Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M7/00—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein

Definitions

• This invention relates to treatment of hot melt ink images and, more particularly, to a system for treating hot melt ink images so as to enhance the quality of the images and, at the same time, prevent cockling and inhibit curling of the substrate which may occur in the processing of the hot melt ink images.
• the- transparency substrate which may be made of a sheet of polyester material such as Mylar, for example, -may be heated to a temperature that is above the glass transition temperature of the substrate material.
• the quality of hot melt ink images on porous substrates may be improved by maintaining the sub- strate at a temperature above its melting point for a selected time.
• the substrate may be supported on a curved platen.
• the response to heating of substrate materials such as transparency substrate polyesters and paper substrates differs and the cockle effect is caused in those substrates in differing ways.
• a web or sheet of paper substrate passes from ambient tempera- ture into a heated zone, it expands so that the width of the web increases but, after the paper has been heated for a period of time (typically 5 to 10 sec ⁇ onds), it loses moisture and shrinks, making the web or sheet narrower.
• the width of a polyester substrate remains larger after it passes into a heated zone so that the cockling effect result ⁇ ing from such passage must be counteracted or pre ⁇ vented in a different way.
• a further object of the invention is to provide a system for treating hot melt ink transparencies to provide improved projection quality of color images.
• An additional object is to provide a continuous process and apparatus for treating hot melt ink images in which the images are heated rapidly and uniformly for a predetermined time period and cooled rapidly at the end of the predetermined period.
• Another object of the invention is to provide a system for reducing curl in hot melt ink transparen ⁇ cies to a level which does not cause deterioration of a projected image.
• a hot melt ink image on a substrate in a controlled manner into a heating zone across a surface which has sufficient curvature to prevent cockle, maintaining the image within the heating zone for a time long enough to permit hot melt ink drops to melt and spread on the substrate, and moving the image in a controlled manner out of the heating zone along a surface which has sufficient curvature to prevent formation of cockle in the substrate.
• the substrate is supported at a reduced curvature or held substantially fla.t in the region of the heating zone between the curved surfaces, and for this purpose, it may be held against the surface of a heated platen.
• the image is moved from the heating zone to a quenching zone where the temperature is reduced at a rapid rate, such as at least 50°C/sec. and, prefer ⁇ ably, at least 500°C/sec.
• quenching is ' effected by moving the substrate into heat-transfer contact with a relatively cold platen.
• the sub ⁇ strate is preferably moved along a surface having, a reverse curvature after quenching. To assure uniform treatment of the hot melt ink image, the substrate is moved continuously through the heating and quenching zones at a uniform rate.
• One form of apparatus for treating hot melt ink images includes a heated platen having a substantially flat center surface and curved surfaces at the inlet and outlet ends, along with a substrate-conveying mechanism for conveying an image-containing substrate across the platen surface at a uniform rate and hold ⁇ ing it against the curved and flat portions of the surface as it is moved across the surface.
• a cooling platen has a quenching zone posi- tioned adjacent to the outlet end of the heated platen and, to assure good heat transfer, the surface of the cooling platen in the quenching zone is preferably curved.
• the cooling platen has a reversely curved surface to receive the substrate after it has passed through the quenching zone.
• Fig. 1 is a schematic sectional view illustrating a representative arrangement for treating hot melt ink images in accordance with the invention.
• Fig. 2 is an enlarged fragmentary view of the arrangement shown in Fig. 1 illustrating the platen arrangement in greater detail.
• the typical embodiment of the invention shown in the drawings comprises an apparatus 10 having a heat- ing zone for heating a hot melt ink print 11 to melt the ink for a selected time period and a quenching zone for quenching the hot melt ink image at the end of the selected time period to produce a print 12 in which the hot melt ink has spread so as to provide improved image quality without objectionable curl.
