JPH0820171A - How to protect the printed image side - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for protecting a printed matter on which an image is formed using a liquid developer for electrostatic charge development which is applied to manifestation of an electrostatic latent image. After forming an image on a material to be printed by an image forming method using a liquid developer, a light-transmitting protective film composed of an aqueous overcoat varnish is formed on the entire surface or a part of the material to be printed on which the image is formed. A method for protecting an image surface of a printed matter, which comprises applying an agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for protecting printed matter on which an image is formed using a liquid developer for electrostatic charge development which is applied to reveal an electrostatic latent image.

[0002]

2. Description of the Related Art In recent years, in the field of hard copy, there has been an active movement toward higher image quality. That is, with the progress of digital technology, it has become possible to ensure high definition at the level of latent image formation as compared with the conventional technology. However, when a powder toner is used as a visualization agent when developing an electrostatic charge, a hard copy having such a high image quality has not been obtained due to the particle diameter of about 10 μm. Therefore, high definition of an image by a liquid developer having a small toner particle size has been newly evaluated in the market.

As is well known, the liquid developer is obtained by dispersing toner particles in an electrically insulating organic liquid, and the toner particles are required to have coloring property, charge property, fixing property and dispersion stability. Therefore, it is composed of pigments, resins, and other additives. In the liquid development method, the toner particles are usually
Charged to the opposite polarity of the electrostatic latent image charge, these toner particles are attracted to the latent image charge in the electrically insulating liquid, migrate to the latent image by electrophoresis, and selectively adhere to the latent image for development. Done.

Printed materials that are currently put into practical use in processes that use liquid developers include plain paper and paper or film coated with a dielectric material. When such an object to be printed is used, it is often the case that a step for improving the adhesion between the object to be printed and the toner and a fixing step are not required. The reason for this is that in the case of the liquid developer, since the toner particle diameter is small as described above, it easily penetrates into the fibers of the paper and it is not necessary to fix it in practice. Secondly, among the materials constituting the toner, the resin that contributes to the fixing property has the property of being soluble or semi-soluble in the solvent, so that the colorant is fixed to the printing medium simply by evaporating the solvent. Because it was possible.

In recent years, a device as described in JP-A-4-507148, that is, an intermediate transfer member is formed without directly transferring the developed liquid developer from the electrostatic latent image carrier to the printing medium. A transfer method has been developed in which the image is not disturbed by transferring through the intermediate transfer member and heating the liquid developer on the intermediate transfer member. The quality of the image on the final substrate according to this method is much higher than that of the image when the normal powder development process is used. It is considered that one of the reasons is that the image is not crushed because the heat roll fixing is not performed.

As described above, unlike the case where the powder toner is used, when the liquid developer is used, the means for fixing the liquid developer on the material to be printed by means such as a heating roller is not particularly required. Moderate fixability is obtained. Therefore, although the image using the liquid developer has high image quality, the gloss is insufficient and the fixing strength, for example, the resistance due to the eraser and the printing target material are different from those of the image using the normal printed matter or powder toner. However, there was a problem such as poor abrasion resistance.

Several proposals have already been made for the protection of image-formed products. For example, JP-A-53-14363
No. 4, a method of forming a solvent-free resin layer on the surface of an image formed on various image supports, and then polymerizing the resin by heat or light to form a protective film for the image. Is proposed. This method has a new problem of how to easily and uniformly form a resin-free resin layer on an image surface obtained by a general image forming method, and is difficult to put into practical use.

Further, attempts have been made to improve the light resistance of dyes by forming a protective layer having a specific spectral characteristic on the image forming surface using the dyes, as disclosed in JP-A-62-280085 and JP-A-62-280086. Has been proposed to. This method is effective in improving the light resistance of dyes, but it is not particularly effective in systems using pigments, and especially when using benzotriazole-based UV absorbers, there is skin irritation and protection. Careful handling may be required when forming the layers.

Further, as described in JP-A-5-323732, in order to improve the gloss of the image surface obtained by using a liquid developer, resin particles having electrophoretic property are used in the image portion or Attempts to develop the entire image have been proposed. Although this method solves the conventional problems, the following new problems occur. That is, the resin particles are not glossy unless they are melted by heat, a new development process needs to be added to develop the resin particles, and it is necessary to design resin particles having electrophoretic properties. .

