Water-dilutable binders, containing latent primary amino groups,

Details Water-dilutable binders, containing latent primary amino groups, Water-dilutable binders, containing latent primary amino groups,

1987-01-23

1988-08-09

Nielsen, Earl

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From phenol, phenol ether, or inorganic phenolate

523415, 523417, 528121, 528229, 528407, C08G 5956

Patent

active

047629037

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to water-dilutable binders for cationic electrocoating finishes, which binders contain latent primary amino groups and are based on reaction products of epoxy resins and polyamines, which contain at least one blocked primary amino group, and, if required, further primary and/or secondary amines.
Cationic electrocoating is a coating process frequently used, in particular, for priming, and in which water-dilutable synthetic resins carrying cationic groups are applied onto electrically conductive articles with the aid of direct current.
The use of modified epoxy resins as binders for cationic electrocoating finishes is known. Water-dilutable modified epoxy resins can be obtained, for example, by reacting polyepoxide compounds with amines and, if appropriate, further modifiers (U.S. Pat. No 4,104,147).
Modified epoxy resins prepared in this manner contain secondary and tertiary amino groups. It is assumed that the low basicity of the tertiary amino groups, in particular, is responsible for the fact that the binders obtained from reaction products of polyepoxide compounds with amines are only poorly dispersible in water and give aqueous systems having a low pH.
In order to overcome these difficulties, attempts were made to introduce primary amino groups into the epoxide binders. This objective was achieved by reacting polyepoxide compounds with a (poly)ketimine containing secondary amino groups or containing hydroxyl groups, and then liberating the protected primary amino group or groups by hydrolysis. (U.S. Pat. Nos. 3,947,339, 4,017,438, 4,104,147 and 4,148,772).
It has been found that the water dispersibility and the electrical deposition properties of the modified epoxy resins are substantially more advantageously affected by increasing the content of primary amino groups than by increasing the content of tertiary amino groups.
Since low molecular weight amines have an adverse effect on the surface properties of the electrically deposited layer, care should be taken to ensure that the binders are free of unconverted amine derivatives.
When primary amino groups are introduced via ketimines containing secondary amino groups, tertiary amino groups, which are not very advantageous, are formed, whereas when ketimines containing hydroxyl groups are used, lower reactivity and selectivity have to be accepted as disadvantages.
It is an object of the present invention to provide water-dilutable modified epoxy resins which have a very high content of primary amino groups and are free of low molecular weight amines.
This object is achieved, according to the invention, if the binders are prepared from polyamine which contains not only a sterically hindered primary amino group but also at least one further primary amino group, and, if required, further liberated by hydrolysis.
The particular advantages achieved with the invention are that, in addition to the raw material base being extended, the component containing the latent primary amino groups is linked to the epoxy resin via a sterically hindered primary amino group, with the result that strongly basic secondary amino groups containing an active H atom are formed, and rapid and quantitative conversions are achieved.
All compounds which contain at least one reactive epoxide group, preferably two reactive epoxide groups, can be employed as component A.
The molecular weight of component A is preferably in the range from 350 to 2000.
Preferred epoxy resins are polyglycidyl ethers of polyphenols, these ethers being prepared from polyphenols and epihalohydrins. For example, the following compounds can be used as polyphenols: 1,1-bis-(4-hydroxyphenyl)-ethane, 1,1-bis-(4-hydroxyphenyl)-isobutane, 2,2-bis-(4-hydroxy-tert.-butylphenyl)-propane, bis-(2-hydroxynaphthyl)-methane, 1,5-dihydroxynaphthalene and phenolic novolak resins.
Polyglycidyl ethers of polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, pentane-1,5-diol, hexane-1,2,6-triol, glycerol and 2,2-bis-(4-hydroxy

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