Apparatus for forming slant, linear easy-to-tear portions on long plastic film

An apparatus for forming slant, linear easy-to-tear portions on a long plastic film, comprising a roll on which the long plastic film passes, pluralities of pattern rolls each partially having a slant, linear stamp on a rolling surface, a shaft to which pluralities of the pattern rolls are fixed, and a first mechanism for moving the shaft in a direction to the roll. Pressure rolls pushing the pattern rolls via rolls fixed to the shaft. A second moving mechanism for moving the pressure rolls in a direction to the pattern rolls, whereby with the pressure rolls pushing the pattern rolls by the second moving mechanism, the stamp of the pattern rolls are pressed onto the elastic film by the first moving mechanism, so that the slant, linear easy-to-tear portions with recesses formed by the pattern projections of the stamp are provided partially and periodically on the plastic film.

FIELD OF THE INVENTION

The present invention relates to an apparatus for efficiently forming slant, linear easy-to-tear portions on a long plastic film.

BACKGROUND OF THE INVENTION

Plastic packages required to have high gas tightness, heat resistance and strength, such as retort pouches, are formed by laminates constituted, for instance, by a film of resins having high heat resistance and high strength, such as polyethylene terephthalate, a highly gas-tight layer such as an aluminum foil, and a sealant layer of cast polypropylene etc. Retort pouches are heated by hot water or a microwave oven, and opened to take out their contents. However, because the pouches have high strength, it is sometimes difficult to open the pouches by hand even if notches are provided on their sides. Particularly as graying population increases people with insufficient grip, there are increasing numbers of people failing to open pouches with notches by hand, sometimes needing scissors.

JP 11-77872 A discloses a method for producing an easy-to-cut laminate film package, comprising irradiating a laminate film comprising a substrate film layer and a sealant layer as thick as ½ or more of the total thickness with laser beams from the sealant layer side, to make the sealant layer thinner, thereby forming a continuous or intermittent half-cut separating line. When a slant, half-cut separating line is formed on a retort pouch by this method, the slant, half-cut separating line should be formed after individual retort pouches are produced, resulting in poor efficiency.

Because stretched films tend to be torn along orientation directions, bags with openings in parallel to orientation directions are easily torn open with notches formed on sides adjacent to the openings. However, such method provides bags tearable only in parallel to openings. Because small openings are preferable in most drinks, fluid foods, etc., packages (bags) with slantly openable portions are desired.

OBJECT OF THE INVENTION

Accordingly, an object of the present invention is to provide an apparatus for forming slant, linear easy-to-tear portions on a long plastic film efficiently.

SUMMARY OF THE INVENTION

As a result of intensive research in view of the above object, the inventors have found that by (a) arranging pluralities of rotatable pattern rolls in a transverse direction of the plastic film, each pattern roll comprising a stamp means having pattern projections for forming easy-to-tear portions (half-cut portions) slantly to a rotation direction, and (b) simultaneously and rotatably pressing the pattern rolls to the plastic film moving on a hard roll, pluralities of slant, linear easy-to-tear portions can be formed periodically on the plastic film. The present invention has been completed based on such finding.

Thus, the apparatus of the present invention for forming slant, linear easy-to-tear portions on a long plastic film comprises (a) a hard roll on which the long plastic film passes, (b) pluralities of pattern rolls each partially having a slant, linear stamp means having pattern projections on a rolling surface, (c) a shaft to which pluralities of the pattern rolls are fixed, (d) a first moving mechanism for moving the shaft in a direction to the hard roll, (e) pressure rolls pushing the pattern rolls directly or indirectly via small-diameter rolls fixed to the shaft, and (f) a second moving mechanism for moving the pressure rolls in a direction to the pattern rolls, whereby with the pressure rolls pushing the pattern rolls directly or indirectly by the second moving mechanism, the stamp means of the pattern rolls are pressed onto the plastic film by the first moving mechanism, so that the slant, linear easy-to-tear portions with recesses formed by the pattern projections of the stamp means are provided partially and periodically on the plastic film.

