Method of priming or one-coat painting of plastics using water-borne paints

The invention relates to a method of priming or one-coat painting of plastics using water-borne paints which comprises employing a water-borne paint which contains an at least partially protonated product of the reaction of PA1 (A) a butadiene- and acrylonitrile-based copolymer containing primary and/or secondary amino groups, or a mixture of such copolymers, and PA1 (B) an organic compound which has a number average molecular weight of from 140 to 10,000 and contains, on statistical average, at least 1.5 epoxide groups per molecule, or a mixture of such organic compounds.

The invention relates to a method of priming or one-coat painting of 
plastics using water-borne paints, and to the use of a water-borne paint 
for priming or one-coat painting of plastics. 
Plastics are increasingly used in virtually all areas, in particular in 
automobile production. In motor vehicles, the aim is for there to be no 
differentiation between the plastic parts and the metallic parts of the 
body, either optically or through lower resistance to stone chipping, 
weathering, etc. In order to achieve this, attempts have been made to 
paint the plastic parts so that there is no differentiation between them 
and the metallic parts of the body with respect to appearance and 
resistance to stone chipping, weathering, etc. However, simple overcoating 
using the paints employed for the metallic parts is unsuccessful due to 
adhesion problems and/or poor low-temperature impact resistance and/or 
poor resistance to stone chipping. In order to overcome these problems, 
plastic parts are painted with a primer, which can then be overcoated with 
a top coat. For ecological and economic reasons, it is desired to employ 
water-borne paints for the primer. When water-borne paints are used for 
priming of plastics, poor notched impact strength and/or poor adhesion 
between the substrate and primer, in particular between the primer and the 
top coat applied thereto, are repeatedly observed. 
The object of the present invention is to provide water-borne paints which 
are suitable for priming or one-coat painting of plastics. These paints 
Should allow, in particular, plastics to be primed in such a manner that 
no, or greatly reduced, problems occur with respect to low-temperature 
impact resistance and/or adhesion. 
This object is achieved, surprisingly, by a method of priming or one-coat 
painting of plastics using water-borne paints which comprises employing a 
water-borne paint which contains an at least partially protonated product 
of the reaction of 
(A) a butadiene-acrylonitrile copolymer having an acrylonitrile content of 
from 5 to 45% by weight and a butadiene content of from 55 to 95% by 
weight which contains, per molecule, on average from 1.4 to 3.0 primary 
and/or secondary amino groups, and optionally tertiary amino groups, and 
has a number average molecular weight of from 500 to 15,000, or a mixture 
of such butadiene-acrylonitrile copolymers, and 
(B) an organic compound which has ia number average molecular weight of 
from 140 to 10,000 and contains, on statistical average, at least 1.5 
epoxide groups per molecule, selected from the group comprising 
glycidyl ethers of aliphatic diols, 
glycidyl ethers of polyphenols, 
aromatic epoxy resins obtainable by allowing the abovementioned glycidyl 
ethers to react with a polyphenol and reacting the resultant product with 
epichlorohydrin, 
glycidyl ethers of polyols obtainable by polymerization of ethylene oxide, 
propylene oxide, tetrahydrofuran or other cyclic ethers, or a mixture of 
such organic compounds, 
where components (A) and (B) are employed in the preparation of the 
reaction product in such amounts that from 1.05 to 20 equivalents of 
reactive amine hydrogen atoms from component (A) are present per 
equivalent of epoxide groups from component (B). 
Suitable compounds for component (A) are butadiene-acrylonitrile copolymers 
containing from 5 to 45% by weight, preferably from 10 to 30% by weight, 
of acrylonitrile and from 55 to 95% by weight, preferably from 70 to 90% 
by weight, of butadiene and containing, per molecule, on average 1.4-3.0 
primary and/or secondary amino groups, and, if appropriate, tertiary amino 
groups. The number average molecular weight of the copolymers is 
advantageously 500-15,000, preferably 2,000-8,000. 
The copolymers containing amino groups can be obtained, for example, by 
reacting butadiene-acrylonitrile copolymers containing carboxyl groups 
with diamines. Such butadiene-acrylonitrile copolymers containing amino 
groups are commercially available (for example HYCAR.RTM. ATBN 1300 X 16, 
1300 X 21 and 1300 X 35). 
In addition, butadiene-acrylonitrile copolymers containing amino groups can 
be prepared by partial hydrogenation of butadiene-acrylonitrile copolymers 
or by the addition reaction of primary amines with butadiene-acrylonitrile 
copolymers containing epoxide groups. 
It is also possible to employ mixtures of butadiene-acrylonitrile 
copolymers containing primary and/or secondary amino groups as component 
(A). 
