JPS61228934A - Molding of blown film and production unit thereof - Google Patents

Abstract

PURPOSE:To correct uneven wall thickness and consequently obtain a film with uniform wall thickness by a method wherein the bubble running between a die and nip rolls is rotated by means of a bubble twisting device. CONSTITUTION:Molten thermoplastic synthetic resin is extruded upwards from the slit 3 of a die 2 into a cylindrical bubble V and, after that, cooled by the cooling air jetted from an air ring 8 and pulled upwards with nip rolls 15. Because the outer peripheral surface of the upward extended bubble V is slidingly contacted with a large number of round pipes arranged on the three vertical stages of a bubble twisting device 22 rotated by a motor 3 so as to be applied with circumferential force simultaneous with the upward proceeding, a twisting force is applied to the bubble V as a whole. The resultant cylindrical bubble V is guided with a stabilizing plate 21 and folded in flat with the nip rolls 15 so as to be taken up by a take-up roller 19 in the form of a sheet-like film. Because beads developed on the peripheral surface of the bubble are dispersed in width direction after the bubble is wound on the take-up roller 19, the resultant film can be taken up in flat.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for dispersing uneven thickness of a cylindrical film formed by inflation molding, and an apparatus for producing the same.

(Prior technology) To mold a film of thermoplastic resin such as polyethylene or polypropylene by the inflation method, the synthetic resin melted in an extruder is extruded through an annular slit in a die, and compressed air is injected into the inside. The film is expanded and stretched to form a cylindrical film, that is, a bubble.

The outer peripheral surface of this bubble is cooled by a cooling device, the bubble is guided by a guide device, and then it is compressed by nip rolls to be folded into two and flattened, and finally wound up on a take-up roll.

Due to manufacturing problems, it is difficult to make the thickness of the film formed by such an inflation method constant.

For example, as shown in Figure 17, which shows an exaggerated change in the cross section of the bubble (a), there are various factors such as dimensional errors due to the wide and narrow groove width of the annular slit of the die, and variations in the viscosity of the molten resin. Depending on the cause, thick portions (b), thin portions (c), or protrusions (d) are formed.

When this bubble (a) is wound up as a two-fold film (e) on a winding roll (f) by a winding machine, as shown in FIGS. 18 and 19, the protrusions ( d)
are stacked in one place in a ring shape.

The thickness g) increases as the wound layer becomes thicker, and permanent deformation occurs in this area, which remains in the film as wrinkles and sag.

Therefore, even if this film (e) is rewound to be used for bag making, for example, it will not become flat, and the uneven surface of this film may be printed or processed into packaging bags. If so, problems will occur.

In other words, the strength of the film becomes non-uniform, making it impossible to increase the production speed. Further, when applying aluminum vapor deposition, etc., uniform plating cannot be achieved, resulting in a poor finish and a decrease in commercial value.

Conventionally, in order to avoid the various problems mentioned above,
Winding methods have been considered to disperse these uneven thicknesses.

One method is to rotate a die to change the relative position of the take-up roll and the film during one winding.

As shown in Fig. 20, a die (q) is rotatably supported on a blade (n) of an extruder (w).
) is brought into sliding contact with the seal portion (r), while rotating the rotational drive means (
p) to rotate it.

Another method is to keep the die fixed and rotate the nip roll around the axis of the bubble, and an apparatus for carrying out such a method is described, for example, in Japanese Patent Publication No. 48-3534, It is publicly known.

Both of the above-mentioned methods attempt to disperse the non-uniformity of the thickness by shifting the relative position of the film wound onto the take-up roll with respect to the winding surface.

As shown in Fig. 21, these winding processes are performed by moving a protrusion (h) formed at a specific position of the film (j) in the width direction of the film (j) in accordance with the number of windings. Changes in the radial thickness (m) of the roll (k) are reduced to eliminate the above-mentioned problems.

(Problems to be Solved by the Invention) However, the method of rotating the die has the following problems.

That is, the rotating die side and the stationary side inevitably have a sliding structure, and it is not easy to prevent resin leakage that occurs from this sliding portion.

