Abstract:
A process treats the surface of a polymeric tampon applicator so as to improve its whitening. The process applies electron beam energy to the applicator in sufficient magnitude and time duration to achieve the desired whitening.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process of improving the whitening, and thus color, of tampon applicators. In particular, the present invention relates to a process that whitens or maintains the whiteness (color) of polymeric tampon applicators, especially biodegradable tampon applicators. 
     Tampon applicators are conventionally manufactured either of a plastic, a cardboard or a paper based material. Plastic tampon applicators are typically manufactured by using an injection molding process. The injection molding process allows desirable features, such as a petal shaped expulsion end and a finger grip to be molded into any desired shape to provide a reliable and high quality product. 
     A disadvantage of some known plastic tampon applicators is that the plastic material is not biodegradable. While such applicators flush, they do not decompose. Therefore, such applicators may accumulate in septic tanks or on screens in wastewater treatment plants and may cause blockages. In addition, plastic tampon applicators typically neither float nor settle to the bottom of settling tanks so they are not easily removed as sludge or by skimmers. 
     2. Description of the Prior Art 
     One plastic material that is dispersible in water and that has been used for tampon applicators is polyvinyl alcohol. Polyvinyl alcohol plastic material for use in tampon applicators is described, for example, in U.S. Pat. Nos. 3,882,196, 3,911,917 and 5,002,526. However, polyvinyl alcohol suffers from discoloration, as well as a strong vinegary odor as described in U.S. Pat. No. 3,882,196 at column 1, line 25 et seq. As further described in U.S. Pat. No. 3,882,196, these problems are resolved prior to injection molding by adding to the polyvinyl alcohol a proton acceptor, such as titanium dioxide, to eliminate the odor, and a white pigment to improve the color to an off-white color. The off-white color, though an improvement, is not pleasingly aesthetic to many women. 
     U.S. Pat. No. 3,657,533 provides a process of preparing bilaterally oriented films of polymers of ethylene (heat shrink films). The process includes a step of irradiating plastic tubing by means of an electron beam for cross linking to provide strength uniformly in the finished heat shrink film product. 
     U.S. Pat. Nos. 5,473,165 and 5,532,495 provide ion beam generators that produce an ion beam characterized by pulses of ion energy for a variety of applications including the modification of the near surface microstructure of various materials including polymers. 
     U.S. Pat. No. 5,454,801 provides a process for forming a polymer coating for the cover of absorbent articles such as sanitary napkins, diapers and the like. The coating is formed of a polymer into a liquid phase and then foamed, either before or after coating, onto the substrate. The foam can be prepared by cross-linking polyethylene and polypropylene either chemically or by radiation provided by an electron gun and then curing the cross-linked polymer by heating. Whiteness of the coating is improved by adding white pigment prior to curing. The curing operation may be performed by means of radiant or thermal energy, for example, heat, ultraviolet light or electron beam. 
     U.S. Pat. No. 5,171,762 provides a process that improves the APHA color (yellowness) of a polymer, particularly polytetrahydrofuran, by subjecting the polymer to microwave energy for a sufficient time to melt the polymer. 
     Thus, the prior art has improved the whiteness of a polyvinyl alcohol tampon applicator by adding white pigment to the polyvinyl alcohol prior to injection molding with the result of an off-white color that is not pleasingly aesthetic to many women. Also, the prior art has irradiated the surface of polymers for the purpose of cross-linking with pulsed ion beams, has prepared foamed polymers by cross-linking with radiation provided by an electron gun, has cured foamed polymers with radiant or thermal energy, for example heat, ultraviolet light or electron beams. Such methods have affected the polymer and are also believed to be expensive. The prior art has attempted to improve the yellowness of polytetrahydrofuran by applying microwave energy for a sufficient time to melt it. Therefore, none of the prior art has improved the whiteness of plastic tampon applicators by simple surface treatment after injection molding. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a process that improves the whiteness or color of a polymeric tampon applicator. 
     It is another object of the present invention to provide such a process that provides a surface treatment to the tampon applicator after injection molding to improve its whiteness. 
     It is still another object of the present invention to provide such a process that subjects the surface of the tampon applicator to electron beam radiation to improve whiteness. 
     It is a further object of the present invention to provide such a process that i s relatively inexpensive. 
