High flexibility epoxy acrylic matting thermal transfer powder coating

Abstract: The purpose of this study is to improve the impact resistance and scratch resistance of methyl acrylic acrylic anti-light powder coating, improve the appearance of coating film, solve the "flowering" and "bright spot" defects caused by the separation of different systems, and successfully applied this powder coating to stainless steel anti-theft door, solve the problem of poor adhesion of powder coating on stainless steel substrate.
The traditional thermal transfer anti-theft door mostly uses the door plate molding after spraying powder coating re-thermal transfer process, due to the influence of the door plate three-dimensional pattern, the transfer process stage often appears in the groove leakage or transfer pattern is not clear defects. The new construction uses the whole flat door plate spray powder coating and then forms the pattern by thermal transfer, and then stamps the door plate into different shapes according to the needs of the process, the advantage of the production process is that the different shapes can be stamped according to the actual needs, and the door plate transfer pattern is clear , good plumpness, the disadvantage is that the post-molding process to use such as punches, bending machines, roller mills and other equipment, if the coating impact resistance and flexibility performance is not good, there will be explosive edge, peeling, shedding and other defects .
Epoxy-based acrylic anti-light powder coating can achieve 10% of the extreme light effect, luster stability, and the system cross-link density, easy to tear paper, transfer pattern clear, widely used in the field of thermal transfer aluminum. However, this kind of powder coating has natural defects, such as poor mechanical performance, it is difficult to pass 50cm backsllow, surface scratch resistance and wear resistance is poor, the surface is easy to bright spots, patterns and other restrictions on the expansion of its application range.
1 Experimental
1.1 Main raw material
-based sealed polyester resin: industrial grade, new material of Shen Jian. Epoxy-based acrylic anti-light resin: industrial grade, Ningbo South China Sea. Curing agent (TGIC): Industrial grade, Huangshan Huahui. Pigments, fillers, powder coating general aid (leveling agent, sabbath fragrance), adhesion promoter, elimination of bright spots or pattern aids, thermal transfer wood grain paper: are commercially available industrial products.
1.2 Experimental instruments and test methods
twin screw extruder; ACM grinder; electrostectrectrometer; oven; special press for thermal transfer; T-bender; differential scanning heat meter (DSC).
the raw materials according to the set formula weighing, pre-mixing, extrusion, powdering, graded after screening electrostitive spraying;
1.3 Reaction Principle
The GMA resins speaking here are based on free-based polymerization of styrene, methyl acrylates, acrylates, methyl acrylic shrinkage glycerides (GMA) and other unsaturated monobodies. Among them, styrene as a hard monog is used to improve the glass transition temperature (Tg) of the resin, methyl acrylates, acrylates as a soft monoid, can improve the flexibility of the coating, GMA for cross-linking monosome, providing curable cross-linked epoxy group, GMA monosome dosage determines the cross-link density of the coating.
This test is intended to use a mixture of curing agent method, epoxy-based acrylic resin and TGIC or HAA together to de-light the carbide polyester, due to the difference between the reaction speed and compatible between the two components, not only the light-loss performance is obvious, but also to make up for the lack of acrylic strength defects, so that the mechanical properties and wear resistance of the coating film can be improved.
1.4 Choice of epoxy acrylic anti-lighting resin
by adjusting the content of GMA can produce different epoxy equivalent products, epoxy equivalent will change the cross-link density of resin curing, according to the relevant literature, in order to obtain a comprehensive anti-light performance, GMA resin The single concentration of GMA should be satisfied between 5% and 30%, more than 30% (corresponding to epoxy equivalent 500) to obtain the actual shiny coating, according to which the market sales of epoxy equivalent between 550 to 700 products for testing.
