US20020115781A1

US20020115781A1 - Coatings and inks based on solvents having negligible photochemical reactivity

Info

Publication number: US20020115781A1
Application number: US09/829,828
Authority: US
Inventors: Daniel Pourreau; Shao-Hua Guo
Original assignee: Arco Chemical Technology LP
Current assignee: Lyondell Chemical Technology LP
Priority date: 1997-02-20
Filing date: 2001-04-10
Publication date: 2002-08-22
Anticipated expiration: 2017-02-20
Also published as: US6462117B1

Abstract

Coating and ink compositions based on organic solvents that have negligible photochemical reactivity and methods for making them are disclosed. The organic solvents have calculated oxidation rate constants of less than about 1×10¹⁰cm³/g·sec, and evaporation rates of not more than about 5 times that of n-butyl acetate. Coatings made by the method of the invention are used for wood, furniture, automotive, container, architectural, coil, aerosol, marine, transportation, industrial, ink, overprint varnish, and road-coating applications.

Description

FIELD OF THE INVENTION

The invention relates to coating compositions and methods of preparing them. In particular, the invention relates to coatings and inks that contain solvents having negligible photochemical reactivity and favorable evaporation rates.

BACKGROUND OF THE INVENTION

Organic solvents, many of which are classified as VOCs, are widely used in traditional coating formulations (including inks). Generally, an organic compound is classified as a VOC unless it has been proven to not participate in atmospheric photochemical reactions. Ordinarily, these are compounds that undergo hydrogen atom abstraction by atmospheric hydroxyl radicals much faster than ethane. VOCS are hazardous to human health because they react with free radicals in the air and generate tropospheric ozone.

Pursuant to the Clean Air Act of 1990, the U.S. Environmental Protection Agency (EPA) recently mandated significant reductions in the amount of VOCS that may be used in coatings. Because of the mandate, the industry has an acute need for good coating solvents that have negligible photochemical reactivity and can therefore be exempt from regulation. Unfortunately, most organic solvents that have the desired low photochemical reactivity are either poor coating solvents or are subject to other regulations. For example, some solvents are classified as “ozone depleters” under the Montreal Protocol; others are regulated by the EPA as “hazardous air pollutants” (HAP solvents). Few organic solvents are valuable for coatings and have low photochemical reactivity, yet are not ozone depleters or HAP solvents.

The EPA has exempted some solvents from VOC status based on their negligible photochemical reactivity. Examples include acetone, methylene chloride, volatile methyl siloxanes, perchloroethylene, and p-chlorobenzyltrifluoride (PCBTF). Unfortunately, these solvents have drawbacks. Acetone and methylene chloride evaporate too fast. In addition, acetone is water-miscible, so coatings made with it absorb moisture too rapidly from the air. Acetone also has appreciable atmospheric photochemistry aside from its reaction with hydroxyl radicals because it strongly absorbs visible and near-UV light. Methylene chloride and perchloroethylene have toxicity concerns. The more exotic solvents, such as methyl siloxanes and PCBTF, are too expensive and are relatively poor coating solvents, as is evidenced by their relatively low Hansen solubility parameters (less than 8.0 (cal/cm ³)^½).

Traditional approaches to reducing the VOC content of coatings and inks have focused in developing new resins, crosslinkers, and reactive diluents that do not require as much solvent to formulate. These approaches have succeeded only marginally in spite of their considerable expense. For example, water-borne coatings, which developed as an alternative to solvent-borne systems, sometimes contain even more VOCs than comparable high-solids formulations, and often give inferior performance. As another example, powder coatings may use little or no VOCs, but they require expensive equipment to apply and cure.

In sum, the coating and ink industry needs solvents that have low toxicity, are inexpensive, are not regulated as HAP solvents or ozone depleters, do not evaporate too rapidly, are good coating solvents, and most important, have negligible photochemical reactivity and could be exempt from VOC regulations.

