Floating type web guiding device

In a floating type web guiding device in which a moving web is guided along a guide surface with fluid jetting holes while being floated above the guide surface, two groups of flow straightening boards are provided respectively at the web lead-in part and the web lead-out part of the guide surface in such a manner that the boards are arranged in parallel with the direction of movement of the web and perpendicular to the web surface, so that the web can be conveyed without rubbing the web surface.

REFERENCE TO RELATED APPLICATIONS 
This invention relates to U.S. Application Ser. No. 005,986, filed Jan. 21, 
1987, entitled AIR JETTING BOX and; U.S. Application Ser. No. 059,985, 
filed June 9, 1987, entitled WEB POSITION DETECTING METHOD; and U.S. 
Application Ser. No. 074,817, filed July 17, 1987, entitled METHOD AND 
APATUS OF NON-CONTACT CONVEYANCE OF A WEB, all assigned to the common 
assignee. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a floating type web guiding device which conveys 
a long belt-like material (hereinafter referred to as "a web"), while 
floating it above its guide surface. This device is used in the 
manufacture of photographic photosensitive materials such as photographic 
films and print paper, photomechanical process materials, magnetic 
recording materials such as magnetic recording tapes, or recording 
materials such as pressure-sensitive copying sheets or heat-sensitive 
copying sheets. 
2. Background of the Invention 
A floating type web guiding device is well known in the art in which a web 
is conveyed along a guide surface having fluid jetting holes or slits. The 
web is conveyed while being floatd above the guide surface. The guide 
surface is arcuate in section so that the direction of conveyance of the 
web is changed while the web is run along the curved guide surface. 
In the floating type web guiding device, the web is stably floated above 
the guide surface in the case where the radius of the guide surface 
arcuate in section is large and the tension of the web is low. On the 
other hand, in the case where the radius of the guide surface is small and 
the tension of the web is high, in order to float the web above the guide 
surface it is necessary to increase the pressure of the fluid serving as 
cushion between the web and the guide surface. When the high pressure 
fluid between the web and the guide surface is discharged from between 
there at a web lead-in part or a web lead-out part of the guide surface 
through which the web is led into or out of the space over the guide 
surface, the web is greatly vibrated or fluttered. As a result, the web 
may be brought into contact with the guide surface. 
In order to prevent the fluttering of the web, a device has been proposed 
by Japanese Patent Application (OPI) No. 93056/1985. In the conventional 
device, guide boards are extended in the direction of movement of the web 
and along the guide surface. 
It is true that the device is effective in supressing the fluttering of the 
web. However, the device is still disadvantageous in that the venturi 
effect is produced between the web and the guide boards, so that the 
pressure of fluid between the web and the guide boards is decreased and 
accordingly the amount of floating of the web is reduced. Therefore, in 
the case where, for instance, a curled web is conveyed by the device, the 
web is liable to contact the guide boards, and the manufactured product 
may not have acceptable quality. 
SUMMARY OF THE INVENTION 
Accordingly, an object of this invention is to provide a floating type web 
guiding device in which, even when the device is miniaturized or the 
tension of a web to be conveyed by the device is high, the fluttering of 
the web is suppressed and the web can be smoothly conveyed without 
contacting guide means such as the guide surface and the guide boards. 
Another object of the invention is to provide a fluid-floated web guiding 
device in which the fluttering is prevented for a web low in rigidity 
(such as a web small in thickness, held at high temperature, or having a 
low strength), and in which the web can be smoothly conveyed without 
contacting guide means such as the guide surface and the guide boards. 
The foregoing objects of the invention have been achieved by the provision 
of a floating type web guiding device in which a moving web is conveyed 
along a guide surface having fluid jetting holes or slits while being 
floated above the guide surface. According to the invention, the device 
comprises two groups of flow straightening boards provided respectively at 
a web lead-in part and a web lead-out part of the guide surface in such a 
manner that each flow straightening board is in parallel with the 
direction of movement of the web and perpendicular to the surface of the 
web.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A floating type web conveying device, a first embodiment of this invention, 
as shown in FIGS. 1(a) and 1(b), comprises an air blowing box 10 with an 
upper, aperture cylindrical plate forming a guide surface 1 which has a 
number of fluid jetting holes 6 and is arcuate in section. In the web 
conveying device, a web 2 is conveyed in the direction of the arrow while 
floating above the guide surface 1 on jets of fluid from holes 6 and 
changes the direction of travel at the guide surface 1. The web conveying 
device further comprises two groups of laterally spaced, flat flow 
straightening boards 3 which are extended respectively from the web 
lead-in part 4 and the web lead-out part 5 of the guide surface 1 in such 
a manner that the boards 3 are in parallel with the direction of movement 
of the web 2 and perpendicular to the surface of the web 2. 
A second embodiment of the invention, a floating type web guiding device, 
is as shown in FIGS. 2(a) and 2(b). In the web guiding device, a web 2 is 
run along a guide surface 1 with fluid jetting slits 7 while floating 
above the guide surface 1. Two groups of flow straightening boards 3 are 
extended respectively from the web lead-in part 4 and the web lead-out 
part 5 of the guide surface 1 in such a manner that the boards 3 are in 
parallel with the direction of movement of the web 2 and perpendicular to 
the surface of the web 2. The upper surfaces of the flow straightening 
boards 3 slope downwards from the flat guide surface 1. Several of the web 
guiding devices shown in FIG. 2(a) and 2(b) are arrangd, for instance, as 
shown in FIG. 3 so that the web is guided in the form of wave. 
