SHEET PROVIDED WITH SAW TEETH MADE OF VULCANIZED FIBERS, CARTON TO WHICH SAID SHEET IS BONDED, AND METHOD OF BONDING

Abstract: A sheet provided with saw teeth to be fixed to a carton case containing a rolled cooking sheet made of synthetic resin film, paper, or metallic foil and to be used for cutting said film, which is characterized particularly in that: said saw teeth are made of vulcanized fiber and, while utilizing stiffness and resilience of said vulcanized fiber as advantages thereof, sheets of moisture-proof film made of synthetic resin are formed on both sides of an original sheet of vulcanized fiber in order to improve wet-absorbing tendency as a drawback of said sheet; and further includes a carton case to which said sheet is bonded as well as a method of bonding said sheet to the carton by making use of said film and ultrasonic fusion-bonding.

Description: The present invention relates to a sheet having a serrated cutting edge for cutting what is called a cooking sheet such as a wrapping film of a synthetic resin, paper sheet and metallic foil, and to a carton case to which the sheet having a serrated cutting edge is adhered. The present invention also includes a method of adhering the sheet having a serrated cutting edge to the carton case. Especially the invention relates to the sheet being made of a vulcanized fibre having a special composition. A material generally called a cooking sheet, such as a wrapping film of a synthetic resin and aluminium foil used in the kitchen, etc. for wrapping foods or the like, is usually rolled up and contained in a paperboard carton case (hereinafter referred to as the "carton"). At the time of use, an end of the film or aluminium foil is pulled out of the carton and cut to a desired length by means of a cutting member or a serrated cutting edge provided on a front portion or a cover portion of the carton (hereinafter referred to as the "cutting edge" or "serrated cutting edge"). The cutting edge provided on the carton is generally made of a metal. Recently a cutting edge made of a vulcanized fibre has been put on the market, because while a metal cutting edge is likely to injure the hand when it is grasped, the vulcanized fibre cutting edge is free from such a possibility. Furthermore, the vulcanized fibre cutting edge may be burned together with the carton when the film or the foil has been used up. While the vulcanized fibre cutting edge has the abovementioned advantages, it also has the disadvantage that because of the properties of the material, the vulcanized fibre cutting edge absorbs moisture and elongates when it is exposed to a moist atmosphere for a long period of time. In an attempt to moisture proof the vulcanized fibre cutting edge, vulcanized fibre blanks have been coated with a melamine resin liquid, glyoxal solution, polyurethane resin liquid, etc. before a cutting edge is formed. However, none of these attempts have been very successful and further improvements are required. If the vulcanized fibre cutting edge is put in the kitchen, for example, which often has a high humidity, the cutting edge may be elongated by moisture in the atmosphere. According to the degree of water-resisting or waterproofing treatment, elongation by moisture absorption may, in an extreme case, partially separate the cutting edge from the carton to which the cutting edge is adhered and reduce the function of the cutting edge. It is a first aim of the present invention to provide a sheet for a cutting edge for cutting material dispensed from within the carton, the cutting edge always having a satisfactory cutting function without being affected by moisture in the atmosphere. In other words, the first aim of the present invention is to provide a vulcanized fibre sheet having a serrated cutting edge, the sheet having a high dimensional stability. It is a second aim of the present invention to improve the shape of the cutting edge so that it can smoothly cut a film of polyvinyl chloride, for example, having a relatively large elongation. It is a third aim of the present invention to provide a novel method of adhering a sheet having a cutting edge to the carton, the method preventing the sheet from peeling off from the carton, even when the sheet is thin. In this method, the cutting edge can be adhered to the paperboard of which the carton is made at the same speed as when a usual metal cutting edge is attached by caulking. Accordingly the present invention is directed to a vulcanised fibre sheet as described in claim 1, a carton as described in claim 9 and a method of bonding as described in claim 13. Advantageous developments are described in sub claims 2 to 8, 10 to 12 and 14 to 15. The moisture-proof film having a low moisture permeability on the two surfaces of the vulcanized fibre sheet having the serrated cutting edge, the moisture-proof film being any one chosen from a polyolefin resin film, polyester resin film and polyvinylidene chloride resin film. Typical examples of the resin film are a polyethylene film, PET film, etc. While the moisture-proof film may be formed directly on the surfaces of the vulcanized fibre, it is also possible to subject the vulcanized fibre to a water-resisting or waterproofing treatment, for example, by applying thereto water-resisting agents such as the melamine resin and glyoxal before the moisture-proof film is formed. To improve the adhesion between the moisture-proof film and the vulcanized fibre, the following means may be used: coating the vulcanized fibre in advance with an anchor coating agent such as polyethyleneimine; or subjecting a resin film to corona discharge before the resin film is applied to the vulcanized fibre so as to form the moisture-proof film. In a usual serrated cutting edge, the shape of each cutting tooth and the distribution of the cutting teeth are of little importance. In the serrated cutting edge formed on the moisture-proof vulcanized fibre blank according to the present invention, the cutting edge has a certain length and, the cutting teeth of the cutting edge are distributed straight. It has been found that if each cutting tooth in the central portion of the cutting edge has the shape of an isosceles triangle and each cutting tooth in the remaining end portions of the cutting edge has the shape of a scalene triangle inclined outward, then the cutting edge can even cut well a film