Specifically, the first apparatus of the present invention comprises (a) a hard roll on which the long plastic film passes, (b) pluralities of pattern rolls each partially having a slant, linear stamp means having pattern projections on a rolling surface, (c) a shaft to which pluralities of the pattern rolls are fixed, (d) a first moving mechanism for moving the shaft in a direction to the hard roll, (e) pressure rolls each pushing each of the pattern rolls from behind, and (f) a second moving mechanism for moving the pressure rolls in a direction to the pattern rolls, whereby with the pressure rolls pushing the pattern rolls by the second moving mechanism, the stamp means of the pattern rolls are pressed onto the plastic film by the first moving mechanism, so that the slant, linear easy-to-tear portions with recesses formed by the pattern projections of the stamp means are provided partially and periodically on the plastic film.

The second apparatus of the present invention comprises (a) a hard roll on which the long plastic film passes, (b) pluralities of pattern rolls each partially having a slant, linear stamp means having pattern projections on a rolling surface, (c) a shaft to which pluralities of the pattern rolls are fixed, (d) a first moving mechanism for moving the shaft in a direction to the hard roll, (e) pluralities of rolls having a smaller diameter than that of the pattern rolls and fixed to the shaft, (f) pressure rolls each pushing each of the small-diameter rolls from behind, and (g) a second moving mechanism for moving the pressure rolls in a direction to the small-diameter rolls, whereby with the pressure rolls pushing the small-diameter rolls by the second moving mechanism, the stamp means of the pattern rolls are pressed onto the plastic film by the first moving mechanism, so that the slant, linear easy-to-tear portions with recesses formed by the pattern projections of the stamp means are provided partially and periodically on the plastic film.

The first moving mechanism preferably comprises first carriers rotatably supporting the shaft, and first guide rails extending perpendicularly to the axis of the hard roll, along which the first carriers are movable in a direction to the hard roll.

It is preferable that the first carriers are always pushed by a resilient member with a small force in a direction away from the hard roll, and that the pattern rolls or the small-diameter rolls are pushed by the pressure rolls to the plastic film against the force of the resilient member.

Each second moving mechanism preferably comprises a second carrier rotatably supporting each pressure roll, and a second guide rail extending perpendicularly to the axis of the hard roll, along which the second carrier is movable in a direction to the hard roll.

The transverse positions of the pattern rolls are adjustable along the shaft.

In the first apparatus, each of the second guide rails is preferably fixed to each table, which is movable along third guide rails extending in parallel to the axis of the hard roll, in a transverse direction of the plastic film, so that the transverse positions of the pressure rolls are adjustable depending on the transverse positions of the pattern rolls.

In the second apparatus, the second guide rails are preferably located at fixed positions, such that each of the pressure rolls comes into contact with the corresponding small-diameter roll.

In one example, the projections of the stamp means are constituted by a large number of hard particles having sharp corners and Mohs' hardness of 5 or more, both sides of the stamp means being defined by grooves on a rolling surface. In another example, the projections of the stamp means comprises a ridge slantly extending on the rolling surface, and one or more edges projecting from an upper surface of the ridge in parallel to the ridge. The edges may be periodically provided with notches.

The pressure rolls are preferably rubber rolls.

The shaft is preferably driven by a motor, such that the pattern rolls rotate at the same peripheral speed as that of the hard roll.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained in detail below referring to the attached drawings, though the present invention is not restricted to them, and various modifications may be made within the scope of the present invention. The explanation of each embodiment is applicable to other embodiments unless otherwise mentioned.

