WO1995025016A1 - Human readable rewritable recording medium - Google Patents

Human readable rewritable recording medium Download PDF

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Publication number
WO1995025016A1
WO1995025016A1 PCT/EP1995/000988 EP9500988W WO9525016A1 WO 1995025016 A1 WO1995025016 A1 WO 1995025016A1 EP 9500988 W EP9500988 W EP 9500988W WO 9525016 A1 WO9525016 A1 WO 9525016A1
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WO
WIPO (PCT)
Prior art keywords
layer
human readable
liquid crystalline
recording medium
rewritable recording
Prior art date
Application number
PCT/EP1995/000988
Other languages
French (fr)
Inventor
Erik De Haan
Stephen James Picken
Robert Jan Van Wijk
Gustaaf Ronald Mohlmann
Original Assignee
Akzo Nobel N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Akzo Nobel N.V. filed Critical Akzo Nobel N.V.
Publication of WO1995025016A1 publication Critical patent/WO1995025016A1/en

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Classifications

    • 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
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/28—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using thermochromic compounds or layers containing liquid crystals, microcapsules, bleachable dyes or heat- decomposable compounds, e.g. gas- liberating
    • B41M5/281—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using thermochromic compounds or layers containing liquid crystals, microcapsules, bleachable dyes or heat- decomposable compounds, e.g. gas- liberating using liquid crystals only

