Package of filter tow bale packed with packing material in a non-hermetic state and manufacturing method thereof

Abstract

The present invention provides a package of a filter tow bale made of cellulose acetate packed with a packing material in a non-hermetic state, which can be stacked in multistage and in which tows in the same bale can be uniformly maintained. The package of the filter tow bale made of cellulose acetate is packed with the packing material in the non-hermetic state, in which the filter tow bale is tightened with the packing material in the package, the filter tow bale has a cubic shape or a rectangular parallelepiped shape with 800 to 1,400 mm in length, 800 to 1,150 mm in width, and 800 to 1,100 mm in height, and a packing initial pressure between a top surface of the filter tow bale and the packing material is 6.3 kPa or less.

Claims

1. A package comprising: a filter tow bale made of cellulose acetate; and a packing material, the filter tow bale packed with the packing material in a non-hermetic state, wherein the filter tow bale has a cubic shape or a rectangular parallelepiped shape with 800 to 1,400 mm in length, 800 to 1,150 mm in width, and 800 to 1,100 mm in height, a packing density of the filter tow bale is 350 kg/m.sup.2 or greater, a packing initial pressure between a top surface of the filter tow bale and the packing material is 6.3 kPa or less, and the package is obtained by i) applying a force to a folded filter tow band in a compression can from an upper surface of the folded filter tow band by a compression plate to compress the folded filter tow band so that an impulse is 1,500 (N.Math.s) or more, and ii) removing the compression can from the folded filter tow band, while keeping compression by the compression plate, to obtain the filter tow bale, and then packing the filter tow bale in the non-hermetic state with the packing material, and iii) releasing pressure by removing the compression plate from the filter tow bale, so that the filter tow bale is tightened with the packing material in the package, the packing density of the filter tow bale is 350 kg/m.sup.2 or greater, and the packing initial pressure between the top surface of the filter tow bale and the packing material is 6.3 kPa or less, wherein the compression plate has a convex at a central part on a surface facing to the folded tow band, the convex having a height of 0 to 40 mm, the impulse is defined by a following calculation: the impulse (N.Math.s)=(the height of the convex portion (mm)/5.4+1)the force applied during the compression (N=kg.Math.m/s.sup.2)a compression time (s), and the packing initial pressure is an average value of pressures measured at three positons including a center of the top surface of the filter tow bale and two portions at vicinity of the corners of the top surface of the filter tow bale 10 minutes after release of the pressure by the compression plate.

2. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 1, wherein the non-hermetic package of the filter tow bale has a central part of the top surface swollen as compared with a peripheral part, and a height of swelling at the central part is 25 mm or less when the peripheral part is taken as a reference.

3. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 2, wherein the packing material comprises a combination of a covering material and a tightening material, and the filter tow bale is covered with the covering material and the tightening material is tightened over the covering material in the package.

4. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 2, wherein the packing material comprises a combination of the covering material and means for integrating the covering material, the covering material is selected from a thin film, paper, a corrugated fiberboard, a synthetic resin sheet, a woven fabric, a non-woven fabric and combinations of these, and the means for integrating the covering material is selected from a surface fastener, an adhesive and a heat seal.

5. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 1, wherein the packing material comprises a combination of a covering material and a tightening material, and the filter tow bale is covered with the covering material and the tightening material is tightened over the covering material in the package.

6. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 5, wherein the covering material is selected from a thin film, paper, a corrugated fiberboard, a synthetic resin sheet, a woven fabric, a non-woven fabric and combinations of these, and the tightening material is a synthetic resin band or a metal band.

7. The package of the filter tow bale packed with the packing material in the non-hermetic state according to any claim 6, wherein the covering material is formed of a material having air permeability, or a material not having air permeability and having a vent hole.

8. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 5, wherein the covering material is formed of a material having air permeability, or a material not having air permeability and having a vent hole.

9. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 1, wherein the packing material comprises a combination of the covering material and means for integrating the covering material, the covering material is selected from a thin film, paper, a corrugated fiberboard, a synthetic resin sheet, a woven fabric, a non-woven fabric and combinations of these, and the means for integrating the covering material is selected from a surface fastener, an adhesive and a heat seal.

