Patent Publication Number: US-5292581-A

Title: Wet wipe

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to disposable wet wiping cloths and the like. More particularly, it is concerned with a new and improved nonwoven fibrous web material having sufficient wet strength to be used as a wet wipe, yet is capable of disintegration within a septic system after a brief period of time. 
     Wiping material of this type typically is prepackaged in a moist environment and is commonly used by consumers for cleansing or wiping parts of the body, particularly when wash water is not readily available or cannot be conveniently used. Travelers find such wipes especially convenient. These wipes have been used for applying or removing makeup or in cleansing other parts of the body, for example, as a substitute for conventional dry toilet paper. 
     As will be appreciated, these premoistened wipes often are disposed of through a sewer or septic system. Thus, while they must have sufficient wet strength to resist tearing and puncturing during use, they also must easily and readily disintegrate within the disposal systems and preferably, when disintegrated, be totally biodegradable. Disposable wipes of this type for personal hygienic use have been known for some time. Typically, they consist of nonwoven webs of fibrous material saturated with a cleansing solution and packaging in their wet condition for easy dispensing. The sheet material is stacked and wrapped in a liquid type package together with a wetting liquid that often includes bacteriacides and other biological control agents as well as perfumes, organism growth inhibitors, and the like. 
     Some wet wipes described heretofore have utilized a pH sensitive water soluble binder adhesive to achieve the requisite wet strength during packaging and use. The binders of such systems exhibit a resistance to weakening during storage, but are much more loosely bonded when the wipe has been immersed in a relatively large amount of substantially neutral water, allowing the wipe to readily break up in the turbulent water movement of the septic or sewer system. One such wet wipe is described in Adams et al U.S. Pat. No. 4,117,187 issued Sep. 26, 1978. Others have suggested the complete elimination of any binder system and rely instead on the hydroentanglement of the fibers within the wet wipe to achieve the requisite strength to process the web into a premoistened towelette for one time use. Such wet wipes readily disentangle when exposed to mild agitation so that they can be readily disposed of in the sewer and septic systems. A wipe of this type is described in U.S. Pat. No. 4,755,421, the disclosure of which is incorporated herein by reference. That patent describes a binder free hydroentangled web material consisting essentially of a blend of rayon fibers and papermaking pulp. While such materials exhibit acceptable absorption characteristics, the strength of such materials, particularly the wet strength thereof, is relatively poor as will be appreciated from the very rapid disintegration or breakup times exhibited by such materials. 
     Unfortunately, the addition of wet strength agents to nonwoven fibrous web materials to improve the wet properties of those materials significantly and deleteriously reduces the absorption characteristics of the fibrous web materials. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes these previous problems in the art and yet achieves excellent wet strength, bulk or thickness, uniform liquid release, and pleasant cloth-like, tactile properties. In addition, the present invention can provide for a wipe material of the type described that qualifies as a totally biodegradable product and maintains an excellent absorption capacity coupled with substantially improved wet strength characteristics. 
     The nonwoven fibrous web material of the invention exhibits improved wet strength, wet thickness and wet toughness, indicative of substantially improved serviceability and resistance to breaking and tearing during converting operations and handling of the material on automated equipment. 
     The disposable nonwoven material of the present invention not only retains the desirable absorption capacity that permits it to absorb and hold a weight of water equal to about five or six times or more the dry weight of the nonwoven material, but also provides sufficient strength to prevent rupturing thereof during use and premature disintegration thereof coupled with an ability to disintegrate within the septic or sewer system in a relatively short period of time and, depending on the composition, totally biodegrade after two or three weeks. 
     Other features and advantages of the present invention will be in part obvious and in part pointed out more in detail hereinafter. 
     These results are achieved by providing a fibrous sheet material of pulp fibers, having at least 5% by weight of man-made fibers, wherein the fibers are initially dispersed within an aqueous dispersing medium containing a wet strength agent. After sheet formation, the web is hydraulically entangled to provide a synergistic effect with the wet strength agent such that the web material exhibits no significant reduction in absorption capacity while incorporating substantially improved wet strength characteristics. 
