Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1999-05-28
2001-01-09
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S447000, C428S690000, C428S913000
Reexamination Certificate
active
06171673
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions for protective films, protective films obtained by curing them and optical recording media having said protective films, particularly to compositions with good lubricity and slidability for protective films, protective films obtained by curing them and optical recording media having said protective films.
PRIOR ART
Recently, optomagnetic recording media have been remarkably widespread as rewritable optical recording media.
FIG. 1
shows such an optomagnetic recording medium in
2
having a transparent plastic substrate
10
such as a polycarbonate. On the transparent plastic substrate
10
are successively formed a first dielectric film
11
, an optomagnetic recording film
12
, a second dielectric film
13
made from a similar material to that of the first dielectric film
11
and a protective film
14
.
When a datum is to be written into the optomagnetic recording medium
2
having the above structure, a magnetic head is entered into contact with the surface of the protective film
14
and the optomagnetic recording film
12
is irradiated with laser from the side of the transparent plastic substrate
10
to partially heat the optomagnetic recording film
12
to its Curie point, then allowed to cool down, during when recording signals are biased from the magnetic head to the optomagnetic recording film
12
so that the desired datum is written.
As the optomagnetic recording medium
2
turns at high speed, during then, the protective film
14
and the magnetic head slide on each other at high speed. Thus, the protective film
14
is desired to have a low friction coefficient. However, a protective film simply obtained by curing a binder material causes the magnetic head or the protective film to be worn or damaged.
Therefore, many attempts have been made to lower the friction coefficient of the protective film. For example, optomagnetic recording media in which a lubricant such as a silicone oil is added in a binder material such as a UV-curable resin have been developed (JPA Nos. 40149/90, 308445/90, 19842/92 and 161088/95).
However, protective films of such recording media still have insufficient characteristics, and the development of a protective film with higher lubricity and slidability is demanded.
In order to solve the above problems of the prior art, the present invention aims to provide a protective film with high lubricity and slidability, a composition capable of forming said protective film and an optical recording medium having said protective film.
SUMMARY OF THE INVENTION
We investigated the reason why protective films of the prior art are insufficient in lubricity and slidability from the viewpoint of combinations of binder materials and lubricants forming the protective films, and obtained the following findings.
If a binder material is used together with a lubricant incompatible with the binder material, the lubricant deposits on the surface of the resulting protective film to show good lubricity.
However, this combination has the drawback that the lubricity decreases with sliding cycles because the lubricant on the surface is wasted by sliding contact with the magnetic head.
A possible means to prevent the decrease of lubricity is to excessively add the lubricant, but the lubricant excessively added causes another problem, i.e. mechanical strength of the protective film is lowered and the excessive lubricant deposits on the surface to attract dust and dirt.
Furthermore, the liquid composition for such a protective film tends to phase-separate over time, so that a homogeneous protective film can not be prepared.
If a binder material is combined with a lubricant compatible with the binder material, the lubricant is taken up in the binder material to fail in an expected lubricity.
If the lubricant here is too excessively added to maintain the balance of compatibility, the lubricant deposits on the surface of the protective film to lower the strength or attract dirt as described above though the lubricity and slidability of the protective film increase.
On the other hand, optomagnetic recording media in which a layer consisting of a lubricant (i.e. lubricating film) is formed on the protective film have also been developed (JPA Nos. 128611/93, 176401/94 and 138589/95) rather than increasing the lubricity of the protective film. In these cases, the protective film itself has high mechanical strength and satisfactory lubricity and slidability, but the lubricating film is extremely sticky so that it tends to attract dust and dirt, which can not be removed once deposited to cause another problem such as crush.
This solution not only requires an additional step of forming a lubricating film on the protective film, but also inevitably involves the use of an organic solvent for diluting the lubricant to be applied as a thin and homogeneous lubricating film.
This concludes that a protective film formed from a binder material mixed with a lubricant incompatible with the binder material should require a technique for incorporating the lubricant incompatible with the binder material as much as possible without depositing on the surface.
Thus, we thought to obtain a composition for protective films in which a lubricant incompatible with the binder material is stabilized.
However, any method that a lubricant incompatible with the binder material is stably dispersed into a binder material has not been known. As a result of our careful studies, we found that, when a lubricant compatible with a binder material (hereinafter referred to as “first lubricant”) and a lubricant incompatible with the binder material but compatible with the first lubricant (hereinafter referred to as “second lubricant”) are mixed into the binder material, the second lubricant is homogeneously and stably dispersed in the binder material.
This is probably because the second lubricant is also dispersed when the first lubricant is homogeneously and stably dispersed in the binder material. The resulting dispersion including the so-called three-component system consisting of a binder material, a first lubricant and a second lubricant in good balance is thought to be very stable by the action of the first lubricant.
The dispersion can be used alone as a composition for protective films or can be added to other kinds of binder materials or the like to prepare a composition for protective films.
When the dispersion is used to be added to other kinds of binder material, the lubricity and slidability of protective films are improved with a slight amount. Thus, an optical recording medium with high lubricity and slidability can be attained simply by applying and curing the resulting composition for protective films on a recording film by a conventional procedure.
The present invention is based on the above findings, and a composition for protective films of present invention comprises a curable binder material, a first lubricant compatible with the binder material and a second lubricant incompatible with the binder material but compatible with the first lubricant.
As a composition for protective films of present invention, silicone lubricants are used for the first lubricant and the second lubricant.
For a composition for protective films of present invention, the first lubricant comprises one or more modified silicone oils selected from propylene oxide-modified silicone oils, ethylene oxide-modified silicone oils or propylene oxide and ethylene oxide-modified silicone oils.
When the above modified silicon oils are used for a first lubricant of a composition for protective films of present invention, the first lubricant is contained at a ratio of 3.0% by weight or less.
On the other hand, a second lubricant of a composition for protective films of present invention comprises an unmodified silicone oil based on dimethyl siloxane.
A composition for protective films of present invention can contain the modified silicone oil at a ratio of 0.01% by weight or more and 3.0% by weight or less.
In a composition for protective films of present inventio
Hayashi Kozaburo
Kominami Hiraku
Tanaka Mieko
Evans Elizabeth
Oliff & Berridg,e PLC
Sony Chemicals Corp.
LandOfFree
Compositions for protective films and optical recording media does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Compositions for protective films and optical recording media, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compositions for protective films and optical recording media will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2436828