Polyester and epoxy resin, their differences. Unsaturated polyester resins in shipbuilding

- general purpose polyester resins obtained by esterification of propylene glycol with a mixture of phthalic and maleic anhydrides. The ratio of phthalic and maleic anhydrides can range from 2:1 to 1:2. The resulting polyester alkyd resin is mixed with styrene in a 2:1 ratio. This type of resin has a wide range of applications: they are used to make pallets, boats, shower rail parts, 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 use of diethylene or dipropylene glycols instead of propylene glycol also gives the resins elasticity. 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 cast polyester buttons. Such resins are often used for decorative casting in the furniture industry and in the manufacture of picture frames. To do this, cellulose fillers (for example, ground nut shells) are introduced into elastic resins and cast into silicone rubber molds. Fine reproduction of wood carvings can be achieved by using silicone rubber molds cast directly from 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 playing balls, safety helmets, fencing, automobile and aircraft parts. To obtain such resins, isophthalic acid is used instead of phthalic anhydride. The process is carried out in several stages. First, the reaction of isophthalic acid with glycol produces a low acid number polyester resin. Then maleic anhydride is added and esterification is continued. As a result, polyester chains are obtained with a predominant arrangement of unsaturated fragments at the ends of the molecules or between blocks consisting of glycol-isophthalic polymer

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

- weather resistant polyester resins, should not turn yellow when exposed to sunlight, for which purpose ultraviolet radiation absorbers are added to 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. This type of resin is used in the manufacture of coatings, exterior panels and lantern roofs.

- chemical 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 ether bonds in the resin. Thus, resins containing “bisglycol” (a product of the reaction 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 production of chemical equipment parts - exhaust hoods or cabinets, chemical reactor bodies and tanks, as well as pipelines.

- fire retardant polyester resins An increase in the resin's resistance to ignition and combustion is achieved by using halogenated dibasic acids, such as tetrafluorophthalic, tetrabromophthalic and chlorendic acids, instead of phthalic anhydride. Further increase in fire resistance is achieved by introducing various combustion inhibitors into the resin, such as esters of phosphoric acid and antimony oxide. Fire-retardant polyester resins are used in the manufacture of exhaust hoods, electrical components, structural panels, and the hulls of some types of naval vessels.

- special purpose resins. For example, using triallyl isocyanurate instead of styrene significantly improves the heat resistance of resins. Special resins can be cured using UV radiation by adding photosensitive 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 polycondensation products of epichlorohydrin with phenols, most often with bisphenol A.

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

Features of epoxy polymers:

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

ü absence of volatile substances during curing,

ü 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 produced by the French chemist Castan 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 the catalytic oxidation of unsaturated compounds.

To use the resin you need a hardener. The hardener can 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 - converted into a solid, infusible and insoluble state. There are two types of hardeners: cold cure and hot cure. If it is polyethylene polyamine (PEPA), then the resin will harden within 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 speed doubles when the temperature increases by 10° C and vice versa. All possibilities to influence the speed of curing come down to this basic rule. In addition to temperature, the polymerization time also depends on the ratio of area to 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, 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 (crack), it is necessary to add plasticizers. They, like hardeners, are different, but all are aimed at giving the resin plastic properties. The most commonly used plasticizer is dibutyl phthalate.

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

Characteristic name	Meaning
Density at 20 °C, g/cm 3	1.16÷1.25
Glass transition temperature, °C	60÷180
Thermal conductivity, W/(m×K)	0.17÷0.19
Specific heat capacity, kJ/(kg K)	0.8÷1.2
Temperature coefficient of linear expansion, °C -1	(45÷65) 10 -6
Heat resistance according to Martens, °C	55÷170
Water absorption over 24 hours, %	0.01÷0.1
Tensile strength, MN/m2	40÷90
Modulus of elasticity (under short-term stress), GN/m 2	2.5÷3.5
Impact strength, kJ/m 2	5÷25
Relative extension, %	0.5÷6
Dielectric constant at 20°C and 1 MHz	3.5÷5
Specific volumetric electrical resistance at 20°C, Ohm cm	10 14 ÷10 16
Dielectric loss tangent at 20°C and 1 MHz	0.01÷0.03
Electrical strength at 20°C, MV/m	15÷35
Moisture permeability, kg/(cm sec n/m 2)	2,1 10 -16
Coeff. water diffusion, cm 2 / h	10 -5 ÷10 -6

