Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-01-10
2002-06-25
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S393500, C162S135000, C162S136000
Reexamination Certificate
active
06410097
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for efficiently producing a silicone-based printing sheet which has an excellent ability to fix a thermal transfer ink thereto and is suitable for use in forming management labels or the like therefrom.
BACKGROUND OF THE INVENTION
The present inventors previously proposed a process for producing a printing sheet by spreading a coating liquid containing a cellulosic polymer and a silicone resin as components on a carrier film comprising a poly(ethylene terephthalate) (PET) film and drying the coating to obtain an ink-receiving layer (JP-A-2000-98902 and JP-A-2000-212304). This printing sheet is intended to be used in such a manner that the ink-receiving layer is peeled from the PET film and ink information is imparted to the thus-exposed surface of the layer by thermal transfer printing to thereby obtain a printed sheet such as a management label. The use of a PET film makes this application possible.
Namely, due to the use of a PET film, the cellulosic polymer segregates and comes to be present in a higher concentration on the PET film side to thereby form an ink-receiving layer having the excellent ability to fix inks thereto. If a carrier film made of a non-polar polymer such as a silicone or olefin polymer is used, the component which segregates and comes to be present in a higher concentration on the carrier film side is the silicone resin, resulting in an ink-receiving layer to which inks are less apt to be fixed and clear ink information is difficult to impart. In the case of using a PET film, however, the ink-receiving layer formed should be peeled off at a high speed in an atmosphere having a temperature as low as about −30° C. partly because of the segregation of the cellulosic polymer. The conventional technique described above hence has a drawback that the production efficiency is low.
SUMMARY OF THE INVENTION
An object of the invention is to provide a process which is for efficiently producing a silicone-based printing sheet and capable of forming an ink-receiving layer which is excellent in the fixability of a thermal transfer ink thereto and can be peeled off easily.
The invention provides a process for producing a printing sheet which comprises spreading a coating liquid containing at least a cellulosic polymer and a silicone resin as components on a carrier film wherein at least a surface layer on the side to be coated with the coating liquid is made of poly (vinylidene fluoride), and drying the coating to form an ink-receiving layer.
According to the invention, by forming an ink-receiving layer on a poly(vinylidene fluoride) surface, not only a cellulosic polymer can be segregated and caused to be present in a higher concentration on the carrier film side to thereby enable the ink-receiving layer to be excellent in the fixability of a thermal transfer ink thereto, but also this ink-receiving layer is not strongly adhered to the poly(vinylidene fluoride) surface and can hence be easily peeled off even at ordinary temperature according to the carrier film comprising the non-polar polymer. Consequently, a printing sheet can be efficiently obtained from which a variety of printed sheets having excellent flexibility can be formed according to circumstances by imparting ink information thereto by an appropriate printing technique, e.g., thermal transfer printing.
The process of the invention comprises spreading a coating liquid containing at least a cellulosic polymer and a silicone resin as components on a carrier film wherein at least a surface layer on the side to be coated with the coating liquid is made of poly(vinylidene fluoride), and drying the coating to form an ink-receiving layer and thereby obtain a printing sheet.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The carrier film is a member for forming an ink-receiving layer thereon, and the film itself does not serve as a component of the printing sheet to be produced. The carrier film for use in the invention is one in which at least a surface layer is made of poly(vinylidene fluoride). Consequently, the carrier film may be one wholly made of poly(vinylidene fluoride), or may be one comprising a supporting substrate made of an appropriate material, such as PET, a polyolefin, paper or a metal foil, and a coating film of poly(vinylidene fluoride) formed on a surface of the substrate.
For forming an ink-receiving layer on the carrier film by coating, a coating liquid is used which contains at least a cellulosic polymer and a silicone resin as components. The cellulosic polymer is used for the purposes of improving ink fixability in thermal transfer printing, enhancing the strength of the printing sheet, etc. One or more suitable cellulosic polymers such as ethyl cellulose can be used.
On the other hand, the silicone resin is used as a substrate for the printing sheet. The silicone resin that can be used is one or more suitable polysiloxanes having structural units represented by, for example, the formula R
x
SiO
y
(wherein R represents an organic group, e.g., an aliphatic hydrocarbon group such as methyl, ethyl, or propyl, an aromatic hydrocarbon group such as phenyl, or an olefin group such as vinyl, a hydrolyzable group such as an alkoxy, or a hydroxyl group; x is 0 to 3; and y is 4 or smaller).
Examples of the silicone resin further include alkyd-modified polysiloxanes, phenol-modified silicone resins, melamine-modified polysiloxanes, epoxy-modified polysiloxanes, polyester-modified polysiloxanes, acrylic-modified polysiloxanes, urethane-modified polysiloxanes, silicones modified with a higher fatty acid ester, higher-alkoxy-modified silicones, and polyether-modified silicones. Such modified silicones may be used alone or in combination of two or more thereof.
From the standpoint of obtaining, for example, Braun tube management labels which withstand even the salvage step in which Braun tubes are treated with hot nitric acid, it is preferred to use as the silicone resin an appropriate MQ resin which is known as, e.g., a tackifier for silicone-based pressure-sensitive adhesives and comprises a polymer comprising monofunctional units M represented by the general formula R
3
SiO—and quadrifunctional units Q represented by the formula Si (O—)
4
. In the general formula, R is the same as defined above.
Printed sheets obtained by imparting ink information to the printing sheet employing the MQ resin can be satisfactorily adhered to, e.g., adherends having curved surfaces. Through a heat treatment, the printed sheets applied can be easily bonded tightly to the adherends to thereby form burned sheets satisfactorily retaining the imparted information. The burned sheets thus formed are excellent in chemical resistance, heat resistance, weatherability, and other properties because the silica yielded from the MQ resin or silicone resin by the burning has been sintered. The burned sheets can be effectively utilized as management labels or the like, for example, from the production of Braun tubes to the salvage thereof.
The printing sheet can be produced in, for example, the following manner. Ingredients including a cellulosic polymer and a silicone resin are mixed together by means of a ball mill or the like using an organic solvent or the like according to need to prepare a coating liquid. This coating liquid is spread on the poly(vinylidene fluoride) side of a carrier film by an appropriate technique, e.g., doctor blade method or gravure roll coater method, and then dried. The resulting dry coating film serving as an ink-receiving layer is peeled from the carrier film to form the target sheet.
In preparing the coating liquid, various ingredients can be incorporated thereinto for the purposes of coloration of the ink-receiving layer to be obtained and of improving the heat resistance, flexibility, and chemical resistance of the ink-receiving layer, ink fixability thereto, etc. Examples of such optional ingredients include inorganic particles and organic compounds such as silicone rubbers, hydrocarbon
Kume Katsuya
Okazaki Katsuyuki
Cameron Erma
Nitto Denko Corporation
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