A fluorinated resin, its preparation method and application

Abstract

The present invention relates to the technical field of marine antifouling coatings, and particularly to a fluorinated resin, a preparation method thereof, and an application thereof in antifouling of marine fixed facilities. The fluorinated resin has the following structural formula: wherein, R1 is (CH 2 ) e (CF 2 ) f CF 3 , e is 1 or 2, and f is a natural integer from 0 to 7; R2, R3, and R4 are independently selected from (CH 2 ) n CH 3 ; a is a natural integer from 2 to 8, and n is a natural integer from 0 to 12. The antifouling coating developed by the present invention not only has good physical and mechanical properties, but also has excellent scrub resistance. At the same time, the smooth low surface energy and self-renewal characteristics of the coating make the attached fouling organisms easy to be removed. This coating adopting a multi-component collaborative antifouling strategy can significantly extend the antifouling validity period, providing an effective solution to the surface antifouling problem of marine fixed facilities, especially new energy facilities such as offshore wind power with an extremely long design life.

Description

Technical Field

[0001] The invention relates to the technical field of marine antifouling coatings, and in particular to a fluorinated resin and a preparation method thereof, and application thereof in the antifouling of marine fixed facilities. Background Art

[0002] With the rapid development of new energy facilities such as offshore wind power and photovoltaic power, the problem of marine biofouling faced by these facilities has become increasingly prominent. Especially for floating offshore new energy facilities, due to their extremely long design life (usually 25 years), long-term static environment and difficulty in routine maintenance, the anti-fouling problem is particularly difficult. At present, the anti-fouling of fixed marine facilities generally adopts ship anti-fouling coating technology.

[0003] The antifouling coatings for ships on the market are mainly divided into the following categories:

[0004] 1. Self-polishing antifouling coating (SPC type) with side chain hydrolyzed resin as the main film-forming material: Self-polishing antifouling coating is mainly composed of self-polishing resin and antifouling agent (copper oxide). It relies on water flow to accelerate the hydrolysis reaction to gradually dissolve the surface of the paint film, continuously release the antifouling agent, and keep the surface of the paint film smooth. Common ones include zinc polyacrylate, copper polyacrylate, and polyacrylate silane. However, the antifouling effect of the above coating depends largely on the movement speed of the hull, which leads to poor antifouling performance in a static environment.

[0005] For example, the prior art CN 110734519 B discloses a low surface energy water-based self-polishing emulsion and a preparation method thereof and a low surface energy water-based self-polishing drag-reducing and antifouling coating: comprising the following raw materials in percentage by weight: 5-15% of fluorine-containing acrylate monomer, 10-20% of acrylic acid silicone monomer, 20-30% of acrylic acid ester monomer, 0.5-1.5% of acrylic acid, 1-2% of emulsifier, 0.3-0.6% of initiator, 0.05-0.1% of sodium bicarbonate, 0.3-0.5% of pH regulator, and the balance is water; the fluorine-containing acrylate monomer is one or more of dodecafluoroheptyl methacrylate, tridecafluorooctyl acrylate and octafluoropentyl acrylate; the acrylic acid silicone monomer is triisopropyl methacrylate and / or triisopropyl acrylate; the acrylic acid ester monomer is one or more of methyl methacrylate, butyl methacrylate, butyl acrylate, hydroxyethyl methacrylate and isobornyl methacrylate. Its antifouling mechanism is self-polishing, and it must have a faster polishing speed to be effective. The polishing rate is 0.19-0.26μm / day (5.7-7.8μm / month). The film thickness is consumed too quickly, and the long-term antifouling performance is poor. Its hydrophobicity is mainly for drag reduction, and is not the main source of antifouling performance.

[0006] 2. Biodegradable antifouling coatings use degradable polyesters such as polycaprolactone (PCL) or polylactic acid (PLA) as film-forming substances, and release antifouling agents to prevent the attachment of fouling organisms through the continuous degradation and peeling of the paint layer. However, the degradation rate of degradable polyesters is uncontrollable, the hydrolysis rate is slow in the early stage, and the acidic products generated by the later degradation will accelerate the degradation of the coating. Therefore, some patents currently disclose dual-solution antifouling coatings, that is, introducing degradable polyester structures into the main chain of antifouling resins to develop main chain degradable self-polishing antifouling resins (CN201310314516.9, CN201710292938.9, CN201910649948.2). The main chain of this type of resin contains a degradable ester bond, and the self-polishing ability of the coating is less dependent on water flow scouring, so its static antifouling effect is improved.

[0007] The above two types of coatings can be called consumable coatings, and their antifouling performance mainly depends on the polishing rate of the coating and the release of the antifouling agent. For common self-polishing coatings, calculated at a polishing rate of 4 to 5 μm / month, a design life of 25 years requires a thickness of at least 1.2 mm. In fact, due to the existence of the saponification layer and the uncontrollable release of the antifouling agent, even if a series of problems caused by excessively thick coatings are not considered, its antifouling time is difficult to support such a long design life.

[0008] 3. Fouling-removing antifouling (FRC) coatings have become a research hotspot for the new generation of antifouling coatings. They usually use organic silicon and / or organic fluorine as film-forming resins. Relying on their low surface energy, elastic and smooth surface, they make it difficult for marine organisms to attach. Even if there is a small amount of attachment, it can fall off under the scouring of water flow, showing excellent antifouling performance and long life. However, this coating requires high-speed water flow to maintain its antifouling performance, and over time, the coating surface may deteriorate due to hydrolysis and aging (Surface Technology, 2022, 51(05): 293-303.). Once the coating is covered with pollutants in seawater, its antifouling performance will also be greatly reduced. In addition, in order to obtain a good static antifouling effect, the current fouling-removing coatings use the characteristics of hydrophilic materials that inhibit protein adhesion. Combining them with organic fluorine silicon materials can form a certain degree of microphase separation structure, which can improve the surface anti-protein adhesion characteristics of organic silicon and enhance static antifouling performance. This technical route has been applied and verified in the products of foreign coating companies such as IP. Patents CN107652887A and CN112940610A also disclose two silicone hydrogels. Although silicone hydrogels have advantages in static antifouling performance, they are soft in texture and have poor mechanical strength.

