Progress modified waterborne polyurethane coatings

Polyurethane ( also known as polyurethane ) is the structure of the main chain polymer containing urethane (-NHCOO-) repeating unit [ 1 ] , usually by the polyisocyanate and active hydrogen-containing polymeric polyol reaction . Waterborne polyurethane (WPU) is water instead of organic solvents as the dispersing medium polyurethane systems , the formation of the WPU emulsion and film has excellent mechanical properties , abrasion resistance, aging resistance , chemical resistance and other characteristics, can be widely for lightweight textile, leather processing , paints , construction and paper industries [ 2 ] .

With the world 's increasing emphasis on environmental protection , more and more scholars committed to the development of waterborne polyurethane coatings , effectively limiting toxic volatile organic solvents. Although water-based polyurethane has some excellent performance, but there are still many shortcomings. Such as low hardness, solvent resistance and poor surface gloss differential , the disadvantages of poor film texture . Since the aqueous polyurethane applications , there are many practical problems , so it needs to be modified [ 3 ] . Its methods include modified epoxy modified acrylic modified silicone-modified , modified nano-materials , composite modification . This paper reviews recent progress in the new two-component waterborne polyurethane modified waterborne polyurethane coatings development and research , and make prospects for future research .

A two-component waterborne polyurethane coatings ·

Two-component waterborne polyurethane coatings is the isocyanate containing active curing agent and an active hydrogen -containing aqueous polyurethane isocyanate reactive composition . Addition reaction between the hydroxyl groups generated by the urethane groups in the molecule two or more , the film forming during the reaction and form a crosslinked structure . Two-component solvent-based polyurethane coatings and waterborne polyurethane coatings combine to form an environment -friendly paint [ 4-5 ] .

Currently , more research is the use of a dispersion polyol ( also called second -generation aqueous hydroxy resin ) preparing an aqueous polyurethane. The polyol preparation method : first synthesized in an organic solvent containing the hydrophilic ionic or nonionic resins segment , the resin melt or solution is then dispersed in water that is obtained . Two-component polyurethane polyol dispersion coating prepared with good performance, good appearance of the coating has excellent mechanical properties , chemical resistance and abrasion resistance , and by adjusting the number of the urethane bond to determine the film properties. Accordingly , polyurethane polyol dispersions are preferably two-component polyurethane coating hydroxyl component .

ZHANG Xu et al [ 6 ] isophorone diisocyanate , a polyether diol , dimethylol propionic acid (DMPA), trimethylol propane (TMP) was prepared from the polyurethane end -NCO prepolymer and then diethanolamine (DEA) to introduce a hydroxyl -terminated polyurethane polyol dispersion component synthetic two-component waterborne polyurethane . Found : When the mass fraction of DMPA 6% -6.5%, DEA mass fraction of 7.61%, TMP content of 3% -5%, nNCO: nOH is 1.5-1.7 , the coating solvent resistance , water resistance, gloss, hardness, optimal . Wu Shenghua et al [ 7] the two-component acrylic latex modified hydrophilic polyol and 1,6 - hexamethylene diisocyanate (HDI) trimer mixture system . The results showed that: when the hydroxyl content of 2.3% , hardness monomer ratio of 1:1 , a polyisocyanate resin, a curing agent and a hydroxyl group -NCO:-OH is 1.2 to 1.4 , the good performance of the resulting coating film . The two-component solvent-based polyurethane coating and coating performance comparison , its overall performance close to the corresponding two-component solvent-based polyurethane coating , and greatly reduce the VOC content , in line with environmental requirements. Lu Cheung et al [ 8] trimethylol propane triacrylate (TMPTA) as internal cross -linking monomers by seed emulsion polymerization and crosslinking monomer synthesis process dropwise hydroxy Break polyacrylate emulsion and prepared as an aqueous two-component polyurethane coatings. Performance tests show that TMPTA was 2% when the total mass of the monomers , the emulsion stability is good , the gel was only 0.26% ; better overall properties of the film hardness, the degree of crosslinking and gloss . ZhouXinhua [9 ] The water-soluble acrylic resin , and 1,6 - hexamethylene diisocyanate (HDI) biuret mixture was diluted with water to prepare an aqueous two-component polyurethane. Experimental results show that the polymer has a core - shell structure , HDI biuret and acrylic resin 12h to complete reaction. The effects of acrylic resin content of two-component waterborne polyurethane performance , results showed : polar acrylic resin and HDI biuret mixed two-component waterborne polyurethane is the degree of crosslinking of the key factors. Tang Jinwei et al [ 10 ] considered diphenyl methane diisocyanate (MDI) waterborne curing agent will create a two-component waterborne polyurethane coatings development situation. MDI hardener two -NCO groups are connected with a benzene ring , the monomer selection, hydrogenation, or change the method of controlling the benzene structure of the active -NCO , even with an aliphatic isocyanate comparable available polyurethane waterborne curing agent .

