Field of the Invention'

This invention relates to cellulosic lacquers comprising polymers containing vinyl ester monomers, and methods for reducing the emission of volatile organic compounds during the application of lacquers to substrates.

Ttørk iiTid of the Invention

Lacquers are a well known type of air drying coating composition comprising film forming polymer and solvent that is usually organic. Often the film forming polymer is a cellulosic resin, such as nitrocellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, ethyl cellulose, or ethylhydroxy ethyl cellulose. Nitrocellulose is one of the most commonly used cellulosic resins in lacquers. A variety of organic solvents are used in lacquers, including active solvents, which dissolve the film forming polymer, and latent solvents, which are unsatisfactory solvents when used alone but become satisfactory solvents when used in combination with an active solvent. In water-borne lacquers, water is used alone or in combination with such organic solvents. Lacquers may contain a variety of other ingredients, including modifying polymers, such as alkyd resins, acrylics, vinyl chloride/vinyl acetate copolymers and ethylene/vinyl acetate copolymers, and diluents, pigments, ^" plasticizers, sanding aids, flattening agents and silicones.

Lacquer films dry primarily by solvent evaporation rather than oxidation or polymerization reactions. Lacquers are therefore advantageous because they frequently dry more quickly than other types of coating compositions and usually do not require baking to form a hard coating. Lacquers containing cellulosic resins with organic solvents are among the fastest drying coating compositions;

consequently they are often preferred for coating wood products, such as furniture, and for automotive repair coatings. However, lacquers sometimes form relatively soft coatings when dry. This may be a disadvantage if the coating is soft enough to be "easily marred or deformed.

Because lacquers usually rely on organic solvents as viscosity reducers to enable easy application to substrates, as the lacquers dry, harmful volatile organic compounds ("VOC") are released into the surrounding atmosphere. Often, conventional lacquers have solids contents only on the order of 10 to 25 weight percent. Due to environmental concerns, it is therefore desirable to increase the solids level and reduce the solvent level in lacquers. Indeed, much emphasis has recently been placed on reducing organic solvents and other sources of volatile organic compounds in all types of coating compositions.

In water-borne lacquers, water is used to achieve low application viscosity in addition to or instead of organic solvents, which helps reduce the amount of volatile organic compounds present in these lacquers. However, when water-borne lacquers are spray coated onto substrates, often an insufficient amount of water evaporates from the spray so the deposited lacquer does not achieve a sufficiently high viscosity for proper film formation. Water has a relatively low evaporation rate when compared to fast evaporating organic solvents, so it has less tendency to evaporate in the spray. Therefore, water-borne lacquers persistently run and sag when applied to substrates because the water content is too high.

Another difficult problem encountered with water-borne lacquers is that line speeds on water-borne lacquer spray lines are often significantly slower than those of organic solvent-borne lacquers, again because water evaporates more slowly from the lacquer than comparable organic solvents. ____.

We have discovered that both organic solvent-borne and water- borne lacquers containing cellulosic resins such as nitrocellulose

may advantageously be formulated at the viscosities necessary for maintaining good fluidity and ease of application with reduced amounts of organic solvent and/or water. This is accomplished by replacing at least a portion of the cellulosic resin conventionally used in such lacquers with at least one polymer containing at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-0-C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons. Using less organic solvent in organic solvent-borne lacquers reduces the amount of harmful volatile organic compounds released from the lacquer during application and drying. Similarly, using less water in water-borne lacquers increases the level of solids in such lacquers, reducing the amount of water that must be evaporated during application of the lacquers to achieve proper film formation and reduced drying time. Moreover, in lacquers containing both organic solvent and water, substitution of at least a portion of the cellulosic resin therein with at least one polymer containing at least one vinyl ester monomer according to the invention advantageously reduces the amounts of organic solvent and water needed in such lacquers.

U.S. Patent No. 5,011,874 to Hoppe, et al., relates to certain lacquers containing cellulose ester/acrylate polymer combinations. These polymer combinations are made by aqueous emulsion polymerization of a cellulose ester with a monomer of the formula atom or a methyl group and R^ denotes a hydrogen atom, an alkyl radical with 1-20 carbons, a cycloalkyl radical with 5 or 6 carbons, -(CH2-CH2-0) _n -R3

(where 3 is H, CH3, or C2H5 and n = 2-50), -C6H5, or -CH ₂ C6H .

Polymer particles essentially 0.1 to 10 microns in size are formed, dried and then added to a solvent. Other monomers, including vinyl esters such as vinyl acetate, vinyl propionate, and vinyl butyrate, may be incorporated into the polymer particles. There is no teaching or suggestion in the Hoppe et al. patent of viscosity reduction ^' or

increasing solids levels in lacquers using polymers containing certain vinyl ester monomers.

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The present invention is directed to a lacquer having a reduced volatile organic compounds content, comprising (i) an organic solvent, (ii) a cellulosic resin, and (iii) a polymer containing at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-0-C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons.

The present invention is also directed to a water-borne lacquer having reduced water content, comprising (i) water, (ii) a cellulosic resin, and (iii) a polymer containing at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-

0-C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons.

The present invention further provides a method of reducing the amount of volatile organic compounds at a given viscosity in a lacquer containing a cellulosic resin and an organic solvent, comprising substituting at least a portion of the cellulosic resin with at least one polymer containing at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-0-

C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons.

