US 2288352 A
Description (OCR text may contain errors)
June 30, 1942. c. L. HENDERSON TRANSFER MACHINE Filed Dec. 24, 1938 2 Sheets-Sheet l June 30, 1942. c. L. HENDERSON TRANSFER MACHINE Filed Dec. 24, 1938 2 Sheets-Sheet 2 Patented June 30, 1942 TRANSFER MACHINE Charles L. Henderson, Appleton, Wis., assignor to Paper Patents Company, Neenah, Wis., a corporation of Wisconsin Application December 24, 1938, Serial No. 241,584
My invention relates generally to the art of photogravure printing and has particular reference to apparatus for transferring a design or pattern to be reproduced by printing to th-- sensitized resist covering on the printing plate or cylinder, preparatory to the etching of such plate or cylinder. More specifically, my invention relates to the light source used in such transfer apparatus.
In carrying out the usual procedures of transferring a design or pattern to the sensitized resist covering for a printing plate or cylinder, it is customary to prepare, by photographic or other means, a transparency having the pattern or design to be reproduced formed thereon. Then, preferably by the use of apparatus ordinarily designated in the art as a transfer machine, this transparency is held in contact with the sensitized resist, and a beam of light of high intensity is passed through the transparency onto the resist with the result that the pattern or design on the transparency is photographically transferred to the resist. The sensitized resist usually comprises a suitable coating applied directly to the plate or cylinder, and after exposure the resist must be developed preparatory to the etching of the plate or cylinder.
During the use of certain of the prior art transfer machines, it has been observed that many of the small opaque areas, especially those having a dimension less than about .0015" are reduced in size, or completely disappear, during the transfer operation. For certain types of work this is not serious, but when it is desired to accurately reproduce patterns or designs with fine detail or to produce intaglio printing surfaces having dot size ink recesses such as are disclosed in my co-pending application Serial No. 105,852, which issued December 5, 1939 as Patent No. 2,182,559, this inability of the prior art transfer apparatus to secure accurate transfer of small areas becomes very serious, and it is with the obviating of this disadvantage that the present invention is concerned.
Reduced to its simplest aspects, my invention consists in the discovery that the tendency of the known transfer machines to eliminate, or reduce the size of, all opaque areas in the transparency below a given minimum dimension during the transfer operation can be eliminated by the use of a particular type of light producing apparatus for exposing the sensitized resist. Somewhat more specifically, my invention involves the discovery that this disadvantage of the prior art producing apparatus so arranged that substantially all of the light rays constituting the beam emitted therefrom are prevented from deviating from the axis or normal direction of propagation of the light source more than a predetermined amount.
The principal immediate use for the present invention is in connection with transfer machines of the general type disclosed in my copending applications Serial No. 130,647 which issued August 29, 1939 as Patent No. 2,170,895, and my co-pending application Serial No. 184,180, which issued August 29, 1939 as Patent No. 2,170,896. Accordingly, in the accompanying drawings I have illustrated certain embodiments of my invention as adapted for use with transfer machines of this general type. It will be understood, however, that the invention is not necessarily limited to any particular type of transfer machine.
In the drawings Figure 1 is a fragmentary perspective view illustrating certain of the structural features of a transfer machine having embodied therein a light source in accordance with the present invention;
Figure 2 is a plan view of the light source constituting a part of the machine of Figure 1;
Figure 3 is a plan view, partially in section, of one of the pressure securing members and the support therefor constituting a part of the machine of Figure 1;
Figure 4 is a sectional view on the general line 44 of Figure 5;
Figure 5 is a sectional view on the general line 55 of Figure 4; and
Figure 6 is a sectional view similar to Figure 5 illustrating a modified form of the invention.
The transfer machine illustrated in the drawings is designed primarily for use in conjunction with printing cylinders. It includes a pair of vertically adjustable bearings Ill carrying the journals 12 at the opposite ends of a printing cylinder, as illustrated at II. The cylinder 'II is thereby rotatably supported about its longitudinal axis in tangential contact with the upper surface of a glass plate I! which serves as a support or carrier for the transparencies, indicated generally at 15, which bear the design or pattern to be transferred to the printing cylinder. The transparency carrier plate I3 is supported so as to be rectilinearly movable in a generally horizontal plane from one end of the machine to the other while in tangential contact with the structures can be overcome by the use of a light 5 cylinder. The various structural details of a machine of this character are illustrated in my co-pending application Serial No. 184,180, no Patent No. 2,170,896.
