Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1995-03-15
2001-07-24
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S690000, C428S690000, C428S690000, C428S522000, C428S900000
Reexamination Certificate
active
06265060
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic recording media, and more particularly to magnetic recording media whose magnetic layers or backside layers, if any, contain a fluorine-containing, solvent-soluble vinyl copolymer having no vinyl chloride or vinylidene chloride substituents. The present invention also relates to such a fluorine-containing vinyl copolymer itself
BACKGROUND OF THE INVENTION
Magnetic recording media generally comprise a magnetic layer coated onto at least one side of a nonmagnetizable substrate. For particulate magnetic recording media, the magnetic layer comprises a magnetic pigment dispersed in a polymeric binder. The magnetic layer may also include other components such as lubricants, abrasives, thermal stabilizers, catalysts, crosslinkers, antioxidants, dispersants, wetting agents, fungicides, bactericides, surfactants, antistatic agents, nonmagnetic pigments, coating aids, and the like.
Some forms of magnetic recording media, such as magnetic recording tape, may also have a backside coating applied to the other side of the nonmagnetizable substrate in order to improve the durability, conductivity, and tracking characteristics of the media. The backside coating also includes a polymeric binder and other components such as lubricants, abrasives, thermal stabilizers, catalysts, crosslinkers, antioxidants, dispersants, wetting agents, fungicides, bactericides, surfactants, antistatic agents, nonmagnetic pigments, coating aids, and the like.
The polymeric binders of the magnetic layer and the backside coating are commonly derived from polymers which require curing in order to provide magnetic recording media with appropriate physical and electromagnetic properties. To prepare such media, the components of the magnetic layer or the backside coating, as appropriate, are combined with a suitable solvent and thoroughly mixed to form a homogeneous dispersion. The resulting dispersion is then coated onto the nonmagnetizable substrate, after which the coating is dried, calendered if desired, and then cured.
The polymeric binders of magnetic recording media are most commonly prepared from polymer blends comprising a hard resin component, i.e., a polymer with relatively high glass transition temperature (T
g
) and modulus, and a soft resin component, i.e. a polymer with relatively low glass transition temperature and modulus. In the past, polyurethane polymers have been widely used as the soft resin component.
Copolymers based on vinyl chloride or vinylidene chloride have been widely used as the hard component of choice for use with polyurethanes, due to their miscibility and functional compatibility with polyurethanes and their relatively high glass transition temperatures, moduli, and hardnesses. Vinyl chloride or vinylidene chloride copolymers, however, tend to degrade over time, releasing gaseous HCl which can change the properties of the media as well as corrode the recording head or the like.
Accordingly, some investigators have described vinyl copolymers used in magnetic recording media, wherein the use of vinyl chloride and vinylidene chloride has been avoided. See, e.g., U.S. Pat. Nos. 5,098,783; 4,876,149; and 4,837,082; and Japanese Publication Nos. SHO 62-30162; SHO 54-84708; SHO 54-46519; and SHO 54-46518.
It is extremely desirable to lubricate the magnetic layer in order to minimize friction between the magnetic layer and the recording/playback head used to transfer signals to and from the magnetic layer. According to one approach for lubricating the magnetic layer, low molecular weight lubricant additives are blended into the dispersion used to form the magnetic layer. However, lubricants internal to the dispersion are not always desirable. Such lubricants may tend to plasticize the polymeric binder and thereby decrease the modulus of the magnetic layer. Further, excess lubricant can exude from the magnetic layer over time, leading to changes in the properties of the magnetic layer as well as to contamination of the head.
In another approach, topical lubricants having a low surface energy such as fluorinated monomers and oligomers may be applied to the surface of a magnetic recording medium such as a rigid disk. Topical lubricants are not generally used for flexible magnetic recording media such as high density diskettes because of the difficulty of providing a thin, uniform lubricant coating on the surface of such media. Incorporation of such fluorinated materials into the dispersion for the magnetic layer of a flexible medium is likewise unsuitable because of the poor solubility of the fluorinated material in common magnetic coating solvents such as methyl ethyl ketone (MEK).
What is needed in the art is a hard resin component of a polymeric binder which has no vinyl chloride or vinylidene chloride components, is soluble in common magnetic coating solvents, and is compatible with other magnetic layer and backside coating components. What is also needed in the art is a way to lubricate magnetic layers without relying solely upon low molecular weight lubricant additives.
SUMMARY OF THE INVENTION
We have now developed a magnetic recording medium whose polymeric binder system comprises a self-lubricating resin which has no vinyl chloride or vinylidene chloride components and which is soluble in methyl ethyl ketone (MEK) and other common solvents. This resin preferably is a hard resin component of the polymeric binder system. “Self-lubricating” means that the hard resin component has lubricating groups pendant from the polymer backbone that enable the polymeric binder to help lubricate the magnetic layer. As a result of using a self-lubricating hard resin component, less low molecular weight lubricant additives, or even no low molecular weight lubricant additives, may be needed.
In one aspect, the present invention concerns a magnetic recording medium comprising a magnetic layer provided on a nonmagnetizable substrate. The magnetic layer comprises a magnetic pigment dispersed in a polymeric binder, the polymeric binder comprising a resin, the resin comprising a nonchlorinated, fluorine-containing vinyl copolymer having pendant nitrile groups, pendant hydroxyl groups, and pendant fluorine-containing groups. Preferably, the vinyl copolymer is a hard resin component of the polymeric binder, the hard resin component having a T
g
of greater than 50° C., and the polymeric binder further comprises a soft resin component having a T
g
of less than 50° C. The vinyl copolymer hard resin component is compatible with other magnetic media formulation components such as the soft resin component of the polymeric binder, pigments, wetting agents and stabilizers. In preferred embodiments of the present invention, one or more components of the polymeric binder may be cured using suitable crosslinking techniques as described below.
In another aspect, the present invention concerns the nonchlorinated, fluorine-containing vinyl copolymer itself
As used throughout this specification, the term “nonchlorinated” means that the fluorine-containing vinyl copolymer contains no covalently bound chlorine atoms. Thus, the term “nonchlorinated” excludes vinyl monomers such as vinyl chloride or vinylidene chloride as monomeric components of the copolymer, but the term “nonchlorinated” does not exclude monomeric components such as (meth)acryloyloxyethyl trimethylammonium chloride in which chlorine is present as a chloride anion.
The term “vinyl” with respect to a polymeric material means that the material comprises repeating units derived from vinyl monomers. As used with respect to a vinyl monomer, the term “vinyl” means that the monomer contains a moiety having a free-radically polymerizable carbon-carbon double bond. Monomers having such moieties are capable of copolymerization with each other via the carbon-carbon double bonds.
The term “compatible” with respect to two materials means that the two materials are capable of forming a mixture in solvent with no apparent phase separation, and may be used together in a blend to provide magnetic layers with excel
Arudi Ravindra L.
Kumar Ramesh C.
Buharin Amelia A.
Imation Corp.
Resan Stevan A.
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