The present invention also is directed to a method of increasing the solids content at a given viscosity of a water-borne lacquer containing a cellulosic resin and water, comprising substituting at least a portion of the cellulosic resin with at least one polymer containing at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-0-C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons.

Finally, the present invention also provides a process for applying a lacquer to a substrate with reduced emission of volatile organic compounds, which comprises:

(1) forming in a closed system a liquid mixture comprising:

(a) a lacquer comprising (i) an organic solvent, (ii) a cellulosic resin, and (iii) a polymer containing at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-0-C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons; and

(b) at least one compressed fluid in at least an amount which when added to the lacquer is sufficient to render the viscosity of the liquid mixture suitable for spraying, wherein the compressed fluid is a gas at standard conditions of 0° C and one atmosphere (STP); and

(2) spraying the liquid mixture onto a substrate to form a coating thereon by passing the liquid mixture under pressure through an orifice to form a spray.

Detailed Description of the Invention

The lacquers of the present invention represent an improvement over known lacquers that contain cellulosic resin. By substituting at least one polymer containing at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-O-C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons, for at least a portion of a cellulosic resin in a lacquer containing the cellulosic resin and an organic solvent or water, at a given viscosity, the amount of solids on a weight percent basis in the lacquer is increased. When the lacquer contains organic solvent, the amount of volatile organic compounds in the lacquer is reduced. This, in turn, reduces emissions of volatile

organic compounds to the atmosphere during application of the lacquer to a substrate.

As is well known to those skilled in the art of lacquers, the various polymers in a lacquer should be compatible with each other and mutually soluble or dispersible in the solvent. That is, gross phase separation should not occur in the lacquer. Lacquers that excessively phase separate, particularly at the time of application to a substrate, might not dry evenly if the various phases do not dry at the same rate. Furthermore, when such phases have different compositions, coating performance can be unacceptable. Lacquers that are substantially homogeneous at the time of application to a substrate are therefore preferred. Accordingly, the cellulosic resin, the polymer containing at least one vinyl ester monomer, and any other modifying polymers present in the lacquer, for example alkyd resins, should be compatible and able to form a substantially homogenous composition in the organic solvent or water.

The cellulosic resin used in the present invention may be any one of those known in the art of lacquers, such as nitrocellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, ethyl cellulose, and ethylhydroxy ethyl cellulose, but is not limited to these cellulosic resins.

The preferred cellulosic resin is nitrocellulose. Any type of nitrocellulose commonly used in lacquers may be employed. Nitrocellulose is made commercially by treating cellulose with mixtures of nitric and εulfuric acids. Typically, the resulting nitrocellulose has a nitrogen content on the order of about 10.5 to about 12.2 percent by weight. Lower nitrogen content nitrocellulose (about 10.7-11.2 percent by weight nitrogen) is more soluble in alcohols, while higher nitrogen content nitrocellulose (about 11.7-12.2 percent) is soluble in esters.

The amount of cellulosic resin in the lacquer is not critical. Generally, the amount of cellulosic resin in the lacquer is less than about 90 percent, preferably less than about 75 percent, more

preferably less than about 60 percent, and most preferably less than about 40 percent, by weight of the total solids in the lacquer. The total solids in the lacquer is all of the nonvolatile components remaining after the organic and/or aqueous solvents evaporate, including the cellulosic resin, the polymer containing at least one vinyl ester monomer, and any other nonvolatile modifying polymers, plasticizers, pigments, or additives. Generally, the amount of cellulosic resin in the lacquer is greater than about 5 percent, preferably greater than about 10 percent, more preferably greater than about 15 percent, and most preferably greater than about 20 percent, by weight of the total solids in the lacquer.

Organic solvent, or water, or both may be used in the lacquer. Useful organic solvents may be selected from any of those conventionally used in formulating lacquers. One organic solvent or a mixture of organic solvents may be used. The total amount of organic solvent and/or water in the lacquer is not critical and is determined by the requirements of each application and method of application. Desirably, the amount of organic solvent and/or water used is less than that which is used conventionally. Generally, the total amount of organic solvent and water in the lacquer is less than about 80 percent, preferably less than about 70 percent, and more preferably less than about 60 percent, by weight of the lacquer. Generally, the total amount of organic solvent and water in the lacquer is greater than about 10 percent, preferably greater than about 20 percent, by weight of the lacquer. A minimal amount of organic solvent or water is desirably used to provide proper application viscosity and film formation characteristics. A blend of organic solvents and water may be used having a range of relative evaporation rates that provide the proper flow properties for application and film formation, as is known to those skilled in the art.

In the case of an organic solvent, at least one active organic solvent and optionally one or more latent organic solvents are used.

Active organic solvents useful in the invention include, for example, ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone, methyl amyl ketone, and the like; esters such as butyl acetate, ethyl acetate, and ethylene glycol monoethyl ether aoetate, and the like; and glycol ethers such as monomethyl ethers of ethylene glycol, monoethyl ethers of ethylene glycol, and monobutyl ethers of ethylene glycol, and the like. Preferably, the lacquer comprises an active organic solvent selected from the group consisting of methyl amyl ketone, methyl ethyl ketone, methyl isobutyl ketone, n-butyl acetate, methyl acetate, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, and mixtures thereof.

Suitable latent organic solvents include, for example, alcohols such as ethanol, isopropanol, sec-butanol, n-butanol, isobutanol, and mixtures thereof.

