RU2766332C1 - Bioprotective polymer powder composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to polymer coating compositions protecting against microbiological damages of metal surface in conditions of high humidity and temperature, as well as used to protect hulls of sea and river vessels, hydrotechnical and other structures against fouling of various kinds of biological habitats of the aquatic environment. Composition includes ultrahigh molecular weight polyethylene with addition of fine low molecular weight polytetrafluoroethylene, as a biocidal additive it contains sodium silicofluoride, copper oxide and zinc oxide, besides, copper oxide and zinc oxide are also an inorganic pigment, and additionally contains aerosil at the following ratio of components, wt%: ultrahigh molecular weight polyethylene 40–55, fine low molecular polytetrafluoroethylene 5–15, sodium silicofluoride 15–24.5, copper oxide 10–17, zinc oxide 4.5–10, aerosil 1–3.

EFFECT: expansion of functional properties of polymer coating and increase of its antimicrobial properties, increase of biostability of polymer composition, improved manufacturability of application by using gas-thermal methods of spraying, improved quality of coatings as a result of reducing roughness of the applied polymer gas-thermal coating from 2–5 to 0.25–0.40 mcm.

1 cl, 2 tbl, 6 ex

Description

The invention relates to compositions of polymeric coatings that protect against microbiological damage to the metal surface under conditions of high humidity and temperature, as well as used to protect the hulls of sea and river vessels, hydraulic and other structures from fouling of various kinds of biological inhabitants of the aquatic environment.

Microbiological damage to coatings is one of the most common cases of biodamage. In conditions of increased risk of microbiological damage, antiseptic compositions containing biocides are used.

Compositions are known that include biocidal additives such as arsenic and lead in their compositions (see RF patent, No. 2123507, IPC C09D5/14, 1998,). The compositions are biologically stable in corrosive environments.

The disadvantage of these compositions is the use as biocidal additives of extremely toxic compounds that are environmentally hazardous to the atmosphere and biologically active media.

Currently, the use of heavy metal compounds is legally limited due to their high toxicity and, consequently, causing environmental damage to the environment when they are used. Therefore, copper compounds are often used, which are highly effective as a biocidal agent and at the same time less toxic when exposed to the environment. The most common biocide is monovalent copper oxide (Cu ₂ O). Typically, antifouling paint contains a synthetic film-forming agent (PSKh-LS, A-15, polyisobutylene, etc.), rosin, copper oxide, a plasticizer, organic solvents (see Gurevich E.S., Rukhadze E.G., Frost A.E. et al. Protection against fouling. - M.: Nauka, 1989, p. 271.). To achieve the desired effect, the content of copper oxide in the coating must be large (for example, 50-70% Cu ₂ O; the dissolution rate of this compound is at least 0.1 g / (m ² * day) (see Chemistry and technology of paint coatings: Textbook for universities, St. Petersburg: KHIMIZDAT, 2008).

Since the 80s. organotin polymer coatings are actively used, including the so-called self-polishing organotin polymer coatings (SPS - self-polishing copolymer). Most often, tributyltin oxide is used for this purpose. Organoelement matter gradually decomposes, releasing tin-containing compounds that inhibit the attachment of fouling larvae (see Cao S., Wang JD., Chen HS., Chen DR. Progress of marine biofouling and antifouling technologies. Review. // Chines Sci. Bull. 2011 V. 56. N 7. P. 598-612.).

However, like copper compounds, tin compounds are extremely toxic. Tin compounds at the concentration required to suppress fouling often result in the death of particularly sensitive individuals and may affect the offspring of surviving individuals. An international convention since 2008 prohibits the use of harsh biocides as additives to coating materials.

Instead of highly toxic organotin compounds, organic additives are introduced - toxic, for example, tetracycline, which inhibits cellular protein synthesis, or less toxic, for example, benzoic, tannic, diethylbarbituric acid, a derivative of vitamin K ₃ , tetramethylethylenediamine, others (see Patent RU No. 1819276, IPC C09D 5 /16, published 2004.10.10., as well as Qu Y.-Y., Zhang S.-F. Preparation and Characterization of novel waterborne antifouling coatings // J. Coat. Technol. Res. 2012. V. 9. N 6. P. 667-674.).

