GB2208622A - Tool usable in the production of an easily openable tightly sealed bag - Google Patents

Abstract

The tool has an array of fine protrusions 10 raised from a surface 9. Each protrusion has a cutting edge 22. The surface 9 may be the circumferential surface of a roller. When pressed into the edge portion of a film it forms a multiplicity of small cuts, which when the film is sealed along edge portions to form a bag, permit the edge to be easily opened by tearing. The protrusions may be formed by cutting into the surface 9 and raising triangular portions 12 leaving indentations 11. <IMAGE>

Description

TOOL USABLE FOR PRODUCTION OF AN EASILY OPERABLE TIGHTLY SEALED BAG This invention relates to a tool for making slits in the edges of a tightly sealed plastic bag, so that it can safely retain the practical strength normally expected of any bag, avoid accidentally sustaining rupture while the bag is being transported or handled, and yet be opened with the force of finger tips.

This application is divided out of Patent Application No 8529597 (GB-A-2169874).

GB-A-2169874 (8529597) in one aspect discloses an easily openable tightly sealed plastic bag formed of a film containing at least a substrate layer and a heat seal layer and possessed of a sealed part, which bag is characterised by the sealed part containing in the substrate layer a multiplicity of through cuts and the through cuts being substantially formed in the edge portion of the bag and partly or wholly closed with the heat seal layer.

In another aspect GB-A-2169874 discloses a method for the production of àn easily openable tightly sealed plastic bag, characterised by forming a multiplicity of through cuts in a film containing at least a substrate layer and a heat seal layer, then folding the film thereby enabling the edge portions containing said through cuts to constitute partly or wholly the sealed edge portions of a bag, and heat-sealing the superposed edges or inner sides thereof thereby completing a tightly sealed bag having at least three edges thereof heat-sealed.

In a third aspect GB-A-2169874 discloses a method for the production of an easily openable tightly sealed bag, characterised by forming a multiplicity of through cuts in a substrate film, binding a heat seal film on one side of the substrate film, then folding the bound films thereby enabling the bordering portions containing said through cuts to constitute partly or wholly the sealed edge portions of a bag, and heatsealing the superposed edges or inner sides thereof thereby completing a tightly sealed bag.

For use in the above methods, this invention, which is divided out of GB-A-2169874, provides a slit imparting tool having blades of fine protrusions linearly aggregated thereon, which tool is characterized by said ine protrusions individually possessing a ridge and said ridge partly or wholly constituting a cutting edge.

In the accompanying drawings: Figure 1 is an end view illustrating a section of the through slits formed in a film prior to heat-sealing with the tool shown in Fig 11 (corresponding to a view taken on line X-X of Fig 3 (b)). Figure 2 is a cross section illustrating the heat-sealed portion of a folded film. Fig 3 (a), (c), (d) are plan views illustrating one end face of a film, (a) showing a state prior to sealing, (c) a state after sealing, (d) a state after sealing with the through slits arranged differently, and Fig 3 (b) an enlarged view of the through slit encircled with a dash and dotted line in (a). Fig 4 and Fig 5 are explanatory diagrams on the mechanism of tearing.

Fig 6 is a diagram illustrating protrusions on a tool in a magnified state. Fig 7 is a cross section illustrating a typical process for the production of such a protrusion. Fig 8 is a perspective view of a fabricating wheel. Fig 9 is an enlarged plan view of part o the circumferential surface of the wheel of Fig 8. Fig 10 is an explanatory diagram illustrating a typical fabrication performed on a film. Fig 11 is a perspective view illustrating a tool having protrusions formed on a flat bar. Fig 12 is a perspective view illustrating a tool having protrusions formed on a plate cut out of a disk. Fig 13 is a micrograph showing a section of a cut in the sealed portion of the tightly sealed bag of the present invention.

A detailed description of the appropriate types of film and their properties for use in an easily openable sealed bag is given in GB-A-2169874.

The present invention concerns a tool which forms a multiplicity of through slits substantially in the edges of a sealed bag produced from the films. The expression "substantially in the edges" denotes that the through slits may be formed in a slightly inner portion from and along the edges or in the edges.

The through cuts or slits may be formed in zigzag pattern as illustrated in Fig 3 (c) or in series as illustrated in Fig 3 (d).

The through cuts or slits do not denote completely opened through holes but denote the cuts left in the substrate layer after being formed through the substrate layer without producing the substrate layer scraps as shown in Fig 2 (a), (b).

