Note: Descriptions are shown in the official language in which they were submitted.
CA 02798032 2012-10-30
Specification
[Title of Invention] APPARATUS FOR CHANGE OF DIRECTION
OF LONG SHEET, AND ARTICLE FLOATING APPARATUS
[Technical Field]
[0001]
The present invention relates to devices for changing (switching) the running
direction of a long sheet, and more particularly, relates to direction
changing devices
for changing the running direction of a long sheet so as to float the running
long
sheet using a pillared perforated container that emits air from its surface.
[0002]
A hollow pillared perforated container termed a "turn bar" has hitherto been
known, which changes the running direction of a running long sheet. The turn
bar
uses air supplied into a perforated container and emitted from the holes of
the
perforated container toward a long sheet, to cause the long sheet to run while
maintaining the state where the long sheet is floating from the perforated
container,
and thereby changes the running direction of the long sheet such that the
perforated
container serves as the changing point.
[0003]
Patent Document 1 discloses a direction changing device (turn roll) for
changing the running direction of a running long sheet (long base material),
the turn
roll including: air supply openings for supplying air to a hollow space within
the turn
roll; and air flow holes provided in the circumferential surface of the turn
roll.
Patent Document I discloses that, to adjust in the width direction of the turn
roll the
amount of emission from the air flow holes, partitions are provided so as to
divide
the hollow space within the turn roll in the width direction of the turn roll,
and for
each of the hollow spaces within the turn roll divided by the partitions,
independent
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air supply openings are provided that can adjust the amount of air supply.
[0004]
Patent Document 2 discloses a direction changing device (object floatation
device) for conveying a long sheet (film-like object) while floating the long
sheet
with a fluid, the direction changing device including: a multilayer surface
formed
with a plurality of thin plates so as to have a fluid hole serving as a
passage for an
externally supplied fluid; a fluid-conveying surface formed near the
multilayer
surface; and fluid flow paths formed between the thin plates, the fluid flow
paths
allowing the fluid to flow from the fluid hole to the fluid-conveying surface.
[0005]
Patent Document 3 discloses a direction changing device (film floatation
direction changing device) for changing the running direction of a running
long sheet
(film), the direction changing device including: a plurality of gas flow holes
formed
in a film-conveying surface; and a horizontally long hollow body. Further,
both axial
ends of the hollow body are fixed to the device body, and a supply tube for
supplying
a compressed fluid is connected within at least one axial end of the hollow
body,
such that the film is conveyed in a non-contact state by emitting air from the
gas
flow holes in the film-conveying surface. In particular, a cross-sectional
shape of a
corner portion of a direction changing member placed at a direction changing
portion
of a conveyance guide used to convey the film by floatation is semielliptical,
elliptical arc, semicircular, or circular arc, and surfaces on the entrance
side and the
detachment side for the conveyed film form linear surfaces parallel to the
conveying
direction of the film. Further, Patent Document 3 also discloses that a string-
like
object is wound at constant intervals around the film-conveying surface having
a
plurality of gas flow holes in the direction changing portion, the film-
conveying
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surface being the surface of a thin plate, whereby spiral gaps are formed on
the
surface so as to have a constant pitch.
[Prior Art Documents]
[Patent Documents]
[0006]
[Patent Document 1] Japanese Patent Laid-open Publication No. 2002-193508
[Patent Document 2] Japanese Patent Laid-open Publication No. 2000-016648
[Patent Document 3] Japanese Patent Laid-open Publication No. 8-245028
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0007]
Each of the conventional direction changing devices floats a long sheet by
applying air emitted from the surface of a perforated container, to the long
sheet at a
high rate. Accordingly, Patent Documents 1 to 3 basically discloses a
technical
content in which the opening areas of air flow holes are reduced in order to
increase
the flow rate of emitted air.
[0008]
However, for the purpose of increasing the flow rate of air, it is necessary
to
use a large high pressure generator for increasing the internal pressure in
the
perforated container. In addition, there has been a problem that air contains
minute
particles (dust) and therefore the use of the direction changing device at a
high flow
rate decreases the air cleanliness in the room. Further, there also has been a
problem
that the emission of a large amount of air into the room raises and scatters
dust
already accumulated in the room and therefore expands dust contamination.
Thus,
the conventional direction changing devices are not suitable for use in the
field
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where high air cleanliness is required, such as a clean room.
[0009]
In view of the above circumstances, it is an object of the present invention
to
provide a direction changing device that can be used even when the internal
pressure
in a perforated container is low, and can reduce the amount of minute
particles in a
room by reducing the amount of air diffusing from the perforated container.
[Means of Solving the Problems]
[0010]
The present inventors have intensively studied to aim the realization of a
direction changing device that can solve the following opposite problems at
the same
time: one is to securely float a long sheet from the surface of a perforated
container
and the other is to decrease the amount of air diffusing from the perforated
container.
In the course of the study, they have examined the use of a porous ceramic
sintered
product as the direction changing device. However, there is fear that the
porous
ceramic sintered product needs a large volume of compressed air to securely
float the
long sheet, resulting in an increase in the installation cost and running cost
of
compressed air supplying equipment. There is also fear that the fine particles
of the
sintered product are stirred up in the air to cause a decrease in the air
cleanness. As a
result of the further study, they have obtained the knowledge that the
formation of a
porous resin layer so as to cover the holes of a perforated container makes it
possible
to securely float a long sheet from the surface of a direction changing device
even if
the internal pressure in the perforated container is set to be relatively low.
