JPH0432380B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is an improvement of a dry developer comprising a carrier and a toner used for developing electrostatic images formed by electrophotography, electrostatic recording, etc. Regarding
In particular, the present invention relates to a positive polarity toner having excellent anti-offset properties and a wax that is effective against fogging.

(Prior Art) In electrophotography, an electrostatic image formed on a photoreceptor is developed by a developer, and then transferred and fixed onto a transfer sheet. As this developer, a dry two-component developer for electrophotography consisting of toner and carrier is known.

In recent years, high-speed copying machines with a copying speed of 50 to 60 sheets per minute have been required, and the developer used in these high-speed copying machines requires a carrier that always maintains the desired polarity and sufficient amount of toner during long periods of use. The amount of charge must be triboelectrically charged. However, with conventional developers, a toner film is formed on the carrier surface due to the opportunity impact of collisions between particles or collisions between particles and the developing machine, or the heat generated by these, resulting in the so-called spent phenomenon, and the charging characteristics of the carrier deteriorate over the usage time. As a result, the replenished toner is developed without being sufficiently charged, resulting in poor images due to fogging, etc., and a large amount of toner scattering, contaminating the inside of the copying machine, making it necessary to replace the entire developer.

In addition, in the case of electrophotographic copying machines aimed at high-speed copying, when the developer image is fused to the fixing substrate, the surface of the heating roller and the developer surface on the fixing substrate come into pressure contact. It has extremely good thermal efficiency and can perform fixing quickly. However, since the developer comes into pressure contact with the heating roller surface in a heated and molten state, a part of the developer adheres to the roller surface and re-adheres to the fixing substrate, which tends to cause the so-called offset phenomenon, which stains the image. . Therefore,
Prevention of offset is an important prerequisite for a developer for a hot roll fixing system.

(Problems to be Solved by the Invention) Various methods have been proposed to prevent developer offset. For example, there is a method in which a liquid or solid resin having mold releasability is mixed with a specific fixing resin to prevent the developer from adhering to the heated roller. In addition, the surface of the heating roller is made of a fluorine-based resin or silicone rubber that is heat resistant and has excellent toner releasability, and a liquid for preventing offset such as silicone oil is supplied to the surface, so that the surface of the heating roller is coated with a film of liquid. A method of coating the surface has been adopted.

Furthermore, among toners for electrophotography, waxes such as polypropylene waxes are commonly used as high-temperature offset prevention agents in toners used in hot roller fixing systems. The charging characteristics of carriers generally have strong negative polarity, so if a large amount of these waxes are used as a high-temperature offset inhibitor in positive polarity toner, the charging characteristics of the toner, which should have positive polarity, will be inhibited. In terms of image characteristics, this causes inconveniences such as increasing copy smudges (B and G) in non-image areas and accelerating deterioration of the two-component developer. Therefore, in positive polarity toners, the amount of wax added is limited as much as possible, and the fixing roller is coated with oil to compensate for the restriction on the amount of wax added.
Although high-temperature offset is prevented, the applied oil is exposed to the heat of the rollers and is one of the causes of dirt inside the copying machine and deterioration of the photoreceptor.

(Means for Solving the Problem) According to the present invention, in order to obtain a positive polarity toner that can obtain sufficient offset prevention properties without applying oil to the fixing roller, a positive polarity consisting of an amine-modified wax is used as an offset prevention agent. By using the wax that has this, high-temperature offset can be prevented and clear, high-quality images without fogging can be obtained, and the amount of wax added can be increased, making the fixing roller part oil-free. became possible.

Generally, in the contact heat fixing method, the surface of a heating body such as a heating roller comes into contact with the toner and melts it to fix the toner.
A so-called offset phenomenon occurs in which a portion of the melted toner or semi-melted toner adheres to the roller and is transferred to subsequent transfer paper, etc. on the surface of the heating element. This occurs when the viscoelasticity of the toner is inappropriate and too small.

In order to prevent such an offset phenomenon, an offset inhibitor is added in addition to the general charge limiting agent. Conventional offset inhibitors include polyolefin waxes such as polyethylene waxes, polypropylene waxes, polybutylene waxes, and oxidized polypropylene waxes, among which polypropylene waxes have been particularly preferably used.

