EP0491846B1 - Reversible or irreversible production of an image - Google Patents

Abstract

PCT No. PCT/EP90/01539 Sec. 371 Date Mar. 13, 1992 Sec. 102(e) Date Mar. 13, 1992 PCT Filed Sep. 12, 1990 PCT Pub. No. WO91/04514 PCT Pub. Date Apr. 4, 1991.A process for the reversible or irreversible production of an image by imagewise exposure of a recording layer to energy in the presence or absence of an electrical and/or magnetic field, resulting in a pattern of surface charges on the surface of the recording layer corresponding to the imagewise exposure to energy. The recording layer consists essentially of an organic material which solidifies in a glass-like manner, is non-photoconductive or substantially non-photoconductive and contains permanent dipoles, in which the pattern of surface charges is produced without or substantially without the formation of free charge carriers by reversible imagewise alignment of at least some of the permanent dipoles present in the recording layer. The process is advantageously carried out using an apparatus which comprises a suitable recording element, devices for imagewise exposure of the recording layer of the recording element to energy, and a counter-electrode which is in direct contact with the recording layer and can be removed therefrom. The pattern of surface charges produced by the process can be toned with liquid or solid toners. The resultant toner image can then either be fixed on the recording layer or transferred from the recording layer to another surface, after which the pattern of surface charges can be erased by exposing the entire surface to energy. A further image can then be produced. In this way, photocopies can be produced without the need to use the high-voltage sources which are necessary in conventional electrophotographic processes.

Description

The present invention relates to a new method for the reversible or irreversible formation of an image by the imagewise action of energy on a recording layer in the presence or absence of an electrical and / or magnetic field, whereby on the surface of the recording layer a pattern of surface charges corresponding to the imaginary action of energy results.

Methods of this type, in which patterns can be generated from surface charges in a wide variety of ways using various physical mechanisms, are known. An example is xerography or electrophotography, in which a photoconductive recording layer, for. B. is charged positively or negatively by means of a high-voltage corona discharge, after which the electrically charged recording layer is exposed imagewise with actinic light. As a result of the exposure, the photoconductive recording layer becomes electrically conductive in its exposed areas, so that the previously generated electrostatic charge can flow off in these areas via an electrically conductive support. This creates a latent electrostatic image on the photoconductive recording layer, which can be developed into a visible image with the aid of suitable liquid or solid toners. This toner image can then be transferred from the recording layer to another surface in a conventional and known manner, resulting in a photocopy. On the other hand, the toner image can also be fixed on the photoconductive recording layer, for example by heating, after which the exposed and therefore toner-free areas of the photoconductive recording layer can be washed away with the aid of suitable liquid developer solvents. The resulting relief layer can then be used for printing purposes, for example. The physical process on which this technique of image-based information recording is based is also known in the scientific literature under the name "Carlson process". In summary, it can be said that in xerography the pattern is formed from surface charges by generating and imagewise removing free charge carriers.

As is known, the xerographic process has disadvantages. So need to generate the high voltage corona discharge to charge the surface DC voltages in the order of 6 kV to 10 kV are applied to the photoconductive recording layer, which raises safety-related and, because of the formation of ozone, also toxicological problems. In addition, because the pattern is formed from surface charges of free electrical charges, the success of the process is affected by the presence of water. This means that excessively high humidity causes premature dissipation of the surface charges even in the dark or prevents sufficient charging of the surface of the photoconductive recording layer. Furthermore, xerography does not allow multiple copies to be made after a single exposure.

A modified xerographic method which overcomes these disadvantages to a certain extent is known from DE-A-15 22 688. In this known method, the pattern of surface charges is generated by irradiating a suitable photoconductive recording layer in the presence of an electric field with a field strength of 1,000 V / cm to 15,000 V / cm over the entire surface. This creates a uniform internal electrical polarization in the recording layer. The surface charge pattern is then formed by local destruction or change in internal polarization. Thus, in contrast to xerography in the narrower sense, the pattern of surface charges is a remanent electrical polarization image, which consists either of electrically positively or electrically negatively charged regions and uncharged regions or of electrically positively and electrically negatively charged regions. This remanent electrical polarization image can be accentuated in the usual and known manner with liquid or solid toners, it being possible to accentuate the remanent electrical polarization image composed of electrically negative and electrically positively charged areas simultaneously with two toners of opposite electrical charge and different colors.

This known method also still has numerous disadvantages. The photoconductive recording layer to be used here is a comparatively thick (15 to 55 »m) inhomogeneous layer made of a photoconductive pigment which is embedded in an electrically insulating carrier. This carrier, which is essential for the known method, prevents the thickness of the recording layer from being reduced. In addition, a very high voltage must still be applied to the photoconductive recording layer so that the process success - the reversible generation of an image - is ensured. Furthermore, it is recommended that Shielding polarized photoconductive recording layer against undesired exposure to light, which generally increases the outlay in terms of apparatus in the known method. Because the known method is still based on the generation of free charge carriers, the polarized photoconductive recording layer is still sensitive to atmospheric moisture, and the electrical charges can balance out again in the heat, which ultimately leads to an unstable image. Furthermore, charge images which are composed of regions of opposite polarization, ie regions which are electrically negatively and electrically positively charged, can only be produced with the aid of a further electrode which lies directly on the photoconductive recording layer and cannot be removed again. However, this additional electrode often reduces the adhesion of the toners to the correspondingly charged areas of the pattern, which drastically deteriorates the quality of the photocopies to be produced. Last but not least, the known method and the photoconductive recording layer used here are not suitable for the reversible generation of an image by imagewise heating of a recording layer with a thermal head or with laser light which is emitted by a semiconductor laser.

EP-A-0 246 500 relates to a layer element with a layer support with a hydrophobic surface and at least one fixed, thin ordered layer applied thereon with a defined uniform and regular structure with a uniform molecular orientation in one direction from a solvent which is soluble in an organic, water-immiscible solvent and / or fusible metallomacrocyclic polymers and their use in electrophotography.

The object of the present invention is to find a new method for the reversible or irreversible formation of an image, in which one of the imagewise effects by imagewise action of energy on a recording layer in the presence or absence of an electric and / or magnetic field on the surface of the recording layer the pattern corresponding to the energy results from surface charges and which no longer has the disadvantages of the prior art.

In addition, it is the object of the present invention to find a new process for producing two-color photocopies, in which a remanent electrical polarization image is formed on the surface of a recording layer, which is composed of electrically positively and electrically negatively charged areas, this new process also should no longer have the disadvantages of the prior art.

Last but not least, it is the object of the present invention to find a new device with which the new method for the reversible or irreversible generation of an image and the new method for producing two-color photocopies can be carried out in a particularly simple and efficient manner.

