AQUEOUS ELECTROPHORETIC DEPOSITION
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Abstract
From an environmental, safety and economic perspective water should be the solvent of choice for electrophoretic deposition under industrial circumstances. However, because of the electrolytic decomposition of water, the majority of EPD is carried out in non-aqueous solvents.
Approaches of the art for aqueous deposition involve the separation of the reaction and deposition front by means of a membrane, the use of palladium electrodes to absorb the formed hydrogen, addition of chemicals to suppress the electrolysis reaction, or lowering voltages below the threshold for water electrolysis. With the first two solutions, the production of coatings is impractical since the deposit is not formed on the electrode, or the electrode material is not suitable since the substrate is usually prescribed by the application. The use of specialty chemicals is expensive and difficult to control. Low voltages have been used to form high quality deposits from aqueous systems but they display very low deposition rates, which are not attractive from an economical perspective.
Present invention provides a system and a means for which high voltages can be used in the electrophoretic deposition from aqueous suspensions without decomposition of water at satisfying deposition rates. It shows that the deposits obtained show a high green density with excellent surface quality.
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Citations
75 Claims
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1-53. -53. (canceled)
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54. A coating process comprising the steps of:
- immersing an electrode or porous substrate placed in front of an electrode in an aqueous medium comprising charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles and subjecting said charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles in an aqueous medium to (asymmetric) unbalanced alternating current (UAC) electric fields, having a frequency and a positive and negative part each having an amplitude and a duration, to deposit electrophoretically said charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles onto said electrode or porous substrate placed in front of an electrode, wherein said amplitude of said unbalanced alternating current (UAC) electric field differs significantly for the positive and negative part, while maintaining an applied signal whose net integral over one period, i.e. average potential, is lower in absolute value than 4V.
- View Dependent Claims (55, 56, 57, 58, 59, 60, 61, 62)
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63. A coating process comprising the steps of:
- immersing an electrode or porous substrate placed in front of an electrode in an aqueous medium comprising charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles and subjecting said charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles in an aqueous medium to (asymmetric) unbalanced alternating current (UAC) electric fields, having a frequency and a positive and negative part each having an amplitude and a duration, to deposit electrophoretically said charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles onto said electrode or porous substrate placed in front of an electrode, wherein said amplitude of said unbalanced alternating current (UAC) electric field differs significantly for the positive and negative part, while maintaining an applied signal whose net integral over one period, i.e. average potential, is lower in absolute value than 4V used to form smooth deposits with no visible defects having a surface with a Ra of 10 nm to 50 μ
m. - View Dependent Claims (64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75)
- immersing an electrode or porous substrate placed in front of an electrode in an aqueous medium comprising charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles and subjecting said charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles in an aqueous medium to (asymmetric) unbalanced alternating current (UAC) electric fields, having a frequency and a positive and negative part each having an amplitude and a duration, to deposit electrophoretically said charged, partially charged or self-charging organic or metallo-organic molecules or colloidal particles onto said electrode or porous substrate placed in front of an electrode, wherein said amplitude of said unbalanced alternating current (UAC) electric field differs significantly for the positive and negative part, while maintaining an applied signal whose net integral over one period, i.e. average potential, is lower in absolute value than 4V used to form smooth deposits with no visible defects having a surface with a Ra of 10 nm to 50 μ
Specification