CA1198958A - Method of cleaning and reclaiming printing screens - Google Patents
Method of cleaning and reclaiming printing screensInfo
- Publication number
- CA1198958A CA1198958A CA000414440A CA414440A CA1198958A CA 1198958 A CA1198958 A CA 1198958A CA 000414440 A CA000414440 A CA 000414440A CA 414440 A CA414440 A CA 414440A CA 1198958 A CA1198958 A CA 1198958A
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- ink
- screen
- water
- cleaning
- surfactant
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Abstract
METHOD OF CLEANING AND RECLAIMING
PRINTING SCREENS
Abstract of the Disclosure Methods of cleaning and reclaiming printing screens which provide synergistic activities are disclosed. Ink cleaning compositions are also disclosed which degrade or solubilize broad classes of printing ink residues on printing screens for quick removal by a pressurized water stream. The compositions are essentially non-aqueous and contain N-methyl-2-pyrrolidone, an oxygenated solvent, such as butyl cellosolve and cyclohexanone, and a surfactant. The compositions meet health and safety standards due to their biodegradability, lack of flammability and high threshold limit values.
PRINTING SCREENS
Abstract of the Disclosure Methods of cleaning and reclaiming printing screens which provide synergistic activities are disclosed. Ink cleaning compositions are also disclosed which degrade or solubilize broad classes of printing ink residues on printing screens for quick removal by a pressurized water stream. The compositions are essentially non-aqueous and contain N-methyl-2-pyrrolidone, an oxygenated solvent, such as butyl cellosolve and cyclohexanone, and a surfactant. The compositions meet health and safety standards due to their biodegradability, lack of flammability and high threshold limit values.
Description
~8~
Related Application I'his application is related to copending, commonly assigned Canadian application serial no. 41~,431, filed ~ctober 28, 19~2.
Background of the ~nvention Screen printing is a well established and sub-stantial industry. Essentially, printin~ screens are im-parted with various designs, art work or printed indicia by rather permanent emulslons on the screen for locali~ed appllcation oE dye pastes or inks used in reproducing the image from the screen. The emulsions surroundin~ the image areas of the printed screens are resistant to inks so that they resist removal during the printin~ process when ink is applied through the screen for reproduction of the images therefrom. The same quali~ies which make emulsions resis-tant to ink and cleaning solvents can make them more diffi-cult to be removed Erom a printed screen. Printing screens are usually made from silk, synthetic fabric or metal materials and, in the practice oE screen printing, it is common to reuse them. This involves a cleaning process whereby ink residue ~rom one printing operation will be removed and cleaned from the screens which permits their storage and later reuse. In the removal of ink, it is sometimes important not to affect the emulsion area which has been imparted to the sreen. Modern day screen printing has evolved rather complex ink or dye formulations which are sometimes very difficult to remove. Agents which may be suitable to clean inks from the screens may also affect the underlying emulsion. Therefore, screen printing lnvolves a balance~ variety of chemical processes in which ~creens are prepared from artwork with semi- to fully-permanent emulsions for reproducinq ink images in a manner such tha-t the emulsion areas resist ink attack. In such operations, the screen is repeatedly clear)ed For filinc~ an~/or subse(luent reuse. It is mab/ . ~
also important that the screen be capable of reclamation when ink image and/or emulsion areas are removed with different types of screen reclaiming solu~ions or agents.
Commercial screen printing shops usually clean or reclaim many screens daily and, for this purpose, employ screen cleaning machines or reclaiming systems. Such cleaning machines or recl~;~;ng systems usually employ recirculating solvents which allow the synthetic or metal screens to be introduced and either cleaned or reclaimed, depending upon production requirements. In addition, other commercial operations involve hand cleaning or recl~;m;ng with various solvents or corrosive agents. During the course o cleaning or recla;~;ng, the screen printer is often in intimate contact with the chemicals or solvents. There are many solvents or agents used in screen cleaning and reclama~ion. The three mos~
c~ orly used agents may be classified as aliphatic hydrocarbons, aromatic hydrocarbons and oxygenated solvents, and less frequently, chlorinated solvents~ Aliphatic hydrocarbons are commonly referred to as "mineral spirits" bu~
more accurately these aliphatic solvents are composed of mixtures of straight-chain and/or branched-chain saturated hydrocarbons. The higher the molecular weight or the number of carbon atoms, the higher the boiling point of the solvent. The!
higher the boiling point, the slower the solvent will evaporate, hence, usually the higher boiling aliphatic hydrocarbons are desirable for use in screen cleaning. The aromatic hydrocarbon solvents include cyclic hydrocarbons containing the benzene ring. These aromatic hydrocarbons are usually more flammable but much stronger in solvation power than the aliphatic type solvents and, similarly, the higher the ~9~
molecular weight for the aromatic hydrocarbon, the higher the boiling range. In contrast to the rather non-polar hydrocarbons, oxygenated solvents are more polar compounds.
Typically, oxygenated solven~s are those having hydroxyl or carbonyl groups, and many of them have considerable solubility in water. Other solvents include chlorinated solvents which are fully~ or semi-chloxinated hydrocarhons and the rarely used fluorinated hydrocarbons of the Freon types.
Today's screen printer thus routineLy deals with a multiplicity of solvents which are used for screen cleaning and reclamation. In the past, when there was perhaps little understanding of the health and safety hazards which printers or wo~kers were exposed to, such solvents were used with impunity. More recently, in view of Federal and State legis-lation, solvents must meet material safety standards. Pro-longed ox repeated sol~ent contact with the skin is generally avoided and, in most instances, because of fl ohility, solvents must be kept away from e~L~ c heat or open flame, and frequently fire departments request their s~orage outside.
Occupational Safe~y and Health ptlm;ni~trations at both Federal and State levels have also placed various restrictions upon the use of solvents and, many may no longer be used. Furthermore, in known processes, hot reclamation systems have been requlred in order to clean or reclaim printing screens, but such systems crsate pollution and hazards which are no longer tolerable. In the search for suitable screen cleaning and reclamation sol-vents or agents, it would be desirable to be able to el;m;n~te the DOT (Department of Transportation) red label which warns of hazardous, fl~ -hle solvents. It would also be desirable to offer cleaning and reclamation composi~ions which are either completely or essentially biodegradable. Another highly desirable objective would be to make available to the industry cleaning and reclamation products having a high threshold limit values (TLV) which means that the amount of aixborne matter provided by such products offers greater safety in breathing.
The above background provides a practical overview of the screen printing industry from the standpoint of the cleaning and reclamation processes to a person of ordinary skill in this art. In addition, in the preparation of this application, patents have been loca~ed which may be considered to relate to the subject matter of this invention. The following is a list of prior patents which may be helpful in understanding this invention without leaving the impression that it is exhaustive or that there may not be more relevant patent art or literature: U.S. Patent Nos. 2,780rl68;
3,459,594; 3,511,657; 3,615,827; 3,642,537; 3,673,099;
3,679,479; 3,706,691; 3,737,38~; 3,764,384; 3,78~,007;
3,796,602; 3,928,065; 3,953,352; 4,024,085; 4,055,515 and 4,070,203. It must be mentioned that these patents have been listed with the knowledge of this invention and even have been obtained from non-analogous arts. Ther~fore, it is not to be in any way inferred that their listing here rapresents the state of the printing screen cleaning or reclamation art.
It is submitted that there is a need for printing screen cleaning and reclamation compositions which are effec-tive in a wide variety of applications. Moreover, it is highly desirable that such compositions, while effective, ~everthe-less, meet environmental health and safety standards~
., Sur~ary of the Invention ~ 'his invention :l~ directed to p~intincJ screen cleaning or reclaiming methods which are generally efEec-tive in solvating or degradiny inks used in the printiny industry. 'rhe methods furlction witll ink cleanirlcJ composi-tions which not only solubili~e or degrade broad classes oE printing inks, but also possess high or no ~lash points, excellent bioclegradabilities and high threshold limit values. Thus, the health and safety of the screen printer or worker in the industry is exceedingly enhanced by this method. In addition, this invention provides for methods of cleaning and reclaiming printing screens which are syner~istically operative whereby inks can be removed and the printed emulsion on the screen may be sensitized for effective removal. In addition, in another of its general aspects, this invention involves a method Eor cleaning or cleanin~ and reclaiming printing screens made of silk, textile, metal or other types, without damaging the screen and to place it in an immediate condition for either stora~e or reuse.
The method o this invention employs the unique compositions disclosed in said copendin~ application serial no. 414,431, which consist essentially of N-methyl-
Related Application I'his application is related to copending, commonly assigned Canadian application serial no. 41~,431, filed ~ctober 28, 19~2.