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

Epoxy resins modified with plasticizers - resins of the K-153, K-115, K-168, K-176, K-201, K-293, UP-5-132 and KDZh-5-20 brands are used for impregnation, pouring, enveloping and sealing of parts and as adhesives, electrical insulating casting compositions, insulating and protective coatings, binders for fiberglass. The composition of the K-02T brand is used for impregnation of multilayer winding products for the purpose of their cementation, increasing 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, petroleum products, industrial and sewage waste), 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. Based on EPOFOM brand resin, casting and impregnating compositions with a high content of reinforcing fabrics and fillers, composite materials and wear-resistant coatings are obtained. EPOFOM is used as an impregnating component of hose material for the repair and restoration of pipelines of sewer networks, pressure networks of cold and hot water supply without dismantling them and removing pipes from the ground (trenchless method).

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

Phenol-formaldehyde resins. In 1909 Baekeland reported the material he had obtained, which he called Bakelite. This phenol-formaldehyde resin was the first synthetic thermoset plastic that did not soften at high temperatures. By 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 its homologues (cresols, xylenols) with formaldehyde. Depending on the ratio of reactants and the nature of the catalyst, thermoplastic (novolac) or thermosetting (resol) resins are formed. Novolac resins are predominantly linear oligomers, in the molecules of which the phenolic nuclei are connected by methylene bridges and contain almost no methylol groups (-CH 2 OH).

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

Features of FFS:

ü by nature - solid, viscous substances that are supplied to production in the form of powder;

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

ü The curing mechanism of resol 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 (resitol) does not melt or dissolve;

ü to harden novolac resins, a hardener is required (usually methenamine is administered, 6-14% by weight of the resin);

ü are easy to modify and modify themselves.

Phenolic resin was first used as an easily molded, high-quality insulator that protected against high temperatures and electrical currents, and then became the main material of the Art Deco style. Almost the first commercial product obtained by pressing bakelite was the ends of the frame of a high-voltage coil. Phenol-formaldehyde resin (FFR) 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 resulting polymers are stable during prolonged heating to 200°C, and for a limited time are able to withstand the effects of higher temperatures for several days at temperatures of 200-250°C, several hours at 250-500°C, several minutes at temperatures of 500-500°C. 1000°C. Decomposition begins at a temperature of about 3000°C.

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

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

Based on FPS, a variety of plastics called phenoplasts are made. Most of them, in addition to the binder (resin), also contain 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 resol resins. Depending on the filler used and the degree of grinding, all press materials are divided into four types: powder (press powders), fibrous, crumb-like 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 a number corresponding to the number of the filler. All press powders can be divided into three large groups according to their intended purpose:

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 from them should not be subjected to significant mechanical loads, 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 resol resins. The products can withstand current voltages of 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 resol resins and fibrous filler, the use of which makes it possible to increase some mechanical properties of plastics, mainly specific impact strength.

Fibers are press materials based on filler - cotton cellulose. Currently, three types of fiberglass are produced: fiberglass, high-strength fiberglass and fiberglass cord. Based on asbestos and resol resin, press materials of the grades K-6, K-6-B (intended for the manufacture of collectors) and K-F-3, K-F-Z-M (for brake pads) 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-like press materials are made from resole resin and pieces (crumbs) of various fabrics, paper, and wood veneer. They have increased specific impact strength.

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

Some properties of coatings based on conventional polyester resins, as well as coatings based on nitrocellulose and urea-formaldehyde varnishes, are given in Table. 122 G From these data it is clear that polished coatings made of polyester resins have a number of advantages compared to 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 flames of smoldering cigarettes and are characterized by excellent frost resistance and increased abrasive resistance.

To achieve a high-quality finish with polyester varnishes, one coat is sufficient, while nitrocellulose and many other varnishes require two or three coats. Films made of polyester resins are resistant to impact loads.

The disadvantages of polyester varnish coatings include the difficulty of removing the coating if it is necessary to apply a new one. Additionally, although polyester coatings are scratch resistant, scratches are more noticeable on them than on nitrocellulose films.