having relatively large elongation. The serrated cutting edge of the sheet may be either formed straight as mentioned above or bent angularly in the lengthwise direction. In the present invention, the serrated cutting edge already formed as mentioned above, especially the sides of each cutting tooth, may be subjected to a water-resisting treatment. In this case, the serrated cutting edge already formed and portions near the cutting edge are subjected to any of the following treatments. One of them is to coat or impregnate the sides of the cutting teeth with an organic solvent solution of any of the above-mentioned resins adapted to have a relatively high fluidity or with a water-resisting agent not mentioned above. Also, a waterproof film may be formed on the serrated cutting edge by applying an ionising radiation curing resin such as an electron beam curing resin (EB resin) and an ultraviolet curing resin (UV resin) to the sides of the cutting teeth and hardening the resin. The hardened waterproof film of the ionising radiation curing resin is very hard so that it prevents moisture from permeating through the sides of the cutting teeth and increases the strength of the cutting edge itself. The water-resisting treatment includes waterproofing treatment for preventing the permeation of moisture. The above-mentioned waterproof film may be formed on the sides of the cutting teeth as a second treatment after a moisture-proof film is formed on the two surfaces of the vulcanized fibre. Also, it is possible to form a moisture-proof film on the two surfaces of the vulcanized fibre blank which is permeated in advance with a waterproofing agent and then form a serrated cutting edge thereon. In the present invention, the vulcanized fibre sheet provided with the serrated cutting edge is attached to a carton as mentioned above. The sheet may be attached to the carton by means of a suitable adhesive (including a pressure-sensitive adhesive). If the following method of adhesion is used, various superior effects as mentioned below will be obtained as compared with the case where the adhesive is used. The method of adhesion comprises placing the sheet having the serrated cutting edge upon a piece of paperboard for the carton, and then adhering the sheet to the paperboard through the moisture-proof film on the surface of the sheet by an ultrasonic adhesion method. It has been confirmed that such adhesion is free from peeling even in a high-humidity atmosphere. Thus, according to the present invention, it is possible to maintain the vulcanized fibre sheet having the serrated cutting edge in a state less liable to be affected by humidity. Therefore, the sheet having the serrated cutting edge has an excellent dimensional stability, even though the sheet is made of vulcanized fibre. Consequently, the serrated cutting edge has good cutting ability. When the sheet is adhered to the carton, the adhesion is strong and free from peeling. Examples of present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view showing an embodiment of a vulcanized fibre sheet having a serrated cutting edge; Figure 2 is an enlarged sectional view taken along line II-II of Figure 1; Figure 3 is a plan view showing a case where a vulcanized fibre blank is provided on both of its two surfaces with a moisture-proof film and then serrated cutting edges are formed thereon in the cross direction perpendicular to the machine direction so as to obtain sheets each having serrated cutting edges; Figure 4 is a plan view showing a case where serrated cutting edges are formed on the vulcanized fibre blank in the machine direction so as to obtain sheets each having serrated cutting edges; Figure 5 is a flattened plan view showing an embodiment of a carton blank provided with one of the sheet having serrated cutting edges; Figure 6 is a perspective view of a carton made by using the carton blank shown in Figure 5, in which the carton is being opened; Figure 7 is a perspective view showing a state in which the carton is open and a cooking sheet rolled up within the carton is being pulled out and cut; Figure 8 is a view showing another carton blank provided with a vulcanized fibre sheet having a serrated cutting edge; Figure 9 is a plan view of a vulcanized fibre sheet having a serrated cutting edge, which shows the shapes and the distribution of the cutting teeth in the serrated cutting edge; Figure 10 is a side view showing a device for adhering the sheet having a serrated cutting edge to a carton blank; Figure 11 is an enlarged sectional view of the device in which a die setting mechanism is open; Figure 12 is an enlarged sectional view of the device in which the die setting mechanism is closed; Figure 13 is an exploded perspective view showing an essential portion of the device; Figure 14 is a schematic plan view explaining a method of adhesion according to the present invention; and Figure 15 is a side view showing a modified example of an ultrasonic adhesion horn. The main material used in the present invention is a vulcanized fibre which, as is generally known, comprises a cotton fibre or chemical pulp made into a base paper without sizing, the base paper being treated with a zinc chloride solution having a certain concentration (Baume degree generally being 65 to 74). The vulcanized fibre has properties intermediate to those of wood and metal. The vulcanized fibre has high elasticity and rigidity, is much lighter than metal and, has a high resistance to various oils. The present invention obtains the above-mentioned sheet having a serrated cutting edge by utilising the properties of the vulcanized fibre and subjecting the vulcanized fibre to special treatment. By adhering the sheet to a carton, the present invention provides a carton having a useful cutting edge which replaces the conventional metal cutting edge. The sheet having a serrated cutting edge has a thickness of 0.2 to 0.5 mm, preferably 0.25 to 0.35 mm. As the thickness decreases, the cutting edge cuts better. In the present invention, a blank of the vulcanized fibre may be used directly as a material for the sheet having a serrated cutting edge. Alternatively, the vulcanized fibre may be made resistant to water in advance by being coated or impregnated with a melamine resin liquid, glyoxal solution, etc. The moisture-proof film may be formed on the surface of the blank by any