• des neuen Verfahrens zur reversiblen oder irreversiblen Erzeugung einer Abbildung durch bildmäßige Einwirkung von Energie auf eine Aufzeichnungsschicht (a) in Anwesenheit oder Abwesenheit eines elektrischen und/oder magnetischen Feldes, wodurch auf der Oberfläche der Aufzeichnungsschicht (a) ein der bildmäßigen Einwirkung der Energie entsprechendes Muster aus Oberflächenladungen resultiert,
• des neuen Verfahrens zur Herstellung zwei- oder mehrfarbiger Photokopien durch Erzeugen eines remanenten elektrischen Polarisationsbildes, welches aus elektrisch positiv und elektrisch negativ geladenen Bereichen zusammengesetzt ist oder solche Bereiche enthält, auf der Oberfläche eine Aufzeichnungsschicht (a) und
• des neuen Geräts zur reversiblen oder irreversiblen Erzeugung einer Abbildung

gelöst werden, wobei sowohl die neuen Verfahren als auch das neue Gerät von einer Aufzeichnungsschicht (a) Gebrauch machen, in welcher das Muster aus Oberflächenladungen bzw. das remanente elektrische Polarisationsbild ohne oder fast ohne Bildung freier Ladungsträger und ohne die Anwendung hoher elektrischer Spannungen durch reversibles bildmäßiges Ausrichten oder durch reversibles bildmäßiges Zerstören der Ausrichtung von permanenten Dipolen erzeugt werden kann.Surprisingly, the object of the present invention was able to be achieved with the help

• of the new method for the reversible or irreversible formation of an image by imagewise exposure of energy to a recording layer (a) in the presence or absence of an electrical and / or magnetic field, whereby on the surface of the recording layer (a) a pattern corresponding to the imagewise exposure to energy results from surface charges,
• the new method for producing two-color or multi-colored photocopies by generating a remanent electrical polarization image, which is composed of electrically positive and electrically negatively charged regions or contains such regions, a recording layer (a) and
• of the new device for the reversible or irreversible generation of an image

be solved, both the new method and the new device making use of a recording layer (a) in which the pattern of surface charges or the remanent electrical polarization image with or without almost no formation of free charge carriers and without the use of high electrical voltages by reversible imagewise alignment or by reversible imagewise destruction of the alignment of permanent dipoles can be generated.

Layers have surprisingly contributed to this solution, which show nematic liquid-crystalline, smectically liquid-crystalline or enantiotropic, ferroelectric smectic liquid-crystalline (S _C *) behavior, so that they either convert to a polarized nematic liquid-crystalline order state and apply them when there is sufficient heat by applying an external electric field cooling in this state can be frozen like a glass or can be switched back and forth between two thermodynamically stable, ferroelectric, smectically liquid crystalline S _C * order states.

• (1) die Aufzeichnungsschicht (a) ein glasartig erstarrendes, nicht oder nur wenig photoleitendes, permanente Dipole aufweisendes organisches Material mit nematisch flüssigkristallinem, smektisch flüssigkristallinem oder ferroelektrischem smektisch flüssigkristallinem Verhalten enthält oder hieraus besteht und daß man hierin
• (2) das Muster aus Oberflächenladungen ohne oder fast ohne Bildung freier Ladungsträger durch reversibles bildmäßiges Ausrichten aller oder eines Teils der in der Aufzeichnungsschicht (a) vorhandenen permanenten Dipole erzeugt, wobei man bildmäßig Wärmeenergie einwirken läßt.

Accordingly, the subject of the present invention is a new method for the reversible or irreversible formation of an image by the imagewise action of energy on a recording layer (a) in the presence or absence of an electric and / or magnetic field, thereby causing on the surface of the recording layer (a) a pattern corresponding to the imaginary effect of the energy results from surface charges, the new method being characterized in that

• (1) the recording layer (a) contains or consists of a vitreous solidifying, non-or only slightly photoconductive, permanent dipole organic material with nematic liquid-crystalline, smectically liquid-crystalline or ferroelectric smectically liquid-crystalline behavior and that one consists in it
• (2) the pattern of surface charges without or almost without the formation of free charge carriers is produced by reversibly imagewise aligning all or part of the permanent dipoles present in the recording layer (a), with thermal energy being allowed to act imagewise.

Another object of the present invention is a new device, with the help of which the new method can be carried out in a particularly simple and efficient manner.

In view of the prior art, it was not to be expected that the object on which the invention was based could be achieved by the new method and by the new device, the extraordinarily numerous advantageous design options of the new method on the one hand and the just as numerous possible uses of the new device on the other hand, they were even more surprising.

In the following, the new method for the reversible or irreversible formation of an image by imagewise exposure of energy to a recording layer (a) in the presence or absence of an electric and / or magnetic field, thereby causing one of the imagewise effects on the surface of the recording layer (a) Energy-related pattern results from surface charges, for brevity referred to as the "inventive method".

For the same reason, the new device, which is used for the reversible or irreversible formation of an image by imagewise exposure to energy on a recording layer (a) in the presence or absence of an electric and / or magnetic field, thereby a on the surface of the recording layer (a) The pattern corresponding to the imaginary effect of the energy results from surface charges, referred to as the "device according to the invention".

The process according to the invention is carried out with the aid of the recording layer (a).

According to the invention, all those recording layers (a) are suitable which contain an organic material having a glassy solidification, non-or only slightly photoconductive, permanent dipoles, or which consist thereof, those recording layers (a) which consist only of such an organic material being very suitable are and are therefore preferred according to the invention.

Accordingly, all the organic materials which solidify glass-like, are not or only slightly photoconductive, have permanent dipoles and in which due to the nonexistent or only low photoconductivity can be used for the production of suitable and highly suitable recording layers (a) to be used according to the invention Expose no or very few free charge carriers can be generated.

These suitable organic materials to be used according to the invention can be low-molecular, oligomeric or high-molecular compounds, and in the case of the high-molecular compounds they can also be cross-linked in two or three dimensions. Of these compounds, the high-molecular ones are used with particular preference for the application according to the invention.

Examples of highly suitable organic materials to be used according to the invention are those with nematic liquid-crystalline, smectically liquid-crystalline or ferroelectric smectic liquid-crystalline behavior. Of these, those with nematic liquid-crystalline and ferroelectric smectic liquid-crystalline behavior are particularly preferred, and those with ferroelectric smectic liquid-crystalline behavior are particularly preferably used.

The compounds with nematic liquid-crystalline behavior which are particularly preferably used for the application according to the invention contain permanent dipoles which usually do not align in such a way that a macroscopic dipole moment results. However, at appropriate temperatures, their permanent dipoles can be oriented in the field direction by an electric field. After the organic material in question has cooled below its glass transition temperature T _G , the orientation of the permanent dipoles is frozen like a glass, so that a macroscopic dipole moment results (cf. US Pat. No. 4,762,912).

Examples of highly suitable compounds with nematic liquid-crystalline behavior that are to be used particularly preferably for the purpose of the invention are from US Pat. No. 4,762,912, EP-A-0 007 574, EP-A-0 141 512 or EP-A -0 171 045 known.