Their disadvantage is the specificity and fragility of the action of organic additives.

Known compositions for applying coatings that are resistant to biologically active media and containing copper compounds in their compositions (see US Patent No. 5571312, IPC 7 C09D 5/16, A01 N 25/00, 1996 and Application DE No. 19606011, IPC 7 C09D5/16, 1997), chromium (see Patent No. 2115680, Russia, IPC C09D 5/10 (1995.01), 1998), zinc (see Patent No. 2415168, Russia, IPC C09D 5/16, 2011). These materials are less toxic than compositions containing mercury, tin, arsenic.

The disadvantage of the compositions is the high content (up to 85 wt. %) of biocides in the unbound state. This leads to rapid leaching of biocides from coatings and does not provide a long-term biocidal effect. In addition, the lack of known biocides of antifouling coatings for marine vessels, both cold and hot applied to the surface to be protected, based on compounds of heavy non-ferrous metals (oxides of copper, lead, mercury, tin, etc.), their organometallic compounds, as well as toxic organic complexes is their ability to accumulate in the cells of plants and animals, the inhabitants of the seas and oceans. This causes ever-increasing irreparable harm to the ecology of the world's oceans, its flora and fauna. As a consequence, through contaminated marine food (fish, animals, algae and other plant products), elevated concentrations of toxic compounds enter the human body.

A composite material is known, including quartz flour, liquid sodium glass, sodium silicofluoride and a hydrophobic component-plasticizer - low molecular weight polyethylene, which is a waste product of high-pressure polyethylene production (see application BY a19990831, IPC C 09 D 5/08, 2001). Composite anticorrosion coatings are highly resistant to acidic environments.

Their disadvantage is low water resistance and a low level of protection against microbiological corrosion due to the low content of the biocidal component. In addition, the applied coating has low adhesion to steel surfaces (no more than 1.5 MPa when tested for peeling with a normally applied load).

The composition of an antifouling composition for coating a surface immersed in water is known, containing a binder (epoxy, acrylic resins, organosilicon compounds, vinyl polymers, styrene polymers, chlorinated rubber, phenolic resins), from 1 to 50% of polytetrafluoroethylene particles, calculated on the dry weight of the composition and from 5 to 95%, based on the dry weight of the antifouling agent composition selected from the group consisting of metallic copper and compounds of copper and zinc, and also constituting a liquid dispersion medium comprising at least one halogenated hydrocarbon (see US Patent No. 4895881, IPC 7 C08J7/04, 1990).

The disadvantage of the composition is the low adhesion to metal surfaces and the inability to use it for the formation of coatings by thermal methods.

The closest in technical essence to the claimed object is a biocidal powder composition based on epoxy and carboxyl-containing polyester resins, their mixtures and polyhexamethylene guanidine hydrochloride as a biocidal ingredient. The biocidal powder coating composition consists of a solid epoxy resin based on bisphenol A with an epoxy equivalent of 715-930 g/mol and/or a carboxyl-containing polyester with an acid value of 26-53 mg KOH/g, a hardener if necessary, a filling regulator, benzoin, pigment and /or filler, and also contains a biocidal additive - polyhexamethylene guanidine hydrochloride together with dicyandiamide in the following ratio, wt. hours: epoxy resin 0-83.1, carboxyl-containing polyester 0-85.4, polyhexamethylene guanidine hydrochloride 4.5-8, dicyandiamide 1.5-7.4, pigments 0-40, fillers 0-12, filling regulator 0, 5-2.1, hardener if necessary 1.7-4.5, benzoin 0.2-0.7 (see Patent RU No. 2700876, IPC C09D 5/14 (2019.05), 2019). This decision was taken as a prototype.

