Multi-core rotary circular die

A multi-core rotary circular die for preparing multi-layer tubular film comprises an inner core which is rotatably fitted in a hollow cylindrical body having a plurality of molten resin inlets and a plurality of middle cores having semi-spherical or spherical surfaces are fitted on the inner core adjacent the one end thereof. The middle cores form the molten resin passages for adjusting the thickness of the molten resin films. The inner core has annular resin storage channels on the periphery thereof and internal resin passages therein connected to the corresponding annular resin storage channels, which are respectively connected to the corresponding molten resin inlets, and an utility feeding passage is also formed in the inner core extending in the longitudinal direction thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improved multi-core rotary circular die 
of the type designed for producing multi-layer tubular film. 
2. Description of the Prior Art 
Heretofore, circular dies of various constructions have been proposed, such 
as, for example, multi-core rotary circular dies which are composed of a 
body having a plurality of inlets for molten resins, an inner core having 
resin feeding passages formed by a plurality of pipes communicating with 
the resin inlets, cores having spherical seal type resin passages 
connected to the resin feeding pipes and cylindrical parts on spherical 
parts of the multiple cores which are fitted at the spherical parts to 
each other, whereby lips are formed, to offer adjustable thickness between 
the cylindrical parts. 
However, in the conventional technology, where a plurality of pipes are 
formed in the inner core by a screwIng manner or the like, the following 
disadvantages have been found: 
AN INNER SIZE OF THE MOLTEN RESIN PASSAGE IS LARGE; THE MOLTEN RESIN 
ADHERES ON THE OUTER AND INNER SURFACES OF THE PIPES OF THE MOLTEN RESIN 
PASSAGE TO CAUSE RESIDENCE OF THE RESIN; IT TAKES A LONG TIME FOR 
DISASSEMBLY AND CLEANING; AND THE UTILITIES OF AIR FOR INFLATION AND WATER 
FOR COOLING A MOLTEN RESIN FILM CAN BE FED BY CONNECTING ROTATABLE JOINTS 
AT THE END OF THE ROTARY SHAFT. 
However, it has been relatively difficult to feed electric power through a 
slip ring to the rotatable part, as it is difficult to provide continuous 
rotation of the die without the slip ring and it is necessary to provide a 
reciprocating turn, whereby the equipment and the operation are 
complicated. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the disadvantages of 
the conventional processes, to improve them, and to provide a multi-core 
rotary circular die which can be easily assembled and disassembled and 
cleaned. 
It is another object of the present invention to provide an improved 
multi-core rotary circular die which is compact and provides a balanced 
propulsive force. 
It is a further object of the present invention to provide a multi-core 
rotary circular die which comprises a plurality of cores of improved 
structure which are fitted on an inner core and are adjustable so as to 
adjust the thicknesses of the molten resin films being extruded and to 
prepare a multilayer film which can be finely wound. 
These objects of the present invention have been attained by providing a 
multi-core rotary circular die which comprises an inner core which is 
rotatably fitted in a hollow cylindrical body having a plurality of molten 
resin inlets, and a plurality of cores having semi-spherical or spherical 
surfaces which are fitted on the inner core to form molten resin passages 
adjustable to vary the thicknesses of the molten resin films being 
extruded, wherein the inner core has annular resin storage channels on the 
periphery thereof and resin passages therein connected to the 
corresponding annular resin storage channels, which are respectively 
connected to the corresponding molten resin inlets, and one or more 
utility feeding passages are formed in the inner core extending in the 
longitudinal direction thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As a result of various studies and experiments, annular or resin type resin 
storage channels and resin passages which are connected to corresponding 
molten resin inlets in a surrounding cylindrical body are formed in the 
inner core in the present invention. It has been found that when a 
stationary molten resin inlet is substantially faced to a molten resin 
passage of an annular or ring design, the pressure of the molten resin is 
low, and the pressure of the molten resin becomes maximum when the 
position of the resin passage is shifted 180 degrees, and that the 
pressure of the molten resin highly affects the flow rate of the extruded 
molten resin. In order to overcome the problem, the outer diameter of the 
inner core is minimized considering the size of the annular resin storage 
channels or the resin passages. As a result, the fluctuation of the flow 
rate of the extruded molten resin can be minimized to .+-.1 to 2%. 
