Machine for hot-printing on paper and foil substrates

Abstract: The invention relates to a machine for hot-printing on paper and foil substrates comprising, on a frame (1a), melting members (5) adapteed to hot melt heat-fusable substances (5c), rollers (4) adjacent to the melting members (5) and adapted to transfer the heat-fusable substances (5c) to a foil substrate (3), heater devices (6) for at least some of the rollers (4) having a plurality of heater bands (6a) housed within the rollers (4) and being each linked to a thermal control of its own, deflector rolls (2) for the foil substrate (3) located downstream of the rollers (4), and cooling devices (2a) for the deflector rolls (2).

Description: The invention relates to a machine for hot-printing on paper and generic sheet substrates, such as light cardboard, plastics sheets, and the like. As is known, printing on offset, photogravure, or sheet rotary presses is currently carried out by a cold process with either single or multiple inking of the paper in the instance of color printing. The paper is liable to become wet in the areas subjected to the liquid ink in a cold condition, and result in smearing, staining, or fouling during its passes over the rollers or the color superimposition steps. To obviate this problem, the paper is quickly dried either by hot air or another means such as UV or IR light, to vaporize off the pigment carriers or solvents. Large fans in a heated enclosure may also be used. However, the paper drying always brings about a number of problems. In fact, since a non-uniform ink application may occur, the dried paper may be just too dry locally, in view of that the drying process to vaporize off the pigment carriers or solvents also changes the optimum relative humidity of the paper, to inhibit in some cases a good further printing in at least four colors. Excess drying may also trigger static electricity phenomena, with resulting sparking, fire, and explosion hazards. Comparable phenomena may also occur with substrates other than paper. Paper, moreover, cannot withstand the mechanical stresses to which it is subjected due to excessive dryness, and break. Further, the extent of the drying process should be controlled in drying systems to suit the amounts of paper to be dried, so as to prevent, for example, a break in the supply of paper from causing excessive drying of paper already in the heating step, with attendant fire hazards. Also known are some apparatus which provide hot-printing, but these apparatus have characteristics which make them definitely inferior in capacity to apparatus for cold-printing on either photogravure or sheet rotary presses. These apparatus are of two types. A first type apparatus only permits of transfer printing because it provides for ink to be transferred from a transfer substrate, over which it has been pre-coated, to a paper or plastics substrate bearing an adhesive. The adhesive on the paper or plastics substrate is caused to swell by heating so as to block the ink of the transfer substrate, as pressed onto the substrate to be imprinted. The transfer substrate is left clean and ink-less on completion of the printing step. This first type apparatus has a low output because it is capable at most of delivering approximately 1800 printed pieces per hour. Furthermore, and above all, it does not allow of four-color printing or superimpositions of inks, and is often prone to smearing. A second type apparatus, see e.g. US-A-2 268 594 provides for the use of rotating rollers which are heated by means of stick electric resistance heaters, or by oil, or steam. The stick resistance heaters, placed inside the rollers to be heated, tend to distort and have a high thermal inertia, that is, are slow to change the magnitudes of the heat exchanges. Thus, the temperature setting is maintained in a coarse fashion, and at any rate with a delay which may be unacceptable at times. The thermal inertia of the sticks is also enhanced by the surrounding air. The oil circulated through the roller interiors cannot be heated to a temperature above 150°C to avoid the risk of cracking and therefore there are provided on the roller outside, which delivers its heat to the paper in rotating, top temperatures of about 100°C, oftentimes inadequate for many heat-fusable inks. To achieve higher temperatures on the rollers, the rollers must be rotated at very low rates, so as to dissipate little heat. but in that case the production output decreases considerably. The heated and pressurized steam circulated through the roller interiors, enables temperatures not above 120°C to be reached on the roller exteriors. In addition, due to the high pressure of the steam, problems are often encountered with the seals which seal off the enclosure defined by the roller. In summary, the cited known second type apparatus, equipped with heated rotating rollers, disallows thermal control of the rollers both in the respect of the achievable temperature value and control of its variations. It is for this reason that said apparatus is restricted to applications which require no high printing accuracy, such as for making chemical or carbon transfer papers, which merely involve the printing of covering substances. Also, even where just covering substances are to be printed, it is still impossible to print on sheet of varying sizes; a partial utilization of the rollers, that is of just a band thereof, greatly aggravates the difficulties pointed out herein above in relation to thermal control. This condition of reduced capacity of hot printing apparatus is quite objectionable because said apparatus not only obviate the problems of cold printing but also, as pointed out by the Applicant, the amount of heat involved in hot printing is less than that to be supplied