Study on the preparation and performance of polyester resins used in outdoor powder coatings

China Paint Online News:
Chen Cheng 1, 2, Li Yong 1, 2, Liu Liang 1, 2, He Tao 1, 2, Zeng Ding 1, 2 (1. China Institute of Electrical Science, Guangzhou 510300;2. Guangzhou Dynasky Materials Technology Co., Ltd., Guangzhou 510300)
Summary: The use of two-step method to synthesize the outdoor weather-resistant powder coating polyester resin, and with FT-IR, UV-Uis was indicated. The effects of methylphenidate (IPA), trihydroxymethyl propane (TMP) and hexydic acid (ADA) on the weather and impact resistance of polyester resins were studied. The results show that with the increase of IPA dosing, the weather resistance of polyester resin is improved and the resistance to shock decreases, with the increase of TMP dosing, the weather resistance of polyester resin is improved, the resistance to shock is improved and then decreased, and with the increase of ADA dosing, the weather resistance performance of polyester resin is decreased and the resistance to impact is improved. The optimized formula synthesizes polyester resins with a 90% light preservation rate (240 h, UVB lamp aging) and excellent impact resistance.
key words: powder coatings; polyester resins; weather resistance; mechanical properties
in the figure classification number: TQ637.82 document identification code: A article number: 1672-2418 (2015) 02-0007-04
0 Introduction
In recent years, with the improvement of people's environmental awareness, the development of environmentally friendly coatings more and more attention. VoC emissions of powder coatings are almost zero, and the pollution to the environment is greatly reduced, which is one of the ideal environmentally friendly coatings.
coating in the outdoor environment by ultraviolet radiation and water, acid rain, oxygen and other effects, will continue to age and degrade, pay to reduce service life. In addition, due to external factors such as collisions, coatings can also cause mechanical damage such as cracks, affecting their service life. Therefore, it is very important to extend the weather resistance and mechanical properties of powder coating to save energy and improve the service life of materials. Polyester resin, as an important part of powder coatings, is the key to optimize the weather resistance and mechanical properties of powder coatings.
the weather resistance or mechanical properties of powder coatings is not a problem under existing technical conditions. Gu Yuxuan and other factors affecting the weather resistance of powder coatings have been systematically studied, Chen Longcai and other factors affecting the impact performance of polyester have been studied. However, to take into account the weather resistance and mechanical properties of powder coatings at present there is still a greater difficulty, mainly subject to the limitations of synthetic polyester resin monomer, so far there is no one at the same time with better flexibility, better weather resistance and cost appropriate monomer. Therefore, the coordinated solution of powder coating weather resistance and mechanical properties has become one of the important directions of polyester resin improvement.
has been gradually restricted due to the potential cancer risk of isocyanuric acid triglycerides (TGIC) curing agents. To this end, domestic enterprises have started the development of low acid polyester resin, in order to reduce the amount of TGIC. In this paper, by studying the effects of different monomers on the weather and impact resistance properties of polyester resins, the synthetic formula of polyester resins was optimized, and 94/6 type low-acid polyester resins were prepared. When using the resin to prepare powder coating, the use of the matching curing agent TGIC is low, reducing emissions, and the prepared coating has excellent weather and impact resistance.
1. Experimental part
1.1 Raw materials
Sequine parabenic acid (PTA), interbenzene (IPA), hexydiacid (ADA), trihydroxymethyl propane (TMP), new glycol (NPG), Isocyanuric acid triglycerides (TGIC), tin monoclonesid oxidation, acidic antidotes (toluene xylene), antioxidants 245, 626, titanium dioxide powder, vanadium sulfate, leveling agent, sabbath, are industrial products.
1.2 polyester resin formula
1.3 polyester resin synthesis process
in order to obtain a high performance polyester resin varieties, the test using two-step synthesis process. The so-called two-step method is relative to the one-step method. One step is to put all the raw materials into the reactor at once for esterization and fusion reaction. The advantage is that the synthesis reaction time is short, the operation is simple, the disadvantage is that the product color is not easy to control, the relative molecular mass distribution of the resin is wide. The two-step method designs the resin synthesis process into two steps: the first step is excessive alcohol, the second step is to synthesize a compound with a certain relative molecular mass, and the second step is to add acid substances to seal and adjust the relative molecular mass, and finally get the appropriate acid value polyester resin. The advantages of this method are uniform distribution of relative molecular mass, easy color control, excellent paint performance, the disadvantage is slightly more complex operation, long synthesis time. The steps are as follows:
formula amount of polyols and polyic acids, catalyst added to the 100 L reactor, stirring well. Under the protection of nitrogen, gradually heated up to about 240 degrees C, reaction 3 h, after reaching the target acid value, viscosity after the addition of acid inflying agent for acid solution, time 3 to 5 h, to achieve the target acid value, viscosity after vacuum shrinkage, 2 to 3 h after the acid value, hydroxy, viscosity and relative molecular quality and distribution of products in line with the requirements. After that, cool down to 210 degrees C, add antioxidants 245 and 626, stir 10 min, and feed. The acid value of the final product is 30 mg. KOH/g, viscosity 6 500 mPa.s.
