JP3511737B2 - Image holding member and image forming method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image holding member provided with a polymer liquid crystal recording layer capable of reversibly changing the light scattering degree by a thermal stimulus and repeatedly recording and erasing an image, and an image holding member. The present invention relates to an image forming method in which continuous copying is performed without performing image exposure each time.

[0002]

2. Description of the Related Art A conventional electrophotographic method comprises a process of repeating charging, image exposure, toner development, transfer of a toner image onto paper, etc. for an electrophotographic photosensitive member, as represented by the Carlson system. In this method, image exposure must be performed each time copying is performed. Therefore, there is a problem that the apparatus becomes complicated and large in size for high speed copying. Also, a large amount of energy was required for image exposure. In order to improve this point, a method has been proposed in which image information is stored in an electrophotographic photosensitive member and a large number of copies are obtained by one image exposure. For example, JP-A-53-102037
JP-A No. 62-2266 and JP-A No. 62-1266 describe a continuous photoreceptor in which a specific compound is added to the photosensitive layer.
However, these persistent photoreceptors have not been satisfactory in terms of duration and contrast. Also,
Japanese Patent Application Laid-Open No. 60-207143 discloses a switching photosensitive member that maintains a photoconductive state. However, this switching photosensitive member also has a problem in maintaining the photoconductive state, and is difficult to put into practical use. On the other hand, as proposed by the present inventors, Japanese Patent Laid-Open No. 5-2
Japanese Patent No. 41480 discloses an image holding member that is used for continuous copying of a large number of sheets by moving conductive particles on the surface of the heat softening layer into the layer to store an image, and an electrophotographic method using the image holding member. There is. With this method of using the image holding member, the image is stored by the movement of particles, so the memory retention is excellent, but since the used image holding member cannot be reused, there is a problem that it must be discarded. there were.

[0003]

Therefore, an image holding member having a recording layer capable of reversibly storing images so that the used image holding member can be reused without being discarded, and the image holding member is used. The advent of imaging methods is desired.

The present invention has been made in view of the above-mentioned actual situation in the prior art. Therefore, it is an object of the present invention to store an image with high maintainability so that the image exposure for each copy is not necessary when a large number of sheets are continuously copied, and the storage is erased after the copy is completed. An object of the present invention is to provide an image holding member that can be reused. Another object of the present invention is to provide an image forming method in which a large number of sheets are continuously copied using the image holding member without performing image exposure for each copying.

[0005]

The image holding member of the present invention comprises:
It is characterized in that a polymer liquid crystal recording layer whose light scattering degree is reversibly changed by thermal stimulation is provided on the electrophotographic photosensitive layer. Further, in the image forming method of the present invention, the light scattering degree is reversibly changed on the electrophotographic photosensitive layer by thermal stimulation.
An image is written by applying a thermal stimulus corresponding to image information to an image holding member provided with a polymer liquid crystal recording layer, and then primary charging, secondary charging by a voltage having a polarity opposite to that of the primary charging or an alternating voltage. A feature of the present invention is that a copy image is continuously produced by repeatedly carrying out an electrophotographic process including steps of charging, exposing the entire surface, developing a toner, and transferring a toner image.
Further, in the image forming method of the present invention, the image written on the recording layer can be erased by heating the image holding member after the production of the copied image is completed. The high fraction of the image bearing member
The sub-liquid crystal recording layer is made transparent over the entire surface, and a copy image is formed by an electrophotographic process consisting of primary charging, secondary charging with a voltage opposite to the primary charging or AC voltage, image exposure, toner development, and toner image transfer. It can also be made.

The structure of the image holding member is shown in FIG.
FIG. 3 is a cross-sectional view of a base structure having a photosensitive layer 2 on the top and a polymer liquid crystal recording layer 3 on the top. As the base 1, a resin film, metal foil, coated paper, metal pipe, plastic pipe or the like, as long as it is used in conventional electrophotographic photoreceptors, can be used made of how.

