RU2392291C2 - Protective coating for metal surfaces - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: coating for metal surfaces includes 3.0% solution of refined sodium carboxymethyl cellulose in amount of 92-100 weight parts, spherical disperse aluminium powder in amount of 5.6-7.6 weight parts, glycerin in amount of 5.0-7.6 weight parts.

EFFECT: enhanced mechanical and adhesive durability of coating.

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Description

The invention relates to a type of protective coatings based on the polymer component of purified sodium carboxymethyl cellulose (a class of polysaccharides) designed to protect metal surfaces from aggressive environments.

Known material designed to protect metal pipelines during pumping of aggressive media (US Pat. No. 2321610 RF: IPC ⁵¹ C09D 101/28, C08L 1/28, B65D 90/06, C08K 3/08, C08K 5/053. Protective coating for metal surfaces / N.M. Antonova, G. G. Melnik. - April 3, 09.01.2007; publ. 10.04.2008, Bull. No. 10). The material contains a 2.0% solution of purified sodium carboxymethyl cellulose, zinc powder PC1 and glycerin in the following ratio of components, parts by weight: 2.0% solution of purified sodium carboxymethyl cellulose 94-100; zinc powder PTs1 0.5-1.5; glycerol 0.9-1.5. EFFECT: invention makes it possible to obtain a coating having predetermined electrophysical characteristics, which ensure that the accumulated aggressive fluid flows through the electric charge pipes to ground loops, is simple to manufacture and apply to the surface, and can be operated in the temperature range 0-200 ° C. The mechanical strength of the obtained coating is 10 MPa, the relative strain value is 17.0%, the adhesive strength is 1 point, and the coating thickness is 70 μm.

The disadvantage of this coating is the duration of manufacture (6 hours), low mechanical strength of the coating.

The closest in composition to the claimed is a protective coating for metal surfaces. (Pat. No. 2266307 RF: MPK7 C08L 1/28, C09B 199/00, C09J 101/28, B65D 90/06. Protective coating for metal surfaces / N.M. Antonova, O.V. Aksenova, V.I. Kulinich, I.A. Neelova. - Application. 23.08.2004; publ. 20.12.2005, Bull. No. 35). The proposed material contains a polymer component - 2.25% solution of purified sodium carboxymethyl cellulose / TU 6-55-39-90 /, which is a sodium salt of cellulose glycolic acid, dispersed aluminum powder dispersed / TU 48-5-226-87 /, and glycerin in the following ratio of components, parts by weight: 2.25% solution of purified sodium carboxymethyl cellulose 98-102, dispersed spherical aluminum powder 0.74-2.5, glycerol 0.74-2.5. The mechanical strength of the obtained coating is 25 MPa, the relative strain is 22.8%, and the coating thickness is 50 μm.

The disadvantage of this coating is the duration of manufacture (10-12 hours).

The objective of the invention is to obtain a protective composite coating resistant to aggressive solvents and polyester unsaturated varnishes, having a thickness of not more than 40 μm, with mechanical characteristics that meet operational requirements, ease of manufacture and application to the surface, environmentally friendly, operated in a wide temperature range (0- 200 ° C).

The problem is achieved due to the fact that the proposed composition, in addition to purified sodium carboxymethyl cellulose / TU 6-55-39-90 /, which is the sodium salt of cellulose glycolic acid, and glycerol additionally contains an aluminum powder fraction with a particle size of 10-20 μm, obtained by sieving from a spherical dispersed aluminum powder containing particles up to 40 microns in size / TU 48-5-226-87 /, in the following ratio of components, parts by weight:

3.0% purified sodium carboxymethyl cellulose solution 92-100 spherical dispersed aluminum powder 5.6-7.6 glycerol 5.0-7.6

