Heat-sealing apparatus and method for forming composite heat seal structure

Abstract

A heat-sealing apparatus for forming a composite heat seal structure, includes a belt conveying, heating and press bonding portion configured to convey and heat a heat seal material to form a band-shaped peelable seal, and a die roll press bonding portion configured to add a linear peelable seal to the band-shaped peelable seal in a longitudinal direction of the band-shaped peelable seal for forming the composite heat seal structure.

Claims

1. A heat-sealing apparatus comprising: a belt conveying, heating and press bonding portion configured to convey and heat a heat seal material to form a band-shaped peelable seal, wherein the belt conveying, heating and press bonding portion comprises: a pair of belts, each of the pair of belts engaged to rollers and configured to travel between the rollers, and a heating body spaced from the pair of belts; and a die roll press bonding portion configured to add a linear peelable seal to the band-shaped peelable seal in a longitudinal direction of the band-shaped peelable seal for forming a composite heat seal structure, the die roll press bonding portion including a linear roller having a linear rib on a peripheral surface of the linear roller in a circumferential direction of the linear roller, and an elastic roller.

2. The heat-sealing apparatus as set forth in claim 1, wherein at least one of the rollers is configured to move in a direction perpendicular to a traveling direction of the pair of belts to control a space between the rollers and change press bonding pressure applied to the heat seal material.

3. The heat-sealing apparatus as set forth in claim 1, wherein the linear rib has a width ranging from 0.05 millimeters (mm) to 0.2 mm and a height ranging from 0.05 mm to 2 mm.

4. The heat-sealing apparatus as set forth in claim 1, wherein a width of a surface of the linear roller in contact with the elastic roll is identical to a width of the band-shaped peelable seal.

5. The heat-sealing apparatus as set forth in claim 1, wherein a peripheral surface of the elastic roller is covered with an elastic material sheet having a hardness of A 50 to A 80.

6. The heat-sealing apparatus as set forth in claim 1, wherein at least one of the linear roller or the elastic roller is configured to move in a direction perpendicular to the longitudinal direction to adjust press bonding pressure.

7. The heat-sealing apparatus as set forth in claim 1, further comprising: a temperature keeping portion between the belt conveying, heating and press bonding portion and the die roll press bonding portion.

8. The heat-sealing apparatus as set forth in claim 7, wherein the temperature keeping portion comprises a temperature keeping plate connected to a heat source.

9. The heat-sealing apparatus as set forth in claim 1, wherein said each of the pair of belts comprises a metal belt.

10. The heat-sealing apparatus as set forth in claim 9, wherein the metal belt comprises at least one of stainless steel, aluminum or brass and has a thickness ranging from 0.01 mm to 0.2 mm.

11. The heat-sealing apparatus as set forth in claim 1, wherein the heating body is surrounded by a belt of the pair of belts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) [FIG. 1] is a graph illustrating schematically the relationship between welding face temperature and bonding strength.

(2) [FIG. 2] is a cross sectional view of a gusset bag applied to press bonding by heating bodies.

(3) [FIG. 3] is a side sectional view showing a state of conducting heat seal by the heating jaw system.

(4) [FIG. 4] is a side sectional view showing a state of conducting heat seal by the band sealer.

(5) [FIG. 5] is a graph showing a relationship between press bonding pressure and sliding strength (frictional force) obtained by using a glass-wool woven fabric impregnated with polytetrafluoroethylene or a stainless steel sheet as the belt material and varying heating body temperature.

(6) [FIG. 6] is a graph showing a relationship between heating time and welding face temperature response obtained by using a glass-wool woven fabric impregnated with polytetrafluoroethylene or a stainless steel sheet as the belt material and varying press bonding pressure.

(7) [FIG. 7] is a graph showing temperature descending after discharge from belt heating.

(8) [FIG. 8] is a graph illustrating schematically variation of welding face temperature with heating time.

(9) [FIG. 9] is a side sectional view illustrating schematically the test method of sealability at flexed portions.

(10) [FIG. 10] is a side sectional view illustrating schematically the heat-sealing apparatus of at least one embodiment of the present application.

(11) [FIG. 11] is a front view of the die roll press bonding portion thereof.

(12) [FIG. 12] is a side sectional view illustrating schematic structure of the temperature regulating portion thereof.

