Polyester and epoxy mixtures are used in high-performance UV powders

UV-cured powder coatings (UV powders) combine the advantages of thermo-cured powder coatings and liquid UV-cured coatings. It differs from ordinary powder coatings in that melting and curing are clearly divided into two processes: after heating, UV-cured powder coating particles melt and flow to form a uniform coating film, which is cross-linked only when exposed to ultraviolet light. The most common crosslinking mechanism used in this technique is free-form reaction: the photoinstration agent in the melt coating film is active by ultraviolet light, and the resulting free-forming free-forming polymerization reaction containing the resin double bonds.
shape and performance of the coating depends on the resin system selected, light triggers, pigments, fillers, additives, powder coating process conditions and curing parameters. The cross-linking rate under specific formulation and curing conditions can be measured by the light differential dynamic thermal analysis method1.
latest research on UV powder coatings has yielded excellent results, achieving smooth coatings at temperatures as low as 100OC2. Both process and economic advantages have contributed to the rapid development of UV powder technology.
1 shows this rapid development, which counts the number of patents filed over the past 30 years.

1996-1998, the number of patent applications for UV powder technology increased rapidly. It should also be mentioned that the "fans" of the UV powder concept were already very active as early as the 1970s.
There are many solid resin systems on the market that can be used to make free-form polymerized UV powders, including acrylic polyester, methyl acrylate polyester and polyacrylate 3, antibutyl diphthalate polyester 4 and its mixture with solid acetylene ether 5, acrylic or methyl acrylic epoxy resin 6, unsaturated polyurethane system 7 and so on. There are also specialized epoxy resins that can be used in UV curing powders based on the photochloric cation process8.
polyester and epoxy mixture developed for UV powder can fully meet the strict requirements of wood, synthetic wood, plastic, metal, etc. Although a "mixed powder" combining polyester and epoxy resins has been known as a thermosolytic powder for more than 20 years, its low temperature (e.g. 120OC) curing can only be "just met" after a long curing time. In contrast, UV-cured powder coating films can meet the most stringent standard9 in just "a few minutes" under heat and ultraviolet radiation.
a polyester/epoxy mixture
methyl acrylic polyester and acrylic epoxy resin for UV powders provides excellent comprehensive performance for curing membranes. Polyester backbone makes the coating show good weather resistance in testing, while epoxy backbone provides good chemical resistance, adhesion and flatness. These UV powders can replace PVC film on medium density fiberboards and offer attractive prospects in the furniture industry.
preparation of polyester/epoxy mixtures is divided into four main steps:
1. At 240OC temperature and the action of a esterification catalyst (e.g. butyltinic acid), phthalates derivatives (PA) in the melt are the same as certain glycols such as neodol (PG) to produce pyrethroid-based stop-chain polyester through a shrink reaction.
2. Keep the molten pyrethroid-based chain polyester temperature below 200OC and add methyl acrylic shrinkage glycery ether (GMA). A quick reaction with the addition of "epoxy/carboxyl" branches methyl acrylic to the end of the polyester chain. Acrylic shrinkage glycery ether has never been used for toxicological reasons. Using appropriate inhibitors, the adhesion of the two bonds can be avoided2.
3. Acrylic acid (AA) is added to a molten bienoxygen resin to produce an epoxy-deacrylate polymer.
4. The methyl acrylic polyester is evenly mixed with the acrylic epoxy resin by extrusion.
the following aspects were studied in the testing of the best formula for polyester/epoxy:
1. Choose aromatic binary acid (PA) between phthalates, isobenzene (PA)
2. Replace the selected aromatic binary acid (PA) with a lipid binary acid such as hexaic acid or 1,4-cyclohexane d'acetic acid.
3. Replace the new glycol with other glycols such as 1,2-ethylene glycol, 1,6-hexanol, or 1,4-cyclohexane methanol.
4. Polyester chains are used with polymethyl group mono-bases such as trihydroxymethylane or triphenyl acid branches. Determine the weight hundred fraction of the selected branching unit according to the Flory equation to avoid polyester collation 10 during synthesis.
table 1 compares a simple methyl acrylic polyester with two mixtures of a type 3 acrylic epoxy resin 11 based on bisphenol-A and chlorinol.
can be seen that the melting viscosity of different systems is obviously different, in which mixture 2 is most conducive to the resin mixture without reducing the glass-state transition temperature Tg conditions to achieve a high flatness of the coating film, to ensure the good storage and handling performance of powder coating.