of the following methods: coating the blank with a resin having a low moisture permeability, the resin being in a state of emulsion or solution, the resin being selected from the polyolefin resin, polyester resin, polyvinylidene chloride resin, etc.; dry laminating the resin in a film state; and extruding the resin in a molten state onto the surface of the blank. A preferable method comprises a polyolefin resin having a low moisture permeability such as polypropylene and methyl pentene polymer being extruded in a molten state onto the surface of the vulcanized fibre blank. In adhering the sheet having a serrated cutting edge to the carton blank, an emulsion of a polyethylene resin, for example may be applied in advance as an adhesion accelerator to the carton blank at a position to which the sheet is to be adhered, a film thus formed in advance increases the adhesion between the sheet and the carton blank. The present invention will now be described in detail with reference to examples and comparative examples. Example 1 First, a method of producing a vulcanized fibre blank used in making the vulcanized fibre sheet having a serrated cutting edge will be described in brief. A paper stuff comprising 50% of NBKP and 50% of NDSP was made into a base paper having a basic weight of 105 g/m 2 . Two pieces of this base paper were immersed in a zinc chloride solution of 69° Be and 40°C, subjected to pressing, adhesion under heat and pressure and air aging, then put into a tank containing a zinc chloride solution of about 30° Be, and aged in a tank containing a zinc chloride solution having a low concentration so that zinc chloride melted away. Then, the base paper was washed in a tank containing hydrochloric acid, and then zinc chloride was removed in a rinsing tank. After being predried, the base paper was coated on its two surfaces with a solution of melamine formalin resin (10 g/m 2 in terms of solid matter), dried by means of a cylinder drier, and further calendered. Thus, a water-resistant vulcanized fibre blank having a thickness of 0.25 mm was obtained. Both of the surfaces of the vulcanized fibre blank were anchored by applying thereto polyethyleneimine in an amount of 3 g/m 2 in terms of solid matter and drying the polyethyleneimine. Then, low-density polyethylene in a molten state was extruded onto the anchored surfaces. Thus, a moisture-proof film comprising a low-density polyethylene layer having a thickness of 20 µm was formed on the two surfaces of vulcanized fibre blank. Now, a vulcanized fibre plate 3 shown in Figures 2 to 4 was obtained, the vulcanized fibre plate 3 comprising a long vulcanized fibre blank 1 provided on its two surfaces with a moisture-proof film 2 which comprises the polyethylene layer. Then, vulcanized fibre sheets 4 having serrated cutting edges were easily obtained by machining the vulcanized fibre plate 3 by means of a serrated cutting edge former or by blanking the vulcanized fibre 3 by means of a press, etc. The vulcanized fibre blank has directional properties attributable to the orientation of the fibre at the time of making the blank. Fibre constituting the blank has a tendency to be arranged in parallel in the paper making direction. Consequently, the physical properties of the blank differ according to the directions of the blank, namely, the machine direction or the lengthwise direction of the blank and the cross direction perpendicular thereto. When the blank has absorbed moisture, the rate of expansion and contraction in the cross direction in Figures 3 and 4 is 6 to 7 times as large as chat in the machine direction. For example, the elongation at a relative humidity of 65 to 90 % (left for 24 hours at an atmospheric temperature of 23°C) in the machine direction is 0.4 %, while that in the cross direction is 2.7 %. Therefore, if serrated cutting edges are formed as shown in Figure 3 in making the blank into sheets having serrated cutting edges and one of these sheets is adhered to a carton, then the sheet having a cutting edge warps on the carton because of the elongation and partially peels off. As a result, the serrated cutting edge loses its sharpness and becomes very dull. If serrated cutting edges are formed in the machine direction as shown in Figure 4, then the above-mentioned problem does not arise because the rate of expansion and contraction in the machine direction is small. In this case, small expansion or contraction offers no problem in practice because such small expansion or contraction corresponds with the expansion or contraction of the carton. It is one of the aims of the present invention to seek to solve the above-mentioned problem of the cross direction. To attain this aim, a moisture-proof film is formed on both surfaces of the blank. According to the present invention, in the blank 3 treated as mentioned above, the serrated cutting edges (see reference symbol 4a or 4b) may be formed either in the machine direction or in the cross direction. In the present invention, the moisture-proof film 2 is formed on both of the surfaces of the blank 1 with the intention mentioned above and then a long rectangular sheet 4 having a serrated cutting edge as shown in Figure 1 is obtained. For example, a flat sheet of 0.8 cm X 30 cm having a thickness of about 0.25 mm was obtained. Example 2 To waterproof the sides of the cutting teeth in the cutting edge 4a of the sheet 4 obtained in Example 1, an epoxy acrylate ultraviolet curing resin having a viscosity of 400 cp, for example, was applied to portions around the serrated cutting edge by means of a suitable gravure roll and then a film of the ultraviolet curing resin was formed on the sides of the cutting teeth in the cutting edge by applying ultraviolet rays thereto. Example 3 A moisture-proof film of polyethylene was formed on the two surfaces of a vulcanized fibre blank in the same way as in Example 1 except that the vulcanized fibre blank had a basic weight of 400 g/m 2 , and then cutting edges were formed by blanking. Thus, a sheet having serrated cutting edges was obtained. The sheet had a thickness of 0.35 mm. The sheet had a cutting edge on each of the two longer sides. The sides of the cutting teeth in each cutting edge were made waterproof in the same way as mentioned above. The moisture-proof film 2 on one of the two surfaces of the sheet 4 having serrated cutting edges was