JP2008189363A - Peeling and breaking seal mixture heat-sealing structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-sealing structure which does not generate resin balls, and also, by which broken bags or pin holes are hard to occur by dispersing a bag breaking stress, and which can perform heat-sealing at a high reliability with inexpensive packaging materials. <P>SOLUTION: This heat-sealing structure has a peeling seal strip and a breaking seal strip in the longitudinal direction of a belt-like heat-seal. The width of the peeling seal strip is 2 to 20 mm, and the width of the breaking seal strip is 1 to 10 mm. The ratio of the width of the peeling seal strip/the width of the breaking seal strip is 0.2 to 20 in the heat-sealing structure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat seal structure in which a peel seal and a tear seal are mixed on the heat bonding surface of a plastic heat seal.

  Heat sealing is applied to the production and sealing of bags and containers using plastic films and sheets.

  In the conventional heat seal, heating is performed in a high temperature region where the heat bonding layer becomes liquid, and the bonding surface is uniformly broken to form a seal.

  On the other hand, in addition to the above-mentioned tear seal, heat seal is also known to have a peel seal, and the inventor has studied the peel seal repeatedly and has filed patent applications (Patent Documents 1 and 2). )

  However, compared to tear seals, peeling seals have a narrower and more subtle heating temperature range. Conventionally, there has been no example of intentionally mixing this tear seal and peel seal, and the need to mix them is also known. It wasn't.

Japanese Patent No. 3811145 Patent No. 3876990

In a seal heated to the state of a conventional tear seal, a force is applied to the seal wire, the adhesive surface does not peel off, and tear occurs at the edge.
In the tear seal, the tear stress is received only at the edge of the heat seal line and not the entire surface.
In a high-temperature heating state in which the adhesive layer is in a liquid state, the adhesive layer melted by the pressure of the heating body protrudes into the heat seal line to form a polyball.

When an external force is applied to the sealed bag or container, it deforms non-uniformly, resulting in a tack with concentrated stress.
When the poly ball formed at the tip of the tack and the heat seal edge match, stress is concentrated on the fine surface, leading to the occurrence of bag breakage and pinholes.

  Conventionally, a thicker adhesive layer or a strong material is selected for this measure, but this method increases the material cost, extends the heating time, or raises the heating temperature. It is not a drastic improvement in the cause of pinholes.

  In the conventional heat sealing method of heating in the tear seal region, the adhesion surface becomes cohesive adhesion, and the tensile strength of the JIS method (Z0238) increases, but the bonding line does not have a destructive force buffering function, so When breaking stress concentrates, it is inevitable that bag breakage and pinholes occur, increasing the thickness of the material and selecting a strong material, which makes it impossible to use the average breakage resistance of packaging materials and increases costs. Yes.

On the other hand, the peel seal has a tensile strength that is lower than that of the seal, but when a fracture stress is applied, it causes interface peeling. Interfacial delamination consumes energy corresponding to the product of delamination strength and delamination area, and therefore has a function of absorbing and absorbing fracture stress.
However, the conventional heated material has a heating temperature zone where the peeling seal is manifested at several degrees Celsius, so there is no appropriate adjustment method and the peeling seal has been avoided.

  An object of the present invention is to provide a heat seal structure that does not generate polyballs, disperses the bag breaking stress, does not easily cause bag breaking or pinholes, and can be heat-sealed with an inexpensive packaging material with high reliability. There is.

  As a result of intensive studies to solve the above-described structure, the present inventor has considered to use a tear seal and a peel seal in combination by providing a peel seal band on the package side of the heat seal. However, this method is not practically realized by performing heat sealing twice. Therefore, further studies were made to develop a method in which the heat seal can be broken in one step to form a seal and a peel seal at the same time. First, a method of giving strength to the heating surface using two heaters was examined, but this could not set the boundary well. Next, a method of placing a base with a gradient on the heating body and forming a tear seal and a peel seal due to the pressure difference of the heat seal was studied. Although this method was successful, it was problematic because of its instability.

  Therefore, further investigation was conducted, and a method of mounting a table with different thermal conductivity on the surface of the heating body was considered, and as a result of repeated experiments, this method can accurately form a peel seal and a tear seal at a predetermined position. Based on this finding, the present invention has been completed.

  That is, the present invention has a peel seal band and a tear seal band in the longitudinal direction of the belt-shaped heat seal, the width of the peel seal band is 2 to 20 mm, the width of the tear seal band is 1 to 10 mm, and the peel seal band This relates to a heat seal structure in which the ratio of the width / breaking seal band width is 0.2-20.

  A region where the heat seal strength increases with increasing heating temperature is called a peel seal (as defined in ASTM F88-00), and the adhesion state is an interfacial adhesion state interfacial adhesion state. When the non-heat-sealed end of the piece heat-sealed by the peel seal is grasped and pulled, as shown in FIG. 1A, the heat-sealed piece does not break and the adhesive surface peels off.

  The region where the tensile strength exceeds the upper limit and becomes flat is called a tear seal (Tear Seal; ASTM F88-00 definition). In this heating region, the adhesive layer becomes liquid, and the adhesive layers on the two adhesive surfaces are mixed.

  In the tear seal, in the cooled state after heating, there is no bonded surface, and the heated part is thicker than the thickness before bonding, so that the bonded part has higher tensile strength than the other parts. The tensile test shows strong results. However, the adhesive layer that has become liquid easily protrudes unevenly at the heat seal edge due to the compression pressure and becomes a poly ball. When the non-heat-sealed end of the piece heat-sealed by this tear seal is grasped and pulled, as shown in FIG. 1 (b), breakage occurs in the immediate vicinity of the heat-sealed line.

  In the tensile test, since the breaking strength of the tearing seal is larger than that of the peeling seal, conventionally, the heating has been considered good. However, as shown in FIG. 2, when an external force is applied to the sealed bag or container, the bag or container is deformed non-uniformly, and thus a tack with concentrated stress is generated. If the poly ball formed on the tip of the tack and the heat seal edge coincide with each other, stress concentrates on a fine surface of 1 mm or less. Since the tear seal is in a state of cohesive adhesion, the fine parts are broken, leading to the origin of broken bags and the generation of pinholes.

  When a flat film or sheet is molded and filled with an article to be packaged, the volume increases, so that tack generation cannot be avoided. In the present invention, the bag breaking stress concentrated on the heat sealing allowance is first peeled off, and peeling is caused by interfacial adhesion of the sealing surface to absorb and buffer the breaking energy. Then, when the pressure-receiving line length of the bag breaking stress is increased to disperse the concentrated stress in a semicircular shape and the load per unit length is decreased, the progress of peeling is stopped. This situation is shown in FIG.

  When peeling progresses and reaches the vicinity of the outer edge of the seal allowance, the strong adhesive force tears to prevent the peeling and prevent the bag from breaking. The energy consumed during this time is broken and becomes several times the yield strength of the seal. In the heating method of the present invention, the peel seal and the tear seal are continuous. Therefore, since it is possible to reliably heat the boundary temperature of the optimum adhesion of the material, it is possible to prevent the formation of poly balls.

(1) Since heating at the boundary temperature between peeling and tearing can be ensured, an optimal adhesion state of the material can be achieved in the heat seal allowance.
(2) When a bag breaking stress larger than the tearing resistance is applied to the heat seal wire, the bag breaking energy can be consumed and buffered by the peeling energy, so that the occurrence of bag breaking and pinholes can be prevented.
(3) Since the temperature can be inclined on the heat seal surface, the peel seal and tear seal state can be made continuous from the inside of the bag or container, so the production of poly balls can be controlled.
(4) Since the bag breaking stress can be dispersed on the adhesive surface, it is possible to prevent the occurrence of defects with an inexpensive packaging material without having to select a material thickness or a strong material.
(5) Since heat seal adjustment can be performed by a rational method, reliability and improvement of heat seal reliability can be achieved.