Introduced into the composition of the prototype biocidal additive - polyhexamethylene guanidine hydrochloride - is characterized by a wide range of biocidal action, effectiveness against bacteria, fungi, molds, algae, viruses, low toxicity for warm-blooded, non-volatile, stable during long-term storage. The biocide is able to maintain sufficient biocidal activity when the composition is applied to the substrate.

However, the biocidal activity of polyhexamethyleneguanidine is insufficient, the fungus resistance of the composition is estimated at 1-2 points, the maximum efficiency of 0 points according to GOST 9.050-75 is not achieved. In addition, the technological features of applying a powder composition (the resulting powder compositions are applied by electrostatic spraying onto a substrate at a voltage of 50 kV, followed by curing of the coating at a temperature of 180-185°C for 20-25) do not allow coating hard-to-reach areas of the protected structure, using open and large surface areas, which limits the scope of the composition. The complex synthesis of polyhexamethyleneguanidine makes its cost, and hence the cost of the composition, quite high.

The technical problem solved by this invention is to increase the biostability of the polymer composition, increase the processability of application through the possibility of using thermal spraying methods, and improve the quality of coatings.

The technical problem posed is solved due to the fact that the bioprotective polymer powder composition, including a polymer binder, a biocidal additive and an inorganic pigment, in accordance with the invention, as a polymer binder, contains ultra-high molecular weight polyethylene with the addition of finely dispersed low molecular weight polytetrafluoroethylene, as a biocidal additive contains sodium fluorosilicon, oxide copper and zinc oxide, and copper oxide and zinc oxide are also inorganic pigment, and additionally includes aerosil in the following ratio, wt. %:

ultra high molecular weight polyethylene 40-55 finely dispersed low molecular weight polytetrafluoroethylene 5-15 sodium silicofluoride 15-24.5 copper oxide 10-17 zinc oxide 4.5-10 aerosil 1-3

The technical result from the use of all the essential features of the invention is to expand the functional qualities of the polymer coating and improve its antimicrobial properties.

Also, the technical result from the use of all the essential features of the invention is to increase the biostability of the polymer composition, improve the processability of application through the possibility of using gas-thermal spraying methods, and improve the quality of coatings.

As a polymer binder in the claimed composition, ultra-high molecular weight polyethylene (UHMWPE) powder with a particle size of 60 - 200 microns is used, with the addition of a fine powder of low molecular weight polytetrafluoroethylene (PTFE) with a particle size of 0.5 - 3.5 microns. UHMWPE is a thermoplastic with high impact and wear resistance, the highest water repellency among polyethylenes, low coefficient of friction, high frost resistance, and high adhesion to metals in the gas-thermal method of coating formation. The addition of finely dispersed low molecular weight PTFE makes it possible to reduce the roughness of the applied thermal thermal polymer coating from 2–5 to 0.25–0.40 µm, which will improve the quality of coatings and have a positive effect, for example, on the speed of ships with coated hulls and on fuel consumption.

As a biocidal additive, it is proposed to use sodium fluorosilicon (GOST 87-77), which has a sufficiently high biocidal activity. Sodium fluorosilicic acid is obtained by reacting fluorosilicic acid with a solution of common salt, sodium sulfate or sodium carbonate.

Copper (II) oxide (GOST 16539-79) and zinc oxide (GOST 10262-73) were used as a pigment and a biocidal additive. Sodium silicofluoride, oxides of copper and zinc, are widely distributed, are not expensive, are produced in the form of a powder with a wide granulation of particles, which allows them to be used as components of a powder mixture in flame spraying.

As a thixotropic filler, it is proposed to use silicon dioxide - aerosil (GOST 14922-77) to impart sedimentation stability to the composite charge during its storage. Aerosil is a highly dispersed highly active amorphous pyrogenic silicon dioxide (SiO ₂ ) with a particle size of 0.005 to 0.040 μm, obtained by flame hydrolysis of high purity silicon tetrachloride (SiCl ₄ ). It is characterized by the maximum specific surface of all powdered fillers, the value of which reaches 380 m ² /g. Increases physical and mechanical properties of elastomers. The silanol groups present on the surface of aerosil particles contribute to the formation of a system of hydrogen bonds between the particles.