In the present invention, the through cuts or slits formed in the substrate layer are to be partly or wholly closed with the heat seal layer. The term "closed" denotes that: (1) the heat seal layer material is filled into the through slits, (2) the heat seal layer material penetrates into the through slits but does not fully fill them. The heat seal layer is heat-sealed around the through slits and closes their openings, and (3) the heat seal layer does not penetrate into the through slits but is fused around them to cover and close their openings.

The expression "wholly closed with the heat seal layer" means that the all numbers of slits are closed with the heat seal layer in one or at least two ways of the above (1), (2), and (3).

The expression "partly closed with the heat seal layer means that: A. Some numbers of the whole slits are closed with the heat seal layer in one or at least two ways of the above (1), (2), and (3), and B. The heat seal layer material penetrates partly into the openings of the slits, or the openings are partly covered with the heat seal layer to narrow the opening area of the slits. But, the slits are not closed as in the above three ways (1), (2), and (3).

The through slits formed without producing film scraps by the present invention are in a slender shape having a length not exceeding 0.5 mm, preferably not exceeding 0.3 mm and exceeding 0.1 mm. As illustrated in Fig. 3, the through cuts 1 are disposed in a transversal direction relative to an edge line 2. Cracks (not illustrated in the drawing) start from the terminals 3, 4 of each through cut 1 shown in Fig. 4.

Virtually no crack is seen to occur at any other point of the through cut. When a group of such through cuts is located substantially on the edge line, tears in the bag start from the inner terminals 4 of the through cuts 1. When such through cuts are located as separated inwards from the edge line 2, the stress exerted as indicated by the arrows in Fig.

4 causes tears to start from the edge line side terminals 3 of the through cuts toward the edge line 2 as indicated by the arrow of dotted line in Fig. 4. After the tears have reached the edge line, the tears begin to propagate in the transversal direction from the other terminals 4 of the through cuts.

The slender through cuts 1 substantially perpendicular to the edge line 2 are disposed ideally at 90" relative to the edge line. In actuality, the through cuts advantageously fulfil their part in this invention so long as they are disposed at angles falling in the range of 70 to 110 , preferably 75 to 105 .

The through cuts formed without producing film scraps means local injuries produced in the film as by causing the relevant portions of the film to be pulled outwardly or by inserting partial cuts in the portions, so that during the infliction of such injuries, absolutely no part is cut out from the film. The through cuts are formed in such portions of the film that are destined to form an edge portion when the opposed ends of the film are heat-sealed to complete a bag. When the film is thick and tough, these through cuts are required to be formed so as to border on the edge line.

When the film is thin, they are desired to be located at a distance of 0.5 to 3 mm inwardly from the edge line.

In accordance with this invention, when the film having the through cuts formed in advance is folded and the opposed ends of the folded film are heat-sealed to form a sealed part of a bag as illustrated in Fig. 1, the molten heat seal layer is allowed to enter the through cuts formed in the substrate layer and substantially fill up the through cuts as illustrated in Fig. 2 (a), (b). Since the through cuts are filled up in their fairly large portions, a possible decrease in the strength of the tightly sealed bag due to the presence of such through cuts can be repressed to the minimum.

In the sealed part of the tightly sealed bag of this invention, the cuts may be distributed, so that those formed in one of the sealed substrate layers of film deviate from those formed in the other substrate layer as illustrated in Fig. 2 (a) or they coincide with those formed in the other substrate layer as illustrated in Fig. 2 (b). Where the material for the substrate layer of the film possesses notably high tear strength, the disposition of the through cuts in their mutually coinciding positions proves more desirable from the standpoint of easy opening of the bag. When the through cuts formed in one of the substrate layers coincide with those formed in the other substrate layer, easy openability of the bag is sufficiently attained even if the pitch Q betueen the cuts is distant as shown in Fig. 3 (c), (d).For example, the pitch Q may be enlarged to about 5 mm. When the through cuts formed in one of the substrate layers do not coincide with those formed in the other substrate layer, it is preferable to fix the pitch Q at not more than 1.5 mm, preferably in the range of about 1.0 to 1.5 mm from the standpoint of the easy opening property. The through cuts may be formed in a single row or in a plurality of rows of at least two. Where the through cuta are formed in a plurality of rows, the width of a group of cuts is desired to be not more than 5 mm, preferably not more than 3.5 mm.

Examples of bags produced with cut edges of this type are disclosed in GB-A-21b.9874 (Figs 6, 7, 8, 9).

