Abstract:
Plastic components exposed to a washing chamber of a washing machine are flame treated to improve the stain resistance of the plastic components. In accordance with the invention, a plastic component is exposed to flame treatment for a sufficient amount of time for a reaction to occur with the plastic component such that at least a surface layer of the plastic component is modified to enhance the resistance of the plastic component to staining. Plastic dishwasher components that may be treated by the flame treatment include a dishwasher tub, a door liner, spray arms, racks, silverware baskets, a pump housing and the like. Plastic washing tubs, agitators, baffles and the like of clothes washing machines could also be advantageously treated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention pertains to the art of washing machines, specifically dishwashers and clothes washing machines, and, more particularly, to plastic washing machine parts having improved resistance to stains and a method of treating the plastic parts to improve stain resistance.  
         [0003]     2. Discussion of the Prior Art  
         [0004]     Typically, interior walls of a dishwasher tub are formed of plastic, generally polypropylene. In addition, the use of plastic for the internal components of dishwashers, such as spray arms, is becoming increasingly popular due to the relatively low cost, light weight, and flexibility of design offered by plastic. However, plastic dishwasher parts, as well as plastic food containers, are prone to staining by food residue. Plastic dishwasher parts are particularly prone to red stains from processed tomato products, such as tomato sauce, ketchup, and spaghetti sauce. Red stains, technically known as carotenoid stains, are caused by lycopene in tomato products. Lycopene is easily absorbed into plastic items and cannot be completely removed by dishwashing detergents.  
         [0005]     Although reducing the ability of a part to be stained may be of interest in certain other fields, the problems associated with staining are of particular concern in connection with plastic dishwasher components. For instance, both a tub and door liner of a dishwasher are typically white in color. During use, if these components are discolored by tomato or other food product stains, the overall appearance of the dishwasher is degraded. Certainly, consumers do not want to put dishes to be cleaned in a dishwasher which has a soiled or otherwise stained washing chamber. As plates or bowls containing tomato or other high staining foods are oftentimes not rinsed prior to loading a dishwasher, the staining foods will tend to drip onto the inner components of the dishwasher. If these staining foods remain on the plastic components for any significant length of time prior to operating the dishwasher, a certain amount of staining is sure to occur.  
         [0006]     Of course, many of the dishwasher parts could be made from materials which would inherently resist staining, such as stainless steel. However, although a market exists for such high-end products, the need to provide a more economically feasible dishwasher leads to the increasing need to employ plastic parts. Some similar problems also exist in connection with clothes washing machines, specifically those incorporating plastic washing tubs or spinners, agitators and/or baffles. Certainly, unsightly stains on these components will lead to customer dissatisfaction. Based on the above, there exists a need to make plastic washing machine parts that are more resistant to staining.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is concerned with treating plastic components of a washing chamber with a flame in order to improve the stain resistance of the plastic components. In accordance with the invention, the plastic components are exposed to a flame for a sufficient amount of time for the flame to react with the plastic components, such that the flame modifies at least a surface layer of the plastic components.  
         [0008]     It has been found that treating washing machine components in this manner significantly alters the resistance of the plastic components to staining, even staining associated with tomato based products which is of particular concern in the art of dishwashers. In connection with a preferred aspect of the invention, plastic dishwasher components that are treated by the flame treatment include: dishwasher tubs, door liners, spray arms, racks, conduits, silverware baskets, pump housings, and the like. For clothes washing machines, plastic tubs or spinners, agitators, baffles and the like are advantageously treated. That is, any plastic component which is arranged in a washing chamber so as to be subject to staining by foods or soiled clothes may be treated in accordance with the present invention.  
         [0009]     Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a view of a dishwasher containing plastic parts treated in accordance with the present invention; and  
         [0011]      FIG. 2  is a side view of a plastic dishwasher part treated in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     With initial reference to  FIG. 1 , the invention will be described with particular reference to a dishwasher  2 . As shown, dishwasher  2  includes a tub  5  which is injection molded of plastic, preferably polypropylene, so as to include integral bottom, side, rear and top walls  8 - 12  respectively. Within the confines of walls  8 - 12 , tub  5  defines a washing chamber  14  within which soiled kitchenware is adapted to be placed upon shiftable upper and lower racks (one of which is indicated at  15 ), with the kitchenware being cleaned during a washing operation in a manner widely known in the art. Tub  5  has attached thereto a frontal frame  16  which pivotally supports a door  20 , having an outer panel  21  and an inner liner  22 , used to seal chamber  14  during a washing operation. In connection with the washing operation, door  20  is preferably provided with a detergent tray assembly  23  within which a consumer can place liquid or particulate washing detergent for dispensing at predetermined cycles of the washing operation. Of course, dispensing detergent in this fashion is known in the art such that this arrangement is only being described for the sake of completeness.  
