Film roll of a thermoplastic resin film

A film roll in which the distance from the center line of the film roll to the edge of the film extending in a film winding direction is slightly changed in a film breadthwise direction.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to a film roll of a thermoplastic resin film. 
More specifically, it relates to a film roll in which the distance from 
the center line of the film roll to the edge of the film extending in a 
film winding direction is slightly changed in a film breadthwise 
direction. 
A thermoplastic resin film typified by a polyester film has been 
commercialized and stored in the form of a roll, which is extremely 
effective in handling, rather than in the form of a sheet. 
Further, the thermoplastic resin film is slit with a razor blade, shear 
blade or the like and rolled to meet user's needs. In order to prevent the 
film as a product from being rolled in a bad shape due to non-uniformity 
in film thickness, that is, to prevent the roll of the film from being 
partially swollen by the successive overlapping of thick portions or 
recessed by the successive overlapping of thin portions of the film, a 
technology for slitting the film in a weaving line, for example, a slit 
width of 10 cm and a cycle of 1 km, without changing the slit width of the 
film, is employed in most cases to diminish non-uniformity in thickness. 
However, even in such a case, the film edges are made uniform extremely 
precisely in order to roll the film into a good shape. 
When the edges of the film are made uniform extremely precisely so as to 
prevent the edge surface of the film roll from becoming irregular as 
described above, the shape of the resulting roll is actually good. 
However, it has been found that the following problem arises when the film 
is actually used. 
That is, the film is used by a user not immediately after production, but 
after a while from production in most cases. Further, when the film is 
slit, the section of the film (resin) is warped by cutting and the cut 
portion is locally thicker than other portions. High pressure is locally 
applied to this edge face portion which has become thick locally (called 
high-edge portion) by contact pressure or tension exerted when the film is 
wound, and blocking occurs between the high-edge portions of the film 
while it is stored after production, thereby causing a process trouble 
such as the breakage of the film. 
It is therefore an object of the present invention to provide a film roll 
of a slit thermoplastic resin film in which high-edge portions are not 
overlapped with one another and blocking does not occur on the edge face 
of the film. 
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 film roll of a thermoplastic resin 
film in which (1) distance between at least one of the two film ends 
extending in a film winding direction of the film roll and the center line 
of the film roll changes in the film winding direction of the film roll, 
(2) the center line average surface roughness Ra.sup.E of each of the two 
edge faces of the film roll is in the range of 3 to 200 .mu.m, (3) the 
maximum depth of the concave portion of the edge faces of the film roll is 
in the range of 50 to 5,000 .mu.m, and (4) the distance between the apices 
of two adjacent convex portions in a diametric direction of the edge face 
is in the range of 200 to 1,000 .mu.m. 
The film roll of the present invention is a roll of a thermoplastic resin 
film. The distance between at least one of the two film ends extending in 
a film winding direction of the film roll and the center line of the film 
roll changes in the film winding direction of the film roll as described 
in (1) above. Distance may change between only one film end and the center 
line or between both the film ends and the center line as described above. 
The center line of the film roll is defined as a straight line parallel to 
the film winding direction at a middle point of the distance between the 
two ends of the film where the distance from an arbitrary straight line 
parallel to the film winding direction becomes maximum. The distance 
between the two ends of the film is defined as the distance between a 
straight line, parallel to the arbitrary straight line and drawn at one 
end of the film where the distance from the arbitrary straight line is 
maximum, and a straight line, parallel to the arbitrary straight line and 
drawn at the other end of the film where the distance from the arbitrary 
straight line, is maximum. 
