JP7791725B2 - Knives for cutting packaging materials and vertical form-fill-seal packaging machines - Google Patents

Description

The present invention relates to a knife for cutting packaging material and a vertical form-fill-seal packaging machine equipped with such a knife, and in particular to a knife for cutting low-stretch packaging material and a vertical form-fill-seal packaging machine equipped with such a knife.

Patent Document 1 discloses a cutting knife that is installed in the cutting device of a packaging machine and that thrusts and cuts cylindrically formed sheet material. This knife comprises a plate-shaped main body, a blade formed on the main body, and cutting blades arranged side by side at a predetermined interval across the width of the blade. The cutting blade is shaped like an isosceles triangle, in other words, V-shaped in a plan view, and comprises a cutting edge, blade base, cutting tip, front blade, and back blade.

The cutting edge forms the V-shaped pointed end of the blade. The base is located on both sides of the cutting edge in the width direction and forms the V-shaped valley of the blade. The cutting edge is a linear portion connecting the cutting edge and base. The front edge is formed on the surface of the blade, includes the cutting edge, extends from the cutting edge toward the base, and is inclined in a direction that reduces the blade thickness. The back edge is formed on the back side of the blade, and has the same cutting edge, base, and cutting edge as the front edge.

The front and back blades formed on the knife described in Patent Document 1 have identically shaped inclined surfaces that are inclined in different directions when viewed from the center of the blade's thickness, and are formed symmetrically on the front and back with the same inclination angle (see, for example, lines 17-20 on page 10 of the publication). As a result, the cross section of the blade in the blade thickness direction, from the cutting edge to the base, is diamond-shaped. When each blade pushes against the packaging material, diamond-shaped cuts are formed in the packaging material, lined up in the width direction.

As each blade continues to push and press, the cut edge of the packaging material gradually becomes larger while forming a similar diamond shape. Then, as each blade continues to push and press, adjacent cut edges in the width direction connect, cutting the packaging material. In other words, while each blade of the knife pushes and presses an area of the packaging material equivalent to the area of the cut edge (thrust and press process), the packaging material is cut with the blades of the knife, gradually enlarging the cut edge of the packaging material (cutting process). This cuts the packaging material.

Japanese Utility Model Application Laid-Open Publication No. 1-176012

Recently, with the growing momentum for environmental awareness and resource conservation on a global scale, such as through the Sustainable Development Goals (SDGs), and the global social issue of marine pollution caused by discarded plastic, attention has been focused on packaging that reduces environmental impact. Most conventional packaging materials are sheet-like films made primarily from petroleum-derived plastic, so attempts are being made to reduce the amount of plastic used by switching to paper packaging made primarily from paper.

Film packaging materials made from plastic materials are thin and flexible, so they stretch appropriately during the pushing and pressing process described above, which, combined with the tearing and slitting process, results in smooth cut edges. On the other hand, paper packaging materials are sheets of tangled fibers such as wood pulp, which are more difficult to stretch than film packaging materials, resulting in insufficient stretching of the paper packaging material during the pushing and pressing process. This causes the paper packaging material to shred during pressing, leaving uncut fibers and other loose fibers at the cut edges, making it impossible to obtain a smooth cut edge.

The present invention was made in consideration of these issues, and aims to provide a packaging material cutting knife that can create smooth cut edges in difficult-to-stretch packaging materials such as paper packaging materials, and a vertical form-fill-seal packaging machine equipped with such a knife.

In order to achieve the above object, one embodiment of a packaging material cutting knife is a knife for cutting packaging material by pushing against it, and includes a plate-shaped main body, a blade portion formed on the main body, and cutting edges that are V-shaped in a plan view and are arranged in parallel at a predetermined interval in the width direction of the blade portion, and the cutting edges each include a cutting edge that forms the pointed end of the V-shape of the cutting edge, blade bases that are located on both sides in the width direction of the cutting edge and form the valleys of the V-shape of the cutting edge, and blades that connect the cutting edge and the blade base and form two sides of the V-shape of the cutting edge. The blade has a tip, a front blade formed on the surface of the blade and extending from the cutting edge to the base along the cutting edge, a back blade formed on the back surface of the blade and having the same cutting edge, base, and cutting edge as the front blade , a ridge line formed at the boundary between adjacent front blades in the width direction and extending from the cutting edge in the extension direction of the blade, and a valley line formed at the boundary between adjacent back blades in the width direction and extending in the extension direction , and the back blade is formed so as to gouge out the back side of the front blade by arranging the valley line opposite the ridge line in the blade thickness direction .

