JP4491424B2 - Heat sealing method - Google Patents

Description

  The present invention relates to a heat sealing method for plastic films and sheets.

  For the production of bags using plastic films and sheets, and for sealing after filling a product into a bag or container, heat sealing using the thermoplasticity of plastic is used.

An outline of a heat sealing method by heating and pressure contact is shown in FIG. In heat sealing, the heat seal layer 1 is brought into contact with the surface, the heating element 3 is brought into contact with the surface layer material 2, and the heat seal layer is heated by heat transfer.
In addition to this, there are also methods in which hot air, ultrasonic waves, electric fields, and magnetic fields are applied to directly heat the heat seal surface, or heat is generated by causing a heat generation phenomenon on the boundary surface.

  In any method, in order to complete heat bonding, it is necessary to set the upper limit of the heating temperature in consideration of the heat resistance of the material to be used, and then to heat the heat seal layer to near the melting temperature or higher.

However, the heat seal part sometimes causes white turbidity or bubbles to be taken in.
Conventionally, as countermeasures, the heat seal temperature has been lowered as much as possible, or a printing layer or an aluminum layer has been provided to shield or obscure them.

  The subject of this invention is providing the heat seal method which solves the problem of taking in of cloudiness and a bubble in a heat seal part.

  As a result of intensive studies to solve the above problems, the present inventor has found that the film material itself has a problem with the cloudiness and bubbles. That is, the solvent and unpolymerized components remain in the heat seal material, and this was vaporized by the heat at the time of heat sealing and foamed. In particular, when the object to be heat-sealed is a laminate including a hydrophilic layer such as polyamide or ethylene-vinyl alcohol copolymer, this hydrophilic layer tends to contain moisture, which is the heat at the time of heat sealing. Vaporizes and foams. Since the liquid vaporized, the volume was increased to about 1000 times, and even if it was a very small amount, a bubble that was visible to the eyes was formed to be clouded.

  And this white turbidity not only worsened the cosmetics, but also deteriorated the heat sealability.

  In view of this, the present inventor has considered increasing the pressure-bonding pressure at the time of heat sealing to suppress the vaporization of moisture as a countermeasure.

As a result, basically, by setting the pressure pressure in heat sealing to be equal to or higher than the water vapor pressure at the heat sealing temperature, not only moisture but also evaporation of solvents and unpolymerized components can be suppressed to solve the problem of bubble generation. did it. Further, when the heat seal temperature is lower than the melting point of the heat seal material, the heat seal material is not yet melted. I found that the problem can be avoided.
The present invention has been made on the basis of these findings, the pressure bonding in heat sealing,
(1) When the heat seal temperature is lower than the melting point of the heat seal material, the water vapor pressure at the heat seal temperature is -0.05 MPa or more,
(2) The present invention provides a heat sealing method characterized in that when the heat seal temperature is equal to or higher than the melting point of the heat seal material, the water vapor pressure at the heat seal temperature is set to 0.13 MPa or higher.

  According to the present invention, it is possible to solve the problem of bubble generation at the time of heat sealing and eliminate the deterioration of the cosmetics due to the generation of bubbles, as well as the deterioration of the heat sealability due to the generation of bubbles. In particular, when the heat seal material is transparent, the transparency of the heat seal portion can also be ensured.

  The kind of heat sealing object to which the present invention is applied is not particularly limited, and can be widely applied to films and sheets. The thickness of the film or sheet is not particularly limited, but is about 20 to 150 μm, usually about 30 to 120 μm.

  The film or sheet may be a single layer or a multilayer. In any case, at least one side is made of a heat seal material. The heat seal material may be a plastic, that is, a thermoplastic resin, but a typical one is a polyolefin, particularly polyethylene or polypropylene. The thickness of the heat sealing material is about 10 to 100 μm, and usually about 20 to 80 μm.