10. The package of the filter tow bale packed with the packing material in the non-hermetic state according to any claim 9, wherein the covering material is formed of a material having air permeability, or a material not having air permeability and having a vent hole.

11. The package of the filter tow bale packed with the packing material in the non-hermetic state according to claim 1, wherein, the height of the convex portion is 5 to 40 mm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The present invention is understood by the following detailed description and attached drawings further completely, however, these drawings are attached only for explanation and do not limit the present invention.

(2) FIG. 1 is a perspective view of a non-hermetic package of a filter tow bale according to the present invention. Note that the drawing is shown in a state where part of a packing material is removed so that the inside is seen.

(3) FIG. 2 is an explanatory view of a measuring method of a packing initial pressure between a top surface of the filter tow bale and the packing material.

(4) FIG. 3 is a view for explaining a manufacturing method of the non-hermetic package of the filter tow bale according to the present invention.

(5) FIG. 4(a) is a cross-sectional view of an upper pressing plate in a thickness direction used in the manufacturing method according to the present invention, and FIG. 4(b) is a plan view of the upper pressing plate. In the drawings, a reference numeral 10 denotes a package, a reference numeral 11 denotes a packing material, a reference numeral 12 denotes a covering material, a reference numeral 13 denotes a tightening material, a reference numeral 15 denotes a filter tow bale, a reference numeral 20 denotes a compression can, a reference numeral 21 denotes a lower pressing plate (lower platen), a reference numeral 22 denotes an upper pressing plate (upper platen), a reference numeral 23 denotes a convex portion, and a reference numeral 24 denotes an inclined surface.

DETAILED DESCRIPTION OF THE INVENTION

(6) <Non-Hermetic Package of Filter Tow Bale>

(7) A filter tow bale which is packed with a packing material in a non-hermetic state (hereinafter abbreviated as a Package in a Non-hermetic State) according to the present invention is in a state where a filter tow bale made of cellulose acetate is tightened with a packing material, and has flat surfaces in such a degree that multistage stacking is possible.

(8) The non-hermetic state in the present invention means that a filter tow bale is covered with a packing material in a state where the filter tow bale can be aerated, and the technology of utilizing the negative pressure as packaging means disclosed in the invention of JP-A 2005-528096 is not included.

(9) Next, the Package in a Non-hermetic State according to the present invention will be explained with reference to FIG. 1.

(10) In the Package in a Non-hermetic State 10, a filter tow bale 15 made of cellulose acetate is tightened with a packing material 11.

(11) The filter tow bale 15 has a cubic shape or a rectangular parallelepiped shape with 800 to 1,400 mm in length, 800 to 1,150 mm in width and 800 to 1,100 mm in height.

(12) As the packing material 11, a material containing a combination of a covering material 12 and a tightening material 13 can be used.

(13) When the packing material 11 containing a combination of the covering material 12 and the tightening material 13 is used, the filter tow bale 15 is covered with the covering material 12 and is tightened with the tightening material 13 over the covering material 12 as shown in FIG. 1.

(14) As the covering material 12, a material selected from a thin film, paper, a corrugated fiberboard, a synthetic resin sheet, a woven fabric, a non-woven fabric and combinations of these can be used.

(15) When using a synthetic resin sheet, a woven fabric or a non-woven fabric as the covering material, a material to which stretchability is imparted by adjusting the thickness, material quality, weaving method and so on, may be used.

(16) When using a material to which stretchability is imparted is used as the covering material, the covering material itself can also perform tightening by covering the tow bale in a state where the covering material is stretched.

(17) As the tightening material 13, a synthetic resin band or a metal band can be used.

(18) A packing material comprising a combination of the covering material and means for integrating the covering material may be used instead of the covering material 12 and the band 13 as the tightening material as shown in FIG. 1.

(19) As the covering material, the same materials as described above can be used.

