Research on the preparation and performance of environmentally friendly water-cured polyurethane waterproof coatings

China Coatings Online News Information
Abstract: Water as a curing agent, volatile and less toxic diphenyl methane diocyanate MDI as a raw material, its formula does not have any volatile and toxic solvents, to prepare environmentally friendly water-cured polyurethane waterproof coatings. The effects of hydro-hydro-polyether polyols, hydro-water chaining agents, gas absorbents and water content on the performance of waterproof coatings were studied. The results showed that the content of NCO was 4.5%, the other parts of the formula remained unchanged, and when the mass of hydrotherm polyether polyol, hydrotherm chaining agent and gas absorbent were 20, 0.4 and 4 respectively, and the water content was 20% of the total mass of A and B, the prepared polyurethane waterproof coating performed best.
key words: eco-friendly; water curing; polyurethane waterproof coatings
in the figure classification number: TU56- 1.65 document identification code: A article number: 1001-702X (2015) 02-0025-05
Currently, the waterproof coatings used on the market are mainly polyurethane waterproof coatings, acrylic waterproof coatings, polymer cement composite waterproof coatings and polymer modified emulsified asphalt waterproof coatings. Among them, polyurethane waterproof coatings with excellent physical and chemical properties and construction properties, has been widely recognized and applied in the construction industry. Polyurethane waterproof coating is divided into single and double parts. Single-group polyurethane waterproof coatings are prone to long curing times and delays due to insufficient humidity in the air. MoCA (3,3-dichloro-4, 4-diamine diphenyl methane, commonly known as moka) is often used as a curing agent in two-component polyurethane waterproof coatings and contains a large number of volatile organic solvents (e.g. toluene, xylene and gumalong resins, etc.). With the enhancement of environmental protection concept and the introduction of environmental regulations, the GB/T19250-2013 "Polyurethane Waterproof Coatings" implemented on August 1, 2014 has added a limit of harmful substances, and now polyurethane waterproof coatings are moving towards environmental protection and healthy direction.
water-cured polyurethane waterproof coating is one of the 6 kinds of environmentally friendly polyurethane waterproof coatings encouraged by the Beijing Municipal Construction Commission, is a polyether-type, solvent-free environmentally friendly high-grade synthetic polymer waterproof coating, compared with the traditional tar-type, petroleum asphalt polyurethane waterproof coating, with solvent-free Volatile, non-toxic, tasteless, construction pollution-free, fast curing and other advantages, in the construction of paint with water as a curing agent, which is significantly different from other single or two-part polyurethane waterproof coating, reflecting the development of polyurethane waterproof coating new ideas, new technology, with broad market prospects.
This paper uses water as a curing agent, with less volatile and less toxic diphenyl methane diocyanate MDI (as compared to TDI) as the raw material to prepare environmentally friendly water-cured polyurethane waterproof coating, its formulation without any volatile and toxic solvents. The effects of hydro-hydro-polyether polyols, hydro-water chaining agents, gas absorbents and water content on the performance of waterproof coatings
1.1 main raw materials
polyether polyol DDL-2000D, relative molecular mass 2000, hydroxy value 56mg KOH// g,f=2, Zibodesin Federal Chemical Co., Ltd.; Polyether polyol WNN-1, relative molecular mass 4800, hydroxy value 35mgKOH/g, f=3, homemade; hydro hydrother polyether polyol PB-9224, relative molecule Mass 7000, hydroxy value 24mgKOH/g, f=3, Nanjing Jinling Petrochemical Co., Ltd.; chlorinated paraffin-52, chlorine content 52%, density 1.25g/cm3, relative molecular mass 420, viscosity (50 oC)3 180mPa.s, Guangzhou Heavy Load Chemical Co., Ltd.; plasticizer, phthalates (DINP), density 0.974g/cm3, relative molecular mass 419, viscosity (20c) 80mPa.s, Nanjing Runbang Chemical Co., Ltd.; Light calcium carbonate, 1250, Jiangxi Province, Bairui calcium carbonate Co., Ltd.; Ultra-fine talcum powder, 600 eyes, Zibo City Zhangdian Shenghua fine chemical plant; wetting dispersant RB-1181, density 1. 06g/cm3, viscosity (20C) 90mPa.s, Guangzhou Leibang Chemical Co., Ltd.; 8 to 115 degrees C, Lake Governor Sheng Chemical Co., Ltd.; Gas absorbent HHJ-1,2000, particle size 6.5 m, homemade; rheumorative additive HHJ-2, homemade; catalyst, february laurel acid dDT tin (T-12), U.S. gas chemistry; isocyanate, diphenyl methane diocyanate MDI-50, isocyanate mass concentration of 33.2%, f-2, Yantai Wanhua polyurethane Co., Ltd.; water, Beijing waterworks.