Background of the ~nvention Screen printing is a well established and sub-stantial industry. Essentially, printin~ screens are im-parted with various designs, art work or printed indicia by rather permanent emulslons on the screen for locali~ed appllcation oE dye pastes or inks used in reproducing the image from the screen. The emulsions surroundin~ the image areas of the printed screens are resistant to inks so that they resist removal during the printin~ process when ink is applied through the screen for reproduction of the images therefrom. The same quali~ies which make emulsions resis-tant to ink and cleaning solvents can make them more diffi-cult to be removed Erom a printed screen. Printing screens are usually made from silk, synthetic fabric or metal materials and, in the practice oE screen printing, it is common to reuse them. This involves a cleaning process whereby ink residue ~rom one printing operation will be removed and cleaned from the screens which permits their storage and later reuse. In the removal of ink, it is sometimes important not to affect the emulsion area which has been imparted to the sreen. Modern day screen printing has evolved rather complex ink or dye formulations which are sometimes very difficult to remove. Agents which may be suitable to clean inks from the screens may also affect the underlying emulsion. Therefore, screen printing lnvolves a balance~ variety of chemical processes in which ~creens are prepared from artwork with semi- to fully-permanent emulsions for reproducinq ink images in a manner such tha-t the emulsion areas resist ink attack. In such operations, the screen is repeatedly clear)ed For filinc~ an~/or subse(luent reuse. It is mab/ . ~
also important that the screen be capable of reclamation when ink image and/or emulsion areas are removed with different types of screen reclaiming solu~ions or agents.
Commercial screen printing shops usually clean or reclaim many screens daily and, for this purpose, employ screen cleaning machines or reclaiming systems. Such cleaning machines or recl~;~;ng systems usually employ recirculating solvents which allow the synthetic or metal screens to be introduced and either cleaned or reclaimed, depending upon production requirements. In addition, other commercial operations involve hand cleaning or recl~;m;ng with various solvents or corrosive agents. During the course o cleaning or recla;~;ng, the screen printer is often in intimate contact with the chemicals or solvents. There are many solvents or agents used in screen cleaning and reclama~ion. The three mos~
c~ orly used agents may be classified as aliphatic hydrocarbons, aromatic hydrocarbons and oxygenated solvents, and less frequently, chlorinated solvents~ Aliphatic hydrocarbons are commonly referred to as "mineral spirits" bu~
more accurately these aliphatic solvents are composed of mixtures of straight-chain and/or branched-chain saturated hydrocarbons. The higher the molecular weight or the number of carbon atoms, the higher the boiling point of the solvent. The!
higher the boiling point, the slower the solvent will evaporate, hence, usually the higher boiling aliphatic hydrocarbons are desirable for use in screen cleaning. The aromatic hydrocarbon solvents include cyclic hydrocarbons containing the benzene ring. These aromatic hydrocarbons are usually more flammable but much stronger in solvation power than the aliphatic type solvents and, similarly, the higher the ~9~
molecular weight for the aromatic hydrocarbon, the higher the boiling range. In contrast to the rather non-polar hydrocarbons, oxygenated solvents are more polar compounds.
Typically, oxygenated solven~s are those having hydroxyl or carbonyl groups, and many of them have considerable solubility in water. Other solvents include chlorinated solvents which are fully~ or semi-chloxinated hydrocarhons and the rarely used fluorinated hydrocarbons of the Freon types.
Today's screen printer thus routineLy deals with a multiplicity of solvents which are used for screen cleaning and reclamation. In the past, when there was perhaps little understanding of the health and safety hazards which printers or wo~kers were exposed to, such solvents were used with impunity. More recently, in view of Federal and State legis-lation, solvents must meet material safety standards. Pro-longed ox repeated sol~ent contact with the skin is generally avoided and, in most instances, because of fl ohility, solvents must be kept away from e~L~ c heat or open flame, and frequently fire departments request their s~orage outside.
Occupational Safe~y and Health ptlm;ni~trations at both Federal and State levels have also placed various restrictions upon the use of solvents and, many may no longer be used. Furthermore, in known processes, hot reclamation systems have been requlred in order to clean or reclaim printing screens, but such systems crsate pollution and hazards which are no longer tolerable. In the search for suitable screen cleaning and reclamation sol-vents or agents, it would be desirable to be able to el;m;n~te the DOT (Department of Transportation) red label which warns of hazardous, fl~ -hle solvents. It would also be desirable to offer cleaning and reclamation composi~ions which are either completely or essentially biodegradable. Another highly desirable objective would be to make available to the industry cleaning and reclamation products having a high threshold limit values (TLV) which means that the amount of aixborne matter provided by such products offers greater safety in breathing.
The above background provides a practical overview of the screen printing industry from the standpoint of the cleaning and reclamation processes to a person of ordinary skill in this art. In addition, in the preparation of this application, patents have been loca~ed which may be considered to relate to the subject matter of this invention. The following is a list of prior patents which may be helpful in understanding this invention without leaving the impression that it is exhaustive or that there may not be more relevant patent art or literature: U.S. Patent Nos. 2,780rl68;
3,459,594; 3,511,657; 3,615,827; 3,642,537; 3,673,099;
3,679,479; 3,706,691; 3,737,38~; 3,764,384; 3,78~,007;
3,796,602; 3,928,065; 3,953,352; 4,024,085; 4,055,515 and 4,070,203. It must be mentioned that these patents have been listed with the knowledge of this invention and even have been obtained from non-analogous arts. Ther~fore, it is not to be in any way inferred that their listing here rapresents the state of the printing screen cleaning or reclamation art.
It is submitted that there is a need for printing screen cleaning and reclamation compositions which are effec-tive in a wide variety of applications. Moreover, it is highly desirable that such compositions, while effective, ~everthe-less, meet environmental health and safety standards~
., Sur~ary of the Invention ~ 'his invention :l~ directed to p~intincJ screen cleaning or reclaiming methods which are generally efEec-tive in solvating or degradiny inks used in the printiny industry. 'rhe methods furlction witll ink cleanirlcJ composi-tions which not only solubili~e or degrade broad classes oE printing inks, but also possess high or no ~lash points, excellent bioclegradabilities and high threshold limit values. Thus, the health and safety of the screen printer or worker in the industry is exceedingly enhanced by this method. In addition, this invention provides for methods of cleaning and reclaiming printing screens which are syner~istically operative whereby inks can be removed and the printed emulsion on the screen may be sensitized for effective removal. In addition, in another of its general aspects, this invention involves a method Eor cleaning or cleanin~ and reclaiming printing screens made of silk, textile, metal or other types, without damaging the screen and to place it in an immediate condition for either stora~e or reuse.
The method o this invention employs the unique compositions disclosed in said copendin~ application serial no. 414,431, which consist essentially of N-methyl-
2~pyrrolidone (herein simply sometimes "N~lP"), an oxygenated solvent and a surfactant. ~s reported therein, a non-aqueous system of these essential components will solubilize and degrade a wide variety of polymeric or other inks currently being employed in the modern screen printin~
industry. The composition has been found to penetrate, emulsify and prevent redeposition of inks during their -- 5 ~
5~
removal from a variety of common printing screens. It has also been discovered that the NMP, oxygenated solvent and surfactant composition must be non-aqueous in order to e~fectively clean screens or to sensitize the cleaned printed screen for subse-quent emulsion removal, if desired.
In this invention, a screen cleaning or reclamation method is provided b~ spra~ing a concentrate of NMP, oxygenated solvent and surfactan~ system (herein sometimes simply "NMP
concentrate") onto a screen surface for a sufficient dwell time to enable solubiliæation or degradation of the ink. Then, the ink may be rinsed with water to remove it from the screen. By this method, the ink is degraded to a point whereby a medlum to high pressuxe, low-volume water spray will permit the complete removal of ink. According to the method of this invention, the NMP concentrate is sprayed onto the screen ink surface.
Spraying a coherent spray of the Nl~P concentrate enables extremely low amounts to be used and degradation may still surprisingly be achieved. It has also been found that, after the ink cleaning step with the N~ concentrate, the printed emulsion is in a sensitized state for r~ val from the screen with a periodate containing emulsion remover. The screen may thus be totally recl~; m~ . Therea~ter, i~ further desired, any image ink residue or "ghost" as the term is used in the trade, may be removed with a caustic solution containing oxygenatçd solvents. By the above sequence, this invention also providas for an overall screen cleaning and reclamation process.
As developed in the background of this invention, hot solvent and alkaline techniques have been employed in the prior art screen cleaning and reclamation. This invention avoids the need for such hot cleaning techniques and ~he associatPd health G
.~
hazards created by such techniques. In another of its aspects, the invention is capable of performance at ambient or room temperature conditions. In this essential respect, it is considered highly unexpected and unobvious that a cleaning and reclamation process could operate at such low or ambient temperatures and be as effective in removing a wide variety of ink compositions. Furthermore, whereas it has been disclosed in prior patents to employ derivatives of pyrrolidone including alkyl pyrrolidones, in cleaning compositions, it has not heretofore been suggested that any such pyrrolidone derivative may be employed in a composition or me~hod for the L~- - val of screen printing ink compositions. Fur~hermore, even where pyrrot;~o~es have been suggested in non-analogous arts, they generally are en~ployed in aqueous systems in contrast to the essentially non-aqu~ous concentrates of this invention. Also~
for purposes of this invention, N-methyl-2 p~L r olidone is essentially required to operate in combination with oxygenated solvents and surfactants in order to achieve the most optimum desired results. In substance, in the screen printiny industry, it has not been heretofore suggested that a non-toxic, biodegradable and very safe cleaning composition may be provided, and still achieve highly desirable cleaning and synergistic reclamation ef~ects, as has been provided by the methods of this invention.
