Low-acid value polyester for HAA system low-temperature curing dry-mixed matting powder coating

Abstract:
By examining the effects of binary alcohol monomers in polyester formulations, studying the effect of acid antidotes on coating properties, and adding a special combination of photostatists to polyesters, the synthesis obtained a low-acid polyester resin suitable for the preparation of low-temperature cured dry-mixed anti-light powder coatings in light alkylamide (HAA) systems.
also studied the curing reaction of powder coating, the results show that the powder coating has a low activity energy, the preparation coating can achieve low temperature curing of 160 degrees C, the gloss is about 28, the coating has good impact resistance and aging resistance, excellent comprehensive performance.Foreword
Powder coatings used outdoors are usually cured with TGIC, but due to the physiological toxicity of TGIC, it has been banned in the European Union and other places, so the use of environmentally friendly and non-toxic HAA instead of TGIC has become a trend in the powder coatings industry

.with the change of people's aesthetic concept and the problem of light pollution caused by high gloss coating, the anti-light powder coating, which can produce soft surface effect, has been more and more widely used.
Dry mixed anti-light method is a commonly used method for the preparation of anti-light powder coating, the method uses different polyesters with large differences in reaction activity in the curing process due to differences in reaction activity, resulting in the coating surface to produce a rough surface on the microscopic to achieve the de-lighting effect, the use of this method without the addition of anti-light additives can obtain 18 to 45 gloss, the overall cost is lower.Currently commonly used HAA system dry mixed light powder coating with polyester curing temperature is generally 180 degrees C higher curing temperature means that more energy needs to be consumed called research shows that the coating curing temperature for every 10 degrees C drop, can save about 10% of the energy

has not yet found a curing promoter suitable for HAA system powder coatings, to ensure that HAA system dry mixed light powder coatings in low temperature curing conditions to cure completely, while taking into account the coating's anti-light performance, impact resistance and weather resistance, can only be optimized through resin formulation and process adjustment.
He Tao and other preparations based on the high and low acid value of benzoic acid-resistant terminal pyrethroid polyester resin, prepared coating can obtain 21 to 26 gloss, excellent weather resistance, but the formula uses TGIC as a curing agent, and curing temperature of 200 degrees C;
Chen Cheng, etc. by adjusting the alcoholic acid ratio, TMA content of high acid components in dry-mixed anti-light polyester, etc., to expand the reaction activity of high and low acid group resins, thereby reducing the gloss of the coating, but synthetic polyester is also using TGIC as a curing agent, curing temperature of 200 degrees C;
Zhou Weiming and others developed a dry mixed anti-light powder coating suitable for HAA system with high, low acid polyester resin, preparation coating in 180 degrees C curing luster can reach 25-35, surface leveling and fineness, the coating curing temperature is high, can not achieve 160 degrees C low temperature curing.This paper, by examining the role of binary alcohols in polyester formulations and studying the effect of acid antidotes on coating performance, and adding a special combination of light stabilizers to polyester, synthesis obtained a low-acid polyester resin suitable for the preparation of HAA system cryogenic cured dry-mixed anti-light powder coating, prepared coating at 160 degrees C curing, with good de-lighting performance and weather resistance.1 Experimental part
1.1 Main raw materials
NPG): BASF Glycol Co., Ltd.;
paraben xylene acid (PTA): Zhuhai BP Chemical Co., Ltd.;
trihydroxymethyl propane (TMP), cyclohexane glycol (CHDM), ethane-butyl propylene glycol (BEPD): Pasto Chemical;
Hydrogenated Bisphenol A (HBPA): Shenzhen Yexu Industrial Co., Ltd.;
2-methyl-1,3-propylene glycol (MPO): Hesse Chemical;
inter-benzoic acid (IPA): Korea KP Chemical Co., Ltd.;
butyldiacid (BDA): Mitsui property;
heterodiacid (ADA): BASF;
parabens (TMA): Jiangsu Zhengdan Chemical;
: Hengyuan Chemical Trading Company;
light stabilizers 234, 2164, 770, 622; double-bond chemicals;
monoclone oxide tin (F4100): Akoma, France;
curing agent T-105, titanium powder, palladium sulfate, annulent, leveling agent: market.