1.2 Main equipment and instruments
cantilevered agitator, RW-20, German IKA company; NDJ-1B type, measuring range 10 to 2×106mPa×, Wuhan Gramo Test Equipment Co., Ltd.;
1.3 Preparation Method
(1)A Part A: Polyether polyols are added to four roast bottles according to design formulation, at speeds of 800r/min, 110 to 120 degrees C, -0.095 to -0.1 Dehydration under MPa vacuum conditions 2.5h, and then remove the vacuum, cool down to 60 degrees C, add MDI, and heat up to 85 to 90 degrees C reaction 3h, test reaction material - NCO content, if very different from the theoretical value, then continue to react to - NCO content unchanged and close to the theoretical value. After cooling down to 50 degrees C and adding chlorinated paraffin, de-bubble 30min under the vacuum conditions of -0.095 to -0.1MPa, you can get the A-part.
(2) B part: plasticizer, chlorinated paraffin, wetting dispersant added to four-mouthed canisters, wait for the temperature to rise to 100 degrees C to add ultra-fine talcum powder, light calcium carbonate, rheumogenic aids, gas absorbers and hydrolytic chaining agents, and then 1200r/min, 11 0 to 120 degrees C and -0.095 to -0.10MPa vacuum conditions dehydrated 2.5h, and finally cooled to 50 degrees C after adding a catalyst, in the -0.095 to -0.10MPa vacuum conditions de-bubble 30min, you can get B parts. Environmentally friendly water-cured polyurethane waterproof coating A, B parts of the basic formula and A, B parts and water matching as shown in Table 1.1.4 performance test method
the prepared waterproof coating according to the design quality ratio weighing, and stir 3 to 5min, so that it mixes evenly, scraped on the Teflon plate, made a thick 1.5mm coating film, in (23±2) degrees C, relative humidity (50±10% of the standard test conditions after maintenance of 7d, sample, test performance. The drying time, dry time, stretch strength, fracture elongation, bond strength and indestructurableness of the coating are tested according to GB/T16777-2008 "Building waterproof material test method"; T529-2008 "Determination of the tear strength of vulcanized rubber or thermoplastic rubber" in the right-angle test piece;
1.5 Principle of Water Curing
The synthetic reaction principle of environmentally friendly water-cured polyurethane waterproof coatings: isocyanate reacts with water, first producing extremely unstable aminomethyl acid (-NHCOOH), which is then rapidly decomposed into amines (-NH2) and carbon dioxide (CO2). If an excess of isocyanate is present, the resulting amine will further react with isocyanate to produce a replacement for isocyanate. Their reaction process is as follows:
Because R-NCO and R-NH2 react faster than water, the above reaction can be written:
by the above reaction can be known, 1 water molecule can react with 2 isocyanate base (-NCO), so water can be regarded as a chaining agent or curing agent, in place of the expensive curing agent MOCA, so that the molecular chain growth, the formation of organic polymer polymer. End-NCO-based polyurethane pre-polyurethane and water reaction to produce polyurethane, the main raw material of polyurethane high-polyurethane is polycyanate, its coating film curing, regardless of the production of urethane bond or arbond bond, are polyurethane. The principle of the reaction of isocyanate with water to produce CO2 gas is used to prepare polyurethane foam, and in the preparation of water-cured polyurethane waterproof coatings, the key is how to eliminate the CO2 generated in the reaction, making it a dense polyurethane elastomer. The addition of gas absorbents eliminates bubbles and results in a dense inner bubble-free coating with no pinholes on the surface.
2. Results and discussion of the effect of
2.1 hydrotherm polyether on the performance of waterproof coatings
According to the experience of producing two-part polyurethane waterproof coating, it is best to use two-function and three-function polyether compounding, and properly control the ratio of the two, which is beneficial to improve the product's stretch strength and fracture elongation. In addition, for environmentally friendly water-cured polyurethane waterproof coatings, hydrother polyether polyols play a very good role in the system.
