JP-2022541533-A5 -

Dates

Publication Date

20230501

Application Date

20190718

Description

This invention relates to the fields of plastic coatings and synthetic leather. This relates, more specifically, to the manufacture of porous polymer coatings, particularly porous polyurethane coatings, using a combination of polyol esters and cationic polymer electrolytes as additives. Plastic-coated fabrics, such as synthetic leather, generally consist of a fabric support material with a porous polymer layer laminated on top, coated with a top layer or topcoat. In relation to this, the porous polymer layer preferably has pores in the micrometer range, is air permeable, and therefore air permeable, i.e., permeable to water vapor, but water resistant. The porous polymer layer often contains porous polyurethane. Currently, porous polyurethane layers are manufactured by a coagulation method that usually uses DMF as a solvent. However, due to environmental concerns, criticism of this manufacturing method is increasing, and it is therefore gradually being replaced by other more environmentally friendly technologies. One of these technologies is based on aqueous polyurethane dispersions called PUDs. These usually consist of polyurethane microparticles dispersed in water, with a solid content typically in the range of 30 to 60% by weight. To manufacture a porous polyurethane layer, these PUDs are mechanically foamed, coated onto a support material (the layer thickness is usually 300 to 2000 μm), and then dried at high temperature. During this drying process, the water present in the PUD system evaporates, forming a film of polyurethane particles. To further enhance the mechanical strength of the film, hydrophilic (poly)isocyanates can be added to the PUD system during the manufacturing process. These can react with free OH groups present on the surface of the polyurethane particles during the drying process, resulting in additional crosslinking of the polyurethane film. The mechanical and tactile properties of the PUD coating manufactured in this manner are largely determined by the cell structure of the porous polyurethane film. Furthermore, the cell structure of the porous polyurethane film affects the air permeability and breathability of the material. In this specification, particularly excellent properties can be achieved by very finely and uniformly distributed cells. A conventional method for influencing the cell structure during the above manufacturing process is to add a foam stabilizer to the PUD system before or during mechanical foaming. The first effect of a suitable stabilizer is that it allows a sufficient amount of air to be incorporated into the PUD system during the foaming process. Secondly, the foam stabilizer directly affects the morphology of the bubbles produced. The stability of the bubbles is also considerably affected by the type of stabilizer. This is particularly important during the drying of the foamed PUD coating, as it can prevent drying defects such as cell coarsening and drying cracks. In the past, polyol esters have already been identified as particularly effective stabilizers for mechanically foamed PUD systems. See, for example, European Patent Application Publication No. 3487945. However, one drawback of polyol esters is that the foam-stabilizing effect of this compound classification can be impaired by the presence of additional auxiliary surfactants, particularly anionic auxiliary surfactants, present in the PUD system. However, the use of auxiliary surfactants is not uncommon, especially in the production of aqueous polyurethane dispersions. Auxiliary surfactants are used in this context to improve the dispersion of polyurethane prepolymers in water and usually remain in the final product. During the mechanical foaming of the polyurethane dispersion, the corresponding auxiliary surfactants can adversely affect the foaming properties of the system, especially when polyol esters are used for foam stabilization. As a result, the amount of air incorporated into the system is often very small, if any, and the resulting foam structure is coarse and irregular. Auxiliary surfactants can also adversely affect the stability of the foam produced, which can cause foam aging during processing of the foamed PUD system, and consequently lead to poor and defective foam coatings. Therefore, the problem that the present invention aims to solve is to provide an additive for the production of a PUD-based foaming system and foam coating that enables efficient foaming and efficient foam stabilization even in a PUD system containing auxiliary surfactants, particularly anionic auxiliary surfactants. Surprisingly, it was found that using polyol esters in combination with cationic polymer electrolytes could solve the aforementioned problems. Therefore, the present invention provides the use of a combination of polyol ester and cationic polymer electrolyte as an additive, preferably as a foaming additive, in an aqueous polymer dispersion, preferably an aqueous polyurethane dispersion, and particular