US2254298A - Method of conditioning cylinders and the like - Google Patents

Description

Patented Sept. 2, 1941 METHOD OF CONDITIONING CYLINDERS AND THE LIKE Charles W. Latham, Maspeth, N. Y., assignor to Smart Platen Process 00.,

Inc., Brooklyn,

No Drawing. Application February 23, 1940, Serial No. 320,423

Claims.

My invention relates to a method of truing cylinders, platens, and the like, and the principles and steps thereof are disclosed herein using an offset printing press by way of example.

In offset lithography the press has at least three cylinders, one to which the printing plate is fastened or strapped, a second or middle one which carries a transfer blanket usually of rubber, and a third cylinder carrying the paper on which the final impression is made. The plate on the plate cylinder is inked by rollers, the image on the plate being transferred to the blanket, and from the blanket to the paper.

It is highly important that during operation the surface of these three cylinders travel at exactly the same number of feet per second, which for purposes of this discussion can be assumed to be the same as rotating the cylinders at exactly the same number of revolutions per minute. If this is not done, there will be smearing and streaking, and a general lack of clarity and definition in the final print. In computing this peripheral speed there must be added to the actual diameters of the plate and blanket cylinders the thickness of the plate and the blanket. respectively, and also sufficient packing behind the blanket to give the necessary printing pressure to obtain adequate transfer. This packing usually consists of sheets of paper and the additional squeeze for printing is best obtained with .004" of packing in addition to whatever is necessary to have the three cylinders uniform in diameter.

Any pressure between the cylinders in excess of that indicated will produce undesirable printing results. However, the cylinders warp and bend under the stresses and strains of continuous work, and are often deformed by bits of cloth, wood and other foreign materials entering between the cylinders. Heretofore, the pressman has endeavored to compensate for such conditions by inserting patches of paper behind the blanket to fillup the hollows and low places in the cylinders, or has resorted to other make- 45 shift ways in his endeavor to maintain an even pressure over the entire surface of the cylinders. It is apparent that such methods cannot be accurate as a practical matter, and one or two thdusandths additional packing on one or more of the high spots of the cylinders will give the excess pressure that causes trouble.

"- ."The known method of reconditioning and truing of cylinders to obtain proper printing pressure is by re-surfacing and regrinding the cylinders which involved dismantling the press,

removing the cylinders, transporting them toa properly equipped plant, building up the surface of the cylinder to an excess thickness, then precision grinding the face of the cylinder, after which the cylinders are reinstalled in the press. Such procedure is expensive and requires the shut-down of the press for a considerable number of days.

It is one object of the present invention to provide a method of permanently building up the low spots of a cylinder or the like without removing the cylinder from its normal mountmgs. i

It is another object of my invention to provide a simple and efficient method of quickly and accurately truing the surface of a cylinder or the like.

It is a further object of my invention to provide a method of building up the working face of a cylinder or the like with base, intermediate and outer layers, each of different character.

It is a still further object of my invention to provide materials of particular characteristics for use in my process for truihg cylinder faces.

Another problem in connection with lithographic and printing presses frequently arises fromthe corrosive effects of certaininks upon metal cylinders. My improved process contemplates the use of coating materials to protect the surface of a cylinder or the like from the corrosive effects of inks and other materials as well as the air.

In practicing my invention, the cylinder being repaired is first properly cleaned and conditioned after whicha base lacquer coating is applied followed by a coating of pigmented lacquer. Any nicks or deep impressions are filled up. The cylinder is now ready for building up the larger hollows thereof to the level of the high spot or spots of the cylinder. A masking cream is applied to the cylinder in such manner that the masking cream covers only the high spots of the cylinder, after which the operator sprays a layer of pigmented lacquer over the entire surface of the cylinden'including the parts covered with the masking cream. The parts of the cylinder to which masking cream was applied are washed off to remove the masking cream and the superimposed layer of pigmented lacquer. Next, masking cream is again applied to the surface of the cylinder in such manner as to cover all the high spots thereof, and this is followed by another layer of pigmented lacquer.