From the compounds with ferroelectric smectic liquid-crystalline behavior which are very particularly preferably used for the application purpose according to the invention, those are to be emphasized which show enantiotropic, ferroelectric smectic liquid-crystalline (S _C *) behavior in thin layers, so that they act between sufficient heat exposure by applying an external electric field two thermodynamically stable, ferroelectric smectically liquid crystalline S _C * order states can be switched back and forth. Such behavior is shown by known maps of chiral mesogenic compounds or groups which contain at least one optically active center. These compounds or groups can form a smectically liquid-crystalline phase, in which the chiral mesogenic compounds or groups as a whole are aligned in parallel by the intermolecular interactions and are joined together to form micro-layers stacked one above the other at equal intervals. These so-called S _C * phases have an electrical spontaneous polarization even in the absence of an external electrical field, this remanent polarization being able to be reoriented by applying an external electrical field, which is why these phases are consequently referred to as "ferroelectric".

gekennzeichnet. Insgesamt führt die Ausrichtung der einzelnen lateralen Dipole der chiralen mesogenen Verbindungen oder Gruppen zu einem makroskopischen Dipolmoment. Indessen führt im allgemeinen der Direktor

in der S_C*-Phase, sofern diese räumlich nicht begrenzt ist, beim Durchgang durch die einzelnen Mikroschichtebenen eine Präzessionsbewegung um die Normale Z aus, d. h. der sogenannte Polarisationsvektor

, welcher die Richtung des Gesamtdipolmoments der Phase angibt, läuft auf einer Helix durch die S_C*-Phase, wodurch ein Gesamtdipolmoment von 0 resultiert.In the ferroelectric, smectically liquid-crystalline S _C * phase, the microlayer structure that is typical for smectically liquid-crystalline phases is present, the molecular longitudinal axes of the chiral mesogenic compounds in the individual microlayers having a tilt angle Til of + α or -α with respect to the layer normal Z. The direction of the inclination or tilt angle Θ of the longitudinal axes of the molecules in a microlayer in relation to the layer normal Z is generally determined by the so-called director

featured. Overall, the alignment of the individual lateral dipoles of the chiral mesogenic compounds or groups leads to a macroscopic dipole moment. However, the director generally leads

in the S _C * phase, provided that this is not spatially limited, a precession movement around the normal Z, that is to say the so-called polarization vector, when passing through the individual microlayer levels

, which indicates the direction of the total dipole moment of the phase, runs on a helix through the S _C * phase, resulting in a total dipole moment of 0.

mit dem äußeren elektrischen Feld wieder übereinstimmt. Diese Umkehrung der Polarisation beruht auf dem "Umkippen" der Moleküllängsachsen der chiralen mesogenen Verbindungen oder Gruppen vom Tiltwinkel Θ von + α in den Tiltwinkel Θ von - α oder umgekehrt. Dabei bildet sich ein neuer ferroelektrischer smektisch flüssigkristalliner S_C*-Ordnungszustand in der Phase aus. Sind diese beiden ferroelektrischen smektisch flüssigkristallinen S_C*-Ordnungszustände thermodynamisch stabil, spricht man von enantiotropem, ferroelektrischem, smektisch flüssigkristallinem S_C*-Verhalten. Da hierbei das "Umkippen" der Moleküllängsachsen der chiralen mesogenen Verbindungen oder Gruppen auf einer Kegelbahn erfolgt, vollzieht sich der Wechsel zwischen diesen beiden S_C*-Ordnungszuständen sehr rasch, weswegen denn auch die Schaltzeiten τ für das Hin- und Herschalten der S_C*-Phase zwischen diesen beiden S_C*-Ordnungszuständen ausgesprochen niedrig sind.However, if such a ferroelectric smectic liquid-crystalline S _C * phase is limited in its thickness and either heated in an external electric field of the appropriate sign and the appropriate orientation or exposed to a very strong external electric field of the appropriate sign and the appropriate orientation, then at exceed a limit field strength dependent on the chiral mesogenic compound used in each case, the direction of the polarization in the S _C * phase is reversed, so that its polarization vector

matches the external electric field again. This reversal of polarization is based on the "tipping over" of the molecular longitudinal axes of the chiral mesogenic compounds or groups from the tilt angle Θ of + α to the tilt angle Θ of - α or vice versa. A new ferroelectric smectically liquid crystalline S _C * order state is formed in the Phase out. If these two ferroelectric smectically liquid crystalline S _C * order states are thermodynamically stable, one speaks of enantiotropic, ferroelectric, smectically liquid crystalline S _C * behavior. Since the molecular longitudinal axes of the chiral mesogenic compounds or groups "tip over" on a bowling alley, the change between these two S _C * order states takes place very quickly, which is why the switching times τ for switching the S _C * back and forth Phase between these two S _C * order states are extremely low.

seine Präzessionsbewegung durch die S_C*-Phase vollführt. In einer solchen makroskopischen Schicht wird die durch die Präzessionsbewegung des Direktors

beschriebene Helix sozusagen spontan "aufgewunden", so daß die chiralen mesogenen Verbindungen oder Gruppen nur noch zwei Möglichkeiten haben, sich zu orientieren.As is known, this behavior is particularly pronounced when the chiral mesogenic compounds are present in a layer whose thickness d is less than the pitch G of the helix along which the director

performs its precessional movement through the S _C * phase. In such a macroscopic layer, the precession movement of the director

described helix "wound" spontaneously, so to speak, so that the chiral mesogenic compounds or groups have only two options for orientation.

Here, such chiral mesogenic compounds and groups to be used according to the invention are very particularly advantageous, in which, after local heating and cooling in the presence of an electric field, one of the two thermodynamically stable (enantiotropic), ferroelectric, smectically liquid-crystalline S _C * order states locally at room temperature can be frozen in a glass-like manner, the chiral mesogenic compounds or groups in question in the other non-heated areas of the organic material either in the other thermodynamically stable ferroelectric smectic liquid-crystalline S _C * order state, in another, not necessarily ferroelectric, liquid-crystalline phase, in disordered Microdomains (scattering centers) or in an isotropic I phase. According to the invention, it is particularly advantageous if the chiral mesogenic compounds or groups are in the other thermodynamically stable, ferroelectric, smectically liquid-crystalline S _C * order state.

There is an additional advantage for the recording layer (a) if the chiral mesogenic compounds or groups contained therein pass into the isotropic I phase below 200 ° C., ie. that is, they have a clearing point below 200 ° C.

In addition, there is an additional advantage for the recording layer (a) to be used according to the invention if the chiral mesogenic compounds or groups contained therein have a phase transition S _C * → S _A *, which is also generally referred to as the Curie temperature T _C , in the temperature range from 50 to 150, preferably 50 to 100, in particular 50 to 90 ° C.

Furthermore, it is of very particular advantage for the recording layer (a) to be used according to the invention if the organic materials containing permanent dipoles contained therein have a glass transition temperature Tg above 25 ° C.

Examples of compounds with enantiotropic, ferroelectric, smectically liquid-crystalline (S _C *) behavior, which are particularly suitable for the application according to the invention, are described in EP-A-0 184 482, EP-A-0 228 703, EP A-0 258 898, EP-A-0 231 858, EP-A-0 231 857, EP-A-0 271 900 or EP-A-0 274 128 or they are described in German patent application P 39 17 196.5.

Accordingly, the recording layers (a) which consist of chiral mesogenic compounds of the type mentioned above or which contain chiral mesogenic groups of the type mentioned above have very particular advantages when used according to the invention and are therefore very particularly suitable for the process according to the invention.

In the excellently suitable recording layers (a) according to the invention, the microlayer planes of the S _C * phase, which is formed by the chiral mesogenic compounds or groups, are oriented perpendicular to the plane of the recording layer (a). In general, the excellently suitable recording layers (a) to be used according to the invention have a ferroelectric spontaneous polarization P _S or a dipole density or a sum of the aligned dipole moments per unit volume of the recording layer (a) used in each case from 1 to 300, advantageously 10 to 300 and in particular 20 to 300 nC / cm².