  An example of the shape of the heat seal provided by the present invention is shown in FIG. The left side of the figure shows an example of a four-side seal bag, and the right side shows an example of a cup container. Needless to say, the three-side seal bag, the two-side seal bag, and only the mouth portion can be applied to the seal bag.

  The heat seal structure of the present invention has a peel seal band and a tear seal band in the longitudinal direction of the belt-shaped heat seal, but the peel seal band is disposed on the inner side (packaged side) and the tear seal band is disposed on the outer side. . Both seal bands are provided continuously unless there are special circumstances, and have a substantially uniform width (exaggerated in FIG. 3).

  The total heat seal width (heat seal allowance in FIG. 4) varies depending on the volume of the bag or container and the capacity of the package, and thus the material and thickness of the film or sheet to be heat sealed, but is usually about 3 to 30 mm. Most of about 5 to 20 mm is about 7 to 15 mm. The width of the peeling seal band is about 2 to 20 mm, preferably about 5 to 10 mm, and particularly preferably about 5 to 8 mm. This width is set in consideration of the range in which the effect of installing the peeling seal is broken and is equal to or twice the breaking energy of the seal, and the dimensions not exceeding the conventional heat seal allowance.

  On the other hand, the width of the tear seal band is about 1 to 10 mm, preferably about 2 to 5 mm, particularly preferably about 2 to 3 mm. This width is sufficient if there is an adhesive surface of 1 mm for the effect of tearing and sealing. However, in order to accurately perform the tear seal, it is preferable that there is a minimum of 2 mm in view of the positioning performance of the apparatus.

  Further, the ratio of the width of the peel seal band / the width of the tear seal band is about 0.2 to 20, preferably about 1 to 5, particularly preferably about 2 to 5 mm. As described above, the effect of consumption of the breaking energy at the peeling seal portion is equivalent to doubled when the peeling is 5 to 10 mm. This ratio is obtained when the dimension of the peel seal is considered based on 2 mm of the tear seal.

  Confirmation of the width of the peel seal band and the tear seal band is based on the heat seal peeling and tear identification method (Patent No. 3876990) and the method of determining the heat seal width (Patent No. 3811145), which the present inventor previously developed. Can be used.

  The heat seal having the structure of the present invention can be formed by using a surface of a heating body of a normal heat seal apparatus provided with a table having different thermal conductivity. That is, a base of a material having a high thermal conductivity is attached to a part where a tear seal is to be formed, and a base of a material having a low thermal conductivity is attached to a part where a peel seal is to be formed. A material with higher thermal conductivity than the heating element can be used for the part where the tear seal is to be formed. However, since the heating element is usually made of a material with higher thermal conductivity, it is the same as this. Material can be used.

  Therefore, a material having a low thermal conductivity (a base using this is referred to as a “heat flow control base”) is used at the site where the peel seal is to be formed. This material is not heat-denatured at the heat seal temperature. For example, a fluororesin such as polytetrafluoroethylene (trade name: Teflon), a sheet-like glass fiber impregnated with a fluororesin, or a sheet-like carbon fiber. A ceramic plate or the like is preferable. The thickness of the base varies depending on the material, the heat seal material, and the like, but may be about 0.1 to 2 mm, usually about 0.1 to 1 mm. Usually, there is no step or gap between the base on which the tear seal is to be formed and the base on which the tear seal is to be formed.

  When the same material as that of the heating element is used at the site where the tear seal is to be formed, a part of the heating element can be trimmed for the size of the heat flow adjusting table, and the heat flow adjusting table can be installed here.

  There are two types of members that can be used for pressure-bonding a material to be heated that is heat-sealed, and both of them are movable types. Further, only one of them may be a heated body, or both may be heated bodies. When both are heating bodies, the heat flow control stand of the present invention is usually provided in both, or on the other hand, it may be sufficient.

