A material generally called a cooking sheet, such as a wrapping film of a synthetic resin and aluminum foil, used in the kitchen, etc. for wrapping foods or the like, is usually rolled up and contained in a paperboard carton case (hereinafter referred to as "carton"). At the time of use, an end of said film or aluminum foil is pulled out of the carton and cut to a desired length by means of a cutting member or a serrated cutting edge provided on a front portion or a cover portion of said carton (hereinafter referred to as "cutting edge" or "serrated cutting edge").
The cutting edge provided on the carton is generally made of a metal. Recently a cutting edge made of a vulcanized fiber has been put on the market because while a metal cutting edge is likely to injure the hand when it is grasped, the vulcanized fiber cutting edge is free from such a possibility. Furthermore, the vulcanized fiber cutting edge may be burned together with the carton when the film or the foil has been used up.
While the vulcanized fiber cutting edge has the above-mentioned advantages, it also has the disadvantage that because of the properties of the material, the vulcanized fiber cutting edge absorbs moisture and elongates when it is put in a moist atmosphere for a long period of time. In an attempt to moisture proof the vulcanized fiber cutting edge, a vulcanized fiber blank has been coated with a melamine resin liquid, glyoxal solution, polyurethane resin liquid, etc. before a cutting edge is formed. However, none of these attempts have been very successful and further improvements are required. If the vulcanized fiber cutting edge is put in the kitchen, etc. which often has a high humidity, the cutting edge may be elongated by moisture in the atmosphere. According to the degree of water-resisting or waterproofing treatment, elongation by moisture absorption may, in an extreme case, partially separate the cutting edge from the carton to which the cutting edge is adhered and reduce the function of the cutting edge.
It is a first object of the present invention to provide a sheet for a cutting edge for cutting a material dispensed from within the carton, said cutting edge always having a satisfactory cutting function without being affected by moisture in the atmosphere. In other words, said first object of the present invention is to provide a vulcanized fiber sheet having a serrated cutting edge, said sheet having a very high dimensional stability.
It is a second object of the present invention to improve the shape of the cutting edge so that it can smoothly cut a film of polyvinyl chloride, etc. having a relatively large elongation.
It is a third object of the present invention to provide a novel method of adhering a sheet having a cutting edge to the carton, said method preventing said sheet from peeling off from the carton, even when the sheet is thin. In this method, the cutting edge can be adhered to the paperboard of which the carton is made at the same speed as when a usual metal cutting edge is attached by caulking,