The lacquer may optionally contain one or more diluents, which have little or no solvating power for the polymers in the lacquer but are employed as viscosity reducers because they are inexpensive compared to active and latent organic solvents. Useful diluents include, for example, aliphatic and aromatic hydrocarbons, such as toluene, xylene, and petroleum naphthas, and the like. Preferably, when diluents are employed with active and latent organic solvents, such diluents evaporate faster than the active and latent organic solvents, so that after the lacquer is applied to a substrate, the active and latent organic solvents will preferentially remain in the lacquer throughout the drying process to aid film formation and to give a smooth coating. The amount of diluent in the lacquer generally ranges from about 0 to about 30 percent by weight of the lacquer, preferably less than about 20 percent by weight of the lacquer.

The polymer used to replace at least a portion of the cellulosic resin contains at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-0-C(=:0)-R, wherein R

is a saturated alkyl group or an aromatic group having 4 to 9 carbons. When R is a saturated alkyl group, such saturated alkyl group preferably has a branched structure. One polymer containing at least one vinyl ester monomer may be used in the lacquer, or two or more different polymers containing at least one vinyl ester monomer may be used in the lacquer. The polymer may be a homopolymer of a vinyl ester of a carboxylic acid having the above formula, or the polymer may be a copolymer each containing at least one vinyl ester monomer that is vinyl ester of a carboxylic acid having the above formula and optionally one or more second monomers.

Examples of useful vinyl ester monomers include vinyl pivalate, vinyl neononanoate, vinyl neohexanoate, vinyl benzoate and vinyl cyclohexanoate. Preferably, the vinyl ester monomer is vinyl pivalate. One (for example when the polymer containing at least one vinyl ester monomer is a homopolymer) or more than one (for example when the polymer containing at least one vinyl ester monomer is a copolymer) vinyl ester monomer may be used.

When the polymer containing at least one vinyl ester monomer is a homopolymer, such homopolymer is preferably selected from poly( vinyl pivalate), poly( vinyl neononanoate), poly( vinyl neohexanoate), poly(vinyl benzoate) or poly(vinyl cyclohexanoate); that is, a polymer made entirely from vinyl pivalate monomer, vinyl neononanoate monomer, vinyl neohexanoate monomer, vinyl benzoate monomer, or vinyl cylcohexanoate monomer. Preferably, such homopolymer is poly( vinyl pivalate). Mixtures of hompolymers may also be used.

When the polymer containing at least one vinyl ester monomer is a copolymer, such copolymer contains at least one vinyl ester monomer that is a vinyl ester of a carboxylic acid having the formula CH2=CH-0-C(=0)-R, wherein R is a saturated alkyl group or an aromatic group having 4 to 9 carbons and optionally a second monomer. Examples of useful second monomers include vinyl acetate, vinyl propionate, vinyl chloride, acrylate esters such as butyl

acrylate, 2-ethylhexyl acrylate and the like, methacrylate esters such as butyl methacrylate, vinyl neodecanoate, vinyl 2-ethylhexanoate, acrylic acid, methacrylic acid, crotonic acid, acrylamide, methacrylamide, acrolein, N,N-dimethylami noethyl methacrylate, isobornyl acrylate, isobornyl methacrylate and mixtures thereof.

In one embodiment of the invention, the second monomer contains at least one polar functionality. Copolymers containing second monomers having at least one polar functionality are particularly compatible with nonoxidizing alkyd resins, which are often used as modifying polymers in cellulosic lacquers. Such polar functionalities include, for example, hydroxyl, carboxyl, amino, amide, cyano, and chloro. Examples of second monomers having polar functionality include vinyl chloride, acrylate esters such as 2- hydroxyethyl acrylate, methacrylate esters such as 2-hydroxyethyl methacrylate, acrylic acid, methacrylic acid, crotonic acid, acrylamide, methacrylamide, acrolein and N,N- diemethylaminoethyl methacrylate.

Copolymers used as the polymer containing at least one vinyl ester monomer generally contain at least about 20, preferably at least about 30, more preferably at least about 40, and most preferably at least about 50, percent by weight of the vinyl ester monomer, based on the total weight of the copolymer.

A particularly preferred copolymer is a vinyl pivalate/vinyl acetate copolymer containing from about 30 to about 75 percent, more preferably from about 35 to about 65 percent, still more preferably from about 40 to about 60 percent, and most preferably about 50 percent, by weight vinyl pivalate monomer, the balance being vinyl acetate monomer.

Generally, the amount of polymer containing at least one vinyl ester monomer in the lacquer depends on the nature of the polymer and its compatibility with the other ingredients of the lacquer. However, in general, the amount of polymer in the lacquer is less than about 95 percent, preferably less than about 90 percent, more

preferably less than about 85. percent, still more preferably less than about 80 percent, and most preferably less than about 75 percent, by weight of the combined weight of the cellulosic resin and the polymer containing at least one vinyl ester monomer, generally, the amount of polymer containing at least one vinyl ester monomer in the lacquer is greater than about 5 percent, preferably greater than about 10 percent, more preferably greater than about 20 percent, still more preferably greater than about 25 percent, and most preferably greater than about 30 percent, by weight of the combined weight of the cellulosic resin and the polymer containing at least one vinyl ester monomer.

