Preparation of two-part water-based polyurethanes based on epoxy resin and their application in wood coatings

Abstract:
In order to improve the room temperature crosslinking speed of two-group water-based polyurethane, N-pyridine ethanolamine was introduced into epoxy resin to prepare epoxy resin-based water-based polyols, which indicated the chemical structure of polyols, and measured its molecular weight, particle size distribution and glass temperature and other major technical parameters. The two-part water-based polyurethane of epoxy resin was prepared in conjunction with polycyanate, and the interlinking reaction process of room temperature was studied by infrared spectroscopy. The results show that the introduction of pyridine base in the molecular structure of polyol accelerates the cross-linking speed of two-group water-based polyurethane

. The two-part water-based polyurethane preparation of water-based wood coating, lacquer film has excellent impact resistance, adhesion, flexibility, gloss, resistance to liquid media, hardness, plumpness and other properties.
keywords:
water-based polyols; two-group water-based polyurethane; epoxy resin; wood coatings
China's annual use of wood coatings about 1 million t, solvent-based wood coatings still dominate, water-based wood coatings annual use of about 50,000t, accounting for about 5% of the total amount of wood coatings. Since 2015, China has started to levy consumption tax on high-volatile organic matter (VOC) paint varieties, water-based wood coatings, as environmentally friendly products, are the development direction of wood coatings, have been included in the Ministry of Industry and Information Technology issued the "State-encouraged list of toxic and harmful raw materials (products) substitutes (2016 version)," the implementation of these environmental protection policies will strongly promote the promotion and application of China's water-based wood coatings. The hardness, fullness, water resistance, heat resistance and high temperature back viscosity of traditional single-group water-based wood coatings are still significantly different from those of traditional two-part solvent-based polyurethane wood coatings. The two-component water-based polyurethane combines the high performance of the two-component solvent-based polyurethane with the low VOC content of the water-based resin, and has excellent properties such as low film temperature, strong adhesion, good wear resistance, high hardness and chemical resistance and good weather resistance, and is the ideal water-based coating resin to replace the solvent-based two-component polyurethane for wood surface decoration and protection. Two-component water-based polyurethane consists of hydroxyl-containing water-based polyol components and low-viscosity polycyanate components containing isocyanate, which are different from the two-component membraneing of organic solvent-based two-component polyurethane, and two-component water-based polyurethane. Membrane process is complex, is a series of water volatile, polyol and polycyanate particles aggregation fusion, polycyanate and polyol reaction, polycyanate and water reaction, such as a series of physical and chemical processes of latex particles between the non-versal film. Therefore, the problem of slow cross-linking film is common.
small molecule seramine can catalycify the reaction of polycyanate and polyols, but it can also catalycify the reaction of polycyanate and water. When the two-part water-based polyurethane coating system is catalytic with small molecule seramine, it is easy to cause paint film bubble problems due to the accelerated reaction of water and isocyanate. Therefore, small molecule schoamine is rarely used as a catalyst for two-group water-based polyurethane coatings. In this paper, the bit-blocking ampicillin is branched into epoxy resin, water-based epoxy resin-based polyols are prepared by hydro-water-modified, and polycyanate cross-linking into a film, which can not only speed up the cross-linking of two-group water-based polyurethane paint film into a film speed, but also obtain a light flat fine paint film. Apply this two-part water-based polyurethane to wood coatings for paint films with excellent properties such as high gloss, high plumpness and high transparency.
1. Experimental Part
1.1 Experimental Raw Materials
Bisphenol A Epoxy Resin (EP): Anhui Hengyuan Chemical Co., Ltd.; N-Pyrethyl ethanolamine, dihydroxymethylate (DMPA), 1,6-hexacyanate (HDI) ): Chemical pure, Aladdin Reagent Co., Ltd.; Acetone, N, N-dmyethanolamine (DMEA): analysis pure, Nanjing Chemical Reagent Co., Ltd.; hydro-modified polyhetide trimer (WT101): solid content 100%, Guangdong Blue Ocean Technology Co., Ltd.
anti-foaming agent: Tego Airex 901W, Germany Created; Thickener: RM-8W, Dow Chemical; Humidifier: Surfynol 104E, Air Chemical; Leveling Agent: RM-2020, Dow Chemical; Diprosteryl glycol butyl ether and diethyl glycol monode: Industrial, Dow Chemistry.