2 · waterborne polyurethane coatings modified

2.1 acrylate -modified

Polyacrylate based material compared with the polyurethane material in water resistance, solvent resistance , weatherability and gloss retention , etc. exhibit good performance , while the polyurethane resin strength , flexibility, and performance aspects of the outstanding performance of the adhesive , so that their have a good combination of complementary , both the overall performance of both [ 11 ] by the modified waterborne polyurethane material . Acrylate (PA) of the aqueous polyurethane (PU) with the chemical modification of the methods of modification and physical modification. Chemical modification is added to the PU emulsion PA , then through a radical polymerization initiator and the obtained hybrid emulsion (PUA). Prepared chemically modified core - shell structure is an effective method in the PU micelles mechanism having a hydrophilic outer surface ionic groups , PA particles having a hydrophobic group and inversely to the outside- swellable PU the particle polymerization , to form the shell PU , PA nuclear core - shell latex particles . Physical modification is the PA and PU physical blending, improve the mechanical properties of the material. Good physical method using a modified PA requirements emulsion ion stability and better affinity for the solvent , otherwise breaking may occur. In addition , paper cups PUA composite emulsion can also be obtained by crosslinking or interpenetrating network (IPN) and other methods. Crosslinked composite emulsion preparation process is complex , can be divided into blending method , capping method and grafting method. IPN refers to a linear PA and PU , respectively , and form a network , the entanglement between the molecular chains is not present.

Wang Qiao et al [ 12 ] using the seed emulsion polymerization method to diacetone acrylamide, hydroxyethyl acrylate functional monomers, adipic acid dihydrazide and polyurethane containing polyisocyanate based curing agent prepared ketone hydrazine , isocyanate based dual self-crosslinking polyurethane - acrylate hybrid emulsion. The study found that the degree of crosslinking emulsion composite film after more than 90% , and significantly improve the hardness , water resistance to organic solvents , has a good application performance. WangXin et al [13 ] first introduced acrylic based on polyurethane backbone and antimony -doped tin oxide (ATO) nanoparticles were prepared by ultrasonic dispersion multifunctional waterborne polyurethane coatings. By infrared spectroscopy (IR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (DTG) and so on structure and properties of coatings were analyzed. Experiments show that , WPUA / ATO coatings with good mechanical properties and thermal stability. WPUA / ATO coating can absorb near-infrared radiation , so it will prevent heat transfer and thermal diffusion effect. Liang Fei et al [ 14 ] were prepared using acrylate-modified core - shell structure waterborne polyurethane emulsion , and characterized by the shape and structure of the emulsion IR, TEM, DSC , etc. ; research polymerization temperature acrylate amount , causing agents influence the type and amount of emulsion and film properties .

