DE60217045T2 - Thermal recording by means of light spot scanning - Google Patents

Description

THE iNVENTION field

The The present invention relates to a method and an apparatus for thermal recording.

general State of the art

The Recording of thermal images or the thermography is a recording process in which images through the use of imagewise modulated Thermal energy be generated. Most of the direct thermal recording materials are of the chemical type. When heated to a certain transformation temperature There is an irreversible chemical reaction and a color image is generated. A particular interesting direct heat imaging element uses an organic silver salt together with a reducing agent. Such a combination can be achieved by a suitable heat source such as e.g. a thermal head, a laser, etc. are displayed.

One Black and white image can be obtained with such a material because the silver ions under the influence of heat to be developed to metallic silver. However, it seems difficult to be a neutral black tone image. In addition, appears to be difficult to obtain a sufficiently high density as required in certain applications (e.g., in graphic applications).

The Thermal recording of information on a thermographic Material by means of the so-called "light spot scanning" is well known in the art.

The thermal recording may be performed by various types of recording devices, for example, a flat-bed type recording (see 1 ), a recording device of the capstan type (see 2 ), an internal drum type recording device ITD (see 3 ) or an external drum type recording device XTD (see 4 . 5 and 6 ). A detailed description of such recording devices can be found eg in EP 0 734 148 and in US 5,932,394 (both in the name of Agfa-Gevaert), so that in the present invention any explicit and in-depth repetition is redundant.

US 5,278,578 shows a method for avoiding streaking in the thermal transfer drum recording using an array of thermal lasers.

Out EP-A 0 485 148 discloses an image recording apparatus for Recording an image by acting on a light beam photosensitive member comprising: a photosensitive member; Light source means for emitting a first and second beam, one of the first and second beam carries image information; and scanning means for scanning the photosensitive member having the first and second beams with a time interval, so that they are on the photosensitive Material overlaps are.

Out EP-A 0 842 782 discloses a method for thermal recording a gradation image on a heat-sensitive recording material (S) with a photothermal conversion agent for converting from light energy to heat energy to develop a color with a density depending on from the heat energy, comprising the following steps: applying a laser beam (L) with a light energy level depending on a gradation one on the heat-sensitive Recording medium (S) to be recorded image; and scanning the thermosensitive Recording medium (S) with the laser beam (L) at a speed of at least 5 m / s.

Out EP-A 1 104 699 discloses a method for recording an image on a thermographic material (m), comprising the following Steps: Providing a thermographic material with a Thermal imaging element (LE), a transparent thermal head (TH) with energized heating elements (Hi) and a radiation beam (L), activating heating elements of the thermal head and imagewise and scan-wise exposure of the imaging element with the aid of the radiation beam, so that the total energy resulting from the thermal head and the radiation beam a level corresponding to a gradation of the on the imaging element having the image to be recorded, wherein the imagewise and scanning exposure carried out is by sending the radiation beam through transparent parts of the thermal head.

Out US 5,990,917 For example, a mechanical scanning laser system with preheating for recording on a thermal recording medium is known.

Out US 5,932,394 A method is known for generating a rasterized reproduction of a halftone image on a lithographic printing plate, comprising the steps of: (1) transporting a thermosensitive imaging element through an exposure region, wherein the imaging element has at least one scan line with multiple microdots, wherein at least one microdot is one effective microdot is; (2) scanwise exposing the thermosensitive imaging element according to rasterized data representative of tones of a halftone image with an amount of radiation rays while transporting the thermosensitive imaging element through the exposure region, wherein at least one of the radiation rays is an effective radiation ray, at any given moment At the moment during exposure, at least two radiation beams of the set of radiation beams impinge on different microdots of a scan line on the imaging element, so that upon completion of the exposure step for each effective microdot of the scan line all effective beams of the set have impacted, the thermosensitive imaging element comprising at least one imaging layer a hydrophilic surface of a lithographic base, the imaging layer comprising hydrophobic thermoplastic polymer particles and a compound comprising is capable of converting light to heat, the compound being present in the imaging layer or a layer adjacent thereto.

thermal Record according to the state technology with the aid of a light spot scanning laser on one thermographic material generally provides sufficient Density only when the energy emitted by the laser beam is so high is that undesirable Side effects occur (e.g., burning, shrinking and irregular expansion). When the energy is reduced to eliminate such side effects, the issue density is unacceptably low.

This Problem applies in particular to Graphical applications, often optical densities above 3.0 or Require 4.0 or even 5.0 D. In addition, often high spatial resolutions from e.g. above 600 or even 1200 dpi or small line widths e.g. under 40 or even 20 μm or fine pixel sizes e.g. fine as 40 or even 20 microns required.

Aspects of invention

A Object of the present invention is to provide a device for thermal recording, which is able to improve images with tone neutrality to deliver.

A Another object of the present invention is to provide a method of recording information that is capable is to deliver images with improved tonal neutrality.

Further Objects and advantages of the invention will become apparent from the following Description.

Short illustration the invention

The The present invention provides a method for recording of information according to claim 1 and a device for thermal Recording an image according to claim 10.

embodiments The present invention is also achieved by the use of mentioned above Process realized in the laser thermography.

Further Advantages and embodiments The present invention will become apparent from the following description and the following drawings.

Full Description of the invention

Short description the drawings

1 schematically shows a recording device of the flat bed type, which is suitable for use in a method according to the present invention.

2 shows a capstan type recording device suitable for use in a method according to the present invention.

3 schematically shows an internal drum type recording device suitable for use in a method according to the present invention.

4 schematically shows an external drum type recording device suitable for use in a method according to the present invention.

5 shows a preferred embodiment of a thermographic laser apparatus suitable for use in a method according to the present invention.

6 Figure 4 is a pictorial view of another thermographic system XTD suitable for use in accordance with the present invention;

7 shows in principle the time evolution of the temperature reached in a thermographic material when applying several scans according to the present invention.

