HC Surface Treatment Network News: Zhang Dongdong, Liu Xiaodong, Sun Jian
(Weifang Hongyuan Waterproof Materials Co., Ltd., Weifang, Shandong 262735)
Abstract: This paper analyzes the causes and hazards of bubbles in polymer cement waterproof coatings, introduces the types and mechanisms of defoaming agents, and explores through experiments the impact of the type, dosage, and compounding ratio of defoaming agents on polymerization. Effect of tensile properties of cement waterproof coating.
Keywords: polymer cement waterproof coating; defoaming agent; tensile strength; elongation at break
Article number: 1007-497X (2015)-04-0010-03 CLC classification number: TU502; TU56+1.65 Document identification code: A
1・Causes and hazards of bubbles in JS waterproof coatings
Polymer cement waterproof coating (hereinafter referred to as JS waterproof coating) is formulated with acrylate, ethylene-vinyl acetate and other polymer emulsions and cement as the main raw materials, adding fillers and other additives. After water evaporation and cement A two-component water-based waterproof coating that solidifies into a film through hydration reaction. JS waterproof coating is mainly composed of liquid material and powder material. When using, the liquid material and powder material should be mixed evenly according to a certain proportion before construction. Due to the nature and usage of JS waterproof coating, it is inevitable to produce bubbles during its production and use, which not only affects the appearance of the coating film, but also affects the tensile properties and waterproofing effect of the coating.
(Jiangxi New Materials Co., Ltd.)
There are two main reasons for the generation of bubbles in JS waterproof coating: First, the main component of the liquid part of JS waterproof coating is polymer emulsion, and surfactants are used in the production process of polymer emulsion, and the viscosity Higher, it is easy to produce bubbles. Secondly, during use, the liquid and powder materials of JS waterproof coating need to be mixed and stirred, and bubbles are easily generated during the stirring process. Therefore, before painting, it is required to let the mixed paint stand for a period of time to allow the bubbles to escape. However, sometimes the standing time is too short, and the bubbles generated have no chance to escape but remain in the coating film. Even if the bubbles burst, Since the coating has lost its fluidity, cracks and pores will also form in the coating film, thus affecting the tensile properties of the JS waterproof coating. In addition, in order to ensure that JS waterproof coating can be applied to the facade without sagging, thickeners or thixotropic agents need to be added during production to increase the viscosity of the coating, making it harder for bubbles to escape. The existence of bubbles not only greatly reduces the effective area of the coating film to resist the action of water pressure, but also easily causes stress concentration around the bubbles, causing the development of fine cracks and causing the coating film to lose its waterproofing effect. Therefore, defoaming agents have become essential additives in JS waterproof coatings.
2. Defoaming mechanism and types of defoaming agents
It is generally believed that defoaming agents need to have two aspects of performance: one is foam suppression performance, which refers to the ability to inhibit the generation of bubbles. Substances with low solubility have better foam suppression properties; the other is foam breaking performance, even if bubbles have already formed The ability to break quickly, and materials with good spreadability (dispersibility) have better foam breaking properties. According to Ross theory, when the defoaming agent is spread on the surface of the solution, it will take away a layer of solution on the adjacent surface, making the liquid film thinner. When the thickness of the liquid film falls below a critical value, it will destroy the stability of the bubble film, causing the bubble film to rupture. . The defoaming process of defoaming agent is shown in Figure 1. The ideal defoaming agent should have both foam-breaking and foam-suppressing properties.
There are many types of defoaming agents used in JS waterproof coatings, including alcohols, mineral oils, fatty acids and fatty acid esters, fatty amides, polyethers, silicones, etc. The defoaming of different defoaming agents The effect is different. This article mainly explores the impact of the use of alcohol defoaming agents, silicone defoaming agents and polyether defoaming agents on the tensile properties of JS waterproof coatings.
3・Experimental part
3.1 Raw materials and equipment
Raw materials: 32.5 grade white cement; 200 mesh quartz powder; 100 mesh quartz sand; 400 mesh heavy calcium carbonate; acrylic emulsion X; plasticizer; bactericide; alcohol defoaming agent L, silicone defoaming agent Agent M, polyether defoaming agent N; water.
Instruments: electronic balance; laboratory dispersion sand mill; hot air aging test chamber; film punching machine and cutting tools; electronic tensile machine.
3.2 Test method
According to the relevant provisions of GB/T23445-2009 “Polymer Cement Waterproof Coating”, the JS waterproof coating is subjected to batching, coating, curing, punching and tensile performance testing.
Pour the prepared JS waterproof coating into the mold after letting it stand for 3 minutes, and use a film maker to make a film at a temperature of (23±2) Place it under standard conditions of ℃ and relative humidity of (50±10)% for 20 hours before applying the film for the second time. After curing for 96 hours under standard conditions, demould, and place the demoulded sample with the reverse side facing up. Curing in a drying oven at (40±2)℃ for 48h, then taking it out and placing it in a desiccator to cool for 2h. Use a microtome to punch the sample into 6 specimens. After marking and marking the thickness, measure the thickness. Select 5 specimens from each specimen for tensile testing, and keep 1 specimen as a spare. The stretching speed of the electronic tensile machine is 200mm/min.
Editor in charge: Zheng Bijia
