US 3532599 A
Description (OCR text may contain errors)
nited States 3,532,599 PROCESS FOR CLEANING WITH ENZYMES Isadore Nathan Cooperman, Plainfielcl, NJ.
(62 Farm Road, Freehold Township, NJ. 07728) No Drawing. Filed Oct. 23, 1968, Ser. No. 770,087 Int. Cl. C12b 1/100 US. Cl. 1953 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to improvements in printing processes whereby equipment can be maintained in a like-new clean condition for extended periods of time. It relates further to a method of cleaning printing equipment whereby accumulated ink deposits can be effectively removed without damage to the surfaces on which the deposits are found. It relates still further to compositions which are useful for practicing the cleaning method of this invention.
Printing inks are generally full-bodied liquids which tenaciously adhere to paper, metal, textile, rubber, plastic and wood surfaces which they contact. These surfaces may be those upon which an image is printed or the surfaces on the parts of printing equipment. The tenacious adherence of ink to surfaces other than those receiving the imprint poses a problem in the care and maintenance of equipment especially rubber rollers and metal printing plates. The ink deposits tend to build up and harden on surfaces which are required to meet close tolerance limits, and the eventual large accumulations can lead to a loss of usefulness of printing plates or rubber covered roller applicators. Cleaning procedures to minimize unwanted accumulation of ink, residues fall into two categories and it is standard operating procedure to clean equipment by either one or both methods after each printing run or at the end of each day of operation.
One method commonly used is to wash with solvents and/or dilute acids. Dilute acids are used in cleaning metal printing plates, and, in the process of removing hardened deposits, the acid also etches the metal and weakens the plate, eventually causing it to be discarded. Solvent washes with alcohol and/or hydrocarbons remove greasy elements of the ink without attacking metal parts; however, organic solvents have a damaging effect on rubber and moreover they do not remove glazing which always forms on the rubber and/or metal surfaces on contact with printing inks.
The other method of cleaning printing equipment is to abrade the surfaces with a material such as finely ground pumice or other abrasive material. Abrasion can be used to clean both metal and rubber parts, and it is an effective approach in that the treated surfaces can be thoroughly cleaned by sufficient abrasion.
By using a combination of these methods, parts can be freed of solvent soluble and insoluble deposits. Generally parts are first washed in a solvent, e.g. a mixture of butanol and aliphatic distillate to remove excess ink. Washing of rubber parts must be carefully and quickly done since the solvent tends to penetrate into the rubber causing it to swell out of shape and lose its ability to absorb Patented Oct. 6, 1970 ink efficiently. The washed parts can be further cleaned by careful abrasion with pumice to remove insoluble glazing resulting from the hardening of gum constituents in many printing inks. The washed and abraded parts are in condition for further use provided these operations were carefully performed and not too often repeated. When a printing plate or a roller is abraded unevenly during cleaning, the unevenness and imbalance interferes with the quality of the copy, the uniformity of ink applications and/or the smoothness of press operation. Thus, though it'is effective for the purpose, the abrading method is not fully satisfactory because it reduces the life of the equipment and can, if improperly done, reduce the quality of the printed image. Accordingly, there is a need in the printing industry for a safe and effective means of cleaning used printing equipment, especially rubber parts, to remove deposits which tend to impair the usefulness and reduce the life of the parts. It is a further object of this invention to provide new compositions which are useful for cleaning printing equipment in a manner which is both efficient and harmless to equipment.
In accordance with the present invention, these and other objects are accomplished in a surprisingly simple and effective manner by the use of enzymatically active cleaning compositions which are capable of decomposing the water and oil insoluble deposits which accumulate on the equipment normally in contact with printing ink. The enzyme attacks and decomposes, probably through hydrolysis, the hardened gum constituents which have deposited on the surfaces of the rollers and printing plates in much the same way as an acid would, except that the enzyme is completely harmless to metal and rubber surfaces whereas acid is not. The enzyme treatment removes, in addition to gum deposits, other components of the ink which had been occluded by the hardened gum.
The present invention is thus useful for cleaning equipment used in procedures where gums are employed in making the imprint. The gum can be a viscosity imparting constituent of the ink or, as in lithography, a part of the solution used to wet the printing plate. Printing inks commonly having a gum component are those used in lithographic, flexographic, rotogravure and letter press processes. Gums which are typically used for this purpose are gum arabic, gum tragacantli, guar gum, starch, aliginate and methylcellulose.
