RU2457228C2 - Method of producing compositions for making antifriction coatings on metal surfaces - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: composition contains polyamide acid-based lacquer, a lubrication mixture, a soot paste, a mica-based paste, an aqueous suspension of polytetrafluoroethylene, polyvinyl pyrrolidone and water. The soot paste contains fine carbon fibres (nanofibres). The lacquer is mixed with the mica-based paste. The obtained mixture is mixed with the aqueous suspension of polytetrafluoroethylene, the soot paste, the lubrication mixture, polyvinyl pyrrolidone and water. The mixture is stirred to a homogeneous composition and an aqueous suspension of a tetrafluoroethylene and hexafluoropropylene copolymer is further added. The invention enables to obtain a homogeneous malleable composition (without formation of agglomerates) upon deposition on metal surfaces of which there is no formation of microreliefs, voids, bubbles and other microdefects in the structure of the coatings, which improves physical-mechanical and tribological characteristics of the coatings. The coating made from said composition can act a priming and a finishing coat.

EFFECT: coating made from the composition using this method has improved antifriction properties.

2 cl, 2 tbl, 6 ex

Description

The invention relates to the field of applying non-stick, corrosion-resistant, wear-resistant and anti-friction coatings that can be used on products used in food, chemical, engineering industries, and also to compositions for coating.

A known method for producing a coating composition containing a dispersion of polytetrafluoroethylene (PTFE), demineralized water, mica (coated with titanium dioxide), a coloring pigment (contains iron oxide, demineralized water, oleic acid, triethanolamine, butylcarbitol, toluene), a mixture containing triethanol acid, toluene, butyl carbitol, the mixture additionally containing methyl methacrylate and a copolymer (40% aqueous dispersion) (see UK patent No. 1557230, class C09D 127/18, 1976).

The composition is prepared by introducing said components into the fluoroplastic dispersion.

As a result of the analysis of this invention, it should be noted that the coating based on the specified composition is not sufficiently resistant to thermal shock, and also has a low thermal resistance, which reduces the service life of the coating under operating conditions.

A known method of producing an antifriction composition by mixing a salt of polyamic acid, which includes furfuryl alcohol and N-methylpyrrolidone, water with a dispersion of white pigment, with a dispersion of polytetrafluoroethylene and a silicone preparation. The dispersion of the white preparation is obtained by mixing titanium dioxide, water and a mixture of triethanolamine and oleic acid (GB No. 1563814, 1976).

However, this composition does not provide sufficient adhesive strength with the substrate and does not have good antifriction properties. Composite materials are known for the manufacture of sliding bearings, mechanical seals and other elements of friction units by mixing polytetrafluoroethylene with inorganic fillers of various chemical nature (Istomin N.P. et al. "Antifriction properties of composite materials based on fluoroplastics" M .: Nauka, 1987, p. .147).

These materials are known as self-lubricating antifriction with a low coefficient of friction, but they have low deformation-strength characteristics, which reduces their performance, and they are not suitable for antifriction coatings. A known method for producing a composite material by mixing polytetrafluoroethylene with an ultrafine inorganic filler β-sialon of the general formula Si 6-x Al ON 8-x, having high wear resistance in combination with high elastic-elastic characteristics, the material is characterized by instability of the friction coefficient and strong wear in the upper the operating limit of the material in the composition of the product (0.5-1.0 wt.) (TU 301-05-120-81) "Low-fluorine-filled compositions of antifriction purpose). This material, in addition, is not used as coatings.

A known method of obtaining a composition for producing an antifriction coating by preparing a solution in an organic solvent of an organofluorine surfactant - an epilameperfluoroxyalkylene or perfluorinated polyalkylene oxide compound in the form of their nitrogen-containing derivatives (RU 2139902, 10.20.1999).

From RU 2278875, 06/27/2006 a method for producing a composition for producing an antifriction material by mixing polytetrafluoroethylene with a fluorine-containing oligomer, for example, Epilam or Foleox brands and a copper-containing carbon filler, is known.

The disadvantages of the known methods is that, firstly, they do not provide a coating having the necessary wear resistance and protecting the product surface from damage, subject to significant loads and high temperatures. This drawback is due to the fact that the known method does not provide deep penetration of a relatively viscous antifriction composition into all micropores, microcracks on the surface of the product and the binding of atomic oxygen and hydrogen, which does not protect the surface layer of metal from corrosion and embrittlement caused by atomic oxygen and hydrogen in these micropores and microcracks, which are sources of the spread of corrosion, does not provide the necessary reduction in the gas permeability of the material. In this case, micropores and microcracks concentrate stress and become centers of destruction of the surface of the product, which increases the coefficient of friction, reduces the service life of the product. In addition, the known method does not allow to remove corrosion products from micropores and microcracks that contribute to corrosion on the metal surface, which increases the coefficient of friction. An insufficient decrease in the gas permeability of the product material, which causes the aging of the product material, and a relatively high coefficient of friction cause an insufficient product life, on the surface of which an antifriction coating is applied in a known manner.