[0011]
A direction changing device for long sheets of the present invention, which
can solve the above problems, comprises a pillared perforated container and a
porous
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resin layer covering holes of the perforated container.
[0012]
In the above direction changing device, it is recommended to take the mode
that the porous resin layer comprises a layered structure of a porous resin
membrane.
[0013]
In the above direction changing device, it is recommended to take the mode
that the porous resin layer comprises a wound structure of a porous resin
membrane.
[0014]
In the above direction changing device, it may be preferred that the porous
resin layer has a thickness of 0.1 to 20 mm.
[0015]
In the above direction changing device, it is recommended to take the mode
that the external surface of the porous resin layer at least partly has a
cylindrical
curved surface.
[0016]
In the above direction changing device, it may be preferred that the porous
resin layer has an air flow coefficient of 100 to 15,000 mL/(cm2.min.MPa).
[0017]
In the above direction changing device, it may be preferred that the porous
resin layer has a variation coefficient of air flow coefficient of not higher
than 30%.
[0018]
In the above direction changing device, it is recommended to take the mode
that the porous resin membrane is a porous polytetrafluoroethylene membrane.
[0019]
In the above direction changing device, it is recommended to take the mode
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that a reinforcing membrane is formed between the perforated container and the
porous resin layer or formed within the porous resin layer.
[0020]
In the above direction changing device, it is recommended to take the mode
that a part of the reinforcing membrane is fixed to the porous resin layer.
[0021]
In the above direction changing device, it is recommended to take the mode
that a liquid repellent agent is added to a surface of the porous resin layer.
[0022]
In the above direction changing device, it may be preferred that one or more
holes each having an internal diameter of not smaller than 1 mm are formed per
20
cm2 of surface area of the perforated container.
[0023]
In the above direction changing device, it is recommended to take the mode
that a compressed gas supplying apparatus is connected to the perforated
container.
[0024]
In the above direction changing device, it can be put into practice in the
mode
that a water vapor generating apparatus is connected to the perforated
container and
the direction changing device is used for food conveyance.
[0025]
Another direction changing device for long sheets of the present invention,
which can solve the above problems, comprises a plurality of object floatation
members arranged in parallel, which members each comprises a pillared
perforated
container and a porous resin layer covering holes of the perforated container.
[0026]
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In the above direction changing device, it may be preferred that a porous
resin
membrane is further provided detachably on the porous resin layer.
[0027]
An object floatation device of the present invention comprises a plurality of
object floatation members arranged in parallel, which members each comprises a
pillared perforated container and a porous resin layer covering holes of the
perforated container.
[Effects of the Invention]
[0028]
According to the direction changing devices of the present invention, the
formation of a porous resin layer so as to cover the holes of a perforated
container
makes it possible to securely float a long sheet from the porous resin layer
even with
a relatively low pressure in the perforated container. In addition, the amount
of air
diffusing from the direction changing device is small, and therefore, air
cleanliness is
improved in a room where the direction changing device is operated.
[Brief Description of the Drawings]
[0029]
[FIG. 1] It is a view showing the production process of a direction changing
device in the mode for carrying out the present invention.
[FIG. 2] It is a view showing the production process of the direction changing
device in the mode for carrying out the present invention.
[FIG. 3] It is a perspective view showing the production process of the
direction changing device in the mode for carrying out the present invention.
[FIG. 4] It is a view showing the usage example of the direction changing
device in the mode for carrying out the present invention.
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[FIG. 5] It is a view showing the usage example of another direction changing
device in the mode for carrying out the present invention.
[FIG. 6] It is a view showing an object conveyance device in the mode for
carrying out the present invention.
[FIG. 7] It is a view showing a test apparatus for the direction changing
devices in Examples of the present invention.
[Mode for Carrying Out the Invention]
[0030]
Direction changing devices of the present invention will be described below
by reference to the drawings. FIGS. I and 2 are views showing the production
process of a direction changing device in the mode for carrying out the
present
invention. FIG. 3 is a perspective view of the completed direction changing
device.
First, as shown in FIG. 1, a hollow pillared perforated container I is
prepared, which
has holes 2 formed in its side surface. Then, as shown in FIG. 2, a porous
resin layer
3 is formed so as to cover the holes 2 of the perforated container 1. This
produces,
as shown in FIG. 3, the direction changing device having the pillared
perforated
container I and the porous resin layer 3 covering the holes 2 of the
perforated
container 1. The porous resin layer 3 may be formed with a monolayer porous
resin
membrane. However, if the porous resin layer 3 has a layered structure
(including a
wound structure) of porous resin membranes, it is possible to secure a
preferred
thickness described later.
[0031]
When a pressurized gas is fed into the perforated container I of the direction
changing device in the mode for carrying out the present invention, the
pressurized
gas passes through the holes 2, further passes through the porous resin layer
3, and
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diffuses to the outside of the direction changing device. Although the state
of the air
flow and the internal pressure distribution on the surface of the porous resin
layer 3
at this time have not been fully elucidated, it is considered that a very
minute air
flow is generated not only in the vertical direction of the porous resin layer
3 but also
isotropically in various directions. Unlike the conventional direction
changing
devices, a large amount of high-rate air flow is not observed, however, a very
smooth
floatation for an object acts near the surface of the porous resin layer 3.
[0032]
The characteristics of such a porous resin material cannot be found in porous
ceramic sintered products and others, which have been simultaneously studied
by the
present inventors.