The cleaning processes of this invention fill an especially important role in the case of lithographic and fleXographic equipment since gum solutions are applied to the equipment all through the printing operations to impart required absorbency characteristics to the printing plate or the offset blankets (rolls). Here, in view of the major amounts of gums which are employed, the problem of gum deposits is particularly frequent and troublesome.
Flexographic printing embraces multilith and collo type procedures in which printing is effected by water base ink transfer to and/or from a rubber or plastic plate for flexographic procedures or to and/or from a gelatine surface for collotype procedures. Gums are used to increase adhesion, impart better transference by increasing viscosity, improves fluid flow of the ink and increases wettability of surfaces. Most commonly employed for this purpose is zein, a proteinaceous gum extracted from corn. Other gums such as gelatine, casein, starch or soya protein have been suggested as substitutes for zein.
In lithography, gum solutions are used as an integral part of the printing process to form a grease repelling coating on the non-printing areas of the printing plate. The areas to which the gum coating does not adhere, are able to absorb the greasy ink and form the imprint. In offset lithography, the printing plate (normally in the form of a cylinder, called the plate cylinder), contacts a rubber covered cylinder (called the blanket cylinder) which in turn makes the imprint by contacting the paper, metal, wood, plastic, or textile which is to be imprinted. The gum solution, normally buffered to an acid pH is applied to the printing plate by means of a series of moistening rollers which transfer the solution from a trough containing it. Each of the moistening rollers eventually builds up a glaze coat which interferes with the resiliency and absorption efliciency of the rollers. In time, gum is transferred by water-in-oil emulsification to the inking rollers, and these likewise lose their essential properties. The gum which is most commonly employed in commercial lithographic operations is gum arabic; a polysaccharide extracted from acacia. Cellulose gum, a synthetic cellulose derivative, is also finding use in commercial operations. Other natural and synthetic gums are also sometimes used, but less frequently.
The choice of enzyme for any given application depends upon the chemical nature of the gum contained in the ink or in the moistening solution (as in the case of lithographic processes). Gums in use today are polysaccharides, cellulose derivatives or proteins. Thus, gum arabic is a polysaccharide, cellulose gum is a cellulosic derivative and zein is a protein. Polysaccharides are decomposed by diastatic and pentosanasic-hexosanasic enzymes. Celluloses are decomposed by cellulases or esterases and proteins are decomposed by proteolytic enzymes. The source of the enzymes used in the present invention is not of critical importance and any of the commercially available materials may be employed herein. In general the enzymatic materials are obtained by the fermentation of various mature seed spores or bacteria on a suitable culture medium. Classic methods for the propagation of these spores or bacteria and the extraction of the enzymatic material are outlined in microbiological textbooks and in US. Pat. No. 1,660,458, issued Feb. 28, 1928; US. Pat. No. 1,421,613, issued July 4, 1922, etc. Very useful enzymatic materials are offered commercially by Rohm and Haas. Rhozyme HP-150 is pentosanasic-hexosanasic is an enzyme which is useful for hydrolysis of polysaccharides such as gum arabic. Cellulase 36 is a cellulase which is useful for the hydrolysis of cellulose gum. Esterases or pectinases because of their activity against cellulosic derivatives, are also useful in the hydrolysis of cellulose gums. Proteinaceous gums such as zein are hydrolyzed by proteolytic enzymes such as Rhozyme A4, Rhozyme J-25, etc. Enzymatic materials are commercially available with or without diluents such as kaolin, salt or other inert materials. Though food grade enzyme products can be used, the present invention can be carried out more economically when technical grade enzymes are employed.
To practice the present invention, it is generally desirable to first remove excess printing ink and unhardened material from the part to be cleaned. In the case of greasy printing inks this can be accomplished by conventional solvent washes. The partially cleaned printing part is then immersed in a solution of the enzyme. Generally, the aqueous enzymatic solution is buffered to an acid pH to provide an environment in which the enzyme is active. The enzyme treat-ment can be conducted at room temperature or slightly higher, e.g. up to about 40 or 50 C. Enzymatic action begins as soon as the printing equipment is contacted with the enzyme composition. Generally, noticeable cleaning is effected after only several minutes of immersion. Longer immersion in the enzyme solution results in more thorough cleaning. There is no diflrculty with allowing the printing part to be immersed in the enzyme solution for a prolonged period since the latter is harmless to either metal or rubber. The concentration of the enzyme in the cleaning solution may vary over Wide limits. Genreally, cleaning solutions with a concentration of L to 30.00 parts of enzyme per 100 parts of cleaning solution are able to provide sufficiently rapid cleaning action while involving economically feasible amounts of the enzymatic material. Larger amounts (e.g. up to 75% or more) of enzyme may be used without danger to equipment but the advantage of reduced cleaning time may not justify the cost of the excess enzyme.