SUMMARY OF THE INVENTION

The invention is a method of preparing a coating composition. The method comprises using as a coating component an organic solvent having negligible photochemical reactivity. Such solvents have an oxidation rate constant of less than about 1×10 ¹⁰cm³/g·sec. This is a calculated or measured rate of hydrogen-atom abstraction from a compound by atmospheric hydroxyl radicals. In addition, the organic solvent has an evaporation rate of not more than about 5 times that of n-butyl acetate.

We surprisingly found that, among thousands of possible organic compounds potentially useful as coating and ink solvents, very few meet the needs of the industry, particularly when current VOC restrictions and relative evaporation rates are taken into account. By including a solvent having an oxidation rate constant of less than about 1×10 ¹⁰cm³/g·sec, and also having an evaporation rate of not more than about 5 times that of n-butyl acetate, formulators can significantly reduce the proportion of photochemically reactive solvent used and still make good coatings.

The invention includes thermoplastic and thermoset coating compositions which comprise an organic solvent having negligible photochemical reactivity. These compositions include a resin or a crosslinker or both. The invention benefits coatings used for wood, furniture, automotive OEM, automotive refinish, container, architectural, coil, aerosol, marine, transportation, industrial maintenance, general industrial, inks, overprint varnishes, and road-coating applications.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The invention is a method of preparing coating compositions, including inks. The method comprises using as a coating component an organic solvent having negligible photochemical reactivity, and also having an evaporation rate of not more than about 5 times that of n-butyl acetate.

By solvents having “negligible photochemical reactivity,” we mean solvents that will undergo free-radical abstraction of a hydrogen atom of the solvent by atmospheric hydroxyl radicals at a measured or calculated rate less than or about equal to the corresponding rate of abstraction of hydrogen atoms from ethane. On a weight basis, this corresponds to an oxidation rate constant of less than about 1×10 ¹⁰cm³/g·sec. Solvents having such low photochemical reactivities are potentially excludable as VOCs under EPA regulations. Solvents preferably used in the method of the invention have oxidation rate constants less than about 5×10⁹cm³/g·sec; most preferred are solvents having oxidation rate constants less than about 3×10⁹cm³/g·sec.

Oxidation rate constants of various coating solvents appear in Table 1 (below). As shown in the table, many traditional coating solvents such as toluene, xylenes, methyl isobutyl ketone, and n-butyl acetate have relatively high oxidation rate constants and are classified by the EPA as VOCS. In contrast, the method of the invention uses solvents having negligible photochemical reactivity such as those listed in the top half of the table (e.g., tert-butyl acetate, dimethyl carbonate).

In addition to negligible photochemical reactivity, organic solvents useful in the method of the invention are limited to those having useful evaporation rates. Some otherwise useful (and currently VOC-exempt) organic solvents have limited value in coatings because they evaporate too rapidly. Examples are acetone and methylene chloride, which evaporate (respectively) roughly 6 and 14 times faster than n-butyl acetate. Organic solvents useful in the invention have evaporation rates of not more than about 5 times that of n-butyl acetate, which is the industry standard for comparison. More preferred organic solvents have evaporation rates of not more than about 3 times that of n-butyl acetate.

Traditional coating solvents classified as VOCs can be included in the method of the invention. These solvents may be critical for maintaining satisfactory coating processability or performance. Preferably, however, at least about 5 wt. % of the total solvent content of coatings made by the method of the invention comprises one or more organic solvents that have negligible photochemical reactivity and also have an evaporation rate of not more than about 5 times that of n-butyl acetate. More preferably, the organic solvent(s) having negligible photochemical reactivity is the major solvent component, i.e., at least about 50 wt. % of the solvent used is one or more solvents that have negligible photochemical reactivity. The solvent having negligible photochemical reactivity may be the only solvent component.

Organic solvents useful in the method of the invention should have good solvent properties for coatings. Preferably, the solvent will have a total Hansen solubility parameter (δ) of at least about 8.0 (cal/cm ³)^½. If the solvent has a δ value less than 8.0 (cal/cm³)^½, it may not adequately solubilize coating components, may give poor film-forming properties, or may contribute to incompletely cured coatings. As noted above, some commercially available organic solvents (e.g., volatile methyl siloxanes and PCBTF) are VOC-exempt, but have 8 values less than 8.0 (cal/cm³)^½. Hansen solubility parameters and methods for calculating them appear, for example, in Polymer Handbook, 3^rded., Brandrup and Immergut, eds. (1989), VII 519-544.