To make possible the photographic transfer of the design or pattern formed in the transparencies to the cylinder, the outer surface of the printing cylinder, in accordance with one commercially successful procedure, is coated with a suitable sensitized resist prior to the transfer operation. The usual commercial re- Bist coating will have a thickness when dry of the transparency carrier plate l3 and the transparencies I! carried thereon onto the resist coated cylinder ll along the line of tangential contact. At the same time, the transparency carrier plate I3 is slowly traversed with rectilinear movement from one end of the machine to the other. The friction along the line of tangential contact between the resist coated cylinder I I and assess:
the transparencies I! located on the carrier plate l3 causes this rectilinear movement of the carrier plate l3 to produce rotation of the cylinder H at a peripheral speed exactly equal to the speed of movement of the carrier plate, as explained in my application Serial No. l84,180. The rate of movement of the carrier plate l3 during this traversing operation is, of course, determinative of thelength of exposure of the resist and may be readily adjusted within any reasonable limits.
To obtain accurate transfer of the design or pattern formed in the transparencies I! to the sensitized resist coating on the cylinder H, it appears necessary that there shall be very intimate contact between the surface of the transparencies l5 carried on the transparency support plate l3 and the cylinder during the transfer operation. Because of ordinary dimensional differences, the obtaining of this intimate contact requires contact pressures along the line of tangential contact of the order of 8 to 10 pounds per linear inch. At the same time. due to the practical necessity of using glass for the transparency carrier plate l3, this pressure must be secured without unduly stressing the plate l3. The presser member I! illustrated particularly in Figures 3 and 4 constitute a pressure securing means which fully meets these requirements.
Each of the presser members I! comprises an elongated structural section, preferably of fiber, for slidably engaging the under surface of the transparency carrier plate I3 with an anti-friction bearing engagement. Because of the considerable length of the presser members I! and the relatively heavy pressures which they must exert, those members are supported at intervals along their length by means of a plurality of uniformly spaced support arms 2|. For reasons which will hereinafter appear, it is desirable that the presser members l'l shall be adjustable toward and away from each other in order that the width of the slot 22 formed therebetween can be varied. Means such as the slot and screw connections 24 between the presser members l1 and the inner ends of the support arms 2| can be used for this purpose.
The support arms 2| are pivotally supported intermediate their ends by two suitably positioned shafts 23 which extend transversely of the machine, and to prevent bending, the shafts 23 are supported intermediate the arms 2i by bearing blocks 25 rigidly attached to the frame of the machine, not shown. The outwardly pro- .iecting end'of each of the support arm; 2| is biased to bring the associated presser member into contact with the under surface of the transparency support plate I3 by a spring 21. as is illustrated in Figure 4, or by other equivalent means.
Through the use of the support arms 2| located at spaced intervals along the length of the presser members II, it is possible to obtain high, uniform contact pressure between the upper surface of the transparencies I! carried on the carrier plate l3-and the surface of the cylinder Ii along the line of tangential contact. Further, since the line of application of the force exerted by the presser members I! is located only a short distance at either side of the line of tangential contact, the transparency carrier plate I3 is sub- .jected to only relatively slight bending stresses during the transfer operation. It is desirable that stop means shall be provided for limiting the upward movement of the presser members 2| in order to minimize any possibility of breaking the transparency carrier plate l3 when the cylinder II is lifted from the contact position.
The light producing apparatus 29, with which the present invention is particularly concerned, includes. as illustrated particularly in Figures 2, 4, and 5, a downwardly flaring light hood 3i and a unitary reflector structure 33 having openings 35 in the side wallsthereof for receiving cooperating pairs of carbons 31 of a plurality of automatic arc lamps. The bottom of the light hood 3| is open and is so proportioned that it aligns with the open top of the reflector structure 33, thereby providing a light directing enclosure for the arc lamp. The top of the light hood 3| is provided with an elongated, relatively narrow slot aperture 33 which is adapted to align with the line of tangential contact between the printing cylinder H and the transparency carrier plate l3. Usually this aperture 39 will have a width of about to The unitary reflector structure 33 illustrated in the drawings is generally rectangular in outline and is provided with flve reflector sections 4|, each of which is arranged to cooperate with the are formed between one of the pairs of carbons 31. Any desired number of reflector sections may, of course, be used, and the reflectors may be of any suitable shape. In the structure illustrated in the drawings the individual reflectors are approximately parabolic longitudinally and approximately elliptic transversely. and the complete reflector structure comprises a bronze alloy casting of hollow wall construction in order that water or other cooling fluid mav be circulated therethrough.