(13) [FIG. 13] is a photograph demonstrating results of inspecting sealability of a bag heat-sealed by the above-mentioned heat-sealing apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

Definition of Temperature Expression Utilized in This Description

(14) First, temperature expressions used in the detailed description of at least one embodiment are explained. Heating temperature: A general term of the temperature heating a material to be heated; in heat-sealing technique, it is basically welding face temperature. Controlled temperature: Controlled value to heat a heating body at a constant temperature. Heating body: Metal block having a heat source and controlled to a prescribed temperature. Heating body surface temperature: Surface temperatures of a heating body are different by the heat transfer from a heating element (heater) and the heat dissipation to periphery, and temperatures of respective heating surfaces are not identical. Temperature of heating surface to be in contact with the material to be heated is defined as “heating body surface temperature”. Welding face temperature: Reached temperature of heat bonding face of a packaging material. Welding face temperature response: Variation response of the temperature of heat bonding face of a packaging material. Heating speed: Variation speed of welding face temperature (° C./s). Equilibrium temperature: Temperature where welding face temperature response constricts/reaches (about 3 times CUT or more). Come up time (CUT): Time of 95% response of equilibrium temperature (s). Interfacial bonding temperature zone: Heating zone where bonding faces are peeled by peeling force. Agglomerate bonding temperature zone: Heating zone where sealant is melted to integrate (molded) 2 surfaces of the sealant. Bonding temperature zone: Connecting region of the temperature zone where interfacial bonding appears and the temperature zone where agglomerate bonding appears, in heat bonding characteristics. Both sides heating: Temperature control function is added to a pair of respective heating bodies. Usually, set at the same temperature. One side heating: One of heating surfaces is allowed to depend on environmental conditions without particular temperature control.

(15) The at least one embodiment is applied fundamentally to the heat seal upon making/sealing packaging bags, and representative bag forms are the following four bags.

(16) (1) 4-sided fin seal bag made by doubling sheets in flat and sealing four sides.

(17) (2) 3-sided fin seal bag made by folding a sheet and sealing three sides.

(18) (3) Pillow type bag made by folding a sheet to face seal areas each other, locating the seal areas around the center of rear side of the packaged product, to render so that only 2 places, i.e. upside and underside, of seal areas can be seen from the front side of the product.

(19) (4) Envelope type bag made by changing the seal portion facing each other in the pillow type bag to envelope type seal where two sheets are superimposed.

(20) The pillow type bag is a modification of the three-sided fin seal bag. First, using a molding tool, the facing line is located around the center of the back of the bag and sealed to form center seal (sealed with facing each other). Thereafter, the upside and underside portions are sealed including folded newly formed center seal portion (fin), and cut.

(21) It is widely utilized because of changing easily from planar form to steric form.

(22) When gussets in 2 lines are formed on both sides of pillow type bag, it becomes gusset bag. Since the gusset bag is possible to be a stereo bag, it has characteristics of good appearance of commercial goods and good efficiency for charging them. Whereas, by rendering gusset bag, problems similar to pillow type bag occur and increase.

(23) Since pillow type packaging bag is excellent in automating ability, it is frequently utilized for soft packaging centering in the field of foods. Moreover, the fin of the center seal exhibits a convenience to exhibit a function of tab upon opening.

(24) The envelope type bag is formed by changing the center seal portion sealed with facing each other of the pillow type bag to 2 sheets piled portion. It is characterized by small step at sealed area and no fin formed by facing seal.

(25) However, it is necessary to provide a sealant having bonding ability on both sides of the material to increase cost, and therefore, its use are restricted.

(26) Film and sheet, which are heat seal materials, are enough to have a heat-sealable layer, and may be formed of single layer or plural layers. In general, it is polyethylene, polypropylene, ethylene copolymers or the like. In addition, not crystallized polyethylene terephthalate and the like are also usable. The thickness of the heat-sealable layer is usually about 3-200 μm, typically about 5-150 μm without limiting specifically thereto. When referring to experimental results, the thickness of the heat-sealable layer to be applied to at least one embodiment is necessary to be 10 μm or more in order to compensate the step portion.

(27) The film or sheet composed of plural layers is constructed by laminating two types or more materials in order to improve printability, resistance to breakage, or gas barrier ability, to adjust rigidity of bags, to prevent adhesion of the material in softened state to the heating plate, or the like. At least, an adhesive layer (sealant) which is the heat-sealable layer, is allocated to one of the surface layers. Heretofore, the design is evaluated “good” to render a great difference in the temperature region applied to the material of the surface layer which becomes the outside layer, and the adhesive layer, and low-temperature solidifying materials were applied.