One embodiment of a vertical form-fill-seal machine is equipped with the aforementioned packaging material cutting knife. It forms the non-stretchable packaging material into a cylindrical shape around a bag-forming tube, and while the formed tubular packaging material is fed in the longitudinal direction of the bag-forming tube, horizontal seals are formed below the bag-forming tube at predetermined intervals along the longitudinal direction of the tubular packaging material. It alternates between forming horizontal seals and filling the tubular packaging material with a filling material, and simultaneously cuts the tubular packaging material at the horizontal seals with the knife to produce bags filled with the filling material.

It is possible to form smooth cut edges on packaging materials that are difficult to stretch.

1 is a perspective view of a vertical form-fill-seal packaging machine according to an embodiment. FIG. FIG. FIG. FIG. FIG. 4 is a cross-sectional view taken along the line AA in FIG. 3. 4 is a cross-sectional view taken along the line BB in FIG. 3. 4 is a cross-sectional view taken along the line CC in FIG. 3. 1A is a front view of each cutting edge, and FIG. 1B is a cross-sectional view of each cutting edge in a direction approaching the base of the blade. These are images taken during the process of cutting a tubular packaging material with a knife: (a) the cut edge of the tubular packaging material when each blade pushes against the tubular packaging material; (b) the cut edge of the tubular packaging material as each blade continues to push against the tubular packaging material; and (c) the cut edge of the tubular packaging material when each blade cuts the tubular packaging material. This is a front view of the bag, clearly showing the cut edges of the horizontal seals cut with a knife. FIG. 10 is a diagram showing the fuzzing of fibers at the cut end of a conventional tubular packaging material.

Figure 1 shows a perspective view of a vertical form-fill-seal packaging machine 1 according to an embodiment. This vertical form-fill-seal packaging machine (hereinafter simply referred to as packaging machine) 1 is equipped with a bag-making tube 2, which extends vertically. The bag-making tube 2 has a hopper 6 at its upper end, through which it receives a supply of filling material such as powder or granular material. In addition, a filling supply device (not shown) is disposed above the packaging machine 1, and the filling supply device supplies a predetermined amount of filling material into the bag-making tube 2 via the hopper 6.

A former 8 is attached above the bag-making tube 2 and below the hopper 6, and a packaging material payout path extends from the former 8 to the packaging material reel 10. Packaging material W is paid out from the packaging material reel 10 via multiple rollers 12. The packaging material W is a low-stretch packaging material, such as a paper packaging material made by laminating and bonding a sheet-like paper material used for the exterior of the bag P and a sheet-like heat-seal material used for the interior of the bag P. The packaging material W paid out from the packaging material reel 10 is guided along the packaging material payout path and led along the former 8 to the outer periphery of the bag-making tube 2.

The packaging material W guided along the former 8 is formed into a tubular shape that surrounds the bag-making tube 2, and this tubular packaging material Wc is guided downward along the bag-making tube 2. As it passes through the former 8, both side edges of the tubular packaging material Wc are overlapped in a predetermined shape, for example, a lapped portion L, forming a seam. The packaging machine 1 is also equipped with a packaging material feeding device. The packaging material feeding device has a pair of packaging material feeders 14.

The packaging material feeders 14 are located below the former 8, on both sides of the outer circumference of the bag-forming tube 2. Each packaging material feeder 14 has an endless suction belt 16, and the tubular packaging material Wc is attracted to the suction belt 14. In this attracted state, the suction belt 14 runs in one direction, causing the tubular packaging material Wc to be fed downward along the bag-forming tube 2.

