US3668032A

US3668032A - Method of making a flexible letterpress mat

Info

Publication number: US3668032A
Application number: US83737A
Authority: US
Inventors: Charles W Bunting; David P Groeber; Louis W Pettlo
Original assignee: Mccall Corp
Current assignee: Mccall Corp
Priority date: 1967-08-28
Filing date: 1970-10-26
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: GB1217889A; US3568595A; DE1761932A1

Abstract

A first portion of a sheet of thermoplastic material is placed on the face of an engraved master plate, and the plate and sheet are positioned between the platens of a hydraulic press. The first portion of the sheet and the master plate are pre-heated and are then pressed together to mold an impression of the face within the first portion of the sheet. The master plate and sheet portion are cooled while the pressure is maintained, after which the pressure is released and the sheet is shifted laterally a precise predetermined distance relative to the master plate while maintaining the angular orientation of the sheet, to position a second portion of the sheet over the face of the master plate. The steps of pre-heating, pressing, cooling and releasing are then repeated to produce a flexible mat having a pair of identical impressions in precise spaced relation and corresponding angular orientation. One or more metal layers are electrolytically deposited on the mat, and the resulting thin sheet of deposited metal is separated from the mat and laminated to a pre-curved reinforcing plate which is trimmed along its edge.

Description

United States Patent Bunting et a1.

[ 1' June 6, 1972 [54] METHOD OF MAKING A FLEXIBLE LETTERPRESS MAT [72] Inventors: Charles W. Bunting; David P. Groeber;

Louis W. Pettlo, all of Dayton, Ohio [73] Assignee: McCall Corporation, New York, NY.

[22] Filed: Oct. 26, 1970 [21] Appl. N0.: 83,737

Related US. Application Data [62] Division of Ser. No. 663,858, Aug. 28, 1967, Pat. No.

3,532,587 10/1970 Ungar et a1. ..l56/249 X Primary Examiner- Carl D. Quarforth Assistant Examiner-Stephen J. Leche'rt, J r. Attorney-Marechal, Biebel, French & Bugg [57] ABSTRACT A first portion of a sheet of thermoplastic material is placed on the face of an engraved master plate, and the plate and sheet are positioned between the platens of a hydraulic press. The first portion of the sheet and the master plate are pre-heated and are then pressed together to mold an impression of the face within the first portion of the sheet. The master plate and sheet portion are cooled while the pressure is maintained, after which the pressure is released and the sheet is shifted laterally a precise predetermined distance relative to the master plate while maintaining the angular orientation of the sheet, to position a second portion of the sheet over the face of the master plate. The steps of pre-heating, pressing, cooling and releasing are then repeated to produce a flexible mat having a pair of identical impressions in precise spaced relation and corresponding angular orientation. One or more metal layers are electrolytically deposited on the mat, and the resulting thin sheet of deposited metal is separated from the mat and laminated to a pre-curved reinforcing plate which is trimmed along its edge.

4 Claims, 10 Drawing Figures PATENTEUJUH 6 I972 SHEET B) W, 7 Mi CHARLES W. HUNTING, DAVID P. GROEBER 8 LOUIS W. PETTLO 1 METHOD or MAKING A FLEXIBLE LETIERPRESS MAT RELATED APPLICATIONS BACKGROUND OF THE INVENTION In the production of part-cylindrical plates for mounting on the rolls of a letterpress, a flexible matrix or mat is made by first pre-heating a flat original engraved plate within a device commonly referred to as a clamshell having internal passageways through which a heating fluid such as steam is circulated. After pre-heating, the engraved plate is removed from the clamshell and a sheet of vinyl is placed on the mat with an overlay of a resilient blanket, and the sandwiched assembly of the plate, vinyl sheet and blanket is inserted within a hydraulic press where substantial pressure is applied to mold in the vinyl sheet an impression of the engraved plate. The sheet and the engraved plate are then cooled within the press while pressure is maintained to form a flexible vinyl mat. One or more metal layers are electrolytically deposited on the mat and the thin sheet of deposited metal is then separated from the vinyl sheet to form a flexible electrotype which is laminated to a pre-curved reinforcing mat and this laminated assembly is trimmed to form the letterpress plate.