SB
Detailed Description of the Invention As delineated above, the method o this invention employs compositions of N-methyl-2-pyrrolidone~ an oxygena~ed solvent and a surfactant~ In a preferred composition, the oxygenated solvents are a co~bination of butyl cellosolve and cyclohexanone. These preferred oxygenated solvents are from the class of glycol ethers, alcohols and ketones, respectively.
Other classes of applicable oxygenated solvents include esters and ethers, and mixed classes thereof. The surfactant is preferably from the group consisting of nonionic or anionic surfactants, or mixtures'thereof, and a specific example of nonionic surfactant is octyl phenoxy (polyethoxy) ethanol of Rohm & Haas, sold under the trademark TRITON X-114 and an organic phosphate ester sold under the trademark GAFAC RP-710 by General ~n~ 1; ne and Film Corporation. Fuxther Pxamples o~
oxygenated solvents from the class of glycol ethers which may be used include methyl cellosoIve, hexyl cellosolve, cellosolve solvent, methyl carbitol, carbitol solvent, butyl carbitol, hexyl carbitol, and the liXe. Other examples of ketones include methyl ethyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, ethyl butyl ketone, isobutyl heptyl ketone, isophorone, diacetone alcohol, acetone, and the like. O~her examples of ethers include butyrolactone, die~hyl carbitol and dibutyl carbitol, and others. Examples of esters include butyl lactate, butyl acetate, butyl carbitol aceta~e, carbitol acetate, butyl cellosolve acetate, cellosolve acetate, 2-ethyl hexyl acetate, amyl ace~ate, methyl cellosolve acetate, formates, and others. Examples of alcohols include amyl alcohol, butyl alcohol, furfurol alcohol, 2~butyne 1,4,diol, , ~_ tetrahydrofurfurol alcohol, and others. Therefore, in accordance with the broader principles o this invention,-oxygenated solvents from the above mentioned classes are suitable for use, dependlng upon the required solvating capacities of the oxygenated solvents in order to obtàin the most desired biodegradability, least flammability and highest threshold limit values to meet or exceed health and safety standards. In accordance with the preferred principles of this invention, however, as mentioned above, there are specific e~amples which meet all of these criteria in the mos~ preferred aspects o this invention. In a generic aspect, the oxygenated solvent facilitates the low viscosity solvating character of the NMP and helps disperse it ~o solubilize or degrade the ink compositions. The NMP is also water active when needed. Thus, the combination of the NMP and the oxygenated solvent provide a coaction between organic co-solvents along with a unique water activity to provide a synergistic action in solvating or degrading of ink compositions on ~creens for removal with water. Yet, it is imperative tha~ the NMP concentrates be essentially non-aqueous during solvation or degradation of ink because any significant water will destroy the effectiveness of NMP in its cleaning power as i~ is used in this invention.
However, the solvated or degraded ink must then be in a state for removal with a low-volume, pressurized stream of water.
In addition to the surfactants mentioned above, other nonionic, anionic, cationic and amphoteric surfactants may be used, as listed primarily in McCutcheon's Detergents and Emulsifiers, 1980 ~dition, MC Publishing Company, Glenrock/ New Jersey. The surfactants aid in the dispexsion and degradation l of the inks for aqueous removal. Surfactants of the anionic "
q type may be (1~ of the group of saponified fatty acids or soaps, or ~2~ of saponified petroleum oil such as sodium salts or organic sulfonates ox sulates or (3) of saponified esters, alcohols or glycols, with the latter being well known as anionic synthetic surfactants. Examples of these anionic surfactants include the alkaryl sulfonates or amine salts thereof such as sulfonates o dodecyl benzene or diethanolamine saLt o dodecyl benzene sulfonic acid. Most of these sulfonates contain many chemical species. The class name given to most of them is "alkylaryl sulfonate". Simply, this means that a paraffinic hydrocarbon is bonded to an aromatic or benzene nucleus and the aromatic portion has been sulfonated.
Examples of saponified fatty acids (C6-C24) are the sodium or potassium salts of myristic, palmitic, stearic, oleic or linoleic acids or mixtures thereof. Also in this class of anionic surfactants are organic phosphate esters including alkali and alkaline earth metal salts of neutral phosphoric acid esters o~ oxylalkylated higher alkyl phenols or aliphatic monohydric alcohols. Aerosol OT is a dioctyl alkali metal sulfosuccinate anionic surfactant made by Cyanamide. The nonionic surfactants suitable for use commonly ha~e hydrophylic portions or side chains usually of the polyoxyalkylene type.
The oil soluble or dispersible part of the molecule i5 derived from either fatty acids~ alcohols, amides or amines. By suitable choice of starting materials and regulation of the length of the polyoxyalkylene chain, the surfactant parts o~
the nonionic detergents may be varied as is well known.
Suitable examples of nonionic surfactants include alkylphenoxy polyoxyethylene glycol, for example, ethylene oxide adduct o o either oc~yl-, nonyl- or tridecyl- phenol and the like~ These ~ 10 --*~rade mark ment~oned nonionic surfactants are usually prepared by~the reaction of the alkyl phenol with ethylene oxide. Commercial products are sold under the trademarks "Triton X-100 or X-114"by Rohm and Haas Co. ox "Tergitol" by Union Carbide and Carbon Corp. which are alkyl phenyl ethers of polyethylene glycol. Othex specific examples of nonionic surfactants include glyceryl monooleate, oleyl monoisopropanolamide sorbitol dioleate, alkylol amides prepared by reacting alkanolamides such as monoisopropanolamine, diethanolamine, or monobutanolamine with fa~ty acids such as oleic, pelargonic, lauric and the like. The cationic surfactants are also well developOed and mainly include betaines and quaternar~ n; um compounds. Some specific examples of be~aines include imidazoline betaines, aliphatic and carboxycyclic betaines, and betaines with hetero atoms in the hydrophobic cha;n~s such as dodecyloxypropyldimethyl aminoacetic acid. Typical of the quaternary ammonium compounds that may be mentioned are dimethyl dicoco ammonium chloride, cetyl pyridinium aceta~e, methyl cetyl pip~xidinium proprionate, N,N dilautyl, N,N
dimethyl ammonium diethophosphate, and the like. Thus, it will be understood that other anionic, cationic, amphoteric or nonionic surfactants may be employed in accordance with the principles of this invention.
The amounts of ingxedients vary over wide ranges, however, it is preferred to use a significant amount of the N-methyl-2-pyrrolidone, i~e., about 30-85% by weight. The oxygenated solvent is usually contained in amount o about 15-35% by weight. The r~m~in~er of the composition comprises a surfactant or a mixture of surfactants within the range of about 1 to about 5% by weight. The NMP concentrates m~y aI~o be supplemented with other organic solvents such as methylene chloride, trlchloroethane, dimethyl sulfoxide and its deriva-tives, fluorocarbons, and freons in amounts of about 10-30% by by weight where additional faster penetrating power may be desired for ink solubilization. Such organic solvents are permitted which would not alter the essential characteristics of the ink cleaning compositions of this invention and may help to enhance activity of the co-solvents in penetrating, emulsifying and accelerating the degradation of ~he inks foir subsequent removal.
In order to fur~her illustrate the invention, refer-ence is made to the specific operating for~llAq detailed hereinafter and detailed methods of cleaning and recla;m;ng a printing screen.
75.72% N-methyl-2-pyrrolidone 18.52~ Butyl Cellosolve
industry. The composition has been found to penetrate, emulsify and prevent redeposition of inks during their -- 5 ~
5~
removal from a variety of common printing screens. It has also been discovered that the NMP, oxygenated solvent and surfactant composition must be non-aqueous in order to e~fectively clean screens or to sensitize the cleaned printed screen for subse-quent emulsion removal, if desired.
In this invention, a screen cleaning or reclamation method is provided b~ spra~ing a concentrate of NMP, oxygenated solvent and surfactan~ system (herein sometimes simply "NMP
concentrate") onto a screen surface for a sufficient dwell time to enable solubiliæation or degradation of the ink. Then, the ink may be rinsed with water to remove it from the screen. By this method, the ink is degraded to a point whereby a medlum to high pressuxe, low-volume water spray will permit the complete removal of ink. According to the method of this invention, the NMP concentrate is sprayed onto the screen ink surface.
Spraying a coherent spray of the Nl~P concentrate enables extremely low amounts to be used and degradation may still surprisingly be achieved. It has also been found that, after the ink cleaning step with the N~ concentrate, the printed emulsion is in a sensitized state for r~ val from the screen with a periodate containing emulsion remover. The screen may thus be totally recl~; m~ . Therea~ter, i~ further desired, any image ink residue or "ghost" as the term is used in the trade, may be removed with a caustic solution containing oxygenatçd solvents. By the above sequence, this invention also providas for an overall screen cleaning and reclamation process.
