Abstract:
An infra-red dryer utilizes high velocity air jets which scrub and break up the moist air layer which clings to the surface of a freshly printed and/or coated sheet. The high velocity air jets are directed through multiple air flow apertures across an array of infra-red lamps onto the freshly printed and/or coated sheets. An extractor exhausts the moisture-laden air from an exposure zone while short wave infra-red radiation heats the ink and/or protective coating. The effective exposure to pressurized air is increased by the air jets which produce a balanced pressure air blanket along the sheet travel path. The moist air layer is displaced from the printed and/or coated sheet and is extracted from the press as the sheet moves through the exposure zone.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 08/116,711 filed Sep. 3, 1993 now U.S. Pat. No. 5,537,925. 
    
    
     FIELD OF THE INVENTION 
     This invention is related generally to accessories for sheet-fed, rotary offset printing presses, and in particular to a dryer for printed materials which utilizes infra-red radiant heat, forced air flow and extraction. 
     BACKGROUND OF THE INVENTION 
     In the operation of a rotary offset press, an image is reproduced on a sheet of paper or some other print stock by a plate cylinder which carries the image, a blanket cylinder which has an ink transfer surface for receiving the inked image, and an impression cylinder which presses the paper against the blanket cylinder so that the inked image is transferred to the paper. In some applications, a protective and/or decorative coating is applied to the surface of the freshly printed sheets. The freshly printed sheets are then conveyed to a sheet delivery stacker in which the finally printed sheets are collected and stacked. 
     The wet ink and coatings should be dried before the sheets are stacked or run back through the press for a second pass, to prevent smearing defects and to prevent offsetting of the ink on the unprinted side of the sheets as they are stacked. Spray powder has been applied between the freshly printed sheets which are to be stacked to improve sheet handling and to separate one delivered sheet from the next sheet to prevent offsetting while the ink and/or coating dries. One limitation on the use of spray powder is that fugitive particles of the spray powder disperse into the press room and collect on press equipment, causing electrical and mechanical breakdowns and imposing a potential health hazard for press room personnel. 
     DESCRIPTION OF THE PRIOR ART 
     Hot air convection heaters and radiant heaters have been employed to reduce the volume of spray powder applied, except for the small amount needed for sheet handling purposes. Hot air convection heaters are best suited for slow to moderate speed press runs in which the exposure time of each printed sheet to the hot air convection flow is long enough that aqueous base inks and coatings are set before the sheets reach the stacker. 
     For high-speed press operation, for example, at 5,000 sheets per hour or more, the exposure time of each printed sheet as it passes through the dryer station is not sufficient to obtain good drying by convection flow alone. Radiant heaters such as infra-red heat lamps provide greater drying efficiency because the short wave length infra-red energy is preferentially absorbed in the liquid inks and coatings to provide rapid evaporation. The infra-red radiant energy releases water and volatiles from the ink and/or coating. Consequently, a humid air layer clings to the printed surface of the sheet as it moves through the dryer, and will be trapped between adjacent sheets in the stack unless it is removed. 
     As press speed is increased, the exposure time (the length of time that printed sheet is exposed to the radiant heat) is reduced. Consequently, the output power of the radiant lamp dryers has been increased to deliver more radiant energy to the printed sheets in an effort to compensate for the reduction in exposure time. 
     The higher operating temperatures of the high-powered lamps cause significant heat transfer to the associated printing unit, coater and press frame equipment, accelerated wear of bearings and alterations in the viscosities of the ink and coating, as well as upsetting the water balance of aqueous coatings. The heat build-up may also cause operator discomfort and injury. 
     OBJECTS OF THE INVENTION 
     The principal object of the present invention is to increase the operating efficiency of a printing press dryer of the type which utilizes radiant lamps to dry inks and coatings on freshly printed and/or coated sheets. 
     A related object of the present invention is to provide a high efficiency, high power output radiant heater which includes improved means for limiting the transfer of heat to nearby parts and press equipment. 
     Another object of the present invention is to increase the effective exposure time of a freshly printed sheet to forced air flow in a printing press dryer so that the printing press may be operated at higher speeds without compromising quality. 