  Films and sheets are often combined with various layers from the viewpoints of improving barrier properties against moisture and oxygen, adjusting rigidity, improving puncture strength, printability, and the like. In some cases, a hydrophilic layer such as polyamide (trade name “nylon”) or ethylene / vinyl alcohol copolymer is incorporated. The inventor has found that the moisture contained in the hydrophilic layer is a major cause of foaming during heat sealing. This foaming problem is mainly a layer in which softening or melting occurs during heat sealing, and thus becomes a serious problem when the hydrophilic layer itself or an adjacent layer softens or melts.

  The apparatus used for the heat seal can be a commercially available one as it is or can be appropriately processed. However, it is preferable to use an apparatus having a reproducibility of the heating temperature of 1 to 3 ° C. and a reproducibility of the compression pressure of 0.01 to 0.05 MPa.

  Strictly speaking, the heat seal temperature in the present invention is the temperature of the heat seal surface of the heat seal material, but usually it is almost the same as the temperature of the heating element to be pressure-bonded, so this is used as the heat seal temperature. . The heat sealing temperature is set according to the purpose of the person performing the heat sealing, and the temperature can also be adopted in the heat sealing method of the present invention. As an example, it may be near the boundary temperature between the peel seal and the tear seal. This has been developed by the present inventor and is described in JP-A-2005-7844.

The method of the present invention is characterized by the pressure applied during heat sealing. That is, what is conventionally performed at about 0.20 MPa is set to a higher pressure for the pressure corresponding to the water vapor pressure at the heat seal temperature. This is to suppress foaming at the time of heat sealing, and since the ease of foaming varies depending on whether or not the heat sealing material is melted into a liquid state at the time of heat sealing, it can be divided into two . The upper limit of the pressure wearing pressure, the upper limit of heat-sealing can be maintained, i.e., an upper limit is not as heat-sealing material can not be maintained a heat seal is extruded from the heat sealed portion by crimping pressure.

  From such a point of view, a spacer can be provided between the heat generating elements that perform heat sealing to restrict the approach distance between the heat generating elements, thereby greatly increasing the upper limit of the pressure bonding pressure. The thickness of the spacer is determined from the range from the place where the heat seal materials are in contact with each other (this is 0%) to the place where the heat seal material is completely extruded (this is 100%). About 70%, preferably about 30-60% is appropriate.

  In addition, a mesh pattern can be applied to the heat seal portion in order to subdivide the remaining traces due to uneven pressure bonding during heat seal. That is, the pitch corresponding to the initial foam size so that the fine foam caused by the fine crimp unevenness caused by the thickness group of the heat sealing object, the surface group of the crimping surface, the deviation in parallelism, etc. does not grow and become large. This is applied to the surface of the pressure-bonded body to control dispersion. The mesh pattern preferably has a depth of about 1 to 30 μm.

  After heat sealing, it is preferable to cool quickly in order to suppress foaming. Examples of the cooling means include cold air suction and pressing of cooling blocks such as cooling rolls.

  The apparatus shown in FIG. 2 was used.

  This apparatus is composed of a pair of heating elements 3 and 3 that move and approach each other to perform heat sealing, and in each case, a heater 7 and a temperature sensor 8 are embedded (only one is shown). The temperature sensor 8 is connected to a temperature adjusting device 9, thereby controlling the heater 7 and adjusting the temperature of the heating element 3.

  A pressure device 10 is attached to one heating element 3, and a pressure source 11 is connected to the pressure device 10 by piping. By controlling this pressure source, the pressure for heat sealing can be adjusted.

  The heat sealing operation using this heat sealing apparatus is automatically performed as follows.

  First, the heater 7 is energized to adjust the surface temperatures of the heating elements 3 and 3 to the same predetermined temperature and wait.

  Next, the two laminated films 5 and 5 are transferred between the heating elements 3 and 3 with the heat seal layers 1 facing each other, and stopped.

  The heating elements 3 and 3 move forward to perform heat sealing and move backward.