activated by corona discharge so that the film had a surface tension of 40 dynes/cm and allowed easy adhesion. Then, the sheet was adhered by means of a pressure sensitive adhesive to a predetermined position in a developed carton blank shown in Figure 5. The construction of the carton will be described with reference to Figures 5 and 6. Reference symbol P represents a carton blank of a paperboard (thickness 0.8 mm) having a basic weight of 350 g/m 2 . Reference symbol 11 represents a rectangular bottom wall panel formed on the blank by fold lines. A longer side, which is a lower side in Figure 5, of the bottom wall panel continues to a front wall panel 12. Another longer side of the bottom wall panel continues through similar fold lines to a rear wall panel 13, top wall panel 14 and cover panel 15 which adjoin one another. The front wall panel 12 and rear wall panel 13 respectively continue through fold lines at both ends or shorter sides to glue flaps 16 and 17. The bottom wall panel 11 continues through fold lines at both ends or shorter sides to side panels 19 each having a flap 18. The cover panel 15 is provided with a pair of inclined perforated lines 20, each continuing to straight perforated lines 21. A finished carton is opened by means of these perforated lines. After being finished, the carton is opened by removing parts of the cover panel 15, which are temporarily attached pieces 23 surrounded by the perforated lines, from the carton body. Also, the cover panel is fixed in place by inserting an insertion piece 22 between the inclined perforated lines 20 into a holding slit 24 provided on the front wall panel 12. The sheet 4 having serrated cutting edges is adhered to the lower surface of the bottom wall panel 11 along a fold line between the bottom wall panel and the front wall panel 12. The sheet is adhered so that its serrated cutting edge 4a protrudes slightly from the fold line. Preferably the sheet to be adhered to the carton is slightly shorter than the longer side of the bottom wall panel 11. In setting up a carton from the developed carton blank, the front wall panel 12, rear wall panel 13 and side panels 19 are vertically erected along fold lines from the bottom wall panel 11, glue flaps 16 and 17 are adhered inside the side plates 19, then a rolled cooking sheet (see reference symbol G in Figure 7) is put into the carton. After that, the opening of the carton is closed by the top wall panel 14 and cover panel 15. Then, the cover plate is fixed to the front wall panel 12 by the spot adhesion H of the temporarily attached pieces 23 thereto. To take out the cooking sheet F contained within the carton as mentioned above, the carton is opened by cutting off the temporarily attached pieces 23, which are spot adhered, along the perforated lines, the end of the wrapping film or sheet F of the roll G is held between the fingers, then a desired length thereof is pulled out. The film, etc. is pulled down along the front wall panel 12 and cut to the desired length by being pushed against the front wall panel 12, that is, by means of the serrated cutting edge 4a protruding from the lower edge of the front wall panel 12. After the cutting, the insertion piece 22 is inserted into the holding slit 24 in the front wall panel 12 to close the carton, thereby preventing dust from entering the carton. Example 4 A description will be given of an example in which the shape of the sheet having a serrated cutting edge, or strictly speaking, the distribution of the cutting teeth thereof, is not straight but bent angularly in the lengthwise direction. In a sheet 5 shown in Figure 8, which is a flat sheet having a serrated cutting edge, the distribution of the cutting teeth thereof in the plan view has a protruded centre in the lengthwise direction and the edge portions on both sides of the centre being inclined toward the ends. This sheet is adhered to a developed carton blank P' which is similar to the carton blank in the above-mentioned example. The sheet 5 having a serrated cutting edge is adhered by means of a pressure sensitive adhesive as used in the above-mentioned example or an adhesive of a hot melt type or any other suitable adhering means to an illustrated position on a cover panel of the carton blank. This carton blank will be described in brief. A cover panel 25 is continuously provided on the upper side of a top wall panel 14. The sheet 5 having a serrated cutting edge, this sheet being different in shape from the sheet in the above-mentioned example, is adhered to the cover panel. A perforated line 26 corresponding to the shape of the sheet 5 is provided on the cover panel. To take out a rolled film or sheet contained within the carton, a separation piece 27 on the outside of the perforated line 26 is cut off along the perforated line 26 and the carton is opened. After the separation piece 27 is separated from the cover panel 25, the serrated cutting edge 4a of the sheet 5 protrudes from the edge of the cover panel. Therefore, it is possible to cut the film or sheet to a desired length by means of the serrated cutting edge. It is to be noted that portions or members of the carton blank P' corresponding to those in the above-mentioned example (see Figure 5) are represented by the same symbols thereas. Example 5 The serrated cutting edge of the sheet according to the present invention may comprise cutting teeth of the same shape, the cutting teeth being uniformly distributed, such being similar to saw teeth made of a metal which have been generally used. A cutting edge having the cutting teeth described below cuts better than the cutting edge mentioned above. A wrapping film having a large elongation, such as a film of polyvinyl chloride, is more difficult to cut than a film having a smaller elongation. This disadvantage is obviated by using a cutting edge having cutting teeth which have the following shapes and distribution. Description will be made with reference to Figure 9. In forming a serrated cutting edge on the vulcanized fibre blank, the cutting teeth near the ends of a rectangular sheet 4 are shaped differently from the cutting teeth in the central portion thereof as shown in Figure 9. Each cutting tooth 4a in the central portion X has the shape of an isosceles triangle having a vertical angle of about 60°. Each cutting tooth 4b on both sides Y thereof has the shape of a triangle in which a < b, where "a" is the length of a side near the end of the sheet and "b" is the length of a side near the central portion, these sides forming the vertical angle . In other words, the vertex of each of these cutting teeth faces outside. In Example 5, two sheets were prepared, one (Example 5A) having a vertical angle  of 58°, the other (Example 5B) having a vertical angle  of 49°. In both of these sheets, the portion Y near each end has a length of about 20 mm and the central portion X has a length of 260 mm. The sheet prepared in Example 1 has cutting teeth shown in Figure 1, all of which have the same shape as the cutting teeth in the central portion. These sheets of Example 1, Example 5A and Example 5B were attached to respective cartons of the same construction, and the cutting quality thereof was tested, the results of which are shown in Table 1. Examples Example 1 Example 5A Example 5B Films cut Note 1 1 : 1 1 : 1.16 1 : 1.47 Note 2 about 60° about 58° about 49° Polyvinylidene chloride Easy to ○ cut Very easy o ○ to cut Easy to ○ cut Polyvinyl chloride Difficult ▵ to cut Possible  to cut Easy to ○ cut Polyethylene Possible  to cut Easy to ○ cut Very easy o ○ to cut Note 1: Two sides forming the vertical angle a : b Note 2: Vertical angle  (pitch 1.5mm) As shown in Table 1 the sheets having a serrated cutting edge according to Example 5 even cut well films of polyvinylidene chloride or polyvinyl chloride having a relatively large elongation. It is assumed that this is because the cutting teeth near the ends, the vertex of each of which faces outside, cut into the film easily at the beginning of the cutting and grasp it surely without slipping. The vertical angle  is preferably within a range of about 45° to 60°. The number of the cutting teeth 4b is above 3, preferably 10. The portion Y near the end has a length of above 4 mm, preferably between 10 and 20 mm. Example 6 Adhering the sheet having a serrated cutting edge according to the present invention to a carton blank by the ultrasonic adhesion method through the moisture-proof film formed on the surface of the sheet will now be described in detail with reference to Figures 10 to 14. It is of course possible to use a usual adhesive such as a pressure sensitive adhesive in adhering the sheet to the carton. It is more advantageous to adhere the sheet to the carton firmly without using any adhesive. Usually, forming the serrated cutting edge by blanking and the adhesion is continuously made mechanically. Therefore, if the adhesive is used, some of it may stick to the blanking die and lower the precision of blanking. If the sheet is fixed to the carton by a heat sealing method without using any adhesive, the cutting edge of the blanking die may expand due to heat, the die engagement being affected thereby, the cutting edge of the die being damaged. To seek to solve the above-mentioned problems, the present invention adheres the sheet having a serrated cutting edge to the carton blank by the ultrasonic adhesion method which is free from these drawbacks. This ultrasonic adhesion method is effective especially when the moisture-proof film is made of a polyolefin resin having a relatively low melting point. Reference symbol 30 in Figure 10 represents an ultrasonic adhering device, which is mounted in an upper bolster 31 of a known die set mechanism for example. The ultrasonic adhering device comprises an ultrasonic generator 30a, an ultrasonic vibrator 30b and a horn 30c. Electric vibrations generated by the ultrasonic generator 30a are converted into mechanical vibrations by the ultrasonic vibrator 30b. Then, the mechanical vibrations are amplified by the horn 30c. The amplified vibrations are transmitted to the moisture-proof film of the sheet having a serrated cutting edge and melts the film by heating it. Thereby the sheet 3, in which the serrated cutting edge 4a has just been formed, is adhered to the carton blank P or P'. The adhesion between the sheet and the carton blank is further increased by coating the adhesion portion of the carton blank in advance with an anchoring agent such as an emulsion of polyethylene imine, polyethylene or polyvinylidene chloride resin, the anchoring agent being dried so as to form a film. In Figures 10 to 12, reference symbol 32 represents an upper plate in the die set mechanism. Immediately below the upper plate 32, there is a holder plate 35 by which an upper cutting edge 34 is held, the clearance 33 between the upper plate 32 and the holder plate 35 being very small. The upper cutting edge 34 is fixed to the lower surface of the holder plate 35. A sheet clamper 36 is disposed under the upper cutting edge 34, there being a certain clearance between the upper cutting edge 34 and the sheet clamper 36. A lower cutting edge 37 corresponding to the upper cutting edge 34 is disposed beside and below the sheet clamper 36, the lower cutting edge 37 and the upper cutting edge 34 facing each other. (See Figure 13.) Reference symbol 38 represents a mount of the lower cutting edge 37, reference symbol 39 representing a lower plate, reference symbol 40 representing a lower bolster, these being adapted to be integrally moved up and down by a cam mechanism or a cylinder mechanism not shown in the Figures. Reference symbol 41 represents a stay bolt embedded in a lower portion of the holder plate 35, the stay bolt 41 passing through the upper cutting edge 34 and the sheet clamper 36. A protruding portion of the stay bolt 41 is provided with a spring 42 which has a tendency to push up the lower surface of the sheet clamper 36. The lower plate 39 has a recess 41a in which the stay bolt 41 sinks when the lower bolster 40 of the die set mechanism moves up. Beside the stay bolt 41, there is a guide rod 43 which gives a small clearance between the sheet clamper 36 and the upper cutting edge 34 by pulling down the sheet clamper 36 within a certain range against the force of the spring 42 when the die set mechanism opens. The guide rod 43 is provided at its top with a bolt head 43a which contacts the upper surface of the sheet clamper 36 as shown by dotted lines in Figure 11. The bolt head 43a pulls down the sheet clamper 36. A blank sheet 3 for forming a serrated cutting edge is sent into the clearance between the sheet clamper 36 and the upper cutting edge 34. The guide rod 43 moves up and down when the die set opens and closes. As the guide rod 43 moves up and down, the bolt head 43a moves through a hole 43b bored through all of the upper cutting edge 34, holder plate 35 and upper plate 32. A carton blank P is supplied to a position under the upper plate 32 so as to oppose the ultrasonic adhesion horn 30c. Beside the die set mechanism, there is a belt conveyor 44 for feeding the blank and pressing rollers 45 above the belt conveyor 44 as shown in Figure. 