US 3635158 A
Very effective and long-lived printing roller has relatively smooth roll surface of long preferably durable fibers with a denier preferably less than 3, bonded together by yieldable binder, at least the outer portion of the surface being porous. Fibrous surface can be provided by helically wrapping a relatively narrow sheet of felted fibers around roll core and cementing it in place under pressure with helical edges carefully butted together. Alternatively a sheet sufficiently wide can be circularly wrapped several times around the core, cemented in place and then ground to a uniform cylindrical surface, or felted tube can be shrunk on. Raising of a little nap on the surface is helpful. Roller removes hickeys when used in inking train and is also good for dampening in dampening train.
Description (OCR text may contain errors)
linite Mates Patent Bndinger A an, M, 11972  ROLLER FOR PRHNTHNG PRESS 3,293,728 12/1966  Inventor: William D. Budinger, 302 River Road, Wilmington, Del. 19809 310O721 8/1963  Filed: Oct. 6, 1969 FOREIGN PATENTS OR APPLICATION S 21 l. N 9 4 5 1 App 6 2 892,984 4/1962 Great Britain ...29/132 mum/ s, m u mm, 495,159 11/1938 Great Britain ..29/ l 30  Continuation-impart of Ser. No. 767980, Oct. 16, a Examiner clyde L coughenour 1968- Attorney-Connolly and Hutz  111.8. Cl ..l0ll/1l4l7, 29/120, 29/132, 57. ABSTRACT 101/348 51 1111. c1. ..B41125/18, B411 27/12 Very effective and long-lived P f roller has @latively  116111 61 seal-c1] 101 /343, 147, 148; 29/120, P Surface 1mg Preferaoly durable fibers i 29/127 131 132; 161/170 n er preferably less than 3, bonded together by yieldable bmder, at least the outer port1on of the surface belng porous.  Reteremes Cited Fibrous surface can be provided by helically wrapping a relat1vely narrow sheet of felted fibers around roll core and ce- UNITED STATES PATENTS menting it in place under pressure with helical edges carefully butted together. Alternatively a sheet suiificiently wide can be 23041678 9/1957 Rockoff "29/121 R circularly wrapped several times around the core, cemented in 218431883 7/1958 Rockoff' 29/132 X place and then ground to a uniform cylindrical surface, or 31345942 10/1967 F 101/348 felted tube can be shrunk on. Raising of a little nap on the sur- 314601222 8/1969 Mitchell 29/132 face is helpful. Roller removes hickeys when used in inking 117891244 1/1931 Mccollum 101/348 train and is also good for dampening in dampening train. 2,775,195 12/1956 Martin ..l01/148 3,147,698 9/1964 Ross ..29/132 UX 10 Claims, 3 Drawing Figures The present application is in part a continuation of application Ser. No. 769,980 filed Get. 16, 1968.
The present invention relates to rollers for planographic printing presses or the like. i
The offset printing industry has long been plagued with the appearance of small blemishes or spots on the finished copy. These defects, called hickeys or fisheyes" by printers, are usually caused by foreign particles such as dirt, bits of paper or dried ink which get into the inking train and from there onto the plate to then interfere with proper ink transfer. l-leretofore the only sure method of removing the foreign particle has been to stop the press and physically scrape the offending particles off the plate.
Some measure of during the run protection has been available through the use of specially prepared inking rollers, called hickey" rollers. Sleeves of polytetrafluoroethylene or other fluorinated plastics, rubber compounded with such plastics, rubber compounded for porosity with blowing agents or dissolved-out materials, or rubber compounds with fiber flock to create a fibrous surface, have all been tried on inking rollers with only limited success. The most effective cleanup roller available in the prior art is probably the oldest. It is made by sewing heavy leather into a sleeve and then fitting this sleeve over a hard (80 Shore A durometer) rubbercovered roller core. With varying degrees of success the foregoing roller surfaces tend to collect and render innocuous foreign particles that may arrive through the inking train or that find their way onto the inked portions of the plate.
Although the best heretofore available, the leather roller is plagued with many disadvantages. It is difficult to clean, gets hard and scratches the plates, and the cover must be frequently retightened.
Among the objects of the present invention is the provision of novel hickey rollers that are not only highly effective but have long maintenance-free lives.
Additional objects of the present invention include the provision of inking and dampening trains containing novel rollers as well as improved techniques for making such rollers.
