JPS589418B2 - Liquid developer for electrostatography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid developer for electrostatography containing a thioindigoid pigment - for visualization of electrostatic latent images formed by electrostatic photography methods such as electrophotography and electrostatic recording. In the case of a wet development method, a liquid developer is used.

Liquid developers generally contain a colorant or resin called a toner in a highly insulating, low dielectric constant organic solvent called a carrier liquid, and a dispersion stabilizer such as a surfactant or a polarity control agent such as a naphthenic acid metal salt or lecithin. During use or storage, the toner is required to exhibit distinct polarity in the developer and to be stably dispersed.

Conventionally, colorants used for coloring such toners include inorganic pigments such as carbon black, phthalocyanine blue, sky blue, rhodamine lake, malachite green lake, methyl violet lake, peacock blue lake, and naphthol green B1 naphthol. Organic pigments such as Green Y, Naphthol Yellow S1 Permanent Red 4R1 Brilliant Fast Scarlet, Hansa Yellow, and Benzidine Yellow are known, but many of them have poor dispersibility and do not have polarity control properties, so these pigments When used or stored for a long period of time, the dispersion stabilizer and polarity control agent may dissolve in the carrier liquid and lose their functionality, causing the toner to aggregate or the polarity to become unclear. This has the disadvantage of causing a decrease in image quality.

In order to improve these drawbacks, proposals have been made to surface-treat the pigment or, in the case of carbon black, to graft it to give the pigment itself dispersibility and polarity controllability, but the results have not yet been satisfactory. has not been obtained.

Furthermore, conventional colorants have poor transparency and coloring power, and are therefore not satisfactory for use in color toners.

The purpose of the present invention is to improve the dispersion stability of toner by using a specific thioindigoid pigment as a toner colorant.
An object of the present invention is to provide a liquid developer for electrostatography that has improved polarity controllability, coloring power, and transparency.

That is, the liquid developer of the present invention has the general formula (where R1==H, R2:=H, R3=Rr:R,
=H, R2-H, R3-C1; R=CH R=CH3, R3=C1; 1
3 tsu 2 R-OCH R-OC3H7,R3-C1;l
At least one selected from thioindigoid thread pigments represented by 3 and R1-CH3, R2-CH3, R3-Br)
It is characterized by containing seeds.

The thioindigoid pigment of the general formula used in the present invention differs from conventional colorants in that it has good dispersibility, and due to its structure, it can clarify the polarity of the pigment itself such as carbon black, and also has good transparency and It has features such as excellent coloring power.

Therefore, without using dispersion stabilizers or polarity control agents,
The dispersion stability and polarity controllability of the toner can be improved, and since no dispersion stabilizer or polarity control agent is used, the liquid developer of the present invention does not cause the toner to aggregate even after long-term use or storage. The polarity is never obscured, so good quality images can be formed at all times.

Furthermore, since the thioindigoid pigment of the present invention has excellent transparency and coloring power, it is particularly suitable for use in color toners that require toner transparency and coloring.

The improvement in the dispersion stability and polarity controllability of the toner is thought to be mainly due to the R3 group, although the R1 and R2 groups (which provide compatibility with the resin and carrier liquid) in the above general formula also play some role.

Next, the structural formula of the thioindigoid pigment having the above general formula is shown.

To make the liquid developer of the present invention, the pigment of the general formula described above, a resin, and a small amount of carrier liquid are kneaded and dispersed using a dispersion machine such as a ball mill or an attritor to form a concentrated toner, which is then diluted with a large amount of carrier liquid. Bye.

As the carrier liquid, highly insulating, low dielectric constant aliphatic or alicyclic hydrocarbons and their halogen derivatives, such as n-hexane, cyclohexane, decalin, kerosene, etc. (commercially available products include Exon's Isopar G, H, Shell Ciel Sol 71 (manufactured by Sekiyu Co., Ltd.).

Further, as the resin, acrylic or methacrylic resin, styrene thread resin, polybutene, rosin-modified maleic acid resin, etc. can be used.

Examples are shown below.

