Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-02
2001-08-14
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S428000
Reexamination Certificate
active
06274649
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an aqueous binder dispersion for cationic electrodeposition coatings based on modified epoxy resins, and to a process for the preparation and use of the dispersion.
Cationic electrodeposition coating is a common coating process, especially for priming, in which water-dilutable synthetic resins carrying cationic groups are applied to electroconductive elements with the aid of direct current.
The use of modified epoxy resins as binders for cationic electrodeposition coatings is known (U.S. Pat. Nos. 4,104,147; 4,260,720; 395,364; 4,268,542).
The modified epoxy resins available hitherto for use in cationic electrodeposition coatings have only poor compatibility with aliphatic hydrocarbons, their elasticity is unsatisfactory, and they give films which cannot easily be overcoated and whose thickness should be further increased.
EP 0 256 020 discloses water-dilutable binders for cationic electrodeposition coatings. In order to prepare the binders, a diepoxide compound, if desired together with at least one monoepoxide compound, is converted to an epoxy resin in a polyaddition reaction carried out at from 100 to 195° C. which is initiated by an initiator which reacts in a monofunctional manner and carries either an alcoholic OH group, a phenolic OH group or an SH group, and the epoxy resin is subsequently modified by means of primary and/or secondary amines or salts thereof and/or the salt of a tertiary amine, a sulfide/acid or phosphine/acid mixture and, if desired, also with a polyfunctional alcohol, a polycarboxylic acid, a polysulfide or a polyphenol.
In order to reduce the viscosity, solvents here must be added before or during addition of the amines. Accordingly, the high solvent content and low solids content are disadvantageous. In particular, the addition of solvents before/during addition of the amines means that excess solvent must be removed again after completion of the preparation of the binder dispersion.
The object of the present invention is accordingly to develop novel binder dispersions based on modified epoxy resins which do not have the abovementioned disadvantages. In particular, the dispersions should have a low solvent content. In particular, the aim is to obviate the need for distillative removal of solvents after preparation of the dispersion.
DETAILED DESCRIPTION OF THE INVENTION
This object is achieved in accordance with the invention by an aqueous binder dispersion for cathodic electrodeposition coatings based on modified epoxy resins containing ammonium groups which is obtainable
A) by reacting
I. a precursor which can be prepared, preferably at temperatures of from 120 to 180° C., particularly preferably from 125 to 150° C., from
a) a diepoxide compound or a mixture of diepoxide compounds and
b) an aromatic or aliphatic compound, preferably containing hydroxyl, carboxyl, phenol and/or thiol groups, or a mixture of such compounds, with reaction of the phenolic hydroxyl groups with epoxide groups,
II. with at least one organic amine or mixture of organic amines at a feed temperature which is reduced to between 60 and 130° C., preferably between 90 and 1150C, to give an epoxide/amine adduct,
B) subsequently or simultaneously reacting the secondary hydroxyl groups with epoxide groups of the epoxide/amine adduct prepared in step A) at temperatures of from 110 to 150° C., preferably at about 130° C., if desired with addition of a catalyst,
C) adding a crosslinking agent, preferably solvent-free, or a mixture of various crosslinking agents, at a temperature of<150° C., preferably 90-130° C.,
D) if necessary neutralizing the mixture, preferably by addition of acids, at temperatures of from 90 to 110° C., and
E) dispersing the mixture obtained in steps A to D in water.
The novel binder dispersions can be obtained from readily accessible starting materials and are distinguished by good compatibility with aliphatic hydrocarbons and high elasticity.
It has been found that the above reaction sequence enables the use of viscosity-reducing solvents to be substantially avoided, and that the resultant binder dispersions surprisingly have an excellent particle size and good sedimentation stability. In addition, it has been found, surprisingly, that the novel binders enable the preparation of aqueous dispersions having high solids contents of from 35 to 45% at the same time as adequately low viscosity.
A high solids content is desirable for economic reasons. For a given reactor size, it allows a high solids yield per production batch to be achieved or, in other words, the production costs per kg of solids can be reduced at high solids contents. However, the solids content cannot be increased to an unlimited extent, since the dispersion must remain of sufficiently low viscosity for the subsequent processing steps, such as, for example, filtration. Experience has shown that the upper limit is a flow viscosity of 25 seconds in a DIN 4 cup.
It is a routine matter to the person skilled in the art to modify the viscosity of an organic binder after it has been protonated by means of acid and dispersed in water. This means that the viscosity of the binder in its organic, non-aqueous state is not necessarily the same as the viscosity in its water-dispersed state. In electrodeposition coating binders, two extreme cases can be observed:
High-viscosity resins can produce both low-viscosity and high-viscosity aqueous dispersions for a given solids content. This also applies to low-viscosity resins. The determining factors are of a complex nature and are generally not fully understood, even by the person skilled in the art. To this extent, the low viscosities of the novel binders with their relatively high solids contents were surprising.
Their use in cationic electrodeposition coatings results in the deposition of thick films which can be readily overcoated. It has been found that the use of component b results in both an increase in elasticity and an increase in the thickness of the deposited films.
Component a in precursor I can be any compound containing two reactive epoxide groups and having an epoxide equivalent weight of below 1000, particularly preferably below 500.
Particularly preferred epoxide compounds are polyphenol diglycidyl ethers prepared from polyphenols and epihalohydrins. Examples of polyphenols which can be employed are the following:
Very particularly preferably: bisphenol A and bisphenol F. Particularly preferably: 1,1-bis(4-hydroxyphenyl)-n-heptane. In addition, 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butylphenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene and phenolic novolak resins are also suitable.
Preferred epoxide compounds are diglycidyl ethers of polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol and bis(4-hydroxycyclohexyl)-2,2-propane.
It is also possible to use diglycidyl esters of polycarboxylic acids, such as, for example, oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, dimerized linolenic acid, etc. Typical examples are glycidyl adipate and glycidyl phthalate.
Also suitable are hydantoin epoxides, epoxidized polybutadiene and diepoxide compounds obtained by epoxidation of an olefinically unsaturated alicyclic compound.
Component b of the precursor I can be an aromatic or aliphatic compound which contains a hydroxyl, carboxyl, phenol or thiol group, or a mixture of such compounds, and reacts in a monofunctional manner with respect to epoxide groups under the reaction conditions prevailing during the preparation of the novel modified epoxy resins.
Component b is preferably a compound of the general formula R
1
—OH, where R
1
can have the following meaning:
R
2
=H, alkyl (preferably having 1 to 20 carbon atoms, particularly preferably t-butyl, nonyl or dodecyl),
R
3
-O- (preferably in the p-position
Grosse-Brinkhaus Karl-Heinz
Heimann Ulrich
Herning Thierry
Jouck Walter
Ott Gunther
Aylward D.
BASF Coatings AG
Dawson Robert
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