8.1 Figure 3 shows three consecutive scan lines on a thermographic material passing through an outer drum.

8.2 shows an enlarged detail of a printed line with a line width b ₁ .

9 FIG. 12 shows a relationship between a control voltage for an acousto-optic modulator and the percentage of the transmitted laser power.

10 Fig. 12 shows an output density on a thermographic material as a function of (i) a pixel distance d _Y to the centerline of a printed line, (ii) a preheat temperature T _p, and (iii) a number of passes n _s .

11 Fig. 10 shows a practical time evolution of the temperature T _m in the thermosensitive element when information is recorded in a single pass.

12 Fig. 10 shows a practical time evolution of the temperature reached in the thermosensitive element when information is recorded by performing a plurality of scans according to the present invention.

13 shows a three-dimensional distribution of the available intensity (or power) of a Gaussian laser beam.

14.1 shows the geometric distribution of the temperature reached in a thermographic material T _m when scanning according to a preferred embodiment of the invention.

14.2 shows the geometric distribution of the temperature reached in a substantially light-insensitive thermographic material T _m when scanning according to another preferred embodiment of the invention.

15 shows the efficiency η of a laser system when using different line thicknesses.

16 shows the efficiency η of a laser system using different spatial resolutions.

17 shows the configuration of a substantially non-photosensitive thermographic material suitable for use within the present invention.

18.1 and 18.2 each show a thermographic system containing a first and a second position of the thermosensitive element with respect to a holding means.

parts list

1

Thermal printing system

5

in the Substantially light-insensitive thermographic material m

10

portable Mirror (e.g., polygon)

12

Strahlungsdetektierungselement

14

holding means (e.g., flat)

15

drum

17

hardcopy printing

18

drive system for the drum

19

laser diode array

20

ink ballpoint radiation beam

21

radiation source

22

filter

23

Spinner engine

24

lens

25

Reference beam of radiation

26

first mirror

27

second mirror

28

modulator

29

concave lens

31

control the drum (temperature, speed)

32

power supply (Polygon, modulator)

33

Speed control of the polygon

34

control the radiation source (including Cooling)

35

control of the video signal

40

line

41

Line length B

42

BOL

43

EOL

44

Line width b ₁

46

Material width W _m

50

time temperature development

51

heating curve

52

cooling curve

55

Ambient temperature T _a

56

Temperature T ₂

57

Transformation temperature T _c

58

Temperature T ₁

59

Firing temperature T _b

61

Three-dimensional Distribution of a Gaussian beam intensity

62

Two-dimensional distribution of the temperature T _m1

63

Two-dimensional distribution of temperature T _m2

65

carrier

66

substratum

67

thermosensitive element

68

protective layer

69

backing

80

supply magazine

81

capstan

82

pulling roller

84

recording system

102

supply magazine

104

Riehmen

105

pulling roller

107

leaf from thermographic material

108

roller

109

roller

110

controller

113

fan

116

Journal outlet

117

keyboard

118

laser source

119

modulator

120

first lens

121

polygon mirror

122

second lens

123

sheet input

124

sheet feeder

125

imaging and processing unit / recording unit

x

Fast scan direction

Y

Slow scan direction

Expressions and definitions

Under The term "laser thermography" becomes a technique Direct thermography understood that a uniform preheating step not by any laser and an imagewise exposure step with the help a laser (See, e.g., EP-A 1 104 699).

Of the Term "thermography" applies to the purpose The present application materials that are not directly photosensitive are, but opposite Heat sensitive or heat sensitive are and being a visible change in a heat-sensitive Imaging material by applying sufficient imagewise expended Heat is achieved will be a change to effect at the optical density. These imagewise applied Heat can from a heat source in the immediate vicinity of the heat-sensitive material may be applied in the heat-sensitive material as Result of the absorption of imagewise applied light the presence of at least one light-to-heat conversion agent in the thermosensitive Material be effected.

Of the Term "thermographic Material "(or complete as "thermographic Recording material ", in the Further indicated by symbol m) comprises a heat-sensitive element or Direct thermal imaging element, which is essentially light-insensitive is, and a carrier.

Of the Print-insensitive means that light is involved in the imaging process not directly involved, but does not exclude that light is indirectly involved, as in the case of light absorption by at least one light-to-heat conversion agent.

Of the Printing essentially light-insensitive does not mean intentional sensitive to light.

The terms "main scan speed v _x " or "processing speed" are used interchangeably, as are the terms "slow scan speed v _y " or "transport speed". The processing direction X and the transport direction Y are shown in many drawings (see 1 . 3 . 4 . 5 and 8.1 ).

For example, if, for economic reasons, a line time t ₁ and a resolution (eg dpi) are known, then the corresponding slow scan speeds v _y can be calculated from the following expression:

Here it is assumed that the resolution in both directions is equal to X and Y, so that symbolically DPI X = DPI Y = DPI (expressed in points / inch) [Eq. 2]

The "transit time" t _s (in s) of a light spot scanning laser system is the time between the beginning of the scanning of a line 40 of pixels (BOL _j ) and starting to scan the same line of pixels (BOL _{j + 1} ). Reference is made to 8.1 which shows three consecutive scan lines on a thermographic material passing through a (stationary) inner drum ITD or, for example, at a (th external drum XTD is attached).

If n _{f represents} the number of surfaces and n _{p represents} the number of revolutions of the polygon mirror (per second), then

For example, some experiments were performed at n _f = 8 and n _p = 1875 (min ^-1 ), resulting in a t _s of about 4 ms / pass. Other experiments with the same spin mirror were performed at n _p = 750 (min ^-1 ), resulting in a t _s of about 10 ms / pass. Still further experiments with the same spin mirror were performed at and n _p = 500 (min ^-1 ) resulting in a t _s of about 15 ms / pass.

