JPS6246856B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Technical Field The present invention relates to a magnetic brush developer for laser printers that employs electrophotography. (2) Background of the Invention The magnetic brush development method has conventionally been applied to copying machines, facsimile machines, electronic printers, etc. Particularly, the features of this method include: (1) being a dry system, (2) not being selective about paper quality in principle, and (3) being capable of high-speed printing. These features are:
It has become even more important in laser printers. As output information from computers becomes more diverse, printers must be able to respond to these diversifications, and in particular, it has been desired to output in kanji in addition to the conventional alphanumeric characters. In response to this need, laser printers have appeared, but since laser printers print using laser light, and the spot diameter of the laser light is approximately 100 to 150 μm, it is difficult to print characters such as kanji. It can be said to be optimal for printing with image properties. (3) Prior Art and Problems As described above, laser printers have many excellent functions, but in order to fully utilize these functions, the performance of the developer must be high. That is, depending on the performance of the developer, the characteristics of the laser printer cannot be fully demonstrated. What kind of performance is required of a developer used in a laser printer? In other words, the objective is to exhibit stable printing performance over a long period of time. A magnetic brush developer is a mixture of iron powder or other ferromagnetic particles and colored resin powder. That is, contact triboelectric charging during mixing causes the toner to electrostatically adhere to the surface of the carrier. The developer is carried to the latent image area by the formation of a magnetic brush, and development is performed by adhering only the toner to the latent image (FIG. 1). As shown in FIG. 1, the developer is stirred in the developing machine, and a mechanical shock is applied to the developer due to this stirring. For this reason, the resin-based toner is fused to the carrier surface. The generation of fused toner (hereinafter referred to as spent toner) makes the carrier surface homogeneous with the toner, and contact triboelectric charging is greatly inhibited. The generation of spent toner stops the function of the developer, and in actual developers, it is necessary to make the carrier and toner difficult to stick to each other. In the development process using a developing machine, charged toner is constantly moving to the latent image, and it is necessary to replenish the developer with a corresponding amount of uncharged toner (FIG. 1). As a result, the counter charge of the toner always remains in the carrier, and as the charge approaches the saturation value, the ability to impart a charge to the toner, that is, the charging property, decreases. However, in order to prevent a decrease in chargeability due to charge up, it is necessary to lower the resistance of the carrier and developer. However, there is a relationship between the chargeability of the developer and the resistivity of the carrier as shown in FIG. 2, and lowering the resistance more than necessary is undesirable because it causes a decrease in the chargeability. On the other hand, the resistivity of the developer plays a very large role in printing. When the latent image toner adheres, there is a development that makes it difficult for the toner to adhere to the central part of the latent image where the density of electric lines of force is low. As a result, when printing a surface image with a certain area, toner adheres only to the peripheral area,
A printing defect occurs in which the center part becomes white. As a method for eliminating such inconveniences, there is a method of controlling printing by applying a bias electric field. A bias electric field is an electrostatic field that is applied between a magnetic brush and a latent image, and this electric field separates toner from the carrier and allows the toner to be transported and adhered to areas with low electric flux density. can. Therefore, by appropriately setting the bias electric field, it becomes possible to control the print density, thicken or thin the print, and further control the area printing. However, the developer
In particular, if the electrical resistivity of the carrier is high, the voltage drop at the magnetic brush portion will be large, and no effective electric field will act between the magnetic brush tip and the latent image surface (the third
figure). Therefore, the resistivity of the carrier must be low to some extent. However, if the resistance of the carrier is too low, the carrier becomes conductive, which not only dissipates the charge of the latent image and causes toner to adhere to it, but also causes the carrier to become conductive.
As shown in FIG. 3, a discharge occurs due to the bias electric field, causing damage to the latent image medium. Furthermore, if a bias electric field is not applied, problems such as severe fogging may occur due to the self-bias caused by the developing current that occurs when the toner moves to the latent image.
