JPH06123964A - Photosensitive microcapsule - Google Patents

Abstract

PURPOSE:To prevent the deterioration in sensitivity due to image forming material and the image noise and to obtain the photosensitive microcapsule excellent in coloring density by incorporating the image forming material by specified wt.% with respect to photosensitive material. CONSTITUTION:The photosensitive microcapsule 10 is composed of an outer shell layer 11 and a core material 12, moreover, the core material 12 is phase- separated into the image forming material 13 and a photosensitive material 14. The outside diameter of the photosensitive microcapsule 10 is preferably to be about several mum-several tens mum, the grain size of the photosensitive microcapsule 10 is preferably to be <=2/3 of the grain size of the photosensitive microcapsule 10. But, it is not confined to this value. And, the photosensitive microcapsule 10 contains the core material in its outside wall part consisting of at least a resin an inorg. material, etc., moreover, by incorporating the image forming material 13 at 0.5-5wt.% per the photosensitive material, the deterioration of sensitivity and the image noise resulted from the image forming material 13 is prevented and excellent coloring density is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photosensitive microcapsule used in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, a color image forming method for forming an image on paper using a microcapsule for image formation containing a dye precursor substance and a photosensitive substance is disclosed in JP-A-59-30.
No. 537.

However, in this image forming method, it was possible to form an image only on so-called special paper on which a developer which reacts with a dye precursor to develop a color was previously coated. Therefore, a method for forming an image on plain paper has been desired. Therefore, the present applicants have proposed photosensitive microcapsules in which a photosensitive substance made of a polymerizable monomer and a core substance made of an image forming substance such as a colored dye or pigment are included.

In this photosensitive microcapsule, the photosensitive substance is polymerized in response to light and its mechanical strength is changed. An image is formed on plain paper by controlling the release amount of the image forming substance by the difference in the intensity.

The method for producing the photosensitive microcapsules is not particularly limited in itself, and is a known method for producing microcapsules such as coacervation method, in-situ polymerization method, and interface method. It can be selected from polymerization methods and the like.

However, the coacervation method has a problem that the water resistance of the capsule film is poor, and the interfacial polymerization method has a problem that the film thickness of the capsule is limited. On the other hand, the in-situ polymerization method has advantages that an inexpensive raw material such as an amino resin can be used, and a membrane wall excellent in water resistance can be formed.

Accordingly, the present applicants constructed the core substance from a hydrophobic substance, emulsifying the core substance in water using an emulsifying dispersant, and surrounding the droplets of the core substance by the in-situ polymerization method. A microcapsule obtained by forming a membrane wall made of a melamine resin is proposed in the specification and drawings attached to the application of Japanese Patent Application No. 4-179754. Since the membrane wall made of this melamine resin is dense and homogeneous as compared with other resins, it has an advantage that the core substance can be stably encapsulated for a long time.

[0008]

However, in the case of producing a photosensitive microcapsule having a melamine resin as a membrane wall by the above-mentioned in-situ polymerization method, the colored substance in the core substance is colored. When the concentration of the image forming material such as dye or pigment becomes high, the thickness of the film wall formed around the core substance becomes insufficient, the strength of the obtained microcapsules becomes insufficient, or a large amount is added to improve it. When the above melamine-formaldehyde prepolymer was added, there was a problem that the obtained microcapsules became aggregates. This phenomenon starts from about 3% of the photosensitive substance, and when it exceeds 5%, encapsulation becomes almost impossible. The inhibition of encapsulation by such dyes and pigments similarly occurs in other methods such as the coacervation method and the interfacial polymerization method.

Further, when the concentration of the image forming material is high, when the light is irradiated corresponding to the image information, the light having the wavelength absorbed by the photosensitive substance is absorbed by the image forming material uniformly dispersed in the core substance. The problem that the sensitivity is significantly reduced due to absorption by the image-forming material, and particularly in a system using photo-curing, a portion which should not release the image-forming material due to photo-curing (formed image Corresponding to the white part), the curing reaction is blocked due to the presence of the image forming material, the photosensitive substance does not sufficiently polymerize and remains rubbery, and the strength is insufficient. There is a problem that the image noise is generated and the image noise is generated.

On the other hand, when the concentration of the image forming material is less than 1% with respect to the photosensitive substance, the encapsulation inhibition as described above does not occur, and the sensitivity is lowered and the curing in the photocuring system is inhibited. Although the problem does not occur, the absolute amount of the image forming material becomes insufficient at the time of image formation, so that the problem that the color density of the formed image becomes insufficient occurs.

The present invention has been made in order to solve the above-mentioned problems, and provides a photosensitive microcapsule which is capable of preventing a decrease in sensitivity and image noise caused by an image forming material and which has an excellent color density. Is intended.