above raw materials are industrial grade.1.2 Experimental Instruments and Equipment
15L Reactor: Self-Assembly; Twin Screw Extruder: SLJ-30AF, Yantai Donghui; Electrostational Spray Gun: BA-28, South China Sea Step SprayIng Complex; Glossy: XGP, Tianjin Xinguang Technology; Chroma meter: CM2300D, Menonda; Impact meter: QCJ, Tianjin Senzda; Cone viscosity meter: DV-II type 'BROOKFIELD Company; differential scanning heater: DSC1, Meitler-Tolido.1.3 polyester resin synthesis process
polyester resin formula is found in Table 1.the monosomes and catalysts, such as alcohols and acids, are put into the 15L reactor according to the formula quantity in Table 1, and the agitator is switched on after nitrogen protection and heating up to 160 degrees C.
heating up slowly to 250 degrees C insulation 4h, control acid value in 4 to 12 mg KOH/g, detect acid values to meet the standard after adding acid antidote and insulation at 240 degrees C 3 to 5h;
reaction to the acid value of 35 to 41 mg KOH/g, cooling to 210 degrees C, began vacuuming until the vacuum degree reached -0.095MPa, the detection acid value dropped to 23 to 27 mg KOH/g, the source obtained low acid polyester resin.the ration of alcohols, acids and other monoliths and catalysts into the 15L reactor according to the formula quantity of Table 1, and turn on the agitator after passing nitrogen protection and heating up to 160 degrees C.
heats up slowly to 250 degrees C insulation 4h, control acid value in 8 to 17 mg KOH/g, test acid value after adding acid antidote and add acid in 240 degrees C: insulation 3 to 5h, reaction to acid value at 65 To 70mgKOH/g, cool down to 210C, start vacuuming until the vacuum degree reaches -0.095MPa, detection acid value dropped to 55 to 57mg KOH/g, the material to obtain high acid polyester resin.
1.4 Powder coatings and coating preparation
powder coating formulations are found in Table 2.According to the formula of Table 2, premixed, and then extruded by the twin screw extruder (extruder I. zone temperature 100 degrees C, II. zone temperature 105 degrees C) extruded, pressed, crushed, oversieve to obtain a low acid powder coating and high acid powder coating.
will be low acid powder coating and high acid powder coating in accordance with the quality ratio of 1:1 fully mixed evenly, the preparation of the resulting powder coating using electrostectric spraying, at 160 degrees C curing 15min, to detect the relevant properties of the coating.1.5 performance test
polyester resin acid value is measured by GB/T6743-2008;
luster is tested according to GB/T9754-2007, coating color difference is tested according to GB/T7921-2008, and impact resistance is measured by GB/T1732-1993;
hardness is determined by GB/T6739-2006, adhesion is determined by GB/T9286-1998, and salt spray resistance is determined by GB/T1771-2007;
water-resistant spot test was conducted according to GSBAL631<> (May 2015), and the glass transition temperature was tested according to GB/T19466.2-2004, with a heating rate of 10r/min and nitrogen atmosphere;
test using QUVSpray (UVB-340) accelerated aging machine (Q-Lab) in accordance with GB/T14522-2008 standards.2 Results and Discussion of the effect of
2.1 binary alcohols on the performance of low acid polyester
Polyols formulated with polyester resins in powder coatings are mainly used with neo-glycol, in addition to polyester formulations will be added to other binary alcohol monomers to improve the performance of polyester or improve the cost-effectiveness of resins.
Such as glycol can give polyester resin a certain flexibility and reduce the cost of resin, hexanol can give polyester resin higher impact resistance, cyclohexane methanol fat ring structure can give polyester resin good weather resistance.
this paper studies the effects of different binary alcohol monomers on the performance of low acid polyester resins, and the experimental results are found in Table 3.
from the results of the Table 3 experiment, it can be seen that polyester resins synthesized with HBPA.CHDM have a higher glass transition temperature than polyester resins that use NPG as binary alcohols alone.
this is because these two monomer structures contain saturated hetease rings, which improves the rigidity of the molecules, so the synthetic polyester has a higher degree of glass transformation than the polyester that simply uses NPG as a binary alcohol;
the molecular structure of HBPA contains 2 saturated hepter rings, which show stronger rigidity when connected with PTA, and the improvement of polyester Tg is more obvious.
in addition, in terms of de-gloss and water-resistant spot performance, coatings prepared with HPPA synthetic polyester have lower gloss and better water spot resistance.
this may be because powder coating dry mixing is the use of high and low acid resin curing process reaction activity difference caused by the coating surface microscopic rough appearance to achieve the de-lighting effect.