An aluminum powder fraction with a particle size of 10-20 μm was obtained using electrostatic sieving on an ELSA-2 electrostatic analyzer. In the work, nickel mesh cloths with exact cell sizes were used. A solution of purified sodium carboxymethyl cellulose of the appropriate concentration was stirred at a frequency of 60 rpm for 10 minutes at a temperature of 60 ° C in a reactor with a frame stirrer and a heating jacket, and the solution was kept for 1 hour until the sodium carboxymethyl cellulose was completely dissolved at the same temperature. Then glycerin and aluminum powder with a particle size of 10-20 μm were added and further mixed for another 10 minutes. The resulting gel-like solution was applied onto a pre-treated 08kp steel surface. A surface with a coating thickness of at least 40 μm was dried for 2 hours at a temperature of (100 ± 2) ° С. The total time of manufacture and drying of the coating does not exceed 3.5 hours. This is due to the absence in the solution of aluminum powder particles with sizes less than 10 microns, prone to the formation of agglomerates and leading to structural inhomogeneity of the coating, as well as an increase in the temperature of mixing the solution and drying of the coating.

The resulting composite coating has mechanical properties at a coating thickness of 40 μm: mechanical strength of the resulting coating σ = 30.6 MPa, relative strain ε = 16.0%, adhesive strength 1 point, which allows to achieve a technical result, which is as follows:

- screening particles of aluminum powder with a size of more than 20 microns leads to a decrease in oxide inclusions, representing a loose oxide film on metal particles. The number of defects on the surfaces of the particles, which are stress concentrators, decreases, and the mechanical strength of the coating increases;

- particles of aluminum powder, having a size comparable to the roughness of the microrelief of the surface to be protected (08kp steel), fill its troughs and are evenly distributed in the coating volume, providing strong adhesion of the coating to the metal surface and high adhesive strength of the coating;

- the availability of aluminum powder provides significant savings in obtaining coatings.

To determine the mechanical characteristics of the coating, 40 μm thick films with particles of aluminum powder with sizes of 10–20 µm, 21–30 µm, and 31–40 µm were made from the solution by pouring. Characteristics - mechanical tensile strength (σ, MPa) and elongation at break (ε,%) were determined in accordance with the method described in OST 84-434-71, adhesive strength according to GOST 16253-70 (here 1 point is the best adhesion, 5 points - unsatisfactory).

The test results are shown in table 1 (examples 1-3). The obtained mechanical characteristics for the composition with aluminum powder, with particles of 10-20 microns in size met operational requirements and are given in table 1 (example 1).

To analyze the processes of joint structure formation of combinations of aluminum powder with particle sizes of 10 ÷ 20 μm, 21 ÷ 30 μm, and 31 ÷ 40 μm, respectively, with purified sodium carboxymethyl cellulose and glycerin, and the influence of these processes on the mechanical characteristics, an electron microscopic analysis of coating samples was performed.

The drawing shows fragments of the surface of the samples of the obtained composite coatings.

With increasing particle size of aluminum, the number of oxide inclusions, the thickness and friability of the oxide film on the particles, the defects on its surface increase and serve as stress concentrators (drawing, A), which leads to a decrease in strength. Smaller particles (10 ÷ 20 μm) have a thinner film without defects, are distributed uniformly in the matrix and cause increased strength of the metal-polymer interface. When the particle size is less than 10 microns, the tendency of the fine fraction to agglomerate both inside and at the coating boundaries prevails. Coagulants from such particles of aluminum powder contribute to improving the adhesion of the coating to the surface to be protected, acting as constricting elements, however, the structural uniformity of the coating, which does not contain larger particles of aluminum powder, is broken, and the strength decreases (Figure B).

The sodium-carboxymethyl cellulose polymer purified without metal powder and glycerin in the coating has a layered structure that promotes crack formation (Figure B). The plasticizer plays the role of a component that reduces internal stresses in the composite and at the “protected surface - coating” interface, increasing mechanical strength by increasing the elastic properties of the coating. The addition of aluminum powder having a particle size of 10 ÷ 20 μm to the composition of the powder allows for a lower coating thickness of 40 μm to obtain higher mechanical characteristics and significantly reduce its drying time.

The combined combination of sodium carboxymethyl cellulose purified with glycerin and aluminum powder with particles of 10 ÷ 20 μm in size allows to obtain a coating with high protective properties, along with mechanical characteristics meeting the operational requirements: fracture strength (σ, MPa), relative deformation (ε, %) and adhesive strength. For three ranges of particle sizes 10 ÷ 20, 21 ÷ 30, 31 ÷ 40 μm, the optimal values were determined in each range using the method of mathematical planning of the experiment: temperature conditions, particle size, combinations of components that provide specified mechanical characteristics that satisfy operational requirements.