(28) This selection is convenient for planar bonding. However, it is not noticed to the fault in design that softening of the surface layer material having flexural stiffness is insufficient in the proper heating temperature range of the adhesive layer to result in an obstacle factor (generation of a through holes) of sealing in a seal containing a flexed portion (Patent Document 3).

(29) The thickness of the film or sheet composed of plural layers is usually about 2-200 μm, typically about 20-120 μm, without limiting specifically thereto.

(30) The heat seal width of the bags may be usual, in general about 3-20 mm, typically about 5-15 mm. The heat seal width may be identical at all heat seal areas, or may be different, for example, between the upside seal portion and the center seal portion.

(31) The composite heat seal structure of at least one embodiment comprises a band-shaped peelable heat seal wherein a peelable seal is provided in band-shaped, and a linear peelable heat seal located therein in the longitudinal direction.

(32) The band-shaped peelable heat seal is provided, in the case of packaging bag, on a side to be opened, and the width is in general about 3-30 mm, typically about 5-15 mm. A preferred bonding strength (heat seal strength) which is a peelable strength, is usually about 2-12 N/15 mm, generally about 2-10 N/15 mm. By setting the bonding strength in this range, the strength can address individual uses having a restriction, such as to be easy to open or to be difficult to open by children

(33) The resistance to bag rupture at the linear seal portion is small because of a minute width (line). When a bag rupture stress is applied to the heat seal edge on the inside of the bag, according to Patent Document 4, the stress is consumed by the peel energy during peeling the band-shaped peelable seal to protect the bag from rupture. The band-shaped peelable heat seal portion is configured exclusively as the place to generate peel energy, and the band-shaped peelable seal is not necessarily required to be complete seal (see FIG. 13).

(34) The width and the depth of the linear seal formed by the linear rib of die roll fundamentally agrees with the width and the height of the linear rib. The width of the linear seal is about 0.05-2 mm, preferably about 0.1-1.5 mm, and the depth is about 0.05-2 mm, preferably 0.1-0.8 mm.

(35) The linear seal portion is enough to achieve sealing, and a suitable adhesive strength is about 2-15 N/15 mm, preferably about 2-12 N/15 mm.

(36) The linear seal is provided in the band-shaped peelable heat seal in its longitudinal direction, and it is preferred to be located not at the center of the band-shaped peelable heat seal but on the side of the outer edge, for example, preferably in the range of about 60-90%, preferably about 60-80% of the total width from the inner edge with keeping at least 5 mm. (Patent Document 4)

(37) The number of the linear seals is basically one, but it is possible to provide plurality, such as two lines or three lines, with increasing local press load, within the range where the function and effects of at least one embodiment is not harmed.

(38) In the case that the heat seal area is curved, it is preferred that the curve pattern of the single linear rib is synchronized with the entry of work, and the linear seal is provided along the curve.

(39) The heat-sealing apparatus of at least one embodiment is to form the composite heat seal structure as above, and comprises a belt conveying, heating and press bonding portion and a die roll press bonding portion.

(40) The belt conveying, heating and press bonding portion is an area to heat a heat-sealing material so as to form the composite heat seal having a predetermined heat seal strength at the next die roll press bonding portion, and is composed of a pair of belts, each of which is engaged by rolls and travels therebetween, and a heating body which is located with a space from the belt.

(41) The number of rolls is basically 2 per each belt, accordingly, the total number is 4. The rolls on the side of entrance of the heat seal material are preferably disposed slightly apart from each other so as to facilitate entering the heat seal material. Whereas, in the area where the heat seal material passes through the heating body portion, the space between both belts is made smaller than the thickness of the heat seal material so as to apply press bonding pressure between the belts.

(42) For that purpose, guide rolls to regulate the space on the entrance side of the heat seal material can be provided on the entrance side to the heating body. Guide rolls can be further provided on the exit side. Usually, one of the rolls engaging the belt is a drive roll, and the other is a follower roll.

(43) The drive roll is provided with a rotation speed control mechanism so as to change traveling speed. Moreover, one or both rolls are made movable in the direction perpendicular to the traveling direction to control the space between the rolls so as to change the press bonding pressure applied to the heat seal material. In the case of providing the guide rolls, it is also to control the space between the guide rolls.