As component (B), organic compounds which have a number average molecular 
weight of from 140 to 10,000 and contain, on statistical average, at least 
1.5, preferably 1.5 to 3.0, particularly preferably 2.0, epoxide groups 
per molecule are employed. It is also possible to employ mixtures of 
compounds of this type as component (B). 
As component (B), glycidyl ethers of aliphatic diols, such as butanediol or 
hexanediol, or glycidyl ethers of polyphenols containing, on statistical 
average, at least two hydroxyl groups per molecule are preferably 
employed. Examples of suitable polyphenols are 
2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 
4,4'-dihydroxybenzophenone,4,4'-dihydroxyphenyl sulfone, 
1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxyphenyl)isobutane, 
2,2-bis(4-hydroxy-tert.-butylphenyl) propane, 
bis(2-hydroxynaphthyl)methane and 1,5-dihydroxynaphthalene. 
In some cases, it is desirable to employ aromatic epoxy resins having a 
relatively high molecular weight as component (B). These can be obtained 
by reacting the abovementioned diglycidyl ethers with a polyphenol, for 
example 2,2-bis(4-hydroxyphenyl)propane, and then further reacting the 
resultant products with epichlorohydrin to give polyglycidyl ethers. 
In addition, diglycidyl ethers of polyols, as obtainable, for example, by 
polymerization of ethylene oxide, propylene oxide, tetrahydrofuran or 
other cyclic ethers, are suitable as component (B). 
To prepare the reaction products to be employed according to the invention, 
components (A) and (B) are generally employed in such amounts that from 
1.05 to 20, preferably from 1.2 to 4.0, equivalents of reactive amine 
hydrogen atoms of component (A) are present per equivalent of epoxide 
groups of component (B). 
Components (A) and (B) are expediently reacted with one another in an 
organic solvent or solvent mixture which is inert towards both amino 
groups and epoxide groups, and at reaction temperatures of 
20.degree.-150.degree. C., preferably 50.degree.-110.degree. C. When the 
epoxide-amine reaction is completed, all or some of the amino groups can 
be neutralized using acids, and the reaction product protonated in this 
way can then be dispersed in water. The reaction product can also be added 
to a water/acid mixture. Organic solvents can then be removed from the 
resultant dispersions by distillation. 
Inorganic and organic acids can be employed for the protonation of the 
reaction products to be employed according to the invention. Preference is 
given to organic acids, such as, for example, formic acid, acetic acid, 
propionic acid or lactic acid. 
The reaction products to be employed according to the invention expediently 
have amine numbers of from 25 to 170, preferably from 40 to 100, mg of 
KOH/g of solid. 
The aqueous dispersions, which can be prepared in the above-described 
manner, of the products, to be employed according to the invention, of the 
reaction of components (A) and (B) can in principle be added to any one- 
or multicomponent water-borne paint which is suitable for priming or 
one-coat painting of plastics. 
The reaction products to be employed according to the invention are 
preferably employed in one- or two-component water-borne paints which 
contain a water-dilutable epoxy resin or a mixture of water-dilutable 
epoxy resins in combination with a crosslinking agent or a mixture of 
crosslinking agents. Water-dilutable epoxy resins are known and 
commercially available (cf., for example, the epoxy resins DOW DER 662 
(Dow Chemicals) and Beckopox EP 384 (Hoechst AG), and the patent documents 
EP-A-272 595, EP-A-81 163, EP-A-346 742, DE-A-26 59 989, DE-A-26 022 22, 
DE-A-26 59 928, DE-A-26 02 221, DE-A-26 02 220, DE-A-26 02 255 and DE-A-23 
32 165). Examples of water-dilutable epoxy resins which can be employed 
are water-dilutable aliphatic, cycloaliphatic or aromatic epoxy resins of 
the glycidyl ether or glycidyl ester type. The water-dilutability of the 
epoxy resins can be achieved, for example, by adding suitable emulsifiers 
and/or by chemical modification of the epoxy resins (for example 
incorporation of hydrophilic molecule segments). A preference is given to 
water-dilutable epoxy resins based on polyglycidyl ethers, preferably 
diglycidyl ethers of polyphenols, preferably diphenols, in particular 
bisphenol A. The epoxy resins employed generally have number average 
molecular weights of from 140 to 5,000. However, it is also possible to 
employ epoxy resins having higher number average molecular weights. In 
principle, the crosslinking agents employed can be any crosslinking agents 
which are suitable for water-dilutable epoxy resins. 
