RU2268277C2 - Method of preparing polysulfide rubber-based anticorrosive coating - Google Patents

Abstract

FIELD: protective coatings.

SUBSTANCE: invention aim is preparation of coatings providing long-term protection of chemical shop equipment under alternate alkali and acid solution action conditions. Protection of equipment, according to invention, is provided by polysulfide sealant having prolonged durability owing to lowered permeability and swelling ability of cured coating material on contact with water and aqueous acid and alkali solutions. Coating is formed by consecutively depositing curable primer and transition adhesive layer onto cleaned metal followed by layer-by-layer application and curing of polysulfide sealant. On the surface of cured coating, additional anti-diffusion polymeric layer based on chlorinated polyvinylchloride resin is formed.

EFFECT: achieved long-term protection of equipment.

Description

The invention relates to the field of production of coatings based on polysulfide rubber used in the technique of anticorrosive protection of metals. The proposed technical solution can be used, for example, for long-term protection of the equipment of chemical shops of power plants, operated under conditions of variable exposure to solutions of acids and alkalis.

A known method of producing coatings of polysulfide rubber by the method of flame or vortex spraying. Rubber grades are used in the form of finely dispersed powders, which, when heated without pressure, can become viscous. The compositions contain a vulcanizing agent and a vulcanization accelerator, which occurs during the spraying process at high temperature. The disadvantage of this method is the high energy intensity and the release of harmful and badly smelling gases, which are the products of thermal decomposition of thiol.

[1] Encyclopedia of Polymers. T. 1. - M .: Soviet Encyclopedia, 1972, p. 644-665.

Known two-component sealants based on liquid thiokol, in particular U-30M. The method of forming coatings by using them does not require the use of elevated temperatures, because vulcanization is realized without heating under the action of a crosslinking agent and a vulcanization accelerator. However, the coating material is characterized by low adhesion to most substrates, low tear resistance, and most importantly, relatively high swelling upon contact with water and acid solutions.

[2] Mudrov O.A., Savchenko I.M., Shitov B.C. Handbook of elastomeric coatings and sealants in shipbuilding. - L .: Shipbuilding, 1982.

There is a method based on the use of varieties of U-30M sealant modified with epoxy resin under the brands U-30MES-5 and U-30MES-10. The content of epoxy in the vulcanizing paste is 5 and 10 mass parts, respectively. The introduction of an epoxy resin provides an acceptable level of adhesive properties of the coating material, but significantly increases the water absorption and swelling in aqueous electrolyte solutions due to the appearance of easily solvable hydroxyl groups in the reaction product of liquid thiol with an epoxy resin.

[3] Averko-Antonovich L.A., Kirpichnikov P.A., Smyslova R.A. Polysulfide oligomers and sealants based on them. - L .: Chemistry, 1983, p. 85-87.

Closest to the proposed technical solution is a method for producing thiokol coatings of cold drying from U-30M sealant by preliminary applying primer and / or adhesive sublayers based on epoxy, chloronairite and other adhesive compositions to sandblasted or single-bonded metal, followed by applying the main coating material and curing it directly on the surface of the protected metal.

[4] Labutin A.A. Corrosion-resistant and sealing materials based on SC. - L .: Chemistry, 1982, p.129-138.

The use of primer-adhesive sublayers leads to the achievement of the necessary adhesion to carbon steel. However, the material of the vulcanized coating of the sealant U-30M with such a protection system does not provide sufficient durability due to the relatively high permeability during operation under conditions of exposure to solutions of acids, alkalis and water.

The effect of increasing the protective ability of a polymer coating against aggressive media as a result of inhibition of the metal corrosion process under the coating depends on the following main factors: permeability, electrical resistance, adsorption of the corrosive agent on the metal surface and the level of adhesive interaction with the substrate.

Known methods of coating formation and the direct nature of the polysulfide vulcanizate do not provide the necessary result in terms of the possibility of a complex effect on these factors.

The traditional gumming with thiol pastes using the spatula method is a laborious and inefficient process. When applying compositions of a more liquid consistency (containing solvents to reduce viscosity) by airless spraying, the porosity of the coating is not guaranteed due to diffusion volatilization of the dissolving agent. The resulting surface or through pores are "weak", defective places that adversely affect the protective properties of the coating.

