METHOD AND APPARATUS FOR CONDITIONING OF CARDBOARD

A method and apparatus are disclosed for conditioning a corrugated cardboard stack by causing air to flow through flutes of the stack from an air intake end to an air discharge end of the stack, air moved by an air moving device being confined to flow only, or at least predominantly, through the flutes.

FIELD OF THE INVENTION

The invention relates to treatment of cardboard, in particular corrugated cardboard, for instance following processing in a conversion apparatus, in order to remove burn fumes and odor caused by laser cutting of the cardboard.

BACKGROUND OF THE INVENTION

The use of laser beams to cut and perforate cardboard (as used in conversion machines such as Highcon Euclid or Highcon Beam available from Highcon Systems Ltd. in Yavne, Israel) creates undesired fumes and odor due to the burning of the cardboard during the process. To reduce the odor, it is common practice to leave the cardboard to ventilate in free air. Even when fans or blowers are used to cause air circulation, it can take a day or more for the smell to be reduced to an acceptable level. Such a method is therefore not efficient, in particular for corrugated cardboard.

An alternative method is described in U.S. Pat. US 10,179,378, which describes removing the smell by heating the cardboard to a temperature as high as 150-260° C. using laser light or in an oven. Such a method is wasteful of energy and dries out the cardboard.

OBJECT OF THE INVENTION

The invention seeks to provide a method and apparatus for conditioning cardboard, by removing fumes and odor more effectively.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a method of conditioning a corrugated cardboard stack, which comprises causing air to flow through flutes of the stack from an air intake end to an air discharge end of the stack by confining air moved by an air moving device to flow only, or at least predominantly, through the flutes. The term “flutes” is used herein to describe the flow channels defined by the corrugations.

After treatment in a conversion machine, cardboard is commonly in the form of individual sheets and the cardboard stack may typically comprise several separate sheets placed one over the other. However, the term “cardboard stack” as used herein is also intended to include cardboard that is coiled into a roll having overlying, or stacked, layers rather than individual sheets and in the ensuing description all references to a stack should be regarded as including a roll.

The invention is predicated on the realisation that, when cardboard is exposed to fumes, such as the fumes that are created during laser cutting, they tend to permeate into the flutes defined by the corrugations. If, as has been the common practice in the past, a corrugated cardboard stack is merely placed in a room in which air circulates, the air flows predominantly around the outer surface of the stack, because it encounters far less resistance that when flowing through the flutes. By guiding the air to ensure that it flows through the flutes, in preference to flowing around the stack, the invention ensures more effective and rapid removal of the fumes and odor.

In some embodiments of the invention, the air moving device may comprise an air extractor connected to the air discharge end of the stack to place the air discharge end under sub-atmospheric pressure and thereby to draw ambient air into the flutes at the air intake end.

Alternatively, or additionally, the air moving device may comprise a fan or blower connected to the air intake end of the stack to raise the air pressure at the air intake end above ambient atmospheric pressure and thereby blow air into the flutes.

In some embodiments, the same air moving device may serve both to reduce the air pressure at the discharge end of the stack and to increase the air pressure at the air intake end, thereby causing air to recirculate through the stack. In this case, to prevent the extracted fumes from recirculating, the recirculated air may be filtered.

As well as removing the smell, in order to preserve certain characteristics of the cardboard, especially its crease readiness quality (i.e. its ability to crease without cracking), it is necessary to control its moisture content. For this reason, after removal of the smell, it is common practice to condition the cardboard by storing it in a moisture-controlled and temperature-controlled room, typically at a temperature in the range of 18-25° C. and a relative humidity of 50-60%RH, for a few days.

In some embodiments, the temperature of the recirculating air is controlled by heating and/or cooling the air to remain within a predetermined range. If desired, the humidity of the recirculating air may additionally, or alternatively, be controlled by a humidifier to remain within a predetermined range.

According to as second aspect of the invention, there is provided an apparatus for conditioning a corrugated cardboard stack, which comprises an air moving device and a shroud to surround the stack so as to confine air moved by the device to flow only, or at least predominantly, through flutes of the cardboard in the stack, from an air intake end to an air discharge end of the stack.

In some embodiments, the shroud may include an element made of a flexible material that is urged to seal against the sides of the stack by an air pressure differential generated by the air moving device.

The air moving device may, in some embodiments, comprise an air extractor connected to the air discharge end of the stack to place the air discharge end under sub-atmospheric pressure and thereby to draw ambient air into the flutes at the air intake end.

Alternatively, or additionally, the air moving device may comprise a fan or blower connected to the air intake end of the stack to raise the air pressure at the air intake end above ambient atmospheric pressure and thereby blow air into the flutes.