Further, as the photosensitive layer 2, Se, CdS,
Inorganic photoconductive materials such as ZnO and organic photoconductive materials (OP
Among C), the same ones as those used for a usual electrophotographic photosensitive member can be used. The photosensitive layer may be functionally separated into a charge generation layer and a charge transport layer. Further, as disclosed in Japanese Patent Laid-Open No. 126035/1979, a hole injecting material such as gold or graphite, or an electron injecting material such as Al or In is provided in order to have charge injecting property from the substrate to the photosensitive layer. The layer may be formed below the photosensitive layer. If the charge injection material is the same material as the substrate, the charge injection layer is unnecessary.

The polymer liquid crystal recording layer 3 has a light scattering degree which is reversibly changed by a thermal stimulus, and the constituent material thereof is, for example, JP-A-59-10930 and JP-A-62-62. 14114, JP-A-63-22306.
6 JP, as described in JP-A-2-2513 discloses such a high-molecular liquid crystal light scattering degree you reversibly change can be cited as typical ones.

[0009] will be explained to the polymer liquid crystal recording layer 3,
The polymer liquid crystal recording layer (hereinafter, simply referred to as “recording layer”) has a multi-domain structure in an initial state and is in a light scattering opaque state, and has a very low light transmittance. Imagewise heating is performed here using a thermal head, laser light or the like to make it isotropic, and then rapidly cooled, the heated portion is fixed in a glass state while maintaining an isotropic transparent state, and the light transmittance increases. When the image is erased, it is possible to return it to the initial light scattering state by uniformly cooling and then gradually cooling it than at the time of recording. Therefore, this recording layer can be reversibly recorded and erased, and can be repeatedly reused. When a thermal head is used as the heating means, the desired conditions can be achieved by controlling the pulse width and energy applied to this. In addition to this, it is also possible to make the initial state transparent and perform cloudy recording. In the recording layer on which an image is thus recorded, there are a light scattering state and a transparent state depending on the image, and the light transmittances are different. There is a photosensitive layer below the recording layer, and if the entire surface of the recording layer is uniformly exposed, the photosensitive layer can be imagewise exposed.

[0010]

[0011]

Further, as the polymer liquid crystal, a main chain type or side chain type polymer liquid crystal in which a mesogenic molecular group exhibiting liquid crystallinity is bonded to the main chain or side chain can be used. Examples of the side chain type polymer liquid crystals include those shown in Structural Examples 1 to 3 below.

[Chemical 1] [In the formula, R represents a hydrogen atom or a methyl group, and n is 1 to
It means an integer of 30, and A represents a mesogen group selected from the following formulas (a) to (k).

[0013]

[Chemical 2] (In the formula, X and Y are each a single bond, -N = N-,
-N (→ O) = N-, -CH = N-N = CH-, -CO
O-, -O (C = O)-, represents a group selected from ethynylene groups, R ¹ represents a group selected from an alkoxy group, a halogen atom, a cyano group, a carboxyl group, and an alkyl group, and p is 1 In the case where p is 2 or more, each R ¹ may be different from each other. )]

Further, as the polymer liquid crystal, a phase-separated polymer obtained by copolymerizing or co-adding a mesogenic monomer and a non-mesogenic monomer and copolymerizing a non-mesogenic component with a polymer side chain. Liquid crystal (for example, JP-A-4
-2182024 and JP-A-6-18866) can also be used. Such a polymer liquid crystal is preferable because the contrast of a recorded image can be significantly improved and the heat-sensitive property can be improved.

Examples of the mesogen monomer include biphenyl type, phenylbenzoate type, cyclohexylbenzene type, azoxybenzene type, azobenzene type, azomethine type, phenylpyrimidine type, diphenylacetylene type,
Examples of such compounds include biphenylbenzoate-based, cyclohexylbiphenyl-based, and terphenyl-based rigid molecules to which an acrylic acid ester, a methacrylic acid ester group, or a vinyl group is bonded via an alkyl spacer having a predetermined length. Representative structural examples of these compounds are shown below. _{CH 2 = C (R a)} -COO- (CH 2) l -O-A CH 2 = C (R a) -COO-A CH 2 = CH- (CH 2) in _l -O-A (wherein, R _a represents a hydrogen atom or a methyl group, and l is 1
Means an integer of 30 and A represents a mesogenic group selected from the formulas (a) to (k). )

