Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1998-12-28
2001-06-05
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S329000, C428S332000, C428S480000, C428S481000, C428S483000, C428S510000, C428S690000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06242077
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyester film which can be used in a magnetic recording medium. More specifically, it relates to a low electrostatic polyester film, has no blocking between films, rarely experiences the transfer of a material to an opposite side of a coating layer caused by blocking and is suitable for use as a base film for a high-density magnetic recording medium having excellent electromagnetic conversion characteristics, dropout resistance and adhesion of a back coat when used in a magnetic recording medium.
BACKGROUND ART
A magnetic recording medium such as a video tape, audio tape, memory tape, magnetic sheet or magnetic disk comprises a base film and a magnetic recording layer formed on the surface of the base film. On a surface opposite to the magnetic recording layer, a slippery back coat layer is formed in many cases to increase slipperiness. As the base film of the magnetic recording medium is mainly used a polyester film. The adhesion of the polyester film to the magnetic recording layer and the adhesion of the polyester film to the slippery back coat layer are important properties. If these adhesion properties are unsatisfactory, the magnetic recording layer and the back coat layer peel off and magnetic characteristics are completely lost in the sound recording, image recording or reproduction step of the magnetic recording medium.
Problems that the Invention Intends to Solve
There are known a large number of polyester base films having improved adhesion. They include, for example, a polyester base film whose surface is subjected to corona discharge, a polyester base film whose surface is coated with an adhesive resin and the like. In order to provide a marked adhesive effect, it is desired to coat the surface of a polyester base film with an adhesive resin.
In recent years, along with an increase in magnetic recording density, the surface of a polyester film used as a base film has been made less rough and more flat. In this case, blocking readily occurs in the roll of a conventional polyester base film coated with an adhesive resin and the film is easily broken or torn when it unrolled in the production process of a magnetic medium.
Particularly, in a vacuum-deposited tape having a magnetic recording thin film layer on the surface of a polyester base film, such as a deposited video tape, the polyester base film has a low surface roughness and hence, the slipperiness of the tape traveling surface must be improved by forming a back coat layer on a side opposite to a magnetic recording layer. When the back coat layer is coated with an adhesive resin by a conventional technology to improve the adhesion of the back coat layer to the polyester film, blocking readily occurs because the surface roughness of the polyester base film is extremely low.
It is considered that this blocking is caused by the fact that moisture contained in the air permeates into the surface of the film or penetrates between surfaces of films and the surfaces of the films become a state that they are adhered to each other by pressure between the films. Although film rolls after film production or before use are kept at low humidity at a plant and it is possible to prevent blocking to a certain degree by strictly controlling storage conditions, there is no radical solution to this problem. Particularly, in the case of a polyester film for a deposited magnetic recording medium, it is impossible to prevent blocking of an adhesive film by the control of humidity alone.
A blocked rolled film may be broken when it is unrolled, or even if it is not broken, a material of a coating layer or polyester film itself may be transferred to a contacting surface by local blocking, and a dropout may be produced when a tape is formed from such a film.
A polyester film which is readily blocked is easily electrified and a high electrostatic film involves such problems that the handling properties of the film greatly deteriorate at the time of film formation and tape formation, sparks generated by electrostatic charge may ignite an organic solvent used for the formation of a tape, the film easily adsorbs suspending dust in the air electrically, and in particular, the dust causes a dropout in a deposited tape and the like which require high-density recording.
It is an object of the present invention to provide a low electrostatic polyester film whose amount of electrostatic charge is small and which is free from blocking between films, rarely experiences the transfer of a material to an opposite side of a coating layer caused by blocking and is suitable for use as a base film for a high-density magnetic recording medium having excellent electromagnetic conversion characteristics, dropout resistance and adhesion of a back coat when it is used in a magnetic recording medium.
Means for Solving the Problems
According to the studies conducted by the inventors of the present invention, it has been found that the above object of the present invention can be attained by a low electrostatic composite polyester film having the following features (1) to (3), which comprises a base film C, a coating layer A formed on one side of the base film C and a coating layer B formed on the other side of the base film C.
(1) The coating layer A is formed of a water-soluble or water-dispersible resin containing inert particles having an average particle diameter of 5 to 100 nm and has protrusions at a density of 1×10
6
to 1×10
8
/mm
2
on the surface and a center line average roughness (Ra−A) of the surface of 0.1 to 2 nm.
(2) The coating layer B comprises 1 to 40 wt % of inert particles having an average particle diameter of 20 to 100 nm and 60 to 99 wt % of a composition containing a water-soluble or water-dispersible resin and the resin-containing composition contains 5 to 85 wt % of a silicone-modified polyester resin or 1 to 30 wt % of silicone or wax based on the layer B.
(3) The base film C is an aromatic polyester film which may contain no inert particles or may contain inert particles having an average particle diameter of 5 to 2,000 nm in an amount of 0.001 to 5.0 wt %.
The present invention is a low electrostatic composite polyester which comprises at least three layers: a polyester base film C, a coating layer A formed on one side of the polyester film C and a coating layer B formed on the other side of the polyester film C and has the improved property of suppressing charging with static electricity by means of the coating layer A and/or the coating layer B and blocking between films.
The low electrostatic composite polyester film of the present invention will be described in detail hereinafter.
The aromatic polyester forming the core layer C of the composite film of the present invention is selected from polyethylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate and the like. Of these, polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are preferred.
The above polyester may be either a homopolyester or a copolyester. Copolymer components that are copolymerizable with polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyoxyethylene glycol, p-xylene glycol and 1,4-cyclohexanedimethanol; other dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid (for polyethylene-2,6-naphthalene dicarboxylate), 2,6-naphthalenedicarboxylic acid (for polyethylene terephthalate) and 5-sodium sulfoisophthalic acid; oxycarboxylic acid components such as p-oxyethoxybenzoic acid; and the like. The amount of the copolymer component is preferably 20 mol % or less, more preferably 10 mol % or less, based on the total of all dicarboxylic acid components.
Further, a polyfunctional compound having a 3 or more functional groups, such as trimellitic acid or pyromellitic acid, may be copolymeri
Osawa Toshifumi
Tojo Mitsuo
Uchida Toshikazu
Copenheaver Blaine
Roché Leanna
Sughru, Mion, Zinn, Macpeak & Seas, PLLC
Teijin Limited
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