Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-06-15
2001-10-30
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S337000, C428S339000, C428S421000, C428S447000, C428S480000, C428S483000, C525S100000, C525S101000, C525S443000, C525S446000, C525S447000, C525S474000, C525S479000
Reexamination Certificate
active
06309730
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field Pertinent to the Invention
The present invention relates to a releasing film. More particularly, the present invention relates to a releasing film superior in thermal stability, surface smoothness and surface flatness, which is useful as a carrier film used in production of a resin sheet, a resin coating or the like from a resin solution, or as a carrier film used in production of a ceramic sheet or the like from a ceramic slurry, or as a protective film for adhesive layer such as adhesive tape or the like. The present invention further relates to a releasing film which allows uniform coating of even aqueous adhesive coating fluid, aqueous resin solution or aqueous slurry and which can be smoothly transferred in production of adhesive coating, resin coating or sheet, or the like.
2. Prior Art
Releasing films are in use as a carrier film in producing a resin sheet, a resin coating, a ceramic sheet or the like.
That is, a resin sheet is produced, for example, by coating (casting), on a carrier film, a solution of a resin obtained by polyvinyl chloride or the like, removing the solvent contained in the solution, by heating, and peeling and removing the carrier film; and is used in applications such as marking sheet and the like.
A resin coating is produced, for example, by dissolving a resin such as an adhesive in a solvent, coating the solution on a carrier film, and removing the solvent by heating.
A ceramic sheet is produced, for example, by dispersing a ceramic powder, a binder, etc. in a solvent, coating the resulting slurry on a carrier film, removing the solvent by heating, and peeling and removing the carrier film.
In recent years, production of such a resin sheet, a resin coating, a ceramic sheet as aforementioned using a releasing film has become frequent. When a ceramic sheet or a resin sheet is used in applications requiring high performances, such as electronic parts, optical parts and the like, the sheet must have a uniform thickness and high surface properties, all of which are superior to conventional levels. A ceramic sheet, when used in production of a ceramic electronic part exemplified as a condenser, is often laminated; for obtaining a condenser of higher electrostatic capacity, the ceramic sheet is becoming thinner and coming to be used in multilayer lamination.
As IC packages or circuit substrates have become more complex, ceramic substrates are moving toward higher functions brought about by multilayer, higher performances, and smaller size and lighter weight, as in laminated condensers. In forming a multilayer circuit, throughholes are formed for layer-to-layer connection by wiring; therefore, accurate production of ceramic sheet and accurate positioning of throughholes are necessary. This is true also for resin substrates.
Hence, such a resin sheet, a ceramic sheet or the like must have a uniform thickness, high accuracy and a smooth surface. In order to produce such a sheet, the facility used for coating a coating fluid such as resin solution, adhesive, ceramic slurry or the like is required to be of high accuracy type, and the carrier film used for production of the above sheet is also required to have surface smoothness of resin sheet after peeling, flatness free from sagging or curling habit, dimensional stability after heat treatment, and good processability in punching, cutting, etc.
As the base film for the carrier film, there are used various films, for example, an olefin-based film (e.g. OPP) and a biaxially oriented polyethylene terephthalate (hereinafter abbreviated to PET in some cases) film. For example, a PET film has, in most cases, a roughened surface by adding a filler or the like for improved windability. Therefore, when a PET film containing a filler and resultantly having a rough surface is used as a carrier film for production of a resin sheet, a ceramic sheet or the like, pin holes may generate when a resin solution or the like has been coated on the carrier film, making it impossible to produce a uniform thin sheet and giving a faulty product, in some cases. When such a sheet is laminated, voids appear easily at the interface of two adjacent layers, in some cases.
When the filler or the like is restricted strictly in the size or the addition amount, the base film comes to have too small a surface roughness. As a result, in the wind-up roll for the film, the film-to-film contact area becomes large, abnormal peeling, etc. arise owing to the blocking, and film slipperiness becomes low; further, in the step of producing a resin sheet or the like, the base film has a problem in transferability, in some cases.
A releasing film, after a resin solution or a ceramic slurry has been coated thereon, is heated for removal of the solvent contained in the solution or the slurry. The heating temperature is, in many cases, close to or higher than the glass transition temperature (Tg) of the base film used in the releasing film. As a result, the releasing film causes dimensional change and thermal deformation such as wrinkles and the produced resin sheet or the like has thickness non-uniformity and poor surface smoothness and is deteriorated in quality. It is feared that with a shortened heating time and an increased heating temperature for improved productivity of the resin sheet or the like, the above quality deterioration appears as a bigger problem. Therefore, a base film of high heat resistance is desired.
A releasing film, before a resin solution or a ceramic slurry is coated thereon, is often wound in a roll form; when the roll is unwound for coating the solution or slurry thereon, the unwound releasing film shows sagging or curling at times. Thereby, the resin sheet coated on the unwound releasing film may have inferior surface flatness. Further, the prepared base film has residual internal stress, depending upon the production conditions thereof; when a resin solution or the like is coated on the releasing film, the residual internal stress is rapidly relaxed, sagging appears locally, and the resin sheet coated has inferior surface flatness.
A releasing film generally has thereon a layer of a silicone resin, a fluororesin or an aliphatic wax in order to allow the film to have releasability. A silicone resin is particularly preferred because it can be easily peeled when released, can be applied on the releasing film in a small layer thickness, and is inexpensive. The silicone resin has a small surface energy (the surface tension (&ggr;S) of the silicone resin is about 19 to 21 dyne/cm) and, therefore, almost uniform coating is possible when there is applied, on the silicone resin, an adhesive coating fluid or a resin solution which are dispersed or dissolved in an organic solvent; however, when there is applied, on the silicon resin, an aqueous adhesive coating fluid or an aqueous resin solution, the applied fluid or solution may be scattered in drops (a state of cissing), because water has a large surface tension (&ggr;L) which is about 73 dyne/cm. In order to alleviate this problem, there are taken a method of using a coating fluid (a resin solution or a slurry) of higher viscosity and a method of adding a surfactant or the like to a coating fluid to reduce the surface tension of the coating fluid. However, the method of using a coating fluid of higher viscosity has a problem in that the leveling in application of the coating fluid is difficult, the thickness of the film formed tends to be nonuniform, and it is difficult to obtain a resin sheet, a resin coating or the like in a thin layer. In case of adding a surfactant invites problems, for example, depending upon the kind and amount of the surfactant added, the sheet obtained has a low strength and it is impossible to obtain a sheet of stable quality.
A resin sheet, a resin coating, a ceramic sheet, etc., which are obtained using a releasing film, are required to have a smaller thickness and a uniform and flat surface. The presence, on the surface of the releasing film, of foreign matter and/or large projections is not preferred
Chen Vivian
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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