US 3853782 A
An alkaline aqueous cleaning solution for removing residue from silk screen stencils and containing active components for removal of residual ink, as well as active components for removal of residual stencil barrier areas. The working solution is inert to the silk utilized in the woven screen, as well as to the metallic frame support.
Description (OCR text may contain errors)
United StatesgPatent [191 Chang SILK SCREEN CLEANER COMPOSITION  Inventor: Edward H. Chang, Burns ville, Minn.
 Assignee: Fremont Industries, Inc.-, Shakopee,
22 Filed: Dec.7, 1972 21 Appl. No: 312,936
 U.S.'Cl 252/139, 252/l56,'252/158, 252/533, 252/534  Int. Cl .1 ..C1ld 3/065  Field of Search..... 252/139, 156, 158, 533, 252/534  References Cited UNITED STATES PATENTS 3,607,764 9/1971 Crotty 252/-l58'X [111' 3,853,782 Dec. 10, 1974 3,681,250 8/1972 Murphy 252/158 FOREIGN PATENTS OR APPLICATIONS 667,292 7/1963 Canada 252/158 Primary Examiner-Leland A. Sebastian  ABSTRACT 7 Claims, N0 Drawings l SILK SCREEN CLEANER COMPOSITION BACKGROUND OF THE INVENTION ward the woven silk as well as to the metallic frames utilized to support the weave.
Silk screen techniques are widely used in certain I areas of technology including graphics, printed circuitry preparation, and the like. Traditionally, the silk weave is maintained or retained in a metallic frame, and a stencil masking material is applied thereto. The masking material traditionally includes polyvinyl acetate-polyvinyl alcohol as a binder together with a photosensitive substance such as sodium chromate, sodium bichromate, or a diazo material. Upon appropriate exposure of the photosensitive material to light, the mask image is prepared and the latent nonpolymerized materials are washed from the screen weave, and the mask is then ready for use. I
While in use, a number of paints or other materials are employed to properly prepare the image on the surface of the substrate or other medium to receive print. Examples of inks which are traditionally used are vinyls, alkyds, latex materials, thermosetting acrylics, lacquers including pigmented and non-pigmented materials, enamels, thermosetting polyethylene terephthalate, polyethylene or polypropylene, along with adhesives. In addition, epoxy-base materials are also utilized.
Following use, it is desirable to remove the residual ink along with any residual stencil masking. In the past, this has traditionally been accomplished by utilizing a two-step process wherein a solvent such as toluol, methyl ethyl ketone, acetone, mineral spirits, or mixtures thereof to dissolve out any of the residual ink. The polyvinyl acetate stencil masking material is resistant to these solvents, and hence a-second operation was necessary wherein an aqueous solution of chlorine, preferably from percent to 7 percent chlorine, was utilized to digest the polyvinyl acetate residue. Such concentrations of chlorine are readily available from commercial bleach mixtures. These operations are time consuming and costly, and hence are not particularly desirable.
In certain instances, conventional paint stripers have been utilized, however the high pH due to high lye content normally adversely affects the aluminum frames. Low alkaline cleaners have been proposed, however they are undesirable in that the emulsion material may be removed, but the residual paint is not. The present invention overcomes these disadvantages by making it possible to utilize a single solution which removes residual ink and residual stencil masking without adversely affecting the metallic aluminum frames.
SUMMARY OF THE INVENTION In accordance with the present invention, an aqueous solution is employed for removing residue from silk screen stencils, wherein the solution contains an alkaline hydroxide along with other components which function as dispersents for pigments and other soils, solvents for the film-forming resins, and an inhibitor to protect the surface of the metallic frames, normally aluminum. The composition provides a working solution which rapidly removes residue from the screen surface, holds the residues in suspension; all of this being accomplished without adversely affecting either the silk weave substance or the metallic frame. I
Therefore, it is a primary object of the present invention to provide an improved cleaner material for re-.
moving residual ink and residual stencil masking materials from silk screens.
It is yet a further-object of the present invention to provide an improved solution for the effective removal of residual ink and stencil masking material from woven silk screens, with the formulations of the present invention being capable of effectively removing this residue without adversely affecting either the silk weave or the metallic frames employed for the weaves.
In accordance with the preferred embodiment of the present invention,.an alkaline concentrate is prepared having the following formulation:
Component vPercent by Weight Potassium hydroxide 3.970 Tetrapotassium pyrophosphate 9.000 Sodium'silicate solids 6.250 Sodium gluconate L875 Sodium ligno sulfonate 0.625 Diethylene glycol monobutyl ether 5.000 Diethylene glycol monoethyl ether 25.000 Octylphenoxyethanol 0.565
Balance water This particular formulation is utilized as a concentrate which is further diluted with water to prepare the ultimate working solution. In this connection, the concentrate is incorporated in water in a quantity ranging from between 10 percent and 60 percent of concentrate, balance water.
