Abstract:
A method is disclosed of preparing a liquid formulation for application as a deposit on a substrate. The method includes the steps of providing a liquid having a first viscosity in a non-evaporative state; and adding an amine-acid adduct to the liquid to form a mixture having a second viscosity greater than the first viscosity. The amine-acid adduct is evaporative such that the amine-acid adduct is substantially completely removed from the deposit in a functionally dry state.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 11/132,520 filed May 19, 2005, which claims priority to U.S. Provisional Patent Application No. 60/572,333 filed May 19, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to liquid formulations designed for application to substrates as coatings, printed patterns or the like, and is concerned in particular with a formulation comprising a mixture of a liquid and volatile viscosity altering components, the latter being substantially completely evaporative when the mixture is applied to a substrate and processed to its functionally dried state. 
     2. Description of the Prior Art 
     There are solutions and dispersions, which are used as coatings or printing inks that are best applied from a very dilute state, such as in a water or non-aqueous medium. In many cases, however, the rheology of these coatings or inks may cause them to flow too freely to allow for proper control of the amount of their application. Further, if discreetly applied, they may flow too freely to maintain their target positions. 
     There exists an abundance of rheology control agents, commonly referred to as “thickening agents”, which can be incorporated in the continuous liquid phase of a system to modify its viscosity to an appropriate level (i.e. one which meets the requirements of the application method). Unfortunately, when used in systems which are subsequently dried, the thickening agent left behind is often of a high enough concentration to adversely affect the performance of the coating or printing. 
     The printing of conductive inks and the application of optical coatings are two non-limiting examples where this dichotomy exists between the requirement of elevated viscosity for application purposes and purity in the functionally dried state. The dielectric properties of residual thickening agents can disadvantageously reduce the conductivity of conductive ink deposits, and the opacity of such residual thickening agents can introduce haze that adversely affects the desired clarity of optical coatings. 
     A need exists, therefore, for coating and ink formulations having rheologies that have been adjusted by the incorporation of thickening agents to achieve viscosities appropriate for the intended application modes, with the thickening agents being substantially completely removed from the resulting coating or ink deposits in their functionally dried states as applied to the substrates. 
     As herein employed, “functionally dried state” means that the volatile components of a liquid mixture have been evaporated to an extent sufficient to place the mixture in condition for its intended use. 
     Again, as herein employed, a component of a liquid mixture is considered to have been “substantially completely removed” when any residue of the component does not prevent the mixture, when in its functionally dried state, from performing its intended use. 
     SUMMARY OF THE INVENTION 
     In accordance with an embodiment, the invention provides a method of preparing a liquid formulation for application as a deposit on a substrate. The method includes the steps of providing a liquid having a first viscosity in a non-evaporative state; and adding an amine-acid adduct to the liquid to form a mixture having a second viscosity greater than the first viscosity. The amine-acid adduct is evaporative such that the amine-acid adduct is substantially completely removed from the deposit in a functionally dry state. 
     In accordance with another embodiment, the invention provides a method of preparing a formulation for application on a substrate. The method includes the steps of providing a liquid having a first viscosity; combining an amine with the liquid; and adding an acid to the liquid amine combination to form a mixture, such that the amine and acid form an amine-acid adduct. The amine-acid adduct comprises more than 10% by weight of said mixture, and the mixture has a second viscosity greater than said first viscosity. The amine-acid adduct is evaporative to a reduced level of less than about 0.1% by weight of the deposit in a functionally dry state as applied to the substrate. 
     In accordance with yet another embodiment, the invention provides a method of coating or printing a substrate with a liquid. The method includes the steps of providing a liquid having a first viscosity; providing an amine-acid adduct; combining the liquid with the amine-acid adduct to form a mixture having a second viscosity greater than the first viscosity; applying the mixture as a deposit on the surface of the substrate; and drying the deposit to a functionally dry state in which the amine-acid adduct is substantially completely removed from the deposit. 
     In accordance with a further embodiment, the invention provides a method of coating or printing a substrate with a liquid. The method includes the steps of providing a liquid having a first viscosity; providing an amine; combining the liquid with the amine; adding an acid to the liquid and amine to form a mixture having a second viscosity greater than the first viscosity, with the amine and acid forming an amine-acid adduct; applying the mixture as a deposit on the substrate; and drying the deposit to a functionally dry state in which the amine-acid adduct is substantially completely removed from the deposit. 
    