As developed in the background of this invention, hot solvent and alkaline techniques have been employed in the prior art screen cleaning and reclamation. This invention avoids the need for such hot cleaning techniques and ~he associatPd health G
.~
hazards created by such techniques. In another of its aspects, the invention is capable of performance at ambient or room temperature conditions. In this essential respect, it is considered highly unexpected and unobvious that a cleaning and reclamation process could operate at such low or ambient temperatures and be as effective in removing a wide variety of ink compositions. Furthermore, whereas it has been disclosed in prior patents to employ derivatives of pyrrolidone including alkyl pyrrolidones, in cleaning compositions, it has not heretofore been suggested that any such pyrrolidone derivative may be employed in a composition or me~hod for the L~- - val of screen printing ink compositions. Fur~hermore, even where pyrrot;~o~es have been suggested in non-analogous arts, they generally are en~ployed in aqueous systems in contrast to the essentially non-aqu~ous concentrates of this invention. Also~
for purposes of this invention, N-methyl-2 p~L r olidone is essentially required to operate in combination with oxygenated solvents and surfactants in order to achieve the most optimum desired results. In substance, in the screen printiny industry, it has not been heretofore suggested that a non-toxic, biodegradable and very safe cleaning composition may be provided, and still achieve highly desirable cleaning and synergistic reclamation ef~ects, as has been provided by the methods of this invention.
SB
Detailed Description of the Invention As delineated above, the method o this invention employs compositions of N-methyl-2-pyrrolidone~ an oxygena~ed solvent and a surfactant~ In a preferred composition, the oxygenated solvents are a co~bination of butyl cellosolve and cyclohexanone. These preferred oxygenated solvents are from the class of glycol ethers, alcohols and ketones, respectively.
Other classes of applicable oxygenated solvents include esters and ethers, and mixed classes thereof. The surfactant is preferably from the group consisting of nonionic or anionic surfactants, or mixtures'thereof, and a specific example of nonionic surfactant is octyl phenoxy (polyethoxy) ethanol of Rohm & Haas, sold under the trademark TRITON X-114 and an organic phosphate ester sold under the trademark GAFAC RP-710 by General ~n~ 1; ne and Film Corporation. Fuxther Pxamples o~
oxygenated solvents from the class of glycol ethers which may be used include methyl cellosoIve, hexyl cellosolve, cellosolve solvent, methyl carbitol, carbitol solvent, butyl carbitol, hexyl carbitol, and the liXe. Other examples of ketones include methyl ethyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, ethyl butyl ketone, isobutyl heptyl ketone, isophorone, diacetone alcohol, acetone, and the like. O~her examples of ethers include butyrolactone, die~hyl carbitol and dibutyl carbitol, and others. Examples of esters include butyl lactate, butyl acetate, butyl carbitol aceta~e, carbitol acetate, butyl cellosolve acetate, cellosolve acetate, 2-ethyl hexyl acetate, amyl ace~ate, methyl cellosolve acetate, formates, and others. Examples of alcohols include amyl alcohol, butyl alcohol, furfurol alcohol, 2~butyne 1,4,diol, , ~_ tetrahydrofurfurol alcohol, and others. Therefore, in accordance with the broader principles o this invention,-oxygenated solvents from the above mentioned classes are suitable for use, dependlng upon the required solvating capacities of the oxygenated solvents in order to obtàin the most desired biodegradability, least flammability and highest threshold limit values to meet or exceed health and safety standards. In accordance with the preferred principles of this invention, however, as mentioned above, there are specific e~amples which meet all of these criteria in the mos~ preferred aspects o this invention. In a generic aspect, the oxygenated solvent facilitates the low viscosity solvating character of the NMP and helps disperse it ~o solubilize or degrade the ink compositions. The NMP is also water active when needed. Thus, the combination of the NMP and the oxygenated solvent provide a coaction between organic co-solvents along with a unique water activity to provide a synergistic action in solvating or degrading of ink compositions on ~creens for removal with water. Yet, it is imperative tha~ the NMP concentrates be essentially non-aqueous during solvation or degradation of ink because any significant water will destroy the effectiveness of NMP in its cleaning power as i~ is used in this invention.
However, the solvated or degraded ink must then be in a state for removal with a low-volume, pressurized stream of water.
In addition to the surfactants mentioned above, other nonionic, anionic, cationic and amphoteric surfactants may be used, as listed primarily in McCutcheon's Detergents and Emulsifiers, 1980 ~dition, MC Publishing Company, Glenrock/ New Jersey. The surfactants aid in the dispexsion and degradation l of the inks for aqueous removal. Surfactants of the anionic "
q type may be (1~ of the group of saponified fatty acids or soaps, or ~2~ of saponified petroleum oil such as sodium salts or organic sulfonates ox sulates or (3) of saponified esters, alcohols or glycols, with the latter being well known as anionic synthetic surfactants. Examples of these anionic surfactants include the alkaryl sulfonates or amine salts thereof such as sulfonates o dodecyl benzene or diethanolamine saLt o dodecyl benzene sulfonic acid. Most of these sulfonates contain many chemical species. The class name given to most of them is "alkylaryl sulfonate". Simply, this means that a paraffinic hydrocarbon is bonded to an aromatic or benzene nucleus and the aromatic portion has been sulfonated.
Examples of saponified fatty acids (C6-C24) are the sodium or potassium salts of myristic, palmitic, stearic, oleic or linoleic acids or mixtures thereof. Also in this class of anionic surfactants are organic phosphate esters including alkali and alkaline earth metal salts of neutral phosphoric acid esters o~ oxylalkylated higher alkyl phenols or aliphatic monohydric alcohols. Aerosol OT is a dioctyl alkali metal sulfosuccinate anionic surfactant made by Cyanamide. The nonionic surfactants suitable for use commonly ha~e hydrophylic portions or side chains usually of the polyoxyalkylene type.
The oil soluble or dispersible part of the molecule i5 derived from either fatty acids~ alcohols, amides or amines. By suitable choice of starting materials and regulation of the length of the polyoxyalkylene chain, the surfactant parts o~
the nonionic detergents may be varied as is well known.
Suitable examples of nonionic surfactants include alkylphenoxy polyoxyethylene glycol, for example, ethylene oxide adduct o o either oc~yl-, nonyl- or tridecyl- phenol and the like~ These ~ 10 --*~rade mark ment~oned nonionic surfactants are usually prepared by~the reaction of the alkyl phenol with ethylene oxide. Commercial products are sold under the trademarks "Triton X-100 or X-114"by Rohm and Haas Co. ox "Tergitol" by Union Carbide and Carbon Corp. which are alkyl phenyl ethers of polyethylene glycol. Othex specific examples of nonionic surfactants include glyceryl monooleate, oleyl monoisopropanolamide sorbitol dioleate, alkylol amides prepared by reacting alkanolamides such as monoisopropanolamine, diethanolamine, or monobutanolamine with fa~ty acids such as oleic, pelargonic, lauric and the like. The cationic surfactants are also well developOed and mainly include betaines and quaternar~ n; um compounds. Some specific examples of be~aines include imidazoline betaines, aliphatic and carboxycyclic betaines, and betaines with hetero atoms in the hydrophobic cha;n~s such as dodecyloxypropyldimethyl aminoacetic acid. Typical of the quaternary ammonium compounds that may be mentioned are dimethyl dicoco ammonium chloride, cetyl pyridinium aceta~e, methyl cetyl pip~xidinium proprionate, N,N dilautyl, N,N
dimethyl ammonium diethophosphate, and the like. Thus, it will be understood that other anionic, cationic, amphoteric or nonionic surfactants may be employed in accordance with the principles of this invention.
The amounts of ingxedients vary over wide ranges, however, it is preferred to use a significant amount of the N-methyl-2-pyrrolidone, i~e., about 30-85% by weight. The oxygenated solvent is usually contained in amount o about 15-35% by weight. The r~m~in~er of the composition comprises a surfactant or a mixture of surfactants within the range of about 1 to about 5% by weight. The NMP concentrates m~y aI~o be supplemented with other organic solvents such as methylene chloride, trlchloroethane, dimethyl sulfoxide and its deriva-tives, fluorocarbons, and freons in amounts of about 10-30% by by weight where additional faster penetrating power may be desired for ink solubilization. Such organic solvents are permitted which would not alter the essential characteristics of the ink cleaning compositions of this invention and may help to enhance activity of the co-solvents in penetrating, emulsifying and accelerating the degradation of ~he inks foir subsequent removal.
In order to fur~her illustrate the invention, refer-ence is made to the specific operating for~llAq detailed hereinafter and detailed methods of cleaning and recla;m;ng a printing screen.
75.72% N-methyl-2-pyrrolidone 18.52~ Butyl Cellosolve
3.04~ Cyclohexanone 2.62% OctyI Phenoxy IPolyethoxy) Etbanol (TRITON X-114~
0.10~ Organic Phosphate Ester tGAFAC RP-710) I
37.86% N-methyl~2-pyrrolidone 9~26~ Butyl Cellosolve 1.52% Cyclohexanone 24.00~ Cellosolve Acetate 26.00% MethyLene Chloride 1.31% Octyl Phenoxy (Polyethoxy~ Ethanol ITRITON X114) 0.05~ Organic Phosphate Ester (G~FAC RP-710) In the alternative to the specific ingredients of Example 2, 50~ o Example 1 may be combined with 26~ of methy lene chloride and 24% cellosolve acetate. Examples 1 and 2 are preferred formulas for ~he N~ cleaning concentrates because of their biodegradability, reduced fl ~hility and low TLV
values.
