Water-based single-component coating as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of coatings, and particularly relates to a water-based single-component coating as well as a preparation method and application thereof. The water-based single-component coating is prepared from hydrophilic pure acrylic emulsion, silicone acrylic emulsion, first titanium dioxide, prefabricated slurry, cellulose, auxiliaries and water. The prefabricated slurry comprises second titanium dioxide, superfine calcium carbonate and water; the particle size of the superfine calcium carbonate is less than 2.0 microns. The hydrophilic pure acrylic emulsion is matched with a certain amount of silicone acrylic emulsion, so that the water resistance and the water permeability of a coating film can be effectively balanced while the stain resistance of the coating film is improved, and the coating has good stain resistance and water resistance and low water permeability. Under the synergistic effect of the superfine calcium carbonate and the second titanium dioxide, the steric hindrance effect of the superfine calcium carbonate can be enhanced, and the dispersity of the second titanium dioxide can be improved, so that the surface flatness and compactness of a coating film are high, and the glossiness, stain resistance and contrast ratio of the coating film are improved. And the first titanium dioxide is matched with the prefabricated slurry containing the second titanium dioxide, so that the contrast ratio, the stain resistance and the glossiness can be better improved.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to a water-based single-component coating and a preparation method and application thereof. Background Art

[0002] With the rapid development of urban viaduct construction, water-based anti-corrosion coating is usually required on the bridge surface. However, the solvent-based coatings currently on the market are expensive and contain a large amount of volatile organic compounds, which are harmful to construction workers and the environment.

[0003] In the field of viaduct coatings, they are generally divided into water-based products and oil-based products. Oil-based coatings are mainly based on oil-based thermoplastic acrylic, chlorinated rubber, acrylic polyurethane or fluoroethylene-vinyl ether coatings (FEVE fluorocarbon coatings). Water-based single-component outdoor coatings are generally single-component water-based high-gloss topcoats, and the stain resistance can generally only reach 15-20%. Generally speaking, single-component high-solid products have lower gloss; high-gloss products generally have poor stain resistance, so it is difficult to take into account high gloss, high solid content, and high stain resistance at the same time.

[0004] Therefore, it is of great significance to provide a coating with high gloss, high solid content and good stain resistance. Summary of the invention

[0005] The present invention aims to solve one or more technical problems existing in the above-mentioned prior art and at least provide a beneficial choice. Specifically, the present invention provides a water-based single-component coating having good gloss, solid content and stain resistance.

[0006] The inventive concept of the present invention: The coating of the present invention includes a hydrophilic pure acrylic emulsion, a silicone acrylic emulsion, a first titanium dioxide, a prefabricated slurry, cellulose, an additive, and water; the prefabricated slurry includes a second titanium dioxide, ultrafine calcium carbonate, and water; the particle size of the ultrafine calcium carbonate is less than 2.0 μm. The present invention uses a hydrophilic pure acrylic emulsion in combination with a certain amount of silicone acrylic emulsion, which can effectively improve the stain resistance of the coating surface. The super-hydrophilic surface design of the coating is effective for both hydrophilic and lipophilic pollutants. Adding a certain amount of silicone acrylic emulsion can make the coating have a certain internal hydrophobic and external hydrophilic effect, which can effectively balance the water resistance and hydrophilicity of the paint film and improve the stain resistance. At the same time, the use of ultrafine calcium carbonate and the second titanium dioxide compound can improve the steric hindrance effect of ultrafine calcium carbonate, improve the dispersibility of the second titanium dioxide, and improve the contrast ratio of the coating. At the same time, the surface flatness and density of the coating are higher, and the gloss and stain resistance of the coating are improved. In addition, the first titanium dioxide is used in combination with the prefabricated slurry containing the second titanium dioxide to improve the contrast ratio, stain resistance and gloss. In short, the components work together to make the coating have high solid content, high gloss, high stain resistance, high weather resistance, high contrast ratio and low water permeability.

[0007] Therefore, a first aspect of the present invention provides a water-based one-component coating.