In another preferred embodiment of the invention, the polymer containing at least one vinyl ester monomer and the vinyl ester momoner itself have glass transition temperatures that enable the lacquer to form a sufficiently hard coating when dried at normal ambient temperatures , i.e., about 20 to about 40 °C. Specifically, the polymer containing at least one vinyl ester monomer has a glass transition temperature which is sufficiently high such that the lacquer forms a solid film at temperatures in the range of about 20 to about 40° C. Preferably the glass transition temperature of the polymer containing at least one vinyl ester monomer is greater than about 40° C, more preferably greater than about 45° C, and most preferably greater than about 50° C. In addition, preferably, the vinyl ester monomer itself has a glass transition temperature greater than about 50°C (when measured as a homopolymer). For purposes of the above, the glass transition temperature is that obtained in the limit of high molecular weight, since the glass transition temperature of a polymer generally varies with molecular weight, with low molecular weights giving lower glass transition temperatures.

Poly( vinyl pivalate) has a glass transition temperature in the range of about 70° to about 86° C and poly( vinyl neononanoate) has a glass transition temperature of about 60° C, in the limit of high molecular weight, making these homopolymers preferred for use as

the polymer containing at least one vinyl ester monomer from the standpoint of glass transition temperature characteristics. Lacquers containing these and like polymers form solid coatings having good hardness at normal ambient temperatures, but still have a sufficiently low application viscosity at higher solids levels.

The polymer containing at least one vinyl ester monomer may be made using any conventional polymerization method, such as solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization. Generally, the polymer is made separately from the rest of the lacquer ingredients, and added thereto as a finished polymer. For example, the vinyl ester monomer(s) and any second monomers may be added along with a polymerization catalyst to a solvent and heated to a temperature generally in the range of about 40° C to about 140° C at standard atmospheric pressure to conduct polymerization. Suitable solvents for conducting the polymerization include, for example, acetates such as n-butyl acetate and n-butyl propionate, ketones such as methyl ethyl ketone and methyl amyl ketone, mineral spirits, xylene and the like. Suitable polymerization catalysts include, for example, azo compounds such as azo-bis-isobutyronitrile, peroxy esters such as t-butyl peroxy-2-ethyl hexanoate, hydroperoxides such as t-butyl hydroperoxide, peroxides such as di-t-butyl peroxide, and the like.

According to the invention, the amount of volatile organic compounds at a given viscosity in a lacquer containing a cellulosic resin and an organic solvent is reduced by substituting at least a portion of the cellulosic resin with the polymer containing at least one vinyl ester monomer. Similarly, according to the invention, the amount of solids at a given viscosity in a water-borne lacquer containing a cellulosic resin and water is increased and the amount of water (and organic solvent, if present) is reduced by substituting at least a portion of the cellulosic resin with the polymer containing at least one vinyl ester monomer. Preferably, at least about 10 percent by weight of the cellulosic resin is replaced with the polymer

containing at least one vinyl ester monomer. More preferably, at least about 15 percent by weight of the cellulosic resin is replaced with at least one polymer containing at least one vinyl ester monomer.

When the polymer containing at least one vinyl ester monomer is substituted into the lacquer for at least a portion of the cellulosic resin at a constant organic solvent concentration, the viscosity of the lacquer decreases. This viscosity decrease is preferably greater than about 30 percent, more preferably greater than about 50 percent, and most preferably greater than about 70 percent. Accordingly, at a given viscosity, the lacquer requires less organic solvent when the polymer containing at least one vinyl ester monomer is present therein. By replacing at least a portion of the cellulosic resin with the polymer containing at least one vinyl ester monomer according to the present invention, the amount of volatile organic compounds in the lacquer is reduced by at least about 5 percent, preferably at least about 10 percent.

The lacquer may contain a variety of optional additives known in the art, including modifying polymers, plasticizers, pigments, sanding aids such as zinc stearate, flattening agents, and flow improving agents such as silicones, provided the additives are compatible with the other ingredients in the lacquer, and do not interfere with the ability of the polymer containing at least one vinyl ester monomer to reduce the viscosity and increase the solids in the lacquer.

One or more modifying polymers may be included in the lacquer to improve its gloss and adhesion. Suitable modifying polymers include, for example, nonoxidizing alkyd resins, ester gum and maleic modified ester gum, toluene sulfonamide formaldehyde polymers, dewaxed damar, vinyl chloride/vinyl acetate copolymers such as Bakelite® VYNC commercially available from Union Carbide Corporation, acrylic polymers, cyclic ketone polymers, sugar-based polymers, and εtyrene-maleic anhydride polymers.

In a preferred embodiment of the invention, the lacquer contains at least one nonoxidizing alkyd resin in addition to a cellulose resin, a polymer containing at least one vinyl ester monomer, and an organic solvent. Suitable nυnoxidizing alkyd resins include, for example, Beckosol® CO9195-02, a short coconut oil alkyd resin commercially available in solution form from Reichhold Chemicals, Inc. and tall oil, fatty acid-based, short oil alkyd resins, such as 57-5735 commercially available from Cargill Chemical Products.

One or more solvent or non-solvent plasticizers may be included in the lacquer to increase its flexibility. Solvent plasticizers also function as solvents for many types of modifying polymers. Suitable solvent plasticizers include, for example, dibutyl phthalate, dioctyl phthalate, n-butyl benzyl phthalate, tricresyl phosphate and triphenyl phosphate. Non-solvent plasticizers include processed vegetable oils, such as castor oil and soybean oil.