However, it is preferred to employ crosslinking agents containing primary 
and/or secondary amino groups. Examples of crosslinking agents of this 
type are: aliphatic polyamines (for example ethylenediamine, 
diethylenetriamine, triethylenetetramine and dipropylenetriamine), 
cycloaliphatic diamines (for example 
3,3'-dimethyl-4,4'-diaminodicyclohexylmethane and isophoronediamine), 
amino-functional, hydrogenated heterocyclic compounds (for example 
N-aminoethylpiperazine) and polyamidoamines, in particular polyamidoamines 
of dimeric fatty acids. 
A preferred crosslinking agent is the product of the reaction of bisphenol 
A diglycidyl ether, isophoronediamine and a polyether-polyol, such as, for 
example, polyethylene glycol. Crosslinking agents of this type are 
commercially available as "Beckopox special curing agent EH 623" (Hoechst 
AG) and are described in EP-A-605. 
It is preferred to formulate the paints which contain a water-dilutable 
epoxy resin as binder and a crosslinking agent containing primary and/or 
secondary amino groups, as two-component systems. It is expedient here to 
prepare one component from the epoxy resin and the protonated reaction 
product and the second component from the crosslinking agent containing 
primary and/or secondary amino groups, if desired together with pigments 
and/or fillers. The component containing the epoxy resin and the 
protonated reaction product generally has a pH of &lt;7.0, and the component 
containing the crosslinking agent containing primary and/or secondary 
amino groups generally has a pH of &gt;7.0. The two components are mixed just 
before application. 
The term "paint" in this description always, unless expressly stated 
otherwise, refers to the complete paint, ie, in two-component systems, the 
paint obtained after mixing the two components. 
The reaction products to be employed according to the invention should be 
incorporated into the water-borne paints in such amounts that the paints 
contain from 5 to 50% by weight, preferably from 10 to 20% by weight, of 
the reaction product, the % by weight data being based on the total amount 
of binders and, if used, crosslinking agents present in the paint. 
Particularly good results are obtained if the amount of reaction product 
employed, the amount of amino-containing crosslinking agent employed and 
the amount of epoxy resin employed are selected so that all 
epoxide-reactive secondary and/or primary amino groups present in the 
reaction product and in the crosslinking agent can react with epoxide 
groups during curing of the paint. 
In addition to the reaction product to be employed according to the 
invention, binders and, if desired, crosslinking agents, it is of course 
also possible for the water-borne paints to contain further conventional 
additives, such as, for example, organic solvents, flow-control agents, 
light stabilizers, rheology aids, pigments, fillers, catalysts, etc. 
The water-borne paints in question generally contain, in the ready-for-use 
state, from 30 to 80% by weight, preferably from 45 to 70% by weight, of 
water, from 0 to 50% by weight, preferably from 0 to 10% by weight, of 
organic solvents, from 1.0 to 25% by weight, preferably from 2 to 10% by 
weight, of the reaction product to be employed according to the invention, 
from 5 to 50% by weight, preferably from 10 to 40% by weight, of binders, 
from 1 to 40% by weight, preferably from 3 to 10% by weight, of 
crosslinking agents, from 0 to 40% by weight, preferably from 5 to 25% by 
weight, of pigments and/or fillers and from 0 to 10% by weight of other 
additives, such as, for example, catalysts, thickeners, flow-control 
agents, etc, the percent by weight data being based on the total recipe of 
the paints in the ready-for-use state ( ie, for example, at spraying 
viscosity). 
Since plastics are generally temperature-sensitive, the water-borne paints 
must generally be cured at temperatures of up to 100.degree. C. in the 
case of thermoplastics and up to 140.degree. C. in the case of thermosets. 
Water-borne paints which contain the reaction products to be employed 
according to the invention can in principle be used for priming or 
one-coat painting of all plastics. Examples of suitable plastics are: ABS, 
AMMA, ASA, CA, CAB, EP, UF, CF, MF, MPF, PF, PAN, PA, PC, PE, HDPE, LDPE, 
PETP, PMMA, PP, PS, SB, PUR, PVC, RF, SAN, PP-EPDM and UP (abbreviations 
in accordance with DIN 7728 T1). Preferred plastic substrates are: 
polycarbonate, polypropylene-EPDM and polyamide. The plastics to be 
painted may of course be polymer blends, modified plastics or 
fiber-reinforced plastics. In many cases, it is expedient to pretreat the 
plastics to be painted, before painting, using suitable methods (for 
example flame treatment, corona treatment, coating with an adhesion 
promoter, such as, for example, chlorinated polyolefins, etc). 
