Polyhydroxy polyurethane resins, which make use of carbon dioxide as a production raw material, are known for some time (see, for example, Patent Documents 1 and 2). Under the current situation, however, the development of their applications has not moved ahead, because these polyhydroxy polyurethane resins are evidently inferior in properties to polyurethane-based resins comparable as high-molecular compounds of similar type.
On the other hand, the global warming phenomenon which can be considered to be attributable to the ever-increasing emission of carbon dioxide has become a worldwide problem in recent years, and a reduction in carbon dioxide emissions has arisen as a critical technical issue for the entire world. The change to renewable resources such as biomass and methane has also become a worldwide trend from the viewpoint of the problem of exhaustible fossil resources (petroleum) (for example, Non-patent Documents 1 and 2).
Under the above-described background, the present inventors put a fresh look on the above-described polyhydroxy polyurethane resins, and have come to realize that the provision of a technology capable of enabling the development of applications of these resins is very effective. Described specifically, carbon dioxide which is a raw material for such polyhydroxy polyurethane resins is a readily-available and sustainable carbon resource, and therefore, the provision of a technology that makes effective use of plastics, in which carbon dioxide has been used as a raw material and is fixed, can find utility as an effective means for resolving problems such as warming and resource depletion which the earth confronts in recent years. The use, if possible, of polyhydroxy polyurethane resins, which can use carbon dioxide as a raw material, for example, in below-described products in which imitation leathers are used will be extremely effective because these products are used in large quantities.
Conventionally, imitation leathers have been widely used in pouches, bags, shoes, furniture, clothing, vehicle interior trim materials, electric appliances, and the like. As resins for these imitation leathers, said resins being useful upon production of these products, polyurethane-based resins are extensively used. It is to be noted that the term “imitation leather” is a generic term for leather-like products manufactured resembling natural leathers. In general, imitation leathers can be roughly divided into artificial leathers, synthetic leathers, and vinyl chloride leathers.
Artificial leathers have a structure closest to that of natural leathers among imitation leathers, and use a non-woven fabric as a base fabric in general. As a common process for the production of an artificial leather, there is, for example, a process to be described hereinafter. After a nonwoven fabric is first impregnated with a solution of a polyurethane-based resin in dimethylformamide (hereinafter abbreviated as “DMF”), the polyurethane-based resin is solidified and dried into a porous form by wet-process film formation (submerged solidification). Subsequently, using it as a base material, its surface may be coated or laminated further with a polyurethane-based resin to provide a surface layer such that a smooth tone is presented, or its surface may be ground to raise fibers such that a suede tone is presented.
On the other hand, synthetic leathers use, as a base fabric, a fabric such as a woven fabric or raised blanket, and depending on their manufacturing processes, are roughly divided into dry-process synthetic leathers and wet-process synthetic leathers in general. For the production of a dry-process synthetic leather, there are two processes, one being to coat a polyurethane-based resin directly on a base fabric and to dry it, and the other to coat a polyurethane-based resin on a sheet of release paper, to dry the polyurethane-based resin into a film, and then to bond the film and a base fabric together with an adhesive. On the other hand, a wet-process synthetic leather can be obtained by impregnating or coating a base fabric with a solution of a polyurethane-based resin in DMF, said solution being similar to that used in the above-described production of the artificial leather, and then subjecting the polyurethane-based resin to submerged solidification and drying to form a porous layer. Further, the dry-process synthetic leather and wet-process synthetic leather obtained as described above may each be coated at a surface thereof with a polyurethane-based resin or provided at a surface thereof with a laminated layer of the resin to present a smooth tone, or may each be ground at a surface thereof to raise fibers such that a suede tone is presented.
As mentioned above, the reduction of carbon dioxide emissions has become a critical worldwide issue. In the field of imitation leathers, more and more makers are also positively working on environmental measures, resulting in a move toward forming imitation leather products by using materials excellent in environmental conservation properties. A great deal of research is hence under way, for example, to reduce VOC (volatile organic compound) emissions as much as possible by using polyurethane-based resins, which are dispersible or emulsifiable in water-based media, in place of polyurethane resins that need to use an organic solvent, or to use plant-derived raw materials as production raw materials from the view point of carbon neutral. However, all the resulting imitation leather products are still different in performance compared with the conventional products, and therefore, are considered to have problems for practical applications. Moreover, these approaches are still insufficient in respect to the realization of the conservation of the current environment on the global scale (Patent Documents 3 to 5).