Process for producing matt coatings on sheetlike substrates

A method for producing matt coatings on sheetlike substrates, comprising the consecutive steps i.-iv.,

• i. providing an uncured coating film of a liquid coating formulation F, curable by UV radiation, on the surface of the substrate to be coated;
• ii. irradiating the coating film with UV radiation which lies substantially in the wavelength range from 250 to 420 nm, with a radiation dose which leads to partial curing of the coating film;
• iii. irradiating the partially cured coating film with UV radiation in the wavelength range from 150 to <250 nm under inert gas;
• iv. irradiating the partially cured coating film with UV radiation which lies substantially in the wavelength range from 250 to 420 nm, or with electron beams, with a radiation dose which leads to full curing of the coating film;
• wherein the coating formulation F comprises at least 80 wt %, based on the total weight of the coating-forming constituents of the coating formulation F, of one or more curable constituents which have ethylenically unsaturated double bonds,
• the coating formulation F further comprising at least one photoinitiator, wherein the coating formulation F comprises at least one oligomer or polymer which carries on average at least 1.5 ethylenic double bonds per molecule and has a number-average molecular weight Mn of at least 450 daltons, and
• the coating formulation F fulfills at least the following features (A) and (B) or (A) and (C) and optionally (D):
• (A) the number of ethylenically unsaturated double bonds, based on the coating-forming constituents present in the coating formulation F, is in the range from 3.0 to 8.0 mol/kg;
• (B) the coating formulation F comprises at least 30 wt %, based on the curable constituents present therein, of an oligomer or polymer or of a mixture of oligomers and/or polymers wherein the ratio α/To of calculated network arc length α in g/mol to the onset temperature To in kelvins of the glass transition, determined by means of differential scanning calorimetry according to DIN EN ISO 11357-2:2014, is at least 1.2;
• (C) the mass-average ratio α/To, averaged over the weight fractions of all curable constituents of the coating formulation F, is at least 1.0;
• (D) the coating formulation F comprises at least one aromatic epoxy acrylate in an amount of at least 20 wt %, based on the total weight of the curable constituents present in the coating formulation F.