Organic solvents useful in the method of the invention preferably contain no reactive halogen atoms, i.e., they contain no chlorine or bromine atoms, but may contain fluorine. In addition, preferred organic solvents are not regulated by the Montreal Protocol as strospheric ozone depleters (e.g., CFCs), and are not classified by the EPA as hazardous air pollutants (HAP solvents; e.g., methylene chloride, perchloroethylene). Preferred organic solvents have relatively low toxicity.

Most or all of the hydrogen atoms in preferred solvents are part of methyl or tert-butyl groups, i.e., they are “primary” hydrogen atoms. For example, in tert-butyl acetate, all of the hydrogen atoms are part of a methyl group or a tert-butyl group, and are all primary hydrogens. Solvents useful in the invention can have secondary or tertiary hydrogens, but preferably such compounds will have an electron-withdrawing group attached to the carbon having the secondary or tertiary hydrogen atom. For example, 2-nitropropane, a solvent useful in the invention, has a tertiary hydrogen, but it is attached to a carbon having a strong electron-withdrawing group (a nitro group) attached to it. Electron-withdrawing groups are well-known to those skilled in the art, and include, for example, nitro, halogen, carboxyl, carbonate, trifluoromethyl, cyano, acetyl, and the like.

Suitable solvents for use in the invention include, for example, nitroalkanes (e.g., 2-nitropropane, nitroethane, nitro-tert-butane), tert-butyl acetate, methyl benzoate, methyl trifluoroacetate, dimethyl carbonate, methyl pivalate, tert-butyl alcohol, propylene carbonate, tert-butyl benzoate, di-tert-butyl carbonate, methyl tert-butyl carbonate, and the like, and mixtures thereof. Most preferred is tert-butyl acetate.

Coating compositions made by the method of the invention are water-borne or solvent-borne, but are preferably solvent-borne. They contain acrylic, vinyl, amino, urethane, epoxy, alkyd, uralkyd, nitrocellulose, melamine, polyols, polyesters, or other resins that are soluble in the organic solvents used. The resins are thermoplastic or thermoset. The thermoset resins have carboxy, hydroxy, epoxy, isocyanate, amino, silane, anhydride, olefin, or allylic functionalities that are cured by reaction with a crosslinker or by self-crosslinking between polymer chains. Suitable crosslinkers include epoxy resins, isocyanates, melamines, and the like. The coatings can be clear or may contain pigments, fillers, or other additives. The coatings can be cured at ambient temperature or at elevated temperature by baking. The coatings cure by radiation, oxidation, or chemical crosslinking.

The invention includes a method of preparing a coating resin. The method comprises polymerizing one or more ethylenic monomers in the presence of an organic solvent having negligible photochemical reactivity and also having an evaporation rate of not more than about 5 times that of n-butyl acetate. Optionally, the polymerization is performed in the presence of a free-radical initiator. The mixture is heated under conditions effective to polymerize the monomers according to well-known techniques. Suitable ethylenic monomers and free-radical initiators are those well known in the art. The ethylenic monomers include, for example, vinyl aromatic monomers, acrylates, allylic alcohols, allylic esters, allylic ethers, cyclic unsaturated anhydrides, vinyl halides, and the like, and mixtures thereof. Peroxides are preferably used as free-radical initiators. If desired, other types of resins can be prepared in the presence of the organic solvent, such as those made by condensation polymerization (e.g., polyethers and polyesters).

The invention includes thermoplastic and thermoset coating compositions. The compositions comprise a resin or a crosslinker or both. In addition, the compositions comprise an organic solvent having negligible photochemical reactivity as measured by an oxidation rate constant of less than about 1×10 ⁻¹³cm³/g·sec, and also having an evaporation rate of not more than about 5 times that of n-butyl acetate.