to cold printing, thereby the savings in energy are substantial. In hot printing, in fact, heat is only supplied for melting the ink or heat-fusable coloring substance, and to maintain it at suitable temperatures during its transfer to paper. In the instance of cold printing, heat is supplied over the entire printed material until the excess liquid is vaporized off and the necessary drying accomplished. Accordingly, the technical task underlying this invention is to provide a machine for hot printing on paper and foil substrates which can substantially obviate the cited drawbacks of cold printing and permit of hot printing even where high printing accuracy and output are required. Within said technical task it is an important object of the invention to provide a machine having a high thermal efficiency and a minimum of dissipated heat not utilized for the printing process. The technical task is substantially accomplished by a machine for hot printing on paper and foil substrates, comprising, on a frame: melting members adapted to hot melt heat-fusable substances, hollow rollers having a cylindrical outer skirt and being adjacent to said melting members and adapted to transfer said heat fusable substances to one said foil substrate being moved past said rollers, heater devices for heating at least some of said rollers characterized in that said heater devices comprise sequentially arranged heater bands inside each heated roller and in contact with said skirt, each of said heater bands being located in a specific zone of said skirt and including electric resistance heaters powered separately from the power supply to the other said heater bands, and deflector rolls for said foil substrate located downstream of said rollers, and cooling devices for cooling at least some of said deflector rolls. The following detailed description of some preferred, but not exclusive embodiments of a hot printing machine is given herein with reference to the accompanying drawings, where: Figure 1 is a general layout diagram of the machine; Figure 2 is a longitudinal section, partly exploded view of a portion of a roller of Figure 1, according to a first embodiment thereof; Figure 3 is a cross-sectional view of the roller of Figure 2 showing the concentrical roller laminations; Figure 4 shows one such lamination or layer in plan view; Figure 5 is a longitudinal section, partly exploded view of a portion of a roller as in Figure 1, according to a second embodiment thereof; Figure 6 is a cross-sectional view of the roller of Figure 5; Figure 7 is an enlarged scale view of a portion of Figure 5; and Figure 8 is a sectional view of an edge element of the roller shown in Figure 5. With reference to the drawing views, the hot printing apparatus or machine according to the invention is indicated at 1 in Figure 1. The machine or apparatus 1 comprises, mounted on a holding frame 1a, a number of deflector members and in particular some deflector or advancing rolls 2 provided for entraining and conveying paper 3, or any other foil substrate, directly after the same has been subjected to the printing operations. Upstream of the deflector rolls 2, there are rollers 4 in the printing zone for transferring heat-fusable substances 5c to the paper 3 or else. The rollers 4 comprise a first roller 4a which transfers the heat-fusable substances from melting members 5. The latter are effective to hot melt the heat-fusable substances and comprise a tray 5a equipped with resistance heaters (Figure 1). The tray 5a is overlaid by a doctoring blade 5b contacting the first roller 4a and adapted to restrict the transfer of heat-fusable substances 5c. The rollers 4 also comprise a second roller 4b contacting the first roller 4a, and a third pressure roller 4c which clamps the paper 3 between the third roller 4c and second roller 4b. Advantageously, at least some of the deflector rolls 2 are cooled by means of cooling devices 2a preferably comprising water circulation circuits and spray nozzles for water to be vaporized. These cooling means 2a may be implemented by technical solutions known per se, and are therefore no further described in detail herein. Cooling some of the deflector rolls 2 enable the penetration of the heat-fusable substances through the paper 3 or else to be blocked. The heat-fusable substance transfer rollers 4 are instead equipped, at least in part, with heater devices 6 placed inside the rollers 4 in contact with a cylindrical metal wall or skirt 7. The latter is of reduced thickness and has a high thermal conductivity and constitutes, along with removable head pieces 8, the load-bearing shell of each roller 4. It is expediently arranged for the heater devices 6 to be subdivided into a plurality of heater bands laid side-by-side along a parallel direction to the main dimension of the rollers 4, and each band has a thermal control independent of the thermal controls for the other bands. In detail of the embodiment shown, the heater devices 6 are subdivided into three heater bands 6a with independent thermal controls, each in contact with a zone of the skirt 7, and engaging in combination the entire skirt 7. The heater bands 6a have uniform thicknesses and are preferably contiguous so as to form a single carpet, as shown in Figure 4. They are formed from a flexible insulating material 9, e.g. silicone, encapsulating electric resistors 10 which are defined by a flexible electric cable bent over and laid such as to leave no empty spaces in each heater band 6a. Electric power supplies are provided separately for each heater band 6a. In each heater band 6a, there are also provided heat sensors 11, such as thermocouples, capable of sensing the temperature and supplying a signal to a control member 12 (Figure 5) adapted to change the amount of the