The known method provides the penetration of the antifriction composition only into part of these pores and microcracks, however, the corrosion products located there due to insufficient cleaning are displaced onto the surface of the product by the antifriction composition, and the quality of the resulting coating is impaired. In addition, as shown by experiments obtained by the known method of coating, they can be in an operable state at relatively low temperatures (up to 150 ° C). Secondly, the method according to RU 2278875, 06/27/2006 receive compositions that are used in mechanical engineering for the manufacture of friction units of machines and mechanisms for various purposes, but not used for coatings on metal surfaces.

The closest in technical essence to the claimed method and the achieved result is a known method for producing non-stick, antifriction coatings on metal surfaces based on F-4D fluoroplastics or a mixture thereof with F-4MDB fluoroplast (based on polytetrafluoroethylene and a copolymer of tetrafluoroethylene with hexafluoropropylene in combination with varnish on based on a polyamido acid from a partially hydrolyzed polyamido acid esterified with mono-ethanolamine in a mixture of solvents of N-methylpyrrolidone, dimethylformamide and Dye, by introducing into the varnish an aqueous suspension of F-4D fluoroplastic or a mixture of it with an aqueous suspension of F-4MDB fluoroplastic and aqueous mate fillers containing mica, molybdenum disulphide and carbon black, pre-rubbed in aqueous solutions containing polyvinylpyrrolidone and OP-10 emulsifier. The composition is mixed and xylene, ethyl cellosolve and then water are introduced in. The composition may contain pigments - titanium dioxide, iron oxides and other additives (monohydric alcohols, oleic acid, etc.). RU Patent No. 2170286 dated November 26, 1999 “Method for coating a metal surface, primer composition and composition for facing”.

Coatings based on this composition, obtained by a known, specified method, have good physicomechanical, anticorrosive properties, have non-stick and antifriction properties, however, the known method has several disadvantages.

The disadvantages, as studies have shown, are in the initial composition system obtained by the known method, by introducing into the varnish based on polyamide acid from partially hydrolyzed polyamide acid esterified with monoethanolamine, in a mixture of solvents N-methylpyrrolidone, dimethylformamide and water, an aqueous suspension of F-4D fluoroplast or mixtures thereof with an aqueous suspension of fluoroplastic F-4MDB, as well as aqueous pastes of fillers containing mica, molybdenum disulfide, carbon black, trapped in aqueous solutions nilpirrolidona and emulsifier OP-10, introduced after stirring solvents - xylene, ethyl cellosolve and water, and may also be administered titanium dioxide, iron oxides and others.

The specified method of introducing components and their mixtures upon receipt of the composite system does not ensure their uniform distribution, dispersion in the mass of components, partial agglomeration of individual components occurs due to the "enveloping" of their solvents of different nature solvating ability.

When a known composition is applied to a metal surface, agglomerates worsen the spreadability of the composition over the surface, which creates a coating thickness difference, uneven concentration of the components in the coating film, which affects the physicomechanical properties, in particular resistance to loads and abrasion, tribological parameters: friction coefficient in different areas surface has different meanings.

The technical task of the invention is the stabilization of the antifriction properties of the coating, increasing the values of the coefficient of friction.

The stated technical problem is achieved by the method of obtaining a composition for producing antifriction coatings on metal surfaces based on an aqueous suspension of polytetrafluoroethylene in combination with a varnish based on polyamic acid, polyvinylpyrrolidone and auxiliary additives, such as fillers, emulsifier, organic solvents and water, and consisting of the following stages: ) the preparation of varnish based on polyamic acid, including:

I - obtaining a solution of polyamic acid by dissolving polyamic acid in a mixture containing N-methylpyrrolidone, monoethanolamine and water at (20-25) ° C;

II - mixing the solution from stage I with a mixture for varnish containing N-methylpyrrolidone, ethyl cellosolve, butinediol;

b) preparation of a lubricant mixture containing an emulsifier based on ethoxylated alkyl phenols, xylene, ethyl cellosolve and water;

c) the preparation of an aqueous paste based on mica containing mica, an emulsifier based on ethoxylated alkyl phenols, polyvinylpyrrolidone and water;

g) the processing of fine fibers with nanoscale mixture for lubrication from stage (b);

e) the preparation of an aqueous carbon black paste containing carbon black, processed fine carbon fibers with nanosizes (from step g), an emulsifier based on ethoxylated alkyl phenols, polyvinylpyrrolidone and water;

g) combining a varnish based on polyamic acid from stage (a) with a paste based on mica from stage (c);

h) combining an aqueous suspension of polytetrafluoroethylene with the components obtained in stages d), g), b), with polyvinylpyrrolidone and water with stirring to obtain a homogeneous finely divided mixture (composition), while the components of the resulting composition are contained in it in the following ratios, wt. hours:

Aqueous suspension of polytetrafluoroethylene 27.8-8.5 Polyamic Acid Varnish 30.0-55.0 Specified carbon black paste 7.3-1.0 Specified Mica Paste 16.0-8.5 Lubricant mixture 10.7-18.8 Polyvinylpyrrolidone 6.0-1.2 Water 2.2-7.0

When preparing this composition for coating, an aqueous suspension of a tetrafluoroethylene-hexafluoropropylene copolymer may be added to the composition.

In the preparation of this composition, finely dispersed carbon fibers with nanosizes used in the preparation of carbon black paste are pretreated with the aforementioned lubricant mixture used to prepare the composition.

As an aqueous suspension of polytetrafluoroethylene in the implementation of the method according to the invention, for example, an aqueous suspension (55-56%) of polytetrafluoroethylene of the brand F-4D (contains polytetrafluoroethylene, an emulsifier based on ethoxylated alkyl phenols, water) is used. As an aqueous suspension of a tetrafluoroethylene-hexafluoropropylene copolymer, for example, an aqueous suspension of F-4MDB (53-54%) is used. As an emulsifier based on ethoxylated alkyl phenols, for example, auxiliary substances OP-6, OP-7, OP-10 are used. As carbon fibers with nanoscale (finely dispersed), for example, finely dispersed carbon fibers with a size of from 0.01-0.1 microns are used.

The following are examples of water pastes based on mica, carbon black paste, lubricant mixtures used in preparing the antifriction coating composition of this invention.

Example 1 (Composition for lubrication in parts by weight):

xylene 2.5-8.9 ethyl cellosolve 6.7-1.5 emulsifier OP-10 2.0-4.2 water 3.7-9.2

Example 2 (paste based on carbon black in parts by weight):

soot 1.2-0.2 fine carbon fibers (with a size of 0.01-0.1 microns) 0.25-0.05 emulsifier OP-10 1,2-0,12 polyvinylpyrrolidone 1.0-0.05 water 2.0-0.40

Example 3 (Pasta based on mica in parts by weight):

mica 1.8-5.6 emulsifier OP-10 0.6-2.0 polyvinylpyrrolidone 0.4-1.3 water 3.7-10.4

Example 4 (Preparation of the composition according to the invention, with a size of 0.01-0.1 microns):

First, a varnish based on polyamic acid is prepared by preparing a solution of polyamic acid in a mixture containing monoethanolamine, N-methylpyrrolidone and water. Next, a varnish mixture containing ethyl cellosolve, N-methylpyrrolidone, butynediol is added to the varnish, and thus a polyamido acid varnish solution with a dry residue of 7.5-9.0% is obtained.

Prepare a paste based on soot (soot paste), a paste based on mica, and also a lubricant mixture. In this case, finely dispersed carbon fibers are pretreated with a lubricant mixture. The resulting polyamic acid based varnish is mixed with the resulting mica-based paste.

In the aqueous suspension of polytetrafluoroethylene F-4D (54-56%), the obtained mixture of varnish based on polyamic acid with a paste based on mica, a mixture for lubrication, a paste based on soot containing these carbon fibers, polyvinylpyrrolidone and water are introduced. After the introduction of each specified mixture (portion) of the components, everything is thoroughly mixed. The prepared composition has a conditional viscosity of 14-20 seconds (according to VZ 246 with a diameter of 4).

Example 5

The composition is prepared analogously to example 4, but in addition, an aqueous suspension of f-4MDB (based on a copolymer of tetrafluoroethylene and hexafluoropropylene) is used in its preparation.

Example 6

The resulting compositions are tested in terms of “appearance”, which reflects the finely dispersed state of the system. For this, a sample of the composition, for example, 10 ml is diluted with 10 ml of water, mixed and poured onto clean photographic glass. In the film obtained on glass, there are no clots, agglomerates not distributed in the total mass of the composition of the components, in contrast to the previously known composition for coating a metal surface. Obtained according to this claimed invention, compositions for antifriction coatings are used both as primers and as facing coatings. The compositions are applied to obtain anti-friction coatings on previously prepared metal surfaces (aluminum, steel, cast iron, etc.).