  FIG. 5 shows a schematic configuration of an example of such a heat sealing apparatus. In this apparatus, both members for pressure-bonding the heated material 6 are heating elements 1-1 and 1-2, electric heaters 2-1 and 2-2 are embedded therein, and a temperature sensor 3 is provided in the vicinity of the heating surface. -1, 3-2 are provided. The electric heaters 2-1 and 2-2 are each connected to a commercial power source via a switch. The temperature sensors 3-1 and 3-2 are connected to the temperature controller 4, and the temperature sensors 3-1 and 3-2 can control the temperature of the heating elements 1-1 and 1-2. (The heating element 1-2 is not shown). As shown on the right both sides of FIG. 5, on the heating surfaces of the heating elements 1-1 and 1-2, the heat flow control bases 5-1 and 5-2 are provided on the left half, and the tear seal is provided on the right half. The flat bases 7-1 and 7-2 to be formed are mounted.

  An enlarged view of the thermocompression bonding part is shown in FIG. In the figure, 1 indicates the thickness of the flat table 7-2 and the heat flow adjusting table 5-2, 2 indicates the tear seal width, and 3 indicates the peel seal width. The thicknesses of the plane table 7-1 and the heat flow control table 5-1 are also usually the same as those of 7-2 and the heat flow control table 5-2.

  When the present invention is applied to a plurality of bag making of two or more, as shown in FIG. 7, the flat bases 7-1 and 7-2 are provided at the center, and the heat flow control bases 5-1 and 5 are provided on both sides. -2 can be provided with a cutting line at the center.

An example in which the present invention is applied to an impulse seal is shown in FIG.
This apparatus includes a fixed base 11 and a vertical moving base 12 that is processed from above and presses the material 6 to be heated, and heat-resistant covers 13 and 14 are attached to the crimping surfaces of both bases 11 and 12. . On the fixed base 11, two heater wires 8 and 9 (only one in the prior art) are installed. As shown in FIG. 8, the two heater wires 8 and 9 are arranged close to each other with the same thickness, and the above-described material having low thermal conductivity, for example, a sheet of Teflon (registered trademark) or the like is used as the heat flow control sheet 10. In addition, one heater wire 9 is laid on the top surface, and the other heater wire 8 is laid on the bottom surface. By installing in this way, the generation of the heat flow difference and the two heater wires 8 and 9 are insulated so as not to cause a step on the surface. Although the heat flow can be adjusted by changing the thickness of the heat flow adjusting sheet, as shown in FIG. 8 (b), the two heater wires 8 and 9 are connected to separate power sources. And precise heating control by the energization time.

  In addition, in the case of ultrasonic seals and electric field seals, peel seals and tear seals can be mixed by installing two rows of heating operation units and adjusting the heating in the same manner as the impulse seal described above.

  In the case of a cup container as shown in the right drawing of FIG. 4, single-sided heating is performed, but in this case as well, a flat table and a heat flow control table are installed on the heating surface, and the set temperature of the heating body is higher than in the case of double-sided heating. Heat sealing can be performed at a high level.

Next, the formation method of the heat seal structure of this invention is demonstrated.
The heat sealing conditions vary depending on the material to be heat sealed. Therefore, first, the relationship between the welding surface temperature of the heat sealing material to be heat sealed and the tensile strength of the material crimped at that temperature is obtained. As a result, for example, the relationship shown in FIG. 9 is obtained.

  This is because if the temperature of the welding surface when the inside of the heat seal surface is heated is 144 ° C. and the temperature of the joint surface between the peel seal heating base and the tear seal heating base is 156 ° C., the heat seal of the peel seal band A continuous peel seal with a strength of 10 N / 15 mm to 50 N / 15 mm. Since the tear seal surface is 160 ° C., the tear seal is heated.

  The heat seal strength of the completed heat seal sample can be seen as a pattern in which the temperature scale from (b) to (a) is replaced with the heating width.