[0009] In addition, the prior art CN 105219217 B discloses a non-dissolving low surface energy antifouling coating for oilfield pipelines, comprising a low surface energy coating component A and a non-dissolving bactericide component B, wherein the components and proportions are as follows by mass percentage: component A: 7.5-8.5% silicone resin; 14-16% epoxy resin; 11-13% acrylic resin; 13-15% tetrafluoroethylene resin; 9-11% chloroether resin; 3.5-4.5% polyvinyl butyral; 7.5-8.5% polypropylene glycol diglycidyl ether; 9. 5-10.5%; rutile titanium dioxide 7-8%; silicon carbide 2.5-3.5%; glass flakes 5.5-6.5%; polytetrafluoroethylene microwax 1.3-1.5%; carbon black 0.4-0.6%; fumed silica thixotropic agent 0.4-0.6%; anti-settling agent 0.8-1.0%; leveling agent 0.3-0.5%; defoaming agent 0.3-0.5%; wetting dispersant 0.3-0.5%; silane coupling agent 0.3-0.5%; accelerator 0.08-0.12%. Tetrafluoroethylene resin is a monomer with functional bodies introduced into the main chain of fluororesin by copolymerization of tetrafluoroethylene monomer and functional monomer. The non-dissolving low surface energy antifouling coating for oil field pipelines can solve the secondary pollution problem of the pipeline network of oil field water injection system. However, although the antifouling coating surface uses a hydrophobic + non-dissolving antifouling agent, it can only effectively resist bacteria and has no antifouling ability for marine organisms, especially invertebrates.

[0010] Prior art CN 100465242C discloses a fluorosilicone block polymer type low surface energy marine antifouling coating and a preparation method thereof. The fluorosilicone block polymer type low surface energy marine antifouling coating is compounded from a base material, a pigment, an additive and a coating solvent. The base material is a polydimethylsiloxane-b-polymethyl methacrylate-b-polyheptafluorobutyl methacrylate ternary fluorosilicone block copolymer, the additives are methyl silicone oil and dioctyl phthalate, and the coating solvent is butyl acetate; the polydimethylsiloxane is 1:1-1:1, the pigment is 1:1-1:1 ... additives are methyl silicone oil and dioctyl phthalate, and the coating solvent is butyl acetate; the polydimethylsiloxane is 1:1-1:1, the pigment is 1:1 The ratio of ternary fluorosilicone block copolymer of alkane-b-polymethyl methacrylate-b-polyheptafluorobutyl methacrylate, pigment, methyl silicone oil, dioctyl phthalate and butyl acetate is: ternary fluorosilicone block copolymer of polydimethylsiloxane-b-polymethyl methacrylate-b-polyheptafluorobutyl methacrylate: pigment: methyl silicone oil: dioctyl phthalate: butyl acetate = 1: 0.1-0.6: 0.02-0.1: 0.02-0.1: 0.2-0.8. However, its antifouling mechanism relies only on low surface energy (super hydrophobic antifouling). Once the surface is contaminated, its antifouling performance is seriously damaged.

[0011] However, those skilled in the art are well aware that, unlike ships, new energy facilities such as floating offshore photovoltaics and offshore wind power are mostly large in size and do not move for a long time. They are in a relatively static marine environment. If the antifouling coating fails, the facilities can hardly be repaired and re-coated with antifouling coating. Therefore, the antifouling coating of marine facilities should have both good antifouling performance and long-term antifouling life to meet application requirements.

[0012] In response to the above needs, the use of multi-faceted synergistic anti-fouling ideas is one of the important ways to solve the anti-fouling problem of marine facilities. The Norwegian company Jotun has developed an anti-fouling coating product for ships, which is designed for use with hull cleaning robots. It makes up for the defect of poor static anti-fouling performance to solve the problem of anti-fouling failure of ship anti-fouling coatings during the period when the ship is docked in the port. However, this product is an anti-fouling coating for hulls based on side-chain hydrolyzed methacrylate silane resin. As mentioned above, the anti-fouling mechanism of consumable anti-fouling coatings determines that it is difficult to have a long-term anti-fouling effect, and frequent cleaning by cleaning robots also seriously affects the life of the coating.

[0013] In fact, in addition to focusing on its static antifouling performance and antifouling life, the antifouling coatings for fixed marine facilities used in conjunction with robots should also have good cleaning resistance. For example, they should have high hardness and adhesion, and maintain excellent mechanical properties after being immersed in seawater. The coating should be able to withstand repeated contact and friction with the brush head without being damaged by active cleaning operations. However, there is currently no technology for long-lasting antifouling coatings that are resistant to cleaning and meet this requirement. Summary of the invention

[0014] The purpose of the present invention is to provide a fluorinated resin having a cleaning resistance and a super hydrophobic layer, and a preparation method thereof and an application thereof in antifouling of fixed marine facilities.

[0015] To achieve the above object, the technical solution of the present invention is as follows:

[0016] A fluorinated resin, the structural formula of which is as follows:

[0017]

[0018] Wherein, R1 is (CH 2 ) e (CF 2 ) f CF 3 , e is 1 or 2, f is a natural integer from 0 to 7; R2, R3, and R4 are independently selected from (CH 2 )nCH 3 ; a is a natural integer from 2 to 8, and n is a natural integer from 0 to 12.

[0019] In a preferred embodiment, in order to obtain a suitable chain length and silicon nucleophilic strength, n is preferably 0, 1, 2, 3, or 4. Too long a length will affect the silicon nucleophilic strength.

[0020] The fluorinated resin provided by the present invention has multiple antifouling properties: a. The hydrolyzable silane ester part enables it to have self-polishing properties, and the antifouling is renewed by hydrolysis on the coating surface; b. The fluorinated part with low surface energy makes it difficult for fouling organisms to adhere to the coating surface; c. The rigid isobornene structure makes microorganisms such as bacteria and algae "unwilling" to adhere to the coating surface, thereby enhancing the antifouling performance; at the same time, the glass transition temperature of the resin is adjusted to make the coating moderately soft and hard.