Definitions

  • the present invention is in the field of human readable rewritable recording media. These media are in the form of sheets, tapes, cards, Tables etc. With rewritable is meant that the written information may be erased and subsequently rewrittten repeatedly.
  • Some known human readable rewritable recording media are based on thermo-sensitive layers having a polymer matrix with higher fatty acid particles dispersed therein. When heated over 120 °C, the higher fatty acid particles are converted into the polycrystalline state and become opaque. This way the necessary parts can be heated and displayed as characters. When reheated to 70-100 °C the material is returned to the monocrystalline state and becomes transparant.
  • These media are described in several publications such as Jetro, January 1994, 94-01-004-03, JP 05262033, JP 05193256, JP 05177975, JP 05169843, JP 05124383, JP 05124382, JP 05038880, JP 04201596, JP 05169843. These recording media are on the market having a metallic like substrate so that opaque characters are written on a metallic like background.
  • Human readable rewritable recording media using this principle have several drawbacks. These media are not used for writing dark characters in an opaque background. For this application said media are less suitable, because the writing must be done slow. There is a demand for human readable rewritable recording media wherein dark characters may be written quickly in a light (opaque) background. A further disadvantage of recording media using this principle is that segregation of the particles occurs in the long run.
  • phase separation liquid crystal polymer is built up from non-liquid crystalline building blocks and liquid crystalline building blocks.
  • the writing principle is based on phase separation between the non-liquid crystalline building blocks and liquid crystalline building blocks. With this principle it is possible to write dark characters in a light background.
  • the drawback of these phase separation based recording media is that it is a rather complicated system wherein there is not much freedom in setting Tgs and Tcs without immediately hampering the contrast.
  • the object of the invention is to provide a human readable rewritable medium which is suitable for writing dark characters quickly in a light background with a good contrast and wherein the phase transition temperatures may be set easily.
  • the invention lies in the fact that the human readable rewritable recording medium comprises:
  • thermosensitive layer which comprises a phase transition liquid crystalline polymer, optionally placed on a transparant substrate, and,
  • thermosensitive layer b) a contrast enhancement layer placed under the thermosensitive layer
  • thermosensitive layer wherein a layer having a low refractive index is present between the thermosensitive layer and the contrast enhancement layer.
  • phase transition liquid crystalline polymers which are used according to the invention are homogeneous and no phase separation occurs.
  • the writing principle is based on phase transition instead of phase separation. This makes the human rewritable medium more stable, also at higher temperatures, and it is possible to write more quickly.
  • This air layer may be obtained by simply not adhering the thermosensitive layer to the contrast layer over the full surface of the layer, but only on distinct places. This may be done by sealing only the outer sides of the layers, or applying a grid of glue lines or dots between the thermosensitive layer and the contrast layer, or placing glass pearls or polymer pearls between the thermosensitive layer and the contrast layer.
  • the glass pearls may be coated with a polymer, so that they adhere thermally on the contrast layer and the thermosensitive layer.
  • thermosensitive layer In another embodiment of the invention a transparant foam film with a low refractive index is placed between the thermosensitive layer and the contrast layer.
  • the thermosensitive layer comprises a liquid crystalline polymer, optionally placed on a transparant substrate.
  • Suitable liquid crystalline polymers are liquid crystalline side chain polymers.
  • the suitability of the liquid crystalline polymers are determined by their phase transition temperatures and the ease to set the Tg and Tc. A rough guideline for the Tg and Tc can be given of how media with a good contrast can be obtained.
  • the Tg should be above room temperature, the difference between Tg and T c should be at least 20°C and not more than 150°C.
  • Liquid crystalline polymers which are preferred are the liquid crystalline polyesters described in EP-A-0478052, and the liquid crystalline polyurethanes described in EP-A-0550105. These liquid crystalline polymers are preferred, because their Tgs and Tcs may be set easily and independent from each other.
  • polyesters according to EP-A-0478052 are obtained by polymerising a monomer mixture comprising diacid chlorides and diols according to the following formula:
  • R 1 -halogen, -R 2 , -OR 2 , , , -CN or -CF 3 ;
  • R 2 -H or an alkyl group having 1-3 carbon atoms
  • R 3 an alkyl group having 1-24 carbon atoms
  • x is an integer in the range of 0 through 6
  • n 0 or 1
  • n is an integer in the range of 0 through 4, and the various R 1 and R 2 groups may be chosen independently from each other.
  • the polyurethanes according to EP-A-0550105 are obtained by polymerising a monomer mixture comprising diisocyanates and diols of the following formula:
  • R 1 -halogen, -R 2 , -OR 2 , , , -CN or
  • R 2 -H or an alkyl group having 1-3 carbon
  • R 3 may represent the same groups as R 1 , but be selected independently of R 1 ;
  • n 0 or 1
  • n 0 or 1
  • y is an integer from 0 through 3;
  • p is an integer from 2 through 4;
  • R 4 an alkyl group having 1-12 carbon atoms
  • x is an integer from 1 through 6;
  • a film may be obtained by solving the polymer in a suitable solvent such as THF/diglyme (4:1), methyl ethyl ketone, cyclopentanone etc. and coating it on a substrate by any suitable method such as meterbar coating, spin coating, gravure coating, reverse roll coating etc.
  • the obtained film may be made homogeneously scattering with the methods described in EP-A-0550105.
  • Suitable substrates are PET, glass, polycarbonate, PVC, ABS, polystyrene, metal, and paper. If a transparant substrate is used, such as PET, it is not necessary to remove the substrate afterwards. When polycarbonate is used, the substrate may be protected with a (transparant) coating to prevent chemical attack from the solvent.
  • the contrast enhancement layer may be any material as long as it has a colour different from the liquid crystalline polymer. Examples are coloured paper, coloured cardboard, coloured plastic substrates or foils, coloured metal substrates or foils (for instance painted or oxidized).
  • homogeneously scattering films (thus a light background) information may be written by locally heating the liquid crystalline polymer above its Tc by means of a thermal printhead needle or a laser.
  • the heated area becomes isotropic and appears coloured, because the coloured contrast enhancement layer is visible through the locally isotropic (thus transparant) film. Owing to the layer having a low refractive index between the contrast layer and the thermosensitive layer a good contrast is obtained.
  • a liquid crystalline polyurethane according to Example 10 of EP-A-0550 105 is solved in THF/diglyme (4:1) and filtrated. Said solution is applied on a 100 micrometers thick PET substrate (Melinex 401 ® , ex ICI) by means of a meterbar. The solvent is removed by drying at room temperature for 5 minutes and subsequent drying at 60 °C for 10 minutes.
  • the film is made homogenously scattering by heating for 2 minutes at 100 °C (Tc minus 10 °) and cooling off with 5° per minute to 78°C
  • the homogenously scattering film is placed on a black plastic substrate, whereby only the outer sides are sealed. Upon writing with a thermal printhead needle a very good contrast is obtained.

