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

1998-12-17

2001-01-02

Mackey, James P. (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

With means cleaning and purifying atmosphere surrounding...

C425S224000, C425S404000, C264S556000

Utility Patent

active

06168412

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 (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. 11 and 12
are respectively a side elevational view and a front elevational view each illustratively showing a prior resin-made membrane formation casting apparatus. Although
FIG. 12
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. 11 and 12
, 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. 11 and 12
, 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 adjusting 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).
In the apparatus shown in
FIGS. 11 and 12
, although the interval between the T die
101
and the casting roll
103
is not necessarily easy to vary because the suction chamber
104
is in a fixed relation to the T die
101
, the adjustment of the interval between the T die
101
and the casting roll
103
is accomplished through the adjustment of the fitting condition of the suction chamber
104
to the T die
101
or through the adjustment in relative position between the casting roll
103
and the T die
101
based upon the movement of the casting roll
103
by the wheels
108
.
However, in such a prior resin-made membrane formation casting apparatus, since the suction of ambient air takes place when the vacuum pump
105
sucks air from the close contact section between the membrane
102
and the casting roll
103
, depending upon the air suction gas quantity, the surface temperature of the inner wall of the suction chamber
104
varies due to the heat transfer between the inner wall surface of the suction chamber
104
and the suction air flows at the atmospheric temperature level.
Particularly, in the case of a large suction gap quantity (high negative pressure), the thermal conductivity rises between the inner wall surface of the suction chamber
104
and the suction air flows at the atmospheric temperature level, so that the surface temperature of the inner wall surface of the suction chamber
104
may decrease to the atmospheric level.
In general, in a resin-made membrane formation casting apparatus for forming a plastic film or a sheet-like resin-made membrane made of a material such as a polyethylene, polypropylene, polyethylene terephthalate and nylon, in the vicinity of an extruding machine for extrusion of a molten resin, particularly, at the periphery of the T die
101
, volatile gases such as a residual monomer, oligomer and additive come into existence, and the volatile gases are sucked and removed from the suction chamber
104
together with air caught up into between the casting roll
103
and the membrane
102
.
At this time, in a state where the surface temperature of the inner wall surface of the suction chamber
104
does down due to the heat transfer between the suction air flows and the inner wall surface of the suction chamber
104
, the volatile gas such as an additive attaches as a volatile matter to the inner wall surface of the suction chamber
104
in a condensed condition. This condensed and attaching volatile matter is accumulated with the passage of time, and drops onto the casting roll
103
to make the casting roll
103
and the membrane
102
dirty, which deteriorates the film quality. In addition, if the attaching and accumulating matter resulting from the drop onto the casting roll
103
gets mixed in the film (membrane
102
), this can cause the film to be broken.
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 resin-made membrane formation casting apparatus which is capable of preventing the drop of the temperature of an inner wall surface of a suction chamber for the absence of attachment of volatile matters onto the inner wall of the suction chamber leading to the contamination of a membrane by the falling of the volatile matters onto a cooling roll.
For this purpose, in accordance with this invention, a casting apparatus for formation of a resin-made membrane is composed of 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 the membrane while cooling, a suction chamber for sucking air from between the membrane and the cooling roll to make the membrane come closely into contact with the cooling roll, and a temperature

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