RU2794172C2 - Method for obtaining composite materials for thin-layer coatings on metal and applying a coating based on composite materials - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: invention relates to the chemical industry and concerns the production of composite materials for thin-layer coatings on metal based on polytetrafluoroethylene, a solution of a salt of polyamide acid and other components that make up these materials, to obtain coatings with non-stick, anti-corrosion and anti-friction properties on various products of food, chemical, engineering, aviation and oil industries. A method for producing composite materials for thin-layer coatings on metal is described, which consists in pouring a solution of polyimide varnish in dimethylformamide into a funnel with holes from one to 10 with a diameter of 2-4 mm, fixed on a tripod above a container with running cold water, compressor supplies air into a container with running cold water, a solution of polyimide varnish flows through the holes in the funnel into a container with water, due to the chaotic seething of water, the streams of varnish in water are formed into a web of solid thin threads with a diameter of 0.5-1.0 mm, the web is washed in distilled water placed on a baking sheet and dried on a baking sheet under natural conditions at 20-25°C, then the resulting web of solid threads is dissolved and stirred until the it is completely dissolved in a solvent mixture containing monoethanolamine, N-methylpyrrolidone, impirons and water, thereby transferring the web of solid threads into a solution of a polyamide acid salt. Then, a solution of a salt of polyamide acid is sequentially introduced into an aqueous suspension of polytetrafluoroethylene F-4D, in combination with impiron, a carbon black paste and a mica-based paste, including a surfactant, as fillers and pigments, a mixture for lubrication, a mixture of solvents consisting of N-methylpyrrolidone, ethyl cellosolve and 1,4-butyndiol, auxiliary and target additives, depending on the functional purpose, while stirring until a homogeneous state. Also described is a method for applying a coating with anti-adhesive, non-stick, anti-corrosion and anti-friction properties based on composite materials for composite materials for thin-layer coatings on metal.

EFFECT: reducing the complexity of the process of obtaining target products, reducing energy and time costs, expanding the arsenal of means for obtaining polyamide in the form of solid thin threads; salts of polyamide acid, as well as composite materials for thin-layer coatings based on polytetrafluoroethylene and other functional components, in order to obtain a coating with non-stick, anti-corrosion and anti-friction properties.

2 cl, 1 dwg, 5 tbl

Description

The invention relates to the chemical industry and concerns the preparation of solutions of salts of polyamic acids based on the resulting web of solid thin threads, as well as composite materials based on fluoroplast and other components of these materials, to obtain coatings with non-stick, anti-corrosion and anti-friction properties on various food, chemical, engineering, aviation, oil industries.

Known methods for producing compositions for coatings on metal for various purposes, in particular: non-stick, anti-adhesive, anti-corrosion, anti-friction, for example, copyright certificate SU 1674554, IPC C08L 79/08, publ. 09/27/2006; patents RU 2071968, IPC C09D 127/18, publ. 01/20/1997; RU 2457228, IPC C09D 127/18, publ. 07/27/2012.

A thin film or solid fibers are obtained from a solution of industrial polyimide varnish containing from (81.5 to 86.5)% - N,N-dimethylformamide (DMF), a highly toxic, oncologically hazardous solvent, especially during thermal firing of coatings based on composite materials , with its content.

In order to reduce the DMF content in materials, first, a solid film with a DMF content (30-32)% is isolated from a solution of polyimide varnish, or hard fibers in the form of a cocoon with a DMF content (15-17)% (taking into account their dry residues), transferring solid film or solid fibers into a polyamic acid salt in an aqueous solution of monoethanolamine and N-methylpyrrolidone.

Aqueous solutions of salts of polyamic acids, together with other components, form composite materials for coatings.

The disadvantages of these inventions are: multi-stage, laborious, energy- and time-consuming in the processes of obtaining both a thin film and fibers in the form of a cocoon, further transferred into a solution of a salt of polyamic acid.

A known method (Patent GB No. 1563814, IPC A47J 36/02, publ. 04/02/1980) for obtaining an anti-friction composition by mixing a polyamic acid salt containing furfuryl alcohol and N-methylpyrrolidone, water with a dispersion of white pigment, with a dispersion of polytetrafluoroethylene and a silicone preparation . In this case, a dispersion of a white preparation is obtained by mixing titanium dioxide, water and a mixture of triethanolamine and oleic acid.

The disadvantage of the invention is the use of DMF together with furfuryl alcohol, which significantly increases the toxicity of the composition; in addition, this composition does not provide the coating with adhesive strength with metals and antifriction properties of the resulting coatings.