Abstract

The present invention is in the field of human readable rewritable recording media. These media are in the form of sheets, tapes, cards, labels, etc. The object of the invention is to provide a human readable rewritable medium which is suitable for writing dark characters quickly in a light background with a good contrast and wherein the phase transition temperatures may be set easily. The invention lies in the fact that the human readable rewritable recording medium comprises: a) a thermosensitive layer which comprises a phase transition liquid crystalline polymer, optionally placed on a transparent substrate, and, b) a contrast enhancement layer placed under the thermosensitive layer, wherein a layer having a low refractive index is present between the thermosensitive layer and the contrast enhancement layer. The layer with the low refractive index may be an air layer. This air layer may be obtained by simply not adhering the thermosensitive layer to the contrast layer over the full surface of the layer, but only on distinct places.

Description

HUMAN READABLE REWRITABALE RECORDING MEDIUM
The present invention is in the field of human readable rewritable recording media. These media are in the form of sheets, tapes, cards, Tables etc. With rewritable is meant that the written information may be erased and subsequently rewrittten repeatedly.
Some known human readable rewritable recording media are based on thermo-sensitive layers having a polymer matrix with higher fatty acid particles dispersed therein. When heated over 120 °C, the higher fatty acid particles are converted into the polycrystalline state and become opaque. This way the necessary parts can be heated and displayed as characters. When reheated to 70-100 °C the material is returned to the monocrystalline state and becomes transparant. These media are described in several publications such as Jetro, January 1994, 94-01-004-03, JP 05262033, JP 05193256, JP 05177975, JP 05169843, JP 05124383, JP 05124382, JP 05038880, JP 04201596, JP 05169843. These recording media are on the market having a metallic like substrate so that opaque characters are written on a metallic like background.
Human readable rewritable recording media using this principle have several drawbacks. These media are not used for writing dark characters in an opaque background. For this application said media are less suitable, because the writing must be done slow. There is a demand for human readable rewritable recording media wherein dark characters may be written quickly in a light (opaque) background. A further disadvantage of recording media using this principle is that segregation of the particles occurs in the long run.
It has been tried to make human readable recording media which are suitable for writing dark characters in a light background. In JP-4218024 (Fuji Xerox) a phase separation liquid crystal polymer is described. Said phase separation liquid crystal polymer is built up from non-liquid crystalline building blocks and liquid crystalline building blocks. The writing principle is based on phase separation between the non-liquid crystalline building blocks and liquid crystalline building blocks. With this principle it is possible to write dark characters in a light background. The drawback of these phase separation based recording media is that it is a rather complicated system wherein there is not much freedom in setting Tgs and Tcs without immediately hampering the contrast.
The object of the invention is to provide a human readable rewritable medium which is suitable for writing dark characters quickly in a light background with a good contrast and wherein the phase transition temperatures may be set easily.
The invention lies in the fact that the human readable rewritable recording medium comprises:
a) a thermosensitive layer which comprises a phase transition liquid crystalline polymer, optionally placed on a transparant substrate, and,
b) a contrast enhancement layer placed under the thermosensitive layer,
wherein a layer having a low refractive index is present between the thermosensitive layer and the contrast enhancement layer.
The phase transition liquid crystalline polymers which are used according to the invention are homogeneous and no phase separation occurs. The writing principle is based on phase transition instead of phase separation. This makes the human rewritable medium more stable, also at higher temperatures, and it is possible to write more quickly.
It appears that when a layer having a low refractive index (approximately 1) is present between the thermosensitive layer and the contrast layer a good contrast is obtained between written parts and the background. The layer with the low refractive index may be an air layer (r.i.= 1). This air layer may be obtained by simply not adhering the thermosensitive layer to the contrast layer over the full surface of the layer, but only on distinct places. This may be done by sealing only the outer sides of the layers, or applying a grid of glue lines or dots between the thermosensitive layer and the contrast layer, or placing glass pearls or polymer pearls between the thermosensitive layer and the contrast layer. When using glass pearls, the glass pearls may be coated with a polymer, so that they adhere thermally on the contrast layer and the thermosensitive layer.