current input to the resistors 10. In particular, it is advantageously arranged for the control member 12 to comprise switch elements, known per se, effective to change the amount of current by alternating conditions of maximum input to breaks in the input. In this way, not only is the initial transition period minimized, but also the demand for local heating is met in a rapid and simple manner, that is heating restricted to a given heater band 6a can be selected where required to deliver more heat owing to the presence of a larger amount of heat-fusable substances thereat. The heater devices 6 are held in contact with the skirt 7 by holder means 13, and the latter are brought out in two preferred embodiments thereof. In the embodiment of Figures 2 and 3, the holding means 13 are a layer of a heat-insulative concrete material 14 cast to a uniform thickness by centrifuging inside the roller 4 a mass of said material in a flowing state. In the embodiment of Figures 5, 6, 7, the holding means 13 are defined by a plate wall 15 made of an aluminum alloy. The wall 15 has corrugations 16 defined by stiffening folds, each laid into a ring substantially concentrical with the skirt 7. The corrugations 16 come into contact with the layer 9, and accordingly, the wall 15 defines, in cooperation with the layer 9, a space 17 containing air. Thus, a heat insulating barrier to the roller 4 interior is created. The outer surface 18 of the wall 15 facing the resistors 10 is suitably coated or treated to provide high heat reflectivity characteristics. For example, it may be mirror finished or polished. The inner surface 19 of that same wall 15 is instead of a dull type. In this way, the heat generated by the resistors 10 is mostly confined to a region close to the skirt 7 by both the space 17 preventing transfer by conduction and the reflective action of the outer surface 18 preventing transfer by radiation. The wall 15 is subdivided into substantially annular, consecutively side-by-side modules which facilitate the assembling of the wall 15 and are adaptable to fit rollers 4 with different lengths. In the embodiment of Figures 5 and 6, there are also shown locating elements inwardly of the wall 15 which comprise a plurality of struts 20 effective to urge the wall 15 in a direction toward the skirt 7. Each strut 20 comprises a bracket element 21 through-penetrated by a screw element 22 which define in combination three active lugs 23 contacting the wall 15. Associated with the screw element 22 are a pair of locknuts 24 and third nut 25 defining a movable body for use to balance the rollers 4. For the printing operations, the skirt 7 of at least some of the rollers 4 (in particular, at least the second roller 4b) are engaged externally, as by means of a highly adhesive glue, with a plastics covering 26 (Figures 5-8), e.g. of the type known in the trade by the name of "Nilograph". This covering has its outer surface screened and etched to delineate the zones to be printed and to facilitate transport of heat-fusable substances. The plastics 26 is advantageous in that it can be removed and enables the same rollers 4 to be used for different printing operations. Provided at one end of the roller 4 and encapsulated in the skirt 7 (Figure 8) is a separating element 27 defined by a headless screw or set screw adapted to urge by its tip a flap of the plastics 26 away from the skirt 7, thus facilitating its full removal whenever in need of replacement. The heat-fusable substances in the tray 5a are formed, for example, by pigments and microcrystalline waxes and indicated at 5c. In particular, where colored covering layers are to be printed, which are intended for removal by scraping off as is typical of many games tied to advertising initiatives, the heat-fusable substances may be a mixture of, powdered aluminum, known as "Argento 177", or alternatively, "Bronzo Pallido 17", to an amount of at least fifty percent; low-density polythene, known as "Eltene 15", to an amount of up to five percent; high-density polythene, known as "Eltene 25", to an amount of up to twenty percent; and a glue, microcrystalline wax, and polythene composition, known as "Luna Melt LM 400", to an amount of up to twenty five percent. Another example of suitable heat-soluble substances for use with the machine or apparatus according to the invention, comprises a mixture of, homogenized pigments to an amount of up to fifty percent; high density polythene to an amount of at least twenty five percent; and a high-melt microcrystalline wax composition, known as "Sepa Melt 87/B", or at any rate having a viscosity of about 2000 cps at 170°C, to an amount of up to twenty five percent. The invention achieves important advantages. In fact, the machine according to the invention makes for a widespread application of hot printing and therefore affords the cited advantages thereof. The temperatures of the rollers 4 is controlled in a simple and highly accurate fashion, sector by sector. It allows temperatures above 180°C to be attained on the roller 4 outer surfaces with quite negligible thermal inertiae. The results to be obtained at these temperatures and with the above-specified inks enable application of thick layers of ink with the utmost accuracy. It is self-evident that the temperature control by different heated bands on each roller also allows alternation of different size papers or substrates during the printing process. The specific structure of the rollers 4 is advantageous in that the heat provided by the resistors is nearly all available to the roller exteriors, for the hot printing process, while minimizing the loss of heat to the roller centers. This also results in a high capability for fast changes of temperature at the paper or substrate during the printing process.

