RU2527997C2 - Composition for thermal barrier coatings - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to compositions for obtaining thermal barrier coatings, which can be applied for an external thermal protection of elements of spacecraft constructions, as well as in construction and aircraft. A composition of the thermal barrier coatings contains dry re-dispersible latex based on copolymers of vinylacetate and ethylene or vinylacetate and vinylversalate as an organic binding agent and a group of filling agents, including vermiculite with the bulk density 95-110 kg/m³ and an average size of particles 1 mm, perlite with the bulk density not more than 100 kg/m³, kaolin, glass microspheres with dimensions 15-200 mcm and the bulk density 240-320 kg/m³ and a fibrous material.

EFFECT: invention provides thermal protection of metal and non-metal constructions against high-temperature rapid aerodynamic heating.

4 cl, 1 tbl

Description

The invention relates to compositions for thermal protection coatings (TZP), which can be used for external thermal protection of structural elements of spacecraft (KA), as well as in other industries, for example, in construction, aircraft,

It is known that for the manufacture of heat-protective coatings (TZP), compositions are used that generally contain the main components: fillers and binders, as well as additives, such as reinforcing fibers, foaming agents, pigments, gel oxides, flame retardants, etc.

Refractory fatty clays, for example kaolin and bentonite, glass or polymer microspheres, as well as various refractory powders of both natural and synthetic origin, namely vermiculite, talc, chamotte, chalk, are used as fillers in the known compositions for fire and heat-protective coatings. . ground quartz sand, aerosil, perlite, porous chamotte, diatomaceous earth, finely ground magnesite, phlogopite, zeolite, salts of phosphoric acid.

Of the greatest interest for the invention in the above fillers are such lightweight heat-resistant materials as vermiculite (RU 2079525, С01D 5/18, 2001; RU 2148066, C09D 5/18, 2000; RU 2415896, C09D 5/18, 2011), perlite ( JP 54014410, 1975; RU 2174527, C09D 5/18, 2001; DE 2227188, 22G 3/48, 1973), glass or polymer microspheres (RU 2039070, 1995; RU 2187433, C09D 5/18, 2002) and kaolin (JP 7002559, C09D 5/18, 1976; RU 2415896, C09D 5/18, 2011).

Reinforcing fiber materials, for example, fiberglass (RU 2249576, C07D 5/18, 2004; DE 2227188, 22G 3/48, 1973: RU 216287 !, C04B 28/34, 2001, are widely used for hardening fire-retardant and especially heat-protective coatings in known compositions. ), granular mineral fiber (RU 2169717, С04В 28/26, 2001), basalt and asbestos fiber (RU 2260029, C09D 5/18, 2003), mullite-siliceous wool (RU 2100310, С04В 28/26). The introduction of a fibrous filler in coating compositions, for example fiberglass, is known to increase the resistance of the coatings to vibration and static loads.

Various organic and inorganic chemical compounds are used as binders in the considered containers. Of the inorganic binders for creating flame retardants for metal, the most widely used are: cement, mainly Portland cement (RU 2415896, C09D 5/18, 2011), water glass (RU 2169717, С04В 28/26, 2001), silicophosphate binder (RU 2079525, C01D 5 / J8, 2001), aluminoborophosphate binder (RU 2103296, C09D 7/00, 2002), polyorganosiloxanes (RU 2028352, C09D 5/04, 1997).

Of the organic binders for heat-protective coatings, the most widely used polymer compounds are, for example, chlorinated rubber, polyurethane, polyesters, phenolic and epoxy resins (PCT WO 91/11498, C09K 21/02, 1991). polyacrylates (WO 2011080364, C09D 5/02, 2011), aqueous dispersions of polymers (latexes). Among the most applicable aqueous dispersions of polymers are acrylic (RU 2208028, C09D 5/18, 2003), styrene-acrylic, polyvinyl acetate and styrene butadiene (RU 2244727, C09D 5/02, 2000; RU 2352601, C09D 5/18, 2008 ; RU 2352601, C09D 5/18, 2006; RU 2148605, C09D 5/18, 2000). By impregnating the fiber materials with solutions or dispersions of these polymers, many different plate and roll heat-shielding materials are used that are used in the construction industry. It should be noted that the listed organic polymers are used both independently and as additives to inorganic binders.