[0021] Based on the same inventive concept, the present invention also claims a method for preparing the fluorinated resin, comprising:

[0022] 1-5wt% of mercaptosilane, 10-30wt% of methacrylic acid fluorine-containing monomer, 30-60wt% of methacrylic acid isobornyl ester monomer, 5-20wt% of methacrylic acid silane ester monomer and initiator are dissolved in a solvent, and reacted at 100-130°C for 20-28h under a nitrogen protection environment; after the reaction, the solvent is removed, and the fluorinated resin is obtained after washing and drying.

[0023] The synthetic route of the fluorinated resin is as follows:

[0024]

[0025] In a preferred embodiment, mercaptosilane is a silane monomer having a mercapto group at one end and an alkoxy group at the other end, preferably (CH 3 (CH 2 ) b O) 3 Si(CH 2 ) a SH; a is selected from any integer in the range of 2-8; b is selected from any integer in the range of 0-4.

[0026] In a preferred embodiment, the mercaptosilane is (3-mercaptopropyl)trimethoxysilane or (3-mercaptopropyl)triethoxysilane.

[0027] Mercaptosilane is an end group modifier, which makes the end group of the fluorinated resin synthesized by the resin trimethoxysilane, so it can react with the hydroxyl-terminated polydimethylsiloxane and the terminal hydroxyl biodegradable resin in the A component.

[0028] In a preferred embodiment, the initiator is any one of cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl hydroperoxide, azobisisobutyronitrile and azobisisoheptanenitrile.

[0029] Isobornyl methacrylate monomer adjusts the Tg of the resin to make it moderately soft and hard. At the same time, its unique norbornene structure can inhibit the adhesion of some marine organisms. Other raw materials cannot be replaced. If styrene is used as a substitute, it will not have the function of inhibiting the adhesion of marine organisms.

[0030] In a preferred embodiment, the methacrylic fluorine-containing monomer is one of 2-(perfluorobutyl)ethyl methacrylate, 2-(perfluorooctyl)ethyl methacrylate, and 2-(perfluorohexyl)ethyl methacrylate.

[0031] In a preferred embodiment, the silyl methacrylate monomer has the following general structure:

[0032]

[0033] R 2 ,R 3 ,R 4 =(CH 2 )nCH 3

[0034] In the formula, n is a natural integer of 0-12. In order to obtain a suitable chain length and silicon element nucleophilic strength, n=0, 1, 2, 3, 4 is preferred.

[0035] In a preferred embodiment, the methacrylate silyl ester monomer includes at least one of trimethylsilyl methacrylate, triethylsilyl methacrylate, triisopropylsilyl methacrylate, triphenylsilyl methacrylate, tri-n-butylsilyl methacrylate, tert-butyldimethylsilyl methacrylate and bis(trimethylsiloxy)methylsilyl methacrylate.

[0036] In a preferred embodiment, the solvent is one of dioxane, butyl acetate and tetrahydrofuran.

[0037] Based on the same inventive concept, the present invention also claims to protect the use of the fluorinated resin in preparing antifouling coatings.

[0038] Based on the same inventive concept, the present invention also claims protection for an antifouling coating, the raw materials of which include component A and component B in a mass ratio of 4-7:1, wherein the component B includes 20-40 parts of the above-mentioned fluorinated resin, 50-70 parts of a silane curing agent, 1-5 parts of a catalyst and 10-25 parts of an organic solvent, and the component A includes 25-40 parts of hydroxyl-terminated polydimethylsiloxane, 5-15 parts of a terminal hydroxyl biodegradable resin, 5-15 parts of corundum powder, 10-30 parts of hydrophobically modified fumed silica, and 1-3 parts of an organic antifouling agent.

[0039] In a preferred embodiment, the preparation method of the hydrophobically modified fumed silica includes: dissolving a long carbon chain silane in an ethanol aqueous solution to prepare a silane solution with a concentration of 3-8wt%, then adding hydrophilic fumed silica, adjusting the pH to 5-7, ultrasonically dispersing at 30-50°C, filtering, washing, and drying to obtain hydrophobically modified fumed silica.

[0040] The hydrophobically modified fumed silica prepared by the present invention can form a cauliflower-like nanostructure on the surface of the hydrophilic fumed silica under the appropriate conditions provided by the present invention, because the modified silane coupling agent has a long alkyl carbon chain, and the surface energy of the silica is reduced. Therefore, after being added to the coating, the hydrophobically modified fumed silica constructs a micro-nano super-hydrophobic structure on the surface of the antifouling coating, similar to the surface of a lotus leaf.

[0041] In a preferred embodiment, the long carbon chain silane is one of dodecyltrichlorosilane, dodecyltrimethoxysilane, hexadecyltrichlorosilane, hexadecyltrimethoxysilane, octadecyltrichlorosilane, octadecyltrimethoxysilane, perfluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane.

[0042] Taking into account the reaction rate and the regularity of the surface microstructure of the modified fumed silica, octadecyltrimethoxysilane is preferred; the long chain helps to form a cauliflower-like nanostructure on the surface of the silica.

[0043] In a preferred embodiment, the viscosity of the hydroxyl-terminated polydimethylsiloxane is 1000-15000 mPa·s; if it is too small, cauliflower-like nanostructures cannot be formed, and if it is too large, the reaction success rate is affected.

[0044] Hydroxyl-terminated polydimethylsiloxane is the main component of silicone resin, which has strong hydrophobicity and is cheaper than fluororesin. Hydroxyl biodegradable resin and hydroxyl-terminated polydimethylsiloxane react with the curing agent to give the coating a certain surface degradability, so that new hydrophobic surfaces are constantly exposed on the coating surface, maintaining the surface's antifouling properties.