Any of the pigments conventionally used in lacquers may be employed in the present invention. Alkaline pigments are generally not preferred for use in nitrocellulose-containing lacquers because they may react with the nitrocellulose during storage, releasing nitrogen oxide vapors. Some metallic pigments, such as bronze-based pigments, may cause gelation in nitrocellulose lacquers.

The lacquer may be applied to a wide variety of substrates, such as wood, printed board, flake board, plastics, metal, cellophane films, paper, foils, and the like.

The lacquers may be applied to substrates by any of the methods used to apply conventional lacquers, such as by spray coating, brush coating, roll coating, dip coating, flow coating, and the like, which are known by those skilled in the art.

The lacquer is particularly suitable for spray coating onto substrates. Suitable methods of spray coating include air spray methods, high-volume low-pressure CΗVLP") spray methods,

airless spray methods, air-assisted airless spray methods, rotary atomizers, electrostatic spray methods, and the like. Lacquers applied by conventional spray coating methods typically contain a relatively high proportion of fast evaporating solvents to provide the low viscosity required for proper atomization. The fast evaporating solvents are designed to evaporate in the spray so that the lacquer is deposited at much higher viscosity, to avoid runs and sags. A relatively low proportion of slow and medium evaporating solvents, which evaporate much less in the spray, are used to provide the proper flow characteristics for droplet coalescence and film formation on the substrate. With the present lacquer, the low atomization viscosities required for spray coating can be obtained by using reduced amounts of solvent, thereby reducing solvent emissions during application.

Air sprays, HVLP sprays, and air-assisted airless sprays typically use lacquers with a viscosity at a temperature of about 25° C that is in the range of from about 30 centipoise to about 150 centipoise, preferably from about 50 to about 100 centipoise, in order to achieve the fine atomization required to obtain high quality coatings.

Airless sprays typically use a wider range of lacquer viscosity, with the viscosity used depending upon the quality requirement of the application. Generally, airless sprays give poorer atomization and a poorer fan pattern than the air spray methods. Lower quality coatings can be applied using a higher viscosity lacquer. Airless sprays typically use lacquers with a viscosity at a temperature of about 25° C that is below about 500 centipoise, preferably below about 300 centipoise, more preferably below about 150 centipoise, and most preferably belqw about 100 centipoise. Typically the viscosity is above about 30 centipoise, preferably above about 50 centipoise.

Airless sprays are formed by passing the lacquer under pressure through an orifice to form a spray. A high pressure drop across the orifice is used to propel the lacquer through the orifice at high velocity. A high velocity liquid film emerges from the orifice

that becomes unstable from shear with the surrounding air and therefore breaks up into droplets. Higher viscosity typically gives poorer atomization for a given spray pressure, so usually a higher spray pressure must be used. Spray pressures typically range from about 300 to about 5000 pounds per square inch (psi), preferably from about 500 to about 4000 psi, and more preferably from about 700 to about 3000 psi. The orifice sizes generally range from about .004-inch to about .072-inch equivalent diameter. The orifice size is selected to give the desired lacquer application rate and proper atomization. Turbulence promoters such as pre-orifices are preferably used to aid atomization.

A preferred method for airless spraying of the lacquer is to heat the lacquer to obtain the viscosity suitable for spraying. Heating the lacquer reduces the viscosity and therefore further reduces the amount of solvent required for spraying. The maximum temperature to which the lacquer may be heated for spraying is generally determined by the thermal stability of the components in the lacquer. The heated spray temperature is generally less than about 150° C, preferably less than about 100° C, still more preferably less than about 80° C, and most preferably less than about 65° C. The heated spray temperature is generally above 30° C, preferably above 40° C, and most preferably above about 45° C. Heated airless sprays can use lacquers that have a higher viscosity than those used with no heating. Typically the viscosity at a temperature of about 25° C is in the range of from about 200 to about 1000 centipoise, preferably from about 300 to about 900 centipoise, and most preferably from about 400 to 800 centipoise. The viscosity of the heated lacquer is preferably reduced to below about 200 centipoise, more preferably to below about 150 centipoise, and most preferably to below about 100 centipoise.

A particularly preferred airless spray process for applying the lacquer to a substrate with further reduced emission of volatile organic compounds is by utilizing a compressed fluid that is a gas at standard conditions of 0° C and one atmosphere absolute pressure

(STP) such as carbon dioxide, as a viscosity reducing diluent for the lacquer. This allows the lacquer already having low solvent content to be sprayed at even lower solvent levels without increasing the viscosity. Accordingly, solvent emissions can be reduced to even lower levels than that achieved by replacement ^' of at least a portion of the cellulosic resin with the polymer containing at least one vinyl monomer.

Typically, the solvent content of the lacquer when spray coated using a compressed fluid is lowered such that the lacquer has a viscosity of about 500 to about 5000 centipoise, preferably from about 700 to about 3000 centipoise, and more preferably from about 800 to about 2500 centipoise, although higher and lower viscosities may also be used.