[0012]

To achieve this object, the photosensitive microcapsule of the present invention comprises an image-forming material such as at least a colored dye and a pigment, and a photosensitive substance whose mechanical strength is changed by irradiation with electromagnetic waves. In a photosensitive microcapsule containing, as a core substance, in an outer wall portion formed of at least a resin or an inorganic substance, the image forming material contains 0.5 to 5% by weight of the photosensitive substance.
It is characterized by being included.

[0013]

In the photosensitive microcapsule of the present invention having the above-mentioned constitution, the image forming material is contained in a proportion of 0.5 to 5% by weight with respect to the photosensitive substance. As a result, encapsulation inhibition during capsule production does not occur, and sensitivity deterioration and insufficient image color density do not occur, so that good image formation can be performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing the structure of a photosensitive microcapsule 10 which is a first embodiment of the present invention.

The photosensitive microcapsule 10 has an outer shell 1
1 and a core substance 12, and the core substance 12 is further phase-separated into an image forming material 13 and a photosensitive substance 14. The outer diameter of the photosensitive microcapsule 10 is preferably several μm to several tens of μm, and the particle size of the image forming material 13 is preferably two thirds or less of the particle size of the photosensitive microcapsule 10. However, it is not limited to this.

The color material constituting the image forming material 13 is
Dyes, pigments, etc. can be used. The dye is preferably a xanthene-based, coumarin-based, merocyanine-based, thiazine-based, azine-based, methine-based, oxazine-based, phenylmethane-based, cyanine-based, azo-based, anthraquinone-based, pyrazoline-based, stilbene-based, quinoline-based, phthalocyanine Examples of the leuco dyes include pigments such as carbon black, yellow lead, red iron oxide, and titanium oxide.
Inorganic pigments such as molybdenum red and organic pigments, more preferably, azo-based, quinacridone-based, phthalocyanine-based, slene-based, isoindolinone-based, anthrapyrinidine-based,
An organic pigment such as a perylene-based pigment can be used.

The photosensitive material 14 is a resin that is sensitive to light and is modified, and includes a photosoftening resin and a photocurable resin. The photocurable resin is usually used by mixing a photoinitiator and a polymerizable substance. The photoinitiator is one that is sensitive to light and initiates polymerization of the resin, and is preferably benzophenone.
Benzoyl alkyl ethers such as benzoyl isopropyl ether, Michler's ketone, metal arene compounds, and 2,4-diethylthioxanthone can be used.

The polymerizable substance is preferably N
-Vinyl-2-pyrrolidone, bisphenol A diacrylate and methacrylate, tripropylene glycol diacrylate and methacrylate, polyethylene glycol diacrylate and methacrylate, pentaerythritol triacrylate and methacrylate, dipentaerythritol hexaacrylate and methacrylate, trimethylolpropane triacrylate and Methacrylate, oligoester acrylate and methacrylate are used. Further, these polymerizable compounds may be used alone or as a mixture of two or more kinds.

The photosensitive microcapsule 10 having the above structure
Can be produced by a method already known in the art. For example, US Pat.
No. 00457, No. 2800458 and the like, a method for phase separation from an aqueous solution, Japanese Examined Patent Publication No. 38-1974.
Japanese Patent Publication No. 42-446, Japanese Patent Publication No. 42-771, etc., the interfacial polymerization method, Japanese Patent Publication No. 36-9168.
In-situ method by polymerization of monomers as disclosed in JP-A-51-9079 and British Patent No. 95280.
No. 7, No. 965074, and the like, but the method is not limited thereto.

As the material for forming the outer shell 11, gelatin, gum arabic, starch, sodium alginate,
Polyvinyl alcohol, polyethylene, polyamide, polyester, polyurethane, polyurea, polyurethane, polystyrene, nitrocellulose, ethyl cellulose, methyl cellulose, melamine-formaldehyde resin, urea-formaldehyde resin, etc. are used, but only the outer shell 11 is sufficiently exposed to light. It is more preferable to use a material that allows the light to pass through.

Here, the image forming material 13 is contained in the photosensitive material 14 in an amount of preferably 0.5 to 5% by weight, more preferably 1 to 3% by weight. 12 are compounded.

Specific examples of the yellow image-forming photosensitive microcapsules in which a film wall is formed around a core material made of a yellow pigment and a photosensitive material having a photosensitivity to light having a wavelength of about 450 nm will be given below.

First, 100 parts by weight of a 1: 1 mixture of polyethylene glycol diacrylate and dipentaerythritol hexaacrylate and 2,2-
2 parts by weight of dimethyl-2-morpholino-4'-methylthioacetophenone, 2 parts by weight of 2,4-diethylthioxanthone, 0.5 parts by weight of 3-thenoyl-7-dimethylaminocoumarin, and a disazo yellow pigment. As described below, a mixture of 0 to 7 parts by weight was ultrasonically dispersed for 5 minutes and heated at 100 ° C. for 10 minutes to obtain a hydrophobic core substance.