(20) As the means for integration, means selected from a surface fastener, an adhesive and a heat seal can be used. The surface fastener performs integration of end portions of the covering material which are close to each other, and the adhesive and the heat seal perform integration of overlapped end portions of the covering material.

(21) As the package 10 according to the present invention is in a non-hermetic state, it is not necessary that the filter tow bale 15 is completely covered with the covering material 12.

(22) When the tow bale is completely covered with the covering material 12, a material having air permeability, or a material not having air permeability and having a vent hole is used as the covering material 12.

(23) A packing initial pressure between a top surface 15a of the filter tow bale 15 and the packing material 12 is 6.3 kPa or less in the package 10.

(24) Here, a packing initial pressure means a pressure after 10 minutes from the completion of packing (when a press pressure is released in FIG. 3(e)).

(25) The packing initial pressure is measured by a method described in examples, and is an average value of pressures at the total of three points, which are a circle (circle mark) 51 including the center point of the top surface 15a, and two points of circles (circle marks) 52 to 55, as shown in FIG. 2.

(26) While it is preferred that a central part and a peripheral part of a top surface 10a of the package 10 is flush with each other, the top surface 10a of the package 10 may have a central part being swollen as compared with a peripheral part as long as the degree of swelling is small.

(27) In the case where the central part of the top surface 10a is swollen as compared with the peripheral part, the height of swelling at the central part is 25 mm or less when the peripheral part is taken as a reference. Even when the central part is swollen as described above, a work of multistage stacking can be facilitated as long as the degree of swelling can be made small.

(28) Unlike the bales as described in the inventions of JP-A 2009-508764 and JP-A 2008-539143 in which the degree of swelling at the central part is small and the degree of swelling in the peripheral part is large to thereby form the flat surface, the package 10 according to the present invention has the central part being flush with the peripheral part or the central part being slightly swollen as compared with the peripheral part. Therefore, a variation in the elastic recovery force in the same tow bale 15 is small.

(29) Accordingly, a fluctuation in tension is small when unwinding the tow from the tow bale 15, therefore, a fluctuation in mass per one filter is also small, thereby obtaining uniform filters.

(30) The filter plug obtained by using the tow bale 15 of the package 10 according to the present invention has a variation in filtering resistance (PDCV) lower than 3.5 when it has a circumference of 20 to 25 mm and a density of 400 to 600 kg/cm.sup.3, and the filter plug has a variation in filtering resistance (PDCV) lower than 3.5 when it has a circumference of 18 mm or less and a density of 350 to 450 kg/cm.sup.3.

(31) <Manufacturing Method of Package>

(32) A manufacturing method of the package of the filter tow bale in the non-hermetic state will be explained with reference to FIGS. 3(a) to (f).

(33) [First Step]

(34) In the first step, a band of filter tow is deposited into a compression can 20 in layers (layers of filter tow 30) as shown in FIG. 3(a).

(35) As a tow for filters, for example, a tow having the total denier of 15,000 to 45,000, in which 2,000 to 30,000 pieces of filaments having a filament denier of 1.5 to 8.2 are gathered, can be used.

(36) When used as a production raw material of a tobacco filter plug, a tow for filters having different filament deniers can be used according to the width of the tobacco filter plug.

(37) When used for the filter plug having a circumference of 20 to 25 mm and a density of 400 to 600 kg/cm.sup.3, a tow for filters having a filament denier of 2.0 to 3.5 and the total denier of 30,000 to 40,000 is preferred.

(38) Further, when used for the filter plug having a circumference of 18 mm or less and a density of 350 to 450 kg/cm.sup.3, a tow for filters having a filament denier of 3.6 to 8.2 and the total denier of 30,000 to 40,000 is preferred.

(39) After that, the compression can 20 filled with the layers of filter tow 30 is moved to a place where a lower pressing plate (lower platen) 21 and an upper pressing plate (upper platen) 22 are arranged opposite to each other in a height direction and placed on the lower pressing plate 21 as shown in FIG. 3(b).

(40) The lower pressing plate 21 is a flat plate.