A tool for producting the cuts will now be described, referring initially to Fig 6 herein. A metallic roll having a multiplicity of slender cutting edges formed on the circumferential surface thereof or a metallic plate having the same cutting edges formed on the flat surface thereof can be advantageouslg used. For example, by making pseudotriangular cuts 21 in a metallic surface 9 and causing metallic portions separated from the metallic surface by the cuts to be raised relative to the bases of the pseudotriangles as axes as illustrated in Fig. 7 , protrusions 10 are created and cut portions remain as depressions 11.The angle which the depression side surfaces of the protrusions 10, namely the bluff surfaces 12, form relative to the metallic surface is desired to exceed 60" and not to exceed 90". The metallic material on which such protrusions as mentioned above have been arranged in at least one straight rou is hardened and used as the tool. Fig. 8 is a perspective view of a processing roll 13 having such protrusions formed on the circumferential surface thereof and Fig. 9 is a plan view illustrating the portion of the processing roll 13 of Fig. 8.

enclosed with a dash and dotted line in an enlarged state.

When the protrusions 10 illustrated in Fig. 6 are pressed against a film, the curved edges of the bluff surfaces 12 function as cutting edges, so that the edges of the bluff surfaces 12 will be straightly inserted into the portions of the film falling under the bluff surfaces 12 side and the outer sloped surfaces 19 will expand the portions of the film by the pressure exerted. As a result, the portions of the film which have admitted the insertion of the bluff surfaces 12 remain flat and the portions which have admitted the outer sloped surfaces 19 are deformed aslant downwardly and strained and come to differ from the level of the remaining portions of the film as illustrated in Fig. 1. The film is provided with the strained portions and the undeformed portions with the cuts therebetween.When the film is heat-sealed, the strained portions of the film are almost returned to their original state to coincide with the level of the remaining portions of the film, but thes still possess the internal strain remained therein and, because of the internal strain, the strength of the film is louered.

Consequently, an important effect that the film is readily torn with the force of fingers from the bordering portion between the strained portion and the unstrained portion.

Unlike the injuries inflicted by insertion of conventional cutting edges, cracks run from the opposite terminals of the through cuts produced as described above. These cracks are highly effective in starting tears in the film. When the through cuts shown in Fig. 1 and formed with the tool illustrated in Fig. 6 are heat-sealed, the portions deformed aslant downwardly are restored substantially to its original flat state as illustrated in Fig. 2 (a), (b).

Fig lOis an explanatory diagram illustrating a typical setup for working on a film by the use of the processing roll illustrated in Fig. 8 . The processing roll 13 and a retainer roll 14 are held in mutual contact and are rotated in opposite directions at one equal peripheral speed. The film 8 is passed through the tuo rolls. During the course of this passage, the film 8 is depressed by the protrusions 10 on the processing roll 13, with the result that through cuts 1 are disposed in the film in the pattern as illustrated in Fig. 3. In the diagram, 15 stands for a roll of film.

In order to form the through cuts in the film, the tool may be used in the shape having protrusions created on the surface of a flat bar as illustrated in Fig. 11 or in the shape having protrusions created on a semicircular plate cut out from a disk as illustrated in Fig. 12.

The tool used in the present invention is desired to be made of a rigid material including a hardened steel and ceramics such as silicon carbide, titanium carbide, and silicon nitride. Where the tool shaped from a metallic material is covered with a thin coat of silicon carbide or titanium carbide, the obtained tool also exhibits outstanding wear-resistance and provides a sharp cutting for a long time.

Now, the methods available for the production of the easily openable tightly sealed bag of this invention will be described below.

These methods are roughly classified into the following two types: (1) The method which comprises inflicting through cuts in a film which has the substrate layer and the heat seal layer joined in advance by lamination and (2) the method which comprises first inflicting through cuts in the substrate layer and subsequently superposing the heat seal layer fast on one of the surfaces of the substrate layer.

The procedure which follows the infliction of the through cuts, namely the procedure which comprises folding the film in such a manner that the portions bearing the aforementioned through cuts will be opposed to each other to form a portion or the entire portion of the sealed edge portions of a bag and heat-sealing the opposed edge portions or the inner sides thereof thereby giving rise to a tightly sealed bag, is applicable commonly to the two major methods (1), (2) mentioned above.