On the other hand, examples of the non-mesogenic monomer include alkyl acrylate and its derivatives, styrene and its derivatives, vinyl acetate, acrylonitrile, vinyl chloride, vinylidene chloride, vinylpyrrolidone, 1-hexene, 1-octene, and crosslinking. Acrylic acid, which is a compound having a reactive group for controlling, ω-carboxy-polycaprolactone monoacrylate, vinyl sulfonate, hydroxyethyl acrylate, hydroxypropyl acrylate, 2-acryloxyethyl acid phosphate, 2-hydroxy-3- Phenoxypropyl acrylate, 2-acryloxyethyl succinate, phthalic acid monoacrylate, 2-acryloxyethyl (2-hydroxyethyl) phthalate, 4-acryloxyalkyloxy benzoi Kuashiddo, glyceryl acrylate, hydroxy group-substituted styrene, acrylamide, N,
N-dimethylaminoethyl acrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, 2-propen-1-ol, 5-hexen-ol, etc. (The acrylic portion of each compound may have a methacrylic structure. ) Is mentioned.

Plural kinds of these mesogenic monomers and non-mesogenic monomers may be used. The amount of copolymerization or co-addition of the above-mentioned mesogenic monomer and non-mesogenic monomer into the polymer liquid crystal is 0.1
The range of ˜70 mol% is preferred. The polymer liquid crystal can be synthesized by using these mesogenic monomers or non-mesogenic monomers by radical polymerization, ionic polymerization or addition to a reactive polymer. The weight average molecular weight of the polymer liquid crystal is in the range of 10,000 to 1,000,000, particularly preferably 20,000 to 500,000.

The above-mentioned polymer liquid crystal is disclosed in JP-A-6-16082.
Crosslinking is preferably performed as described in JP-A-5, and a crosslinked polymer liquid crystal having a multi-domain structure is particularly preferable. By cross-linking the polymer liquid crystal as a multi-domain structure composed of an aggregate of domains having a specific size having optical anisotropy, high speed and stable recording and erasing can be realized. The multi-domain structure refers to a structure composed of an assembly of a plurality of minute domains having optical anisotropy (birefringence) and strongly scatters light. Particularly, when the size of the domain in the multi-domain structure is in the range of 0.2 to 2.0 μm in diameter at the maximum of the distribution number of the domain, light is scattered most strongly, which is preferable. The cross-linking of the polymer liquid crystal is carried out after forming the polymer liquid crystal as a recording layer,
It is done by adding heat, light, electron beams, etc. As the polymer liquid crystal to be crosslinked, one containing the above-mentioned reactive group as one component of the main chain or the side chain is used.

Components other than the above may be added to the recording layer for the purpose of improving the characteristics. For example, antioxidants such as hindered amines and hindered phenols for the purpose of improving weather resistance, and anthraquinone-based, styryl-based, various dichroic dyes such as azomethine-based and azo-based for the purpose of improving display contrast, Various fluorescent dyes are added for the purpose of improving the light scattering property. In order to efficiently perform thermal writing by laser light, a laser light absorbing dye, for example, 780
When a general semiconductor laser having a wavelength of up to 830 nm is used, it is also effective to add a near infrared absorbing dye such as phthalocyanine, squarylium or azurenium. The addition amount of the various components listed above is 0.01 to the composition.
A range of 5% by weight is preferred. On the other hand, it is also effective to add a release agent in order to prevent adhesion when the base material coated with the recording layer is wound up during production. In addition to the above, a low molecular weight liquid crystal compound may be added to the polymer liquid crystal within the range of 1 to 20% by weight.

An intermediate layer may be present between the photosensitive layer and the recording layer in order to improve coatability and adhesion. Since this intermediate layer is also a part of the insulating layer, the higher the electric resistance, the more preferable. Further, an undercoat layer similar to that in a usual electrophotographic photoreceptor may be provided between the substrate and the photosensitive layer. Further, it is effective to provide a protective layer on the surface of the recording layer in order to protect the recording layer from deterioration such as abrasion. The protective layer is preferably made of a material having high heat resistance, high hardness and low friction, such as a thermoplastic or thermosetting type or an ultraviolet curing type,
An electron beam curing type fluorine resin, silicone resin, acrylic resin, urethane resin, epoxy resin or the like is used. In the protective layer, powders of silica, calcium carbonate, barium sulfate, fluororesin, silicone resin, etc. are dispersed for the purpose of improving the contactability with the thermal head when writing an image and improving the cleaning property of residual toner. You may.