(41) A packing material (covering material) (not shown) and a synthetic resin band 40 serving as a tightening material are arranged on the lower pressing plate 21. The synthetic resin band 40 is inserted into a plurality of grooves 26 formed in the lower pressing plate 21.

(42) The method itself in which a material corresponding to the packing material is previously arranged in pressing means is well known and described in, for example, JP-A 2010-254376 and shown in FIG. 2, and described in JP-A 2011-213354 and shown in FIG. 2 and FIG. 4.

(43) [Second Step]

(44) In the second step, the layers of filter tow 30 are compressed by the upper pressing plate 22 from an upper side as shown in FIG. 3(c).

(45) The upper pressing plate 22 can apply a pressure by a hydraulic rod 25.

(46) The upper pressing plate 22 has a convex portion 23 in the central part and has a flat surface portion 24 in a peripheral part.

(47) The convex portion 23 and the flat surface portion 24 have the plurality of grooves 26 for inserting the synthetic resin band 40, and the synthetic resin band 40 serving as the tightening material is inserted into the grooves 26.

(48) In one example, the convex portion 23 is a mountain-like protrusion having an inclined surface or a stepped surface. That is, the convex portion 23 includes a flat top surface 23a and an inclined surface 23b as shown in FIGS. 4(a), (b). The inclined surface 23b may also be a stepped surface.

(49) A height H of the convex portion 23 from the flat surface portion 24 is preferably 0 to 40 mm, and more preferably 5 to 40 mm and further preferably 10 to 38 mm.

(50) As an area ratio between the convex portion 23 and the flat surface portion 24 in the upper pressing plate 22, an area of the convex portion 23 is preferably 95% or more, and more preferably, 98% or more.

(51) As an area ratio between the top surface 23a and the inclined surface 23b in the convex portion 23, an area of the flat top surface 23a is preferably 10 to 40%, and more preferably, 15 to 30%.

(52) In the second step, compression is performed so that an impulse (N.Math.s) calculated from the following formula is preferably 1,500 N.Math.s or more, and more preferably, 1,500 to 15,000 N.Math.s.
Impulse (N.Math.s)=(height of convex portion (mm)/5.4+1)force by pressing means at the time of compression (N=kg.Math.m/s.sup.2)compression time(s)
(5.4 and 1 in the formula are constants based on manufacture data accumulated for a long period of time, which indicate a known impulse (hereinafter impulse 1) obtained from the force by the pressing means at the time of compression (N=kg.Math.m/s.sup.2)compression time (s).)

(53) In the second step, a plate composed only of a flat surface (not having the convex portion 23) can be used as the upper pressing plate 22.

(54) When using the upper pressing plate 22 composed only of the flat surface, compression is performed so that a prescribed impulse is obtained.

(55) [Third Step]

(56) In the third step, as shown in FIG. 3(d), after the compression by the upper pressing plate 22 is stopped, the compression can 20 used for compression is moved and removed, then, the filter tow bale 15 is packed with the packing material (only the synthetic resin band 40 is shown in the drawing) so that the filter tow bale 15 is in a non-hermetic state.

(57) To stop the compression in the third step means to stop applying the pressure by the hydraulic rod 25. As the upper pressing plate 22 itself is in the state of FIG. 3(d), the filter tow bale 15 is in a state where at least a pressure by an own weight of the upper pressing plate 22 is applied.

(58) In the state shown in FIG. 3(d), packing is performed so that a packing initial pressure between the top surface 15a of the filter tow bale 15 and the packing material 12 is 6.3 kPa or less.

(59) [Fourth Step]

(60) In the fourth step, the filter tow bale is released from the pressure by lifting the upper pressing plate 22 to thereby obtain the package 10 as shown in FIGS. 3(e), (f).

(61) While the top surface 10a of the package 10 is a flat surface in the state shown in FIG. 3(e) obtained immediately after the upper pressing plate 22 is lifted, the central part of the top surface 10a may be slightly swollen with a lapse of time.

(62) However, since a height of swelling at the central part at this time is 25 mm or less when the peripheral part is taken as a reference, the work of multistage stacking is facilitated.