In general, the recording layer (a) to be used according to the invention, which is very excellently suitable, has a thickness d of 0.1 to 20 μm. If it is more than 20 »m thick, there may be a loss of bistability under certain circumstances, whereas a thickness d of> 0.1» m may cause it to deform, for example due to capillary effects. The thickness range from 0.1 to 20 »m thus represents an optimum within which the thickness d of the recording layer (a) can be varied widely and can be adapted to the respective requirements, which arise from the desired application-related property profile on the one hand and the physical chemical properties the organic materials used on the other hand result. Within this thickness range that of 0.1 to 10, advantageously 0.1 to 8, and in particular 0.2 to 5 »m, should be emphasized again in particular because the outstanding recording layers (a) of this thickness range have very particular advantages when carrying out the process according to the invention, in particular show a higher sensitivity to the imaginary energy effect and a better stability of the remanent electrical polarization image.

• den niedermolekularen chiralen mesogenen Verbindungen mit enantiotropem, ferroelektrischem smektisch flüssigkristallinen (S_C*)Verhalten oder aus
• den vernetzten oder unvernetzten Polymeren, welche chirale mesogene Seitengruppen mit enantiotropem, ferroelektrischem smektisch flüssigkristallinem (S_C*)Verhalten zeigen,

nach den üblichen und bekannten Techniken der Herstellung dünner Schichten erzeugt.The production of the recording layers (a) to be used according to the invention has no special features in terms of method, but instead is made from the conventional and known suitable organic materials described above, some of which are commercially available, but in particular from

• the low molecular weight chiral mesogenic compounds with enantiotropic, ferroelectric smectic liquid crystalline (S _C *) behavior or from
• the crosslinked or uncrosslinked polymers which show chiral mesogenic side groups with enantiotropic, ferroelectric, smectic, liquid-crystalline (S _C *) behavior,

produced according to the usual and known techniques for producing thin layers.

Examples of suitable techniques for the production of thin layers of low-molecular chiral mesogenic compounds of the type mentioned and the compounds themselves are z. B. from US-A-4 752 820, WO-A-87/07890 or WO-A-86/02937 known.

Furthermore, EP-A-0 184 482, EP-A-0 228 703, EP-A-0 258 898, EP-A-0 231 858, EP-A-0 231 857, the EP-A-0 271 900 and EP-A-0 274 128 disclose the techniques for producing thin layers of crosslinked or uncrosslinked polymers with chiral mesogenic side groups of the type mentioned, and the polymers themselves, or they are described, for. B. in German patent application P 39 17 196.5 described in detail. The techniques mentioned herein for the production of thin layers and the polymers used here are particularly preferably used for the production of the recording layers (a) to be used according to the invention.

To carry out the method according to the invention, the recording layer (a) to be used according to the invention is applied to the orientation layer (e) in the desired suitable thickness in a customary and known manner electrically conductive support (b), which contains at least one dimensionally stable support layer (c), an electrode layer (d) and the orientation layer (e) one above the other in the order given, resulting in a recording element (A, D, E), which at least contains said layers (c), (d), (e) and (a) one above the other in the order given.

Examples of dimensionally stable carrier layers (c), electrode layers (d) and orientation layers (e), which are suitable for the construction of the recording element (A, D, E) to be used in the method according to the invention, can be found in the patents WO-A-86 / 02937, WO-A-87/07890, US-A-4 752 820, GB-A-2 181 263, US-A-4 752 820, EP-A-0 184 482, EP-A-0 205 187, EP-A-0 226 218, EP-A-0 228 703, EP-A-0 231 857, EP-A-0 231 858, EP-A-0 258 898, EP-A-0 271 900 or EP- A-0 274 128 or they are described in German patent application P 39 17 196.5.

When carrying out the method according to the invention, an imagewise action of energy on the recording layer (a) in the surface thereof in the presence or absence of an electrical and / or magnetic field results in a pattern of surface charges corresponding to the imaginary action of the energy, i. i.e., a retentive electrical polarization image is generated. This remanent electrical polarization image is composed either of electrically positive and electrically negatively charged areas or of electrically positively or electrically negatively charged areas and uncharged areas, or it contains these areas.

According to the invention, this pattern is generated from surface charges or the remanent electrical polarization image with no or almost no formation of free charge carriers by the reversible imagewise alignment of all or part of the permanent dipoles present in the recording layer (a).

• (i) in Abwesenheit eines elektrischen und/oder magnetischen Feld durch reversibles bildmäßiges Zerstören der Ausrichtung eines Teils der in der Aufzeichnungsschicht (a) vorhandenen ausgerichteten permanenten Dipole,
• (ii) in der Gegenwart eines elektrischen und/oder magnetischen Feldes durch reversibles bildmäßiges Verändern oder Umkehren der Ausrichtung eines Teils der in der Aufzeichnungsschicht (a) vorhandenen ausgerichteten permanenten Dipole oder
• (iii) in der Gegenwart eines elektrischen Feldes durch reversibles bildmäßiges Ausrichten eines Teils der in der Aufzeichnungsschicht (a) vorhandenen nicht ausgerichteten permanenten Dipole

bei der bildmäßigen Einwirkung von Energie auf die Aufzeichnungsschicht (a) geschehen.According to the invention, this can

• (i) in the absence of an electric and / or magnetic field by reversibly imagewise destroying the orientation of a portion of the aligned permanent dipoles present in the recording layer (a),
• (ii) in the presence of an electric and / or magnetic field by reversibly imagewise changing or reversing the orientation of a portion of the aligned permanent dipoles or present in the recording layer (a)
• (iii) in the presence of an electric field by reversibly imagewise aligning a portion of the non-aligned permanent dipoles present in the recording layer (a)

in the imagewise action of energy on the recording layer (a).

According to the invention, the imagewise effect of thermal energy is advantageous, the use of laser light, in particular that emitted by semiconductor lasers, or a conventional and known thermal head being particularly advantageous.

When using laser light, it is recommended that the recording layer (a) contain customary and known components, which may be chemically bonded to the organic material in question, which strongly absorb the laser light, and / or that the recording layer (a) be a conventional and known one Layer rests, which strongly absorbs the laser light.

The pattern of surface charges or the remanent electrical polarization image resulting here in the procedure according to the invention can, after its intended use, either through the full-surface exposure to energy in the presence or absence of an electrical and / or magnetic field without the formation of free charge carriers with full alignment of all in the recording layer (a ) existing permanent dipoles or with complete destruction of the orientation of the permanent dipoles present in the individual areas of the pattern or image. Here too, thermal energy is advantageous according to the invention.

According to the invention, a new pattern of surface charges or a retentive electrical polarization image can be generated in the recording layer (a) after the deletion, which is why the method according to the invention is reversible.

An example of a preferred use according to the invention of the pattern of surface charges or the remanent electrical polarization image is its accentuation with liquid or solid toners, after which the resulting toner image can be transferred to another surface, thereby photocopying the pattern or image on the other surface arises.

According to the invention, the emphasis can then be repeated, ie it can be from a pattern of surface charges or from a remanent one electrical polarization image several photocopies can be obtained, which is a very special advantage of the inventive method. However, the pattern or image present in the recording layer (a) can be erased again in the manner mentioned above, after which a new pattern or image can be produced in the manner according to the invention and, after being re-emphasized, used for copying purposes.

