Research on polyester resins for special functional series of powder coatings

Research on special functional series polyester resins for powder coatings
Wu Deqing
Abstract:
polyester resins are very important raw materials for powder coatings, in order to meet market demand, Shen Jian company opened a series of energy-saving low-temperature rapid curing resins; This paper discusses the technical points of developing these resins and compares the performance of the resin products developed.
1 Foreword
thermostate powder coating polyester is widely used at home and abroad, with the market for powder coating and coating performance requirements are getting higher and higher, our company for market demand and customer requirements, combined with domestic and foreign polyester resin performance characteristics, developed four types of polyester: (1) energy saving Type low temperature fast curing polyester; (2) fine art composite powder coating polyester; (3) high gloss, high level, high performance powder coating polyester; (4) ultra-high weather resistance, heat resistance, yellow degeneration-resistant pure polyester
China
.
2 reaction principle
-based polyester resin is chemically synthesized by polyic acids and polyols, the key is to RCOOR' represented by the ester polymer, the polymer inside or at its ends are with one or more functions, polymer structure not only requires a certain degree of polymerization, but also requires a certain degree of branching function, the molecular interior not only exists more than two nirhea-based, but also the molecular ends with arbond-based sealing end, the entire synthesis process is divided into ester, polysorme, Acid solution and other steps, with chemical reactions expressed as follows:
3 the effect of raw material selection on polyester performance

3.1 The main raw materials
polyols are: glycol, glycol, neo-glycol, 2-methyl propylene glycol, 1,6-glycol, 1,4-ring glycol, propylene glycol, trihydroxy methamphetamine, tyrannol and so on.
polyacids are: benzoic acid, interbenzoic acid, diacid, diacid, pyrethroid acid, phthalates, parabens and so on.
catalysts are mainly metal tin, lithium organic matter, promoters are mainly seasonal ammonium salts, aromatic base , hexylamide, mimi, and other antioxidants, brighteners.
3.2 Pyride polyester resin design target
- low crystallization, the average molecular weight (Mn) between 2000 to 7000, easy to crush into powder.
- Melting range: the melting temperature of the resin used in the house is 100 to 115 degrees C, and the melting temperature of the outdoor resin is 110 to 125 degrees C.
- stable storage, no blocking phenomenon, glass temperature Tg 53 to 70 degrees C.
- resin color is light and transparent, is conducive to the preparation of light color high decorative powder coating.
- with a certain reaction group, can cure into film, with good overall paint performance.
3.3 Effects of major materials on polyester properties
The vast majority of the properties of powder coatings are determined by the substrate, and the problem is that many of the required properties are contradictory, it is important to grasp the molecular weight, adhesion, adhesion, degree, glass temperature and softening point, acid value of the moderate balance, find the best trade-off point, so that the paint production has the best processing characteristics, at the same time in storage has good stability, in the application has a good leveling and other integrated properties.
3.3.1 Effect of polyols on polyester properties
Straight-chain binary alcohols can improve the flexibility of polyester resins and increase molecular weight, but straight-chain binary alcohols have no space shielding base, which is detrimental to reducing the glassing temperature of polyester and the water resistance of powder coatings.
From the structural point of view, methyl binary alcohol has two hydroxyl, the reaction speed is accelerated, methyl shielded polyester in the ester key to reduce flexibility and appear rigid, molecular structure compact so that polyester has a higher glass temperature and powder coating anti-fouling.
To determine a reasonable polyol ratio is very important to obtain excellent performance polyester, usually with the increase in the proportion of tri-official energy or poly-official alcohol, resin system active cross-linking group increased, cross-link density increased, coating film performance and storage stability is good, softening point correspondingly improved, but the appearance and gloss of the coating is poor, easy to glue, dlycol and triamol generally controlled between 1:0.4 to 0.5.
3.3.2 Effects of pyric acid or anhydride on polyester properties

is a compound of the triceptic group, when cross-linked with the curing agent, the reaction activity is high, the cross-link density is high, so the mechanical properties are good. Between benzoic acid and benzene is a compound of diorine, in esterification will form too much internal esters to reduce the number of official energy groups, in the final cross-linking due to changes in the official energy group, resulting in differences in the physical mechanical properties of coating film.
