DE2807141A1 - Corrosion resistant protective coating for metals esp. car under-body - is a thixotropic mixt. of synthetic rubber latex, inorganic pigments and water soluble alkyd resin - Google Patents

Abstract

Thioxotropic corrosion resistant coating compsns. for metals are based on (a) synthetic butadiene-styrene and/or butadiene-acrylonitrile and/or butadiene-acrylonitrile-styrene copolymer rubbers, (b) inorganic pigments with a low water requirement, (c) organic plasticisers, (d) water dilutable alkyd resin thickener/binders, (e) (in)organic destabilisers such as Na silicofluoride, organopolysiloxane and zinc-ammonium complex salts in amts. of 0.1-10 pts. wt. per 100 pts. wt. dispersion solids, and (f) opt non-ionic surfactants and electrolytes. The compsns. may also contain cross-linking agents such as sulphur based agents, polyvalent metals salts, water soluble melamine-formaldehyde or melaminine-urea resin. The coatings are esp. useful for corrosion protection of iron and steel, partic. for car underbody protection. The coatings can be dried and cured in a single stage at up to 150 degrees C without the formation of cracks and bubbles, and the cured coatings have excellent adhesion and resistance to stone chipping and to chemical agents such as salts, oil and petrol.

Description

Thixotropic coating masses based on dispersion for

Corrosion Protection of Metals The invention relates to thixotropic coating compositions Dispersion-based for the protection of metals against corrosion, for example iron and steel, which has a durable, adhesive, highly elastic, moisture-proof and chemical-resistant protective film of high layer thickness can form and the front are especially suitable for car underbody protection.

As is known from DT-OS 2 012 463, a coating compound can be used on a dispersion basis from a dispersion of a butadiene / styrene / unsaturated carboxylic acid mixed polymerizate and in layer thicknesses of 200 to 2000 / um for weatherproof sealing of iron and steel exterior surfaces.

The main disadvantage of this invention is that it is completely inadequate Ability to dry the coating compound mentioned.

The drying must either be at room temperature or at a maximum of up to to be done to 11000. At higher drying temperatures, cracks and blisters form in the corrosion protection film as well as to peeling phenomena at the coating compound interface - metal. This means that this mass is suitable for large-scale use where it is short Drying times are important (e.g. car underbody protection) and therefore high temperatures of approx. 1500G are necessary, cannot be used.

In addition, the above-mentioned coating compounds are applied on metal surfaces with higher layer thicknesses (1000 to 2000 µm) even with mild ones Quality-reducing cracks. Another disadvantage of the described Coating compounds is the non-use of plasticizers, there at low temperatures the mixtures become very brittle and very easy to remove Splinter metal surface. In addition, through the use of fillers With a high water requirement, the flushability of the dispersion is limited from the outset and the realization of great layer thicknesses in good quality may be too small Solids content of the coating compound made difficult. The same applies to the use common, highly hydrophilic thickeners. The aim of the invention is to overcome the disadvantages to eliminate the known coating compounds for the corrosion protection of metals.

The drying of the coating mass should take place above 110 ° C, without cracking or blistering in the anti-corrosion film or peeling phenomena at the interface between coating compound and metal. The protective film formed is higher The layer thickness should be durable, adhesive, highly elastic and resistant to moisture and chemicals be.

The invention is based on the object of thixotropic coating compositions based on polymer dispersions, inorganic and organic additives develop in solid, liquid, dispersed, dissolved and emulsified form, which can be applied to metal surfaces by spraying, painting or spatula and can be baked immediately after application at around 1500C. This should the above requirements for the protective film must be guaranteed.

According to the invention, the object is achieved by combining synthetic Elastic dispersions based on butadiene-styrene and X or butadiene-acrylonitrile and / or Butadiene-acrylonitrile-styrene (all latices carry functional groups, preferably Carboxyl groups) with inorganic pigments that have a low water requirement, organic plasticizers and thickeners based on water-thinnable alkyd resins then dissolved if a brief phase separation period in the course of the heating of the coating composition between the solid matter and the dispersion water is achieved.