Any desired technique can be used for applying coatings made by the method of the invention. Suitable techniques include, spraying, brushing, lay down, dipping, or other methods. The coatings can be applied to coated or uncoated metal, plastic, glass, concrete, asphalt, or other hard surfaces. Coatings made by the method of the invention are used in wood, furniture, automotive OEM, automotive refinish, container, architectural, coil, aerosol, marine, transportation, industrial maintenance, general industrial, inks, overprint varnishes, and road-coating applications. The examples below show just a few possible formulations that contain reduced levels of photochemically reactive solvents. The performance characteristics of these coatings should rival those of the comparative examples with larger proportions of photochemically reactive solvents.

Example 23 and Comparative Example 24 show properties of a two-component polyurethane coating made from a hydroxy-acrylic resin. The examples show that excellent coating properties are maintained when tert-butyl acetate is used in place of n-butyl acetate to give a formulation with an 11 wt. % reduction in the content of photochemically reactive organic solvent.

The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.

EXAMPLE A

Preparation of a Zero-VOC Acrylic Resin Solution

Tert-butyl acetate (150 g) is charged to a glass polymerization reactor equipped with reflux condensor, heating mantle, and addition funnel. A mixture of styrene (42 g), methyl methacrylate (42 g), butyl acrylate (35 g), butyl methacrylate (147 g), hydroxyethyl acrylate (84 g), and benzoyl peroxide (20 g) is cooled to 5° C. and is then charged to the addition funnel. The tert-butyl acetate is heated to reflux (98° C.), and the monomer mixture is added gradually over 4 h. The mixture is refluxed for an additional hour after monomer addition is complete. The reactor contents are cooled to room temperature, and the mixture is discharged. The resulting hydroxy-functional acrylic resin solution is expected to have a solids content of about 70 wt. %. The solid component of the resin solution has a hydroxyl number within the range of about 110 to 120 mg KOH/g.

TABLE 1


Oxidation Rate Constants¹of Coating Solvents (cm³/g.sec)

	tert-butyl acetate	2.3 ×10⁹
	dimethyl carbonate	2.9 ×10⁹
	methyl tert-butyl carbonate	3.3 ×10⁹
	di-tert-butyl carbonate	3.5 ×10⁹
	methyl benzoate	3.7 ×10⁹
	propylene carbonate	4.1 ×10⁹
	ethane (for comparison)	5.4 ×10⁹
	tert-butyl benzoate	7.7 ×10⁹
	tert-butyl alcohol	8.8 ×10⁹
	n-butyl acetate	2.5 ×10¹⁰
	toluene	3.9 ×10¹⁰
	methyl isobutyl ketone	8.5 ×10¹⁰
	xylenes	1.3 ×10¹¹


	#reported by Atkinson. See, for example, R. Atkinson, Int. J. Chem. Kinet., 19 (1987) 799, and R. Atkinson, Environ. Tox. Chem., 7 (1988) 435. The rates here are
	#reported in cm³/g . sec to correct for volatility and to normalize for differing numbers of hydrogen atoms. To convert a rate in cm³/molecule.
	#sec to a rate in cm³g . sec, multiply the former by 6.022 × 10²³molecules per mole, and divide by the molecular weight (g/mole) of the solvent.

Example 1 and Comparative Example 2

2K High-Solids Acrylic-Urethane Gloss

Clearcoat for Air-Dry Applications

	Example	1	C2

Part A: Acrylic Polyol
G-CURE 105P70 acrylic polyol¹	800	800
methyl amyl ketone	0	80
tert-butyl acetate	80	0
dibutyltin dilaurate (2% in methyl	7.0	7.0
ethyl ketone)
Part B: Isocyanate
LUXATE FIT-2000 isocyanate	200	200
adduct²
propylene glycol methyl ether	16.6	33.3
acetate
methyl ethyl ketone	0	33.3
tert-butyl acetate	49.9	0
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	2.4	3.3
reactive #s per # of solids applied	0.35	0.52

