LU85060A1 - THERMOSETTING COATING COMPOSITION - Google Patents

Description

THERMOSETTING COATING COMPOSITION

The present invention relates to a thermosetting coating composition and in particular to a coating composition comprising as a binder a mixture of a saturated hydroxylated polyester, a crosslinking agent of the amino compound type, and a blocked acid catalyst.

It is well known that acid catalysts are frequently used to accelerate the crosslinking reaction of thermosetting compositions.

However, the simple addition of an acid catalyst has the disadvantage of increasing the viscosity during storage and consequently reducing the duration of use of the composition.

In order to overcome this drawback, it was first proposed to use blocked acid catalysts, which consist of the addition product of an organic or inorganic acid with an organic compound, such as amines, the product formed being thermally decomposable. , regenerating the acid at the time of its decomposition. However, this type of product does not allow the compositions to be cooked at reduced temperature, while maintaining good chemical resistance of the coating.

In addition, the presence of an amino compound in the adduct causes unwanted colorations in the finished product.

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It has also been proposed to use difunctional acid compounds blocked in the same manner as above in order to further improve the storage stability of the compositions. However, they have the same disadvantages as the previous catalysts from the point of view of baking temperature and chemical resistance of the coating formed.

It has also been proposed to block the difunctional acid catalysts in another way, for example by forming a pitch adduct; oxime type. However, these types of blocked catalysts no longer make it possible to reduce the firing temperature or to obtain good chemical resistance of the coating.

There is therefore a need for thermosetting coating compositions containing a blocked acid catalyst and making it possible to significantly reduce the baking temperature, while improving the chemical resistance of the coating and maintaining the storage stability properties at their level. usual.

The subject of the present invention is a thermosetting coating composition comprising, as a binder, a saturated hydroxylated polyester, a crosslinking agent of the amino compound type and an adduct of an epoxide and of a difunctional sulfonic acid, which can be baked. at a lower temperature while ensuring good chemical resistance to the coating, in particular when it covers a thick primer on a metal support.

A subject of the invention is also a thermosetting coating composition comprising as a binder a saturated hydroxylated polyester, a crosslinking agent of the amino compound type and a product of addition of an epoxide and of a sulfonic acid having good storage stability properties.

The thermosetting coating composition of the present invention is characterized in that it comprises as a binder a V ^ comprising a saturated hydroxylated polyester, a crosslinking agent of the amino compound type and an adduct of an epoxide and a difunctional sulfonic acid, as a catalyst for the crosslinking reaction.

The crosslinking agent used in the binder mixture of the composition of the invention is generally an amino derivative. As examples of suitable amino derivatives, mention may be made of the reaction products of aldehydes, such as formaldehyde, with substances having one or more amino groups, such as, for example, melamine, urea, dicyan -diamide or else benzoguanamine, and mixtures thereof. Amino compounds modified with alcohols can also be used. As these products have only very low compatibility with the second component of the binder, in this case polyester, it is preferable to use amino derivatives of low molecular weight, having a defined structure as well as better miscibility. with the other component. By way of particularly suitable examples, mention may be made of dimethylolurea, tetramethylol-benzoguanamine, trimethylolmelamine or hexamethylolmelamine or their partially or completely etherified derivatives. However, it is preferred to use hexamethyl melamine etherified with alcohols having from 1 to 4 carbon atoms.

The second component of the binder mixture is a saturated polyester with hydroxyl groups. Generally the hydroxylated index of the polyesters used is between 15 and 200, and generally between 30 and 100.

Among the polyesters which can be used in the composition of the invention, mention may in particular be made of the condensation products of saturated diols and / or higher polyols with aromatic and / or cycloaliphatic dicarboxylic acids free of ethylenic unsaturation, and acids saturated aliphatic dicarboxyls.

Examples of diols which can be used to prepare the polyester include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3- butanediol, 1,4-butanediol, 2,2-dimethylpropane 1,3 diol, 1,6 hexanediol, 2-ethylhexane-1,3-diol, 1,2-cyclohexanediol, 1,4 cyclohexanediol, 1,2-bis (hydroxymethyl) -cyclohexane, 1,3-bis (hydroxymethyl) -cyclohexane, 1,4-bis (hydroxymethyl) - cyclohexane, X-, 8-bis (hydroxymethyl) -tricyclo (dj.2. l.cTj decanes where the values 3,4 or 5 are assigned to X, diethylene glycol, triethylene glycol, dipropylene glycol and tripropylene glycol. Cycloaliphatic diols can be used in their cis or trans form or in as a mixture of the two isomers.