A vertical sealer 18 that can be opened and closed is located near the bag-making tube 2. The vertical sealer 18 is located between a pair of packaging material feeders 14 when viewed circumferentially around the bag-making tube 2, and heat-seals the wrap portion L of the tubular packaging material Wc, bonding both side edges together to form a vertical seal portion Sv on the bag P. As a result, after passing through the vertical sealer 18, both side edges of the tubular packaging material Wc are completely closed.

An openable and closable horizontal sealer 20 is positioned below the bag-making tube 2. The horizontal sealer 20 has a pair of heater blocks 20a, 20b. Each heater block 20a, 20b has a built-in heater. Each heater block 20a, 20b extends horizontally, which is the direction across the tubular packaging material Wc, and moves toward and away from each other in the radial direction of the bag-making tube 2 within the horizontal plane. This allows the horizontal sealer 20 to open and close.

When the horizontal sealer 20 closes, the heater blocks 20a, 20b pinch the tubular packaging material Wc from the front and back, forming a horizontal seal Sh on the tubular packaging material Wc. One of the heater blocks 20a, 20b, the heater block 20a, holds a knife 22 for cutting the packaging material. The other of the heater blocks 20a, 20b, the heater block 20b, has a blade receiving groove 24 formed in it to receive the knife 22. When the horizontal sealer 20 closes, the knife 22 slides horizontally toward the blade receiving groove 24, pushing and cutting the horizontal seal Sh.

The series of operations of the packaging machine 1 configured in this manner is described below. The packaging machine 1 forms the packaging material W into a tubular shape around the bag-forming tube 2, and while the formed tubular packaging material Wc is fed in the longitudinal direction of the bag-forming tube 2, i.e., downward, the vertical sealer 18 forms vertical seals Sv. Next, below the bag-forming tube 2, the horizontal sealer 20 forms horizontal seals Sh at predetermined intervals along the longitudinal direction of the tubular packaging material Wc. Meanwhile, the formation of horizontal seals Sh and the filling of the tubular packaging material Wc are alternately performed. At the same time, the knife 22 cuts the tubular packaging material Wc at the horizontal seals Sh. This produces bags P filled with the filling material.

Figure 2 shows a plan view of the knife 22. The knife 22 thrusts and cuts the tubular packaging material Wc in the horizontal seal section Sh in the horizontal sealer 20. The plate-shaped main body 26 of the knife 22 is formed with a bolt insertion hole 28 for holding the knife 22 to the heater block 20a and two engagement notches 30. The main body 26 also has a cutting edge 32.

A large number of blades 34 are arranged in the width direction X of the blade portion 32 at a predetermined interval D (e.g., 5 mm pitch). In other words, the width dimension of the blades 34 in the width direction X is the interval D. Each blade 34 has two front blades 36. A back blade 38 (shown by dashed lines) is formed on the back surface opposite each front blade 36 of the blade 34. The direction perpendicular to the width direction X of the blade portion 32 is defined as the extension direction Y of the blades 34.

Figure 3 shows an enlarged view of the front blade 36. Each blade 34 has a cutting edge 40, a base 42, and a cutting tip 44. The cutting edge 40 forms the V-shaped pointed end of the blade 34. The base 42 is located on both sides of the cutting edge 40 in the width direction X and forms the V-shaped valley of the blade 34. The cutting tip 44 connects the cutting edge 40 and the base 42 and forms two sides of the V-shape of the blade 34. The front blade 36 extends along the cutting tip 44 from the cutting edge 40 toward the base 42.

More specifically, the front edge 36 has a rectangular inclined surface. Furthermore, a ridge line 46 is formed on the cutting edge 34 at the boundary between adjacent front edge 36 in the width direction X. The ridge line 46 extends from the cutting edge 40 in the extension direction Y and has a base point 48 at the end opposite the cutting edge 40. The blade base 42 is located on the same line as the base point 48 in the width direction X, or on the cutting edge 40 side of the base point 48 in the extension direction Y. The ridge line 46 extends in the extension direction Y from the base point 48 on the surface of the cutting edge 34 to the cutting edge 40. Furthermore, a first valley line 50 is formed on the surface of the cutting edge 34 at the boundary between adjacent cutting edges 34 in the width direction X.