When the easily openable tightly sealed bag is produced by inflicting through cuts in the film by the above method (1), folding the film in such a manner that the portions bearing such through cuts will be superposed to form a portion or the entire portion of the sealed edge portions of a bag and heat-sealing the opposed edge portions thereby forming a sealed part in the completed bag, the through cuts are partly or wholly blocked with a heat seal layer as illustrated in Fig. 2 (a), (b) and they are distributed only in the heat-sealed portions.When the opposed edge portions are heat-sealed on their inner sides, the through cuts are distributed in the heat-sealed portions and in the nonheat-sealed portions falling outside the heat-sealed portions and the through cuts distributed in the heat-sealed portions are partly or wholly blocked with the heat seal layer and the through cuts distributed in the nonheat-sealed portions are not blocked with the heat seal layer.

When the easily openable tightly sealed bag is produced by inflicting through cuts in the substrate layer and superposing the heat seal layer thereon by the method of (2) and heat-sealing the opposed edge portions to form a sealed part in the completed bag, the through cuts are partly or wholly blocked with the heat seal layer and they are distributed only in the heat-sealed portions. In this case, when the inner sides of the edge portions are heat-sealed, the through cuts are distributed in the heat-sealed portions and in the nonheat-sealed portions alike and these through cuts in both the heat-sealed portions and the nonheat-sealed portions are partly or wholly blocked with the heat seal layer.

Example 1 [Hanufacture of device for imparting through cuts] Fig. 6 is a perspective view of protrusions 10 on a through cuts imparting device of this invention in a magnified state. As illustrated in Fig. 7, cuts 21 are made in a flat, smooth metallic surface 20. Then, the surface portions separated from the metallic surface in consequence of the work of making cuts 21 are raised substantially upright as indicated by the arrow of Fig. , there are formed bluff surfaces 12 as illustrated in Fig. 7'. The bluff surfaces 12 has on their backs formed outer sloped surfaces 19 by the flat, smooth metallic surface pulled up through the medium of ridge lines 22. By 11 are denoted depressions which are formed in the flat, smooth metallic surface by the insertion of the cuts.The angle which the bluff surfaces 12 form relative to the flat, smooth metallic surface 20 is required to exceed 60" and desired to fall in the range of 80" to 100 . The metallic material on which the protrusions of the shape described above are formed in a large number is hardened and used as a cutting blade of this invent ion.

Since the ridge lines 22 are formed by the cuts made in the metallic surface, they are naturally sharp and constitute escellent cutting edges. In the present working example, the protrusions 10 have a width of 0.4 mm at their foots. As illustrated in Fig. 8 , these protrusions 10 are disposed in at least one row on the circumferential surface of a processing roll 13. Fig. 9 is a plan view illustrating the portion of the roll 13 indicated by a dash and dotted line in Fig. 8 in a magnified state. When this processing roll 13 is rotated and the protrusions 10 are brought into pressed contact with the film, the ridge lines 22 function as cutting edges to inflict a linearly arranged group of fine slender cuts in the film.Since the cutting edges are each in the form of a mountain, the length of the cuts inflicted in the film can be varied by regulating the pressure with which the cutting edges are pressed into the film. This device wears slowly and enjoys high durability because the cutting blades have an appreciable thickness.

Example 2 [Production of easily openable tightly sealed bag]: A composite laminated film of 720 mm in width and 74 gm in total thickness consisting of the following structure uas prepared by an extrusion laminating method: PETtl2/AC/LDPEls/AQ7/IR40 wherein, PET12: biaxially stretched polyester film (E-5100 produced by Toyobo K. K.) ..... 12 m in thickness AC : imine type anchor coat agent (WS-680 produced by Matsuoto Seiyaku K. K.) ..... 0.01 g/m2 of solid content LDPE15: low-density polyethylene (Suntech LD, L-1850A produced by Asahi Kasei Kogyo K. K.) 15 m in thickness ..... 15 m in thickness Al7 : flexible aluminum foil (produced by Tokai Kinzoku K.K.) ..... 7 m in thickness IR40 : ionomer (Himiran 1652 SR, produced by Nitsui-Du Pont Polychemical K. K.) ..... 40 m in thickness A group of cuts was inflicted in the above laminated film with the device of Example 1.

As illustrated in Fig. 10, the processing roll 13 and the retainer roll 14 are held in mutual contact and are rotated in oposite directions at one equal peripheral speed.

The film 8 is passed through the two rolls. During the course of this passage, the film 8 is pressed by the protrusions 10 of the processing roll 13. This film 8 is fed from the roll 15. Consequently, through cuts are formed in three rows, two at a distance of 10 mm from the opposite edges of the film 8 and one at the center of the width of the film. Then, by cutting the film along the central array of through cuts, there are obtained two strips of film each measuring 350 mm in width.