     A better understanding of these advantages, features, properties and relationships of the invention will be obtained from the following detailed description which sets forth an illustrative embodiment and is indicative of the way in which the principles of the invention are employed. 
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The nonwoven fibrous web materials formed in accordance with the invention are made by a wet paper making process that involves the general steps of forming a fluid dispersion of the requisite fibers, depositing the dispersed fibers on a fiber collecting wire in the form of a continuous sheet-like web material and hydroentangling the material without any postformation bonding treatment. The fiber dispersion incorporates up to 2% by weight, preferably about 1% by weight, of a wet strength additive and, following sheet formation, is hydroentangled to provide the desired synergistic strength and absorbency characteristics. 
     The fiber dispersion may be formed in a conventional manner using water as the dispersant or by employing other suitable liquid dispersing media. Preferably, aqueous dispersions are employed in accordance with known paper making techniques and, accordingly, a fiber dispersion is formed as a dilute aqueous suspension or furnish of paper making fibers. The fiber furnish is then conveyed to the web-forming screen or wire, such as a Fourdriner wire of a paper making machine, and the fibers are deposited on the wire to form a fibrous web or sheet which is subsequently hydroentangled. The sheet or web is dried in a conventional manner, but is not treated with any postformation bonding agent. 
     The fiber furnish is a blend of natural pulp and man-made fibers. The pulp component of the fiber furnish is the major component and can be selected from substantially any class of pulp and blends thereof. Preferably the pulp is characterized by being entirely natural cellulosic fibers and can include cotton as well as wood fibers, although softwood paper making pulp, such as spruce, hemlock, cedar and pine are typically employed. Hardwood pulp and non-wood pulp, such as hemp and sisal may also be used. 
     As mentioned, the nonwoven web material also contains a significant concentration of man-made fibers blended with the wood pulp. The typical man-made fiber is regenerated viscose rayon. However, as will be appreciated, the man-made fiber component is not limited to viscose rayon, but can include other cellulosic fibers. For example, cellulose acetate, polyester, nylon or polypropylene fibers also may be used. To assure complete biodegradability, the man-made fibers preferably are of a cellulosic character and non-cellulosic fibers are not employed. 
     Although substantially all commercial paper making machines, including rotary cylinder machines, may be used, it is desirable where very dilute fiber furnishes are employed to use an inclined fiber-collecting wire, such as that described in U.S. Pat. No. 2,045,095 issued to F. H. Osborne on Jun. 23, 1936. The fibers flowing from the headbox are retained on the wire in a random three-dimensional network or configuration with slight orientation in the machine direction while the aqueous dispersant quickly passes through the wire and is rapidly and effectively removed. 
     As mentioned, the fiber furnish consists of a mixture of not only natural cellulosic fibers, but also man-made fibers such as viscose or acetate rayon. The man-made fibers are preferably of a low denier of about 1-6 denier per filament (dpf). Generally, the lower denier materials are of slightly shorter length than the higher denier in view of the tendency of the lower denier fibers to entangle prior to deposition on the web forming screen. For example, 3 dpf rayon fibers can be used at lengths of about 1/2 inch, while it is preferred to use a 1.5 dpf fiber at a length of about 5/16 inch. As will be appreciated, longer fibers may be used where desired so long as they can be readily dispersed within the aqueous slurry of the other fibers. Although the amount of synthetic fibers used in the furnish may also vary depending upon the other components, it is generally preferred that less than 50 percent by weight be employed. Typically, the man-made content is at least 5 percent by weight with 5-30 percent by weight of rayon being used in most cases. 
     In addition to the man-made fibers and the conventional paper making fibers of bleached kraft, the furnish of the present invention may include two distinctively different types of natural fibers that uniquely combine to provide the desired absorbency, bulk and wet tactile properties sought after in the wet tissues of the type described. As mentioned, some strength is imparted by the kraft fibers. However, additional strength and absorbency is achieved in accordance with the present invention by including long vegetable fibers and particularly the extremely long, natural, unbeaten fibers such as manila hemp, caroa, flax, jute and Indian hemp. These very long natural fibers supplement the strength characteristics provided by the bleach kraft and, at the same time, provide a limited degree of bulk and absorbency coupled with a natural toughness and burst strength. Accordingly, the manila hemp or comparable fibers may be included in varying amounts, typically at about 5-30 percent by weight. Generally, the inclusion of such fibers is preferred, but the total amount thereof is kept at about 10 percent by weight in order to achieve a proper balance of desired properties in the end product. 
     Using a conventional paper making technique, the fibers are dispersed at a fiber concentration within the range of 0.5-0.005 percent by weight, and are preferably used at a fiber concentration of about 0.2-0.02 percent by weight. As will be appreciated, paper making aids, such as dispersing agents, may be incorporated into the fibrous slurry together with the aforementioned wet strength agents. These materials constitute only a minor portion of the total solid weight of the fiber furnish, typically less than one percent by weight, and facilitate uniform fiber deposition while providing the web in its wet condition with sufficient integrity so that it will be capable of retaining its integrity during the hydroentangling operation. These dispersants may include natural materials, such as guar gum, karaya gum and the like as well as man-made resin additives. The dilute aqueous fiber furnish is fed to the headbox of the paper making machine and then to the fiber-collecting wire thereof where the fibers are deposited to form a continuous web or sheet. Preferably the base web material is hydroentangled prior to the drying operation, although drying may occur immediately after web formation in a conventional manner by passing the newly formed web over a number of heated dryer drums. However, in accordance with the preferred mode of operation, the sheet material prior to drying is hydroentangled so that during the subsequent drying operation, the wet strength additive incorporated therein will tend to cure and provide the desired wet strength characteristics without significantly hampering or detracting from the high absorbency characteristics imparted to the web by the hydroentangling operation. 
     The wet strength agent added to the fiber furnish prior to web formation may include any one of a number of well-known materials suited for pre-formation addition to the fiber furnish. This may include various resins, such as the polyacrylamide sold by American Cyanamide under the trade designation Parez 631; however, the preferred material is a polyamide-epichlorohydrin resin. It is a cationic, water-soluble thermosetting reaction product of epichlorohydrin and a polyamide and contains secondary amine groups. A typical material of this type is sold by Hercules Chemical Company under the trademark &#34;Kymene 557&#34;. Resins of this type are more fully described in Jones et al U.S. Pat. No. 4,218,286 issued Aug. 18, 1980, the disclosure of which is incorporated herein by reference. The water soluble, cationic thermosetting epichlorohydrin-containing resin is usually employed in amounts well less than 2 percent, that is, in the range of 0.01-1.5 percent by weight, with the preferred amount being in the range of 0.5-1.3 percent by weight. 
     Typically, the hydroentangling operation is carried out in the manner set forth in Viazmensky et al U.S. Pat. No. 5,009,747 issued Apr. 23, 1991. While that patent relates to a fiber web having a significantly higher man-made fiber content, preferably within the range of 40-90 percent man-made fiber, the hydroentangling operation described therein can efficaciously be employed with the web material of the present invention. Thus, as also stated in the aforementioned U.S. Pat. No. 4,755,421, the hydroentanglement treatment entangles together the fibers forming the web in such a manner as to provide total energy input of less than about 0.2 horsepower-hours per pound of web. The total energy required to treat the web can range from as low as 0.002 and typically falls within the range of 0.01-0.15 horsepower-hours per pound of web. 
     The basis weight for the nonwoven web material of the present invention typically is in the range of about 20-110 grams per square meter. The preferred material exhibits a basis weight of about 35-95 grams per square meter. 
     The expression &#34;absorptive capacity&#34; as used herein refers to the capacity of the material to absorb liquid (i.e., water or aqueous solution) over a period of time and is related to the total amount of liquid absorbed and held by a material at its point of saturation. The total absorptive capacity is determined by measuring the increase in the weight of the sample material resulting from the absorption of a liquid. The general procedure used to measure the absorptive capacity conforms to Federal Specification No. UU-T-595C and is expressed as a percent of the weight of liquid absorbed divided by the weight of the sample in accordance with the following equation: ##EQU1## Disposable wet wipes of the type described in the application will typically have an absorptive capacity of at least 500 percent, with most webs having an absorptive capacity of about 600 percent and more. These webs are readily adapted for generally family use as a wet hygienic wiping towel that will retain its strength characteristics despite packaging and prolonged storage in a wet condition. Surprisingly, these desired strength characteristics are achieved within a product that exhibits a very low density and high bulk characteristics. The resultant wipes are odor free, although preservative as well as perfumes or scents may be added. The moisturizing or wetting ingredients are mainly water that may contain other conventional ingredients such as bactericides, fungicides, bacteriostats, glycerine, lanolin, and the like. 
    
