Unsaturated polyester resins used in reinforced plastics are products of the interaction of reactive polymers and monomers. this combination was proposed by C. Ellis in the 30s, who discovered that unsaturated polyester resins obtained by reacting glycols with maleic anhydride cured into insoluble solid material by adding a peroxide initiator. Ellis patented this discovery in 1936.

Ellis later discovered that more valuable products could be obtained by reacting an unsaturated polyester alkyd resin with monomers such as vinyl acetate or styrene. The introduction of monomers significantly reduces the viscosity of the resin, which makes it easier to add initiator to the system and allows the curing process to be more vigorous and complete. In this case, the polymerization of the mixture is faster than each component separately. The right to this process was claimed in 1937; it was patented in 1941. The new materials met certain industrial needs. Now, more than 40 years later, the annual unsaturated polyester resin in the US has reached ~0.5 Mt.

Unsaturated polyester resins have a variety of properties. At room temperature, liquid resins are stable for many months and even years, but with the addition of a peroxide initiator, they solidify in a few minutes. Curing occurs as a result of an addition reaction and the transformation of double bonds into simple ones; it does not form any by-products. Styrene is most commonly used as the addition monomer. It interacts with the reactive double bonds of polymer chains, crosslinking them into a strong three-dimensional structure. The curing reaction takes place with the release of heat, which in turn contributes to a more complete process. It has been found that usually about 90% of the double bonds present in the polymer enter into the reaction during the curing of the resin. 28

Polyester resins are used in a wide range of products including boats, building panels, automotive and aircraft parts, fishing rods and golf clubs. Approximately 80% of polyester resins produced in the USA are used with reinforcing fillers, mainly fiberglass. Non-reinforced polyester resins are used in the production of buttons, furniture, artificial marble and body putty.

Unlike most other plastics, which are made from a single ingredient, the polyester resins used in AP; contain several components (resin, initiator, filler and activator). Both the chemical nature and the ratio of these components can vary, which makes it possible to obtain a large number various types polyester resins. When creating any polyester resin, they try to give it the properties necessary for a particular application.

Maleic anhydride is used as a source of reactive double bonds for a large number of unsaturated polyester resins. When it interacts with glycols (usually propylene glycol is used), linear polyester chains with a molecular weight of -1000 ... 3000 are formed. Despite the lower cost of ethylene glycol compared to the cost of propylene glycol, the former is used only to obtain a few special resins. This is due to the poor compatibility of ethylene glycol-based polyesters with styrene. In the process of esterification, the cis-configuration of maleic anhydride passes into the fumaric transstructure. This is useful due to the greater reactivity of the double bonds of the fumaric fragment in the reaction with styrene. Thus, a high degree of trans isomerization is an important factor in the production of reactive polyester resins. Despite the high degree of maleic anhydride isomerization, which reaches more than 90%, more expensive fumaric acid is used to obtain polyester resins with increased reactivity.

Other diaxial acids or anhydrides, such as adipic and isophthalic acids or phthalic anhydride, are often added to the base reagent to measure the final properties of the resin and control the number of double bonds. A typical polyester resin structure is shown below (where ^ is the alkyl or aryl group of the modifying dibasic acid or anhydride):

O O CH3 O O CH3 I

H [O-C-R-C-O-CH-CH2-O-C-CH=CH-C-O-CH-CH2 Jn he.

Due to the variety of properties and low cost, polyester resins are widely used for various products. However, processors lack knowledge of polyester resin chemistry and require ongoing technical assistance. Resin suppliers provide consumers with complete information on resin types, manufacturing techniques, prices and properties. Initiator suppliers also provide advice on the use of their products in combination with various activators and inhibitors.

The rapid development of research and application of wound materials has led to the creation of a large number of specifications and standards for their testing methods. The following ASTM standards are of interest: ASTM D2290-76. Determining the limit...

A number of tests should be carried out at elevated temperatures. It depends on the type of composite material and its area of ​​application. Conventional composites should not lose strength and modulus after half an hour exposure at a temperature of ...

Index Initial values ​​After holding at a depth of 1737 m for 1045 days Index Initial values ​​After holding at a depth of 1737 m for 1045 days А0Ж(MPa £ssh, GPa …

Polyesters are called such polymers, in the chains of macromolecules of which there are oxygen containing ether groups of the form - C - O - C - or ester groups of the form

The first type of polyesters is called polyethers, and the second type is polyesters. In woodworking, poly- or oligoesters are used in significant volumes.

Complex poly- or oligoesters are divided into saturated and unsaturated.

There are no multiple double bonds in the chains of molecules of saturated poly- or oligoethers. Saturated polyesters are obtained by polycondensation of saturated dibasic acids (or their anhydrides) with dihydric or trihydric alcohols.

Saturated oligoesters obtained in the presence of vegetable oils are called alkyd resins.

Saturated oligoether based on ethylene glycol dihydric alcohol and adipic acid has the following structure:

Unsaturated polyesters are obtained by polycondensation of unsaturated (unsaturated) dibasic acids (or their anhydrides) with diatomic or trihydric alcohols, therefore, in the chains of molecules of the resulting oligomers or polymers there is a reactive double bond - R - CH \u003d CH - R -.

An unsaturated polyester based on unsaturated maleic anhydride and ethylene glycol dihydric alcohol has the form:

The following polyester resins are widely used in woodworking:

Saturated alkyd oligoesters (glyphthals and pentaphthals), as well as

unsaturated polyether maleates or polyester acrylates.

Alkyd glyphthalic resins are synthesized by condensation of glycerol with phthalic anhydride in the presence of fatty acids of vegetable oils in the melt at a temperature of 220-240 0 C. Oligomers of the following structure are obtained:

As a result of condensation, linear and branched thermosetting oligomers are formed, which subsequently slowly solidify due to the interaction of the remaining reactive hydroxyl - OH and carboxyl groups - COOH and form network insoluble and infusible coatings.

External signs of glyphthals. These are highly viscous sticky translucent substances. The color of glyphthals is from light yellow to yellow-brown.

Basic properties. Glyphtals have a molecular weight of 1500 to 5000. They are soluble in toluene, alcohol, xylene, white spirit. Usually, glyphtals are immediately dissolved in organic solvents and solutions are obtained with an oligomer (glyphthal) concentration of 40-60%. The density of solutions is 900 - 1050 kg/m 3 .

Glyftals are thermoplastics and at room temperature they slowly cure or "dry out" as they usually say. In the absence of vegetable oils, significant shrinkage of the material is observed during curing and, after "drying", brittle coatings are formed.

To reduce shrinkage, accelerate curing and increase the elasticity of coatings, glyptals are modified with vegetable oils.

Depending on the amount of added oil, the following types of glyphthals are distinguished:

· Super-skinny GF. They contain less than 34% oil.

Skinny glyphtals with an oil content of 34% to 45%.

· Medium GF, in which vegetable oil from 46% to 55%.

· Fatty glyphtals contain from 56% to 70%.

· And very greasy glyphthals, in which oils can be more than 70%.

The operating temperature of cured coatings based on glyphthals is from - 20 0 С to + 100150 0 С.

The use of glyphthals. Glyphthalic resins (oligomers) are mainly used:

as the main component (base) of paints and varnishes (finishing) materials, such as varnishes, enamels, paints, primers

as a base for adhesives

as a binder in the production of fiberglass,

for the impregnation of textured and opaque papers in the production of paper resin films for furniture lining.

