Glifthal resins are the most common types of polyester ( alkyd ) resins and are polycondensation products of glycerol with phthalic anhydride . For various needs, resins are produced in a pure and modified form. Unmodified resin has a hard and brittle structure, transparent in a thin layer. Color - from yellow to dark brown. [one]
In its pure form, glyphthalic resins are rarely used because of a number of disadvantages: fragility, limited solubility, a tendency to gelation, incompatibility with many components of varnishes. To cure them, a high temperature and a long exposure time are required. The main application are glyphthalic resins modified with various additives. They have better solubility in organic solvents, compatibility with other film-forming substances. As modifying substances, vegetable oils, fatty and resin acids are used. Glyphthal resins are characterized by high electrical insulating properties and good water resistance, which allows them to be widely used for the manufacture of electrical insulating plastics, electrical insulating varnishes and paints and varnishes. Glyphthal resins have an increased heat resistance of up to 150 ° C. They differ from bakelite resins in their increased elasticity , resistance to aging at elevated temperatures, and high adhesion .
Content
Education Process
The process technology for producing pure resin consists of preheating glycerol (29.2% or 2 mol) in a reactor to 120 ° C, adding phthalic anhydride (70.8% or 3 mol), heating the molten and mixed mass to 190-200 ° C. , curing, subsequent curing and grinding. Modified resins are prepared using free fatty acids, castor oil, or in a more complicated way — by cleaving vegetable oils in pure form, followed by transesterification using the alcoholysis method. [one]
Unmodified Resins
At the beginning of the process, due to the esterification of the hydroxyl groups of glycerol, acid monoesters arise, while the acidity of the mixture is greatly reduced. Then glycerol diesters are formed. As a result of the further condensation reaction, which is accompanied by the release of water, polymers of various structures and different molecular weights are formed. The reaction of the formation of acid esters is accompanied by the release of heat without the release of water, at high speed. Condensation of acid esters proceeds more slowly and is accompanied by the conversion of linear molecules to branched and cross-linked. The acid number and the number of hydroxyl groups are reduced. [2]
In the final stage of the process, the polymerization rate increases and the solubility decreases. The reaction is stopped earlier in order to obtain a soluble product, since there is a danger of gelation - the transition of the resin from a liquid and flowing into an insoluble three-dimensional polymer.
Modified Resins
The initial stage passes through the monoglyceride with the formation of an acid ester, which can enter into further condensation with similar compounds or with molecules of the main components. Resins with low acidity and high elasticity are formed. With further heating and due to double bonds of fatty acids, resins can be converted into a three-dimensional polymer. With an increase in the fat content of the composition, a decrease in the polymerization rate, a decrease in hardness, and an increase in solubility in petroleum hydrocarbons occur.
Resin based on ricinoleic acid (castor oil) is widely used as modifying additives. Paraffin- based synthetic hydroxycarboxylic acids are also used. The introduction of saturated fatty acids (e.g. stearic acid) increases the heat resistance of the resin. In some recipes, resin acids ( rosin ) are used, which gives shine and hardness to the varnish film. Unsaturated fatty acids can achieve curing of the varnish film at 20 ° C.
Application
Glyphthalic resins are widely used in the manufacture of glyphthalic varnishes and enamels for cold and hot drying, as well as in the manufacture of nitro-varnishes and nitro-paints. Films obtained from varnishes on glyphthalic resins have good hardness, elasticity and do not soften.
- Gliftal resin modified with fatty acids of drying oils ( linseed , wood ) is used to make varnishes that dry well in air, forming elastic and weather-resistant films.
- When fatty acids are modified with semi-drying and non-drying oils ( sunflower , cotton ), glyphthalic resin is used for the preparation of hot-dried varnishes.
- Castor oil fatty acid resins (resil resins) are used in the manufacture of nitrocellulose varnishes.
- Gliphthalic resins with a high content of fatty acids (fatty resins) are used as a primer on glyphthalic varnishes.
- Gliphthalic resins with a lower fatty acid content (skinny resins) are used to make putties . [3]
When marking packages of paints based on glyphthalic resin, the letter designation GF is used .
See also
- Polyesters
- Alkyd resins
Notes
- ↑ 1 2 A. Vorobyov / Components and technologies. No. 6, 2003 // Polyester resins
- ↑ Unmodified glyphthalic resins
- ↑ Polyester (alkyd) resins