Metal salts of phosphoric acid esters as cross linking...

Details Metal salts of phosphoric acid esters as cross linking... Metal salts of phosphoric acid esters as cross linking...

1999-11-09

2002-01-01

Wood, Elizabeth D. (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Organic compound containing

C502S150000, C502S156000, C502S159000, C502S161000, C502S171000, C502S172000, C525S438000, C525S533000, C525S534000, C525S934000, C528S087000, C528S088000, C528S089000, C528S092000, C528S220000, C528S236000, C528S237000, C528S242000

Reexamination Certificate

active

06335304

ABSTRACT:

INTRODUCTION
The present invention is directed to a catalyst for the epoxy reaction with carboxyl and or anhydride functional compounds for use in coating, sealant, adhesive and casting applications. More particularly, the present invention is directed to the use of zinc or tin (II) salts of a mono- or di-ester of phosphoric acid (also referred to as alkyl acid phosphate) having the structure:
(RO)
n
—P(═O)—(OH)
m
wherein n+m═3 and n is between 2 to 1 preferably between 1.7 to 1.2 and the metal counter ion Zn or Sn (II) is in a molar equivalent ratio of 0.7 to 1.5 per mole of the alkyl acid phosphate. The use of Zn or Sn(II) alkyl acid phosphate as a catalyst in the epoxy-carboxylanhydride reaction improves the stability of the reactants at room temperature and avoids yellowing or blistering in the coating produced. Furthermore, the improved stability of the reactants in the presence of the catalyst enables a single packaged product for the epoxy-carboxy/ahydride mixture.
BACKGROUND OF THE INVENTION
It has been long recognized that epoxy compounds react with carboxylic acids or with anhydrides. It is also known that this reaction can be catalyzed. Antoon and Koenig (
J. Polym. Sci
., Polym. Chem. Ed. (1981) 19(2):549-70) studied the mechanism of catalysis by tertiary amines of the reaction of anhydrides with epoxy resins, typically a glycidyl ether of bisphenol. They pointed out that it is the quaternary ammonium salt zwitterion that initiated the polymerization reaction. Matejka and Dusek studied the reaction of phenylglycidyl ether model compounds with caproic acid in the presence of a tertiary amine as the catalyst (
Polym. Bull
. (1986) 15(3):215-21). Based on their experimental data, they suggested that this is an addition esterification process.
Metal salts and amines have been used as catalysts for the epoxycarboxyl/anhydride reaction. For example, 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), a strong basic amine and its salts are being promoted as catalysts for epoxy-carboxyl/anhydride polymer systems. It is known that the salts of amines usually improved the pot life of such polymer systems. Whittemore et. al. (U.S. Pat. No. 3,639,345) disclosed thermosetting resins using an epoxy functional bisphenol A and a trimellitic anhydride ester with an amine, an imidazole or an aminoalkyl phenol, as the catalyst.
Metal salts or Lewis acid catalysts are also promoted for epoxy resins. The metal salts has found applications as catalysts for epoxycarboxyl/anhydride coatings. The catalytic effect of metal salts was recognized by Connelly et. al. (ZA 6,907,152) who described the use of zinc acetate, chromium acetate, iron octoate, zinc naphthenate, cobalt naphthenate and manganese naphthenate as catalysts. Metal salts of Mg, Ca, Sr, Ba, Zn, Al, Sn and Sb have been disclosed by Lauterbach (U.S. Pat. No. 4,614,674) as catalysts in combination with waxes as matting agents for powder coatings. Wright et. al. disclose (U.S. Pat. No. 4,558,076) a fast curing coating formulation comprising a carboxyl functional polymer, a tertiary amine, a polyepoxide and an Al, Ti, or Zn alkoxide or complex as the catalyst.
A major problem with the known catalysts is the poor stability of the combination of the epoxy and carboxyl/anhydride reactants at ambient room temperature. The increase in viscosity requires the epoxy and the carboxyl/anhydride compounds to be formulated into two separate packages. A further problem is the yellowing tendency of amines during the bake or heating cycle. In addition, it is known that the use of amines result in films that are sensitive to humidity leading to blistering of the film. It would be desirable to have a catalyst that does not require the separate packaging of epoxy and carboxyl/anhydride reactants and does not cause yellowing or sensitivity to humidity leading to blistering