Next, an image forming method using the above image holding member will be described. First, in the image holding member of the present invention,
Writing is performed by applying a thermal stimulus according to image information with a thermal head or the like. As a result, an image having a reversibly changed light scattering degree is formed on the recording layer.

Since the recording layer has a high electric insulation property, when the image holding member is charged, electric charges are accumulated in the recording layer and it becomes difficult to repeatedly make a copy. Therefore, in the image forming method of the present invention,
After recording an image on the recording layer, the image holding member is subjected to primary charging and secondary charging with a voltage opposite to that of the primary charging or an AC voltage, and then a whole surface is exposed to form a latent image. . This will be described with reference to FIG. 2. These steps are performed on an image holding member having an electrically insulating layer provided on a photosensitive layer having a charge injection layer as described in JP-A-54-126035. It is similar to the forming method.

FIG. 2 illustrates a state in which the electrophotographic process is performed on the image holding member on which an image is recorded, and the light scattering portion 3 in which the right side portion of the recording layer is in the light scattering state.
1, the left part represents the transparent part 32 in the transparent state. When the photosensitive layer is positively charged, first, as shown in FIG. 2A, the surface of the image holding member is primarily charged to a negative voltage. Photosensitive layer 2
Positive charges are injected from the side of the substrate 1 to accumulate the positive charges. Then, as shown in FIG. 2B, when the secondary charging is performed with a positive voltage having the opposite polarity to the primary charging, the negative charges on the surface of the image holding member are neutralized. In this case, the negative charges on the surface of the member may be erased by AC charging. In any case, it suffices that no charges remain on the surface of the image holding member. At this time, the positive charges accumulated in the photosensitive layer remain trapped and negative charges are induced on the substrate side. After that, Fig. 2 (3)
As shown in (4), the entire surface of the image holding member is exposed to light 4 for the entire surface exposure that matches the light attenuation characteristics of the photosensitive layer. Since the light does not reach the photosensitive layer in the light scattering portion 31, the positive charge of the photosensitive layer remains, but the light is transmitted in the transparent portion 32, so that the photosensitive layer is exposed and the positive charge is attenuated. The surface potential of the image holding member is high at the portion where the positive charge remains on the photosensitive layer and is low at the charge attenuating portion, whereby a latent image is formed. In the present invention, the secondary charging and the whole surface exposure may be performed at the same time.

Then, the latent image is developed with toner, and the obtained toner image is transferred to a sheet to obtain a copy image. Figure 2 above
By repeating the steps after the step shown in (1), the copied images can be continuously obtained. After the required number of copies have been completed, the image on the recording layer can be erased by heating the image holding member. This allows the image bearing member to be reused for subsequent imaging. The above is a continuous mode image forming method that does not require image exposure for each copy. However, if the entire recording layer is made transparent, image exposure is performed after primary charging and secondary charging, so that each image is exposed one by one. Images can be created in the copy mode for making copies.

[0025]

EXAMPLES In the following examples, "parts" represent parts by weight. Example 1 A 100 μm-thick polyester film (manufactured by Toyo Metalizing Co., Ltd.) on which a nickel-chromium alloy was deposited was used as a substrate. The nickel-chromium alloy layer ensures conductivity and also functions as a hole injecting electrode. On top of this, N, N '
A coating solution for forming a charge transport layer consisting of 10 parts of diphenyl-N, N'-bis (m-tolyl) benzidine and 10 parts of a polycarbonate resin was applied with a roll coater to give a film thickness of 18
A μm charge transport layer was formed. Next, 3 of chlorogallium phthalocyanine (see JP-A-5-98181) is used.
Parts are polyvinyl butyral resin 1 part, n-butanol 2
The dispersion liquid dispersed in a solution of 0 part was applied on the charge transport layer to form a charge generation layer having a film thickness of 0.12 μm. As a result, a photosensitive layer composed of the charge transport layer and the charge generation layer was formed. On the formed photosensitive layer, an isopropanol solution of an ultraviolet curable acrylic resin (trade name: DPCA, manufactured by Nippon Kayaku Co., Ltd.) was applied and irradiated with ultraviolet rays to be cured to form an intermediate layer having a thickness of 3 μm. . This intermediate layer has the function of improving the solvent resistance of the photosensitive layer.