The apparatus of the present invention for forming slant, linear easy-to-tear portions100on a long plastic film1comprises (a) a hard roll11on which a long plastic film1passes, (b) pluralities of pattern rolls13each partially having a slant, linear stamp means13ahaving pattern projections on a rolling surface, (c) a shaft15to which pluralities of pattern rolls13are fixed, (d) a first moving mechanism for moving the shaft15in a direction to the hard roll11, (e) pressure rolls21pushing the pattern rolls13directly or indirectly via small-diameter rolls18fixed to the shaft15, and (f) a second moving mechanism for moving the pressure rolls21in a direction to the pattern rolls13, whereby with the pressure rolls21pushing the pattern rolls13directly or indirectly by the second moving mechanism, the stamp means13aof the pattern rolls13are pressed onto the plastic film1by the first moving mechanism, so that the slant, linear easy-to-tear portions100with recesses formed by the pattern projections of the stamp means13aare provided partially and periodically on the plastic film1.

[1] First Apparatus for Forming Easy-to-Tear Portions

As shown inFIGS. 1-3, the first apparatus of the present invention for forming easy-to-tear portions comprises (a) a hard roll11on which a long plastic film1passes, (b) pluralities of (4 in the depicted example) pattern rolls13each partially having a slant, linear stamp means13ahaving pattern projections on a rolling surface, (c) a shaft15driven by a motor M, to which pluralities of pattern rolls13are fixed, (d) a first moving mechanism for moving the shaft15in a direction to the hard roll11, (e) pressure rolls21each pushing each of the pattern rolls13from behind, and (f) a second moving mechanism for moving the pressure rolls21in a direction to the pattern rolls13, whereby with the pressure rolls21pushing the pattern rolls13by the second moving mechanism, the stamp means13aof the pattern rolls13are pressed onto the plastic film1by the first moving mechanism, so that the slant, linear easy-to-tear portions100with recesses formed by the pattern projections of the stamp means13aare provided partially and periodically on the plastic film1.

The first moving mechanism preferably comprises a pair of first carriers17,17rotatably supporting the shaft15, and a pair of first guide rails19,19extending perpendicularly to the axis of the hard roll11, along which the first carriers17,17are movable in a direction to the hard roll11. The first carriers17and the first guide rails19may have known structures.

Each second moving mechanism preferably comprises a second carrier22rotatably supporting each pressure roll21, and a second guide rail25extending perpendicularly to the axis of the hard roll11, along which the second carrier22is movable in a direction to the hard roll11. The second carriers22and the second guide rails25may have known structures.

The hard roll11supporting the plastic film1while forming the easy-to-tear portions100is preferably a metal roll, though its material is not restricted as long as its surface is sufficiently hard. To control the moving speed of the plastic film1, another hard roll12is preferably arranged opposite to the hard roll11, such that a pair of hard rolls11,12can grip the plastic film1. The hard roll11is driven by a motor (not shown), and the surface-smooth roll12opposing the hard roll11is preferably a follower roll rotating by the movement of the plastic film1. Because the plastic film1is gripped by a pair of hard rolls11,12, it is under sufficient tension while the easy-to-tear portions100are formed on the plastic film1on a surface of the hard roll11.

As shown inFIG. 2, pluralities of pattern rolls13for forming a large number of recesses constituting the easy-to-tear portions100on the plastic film1are fixed to one shaft15with predetermined intervals. Each pattern roll13is preferably a metal roll having one slant, linear stamp means13aon a rolling surface. As shown inFIGS. 5 and 7, the stamp means13aextends on the rolling surface of the pattern roll13slantly (for instance, at 45°) to the axis of the pattern roll13.

As shown inFIGS. 4-6, the first example of the stamp means13acomprises projections constituted by a large number of hard particles having sharp corners and Mohs' hardness of 5 or more. Grooves13b,13bare formed on both sides of the stamp means13a. The grooves13b,13bon both sides form sharp edges of the stamp means13a, providing the easy-to-tear portions100with sharp edges. The hard particles are preferably fine diamond particles, which are attached to a metal roll surface with a nickel plating, etc. The average particle size of hard particles is determined depending on the thickness and layer structure of the plastic film1. For instance, when the plastic film1is a laminate constituted by a 15-μm-thick polyethylene terephthalate (PET) layer, a 20-μm-thick nylon layer, an aluminum foil, and a 40-μm-thick polyethylene (sealant) layer, the PET layer and the nylon layer should be sufficiently cut. Accordingly, the average particle size of hard particles is preferably in a range from 30 μm to 200 μm, such that recesses can be formed to the depth near 15 μm+20 μm=35 μm. The percentage (area ratio) of hard particles on the surface of the stamp means13ais generally 10-50%, preferably 15-30%.

