EP-4114884-B1 - HIGH TEMPERATURE CROSS-LINKING DISPERSION

Inventors

• DOERR, SEBASTIAN
• JANßEN, Petra
• GIPPERICH, INGO

Dates

Publication Date

20260513

Application Date

20210301

Claims (10)

1. Process for preparing at least one blocked polyisocyanate, comprising the following steps: (A) reacting at least one polyisocyanate with at least one thermally eliminatable blocking agent selected from the group consisting of primary, monofunctional alcohols and mixtures thereof, in order to obtain at least one partly blocked polyisocyanate, (B) reacting the at least one partly blocked polyisocyanate from step (A) with at least one nonionic hydrophilizing agent in order to obtain an intermediate, (C) reacting the intermediate obtained in step (B) with at least one thermally eliminatable blocking agent selected from the group consisting of primary, monofunctional alcohols and mixtures thereof, in order to obtain the at least one blocked polyisocyanate, (D) dispersing the at least one blocked polyisocyanate obtained in step (C) in water.
2. Process according to Claim 1, characterized in that polyisocyanates used are the compounds of relatively high molecular weight that have isocyanurate, urethane, allophanate, biuret, iminooxadiazinetrione, oxadiazinetrione and/or uretdione groups and are based on aliphatic and/or cycloaliphatic diisocyanates.
3. Process according to Claim 2, characterized in that the compounds of relatively high molecular weight that have biuret, iminooxadiazinedione, isocyanurate and/or uretdione groups are based on hexamethylenediamine diisocyanate, isophorone diisocyanate and/or 4,4'-diisocyanatodicyclohexylmethane.
4. Process according to any of Claims 1 to 3, characterized in that the at least one thermally eliminatable blocking agent used in step (A) and the at least one thermally eliminatable blocking agent used in step (C) are identical.
5. Process according to any of Claims 1 to 4, characterized in that the at least one nonionic hydrophilizing agent is at least one polyoxyalkylene ether containing at least one hydroxyl or amino group.
6. Process according to any of Claims 1 to 5, characterized in that the blocked polyisocyanate in aqueous dispersion has an average particle size of 10 to 400 nm, more preferably 20 to 200 nm, determined in each case by means of laser correlation spectroscopy after dilution of the sample with demineralized water.
7. Blocked polyisocyanate obtainable by a process according to any of Claims 1 to 6.
8. Use of the blocked polyisocyanate according to Claim 7 for production of coating compositions, adhesives, sealants or elastomers.
9. Coating composition, adhesive, sealant or elastomer comprising at least one blocked polyisocyanate obtainable by a process according to any of Claims 1 to 6, or according to Claim 7.
10. Substrates provided with coatings obtainable using the at least one blocked polyisocyanate obtainable by a process according to any of Claims 1 to 6, or according to Claim 7.

Description

The present invention relates to a process for the preparation of at least one blocked polyisocyanate, comprising the steps (A) reacting at least one polyisocyanate with at least one thermally releasable blocking agent selected from the group consisting of primary, monofunctional alcohols and mixtures thereof to obtain at least one partially blocked polyisocyanate, (B) reacting the at least one partially blocked polyisocyanate from step (A) with at least one nonionic hydrophilizing agent to obtain an intermediate, (C) reacting the intermediate obtained in step (B) with at least one thermally releasable blocking agent selected from the group consisting of primary, monofunctional alcohols and mixtures thereof to obtain the at least one blocked polyisocyanate, (D) dispersing the at least one blocked polyisocyanate obtained in step (C) in water, a correspondingly obtained blocked polyisocyanate, the use of this blocked polyisocyanate for the preparation of coatings, adhesives, sealants or elastomers, and providing substrates with coatings available using the at least one blocked polyisocyanate according to the invention. In recent years, the importance of waterborne paints and coatings has increased significantly due to increasingly stringent emission regulations regarding solvents released during paint application. Although waterborne paint systems are now available for many applications, they often cannot achieve the high quality level of conventional, solvent-based paints in terms of solvent and chemical resistance, elasticity, and mechanical stress. Even waterborne coating systems based on aqueous polyurethane dispersions often still contain significant amounts of solvents. Avoiding these solvents in polyurethane dispersions is generally not possible, as the production of such dispersions via prepolymers often requires solvents, or a so-called co-solvent (coalescence agent) must frequently be added to the dispersions to lower the minimum film formation temperature. This ensures that sufficiently hard layers are formed during coating at or below room temperature. The storage stability of PUR dispersions and coating formulations is also frequently compromised without solvents. For example, the solvent N-methylpyrrolidone (NMP) is still sometimes used in aqueous dispersions and coatings. One example is carboxylic acid hydrophilized polyisocyanate crosslinker dispersions with dimethylpyrazole-blocked ion exchangers. Isocyanate groups, which are found, for example, in EP-A 0 942 023 These crosslinking dispersions, as well as the lacquers produced from them, contain NMP as a co-solvent. A solvent-free production of the in EP-A 0 942 023 The described DMP-blocked polyisocyanate crosslinker, achieved by omitting the solvent, is not possible due to viscosity reasons. The in WO 1997/012924 The described non-ionic hydrophilic polyisocyanate crosslinker dispersions with pyrazolically blocked isocyanate groups contain approximately 7 wt% butyl glycol as a co-solvent. Similar to NMP, this is characterized by a relatively high boiling point. Separation for the production of solvent-free, aqueous dispersions is not possible. In DE 19914885 Polyurethane dispersions with dimethylpyrazole-blocked isocyanate groups for the production of glass fiber sizing are described. These dispersions are prepared using an organic solvent, which is removed from the dispersion by distillation after dispersion in water. In DE 3613492 An acetone-based process for the production of solvent-free polyurethane-polyurea dispersions is described. The prepolymer, which in this case is not blocked, is prepared in a 20 to 50 wt% solution in a volatile organic solvent, such as acetone, and the solvent is removed by distillation after dispersion in water. The replacement of NMP in the procedure according to EP-A 0 942 023 by acetone in amounts of 50 or 62 wt% as in DE 19914885 This leads to DMP-blocked polyisocyanate crosslinkers, which, however, are not stable in storage. DE 10 2006 025313 A1 This document discloses a process for the production of aqueous, solvent-free polyurethane crosslinker dispersions with pyrazole-blocked isocyanate groups. According to this process, the blocked polyisocyanates are obtained by reacting the polyisocyanate with a thermally cleavable blocking reagent, followed by a hydroxycarboxylic acid and a di- or polyfunctional chain-extending component. The aqueous dispersions thus obtained are well-suited for the production of solvent-resistant stoving enamels, but exhibit only limited stability in some formulations. EP 0 802 210 A1 refers to aqueous or water-dilutable blocked polyisocyanates that enable the production of one-component polyurethane coatings which can be baked at comparatively low temperatures of 130 to 150 °C, with a significantly reduced thermal yellowing, a method for their manufacture and their use. US 2019/315910 A1 refers to a blocked isocyanate containing a latent isocyanate group which is an isocyanate