Cationically curable composition and method for the joining, casting and coating of substrates using the composition

A method for the joining, casting, molding, sealing and coating of substrates using a cationically curable composition, the method comprising:

• a) providing a cationically curable composition at least one cationically polymerizable component, a first photoinitiator for cationic polymerization, and a second photoinitiator for cationic polymerization, wherein the second photoinitiator comprises an aryl sulfonium salt;
• b) dosing the composition onto a first substrate;
• c) activating the composition by irradiation with actinic radiation of a first wavelength λ1, wherein an open time of the composition, during which the composition remains liquid, is started by activating the composition;
• d) optionally supplying a second substrate to the activated composition on the first substrate, thus forming a substrate composite, and, furthermore, optionally aligning both substrates with one another;
• e) fixing the activated composition by irradiation with actinic radiation of a second wavelength λ2, wherein skin formation takes places and the open time of the composition ends;
• and
• f) optionally heating the fixed composition on the first substrate or in the substrate composite,
• wherein the cationically curable composition has a higher proportion of amount-of-substance of the second photoinitiator as compared to the first photoinitiator, and
• wherein the cationically curable composition comprises the at least one cationically polymerizable component and the first photoinitiator releasing an acid when irradiated with actinic radiation of a first wavelength λ1, as well as the second photoinitiator releasing an acid when irradiated with actinic radiation of a second wavelength λ2, wherein the second wavelength λ2 is shorter than the first wavelength λ1, wherein the first and the second photoinitiators are selected such that the first photoinitiator can be activated at a first wavelength λ1 of 460 nm without the second photoinitiator being activated simultaneously,
• wherein, after activation of the first photoinitiator, an absorption band of the second photoinitiator at a wavelength λ2 of 365 nm is above the absorption of the first photoinitiator and the decomposition products formed after the activation so that the second photoinitiator, after activation of the composition in step c), shows an absorption of actinic radiation of the second wavelength λ2 in the composition that is sufficient to activate the second photoinitiator in step e).