Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2000-03-28
2002-11-12
Beck, Shrive P. (Department: 1762)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S423100, C428S480000, C428S904000, C427S245000, C427S246000, C427S389900, C427S393500
Reexamination Certificate
active
06479153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a leather-like sheet and the process for producing it. More specifically, the present invention relates to leather-like sheets, and a process for producing such sheets in which a fibrous substrate comprising an ordinary fiber or a microfine fiber is impregnated with a specific composite resin emulsion and then the emulsion is solidified. The leather-like sheet of the present invention has far more satisfactory softness and fulfillment feeling than conventional leather-like sheets obtained by first impregnating a fibrous substrate with an emulsion type resin and then drying and solidifying the resin. The leather-like sheets of the present invention have good endurance, an excellent and high-grade hand feel, and feel like natural leather.
2. Discussion of the Background
Until now, artificial leathers used as substitutes for natural leathers were made by impregnating a fibrous substrate with a resin binder, such as a polyurethane. One of two processes are typically used for producing artificial leather sheets: the wet process and the dry process. In the wet process, a fibrous substrate is impregnated with a solution in which a resin component is dissolved in an organic solvent, for example a polyurethane dissolved in dimethylformamide. The resulting impregnated fibrous sheet is then immersed in a non-solvent such as water to solidify the resin component. In the dry process, a fibrous substrate is impregnated with either a solution of a resin component dissolved in an organic solvent or an emulsion of the resin component dispersed in water, and then the resulting impregnated fibrous sheet is dried to solidify the resin component.
The wet process makes it possible to obtain a sheet having a hand feel property more similar to that of natural leather than the dry process, but the wet process suffers from poor productivity. Another problem with the wet process is that harmful organic solvents, such as dimethylformamide, are indispensable. On the other hand, such harmful organic solvents are not required for the resin emulsions which may be used in the dry process. However. the hand feel of sheets made by the dry process is far poorer than that of sheets made by the wet process. This is because in sheets prepared by the dry process, the resin moves in the fibrous substrate during the drying step, to produce a structural form in which fibers are strongly restrained in localized regions, thereby causing the softness of the sheet to be lost and making its hand feel hard. If the amount of adhesion of the resin to the fibers is reduced so as not to damage the flexibility of the sheet, the hand feel is that of the fibrous substrate, such as a nonwoven fabric, and thus a leather-like hand feel cannot be obtained. However, if the amount of adhesion of the resin is increased so as to obtain fulfillment feeling and a leather-like hand feel, the softness of the sheet is reduced, and therefore the sheet becomes hard. In either case, it is impossible to obtain a high-grade hand feel like that of natural leather. This is true in a dry process using either a resin emulsion or organic solvent solutions of the resin.
In the dry process, it may be possible to add a softener subsequent to the addition of the resin in order to improve the softness of the leather-like sheet. However, this would require the additional step of adding the softener, which would result in reduced productivity. Furthermore, even if a softener is added, it is still difficult to obtain a high-grade hand feel like that of natural leather.
Specific examples of methods in which an emulsion resin was used include a method of impregnating a fabric with a mixed resin emulsion consisting of a polyurethane emulsion and a polyacrylic ester emulsion, then treating the resulting impregnated sheet with hot water to produce a base fabric for artificial leather (Japanese Patent Application Laid-Open No. 128078/1980). In addition, a method of adding a solution of inorganic salts dissolved in an aqueous polyurethane emulsion having an average particle size of 0.1 to 2.0 &mgr;m to a nonwoven fabric sheet comprising a fiber layer made mainly of a microfine fiber having a monofilament fineness of 0.5 denier or less, and then drying the resultant impregnated sheet with heat to produce an artificial leather, was suggested (Japanese Patent Application Laid-Open No. 316877/1994). It is unclear whether the artificial leathers obtained by these methods have sufficiently improved softness and hand feel.
For the above-mentioned reasons, the wet process is currently the exclusive process adopted in the industry for producing artificial leather. The wet process is capable of producing high-quality artificial leather but has the disadvantages of having low productivity and requiring the use of an organic solvent.
However, the dry process does not require the use of any organic solvents. Consequently, the dry process has many benefits, such as being environmentally acceptable, providing a safe working environment, being very simple to operate, and so on. For this reason, there has been strong demand for development of a technique for producing a leather-like sheet that is satisfactorily soft and dense and has high quality, using an aqueous resin emulsion.
A sheet whose fibrous substrate is composed of a microfine fiber has good hand feel like that of natural leather and is used as a so-called high-class suede-like artificial leather. A typical example of a method of producing such sheets includes the method (1) of:
(a) impregnating a fibrous substrate comprised of a sea-island type microfine fiber forming composite spun fiber or blend spun fiber, with an organic solvent solution of a resin,
(b) wet-solidifying the resin,
(c) forming the microfine fiber by dissolving and removing and/or decomposing and removing the sea component with an organic solvent, an alkali solution, or the like, leaving behind the island component of the sea-island type fiber as a microfine fiber. Alternatively, another example of a method for producing such sheets, method (2), includes:
(a) forming a substrate comprising an already formed microfine fiber,
(b) impregnating the substrate with an organic solvent solution of a resin, and
(c) wet-solidifying the resulting resin saturated substrate.
However, such methods also have the above-discussed problems. If the amount of adhesion of the resin to the fiber is low enough so that the hand feel is soft, the resulting sheet has the hand feel properties of the fibrous substrate, which is not dense.
In light of this background, there is a strong demand for methods of making leather-like sheets using an environmentally acceptable aqueous resin emulsion which provides a safe working environment, and a simple production process. This process should also be capable of using fibrous substrates comprising a microfine fiber and capable of producing a high-quality leather-like sheet having excellent softness and fulfillment feeling.
SUMMARY OF THE INVENTION
An object of the present invention is to provide leather-like sheets that have excellent softness and fulfillment feeling, and have good hand feel, hand feel and physical properties like&those of natural leather and high quality suede, by a process which uses a specific resin emulsion.
The inventors have found that if a specific composite resin emulsion capable of being thermally gelled is used as a resin emulsion to impregnate a fibrous substrate, and the emulsion is then gelled, the resulting composite resin is solidified without restraining the fibers and the resin fills in between the fibers. The inventors also have found that such composite resin emulsions make it possible to provide a high quality leather-like sheet that has excellent softness and fulfillment feeling, and has very good hand feel, feel and physical properties like those of natural leather.
Furthermore, the inventors have found that if a fibrous substrate comprised of a microfine fiber-forming fiber is impregnated with an emulsion of a therma
Adachi Hideaki
Kato Mitsuru
Beck Shrive P.
Crockford Kirsten A.
Kuraray Co. Ltd.
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