Since there is no suitable sealing material, the accuracy of the finishing dimensions of this sliding part is increased to minimize the gap between the two, but if bearings are used for this reason, the die will become hot. , the life of this bearing will be shortened.

Further, rotating the die requires simultaneously rotating an air ring and a bubble cooling blower provided on the die.

In order to prevent these from rotating, they must be constructed separately from the die.

In any case, the problem arises that the entire device becomes complicated and large.

Furthermore, when using low-density polyethylene (LDPE) or high-density polyethylene (HDPE).

It is necessary to clean the resin path and disassemble the device, but as described above, disassembling the complicated device is time-consuming.

Furthermore, when forming the blown film, there is a problem that the effect of dispersing uneven thickness is small because the area over which the force that twists the bubbles is applied is small.

As described in the above-mentioned publication, the method of rotating the other nip roll is to use an end face position correction device to correct the deviation in the width direction of the film being wound. However, there was a problem in that the structure of the single winding device was complicated.

(Means for Solving the Problems) An object of the present invention is to solve the above-mentioned problems by rotating bubbles between a die and a nip roll using a bubble twisting device with a relatively simple structure. The object of the present invention is to provide a method for forming a blown film and an apparatus for manufacturing the same.

In the present invention, a molten thermoplastic resin is extruded through an annular slit of a die and then cooled to form a cylindrical bubble, and the outer peripheral surface of the bubble is brought into sliding contact with a holding member that moves around the bubble. A blown film forming method characterized by twisting a bubble and then flattening the bubble with a stabilizer plate and a nip roll, and extruding a molten thermoplastic resin through an annular slit to form a cylindrical bubble. A blown film manufacturing apparatus comprising: a die that cools the bubbles, an air ring that cools the bubbles, a stabilizer plate that is provided facing the die and flattens the bubbles, and a nip roll that feeds the film by sandwiching the film therebetween. It is an object of the present invention to provide a blown film manufacturing device characterized in that a bubble twisting device is provided between the device and a nip roll to hold bubbles and apply rotational force to the bubbles in the circumferential direction. .

(Embodiment) First, a blown film manufacturing apparatus according to the present invention will be explained in detail based on an embodiment shown in FIGS. 1 to 6, and then a molding method will be explained.

(1) is an extruder, (2) is a die, and an annular slit (3) is cut in the upper surface of the die (2).

In the center of the die (2), there is an exhaust pipe (4) that passes through it in the vertical direction and is open at the upper end, and this exhaust pipe (4).
Air supply pipes (5) are each provided concentrically housed within.

The base end of the air supply pipe (5) is connected to an air compressor (6), and the base end of the exhaust pipe (4) is adapted to exhaust air via a regulating valve (7).

(8) is a hollow annular air ring, and an annular air outlet (8a) is formed on the inner peripheral surface of the air ring.

The lower surface of the air ring (8) is placed on a mounting ring (9) provided around the upper surface of the die (2), and the annular chamber (8b) is connected to an air cooling unit via a pipe (10). (11).

A frame (14) is mounted on one of the upper ends of the support (13) erected from the base (12), facing the die (2).
is installed. A horizontal shaft (15a) (15a) is pivotally attached to this frame (14).
5a) (15a) has a pair of nip rolls (15) (
15) are fixed to each other and are rotationally driven by a rotational drive means (16).

A guide roller (17
), and a rotary drive means (1) is provided on the lower side thereof.
8) and a winding roller (19) rotated by the winding machine (20).

(21) is a stabilizer plate whose upper end is connected to the frame (1).
4), and a plurality of guide rollers (21b) pivotally connected to parallel shafts passing through the frame (21a) horizontally. has been done.

Next, the bubble twisting device (22) provided between the die (2) and the nip roll (15) will be explained.

(23) is a board, which has an annular shape with a circular hole (23a), and whose lower surface is attached to a horizontal frame (25) via a thrust self-aligning roller bearing (24), and is rotatable around a vertical axis. is supported by.