As shown inFIGS. 7-10, the second example of the stamp means13acomprises a ridge131formed slantly on the rolling surface, and pluralities of parallel edges132projecting from an upper surface of the ridge131. To make the edges132easily bite the plastic film1, the edges132may be provided with notches134periodically. The edges132of the stamp means13aare obtained by cutting a rolling surface of the metal roll to form the ridge131, and then forming pluralities of parallel grooves133on the upper surface of the ridge131by a grinder. The edges132are high enough to cut the plastic film1as deep as preferably about 35 μm in the above example. Specifically, the height of the edges132is preferably about 100-300 μm. In order that the edges132have sufficient strength and hardness, a metal roll having the stamp means13ais preferably made of high-speed steel, tool steel, cemented carbides, etc. Though plural lines of edges132are arranged in the depicted example, the apparatus of the present invention is not restricted thereto, but may have a line of edges132. Though the stamp means13ahaving the ridge131with edges132is integral with each pattern roll13in the depicted example, they may be separate members. In this case, the stamp means13ais preferably made of high-speed steel, tool steel, cemented carbide, etc., and a roll body is preferably made of stainless steel.

As is clear fromFIGS. 2 and 14, both ends of the shaft15, to which pluralities of pattern rolls13are fixed, are rotatably supported by a pair of first carriers17,17, a motor M being mounted to one end of the shaft15. Each first carrier17,17is movable along each first guide rail19,19in a direction perpendicular to the axis of the hard roll11. A tip end (on the side of the hard roll11) of each first guide rail19,19is provided with a stopper19a,19aand a coil spring19b,19bfixed to the stopper19a,19a. Accordingly, while the pressure rolls21do not push the pattern rolls13, the first carriers17,17retreat to positions determined by stoppers19c,19cprovided on the rear ends of the first guide rails19,19, such that the pattern rolls13are sufficiently separate from the hard roll11. Further, there is preferably a gap between the pressure rolls21and the pattern rolls13.

Because the transverse positions of the pattern rolls13should be set depending on the size of packages (bags) to be produced and the positions of easy-to-tear portions100, they should be adjustable along the shaft15. In addition, to control the depth of easy-to-tear portions100precisely, the pattern rolls13should be positioned with precise gap relative to the hard roll11. To this end, the pattern rolls13should rotate coaxially with the shaft15perfectly. Accordingly, the pattern rolls13are preferably shrink-fit or screwed to the shaft15.

When the pattern rolls13are shrink-fit to the shaft15, as shown inFIG. 11, a shaft15having a flat surface15aand pattern rolls13each having in its inner surface a flat surface13ccorresponding to the flat surface15aare combined. In all pattern rolls13, the positions (rotation positions) of the stamp means13arelative to the flat surfaces13care the same. With the flat surface15aof the shaft15engaging the inner flat surfaces13cof the pattern rolls13, the stamp means13aof all pattern rolls13are located at the same rotational position. Thus, pluralities of easy-to-tear portions100formed by one rotation of pluralities of pattern rolls13are aligned in a transverse direction of the plastic film1.

FIGS. 12(a) and12(b) show one example of pattern rolls13screwed to a shaft15. This example uses (a) a shaft15having a flat surface15awith a threaded hole, (b) pattern rolls13each having a flat surface13ccorresponding to the flat surface15ain its inner surface, a flat surface13din parallel to the flat surface13cin its outer surface, and a threaded hole penetrating from the flat surface13cto the flat surface13d, and (c) a screw16threadably engaging each threaded hole of the shaft15and the threaded hole of each pattern roll13. In all pattern rolls13, the positions (rotation positions) of the stamp means13arelative to the flat surfaces13c(13d) are the same. With the flat surface15aof the shaft15engaging the inner flat surfaces13cof the pattern rolls13, and the screws16threadably engaging the threaded holes of the shaft15and the threaded holes of the pattern rolls13, the stamp means13aof all pattern rolls13are located at the same rotational position. Thus, pluralities of easy-to-tear portions100formed by one rotation of pluralities of pattern rolls13are aligned in a transverse direction of the plastic film1.