[0008] Specifically, the water-based single-component coating includes a hydrophilic pure acrylic emulsion, a silicone acrylic emulsion, a first titanium dioxide, a prefabricated slurry, cellulose, an additive, and water;

[0009] The prefabricated slurry includes a second titanium dioxide, ultrafine calcium carbonate and water;

[0010] The particle size of the ultrafine calcium carbonate is less than 2.0 μm.

[0011] Preferably, the hydrophilic pure acrylic emulsion has a solid content of 57-59% and a minimum film-forming temperature of 8-32°C.

[0012] Preferably, the hydrophilic pure acrylic emulsion is Budford RS2808A.

[0013] Preferably, the solid content of the silicone acrylic emulsion is 48-50%, and the minimum film-forming temperature is 20-24°C.

[0014] Preferably, the silicone acrylic emulsion is Badful NPT907.

[0015] Preferably, the mass ratio of the first titanium dioxide to the second titanium dioxide is (0.27-1):1; further preferably, the mass ratio of the first titanium dioxide to the second titanium dioxide is (0.3-0.9):1.

[0016] The mass ratio of the first titanium dioxide to the second titanium dioxide of the present invention is (0.27-1):1. According to the different particle sizes of ultrafine calcium carbonate and titanium dioxide, the suitable addition ratio of the second titanium dioxide and ultrafine modified calcium carbonate can improve the steric hindrance effect of ultrafine calcium carbonate, improve the dispersibility of the second titanium dioxide, and improve the contrast ratio of the coating. At the same time, the surface flatness and density of the coating are higher, the glossiness and stain resistance of the coating are improved, and the carbon emissions can be reduced to a certain extent to meet the low-carbon environmental protection requirements.

[0017] Preferably, the first titanium dioxide and the second titanium dioxide are both rutile.

[0018] Preferably, the first titanium dioxide and the second titanium dioxide both include at least one of titanium dioxide R706 and titanium dioxide R996.

[0019] Preferably, the particle sizes of the first titanium dioxide and the second titanium dioxide are both 0.27-0.45 μm; further preferably, the particle sizes of the first titanium dioxide and the second titanium dioxide are both 0.3-0.4 μm.

[0020] Preferably, the Mohs hardness of the first titanium dioxide and the second titanium dioxide is greater than 5.5; further preferably, the Mohs hardness of the first titanium dioxide and the second titanium dioxide is greater than 6; further preferably, the Mohs hardness of the first titanium dioxide and the second titanium dioxide is 6.5.

[0021] Preferably, the oil absorption of the ultrafine calcium carbonate is 16-30 g / 100 g; further preferably, the oil absorption of the ultrafine calcium carbonate is 18-27 g / 100 g.

[0022] Preferably, the ultrafine calcium carbonate is Omya Calcigloss-IK high-gloss functional calcium carbonate.

[0023] Preferably, the auxiliary agent includes at least one of an antifreeze-thaw auxiliary agent, a film-forming auxiliary agent, a wetting agent, a dispersant, a pH regulator, a bactericide, an anti-settling agent, a mildew inhibitor, and a defoaming agent.

[0024] Preferably, the coating includes, by mass, 45-65 parts of hydrophilic pure acrylic emulsion, 2.7-11 parts of silicone acrylic emulsion, 6.5-16.5 parts of first titanium dioxide, 9-33 parts of prefabricated slurry, 0.1-0.55 parts of cellulose, 0.27-1.6 parts of antifreeze-thaw aid, 0.45-5.5 parts of film-forming aid, 0.1-0.33 parts of wetting agent, 0.1-0.65 parts of dispersant, 0-0.11 parts of pH regulator, 0-1.1 parts of bactericide, 0.1-0.33 parts of anti-settling agent, 0.45-2.2 parts of mildewcide, 0.5-11 parts of defoaming agent, and more than 0 parts and less than or equal to 30 parts of water.

[0025] Further preferably, the coating includes, by weight, 50-60 parts of hydrophilic pure acrylic emulsion, 3-10 parts of silicone acrylic emulsion, 7-15 parts of first titanium dioxide, 10-30 parts of prefabricated slurry, 0.2-0.5 parts of cellulose, 0.3-1.5 parts of antifreeze-thaw aid, 0.5-5 parts of film-forming aid, 0.1-0.3 parts of wetting agent, 0.1-0.6 parts of dispersant, 0-0.1 parts of pH regulator, 0-1 parts of bactericide, 0.1-0.3 parts of anti-settling agent, 0.5-2 parts of mildewproof agent, 3-10 parts of defoaming agent, and more than 0 parts and less than or equal to 28 parts of water.