(44) The belt may be conventional, such as polytetrafluoroethylene impregnated glass-wool woven fabric, but that made of metal is preferred in order to raise thermal efficiency.

(45) This was demonstrated by measuring a response of welding face temperature with a gap of 0.1 mm using a polytetrafluoroethylene impregnated glass-wool woven fabric 0.25 mm in thickness as a representative conventional belt and a stainless steel sheet 0.04 mm in thickness as a representative metal belt. The press bonding pressure was varied at 0.03 MPa, 0.09 MPa, 0.18 MPa, and the response was measured by applying the MTMS kit (JP 3465741). The results are shown in FIG. 6.

(46) As shown in the figure, it can be seen that the response of polytetrafluoroethylene with a gap of 0.1 mm (not in contact) is considerably slower than the other measured results. In the press bonding pressure from 0.03 MPa to 0.09 MPa, the responses of welding face temperature are faster. As far as heating response, high press bonding pressure is effective.

(47) When the effect of the press bonding pressure raising the heating response is reviewed by the sliding frictional force which is another parameter, as shown in FIG. 5, it can be seen that there is a great problem with increasing the press bonding pressure.

(48) The come up time (CUT) of the non-contact welding face temperature response of stainless steel sheet 0.04 mm applicable to the belt material is demonstrated to be about 0.7 second, and it is much faster than the response of polytetrafluoroethylene impregnated sheet 0.25 mm at a press bonding pressure of 0.18 MPa. Since the frictional force of stainless steel sheet is very great under pressing, there is a problem with practicability is its use. However, under non-contact conditions, in frictional force is zero, and therefore, the problem of the metal belt is solved. As a whole, the superiority of the belt made of metal, represented by stainless sheet was confirmed.

(49) The belt made of metal is formed by a high heat-conductive material which is resistant to rusting under heating at about 200° C., such as stainless steel, aluminum or brass, and the thickness is about 0.01 to 0.2 mm. The width is the same as the heat seal width or slightly wider than it. Since the heat seal width is usually about 5-20 mm, a suitable belt width is about 5-25 mm. As to the surface, both surfaces are smooth.

(50) The heating body is to heat the heat seal material through the belt, and commonly formed of a heat-conductive material resistant to rusting under heating at about 250° C., such as stainless steel, aluminum or brass. As the heat source of the heating body, an electric heater is commonly used, and is set on the inside of the heating body.

(51) The heating surface of the heating body is made in a form of long rectangle, and the length is set so that necessary heating can be achieved. The width is, in general, made greater than the heat seal width by about 5-10 mm.

(52) The heating body is located with a space from the belt, in order to prevent it from damaging by the sliding of belt. The space is set to render the press bonding pressure between the belt and the heating body 0.02 MPa or less, preferably 0.01 MPa or less. When the space is too great, heat efficiency is degraded. Therefore, the upper limit of the space is about 0.2 mm, preferably about 0.1 mm. For that purpose, it is preferably to provide a mechanism of moving the heating body to adjust the space from the belt.

(53) The die roll press bonding portion is an area to form the composite heat seal structure by press bonding the heat seal material of which the prescribed portion has been heated in the belt conveying, heating and press bonding portion, and is composed of a linear roll and an elastic roll.

(54) The linear roll is a rigid roll made of a metal, such as stainless steel or brass, or a ceramic, coated with polytetrafluoroethylene, DLC or the like.

(55) The diameter is about 40 to 100 mm, and the width of the surface to be in contact with the elastic roll is identical with the width the band-shaped peelable seal. The height and width of the linear rib are allowed to agree with the linear seal to be formed.

(56) Although the linear roll may be provided with a heating mechanism, it is not so effective because the time in contact with heat seal material is shorter than the heat response of the material. To raise temperature by the heat inertia caused by continuous operation is in a preferred direction.

(57) The elastic roll may be made of an elastic body as a whole, or may be a common roll of which the peripheral surface is covered with an elastic body sheet. The material of the elastic body may be any one having a necessary elasticity and resistance to heat-sealing temperature, and for example, silicone rubber can be employed. Preferred one has a thickness of about 3-5 mm and a hardness of about A 50-A 80.

(58) The diameter of the elastic roll is in general about 40-100 mm which is decided by considering the consumption of the elastic body during continuous operation. The width is preferably set so as to form margins of 2 mm or more on both sides where the linear roll does not press.