It has been found desirable to avoid the transfer operation of the pre-heated engraved plate from the clamshell to the high pressure press after adding the vinyl sheet and blanket to increase efficiency in producing a mat and to avoid heat loss from the plate during the transfer. Furthermore, for efficiently printing some smaller books or magazines, it is frequently desirable to form a mat having a pair of identical impressions in precise registration for producing a two-on letterpress plate on which two impressions are spaced circumferentially in relation to the roll of the letterpress on which the plate is mounted.

SUMMARY OF THE INVENTION The present invention is directed to an improved method and apparatus for efficiently producing a flexible vinyl mat and which is especially suited for forming a two-on mat or a four-on mat having corresponding pairs of identical impressions all in precise registration. Thus the method and apparatus of the invention provide for efficiently constructing either two-on or four-on letterpress plates and thereby substantially reduce the time required to mount and align a set of plates on the plate cylinders of the letterpress for a particular printing job.

According to a preferred embodiment of the invention, a two on mat is produced by securing an engraved master plate to the center section of a flat lower press member which slidably supports a U-shaped frame to which is secured a sheet of vinyl. Cooling fluid is circulated through passageways fonned within each end section of the press member and cooling and heating fluid are alternately circulated through a passageway within the center section directly under the engraved plate.

The lower press member, master plate and the vinyl sheet are carried into a hydraulic press where a portion of the vinyl sheet is held in light contact with the engraved face of the master plate by a resilient blanket mounted on an upper press member while the master plate and vinyl sheet are pre-heated by circulating steam through the center section of the lower press member. After the master plate reaches a predetermined temperature, the sheet of vinyl is pressed against the engraved face of the plate by raising the lower press member toward the upper press member.

As the high pressure is being applied, cool water is circulated through the center section of the lower press member in place of the steam to cool the corresponding portion of the vinyl sheet while the remaining portion of the vinyl sheet is maintained cool by the water being circulated through the adjacent end section of the lower press member. After one impression is made in the vinyl sheet, the sheet is shifted a predetermined distance by sliding the frame laterally and a second impression is formed within the vinyl sheet by repeating the above procedure. As a result, two identical impressions can be quickly formed within the'sheet with the impression disposed in precise registration.

Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of apparatus for forming a flexible mat in accordance with the invention; 1

FIG. 2 is a perspective view of a vinyl sheet and the upper and lower press members forming a part of the apparatus shown in FIG. 1;

FIG. 3 is a plan view of the lower press member with two engraved plates mounted thereon;

FIG. 4 is an elevation view of the upper and lower press members as taken generally on the line 4-4 of FIG. 3;

FIG. 5 is a section of the lower press member taken generally on the line 5-5 of FIG. 3;

FIG. 6 is a side elevational view of the upper press member and a section of the lower press member taken generally on the line 66 of FIG. 3;

FIG. 7 is a schematic flow diagram showing the circulation of heating and cooling fluid throughthe lower press;

' FIG. 8 is a view of a typical mat formed in accordance with the invention and having two sets of two-on impressions;

FIG. 9 is a fragmentary section of the lower press member as taken generally on the line 99 of FIG. 5; and

FIG. 10 is an enlarged fragmentary section as taken on the line 10-10 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a hydraulic molding press 15 of the type manufactured by Ostrander-Seymour Company, Melrose Park, Illinois, and generally includes a base 16 which supports a table 18 movable horizontally between an extended position (FIG. 1) and a retracted position (not shown) under a head portion 20 where the table is moved vertically by a hydraulic cylinder (not shown) mounted on the base 16. An automatic recorder controller 22 is mounted on the head portion 20 and is connected to control the horizontal and vertical movements of the table 18 in accordance with a pre-selected temperature sequence as explained later.

In accordance with the invention, a lower press member 25 in the form of a rectangular plate is mounted on the upper surface of the table 18. The press member 25 includes a base portion 26 (FIG. 6) having a pair of parallel spaced slots 28 (FIG. 5) which divide the base portion 26 into a pair of end sections 29 on opposite sides of a center section 30. A strip 32 of insulation material, such as a strip of polytetrafluorethylene, is mounted within each of the slots 28 as shown in FIG. 10.

The base section 26 of the press plate 25 is provided with a longitudinal flat edge surface 34 (FIG. 6) to which an edge portion 35 is secured by a series of screws 36. A longitudinally extending slot 38 of rectangular cross section is formed within the edge section 35 having the surface 34 as one side, and a corresponding parallel spaced slot 39 formed within the base portion 26. A U-shaped frame 45 (FIG. 3) includes a pair of parallel spaced legs 46 which are slidably mounted within the

corresponding slots

38 and 39 within the press member 25. The legs 46 are rigidly connected by a bar 48 and each leg is provided with a longitudinally extending slot 49.