[0033]
FIG. 4 is a view showing the example of use of the direction changing device
in the mode for carrying out the present invention. In FIG. 4, a long sheet
(e.g., one
used as a conveyor belt for articles) is hooked around half the direction
changing
device, and a pressurized gas is fed into the perforated container I in this
state,
whereby air diffuses from the surface of the porous resin layer 3. This causes
the
long sheet to float, and therefore, the long sheet runs smoothly.
[0034]
As the material forming the porous resin layer 3, there can be used various
porous films made of resins which may include polyolefins such as polyethylene
and
polypropylene; polyvinyl chloride; polyamide; polycarbonate; polyphenylene
ether;
polyethylene terephthalate; polybutylene terephthalate; polyurethane; their
mixtures;
and their layered products. In particular, ultrahigh molecular weight
polyolefins and
polytetrafluoroethylene (PTFE) may be preferred because they have high melting
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viscosities, and therefore, even if some heat is applied to the porous resin
layer 3
after its production, the forms of pores are not significantly changed.
[0035]
In the above resins, polytetrafluoroethylene has high melting viscosity, high
heat resistance, and small amounts of gas and dust generation, and therefore,
it may
be more preferred when the direction changing device is used for applications
such
as clean rooms. Further, polytetrafluoroethylene has excellent surface release
properties, and therefore, even if the supply of the pressurized gas into the
perforated
container I is stopped due, for example, to an electric power failure during
the
running of the long sheet, the porous resin layer 3 and the long sheet
relatively
smoothly slide even while being in contact with each other. This makes it
possible to
minimize the damage of the long sheet caused by the sudden stoppage of the
entire
device system. Thus, the use of polytetrafluoroethylene as the material
forming the
porous resin layer 3 produces a very advantageous effect, even in the state
where the
pressurized gas is supplied.
[0036]
In addition, the use of PTFE as the material of the porous resin layer 3 makes
it possible to use the direction changing device in the temperature range of
from very
low temperatures, e.g., minus 100 C, to high temperatures, e.g., 260 C. If the
direction changing device is connected to a vapor generator for supplying
heated
water vapor having a high heat capacity into the perforated container 1, it is
also
possible to convey food while cooking it.
[0037]
As the porous resin membrane forming the porous resin layer 3, there can be
used a membrane having a porous structure obtained by the phase separation
method;
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a membrane having a porous structure obtained with a pore-forming agent; and a
membrane having a porous structure obtained by expansion processing. When a
pore-forming agent is used, a large content of filler as the pore-forming
agent makes
the pore size distribution wider, and the filler is likely to be removed.
Thus, it is
desirable that the content percentage of the filler may be not greater than
50% by
mass.
[0038]
When the porous resin membrane is formed by expansion processing, using a
polytetrafluoroethylene material, the porous resin membrane can be obtained by
extruding a mixture of a PTFE fine powder and a lubricant to produce a formed
product (paste-formed product); removing the lubricant from the formed
product;
and then expanding the formed product thus treated. The paste-formed product
to be
expanded can be any of unbaked, semi-baked, and baked products. The unbaked
products may be more preferred because of their excellent self-welding
properties.
The expansion method may be any of uniaxial, simultaneous biaxial, and
sequential
biaxial expansion methods, each carried out at or below the melting point of
PTFE.
Specifically, for example, the methods disclosed in the following publications
can
serve as useful references: Japanese Patent Publication Nos. 56-45773, 56-
17216;
53-55378, and 55-55379; Japanese Patent Laid-Open Publication Nos. 59-109534
and 61-207446.
[0039]
It is recommended that the porosity of the porous resin membrane may be, for
example, not lower than 40% (preferably not lower than 60% and more preferably
not lower than 70%) and not higher than 95% (preferably not higher than 93%
and
more preferably not higher than 90%). The porosity of the porous resin
membrane
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can appropriately be adjusted by the expansion ratio. The reason why the
porosities
as described above are recommended is as follows: when the porosity is too
low, the
air flow resistance of the porous resin layer 3 becomes increased, and
therefore, a
pressurized gas having a high pressure is required in order to float the long
sheet.
On the other hand, the upper limit of the porosity is not particularly
limited, but the
above range is recommended, because when the porosity is too great, the porous
resin layer 3 cannot completely make uniform the air flow from each of the
holes 2
of the perforated container 1.
[0040]
The porosity of the porous fluororesin membrane can be calculated based on
formula (1) described below, using an apparent density D2 obtained by
measuring the
mass W and apparent volume V including holes, of the porous fluororesin
membrane
(D2 = W/V in units of g/cm3), and a true density when no holes are formed (2.2
g/cm3
in the case of PTFE). In this connection, the thickness used to calculate the
volume
V can be set to be the average thickness measured with a dial thickness gauge
(the
measurements of the average thickness were made using "SM-1201 ", available
from
Teclock Corporation, in the state where no load was applied other than the
spring
load of the gauge body).
Porosity [(2.2 - D2) / 2.2)] x 100 (1)
[0041]
The thickness of a single porous resin membrane is not particularly limited.
The total thickness of the porous resin layer 3 (the thickness of a single
porous resin
membrane in the case where the porous resin membrane is a monolayer; and the
total
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thickness of the porous resin membranes in the case where a plurality of
porous resin
membranes are layered) may be, for example, not smaller than 0.1 mm,
preferably
not smaller than 0.4 mm, and more preferably not smaller than 1 mm. This is
because if the total thickness of the porous resin layer 3 is too small, there
occurs
phenomenon that the porous resin layer 3 may be removed to bulge outward away
from the perforated container I due to the pressure of the pressurized gas.