experiment using hydrother polyol PB-9224, it is in the water-cured polyurethane coating film reaction as the main raw material to participate in cross-linking reaction, but also as a new type of surfactant, enhance the compatible between the various groups, especially the curing agent water and other parts, and thus improve the film-forming of polyurethane coating. According to table 1 formulation, the other parts remain unchanged, by increasing the amount of hydro-hydro polyether polyol PB-9224 to replace the amount of polyether polyol DDL-2000D, to investigate its impact on the performance of environmentally friendly water-cured polyurethane waterproof coating, the results can be seen in Figure 1.As can be known from Figure 1, with the increase of hydrother polyol PB-9224 dosage, the fracture elongation rate of environmentally friendly water-cured polyurethane waterproof coating shows the trend of first increasing and then decreasing, while the stretch strength, tear strength and -NCO content gradually increase; 4 molecular mass is large, high official energy, and polyether polyol DDL-2000D molecular mass is small, low official energy, in the calculation of - NCO content, with the increase of PB-9224 dosing, DDL-2000D dosing decreased, resulting in - NCO content increased. One of the reasons is that when the content of NCO increases, the curing crosslink density of the coating increases, the rigid chain segment increases, the polar group increases, it is easy to form hydrogen bonds, which makes the stretch strength of the coating film increase, the fracture elongation rate and tear strength also increase; The increase of the molecular group limits the movement of the molecular chain in the process of stretching, resulting in a decrease in the fracture elongation of the coating and an increase in the tear strength, in addition, the increase of the NCO content increases the density of CO2 produced during the reaction between NCO and H2O, resulting in a CO2 escape rate less than the CO2 generation rate, which can easily cause bubbles on the surface and cross-section of the coating film, and thus reduce the fracture elongation rate. Second, the appropriate addition of high-level hydrothermical polyether PB-9224, can improve the stretch strength and fracture elongation rate at the same time, but excessive dosage, coating curing will form too many physical cross-linking points, cross-linking network density is higher, strength is higher, elongation is reduced, and low-level polyether DDL-2000D can make the linear structure ratio in high-level polyester, flexibility is better, strength is lower. Third, hydro-hydro polyether PB-9224 can reduce the surface tensor pressure of the substance and enhance the compatibness of various components in the system, especially in the water-involved reaction, can improve the uniformity of the coating film, and ultimately improve the coating performance.
According to the above analysis, the other ingredients in the formula remain unchanged, when the hydrotherm polyether PB-9224 mass is 20, - NCO content of 4.5%, the preparation coating film-forming performance is the best, tensile strength of 3.2MPa, fracture elongation rate of 890%, tear strength of 19N/mm, in line with GB/T19250-2013 requirements.
2.2 Effect of hydrophobic chaining agent on the performance of waterproof coatings
Hydro-water chaining agent refers to the introduction of hydrophobic groups of chaining agents, such chaining agents are often used as special raw materials in water-based polyurethane (WPU) preparation, and its application in polyurethane waterproof coatings is rarely studied, especially in water-cured polyurethane waterproof coatings. Currently commonly used hydro-hydroploric chaining agents are pyridine-type chain-expanding agents, mainly 2,2-hydroxymethyl acid (DMPA) and 2,2-hydroxymethylbutyric acid (DMBA) 2 kinds, of which DMPA earlier use time, It is also the most commonly used at present, but its melting point is high (180 to 185 degrees C), it is difficult to heat and melt, need to add organic solvents (e.g. N-methyl pyridoxine, acetone, etc.) to dissolve it, and the solubility is small. DMBA has a special molecular structure, in organic solvents have better solubility, and low melting point (110 to 115 degrees C), can be solvent-free, more environmentally friendly products, known as a new generation of green-friendly chain-expanding agent.
in order to facilitate the preparation of environmentally friendly water-cured polyurethane waterproof coating, and do not introduce toxic organic solvents, this experiment selected DMBA as a hydro-water chaining agent for research. The quality of PB-9224 in the formula is 20, the other parts remain unchanged, by increasing the amount of hydro-water chaining agent DMBA, to investigate its impact on the performance of environmentally friendly water-cured polyurethane waterproof coating, the results can be seen in Table 2.can be seen from Table 2, with the increase in the amount of hydro-water amplification chain agent DMBA, the stretch strength and tear strength show a tendency to increase first and then decrease, and the fracture elongation rate gradually increases. Due to the hydrophobic chaining agent DMBA molecular structure contains 2 hydroxymethyl groups and 1 new pyridine base, and more than 1 methane than DMPA, resulting in a greater distance between nihilone and methane, nihilone and isocyanate space resistance is reduced, so that the chain expansion reaction is easier to carry out, increase the high The flexibility of the polylysum, which in turn improves the elongation, the appropriate amount of DMBA can make the stretch strength and fracture elongation rate of waterproof coating increase at the same time, such as excessive, more reaction points due to the expansion of the chain make the crosslink point relatively reduced, the solid crosslink density decreases, the stretch strength decreases, further reduces the tear strength;