[0026] Preferably, the cellulose comprises hydroxyethyl cellulose.

[0027] Preferably, the hydroxyethyl cellulose includes at least one of HBR250 cellulose and HHBR250 cellulose.

[0028] Preferably, the antifreeze-thaw aid includes at least one of propylene glycol (PG) and ethylene glycol.

[0029] Preferably, the film-forming aid includes at least one of 2-methyl-propionic acid, 2,2,4-trimethyl-1,3-pentanediol monoester, and polyol monobutyl ether.

[0030] Preferably, the film-forming aid comprises carbon dodecanol ester; further preferably, the film-forming aid comprises carbon dodecanol ester of Eastman.

[0031] Preferably, the wetting agent is a nonionic surfactant.

[0032] Preferably, the wetting agent includes at least one of Klein Genapol PF20 and Emulsogen LCN070.

[0033] Preferably, the dispersant comprises at least one of polypropionate, polystyrene salt and maleate.

[0034] Preferably, the dispersant includes AD 504 from Sanyo Chemical Fine Chemicals Nantong Co., Ltd.

[0035] Preferably, the pH adjuster comprises 2-amino-2-methyl-1-propanol.

[0036] Preferably, the pH adjuster is AMP95.

[0037] Preferably, the bactericide includes at least one of formaldehyde-releasing agents, isothiazolones and benzamimidazoles.

[0038] Preferably, the bactericide includes BIOBAN 623A of Dow, BW20 of Thor Specialty Chemicals (Shanghai) Co., Ltd. and preservative of Thor Specialty Chemicals (Shanghai) Co., Ltd. At least one of LPC5.

[0039] Preferably, the anti-settling agent includes at least one of sepiolite, bentonite, high viscosity attapulgite, and organically modified hectorite clay.

[0040] Preferably, the anti-settling agent includes Bentone DY CE produced by Deqian (Shanghai) Chemical Co., Ltd.

[0041] Preferably, the mildew preventer includes at least one of dibromocyanopropionamide (DBNPA), isothiazolinones, phenylimidazoles, substituted aromatic hydrocarbons, and dithiocarbamates.

[0042] Preferably, the antifungal agent includes AA146 from LANXESS (Changzhou) Co., Ltd.

[0043] Preferably, the defoamer comprises a mineral oil / silicone composite defoamer.

[0044] Preferably, the defoaming agent comprises BASF Foamaster NXZ.

[0045] Preferably, the prefabricated slurry further comprises at least one of a dispersant and a defoaming agent.

[0046] Specifically, in the prefabricated slurry, the selectable types of the dispersant and defoamer are the same as the dispersant and defoamer in the above-mentioned coating.

[0047] Preferably, the prefabricated slurry further comprises a dispersant and a defoamer, and by weight, the prefabricated slurry comprises 9-22 parts of ultrafine calcium carbonate, 45-70 parts of a second titanium dioxide, 0.45-3.3 parts of a dispersant, 0.45-3.3 parts of a defoamer, and 4.5-16.5 parts of water.

[0048] Further preferably, the prefabricated slurry also includes a dispersant and a defoamer, and in parts by mass, the prefabricated slurry includes 10-20 parts of ultrafine calcium carbonate, 50-65 parts of the second titanium dioxide, 0.5-3 parts of the dispersant, 0.5-3 parts of the defoamer, and 5-15 parts of water.

[0049] The second aspect of the present invention provides a method for preparing the water-based single-component coating according to the first aspect of the present invention.

[0050] Specifically, the method for preparing the water-based single-component coating comprises the following steps:

[0051] The coating is prepared by mixing various raw material components.

[0052] Preferably, the method for preparing the prefabricated slurry comprises the following steps:

[0053] The raw material components are mixed to prepare the prefabricated slurry.

