JPS63183453A - Developer for electrophotography - Google Patents

Abstract

PURPOSE:To improve the fixability, offsetting resistance and shelf stability of a developer by using a vinyl polymer having maximal values of number average mol.wt. in specified low and high molecular regions and contg. a prescribed percentage of the low molecular region as a fixing medium. CONSTITUTION:A polymer synthesized from a vinyl monomer by suspension polymn. or other method, e.g., a styrene-n-butyl acrylate copolymer is used as a fixing medium in a developer. The polymer has maximal values of number average mol.wt. in the low molecular region of 4X10<3>-7X10<3> and in the high molecular region of 2X10<5>-5X10<5> measured by gel permeation chromatography and contains 65-85wt.% low molecular region. In case of <65% low molecular region, the fixability of the resulting developer is lowered. In case of >85% low molecular region, the continuity of thermal properties between the low and high molecular regions is unbalanced to deteriorate the shelf stability.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an electrophotographic developer, and more particularly, it has storage stability that can be used widely from low-speed copying machines to high-speed copying machines;
This invention relates to a developer with excellent offset resistance and fixing properties.

[Prior art]

In electrophotography, an electrostatic image is generally formed on the surface of a photoreceptor made of a photoconductor, and a developer is applied to the latent image using a developing means such as a magnetic brush to make it visible. After being transferred to transfer paper, it is fixed to obtain a copy.

Developers used in such electrophotography include one-component developers in which a colorant, charge control agent, etc. are dispersed in a fixing medium, or two-component developers in which a carrier is mixed. It has been known.

These developers are required not only to be able to provide good images but also to have storage stability, offset resistance, and stability. Conventionally, various improvements have been made in resins used as fixing media with respect to such characteristics. For example, in Japanese Patent Publication No. 51-23354, it was proposed to use a crosslinked vinyl polymer to maintain a balance between offset properties and fixing properties. An attempt was made to improve the storage stability by mixing resins such that the resin has a maximum value in the range of 3.5 to 40. It has been proposed to improve fixing properties by using resin.

[Problem that the invention seeks to solve]

However, in any of the prior art mentioned above, although the storage stability and offset I resistance of the developer are improved to some extent by using a crosslinked resin, the adhesion to the transfer paper (anchor effect) is small. , when used in high-speed copying machines, etc., there is a tendency for poor fixing to occur.

In addition, if the low molecular weight region and the high molecular region exist far apart at the maximum value of the molecular weight (GPC), each region will react differently to heat and the thermal properties will become discontinuous, resulting in extreme blocking and storage. Stability deteriorates and an offset phenomenon occurs. Furthermore, the Mw/Mn of the resin used cannot be used to determine storage stability, anti-offset properties, or fixing properties, and stable properties cannot always be obtained. It was not possible to obtain sufficient fixing stability while ensuring offset resistance.

[Means for solving problems]

As a result of repeated research to solve the above problems, the inventor of the present invention found that
By using as a fixing medium a resin that is made of a non-crosslinked vinyl polymer and whose number average molecular weight (Mn) as measured by GPC (gel permeation chromatography) has two maximum values in adjacent regions. It has been found that excellent storage stability, offset resistance and fixing properties can be obtained.

That is, the present invention provides an electrophotographic developer containing a fixing medium and a colorant as main components, wherein the fixing medium is a polymer synthesized from a vinyl polymer, and the GPC (gel The number average molecular weight measured by permeation chromatography has maximum values in the low molecular weight range of 4 x 103 to 7 XIO" and the high molecular weight range of 2 x 105 to 5 x 10', and It is characterized in that the ratio is 65 to 85% by weight of the entire polymer.

The present invention will be explained in detail below.

The fixing medium used in the developer of the present invention is mainly composed of a polymer synthesized from vinyl monomers, and its molecular weight distribution measured by GPC (gel permeation chromatography) is As shown in Figure 1, the low molecular weight range of 4 x 103 to 7 x 103 and the 2 x
One of its characteristics is that it has a two-peak distribution with maximum values in the polymer region of 105 to 5XIO3. That is, if the maximum value of the low molecular weight region is less than 4XIO'', not only will the storage stability of the developer itself deteriorate, but also offset of fixing will easily occur, and the doctor blade, photoreceptor, blade, etc. in the developing device will be affected. If the maximum value of the high molecular weight region exceeds 5 x 105, the continuous change in thermal properties with the medium of the low molecular weight region will be inhibited, resulting in storage stability. Furthermore, if the two maximum values deviate from the above-mentioned range and approach each other, not only will sufficient fixing performance not be obtained, but offset will likely occur.