Samples of polymer composite coatings were obtained by thermal spraying of a powder mixture, including the following operations: preparation of a dry powder mixture according to the claimed composition, flame spraying of the composition on steel samples.

The following components were chosen for the preparation of the composite mixture: UHMWPE powder of the trade mark Hostalen GUR 4120 (particle size 100 - 160 μm), manufacturer "Ticona" (Germany); low molecular weight PTFE powder with a particle size of 0.5 - 3 μm, obtained by a thermogasdynamic method, manufacturer Vladforum LLC (RF) according to TU 2213-001-15259672 - 2016; biocidal additive of sodium fluorosilicon according to TU 113-08-587-86, manufacturer of JSC Apatit, Saratov region; copper (II) oxide powder (GOST 16539-79); zinc oxide powder (GOST 10262-73); Aerosil powder (pyrogenic silica) brand A-300, GOST 14922-77, particle size 0.005 ... 0.040 μm, with the following ratio of components, wt. %:

ultra high molecular weight polyethylene 40-55 finely dispersed low molecular weight polytetrafluoroethylene 5-15 sodium silicofluoride 15-24.5 copper oxide 10-17 zinc oxide 4.5-10 aerosil 1-3

The powder components of the composition were dried in a ShS-80-01 oven at a temperature of 80°C for 2 hours before preparing the mixture. Ingredients were weighed on desktop electronic scales "SHTRIKH M 6-2", NPV modification. Composite charge was made by sequential mixing of ingredients in a laboratory grain mill LM 200 with water-cooled chamber.

The prepared polymer powder composite mixture was applied in the form of a coating on the surface of plates made of St-3 steel by the method of flame spraying - the process of melting or heating powder particles in a flame to a highly plastic state, accelerating them in a torch and applying them to the prepared surface of the part. To form the coatings, a polymer powder thermospray OIM 050.00.00.000 manufactured at the Joint Institute of Mechanical Engineering of the National Academy of Sciences of Belarus was used, which is used for flame spraying of coatings with powders of polymeric thermoplastic materials with a melting temperature of 90 to 400°C.

Flame spraying modes: working pressure of gases, MPa, no more than: air - 0.5; propane - 0.2; gas consumption, m ³ /h: air - 20; propane - 0.9; spraying distance - 210 mm.

Coatings were applied to steel specimens intended for roughness assessment to determine resistance to mold fungi GOST 9.050-75. “Paint coatings. Methods of laboratory testing for resistance to mold fungi” and according to GOST 9.048-89, as well as for samples intended for studying the adhesion of coatings by the pull-off method with a normally applied load.

Table 1 presents examples of quantitative and qualitative compositions of the claimed composition (examples No. 1-4), as well as examples of compositions that go beyond the claimed limits (control examples No. 5-6).

Table 1 - Compositions of the claimed composition

Mixture components The content of the component, wt. % Examples of coatings with the claimed composition Test Cases one 2 3 4 five 6 Ultra high molecular weight polyethylene 40 47 52 55 39 56 Polytetrafluoroethylene 15 10 7 five 17 3.5 Sodium silicofluoride 15 eighteen 21 24.5 27 12 copper oxide 17 15 13 10 nine 17.5 zinc oxide 10 8 6 4.5 4 10.5 Aerosil 3 2 one 1.0 4 0.5

For metal structures and structures operated in conditions of high humidity or in water with a high content of bacteria, fungi and algae, an abundance of defects associated with exposure to metabolic products of microorganisms, the most viable of which are mold fungi, is typical. Studies of the properties of coatings from the compositions of the claimed polymer powder composition for resistance to the most common and aggressive mold fungus Aspergillus niger and Aspergillus penicilloides was carried out according to GOST 9.050-75. “Paint coatings. Methods of laboratory testing for resistance to mold fungi” and according to GOST 9.048-89. The essence of the method lies in the fact that samples of materials are kept under conditions of natural infection with mold fungi and the microbiological resistance of the material is determined by the degree of growth of microorganisms on its surface.