[0054] Preferably, ultrafine calcium carbonate, titanium dioxide, dispersant and defoamer are added into water under stirring, and then stirred at high speed to obtain the prefabricated slurry.

[0055] Preferably, the stirring speed is 400-600 r / min; further preferably, the stirring speed is 450-550 r / min; further preferably, the stirring speed is 500 r / min.

[0056] Preferably, the rotation speed of the high-speed stirring is 1300-1700 r / min, and the time of the high-speed stirring is 13-18 min; further preferably, the rotation speed of the high-speed stirring is 1400-1600 r / min, and the time of the high-speed stirring is 14-16 min; further preferably, the rotation speed of the high-speed stirring is 1500 r / min, and the time of the high-speed stirring is 15 min.

[0057] The third aspect of the present invention provides an application of the water-based single-component coating according to the first aspect of the present invention in the field of bridges.

[0058] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0059] (1) The present invention uses a hydrophilic pure acrylic emulsion in combination with a certain amount of silicone acrylic emulsion, so that the hydrophobic and exophylic properties of the coating surface are enhanced. This hydrophobic and exophylic coating can effectively improve the stain resistance of the coating surface, and at the same time can well balance the water resistance of the coating, that is, it can effectively take into account both the stain resistance and water resistance. A certain amount of small molecule silicone acrylic emulsion can be evenly dispersed in the pure acrylic emulsion system by hydrogen bonding during cross-linking and curing, so that after the entire coating is cured and formed, a large amount of hydrophilic pure acrylic emulsion cross-links and cures to improve the hydrophilicity of the coating surface, so that the coating has a better stain resistance effect, and a small amount of small molecule silicone acrylic emulsion forms a silicon-oxygen bond inside the coating to provide a certain coating water resistance, so that the coating has a lower water permeability and water resistance.

[0060] (2) The present invention uses ultrafine calcium carbonate and a certain amount of second titanium dioxide to prepare a premixed slurry, so that the ultrafine calcium carbonate can effectively disperse a part of the titanium dioxide by utilizing the steric hindrance effect. The two work together to obtain a higher surface flatness and density of the coating, and improve the glossiness, stain resistance and contrast ratio of the coating. In addition, the first titanium dioxide is used in combination with the prefabricated slurry containing the second titanium dioxide to better improve the contrast ratio, stain resistance and glossiness. The components work together, and on the basis of the solid content of the coating being greater than 60%, the stain resistance of the coating can reach 3-4%, the gloss can reach about 65-70%, and it has high weather resistance, high contrast ratio and low water permeability. At the same time, a certain amount of ultrafine calcium carbonate replaces titanium dioxide, which can reduce a certain amount of titanium dioxide, reduce carbon emissions to a certain extent, and meet low-carbon environmental protection requirements. DETAILED DESCRIPTION

[0061] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be noted that the following embodiments do not limit the protection scope of the present invention.

[0062] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0063] Example 1

[0064] A water-based one-component coating, comprising, by weight:

[0065]

[0066] Wherein, by weight, the prefabricated slurry includes 16.4 parts of water, 15 parts of ultrafine calcium carbonate, 65 parts of titanium dioxide R706, 0.6 parts of dispersant and 3 parts of defoaming agent.

[0067] A method for preparing a water-based single-component coating comprises the following steps:

[0068] The raw material components are mixed to prepare a water-based single-component coating.

[0069] The method for preparing the prefabricated slurry comprises the following steps:

[0070] Water was added to the container and stirred at a speed of 500 r / min, and then ultrafine calcium carbonate, titanium dioxide, dispersant and defoamer were added, and the speed was adjusted to 1500 r / min and stirred at high speed for 15 minutes to prepare a prefabricated slurry.

[0071] Example 2

[0072] A water-based one-component coating, comprising, by weight:

[0073]

[0074] Among them, the prefabricated slurry includes 16.4 parts of water, 10 parts of ultrafine calcium carbonate, 70 parts of titanium dioxide R706, 0.6 parts of dispersant, and 3 parts of defoaming agent, calculated by mass.

[0075] The preparation method of a water-based single-component coating comprises the following steps:

[0076] The raw material components are mixed to prepare a water-based single-component coating.