According to the present invention, it is also important that the low molecular weight region of the double peak distribution accounts for 65 to 85% by weight of the entire polymer. If the ratio of the low molecular weight region is less than 65% by weight, the fixing properties will deteriorate, and if it exceeds 85% by weight, the continuity of thermal properties with the high molecular weight region will be unbalanced and the storage stability will be extremely poor.

These characteristics are due to the resin medium having a maximum value in the region of 4 × 103 to 7 × 103, and the resin medium having a maximum value in the region of 2 × 103 to 5 × 10
It cannot be obtained simply by a mixture with a resin medium having a maximum value in the region of 5, but it needs to be a single polymer mixed and reacted in a molecular state. Therefore, in producing the polymer in the present invention, polymerization is carried out by a known polymerization method such as a bulk polymerization method, a solution polymerization method, or a suspension method. Among these polymerization methods, suspension polymerization is preferred from the viewpoint of polymerization stability and reduction in manufacturing costs. Specifically, a low molecular weight polymer and a high molecular weight polymer, which have been prepolymerized using a vinyl monomer, are dissolved in a solvent and reacted intermolecularly to form a chemically and physically intimate bond. Since this reaction is a polymer reaction called a graft reaction, the polymer as a polymer component and a polymer as a low molecular component show continuous changes in thermal properties as a whole, resulting in excellent storage stability, offset resistance, and fixing properties. etc. can be obtained. In addition, during the polymerization, a molecular weight regulator, a chain transfer agent, etc. may be added as necessary.

Vinyl monomers used in the present invention include vinyl aromatic compounds such as styrene, α-methylstyrene, P-chlorostyrene, and vinyltoluene, or substituted products thereof, acrylic acid, methyl acrylate, ethyl acrylate, and acrylic acid. Butyl acrylate, octyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, α-chloromethyl methacrylate, acrylonitrile, methacrylonitrile, monocarboxylic acids such as acrylamide, maleic acid, etc. acids, dicarboxylic acids or substituted products thereof such as butyl maleate, methyl maleate, dimethyl maleate, vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, vinyl ketones such as vinyl methyl ketone,
Vinyl ethers such as vinyl methyl ether and vinyl ethyl ether can be used alone or in combination of two or more.

According to the present invention, the above-mentioned polymer made of vinyl monomer is contained in the fixing medium in a proportion of 50''A or more, and other resins such as polyester resin, polyamide resin, epoxy resin, terpene resin, etc. It can be used in combination with resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc.

It is also possible to add various waxes such as low molecular weight olefin resins such as low molecular weight polypropylene and low molecular weight polyethylene, paraffin wax and carnauba wax as anti-offset agents in a proportion of 2 to 20% by weight based on the entire medium. At this time, these anti-offset agents can be simply kneaded with the above-mentioned resins, but they can also be made to coexist during polymerization of the fixing medium.

As colorants, seven types of pigments and dyes including carbon blank can be used, and in -component type developers, magnetic substances such as magnetite and ferrite can be used at a ratio of 20 to 60% by weight based on the total amount of the developer. It can also be blended.

Furthermore, if desired, in addition to the quaternary ammonium compound, charge control agents such as azo complex salts, nigrosine, nigrosine base, basic dyes such as crystal violet, etc. can be used.

The above-mentioned fixing medium, colorant, and charge control agent are weighed and mixed in a predetermined proportion, then kneaded by a known kneading means such as a three-roll or twin-screw press, and then pulverized and classified to obtain an average particle size. The developer becomes 5 to 15 μm.

The obtained developer can be improved in fluidity,
In addition to dry silica, wet silica, dry alumina, and titania, surface treatments using silicone oil, silicone oil modified with amino groups, mercapto groups, etc., and aminosilane coupling agents are used to control electrical charges. The surface can also be treated with an agent. In addition, these surface treatment agents have a BET specific surface area of 50 to 400 m
It is preferable to use 27 g of fine powder, and the amount added is preferably 1 to 5 parts by weight per 100 parts by weight of the developer.

The invention will now be explained with the following examples.