The results show that , PUA composite emulsion product was prepared having a core - shell structure at a polymerization temperature of 70 ℃ -75 ℃, oil-soluble initiator, azobisisobutyronitrile , the amount of 2.0 % to 2.5 % to obtain better performance emulsion , PUA film water resistance , stability and a significant improvement in mechanical properties . Parmar [15] , such as the use of epoxy - acrylate graft copolymer prepared with PU modified PUA emulsion. The results show that the modified electrochemical properties and mechanical properties of the emulsion and film has improved significantly. FU and blue [ 16] In trimethylol propane (TMP) as crosslinker EP -modified PU, then methyl methacrylate (MMA) free radical polymerization, epoxy urethane - acrylate (WPUEA ) hybrid dispersion. The results show that the modified epoxy resin EP and MMA WPU, preparation of EP / PUA excellent dispersion properties , WPUEA modified film has good mechanical properties and solvent resistance.

2.2 Epoxy -modified

Epoxy (EP) materials with high mechanical properties , strong bond , good stability and excellent processing performance, etc., and contains lively epoxy, PU reaction can be directly involved [17 ] . Common epoxy-modified isocyanate is a hydroxyl group reactive with an epoxy resin , so that between the network between the PU and EP have certain chemical links , form an interpenetrating network structure , to improve the mechanical properties of the PU coating , solvent resistance, water resistance and heat resistance . EP modified method often used in mechanical blending and copolymerization . A carboxyl group and the hydrophilic group and the polyether segment EP -free chemically blended PU mechanical binding , hydrophobic interactions using the EP and PU , the PU coated EP so as to achieve the purpose of modification . The copolymerization reaction is grafted onto the EP PU chain. In short, the method of forming the emulsion blend has better stability than the copolymerization .Sellotape


QuJinqing [18] In EP, polyether, toluene diisocyanate (TDI) and dimethylolpropionic acid (DMPA) as a main raw material for preparing an aqueous polyurethane coating . Studies have shown that the aqueous polyurethane coating with lower hardness and tensile strength values ​​of the epoxy resin and the epoxy value increases with the decrease of elongation at break . After adding the resin used in the experiment the way to improve the stability of the waterborne polyurethane emulsion . Performance tests show that after waterborne polyurethane modified epoxy resin coated with high hardness, solvent resistance and good.黄先威et al [ 19 ] studied the amount of modifier EP , adding affects the way , the reaction temperature on emulsion stability , analysis of the factors affecting the performance of the coating , the experimental results show that when the EP mass fraction more than 7% , the pre- polymer viscosity is too large, and the emulsion stability deteriorated . Because with the EP may increase , increasing crosslinks formed between the latex particles and precipitation. Wang Huan et al [20 ] E-44 of epoxy resin as modifier , isophorone diisocyanate (IPDI), dimethylol propionic acid (DMPA), polyester polyol (POL-220), poly polyol (PPG-220) and other raw materials for the synthesis of a series of experiments epoxy resin modified waterborne polyurethane emulsion . Studied the epoxy , DMPA and polyester polyols addition on emulsion and film properties . Experimental results show that : the mechanical properties of the modified resin, a water resistance and thermal properties of the polymer film are improved. When W ( polyester ) = 20.0%, W (DMPA) = 3.9%, W (E-44) = 8% , the best overall performance of waterborne polyurethane modified . Wei et al [ 21 ] to isophorone diisocyanate (IPDI), poly adipic acid 1,4 - butanediol ester (PBA), hexamethylene diisocyanate (HDI) as the main raw material experiments to a 4 - butanediol chain extender is a small molecule , with sodium ethylene diamine group b is a hydrophilic chain extender , epoxy resin E-51 as a modifier , prepared by a solid content of 50% sulfonate -type epoxy resin modified waterborne polyurethane emulsion (SWPU). Experiments discussed the emulsion particle size and distribution and the impact on the amount of the epoxy film mechanical properties ; using DTG, IR, NMR and other means of detection of the film 's structure and thermal stability were analyzed . The results showed that: the epoxy and hydroxyl groups involved in the reaction of the epoxy groups , and generates a new aqueous polyurethane structure ; with increasing ethylene content, the wider the particle size distribution of the emulsion ; When the amount is less than 4% of ethylene , the tensile strength increased significantly ; thermal stability of the film increases with the amount of epoxy .

