DE1669135A1 - Process for the electrophoretic coating of workpieces - Google Patents

Description

FARBENFABRIKEN BAYER AG

? 9. July 1966

LE VE R KU S E N - Bayerwerk

Fri / Ko.

PATENT DEPARTMENT Electrophoretic coating process

of workpieces

The process of electrophoretic painting has been around for a long time for the coating of metal parts introduced in practice. Preferred binders to be applied electrophoretically real or colloidal, predominantly aqueous solutions of alkyd resins, melamine-formaldehyde resins, epoxy and acrylate resins are used. These resins in solution form have proven to be largely free of interference in the electrophoretic process due to their ability to be applicable, well established.

When using polymer emulsions or dispersions, however, problems arise which prevent the use of this binder class have so far restricted the electrophoretic coating process: For example, those with emulsion polymers show produced coatings have an unsatisfactory throwback, i.e. the thickness of the applied layer is at the edges and burrs of the workpiece insufficient. The emulsifier content of the emulsions leads to disturbances in the electrophoretic structure of the paint layer, Sometimes there are even disturbances caused by electrolysis the material surface. Often the gloss of the polymer dispersions applied electrophoretically is also satisfactory No coatings. For example, the amperage-time

Curve with styrene-butadiene emulsions at the beginning a constant or even increasing amperage, which leads to the formation of spongy layers with poor mechanical properties, especially in unbaked condition, leads (see paint and varnish TO, no. 4, pp. 271-279 (1964)).

The aim of the present method is for the use to find suitable polymer emulsions as coating compositions to be applied electrophoretically.

These emulsions should give a coating that is good mechanical properties shows good throwing power and good gloss even in the non-baked state. In addition, the Solvent fastness should be very good after a stoving process to be carried out at the lowest possible temperature. So satisfy Acrylate dispersions used in this regard for electrophoretic coating purposes are not used because they are intense Active solvents such as hot esters of the lower fatty acids, dimethylformamide or dimethyl sulfoxide are not indifferent are, while coatings produced with the help of butadiene-styrene emulsions in addition to interference with the electrophoretic Layer structure show insufficient resistance to aging.

From US Pat. No. 2,530-366 it is known to mill or knead polyethylene with half-esters of copolymers of maleic anhydride and then to disperse this mixture in an aqueous basic medium in order to carry out electrophoretic coatings with the resulting emulsion. However, this process works with large amounts of an emulsifier, which is incompatible with the polyethylene and later leads to reduced values in terms of water resistance and electrical properties

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leads. Because in this dispersion system of the pesticide particles enveloping emulsifier is the landing carrier, but not the actual polymer, has the still moist, freshly applied Coating with a considerable volume has insufficient mechanical strength and only achieves this during stoving, with the polymer particles merge. In addition, these ultimately have deposited on the material surface through fusing Coatings obtained from polyethylene particles have only a low resistance to attack by hydrocarbons.

A process has now been found for the production of electrophoretic coatings with the aid of polymer emulsions optionally containing additives, which is characterized in that polymer emulsions from copolymers of ethylene and acrylic and / or methacrylic acid and optionally their esters are used, 3-95 wt. % of the carboxyl groups present are in salt form.

The present process for the preparation of electrophoretic Coatings based on polymer emulsions optionally containing pigments and fillers as additives to coatings that, when freshly applied, have good mechanical properties with good grip and after baking have excellent gloss and very good solvent resistance.

In particular, according to the present invention, polymer emulsions are used used, those from copolymers e.g. of ethylene

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and acrylic acid and / or methacrylic acid and optionally their esters are built up and have a content of 5 - 75 wt. $, preferably 5-40 wt. <$> copolymerized acrylic and / or methacrylic acid units with ri values of the copolymers of 0.05 - 1, measured in cyclohexanone at 100 0.

The ethylene copolymers containing carboxyl groups of the present invention are used in the form of their alkali metal, ammonium salts or amine salts, preferably in the form of the Na or K salts. Here are 3-95 # »bevoreugt 5-75 wt be neutralized # of carboxyl groups..

The solids content of the dispersions used is 3 to about 60% by weight, preferably 10-45% by weight .