A threaded stud 55 (FIGS. 3 and 6) extends through the base portion 26 and has an inner end portion 56 which is received within the corresponding slot 49. Another threaded stud 55 extends through the edge portion 35 of the lower press member 25 and has an inner portion 56 received within the slot 49 of the other leg 46 so that the studs 55 cooperate to retain the frame 45 on the lower press member 25. A lock nut 58 is mounted on each of the studs 55 for securing the studs rigidly to the lower press member after it is properly adjusted.

A vertically extending pin 60-(FIG. 3) is mounted on the end portion of each leg 46 of the frame 45, and a pair of L- shaped stop members 62 are mounted on one end of the press member 25 by screws 63 and extend into the

slots

38 and 39 for engaging the end surfaces of the legs 46 and thereby limit the movement of the frame 45 to the right (FIG. 3). The studs 55 limit the movement of the frame to the left.

' Referring to FIGS. and 10, the center section 30 of the lower press member 25 has a flat top surface 65 which is spaced slightly below the corresponding top surface 66 of the adjacent end sections 29 and forms a recess between the insulation strips 32 for receiving two originalor master plates P, and P each having an engraved face. Each master plate is secured to the center section 30 by a pair of screws 68 and the engraved face of each master plate projects slightly above the top surfaces 66 of the end sections 29 by approximately 0.010 inch.

Referring to FIG. 9, each end section 29 and the center section 30 of the press member 25 is provided with a series of parallel spaced passageways 70 which extend laterally between the

slots

38 and 39 and are connected on opposite ends by longitudinally extending passageways 72. A series of plugs 74 are press-fitted into the passageways 72 and a series of threaded plugs 76 close the corresponding ends of the passageways 70 to form a serpentine-like flow path between an inlet port 77 and an outlet port 78. Referring to FIG. 6, the inlet and outlet ports are formed within the press member 25 under the rail 39 and are connected to the adjacent passageways 72 by short vertically extending passageways 80 (FIG. 6) which are closed at the bottom of the press member by corresponding plugs 82.

Referring to FIG. 7, the inlet ports 77 of the end sections 29 of the press member 25 are connected by lines 85 to a water supply line 86 through a flexible line 87 and including a manual shutofi valve 88. The discharge ports 78 of each end section 29 are connected by

lines

90 and 91 through a flexible line 92 to a drainline 94 having a check valve 95. The inlet port 77 of the center section 30 of the press member 25 is connected by a line 97 and a flexible line 98 to a steam supply line .100 in which is mounted solenoid control valve 102, a manual shutoff valve 103, a pressure gage 104 and a pressure regulator l05..The lines- 97 and 98 are also connected to a water supplyline 108 having a check valve 109, a solenoid controlled valve 110 and a manual shutoff valve 111. The water supply line 108 connects with the .water supply line 86.

- The outlet port'78 of the center section 30 is connected by a line 1 15 and flexible line 116 to a drain line 1 18 which is normally connected to the drain line 94 through a three-way solenoid controlled valve 120. A condensate line 122 connects the valve 120 to the drain' line 94 on the opposite side of the check valve 95 and is provided with a strainer 124, a steam trap 125 and a check valve 126. The solenoid controlled valves 102, I and 120 are actuated by the recorder controller 22 which is controlled by a thennocouple 130 mounted within the center section 30 of the press member 25. Leads 132 connect the thermocouple 130 to the controller 135.

Referring to FIGS. 2, 4 and 6, a stationary upper press member 140 in the form of a rectangular plate, is mounted within the head 20 of the press and is disposed directly above the center section 30 of the lower press member 25 when the table 18 is retracted. The upper press member 140 includes end mounting flanges 141 and may be provided with internal passageways 142 (FIG. 6) corresponding to the '

passageways

70 and 72 within the center section 30 of the lower press member 25, for heating and cooling the upper press member simultaneously with the center section 30. Ex-

perimentation has shown, however, that the additional heating 'andcooling of the upper press member 140 is not necessary to obtain satisfactory performance of the apparatus.

A resilient rectangular blanket 145, preferably of a rubberfabric material and having a uniform thickness, extends over the bottom flat surface 146 of the upper press member 140. The blanket has opposite end portions which extend into corresponding grooves 148 formed within the preset member and the end portions are secured by corresponding clamping bars 149.