In the carboxylization reaction, the resin acid price increased with the increase in the amount of benzoic acid, but the softening point decreased, the coating film performance is good because when the acid equivalent increases, the resin acid price is high, that is, to participate in the curing reaction of the carboxyl energy group, resin activity is large, curing cross-link density is high.
3.3.3 Effects of catalysts, additive types and dosing on synthetic resins
in resin synthesis, in order to make the reaction completely thorough, speed up the reaction process, save energy, save labor, often add the right amount of catalysts. The addition of a promoter can improve the speed of powder filming and reduce the curing temperature, add some antioxidants to improve the appearance of the resin, and add a detergent can improve the luster of the film after powdering. The selection and determination of dosage of these additive types is particularly important. Additive addition not only increases costs, but also sometimes backfires;
reaction catalysts generally used in degradation reactions are metal compounds, especially metal carbonates, which are used at about 0.15%. The reaction time is long and the resin color is darker when the catalyst dosing is small, but the binary alcohol is easy to lose, and ultimately affects the coating performance.
in the carboxylization reaction, we generally choose metal tin organic compounds as catalysts, the dosing is controlled at 0.04% to 0.05%. Catalyst dosing less can not achieve the effect, increase the reaction time;
reaction promoters generally use methazole or ammonium salts. Mimi's performance improvement is obvious, but not good to grasp, excessive will cause the surface leveling of the coating film after powdering and orange peel, ammonium salt improper dosage not only affects the appearance of the coating film, but also has an impact on storage stability.
antioxidants generally use phosphates or blocked phenols.
4 Synthesis route
polyester resin synthesis route is shown in Figure 1, changing the reaction temperature, stirring speed, feeding time, inert gas, compression poly, system pressure and other conditions will affect the performance of polyester.
in the reactor equipped with stirring, heat, reflow column, condenser in the order of preol after acid feeding and heating dissolve, when the temperature rises to 160 to 190 degrees C reaction water, strictly control the gas phase Top temperature, control the refring index of water within 1.337, the final temperature control at 240 to 250 degrees C insulation until the material is transparent, monitor AV and viscosity to the end point, and then cool the chip broken packaging.
5 Research on polyester resins for functional powder coatings
5.1 Energy-saving low-temperature fast-curing resins
Through the study of materials and mechanisms, the molecular structure of resin products is constantly adjusted, higher active groups are introduced, and efficient catalytic promoters are selected, thereby reducing system reaction activatability, improving resin reaction activity and achieving effectiveness The purpose of reducing the curing temperature of powder coating and shortening the curing time has realized the solidification of the resin from 150 to 180 degrees C/5 to 10min, which can replace the conventional resins cured from 180 to 200 degrees C/10 to 20min, saving energy and improving the work efficiency of downstream products. The SJ-3-G resin is a polyester that we have developed that can be cured at 150 degrees C/8 to 10min, and SJ-3-AT and SJ-4-D, which can be developed at the request of Haier, which can be developed at 160 degrees C/8 to 1 0min curing products; SJ-5-C polyester can be cured at 160 degrees C/10 to 15min; SJ-6-B is a low-curing agent dosage that can be cured at 160 degrees C/5 to 10min.
5.1.1 The principle of reaction synthesis explains that
(1) improves the activity of the resin reaction group
The selected aromatic carboxylic acid (benzoic acid, interbenzene) and branched-chain fatty alcohols (already nitric acid, ethylene glycol) need to contain at least two hydrogenic groups, the dosing is about 5% to 30%, while controlling the amount of triamol to prevent gelization. All monosomes are ratiod from 1:1.1 to 1.5, and flexible long-chain monotones are introduced as far as possible in the molecular chain segment, so that the normal low temperature fast curing resin can be made.