According to the present invention, a desired number of utility feeding 
passages are formed in the inner core in a longitudinal direction thereof. 
In one utility feeding passage, electric wire for the heater of the 
circular die is disposed so as to feed electric power through a slip ring 
to the heater. When a slip ring is not used, the circular die cannot be 
continuously rotated, but it must be reciprocally turned, whereby the 
structure and the operation have been complicated. 
In the circular die of the present invention, the electric wire is disposed 
in one of the utility feeding passages whereby electric power can be 
easily fed through the slip ring and the circular die can be continuously 
and smoothly rotated in one direction. 
The cores used in the two embodiments of the present invention described 
herein have, respectively, a semi-spherical surface or a spherical 
surface. A structure having spherical surfaces is known to have a high 
degree of freedom in the design of passages in a circular die, but the 
preparation, assembly and disassembly of such a circular die are not easy 
and require a long time. The molten resins used for the circular die 
include low density polyethylene, high density polyethylene, ethylene 
vinylacetate copolymer, polypropylene, ionomer, nylon 6 and the like. For 
example, a multi-layer film is preferably formed with low density 
polyethylene for an inner layer, ionomer for the middle layer and nylon 6 
for the outer layer. 
Referring now to FIGS. 1 and 2, a multi-core rotary circular die which 
includes a middle core having an outer semi-spherical surface and disposed 
on an inner core, will be illustrated. A hollow cylindrical body 1 made of 
metal or the like is fixed on a table 2, made of metal or the like, by 
fastening means 3, such as bolts. Three molten resin inlets 4a, 4b and 4c 
are formed through the wall of the hollow cylindrical body 1 at suitable 
positions on the outer surface thereof. An inner core 5, made of metal or 
the like, is rotatably fitted in the hollow cylindrical body 1 and 
includes a utility feeding passage 10 extending longitudinally and passing 
through the axial center of the inner core. The inner core 5 has ring type 
or annular resin storage channels 6a, 6b and 6c and internal 
longitudinally extending resin passages 7a, 7b and 7c, which are 
respectively connected to the corresponding molten resin inlets 4a, 4b and 
4c. 
A cooling water pipe W for cooling the multi-layer molten resin film and an 
air pipe A for inflating the multi-layer molten resin film, which are 
connected to a multi-layer circular die 12, are disposed inside of the 
utility feeding passage 10. Suitable circular seals 8, as O-rings, are 
disposed between the hollow cylindrical body 1 and the inner core 5, 
between the annular storage channels, so as to prevent contamination of 
the molten resins. Molten resin leakage grooves 9 are disposed between the 
hollow cylindrical body 1 and the inner core 5 and between respective 
pairs of seals 8 disposed between such resin storage channels. 
Another utility feeding passage 11, which is similar to the utility feeding 
passage 10, is formed in parallel relation to the axial utility feeding 
passage 10 in the inner core extending in the longitudinal direction 
thereof. 
An electric wire E is disposed in this other utility feeding passage 11 and 
electric power is fed through a slip ring S so as to continuously and 
smoothly rotate the circular die in one direction. 
The multi-core circular die 12 is fastened on one end of the inner core 5 
by a nut 13. Middle cores 16, 17 and 18, having semi-spherical surfaces 
are disposed in the circular die 12, and molten resin passages 19 and 21, 
and one other, not shown, are connected to the spaces between the cores. 
A die lip 22 is connected to the spaces. A key 14 is disposed between the 
upper part 5a of the inner core 5 and the lower middle core 16 to rotate 
the multi-core circular die 12 with the inner core 5. A bearing 15 is 
disposed between the table 2 and the inner core 5 to hold the inner core 
5. A motor M, a sprocket SR, a rotary joint C having four necks, a slip 
ring S, and an electric wire E are also provided. 
An inlet C.sub.1 for feeding air to the upper part of the mandrel is 
provided in the larger of the four necks of the rotary joint, a water 
outlet C.sub.2 is provided in the next smallest neck, an outlet C.sub.3 
for discharging from the mandril is provided in the third neck and a water 
inlet C.sub.4 is provided at the rotary joint C. 