To achieve this phase separation, the dispersion mass are destabilizing Agents of an inorganic or organic nature are added. Such destabilizing Agents are sodium silicofluoride with 0.4-10 parts by weight, optionally in combination with electrolytes such as sodium sulfate, or organopolysiloxanes with 0.1 - 6.0 Parts by weight, optionally in combination with nonionic surface-active Substances and electrolytes, or zinc-ammonium complex salts with 0.5 - 8.0 parts by weight, in each case based on 100 parts by weight of dispersion solid or mixtures of the named substances.

It is surprising that with the addition of suitable combinations of destabilizing Agents that become effective when heated, even with high layer thicknesses up to 2000 / um good film formation is achieved even if drying is carried out at the same time is carried out with the baking at approx. 1500C. It is also surprising that according to the invention coating compositions made from a wide variety of butadiene-styrene and Butadiene-acrylic copolymers and butadiene-styrene-acrylonitrile copolymers with functional groups can be produced if the solids content of the Coating mass 50 ffi and the solids content of the husgang dispersion exceed 40% and that not only, as can be seen from DT-OS 2 012 463, certain butadiene-styrene latices can be used.

The mixtures according to the invention are based on those used in manufacture Easily produced by machines commonly used in emulsion paints. They exhibit a very good storage stability, with sedimentation or floating phenomena being practical do not occur. These products are great for running Metal corrosion protection work, e.g. coating of car underbody panels, insert. They are characterized by excellent processability especially when applying with a spray gun.

After drying and baking, immediately after application can be carried out in one operation at temperatures up to 150 0C, smooth, closed, well-adhering, elastic protective films in thicknesses up to approx. 2000 μm that protect against the damaging effects of weather and chemicals (e.g. Climatic changes, salt pollution) are extremely resistant0 An addition of cross-linking Agents for the coating compositions according to the invention are possible, such agents zoBe are polyvalent metal ions, melamine-formaldehyde or melamine-urea resins and vulcanization mixtures of sulfur, zinc oxide and organic vulcanization accelerator0 The addition of such agents improves the already good metal adhesion of the invention Further Corrosion Protection Compounds The invention is based on exemplary embodiments below Example 1 is explained in more detail in a dissolver with a capacity of 500 kg 160 kg of a butadiene-acrylonitrile latex with functional groups, a Submitted solids content of 41% and an acrylonitrile content in the polymer of 38%, The following are added one after the other to the latex while stirring: 19.2 k water-thinnable Alkyd resin 8.0 kg melamine-formaldehyde resin 2.5 kg organopolysiloxane 240.0 kg pigment paste the following composition: water 120.0 parts by weight non-ionic surfactant 1o0 "II Dispersing aid 1 based on polyacrylate 1.5 "" alkali polyphosphate 1.2 defoamer 1.9 t t zinc oxide 6.0 titanium dioxide rutile 15.0 Iron oxide black 160.0 Parts by weight kaolin 30.0 tt chalk 90.0 polyamide fibers approx. 3 mm long The mixture is adjusted to a pH value of 8 - 10 and thereby maintains its thixotropic Character in connection with the use of the alkyd resin.

The mixture is electrophoretically applied with a spray gun or otherwise primed sheet steel sprayed on and with a wet layer thickness of 1000 μm, dried and baked in a drying oven at 1400 ° C. for 40 minutes. After baking, a firmly adhering, crack-free and bubble-free layer is obtained, which is subjected to the tests summarized in Table 1.

Example 2 The conditions are the same as in Example 1160 kg of a butadiene-styrene latex with functional groups, a solids content of 50% and a styrene content in the polymer of 60%. The latex will be added one after the other with stirring: 19.2 kg of water-thinnable alkyd resin 12.0 kg Vulcanization paste based on sulfur (50% solids) 240.0 kg pigment paste accordingly Example 1 Then proceed as in Example 1. Exam Results are included in Table 1.

Example 3 Under the same conditions as in Example 1 160 kg of a butadiene-styrene-acrylonitrile latex with functional groups, a Solids content of 47%, a Stvrol content of 22% and an acrylonitrile content submitted by 33 Xo in the polymer. The following are added one after the other to the latex while stirring: 19.2 kg water-thinnable alkyd resin 0.6 kg sodium silicofluoride dispersion 50% 240.0 kg pigment paste according to Example 1 The procedure in Example 1 is then continued procedural test results are shown in Table 1.