Examples of aromatic dicarboxylic acids or aliphatic cycloaliphatic * there may be mentioned phthalic acid, isophthalic acid, terephthalic "lic, hexahydroterephthalic, tetrahydrophthalic, hexahydrophthalic, hexahydroisophthalic, or endomethylene tetrahydrophthalic endoéthylène, hexachloro-endomethylene-tetrahydrophthalic or tétrabromophatlique.

Cycloaliphatic dicarboxylic acids can be used in their cis or trans form or in the form of a mixture of the 2 isomers.

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As examples of saturated aliphatic dicarboxylic acids, mention may be made of succinic, glutaric, adipic, suberic, sebacic, decanedicarboxylic, 2,2,4 trimethyladipic acids. It is also possible to use unsaturated dicarboxylic acids but in small quantities, such as for example the acids chosen from the group comprising maleic acid, fumaric acid, itaconic or citraconic acid.

In addition to the free dicarboxylic acids, it is also possible to use their lower alcohol esters such as, for example, dimethyl, diethyl or dipropylic esters. If the dicarboxylic acids form anhydrides, these can also be used, such as for example phthalic, hexahydrophthalic, tetrahydrophthalic, succinic, glutaric and maleic anhydrides.

The polyesters obtained from the above-mentioned compounds and used subsequently in the compositions of the invention generally have a molecular weight of between 240 and 4000.

It is also possible to use other types of polyesters in the composition of the invention, in particular those constituted by hydroxylated alkyd resins.

As examples of alkyd resins, mention may be made of the reaction products of diols and / or polyols with aromatic, cycloaliphatic or aliphatic dicarboxylic acids, as well as with fatty acids.

The fatty acids which can be used are chosen from the group comprising caproic, caprylic, pelangonic, lauric, myristic, palmitic, stearic, arachidic, behenic, oleic, linoleic, linolenic acids, and their mixtures in the form of acids obtained from of

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- 6 - natural oils such as linseed, castor, tallow, soy, peanut or coconut oils.

Unsaturated carboxylic acids can also be used, but in small amounts. It is also possible to use synthetic fatty acids, such as for example 2-ethylhexylic acids, 0 (-alkyl-carboxylic acid, isononic acid or mixtures of synthetic fatty acids having from 7 to 9 carbon atoms. Esters and natural oils free acids can also be used in the preparation of alkyd resins.

The two components of the thermosetting binder are subjected to a crosslinking reaction to form a final coating. This reaction <* can be influenced by an acid catalyst.

Although many acid catalysts have already been used to catalyze this type of reaction, the Applicant has unexpectedly found that by using a compound of a difunctional sulfonic acid blocked with a monoepoxy compound, as catalyst , not only did they retain the good storage stability properties thanks to the blocking of the acid, but in addition, this catalyst had the advantage of being able to carry out the crosslinking reaction at a significantly lower temperature.

The catalyst used in the composition is in the form of an adduct between a difunctional sulfonic acid and an epoxy compound.

This type of catalyst also has the advantage of not causing unwanted coloring in the final coating.

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As difunctional sulfonic acids which can be used in the adduct, mention may be made of polyalkylaromatic polysulfonic acids, in particular those having a molecular weight of approximately 500 and comprising at least two alkyl or branched groups and at least two sulfonic acid groups attached to an aromatic ring, their isomers and mixtures thereof.

A typical catalyst can in particular be obtained using a benzenedisulfonic acid substituted by at least two alkyl groups having a total of 20 carbon atoms, such as didecylbenzenedisulfonic acid or tetrapentylbenzenedisulfonic acid. The benzene ring can be substituted by at most 3 sulfonic acid groups and two alkyl groups; in the latter case, the appropriate acids are those in which the 2 alkyl groups together have a total of at least 13 carbon atoms. Although benzene is generally used as aromatic compound, it is also possible to use others having a polycyclic aromatic nucleus, such as, for example, naphthalene, anthracene, phenanthrene, etc. When these types of aromatic compounds are used, several variants exist for the position of the substituents.