Properties of coatings of various types

Index
	nitrocellulose	urea-form-. aldehydic	polyester
Solvent resistance			Very good
Scratch resistance
Resistance to pollution	Excellent	Excellent	Very good
Color stability.	Excellent	Very good
Moisture resistance.	Very good	Excellent	Very good
Transparency	Very good	Excellent	Very good
		Great	Very good
Chemical resistance	Excellent		Very good
Fire resistance			Excellent
Heat resistance
Thickness of coating applied in one step, mm
Cost of 1 m of coating in one layer, cents

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

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 produced in the presence of air from a conventional type of 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.

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

Free radicals formed as a result of 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, radicals arising from the decomposition of peroxides interact preferentially

This reaction occurs extremely quickly®. 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 has been 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.

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

a) modification of acid reagents used in the synthesis of polyesters;.

b) modification of alcohol reagents;.

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

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

e) use of drying oils;

f) the use of polyesters with a high softening point;.

g) introducing waxes or other floating additives into resins;

h) protection of the coating surface with polyester films;.

i) hot drying.

Modification of acid reagents.

Industrial production of polyester varnishes based on tetrahydrophthalic anhydride has recently been organized. These varnishes form non-stick 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 tetrahydrophthalic anhydride and properties of resins based on them

Starting Reagents	Composition, mole
Tetrahydrophthalic anhydride.... ......
Fumaric acid....
Maleic anhydride. .
Diethylene glycol.....
1,2-Propylene glycol. . .
Dipropylene glycol....
Polyglycol E-200....

Properties of resins

Acid number, mg KOH/g.......
Degree of esterification, %
Gardner viscosity at 20° C..........
Gardner chromaticity. .
Density at 25°C, g
Scratch resistance, g

Films were prepared from polyester resins of this type, into the formulation of which glycerin, tris-(2-carboxyethyl)-isocyanurate or a certain amount of malic acid were introduced. In table Figure 124 shows the effect of the listed reagents (modifiers) on the hardness of films manufactured 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% cobalt introduced in the naphthenate composition 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 when using resins of the other two types.

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

Steel coatings obtained from the three named resins are very elastic; When using polyesters modified with glycerol and tris-(2-carb-oxyethyl)-isocyanurate, the flexibility of coatings on aluminum is insufficient, while coatings made from a third formulation of resin are characterized by good elasticity. Films made from it are also superior to others in 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 have a significant effect on the properties of the coatings.

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

diethylene glycol 1,2-propylene glycol or dipropylene glycol (see Table 123). A change in the ratio of fumaric and tetrahydrophthalic acids also has a great influence. Thus, the scratch resistance of films increases with increasing this ratio and decreases with the introduction of propylene and dipropylene glycol into the composition of the original 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. Films made from polyesters modified with tetrahydrophthalic anhydride are more hard and shiny than films based on phthalates.

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

TABLE 125.

Recipes of tetrahydrophthalates with added modifiers and properties of resins based on them

Starting Reagents	Composition, mole
Tetrahydrophthalic anhydride
Fumaric acid
Diethylene glycol
G licerin
Apple acid
Tris-(2-carboxyethyl)-isocyanurate
Properties
Acid number, mg KOH/g
Degree of esterification, %
Gardner-Holt viscosity at 25°C
Density at 25° C, gsm
Gardner chromaticity
Maximum compatibility with styrene, %

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 overall 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% cobalt, introduced in the form of cobalt-naphthenate.

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

Rice. 42. The influence of the ratio of acid reagents in the polyester formulation on the scratch resistance of films made from cured resins. The numbers on the curves indicate the styrene content in the initial solutions.

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

The tackiness of coatings made from polyesters with a high degree of unsaturation (high fumaric acid content) disappears faster than when using products with a low degree of unsaturation, although polyesters modified with tetrahydrophthalic anhydride in all cases are characterized by the formation of non-tacky films.

It should be noted that such coatings do not always have satisfactory hardness and scratch resistance (Table 126). Thus, films produced using diethylene glycol polyethers are characterized by better hardness and scratch resistance than coatings based on 1,2-propylene glycol polyethers. 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 reduces the scratch resistance of the films.

TABLE 126.