These steps are repeated successively until all parts of the cylinder are brought up even. with the highest areas thereof, after which a final surface lacquer coating is applied. The characteristics of the materials used, as well as'the details of operation in carrying out the steps of my process, as well as the drying times, etc., are all fully explained hereinafter.

' In the course of usage of an offset press, the.

most seriously affected cylinders are the blanket and impression cylinders. At times the plate cylinder may be affected also, but this is not so usual partly because the surface is protected by the plate. The carrying out of the invention will be described in connection with conditioning the blanket and impression cylinders and on the assumption that the plate cylinder is in perfect condition or substantially so.

It will be understood, however, that the same principles are applicable to conditioning the cylinders of lithographing and printing presses, as well as cylinders and platens used for many other purposes outside of the printing field as, for example, in the making of paper and the making of paper doilies, napkins, and the like, in which parts are cut out to give lace effects, and advertising mounting cut-outs.

The first step of this process is to clean and condition the cylinder to be built up. In offset lithographing presses, the working face of the cylinder becomes covered with oil and grease, some of which has penetrated into 'the pores of the metal, and must be removed, along with other foreign matter, preferably down to the base metal of the cylinder. of course, dry ink, rust spots, and otheradhering matter may be quickly removed from the cylinder by scraping and sandpapering, after which the cylinder should be thoroughly washed with a solvent and softener for the ink. Such softeners are usually of agesoline nature, such as xylol, and of light viscosity. This washing of the cylinder must be sufficient to remove all surface grease. after which the cylinder is coated with a substance of a nature to saponify and emulsify ink and the ingredients thereof, and to penetrate into the pores of the metal to clean the same as well as the surface of the cylinder.

One such substance which I have found to be satisfactory consists of a. caustic alkali, such as lye, water, and a small quantity of starch, such as ordinary laundry starch, mixed to form a paste which can be applied to the cylinder and allowed to remain thereon. This coating must completely cover the cylinder and preferably should be a thick coating which will be allowed to remain on the cylinder at least one halfhour.

After this elapsed time, the caustic coating must be thoroughly washed off, which is preferably done with water and sponge.

While the cylinder is wet from washing off the caustic, the cylinder should be washed next with a solution which will neutralize the caustic alkali, and at the same time remove any iron oxide that may remain on the cylinder. I have found ten percent solution of acetic acid to be satisfactory for these purposes, under normal conditions. Other acids may be used in a solution having a pH range of from 2 to 3. i

The whole cylinder should be washed off with this acid solution at least three times which should be suiiicient to remove any traces of the caustic alkali and to start removal of the iron oxide. Whether this removal is by reduction or dissolution of the iron oxide, or both, is immaterial, the desired eifect being to attack the face ,of the cylinder so as to roughen the same slightly in preparation for receiving the following coatings. It is desirable that several additional applications oi the acid solution should be made, each without waiting for the preceding application todry, so as to get down to the base metal of the cylinder, but apparently it is not necessary that every trace of the iron oxide should be removed.

After the last washing with the acid solution, and without drying the cylinder, the cylinder is washed with clear water until it is entirely clean. This water will cause the formation of a very slight amount of iron oxide, which is not harmful, the water being promptly worked off the cylinder by means of a cloth saturated in the solvent of gasoline nature first referred to above. This working over the surface of the cylinder should continue until the surface is substantially uniform in color, which will be a very light yellow.

It will be understood that with cylinders, etc., not used in a printing press, that there may not be the necessity-for using the caustic coating referred to above, and that substitutions in the above materials may be necessary or advisable in order to meet conditions in the different fields.

The important thing is that all foreign matter should be removed from the cylinder surface to be treated, as well as the surface pores, and that the surface should be slightly roughened. If the acid treatment does not produce sufficient roughening of the surface, then mechanical methods of roughening may be used, such as sand blasting, grinding, etc.