As illustrated in Fig. 1, the portions of the obtained film which were cut into with the bluff surfaces of the device remained flat and the portions which received the insertion of the outer sloped surfaces were deformed aslant downwardly, resulting in formation of the uneven film surfaces at the cut portions with the cuts therebetween. It was observed that the opposite terminals of each through cut were cracked.

From the obtained film, pillow type gusset bags each having the three edge portions heat sealed and containing 250 g of instant coffee were produced by the use of an automatic bag making and bag-filling machine.

In the sealed part of each of the bags so produced by the automatic bag-making and bag-filling machine, the through cuts were wholly blocked with the heat seal layer. When the opposed edge portions are heat-sealed by the automatic bag-making and bag-filling machine, they are so positioned that the through cuts in one of the edge portions will deviate from those in the other edge portion.

During the course of the production of bags, the transportation of the produced bags, or the storage thereof, the film retained sufficient strength without suffering any trouble. The bags consequently obtained could be opened with the force of finger tips at any desired point in the longitudinal heat-sealed portions.

In this working example, the protrusions were arrayed orderly. The protrusions, if distributed irregularly, could be expected to bring about the effect aimed at by this invention so long as they were formed with sufficient density.

Example 3: A composite laminated film of 770 mm in width and 70 m in thickness consisting of the following structure was prepared by an extrusion laminating process: ONE /AC/PE2 S/EVA3o wherein, ON@15 : biaxially stretched 6-nylon film (Embrem produced by UNITIKA, Ltd.) ..... 15 m in thickness AC : isocyanate type anchor coat agent (prepared by mixing EL-200 and CAT-200 both produced by Toyo Photon K. K. in the ratio of 13 : 1) ..... 0.02 g/m2 of solid content PE25 : low-density polyethylene (Suntech LD, L-1850A produced by Asahi Kasei Kogyo K.K.) ..... 25 m in thickness EVE30 : ethylene-vinyl acetate copolymer resin (Suntech EVA, EL-0990 produced by Asahi Kasei Kogyo K. K.) ..... 30 m in thickness The above isocyanate type anchor coat agent was applied to the biaxially stretched 6-nylon film by a gravure coating method. The low-density polyethylene layer and the ethylene-vinyl acetate copolymer resin layer were superposed to each other by a tandem extrusion laminating method.

A croup of cuts was inflicted in the above laminated film with the device illustrated in Fig. 8 without giving rise to any waste scraps of the film.

The ethylene-vinyl acetate copolymer constituted the heatseal layer. On the circumferential surface of the processing roll 13, protrusions of the shape illustrated in Fig. 7 having the maximum width of 0.5 mm are arrayed in a total of four zigzag rows, two each at a center-to-center distance of 0.5 mm from the central zone of flat, smooth surface 1.5 mm in width left at the center of the width of the peripheral surface. Then, by following the procedure of Example 1, through cuts were inflicted in the portions at a distance of 10 mm from the opposite edges at an interval of 250 mm of width.Then, the film was cut in the centers of the arrayed groups of cuts to obtain the strips of film having a width of 250 mm and containing groups of through cuts in the portions at a distance of not less than 0.75 mm from the opposite edges of the film.

As illustrated in Fig. 1, the portions of the obtained film which were cut into with the bluff surfaces of the device remained flat and the portions which received the insertion of the outer sloped surfaces were deformed aslant downwardly, resulting in formation of the uneven film surfaces at the cut portions with the cuts therebetueen. It was observed that the opposite terminals of each through cut were cracked.

From the film so obtained, pillow type bags each having the edge portions heat-sealed and containing 250 g of a piece of devi 1's-tongue jelly were produced by the use of an automatic bag-making and bag-filling machine. A micrograph illustrating the sealed portion containing cuts is shown in Fig.17..

In each of the bags so produced by the automatic bag-making and bag-filling machine, the through cuts were partly blocked with the heat seal layer. During the heat sealing of the opposed edge portions with the automatic bag-making and bag-filling machine, these edge portions were so positioned that the through cuts in one of the edge portions deviate from those in the other edge portion.

During the course of the production of bags, the transportation of the produced bags, or the storage thereof, the film retained sufficient strength without suffering any trouble. The bags consequently obtained could be opened with the force of finger tips at any desired point in the longitudinal heat-sealed portions.