Of greatest interest to the present invention is the composition used to obtain a heat-resistant layer of a multilayer combined polymer coating applied first on a substrate in the manufacture of this coating (RU 2352601, C09D 5/18, 2008). This known composition in its qualitative composition is closest to the proposed composition and is selected as a prototype. It includes a water-dispersion binder, which may be a polymer latex composition, based on copolymers of acrylate, styrene, vinyl acetate, butadiene-styrene copolymer, polyurethane, polyvinyl chloride. Specifically, this prototype gives an example of a composition comprising a polymer latex composition (20-60 wt.%) Containing polyvinyl acetate latex and / or dimethyl acrylate latex, or a dispersion of methylphenylsiloxane resin ("silikofen") or an epoxy resin (ED-20) with a hardener. As a filler, a mixture of hollow glass microspheres with a diameter of 35-200 microns and various bulk density (70-650 kg / m ³ ) and / or a mixture of polystyrene microspheres with a diameter of 10-500 microns and bulk density 50-650 kg / is introduced into the known composition m ³ . In addition, the known composition contains other auxiliary target additives: pigments, flame retardants, corrosion inhibitors, surfactants, for example, neonol, ethoxylated monoalkylphenols, etc. Then, if necessary, apply one or more layers of fiberglass using phosphate glue and then apply one or more layers of polymer intumescent fire-retardant paint. This flame retardant outer layer includes a polymer binder (polymer aqueous dispersions, for example styrene-acrylic, styrene-butadiene, polyvinyl acetate) and intumescent additives, the so-called porophores (polyalcohols, organic amines or amides, melamine, urea).

Thus, the selected prototype qualitatively and quantitatively differs from the proposed composition and is part of a complex composition for the formation of a multilayer coating, the formation of which requires intermediate drying of each layer and is time-consuming. In addition, the use of glued fiberglass as an interlayer reinforcing component is unacceptable for TZP applied to complex product profiles.

The disadvantages of the composition of the inner heat-protective layer. selected as a prototype, one can primarily attribute the use of an organic polymer as a binder aqueous dispersion. Although water-dispersion latexes have important advantages compared with solutions of organic resins in toxic solvents, such as fire and explosion safety, a high concentration of the target component, and the absence of emission of harmful substances during the manufacture of coatings, they nevertheless have significant disadvantages. The use of aqueous dispersions of latexes also causes a number of difficulties: the inability to work with them at low temperatures, the inconvenience and disadvantage of transporting and storing large volumes of water-dispersion compositions, the difficulty of accurate dosages of components directly at the coating sites.

It is known from practice that latexes of acrylate copolymers, most often butyl acrylate, are the highest quality binders for a wide variety of finishing materials, since they have high adhesion, high resistance to hydrolysis and aging, and the service life of materials based on them can reach 25 years. But they are characterized by high cost and are the most expensive group of latexes.

Among the listed latexes, the styrene butadiene latexes are also mentioned in the prototype composition. However, it is known that styrene-butadiene latexes are widely used in the manufacture of finishing materials in construction, but are characterized by the fact that their use causes rapid film aging due to oxidation of residual double bonds, which limits the service life of the resulting coatings.

As an example of a binder in the prototype composition, it is also proposed the use of solutions of epoxy resin ED-20 in toxic solvents, which is the most undesirable component of the composition.

As can be seen from the descriptions of the patent documents cited above. the considered heat-resistant compositions are not intended for the space industry and in many respects cannot be applied in this technical field.

In accordance with operating conditions, special stringent requirements are imposed on coatings for structural elements of spacecraft.