The rotary part R of the device thus includes the inner core 5, the 
multi-core circular die 12, the middle cores 16, 17 and 18, the die lip 22 
and the slip ring S, while the stationary part ST includes the hollow 
cylindrical body 1 and the table 2. 
FIG. 4 shows the semi-spherical surface of the middle core 18, wherein the 
resin passage 21 is communicated with the space between the semi-spherical 
surface and the circular die 12. Also, as shown, a groove manifold is 
formed from the lower part of the semi-spherical surface to the opposite 
upper part of the semi-spherical surface, the width of the groove 
gradually decreasing from the lower part to the upper part of the 
spherical surface, as shown also by the dotted lines in FIG. 1. The slant 
angle of the groove manifold depends upon the size of the semi-spherical 
surface. The depth of the groove can be constant and also can be decreased 
from the lower part to the upper part of the spherical surface. 
The space between the inner spherical surface of the core 18 and the outer 
spherical surface of the adjacent middle core 17 can be constant and can 
also be decreased from the lower part to the upper part, and is, for 
example, 0.1 to 5 mm, preferably 0.2 to 2 mm, and especially 0.5 to 1.5 
mm. The space at the semi-spherical surface and the groove can be selected 
so as to provide uniform flow rate around the die lip 22. The slant 
tapered groove as the manifold on the semi-spherical surface is remarkably 
effective for attaining the uniform flow rate. If desired, the slant 
tapered groove can be formed on the inner semi-spherical surface of the 
circular die 12 instead of the outer semi-spherical surface of the middle 
core. The same type of slant tapered groove can be formed for each of the 
spaces connected to the resin passages, such being shown by dotted lines 
in FIG. 1. 
Adjustment of the space at the semi-spherical surface and the cylindrical 
surface to the die lip can be attained by screwing the bolts 23, 24, 25 
and 26, shown in FIG. 1. 
The resin passages 19, 21 and the third such, not shown, are respectively 
connected to the ring type resin storages 6a, 6c, 6b, which can be grooves 
carved on the outer surface of the rotatable inner core 5, as shown in 
FIG. 1 or on the inner surface of the stationary hollow cylindrical body 
1. Likewise, the seals 8 for preventing leakage of the molten resin from 
the annular resin storage channels can be fitted on the outer surface of 
the rotatable inner core 5 or on the inner surface of the stationary 
hollow cylindrical body 1. 
It is a novel feature of the invention to form the passages from the 
annular resin storage channels 6a, 6b and 6c through the resin passages 
19, 21 and other, not shown, to the slant tapered grooves in the 
semi-spherical parts. It is also a novel feature of the invention to form 
the middle cores with a semi-spherical portion and a cylindrical portion. 
The middle cores can be easily disassembled and the spaces between the 
middle cores and the circular die are finely adjustable and the slant 
tapered grooves on the semi-spherical parts improve the uniform flow rates 
of the molten resins. 
Referring now to FIG. 5, another embodiment of the multi-core rotary 
circular die of the present invention is illustrated, wherein molten resin 
inlets 4 are similarly formed through the wall of a hollow cylindrical 
body 1 and an inner core 5 is rotatably fitted in the hollow cylindrical 
body 1, but spherical middle cores 16, 17 and 18 are provided at the upper 
part. The inner core 5 has the annular resin storage channels 6 and the 
resin passages 7 which are respectively connected to the corresponding 
molten resin inlets 4. Thus, the parts of the hollow cylindrical body 1 
and the inner core 5 are substantially the same as those of the embodiment 
shown in FIG. 1, with the exception essentially of the middle cores 16, 17 
and 18 having spherical surfaces instead of semi-spherical surfaces. The 
middle core 17 can be of a separatable form so as to contact on the 
spherical surface of the middle core 16. The middle core 18 and the 
circular die 12 are also separatable so as to contact on the spherical 
surfaces thereof At the lower part of the spherical surface, the middle 
cores 16, 17 and 18 and the circular die 12 are rotatably fitted so as to 
adjust the spaces between the upper spherical surfaces of the middle cores 
and the circular die by the adjusting bolts 23 and 24. 