The same air moving device may, in some embodiments, serve both to reduce the air pressure at the discharge end of the stack and to increase the air pressure at the air intake end, thereby creating an air recirculation circuit passing through the flutes of the cardboard in the stack. In such an embodiments, the recirculation circuit may include a filter, for example containing activated carbon.

For improved conditioning of the cardboard, the recirculation circuit may additionally include at least one of(i) a heater or cooler for maintaining the temperature of the recirculating air within a predetermined range,(ii) a humidifier for maintaining the humidity of the recirculating air within a predetermined range,(iii) an ozoniser for introducing ozone into the recirculating air, and(iv) and atomiser for introducing airborne material into the recirculating air.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG.1shows a stack10made up of cardboard sheets that have all been stacked with the same orientation, that is to say with all the corrugations lying parallel to one another. Each sheet may have been pre-treated in a conversion machine, such as a Highcon Euclid or a Highcon Beam machine. The cutting of cardboard using a laser by such machines generates fumes that create an unpleasant odor. WhileFIG.1shows a cubic stack of individual sheets, as previously mentioned, the invention is equally applicable to removing odor from a roll of cardboard, which may have acquired an odor through improper storage or exposure to fumes.

In order to reduce the smell, the present invention proposes flowing air in the direction indicated by the arrows12inFIG.1, that it to say with the air flowing through flutes defined by the corrugations of the cardboard, rather than around the stack10. In this way, most of the cardboard is placed in the immediate vicinity of the air flow, being spaced from the air flow preferably by less than a few millimetres, or even less than one millimetre.

If a cardboard stack is merely left to ventilate, any air flow that takes place through the flutes of the stack is almost insignificant. This is because, even if the stack is placed in air stream, the flow resistance around the stack is much less that the flow resistance through the stack. To achieve the desired air flow through the stack, embodiments of the invention therefore confine the air flow, so as to prevent it as much as practicable from flowing around the outside of the stack.

InFIG.2, ambient air is sucked through the stack10in the direction of arrows12by means of an air extractor24. The intake end of the extractor24is connected to a plenum20. The plenum20has on its front side28facing the stack10, a mouth, which may be covered by a grille, against which the stack10is placed. A shroud22in the form of a skirt of a flexible material is attached to front side28of the plenum20and surrounds the mouth and the stack10.

In use, the stack10is transported, for example by means of a forklift truck, and placed in front of the mouth in the front side28of the plenum20and the shroud22is loosely placed over the sides of the stack10. When the extractor24is then operated, the low pressure created in the plenum20sucks the shroud into intimate contact with the stack10and the against the grille, so that no air can flow around the stack10. Instead, the moved air follows the path indicated by the arrows12and flows through the flutes defined by the corrugations int the stack into the plenum20, being then discharged to atmosphere through an exhaust duct26of the extractor24.

The use of a flexible, air-impermeable material, as a shroud22has been found effective as it can form a good seal against the stack10, even if the cardboard sheets in the stack10are not perfectly aligned. It should be clear to the person skilled in the art that other means may be employed to shroud the stack in order to prevent or minimise the flow of air around the stack10. For example, slidable shutter plates may be mounted on the front side28of the plenum, or the mouth may be surround by an inflatable bladder or a ring of compressible, closed cell, foam.

In the embodiment ofFIG.2there is no air recirculation, and the apparatus relies only on drawing ambient air into the stack10and discharging the air, together with any scavenged fumes, into the ambient atmosphere through the exhaust26. If desired, a filter may be placed in the plenum20or in the exhaust duct26to reduce pollution of the ambient air.

The embodiment ofFIG.3is a modification of the embodiment ofFIG.2and, in order to avoid repetition, like parts have been reallocated the same reference numerals. The essential difference between the embodiment ofFIG.3and that ofFIG.2is that the air discharged through the exhaust duct26of the extractor24is recirculated, via an air duct30and a horn32, back to the air intake side of the stack10so that much of the air is recirculated and only a small proportion escapes to the ambient atmosphere through the gap between the horn32and the stack10. By increasing the pressure differential across the stack, the embodiment ofFIG.3allows the air flow rate to be nearly doubled and this has been found to improve odor removal even in the absence of a volatile organic compound (VOC) filter.

FIG.3also shows that a VOC filter34may be mounted in the plenum, to neutralise the fumes scavenged from the stack10. The filter may for example be an activated carbon filter. As previously mentioned, such a filter may also be included in the embodiment ofFIG.2.

FIG.3also shows an ozoniser36is provided to introduce ozone into the air entering the stack10. The ozone, which may be generated for example by an ultraviolet lamp, has a sterilising effect and also assists in regeneration of the activated carbon filter34. Ozone may alternatively be generated by commercially available ozonisers, as available for example by Ecozone Technologies in Hasharon Industrial Park, Kadima, Israel (https://ecozone-technologies.com/). Various walls have been shown inFIGS.3and4in dotted lines, this being to indicate that air is allowed to pass through them.

