Apparatus and method for sterilizing an aseptic web

[0002] This application claims the priority of U.S. Provisional Patent Application Ser. No. 60/0974,462, filed on Aug. 21, 1998.

[0003] The present invention relates to a new improved method and apparatus for sterilizing paperboard material used for aseptic liquid containers commonly used for beverages. The method and apparatus, as taught herein, is especially useful for, but not necessarily limited too, gable top containers having a fitment attached thereto for pouring the liquid contents from the container.

[0004] The paperboard container having a fitment, or pour spout, from which the liquid inside may be easily poured therefrom is fast becoming a standard in the milk and juice carton industry. In order to place a fitment on the typical paperboard container a hole must first be punched or cut out of the carton's surface. The presence of this hole increases the complexity of the sterilization process.

[0005] FIG. 1 presents a schematic crossection of typical prior art apparatus for sterilizing paperboard material used for liquid containers. An application roller rotatingly dips into a reservoir of sterilant, typically hydrogen peroxide. The paper board stock to be sterilized is passed through a nip between the application roller and the back up roller thereby flooding the hydrogen peroxide upon the surface of the paperboard. The flooded paperboard is then passed through a nip between the back up roller and doctor roller whereby excess hydrogen peroxide is removed from the paperboard and drips back into the reservoir.

[0006] Although this process has worked well for paperboard having a continuous surface without holes therein, for the receipt of a fitment, the doctor roller/backup roller combination is unable to remove the excess sterilant that collects within the gap, or opening, presented between the doctor roll and the backup roller by the presence of the fitment hole. Thus as the sterilized paperboard is discharged from the doctor roller/backup roller nip the accumulated sterilant, within the fitment hole flows across the paperboard leaving an undesired residual of sterilant upon the board. Similarly, for paper board having surface irregularities such as score lines etc. the prior art method of sterilization causes a build up of sterilant in the areas of surface area height differentials thereby leaving globules or droplets of sterilant upon the paperboard surface. Subsequently the, system used to dry the sterilant from the board is unable to dry the residual sterilant and many times producing a sterilized paperboard having a hydrogen peroxide residual greater than 0.5 parts per million, the industry standard.

[0007] The disadvantages of the prior art are overcome by the present invention. By the apparatus and method of the present invention an anilox roller is submerged in a bath of sterilant. As the surface of the anilox roller rotates upward out of the sterilant, excess sterilant is removed from the surface by a typical doctor blade. The paperboard web is then passed through a nip between the anilox roller and a backup or pressure roller. The sterilant retained within the pores of the anilox roller are thusly transferred from the anilox roller, in a printing like manner, as the paperboard web passes through the nip, and is deposited upon the paperboard thereby sterilizing the paperboard.

[0008] FIG. 1 shows a schematic crossection of a typical prior art machine.

[0009] FIG. 2 shows a schematic crossection of the apparatus for practicing the present invention.

[0010] FIG. 3 presents a pictorial view of a typical anilox roll suitable for practicing the present invention.

[0011] FIG. 4 is a partial enlarged view of the surface of the anilox roll as shown in FIG. 3.

[0012] FIG. 5 is a crossectional view taken along line 5—5 of FIG. 4.

[0013] Referring now to FIG. 2, a crossectional schematic is shown of the apparatus 10 suitable for the practice of the present invention. An anilox printing roller 12 is rotatingly submerged and passed through a bath of sterilant 14 where the micro pores on the cylindrical surface of the anilox roll fill with sterilant. A trailing edge doctor blade 16 wipes excess sterilant from the surface of roll 12. Paper board 20 is continuously passed through the nip between anilox roll 12 and pressure roll 18 whereby the sterilant contained within the pores 11 of roll 12 is deposited upon paperboard 20 thereby sterilizing the paperboard surface. The wetted paperboard is then passed through a drying apparatus (not shown) and on to the filling machine.

[0014] Anilox roll 12 is similar to the anilox roll as used in the rotogravure printing process. We have found that a anilox roll comprising a laser engraved, plasma coated, ceramic covered metal roll having a uniform distribution of micro cells or pores about its cylindrical surface has performed well. The surface of roll 12 has 100 percent of its cylindrical surface engraved with a uniform array of pores having a 300 line count and 6 billion cubic microns per square inch (BCM).

[0015] An alternate method may, in addition, include a rubber transfer roll (not shown) whereby the transfer roll would rollingly engage the anilox roller whereby the sterilant would be deposited upon the transfer roll. The transfer roll would then deposit the sterilant upon the paperboard web.

[0016] Also an alternate embodiment may be structured whereby the sterilant is sprayed upon anilox roller as opposed to submerging the roll in the sterilant.

[0017] By use of the method and apparatus disclosed above the sterilant is uniformly deposited upon the paperboard surface only. Thus none of the sterilant is floodingly deposited in hole cut outs intended for fitment application thereby eliminating the undesirable collection of residual sterilant upon the paperboard.

[0018] Having described the preferred embodiments of the present invention, and several of its benefits and advantages, it will be understood by those of ordinary skill in the art that the foregoing description is merely for the purpose of illustration and that numerous substitutions, rearrangements, and modifications may be made in the invention without departing from the scope and spirit of the appended claims.