  Therefore, first, a heat flow control table is designed. The surface temperature of the heating elements 1-1 and 1-2 is set to be 3 to 5 ° C. higher than the above (a), and the thickness of the heat flow adjusting table made of the material to be used is changed from the outer edge of the heat flow adjusting table. The welding surface temperature sensor is sandwiched between the materials to be heated so that the welding surface temperature sensor is positioned at 1 mm and in the vicinity of the midpoint of the flat base margin, and the relationship between the pressure bonding time and the welding surface temperature is obtained. As a result, for example, a graph as shown in FIG. 10 is obtained. From this result, first, the time when the welding surface temperature reaches (a) when the heat flow adjusting table is not provided (line of all the pressure bonding surfaces in FIG. 10) is obtained, and this is set as the heat sealing pressure bonding time. And the thickness of the heat flow control stand which becomes the welding surface temperature which can form a peeling seal in this crimping time is selected. In the example of FIG. 9, the temperature at which the peel seal is formed is 144 to 153 ° C. Therefore, the thickness of the heat flow adjusting table corresponding to the lower limit of 144 ° C. is about the welding surface temperature within this temperature range in FIG. Set to about 0.3 mm.

  When the design of the heat flow adjusting table is completed in this way, the heat flow adjusting table and the flat table are attached to the heating surfaces of the heating elements 1-1 and 1-2, and heat sealing is performed to form the heat seal of the structure of the present invention. can do. What is necessary is just to use those in the design of said heat flow control stand for the setting temperature and crimping | compression-bonding time of the heating bodies 1-1 and 1-2 in that case.

  As the material to be heated 6, a packaging material with a total thickness of 0.09 mm, which is used in retort packaging on the market, is used, and the relationship between the welding surface temperature and the tensile strength is patented. It calculated | required by the method of 3465741 description, and the result shown in FIG. 9 was obtained. From this result, the welding surface temperature was set to 160 ° C. ((a) in the figure) as the lowest temperature at which a torn seal could be reliably obtained.

A heat sealing apparatus having the configuration shown in FIG. 5 was used. Each of the heating elements 1-1 and 1-2 of this apparatus has a length of 3.5 cm, a width of 3 cm, a length of 20 cm, and a heating surface cost of 1.7 cm, and this is 400 w, a thickness of 0.8 cm, and a length. 20 cm electric heaters 2-1 and 2-2 were attached. In order to reduce the temperature unevenness in the length direction, a heat pipe (not shown) was mounted between the electric heaters 2-1 and 2-2 and the surfaces of the heating elements 1-1 and 1-2. As the temperature sensors 3-1 and 3-2, a fine electric cane having a wire diameter of 0.2 mm was used. The electric heaters 2-1 and 2-2 were adjusted by an ON-OFF method having a PID function. The welding surface temperature was measured with the apparatus used in Japanese Patent No. 3465741.

  The set temperature of the heating elements 1-1 and 1-2 is set to 165 ° C., and a Teflon (registered trademark) sheet having a thickness of 0.2 mm, 0.3 mm, or 0.4 mm is attached to each sample as a heat flow control table. The weld surface temperature at the center of the flat table and 1 mm from the outer edge of the heat flow control table was measured with the two sensors interposed. The result is shown in FIG. The thickness of the heat flow adjusting table was determined to be 0.3 mm, and the heating time was determined to be 0.38 seconds.

  Therefore, on both heating surfaces of the heating elements 1-1 and 1-2, a 0.3 mm Teflon sheet is 9 mm wide (3 in FIG. 6), and the remainder is a stainless steel sheet of the same material as the 0.3 mm heating body. (2 in FIG. 6) 5 mm was attached.