• the heating zone is formed by a substrate heating platen 13, described in greater detail hereinafter, to which the print 11 is supplied by an input drive roll 14 and a cooperating pinch roll 15.
• a cooling platen 16, also described hereinafter, has a cooperating drive roll 17 to receive the print 11 from the heating platen 13 and quench the hot melt ink image thereon while moving the print away from the heating zone.
• the cooling platen 16 has two a-rrays of cooling fins 18 and 19 and the en ⁇ tire hot melt ink image treatment arrangement is en ⁇ closed in a housing 20.
• a spring device 21 supported by the interior surface of the housing 20 has a spring arm 22 which urges the surface 23 of the cooling platen 16 against the output drive roll 17, the cool ⁇ ing platen being pivotally supported by a shaft 24 near the end of an arm 25 adjacent to the pinch roll 15.
• the housing is arranged to permit circulation of air either by convection or by a fan (not shown) past the arrays of fins 18 and 19 to remove heat from the cooling platen and maintain the temperature of that platen within a desired range, such as below 55°C, to assure rapid cooling of the hot melt ink in the image on the substrate after it leaves the heating zone.
• a fan not shown
• the cooling platen may be cooled by liquid circulation or by a thermoelectric cooling device.
• the heating platen 13 includes an electric heater 26 mounted at the rear surface of a platen body 27 and covered by a layer of insulation 28 which also fills the gap between the heating and cooling platens to inhibit direct heating of the adjacent portion of the cooling platen 16. Alternatively, if desired, an air gap may be provided between the adjacent ends of the heating and cooling platens.
• the sub ⁇ strate 30 should be heated in the heating zone to a controlled temperature above the melting point of the ink, such as, for example, 95°C, for a period of, for example, 0.5 to 10 sec. and, preferably, 1 to 5 sec, preferably by contact heat transfer.
• a guide member 31, spaced from a substrate- engaging surface 32 of the heated platen body 27, is positioned to enclose the heating zone and to guide the leading and trailing edges of the substrate 30 as it is driven by the input rolls 14 and 15 through the heating zone and into the nip between the cooling platen 16 and the output drive roll 17. Accordingly, the temperature of the platen body 27 is maintained at a desired level above the melting point of the ink and the drive rolls 14 and 17 are arranged as described hereinafter to maintain each portion of the transpar ⁇ ency 11 in the heating zone for the desired length of time.
• the temperature of the substrate will approach the temper ⁇ ature of the platen at a rate with a thermal time constant, i.e . ., the time in which the temperature difference is reduced by 63%, of approximately 0.05 sec. to 0.10 sec.
• a thermal time constant i.e . ., the time in which the temperature difference is reduced by 63%, of approximately 0.05 sec. to 0.10 sec.
• the heated substrate- engaging surface 32 of the platen 27 has a curved surface section 33 at the input end, a substantially flat central section 34, and another curved section 35 at the output end of the heating zone.
• Cockle of the substrate not only detracts from the appearance of the print but, more importantly, causes portions of the substrate to be held out of contact with the heating and cooling platens.
• separation of the substrate from the platen surface by more than about 1 or 2 mils (0.025 or 0.05mm) can: increase the heat transfer time constant by a factor of two or more so that the desired heating and cooling rates may not be achieved.
• the curved surfaces 33 and 35 are arranged to have a curvature which is sufficient to prevent cockle of the substrate 11 as it moves between room tem- perature at the input end and the high-temperature heating zone and between the heating zone and the low-temperature cooling platen.
• these curved surfaces may have a radius of less than 8 cm. and preferably 3 cm. to 5 cm.
• the central section 34 of the heating platen is preferably flat but, if de ⁇ sired, it may be slightly curved, so long as the curvature imparted to a transparency substrate during its passage along the heating platen is not great enough to prevent it from being overcome by the subse ⁇ quent decurling action of the cooling platen.
• the radius of curvature of the central section 34 is at least 5. cm.
• the optimum curvatures of the input and output surfaces 33 and 35, and of the center section 34, if curved, depend upon the ambient temperature, the pro ⁇ cessing temperature, which is related to the melting temperature of the ink, and the glass transition cem- perature of the substrate. Of course, if the glass transition temperature of the substrate is above the processing temperature, the curvatures will not cause the substrate to curl and, as long as the radius is small enough to prevent cockle, the values of the curvatures are not important.
