US 3615791 A
Description (OCR text may contain errors)
1  Assignee United States Patent  Inventors  LACQUER EMULSIONS FOR LITHOGRAPHIC PLATES AND METHOD FOR THEIR MANUFACTURE 24 Claims, No Drawings  US. Cl l06/l70, 96/33, 96/48 R, 96/49,101/456,101/457,
106/209, 260/29.2 R, 260/29.2 M, 260/29.2 TN,
260/29.2 UA, 260/29.3, 260/29.6 R, 260/29.6
AN, 260/29.6 MH, 260/37 SB, 260/37 PC, 260/37  Int. Cl C086 21/04, G03f7/00, B41m 5/00  Field ofSearch 106/170; 96/33, 48, 49; 101/463, 464, 465, 466, 456, 457;
260/29.2, 29.2 M, 29.3, 29.6 EM, 29.6 ME, 29.6
MH  References Cited UNlT ED STATES PATENTS 3,276,360 10/1966 Stimson et a1 260/29.6
2,410,382 10/1946 Kaplan 106/170 2,591,904 4/1952 Zola 106/238 2,637,705 5/1953 Auer 106/170 3,019,105 1/1962 Adams 106/170 3,019,106 1/1962 Adams 106/170 2,754,279 7/1956 Hall 96/33 OTHER REFERENCES Perry-Chemical Engineers Handbook (3rd Ed.) (McGraw- Hill) (N.Y.) (1950) TP 155 p4, pages 1167- 1169.
Modern Plastics Encyclopaedia 1965 (Sept. 1964) (Me- Graw-l-lill) (N.Y.) p.528 Primary Examiner-Morris Liebman Assistant Examiner-H. H. Fletcher Attorney-Owen, Wickersham & Erickson LACQUER EMULSIONS FOR LITHOGRAPHIC PLATES AND METHOD FOR THEIR MANUFACTURE This invention relates to improvements in lacquer emulsions for lithographic plates and in a method for their manufacture. More particularly, it relates to an oleophilic emulsion applied to exposed presensitized lithographic plates for simultaneously developing the plates after light exposure, desensitizing the nonimage areas, and applying a film of an ink-attractive lacquer on the plate surface.
Presensitized plates have become quite popular in the lithographic industry. A "presensitized plate is one that has been coated with a stable, light-sensitive material and is capable of being stored before use for long periods of time under ordinary temperature and humidity conditions. As such plates have become more popular, interest has arisen in how to simplify the processing after exposure to a light source through a negative or stencil, to produce the desired image. The most common method has heretofore involved four steps: (1) developing the light-exposed plate with a suitable solvent to remove the unexposed areas of light-sensitive material, (2) drying the developed plate, (3) treating the plate with a lithographic desensitizing solution to render the nonimage areas ink-repellent, and (4) rubbing the image areas with ink or a colored lacquer emulsion to render them plainly visible and to increase their chemical resistance and ink receptivity. The three main operations (excluding the drying step) were separate and distinct-a procedure which has been especially objectionable in commerce because of the time it has taken and because of additional processing equipment that it has required.
Accordingly, compositions have been introduced which simultaneously perform the three operations of developing, desensitizing, and lacquering. Heretofore, these materials have run into various difficulties. Some have been suitable for only one type of light sensitive coating. Some have resulted in rather short press runs, due either to loss of image or to the plates becoming plugged after a relatively small number of impressions have been run. Others were unreliable, producing immediate plugging in some instances and being unpredictable in their behavior. Some lacquer emulsions have not stored well, settling out after standing for a few weeks and being difficult to reconstitute uniformly. In some the lacquer emulsion has tended to attack the image areas of the lithographic plate upon prolonged contact. In others, the lacquers have not served as adequate protection for the developed plate.
The present invention is directed to solving these and other problems.
One object of the invention is to provide a chemically and physically stable, long-lasting emulsion which will simultaneously develop and desensitize the nonimage areas of lithographic plates and deposit on their image areas a colored resin film of abrasive-and-chemical resistant lacquer.
Another object of this invention is to provide a lacquer type of emulsion which is suitable for processing lithographic plates, no matter what type of commercially used light-sensitive coatings are involved.
Another object is to provide an oleophilic lacquer emulsion which will not attack the image areas of the lithographic plate upon prolonged contact.
Another object is to provide a talc-free, stable, lacquer emulsion for lithographic plates.
An additional object is to provide a lacquer emulsion which significantly contributes to the press life and inking and printing qualities of the lithographic plates processed thereby. Our new lithographic lacquer emulsions offer increased solvent resistance, thereby improving the length of run on the press by minimizing the solvent effects from press fountain solutions, clean-up solutions, and ink solvents. They also provide increased abrasion resistance, thereby improving the length of run on the press by minimizing abrasion effects from press ink rollers, water rollers, and blanket.
Another object of the invention is to provide lacquer resins which require no further curing for use in lithographic printmg.
Other objects, features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of some preferred embodiments.
The present invention provides an oil-in-water developer, desensitizer and lacquer emulsion for lithographic printing plates comprising a two-phase liquid composition having a nonaqueous resinous phase characterized by certain types of resins. Our new emulsion may be prepared relatively simply and is very effective for processing lithographic plates having various types of light-sensitive coatings.
Specifically, the emulsion of this invention is a two-phase liquid composition having (1) an aqueous phase that includes an aqueous desensitizing solution and (2) a nonaqueous resinous phase comprising (a) an essentially water-insoluble solvent and (b) a generally high-molecular weight oleophilic, water-insoluble resin with particle size less than 500 microns. The emulsion may also contain various other ingredients in both the aqueous and nonaqueous phases, such as a wetting agent, a pigment, or a thickening agent. These features are explained in more detail below.
In the past, lacquer emulsions for the development of lithographic printing plates were produced from low-molecularweight resins, such as epoxy and novolak resins, the highest molecular weight of such resins generally being about 2,500 to 4,000; these emulsions required curing in order to be suitable for use in lithographic processes.
Our new lithographic emulsions are characterized by resins that provide increased chemical resistance and physical strength, properties generally attributed to medium and high molecular weight resins. Various resins with molecular weights varying from as low as 3,000 for some resins to over l00,000 in others are operable. Generally, resins with molecular weights ranging from 10,000 to over l00,000 are preferred.