     Yet another object of the present invention is to provide an improved radiant heat dryer of the character described which includes means for removing the humid air layer from the surface of a freshly printed sheet and extracting it from the press, thereby accelerating the drying process. 
     SUMMARY OF THE INVENTION 
     The foregoing objects are achieved according to the present invention by a combination forced air and radiant heat dryer in which the exposure to forced air flow is increased by broadening the air base. Forced air at high pressure is discharged uniformly through precision holes located directly above an array of infra-red lamps onto a freshly printed and/or coated sheet as it moves along a sheet transport path to a delivery stack. 
     According to one aspect of the present invention, the moist air layer is displaced from the surface of the printed sheet by high-velocity air jets which scrub and break-up the moisture-laden air layer that adheres to the printed surface of the sheet. The high-velocity air jets create turbulence which overcomes the surface tension of the moisture and separates the moisture laden air from the surface of the paper. The moisture laden air becomes entrained in the forced air flow and is removed from the press as the moisture laden air is extracted. 
     Effective exposure to the forced air flow is increased by multiple air jets, in which the air jets are arranged to deliver a substantially uniform blanket of the high velocity air across the sheet transport path. Preferably, the high velocity air jets are uniformly spaced with respect to each other along the sheet delivery path. Since the release of moisture and other volatiles from the ink and/or coating occurs continuously during exposure in response to the absorption of infra-red radiation, the moisture laden air layer is displaced continuously from the printed sheet as the printed sheet travels through the dryer and crosses the multiple air jets. 
     After a printed sheet exits the dryer, and before the arrival of the next successive printed sheet, residual moisture-laden air is completely exhausted from the press by an extractor. According to this arrangement, the drying of each printed sheet is accelerated before it is placed on the delivery stack. If a protective coating is applied over the ink, the coating is completely dried and a dry film is established over the wet ink. This permits the ink to thoroughly cure under the coating after stacking, thus eliminating the need for spray powder to control offsetting. 
     Operational features and advantages of the present invention will be understood by those skilled in the art upon reading the detailed description which follows with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side elevational view in which the dryer of the present invention is installed in a four color offset rotary printing press; 
     FIG. 2 is a simplified side elevational view showing the installation of the dryer of the present invention in the delivery conveyor section of FIG. 1; 
     FIG. 3 is a perspective view, partially broken away, showing installation of the dryer assembly of FIG. 2 on the gripper chain guide rails; 
     FIG. 4 is a simplified schematic diagram showing the principal dryer components of the present invention; 
     FIG. 5 is a sectional view of the improved dryer of the present invention taken along the line  5 — 5  of FIG. 4; 
     FIG. 6 is an elevational view, partially in section, of the dryer assembly shown in FIG. 2; and, 
     FIG. 7 is a top plan view, partially in section, of the dryer assembly shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As used herein, the term “processed” refers to various printing processes which may be applied to either side of a sheet or web, including the application of inks and/or coatings. The term “substrate” refers to sheets or web stock. 
     Referring now to FIG. 1, the dryer  10  of the present invention will be described as used for drying freshly printed substrates, either sheets or web stock, which have a protective and/or decorative coating which has been applied in a sheet-fed or web-fed, rotary offset or flexographic printing press. In this instance, the dryer  10  of the present invention is mounted on the guide rails of the delivery conveyor of a four color printing press  12  which is capable of handling individual printed sheets having a width of the approximately 40″ (102 millimeters) and capable of printing 10,000 sheets per hour or more, such as that manufactured by Heidelberg Druckmaschinen AG of Germany under its designation Heidelberg Speedmaster 102V. 
     The press  12  includes a press frame  14  coupled on the right end to a sheet feeder  16  from which sheets, herein designated S, are individually and sequentially fed into the press, and at the opposite end, with a sheet delivery stacker  18  in which the finally printed sheets are collected and stacked. Interposed between the sheet feeder and the sheet delivery stacker  18  are four substantially identical sheet printing units  20 A,  20 B,  20 C and  20 D which can print different color inks onto the sheets as they are moved through the press. 