A known method (patent RU 2021296, IPC C08G 73/10, publ. 10/15/1994) for obtaining a composition for an anti-adhesive coating, which consists in the initial manufacture in an amide solvent of the reaction product of 4,4'-diaminotriphenylamine or its mixture with a number of other substituted diamines with dianhydride formulas O=(COz)=Ph-X-Ph=(COz)=O or mixtures thereof with other dianhydrides, followed by conversion into a salt and depositing it on a metal substrate.

The disadvantage of this anti-adhesive coating is the duration of the holding process of the resulting solution before applying it to metal products, from 30 minutes to 5 days; the duration of the heat treatment cycle for each deposited layer is from 130 min to 200 min, without taking into account the time of temperature rise from stage to stage. Such a cycle of time and energy is costly and unprofitable.

The closest in technical essence to the claimed invention is (Patent RU 2557530, IPC C08G 73/10, publ. 20/07/2015) supplements."

A well-known patent describes a method for producing a solution of a polyamic acid salt used as an additive, and a method for producing coatings based on fluoroplast with the addition of a polyamic acid salt. The known method includes the formation of a cocoon by introducing (13.0-13.5) wt.% solution in dimethylformamide into distilled water, with stirring at a speed of 50 rpm. Next, the cocoon is washed with distilled water, dividing it into individual fibers, natural air drying and subsequent stepwise drying, first at 120-130 ° C for 60 minutes in a drying cabinet, then in a vacuum thermostat, holding them at (79- 81)°C and a pressure of about 1 atm, to reduce the DMF in the fibers to 3.68 wt.%, followed by obtaining a salt of polyamic acid - an additive from the obtained fibers, by dissolving them in a mixture containing N-methylpyrrolidone, monoethanolamine and water. A method for producing composite materials based on fluoroplast with the addition of a solution of a salt of polyamic acid and other target additives is also described.

The disadvantages of this method are: the complexity and loss in the separation of the obtained solid fibers, pressed in the form of a dense cocoon around the rod and the blades of the stirrer, by cutting it; a large expenditure of time for the separation of fibers pressed together and their grinding (all work is done manually); long drying period - (3-4) days in a fume hood with warm air supply (35-40)°C, then in a vacuum thermostat at (79-81)°C and a pressure of 1 atm for 60 minutes until a dry residue of 96, 32%; the resulting fibers can be dried in natural conditions, using only warm air, but for a longer time (up to 6 days), to a dry residue content of (90-92)%; prolonged dissolution of fibers having a diameter of (2.0-3.0) mm, within (6-8) hours; the content between the compressed fibers - a layer of non-hydrolyzed initial solution of polyimide varnish, which makes it difficult to separate the fibers, increases waste and reduces the quality of solid fibers; instability in the content of dry residue in the form of fibers and in the resulting solution of a salt of polyamic acid based on them, which leads to instability of the viscosity and dry residue in the resulting composite materials.

The technical task of the claimed invention is to obtain solid thin filaments, with a small diameter, which reduces the time of their drying and - dissolution in a solvent solution, when transferring solid thin filaments into a solution of a polyamic acid salt.

The technical result consists in reducing the complexity of the process of obtaining the target products, reducing energy and time costs, expanding the arsenal of means for obtaining the shape of solid thin threads; salts of polyamic acid, as well as composite materials for thin-layer coatings based on fluoroplast and other functional components, in order to obtain a coating with non-stick, anti-corrosion, anti-friction properties.

The set technical task and the technical result in terms of the method for producing composite materials for thin-layer coatings on metal are achieved by pouring a solution of industrial polyimide varnish in dimethylformamide (DMF) into a funnel with holes from 1 to 10 pcs. 2-4 mm in diameter, mounted on a tripod over a large volume container with running cold water, the polyimide varnish solution flows freely through the holes in the funnel in a thin stream (s) into the container with water, when air is supplied by the compressor to the water, its chaotic seething is created, with In this case, the streams of varnish in water are formed into a web of solid thin threads of light yellow color, with a diameter of 0.5-1.0 mm, the resulting web of solid thin threads is washed in distilled water, dried on a baking sheet under natural conditions at 20-25 ° C, the resulting a web of solid thin light yellow filaments into a solution of a polyamic acid salt, by dissolving them and stirring in a mixture of solvents containing monoethanolamine, N-methylpyrrolidone, impiron and water, until they are completely dissolved, they are introduced into an aqueous suspension of polytetrafluoroethylene, in combination with surface- active substance, impiron, inorganic fillers and pigments in a pasty state, solvents, auxiliary and target additives.

The set technical task and the technical result in terms of the coating method based on composite materials are achieved by the fact that composite materials consisting of combined: aqueous suspensions of polytetrafluoroethylene, solutions of salts of polyamic acids based on a web of solid thin filaments, a mixture of solvents containing N-methylpyrrolidone, ethyl cellosolve, 1,4-butyndiol, surfactant, impirons, pastes of inorganic fillers that provide coating properties, pigments that provide color - decorative effect, solvents, auxiliary and target additives, are applied in layers from one to 5-8 layers by pneumatic spraying at a pressure of 2 .5-3.5 atm on prepared metal products, preliminary heat treatment of each coating layer is carried out at 80-100°C with final heat treatment at 360-450°C for 40-60 minutes.