Claims: A machine for hot-printing on paper and foil substrates, which comprises, on a frame (1a): melting members (5) adapted to hot melt heat-fusable substances(5c), hollow rollers (4) having a cylindrical outer skirt (7) and being adjacent to said melting members (5) and adapted to transfer said heat-fusable substances to one said foil substrate (3) being moved past said rollers (4), heater devices (6) for heating at least some of said rollers (4) characterised in that said heater devices (6) comprise sequentially arranged heater bands (6a) inside each heated roller (4) and in contact with said skirt (7), each of said heater bands (6a) being located in a specific zone of said skirt (7) including electric resistance heaters (10) powered separately from the power supply to the other said heater bands (6a), and deflector rolls (2) for said foil substrate (3) located downstream of said rollers (4), and cooling devices (2a) for cooling at least some of said deflector rolls (2). A machine according to Claim 1, wherein there are provided a heat sensor (11) located at each said heater band (6a), and a control member (12) located outside said rollers (4) and connected to each said heat sensor (11) and to said electric resistors (10) in each said heater band (6a), said control member (12) being operative to change the amount of the current input to said resistors (10). A machine according to Claim 1, wherein each said heater band (6a) comprises a flexible insulating material (9) encapsulating said electric resistors (10), said electric resistors (10) being formed from at least one flexible electric cable bent over and laid to engage substantially all of said heater band (6a). A machine according to Claim 2, wherein said control member (12) comprises switch elements known per se and adapted to alternate condition of maximum electric current delivery to conditions of broken delivery, the thermal control of each said heater band (6a) being accomplished by alternating said conditions. A machine according to Claim 1, wherein there are provided holding means (13) for said heater devices (6), located inside said rollers (4) and adapted to hold said heater devices (6) in contact with said skirt (7) and to hold the heat developed by said heater devices (6) within a zone of said rollers (4) close to said skirt (7). A machine according to Claim 5, wherein said holding means (13) comprise a layer of a concrete material (14) having a substantially uniform thickness and being placed in contact with said heater devices (6) and adapted to support and hold the latter in contact with said skirt (7). A machine according to Claim 5, wherein said holding means (13) comprise a wall (15) partly spaced apart from said heater devices (6) and defining at least one thermally insulative space (17) therewith. A machine according to Claim 7, wherein said wall (15) has a reflective surface(19) facing said heater devices (6). A machine according to Claim 7, wherein said wall (15) has corrugations partly in contact with said heater devices (6). A machine according to Claim 7, wherein there are provided adjustable locating elements comprising a plurality of struts (20) arranged to urge said wall (15) toward said skirt (7), wherein said struts (20) comprise a bracket element (21) and an operational screw element (22) through-penetrating said bracket element (21), said bracket element (21) and said screw element (22) defining in combination three lugs (32) acting on said wall (15), and wherein said screw element (22) has at least one movable balance body (25) thereon. A machine according to Claim 1, wherein at least in part said rollers (4) have, above said skirt (7), a plastics covering (26) glued to said skirt (7) and having an outer surface adapted to transfer said heat-fusable substances (5c). A machine according to Claim 11, wherein there is provided at least one separating element (27) defined by a screw encapsulated by said skirt (7) and threadable down to a position of at least partial projection from said skirt (7), against said plastics (26), to facilitate the separation thereof. A roller for a machine for hot-printing on paper and foil substrates, which comprises: a cylindrical skirt (7) adapted to transfer heat-fusable substances (5c) to said foil substrate (3), heater devices (6) located inside said roller (4), characterised in that said heater devices (6) are in contact with said skirt (7) and comprise a plurality of sequentially arranged heater bands (6a), each said heater band (6a) being located at a specific zone of said skirt (7) and each having electric resistance heaters (10) powered separately from the power supply to the other said heater bands (6a), and holding means (13) engaging said heater devices (6) and defining at least one space (17) therewith adapted to limit the loss of heat by conduction, said holding means (13) including wall (15) having a reflective surface (19) facing said heater devices (6) and adapted to limit the loss of heat by radiation.

Inventors: VIGANO' VITTORIO, VIGANO', VITTORIO
Applicants: VITTORIA INDIRIZZI CONPIT SRL, VITTORIA INDIRIZZI CONPIT S.R.L.
Application year: 1989
Main classification: B41F17
IPC codes: B41F17, B41M1, B41F23, B41F13, B41F16, B41F31, B41F9