Rosin-modified phenolic resin is mainly composed of rosin, alkylphenol, polyol and formaldehyde, etc. After a certain condensation polymerization reaction to obtain high molecular weight, low acid value resin. Due to its unique honeycomb structure characteristics, it can be well wetted with pigments, and it can get a certain viscoelastic binder by proper reaction with gel agents, which is widely used in lithographic inks. The experimental results show that the performance of the resin depends largely on the type of alkylphenol. The phenols currently used in rosin-modified phenolic resins are tert-butylphenol, octylphenol, nonylphenol, dodecylphenol, etc. There are also phenol, bisphenol A, which is poor in oil solubility. The use of higher alkylphenols makes the resin have good solubility, higher viscosity and larger molecular weight, which can basically meet the needs of high-speed printing and the large-scale use of aromatic-free mineral oil. The length and the degree of branching of the alkyl phenol have a great influence on the reactivity of the condensate, the softening point and the capacity of the rosin modified resin.
One. Synthesis process of rosin modified phenolic resin
Rosin modified phenolic resin is still characterized by the traditional synthesis process. The characteristic of the one-step method is that phenol, aldehyde and other raw materials are directly reacted with rosin after mixing, the process is simple, but the subsequent steps such as temperature increase control requirements are high; the two-step method is characterized by the pre-synthesis of phenolic condensate intermediates, and then with rosin The system reacts to form a resin with low acid value, high softening point, and considerable molecular weight and certain mineral oil solvent solubility through each specific reaction stage.
1. One-step process
One-step reaction principle:
① Synthesis of resol phenolic resin:
Add alkylphenol to the molten rosin, paraformaldehyde exists in the system as particles, then decomposes into monomer formaldehyde, and polycondensation occurs with the alkylphenol.
② Formation of methine quinone
Dehydration at elevated temperature. During the heating process, the activity of the methylol group in the system increases rapidly. Dehydration within the methylol molecule occurs, and the condensation etherification reaction between the methylol molecules forms various phenolic forms with different degrees of polymerization. Condensate.
③Addition of rosin with methine quinone and maleic anhydride
Add maleic anhydride at 180℃, use the unsaturated double bond of maleic anhydride and the double bond of rosin acid, at the same time, dimethyl quinone and rosin acid also undergo Diels-Alder addition reaction to form maleic anhydride. Benzodihydrofuran compound.
④Esterification of polyol
The presence of a large number of carboxyl groups in the system will destroy the balance of the system and cause the resin to become unstable. Therefore, we add a polyol, and use the esterification reaction between the hydroxyl group of the polyol and the carboxyl group in the system to reduce the acid value of the system. At the same time, through the esterification of polyol, a polymer suitable for offset printing ink is formed.
2. Two-step process
Two-step reaction principle:
① Under the action of a special catalyst, formaldehyde forms a variety of resol phenolic oligomers containing a large amount of active methylol in the solution of alkylphenol. Since the system has no inhibitory effect of rosin acid, it is possible to synthesize condensates of more than 5 phenol structural units.
②The polyol and rosin are esterified at high temperature, and under the action of an alkaline catalyst, the desired acid value can be reached quickly.
③ In the reacted rosin polyol ester, slowly add the synthetic resole phenolic resin, control the rate and temperature of the drop, and the drop is completed. Dehydration at elevated temperature eventually forms the desired resin.
The advantage of the one-step process is that the waste is removed in the form of steam, which is easy to handle in an environmentally friendly manner, but the phenolic condensation reaction that occurs in the molten rosin is prone to many side reactions due to the high reaction temperature and uneven dissolution, so the detection and quality of the condensation product Adjustment is difficult to control and it is difficult to obtain stable resin products. The advantage of the two-step method is that phenolic condensation oligomers with relatively stable structure and composition can be obtained, each reaction stage is easier to monitor, and the product quality is relatively stable. The disadvantage is that the traditional phenolic slurry condensate must be acid-neutralized and rinsed with a large amount of water for many times to remove salt before it can react with rosin, which generates a large amount of phenol-containing wastewater, which causes great damage to the environment and consumes a lot of time.
One-step method and two-step method are right or wrong, and have been the focus of ink manufacturers for a long time. However, with the successful development of the no-wash method to synthesize the phenolic condensate process route, it has effectively promoted the more rationalization of the two-step process route.
Second. Development of resin binder
Ink binders are still dominated by rosin-modified phenolic resins. Looking at a large number of patent documents published in recent years, the main work still focuses on how to choose alkylphenols, fatty acids or fatty acid-modified alkyd resins, and various modifications. Sexual craftsmanship. In addition to adapting to the trend of ink solvent dearomatic hydrocarbons, general lithographic inks contain aromatic hydrocarbon solvents of 10% to 30%, the removal of aromatic hydrocarbons to less than 1%, the aniline point will rise above 10 ℃, which will greatly reduce the solubility of the resin and make the ink The fluidity and gloss become worse, and it is necessary to use a more soluble resin to adapt to it. To meet the needs of manufacturing lithographic inks by the squeeze water process, manufacturing lithographic inks by the squeeze water process is considered to be the most efficient, good quality, and low-cost production method that kneads and dehydrates wet pigments and binders at a certain temperature The pigment particles can be directly dispersed into the ink binder. According to the size and surface treatment of the pigment particles, the binder must be controlled to have the appropriate surface tension and water resistance. The low polarity, high solubility, and high molecular weight rosin must be controlled. The connecting material made of modified phenolic resin is suitable for the manufacturing process of water extrusion ink.
The development of inks is inseparable from the development of resins, adapting to the development of the printing industry, stabilizing the quality of resin products, perfecting production processes, and developing new products will be the focus of future development of resins.