Study On Curing Conditions And Performance Of Film Formed By Cross-linking Agent HMMM With Two Resins

Water-based coatings have attracted much attention due to their environmental protection and high safety,and the application of etherified melamine-formaldehyde resin as cross-linker in coatings is in great demand.The cross-linking properties of methyl etherified melamine-formaldehyde resin with film-forming materials of mainstream coatings were studied,it is of great significance to the performance optimization of etherified melamine-formaldehyde resin and the formulation design of water-based coatings.Based on the technical requirements of the cooperative enterprise,in this paper,water-borne acrylic resin and water-borne polyurethane were selected to be cross-linked with etherified melamine formaldehyde resin to form films:a)to discuss the influence of main factors on the properties of curing films;b)to optimize the curing conditions of curing films by orthogonal experimental design;c)to compare the properties of curing films with water-borne acrylic resin and water-borne polyurethane respectively.It provides theoretical guidance for the application of methyl etherified melamine-formaldehyde resin in the field of waterborne coatings.The findings were as follows:1.Curing film formed by cross-linking of waterborne acrylic resin and methyl etherified melamine formaldehyde resin.The optimum curing conditions were as follows:the ratio of water-borne acrylic resin to methyl etherified melamine formaldehyde resin was 3:1,curing time was 40 min,curing temperature was 145℃.Under the optimum curing conditions:the gloss of the cured film was 71.3 GS,the adhesion 1 grade,the flexibility was mm,the hardness 2H,the thickness 22μm,the rate of absorbing solution（salt）4.6%,the rate of absorbing solution（acid）37.4%,the rate of absorbing solution（alkali）9.9%,the rate of absorbing solution（alcohol）33.9%,the water absorption rate 9.5%,and the crosslinking degree was 97.0%.Compared with water-borne acrylic resin,the water absorption of cured film decreased significantly,while the crosslinking degree increased significantly.The cured film contained-NH-,-OH,carbonyl,the triazine ring,ether and other functional groups.2.The thermal decomposition of water-based acrylic resin and methyl etherified melamine formaldehyde resin compound cross-linking film formation could be roughly divided into four stages.The main pyrolysis stage of curing film formation was300～460℃.Compared with water-based acrylic resin,this stage loses weight.The difference was obvious.Using the FWO method,the KAS method,the Starink method,the C-R method to calculate the mechanism function of curing film in the main pyrolysis stage was G（α）=（1-α）^-1-1;the reaction mechanism belongs to chemical reaction;the activation energy of the reaction was 224.80 k J·mol^-1,and the pre-exponential factor was 3.56×10¹⁶ min^-1.With the increase of the relative conversion,the activation energy of the cured film decreased at first and then increased.3.Water-based polyurethane and methyl etherified melamine formaldehyde resin compounded cross-linking and cured to form a film.The optimized curing conditions:solid ratio of waterborne polyurethane and methyl etherified melamine formaldehyde resin was 7.0:1,curing time 60min,and curing temperature 145℃.Under the optimized curing conditions:the cured film gloss 81.7Gs,the adhesion level 1,the flexibility 1mm,the hardness 4H,the thickness 21μm,the liquid absorption rate（salt）1.9%,and the liquid absorption rate（acid）1.1%,the liquid absorption rate（alkali）0.9%,the liquid absorption rate（alcohol）82.6%,the water absorption rate was 1.7%,and the crosslinking degree was 93.6%.Compared with water-based polyurethane,there was a significant difference in the liquid absorption rate（alcohol）of the cured film,the water absorption rate slightly reduced,and the crosslinking degree was slightly increased.The cured film contains functional groups such as the triazine ring and ether.4.The thermal weight loss of the composite film of waterborne polyurethane and etherified melamine formaldehyde resin was significantly different in the third stage.By using the FWO method,the KAS method,the Starink method and the C-R method,the mechanism function of curing film at 260～360℃,the third stage was G（α）=[（1-α）^-13-1]²,which fits the Z-L-T equations.The reaction mechanism was three-dimensional diffusion,the activation energy 276.00 k J·mol^-1,and the pre-exponential factor was 1.76×10²² min^-1.With the increase of the relative conversion,the activation energy of the cured film decreased rapidly.Water-borne acrylic resin and water-borne polyurethane were cross-linked with methyl etherified melamine-formaldehyde resin to form a composite film.The comprehensive performance of the composite films was improved under the optimized curing conditions.The reaction activation energy of the composite curing film of water-borne acrylic resin and etherified melamine-formaldehyde resin was higher than that of water-borne acrylic resin at the main pyrolysis stage,which indicated that the thermal stability of the cured film was better than that of water-borne acrylic resin at that stage,the application of etherified melamine formaldehyde resin crosslinker is helpful to improve the thermal stability of the coating.It has important theoretical guidance significance for the application of methyl etherified melamine formaldehyde resin in waterborne coatings.