The change of the distance in (1) above is that at least one of the two 
film ends extending in a film winding direction of the film roll satisfies 
the following equations (1) to (4): 
when 0.ltoreq.x.ltoreq.k.sub.1 and 12.5.ltoreq.k.sub.1 
.ltoreq.2.5.times.10.sup.6, 
EQU y=ax (1) 
wherein y is a difference (mm) between the distance from the center line of 
the film roll to any position of the end of the film in a film breadthwise 
direction and the distance from the center line of the film roll to a 
position of the end of the film where the distance from the center line of 
the film roll in the film breadthwise direction is minimum, x is a 
distance (mm) in a film winding direction from the position of the end of 
the film where the distance from the center line of the film roll in the 
film breadthwise direction is minimum, to any position of the end of the 
film, and 4.times.10.sup.-6 .ltoreq.a.ltoreq.4.times.10.sup.-3, 
when k.sub.1 .ltoreq.x.ltoreq.k.sub.2, 12.5.ltoreq.k.sub.1 
.ltoreq.2.5.times.10.sup.6 and 12.5.ltoreq.k.sub.2 
.ltoreq.3.5.times.10.sup.6, 
EQU y=b (2) 
wherein x and y are the same as defined in the above equation (1), and 
0.05.ltoreq.b.ltoreq.10, 
when k.sub.2 .ltoreq.x.ltoreq.k.sub.3, 12.5.ltoreq.k.sub.2 
.ltoreq.3.5.times.10.sup.6 and 25.ltoreq.k.sub.3 .ltoreq.6.times.10.sup.6, 
EQU y=-cx+d (3) 
wherein x and y are the same as defined in the above formula (1), and 
4.times.10.sup.-6 .ltoreq.c.ltoreq.4.times.10.sup.-3 and 
1.ltoreq.d.ltoreq.24, and 
when k.sub.3 .ltoreq.x.ltoreq.k.sub.4, 25.ltoreq.k.sub.3 
.ltoreq.6.times.10.sup.6 and 25.ltoreq.k.sub.4 .ltoreq.7.times.10.sup.7, 
EQU y=e (4) 
wherein x and y are the same as defined in the above equation (1), and 
0.ltoreq.e.ltoreq.5 (provided that k.sub.1 .ltoreq.k.sub.2 &lt;k.sub.3 
.ltoreq.k.sub.4). Alternatively, the change is that at least one of the 
two film ends extending in the film winding direction satisfies the 
following equation (5): 
when 0.ltoreq.x.ltoreq.k and 0.ltoreq.k.ltoreq.7.times.10.sup.6, 
EQU y=A{sin(ax+3/2.times..pi.)+1} (5) 
wherein .pi./(7.times.10.sup.6).ltoreq.a.ltoreq..pi./(1.times.10.sup.3) and 
0.05.ltoreq.A.ltoreq.10, and x and y are the same as defined in the above 
equation (1). 
The change which satisfies the equation (5) out of the above equations is 
preferred for practical application. 
The change of the end(s) of the film can be easily controlled by a 
programmed computer when the film is slit. 
As described in (2) above, the film roll of the present invention is 
characterized in that the center line average surface roughness Ra.sup.E 
of the edge face of the film roll is in the range of 3 to 200 .mu.m. When 
Ra.sup.E is less than 3 .mu.m, high pressure is applied to a high-edge 
portion and blocking occurs between the high-edge portions of the film, 
thereby causing a process trouble such as the breakage of the film. On the 
other hand, when Ra.sup.E is more than 200 .mu.m, the film is rolled in a 
bad shape disadvantageously. 
Ra.sup.E is preferably in the range of 5 to 200 .mu.m, more preferably 5 to 
100 .mu.m, particularly preferably 10 to 100 .mu.m. 
As described in (3) above, the film roll of the present invention is 
further characterized in that the maximum depth of the concave portion of 
the end face is in the range of 50 to 5,000 .mu.m. This maximum depth is 
preferably in the range of 50 to 3000 .mu.m, more preferably 100 to 2000 
.mu.m. 
As described in (4) above, the film roll of the present invention is still 
further characterized in that the distance between the apices of two 
adjacent convex portions in a diametric direction of the edge face is in 
the range of 200 to 1,000 .mu.m. This distance is preferably in the range 
of 200 to 800 .mu.m, more preferably 300 to 800 .mu.m. 
Any thermoplastic resin films are acceptable as the thermoplastic resin 
film of the present invention. The thermoplastic resin film which the 
present invention concerns is preferably an aromatic polyester film, 
particularly preferably a biaxially oriented polyethylene terephthalate 
(PET) film or a biaxially oriented polyethylene-2,6-naphthalene 
dicarboxylate (PEN) film. 
The thermoplastic resin film used in the present invention may contain such 
additives as a stabilizer, a colorant and an antistatic agent. It is 
particularly preferred to have various inert solid fine particles 
contained in the polymer to make the film surface rough so as to improve 
slipperiness. 
A biaxially oriented aromatic polyester film which is one of the 
thermoplastic resin films used in the present invention can be produced by 
melt-extruding a fully dried aromatic polyester at a temperature between 
its melting point and (melting point +70).degree. C. and quenching it on a 
casting drum to obtain an unstretched film, biaxially stretching the 
unstretched film sequentially or simultaneously, and heat setting the 
biaxially oriented film. The biaxial stretching is preferably sequential 
biaxial stretching. The unstretched film is preferably stretched to 2.3 to 
6.5 times in a longitudinal direction at 70 to 170.degree. C. and to 2.3 
to 6.5 times in a transverse direction by a stenter at 70 to 150.degree. 