For performing the actual cleaning operation, the working solution is placed in a tank and the screen desired to be cleaned is immersed in the tank fora period of approximately 15 minutes. Such immersion is normally sufficient to remove approximately percent of the soil present on the screen, and effectively softens the polyvinyl acetate resist. Obviously, if the material were to be heated, the immersion time could be shortened.
Thereafter, the screen is subjected to a spray rinse with the same working solution, with the rinse preferably being achieved with a nozzle capable of dispensing a discharge of approximately 2 gallons per minute at 500 psi. This will effectively remove the soil from the screen and after rinsing and drying, the screen is suited for re-use.
In certain instances, silk screens are prepared utilizing multi-filament or monofilament polyester or nylon materials. The working solution of the present invention has been found to be non-harmful to these fabrics. Also, in addition to aluminum, steel and wood frames are in use, neither of which are adversely affected by the working solutions of the-present invention.
The working solutions of the present invention are operational without requiring the use of flammable solvents or chlorine bleaches, both of which are difficult for handling. Also, the surface active agents which are employed in the material are biodegradible, and thus provide an advantage in ultimate disposal.
The formulations have long tank life, and exceptionally long shelf life. Thus, unusual precautions are not required for use.
In the working solution, elevated temperatures are not an absolute requirement, however it has been found that temperatures in the range of from 180 F. to 200 F. are desirable from the standpoint of cleaning efficiency.
In the' preparation of dilute working solutions, it has been found that a workable range may be expressed as follows:
Component Percent by Weight Potassium hydroxide Tetrapotassium pyrophosphate Sodium silicate solids Sodium gluconate Sodium ligno sulfonate Diethylene glycol monobutyl ether Diethylene glycol monoethyl ether Nonionic surface active agent selected from the group consisting of octyphenoxyethanol and nonylphenoxyethanol Balance water For most operations, however, and for the preparation of a solution which is usable with all inks, particularly those as set forth hereinabove, the following formulation is recommended:
Component Percent by Weight This compositional range has been found particularly desirable for use with paints of the following composition or formulation; vinyls, alkyds, latex materials, thermosetting acrylics, lacquers including pigmented and non-pigmented materials, enamels, thermosetting polyethylene terephthalate, polyethylene or polypropylene, along with adhesives.
In certain instances, highly cured epoxy-base paints are removed with a certain amount of difficulty, how ever the composition of the present invention is useful in removing epoxy-base paints which have not become totally or completely cured on the surface of the screen.
In the formulation, potassium hydroxide is preferred, however it is understood that the hydroxide may be an alkaline earth hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide. This component in the formulation is an alkaline donor which enhances the cleaning function, as well as providing a neutralization source for acidic soil. Furthermore, potassium hydroxide functions as a silicate stabilizer as a potassium ion donor in the system.
The tetrapotassium pyrophosphate, in addition to functioning as a water softener in the working solution, is a strong dispersent for pigments dissolved in the cleaning operation.
Sodium gluconate, also identifiable as the sodium salt of 2, 3, 4, 5, 6 pentahydroxy-l-hexanoic acid, and the sodium ligno sulfonate function as strong dispersents for removed soil, and also operate to complex metallic ions present in the soils. In addition, these materials function as an anti-scale and sludge conditioner.
Sodium lignosulfonate is the sodium salt of lignin sulfonic acid. While the exact structure of lignin has not as yet been determined, it is known to be a polymer with an average molecular weight of about 10,000. The repeating monomer unit is guar-acyl propane having the structural formula as follows:
Sodium silicate solids are employed having'a Na O/- SiO ratio of l: 1.6 up to about 123.22. This range of materials has been found to be useful. The sodium silicate provides a strong corrosion inhibitor for soft metals such as aluminum, and also provides for a substantial degree of detergency.
The diethylene glycol monobutyl ether and the diethylene glycol monoethyl ether are employed for their properties of strong penetrants and solvents for the film-forming resins. They have low odor, are water soluble, with high boiling points.
The nonionic surface active agent is preferably selected from the group consisting of octyphenoxyethanol and nonylphenoxyethanol. These materials have a high cloud point (normally above C. are biodegradable, and alkaline stable. They tend to reduce the surface tension and therefore aid in rinsing after film removal. Other nonionic or anionic surface active agents may be used if desired. Anionic surface active agents which may be utilized successfully are sodium alkylbenzene sulfonate materials which are, of course, widely used for these purposes. These materials are commercially available.
These materials are a class of synthetic anionic surface active agents represented by the general formula:
U iCHflHlOlFcmom-o 5 03M wherein R is a straight or branched chain saturated hydrocarbon group having from about 8 to about 18 carbon atoms, such as a straight or branched group, such as octyl, nonyl, decyl, dodecyl and the like; A is either oxygen, sulfur, a carbonamide group, thiocarbonamide group, a carboxylic group or thiocarboxylic ester group, x is an integer from 3 to 8 and M is preferably sodium, but may be either hydrogen, potassium, ammonium, an organic amine such as ethanolamine, diethan- '5 olamide, triethanolamine, ethylene diamine or the like.