On the other hand, 4-acryloxyhexyloxy-4'-cyanobiphenyl as a mesogenic monomer,
As a reactive non-mesogenic monomer, 2-hydroxyethyl methacrylate was polymerized by using azobisisobutyronitrile as an initiator and 2-butanone as a solvent, and was precipitated and purified with methanol to be represented by the following structural formula I. A polymer liquid crystal was obtained.

[Chemical 3] However, the weight average molecular weight (polystyrene conversion by GPPC) was 80,000, Tg (glass transition point) was 40 ° C, and Ti (liquid crystal phase-isotropic phase transition point) was 115 ° C. 100 parts of the above-mentioned polymer liquid crystal, 4 parts of 4,4'-diphenylmethane diisocyanate as a cross-linking agent, and 2-butanone 1 as a solvent.
50 parts and 150 parts of toluene, and 0.01 part of a silicone-based release agent (trade name: KS778, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to prepare a mixed solution, which was coated on the intermediate layer with a roll coater. Then, after drying at 80 ° C. for 2 minutes, the film was wound into a roll, put in a dryer and heated at 60 ° C. for 24 hours to crosslink. The formed recording layer scattered light and became cloudy. The film thickness of the recording layer was 6 μm. Then, a coating liquid made of an ultraviolet curable resin (trade name: Aronix, manufactured by Toagosei Co., Ltd.) in which 1% by weight of silica particles having an average particle diameter of 1 μm was dispersed was applied onto the recording layer using a roll coater, and a high pressure mercury lamp was applied. When used, it was cured to form a protective layer having a thickness of 3 μm. The film obtained by these operations has a form in which an insulating layer having a total thickness of 12 μm is provided on the photosensitive layer, the volume resistivity of these three layers is 10 ¹⁵ Ωcm or more, and the insulating property is Was enough.
Then, the film is cut into 350 mm × 500 mm,
It was processed into a belt shape to obtain an image holding member.

On the obtained image holding member, 8 dots / mm,
When an image was written using a thermal head of 0.3 mJ / dot, the recording layer of the printing part became transparent.
Subsequently, the image holding member was subjected to primary corona charging so as to have a potential of -500V. Next, when charged to +800 V and uniformly irradiated with white light on the entire surface, the potential of the image printing portion was discharged to zero or 50 V or less, while the white turbid non-printing portion was +500 V. This latent image was developed with a two-component positively charged developer, and the obtained toner image was transferred to a transfer material to obtain a copy image having high contrast. This process was repeated at a speed of 100 sheets per minute. As a result, it was confirmed that there was no problem even when continuous 2000 sheets were copied. After the operation was completed, when the image holding member was passed through a heat roll heated to 130 ° C., the printing part returned to the cloudy state again, and it could be used as in the initial stage.

Example 2 In Example 1, when the image holding member was passed through a heat roll heated to 130 ° C. and immediately thereafter passed through a roll at 20 ° C., the recording layer became transparent over the entire surface. Using this image holding member, image exposure was carried out after primary charging of -500V and then secondary charging of + 800V. As a result, the character portion (black portion) of the image was + 500V and the solid portion (white portion) of the image was A latent image of + 50V was formed. This latent image was developed with a two-component negatively chargeable developer, and the formed toner image was transferred to a transfer material to produce a copied image. By repeating this operation, different copy images could be obtained one by one.