More than 70% of the total volume of produced alkyd polyester resins is used for the manufacture of varnishes and enamels. Coatings or glue joints after curing glyptals have anti-corrosion properties, pleasant appearance, good weather resistance and heat resistance up to 150 0 С.

In addition to oils for accelerated curing, accelerators are added to glyphthals - driers, mainly naphthenates or resinates of cobalt and manganese.

Pentaphtali (PF)

Alkyd pentaphthalic resins are obtained in the same way as glyphthalic resins, but instead of glycerin, a tetrahydric alcohol, pentaerythritol, is used. Get oligomers of the following structure:

As a result of condensation, branched thermosetting oligomers are first formed, which are subsequently cured due to the interaction of the remaining reactive hydroxyl - OH and carboxyl groups - COOH and form a network of insoluble and infusible coatings. The reactivity of pentaerythritol is higher than that of glycerin, so the curing of pentaphthals is faster and easier.

The external signs of pentaphthals are the same as those of glyphthals.

The main properties and applications of pentaphthals are similar to those of glyphthals.

During the curing of pentaphthalic alkyd resins, brittle coatings are also obtained and shrinkage of the material is observed, therefore alkyd pentaphthalic resins are modified with oils, urea-formaldehyde oligomers, organosilicon liquids, nitrocellulose, and other reagents. To speed up the "drying" of coatings, desiccants are also introduced into pentaphthals.

After modification, the curing rate of pentaphthals increases. Cured coatings based on pentaphthals have greater mechanical strength, service life and temperature limits of operation than coatings based on glyphthals.

Products protected by coatings based on alkyd resins can be used outdoors. Alkyd varnishes, enamels (for example, PF-115 enamel), primers, putties cover car bodies, subway cars, agricultural machinery, refrigerator cases, parquet floors, window frames, furniture details, skis and other products.

Materials based on glyphthalic alkyd resins are marked with the letters GF, based on pentaphthalic resins - with the letters PF.

Polyethylene terephthalate (PET or PET)

Polyethylene terephthalate also belongs to the group of saturated polyesters.

A saturated polyester based on ethylene glycol dihydric alcohol and terephthalic acid has the following structure:

External signs of polyethylene terephthalate. Crystalline PET is a white solid and odorless substance. Amorphous PET is a transparent, colorless polymer. Heavier than water. At temperatures above 100°C, polyethylene terephthalate is hydrolyzed (destroyed) by alkali solutions, and at 200°C even by water.

Basic properties. PET is a thermoplastic having a density of 1380 - 1400 kg / m 3 and a melting point of ~ 255 - 265 0 C. Softening temperature of ~ 245 - 248 0 C. It has high chemical resistance; in the cold, it does not dissolve in water, in traditional organic solvents, in dilute solutions of acids and alkalis. Stable in solutions of bleaching agents. It dissolves only when heated to 40 - 150 0 C in aromatic (similar in structure) hydrocarbons, such as phenol, cresol, in an alcohol-benzene mixture. Resistant to moths and microorganisms, good dielectric. Polyethylene terephthalate is characterized by high strength, resistance to abrasion and repeated deformations during stretching and bending; it is steady against action of light, x-ray, - beams. Temperature range of operation from - 60 0 С to + 170 0 С.

The use of polyethylene terephthalate. About 80% of all PET produced is used for the production of lavsan fibers. Other trade names for the fiber are terylene, dacron, tetheron, elan, tergal, tesil. The fibers do not wrinkle, have high strength, elasticity, are resistant to light and abrasion. The properties are close to acetate fibers. Modified fibers are well dyed.

PET fibers are used to make technical fabrics for overalls, tarpaulins, fishing nets, ropes, fire hoses, and belts. In addition, furniture and drapery fabrics for upholstery of upholstered furniture are produced from PET fibers.

About 20% of the produced PET is used for film production. The films are transparent, durable, do not let water vapor, oxygen, nitrogen and solvent vapors through. In this regard, they are used for food packaging, for the manufacture of bottles for carbonated drinks and juices. In addition, films are used as a substrate for various tapes for audio and sound recording, in the production of film and photographic films.

Unsaturated oligo- and polyesters

Among unsaturated polyesters, the most common products of the condensation of maleic anhydride with ethylene glycol, which are called oligoethermaleinates and have the following structure:

The resulting oligoethermaleinates contain an unsaturated bond - R - CH 2 = CH 2 - R -, which can be easily cured at room temperature without the release of low molecular weight by-products.

External signs of oligoethermaleinates. They are clear, colorless liquids of low viscosity. They let in 92% of sunlight. Do not change the natural color of the wood.

Basic properties. Oligoethermaleinates - thermoplastics with a density of 1100-1500 kg / cm 3; have a molecular weight of 300 to 3000 and are readily soluble in organic solvents and monomers. Solutions of oligoethermaleinates have a low viscosity, are transparent and do not change the natural color of the wood. They have good adhesion to fiberglass, paper and metals. When "drying", i.e. curing with the formation of a strong polymer of a network structure, minimal shrinkage of the coatings is observed.

As a rule, unsaturated oligoesters are dissolved at T = 70 0 C in the monomer (most often in styrene) and 60-75% solutions are obtained. These solutions are called unsaturated polyester resins NPS. They serve as the basis of binders in the production of fiberglass, are used for the impregnation of papers and for the manufacture of varnishes, enamels and primers.

Accelerated curing of coatings is carried out either by heating, or under the action of ultraviolet (UV) or infrared (IR) rays, or under the influence of an accelerated electron beam (EBE). Curing (crosslinking) of molecules occurs due to the opening of double bonds in the molecules of oligoethers and in the molecules of the styrene monomer, as a result of which the molecules of the oligoether are crosslinked by "bridges" of styrene molecules.

To eliminate brittleness, increase elasticity and mechanical strength of coatings, unsaturated oligo-(poly)ethers are modified with saturated acids (adipic, sebacic, phthalic). Coatings based on modified polyesters are hard, mechanically strong, glossy, have good electrical insulating properties and are resistant to water, gasoline, oils and dilute acids. Coatings are resistant to temperatures of +80 - +100 0 С.

The use of unsaturated poly- and oligoesters. From them, insulation is obtained in electrical and radio engineering, cements, self-leveling floors, as well as fiberglass. Fiberglass is used for the manufacture of bodies, bumpers, tuning parts for cars. From fiberglass impregnated with unsaturated polyester, the hulls of boats and boats are formed, and damage is repaired on the bodies of cars, boats and boats. Unsaturated polyester resins are cheaper and more convenient than epoxy resins. They are less viscous, easy to apply and cure quickly with normal conditions. Unsaturated polyester resins are well combined with various pigments, dyes, plasticizers and dry bulk fillers (chalk, talc, sand, kaolin, etc.). Decorative items are made from them by pouring into molds: accessories, figurines, buttons, etc. haberdashery products, polymer concrete and artificial stone (furniture countertops, window sills, skirting boards, fireplace lining, sinks, bathtubs, sinks, tiles).

Varnishes and primers based on unsaturated polyesters are conventionally denoted by the letters PE, PN, NPS. Lacquers are used for furniture finishing according to the highest class, for finishing television and radio equipment (for example, cold-drying varnish of the PE-265 brand).

Asbestos-cement and wood-fiber boards, honeycomb plastics and other materials are glued together with polyester adhesives.

