Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Patent
1999-01-12
2000-12-12
Nakarani, D. S.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
428451, 428910, B32B 2730, B32B 2736
Patent
active
061595950
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a release film. More particularly, the present invention relates to a release film which is useful as a protective film for an adhesive coating formed using a coating solution or as a carrier film for formation of a resin sheet, a resin coating, a ceramic sheet or the like from a solution or a slurry and which undergoes very small dimensional change during the heat treatment conducted at the time of applying a coating solution, a resin or the like.
BACKGROUND ART
A release film is widely used as a protective film for a variety of adhesive coatings. An adhesive coating is generally formed by coating a coating solution comprising an adhesive and a solvent, on a base film and heating the coated base film to remove the solvent. A release film is laminated on a surface of the thus-formed adhesive coating and serves as a protective film.
A release film is also used as a carrier film for formation of a resin sheet, a resin coating, a ceramic sheet or the like. For example, a resin sheet is formed by coating a resin solution, obtained by dissolving a vinyl chloride resin or the like in a solvent, on a release film (carrier film) and heating the coated carrier film to remove the solvent. The thus-formed resin sheet is separated by peeling from the carrier sheet, and used, for example, as a vinyl chloride sheet for a marking sheet. A resin coating is formed by coating a coating solution comprising a solvent and a resin such as an adhesive and the like, on a carrier film and heating the coated carrier film to remove the solvent. A ceramic sheet is formed as a ceramic green sheet by coating a slurry, obtained by dispersing a ceramic powder, a binder, etc. in a solvent, on a carrier film and heating the coated carrier film to remove the solvent.
An organic solvent has been conventionally used as the above solvent. Recently, however, water is used more often than the organic solvent. That is, an aqueous adhesive solution such as emulsion has started to be used in the coating solution containing an adhesive, and a water-dispersed slurry has started to be used to coat the above slurry. The reason is that the use of water makes it very easy to handle the coating solution in the steps of adjusting the concentration of the aqueous adhesive solution or slurry, coating the same, and heating the same to remove a solvent because water, unlike an organic solvent, is free from the risk of fire or environmental pollution.
Water, however, has a larger surface tension ((.gamma.L) of about 73 dyne/cm) than an organic solvent. Therefore, when an aqueous coating solution such as an aqueous adhesive solution or a water-dispersed slurry is coated on a release layer having a small surface energy (for example, a silicone-based release layer has a surface tension (.gamma.S) of about 19 to 21 dyne/cm), the coating solution is scattered in droplets on the surface of the release film (this may be referred to as "cissing" hereinafter), and no uniform film can be obtained, which is a serious problem.
To alleviate the problem, it is conceivable to use a coating solution (resin solution or slurry) having a higher viscosity or to add a surfactant or the like to the coating solution in order to reduce the surface tension of the coating solution. However, these measures have the following problems; that is, if the coating solution (resin solution or slurry) having a higher viscosity is used, it is difficult not only to level the surface, namely, to make the thickness of the coating solution uniform at the time of coating, but also to reduce the thickness of a resin sheet, a resin coating, a ceramic sheet or the like. On the other hand, if a surfactant is added to the coating solution, the resulting sheet may have a reduced sheet strength depending on the kind and amount of the surfactant used, whereby products having stable quality cannot be obtained.
As for reducing the thickness of a resin sheet, a resin coating, a ceramic sheet or the like, when an organic resin such as acrylic resin or alkyd res
REFERENCES:
patent: 4426469 (1984-01-01), Marzola et al.
patent: 5932352 (1999-08-01), Higgins
Nakarani D. S.
Teijin Limited
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