    
     DETAILED DESCRIPTION 
     The present invention employs the amine carbamate as a viscosity control agent for a range of solutions/dispersions from hydrocarbons to alcohols to water. Primary and secondary amines are candidates; tertiary amines are not useful. 
     The amines, when treated with CO 2  form the amine carbamate (and with water can form the amine carbonate). This zwitter ion salt formed can, as is the case of fatty acid esters and salts, be used to alter the rheology of a liquid in which such salts are compatible. 
     The use of amines, especially those that have a boiling point at about the temperature of that of the solvent or the continuous phase of a liquid mixture, allows the carbamate (carbonate) to break down (release CO 2 ) and the amine to evaporate off with the other volatile components of the mixture. In the course of applying the mixture to a substrate and processing it to its functionally dried state, the carbamate (carbonate) is substantially completely removed, with any residue being as low as 0.2%, typically less than 0.1%, preferably less than 0.01%, and most preferably less than 0.001% by weight of the thus applied and processed mixture. 
     Applications where this type of rheology control is advantageous include, for example:
         (a) Nanotechnology, where the elements being coated are often in very dilute concentration, but the coatings need a higher viscosity to allow even placement. This is of particular interest when dealing with carbon nanotubes, where viscosity control not only facilitates application, but also has a stabilizing effect in preventing the nanotubes from entangling in the carrier liquid, thus agglomerating and falling out of the carrier liquid before coating, discrete coating, or printing.   (b) The application of optical coatings, e.g., for film based vision driven user interfaces (displays, touchscreens), clear protective coatings for graphics, etc., where clarity of the functionally dried deposit is a prime requirement.   (c) Other contamination-sensitive coatings that are used in electronic product fabrication. For example, use of “ink jet” type of coatings (printing) used in placement of resist coatings; or adhesion treatments for discrete placement of conductive elements in a circuit.       

     In the following examples, liquid mixtures were prepared using one or more of the following components:
     CNT Ink Concentrate (3000 ppm CNT) obtained from Eikos in Franklin, Mass.   Solvent Ink Concentrate #7633-41P obtained from Raffi &amp; Swanson in Wilmington, Mass.   Diluting Acrylate IBOA (Isobornyl Acrylate) obtained from Surface Specialties UCB in Smyrna, Ga.   UV Coating ECX 4019 obtained from Cognis Corporation in Ambler, Pa.   

     Example 1 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Conductive Ink 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 WB Carbamate: 
                 sec-Butyl Amine 
                 90 grams 
               
               
                   
                 Water 
                 10 grams 
               
               
                   
                 CO 2   
                 Bubble through until 
               
               
                   
                   
                 viscosity 11,500-12,500 cP 
               
               
                 CNT Ink 
                 CNT Ink Concentrate 
                  1% 
               
               
                 Formula: 
                 (3000 ppm CNT) 
               
               
                   
                 Water 
                 21% 
               
               
                   
                 Solvent (IPA) 
                 50% 
               
               
                   
                 Carbamate 
                 28% 
               
               
                   
                   
                 100%  
               
               
                   
               
               
                 Starting viscosity of ink concentrate 30-100 cP 
               
               
                 Final viscosity of mixture 1500-2000 cP 
               
             
          
         
       
     
     Example 2 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Optical Coating 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Carbamate: 
                 n-Butyl Amine 
                 50 grams 
               
               
                   
                 Solvent 
                 50 grams 
               
               
                   
                 CO 2   
                 Bubble through until 
               
               
                   
                   
                 viscosity 10,000 cP 
               
               
                 Solvent Ink Formula: 
                 Solvent Ink Concentrate 
                 10% 
               
               
                   
                 Solvent 
                 70% 
               
               
                   
                 Carbamate 
                 20% 
               
               
                   
                   
                 100%  
               
               
                   