Some properties of coatings based on the renewal of polyester resins of the usual type, as well as coatings based on nitrocellulose and urea-formaldehyde varnishes are given in Table. 122 G From these data it clearly follows that polished polyester resin coatings have a number of advantages over other materials.

They are characterized by exceptionally high gloss, transparency, excellent appearance, resistance to water, solvents and many other chemicals. In addition, polyester coatings are resistant to the flame of smoldering cigarettes and are characterized by excellent frost resistance and increased abrasion resistance.

Polyester lacquers require a single coat to achieve high quality finishes, while nitrocellulose and many other lacquers require two or three coats. Films made of polyester resins are resistant to impact loads.

The disadvantages of coatings made of polyester varnishes include the difficulty of removing the coating in case it is necessary to apply a new one. In addition, although polyester coatings are scratch resistant, scratches are more visible on them than on nitrocellulose films.

Properties of various types of coatings

As already noted, sometimes in the manufacture of furniture they do not strive to achieve the high gloss characteristic of polyester coatings.

The processing of polyester varnishes is difficult due to the need to use two-component systems, as well as due to the inhibition of their curing process by atmospheric oxygen. The last drawback has now been overcome thanks to the development of special techniques.

It is known that the surface layer of a coating made in the presence of air from conventional type polyester resin remains uncured for a long time. If the film is cured not in air, but, for example, in a nitrogen atmosphere, the process is not inhibited by atmospheric oxygen and the coating is completely cured.

When producing laminates or castings, oxygen inhibition does not play a significant role, since the surface in contact with air is relatively small compared to the volume of the product. Typically, curing is accompanied by a significant release of heat, which contributes to the formation of additional free radicals.

The drying of polyester resins in films (when the surface to volume ratio is very high) proceeds practically without increasing the temperature in the mass, since the heat of reaction in this case quickly dissipates and the formation of free radicals due to heating does not occur.

Free radicals resulting from the breakdown of peroxides or hydroperoxides initiate the copolymerization reaction of fumarates or maleates with a monomer, such as styrene. Free radicals react with styrene and fumarate (or maleate) groups of polyester, and free radicals are formed according to the following schemes:

In the presence of oxygen, the radicals arising from the decomposition of peroxides interact predominantly

This reaction is extremely fast. Thus, in the surface layer of solutions of unsaturated polyesters in styrene, the concentration of active free radicals in the presence of air decreases at a high rate, which greatly slows down the initiation of copolymerization.

It was shown that during the polymerization of styrene at 50°C, the reactivity of free radicals formed from peroxides in reactions with oxygen is 1-20 million times greater than in reactions with styrene.

Probably the most important step in the development of the polyester varnish industry was the invention of ways to eliminate the inhibitory effect of oxygen on the curing process by chemically modifying polyesters. Currently, the following methods are known for obtaining polyester varnishes, the drying of which is not subject to the inhibitory effect of atmospheric oxygen:

a) modification of acidic reagents used in the synthesis of polyesters;

b) modification of alcohol reagents;

c) modification of cross-linking agents (monomers);

d) the introduction of polymers capable of interacting with polyester resins;

e) the use of drying oils;

e) the use of polyesters with a high softening point;

g) introduction of waxes or other pop-up additives into resins;

h) coating surface protection polyester films;.

i) hot drying.

Modification of acid reagents.

Recently organized industrial production polyester varnishes based on tetrahydrophthalic anhydride ''. These varnishes form non-tacky films that dry well in air and have hardness, rigidity and excellent gloss. In table. 123 shows typical formulations and properties of polyesters synthesized using tetrahydrophthalic anhydride.

TABLE 123.

Formulations of polyesters modified with tetrahydrophthaleft anhydride and properties of resins based on them

Resin Properties

From polyester resins of this type, in the formulation of which glycerol, tris-(2-carboxyethyl)-isocyanourate or some amount of malic acid was introduced, films were obtained. In table. 124 shows the effect of the listed reagents (modifiers) on the hardness of films made at 25 ° C and 50% relative humidity in the presence of 1.5% (by weight) of a 60% solution of methyl ethyl ketone peroxide and 0.021% of cobalt introduced in the composition of naphthenate cobalt.

TABLE 124.

Sward-Rocker hardness of films based on tetrahydrophthalates synthesized with various additives

From the data in Table. 124 it follows that the hardness of coatings based on polyesters containing tris-(2-carboxyethyl)-isocyanurate units is higher than in the case of using resins of the other two types.

Obviously, all these modifiers increase the activity of the polyester in the reactions of three-dimensional network formation. There is evidence in the literature that the use of glycerol in the synthesis of tetrahydrophthalates is very promising.

Coatings on steel obtained from the three named resins are very elastic; when using polyesters modified with glycerol and tris-(2-carboxyethyl)-isocyanurate, the flexibility of the coatings on aluminum is insufficient, while the resin coatings of the third formulation have good elasticity. Films made from it also outperform others in terms of impact resistance.

It was found that changing the ratio of polyester and styrene or the amount and composition of the initiator and accelerator does not significantly affect the properties of the coatings.

On the contrary, significant differences in the properties of the coatings are observed when replacing polyester in the formulation.

diethylene glycol 1,2-propylene glycol or dipropylene glycol (see table. 123). A change in the ratio of fumaric and tetrahydro-phthalic acids also has a great influence. Thus, the scratch resistance of films increases with an increase in this ratio and decreases with the introduction of propylene and dipropylene glycol into the composition of the initial polyester.

Since the reactivity of tetrahydrophthalic anhydride in reactions with glycol is higher than that of phthalic anhydride, the polycondensation process can be carried out at lower temperatures. Polyester films modified with tetrahydrophthalic anhydride have higher hardness and gloss than films based on phthalates.

As already mentioned, the patent literature provides data on modifying the properties of tetrahydrophthalates by introducing glycerol, malic acid, or tris-(2-carboxyethyl)-isocyanurate into the polyester formulation (Table 125).

TABLE 125.

Formulations of tetrahydrophthalates with additives of modifiers and properties of resins based on them

In all three recipes given in. table, the molar ratio of tetrahydrophthalic anhydride and fumaric acid was 1:1. Acid modifiers were introduced in an amount corresponding to 0.5 g-equiv of carboxyl groups, and the total ratio of carboxyl and hydroxyl groups was 1: 1.05. From the synthesized polyesters, 50% solutions in styrene were prepared and films were obtained in the presence of a 1.5% solution (60%) of methyl ethyl ketone peroxide and 0.021% of cobalt introduced in the form of cobalt α-naphthenate.

All of these films passed the scratch resistance test for 30 days. In all cases, the scratch resistance of the films increased with time. Heat treatment at 50°C also had a positive effect; at the same time, high durability of the coatings was achieved.

Rice. 42. Influence of the ratio of acidic reagents in the polyester formulation on the scratch resistance of films from cured resins. The numbers on the curves are the content of styrene in the initial solutions.

It has been found that the scratch resistance of coatings increases with increasing resin crosslink density (Fig. 42). As can be seen from the figure, within the studied limits, cured products based on more concentrated styrene solutions have better resistance.

The tackiness of coatings made of highly unsaturated polyesters (with a high content of fumaric acid) disappears faster than when using products of a low degree of unsaturation, although for polyesters modified with tetrahydrophthalic anhydride, in all cases, the formation of non-tacky films is characteristic in air.