It is thought that there is an optimum range for the resistivity of the carrier, together with the chargeability of the developer. In a developer composed of carrier and toner, a factor that influences printing characteristics is the amount of charge per unit weight of toner (hereinafter referred to as tp). It is not preferable that tp is too low or too high, and 10 to 20 μC/g is appropriate. There are several factors that affect the tp value of a developer, but the surface condition of the carrier is considered to be particularly important. The degree of curing of the polytadiene in the coating layer greatly influences the tp value. Therefore, when the amount of curing agent is small, that is, when the degree of curing is low, tp is not stable and decreases as printing progresses. Furthermore, as the amount increases, the coating layer hardens and shrinks rapidly, causing cracks and preventing the formation of a strong coating layer. There is an optimum amount of curing agent to be mixed. The surface of the carrier is made non-adhesive by forming a Teflon film on its surface. However, Teflon film has high electrical resistivity, the coating layer is brittle, and the quenching temperature is high (300℃).
above) and other inconveniences. Generally, dispersing carbon is considered to reduce the resistance of the coating layer, but it is difficult to uniformly disperse carbon in the coating resin, and carbon particles are removed from the coating layer while stirring the developer. It will come off. Toner is mainly composed of colored resin powder, and is triboelectrically charged when it comes into contact with a carrier.The toner is then carried by the carrier to the latent image area, developed, and then transferred to paper and fixed. The printing process ends. Here, fixing is a process in which the image transferred to the paper is a powder image, and this is brought into close contact with the paper. Fixing methods include 1 oven fixing, 2 pressure fixing, 3 heat pressure fixing, 4 flash fixing, and 5 solvent fixing, but 1 to 4 can be said to be the main ones. These fuse toner to paper using heat, pressure, or the like. Therefore, if fixing is attempted with less energy, a resin with a low melting point will be used as the base material, which will cause the following problems. On the other hand, in order to avoid this problem, there is a tendency to raise the melting point of the resin, which causes poor fixing. The above-mentioned problems are as follows.
The toner fusing to the first carrier and the toner fusing to the second photoconductor drum both significantly reduce the printing function and sometimes cause the printing function to be lost. Since the developer is stirred in the developing machine, a mechanical impact force is applied between the toner and the carrier.
Therefore, the resin-based toner is softened by this impact and fused to the carrier surface. As a result, an effect similar to that obtained by coating the carrier surface with toner is obtained, and the toner cannot be sufficiently charged. For this reason, as mentioned above, the carrier surface is coated with a resin that is non-adhesive to the toner, but in order to further prevent adhesion, it is necessary to make the toner itself difficult to adhere to. . A similar amount of toner remains on the photoconductor drum even after the transfer to paper is completed. This residual toner will interfere with the next printing process, so it is removed by a fur brush. At this time, the toner particles are struck onto the photocon surface by the fibers forming the brush and are fused to the photocon surface. The fusion of toner onto the photocon surface not only reduces the photosensitivity of the photocon, but also causes afterimages on prints. To overcome such disadvantages, it is necessary to make the toner particles non-adhesive, and this is especially effective when it is difficult to make the surface itself non-adhesive, such as the surface of a photocon. Therefore, in order to prevent the toner from adhering to the carrier and photocon, it is necessary to prevent the toner from adhesion without increasing the melting point. (4) Purpose of the Invention The purpose of the present invention is to have excellent mechanical strength, low heat treatment temperature, excellent non-adhesiveness to toner,
Another object of the present invention is to provide a magnetic brush developer for a laser printer, which comprises a carrier having a coating layer having a relatively low electrical resistivity, and a toner having excellent non-adhesion to the carrier and photoconductor drum. (5) Structure of the Invention The above-mentioned object of the present invention is to form a polymer chain containing 50% or more of 1,2-polybutadiene units having side chain double bonds in which Fe ₃ O ₄ powder is dispersed and having a number average molecular weight of 10,000 to 10,000.