According to this spray coating process, a liquid mixture is formed by combining in a closed system the lacquer with at least one compressed fluid in at least an amount which when added to the lacquer is sufficient to render the viscosity of the liquid mixture suitable for spraying. Preferably, the viscosity of the liquid mixture is less than about 200 centipoise, more preferably less than about 100 centipoise, and most preferably less than about 50 centipoise. The liquid mixture is sprayed onto a substrate to form a coating thereon by passing the liquid mixture under pressure through an orifice to form a spray.

As used herein, "compressed fluid" is a fluid in the gaseous state, the liquid state, or a combination thereof, or is a supercritical fluid, depending upon (i) the particular temperature and pressure to which it is subjected, (ii) the vapor pressure of the fluid at that particular temperature, and (iii) the critical temperature and critical pressure of the fluid, but which is in its gaseous state at standard conditions of 0° C temperature and one atmosphere absolute pressure (STP). As used herein, a "supercritical fluid" is a fluid at a temperature and pressure such that it is at, above, or slightly below its critical point.

Compounds that may be used as compressed fluids include but are not limited to carbon dioxide, nitrous oxide, xenon, ethane, ethylene, propane, propylene, and mixtures thereof. Preferably, the compressed fluid has appreciable solubility in»the cellulosic resin and the polymer containing at least one "vinyl όster monomer, is inert, and is environmentally compatible. Preferred compressed fluids are carbon dioxide and ethane. Carbon dioxide is the most preferred compressed fluid. The compressed fluid should be used in the liquid mixture generally in an amount of at least about 10 percent, preferably greater than about 15 percent, more preferably greater than about 20 percent, and most preferably greater than about 25 percent, based on the total weight of the liquid mixture, in order to give sufficient viscosity reduction. The compressed fluid is generally used in an amount less than about 60 percent, preferably less than about 50 percent, by weight of the liquid mixture. The compressed fluid is preferably used in an amount that is below the solubility limit in the lacquer at the spray temperature and pressure used, to avoid formation of a liquid compressed fluid phase that can extract solvent from a lacquer phase and thereby increase the spray viscosity, which can give poorer atomization, and the deposition viscosity, which can give poorer film formation. Viscosity reduction is greatest at the solubility limit.

Methods and apparatus for spray coating using compressed fluids at temperatures and pressures at which the compressed fluid is a supercritical fluid are described in the following U.S. Patents: No. 4,923,720 to Lee, et al.; No. 5,009,367 to Nielsen; No. 5,057,342, No. 5,106,650; and No. 5,108,799 to Hoy, et al.; and No. 5,171,613 to Bok, et al., the disclosures of which are incorporated herein by reference. As disclosed in these patents, compressed fluids such as carbon dioxide are not only effective viscosity reducers, they can produce a new airless spray atomization mechanism called a decompressive spray. Decompressive sprays can have finer droplet size than conventional airless sprays and a feathered spray pattern needed to

apply high quality coatings. A decompressive spray is formed by rapid expansion of the compressed fluid as a gas as it is released from solution in the liquid mixture during depressurization in the spray orifice. Decompressive sprays typically have a rounded, parabolic-shaped spray fan instead of the sharp angular fans typical of conventional airless sprays. The spray also typically has a much wider fan width than conventional airless sprays produced by the same spray tip. Furthermore, no liquid film is visible as the spray emerges from the spray tip. As used herein, "decompressive spray" is understood to mean to a spray, spray fan, or spray pattern that has the preceding characteristics. Preferably, the amount of compressed fluid in the liquid mixture is sufficiently high to produce a decompressive spray of the lacquer.

The liquid mixture of lacquer and compressed fluid may be prepared for spraying by any of the spray apparatus disclosed in the aforementioned patents or other apparatus. Such apparatus may also be a UNICARB® System Supply Unit and spray guns manufactured by Nordson Corporation to proportion, mix, heat, and pressurize coating compositions with compressed fluids such as carbon dioxide for spray application.

The following examples further illustrate the invention. In these examples, the following terms are understood to have the following meanings:

Solution Compatibility - Homogeneity of a lacquer as measured by visual inspection for phase separation in a glass container.

Clarity - Translucency of a dry coating made from a lacquer as measured by visual inspection of the dry coating for haze or cloudiness.

Repairabilitv - Ability to repair marks made on a dry coating made from a lacquer, as measured by scratching the coating with the end of a hard object, such as a paper clip, then lightly rubbing the scratched area of the dry coating with a cloth saturated with methyl

amyl ketone, thereby disolving the coating material around the scratch, and observing whether the scratch disappears when the area dries.

Pencil Hardness ~ Hardness of a dry coating made from a lacquer as measured by ASTM D3363.

60° Gloss -- Gloss of a dry coating made from a lacquer as measured using a Pacific Scientific Glossgard® II glossmeter at a 60 angle from the surface of the coating.

Spotting Test ⁽ Water ⁾ - Water resistance of a dry coating made from a lacquer as measured by placing a large drop of water on the coating, covering it with a watch glass, and observing after three days whether a spot remains on the coating when the water is removed from the coating with a paper towel.

S ^p ottin ^g Test ⁽ Ethan ol ⁾ - Resistance of a dry coating made from a lacquer to an ethanol/water solution, performed in the same manner as the Spotting Test (water), except using a drop of a 50 weight percent solution of ethanol in water for six hours on the coating.

Alkvd 1 - A nonoxidizing, short coconut oil alkyd resin, commercially available in solution form as Beckosol® CO9195-02 from Reichhold Chemicals, Inc.