Example 1 Pigment No. 1 30g
Styrene/lauryl methacrylate = 10/90 (weight ratio) copolymer 65g Isopar 0
A mixture consisting of 100 g was kneaded and dispersed in a ball mill for 80 hours to obtain a concentrated toner, and then 20 g of the mixture was diluted with 1 liter of Isopar G to prepare a liquid developer.

Next, an electrostatic latent image was formed on zinc oxide/resin dispersion thread photosensitive paper using the negative image as an original by a conventional method, and development was performed using the developer described above, resulting in a red positive image with an image density of 0.63. Obtained.

The toner particle size of this developer was 0.25 μm.

Further, this developer was allowed to stand for 80 days at 50° C. for forcible deterioration, and then developed in the same manner. When the image density was 0.60, there was almost no change.

Further, the particle size of the toner at this time was 0.26 μm, with almost no change observed, and a liquid developer was prepared in the same manner as in Example 1, except that the thioindigoid pigment shown in the comparative example was used instead.

Next, when an electrostatic latent image was developed using this developer in the same manner as in Example 1, the density of the obtained image was as low as 0.54, and the image density after forced deterioration was even higher at 0.46. decreased.

The particle size of the toner was 0.30 μm immediately after preparation and 0.33 μm after forced deterioration, which did not change much, but was larger than that of Example 1.

Example 2 A mixture consisting of 15 g of pigment No. 2, 50 g of a copolymer of lauryl methacrylate/acrylic acid = 90/10 (weight ratio), and 80 g of Isopar 6 was kneaded and dispersed in an attrique for 15 hours to produce a highly transparent concentrated toner.

The particle size of this toner is 0.20μ, and the viscosity is 20
It was cps.

Next, after forced deterioration in the same manner as in Example 1, the particle size and viscosity were measured, and the results were 0.22μ and 25μ, respectively.
It just changed to cps.

Furthermore, 10 g of concentrated toner at the initial stage of production was diluted with 2 liters of Isopar G to prepare a liquid developer for magenta, and an electrostatic latent image formed in the same manner as in Example 1 was developed, resulting in a color copy image with good color reproduction. It was done.

The reason why the color reproduction was so good is thought to be due to the small particle size of the toner and the high transparency of the toner.

Example 3 Carbon black (Mitsubishi Kasei MA-11) 10.
9 Pigment Sou 5 1g Phthalocyanine Blue - 3g Rosin modified maleic acid resin (MRP manufactured by Tokushima Essential Oils) 50g
Isopar G 100g
After kneading and dispersing the mixture in a ball mill for 25 hours to create a concentrated toner, 15 g of the mixture was mixed with Isopar G2L.
It was dispersed into a liquid developer.

When this developer was used for development in the same manner as in Example 1, an image with a density of 1.25 and good sharpness was formed.

For comparison, a liquid developer was prepared in the same manner as in this example except for pigment No. 5, and development was performed, but the concentration was 0.82.
An image with poor sharpness was obtained.

Example 4 Carbon black (Mitsubishi Kasei MA-11) 20
A mixture consisting of 5 g of pigment No. 3, 65 g of styrene-butadiene copolymer, and 120 g of Isopar G was kneaded and dispersed in an attritor for 8 hours to obtain a concentrated toner, and 30 g of the mixture was diluted with 2 liters of Isopar G to prepare a liquid developer.

The toner particle size of this developer was 0.23μ.

When this developer was used for development in the same manner as in Example 1, an image with a density of 1.28, good sharpness, and no bleeding was formed.

On the other hand, for comparison, a liquid developer (toner particle size 0.32μ) was prepared in the same manner as in this example except that pigment No. 3 was removed, and development was performed in the same manner. A poor and smeared image was formed.

Next, these two types of developers were forced to deteriorate in the same manner as in Example 1, and the particle size was measured.
There was no change at all, and almost no sedimentation occurred, whereas the comparative product had a considerably large value of 0.43μ, and moreover, toner lumps were sedimented.

Claims (1)

[Claims] (However, R1=H, R2=H, R3=Br :R1=
H, R2=H, R3=C1; R1-CH3, R2-CH3, R3-C1; R1-
OCH3, R2-OC3H7, R3-C1; and R0=
A liquid developer for electrostatic photography containing at least one selected from thioindigoid pigments represented by CH3, R2-CH3, R3-Br).