UV curing of powder coatings
are made from methyl acrylic polyester and its mixtures for UV curing testing. The coating formula is listed in Table 2, and the heating/curing curve used in the test is shown in Figure 2.
first use of medium-infrared radiation melted powder particles, the second step using conflowal heating to form a coating film, the third step using ultraviolet radiation to cure the coating film. Ultraviolet radiation always increases the surface temperature, but the measurements clearly show that the temperature is completely controlled except for the surface, not more than 110oC in less than 3 minutes of the entire test cycle, and the curing time is much shorter than the time required for the thermosysty powder to cure around 140oC.
the conversion of the polyester/epoxy UV powder to show greater responsiveness when the dose of UV exposure is low (Table 3). The quality of double-bond conversion was tested by methyl ethyl ketone scrub.
Tg and melting viscosity optimization
synthesis reactions using phthalates derivatives (PA) produced by methyl acrylic polyester, Tg is very close, but melting viscosity varies greatly. Polyester is mixed with acrylic epoxy resins with high Tg and low melting viscosity, providing a low melting viscosity binding agent that optimizes coating flatness (Table 4).
in order to achieve a lower melting viscosity of binding agents containing methyl acrylic polyester A and acrylic epoxy resins, five modifiers were studied.
1. Polyester branching unit of natural weight percentage.
2. Phthalates derivatives (PA) are partially replaced by hethyl disic (a long-chain lipid binary pyridine).
3. Replace the new glycol (NPG) with 1,6-hexalycol (a long-chain adipose glycol).
4. Replace type 3 epoxy resins with a type 2 acrylic epoxy resin that is also based on bisphenol-A and chlorinol.
5. Replace aromatic epoxy resins with a fatty epoxy resin based on hydrogenated biphenol-A.
properties of the resin are listed in
5, the modifiers 4 and 5 reduce Tg to unacceptable levels. It is important to remember that for every 1% oxymedone light trigger added to the binding agent, the Tg of the binding agent is reduced by about 2oC12. Powders based on these two systems produce extrusions that are difficult to refine into powders during handling and storage. When the powder is stored, there are some lumps, and some melting bonding occurs during the transfer of the powder from the feeder to the spray gun. Of course, if these problems can be easily solved (e.g. using air conditioning work areas, refining with cooling grinders, etc.), then both combinations can form a flat coating film.
example of high-performance powder coating research
flating sublight film UV powder
obtains a flat methylene finish for metal and medium density fiberboards by mixing specific polyester and epoxy resins. Flat varnishes can be successfully painted on hardwood, veneer composite plates (e.g. birch, powder ash composites, birch) and PVC for elastic flooring. The epoxy components in the binding agent enhance the chemical resistance of all coatings. The binding agent with modifier 1 has the optimum flatness (Table 5) and the powder has no serious handling and storage problems.
Music furniture UV powder
polyester and epoxy structure combined to allow UV powder to be applied to medium density fiberboards and tested by DIN 68861 standards, including chemical resistance, wear resistance, scratch resistance and heat resistance. The results of the test were detailed in four recently published papers9, 13-15.
polyester/epoxy ratio has an effect on accelerated weather resistance test results: the more polyester in the binding agent, the lighter the paint yellowing phenomenon. If this accelerated weather resistance test must be passed, a trade-off must be found between UV resistance and chemical resistance or flatness.
UV powders that increase adhesion to metals
UV curing powders based on polyester/epoxy mixtures show excellent adhesion on metal substrates, and high adhesion means strong corrosion resistance. The copper-accelerated salt spray test (CASS) in accordance with ASTM B 368 standards is used to analyze the corrosion resistance of varnish and white paint painted on yellow chromium and electrolytic chrome steel1.
Plastic varnish
When painted as a transparent protective layer on PVC, elastic floor tiles or original sheet molding (SMC) plates, polyester/epoxy mixtures give UV powders a high degree of flexibility and chemical resistance13. The wear resistance of matte varnish is also very good, but further research is needed to obtain full light varnish.
UV curing toner
and a toner manufacturer found that the use of (meth) acrylic polyester/epoxy mixture as a toner binding agent, melting and UV curing can obtain the desired toner performance.
conclusion
Polyester and epoxy mixtures are used in UV powders for excellent flatness, adhesion and chemical resistance in wood furniture, metals, plastics and toners. In order to obtain the best combination of low melting viscosity and glass transition temperature above 45 degrees C, structural change studies were carried out, resulting in the elimination of serious handling and storage problems of UV powder.
A core structure is designed by mixing methamphetamine polyester based on phthalates and new glycol with acrylic and reaction products of type 3 epoxy resins (produced by the polymerization of biphenol-A and chlorocol).
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