The length of each flow straightening board 3 in the direction of movement 
of the web 2 and the height (or width) in the direction perpendicular to 
the web surface should be increased as much as possible in order to 
improve the flow straightening effect. It is desirable that the length in 
the direction of movement of the web is at least in a range of from 50 mm 
to 150 and the height (or width) in the direction perpendicular to the web 
is at least in a range of from 10 mm to 30 mm. The smaller the distance 
between the adjacent flow straightening boards 3, the higher is the flow 
straightening effect. However, it is practical that the flow straightening 
boards 3 are arranged at intervals of the order of 20 mm to 100 mm. It is 
effective both in reducing the floating of the web and in lowering the 
venturi effect to design the thickness of each flow straightening board in 
such a manner that the surface of the board in parallel with the web 
surface is as small as possible. Therefore, it is preferable that the flow 
straightening boards are small in thickness, for instance 1 mm to 2 mm. 
The material of the flow straightening boards should be such that the 
boards satisfy the above-described requirement of thickness and have 
sufficiently high mechanical strength. Therefore, the flow straightening 
boards may be made of a metal plate such as an iron plate, stainless steel 
plate or aluminum plate, or a plastic plate. 
Since the flow straightening boards are provided as described above, the 
flow of gas at the web lead-in part and the web lead-out part of the guide 
surface can be satisfactorily straightened in parallel with the direction 
of movement of the web, and near the flow straightening boards, the 
vibration of the web can be suppressed while the web is kept sufficiently 
floated above. 
The technical concept of the invention is applicable to the air blowing 
boxes in a web guiding device in which the web is supported by an air flow 
so that it is conveyed while being floated in wavy form as shown in FIG. 
3. 
Examples of the webs handled by the web guiding device of the invention are 
webs of paper, plastic film, metal, resin-coated paper, and synthetic 
paper. The plastic film is made of, for instance, polyolefin such as 
polyethlene or polypropylene, vinyl copolymer such as polyvinyl acetate, 
polyvinyl chloride or polystyrene, polyamide such as 6,6-nylon or 6-nylon, 
polyester such as polyethylene terephthalate or 
polyethylene-2,6-naphthalate, or cellulose acetate such as polycarbonate, 
cellulose triacetate or cellulose diacetate. Typical example of the resin 
of the resin-coated paper are polyethlene and polyolefin. However, the 
resin is not always limited thereto. The metal web may also be an aluminum 
web. 
In general, in a web guiding device of the above-described type, the 
pressurized fluid between the web and the guide surface is quickly 
discharged at the web lead-in part and the web lead-out part of the guide 
surface. In this operation, since the streams of fluids jetted from the 
number of fluid jetting holes are not always the same in direction, the 
streams of fluid collide with one another to vibrate the web. In this 
case, the web is greatly fluttered especially by the streams of fluid 
which flow in the direction of width of the web. 
However, in the web guiding device of the invention, the flow straightening 
boards are provided at the web lead-in part and the web lead-out part of 
the guide surface in such a manner that the boards are in parallel with 
the direction of movement of the web and perpendicular to the web surface 
as was described before, and therefore the streams of fluid are in 
parallel with the direction of movement of the web, and the fluttering of 
the web can be suppressed. 
In this operation, the web is steadily kept floated above the flow 
straightening boards, and the fluttering of the web is minimized. Thus, 
the web is never brought into contact with the guide surface. 
SPECIFIC EXAMPLE 
Under the conditions that, in FIG. 1, the guide surface 1 had a radius r of 
200 mm and a polyethylene terephthalate film 2 having a thickness of 120 
micrometers was conveyed with an amount of floating of 15 mm and a tension 
of 10 kg/1000 mm, the fluttering of the web 2 was measured with a laser 
displacement gage. 
When the flow straightening boards were removed from the web guiding 
device, the amplitude of the fluttering was 16 to 20 mm. On the other 
hand, in an embodiment of the invention, the device is provided with a 
plurality of flow straightening boards having a length of 150 mm in the 
direction of movement of the web, a height (or width) of 15 mm in the 
direction perpendicular to the web surface and a thickness of 5 mm and 
arranged at intervals of 80 mm. In this case, the amplitude of the 
fluttering was as small as 5 to 8 mm. 
As was described above, in the floating type web guiding device of the 
invention, the flow straightening boards for regulating the streams of 
fluid are extended from the web lead-in part and the web lead-out part of 
the guide surface, so that the web is conveyed while being steadily 
floated above the guide surface. That is, the fluttering of the web is 
suppressed. Thus, the web can be stably and smoothly conveyed over the web 
guiding device of to the invention. 
When a thin web low in rigidity is to be conveyed, the employment of the 
floating type web guiding device according to the invention is especially 
effective in suppressing the fluttering of the web. 
Furthermore, in the case also when the pressure of the fluid between the 
web and the guide surface is high, the fluttering of the web can be 
suppressed in the web guiding device of the invention. Therefore, the web 
guiding device can be miniaturized (the radius of the guide surface can be 
reduced), which contributes to a reduction of the manufacturing cost of 
the entire web conveying equipment. For the same reason, the web can be 
smoothly conveyed even under high tension.