Web takeup roll

A web takeup roll includes a web takeup core and a shape-memory resin layer provided on an outer circumference of the web takeup core. In the present web takeup roll, a modulus of elasticity of the shape-memory resin layer changes with temperature.

BACKGROUND OF THE INVENTION 
This invention relates to an improvement of the roll that is to be loaded 
in a takeup unit for coating or otherwise treating the surface of an 
elongated web of support (hereunder referred to simply as "a web") such as 
paper, a plastic film or a thin metal sheet. 
Products obtained by coating or otherwise treating the surface of webs are 
extensively used in industry. Since many of those products are made from 
expensive materials as typically exemplified by photo-graphic materials, 
it is desired to produce them with the highest possible yield. 
One of the causes that have lowered the yield of those products is 
transfer, or a phenomenon in which the shape of the foremost or leading 
end of a web wound onto a takeup roll is transferred under the web takeup 
pressure onto overlying turns of the web having a coating or a layer of 
surface treatment. Stated more specifically, a product of interest is 
wound onto the web takeup roll by first joining its leading end to the 
roll with adhesive tape, by application of static electricity or by some 
other means and by then winding successive turns of the web over the 
leading end of the web which takes on various shapes such as a slanting 
line, a circular arc, sawteeth and a triangle. As a result, a step, or a 
difference in level, that corresponds to the web thickness will occur 
between the surface of the roll and the shape of the leading end of the 
web and as successive turns of the web are taken up by the roll, a shape 
that is similar to that of the leading end of the web will develop in the 
stepped area in an amount that is proportional to the web takeup pressure. 
The coating or the layer of surface treatment on the surface of the web in 
that area undergoes plastic deformation and, if the product is a 
photographic material, this will cause pressure fog, uneven thickness and 
other defects that contribute to a lower yield of the final products. The 
extent of the occurrence of such defective products due to transfer is 
variable with the constituent material of the web, the diameter of the 
takeup roll, its constituent material and the condition of the takeup 
operation but, typically, such defective products occur as soon as the 
takeup operation starts and continues until several to several tens of 
turns of the web are wound up. 
Under the circumstances, it was previously attempted to eliminate the 
adverse effects of "transfer" by increasing the diameter of the takeup 
roll or taking up the web with the takeup tension being reduced for the 
first several turns of the web. However, the increase in the diameter of 
the takeup roll results in an increase in its weight, causing 
inconvenience in transport and storage aspects. Lower takeup tensions can 
cause substantial misalignment in overlapping turns of the web and the 
range of conditions that can be adopted is also limited. Another current 
practice is to use adhesive tape that is as thin as possible but the 
effectiveness of this approach which is solely directed to the reduction 
in thickness is limited. 
With a view to alleviating the adverse effects of the steps, an attempt has 
been made to wrap a soft material such as polyurethane rubber around the 
surface of the take up roll. This method has proved to be effective in the 
initial period but has no long-term utility on account of deterioration 
with time. With prolonged use, the elastic property of the rubber 
decreases and the inherent cushioning effect cannot be achieved. In 
addition, the rubber sheds off as particles that can potentially be 
incorporated into the final product. 
Several methods have been proposed to solve those problems: in one method, 
the circumference of a takeup roll is covered with a soft elastomer that 
is formed of a leather-like sheet having a surface hardness of 55-90 
degrees (see Unexamined Published Japanese Patent Application No. 
41382/1988); in another method, the circumference of a takeup roll is 
covered with a rubber layer having a hardness of 20-60 degrees (see 
Unexamined Published Japanese Utility Model Application No. 11470/1988); 
in still another method, the surface of a takeup roll is provided with a 
stepped cutout that corresponds to the shape of the leading end of the 
sheet which is to be wound onto the roll (see Unexamined Published 
Japanese Utility Model Application No. 41072/1988). 
As described above, the use of a soft surfacing material and the provision 
of steps on takeup rolls have been the two recent approaches taken to 
alleviate the transfer of steps that occurs in the first several turns of 
the web or sheet is attached. However, the first approach which uses 
rubber or some other suitable soft material on the surface of a takeup 
roll suffers disadvantages associated with rubber deterioration, its 
recovery and compatibility with film securing tape. The second approach 
involves so much difficulty in achieving registry between the cut end of a 
film and the stepped area of the takeup roll that no proper adjustments 
can be made if the film thickness varies. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished under these circumstances and 
has as an object providing a web or film takeup roll that is adjustable to 
various film thicknesses, that experiences minimum materials 
deterioration, that features effective recovery, and that has good 
compatibility with film securing tape. 
This object of the present invention can be attained by a web takeup roll 
having a web takeup core and a shape-memory resin layer formed on an outer 
circumference of the web takeup core.