EXAMPLES

Examples 1 to 7 and Comparative Examples 1 to 8

(63) Packages of examples and comparative examples were fabricated by the steps shown in FIGS. 3(a) to (f).

(64) [First Step: FIGS. 3(a), (b)]

(65) A filter tow having a filament denier of 2.0 to 3.5 and the total denier of 30,000 to 40,000 was used.

(66) The compression can 20 made of metal having a rectangular parallelepiped shape with 1,200 mm in a long edge, 950 mm in a short edge and 4,000 mm in height was used, and a filter tow of 625 kg was put into the can.

(67) [Second Step: FIG. 3(c)]

(68) As shown in FIG. 3(c), the layers of tow 30 were compressed by the upper pressing plate 22 in compression conditions shown in Table 1 to obtain bales with a packing density of 550 kg/m.sup.3.

(69) The upper pressing plate 22 composed only of the flat surface (the height (H) of the convex portion is 0 mm in Table 1) was used in the examples 1, 2 and the comparative examples 1 to 3.

(70) In other examples, the upper pressing plate 22 having the convex portion 23 as shown in FIG. 3 was used. The heights (H) of the convex portions are shown in Table 1.

(71) [Third Step; FIG. 3(d)]

(72) After a compression time shown in Table 1 was passed, packing was performed by strapping bands from directions orthogonal to each other as shown in FIG. 1 so as to be in the non-hermetic state.

(73) Two pieces of a film made of polyethylene resin and an inserting paper (the inserting paper is arranged in the outside) were used as the covering material 12, and five bands made of polyethylene-telephthalate resin (width 15 mm) were used as the synthetic resin band 13 (two bands in the same direction and three bands in orthogonal direction were used).

(74) [Fourth Step; FIGS. 3(e), (f)]

(75) After the packing, the pressure was released to obtain the package 10.

(76) The packing initial pressure of the package 10 was measured.

(77) In addition, after allowing the obtained package to stand for 24 hours at room temperature, a swelling on the top surface was measured. The swelling on the top surface was provided by placing a flat plate (10 kg) on the top surface and measuring distances between four corners and the flat plate to obtain an average value thereof.

(78) <Measuring Method of Packing Initial Pressure>

(79) Measurement was made by using a film-type sensor having 14 mm in width, 205 mm in length and 0.208 mm in thickness (a circle having a diameter of 9.5 mm at the tip of the sensor is an effective sensing area, the maximum loads 4.4 N and 110 N; pressure-voltage conversion type) (brand name: Flexi Force, manufactured by NITTA Corporation).

(80) The measurement was made 10 minutes after the release of pressure in the step of FIG. 3(e).

(81) As the measurement method, the covering material was cut for approximately 20 mm in the vicinity of three points of the circle 51, the circle 53 and the circle 55 shown in FIG. 2, and measurement was performed by inserting the film-type sensor so that the effective sensing area (connected to an external circuit) was positioned at the circle 51, the circle 53 and the circle 55.

(82) The synthetic resin band 13 does not exist at positions of the circle 51, the circle 53 and the circle 55.

(83) Test Example 1 (Evaluation of Multistage Stacking Property)

(84) Stability when stacking packages in four stages was evaluated by using the obtained packages. Wooden pallets were interposed between a floor surface and the lowermost package and between respective packages.

(85) In the four-stage stacking as the above, states of contacts between the pallets interposed between respective packages and the top surfaces of the packages were observed by the naked eyes and evaluated. Packages in which the pallet contacts the top surface of the package were evaluated as good, while packages in which the pallet does not contact the top surface even in a part were evaluated as poor.

(86) Text Example 2 (Evaluation of Pressure Drop when Processed into Tobacco Filter)

(87) Pressure drop was evaluated when the tow bales of respective packages according to the examples and the comparative examples were used and processed into tobacco filters.

(88) A tow of cellulose acetate fiber was opened or bloomed using a rod making machine for manufacturing tobacco filters (KDF2/AF1) to have approximately 5 cm to 20 cm in width, and after uniformly spraying 6 parts by mass of triacetin relative to 100 parts by mass of the tow, the tow was opened or bloomed with an air stream, introduced into a trumpet-shaped convergence tube, wound up using wrapping paper, and then cut by a cutter, thereby to obtain a filter.