The resins used in our lithographic lacquer emulsions form an ink-receptive, chemical-resistant resin image on the plate during development, so that this resin image is resistant to lithographic fountain solutions and lithographic inks. This resin image also has the physical strength to withstand demanding printing conditions. Further, the resin image is resistant to weak acids, such as phosphoric acid, and to the other chemicals used in lithographic fountain solutions, such as ammonium dichromate, sodium phosphate, urea, nitric acid, water, and natural gums. (Lithographic fountain solutions are operated at a pH 3.5 to 5.5 and are in direct contact with the lithographic plate.) The resin image is also resistant to alcohols, such as isopropanol, to mixtures of alcohols and water of the types used on lithographic presses equipped with "Harris Micro-Flo" or Dahlgren Dampeners." It is also resistant to aliphatic hydrocarbons, mineral oils, drying oils, linseed oil varnish, wetting agents, modifiers, petroleum fractions, wax, extenders, driers, pigments and resins, which are used to make lithographic inks. Not only is the resin image insoluble in the above ink constituents, but the resin is not swelled or softened by them so as to result in damage to the resin image under printing conditions.
The resins used in the lithographic emulsions of this invention can be characterized in terms of chemical resistance as those resins which are most resistant to water, alcohols, weak acids and aliphatic hydrocarbons generally, but soluble in cyclehexanone, isophorone, xylene, chlorinated benzene, methyl ethyl ketone, and other water-immiscible aliphatic ketones, such as methyl isobutyl ketone, ethyl butyl ketone, methyl isomyl ketone and diisobutyl ketone. They are also soluble in water-immiscible esters of aliphatic acids and aliphatic alcohols, such as amyl acetate and methylamyl acetate.
The resins used in this invention are further characterized by a low water absorption, as may be indicated by the A.S.T.M. Test Method D-570 and reported in the plastics properties chart in Modem Plastics Encyclopedial966." Water absorption is the amount of water absorbed when a test-piece of plastic of specified dimensions is immersed in water for the test-specified time. Resins with water absorption of less than 1 percent arepreferred, and resins with water absorption over 5 percent may be damaged by water or fountain solution absorption on the lithographic press.
The resins used in the lithographic emulsions of this invention can be characterized in terms of physical strength as the hardest resins, as determined by the Rockwellhardness tests, as indicated by the A.S.T.M. Test Method D-785 reported in "Modem Plastics Encyclopedia-1966. Hardness expresses resistance to deformation and is a complex property; when assessed by indentation or penetration methods, factors such as elastic modulus, yield strength, plasticity, and time are involved. Resins with Rockwell, M-scale Hardness of M-SO to M-l00 are operable, and those with M-70 to M-l00 are preferred. These hardnesses enable our resins to withstand the printing conditions on a lithographic press.
The resins used in this invention may further be characterized as toughest resins, toughness also enabling them to withstand printing conditions on a lithographic press. Impact strength represents the resistance, or toughness, of a rigid material to a sudden application of a mechanical load. It is conventionally assessed by measurement of the energy required to fracture a standard test-piece under standard conditions. lmpact strength may be determined by the lzod Test according to A.S.T.M. Test Method D-256 reported in Modern Plastics Encyclopedia-1966." Impact strengths of l to 20 foot-pounds per inch of notch are preferred.
Since lithographic plates are mounted on presses by wrapping the plates around plate cylinders, it is important for the resin image of a lithographic plate to have flexural strength. Static flexural strength, sometimes known as crossbreaking strength, or modulus of rupture, represents the maximum stress developed in the surface of a prescribed barshaped test piece, when it is supported near its ends and loaded at the center until failure occurs. Flexural strength is measured by A.S.T.M. Test Method D-790 reported in Modern Plastics Encyclopedia-I966. Flexural strengths of 1000 to 23,000 p.s.i. are operable, with 10,000 to 23,000 p.s.i. preferred.
Other conditions on a lithographic press call for resins with high tensile strength and high percent elongation. Tensile strength may be determined by A.S.T.M. Test Methods D-638 and D-651, and elongation may be determined by A.S.T.M. Test Method D-638 reported in Modern Plastics Encyclopedial966. Tensile strength, or tenacity, is the maximum tensile stress to which a material can be subjected before it breaks. Elongation or extension at break is the maximum tensile strain to which a material can be subjected before it breaks. Tensile strengths of 1000 to 13,000 p.s.i. are operable with 5000 to 13,000 p.s.i. preferred. Elongation ranging from 2 percent to 1000 percent are operable with percent and 1000 percent preferred.
We have found that lithographic plates treated-with emulsions containing our preferred resins (characterized by increased chemical resistance, increased physical strength, and increased molecular weight) consistantly out-perform current commercial emulsions.
However, there was a difficult problem to solve before the preferred resins could be used in lithographic lacqueremulsions. it was found that emulsions of these preferred resins were unstable in storage and in transit, which may involve movement from coast to coast. Their instability resulted in particle separation on storage, and, when they were used to develop plates, caused nonuniform particle buildup on the plate solids, caused image plugging or bridging on fine halftone screens, and caused particle spots in the background areas of the plate.
Study has shown that the preferred, the more chemically resistant and physically strong resins, are more difficult to emulsify. Normal mixing machines (such as a Cowles Dissolver) and milling machines (such as a Morehouse Mill) gave particle sizes of the resulting emulsion in excess of 500 microns. Furthermore, it has been found that emulsions using these resins with many particle sizes in excess of 500 microns tended to agglomerate in storage, causing particle separation and failure of the emulsion.
An important finding, a discovery constituting a significant feature of this invention, is that emulsions of resins of the preferred chemically resistant physically strong type cannot be relied on and do not give consistent results, where particle sizes are as large as 500 microns. Stability and success is attained in our invention by using particle sizes no larger than 500 microns and no smaller than 1 micron,preferably about 10 to 50 microns.
Our desired range of particle sizes of the resins has been attained by .using homogenizers, such as a Manton-Gaulin Homogenizer, Model l5M-8TA Laboratory Submicron Dispenser, single-stage, manufactured by Manton-Gaulin Manufacturing Co., Inc-Everett, Mass., and by using them at pressures between 500 and 9000 p.s.i., preferably about 2500 p.s.i. The resulting lacquer emulsion has a 10-50 micron particle size range and is stable on storage and in transit.
In the past, the lacquer emulsions for lithographic plates have generally been stabilized by the use of thickeners. The preferred thickeners have been chemically inert, nonabrasive,
operative at approximately pH 3, and thixotropic, examples being talc and fine silica, such as Cab-O-Sil of Cabot Corporation. in some lacquer emulsions the use of Cab-O-Sil has helped to prevent phase separation of the oil and water phases on standing, but it has no effect on the particle size of the emulsion. When Cab-O-Sil is used in our preferred lacquer emulsion, it does not in and of itself provide suitable stability in storage.