10. The sheet 3, not having a serrated cutting edge, is supplied through nip rollers 46 to the die set mechanism. The relationship between the upper cutting edge 34 and the lower cutting edge 37 is shown in Figure 13, each of them having a serrated cutting edge, these cutting edges being engageable with each other. When the die set mechanism is in an open state as shown in Figure 11, the carton blank P is supplied by means of the belt conveyor 44 and the pressing rollers 45 to a position under the upper plate and directly below the adhesion horn 30c as shown by an arrow, the blank sheet 3 for forming a serrated cutting edge being supplied between the upper cutting edge 34 and the sheet clamper 36. When the die set mechanism is in an open state, the bolt head 43a of the guide rod 43 pushes down the sheet clamper 36 as shown in Figure 11. Therefore, a certain clearance is formed between the clamper 36 and the upper cutting edge 34. Through this clearance, the blank sheet 3 is intermittently supplied from the nip rollers 46. After the blank sheet is supplied, the die set mechanism starts closing. Then, the bolt head 43a moves upward, thus the pushing down of the sheet clamper 36 by the bolt head 43a being released. Now, the sheet clamper 36 is pushed toward the upper cutting edge 34 by the force of the spring 42 attached to the stay bolt 41. Therefore, the sheet 3 is firmly held between the clamper 36 and the upper cutting edge 34. The sheet 3 for forming a serrated cutting edge is supplied as mentioned above so that a certain length thereof protrudes from the upper cutting edge 34 over the lower cutting edge 37 as shown in the Figure. Then, the die set mechanism starts closing as shown in Figure 12. Now the lower cutting edge 37 moves upward and cuts the blank sheet 3 to form a serrated cutting edge. At the same time, the lower cutting edge 37 pushes up the sheet having the serrated cutting edge against a predetermined portion of the carton blank P waiting above the sheet as shown in Figure 12. By the pushing of the sheet against the carton blank, a pressure-sensitive switch (not shown) of the, ultrasonic adhering device 30 is turned on to start the adhering device. The adhering device melts the moisture-proof film formed on the surface of the sheet to adhere the sheet 3 to the predetermined portion of the carton blank P. After the adhesion is finished, the die set mechanism opens and the carton blank to which the sheet having the serrated cutting edge has been adhered is taken out of the die set mechanism. Then, a new carton blank and a new blank sheet are supplied, the blank sheet being adhered to the carton blank in the same way as mentioned above. According to the above-mentioned example, the vulcanized fibre sheet having a serrated cutting edge is adhered through the moisture-proof film formed on the surface of the sheet to the carton blank without using any adhesive. Therefore, the serrated cutting edge can be attached to the carton quickly, surely and at a low cost. In experiments made by the inventors, a rectangular sheet having a serrated cutting edge, 0.35 mm thick, 30 cm X 0.8 cm, was adhered to a carton blank at a speed of 120 shots per minute. This adhesion speed is almost equal to the speed at which a conventional metal cutting edge is fixed to a carton blank. Adhesion tests were made to compare sheets adhered to carton blanks as mentioned above with sheets adhered to carton blanks by other adhering means. The results of the test are shown in Table 2 below. (Adhesion Test) Thickness of sheet having serrated cutting edge PE Film supersonic adhesion Adhesive of 2-liquid type used Adhesive of 1-liquid type used Hot-melt adhesive used Epoxy resin used 0.25 mm ○ X X X ○ 0.35 mm ○ X ○ ○ ○ Test conditions: 40°C, 90% RH, 24 Hr Note: Epoxy resin has good adhesion but extremely low productivity because its curing time is long. As is apparent from the table above, satisfactory adhesion was confirmed after the sheets were let alone in a high-humidity atmosphere for 24 hours, even in the case of thin sheets having a serrated cutting edge. The ultrasonic adhering device is not limited to the device described above and may comprise a vibrator 30a and a horn 30c, energy generated by the vibrator 30a being converted into vibrations in the vertical direction by the horn as shown in Figure 15. As apparent from the description above, in the present invention, the die set mechanism may contain therein, for example, the ultrasonic adhering device and the serrated cutting edge forming device, the forming device comprising the upper cutting edge and the lower cutting edge, a blank sheet being cut to a predetermined width by utilising the opening and closing operations of the die set, the sheet being adhered to a predetermined position of a carton blank by means of the ultrasonic adhesion method. The carton blank may preferably be pattern coated in advance at a position, to which the sheet having a serrated cutting edge is to be adhered, with a substance which facilitates adhesion, then the carton blank is supplied to the die set mechanism. The substance may be, for example, an emulsion of denatured polyethylene. The substance increases the adhesive strength of the ultrasonic adhesion method as well as the adhesion speed. The present invention is not limited to the examples described above and may be modified in various ways within the scope of the invention. Effects of the Invention To confirm the effects of the moisture-proof film in the present invention, the following tests were made by means of the following samples: Sample A: Blank sheet prepared in accordance with Example 3. This was prepared by impregnating a vulcanized fibre sheet having a basic weight of 400 g/m 2 (thickness 0.35 mm) in advance with a melamine resin solution (concentration 5%), the sheet being dried, and then a low-density polyethylene film having a thickness of 20 µm being