Thermal Dye Transfer Printing Uniformity Corrections

Thermal Dye Dye Transfer Printing Printing Uniformity Uniformity Corrections Corrections A.R. Lubinsky Research Research Laboratories, Laboratories, Eastman Eastman Kodak Company Rochester, New Rochester, New York York 14650

ABSTRACT ABBIBAçI A brief introduction to continuous tone, dye sublimation sublimation transfer printing printing using a thermal head density head is is given. given. Two Two problems problems that that can can arise arise in in such such aa method method of of printing printing are are discussed: discussed: density non-uniformities non -uniformitiesdown downthe the page pagedue dueto tothe theaccumulation accumulationofofheat heatininthe thethermal thermalhead, head, and density non-uniformities non -uniformitiesacross acrossthe thepage pagedue duetotovariations variationsinin electrical, electrical, thermal thermal or or mechanical mechanical properties across the line of heating elements. Measurements Measurements and and analyses analyses of these these effects are presented. Correction methods are proposed and implemented, implemented, and and results results are are shown shown for each of these problems.

1. INTRODUCTION

and in in thermal dye transfer media2 Recent advances advances in in thermal thermal head1 headl and medial technologies technologies have have resulted resulted in in large large improvements improvements in in the the level level of of image image quality quality obtainable obtainable from from thermal thermal printing. printing. The continuous continuous-tone hard-copy has begun begun to to -tone color hard -copy output output quality quality achievable achievable in in some systems3 has rival rival the the established established standard standard of photographic photographic print print quality. quality. The The emergence emergence of of electronic electronic printing technologies with improved capabilities has opened opened up up new areas areas for possible application; for example, areas associated with high high image image quality quality requirements. requirements. The present paper describes some work on thermal thermal dye dye transfer printing, printing, to extend performance towards higher quality applications by by correcting correcting some some image image quality problems. problems. The approach used here here is is one of of compensating compensating for for certain certain hardwarehardware-induced induced artifacts by software Such methods methods are are easy easy to implement in electronic systems, software corrections.^ corrections.5'6 Such systems, and and are are often often useful when more direct methods are not possible possible or or are are less less than than satisfactory, for certain certain applications.

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PRINTING 2. THERMAL DYE TRANSFER PRINTING

Receiver

Dye /Binder

Thermal Head

Figure 1. Thermal printing. printing. Figure 1. Thermal The elements of thermal dye transfer printing are shown shown schematically in Figure 1. The system system is characterized by relative simplicity and quietness of operation. operation. Print media comprising comprising a receiver layer and a dye/binder layer are brought into contact with with a thermal head. individually addressable head. The The head consists of a linear array of individually addressable resistive heaters. Each heater in amount of of heat heat to to the the dye dye/binder in the line array supplies aa varying amount /binder layer, which in turn turn causes a varying varying amount of dye to diffuse to the the receiver. receiver. After aa line of picture elements (pixels) moved, new image (pixels) is printed in in this way, the roll is moved, image information information is loaded, loaded, and a new line of pixels may be printed.

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Media

dye , ,t)t)-- heat y, zz dye T(x, y, Calculate T(x, heat transfer transfer (x,y) - mass transfer Calculate Calculate m/A (x,y) Results:

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A* 200 Low Heat Model results. Heat Figure Low Figure 2. 2. Model

High Heat

In Figure 2, some results from a model analysis of thermal dye transfer printing are shown. Heat transfer calculations are used to find the temperature temperature as a function of spatial position model for mass mass transfer is used to find the position and time in the dye/binder layer. A separate model heat", "lowheat for "low shown for are shown Results are receiver. Results the receiver. to the diffuses to mass/area of dye which diffuses ", a small of method heat".". ItIt is "high heat number of heat pulses per is interesting interesting that in this of for "high and for pixel, and per pixel, printing, both the amount and the area coverage of dye in in each each pixel pixel changes as the input number of heat pulses changes. Considerable energy is required to drive the array of heating heating resistors, and only part of moving print media. media. The remaining that energy is effective in raising the temperature of the moving surrounding material, energy will raise the temperature of the surrounding material, and and this might be expected to density. Secondly, it is clear that print density. have an an effect effect on on print that ifif any any one one of of the the array array of of heater heater have elements differs from its neighbors in its resistance (or any other relevant property), then its response to to aa given given input and the the resulting resulting print print density density will will also also differ. differ. We We now now discuss discuss these these response two problems in more detail.

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3. DOWNDOWN-THE-PAGE 3. THE -PAGE NON-UNIFORMITY NON -UNIFORMITY

Measurements of print density density down down the the page page were resistor in in the Measurements of print were made made when when each each resistor the thermal thermal head was with the the same same number number of of pulses pulses per per pixel. pixel. The The number numberofofpulses head was driven driven with /pixel and pulses/pixel and several other In all several other printer printer parameters parameters were were varied. varied. In all cases cases the the density density was was found found to to increase, increase, in in aa non non-uniform -uniformway, way, down down the the page. page. The The results results are are shown shown in in Figure Figure 3. 3. dd (cm) (cm)

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Figure Corrected vs. vs. uncorrected uncorrected prints. Figure 6. 6. Corrected

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4. 4. ACROSS-THE-HEAD ACROSS -THE -HEAD NON-UNIFORMITY NON -UNIFORMITY

In Figure Figure 77 are shown some examples of of the the variation variation in in density density across across the the width width of of aa In are shown some examples thermal print head for identical inputs to each element of thermal print head for identical inputs to each element of the the line line array. array. The The density density differences differences are noticeable. noticeable. Furthermore, Furthermore, the the difference difference in in the are the density density produced produced by by different different heating heating elements increases increases as as the the number number of of heat heat pulses pulses increases. elements increases. IfIf uncorrected, uncorrected, unwanted unwanted bands bands and and streaks prints can can result. result. streaks on on the the output output prints e 0.4 04 o .g

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