NO743651L - - Google Patents

Description

In heat curable coatings

for melt coating.

The object of claim no* ....... (patent application no. 3240/72) is in hot curable pjilfiver-shaped coverings of a binder consisting of a polyester containing a hydroxyl group and a masked polyisocyanate and possibly further common additives. These coating agents are characterized in that the binder consists of A) to 30 to 45 weight? of a polyester of an average molecular weight from. 500 to 6000, an acid number below 20, an OH number from 400 to 800 and a softening point from 80 to 150°C, prepared from a mixture, ;I) of 90 to 10 mol% of isophthalic acid or its esters and 10 to 90 mol >S terephthalic acid or its esters and II) a mixture of 70 to 100 mol? of one or more saturated aliphatic polyols with 4 to 6 OH groups with 30 to 0 molSS of one or more aliphatic saturated glycols, whose hydroxyl groups are separated from each other by at least 3 C atoms and B) to 55 to 70 weight? of a di- or polyisocyanate, whose isocyanate group is completely or partially masked with a heat-releasable lactam and ;fl). up to. 2 weight$ of an accelerator. According to the teaching aom appears from the above-mentioned patent, this coating agent is applied as usual in powder form to the surface which is to protect^^, e.g. by dusting or electrostatic spraying and the coating is produced by heating. The firing temperatures are at 150 and 250°C, preferably 180 to 200°C, the firing times are at 10 to 60 minutes, preferably at 20 to 40 minutes. ;It has now been found that the same in heat curable;J coating agents are excellently suitable for application from the melt* The application from the melt takes place solvent-free at temperatures between; 80 and 140°C, preferably between 100 and 120°C according to the usual methods for this purpose, especially by vaising or rakling. The applied coating agent is then cured at temperatures above 150°C into hard, elastic, climate-resistant coatings. > The method of applying coating from melt instead of from. solutions in organic solvents are known using thermoplastic plastics. LiléLedes belongs to the state of the art in hot-melt adhesives, i.e. thermoplastics that are applied in a molten state as an adhesive. One application of such thermoplastics for coating metallic substrates instead of a burn-in coating does not lead to hard and resistant surfaces, their scratch sensitivity is so great that the climate resistance is not present to the desired degree. • When trying to use heat-setting binders instead of the thermoplastics, as is common in burn-in varnishes for industrial painting, it turns out that the solvent-free in the melt flow at the temperatures to be used already partially gel after minutes. Moreover, the viscosity of the melt is already so high at the start that an application by vaising or

-' Rakling is not possible.

It was therefore surprising that the powder coatings mentioned in the above-mentioned patent are thus excellently suitable agents for hot-melt coating. Example 1.

A coating agent produced according to the regulations in DOS 2,146,841, example 4, is heated at 120°C and thereby melted while stirring and applied in a liquid state with a film coating triangle resp. a lacquer dumbbell on electrolytically diluted tin as it is usually processed in the tin packaging industry. With a gap width of 25 µm, the pull-off speed is set so that a film thickness of 10 µm is produced. After burning in for 15 min- . otter at 180°C gives a very well-flowing, smooth, colorless coating which has the following properties: Erichsenverdi (DIM 53 156): The tin cracks before the varnish coating.

Bending test (ECCA standard; 0.3 mm tin): T 0.

Sterilization test (1 hour 121°C hot steam):

All right. Example 2. ,

The coating agent used in example 1 is pigmented

in melt flow at 120°C when adding 35 wt? titanium dioxide (a rutile type produced by the chloride method under the trade name "Kronos titanium dioxide Cl 220") under a dissover and then applied as described in example 1 to electrolytically diluted tin,

with a slot width of 5OyU, the application speed is chosen so that

a coating of approx. 50 g per tin plate of 840 mm x 680 mm. After firing at 180°C for 15 minutes, a high-gloss, brilliant continuous white topcoat is obtained, which has the same properties as described in example 1. The degree of gloss according to Lange measured with 45°

optics, located at 123?. The varnishing can be punched, pressed, and over-; can be painted and can be folded.

Example 3 » The pigmented coating agent referred to in example 2 is applied at 120°C in a molten state to a coating heated with steam at 120°C and applied to it in the usual way for coil coating with a strip of tin flowing from the coil (steel sheet of 0.5 mm thickness),. A film of 25/U thickness applied to the coater at a belt speed of 16 m/pinnut shows, after baking at 300°C for 85 seconds, an impeccable course of high gloss and has the following properties:

Erichsen value (DIN 53 156): 8.7 mm. >..Indentation hardness (DIN 53 153): 115.,

Gloss level according to Lange (45° optics): $112.

Bending test: Tl. The climate resistance of the paintwork was measured in an Atlas Weatherometer with carbon arcs and is practically equal to that of a commercial automotive topcoat based on alkyd-melamine resin.

Claims (2)

1. Use of a heat-curable coating agent from a binder consisting of a hydroxyl group-containing polyester and a masked polyisocyanate and possibly further common additives, the binder consisting of A) to 30 to 45 weight? of one polyester with average molecular weight from 500 to 6000, an acid number below 20, an OH number from 400 to 800b g a softening temperature from 80 to 150°C, prepared from a mixture I) of 90 to 10 mol? isophthalic acid or their esters and 10 to 90 mol? terephthalic acid or its esters and II) a mixture of 70 to 100 mol? of one or more saturated aliphatic polyols with 4 to 6 OH groups "■" with 30 to 0 mol? of one or more aliphatic saturated glycols, whose hydroxyl groups are separated from each other by .at least 3,C atoms and B) to 55 to 70 weight? of a di- or polyisocyanate, whose isocyanate group is fully or partially masked with heat-releasable lactam, and C) up to 2 weight? of an accelerator and possibly further common additives, production of heat-curable coatings by application in a molten state and subsequent curing by burning in. 2. By melt application achieved, burned-in coating using the binder specified in claim 1..