Example 4 Under the same conditions as in Example 1, with a pigment paste of the following composition worked water 135.0 parts by weight non-ionic Surfactant 1.0 "" Dispersing aid 2.0 "" based on polyacrylate alkali polyphosphate 2.0 "defoamer 1.6 rutile titanium dioxide 120.0 black iron oxide 90.0" kaolin 80.0 "Chalk 170.0" test results are shown in Table 1.

Example 5 This example is used for comparison with a coating compound according to DT-OS 2 012 463. A mixture of the following composition is produced: 52.0 parts by weight of butadiene-styrene latex with functional groups, 48% solids and a pH of 8.5 7.0 11 "iron oxide black 21.0 21" aluminum silicate 2.0 o "" silicon carbide 0.5 ", magnesium montmorillonite 0.7" "thickener based on polyacrylate 0.3 11 defoamer 0.2 11 11 cobalt naphtenate solution 0.3 parts by weight Wetting Agent 1.5 "" Butyl Glycol 14.5 "" Water This mixture is made accordingly Example 1 processed further.

Test results are shown in Table 1.

Table 1 Test results of the examples of the mixture according to Example 1 2 3 4 5 Test method: cracked surface appearance of the crack and bubble free pale burned film stone chipping test - downpipe method (kg) 35 50 40 50 night - Emission method (sec) 40 65 40 6C testable tear-off test according to 24.7 26.8 29.5 23.1 TGL 27 608 (N / cm²) aerosol test after every 1500 hours TGL 18 754 sheet 3 every 1500 Hours mineral oil compatibility all compatible according to TNL 12 829 compatibility with seasonal metal protection agent all compatible according to TNL 12 829 gasoline resistance all resistant according to TNL 12 903 brine-cold-exchange no reduction in quality storage (25 cycles) Description of the test methods rockfall test (downpipe method): At the bottom of a vertical pipe 2.5 m long and 2 inches in diameter the sheet metal coated with the anti-corrosion compound becomes at an angle of 450 appropriate. From above, through the downpipe, hard gravel with a grain size of 0.5 - 1.2 mm until the protective layer on the metal sheet is penetrated. Then the required amount of gravel is weighed.

Stone chipping test (radiation method): barley: commercially available Vacublast device Blasting material: Granulated phosphor slag with a grain size of 1.0 - 1.6 mm Blasting pressure: 4.0 - 4.5 atü Blasting time: until the protective layer is irradiated Brine cold alternating test: The test specimen is exposed to the following loads: Immerse in 5% saline solution at + 20 ° C for 6 hours; then without intermediate drying 18 hours of cold storage at - 200C. After 25 cycles, the assessment is carried out Examination of the mechanical characteristics of the protective layer.

Claims (4)

Claims 1. Thixotropic coating compositions based on dispersion for the corrosion protection of metals, for example iron and steel, preferably for car underbody protection, characterized by a combination of synthetic Elaatdispersionen with functional groups based on butadiene-styrene and / or Butadiene-acrylonitrile and / or butadiene-acrylonitrile-styrene copolymers with inorganic ones Pigments that have a low water requirement, organic plasticizers as well Fasteners based on water-thinnable alkyd resins and destabilizing inorganic or organic agents such as sodium silicofluoride, organopolysiloxanes or zinc-ammonium complex salts, individually or in a mixture, in amounts from 0.1 to 10 parts by weight per 100 parts by weight of dispersion solid, optionally with non-ionic surfactants and electrolytes. 2. Coating composition according to claim 1, characterized in that after application to a metal surface in one operation at temperatures is dried and baked up to approx. 150 ° C. 30 Coating compound according to Claim 1, characterized in that they cross-linking agents, e.g. sulfur-based, polyvalent metal salts, water-soluble ones Contains melamine-formaldehyde resins or melamine-urea resins. 4. Coating composition according to claim 1, characterized in that the fillers have a low water requirement.