         [0013]     Disposed within tub  5  and, more specifically, mounted within a central opening formed in bottom wall  8  of tub  5  is a pump and filter assembly  30 . Extending about a substantial portion of pump and filter assembly  30 , at a position raised above bottom wall  8 , is a heating element  44 . In a manner known in the art, heating element  44  preferably takes the form of a sheathed, electric resistance-type heating element. In general, pump and filter assembly  30  is adapted to direct washing fluid to a lower wash arm  47  and an upper wash arm (not shown). Dishwasher  2  has associated therewith a drain hose  85  including at least one corrugated or otherwise curved portion  89  that extends about an arcuate hanger  92  provided on an outside surface of side wall  10 . Drain hose  85  is also preferably secured to tub  5  through various clips, such as that indicated at  94 . In any event, in this manner, an upper loop is maintained in drain hose  85  to assure proper drainage in a manner known in the art. Actually, a detailed description of the exact structure and operation of pump and filter assembly  30  of dishwasher  2  does not form part of the present invention, but is rather set forth in pending U.S. application Ser. No. 10/186,739 entitled “Dishwasher Pump and Filtration System” filed Jul. 2, 2002, incorporated herein by reference. In addition, a silverware basket  100  is shown positioned in rack  15  in a manner known in the art.  
         [0014]     The present invention is actually directed to providing various components of dishwasher  2  with an increased resistance to stains. In general, the process includes exposing plastic dishwasher parts to a flame treatment for an amount of time sufficient to allow the flame treatment to react with the plastic parts. It has been unexpectedly found that the reaction that takes place between the plastic parts and the flame treatment modifies the surface of the plastic parts such that the parts exhibit increased resistance to stains.  
         [0015]     Essentially, any plastic dishwasher part that is susceptible to stains from contact with food residue may be treated by the process of the invention. The plastic dishwasher parts that may be treated include, but are not limited to, walls  8 - 12 , a shiftable upper rack (not shown), shiftable lower rack  15 , inner liner  22  of door  20 , dispensing assembly  23 , lower wash arm  47 , an upper wash arm (not shown), at least the housing for pump and filter assembly  30 , basket  100 , and the like. However, for discussion purposes, reference will be made to  FIG. 2  in discussing the treatment of a representative plastic dishwasher part which is generically referred to as plastic part  150 . Preferably, plastic part  150  includes a main body  155  which is molded of polypropylene. Main body  155  has at least one surface  158  exposed to washing chamber  14 .  
         [0016]     The treatment in accordance with the invention includes exposing plastic part  150  to one or more flames, such as an assembly line system of gas burners or torches, placed in close proximity to surface  158  of plastic part  150 . Since the distance between each flame and surface  158  of plastic part  150  affects the degree of surface modification, the visible blue portion of the flame is preferably kept no more than one inch from surface  158  of plastic part  150 . The airflow of the burner is preferably in the order of 6 ounces per square inch and the burner speed is approximately 65 feet per minute. Plastic part  150  remains in contact with the flame for a sufficient amount of time for the flame to modify at least surface  158  of plastic part  150 . However, the parameters may be adjusted in order to modify the results. For example, the dwell time of the flame treatment may be determined and adjusted according to the depth of plastic part  150  and the desired depth of treatment.  
         [0017]     Surface  158  of plastic part  150 , treated by the method of the invention, also exhibits improved surface energy or wettability, as well as enhanced drying characteristics as water tends to spread out on the components instead of beading into large droplets. Adjustments may be made to various parameters, such as burner speed and airflow, in order to achieve the equivalent of a plasma index of 45, which has been proven to be optimum for improving the wettability of plastic part  150 .  
         [0018]     As indicated above, plastic parts  150  that have undergone the flame treatment of the present invention have improved resistance to staining when compared to plastic parts that have not been treated. For example, a test was carried out to measure the difference in the stain resistance of plastic dishwasher parts that have been treated with the flame treatment of the invention versus parts not treated, wherein two dishwasher tubs were subjected to several wash cycles. Prior to the initial wash cycle, dishes soiled with tomato sauce and the like were placed within the washing chamber of each dishwasher. No cleaning or other modification of the dishwashers took place between cycles. One dishwasher included plastic parts which had been treated in accordance with the present invention and the other dishwasher included identical parts which were not treated. The change in color of the plastic parts was observed after each wash cycle and at the completion of all wash cycles. The plastic parts of the flame treated dishwasher unexpectingly showed little to no staining, i.e. substantially no change in lightness and color, while the untreated plastic parts contained seemingly irreversible staining.  
         [0019]     The treated plastic dishwasher components have been found to not develop carotenoid stains caused by foods that contain lycopene. In any case, it should be readily apparent that treating plastic dishwasher components in accordance with the invention makes the components significantly more resistant to being stained from even the worst types of staining food substances typically experienced in connection with a domestic dishwasher. For a relatively minor incremental cost, various washing machine components can be treated to provide a long-lasting, more aesthetically appealing and overall hygienic washing chamber arrangement. Although described with reference to a preferred embodiment of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, although the invention is seen to have particular use in connection with treating dishwasher components, other washing machine components, such as clothes washing machine tubs or spinners, as well as agitators and baffles located in the tubs, can be made of plastic and benefit from the invention for generally corresponding reasons. Treating these washing machine components in a corresponding manner can prevent staining from various soils removed from clothing, as well as dyes which are inherently drawn from certain clothing during washing operations. In general, the invention is only intended to be limited by the scope of the following claims.