Surface properties of coatings made of polyester resins modified with tetrahydrophthalic anhydride

As already noted, the scratch resistance of films obtained from tetrahydrophthalate solutions increases with time and becomes constant only 12-16 days after their application. Maximum Svard-Roker hardness values ​​are usually achieved one week after film application.

Tetrahydrophthalate-based coatings are superior in scratch and impact resistance to coatings made using industrial-grade polyester resins that do not contain waxy additives. However, they are inferior to them in hardness.

Modification of alcohol reagents.

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

However, they have not found industrial application. Much later, in Germany and the USA, it was simultaneously established that the introduction of residues of p-unsaturated ethers 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 series of p, y-alkenyl ethers of mono- or polyhydric alcohols. It has been found that by partially replacing (in polyester formulations) conventional glycols with α-allyl glycerol ether, products are formed from which hard and scratch-resistant coatings can be obtained.

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

Residues of benzyl alcohol ethers have a similar effect. This analogy is clear 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 their strength, elasticity and scratch resistance.

Thus, the presence of an ether group in polyester molecules determines the production of “non-inhibited” varnishes. In 1962, a report was published on polyesters synthesized using trimethylolpropane diallyl ether. The polyester was obtained by condensation of 214 wt. including diallyl ether of trimethylolpropane with 74 wt. parts of phthalic anhydride until the acid number is 24. The product, viscous at room temperature, was dissolved in xylene, after which 0.03% cobalt drier was added to the solution. Then the ability of the solution to dry was tested using the V.K. Drying Recorder device (varnish layer thickness - 0.038 mm). The test results are given in table. 127.

TABLE 127

Films obtained by the method 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 cobalt drier, such films do not dry for a long time.

A patent has recently been received for a method for producing 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 products of the addition of ethylene or propylene oxides to the above-mentioned glycols is also described (the molar ratio of oxide: glycol ranges from 2: 1 to 5:1).

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

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

The use of allyl ethers was mentioned above.

The introduction of allyl alcohol ether residues into the side chain of alcohol reagents is carried out using 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 allylic groups. Jenkins, Mott and Wicker expressed the "functionality" of such polyesters as the average number of allylic groups per molecule.

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

To obtain varnishes that dry on. air, it is necessary to introduce a certain amount of allylic ether residues into the polyester composition, which is determined experimentally. The presence of these residues on the polyester side chain means that gelation may occur during the polycondensation process before the optimum molecular weight of the product is reached. The relationship between the content of allylic 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 equimolecular amounts of maleic and phthalic anhydrides.

TABLE 128

		Maximum molecular weight of polyester that can be achieved without gelation	"Allyl functionality" of polyester

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

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

It has been established that 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 coatings, polyesters containing at least 0.33 mol of the same component are used.

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

Scratch-resistant coatings are made from polyesters containing 1.45 g-mol 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 easily be destroyed by strong acids. To prevent this unwanted side reaction, special precautions must be taken.

Recently, the patent literature has reported the combined use of a conventional polyester and a polyester based on an unsaturated acid, a saturated diol and an unsaturated diol containing p, y-unsaturated ether residues:

An example 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. Polyesters of two types, each of which contains unsaturated groups of only one kind, are little prone to homopolymerization, are mixed at room temperature and obtained as follows thus a resin whose curing does not inhibit atmospheric oxygen.

One of the most important characteristics of solvent monomers used in paint and varnish compositions is their vapor pressure. From this point of view, the use of styrene is undesirable, since a significant amount of styrene evaporates from thin materials.

films, especially with long drying times. For the manufacture of polyester varnishes, it is advisable to use low-volatile 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.

Polyallyl ethers meet these requirements: they combine well with polyesters to form low-viscosity compositions that have no surface tack when cured. Such monomers easily enter into copolymerization with polyesters and do not form homopolymers under these conditions. Below are data on the temperatures developing in the mass of polyester resins during their curing process:

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

It is interesting to note that p-allyl ethyl 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.

Polyallyl ethers can be prepared 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 mixtures with polyesters.

As the content of allyl groups increases, the ability of resins to form non-stick coatings improves. Properties of films obtained during curing.

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

TABLE 129.

	nality. monomer	Quantity. allylic. mol/100 2 resins	Resistance to scratching in 18 hours	Time until.	Viscosity. monomer.
Glycerol diallyl ether....
Glycerol acetate diallyl ether
Tetraallyl ether bis-glycerinace-tata.......
Octaallyl ester of tetraglycerol ester of pyro-mellitic acid.......

