WO2004104121A1

WO2004104121A1 - Crosslinkable coating systems containing carboxyalkylcellulose esters

Info

Publication number: WO2004104121A1
Application number: PCT/US2004/013983
Authority: WO
Inventors: Ronald Todd Obie
Original assignee: Eastman Chemical Co
Current assignee: Eastman Chemical Co
Priority date: 2003-05-16
Filing date: 2004-05-05
Publication date: 2004-12-02
Anticipated expiration: 2005-11-16

Abstract

An aminoplast crosslinker system is disclosed having improved cure speed as measured by mar resistance and block and print resistance test results. A carboxyalkyl cellulose ester, such as carboxymethyl cellulose acetate butyrate, is dissolved in a solvent, such as methanol or ethanol, and subsequently blended with an aminoplast crosslinker. This mixture may be used as such, or may be added to a mixture containing an alkyd resin or any other compatible polymer. The finished mixture can then be catalyzed with PTSA or any other catalyst material. In a coating, the system provides dramatically improved cure response and print and block resistance over a crosslinker containing an acrylic polyol or Styrene Allyl Alcohol, while at the same time providing improved flow and leveling.

Description

Crosslinkable Coating Systems Containing Carboxyalkylcellulose Esters

FIELD OF THE INVENTION

The invention relates to crosslinking compositions, and more specifically, to crosslinking coating compositions containing carboxyalkyl cellulose esters. The inventive coating compositions exhibit improved cure properties over comparable crosslinking compositions lacking such esters.

BACKGROUND OF THE INVENTION

Aminoplast and phenolplast resins are the two most common types of crosslinking resins, and can be used to crosslink coating compositions containing a variety of polymer resins or binders. This crosslinking results in improved coating cure speed, and in improved physical properties in the coating compared to coating compositions that cure via physical drying, or via thermoplastic or oxidative curing. Aminoplast and phenolplast crosslinkers essentially function by reaction of functional groups on the crosslinker with functional groups of the polymer resin. Examples of polymer resins that can be cured via crosslinking include alkyd, polyester, epoxy, acrylic, and siloxane resins. Reactive functionalities of these polymer resins include hydroxyl, carboxyl, epoxy, and amine functionalities.

Phenolplast or phenolic crosslinking resins are typically made by reacting phenols with formaldehyde, through a condensation reaction, to yield a phenol-formaldehyde resin, though aldehydes other than formaldehyde may also be used. Phenol-formaldehyde resins thus consist of aromatic rings linked by methylene or oxymethylene groups. Thermosetting phenol- formaldehyde resins are typically used to develop container coatings, and may be blended with the backbone resins already described. Aminoplast or amino-formaldehyde crosslinking agents are made by reacting formaldehyde with an amine through a condensation reaction, followed by alkylation of the resulting methylol groups with an alcohol. The chemical and physical properties of the aminoplast resin or crosslinker are determined by the choice of amine used in the condensation reaction, the molar ratio of amine to formaldehyde, the choice of alkylation alcohol, and the degree of alkylation of the methylol groups formed during the condensation reaction.

There are primarily four types of aminoplasts used in industrial coatings: urea-formaldehyde crosslinkers, melamine-formaldehyde crosslinkers, benzoguanamine-formaldehyde crosslinkers, and glycoluril-formaldehyde crosslinkers. Henk van Dijk presents a more detailed view of the chemistry and properties of these crosslinkers and their use in "The Chemistry and Application of Mio Crosslinking Agents or Aminoplasts" Volume V, Part II, Edited by Dr P.K.T. Oldring PhD BA, John Wiley and Sons in association with SITA Technology Limited, incorporated herein by reference. Further details of chemistry and properties can be found in "Amino Coatings Resins Their Invention and Reinvention" copyright 1986, 1995 Cytec Industries

Inc., incorporated herein by reference. Aminoplast crosslinkers are used in both solvent-based and water-based systems.

Improved cure speeds are important for increased article processing speeds and lower energy requirements. However, when only faster cure speed is taken into account, the demands of water-resistance, detergent- resistance, and the overall physical properties, may suffer. Urea- formaldehyde resins are typically used in coatings when faster cure speeds are desired. Melamine-formaldehyde resins are used when improved water, detergent, and overall physical properties are desired, and are not obtained with urea-formaldehyde resins. However, melamine-formaldehyde resins are typically slower in cure speed than are urea formaldehyde resins.