(59) At least, one of the linear roll or the elastic roll has a structure capable of moving freely in the vertical direction under a necessary load so that they accommodate the total variation of the thickness of heat seal material and deformation of the elastic roll by compression. Moreover, they are arranged to adjust the press bonding pressure to a prescribed value.

(60) Both of the linear roll and the elastic roll are driven at the same number of revolutions so as to be conformed to the traveling speed of the heat seal material conveyed from the belt conveying, heating and press bonding portion.

(61) It needs that the peripheral speed of the die roll is exactly matched with the speed of the conveying belt, and therefore, the same driving source is used of the belt and the die roll, or the number of revolution is electrically controlled.

(62) Incidentally, the inventor found that temperature of the heat seal material descends between the belt conveying, heating and press bonding portion and the die roll press bonding portion, and this is possible to become a problem upon heat-sealing. Namely, the heat seal material is transferred from the belt conveying, heating and press bonding portion to the die roll press bonding portion through a space. The temperature lowering of the heat seal material therebetween was measured, and the results are shown in FIG. 7.

(63) In order to achieve the anticipated seal surely, it is necessary to restrain the temperature lowering within 2° C. than the set value of the welding face temperature at the heating portion. The temperature lowering was 0.4 s/2° C. in the exposed state at room temperature, and was 1.1 s/2° C. in the case of keeping the temperature at the temperature of the belt. Thus, it was found that the heat-sealing of at least one embodiment can be ensured by the protection to keep the temperature. (see FIG. 7)

(64) The discharge speed of heat seal material varies according to the prescribed conditions of heating at the belt conveying, heating and press bonding portion. The relationship between the diameter of the die roll and the transit time of transfer dimension (the length of temperature keeping space) from the drive roll 31 was pursued by trial calculation, and the results are shown in Table 1. The transit time is investigated in the case of the die roll diameter 50 mmφ.

(65) The transit time is 0.6 s for the belt speed 10 m/min, 1.0 s for 6 m/min and 1.6 s for 5 m/min. It was found that, in every case, the welding face temperature response is beyond the proper range by the transfer in exposed state, and therefore, it is difficult to complete bonding by the separated die roll. Using the belt speed of 1.0 s as a criterion, combinations of belt speed and roll diameter are divided by a bold line in Table 1. In the application range of belt speed and roll diameter which are commonly used, active temperature keeping having a heating function is required.

(66) Temperature keeping plates which were connected to a heat source were provided. The gap between each temperature keeping plate and heat seal material was made 2-5 mm so as not to restrain the transfer of the heat seal material. The heating by the temperature keeping plates is enough to be set at a temperature higher than the welding face temperature at the belt conveying, heating and press bonding portion by about 5° C. and precise temperature control is not required.

(67) By the construction of the temperature keeping plate, the single linear seal and planar press bonding can be ensured even under low speed operation conditions.

(68) The heat-sealing with the composite structure using such an apparatus is conducted by heating the heat seal material to be rendered at a proper temperature in the belt conveying, heating and press bonding portion, and by pressing it to be rendered at a proper press bonding in the die roll press bonding portion.

(69) The heating conditions are different according to heat seal material, temperature and length of heating body, and conveying speed.

(70) TABLE-US-00001 TABLE 1 Roll Belt speed (m/min) diameter Temp. keeping [In frame is transit time of temp. keeping space (s)] (mm) space (mm) 1 2 3 4 5 6 7 8 9 10  20  40  2.4 1.2 0.8 0.6 0.48 0.4 0.34 0.30 0.27 0.24  30  60  3.6 1.8 1.2 0.9 0.72 0.6 0.51 0.45 0.41 0.36  40  80  4.8 2.4 1.6 1.2 0.96 0.8 0.68 0.60 0.54 0.48  50 100  6.0 3.0 2.0 1.5 1.20 1.0 0.85 0.75 0.68 0.60  60 120  7.2 3.6 2.4 1.8 1.44 1.2 1.02 0.90 0.81 0.72  70 140  8.4 4.2 2.8 2.1 0.81 1.4 1.19 1.05 0.95 0.84  80 160  9.6 4.8 3.2 2.4 1.92 1.6 1.36 1.20 1.08 0.96  90 180 10.8 5.4 3.6 2.7 2.16 1.8 1.53 1.35 1.22 1.08 100 200 12.0 6.0 4.0 3.0 2.40 2.0 1.70 1.50 1.35 1.20

(71) Referring to the response of welding face temperature of the heat seal material, the combination of the length of heating body and belt speed is selected to decide heating time by the following formula:

(72) Provided that ⋅Length of heating body: L (m), ⋅Conveying speed of belt: V (m/s), ⋅Necessary heating time: t (s) (measured by utilizing “MTMS” kit)
[Mathematical 2]
t=L/N (s)  (1)

(73) It is necessary that this time is longer that the response time set from the integrated welding face temperature response of the belt material and the heat seal material.