Before describing in detail the cleaning and re-claiming of printing screens emloying the methods of this invention, an unders~n~i ng of certain underlying facts or terms is impox~ant. First of all, the ink side o~ the printing screen is alternately c~lled the squeegee side, thQ well side, or the front side, but for purposes of this description-it will be called the ink side. The opposite side o the screen is called the back side, down side or print-contact side. Again, for purposes of this description, it will be called the print~
contact side. The term "ink" will be the generic term for many of the compositions that are employed in tha practice of screen printing including dyes or inks commonly referred to as flexible enamels, synthetic enamels, fast-dry enamels, flexible l3 lacquers, industrial lacquers, flat vinyl ink, vinyl half-tone ink, fluorescent vinyl ink, gloss vinyl ink, satin vinyl ink, flock adhesive, transparent ink, me~allic powders, acrylic ink, plastisol ink, mylar ink, textile ink, among many other types of inks. For general information on ink compositions, refer-ence may be had to the catalog by KC Graphics, Inc. 1978-1979, copyright 1978 by KC Graphics, Inc. Reerence may also be had to "Te~tile Screen Printing" by Albert ~osloff, Second Edition, International Standard Book Number 0-911380-39~6 (1976). These sources will also serve as backyround information for the inks which may b~ cle~n~ with the inventive cleaning compositions.
As developed above, the printing screen may be made from a number of materials and may have various mesh sizes. A mono-ilament screen is a single strand of material for example of polyester, nylon, stainless steel, silk, chrome-plated wire, o~
other things r which is woven into a specific number of squares per a d; -nsionr i.e., a 230 mesh means 230 open squares per square inch. A multi-f;1~Qnt screen is comprised of a sexies of strands of similar materials just mentioned, braided before weaving into the mesh measurement, i.e., 12xx150 mesh would mean lZ interwoven strands subsequently woven into 150 open squares per square inch and, where the cross-over points of mesh occur, pigment can get into the strands and ma~ become extremely hard to L~...ove. Thus, it may be determined by this description of either the mono-filament or the multi-filament screens that the requirements for complete removal of ink residue, for instance, may differ due to the construction of the screen. In particular, that last residue often referred to in the art as "ghost" or "haze" would be more readily apparent in the multi-filament screens where pigment can get into the strands and becomes very hard to remove. There are a number of classes of emulsions which ini~ially cover the print-contact side of the screen. For ins~ance, a direct emulsion is a water-reducible substance which cures to a temporary, non-removable substance when exposed to specific wavelengths of light. For instance, the art work can be placed over the fresh emulsion while it is still reactive to water and exposed to halide light, at which time the part of the emulsion not expos~d to the light~ because it is covered with the art, stays water reactive. After a certain shooting or light exposure time, the art i5 Le...Oved~ the screen is then flushed with water and the part that has not been exposed to the light is flushed out, leaving the emulsion-void image area through which the ink 1OWS through the screen for printing. The measure of difficulty of emulsion removal also relates to the number o coats ~hich are put on the mesh, that is, dried and reapplied, and so orth, until you have between, for instance, 2 to about 5 coats of emulsion. Thus, the degree of dificulty in removing emulsion depends upon a number of factors including the number of coats, whether i~ is strongly sensitized, the exposure time, type of light activa~ion and chemical hardeners used after emulsion development, among other factors.
In view of the above background, the cleaning composition of Example 1 is a liquid non-aqueous solvent con~entrate having a flash point of approximately 200F (95C) and it is designed to remove a large variety of inks and paints from screens. In another eature of the method, NMP
concentrate of Example 1 prepares or sensitizes many common emulsions for subsequent removal with a low-volume, high pressure water rinsing. It i5 fast, efficient, economical by 1~
~L~8~
its capability of low-volume usage~ biodegradable and does not carry the red label (DOT fl~mm~ble~ solven-t designation. It is also safe on all screens and can be left on screens for extended periods prior to rinsing for cleaning. In the method of this invention, the ink side of the screen is sprayed in a light even pattern with a cohesive spray to prevent volatilization, followed by a dwell time of about 2-5 minutes.
A pressuriæed unit is operated for example under about 30 to 100 psi (typically 40 psi~ to provide a coheren-t stream of concentrate from a nozzle about 6" to 12" away rom the screen.
Mists are avoided. After the spray treatment, the degraded inks are then easily removed by a light to high pressure, i.e., approximately 50 to 1000 psi, low-volume ~ater rinse.
Lo~-volume means 2 - 4 gallons per minute. A an spray has been found preferred to provide a balance of force and quantity. A suitablè fan spray nozzle is the UniJet 65/01 manufactured by Spraying Systems Company of Wheaton, Illirois.
It is important, as developed above, that the screens on which the ink will be solubilized or degraded are free fxom water '0 prior to cleaning. The presence of water either in khe N~
concentrate or on the screen greatly destroys the effectiveness of the composition.
It has been found that tAe most preferred cleaning technique for achieving the advantages of the invention is the method ~hereby the cleaning concentrate is sprayed onto the ink side of the screen in a light even pattern and allo~ed to dwell for a short period of time, i.e., several minu~es up to several hours~ depending upon the factors involved in the cleaning system, composikion of the inks, production timing, and so forth. During the dwell time, the liquid cleaning concentrate - lfi -*trade mark ~ .
penetrates, emulsifies and solubilizes the ink. The ihk stays on the screen, but its ormer ink character is destroyed.
During the dwell ~ime, the co-solvent actions of N-methyl-2-pyrrolidone and the oxygenated solvent are at work. Further-more, the surfactant is penetrating the ink composition for dispersion and to aid in later ink removal by water. The coaction of all three ingredients permits the solubilization or degxadation of the ink permitting it ~o be dispersed easily for removal. The ~-methyl-2-pyrrolidone provides water activity to the composition for removal with water~ however, water must be under pressurized conditions such that the ink composition may be blown out, i.e., blo~n away from the screen. Thus, the composition is a delicate balance of ingredients whereby organic c~mronents of the ink may be solubilized or degraded by both the N-methyl-2-pyrrolidone and oxygenated solvents.
Furthermore, even though water during the presence of the soluhilization and degradation of the ink would be detrimental to the activity of N-methyl-2-pyrrolidone, nevertheless, the degraded ink in the presence of the NMP and cosolvent is water-active and may be L~.~.ov~d from the screen with a pres-surized fan of low-volume water rinse. In this connection it is preferred to employ a slicing fan or stream of water and sweeping it across the screen rom the bottom upwards in a ~nner such that the ink may be removed without redeposition.
The composition of ~xample 2 above is employed in the same manner for cleaning as the li~uid solvent concentrate of Example 1. However, the presence of methylene chloride tends to enhance the penetration of the entire composition and cellosolve ace~ate enhances the wa~er solubility of the composition. Other organic solvents which may be substituted ~&-., P3~
for ~he methylene chloride include other chlorinated solvents like l,l,l-trichloroethane, dimethyl sulfoxide, its derivatives and fluorocarbons ox Freons, In either case, the addition of such an organic solvent which enhances penetration, may also tend to evaporate and, therefore, has a much shorter wet life or dwell time on the screen. For instance, whereas the composition of Claim 1 may be left on the screen surface for a number of hours, the composition of Example 2 i5 usually employed for several minu~es, i.e., between 2-5 minutes for example. It is to be further understood that the ink solubilizer of Example 1 may be sequentially used in combination with the cleaning concentrate of Example 2. For instance, during the course of a cleaning operation, the ink may be solubilized with the Example 1 concentrate where~an operation may require screens to be left from production for a period of time up to several hours prior to the rinse .~ val of the ink. In such a case, the dwell time may be followed by a fresh degrading concentrate of Example 2 so that the residue may be activated for subsequent removal with a low-volume, high pressure water rinse. Furthermore, the amounts of the mate xials sprayed onto the substrate vary but normally they are withLn the range of several ounces per several ~quare ~eet, for example, 2-4 ounces per 6 foot square of screen.
Thus, in a preferred aspect, the me~hod of this invention involves spraying of the conc~ntrates of either of the Examples 1-2 onto a screen. The spray is an economieal and low volume usage followed by dwell time to solubilize and/or degrade the ink. Thereafter, a low-vol~me, high pressure water stream is directed at the substrate, preferably a fan spray is employed to slice through and help remove the destroyed ink , _~
. ..
~J~
composition. If the solubilized and degraded screen were simply dipped in water, the inks would set up and the screen would not be efectively cleaned. There is a balance between the force and the quantity of the water which is employed which will be understood by the person of ordinary skill in the art in view of this description.
It has been observed in connection with the method of cleaning the screens with a low area coverage spray, that a light mist may tend to settle on o~her remaining areas of degraded inks. It has been found th~t this problem can be alleviated or overcome by the addition of another component into the concentrate. That COmpQnent may be characterized as a hydrophobic additive and in particular it has been found that synthetic water soluble oils sold under the trademark UCON are satisfactory. Depending upon the amount of water mist or back-lash that is to be expected from the water rinse out, par~
of the surfactant package or liquid NMP concentrake may contain a water dispexsible oil which functions initially as a water repellant to a ligh~ water spray or mist, but readily allows a low volume, pressurized stream of water to removs the ink compositions previously degraded and solubilized by the NMP
concentrate. Such water soluble oils are of the class ~f polyalkylene glycols, commonly known as UCON lubricants manufactured by Union Carbide Corporation, but other types and mixtures thereo could be used of dif~ering water solubility.