The foregoing as well as further objects of the present invention will be more fully understood from the following description of several of its exemplifications, reference being made to the accompanying drawings in which:
FIG. l is a perspective view of one end of a printing roller embodying the invention;
FIG. 2 is a vertical sectional view of a fibrous sheet that can be used to make such a roller; and
FIG. 3 illustrates an inking and dampening train in which rollers of the present invention are incorporated.
The printing press roller of the present invention has a surface of densely felted long fibers with a denier preferably less than 3 bonded together by a yieldable binder, the outer surface of the roller being finished to give a velvety texture.
Referring to the drawings, the roller of FIG. ll has a fibrous sleeve 12 firmly cemented on a rubber core 114 which is in turn mounted on a solid or hollow shaft 16 that may be made of a metallike steel or aluminum. The rubber core 14 is preferably an oil-resistant rubberlike neoprene or poly-2- chlorobutadiene although natural rubber or any other kind of rubber including silicone rubber can also be used, and preferably has a durometer hardness of 20 to 50 Shore A, or even less. In order to provide a longer life, the rubber is usually vulcanized to the shaft although it can be merely cemented in place, or held by frictional forces alone as by forming the core with an inner diameter smaller than the outer diameter of the mandrel and forcing the core over the mandrel with the help of a lubricant and a tapered pilot.
The following examples illustrate more completely the construction and physical properties of typical rollers of this invention.
EXAMPLE l A conventional roller for ink or water form positions is used in accordance with this example as the starting material for making a roller of the present invention. The three, positions ill through M are ink form positions and 54 is a water form position. The roller has previously been covered with a soft 15 to 30 durometer Buna N rubber. To convert such roller, the rubber covering is ground to a diameter 0.090 inch under the press manufacturers specified size. it is then painted with a suitable adhesive such as a flexible epoxy made by mixing 60 parts by weight of a low-molecular weight epichlorhydrinbisphenol-A condensate with 40 parts by weight of the polyamide condensation product of dimerized coconut oil acids with triethylene tetramine (equal parts), and 50 parts by weight methyl ethyl ketone. Such an adhesive is available from the Shell Chemical Co. as Epon 828 and Curing Agent V-25.
On top of the adhesive is wrapped a. %-inch thick sheet of high-density felt of 1.5 denier polyester fibers about threefourth inch long that has been previously slit into a strip having a width two times the diameter of the ground starting roller. A single layer of the strip is helically wrapped around the roller using great care to butt the adjacent helical strip edges tightly together. The start and finish ends of the strip are held in place with short lengths of adhesive tape, and a 3%- inch wide nylon parachute tape is helically wrapped over the felt under about 75 pounds of tension. The ends of the nylon pressure wrap are tied together and the wrap is kept on until the adhesive has cured. This generally takes about 24 hours.
Because of the overwrap tension, the felt will be crushed somewhat and matted. This condition is relieved after the ad hesive cure is completed and the overwrap removed, by then placing the roller in a 200 F. oven for 6 hours and allowing the felt to rebound.
The felt-covered roller is next soaked in an aqueous dispersion of polytetrafluoroethylene having a specific gravity of about 1.16. The felt is quite porous and with polymer particles about 0.5 micron in size adequate impregnation takes place in about 1 hour at room temperature. The thus impregnated dispersion is freeze coagulated in the felt by removing the roller from the dispersion and promptly dunking it in a bath of dry ice and acetone. It is then placed on a drying rack and the water allowed to evaporate off. When dry the roller is ready for further impregnation.
A suitable impregnation for this purpose may be made by suspending /2 micron polyvinylchloride resin particles in four times their weight of dioctyl phthalate. The impregnation is accomplished by filling the lower half of a large vacuum tank with the resulting suspension. The roller is then suspended in the tank just above the liquid level and the air evacuated. When the system reaches a sufficiently complete vacuum (50-100 microns), the roller is allowed to drop below the surface of the liquid. The system is then opened to the atmosphere and the roller allowed to soak for about an hour, after which it is placed in an oven to cure for four hours at 280 IF. This converts the polyvinylchloride-dioctyl phthalate mixture to a solid yieldable plastisol having a 15 to 20 Shore A durometer. After cooling the roller is placed in a lathe and ground to proper size with an abrasive wheel. The desired nap is then raised by wetting the ground roller with mineral spirits and sanding while wet with No. grit garnet paper. Best results are obtained if the roller is spun in a lathe at 500-! ,000 rpm. while pressing the sanding paper against it and moving the paper from one end of the roller to the other, changing the spinning direction after each pass with the paper. The roller can then be wiped dry and is ready for use.