On the upper surface near the outer periphery of the substrate (23), there are two circular holes (27a), upper and lower, which are parallel to the substrate (23), formed by pillars (26) erected at equal intervals along the circumference. (2
7) (27) is fixed.

Bubble holding devices (28) having a structure which will be described in detail later are attached concentrically to the upper surfaces of each of these substrates (23) (27).

Further, a tune (29) is fixed to the outer peripheral surface of the board (23), and this chain (29)
The sprocket (3o) that meshes with is rotated by a rotational drive means, that is, a motor (31) with a reduction gear.

Next, the bubble holding devices (28) will be explained, but since they all have the same structure, the one in the center of the three above and below will be explained.

(32) is a rotating body, consisting of an annular upper ring (33), a lower ring (34) having an annular groove (34a) on its inner circumferential surface, and spaced between them at equal intervals along one circumference. It consists of six vertical connecting rods (35), and has a cage shape with open upper and lower end surfaces.

Six short shafts (36a) are protruded from the upper surface of the slightly inner edge of the circular hole (27a) of the substrate (27) at equal intervals along one circumference.

Six vertical rollers (36) pivotally mounted on the upper end of each short shaft (36a) are connected to the annular groove (34a) of the rotating body (32).
It is removably inserted into the shaft, and is rotatably supported around a vertical axis.

Along one circumference at the bottom of the outer peripheral surface of the lower ring (34).

A chain (37) is wound around the chain (37), and a sprocket (39) is attached to the output shaft of a rotational drive means, that is, a motor (38) provided on the base plate (27).
are interlocking.

Therefore, by rotating the motor (38) in the forward or reverse direction,
The rotating body (32) is rotated forward and backward around a vertical axis.

On the upper surface of the upper ring (33) near the circular hole (33a),
Twenty-four pins (40) are provided protruding along the circumference, and the outer ends of horizontal arms (41) are pivotally connected to each pin (40). The inner end is
They each protrude into the circular holes (33a) (see Fig. 5).

3 and 4 show the state in which only one arm (41) is attached in order to make the configuration easier to understand, and the following explanation will be mainly based on these drawings.

The inner end of the arm (41) has a mounting hole (
A mount (42) having 42a) is provided for rotation about a vertical axis.

A circular hole (27a) in the substrate (27) corresponding to a position that is approximately symmetrical about the centers of the pin (40) and the circular hole (34a).
A mounting tool (43) having a mounting hole (43a) opening on the top surface is provided on the inner edge so as to be rotatable around a vertical axis.

(44) is a holding member made of a flexible synthetic resin material, that is, a circular tube, the upper end of which is connected to the mounting hole (42).
In a), the lower end is also fitted into the mounting hole (43a),
It is attached between the up leg (33) and the base plate (27) so that its planar shape forms an arc.

By installing 24 circular tubes (44) configured in this manner at equal intervals on the circumference between the upper ring (33) and the base plate (27), as shown in FIG. On the inner peripheral surface of the circular tube (44), although it is a pseudo circle, there is a
An enveloping circle (S) close to a circle is formed.

As will be described later, it slides into contact with the outer peripheral surface (u) of a bubble (indicated by an imaginary line) passing through this valve holding device (28), holds it, and applies a force that twists it around a vertical axis. It is now possible to grant.

To change the radius of the envelope circle (S), as shown in Figure 4,
The motor (38) is driven and the sprocket (39) is turned counterclockwise to rotate the one-rotator (32) clockwise by a required angle as shown by the arrow (1).

Then, the circular tube (44) is moved to the position shown by the imaginary line and deformed so that the radius of curvature becomes smaller.

Therefore, as shown in Fig. 6, these 24 circular tubes (
The radius of the envelope circle formed by 44) is smaller than the radius of the envelope circle in FIG.

Next, the operation of the blown film manufacturing apparatus according to the present invention as described above will be explained, and a forming method for dispersing the uneven thickness of the blown film according to the present invention will also be explained.