(74) If the heat transfer (heating during sliding) between heating body and belt is carried out equivalent to the heating jaw system, the heating mechanism of the band sealer can be developed equivalent to the theory of the heating jaw system.

(75) The response of welding face temperature can be measured by using the surface temperature of heating body as a parameter. The model is shown in FIG. 8.

(76) The response of welding face temperature becomes finally asymptotic. But, it becomes an asymptotic line at the arrival point, and it is actually difficult to define the response.

(77) Then, the inventor defines CUT (Come Up Time) by employing 95% arrival time.

(78) Provided that ⋅Arrival temperature of welding face temperature response (equilibrium temperature); Te, ⋅Start temperature (room temperature); Tr,
[Mathematical 3]
T.sub.95=(Te−Tr)×0.95+Tr  (2)

(79) The time to arrive at T.sub.95 is read from the data of welding surface temperature response obtained by using “MTMS” kit to get the CUT value.

(80) In the case of Tr; 20° C., Te; 120° C., 150° C., T.sub.95 is calculated to obtain 115° C., 143.5° C. The difference between the CUT are the equilibrium temperature is 5° C., 6.5° C.

(81) In the case of practicing heat bonding (heat-sealing), referring to the response characteristics like FIG. 8, T1 is selected which is near the target temperature and slightly higher (2-3° C.) than it, as the heating body surface temperature. Alternatively, a much higher temperature, such as T2 or T3 is employed, and the heating temperature is set by the time control at the time of passing T1.

(82) If the welding face temperature is selected around T1, it is characterized by a great allowance time against the necessary welding face temperature. Whereas, by the heating at a transient temperature on the high temperature side, the heating time is short, but the range of proper time becomes very narrow. Therefore, it requires a high degree time control, and has a defect that the finish is unstable.

(83) The heating time of one work is determined by the integration of three points, i.e. the length of heating body, belt speed and heat transfer response properties between sliding belt and work. The heating times determined by the relationship between the length of heating body and belt speed are shown in Table 2.

(84) Each passing (heating) time shown here decides the design conditions and operation conditions compared with the heat transfer response of belt and heat seal material described as above.

(85) Since the length of heating body is decided upon its manufacture, it cannot be selected in operation.

(86) In the case of the heating body having a length of 200 mm, when polytetrafluoroethylene belt 0.25 mm in thickness is used, and heating time of 3.0 s can be ensured by adjusting the press bonding pressure minor, the fastest belt speed (upper limit of the speed) is 4 m/min. The speed up more than this falls in transient heating conditions where heating conditions become unstable.

(87) TABLE-US-00002 TABLE 2 Table of passing (heating) times decided by heating body length and belt speed Table of passing (heating) time (s) Heating body Belt speed (m/min.) length (mm) 1 2 3 4 5 6 7 8 100  6.0  3.0 2.0 1.5 1.2 1.0 0.85 0.75 200 12.0  6.0 4.0 3.0 2.4 2.0 1.7  1.5  300 18.0  9.0 6.0 4.5 3.6 3.0 2.6  2.3  400 24.0 12.0 8.0 6.0 4.8 4.0 3.4  3.0 

(88) In the case of non-contact stainless steel sheet system, since 1 s of the heating time can be applied, the speed of the belt can be extended to 6 m/min for the length of heating body of 100 mm. For 200-400 mm, speed up to 8 m/min or more is possible.

(89) Thus, it could be proved the superiority of the non-contact system of sliding belt by the separation of heating and press bonding functions of at least one embodiment. Even in a low speed range, there is no problem if a countermeasure against temperature lowering of heat seal material is provided, such as by mounting a temperature keeping plate 41.

(90) Moreover, the press bonding pressure at the die roll press bonding portion is also different according to the heat seal material and heating temperature (softening properties).