The analyzed sources focus on increasing adhesion at the metal – sealant interface [2-4]. However, these solutions do not contribute to the realization of the main goal - to reduce the degree of swelling of the coating material and increase its durability, especially when used in such specific conditions as the variable exposure to aqueous solutions of acid and alkali. In this regard, it is obviously advisable to apply an additional polymer layer, the functional purpose of which is to reduce permeability due to barrier inhibition of diffusion of the medium into the coating material.

The technical task implemented by the proposed method is to obtain a protection system based on a polysulfide sealant, which increases the durability of the coating by reducing the permeability and degree of swelling of the vulcanized coating material in contact with water and aqueous solutions of acid and alkali.

The stated technical problem is solved by sequentially applying a cured primer layer of epoxy resin-based EP-0010 based on epoxy resin in combination with an amine type hardener, a transition adhesive undercoat of polysulfide sealant U-30M based on grade 1 liquid thiol, a filler, curing agent, vulcanization accelerator - diphenylguanidine in combination with epoxy resin ED-20 and hardener polyethylene polyamine, followed by layer-by-layer n application and vulcanization of the U-30M polysulfide sealant, while on the surface of the vulcanized coating an anti-diffusion polymer layer is additionally formed from XB-784 varnish based on chlorinated polyvinylchlorinated resin dissolved in a mixture of volatile organic solvents with the addition of a plasticizer.

The analysis of technology, including a search by patent and scientific and technical sources of information and identification of sources containing information about analogues of the invention, allowed to establish that the applicant has not found an analogue characterized by features identical to all the essential features of the claimed invention, but determined from the list of analogues of the prototype, as the closest analogue in terms of the totality of features, it was possible to identify the set of essential technical results regarding distinctive signs in the claimed object set forth in the claims. Therefore, the invention meets the requirement of "novelty" under applicable law.

To verify the conformity of the claimed invention to the requirements of the inventive step, the applicant searched for known solutions in order to identify features that match the features of the invention that are distinctive from the prototype, the results of which show that the invention does not explicitly follow from the prior art, as the prior art defined by the applicant , the influence of the conversion provided for by the essential features of the invention on the achievement of the technical result is not revealed. Therefore, the invention meets the requirement of "inventive step" under applicable law.

The essence of the sequence of technological operations and the used component composition of the polymer coating system is as follows.

When sandblasting or shot blasting, the metal surface becomes rough and is activated as a result of an increase in polarity due to the formation of metal oxides. Subsequent application of a primer based on a polar epoxy film former ensures a high degree of adhesive interaction in the substrate-adhesive system. In addition, the use of a cured primer putty helps to smooth out the overall surface topography and improve contact conditions with the following coating layers.

The cured primer layer is a three-crosslinked, high modulus and inelastic product. Consequently, when a polysulfide sealant is applied directly onto it, which does not have its own adhesion and forms a low-modulus elastic material after vulcanization, the latter can peel off with violation of coating continuity and subsequent introduction of an aggressive medium at the interface. In this regard, it is necessary to use a transition sublayer, which has an "affinity" for both the primer layer and the vulcanized coating material. In this case, a sufficiently high adhesion between the layers is ensured and the difference between their elastic moduli, linear expansion coefficients, and the level of internal stresses is compensated.

In terms of achieving the desired technical result, it is crucial that a vulcanized coating based on a polysulfide sealant contains an additional anti-diffusion layer formed from chlorinated polyvinyl chloride resin. The presence of such a layer from a reasonably selected film former determines the following.

Firstly, the mechanical microporosity of the surface of the polysulfide vulcanizate is reduced due to the leveling (overlapping) of existing defects formed after the volatilization of the dissolving agent during coating formation.

Secondly, the ability of the material to prevent the penetration of an aggressive environment to the protected surface as a result of one-sided diffusion due to inhibition of the transfer of corrosive components through the main polysulfide coating and primer layer is increased.

Thirdly, the ionic permeability of the coating system as a whole is reduced by providing a certain diffusion selectivity by applying polymer layers of different chemical nature and thickness.

The choice of chlorinated polyvinyl chloride resin as the basis for the anti-diffusion layer is due to the fact that it is a polar polymer capable of forming coatings with high weather and water resistance, strength and elasticity, as well as resistance to mineral acids and alkalis.

To implement the proposed method using the following materials.

As a cured primer, an EP-0010 grade epoxy putty (GOST 10277-76) is used in combination with an amine type hardener, for example, polyethyleneamine (PEPA) according to TU 6-02-1099-83.

