JPS6327708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to electrophotographic toners, and more particularly to improved electrophotographic toners and methods of making the same.

Conventionally, as an electrophotographic method, U.S. Patent No.
Various methods are described in Japanese Patent Publication No. 2297691, Japanese Patent Publication No. 42-23910, Japanese Patent Publication No. 43-24748, etc., but in general, photoconductive substances are used to coat photoreceptors by various means. An electrical latent image is formed on the paper, then the latent image is developed using toner, and if necessary, the powder image is transferred to paper, etc., and then fixed by heating or solvent vapor, etc., to obtain a copy. be.

Examples of methods for visualizing electrical latent images using toner include the magnetic brush method described in U.S. Pat. No. 2,874,063, the cascade development method described in U.S. Pat. No. 2,618,552, and the
The powder cloud method described in No. 2221776 is known. Needless to say, fixing the toner image is an important step in any of these developing methods.

Especially when considering application to high-speed copying machines, since a heat roll fixing device is used, the toner image and the heat roll come into contact in a heated and molten state during fixing, so a part of the toner image adheres to the heat roll surface and is transferred. It is required that so-called offset does not occur.

Obtaining toner that does not cause such offset becomes more difficult when considering application to so-called labor-saving high-speed copying machines, which do not use a lot of power in the fuser and use heat rolls. encounter problems.

In other words, in order to prevent offset from occurring, the binder polymer used in toners is required to be as strong as possible, but on the other hand, in order to give the high molecular weight polymers used for this purpose sufficient melt fluidity, they must be heated to considerably high temperatures. The toner must be heated, which does not meet the requirement of saving labor. In other words, in order to save labor,
It is required to fix at a low temperature, and in order to meet this requirement and flow well even at a low temperature, it is preferable to use a resin that not only has a low glass transition point but also has a molecular weight as low as possible. However, resins with low molecular weight naturally lack toughness and are therefore prone to offset.

Conventionally, toner toughening to prevent offset has been carried out by using a high molecular weight polymer with an average molecular weight of about 100,000 or more, and such high molecular weight polymers are usually made from vinyl-based polymers by conventional radical polymerization methods. There is no need to use a vinyl polymer because it can be easily obtained. In order to fix toners using these high molecular weight vinyl polymers at low temperatures, methods include lowering the glass transition point of the polymer as low as possible without causing blocking, or lowering the fixing temperature by adding a plasticizer. There is.

However, these methods not only lower the fusing point (the lowest temperature at which complete fusing occurs), but also lower the hot offset temperature (the temperature at which offset begins to occur), and therefore the temperature between the fusing point and the hot offset temperature decreases. The result is that the temperature range, the so-called fusing temperature, is simply shifted to the lower side.

This causes new problems such as frequent occurrence of offsets and streaks due to the instability of the toner at high temperatures, thereby negating the advantage of lower fixing temperatures. If you lower the glass transition point of the polymer or add a plasticizer in anticipation of a decrease in the hot offset temperature, if you compensate for the decrease in fixing temperature by increasing the weight average molecular weight, it will certainly work. Although it is possible to prevent the hot offset temperature from decreasing, the increase in viscosity due to the increase in molecular weight lowers the glass transition point and reduces the effect of adding a plasticizer, making it impossible to lower the fixing temperature sufficiently.

On the other hand, condensation resins such as polyester resins and epoxy resins have a low glass transition point, unlike vinyl polymers, and low molecular weight resins can be easily obtained. This means that low temperature fixing toners can be easily obtained using these resins.

However, since these resins are low molecular weight resins, offset is severe and they cannot be used as toners for heat rolls. Surprisingly, even if these polyester and epoxy resins are made to have a high molecular weight, the molecules do not have flexibility, so the elastic properties during melting required for offset resistance cannot be obtained, which is even more undesirable. In addition, only the toughness in the solid state increases, and the pulverization process of melt-mixing with the colorant and pulverizing it to form a toner becomes extremely difficult. Heat roll toners using polyester or epoxy resins have not been used in the past because of the difficult problems described above.