Example 3 A CdS photoconductive layer (thickness 30 μm) having a 160 mmφ × 340 mm aluminum pipe as a base and a vinyl chloride-vinyl acetate copolymer as a binder resin was formed thereon. A methanol butanol solution of a copolymer nylon resin (trade name: CM8000, manufactured by Toray) was dip-coated on the formed photoconductive layer to form a 2 μm thick intermediate layer.
An insulating layer having a film thickness of 15 μm and made of the same ultraviolet curable resin as that of Example 1 was further formed on the formed intermediate layer. The same mesogenic monomer as described in Example 1, 2-hydroxyethyl methacrylate as the reactive non-mesogenic monomer, and butyl acrylate as the non-mesogenic monomer were used and copolymerized in the same manner as in Example 1 with the following structural formula II. The polymeric liquid crystals shown were synthesized.

[Chemical 4] However, the weight average molecular weight (in terms of polystyrene by GPC) was 50,000, Tg was 40 ° C, and Ti was 90 ° C. 100 parts of polymer liquid crystal purified by precipitation with methanol,
3 parts of hexamethylene diisocyanate, which is a polyfunctional isocyanate compound as a cross-linking agent, and 150 parts of 2-butanone and 150 parts of toluene are added as a solvent, and the resulting solution is applied onto the insulating layer to form a film having a thickness of 6 μm. A recording layer was formed. After drying at 80 ° C. for 2 minutes, it was heated in an oven at 60 ° C. for 24 hours to crosslink. Further Example 1
A protective layer was formed in the same manner as in. By these operations,
An insulating layer having a total thickness of 26 μm was formed.

When an image was written on the obtained cylindrical image-holding member with a thermal head, the recording layer in the printing portion became transparent. Subsequently, when primary corona charging of +1500 V, secondary AC neutralization and simultaneous whole surface exposure were performed, the potential of the printing portion was zero or +50 V or less, and the potential of the non-printing portion was +500 V. In this state, the toner image was developed with a one-component negatively charged developer, and the obtained toner image was transferred to a transfer material. As a result, a copy image with a developed printed portion was obtained. By repeating these steps in the same manner as in Example 1, a good copy could be obtained. Moreover, it was possible to return to the initial state by heating similarly.

[0031]

Since the image holding member of the present invention has the above-mentioned structure, it is possible to write and store an image with high maintainability, and to erase the written image after copying is completed, It can be used. The image forming method of the present invention using the same does not require image exposure for each copy, and after the image is first written, copies can be continuously produced without image exposure. it can. Also,
After the copy making operation is finished, the written image can be erased by heating the image holding member, and the image holding member can be repeatedly used.

[Brief description of drawings]

FIG. 1 shows a sectional view of an image holding member of the present invention.

FIG. 2 is a diagram for explaining an image forming method of the present invention.

[Explanation of symbols]

1 ... Substrate, 2 ... Photosensitive layer, 3 ... Polymer liquid crystal recording layer, 31 ...
Light scattering part, 32 ... Transparent part, 4 ... Light for whole surface exposure.

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Claims (4)

(57) [Claims] 1. An image holding member comprising an electrophotographic photosensitive layer and a polymer liquid crystal recording layer having a light scattering degree reversibly changed by thermal stimulation. 2. A thermal stimulus corresponding to image information is applied to an image holding member comprising a polymer liquid crystal recording layer having a light scattering degree reversibly changed by thermal stimulus on the electrophotographic photosensitive layer. Image writing, then primary charging, secondary charging with a voltage opposite to the polarity of the primary charging or an alternating voltage,
An image forming method characterized in that electrophotographic processing consisting of steps of whole surface exposure, toner development, and toner image transfer is repeatedly carried out to continuously produce copied images. 3. The image forming method according to claim 2, wherein after the copy image is produced, the image holding member is heated to erase the image written in the polymer liquid crystal recording layer. 4. A thermal stimulus on the electrophotographic photosensitive layer.
Providing a polymer liquid crystal recording layer that reversibly changes the light scattering degree
The polymer liquid crystal recording layer is made transparent over the entire surface by applying a thermal stimulus to the image holding member, and is subjected to primary charging, secondary charging with a voltage having an opposite polarity to the primary charging or AC voltage, image exposure,
An image forming method for producing a copy image by an electrophotographic process including a step of developing a toner and transferring a toner image.