Further, it
is not possible to completely make uniform the air flow from the holes 2 of
the
perforated container 1. In this connection, the pore diameter of the porous
resin
membrane may be about 0.2 to 10 gm, preferably about 0.2 to 5 gm.
[0042]
On the other hand, if the total thickness of the porous resin layer 3 is too
great, it becomes difficult to prevent the pressurized gas from leaking in the
directions of the sides of the porous resin layer 3. Further, an increase in
the air flow
resistance of the porous resin layer 3 requires a pressurized gas having a
very high
pressure in order to float the long sheet. Thus, the total thickness of the
porous resin
layer 3 may be, for example, not greater than 20 mm, preferably not greater
than 15
mm, and more preferably not greater than 10 mm.
[0043]
As the layered form of the porous resin membrane, for example, it is possible
to wind a plurality of porous resin membranes concentrically around the
perforated
container 1. In particular, one closer to the perforated container I may
preferably
have higher porosity in the layered form of a plurality of porous resin
membranes. A
porous resin membrane having low porosity is, on the one hand, effective in
allowing
air to uniformly diffuse, but is, on the other hand, likely to cause clogging
from dust
in the air, and therefore, may lack stable driving performance over a long
period of
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time. Accordingly, it is effective to use a porous resin membrane having high
porosity, which is unlikely to cause clogging, on the perforated container 1
side of
the direction changing device, and use a porous resin membrane having low
porosity,
which is effective in allowing air to uniformly diffuse, on the outer side of
the
direction changing device. For example, the porosity of the porous resin
membrane
closest to the perforated container I is set to be equal to or greater than
1.5 times,
more preferably equal to or greater than 2 times, and still more preferably
equal to or
greater than 3 times, the porosity of the porous resin membrane on the
outermost
surface side of the direction changing device.
[0044]
As another layered form of the porous resin membrane, it is possible to wind
a single porous resin membrane around the perforated container 1. Such winding
is
preferred because after being wound around the perforated container 1, the
porous
resin membrane may be caused to contract by heating, and thereby is fixed to
the
perforated container 1. To float a long sheet 6, the vicinity of the surface
of the
porous resin layer 3 serves as an important part, and therefore, this part
needs to be
secured as a space where nothing is placed. Accordingly, it is not desirable
that the
porous resin layer 3 may be fixed using some instrument at the outer side of
the
porous resin layer 3. Thus, the layering by winding as described above is
effective
as fixing means using the heating contraction of the porous resin membrane,
and
therefore, it may be extremely preferred as the form of the direction changing
device
of the present invention. A preferred number of windings may be, for example,
not
less than two, more preferably not less than five, and still more preferably
not less
than seven, around the perforated container 1. There is no particular upper
limit to
the number of windings. From the viewpoint of the production efficiency of the
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direction changing device, the number of windings may be, for example, not
more
than 100, preferably not more than 50.
[0045]
In the layering of the porous resin membrane, it is effective to carry out
vacuum treatment on the direction changing device before heat treatment, in
order to
remove the air present between the layers. If necessary, it is also possible
to use an
adhesive of, for example, a thermoplastic resin fine powder or a heat-curable
resin
such as an epoxy resin, to adhere the layers of porous resin membranes
together. It is
possible to use not only a technique of simply applying an adhesive to the
surface of
a porous resin membrane, but also, for example, a technique of impregnating
the
pore portions of a porous resin membrane with an adhesive of a heat-curable
resin;
drying the resulting product to thereby become semi-cured (B-staged); layering
the
resulting product; and carrying out heat treatment.
[0046]
It is desirable that the air permeation coefficient (K: an index of air flow
resistance in units of mL/(cm2.min.MPa); hereinafter, the units may
occasionally be
omitted) of the porous resin layer 3 may be set to be 100 to 15000. This is
because
when the air permeation coefficient (K) is set to be not smaller than 100, it
is
possible to float the long sheet more securely. Further, when the air
permeation
coefficient (K) is smaller than 100, it may be necessary to very increase the
surface
smoothness of the porous resin layer 3, which is not economical.
[0047]
On the other hand, when the air permeation coefficient (K) is greater than
15000, there is fear that a large volume of compressed air is required,
resulting in an
increase in the installation cost and running cost of compressed air supplying
CA 02798032 2012-10-30
equipment. Further, when the long tape 6 to float is placed on an action
surface as
the surface of the porous resin layer 3, the diffusion of compressed air from
the holes
under the long tape 6 is greatly prevented, and therefore, it is not possible
to obtain
stability. Accordingly, it is desirable that the air permeation coefficient
(K) may be
set to be not greater than 15000. The air permeation coefficient (K) may more
preferably be set to be 300 to 10000, still more preferably 500 to 7000.
[0048]
The air permeation coefficient (K) can be measured in such a manner as
described above. First, compressed air having a constant pressure (MPa) is
supplied
to the perforated container 1, and the amount of air (mL/min) diffusing on the
floatation action surface as the surface of the porous resin layer 3 is
measured (using
a high precision film flow meter SF-1 U, available from HORIBA STEC, Co.,
Ltd.).
Then, the measured value of the amount of diffusing air is divided by a
measurement
area (cm2) to obtain the amount of emission V per unit area (mL/cm2.min).