(89) A filter rod having a circumference of 24.2 mm and a length of 100 mm was obtained. The winding velocity was 600 m/min.

(90) A pressure drop (mmWG) relating to the filter rod having the length of 100 mm was measured by using an automatic pressure drop measuring instrument (QTM-6 manufactured by CERULEAN UK) in a condition of an air flow rate 17.5 ml/sec).

(91) Average values (x) and standard deviations (a) of the pressure drop (PD) were calculated from measurement data, and PDCV was calculated by a formula: /x100.

(92) Evaluations were indicated as good when PDCV was lower than 3.5 and evaluations were indicated as poor when PDCV exceeded 3.5. When PDCV is lower than 3.5, the smoking flavor obtained when using as the tobacco filter is not badly affected.

(93) TABLE-US-00001 TABLE 1 Second step Package Test result Convex Pressing Compression Compression Impulse Packing initial Multistage portion (H) area pressure time (H/5.4 + 1) pressure Swelling stacking height (mm) (m.sup.2) (MPa) (second) Impulse 1 Impulse 1 (MPa) height (mm) property PDCV Example 1 0 1.13 3.5 600 1526 1,526 5 25 Good Good Example 2 0 1.13 3.5 2100 1675 4,675 5 20 Good Good Comparative 0 1.13 3.5 60 187 187 40 45 Poor Good Example 1 Comparative 0 1.13 3.5 240 666 666 25 30 Poor Good Example 2 Comparative 0 1.06 1.3 120 133 133 50 60 Poor Good Example 3 Example 3 10 1.13 3.5 360 962 2,744 5 25 Good Good Comparative 10 1.06 1.3 180 192 548 30 38 Poor Example 4 Comparative 10 1.13 3.5 60 187 534 30 35 Poor Example 5 Example 4 25 1.13 35 240 666 3,750 5 25 Good Comparative 25 1.13 35 60 187 1,054 15 35 Poor Example 6 Example 5 38 1.13 3.5 60 187 1,504 5 25 Good Good Example 6 38 1.13 3.5 240 666 5,353 5 20 Good Good Example 7 38 1.13 3.5 600 1526 12,268 5 20 Good Good Comparative 38 1.06 1.3 120 133 1,066 15 30 Poor Good Example 7 Comparative 60 1.13 3.5 60 187 2,267 5 25 Good Poor Example 8

(94) As apparent from Table 1, in packages according to the present invention, heights of swelling in the central part were low (25 mm or less), therefore, both the multistage stacking property and PDCV when processed into the tobacco filters were good.

(95) From comparison between examples 1, 2 and examples 3 to 7, it was found that using the pressing means having the convex portion in the central part and the flat surface portion in the peripheral part was a preferable manufacturing method in consideration of the number of equipment needed at the time of manufacture as the compression time was reduced.

Examples 8 to 10 and Comparative Examples 9 to 13

(96) Packages of examples and comparative examples were fabricated by steps shown in FIGS. 3(a) to (f).

(97) [First Step; FIGS. 3(a), (b)]

(98) Filter tows having filament deniers and total deniers shown in Table 2 were used.

(99) The compression can 20 made of metal having a rectangular parallelepiped shape with 1,200 mm in a long edge, 950 mm in a short edge and 4,000 mm in a height was used, and a filter tow of 625 kg was put into the can.

(100) [Second Step; FIG. 3(c)]

(101) As shown in FIG. 3(c), the layers of tow 30 were compressed by the upper pressing plate 22 in compression conditions shown in Table 1 to obtain bales with packing densities shown in Table 2.

(102) The upper pressing plate 22 composed only of the flat surface (the height (H) of the convex portion is 0 mm in Table 1) was used in the example 9 and the comparative examples 9 to 11, 13.

(103) In other examples, the upper pressing plate 22 having the convex portion 23 as shown in FIG. 3 was used. The heights (H) of the convex portions are shown in Table 1.