200,000, or a polymer made by adding dicumyl peroxide to a 1,4-cis polybutadiene cyclized product, coats the base iron powder, and heat-treats the carrier to harden the resistivity. This can be achieved by a magnetic brush developer for laser printers, which is characterized in that it contains carrier particles of 10 ⁵ to ^{10 7} Ωcm. Fe ₃ O ₄ powder is easily dispersed in the coating resin varnish, exhibits conductivity close to that of a conductor, and is also a charge control agent. Therefore, by dispersing Fe ₃ O ₄ powder in a coating resin and coating it, it is possible to achieve both low resistance and non-tackiness of the carrier. Furthermore, in order to lower the resistance of the carrier, the resistivity of the base iron powder is also involved, and if the base material itself has a high resistance, it cannot be expected to significantly lower the resistance through coating treatment.
Figure 4 shows the same coating (coating thickness 1.0 μm) using various iron powders with different resistivities as base materials.
Volume ratio of m-butadiene polymer/Fe ₃ O ₄ = 1:1)
This shows the resistivity of the carrier when subjected to Next, when coating iron powder with a resistivity of 10 ³ Ωcm or less, the volume ratio of butadiene polymer/Fe ₃ O ₄ is R _v , and the change in resistivity with respect to this is shown in Figure 5A. show. This result R
The resistivity is almost constant when _v ≦2, but when R _v >2
is rapidly increasing. From this, it is preferable that R _v ≦2 from the viewpoint of manufacturability and stability, that is, less variation in resistivity. The charge imparting ability K of the carrier to the toner is 10 when R _v ≦2, as shown in Figure 5B.
It is almost stable at ~20 μC/g, but increases rapidly when R _v >2. The relationship with these volume ratios shows the same tendency both when the particle size of the iron powder is 80 μm (a) and when it is 140 μm (b). As shown in FIG. 5A, the electrical resistivity of the carrier of the present invention is 10 ⁵ to 10 ⁷
It is Ωcm. When the volume ratio of butadiene polymer/Fe ₃ O ₄ is expressed, it is preferably 1/8 to 2/1, more preferably 1/4 to 1/1. When this ratio is less than 1/8, /
The amount of binder resin relative to Fe ₃ O ₄ is small, the coating layer is brittle, and the /Fe ₃ O ₄ particles come off from the coating layer during printing. On the other hand, if it is larger than 2/1, the electrical resistivity of the carrier increases as described above, making it impossible to achieve our objective. The butadiene polymer coating the carrier iron powder is a polymer containing 50% or more of 1,2-polybutadiene units having side chain double bonds in the polymer chain and having a number average molecular weight of 10,000 to 200,000, or 1,4
- A cyclized product of cis polybutadiene, or a cyclized product of a copolymer of styrene or acrylonitrile containing 50% or more of 1,4-cis polybutadiene,
A resin obtained by adding dicumyl peroxide to this polymer, coating it, and curing the polymer by heat treatment is used. If the content of 1,2-polybutadiene units having side chain double bonds is less than 50%, the non-adhesive properties of 1,2-polybutadiene will be lost. When the number average molecular weight of polbutadiene is less than 10,000, the resin before curing is semisolid or liquid, so carriers tend to associate with each other when forming a coating layer. If it is larger than 200,000, it becomes difficult to dissolve in the solvent, and the resin solution concentration for performing the desired coating cannot be obtained. A cyclized copolymer of styrene or acrylonitrile containing 1,4-cis polybutadiene is 1.4
- Contains less than 50% cis-polybutadiene,
The inherent non-stick property of 1,4-cis polybutadiene is lost. The carrier iron powder preferably has an average particle size of 50 to 500 μm. If the particle size is smaller than 50 μm, the carrier will adhere to the latent image along with the toner, resulting in a decline in print quality.If the particle size is larger than 500 μm, fine patterns, such as kanji characters that require high resolution, will Sufficient printing becomes impossible. Disperse in resin of carrier coating layer/
The average particle size _{of Fe3O4} powder is 0.1~1.0μm, furthermore 0.1~
0.5 μm is preferred. When the average particle size is smaller than 1.0 μm, the particles tend to aggregate more strongly, making it difficult to uniformly disperse them in the coating layer. If the diameter is larger than 1.0 μm, the Fe ₃ O ₄ particles will stick out from the coating layer, and the carrier particles will collide with each other.