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

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

Of great practical importance is the fact that any unsaturated polyester can be made “non-inhibited” by adding the appropriate monomer.

Indeed, it is much easier to inject into the resin. monomers are ethers of allyl alcohol, which modify the polyester chains. There is information about 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 on their own are not effective enough to allow the varnish to air dry to form a high quality finish. It should also be noted that when using styrene-containing resins, the ratio of polyester and styrene may be disrupted, in particular due to the evaporation of styrene, which reduces the depth of curing of the resin. In this regard, it is necessary to take into account losses due to evaporation, penetration into the substrate or spraying and introduce excess styrene into the varnish composition (5-10%). In addition, when using styrene as a solvent monomer, polyesters of high molecular weight should be used.

Organic supplements

It has been found that paraffin wax can be used to remove the surface stickiness of 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 that prevents the inhibitory effect of atmospheric oxygen. This method of obtaining non-stick coatings has been successfully used in the production of polyester resins and varnishes. Other “floating” additives are also known, such as stearates, which, however, are not used as widely as paraffin.

Typically, wax-like additives are introduced in an amount of 0.01 to 0.1 wt.%. After the coating has dried (3-5 hours after its application), the paraffin film is removed by grinding with abrasive materials. Subsequent polishing of the ground coating results in a mirror-like surface. Sanding is quite a difficult process, as wax-like additives clog the sanding paper.

The need for additional operations - grinding and polishing - is a serious obstacle that complicates the use of polyester varnishes. However, it is still not possible to obtain shiny coatings from resins containing wax-like additives without additional processing. It should also be noted that floating 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 as the paraffin floats; After grinding and polishing, this process may continue, especially under the influence of heat or ultraviolet irradiation.

A decrease in adhesion can be avoided by first applying a varnish that does not contain waxy additives, and after some time, a paraffin solution. In this case, paraffin is only on the surface of the coating.

The introduction of small amounts of cellulose acetobutyrate gives varnishes the ability to form non-stick films when drying in air and has a number of additional advantages:

a) prevents runoff from vertical surfaces;.

b) accelerates gelation;.

c) prevents the formation of cavities and irregularities;.

d) increases surface hardness;.

e) increases the heat resistance of the coating.

To prepare non-inhibited varnishes, low-molecular-weight cellulose acetobutyrate is added to the polyester at 150°C and, after its complete dissolution, a solvent monomer is added. If the polyester is first dissolved in the monomer, then acetobutyrate is introduced into the solution at approximately 95 ° C; in this case, loss of monomer (1-2%) due to evaporation is possible. Cellulose acetobutyrate not only improves the quality of varnishes and coatings, but is also a thickener and viscosity regulator for varnishes. 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, uncured layer of polyester resin. By obtaining such a surface coating immediately after applying the polyester resin, it is possible to avoid incomplete curing of the surface layer of the resin.

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 occurring.

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

However, such products are not widely used, which can be explained by 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 the acids of drying oils. In addition, some of these products do not copolymerize well with styrene or maleate units and cause the film to discolor as it ages.

Another method for obtaining non-tacky coatings is the use of polyesters, which, even in the uncured state, are so rigid that films based on them can be polished without clogging the polishing material.

Typically, the hardness of polyesters and their softening point are interrelated. Polyesters with a softening point above 90° C are suitable for producing non-stick coatings. In Chap. 6 shows that the softening temperature 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. A similar effect on these properties is exerted by the introduction of polar groups into the polyester chain.

Thus, by using appropriate components or introducing specific groups into polyesters, their softening temperature can be significantly increased.

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

o-phthalic f-maleic

A similar effect on the properties of polyesters is exerted by the introduction of amide groups by partially replacing the glycols used in the synthesis with ethanolamine or ethylenediamine.

This effect was observed, for example, in the case of replacing more or less of propylene glycol with amines during the synthesis of polypropylene glycol maleinate isophthalate (the molar ratio of acid reagents is 1: 1).

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

Usually, obtaining unsaturated polyesters with a high softening point is not particularly difficult, but varnishes based on them have a number of significant disadvantages. Thus, cured coatings, although hard, are brittle and sensitive to solvents. With alternating cooling and heating, films tend to crack. These disadvantages are mainly related to losses.