Further,
similar measurements are carried out by making various changes in the pressure
P
(MPa) of compressed air to be supplied to the perforated container 1. Then,
the
measured values are plotted on a graph where the horizontal axis represents
the
supply pressure (P) and the vertical axis represents the amount of emission
(V), and
the inclination of the obtained straight line is defined as the air permeation
coefficient (K). That is, the following formulas (2) and (3) are obtained, and
therefore, the air permeation coefficient (K) can be specified.
V (mL/cm2.min) = KP (2)
K (mL/(cm2.min.MPa)) = V/P (3)
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[0049]
It is desirable that the values of the air permeation coefficient (K) should
not
vary significantly between different regions of the porous resin layer 3. This
is in
order to float the long sheet 6 in a balanced and stable manner. Accordingly,
the
variation coefficient of the air permeation coefficient may preferably be not
higher
than 30%, more preferably not higher than 15%. When the variation coefficient
(C)
is higher than 30%, there is fear that the stability of floatation may be
deteriorated.
In particular, when the long tape 6 has a narrow width, there is possibility
that the
long tape 6 may lack the stability of floatation.
[0050]
The variation coefficient (C) can be measured in such a manner as described
below. First, the floatation action surface as the surface of the porous resin
layer 3 is
divided into five equal sections. The air permeation coefficient (K) is
measured at a
measuring point representing each section, and the variation coefficient (C)
of the air
permeation coefficient (K) can be calculated according to formula (4)
described
below, using the average value (Km) and the value of the standard deviation
((Y) of
five measured values of the respective five sections.
C (%) = (a/Km) x 100 (4)
[0051]
A reinforcing membrane may preferably be formed between the perforated
container I and the porous resin layer 3, or within the porous resin layer 3.
This is in
order to prevent the porous resin layer 3 from being removed to bulging
outward
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away from the perforated container I due to the pressure of the pressurized
gas. For
example, the reinforcing membrane can be inserted between porous resin
membranes
to be layered. As the material of the reinforcing membrane, there can be used
materials having strength and rigidity without impairing air permeability,
such as
glass fiber woven fabrics; carbon fiber woven fabrics; nonwoven fabrics; woven
fabrics made of super engineering plastic fibers, e.g., aramid and Teflon
(registered
trademark); and stainless meshes. The position where the reinforcing membrane
is
placed may be any of a position close to the perforated container 1, a
position far
from the perforated container 1, and a position between the close and far
positions.
When the reinforcing membrane is placed at a position close to the perforated
container 1, it is possible to expect the function of distributing the
pressurized gas
throughout the porous resin layer 3, and the buffer function of reducing
pressure.
When the reinforcing membrane is placed at a position far from the perforated
container 1, the thickness of the porous resin membrane forming the outermost
layer
may be not smaller than 100 gm, preferably not smaller than 150 gm, and more
preferably not smaller than 200 gm, in order to prevent the irregularities of
the
reinforcing membrane from affecting the surface of the porous resin layer 3
(i.e., in
order not to disrupt the laminar flow properties of the pressurized gas
diffusing from
the surface of the porous resin layer 3).
[0052]
When porous resin membranes are adhered together, or a porous resin layer
(membrane) and the reinforcing membrane are adhered together, it is desirable
that
the adhesion may be carried out only in a part of the porous resin layer
(membrane).
This is in order not to inhibit a gas from passing through the porous resin
layer.
When fusion bonding is carried out using a reinforcing membrane having air
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permeability and fusion bonding properties, the fusion bonding may be carried
out
all over the porous resin layer.
[0053]
In this connection, heat-curable resins such as phenol and polyimide can also
be used as the material of the reinforcing membrane. These materials, however,
cannot be self-welded, and therefore, require an adhesive. There is fear that
clogging
of pores may occur from the adhesive. Thus, when such a resin material is
used, it is
desirable that the resin material may be layered with the porous resin
membrane in
the state where the resin material is semi-cured (B-staged), before being
completely
cured.
[0054]
The surface of the porous resin layer 3 may preferably be subjected to
antistatic treatment, or a liquid-repellent agent (e.g., a liquid-repellent
polymer) may
preferably be added to the surface of the porous resin layer 3 for
waterproofing and
antifouling. As the method of antistatic treatment, there can be used, for
example,
treatment with an antistatic agent containing a quaternary ammonium
surfactant, or
with an antistatic agent containing conductive fine powder such as silicate,
carbon
nanotube, or carbon nanofiber. As the method of waterproof/antifouling
treatment,
there can be used, for example, coating the surface of the porous resin layer
3 with a
water/oil-repellent polymer. This treatment makes it possible to prevent
various
contaminants such as machine oils and water droplets from penetrating into, or
being
held in, the pores of the porous resin layer 3. The contaminants reduce the
air
permeability of the porous resin layer 3. In this connection, the "liquid-
repellent
agent" as used in the claims and the specification refers to a substance
having the
property or function of repelling a liquid, and examples of the "liquid-
repellent
19
CA 02798032 2012-10-30
agent" may include "water-repellent agents", "oil-repellent agents", and
"water/oil-
repellent agents".
[0055]
The material of the perforated container I is not particularly limited, but
there
can be used a stainless material or a resin material. It is desirable that in
the surface
of the perforated container 1, one or more holes each having an inner diameter
of not
smaller than 1 mm may be formed per 20 cm2 of surface area of the perforated
container.
[0056]
As described above, the present inventors also have simultaneously studied a
porous ceramic sintered product in contrast with a porous resin material.
Thus,
findings obtained from these studies will be described for confirmation. The
pore
structure of a porous ceramic sintered product is determined by the particle
diameter,
the shape, and the sintering method of fine powder, which is a raw material.
