HK1227050A1 - Primer compositions for application to sheet materials and methods of applying same - Google Patents

Description

Primer composition for application to sheet and method of applying same

Cross Reference to Related Applications

This application is a continuation-in-part of U.S. patent application serial No.13/786516 filed on 6/3/2013, which U.S. patent application serial No.13/786516 claims the benefit of U.S. provisional application serial No.61/661532 filed on 19/6/2012, both of which are incorporated herein by reference.

Technical Field

The present invention relates to a primer composition for application to a sheet material, a method of applying the primer composition to a sheet material.

Background

Sheet materials used in construction and other applications often require corrosion resistance. Such as steel and other types of metal roofing sheets, must withstand exposure to environmental conditions for extended periods of time. Galvanized steel roofing sheets are typically pretreated with a chromium-containing composition to increase corrosion resistance. Such pre-treatment may be performed on long steel strips, which are then wound into rolls for subsequent use.

Disclosure of Invention

One aspect of the present invention provides a fast-curing waterborne primer coating composition comprising water, a latex resin and corrosion inhibiting particles.

Another aspect of the invention provides a coated metal sheet comprising a metal substrate and a cured primer coating covering at least a portion of the metal substrate, wherein the cured primer coating comprises a latex resin and corrosion-inhibiting particles and is cured at a temperature of less than 350 ° F for less than 10 seconds.

Another aspect of the invention provides a method of coating a sheet metal substrate comprising applying a primer coating composition comprising water, a latex resin and corrosion inhibiting particles to the sheet and curing the primer coating composition at a temperature of less than 350 ° F for a time of less than 10 seconds.

Brief Description of Drawings

FIG. 1 is a schematic side view, in part, illustrating a method of applying a primer coating to a metal sheet in a roll mill including the use of a roll coater to apply a primer coating composition to the sheet and use in accordance with an embodiment of the present invention.

Detailed Description

FIG. 1 schematically illustrates a roll coating process for applying a primer coating composition to a sheet material in accordance with one embodiment of the present invention. In the embodiment shown, the coating operation may be carried out in a conventional rolling mill. Metal sheets such as galvanized steel, aluminum, etc. are provided in strips 5 which are fed under counter-rotating coating rolls 20 and 22 supplied with a quantity (application of) primer coating composition 24. The base sheet may be of any desired thickness, for example 0.5-3 mm. For example, in certain embodiments the galvanized steel roofing sheet may be 0.5 to 2mm thick. The uncoated strip 5 is passed under coating rollers 20 and 22 where a layer of primer coating composition 24 is deposited onto the upper surface of the sheet. After the primer coating composition 24 is deposited onto the strip 5, the coated strip 10 is passed through an oven 30 or any other known type of heating device such as an IR heat source to rapidly cure the primer coating composition. The coated sheet 10 may be formed into a roll 26 for storage and transport for use in various applications.

During the roll coating process, the primer coating composition is typically applied to sheet 5 at a wet film thickness of at least 1 micron, typically at least 1 or 5 microns. In certain embodiments, the wet film thickness of the coating material is 5 to 15 or 20 microns. In certain embodiments, the deposition rate of the coating composition may be at least 200ft/min, typically at least 300ft/min or 350 ft/min.

After application, the primer coating composition typically dries and cures quickly (with minimal VOC emissions). As used herein, the terms "fast cure" and "rapidly curable" mean that the primer coating composition is fully cured in a reduced amount of time when subjected to elevated temperatures as compared to conventional primer compositions of the art (which are typically applied to metal substrates). The curing time is typically less than 20 seconds, for example less than 10 or 5 seconds. Typical curing temperatures are below 350 ° F, for example below 300 ° F or 250 ° F. In certain embodiments, the cure time may be less than 3 or 2 seconds, or less, at a temperature of 220 ° F or 200 ° F.

The dry film thickness of the primer coating may typically be greater than 1 micron, for example greater than 2 or 3 microns. In certain embodiments, the dry film thickness of the primer coating may be 3 to 10 or 20 microns.

The primer coating composition of the present invention may be water-based. In certain embodiments, water may comprise 20 to 80 weight percent, such as 50 to 65 weight percent, of the primer coating composition. In certain embodiments, the primer coating composition comprises less than 10 wt% organic solvent, for example less than 7 or 4 wt%, based on the total weight of the composition. The resin solids content of the primer coating composition can be relatively high, such as greater than 35 or 40 weight percent, based on the total weight of the composition.