More modern methods of preventing the inhibitory effect of atmospheric oxygen, which were described in the previous paragraphs, make it possible to obtain high-quality coatings without significantly increasing the cost of materials.

Surface protection using polymer films.

This method consists of protecting the paint surface with cellophane or terylene film and thus preventing the inhibiting effect of oxygen on the curing of polyester resins. In addition, when films are used, there is no noticeable loss of styrene due to evaporation. This method of surface protection is also used in the manufacture of certain types of laminates and when curing the outer layer of fiberglass. This method is not of practical interest for obtaining other types of coatings.

"Hot" curing.

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

Some baked polyester varnishes have been reported to produce coatings comparable in hardness to melamine alkyd resin coatings. Such varnishes are cured using infrared heating at 100° C for 5 minutes. This results in shiny coatings that do not require special polishing.

COPOLYMERIZATION OF TWO-COMPONENT SYSTEMS.

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

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 17N0 have shown, the tensile strength decreases with increasing polyethylene glycol content in the polyester composition due to a decrease in the density of cross-links. At the same time, the elasticity of the copolymers increases sharply and, having reached a maximum, begins to decrease as a result of an increase in the intermolecular interaction of the 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 original polyester is monotonic [L-N. Sedov, P. 3. Li, N. F. Pugachevskaya, Plast, masses, No. 11, 11 (Shbb); Report at 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 hardening. Both compositions are made in liquid form, but can have different properties.

What is epoxy resin?

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

When epoxy resin is combined with a hardener, strong and hard products are obtained. Epoxy resin is resistant to aggressive elements; they can dissolve when exposed to acetone. 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 resin hardens at temperatures from -10 to +200 degrees.

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

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

Application of epoxy resin

Epoxy resin serves as a high-quality adhesive material. It is capable of gluing wood, aluminum or steel, and other surfaces that do not have pores.

Epoxy resin is used to impregnate fiberglass; this material is used in automotive and aircraft manufacturing, electronics, and in the production of fiberglass for construction. Epoxy resin can serve as a waterproofing coating for floors or walls with high humidity. The coatings are resistant to aggressive environments, so the material can be used for finishing external walls.

After hardening, a durable and hard product is obtained that is easy to sand. Fiberglass products are made from this material; they are used in households, industry, and as room decoration.

What is polyester resin?

The basis of this type of resin is polyester; to harden the material, solvents, accelerators or inhibitors are used. The composition of the resin has various properties. This 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 resin has low physical and mechanical properties compared to epoxy material, and is also low in cost, which is why it is in great 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 the product to be used for the manufacture of fiberglass products, that is, canopies, roofs, shower stalls 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 product is used. The type of this product is selected depending on the coating. When using polyester resin indoors, when moisture and aggressive substances do not reach the surface, orthophthalic gelcoats are used. At high humidity, use isophthelic-neopentyl or isophthalic agents. Gel coats are also available in a variety of qualities and may be fire or chemical resistant.

The main advantages of polyester resin

Polyester resin, unlike epoxy resin, is considered more in demand. She 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 the environment and health.

When combined with glass materials, the product has increased strength, even exceeding steel. No special conditions are required for hardening; the process occurs at normal temperatures.

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

Work with polyester resin is easier, and the cost of the material allows you to save on costs. But to obtain 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, under what conditions it will be applied; the type of surface also plays an important role. Epoxy resin costs more than polyester resin, but is more durable. The adhesive property of epoxy resin exceeds any material in terms of strength; this product reliably connects various surfaces. Unlike polyester resin, epoxy composition has less shrinkage, has high physical and mechanical properties, less moisture permeability, and is wear-resistant.

But unlike the polyester composition, epoxy resin hardens more slowly, which leads to slower production of various products, for example, fiberglass. Also, working with epoxy resin requires experience or careful handling; further processing of the material is more difficult.

During exothermic curing, when the temperature rises, the material can lose its viscosity, which makes it difficult to work with. Basically, epoxy 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 resin, this will significantly reduce costs and simplify the work. When using epoxy-type resin, it is necessary to protect your hands with gloves and your respiratory organs with a respirator to avoid burns when using hardeners.