The attached photo illustrates the resulting web of solid thin threads with a diameter of 0.5-1.0 mm.

The following are specific examples illustrating the claimed group of inventions, but not limiting it.

The method of obtaining composite materials for thin-layer coatings on metal is carried out as follows.

A solution of industrial polyimide varnish in dimethylformamide in an amount of 1.0 kg is poured into a funnel with one or more holes with a diameter of 4 mm, mounted on a tripod over a container with a volume of 35 liters with running cold water. The polyimide lacquer solution flows freely through the hole(s) in the funnel in a thin stream(s) into a container of water. When air is supplied by the compressor to the water, its chaotic seething is created, while the streams of varnish in the water form into a web of solid thin threads of light yellow color, 0.5-1.0 mm in diameter.

The resulting web of solid thin threads is washed in distilled water, dried on a baking sheet under natural conditions at 20-25 °, yield - 210 g.

First, 282 g of a solution is prepared to transfer the obtained cobweb of solid thin filaments into salt, containing: water, monoethanolamine, impiron, N-methylpyrrolidone, in a weight ratio of 15.1:10.0:2.1:1.0, respectively.

50.0 g of a cobweb of hard thin threads, 0.5-1.0 mm in diameter, is introduced into the resulting solution in portions, without grinding it, with periodic stirring and addition of the cobweb, for 1.5-2 hours. The resulting solution of a salt of polyamic acid, based on a web of hard thin filaments with a diameter of 0.5-1.0 mm, weighing 332 g, is transparent, has an amber color, a dry residue of 10.3%, a viscosity of 20.5 s according to VZ 246, with a hole diameter - 4 mm.

First, the prepared solution of the polyamic acid salt obtained by the method described above is mixed with a solvent mixture for the PAA salt solution containing N-methylpyrrolidone, ethyl cellosolve, 1,4-butyndiol in a weight ratio of 1.0:5.4:3.3, respectively.

Next, a lubricant mixture is prepared containing an emulsifier based on ethoxylated alkylphenols, o-xylene, ethyl cellosolve and water, in a weight ratio of 2.0:2.0:1.0:2.5, respectively.

Next, a mica-based aqueous paste is prepared containing mica, an emulsifier based on ethoxylated alkylphenols, impiron, and water in a weight ratio of 3.9:1:5.5:2.3, respectively.

Further, an aqueous carbon black paste is prepared containing an emulsifier based on ethoxylated alkylphenols, impiron and water in a weight ratio of 4.4:1:2.5:1.7, respectively.

A polyamic acid salt solution based on a web of hard fine filaments, diluted with a mixture of solvents for a polyamic acid salt, a mica-based paste and a carbon black-based paste (as pigments and fillers) is combined.

Carry out the combination of an aqueous suspension

polytetrafluoroethylene with the components obtained in the previous stages, impiron and water, with stirring until a homogeneous composition is obtained with the following content of components, parts by weight:

The composition for anti-friction coatings may additionally contain an aqueous suspension of a copolymer of tetrafluoroethylene with hexafluoropropylene.

The following are examples of recipes for the following formulations:

1. The composition of the solution for obtaining a salt of polyamic acid from a web of thin solid filaments;

2. The composition of the mixture for transferring the web of thin solid threads into a solution of a salt of polyamic acid;

the composition of the solvent mixture for the PAK salt; lubrication mixture composition, carbon black paste composition, mica-based paste composition.

The composition of the salt solution of polyamic acid from thin solid threads with a diameter of 0.5-1.0 mm, in parts by weight:

The composition of the mixture of solvents for varnish salts of polyamic acids, in wt.h.

The composition of the mixture for lubrication, wt.h.:

The resulting compositions are tested in terms of "appearance", which reflects the finely dispersed state of the system. To do this, a sample of the composition, for example, 10 ml, is diluted with 10 ml of distilled water, mixed and poured onto a clean photographic glass. In the film obtained on glass, there are no clots, agglomerates, components not distributed in the total mass of the composition.

The method of applying coatings based on composite materials is carried out as follows.

