REN Pei-xian, WANG Cai-jian, FU Qiu-mang (Shijiazhuang Paint Company, Shijiazhuang 050051, Hebei, China)
Abstract: This paper introduces a method of preparing solvent-free epoxy putty for concrete substrates, focusing on the screening process of solvent-free epoxy resin, curing agent, low oil absorption pigment and filler, and diluent. The prepared putty not only meets customer construction needs and various product standards, but also meets the environmental standards of low VOC, and has a good market prospect.
With the continuous promulgation of national environmental protection policies, people’s awareness of environmental protection continues to increase, and the types of coatings used for anticorrosion and decoration of outdoor concrete bridges or other concrete infrastructures that meet national and industry environmental protection requirements have received great attention from all walks of life. The traditional solvent supporting products used for the protection of concrete substrates used before will be gradually eliminated by the market. The development of low-VOC concrete substrate protective coating products is imminent.
There are many holes on the concrete surface and the flatness is poor. Usually, a composite coating is used to achieve the purpose of protection. The relatively large and indispensable filling material in the composite coating is the putty layer. Due to the strong alkalinity of concrete, epoxy system closed primer is usually selected with epoxy putty, and then matched with epoxy midcoat, polyurethane or fluorocarbon topcoat to achieve the purpose of overall protection. To obtain environment-friendly epoxy putty, it is necessary to take into account the current status of outdoor construction, VOC emissions, workability, dryness, and engineering progress. Solvent-free epoxy putty should be the first choice.
Combined with “Corrosion-resistant coating of solvent-free epoxy liquid coatings” (GB / T 31361-2015), “Solvent-free anticorrosive coatings” (HG / T 5177-2017), “Limits of volatile organic compounds in architectural coatings and adhesives Value Standards “(DB13 / 3005—2017) and the third-generation nuclear power AP1000  requirements for solvent-free epoxy putty products, and at the same time to meet the actual needs of outdoor customers in construction, this experiment passed the epoxy resin, curing agent 5. Screening of raw materials such as low oil absorption pigments, fillers, thinners, etc., a solvent-free epoxy putty used in concrete infrastructure, with good versatility and compatibility, has a broad market prospect and economic benefits.
1.1 Experimental raw materials and equipment The
experimental raw materials and main equipment are shown in Tables 1 and 2.
1.2 Experimental ideas
The VOC of solvent-free liquid epoxy putty mainly comes from the resin, solvent and auxiliaries added in the system. In order to obtain a low VOC putty variety that does not affect the construction cycle, it is necessary to control the consistency of the putty between 8 and 9, so it is necessary to choose a low molecular weight epoxy resin (100% solid content, low viscosity liquid epoxy resin). Resin), filler with low oil absorption, additives with viscosity reducing effect and reactive diluent, and the best compatibility ratio between the components is screened out. At the same time, the overall performance of the prepared coating meets product technical standards.
1.3 Color paint experimental formula
The preliminary reference formula for this experiment is shown in Table 3.
1.4 Preparation process and performance testing
Production process: Add epoxy resin to the mixing tank, add the modification assistant under the stirring condition at 800 r / min, add the anti-settling agent and stir for 10 min, and then mix at 500 r / min Add the live diluent at a speed, add the pigments and fillers in the formula in Table 3 in order while stirring, add the diluent according to the viscosity, and stir at a high speed to a fineness of <70 μm to complete the preparation of the colored paint.
According to a certain mass ratio, the color paint component (component A) and the curing agent component (component B) are mixed, and they can be applied after 5 to 10 minutes of curing.
The prepared putty was subjected to density determination and calculation of VOC content under putty construction viscosity. At the same time, according to the technical specifications of the third-generation nuclear power AP1000 solvent-free epoxy putty product, a sample preparation of the putty was performed, and the performance of the putty was tested.
2 Experimental results and discussion
2.1 Selection of epoxy resin The
most important thing in preparing solvent-free epoxy putty is to select a suitable epoxy resin with a full solid content and low viscosity. After preliminary experiments, three types of 100% solid content and viscosity are selected. For small molecular epoxy resins below 30 000 mPa · s, the index parameters are shown in Table 4.
Epoxy resin 1, epoxy resin 2, and epoxy resin 3 were prepared into component A of the colored paint according to Table 3, which are Scheme 1, Scheme 2, Scheme 3, respectively, and the curing agent of component B (the amine value of the curing agent). (NV = 100%) for maturation in specific periods, as shown in Table 5 [m (A component): m (B component) = 10: 4].
Test the workability and adhesion of the cured putty and calculate the VOC content. The specific results are shown in Table 6.