Next, Gohsenol NL- manufactured by Nippon Synthetic Chemical Industry Co., Ltd.
05 (PVA: polyvinyl alcohol) 5% aqueous solution 1
When 100 parts by weight of the core substance and 100 parts by weight of the core substance were mixed and rotated by a homogenizer at 5000 rpm for 5 minutes, an O / W emulsion dispersion in which a hydrophobic substance was emulsified in water was obtained.

Separately, powdered melamine 126
g (1 mol) and formalin (37% formaldehyde aqueous solution) 203 g (equivalent to 2.5 mol of formaldehyde)
Was mixed, the pH was adjusted to 7.5, the mixture was heated at 80 ° C. for 30 minutes and then cooled to obtain a transparent aqueous solution of the initial condensate of melamine.

Then, the O / W emulsion dispersion was diluted with 3 times deionized water, 20 parts by weight of the melamine initial condensate aqueous solution was further added, and the pH of the dispersion was stirred with ammonium chloride to pH 5.5. After adjusting the temperature to 80 ° C., the temperature was raised to 80 ° C., the temperature was maintained for 4 hours, the temperature was lowered to 30 ° C., the pH was adjusted to 8, and the mixture was filtered and washed to obtain a dispersion liquid of photosensitive image forming microcapsules for yellow image formation.

At this time, 0, 0.3, 0.5, 1, 3, 5, 6, 7 parts by weight of the disazo yellow pigment is added to the photosensitive microcapsules so as to have an average particle size, sensitivity, and The image density when pressure-developed (compressed) without exposure is shown in FIG.

This was prepared by adding a 10% aqueous solution of PVA as a binder to the slurry of the above-mentioned photosensitive microcapsules and applying it on a PET film having a thickness of 50 μm and drying it to obtain a sample for sensitivity measurement and image density measurement. .
The average particle size was measured using a Coulter counter, the sensitivity was measured using a Narumi Shokai spectral sensitivity measuring instrument, and the image density was measured using a Macbeth reflection density measuring instrument RD914.

It is clear from FIG. 2 that encapsulation becomes impossible when the pigment concentration exceeds 5 parts by weight, and the pigment concentration is 3%.
If the amount is more than about 50 parts by weight, the sensitivity is reduced to half or less as compared with the case of no pigment (the content of the pigment is 0 parts by weight). Regarding the image density, when the amount is less than 0.5 part by weight, the reflection density is 1
It is much lower than, and the concentration is insufficient. Therefore, comprehensively judging the ease of making capsules, the sensitivity, and the image density, it is appropriate that the pigment concentration is in the range of 0.5 to 5 parts by weight, and further preferably 1 to 3 parts by weight. I got the result.

In the photosensitive microcapsule 10 having the above-mentioned image forming material concentration, when the light is irradiated corresponding to the recorded image, the photosensitive material 14 is not exposed to the image forming material 13. Photoreaction inhibition due to the presence in an excessive amount does not occur, the sensitivity of the photosensitive substance 14 is prevented from being lowered, and at the same time, the occurrence of image noise due to insufficient curing of the capsules on the white background portion of the formed image can be prevented. .

Further, since the existing amount of the image forming material in the above range is sufficient for image formation, the color density of the formed image is not insufficient.

The present invention is not limited to the embodiments described in detail above, and various modifications can be made without departing from the spirit of the invention.

[0034]

As is apparent from the above description, the photosensitive microcapsule of the present invention comprises an image forming material such as at least a colored dye and a pigment, and a photosensitive substance whose mechanical strength is changed by irradiation with light. As a core substance, the core substance is contained in the outer wall portion formed of at least a resin or an inorganic substance, and the image forming material further comprises:
When it is contained in an amount of 0.5 to 5% by weight with respect to the photosensitive substance, it is possible to prevent sensitivity deterioration and image noise due to the image forming material and to exhibit excellent color density.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a photosensitive microcapsule of the present invention.

FIG. 2 is a diagram showing the results of measuring the average particle size, the sensitivity, and the image density by specifically producing the photosensitive microcapsules of the present invention at a plurality of pigment concentrations.

[Explanation of symbols]

 10 Photosensitive Microcapsule 11 Outer Shell 12 Core Material 13 Image Forming Material 14 Photosensitive Material

Claims (1)

[Claims] 1. A core comprising at least an image forming material such as a colored dye or a pigment, and a photosensitive substance whose mechanical strength is changed by irradiation of light, as a core substance, and the core is provided in an outer wall portion formed of at least a resin or an inorganic substance. A photosensitive microcapsule containing a substance, wherein the image forming material is contained in an amount of 0.5 to 5% by weight based on the photosensitive substance.