It is,
however, extremely difficult and costly to make the sizes of the pores uniform
and
align the directions of the pores. In the present invention, a porous resin
material is
used, of which pore structure is easy to control. This greatly makes uniform
the
distribution of the pores of the porous resin membrane in the thickness
direction and
aligns the directions of the pores, and therefore, aligns the vectors of a
pressurized
gas diffusing on the surface of the porous resin membrane. This makes it
possible to
float an object to float by uniformly supporting it. That is, pores having a
pore
diameter in units of micron or submicron are uniformly and densely distributed
in the
aligned direction. This makes it possible to obtain a gas laminar flow having
excellent static pressure characteristics from a pressurized gas having a low
pressure.
In contrast, the pore structure of the porous ceramic sintered product is
isotropic in a
CA 02798032 2012-10-30
three-dimensional manner. Accordingly, a pressurized gas diffuses also from
surfaces (end surfaces) other than the surface opposing an object to float.
For
example, the end surfaces are sealed by applying a heat-curable resin or the
like to
the end surfaces and curing the heat-curable resin, which, however, is a very
time-
consuming work. In the present invention, the porous resin has a soft
structure, and
therefore, it is possible to easily seal the end surfaces only by mechanically
compressing or heat-compressing the end surfaces. Further, the porous ceramic
sintered product is generally formed as a large bulk object, and is cut into a
required
shape, or is worked into a required shape by sintering and forming with a
mold.
Thus, the porous ceramic sintered product has the demerit that cutting step
and mold-
forming step complicate the production process. In this respect, it is also
one of the
merits of the direction changing device of the present invention that it is
easy to
produce.
[0057]
FIG. 5 is a view showing the usage example of another direction changing
device in the mode for carrying out the present invention. In FIG. 5, a
direction
changing device comprises a plurality of object floatation members 13 arranged
in
parallel, which members each comprises a pillared perforated container I and a
porous resin layer 3 covering holes 2 of the perforated container 1. A long
sheet 6 is
hooked around about half the direction changing device, and a pressurized gas
is fed
into each of the perforated containers I in this state, whereby air diffuses
from the
surfaces of the porous resin layers 3. This causes the long sheet 6 to float,
and
therefore, the long sheet 6 runs smoothly.
[0058]
In the example of FIG. 5, the object floatation members 13 are arranged in a
21
CA 02798032 2012-10-30
circular shape. A plurality of object floatation members 13, however, only
need to be
arranged in parallel (i.e., such that the object floatation members are
directed in the
same direction), and may be arranged in, for example, an ellipsoidal shape.
[0059]
In the above-described direction changing device in the mode for carrying out
the present invention, a porous resin membrane (not shown) may preferably be
further provided detachably on each of the porous resin layers 3. This is
because
even when a liquid, a sticky object, or the like has become attached to the
porous
resin membrane during the operation of the direction changing device, the
porous
resin membrane may be replaced with another porous resin membrane. This
greatly
facilitates the maintenance of the direction changing device. The material of
the
porous resin membrane may be similar to that of the porous resin membrane
included
in the porous resin layer 3, and may most preferably be a porous PTFE
material.
[0060]
FIG. 6 shows an object floatation device derived from the direction changing
device of the present invention. As shown in FIG. 6, object floatation members
13,
each having a porous resin layer 3 on the surface of a perforated container 1,
are
arranged in parallel, whereby a conveyed object 12 can be conveyed by floating
it.
When the conveyed object 12 is heavy, the perforated container I may have a
prismatic shape. This increases the area of the surface of the porous resin
layer 3
opposing the conveyed object 12, and therefore, increases floatation.
Alternatively,
it is also possible to increase floatation by laying numerous perforated
containers 1
each having a reduced diameter. Although the object floatation device of the
present
invention is different in an object to float from the direction changing
device of the
present invention for changing the running direction of a long sheet; however,
these
22
CA 02798032 2012-10-30
devices are the same in the variations of the perforated container I and the
porous
resin layer 3 that can be used, and the same in the effects that can be
enjoyed. Thus,
the variations and the effects are not described in detail.
[0061]
In the example of FIG. 6, the object floatation members 13 are arranged on
the same plane. A plurality of object floatation members 13, however, only
need to
be arranged in parallel, and the object floatation members 13 may be arranged
on a
curved surface.
[Examples]
[0062]
The direction changing devices in Example of the present invention will be
described below by reference to Examples and Reference Examples. As a matter
of
course, the present invention is not limited to these Examples.
[0063]
1. Evaluation Apparatus
FIG. 7 is a view showing a test apparatus for the direction changing devices
in
Example of the present invention. In FIG. 7, a direction changing device 4 and
guide
rails 9 are fixed on a test bench 5. On the direction changing device 4 having
a
perforated container I and a porous resin layer 3, a long sheet 6 was hooked
such
that one end of the long sheet 6 was attached to a fixing bar 8 and the other
end of
the long sheet 6 was attached to a weight 7. An adhesive tape was used as the
long
sheet 6, and the pressure-sensitive adhesive side of the adhesive tape was
opposed to
the long sheet 6. A compressed gas supply apparatus (e.g., a compressor) 11
was
connected to the direction changing device 4 by a gas supply hose 10. A
pressurized
gas supplied from the compressed gas supply device 11 was introduced to the
23
CA 02798032 2012-10-30
direction changing device 4, and thereby floated the long sheet 6. The fixing
bar 8
was shifted along the guide rails 9 in the horizontal direction in this state,
whereby
the direction of the adhesive tape as the long sheet 6 was changed by 90
degrees on
the direction changing device 4.