As shown inFIGS. 3 and 12(b), adjacent pattern rolls13,13on both sides of a centerline1a, along which the plastic film1is cut, should have stamp means13a,13aarranged in a “separated V form.” Though the longitudinal length (length along the shaft15) of the stamp means13ais less than the longitudinal length of the pattern rolls13to secure the fixing of the pattern rolls13to the shaft15in the depicted example, the stamp means13aand the pattern rolls13may of course have the same longitudinal length.

FIGS. 13(a)-13(c) show another example of pattern rolls13screwed to a shaft15. In this example, each pattern roll13has an axial notch13ein its inner surface, while the shaft15has an axial ridge15bto be received in the notch13ein its outer surface. A combination of the axial notch13eand the axial ridge15bacts as a rotation-preventing key. The pattern rolls13are provided with flanges14,14on both longitudinal sides. After the shaft15is inserted into the pattern rolls13with the axial ridge15breceived in the axial notches13e, the flanges14,14are fixed to the shaft15by screws16,16.

The pattern rolls13are rotated by a motor M mounted to one end of the shaft15. Thus, the long plastic film1passes through a gap between the hard roll11and the pattern rolls13both driven by motors. Because the easy-to-tear portions100should be formed on the plastic film1precisely periodically, the peripheral speed of the hard roll11(the moving speed of the long plastic film1) should be precisely equal to the peripheral speed of the pattern rolls13. To this end, sensors (not shown) for measuring the moving speed of the long plastic film1and/or the peripheral speed of the pattern rolls13are provided, to control them such that their difference becomes zero.

Though feedback control may be used, more precise control is preferably conducted by setting an initial peripheral speed of the pattern rolls13slightly less than the moving speed of the long plastic film1, and then controlling the moving speed of the plastic film1and/or the peripheral speed of the pattern rolls13to increase the peripheral speed of the pattern rolls13relative to the moving speed of the plastic film1, such that their difference becomes zero. The initial peripheral speed of the pattern rolls13is preferably 95-99% of the moving speed of the long plastic film1. Such control is conducted because the diameter of each pattern roll13inevitably has a dimensional error, which leads to the periodic interval error of easy-to-tear portions100. For instance, if the pattern rolls13were follower rolls, the rotation of the pattern rolls13accumulates the above error, so that the periodic intervals of the easy-to-tear portions100would undesirably deviate from the predetermined range. To avoid such error, control is conducted to make the difference between the moving speed of the plastic film1and the peripheral speed of the pattern rolls13zero.

The pressure rolls21for pushing the pattern rolls13are preferably rubber rolls, to protect the stamp means13aof the pattern rolls13, and to increase a friction coefficient between the pressure rolls21and the pattern rolls13. Also, to precisely control the positions and depth of easy-to-tear portions100formed on the plastic film1, the precise position control of the pressure rolls21is needed. Accordingly, each second moving mechanism for moving each pressure roll21in a direction to the pattern roll13comprises a second carrier22rotatably supporting each pressure roll21, and a second guide rail25extending perpendicularly to the axis of the hard roll11, along which the second carrier22is movable in a direction to the hard roll11. As shown inFIG. 14, each second guide rail25is fixed to each table27.