Our new emulsion is also preferably characterized by being talc-free. In the past, particle sizes of lacquer emulsions were sometimes reduced by using talc, the particle size-reduction being due to internal grinding action during mixing and milling processes. However, talc has the following disadvantages in lacquer emulsions for the development of lithographic printing plates:
1. The talc has separated on standing, resulting in an unstable emulsion which had to be redispersed by shaking, etc., prior to application of the lacquer emulsion to the lithographic plate.
2. The talc has damaged the lithographic plate by abrasion of the plate during lacquer emulsion application.
3. The presence of tale in the resin coating on a lithographic plate has reduced the length of run on the press.
Hence, the importance of our new emulsion being talc-free. However, talc can be used if desired, so long as it is understood that the results will be somewhat poorer. This will be further explained below. 7
The resins used in the lacquer emulsions of this invention are those having the properties discussed above and include vinyl chloride-vinyl acetate copolymer resins, vinylidene chloride-acrylonitrile resins, polyvinyl formal, acetal, and butyi'al resins, polycarbonate resins, polystyrene resins, acrylic ester resins, bisphenol fumarate polyester resins, silicone resins, polyurethane resins, cellulose acetate resins, .and phenoxy resins.
The vinyl chloride-vinyl acetate copolymer resins are exemplified by the resins sold by Union Carbide Corporation under the trade designation Bakelite vinyl resin VYHH, a copolymer having a chemical composition of approximately 87 percent vinyl chloride and 13 percent vinyl acetate. This material is supplied as a dry white powder or in a relatively strong solvent-diluent solution such as about 50 percent ketone solvent and 50 percent toluene diluent. The molecular weight is about 50,000, and the resin gives a desirable balance between chemical resistance, solubility, film strength, and thermoplasticity. It should be contrasted with the much less resistent and weaker forms of polymers of low molecular weight made from the same monomers. We do not include resins of this type having a molecular weight below about 10,000.
The vinylidene chloride-acrylonitrile resins are exemplified by the thermoplastic, solvent-soluble copolymers of vinylidene chloride and acrylonitrile sold by The Dow Chemical Company under the trade designation Saran Resin F-120, a tough, film-forming lacquer resin sold in two viscosity types (200 cps. and 1,000 cps.). It may be dissolved in methyl ethyl ketone. In uses where high resistance and barrier properties are needed, and where a solvent system can be tolerated, these coatings are superior to other commercially available products. The molecular weights are about 50,000 to 100,000. We do not include in our coverage resins of this type having molecular weights below about 10,000.
The polyvinyl formal resins are exemplified by the resins sold by the Shawinigan Resins Corporation under the trade designation Formvar 7/70. These are also polyvinyl acetals and polyvinyl butyrals (Butvar). For example, polyvinyl acetals are prepared from aldehydes and polyvinyl alcohols. Polyvinyl alcohols are high molecular weight synthetic resins containing varying percentages of hydroxyl and acetate groups produced by hydrolysis of polyvinyl acetate. Polyvinyl alcohols partially or completely hydrolyzed, in various molecular weight grades, are used in producing commercial polyvinyl acetals. As a general rule, the substitution of butyral or formal groups for acetate groups results in a more hydrophobic polymer with increased toughness and adhesion. Formvar 7/70 has a molecular weight of about 21,000. We include in this invention this class of resins when the molecular weight is above 10,000, preferably 20,000 to 100,000.
The polycarbonate resins are exemplified by the resins sold by the General Electric Company under the trade designation Lexan type 8070-112, films that are transparent, clear, thermoformable, heat scalable, strong, tough and strain resistant. The molecular weight is about 20,000 to 50,000 and we include such resins in this invention when the molecular weight is above 10,000.
The polystyrene resins are exemplified by the biaxially oriented polystyrene films sold by the Plax Corporation under the trade designation Polyflex. These films have excellent resistance to weak acids, weak alkalies, greases, and oils and have good resistance to strong acids, strong alkalies, alcohols and most organic solvents. The molecular weight is over 100,000. We include such high molecular weight polystyrenes in this invention, but not those whose molecular weight is below 10,000.
The acrylic ester resins are exemplified by the polymers of esters of acrylic and methacrylic acids sold by the Rohm & Haas Company under the trade designation Acryloid A-l0. Acryloid resins have excellent resistance to water, alcohol, alkalies, acids, oils and greases. Acryloid resins have outstanding durability and flexibility. Acryloid A-lO is the hardest of the acryloid group. It is sold in solution as a 30 percent solids content in Cellosolve acetate with a viscosity of 710-850 cps. at 30 C. its molecular weight is about 5,000 to 10,000 and these are among the lower molecular weight materials included in this invention.
The bisphenol fumarate polyester resins are exemplified by the corrosionqesistant polyester resins sold by Atlas Chemical Industries, Inc. under the trade designation Atlac 3825, a patented (U.S. Pat. No. 2,634,251) corrosion-resistant polyester resin used in making highly corrosion-resistant glassreinforced plastic tanks for food processing, etc. its molecular weight is about 20,000 to 50,000, and we include such resins having a molecular weight above 10,000.
The silicone resins are exemplified by the pure silicone resins sold by General Electric Company under the trade designation Silicone Resin SR-82, a hard resin that air dries to a tack free film which, when cured, has better solvent resistance than other silicone resins. lts molecular weight is about 3,000, and has about as low a molecular weight as is acceptable in this invention. In use, extensive cross-linking occurs spontaneously.
The polyurethane resins are exemplified by a class of blocked polyurethane prepolymer resins sold by Trancoa Chemical Corporation under the trade designation Tranco8-A Polyurethane. These are isocyanate-terminated polymers whose isocyanate groups have been reacted with phenol to form a thermally unstable linkage. These resins can be heated to drive off phenol, and the isocyanate groups then react with the previously added polyol system. Tranco 8-A resins have outstanding abrasion resistance, toughness, chemical resistance, hardness and flexibility. The molecular weight is about 8,000, and we include such resins having a molecular weight over about 3,000.
The cellulose acetate resins are exemplified by a class of cellulosic resins sold by Celanese Corporation of America under the trade designation Cellulose Acetate HBML-70, a low viscosity resin for molding compounds, cost film, extruded film, sheeting, cements, lacquers, dope coatings. The molecular weight is about 50,000 to 100,000, and we include such resins when the molecular weight is above about 10,000.