The next step in truing the cylinder is to apply the first of a series of coatings to build up the same, immediately preceding which operation the cylinder should be washed with any usual lacquer thinner or alcohol to insure that the surface is free from moisture, grease and dust.

The initial or base coating applied to the cleaned face of the cylinder is preferably a nitrocellulose base .clear lacquer primer, desirably having a plasticiser therein, so that the finished coating is smooth and continuous. This lacquer has the further characteristics of being able to penetrate into the pores of the base metal of the cylinder and adheres firmly to the same; relatively slow drying, and such as to leave a tough, clear, somewhat resilient coating. Any usual type of spray gun is used to apply this coating, preferably as a wet spray, so as to leave a coating of substantial thickness, viz., of the order of .005". Of course, the coating also must be of a nature to firmly bond with the following lacquer coating.

The base coating should be allowed to dry for at least a half an hour, and preferably for one hour. It is also desirable that the cylinderbe rotated during this drying so as to insure an evenly distributed coating. In applying the base coating, care should be taken to completely cover the edges as well as the face of the cylinder so as to leave no opening for moisture to creep in, thereby starting undesired rust formation under the coatings. This same technique is used in connection with the second coating which is to be applied as soon as the initial coating is dry.

The second coating and all of the subsequent build-up coatings are also sprayed on. This second coating is a pigmented nitro-cellulose base lacquer, which also preferably contains a plasticiser, and is desirably quick drying. The pigmentation is preferably bronze, or other metal, in the form of a powder having a particle size such as will pass through a 200 to 400 mesh screen. We have found bronze having a particle size equivalent to 325 mesh to be very satisfactory in providing a coating of approximately .005" in thickness. A lacquer thinner is used to provide a lacquer of a consistency of thin syrup.

The cylinder is now ready to have the intermediate coatings applied to build up the low spots thereof to the level of the high spots of the cylinder, which is accomplished in the following manner. According to this process it is desirable to mask the high spots of the cylinder so that subsequent lacquer coatings will not adhere thereto. In a printing press the masking material can be applied in the form of a cream by means of the normal inking rollers. My masking cream comprises approximately equal parts of a printing ink, a blank fix, such as barium sulphate pigment and a stock consisting of a soap which is high in alkali content, an oil such as lard oil, the soap and oil being of a character to saponify the ink, and enough water to form a soft paste. The same are mixed to a consistency such that a substantial film will be transferred to the cylinder.

In an offset press, and assuming that it is the normal blanket cylinder that is first being conditioned, a blanket is attached to the normal plate cylinder, in place of a plate. 'The inking mechanism is operated in the usual manner to apply a thick, even coat of masking cream to the entire blanket. i

When these preparations are made, and even before the masking cream is applied to the blanket, the normal adjustments of the spacing between the plate and blanket cylinders is made until only a light contact pressure exists between the blanket on the plate cylinder and the high spots'of the face of the normal blanket cylinder. After the cylinders are brought to contact position the adjustments are locked in place, and the coated blanket and cylinder being conditioned are rotated. The high spots on the face of the blanket cylinder will receive a layer of the masking cream, which will cover the same. Those parts of the cylinder which have no masking cream thereon are the low spots which need to be built up.

Of course, it has been assumed that dents and nicks in the base metal of the cylinder have been filled, which I prefer to do after the application of the base coatings referred to above and before first applying masking cream to the cylinder.

Having applied a coating of masking cream to the high spots of the cylinder, the operator then applies the first of the intermediate coatings, which consists in spraying over the entire face of the cylinder, including the parts which have received the masking cream, a coating of the pigmented lacquer referred to above.