It should be noted that such coatings do not always have satisfactory hardness and scratch resistance (Table 126). Thus, films produced using diethylene glycol polyesters have better hardness and scratch resistance than coatings based on 1,2-propylene glycol polyesters. Replacing diethylene glycol with 1,3-butylene-, 1,4-butylene-, and neo-pentyl glycol, 2-methyl-2-ethyl-1,3-pentanediol, or hydrogenated bisphenol A eliminates surface tack, but worsens the scratch resistance of the films.

TABLE 126.

Surface Properties of Polyester Resin Coatings Modified with Tetrahydrophthalic Anhydride

As already noted, the scratch resistance of films obtained from solutions of tetrahydrophthalates increases with time and becomes constant only 12–16 days after their application. Peak Sward-Rocker hardness values ​​are usually reached one week after film application.

Coatings based on tetrahydrophthalates are superior in scratch and impact resistance to coatings made using polyester resins industrial type containing no waxy additives. However, they are inferior to them in hardness.

Modification of alcohol reagents.

In the early stages of research, it was proposed to use diols of a special type, for example, endo-methylenecyclohexyl-bis-methanediol (a product of the Diels-Alder reaction) or 4,4- (dioxydicyclohexyl) -alkanes, to obtain so-called "non-inhibited" varnishes. These compounds have been used to partially or completely replace conventional type glycols. Since coatings based on such polyesters turned out to be insufficiently hard and resistant to scratching and solvent action.

supporters, they did not find industrial applications. Much later, in the FRG and the USA, it was simultaneously established that the introduction of p-unsaturated ether residues into polyesters leads to a noticeable decrease in the inhibitory effect of atmospheric oxygen on the curing process of polyester resins.

The consequence of this discovery was the use for this purpose of a number of p, y-alkenyl ethers of mono- or ^-polyhydric alcohols. It has been found that partial replacement (in the polyester formulation) of conventional glycols with α-allyl ester of glycerol results in products that can be used to produce hard and scratch-resistant coatings.

The presence of an allyl group in the polyester composition does not in itself prevent the inhibitory effect of atmospheric oxygen on the curing process. To render polyesters non-inhibitable, the allyl group must be bonded to an oxygen atom forming an ether bond.

A similar effect is exerted by the residues of ethers of benzyl alcohol. This analogy is understandable if we consider the structure of these compounds:

It was soon discovered that the curing of polyesters synthesized from polyalkylene glycols was also not inhibited by atmospheric oxygen. Coatings based on polyesters of this type (fumaric acid was used as an unsaturated reagent) were distinguished by strength, elasticity, and scratch resistance.

Thus, the presence of an ether group in polyester molecules leads to the production of "non-inhibited" varnishes. In 1962, a report was published on polyesters synthesized using trimethylol propane diallyl ether. The polyester was obtained by condensation 214 wt. including diallyl ether of trimethylolpropane with 74 wt. h. phthalic anhydride to achieve an acid number of 24. Viscous at room temperature, the product was dissolved in xylene, and then added to a solution of 0.03% cobalt desiccant. The ability of the solution to dry was then tested using a VK Drying Recorder (lacquer layer thickness 0.038 mm). The test results are given in table. 127.

TABLE 127

The films obtained as described above are characterized by good resistance to heat and ultraviolet radiation, resistance to paraffin oil and good electrical insulating properties. In the absence of a cobalt desiccant, such films do not dry out for a long time.

A patent has recently been obtained for a method for the production of air-drying polyesters based on aliphatic alcohols containing 2-7 ether groups in the chain. Triethylene-, tetraethylene-pentaethylene-, hexaethylene- and pentabutylene glycol are used as such alcohol reagents. The use of addition products of ethylene or propylene oxides to the glycols mentioned above (the molar ratio of oxide:glycol is from 2:1 to 5:1) is also described.

mix 100 wt. including the resulting solution with 4 wt. hours of 50% cyclohexanone peroxide paste and 4 wt. including a 10% solution of cobalt naphthenate and cast the film. Film curing begins after 8 minutes and is accompanied by a strong exothermic effect.

Thin coatings are fully cured in 6 hours and can be successfully polished 8 hours after varnishing. The resulting films are elastic and resistant to scratching. If such a varnish is applied to a tree and a ball is dropped from a height of 1.5 m onto the resulting coating, a dent appears on the surface, but no cracks form.

The use of allyl ethers has been mentioned above.

The introduction of allyl alcohol ether residues into the side chain of alcohol reagents is carried out according to the Williamson method. The most accessible compounds of this group are partial allyl ethers of polyhydric alcohols. One of the most important characteristics of polyesters obtained using these esters is the content of side allyl groups. Jenkins, Mott and Wicker expressed the "functionality" of such polyesters as the average number of allyl groups per molecule.

The relationship of "allyl functionality" and molecular weight of polyesters based on maleic anhydride, propylene glycol and glycerol monoallyl ether is shown below:

To obtain varnishes that dry on. air, it is necessary to introduce a certain amount of allyl ether residues into the polyester composition, which is determined experimentally. The presence of these residues in the side chain of the polyester leads to the fact that during the polycondensation may occur gelation before the optimum molecular weight of the product is reached. The relationship between the content of allyl groups and the molecular weight at which gelation occurs is shown in table. 128 using the example of a polyester synthesized from propylene glycol, glycerol monoallyl ether and an equimolecular amount of maleic and phthalic anhydrides.

TABLE 128

The maximum achievable molecular weight cannot. be increased by reducing the content of maleic anhydride in the polyester formulation.

The properties of films made from styrene-containing resins improve with an increase in the content of allyl ether residues in the original polyester. So, when replacing 80 mol. % propylene glycol monoallyl ether glyceride produce polyesters that form strong, tough films that are resistant to solvents and fingernail scratches. If only 30% propylene glycol is replaced with glycerol allyl ether in the polyester formulation, the surface of the coating is easily scratched with sandpaper.

It has been established that in order to obtain coatings with good gloss after polishing, it is necessary to use polyesters containing about 0.15 mol of allyl ether per 100 g of polyester; to achieve high scratch resistance of the coatings, polyesters containing at least 0.33 mol of the same component are used.

Similarly, when using diallyl ether of glycerol as an agent that causes termination of the polycondensation chain, well-polished films are formed when 0.3 mol of this compound (per 100 g of polyester) is introduced into the polyester composition.

Scratch resistant coatings are made from polyesters containing 1.45 g mole of diallyl ether residues.

One of the main obstacles to the use of p,y-unsaturated ethers is the relative complexity of the synthesis of polyesters based on them. This is primarily due to the fact that the unsaturated units of the main and side chains tend to copolymerize. In addition, during the polycondensation of a,p-unsaturated acids with p,y-unsaturated diodes, the ether group can be easily destroyed by strong acids. Special precautions must be taken to prevent this unwanted side reaction.

Recently in the patent literature data have been given on the combined use of a polyester of a conventional type and a polyester based on an unsaturated acid, a saturated diol and an unsaturated diol containing residues of p, y-unsaturated ethers:

Examples of such p, y-unsaturated ether alcohols are the mono-w diallyl ethers of trimethylolethane, butanetriol, hexanetriol, and pentaerythritol. Mention is also made of the use of dicarboxylic acids containing allyl groups, for example, a-allyloxysuccinic and a, p-diallyloxysuccinic. thus a resin whose curing does not inhibit the oxygen in the air.

