Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-05-20
2002-04-30
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S327000, C428S407000, C428S447000, C428S480000, C428S483000, C428S900000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06379774
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a composite polyester film and to a magnetic recording medium. More specifically, it relates to a composite polyester film whose amount of electrostatic charge is small and which is free from blocking, rarely chipped and suitable for use as a base film for a high-density magnetic recording medium having excellent electromagnetic conversion characteristics, adhesion to a magnetic layer and adhesion to a back coat and to a magnetic recording medium comprising the same as a base film.
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 layer formed on the surface of the base film. On a surface opposite to the magnetic layer, a slippery back coat layer is formed in many cases to achieve 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 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 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.
Polyester films having improved adhesion include one whose surface is subjected to corona discharge, one whose surface is coated with an adhesive resin, and the like. In order to provide a marked adhesion effect, it is said that the surface of a polyester base film is desirably coated with an adhesive resin.
In recent years, along with an increase in magnetic recording density, the surface of a polyester film used has been made less rough and more smooth. In this case, blocking readily occurs when a conventional polyester film coated with an adhesive resin is rolled and the film is easily broken or torn when it is unrolled in the production process of a magnetic medium.
Particularly, in a deposited tape having a magnetic metal thin film formed on the surface of a polyester film by vacuum deposition, such as a deposited video tape, the base film used 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 side. When the surface of the polyester film 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 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 the contact surfaces of films and the contact surfaces of the films become a state that they are adhered to each other by pressure between the films. Film rolls after film production or before using to base films are kept at low humidity at a plant. Although 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 during storage.
A polyester film which is readily blocked is easily electrified with electricity 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, and the film easily adsorbs suspending dust in the air electrically, thereby causing a drop out in a deposited tape and the like which require high-density recording.
JP-A 61-5941 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses an adhesive polyester film for use as a base film for a magnetic metal thin film deposited magnetic recording medium, which comprises a smooth polyester film having an Ra value of 0.002 to 0.030 &mgr;m and a polymer layer formed on both sides of the polyester film, wherein at least one of the polymer layers is essentially composed of an adhesive resin and 0.1 to 30 wt % of silicone based on the adhesive resin and a magnetic layer is formed on the other polymer layer. Polyurethanes, polyester ether copolymers, water-soluble polyester copolymers and polyester copolymers containing a polyethylene glycol-sulfonic acid alkali metal salt are enumerated as the adhesive resin. It is disclosed that the silicone compound usable is a compound having a chain component represented by the following formula:
wherein R
1
is CH
3
, C
6
H
5
or H, R
2
is CH
3
, C
6
H
5
, H or functional group (such as an epoxy group, amino group or hydroxyl group), and n is an integer of 100 to 7,000.
JP-A 10-261215 discloses a polyester film for a magnetic recording medium which comprises a polyester film having a surface A with an SRa value of 2 to 4 nm and an SRz value of 10 to 40 nm and a coating layer formed on the other surface B of the polyester film, the coating layer comprising 20 to 80 wt % of an adhesive polymer prepared by copolymerizing a fluorine compound or a silicon compound and fine particles existent in the coating film and/or on the surface of the coating film, a ferromagnetic metal thin layer being formed on outside of the surface A, and a back coat layer being formed on outside of the coating layer.
JP-A 10-261216 discloses a polyester film for a magnetic recording medium which comprises a polyester film having a surface A with an SRa value of 2 to 4 nm and an SRz value of 10 to 40 nm and a polymer layer essentially composed of an adhesive resin formed on the other surface B of the polyester film, the adhesive resin being prepared by copolymerizing 0.1 to 30 wt % of a fluorine compound or silicon compound, a ferromagnetic metal thin film layer being formed on outside of the surface A and a back coat layer being formed on outside of the polymer layer.
WO98/49008 discloses a low electrostatic composite polyester film which is a composite film comprising a base film C, a coating layer A on one side of the base film C and a coating layer B on the other side of the base film C, wherein
(1) the coating layer A is made from a water-soluble resin or water-dispersible resin containing inert particles having an average particle diameter of 5 to 100 nm and has protrusions on the surface at a density of 1×10
6
to 1×10
8
/mm
2
and a center line average surface roughness (Ra-A) 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 water-soluble resin- or water-dispersible resin-containing composition which 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; and
(3) the base film C is an aromatic polyester film which does not contain inert particles or contains inert particles having an average particle diameter of 5 to 2,000 nm in an amount of 0.001 to 5.0 wt %.
This composite polyester film is used as a base film for producing a magnetic recording medium having a magnetic recording layer on outside of the coating layer A.
It is an object of the present invention to provide a composite polyester film whose amount of electrostatic charge is small and which is free from blocking, rarely chipped and suitable for use as a base film for a high-density magnetic recording medium having excellent electromagnetic conversion characteristics, adhesion to a magnetic layer and adhesion to a back coat.
It is another object of the present invention to provide a composite polyester film having a back coat layer having new composition and the above characteristic properties.
It is a further object of the present invention to provide a composite polyester film having a coating layer havi
Osawa Toshifumi
Tojo Mitsuo
Uchida Toshikazu
Teijin Limited
Thibodeau Paul
Zacharia Ramsey
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