Melamine-formaldehyde crosslinkers are therefore often selected because of their improved performance and pot/shelf life as compared to urea formaldehyde-crosslinkers. However, this can mean a compromise between cure speed and performance, due to the slower cure speeds of the melamine formaldehyde resins.

Products have been developed to address this problem. For example, Resimene 797, available from Monsanto/Solutia, is a hexamethoxy- methylmelamine-based crosslinker blended with 20% styrene allyl alcohol. Resimene 2040, also available from Monsanto/Solutia, is a hexamethoxy- methylmelamine-based crosslinker blended with 40% styrene allyl alcohol, based on total solids of the crosslinker. Modacure, another product of Monsanto/Solutia, is a hexamethoxymethylmelamine-based crosslinker modified with up to 60% styrene allyl alcohol, based on total crosslinker solids. The styrene allyl alcohol in these products, a polyol, is used to modify melamine in such a way as to produce a faster curing melamine. These resins thus show improved cure response compared to the typical commercially available melamine-formaldehyde resins.

WO 01/60882 describes alkoxymethyl melamine crosslinkers, having reduced levels of imino groups, that yield improved cure response.

U. S. Pat. No. 4,1119,762 describes blends of a liquid hexamethoxymethyl- melamine with 1 ,4-cyclohexane dimethanol and a polyether polyol.

Solutia has also introduced Resimene CE-7103, a product that yields improved cure response for melamine-formaldehyde resins. Resimene CE-7103 is a highly etherified, low molecular weight, co-etherified melamine-formaldehyde resin. It is said to provide crosslinked coating systems requiring lower temperature cure, reduced catalyst requirements, lower evolved formaldehyde, improved flexibility, lower free formaldehyde, and lower viscosity and VOC.

Cytec has introduced Cymel 104 and 105 to address improved cure response in MF resins. Cymel 104 resin is an 80/20 solids blend of Cymel 303 resin (a highly methylolated, highly methylated melamine resin) with REACTOL 180 polyol (a hydroxyl-functional resin supplied by Eastman Chemical Co., Kingsport, TN); Cymel 105 resin is a 60/40 solids blend of Cymel 303 and REACTOL 180. These products are claimed to show , improved cure response, higher film hardness, and improved corrosion resistance relative to 100% Cymel 303 resin.

There remains a need however, for aminoplast resins having even faster cure response, while maintaining satisfactory properties in the resulting coating.

BRIEF SUMMARY OF THE INVENTION

The invention provides a crosslinking coating composition, containing an aminoplast crosslinker, and having improved cure speed over traditional aminoplast crosslinkers, as measured by mar resistance, block resistance, and print resistance tests. According to the invention, carboxyalkyl cellulose esters, relatively hydrophobic polymers containing both acid groups and hydroxyl groups, are dissolved in a solvent and subsequently blended with an aminoplast crosslinker. In one embodiment, carboxy- methylcellulose acetate butyrate is dissolved in methanol or ethanol and subsequently blended with a liquid hexamethoxymethylmelamine. This mixture may be used as is; added to a mixture containing an alkyd resin; or added to a mixture containing any other compatible polymer composition. The finished mixture can then be catalyzed with PTSA or any other catalyst material. As a coating, the mixture of carboxymethylcellulose acetate butyrate and a liquid hexamethoxymethylmelamine provides dramatically improved cure response and print and block resistance over a crosslinker containing an acrylic polyol or Styrene Allyl Alcohol. At the same time, the mixture provides improved flow and leveling.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an aminoplast crosslinker having improved cure speed, as measured by mar resistance, block resistance, and print resistance test results. According to the invention, carboxyalkyl cellulose esters, relatively hydrophobic polymers containing both acid groups and hydroxyl groups, are dissolved in a solvent, and subsequently blended with a crosslinker, and especially an aminoplast crosslinker. In one embodiment, carboxymethylcellulose acetate butyrate is dissolved in methanol or ethanol and subsequently blended with a liquid hexamethoxymethylmelamine to obtain a crosslinker system blend. This blend may be used as such; added to a mixture containing an alkyd resin; or added to a mixture containing any other compatible polymer. The final mixture may then be catalyzed with PTSA, or with any other suitable catalyst material.

As a coating, the blends provide dramatically improved cure response and print and block resistance over a crosslinker containing an acrylic polyol or styrene allyl alcohol as the polyol. At the same time, the carboxymethylcellulose acetate butyrate /liquid hexamethoxymethylmelamine blend provides improved flow and leveling. Other amino and phenolplast resins are also useful according to the invention, such as Tris alkoxy carbonyl triazine type products, for example.