The thermoplastic synthetic resin heated and melted in the extruder (1) is extruded upward through the slit (3) of the die (2) to form a cylindrical bubble (V), and inside it is , while compressed air is blown in from the air supply pipe (5), its outer peripheral surface is cooled by cooling air from the air outlet (8a) of the air ring (8), and is further cooled upward by the nip roll (15). be lifted up.

Bubble (V) expanded to a predetermined radius and stretched upward
The outer peripheral surface of the bubble twisting device (22), which is rotated by the motor (31), is in sliding contact with a large number of circular tubes (44) in bubble holding devices arranged in three stages above and below, so that the outer circumferential surface of In order to receive force in the circumferential direction, bubbles (
V) will be subjected to torsional force as a whole.

That is, as shown in FIG.
) when receiving a force in the circumferential direction.

The initial position of the protrusion <X> generated on the bubble (V) is (
X I), this position is due to the twist of the bubble,
It draws a spiral trajectory, and after a certain period of time, the position (
x2).

This cylindrical bubble (V) is guided by a stabilizer plate (21) and folded flat by nip rolls (15) (15), and the sheet-shaped film is folded into a single take-up roller (19).
).

Therefore, the protrusions (X) generated in the bubble phase are dispersed in the width direction after being wound around the take-up roller (19) as described above, so that the film can be wound flat. .

(Modification) In the first embodiment described above, the bubble twisting device (22
), the three bubble holding devices were rotated 360 degrees by a single rotary drive means; instead, one
Rotate 180 degrees in the circumferential direction.

It may be made to move back and forth.

In addition, in FIG. 7, as shown by imaginary lines, each bubble holding device (28) has a separate rotary drive means (45).
may be provided respectively, and the rotational force in the circumferential direction applied to the bubble (V) may be changed for each stage to enhance the twisting effect.

What is shown in FIG. 8 is that the rotating part (46a) at the upper part of the air ring (46) provided on the die (2) can rotate around a vertical axis, and the one-rotation driving means ( This figure shows another embodiment in which a bubble twisting device (22) is mounted and fixed on this rotating part (46b) linked to the bubble twisting device f(47).
22) and the air ring (46) can be rotated at the same time.

Figures 9 to 13 show the bubble holding device used in the first embodiment of the present invention! (28) holding member (44
), and these will be described below.

(48) in FIG. 9 is an annular holding member, which includes an annular main body (48a), which is rotatably supported by the main body (48a) and rotated by a rotational drive means, that is, a motor (49). It consists of a hollow ring (48b).

The annular chamber (48c) of the hollow ring (48b) has an annular slit (48d) on its inner periphery and communicates with a hole (48e) facing upward and downward in the main body (48a), and this hole (486) It is connected to a vacuum pump (not shown), and a bubble (V) is formed in the slit (48d).
It is designed to be able to suck the outer peripheral surface of the

Instead of this holding member (48), a fixed ring member can also be used.

Figure 10 shows that by assembling six horizontal bars (50a) into a regular hexagon in a basket (sob),
A holding member (51) is formed, and the outer circumferential surface of the bubble is brought into sliding contact with the inner circumferential surface of this hexagon.

FIG. 11 shows a member holding an iris ring (53) of a known device in which a large number of thin plates (53a) are spirally arranged in an enveloping circle within an annular frame (52). It is used as a.

Fig. 12 shows a wire iris ring (54) of a known device having a plurality of wires (54a) in place of the thin plate (53a) described above, so that it can be brought into sliding contact with the outer peripheral surface of the bubble with this envelope circle. It has become.

FIG. 13 shows an arm (57) pivotally connected to equally spaced pins (56) on the upper end surface of a cylinder (55), parallel to the traveling direction of the bubble (58). As shown in FIG.

1413I corresponds to FIG. 3 in the first embodiment, and a flexible cylinder (59) in place of the cylinder (44) contains a cooling medium, e.g. This figure shows an example of a structure that allows air to pass through.

In this case, the upper ring (60) and the lower ring (61) are provided with conduits (62) (6
3), and both ends of a cylinder (59) serving as a holding member are communicated with these conduits (62) and (63).