Example A styrene-〇-butyl acrylate copolymer having the molecular weight distribution shown in Table 1 was prepared by a suspension polymerization method, and 50% by weight of each resin, 45% by weight of magnetite, 4% by weight of low molecular weight polypropylene, and an electric charge. After mixing the control agent at a ratio of 1% by weight, it was kneaded in a twin-screw extruder, and then crushed and classified to obtain an average particle size of 1.
A developer with a thickness of 1 μm was obtained.

100 parts by weight of this developer was treated with 1 part by weight of hydrophobic silica, and then placed in a developing device of Kyocera's Compact Laser F-1010 to perform reversal development. The drum was made of 5e-As, the fixing temperature was set at 195° C., and the copying test was conducted at a speed of 10 sheets/min.

The resulting images were examined for fixation rate, anchor effect, and offset property, and also evaluated for image quality.

The fixing rate was calculated by re-measuring the density of the pattern by reciprocating the pattern 10 times in the vertical direction using a cylindrical weight (diameter 50 mm) with a 1 kg load attached to a cotton cloth.

The anchor effect was examined by pasting an adhesive tape on a 20 x 100 mm 25x dot density area and then peeling it off to examine the degree of adhesion of the I-ner to the paper. Additionally, 50% of each developer
The condition G (fluidity, blocking property) after being left in an atmosphere at ℃ for 100 hours was examined to evaluate the storage stability.

Furthermore, the proportion of the low molecular weight region in the fixing medium was determined from the area ratio of the low molecular weight region bordering on the minimum value in the peak distribution in the molecular weight distribution map.

In addition, the characteristic evaluation in the table is as follows.

Fixation rate ◎: 95% or more 0190-95% △; 80-90% ×; 80% or less Anchor effect ◎: Hardly peels off ○: Slightly peels △: Severely peels ×: Preservability with all peeling ◎: Not at all No change ○: Soft caking △: Weak blocking occurred ×; Offset property with severe aggregation and bulging
○: Does not occur at all △: Occurs slightly ×: Image quality with severe offset and dirt on the fixing roller ◎: High density and no fog ○:
Slight staining △: Severe bleeding ×: Smearing and fogging [margins below] = 11- As is clear from Table 1, there are 4 peaks in the low molecular weight range XI
If it is lower than O3 (Ihl), the fixing property is good, but the storage stability, offset property, and image quality are poor.

On the other hand, when it exceeded 7 XIO' (lk6), the fixing performance deteriorated. On the other hand, when the peak in the high molecular region is less than 2XIO3 (II & 17), storage stability, offset resistance, and image quality deteriorate, and when it exceeds 7XIO' (11k18)
, fixability, storage stability, and offset resistance are all insufficient.

Even if the peaks of the low molecular weight range and high molecular weight range are within the ranges specified in the present invention, when the low molecular weight range is small (1hIO), both properties are insufficient, and conversely, when the low molecular weight range is large (Null), the fixing properties are not good. However, storage stability and offset image quality are poor.

When two types of resins with different number average molecular weights are mixed (
N[L9] The fixing property was good, but the storage stability was poor.

In contrast to these comparative examples, samples Nos. 2 to 5 of the present invention were all excellent in fixing properties, and were also excellent in storage stability, offset property, and image quality.

〔Effect of the invention〕

As detailed above, the electrophotographic developer of the present invention has thermal properties because the fixing medium is mainly composed of a single polymer having a number average molecular weight distribution in a specific low molecular weight region and a specific high molecular weight region. is continuous from the low molecular weight region to the high molecular weight region, thereby providing stable fixing properties, anti-offset properties, and storage stability regardless of copying speed and fixing temperature. Also,
The ability to respond to a wide range of fixing temperatures makes it possible to downsize the fixing device. Furthermore, since it has excellent fixing properties, especially adhesion, it has the advantage that excellent fixing properties can be obtained regardless of the thickness and surface roughness of the copy paper.

[Brief explanation of the drawing]

Figure 1 shows the GP of the fixing medium used in the developer of the present invention.
This is an example of a molecular weight distribution diagram obtained by method C.

Claims (1)

[Claims] In an electrophotographic developer whose main components are a fixing medium and a colorant, the fixing medium contains a polymer synthesized from vinyl monomers, and the polymer is subjected to GPC (gel permeation chromatography). The number average molecular weight measured by An electrophotographic developer characterized in that the proportion of the low molecular weight region is 65 to 85% by weight of the entire polymer.