1.2 Synthesis of water-based epoxy-based polyols
the N-based ethanolamine and biphenol A epoxy resin into a four-mouth flavonoid with heating devices, thermometers, agitators and condenser tubes, adding a moderate amount of acetone, heating and stirring, reflow reaction 5 h, to obtain yellow transparent bisphenol A epoxy-based polyol BBP propone solution (type 1). Then proportionally add DMPA and HDI to continue the reflow reaction of about 5 h, and then use the amount of DMEA with DMPA and other substances to median, continue to reflow reaction 30 min. After the reaction stopped heating, drip water stirring dispersed to the system solid content of 40%, after cooling decompression steamed acetone, milky white with blue bisphenol A epoxy resin-based polyol (WBBP) water dispersion.
1.3 Epoxy resin-based two-part water-based polyurethane wood paint preparation
the bisphenol A epoxy resin polyol water dispersion WBBP and polyocyanate curing agent WT101 by hydroxyl and isocyanate-based substance ratio of 1:1.4 in conjunction with the preparation of bi-group water-based polyurethane system. The epoxy resin-based two-part water-based polyurethane is used in the preparation of water-based wood finishes, the basic formula as shown in Table 1. Spray the water-built wood lacquer on a primer-treated board surface. The film-forming process at room temperature was examined, and the performance of the paint film was determined after the full cross-linking of the film was determined.
table 1 epoxy resin-based two-part water-based polyurethane wood lacquer1.4 Instrument and Test Method
1.4.1 Infrared Spectroscopy
Infrared analysis using the German Bruker-ALPHA Fourier infrared spectrometer using attenuation full reflection method for infrared analysis, scanning range of 4000 cm-1 to 500 cm-1.
1.4.2 MRI Spectroscopy
using the German Bruker 500 MHz Avance DRX-type MRI spectrometer for nuclear magnetic analysis, based on CDCl3 as a solvent, TMS.
1.4.3 gel permeation chromatography
dissolves the sample in a tethydrofuran solution using a filter with a pore of 0.45 m (Nylon, Millex-N) H 13 mm Syringes Filters, Millipore, US) filters and then uses water1550 gel permeation chromatography (GPC) to determine the relative molecular mass of the sample using a tethydrofuran as the flow phase. The detectors are Water2487 UV detector and Water2414 refring index analyzer, the column is Style HR1, HR2, flow phase flow rate of 1 mL/min, and the relative molecular mass and distribution of polymers are determined by using single dispersion polystyrene as a sample.
1.4.4 Laser particle size analysis
After diluting epoxy resin-based polyol water dispersion with distilled water to a solid content of 1%, the particle size distribution was determined using the Nano ZS ZEN3600 nanometric analyzer.
1.4.5 glass transition temperature measurement
the glass transition temperature (Tg) of the polyol sample was measured using the Diamond Differential Scan Heat (DSC) analyzer. It is called to take 6 to 8 mg sample, press into the closed aluminum crucible, pure radon calibration, empty crucible to make a reference sample, nitrogen flow of 50 mL/min, heating range -50 to 150 degrees C, heating rate of 20 degrees C/min.
1.4.6 Paint film performance measurement
the epoxy resin-based two-part water-based polyurethane into a water-based wood paint, according to the "indoor decoration of water-based wood coating" (GB/T 23999-2009) to determine the paint and paint film performance.
2. Discussion and results
2.1 BPA epoxy resin-based polyol structure degeneration
2.1.1 Infrared spectral analysis
the infrared spectroscopy of BPA epoxy resin and polyol products BBP and WBBP is shown in Figure 1.
1 FT-IR spectra of BBBP and WBBP products BBBP and WBBP
as can be known from Figure 2, 913 cm-1 aerosol in the spectrum of Bisphenol A epoxy resins The characteristic peak of the base, and the characteristic peak of the end epoxy base at 913 cm-1 in the BBP map disappeared, indicating that the epoxy-based and amine-based open-loop addition reactions occurred between biphenol A epoxy resin and pyrethromyl ethanol. At 1703 cm-1 in the WBBP spectrum, a niobium-based feature peak appeared, indicating that isocyanate-based and polyol hydroxyl reactions produced amino methylate bonds, while 2272 cm-1 did not appear isocyanate-based characteristic peaks, indicating that isocyanate reaction is complete. WBBP has a strong hydroxyl feature peak at 3341 cm-1, which is also consistent with the chemical structural characteristics of the target product polyol.
2.1.2 MRI spectra
disphenol A epoxy resins and polyol products BBP and WBBP are shown in Figure 2.