[0045] In a preferred embodiment, the hydroxyl-terminated biodegradable resin is one of hydroxyl-terminated polylactide (OH-PLA-OH), hydroxyl-terminated polycaprolactone (OH-PCL-OH), hydroxyl-terminated aliphatic carbonate (OH-APC-OH), and hydroxyl-terminated polylactic acid-glycolic acid copolymer (OH-PLGA-OH).

[0046] In a preferred embodiment, the organic solvent is a mixture of one or more of butyl acetate, ethylene glycol monobutyl ether, propylene glycol methyl ether acetate, and xylene.

[0047] In a preferred embodiment, the organic antifouling agent is one of zinc pyrithione (ZPT), 4,5-dichloro-2-octyl-4-isothiazolinone (DCOIT), and 2-(p-chlorophenyl)-3-cyano-4-bromo-5-trifluoromethyl-pyrrole (ECONEA); preferably DCOIT, which has a broad spectrum of activity against hard shells, soft shells and algae.

[0048] In a preferred embodiment, the silane curing agent includes any one of tetraethyl orthosilicate, tetraethyl orthosilicate condensate, methyl orthosilicate, methyltriacetoxysilane, and n-butyl titanate, or a combination of two or more thereof.

[0049] In a preferred embodiment, the catalyst is one of stannous octoate, dibutyltin dilaurate or dibutyldiacetyltin.

[0050] The fluorinated resin and other resins in the coating are not simply physically blended. During the film-forming process, they can participate in the cross-linked curing network of the coating resin through covalent bonds via the siloxane structure of the macromolecular end group (organic silicon cross-linking reaction of hydroxyl and alkoxysilane).

[0051] In the present invention, the hydrophobic organosilicon resin and the wear-resistant corundum give the coating scrub resistance; the micro-nano structure of the hydrophobically modified fumed silica, the fluorinated resin and the organosilicon cooperate to realize the surface super-hydrophobicity; the fluorinated resin and the terminal hydroxyl degradable resin cooperate to realize the surface self-renewal function of the coating. The selection of raw material components and the compound combination and synergistic effect in the preparation process make the antifouling material have the characteristics of scrub resistance, surface super-hydrophobicity and surface self-renewal, showing good antifouling performance and fouling release performance; the coating has the advantages of both self-polishing and fouling release antifouling mechanisms, and the antifouling performance is not affected by the surface renewal speed, while avoiding the failure of the super-hydrophobic microstructure caused by surface pollution.

[0052] Based on the same inventive concept, the present invention also claims a method for preparing the antifouling coating, comprising:

[0053] (1) Preparation of component A: dissolving hydroxyl-terminated polydimethylsiloxane and terminal hydroxyl biodegradable resin in an organic solvent, adding corundum powder, hydrophobically modified fumed silica and an organic antifouling agent, and sand-milling for 15-30 minutes to obtain component A;

[0054] (2) Preparation of component B: uniformly mixing the fluorinated resin, the silane curing agent and the catalyst to prepare component B;

[0055] (3) Component A and component B are mixed evenly in a mass ratio of 4 to 7:1 to obtain an antifouling coating.

[0056] Based on the same inventive concept, the present invention also claims to protect the application of the antifouling coating in antifouling of fixed marine facilities.

[0057] The present invention provides a multi-mechanism synergistic long-term antifouling coating, which is particularly suitable for offshore new energy facilities and has the characteristics of long-term antifouling, cleaning resistance and surface self-renewal. The surface of this coating adopts wear-resistant micro-nano structure and fluorosilicone resin to construct a super-hydrophobic layer to prevent the attachment of marine organisms. In addition, by introducing hydrolyzable / degradable components, the coating can achieve a certain degree of self-renewal, solving the problem of reduced antifouling performance of traditional FRC coatings due to surface aging. The low surface energy and self-renewal properties of the coating make it easy to remove attached fouling organisms. At the same time, the coating exhibits excellent cleaning resistance and can withstand the cleaning operations of the brush head or high-pressure water flow of the cleaning robot. Therefore, the coating of the present invention is used in combination with an underwater cleaning robot to provide long-term antifouling protection for marine fixed facilities, which is very suitable for new energy facilities such as offshore wind power with ultra-long design life.

[0058] Generally speaking, the greater the hardness, the more wear-resistant it is. The resin of the coating of the present invention forms a silicone cross-linked network, which is a thermosetting resin with high hardness and good scrub resistance. The added corundum powder is a recognized wear-resistant filler, which further improves the wear resistance. For silicone hydrogel coatings, because the coating is hydrophilic and soft in water, it is not scrub-resistant. The coating is hydrophobic and has a large cross-linking density, so the hardness of the formed coating is large. In the present invention, the anti-fouling performance of the coating does not conflict with its scrub resistance, so the performance of both can be taken into account.

[0059] The coating does not use copper-containing antifouling agents such as cuprous oxide and cuprous thiocyanate, and is highly environmentally friendly and has no destructive impact on the marine ecological environment. After polishing, the super-hydrophobic micro-nano structure of the coating still exists on the surface. Therefore, the coating can be used in conjunction with underwater robot cleaning to greatly extend the antifouling period. By reasonably designing the film thickness, the effective period can reach more than 10 years, meeting the long-term antifouling needs of large ships. It can be widely used in the protection of surface marine biological fouling of marine engineering facilities and structures such as docks, drilling platforms, piers, piles, etc., and has good potential economic benefits.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. The coating prepared by the present invention combines multiple antifouling mechanisms and has the advantages of self-polishing and fouling release coatings. Its antifouling effect is mainly independent of the coating renewal speed and the release of antifouling agents, such as Figure 1 As shown, the coating relies on the micro-nano structure and low surface energy of the surface to achieve super-hydrophobicity, thereby promoting the natural shedding of contaminants. In addition, the coating automatically renews the aged part of the surface through the hydrolysis / degradation process, so that the attached contaminants are removed, effectively solving the problem of the performance degradation of the traditional micro-nano structure super-hydrophobic surface when covered by contaminants.

