Experimental development of the hottest water-base

2022-09-19
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Experimental development of water-based flexographic ink II

3 results and discussion

3.1 composite of water-based binder

3.1.1 Maleic Anhydride Addition rosin resin synthesis

Maleic Anhydride Addition rosin resin is composed of maleic anhydride and rosin through 1:4 addition and esterification with polyols. The structure and properties of the resin have a decisive impact on the printability and printability of ink. When synthesizing Maleic Anhydride Addition rosin resin, the following factors should be paid attention to:

1) the dosage ratio of rosin and maleic anhydride. When Rosin/maleic anhydride = 1.14 (molar ratio), the obtained resin has ideal properties in the preparation of ink binder. When Rosin/maleic anhydride is greater than 1.14, because rosin products are mainly used in automotive interior and exterior decoration and aviation, high-speed rail, marine composite profiles, the so-called high cooling content increases the brittleness of the resin, the wear resistance of ink printing film becomes poor, and the powder is imprinted; When Rosin/maleic anhydride is less than 1.14, the functionality of the system increases, resulting in an increase in the possibility of gelatinization during late esterification, and the water solubility of the resin becomes poor

2) dosage of polyol. The purpose of esterification of the addition resin with polyol is to improve the molecular weight of the resin and endow the resin with excellent physical and mechanical film-forming properties. However, in order to ensure that the resin has enough salifying property to determine the good water solubility of the resin, the addition resin can only be partially esterified to form a semi ester resin, that is, a part of the carboxyl group (-cooh) in the addition resin molecule has not been esterified, and the reactive active group is reserved for the later salifying. The dosage of pentaerythritol should account for 8% - 10% of the total resin

3) acid value of addition resin. The acid value of the resin is an index to measure the active carboxyl content in the molecular structure of the resin. The acid value is low, the water solubility of the resin is poor, but the hardness and gloss of the resin are good. On the contrary, the acid value of the resin is high, the water solubility of the resin is good, and the wettability to pigments and fillers is good, but the hardness and gloss of the resin are poor, and the water resistance is poor. The comprehensive result is that the acid value of the addition resin should be controlled within the range of 145mgkoh/g ~ 155mgkoh/g

4) conditions of process operation. The addition conditions of resin are mainly the addition temperature and time. The addition reaction between rosin and maleic anhydride is an exothermic reaction. In addition, maleic anhydride is very easy to sublimate. During the process operation, when the rosin melts, maleic anhydride should be added to the reaction system at a lower temperature. The initial temperature of maleic anhydride should be controlled at 160 ~ 170 ℃. When maleic anhydride is added, the system will automatically rise to 210 ~ 220 ℃, and the system temperature will decline after holding for 2 hours, The addition reaction reaches the end point; Esterification conditions: after addition, pentaerythritol is added into the system, and the acid value is measured at 260 ~ 265 ℃. At this stage, the air duct should be increased to make the acid value qualified in a short time as far as possible, so as not to deepen the color of the resin

3.1.2 design of lotion acrylic resin

lotion acrylic resin is copolymerized by lotion with derivatives of acrylic acid and other ethylene monomers initiated by water-soluble initiator. In order to meet the preparation requirements of water-based flexographic ink, the following factors are mainly considered in resin design:

1) functionality of acrylic resin. The functionality of acrylic resin depends on the carboxyl functional group in the copolymer molecular structure, which can be neutralized and salted in the later stage and give the resin water solubility. The carboxyl group in the copolymer molecular structure is introduced by acrylic monomer. In the copolymer design, the amount of acrylic monomer is too low, the mixing of acrylic lotion and addition resin solution becomes worse, and separation occurs, which makes the stability of ink worse. Too high amount of acrylic monomer will slow down the dryness of ink, reduce the wear resistance of printing film, and deteriorate the water resistance. According to the results of orthogonal test, the ideal dosage of acrylic monomer should be controlled in the range of 25% - 45%

2) film forming property of acrylic resin. The film-forming property of acrylic resin is mainly characterized by the glass transition temperature (TG) of the copolymer. According to the contribution of each monomer to the glass transition temperature of the copolymer, the monomer can be divided into hard monomer and soft monomer. The influence of each monomer on the glass transition temperature of the copolymer can be determined by the empirical formula 1/tg=w1/tg1+w2/g2t++ W1/tg1 determine the amount W1 of each monomer according to the expected TG and the TG1 of each monomer homopolymer. The Tg of the copolymer is too high, the printing film is brittle, and the powder is easy to fall off; The Tg of the copolymer is too low, the printing film is sticky, and the gloss is low. When the Tg of the copolymer is 65 ~ 85 ℃, the prepared water-based flexographic ink has satisfactory printability

3) the process of acrylic resin synthesis. Acrylic resin is polymerized by seed lotion. First, the polymerization system is polymerized at a lower temperature (75 ~ 85 ℃) to produce active seeds, and then the polymer material chelated with zn2+ and 4-butylammonium bromide act together to further polymerize the active seeds with unpolymerized monomers at a higher temperature (85 ~ 95 ℃). By using this seed lotion polymerization, all monomers in the reaction system can participate in the copolymerization. The test results show that there is no free monomer in the system. On the one hand, the yield of copolymer can be improved by seed lotion polymerization, and the lotion is safe and environmental friendly because there is no free monomer in it; On the other hand, the obtained lotion and Maleic Anhydride Addition rosin resin solution have good mixing, which enables enterprises from top to bottom to actively fulfill the provisions of risk management and control, and meet the preparation requirements of water-based flexographic ink. (to be continued)

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