The invention can be further illustrated by the following examples of preferred embodiments, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLES

Example 1

Into a stainless steel mixing vessel was charged 66.0 grams of methanol. 34.0 grams of Carboxymethylcellulose acetate butyrate, lot # KP0003B, available from Eastman Chemical Company, Kingsport, Tennessee was added slowly and mixed until dissolved. To this mixture was added 136.0 grams of Cymel 300, a liquid hexamethoxymethylmelamine, available from Cytec Industries, and the mixture mixed until uniform. The resulting mixture provided a clear film when drawn down onto a Leneta Chart Form 7B (available from Leneta Inc), by 1.5mil bird bar and allowed to air dry 15 minutes and force dried 10 minutes at 66°C. Addition of 3 weight percent Cycat 4040 catalyst, a 40% solution of Para toluene sulfonic acid in isopropanol, available from Cytec Industries, resulted in a clear, less tacky film after air drying 15 minutes and force drying 10 minutes at 66°C.

Examples 2 - 7

In examples 2-7, the carboxymethylcellulose acetate butyrate-modified hexamethoxymethylmelamine solution of example 1 was added to a coating based on a short oil alkyd resin (Duramac 207-1205, available from Eastman Chemical Co., Kingsport, TN), and the results compared to the cure and appearance of Resimene 2040, a 40% styrene allyl alcohol- modified hexamethoxymethylmelamine crosslinker available from Solutia.

Print resistance was checked by performing 6 mil draw downs on plate glass. The draw downs air-dried for 15 minutes, cured for 10 minutes @ 66C, and cooled for 5 minutes. A 2 psi and 4 psi print test was applied for 2 hours. Clarity, mar resistance, and flow and leveling were evaluated by 1.5 mil draw downs and 6 mil draw downs on Leneta Form 7B. These draw downs cured on the same schedule as those on the plate glass. The results are detailed below in Table 4.

In comparing Example 6 to Example 7, it can be seen that the Example 1 carboxymethylcellulose acetate butyrate/Melamine blend results in better print/block and mar resistance and better overall hardness than Resimene 2040. The Example 1 modified coating results in a more hazy appearance on plate glass however. Examples 8 - 21 detail studies evaluating compatibility of the carboxymethylcellulose acetate butyrate /Melamine blend of Example 1 with various alkyd resins. Alkyd resins are often used as backbone resins in aminoplast based coatings. Alkyd resins are the reaction product of a dibasic acid such as phthalic acid with an alcohol such as glycerol.

Typically, reaction of a stoichometric ratio of acid groups of phthalic acid to hydroxyl groups on glycerol results in a hard brittle polyester mass. These resins are typically defunctionalized by the addition of fatty acids of various types. These fatty acids are classified by chemical type such as soybean, linseed, or tall oil, for example, and by whether the oil is non-drying or drying (i.e., is saturated or unsaturated). Thus alkyd resins are the reaction products of a dibasic acid such as phthalic acid, a polyol such as glycerol: and a fatty acid such as linseed oil. (There are other modifications that may be made as well.) The amount of defunctionalization, i.e., the amount of fatty acid used, provides a third classification of the alkyd, i.e., oil length.

Thus short oil alkyds are those that contain ≤40% oil, medium oil alkyds are those that contain oil contents of 40 - 50% while long oil alkyds contain >55% oil.

Although excellent clarity is often necessary for topcoats, it is not necessarily a requirement for sealers and for primers and other pigmented coatings. It is therefore useful to know the compatibility properties of various backbone resins.

Akzo 21-1106 is a short oil coconut alkyd available from Akzo Nobel Akzo 11-1135 is a short oil coconut alkyd available from Akzo Nobel Akzo 21-3801 is a long raw castor oil alkyd available from Akzo Nobel Aroplaz 2575X60 is a short oil coconut alkyd available from Reichhold Beckosol 12-035 is a short oil coconut alkyd available from Reichhold Chempol 501-0127 is a medium oil castor oil alkyd available from CCP Chempol 501-3231 is a high solids coconut oil alkyd available from CCP

Duramac 201-1167 is a long oil sunflower oil alkyd available from Eastman

Chemical Co., Kingsport, TN.

Duramac 207-2742 is a chain stopped sunflower oil alkyd available from

Eastman Chemical Co., Kingsport, TN.

Duramac 57-5816 is a long oil sunflower oil alkyd available from Eastman

Chemical Co., Kingsport, TN.