Details on the preparation of such polymer dispersions are given, for example, in the German patent applications F 48 631 IVd / 39b, F 34 024 IVb / 39c and F 30 2.19 IVb / 39c are given.

As esters of acrylic and methacrylic acid come into question: Esters with 1 to 8 carbon atoms in the ester alkyl, which are optionally by Hydroxyl groups can be substituted.

Acrylic or methacrylic acid esters with 1-4 C atoms in the ester alkyl are preferably used. A special interest have the 2-hydroxyethyl or 2-hydroxypropyl esters of Acrylic or methacrylic acid, especially the 2-hydroxypropyl ester of the acids mentioned.

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Examples of copolymerizable acrylic (methacrylic) acid esters are: (methacrylic acid methyl ester, (meth) Acrylic acid ethyl ester, (meth) acrylic acid propyl ester, (meth) Acrylic acid isopropyl ester, (meth) acrylic acid butyl ester, (meth) acrylic acid isobutyl ester, (meth) acrylic acid-2-ethylhexyl ester, (Meth / acrylic acid octyl ester, (meth) acrylic acid 2-hydroxyethyl ester, (Meth) acrylic acid-2-hydroxypropyl ester or mixtures thereof.

Since the transition from pure polymer dispersion to colloidal polymer solution has a flowing character and the carboxyl group content of the polymer as well as its degree of neutralization and the contaminant content of the system is dependent The terms latex, polymer dispersion or emulsion used in the application should not be regarded as restrictive be.

Although those for the electrophoretic coating process The polymer dispersion to be used is excellent for the preparation The addition of pigments, dyes, fillers or plasticizers is in principle suitable for clear coatings possible, as well as a mixture with other (colloidal) solutions or latices of polymers or crosslinkers can be. In this case, however, due to the colloid chemical and electrical property changes hardly predictable of the system, the conditions for optimal electrophoretic deposition can be determined empirically.

Also a follow-up treatment of the freshly cast down coatings for example by spraying or dipping with other coating agents, Crosslinking solutions, dyes or hydro

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phobia is possible without further ado.

Although the proposed types of polymer emulsions are particularly good for electrophoretic coating Workpieces made of iron or mainly iron-containing metal types are suitable, the coating of non-ferrous metals succeeds, such as copper, zinc and their alloys, bronze, precious metals and also other electrically conductive or made conductive ones (Graphite, chrome-plated) materials as well.

The temperature of the coating bath should be between 0 and 9Q ⁰ C, preferably from 5 to 55 are G ^0.

Adjust the voltages and currents used according to the technological values of the system: workpiece and coating equipment, i.e. they are of the size of the workpiece as well as its geometry, but also depends on the desired deposition rate, layer thickness and possibly added auxiliaries and additives; material constants also play a role of the workpiece a role. Although the voltages to be selected can be determined empirically from case to case be said that they will preferably be above 50 volts.

The following examples are intended to explain the process without, however, restricting it to these. The specified parts are parts by weight, unless otherwise noted.

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Latex 1:

6,000 parts of copolymer of ethylene and 19% by weight of acrylic acid (^ value, measured in cyclohexanone at 100 G, 0, 55) are placed in an autoclave _{with 200 parts of NaOH and 10,000 parts of H 2 O}

120 ⁰ O converted into an approx. 40 $ latex.

The "intrinsic viscosity" is understood by the - "^ - value.

Latex 2:

The procedure is the same as for Latex 1, but KOH is used instead of NaOH.

Latex 3:

6000 parts of the Athylencopolymerisats used in Latex 1 are dissolved with 54 000 parts water and 600 parts of triethylamine with vigorous stirring at 90 ⁰ C in an emulsion with a Pestkörpergehalt of about 10 wt.%.

Latex 4:

6000 parts of copolymer of ethylene and 15 wt. <F ₀ methacrylic ΟΊ value in cyclohexanone at 100 ⁰ C, 0.87) are mixed with 250 parts NaOH and 10,000 parts of water at 140 ⁰ C in a 40 $ Latex convicted.