One additional step may be added if desired. To prevent later penetration and swelling by ink solvents and press wash chemicals, the rubber exposed at the ends of the roller may be sealed with a suitable barrier material. A flexible epoxy cement such as the above-described adhesive is quite satisfactory for this purpose.
The roller of this example has an essentially nonporous smooth 15-20 durometer Shore A surface out of which project millions of short fibers. Because of the mechanical interlocking imparted by the felting process, the fibers are anchored securely into the roller. In contrast to a surface produced by compounding flock into rubber, the nap of this roller will not easily pull out. Equally important, this rollers durability is derived primarily from the interlocking fibers. Tough binder/fillers with their corresponding hardness are therefore not required and advantage can be taken of the yieldability of extremely soft binder/fillers.
Good rollers can also be made with a more porous surface in which case the binder applied to the fibers does not fill the pores between the fibers and should have a tensile strength of at least about 1,200 pounds per square inch, as in the following example.
EXAMPLE II The sleeve 12 is made of sheet of felted fibers such as described in example 1 of U.S. Pat. No. 3,067,483 granted Dec. 1 l, 1962, but needle-punched from a thicker mat so that it has a thickness of 0.075 inch. The remainder of the procedure of that example is followed up until the buffing step. Instead of buffing, the substrate is then slit into the form of an elongated strip with parallel side edges, the core is coated with a flexible adhesive, and the strip helically wrapped around the coated core. A helix angle of about 40 to 50 with respect to the axis of the core is very suitable, and the strip width can be from one to 2% times the diameter of the roll to be covered. Care is taken during the wrapping to have the abutting edges of the substrate free of adhesive and in uniformly close engagement with each other throughout the wrap. The assembly is then placed under radially directed pressure until the adhesive is fully cured.
It is helpful to seal the sheet surface which comes in contact with the adhesive as by coating the surface with a layer that renders it effectively nonporous and thus keeps the adhesive from soaking into the sheet. One very desirable sealing technique is to spread on the sheet a 0.005-inch thick coating of a butadiene-acrylonitrile rubber mixture as follows (in parts by weight):
100 parts uncured butadiene-acrylonitrile rubber such as Hycar l032 5 parts zinc oxide 1.5 parts sulfur 75 parts carbon black parts benzothiazyl disulfide 1 part stearic acid 800 parts dry methyl ethyl ketone and then curing the rubber by passing the coated sheet through a curing oven maintaining a dwell of 10 minutes at a temperature of 280 F. The cured sheet is then slit into a strip having a width equal to 2.2 times the diameter of the roller to be covered. It is now ready to be wrapped on the adhesivecoated roller.
The adhesive used may be any one of the well known and commonly available rubber-bonding adhesives. Because the fibrous substrate offers excellent opportunity for mechanical bond, it is only necessary to match the adhesive to the particular type of rubber on the roller being covered. A flexible epoxy adhesive such as that of the first example is particularly effective for bonding the substrate to most commonly used rubber cores. The surface of the rubber core is preferably prepared for receiving the adhesive by wiping it with a solventlike methyl ethyl ketone or acetone or methyl chloroform.
The curing pressure can be applied by a toroidal ring of fiexible rubber or other air-impervious material fitted with an air valve like an automobile tire tube. The ring has a central diameter into which the wrapped core is inserted with its axis aligned with the toroidal axis, after which the ring is inflated to cause the wrapped core to be squeezed. A pressure of about 50 pounds per square inch is very effective. Curing is completed in about 24 hours, and can be hastened by heating to temperatures of 120 to 250 F. During the pressuring and curing care should be taken not to permit any shifting of the wrap.
When the curing tape is used for pressurizing, higher pressures may be obtained by dampening the tape with water before wrapping and allowing it to dry and shrink after wrapping. Excessive pressure may cause irreversible crushing of the substrate, and is preferably avoided although such a crushed substrate can still be used.
