Self-crosslinking water-dilutable binders

Details Self-crosslinking water-dilutable binders Self-crosslinking water-dilutable binders

2001-11-02

2003-12-30

Dawson, Robert (Department: 1712)

Stock material or miscellaneous articles

Composite

Of epoxy ether

C427S372200, C523S416000, C523S417000, C523S424000, C525S405000, C525S500000, C525S510000, C525S526000, C528S118000, C528S123000, C528S162000, C528S250000, C528S254000, C528S259000, C528S421000

Reexamination Certificate

active

06670041

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to water-dilutable binders which are self-crosslinking at room temperature.
BACKGROUND OF THE INVENTION
Film-forming binders based on reaction products of Mannich bases and epoxy resins are described in a series of publications. According to DE-A 20 33 770, 23 20 301, 23 57 045, 24 19 179, 25 41 801, 25 54 080, 27 11 385 and 30 45 251, Mannich bases obtained from polyhydric phenols, secondary amines and formaldehyde are reacted with epoxy resins, it being possible for both the phenols and the epoxy resins to be subjected to modifications of various kinds with, for example, monoblocked diisocyanates, other phenols or metal salts.
As is evident from the cited references, binders of this kind require baking temperatures of around 190° C. for crosslinking, and even then the films by no means meet the automobile industry's practical requirements in terms, for example, of salt spray resistance. Moreover, the crosslinking of these products is accompanied by elimination of formaldehyde and amines, which may lead to a pollution of the environment. The purpose of a large number of the abovementioned modifications is therefore less to improve the film properties, but rather to reduce the amount of elimination products. In the case of modification with monoblocked diisocyanates, for instance, it is explicitly stated in DE-A 25 54 080 that the isocyanate groups contribute little to the crosslinking and serve only to trap liberated amines.
WO 83/00872 discloses cathodically depositable electro-deposition coating binders which are obtained by cocondensation of partially defunctionalized epoxy resins and phenolic resols and simultaneous or subsequent reaction of the epoxide groups with primary or secondary amines. A substantial disadvantage in the preparation of these products lies in the need to prepare the phenolic resols, which is known to involve a considerable amount of time and to result in relatively large amounts of phenol- and salt-containing wastewaters. Moreover, any salt residues in the resin may lead to defects in the course of electrodeposition.
GB-A 2,050,381 discloses cathodically depositable coating compositions which are obtained by mixing epoxy resin-amine adducts and etherified phenol-formaldehyde resins and/or amino resins and heating the mixtures to at least 50° C. A partial condensation of the components is intended to improve the emulsion stability of the protonated products in water, in comparison to simple mixtures of the stated components. In the epoxy resin-amine adducts that are used in accordance with this reference, the amino groups present are substantially tertiary amino groups, since the reaction takes place under conditions which lead to a substantially complete reaction of the amino hydrogens. Because of their structure, products of this kind require baking temperatures of more than 170° C. for adequate crosslinking.
SUMMARY OF THE INVENTION
It has now been found that reaction products of epoxy-amine adducts with formaldehyde and compounds which are able to form condensation resins with formaldehyde may be formulated to give binders which are self-crosslinking at room temperature. The reaction is preferably conducted not between a preformed formaldehyde condensation resin and epoxy-amine adducts but instead with epoxy-amine adducts, formaldehyde resin formers and formaldehyde or a formaldehyde source each separately present in the reaction mixture at the start of the reaction.
The invention accordingly provides water-dilutable binders which are self-crosslinking at room temperature, comprising reaction products ABF of epoxy-amine adducts A and formaldehyde resin formers B selected from phenols B1, (substituted) ureas B2, melamine B3, guanamines B4, and mixtures of said resin formers, with formaldehyde F or compounds which release formaldehyde under the reaction conditions, such as paraformaldehyde or trioxane.
The term “water-dilutable” refers to those binders which—after partial neutralization if appropriate—form stable mixtures with water which do not undergo macroscopic phase separation or sedimentation when stored at room temperature (20° C.) over at least 4 weeks.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The epoxy-amine adducts A are obtained by reacting epoxy resins A1 containing at least 2 epoxide groups per molecule and having a specific epoxide group content SEC of from 1.0 to 5.6 mol/kg with aliphatic amines A2 having from one to twenty, preferably from 4 to 18 carbon atoms and containing at least one primary amino group and, if desired, another primary or tertiary amino group, and, if desired, a compound A3 containing at least one carboxyl group or at least one secondary amino group. The reaction is conducted in such a way that, when it is at an end, epoxide groups can no longer be detected in the reaction mixture.
The epoxy resins A1 which can be used for the invention are commercially available customary diepoxide or polyepoxide compounds, such as are obtained by reaction of polyhydric phenols, especially bisphenol A, or phenol novolaks and epichlorohydrin. If desired it is also possible to use other epoxy resins, based for example on polyols. Products of this kind are known to the skilled worker and are described in large numbers in the literature. For the process of the invention it is preferred to use epoxy resins based on bisphenol A or phenol novolaks having a specific epoxide group content SEC of from 1.0 to 5.6 mol/kg (“epoxide equivalent weight” of from 180 to 1000 g/mol).
Preferred amines A2 are primary monoalkylamines, especially those whose alkyl radical contains 4 or more carbon atoms, or primary alkylenediamines or diamines which in addition to the primary amino group contain a tertiary amino group as well, e.g., a dialkylamino group. As preferred representatives, mention may be made of n-butylamine, isobutylamine, hexylamines, especially n-hexylamine, 2-ethylhexylamine, ethylenediamine and its homologues such as 1,2 and 1,3-diaminopropane, 1,4-diaminobutane, and 1,6-diaminohexane, and also primary-tertiary diamines, such as dimethylaminopropylamine, diethylaminopropylamine and homologues of this series. Particular preference is given to using mixtures of alkylamines and/or alkylenediamines and dialkylamino-alkylamines.
The modifiers A3 are selected from carboxyl compounds and compounds containing at least one secondary amino group.
Preference is given to using, for example, carboxyl-containing adducts of maleic anhydride with unsaturated oils and/or unsaturated hydrocarbon compounds whose anhydride groups have been opened by monoesterification with monohydroxy compounds, where the free carboxyl groups, if desired, in part are reacted with monoepoxide compounds. By means of such modification it is possible to substantially improve the film surface and the flexibility of the films.
The carboxyl compounds of this kind suitable for modifying the epoxy resin-amine adduct are obtained in conventional manner by subjecting maleic anhydride to addition reaction with unsaturated oils, examples being tung oil, linseed oil, dehydrated castor oil, soybean oil, sunflower oil, and similar natural oils. As starting material it is also possible to employ synthetically prepared hydroxyl-free esters of the fatty acids present in the abovementioned oils, and/or of tall oil fatty acids, with polyols. As polyene compounds it is preferred to employ unsaturated, low molar mass hydrocarbon polymers or oligomers for reaction with maleic anhydride. Examples of this class of compound are the so-called polybutadiene oils, viz. liquid oligomers of butadiene with a variety of stereospecific structures or the corresponding oligomers of pentadienes or cyclopentadiene, the use of mixed oligomers also being possible. These compounds normally have molar masses (weight averages MW) of between 400 and 3 000 g/mol. It is of course also possible to employ mixtures of these oligomers in order to form adducts with the maleic anhydride.
The amount of maleic anhydride is chosen such that the carboxyl compound prepar

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