• the radius of curvature required to prevent cockle is given by the equation:
• ⁇ T* ⁇ E is Young's Modulus of the substrate material at the processing temperature
• t is the thickness of the substrate
• k is a constant
• ⁇ T is the difference between the processing temperature and the lower of the inlet temperature and the quenching temperature
• ⁇ is the thermal expansion coefficient of the substrate material. Since Mylar has a high Young's Modulus and a low thermal expansion coefficient, it is a preferred material for use as a transparency sub ⁇ strate.
• the angular length of each of the input and output curved surfaces, i.e . ., the portion 33 and the portion 35 together with the adjacent insula ⁇ tion and cooling platen surfaces, should be great enough to provide good mechanical stability of the curved substrate.
• the angular length of those surfaces is preferably at least 10° and desirably 15°.
• the output drive roll 17 is arranged to drive the substrate at a rate faster than it is driven by the input drive roll 14, and the input drive roll has a one-way clutch arranged to permit the substrate to turn it while causing sufficient drag to hold the substrate against the surface 32 of the platen 27.
• the slower speed cf the input drive roll 14 is selected to permit the leading edge of the substrate 11 to be retained in the heating zone for a slightly longer period to compen ⁇ sate for any lack of close contact with the surface 32 before the substrate is engaged between the drive roll 17 and the surface 23 of the quench platen 16.
• the input drive roll 14 may be ar ⁇ ranged to advance the substrate 11 at a rate of about 0.5 cm/sec
• the output drive roll 17 is ar ⁇ ranged to drive the substrate at a rate of about 1 cm/sec.
• this arrangement provides a residence time in the heating zone of about 5 sec. for the leading edge of the substrate which is not held tightly against the surface 32, since it has not been engaged by the output drive roll 17, and a resi- dence time of about 2.5 sec. for the rest of the sub ⁇ strate 11, which, except for the trailing end, is held tightly against the heated surface 32 of the platen after the leading edge has been engaged by the output drive roll 17.
• the substrate drive speed provided by the drive roll 17 is in the range from about 0.25 to 5 cm/sec. and, desirably, the drive speed is in the range from 0.5 to 2 cm/sec.
• the angular length of the input curved surface section 33 may be about 10°, providing a linear curved surface length of about 0.6 cm, and the angular length of the output curved surface section 35 may be about 5°, providing a curved surface length of about 0.3 cm so that, at a drive speed of 1 cm/sec, the residence time of the portion of the substrate in contact with the output curved surface is only about 0.3 sec.
• the substrate is held close to or against the flat portion 34 of the platen for about 1.6 sees.
• the sub ⁇ strate will no.t necessarily be held in complete con ⁇ tact with the platen surface 32 along the entire length of the center section 34.
• polyester material of a substrate such as Mylar is thus held against the flat or sub ⁇ stantially flat surface portion 34 during a large portion of its passage through the heating zone and for a time which is long enough to permit the sub ⁇ strate material to relax, it retains less of the curvature resulting from its passage along the curved surface portions of the platen surface 32.
• the cooling platen 16 has a quenching zone 36 adjacent to the output end of the heating zone which receives the substrate 30 as it passes out of the heating zone and quenches the ink image thereon at a rapid rate to avoid crystallization and frosting.
• the cooling platen temperature in the quenching zone 36 should be low enough to cool the ink at a rate of at least 50°C/sec. and, preferably, at least 500°C/sec. Cooling by contact heat transfer to a metal or other heat-conductive surface is adequate. ' for this purpose, as long as the quench surface is maintained adequately below the melting temperature of the ink.
• the cooling platen temperature in the quenching zone is at least 10°C below the melt ⁇ ing point of the ink and, desirably, it is at least 30°C below the melting point.
• a quenching zone temperature 30°C below the ink melting point and a substrate moving at a rate of about 1 cm/sec molten ink on the substrate will solidify in substantially less than one second and, preferably, less than one-half second, corresponding to a distance of less than 1 cm. so that a quenching zone 36 having a length of 1 cm. should be sufficient. Therefore, if the drive roll 17 engages the surface of the substrate 30 containing the ink drops at least 1 cm.
