CS195782B1 - Method of producing alkyde resins - Google Patents

Description

The invention relates to a process for the preparation of alkyd resins, particularly suitable as binders for primers, which can be overcoated with both synthetic and nitrocellulose enamels.

Alkyd resins currently constitute a very large group of lacquer binders. In addition to types with a very versatile use, paint manufacturers often place very special requirements on certain types. Thus, only the type of alkyd that is resistant to aliphatic, aromatic and oxygenated solvents after drying is applicable to the primer, since additional layers of synthetic or nitrocellulose coating compositions containing said solvents are applied to the primer. Conventional types of flax or soy alkyd are unsuitable for this purpose. The paints do not give off aromatic and oxygenated solvents, especially esters, they break up and cause paint defects (lifting, wrinkling, snake skin structure). Therefore, alkyds containing a higher proportion of wood oil, which contains conjugated fatty acids, have been used for this purpose so that the coating has a higher crosslinking density after drying. Modifications of inorganic-wood alkyds with phenolic or alkyl resol resins are also known which further reduce solvent attack. However, the use of both components has disadvantages and limitations. There is a shortage of wood oil worldwide. Due to the conjugated fatty acids, the alkyds prepared therefrom have a higher tendency to gelatinize in production 1 during storage as well as to be highly cruel.

These disadvantages are solved by the invention according to which alkyds can be prepared for primers without the use of wood oil by reacting vegetable oils, polyols and carboxylic acids in two stages. SUMMARY OF THE INVENTION In the first step, it is reacted in an inert atmosphere at a temperature of 235 DEG to 260 DEG C. and for 1 to 3 hours with an iodine value of at least 178 g J / 100 g with pentaerythritol in a molar ratio of 0.20 to 260. 0.45 with catalysis of 40 to 250 g of lead and / or calcium oxide based on 1 kgmol of oil.

The reaction mixture is then cooled to 160 to 200 ° C and the partial esters thus obtained are subjected to a second step in an inert gas or azeotropic solvent medium, gradually increasing the reaction temperature to not more than 260 ° C, until the acid number falls below 15 mg KOH / gs. phthalic anhydride and benzoic acid in a molar ratio of 1.5 to 2.5 and in an amount such that the starting ratio of hydroxyl to carboxylic equivalents is 1.1 to 1.3. The resulting product is finally cooled and optionally dissolved in aromatic solvents, preferably xylene, and / or white spirit, optionally mixed with oxygenated solvents to a 40-90% solution.

The prepared alkyl serves as a binder for paints, especially for the preparation of primers. The prepared coatings dry very quickly and are recoatable and overcoated with another layer of synthetic or nitrocellulose paints. This completely eliminates the need to use wood oil, which is a worldwide scarcity, for the synthesis of alkyds.

The basic raw material is linseed oil, for which it is important that its unsaturation, expressed as an iodine value, would not fall below 178 g J / 100 g. This condition, together with others, ensures the formation of a mesh of sufficient density. The other conditions imposed on linseed oil are the same as for all other types of alkyds. Another raw material is pentaerythritite, which is a technical mixture of mono-, di- and tripentaerythrite with a minimum content of 94% by weight. monopentaerythritol.

Phthalic anhydride and benzoic acid are used as carboxylic acids. Both benzoic acids prepared by decarboxylation of phthalic acid and acids prepared by contacting may be used.

The alkyds according to the invention are prepared as follows:

Flaxseed oil was charged to the reactor and stirred at 20-60 ° C with vigorous stirring. Pentaerythritol and the catalyst are added. The reaction mixture is then heated to 240 DEG-260 DEG C. for 2 to 4 hours while introducing the inert gas, and the alcoholysis is allowed to proceed. The course can be monitored either by miscibility with methanol, preferably by changes in electrical conductivity. It stops when the optimum is reached (miscibility with methanol is at least 2.5: 1). The alcoholysis is completed within 1 to 3 hours of heating to 240 to 260 ° C. The mixture is then cooled to 160-200 ° C and benzoic acid and phthalic anhydride (or derivatives thereof) are added with stirring. The further procedure is then dependent on the equipment above the reactor. In the melting process, the reactor is sealed and a small stream of inert gas (nitrogen, CO 2, combustion gases) is discharged by the reaction water evolution. In the azeotropic process, 2 to 3 wt. (based on feed) of an azeotropic solvent such as xylene, and water is distilled off as an azeotrope. In both cases, the temperature is gradually raised, up to a maximum of 260 ° C, the usual range being 240 to 260 ° C. Polyesterification was terminated when the acid number fell below 15 mg KOH / g. The product is cooled and discharged into a container, or after cooling to 130-170 ° C. Celsius is diluted to 40-90% with aromatic solvents, white spirit, or mixtures thereof with oxygenated solvents, in particular ketones, esters and alcohols.

