Coating knowledge: spray polyurea coating with hydrophobic polyol

Core tip: since it was developed by researchers of Texaco chemical company in the mid-1980s, spray polyurea paint has been widely recognized in the paint market Compared with other coating alternative technologies (such as epoxy and acrylic), spray polyurea has a unique advantage because of its application performance under extreme conditions These properties include rapid curing and put into use, low temperature curing (below 0 ℃), insensitive to moisture, low VOC content and excellent physical and mechanical properties These characteristics, together with the improvement of construction equipment, promote polyurea to become a leading technology in related fields, such as secondary sealing, corrosion prevention and anti-corrosion Which is the price of Dajin diatom mud Recommended brief introduction: which is the price of Dajin diatom mud? How to buy genuine diatom mud? Guangdong diatom mud agent suggests placing a basin of cold water in the air conditioning room, so that the diatom mud wall can breathe effectively The feature of the breathing wall is obvious When the indoor air is dry, the diatom mud wall will release the absorbed water quickly Put it out to help regulate the indoor dry humidity It is suggested to place a basin of cold water in the air conditioning room, so that the wall of diatom mud can breathe effectively The feature of the wall that can breathe is obvious When the indoor air is relatively dry, the wall of diatom mud will absorb the water Paint House News: since it was developed by researchers of Texaco chemical company in the mid-1980s, spray polyurea paint has been widely recognized in the paint market Compared with other coating alternative technologies (such as epoxy and acrylic), spray polyurea has a unique advantage because of its application performance under extreme conditions These properties include rapid curing and put into use, low temperature curing (below 0 ℃), insensitive to moisture, low VOC content and excellent physical and mechanical properties These characteristics, together with the improvement of construction equipment, promote polyurea to become a leading technology in related fields, such as secondary sealing, corrosion protection, waterproof membrane and tank lining The chemistry of polyurea coatings can be divided into two parts: (1) pure polyurea and (2) hybrid polyurea, both of which are based on the chemical reaction of isocyanate curing Pure polyurea coating is the result of one-step reaction between isocyanate terminated prepolymer and curing blend containing only amine terminated resin and chain extender On the other hand, hybrid polyurea is the product of isocyanate terminated prepolymer, which reacts with the cured blend containing hydroxyl and amine terminated resin and chain extender Although there is little difference between pure polyurea and hybrid polyurea in physical and mechanical properties, catalyst should be added to hybrid polyurea to maintain the same level of reaction activity as pure polyurea Due to the competitive reaction between water and hydroxyl terminated resin and reactive isocyanate group, hybrid polyurea becomes sensitive to moisture, and bubbles will form when there is high content of water The chemical process of pure polyurea has occupied the main market of spray polyurea, but recently the development of hybrid polyurea spray coating has become a new hot spot Formula designers are using the performance advantages of hybrid polyurea to improve some properties of spray polyurea coatings These properties include mechanical properties, heat resistance and chemical resistance However, the availability of amine terminated resins, such as polyether amines, is limited in design, and hydroxyl terminated resins (such as polyols) have a wide range of variability These polyols can be different in main chain structure, relative molecular weight and functional group The hybrid polyurea coating with high performance can be developed by using these characteristics, and its performance level can not be achieved by using typical pure polyurea technology For example, a recently published paper shows that the hydrocarbon resistance of polyurea can be improved by adding polyester polyol to the main chain of polymer 2 By introducing polyester polyol into the formulation, the author can develop excellent xylene resistant coatings Xylene is an aggressive chemical often encountered in the oil and gas industry Polyurea can be used for secondary sealing and container lining We recently launched a new hydrophobic vorapel Gamma Polyol 3 These polyols have been used to prepare casting polyurethane elastomer, which shows excellent moisture resistance and good water-soluble acid resistance (such as 10% hydrochloric acid and 30% sulfuric acid) As water-soluble acids are more and more used in sewage treatment, chemical treatment, steel pickling, oil and natural gas recovery and other fields, we develop hybrid polyurea spray coating to expand the effectiveness of these hydrophobic polyols When applied to reinforced concrete, this material can provide a good coating with good mechanical properties, good adhesion and resistance to high concentration of acid The prepolymer was synthesized in a 15 liter glass reactor equipped with a thermometer, a top agitator, a nitrogen inlet and a nitrogen outlet for continuous nitrogen flow In the first step, the polyol is added to the reactor, and a few drops of benzoyl chloride are added at the same time, and the temperature is heated to 50 ℃ Once the polyol is in equilibrium, the liquid methylene diphenyl isocyanate (MDI) is added to the reactor in two parts within one hour After adding each equal part of isocyanate, carefully monitor the temperature of the reactor to ensure that the temperature will not rise due to the exothermic reaction between polyol and isocyanate After the last part of isocyanate was added, the reactor was heated to 70 ℃ and kept at this temperature for 3 hours The reactor was then cooled to 50 ° C to prevent thermal burns and the prepolymer was packed in a clean, dry metal tank for storage The prepolymer prepared by this method has a shelf life of up to six months Resin blends