First of all, heat-proof coatings must withstand without cracking and shedding a sharp rise in temperature to 800 ° C for 10 minutes (thermal shock) under high aerodynamic loads and strong vibration. At the same time, the surface temperature of spacecraft structures (the head fairing of the launch vehicle, compartments, garrots, manhole covers, etc.) under a heat-shielding coating should not exceed 150 ° C, while the temperature developing on the outside of the head fairing rises up to values 800-1200 ° С. According to thermal characteristics, the material used for these purposes should provide thermal conductivity - not more than 0.102 W / m K and heat capacity not less than 1.6 kJ / kg. Thus, TZP should provide power protection of metal and nonmetallic structures from high-temperature high-speed aerodynamic heating in operating conditions. When the material is heated, there should be no through cracks and delaminations from the surface of the protected structure.

In addition, TZP should have low density, but high strength and elasticity, high adhesion to metal and carbon fiber, and also during the coating process no harmful substances should be released into the air of the working area, but at the same time, color change, coking and the emission of volatile substances.

The main task of creating a new heat-shielding material for this purpose, in addition to the listed physical, mechanical and thermal characteristics, is to achieve a minimum coating density, which allows to increase the payloads of spacecraft.

The purpose of the new invention is to develop an environmentally friendly multicomponent dry composition with a low density for the manufacture of heat-resistant coatings that satisfy the set of the above requirements for physical, mechanical and thermal characteristics.

The proposed composition for thermal barrier coatings contains dry redispersible latex as an organic binder, which is a copolymer of vinyl acetate and ethylene or vinyl acetate and vinyl versalate, and also as fillers it contains: vermiculite with a bulk density of not more than 95-110 kg / m ³ and an average particle size of 1 mm perlite with a bulk density of not more than 100 kg / m ^3, kaolin, glass microspheres with sizes of 15-200 microns and a bulk density of 240-320 kg / m ^3, made of borosilicate soda glass, and a fibrous material at a track boiling ratios of mixture components (.% by weight): vermiculite - 4-19, perlite - 4-19, kaolin - 2-4, glass microspheres - 11-26, fibrous material - 2-8, dry redispersible latex - the rest.

The composition additionally as a binder contains cement in an amount of 2-14 wt.%.

As the fibrous material, the composition preferably contains cellulose fibers or ground glass fiber.

The composition, preferably as a redispersible latex, contains copolymers of vinyl acetate and ethylene.

The proposed composition of the dry powder mixture includes all the necessary ingredients in dry form. After mixing with water, it can be used to obtain coatings by known mechanical or manual methods.

The composition has common features with the composition of the prototype: it contains latex as a binder, glass microspheres as a filler.

However, the proposed method uses preferably glass microspheres ranging in size from 15 to 200 μm, mainly from 15 to 125 μm, with a low bulk density of 240-320 kg / m ³ of chemically stable sodium borosilicate glass, which have good compatibility with most polymers. The choice of the claimed quantitative range of microsphere content in the composition (11-26 wt.%) Is explained by the fact that the introduction of less than 11 wt.%, The microspheres have a weak effect on the totality of the properties of the heat-shielding composition, and the introduction of more than 26 wt.%, Leads to a decrease in the elasticity of the coating .

In contrast to the prototype, the proposed composition contains, in addition to microspheres, other light fillers, namely vermiculite and perlite, which are recognized as unique in their structure and properties. The introduction of these materials significantly increases the heat-shielding properties of the coating and reduces its density. The proposed composition also includes additives of reinforcing fibrous material, kaolin, designed to increase the strength of TZP. For the same purposes, the composition may contain a certain amount of cement.

Perlite is known to be volcanic glass. It contains oxides of silicon, aluminum, sodium, potassium, iron, calcium and magnesium, as well as from 2 to 5% water. It is inert, has a low bulk density (within 100 kg / m ³ ). In the proposed composition, it is introduced in an amount of 4-19 wt.%, Which significantly reduces the density of TZP. A decrease in the percentage of perlite below 4 wt.% Does not significantly affect the density of the coating, an increase of more than 19 wt.% Leads to the appearance of shrinkage and cracking in the coating when exposed to high temperatures.