formed on the two surfaces of the sheet. Sample B: This was prepared by impregnating a vulcanized fibre sheet having the same basic weight as above (thickness the same as above) in advance with a melamine resin solution (concentration 5%). Sample C: This was prepared by impregnating a vulcanized fibre sheet having the same basic weight as above (thickness the same as above) in advance with a melamine resin solution having a concentration of 5 %, and the sheet being coated with an urethane resin liquid in an amount of 15 g/m 2 (solid matter). Rectangular sheets having a width of 8 mm and a length of 100 mm were cut out of each of the samples. The direction in which the serrated cutting edge was to be formed was the lengthwise direction of each sheet as shown in Figures 3 and 4. Two types of these rectangular sheets were obtained. In one of the two types, the lengthwise direction was parallel to MD (shown as "long." in Tables 3 and 4 below). In the other of the two types, the lengthwise direction was parallel to CD (shown as "lat." in Tables 3 and 4 below). The samples were tested as to the degrees of the contraction and elongation thereof according to the differences of humidity. The tests were made as follows: Each of the, samples was left alone in an atmosphere of 23°C and 65% RH for 24 hours and the elongation in the lengthwise direction of each sample was determined, the value of the elongation serving as a reference value. Then, each sample was left alone in an atmosphere of 20% RH or 90% RH for a certain period of time (for hours shown in the tables below). Now, the degree of contraction or elongation, that is. the ratio of contraction or elongation to the reference value by the change of conditions was determined. Tables 3 and 4 show the ratio of contraction or elongation in terms of percentage. As apparent from Tables 3 and 4, according to the present invention, even the vulcanized fibre sheet, which is relatively easily affected by moisture in the atmosphere, can be made less liable to be affected by humidity by the moisture-proof film formed on the surface thereof. The moisture-proofing treatment by forming the moisture-proof film according to the present invention has effects much better than conventional water-resistant articles by the melamine resin, urethane resin, etc. Preferably, the moisture-proof film is a polyolefin resin film having a relatively low moisture permeability. The water-resisting or waterproofing treatment by a melamine resin, urethane resin, for example has been considered to be indispensable. However, according to the present invention, the use of the moisture-proof film decreases the necessity of the treatment and it is possible to dispense with the expensive urethane resin. As a result, it is possible to provide a practical and less expensive product. The vulcanized fibre laminated with polyethylene is compared with the vulcanized fibre coated with a urethane resin as follows: The unit price of the resin used in the former is only 1/5 of the unit price of the resin used in the latter. The efficiency of treatment in the former is 30 times as large as the efficiency of treatment in the latter. Therefore, the product of the present invention is inexpensive. Thus, in the present invention, the vulcanized fibre sheet provided with the moisture-proof film is used as a blank, and a serrated cutting edge is formed on the vulcanized fibre sheet by utilising its very high elasticity and rigidity. Therefore, the serrated cutting edge is free from deformation or damage by an external force and always cuts very well. The sheet of the present invention maintains its dimensional stability even when it is kept in a kitchen, for example, having a high humidity. Therefore, the sheet having a serrated cutting edge according to the present invention is suitable for cutting cooking sheets of a resin film, paper, metal foil, treated paper, etc. used for packing foods. Since the sheet having a serrated cutting edge is made of the vulcanized fibre, the sheet does not injure fingers, even when it is attached to a carton. After use, the whole carton having the sheet may be burned as it is, with no residue being left, unlike conventional metal cutting edges. The sheet having a serrated cutting edge and attached to a carton is almost free from dimensional change by moisture in the atmosphere. Especially, there is no relative dimensional change by moisture in the atmosphere between the sheet and the paperboard forming the carton. Therefore, the sheet attached to the carton is free from being removed therefrom or deformed by moisture and has a stable cutting ability. The contraction and elongation by moisture of the paperboard forming the carton are shown in Tables 3 and 4 above. As compared with a serrated cutting edge in which all the cutting teeth have the shape of a uniform isosceles triangle, a serrated cutting edge in which each cutting tooth in the end portions of the cutting edge has the shape of a scalene triangle inclined outward, cuts surely into a film without slipping and is effective in cutting films having a large elongation such as polyethylene film and polyvinyl chloride film. If the sheet having a serrated cutting edge is adhered to the carton by means of the ultrasonic adhesion method of the present invention and by utilising the moisture-proof film, then the following advantages will be obtained: (1) Since no adhesive is used, the production cost is reduced and the sheet can be adhered to the carton at a speed equivalent to the speed of attaching conventional metal cutting edges to the carton. (2) No adhesive sticks to the die cutting edges for forming the serrated cutting edges. (3) Adhesion by utilising ultrasonic waves does not transmit heat to the die cutting edges. Therefore, the die cutting edges are free from troubles such as damages by improper engagement. (4) When a metal edger shown in Figure 10, which is an example of the machine for forming a serrated cutting edge, is used, it is possible to adhere the sheet having a serrated cutting edge to a carton blank by a single process by means of the ultrasonic adhesion method. After use, carton cases including the sheets of the present invention can be burned as they are or recycled as a waste paper pulp. Thus, the present invention is useful also in saving resources and preventing environmental contamination.