Example 3 and Comparative Example 4

White Polyester-Urethane 2K Air-Dry Coating¹

	Example	3	C4

Part A
5760 polyester resin solution²	28.9	28.9
TITANOX 2090 titanium dioxide³	37.3	37.3
n-butyl acetate	0	9.45
tert-butyl acetate	9.45	0
soya lechithin	0.32	0.32
BYK 300 additive⁴	0.40	0.40
dibutyltin dilaurate	0.040	0.040
Part B
DESMODUR N-75 isocyanate adduct⁵	0	19.9
LUXATE HT2000 isocyanate adduct⁶	14.9	0
ethylene glycol ethyl ether acetate	0	3.72
tert-butyl acetate	4.97	0
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	1.1	2.6
reactive #s per # of solids applied	0.087	0.27

Example 5 and Comparative Example 6

White Alkyd Topcoat¹

	Example	5	C6

5720 alkyd resin solution²	48.7	48.7
TITANOX 2090 titanium dioxide³	29.2	29.2
BYK 300 additive⁴	0.20	0.20
n-butyl acetate	0	20.3
tert-butyl acetate	20.3	0
cobalt (18%) drier	0.13	0.13
zirconium (18%) drier	0.39	0.39
ACTIV-8 additive⁵	0.20	0.20
EXKIN #2 anti-skinning agent⁶	0.14	0.14
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	1.9	3.5
reactive #s per # of solids applied	0.20	0.50

Example 7 and Comparative Example 8

Polyester Urethane Furniture Coating¹

	Example	7	C8

MULTRON R-12A polyester	275	275
polyol²
MODAFLOW resin modifier³	1.0	1.0
DESMODUR HL isocyanate adduct²	370	370
toluene	0	179
ethylene glycol ethyl ether acetate	65	175
tert-butyl acetate	289	0
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	2.8	4.4
reactive #s per # of solids applied	0.43	1.0

Example 9 and Comparative Example 10

Acrylic-Nitrocellulose Aircraft White Gloss Coating¹

	Example	9	C10

RBH White titanium dioxide	23.8	23.8
dispersion #6610²
½ sec RS nitrocellulose³	5.90	5.90
ACRYLOID B-82 acrylic resin⁴	28.6	28.6
dioctyl phthalate	5.40	5.40
toluene	0	7.16
methyl ethyl ketone	0	13.1
tert-butyl acetate	36.3	0
methyl isobutyl ketone	0	16.0
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	3.8	5.2
reactive #s per # of solids applied	0.58	1.5



Example 11 and Comparative Example 12
Epoxy-Amine Clear Can Coating1

Example

11

C12

EPON 1001 B-80 epoxy resin²	246	246
UNJ-RLEZ 2100P75 curing agent³	250	250
n-butyl alcohol	84.0	84.0
n-propyl alcohol	0	62.0
toluene	0	45.6
methyl butyl ketone	0	21.5
tert-butyl acetate	158	0
ethylene glycol ethyl ether	50.0	78.5
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	3.2	4.0
reactive #s per # of solids applied	0.64	1.1

Example 13 and Comparative Example 14

Black Acrylic Lacquer for Wood Coatings¹

	Example	13	C14

ACRYLOID B-99 acrylic resin	7.67	7.67
solution²
ACRYLOID B-48N solid acrylic	117	117
resin²
carbon black	3.83	3.83
toluene	0	144
xylenes	38.0	368
ethylene glycol ethyl ether acetate	62.8	123
tert-butyl acetate	534	0
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	3.7	6.3
reactive #s per # of solids applied	0.85	5.2

Example 15 and Comparative Example 16

Blue Flexographic Ink¹

	Example	15	C16

SUNFAST BLUE 249-2083 dye²	6.32	6.32
ACRYLOID DM-55 acrylic	2.11	2.11
resin³
ACRYLOID B-72 acrylic resin³	23.1	23.1
n-propyl acetate	0.72	21.2
ethyl alcohol (denatured)	23.6	38.6
tert-butyl acetate	42.2	0
ethyl acetate	0	8.70
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	3.7	5.3
reactive #s per # of solids	0.83	2.2
applied



Example 17 and Comparative Example 18
Beige Polyester-Melamine Baking Enamel for Coil Coatings¹