Using this heat sealing apparatus, heat sealing was performed under the following conditions.
Heater surface temperature: 165 ° C
Crimping time: 0.38 seconds Heat flow control base material: Teflon (registered trademark)
Heat flow control stand thickness (1): 0.3 mm
Peel off seal (3): 9mm
Tear seal allowance (2): 5mm
Initial pressure bonding pressure: 0.1 Mpa

  The result of the tensile test of the obtained mixed heat seal sample of peel seal and tear seal is shown by a solid line in FIG. The result of a similar tensile test performed on a heat seal sample with only a tear seal performed at 170 ° C. based on the result of thermal analysis without providing a heat flow adjusting table is also shown by a broken line in FIG.

  As shown in FIG. 11, in the hybrid heat seal of the present invention, the rising was slow and the adhesion surface peeling was clearly observed. The tensile strength was 57 N / 15 mm, which was the maximum value, and the peeling progressed and the film was broken at about 0.85 cm (d) in the seal area. Up to about 0.8 cm, it was a good peel seal at the boundary region between the peel seal and the tear seal.

  On the other hand, the heat seal sample with only a tear seal has a fast rise, reaches the yield point (c) with a peel dimension of 0.35 cm, and breaks at a tensile strength of 51 N / 15 mm, which is smaller than the tensile strength of the boundary region of the present invention. did.

  The tensile strength at each point is a response to a small tensile change at each point. That is, the work amount at each measurement point is the sum of up to the fracture of [(strength; N) × (tensile distance between samplings)] / [(tensile speed) × 15 mm]. If the pulling speeds are the same, the present invention and the conventional heat seal surface breakage protection can be compared by indexing comparison of the calculation area. In order to evaluate the superiority, from the results shown in FIG. 9, the integration of the conventional method was performed at point (c), and the integration range of the hybrid method of the present invention was performed up to (d) point. The conventional method obtained 9.9, and the hybrid method obtained 41.

  Since this numerical value can be evaluated by replacing it with the energy consumption ability with respect to the external stress of the bonding surface, even if the bonding surface is partially peeled off by hybrid heating, it can be evaluated that the heat seal allowance is functioning effectively for bag breakage prevention.

  The heat seal structure of the present invention has the advantages that the heat seal edge can be prevented from being broken and broken, it is not necessary to increase the thickness of the material to prevent breakage, and the reliability of the heat seal can be assured. There is a possibility to replace heat sealing.

It is a schematic diagram which shows the state of the tearing seal in a tension test. It is a schematic diagram explaining the stress concerning a heat seal part by external pressure. It is a figure which illustrates typically a state when peeling stress is applied to the heat seal structure of this invention. It is a figure which shows the example of a heat seal shape. It is the figure which showed typically the example of the heat seal apparatus which forms the heat seal structure of this invention. It is the elements on larger scale of FIG. It is a figure which shows the state which manufactures a continuous bag with the heat seal structure of this invention. It is the figure which showed typically the other example of the heat seal apparatus which forms the heat seal structure of this invention. It is the graph which showed the change of the welding surface temperature and tensile strength at the time of heat-sealing. It is a graph which shows the crimping time change of the welding surface temperature by changing the thickness of a heat flow control stand. It is the graph which performed the tension test about the heat seal structure of this invention, and the conventional tear seal, and showed the change of peeling distance, and the change of tensile strength.

Explanation of symbols

1-1, 1-2 Heating body 2-1, 2-2 Electric heater 3-1, 3-2 Temperature sensor 4 Temperature controller 5-1, 5-2 Heat flow control base 6 Materials to be heated 7-1, 7 -2 Flat bases 8 and 9 Heater wire 10 Heat flow control sheet 11 Fixed base 12 Vertically movable bases 13 and 14 Heat resistant cover

Claims (2)

It has a peel seal band and a tear seal band in the longitudinal direction of the belt-shaped heat seal, the width of the peel seal band is 2 to 20 mm, the width of the tear seal band is 1 to 10 mm, and the width of the peel seal band / the tear seal band Heat seal structure with a width ratio of 0.2 to 20 A heat sealing apparatus, wherein at least two stands having different thermal conductivities are mounted in a longitudinal direction of a heating surface of a heating body.

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