By the time the operator has completed applying this coat of lacquer to the cylinder, that which was first applied is dry, but if not the cylinder may be allowed to dry for a few minutes, preferably while rotating. The operator then washes off all the high spots of the cylinder which contain the masking cream and an overlying coating of lacquer, by using a, cloth saturated in a solvent and softener for the ink, such as xylol referred to above. These spots are easily identified because there is a certain amount of coagulation takes place between the newly applied coating of lacquer and the masking cream, which makes that portion of the cylinder surface different in appearance from the remainder of the face of the cylinder. This method of removing the applied coating of lacquer and the masking cream prevents the formation of any ridges around the high spots of the cylinder so that at the end of the building up process the cylinder will have a smooth and continuous surface.

This operation completed, a fresh coating of masking cream is applied, using the .same press adjustments that were used to apply the initial coating of masking cream. This second coating of masking cream is applied in the same way, and this time in addition to the high spots initially covered, it is probable that there will be additional high spots which also will receive the masking cream coating.

The operator then sprays upon the entire face of the cylinder and including the portions covered with masking cream, another coating of the pigmented lacquer, after which the high spots are again washed off. These steps of applying the masking cream, applying a coating of pigmented lacquerto build up the low spots, washing off the masking cream to remove the unwanted lacquer coating, and then remasking the cylinder, are repeated in that order until finally the whole surface of the blanket cylinder receives an even coating of masking cream.

Of course, there would be no objection 'to an experienced operator filling up a particularly hollow spot with several coatings of the building up lacquer before applying a coating of masking cream, but at all times great care must be taken not to overlap the high spots with a build-up coating unless there is masking cream over-the high spots. Also, it is desirable that there be only one coating of build-up lacquer applied over an area having masking cream thereon so as to insure the complete removal of both masking cream and unwanted lacquer, which would otherwise produce ridges in the surface.

Having reached the point where the surface of the cylinder is completely trued up, as shown by the complete layer of masking cream thereover, it is desirable that one additional coating of pigmented lacquer be applied over the entire builtup surface of the cylinder as soon as the masking cream is washed off.

Thus, the surface of the cylinder will be uniform in color, which might not be the case where I there have been alternate masking cream and pigmented lacquer coatings on different spots of the cylinder.

In any event my process contemplates applying one or more final finish coatings of a clear lacquer, chosen to provide a hard and glossy surface, over the face of the cylinder. This lacquer is also denser than the two preceding lacquers referred to.

Having thus conditioned the blanket cylinder, the impression cylinder is trued up in exactly the same manner with the exception that the blanket is applied to its cylinder, a plate is put in place on the plate cylinder, and in this case the masking cream is transferred from the plate to the blanket and thence to the impression cylinder.

It may be noted that in place of the masking cream described above, other masking creams can be used, as well as any of the types of wax compounds normally used in lithographing inks to prevent smearing when printed sheets are piled on each other. Also, instead of metal powders as referred to above, other pigments may be used in the lacquer coatings.

Furthermore, while the application of masking cream from the normal inking rollers has been referred to here, it will be understood that any other arrangement could be used which will insure a uniform coating of masking cream from a level surface being brought into contact with the high spots of the cylinder being conditioned.

From the foregoing description, it will be seen that I have provided a process for building up cylinders, platens and the like to have a smooth, even surface, thus providing a cylinder of uniform diameter, without the necessity for any re-grinding and without removing the cylinders, etc., from their normal places of use, although of course this might be done.

This invention contemplates the use of adherent coatings of one or more materials which are, applied to the surface as a fluid and which dry or set to provide a hard and even surface. In addition to lacquers and materials of that class, resins, metals and plastics may also be used.

Other modifications may be made in the materials used, and in the order of the steps of the process, and even omitting certain steps, without departing from the spirit and scope of my invention, and such modifications or changes are intended to be covered by the appended claims.