On the other hand, when considering the case where toner is mixed with a carrier and used as a developer, whether it is a cascade method or a magnetic brush method, only the toner is separated from the developer mixture and directly participates in development. However, in this case, the efficiency of developing the electrostatic latent image on the drum and the efficiency of transferring it to paper etc. are extremely important issues regarding toner. In order to improve these development efficiency and transfer efficiency, attempts are often made to add a charge controller as an additive, but in this case, if the charge controller is not uniformly dispersed in the toner, the desired effect cannot be obtained. Or, the toner quality becomes unstable.

In the case of polyester or epoxy resins that can easily incorporate a functional group that acts as a charge controller into the molecular structure of the resin, the dispersibility of the charge controller, such as when the above-mentioned charge controller is physically mixed from the outside, is You don't have to worry about problems like this.

These properties are the reason why many toners using polyester and epoxy resins exhibit excellent development characteristics. Of course, it is possible to achieve the same excellent development properties as using polyester resin or epoxy resin by introducing a functional group with a charge controller effect into the side chain of vinyl polymer, but styrene These polymers have the disadvantage that they maintain a lower glass transition point than polyester resins and epoxy resins, and it is difficult to reduce their molecular weight.

Therefore, it is extremely difficult to obtain toner materials with a low melting point comparable to polyester resins and epoxy resins. Without impairing the excellent low-temperature fixing and developing properties of polyester resins and epoxy resins,
The above description should have amply clarified that there is a need for a toner that does not cause offset up to a temperature comparable to that of toners using large molecular weight vinyl polymers in heat roll fixing.

Also, if a low melting point material comparable to polyester resins and epoxy resins can be obtained using vinyl polymers with functional groups that act as charge controllers,
It has also become clear that there is a desire to obtain a toner for heat rolls without impairing its low-temperature fixability and development characteristics.

These toners are required to have an extremely low molecular weight, a low-temperature melting material with a low softening point, a highly fluid polyester resin, an epoxy resin, or a vinyl polymer with a functional group that acts as a charge controller, and a weight average molecular weight of several dozen. This is achieved by using the former as a major component in a blend of polymers with a large molecular weight of 10,000 or more.

Specifically, the molecular weight is 1000-4000 and the glass transition point is
Melt index at 40-60℃ and at 110℃ (load 2160gr, orifice inner diameter 2.0955±
0.0051mm, length 8.000±0.025mm) is 50~200gr/
10 min low melting temperature, highly fluid polyester resin, epoxy resin, or vinyl polymer with a functional group that acts as a charge controller, and a large molecular weight polymer with a glass transition point of 35 to 60°C and a weight average molecular weight of 500,000 or more. said low melting temperature;
50 to 95% by weight of highly fluid resin (depending on the toner contained, extremely low minimum fusing temperature of approximately 120 to 130°C in a fusing test using a 720 Xerox copier, and hot offset temperature) Toner with a temperature of about 200°C can be easily obtained.

However, these toners consist of a blend of materials that exhibit the extreme properties described above.
It has the disadvantage that its properties, particularly its rheological properties, vary significantly with a slight variation in the composition ratio.

In other words, even a slight increase in the amount of low molecular weight components greatly increases the likelihood of offset occurring.

On the other hand, if the amount of the high molecular weight component is even slightly too large, the minimum fixing temperature will suddenly increase, and the grinding speed will decrease when producing toner, which is a major drawback.

Therefore, the resin composition range that balances low melting point properties, offset resistance, and good manufacturability is extremely narrow, which has the undesirable result of requiring much tighter control than usual over toner manufacturing conditions. .