A preferred high molecular weight one is UCON 50-HB5100~
Specific compounds include polyalkylene gly501s, i.e~, an oxirane polymer, CAS Registration No. 9038-95-3 or ethoxylatecl lanolin or ethoxylated castor oil. However, it is preferred Jq that the oils of the types described herein do not leave a residue on the screen after an adequate water rinse.
When the printing screen is to be ~otally reclaimed, that is, cleaned and the emulsion removed completely, the process is as follows. When the process of printing is com-pleted~ the operator cards or squeegees off any xesidual ink that is on the ink side of the screen, as well as any ink from the print-contact side. From a very prac~ical standpoint, inks are ~p~n~ive and an attempt is made to return as much of the ink as possible. From a standpoint of cleaning, more excess ink requires more cleaning concentrate in order to remove the ink and reclaim the screen without haæe o~ ghost residue.
After the screen is well carded, either before or after L~l,.oval from the press, and the cleaning process begins. If the process is to be an ;mme~;~te reclaim, either the co~centrate of Example l or 2 may be used, generally speaking, depending on ink type. Bither concentrate is sprayed on the ink s~de of the screen and then moved to the reclaim area. In the process of ; d;~te recl~;m;ng, within about 5-10 minutes after the application of either of the compositions of ~rl es 1 or 2, immediate recl ~;m; ng should be ~ -nc~d. After spraying with either concentrate, the image is flushed out from the print-contact side of the screen with high pressure water, as developed above, and this clears all or practically all of the ink. At the same time, the entire surface of the emulsion is wetted with water to prepare it for the application o a periodate-containing emulsion L~ ver. It has been found that there is a synergistic action resulting from use of the non-aqueous concentrate of Example 1 or 2 whose residue ~ jn!~
even after the watex spray such that the emulsion is sensitized ,~o ~--for faster removal. It is theorized, however, that in the immediate reclaim process, the emulsion is somehow softened or made more permeable for the treatment with a periodate-containing emulsion remover. A suitable example of an emulsion remover is exemplified by Example 3.
94.096~ Water 2.880% Sodium Meta Periodate 3.000~ Monosodium Phosphate~ Anhydrous 110 grams/1000 pounds water of an Anionic Surfa~tant Package of Equal Amounts of GAFAC RP-710, identif.ied above and CALSOFT F-90 Isodium dodecylbenzene sulfonate) The above periodate cont~;~;ng remover is then sprayed onto the screen surface on the print side and is per-mitted to dwell there anywhere from about 15 seconds to several minutes. This is generally an adequate time for degradation ~of the emulsion. Again a high pressure spray is employed to clean the emulsion from the screen. As developed above, it is important that residual effect of the concentrate of Examples 1 or ~ after the water spray be utilized immediately by following with an application of the periodate-containing emulsion re-mover. It has been proven that when more time elapses, for instance one-half hour, the emulsion will be taken off with greater difficultv. Accordingly, there is a synergism between the residual effect of the cleaning compositions of this invention insofar as they coact with such periodate con~ining emulsion removers and provide the complete xemoval o~ the emulsion.
*trade mark Finally, in the event that there is a residual ghost image as explained above, especially in connection with a multi-filament screen, a ghost or image remover may be employed. It is to be noted, however, that although there are at some time residual images, they are not necessarily a hindrance to further use of the screen and some screen printers axe not particular where there is a tinge of residue as long as the mesh squares themsel~es are no~ blocked in the screen. If a ghost or haze remover is used, it is typically a caustic solution of oxygenated solvents. The reason for such usage is that they are water rinsable or soluble and leave no residue to cause emulsion pro~lems later. In the case of the ghost or haze removers o~ this type it is necessary to brush, roll or card them on as opposed to spraying because Qf the enhanced viscosity. A typical composition is as follows:
31.64~ Cyclohexanone 19.40% Cellosolve Acetate 38.83~ 50dium Hydroxide 50 9.61~ DOWFAX 2Al Solution (sodium Didodecylphenoxy-benzenedisulfonate 70%, sodium dodecylphenoxy-benzenedisul~onate 30%) 0.01% Brilliant Milling Red Dye O.51~ GAFAC RP-710 ~identified above) For screens which will be delayed in processing but which will be totally reclaimed, it is important to destroy the ink so that at some time thereafter, that is in a matter of hours, the screen may be treated. For instance, the compo-sition of Example 1 is sprayed onto the ink side and, again~
this is a cohesive spray of the type referred to above without *traae mark ~,' !
5~
mist so as to reduce volatilization. The screen is thus wet and the ink tends to stay wet for a period of time. However, if there is a lapse of time before it goes to the screen shop for complete removal of the emulsion, there will be some ~endency for drying and possibly some run-down on the print side of the screen. I this develops, then the print side of the screen may be resprayed with a composition of Example 2 which acts to freshen up the solubilized residue after treat-ment with the composition of Example 1 to degrade the ink upon ~eing contacted with the water spray. At this poin~, upon respraying the print-contac~ side of the screen with a concen-trate of Example 2, the emulsion is sensit.ized or conditioned ~or the subsequent action with the emulsion cleaner as men-tioned above. Again, if a ghost or haze occurs, the ghost remover may be employed as set forth above.
One of the very significant aspects of the cleaning and reclAim;ng procedures i5 that no urther screen degreasing is required as is required when products typically availabie i~
the prior art have been used on screens to remove the inks and emulsions. In the past, toluene, acetone, bleach, trisodium phosphate, and other solvents or cl~n; n~ agents of the type indicated in the background of this invention have been employed in order to ~1 im- n~te screen oily residue at the end of processing. Accordingly, this invention o~fers a highly advantageous system for the complete cleaning of inks and emulsions from printing screens in a manner heretofore n~chi eved.
In view of the above detailed descrip~ion, printing screen cleaning and reClA;mlng methods are provided with distinct advantages over the methods now available. In ~3 5~
addition, methods of employing the compositions of this inven-tion have been provided which are unique and operate syner-gistically with other compositions in the process of cleaning and reclaiming screens. In view of the above detailed descrip-tion, it will be apparent to a person of ordinary skil1 in the art that deviations may be made from the specific examples and methods of operation without departing from the spirit and scope of this invention.
What is claimed is:
;2 't _~_
0.10~ Organic Phosphate Ester tGAFAC RP-710) I
37.86% N-methyl~2-pyrrolidone 9~26~ Butyl Cellosolve 1.52% Cyclohexanone 24.00~ Cellosolve Acetate 26.00% MethyLene Chloride 1.31% Octyl Phenoxy (Polyethoxy~ Ethanol ITRITON X114) 0.05~ Organic Phosphate Ester (G~FAC RP-710) In the alternative to the specific ingredients of Example 2, 50~ o Example 1 may be combined with 26~ of methy lene chloride and 24% cellosolve acetate. Examples 1 and 2 are preferred formulas for ~he N~ cleaning concentrates because of their biodegradability, reduced fl ~hility and low TLV
values.
Before describing in detail the cleaning and re-claiming of printing screens emloying the methods of this invention, an unders~n~i ng of certain underlying facts or terms is impox~ant. First of all, the ink side o~ the printing screen is alternately c~lled the squeegee side, thQ well side, or the front side, but for purposes of this description-it will be called the ink side. The opposite side o the screen is called the back side, down side or print-contact side. Again, for purposes of this description, it will be called the print~
contact side. The term "ink" will be the generic term for many of the compositions that are employed in tha practice of screen printing including dyes or inks commonly referred to as flexible enamels, synthetic enamels, fast-dry enamels, flexible l3 lacquers, industrial lacquers, flat vinyl ink, vinyl half-tone ink, fluorescent vinyl ink, gloss vinyl ink, satin vinyl ink, flock adhesive, transparent ink, me~allic powders, acrylic ink, plastisol ink, mylar ink, textile ink, among many other types of inks. For general information on ink compositions, refer-ence may be had to the catalog by KC Graphics, Inc. 1978-1979, copyright 1978 by KC Graphics, Inc. Reerence may also be had to "Te~tile Screen Printing" by Albert ~osloff, Second Edition, International Standard Book Number 0-911380-39~6 (1976). These sources will also serve as backyround information for the inks which may b~ cle~n~ with the inventive cleaning compositions.
As developed above, the printing screen may be made from a number of materials and may have various mesh sizes. A mono-ilament screen is a single strand of material for example of polyester, nylon, stainless steel, silk, chrome-plated wire, o~
other things r which is woven into a specific number of squares per a d; -nsionr i.e., a 230 mesh means 230 open squares per square inch. A multi-f;1~Qnt screen is comprised of a sexies of strands of similar materials just mentioned, braided before weaving into the mesh measurement, i.e., 12xx150 mesh would mean lZ interwoven strands subsequently woven into 150 open squares per square inch and, where the cross-over points of mesh occur, pigment can get into the strands and ma~ become extremely hard to L~...ove. Thus, it may be determined by this description of either the mono-filament or the multi-filament screens that the requirements for complete removal of ink residue, for instance, may differ due to the construction of the screen. In particular, that last residue often referred to in the art as "ghost" or "haze" would be more readily apparent in the multi-filament screens where pigment can get into the strands and becomes very hard to remove. There are a number of classes of emulsions which ini~ially cover the print-contact side of the screen. For ins~ance, a direct emulsion is a water-reducible substance which cures to a temporary, non-removable substance when exposed to specific wavelengths of light. For instance, the art work can be placed over the fresh emulsion while it is still reactive to water and exposed to halide light, at which time the part of the emulsion not expos~d to the light~ because it is covered with the art, stays water reactive. After a certain shooting or light exposure time, the art i5 Le...Oved~ the screen is then flushed with water and the part that has not been exposed to the light is flushed out, leaving the emulsion-void image area through which the ink 1OWS through the screen for printing. The measure of difficulty of emulsion removal also relates to the number o coats ~hich are put on the mesh, that is, dried and reapplied, and so orth, until you have between, for instance, 2 to about 5 coats of emulsion. Thus, the degree of dificulty in removing emulsion depends upon a number of factors including the number of coats, whether i~ is strongly sensitized, the exposure time, type of light activa~ion and chemical hardeners used after emulsion development, among other factors.