The cured roller is removed from the pressurizing and should not show excess adhesive. It can now be inserted in the inking train, as by fitting its shaft in the roller journals of an inking train. it is preferred however to dress the cured hickey roller, as by subjecting it to a grinding operation that removes a small amount, 0.05 to 0.020 inch, of the surface and assures its accurate cylindrical shape. The grinding is easily effected with an ordinary No. 24 grit abrasive grinding wheel mounted on a lathe or roll grinder in the manner customary to the rubber roll-making industry.
For best results the sleeve should be further impregnated with additional binding agent to improve both its operating life and function. Polyurethane and polyurea impregnants are particularly suitable for this purpose. The following impregnant is a highly effective one:
parts polyurethane of tetramethylene ether glycol and toluene diisocyanate with an available isocyanate content of 4.10 percent 12.5 parts 4,4'-methylene-bis-(2-chloraniline) 0.2 parts adipic acid 300 parts anhydrous acetone.
About 5 minutes are required to thoroughly saturate the substrate, after which the roller may be removed and the acetone allowed to evaporate.
Any other strong flexible resin used in synthetic leathers makes a suitable impregnant when dissolved or dispersed to provide an impregnating composition of suitably low viscosity. Even for the more porous constructions more than one impregnating step can be used, and in each step the need not be the same. The roller of this example can thus be improved somewhat by preceding the final impregnation with a polytetrafluorethylene impregnation as in example I.
The total weight of nonvolatile impregnant in the sleeve can be as little as about 10 percent of the total weight of the impregnated substrate.
The binders must be curable at temperatures that do not deleteriously affect the fibers or the roller core when such a core is used. Typically the cure temperatures should be under about 300 F. and just about all resins meet this condition. The binder should also be resistant to inks and solvents normally encountered in offset printing. Elastomeric binders are much to be preferred as compared with nonelastomeric ones, and they may be thermoplastic or thermosetting. impregnating compositions that have a viscosity greater than 5 poises do not penetrate well into the substrate and are accordingly not desirable unless vacuum impregnated.
After any solvent or suspending medium present has evaporated from the impregnated substrate the binder is cured and the roller may be given its final dress grinding. Curing of the foregoing binder may be accomplished in 7 days at room temperature but is preferably conducted for 3 hours at 212 F. The intermediate grinding can be omitted where there is a finish grinding.
The final grinding process leaves a very fine nap on the roller surface. It is generally desirable to enhance this nap as by sanding in the manner indicated above.
The product of this example (as well as that of the first example) has no visible seam. It has a soft downy feel in spite of an apparent surface hardness of 65-75 durometer Shore A. When properly installed on a wet-ofi'set press in the first inking position over the plate, its hickey-removal action is of outstanding superiority and its surface texture does not print through to the work. It seems to have little or no tendency to scratch or abnormally wear the plate, and surprisingly, it can usually be cleaned of ink using a normal in-press washup.
The substrate i2 is preferably at least mils thick to provide the desired hickey removal. The thickness can be substantially greater than 15 mils and as much as one-half inch or more, but the effectiveness of the roller does not improve significantly after the thickness is increased beyond about 80 mils. The fibers can be of any kind, either hydrophilic, hydrophobic, oleophilic, or oleophobic. The desired porosity with respect to printing inks can be obtained with any of these types of fibers such as polyamide, polyimide, polyester, protein for example wool or silk, polyesteramide, regenerated cellulose, cellulose acetate, cellulose nitrate, cellulose butyrate, rayon, linen, cotton, ramie, bagasse, hemp, rubber, metals. The more durable and wear-resistant fibers such as polyamide, polyethyleneterephthalate and polyacrylonitrile are preferred. Brittle fibers are not suitable.
It is also important to have the fibers securely felted together so that they better withstand the flexing the substrate undergoes in use. Crinkled fibers that are very thin and at least one-fourth inch long, preferably at least one-half inch long, before crinkling are used for this reason. The crinkling can be carried out by heat processing, with or without solvent, by mechanically curling or in any other effective way, and the fibers can have a cross section that is circular, elliptical, flat or even crescent shaped, the latter shapes enabling more drastic crinkling. The felting of the fibers together can be accomplished by needle-punching batts as in the above example, or then can be wet-felted like paper is, or dry-felted like mens hats are. The mechanical interlocking provided by the felting contributes much of the strength found in the finished roll.
In general the substrate does not have to have any binder when it is first wound on the core or shaft, but the presence of a little binder, even 5 percent by weight of the fibers, strengthens the sheet and makes it easier to wrap as well as keep aligned.