The terminology phenoxy resin as used herein refers to the high molecular weight polyhydroxy ethers. These compounds are generally formed by copolymerization of bisphenol A [2, 2-bis (p-hydroxyphenyl) propane] and epichlorhydrin. Phenoxy resins usually have a molecular weight of at least about 20,000, generally 20,000 to 30,000 or even higher as for example 80,000 or even 200,000 if desired. Additionally, phenoxy resins have an essentially linear molecular structure and do not require chemical curing to be suitable for use in lithographic processes. The phenoxy resins used in this invention are commercially available from a number of sources, with specific examples of suitable resins being those sold by the Union Carbide Corporation under the trade designation Bakelite PKDA, PAHJ, PKHC, and PKHH resins. Further illustrative examples of suitable such resins are those commercially available from the Shell Chemical Company under the trade designations Eponol 55 and Eponol 53B40. Reference may also be made to Modern Plastic's Encyclopedia for 1964, Vol. 4l/No. 1A, pages 209 and 210 for a more detailed discussion of such compounds.
To form the nonaqueous resinous phase of the emulsion, a selected resin is dissolved in an essentially water-insoluble sol vent, i.e., a solvent which has a solubility of no more than about 2.4 grams per ml. or less in water at room temperature. illustrative examples include cyclohexanone, isophorone, methyl ethyl ketone, xylene, chlorinated benzene, and other water immiscible aliphatic ketones, such as methyl isobutyl ketone, ethyl butyl ketone, methyl isoamyl ketone and diisobutyl ketone. Other examples include water-immiscible esters of aliphatic acids and aliphatic alcohols such as amyl acetate and methyl amyl acetate.
The resinous phase of an emulsion may also include a wetting agent, or surfactant, which contributes to the stability of the emulsion. To be suitable, the wetting agent must not react chemically with the ingredients of the lacquer to convert a hydrophilic surface into an oleophilic surface; accordingly it is preferred to use nonionic surface active agents. Suitable materials include various polyol compounds, such as are marketed by the Wyandotte Chemical Corporation under the trade name Pluronic, typified by a hybrid compound of watersoluble polyoxyethylene chains added to both ends of waterinsoluble polyoxypropylene. These materials are available in various molecular weights and percentages of hydrophilic polyoxyethylene content. For one example, Pluronic F-68 has the formula Compounds are formed by adding to both ends of water-insoluble polyoxypropylene chains water-soluble polyoxyethylene groups. in the formula, (a) and (0) refer to the number of polyoxethylene group on the ends and (b) refers to the number of water-insoluble polyoxypropylene group. For Pluronic F-68, (b) is approximately 30 and has a typical molecular weight of 1750. HO(O-CH -CH,-O)a and l-lc(O-Cl-I Cl-l represent 80 percent of weight of the molecule. The value of (a) is approximately 57 and the value of (c) is approximately 57. The total molecular weight of Pluronic F-68 is about 8750. It comes in the form of white flakes with a melting point of 51 C. Minimum. The pH of 0.25 percent Solution at 25 C. is 6.5-7.5.
Other wetting agents which can be used in this invention are Sterox AJ and Tergitol NPX. Sterox AJ is an 85 percent active aqueous dispersion of a nonionic surface active material based upon a substituted phenol and ethylene oxide; it contains 85 percent surfactant, 14 percent inorganic slat, and 1 percent water, and is a product of the Monsanto Chemical Company. Tergitol N PX is a 100 percent active anhydrous nonionic surface active material based upon nonyl phenyl polyethylene glycol ether and is a product of Union Carbide Chemicals Company.
If desired, the resinous phase of the composition may also include a pigment which will form an easily visible color with the resin on the image areas of the plate to facilitate inspection of the finished plate and serve to indicate the presence of the lacquer after the plate has been in service on the press. The pigments should be easily dispersed and contribute to the stability of the dispersion and the oleophilic properties of the resin film. Suitable pigments may be readily selected by those skilled in the art; illustrative examples include the following commercially available pigments; Neo Spectra Mark III and Peerless Black 155 (for black), Naphthol Red B (for red), and Monastral Blue and Carbanthrene Blue (for blue). A preferred pigment is Naphthol Red B, because the resin film subsequently produced has less tendency to blind and the pigment is easily dispersible. The pigment is generally desirable but not necessary, and not all pigments are equally satisfactory; in addition to those listed earlier, others may be selected by trial and error. Some important properties of good pigments for this purpose are case of wetting out and dispersing, the stability of their dispersions, and their contribution to the oleophilic properties of the resin film.
The concentration of resin in the solvent may be varied to a considerable extent, ranging from a very small quantity of resin up to the saturation point, but at the lower concentrations, extensive working of the lacquer on'the plate will be required to deposit a layer of resin of adequate thickness. As a result, it is preferred to maintain the concentration in the range of from approximately 5 percent by weight of the solvent up to the saturation point, which will normally be at approximately lO percent by weight of resin. When working with certain light-sensitive coatings, however, as will be explained, the concentration of resin may be as low as approximately 1 to 2 weight percent.
The proportions of the wetting agent and pigment which may be used, also vary in concentration, depending upon the practical working conditions; consequently, the desirable quantities of each ingredient will be determined for each operation. In general, the concentrations of each of these ingredients will not exceed approximately percent by weight based on the solvent.
As indicated previously, the aqueous phase of the lacquer emulsion includes an aqueous desensitizing solution; this helps in formation of an oil-in-water emulsion and also is valuable for its action in the processing of lithographic plates, as it dissolves the nonlight-hardened, light-sensitive material (if this is aqueous and acid soluble) and leaves a protective film of a hydrophilic colloid over the plate. Many such solutions are 65 known and are suitable for use in this invention; one such desensitizing solution has a composition as follows:
Exam ple l- Desensitizer Ingredient Amounts by volume in water. 2% 17 Methyl Cellosolve Formaldehyde solution in water. 37%
Sterox Al is an percent active aqueous dispersion of a nonionic surface active material based upon a substituted phenol and ethylene oxide. It contains 85 percent surfactant, 14 percent inorganic salt, and 1 percent water. and is a product of the Monsanto Chemical Company.
Other desensitizing solutions may, however, be used, such solutions generally comprising a water solution of a hydrophilic colloid, such as gum arabic, and an acidic desensitizing agent, such as phosphoric acid or the salt of such acid. r? aq ueous phase of the emulsion composition may also, if desired, include a suitable thickening agent to give the emulsion 3. false body and thus increase the stability of the emulsion. Numerous suitable such agents are known in the art and are commercially available, an illustrative example being a pyrogenic silica compound commercially available from Cabot Corporation under the Cab-O-Sil" trade name and used to thicken polar systems. its particle size is about 0.015 micron; its surface area is about 200 M/gm.; and its bulk density is about 2.2 lbs/cubic ft. Also, if desired, for any given concentration of this particular silica compound, the amount of false body can be increased by adding a nonionic or a long chain cationic amine wetting agent in the quantity up to approximately lO percent by weight of the amount of silica material. Because of its fine particle size, 0.015 microns, this material tends to produce a slight scouring action on a plate surface which at times is beneficial.