In view of the above background, the cleaning composition of Example 1 is a liquid non-aqueous solvent con~entrate having a flash point of approximately 200F (95C) and it is designed to remove a large variety of inks and paints from screens. In another eature of the method, NMP
concentrate of Example 1 prepares or sensitizes many common emulsions for subsequent removal with a low-volume, high pressure water rinsing. It i5 fast, efficient, economical by 1~
~L~8~
its capability of low-volume usage~ biodegradable and does not carry the red label (DOT fl~mm~ble~ solven-t designation. It is also safe on all screens and can be left on screens for extended periods prior to rinsing for cleaning. In the method of this invention, the ink side of the screen is sprayed in a light even pattern with a cohesive spray to prevent volatilization, followed by a dwell time of about 2-5 minutes.
A pressuriæed unit is operated for example under about 30 to 100 psi (typically 40 psi~ to provide a coheren-t stream of concentrate from a nozzle about 6" to 12" away rom the screen.
Mists are avoided. After the spray treatment, the degraded inks are then easily removed by a light to high pressure, i.e., approximately 50 to 1000 psi, low-volume ~ater rinse.
Lo~-volume means 2 - 4 gallons per minute. A an spray has been found preferred to provide a balance of force and quantity. A suitablè fan spray nozzle is the UniJet 65/01 manufactured by Spraying Systems Company of Wheaton, Illirois.
It is important, as developed above, that the screens on which the ink will be solubilized or degraded are free fxom water '0 prior to cleaning. The presence of water either in khe N~
concentrate or on the screen greatly destroys the effectiveness of the composition.
It has been found that tAe most preferred cleaning technique for achieving the advantages of the invention is the method ~hereby the cleaning concentrate is sprayed onto the ink side of the screen in a light even pattern and allo~ed to dwell for a short period of time, i.e., several minu~es up to several hours~ depending upon the factors involved in the cleaning system, composikion of the inks, production timing, and so forth. During the dwell time, the liquid cleaning concentrate - lfi -*trade mark ~ .
penetrates, emulsifies and solubilizes the ink. The ihk stays on the screen, but its ormer ink character is destroyed.
During the dwell ~ime, the co-solvent actions of N-methyl-2-pyrrolidone and the oxygenated solvent are at work. Further-more, the surfactant is penetrating the ink composition for dispersion and to aid in later ink removal by water. The coaction of all three ingredients permits the solubilization or degxadation of the ink permitting it ~o be dispersed easily for removal. The ~-methyl-2-pyrrolidone provides water activity to the composition for removal with water~ however, water must be under pressurized conditions such that the ink composition may be blown out, i.e., blo~n away from the screen. Thus, the composition is a delicate balance of ingredients whereby organic c~mronents of the ink may be solubilized or degraded by both the N-methyl-2-pyrrolidone and oxygenated solvents.
Furthermore, even though water during the presence of the soluhilization and degradation of the ink would be detrimental to the activity of N-methyl-2-pyrrolidone, nevertheless, the degraded ink in the presence of the NMP and cosolvent is water-active and may be L~.~.ov~d from the screen with a pres-surized fan of low-volume water rinse. In this connection it is preferred to employ a slicing fan or stream of water and sweeping it across the screen rom the bottom upwards in a ~nner such that the ink may be removed without redeposition.
The composition of ~xample 2 above is employed in the same manner for cleaning as the li~uid solvent concentrate of Example 1. However, the presence of methylene chloride tends to enhance the penetration of the entire composition and cellosolve ace~ate enhances the wa~er solubility of the composition. Other organic solvents which may be substituted ~&-., P3~
for ~he methylene chloride include other chlorinated solvents like l,l,l-trichloroethane, dimethyl sulfoxide, its derivatives and fluorocarbons ox Freons, In either case, the addition of such an organic solvent which enhances penetration, may also tend to evaporate and, therefore, has a much shorter wet life or dwell time on the screen. For instance, whereas the composition of Claim 1 may be left on the screen surface for a number of hours, the composition of Example 2 i5 usually employed for several minu~es, i.e., between 2-5 minutes for example. It is to be further understood that the ink solubilizer of Example 1 may be sequentially used in combination with the cleaning concentrate of Example 2. For instance, during the course of a cleaning operation, the ink may be solubilized with the Example 1 concentrate where~an operation may require screens to be left from production for a period of time up to several hours prior to the rinse .~ val of the ink. In such a case, the dwell time may be followed by a fresh degrading concentrate of Example 2 so that the residue may be activated for subsequent removal with a low-volume, high pressure water rinse. Furthermore, the amounts of the mate xials sprayed onto the substrate vary but normally they are withLn the range of several ounces per several ~quare ~eet, for example, 2-4 ounces per 6 foot square of screen.
Thus, in a preferred aspect, the me~hod of this invention involves spraying of the conc~ntrates of either of the Examples 1-2 onto a screen. The spray is an economieal and low volume usage followed by dwell time to solubilize and/or degrade the ink. Thereafter, a low-vol~me, high pressure water stream is directed at the substrate, preferably a fan spray is employed to slice through and help remove the destroyed ink , _~
. ..
~J~
composition. If the solubilized and degraded screen were simply dipped in water, the inks would set up and the screen would not be efectively cleaned. There is a balance between the force and the quantity of the water which is employed which will be understood by the person of ordinary skill in the art in view of this description.
It has been observed in connection with the method of cleaning the screens with a low area coverage spray, that a light mist may tend to settle on o~her remaining areas of degraded inks. It has been found th~t this problem can be alleviated or overcome by the addition of another component into the concentrate. That COmpQnent may be characterized as a hydrophobic additive and in particular it has been found that synthetic water soluble oils sold under the trademark UCON are satisfactory. Depending upon the amount of water mist or back-lash that is to be expected from the water rinse out, par~
of the surfactant package or liquid NMP concentrake may contain a water dispexsible oil which functions initially as a water repellant to a ligh~ water spray or mist, but readily allows a low volume, pressurized stream of water to removs the ink compositions previously degraded and solubilized by the NMP
concentrate. Such water soluble oils are of the class ~f polyalkylene glycols, commonly known as UCON lubricants manufactured by Union Carbide Corporation, but other types and mixtures thereo could be used of dif~ering water solubility.
A preferred high molecular weight one is UCON 50-HB5100~
Specific compounds include polyalkylene gly501s, i.e~, an oxirane polymer, CAS Registration No. 9038-95-3 or ethoxylatecl lanolin or ethoxylated castor oil. However, it is preferred Jq that the oils of the types described herein do not leave a residue on the screen after an adequate water rinse.
When the printing screen is to be ~otally reclaimed, that is, cleaned and the emulsion removed completely, the process is as follows. When the process of printing is com-pleted~ the operator cards or squeegees off any xesidual ink that is on the ink side of the screen, as well as any ink from the print-contact side. From a very prac~ical standpoint, inks are ~p~n~ive and an attempt is made to return as much of the ink as possible. From a standpoint of cleaning, more excess ink requires more cleaning concentrate in order to remove the ink and reclaim the screen without haæe o~ ghost residue.
After the screen is well carded, either before or after L~l,.oval from the press, and the cleaning process begins. If the process is to be an ;mme~;~te reclaim, either the co~centrate of Example l or 2 may be used, generally speaking, depending on ink type. Bither concentrate is sprayed on the ink s~de of the screen and then moved to the reclaim area. In the process of ; d;~te recl~;m;ng, within about 5-10 minutes after the application of either of the compositions of ~rl es 1 or 2, immediate recl ~;m; ng should be ~ -nc~d. After spraying with either concentrate, the image is flushed out from the print-contact side of the screen with high pressure water, as developed above, and this clears all or practically all of the ink. At the same time, the entire surface of the emulsion is wetted with water to prepare it for the application o a periodate-containing emulsion L~ ver. It has been found that there is a synergistic action resulting from use of the non-aqueous concentrate of Example 1 or 2 whose residue ~ jn!~
even after the watex spray such that the emulsion is sensitized ,~o ~--for faster removal. It is theorized, however, that in the immediate reclaim process, the emulsion is somehow softened or made more permeable for the treatment with a periodate-containing emulsion remover. A suitable example of an emulsion remover is exemplified by Example 3.
