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    Home > Coatings News > Paints and Coatings Market > Research preparation of alcohol-soluble polyurethane closed primers

    Research preparation of alcohol-soluble polyurethane closed primers

    • Last Update: 2020-12-26
    • Source: Internet
    • Author: User
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    Abstract: The use of environmentally friendly solvents instead of toluene and other toxic solvents, the preparation of alcohol-soluble polyurethane closed primer, reduce environmental pollution. Various factors affecting the performance of closed primer are discussed.
    key words: alcohol-soluble polyurethane closed primer, environmentally friendly paint, development
    in the figure classification number: TQ630.7 document identification code: A article number: 1009-1696 (2013) 0 1-0013-02
    0 Introduction
    At present, the general furniture factory due to cost reasons, most of the choice of poor texture, soft, porous substrate, some wood substrate also has a lot of wood grain, pipe, pores and so on. When the pores are more, the gap is deep, which contains more air, easy to produce bubbles, pinholes, tweezers and other ills, generally to spray closed primer on the substrate closed treatment. Closed primer penetration is strong, can effectively fill the substrate pores, block the residual small amount of moisture and volatile substances in the wood outward diffusion, effectively close the substrate, slow down the wood due to moisture absorption caused by deformation, while preventing the upper coating from seeping into the wood, to a certain extent to improve the film plumpness, to prevent the coating subsidence. At present, the use of polyurethane closed primer due to low solid content, solvent emissions, do not meet environmental protection requirements.
    In this paper, an alcohol-soluble polyurethane closed primer, free TDI (toluene diocyanate) is developed, diluted with alcohol-based low-toxic solvents, which can improve the operating environment and reduce injury to operators.
    1. Experimental part
    1.1 Raw materials
    TDI (toluene isocyanate, 80/20), trihydroxymethyl propane, polyester polyol, monool functional monomer, antioxidants, catalysts, propylene glycol methyl ether acetate, ethanol, leveling agent, defoaming agent, are all industrial products.
    1.2 Synthesis process
    in turn in the reaction bottle to add TDI, propylene glycol methylene acetate, trihydroxymethyl propane, polyester polyols and antioxidants, heat up to 60 degrees C reaction 1h, and then heat up to 72 to 75 degrees C insulation 2h, and then heat up to 80 to 8 4 degrees C insulation 1h, cool down to 60 degrees C, add a unitol functional monolith, in 60 to 65 degrees C reaction 1h after the start of the determination - NCO content, - NCO content qualified, add the remaining propylene glycol methyl ether acetate, as well as ethanol, leveling agent and desmodulator, mixing well, feeding.
    1.3 Performance indicators
    Color: <1;
    viscosity (coated 4 cups, 25 degrees C): 22 to 28s;
    solid content: 43% to 47%;
    -NCO content: <0.1%;;
    free TDI: <0.01%;
    table dry time: 40min;
    Dry time: 6h;
    Hardness: HB;
    Adhesion: Level 1;
    :
    : Spray polyurethane finish no adverse.
    2. Results and discussion
    2.1 reaction temperature effect
    TDI and polyol addition reaction is heat release reaction, the higher the reaction temperature, the more heat given by the outside world, the more easily oxidized, the darker the color of the product, at the same time the faster the reaction speed, the more unfazed the control of the reaction, the more unstable the process, the relative molecular mass of the product is difficult to control, the resulting polymer is too much, the performance of poor solution, high viscosity, and even the possibility of gel. In addition, theoretical studies show that there are differences in the reaction activity of 2 -NCO-based in TDI molecules, and in polyurethane coatings, people often use the characteristics of 4-bit-NCO-based reaction activity, so that 4-bit-NCO-based priority addition or polymerization, leaving 2 bits-NCO-NCO and hydroxyl resin cross-linking reaction. The greater the relative activity gap between 4-bit-NCO-based and 2-bit-NCO-based, the more uniform the distribution of the relative molecular mass of synthetic products, the better the solubility, and the better the storage stability. With the increase of temperature, the difference of reaction activity gradually becomes smaller, the higher the reaction temperature, the smaller the activity difference of 2 -NCO groups in TDI molecules, so that the more uneven the distribution of the relative molecular mass of the product, the worse the performance of the product. However, the reaction temperature is too low, the required reaction time is long, TDI reaction is not complete, excessive residual TDI, resulting in the reaction later added to the immedol material reaction to generate a large number of low relative molecular mass products, so that the product storage stability is poor, paint film hardness is low, easy to granulate.
    this reaction is selected at 60 to 65 degrees C to make -NCO-based and -OH-based reactions, and insulation at 70 to 72 degrees C, so that the reaction is carried out smoothly, and then heated up to 80 to 84 degrees C, at this temperature to promote swimming Further reaction from the TDI monomer, reduce the free TDI content, and finally add the monool functional monomer, so that the pre-oxide-NCO-based and monool functional monomer reaction, so that the free TDI content tends to zero, the final reaction is easy to control.
    2.2 n (-NCO)/n(-OH) ratio
    In the synthesis of polyurethane pre-polymers, the n(-NCO)/n(-OH) ratio affects the stability of the reaction process, the storage stability of the product and the size and distribution of the compound relative to molecular mass, thus affecting the performance of the coating. Generally reduce the n (-NCO)/n (-OH) ratio, can reduce the free TDI content, but the synthetic products relative to molecular mass, high viscosity, unstable process, easy to glue. However, the n(-NCO)/n(-OH) ratio increased and the free TDI content was high. In this reaction, using the difference between the 4-bit and 2-bit-NCO-based reaction activity of TDI, the 4-bit-NCO-based priority reaction generated pre-concentration, leaving behind a 2-bit-NCO-based and monool functional monomer reaction. If the value of n (-NCO)/n (-OH) is too low to close all hydroxyl, then the coating film crosslinking degree is low, solvent resistance, chemical resistance and water resistance is reduced, and even the coating film is soft or can not form a dense paint film;
    effect of table 1 n (-NCO)/n(-OH) ratio
    is visible from Table 1: When n (-NCO)/n(-OH) <1.9, the product has a large viscosity, n (-NCO)/n (-OH) >2.3, although the pre-cluster viscosity is low, but the coating surface is prone to shrink holes. Through the test, it is determined that n (-NCO)/n(-OH) is 1.9 to 2.1, the coating performance is better.
    2.3 solvent impact
    in the synthesis of polyurethane pre-polymer, generally selected xylene and butyl acetate and other solvents, in the production and construction process, the release of solvents with a high physiological toxicity, pollution to the environment. Propylene glycol methyl ether acetate because of its low toxicity, strong solubility, more and more widely used in the coating industry, and ethanol is a regenerative non-toxic solvent, the two are used instead of toxic and harmful solvents, reduce the emission of harmful substances, to meet environmental protection, safety and health requirements. When the amount of propylene glycol methyl ether acetate is too large, the paint film drys for a long time, and the ethanol dosing is too much, then the paint film is prone to whitening. The test showed that the paint film had excellent performance when the ratio of propylene glycol methyl ether acetate to ethanol was 2:8.
    3. Conclusion
    prepared a polyurethane closed primer, the selection of propylene glycol methyl ether acetate, ethanol and other non-toxic solvents, instead of toxic and harmful solvents, no free TDI, ethanol dilution, easy to use, energy saving, harmful substances content is effectively controlled, not only to protect the health of production operators and construction personnel, but also conducive to environmental protection, environmentally friendly paint products.
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