Vermiculite is a product of secondary alteration (hydrolysis and subsequent weathering) of dark mica biotite and phlogopite. Represents large lamellar crystals of golden yellow, brown, yellowish-brown, bronze yellow or greenish-blackish color. When heated to a temperature of 900-1000 ° C, the volume of the original mineral increases in volume by 15-25 times. The industry uses the expanded vermiculite obtained in this way - a light heat-resistant material of a finely scaled structure. Vermiculite is part of many fire retardant coatings, and is also used as a heat-insulating aggregate of fire-resistant structures in the compositions of heat and sound insulating building mixtures (RU 2169717, С04В 28/26; RU 20779525, C01D 5/18, 2001). When using ground vermiculite with a particle size of 3 to 10 μm (RU 2148066, C09D 5/18, 2000), high density densitizers are obtained that are not acceptable for solving the task.

In the inventive composition, it is proposed to use vermiculite of light grades KVV-2 and KVV-4 with a bulk density of not more than 110-95 kg / m ³ with an average particle size of about 1 mm. Vermiculite is introduced into the composition in the same amounts as perlite (4-19 wt.%). A decrease in the proportion of vermiculite below 4 wt.% Does not affect the decrease in the density of the coating, an increase of over 20 wt.% Leads to a decrease in the elasticity of the coating.

The proposed method also uses a small additive of kaolin as a refractory light filler, which helps to increase the ductility and astringent properties of the composition. Enriched kaolin of grades KR-1 and KR-2 according to GOST 19608-84 is preferred. Kaolin is introduced into the proposed composition in an amount of 2-4 wt.%. In case of underestimation of the amount of kaolin below 2 wt.%, An increase in the ductility of the composition after exposure to high temperatures is not achieved; in case of overstatement of more than 4 wt.% - the density of the fire retardant coating increases.

As a fibrous material, the composition, for example, contains ground fiberglass of the TIAS brand with a fiber length of 0.05-1.0 mm and a bulk density of 250-300 kg / m ³ or materials from natural cellulose fibers. A good result is shown, for example, by a composition containing fibers of the trademark "TC" of the German company CFF GmbH & Co.KG. Products brand "TS", as you know, is made from technical cellulose, has a fiber length of 20-2500 microns with a diameter of about 25 microns and a bulk density of 20-250 kg / m ³ . Such fibers have a high tensile strength, are inert to acids and bases in the pH range from 4 to 12, physiologically and toxicologically safe.

It should be noted that the use of the above fillers in the claimed amounts having different characteristics, such as the structure and shape of the particles, surface morphology, and dispersion, allows to obtain light coatings with high strength. The proposed composition as an organic binder contains dry redispersible latex, which allows you to make the composition for thermal protection coatings in the form of a dry mixture of powder components, which is technologically, environmentally and economically preferable compared to using a water-dispersion composition as a binder. As dry redispersible latexes in the claimed composition, known homo- and copolymers of vinyl acetate, ethylene and vinyl versalate are used, as well as copolymers of vinyl acetate, acrylic ester and versatic acid vinyl ester. It is preferable to use copolymers of vinyl acetate and ethylene, for example, VINNAPAS 705 5N, 4042H, 4023H or copolymers of vinyl acetate and versalate of various brands of the NEOLITH series. Dry latexes are obtained by spray drying of water-dispersed polymers and retain their properties during repeated dispersion (redispersion).

Dry mixtures of the proposed composition are obtained by mixing the components in mills of various types. For example, in laboratory conditions, a mill of the MShL-1P brand can be used to mix the components of the mixture, in which mixing is performed in porcelain drums without grinding media for 0.5 hours.

For the manufacture of TZP, the dry mixture obtained from the listed components is mixed with water directly at the production site before application to the product.

The advantages of the proposed structure are that:

- the composition provides the thermal characteristics necessary for the operating conditions: thermal conductivity 0.07-0.1 W / m K, heat capacity 1.0-1.2 kJ / kg K and provides the temperature under the heating current during the critical heating time at 800 ° C not above 110-130 ° C;

- the combination of physico-mechanical characteristics of a coating made from a dry mixture: density, tensile and compressive strength under extreme loads (elasticity), adhesion to substrates made of metal alloys, carbon fiber reinforced plastic and fiberglass plastic provide operational qualities of the coating under extreme conditions, excluding delamination, cracking and resistance to vibration.

