Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-03-23
2003-07-08
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S448000, C428S451000, C428S452000, C525S477000, C427S387000, C427S515000, C427S356000, C427S421100, C427S428010
Reexamination Certificate
active
06589659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet that is coated with silicone compounds in order to heighten the effect of preventing adhesion of stains and a process for preparing the sheet. More particularly, the invention relates to a sheet highly effective in preventing adhesion of stains which has a multi-layer construction coated with silicone compounds different in surface tension and a process for preparing the sheet.
2. Description of the Related Art
In recent years, there are a variety of sheets formed of fabric, non-woven fabric, or resin sheets that have undergone a water-repelling treatment. Examples of such sheets include raincoats, bibs for babies and infants, aprons, lunch mats, tablecloths, boots, underwear, and back sheets of sanitary goods such as diapers and sanitary napkins. This treatment is carried out to prevent adhesion of stains, to allow stains to wash out easily even though the sheets are stained, or to prevent water or stains from oozing through the sheets.
For the water-repelling treatment, sheets are coated, for example, with rubber, resins, or silicone oil. For example, Japanese Patent Laid-Open No. 194183/1985 discloses cloth where a fiber construction treated with a silicone type water repellent is coated with film formed of silicone rubber. However, this cloth can not prevent adhesion (sticking) of stains effectively even though it can repel water.
In order to prevent adhesion (sticking) of stains, sheets need still higher water repellency. For example, blood is a liquid that contains water as solvent. The surface tension of the water is about 73.0 mN/m in its standard condition and on the other hand, the surface tension of the blood is about 54.0 mN/m. Accordingly, for preventing adhesion of stains such as blood, the sheets require still higher water repellency. In addition, for blood or a protein-containing liquid to be scattered at meals, it is irrational to evaluate its adhesion only by surface tension. For example, albumin and globulin in blood and various proteins contained in a liquid to be scattered at meals have a three-dimensional structure and in addition, have various groups such as amino groups and carboxyl groups. Consequently, protein-containing stains exhibit very high adhesion as compared with water molecules having a strong tendency to cohere to themselves, caused by hydrogen bonds. Therefore, the development of sheets that have still higher water repellency and are highly effective of preventing adhesion of stains has been in demand.
In addition, conventional water repellents having low resistance to friction have a disadvantage of deteriorating in water repellency due to flaking off or producing cracks on the surface by the use in a short period of time. For improvement in anchoring effect to base materials, modification of the molecular structures of the water repellents themselves or addition of an anchoring agent (such as hot melt adhesive, urethane curing agent or the like) to the water repellents is carried out. However, practice of these methods results in deterioration in water repellency of the repellents.
SUMMARY OF THE INVENTION
The present invention is to solve the problems described above and has an object to provide a sheet having high water repellency that can prevents adhesion of protein-containing stains.
Another object of the invention is to provide a sheet that can maintain high water repellency and high effectiveness in preventing adhesion of stains in spite of friction working on its surface.
According to a first aspect of the invention, there is provided a sheet highly effective in preventing adhesion of stains, which comprises a base sheet, a first silicone compound layer formed on the surface of the base sheet, and a second silicone compound layer further formed on the surface of the first silicone compound layer, the second silicone compound layer having a lower surface tension than the first silicone compound layer. A process for preparing this sheet comprises the steps of forming a primary coat of the first silicone compound (i.e., the first silicone compound layer) on the surface of the base sheet; curing the primary coat; and forming a surface coat of the second silicone compound (i.e., the second silicone compound layer) having a lower surface tension than the first silicone compound on the surface of the primary coat.
According to a second aspect of the invention, there is provided a sheet highly effective in preventing adhesion of stains, which comprises a base sheet and a layer formed on the surface of the base sheet, wherein the layer comprises a mixture of a first silicone compound and a second silicone compound having a lower surface tension than the first silicone compound, and the second silicone compound appears on the surface of the layer more than the first silicone compound. A process for preparing this sheet comprises the steps of: forming a coat of a mixture of the first silicone compound and the second silicone compound having a lower surface tension than the first silicone compound on the base sheet; and crosslinking the silicone compounds in a condition where the second silicone compound is transferred to the surface side of the coat and first silicone compound is transferred to the base sheet side of the coat. Alternatively, the sheet may be prepared by a process comprising the steps of: forming a coat of a mixture of the first silicone compound and the second silicone compound having a lower surface tension than the first silicone compound on the base sheet; and crosslinking the silicone compounds so that the second silicone compound appears on the surface of the coat more than the first silicone compound by bleeding.
These sheets of the invention are coated with silicone on the surfaces and therefore, exhibit high water repellency. Moreover, they can prevent to a great extent the adhesion of protein-containing stains. In these sheets, still moreover, friction of the surfaces coated with the silicones does not cause deterioration in these effects.
The term “surface tension” as used for the silicone compounds in the invention means a surface tension of silicone compound in a liquid state. However, even after the silicone compounds are fixed (or solidified), it is preferable that the surface tension of the first silicone compound is higher than the surface tension of the second silicone compound.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, the presence of the first silicone compound having a certain surface tension on the base sheet side and the presence of the second silicone compound having a lower surface tension than the first silicone compound on the surface side result in heightening the effect of preventing the adhesion of stains. The sheets of the invention that are highly effective in preventing the adhesion of stains can be prepared by any one of the following three methods.
(1) A method where the first silicone compound is applied to the surface of a base sheet and then crosslinked to form a primary coat (layer) and after fixing the primary coat, the second silicone compound having a lower surface tension than the first silicone compound is applied to the surface of the primary coat to form a surface coat (layer).
(2) A method where a mixture of the first silicone compound and the second silicone compound having a lower surface tension than the first silicone compound is applied to the surface of a base sheet to form a coat (layer) and the silicone compounds are crosslinked in a condition where the second silicone compound is transferred to the surface side of the coat and the first silicone compound is transferred to the base sheet side of the coat.
(3) A method where a mixture of the first silicone compound and the second silicone compound having a lower surface tension than the first silicone compound is applied to the surface of a base sheet to form a coat (layer) and after crosslinking, the major portion of the second silicone compound is allowed to come to the surface of the coat by blee
Imai Shigeo
Tsuboi Hiroshi
Darby & Darby
Dawson Robert
Uni-Charm Corporation
Zimmer Marc S
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