In the compositions of the invention, use is preferably made, as a difunctional sulfonic acid, of naphthalene polysulfonic acids ‘substituted by alkyl groups having from 6 to 12 carbon atoms, such as, for example, dinonylnaphthalene disulfonic acid.

The second constituent of the additive product is an epoxy compound such as aliphatic and / or aromatic epoxy resins, for example based on bisphenol A, or an epoxy compound such as glycidic esters of branched fatty acids, glycidic ethers, epichlorohydrin, styrene epoxide, butadiene diepoxide and / or epoxidized polybütadienic oils.

As epoxy compound, use is preferably made of epoxy resins based on bisphenol A, or glycidic esters of branched fatty acids, such as glycidyl versatate.

”The adduct used in the present invention is prepared by mixing the two pure components or in solution, used in a proportion such that there is from 0.1 to 1 sulfonic acid group per epoxy group, and by heating the resulting mixture for 20 to 60 minutes at a temperature between 20 and 150 ° C, preferably between 60 and 80 ° C.

The adduct can be added * to the composition as such or in solution. Generally, an amount of adduct of between 0.1 and 20%, preferably between 0.1 and 5% by weight, relative to the weight of the binder, is used.

The compositions comprising the saturated hydroxylated polyester, the crosslinking agent as well as the blocked catalyst, may contain, in addition to the usual pigments, other additives such as spreading agents as well as possibly other binders. These compositions are applied by * methods known to those skilled in the art, in particular by means of a brush, roller, spray gun or even a soaking bath. They can also be applied using an electrostatic process.

After application, the compositions of the invention are crosslinked by subjecting them to a heat treatment at a temperature of between - 100 and 300 ° C. · One of the advantages of the compositions of the invention lies in the fact that for the same temperature furnace, the residence time is significantly reduced therein. In other words, it is possible, by keeping the same residence time, to reduce the crosslinking temperature.

The compositions of the invention are particularly applicable * for covering metal plates protected against corrosion by a thick layer of primer. By thick layer is meant a thickness greater than 10 ^ / mt. The Applicant has in fact observed that by using the compositions of the invention, coatings having good chemical resistance were obtained, which it was not possible to obtain with the usual coatings.

The following examples are given in order to better illustrate the compositions of the invention but without limiting the scope thereof. Example 1 a) Preparation of the hydroxylated polyester

A mixture comprising 250.6 g of ethylene glycol, 400.6 g of neopentyl glycol, 321.7 g of 1.4 butanediol, 668.5 g of terephthalic acid, 901.1 g was heated to 250 ° C. isophthalic acid and 153.3 g of adipic acid, in the presence of. 2.3 g of dibutyltin oxide. 378 g of water were collected. The product obtained had an acid index of v - between 6 and 12 mgr KDH / gr. It was then diluted in 2300 g of an aromatic solvent (sold under the name SOLVESSO 200).

b) Preparation of the blocked acid catalyst

20 g of a solution of dinonylnaphthalene di-4 were mixed.

- 10 - sulfonic at 55% in isobutanol with 30 g of the glycidic ester of a fatty acid q (branched characterized by an epoxy weight equivalent of 240-250 (product sold by Shell under the name CARDURA E 10 The reaction between these two compounds was exothermic, the mixture was stirred for 30 minutes and then diluted with 50 g of aromatic solvent (sold under the name SOLVESSO 200). The solution obtained contained 0.41 v milliequivalents acid / gr potentially available, c) Preparation of the composition

A paint was prepared containing by weight 44 parts of the polyester prepared in paragraph a) 4.1 parts of commercial hexamethoxymethyl melamine 26 parts of titanium dioxide 25.4 parts of aromatic solvent (SOLVESSO 200) 0.5 parts of blocked acid catalyst prepared in paragraph b).

The viscosity of this paint, measured using the DIN 4 viscosimeter was 80 sec. After 1 week of storage at 40 ° C., a viscosity of 83 sec was measured; and after 2 weeks, 82 sec.

This paint was applied to an aluminum plate 0.6 mm thick and it was subjected to a heat treatment by passing through an oven at 340 ° C for 30 seconds. The peak metal temperature was 232 ° C.