Example 1. Samples obtained using fractions with particle sizes of aluminum powder 10 ÷ 20 microns.

A gelled 3.0% purified sodium carboxymethyl cellulose solution contained over 100 g of a solution of 5.6 g of aluminum powder with a particle size of 10 μm and 7.6 glycerol. By pouring from the obtained gel solution, a film with a thickness of 40 μm was prepared, dried at a temperature of 100.0 ° C.

The mechanical characteristics — fracture strength (σ, MPa) and elongation at break (ε,%) —determined in accordance with the method described in OST 84-434-71, on a tensile testing machine RM-4, providing a moving gripping speed relatively stationary 2.5 mm / min, the values of the adhesive strength of the coating to the surface of the steel 08 kp according to GOST 16253-70.

The values of mechanical strength (σ), relative deformation (ε) and adhesive strength satisfy the operational requirements. The results are shown in table 1.

The coating is heat-resistant in the temperature range ≤200 ° С.

Example 2. Samples obtained using a powder fraction with sizes of 21 ÷ 30 microns.

Samples were obtained on the basis of a 2.3% solution of sodium carboxymethyl cellulose purified with the addition of 1.7 g of aluminum powder with a particle size of 28 μm and 0.6 g of glycerol to 100 g of the solution as described above. A film with a thickness of 40 μm was dried at a temperature of 44.0 ° C and tested as described in example 1. The test results are shown in table 1.

The mechanical strength (σ) is low, the relative deformation (ε) meets the operational requirements, and the adhesive strength is high. The results of mechanical tests do not meet operational requirements and are given in table 1.

The coating is heat-resistant in the temperature range ≤200 ° С.

Example 3. Samples obtained using a powder fraction with sizes of 31 ÷ 40 microns.

A gelled 2.7% purified sodium carboxymethyl cellulose solution contained over 100 g of a solution of 3.5 g of aluminum powder with a particle size of 40 μm and 0.8 g of glycerol. A film with a thickness of 40 μm was dried at a temperature of 43.8 ° C and tested as described in example 1. The test results are shown in table 1. The results of mechanical tests do not meet operational requirements.

The coating is heat resistant in the temperature range ≤200 °.

The compositions indicated in examples 1, 2, 3 were tested for resistance to aggressive environments. For this, coated steel samples (coating thickness 40 μm) were dried for 2 hours at a temperature of (100 ± 2) ° С and tested for resistance to aggressive media - solvents and polyester varnish. The test results are shown in table.2.

The ratio of the weight parts used in examples 1, 2, 3, are shown in table.3.

From the described examples it is seen that the best quality coating is obtained on the basis of the composition described in example 1.

Table 1 σ, MPa ε,% Adhesion points Note 30.6 16,0 one Example 1 11.8 12.0 one Example 2 10.8 16,0 2 Example 3

table 2 Sustainability Note Solvents Unsaturated polyester varnishes Toluene Ethyl acetate Acetone Ethanol Styrene PE-246 + + + + - + Example 1 + + + + + + Example 2 + + + + - - Example 3

Table 3 Weight ratio The solution of sodium carboxymethyl cellulose purified Aluminum powder Glycerol Particle size, microns Coating drying temperature, ° С Note 3.0% - 100 parts by weight 5.6 parts by weight 7.6 parts by weight 10 100.0 Example 1 2.2% - 100 parts by weight 1.7 parts by weight 0.6 parts by weight 28 44.0 Example 2 2.7% - 100 parts by weight 3.5 parts by weight 0.8 parts by weight 40 43.8 Example 3

Claims (1)

A protective coating for metal surfaces containing a purified sodium carboxymethyl cellulose solution, spherical dispersed aluminum powder and glycerin, characterized in that a 3% purified sodium carboxymethyl cellulose solution is used, and a spherical dispersed aluminum powder with a particle size of 10-20 μm in the following ratio components, parts by weight:
3.0% purified sodium carboxymethyl cellulose solution 92-100 spherical dispersed aluminum powder 5.6-7.6 glycerol 5.0-7.6

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