               
               
                 Starting viscosity of concentrate 100-200 cP 
               
               
                 Final viscosity of concentrate 1000-1200 cP 
               
             
          
         
       
     
     Example 3 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Optical Coating 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Carbamate: 
                 n-Propyl Amine 
                 20 grams 
               
               
                   
                 Diluting Acrylate 
                 80 grams 
               
               
                   
                 CO 2   
                 Bubble through until 
               
               
                   
                   
                 viscosity 10,000 cP 
               
               
                 UV Coating Formula: 
                 UV Coating 
                 79% 
               
               
                   
                 Carbamate 
                 21% 
               
               
                   
                   
                 100%  
               
               
                   
               
               
                 Starting viscosity of UV coating 200-250 cP 
               
               
                 Final viscosity of mixture 1500-1800 cP 
               
             
          
         
       
     
     The mixtures of Examples 1-3 were applied to a clear polyester film using a Meyer drawdown rod and processed to their functionally dried state in a laboratory oven at 70° C. for one minute. The resulting dried deposits were tested for residual carbamate components using a pHydrion Insta-Check Surface pH Pencil (available from VWR International of West Chester, Pa., U.S.A.). In each case, the pH reading ranged between 5 and 6. 
     Based on the definition of pH (the chemical fact that pH is the negative logarithmic function of the concentration of the hydrogen ion, written as the equation pH=−log [H + ] from Holtzclaw et. al.  General Chemistry, p.  459, 1984, D. C, Heath and Co., Lexington, Mass.), the higher the concentration of the hydrogen ion, the lower the pH. Any residual amine component of the carbamates would decrease the hydrogen ion concentration and thereby increase the pH as measured in this test. 
     Using this method of calculation, and based on the pH readings recited above, the residual carbamate concentrations in the functionally dried residues of Examples 1-3 were determined to be in the range of 7.3×10 −6 %. To the extent present at such reduced levels, any residual carbamate was observed to have no significant adverse impact on the conductivity of the ink of Example 1, or on the clarity of the coatings of Examples 2 and 3. 
     Zwitter ion adducts of amines can be formed with materials other than CO 2 . Carbon disulfide (CS 2 ) also forms stable amine salts, as do hydrogen chloride (HCl) and low boiling temperature organic acids (e.g. acetic acid, formic acid, propionic acid). However, CO 2  has the advantage of being of minimal toxicity and is a relatively weak acid, which may be a benefit to some of the coatings being treated. 
     Another advantage is that few amine carbamates/carbonates are stable much above 100° C. Thus a CO 2 -based adduct, being easier to break down, has an excellent overall fugitive property. 
     As an alternative to making an amine adduct and then adding the adduct to a coating (or printing) system, the amine may be added directly to the coating, followed by addition of the CO 2 , CS 2 , etc. so as to form the amine adduct in-situ. In all cases, upon drying, the amine carbamate would decarboxylate, and then the amine could be driven off. The temperature needed would depend on the amine and whether or not the regenerated amine was needed to play a roll in maintaining coating “wet out” during the drying process. 
     The printed or coated mixtures of the present invention may be dried to their functionally dried state by various methods, e.g., thermal drying, air drying, infrared drying, microwave drying and vacuum drying. 
     Amines useful in the present invention may be selected from the group listed below in Table 1. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Amine 
                 B.P. ° C. 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Morpholine 
                 129 
               
               
                   
                 N-ethyl-n-butyl amine 
                 91 
               
               
                   
                 n-butyl amine 
                 78 
               
               
                   
                 sec-butyl amine 
                 63 
               
               
                   
                 t-butyl amine 
                 46 
               
               
                   
                 n-propyl amine 
                 48 
               
               
                   
                 n-pentyl amine 
                 104 
               
               
                   
                 di-n-butylamine 
                 129 
               
               
                   
                 N-methyl-n-butylamine 
                 91 
               
               
                   
                 Ethylene diamine 
                 117 
               
               
                   
                 AMP (2 amino-2-methyl-1-propanol) 
                 166 
               
               
                   
                 DMEA (dimethyl, ethanol amine) 
                 135