One of the most important characteristics of solvent monomers used in paint compositions is their vapor pressure. From this point of view, the use of styrene is undesirable, since a noticeable amount of styrene escapes from the thin ones.

films, especially with long drying times. For the manufacture of polyester varnishes, it is advisable to use low-volatility monomers capable of active copolymerization with maleates and fumarates in the presence of atmospheric oxygen. The ability of monomers to mix with polyesters to form low-viscosity solutions is also of great importance.

Polyallylic ethers meet these requirements: they are well combined with polyesters, forming low-viscosity compositions that, in the cured state, do not have surface tack. Such monomers readily enter into copolymerization with polyesters and do not form homopolymers under these conditions. Below are data on the temperatures that develop in the mass of polyester resins during their curing:

Compounds with allyloxy groups readily copolymerize with fumarates. Thus, p-allyloxyacetate forms copolymers with diethyl fumarate at various ratios of reagents.

It is interesting to note that p-allyloxyethyl acetate does not copolymerize with styrene, and when this ester is introduced into styrene-containing polyester resins, it probably reacts only with the fumarate groups of the polyester.

Polyallylic ethers can be obtained from melamine derivatives or by esterification of glycerol allyl ethers with phthalic anhydride. Although such monomers copolymerize well with fumarates, in many cases their use is complicated by the fact that they form highly viscous blends with polyesters.

With an increase in the content of allnl groups, the ability of resins to form non-tacky coatings improves. Properties of films obtained by curing.

compositions consisting of three parts of polyester and two parts of polyallyl monomers of various types are shown in table. 129.

TABLE 129.

Jenkins, Mott and Wicker investigated the effect of the amount of tetraallyl ether of bis-glycerol adipate on the properties of polyester coatings (Table 130).

The authors have shown that the composition must contain at least 40% monomer in order to obtain scratch-resistant hard coatings. This amount corresponds to 0.35 g-eq of allyl groups per 100 g of solution and is close to the optimal content of side allyl groups in the polyester chain (see previous section).

big practical value has the circumstance that any unsaturated polyester can be rendered "non-inhibitable" by the addition of the appropriate monomer.

Indeed, it is much easier to introduce into the resin. monomers are ethers of allyl alcohol than to modify polyester chains. There is evidence of a decrease in the inhibitory effect of atmospheric oxygen when aromatic monomers containing at least two isopropenyl radicals, for example, diisopropenylbenzene, are added to polyester resins. However, such compounds alone are not effective enough to allow the varnish to air dry to form a high quality coating. It should also be noted that when using styrene-containing resins, the ratio of polyester and styrene can be violated, in particular, due to the evaporation of styrene, which causes the depth of resin curing to decrease. In this regard, it is necessary to take into account losses due to evaporation, penetration into the substrate or spraying, and to introduce an excess of styrene (5-10%) into the composition of the varnish. In addition, when using styrene as the solvent monomer, higher molecular weight polyesters should be used.

Organic Supplements

It has been found that paraffin wax can be used to remove surface tack from polyester coatings. It is soluble in the original resin, but during the curing process it is almost completely released from it, forming a protective film on the surface of the coating, which prevents the inhibitory effect of atmospheric oxygen. This method of obtaining non-tacky coatings has been successfully used in the production of polyester resins and varnishes. Other "pop-up" additives are known, such as stearates, which, however, are not used as widely as paraffin.

Typically, wax-like additives are added in an amount of 0.01 to 0.1% by weight. After the coating has dried (3-5 hours after its application), the paraffin film is removed by grinding with abrasive materials. During subsequent polishing of the polished coating, a mirror surface is formed. Sanding is a rather* difficult process as the wax-like additives clog sandpaper.

The need for additional operations - grinding and polishing - is a serious obstacle to the use of polyester varnishes. However, it has not yet been possible to obtain brilliant coatings from resins containing wax-like additives without additional processing. It should also be noted that the pop-up additives minimize the loss of styrene from evaporation.

One of the disadvantages of polyester varnishes of this type is the deterioration of the adhesion of films based on them to the substrate due to the migration of wax or paraffin into it.

The surface layer of coatings becomes cloudy in the process of paraffin floating; after grinding and polishing, this process can continue, especially under the influence of heat or ultraviolet radiation.

Reduced adhesion can be avoided by first applying a varnish that does not contain wax additives, and after a while, a paraffin solution. In this case, the paraffin is only on the surface of the coating.

The introduction of small amounts of cellulose acetate butyrate gives varnishes the ability to form non-tacky films when dried in air and has a number of additional advantages:

a) prevents runoff from vertical surfaces;

b) accelerates gelation;

c) prevents the formation of shells and irregularities;

d) increases surface hardness;

e) increases the heat resistance of the coating.

For the preparation of non-inhibited varnishes, low molecular weight cellulose acetobutyrate is added to polyester at 150 ° C, and after its complete dissolution, a solvent monomer is added. If the polyester is first dissolved in the monomer, then the acetobutyrate is introduced into the solution at approximately 95°C; in this case, monomer losses (1-2%) due to evaporation are possible. Cellulose acetobutyrate not only improves the quality of lacquers and coatings, but also acts as a thickener and viscosity regulator for lacquers. To effectively prevent the inhibitory effect of oxygen, a layer of varnish based on butyrate and urea-formaldehyde resin is sometimes applied over a freshly applied unpolymerized layer of polyester resin. By obtaining such a surface coating directly after the application of the polyester resin, incomplete curing of the surface layer of the resin is avoided.

A method to avoid gelation is to react the carboxyl-terminated polyester with a partially epoxidized alkyd resin based on drying oil acids. These compounds react at relatively low temperatures, which prevents the Diels-Alder reaction from proceeding.

Air-drying polyesters are also obtained by reacting a diglyceride, a hydroxyl-terminated polyester, and a diisocyanate.

However, such products have not been widely used, which can be explained by the serious difficulties encountered in their production. To give polyesters the ability to dry in air, it is necessary to introduce into their composition a significant amount of compounds based on acids of drying oils. In addition, some of these products copolymerize poorly with styrene or maleate units and cause discoloration of the film as it ages.

Another way to obtain non-tacky coatings is to use polyesters, which, even in the uncured state, are so stiff that films based on them can be polished without clogging the polishing material.

Generally, the hardness of polyesters and their softening point are related. Polyesters with a softening point above 90 ° C are suitable for obtaining non-tacky coatings. In Ch. 6 shows that the softening point can be increased in several ways. For example, when using cyclic diols such as cyclohexanediol, it is possible to obtain polyesters with increased hardness and softening point. The introduction of polar groups into the polyester chain has a similar effect on these properties.

Thus, by using appropriate components or introducing specific groups into polyesters, it is possible to significantly increase their softening point.

Propylene glycol f--j- hydrogenated bisphenol A*. . . .

o-Phthalic f-maleic

The introduction of amide groups through the partial replacement of ethanolamine or ethylenediamine used in the synthesis of glycols has a similar effect on the properties of polyesters.

Such an effect was observed, for example, in the case of replacing a greater or lesser part of propylene glycol with amines in the synthesis of polypropylene glycol maleate isophthalate (the molar ratio of acidic reagents is 1: 1).

Comparing the effect of equimolecular amounts of monoethanolamine and ethylenediamine on the softening point of polyesters, we can conclude that ethylenediamine is more effective (Table 132).