[0062] 2. The antifouling coating developed by the present invention is highly compatible with the underwater cleaning robot system, and not only has good physical and mechanical properties, but also has excellent scrub resistance. The super-hydrophobic property of the coating remains stable during scrubbing and polishing and will not be destroyed. At the same time, the smooth, low surface energy and self-renewal properties of the coating make it easy to remove attached fouling organisms. This coating that adopts a multi-element synergistic antifouling strategy can significantly extend the antifouling effectiveness period (up to more than 10 years), and provides an effective solution for the surface antifouling problem of marine fixed facilities, especially new energy facilities such as offshore wind power with extremely long design life. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 A schematic diagram of the antifouling mechanism of the antifouling coating prepared in the present invention;

[0064] Figure 2 This is a SEM image of the hydrophobic fumed silica prepared in the present invention;

[0065] Figure 3 H NMR spectrum of fluorinated resin 1

[0066] Figure 4 The water contact angle of the antifouling coating prepared in Example 1;

[0067] Figure 5 This is a high-magnification SEM image of the coating surface microstructure before and after the scrubbing test in Example 3. DETAILED DESCRIPTION

[0068] The present invention is further described below in conjunction with the accompanying drawings. The present invention can be better understood according to the following examples. However, it is easy for those skilled in the art to understand that the specific material ratios, process conditions and results described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims. The methods of the present invention are conventional methods unless otherwise specified, and the materials can be obtained from public commercial channels unless otherwise specified.

[0069] Preparation of Hydrophobically Modified Fumed Silica

[0070] Octadecyltrimethoxysilane (375 g, 1 mol) was dissolved in 1 L of anhydrous ethanol, and then deionized water (5.4 g, 0.3 mol) was added and stirred evenly, and then 720 g of hydrophilic fumed silica (40 nm) was added to the above solution and dispersed evenly, and the pH was adjusted to 7. Finally, ultrasonic treatment was performed at 25°C for 1 min, and the mixture was filtered, washed with ethanol, and vacuum dried to obtain hydrophobically modified fumed silica. The surface morphology of the prepared hydrophobically modified fumed silica is as follows: Figure 2 shown.

[0071] Preparation of fluorinated resin 1

[0072] First, (3-mercaptopropyl)trimethoxysilane (3.93 g, 20 mmol), 2-(perfluorobutyl)ethyl methacrylate (20 g, 60 mmol), isobornyl methacrylate (31.2 g, 140 mmol), trimethylsilyl methacrylate (6.1 g, 40 mmol) and BPO (0.18 g, 0.3% based on the mass of monomers) were dissolved in 100 ml of dioxane, and then added into a 250 mL three-necked flask and heated under N 2 The reaction was carried out at 110°C for 12 hours. After the reaction was completed, the excess solvent was removed by a rotary evaporator, and the product was washed with excess methanol. The product was placed in a vacuum drying oven at 50°C for 24 hours to obtain a white solid. Its chemical structure was characterized by nuclear magnetic resonance ( Figure 3 ), proving that the fluorinated resin 1 was successfully prepared.

[0073] Preparation of fluorinated resin 2

[0074] First, 3-mercaptopropyl)trimethoxysilane (3.93 g, 20 mmol), 2-(perfluorohexyl)ethyl methacrylate (13.1 g, 30 mmol), isobornyl methacrylate (15.6 g, 70 mmol), triisopropylsilyl methacrylate (7.26 g, 30 mmol) and BPO (0.18 g, 0.3% based on the mass of monomers) were dissolved in 100 ml of dioxane, and then added into a 250 mL three-necked flask and heated under N 2 The reaction was carried out at 110°C for 12 hours. After the reaction was completed, the excess solvent was removed by a rotary evaporator, and the product was washed with excess methanol. The product was placed in a vacuum drying oven at 50°C for 24 hours to obtain a white solid. Its chemical structure was characterized by nuclear magnetic resonance, and the results were similar to Figure 3 .

[0075] Preparation of fluorinated resin 3

[0076] Compared with fluorinated resin 1, the only difference is that (3-mercaptopropyl)trimethoxysilane (3.93 g, 20 mmol) is not added. The other preparation processes are the same as those of fluorinated resin 1 to obtain fluorinated resin 3.

[0077] Example 1

[0078] Preparation of component A: 25 parts by weight of hydroxyl-terminated polydimethylsiloxane and 10 parts by weight of hydroxyl-terminated polycaprolactone (OH-PCL-OH, M n =10-20 kDa) was dissolved in 30 parts by weight of butyl acetate, 15 parts by weight of corundum powder (800 mesh), 15 parts by weight of hydrophobically modified fumed silica, and 5 parts by weight of DCOIT antifouling agent were added, and sanded for 20 minutes to obtain component A.

[0079] Preparation of component B: 20 ​​parts by weight of fluorinated resin 1, 55 parts by weight of ethyl orthosilicate curing agent and 2 parts by weight of dibutyltin dilaurate catalyst component are dissolved and mixed uniformly in 23 parts by weight of xylene to prepare component B;

[0080] When the coating is used, component A and component B are mixed evenly in a mass ratio of 7:1 and cured for 5 to 8 hours to obtain the antifouling material. The static water contact angle test results of the antifouling coating are as follows: Figure 3 As shown, it is about 157°, and its surface micro-nano structure and low free energy make it super hydrophobic.