- technologically, the use of a dry mixture, including all the necessary ingredients of the coating, is appropriate and not laborious;

- the proposed composition of the dry mix is environmentally friendly, because it is water-soluble and when using the dry mix does not have to use organic toxic solvents or water-dispersible polymers;

- the use of the proposed composition is economically advantageous, since it is created using inexpensive and affordable lightweight inorganic fillers and fibrous materials that have not previously been used in space technology.

Below the invention is illustrated by the Table, which gives examples of compositions for the manufacture of heat-protective coatings. These examples do not limit the possibility of compiling compositions of the same qualitative composition, differing in the quantitative ratios of the components, but chosen within the claimed numerical limits (without expanding the scope of the claims).

Table Component The proportion of the component, wt.% Sample No. one 2 3 four 5 6 7 8 9 10 Vermiculite eighteen 19 max fourteen fifteen 13 eleven four 4 min 16 12 Perlite 17 19 fourteen fifteen fourteen eleven four four fifteen 13 Microspheres 17 16 17 fourteen fifteen eleven twenty 26 fifteen 13 Kaolin 2 four 2 four 3 2 2 four four 2 Cement fourteen 10 10 8 3 four 2 - 10 2 Technogel 2 - 8 - 2 - - 2 2 TIAS - 2 - 2 - 3 8 8 - Neolithic 4400 - - - - - - - 56 Winnapas 4023 - - - - 52 58 - 60 40 - Winnapas 4042 - - - 40 - - - - Winnapas 7055 thirty thirty 35 - - - 60 - σ _us .SS, kg / m ³ 326 256 285 307 377 400 325 372 311 273 ρ TZP, kg / m ³ 379 354 374 402 499 556 527 481 338 382 σ _growth , MPa 1.4 0.33 0.44 0.8 1,1 0.8 0.9 1.4 σ _compress MPa 1.9 0.94 0.91 2.1 1,2 0.8 1.7 1.9 σ _neg. MPa 0.38 0.44 0.45 1,66 λ, W / m K 0.0085 - 0.07-0.1 0.009 - 0.0085 C _r , kJ / kg K 1.0-1.2 - 1.0-1.2 1,1 - 1.0-1.2 Тпод ТЗП, ° С 310 - 140 105 - 110 Legend: σ _us. SS - bulk density of the dry mixture; σ _otp — _ultimate compressive stress; ρ ТЗП - density of heat-shielding coating; λ - thermal conductivity coefficient:
σ _rast - tensile stress; With _p - specific heat;
Т under ТЗП - temperature on the inner side of the substrate after exposure to a thermal load of 800 ° С 10 min.

Claims (4)

1. The composition for thermal barrier coatings containing a latex organic binder and a group of fillers, including glass microspheres, characterized in that the quality of the organic binder contains dry redispersible latex, which is a copolymer of vinyl acetate and ethylene or vinyl acetate and vinyl versalate, and also as fillers contains: vermiculite with bulk density of 95-110 kg / m ³ and an average particle size of 1 mm, perlite with a bulk density of not more than 100 kg / m ³ , kaolin, glass microspheres with dimensions of 15-200 microns and bulk density of 240-320 kg / m ³ made of sodium borosilicate glass and fibrous material with the following ratios of the components of the mixture, wt.%:
Vermiculite 4-19 Perlite 4-19 Kaolin 2-4 Glass microspheres 11-26 Fiber material 2-8 Latex Rest 2. The composition according to claim 1, characterized in that it additionally contains cement in an amount of 2-14 wt.% As a binder. 3. The composition according to claim 1, characterized in that as the fibrous material, preferably, contains cellulose fibers or ground glass fiber. 4. The composition according to claim 1, characterized in that, preferably, as a redispersible latex contains copolymers of vinyl acetate and ethylene.