Claims: A vulcanized fibre sheet (4) having a serrated cutting edge (4a), comprising a vulcanized fibre blank (1), characterised in that it has two outer surfaces provided with a moisture-proof film (2) composed of a low-density polyethylene film, the serrated cutting edge (4a) being formed on at least one edge of the sheet (4). A vulcanized fibre sheet according to claim 1, characterised in that the moisture-proof film (2) is formed over a water-resisting agent applied to the vulcanized fibre blank (1). A vulcanized fibre sheet according to claim 1 and claim 2, characterised in that the sheet (4) has the shape of a rectangle and a plurality of cutting teeth provided on a cutting edge thereof, each cutting tooth (4a) in a central portion (X) of the cutting edge having the shape of an isosceles triangle, each cutting tooth (4b) provided at two outer end portions (Y) of the cutting edge having the shape of a scalene triangle inclined away from the central portion (X) of the cutting edge. A vulcanized fibre according to claim 2 and any claim read appendant thereto, characterised in that the water-resisting agent is a melamine resin or glyoxal. A vulcanized fibre sheet according to any preceding claim, characterised in that the serrated cutting edge (4a) has a thickness of between 0.2mm and 0.5mm. A vulcanized fibre sheet according to any preceding claim, characterised in that the serrated cutting edge (4a) has a thickness of between 0.25mm and 0.35mm. A vulcanized fibre sheet according to claim 3 and any claim read appendant thereto, characterised in that the scalene triangle has a vertical angle of about 58°. A vulcanised fibre sheet according to claim 3 and any claim read appendant thereto, characterised in that the scalene triangle has a vertical angle of about 49°. A carton to which a vulcanized fibre sheet (4), having a serrated cutting edge (4a) and two outer surfaces is adhered, the carton having a carton body and a cover, the carton body comprising a bottom wall panel (11), a front wall panel (12), a rear wall panel (13) and side panels (19), the cover covering the opening of the carton body, characterised in that a moisture-proof film (2) is formed on the two outer surfaces of the vulcanized fibre sheet (4), the moisture-proof film (2) being a low-density polyethylene film. A carton according to claim 9, characterised in that the sheet (4) is adhered to a dried polyethylene emulsion applied to a carton blank. A carton according to claim 9 or claim 10, characterised in that the serrated cutting edge (4a) has a thickness of between 0.2mm and 0.5mm. A carton according to any one of claims 9 to 11, characterised in that the serrated cutting edge (4a) has a central portion (X) with a plurality of cutting teeth (4a) having the shape of an isosceles triangle and two outer portions (Y) having a plurality of cutting teeth (4b) having the shape of a scalene triangle inclined away from the central portion of the serrated cutting edge (4a). A method of adhering a vulcanized fibre sheet (4) having a serrated cutting edge (4a) to a carton blank (P), the carton blank (P) comprising a bottom wall panel (11), a front wall panel (12), a rear wall panel (13), side panels (19) and a cover (15), characterised in that the method comprises the steps of forming a moisture-proof film (2) composed of a low-density polyethylene film on the vulcanized fibre sheet (4), and adhering the vulcanized fibre sheet (4) through the moisture-proof film (2) to a predetermined portion of the carton blank (P) by an ultrasonic adhesion method. A method according to claim 13, characterised in that the serrated cutting edge (4a) has a thickness of between 0.2mm and 0.5mm. A method according to claim 13 or claim 14, characterised in that the serrated cutting edge (4a) has a central cutting portion (X) with a plurality of cutting teeth (4a) having the shape of a isosceles triangle and two outer portions (Y) having a plurality of cutting teeth (4b) having the shape of a scalene triangle inclined away from the central portion of the serrated cutting edge (4a).

Inventors: IKEDA KEIICHI, MIKAMO HIROAKI, SANO MITSUHIRO, SHOJI ISAO, WAKABAYASHI NOBUO, IKEDA, KEIICHI, MIKAMO, HIROAKI, SANO, MITSUHIRO, SHOJI, ISAO, WAKABAYASHI, NOBUO, IKEDA, KEIICHI, FUJI-KAKO JIGYOSHO OF, MIKAMO, HIROAKI, FUJI-KAKO JIGYOSHO OF, SANO, MITSUHIRO, FUJI-KAKO JIGYOSHO, SHOJI, ISAO, 101, VILLA SUNSHINE, WAKABAYASHI, NOBUO, FUJI-KAKO JIGYOSHO OF
Applicants: OJI PAPER CO, TOYO FIBRE CO LTD, OJI PAPER CO., LTD., TOYO FIBRE CO., LTD.
Application year: 1992
Main classification: B65D5
IPC codes: B26D3, B26D1, B26D7, B31B1, B26F3, B29C65, B29C69, B26F1, B65H35, B65D83