Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1998-07-21
2001-04-24
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S212000, C428S216000, C428S323000, C428S336000, C428S480000
Reexamination Certificate
active
06221461
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a biaxially oriented laminate polyester film. More specifically, it relates to a biaxially oriented laminate polyester film which enables the direct recycling of a reproduction polymer for the production of a film (to be referred to as “self-recyclability” hereinafter), has excellent electromagnetic conversion characteristics as a base film for a high-density magnetic recording medium and excellent winding and handling properties as a base film.
A biaxially oriented polyester film typified by a polyethylene terephthalate film is used for a wide range of applications, particularly as a base film for a magnetic recording medium, due to its excellent physical and chemical properties.
Along with recent efforts made to increase the density and capacity of a magnetic recording medium, a base film is desired to be flatter and thinner. However, when the surface of the base film is flattened to maintain excellent electromagnetic conversion characteristics, its slipperiness becomes insufficient. For instance, when the base film is rolled, it is wrinkled or has blocking with the result that the surface of the film roll becomes uneven, thereby reducing the yield of products and narrowing the appropriate ranges of tension, contact pressure and speed for winding the base film, whereby it is made extremely difficult to wind the base film. When the slipperiness of the base film is low in the film processing step, the friction of the base film with a metal roll increases, thereby producing abrasion dust which causes the lack of a magnetic recording signal or drop-out.
To improve the slipperiness of a polyester film, the following two methods to impart unevenness to the film surface are generally employed: (i) one in which inert particles are deposited from a residual catalyst in a raw material polymer in the production process and (ii) one in which inert particles are incorporated. Generally speaking, the larger the size and content of particles contained in the film the more the slipperiness of the film is improved.
Meanwhile, as described above, the surface of a base film is desired to be as even as possible in order to improve electromagnetic conversion characteristics. When a magnetic recording medium is formed from the base film having a rough surface, the unevenness of the surface of the base film appears on the surface of a magnetic layer even after the formation of the magnetic layer, thereby deteriorating electromagnetic conversion characteristics.
In this case, the larger the size and content of particles contained in the base film the greater the surface roughness of the base film becomes, thereby deteriorating electromagnetic conversion characteristics.
To improve both winding properties and electromagnetic conversion characteristics, which are contradictive to each other, there is a widely known means for having a base film laminated, in which one surface on which a magnetic layer is formed, of the base film is flattened for improving electromagnetic conversion characteristics and the other surface thereof is roughened for improving slipperiness.
In this case, a lubricant having a small particle diameter is used or the amount of the lubricant added is reduced to flatten the layer on the side on which the magnetic layer is formed whereas a lubricant having a large particle diameter is used or the amount of the lubricant added is increased to roughen the layer on the other side (running surface side) on which no magnetic layer is formed.
That is, the flat layer on the coating surface side and the rough layer on the running surface side greatly differ from each other in the characteristic properties of a lubricant used, such as species, particle diameter and amount.
In the case of a single-layer film, film waste produced in the production process of a film is recovered and made into chips, and the obtained chips can be recycled directly for the production of the film. In the case of a laminate film, however, the lubricant composition of chips recovered from a laminate film differs from the lubricant compositions of a rough layer and a flat layer of the laminate film. Therefore, when such chips are used for the production of a laminate film, the lubricant composition of a layer made from the recycled chips suffers a change, resulting in causing changes in the characteristic properties of the film.
Meanwhile, it has recently been proposed to use chips recovered from the laminate film in an intermediate layer portion (core layer portion) of a three-layer laminate film.
In this method, however, the intermediate layer portion must be thick enough to consume chips recovered from the laminate film as well as chips recovered from the three-layer laminate film. Therefore, the three-layer laminate film must be extremely thick. When chips containing a lubricant having a large particle diameter or a large amount of a lubricant are used even in an intermediate portion, they influence the formation of protrusions on a surface layer portion. Therefore, the use of the chips is limited.
As described above, a magnetic recording medium having a higher density and larger capacity and a base film having a smaller thickness have recently been demanded. Therefore, the thickness of the above three-layer laminate film is reduced, and it is substantially difficult to recycle chips recovered from the laminate film for the intermediate layer of the above three-layer film.
It is therefore the current situation that the chips recovered from the laminate film is scrapped, thereby boosting the costs of the film. Such scrapped films are disposed of as industrial waste but it is now difficult to dispose of such films.
It is an object of the present invention to provide a biaxially oriented laminate polyester film which enables the direct recycling of a reproduction polymer for the production of a film, that is, to provide a biaxially oriented laminate polyester film having self-recyclability.
It is another object of the present invention to provide a biaxially oriented laminate polyester film which has self-recyclability and excellent winding and handling properties and which can be used as a base film for a high-density magnetic recording medium having excellent electromagnetic conversion characteristics.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, the above objects and advantages of the present invention can be attained by a biaxially oriented laminate polyester film composed of polyester compositions and comprising two adjacent layers which differ from each other in surface roughness, wherein:
each of the layers contains at least two different lubricant particles, and each of two members out of the lubricant particles of one layer and each of two members out of the lubricant particles of the other layer have the same substrates and the same average particle diameters, respectively, and are contained in such amounts that satisfy the following expressions (1) to (3):
W
A
(
I
)/
W
A
(
II
)=(0.95-1.05)×
W
S
(
I
)/
W
B
(
II
) (1)
W
A
(
I
)<
W
B
(
I
) (2)
W
A
(
II
)<
W
B
(
II
) (3)
wherein W
A
(I) is a content (wt %) of lubricant particles I having the largest average particle diameter out of the lubricant particles contained in the first layer (layer A), W
A
(II) is a content (wt %) of lubricant particles II having the second largest average particle diameter out of the lubricant particles contained in the first layer, W
B
(I) is a content (wt %) of lubricant particles I having the largest average particle diameter out of the lubricant particles contained in the second layer (layer B), and W
B
(II) is a content (wt %) of lubricant particles II having the second largest average particle diameter out of the lubricant particles contained in the second layer.
The polyester in the present invention is an aromatic polyester comprising an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as
Kobayashi Ieyasu
Osawa Toshifumi
Le H. Thi
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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