Fe ₃ O ₄ particles may come off. The thickness of the carrier coating layer is 0.1~10.0μ
m, more preferably 0.5 to 1.5 μm. If it is smaller than 0.1 μm, it becomes difficult to uniformly disperse the Fe ₃ O ₄ particles and the adhesion effect becomes weaker. If it is larger than 10.0 μm, the electrical resistance of the coating layer increases and the original purpose cannot be achieved. The amount of dicumyl peroxide added to the carrier coating polymer is based on 100 parts by weight of the polymer.
0.1 to 10 parts by weight, more preferably 1 to 5 parts by weight. If it is less than 0.1 part by weight, the coating layer will be insufficiently cured and will not exhibit sufficient charge imparting properties. If it is more than 10% by weight, the ability to impart charge to the toner becomes excessive, making it necessary to print with a high toner concentration, resulting in a decrease in printing quality. If the mixing ratio of toner particles to carrier is less than 1% by weight, sufficient print density cannot be obtained, and if it is more than 6% by weight, toner particles cannot come into contact with the surface of the carrier, resulting in the generation of uncharged toner. This results in a decrease in print quality. The binder resin of the toner has a melting point of 60 to 160°C, an epoxy equivalent of about 450 to about 5,500, a weight average molecular weight of about 900 to about 8,250, and a content of bisphenol A glycidyl ether with a degree of polymerization of 4% by weight or less. Certain bisphenol/epichlorohydrin type epoxy resins are preferred. If the melting point of the binder resin is lower than 60°C, it is undesirable because it tends to cause blocking when used as a toner. If the temperature is higher than 160°C, the fixing property to paper will be poor. When the epoxy equivalent is less than 450, the melting point is 60℃
As it becomes lower, blocking becomes more likely to occur as described above. Also, if it is larger than 5500, the melting point is 160
If it becomes higher than ℃, it will cause poor fixing performance. When the weight average molecular weight is less than 900, the melting point is 60
It will be lower than ℃. Moreover, when it is larger than 8250, the melting point becomes higher than 160°C. The content of montan acid wax, which is an adhesion inhibitor for toner particles, does not have to be included, but if it is more than 1% by weight,
This is not preferable because it causes the following drawbacks. If the amount of wax added is small, the anti-stick effect will be poor, and if the amount added is large, the wax will seep out and adhere to the developer and photoconductor drum. In toners based on epoxy resin, 1 to 5% by weight will cause filming on the drum, and if it exceeds 5% by weight,
Due to the oozing effect, the contrast decreases due to wax adhesion and fogging in the back shadow area becomes noticeable. It has been found that the fusion to the photoconductor drum and carrier surface depends on the proportion of bisphenol A glycidyl ether with a degree of polymerization of 0 contained in the base resin rather than on the molecular weight of the epoxy base material. In particular, when the proportion of bisphenol A glycidyl ether with a degree of polymerization of 0 exceeds 4% by weight, fusion is remarkable. Therefore, it has been found that the original objective can be achieved by adjusting the mixing ratio of bisphenol A glycidyl ether having a degree of polymerization of 0 to 4% by weight or less, and by adjusting the amount of Montan acid wax added to 0 to 1% by weight. If the carbon content of the toner is less than 0.6% by weight, sufficient print density cannot be obtained in printing.
On the other hand, if it exceeds 8% by weight, the softening point and melting degree will increase and the fixing properties will deteriorate. Toner does not need to contain dye, but 5% by weight
If it exceeds this, the charging property will decrease. The adhesive resin content of the toner is the amount remaining after subtracting the above carbon, dye, and fusing inhibitor from the toner weight. Note that the average particle size of the toner is preferably 5 to 30 μm, more preferably 5 to 25 μm. If it is smaller than 5 μm, the fine toner particles have a specific charge (amount of charge per unit weight).
