Casting apparatus for formation of resin-made membrane

Details Casting apparatus for formation of resin-made membrane Casting apparatus for formation of resin-made membrane

1998-04-17

2001-08-14

Nguyen, Nam (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Means casting fluent stock operably associated with shaping...

C118S101000, C118S202000, C425S066000, C425S278000, C425SDIG001

Reexamination Certificate

active

06273704

ABSTRACT:

BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention is for the purpose of forming a film-like or sheet-like resin-made membrane (signifying a thin-film), and relates to a resin-made membrane formation casting apparatus suitably used, for example, as a biaxial oriented film machine, a non-oriented film machine, a sheet machine, and others.
2) Description of the Related Art
FIGS. 31 and 32
are respectively a side elevational view and a front elevational view each illustratively showing a prior resin-made membrane formation casting apparatus. Although
FIG. 32
shows only one end portion side of the prior apparatus in its width direction, the other end portion side is constructed in a similar way.
As shown in
FIGS. 31 and 32
, the prior apparatus is equipped with a T die
101
for extruding a molten resin from an extruding machine (not shown) into a film-like or sheet-like membrane
102
, a casting roll (cooling roll)
103
for receiving the membrane
102
extruded from the T die
101
on its outer circumferential surface to cool and deliver the membrane
102
, and a suction chamber (vacuum box)
104
for stably making the membrane
102
come closely into contact with the surface of the casting roll
103
.
In this constitution, the casting roll
103
is supported by a roll supporting shaft
106
to be rotatable with respect to a side frame
107
.
The suction chamber
104
is fixedly secured on one side surface of the T die
101
. Further, a vacuum pump
105
is in a coupled relation to the suction chamber
104
so that, when this vacuum pump
105
is placed into operation, the air between the membrane
102
and the casting roll
103
is sucked through an opening section
104
a
of the suction chamber
104
.
The opening section
104
a
is made throughout the overall width of the membrane
102
in the proximity of a portion where the membrane
102
starts to come closely into contact with the outer circumferential surface of the casting roll
103
. Further, a seal gap
104
b
is defined between the suction chamber
104
and the casting roll
103
. The dimension of the seal gap
104
b
is set to ensure a required suction force (pressure reduction level) at the close contact section between the membrane
102
and the casting roll
103
concurrently with allowing the rotation of the casting roll
103
. In
FIGS. 31 and 32
, reference numeral
108
represents wheels to be used when shifting this apparatus.
With the above-mentioned constitution, the resin molten by the non-shown extruding machine passes through the T die
101
to be extruded into a film-like or sheet-like membrane
102
which in turn, is placed on the outer circumferential surface of the casting roll
103
to be cooled for formation.
At this time, the air within the suction chamber
104
is sucked by the vacuum pump
105
so that the air in the close contact section between the membrane
102
and the casting roll
103
is sucked through the opening section
104
a
of the suction chamber
104
. Whereupon, that close contact section is pressure-reduced to discharge the air taken in between the membrane
102
and the casting roll
103
, with the result that the membrane
102
made of the molten resin can stably be brought into contact with the casting roll
103
.
In this case, depending upon the kind of resin, on the condition that an interval between the T die
101
and the casting roll
103
is small, the orientation of the molten resin due to its extension is not relieved, but the resin is cooled and solidified on the casting roll
103
, and hence, a necessary film characteristic (membrane characteristic) is unobtainable. In addition, under the condition that the interval between the T die
101
and the casting roll
103
is small, the microscopic surface irregularities occurring at the exit of the T die
101
is unreducible in the extension interval, and after being cooled and solidified, they remain as the surface roughness, thereby deteriorating the film quality (membrane quality).
Accordingly, a way of varying the interval between the T die
101
and the casting roll
103
in accordance with kinds of resins can be taken in order to attain the necessary film characteristic (membrane characteristic). However, in the prior apparatus shown in
FIGS. 31 and 32
, since the suction chamber
104
is fixed with respect to the T die
101
, difficulty is encountered to vary the interval between the T die
101
and the casting roll
103
.
For instance, even if, in the prior apparatus shown in
FIGS. 31 and 32
, the casting roll
103
is lowered to enlarge the interval between the T die
101
and the casting roll
103
, the seal gap
104
b
between the suction chamber
104
and the casting roll
103
results in enlargement to make it difficult to obtain a necessary suction force, so that the removal of the air taken in between the membrane
102
and the casting roll
103
becomes impossible, with the result that it is impossible to stably make the membrane
102
come closely into contact with the casting roll
103
.
Furthermore, according to an experiment, in the case of forming the membrane
102
through the use of a casting apparatus based upon the above-mentioned suction chamber
104
, the configuration of the vacuum space defined by the membrane-like molten resin immediately after being discharged from the T die
101
, the outer circumferential surface of the casting roll
103
and the tip portion of the suction chamber
104
, or the occurrence or non-occurrence of the flow of the outside air into that vacuum space, has influence on the stably closely contacting condition of the membrane
102
with the casting roll
103
in accordance with the conditions such as the kind of resin material being, the resin viscosity when molten, the thickness of the membrane
102
and the formation speed. Particularly, in the case of a resin with a relatively low extension viscosity, the outside-air flow situation into the vacuum space affects the stably close contact of the membrane
102
with the casting roll
103
.
For this reason, troubles take place; for example, the membrane
102
vibrates (swings) or is brought into the interior of the suction chamber
104
, and particularly in the case of high-speed formation of the membrane
102
, that influence becomes more serious. For example,
FIG. 33
shows an outside-air inflow situation (the dotted arrows denote air flows) in a cross section taken along a line S—S of
FIG. 31
, and, as shown in
FIG. 33
, the membrane
102
vibrates (swings) or is brought into the interior of the suction chamber
104
due to the occurrence of the dynamic pressure at a portion designated at B
2
and the eddy caused by the suction at a portion depicted at B
1
, which hinders the speed-up of the membrane formation.
SUMMARY OF THE INVENTION
The present invention has been developed with a view to eliminating the above-mentioned problems, and it is therefore an object of this invention to provide a casting apparatus for resin-made membrane formation which is capable of accomplishing the stable pressure reduction by a suction chamber without depending upon the dimension of the interval between a die and a cooling roll and of appropriately setting the interval between the die and the cooling roll irrespective of the kind of resin being employed so that the necessary membrane characteristic is securable to improve the quality of a resin-made membrane.
For this purpose, in accordance with the present invention, a casting apparatus for resin-made membrane formation comprises a die for extruding a molten resin into a membrane, a cooling roll for receiving the membrane extruded from the die on its outer circumferential surface to deliver it while cooling, and a suction chamber for sucking air between the membrane and the cooling roll so that the membrane is brought closely into contact with the surface of the cooling roll, wherein the suction chamber is disposed independently of the die and is located to define a necessary seal gap with respect to the cooling roll, and a mechanism for imparting c

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