(91) The sealing at a flexed portion by plastic deformation varies according to each material. The sealing stress at the flexed portion is measured by the test developed by the inventor, shown in FIG. 9.

(92) The temperature T° C. of a heating bar provided with a single linear rib in a form of a half circle 0.5 mm in height is raised gradually, and pressing strength is changed. Thus, a combination of the temperature and press bonding pressure capable sealing is investigated.

(93) The measured results are converted to linear load per 1 cm of single linear rib of the heating bar to seek standardization of the measured results.

(94) A specimen is folded back to construct two flexed portions, and a LLDPE film about 10 μm in thickness is put therebetween in contact with the specimen. The specimen is heated to the surface temperature of T° C., and pressing load is changed. A flaw detecting solution is dripped to the flexed portion of the finished specimen, and the sealability is inspected visually using a loupe or microscope, according the evaluation technique developed by the inventor.

(95) The test was conducted using OPP (biaxially stretched polypropylene having Young's modulus of about 2,000) which is the hardest and most difficult to seal among the packaging materials supplied on the market, and the results are summarized in Table 3.

Application Example of Patent Document 3

(96) TABLE-US-00003 TABLE 3 Qualification test of sealability at flexed portion of highly rigid material (example) Heating temperature (band surface temp.) [° C.] 110 114 116 118 120 126 134 140— Established 120 83 42 42 31 31 26 Generation of strength of shrinkage in- seal (N/cm) applicable due to melted state Rupture Softening Eligible range Shrinkage begins begins Specimen material: OPP; 40 μm + Material to detect seal: LLDPE; 15 μm

(97) Linear load of 26-120 N/cm was applied at each heating temperature (surface temperature of heating body).

(98) From the results, it was found that when a high pressing load was applied at 110° C. where softening does not occur, the press bonding portion is whitened and crumbled, and it is difficult to seal out of softening temperature range.

(99) At 114° C. where softening begins, linear load of 83 N/cm was required.

(100) Further raising the temperature, the linear load was lowered to 42 N/cm from 116° C., and sealing by practical load could be achieved. Since the material was biaxially stretched, shrinkage occurred at a temperature to close its melting point. Therefore, the upper limit of applicable temperature is around 140° C.

(101) It was found that the applicable temperature range is from 116 to less than 140° C. only for the purpose of sealing.

Embodiments

(102) A side view of a schematic structure of a heat-sealing apparatus which is at least one embodiment of the present application is illustrated in FIG. 10, and a front view of the die roll press bonding portion thereof is illustrated in FIG. 11.

(103) The belt conveying, heating and press bonding portion 3 is composed of a pair of belts 33 made of stainless steel 0.04 mm in thickness which is engaged between rolls 31, 32 and travels, and heating bodies 34 disposed with a space of 0.1 mm from the belt 33, respectively.

(104) In the case of the heating body having a length of 200 mm, when polytetrafluoroethylene belt 0.25 mm in thickness is used, and heating time of 3.0 s can be ensured by adjusting to the minor press bonding pressure, the fastest belt speed (upper limit of the speed) is 4 m/min. The speeding up more than this falls in transient heating conditions where heating conditions become unstable.

(105) Both of the rolls 31 on the left side in FIG. 10 are drive rolls and the rolls 32 on the right side are follower rolls. The drive rolls 31 and the follower rolls 32 facing each other respectively are rendered to adjust the space to vary the press bonding pressure applied on work 1. The drive rolls 31 are designed to change rotation speed to change traveling speed of work 1.

(106) Both heating bodies 34 are in a form of rectangular parallelepiped having a length of 200 mm, and a heater 341 is embedded on the inside. A heating pipe 342 and a sensor 343 to measure surface temperature of the heating body are further embedded on the side of belt surface.

(107) Both heating bodies 34 are designed to adjust the space from the belt 33.

(108) The die roll press bonding portion 2 is composed of a linear roll 21, of which the peripheral surface, a single linear rib having a section of half circle 0.3 mm in height is provided, and an elastic roll 22. The elastic roll 22 has a width of 25 mm and has a structure made of a common roll which is covered with a sheet of silicone rubber elastic body 221 4 mm in thickness having a hardness of A 70.

(109) The linear roll 21 has a width of 20 mm and a diameter of 50 mmφ. As shown in FIG. 11, a press bonding pressure adjusting spring 23 is attached to the shaft, and thereby, the press bonding pressure of the linear roll 21 can be adjusted by the application of spring pressure.

