other major materials and equipment: isocyanuric acid trisornate glycerides (TGIC), B1530, chin white powder, vanadium sulfate, powder coating additives (leveling agent, brightener, sabbath, wax powder, etc.). Equipment has: twin screw extruder, high-speed 10-wheeler, electrostectrective spraying equipment, high-temperature oven, hot painting machine and so on.
2.2 Preparation of thermal transfer powder coatings
According to the formula designed in Table 2, accurately weigh polyester resin, curing agents, additives and pigments for adequate premixing, melting out cooling and crushing, and then using a high-speed shredder grinding powder through the sieve spray plate, solidified to make a hot transfer base powder sample. Finally, the model is obtained by thermal transfer by hot painting machine.
table 1, the higher the acid value (hydroxy) of the resin, the higher the reaction activity of the resin. From the comparison of the experiments in Table 2, the higher the resin acid value (hydroxy value), the greater the crosslink density of the coating, and the higher the hardness of the coating after curing. Generally speaking, the higher the crosslink density of polyester resin for wood transfer, the higher the hardness, the texture of transfer is not only clear, easy to tear paper, but also after transfer coating retention is greatly reduced.
But as the acid value of the resin increases, the amount of TGIC (B1530) of resin and reaction curing increases, the gel time becomes shorter, the reaction activity increases, the level of the coating will be worse, while the cured coating has the disadvantages of large brittleness and poor mechanical performance. Therefore, in order to ensure a higher cross-link density of powder, high leveling and hardness, you can choose two resins with high and low acid value (hydroxy value) to prepare the wood grain powder with good transfer effect.
2.3 Two different acid values (hydroxy) resin compounding using the preparation of wood-printed powder
using two different acid values (hydroxy) resin combination, so that the coating has a high cross-link density and hardness, to ensure that the cured coating has excellent leveling and tearing effect, reduce the presence of oil after transfer. The formula is designed as Table 3.
Through 2 and 3 experiments, it is shown that the hardness of wood-grain powder made of formula 1 is higher than that of a single component, indicating that the addition and compounding of high acid resin C increases the cross-link density of the cured coating, which improves the hardness of the coating and turns Printing effect has been improved, but there is still the phenomenon of printing after transfer, which is related to the structure and reaction activity of resin A itself, resin A itself has a lower acid value, a low crosslink density of curing coating, even if the addition of high acid resin C can not make it 100% curing.
the transfer effect is improved after adding the high acid resin, the leveling is good, and the transfer is oil-free. The addition of some of the hydroxyl polyurethanes in Formula 3, 4 has improved the phenomenon of coating paper after low-light polyurethane curing. Experiments from 2 and 3 show that the addition of high acid value (hydroxy) resin can effectively improve the cross-link density and hardness of wood-printed powder, thus improving the transfer effect of wood-printed powder.
effects of 2.4 additives on wood-print transfer
When designing wood-print powder formulations, additives are often added to improve coating performance. Commonly used additives are leveling agents, moisturizers, scents, curing promoter, wax powder and so on. The leveling agent and wetting agent play a role in improving the leveling. Some studies show that leveling agent, wetting agent after the coating curing will migrate to the coating shows that excessive will affect the transfer effect, so that the transfer coating is easy to leave an oil mark, so in the formulation design to add a moderate amount. The sabbath mainly plays the role of degassing in the formula, and it has little effect on the clarity of woodprint transfer.
is usually added to the aluminum profile powder coating a certain amount of wax powder, used to improve the anti-scratch performance of the coating, to achieve a smooth effect. The surface contact of the thermal transfer process is a physical process, so the size of the wax powder interface pressure has a great influence on the transfer effect. Experimental data in relevant literature show that the smaller the surface stress of wax powder, the easier it is to tear paper for transfer. However, the amount of wax powder added too much affects the clarity of the texture, so the amount of wax powder should be appropriate when designing the wood-print formula.
to increase the reaction activity of wood-print powder polyester, so that the coating can be fully cured, usually the formulation of a certain amount of curing promoter. However, pay attention to its addition, adding too much will affect the leveling effect of the coating.
The transfer effect of thermal transfer powder coating mainly depends on the reaction activity of the resin, the cross-link density of the coating is large, the hardness is high, the transfer pattern is clear, easy to tear paper, after transfer is not easy to leave printing. In summary, in the design of wood-print powder coating formulation, should choose a high reactive activity, a high degree of curing polyester resin, or through high and low acid value (hydroxy value) re-use, in order to ensure that the cured coating has a higher cross-link density has a better leveling performance and transfer effect. At the same time, in the design of the formula should pay attention to the addition of various additives, in order to ensure that the optimization of the formula to achieve a good transfer effect.