To test the biostability of samples of composite coatings to fungi, an aqueous suspension of microorganisms was used, the composition of which is given in GOST 9.048-89 (1 ml of the suspension contains 1–2 million spores of each test culture included in the mixture). Samples of composite coatings in Petri dishes were placed in desiccators, in which a relative humidity of 95–98% and a temperature of 27–31°C were maintained. The tests were carried out for 28 days. After the specified period, the samples were removed from the desiccator, examined at an illumination of 200-300 lux with the naked eye, as well as using a microscope at a magnification of ^50-60x , and the fungus resistance was evaluated in points according to the degree of fouling of the surface of the materials on a 6-point scale.

In the case when the germination of spores and conidia is not detected under the microscope, the biostability of the material corresponds to 0 points, if germinated spores and slightly developed mycelium are found under the microscope - 1 point, the formation of mycelium in the form of branching hyphae with sporulation - 2 points, with barely visible to the naked eye mycelium and sporulation - 3 points. In the case when the development of fungi covering less than 25% of the test surface is clearly visible to the naked eye, biostability is 4 points, intensive growth of fungi, abundant development of mycelium over an area of more than 25% of the surface - 5 points.

The results of studies of adhesion of coatings, their roughness and resistance to mold fungi are shown in Table 2.

Table 2 - Properties of sprayed coatings of the claimed composition and control samples

Coating No. Properties of applied coatings Adhesion strength with the base, MPa Roughness, µm Mushroom resistance, score Prototype 6.1 2.5 12 one 7.6 0.30 0 2 7.9 0.40 0 3 8.4 0.75 0 4 9.2 1.0 0 five 6.9 2.3 one 6 7.1 0.30 2

The analysis of the obtained results showed that when applying coatings from the developed composition of the polymer powder composite mixture by flame spraying, the surface to be protected is characterized by the highest possible biostability (0 points) in relation to the most aggressive mold fungi, which indicates a higher protective ability of this material compared to the prototype and control samples. In this case, as follows from the above data, sodium silicofluoride plays a decisive role in the biocidal properties of the composite coating (example 6). Despite the high total content of widely used known biocides of zinc oxide and copper according to example 6, with a decrease in the composition of the sodium silicate fluoride powder composition, the biostability index is 2, that is, there is a decrease in fungus resistance. With a low content of polytetrafluoroethylene in the composition, the biostability index is high - 0 points, but at the same time the roughness of the coating increases (example 4).

Thus, due to the implementation of the distinctive features of the invention (together with the features indicated in the restrictive part of the formula), important new properties of the object are achieved:

- the optimal ratio of ingredients expands the functional qualities of the polymer coating;

- the presence of bactericidal additives in the compositions (sodium fluorosilicon, oxides of copper and zinc) increases the antimicrobial properties.

The claimed bioprotective polymer powder composition can be manufactured using the specified known components included in its composition within the stated limits. As tests have shown, when changing the limit values of the quantitative composition of the components, both in the direction of exceeding and decreasing the values, the claimed technical result is not achieved.

The claimed invention can be used in various industries where protection from microbiological damage to the metal surface is required under conditions of high humidity and temperature, for example, to protect the hulls of sea and river vessels, hydraulic and other structures from fouling of various kinds of biological inhabitants of the aquatic environment.

Claims (2)

A bioprotective polymer powder composition for coatings, including a polymer binder, a biocidal additive and an inorganic pigment, characterized in that it contains ultra-high molecular weight polyethylene with the addition of finely dispersed low molecular weight polytetrafluoroethylene as a polymer binder, and contains sodium fluorosilicide, copper oxide and zinc oxide as a biocidal additive, moreover, the oxide copper and zinc oxide are also inorganic pigment, and additionally includes aerosil in the following ratio, wt. %: ultra high molecular weight polyethylene 40–55 finely dispersed low molecular weight polytetrafluoroethylene 5–15 sodium silicofluoride 15–24.5 copper oxide 10–17 zinc oxide 4.5–10 aerosil 1–3