Polyester synthesized with HBPA has a higher Tg, compared with the low Tg polyester molecular chain, its molecular chain movement at high temperature is relatively not intense, the molecular chain gap is small, high temperature water vapor is difficult to enter the polyester coating
2.2 Effects of acidic antidotes on the performance of low acid polyester
The two-part dry-mixed anti-light powder coating de-lighting principle is to use the reaction activity differences of the polyester powder parts of the low-acid value to form a coarse microstructure of the de-lighting surface.
generally speaking, the high acid polyester powder component reaction activity is high, the low acid polyester powder component reaction activity is low, the greater the difference in activity between the two, the lower the coating gloss obtained.
but the specific application in the field of low temperature curing, in addition to the coating gloss reduction, but also need to pay attention to the low-activity low-acid polyester powder components in low-temperature curing conditions can be completely cured.
therefore, different types of acid antidotes were selected to give different reaction activities to polyester resin end steryl, and the effect of the type of acid antidote on the performance of low acid polyester resins was studied, and the results were found in Table 4.
From the results of table 4 experiments, it can be seen that polyester prepared with PMDA as an acid antidote has the best impact resistance and low gloss, and polyester with ADA as an acid antidote has the lowest luster, but poor impact resistance.
This is because the use of ADA as an acid-based polyester resin due to the end of the azithyl for ADA, the activity is relatively low, so its reaction activity with high acid polyester parts is very different, more likely to form a rough surface of microstructure, lower gloss;
, the coating may not cure completely under low temperature curing conditions due to its low reaction activity, so the impact resistance of the anti-light coating is poor.
pmDA as an acid antidote, the coating is relatively fully cured and has the best impact resistance due to the high reactive activity of the pyrethromium provided by PMDA at the end of the molecular chain. . HaA system powder coating curing process to generate water, vaporization will take away heat, so it is not possible to test the DSC HAA system powder coating curing process of energy changes to study the degree of curing under low temperature curing polyester resin.
In this paper, DSC tested different kinds of acid antidote synthetic polyester at 160 degrees C low temperature and 180 degrees C conventional temperature curing coating people, through the coating Tg;
From the results of Figure 1, it can be seen that when ADA is an acid antidote, the coating Tg difference is greatest under temperature curing conditions of 160 degrees C and 180 degrees C, which indicates that polyester synthesized with ADA as an acidic agent has low reaction activity under low temperature curing conditions, and the resin cannot be completely cured at 160 degrees C.
and PMDA cures at 2 temperatures results in the smallest difference in coating Tg, indicating that the polyester coating is basically cured completely, so its coating is the most impact-resistant. 2.3 Curing reaction analysis
the active energy of the powder coating curing system can be derived from the Alenius equation, and the active energy calculation formula is shown in the formula (1). : Tgel-curing system adhesion time; R-universal gas constant; T-curing temperature; C-constant. According to this formula, the surface active energy of powder coating system can be calculated by Integel and 1/T. test results for the adhesion time of powder coatings prepared from self-synthetic low acid polyesters and conventional low acid polyesters at different temperatures are available in Table 5.
based on the data in Table 5, the Intgel-1/T relationship curve is graphed by Intgel and 1/T, as shown in Figure 2. the curve data obtained in Figure 2 is fitted, and the results are shown in Table 6. From the table 6 data fitting results, it can be seen that the self-synthetic low acid polyester powder coating has a lower activated energy than conventional low acid polyester powder coating, so it has a higher activity under low temperature curing conditions, can be cured at a lower reaction temperature, thus ensuring that the powder coating can have good impact resistance and weather resistance after curing, which is also compared with the previous document.