To work with polyester resin, no special knowledge or experience is required; the material is easy to use, does not emit toxic elements, and is low in cost. Polyester resin can be used to treat various surfaces, but the coating requires additional treatment with a special agent. Polyester resin is not suitable for gluing 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.

To make a composition from polyester resin, much less catalyst is required, this also helps to save money. The polyester composition hardens faster than epoxy material, within three hours, the finished product has elasticity or increased bending strength. The main disadvantage of polyester material is its flammability due to the styrene content.

Polyester resin should not be applied on top of epoxy material. If the product is made or patched with epoxy resin, then it is better to use it for future restoration. Polyester resin, unlike epoxy, can shrink significantly; it must be used to do all the work at once 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 epoxy and polyester compositions.

First, degreasing is carried out; for this, various solvents or detergent compositions are used. There should be no greasy stains or other contaminants on the surface.

After this, grinding is performed, that is, the top layer is removed; if the area is small, sandpaper is used. For large surfaces, special grinding machines are used. Remove dust from the surface using a vacuum cleaner.

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

Results

It is much easier to work with polyester resin; this material helps to save on costs, since it has a low cost, it hardens quickly, and does not require complex processing. Epoxy resin is characterized by high strength, adhesive properties, and is used for casting individual products. When working with it, you must be careful; further processing is more difficult. When working with such compounds, it is necessary to protect your hands and respiratory organs with special means.

The modern chemical industry produces many types of resins used in various industries and in the production of composite materials. Among this variety, epoxy and polyester thermosetting resins are most actively used.

They, unlike thermoplastics, do not return to their original (liquid) state under the influence of heat after curing. Both resins have a liquid, syrupy consistency, but each has a number of specific properties.

A synthetic oligomeric compound that is not used in its pure form, but only with a polymerizing component (), in combination with which the resin exhibits its unique qualities. The ratio of epoxy resin to hardener has wide limits.

Due to this, the final compositions are varied and used for different purposes. These are both tough and hard, resembling rubber in consistency, and materials stronger than steel. The polymerization reaction is irreversible. Cured resin does not melt or dissolve.

Application area

Epoxy materials have unlimited possibilities for use. Traditionally they are used as:

• impregnating agent for glass fibers, fiberglass, gluing various surfaces;
• waterproofing coating of walls and floors, including swimming pools and basements;
• chemically resistant coatings for interior and exterior finishing of buildings;
• products that increase strength and water resistance for wood, concrete and other materials;
• raw materials for casting forms subjected to cutting and grinding in the production of fiberglass products in the electronics industry, construction, household, design work.

Advantages and disadvantages of epoxy

Polymer two-component compositions, which include a hardener and epoxy resin, have many undeniable advantages, including:

• high strength of the formed joints;
• minimum degree of shrinkage;
• low sensitivity to moisture;
• improved physical and mechanical parameters;
• polymerization temperature in the range from -10 to +200 degrees Celsius.

The unlimited number of variations of created compounds and many positive characteristics have not made epoxy resins more in demand than polyester resins. This is due to the disadvantage of this polymer, such as cost. This is especially true on an industrial scale, when the amount of resin used for impregnation is large.

Why are epoxy resins needed?

This two-component compound is used quite rarely as a construction material, but there are situations in which it has proven itself to be the best. Today it is almost impossible to find a better adhesive composition than epoxy resin.

It serves as an excellent protective coating and is recommended for use when gluing various materials. These include a variety of wood species, metals such as steel and aluminum, and any non-porous surfaces. With its help, you can improve the performance qualities of fabric materials, but not in cases of working with large volumes. The latter is due to high costs.

Epoxy adhesive

A special epoxy composition with high strength adhesion to many materials, available both rigid and elastic.

If the glue is intended to be used exclusively for household needs, it is enough to purchase a composition that does not require compliance with any strict proportions. Such “kits” are sold in the form of a cold-type resin and hardener. Most often, they already come in the required ratio, which can vary from 100:40 to 100:60.

The use of this type of glue is not limited solely to household needs. The composition is actively used in a wide variety of fields, including even aircraft manufacturing. The proportions and types of hardeners are different. It all depends on what purpose the glue is used for.