The annular resin storage channels 6a, 6b and 6c are connected through the 
resin passages 7a, 7b and 7c and the resin passages 19, 21 and the one, 
not shown, and the spaces between the upper spherical surfaces to the die 
lip 22. The die lip 22 is formed with separatable parts which are held in 
the circular die 12. The thickness of the molten resin film can be 
adjusted by the adjusting bolts 23 and 24, and by bolts 25 and 26 for 
holding the die lip 22. The spaces between the middle cores and the 
circular die can be the same as those of the semi-spherical form, and are 
formed on the upper spherical parts, and can be constant and can also be 
decreased from the largest diameter part to the upper part. Each of the 
manifold of grooves can be formed as slant tapered grooves, which can be 
the same as those in the middle cores of the semi-spherical form. The 
shape of the slant tapered groove can be decided so as to attain a uniform 
flow rate. It is preferable, however, to form the slant tapered grooves as 
shown by the dotted lines in FIG. 5. 
The electric wire E of a band heater for heating the die, not shown, the 
nut 13 for fastening the inner core 5, the holder 14 for connecting the 
inner core to the middle core 16, and the other parts are substantially 
the same as those of FIG. 1, except for the spherical inner cores 16, 17 
and 18 and the circular die 12 having an inner spherical surface. 
The operation of the multi-core rotary circular die of the invention will 
be illustrated. For example, low density polyethylene is fed from the 
molten resin inlet 4a through the ring type resin storage 6a and the resin 
passage 7a, which are formed in the rotated inner core 5, to the resin 
passage 19 for the inner layer of space between the middle cores 16 and 17 
of the three layer circular die 12. Ionomer resin and nylon 6 are 
respectively fed from the molten resin inlets 4b and 4c through the resin 
passages 7b and 7c to the resin passage for the middle layer and the resin 
passage 21 for the outer layer of the middle cores 17 and 18 of the three 
layer circular die 12. The molten resin film for the three layer tube can 
be extruded from the die lip 22 and the thickness of the molten resin film 
can be adjusted by the adjusting bolts 23, 24, 25 and 26. 
Thus, in the multi-core rotary circular die of the present invention, a 
plurality of annular or ring type resin storage channels connected to 
respective longitudinally oriented resin passages are formed in the inner 
core, and a desired number of utility feeding passages are also formed 
passing axially through the inner core. Accordingly, a compact apparatus 
can be prepared and the assembly, disassembly and cleaning of the circular 
die are easily accomplished. The circular die can be continuously and 
smoothly rotated in one direction and the operational efficiency can be 
improved because electric power is fed through a slip ring connected to an 
electric wire disposed in one of the utility feeding passages. 
According to the invention, when the type of molten resin is to be changed, 
in order to attain a complete exchange of the molten resin, the outer 
diameter of the inner core 5 has been minimized and the resin storage 
channels 6a, 6b and 6c are formed by plating hard chromium or the like to 
provide smooth flow in the resin exchange. On the other hand, the molten 
resin may be easily retained by inserting plugs in the hollow cylindrical 
body in the positions facing the molten resin inlets 4a, 4b and 4c, and 
the plugs are taken out for the resin exchange operation and the molten 
resin is extruded from the opening, whereby the resin exchange can be 
attained for a short time. 
In one example of the operation of the apparatus of the invention, 
excellent three layer resin film F was obtained by extruding low density 
polyethylene as an inner layer, ionomer resin as the middle layer and 
nylon 6 as the outer layer through a multi-core rotary circular die having 
a hollow cylindrical body with an outer diameter of 300 mm and an inner 
diameter of 200 mm, an inner core having an outer diameter of 200 mm and a 
rotary speed for the rotary part R of 1 turn per 10 to 15 minutes. In the 
above-mentioned embodiment, a plurality of cores having semi-spherical 
surfaces as shown and illustrated were employed. However, it is clearly 
understood that a person skilled in the art could apply the same 
structure, using a plurality of cores having spherical surfaces, as 
already described. 
Obviously many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims, the present invention may be 
practiced otherwise than as specifically described herein.