If the diameter is larger than 25 μm, the specific charge becomes small and the amount of charge is insufficient, making it impossible to obtain sufficient print quality. (6) Examples and Comparative Examples [Example 1] TS-200R (manufactured by Nippon Steel Powder, average particle size) was used as the base iron powder.
80μm), 1,2-polybutadiene RB-810 (manufactured by Japan Synthetic Rubber), Fe ₃ O ₄ powder for coating resin
EPT-500 (manufactured by Toda Kogyo, average particle size 1 μm) was used. First, 25g of polybutadiene, 100g of Fe ₃ O ₄ powder
g, Trichlene 1 Furthermore, 0.25 g of dicumyl peroxide and 50 pieces of 15 mmφ iron powder were placed in a polyethylene wide-mouth bottle, and rotated for about 1 hour (150 rpm) on a ball mill stand to dissolve Fe ₃ O ₄ in the polybutadiene varnish.
was dispersed. Next, after the stirring was completed, 5 kg of base iron powder was added to the wide-mouthed bottle, and while rotating and stirring (100 rpm), the trichlene vapor generated inside the container was removed by a pump. When this process was continued for about 5 hours, most of the predetermined trichlene was removed, and a uniform coating layer of about 1 μm was formed on the surface of the iron powder particles. Next, the coated carrier was placed in a rotary furnace and heat treated at 180°C for 2 hours. After the heat treatment was completed, it was classified using a #100 sieve, and those that passed through the sieve were collected as good products. Next, the epoxy equivalent is 950 and the weight average molecular weight is 1400.
and 92.5 parts by weight of a bisphenol A/epichlorohydrin type epoxy resin having a melting point of 100°C and containing about 3.0% by weight of bisphenol A glycidyl ether with a degree of polymerization, 3 parts by weight of carbon black, 5 parts by weight of nigrosine-based dye, and montanic acid. 0.5 part by weight of ester wax was kneaded in a kneader heated to 100°C. Next, the kneaded product was pulverized using a jet pulverizer, and then classified using an air classifier to obtain a toner. Developer A having a toner concentration of 3% by weight was prepared using this toner and the coated carrier described above, and a printing test was conducted using an F-6700D laser printer under the test conditions shown in Table 1.

[Comparative example 1]

The toner and carrier configurations were almost the same as in Example 1. However, /Fe ₃ O ₄ powder was not used for the carrier, and 1,2-polybutadiene was used for the coating. In this case, when a similar experiment was conducted with a toner concentration of 4% by weight, the charge imparting ability began to decline after 20,000 sheets were exceeded. Further, in this case, the resistance of the carrier was 10 ¹¹ Ωcm or more, and printing control by bias was impossible.
(Effect of Fe ₃ O ₄ ) [Comparative Example 2] The carrier was the same as in Example 1, the toner was the same as in Example 1 except for the montan acid wax, and bisphenol with a degree of polymerization of 0 was used as the base resin. It was replaced with one containing 4 parts by weight or more of Acricidyl ether. Filming began to occur on the drum when the number of sheets exceeded 4,000, and when the number of sheets exceeded 10,000, the toner fused onto the drum began to be transferred to the paper. (Effects of wax and base resin) [Comparative Example 3] Both the toner and carrier were the same as in Example 1, but when dicumyl peroxide was added in an amount of 0.1 to 0.5% by weight based on the coating resin, charge imparting ability was achieved for 50,000 sheets or more. Furthermore, at 5 to 10% by weight, the charge imparting ability becomes too high, and in order to perform optimal printing, the toner concentration needs to be 5 to 6% by weight.