Duramac 52-5205 is a short oil coconut oil alkyd available from Eastman

Chemical Co., Kingsport, TN.

EPS 6560 is a medium oil coconut alkyd available from Engineered

Polymer Systems. The alkyds of Examples 11, 12, and 15 produced clear films. These alkyds were then used to make formulations as described in examples 22 - 24 below.

Resimene 2040 was put into a formulation similar to Example 23. That formulation is given in Table 9 as comparative example 25 below.

Table 9.

Ex 25 - Addition of Resimene 2040 in B9P473B Type Formulation

Item Weight (g)

Xylene 6.55

Butyl Acetate 30.30

PM Acetate 12.28

Solvesso 100 4.09

Ethanol 0.82

Isopropanol 8.19

Methanol 8.19

Isobutanol 4.09

Add with agitation

Aroplaz 2575X60 38.21

Add with agitation

Resimene 2040 49.13

Total 161.85

Viscosity, #2 Zahn Signature Cup @ 80F 13.85 s

Portions of the formulations in Tables 8 and 9 were catalyzed with 3% Cycat 4040 and evaluated for clarity, flow and leveling, and print resistance as detailed in Table 15. The draw downs applied onto Form 7B paper air- dried for 15 minutes and cured at 66C for 10 minutes. Print resistance was evaluated by 6mil draw downs on plate glass, which air-dried for 15 minutes, cured at 66C for 10 minutes, and cooled 5 minutes. Then 2psi and 4psi print tests were applied for 2 hours. Table 10 details the results obtained.

All coatings resulted in clear films. Comparison of the print resistance of Example 23, CMCAB /Melamine blend formulated with Aroplaz 2575X60, to the print resistance of Example 25, Resimene 2040 formulated with Aroplaz 2575X60 shows that the CMCAB /Melamine blend is better for print resistance. As a further example of the improvement in cure of the present invention, panels were developed using the samples of Examples 2 and 3 (See Tables 2 and 3). Examples 26 describe the catalysis of the Example 2 coating which consists of CARBOXYMETHYL CELLULOSE ACETATE BUTYRATE/Melamine (Example 1) and Duramac 207-1205 Coconut oil alkyd with Cycat 4040, a 40% solution of para toluene sulfonic acid. Example 27 describe the catalysis of the Example 3 coating which consists of Resimene 2040 and Duramac 207-1205 coconut alkyd with Cycat 4040, a 40% solution of para toluene sulfonic acid. Examples 28 and 29, describe panel development for comparison of these coatings Para toluene sulfonic acid catalyzed coatings. Examples 30 and 31 describe these same coating examples but catalyzed with Kcure 129B, a methane sulfonic acid catalyst available from King Industries. Examples 32 and 33 detail panels developed utilizing these methane sulfonic acid catalyzed examples.

Example 28, CMCAB /Melamine blend formulated with Duramac 207-1205 Alkyd, shows faster cure response as a sealer resulting in significantly improved sanding; it also shows better spray flow and leveling, better print, and better mar resistance as compared to Example 29, Resimene 2040 formulated with Duramac 207-1205 Alkyd. However, Example 28 results in a less glossy film.

Both Example 32, CMCAB /Melamine blend formulated with Duramac 207- 1205 Alkyd, and Example 33, Resimene 2040 formulated with Duramac 207-1205 Alkyd, catalyzed with Kcure 129B, methane sulfonic acid cure faster than these same products catalyzed with para toluene sulfonic acid; however the panel developed with Example 32, CMCAB /Melamine blend formulated with Duramac 207-1205 Alkyd, results in better initial hardness at the sealer stage, better blister resistance, better flow and leveling, better print resistance, and better slip resistance. Again, however, Example 32, CMCAB /Melamine blend formulated with Duramac 207-1205 Alkyd, results in a less glossy panel.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

I claim:

1. A coating composition, comprising: a carboxyalkyl cellulose ester; a crosslinking resin; and one or more binder resins.

2. The coating composition according to claim 1, wherein the crosslinking resin is at least one member selected from the group consisting of an aminoplast crosslinking resin and a phenolplast crosslinking resin.

3. The coating composition according to claim 2, wherein the carboxyalkyl cellulose ester is a carboxymethyl cellulose ester.

4. The coating composition according to claim 2, wherein the carboxyalkyl cellulose ester is carboxymethyl cellulose acetate butyrate.

5. The coating composition according to claim 1, wherein the crosslinking resin is a melamine resin.