Conventionally, in the field of printing ink, it has been common to apply a coating material called an overprint varnish (abbreviated as OP varnish) for the purpose of giving gloss to a printed matter or protecting a printed surface to improve abrasion resistance. Is done in a regular manner.

OP varnishes can be classified into the following four types according to their composition (printing ink introduction. Jiro Aihara. Press Society Press). That is, solvent-based OP varnish, water-based OP varnish,
Thermosetting OP varnish and ultraviolet curing OP varnish have been put to practical use.

[0012]

DISCLOSURE OF THE INVENTION The inventors of the present invention have problems and gloss that images obtained by a copier or a printer using a liquid developer are inferior in various resistances such as light resistance and abrasion resistance. As a result of a thorough study on market demands for improvement in image quality due to lack of image quality, a water-based OP varnish is preferably applied to the entire surface or a part of the image-formed substrate. Found a method which is satisfactory in terms of safety, cost and ease of coating by forming a light-transmitting film made of a vinyl resin composition in an aqueous OP varnish. Came to.

[0013]

An image is formed on an object to be printed by an image forming method using a liquid developer, and then an aqueous OP varnish, preferably an aqueous OP varnish, is formed on the entire surface or a part of the object on which the image is formed. Provides an image protection method characterized by forming a light-transmissive film made of a vinyl-based aqueous OP varnish.

As described above, various materials have been proposed as conventional OP varnishes. However, when an ultraviolet curable resin is used, the adhesiveness to the liquid developer is insufficient, resulting in adhesion. As a result of a peeling test using a tape, there was a problem that the tape was peeled from the interface between the varnish and the toner. Further, when the solvent-type OP varnish is used, the solvent vapor generated in the drying step is not environmentally preferable. In addition, the use application may be limited by the solvent remaining on the coated surface. Furthermore, it has been found that the thermosetting and UV-curable OP varnishes have drawbacks such as severe drying conditions or the need for special equipment.

From the above examination, as a protective material in the image protection method of the present invention, from the standpoint of environmental safety, the standpoint of drying conditions / apparatus, and the standpoint of the image protection effect, water-based OP
The use of varnish proved suitable.

The aqueous OP varnish depends on the resin skeleton used,
It can be classified into vinyl type, polyester type and polyamide type. However, the vinyl-based water-based OP varnish is suitable because of the storage stability of the OP varnish itself and the difficulty of controlling the molecular weight for water solubilization. Generally, a vinyl-based aqueous OP varnish has a cationic property, an anionic property, or an anionic property depending on the type of hydrophilic functional group introduced into the vinyl skeleton.
It can be classified as nonionic. As the vinyl-based aqueous OP varnish that can be used in the present invention, the above-mentioned three types can be used, but the anionic type is more preferable from the viewpoint of stability.

It is not necessary to add the anti-friction agent, the defoaming agent, the preservative and the solubilizing agent, which are added to general printing inks.
It is preferable because it improves the performance of the P varnish.

The composition of the toner particles in the liquid developer as the image forming material used in the present invention is not particularly specified, and conventionally known ones can be used. Generally, the toner particles are composed of a fixing agent for fixing the toner particles to the printing medium and a colorant such as a pigment or dye for visualization. The fixing agent may be any resin that is insoluble or swellable in the carrier liquid. Specifically, for example, polyethylene resin, methacrylic resin, acrylic resin, styrene resin, vinyl acetate resin, ester resin, amide resin, phenol modified alkyd resin, epoxy resin, linseed oil modified alkyd resin, coumarone-indene resin, phenol- Formalin resin, rosin resin, styrene-butadiene rubber, cyclized rubber and the like are used.

As the colorant for the liquid developer used in the present invention, known pigments, dyes, or a mixture of both, which have been conventionally used in the liquid developer, can be used.
For example, Hansaelo, Benzijinelo, Benzijin Orange, Fast Red, Brilliant Carmine 3B,
Examples thereof include copper phthalocyanine blue, phthalocyanine green, spirit black, oil blue, alkali blue, rhodamine 6B, nigrosine, carbon black, dichloroquinacridone, and isoindolinone.
Further, surface-treated pigment, polymer-grafted carbon and the like can also be used.