     These and other objects of the present invention will be accomplished by the process of the present invention that improves the whiteness of a polymeric tampon applicator by applying to its surface a beam of electrons, sufficient in energy and time duration to whiten the color of the tampon applicator. The tampon applicator is preferably a biodegradable tampon applicator. The preferred biodegradable tampon applicator is made of polyvinyl alcohol. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure. 
     FIG. 1 is a diagram illustrating the irradiation system used by the process of the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     The process of the present invention treats the surfaces, especially the outer surface, of a polymeric tampon applicator with electron beam energy to whiten discernibly the outer surface. Whiten means a whiter color of the surface than would have been absent the present process. 
     The process of the present invention is applied after the formation of the tampon applicator. Moreover, the process is effective to improve whiteness even though nothing needs to be added to the polymer. The process of the present invention can be applied to a polymeric tampon applicator that may or may not be biodegradable. Thus, the polymeric tampon applicator can be plastic, which may or may not be biodegradable, or biodegradable polymers. However, the present invention is particularly useful for biodegradable tampon applicators where the whiteness of the surface of the tampon applicator has been problematic. 
     The biodegradable polymer tampon applicator is preferably polyvinyl alcohol. However, other polymers such as starch, polyacrylic acids, polyvinylpyrrolidone or polyethylenimine can also be used. The polyvinyl alcohol contains white pigment, for example, titanium dioxide. The white pigment is mixed with the polyvinyl alcohol material prior to its formation into a tampon applicator as by extruding or injection molding. After formation, the applicator has an off white color as pointed out by the aforementioned U.S. Pat. No. 3,882,196. 
     Referring to the drawings and, in particular, to FIG. 1, there is provided an electron beam radiation system generally represented by numeral  10 . The electron beam radiation system  10  may be employed in the process of the present invention. The electron beam radiation system  10  includes an electron gun  11  that receives operating power from a power source  12 . The power source  12  is under the control of a controller  13 . The electron gun  11  is arranged to emit an electron beam  14 . 
     The electron beam  14  is positioned incident on a surface of a tampon applicator  15  that is to be treated, preferably the outer surface of the tampon applicator. The tampon applicator  15  is preferably situated in a carrier  16 . The carrier  16  is moved past the electron gun  11  in the direction indicated by arrow  18 . However, it should be understood that the carrier  16  can reciprocate back and forth or move in the direction opposite that shown in FIG.  1 . 
     The electron gun  11  is positioned from the carrier  16  so that the gun does not physically contact the outer surface of the tampon applicator  15 . The actual distance between the end of the electron gun  11  and the outer surface of the tampon applicator  15  is such that the gun or electron beam  14  will not melt or damage the structure of the outer surface, but preferably will otherwise optimize the desired effect of the electron beam incident on the outer surface. 
     The speed of travel of the tampon applicator  15 , and thus outer surface, past the electron gun  11  is about 20 feet per minute. As shown in FIG. 1, the electron gun  11  applies the electron beam  14  continuously to the outer surface of the tampon applicator  15  as the tampon applicator is passed by the gun. 
     It is believed that the electron beam  14  irradiates the near outer surface microstructure of the tampon applicator  15  to alter the chemical characteristics of the near outer surface structure or microstructure. This results in a whitening of the tampon applicator  15 . 
     Improved whitening can be achieved when the electron gun  11  applies an electron beam dosage of about 2 to 10 Mrad(millions of radiation absorbed doses) to the outer surface to be treated. The degree of whiteness achieved is proportional to the electron beam dosage applied, in that, a dosage of 10 Mrad produces a greater whitening effect than a dosage of 2 Mrad. However, it has been found in practice that the desired whitening effect is achieved when the electron gun  11  operates at 9.5 Mev (millions of electron volts) with a power output of 150 kilowatts for a dosage of 2 to 2.2 Mrad applied continuously to a biodegradable polyvinyl alcohol tampon applicator  15  passed by the electron beam  14  at a rate of travel of about 20 ft/min. However, the operation of the electron gun  11 , and thus the electron beam  14  emitted, will vary dependent upon the material of the tampon applicator  15  and, in particular, the outer surface to be treated. Nonetheless, the present invention provides for a discernible whitening on the surface, preferably the outer surface, of all polymeric tampon applicators, especially biodegradable polymers, by the application of an electron beam. The criteria is that the electron beam is applied after the formation of the tampon applicator  15  and it provides discernible whitening, as measured by color measurement equipment and/or as discernible to the human eye. 
     The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims.