Process for dry-cleaning or de-oiling by means of a perchloroethylene base composition
The present invention concerns a process for dry cleaning and de-oiling textiles, for the purpose of preventing stains from being redeposited on a textile substrate of natural, artificial or synthetic fibers or a mixture of such fibers, and thus holding the soiling or staining substances of the substrate in suspension in the liquid bath in the course of the cleaning or de-oiling operation. 
     The invention also concerns a perchloroethylene base composition for dry cleaning and de-oiling textiles, for the purpose of preventing the stains on a substrate from being redeposited thereon. 
     It is known that, when carrying out dry cleaning or de-oiling operations by means of perchloroethylene, on woven or knitted textiles, the stains which are removed from the textiles have a tendency to be redeposited on the textiles, particularly when the perchloroethylene is not regularly regenerated. This accentuates the phenomenon of &#34;greying&#34; of the textiles, which is more easily observed on white or light-colored fabrics. 
     The fabrics which may be involved in this redeposition are multiple and the complexity of the phenomenon depends mainly on the diversity of the fibers involved in the same cleaning bath and on the hygrometry of the ambient atmosphere. 
     Various anti-redeposition agents have heretofore been proposed for washing textiles in aqueous medium, in particularly cellulose derivatives. 
     For the purpose of cleaning in organic solvent medium, it is known from French Pat. No. 1.386.783 and its addition No. 89.341 that certain reinforcing agents have an anti-redeposition action, in particular oxazines or substituted amides having more than 10 carbon atoms. 
     However, these agents, whether those used in aqueous medium or those used in an organic solvent medium, have the drawback of not being distillable. Accordingly, when regenerating the spent perchloroethylene by distillation, such agents remain at the bottom of the still with the soils or stains and other heavy residual substances, and therefore can no longer be recovered. In other words, these anti-redeposition agents of the prior art must be systematically added to each regeneration operation of the soiled solvent medium. 
     The object of the present invention is to avoid redeposition thereby markedly to limit the &#34;greying&#34; phenomenon, during the dry cleaning or de-oiling operation of textiles of synthetic, artificial, natural or mixed fibers, while making it possible to recover and re-use the anti-redeposition agent of the invention, by distillation with the perchloroethylene during each bath regeneration stage. 
     The applicants have surprisely found that it was possible very substantially to reduce the redeposition of staining matter, by using, in suitably stabilized perchloroethylene, compounds selected from the group consisting of nitroalkanes having from 1 to 4 carbon atoms and mixtures thereof. 
     British Pat. No. 693.792 proposes incorporating a stabilizing amount of a nitroalkane comprising from 1 to 3 carbon atoms and/or its chlorine derivatives, as a stabilization agent for crude perchloroethylene as manufactured, or for purified perchloroethylene in regard to its oxidation on contact with air, or metal surfaces, and/or in the event of its being exposed to light, heat and/or humidity. The stabilizing amount may vary from 0.01 to 1% by weight with respect to the perchloroethylene. 
     The applicants have observed that, with such a stabilizing amount of nitroalkanes as high as 1% by weight in perchloroethylene, the effect against the &#34;greying&#34; phenomenon of textiles is wholly insufficient and indeed negligible. 
     The invention therefore concerns a process for antiredeposition of staining substances, when dry cleaning or de-oiling, by means of suitably stabilized perchloroethylene, the process being characterized in that the &#34;greying&#34; phenomenon of the textiles is markedly reduced when a sufficient amount of an additive represented by a nitroalkane having from 1 to 4 carbon atoms or a mixture of at least two such nitroalkanes is added. 
     Generally, the applicants have found that the desired anti-redeposition effect is apparent when at least 1.25% by weight of the nitroalkane additive is added to the perchloroethylene. 
     The upper limit of the amount of the nitroalkane additive to be added corresponds to that which results in an undesirable secondary action, such as a perceptible deterioration in the textile fiber, a detrimental effect on colored textiles, a tendency to attack the flexible joints of the dry cleaning or de-oiling apparatus. For example, up to 10% by weight of the nitroalkane additive may very well be added, without observing any harmful secondary effect. 
     In a preferred form of the invention, the nitroalkane additive used is one that is highly soluble in perchloroethylene, but of very low solubility in water, and its boiling point does not differ by more than 15° C. from the boiling point of perchloroethylene so as to permit co-distillation of the nitroalkane additive with perchloroethylene. 
     Additives meeting these requirements is represented by nitroethane, nitro-1 propane, 2-nitro propane and mixtures of such compounds with each other. 
     The applicants have found in fact that very good results in regard to anti-redeposition of soiling material are achieved by adding to the perchloroethylene from 2 to 5% by weight of nitroalkanes having 2 to 3 carbon atoms. 
     When carrying out operations of regenerating perchloroethylene by distillation of the spent dry-cleaning or de-oiling baths, the nitro-ethane and propane derivatives undergo co-distillation with the perchloroethylene. This makes it possible for the perchloroethylene, which is regenerated in this way, to be re-used directly as an anti-redeposition composition, while substantially preserving its initial composition. 
     The perchloroethylene may be stabilized by any suitable stabilization agent, in particular those which are compatible with the presence of the C 1  -C 4  nitroalkane additive such as, inter alia, and without this list of compounds being limiting: butylene oxide, tertio-butanol, N-methylpyrrole, n-butanol, diisobutylene, isopropyl acetate and more particularly epichlorohydrin, taken separately or in the form of a mixture of at least two of such compounds. 
     The anti-redeposition process according to the invention may also include the addition of auxiliary substances which are currently employed in dry cleaning, for example cleaning reinforcing agents represented by anionic, cationic or non-ionic surface active agents, such as: alkylsulphonates, alkylarylsulphonates, more particularly Ca dodecylbenzenesulphonate, products of ethoxylation of fatty alcohols and fatty acids, fatty alcohol sulphates, petroleum sulphonates, alkyl polyglycol ethers, alkylphenol polyglycol ethers, more particularly oxyethylenated nonylphenol having 12 ethylene oxide mols, color brightening agents, finishing agents, antistatic agents and water-proofing agents. Each of these auxiliary substances may be used in the usual proportions, for example, from 1 to 10 g per liter of perchloroethylene-based bath, insofar as it is compatible with the presence of the nitroalkane additive of the invention. 
     In addition, the process of the invention may comprise the addition of water in proportions which may be up to about 5 to 6% and more particularly from 2 to 3% by weight relative to the textile to be cleaned. The water may originate from the moisture provided by the textiles themselves and/or by the commercial cleaning reinforcing agents which contain between 4 and 30% and usually from 8 to 14% of their weight of water. Occasionally, additional amounts of water are added (about 2 to 4% by weight relative to the textiles to be cleaned) to the cleaning bath containing the reinforcing agents in order to improve the cleaning effect relative to so-called &#34;meager&#34; soiling substances. 
     The invention also concerns a composition or bath useful in dry cleaning and de-oiling textiles, to prevent &#34;greying&#34; or redeposition of stains on textiles comprising natural, artificial or synthetic fibers or mixtures of such fibers, during the dry cleaning and de-oiling operations, by means of suitably stabilized perchloroethylene, possibly containing up to 6% by weight water with respect to the textiles to be treated and the usual auxiliary substances, more particularly cleaning reinforcing and anti-static agents, each of said auxiliary substances may be present in amounts from 1 to 10 g per liter of said composition, which composition is characterized in that it contains, besides the perchloroethylene and its suitable stabilization agents, from 1.25 to 10% and preferably from 2 to 5% by weight of an additive represented by at least one nitroalkane compound having from 1 to 4 carbon atoms, as an anti-redeposition additive. 
     In a preferred embodiment of the invention, the composition contains, as the anti-redeposition additive, a compound selected from nitroethane, 1-nitropropane, 2-nitropropane and mixtures thereof. 
     The mode of operation permitting evaluation of the &#34;greying&#34; phenomenon of textiles, was as follows: a dispersion of 10 g of staining matter in 1 liter of the perchloroethylene-based composition to be tested was prepared by agitation at ambient temperature for 5 minutes in a container. 
     The staining matter used had the following composition by weight: 
     
         ______________________________________                                    
                     Parts                                                
______________________________________                                    
clay                   7.175                                              
whiting                2.000                                              
brown iron oxide       0.125                                              
carbon black           0.075                                              
wood charcoal          0.625                                              
sand                   90.000                                             
______________________________________                                    
 
    
     and corresponds to the British Standard B 54088-1766 &#34;Standard Oil CTL/V.&#34; 
     The samples of textiles studied were bleached without finishing and comprised: 
     100% polyester weighing 268 g/m 2   
     65% polyester 35% cotton mixture weighing 170 g/m 2   
     100% 6/6 polyamide weighing 170 g/m 2   
     100% polyacrylonitrile (registered trademark Crylor) weighing 230 g/m 2   
     100% wool weighing 178 g/m 2 . 
     These samples were kept for 48 hours in a room maintained at a temperature of 20° C. and 65% relative humidity, and stored in closed containers until the moment of the test. 
     A sample piece of 3.4 g of each of the five textiles mentioned above was then introduced into a miniature-size dry cleaning machine which was set in operation. 
     Without stopping the machine, the staining matter prepared as indicated above was then poured onto the textile samples, and operation was continued at a bath temperature of about 25° C. for a period of 5 minutes, before centrifuging for 10 seconds. The samples were dried for 10 minutes at a temperature of 60° C. 
     Each of the samples treated in this way, and &#34;greyed&#34; to a greater or lesser extent, was subjected to an operation of determining the reflectance index by means of the &#34;Reflection meter 670&#34; of the company &#34;Photovolt&#34; (United States of America) provided with a green filter. 
     The apparatus was set up to 100 for each bleached but untreated textile, and a reflectance index was measured for each &#34;greyed&#34; sample. 
     The figure value of the &#34;greying&#34; phenomenon is represented by the difference between 100 and the value of the reflectance index measured for each sample. The less the &#34;greying&#34; phenomenon, the closer this index will be to the value of 100. 
    
    
     In the following examples which illustrate the various aspects of the invention in non-limiting manner, the stated percentages of the components of the various compositions are expressed by weight. 
     EXAMPLES 1 to 6 
     Using the mode of operation set out above, the &#34;anti-greying&#34; effect or anti-redeposition effect of various compositions based on initially stabilized perchloroethylene, in which different proportions of nitroethane, 1-nitropropane and/or 2-nitro propane were incorporated, is examined. 
     The starting perchloroethylene was stabilized by 0.02% of epichlorohydrin and 0.002% of N-methylpyrrole. 
     Following Table I summarizes the results obtained. This table also shows a reference test carried out with a composition which did not contain nitroalkane according to the invention. 
     
                                           TABLE I                                 
__________________________________________________________________________
                   65/35                                                  
                       100%                                               
                           100%                                           
                100%                                                      
                   poly-                                                  
                       6/6 poly-                                          
Exam-                                                                     
    Composition poly-                                                     
                   ester                                                  
                       poly-                                              
                           acrylo-                                        
                               100%                                       
ples                                                                      
    in % by wt.                                                           
            Fiber                                                         
                ester                                                     
                   cotton                                                 
                       amide                                              
                           nitrile                                        
                               wool                                       
__________________________________________________________________________
                Measure of reflectance index                              
Refer-                                                                    
    Stabilized                                                            
ence                                                                      
    perchloro-                                                            
            100 52 80  68  61  81                                         
    ethylene                                                              
1   Stabilized                                                            
    perchloro-                                                            
    ethylene                                                              
            96  89 88  93  72  92                                         
    nitroethane                                                           
            4                                                             
2   Stabilized                                                            
    perchloro-                                                            
    ethylene                                                              
            96  81 84  89  71  87                                         
    1-nitropropane                                                        
            4                                                             
3   Stabilized                                                            
    perchloro-                                                            
    ethylene                                                              
            96  80 88  93  73  90                                         
    2-nitropropane                                                        
            4                                                             
4   Stabilized                                                            
    perchloro-                                                            
    ethylene                                                              
            96                                                            
    nitroethane                                                           
            1   83 86  92  71  90                                         
    1-nitropropane                                                        
            1                                                             
    2-nitropropane                                                        
            2                                                             
5   Stabilized                                                            
    perchloro-                                                            
    ethylene                                                              
            96  80 85  91  70  89                                         
    1-nitropropane                                                        
            2                                                             
    2-nitropropane                                                        
            2                                                             
6   Stabilized                                                            
    perchloro-                                                            
    ethylene                                                              
            96  88 88  93  73  90                                         
    nitroethane                                                           
            2                                                             
    2-nitropropane                                                        
            2                                                             
__________________________________________________________________________
 
    
     These results show a marked improvement in anti-redeposition when the nitroalkanes of the invention are incorporated in the stabilized perchloroethylene, compared to stabilized perchloroethylene which does not contain nitroethane, 1-nitropropane and/or 2-nitropropane as an anti-redeposition additive. 
     EXAMPLES 7 to 10 
     Operation was similar to Examples 1 to 6, except that a mixture of cleaning reinforcing agents having the following composition was also added to the perchloroethylene-based bath: 
     
         ______________________________________                                    
                           %                                              
______________________________________                                    
oxyethylenated nonylphenol having 12 ethylene                             
oxide mols                   32                                           
calcium dodecyl benzenesulphonate (with 30%                               
water)                       43                                           
polyglycol having a mean molecular weight of                              
about 300                     5                                           
butylglycol                  20                                           
______________________________________                                    
 
    
     The water added to the bath (apart from the water provided by the reinforcing agents and the textiles) represents about 0.8 g/l of bath, which corresponds approximately to a water content of 4% relative to the fibers. The results observed are set forth in the following Table II, which also shows corresponding reference tests performed with compositions not containing the nitroalkanes of the invention. 
     
                                           TABLE II                                
__________________________________________________________________________
                    65/35                                                 
                        100%                                              
                            100%                                          
                 100%                                                     
                    poly-                                                 
                        6/6 poly-                                         
Exam-                                                                     
    Initial      poly-                                                    
                    ester-                                                
                        poly-                                             
                            acrylo-                                       
                                100%                                      
ples                                                                      
    bath composition                                                      
             Fiber                                                        
                 ester                                                    
                    cotton                                                
                        amide                                             
                            nitrile                                       
                                wool                                      
__________________________________________________________________________
                 Measure of reflectance index                             
Refer-                                                                    
    Stabilized                                                            
ence                                                                      
    perchloro-                                                            
             100 52 80  68  61  81                                        
    ethylene                                                              
Refer-                                                                    
    Stabilized                                                            
ence                                                                      
    perchloro-                                                            
    ethylene 100                                                          
    Cleaning re- 58 70  74  71  76                                        
    inforcing agts                                                        
             2 g/l                                                        
Refer-                                                                    
    Stabilized                                                            
ence                                                                      
    perchloro-                                                            
    ethylene 100                                                          
    Cleaning re- 76 74  80  74  74                                        
    inforcing agts                                                        
             2 g/l                                                        
    water    0.8 g/l                                                      
7   Stabilized                                                            
    perchloro-                                                            
    ethylene 96                                                           
    2-nitropropane                                                        
             4   82 83  89  83  89                                        
    Cleaning rein-                                                        
    forcing agts                                                          
             2 g/l                                                        
8   Stabilized                                                            
    perchloro-                                                            
    ethylene 96                                                           
    1-nitropropane                                                        
             4   78 85  89  83  90                                        
    Cleaning rein-                                                        
    forcing agts                                                          
             2 g/l                                                        
    water    0.8 g/l                                                      
9   Stabilized                                                            
    perchloro-                                                            
    ethylene 96                                                           
    2-nitropropane                                                        
             2                                                            
    1-nitropropane                                                        
             1   80 82  89  80  89                                        
    nitroethane                                                           
             1                                                            
    Cleaning rein-                                                        
    forcing agents                                                        
             2 g/l                                                        
10  Composition                                                           
    of Example 9                                                          
             100 78 84  88  80  89                                        
    water    0.8 g/l                                                      
__________________________________________________________________________
 
    
     It will be seen that with the compositions of Examples 7 and 9, the results obtained are very good, taking into account the very large amount of staining substances added relative to the weight of textiles treated. 
     In the presence of water (composition of Examples 8 and 10), the results remain substantially the same as those obtained with the compositions of Examples 7 and 9. 
     On the basis of these results, it will be seen that the addition of reinforcing agents to the stabilized perchloroethylene alone is not capable of improving the anti-redeposition properties of the bath, except, and on average to a small v extent, in the case of the synthetic fibers. In the presence of reinforcing agents and water, the good results obtained with the compositions of Examples 8 and 10 are at least maintained if not improved, as is the case for wool. 
     EXAMPLES 11 to 14 
     These examples illustrate the continuous de-oiling of knitted articles. In order to facilitate the knitting of such fibers as 100% polyester, 100% polyacrylonitrile, 100% wool, polyamide, polyester-cotton, they are coated with mineral oils (synthetic fibers) or oleins (wool). These fibers are knitted on industrial looms and issue in a tubular form. 
     The staining on these knitted articles essentially results from the dust on the floors when the articles fall from the carriages or the looms. 
     These knitted articles are de-oiled discontinuously in the same manner as for the dry-cleaning operation. For this purpose, use is made of dry-cleaning machines of large capacity (from 50 to 150 kg of working load) with stabilized perchloroethylene, as in Examples 1 to 6, without the addition of cleaning reinforcing agent or water, in which the nitroalkanes of the invention are incorporated. 
     Table III hereinafter shows the results obtained. 
     
                                           TABLE III                               
__________________________________________________________________________
                    65/35                                                 
                        100%                                              
                            100%                                          
                 100%                                                     
                    poly-                                                 
                        6/6 poly-                                         
Exam-                                                                     
    Initial      poly-                                                    
                    ester-                                                
                        poly-                                             
                            acrylo-                                       
                                100%                                      
ples                                                                      
    both composition                                                      
             Fiber                                                        
                 ester                                                    
                    cotton                                                
                        amide                                             
                            nitrile                                       
                                wool                                      
__________________________________________________________________________
                 Measure of reflectance index                             
Refer-                                                                    
    Stabilized                                                            
ence                                                                      
    perchloro-                                                            
    ethylene 100 71 82  75  66  85                                        
11  Stabilized                                                            
    perchloro-                                                            
    ethylene 96  91 90  94  74  93                                        
    nitroethane                                                           
             4                                                            
12  Stabilized                                                            
    perchloro-                                                            
    ethylene 96  83 88  93  72  90                                        
    1-nitropropane                                                        
             4                                                            
13  Stabilized                                                            
    perchloro-                                                            
    ethylene 96  85 90  94  76  92                                        
    2-nitropropane                                                        
             4                                                            
14  Stabilized                                                            
    perchloro-                                                            
    ethylene 96                                                           
    nitroethane                                                           
             1   89 90  93  74  82                                        
    1-nitropropane                                                        
             1                                                            
    2-nitropropane                                                        
             2                                                            
__________________________________________________________________________
 
    
     This table shows the significant improvement in respect of anti-redeposition when nitroalkanes of the invention are incorporated in the stabilized perchloroethylene, relative to the reference comprising stabilized perchloroethyelene alone.