CS248787B1 - Process for preparing isophthalic acid alkyd resins - Google Patents

Abstract

The solution relates to a method for preparing alkyd resins carried out in two stages, with the first stage performing transesterification and the second stage polyesterification of the obtained intermediate product with polyalcohols. The purpose of the invention is to improve the solubility of isophthalic acid in the reaction mixture, which leads to an acceleration of the acidolysis process, a decrease in the reaction temperature and thus to energy savings and an increase in the production capacity of the device. This is achieved by subjecting vegetable oils or their mixtures with acyclic monocarboxylic acids containing 7 to 22 carbon atoms to transesterification with technical isophthalic acid in the presence of a monohydric to tetrahydric alcohol or alkyl ether alcohol and optionally organic solvents until an acid number of 80 to 150 mg KOH . g"1 is achieved.

Description

The invention relates to a process for the preparation of isophthalic acid alkyd resins by a two-step solvent process.

Among the most widespread synthetic binders of paints are alkyds. They are reaction products of polyalcohols, aromatic dicarboxylic and acyclic monocarboxylic acids. The synthesis of alkyds is based on a direct one-step esterification of the starting components or more often on a two-step process. It is based on natural oils which are first subjected to alcoholysis or acidolysis and then to esterification.

Depending on the amount of acyclic monocarboxylic acids or starting oils, the alkyds are distinguished by an oil length ranging from 25% to 75%. Depending on the type of oil used, the alkyds are divided into drying and non-drying (J. Mleziva et al .: Polyesters, their production and processing, 2nd ed., Prague, SNTL 1978). Most alkyds are well pigmented, have excellent film-forming properties, and the coating films are cured by drying or firing. The coatings obtained are adhesive, chemically resistant and durable. The drying alkyds dry in the air in the presence of desiccants already at room temperature. Non-drying alkyds need the addition of curable binders and firing at temperatures between 120 ° C and 180 ° C for crosslinking.

Alkyd resins are branched polyesters in terms of their structure, where, in addition to the acyclic monocarboxylic acids, almost always dicarboxylic acids, most frequently benzene dicarboxylic acids, act as carboxyl components. Depending on the type of dicarboxylic acid used, the preparation process can also be adapted. Most often it is based on vegetable oils, which are subjected to transesterification by polyalcohols. When isophthalic acid is used, the vegetable oil may also be transesterified at 250 to 280 ° C (British patent 923 857, Belgian patent 831 587). After the transesterification, the preparation of the alkyd resin is completed by addition of a polyol and subsequent polyesterification with water removal. The problem in this synthesis is the low solubility of isophthalic acid in the reaction mixture and its escape by sublimation.

These problems are solved by the present invention, which relates to a process for preparing alkyd resins based on technical isophthalic acid, polyalcohols, vegetable oils and possibly other reactants in two stages, wherein in the first stage vegetable oils are re-esterified at temperatures of 250 to 280 ° C. isophthalic acid and in the second step, the preparation is completed by polyesterification of the intermediate obtained with polyalcohols or other components at temperatures of 220 to 260 ° C until the acid value of the end product is below 15 mg KOH. G

The essence of the invention is that vegetable oils or mixtures thereof with acyclic monocarboxylic acids having 7 to 22 carbon atoms are subjected to transesterification with isophthalic acid in the presence of 0.5 to 15% by weight. % of a monovalent to tetravalent alcohol or an alkyl ether alcohol, and optionally 1 to 15 wt. organic solvents from the group of aromatic hydrocarbons boiling in the range of 110-150 ° C, ketones and ether esters until the acid value of the resulting reaction intermediate is 80-150 mg KOH. g.

All types of isophthalic acid oil alkyds can be prepared as described. The addition of a proportion of monovalent to tetravalent acyclic alcohol or alkyl ether alcohol, preferably volatile monoethylene glycol, monopropylene glycol, in addition to the optional addition of the specified organic solvents, already removes a number of well known difficulties in the preparation of isophthalic alkyds in the first step of the reaction. Above all, the sublimating isophthalic acid leakage from the reaction mixture and thus the abnormality of the resin and the loss of valuable raw material. In addition, subsequent blockage of the transfer tube and coolers leads to the necessity of dismantling the equipment or difficult cleaning.

By improving the miscibility of the reaction components with one another in the presence of alcohols and the specified organic solvents, the reaction or the reaction is significantly shortened. the reaction can be carried out at the same rate at temperatures 10 to 20 ° C lower than those previously known. This leads to energy savings and increased production capacity of the plant.

The starting reactants of the alkyds of the present invention are vegetable oils or acyclic monocarboxylic acids, polycarboxylic acids, polyalcohols, monocarboxylic aromatic acids or functional or substituent derivatives thereof. Furthermore, organic solvents are also used.

Of the vegetable oils, non-drying, semi-drying or drying oils are used, in particular castor oil, castor oil, soybean, sunflower, rapeseed, safflower, linseed or acyclic monocarboxylic acids derived therefrom. Synthetic acyclic monocarboxylic acids may also be used.

Cyclic carboxylic acids and their derivatives include, in particular, industrial isophthalic acid, which always contains 1 to 25% terephthalic acid. Further, they are orthophthalic, tetrachlorophthalic, tetrahydrophthalic, 3,6-endomethylenetetrahydrophthalic and hexahydrophthalic anhydrides. Naphthalenedicarboxylic acids, dimerized unsaturated acyclic acids, trimellitic or pyromellitic anhydride can also be used. In addition to the most commonly used aromatic dicarboxylic acids, aromatic monocarboxylic acids such as benzoic acid, p-tert-butylbenzoic acid, m- and p-hydroxybenzoic acid are optionally added.