[0077] The method for preparing the prefabricated slurry comprises the following steps:

[0078] Water was added to the container and stirred at a speed of 500 r / min, and then ultrafine calcium carbonate, titanium dioxide, dispersant and defoamer were added, and the speed was adjusted to 1500 r / min and stirred at high speed for 15 minutes to prepare a prefabricated slurry.

[0079] Example 3

[0080] A water-based one-component coating, comprising, by weight:

[0081]

[0082] Among them, calculated by mass, the prefabricated slurry includes 16.4 parts of water, 15 parts of ultrafine calcium carbonate, 65 parts of titanium dioxide R996, 0.6 parts of dispersant, and 3 parts of defoaming agent.

[0083] The preparation method of a water-based single-component coating comprises the following steps:

[0084] The raw material components are mixed to prepare a water-based single-component coating.

[0085] The method for preparing the prefabricated slurry comprises the following steps:

[0086] Water was added to the container and stirred at a speed of 500 r / min, and then ultrafine calcium carbonate, titanium dioxide, dispersant and defoamer were added, and the speed was adjusted to 1500 r / min and stirred at high speed for 15 minutes to prepare a prefabricated slurry.

[0087] Comparative Example 1

[0088] The only difference between Comparative Example 1 and Example 3 is that no prefabricated slurry is added in Comparative Example 1, and in order to keep consistent with the total amount of titanium dioxide added in Example 3, conventional calcium carbonate is used instead of ultrafine modified calcium carbonate, the amount of titanium dioxide R996 is 24.6 parts, the amount of calcium carbonate CC700 is 3.6 parts, and the amount of water is 8.7 parts, and the rest is the same as Example 3.

[0089] Comparative Example 2

[0090] The difference between Comparative Example 2 and Example 3 is that Comparative Example 2 uses an equal amount of hydrophilic pure acrylic emulsion RS2808A to replace the silicone acrylic emulsion NPT907, and the rest is the same as Example 3.

[0091] Comparative Example 3

[0092] The only difference between Comparative Example 3 and Example 3 is that in Comparative Example 3, all the titanium dioxide is used to prepare the slurry, and the first titanium dioxide is not added separately to the coating, that is, the amount of the prefabricated slurry is 36 parts, the ultrafine calcium carbonate in the prefabricated slurry is 10 parts, the titanium dioxide is 68.3 parts, and the water amount is 1.9 parts, which is the same as Example 3.

[0093] Performance Testing

[0094] The coatings prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. The specific test items and test methods are shown in Table 1.

[0095] Table 1: Test items and test methods

[0096]

[0097]

[0098] The performance test results of the coatings of Examples 1-3 and Comparative Examples 1-3 are shown in Table 2.

[0099] Table 2: Performance test results of coatings of Examples 1-3 and Comparative Examples 1-3

[0100]

[0101] It can be seen from Table 2 that the coating prepared by the present invention has a high solid content, good stain resistance, gloss, contrast ratio, good scrub resistance, resistance to artificial aging, algae resistance, mildew resistance, and low water permeability.

[0102] It can be seen from Comparative Example 1 and Example 3 that even though the addition amounts of titanium dioxide, pure acrylic emulsion and silicone acrylic emulsion in Comparative Example 1 are the same as those in Example 3, only ordinary calcium carbonate is used in Comparative Example 1 without ultrafine calcium carbonate, and ordinary calcium carbonate is added to the formula in a conventional manner, so that the contrast ratio, stain resistance, water resistance and gloss of Comparative Example 1 are lower than those of Example 3, indicating that pre-preparing a prefabricated slurry with part of titanium dioxide and ultrafine calcium carbonate, and then mixing it with the remaining titanium dioxide to prepare the coating, plays an important role in improving the contrast ratio, stain resistance and gloss of the coating.

[0103] It can be seen from Comparative Example 2 and Example 3 that Comparative Example 2 uses an equal amount of pure acrylic emulsion RS2808A to replace the silicone acrylic emulsion NPT907, that is, does not contain silicone acrylic emulsion, so that the stain resistance, artificial aging performance and water permeability of Comparative Example 2 are significantly reduced, indicating that the compounding of pure acrylic emulsion and silicone acrylic emulsion can improve the stain resistance of the coating while also improving the artificial aging resistance of the coating, improving the water resistance of the coating, and reducing the water permeability of the coating.