In another embodiment of the invention a transparant foam film with a low refractive index is placed between the thermosensitive layer and the contrast layer.
As mentioned above, the thermosensitive layer comprises a liquid crystalline polymer, optionally placed on a transparant substrate. Suitable liquid crystalline polymers are liquid crystalline side chain polymers. The suitability of the liquid crystalline polymers are determined by their phase transition temperatures and the ease to set the Tg and Tc. A rough guideline for the Tg and Tc can be given of how media with a good contrast can be obtained. The Tg should be above room temperature, the difference between Tg and Tc should be at least 20°C and not more than 150°C.
Liquid crystalline polymers which are preferred are the liquid crystalline polyesters described in EP-A-0478052, and the liquid crystalline polyurethanes described in EP-A-0550105. These liquid crystalline polymers are preferred, because their Tgs and Tcs may be set easily and independent from each other.
The polyesters according to EP-A-0478052 are obtained by polymerising a monomer mixture comprising diacid chlorides and diols according to the following formula:
Figure imgf000006_0001
wherein R1 = -halogen, -R2, -OR2,
Figure imgf000006_0002
,
Figure imgf000006_0003
, -CN or -CF3;
R2 = -H or an alkyl group having 1-3 carbon atoms; R3 = an alkyl group having 1-24 carbon atoms;
A = -CN, -NO2, -CH=C(CN)2, -H, -OR3, -CF3, or
,
Figure imgf000006_0004
x is an integer in the range of 0 through 6
Z : -(CR2=CR2)n-(CR2=Y)m-,-O-C(O)- or -C(O)-O-; Y : =CR2-, =C-CN or =N;
m is 0 or 1,
n is an integer in the range of 0 through 4, and the various R1 and R2 groups may be chosen independently from each other. For further information reference may be had in EP-A-0478052. The polyurethanes according to EP-A-0550105 are obtained by polymerising a monomer mixture comprising diisocyanates and diols of the following formula:
Figure imgf000007_0001
wherein R1 = -halogen, -R2, -OR2,
Figure imgf000008_0001
,
Figure imgf000008_0002
, -CN or
-CF3;
R2 = -H or an alkyl group having 1-3 carbon
atoms;
R3 may represent the same groups as R1 , but be selected independently of R1;
n is 0 or 1;
m is 0 or 1;
y is an integer from 0 through 3;
p is an integer from 2 through 4;
R4 = an alkyl group having 1-12 carbon atoms;
x is an integer from 1 through 6;
Z = -C=N-, -N=C-,
Figure imgf000008_0003
,
Figure imgf000008_0004
, -C=C-. For further information, reference may be had in EP-A-0550105.
A film may be obtained by solving the polymer in a suitable solvent such as THF/diglyme (4:1), methyl ethyl ketone, cyclopentanone etc. and coating it on a substrate by any suitable method such as meterbar coating, spin coating, gravure coating, reverse roll coating etc. The obtained film may be made homogeneously scattering with the methods described in EP-A-0550105. Suitable substrates are PET, glass, polycarbonate, PVC, ABS, polystyrene, metal, and paper. If a transparant substrate is used, such as PET, it is not necessary to remove the substrate afterwards. When polycarbonate is used, the substrate may be protected with a (transparant) coating to prevent chemical attack from the solvent. The contrast enhancement layer may be any material as long as it has a colour different from the liquid crystalline polymer. Examples are coloured paper, coloured cardboard, coloured plastic substrates or foils, coloured metal substrates or foils (for instance painted or oxidized).
In the homogeneously scattering films (thus a light background) information may be written by locally heating the liquid crystalline polymer above its Tc by means of a thermal printhead needle or a laser. The heated area becomes isotropic and appears coloured, because the coloured contrast enhancement layer is visible through the locally isotropic (thus transparant) film. Owing to the layer having a low refractive index between the contrast layer and the thermosensitive layer a good contrast is obtained.
The invention is illustrated with an unlimitative example below. EXAMPLE 1
A liquid crystalline polyurethane according to Example 10 of EP-A-0550 105 is solved in THF/diglyme (4:1) and filtrated. Said solution is applied on a 100 micrometers thick PET substrate (Melinex 401 ®, ex ICI) by means of a meterbar. The solvent is removed by drying at room temperature for 5 minutes and subsequent drying at 60 °C for 10 minutes.
The film is made homogenously scattering by heating for 2 minutes at 100 °C (Tc minus 10 °) and cooling off with 5° per minute to 78°C
(Tg).
The homogenously scattering film is placed on a black plastic substrate, whereby only the outer sides are sealed. Upon writing with a thermal printhead needle a very good contrast is obtained.

