Rosin resin acids contain double-chain and carboxyl-active genes, with conjugated double bonds and typical carboxyl group reactions. In addition to being prone to oxidation and isomerization, rosin also has double bond reactions such as disproportionation, hydrogenation, addition, and polymerization.
At the same time, it also has carboxyl reactions such as esterification, alcoholization, salt formation, decarboxylation, and aminolysis.
The secondary reprocessing of rosin is based on the characteristics of rosin with double bonds and carboxyl groups, and the rosin is modified to generate a series of modified rosin, which improves the use value of rosin.
Rosin resin is used in the adhesive industry to increase viscosity, change adhesive stickiness, cohesive properties, etc.
Rosin resin is a tricyclic diterpenoid compound, obtained in monoclinic flaky crystals in aqueous ethanol. The melting point is 172~175°C, and the optical rotation is 102° (anhydrous ethanol). Insoluble in water, soluble in ethanol, benzene, chloroform, ether, acetone, carbon disulfide and dilute aqueous sodium hydroxide solution.
It is the main component of natural rosin resin. Esters of rosin acids (such as methyl esters, vinyl alcohol esters, and glycerides) are used in paints and varnishes, but also in soaps, plastics, and resins.
It is a polyol ester of rosin acid. Commonly used polyols are glycerol and pentaerythritol. The polyol rosin ester is a light yellow transparent solid with a softening point of 90-110°C and an acid value of 10-20. Used to make paint, the quality is slightly higher than that of rosin calcium soap.
The softening point of pentaerythritol rosin ester is higher than that of glycerol rosin ester, and the drying performance, hardness, water resistance and other properties of the varnish are better than those of the varnish made of glycerol rosin ester.
If the corresponding ester made from polymerized rosin or hydrogenated rosin is used as raw material, the tendency of discoloration is reduced, and other properties are also improved to a certain extent. The softening point of polymerized rosin ester is higher than that of rosin ester, while the softening point of hydrogenated rosin ester is lower.
Rosin esters are refined from rosin resins. Rosin resin is made by esterification of rosin. For example, rosin glyceride is made of rosin by esterification of glycerol.
The main component of rosin resin is resin acid, which is a mixture of isomers with the molecular formula C19H29 COOH; rosin ester refers to the product obtained after the esterification of rosin resin, because it is a different substance, so it is impossible to say whose scope it is. big.
Rosin-modified phenolic resin is still mainly characterized by the traditional synthesis process. The one-step process is to mix phenol, aldehyde and other raw materials with rosin and then react directly.
The process form is simple, but the control requirements such as subsequent heating are relatively high; the two-step process is to synthesize the phenolic condensate intermediate in advance, and then react with the rosin system.
Each specific reaction stage eventually forms a resin with a low acid value, a high softening point, and a comparable molecular weight and a certain solubility in mineral oil solvents.
1. One-step process Reaction principle:
① Synthesis of resole phenolic resin: Alkylphenol is added to the molten rosin, and paraformaldehyde exists in the system in granular form, and then decomposes into monomer formaldehyde, which undergoes a polycondensation reaction with alkylphenol.
② Formation of methine quinone: dehydration at elevated temperature, in the process of heating up, the activity of methylol in the system increases rapidly, the dehydration within the methylol molecule occurs, and the condensation etherification reaction between the methylol molecules occurs, forming A variety of phenolic condensates with different degrees of polymerization are available.
③ Addition of rosin to methine quinone and maleic anhydride: Add maleic anhydride at 180 °C, use the unsaturated double bond of maleic anhydride and the double bond in rosin acid to add, and simultaneously add methine quinone to rosin. The acid also undergoes a Diels-Alder addition reaction to produce maleic anhydride chromofuran compounds.
④ Esterification of polyol: The existence of many carboxyl groups in the system will destroy the balance of the system and cause the instability of the resin.
Therefore, we add polyols and use the esterification reaction between the hydroxyl groups of polyols and the carboxyl groups in the system to reduce the acid value of the system. At the same time, through the esterification of polyols, high polymers suitable for offset printing inks are formed.
2. Two-step process Reaction principle:
① Under the action of a special catalyst, formaldehyde forms a variety of resole phenolic oligomers containing a large amount of active methylol in the solution of alkylphenol. Since the system has no inhibitory effect of rosin acid, condensates with more than 5 phenolic structural units can be synthesized.
② Polyol and rosin are esterified at high temperature, and under the action of basic catalyst, the required acid value can be reached quickly.
③ In the rosin polyol ester that has been reacted, slowly add the synthesized resole phenolic resin dropwise, control the dropwise addition rate and temperature, and complete the dropwise addition. Dehydration at elevated temperature, and finally the desired resin is formed.
The advantage of the one-step process is that the waste is removed in the form of steam, which is easy to deal with in environmental protection. However, the phenolic condensation reaction that occurs in the molten rosin is prone to many side reactions due to high reaction temperature and uneven dissolution.
The adjustment is difficult to control, and it is not easy to obtain stable resin products. The advantage of the two-step method is that a phenolic condensation oligomer 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 pulp condensate must be neutralized by acid and rinsed with a large amount of water to remove salt before it can react with the rosin, resulting in a large amount of phenol-containing waste water, which causes great damage to the environment and consumes a lot of time.
The question of the right and wrong of one-step and two-step processes has long been the focus of ink manufacturers. But recently, with the successful development of the no-wash method for synthesizing phenolic condensate, the rationalization of the two-step synthesis method has been strongly promoted.