Example

17

C18

5781 polyester poiyoi resin²	27.9	27.9
CYMEL 350 melamine resin³	11.7	11.7
titanium dioxide pigment	28.1	28.1
carbon black pigment	0.070	0.070
yellow iron oxide pigment	0.84	0.84
silica flatting agent	2.96	2.96
acid catalyst	1.27	1.27
propylene glycol methyl ether	7.59	17.6
acetate
n-butyl acetate	0	9.50
methyl pivalate	19.5	0
Pounds (#) of photochemically
reactive solvent
reactive #s per gallon	1.4	3.2
reactive #s per # of solids applied	0.12	0.39

Example 19 and Comparative Example 20

SAA Resinous Polyol—Urethane Clearcoat for Wood¹

	Example	19	C20

Part A
SAA 103 resinous polyol²	150	150
n-butyl acetate	0	200
tert-butyl acetate	200	0
Part B
LUXATE HT2000 isocyanate adduct²	70.0	70.0
n-butyl acetate	0	20.0
tert-butyl acetate	20.0	0
Pounds (#) of photochemically reactive solvent
reactive #s per gallon	0	4.0
reactive #s per # of solids applied	0	1.0

Example 21 and Comparative Example 22

One-Component Thermoplastic Acrylic Clearcoat

Example	21	C22

ACRYLOID B-82 solid acrylic resin¹	150	150
n-butyl acetate	0	225
tert-butyl acetate	225	0
Pounds (#) of photochemically reactive solvent
reactive #s per gallon	0	4.9
reactive #s per # of solids applied	0	1.5

Example 23 and Comparative Example 24

Two-Component Hydroxy-Acrylic Polyurethane Coating

Example	23	C24

G-CURE 105P70 acrylic polyol¹	100	100
T-12 catalyst²(1 wt. % in toluene)	1.9	1.9
silicone flow additive (10%)	0.34	0.34
LUXATE HT-2000 isocyanate adduct³	25.5	25.5
ethylene glycol ethyl ether acetate	25.0	25.0
methyl amyl ketone	25.0	25.0
n-butyl acetate	0	25.0
tert-butyl acetate	28.0	0
Coating Properties
Pot life (sec, Zahn #2 cup) T = 0;	21.1; 29.7	21.2; 29.9
T = 4 h
Dry time (h, 21.5° C., 59% rel. hum).	0.25; 1.5; 2.0;	0.20; 1.4; 1.6;
evap time; gel time; dry time; total	3.0	3.2
Film thickness (mil)	2.8	2.7
Gloss (20°); (60°)	88; 95	88; 95
Pencil hardness; Pendulum hardness	4 H; 89	4 H; 91
Forward, reverse impact (in./lb.)	160+; 160+	160+; 160+
Adhesion	pass	pass
DOI	90	90
Photochemically reactive pounds	3.8	4.3
per gallon
Chemical & solvent resistance, 30 min.:	no change	no change
10% HCI, 10% HOAc, 10% NaOH,
xylenes,
MEK; MEK 100 double rubs

Example 25 and Comparative Example 26

Thermoset Overprint Varnish¹

Example	25	C26

CAP 482-0.5 cellulose acetate propionate²	10.8	10.8
BECKAMINE 21-511 urea resin³	18.0	18.0
acid catalyst	0.050	0.050
ethyl alcohol (denatured)	24.5	49.5
ethyl acetate	0	21.2
methyl pivalate	46.2	0
Pounds (#) of photochemically reactive solvent
reactive #s per gallon	4.4	5.7
reactive #s per # of solids applied	1.4	3.5

The preceding examples are meant as illustrations; the following claims define the scope of the invention. [0039]

Claims

We claim:

1. A method of preparing a coating composition, said method comprising using as a coating component an organic solvent having negligible photochemical reactivity as measured by an oxidation rate constant of less than about 1×10¹⁰cm³/g·sec, and also having an evaporation rate of not more than about 5 times that of n-butyl acetate.

2. The method of claim 1 wherein the organic solvent has a total Hansen solubility parameter of at least about 8.0 (cal/cm³)^½.