Figure 4 shows an enlarged view of the rear blade 38. The rear blade 38 is formed on the rear surface of the blade 34, opposite the front blade 36, and has the same cutting edge 40, blade base 42, and cutting tip 44 as the front blade 36. Specifically, the rear blade 38 has a triangular inclined surface. Furthermore, a second valley line 52 is formed at the boundary between adjacent rear blades 38 in the width direction X on the blade 34. Furthermore, on the rear surface of the blade 34, the boundary between adjacent blades 34 in the width direction X forms the apex of the triangle of the rear blade 38, and the blade base 42 is located at this apex.

Figures 5 to 7 show cross-sectional views taken along the arrows A-A, B-B, and C-C of Figure 3, respectively. Figure 5 shows a cross-section taken along the ridge line 46 of the cutting edge 34. Figure 6 shows a cross-section at an angle inclined relative to the extension direction Y at the location where both the front cutting edge 36 and the back cutting edge 38 of the cutting edge 34 are present. Figure 7 shows a cross-section taken along the first valley line 50 of the cutting edge 34.

As is clear from Figures 5 to 7, the front blade 36 is inclined in a direction that reduces the thickness t1 of the cutting edge 34 in the blade thickness direction Z. On the other hand, as is clear from Figures 5 and 6, the back blade 38 is formed to hollow out the back side of the front blade 36 due to the presence of the second valley line 52, and is inclined in a direction that reduces the thickness t2 of the front blade 36 in the blade thickness direction Z.

Figure 8 shows (a) a front view of each blade 34 (specifically, three blades) as viewed in the extension direction Y, and (b) to (e) stepwise cross-sectional views of each blade 34 as they approach the base 42. By reducing the thickness t2 of the front blade 36 in conjunction with the formation of the back blade 38, the area of the cross section S in the blade thickness direction Z, from the cutting edge 40 to the base 42 of the blade 34, is significantly reduced compared to the conventional diamond-shaped cross section S. Specifically, the cross section S is a concave rectangle in all cross sections shown in Figures 8(a) to (e).

Figure 9 shows captured images of (a) each cut edge 54 of the tubular packaging material Wc when each blade 34 pushes against the tubular packaging material Wc, (b) the cut edge 54 of the tubular packaging material Wc as each blade 34 continues to push, and (c) the cut edge 54 of the tubular packaging material Wc when each blade 34 cuts the tubular packaging material Wc during the process of cutting the tubular packaging material Wc with the knife 22. As each blade 34 pushes against the tubular packaging material Wc, recessed rectangular cut edges 54 are formed in the tubular packaging material Wc lined up in the width direction X, as shown in Figure 9(a).

As each blade 34 continues to push, the cut edges 54 in the tubular packaging material Wc gradually become larger while forming similar concave rectangular shapes, as shown in Figure 9(b). Then, as shown in Figure 9(c), as each blade 34 continues to push, adjacent cut edges 54 in the width direction X connect, thereby cutting the tubular packaging material Wc.

That is, while the blades 34 of the knife 22 are thrusting against a portion of the tubular packaging material Wc equivalent to the area of the cut edge 54 (thrust-pushing process), the blades 44 of the knife 22 cut through the tubular packaging material Wc, gradually enlarging the cut edge 54 of the tubular packaging material Wc (slitting process). The lower portion of the cut edge 54 shown in Figure 9 has a shape that corresponds to the recessed portion of each blade 34, which has a concave rectangular cross section. Therefore, when the blades 34 thrust against the tubular packaging material Wc in the thrust-pushing process, the tubular packaging material Wc is cut without the blades 34 exerting much pressure on the packaging material W below the cut edge 54.

Figure 10 shows a front view of the bag P, clearly showing the cut edges 54 of the horizontal seals Sh cut by the knife 22. The cut edges 54 in the tubular packaging material Wc at the horizontal seals Sh are formed at the top and bottom ends of the bag P. The cut edges 54 have a peak-valley wave pattern that follows the outer edge of the concave rectangular cross section of each blade 34. Both the peaks and valleys of this wave pattern are smooth, and as is clear from Figure 9(c), no uncut portions such as frayed fibers of the tubular packaging material Wc remain at the cut edges 54.