The primer coating composition may have little or no Volatile Organic Content (VOC). For example, the primer coating composition can comprise less than 1.5 wt% VOC, such as less than 1 or 0.5 wt% VOC, based on the total weight of the composition. In certain embodiments, the primer coating composition is substantially free of VOCs.

According to an embodiment of the invention, the primer coating composition comprises a latex resin. The latex resin may or may not be self-crosslinking. The latex resin typically comprises 20 to 60 weight percent, such as about 30 to about 50 weight percent, of the primer coating composition. In certain embodiments, suitable monomers for preparing the latex resin may include vinyl aromatic monomers such as styrene, cycloaliphatic monomers such as cyclohexyl methacrylate, and long chain aliphatic monomers such as 2-ethylhexyl acrylate, MMA, and/or 2-ethylhexyl methacrylate. Other types of monomers include cyclohexene, 2-ethyl-1-hexene, cyclohexanol, alpha-methylstyrene, 2-ethylhexanol, 2-ethylhexyl acetate, methyl-4-phenyl butyrate, methyl myristate and/or methyl palmitate.

In certain embodiments, the monomers used in the latex resin include vinyl aromatic compounds, such as vinyl aromatic monomers, which in certain embodiments comprise compounds having a calculated Tg of at least 100 ℃. Specific examples of vinyl aromatic compounds are styrene (whose calculated Tg is 100 ℃), alpha-methylstyrene (whose calculated Tg is 168 ℃), vinyltoluene, p-methylstyrene, ethylvinylbenzene, vinylnaphthalene, vinylxylene, alpha-methylstyrene dimer (meth) acrylate, pentafluorostyrene, and the like. In certain embodiments, styrene or another vinyl aromatic monomer may be the most predominant monomer of the resin, on a weight percent basis.

In certain embodiments, the monomers of the latex resin include cycloaliphatic (meth) acrylate monomers, such as trimethylcyclohexyl acrylate, t-butylcyclohexyl acrylate, dicyclopentadiene (meth) acrylate, trimethylcyclohexyl methacrylate (calculated Tg of 98 ℃), cyclohexyl methacrylate (calculated Tg of 83 ℃), isobornyl methacrylate (calculated Tg of 110 ℃), 2-ethylhexyl methacrylate, tetrahydrofurfuryl methacrylate, 3, 5-trimethylcyclohexyl methacrylate (calculated Tg of 125 ℃), and/or 4-t-butylcyclohexyl methacrylate, among others.

In certain embodiments, the monomers of the latex resin include alkyl (meth) acrylates, which in certain embodiments comprise compounds having a calculated Tg of at least 100 ℃. A specific example of the alkyl (meth) acrylate is C (meth) acrylate₁-C₂₄Alkyl esters, such as methyl (meth) acrylate (which has a calculated Tg of 105 ℃), propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, octadecyl (meth) acrylate and nonadecyl (meth) acrylate, and mixtures thereof. Other monomers include, for example, nitriles such as acrylonitrile and/or methacrylonitrile.

Some non-limiting examples of latex resins that can be used in the primer coating compositions of the present invention are commercially available from Nuplex, Lubrizol, Rohm and Haas, Alberdingkeley Company, Omnova and DSM Neoresins, e.g., Joncryl 1982, Carososet CR-781, Alberdingk AC 2403, Alberdingk 2360, NeocrylXK-98, and the like.

The average particle size of the latex resin may be 50nm-300nm, for example 60nm to 100 or 150 nm; glass transition temperature (T)_G) Is-20 to 100 ℃, typically 0 to 20 or 50 ℃; and an acid number of 0 to 20, typically 2 to 10.