     As illustrated in FIG. 1, each sheet fed printing unit is of conventional design, each unit including a plate cylinder  22 , a blanket cylinder  24  and an impression cylinder  26 . Freshly printed sheets from the impression cylinder  26  are transferred to the next printing unit by transfer cylinders T 1 , T 2 , T 3 . A protective coating is applied to the printed sheets by a coating unit  28  which is positioned adjacent to the last printing unit  20 . The coating unit  28  is preferably constructed as disclosed in my U.S. Pat. No. 5,176,077, which is incorporated herein by reference. 
     The freshly printed and coated sheets S are transported to the delivery stacker  18  by a delivery conveyor system, generally designated  30 . Referring now to FIG. 1, FIG.  3  and FIG. 5, the delivery conveyor  30  is of conventional design and includes a pair of endless delivery gripper chains  32 A,  32 B shown carrying laterally disposed gripper bars  34  (FIG. 5) having a gripper element G for gripping the leading edge E of a freshly printed sheet S as it leaves the impression cylinder  26 . As the leading edge E of the printed sheet S is gripped by the gripper G, the delivery chains  32 A,  32 B pull the gripper bar  34  and sheet S away from the impression cylinder and transports the freshly printed and coated sheet to the sheet delivery stacker  18 . 
     Prior to delivery to the sheet delivery stacker  18 , the freshly printed sheets are dried by a combination of infra-red thermal radiation, forced air flow and extraction. Referring now to FIG. 2, FIG. 3, FIG.  4  and FIG. 5, the dryer  10  includes as its principal components a dryer head  36 , a radiant heat lamp assembly  38 , and an extractor head  40 . As shown in FIG.  3  and FIG. 5, the dryer head  36  is mounted on the upper section  42 A of a chain guide rail  42 , and likewise on the upper chain guide section  44 A of a chain guide rail  44 . In this position, the dryer head  36  is extended across and spaced from the sheet travel path P (FIG.  4 ). 
     The dryer head includes a housing  46  defining an air distribution manifold chamber  48 . The air distribution manifold housing includes multiple inlet ports  50 A,  50 B,  50 C and  50 D for receiving pressurized air through a supply duct  52  from a blower fan  54 . As shown in FIG. 7, the air distribution manifold housing  46  includes a distribution panel  56  which is intersected by multiple discharge ports  58  which are oriented for discharging pressurized jets of air toward the sheet travel path. The discharge ports  58  are uniformly spaced so that a uniform blanket of pressurized air is produced across the processed side of a sheet S as it moves through the dryer. 
     Referring now to FIG.  6  and FIG. 7, the heat lamp assembly  38  includes an array of heat lamps  60  extending transversely with respect to the sheet travel path P substantially in parallel relation with each other. The radiant heat lamps  60  are supported between the sheet travel path P and the air distribution manifold by end brackets  62 ,  64 . The ends of each heat lamp project through circular apertures formed in the end brackets. Each heat lamp  60  includes electrodes  60 A,  60 B which are electrically connected to power buses  66 ,  68  by flexible, conductive straps  70 ,  72 , respectively. According to this arrangement, each heat lamp  60  is free to expand and contract longitudinally in response to thermal cycling. 
     Each heat lamp  60  is preferably an infra-red radiant lamp having an output in the short wavelength (near) infra-red region (from about 0.70 to about 1.50 micrometers). The power dissipation of each infra-red lamp may be selected from the range of 500 watts-2 kw. In the exemplary embodiment, each lamp is a short wavelength infra-red quartz lamp having an electrical power rating of 1 kw. 
     Referring now to FIG. 2, FIG. 4, FIG.  5  and FIG. 6, the extractor head  40  is mechanically attached to the lower guide rail section  42 B of the chain guide rail  42 , and likewise is connected to the lower chain guide rail  44 B on the opposite side. The extractor head  40  is positioned facing the back side of a freshly processed sheet as it moves along the sheet travel path. According to this arrangement, an exposure zone  74  is bounded between the dryer head  36  and the extractor head  40 , and is substantially co-extensive with the length and width of the radiant heat lamp assembly  38 . 