(110) By using an air cylinder as the pressing apparatus, press bonding load can be adjusted easily by the control of air pressure. Furthermore, automatic vertical motion can be made under constant press bonding. Moreover, upon standing by the operation, the elastic roll 22 can be released from the load easily to decrease the wear of the elastic roll.

(111) The linear roll 21 and the elastic roll 22 are engaged by a gear to synchronize their rotation. As a drive source, motor capable of conducting fine adjustment electrically is used, and their speed is agreed with the entering speed of work.

(112) Between the belt conveying, heating and press bonding portion and the die roll press bonding portion, a temperature keeping portion 4 is provided.

(113) This temperature keeping portion 4 has, of which the section is as shown in FIG. 12, a structure where two temperature keeping plates 41 are disposed in parallel on the upper and lower sides, and the right sides of the plates are fixed by a heating body including a heater 421, and the outer surface is covered by a temperature keeping material 43.

(114) When heat-sealing is carried out using the apparatus as above, first, work 1 is conveyed from the right side in FIG. 10 followed by the arrow dotted line and entered from the space between rolls 32, 32. Then, while it is nipped by a pair of the belts 33, 33 and conveyed, it is heated from the upper and lower sides by the heating bodies 34, 34, and the heat seal layers are softened to be made into an interfacial bonding state.

(115) Subsequently, the work 1 is released from the rolls 31, 31, and delivered to the die roll press bonding portion 2 while the temperature is kept by temperature keeping plates 41. Then, the work 1 is pressed by the linear roll 21 and the elastic roll 22, and is locally sunk into the elastic body 221 by the single linear rib 211 to form a single linear seal and transfers to press bonding of planar portions. 2 sheet portions are press bonded by the elastic body caused by its fluidity deformation corresponding to the difference in step between a 4 sheet portion and 2 sheet portions.

(116) A laminated sheet composed of OPP 25 μm in thickness and an agglomeration destructed sealant 30 μm in thickness was used as a heat seal material to which Patent Document 3 was applied.

(117) This was heated at 123° C. as the heating body surface temperature, at a conveying speed of 4 m/min for 3 seconds in the belt conveying, heating and press bonding portion, and the heat seal material discharged after 1.5 seconds from the temperature keeping plates was press bonded to form a composite heat seal structure at a press bonding pressure of 40 N/cm (die roll press bonding linear load 40 N) in the die roll press bonding portion. It is the characteristics of at least one embodiment that since press bonding is carried out separately by utilizing linear deformation, it is enough only by the application of press bonding properties to seal, irrespective of the heat seal size of packaging bag.

(118) As to the heat seal, the total width of band-shaped portions was 15 mm and the width of linear seal portion was 0.3 mm, and the heat seal was peelable seal capable of opening at about 8 N by nipping to pull it. A flaw detecting solution was dropped on the inside heat seal line to confirm the complete seal by the single linear seal in the whole heat seal area including step portions. A photograph of the state is shown in FIG. 13.

INDUSTRIAL APPLICABILITY

(119) The heat-sealing apparatus and the heat-sealing method of at least one embodiment can be sealed efficiently even a packaging bag having a step portion on the heat seal surface, such as pillow type bag or a gusset bag, and they can be utilized widely for the heat-sealing of packaging bags, etc.

DESCRIPTION OF REFERENCE SINGS

(120) 1 Heat seal material (work) 2 Die roll press bonding portion 21 Linear roll 211 Single linear rib 22 Elastic roll 221 Elastic body 23 Press bonding pressure adjusting spring 3 Belt conveying, heating and press bonding portion 31 Drive roll 32 Follower roll 33 Belt 34 Heating body 341 Heater 342 Heating pipe 343 Heating body surface temperature sensor 4 Temperature keeping portion 41 Temperature keeping plate 42 Heating body 421 Heater 43 Temperature keeping material 5 Heating jaw type heat sealer 51 Heating body 511 Heater 512 Heating pipe 513 Temperature control sensor 514 Heating body surface temperature 52 Covering material 53 Intermittent motion 6 Band sealer 61 Drive roll 62 Sliding belt 63 Heating body 631 Heater 632 Heating pipe 633 Temperature control sensor 634 Heating body surface temperature 7 Welding face temperature