The "total line time t ₁ " of a light spot scanning laser system is the time between the beginning of printing a line of pixels and the beginning of printing the next line of pixels in the printer transport direction Y (often referred to as "slow scan or sub scan direction"; so-called "fast scan or main scan direction X").

Since n _{s represents} the number of passes, it follows that

Equations 3 and 4 were used to calculate characteristic values for the next table in preparation for a practical experiment, with the same polygon mirror (n _f = 8) rotating at different speeds (see n _P = 205 to 2500 min ^-1 ).

The term "line width b ₁ " may self-explain and is (with the reference number 44 ) in 8.2 shown. The following equation applies:

In a later section on comparative experiments, the physical origin of a line width b _{1 is described} with reference to FIG 14.1 which explains the geometric distribution achieved in a first thermographic material 62 the temperature T _m during scanning according to a preferred embodiment, and with reference to 14.2 representing the geometric distribution achieved with a second, substantially light-insensitive thermographic material m ₂ 63 the temperature T _m when scanning with a second preferred embodiment shows.

By "spatial resolution" is meant the precision (or distance) at which an image is reproduced, measured in terms of the number of lines that can be distinguished in an image, eg expressed in lines / mm or in dots per inch (dpi). The highest resolution that can be achieved with a thermographic system is symbolized here by dpi _upp .

The "pixel writing time t _P " (expressed in s) means the time required to write a pixel. The following mathematical relationship between the pixel writing time t _P (expressed in s), the spatial resolution (expressed in points per inch DPI) and the velocity v _x (expressed in m / s):

The term "efficiency η of the radiation beam" is defined in relation to a geometric distribution of the available intensity (or power) of the radiation beam (eg, a Gaussian laser beam as in FIG 13 shown) and comprises the ratio of the (quasi) total area of such intensity curve to the area of the intensity curve after limiting to temperatures of the substantially light-insensitive thermographic material m to temperatures above the transformation temperature T _C. These surfaces can be calculated using a specific integral calculus.

A "template" is any Expression or any screen output containing information as a picture in the form of variations in optical density, transmission or opacity. Each template consists of a series of picture elements called "pixels". At the present Registration will be the terms Pixel and point also considered equivalent. According to the present Invention can be also the expressions Pixel and point on an input image (known as template) as well as an output image (as screen output or as Expression, e.g. known as Print).

In the present application, a "pixel output D _o, " or "output D _o " for short, includes quantification of a pixel printed on a thermographic material, which quantification may relate to characteristics such as density (symbolized by D), size, and so on.

In The following sections explain some more specific expressions.

thermographic material

The substantially light-insensitive thermographic material m having a firing temperature T _b used in the present invention comprises a heat-sensitive element having a transformation temperature T _c , a support and at least one light-to-heat conversion agent. The substantially light-insensitive thermographic material m may be opaque or transparent. The thickness of the thermosensitive element is generally in the range of about 7 to 25 μm (eg, 20 μm), and the thickness of the support is generally in the range of about 60 to 180 μm (for example, 175 μm). Suitable support materials include polyethylene terephthalate.

The substantially light-insensitive thermographic material m may further comprise a substrate or substrate layer 66 with a typical thickness of about 0.1 to 1 μm (eg 0.2 μm) and / or a protective layer 68 with a typical thickness of about 2 to 6 μm (eg 4 μm) on the same side of the support as the heat-sensitive element (for numbering see 17 ). Optionally, on the other side of the carrier 65 a backing layer 69 be provided which contain an anti-static and / or matting agent (or roughening agents or spacers, expressions that are often used as synonyms) to prevent sticking and / or to support the transport of the substantially light-insensitive thermographic material m. Further details about the configuration of such a substantially light-insensitive thermographic material m are out EP 0 692 733 known.

The Light-to-heat conversion agent are preferred for visible light is transparent and found in the heat-sensitive Element and / or in an adjacent layer thereto as a dispersion solid particles, a solution or partly as solid particles and partly as a solution in them. Suitable light-to-heat conversion agents include infrared-absorbing dye and absorbent. The light-to-heat conversion agents are preferably together homogeneously or separately in the heat-sensitive Element, a constituent layer of the heat-sensitive element and / or an adjacent layer of the heat-sensitive Elements distributed.

The thermosensitive element contains the ingredients required to effect the image formation reaction. The element may comprise a layer system in which the ingredients required to effect the image formation reaction are dispersed in different layers under the condition that the components active in the image formation reaction are in reactive association with each other, ie, during the heat development process, one type of active ingredient must be present so as to be able to diffuse to the other types of active ingredients, that the image formation reaction can occur.

Any type of thermosensitive material having various image formation reactions may be used in the present invention. A preferred thermographic material for use in the present invention is the so-called "Laser Induced Dye Transfer System LIDT", which is incorporated herein by reference US 5,804,355 is described. A preferred image-forming reaction is the reaction of one or more substantially light-insensitive organic silver salts with one or more reducing agents, wherein the reducing agents are such that they can diffuse to the particles of a substantially light-insensitive organic silver salt such that reduction to silver occurs can.

preferred essentially light-insensitive organic silver salts for use in the substantially light-insensitive thermographic material, used in the present invention are essentially light-insensitive silver salts of an organic carboxylic acid, wherein essentially light-insensitive silver salts of a fatty acid such as about silver behenate are particularly preferred.

The so-called "transformation temperature or threshold value T _c " is defined as the minimum temperature of the substantially light-insensitive thermographic material m required for a given period of time to cause an image formation reaction to form a visually perceptible image.

As the temperature of the substantially non-photosensitive thermographic material increases above T _c , the recording density continues to increase, but generally not linearly. A substantially light-insensitive thermographic material used according to the present invention generally has a value T _c between 75 and 120 ° C, in particular between 80 and 110 ° C.