Usually, obtaining unsaturated polyesters with a high softening point does not pose any particular difficulties, however, varnishes based on them have a number of significant drawbacks. Thus, cured coatings, although hard, are brittle and sensitive to solvents. Under alternating cooling and heating, the films tend to crack. These shortcomings are mainly related to losses.

More modern methods prevent the inhibitory effect of atmospheric oxygen, which were described in the previous paragraphs, make it possible to obtain coatings High Quality without a significant increase in the cost of materials.

Surface protection with polymer films.

This method consists in protecting the paint surface with a cellophane or terylene film and thus preventing oxygen from inhibiting the curing of polyester resins. In addition, in the case of the use of films, no noticeable loss of styrene due to evaporation is observed. This method of surface protection is also used in the manufacture of certain types of laminates and in the curing of the outer layer of glass-reinforced plastics. For obtaining other types of coatings, this method is of no practical interest.

"Hot" curing.

Hard polyester coatings are obtained by curing resins at temperatures of the order of 100° C. or higher. There is no need to use specific additives or special types of polyesters. In the process of curing at high temperatures, significant losses of styrene are possible, which adversely affects the quality of the surface of the coating. In this regard, it is advisable to use resins containing high-boiling monomers.

Some stoving polyester lacquers have been reported to produce coatings comparable in hardness to melamine alkyd resin based coatings. Such varnishes are cured using infrared heating at 100°C for 5 minutes. In this case, brilliant coatings are formed that do not require special polishing.

COPOLYMERIZATION OF TWO-COMPONENT SYSTEMS.

This section discusses the patterns of copolymerization proceeding with the participation of free radicals. Free radicals can be generated in a variety of ways, including thermal or photochemical degradation of compounds such as organic ones.

As tests of copolymers with styrene of mixed unsaturated polyesters of low molecular weight glycols (ethylene glycol, Di- and triethylene glycol) and polyethylene glycol of molecular weight 17D0 showed, the tensile strength decreases with an increase in the content of polyethylene glycol in the polyester composition due to a decrease in the cross-link density. At the same time, the elasticity of copolymers sharply increases and, having reached a maximum, begins to decrease as a result of an increase in the intermolecular interaction of polyester units. When using polyethylene glycol with a molecular weight of 600, the dependence of the relative elongation of the polymer on the composition of the initial polyester has a monotonic character [L-N. Sedov, P. 3. Li, N. F. Pugachevskaya, Plast, masses, No. 11, 11 (Shbb); Report on the 2nd International Conference on fiberglass and casting resins, Berlin, 1967]. - Approx. ed.

Epoxy and polyester resins are thermosetting, due to this quality, they are not able to return to a liquid state after curing. Both compositions are made in liquid form, but are capable of possessing different properties.

What is epoxy resin?

Epoxy type resin is of synthetic origin, it is not used in its pure form, a special agent is added to solidify, that is, a hardener.

When combining epoxy resin with a hardener, strong and solid products are obtained. Epoxy resin is resistant to aggressive elements, they are able to dissolve when acetone enters. Cured epoxy resin products are distinguished by the fact that they do not emit toxic elements, and shrinkage is minimal.

The advantages of epoxy resin are low shrinkage, resistance to moisture and wear, and increased strength. The solidification of the resin occurs at temperatures from -10 to +200 degrees.

Epoxy type resin can be hot cured or cold cured. With the cold method, the material is used on the farm, or in such enterprises where there is no possibility of heat treatment. hot way used for the manufacture of high-strength products that can withstand heavy loads.

The working time for an epoxy type resin is up to one hour, since then the composition will begin to harden and become unusable.

Epoxy Resin Application

Epoxy type resin serves as a high-quality adhesive material. It is able to bond wood, aluminum or steel, and other non-porous surfaces.

Epoxy-type resin is used to impregnate fiberglass; this material is used in the automotive and aviation industries, electronics, and in the manufacture of fiberglass for construction. Epoxy resin can serve as a waterproofing coating for floors or walls with high humidity. Coatings are resistant to aggressive environments, so the material can be used for finishing external walls.

After solidification, a durable and hard product is obtained, which can be easily polished. Fiberglass products are made from such material, they are used in the household, industry, and as room decor.

What is polyester resin?

The basis of this type of resin is polyester; solvents, accelerators or inhibitors are used to solidify the material. The composition of the resin has different properties. It depends on the environment in which the material is used. Frozen surfaces are treated with special compounds that serve as protection against moisture and ultraviolet radiation. This increases the strength of the coating.

Polyester-type resin has low physical and mechanical properties compared to epoxy material, and is also characterized by low cost, due to which it is actively in demand.

Polyester resin is used in construction, mechanical engineering, and the chemical industry. When combining resin and glass materials, the product hardens and becomes durable. This allows you to use the tool for the manufacture of fiberglass products, that is, canopies, roofs, shower cubicles and others. Also, polyester resin is added to the composition in the manufacture of artificial stone.

The surface treated with polyester resin needs additional coating; for this, a special gelcoat agent is used. The type of this tool is selected depending on the coverage. When using polyester resin indoors, when moisture and aggressive substances do not get on the surface, orthophthalic gelcoats are used. At high humidity, isophthalic-neopentyl or isophthalic agents are used. Gelcoats are also available with different qualities, they can be resistant to fire or chemicals.

The main advantages of polyester resin

Polyester resin, in contrast to the epoxy composition, is considered more in demand. It also has a number of positive qualities.

• The material is hard and chemical resistant.
• The resin has dielectric properties and wear resistance.
• When used, the material does not emit harmful elements, therefore it is safe for environment and health.

When combined with glass materials, the agent has increased strength, even exceeding steel. No freezing required special conditions The process takes place at ordinary temperature.

Unlike epoxy, polyester resin has a low cost, so coatings are cheaper. The polyester-type resin has already started the curing reaction, so if the material is old, then it may have a solid appearance, and is unsuitable for work.

Polyester-type resin is easier to work with and the cost of the material saves on costs. But to get a more durable surface or high-quality bonding, epoxy material is used.

Differences between polyester and epoxy resin, which is better?

Each material has a number of advantages, and the choice depends on the purpose of the product used, that is, in what conditions it will be applied, the type of surface also plays an important role. Epoxy type resin has a higher cost than polyester material, but it is more durable. The adhesive property of epoxy exceeds any material in strength, this tool reliably connects various surfaces. Unlike polyester resin, the epoxy composition has less shrinkage, has high physical and mechanical properties, less moisture passes through, and is resistant to wear.

But unlike the polyester composition, epoxy resin hardens more slowly, this leads to a slowdown in the manufacture of various products, such as fiberglass. Also, to work with epoxy requires experience or careful handling, further processing of the material is more difficult.

With exothermic curing, during temperature rise, the material is able to lose viscosity, which makes it difficult to work. Basically, epoxy-type resin is used in the form of glue, as it has high adhesive qualities, unlike polyester material. In other cases, it is better to work with polyester-type resin, this will significantly reduce costs and simplify the work. When using epoxy-type resin, it is necessary to protect hands with gloves, and respiratory organs with a respirator, so that when using hardeners, you do not get burns.

To work with polyester-type resin, special knowledge and experience are not required, the material is easy to use, does not emit toxic elements, and is notable for its low cost. Polyester resin can be used on various surfaces, but the coating needs additional processing. special means. Polyester resin is not suitable for bonding various materials; it is better to use an epoxy mixture. Also, for the manufacture of decorative products, it is better to use epoxy resin, it has high mechanical properties and is more durable.