    
     The following examples are given for purposes of illustration only in order that the present invention may be more fully understood. These examples are not intended to in any way limit the practice of the invention. Unless otherwise specified, all parts are given by weight. 
     EXAMPLE I 
     A fiber furnish was prepared from 95% Alberta Hibrite wood pulp and 5% of 1.5 denier 3/8 inch rayon fibers. To the furnish was added 1.0% by weight of a water soluble cationic thermosetting wet strength resin (Kymene-557). The fibers were dispersed at a concentration of about 0.02% and formed into a nonwoven web material. The resultant web material was hydroentangled using the procedure outlined in U.S. Pat. No. 5,009,747 at an energy level of 0.0258 horsepower-hours per pound of web and then the web was dried. Absorption capacity measurements were taken of the web material and the result is set forth in Table 1 as Sample 1-D. Comparative absorption capacity results are set forth for Samples 1-A through 1-C where either the wet strength agent or the entanglement or both were omitted. 
     
                       TABLE 1                                                     
______________________________________                                    
        Wet Strength             Absorption                               
Sample  Additive      Entanglement                                        
                                 Capacity                                 
______________________________________                                    
1-A     None          None       450%                                     
1-B     Yes           None       325%                                     
1-C     None          Yes        463%                                     
1-D     Yes           Yes        598%                                     
______________________________________                                    
 
    
     As can be seen from Table 1, the addition of the wet strength agent to the non-entangled nonwoven web results in an expected loss of absorption capacity. However, the combination of wet strength additive and hydroentanglement, as shown in Sample D, results in an unexpected improvement in the absorption capacity of the web material made in accordance with the invention. 
     EXAMPLE II 
     The procedure of Example I was repeated with substantially the same comparisons except that the composition of the fiber furnish was varied to show the effect of altering the pulp and rayon content. The entanglement energy level employed was 0.1115 horsepower-hours per pound of web on all samples. The properties of the resultant materials are set forth in Table 2. 
     As will be noted from Table 2, the combination of wet strength agent and entanglement enhances the wet properties of the material but surprisingly does not significantly adversely impact the improved absorption capacity of the resultant web materials. 
     EXAMPLE III 
     To determine the effect of varying the amount of wet strength additive, a series of nonwoven web materials were prepared in accordance with the procedure of Example I. In each instance the web materials were identically hydroentangled and the only variable was the amount of wet strength resin added to the fiber furnish. As reported in Table 3, even small amounts of resin were effective to improve the wet tensile of the nonwoven web material with the properties appearing to optimize at approximately 1% of resin addition. 
     
