Recloseable retort pouch

Details Recloseable retort pouch Recloseable retort pouch

2000-02-28

2004-04-13

Kim, Eugene (Department: 3721)

Manufacturing container or tube from paper; or other manufacturi

Container making

Pliable container

C493S213000

Reexamination Certificate

active

06719678

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention generally relates to retort pouches for materials, such as food products. More particularly, the present invention relates to a retort pouch which is suitable for wet food and which can be easily opened and reclosed.
Closable pouches having an integral zipper or fastener are well known in the art of packaging dry foods. These pouches are often rectangular, made of a web material, and have heat-sealed portions at both side and bottom edge portions. A top opening portion is often provided with means for repetitively opening and reclosing the opening, such as a zipper fastener fastened to the inner surfaces thereof, and extending from one side edge to the opposite side edge. The top opening portion is usually heat-sealed until the product is to be used. In order to open the pouch, the pouch is manually cut between the top heat-sealed portion and the zipper portion, and the top edge is removed. If any product remains in the pouch after being opened, the pouch can be reclosed and reopened by means of a zipper comprising a ridge and trough arranged in registration on the inner surface of the front and back panels of the pouch.
One pouch manufacturing technique is described in U.S. Pat. No. 5,542,902 to Richison et al. In this process, a single web is divided into two portions, with one portion being placed beneath the other. A zipper closure and a base gusset are oriented between the two portions, and then front and back panels of the pouch (formed of the two slit portions of the web) are heat-sealed to one another along their edges to form the pouch.
However, when pouches are to be used to hold retort food, an oxygen blocking capability and adequate strength at the high sterilization temperatures are required. It has been disclosed that these goals am attainable by forming the wall portions of the pouch from a laminated film consisting of four layers, the outermost of which is polyester (hereinafter “PET”), followed by aluminum foil (hereinafter “Al”), then BiOriented Nylon (hereinafter referred to as “BONyl”) and the innermost of a non-oriented or cast polypropylene film (hereinafter “CPP”). It is also known to provide a laminated film consisting of the same four layers of material in the following arrangement: outermost is PET, then BONyl, then Al, and the innermost layer of CPP. The foil layer provides a barrier to air, humidity and light and therefore should preferably be preserved intact until the product reaches the consumer.
The feature of stand-up capability has been achieved by adding a separate gusset between the bottom parts of the two webs, or by adding a flap to the bottom of a single sheet which is intended to be folded in two, thus forming two leaves with the flap as a gusset serving as a base of a stand-up pouch. The aforementioned laminated films have sufficient strength so that pouches made from them withstand the high temperatures and pressures generated during the retort process without bursting and releasing their contents or otherwise losing their hermetic sealing and loss of the required food sterility. This means, however, that great force is required in order to tear them, so as to open the pouch in the first place. Thus, generally a knife or scissors are required in order to cut the laminated film.
To address this problem of difficulty of opening, it has been suggested to utilize a tape formed of an oriented plastics material at a position between the top edge and the zipper. The oriented tape is arranged for easy cutting in one direction. However, placing such tapes on the pouch reduces the efficiency of the pouch producing process, and results in higher costs per pouch.
It is also known, for example from U.S. Pat. No. 3,790,744 to Bowen, to utilize laser energy to provide a weakened line in the laminate web material, so as to form a tear line in the laminate, and from EP 0 473 517 to American National Can Company to provide laser scoring in two close parallel lines across a non-reclosable laminate pouch to create a tear line. Generally, the laser scoring is performed on the individual webs while they are in the slitter, before assembly of the pouch. When it is time to assemble the pouch, there is often a problem of ensuring that the score lines on the front and back panels of the pouch are in registration with one another, which is required in order to obtain good tear performance.
However, as described by Richison, it is extremely difficult to ensure the precision of registration required for a good tear. The teachings of EP 0 473 517 attempt to compensate for this lack of precision by providing two or three close parallel laser scored lines, about ⅛″ to {fraction (1/16)}″ apart on the same surface. While this might address the tear performance caused by imprecisely aligned webs, it requires the use of two or three times as many lasers, thereby greatly increasing the expense of the production process. In addition, the disclosed method of scoring of two lines so close to one another can detrimentally affect the mechanical properties of the pouch, thereby affecting its suitability for use with wet materials in a retort process, due to the extreme conditions generated by the process.
An alternative method of facilitating the removal of the top portion of the pouch is disclosed in EP 0 345 930 to Kabushiki Kalsha Hosakawa Yoko where it is taught to subject the inner layer of the laminate to surface roughening treatment by an abrasive roller for forming a surface roughened zone of small width. The mechanical strength of the laminate in this surface roughened zone is reduced, so as to facilitate cutting of the sheet therealong. In theory, this treatment is effected only on the internal cast polypropylene layer or on the outer polyester layer. In practice, this is problematic since it applies an abrasive mechanical means to the laminate. Since it is very difficult to control the depth of the recesses cut by the abrasive, this can lead to the creation of pinholes in the adjacent air impermeable layer, thereby permitting air and moisture to contact the contents of the pouch.
Known stand-up pouches, which are intended for retort, are mostly suitable only for use with dry contents (i.e. having moisture content significantly below 2%, usually as little as 1.2% or less). Examples of dry foods are dry dog food, dried soup mixes, dried gravy mixes, dried, cake mixes, dried pudding mixes. This is so because the use of flexible retort packages (instead of conventional cans) for liquid or partially liquid foods (for example having moisture content greater than 2%), such as soup, gravy, purse, sauces, toppings, condiments, etc., poses particular challenges. Usually, food material is packed in a retort pouch and then transferred to an autoclave where it undergoes a sterilization process at high temperatures, above 121° C. and pressure of about 2 atm. The volume of water increases many hundreds of times when it turns into steam and the energy released by the steam is much higher than that released by the water at 100° C. Thus, in packages with liquid or wet products, the pressure and steam temperatures produced inside the package even by a small quantity of evaporated water are much higher than with dry foods, dramatically increasing the resistance requirements of the components used, including the different webs, adhesives and dyes. For this reason, at present, most of the canning industry utilizes metal cans, whose resistance at high temperatures and pressures are greater than those of flexible, plastic webs. During the retort process with flexible packages, it is necessary to work with special autoclaves wherein it is possible to apply opposing, external, pressure of about 2 atm, as well as tight control over the cooling phase, in order to prevent the packages from bursting.
The particular sensitivity of the stand-up pouch to the pressures created during the retort process, as compared with other packages, arises from the complicated make-up of the pouch, and the various heat-seals required t

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