for curing prepolymers are prepared by adding raw materials directly into a clean, dry metal tank Although no specific order of addition is mandatory, in this case, the order of addition of raw materials is from the lowest to the highest according to the mass concentration in the formula If catalyst is used, the catalyst shall be weighed carefully on the analytical balance and diluted with 40-50g resin mixture before adding The material is mixed with a high-speed mixer at a speed of about 1000 rpm and put into use immediately The elastomer coating is prepared by isotherm PM or other suitable multi-component high-pressure spraying equipment Distribute the material at a static pressure of 2000 psi and spray it with a gunner fusion cleaning gun or a problerap-2 polyurea spray gun Spray the sample on low surface energy materials, such as polyethylene, and the coating can be peeled off within 20-30 minutes after spraying The sample used for adhesion test is applied to the steel plate with a thickness of ¼ inch, and the steel plate is sandblasted to a roughness of 2-4mm according to sspc10 standard All samples were dried at room temperature for 7 days prior to physical and chemical tests Hardness shall be tested in accordance with ASTM Test method standard D2240; tensile strength and elongation at break shall be tested in accordance with ASTM Test method standard d1708 or D412 Tear strength (c-head) shall be determined in accordance with ASTM Test method standard d624 The hydrolytic stability was determined by immersing a 2 × 2-inch specimen (3 mm thick) in water for 2 weeks at a test temperature of 95 ℃ After soaking, pat the sample dry, weigh it, and store it in a plastic bag before tensile test to prevent moisture from volatilizing The chemical resistance shall be tested in accordance with ASTM Test Method d534-95, and the 2 × 2 inch specimen shall be immersed in the required medium at 25 ℃ for 7-21 days Then rinse the sample with water, pat it dry, and store it in a plastic bag before the tensile test Pull off adhesion test shall be conducted according to ASTM Test method standard d4541, and self calibration (type IV) pneumatic adhesion tester shall be used For the sample impregnated with chemical medium, dry the sample at 25 ℃ for 1 week and then bond the test column to the coating surface Results and discussion the physical and mechanical properties of hybrid spray polyurea coating based on hydrophobic vorapel polyol were evaluated and compared with those of pure polyurea coating For this study, two methods were used to introduce the vorapel polyol into the formula In the first method, a 16% NCO prepolymer (prepolymer 2) obtained from vorapel is cured with a standard polyurea resin blend containing polyamine In the second method, the same 16% NCO capped prepolymer was cured with a resin blend which also contained vorapel polyol The samples obtained by these two methods contain nearly 25% (mass ratio) of voratel (hereinafter referred to as vorastar Gamma 7000 pure polyurea) and 50% (mass ratio) of vorapel (hereinafter referred to as vorapel 7000 hybrid polyurea) As shown in Table 1, the addition of the above vorapel polyols to the NCO terminated prepolymer has little effect on the viscosity of the prepolymer However, when polyether amines were replaced with vorapel polyols, the viscosity of the resin decreased significantly From the practical point of view, compared with the pure polyurea system, the lower viscosity is more convenient for the correct mixing of 1:1 formula, allowing the system to be treated at a lower temperature The material can be treated at a lower temperature to provide more flexibility for spraying construction equipment Viscosity at a given temperature is used as a method to control the pressure difference between isocyanate and resin proportioning pump Keeping the pressure difference < 100 psi ensures that the material can be sprayed and mixed in the desired 1:1 ratio The reactivity of all elastomer systems is highly dependent on the selection of resin curing agent blends As shown in Fig 1, the effective gelling time of two blends based on polyether amine / detda resin is 3-5 seconds, and the surface drying time is 7-10 seconds The blending time of the VORAPEL polyol in the resin blend was prolonged to 7 seconds, and the drying time was 20 seconds Surprisingly, the addition of vorapel to the formulation did result in a moderate increase in the hardness of the coating The shore a hardness of hybrid polyurea containing only vorapel polyol is 90, while that of pure polyurea is only 85 In general, when polyether amine containing resin blends are used in pure polyurea materials, excellent mechanical properties such as elongation and tear strength can be obtained The difference of stress-strain properties of pure polyurea materials is also reflected in their heat flow curves, which are obtained by DMTA analysis in the temperature range of - 100 ℃ to 200 ℃ Trace Tan δ and storage modulus (G ') of each system, as shown in Figure 1 Compared with the hybrid polyurea (25 MPa), the vorastar 7000 pure polyurea material has a much higher storage modulus (about 80 MPa) at room temperature The polymer with high storage modulus needs more stress to stretch the material (strain), so it can get more ultimate tensile strength and elongation On the other hand, high hardness polymers, such as vorapel hybrid materials, need less force to stretch materials, which is a preferred choice for applications such as waterproofing The high temperature stability of vorastar 7000 hybrid polyurea also showed moderate improvement The tan δ curves show that the two pure polyurea materials can undergo the melting transition at about 150 ℃, while the melting temperature of hybrid polyurea is over 200 ℃ To assess the ability of the polyol vorapel to change the overall hydrophobicity of elastomer samples, our initial efforts focused on measuring the hydrolytic stability Since polyurea is known to exhibit excellent hydrolysis stability under normal environmental conditions, we chose a more stringent set of conditions to test our materials The data in Table 2 show the changes in mass and mechanical properties after 14 days of immersion in deionized water at 95 ° C