[0081] Example 2

[0082] Preparation of component A: 30 parts by weight of hydroxyl-terminated polydimethylsiloxane and 5 parts by weight of hydroxyl-terminated polylactide (OH-PLA-OH, M n =20-30 kDa) was dissolved in 22 parts by weight of propylene glycol methyl ether acetate, 15 parts by weight of corundum powder, 20 parts by weight of hydrophobically modified fumed silica, and 8 parts by weight of an organic antifouling agent ZPT were added, and sand-milled for 20 minutes to obtain component A;

[0083] Preparation of component B: 30 parts by weight of fluorinated resin 2, 50 parts by weight of n-butyl titanate curing agent and 1 part by weight of stannous octoate catalyst component are dissolved and mixed uniformly in 19 parts by weight of xylene to prepare component B;

[0084] When the coating is used, component A and component B are evenly mixed in a mass ratio of 5:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0085] Example 3

[0086] Preparation of component A: 30 parts by weight of hydroxyl-terminated polydimethylsiloxane and 10 parts by weight of hydroxyl-terminated polylactic acid-glycolic acid copolymer (OH-PLGA-OH) were dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder, 35 parts by weight of hydrophobically modified fumed silica, and 3 parts by weight of Econea organic antifouling agent were added, and sand-milled for 20 minutes to obtain component A;

[0087] Preparation of component B: 35 parts by weight of fluorinated resin 2, 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0088] When the coating is used, component A and component B are evenly mixed in a mass ratio of 6:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0089] Example 4

[0090] Preparation of component A: 40 parts by weight of hydroxyl-terminated polydimethylsiloxane and 15 parts by weight of hydroxyl-terminated polylactic acid-glycolic acid copolymer (OH-PLGA-OH) were dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder, 20 parts by weight of hydrophobically modified fumed silica, and 3 parts by weight of Econea organic antifouling agent were added, and sand-milled for 20 minutes to obtain component A;

[0091] Preparation of component B: 35 parts by weight of fluorinated resin 2, 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0092] When the coating is used, component A and component B are evenly mixed in a mass ratio of 6:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0093] Comparative Example 1

[0094] Based on Example 3, no hydrophobic fumed silica was added to component A. 30 parts by weight of hydroxyl-terminated polydimethylsiloxane and 10 parts by weight of hydroxyl-terminated polylactic acid-glycolic acid copolymer (OH-PLGA-OH) were dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder and 3 parts by weight of Econea organic antifouling agent were added, and sand-milled for 20 minutes to obtain component A;

[0095] Preparation of component B: 35 parts by weight of fluorinated resin 2, 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0096] When the coating is used, component A and component B are evenly mixed in a mass ratio of 4:1 and cured for 5 to 8 hours to obtain the antifouling material.

[0097] Comparative Example 2

[0098] Based on Example 3, no degradable hydroxyl-terminated resin is added to component A. 30 parts by weight of hydroxyl-terminated polydimethylsiloxane is dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder, 35 parts by weight of hydrophobically modified fumed silica, and 3 parts by weight of Econea organic antifouling agent are added, and sand-milled for 20 minutes to obtain component A;

[0099] Preparation of component B: 35 parts by weight of fluorinated resin 2, 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0100] When the coating is used, component A and component B are evenly mixed in a mass ratio of 5.5:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0101] Comparative Example 3

[0102] Based on Example 3, fluorinated resin 2 was not added to component B. Preparation of component A: 30 parts by weight of hydroxyl-terminated polydimethylsiloxane and 10 parts by weight of hydroxyl-terminated polylactic acid-glycolic acid copolymer (HO-PLGA-OH) were dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder, 35 parts by weight of hydrophobically modified fumed silica, and 3 parts by weight of Econea organic antifouling agent were added, and sand-milled for 20 minutes to obtain component A;

[0103] Preparation of component B: 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0104] When the coating is used, component A and component B are evenly mixed in a mass ratio of 5.5:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0105] Comparative Example 4

[0106] On the basis of Example 3, fluorinated resin 3 was added to component B. Preparation of component A: 30 parts by weight of hydroxyl-terminated polydimethylsiloxane and 10 parts by weight of hydroxyl-terminated polylactic acid-glycolic acid copolymer (OH-PLGA-OH) were dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder, 35 parts by weight of hydrophobically modified fumed silica, and 3 parts by weight of Econea organic antifouling agent were added, and sand-milled for 20 minutes to obtain component A;

[0107] Preparation of component B: 35 parts by weight of fluorinated resin 3, 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0108] When the coating is used, component A and component B are evenly mixed in a mass ratio of 6:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0109] Comparative Example 5

[0110] Based on Example 3, hydroxyl-terminated polydimethylsiloxane was not added to component A. Preparation of component A: 10 parts by weight of hydroxyl-terminated polylactic acid-glycolic acid copolymer (OH-PLGA-OH) was dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder, 35 parts by weight of hydrophobically modified fumed silica, and 3 parts by weight of Econea organic antifouling agent were added, and sand-milled for 20 minutes to obtain component A;

[0111] Preparation of component B: 35 parts by weight of fluorinated resin 2, 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0112] When the coating is used, component A and component B are evenly mixed in a mass ratio of 6:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0113] Comparative Example 6

[0114] On the basis of Example 3, the B component does not add the fluorinated resin 2, but only adds the raw materials for preparing the fluorinated resin 2. Preparation of component A: 30 parts by weight of hydroxyl-terminated polydimethylsiloxane and 10 parts by weight of hydroxyl-terminated polylactic acid-glycolic acid copolymer (OH-PLGA-OH) are dissolved in 17 parts by weight of butyl acetate, 5 parts by weight of corundum powder, 35 parts by weight of hydrophobically modified fumed silica, and 3 parts by weight of Econea organic antifouling agent are added, and sand-milled for 20 minutes to obtain component A;

[0115] Preparation of component B: 35 parts by weight of the mixture, 50 parts by weight of methyltriacetoxysilane curing agent and 3 parts by weight of stannous octoate catalyst are dissolved and mixed evenly in 12 parts by weight of butyl acetate to prepare component B;

[0116] Dissolve 3-mercaptopropyl)trimethoxysilane (3.93 g, 20 mmol), 2-(perfluorohexyl)ethyl methacrylate (13.1 g, 30 mmol), isobornyl methacrylate (15.6 g, 70 mmol), triisopropylsilyl methacrylate (7.26 g, 30 mmol) and BPO (0.18 g, 0.3% based on the mass of the monomers) in 100 ml of dioxane and mix well to obtain a mixture;

[0117] When the coating is used, component A and component B are evenly mixed in a mass ratio of 6:1, and cured for 5 to 8 hours to obtain the antifouling material.

[0118] The components of the embodiments and comparative examples are listed in Table 1 and Table 2.