On the other hand, Figure 11 shows fiber fluffing 56 that occurred at the cut edge 54 of the tubular packaging material Wc in the conventional method. The cut edge 54 of the conventional tubular packaging material Wc has fiber fluffing 56 of the tubular packaging material Wc at the peaks of the corrugated peaks and the corners of the valleys. This is because packaging material W is more difficult to stretch than film packaging, and in the conventional case where the cross section S of the blade 34 is diamond-shaped, the tubular packaging material Wc is not stretched sufficiently during the pushing process, causing the tubular packaging material Wc to be torn apart.

Specifically, as the knife 22 pushes and pushes, the portion of the tubular packaging material Wc shown in Figure 11 that forms the cut edge 54 (the upper end of the bag P) is pushed in by the blade 34, and is pulled by the blade 34 while being pulled downwards by the blade 34. The tubular packaging material Wc, which is made from a packaging material W that is difficult to stretch, is pulled by the blade 34 beyond the tensile strength limit of the packaging material W before the cut is completed, and is torn by the blade 34, causing fuzzing 56 at the cut edge 54.

Such fuzz 56 not only prevents the formation of a smooth cut edge 54, but also reduces the quality of the bag P by causing other objects to get caught on the fuzz 56 when they come into contact with it, and by causing paper dust when the fuzz 56 falls off.

As described above, in the packaging cutting knife 22 of this embodiment, the thickness t2 of the front blade 36 is reduced by forming the back blade 38. As a result, the front blade 36 and back blade 38 have inclined surfaces that slope in the same direction when viewed from the center of the thickness of the blade 34, and are formed asymmetrically on the front and back with different cutting angles. This reduces the area of the cross section S in the blade thickness direction Z from the cutting edge 40 to the blade base 42 of the blade 34.

By reducing the area of the cross section S of the blades 34, the tubular packaging material Wc is cut without each blade 34 pressing too hard against the packaging material W below the cut edge 54. In other words, because the area of the cut edge 54 of the tubular packaging material Wc is smaller than before, the importance of the pushing and pushing process described above can be reduced. Therefore, when cutting the tubular packaging material Wc with the knife 22, the importance of the tearing process described above becomes relatively greater, allowing for a smooth cut edge 54 to be formed in the tubular packaging material Wc.

Specifically, the cross section S in the blade thickness direction Z from the cutting edge 40 to the blade base 42 of the blade 34 is a concave rectangle. This allows the cut edge 54 of the tubular packaging material Wc to be formed into a wavy, peak-valley pattern without fuzzing 56, along the outer edge of the concave rectangular cross section of each blade 34. Furthermore, the blade base 42 is located on the same line in the width direction X as the base point 48 of the ridge line 46, or closer to the cutting edge 40 than the base point 48 in the extension direction Y.

As a result, when the blade base 42 of the cutting edge 34 reaches the tubular packaging material Wc during the process of cutting the tubular packaging material Wc with the knife 22, the ridge line 46 is reliably positioned at the peak of the incision 54 of the tubular packaging material Wc. Therefore, as shown in Figure 9(c), the incisions 54 are connected, making it possible to maintain the cross section S as a concave rectangle until the tubular packaging material Wc is cut. This makes it possible to more reliably form smooth incisions 54 in the tubular packaging material Wc.

Furthermore, the spacing D between the blades 34 arranged in the width direction X of the blade portion 32 is preferably 5 mm. By arranging the blades 34 in a row with a shorter spacing D than conventionally, fraying 56 on the cut edge 54 can be more effectively prevented.

This concludes the description of the embodiment, but the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the knife 22 can cut difficult-to-stretch packaging materials other than paper packaging materials, and can be used to cut packaging materials W of all shapes other than tubular packaging material Wc. Furthermore, if used to cut packaging material W, the knife 22 may be used in packaging machines of packaging types other than the vertical form-fill-seal-seal packaging machine 1 shown in the embodiment.

The knife 22 can also be used to cut packaging material W in devices other than packaging machines. Furthermore, the cross section S of the blade 34 is not limited to a concave rectangle. Specifically, the thickness t2 of the blade 36 can be reduced by forming the back blade 38. In other words, the front blade 36 and the back blade 38 can be formed as inclined surfaces that are inclined in the same direction when viewed from the center of the blade 34's thickness, and can be formed asymmetrically on the front and back with different cutting angles.