[0064]
(Example 1)
As the perforated container 1, there was used a stainless pipe having four
holes each having a diameter of 5 mm in its central portion at equal intervals
in the
circumferential direction. The stainless pipe had an outer diameter of 34 mm,
an
inner diameter of 28 mm, and a length of 150 mm; both ends of the stainless
pipe
were welded and sealed with stainless plates each having a thickness of 2 mm;
and a
hole was formed at one end so that a connector of the gas supply hose 10 was
attached to the one end.
[0065]
As the porous resin membrane, there was used a bi-directionally expanded
porous PTFE film (available from W.L. Gore & Associates Co., Ltd.; film
thickness:
125 pm; and apparent density: 0.436). The bi-directionally expanded porous
PTFE
film was produced from PTFE fine powder available from Daikin Industries, Ltd.
(product name: Polyflon F 104) through the respective steps of paste
extrusion,
rolling, lubricant drying, expansion, and baking. The bi-directionally
expanded
porous PTFE film was cut into a size having a width of 250 mm and a length of
3 m
when used.
[0066]
As the reinforcing membrane, there was used a woven fabric made of
expanded PTFE (available from W.L. Gore & Associates Co., Ltd.; single fiber
24
CA 02798032 2012-10-30
fineness: 380 deniers; and basis weight: 183 g/m2), and the woven fabric was
cut into
a size having a width of 250 mm and a length of I m.
[0067]
On a glass plate, the bi-directionally expanded porous PTFE film and the
expanded PTFE woven fabric prepared as described above were spread in overlap
with each other so as to have the same width, while being extended so as not
to make
wrinkles. In this connection, at the front end portion, an overlap was made
such that
the front end of the bi-directionally expanded porous PTFE film was placed 10
cm
ahead of the front end of the expanded PTFE woven fabric.
[0068]
The stainless pipe described above was placed on the bi-directionally
expanded porous PTFE film at the front end portion of the spread
bidirectionally
expanded porous PTFE film and expanded PTFE woven fabric. Then, the bi-
directionally expanded porous PTFE film and the expanded PTFE woven fabric
were
wound concentrically around the stainless pipe, while tension was applied
thereto so
as not to make sag and wrinkles, such that the bi-directionally expanded
porous
PTFE film at the front end portion was placed on the stainless pipe side (the
innermost layer side).
[0069]
The stainless pipe, around which the bi-directionally expanded porous PTFE
film and the expanded PTFE woven fabric had been wound, was placed in an oven
while being mounted on a jig that supported the stainless pipe at both ends,
and was
subjected to heat treatment at 340 C. The product thus treated was removed
from
the oven about 10 hours later, while remaining mounted on the jig, and was
cooled to
room temperature by natural cooling.
CA 02798032 2012-10-30
[0070]
Then, the portions of the bi-dierctionally expanded porous PTFE film and the
expanded PTFE woven fabric, which portions protruded from both ends of the
stainless pipe, were cut off with a cutter knife, such that the film and the
woven
fabric have a width of 150 mm (the same as the length of the stainless pipe).
Further,
both ends of the stainless pipe were fastened by stainless hose bands
(available from
TOYOX Co., Ltd.; product name: Escargot). By the above method, a direction
changing device (1) was obtained, around which the bi-directionally expanded
porous PTFE film and the expanded PTFE woven fabric were wound. In this
connection, the outermost diameter of the direction changing device (1) was 42
mm.
[0071]
(Example 2)
As the porous resin membrane, there was used a uniaxially expanded porous
PTFE film (available from W.L. Gore & Associates Co., Ltd.; film thickness:
165
m; and apparent density: 0.564). The uniaxially expanded porous PTFE film was
produced from PTFE fine powder available from Daikin Industries, Ltd. (product
name: Polyflon F104) through the respective steps of paste extrusion, rolling,
lubricant drying, expansion, and baking. The uniaxially expanded porous PTFE
film
was cut into a size having a width of 250 mm and a length of 4 m.
[0072]
As the reinforcing membrane, there was used a woven fabric made of
expanded PTFE (available from W.L. Gore & Associates Co., Ltd.; fineness: 380
deniers; and basis weight: 183 g/m2), and the woven fabric was cut into a size
having
a width of 250 mm and a length of 50 cm when used.
[0073]
26
CA 02798032 2012-10-30
A direction changing device (2) was obtained under other conditions similar
to those of Example 1. The outer diameter of the direction changing device (2)
was
39 mm.
[0074]
(Example 3)
As the porous resin membrane, a polypropylene porous membrane (product
name: NG100, available from Tokuyama Corporation; thickness: 110 m) was cut
into a size having a width of 250 mm and a length of 2 m.
[0075]
As the reinforcing membrane, a 300 mesh stainless screen (available from
Mesh Corporation; wire diameter: 30 m) was cut into a size having a width of
150
mm and a length of 2 m.
[0076]
Around a stainless pipe, which was the same as in Example 1, the stainless
screen was first wound concentrically, and the polypropylene porous membrane
was
then wound concentrically without making wrinkles. Around the resulting
product, a
uniaxially expanded porous PTFE film, which was the same as in Example 2, was
further wound five times. The uniaxially expanded porous PTFE film was used
because it contracts when subjected to heat treatment and has the effect of
fastening.