The preparation of metal surfaces is carried out in any of the ways known for this metal, which ensures the complete absence of grease (oil) and other contaminants (degreasing, etc.). The composition is applied by known methods, for example, by aerosol spraying or rolling. On the prepared metal surface, the composition is applied to obtain a coating according to the invention in several layers. The number of applied layers, their thickness are determined by the specific purpose, operating conditions of the resulting coating, type (type) of products on which the composition is applied (plain bearings, molds, gas-dynamic bearings, thermocouples, etc.). The total thickness of the applied multilayer coating can be 40-55 microns, with a thickness of one layer from 3 to 19 microns.

After each applied coating layer according to this invention, drying is provided at 75-85 ° C for 5-10 minutes and heat treatment at 275-310 ° C for 10 to 30 minutes. The final heat treatment of the coating based on the composition of the invention is carried out at 350-400 ° C. The coating is subjected to the following tests:

- for adhesion, points - 1;

- tensile strength, kgf / cm ² - does not separate from the substrate;

- impact strength kg - 50 - no defects;

- bending strength - 1 - no defects;

- tensile strength - no defects (cracks, delamination);

- wear;

- coefficient of thorns in the dynamic loading mode with a load on the sample of 6.7 kg.

Table 1 presents data on the antifriction properties of coatings based on the composition obtained by the method according to the claimed invention.

Table 1 Parameter Name At the beginning of the test At the end of the test reference actually reference actually 1. Linear wear, microns - - n.b. 4.0 1,0 2. The coefficient of friction is static n.b. 0.14 0,027 n.b. 0.24 0.119 3. Friction coefficient: dynamic n.b. 0.5 0.385 Resource in loading cycles

Table 2 presents examples of compositions obtained by the claimed method

table 2 Name of components The ratio of components, parts by weight one 2 3 1. Varnish based on polyamic acid (PAK varnish) 30,0 35.0 55.0 2. Carbon black paste 7.3 3.8 1,0 3. Mica based pasta 16,0 12.3 8.5 4. Lubricant mixture 10.7 15,2 18.8 5. Aqueous suspension of polytetrafluoroethylene F-4D (56%) 27.8 23.0 8.5 6. Polyvinylpyrrolidone 6.0 3,7 1,2 7. Water 2.2 7.0 7.0

As follows from the above data, the coating of the compositions obtained by the method according to the claimed invention almost 2 times exceeds the tribological properties of the coating obtained by the previously known method: the initial static coefficient of friction is reduced from 0.14 to 0.027; linear wear from 4 microns (by reference) is reduced to 1 micron. In addition, due to the finely dispersed composite system, the resulting coatings are completely free from defects (micropores, voids, bubbles), which also contributes to an increase in the tribological characteristics of the coatings.

Claims (2)

1. A method of obtaining a composition for producing anti-friction coatings on metal surfaces based on an aqueous suspension of polytetrafluoroethylene in combination with a varnish of polyamic acid, polyvinylpyrrolidone, excipients, such as fillers, emulsifier, organic solvents, water, characterized in that it consists of the following stages:
a) the preparation of varnish based on polyamic acid, including
I - obtaining a solution of polyamic acid by dissolving polyamic acid in a mixture containing N-methylpyrrolidone, monoethanolamine and water;
II - mixing the resulting solution from stage 1 with a mixture for varnish containing N-methylpyrrolidone, ethyl cellosolve, butinediol;
b) preparation of a lubricant mixture containing an emulsifier based on ethoxylated alkyl phenols, xylene, ethyl cellosolve and water;
c) the preparation of an aqueous paste based on mica containing mica, an emulsifier based on ethoxylated alkyl phenols, polyvinylpyrrolidone and water;
d) processing of finely dispersed carbon fibers with nanosized lubricant mixture from stage (b);
e) preparation of an aqueous carbon black paste containing carbon black, treated fine carbon fibers from step (d), an emulsifier based on ethoxylated alkyl phenols, polyvinylpyrrolidone and water;
g) combining a varnish based on polyamic acid from stage (a) with a paste based on mica from stage (c);
h) combining an aqueous suspension of polytetrafluoroethylene with the components obtained in stages (e), (g), (b) with polyvinylpyrrolidone and water, with stirring, until a homogeneous composition is obtained with the following content of components, parts by weight:
Aqueous suspension of polytetrafluoroethylene 8.5-27.8 Polyamic Acid Varnish 30.0-55.0 Specified carbon black water paste 1.0-7.3 Mica Paste 8.5-16.0 Lubricant mixture 10.7-18.8 Polyvinylpyrrolidone 1.2-6.0 Water 2.2-7.0 2. A method of obtaining a composition for producing anti-friction coatings according to claim 1, characterized in that it further comprises an aqueous suspension of a tetrafluoroethylene-hexafluoropropylene copolymer.