The present invention provides a novel wax made of an amine-modified polyolefin wax for use in electrophotographic toners. Here, the amine-modified wax is a polyolefin wax at least partially graft-modified with a vinyl monomer having a tertiary amino group. The amine-modified wax is obtained by grafting a vinyl monomer having a tertiary amine group and a polyolefin wax or an oxidized polyolefin wax through a radical polymerization reaction using a radical initiator to form an amine-modified wax. Such modified wax has a weight average molecular weight of 1000.
~45,000, particularly preferably a weight average molecular weight of about 20,000 to 30,000, and an amine value of 20 to 100. Further, these amine-modified waxes preferably have a softening point of 100 to 180°C, particularly 130 to 160°C. Specifically, vinyl monomers having a tertiary amino group include N,N-dimethylaminomethyl methacrylate, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl methacrylate, and N,N-diethylaminopropyl. Examples include methacrylate, N,N-dimethylaminoethylmethacryamide, N,N-dimethylaminopropylmethacryamide, and N,N-diethylaminopropylmethacryamide. Also, olefinic hydrocarbons having 1 to 6 carbon atoms, such as ethylene, propylene, butylene, styrene, vinyl chloride, acrylic esters, methacrylic esters, and other ethylenically unsaturated monomers and alkylene polyamines, reaction products or oxidized It is also possible to use amine-modified hydrocarbon waxes obtained by reacting polyolefin waxes with alkylene polyamines such as ethylene diamine.

An example of manufacturing the amine-modified polyolefin wax used in the present invention is shown below.

Polyethylene wax (number average molecular weight Mn 1220, weight average molecular weight Mw 1550, Mw/Mn 1.27, melting point 104.5℃, density
4.5 kg (0.95 g/cc) was added and melted at 120°C with stirring. Add 224g of 2-t-butylazo-2-cyanopropane to this and 500g of dimethylaminoethyl methacrylate (10% by weight of the total amount with wax).
The entire solution was added dropwise over 45 minutes, kept at 120°C for an additional 15 minutes, cooled, solidified, crushed and dried to obtain 5 kg of white modified wax.

This product was separated into a predetermined graft-modified wax and a polymer of amino group-containing vinyl monomer by a solvent fractionation method, and as a result of filtering, the modified wax was found to be a composition with excellent homogeneity.

In carrying out the present invention, a positive polarity toner that can sufficiently prevent offset without applying oil to the fixing roller is used, for example, as a wax material such as amine-modified polypropylene wax (for example, a product manufactured by Sanyo Chemical Co., Ltd.). QN-7700) is used in an amount of 3 to 9% by weight based on 100 parts by weight of the total composition of the toner, including synthetic resin, carbon black, colorant, charge control agent, etc.
It has become necessary to use a high-temperature offset, which makes it possible to obtain clear, high-quality copies. Regarding the amount of these waxes used, it is appropriate to use this range because if the amount is less than 3% by weight, the effect will be small and if the amount used is too large (more than 9% by weight), there will be adverse effects such as toner adhesion to non-image areas. Furthermore, there is no problem in using these amine-modified polyolefin waxes in combination with conventional unmodified polyolefin waxes.

The toner constituting the developer of the present invention is made of synthetic resins such as polystyrene, styrene-acrylic copolymers, unsaturated polyesters, polyvinyl chloride, polyvinyl acetate, phenolic resins, and epoxy resins.
5 to 15 parts by weight of a coloring agent such as carbon black or chromium metal-containing dye, and 1 to 5 parts by weight of a charge control agent.
It can be manufactured by using part by weight as a raw material, mixing a predetermined amount of the amine-modified polyolefin wax, melting/kneading, pulverizing and classifying.