The Tse $55.: as a th ick ener in the emulsion is not recommended because the tale particle size ranges from 0.5 microns to 40 microns and can cause damage to the plate surface and can reduce the length of run by weakening the lacquered image.
A second solvent may also be used in the emulsion to slow down the evaporation rate of the organic solvent employed in the resinous phase. The use of such a solvent makes it possible to work the emulsion over the plate for a longer period of time without its drying and forming a dry film on the nonprinting areas. To achieve this result, the solvent must be water miscible, and hence it is normally included in the aqueous phase of the composition before the thickening agent is added, although it may be added as a part of the resinous phase, where in conjunction with the organic solvent therein, it acts as a solvent for the resin. Suitable examples of such a solvent include Carbitol acetate (diethylene glycol monoethyl ether acetate), Cellosolve acetate (ethylene glycol monoethyl ether acetate), methyl Cellosolve (ethylene glycol monomethyl ether), dioxane, and any of the available Dowanol mixtures (glycol ethers produced by reaction of alkylene oxides with alcohols).
When the second, water-misciblesolventand thethickenfig agent are both included in the aqueous phase of the composition, a relatively small quantity of the solvent will generally be used, preferably a maximum of approximately 10 percent by volume. Similarly, the thickening agent will preferably be a maximum of approximately 5 percent by weight, with about 2 to 4 weight percent being preferred, although the quantities of each of these ingredients may be varied if desired.
The lacquer emulsion of this invention is suitable for use with lithographic plates using any of the available supports, including metal and paper types, which have been coated with any of the various available light-sensitive materials including any of the family of diazo resins and the light-sensitive materials of the cinnamate photopolymer type, such as those disclosed in US. Pat. No. 2,610,210 and British Pat. No. 794,572.
When the lacquer emulsion is to be used with a cinnamate type photopolymer, the composition includes a solvent for removing the unexposed cinnamate polymer from the surface of the plate. This solvent is so selected that it does not cause appreciable swelling and softening of the light-exposed polymer, for if this occurs, the emulsion will not operate satisfactorily due to the fact that rubbing of the plate with the emulsion will smear the image areas. When the emulsion is to be used with such photopolymers, the resin content of the resinous phase will generally only be approximately 1 to 2 percent by weight, based on the solvent content, to accommodate the additional solvent. When preparing such an emulsion for use with a cinnamate-type photopolymer, the additional solvent may be added either to the resinous phase, as mentioned, or to the crude emulsion before going to the colloid mill or to the finer emulsion coming out of the mill, but in any case it should be added with agitation.
Illustrative examples of suitable formulations follow.
Example 2-Acrylie ester resin lacquer Parts by weight Ingredient 14 B (Water Phase) The oil phase (portion A) is preferably prepared by first dissolving the acrylic ester resin in cyclohexanone, then dissolving the wetting agent in that solution, next adding the pigment into the solution, and stirring the solution until the pigment is wet. Then the mixture is preferably run through a colloid mill to obtain a suitable dispersion; a reading of at least three on the fineness of grind gage calibrated in steps from 0.0000 to 0.001 is satisfactory. This dispersion step is optional.
The Carbitol acetate and isophorone are added to slow down the evaporation rate of the organic solvent mixture, thereby making it possible to work the emulsion over the plate longer without its drying and forming a dry film on the nonprinting areas. These two materials may be omitted to advantage when it is desired to have a more rapid buildup of the lacquer on the image, as, when processing smaller sized plates, as in example 3.
The pigment gives the resin deposited on the image an easily visible color, facilitating inspection of the finished plate and serving to indicate the presence of the lacquer after the plate has been in service on the press.
The wetting agent is used to produce a suitable emulsion in terms of kind and stability; it must not convert a water-loving surface to an oil-loving surface; so it is preferred to use nonionic surface-active agents.
The solvent (e.g., cyclohexanone) for portion A must be essentially water-insoluble so as to provide a separate phase which can be emulsified into the water phase. It must, of course, be a solvent for the resin being used and preferably it should have a fairly rapid rate of release from the resin film; this is judged by noting if the resin layer over the lithographic image is easily dissolved away by commonly used solvents such as turpentine or the kerosene types of solvents found in heat-set or quick-set inks. When photopolymer plates are to be processed, it is necessary that this solvent be able to dissolve the nonlight-struck polymer without appreciably swelling and softening the light-struck polymer.
The water phase (portion B) is prepared by adding the wetting agent and thickening agent to the desensitizer and stirring until a thickening is produced.
The silica (Cab-O-Sil) is added to give the emulsion a false body which increases the stability of the dispersion. For any concentration of this silica, the amount of false body can be further increased by adding the nonionic wetting agent in an amount up to one-tenth of the amount of the silica. A wetting agent such as a long chain cationic amine will also increase the thickening efficacy in a similar way. Because of its fine particle size this pyrogenic silica has a scouring action on the plate surface, and at times this may be beneficial. The presence of this material in the lacquer film has not tended either to weaken it or to decrease its ink attractiveness. Its function in the formula is not critical and it may be omitted.
The desensitizer is necessary for the formation of the ink in water emulsion and also for its action on processing the lithographic plate. This action is twofold: (I) it dissolves off the nonlight-hardened sensitizer if this is aqueous, acid soluble and (2) it leaves over the plate a protecting film of water-loving colloid.
in mixing, the water phase can be added to the oil phase, or the oil phase can be added to the water phase without impairing the performance of the emulsion.
The water phase, may for example, be slowly added to the oil phase, with stirring to produce a coarse oil-in-water emulsion, and the coarse emulsion is then run through a homogenizer so as to produce a desired fineness of dispersion of the oil phase. The finer the dispersion, the creamier or the more viscous the emulsion; a reading of at least three on fineness or grind gauge is considered satisfactory.
The proportions as given in the formula are not critical. As indicated above, some materials can be omitted entirely or greatly decreased in amounts. The amounts of the other components can be varied :10 percent without seriously impairing the working properties or the performance of the emulsion.
The emulsion is used by pouring a small pool of the emulsion liquid onto the exposed plate and working the liquid thoroughly over the plate surface with a wad of absorbent cotton or with a sponge.
Example 3-Treatment of a plate with lacquer of Example I.