Fibers at least one-half inch long, measured in uncrinkled form, should be used for needle punching.
The fibrous substrate of the present invention has sufficient resiliency so as to provide good hickey-picking even if held on an unyielding core. For such purposes it is desirable to have the substrate at least 80 mils thick directly adhered to a wood or metal core for example.
The use of a yieldable core has advantages, particularly when the yieldability corresponds to the -50 durometer hardness referred to above.
The presence of a seam or other interruption in the uniformity of the outer surface of the sleeve is undesirable since such interruption will frequently print through to the finished work. it is for this reason that care should be taken to accurately abut the edges of the substrate used to form the sleeve. When the substrate used to form the sleeve has a thickness as high as 8 percent or so of the outer radius of the core, the spiral winding tends to cause the outer surface of the sleeve to be stretched and pull the side edges toward each other. This has the effect of giving these edges a bevelled appearance and prevents the edges from being butted together over their entire depth. This difficulty can be minimized by giving the side edges an initial reverse bevel. PEG. 2 illustrates a strip lift of the substrate of the present invention with reverse tapers 20 at the side edges extending between the outer surface 21 and the inner surface 22. Bevels 20 of as little as 10 to 20 measured away from perpendicularity with respect to the outer and inner surfaces, are adequate in most cases to permit accurate abutting of sheets 40 to 200 mils thick and the preparation of a sleeve that shows no seam, particularly after a light grind dressing.
A seamless construction can also be provided by wrapping several turns of the substrate in an unhelixed manner around the core. The leading edge of such a wrapped sheet can extend parallel to the cores longitudinal axis and the trailing end of the last turn can extend far enough to overlie the leading end. Cementing the above wrap in place on the core as well as cementing the turns to each other followed by a grinding to make theexternal surface truly cylindrical, will provide all the characteristics of a seamless surface. if the adhesive is the same as the binder, the ground juncture at the trailing end of the last turn cannot be visually distinguished.
The use of a single turn of a sheet where the advanced and trailing ends abut against each other, is not desirable. During the use of the hickey rollers of the present invention the sleeves are subjected to considerable inward deflection and this develops extremely large stresses that can damage a butt joint of this type. The multitum arrangement or the helical arrangement withstands such deflection very effectively, and good adhesion to the core is a considerable help in this connection. At least a little pressure should be applied during the cementing to improve the adhesion, but the pressure should not be so great as to excessively distort the materials. A range of from about 1 to about pounds per square inch is generally effective.
EXAMPLE ill Parts by Weight Material Solution A Solution B High acrylonitrile uncured butadiene-acrylonitrile polymer 100 100 Zinc oxide 5 5 Sulfur 6 0 Channel black 56) 50 Cournarone-indene resin m.p.-25C. 25 2s Aldolalpha-naphthylamine 5 5 Mercapto benzothiazole O 6 Dry methyl ethyl ketone 800 800 immediately prior to use, 2.5 parts of butyraldehyde-aniline condensation accelerator in an equal amount of methyl ethyl ketone are added to solution B. Solutions A and B are then mixed together in equal parts and applied by spreading or brushing onto the roller. Sufficient solution should be applied so that after solvent evaporation an adhesive film about 0.003 inch thick will remain.
The fibrous substrate used is a polyimide fiber sheet 0.085 inch thick weighing about 9 ounces per square yard, and needle punched from a batt of 2-inch long fibers that have been mechanically curled and have a denier of about I. The sheet is not impregnated with a binder before cementing and is not given a preliminary seal coating. It is otherwise applied, impregnated, cured and finished in the same manner described in example ll except that it is cut into a strip 2.4 times the diameter of the roll core and the impregnant is the one described in example VI of U.S. Pat. lilo. 3,000,757 granted Sept. 19, 1961.
The rollers of the last two examples have substrates which are essentially entirely porous throughout their depth except for those levels at which a sealing layer was applied or adhesive was used to secure the substrate to the core or to secure one layer of substrate to another. For some purposes however, less porosity is desired, as for example where the roller is to be very easily cleaned of ink. One way to reduce the porosity is to impregnate the substrate until all its pores are filled, as in example l. Alternatively, the helically wound hickey roller of examples I! and Hi can, after mixing of the last impregnant, be subjected to additional impregnation and curing until it is no longer absorbent. Another method of reducing porosity is to fill the pores with fine particles of polytetrafluoroethylene or polytrifluoromonochloroethylene.
