Preparation method for low-color number environment-friendly polyurethane curing agent

Abstract

The invention discloses a preparation method for a low-color number environment-friendly polyurethane curing agent. The method comprises the following steps of 1, continuously reacting dihydric alcohol, trimethylolpropane and toluene diisocynate to generate prepolymer reaction liquid by using a continuous reaction device, wherein the trimethylolpropane is fed in a batch addition way; 2, separating the prepolymer reaction liquid by using two stages of film evaporators, pumping evaporation residues obtained by separation into a diluting tank by using a pump, and performing diluting to obtain low-free isocyanate monomer content polyurethane curing agent. The method has the advantages that the whole production process is continuous, the use of a solvent is avoided, reaction heat is maximally utilized, the method is energy-saving and environmentally friendly, the color of a product is improved, and the quality of the curing agent product is improved.

Description

technical field [0001] The invention relates to a preparation method of a low-color environment-friendly polyurethane curing agent. Background technique [0002] The coating film of polyurethane coating has the advantages of high hardness, good toughness, strong chemical resistance and fast drying. It is one of the most widely used solvent-based coatings with excellent performance. Polyurethane coatings are composed of two components, one is a hydroxyl component such as alkyd resin, polyester resin or acrylic resin, and the other key component is a polyurethane curing agent polymerized from isocyanate monomer and alcohol. [0003] Since the polyurethane curing agent uses isocyanate monomer as raw material, it is inevitable that there will be a certain amount of isocyanate monomer residue. In principle, the less residual isocyanate monomer the better. However, at present, domestic toluene diisocyanate (TDI) adduct curing agents are all chemical processes. The advantages of t...

AI Technical Summary

Problems solved by technology

However, at present, domestic toluene diisocyanate (TDI) adduct curing agents are all chemical processes. The advantages of this process are that the synthesis process is simple, no additional separation is required, and the cost is low, but the inevitable disadvantage is: free TDI monomer High content, generally around 1% to 2%, is very unfavorable to human health, leading to potential health problems; high molecular weight, high viscosity, can only be used for the preparation of low-end coatings

The above two dehydration processes also have defects: one is that the solvent is refluxed for dehydration, and the solvent itself will consume the hydroxyl organic matter, especially ketone solvents, which may easily cause the quality of the raw material of the hydroxyl organic matter to deteriorate; the other is that the dehydration temperature is high, and it is also easy to cause The quality of organic matter deteriorates, for example, trimethylolpropane (TMP) tends to turn yellow when the temperature is higher than 105°C, which is not conducive to the synthesis of low-color products

[0007] The process of synthesizing polyurethane prepolymer in the above patents is a batch reaction, which is not conducive to the control of product quality, and the difference between batches cannot be avoided

The reaction between NCO in TDI and OH in alcohol is a violent exothermic reaction. Improper temperature control will cause the color number of the prepolymer reaction liquid to be high. To control the violent exothermic reaction process, a large amount of condensed water is required to cool down, which will increase a lot of energy consumption

The reaction process in the above-mentioned patents does not mention how to control the temperature of the reaction, and the introduction of a solvent in the reaction process can reduce the viscosity in the reaction process, but the reaction time is prolonged due to the reduction of the concentration of isocyanate, and impurities in the solvent, Moisture, etc. will have an adverse effect on product quality, which is not conducive to the synthesis of water-white products

In addition, due to the low boiling point of the solvent, a large amount of solvent will be lost during the distillation process, which is not environmentally friendly, and the evaporated solvent will damage the vacuum system, which is not conducive to maintaining the vacuum degree, thus affecting the operation of the device and the stability of free monomers take off

The recovered solvent and TDI monomer are mixed together, because the loss of solvent and TDI cannot be measured, which makes the recycling process complicated and difficult, and the above-mentioned literature does not give a specific recycling plan

[0008] Therefore, it is necessary to solve the problems of poor product quality stability, high energy consumption in the reaction and separation process, unenvironmental protection in the separation process, complicated and difficult solvent and monomer recycling process in the prior art, and find a new preparation method.