C., and then heat set at 150 to 250.degree. C. under tension or under 
limited shrinkage. The heat setting time is preferably 10 to 30 seconds. 
The stretching conditions of the film in the longitudinal and transverse 
directions are preferably such conditions that the physical properties of 
the obtained biaxially oriented polyester film should satisfy required 
properties, for example, that physical properties of the film stretched in 
one direction should be almost equal to those in the other direction. In 
the case of simultaneous biaxial stretching, the above stretching 
temperature, stretching ratios, heat setting temperature and the like can 
be applied. 
So-called three-stage or four-stage stretching that the biaxially oriented 
polyester film is further stretched in a longitudinal direction and/or 
transverse direction may be employed as required. In the four-stage 
stretching, the unstretched film is stretched to 1.8 to 2.8 times in a 
longitudinal direction at 70 to 150.degree. C. and to 3.5 to 5 times in a 
transverse direction by a stenter, heat set (intermediate heat setting) at 
100 to 170.degree. C. for 10 to 30 seconds, stretched to 1.5 to 3.0 times 
in a longitudinal direction at 110 to 180.degree. C. and to 1.2 to 2.4 
times in a transverse direction by the stenter at 110 to 190.degree. C., 
and further heat set at 150 to 250.degree. C. for 10 to 30 seconds under 
tension. 
The thus produced biaxially oriented aromatic polyester film to be used in 
the present invention preferably has a thickness of 1 to 500 .mu.m, more 
preferably 3 to 350 .mu.m, particularly preferably 3 to 25 .mu.m. 
The film used in the present invention preferably has a center line average 
surface roughness Ra.sup.S of at least one surface in the range of 10 nm 
or less. The film may be a multi-layer laminate film consisting of two or 
more layers. 
In the slit film to be used for the film roll of the present invention, 
when the change of (1) above satisfies the above equations (1) to (4), it 
is a periodical change that one cycle is formed by changing x from 0 to 
k.sub.4, whereas when the change of (1) above satisfies the above equation 
(5), it is a periodical change that one cycle is formed by changing x from 
0 to k. 
The width of the film roll of the present invention can be in the range of 
100 mm to 5 m, preferably 100 mm to 1,500 mm. The diameter of the film 
roll can be in the range of 100 mm to 1 m, preferably 200 mm to 800 mm. 
The length of the rolled film is preferably in the range of 1,000 to 
50,000 m, more preferably 3,000 m to 30,000 m. 
The thermoplastic resin film, particularly biaxially oriented aromatic 
polyester film, forming the film roll of the present invention is 
advantageously used as a base film for a magnetic recording medium. 
The following examples are given to further illustrate the present 
invention. 
The values of properties in the present invention were measured and defined 
as follows: 
(a) Center Line Average Surface Roughness 
Replicas of 5 arbitrary sites of the edge face portion of the roll are 
prepared with a mixture of DE-SI-CON of Toyo Kagaku Kenkyusho and a 
special curing agent. The replicas are cut in a diametric direction of the 
roll and the cut sections thereof are observed through a microscope. A 
photomicrograph of each of the sections is taken in such a way that the 
length (Lx) in the diametric direction of the roll is to be in the range 
of 1 to 5 mm. 
The images of the photomicrographs are processed by the LEX-FS image 
processing analyzer of Nifleco Co., Ltd. and a value obtained from the 
following equation is defined as film surface roughness when the obtained 
center line roughness is expressed by z=f(x). 
##EQU1## 
(2) Depth of Concave Portion and Interval Between Apices of Two Convex 
Portions of Edge Face of Film Roll 
To measure the depth of a concave portion and the interval between the 
apices of two adjacent convex portions of the edge face of a film roll, 
replicas of 5 sites prepared in the same manner as in the above 
measurement of the "surface roughness" are cut in a direction parallel to 
the diametric direction of the roll, a photomicrograph of each of the 
sections is taken in such a way that the length (Lx) in the diametric 
direction of the film roll is to be 5 mm, and the average value of the 5 
maximum lengths out of Lx's is defined as the depth of the concave portion 
of the edge face. 
The average value of five minimum intervals between the apices of adjacent 
convex portions spaced apart from each other by 0.1 mm or more is defined 
as the interval between apices.