Composite materials obtained according to this invention for thin-layer coatings on metal are applied to previously prepared surfaces of products made of aluminum, steel, etc. The preparation of metal surfaces is carried out by any of the methods known for this metal, ensuring the complete absence of fatty (oil) and other contaminants. The compositions are applied by known methods, for example by pneumatic spraying or roller rolling. The coating composition is applied in several layers. The number of applied layers, their thickness are determined by the purpose, operating conditions of the product on which the composition is applied. The total thickness of the applied multilayer coating can be 40-55 microns, with the thickness of one layer from 3 to 10 microns. After each applied layer of the coating according to this invention, heat treatment is provided at 80-100°C for 5-10 minutes. The final heat treatment of the coating based on the composition according to the invention is carried out at 360-450°C for 40-60 minutes.

Samples of products coated on the basis of composite materials are subjected to the following tests, depending on the operational purpose of the coatings:

- for adhesion, score - 1;

- tear strength, 1650 kgf/cm - does not separate from the substrate;

- impact strength, 50 - no defects;

- bending strength - 1 mm - no defects;

- drawing strength (press stamping of a product from sheet metal) - no defects;

- for linear wear, microns at 1 km of run - less than 1;

- coefficient of friction in dynamic loading mode, with a load on the sample of 6.7 kg, are given in Table 4.

The ratio of components in composite materials is given in Table 5.

As follows from the above test results, coatings based on composite materials, obtained by the claimed method, have indicators similar to the results in a known method: linear wear; static coefficient of friction at the end of the test; dynamic coefficient of friction at the end of the test.

In the resulting coatings, as well as in the well-known solutions described above, there are no defects (micropores, voids, bubbles). This confirms the continuity and fineness of the composite system. Form - in the form of solid fibers with a diameter of up to 3 mm or in the form of a web of solid thin threads with a diameter of 0.5-1.0 mm does not affect the basic properties of coatings based on composite materials obtained in the presence of solutions of polyamic acid salts from these hard fibers or cobwebs.

The difference affects only the method (technology) for obtaining fibers and cobwebs in the well-known decision according to the patent of the Russian Federation 2557530 dated 06/14/2013 and the claimed method, taking into account the complexity and efficiency.

However, it should be noted that the coatings according to the claimed method have slightly improved non-stick properties than the properties of the coatings according to the previously declared method, in particular: without residue and help, it is completely easy to remove with a water jet, which is observed on the coatings according to the claimed method, while burnt milk is removed from the coating obtained according to known inventions only with prolonged exposure to a water jet or is completely removed only with a napkin. Reduced non-stickiness (non-stickiness of food) of the coating is confirmed by removing bread rolls from baking forms after 2 weeks of operation, d.b. - within (8-12) months.

The reason for the increase in the non-stick properties of coatings based on composite materials in the claimed invention can be explained by the greater compaction of the applied composition during the formation of the coating at the initial stages of heat treatment of wet layers, due to the greater binding of the molecules of the polyamic acid salt solution based on finely structured threads, compared with large fibers.

The present invention allows to reduce energy and time costs, the complexity of technological processes for obtaining intermediate and target products: solid thin threads with a diameter of 0.5-1.0 mm; polyamic acid salt solution, and composite materials for thin-layer coatings based on fluoroplast and other functional components, in order to obtain a coating with non-stick, anti-corrosion, anti-friction properties.

Claims (2)

1. A method for producing composite materials for thin-layer coatings on metal, which consists in pouring a solution of polyimide varnish in dimethylformamide into a funnel with holes from one to 10 with a diameter of 2-4 mm, fixed on a tripod above a container with running cold water, air is supplied by a compressor into a container with running cold water, a solution of polyimide varnish flows through the holes in the funnel in a stream into a container with water, due to the chaotic seething of water, the varnish streams in water form into a web of solid thin threads with a diameter of 0.5-1.0 mm, the web is washed in distilled water, placed on a baking sheet and dried on a baking sheet under natural conditions at 20-25 ° C, then the resulting web of solid threads is dissolved and stirred until completely dissolved in a mixture of solvents containing monoethanolamine, N-methylpyrrolidone, impyrones and water, thereby transferring the web of solid threads threads into a solution of a salt of polyamic acid, after which a solution of a salt of polyamic acid is sequentially introduced into an aqueous suspension of polytetrafluoroethylene F-4D, in combination with impiron, a soot-based paste and a mica-based paste, including a surfactant, as fillers and pigments, a mixture for lubricants, a mixture of solvents, consisting of N-methylpyrrolidone, ethyl cellosolve and 1,4-butyndiol, auxiliary and target additives, depending on the functional purpose, with stirring until a homogeneous state. 2. A method of applying a coating with anti-adhesive, non-stick, anti-corrosion, anti-friction properties based on composite materials obtained by the method according to claim 1, which consists in preparing the metal surfaces of the product by removing fatty contaminants and applying a coating, characterized in that the coating is applied in layers from one to 5-8 layers, preliminary heat treatment of each coating layer is carried out at 80-100°C with final heat treatment at 360-450°C for 40-60 minutes.

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