2.3 silicone modified

Silicone repeating silicon-oxygen bond is a main chain , a polymer of an organic group connected to the silicon atom. And the silane monomer is usually collectively referred to as the polysiloxane silicone . Silicone has a fire , weather , water , and good stability . Research scholars advantages of polyurethane and silicone combine to give excellent performance materials.

殷锦捷et al [ 22 ] using the appropriate ratio of silicone and epoxy composites modified polyurethane coatings, polyurethane prepolymer discussed monomeric toluene diisocyanate (TDI) and polyether glycols (DL2000) , the modifier the addition amount , reaction time , reaction temperature and other factors result in the modification . And composite modified film characterization. The results showed that the mechanical strength of the product coating , adhesion , water absorption , thermal stability and acid resistance and other indicators are very good improvement after modification . High Mingchih et al [ 23 ] were prepared by emulsion with core - silicone modified waterborne polyurethane shell structure - acrylate hybrid emulsion. Total reflection infrared spectroscopy and photoelectron spectroscopy analysis showed that the surface of polyurethane - acrylate molecular chain has chemical type silicone segments and siloxane segments have a surface enrichment trend. Further , as the silicone content of the film increases the water contact angle increases , the water resistance is improved. Round Kang et al [ 24 ] synthesized silicone-modified WPU ( waterborne polyurethane ) using acetone emulsion. The results showed that: a silane coupling agent (KH-550) , and dimethylol propionic acid (DMPA) the feeding method on a larger stability of the aqueous polyurethane emulsion ; When W (DMPA) = 3% -5%, aqueous polyurethane the stability of the emulsion and the water resistance of the film is better . Wu Xiaobo , etc. [ 25 ] Preparation of modified waterborne polyurethane (PUDS) emulsion and coating . Experimental results show that the silicone to have access to a molecular chain of the aqueous emulsion stability and good heat resistance . Within a certain range to improve silicone oil content, hardness, and thermal decomposition temperature of the product increases , the water absorption decreased. In the amino silicone content of 6 % ​​to 9 %, the modified product with the best overall performance. Song Jianhua et al [ 26 ] using the two -step synthesis of epoxy four coordinated silicon (ETCS) modified waterborne polyurethane. The results showed that the emulsion was prepared in a translucent blue , particle radius , good stability ; coating film having high heat resistance , low water absorption characteristics. ETCS synthesis using as the aqueous polyurethane chain extenders are the various aspects of improved performance .Washi tape


Over 2.4 yuan modification method

Fang Zhenhua , etc. [ 27-28 ] with diethyl isophorone diisocyanate (IPDI), polyethylene glycol (PEG), bis (hydroxymethyl) propionic acid (DMPA) and hydroxyethyl acrylate (HEA) as the main raw material, the use of melamine as a modifier , prepared new polyurethane UV-curable coatings (UVWPU). Using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) and mechanical testing to test the performance of the coating . The results showed that the modified UV-WPU film has good high temperature , water resistance and mechanical properties. Optimum amount of melamine was 4.7% , after modification coating the glass transition temperature (Tg) increased by 20.4 ℃ and weight loss temperature increased 105 ℃. In addition, the research team also uses bisphenol A UV curable waterborne polyurethane coatings for modification experiments to study the effects of bisphenol A modified emulsion and film properties . The results show that , DMPA Increase in the amount of the emulsion storage stability , the average particle size increases with the content of the smaller DMPA ; various aspects of performance UVWPU modified bisphenol A cured film were improved . ZhangSigang [29 ] The aqueous polyurethane of microcrystalline cellulose was modified to test the potential number and size of the electric analysis hydrophilic group , found that the more strongly hydrophilic molecular chain , resulting in the dispersed particles is easier to improve the emulsion stability. In Yoshida et al. [ 30 ] castor oil , polyether glycol (PPG220), toluene diisocyanate (TDI), dibutyltin dilaurate (DBTDL), dimethylol propionic acid (DMPA), epoxy resin (E -44 ) , hydroxyethyl acrylate (HEA), trimethylol propane (TMP), epoxy-modified acrylic acid, methyl methacrylate (MMA), butyl acrylate (BA), triethanolamine (TEA), b diamine (EDA). Studied waterborne epoxy modified acrylic polyurethane coatings . The use of epoxy resin with a high modulus, high strength and good chemical resistance , etc., may be directly involved in synthesis of waterborne polyurethane , acrylic emulsion in another section also access the epoxy , so that part of the reticular formation Finally, the synthesis of epoxy resin modified waterborne PUA water resistance , abrasion resistance, alcohol , etc. has been significantly changed. As can be seen from the water-based coatings performance test results obtained , the hardness of H, excellent wear resistance, breaking the single-component waterborne polyurethane coatings soft coating , water resistance, alcohol resistance shortcomings of poor , can be widely used in high performance waterborne wood furniture coatings.Masking tape