A charge adjusting agent can be added to the liquid developer used in the present invention. As the charge adjusting agent,
Naphthenic acid, octenoic acid, oleic acid, stearic acid,
Metal salts of fatty acids such as lauric acid, metal salts of sulfosuccinate, oil-soluble sulfonic acid metal salts described in JP-B-45-556, abietic acid or hydrogenated abietic acid described in JP-B-48-25666 Metal salt of Japanese Patent Publication Sho 5
Alkylbenzene sulfonic acid Ca described in JP-A-5-2620
Salts, aromatic carboxylic acid or sulfonic acid metal salts described in JP-A-52-107837, nonionic surfactants such as polyoxyethylated alkylamines, lecithin, oils and fats such as linseed oil, polyvinylpyrrolidone All known charge-imparting agents and preparation agents such as organic acid esters of polyhydric alcohols can be used.

The method for producing the liquid developer used in the present invention is a method in which a colorant, a resin and, if necessary, other additives are added and wet-dispersed in an electrically insulating liquid by a disperser such as a sand mill. A method in which a colorant, a resin, and other additives, if necessary, are heated and kneaded by a two-roll twin-screw extruder or the like in advance and then dry-pulverized or wet-pulverized as it is. Also, if necessary, heat a monomer that is soluble in a non-polar solvent together with a polymerization initiator,
By stirring, a polymerization reaction is caused to occur, and the colorant is dispersed in the resulting insoluble polymer resin particles,
A method of mixing is also available.

[0022]

EXAMPLES The present invention will be described below based on examples.
In the examples, "part" means "part by weight" and "%" means "% by weight".

[Example 1] Polyethylene resin ("Mitsui High Wax 4202E" manufactured by Mitsui Petrochemical Co., Ltd.) 40 parts Carbon black ("Mitsubishi Color Carbon # 44" manufactured by Mitsubishi Kasei Co., Ltd.) 2 parts Isopa H (Exxon) 160 parts Each of the above mixtures was wet-dispersed for 30 hours to obtain a concentrated developer. Isopa H was added to adjust the developer to a solid content of 1.5%. Zirconium octylate was added to 1000 parts of the obtained developer.
0.2 parts was added to prepare a developing solution for image evaluation. Put this in a liquid development copier ("Savin870" manufactured by Sabin),
The reflection density of the solid portion of the obtained image was measured by a reflection densitometer (“Macbeth RZ-918” manufactured by Macbeth Co.). As a result, the image density was 1.38. Further, the obtained image was good with no stain on the non-image area.

Next, Toyo Litho Coat 415 Varnish (trade name, manufactured by Toyo Ink Mfg. Co., Ltd.) is treated with water / IPA.
(Isopropyl alcohol) is adjusted to a viscosity that can be applied by a bar coater with a 1/1 dilution solvent.
Was coated on the above image with a thickness of 3 μ (dry film thickness). Then, after drying in a 60 ° C. oven for 30 seconds, the reflection density of the solid portion was measured under the above measurement conditions, and as a result, the image density was 1.60.

Example 2 Polyethylene-methacrylic acid copolymer 40 parts (Mitsui DuPont Polychemical Co., Ltd. “HIMIRAN 1856”) Carbon black “Mitsubishi Color Carbon # 44” 2 parts ISOPA G (Exxon) 160 parts Each mixture was wet-dispersed for 18 hours to obtain a concentrated developer. Then, a developer for image evaluation was prepared in the same manner as in Example 1 to form an image, and the density of solid areas was measured. As a result, the reflection density was 1.25.

Next, Toyo Litho Coat 300A varnish (trade name, manufactured by Toyo Ink Mfg. Co., Ltd.) was adjusted to a coatable viscosity by a bar coater with a diluting solvent containing 1/2 of water / IPA, and 3 μm was prepared with a bar coater # 4. The thickness (dry film thickness) was applied on the image. Then 30 at 60 ℃ oven
After second drying, the reflection density of the solid portion was measured under the above measurement conditions, and as a result, the image density was 1.56.

[0027]

According to the present invention, various performances of an image surface using a liquid developer as an image forming material are improved. For example, the improved glossiness resulted in higher reflection density and improved other resistances such as abrasion resistance and tape peeling resistance.

Claims (2)

[Claims] 1. A light-transmitting material comprising an aqueous overcoat varnish formed on an entire surface or a part of an image-formed object after the image is formed on the object by an image forming method using a liquid developer. A method for protecting an image surface of a printed matter, which comprises applying the protective agent of 1. 2. The method for protecting an image surface of a printed matter according to claim 1, wherein the water-based overcoat varnish is a vinyl resin.