Claims

1. Human readable rewritable recording medium, comprising:
a) a thermosensitive layer which comprises a phase transition liquid crystalline polymer, optionally placed on a transparant substrate, and
b) a contrast enhancement layer placed under the thermosensitive layer,
wherein a layer having a low refractive index is present between the thermosensitive layer and the contrast enhancement layer.
2. Human readable rewritable recording medium, according to claim 1, characterised in that the layer having a low refractive index is an air layer.
3. Human readable rewritable recording medium, according to claim 1, characterised in that the layer having a low refractive index is a transparant foam film.
4. Human readable rewritable recording medium, according to claim 1, characterised in that the liquid crystalline polymer is a liquid crystalline side chain polymer.
5. Human readable rewritable recording medium, according to claim 1 characterised in that the liquid crystalline polymer is a liquid crystalline polyester obtained by polymerising a monomer mixture comprising diacid chlorides and diols according to formula:
Figure imgf000011_0002
wherein R1 = -halogen, -R2, -OR2,
Figure imgf000011_0001
,
Figure imgf000011_0003
, -CN or -CF3;
R2 = -H or an alkyl group having 1-3 carbon atoms; R3 = an alkyl group having 1-24 carbon atoms;
A = -CN, -NO2, -CH=C(CN)2, -H, -OR3, -CF3, or
,
Figure imgf000011_0004
x is an integer in the range of 0 through 6
Z : -(CR2=CR2)n-(CR2=Y)m-,-O-C(O)- or -C(O)-O-;
Y : =CR2-, =C-CN or =N;
m is 0 or 1,
n is an integer in the range of 0 through 4, and the various groups R1 and R2 may be chosen independently from each other. Human readable rewritable recording medium, according to claim 1, characterised in that the liquid crystalline polymer is a liquid crystalline polyurethane obtained by polymerising a monomer mixture comprising diisocyanates and diols according to formula :
Figure imgf000012_0001
wherein R1 = -halogen, -R2, -OR2,
Figure imgf000013_0001
,
Figure imgf000013_0002
, -CN or
-CF3;
R2 = -H or an alkyl group having 1-3 carbon
atoms;
R3 may represent the same groups as R1, but be selected independently of R1;
n is 0 or 1;
m is 0 or 1;
y is an integer from 0 through 3;
p is an integer from 2 through 4;
R4 = an alkyl group having 1-12 carbon atoms;
x is an integer from 1 through 6;
Z = -C=N-, -N=C-,
Figure imgf000013_0003
,
Figure imgf000013_0004
, -C=C-
PCT/EP1995/000988 1994-03-16 1995-03-16 Human readable rewritable recording medium WO1995025016A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP94200676.8 1994-03-16
EP94200676 1994-03-16

Publications (1)

Publication Number Publication Date
WO1995025016A1 true WO1995025016A1 (en) 1995-09-21

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Country Status (1)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0216082A (en) * 1988-07-04 1990-01-19 Sony Corp Erasable thermal recording method
JPH0387293A (en) * 1989-08-31 1991-04-12 Toshiba Corp Recording and erasing method and recording medium adapted thereto
EP0535930A1 (en) * 1991-10-04 1993-04-07 Oki Electric Industry Co., Ltd. Thermoreversible recording material, thermoreversible recording medium and recording method

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0216082A (en) * 1988-07-04 1990-01-19 Sony Corp Erasable thermal recording method
JPH0387293A (en) * 1989-08-31 1991-04-12 Toshiba Corp Recording and erasing method and recording medium adapted thereto
EP0535930A1 (en) * 1991-10-04 1993-04-07 Oki Electric Industry Co., Ltd. Thermoreversible recording material, thermoreversible recording medium and recording method

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 14, no. 155 (M - 0954) 26 March 1990 (1990-03-26) *
PATENT ABSTRACTS OF JAPAN vol. 15, no. 260 (M - 1131) 2 July 1991 (1991-07-02) *

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