As long as these conditions are met, the cross section S of the blade 34 can be modified into various shapes depending on the required shape of the cut edge 54 of the packaging material W. For example, the cross section S in the blade thickness direction Z from the cutting edge 40 to the blade base 42 of the blade 34 may have arc-shaped corners rather than a concave rectangle with acute corners.

The cross section S may also be triangular in shape when the blade base 42 is positioned on the same line in the width direction X as the base point 48 of the ridge line 46, or closer to the cutting edge 40 than the base point 48 in the extension direction Y. This reduces the area of the cross section S of the blade 34 compared to when the cross section S is at least diamond-shaped. Furthermore, by connecting the cut edges 54, the cross section S can be maintained in a triangular shape until the tubular packaging material Wc is cut, allowing for smooth cut edges 54 to be formed in the tubular packaging material Wc.

REFERENCE SIGNS LIST 1 Vertical form-fill-seal packaging machine 2 Bag-forming tube 22 Knife 24 Blade receiving groove 26 Main body 32 Blade portion 34 Blade 36 Front blade 38 Back blade 40 Cutting blade 42 Blade base 44 Blade tip 46 Ridge line 48 Base point D Spacing P Bag S Cross section Sh Horizontal seal portion t2 Thickness W Packaging material Wc Cylindrical packaging material X Width direction Y Extension direction Z Blade thickness direction

Claims (7)

A knife for cutting packaging material that pushes and cuts difficult-to-stretch packaging material,
A plate-shaped main body;
a blade portion formed on the body;
and cutting edges arranged side by side at predetermined intervals in the width direction of the blade portion and having a V-shape in a plan view.
The cutting tool is
a cutting edge forming the V-shaped pointed end of the cutting tool;
a blade base that is located on both sides of the cutting edge in the width direction and forms the V-shaped valley of the cutting edge;
a cutting edge that connects the cutting edge and the blade base and forms two sides of the V-shape of the blade;
a front edge formed on a surface of the cutting tool and extending from the cutting edge toward the base along the cutting edge;
a back blade formed on the back surface of the cutting element and having the same cutting edge, blade base, and cutting edge as the front blade ;
a ridgeline formed at a boundary between the front blades adjacent in the width direction and extending from the cutting edge in the extending direction of the blade;
a valley line formed at a boundary between the back blades adjacent in the width direction and extending in the extension direction;
Equipped with
The back blade is formed so as to gouge the back side of the front blade by arranging the valley line opposite the ridge line in the blade thickness direction . The packaging material cutting knife of claim 1, wherein the front blade and the back blade have inclined surfaces that are inclined in the same direction when viewed from the center of the blade's thickness, and are formed asymmetrically with different cutting angles on the front and back. The packaging material cutting knife according to claim 2, wherein the cross section of the blade in the blade thickness direction from the cutting edge to the blade base is a concave rectangle. 4. The packaging material cutting knife according to claim 1 , further comprising a base point at the end of the ridge line opposite the cutting edge, and the base of the blade is located on the same line as the base point in the width direction or on the side of the cutting edge relative to the base point in the extension direction. A packaging material cutting knife according to any one of claims 1 to 4, wherein the spacing between the cutting edges arranged in the width direction of the blade portion is 5 mm. A packaging material cutting knife according to any one of claims 1 to 5, wherein the front blade has a rectangular inclined surface, while the back blade has a triangular inclined surface. A vertical form-fill-seal packaging machine equipped with the packaging material cutting knife according to any one of claims 1 to 6,
A vertical form-fill-seal packaging machine that forms the packaging material into a tubular shape around a bag-forming tube, and while the formed tubular packaging material is fed out in the longitudinal direction of the bag-forming tube, forms horizontal seals below the bag-forming tube at specified intervals in the longitudinal direction of the tubular packaging material, alternately forms the horizontal seals and fills the tubular packaging material with a filling material, and simultaneously cuts the tubular packaging material at the horizontal seals with the knife to produce bags filled with the filling material.