3. The method of claim 1 wherein the organic solvent contains no chlorine or bromine atoms.

4. The method of claim 1 wherein the organic solvent is selected from the group consisting of nitroalkanes, tert-butyl acetate, methyl benzoate, methyl trifluoroacetate, dimethyl carbonate, methyl pivalate, tert-butyl alcohol, propylene carbonate, tert-butyl benzoate, di-tert-butyl carbonate, and methyl tert-butyl carbonate.

5. The method of claim 1 wherein the organic solvent is tert-butyl acetate.

6. The method of claim 1 wherein the oxidation rate constant is less than about 5×10⁹cm³/g·sec.

7. The method of claim 1 wherein the oxidation rate constant is less than about 3×10⁹cm³/g·sec.

8. The method of claim 1 wherein the organic solvent comprises at least about 5 wt. % of the total solvent component of the coating composition.

9. The method of claim 1 wherein the organic solvent having negligible photochemical reactivity comprises the major solvent component of the coating composition.

10. A method of preparing a coating composition, said method comprising using as a coating component an organic solvent having negligible photochemical reactivity as measured by an oxidation rate constant of less than about 1×10¹⁰cm³/g·sec, and also having an evaporation rate of not more than about 5 times that of n-butyl acetate, a total Hansen solubility parameter of at least about 8.0 (cal/cm³)^½, and no chlorine or bromine atoms.

11. The method of claim 10 wherein the organic solvent is selected from the group consisting of nitroalkanes, tert-butyl acetate, methyl benzoate, methyl trifluoroacetate, dimethyl carbonate, methyl pivalate, tert-butyl alcohol, propylene carbonate, tert-butyl benzoate, di-tert-butyl carbonate, and methyl tert-butyl carbonate.

12. The method of claim 10 wherein the oxidation rate constant is less than about 5×10⁹cm³/g·sec.

13. The method of claim 10 wherein the organic solvent comprises at least about 5 wt. % of the total solvent component of the coating composition.

14. A method of preparing a coating resin, said method comprising polymerizing one or more ethylenic monomers in the presence of an organic solvent having negligible photochemical reactivity as measured by an oxidation rate constant of less than about 1×10¹⁰cm³/g·sec, and also having an evaporation rate of not more than about 5 times that of n-butyl acetate.

15. The method of claim 14 wherein the polymerization is performed in the presence of a free-radical initiator.

16. The method of claim 14 wherein the oxidation rate constant is less than about 5×10⁹cm³/g·sec.

17. The method of claim 14 wherein the solvent is selected from the group consisting of nitroalkanes, tert-butyl acetate, methyl benzoate, methyl trifluoroacetate, dimethyl carbonate, methyl pivalate, tert-butyl alcohol, propylene carbonate, tert-butyl benzoate, di-tert-butyl carbonate, and methyl tert-butyl carbonate.

18. The method of claim 14 wherein the solvent is tert-butyl acetate.

19. A thermoplastic or thermoset coating composition which comprises:

(a) an organic solvent having negligible photochemical reactivity as measured by an oxidation rate constant of less than about 1×10¹⁰cm³/g·sec, and also having an evaporation rate of not more than about 5 times that of n-butyl acetate; and

(b) one or more components selected from the group consisting of coating resins and crosslinkers.

20. The composition of claim 19 wherein the oxidation rate constant is less than about 5×10⁹cm³/g·sec.

21. The composition of claim 19 wherein the organic solvent is selected from the group consisting of nitroalkanes, tert-butyl acetate, methyl benzoate, methyl trifluoroacetate, dimethyl carbonate, methyl pivalate, tert-butyl alcohol, propylene carbonate, tert-butyl benzoate, di-tert-butyl carbonate, and methyl tert-butyl carbonate.

22. The composition of claim 19 wherein the organic solvent is tert-butyl acetate.

23. The composition of claim 19 comprising a crosslinker selected from the group consisting of polyisocyanates and isocyanate-terminated prepolymers.

24. A wood, furniture, automotive OEM, automotive refinish, container, architectural, coil, aerosol, marine, transportation, industrial maintenance, general industrial, ink, overprint varnish, or road coating made from the composition of claim 19.

25. A thermoplastic or thermoset coating composition which comprises tert-butyl acetate and one or more components selected from the group consisting of coating resins and crosslinkers.