In addition to the difficulty of managing toner manufacturing conditions, as far as the balance of the above three types of characteristics is concerned,
It is inevitable that there is a limit to the toner properties that can be achieved. For example, even if the amount of low molecular weight components is increased to lower the minimum fixing temperature, the amount of low molecular weight components cannot be increased beyond a certain level in order to suppress the occurrence of offset, and the amount of high molecular weight components cannot be increased to obtain a sufficiently high offset temperature. Even if an attempt is made to increase the amount, there is a disadvantage in that the minimum fixing temperature increases, so there is a limit to increasing the amount of high molecular weight components.

Therefore, the object of the present invention is to combine the property of a toner made only of a vinyl polymer with a sufficiently high molecular weight with no offset even at high temperatures, and the use of a polyester resin, an epoxy resin, or an epoxy resin with a sufficiently low molecular weight and a low glass transition point, or a toner having a charge controller function. In order to obtain a toner that has both the excellent low-temperature fixing properties and development properties of a toner made only of vinyl polymers with functional groups, it is desirable to improve the offset resistance by adding a small amount of additive material, not more than a few percent. By making this possible, it is possible to achieve stability in manufacturing toners made of materials exhibiting the above-mentioned extreme properties, and to expand the degree of freedom in changing the composition to improve various toner properties. .

The above object is achieved by an electrophotographic toner characterized by containing 5% by weight or less of fibrous polytetrafluoroethylene inside toner particles consisting of a binder resin and a colorant, This electrophotographic toner contains a small amount of powdered polytetrafluoroethylene that can be fibrillated in an amount of 5% or less based on the toner weight during melt-kneading for toner production.
It is preferably produced by adding 0.01 to 1.0% and kneading the mixture in an intensive mixer to fiberize the polytetrafluoroethylene.

It is a well-known fact that fibrous fine powder polytetrafluoroethylene is used by dispersing it in toner particles. For example, its use is disclosed in Japanese Unexamined Patent Publication No. 52-23941. However, its purpose is to reduce the formation of toner films on the surface of the photoconductor, not to improve the rheological properties of the toner, as is the object of the present invention.

In addition, the method of fiberizing fine powder polytetrafluoroethylene disclosed herein involves mixing fine polytetrafluoroethylene powder with fine powder that has already been used as a toner, and forming polytetrafluoroethylene fine powder into fibers. The mixture is subjected to a treatment for

The present invention provides a method for fiberizing polytetrafluoroethylene in a melt-kneading process in which heat and shear force are applied, which must be passed through in order to uniformly mix a binder resin and a colorant in a toner manufacturing process. This method of making polytetrafluoroethylene into fibers is a novel and outstanding method that has not even been predicted in the past. That is, according to the method of the present invention, an appropriate amount of polytetrafluoroethylene fine powder is mixed with a binder resin and a colorant, and this mixture is melt-kneaded in an intensive mixer and then pulverized. When observing the dispersion of ethylene using a scanning electron microscope, it can be seen that the toner particles are trapped in the polytetrafluoroethylene fibers spread throughout the toner system.

The present invention is based on the extremely novel discovery that fiberization of polytetrafluoroethylene is carried out during the toner manufacturing process, and the present inventors have surprisingly found that polytetrafluoroethylene is fiberized by less than a few percent, usually less than 1%. The present invention has been completed by the discovery that by adding polytetrafluoroethylene, the hot offset temperature of the toner can be increased without affecting other properties.

The presence of fibrous polytetrafluoroethylene increases the hot-offset temperature of the toner because of the loose and extensive crosslinking or entangling of the entire toner system, which is required in the toner for offset resistance. This is thought to be because fiberized polytetrafluoroethylene satisfies this condition.

If the fibrous polytetrafluoroethylene is too tightly crosslinked or intertwined, its melt fluidity will deteriorate, which not only has a negative effect on fixing properties, but also hinders the development of the elastic properties necessary for offset resistance. It also inhibits.

It is also undesirable for the same reason as mentioned above to have entanglement or crosslinking in the toner system only locally.

According to the method of the present invention, the condition that the entire toner system is loosely and largely crosslinked or intertwined, which is necessary for the offset resistance of the toner, can be achieved by using a few percent or less of fibrous polytetrafluoroethylene. This is extremely important.