The primer coating composition also includes at least one corrosion inhibiting material such as chromium-containing or non-chromium-containing particles. As used herein, the term "corrosion inhibiting" particles means particles that, when incorporated into the primer coating composition of the present invention, provide a salt spray corrosion resistance of at least 1000 hours and no visible corrosion sites on the surface, as measured by the ASTM B117 standard test. In certain embodiments, the corrosion-inhibiting particles may be provided in the form of a pigment or toner, which typically has an average particle size of 0.1 to 5 microns, such as 0.2 to 3 microns or 0.5 to 1.5 microns. The corrosion inhibiting particles are typically present in an amount of 1 to 30 weight percent, based on the total weight of the primer coating composition, e.g., 2 or 3 to 25 weight percent. In certain embodiments, the corrosion-inhibiting particles comprise at least 5 or 8 weight percent, or at least 10 or 12 weight percent of the primer coating composition.

According to certain embodiments of the invention, the coating is substantially free of chromium. In such embodiments, chromium is not intentionally added to the coating composition and is present only at trace levels or as an impurity. In such embodiments, examples of chromium-free corrosion-inhibiting particles include silicates such as calcium silicate, oxides, phosphosilicates (phosphorosilicates), phosphates, silicon dioxide, and the like. In certain embodiments, silica may be added to the primer coating composition in an amount of 15 to 30 weight percent, such as 20 to 25 weight percent. Some examples of silica include Lo-Vel275 silica from PPG Industries and Aerosil 200 silica from Air Products.

In certain embodiments, chromate-containing materials may be added to the primer coating composition. Examples of chromium-containing corrosion-inhibiting particles include chromates such as strontium chromate and the like. The chromium containing particles may be added in the amounts described above. In certain embodiments, the chromium-containing corrosion inhibiting particles comprise at least 3 wt.%, such as 5 to 20 wt.%, or 8 to 18 wt.%, or 10 to 15 wt.%, based on the total weight of the primer coating composition.

In addition to the latex resin and the corrosion inhibiting particles, the primer coating composition may further comprise at least one coalescent in an amount of up to 10 weight percent, such as in an amount of 2 to 3 weight percent, based on the total weight of the primer coating composition. Examples of suitable coalescing agents include butyl carbitol, which is commercially available from the Dow Chemical Company, Dowanol DPM, Dowanol DPnB, Dowanol PPh, butyl cellosolve or Dowanol DPnP. According to an embodiment of the invention, the coalescing agent forms a thin film around the latex resin particles which aids their coalescence. The improved coalescence of the latex resin particles may result in very fine particle sizes and uniform microstructures that may provide improved corrosion protection compared to other types of coatings having larger resin particle sizes. For example, according to certain embodiments of the invention, the average resin particle size may be less than 150nm, such as less than 100 or 80 nm.

In certain embodiments, the wax may be added to the primer coating composition in an amount up to 10 weight percent, such as 0.5 to 3 weight percent, based on the total weight of the coating composition. Suitable types of waxes include Ceraflour 913, Worleeadd352, Aquamat 272, Aquamat 270, Aquocer 539, and combinations thereof. For example, the wax sold under the name Aquamat 272 by BYK Chemie may be used. The type and amount of wax can be controlled to improve the scratch resistance of the coated sheet. The use of wax additives can reduce or prevent scratching during the winding and unwinding process, as well as during subsequent topcoat application and/or installation and use of the coated sheet, for example when the coated sheet is formed into a coil. In certain embodiments, the amount of wax added to the primer coating composition is limited to avoid unwanted slippage when the coated sheet is wound up, for example to prevent unwanted "nesting" of the roll due to low friction between adjacent roll layers.

Various other additives may optionally be added to the primer coating composition according to certain embodiments of the present invention. For example, suitable additives include thickeners, defoamers, surfactants, rust inhibitors, pH control agents and toners such as titanium dioxide and the like (which are commonly used in primers).

Suitable thickeners include Acrysol ASE-60, Aquatix 8421, DSX-1550 and Laponite RD. When used, such thickeners may be present in an amount of up to 7 weight percent, such as from 0.5 to 4 weight percent, based on the total weight of the primer coating composition.

Suitable defoamers include BYK-011, BYK-20, BYK-32, BYK34, and Drewplus L-419 available from Ashland in an amount of up to 2 wt%, for example, 0.1 to 0.5 wt%, based on the total weight of the primer coating composition.

Suitable surfactants include Zonyl FSP from DuPont, Surfynol104E, BYK 346, and BYK 348 from Air Products in amounts up to 2 weight percent, for example, from 0.1 to 0.5 weight percent, based on the total weight of the primer coating composition.

Suitable rust inhibitors include Halox 550, Halox Flash X-150, 330, Halox SZP-391, ammonium benzoate and sodium nitrite, typically in amounts of up to 1 weight percent, e.g., 0.4 to 0.6 weight percent, based on the total weight of the primer coating composition.

In certain embodiments, the primer coating composition is substantially free of certain metal salts such as metal phosphates, phosphocarbonates, and phosphosilicates. For example, the composition may be substantially free of zinc phosphate, calcium phosphosilicate and/or calcium rich silica.

Suitable pH control agents include any water soluble amine such as Dimethylethanolamine (DMEA), available from Avecia, typically in an amount of up to 1% by weight, such as 0.01 to 0.2% by weight, based on the total weight of the primer coating composition.

In certain embodiments, at least one colored pigment or toner may be added to the primer coating composition. The colored pigments and toners are different from reflective interference pigments and include conventional inorganic and organic pigments such as those found in conventional paints and primers. For example, different Color pigments are listed in the Dry Color Manufacturers Association (DCMA) classification. In contrast to platy and platy reflective interference pigments having relatively high aspect ratios, such colored pigments and toners typically comprise particles having a substantially equiaxed morphology, for example, an aspect ratio of about 1: 1. one suitable type of colored pigment comprises TiO in an amount of up to 35 wt.%, e.g., 1-25 wt.%₂Based on the total weight of the primer coating composition. Aqueous white toner commercially available from PPG Industries and corosperse 176E chromium toner commercially available from Wayne Pigments are examples of suitable toners.

In certain embodiments, electrically conductive particles, such as grapheme carbon particles, may be added to the primer coating composition in an amount of up to 5 weight percent or greater, such as from 1 to 2 weight percent, based on the total weight of the primer coating composition. Such grapheme carbon particles may provide improved thermal emissivity properties. The grapheme carbon particles may be obtained from commercial sources or may be manufactured according to the methods and apparatus described in U.S. application serial nos. 13/249315 and 13/309894, which are incorporated herein by reference.

The following examples illustrate various aspects of the present invention, but are not intended to limit the scope of the invention.

Examples

A primer coating composition containing chromium or non-chromium corrosion inhibiting particles was prepared as described in table 1 below. Sample No.1 contains a chromium toner, while sample No.2 is chromium-free.

TABLE 1

Primer coating composition

The components listed in table 1 were added together in the order described, with gentle stirring. The primer coating composition was allowed to equilibrate overnight prior to panel preparation. The following day the viscosity and pH were checked. The primer coating composition was applied to three different types of substrates using a wire draw down bar. The three types of substrates are hot dip galvanized steel, aluminum and steel, and are coated with zinc and aluminum, which are commercially available under the designation Galvalume. The coated panel was placed in a conveyor oven set at a temperature of 260 ℃ and a linear velocity sufficient to obtain a peak metal temperature of 190 ° F within a two second residence time. Some of the primer-coated panels were then coated with three different types of topcoats: a high bake waterborne topcoat, commercially available from PPG under the name Environ; a solventborne polyester-based topcoat commercially available from PPG under the name Truform; and a water-borne topcoat commercially available from PPG under the name Environ MCL. Control panels comprising conventional chrome-containing and chrome-free primers were also made by applying either a chrome urethane primer from PPG, or a non-chrome urethane primer from PPG. The conventional polyurethane primer is applied by a similar method as described above except that a longer cure time of at least 30 seconds at a higher peak metal temperature of 450 ° F is required to fully cure the polyurethane primer. The coated panels were tested and the results are shown in the table below.

TABLE 2

Primer only

TABLE 3

Primer and water-based high baking system Environ top coat

TABLE 4

Primer and Truform solvent polyester topcoat

TABLE 5

Primer and low baking aqueous Solar White topcoat

In the preceding tables, the T-bend test was performed according to the standard ASTM D4145 test; the reverse (Rev) impact test was performed according to ASTM D2794, the X-score adhesion test was performed according to ASTM D3359, and the MEK damage (Mar) test was performed according to ASTM D5402. The pencil hardness test was performed according to ASTM D3363, where a pencil was held firmly against the primer coating at a 45 degree angle and pushed away from the operator with a 0.25 inch stroke (stroke). Sufficient pressure is applied downward and forward to cut or scrape the film. This process was repeated along the hardness scale until a pencil was found to not cut through the film to the substrate. The hardness scale is: 6B (very soft) to 6H (very hard).

TABLE 6

Corrosion test results

TABLE 7

TABLE 8

The panels were placed in a 95F/5% NaCl solution chamber (cabin) for 1216 hours with taped (taped) trimmings according to the ASTM B117 salt spray test listed in the previous table. The panel was then removed from the chamber and the face of the panel was visually evaluated for any red or white rust, black spots and bubble defects.

For purposes of this detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of "or" means "and/or" unless explicitly stated otherwise, even though "and/or" may be explicitly used in certain instances.

Those skilled in the art will readily appreciate that changes may be made to the invention without departing from the concepts disclosed in the foregoing description. Such variations are to be considered as included in the following claims unless the claims, by their language, expressly state otherwise. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims (22)

1. A fast-curable waterborne primer coating composition comprising:

water;

a latex resin; and

corrosion inhibiting particles.

2. The rapidly curable waterborne primer coating composition of claim 1, wherein the composition is capable of curing at a temperature of less than 350 ° F in less than 10 seconds.

3. The rapidly curable waterborne primer coating composition of claim 1, wherein the corrosion-inhibiting particles comprise chromium and the corrosion-inhibiting particles are present in an amount of at least 3 weight percent based on the total weight of the coating composition.

4. The rapidly curable waterborne primer coating composition of claim 3, wherein the corrosion inhibiting particles comprise strontium chromate.

5. The rapidly curable waterborne primer coating composition of claim 1, wherein the corrosion-inhibiting particles are substantially free of chromium and the corrosion-inhibiting particles are present in an amount of at least 5 weight percent based on the total weight of the coating composition.

6. The rapidly curable waterborne primer coating composition of claim 5, wherein the corrosion inhibiting particles comprise a silicate, an oxide, a phosphate, a phosphosilicate, or a silica.

7. The rapidly curable waterborne primer coating composition of claim 1, wherein the corrosion inhibiting particles comprise silica and the corrosion inhibiting particles are present in an amount of at least 10 percent by weight based on the total weight of the coating composition.

8. The rapidly curable waterborne primer coating composition of claim 1, wherein the latex resin is self-crosslinking and is prepared from at least one vinyl aromatic monomer.

9. The rapidly curable waterborne primer coating composition of claim 1, wherein the primer coating composition has a volatile organic content of less than 1.5 weight percent, based on the total weight of the composition.

10. The rapidly curable waterborne primer coating composition of claim 1, further comprising a coalescent, a wax, a viscosity enhancer, a thickener, a colored pigment, and/or a colored toner.

11. A coated metal sheet comprising:

a metal substrate; and

a cured primer coating covering at least a portion of the metal substrate, wherein the cured primer coating comprises a latex resin and corrosion-inhibiting particles and is cured at a temperature of less than 350 ° F for less than 10 seconds.

12. The coated metal sheet of claim 11, wherein the corrosion-inhibiting particles comprise strontium chromate and/or silica.

13. The coated metal sheet of claim 11, wherein the cured primer coating has a dry film thickness of at least 1 micron.

14. The coated metal sheet of claim 11, wherein the metal is in the form of a coil.

15. A method of coating a sheet metal substrate comprising:

applying a primer coating composition comprising water, a latex resin, and corrosion-inhibiting particles to the sheet; and

the primer coating composition is cured at a temperature of less than 350 ° F for a time of less than 10 seconds.

16. The method of claim 15, wherein the primer coating composition is applied at a wet film thickness of at least 1 micron.

17. The method of claim 15, wherein the primer coating composition has a volatile organic content of less than 1.5 wt.%.

18. The method of claim 15, wherein the primer coating composition is applied by roll coating.

19. The method of claim 18, wherein the primer coating composition is applied at a rate of at least 200 ft/min.

20. The method of claim 15, wherein the primer is cured by passing the sheet and applied primer coating composition through an oven at a temperature of less than 250 ° F for a time of less than 5 seconds.

21. The method of claim 15, further comprising applying a top coat over at least a portion of the primer coat.

22. The method of claim 15, further comprising forming the coated metal sheet into a coil.