DETAILED DESCRIPTION OF THE INVENTION 
The web takeup roll of the present invention may itself be made of various 
materials including a metal, a resin, etc. 
Details of the shape-memory resin to be used in the present invention are 
given in the textbook entitled "Technology of the Next-Generation 
Actuator" which was written by S. Hayashi of Mitusbishi Heavy Industries, 
Ltd. and which was used at the seminar held by The Japan Society of 
Mechanical Engineers in January 1990. The shape-memory resin is defined in 
that textbook as "a resin which, if deformed at one temperature, will 
completely recover its original shape on being raised to a higher 
temperature and which will exhibit this phenomenon in an observable state 
over a useful temperature range." There are four resins that are currently 
available on the market as common shape-memory resins and they are 
transpolyisoprene, polynorbornene, a styrene-butadiene copolymer and 
polyurethane. All of these resins have been verified to develop the 
shape-memory effect. 
FIG. 2 is a graph showing how the modulus of elasticity of the shape-memory 
resin changes with temperature. In order to insure that two different 
regions, a rubber region and a fluid region, are developed distinctly, 
each of the currently available commercial shape-memory resins is composed 
of two phase. One is a fixing phases that helps the resin retain a certain 
shape and the other is a reversible phase that reversibly undergoes 
softening and hardening to develop the shape-memory effect. 
Consisting of those two phases, the shape-memory resin can cause the 
following phenomena, in the order written, in response to temperature 
changes: 
(1) molding: 
(a) the resin is held above a certain temperature to become softened 
(thermally melted into a fluid region); 
(b) the resin is cooled to a certain shape A (the original shape is given 
in a rubber region); 
(2) setting: 
(c) an external force is applied to deform the resin from shape A to 
another shape B (the resin remains in the rubber region); 
(d) with shape B retained, the resin is further cooled; in this state, 
shape B is retained even if the external force is removed (the resin is in 
a glass region); 
(3) shape recovery: 
(e) the resin reverts to shape A upon heating to the temperature at which 
only the reversible phase will soften (the resin is in the rubber region). 
The shape-memory resin is capable of repeating steps (c)-(e) and hence 
develops the shape-memory effect through many cycles. 
The temperatures associated with the fixing and reversible phases differ 
from one resin to another but it is essential for the development of the 
shape-memory effect that the modulus of elasticity makes a substantial and 
abrupt change with temperature in the reversible phase (see Unexamined 
Published Japanese Patent Application Nos. 169314/1982, 85210/1983, 
11315/1984, 227438/1984, 36538/1985 and 264057/1986) . 
An embodiment of the present invention is described below with reference to 
FIG. 1. As shown, a shape-memory resin layer 1 is applied to the surface 
of a roll 2 and heated above the temperature where the fixing phase of the 
resin freezes. the resin layer is then cooled to freeze the fixing phase. 
Just prior to the winding up of a web, the surface of the roll is heated 
above the rubber transition temperature of the resin (i.e., above the 
reversible phase freezing point but below the fixing phase freezing point) 
and the web is subsequently taken up by the roll. At the heating 
temperature, the surface of the roll is elastic like rubber so that the 
leading end of the web attached to the roll puts a stress on the rubber 
surface to cause deformation (B). When the roll cools during or after the 
winding up of the web, the surface of the roll makes a transition to the 
glass phase and the shape B of the leading end of the web is left as 
indentation on the roll surface. For using the same roll in order to wind 
up another web, it need only to be heated again, whereupon it reverts to 
the original cylindrical shape (A). 
There is no particular limitation on the method of forming a layer of 
shape-memory resin on the surface of a takeup roll. In one method, a film 
of shape-memory resin is first prepared by either coating or molding and 
then attached to the surface of a roll. Alternatively, a layer of 
shape-memory resin is directly coated onto the surface of a cylindrical 
roll. 
The web to be used in the present invention may be selected from a broad 
range of materials including paper, plastic films, resin coated paper, an 
aluminum web, and synthetic paper. Plastic films may be made of various 
materials including polyolefins such as polyethylene and polystyrene, 
vinyl polymers including polyvinyl acetate, polyvinyl chloride and 
polystyrene, polyamides such as nylon 6,6 and nylon 6, polyesters such as 
polyethylene terephthalate and polyethylene-2,6-naphthalate, 
polycarbonates, and cellulose acetate such as cellulose triacetate and 
cellulose diacetate. Resins for use in resin coated paper are typified by, 
but not limited to, polyolefins such as polyethylene. 
The following example is provided for the purpose of further illustrating 
the present invention but is in no way to be taken as limiting. 
A cylindrical aluminum roll (i.d., 270 mm; o.d., 290 mm; wall thickness t, 
10 mm; length, 1600 mm) was coated on the outer surface with a 
shape-memory polyurethane resin layer 1 in an annular form that had an 
inside diameter (i.d.) of 290 mm, an outside diameter (o.d.) of 300 mm and 
a wall thickness of 5 mm. Before takeup operation, the roll was heated to 
a temperature of 30.degree.-100.degree. C. (preferably 
30.degree.-50.degree. C.) to remove any residual transfer of steps that 
had occurred in the previous windup operations. After thus leveling off 
the roll surface, a web consisting of a photographic material coated on a 
100-.mu.m thick polyethylene terephthalate film was wound onto the roll. 
During the takeup operation, the roll was cooled to a temperature of 
5.degree.-25.degree. C., preferably 15.degree.-25.degree. C. The leading 
end of the wound film bit into the surface of the shape-memory resin to 
produce indentation, so that the shape of that leading end of the film was 
not at all transferred onto the surface of the overlaying photographic 
material. After unwinding the film, the roll could be repeatedly used for 
taking up other webs by heating to a temperature of 30.degree.-100.degree. 
C. 
The web takeup roll of the present invention can be repeatedly used to wind 
up varying thicknesses of webs without deterioration. The surface of the 
roll achieves good recovery to the original shape and also has good 
compatibility with film securing tape. Webs and other film products can be 
wound up by this roll without causing any transfer of the leading end of 
the web or cut end of the film securing tape. Because of these features, 
the takeup roll of the present invention makes great contribution to 
improvements in the quality and yield of the final coated products.