[0119] Table 1. Coating composition of the examples

[0120]

[0121]

[0122] Table 2 Coating composition of Example 3 and Comparative Example

[0123]

[0124] With reference to GB / T5370-2007 standard, shallow sea board hanging was carried out in Qingdao waters for half a year, and the anti-fouling effect was scored, with 100 points as the full score.

[0125] The polishing rate test was carried out with reference to GB / T31411-2015 standard.

[0126] Refer to GB / T 5210-2006 and use a pull-off adhesion tester to measure the adhesion of the coating after immersion.

[0127] Refer to GB / T 6739-2022 to test the pencil hardness of the coating.

[0128] The coating polishing (thickness loss) was performed as follows: different antifouling coatings were applied on epoxy resin panels, immersed in natural seawater, and the thickness loss of the coatings was characterized by a laser film thickness meter at regular intervals.

[0129] Scrub resistance test: There is currently no standard test method for the cleaning resistance of antifouling coatings. Therefore, the scrub resistance test method is specified in the following application scenarios: Take out the sample after soaking in artificial seawater, gently absorb the water droplets on the surface with a wipe paper, and weigh M 0 After rubbing the same area of ​​the surface back and forth 400 times with a brush, rinse the surface with artificial seawater, and gently absorb the water droplets on the surface with a wipe paper, weigh M w . Use "M 0 -M w " stands for cleaning resistance. The larger the value, the worse the scrubbing resistance. After the test, retest the water contact angle of the test sample. (The test samples have the same area, the same coating, and the brush wires are the brush wire models commonly used in cleaning robots.

[0130] The test results are shown in Table 3.

[0131] Table 3 Performance of each embodiment and comparative example

[0132]

[0133] It is not difficult to find from Table 2 combined with the accompanying drawings:

[0134] The antifouling scores of Examples 1 to 4 in the half-year shallow sea hanging board experiment were all 95 or above, showing excellent static antifouling effects. The three coatings showed excellent scrub resistance, and their contact angles were all over 150 degrees, showing super hydrophobic properties. Even after 400 scrubbings, the contact angle remained stable, thus maintaining the characteristics of the super hydrophobic surface. Figure 4Scanning electron microscope (SEM) images of the coating of Example 1 before and after scrubbing are shown. Before scrubbing, the surface of the coating of Example 1 exhibits a micro-nano rough structure. Although the surface morphology after the scrubbing test is different from that of the original coating, the surface of the coating after abrasion still maintains the micro-nano rough structure, which is the key to the coating maintaining its superhydrophobicity.

[0135] Comparative Example 1 is based on Example 3, and the coating does not contain hydrophobic fumed silica, and its contact angle is only 119°, which once again confirms that the micro-nano structure formed by hydrophobic fumed silica on the coating surface is the key factor for the coating to have super hydrophobicity. It is precisely because of the difference in surface contact angle that the antifouling performance of Comparative Example 1 is poor, and the antifouling score is 87. In addition, its scrub resistance is significantly reduced compared with Examples 1 to 3. This may be due to the low pigment-to-base ratio of the coating, resulting in a high content of resin components in the coating, and the paint film is soft and therefore not scrub-resistant, which can also be confirmed from the test results of the pencil hardness of the coating.

[0136] Comparative Example 2 is based on Example 3, but the coating does not contain a degradable hydroxyl-terminated resin. Therefore, Comparative Example 2 has almost no thickness loss (0.1 μm) after static immersion, and it is difficult to achieve surface renewal in static seawater. Therefore, although its contact angle is not much different from that of Example 3, it lacks a renewable surface, and thus has poor static antifouling performance, with a score of 89 points.

[0137] Comparative Example 3 is based on Example 3, but the coating does not contain fluorinated resin 2, and the surface free energy is higher, so the contact angle of Comparative Example 3 is only 136°, and the polishing rate of its coating is significantly lower than that of Example 3, so the anti-fouling score is only 83 points.

[0138] Comparative Example 4: On the basis of Example 3, component B adds fluorinated resin 3 to replace fluorinated resin 2. Since fluorinated resin 3 does not contain trimethoxysilane end groups, it cannot participate in the construction of the coating cross-linked network through coupling reaction, but is combined with other raw materials in a physical mixing manner, which reduces the cross-linking density and cohesion of the coating. Although its initial hydrophobicity (154°) is not much different from that of Experiment 3, after 400 scrubbings, the coating contact angle dropped significantly to 121°, and the scrubbing resistance was also significantly reduced (210 mg). This phenomenon is attributed to the reduction in the degree of cross-linking of the coating, resulting in poor wear resistance, and the fluorinated components on the surface of the coating are worn out in large quantities during the scrubbing process. Therefore, the adhesion and pencil hardness of the coating are lower than those of Experiment 3, which is mainly due to the low cohesion of the coating. Despite this, the antifouling score of the coating is still 95, indicating that its antifouling performance is basically unaffected.

[0139] Comparative Example 5 is based on Example 3, but component A does not add hydroxyl-terminated polydimethylsiloxane (the main film-forming resin). Due to the lack of the main film-forming resin, the scrub resistance of the coating is very poor (560 mg). After being immersed in natural seawater, it bubbles and falls off, and has poor adhesion, so it is impossible to perform an anti-fouling score.

[0140] Comparative Example 6 is based on Example 3, but fluorinated resin 2 is not added to component B, and only the raw materials (monomers) for preparing fluorinated resin 2 are added. Its initial water contact angle is 158°, and it has a super-hydrophobic surface. However, after 400 scrubbings, although the scrubbing resistance does not decrease significantly, the contact angle of the coating drops to 129°. This is because the fluorinated small molecule monomer migrates to the coating surface, and the content of the fluorinated small molecule monomer on the surface decreases after scrubbing. The antifouling performance of the coating is similar to that of Comparative Example 3, indicating that the raw materials of fluorinated resin 2 added to component B and the raw materials without fluorinated resin 2 have the same antifouling effect. This is because during the seawater immersion process of the coating of Comparative Example 6, the added small molecule raw materials will quickly migrate and release from the coating, thereby failing.