A presensitized aluminum lithographic plate with a lightsensitive diazo coating thereon (Fairmount Chemical Companys Diazo Resin No. 4) was subjected to ultraviolet light through a negative pattern. The plate was thereafter rubbed up with an emulsion composition corresponding to example 2 to remove the nonimage areas from the surface of the plate, leaving a hydrophilic layer thereon, and depositing a protective, colored film of acrylic ester on the light-exposed image areas. After drying, the image of the plate could be seen in the areas where the diazo resin had been exposed. A good image on a clean background was obtained by use of this formulation on a plate, and the plate was subsequently press tested for over 18,000 impressions with no evidence of image failure. Example 4-Modification of Example 2 This formula has no carbitol acetate or isophorone and uses a different pigment. This formula will build up a lacquer film on the image more readily. The preparation is like that for example 2, accommodating the omission of some ingredients.
The preceding examples are particularly suited to diazosensitized negative-working plates of the presensitized or wipe-on types.
Some modification is desirable for processing a plate sensitized with a negative-working photopolymer of the cinnamate type such as taught in US. Pat. No. 2,610,120 (Minsk) and British Pat. No. 794,572 (Gestetner). The modification consists of using an added amount of a solvent suitable to dissolve the nonlight-struck polymer while causing the minimum amount of swelling and softening to the light-struck polymer. If there is too much softening and swelling, the emulsion won t work because rubbing the plate will cause smearing of the image.
Ingredient Parts by weight Cyclohexanone 800 Acrylic ester rerin (Acryloid A-l) 300 Nonionic wetting agent (Pluronic F-68) 76 Pigment (Naphthol Red B) 100 Desenritizer 3860 Thickening agent (Cab-O-Sil) I38 Carbitol acetate 500 Cyclohexanone 1840 The Carbitol acetate and second amount of cyclohexanone are added either to the crude emulsion before it is put through the colloid mill or to the finer emulsion coming from the mill; in any case they should be added with agitation.
Example 6- Lacquer employing polyvinyl formal resin Thickening agent (Cab-O-Sil) l 1.5
The water phase B is added slowly to the oil phase A, and the resulting mixture is preferably homogenized at approximately 1000 p.s.i.
Example 7Treatment of a plate with the lacquer of Example 6 A presensitized aluminum lithographic plate with a lightsensitive diazo coating thereon (Fairmount Chemical Companys Diazo Resin No. 4) was subjected to ultraviolet light through a negative pattern. The plate was thereafter rubbed up with an emulsion composition corresponding to example 6 for approximately 2 minutes to remove the nonimage areas from the surface of the plate, leaving a hydrophilic layer thereon and depositing a protective colored film of polyvinyl formal on the light-exposed image areas. After drying, the image of the plate could be seen in the areas where the diazo resin had been exposed. A good image on a clean background was obtained by use of this formulation on a plate, and the plate was subsequently press-tested for over 18,000 impressions with no evidence of image failure.
Example 8Plate treatment with various lacquers having different resin bases.
Example 7 is repeated, using the same procedure and same ingredients in the same amount except for the resin. Various other resins are substituted on a weight-for-weight basis in place of the Formvar 7/70, and the number of press impressions shown below was obtained for each resin as shown, with no evidence of image failure:
resin. Saran F-l20 (Dow Chemical Co.) Polycarbonate Resin. Lexln l8,000 (General Electric Company) Polystyrene Resin, Polyflex l8,000 (Plax Corporation) Bisphenol fumarate-Polyester Resin, Atlac l8,000 (Atlas Chemical Industries) Polyurethane Resin, Tranco 8-A 18.000 (Trancoa Chemical Corp.) Cellulose Acetate resin HlML- 6,000
(Celanese Corporation) Example 9-Simplified lacquers like those of Examples 6 and This formula is like that of examples 6 and 8, but has no Carbitol acetate or isophorone and uses a different pigment. This formula builds up a lacquer film on the image more readily than in examples 6 to 8.
Ingredient Parts by weight Cyclohexanone 122.9 Resin 5.] Nonionic wetting agent,
(Pluronic F-68) 7.0 Pigment, (Peerless Black I55) 7.0 Desensitizer 346.5
Thickening agent, (Cab-O-Sil) I LS In separate instances, each of the resins of examples 6 to 8 are employed, with results similar to those of examples 6 to 8, except as noted above.
Example 10. Adaptation of lacquers to cinnamate plates.
Examples 6 and 8 are particularly suited to diazo-sensitized negative workingplates of the presensitized or wipe on types. For a plate sensitized with a negative working photopolymer of the cinnamate type the following modification is preferred.
Each of the resins of examples 6 and 8 are used separately in the amount shown above.
Example 1 l-Silicone resin lacquer Parts by Ingredient weight A (Oil Phase) Silicone Resin SR-82 (General Electric Co.) l7 Cyclohexanone l2l lsophorone 37 Carbitol acetate 81 Non-ionic wetting agent (Pluronic F-68) l0 Pigment (Naphthol B Toner Red) l4 B (Water Phase) Desensitizer, as in Example I 693 Non-ionic wetting agent (Pluronic F-68) .4 Thickening agent (Cab-O-Sil) 23 The water phase was added slowly to the oil phase, and the resulting mixture was homogenized with a hand homogenizer .1 the light-exposed image areas. After drying, the image of the plate could be seen in the areas where the diazo resin had been exposed. A good image on a clean background was obtained by use of this formulation on a plate, and the plate was sub- Homogenizing pressure adjustments made from the same crude lacquer emulsion, based on example I4 with phenoxy resin, resulted in the following results:
sequently press-tested for over 14,000 impressions with no Sample No. Homogenizer Particle Size evidence of image failure. '"W' Example l3-Lacquer of Example 11 simplified This fonnula is like that of Example 11 but has no Carbitol acetate or isophorone and uses a different pigment. Thi fo 10 g f 'af 8 [burner rpm :83
or r argert an mula bullds up a lacquer film on the image more readily. 3' "mounted I 500 I00 4. Homogenized 2500 I00 Ingredient Parts by weight Homqenind 50 s. u v J 4500 40 7. Homogenized 6000 10 Cycbhemone 239 a. Homogenized 9000 10 Silicone Resin SR-IZ l7 Nonionic wetting agent I4 (Pluronic F68) Pigment (Peerless Black 155 I4 The above particle sizes were measured from freshly ww. in ewnple I prepared lacquer samples and again from the same samples Thickening Agent (Cab-O-Sil) 23 Example l4-Lacquer of Example 13 3 adopted for cinnamate plate For a plate sensitized with a negative working photopolymer of the cinnamate type the following modification is preferred to examples I1 and 13.
Example l5--An alternate Ingredient Parts by weight Resinous Phase A Rerin I00 Cyclohexanone I000 Nonionic wetting agent 66 Pigment 40 Aqueous Phase B Desenritizer 3370 Thickening Agent I Carbitol Acetate 450 The resin may be any of those shown in the preceding examles.