To produce a mat with the apparatus constructed in accordance with the invention, a sheet 155 (FIGS. 2 and 3) of thermoplastic material such as vinyl and having a pair of prepunched holes 156, is mounted on the frame 45 so that the pins 60 project into the holes 156. The valve 88 is opened so that cooling water is continuously circulated through the end sections 29 of the lower press member 25 thereby cooling the top surfaces 66 of the end sections 29.

The recorder controller 22 is manually actuated to initiate a predetermined cycle which begins with retracting the table 18 under the head 20. The table 18 and lower press member 25 are then moved upwardly with relatively light pressure so that the sheet 155 of vinyl lightly contacts the blanket 145 on the upper press member 140 and is thereby held in light contact with the engraved faces of the master plates P, and P When the table is retracted, it actuates a switch which opens the solenoid controlled valve 102 and closes the valve 110. When the controller 22 senses a temperature rise through the thermocouple 130, valve is actuated to connect return line 118 to the condensate line 122 so that steam is circulated through the center section 30 of the lower press member 25 which raises the temperature of the master plates P, and P, and the overlying portion of the vinyl sheet 155.

When the center section 30 of the lower press member 25 reaches a predetermined curing temperature, which can be adjustably set, the thermocouple signals the controller 22 which energizes the hydraulic cylinder within the press 15 so that it applies full force upwardly on the table 18. As a result, the engraves faces of the plates P, and P are pressed into the vinyl sheet thereby producing corresponding impressions I, and I within the sheet as illustrated'in FIG. 8 on the righthand portion of the sheet 155.

Substantially simultaneously with the: application of full pressure on the lowerpress member 25 against the upper press member 140, which produces a force on the order of twelve tons, therecorder controller 22 closes the valve 102, opens the valve 1 10 and actuates the valve 120 so that the line 1 18 is connected directly to the drain line 94. Thus the temperature of the center section 30 of the lower press member 25 and the master plates P, and P and the vinyl sheet 155 begins to drop. When the temperature of the center section 30 reaches a predetermined lower limit, which can be adjustably set, the thermocouple 130 signals the controller 22 which actuates the hydraulic cylinder in the press 15 to lower the table 18 and thereby release the pressure between the upper and lower press member, after which the table 18 automatically returns to its extended position as shown in FIG. 1.

After one set of impressions I and I, are formed within the vinyl sheet 155 from the master plates P, and P,, the frame 45 and sheet 155 are moved to the right (FIG. 3) until the ends of the legs 46 engage the stop members 62. In this position, the right-hand portion of the vinyl sheet 155 which has the impressions I, and I is positioned adjacent the top surface 66 of the right end section 29 of the lower press member 25 and the left end portion of the sheet is positioned over the engraved faces of the master plates P, and P The recorder controller 22 is actuated again so that the operational steps of the cycle described in the preceding paragraphs are repeated automatically which results in producing a sheet 155 having another set of impressions I and I, (FIG. 8) in precise registration to the corresponding first set of impressions I, and I The sheet 155 is then cut or sheared along the line to produce two mats each having a pair of identical impressions in precise registration. Each mat is then used to produce atwo-on letterpress plate using the same procedure as mentioned above for producing a plate with a single impression. That is, one or more metal layers are electrolytically deposited on each mat. The resulting thin sheet of deposited metal is separated from the mat to form a flexible electrotype which is laminated to a pre-curved reinforcing mat or plate. The plate is then trimmed to form a letterpress plate.

From the drawings and the above description, it can be seen that the apparatus and method for producing a mat in accordance with the invention provides several desirable features and advantages. For example, by connecting the center section 30 of the lower press member 25 to corresponding water and steam supply and discharge lines having automatically controlled valves, the center section 30 may be heated within the press for pre-heating the master plates and the vinyl sheet and then cooled while-full pressure is applied between the press members to produce a mat without requiring the transfer of .the master plate from a pre-heating clamshell to a molding press. As a result, the time required for forming an impression within the vinyl sheet is significantly reduced. In addition, the cooling under pressure prevents shrinkage of the image.

The slidable frame 45 and its cooperation with the three section lower press member 25 also provide important features of the invention. That is, the frame 45 provides for shifting the vinyl sheet 155 by a precise predetermined distance after one impression is made so that a second identical impression can be formed within the sheet in precise registration with the first impression. The continuous cooling of the end sections 29 is effective to prevent the adjacent portion of the overlying half portion of the vinyl sheet from being heated when the other half portion is being heated and pressed against the face of the master plate, and thereby prevents warping and distortion of the adjacent portion of the vinyl sheet.