On the other hand, the carrier used in the present invention is made of iron oxide powder with a particle size of 100 to 200 μm as a core material, ferrite such as nickel or cobalt, granulated magnetite, etc., and silicone resin, fluororesin, polymethyl acrylate, etc. on the surface. , polyacrylic acid esters such as polyethyl acrylate, n-butyl polyacrylate, and isobutyl polyacrylate, resins such as acrylonitrile, acrylamide, and vinyl isobutyl ether are coated to increase the resistivity.
A resin-coated carrier having a resistance of 10 ¹⁰ to 10 ¹⁶ Ω-cm is used. The above-mentioned iron powder, ferrite, granulated magnetite, etc. without resin coating are used.

(Example) The present invention will be explained below with reference to Examples.

Example 1 A material obtained by coating iron oxide powder with an average particle size of about 150 μm with silicone resin in a fluidized bed was placed in an electric furnace and fired at 250° C. for 2 hours to obtain a carrier.
On the other hand, styrene-acrylic copolymer resin spherical powder
Mw12.3× ¹⁰⁴ , Mn0.47× ¹⁰⁴ , Tg66°C) with an average particle diameter of 10 μm 93 parts by weight Amine-modified polypropylene (amine value 40 QN-7700 manufactured by Sanyo Chemical Co., Ltd.) 5 parts by weight Carbon black ( Taipiroxide #9575 manufactured by Dainichiseika Chemical Co., Ltd. 5 parts by weight Charge control agent; Nigrosine dye (Bontron No.
4 (manufactured by Orient Chemical Co., Ltd.) 2 parts by weight or more of the mixture was melted in a roll mill for 20 minutes, kneaded, cooled, coarsely pulverized in a mill, and further finely pulverized in a supersonic jet mill, with an average particle size of 10 to 15μ.
m toner was obtained. Furthermore, a dry two-component developer for electrophotography of the present invention was prepared by mixing toner at a ratio of 5% by weight with respect to the carrier iron powder.

When this developer was put into a high-speed continuous copying machine (30 copies/minute) and a continuous copying durability test of 500,000 copies was conducted,
The image density (I・D) measured by the Macbeth reflection densitometer is approximately 1.35, the background dirt (B・G) in the non-image area is approximately 0.4 to 0.6, and the amount of triboelectric charge (Q/
M) was 35 μс/g and was stable during continuous copying, with no offset phenomenon or stain on the fixing roller, and clear images were obtained.

The amine value here refers to the number of mg of KOH equivalent to the amine alkali present in 1 g of the sample, and is expressed by the following formula.

Amine value = 0.5N-HCJ titration (ml) x 0.5 x f x 56.11/feed (g
) However, f = 0.5N factor of HCl aqueous solution Comparative example Suspension polymerized product of styrene-acrylic copolymer resin spherical powder (Mw 12.3×10 ⁴ , Mn 0.47×10 ⁴ , Tg 66°C) with an average particle diameter of 10 μm 93 weight Parts Polypropylene wax (Viscol 550P manufactured by Sanyo Chemical Co., Ltd.) 3 parts by weight Carbon black (Tipyroxide #9575 manufactured by Dainichiseika Chemicals) 5 parts by weight Charge control agent; Nigrosine dye (Bostron No.
A toner was prepared in the same manner as in Example 1 using 2 parts by weight (manufactured by Orient Chemical Co., Ltd.) to prepare a dry two-component developer for electrophotography as a comparative example.

When this developer was subjected to a continuous copy durability test using a high-speed continuous copying machine in the same manner as in Example 1, toner adhesion to non-image areas (B and G) was observed, and offset and fixing rollers were stained. .

(Effects of the Invention) As described above, the present invention uses an amine-modified polypropylene wax in the toner to achieve
It is now possible to use a larger amount of wax than conventional wax without interfering with the charging properties of positive polarity toner, and it has also become possible to use oil-free fuser rollers, which reduces dirt and exposure inside the copying machine. It has the advantage of preventing body deterioration.

Claims (1)

[Claims] 1. In a dry two-component developer for electrophotography consisting of a carrier and a positive polarity toner, an amine-modified polyolefin wax having an amine value of 20 to 100 is added to the positive polarity toner in a total of 100 parts by weight of the composition constituting the toner. A dry two-component developer for electrophotography, characterized in that it contains 3 to 9% by weight.