Therefore, if the cylinder (59) is cooled, the bubble held in sliding contact with the cylinder (59) is given a twisting force and is also cooled, which has the advantage of improving productivity.

A perforated conduit member (65) having holes (64a) on the outer peripheral surface to allow the cooling medium to flow out as shown in FIG. 15, or a perforated conduit member (65) having slits (64b) as shown in FIG. ) in place of the cylinder (59) shown in FIG. 14, the cooling effect can be further enhanced.

(Effects of the Invention) As described above in detail, according to the method for forming a blown film according to the present invention, bubbles are twisted between a goo and a nip roll.

There is an advantage that uneven thickness is dispersed, the winding state of the bubble is stabilized, and productivity is improved.

In addition, the torsional force on the bubble tilts the molecular arrangement and increases the strength of the film, and the torsional force stretches the thick part before solidification, correcting uneven thickness, and creating a uniform wall thickness. There is an advantage that a film can be obtained.

This has the effect of combining the advantages of both the conventional method of rotating a die and the method of rotating a nip roll.

Further, in order to carry out the molding method according to the present invention.

Since it is only necessary to add a bubble twisting device to the conventional manufacturing equipment, there is an advantage that there is no need to invest a large amount of new equipment cost.

The blown film manufacturing apparatus according to the present invention includes:
Since it has a relatively simple structure, it has the advantage of being inexpensive to manufacture.

In addition, since bubble inflation molding requires the same steps as the conventional method and no new steps are added, it has the advantage of improving quality while increasing productivity.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view showing a first embodiment of the blown film manufacturing apparatus according to the present invention, and FIG. 2 is a perspective view showing only the bubble holding device taken out. FIG. 3 is a vertical cross-sectional view showing the installation state of only one circular pipe in FIG. 2, FIG. 4 is a plan view, and FIG. 5 is a plan view of FIG. 2. FIG. 7 is a schematic configuration diagram for explaining the twisting of bubbles; FIG. 8 is another implementation of the bubble twisting device. FIG. 9 is a front view showing an example; FIG. 9 is a longitudinal sectional view of a ring-shaped holding member;
FIG. 11 is a perspective view showing another embodiment of the bubble holding member, and FIG. 11 is a plan view of the iris ring. Fig. 12 is a plan view of the wire iris ring;
10 is a schematic plan view showing another embodiment of the bubble holding member different from FIG. 10. Figure 14 is the third! ! FIG. 15 is a partially cutaway front view showing a perforated conduit member in an embodiment different from the cylinder used in FIG. 14. FIG. FIG. 16 is a front view showing a perforated conduit member different from that in FIG. 15, and FIG. 17 is a cross-sectional view of a bubble formed by the conventional inflation method. FIG. 18 is a perspective view showing a film wound around a take-up roll. FIG. 19 is a longitudinal cross-sectional view showing how the film is wound by a conventional winding method, and FIG. 20 is a partially cutaway front view showing a conventional rotary die device. FIG. 21 is a longitudinal cross-sectional view showing the state of winding of a film in which thick portions are dispersed. (1) Extruder (2) Die (3) Slit (4) Exhaust pipe (5) Air supply pipe (6
) Air compressor (7) Regulating valve (8) Air ring (11) Air cooling unit (13) Support column (14)
Frame (15) Nip roll (16) (
18) Rotation drive means (19) Take-up roller (21) Stabilizer plate (22) Bubble twisting device (23) Substrate (24) Thrust self-aligning roller bearing (25
) Horizontal frame (27) Substrate (28) Bubble holding device! (29) Chain (30) Sprocket (31) Motor with reducer (32) Rotating body
(33) Upper ring (34) Lower ring (3
6) Vertical roller (37) Chain (38) Motor (39) Sprocket (40) Pin (41)
) Arm (42) (43) Mounting tool (44
) Holding member (circular tube) (45) Rotation drive means (46
) Air ring (46a) Rotating part (47) Rotation drive means (48) Holding member (49) Motor
(53) Iris ring (54) Wire iris ring (55) Cylinder body (57) Arm (59) Circular tube (60) Upper ring (61) Lower ring
(62) (63) Conduit (65) Perforated conduit member Figure 5 Figure 6 Figure 7 Figure 8 F