Example l6-Homogenization of the emulsion The emulsion of example 14 may be homogenized by a Manton-Gaulin Homogenizer Model 15 M-8TA Laboratory Submicron Disperser, single stage, at 2500 p.s.i. The basic principle of homogenization is the control of velocity through an adjustable, restricted orifice. The product at high pressure enters a controlled clearance area between the homogenizing valve and seat. At this point, energy which has been stored as pressure is instantaneously released as a high velocity stream. Velocity is a function of homogenizing pressure and may be in excess of 57,000 ft. per minute. In the high velocity area, between the homogenizing valve and seat, the product is subjected to intense turbulence, hydraulic shear, and cavitation. The product then emerges from the controlled clearance area and impinges with shattering force and change of direction on the impact ring. This series of actions, occurring in as short an interval as a microsecond, is the homogenizing process.
after ten months and showed no variation in particle size due to aging. As homogenizing pressures become greater, the particles of the dispersed phase become smaller and the time needed by the lacquer to cast a resin film on the image becomes longer. Homogenizer pressures from about 500 p.s.i. to about 9000 p.s.i. are operable; however, the preferred pressure range is from about 1500 p.s.i. to about 3000 p.s.i. Particle sizes from 1 micron to 500 microns are operable; however, the preferred particle size is about 50 microns.
The above lacquers were used with a 2" 3Xl" damp sponge to rub up a (l0"Xl6% 0.009") presensitized smooth micro surfaced aluminum lithographic plate with a light-sensitive diazo coating thereon (Fairmount Chemical Company's Diazo Resin No. 4), which had been exposed to ultraviolet light through a line halftone screen negative pattern containing l0,20,30,40,50,60,70,80,90 percent halftone screens and solids. The plates were all developed in 81 to 92 seconds except that the test lacquer No. 8, homogenized at 9000 p.s.i., required 97 seconds to rub up. Differences in developing speeds of different particle size emulsions are more evident on 77"X58b:: 0.020" plates and on brush and ball grained plates.
Samples No. 1 (Crude Mix) and No. 2 (Colloid-Milled Emulsion) showed evidence of particle separation in the emulsion, resulting in nonuniform particle buildup on the plate solids, image plugging or bridging on the 70-80-90 percent halftone screens, and particle spots on the background areas of the plate.
Samples Nos. 3 through 8 all resulted in a uniform lacquer deposit with no plugging in the halftone screens.
Press tests of the above plates resulted in plugging in halftones of Samples No. 1 (Crude Mix) and No. 2 (Colloid- Milled Emulsion), but all other plates, Samples Nos. 3 through 8 printed well on the press without plugging.
Example l4-A talc free lacquer used in a plate.
A presensitized aluminum lithographic plate with a lightsensitive diazo coating thereon (Fairmount Chemical Company's Diazo No. 4) was subjected to ultraviolet light through a negative pattern. The plate was thereafter rubbed up with an emulsion composition corresponding to example 15, in which the wetting agent was Pluronic F68, the pigment was Naphthol Red B, the resin was Bakelite Phenoxy PKl-IS, and the thickening agent was Cab-O-Sil. It tool approximately 1 minute to remove the nonimage areas from the surface of the plate. After working with the emulsion, the plate had a protective film of hydrophilic material over the nonimage areas and a colored phenoxy film on the light-exposed image areas. After drying, the image of the plate could be seen in the areas where the diazo resin had been exposed. A good image on a clean background was obtained by use of the plate, and the plate was subsequently press-tested for 100,000 impressions. Example 18. Comparison of Example 17 with a lacquer containing 5 percent talc.
The procedure and composition of example 16 was followed except that 5 percent talc was added to the lacquer emulsion. After rubbing the emulsion for about 1 minute, the nonlight exposed areas of the light-sensitive material were removed from the surface of the plate by the emulsion, and the protective lacquer film was applied over the image areas thereof. The thus-developed plate was subsequently used on a printing press in standard lithographic processes with clear and distinct images being produced.
The lacquer made as example 17 (no talc) and the lacquer made as example 18 (talc added) were used to process sections of the same plate which was press-tested. This press test was re-run two additional times, and lacquer example 18 with talc averaged 35 percent shorter length of run than lacquer example l7 with no talc added.
Example l9Phenoxy cinnamate plate treatment.
The general procedure of Examples 17 and I8 was followed, but in this example, the light-sensitive material was an improved phenoxy-cinnamate photopolymer, and the emulsion composition was that disclosed in example 10 herein, the resin, wetting agent, pigment, and thickening agent being the same as in example 17. The plate was rubbed up with this emulsion for approximately 3 minutes, and, after drying, the image was clearly visible in the light-exposed areas. A good, clear image on a clean background was subsequently obtained by use of the plate, and the plate was press-tested for 50,000 impressions.
It will thus be appreciated that the objects of this invention have been achieved by the described lacquer emulsion which is capable of being used with various lithographic surfaces and light-sensitive materials, with the resin being selectively attracted to the image areas of the plate as opposed to the nonimage areas to avoid scumming or smearing and thus produce plates with good press life and inking and printing qualities. Also, the lacquer emulsion of this invention has sufficiently low solvent-retention characteristics so that a tackfree lacquer film may be provided over the image areas to prevent damage by fingerprints or other improper handling and sufficiently hard and durable to provide adequate protection for the image.
To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.
1. A lacquer emulsion for treating exposed lithographic plates, comprising a two-phase liquid emulsion including in combination 1. an aqeous phase containing a desensitizer for removing unexposed areas from said plate, and
2. a nonaqueous phase consisting essentially of:
a. an essentially water-insoluble solvent having a solubility of no more than about 2.4 grams per 100 ml. of water at room temperature and b. a water-insoluble oleophilic resin dissolved in said solvent, and being present in a range of from a small but effective amount up to saturation in said solvent, said resin being of the type resistant to lithographic fountain solutions, lithographic inks, weak acids, alcohols, aliphatic hydrocarbons, and drying oils and having water absorption less than percent, said resin having when dry, at Rockwell hardness of about M-50 to about M-JOO, an impact strength of about 1 to about 20 footpounds per inch of notch, flexural strength between about 1000 and about 23,000 p.s.i., and tensile strength of about 1000 to about 13,000 p.s.i., said nonaqueous Phase being dispersed in said aqueous phase with the particle size of the nonaqueous phase particles being between about and about 500 microns.
2. The emulsion of claim 1 wherein said particle size lies between 10 and 50 microns.
3. The emulsion of claim 1 being talc-free.
4. The emulsion of claim l containing an oleophilic dispersion-stable pigment in said nonaqueous phase.
5. The emulsion of claim 1 containing in said nonaqueous phase a nonionic surfactant.
6. The emulsion of claim 1 containing in said aqueous phase a thickening agent having a particle size lower than one-tenth of a micron.