• the ink will be solidified before the drive roll engages • the surface, thereby preventing any flattening or other deformation of the ink drops which might degrade the projected image quality of the transparency. This also avoids any offsetting of soft ink onto the drive roll which could produce image defects in a subsequent portion of the same print or other prints.
• the surface of the insu ⁇ lating layer 28 between the heating platen and the cooling platen and the surface 23 of the cooling platen in the quenching zone have the same curvature as that of the region 35 of the heating platen surface 32. This not only prevents cockle, but also assures good contact of the substrate with the surface 23 of the cooling platen in the quenching zone to provide good heat transfer so that any molten ink drops on the substrate are solidified before they reach the output drive roll. For example, if the quenching time is 150 milliseconds and the substrate is driven at 1 cm/sec, a quenching zone length of a few millimeters is suffi ⁇ cient.
• the radius of cur ⁇ vature of the reverse curved surface 36 should be less than that of the surfaces 33 and 35 and, desirably, the radius of curvature is less than half that of the surfaces 33 and 35.
• the radius of the surface 37 is about one-quarter of that of the surfaces 33 and 35, i . .e. , about one cm.
• the effect on decurling is surprising because the stress in a 4-mil (0.1mm) Mylar substrate in the 1 cm.. radius curvature section 36 is only about 2,500 psi, which is less than 25% of the yield strength of the material at a cooling platen temperature of about 45°C.
• a print 11 having solid hot melt ink drops 38 which were deposited on the surface of the substrate 30 during ink jet printing is passed through a heating zone having a platen temperature of about 95°C at a rate of 1 cm/sec.
• the solid ink drops which have a melting point of about 80°C, are melted and permitted to spread on the surface of the substrate to produce drops 39 hav- ing a larger area and an increased radius of curva ⁇ ture, resulting in improved image quality as described in the above-mentioned Fulton et al. patent and the Hoisington et al. application.
• the drops 38 and 39 which may, for example, be about 0.1-0.2 mm.
• the thermal transfer time constant is about 0.1 sec, causing the temperature of the sub ⁇ strate and its ink image to be reduced by about 32°C (63% of the difference between 95°C and 45°C) to about 63°C in about 0.1 sec or about 1 mm. of substrate motion into the quenching zone.
• the average rate of cooling during this time period is 320°C/sec , but the initial cooling rate during the time in which the temperature is reduced to a level below the 80°C melt- ing point is higher since the cooling rate is a nega ⁇ tive exponential.
• the tem ⁇ perature falls to about 52°C and the ink temperature continues to approach 45°C as the substrate moves along the cooling platen.
• Such rapid cooling prevents significant crystal ⁇ lization and frosting of the ink image and assures that the ink drops 39 are solidified before they are engaged by the drive roll 17.
• the sub ⁇ strate 11 i-s driven around the reverse-curvature sur- face 37 of the platen which results in substantial elimination of any curvature caused by passage of the substrate 30 along the curved surfaces 33 and 35 while at an elevated temperature.

Landscapes

• Ink Jet (AREA)
• Particle Formation And Scattering Control In Inkjet Printers (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)
• Accessory Devices And Overall Control Thereof (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Ink Jet Recording Methods And Recording Media Thereof (AREA)

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Publications (1)

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Citations (5)

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• 1989
  • 1989-10-02 US US07/416,158 patent/US5023111A/en not_active Expired - Lifetime
• 1990
  • 1990-09-04 WO PCT/US1990/004997 patent/WO1991004799A1/en not_active Ceased
  • 1990-09-04 EP EP90915362A patent/EP0447533B1/en not_active Expired - Lifetime
  • 1990-09-04 KR KR1019910700520A patent/KR950000774B1/ko not_active Expired - Fee Related
  • 1990-09-04 JP JP2514317A patent/JPH03505187A/ja active Granted
  • 1990-09-04 AT AT90915362T patent/ATE110031T1/de not_active IP Right Cessation
  • 1990-09-04 DE DE69011663T patent/DE69011663T2/de not_active Expired - Fee Related
  • 1990-09-12 CA CA002025184A patent/CA2025184C/en not_active Expired - Fee Related
• 1991
  • 1991-02-06 US US07/651,321 patent/US5980981A/en not_active Expired - Lifetime

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