1.5 polyester resin
because the higher the value of polyester resin acid, the greater the cross-link density, the mechanical properties of the coating film such as bending, impact deterioration. If the acid value of the coating film is low, cross-link density is small, although the flexibility of the coating is enhanced, but the transfer is easy to stick paper, affecting the appearance. Therefore, the selection of medium acid AV , 30 to 35 mg / KOH flexibility is better polyester, can not only ensure the transfer of non-stick paper, but also have relatively good bending performance.
different manufacturers of acid values between 30 to 35 mg / KOH polyester, with the same epoxy acrylic resin (Ww - 700) for light-off testing, the results are listed in Table 1.
From the experimental results can be seen that the viscosity on the surface gloss, flow level, bright spot, flowering has an impact, high viscosity, coating film gloss high, the surface does not have bright spots, patterns, but the surface level difference, low viscosity, low coating gloss, flow leveling good, but the coating surface easy bright spots, patterns, so if you want to pursue the appearance of the coating film, should choose medium or medium lower mucosa value of polyester.
1.6 curing agent
Poor mechanical performance is a common disease of GMA's anti-lighting system, curing agents can be selected to improve the mechanical performance of GMA's anti-light formulation. Such suitable curing agents are TGIC and HAA, but due to the low glassing temperature of HAA curing coating, transfer of secondary heating can easily lead to sticky paper, so choose TGIC to participate.
TGIC usage is also critical. The amount of less gloss is low, the mechanical performance is poor, and the surface is easy to pattern; GMA anti-light coating cross-link density, coating flexibility is poor, and styrene and other hard monobodies affect flexibility, experiments show that to ensure very good flexibility, TGIC dosing at 2% is necessary.
1.7 to improve the appearance of the surface, to solve the bright spot defects
epoxy acrylic anti-light surface easy to highlight, pattern, some turtle pattern is very obvious. The experimental conclusions obtained from Table 1 show that polyester A, polyester B, polyester C surfaces have bright spots or patterns, because of the low viscosity of the system, styrene and other hard monomer floating to the coating surface to produce bright crystal points. If the viscosity of the system is too low, the styrene hard monosylene chain section floats, forming a turtle pattern.
test, the main difference in the elimination of bright spots is to improve viscosity and reduce solubility.
(1) improve the production process and reduce the extrusion temperature. Double screw extruder screw melting section temperature in 70 to 80 degrees C is good, extrusion temperature is low, mixing difference, acrylic resin and polyester is not easy to layer, the resulting coating bright spot defects improved significantly;
(2) add the appropriate amount of fillers or additives to improve the viscosity of the system, touch fillers such as talcum powder can improve the system viscosity, the amount of use should not exceed 5%, otherwise affect the appearance of flow level and bending performance. After testing, the appropriate amount of added gas phase silica can improve the viscosity of the system, eliminate bright spots, but the amount of addition should be 1%, otherwise not only will seriously affect the leveling and mechanical performance, but also will lead to the gloss is not expected to rise.
, of course, the above method is only complementary to the elimination of bright spots, the key factor is polyester and epoxy acrylic resin matching.
1.8 Increase the adhesion of powder coating to stainless steel
stainless steel surface is usually smooth, spray powder on the surface, often appear paint drop or poor adhesion defects, in order to improve the adhesion of powder coating on stainless steel substrate, before spraying should be stainless steel Necessary polishing to increase the roughness of the interface is not enough, but over time, the delayed adhesion and bending performance of the coating film after curing will decline, and the addition of adhesion promoters to the formulation can be used to solve the immediate bending and delay bending properties.
1.9 Final powder coating formulation and performance
after polyester, lightener selection, as well as the assessment of the impact of TGIC dosage, wear resistance scratch resistance, surface highlights improvement, adhesion improvement, etc. to determine the final formula, powder, powder coating and coating performance testing, powder coating formulation and coating performance as shown in Table 2, Table 3, transfer and bend effect as shown in Figure 3, Figure 4.
2 Conclusion
by selecting the right polyester and GMA acrylic resin, and with the curing agent TGIC, and in the formulation to add the appropriate amount of tentacleance assistance and adhesion promoter, the resulting low-light bend transfer powder coating, not only has excellent appearance and transfer performance, but also has excellent flexibility, high adhesion, can be used in the field of anti-theft transfer door bending.
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