The compositions of the present invention can include any inert diluent (for example, as a suspending agent) which does not deactivate the active enzyme component. Among such diluents are diatomaceous earth, kaolin clay, salt, silica, talc, hydrous magnesium, aluminum silicates and their organic derivatives and acid buffers such as citrate, tartrate or acetate. Generally, since the enzymes are active under acidic conditions, it is desirable to include one of the above-mentioned acid buffers in the compositions of the present invention. It is an advantage of this invention that the enzymatic material is not deactivated by organic solvents which are capable of dissolving the greasy components of ink. This compatibility permits the formulation of the enzymatic material as a dual function composition capable of exerting both hydrolytic and solvent action. Thus, it is possible to prepare a composition of the proteolytic, diastatic, pentosanasic-hexosanasic or esterasic enzyme or combinations thereof in organic solvents such as the aromatic hydrocarbons (e.g. benzene, toluene, or xylene), the aliphatic hydrocarbons (e.g. hexane, heptane and octane) or other solvents such as ethanol, ethyl acetate or ether. The concentration of the enzyme in the organic solvent should generally be in the range of 1 to 30 weight percent. The composition can contain an emulsifier which will allow the organic solvent to mix with water when water is added to activate the enzyme. The resulting emulsion will be found to be effective for removing glaze and also oil-soluble ink components from the printing equipment to be cleaned.
The cleaning compositions of the present invention can be applied to the equipment to be cleaned without disassembling it. Thus, for example, if it is desired to clean the moistening rollers in lithographic equipment the trough in which the moistening solution is generally kept can be emptied and the enzymatic composition of the present invention placed therein. By rotating the rollers in the trough containing the enzymatically active cleaning solution, the rollers are constantly brought into contact with the cleaning solution and after a suitable period of time become clean. Alternatively, a cloth can be dampened with the enzymatic cleaning material and used to apply it to the part to be cleaned. After a suitable period of time the enzymatic material can be removed by washing with water. The cleaned part will be notably free of glaze and any other material which may have been occluded by the glaze forming substance. The cleaned part can be returned to service Without any further treatment.
A typical composition for cleaning lithographic printing plates or rubber rollers has the following formulation:
Parts Rhozyme HP-150 enzyme 10 Water If it is desired, a lithographic cleaning solution can be prepared to contain both enzymatically active material and organic solvent. An example of such a composition is:
Parts Rhozyme HP- enzyme 10 Laktane solvent 6O Ethanol 40 A useful composition for cleaning fiexographic equipment has the following composition:
.Parts RhozymeA-40 enzyme, Rhozyme L25 enzyme 15 Ethyl acetate 25 Laktane solvent 75 The following example is presented to further illustrate the present invention.
EXAMPLE 1 green (the original color of the rubber roller) and considerable softening of the roller was noted. Previous cleaning of the roller with organic solvents only had left the roller in a hardened and black condition.
What is claimed is:
1. A process for cleaning printing equipment to remove hardened gum deposits from the surface thereof which comprises immersing the equipment to be cleaned in an aqueous composition containing at least one enzyme selected from the group consisting of a cellulose, a diastase, a pentosanase-hexosanase, a protease or an esterase and maintaining the printing part in said enzymatic composition until the gum deposits have been substan- Cir tially hydrolyzed to water-soluble decomposition products.
2. The process of claim 1 wherein the printing part is a rubber covered cylinder used for lithographic or fiexographic printing.
3. The process of claim 1 wherein the printing part is a printing plate used in lithography.
4. The process of claim 1 wherein a pentosanasic-hexosanasic enzyme is used.
5. The process of claim 1 wherein the deposit to be hydrolyzed is gum arabic or cellulose gum.
References Cited UNITED STATES PATENTS 649,169 5/1900 Jobbins 195-2 XR 1,421,613 7/1922 Takamine 195--4 1,430,523 9/1922 Jenny et al. 195-2 1,877,097 9/1932 WaHerstein 1954 2,607,359 8/1952 Oesting 134-42 XR 2,742,398 4/1956 Zobell 134-42 XR 3,220,928 11/ 1965 Brenner 195-2 MORRIS 0. WOLK, Primary Examiner J. T. ZATARGA, Assistant Examiner US. Cl. X.R.