EXAMPLE I The roller produced in accordance with example III is immersed in an aqueous dispersion of polytetrafiuoroethylene containing 50 percent by weight polytetrafiuoroethylene particles having a size of approximately half a micron. After thorough saturation the roller is removed from the dispersion and cooled to F. by placing it in a container held in an isopropyl alcohol bath containing dry ice to flocculate the polytetrafluoroethylene particles so that they are no longer suspended. The roller then is removed from the freeze container and exposed to the atmosphere at room temperature to permit its ice content to melt and evaporate. The treatment is then repeated, this time the impregnation being carried out in a vacuum tank with a dispersion having 50 percent resin, the dried product can then be ground to finished dimensions and napped.
The polytetrafiuoroethylene particles in the pores of this roller are apparently free to move about to some extent. This may explain why the filler has some of the same yieldability characteristics as that of example I. Since the internal pores are essentially filled, the cleanability of this roller approaches that of example I.
To help prevent filler particles such as the polytetrafluoroethylene from being pulled out of the surface, that surface can be given a supplemental impregnation with a binder such as that of example ll.
EXAMPLE V A roller like that produced in the first example but having polyamide fibers in the substrate in place of the polyethyleneterephthalate fibers, is vacuum impregnated with a solvent-free liquid cureable urethane resin instead of the polyvinyl chlorideplastisol. The urethane is cureable to a to 25 durometer Shore A hardness. A single impregnation with the urethane is sufficient to provide the desired imperviousness, after which the impregnant is cured, the roller ground and finally napped with No. 100 aluminum oxide sandpaper to raise a nap 3-15 mils high.
The product of this example exhibits cleanability and hickey-removal characteristics intermediate between those of the other examples. It is particularly useful on high-speed equipment where cleaning case is more important than optimizing hickey removal. Because the abrasion resistance of the fiber is substantially higher than that of the soft filler, the roller, as it wears, will continually maintain a napped surface.
The following is an example of a multiple-layer smooth-surfaced construction.
EXAMPLE VI A rubber-covered roll core as in example [I] and inches long has its rubber surface coated with rubber cement, and a layer of the same cement is applied to one face of a lOl-inch wide fiber sheet 18 inches long. The fiber sheet is an impregnated 0.030-inch thick air-felted web of 2.5 denier shrinkable polyamide fibers l te-inch long that after felting has been thermally treated to curl the fibers. The impregnation was with 20 percent by weight of the binder described in example 4 of US. Pat. No. 3,100,721. The cement-coated substrate is wrapped around the cement-covered roll core a little more than two turns, tension being applied at the end of the first turn. The outer end of the wrap is held down with pressure-sensitive tape, and the assembly placed under pressure until the cement cures. The assembly is impregnated with the binder described in example I of U.S. Pat. No. 3,214,290 granted Oct. 26, 1965, to increase the binder content to 40 percent. After curing, the roll is ground down to an overall diameter 0.100 inch larger than that of the core. This leaves an apparently seamless construction, but the impregnation is greater in the outside turn than in the inside turn of the substrate. The impregnation into the inside turn is hampered by the layer of cement between the turns, so that it takes place primarily through the narrow thickness of the sheet that connects the turns as well as through the exposed edges. While such a roll can be used to pick hickeys very effectively, it is difficult to clean free of printing ink because the ink works its way into the lower turn and only washes out with difficulty. Such a roll is quite suitable however for pore filling as in examples l and IV for instance. For such pore filling it is only necessary to make sure the edges and outer turn are filled and that they seal any residual porosity in the inner turn.
EXAMPLE Vll A roll is prepared for bonding as in example I. The felt sheet is prepared from retractable polytetrafluoroethylene fiber This felt is slit into a strip having a width approximately 1.5 times the roll core diameter and wrapped carefully on the adhesive-coated roller, as in example I. The assembly is then overwrapped with nylon tape except that tension must not be allowed to exceed 10 pounds per inch of width. Excessive tension unnecessarily compresses the felt and causes strikethrough of the adhesive.
After curing it will be noted that the felt has bonded very well to the surface of the roll core, even though the adhesive will not actually bond to the fiber material. Bond is effected through encapsulating the inner fibers and mechanically locking them in place.
lmpregnation and finishing are accomplished as in example I. It is important during grinding that the roller be turned slowly and wheel kept clean and sharp.