94.096~ Water 2.880% Sodium Meta Periodate 3.000~ Monosodium Phosphate~ Anhydrous 110 grams/1000 pounds water of an Anionic Surfa~tant Package of Equal Amounts of GAFAC RP-710, identif.ied above and CALSOFT F-90 Isodium dodecylbenzene sulfonate) The above periodate cont~;~;ng remover is then sprayed onto the screen surface on the print side and is per-mitted to dwell there anywhere from about 15 seconds to several minutes. This is generally an adequate time for degradation ~of the emulsion. Again a high pressure spray is employed to clean the emulsion from the screen. As developed above, it is important that residual effect of the concentrate of Examples 1 or ~ after the water spray be utilized immediately by following with an application of the periodate-containing emulsion re-mover. It has been proven that when more time elapses, for instance one-half hour, the emulsion will be taken off with greater difficultv. Accordingly, there is a synergism between the residual effect of the cleaning compositions of this invention insofar as they coact with such periodate con~ining emulsion removers and provide the complete xemoval o~ the emulsion.
*trade mark Finally, in the event that there is a residual ghost image as explained above, especially in connection with a multi-filament screen, a ghost or image remover may be employed. It is to be noted, however, that although there are at some time residual images, they are not necessarily a hindrance to further use of the screen and some screen printers axe not particular where there is a tinge of residue as long as the mesh squares themsel~es are no~ blocked in the screen. If a ghost or haze remover is used, it is typically a caustic solution of oxygenated solvents. The reason for such usage is that they are water rinsable or soluble and leave no residue to cause emulsion pro~lems later. In the case of the ghost or haze removers o~ this type it is necessary to brush, roll or card them on as opposed to spraying because Qf the enhanced viscosity. A typical composition is as follows:
31.64~ Cyclohexanone 19.40% Cellosolve Acetate 38.83~ 50dium Hydroxide 50 9.61~ DOWFAX 2Al Solution (sodium Didodecylphenoxy-benzenedisulfonate 70%, sodium dodecylphenoxy-benzenedisul~onate 30%) 0.01% Brilliant Milling Red Dye O.51~ GAFAC RP-710 ~identified above) For screens which will be delayed in processing but which will be totally reclaimed, it is important to destroy the ink so that at some time thereafter, that is in a matter of hours, the screen may be treated. For instance, the compo-sition of Example 1 is sprayed onto the ink side and, again~
this is a cohesive spray of the type referred to above without *traae mark ~,' !
5~
mist so as to reduce volatilization. The screen is thus wet and the ink tends to stay wet for a period of time. However, if there is a lapse of time before it goes to the screen shop for complete removal of the emulsion, there will be some ~endency for drying and possibly some run-down on the print side of the screen. I this develops, then the print side of the screen may be resprayed with a composition of Example 2 which acts to freshen up the solubilized residue after treat-ment with the composition of Example 1 to degrade the ink upon ~eing contacted with the water spray. At this poin~, upon respraying the print-contac~ side of the screen with a concen-trate of Example 2, the emulsion is sensit.ized or conditioned ~or the subsequent action with the emulsion cleaner as men-tioned above. Again, if a ghost or haze occurs, the ghost remover may be employed as set forth above.
One of the very significant aspects of the cleaning and reclAim;ng procedures i5 that no urther screen degreasing is required as is required when products typically availabie i~
the prior art have been used on screens to remove the inks and emulsions. In the past, toluene, acetone, bleach, trisodium phosphate, and other solvents or cl~n; n~ agents of the type indicated in the background of this invention have been employed in order to ~1 im- n~te screen oily residue at the end of processing. Accordingly, this invention o~fers a highly advantageous system for the complete cleaning of inks and emulsions from printing screens in a manner heretofore n~chi eved.
In view of the above detailed descrip~ion, printing screen cleaning and reClA;mlng methods are provided with distinct advantages over the methods now available. In ~3 5~
addition, methods of employing the compositions of this inven-tion have been provided which are unique and operate syner-gistically with other compositions in the process of cleaning and reclaiming screens. In view of the above detailed descrip-tion, it will be apparent to a person of ordinary skil1 in the art that deviations may be made from the specific examples and methods of operation without departing from the spirit and scope of this invention.
What is claimed is:
;2 't _~_
Claims (23)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of cleaning a printed screen having an image and a residue of ink on the surface thereof which comprises the steps of spraying at room temperature the printed screen ink residue with a non-aqueous biodegradable liquid composition of N-methyl-2-pyrrolidone, an oxygenated solvent and a surfactant, allowing the composition to dwell on the ink surface for a sufficient period of time to degrade the ink residue and removing the degraded ink residue by rinsing with a pressurized stream of water without removing the printed image.
2. The method of Claim 1 comprising the additional step of mechanically agitating said compositions on said screens under non-aqueous conditions before rinsing.
3. The method of Claim 1 wherein the composition contains tetrahydrofurfuryl alcohol.
4 The method of Claim 1 wherein rinse water is applied as a fan spray.
5. The method of Claim 1 wherein waster rinse is a pressurized low-volume water rinse.
6. The method of Claim 1 wherein the oxygenated solvent is selected from the group consisting of butyl cello-solve, cellosolve acetate and cyclohexanone, and mixtures thereof.
7. The method of Claim 6 wherein the dwell time of said ink surface is from about several minutes up to several hours.
8. The method of Claim 7 wherein after several hours dwell time the degraded ink is treated with a liquid concen-trate of N-methyl-2-pyrrolidone, an oxygenated solvent, methylene chloride, and a surfactant prior to rinsing.
9. The method of Claim 1 conducted under room temperature conditions.
10. The method of Claim 1 wherein said surfactant is selected from the class consisting of nonionic, anionic and amphoteric surfactants, and mixtures thereof.
11. The method of Claim 1 wherein said liquid compo-sition comprises a non-aqueous mixture consisting essentially of aobut 30 to about 85% N-methyl-2-pyrrolidone, about 10-35%
of an oxygenated solvent and about 1-5% of a surfactant.
of an oxygenated solvent and about 1-5% of a surfactant.
12. The method of Claim 1 wherein said liquid composition additionally includes a water dispersible oil.
13. The method of Claim 12 wherein said water dispersible oil is selected from the group consisting of polyalkylene glycol, ethoxylated lanolin and ethoxylated castor oil.
14. A method of cleaning and recycling a printing screen having an image of an emulsion and a residue of ink on the surface thereof which comprises the steps of spraying at room temperature the printing screen ink residue with a non-aqueous biodegradableliquid ocmpositon of N-methyl-2-pyrrolidone, an oxygenated solvent and a surfactant, allowing the composition to dwell on the ink surface for a sufficient period of time to degrade the ink residue, removing the degraded ink residue by rinsing with a pressurized stream of water, contacting within a short time the water-rinsed screen with a periodate-containing emulsion remover, and flushing the resultant screen with a stream of pressurized water to remove the emulsion image.
15. The method of Claim 14 wherein the periodate containing emulsion remover is an aqueous solution of sodium metaperiodate.
16. The method of Claim 15 wherein said periodate-containing emulsion remover additionally contains an anionic surfactant.
17. The method of Claim 14 wherein after the last water flush a caustic solution of oxygenated solvent is applied to the screen to remove ghost images.
18. The method of Claim 17 wherein the caustic solution of oxygenated solvent comprises a solution of sodium hydroxide, an oxygenated solvent from the group consisting of cyclohexanone, cellosolve acetate and mixtures thereof and a surfactant.
19. The method of Claim 14 wherein said surfactant is an anionic surfactant.
20. The method of Claim 14 wherein, after said dwell time and prior to the first water rinse, spraying a composition onto the resultant screen residue comprising N-methyl-2-pyrrolidone, an oxygenated solvent, a surfactant, and an organic solvent from the group consisting of methylene chloride, dimethylsulfoxide and chloroform is sprayed on said residue.
21. The method of Claim 20 conducted under room temperature conditions.
2 The method of Claim 14 wherein said liquid composition additionally includes a water dispersible oil.
23. The method of Claim 22 wherein said water dispersible oil is selected from the group consisting of polyalkylene glycol, ethoxylated lanolin and ethoxylated castor oil.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US32778381A | 1981-12-07 | 1981-12-07 | |
| US327,783 | 1981-12-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1198958A true CA1198958A (en) | 1986-01-07 |
Family
ID=23278047
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000414440A Expired CA1198958A (en) | 1981-12-07 | 1982-10-28 | Method of cleaning and reclaiming printing screens |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS58104796A (en) |
| CA (1) | CA1198958A (en) |
| MX (1) | MX161511A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4453984A (en) * | 1982-06-30 | 1984-06-12 | International Business Machines Corporation | Method for removing electrically conductive paste from a screening mask |
| JPH0673995B2 (en) * | 1987-07-28 | 1994-09-21 | 神東塗料株式会社 | Reproduction method of rotary screen gauze for printing |
| JPH0679852A (en) * | 1992-07-13 | 1994-03-22 | Sanyo Chem Ind Ltd | Cleansing for screen printing board |
| CN106274123A (en) * | 2016-08-16 | 2017-01-04 | 东莞市五株电子科技有限公司 | A kind of half tone regeneration method |
-
1982
- 1982-10-28 CA CA000414440A patent/CA1198958A/en not_active Expired
- 1982-12-06 JP JP21381082A patent/JPS58104796A/en active Pending
- 1982-12-07 MX MX19547882A patent/MX161511A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| MX161511A (en) | 1990-10-19 |
| JPS58104796A (en) | 1983-06-22 |
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