The "firing temperature T _b " of a substantially light-insensitive thermographic material m is the lowest temperature at which any firing could occur, regardless of which layer this might be (eg in a carrier 65 , in a substrate layer 66 , in a thermosensitive element 67 , in a protective layer 68 and / or in a backing layer 69 , see for numbering 17 ).

Device for thermal Recording an image in a substantially light-insensitive thermographic material

Aspects of the present invention are realized by an apparatus for thermally recording an image in a substantially non-photosensitive thermographic material m having a firing temperature T _b , the substantially non-photosensitive thermographic material m being a thermosensitive element having a transition temperature T _c , a support and at least one Light-to-heat conversion means comprises means for generating a radiation beam 20 with wavelengths λ, which is absorbed by the light-to-heat conversion means, and an optical means for scanning a line 40 of the substantially light-insensitive thermographic material m with the radiation beam 20 at various positions along a scan direction at each point in a scan cycle.

According to a first embodiment of the device according to the present invention, the radiation beam 20 be modulated according to the information to be recorded.

According to a second embodiment of the device according to the present invention, the optical scanning means can heat the line of the substantially light-insensitive thermographic recording material m to a first predetermined temperature T ₁ above the transformation temperature T _c and below the firing temperature T _b of the substantially light-insensitive thermographic material m ,

According to a third embodiment of the device according to the present invention, the device further comprises means for cooling the line 40 of the substantially light-insensitive thermographic material m to a second predetermined temperature T ₂ below the transformation temperature T _c .

According to a fourth embodiment of the device according to the present invention, the device further comprises means for re-scanning the line of the substantially light-insensitive thermographic material m at a frequency n _s , wherein the radiation beam is identically modulated according to the information to be recorded.

6 Fig. 10 is a pictorial view of a thermal recording apparatus according to the present invention.

According to a fifth embodiment of the device according to the present invention, the thermographic material may be attached to a holding means 14 (which could be a flatbed), eg on an external drum 15 to be attached.

According to a sixth embodiment of the device according to the present invention, the thermographic material may be attached to a holding means 14 , for example, a drum, which can heat the substantially light-insensitive thermographic material to a preheat temperature T _p below a transformation temperature T _c of the substantially light-insensitive thermographic material.

According to a seventh embodiment of the apparatus according to the present invention, the means for generating a radiation beam 20 a laser beam.

According to an eighth embodiment of the device according to the present invention, the means for generating a radiation beam 20 a coherent light source ( 11 ) comprising a semiconductor or diode laser (optionally fiber-coupled), a diode-pumped laser (such as a neodymium laser), or an ytterbium fiber laser.

According to a ninth embodiment of the device according to the present invention, the means for generating a radiation beam 20 an infrared or near-infrared laser beam, eg with an emission in the wavelength range λ = 700-1500 nm. Suitable lasers include an Nd-YAG laser (neodymium-yttrium-aluminum garnet, 1064 nm) or an Nd-YLF laser (neodymium Yttrium lanthanum fluoride, 1053 nm). Suitable laser diodes usually emit, for example, at 830 nm or at 860-870 nm.

If a laser sweeps over the thermographic material, the temperature rises on the recorded pixels on and in the thermosensitive element comes it to an image formation process e.g. Reduction of a substantially light-insensitive silver salt of the thermographic material, and a perceptible picture appears. After writing a transported first line (not shown in drawing Figure 6) Motor the drum one step.

According to a tenth embodiment of the device according to the present invention, the means for generating a radiation beam 20 a laser beam (eg a YAG-doped Ytterbium laser Yb-YAG which emits a beam of 1030 nm with a continuous power of 20 W, eg "DisKlaser" type, available from NANOLASE), from a modulator 28 , eg an acoustic modulator, which can be activated or deactivated.

6 shows that the laser beam 20 from a first mirror 26 is deflected, passing through a modulator 28 For example, an acoustic modulator that can be activated or deactivated passes. When activated, the laser beam passes to a second mirror 27 and can pass through two lenses to adjust the (vertical) beam diameter and then come to a moving mirror 10 , eg a polygon with eight faces.

This polygon turns the beam over an fθ lens 29 to a toroidal lens (not explicitly shown) which focuses the beam onto the substantially light-insensitive thermographic material.

According to one Eleventh embodiment the device according to the present invention Invention, the optical scanning means comprises a light deflecting means for deflecting the laser beam to be substantially non-photosensitive scanning thermographic material m with the deflected laser beam, like a polygon mirror. The radiation beam scans faster or slower over the substantially light-insensitive thermographic material m, depending on the speed of the moving components in the optical scanning means, such as a polygon mirror.

According to one twelfth embodiment the device according to the present invention Invention, contains the Device further a further heating means.

According to a thirteenth embodiment of the apparatus according to the present invention, the apparatus further includes another heating means comprising an outer drum, such as in FIG 4 and 8.1 shown and off US 5,932,394 known.

4 schematically shows an external drum type recording device with a so-called "imaging array" (eg, a laser array). In such an embodiment, a carriage must be an array 19 from eg laser diodes, at least twice from one side (eg BOL) of the drum 15 move to the other side (eg EOL) of the drum (or sweep that area). Although this appears to require a longer line time (due to the mechanical movements of the carriage), it must be emphasized that such an array preferably scans the substantially non-photosensitive thermographic material m (5) simultaneously with at least two laser beams (sometimes referred to as "comb-like"). , whereby one gains (because of the electro-optical simultaneity) at line time.

According to a fourteenth embodiment of the apparatus according to the present invention, the apparatus further includes another heating means comprising a transparent thermal head (disclosed in U.S. Pat 5 not shown separately) as known from EP-A 1 104 699.