1.4 Preparation of powder coatings and coatings
prepare powder coatings according to the basic formula of Table 2, the process is: ingredients →mixed→ extruded→ press →shred→ sieve→ products. The prepared powder coating is electrostectrulated and cured according to certain curing conditions, and the coating and coating performance are tested.
1.5 samples are not available for
FT-IR: Analysis of the structure of the sample using the Nexus 670 Fourier Transform infrared Spectrometer of Nicolet, USA.
UV-Vis: The ultraviolet absorption performance of the sample was analyzed using the TU-1901 dual-beam UV visible termosometer of Beijing General Instruments Co., Ltd.
weather resistance test: the U.S. Q-Lab company QUV/Spray model artificial aging box for weather resistance testing. Cycle conditions: UVB60 ×4× h light; Irradiance: 0.71 W/m2. Impact performance test: by reference to GB/T 1732-1993 paint film impact resistance measurement.
2. Results and
infrared analysis of 2.1 polyester resins
FT-IR spectra in Figure 1.
as can be seen from Figure 1, the wide and scattered absorption peaks near 3 276 cm-1 are arbond-OH absorption peaks, the C-H characteristic key absorption peaks of alkanes near 2,963 cm-1, the ester-based C-O characteristic absorption peaks near 1,713 cm-1, and the ester-based C-O characteristic absorption peaks near 1,266 cm-1. The characteristic absorption peak of the C-O key, the characteristic absorption peak of the benzene ring at 1 600 cm-1, 1 585 cm-1, 1 500 cm-1, 1 450 cm-1, and the C-C absorption peak of no olefins in 1,675 cm-1 to 1 640 cm-1. As can be known from the figure, the synthetic polyester is an aromatic end pyridine-based saturated polyester resin.
2.2 IPA dosing on the weather resistance and impact resistance of powder coatings
Figure 2 shows the effects of different IPA contents on the weather resistance and impact resistance of polyester resins (shocks are recoil results, the same below). As can be seen from the figure, with the increase of IPA dosing, the weather resistance of polyester coating increases, and the resistance to shock shows a downward trend.
degradation of polyester coatings during outdoor use is mainly associated with UV exposure. Figure 3 shows the UV spectra of polyester resins obtained from different IPA dosing. It can be shown from the figure that when the amount of IPA increases, the UV absorption strength of polyester resin decreases, thus reducing the degradation of the polymer and improving weather resistance. However, because IPA is a non-symmetrical structure, the resin synthesized by it has poor remnological properties and is more prone to breakage of the molecular chain under the action of external forces, resulting in a decrease in its impact resistance.
effects of 2.3 TMP dosing on the weather and impact resistance of powder coatings
Figure 4 shows the effects of TMP dosing on the weather and impact resistance of polyester coatings. As can be seen from the figure, with the increase of TMP dosing, the weather resistance of the coating is gradually increasing, but the mechanical performance is increased and then decreased. TMP is a polyol for 3-unit group, because the monomer molecule does not contain β hydrogen atoms, which is helpful to improve the weather resistance of polyester resin. The structure of the monomer can also play a role in improving cross-link density, so that molecules from long-chain structure to mesh structure, thereby improving the impact resistance of polyester. However, an over-addition can cause the coating to be too hard, reducing the flexibility of the coating, and can also cause a rapid increase in viscosity and even the production of gels. Therefore, the amount added is not easy to be excessive.
effects of 2.4 ADA dosing on the weather resistance and impact resistance of powder coatings
Figure 5 shows the effect of ADA additions on the weather resistance and aesthetic properties of polyester coatings. As can be seen from the figure, with the increase of ADA dosing, the impact resistance of polyester resin is improved. ADA is a fatty binary acid that increases the softness of the polyester polymer chain, thereby improving its impact resistance. Because ADA monomer contains more β hydrogen atoms, it is easier to absorb energy and cause the molecular chain to break, so the addition of ADA will have a greater impact on the weather resistance of polyester resin.
3 conclusion
two-step method is used to synthesize polyester resin for outdoor weather-resistant powder coatings. The results of infrared analysis show that the synthetic polyester resin is an aromatic end pyridine-based saturated polyester resin. With the increase of IPA dosing, the weather resistance of polyester resin is improved and the resistance to shock decreases, with the increase of TMP dosing, the weather resistance of polyester resin is improved, the resistance to impact is improved and then decreased, and with the increase of ADA dosing, the weather resistance performance of polyester resin is decreased and the resistance to shock is improved. The optimized formula synthesizes polyester resins with a 90% light preservation rate (240 h, UVB lamp aging) and excellent impact resistance.
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