# US 7,608,375 B2 · Liquid developer and image forming apparatus using the same

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- Number: US 7,608,375 B2
- Document ID: US7608375B2
- Status: Granted
- Kind: B2
- Application number: 11/565,956
- Filed: 2006-12-01
- Published: 2007-06-07
- Granted: 2009-10-27
- Earliest claimed: 2005-12-02
- Assignees: Seiko Epson Corporation
- Inventors: Nobuhiro Miyakawa
- Web page: https://patentgrep.com/patent/US7608375B2

## CPC

- G03G 9/1355: {Ionic, organic compounds}
- G03G 9/125: characterised by the liquid
- G03G: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY

## Abstract

A liquid developer includes a positively chargeable pigment, a carrier liquid formed of a vegetable oil, and an antioxidant formed of a phosphorous acid ester compound.

## Claims

### Claim 1

A liquid developer comprising a positively chargeable pigment, a carrier liquid formed of a vegetable oil, and an antioxidant formed of a phosphorous acid ester compound, wherein the phosphorous acid ester compound is in an amount of 0.2% to 5.0% by weight.

### Claim 2 (depends on 1)

The liquid developer according to claim 1, wherein the vegetable oil contains at least 50% by weight of oleic acid component.

### Claim 3 (depends on 1)

The liquid developer according to claim 1, wherein the phosphorous acid ester is at least one selected from triphenyl phosphite, trioleyl phosphite, diphenyl mono(2-ethylhexyl) phosphite, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyl tetra (tridecyl) pentaerythritol tetraphosphite, and tetra(C12-C15 alkyl) 4,4′-isopropylidenediphenyl phosphite.

### Claim 4 (depends on 1)

The liquid developer according to claim 1, further comprising a phenolic antioxidant as the antioxidant.

### Claim 5 (depends on 4)

The liquid developer according to claim 4, further comprising 0.05% to 0.3% by weight of a phenolic antioxidant.

### Claim 6 (depends on 5)

The liquid developer according to claim 5, wherein the phenolic antioxidant is at least one selected from 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-methoxyphenol.

### Claim 7 (depends on 4)

The liquid developer according to claim 4, wherein the vegetable oil contains at least 50% by weight of triglyceridic oleic acid component.

### Claim 8 (depends on 4)

The liquid developer according to claim 4, wherein the phosphorous acid ester is at least one selected from triphenyl phosphite, trioleyl phosphite, diphenyl mono(2-ethylhexyl) phosphite, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyl tetra (tridecyl) pentaerythritol tetraphosphite, and tetra(C12-C15 alkyl) 4,4′-isopropylidenediphenyl phosphite.

### Claim 9

An image forming apparatus comprising a liquid developer as the developer for developing an electrostatic latent image formed on an electrostatic latent image carrier, wherein the liquid developer comprises a positively chargeable pigment, an antioxidant formed of a phosphorous acid ester compound, and a carrier liquid formed of a vegetable oil, wherein the phosphorous acid ester compound is in an amount of 0.2% to 5.0% by weight.

### Claim 10 (depends on 9)

The image forming apparatus according to claim 9, further comprising a phenolic antioxidant as the antioxidant.