Preparation of epoxy resins and glue

Mixing resin and hardener when creating an adhesive solution in small quantities does not require any special conditions. Both an overdose and a lack of polymerizing agent are acceptable. The recommended (standard) proportion is 1:10. If the resin is prepared in large quantities, for example, for pouring into a mold to make fiberglass products, then both the selection and work with components must be approached responsibly and carefully.

When purchasing resin and hardener, it is necessary to clarify their purpose. The resin, if it is necessary to prepare several kilograms of the composition, is preheated. Only after this are added polymerizing components and plasticizers. The presence of harmful vapors emitted requires the use of personal protective equipment. Failure to follow safety rules can result in burns and the development of respiratory diseases.

Epoxy resin usage time

This parameter is most important when working with compounds, since the period during which they remain viscous or liquid and are suitable for processing has its limitations. The “working time” of the composition depends on several factors that must be taken into account during the preparation of the compound.

Curing of some compounds occurs at a temperature of -10, others - above +100 degrees. As a rule, you can work with the composition from half an hour to an hour. If it hardens, it will become unusable. Therefore, when preparing compositions, you need to clearly control both the amount of hardener and the temperature of the resin.

It is a product of the petrochemical industry, the main component of which is polyester. For polymerization (hardening), components such as solvents, initiators, inhibitors, and accelerators are added to it. The composition of polyester resins may be changed by the manufacturer depending on the specific application.

Hardened surfaces are coated with a special substance (gelcoat), which increases the strength and resistance of the coating to ultraviolet radiation, moisture and water. The physical and mechanical properties of polyester resins are significantly lower than epoxy resins, but due to their low cost, they are the most popular.

Scope of use

Polyester resin is actively used in industries such as mechanical engineering, chemical industry, and construction. The resin is especially strong when combined with glass materials in the construction industry.

The combination of these two materials allows this type of resin to be used in the production of fiberglass, from which high-strength and mechanically resistant canopies, roofs, wall partitions, shower stalls and other similar products are made. This type of resin is one of the components in the production process of artificial stone, significantly reducing the cost of finished products.

Polyester Resin Coatings

Finished products made of polyester resin, given their not the highest physical and mechanical properties, need to be protected with gelcoat. The type of this special substance depends on the application of the final product.

Products that are not exposed to an active chemical environment or water and are used indoors are covered with orthophthalic gelcoats, and in conditions of high humidity or difficult climates, for example, in shipbuilding, swimming pools, baths - isophthelic-neopentyl and isophthalic. There are special-purpose gelcoats that can be fire-resistant or have increased resistance to chemical compounds.

Advantages of polyester

Polyester resins, unlike epoxy resins, are a more popular structural material, and in the cured state they have the following advantages:

• hardness;
• resistance to chemical environments;
• dielectric properties;
• wear resistance;
• absence of harmful emissions during operation.

In combination with fiberglass fabrics, they have similar, and sometimes even higher, parameters than structural steel. The cheap and simple production technology inherent in these resins is due to the fact that they harden at room temperature, but at the same time they shrink slightly.

This eliminates the need for bulky heat treatment units. Considering this and the fact that polyester resins are half the price of epoxy resins, the cost of the final product is low. All this makes the use of polyester-based resins beneficial for both the manufacturer and the buyer.

Flaws

The disadvantages of polyester resins include the use of a flammable and toxic solvent such as styrene during the production process. Many manufacturers have stopped using it, so when purchasing resin, you need to pay attention to the composition.

Another disadvantage of the composition is the flammability of the resin. In its unmodified form, it burns like hardwood. To solve this problem, manufacturers introduce powder fillers with fluorine and chlorine or carry out chemical modification.

Nuances of choice

Polyester resins are supplied in a “started” polymerization reaction, that is, after a certain time they turn into a solid state. And if you purchase old resin, it will not have the declared properties and characteristics. Many manufacturers provide a guarantee of freshness for their products.

The shelf life of polyester resins is about six months. If you follow storage rules, for example, keep the composition in the refrigerator without freezing, you can use the resin throughout the year. Avoid exposure to direct sunlight and ambient temperatures above +20 degrees.

Epoxy and polyester resins

Working with polyester resins is much easier than with epoxy resins, and their cost is lower. However, when choosing a material for reliable gluing of surfaces or casting of decorative products, it is recommended to give preference to epoxy compounds.