According to the invention, the remanent electrical polarization image generated in the manner according to the invention, which is composed of regions containing electrically positive and negatively charged electrons or contains these regions, can be simultaneously or successively accentuated with at least two liquid or solid toners of opposite electrical charge, as a result of which a two-colored or multicolored A toner image is formed which, after being transferred from the recording layer (a) to another surface, provides a two-color or multi-color photocopy. Further advantages are obtained if at least two toners are used which have a strong optical contrast. Here too, according to the invention, several photocopies can be obtained from one and the same retentive electrical polarization image.

However, it is also possible to accentuate the pattern of surface charges generated in the manner according to the invention or the remanent electrical polarization image with at least one liquid or solid toner, after which the resulting toner image is fixed, for example by heating. It goes without saying that this fixed toner image produced in the method according to the invention can no longer be deleted, which is why this embodiment of the method according to the invention is irreversible. However, this is offset by the fact that the fixed toner image can be washed out by washing out its unstressed areas with the aid of suitable developer solvents, which results in a relief layer on the recording element which, inter alia, can be used for printing purposes.

The method according to the invention can be carried out with a wide variety of devices.

According to the invention, however, it is advantageous if the device according to the invention is used to carry out the method according to the invention.

The device according to the invention comprises at least one of the recording elements (A, D, E) described in detail above, at least one counterelectrode (C, F), and at least one energy source or device (B) which is used for the imagewise action of energy on the recording layer (a ) serves.

According to the invention, it is advantageous if the device (B) for imagewise exposure to energy contains a laser light source (G), in particular a semiconductor laser, or a conventional and known thermal head (G).

It is also advantageous according to the invention if the counter electrode (C, F) is arranged so that it can be removed from the recording element (A, D, E) again. The counter electrode (C, F) is advantageously in direct contact with the recording layer (a, D). It can be in the form of a flat or curved plate or in the form of a roller which is moved in relative movement over the recording element (A, D, E) at a suitable speed. The counter electrode (C, F) is connected in the opposite direction to the electrode layer (d) of the electrically conductive carrier (b). The surface of the counter electrode (C, F) can be covered by a conventional and known polysiloxane layer or Teflon layer (h).

Furthermore, it is advantageous according to the invention if the surface of the counterelectrode (C, F) is either structured in such a way that it acts as an orientation layer (g), or is covered by an orientation layer (g) which either has the composition and structure of the Orientation layer (s) of the recording element (A, D, E) corresponds to or differs therefrom. Furthermore, the counter electrode (C, F) can be heated and / or have a relief-like surface.

The device according to the invention can contain a flat or a roller-shaped recording element (A, D, E).

If the device according to the invention contains a flat recording element (A, D, E), then either the flat or the curved plate-shaped counterelectrode can be pressed onto the recording layer (a) of the recording element (A, D, E), the full area of the recording layer ( a) or only a part of it is covered by the counter electrode (C, F). However, the roller-shaped electrode (C, F) can also be used, which is then, preferably in the full width of the recording element (A, D, E), moved in relative motion at a suitable speed over its recording layer (a).

However, if the device according to the invention contains a roller-shaped recording element (A, D, E), then either the flat or the curved plate-shaped counterelectrode (C, F) can be used, via which the roller-shaped recording element (A, D, E) moves in relative motion moving at an appropriate speed. However, the roller-shaped counter electrode (C, F) are used, which is rotated against the roller-shaped recording element (A, D, E) in the manner of a calender at a suitable speed, which is particularly advantageous according to the invention.

Furthermore, the device according to the invention can have at least one device (H) for emphasizing the pattern of surface charges with solid or liquid toners generated in the recording layer (a), at least one device (I) for transferring the toner image from the recording layer (a) to another Surface or alternatively at least one device (J) for fixing the toner image, at least one device (K) for the full-surface action of energy, in particular thermal energy, on the recording element (A, D, E), which is also in the counter electrode (C, F ) can be included, and contain at least one device (L) for generating electrical and / or magnetic fields which can penetrate the entire area of the recording element (A, D, E).

In addition, the device according to the invention contains conventional and known electrical and / or mechanical devices which are useful for controlling the device according to the invention, such as electrical and / or mechanical control systems and servomotors. In addition, the device according to the invention can be connected to and controlled by a process computer.