Much less catalyst is required to make a compound from polyester resin, which also helps to save money. Dries polyester compound faster than epoxy material within three hours, ready product has elasticity or increased flexural strength. The main disadvantage of polyester material is its combustibility, due to the content of styrene in it.

Polyester resin must not be applied on top of epoxy. If the product is made or patched with epoxy resin, then in the future it is better to use it for restoration. A polyester-type resin, unlike an epoxy composition, can shrink significantly, it must be done immediately all the work in two hours, otherwise the material will harden.

How to properly prepare the surface for processing?

In order for the resin to adhere well, the surface must be properly treated, such actions are performed using an epoxy and polyester composition.

First, degreasing is performed, for this, various solvents or detergent compositions are used. The surface must be free of grease or other contaminants.

After that, grinding is performed, that is, the top layer is removed, with a small area, they are used sandpaper. For large surfaces, special grinding machines are used. Dust is removed from the surface with a vacuum cleaner.

During the manufacture of fiberglass products or when re-applying the agent, the previous layer is covered with resin, which has not had time to completely harden and has a sticky surface.

Results

Polyester resin is much easier to work with, this material helps to save on costs, as it has a low cost, it quickly hardens, and does not need complex processing. Epoxy-type resin is characterized by high strength, adhesive ability, and is used when casting individual products. When working with it, you must be careful, further processing is more difficult. During work with such compounds, it is necessary to protect the hands and respiratory organs with special means.

- polyester resins general purpose obtained by esterification of propylene glycol with a mixture of phthalic and maleic anhydrides. The ratio of phthalic and maleic anhydrides can vary from 2:1 to 1:2. The resulting polyester alkyd resin is mixed with styrene in a ratio of 2:1. Resins of this type have a wide range of applications: they are used for the manufacture of pallets, boats, parts of shower racks, swimming pools and water tanks.

- elastic polyester resins instead of phthalic anhydride, linear dibasic acids (adipic or sebacic) are used. A more elastic and soft unsaturated polyester resin is formed. The diethylene or dipropylene glycols used instead of propylene glycol also impart elasticity to the resins. The addition of such polyester resins to general purpose rigid resins reduces their brittleness and makes them easier to process. This effect is used in the production of molded polyester buttons. Such resins are often used for decorative molding in the furniture industry and in the manufacture of picture frames. To do this, cellulose fillers (for example, crushed walnut shells) are introduced into elastic resins and cast into silicone rubber molds. Fine reproduction of wood carvings can be achieved by using silicon rubber molds cast directly on the original carvings.

- elastic polyester resins occupy an intermediate position between rigid general-purpose resins and elastic ones. They are used to make impact-resistant products such as balls, crash helmets, fences, automotive and aircraft parts. To obtain such resins, isophthalic acid is used instead of phthalic anhydride. The process is carried out in several stages. First, by reacting isophthalic acid with glycol, a low acid number polyester resin is obtained. Then add maleic anhydride and continue the esterification. As a result, polyester chains are obtained with a predominant arrangement of unsaturated fragments at the ends of molecules or between blocks consisting of a glycol-isophthalic polymer.

- low shrinkage polyester resins when molding fiberglass reinforced polyester, the difference in shrinkage between resin and fiberglass results in pitting on the surface of the product. The use of low shrinkage polyester resins reduces this effect, and the cast products thus obtained do not require additional sanding before painting, which is an advantage in the manufacture of automotive parts and household electrical appliances. Polyester resins with low shrinkage include thermoplastic components (polystyrene or polymethyl methacrylate), which are only partially dissolved in the original composition. During curing, accompanied by a change in the phase state of the system, the formation of microvoids occurs, compensating for the usual shrinkage of the polymer resin.

- weather resistant polyester resins, should not turn yellow when exposed to sunlight, for which UV absorbers are introduced into its composition. Styrene can be replaced by methyl methacrylate, but only partially, because methyl methacrylate does not interact well with the double bonds of fumaric acid, which is part of the polyester resin. Resins of this type are used in the manufacture of coatings, exterior panels and skylight roofs.

- chemically resistant polyester resins ester groups are easily hydrolyzed by alkalis, as a result of which the instability of polyester resins to alkalis is their fundamental disadvantage. An increase in the carbon skeleton of the original glycol leads to a decrease in the proportion of ester bonds in the resin. Thus, resins containing "bisglycol" (the reaction product of bisphenol A with propylene oxide) or hydrogenated bisphenol have a significantly lower number of ester bonds than the corresponding general purpose resin. Such resins are used in the manufacture of parts of chemical equipment - fume hoods or cabinets, housings of chemical reactors and tanks, as well as pipelines.

- flame retardant polyester resins an increase in the resistance of the resin to ignition and combustion is achieved by using halogenated dibasic acids instead of phthalic anhydride, for example, tetrafluorophthalic, tetrabromophthalic and "chlorendic". A further increase in fire resistance is achieved by introducing various flame retardants into the resin, such as phosphoric acid esters and antimony oxide. Flame retardant polyester resins are used in fume hoods, electrical components, building panels, and in the hulls of some types of naval vessels.

- resin special purpose . For example, the use of triallyl isocyanurate instead of styrene significantly improves the heat resistance of resins. Specialty resins can be cured with UV radiation by incorporating photoactive agents such as benzoin or its ethers.

Epoxy resins - oligomers containing epoxy groups and capable of forming cross-linked polymers under the action of hardeners. The most common epoxy resins are the products of polycondensation of epichlorohydrin with phenols, most often with bisphenol A.

n can reach 25, but epoxy resins with less than 10 epoxy groups are most common. The higher the degree of polymerization, the thicker the resin. The lower the number on the resin, the more epoxy groups the resin contains.

Features of epoxy polymers:

ü the possibility of obtaining them in liquid and solid state,

ü absence of volatile substances during curing,

ü the ability to cure in a wide temperature range,

ü slight shrinkage,

ü non-toxic in the cured state,

ü high values ​​of adhesive and cohesive strength,

ü Chemical resistance.

Epoxy resin was first obtained by the French chemist Kastan in 1936. Epoxy resin is obtained by polycondensation of epichlorohydrin with various organic compounds: from phenol to edible oils (epoxidation). Valuable grades of epoxy resins are obtained by catalytic oxidation of unsaturated compounds.

Resin requires a hardener. The hardener may be a polyfunctional amine or anhydride, sometimes an acid. Curing catalysts are also used. After mixing with a hardener, the epoxy resin can be cured - transferred to a solid, infusible and insoluble state. There are two types of hardeners: cold curing and hot curing. If it is polyethylenepolyamine (PEPA), then the resin will harden in a day at room temperature. Anhydride hardeners require 10 hours of time and heating to 180 °C in a heat chamber.

The ES curing reaction is exothermic. The rate at which the resin cures depends on the temperature of the mixture. The higher the temperature, the faster the reaction. Its rate doubles when the temperature rises by 10°C and vice versa. All possibilities to influence the cure rate come down to this basic rule. The polymerization time, in addition to the temperature, also depends on the ratio of the area to the mass of the resin. For example, if 100 g of a mixture of resin and hardener turns into a solid state in 15 minutes at an initial temperature of 25 ° C, then these 100 g, evenly spread over an area of ​​1 m2, will polymerize in more than two hours.