Although the main field of application is the preparation of primers, they can serve alone or in combination with other types of alkyds as a binder for air-drying enamels, when combined with amino resins for coatings and acid cured coatings.

He did

To a reaction flask equipped with a stirrer, a thermometer and an azeotrope was charged 1172 g (1.33 g of molybdenum oil with an iodine number of 184 g J / 100 g) and with stirring 424 g (3.03 gmol) of pentaerythritol and 0.15 g of lead oxide (112 g / kgmol of oil) Under nitrogen, heat the contents of the flask to 245 ° C, at which point the first sample is taken, followed by 15 min intervals. Cool to 170 ° C and add 204 g of benzoic acid (1.67 gmol) and 616 g of phthalic anhydride (4.17 gmol) with a ratio of hydroxyl to carboxylic equivalents of 1.15 and a molar ratio of anhydride to monocarboxylic acid of 2, 5. Add 100 g of xylene and gradually raise the temperature to 260 ° C with constant removal of the reaction water in the form of azeotrope with xylene. It is cooled to 130 ° C and diluted with a 1: 1 wt.% naphtha - xylene mixture. 60% solution. The product obtained has a consistency of 60 s (volume no. 4 ČSN 673013) and a color of 6 mg J. to stage B5 in 10 h (ČSN 673053). The prepared primer dries to stage A in 15 minutes, to stage B5 in 2 hours. After 2 hours it is recoatable and can be overcoated with synthetic enamels and in 24 hours with nitrocellulose enamel.

Example 2

To a reaction flask equipped with a stirrer, thermometer, and condenser was charged 639 g of linseed oil (0.73 gmol) having an iodine number of 178 g J / 100 g, heated to 100 ° C and 476 g of pentaerythritol and 0.06 grams were added with stirring. CaO and 0.06 g Pb (100 g CaO and 100 g PbO per kgmol of oil). The contents of the flask were heated to 250 ° C while nitrogen was passed and the mixture was cooled to 170 ° C after reaching the maximum electrical conductivity of 2.5 hours under these conditions. 305 g of benzoic acid are added, and the reaction mixture is heated to 230 ° C under nitrogen and maintained to an acid number below 30 mg KOH / g. The contents were then cooled to 180 ° C and 555 g of phthalic anhydride was added and gradually heated to 240 ° C while evacuating the reaction water through a stream of nitrogen. The reaction was terminated when the acid number fell below 15 mg KOH / g. Cool and dilute with a 1: 8: 1 white spirit: xylene: methanol mixture to a 85% solution. The product obtained has a consistency of 175 s (no. 4 ČSN 673013) and a color of 100 mg J. After siccativation (0.04 wt% Co as a metal on the wall) it dries to stage A in 20 minutes and to stage B5 in 6 hours (ČSN 673 053). The prepared primer dries to Stage A in 15 minutes and Stage B5 in 2 hours. In 1.5 hours it is recoatable with synthetic enamels and in 24 hours with nitroemail.

Claims (1)

SUBJECT Process for preparing alkyd resins suitable in particular as a binder for primers by the reaction of vegetable oils, polyols and carboxylic acids in two steps, characterized in that in the first step it is reacted in an inert atmosphere at a temperature of 235 to 260 ° C and for 1 to 3 hours Linseed oil with an iodine value of at least 178 g J / 100 g with pentaerythritol in a molar ratio of 0,20 to 0,45 with a catalysis of 40 to 250 g of lead and / or calcium oxide based on 1 kgmol of oil and the reaction mixture is then cooled to 160 g up to 200 ° C, and the partial esters thus obtained are broken down in an inert gas or azeotropic solvent medium in a second stage of the synthesis, gradually increasing the reaction temperature to not more than 260 ° C until the acid number falls below 15 mg KOH / g by polyesterification with phthalic anhydride and benzoic acid. a molar ratio of 1.5 to 2.5 and in an amount such that the starting ratio of hydroxyl to carboxyl The resulting product was cooled and optionally dissolved in aromatic solvents, preferably xylene and / or white spirit, optionally mixed with oxygenated solvents, to a 40-90% solution.