• 1. Zwischen der walzenförmigen Gegenelektrode (C, F) und der Elektrodenschicht (d) des Aufzeichnungselements (A, D, E) wird eine geeignete Spannung im Bereich von 1 bis 100 V angelegt. Hiernach wird die walzenförmige Gegenelektrode (C, F) mit einer geeigneten Geschwindigkeit in relativer Bewegung über die Aufzeichnungsschicht (a) des Aufzeichnungselements (A, D, E) hinweggeführt. Dadurch werden die in der Aufzeichnungsschicht (a) vorhandenen permanenten Dipole vollflächig ausgerichtet. Unmittelbar hinter der sich bewegenden walzenförmigen Gegenelektrode (C, F) erfolgt die bildmäßige Einwirkung von Energie, wodurch das Muster aus Oberflächenladungen oder das remanente elektrische Polarisationsbild resultiert. Das Aufzeichnungselement (A, D, E), welches nun das Muster oder das Bild enthält, wird dann in relativer Bewegung mit einer auf die Bewegung der walzenförmigen Gegenelektrode (C, F) abgestimmten Geschwindigkeit zu der Betonerungsvorrichtung (H) geführt und dort betonert. Hiernach wird das betonerte Aufzeichnungselement (A, D, E) in relativer Bewegung mit der abgestimmten Geschwindigkeit zu der Vorrichtung (I) für das übertragen des Tonerbildes von der Aufzeichnungsschicht (a) auf eine andere Oberfläche geführt. Hiernach kann entweder das tonerfreie Aufzeichnungselement zur Betonerungsvorrichtung (H) und zur Vorrichtung (I) zum übertragen des Tonerbildes zurückgeführt werden, wodurch zwei oder mehr Kopien des ursprünglichen Musters oder Bildes erzeugt werden können, oder es kann zum Löschen des Musters oder des Bildes die walzenförmige Elektrode (C, E) in abgestimmter relativer Bewegung erneut über das Aufzeichnungselement (A, D, E) hinwegbewegt werden.
• 2. Statt zu einer Vorrichtung (I) zum übertragen des Tonerbildes von der Aufzeichnungsschicht (a) auf eine andere Oberfläche geführt zu werden, kann das betonerte Aufzeichnungselement (A, D, E) zu einer Vorrichtung (J) zum Fixieren des Tonerbildes bewegt werden, wonach das Aufzeichnungselement (A, D, E) zur Weiterverarbeitung in geeigneter Weise das erfindungsgemäße Gerät verläßt.
• 3. An das Aufzeichnungselement (A, D, E) mit einer nicht vollflächig ausgerichteten Aufzeichnungsschicht (a) wird ein senkrecht zu der Aufzeichnungsschicht (a) orientiertes elektrisches Feld angelegt. Hiernach wird die Aufzeichnungsschicht (a) bildmäßig erwärmt, wodurch das Muster aus Oberflächenladungen oder das remanente elektrische Polarisationsbild entsteht. Hiernach wird das Aufzeichnungselement (A, D, E) in relativer Bewegung mit einer geeigneten Geschwindigkeit wie unter Ziffer 1. beschrieben zu den Vorrichtungen zum Betonern (H) und zum übertragen des Tonerbilds von der Aufzeichnungsschicht (a) auf eine andere Oberfläche (I) oder, alternativ hierzu, zu einer Vorrichtung (J) zum Fixieren des Tonerbildes geführt. Sofern das in der Aufzeichnungsschicht (a) vorhandene Muster oder Bild wieder gelöscht werden soll, wird die Aufzeichnungsschicht (a) so hoch erhitzt, daß die bildmäßige Ausrichtung der permanenten Dipole in der Aufzeichnungsschicht (a) wieder zerstört wird.
• 4. Diese Ausführungsform wird wie unter Ziffer 1. beschrieben durchgeführt, nur daß zum Zwecke der Erzeugung eines remanenten elektrischen Polarisationsbildes, welches aus elektrisch positiv und elektrisch negativ geladenen Bereichen zusammengesetzt ist, bei der bildmäßigen Einwirkung von Energie an die Aufzeichnungsschicht (a) vollflächig ein elektrisches Feld angelegt wird, dessen Feldlinien die Aufzeichnungsschicht (a) durchdringen, und daß das remanente elektrische Polarisationsbild in der Betonerungsvorrichtung (H), vorteilhafterweise sukzessive, mit zwei optisch stark kontrastierenden Tonern entgegengesetzter elektrischer Ladung betonert wird, wodurch ein zweifarbiges Tonerbild entsteht. Dieses wird in der gleichen Weise, wie sie bei der Ausführungsform unter Ziffer 1. beschrieben wird, zur Herstellung von Photokopien verwendet, welche nun aber zweifarbig sind.
• 5. Bei dieser Ausführungsform wird zwischen der walzenförmigen Gegenelektrode (C, F) und der Elektrodenschicht (d) des Aufzeichnungselements (A, D, E) eine geeignete Spannung im Bereich von 1 bis 100 V angelegt. Hiernach wird die walzenförmige Gegenelektrode (C, F) mit einer geeigneten Geschwindigkeit in relativer Bewegung über die Aufzeichnungsschicht (a) des Aufzeichnungselements (A, D, E) hinweggeführt. Im Unterschied zu der unter Ziffer 1. beschriebenen Ausführungsform werden hierbei die Temperatur und die Feldstärke so gewählt, daß die Aufzeichnungsschicht (a) nicht vollflächig ausgerichtet wird. Unmittelbar hinter der sich bewegenden walzenförmigen Gegenelektrode (C, F) erfolgt die bildmäßige Einwirkung von Energie, wodurch ein erstes Muster aus Oberflächenladungen oder ein erstes remanentes elektrisches Polarisationsbild resultiert. Hiernach wird dieser Abbildungsvorgang oder Verfahrensschritt wiederholt, nur daß zu diesem Zweck die Spannung zwischen der walzenförmigen Gegenelektrode (C, F) und der Elektrodenschicht (d) umgepolt wird und daß hierbei ein vom ersten remanenten elektrischen Polarisationsbild verschiedenes zweites Polarisationsbild mit entgegengesetzten elektrischen Oberflächenladungen gebildet wird. Im Anschlup daran wird das Aufzeichnungselement (A, D, E), dessen Aufzeichnungsschicht (a) elektrisch positive und elektrisch negative Bereiche enthält, in der gleichen Weise, wie sie bei der Ausführungsform unter Ziffer 4. beschrieben wird, zur Herstellung zweifarbiger Photokopien verwendet.

The method according to the invention can in principle be carried out in five ways, which is explained below by way of example:

• 1. A suitable voltage in the range from 1 to 100 V is applied between the cylindrical counter-electrode (C, F) and the electrode layer (d) of the recording element (A, D, E). Thereafter, the roller-shaped counter electrode (C, F) is guided over the recording layer (a) of the recording element (A, D, E) at a suitable speed in relative movement. As a result, the permanent dipoles present in the recording layer (a) are aligned over the entire surface. Immediately behind the moving roller-shaped counterelectrode (C, F) is the imaginary effect of energy, which results in the pattern of surface charges or the remanent electrical polarization image. The recording element (A, D, E), which now contains the pattern or the image, is then guided in relative movement at a speed which is matched to the movement of the roller-shaped counterelectrode (C, F) to the concreting device (H) and is concrete-stressed there. After that it will toned recording element (A, D, E) in relative motion at the tuned speed to the device (I) for transferring the toner image from the recording layer (a) to another surface. Thereafter, either the toner-free recording element can be returned to the emphasizing device (H) and the device (I) for transferring the toner image, whereby two or more copies of the original pattern or image can be produced, or the roller-shaped one can be used to delete the pattern or the image Electrode (C, E) are moved again in a coordinated relative movement over the recording element (A, D, E).
• 2. Instead of being guided to a device (I) for transferring the toner image from the recording layer (a) to another surface, the concreted recording element (A, D, E) can be moved to a device (J) for fixing the toner image , after which the recording element (A, D, E) leaves the device according to the invention in a suitable manner for further processing.
• 3. An electric field oriented perpendicular to the recording layer (a) is applied to the recording element (A, D, E) with a recording layer (a) not aligned over the entire surface. Thereafter, the recording layer (a) is heated imagewise, whereby the pattern of surface charges or the remanent electrical polarization image is formed. Thereafter, the recording element (A, D, E) moves in relative motion at a suitable speed as described under item 1. to the devices for concreting (H) and for transferring the toner image from the recording layer (a) to another surface (I) or, alternatively, to a device (J) for fixing the toner image. If the pattern or image present in the recording layer (a) is to be erased again, the recording layer (a) is heated to such an extent that the imagewise alignment of the permanent dipoles in the recording layer (a) is destroyed again.
• 4. This embodiment is carried out as described under number 1, except that for the purpose of generating a remanent electrical polarization image, which is composed of electrically positive and electrically negatively charged areas, the entire surface is exposed to the imagewise action of energy on the recording layer (a) electric field is applied, the field lines of which penetrate the recording layer (a), and that the remanent electrical polarization image in the emphasizing device (H), advantageously successively, is emphasized with two optically strongly contrasting toners of opposite electric charge, whereby a two-tone toner image is created. This is used for the production of photocopies in the same manner as described in the embodiment under number 1, but which are now two-tone.
• 5. In this embodiment, a suitable voltage in the range of 1 to 100 V is applied between the cylindrical counter-electrode (C, F) and the electrode layer (d) of the recording element (A, D, E). Thereafter, the roller-shaped counter electrode (C, F) is guided over the recording layer (a) of the recording element (A, D, E) at a suitable speed in relative movement. In contrast to the embodiment described under number 1, the temperature and the field strength are selected so that the recording layer (a) is not aligned over the entire surface. Immediately behind the moving roller-shaped counterelectrode (C, F) is the imaginary effect of energy, which results in a first pattern of surface charges or a first remanent electrical polarization image. Thereafter, this imaging process or process step is repeated, except that for this purpose the voltage between the cylindrical counter-electrode (C, F) and the electrode layer (d) is reversed and that a second polarization image with opposite electrical surface charges is formed which is different from the first remanent electrical polarization image . Subsequently, the recording element (A, D, E), the recording layer (a) of which contains electrically positive and electrically negative regions, is used for producing two-color photocopies in the same manner as is described in the embodiment under item 4.