According to Table 6, it can be concluded that Scheme 2 and Scheme 3 can guarantee the normal construction of the product, and have good adhesion, can meet the customer’s construction requirements, and also meet the solid content requirements of solvent-free products, reducing the impact on the construction workers lowest.
It can be seen from Table 7 that the elongation and volume solids of Scheme 2 are better than Scheme 3, but the drying time, adhesion, and Shore hardness of Scheme 3 are better than Scheme 2. In addition, the price of the resin used in scheme 2 is much higher than that used in scheme 3, so the resin used in scheme 3 is the first choice for the next experiment when all the performance indicators are qualified.
2.2 Selection of curing agent
Since the prepared coating is a solvent-free epoxy putty, according to accumulated experience, the curing agent should be selected as a low viscosity fatty amine curing agent with a solid content of 100% and a longer activation period. The following two curing agents were selected for paint matching and performance test comparison. Details of curing agents are shown in Table 8.
It can be seen from Table 8 that both curing agents are low-viscosity aliphatic modified amines, and basically no difference can be seen from the data. In order to screen a cost-effective curing agent, the performance of the two-component formulation needs to be adjusted. test. The specific test results are shown in Table 9.
From the comparison data of curing agent in Table 9, curing agent a has a poor elongation, which is close to the standard requirements, and various performance indicators of curing agent a are lower than curing agent b. Therefore, it is more suitable to use curing agent b as the curing agent of the solvent-free putty product.
2.3 Screening of
low oil absorption fillers The addition of low oil absorption talc powder is beneficial to reduce the viscosity of the system, easy to apply and prolong the activation period of solvent-free epoxy resin. However, because low oil absorption talc powder contains more calcium carbonate, so Will affect the sanding performance of putty products. Therefore, comparative experiments are needed to determine the appropriate addition amount. The specific experimental scheme and test results are shown in Table 10. It can be seen from Table 10 that with the increase of the amount of low oil absorption talc, the activation period and consistency of the putty have a significant improvement effect, and the workability of the putty has improved, but excessive addition will make the abrasiveness of the putty worse. Worse. On the whole, the low oil absorption talc powder is most suitable when the ratio is 2.
2.4 Screening of
thinners The selection of thinners is very important. Appropriate thinners can significantly improve the viscosity-reducing effect of the system and help design solvent-free epoxy putty products that have good application viscosity while meeting the requirements of solvent-free products. Relevant laws and regulations require, and the added diluent must not affect the drying and subsequent related performance. In this experiment, three inactive diluents were selected for the experiment. The viscosity of the mixture was measured after mixing the three diluents with the epoxy resin, and the varnish was prepared after the prepared mixture was mixed with the curing agent to determine the relevant data of the varnish. See Table 11.
According to the process, three types of diluents were used to prepare putty samples, and the technical data of related epoxy putty were examined. The specific experimental results are shown in Table 12.
Based on the above experimental data, we can see that although the viscosity reduction effect of 2 # thinner is better than the other two products, its hardness is slightly lower; and the comprehensive evaluation of 3 # thinner, whether it is the drying rate or 7d Product hardness and abrasiveness can meet the design requirements. Therefore, 3 # diluent was selected as the diluent for this experiment.
3 Experimental formula and performance
Through the above experiments, the experimental formula of the solvent-free putty product was finally determined, as shown in Table 13.
After screening the main materials of the solvent-free putty products, the VOC content of the coating construction is controlled, and the performance is in line with “Corrosion-resistant coating of solvent-free epoxy liquid coatings” (GB / T 31361-2015), “solvent-free anticorrosive coatings” (HG / T 5177-2017), “Standards for Limits of Volatile Organic Compound Content in Architectural Coatings and Adhesives” (DB13 / 3005-2017) and other standards, and the requirements of the third-generation nuclear power AP1000 for solvent-free epoxy putty products, Refer to the ARMORSEA L 33EPOXY PRIMER specification for the testing indicators. Table 14 shows the performance indicators of the final product.
This experiment successfully screened epoxy resin, curing agent, filler, and diluent to successfully prepare a solvent-free epoxy putty for concrete substrates that meets environmental protection requirements, and reached the following conclusions.
(1) Through screening of properties such as adhesion and tensile strength, epoxy resin a and curing agent b were determined as the solvent-free epoxy resin and curing agent in this experiment.
(2) The filler with low oil absorption can significantly reduce the construction viscosity of the product, and the optimal addition amounts are 5% and 20%, respectively.
(3) By adding a suitable diluent, it can ensure that the product has better workability and a relatively long activation period. It can reduce the construction viscosity without affecting the subsequent drying time and sanding performance.