5 shows a preferred embodiment of a laser thermography device suitable for use in a method according to the present invention. In 5 is reference number 5 the thermal imaging element, 17 a hardcopy expression, 20 a laser beam, 102 a supply magazine, 104 a belt, 105 a tension roller, 108 a roller, 109 a roller, 110 a controller, 113 a fan, 116 exposed and processed leaves, 117 a keyboard, 118 a laser source, 119 a modulator, 120 a first lens, 121 a polygon mirror, 122 a second lens, 123 blank sheets to be exposed, 124 a sheet feeding device, 125 an imaging and processing unit, 126 a pressure roller. A detailed description of a laser thermal printer can be found in DE-A 196 36 235.

According to a fifteenth embodiment of the apparatus according to the present invention, the apparatus includes controllable parameters comprising 1) specifications of the substantially light-insensitive thermographic material m and the light-to-heat converting means, 2) temperature T _{p of} the drum, 3) position 4) power of a laser, 5) input of a modulator, 6) transport velocity v _y of the substantially light-insensitive thermographic material m, 7) speed n _{p of} a rotating optical means, 8) number n _s of passes during a line time t ₁ .

According to one sixteenth embodiment the device according to the present invention Invention, concludes the device made a transparent thermal head.

Method of recording of information

Aspects of the present invention are realized via a method for recording information (eg, image data and bar codes), comprising the following steps:
Providing a device for thermal recording 1 , a substantially light-insensitive thermographic material m (5), the thermographic material having a firing temperature T _b (eg, about 300 ° C) and a heat-sensitive element having a transition temperature T _c (eg in the range between 80 ° C and 110 ° C the specific type of thermographic material), a support and at least one light-to-heat conversion agent;
Generating a radiation beam 20 having wavelengths λ which is absorbed by the light-to-heat conversion means and modulated according to the information to be recorded (ie imagewise);
Scan a line ( 40 in 8.1 ) of the substantially non-photosensitive thermographic material m a first time with the radiation beam, whereby the line of the substantially light-insensitive thermographic material m to a first predetermined temperature T ₁ above the transformation temperature T _c and below the firing temperature T _b of the substantially light-insensitive thermographic material m is heated; and re-canning the same line of the substantially light-insensitive thermographic material m at a frequency n _s , wherein the radiation beam is identically modulated in accordance with the information to be recorded.

7 indicates the time evolution of the temperature reached in a thermographic material Applying multiple scans in accordance with the present invention.

In 11 and 12 Various experiments are shown in which the first predetermined temperature T _{1 was} about 200 ° C.

According to a first embodiment of the method according to the present invention, the method further comprises cooling the line 40 of the substantially light-insensitive thermographic material m to a second predetermined temperature T ₂ below the transformation temperature T _c , with non-forced cooling, ie natural, physical decay of the temperature with time, being preferred. Examples of forced cooling is cooling with a blower.

In general, the second predetermined temperature T _{2 is} between the transformation temperature T _c and the ambient temperature T _a . In a preferred embodiment, the second predetermined temperature T _{2 is} almost at the ambient temperature T _a . In a further preferred embodiment, wherein a substantially non-photosensitive thermographic material m with a holding means 14 is in contact (for example, it is flat, as in 1 shown, or it is for example cylindrical, as from a drum 15 in 3 - 6 and 8.1 shown), the second predetermined temperature T _{2 is} at the so-called preheat temperature T _p , so that T ₂ = T _p (see 7 ). In those embodiments in which the retaining means 14 or the drum 15 is not preheated, the temperature T _{p is} the ambient temperature T _a (such that T ₂ = T _p = T _a ).

According to a second embodiment of the method according to the present invention, the method further comprises removing the substantially non-photosensitive thermographic material m from the thermal recording device 1 , whereby a hardcopy expression (in 5 by reference number 17 specified) of the information is supplied.

According to a third embodiment of the method according to the present invention, an upper limit of the spatial resolution (dpi _upp ) is controlled by determining a main scanning speed v _y in relation to the first predetermined temperature T ₁ .

For example, when it is desired for a given substantially non-photosensitive thermographic material m and for a given predetermined temperature T ₁ , a spatial resolution in a hardcopy printout 17 to increase to a required value dpi _upp , the main scanning speed v _{x could be} increased.

The velocity of the radiation beam above the substantially non-photosensitive thermographic material increases with the rotational speed of the rotating polygon. Due to the normally non-squared distribution of the intensity of the laser beam (see 13 ) receives only a portion of the irradiated thermographic material above the transition temperature T _c temperature (see 14.1 and 14.2 ). At a higher main scanning speed v _x , smaller lines are thus recorded. If the slow scan speed v _y is also increased accordingly, a higher spatial resolution is obtained, ie dpi _upp .

Since at a higher main scanning speed v _x, a reduced efficiency η of the laser system is observed (see, for example, US Pat 15 To be explained later), it may be necessary to increase the number of passes n _s to obtain a sufficiently high density.

According to a fourth embodiment of the method according to the present invention, the method further comprises a step of controlling a spatial resolution (dpi) of the hardcopy printout 17 in that the first temperature T _{1 is} chosen to be considerably higher than T _c .

In certain circumstances, the first temperature T _{1 is} relatively close to T _c (as in FIG 14.1 for a thermographic material scanned at a fairly high main scanning speed v _x ), resulting in thinner lines.

In other preferred circumstances, the first temperature T _{1 is} relatively far from T _c (as in FIG 14.2 for the same thermographic material scanned at a relatively low main scanning speed V _x ), resulting in obtaining thicker lines.

If desired, the spatial resolution (dpi) for a hardcopy printout 17 to increase, eg to the upper limit dpi _upp for a given substantially non-photosensitive thermographic material m and for a given main scanning speed v _x , the first temperature T _{1 should be} reduced.