Alkvd 2 - A tall oil, fatty acid-based, short oil alkyd resin, commercially available as 57-5735 from Cargill Chemical Products.

Example 1

This example illustrates the preparation of four vinyl pivalate homopolymers, namely poly(vinyl pivalate) polymers, designated as Polymers 1 to 4, which may be used as polymers containing at least one vinyl ester according to the present invention.

Polymers 1 to 4 were each prepared in the following manner. A two-liter, four-neck, round bottom flask, equipped with a condenser and a mechanical stirrer, was charged with 200 grams of vinyl pivalate monomer and 270 grams of n-butyl acetate solvent. The

monomer/solvent mixture was then sparged with nitrogen for ten minutes and heated to the temperatures shown below (Table 1). A solution of azo-bis-iso-butyronitrile (AIBN) catalyst in n-butyl acetate was then added to the monomer mixture. An induction period of two to thirty minutes occurred in each case hefore polymerization began, which was evidenced by a sudden exotherm. The temperature was maintained at the levels shown (±3° C) for four hours. A second solution of AIBN in n-butyl acetate was then added to the reaction mixture, which was then allowed to cook for two more hours. Table 1 indicates the total amount of AIBN catalyst added to each reaction mixture.

In the case of Polymer 4, 0.37 weight percent of a chain transfer agent, 3-mercapto-l-propanol, with the amount based on the vinyl pivalate monomer, was added to the flask containing the solvent and monomer to reduce the molecular weight and change the polydispersity of the resulting polymer. The 3-mercapto-l-propanol was added to the flask by a pump over a period of two hours, starting thirty minutes after polymerization began.

After cooling to room temperature, the resulting poly(vinyl pivalate) homopolymer solution was concentrated to 60 weight percent polymer by using vacuum distillation. The physical properties of Polymers 1 to 4 are given in Table 1. The viscosities were measured at 25° C using a Brookfield viscometer, with 60 weight percent polymer solution in n-butyl acetate.

This example compares a conventional nitrocellulose lacquer (Lacquer A) with several lacquers (Lacquers 1 to 4) in which some or all of the nitrocellulose was replaced with poly( vinyl pivalate) (Polymer 1 from Example 1).

Lacquers 1 to 4 were each made by mixing a 60 weight percent solution of Polymer 1 in n-butyl acetate and a 70 weight percent solution of nitrocellulose in isopropanol, in the Polymer 1 : nitrocellulose weight ratios indicated below (Table 2). Each of the Lacquers 1 to 4 was then diluted to 30 weight percent total solids. Lacquer A was made by mixing nitrocellulose and dioctyl phthalate plasticer in a weight ratio of 80:20 with n-butyl acetate solvent to give 30 weight percent total solids.

The Solution Compatibility, Clarity, Repairability, Pencil Hardness, 60° Gloss, Spotting Test (Water), and Spotting Test (Ethanol) were measured for each lacquer and the results are shown below (Table 2). Lacquers 1 to 4, which contained various amounts of Polymer 1, each demonstrated good Solution Compatibility, Clarity, Repairability, and Pencil Hardness and each had no spotting with either water or ethanol solution. The 60° Gloss measurements of Lacquers 1 to 4 were somewhat lower relative to that of Lacquer A, which was probably a result of either a slight dry film incompatibility

between Polymer 1 and the nitrocellulose or the absence of plasticizer in Lacquers 1 to 4.

TABLE 2

This example compares a conventional nitrocellulose lacquer (Lacquer B) with several lacquers (Lacquers 5 to 7) in which some or all of the nitrocellulose was replaced with poly( vinyl pivalate) (Polymer 3 from Example 1).

Lacquers 5 to 7 and Lacquer B were each made by combining a 60 weight percent solution of Polymer 3 in n-butyl acetate, a 70 weight percent solution of nitrocellulose in isopropanol, dioctyl phthalate plasticizer, and a solvent mixture having a 3.5:1 weight ratio of methyl amyl ketone to n-butyl alcohol. The amounts of Polymer 3, nitrocellulose, and dioctyl phthalate, as weight percentages of the total solids in each lacquer, are given below (Table 3). Each lacquer contained 31 weight percent total solids.

The Brookfield viscosity (centipoise, 25° C), film thickness (millimeter), Pencil Hardness, and 60° Gloss were measured for each lacquer and the results are shown below (Table 3). Lacquers 5 to 7, which contained various amounts of Polymer 3, each had reduced

viscosity compared with Lacquer B. For example, Lacquer 5, which contained only two-thirds the amount of nitrocellulose in Lacquer B, because one-third of the nitrocellulose polymer was replaced with poly( vinyl pivalate), had a viscosity of about 40 ^* percent that of Lacquer B, while the hardness and gloss of Lacquer 5 were substantially maintained relative to Lacquer B.

This example illustrates the preparation of three copolymers, Polymers 5 to 7, containing various amounts of vinyl pivalate monomer and vinyl acetate (second) monomer, which may be used as polymers containing at least one vinyl ester monomer according to the present invention.

Polymers 5 to 7 were each prepared in the same manner as Polymer 1 in Example 1, except vinyl acetate monomer was substituted for 25, 35 and 50 weight percent of the vinyl pivalate monomer in Polymers 5, 6 and 7, respectively. The physical properties of Polymers 5 to 7 are shown in Table 4. The viscosities were measured at 25° C using a Brookfield viscometer, with a 60 weight percent solids solution in n-butyl acetate.