Examples A composite laminated film was prepared by following the procedure of Example 3 except that through cuts were inflicted in the biaxially stretched 6-nylon film with the device illustrated in Fig. 8 immediately prior to laminating in the process of extrusion lamination.

Then, by following the procedure of Example 3, the laminated film was cut at the center of the groups of cuts, to afford two strips of film having a width of 250 mm and containing through cuts in the portions at a distance of 0.75 mm inwardly from the opposite edges of the film. The ethylene-vinyl acetate copolymer constituted the heat seal layer.

From the film so obtained, pillow type bags each having the edge portions heat-sealed and containing 250 g of a piece of devil's-tongue jelly were produced by the use of an automatic bag-making and bag-filling machine.

By visual inspection, the cuts in the tightly sealed bag produced by the automatic bag-making and bag-filling machine were found to be wholly blocked with the heat seal layer.

During the course of the production of bags, the transportation of the produced bags, or the storage thereof, the film retained sufficient strength without suffering any trouble. The bags consequently obtained could be opened with the force of finger tips at any desired position in the longitudinal heat-sealed portions.

Example 5-: A composite laminated film consisting of a stretched nylon film (15 am in thickness) coated with vinylidene chloride resin as a substrate layer and a linear low-density polyethylene (25 am in thickness) as a heat seal layer and measuring 820 mm in width and 40 m in total thickness was us-ed to produce vacuum-packed bags for domestic use with a bag-making machine capable of sealing three sides.

The laminated film used in this Example had the following structure in detail: KONZls/adhesive/L-LDPE2s wherein, KON2ls : polyvinyl idene chloride-coated biaxially stretched 6-nslon (Hahden film, KN 8002 produced by Tosobo K. K.) ..... 17 m in thickness Adhesive: isocyanate type adhesive (prepared by mixing AD-335AT and CAT-lO both produced by Topo Photon K. K. in the ratio of 100 : 6) ..... 2 m in thickness (2-3 g/m2 of solid content) L-LDPE2s: linear low-density polyethylene (Tocello TUX-FC produced by Tokyo Cellophane K.K.) ..... 25 m in thickness The polyvinyl iden chloride coat surface of the above polyvinyliden chloride coated biaxially stretched 6-nylon was applied with the isocyanate type adhesive by a gravure coater. The linear low-density polyethylene layer had its one surface subjected to corona discharge treatment. This treated surface was applied to the above adhesive-applied surface. Then, the above plies were subjected to a dry laminating method to produce a composite film.

In the process of forming the bags, the film taken out of the source of supply was folded half and a group of through cuts was inflicted with the device illustrated in Fig. 8 in the portions which constitute the longitudinal sealed portions and the end portions of the bags to be made.

Then, the film was heat-sealed to obtain the bags of 200 mm in width and 300 mm in length whose three end portions had been sealed.

Through cuts were formed in one end portion of the film folded into two (410 mm in width), in a portion at a distance of 200 mm inwards from the aforesaid end portion, and in a portion at a distance of 10 mm inwards from the other end portion. The remaind margin of 10 mm was cut off.

The bags thus produced had their two longitudinal end portions and one lateral end portion heat-sealed, and the top end was not sealed. The two longitudinal heat-sealed end portions contained a group of cuts in the width of about 2 mm to the whole longitudinal length of the bags. All the cuts had been covered with the heat seal layer.

During the course of the transportation of the produced bags, the storage thereof, or the handling in filling the bag in a house, the bag caused no trouble. The bag could be opened with the force of finger tips at any desired point in the longitudinal sealed portions.

Claims (4)

1. A slit imparting device having blades of fine protrusions linearly aggregated thereon, which device is characterized by said fine protrusions individually possessing a ridge and said ridge partly or wholly constituting a cutting edge.

2. A slit imparting device according to Claim 1, wherein said blades of fine protrusions are disposed on a circumferential surface of a rotary roll or disk.

3. A slit imparting device according to Claim 1, wherein said blades are hardened metallic blades, ceramics or metallic blades coated with ceramics.

4. A slit imparting device according to Claim 1, wherein said fine protrusions are produced by making cuts into the flat smooth surface of a metallic material for said device and are formed of outer sloped surfaces resulting from said flat smooth being raised by said cuts -inserted thereunder and bluff surfaceswresulting from insertion of said cuts under said flat smooth surface of the metallic material and ridges jointly formed by said outer sloped surfaces and said bluff surfaces constitute themselves cutting blades.