(2) control of molecular structure
We take step-by-step segment control in synthetic process control, and obtain a resin with a narrow molecular weight distribution through the effective control of the instrument. According to the active concepts such as official energy groups, the polymerization distribution of linear aggregators is derived, with the degree of reaction P instead of chain growth, the average polymerization and the reverent polymerization are:
Xn s 1/1-P
Xw s 1 s P/1-P
molecular weight distribution width is: Xw/Xn s 1 s P ≈ 2.
to obtain a higher reaction activity and a moderate reaction rate.
(3) Application of curing promoter
in energy-saving low-temperature fast curing resin curing promoter is particularly prominent, in order to speed up the film-forming speed, reduce the active energy of the reaction, in order to achieve the goal of reducing the curing temperature, we use a new -salt curing promoter, and by adding a few nitrogen-containing hybrid compounds and other mixture promoter effectively reduce the powder-forming film-forming energy, to reduce the curing temperature, accelerated curing speed.
according to the above-mentioned process we design and develop a variety of polyester products performance and comparison with similar products at home and abroad see Table 1, Table 2 and Table 3.
table 1 and table 2, the performance indicators of SJ series products reach the same performance indicators of similar products abroad.
table above reflects that SJ-3-G, 3-AT, 5-C, 4-D have certain advantages over similar products at home and abroad, especially in mechanical properties and gloss.
5.1.2 Three waste and treatment
energy-saving low-temperature rapid curing resin, no exhaust gas, slag production, only a small amount of esterified water, esterified water contains trace amounts of acid, alcohol and esters, esterified water discharged into the company's sewage bio-chemical pool centralized treatment.
5.1.3 Test Results
(1) SJ-3-AT compared to other similar products, whether resin performance indicators or secondary performance has certain advantages, coating leveling and coating gloss is particularly prominent, the product in Haier a large number of applications to prove its success.
(2) SJ-3-G has significantly reduced curing time, reduced curing temperature, energy saving and consumption-saving advantages compared with other similar products, and polyester performance and secondary performance indicators are similar.
(3) SJ-5-C compared with other similar products, in the same curing conditions with excellent mechanical performance, resin secondary performance indicators advantages are obvious, with good water and boiling, salt spray resistance, the product is currently used in a large number of Korean-funded enterprises.
(4) SJ-4-D has excellent mechanical properties, anti-flow, pinhole resistance and yellowing resistance compared to other similar products.
5.2 Development of polyester
5.2.1 resins for high gloss, high level, high performance powder coatings
Straight chain alcohol flexible structure, adjust the alcohol-acid ratio, the use of more efficient promoter, we have developed a series of resins, with low viscosity, high glassing temperature, long adhesion time, sufficient fluidity, ideal toughness characteristics, to achieve secondary performance gloss in more than 95%, coating membrane model flat and clear. Storage performance of 45 degrees C baking more than 24h, so that the powder coating in the overall performance has been upgraded. The resin products we design and develop are described below.
(1) SJ-3-F is a specially developed high-performance resin based on market and customer needs to meet high gloss and high leveling. This model is the choice of PTA, MPDI, NPG, TMP, EG and other polyols, acid single system prepared end-to-end pyride resin. We used TMA acid desealing end curing agent, abandoned the traditional seasonal ammonium salt promoter, and selected a new liquid amine promoter, and achieved very good results. The structure of SJ-3-F polyester uses straight-chain alcohols and acids, and controls the appropriate alcohol-acid ratio, reduces the viscosity of the resin system, so that the reaction activity of the resin is controlled in a moderate range, thus obtaining a balance of leveling and mechanical properties, as well as a very high gloss.
(2) SJ-4-ET was developed specifically for the high demand for coating flat, gloss, impact, weather resistance and powder storage stability in the aluminum alloy spraying market. We use MPDI with part of the side methyl branch chain to replace a certain amount of glycol, in order to improve the flexibility and hydrolysis resistance of the coating film, at the same time through the IPA and long chain has diic acid ratio adjustment, greatly reduced the viscosity of the resin system, so that the resin has a more suitable alicic acid ratio, reached the expected glass temperature.
(3) SJ-3-A, 3-D, 3-E, 5-A, 6-BT, 4-F are high gloss, high level, high-performance powder coatings specially developed to meet the needs of our specific customers, the series of products using special production