Latex 5:

6000 parts of copolymer of 65 wt. ^ Ethylene, 10 wt. # Of ethyl acrylate and 25 wt. $ Methacrylic acid (^ value, measured in cyclohexanone at 100 ⁰ C, 0.71) are dissolved in 12, 000 parts of t-butanol. A solution of 220 parts of NaOH is then used at 80 ^{° C.}

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13,000 parts of water are added and the alcohol is distilled off with vigorous stirring, leaving an approx. 39 # strength latex

latex 6:

6000 parts of copolymer of 75 parts ethylene, 20 parts of acrylic acid and 5 parts Oxypropylmethacrylat (τ ^ value, measured in cyclohexanone at 100 ° C, 0 "43) are dissolved in 12, 000 parts of t-butanol and at 80 ⁰ C with stirring with a solution of 300 part ,, ;; NaOH is added in 13,000 parts of water. The alcohol is then distilled off. A 40 # late is left behind

Latex 7:

Like latex 1, only a copolymer of ethylene and 9 GeT »v /> acrylic acid is used (- ^ - value, measured in cyclohexanone at 10C ¹ " * ",,

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A sheet metal (65 χ 165 x 0.3 mm) is used for coating tests. The polymer dispersion is diluted to the desired target body content, filled into a container connected as a cathode, brought to the test temperature and then the test body connected as an anode is immersed for a while
is gently stirred. The individual test conditions can be found in the following table:

Example No. 123 4 56789

Latex No. 112 3 4 5 6 7 1

Latex diluted to 20 2 5 20 10 40 20 20 25 30

Weight? 6 fixed salary

Temperature ( ⁰ C) of the 35 30 35 25 45 35 35 35 12 coating bath

Test material Fe Cu Fe VpA® Fe Fe VpA® Fe Fe

sheet metal (anode)

Voltage (V) 120 120 125 130 110 120 120 120 100

Initial current 8 118.5 6 15 9 8 7 10

strength (A)

End current (mA)

Duration of experiment 30 25 40 50 15 30 35 50 70

(sec)

Drying temperature 90 120 90 HO 100 90 150 130 95

( ⁶ C)

achieved shift 25 30 30 35 15 20 25 30 40

thick ψ-)

Erichsen value of

dry coating 888888888

mm

= Stainless steel

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8th 1 1 8th, 5 6th 1 5 9 8th 7th 10 1 1 8th 10 1 0 10 8th 5

to

At first a considerable current flows, but it flows very quickly decreases as the specimen surface is coated. The test sheet under tension is then lifted out and rinsed with water. In all cases a firmly adhering, almost dry-to-the-touch coating is deposited which is mechanically so strong that it is not damaged by manipulation with the test body. Afterward the coating is dried at an elevated temperature.

In all cases the coatings are good gloss, more excellent Resistance to solvents such as aliphatics, aromatics, esters, water, organic and inorganic acids or also strong solvents like dimethylformamide, dimethylacetamide, Dimethyl sulfoxide. For testing purposes, a cotton ball soaked with solvent is placed on the coating for 30 minutes and then checked whether swelling or detachment of the coating from the workpiece occurs.

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Claims (4)

'"'; -ht ^ iSnfiert j patent claims: * ~ M * ,, 1.) Process for the production of electrophoretic coatings with the aid of polymer emulsions optionally containing additives, characterized in that as Polymer emulsions those made from copolymers of ethylene and meth- and / or acrylic acid and, if appropriate, their esters used, with 3 - 95 $ of the carboxyl groups present in salt form. 2.) Process according to claim 1, characterized in that polymer emulsions from copolymers of ethylene and acrylic acid and / or methacrylic acid and optionally their esters with a content of 5-75 wt. # copolymerized acrylic and / or methacrylic acid units with ^ values of the copolymers of 0.05-1, measured in cyclohexanone at 100 ° C., are used where 3-95 # of the carboxyl groups present are in salt form. 3.) Process according to claim 1 and 2, characterized in that the ethylene copolymers 5-40 wt. $ Acrylic and / or methacrylic acid units built-in included. 4.) Process according to claim 1 and 2, characterized in that the carboxyl groups are in the form of their sodium or potassium salts are present. , Le A 10 162 -11- 109823/1807 ORIGINAL I