The water-borne paints which contain the reaction products to be employed 
according to the invention are preferably employed for priming of plastics 
and can be applied, for example, by spraying, knife coating or dipping. 
The plastics primed in this way can easily be overcoated, for example, 
with one-coat solid or metallic finishes or with two-coat solid or 
metallic finishes of the base coat/clear coat type.

The invention is described in greater detail in the examples below. 
1. Preparation of an aqueous dispersion of the reaction product to be 
employed according to the invention 
359.8 g of HYCAR.RTM. ATBN 1300 X 16 (butadiene-acrylonitrile copolymer 
containing secondary amino groups, containing 16% by weight of 
acrylonitrile and having a number average molecular weight of 3,500-3,800, 
and obtainable by reacting a butadiene-acrylonitrile copolymer containing 
terminal carboxyl groups with aminoethylpiperazine) are dissolved in 174 g 
of toluene, 46.3 g of a polytetrahydrofuran diglycidyl ether having an 
epoxide equivalent weight of approximately 420 are added, and the mixture 
is stirred at 80.degree. C. until virtually no epoxide groups are 
detectable (after about 10 hours). The mixture is then diluted using 68.4 
g of ethylene glycol monobutyl ether and 116.0 g of isobutanol and cooled 
to 40.degree. C. 6.4 g of glacial acetic acid and 1,588 ml of 
demineralized water are then added over the course of one hour. The 
resultant dispersion is freed from organic solvents under reduced pressure 
and adjusted to a solids content of 21.5% by weight using demineralized 
water. The amine number of the reaction product is 61.2 mg per g of solid. 
2. Preparation of a paint component containing cross-linking agents 
170 g of an 80% strength aqueous solution of the epoxy resin crosslinking 
agent Beckopox EH 623 (manufacturer: Hoechst AG) are predispersed using 
460 g of water, 180 g of talc, 320 g of TiO.sub.2, 2 g of flame black, 8 g 
of Bentone SD 2 (Kronos Titan GmbH) and 19 g of Borchigel L75 (50% 
strength in water, Gebruder Borchers), and the dispersion is ground in a 
ball mill to a particle size of 15 .mu.m. 100 g of water are subsequently 
incorporated into the ground product. 
3.1 Preparation of a paint component containing binders and the reaction 
product to be employed according to the invention 
62.6 g of the dispersion described under point 1 and 92 g of an aqueous 
epoxy resin dispersion based on bisphenol A diglycidyl ether (Beckopox EP 
384, manufacturer: Hoechst AG) are mixed. 
3.2 Preparation of a paint component containing a styrene-butadiene rubber 
dispersion instead of the reaction product to be employed according to the 
invention 
29.2 g of an aqueous 50% strength styrene-butadiene rubber dispersion 
(Lipaton X 5521, manufacturer: Huls AG) and 84.3 g of the epoxy resin 
dispersion described under 3.1 are mixed. 
4. Preparation and application of the paints, and testing 
4.1 126 g of the paint component as per point 2 are mixed with 154.5 g of 
the paint component as per point 3.1, and the mixture is adjusted to a 
viscosity (spraying viscosity) of 25-27 sec. (DIN 4 cup) using 
demineralized water. A polycarbonate sheet which has been cleaned using 
isopropanol is sprayed with the resultant paint (dry film thickness: 25-30 
.mu.m), and the film is cured at 80.degree. C. for 30 minutes after an 
evaporation time of 10 minutes at room temperature. A commercially 
available metallic base coat and a commercially available clear coat are 
subsequently applied on top by the wet-on-wet method, and the coatings are 
baked at 80.degree. C. for 45 minutes. After storage for 3 days at room 
temperature, the painted substrates obtained in this way are tested for 
adhesion (crosshatch test in accordance with DIN 53 151) and for 
low-temperature impact strength (penetration test in accordance with DIN 
53 443, part 2). The results are shown in Table 1. 
4.2 126 g of the paint component as per point 2 are mixed with 113.5 g of 
the paint component as per point 3.2, and the mixture is processed further 
as described under point 4.1. The substrate painted with this paint is 
tested in the same way as the substrate obtained as per point 4.1 The test 
results are shown in Table 1. 
4.3 126 g of the paint component as per point 2 are mixed with 84.4 g of 
the epoxy resin dispersion described under point 3.1, and the mixture is 
processed further as described under point 4.1. The test results of the 
substrate painted using this paint are given in Table 1. 
TABLE 1 
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Test results 
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Finish as per point 
4.1 4.2 4.3 
Crosshatch test 0 0 0 
Temperature of the 
-20.degree. C. 
-6.degree. C. 
0.degree. C. 
transition (determined 
in the penetration test) 
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