[0077]
The stainless pipe was placed in an oven while being mounted on a jig, which
was the same as in Example 1, and subjected to heat treatment at 155 C. The
product thus treated was removed from the oven about 5 hours later, while
remaining
mounted on the jig, and was cooled to room temperature by natural cooling.
[0078]
27
CA 02798032 2012-10-30
A direction changing device (3) was obtained by subsequently carrying out
the same treatment as in Example 1. The outer diameter of the direction
changing
device (3) was 37 mm.
[00791
The air permeation coefficient (K) of the porous resin membrane and the
coefficient of variation (C) of the air permeation coefficient (K) in each of
the above
direction changing devices (1) to (3) are shown in Table I below.
28
CA 02798032 2012-10-30
0 0 0
>C >C >C
O cC
O O O >C >C >C
v N
pip O
O
U O
a CO
>C 4 >C >C >C
CO
O O O a . a
L cd
~y:y Q-I
0 0
O >C >C >C N
N
O
nC
ti c
S]. 0..
o_ O O O >C >C >C
L
a
a
O O a X >C >C
^ c
o a~
. . U O 00 O .--i
F W N M
O O
U O O Cl
00 O O O
M N
Q O
0
p N O C .N O C.M. 0 0 O 0 O C p
00 -0 p. U by v =v . U U 'Cp v U ' U M v U W (U
Q chi =n (~ C d [j C) b Q d Q v .b = b
CA 02798032 2012-10-30
[00811
(Reference Example 1)
A commercially available porous pipe made of ultrahigh molecular weight
polyethylene (available from Kabushiki Gaisha Someya Seisakusho; inner
diameter:
30 mm; outer diameter: 40 mm; thickness: 5 mm; length: 150 mm; and average air
hole diameter: 5 gm) was used without modification as a direction changing
device
(4).
[0082]
(Reference Example 2)
A commercially available porous pipe made of ultrahigh molecular weight
polyethylene (available from Kabushiki Gaisha Someya Seisakusho; inner
diameter:
30 mm; outer diameter: 40 mm; thickness: 5 mm; length: 150 mm; and average air
hole diameter: 15 gm) was used without modification as a direction changing
device
(5).
[0083]
(Reference Example 3)
A commercially available diffuser tube made of porous ceramics (product
name: Air Stone NR-5304, available from IWAKI Co., Ltd.) was used without
modification as a direction changing device (6).
[0084]
The air permeation coefficient (K) of the porous pipe or the diffuser tube and
the coefficient of variation (C) of the air permeation coefficient (K) of each
of the
direction changing devices (4) to (6) are shown in Table I above.
[0085]
2. Evaluation Method
CA 02798032 2012-10-30
The direction changing devices (1) to (6) were each attached to the test
apparatus as shown in FIG. 7, and were tested for change in the running
direction of
an adhesive tape. A load of 100 g/cm was applied to an adhesive tape (product
name: No. 3705 Super, available from Nitto Denko Corporation; width: 5 cm) by
dangling the weight 7 of 500 g by the adhesive tape. The pressure-sensitive
adhesive
surface was opposed to the direction changing device, and the adhesive tape
was
caused to reciprocate in the longitudinal direction on the direction changing
device in
the state where the running direction was changed by 90 degrees (FIG. 7).
Thus, it
was determined whether or not the adhesive tape was able to be shifted without
being
affected by the pressure-sensitive adhesive (the first test).
[0086]
In addition, after being left in this state for an hour, the adhesive tape was
shifted again in the longitudinal direction. Thus, it was determined whether
or not
the adhesive tape was able to be shifted without being affected by the
pressure-
sensitive adhesive (the second test).
[0087]
Table I shows the results of the tests carried out by changing the pressure of
the pressurized gas to 0.05 MPa, 0.1 MPa, 0.2 MPa, and 0.3 MPa. The direction
changing devices used were six types, i.e., (1) to (6). Table I shows the
results of the
tests carried out in the initial state of the operation of each direction
changing device
(the first test), and the results of the tests carried out an hour later (the
second test).
[0088]
The evaluation criteria of Table I are as follows:
0: the adhesive tape is able to be shifted without being affected by the
pressure-sensitive adhesive.
31
CA 02798032 2012-10-30
0: the adhesive tape is affected by the pressure-sensitive adhesive such that
jams occur in places.
X: the adhesive tape is not able to be shifted because the pressure-sensitive
adhesive is adhered to the direction changing device.
[0089]
As can be seen from the test results shown in Table 1, in the direction
changing devices (4) to (6) using a porous pipe made of ultrahigh molecular
weight
polyethylene or a porous pipe made of porous ceramics, a slight improvement
was
found when the pressure of the pressurized gas was increased to 0.3 MPa.
However,
at lower pressures, the adhesive tape was not able to be shifted because the
pressure-
sensitive adhesive became adhered to the direction changing device. In
contrast, in
the direction changing device (1) to (3) as Example of the present invention
using a
porous resin membrane, the state of the floatation of the adhesive tape was
excellent.
Thus, the adhesive tape was able to be shifted very smoothly without being
affected
by the pressure-sensitive adhesive.
[Explanation of Numerals]
[0090]
1 Perforated container
2 Hole
3 Porous resin membrane
4 Direction changing device
5 Test bench
6 Long sheet
7 Weight
8 Fixation bar
32
CA 02798032 2012-10-30
9 Guide rails
Gas supplying hose
11 Compressed gas supplying apparatus
12 Conveyed object
5 13 Object floatation member
33