During the transfer operation, an arc will be established and maintained between each of the cooperating pairs of carbons 31 by automatic mechanisms, not illustrated, and the light from these arcs will be directed by the reflectors 4| and the light hood 3| through the slot aperture 39 as a narrow beam of very high unit density. Since the slot aperture 39 aligns with the slot 22 between the presser members H and the line of tangential contact between the cylinder H and the transparencies l carried on the carrier plate l3, this narrow beam after passing through the transparencies will impinge upon the resist coating of the cylinder ll coincident with the line of tangential contact between the transparencies and the cylinder. The spacing of the presser members I! will determine the width of the beam.
In the prior art apparatus, the light source was so arranged that the beam of light emitted therefrom included large numbers of rays having their axes of propagation angularly disosed through wide angles with respect to the normal axis of propagation to the light source, i. e. the beam from the light source included large numbers of rays which impinged upon the under surface of the transparency support at various angles of incidence from small angles to angles approximating the normal to that surface (90). Light sources of this character, as stated previously, inherently produce inaccurate transfer of small opaque areas in the transparencies to the resist coating on the printing cylinder, and under certain circumstances result in the complete elimination of such areas during the transfer operation, a very serious matter when the transparency consists entirely of a plurality of dot sized images such as is the case following certain of the commercial procedures.
I have found, however, that if the light source is provided with means so arranged that the light beam emitted from the light source includes substantially no rays which diverge from the normal axis of propagation of the light source beam more than about 60, 1. e. if the beam contains substantially no rays incident upon the under surface of the transparency carrier plate (and. the cylinder) along the line of tangential contact at an angle of incidence less than 30, this difficulty will be overcome to a considerable extent, and a reasonably accurate transfer of the small areas will be effected. This 60 deviation (or 30 incidence) is in the nature of a limiting figure, and the better results are obtained when the deviation is limited to a value smaller than 60. Apparently the smaller the angle of deviation the better the results.
While it is probable that various means can be employed for producing a light beam having the above stated characteristics, the means which I have found most satisfactory consists in the provision of a plurality of bafiies 43 located transversely of the reflectors 4| and light hood 3|, as illustrated in Figures 4, 5, and 6 of the drawings. The effect of these baffles is to confine the individual light rays which constitute each of the secondary beams, produced by the individual light source-reflector combinations, within a single solid angle of such dimensions that few, if any, of these rays will diverge from the normal axes of propagation of the secondary beams (indicated by the lines 41 in Figure 6) more than 60. The axes 41 of the secondary beams are, of course, parallel with the normal axis of propagation of the combined beam. When apparatus of this character is properly located with respect to the transparency carrier plate and the cylinder, that is, with the normal axis of propagation thereof substantially perpendicular to the plane of the under surface of the transparency support plate and with the slot 39 in substantial register with the line of tangential contact between the transparencies and the cylinder, the beam produced by such apparatus will meet the requirements enumerated above.
The construction of Figure 6.is illustrative of apparatus wherein the deviation of the individual rays constituting the light beam reaches the maximum permissive amount. In the construction illustrated in this figure, the axis of propagation of the beam as a whole and ofeach of the secondary beams produced by the individual light source-reflector combinations is substantially perpendicular to the under surface of the transparency carrier plate l3. Further, the length of the baflles 43 is such that all of the rays constituting each of the secondary beams produced by the individual light source-reflector combinations, and hence all of the rays constituting the beam produced by the entire apparatus as a whole, contain few, if any, rays incident upon the under surface of the transparency carrier plate at angles smaller than 30. If the baffles 43 are shorter than illustrated in Figure 6 the advantages of the invention in minimizing the reduction or loss of small opaque areas during the transfer operation will not be attained.
For the maximum benefit, however, it appears that the light source must meet a further requirement. Particularly, when the apparatus comprises a plurality of light source-reflector combinations arranged side by side, as illustrated in Figures 5 and 6, it is necessary not only that the beam produced by each reflector-light source combination and the beam produced by the ap paratus as a whole shall contain no rays incident upon the under surface of the transparency carrier plate at angles less than 30 (i. e. shall contain no rays which deviate from the axis of propagation of the beam more than but also that the secondary beams produced by adjacent reflector-light source combinations shall be confined within a solid angle which overlaps exactly one-half of the distance which is illuminated by the next adjacent reflector-light source combination. Stated somewhat differently, this means that the length of the baffles 43 must be such, relative to the proportions of the individual reflectors and the spacing between the reflectorlight source combinations and the under surface of the transparency support plate, that the rays of maximum deviation emitted from each light source-reflector combination shall intersect the under surface of the transparency support plate substantially conincident with the point of intersection of the axis of propagation of the next adjacent light source-reflector combination.