[0141] Therefore, the above results show that the multi-mechanism synergistic long-lasting antifouling coating prepared by the present invention, through the selection of raw material components and the compound combination and synergistic effect during the preparation process, enables the antifouling material to have the characteristics of scrub resistance, surface superhydrophobicity and surface self-renewal.

[0142] The super-hydrophobic micro-nanostructure on the coating surface is still maintained after 400 scrubbings. The high-magnification SEM images of the coating surface microstructure of the antifouling coating of Example 3 before and after 400 scrubbing tests are shown in FIG. Figure 5 As shown, the results of Examples 1-2 and 4 are similar. This shows that the antifouling performance of the coating is basically unaffected after scrubbing, so the long-term antifouling performance of the coating can be guaranteed by cooperating with an underwater scrubbing robot. The polishing rate of the coating is less than 2.2 μm / month. Considering that the conventional design film thickness of the current ship antifouling paint is 300-500 μm, and considering the thickness loss caused by the scrubbing of the coating by the underwater cleaning robot, the antifouling period can be up to more than 10 years. It can be widely used in marine engineering facilities and structures such as docks, drilling platforms, piers, piles, etc. for surface marine biological fouling protection, and has good potential economic benefits.

[0143] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fluorinated resin, characterized in that: Its structural formula is as follows: Where R1 is (CH2) e (CF2) f CF3, e is 1 or 2, f is a natural integer of 0-7; R2, R3, R4 are independently selected from (CH2) n CH3; a is a natural integer of 2-8; n is a natural integer of 0-12; x, y, z are the mass fraction ratio of the three polymerization units, x:y:z is 30-60:10-30:5-20.

2. The fluorinated resin according to claim 1, characterized in that n is 0, 1, 2, 3 or 4.

3. The method for preparing a fluorinated resin according to claim 1 or 2, characterized in that: include: 1-5wt% mercaptosilane, 10-30wt% methacrylic acid fluorinated monomer, 30-60wt% methacrylate isobornyl monomer, 5-20wt% methacrylate silane monomer and initiator are dissolved in a solvent, and reacted at 100-130°C for 20-28h under nitrogen protection; after the reaction, the solvent is removed, washed and dried to obtain a fluorinated resin; mercaptosilane is a silane monomer having a mercapto group at one end and an alkoxy group at the other end, and the structural formula is (CH3(CH2) b O)3Si(CH2) a SH; a is selected from any integer in the range of 2-8; b is selected from any integer in the range of 0-4; the methacrylic acid fluorinated monomer is one of 2-(perfluorobutyl)ethyl methacrylate, 2-(perfluorooctyl)ethyl methacrylate, and 2-(perfluorohexyl)ethyl methacrylate; the methacrylic acid silane ester monomer has the following general structure: Wherein, n is a natural integer of 0-12.

4. The preparation method according to claim 3, characterized in that: The mercaptosilane is (3-mercaptopropyl)trimethoxysilane or (3-mercaptopropyl)triethoxysilane.

5. The preparation method according to claim 3, characterized in that: The methacrylate silane ester monomer includes at least one of trimethylsilyl methacrylate, triethylsilyl methacrylate, triisopropylsilyl methacrylate, triphenylsilyl methacrylate, tri-n-butylsilyl methacrylate, and tert-butyldimethylsilyl methacrylate.

6. An antifouling coating, characterized in that: The raw materials include component A and component B in a mass ratio of 4-7:1, and the component B includes 20-40 parts by weight. The fluorinated resin as claimed in claim 1 or 2, 50-70 parts of a silane curing agent, 1-5 parts of a catalyst and 10-25 parts of an organic solvent; component A comprises 25-40 parts of a hydroxyl-terminated polydimethylsiloxane, 5-15 parts of a terminal hydroxyl biodegradable resin, 5-15 parts of corundum powder, 10-30 parts of a hydrophobically modified fumed silica and 1-3 parts of an organic antifouling agent.

7. The antifouling coating according to claim 6, characterized in that: The preparation method of the hydrophobically modified fumed silica comprises: dissolving a long carbon chain silane in an ethanol aqueous solution to prepare a silane solution with a concentration of 3-8wt%, then adding hydrophilic fumed silica, adjusting the pH to 5-7, ultrasonically dispersing at 30-50°C, filtering, washing and drying to obtain the hydrophobically modified fumed silica; the long carbon chain silane is one of dodecyltrichlorosilane, dodecyltrimethoxysilane, hexadecyltrichlorosilane, hexadecyltrimethoxysilane, octadecyltrichlorosilane, octadecyltrimethoxysilane, perfluorooctyltrimethoxysilane and heptadecafluorodecyltrimethoxysilane.

8. The antifouling coating according to claim 6, characterized in that: The viscosity of the hydroxyl-terminated polydimethylsiloxane is 1000-15000 mPa·s.

9. The antifouling coating according to claim 6, characterized in that: The hydroxyl-terminated biodegradable resin is one of hydroxyl-terminated polylactide, hydroxyl-terminated polycaprolactone, hydroxyl-terminated aliphatic carbonate, and hydroxyl-terminated polylactic acid-glycolic acid copolymer.

10. The antifouling coating according to claim 6, characterized in that: The organic solvent is a mixture of one or more of butyl acetate, ethylene glycol monobutyl ether, propylene glycol methyl ether acetate and xylene.

11. The antifouling coating according to claim 6, characterized in that: The organic antifouling agent is one of zinc pyrithione (ZPT), 4,5-dichloro-2-octyl-4-isothiazolinone (DCOIT), and 2-(p-chlorophenyl)-3-cyano-4-bromo-5-trifluoromethyl-pyrrole (ECONEA).

12. The antifouling coating according to claim 6, characterized in that: The silane curing agent includes any one of tetraethyl orthosilicate, tetraethyl orthosilicate condensate, methyl orthosilicate, methyl triacetoxysilane, and n-butyl titanate, or a combination of two or more thereof.

13. Use of the antifouling coating according to any one of claims 6 to 12 in antifouling of marine fixed facilities.

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