Zhao et al [ 31 ] studied the ketone and hydrazine crosslinking waterborne polyurethane modified silane coupling double . Diethanolamine (DEA) and diacetone acrylamide (DAAM) Michael addition reaction occurs synthesis of novel polyurethane chain extender DDP (N-[(1,1 - dimethyl-2 - acetyl ) ethyl ]-β- glyoxylic aminopropionamide ) . With trimethylolpropane (TMP), polytetrahydrofuran diol (PTMG1000), isophorone diisocyanate (IPDI), dimethylol propionic acid (DMPA) as the main raw material, the use of γ- aminopropyltriethoxysilane triethoxysilane (KH550) capped on the basis of the modified polyurethane , containing keto carbonyl diol N-[(1,1 - dimethyl-2 - acetyl ) ethyl ]-β- dihydroxy- ethylamino propanamide (DDP) and 1,4 - butanediol (BDO) chain extender to prepare the side chain keto group -containing polyurethane emulsion . By adding adipic acid dihydrazide (ADH), at room temperature to obtain self-crosslinking one hydrazine crosslinking and silane coupling dual modified waterborne polyurethane emulsion . The results showed that only showed good emulsion stability and water resistance , and one hydrazide crosslinking structure is introduced to improve the thermal stability of the coating. HanYafang et al [ 32 ] using flaxseed oil on waterborne polyurethane coatings modified to study the effects of flaxseed oil ammonolysis reaction time and temperature on the structure and properties of waterborne polyurethane coatings for . Experimental structural response of waterborne polyurethane coatings at temperatures between 102 ℃ -118 ℃, reaction time 80min conditions formed by IR spectroscopy . The results show that the drying time of the coating contacting the modified significantly reduced , and stable at room temperature up to 3 months.

3 · Outlook

With further research on waterborne polyurethane synthetic polyol dispersions of two-component waterborne polyurethane coatings will become easy construction , to meet some special purpose. Research on waterborne polyurethane coatings can further develop high-performance, defect-free water-based polyurethane coating systems. Depend on the characteristics of polyurethane molecules can be cut to introduce special features molecular structure enriched polyurethane coating versatility , and constantly open up the field of application of waterborne polyurethane coatings.

Environmentally friendly waterborne polyurethane coatings has become one of the mainstream of the development of the coatings industry , but compared with solvent-based polyurethane coatings, waterborne polyurethane coatings there is low water resistance and solvent resistance, hardness and poor slow drying and other shortcomings. To use a variety of new modified method developed taking into account the special properties of waterborne polyurethane coatings to improve the performance of innovative design research ideas , with the right mix of new and conventional means of this type of modification means to enhance the performance of polyurethane . Meanwhile , grafting, filling and multi mutual improve performance polyurethane coatings also wear a good research network .Wholesale masking tape