(104) [Third Step; FIG. 3(d)]

(105) After a compression time shown in Table 3 was passed, packing was performed by strapping bands from directions orthogonal to each other as shown in FIG. 1 so as to be in the non-hermetic state.

(106) Two pieces of a film made of polyethylene resin and an inserting paper (the inserting paper is arranged in the outside) were used as the covering material 12, and five bands made of polyethylene-telephthalate resin (width 15 mm) were used as the synthetic resin band 13 (two bands in the same direction and three bands in orthogonal direction were used).

(107) [Fourth Step; FIGS. 3(e), (f)]

(108) After the packing, the pressure was released to obtain the package 10.

(109) The packing initial pressure of the package 10 was measured.

(110) In addition, after allowing the obtained package to stand for 24 hours at room temperature, a swelling on the top surface was measured. The swelling on the top surface was provided by placing a flat plate (10 kg) on the top surface and measuring distances between four corners and the flat plate to obtain an average value thereof.

(111) Evaluation of the multistage stacking property of the test example 1 was made by using respective packages of the examples and the comparative examples. Results are shown in Table 3.

(112) By a test example 2, pressure drop was evaluated when the tow bales of respective packages according to the examples and the comparative examples were used and processed into tobacco filters. A filter rod having a circumference of 16.5 mm and a length of 100 mm was fabricated and used in the test example 2. Results were shown in Table 3.

(113) TABLE-US-00002 TABLE 2 Filament Packing density denier Total denier (kg/m.sup.3) Example 8 6 17,300 450 Example 9 6 17,300 400 Example 10 6 17,300 350 Comparative 3.1 29,800 500 Example 9 Comparative 6 17,300 400 Example 10 Comparative 6 17,300 390 Example 11 Comparative 6 17,300 400 Example 12 Comparative 6 17,300 500 Example 13

(114) TABLE-US-00003 TABLE 3 Second step Package Test result Convex Pressing Compression Impulse Packing initial Multistage portion (H) area Compression time (H/5.4 + 1) pressure Swelling stacking height (mm) (m.sup.2) pressure (MPa) (second) Impulse 1 Impulse 1 (kPa) height (mm) property PDCV Example 8 38 1.13 3.5 60 187 1,504 5 25 Good Good Example 9 0 1.13 3.5 600 1,526 1,526 5 25 Good Good Example 10 38 1.13 3.5 600 1,526 12,268 5 20 Good Good Comparative 0 1.13 3.5 600 1,526 1,526 5 25 Good burst Example 9 Comparative 0 1.13 3.5 60 187 187 40 45 Poor Good Example 10 Comparative 0 1.06 1.3 120 133 133 50 60 Poor Good Example 11 Comparative 60 1.13 3.5 60 187 2,267 5 25 Good Poor Example 12 Comparative 0 1.13 3.5 60 187 187 60 60 Poor Poor Example 13

(115) As apparent from Table 3, heights of the swelling in the central part were low (25 mm or less) in the packages according to the present invention, therefore, both the multistage stacking property and PDCV when processed into the tobacco filter were good.

(116) From comparison between example 8 and example 9, it was found that using the pressing means having the convex portion in the central part and the flat surface portion in the peripheral part was a preferable manufacturing method in consideration of the number of equipment needed at the time of manufacture as the compression time was reduced.

(117) Furthermore, it was confirmed that, with the filter tows having different thicknesses (different filament deniers) used in the examples 1 to 7 in Table 1 and the examples 8 to 10 in Table 3, the same results were obtained by adopting the manufacturing method according to the present invention.

(118) Variation in quality of filter tows in the same bale is small in the packages in which the filter tow bale is packed with the packing material in the non-hermetic state, therefore, the filter tow bale of the package can be used as the filter plug for tobacco.

(119) The present invention has been described as the above. The present invention naturally includes various modifications in a range thereof, and these modifications do not depart from the range thereof. All regarded as modifications of the present invention by those who have normal knowledge in the technical field is included in the range of claims described below.