EXAMPLE 1 
Dimethyl terephthalate and ethylene glycol were polymerized in accordance 
with a commonly used method by adding manganese acetate as an ester 
interchange catalyst, antimony trioxide as a polymerization catalyst and 
phosphorous acid as a stabilizer to obtain polyethylene terephthalate A 
which contained substantially no inert particles. 
Polyethylene terephthalate B containing silica particles having an average 
particle diameter of 0.5 .mu.m was obtained in the same manner as 
described above. 
These polyethylene terephthalates A and B were dried at 170.degree. C. for 
3 hours and supplied separately to two extruders to be melt extruded at a 
melting temperature of 290.degree. C. using a multi-manifold co-extrusion 
die. A sheet extruded from the die was quenched to obtain a 82 .mu.m-thick 
unstretched film. 
The obtained unstretched film was preheated, stretched to 3.2 times in a 
longitudinal direction between low-speed and high-speed rolls at a film 
temperature of 95.degree. C., and quenched. Thereafter, a water-soluble 
coating solution containing a water-soluble acryl-modified polyester resin 
and acryl particles having an average particle diameter of 30 nm was 
coated on the polyethylene terephthalate A side of the longitudinally 
stretched film to a thickness of 0.005 .mu.m (0.015 .mu.m after stretching 
and drying). The coated film was then supplied to a stenter to be 
stretched to 4.1 times in a transverse direction at 110.degree. C. The 
obtained biaxially oriented film was heat set with hot air at 220.degree. 
C. for 4 seconds to obtain a 5.9 .mu.m-thick biaxially oriented laminate 
polyester film. 
This laminate film was slit to ensure that one end of the film in a film 
winding direction satisfies the following equations (1)' to (4)' and that 
the other end of the film also satisfies the same equations, and 5,000 m 
of this slit laminate film was wound around a rubber roll having an Asker 
hardness of 50.degree. to a width of 500 mm at a contact pressure of 50 
kg/m. 
EQU y=4.times.10.sup.-5 x(0.ltoreq.x.ltoreq.25,000) (1)' 
EQU y=1.0(x=25,000 to 28,000) (2)' 
EQU y=-4.times.10.sup.-5 x+2.12(28,000.ltoreq.x.ltoreq.53,000) (3)' 
EQU y=0(x=53,000 to 56,000) (4)' 
y and x are the same as defined in the above equations. The end of the film 
changed periodically such that one cycle was formed by changing x from the 
above equations (1)' to (4)'. 
Other characteristic properties of the obtained roll are shown in Table 1 
below. 
After the roll was left to stand at a relative humidity of 80% and a 
temperature of 60.degree. C. for 3 days, the film was unrolled at a rate 
of 100 m/min. No blocking occurred on the edge face. Therefore, the film 
roll was extremely good. 
Comparative Example 1 
A biaxially oriented polyester film was produced in the same manner as in 
Example 1 except that the ends of the film were not processed. 
The characteristic properties of the obtained roll are shown in Table 1. 
The film was unrolled after it was left to stand in the same manner as in 
Example 1. Blocking occurred on the edge face and the film was broken 
while it was unrolled. 
EXAMPLE 2 
The same procedure of Example 1 was repeated except that the film was slit 
to ensure that one end of the film satisfied the following equation (5)' 
and the other end also satisfied the equation. 
##EQU2## 
The characteristic properties of the obtained roll are shown in Table 1. 
This roll was left to stand in the same manner as in Example 1 and the 
film was unrolled and observed. No blocking occurred on the edge face and 
the film roll had a good shape. 
TABLE 1 
__________________________________________________________________________ 
Interval between the 
Center line average Maximum depth of apices of two adjacent 
surface roughness on concave portion of convex portions of 
edge face of roll (.mu.m) edge face of roll (.mu.m) edge face of roll 
(.mu.m) Blocking 
__________________________________________________________________________ 
Example 1 
19 300 400 No 
Example 2 21 500 500 No 
Comparative 1 5 -- Yes 
Example 1 
__________________________________________________________________________ 
As described above, in the prior art, high pressure is applied to a 
high-edge portion, which is produced when the film is slit, by contact 
pressure or tension applied when the film is wound, and blocking occurs 
between the high-edge portions of the film, thereby causing a process 
trouble such as the breakage of the film. 
The present invention, on the contrary, can provide a film roll of a 
thermoplastic resin film in which high-edge portions are not overlapped 
with one another and blocking does not occur on the edge face of the film.