Instead of producing two two-on mats as shown in FIG. 8, it can be seen that the master plates P and P could be formed integrally or rigidly connected with the corresponding engraved faces in precise registration so that a four-on" mat could be produced with all of the impressions in precise registration. A typical application for a four-on mat would be for producing a letterpress plate having two-on" double page impressions. By providing an automatic control system as shown I in FIG. 7 for circulating steam or water through the center section 30 of the lower press member 25, and controlling the operation of the system by a then'nocouple which senses the temperature of the center section 30, each mat receives the same treatment so that the impressions on each mat of a color set will have precisely the same registration and thereby substantially reduces the time for mounting and positioning the plates on the plate cylinders of the letterpress.

While the method herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise method, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

l. A method of making a multiple impression letterpress plate, comprising the steps of positioning a first portion of a sheet of thermoplastic material in overlying relation with an engraved-like face of a master plate, positioning said master plate and the overlying first portion of said sheet between first and second press members of a reciprocating press, preheating said master plate and said first portion of said sheet to a predetermined temperature, moving said first and second press members together to effect pressing of said first portion of said sheet with a predetermined pressure against said face of said master plate to mold an impression of said face within said first portion of said sheet, cooling said master plate and said first portion of said sheet, moving said first and second press members apart for releasing said pressure, shifting said sheet laterally a predetermined distance relative to said master plate while maintaining precise angular orientation of said sheet relative to said masterplate for positioning a second portron of said sheet in overlying relation withsaid face of said master plate, repeating said pre-heating, pressing, cooling and releasing steps to fonn a mat having a pair of identical impressions in precise spaced relation and corresponding angular orientation and with each impression conforming to said face of said master plate, coating metal onto said mat to form a layer of metal corresponding to the impressions on said mat, separating said layer of metal from said mat to form a metal sheet having a corresponding pair of identical impressions, and laminating said metal sheet to a curved reinforcing plate.

2. A method as defined in claim 1 including the step of holding said sheet of thermoplastic material in light contact with said face of said master plate during said preheating by lightly pressing said second press member toward said first press member to effect said pre-heating said sheet of thermoplastic material.

3. A method as defined in claim 1 wherein said master plate and each portion of said sheet are pre-heated by circulating heating fluid through a passageway formed in said first press member, and said master plate and each portion of said sheet are cooled by circulating cooling fluid through said passageway in place of said heating fluid.

4. A method as defined in claim 1 including the steps of cooling said second portion of said thermoplastic sheet during said pre-heating, pressing and cooling of said first portion of said sheet to prevent warping of said second portion of said sheet, and cooling said first portion of said sheet while preheating, pressing and cooling of said second portion to prevent warpingof said first portion of said sheet.

Claims

1. A method of making a multiple impression letterpress plate, comprising the steps of positioning a first portion of a sheet of thermoplastic material in overlying relation with an engravedlike face of a master plate, positioning said master plate and the overlying first portion of said sheet between first and second press members of a reciprocating press, preheating said master plate and said first portion of said sheet to a predetermined temperature, moving said first and second press members together to effect pressing of said first portion of said sheet with a predetermined pressure against said face of said master plate to mold an impression of said face within said first portion of said sheet, cooling said master plate and said first portion of said sheet, moving said first and second press members apart for releasing said pressure, shifting said sheet laterally a predetermined distance relative to said master plate while maintaining precise angular orientation of said sheet relative to said master plate for positioning a second portion of said sheet in overlying relation with said face of said master plate, repeating said pre-heating, pressing, cooling and releasing steps to form a mat having a pair of identical impressions in precise spaced relation and corresponding angular orientation and with each impression conforming to said face of said master plate, coating metal onto said mat to form a layer of metal corresponding to the impressions on said mat, separating said layer of metal from said mat to form a metal sheet having a corresponding pair of identical impressions, and laminating said metal sheet to a curved reinforcing plate.

4. A method as defined in claim 1 including the steps of cooling said second portion of said thermopLastic sheet during said pre-heating, pressing and cooling of said first portion of said sheet to prevent warping of said second portion of said sheet, and cooling said first portion of said sheet while pre-heating, pressing and cooling of said second portion to prevent warping of said first portion of said sheet.