The coating thus obtained had an average thickness of 20 ^^.

The crosslinking and therefore the chemical resistance of the coating was evaluated by the resistance to methyl ethyl ketone: no alteration of the film was observed after 100 double passes with a cloth soaked in methyl ethyl ketone.

Example 2

A hydroxylated polyester and a blocked acid catalyst were prepared in the same manner as that described in Example 1.

The paint composition described in paragraph c) of Example 1 was applied to a 0.75 mm thick galvanized steel plate and it was subjected to a heat treatment by passing through an oven at 340 ° C. for 55 seconds. The peak metal temperature was 232 ° C.

The coating thus obtained was tested from the point of view of chemical resistance to the solvent, according to the method described in Example 1.

No change in the paint film was detected after 100 double passes with the cloth soaked in methyl ethyl ketone.

Example 3

A 0.75 mm thick galvanized steel plate was covered with a layer of paint, the composition of which was given in paragraph c) of Example 1.

This paint was subjected to heat treatment by passing through an oven at 340 ° C for a period of 45 seconds. The peak temperature of the metal was 225 ° C.

On this paint, serving as a primary coating, the same paint composition was then applied as that described above. It was subjected to heat treatment by passage through an oven.

The average total thickness of the coating after heat treatment was 40m,

The operating conditions of the heat treatment as well as the properties of the coating obtained are indicated in Table 1 below.

By way of comparison, a layer of paint obtained with the same polyester and the same crosslinking agent as those described in Example 1 was applied to the primary paint, except that a blocked acid catalyst was used. by the adduct between para-toluene sulfonic acid and the glycidic ester of a U-branched fatty acid characterized by an epoxy weight equivalent of 240-250 (product sold by Shell under the name CARDURA E 10). The catalyst solution contained 0.526milliequivalent acid / gr potentially available. This catalyst is monofunctional.

The paint composition included (quantities expressed in part by weight) 44 parts of the polyester prepared in Example 1, paragraph a) 4.1 parts of commercial hexamethoxymelamine 26 parts of titanium dioxide 25.4 parts of aromatic solvent (SOLVESSO 200) 0.388 parts of the blocked monofunctional acid catalyst.

This coating was subjected to heat treatment by passage through an oven. The operating conditions of this treatment as well as the properties of the coating obtained are indicated in Table I below.

Claims (9)

1. A thermosetting coating composition characterized in that it comprises as a binder a mixture comprising a saturated hydroxylated polyester, a crosslinking agent of the amino compound type and an adduct of an epoxy compound and of a difunctional sulfonic acid in as a catalyst for the crosslinking reaction. 2. Composition according to claim 1 characterized in that it comprises from 0.1 to 20%, preferably from 0.1 to 5% by weight, based on the binder, of the adduct between the difunctional sfulfonic acid and the epos ^ compound. • 1 - 14 - 'Μ 3. Composition according to any one of claims 1 and 2, characterized in that the adduct comprises an amount of sulfonic acid such that there is from 0.1 to 1 acid group per epoxy group. 4. Composition according to any one of claims 1 to 3, characterized in that the difunctional sulfonic acid used comprises at least two alkyl radicals · linear or branched and at least two sulfonic acid groups attached to an aromatic ring. 5. Composition according to claim 4 characterized in that the difunctional sulfonic acid is chosen from the group of naphthalene polysulionic acids substituted by alkyl radicals having from 6 to 12 carbon atoms. 6. Composition according to claim 5 characterized in that the difunctional sulfonic acid is dinonylnaphthalene disulfonic acid. 7. Composition according to any one of claims 1 to 6 characterized in that the epoxy compound used in the adduct is chosen from the group comprising epoxy resins based on bisphenol A and glycidic esters of branched fatty acids in alpha position. 8. Composition according to any one of the preceding claims, characterized in that it comprises a saturated hydroxylated polyester, a crosslinking agent of the amino compound type and 0.1 7. by weight, based on the binder, of a catalyst formed. by the adduct between dinonylnaphthalene disulfonic acid and the glycidic ester of a fatty acid branched in position 0 (having an epoxide weight equivalent of 240-250. 9. Thermosetting coating obtained with the compositions described in any one of the preceding claims.