Metal salts such as zinc carboxylates have been shown to be effective catalysts in the above referenced patents. However, the problem with di and polyvalent metal salts is salt formation with the carboxyl groups of the reactant through ionic crosslinking leading to an instant increase in viscosity or gelation. Although covalent bonds are not formed in this process, this reaction can lead to very highly viscous formulations with poor flow quality resulting in poor film properties.
A class of metal alkyl acid phosphates which effectively catalyze the reaction of epoxy-carboxyl/anhydride have been developed. The use of these catalysts in the coating process not only reduce yellowing, but also provided excellent room temperature stability and excellent humidity resistance. The improved stability with the use of the metal alkyl acid phosphates of the invention provides for the formulation of a single packaged product.
SUMMARY OF THE INVENTION
The present invention provides a metal (M) alkyl acid phosphate catalyst wherein the alkyl acid phosphate has the formula:
(RO)
n
—(P═O)—(OH)
m
and wherein:
a. each R is selected from the group consisting of:
a C
1
to C
18
alkly, cycloalkyl, or aryl;
a linear or branched C
6
to C
18
alkyl substituted with —(O—CH
2
—CH
2
—)
o
or —(O—CH—CH
3
—CH
2
—)
p
, wherein o or p is from 1 to 20; and
a &bgr;-hydroxyethyl compound, R′—X—CH
2
—CH—OH—CH
2
—, wherein R′ is a C
6
to C
18
alkyl or cycloalkyl or aryl, X is either —CH
2
—, —O— or —COO—;
b. n+m=3 and n is between 2 to 1; and
c. M is Zn or Sn (II) in a mole equivalent of 0.7 to 1.5 moles per mole of alkyl acid phosphate.
When R is a linear or branched alkyl substituted with —(O—CH
2
—CH
2
—)
o
or —(O—CH—CH
3
—CH
2
—)
p
, it may be the reaction product of a C
6
to C
18
alcohol with ethylene oxide or propylene oxide. When R is a &bgr;-hydroxyethyl compound, it may be the reaction product of an epoxide with phosphoric acid to provide R′—X—CH
2
—CH—OH—CH
2
—, wherein R′ is an alkyl or cycloaliphatic or aromatic radical with between C
6
to C
18
carbons, X is —CH
2
—, —O—, or —COO—. The length of the R or R′ chain controls the solubility of the compound in solvents and the compatibility of the compound with other resins.
The catalysts of the present invention are prepared by reacting a zinc or tin (II) alkoxide, oxide or carboxylate with an alkyl or aryl phosphoric acid. The metal alkyl or aryl acid phosphates are useful for catalyzing the reaction between an epoxy compound and a carboxyl compound selected from the group consisting of a carboxylic acid and an anhydride.
LIST OF REFERENCES
1. Antoon and Koenig,
J. Polym. Sci
., Polym. Chem. Ed. (1981) 19(2):549-70.
2. Matejka and Dusek,
Polym. Bull
. (1986) 15(3):215-21.
3. Wright et. al, U.S. Pat. No. 4,558,076.
4. Whittemore et. al. U.S. Pat. No. 3,639,345.
5. Connelly et. al. ZA 6,907,152.
6. Lauterbach, U.S. Pat. No. 4,614,674.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a catalyst, a metal (M) salt of an alkyl acid phosphate with the formula:
(RO)
n
—(P═O)—(OH)
m
wherein:
a. each R is selected from the group consisting of:
i) a C
1
to C
18
alkyl, cycloalkyl, or aryl;
ii) a linear or branched C
6
to C
18
alkyl substituted with —(O—CH
2
—CH
2
—)
o
or —(O—CH—CH
3
—CH
2
—)
p
, wherein o or p is from 1 to 20; and
iii) a &bgr;-hydroxyethyl compound, R′—X—CH
2
—CH—OH—CH
2
—, wherein R′ is a C
6
to C
18
alkyl or cycloalkyl or aryl, and X is either —CH
2
—, —O— or —COO—;
b. n+m=3 and n is between 2 to 1; and
c. M is Zn or Sn (II) in a mole equivalent of 0.7 to 1.5 moles per mole of alkyl acid phosphate.
When R is a linear or branched alkyl substituted with —(O—CH
2
—CH
2
—)
o
or —(O—CH—CH
3
—CH
2
—)
p
, it may be the reaction product of a C
6
to C
18
alcohol with ethylene oxide or propylene oxide. When R is a &bgr;-hydroxyethyl compound, it may be the reaction product of an epoxide with phosphoric acid to provide R′—X—CH
2
—CH—OH—CH
2
—, wherein R′ is an alkyl or cycloaliphatic or aromatic radical with between C
6
to C
18
carbons, X is —CH
2
—, —O— or —COO—. The length of the R or R′ chain controls the solub

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