2 BPA epoxy resins and polyol products BBP and WBBP 1H NMR spectra
Figure 3 BPA epoxy resins and polyol products BBP and WBBP 13C NM R-spectrum is visible from Figure 3, BBP map δ s 44.2, 49.1 epoxy-based mid-carbon and uncle carbon characteristic peak disappeared. After the base and the amine-based opening ring are added, the chemical displacement of the two carbons of the epoxy base moves to the low field, which appears in δ, 56.1, 67.1 δ, respectively; 59.3 there are characteristic peaks of Pyrides linked to N, and new characteristic peaks of benzene ring skeleton carbon appear at δ to 127 to 140, which is the characteristic peak of benzene cyclic carbon in niacin-based ethanol. Compared with the BBP spectrum, the characteristic peaks of methane carbon in the WBBP map are enhanced by the introduction of heterocyanate, δ which is 26 to 30.
2.1.3 Gel permeation chromatography
the number of epoxy resins and polyol products BBP and WBBP was measured by gel permeation chromatography (GPC), as shown in Figure 4.
Figure 4 Molecular weight distribution curves of BBBP and WBBP, biphenol A epoxy resins and polyol products
as shown in Figure 4, with the polymerization reaction of the addition, the outflow time of the product is shorter than that of the reactant and the relative molecular mass is increased. With polystyrene as the ratio, the number of epoxy resins and their polyol products BBP and WBBP were measured relative to molecular mass of 1532, 2020 and 3186, respectively.
2.1.4 Laser particle size analysis
the effect of DMPA niobide-based median on the distribution of EPOX-based polyol WBBP dispersion particle size was examined by laser particle size analysis, and the results are shown in Figure 5.
effect of water neutrality on the particle size distribution of WBBP water dispersion
As can be known from Figure 5, with the improvement of neutrality, the particle size of WBBP water dispersion is enhanced and the particle size of dispersion is gradually reduced. When the mesosurm is 60%, the water dispersion has no blue light, the particle size is twin peak distribution, and there is a strong particle size distribution peak in the 1 to 2 m range, the sedimentation 7 d has precipitation, the water dispersion stability is poor≥
2.1.5 DSC analysis
the glass transition temperature (Tg) of bisphenol A epoxy-based polyol products was measured by DSC, as shown in Figure 6.
Figure 6 DSC curve of biphenol A epoxy resin-based polyol products
as can be known from Figure 6, BBP and WBBP products were heated twice in the range of -20 to 120 degrees C, and the Tg measured by the second heating of the same sample was higher than the Tg value measured in the first heating. This is due to the BBP and WBBP surface rich in hydroxyl and other hydrophobic groups, there will be varying degrees of water absorption affecting Tg values, and the second heating removed the effects of water, the measured Tg value is more accurate. It can also be seen from the DSC curve that the Tg value of WBBP2 heating is more different (approximately 10 degrees C), and this result is consistent with the chemical structure characteristics of the product, because WBBP is a further hydro-hydro modified BBP, more prone to water absorption affecting Tg.
2.2 epoxy resin-based two-part water-based polyurethane room temperature cross-linking membrane process
Ester system, in the temperature of 25 degrees C, humidity of 60% of the environment cross-curing, the use of infrared spectroscopy to observe the two-group water-based polyurethane cross-linking reaction process isocyanate vibration absorption peak changes, as shown in Figure 7.
7 WBBP infrared spectroscopic analysis of the cross-linking reaction process of water dispersion
as can be known from Figure 7, WBBP is connected to ampicillin ethanol, polyols due to the molecular structure containing seramine groups, cross-linking reaction speed with isocyanate Speed up, after 4 d under room temperature conditions - NCO base group basically disappeared, paint film curing completely, and the literature reported that the ordinary two-group water-based polyurethane room temperature conditions paint film to achieve the best performance needs 7 to 14 d. And because of the large bit resistance effect of introducing schoamine-based groups in WBBP structure, the reaction of catalytic hydroxyxyl and isocyanate and water and isocyanate-based is mild.
2.3 epoxy resin-based two-part water-based polyurethane wood coating performance

table 2 epoxy resin-based two-part water-based polyurethane wood paint performance  Note: (1)0h, 3h, 4h for different active periods;
By Table 2, biphenol A epoxy resin as a multi-alcohol main chain into the two-group water-based polyurethane coating, can achieve epoxy resin and polyurethane performance complement each other, prepared water-based wood coating, its paint film has excellent impact resistance, adhesion, flexibility, hardness, gloss, plumpness and liquid-resistant media performance, can reach the performance level of solvent-based bi-group polyurethane. From Table 2 different construction active period paint film gloss data can be found, WBBP and polycyanate curing agent prepared