  The laminated films 5 and 5 that have been heat-sealed move immediately and are cooled by the cooling press at the heat-sealed part, and the heat-sealing is completed.

The heat sealing test of the following laminated film 5 was done using this apparatus.
PET12μm / Nylon 15μm / CPP60μm
PET: Polyethylene terephthalate CPP: Unstretched polypropylene
Melting point 150 ° C, softening start temperature 138 ° C (actual measured value)
Nylon contains 10% by volume of water.
The pressure bonding time was set to 5 to 10 seconds by setting the heating element to the target temperature, and the foaming state of the heat seal part was evaluated by changing the heating temperature and pressure bonding pressure. The obtained results are shown in Table 1.

  Each heat seal state when it is obtained by the method of the present invention with increased pressure bonding pressure when it is performed at a pressure bonding pressure of 0.2 MPa is shown in the photograph of FIG. The crimping pressure in the method of the present invention is 0.3 MPa or higher at 145 ° C., 0.5 MPa or higher at 150 ° C., and 0.57 MPa or higher at 155 ° C.

  Next, FIG. 4 shows the results of measuring the tensile strength of heat sealing performed at a pressure of 0.2 MPa and heat sealing performed by adjusting the pressure of pressure while changing the heat sealing temperature. The tensile strength was measured according to JISZ0238. In the heat seal obtained by the method of the present invention, no bubbles were observed on the heat seal surface, whereas in the heat seal performed at a pressure of 0.2 MPa, the water vapor pressure of 0.2 MPa was 134 ° C., so the test temperature range In all, bubbles are generated in the heat seal portion, and the tensile strength is lower than that of the heat seal obtained in the present invention. From this result, it was also confirmed that the heat seal deterioration was improved by the present invention.

  In this case, as shown in FIG. 3, the spacer 4 was arranged on one heat generating body 3, and the lower limit of the crimping allowance was regulated to perform heat sealing. The height of the spacer 4 was the same as the total thickness of the two laminated films 5 and 5 and the total thickness was −20 μm and the total thickness was −40 μm.

  As a result, foaming was large in [0], and foaming was successfully suppressed in [-20 μm] and [−40 μm]. In [-20 μm], there was little protrusion of the adhesive layer. Since the heat seal layer of the test material is 60 μm, it was found that the pressure bonding allowance is preferably about 30 to 60% of the adhesive layer.

  Although the method of the present invention can be widely applied to a heat sealing method, a laminated film including a hydrophilic layer can be heat-sealed without causing a foaming problem, and thus is effective for heat-sealing this laminated film.

It is the schematic which shows a heat seal state. It is a figure which shows schematic structure of the heat seal used in the Example of this invention. It is a figure which shows the state which provided the heat generating body center spacer of FIG. It is a graph which shows the relationship between the tensile strength of each heat seal obtained by the method of this invention, and the conventional method, and heat seal temperature. It is a photograph which shows the state of each heat seal obtained by the method of this invention and the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat seal layer 2 Surface layer material 3 Heat generating body 4 Spacer 5 Laminated film 7 Heater 8 Temperature sensor 9 Temperature control apparatus 10 Pressurization apparatus 11 Pressure source

Claims (4)

Pressure bonding pressure in heat sealing
(1) When the heat seal temperature is lower than the melting point of the heat seal material, the water vapor pressure at the heat seal temperature is -0.05 MPa or more,
(2) When the heat seal temperature is equal to or higher than the melting point of the heat seal material, the water vapor pressure at the heat seal temperature is set to 0.13 MPa or higher.   2. The heat sealing method according to claim 1, wherein the object to be heat sealed is a laminated film including a hydrophilic layer.   The heat sealing method according to claim 1 or 2, wherein a pressure bonding allowance of the heat sealing portion is 20 to 70% of a layer thickness of the heat sealing material.   The heat sealing method according to claim 1, 2 or 3, wherein the heat sealing part is subjected to mesh processing.

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