• 2020-04-10

1.WPU extinction resin
Thometzsk et al. introduced a method for preparing low gloss powder coatings and discussed the factors affecting glossiness.In contrast, liquid coatings are easier to produce low-gloss coatings because the roughness of these particles tends to produce the desired low gloss as pigments and additives are deposited on the film surface during drying.The main preparation method of WPU matte coating is to add silica matting agent into the WPU dispersion and prepare it with defoaming agent, curing agent, thickening agent and leveling agent.The preparation method of WPU finishing agent for extinction type synthetic leather is to add extinction powder to make the finishing agent produce extinction effect.
Silica as a matting agent has a series of advantages: chemical stability, high matting efficiency, good transparency, less addition and good storage.Silica matting agent mainly consists of gaseous silica, precipitated silica and silica gel.However, when silica is used as a matting agent, such factors as pore volume, average particle size and particle size distribution, dry film thickness and whether the particle surface is treated or not will affect the matting effect.The addition of matting agent to reduce the gloss of paint at the same time also brings many disadvantages, such as the stability of the emulsion, viscosity increase;The coating increased brittleness, easy to break off, corrosion resistance, scratch resistance, bending resistance and other properties.The properties of waterborne matte varnish made by using matting emulsion and adding traditional matting powder were studied respectively. It was found that with the increase of matting powder, the viscosity of the varnish decreased rapidly.
Polyurethane is a polar elastomer with poor compatibility with silica.Therefore, it is necessary to use auxilaries or organically modified silica matting agents in the preparation process to make the silica matting agent stable and evenly dispersed in the WPU dispersion.Therefore, the production process is complicated and the cost increases.

2.WPU self-extinction resin
Self - extinction (matting)resin is not to add any matting agent, extinction powder, resin itself can produce low gloss effect.
In this paper, a kind of uniform polyurethane particles with the structure of microspheres were produced without adding matting agent, so as to produce a rough polyurethane film and produce the expected matting effect.Since made WPU matting resin, isophorone diisocyanate (IPDI), glycol (PTMG), polytetrahydrofuran dihydroxy methyl propionic acid (DMPA) as the prepolymer reaction monomer, 2 - [(2 aminoethyl) amino] ethyl sulfonic acid sodium (A95), after the hydrazine hydrate as chain extender, bismuth acid as catalyst, triethylamine (TEA) as the neutralizer was not add the matting agent since the matting resin.The prepared WPU matting resin film was analyzed by scanning electron microscope (SEM) and atomic force microscope (AFM).These surface microstructure are the most important conditions for producing low gloss.The extinction property of WPU self-extinction resin obtained by this method conforms to the extinction principle.The glossiness of film measured by burnish meter belongs to flat light range.The experimental results showed that the prepolymer was heated in sections, the catalyst dosage was 0.016%, the hydrazine hydrate was used as the chain extender, and the added amount was controlled at about 45%, and the DMPA was 2.6% (wt).Mass fraction, the same below), the pt-mg with molecular weight of 1000 is the soft segment, the A95 is 0.084%, and the R value is between 1.7 and 2.1, the polyurethane can obtain the emulsion with excellent stability and the WPU coating with good optical effect.
The preparation method of WPU self-extinction resin was developed, that is, the graft of acrylic acid which can absorb light was introduced, and the water resistance and solvent resistance of WPU resin were greatly improved.A kind of self-extinction WPU resin was developed. When the film dried and lost water, the micro-roughness of the surface increased, the gloss decreased, and the extinction effect was achieved.A kind of polyurethane A component with large particle size and crosslinked structure was synthesized and mixed with B component with small particle size.
A series of matting emulsions of polyacrylic acid series were prepared, including polyurethane - acrylate composite matting emulsions.WPU- acrylate composite emulsion was synthesized by semi - continuous emulsion polymerization.Transmission electron microscopy (TEM) showed that the morphology of latex particles changed from the original core-shell structure to an irregular half moon shape after neutralization by N, n-dimethyl ethanolamine.When the content of polyurethane is high, due to the compatibility difference between the two phases, the latex particles form microphase separation, which causes the uneven shrinkage of the emulsion film, resulting in a concave structure on the film surface and extinction.

3.Modification of WPU self-extinction resin
Due to the fact that WPU self-extinguishing resin is not added with extinction agent, its water resistance and thermal stability are poor. In order to improve the comprehensive performance of WPU self-extinguishing resin and expand the use range, it is necessary to conduct modification research on it.
EP crosslinking modified WPU self - extinction resin was synthesized by using EP as crosslinking modifier and taking full advantage of the hydroxyl group of EP and epoxy group to participate in the reaction.EP has the advantages of high modulus, high strength, strong adhesion, low molding shrinkage and good chemical stability, etc. The mechanical properties, heat resistance, water resistance and solvent resistance of the modified WPU matting resin coating film are obviously improved.The performance of WPU resin before and after modification was tested and analyzed. With the increase of EP content, the water absorption decreased, the water contact Angle increased, and the water resistance improved.The uncrosslinked modified WPU was precipitated (redispersible) after long storage, while the modified WPU after EP was emulsified with deionized water could form a regular microsphere-type stable emulsion. However, when the content of EP was too high, the stability became worse.The content of 5.0% EP was the most suitable, and the extinction performance and emulsion stability of the modified WPU extinction resin were good.
High solid content of WPU modified by epoxy resin matting resin, discusses the main factors influencing the high solid content, and the surface microstructure of the WPU film, extinction properties, hydrolysis resistance, thermal properties, mechanical properties and rubbing fastness, found that after the modification of epoxy resin, WPU film surface micro rough, comply with the requirements for extinction, and excellent comprehensive performance.
The development of WPU matting coatings is fast, but there are still some problems in application.Without adding matting agent, the matting resin can avoid the influence of matting agent on the performance, and also can achieve the same performance with the presence of silica and other matting agent, which is a breakthrough and improvement.Of course, this method of resin, performance is not perfect, so it needs to be further improved.In the future, it is necessary to strengthen the development of the production process is simple, excellent performance of the extinction resin, preparation of more excellent WPU coating.

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