As shown inFIGS. 1,15and16, each second carrier22comprises a support member23rotatably supporting the pressure roll21, a holder24telescopically receiving the support member23, a load cell51set in the holder24, and a rod65fixed to a vertical frame63of the second carrier22and supporting the load cell51via a coil spring52. The holder24may be provided with a key member (not shown) for preventing the rotation of the support member23. The support member23has a two-pronged tip end portion for rotatably supporting a shaft21aof the pressure roll21. A rear end of the support member23abuts the load cell51, which measures a load applied to each pressure roll21. When a load applied to the pressure roll21exceeds a predetermined level, the coil spring52is compressed, reducing the pushing force of the pressure roll21to the pattern roll13, thereby preventing damage to the long plastic film1and the apparatus.

The second carrier22movable along the second guide rail25on the table27comprises a screw shaft33rotatably supported by a vertical frame31of the table27, a nut member35threadably engaging the screw shaft33for converting the rotation of the screw shaft33to a linear motion, a carrier body37fixed to the nut member35, and a guide member39provided on a lower surface of the carrier body37such that it engages the second guide rail25on the table27. The screw shaft33and the nut member35constitute a so-called ball screw. Mounted to a rear end of the screw shaft33is a pulley45connected to a motor43via a driving belt41.

Because the transverse positions of the pattern rolls13differ depending on the size of packages (bags) to be produced and the positions of the easy-to-tear portions100, the transverse positions of the second carriers22each rotatably supporting each pressure roll21should be adjustable depending on the transverse positions of the pattern rolls13. Accordingly, as shown inFIGS. 1,2and14, the first apparatus for forming easy-to-tear portions comprises a third moving mechanism under the table27. The third moving mechanism comprises a pair of third guide rails49a,49bdisposed on an upper surface of a horizontal frame47of the apparatus, and a pair of guide members51a,51bengaging the third guide rails49a,49b. The table27is also provided with a linear clamp53engaging the third guide rail49afor providing the table27with a fixed axial position, and the linear clamp53comprises a clamp arm53a. When the clamp arm53ais rotated after the guide members51a,51bare moved to a desired position along the third guide rails49a,49b, the linear clamp53strongly engages the third guide rail49a, so that the transverse position of each pressure roll21can be set precisely. By the third moving mechanism, the transverse positions of the pattern rolls are adjustable depending on the transverse positions of the pattern rolls. To adjust the vertical position of the table27, a vertically shifting mechanism may be mounted to the horizontal frame47.

For instance, when easy-to-tear portions100are formed on a long plastic laminate film1having a sealant layer by the first apparatus, the pattern rolls13are first transversely positioned on the shaft15by a shrink-fitting method or a screwing method, according to the intervals of the easy-to-tear portions100. Because one side of a package (bag) is usually a fold, the easy-to-tear portions100are preferably formed near a side opposing the fold. Namely, plural pairs of pattern rolls13are fixed to the shaft15, such that pairs of easy-to-tear portions100are arranged preferably in a separated inverse V form on a ribbon101for forming a bag as shown inFIG. 3.

Next, a long plastic film1is caused to pass through a pair of hard rolls11,12with a sealant layer of the plastic film1upward (facing the hard roll11).

Because the pressure rolls21do not abut the pattern rolls13at their retreated positions as shown inFIG. 2, the first carriers17,17retreat to the stoppers19c,19cby the coil springs19b,19b. The motor43is driven to rotate the screw shaft33via a belt41, moving each pressure roll21forward until it comes into contact with each pattern roll13. By further operation of the motor43, the pressure rolls21push the pattern rolls13, because the first carriers17,17are movable along the first guide rails19,19in a direction to the hard roll11. As a result, the stamp means13aof the pattern rolls13are pressed onto the plastic film1on the hard roll11as shown inFIGS. 17(a) and17(b).