Compounds illustrative of the sulfated oxyethylated alkyl phenol class of anionic surface active agents include ammonium nonylphenoxy tetraethylenoxy sulfate, sodium dodecylphenoxy triethyleneoxy sulfate,
ethanolamine decylphenoxy tetraethyleneoxy sulfate and potassium octylphenoxy triethyleneoxy sulfate.
These materials are also commercially available.
Working solutions having the following specific formulations were prepared.
EXAMPLE 1 Percent Component by Weight Potassium hydroxide 0.397 Tetrapotassium pyrophosphate 0.9 Sodium silicate solids (Na O/SiO 1:3;22) 0.625 Sodium gluconate 0.1875 Sodium ligno sulfonate 0.0625 Diethylene glycol monobutyl ether 0.5 Diethylene glycol monethyl ether 25 Octylphenoxyethanol 0.0565 Balance water This formulation provided good results.
EXAMPLE 2 Percent I Component by Weight Potassium hydroxide l.99 Tetrapotassium pyrophosphate 4.5 Sodium silicate solids (Na o/SiO 1:1.6) 3. l25 Sodium gluconate 0.938 Sodium ligno sulfonate 0.313 Diethylene glycol monobutyl ether 2.5 Diethylene glycol monoethyl ether 12.5 Nonylphenoxyethanol 0.238 Balance water.
i This formulation provided good results.
EXAMPLE 3 Percent Component by Weight Potassium hydroxide 1.32 Tetrapotassium pyrophosphate 3.0 Sodium silicate solids Nap/$0, 1:1.6) 2.08 Sodium gluconate 0.625 Sodium ligno sulfonate 0.208 Diethylene glycol monobutyl ethe 1.67 Diethylene glycol monethyl ether 8.33 Sodium dodecylphenoxy-triethyleneoxy sulfate 0. l 88 Balance water This formulation provided good results.
. EXAMPLE 4 Percent Component by Weight Potassium hydroxide 1.32 Tetrapotassium pyrophosphate 3.0 Sodium silicate solids 2.08 Sodium gluconate 0.625 Sodium ligno sulfonate 0.208 Diethylene glycol monbutyl ether L67 Diethylene glycol monoethyl ether 8.33 Potassium octylphenoxy triethyleneoxy sulfate 0. I88
Balance water screens.
- I claim: 7
1. An alkaline aqueous cleaning solution for removing residue from silk screen stencils andhaving the following formulation:
Percent Component by Weight An alkaline earth hydroxide selected from the group consisting of sodium and potassium hydroxides .3 to 2 Tetrapotassium pyrophosphate 7 to 4 Sodium silicate solids (Na,O/SiO l:l.6 Y
to 1:322) I 5 to 3 Sodium gluconate 15 to 1 Sodium ligno sulfonate 05 to .3 Diethylene glycol monobutyl ether 25 to 2 5 Diethylene glycol monoethyl ether 2 to 20 Surface active agent selected from the group consisting of nonionic and anionic surface active agents 04 to .4
Balance water 2. The alkaline aqueous cleaning solution as defined in claim 1 being particularly characterized in that said alkaline earth hydroxide is potassium hydroxide.
3. The alkaline aqueous cleaning solution as defined in claim 1 wherein said surface active agent is selected from the group consisting of octylphenoxyethanol and nonylphenoxyethanol.
4. The alkaline aqueouscleaning solution as defined in claim 1 being particularly characterized in that said.
solution has the following formulation:
Component Percentby Weight Potassium hydroxide .5 to L5 Tetrapotassium pyrophosphate l to 3 Sodium silicate solids l to 2 Sodium gluconate .2 to .5 Sodium ligno sulfonate .l to .2 Diethylene'glycol monobutyl ether 1 to 1.5 Diethylene glycol monoethyl ether 3 to 7 Nonionic surface active agent selected from the group consisting of .05 to. l5
octylphenoxyethanol and nonylphenoxyethanol Balance water 5. An alkaline aqueous cleaning solution concentrate for the preparation of working solutions to remove residue from silk screen stencils and having the following formulation:
Component Percent by Weight Potassium hydroxide 3.970 Tetrapotassium pyrophosphate 9.000 Sodium silicate solids 6.250 Sodium gluconate 1.875 Sodium ligno sulfonate 0.625 Diethylene glycol monobutyl ether 5.000 Diethylene glycol monoethyl ether 25.000 Octylphenoxyethanol 0.565
Balance water 6. The method of cleaning silk screen printing stencils after use which comprises:
,a. immersing said stencil in a solution of the following formulation:
Percent by Weight Component in Water 043970 to 1.588 0.9000 to 3.600
0.6250 to 2.500 0.1875 to 0.750 0.0625 to 0.250 0.5000 to 2.000 2.5000 to l0.000
Continued Percent by Weight Component in Water Surface active agent selected from from the group consisting of octylphenoxyethanol and nonylphenoxyethanol Balance water b. and thereafter rinsing and drying.
7. The method of cleaning silk screen printing stencils as defined in claim 6 being particularly characterized in that said alkaline earth hydroxide is potassium hydroxide.