The method according to the invention has numerous special advantages: it can be carried out without the use of very high voltages, which means that numerous safety-related problems are eliminated. Because no or very few free charge carriers are generated when it is carried out, it is insensitive to air humidity and heat. No light shields are necessary for its implementation. In addition, it can be carried out with the aid of homogeneous, thin recording layers which are outstandingly suitable for imagewise heating with laser light, in particular with that emitted by semiconductor lasers, or with a thermal head. In addition, both the method according to the invention and the device according to the invention are extremely variable, so that they can be used with advantage in a wide variety of embodiments.

Examples example 1 Reversible generation of an image using the method according to the invention

Test specification:

welches enantiotrope ferroelektrische smektisch flüssigkristalline Eigenschaften hat und das folgende ¹H-Kernresonanzspektrum aufweist (δ in ppm; Tetramethylsilan als interner Standard):
1,00-2,80 (Multiplett m, al-H)
3,80-4,15 (m, 4H, OCH₂)
5,28-5,36 (m, 1H, OCH)
6,95-8,27 (m, 12 ar-H).For the implementation of the method according to the invention, a recording element was first produced which had a glass plate as a dimensionally stable support layer, a 0.7 »m thick, conductive, transparent electrode layer made of indium tin oxide (ITO), a rubbed polyimide layer, which is more commonly known Were prepared by spinning a 3% solution of a polyimide precursor (Liquicoat® ZLI 2650 from Merck AG), drying the resulting nap layer, baking the polyimide precursor layer at 300 ° C. for 4 hours and rubbing the polyimide layer thus obtained with a velor cloth and a 1.2 »m thick recording layer made of the polymer,

which has enantiotropic ferroelectric smectic liquid crystalline properties and has the following ¹H nuclear magnetic resonance spectrum (δ in ppm; tetramethylsilane as internal standard):
1.00-2.80 (multiplet m, al-H)
3.80-4.15 (m, 4H, OCH₂)
5.28-5.36 (m, 1H, OCH)
6.95-8.27 (m, 12 ar-H).

This polymer was applied by knife coating its 10% strength solution in tetrachloroethane onto the polyimide layer in such a way that after drying the recording layer remained with the thickness indicated above.

After application in the manner described above, the recording layer was briefly heated to above 160 ° C., after which the recording layer was present as an isotropic melt.

After cooling to room temperature, the recording layer had a polydomain structure with a homogeneous planar orientation over the entire surface. The homogeneous planar orientation means that the microlayer planes of the smectic layers in the material of the recording layer were all perpendicular to the plane of the recording element.

The homogeneously planar-oriented recording layer was now brought into direct contact with an ITO electrode layer (image electrode) which had been etched image-wise and which was coated in a customary and known manner by image-wise etching of a full-area ITO electrode on a glass plate and by coating of the resulting electrode image relief with a thin layer of Teflon with non-stick properties. Thereafter, a DC voltage of 50 volts was applied between the image electrode and the electrode layer of the recording element, while the recording layer was briefly heated to a temperature of 120 ° C. The simultaneous exposure to heat and an electric field polarized the recording layer where it was in contact with the image electrode. After that, the recording layer was rapidly cooled to room temperature and the image electrode was removed from the recording layer.

In this way, a polarization image resulted in the recording layer, which was accentuated with the aid of a conventional and known electrophotographic developer. In this case, the toner adhered to those points on the recording layer which had previously been in direct contact with the image electrode and had thereby been polarized. The overall result was a positive toner image of the electrode image relief, which could be easily transferred to another surface, for example a paper. After this, the imaging process could be repeated several times in the manner according to the invention without the imaging quality being lost.

Example 2 Reversible generation of an image using the method according to the invention

Test specification:

The recording element of Example 1 was now brought into full contact with a flat Teflon-coated metal electrode (counter electrode). Here too, care was taken to ensure that the direct contact did not cause the recording layer of the recording element was deformed. After a direct voltage of 50 volts was applied between the counter electrode and the electrode layer of the recording element, the recording layer was heated to 120 ° C. and thereby polarized over the entire surface. After the recording layer had cooled to room temperature, the counter electrode was removed again.

With the help of a commercially available thermal head, as is usually used for thermal transfer printing, image-wise information was now written into the fully polarized recording layer of the recording element. The locations of the fully polarized recording layer which came into brief contact with the thermal head were depolarized, which resulted in a negative polarization image of the image information transmitted with the thermal head. This toner image could also be toned using a conventional electrophotographic developer, after which the toner image thus obtained on the recording member could be easily transferred to paper.

After the transfer, the recording element was available for further imaging cycles.

Claims (34)

1. A process for the reversible or irreversible production of an image by imagewise exposure of a recording layer (a) to energy in the presence or absence of an electrical and/or magnetic field, resulting in a pattern of surface charges on the surface of the recording layer (a) corresponding to the imagewise exposure to energy, wherein

   (1) the recording layer (a) contains or comprises an organic material which has a nematic liquid-crystalline, smectic liquid-crystalline or ferroelectric smectic liquid-crystalline behavior which solidifies in a glass-like manner, is not or only slightly photoconductive and contains permanent dipoles, and wherein

   (2) the pattern of surface charges is produced therein without or virtually without formation of free charge carriers by reversible imagewise alignment of all or some of the permanent dipoles present in the recording layer (a), the energy used for imagewise exposure being thermal.
2. A machine which serves for the reversible or irreversible production of an image by imagewise exposure of a recording layer (a) to energy in the presence or absence of an electrical and/or magnetic field, resulting in a pattern of surface charges on the surface of the recording layer (a) corresponding to the imagewise exposure to energy, and which comprises

   (A) at least one recording element, containing

   (a) a recording layer which is suitable for the process, and

   (b) an electroconductive substrate,

   (B) at least one device for imagewise exposure of the recording element (A) to energy, and

   (C) at least one electrode (counterelectrode) connected opposite the electroconductive substrate (b),

   wherein

   (D) the recording layer (a) contains or comprises an organic material which has a nematic liquid-crystalline, smectic liquid-crystalline or ferroelectric smectic liquid-crystalline behavior which solidifies in a glass-like manner, is not or only slightly photoconductive and contains permanent dipoles, and in which the pattern of surface charges is produced without or virtually without formation of free charge carriers by reversible imagewise alignment of all or some of the permanent dipoles present in the recording layer (a),

   (E) the electroconductive substrate (b) contains at least

   (c) one dimensionally stable carrier layer,

   (d) one electrode layer and

   (e) one alignment layer,
   in the stated sequence one on top of the other, the recording layer (a) being directly on top of the alignment layer (e),

   (F) the counterelectrode (C) is in direct contact with the recording layer (a) and is arranged in such a manner that it can be removed again from the recording element (A, D, E), and in such a manner that it has either the form of a planar or curved plate or the form of a roller which can be passed over the recording element (A, D, E) in apparent motion, and wherein

   (G) the device (B) for the imagewise exposure to energy contains at least one laser light source or a thermal printing head.
3. A process for the reversible or irreversible production of an image by imagewise exposure of a recording layer (a) to energy in the presence or absence of an electrical and/or magnetic field, resulting in a pattern of surface charges on the surface of the recording layer (a) corresponding to the imagewise exposure to energy, which comprises the following process steps:

   (1) application of a 0.1 to 20 »m thick recording layer (a) which solidifies in a glass-like manner and is not or only slightly photoconductive and has a nematic liquid-crystalline or enantiotropic, ferroelectric smectic liquid-crystalline (S_C*) behavior and, at sufficiently high temperature by applying an external electrical field, can either be converted into a polarized nematic liquid-crystalline ordered state and frozen in this state in a glass-like manner on cooling or can be switched back and forth between two thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states, to the alignment layer (e) of an electroconductive substrate (b), which contains a dimensionally stable carrier layer (c), an electrode layer (d) and an alignment layer (e) one on top of the other, resulting in a recording element (A, D, E),

   (2) alignment of the recording layer (a) over the entire surface into the polarized nematic liquid-crystalline ordered state or into one of its thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states by warming the entire surface of the recording layer (a) in the electrical field between the electrode layer (d) and a counterelectrode (C, F), which is arranged in such a manner that it can be removed from the recording element (A, D, E), is connected opposite the electrode layer (d), is in direct contact with the recording layer (a) and is covered either by an alignment layer (g) or a polysiloxane layer (h) or whose surface serves as an alignment layer (g), the counterelectrode (C, F) either having the form of a curved or planar plate or the form of a roller which is passed over the recording element (A, D, E) in apparent motion at a suitable speed,

   (3) imagewise warming of the recording layer (a) aligned over the entire surface in the presence or absence of an electrical field by means of a laser beam or a thermal printing head, forming a pattern which comprises areas which are stable at room temperature, in which either a non-polarized nematic liquid-crystalline ordered state, the other thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered state, another liquid-crystalline ordered state, unordered micro-domains (centers of scattering) or an isotropic I phase is present, and

   (4) toning the pattern in the absence of an electrical field with solid or liquid toners.
4. A process as claimed in claim 3, which comprises at least one of the following process steps:

   (5) the toner image resulting from process step (4) is transferred from the recording layer (a) to another surface,

   (6) the pattern is erased after process step (5) by repeating process step (2), and

   (7) the toner image resulting from process step (4) is fixed on the recording layer (a).
5. A process for the reversible or irreversible production of a positive image by imagewise exposure of a recording layer (a) to energy in the presence or absence of an electrical and/or magnetic field, resulting in a pattern of surface charges on the surface of the recording layer (a) corresponding to the imagewise exposure to energy, which comprises the following process steps:

   (1) application of a 0.1 to 20 »m thick recording layer (a) which is non-polarized nematic or not aligned over the entire surface, which solidifies in a glass-like manner and is not or only slightly photoconductive and has a nematic liquid-crystalline or enantiotropic ferroelectric smectic liquid-crystalline (S_C*) behavior and, at sufficiently high temperature by applying an external electrical field, can either be converted into a polarized nematic liquid-crystalline ordered state and frozen in this state in a glass-like manner on cooling or can be switched back and forth between two thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states, to the alignment layer (e) of an electroconductive substrate (b) which contains a dimensionally stable carrier layer (c), an electrode layer (d) and an alignment layer (e) one on top of the other, resulting in a recording element (A, D, E),

   (2) imagewise warming of the recording layer (a) which is non-polarized nematic or not uniformly aligned over the entire surface, in the presence of an electrical field by means of a laser beam or a thermal printing head, forming a pattern which comprises areas which are stable at room temperature in which either a polarized nematic liquid-crystalline or one of the two thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states of the recording layer (a) is present, and

   (3) toning the pattern in the absence of an electrical field with solid or liquid toners.
6. A process as claimed in claim 5, which comprises one of the following process steps:

   (4) the toner image resulting from the process step (3) is transferred from the recording layer (a) to another surface,

   (5) the pattern is erased after process step (4) by warming the entire surface of the recording layer (a) in the absence of an electrical field, or

   (6) the toner image resulting from process step (3) is fixed on the recording layer (a).
7. A process for the production of two- or multi-color photocopies by producing a residual electrical polarization image composed of positively and negatively electrically charged areas on the surface of a recording layer (a), which comprises:

   (1) application of a 0.1 to 20 »m thick recording layer (a) which solidifies in a glass-like manner and is not or only slightly photoconductive having an enantiotropic, ferroelectric smectic liquid-crystalline (S_C*) behavior and, at sufficiently high temperature by applying an external electrical field, can be switched back and forth between two thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states, to the alignment layer (e) of an electroconductive substrate (b), which contains a dimensionally stable carrier layer (c), an electrode layer (d) and an alignment layer (e) one on top of the other, resulting in a recording element (A, D, E),

   (2) alignment of the recording layer (a) over the entire surface into one of its thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states by warming the entire surface of the recording layer (a) in the electrical field between the electrode layer (d) and a counterelectrode (C, F), which is arranged in such a manner that it can be removed from the recording element (A, D, E), is connected opposite the electrode layer (d), is in direct contact with the recording layer (a) and is covered either by an alignment layer (g) or a polysiloxane layer (h) or whose surface serves as an alignment layer (g), the counterelectrode (C, F) either having the form of a curved or planar plate or the form of a roller which is passed over the recording element (A, D, E) in apparent motion at a suitable speed,

   (3) imagewise warming of the recording layer (a) aligned over the entire surface in the presence of an electrical field by means of a laser beam or a thermal printing head, forming a residual electrical polarization image which comprises areas which are stable at room temperature in which in each case one of the two thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states of the recording layer (a) is present, and

   (4) toning the residual electrical polarization image with two liquid or solid toners of opposite electrical charge.
8. A process for the production of two- or multi-color photocopies by producing a residual electrical polarization image composed of positively and negatively electrically charged areas on the surface of a recording layer (a), which comprises:

   (1) application of a 0.1 to 20 »m thick recording layer (a) which solidifies in a glass-like manner and is not or only slightly photoconductive having an enantiotropic, ferroelectric smectic liquid-crystalline (S_C*) behavior and, at sufficiently high temperature by applying an external electrical field, can be switched back and forth between two thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states, to the alignment layer (e) of an electroconductive substrate (b), which contains a dimensionally stable carrier layer (c), an electrode layer (d) and an alignment layer (e) one on top of the other, resulting in a recording element (A, D, E),

   (2) imagewise warming of the recording layer (a) in the presence of the electrical field between the electrode layer (d) and a counterelectrode (C, F), which is arranged in such a manner that it can be removed from the recording element (A, D, E), is connected opposite the electrode layer (d), is in direct contact with the recording layer (a) and is covered either by an alignment layer (g) or a polysiloxane layer (h) or whose surface serves as an alignment layer (g), the counterelectrode (C, F) either having the form of a curved or planar plate or the form of a roller which is passed over the recording element (A, D, E) in apparent motion at a suitable speed, by means of a laser beam or a thermal printing head, forming a residual electrical polarization image which comprises areas which are stable at room temperature in which in each case one of the two thermodynamically stable, ferroelectric smectic liquid-crystalline S_C* ordered states of the recording layer (a) is present,

   (3) repeating process step (3) in the presence of the reversed electrical field, forming a second residual electrical polarization image which is different from the first polarization image, having opposite electrical surface charges, and

   (4) toning the residual electrical polarization image with at least two liquid or solid toners of opposite electrical charge.
9. A process as claimed in claim 7 or 8, wherein at least two toners are used which are optically highly contrasting.
10. A process as claimed in claim 1 or 3 or 4 or 5 or 6 or 7 or 8 or 9, which is carried out using a machine as claimed in claim 2.