The average depth of recesses constituting the easy-to-tear portions100, which are formed on the plastic film1by the stamp means13aof the pattern rolls13, is determined by pressure applied to the pattern rolls13by the pressure rolls21. Because pressure to the pattern rolls13is known from a load applied to the pressure roll21, the position of each pressure roll21is determined according to a signal from the load cell51. As shown inFIGS. 1 and 17(a), a line connecting the center of each pressure roll21to the center of each pattern roll13is preferably horizontal. When the long plastic film1passes between the hard roll11and the pattern rolls13in this state, a large number of recesses are formed correspondingly to the pattern projections of the stamp means13aon the long plastic film1. Because the stamp means13aare provided partially and slantly on the rolling surface of each pattern roll13, the easy-to-tear portions100periodically formed by the stamp means13aare slant to the longitudinal direction of the long plastic film1as shown inFIG. 3.

Because each pair of pattern rolls13have stamp means13aslant in opposite directions, plural pairs of easy-to-tear portions100in a separated inverse V form are formed as shown inFIG. 3. Because lines of two pairs of easy-to-tear portions100are formed on a long plastic film1in the depicted example, the plastic film1is cut to half along a centerline1a, and each resultant ribbon101,101is folded along a longitudinal line1bas shown inFIGS. 3 and 18, resulting in the complete overlapping of pairs of easy-to-tear portions100(step A). Next, each folded plastic ribbon101is longitudinally heat-sealed along a line connecting outer edges100aof the easy-to-tear portions100, and a side margin is cut off along the resultant first heat-sealed portion103, to obtain a flat, tubular ribbon105(step B). Further, second heat-sealed portions107are formed along transverse lines1cnear the easy-to-tear portions100, and the tubular ribbon105is cut to individual bags109(step C). After filling individual bags109with a content, their openings are heat-sealed (forming third heat-sealed portions111), to obtain content-filled bags113(step D). The formation of a notch115in the third heat-sealed portion111near the easy-to-tear portion100makes it easy to open the bag113along the easy-to-tear portion100.

[2] Second Apparatus for Forming Easy-to-Tear Portions

As shown inFIGS. 19-21, the second apparatus of the present invention for forming slant, linear easy-to-tear portions100on a long plastic film1comprises (a) a hard roll11on which a long plastic film1passes, (b) pluralities of (4 in the depicted example) pattern rolls13each partially having a slant, linear stamp means13ahaving pattern projections on a rolling surface, (c) a shaft15to which pluralities of pattern rolls13are fixed, (d) a first moving mechanism for moving the shaft15in a direction to the hard roll11, (e) pluralities of rolls18having smaller diameters than those of the pattern rolls13, which are fixed to the shaft15, (f) pressure rolls21each pushing each of the small-diameter rolls18from behind, and (g) a second moving mechanism for moving the pressure rolls21in a direction to the small-diameter rolls18, whereby with the pressure rolls21pushing the small-diameter rolls18by the second moving mechanism, the stamp means13aof the pattern rolls13fixed to the shaft15are pressed onto the plastic film1by the first moving mechanism, so that the slant, linear easy-to-tear portions100with recesses formed by the pattern projections of the stamp means13aare partially and periodically formed on the plastic film1.

The first moving mechanism preferably comprises a pair of first carriers17,17rotatably supporting the shaft15, and a pair of first guide rails19,19extending perpendicularly to the axis of the hard roll11, along which the first carriers17,17are movable in a direction to the hard roll11. The first carriers17and the first guide rails19may have known structures.

Each second moving mechanism preferably comprises a second carrier22rotatably supporting each pressure roll21, and a second guide rail25extending perpendicularly to the axis of the hard roll11, along which the second carrier22is movable in a direction to the hard roll11. The second carriers22and the second guide rails25may have known structures.

With respect to the structures of the hard rolls11,12, the pattern rolls13, the pressure rolls21and the second carriers22, the fixing methods of the pattern rolls to the shaft15, and the control of the peripheral speed of the hard roll11(moving speed of the long plastic film1) relative to the peripheral speed of the pattern rolls13, the second apparatus may be the same as the first apparatus.