This increases the resistivity of the developer, making bias control impossible. [Example 2] Cyclization 1 with a cyclization rate of 60% as a coating resin,
All composition ratios were the same as in Example 1 except that 4-cis polybutadiene (CLBR, manufactured by Nihon Gosei Rubber) was used. As a result of the printing test, the printing quality, printing stability, toner adhesion to the carrier, etc. were all the same as in Example 1. [Example 3] The carrier and toner configuration were almost the same as those described in Example 1, but the iron powder was changed from TS-200R to ST-
200 (manufactured by Kanto Denka, average particle size 140 μm) and the amount used was 10.0 kg, but the same as Example 1 was used. When a printing test was carried out using a developer composed of these toners and carriers, properties equivalent to those of Example 1 were obtained in terms of printing quality, charge imparting ability of the carrier, and fusion of the toner to the drum. However, although the toner fusion of the carrier was as low as 0.15% even after 200,000 sheets, the resistance value of the carrier was as high as 10 ⁸ Ωcm, making it impossible to control printing by bias as effectively as in Example 1. (7) Effects of the Invention According to the present invention, it is possible to reduce the adhesion of toner to the carrier and the photoconductor drum, and the charging characteristics are stabilized over a long period of time due to the effect of lowering the resistance of the carrier. It is possible to obtain a developer having excellent printing properties.

[Brief explanation of the drawing]

Fig. 1A is an explanatory diagram showing the operation of a laser printer, Fig. 1B is an explanatory diagram of a magnetic brush developer, and Fig. 2 is a graph showing the relationship between the carrier's ability to impart charge to toner and resistivity. and the third A
The figure is an explanatory diagram of a developing brush to which a bias electric field is applied, Figure 3B is an explanatory diagram of the developing process for screen printing, and Figure 4 is the relationship between the resistivity of the carrier and the resistivity of the carrier base iron powder. FIG. 5A is a graph showing the relationship between the volume ratio of butadiene polymer/Fe ₃ O ₄ powder and the resistivity of the carrier,
Figure 5B is a graph showing the relationship between the volume ratio of butadiene polymer/Fe ₃ O ₄ powder and the ability of the carrier to impart a charge to the toner, and Figure 6 is a graph showing the relationship between the number of prints, the amount of fused toner (F), and the amount of fused toner (F). It is a graph showing the relationship with charge imparting ability (K). 1...Developer, 2...Carrier, 3...Toner, 4...
Photocon drum, 5... Charger, 6... Laser light, 7... Latent image area, 8... Developing area, 9... Developing machine,
10... paper, 11... fur brush, 12... fixing device,
a... Carrier (average particle size 80 μm), b... Carrier (average particle size 140 μm), F... Amount of fused toner, K... Charge imparting ability.

Claims (1)

[Claims] 1. The ratio of polymer: Fe ₃ O ₄ is 1:8 to 2:1.
1 with side chain double bonds dispersed with Fe ₃ O ₄ powder,
A polymer having a number average molecular weight of 10,000 to 200,000 and containing 50% or more of 2-polybutadiene units in the polymer chain, or 1,4 having a number average molecular weight of 10,000 to 200,000.
- Contains a carrier with a resistivity of 10 ⁵ to 10 ⁷ Ωcm, which is a mixture of cis-polybutadiene cyclized product and dicumyl peroxide, coated on iron powder as a base material, and heat-treated to harden the polymer. A magnetic brush developer for laser printers featuring: 2 The average particle size of the iron powder of the carrier base material is 50 to 500μ
The developer according to claim 1, which is m. 3. The developer according to any one of claims 1 to 2, wherein the resistivity of the iron powder of the carrier base material is 10 ³ Ωcm or less. 4 Disperse in carrier coating polymer
The developer according to any one of claims 1 to 3, wherein the Fe ₃ O ₄ powder has an average particle size of 0.1 to 1.0 μm. 5 The thickness of the carrier coating layer is 0.1 to 10μ
The developer according to any one of claims 1 to 4, which is m. 6. The developer according to claim 1, wherein the dicumyl peroxide added to the carrier coating polymer is 0.1 to 10 parts by weight per 100 parts by weight of the polymer.