JPS6232466A - Imaging material for electrophotography - Google Patents

Abstract

PURPOSE:To upgrade a color image and to form a particularly bright and sharp image by putting spheroidized particles having a high refractive index into an imaging material. CONSTITUTION:The imaging material for electrophotography contains transparent spherical particles 1 having >=1.4 refractive index. Incident light transmits the particles 1 and arrives at an inorg. pigment 2 or org. pigment 3 distributed in the color image. The light scattered and reflected therein is again reflected in substatially the same direction as the direction of the incident light by the lens effect of the particles 1 and arrives at an observer's eyes. The material for the spherical particles is selected by taking the actual ease of use into consideration, regardless of org. and inorg. materials. Spheroidization is executed in the polymn. stage of each polymer to produce the spherical particles.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD This invention relates to electrophotographic imaging materials, particularly toners having retroreflective properties.

2. Description of the Related Art Electrophotographic image forming methods are well known, and various requirements are placed on the characteristics of the images. Especially since color images have been formed, there has been a demand for improvements in image quality, and some of these include measures that are better recognized by the observer's eyes, that is, improvements in visibility. For this purpose, edges such as lacquering are insufficient.

Purpose: In order to meet the above requirements, the present invention provides an electrophotographic developing material that makes use of the retroreflective ability of transparent spherical particles to form images that stand out even in the dark and give an effective impression. is intended to provide.

Structure The structure of the present invention for achieving the above object has a refractive index of 1.
．． This is an electrophotographic imaging material containing 4 or more transparent spherical particles.

Retroreflectivity is a phenomenon as shown in the drawing, in which incident light passes through transparent spherical particles 1 and reaches inorganic pigments 2 or organic pigments 3 distributed within a color image. The scattered and reflected light is again reflected in almost the same direction as the incident light by the lens effect of the transparent spherical particles 1, and reaches the observer's eyes. This retroreflectivity is extremely effective for visibility, especially in a dark environment, and has a great influence on the usefulness of images produced by electrophotography.

The retroreflection ability depends on the particle size of the spherical particles, the refractive index, the degree of circularity, the amount of mixture in the imaging material, etc., but the refractive index has the highest contribution rate.

The higher the refractive index, the higher the retroreflection brightness, but as a result of various experiments, it was found that spherical particles with a refractive index of 1.4 or more are required.

The material of the spherical particles may be selected in consideration of practical ease of use, regardless of whether it is an organic material or an inorganic material.

Glass is a typical inorganic material, and examples of its types include Na20-CaO-3iO2, Na20-
B203-AI 203-3iO2 series, +go-Ca
O-8203-AI 203-3iOz series, Li 20
(Na20)At 203-3i02 series, Na20-
Ba0-AI 203-3i02 series, Li 20-Al
203-3iO2 system, Li 20-AI 203-8
iOz-TiO2 system, Li20-Al 203-3i0
2-P20 s system, Li 20-Al 20 a-3i
02-Zr02 series, Na20-Ca0-At 20 s
-3iO2 system, Li 20-Hg0-Al 203-
3iOz series, Li 20-P20s-A (JzO series, K
2O-BaO-8iO2 system, B203-La 20-
PbO system, 8203-La 2O-BaO system, 8203
-AI 203-CaO system, NaF-Ti02-3i
Oz series, Tl 20 (Na20)-At 203-3i
O2 system, V205-Ba0-P2Os system, B203-T
iOz-BaO system, Fe203-Hno(BaO)-L
There are i20-8iO2 series and Karasu, which can be selected according to the purpose.

Organic materials include spherical particles of polymers. Examples of such materials include the following: polymethacrylate, polystyrene, styrene-acrylonitrile copolymer, polyvinyl chloride (rigid), polypropylene, various types of low-density, medium-density, and high-density polyethylene, polycarbonate, polyamide (nylon 6.6) , allyl diglycol carbonate, poly4 methylpentene 1, polychlorostyrene,
Polytrifluoroisopropyl methacrylate, polydimethylsiloxane, polyvinyl acetate, polyisobutylene, polyvinylidene chloride, polytrifluorochloroethylene, cellulose acetate, cellulose acetate butyrate, cellulose nitrate, polyacetal, epoxy resin, polyester resin, phenol resin, urea Resin etc.