The product of this example exhibits hickey-removal qualities almost comparable to that of the first example. By virtue of the polytetrafluoroethylene fiber, it is somewhat easier to clean.
Another feature of the hickey rollers of the present invention is that their operation may be further improved by driving them at a rotational rate somewhat different from that required to merely roll across the plate. By gearing these hickey rollers so that their rotational speed is l to 5 percent greater or smaller than they would have if impelled by the rolling action on the plate, they are given a wiping effect which increases the hickey-removal action. Care must be taken however in that this mode of operation may cause the plate to wear prematurely. In practice, if this mode is to be used it is done intermittently.
FIG. 3 shows an offset printing roll assembly having a plate cylinder 30 on which the printing plate is secured as by cementing, and a train of inking rollers 31 through 38 and 41 through 44 that carry ink from an ink trough 45 and apply it to the surface of the plate. Hickey rollers of the present invention are generally used for one or more of the plate-contacting rollers 41 through 44. The other rollers in the inking train can be the usual rubber rollers.
A train of dampening rolls 51 through 54 are conventionally used to moisten the plate from a water trough 56. A blanket cylinder 58 receives the ink from the inked portions of the printing plate, and transfers it to the printed sheets 60 with the help of a back up or pressure cylinder 59.
The rollers of the present invention are receptive to water and dampening solutions, as well as to hydrophobic printing ink. l-leretofore, dampening rollers have been bare rubber rollers or rubber rollers covered with cloth, flannel, molletin,
paper wrap or hard paper sleeves. All of the foregoing have individual disadvantages but share the common disadvantage of difficulty in control. Because they lack dimensional stability or uniform water receptivity, they cannot apply a sufficiently uniform film of water to the plate. The rollers of this invention exhibit great dimensional stability and have a uniform, mechanically water receptive surface. Because of the dimensional accuracy obtainable, it is possible to set these rollers very lightly (barely touching) the plate. This is desirable as it provides better dampening and is less likely to feed ink back up the dampening train. When used in this manner, it is desirable to equip the roller with drive trucks as described in U.S. Pat. No. 3,296,964 issued Jan. 10, 1967.
Because the rollers of this invention will carry both ink and water simultaneously, they offer special advantages when used in the dampening systems described in US. Pat. Nos. 3,168,037 granted Feb. 2, 1965, and 3,343,484 granted Sept. 26, 1967. The roller should be substituted for that shown as No. 12 in FIG. 1 of US. Pat. No. 3,168,037. its use here permits improved dampening with a lower alcohol content than otherwise possible. Reduction of the alcohol content is a cost saving measure as well as a safety feature.
As an ink form roller, the rollers of the present invention should not be permitted to accumulate ink that is allowed to compact and harden in the pores of the substrate. If this happens the surface nap tends to break off, leaving a hard surface of greatly reduced effectiveness.
The roller construction of example i tends to prevent this condition by having the internal pores filled with a soft binder and thereby preventingink penetration below the surface. Because the binder is so soft and compliant, the fibers wear resistance is greatly improved. Working against the plate, the soft binder allows the fibers to bend with a much greater radius than would otherwise be possible. The greater bending radius reduces fatigue and keeps fiber breakoff to a minimum. it also appears that the soft and somewhat tacky nature of the binder helps in picking hickeys off the plate.
The nap raised on the surface of these rollers is particularly important to their use. The nap height or protruding fiber length can be controlled during the final sanding operation. in general, coarse grit papers such as No. 60 or No. 80 used on a roller wet with mineral spirits will yield long nap fibers with a height of l520 mils or more. Fine papers such as No. 220 used dry will give a very t'uie nap of l to 3 mils height. Although the choice of nap height is usually a matter of individual preference among press operators, some generalizations can be made.
When used as a hickey roller, long naps tend to be most effective. However, in the last inking position (No. 41 in FIG. 3), long-napped rollers may leave a pattern in the print. For this position, fine-napped rollers are preferred.
As a dampener, rollers of this invention are usually preferred with a fine nap when used against the plate. Water train rollers such as the ductor (No. 52 in FIG. 3) usually require the longer nap to carry sufficient dampener solution. For ductors or dampening rollers, many pressmen prefer the fully porous roller of example ll. The porous roller will carry a reservoir of solution which is frequently considered helpful.