In the embodiment ofFIG.4, like parts have again been allocated the same reference numerals. As in the embodiment ofFIG.3, the air in this embodiment is recirculated but instead of flowing through an air duct, it flows through a housing comprises of a stationary part40and a pivotable cover42, show in solid lines in its closed position and in dotted lines in an open position. In addition to an ozoniser36, as previously described, various devices are arranged within the housing40,42.

Reference numeral44represents temperature control equipment, that may comprise a heater and/or a cooler, for maintaining the temperature of the recirculated air within a predetermined desired range. A humidifier46is provided to regulate the relative humidity of the air.

InFIG.4, an atomiser48is also provided to spray airborne material into the air. The sprayed material may be any desired treatment solution, for example it may be a perfume or an anti-bacterial compound.

FIG.4also shows that sensors50and52may be mounted in the housing to monitor desired parameters of the recirculating air, such as its temperature and relative humidity, the output of the sensor being provided to a control circuit that controls the operation of the heater/cooler and humidifier.

It is additionally possible to use as a sensor an ‘artificial nose’, such as Cyranose 320 commercially available from Sensigent in Baldwin Park, CA, USA or any other suitable smoke detector) in order to “smell” the level of fumes or odor removal which may also allow for automatic stopping of the conditioning operation when the level of odor reduction (or level of moisture) is achieved.

The embodiment ofFIG.4offers the advantage that when the cover42is open, there is unhindered access to the mouth of the plenum20. A stack10can therefore readily be placed in front of the plenum20and the shroud22deployed to seal around the stack10. When next the cover42is pivoted into its closed position, a closed recirculation path, represented by the arrows12in the drawing, is created and clean air at a desired temperature and relative humidity can be circulated through the flutes of the stack10to remove any odor and also condition the cardboard.

If the pre-processed cardboard sheets have cuts in them, when they are stacked they may create paths for air to enter or exit from the stack, other than through its intake and discharge ends. If a shroud of flexible material is used, it may block air flow through these additional paths to ensure that air flow through the entire length of the flutes.

FIG.4also shows that an exhaust port54may be provided in the stationary part40of the housing. The port may be kept closed during air recirculation and only opened to vent the housing and discharge accumulated VOC’s to atmosphere between operating cycles. Alternatively, a proportion of the recirculating air may be discharged during operation and replenished with clear air, whereupon an intake port56containing a one-way valve may be provided in the cover42.

The inventors have found that a suitable temperature range for heating the recirculating air is 30° - 80° C., preferably 40° - 60° C. An air flow through flutes at a speed of 0.3 - 15 m/s, preferably 2.5 - 10 m/s, for a period of only 3 - 15 min was found to suffice for effective removal of odors.

To compensate for paper moisture loss due to the heating, the humidifier may be controlled to maintain the relative humidity of the circulating air at 40-80%, and more preferably 50-70%.

To assess the effect of using a flexible shroud to cause air to flow primarily through the flutes of the cardboard of the cardboard stack, comparisons were conducted: stacks of corrugated cardboard sheets that had been cut to the same size (1050 mm × 750 mm) with a laser cutter were subjected to airflow in an open configuration similar to that shown inFIG.2, with and without the use of a shroud. In the case without the shroud, the stack was arranged to so that one end of the stack approximately fit the hard-edged opening of the airflow device, but there were gaps around the edges of that opening. The actual configuration used is shown inFIG.5, in which the stack of cardboard sheets10is piled on a pallet60, and aligned so that one end of the stack (that opposite the viewer) is within the aperture that is created by the bottom of the opening in the apparatus (which is the same height as the pallet) and sliding shutters62,64and66; the gap along the top of the stack is indicated by68, and there are also gaps (not seen) along the vertical edges of the stack. When the shroud was used, the gaps were covered.FIG.6shows the actual configuration used when the shroud was employed. Airflow speed was measured by placing an airflow measurement device (MRC Anemometer catalog no. AM-4207SD, www.mrclab.com/anemometertype-kj-temp-data-logger-1), at the front center the stack, directly in front of the end where the air flowed into the stack. Effectiveness in removing the odor that remained from the laser cutting was assessed by the Robinson method (similar to European standard EN 1230-2): each of seven trained panelists evaluated the level of odor by putting the laser-cut portion of the topmost sheet close to his nose and rating the smoke smell on a scale of 1-10, with 1 being the smell of uncut carton and 10 being the smell of the carton immediately after being cut with a laser. “Extraction time” was the time it took for the average odor rating to be reduced to 2 under the same airflow speed. Results are presented in Table 1 below. Assessments were done for both B flute and E flute type cardboard.

These results show that the use of a flexible shroud significantly increases the airflow through the flutes and reduces the time required to remove the odor that results from laser cutting the corrugated cardboard.