To produce spherical particles, each polymer is spherical during polymerization. Regarding acrylic materials, polymer particles of around 100 microns can be produced by pearl polymerization. Intermediate particles of about 10 to 50 microns can be produced by seed emulsion polymerization, dispersion polymerization, etc.

Spherical particles that are difficult to form by polymerization can be obtained by drawing a molten polymer.

The particle size of the spherical particles is determined by the intended imaging system.

The reason for this is that in order to exhibit the retroreflective ability of the transparent spherical particles, the spherical particles must protrude from the color image layer as shown in the drawing. For example, in the case of a dry toner development method using a magnetic brush, 2
~3 layers of dry toner are required, and the thickness is 100
It seems to be around μ. Heat and fix this 5
Assuming that the diameter is about 0μ, the maximum diameter of a spherical particle will be 100μ if half of it is buried in a single layer of toner.

The ideal shape of a spherical particle is a true sphere, but Wadell's true sphericity, which is known as the definition of sphericity, is 14! =
s/S where S=surface area of a sphere having the same volume as the actual particle S=surface area of the actual particle is desirably 0.95 or more.

The optimum mixing ratio of spherical particles to the imaging material varies depending on the imaging method, but the appropriate amount is usually 2 to 70 wt%, preferably 5 to 30 wt%.

Hereinafter, the present invention will be specifically explained with reference to Examples.

Note that all amounts (parts) of each component described in Examples are parts by weight.

Example 1 As described above, each of yellow, cyan, and magenta color toners having a particle size of 12 μm was obtained by premixing the raw materials of the three compositions using a Henschel mixer, heating mixing using two rolls, pulverizing, and classifying the raw materials.

A developer was prepared by mixing 95 parts of 200/300 mesh type carrier iron powder and 10 parts of 40 μm spherical particles of polymethyl methacrylate with a refractive index of 1.49 into 5 parts of this toner.

A color image consisting of three colors was formed by performing development and transfer three times using these three types of developers.

This color image was fixed using a heater roller that was a relatively elastic material.

Microscopic observation of the produced color image confirmed that about half of the polymethyl methacrylate particles were exposed on the surface.

Comparative Example 1 A color image was produced in the same steps as in Example 1 using a developer produced without containing polymethyl methacrylate particles.

The visibility of each color image of Example 1 and Comparative Example 1 was compared using the following method.

Each color image was placed under constant illumination, and the viewing distance of the color image pattern was set by a panelist.

In Example 1, it was possible to distinguish colors even at a distance of 10 rrt, but in Comparative Example 1, it was necessary to keep the distance to color separate approximately 1# line images under 500 lux illumination within 3 TrL.

Example 2 2 Colloidal polymer liquid of ethylhexyl methacrylate (solid content 25%) 160 parts Monoazo pigment 2 parts Calcium naphthenate 2 parts Isopar) 1
A mixture consisting of 480 parts was kneaded in a ball mill for 48 hours to prepare a concentrated toner. Part 20
Isopar H
232 to obtain a yellow liquid developer.

On the other hand, developers containing cyan and magenta spherical particles were produced in the same manner using a copper phthalocyanine pigment and an azo lake pigment instead of the monoazo pigment, respectively.

Using these three color developers, development and transfer were performed three times to form a color image consisting of three colors.

This color image was fixed by simple hot plate fixing. Microscopic observation of the formed color image revealed that about half of the spherical glass particles were exposed on the surface.

Comparative Example 2 In Example 2, a developer was prepared without adding glass particles. Then, a color image containing no spherical particles was formed using the same steps as in Example 2.

The visibility of the color images produced in Example 2 and Comparative Example 2 was compared. The method is the same as in Example 1 and Comparative Example 1. The result was 17 m for Example 2.
However, in the case of Comparative Example 2, color separation could not be performed unless the distance was within 5 m.

As explained above, according to the present invention, by incorporating spherical particles with a high refractive index into a developing material (developer),
It is possible to improve the quality of color images, especially to form bright and clear images.

[Brief explanation of the drawing]

The drawing is an explanatory diagram showing the retroreflectivity of the electrophotographic imaging material of the present invention. 1... Transparent spherical particles 2... Inorganic pigment 3.
・・Organic pigment

Claims (1)

[Claims] A visualization material for electrophotography, characterized in that it contains transparent spherical particles with a refractive index of 1.4 or more.