14.1 and 14.2 also illustrate another embodiment of the present invention. For an equal upper limit of the temperature T _m , the spatial resolution (dpi) of the hardcopy printout 17 by selecting the type of thermographic material, in particular with respect to the transformation temperature T _c , when, for example, a device is to comprise two or more film cassettes comprising at least two types of thermographic materials, such as m ₁ and m _2, with respective transformation _temperatures T _c1 and T _c2 .

In general, shows 14.1 the geometric distribution achieved in a thermographic material 62 the temperature T _m when scanning according to a preferred embodiment, and 14.2 shows the geometric distribution achieved in a thermographic material 63 the temperature T _m when scanning according to a second preferred embodiment.

More in detail shows from one point of view 14.1 the geometric distribution of the temperature T _m achieved in a thermographic material when scanning with a high-speed laser beam; and 14.2 shows the geometric distribution of the temperature T _m achieved in a thermographic material when scanning with a low-speed laser beam. From another point of view shows 14.1 the geometric distribution of the temperature T _m achieved in a first, substantially light-insensitive thermographic material m ₁ when scanning with a laser beam; and 14.2 shows the obtained in a second, substantially light-insensitive thermographic material m ₂ geometric distribution of the temperature T _m when scanning with a same laser beam.

It can be quite clear that in a process according to the present invention, the firing temperature T _{b must} not be exceeded (see 7 . 11 and 12 ).

11 shows the actual time evolution of the temperature T _m in the thermosensitive element when recording information in a single pass, 12 FIG. 14 shows the actual time evolution of the temperature T _m reached in the thermosensitive element when information is recorded, by applying multiple scans according to the method of the present invention. Applying multiple scans eliminates unwanted side effects such as warping, staining and burning.

According to a fifth embodiment of the method according to the present invention, the frequency n _s comprises at least twice (n _s ≥ 2, see also FIG 7 . 10 and 12 ).

According to a sixth embodiment of the method according to the present invention, the frequency n _s is defined so that a desired pixel output (D _o ) is achieved.

In some circumstances, the first temperature T _{1 is} relatively close to T _c (as in FIG 14.1 shown), resulting in thinner lines being obtained, so that more passes must be made to have sufficient density in the output pressure 17 to get (especially in the middle of the line width 44 , please refer 8.2 . 10 . 14.1 and 14.2 ).

In other preferred circumstances, the first temperature T _{1 is} relatively far away from T _c (as in FIG 14.2 shown), which gives thicker lines and generally requires fewer passes.

According to a seventh embodiment of the method according to the present invention, an upper limit of the spatial resolution (dpi _upp ) is controlled by determining an energy radiated from the radiation beam with respect to a main scanning speed v _x .

The Laser output must generate sufficient energy, so that with the essentially light-insensitive thermographic material m a desired one Density can be maintained. If a laser is the thermographic material scans, the temperature rises on the recorded pixels, it comes to the image formation reaction and a perceptible image appears. After writing a first line transports one (Not shown in the drawing Figure 6) engine to the drum one step.

According to an eighth embodiment of the method according to the present invention, the method further comprises a step of defining a position (where the scanning of the substantially light-insensitive thermographic material m is performed) of the heat-sensitive element with respect to a holding means 14 or a drum 15 , Reference is made to 18.1 respectively. 18.2 showing a thermography system having a first position and a second position (REPL versus RPEL) of the thermosensitive element with respect to a holding means 14 or a drum 15 contains.

According to a ninth embodiment of the method according to the present invention, the method further comprises a step of further heating (also referred to as "background heating or preheating") of the substantially light-insensitive thermographic material m to a preheat temperature T _p before and / or during the scan of which with the radiation beam (see 5 and 7 ).

17 (not to scale) shows a cross-section of a configuration of a substantially light-insensitive thermographic material m suitable for use in the present invention.

According to one tenth embodiment the method according to the present Invention, includes the substantially light-insensitive thermographic Material m a heat-sensitive Element consisting of at least one layer, the heat-sensitive Element is a substantially light-insensitive organic silver salt and a reducing agent therefor in a heat relationship comprising, wherein the reducing agent in a layer of the thermosensitive Elements that are the essentially light-insensitive organic Contains silver salt, and / or in an adjacent layer of the heat-sensitive element such, that the reducing agent is present such that it is in a thermal working relationship with the substantially light-insensitive organic silver salt located.

According to one Eleventh embodiment the method according to the present Invention, the method further comprises a step of further Heating the substantially light-insensitive thermographic Material m with a transparent thermal head.

moreover It may be additional to the Gaussians and non-Gaussian radiation intensities be advantageous to shape the writing point such that it becomes a "cylinder" writing spot. This can e.g. by so-called diffractive optical elements (DOE) happen.

According to one twelfth embodiment the method according to the present Invention, that concludes essentially light-insensitive thermographic material Image forming layer on a hydrophilic surface.

industrial application

The Apparatus for thermal recording of an image according to the present invention This invention is used to record information in the Substantially light-insensitive thermographic materials for medical and graphic applications.

EXAMPLES

All experiments were performed on an XTD embodiment as in 6 shown performed. The practical dimensions of this system (see also 8.1 ): the diameter D _{d of} the drum 15 was 70 mm, the width of the drum 15 was 250 mm and the width W _m ( 46 ) of the thermographic material was 200 mm.