Claims (19)

[Claims] (1) Molten thermoplastic resin is extruded through an annular slit of a die and then cooled to form a cylindrical bubble, and the outer peripheral surface of the bubble is brought into sliding contact with a holding member that moves around the bubble. 1. A method for forming a blown film, which comprises twisting a bubble using a stabilizer and a nip roll, and then flattening the bubble using a stabilizer plate and a nip roll. (2) A die that extrudes molten thermoplastic resin through an annular slit to form a cylindrical bubble, an air ring that cools the bubble, and a stabilizer plate that is provided opposite the die and flattens the bubble. and a nip roll for feeding the film, a bubble twisting device that holds the bubble between the die and the nip roll and applies rotational force to the bubble in the circumferential direction. A blown film manufacturing device characterized by being provided with. (3) A patent claim characterized in that the bubble twisting device comprises a holding member that slides into contact with the outer periphery of the bubble, and a rotational drive means that rotates the holding member in the circumferential direction with respect to the central axis of the bubble. The blown film manufacturing apparatus according to item (2). (4) The bubble twisting device is mounted on an air ring provided on the die so as to rotate around a vertical axis, and is adapted to be rotated by rotational drive means of the air ring. The blown film manufacturing apparatus according to item 2) or item (3). (5) A patent claim characterized in that the bubble twisting device is provided with a plurality of holding members that are in sliding contact with the outer periphery of the bubble, and respective rotational drive means so that the holding members can rotate independently of each other. The blown film manufacturing apparatus according to item (3). (6) The blown film manufacturing apparatus according to claim (3), wherein the holding member is an iris ring in which a large number of thin plates are spirally arranged to form an enveloping circle. (7) The blown film manufacturing apparatus according to claim (3), wherein the holding member is a plurality of elastic bodies arranged to form an enveloping circle. (8) The blown film manufacturing apparatus according to claim (3), wherein the holding member is a tube through which a cooling medium can pass through the hollow part. (9) The blown film manufacturing apparatus according to claim (3), wherein the holding member comprises a perforated conduit member capable of allowing the cooling medium to flow out onto the outer peripheral surface. (10) Claim No. 1, wherein the holding member is a ring.
The blown film manufacturing apparatus according to item 8) or item (9). (11) The blown film according to claim (8) or (9), wherein the holding member is made of a plurality of flexible tube members and is in contact with the bubble with its envelope circle. Manufacturing equipment. (12) Claim No. 8, wherein the holding member is a plurality of tube members arranged in a polygonal shape intersecting the direction of travel of the bubble, and the inscribed circle of the holding member is in sliding contact with the outer periphery of the bubble. or (9). (13) the holding member is parallel to the traveling direction of the bubble;
The apparatus for producing a blown film according to claim 8 or 9, which is a plurality of tubes arranged along the circumference. (14) According to claim (3), the holding member is arranged in the form of a polygon that intersects with the traveling direction of the bubble, and whose inscribed circle is a bar material that slides into contact with the outer circumference of the bubble. The blown film manufacturing apparatus described above. (15) the holding member is parallel to the traveling direction of the bubble;
The blown film manufacturing apparatus according to claim 3, wherein the blown film manufacturing apparatus is a plurality of rods arranged along the circumference. (16) The blown film manufacturing apparatus according to claim (3), wherein the holding member is a polygonal body capable of forming an inscribed circle. (17) The blown film manufacturing apparatus according to claim (3), wherein the holding member is an annular ring. (18) The blown film according to claim (17), wherein the ring has a slit connected to a vacuum pump on its inner peripheral surface, and the outer peripheral surface of the bubble can be sucked by the slit. manufacturing equipment. (19) The blown film manufacturing apparatus according to claim (18), wherein the ring is rotated by rotational drive means.