As an adhesive sublayer, a mixture of polysulfide sealant of the U-30M grade (GOST 13489-79) with an epoxy resin of the ED-20 grade (GOST 10587-84) is used. The hardener of the adhesive sublayer is PEPA.

The U-30M polysulfide sealant is made of brand 1 liquid thiol, carbon black as a filler, a curing agent - manganese dioxide dispersed in a phthalate ester plasticizer and a vulcanization accelerator. It is produced in accordance with GOST 13489-79 and is supplied in the form of three components: U-30M sealant, vulcanizing paste No. 9, and diphenylguanidine (DFG) vulcanization accelerator.

The basis of the diffusion layer is a film-forming composition of chlorinated polyvinyl chloride resin grade PSX-L in the form of varnish ХВ-784 (GOST 7313-75), which is a solution of this polymer in a mixture of volatile organic solvents with the addition of a plasticizer.

Solvent R-4 (GOST 7827-74) is used as a diluting agent with which the initial working viscosity of the primer layer, adhesive undercoat, sealant and varnish ХВ-784 is regulated.

Concrete example

Samples of dimensions 70 × 70 × 1 mm are made of steel-3. The surface of the samples is prepared by sandblasting or shot blasting.

Prepare the working composition of the primer layer based on EP-0010 putty, PEPA hardener and R-4 solvent. Dosing of components (mass ratio putty: hardener) is carried out in accordance with the passport recommendations for this batch of putty. Solvent R-4 is used in amounts necessary to achieve optimal viscosity, depending on the method of applying the working composition. The components are mixed thoroughly to evenly distribute the hardener in the bulk. Then the primer layer is applied on all sides to the surface of the samples in one layer. The curing time of the primer is 24 hours at a temperature of 18-20 ° C.

To prepare the working composition for the cured transitional adhesive sublayer, the components are taken in the following ratio, parts by weight:

epoxy resin ED-20 one hundred polysulfide sealant U-30M twenty PEPA hardener 10 solvent R-4 thirty

The calculated quantities of U-30M sealant and ED-20 epoxy are loaded into separate containers and diluted with solvent R-4 to a viscosity of 40-50 s according to VZ-4 at 20 ° C. Both solutions are poured into one container, again thoroughly mixed until a homogeneous mass is obtained (for at least 5 minutes).

The life time of the curable composition at a temperature of 18-20 ° C is 1-1.3 hours. Full cure time 24 hours.

To carry out the next technological operation (layer-by-layer deposition and vulcanization of a polysulfide sealant) materials are used in the following ratio of components, parts by weight:

polysulfide sealant U-30M one hundred vulcanizing paste No. 9 9 accelerator DFG 0.2 solvent R-4 fifteen

The required amount of pre-mixed polysulfide sealant is taken, the calculated amount of P-4 is introduced into it and mixed. Add the calculated dosage of the vulcanizing paste, which is also mixed before sampling. Intensive mixing of the composition is carried out for 3-5 minutes. The required amount of DPH is added to the resulting homogeneous mixture and finally mixed. Potlife is 2-4 hours.

The surface of the samples from all sides is covered with a composition in one layer and cured for 24 hours at a temperature of 16-20 ° C.

The thickness of the formed single-layer coating when applied by airless spray is 100-120 microns.

Subsequent layers are applied and cured in the same way. Depending on the required coating thickness, the required number of layers is applied. So, for example, to obtain a coating with a thickness of 1.5 mm, 14-15 layers of sealant are applied.

Next, an anti-diffusion polymer layer is formed on the entire surface of the samples by, for example, air spraying of varnish XB-784, which is thoroughly mixed before use.

If necessary, the varnish is diluted to a working viscosity with solvent R-4 (viscosity according to VZ-4 19-23s at 20 ± 2 ° С for air spraying).

Claims (1)

A method of obtaining an anti-corrosion coating by sequentially applying a cured primer layer of epoxy resin-based EP-0010 epoxy-based filler in combination with an amine-type hardener, a transition adhesive undercoat of polysulfide sealant U-30M based on liquid thiol, filler, vulcanizing agent on sandblasted or homogenized metal vulcanization accelerator - diphenylguanidine, in combination with epoxy resin ED-20 and hardener polyethylene polyamine, followed by layering the cross-linking and vulcanization of the U-30M polysulfide sealant, characterized in that an anti-diffusion polymer layer of XB-784 varnish is additionally formed on top of the vulcanized coating based on chlorinated polyvinyl chloride resin dissolved in a mixture of volatile organic solvents with the addition of a plasticizer.