• 1) Thermografische Spezifikationen des im Wesentlichen lichtunempfindlichen thermografischen Materials m und des IR-Absorbers (z.B. spektrale Bandbreite und Empfindlichkeit) wurden aus einer Matrix von zur Verfügung stehenden Werten ausgewählt.
• 2) Die Temperatur T_p der Trommel 15 wurde in einem Bereich zwischen 30°C und 150°C, besonders bevorzugt zwischen 50°C und 120°C, gesteuert und aller typischsten auf diskrete Werte von 70, 75, 80, 85, 90 und 100°C eingestellt.
• 3) Hinsichtlich der Position des thermografischen Materials 5 bezüglich der Trommel 15 wurden die Einflüsse von zwei Möglichkeiten (in 18.1 und 18.2 als REPL gegenüber RPEL erwähnt) untersucht.
• 4) Die Strahlungsquelle 21 war ein YAG-dotierter Yb-Laser mit einer Wellenlänge λ von 1030 nm. Eine verfügbare Leistung von 20 Watt (im Dauerstrichmodus) führte dazu, dass etwa 9 Watt auf das thermografische Material 5 auftrafen. Manchmal sind niedrigere Werte für die Leistung gewählt worden, indem die Stromversorgung reduziert wurde (z.B. entsprach ein Steuerstrom von 45 A einer Leistung von 20 W).
• 5) Die Eingabe V_c,m eines Modulators 28, insbesondere die Stromversorgung zu einem akustooptischen Modulator AOM (insbesondere ein AOM wie z.B. Typ 1110AF_AIFO_2, von CRYSTAL TECHNOLOGY CORPORATION geliefert) war allgemein auf 1 Volt eingestellt, was eine Ausgabe P_o,m von etwa 93% ergab (siehe auch 9, die eine Beziehung zeigt zwischen einer Steuerspannung V_c,m zu einem akustooptischen Modulator und dem Prozentsatz der übertragenen Laserleistung P_o,m).
• 6) Die Transport- oder Langsamscangeschwindigkeit v_y des im Wesentlichen lichtunempfindlichen thermografischen Materials m lag im Bereich von zwischen 0,35 und 4,5 mm/s. Zu besonders getesteten Geschwindigkeiten zählten 0,35, 0,42, 0,52, 0,70, 1,05, 1,25 und 2,00 mm/s.
• 7) Die Geschwindigkeit n_p des sich drehenden optischen Mittels (z.B. ein Spiegel oder ein Polygon) lagen im Bereich zwischen 250 und 3500 min^-1. Besonders getestete Geschwindigkeiten waren 444, 500, 750 und 1875 min^-1.
• 8) Die Anzahl n_s an Durchgängen (während einer Linienzeit t₁) n_s lag im Bereich zwischen 1 mal und 400 mal. Besonders getestete Werte waren 3, 6, 12, 18, 24, 30, 42, 50, 63, 100, 200 und 400 Durchgänge.

A preferred embodiment of the present invention has been tested and thoroughly evaluated. The controllable parameters mentioned above are summarized in the following paragraph.

• 1) Thermographic specifications of the substantially light-insensitive thermographic material m and the IR absorber (eg, spectral bandwidth and sensitivity) were selected from a matrix of available values.
• 2) The temperature T _{p of} the drum 15 was controlled in a range between 30 ° C and 150 ° C, more preferably between 50 ° C and 120 ° C, and most typically set to discrete values of 70, 75, 80, 85, 90, and 100 ° C.
• 3) With regard to the position of the thermographic material 5 concerning the drum 15 were the influences of two possibilities (in 18.1 and 18.2 mentioned as REPL over RPEL).
• 4) The radiation source 21 was a YAG-doped Yb laser with a wavelength λ of 1030 nm. An available power of 20 watts (in continuous wave mode) resulted in about 9 watts being applied to the thermography material 5 auftrafen. Sometimes lower power values have been chosen by reducing the power supply (eg a control current of 45 A was equivalent to a power of 20W).
• 5) The input V _{c, m of} a modulator 28 In particular, the power supply to an acousto-optic modulator AOM (especially an AOM such as type 1110AF_AIFO_2, supplied by CRYSTAL TECHNOLOGY CORPORATION) was generally set to 1 volt, giving an output P _{o, m} of about 93% (see also US Pat 9 showing a relationship between a control voltage V _{c, m} to an acousto-optic modulator and the percentage of transmitted laser power P _{o, m} ).
• 6) The transport or slow scan velocity v _y of the substantially light-insensitive thermographic material m was in the range of between 0.35 and 4.5 mm / s. Specially tested speeds were 0.35, 0.42, 0.52, 0.70, 1.05, 1.25 and 2.00 mm / s.
• 7) The speed n _{p of} the rotating optical means (eg a mirror or a polygon) ranged between 250 and 3500 min ^-1 . Specially tested speeds were 444, 500, 750 and 1875 min ^-1 .
• 8) The number n _s of passes (during a line time t ₁ ) n _s ranged between 1 and 400 times. Specifically tested values were 3, 6, 12, 18, 24, 30, 42, 50, 63, 100, 200 and 400 passes.

It should be noted that the line time t ₁ can be derived from the transit time t _s (see n _p and Equation 4) and from the number n _s of passes. The t ₁ values tested were 20, 30, 40, 50, 60, ... 225, 630 to 1260 ms.

During the Test program, which led to the present invention have been carried out in-depth experiments. For reasons of brevity In the following two groups of experiments are described in detail to the To illustrate the invention clearer.

• (i) einer Pixelentfernung d_Y (z.B. im Bereich von –50 μm bis +50 μm) von der Mittelachse c_L einer gedruckten Linie 40 (siehe auch 8.2),
• (ii) eine Hintergrunderhitzungs- oder Vorerhitzungstemperatur T_p (z.B. 90°C oder 100°C) und
• (iii) eine Anzahl von Durchgängen n_s (z.B. im Bereich von 3 mal bis 30 mal).

10 records the results of the first set of experiments and shows an output density (up to 4.5 D) for a substantially light-insensitive thermographic material m as a function of:

• (i) a pixel distance d _Y (eg, in the range of -50 μm to +50 μm) from the central axis c _{L of} a printed line 40 (see also 8.2 )
• (ii) a background heating or preheating temperature T _p (eg 90 ° C or 100 ° C) and
• (iii) a number of passes n _s (for example in the range of 3 times to 30 times).

