JPS6222845B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for heat sealing and heat shrinking films.

It is common practice to prevent contamination of articles to be exposed for sale by packaging each article in a sealed film of thermoplastic material. The standard method of packaging and sealing is to place the article on a film and wrap it. The final step in packaging technology is rolling or transporting the article to a hot plate or ultrasonic electrode so that an overlapping part of the packaging material lies between the flat surface of the article and the plate. . As a common modification, the film is heat-shrinked to the contour of the article by passing the article through a heat-shrink tunnel.
These two operations can be combined and performed by a single device. An example of such a conventional method is disclosed in Japanese Patent Publication No. 38-19199.

Problems to be Solved by the Invention According to the conventional method, when a product is wrapped in a film and heat-sealed and heat-shrinked by blowing high-temperature air, there is a risk that the film packaging becomes incomplete. That is, according to the conventional method, when wrapping a product with a film, the edges of the film are simply overlapped, and then hot air is blown over the film. As a result, the edges of the film may shift, making it impossible to properly connect and seal the edges of the film.
Furthermore, according to the conventional method, the edges of the film are heat-sealed and the entire film is heat-shrinked using a flow of high-temperature air from above. For this reason,
Heat shrinkage occurred before the edges of the film were properly heat-sealed, causing the edges of the film to shift and not be able to be properly heat-sealed.

Means for Solving the Problems According to the present invention, the above-mentioned problems are solved in a method for heat-sealing and heat-shrinking a biaxially oriented polymer film wrapped around a product in one operation: (a) (b) packaging the product in said film and overlapping the edges of said film on one surface of said product to form a package; and (b) placing said product face down on a conveyor allowing free flow of air from below. (c) conveying the package into a substantially air-locked tunnel; and (d) directing a jet of hot air through the conveyor and into the tunnel beneath the package. (e) sealing the package by applying the overlapping layers of the film to the facing surface, thereby bringing the overlapping layers of the film into close contact with the bottom surface of the product; (f) continuously forcing the hot air from within the tunnel while air is forced into the tunnel from below; and (g) cooling the film after the package is removed from the tunnel.

Further in accordance with the present invention, the method of the present invention as described above is provided in an apparatus for heat-sealing and heat-shrinking a biaxially oriented polymer film wrapped around a product in one operation, in which: (a) air is freely allowed to flow from below; (b) a substantially airlocked tunnel through which the conveyor and the packages thereon pass; and (c) a number of holes below the upper track of the conveyor and below the tunnel. (d) a fan; (e) a heater; (f) a duct for directing air from the fan to the bottom of the plate; by an apparatus for heat sealing and heat shrinking a film, the apparatus being arranged to heat air, and further comprising: (h) an air outlet from the tunnel to the inlet of the fan; This is preferably carried out.

The first step toward overcoming the difficulties previously found is to use films that can withstand higher temperatures. One such film is a biaxially oriented polyolefin that has been cross-linked by radiation. Compared to previously used films, such film materials are stronger and have higher shrinkage, so they will pull down to irregularities on the article to be packaged. It also has the useful property of being stable in its new form after heat shrinkage,
Other films, on the other hand, tend to stretch and may therefore become loose on their contents. Because shrinkage, welding, and burnout temperatures are higher for irradiated films than for non-irradiated films, methods suitable for this irradiated film may not be suitable for other films.

Shrinkage tunnels are well known and known patterns and methods can be applied in the present invention. The heat for sealing and shrinking is carried by air, which is heated by electrically resistive elements and blown against the overlapping portions of the film to be sealed. By using hot air at a high rate per minute, the arrangement is such that heat is transferred from the air to the film very well. As a result, the sealing and shrinking is carried out so quickly that the conveyor passing the packages through the shrink tunnel can run faster and the output can be made much higher.

According to current practice, the air supply is divided into two streams. One stream provides a heat sealing jet while the other provides another heat shrinking jet. According to the invention, the air supply is not divided. The entire air is directed towards the heat sealing jet and the area to be sealed at the bottom of the package. The same air passes upward to form a curtain of hot air that surrounds the package and provides heat to shrink the film. The double-walled shrink tunnels traditionally used to direct air for heat shrinking are no longer used, and are no longer used to any significant extent, although previously promising prior to sealing. It has been found that pre-shrinking reduces the overlap of the film forming the seal and even opens up the gaps, effectively eliminating the seal.

The surfaces of the films that are welded together to form a seal must clearly contact each other. By placing the packaged articles on the overlapping portions of the film, the surfaces are at least made mutually consistent, but contact is ensured, especially when the articles are irregular, and with light article weights. It is difficult to do so. It has already been explained that shrinkage of the film brings the film face down into contact with the packaged article and thus other layers of the film, but shrinkage prior to sealing is undesirable. The various layers that are to be sealed together in this way may and often will not touch. According to the invention, the various layers of the film are secured with a jet of high velocity air, and sealing effectively over the entire surface and areas of the packaged article is essential, so that in practice the There must be a high velocity jet of hot air over one surface.

After sealing and shrinking, the film can be cooled at room temperature or with a stream of cold air. This may be conveniently done by incorporating a tunnel similar to the seal/shrink tunnel in the same device, but this is not required.

In the accompanying drawings, two tunnels are shown as two parts of a single device, through which the packaged articles pass without intermediate handling.
This has the following advantages: 1. Welding between the packages is prevented, 2. The seals are hardened before handling the packages, and 3. Workers' hands are prevented from getting burnt.

EXAMPLE The illustrated device is constructed by means of a frame structure, which can advantageously be made from steel angles 3.
Supports a horizontal use surface 1. Juan 5 and 7,
Drive motors 9, 10 and 11 and other accessories are contained within the frame structure. The frame structure is surrounded by panels 13. Panel 13
can be made from stainless steel or other materials that are satisfactory in terms of hygiene and maintenance. The illustrated fan and motor arrangement has been found to be convenient for maintenance. Other arrangements can also be adopted.

Canopy 15 is suitably insulated and covers a portion of the sealing and shrinking use surface, and when the cooling device is incorporated into the sealing/shrinking device, second canopy 17 covers the cooling zone. Each canopy forms a tunnel with openings to the left and right in FIG. The opening is covered with a curtain made of a soft, heat-resistant material, such as silicone rubber or polytetrafluoroethylene. The inner curtain 21 further isolates the hottest zone. The curtains are supported by a frame, such as 23, from which they can be slid off for cleaning.

The packaged articles are conveyed through one or two tunnels by a conveyor. The packaged articles are placed on the stack of film and placed at the end of the conveyor. The end of the conveyor is on the left in FIG. 1 and moves continuously to the right. For packaging the cut meat pieces, the conveyor is conveniently 75 cm wide, which provides space for four normal cut meat pieces side by side. For larger articles, the conveyor can of course be wider than this. It must be able to withstand temperatures of at least 250 ° C, must allow free passage of air from below, and must be hygienic.

A conveyor that has been found to be suitable is indicated at 25. This is a belt consisting of horizontal bars approximately 1 cm in diameter between links similar to those used in motorcycle chains. Chains move at high speeds and support significant loads, so
Requires support. Metal passages may be unsatisfactory since small pieces of metal can wear out and contaminate the package. What has proven convenient is a system of channels 26, which are L-shaped in cross-section and made from a non-metallic material capable of withstanding high temperatures. A variety of proprietary materials for use in support are satisfactory.

The rod can be coated with a material such as silicone rubber to which the film material will not adhere. Ordinary means, e.g. 27
Means as shown adjusts the tension in the chain.
11 3/4 horsepower motor operating at 1400 rpm
is a variable gear (not shown) and sprocket 2
9 drives the chain at a speed of up to 30 m/min. Guard plate 31 keeps workers away from the machine.

Hot air for sealing and shrinking is 2 horsepower;
It is supplied by a fan 5 driven by a motor 9 at 2800 rpm through a V-shaped belt and a pulley, which sets the air velocity at the package to be sealed between 500 m/min and 3000 m/min. selected. For economic reasons and to facilitate reaching the required high temperatures, hot air is circulated in a closed system. The fan has 3 primary heaters.
3 into the tunnel inlet duct containing the secondary heater 35 and thence into the sealing/shrinking tunnel 37;
It then discharges through holes 39 in the tunnel floor to the exit duct. Curtains 19 and 21 minimize loss of hot air. Heat with sealer fan 5
Further conservation can be achieved by delaying the inlet and outlet ducts with ceramic fiber blankets (not shown).

Heaters 33 and 35 are divided into two groups. One group is rated for 4.5KW and is permanently connected. The other group is rated at 13.5KW and is limited by an adjustable temperature controller (not shown). The temperature is indicated by a vapor pressure thermometer 40 in the tunnel.

An important part of the invention is the method by which hot air is provided to the package to be sealed and heat-shrinked. As already mentioned, hot air is distributed at the bottom of the packaging,
That is, it is sprayed at high speed onto the stacked portions of the packaging material. What is required is a jet that is approximately uniform across the bottom of each package so that the film is propelled against the bottom of the product and against the stacked surface of the film, and the packages are stacked. It will seal very quickly over the exposed area. The hot high velocity air continues to rise around the package and the film is shrunk on all sides. In order to induce the necessary distribution of hot air, the floor of the seal/shrink tunnel has a row of holes and is a plate 41 located between the inlet duct and the conveyor 25. Each hole is at least 9 mm in diameter and the hole spacing is approximately 50 mm. The holes can be individually plugged to provide optimum distribution of air across the bottom of the package to be sealed. Generally, what is required is a uniform distribution over the bottom, but whether this is suitable in each case depends on the shape of the package and can be found by simple experimentation.

Due to the high velocity of the air entering the tunnel through which it passes and the large holes in plate 41, the rate at which hot air enters the tunnel is high. This speed is
It has been found that the air should exceed 25 m ³ /min per m ² of conveyor through which it passes. This high flow rate is
In combination with the high temperature of the air, as already mentioned, heat is transferred from the air to the package very well.

The jet plate lies below the rod of the conveyor 25 and is therefore difficult to clean. An effective plate 43 is attached to the top of plate 41 and correspondingly drilled with holes. The plate 43 can be slid off the tunnel and cleaning is thus facilitated.

Conveyor belt speed and air temperature and speed are interrelated. For normal meat slices, the belt speed is up to 30m/min, the air temperature at the seal is 120℃~250℃ and the air velocity is
It was found that it can be between 500m/min and 3000m/min. At a belt speed of 12 m/min, using a biaxially oriented polyolefin film cross-linked by radiation, the optimum temperature range is 200 m/min.
°C to 210 °C, and the amount of air required is from 17 m ³ /min at a pressure equal to 11 cm of water.
It was found to be 20m ³ /min.

As is clear from the drawing, the cooling tunnel 17,
The cooling fan 7 and the arrangement for supplying cooling air are comparable to those commonly used for sealing, but the fan and its motor are small and the air is drawn from the atmosphere or, if necessary, from some type of cooler. , taken in, and emitted into the atmosphere. Of course, there is no heating and the fan is not delayed. It was not found necessary to attach a perforated plate 43 to the cooling tunnel.

In use, the equipment will normally be fed from a charging conveyor and discharged to a table or conveyor. Auxiliary rollers, e.g.
It will be seen that what is indicated at 45 in the figure is advantageous.

Compared to existing methods and equipment, the present invention delivers hot film more forcefully and in a shorter amount of time per package so that the overlapped joint seals over an area and not just in high spots. be done. This prevents air from entering or exiting the meat and holds the film tightly against the tensile forces of contraction. Using the same strong supply of hot air, the film can also be shrunk much more completely than it currently does.

The thickness of the film is initially about 0.03 mm and increases to an average of about 0.08 mm and in some cases to 0.25 mm. At these thicknesses, the polyolefin films preferred for this invention are strong enough to remain intact even on the sharp edges of bone. moreover,
The film is pulled down over the surface of the meat. In test experiments, only approximately 1
It was found that % should be repackaged.

Because of the high speed of sealing and shrinkage, the conveyor belt speed can be increased from the conventional 7.5-9 m/min to more than 20 m/min. Additionally, the width of the belt can be increased, resulting in more product for a given length of seal/shrink tunnel.

Although the preferred film is one that is compatible with sealing at high temperatures, the apparatus and method can be modified only within a controlled manner to heat seal and shrink packages wrapped in low temperature sealing films. You will find that it can be used.

[Brief explanation of the drawing]

FIG. 1 further shows the drive arrangement for the sealing fan, and in FIGS. 2 and 3 line A--A
FIG. 2 is a partial schematic vertical cross-sectional view of one embodiment of the present invention in FIG. 2 is a cross-sectional view of the same embodiment taken along line BB in FIG. 1; FIG. FIG. 3 is a plan view of the embodiment with the lid removed. 1...Horizontal usage surface, 5, 7...Fan, 15...Canopy, 17...Second canopy, 25...Conveyor, 33...Primary heater, 35...Secondary heater,
37... Seal/contraction tunnel, 39... Hole, 41
...board.

Claims (1)

[Claims] 1. A method of heat-sealing and heat-shrinking a biaxially oriented polymer film wrapped around a product in one operation, comprising: (a) packaging the product within the film; overlapping the edges of the film at the surface to form a package; (b) placing the package with the surface down on a conveyor allowing free flow of air from below; (c) conveying the package into a substantially air-locked tunnel; (d) directing a jet of hot air through the conveyor and into the tunnel to overlapping layers of film on a downwardly facing surface of the package; (e) preventing the hot air from flowing upwardly and around the package; (f) continuously evacuating the hot air from within the tunnel while air is being forced into the tunnel from below; (g) allowing the package to shrink. A method of heat sealing and heat shrinking a film comprising cooling the film after exiting the tunnel. 2. The method according to claim 1, wherein the film is a polyolefin. 3. A method according to claim 1 or 2, wherein the package is cooled in another tunnel. 4. A method according to any one of claims 1 to 3, wherein heated air forced onto the conveyor by a fan is circulated from the tunnel to the air intake path of the fan. 5. The method according to any one of claims 1 to 4, wherein the product is meat. 6. An apparatus for heat-sealing and heat-shrinking biaxially oriented polymeric films wrapped around a product in one operation, comprising: (a) a horizontal conveyor through which air can flow freely from below; and (b) said conveyor and its a substantially airlocked tunnel through which the upper package passes; (c) a plate below the upper track of the conveyor and having a number of holes below the tunnel; (d) a fan; and (e) a heater. (f) a duct directing air from the fan to the bottom of the plate; (g) the heater positioned to heat the air before it reaches the plate; (h) and An apparatus for heat sealing and heat shrinking a film, further comprising an air outlet from the tunnel to an inlet of the fan. 7. In a patent claim in which the plate with said holes is overlaid by another plate with other holes which occupy the same space as these below, said other plate being removable for said cleaning. The device according to scope item 6. 8. An apparatus as claimed in claim 6 or claim 7, including another tunnel on the conveyor and directing cooling air to the packages as they pass through the tunnel.