In order for the epoxy resin together with the hardener in the cured state to be more plastic and not break (do not crack), plasticizers must be added. They, like hardeners, are different, but all are aimed at giving plastic properties to the resin. The most commonly used plasticizer is dibutyl phthalate.

Table - Some properties of unmodified and unfilled diano epoxy resins.

Epoxy-Diane resins of grades ED-22, ED-20, ED-16, ED-10 and ED-8, ​​used in the electrical, radio-electronic industry, aircraft, shipbuilding and mechanical engineering, in construction as a component of casting and impregnating compounds, adhesives, sealants, binders for reinforced plastics. Solutions of epoxy resins grades ED-20, ED-16, E-40 and E-40R in various solvents are used for the manufacture of enamels, varnishes, fillers and as a semi-finished product for the production of other epoxy resins, casting compositions and adhesives.

Epoxy resins modified with plasticizers - resins of grades K-153, K-115, K-168, K-176, K-201, K-293, UP-5-132 and KJ-5-20 are used for impregnation, pouring, enveloping and sealing parts and as adhesives, electrical insulating potting compositions, insulating and protective coatings, binders for fiberglass. Composition grade K-02T is used for impregnation of multilayer winding products in order to cement them, increase moisture resistance and electrical insulating properties.

Modified epoxy resins of the EPOFOM brand are used at various industrial and civil facilities as anti-corrosion coatings to protect metal and concrete building structures and capacitive equipment from the effects of chemically aggressive environments (especially acids, alkalis, oil products, industrial and sewage effluents), precipitation and high humidity. . These resins are also used for waterproofing and monolithic self-leveling coatings of concrete floors, priming and applying a finishing layer. EPOFOM grade resin is used to produce casting and impregnating compositions with a high content of reinforcing fabrics and fillers, composite materials and wear-resistant coatings. EPOFOM is used as an impregnating component of a hose material for the repair and restoration of pipelines of sewer networks, pressure networks of cold and hot water supply without their dismantling and extraction of pipes from the ground (trenchless method).

Compositions of the EZP brand are used to cover storage containers for wine, milk and other liquid food products, as well as various kinds liquid fuel(gasoline, kerosene, fuel oil, etc.).

Phenol-formaldehyde resins. In 1909, Baekeland reported on the material he had received, which he called Bakelite. This phenol-formaldehyde resin was the first synthetic thermoset plastic that did not soften at high temperatures. After carrying out the condensation reaction of formaldehyde and phenol, he obtained a polymer for which he could not find a solvent.

Phenol-formaldehyde resins are polycondensation products of phenols or their homologues (cresols, xylenols) with formaldehyde. Depending on the ratio of the reactants and the nature of the catalyst, thermoplastic (novolacs) or thermosetting (resols) resins are formed. Novolac resins are predominantly linear oligomers, in the molecules of which the phenolic cores are connected by methylene bridges and contain almost no methylol groups (-CH 2 OH).

Resole resins are a mixture of linear and branched oligomers containing a large number of methylol groups capable of further transformations.

FFS features:

ü by nature - solid, viscous substances that enter the production in the form of a powder;

ü for use as a matrix, melt or dissolve in an alcohol solvent;

ü The curing mechanism of resole resins consists of 3 stages. At stage A, the resin (resol) is similar in physical properties to novolacs, because dissolves and melts, at stage B the resin (resitol) is able to soften when heated and swell in solvents, at stage C the resin (resit) does not melt and does not dissolve;

ü for curing novolac resins, a hardener is required (usually urotropine is introduced, 6-14% by weight of the resin);

ü easy to modify and modify themselves.

Phenolic resin was first used as an easy-to-form, high-quality insulator that protected against high temperatures and electric current, and then became the main material of the Art Deco style. Practically the first commercial product obtained by pressing Bakelite is the ends of the high-voltage coil frame. Phenol-formaldehyde resin (PFR) has been produced by industry since 1912. In Russia, the production of cast resites under the name Carbolite was organized in 1912-1914.

Phenol-formaldehyde binders are cured at temperatures of 160-200°C using significant pressure of the order of 30-40 MPa and above. The polymers obtained as a result are stable upon prolonged heating up to 200°C, and for a limited time they are able to withstand the action of higher temperatures for several days at temperatures of 200-250°C, several hours at 250-500°C, several minutes at temperatures of 500- 1000°C. Decomposition begins at a temperature of about 3000°C.

The disadvantages of phenol-formaldehyde resins include their fragility and high volumetric shrinkage (15-25%) during curing, associated with the release a large number volatile substances. In order to obtain a material with low porosity, it is necessary to apply high pressures during molding.

Phenol-formaldehyde resins grades SFZh-3027B, SFZh-3027V, SFZh-3027S and SFZh-3027D are intended for the production of heat-insulating products based on mineral wool, fiberglass and for other purposes. Phenol-formaldehyde resin grade SFZh-3027C is intended for the production of foam plastic grade FSP.

On the basis of FFS, a variety of plastic masses, called phenolics, are made. The composition of most of them, in addition to the binder (resin), includes other components (fillers, plasticizers, etc.). They are processed into products mainly by pressing. Press materials can be prepared on the basis of both novolac and resole resins. Depending on the filler used and the degree of grinding, all press materials are divided into four types: powder (press powder), fibrous, crumbly and layered.

The designation of press powders most often consists of the letter K, denoting the word composition, the number of the resin on the basis of which this press material is made, and the number corresponding to the filler number. All press powders according to their purpose can be divided into three large groups:

Powders for technical and household products (K-15-2, K-18-2, K-19-2, K-20-2, K-118-2, K-15-25, K-17-25, etc. etc.) are made on the basis of novolac resins. Products made of them should not be subjected to significant mechanical stress, high voltage current (more than 10 kV) and temperatures above 160°C.

Powders for electrical insulating products (K-21-22, K211-2, K-211-3, K-211-4, K-220-21, K-211-34, K-214-2, etc.) are made in most cases on the basis of resole resins. Products withstand the action of current voltage up to 20 kV at temperatures up to 200°C.

Powders for special-purpose products have increased water and heat resistance (K-18-42, K-18-53, K-214-42, etc.), increased chemical resistance (K-17-23. K-17- 36, K-17-81, K-18-81, etc.), increased impact strength (FKP-1, FKPM-10, etc.), etc.

Fibrous press materials are prepared on the basis of resole resins and fibrous filler, the use of which makes it possible to increase some mechanical properties of plastics, mainly specific impact strength.

Fibers - press materials based on filler - cotton cellulose. Currently, three types of fiberglass are produced: fiberglass, high-strength fiberglass and fiberglass cord. On the basis of asbestos and resole resin, press materials of grades K-6, K-6-B (intended for the manufacture of collectors) and K-F-3, K-F-Z-M (for brake shoes) are produced. Press materials containing glass fiber are called fiberglass. It has higher mechanical strength, water and heat resistance than other fibrous press materials.

Crumb press materials are made from resole resin and pieces (crumbs) of various fabrics, paper, wood veneer. They have increased specific impact strength.

Laminated press materials are produced in the form of large sheets, plates, pipes, rods and shaped products. Depending on the type of filler (base), sheet laminates are produced in the following types: textolite - on cotton fabric, fiberglass - on glass fabric, asbestos-textolite - on asbestos fabric, getinaks - on paper, wood-laminated plastics - on wood veneer.