The alcohol component of the alkyds consists of polyalcohols having 2 to 6 hydroxyl groups. The technically most important polyalcohols are glycerol and pentaerythritol. Ethylene glycol, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, 1,2,6-hexanetriol, 1,2,3-trihydroxybutane, 2,3,4-pentanetriol, propylene glycol and sorbitol are also used. The polyalcohols are used singly or in mixtures with one another.

The first step of the preparation of the alkyds of the present invention is acidolysis and simultaneous esterification with a proportion of polyalcohol in the presence of organic solvents;

For the first stage, the most suitable solvents are ketones and ester esters and combinations thereof with aromatic hydrocarbons, the second stage being conducted in the presence of aromatic hydrocarbons or mixtures thereof with ketones. As the ketone, for example, cyclohexanone, methylcyclohexanone, methyl isobutyl ketone, aromatic hydrocarbons such as xylene and toluene can be used. Furthermore, ethers such as methoxyethylene glycol acetate, ethoxyethylene glycol acetate can also be used. The solvents in the first phase contribute to the flushing of isophthalic acid. They can be used both individually and in mixtures with one another.

According to the invention, the most common preparation is as follows: The synthesis takes place in a stirred reactor equipped with a heating and cooling device, an azeotrope adapter and optionally a viscosity measuring device. The process is carried out in a two-step process by first reacting the vegetable oils with industrial isophthalic acid, a small amount of polyalcohol and optionally a monocarboxylic acid at a temperature of 250 to 280 ° C for 0.2 to 3 hours. The reaction proceeds without catalyst in the presence of organic solvents. A polyalcohol and optionally other monocarboxylic and / or dicarboxylic acids or derivatives thereof are added to the resulting equilibrium mixture. The monocarboxylic acids may also be added in the first step. The invention is illustrated by the following examples.

He did

A reactor equipped with a reflux condenser, a condenser and a separating vessel was charged with 455 wt. parts by weight of soybean oil and 330 wt. parts of technical isophthalic acid (terephthalic acid content is 1%) and 8 wt. parts of ethylene glycol.

After closing the reactor, 16 wt. parts of a 1: 1 mixture of methylcyclohexanone-xylene and the reaction mixture was heated to 270 ° C. After 50 minutes from reaching this temperature, the reactor is cooled to 170 ° C and 35 wt. 156 parts by weight of p-tert-butylbenzoic acid; parts of glycerol. 20 wt. parts of xylene and then gradually heated to 240 ° C while distilling off the reaction water and the added solvents. The reaction was terminated when the acid number fell below 10 mg KOH.g. The solvent mixture was distilled off and used to prepare another methylcyclohexanone-xylene mixture.

Example2 '

In a reactor equipped with a reflux condenser, a condenser and a separating vessel, 635 wt. 187 parts by weight of flaxseed oil are added, with vigorous stirring. parts by weight of technical isophthalic acid (terephthalic acid content 25%), 30 wt. parts of benzoic acid and 6 wt. parts of glycerol.

35 wt. parts of methyl isobutyl ketone and the reaction mixture was heated to 260 ° C. After 1.5 hours of reaching this temperature, the reactor contents were cooled to 160 ° C and 108 wt. parts of pentaerythritol. After addition of 30 wt. parts of xylene, the reactor contents are heated to 230 ° C. The reaction proceeds while distilling off water and added solvents and terminating when the acid number drops below 7 mg KOH.g.

Example 3

A reactor having a reflux condenser, a condenser and a separating vessel was charged with 248 wt. parts of soybean oil, 102 wt. parts of fatty acids of dehydrated castor oil, 343 wt. parts of technical isophthalic acid (terephthalic acid content 5%) and 20 parts by weight of pentaerythritol.

After adding 38 wt. of methylcyclohexanone-ethoxyethylene glycol acetate was heated to 280 ° C. After 0.5 h from reaching the temperature, the reactor contents were cooled to 175 ° C and 249 wt. parts of trimethylolpropane and 50 wt. parts of toluene. The reactor is heated to 240 ° C and polyesterification is carried out while distilling off the solvent / water mixture. This was terminated when the acid number fell below 12 mg KOH.g

For comparison, parallel experiments 1A, 2A, 3A were conducted without the proportion of polyalcohol and solvents in acidolysis. The acidolysis times were prolonged as follows: 1A for 2 hours, 2A for 3.5 hours, 3A for 1 hour. In all cases, experiments A also showed a strong sublimation of isophthalic acid.

Claims (1)

The process for preparing alkyd resins based on technical isophthalic acid, polyalcohols, vegetable oils and possibly other reactants is carried out in two stages, the first stage at 250 to 280 ° C being transesterified with isophthalic acid and the second stage completing the preparation. by polyesterification of the intermediate obtained with polyalcohols or other components at temperatures of 220 to 260 ° C until the end product has an acid value below 15 mg KOH.g, characterized in that the vegetable oils or their mixtures with acyclic monocarboxylic acids containing 7 to 22 carbon atoms are subjected to % transesterification with isophthalic technical acid in the presence of 0.5 to 15 wt. % of a monovalent to tetravalent alcohol or an alkyl ether alcohol and optionally 1 to 15 wt. organic solvents from the group of aromatic hydrocarbons boiling in the range of 110-150 ° C, ketones and ether esters until the acid value of the resulting reaction intermediate of 80-150 mg KOH.g ^{-1 is} reached.