The rollers of this invention tend to be superior to conventional molletin rollers by reason of greater uniformity, easier dampening control and less tendency to shed lint.
The felted layer of the present invention can be preformed as a shrinkable tube that is slipped over the core and then shrunk down to securely grip the core and hold itself in place with adhesive. Thermally shrinkable stretched polyethylene terephthalate fibers when air felted on a cylindrical form make an effective tube for such a construction.
While as indicated above fiber deniers less than about 3 are desired, fiber substrates can be used when the fiber denier is as high as 5, particularly in a dampening roller. Also the fiber ends can be split so as to provide the desired denier in the ends and thus give good roll operation although the body of the fiber is too thick to be really effective.
The polytetrafluoroethylene impregnation step of example I can be omitted without seriously reducing the rollers effectiveness. it is included for two reasons:
1. Finish grinding is made somewhat easier because the polytetrafiuoroethylene particles improve the powdering of the waste and reduce the tendency of the grinding wheel to load. This effect allows the roller to grind cooler and minimizes the chance of degrading the binder or tiller.
2. in use the polytetrafluoroethylene appears to improve the hickey removal quality of the roller and slightly extend nap life. These effects may be due to an electrostatic charge developed on the roller which causes the nap to stand on end.
Freeze coagulation of the polytetrafluoroethylene dispersion is similarly not mandatory. it is helpful because it tends to improve the uniformity of particle deposition in the fiber matrix.
Whether or not the polytetrafiuoroethylene is used in the roller of example l, other materials may be substituted for the polyvinylchloride plastisol. In the example 1 construction, the polyvinylchloride plastisol serves to fill all the pores and also helps hold the fibers in place. The exact nature of such impregnant is not important so long as it is very soft and will withstand the environment in which it will be used. Successful impregnation to make nonporous rollers of this invention can be effected by using gels or plastisols of other polymers as well as by using liquid elastomer systems. Liquid rubbers of the Buna N, polysulfide, silicone or butyl classes are suitable although the liquid urethane systems most easily lend them selves to this application. Single or two component urethanes may be used provided they are soft enough or plasticized sufficiently to bring their lDurometer below 25 Shore A. A du rometer hardness of 5-10 Shore A is preferred. A suitable urethane impregnant may be prepared as taught in US. Pat. No. 3,456,037 granted July 15, 1969.
The most pore-free impregnation products are more readily obtained from impregnating fonnulations relatively free of volatile ingredients. Nonreactive, nonvolatile, liquids should also be avoided for pore-free impregnation products except in amounts absorbed by the solids that are present.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
What is claimed:
1. A printing press inking system including a printing-platecontacting roller having a roll surface of a preconstituted dense felt of flexible fibers at least one-half inch long with a denier less than about 3, bonded together by a soft yieldable hinder, the felt being at least 15 mils thick and the fibers projecting as a velvety nap from the bonded-together surface.
2. A printing press roller having a roll surface of a preconstituted dense felt of flexible fibers which are at least one-half inch long with a denier less than about 5 and are bonded together by a soft yieldable hinder, the felt being at least 15 mils thick with its pores substantially completely filled and the fibers projecting as a velvety nap from the filled surface.
3. The combination of claim 2 in which the fibers are crinkled polyester, polyamide, polyimide or polyacrylonitrile fibers.
4. The combination of claim 2 in which the binder is an elastomer having by itself a hardness no greater than about 25 durometer Shore A.
5. The combination of claim 2 in which the binder is a polyurethane or polyurea elastomer.
6. The combination of claim 2 in which the pores are filled with a material less abrasion-resistant than the fibers and the nap is at least about 3 mils high.
7. The combination of claim 2 in which the fibers have a denier less than about 3 and'the pores of the felt are partially filled with polytetrafiuoroethylene particles.
10. A printing press plate dampening system having a set of dampening rollers in which set one of the rollers is the roller of claim 2.
WEB-2 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Januarv 18, 1972 Patent No. 3,625,168 Dated Inventor-(K25 WILLIAM D RUDINGER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 1, line 3, change "769,980" to 767,980
Column 2, line numbered 5, change "The three" to Signed and sealed this 13th day of June 1972.
EDWARD M.DFLJEICHER,Jfi ROERT GQITSCHALK Commissioner of Patents Attesting Officer