[0104] It can be seen from Comparative Example 3 and Example 3 that titanium dioxide is not added separately in Comparative Example 3, but titanium dioxide is added to all the prefabricated slurry, so that the contrast ratio, stain resistance and glossiness of Comparative Example 3 are lower than those of Example 3, indicating that the use of the first titanium dioxide in combination with the prefabricated slurry containing the second titanium dioxide can improve the contrast ratio, stain resistance and glossiness.

[0105] In summary, the present invention uses a hydrophilic pure acrylic emulsion with a certain amount of silicone acrylic emulsion, which can effectively improve the stain resistance of the coating surface and balance the water resistance of the coating film. Ultrafine calcium carbonate is compounded with a certain amount of the second titanium dioxide to prepare a prefabricated slurry, so that the ultrafine calcium carbonate effectively disperses a part of the titanium dioxide by utilizing the steric hindrance effect. The two work together to obtain a higher surface flatness and density of the coating film, and improve the gloss, stain resistance and contrast ratio of the coating film. In addition, the first titanium dioxide needs to be used in combination with a prefabricated slurry containing the second titanium dioxide to better improve the contrast ratio, stain resistance and gloss. The components work together so that the coating has a stain resistance of 3-4%, a gloss of about 65-70%, a contrast ratio of up to 95-97%, and a water permeability of ≤0.5mL on the basis of a solid content greater than 60%, and the comprehensive performance of the coating is greatly improved.

[0106] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A coating, characterized in that: Including hydrophilic pure acrylic emulsion, silicone acrylic emulsion, first titanium dioxide, prefabricated slurry, cellulose, additives, and water; The prefabricated slurry includes a second titanium dioxide, ultrafine calcium carbonate and water; The particle size of the ultrafine calcium carbonate is less than 2.0 μm.

2. The coating according to claim 1, characterized in that The mass ratio of the first titanium dioxide to the second titanium dioxide is (0.27-1):

1.

3. The coating according to claim 1, characterized in that The oil absorption of the ultrafine calcium carbonate is 16-30g / 100g.

4. The coating according to claim 1, characterized in that The auxiliary agent includes at least one of an antifreeze-thaw auxiliary agent, a film-forming auxiliary agent, a wetting agent, a dispersant, a pH regulator, a bactericide, an anti-settling agent, a mildew preventer, and a defoaming agent.

5. The coating according to claim 4, characterized in that The coating comprises, by weight, 45-65 parts of hydrophilic pure acrylic emulsion, 2.7-11 parts of silicone acrylic emulsion, 6.5-16.5 parts of first titanium dioxide, 9-33 parts of prefabricated slurry, 0.1-0.55 parts of cellulose, 0.27-1.6 parts of antifreeze-thaw aid, 0.45-5.5 parts of film-forming aid, 0.1-0.33 parts of wetting agent, 0.1-0.65 parts of dispersant, 0-0.11 parts of pH regulator, 0-1.1 parts of bactericide, 0.1-0.33 parts of anti-settling agent, 0.45-2.2 parts of mildewproof agent, 0.5-11 parts of defoaming agent, and water greater than 0 parts and less than or equal to 30 parts.

6. The coating according to claim 1, characterized in that The prefabricated slurry also includes at least one of a dispersant and a defoamer.

7. The coating according to claim 6, characterized in that The prefabricated slurry also includes a dispersant and a defoamer, and by weight, the prefabricated slurry includes 9-22 parts of ultrafine calcium carbonate, 45-70 parts of the second titanium dioxide, 0.45-3.3 parts of the dispersant, 0.45-3.3 parts of the defoamer, and 4.5-16.5 parts of water.

8. The method for preparing the coating according to any one of claims 1 to 7, characterized in that: The following steps are involved: The coating is prepared by mixing various raw material components.

9. The preparation method according to claim 8, characterized in that: The method for preparing the prefabricated slurry comprises the following steps: The raw material components are mixed to prepare the prefabricated slurry.

10. Use of the coating according to any one of claims 1 to 7 in the field of bridges.

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