Apparatus satisfying this last requirement is illustrated in Figure 5 where the lines 49 are representative of the solid angles within which each of the secondary beams produced by the light source-reflector combinations is confined by the baffles 43, and the lines 5| are illustrative of the axes of propagation of the individual light source-reflector combinations. The provision of an apparatus meeting the basic requirement (i. e. having no beam deviating from the axis of propagation more than 60), and also the requirement just described. necessarily involves an accurate correlation of the proportions of the reflectors 4|, the length of the baffles 43, and the spacing between the reflector-light source combinations and the under surface of the transparency support plate 13. Regardless of whether or not the full refinements of the Figure 5 structure are used, it is desirable to minimize the deviation of the constituent rays of the secondary and complete beams from the axis of propagation thereof as much as possible (i. e. to maximize the angle of incidence of the constituent rays). At the same time, to secure the best possible results the baflles should be so proportioned that each unit of length along the line of tangential contact is illuminated by two, and two only, of the individual light source-reflector combinations, as illustrated in Figure 5 and described above.
In a specific example of the Figure 5 construction, each of the reflectors had a dimension F of approximately 6 inches and a dimension at right angles to the F dimension of about 12 inches. The carbons 31 were located so that the arcs drawn therebetween were approximately inches from the upper surface of the transparency carrier plate l3, and the baffles 43 extended to within 5 inches of the upper surface of the carrier plate IS. The slot aperture 22 in this embodiment of the invention had a length of 50 inches and a width of .010 inch, and the bailles had a thickness of approximately .06 inch. The light emitted from the slot aperture during the operation of the apparatus was found to include no ray deviating from the normal axis of propagation of the light source more than about 59, or what is the same thing, no ray incident upon the under side of the transparency carrier plate l3 along the line of tangential contact between the transparencies and the printing cylinder at an angle of incidence less than about 31. Further, the dimensions of the various structural elements of the light source are so correlated that each unit of length along the line of tan gential contact is illuminated by two, and two only, light source-reflector combinations, as illustrated in Figure 5.
In the foregoing I have described the features of an improved light source or light producing apparatus for use in transfer apparatus of the general type wherein a design or pattern to be printed is photographically transferred to the resist covering for a printed plate or cylinder prior to the etching of such plate or cylinder. It will be understood that various light producing apparatus may be evolved utilizing the principles which Ihave disclosed in the foregoing, and also that light producing apparatus according to my invention may be used in conjunction with various types of transfer machines. It is my desire, therefore, that the accompanying claims shall be accorded the broadest reasonable construction consistent with the language appearing therein and the prior art.
I claim the following as my invention:
1. In a transfer machine of the class described, in combination, a generally that transparency carrier plate supported for rectilinear movement in a plane substantially coincident with the surface thereof, a transparency having opaque areas of variable size depending upon tonal range supported on said transparency carrier plate, means for rotatably supporting a sensitized coated printing roll in contact with said transparency, said printing roll being rotated on rectilinear movement of said transparency carrier plate, means, which includes a plurality of light source-reflector combinations arranged size by side, for directing a narrow concentrated beam of light onto and through a narrow elongated portion of said transparency carrier plate, and means for so confining the light produced by each of said light source-reflector combinations that each unit of length along the illuminated portion of said carrier plate is illuminated by two, and two only, of said light source-reflector combinations, said light confining means preventing substantial reduction in size of said opaque areas in the transparency on transfer thereof,
2. In a transfer machine of the class de scribed, in combination, a generally flat transparency carrier plate supported for rectilinear movement in a plane substantially coincident with the surface thereof, a transparency having opaque areas of variable size depending upon tonal range supported on said transparency carrier plate, means for rotatably supporting a sensitized coated printing roll in contact with said transparency, said printing roll being rotated on rectilinear movement of said transparency carrier plate, means, which includes a plurality of light source-reflector combinations arranged side by side, for directing a narrow concentrated beam of light onto and through a narrow elongated portion of said transparency carrier plate, and baiile means for so confining the light produced by each of said light sourcereilector combinations that the light rays of maximum deviation emitted from each light source-reflector combination intersect the surface of said transparency carrier plate substantially coincident with the point of intersection of the normal axis of propagation of the next adjacent light source-reflector combination, said baflle means preventing substantial reduction in size of said opaque areas in the transparency on transfer thereof.
CHARLES L. HENDERSON.