• i) mehr Durchgänge zu einer höheren Dichte führen; mehr Durchgänge führen zu einer breiteren Linienbreite;
• ii) für eine Hintergrundtemperatur T_p = 90°C sind mindestens 30 Durchgänge erforderlich, um eine akzeptable Dichte zu erhalten;
• iii) für eine Hintergrundtemperatur T_p = 100°C sind mindestens 12 Durchgänge erforderlich, um eine akzeptable Dichte zu erhalten;
• iv) eine höhere Hintergrundtemperatur ermöglicht ein schnelleres Aufzeichnen, doch nimmt die Auflösung des Ausgabebilds ab; und
• v) durch Aufzeichnen gemäß der vorliegenden Erfindung lässt sich ohne Verlust an Tonneutralität eine Dichte D > 4,0 erhalten.

From these experiments it can be concluded that:

• i) lead more passes to a higher density; more passes lead to a wider line width;
• ii) for a background temperature T _p = 90 ° C, at least 30 passes are required to obtain an acceptable density;
• iii) for a background temperature T _p = 100 ° C, at least 12 passes are required to obtain an acceptable density;
• iv) a higher background temperature allows for faster recording, but decreases the resolution of the output image; and
• v) by recording according to the present invention, a density D> 4.0 can be obtained without loss of tonal neutrality.

15 and 16 record the results of the second set of experiments, which confirms that: (i) higher polygon speed normally results in smaller linewidth and hence higher spatial resolution, but also ii) higher polygon speed for lower efficiency η led the thermographic system. If a given system and a particular substantially light-insensitive thermographic material are given m, our spatial resolution tests resulted 15 showing the efficiency η of the laser system when different line thicknesses were applied, and too 16 showing the efficiency η of the laser system when different spatial resolutions were applied.

To make sure that the term "efficiency η of the radiation beam" is well understood, it becomes apparent 14.1 Reference is made, in which the obtained in a first, substantially light-insensitive thermographic material m ₁ geometric distribution of the temperature is shown in scanning with a Gaussian laser beam, and on 14.2 which shows the geometric distribution of the temperature when scanning with a same Gaussian laser beam achieved in a second, essentially light-insensitive thermographic material m ₂ . It should be noted that according to the present invention, high spatial resolutions of, for example, over 600 or even 1200 dpi and small line widths of eg less than 40 or even 20 μm are obtained.

After this preferred embodiments of the present invention in detail is now apparent to those skilled in the art, that numerous modifications can be made to it, without from the scope of the invention as defined in the appended claims, departing.

Claims (12)

A method of recording information comprising the steps of: - providing a thermal recording device ( 1 ), a substantially light-insensitive thermographic material m ( 5 ), wherein the thermographic material has a firing temperature T _b and comprises a heat-sensitive element having a transformation temperature T _c , a support and at least one light-to-heat conversion agent; - generating a radiation beam ( 20 ) having wavelengths λ which is absorbed by the light-to-heat conversion means and modulated according to the information to be recorded; - Scan a line ( 40 ) of the substantially non-photosensitive thermographic material m a first time with the radiation beam, whereby the line of the substantially light-insensitive thermographic material m to a first predetermined temperature T ₁ above the transformation temperature T _c and below the firing temperature T _b of the substantially light-insensitive thermographic material m is heated; and characterized by the step of: re-canning the same line of the substantially light-insensitive thermographic material m at a frequency n _s , wherein the radiation beam is identically modulated according to the information to be recorded. The method of claim 1, wherein the method further comprises the step of: cooling the line of substantially non-photosensitive thermographic material m to a second predetermined temperature T ₂ below the transformation temperature T _c . The method of claim 1, wherein an upper limit of the spatial resolution (dpi _upp ) is controlled by determining a main scanning speed v _x in relation to the first predetermined temperature T ₁ . Method according to one of claims 1 to 3, wherein the frequency n ₅ comprises at least twice (n _s ≥ 2). The method of claim 4, wherein the frequency n _{s is} defined such that a desired pixel output (D _a ) is achieved. The method of claim 1, wherein an upper limit of the spatial resolution is controlled by determining an energy radiated from the radiation beam in relation to a main scanning speed v _x . The method of claim 1, further comprising the step of further heating the substantially non-photosensitive thermographic material m to a preheat temperature T _p before and / or during scanning thereof with the radiation beam. A method according to claim 1, further comprising a step of defining a position of the thermosensitive element with respect to a holding means (Fig. 14 ) or a drum ( 15 ). Method according to one of the preceding claims, wherein the substantially light-insensitive thermographic material m a heat-sensitive Element comprises, which consists of at least one layer, wherein the heat sensitive Element is a substantially light-insensitive organic silver salt and a reducing agent for it in a heat relationship with, wherein the reducing agent in a layer of the thermosensitive Elements, which is the substantially light-insensitive organic silver salt contains and / or in an adjacent layer of the heat-sensitive element such, that the reducing agent is present such that it is in a thermal working relationship with the substantially light-insensitive organic silver salt located. Contraption ( 1 ) for thermally recording an image in a substantially lichtunempfindli thermographic material m having a firing temperature T _b , wherein the substantially light-insensitive thermographic material m comprises a heat-sensitive element having a transformation temperature T _c , a support and at least one light-to-heat conversion means, - means for generating a radiation beam ( 20 ) having wavelengths λ which is absorbed by the light-to-heat conversion means; and - optical means for scanning a line ( 40 ) of the substantially light-insensitive thermographic material m with the radiation beam ( 20 at various positions along a scan direction at any one time in a scan cycle, characterized in that the apparatus further comprises means for rescanning the line of substantially non-photosensitive thermographic material m at a frequency n _s , the radiation beam being identically modulated according to the information to be recorded becomes. The device of claim 10, further comprising additional Heating means. Use of a method according to claim 1 in laser thermography.