I claim:

1. The method of conditioning the surface of a cylinder which consists in cleaning the surface to be treated, spray coating the surface with a lacquer primer, spray coating a metal pigmented lacquer thereover, masking the high spots of the surface with a material to prevent formation of a continuous film thereover, spray coating a metal pigmented lacquer over the masked and unmasked portions of the surface, washing off the masked portions, remasking the high spots of the surface and recoating the whole surface with metal pigmented lacquer until the low spots of the surface are built up to the level of the highest areas of the surface, and spray coating the entire surface with a protective lacquer film.

2'. The method of conditioning the surface of a cylinder which comprises cleaning the surface to be treated, spray coating the surface with a lacquer primer, masking the high spots of the surface with a material to prevent formation of a continuous film thereover, spray coating a pigmented lacquer over the masked and unmasked portions of the surface, washing off the masked portions, remasking the high spots of the surface and recoating the entire surface with pigmented lacquer until the low spots of the surface are built up to the level of the highest areas of the surface, and spray coating the entire surface with a protective lacquer flhn.

3. The method of conditioning the surface of a cylinder which comprises cleaning the surface of the cylinder to be treated, spray coating the surface with a base material while rotating the cylinder and drying the coating while rotating the cylinder to provide an even surface, masking the high spots of the surface with a removable material applied from a true surface, spray coating the masked and unmasked portions of the surface with a material while rotating the cylinder, removing the masking material and coating thereover, alternately masking the high spots of the surface, coating the surface and removing the masking material uriiil the low spots are built up to the level of the -ghest areas of the surface, and spray coating the entire surface with a protective material.

4. The method of conditioning the'surface of a cylinder and the like which comprises cleaning and roughening the surface to be treated, spray coating the surface with a' base priming material, spray coating thereover a covering material which provides an even surface, masking the high spots of the surface with a removable material, and spray coating the low spots of the surface with at least one layer of build-up material until the same are built up to the level of the highest areas of the surface, and spray coating over the entire surface a protective material.

5. The method of conditioning the surface of a cylinder which comprises preparing the surface to be treated, applying thereover at least one adherent, setting coating of material, alternately masking the high spots of the surface with a removable material applied from a true surface and applying adherent, setting coatings of material to the low spots of the surface until the same are built up to the level of the highest areas of the surface, removing the masking material, and applying at least one adherent, setting coating of materials to provide the desired working face.

6. The method of conditioning the surface of a cylinder which comprises preparing the surface to be treated, applying thereover at least one adherent, setting coating of material, alternately masking the high spots of the surface with a removable material applied from a true surface and applying adherent, setting coatings of material to the low spots of the surface until the same are built up to the level of the highest areas of the surface, removing the masking ma terial, and applying at least one-adherent, setting coating of materials to provide the desired working face, each of said adherent coatings having different characteristics as to density thereof.

'7. The method of resurfacing and truing the face of a cylinder which comprises cleaning and roughening the face of the cylinder, applying thereover a somewhat resilient base coating, applying thereover a covering coating, alternately masking the high spots of the cylinder face and applying a build-up coating to the low spots of the face until the same are built up to the level of the highest areas of the face, removing the masking material, and applying at least one finishing coating of a nature to produce a hard outer surface.

8. The method of truing the surface of a cylinder which comprises cleaning and preparing the surface to 'be treated, applying thereto an over-all lacquer priming coat, alternately masking the high spots of the cylinder surface and applying abuild-up coating of lacquer to the low spots thereof until the same are built up to the level of the highest areas of the surface-removing the masking material, and applying at least one over-all finishing coating of lacquer.

9. The-method of truing the surface of a cylinder which comprises cleaning and roughening the surface to be treated, applying thereto an over-all lacquer'priming coat," applying thereover another lacquer coating, alternately masking the high spots of the cylinder surface and applying a build-up coating of lacquer to the low spots thereof until the same are built up to the level of the highest areas of the surface, re-

spots of the cylinder surface and applying a build-up coating of pigmented lacquer to the low spots thereof until the same are built up to the level of the highest areas of the surface, removing the masking material, and applying at least one over-all finishing coating of lacquer.

CHARLES W. LATHAMQ