                                           TABLE 2                                 
__________________________________________________________________________
                                        (g)                               
(%)                  (%)   (g/25 mm)                                      
                                  (g/cm/cm.sup.2)                         
                                        Wet  (microns)                    
Fiber Comp.                                                               
           Wet       Absorption                                           
                           Tensile                                        
                                  Toughness                               
                                        Tongue                            
                                             Thickness                    
Sample                                                                    
    (Pulp/Rayon)                                                          
           Additive                                                       
                Entangle                                                  
                     Capacity                                             
                           Dry                                            
                              Wet Wet   Tear Wet                          
                                                Dry                       
__________________________________________________________________________
2-A 95/5   No   No   455   3173                                           
                               85  1.6  176  180                          
                                                263                       
2-B 95/5   No   Yes  668   1330                                           
                              242 22.3  287  227                          
                                                478                       
2-C 95/5   Yes  Yes  643   1673                                           
                              545 52    315  323                          
                                                548                       
2-D 90/10  No   No   465   3119                                           
                              174 7     213  202                          
                                                245                       
2-E 90/10  No   Yes  648   1531                                           
                              361 29.1  369  241                          
                                                490                       
2-F 90/10  Yes  Yes  684   1831                                           
                              580 54.7  415  280                          
                                                631                       
2-G 85/15  No   No   478   3380                                           
                              195  7.2  218  234                          
                                                266                       
2-H 85/15  No   Yes  639   1659                                           
                              349 27.9  431  281                          
                                                360                       
2-I 85/15  Yes  Yes  660   2134                                           
                              566 48.4  424  353                          
                                                398                       
2-J 80/20  No   No   550   2820                                           
                              184  5.7  240  231                          
                                                243                       
2-K 80/20  No   Yes  648   1860                                           
                              512 37.4  466  282                          
                                                479                       
2-L 80/20  Yes  Yes  703   2019                                           
                              627 55.6  435  333                          
                                                455                       
2-M 70/30  No   No   546   2473                                           
                              140  7.1  210  235                          
                                                243                       
2-N 70/30  No   Yes  666   1918                                           
                              856 73    515  288                          
                                                450                       
2-O 70/30  Yes  Yes  647   2186                                           
                              1139                                        
                                  103   661  307                          
                                                495                       
__________________________________________________________________________
 
    
     
                       TABLE 3                                                     
______________________________________                                    
         (g/25 mm)  (g/cm/cm.sup.2)                                       
                                 (%) Wet                                  
(%)      Wet tensile                                                      
                    Wet Toughness                                         
                                 Elongation                               
Resin Amt.                                                                
         MD     CD       MD   CD     MD   CD                              
______________________________________                                    
0        120    120      10   10     23   27                              
0.3      270    225      10   15     8    20                              
0.7      400    338      17   23     9    21                              
1.0      510    425      21   30     9    21                              
1.3      550    380      17   24     7    19                              
______________________________________                                    
 
    
     EXAMPLE IV 
     The effect of the wet strength resin on the breakup time of the nonwoven web material when slightly agitated in water is exemplified in Table 4. 
     In this example, two slightly different fiber furnishes were prepared both with and without a wet strength additive. All sheets were hydroentangled in exactly the same manner at an energy level of 0.0636 horsepower-hours per pound of web and the wet strength characteristics thereof were measured. 
     
                                           TABLE 4                                 
__________________________________________________________________________
           85% Howe Sound Pulp                                            
                         80% Howe Sound Pulp                              
           15% Rayon 1.5 d × 9 mm                                   
                         20% Rayon 1.5 d × 12 mm                    
           No Kymene                                                      
                  1% Kymene                                               
                         No Kymene                                        
                                1% Kymene                                 
__________________________________________________________________________
Wet tensile MD                                                            
           300     790   490    1060                                      
(g/25 mm) CD                                                              
           310    1010   450     930                                      
Wet toughness MD                                                          
            29     50     42     94                                       
(g/cm/cm.sup.2) CD                                                        
            26     78     42     84                                       
Breaking time (sec)                                                       
            25    NB      30    NB                                        
__________________________________________________________________________
 NB  Does not break up in the water                                       
 
    
     EXAMPLE V 
     The effect of the addition of the wet strength agent on the toughness of the nonwoven fibrous web material was determined by preparing two separate fiber furnishes. The measurements were made on the nonwoven web material after hydroentanglement as set forth in Example I. 
     As clearly evidenced by the figures set forth in Table 5, the addition of the wet strength agent significantly enhances the wet toughness of the nonwoven web material. 
     
                       TABLE 5                                                     
______________________________________                                    
       Wet Toughness (g/cm/cm.sup.2)                                      
Wood Pulp/                                                                
         No Additive      1% Additive                                     
Rayon Ratio                                                               
         MD       CD     Avg.   MD   CD     Avg.                          
______________________________________                                    
70/30    35.9     41.2   38.6   75.3 45     60.2                          
95/5      9.8     11.8   10.8   49.9 30.7   40.3                          
______________________________________                                    
 
    
     As will be appreciated to persons skilled in the art, various modifications, adaptations, and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.