This example compares a conventional nitrocellulose lacquer (Lacquer C) with several lacquers (Lacquers 8 to 14) in which some or all of the nitrocellulose was replaced with poly( vinyl pivalate) or vinyl pivalate/vinyl acetate copolymers.

Lacquers 8 to 14 and Lacquer C were each made by combining a 60 weight percent solution of one of Polymers 1, 5, 6, or 7 in n-butyl acetate; a 70 weight percent solution of nitrocellulose in isopropanol; a 75 percent weight solution of Alkyd 1 in methyl amyl ketone; dioctyl phthalate plasticizer; and a solvent mixture having a 3.5:1 weight ratio of methyl amyl ketone to n-butyl alcohol. The amounts of Polymers 1, 5, 6, or 7 and nitrocellulose in each lacquer, as weight percents of the combined weight of Polymers 1, 5, 6 or 7 and nitrocellulose, are shown below (Table 5). The combined weight of Polymers 1, 5, 6, or 7 and nitrocellulose was 40 weight percent of the total solids in each lacquer. The amount of Alkyd 1 in each lacquer was 49.6 weight percent of the total sohds, while the amount of dioctyl phthalate plasticizer in each lacquer was 10.3 weight percent of the total solids. Each of Lacquers 8 to 14 and Lacquer C contained 45 weight percent total solids.

The Solution Compatibility, viscosity, Pencil Hardness, and 60° Gloss were measured for each lacquer and the results are shown below (Table 5).

ΪΔELEJi

Lacquer JL 1Q .11. 02_ _ιa. _14_

33

33 67

67 67 33

Good 600

0.9 t\3

B 46

In Lacquers 8, 10, and 12, Solution Compatibility was not achieved, which was probably due to incompatibility between Alkyd 1 and the vinyl pivalate in Polymers 1, 5, and 6. However, Lacquers 9, 11, 13, and 14 had good Solution Compatibility.* This indicates that for this particular lacquer system, which contains ^' a combination of nitrocellulose and Alkyd 1, vinyl pivalate/vinyl acetate copolymers that contain increased amounts of vinyl acetate are preferred.

The data in Table 5 also indicate that the viscosities of Lacquers 9, 11, 13, and 14 were substantially reduced compared with Lacquer C. Therefore, replacement of at least a portion of the nitrocellulose in Lacquer C with vinyl pivalate/vinyl acetate copolymers reduced the viscosities of the resulting lacquers greatly.

Example 6 The solids contents of Lacquers 13 and 14 in Example 5 were increased in order to adjust the viscosity of both lacquers to 1250 centipoise, the viscosity of Lacquer C. At a viscosity of 1250 centipoise, the volatile organic compound (VOC) contents of Lacquers 13 and 14 and of Lacquer C were as follows:

Lacquer £ 13. H

Viscosity, cP Solids, weight % VOC, lb/gal VOC/Solids, lb/lb

The levels of volatile organic compounds in Lacquers 13 and 14, on the basis of pounds of VOC per gallon of lacquer, were reduced by about 5 percent and about 10 percent, respectively, compared with Lacquer C. The emissions of volatile organic compounds from Lacquers 13 and 14, when compared on the basis of an equal amount of applied coating solids ("VOC/Solids, lb/lb"), were reduced by about

12 percent and about 24 percent, respectively, compared with Lacquer C.

Lacquers 13 and 14 were particularly suitable for spray application using compressed fluids such as carbon dioxide to dilute the lacquer to a sprayable viscosity. In addition to the reduction in volatile organic compounds achieved by substitution of a polymer containing at least one vinyl ester monomer for a portion of the nitrocellulose in these lacquers, spray coating with a compressed fluid would allow additional, significant reduction in volatile organic compounds usage over that of Lacquer C.

Example 7

This example compares a conventional nitrocellulose lacquer (Lacquer D) with a similar lacquer (Lacquer 15) in which 37.5 weight percent of the nitrocellulose was replaced with poly( vinyl pivalate) (Polymer 4).

Lacquer D was made by mixing 40 weight percent nitrocellulose (as a 70 weight percent solution of nitrocellulose in isopropanol), 49.6 weight percent Alkyd 2, and 10.3 weight percent dioctyl phthalate in a solvent mixture having a 3.5:1 weight ratio of methyl amyl ketone to n-butyl alcohol, to produce a lacquer containing 44.56 weight percent total solids. Lacquer 15 was made in the same manner, except 37.5 weight percent of the nitrocellulose was replaced with Polymer 4.

The solids contents of Lacquers D and 15 were adjusted so that the viscosity of both lacquers was 1250 centipoise. At this viscosity, the levels of volatile organic compounds (VOC) in Lacquers D and 15 were as follows:

Lacquer Viscosity, cP Solids, weight % VOC, lb/gal VOC/Solids, lb/lb

The level of volatile organic compounds in Lacquer 15, on the basis of VOC per gallon of lacquer, was reduced by about 12 percent from that of Lacquer D. The emission of volatile organic compounds from Lacquer 15, when compared on the basis of an equal amount of applied coating sohds ("VOC/Solids, lb/lb"), was reduced by about 22 percent, compared with Lacquer D. Lacquer 15 was suitable for spray coating application using compressed fluids to provide significant, additional reduction in VOC emissions.