As is clear fromFIGS. 20 and 22, both ends of the shaft15, to which pluralities of pattern rolls13are fixed, are rotatably supported by a pair of first carriers17,17, a motor M being mounted to one end of the shaft15. Each first carrier17,17is movable along each first guide rail19,19in a direction perpendicular to the axis of the hard roll11. With respect to the structures of the first guide rails19,19, the second apparatus may be the same as the first apparatus. While the pressure rolls21do not push the pattern rolls13, the first carriers17,17retreat to positions determined by stoppers19c,19cprovided on the rear ends of the first guide rails19,19, such that the pattern rolls13are sufficiently separate from the hard roll11. Further, there is preferably a gap between the pressure rolls21and the small-diameter rolls18.

To precisely control the positions and depth of easy-to-tear portions100formed on the plastic film1, the precise position control of the pressure rolls21is needed. Accordingly, each second moving mechanism for moving each pressure roll21in a direction to the small-diameter roll18comprises a second carrier22rotatably supporting each pressure roll21, and a second guide rail25extending perpendicularly to the axis of the hard roll11, along which the second carrier22is movable in a direction to the hard roll11. As shown inFIG. 14, each second guide rail25is fixed to each table27.

For instance, when easy-to-tear portions100are formed on a long plastic laminate film1having a sealant layer by the second apparatus, the pattern rolls13are first transversely positioned on the shaft15by a shrink-fitting method or a screwing method, according to the intervals of the easy-to-tear portions100. Because one side of a package (bag) is usually a fold, the easy-to-tear portions100are preferably formed near a side opposing the fold. Namely, plural pairs of pattern rolls13are fixed to the shaft15, such that pairs of easy-to-tear portions100are arranged preferably in a separated inverse V form on a ribbon101for forming a bag as shown inFIG. 21.

Next, a long plastic film1is caused to pass through a pair of hard rolls11,12with a sealant layer of the plastic film1upward (facing the hard roll11).

Because the pressure rolls21do not abut the pattern rolls13at their retreated positions as shown inFIG. 20, the first carriers17,17retreat to the stoppers19c,19cby the coil springs19b,19b. The motor43is driven to rotate the screw shaft33via a belt41, moving each pressure roll21forward until it comes into contact with each small-diameter roll18. By further operation of the motor43, the pressure rolls21push the small-diameter rolls18, because the first carriers17,17are movable along the first guide rails19,19in a direction to the hard roll11. As a result, the stamp means13aof the pattern rolls13are pressed onto the plastic film1on the hard roll11as shown inFIGS. 24(a) and24(b).

The average depth of recesses constituting the easy-to-tear portions100, which are formed on the plastic film1by the stamp means13aof the pattern rolls13, is determined by pressure applied to the small-diameter rolls18by the pressure rolls21. Because pressure to the small-diameter roll18is known from a load applied to the pressure roll21, the position of each pressure roll21is determined according to a signal from the load cell51. As shown inFIGS. 19 and 24(a), a line connecting the center of each pressure roll21to the center of each small-diameter roll18is preferably horizontal. When the long plastic film1passes between the hard roll11and the pattern rolls13in this state, a large number of recesses are formed correspondingly to the pattern projections of the stamp means13aon the long plastic film1. Because the stamp means13aare provided partially and slantly on the rolling surface of each pattern roll13, the easy-to-tear portions100periodically formed by the stamp means13aare slant to the longitudinal direction of the long plastic film1as shown inFIG. 21.

Because each pair of pattern rolls13have stamp means13aslant in opposite directions, plural pairs of easy-to-tear portions100in a separated inverse V form are formed as shown inFIG. 21. Because lines of two pairs of easy-to-tear portions100are formed on a long plastic film1in the depicted example, the plastic film1is cut to half along a centerline1a, and each resultant ribbon101,101is folded along a longitudinal line1bas shown inFIGS. 21 and 18, resulting in the complete overlapping of pairs of easy-to-tear portions100(step A). Subsequently conducting the same steps B, C and D as in the first apparatus for forming easy-to-tear portions, content-filled bags113are obtained. As in the first apparatus, the formation of a notch115in the third heat-sealed portion111near the easy-to-tear portion100makes it easy to open the bag113along the easy-to-tear portion100.