7. The emulsion of claim 6 wherein said thickening agent is pyrogenic silica having a particle size of about 0.015 micron.
8. The emulsion of claim 7 having a surfactant in conjunction with said silica and chosen from the class consisting of nonionic surfactants and cationic amine surfactants.
9. The emulsion of claim 1 having a water-miscible solvent for delaying evaporation of said water-insoluble solvent.
10. The emulsion of claim 1 wherein the resin has a molecular weight above 3000.
ll. The emulsion of claim 1 wherein the resin has a molecular weight of more than. 10,000.
12. The emulsion of claim 1 wherein the resin is chosen from the group consisting of a. vinyl chloride-vinyl acetate copolymer resins having a molecular weight in excess of 10,000,
b. vinylidene chloride-acrylonitrile resins having a molecular weight in excess of 10,000,
c. polyvinyl formal resins having a molecular weight over d. polyvinyl acetal resins having a molecular weight in excess of 10,000,
e. polyvinyl butyral resins having a molecular weight in excess of 10,000,
f. polycarbonate resins having a molecular weight in excess g. polystyrene resins having a molecular weight in excess of h. acrylic ester resins having a molecular weight in excess of i. bisphenol-fumarate polyester resins having a molecular weight in excess of 10,000
j. silicone resins having a molecular weight no lower than about 3,000,
k. polyurethane resins having a molecular weight over l. cellulose acetate resins having a molecular weight over 10,000, and
m. phenoxy resins having a molecular weight of at least 13. The emulsion of claim 12 wherein the solvent is selected from the group consisting of cyclohexanone, isophorone, xylene, chlorinated benzene, methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, methyl isoamyl ketone, and diisobutyl ketone.
14. A lacquer emulsion for treating exposed lithographic plates, comprising a homogenized talc-free two-phase liquid emulsion including in combination 1. an aqueous phase consisting essentially of a desensitizer for removing unexposed areas from said plate, and
2. a nonaqueous phase consisting essentially of a. an essentially water-insoluble solvent having a solubility of no more than about 2.4 grams per ml. of water at room temperature and b. a water-insoluble oleophilic resin dissolved in said solvent, and being present in the range of from a small but effective amount up to saturation in said solvent, said I resin being of the type resistant to lithographic fountain solutions, lithographic ink, weak acids, alcohols, aliphatic hydrocarbons, and drying oils and having water absorption less than 5 percent, said resin having when dry, a Rockwell hardness of about M-50 to about M-lOO, an impact strength of about 1 to 20 footpounds per inch of notch, flexural strength between about 1000 and about 23,000 p.s.i., and tensile strength of about 1000 to about 13,000 p.s.i., said nonaqueous phase being dispersed in said aqueous phase and so homogenized that the particle size of the nonaqueous phase particles is between about 10 and about 500 microns.
15. The emulsion of claim 14 wherein said particle size lies between and 50 microns.
16. The emulsion of claim 14 containing an oleophilic dispersion-stable pigment in said nonaqueous phase, a nonionic surfactant in said nonaqueous phase, and a thickening agent in said aqueous phase having a particle size lower than one-tenth of a micron.
17. The emulsion of claim 14 wherein said aqueous phase constitutes 60 to 80 percent of the emulsion, said nonaqueous phase having the resin-to-solvent percentage between a l percent and a saturated solution.
18. A method for producing a lacquer emulsion for treating exposed lithographic plates, comprising the steps of 1. making an aqueous phase consisting essentially of a desensitizer for removing unexposed areas from said plate,
2. making a nonaqueous phase by dissolving a water-insoluble oleophilic resin in essentially water-insoluble solvent having a solubility of no more than about 2.4 grams per 100 ml. of water at room temperature, said resin being present in a range of from a small but effective amount up to saturation in said solvent, said resin being of the type resistant to lithographic fountain solutions, lithographic ink, weak acids, alcohols, aliphatic hydrocarbons, and drying oils and having water absorption less than 5 percent, said resin having when dry, a Rockwell hardness of about M-SO to about M-l00, an impact strength of about 1 to about 20 foot-pounds per inch of notch, flexural strength between about 1000 to about 23,000 p.s.i., and tensile strength of about 1000 to about 13,000 p.s.i.,
3. mixing said aqueous and said nonaqueous phases, and
4. homogenizing the mixture so as to make the emulsion particle sizes of the nonaqueous phase particles lie between about 10 and about 500 microns.
19. The method of claim 18 wherein said particle size lies between 10 and 50 microns.
20. The method of claim 18 wherein the homogenizing step is carried out at between 500 and 900 p.s.i.
21. The method of claim 20 wherein the homogenizing step is carried out at between about 1500 to about 3000 p.s.i.
22. The method of claim 18 wherein in said step (2) an oleophilic dispersion-stable pigment is introduced into and dispersed in said nonaqueous phase.
23. The method of claim 18 wherein in said step (1), a nonionic surfactant and a thickening agent having a particle size lower than one-tenth of a micron are mixed with said desensitizer.
24. The method of claim 23 wherein said thickening agent is pyrogenic silica having a particle size of about 0.0 l 5 micron.
i i I! t I! mg? I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,615, 791 Dated October 26, 1971 lnventol-(s) Daniel C. Thomas and Charles T. Hathaway It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
r- 001. 2, line 63, "cyclehexanone" should read 1 cyclohexanone--; line 66, 'isomyl" should read --isoamyl--. Col. 3, line 54, "and should read --to--. C01. 7, line 12, "slat" should read --salt-. Col. 8, line 74, "No. 2,6l0 ,2l0" should read --No. 2,6lO,l20--. Col. 9, line 32, "Napthol' should read --Naphthol--. Col. 10, line 68 "B" should be moved up one line to be on the same line as "Desensitizer (as in Example 1)". Col. 13, line 22, "13 3" should read --l3--, and "adopted" should read --adapted--; line 33, between "(Pluronic F-68) and "Desensitizer, as in example 1" insert --Pigment Naphthol Red B)-- in the ingredient column, and between 76 and "3860" insert --l00-- in the parts by weight column; line 40, after "alternate" insert --formula-. Col. 14, line 31, "16 3/8" should read --l6 3/8"--; line 41, "58b::" should read --58"-; line 54, "Example 14'' should read --Example l7--; line 63, "tool" should read --took-. Col. 18, line 13, "900" should read --9000- Signed and sealed this 2nd day of May 1972.
EBMLRD M.F'L'ETCH11",'JR. ROBERT GOTTSCHALK Attesting; Officer Commissioner of Patents