     Referring again to FIG. 5, the extractor head  40  includes housing panels  41 ,  43  defining an air extractor manifold chamber  76  on laterally opposite sides of the exposure zone. Each manifold chamber  76  has an inlet port  88  coupled in air flow communication with the exposure zone  74 . The extractor head  40  also includes an air circulation passage  78  which is enclosed between a lower manifold panel  80  and a support plate  82 . The support plate  82  defines the lower boundary of the exposure zone  74 , and limits downward deflection of the trailing end of the sheet S. The support plate  82  is reinforced by multiple ribs  83  which extend between the support plate and the manifold panel  80 . 
     The support plate  82  and the ribs  83  serve as a heat sink for conducting thermal energy out of the exposure zone  74 , in response to heat exchange with cooling air flowing through the air circulation passage  78 . The air circulation passage  78  has an inlet port  84  connecting the air circulation passage in flow communication with a source of cooling air (for example ambient air), and a vent port  86  connecting the air circulation passage  78  in air flow communication with the extractor manifold chamber  76 . 
     As shown in FIG.  4  and FIG. 5, the extractor manifold inlet port  88  is coupled in air flow communication with the exposure zone  74  for extracting heat and moisture laden air out of the dryer. The extractor manifold chamber  76  is coupled in air flow communication with an exhaust blower fan  90  by an air duct  92 . The air flow capacity of the exhaust blower fan  90  is preferably about four times the flow capacity provided by the forced air blower fan  54 . This will ensure that the exposure zone  74  is maintained at a pressure level less than atmospheric, thereby preventing the escape of hot, moisture laden air into the press room. 
     Referring now to FIG. 4, FIG. 5, and FIG. 7, a reflector plate  94  is mounted intermediate the air distribution panel  56  and the heat lamp assembly  38 . The reflector plate is intersected by multiple air flow apertures  96  which are disposed in air flow communication with the discharge ports  58  which are formed in the distribution panel  56 . The air flow apertures  96  are oriented to direct jets  98  of pressurized air through the heat lamp assembly and onto a printed and/or coated (processed) sheet S moving along the sheet travel path. 
     According to one aspect of the present invention, the multiple air flow apertures are arranged in linear rows  100 ,  102 ,  104 ,  106  and  108  which extend transversely with respect to the direction of sheet travel. The rows are longitudinally spaced with respect to each other along the sheet travel path. Each air jet expands in a conical pattern as it emerges from the air flow aperture  96 . Expanding air jets from adjacent rows overlap along the sheet travel path, thereby producing a turbulent air blanket which scrubs the processed side of the sheet S as it moves through the exposure zone. Preferably, balanced air pressure is applied uniformly across the sheet S to ensure that the moist air layer is completely extracted. 
     Referring again to FIG.  5  and FIG. 7, the air distribution manifold discharge ports are arranged in similar linear rows which are spaced with respect to each other and are aligned with the rows in the reflector plate. In this arrangement, the discharge ports  58  in each row of the distribution manifold are aligned in flow registration with the air flow apertures  96  in each row of the reflector plate, respectively. Preferably, the air flow apertures  96  in the reflector plate are substantially centered with respect to adjacent heat lamps  60  whereby each pressurized air jet  98  is directed through one of the longitudinal spaces between adjacent lamps (see FIG.  5 ). 
     As shown in FIG. 5, the sheet support plate  82  faces the radiant heat lamps across the exposure zone  74  and is disposed substantially in alignment with the sheet travel path P for engaging the back side of a freshly processed sheet S as it is travels through the exposure zone. The leading edge E of the sheet S is gripped by the gripper means G, and the depending body portion of the sheet S rides on a thin air cushion AC along the support plate  82 . 
     Referring again to FIG.  4  and FIG. 6, the reflector plate  94  is pre-stressed to assume the form of a convex arch under ambient temperature conditions, and approaches a flat plate configuration under production operating temperature conditions. According to this arrangement, the reflector plate  94  is prevented from touching the infra-red lamps  60  during production. The reflector plate  94  has side edge portions  94 A,  94 B which are mounted on first and second shoulder brackets  110 ,  112 , respectively, on opposite sides of the dryer head. The shoulder brackets limit thermally induced deflection movement of the reflector plate  94  toward the heat lamps, while accommodating thermally induced lateral expansion and contraction movement of the reflector side edge portions  94 A,  94 B, respectively. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.