The fact that such a small amount of fiberized polytetrafluoroethylene improves the offset gradient and has no adverse effect on other toner properties is that the composition of the main binder polymer of the toner is mostly low-temperature fixing. , which means that it can be determined with manufacturability as the main focus, and therefore, the above-mentioned balance among low-temperature fixability, manufacturability, and offset resistance can be achieved relatively easily. In other words, sufficient low-temperature fixability and good manufacturability can be achieved by adding a large amount of low-molecular-weight components even if offset resistance is sacrificed to some extent; By adding such a component, it is possible to achieve manufacturing stability in which the fixing temperature does not increase even if there is a slight change in composition.

A decrease in the offset temperature due to the presence of an excessive amount of low molecular weight components is prevented by the fibrous polytetrafluoroethylene.

The polytetrafluoroethylene that can be made into fibers used here is suitably the polytetrafluoroethylene for dust control manufactured by Hershey Co., Ltd. in the United States. Fluoroethylene does not exhibit any dust control properties.

The above-mentioned polytetrafluoroethylene includes an aqueous colloid dispersion type and a fine powder type, but the fine powder type is suitable for the purpose of the present invention.

The method of the present invention, which aims to improve the offset gradient by adding polytetrafluoroethylene fine powder that can be made into fibers, balances low-temperature fixability, manufacturability, and offset resistance. It is particularly effective for toners that use a blend of an extremely low molecular weight polymer and an ultra-high molecular weight polymer as the binder polymer, which is difficult to control. The objective can also be satisfactorily achieved by increasing the weight average molecular weight of. However, in such a case,
When a large weight average molecular weight that cannot be achieved without the use of a crosslinking reaction is required, it is generally difficult to control the crosslinking reaction during polymerization, so the molecular weight of the polymer used varies from lot to lot, making it difficult to maintain offset resistance at a constant level. I run into problems that I can't control.

In such cases, the molecular weight of the polymer should be kept at a level that can be controlled during polymerization, and by introducing fibrous polytetrafluoroethylene into the Henner system, it is possible to exhibit rheological properties equivalent to those of a crosslinked polymer. Can be done. This eliminates problems such as lot-to-lot variation when using crosslinked polymers as described above.

Any suitable pigment or dye can be used as a colorant for the toner powder in the toner of the present invention. Toner colorants are well known and include carbon black, nigrosine dye, aniline blue, alcohol blue, chrome yellow, ultramarine blue, monoline yellow,
Examples include methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal and mixtures thereof. The pigment or dye must be present in the toner in an amount sufficient for it to strongly color the toner so that it forms a clearly visible image on the paper. Thus, for example, where conventional xerographic reproduction of printed documents is desired, the toner may be formed using a black pigment, such as carbon black, or a black dye, such as Amaraplast black dye. Pigments are preferably used in an amount of about 3 to 20% by weight based on the total weight of the colored toner, or if the toner colorant used is a dye, only a small amount of the colorant should be used. Bye.

Toners according to the present invention may be made by any known toner mixing and grinding method. All ingredients are thoroughly mixed, for example, by blending, mixing and grinding all the ingredients, and then the resulting mixture is pulverized. Other well-known methods of forming toner powders include ball milling the colorant, resin, and solvent and spray drying the toner formulation mixture.

In order to use the electrophotographic toner according to the present invention by a cascade development method, a magnetic brush development method, a C. shell development method, etc., the toner must have an average particle size of about 30 microns or less expressed as a weight percentage. However, it is desirable for this average particle size to be between about 4 and 20 microns to produce optimal results. Particle sizes slightly less than 1 micron are desirable for use in powder cloud development.

Coated and uncoated carriers used in cascade development, magnetic brush development, C-shell development, etc. are well known;
carrier particles if the toner powder acquires a charge of opposite polarity to that of the carrier particles when the carrier particles are brought into intimate contact with the toner powder such that the toner powder adheres to and surrounds the carrier particles; may be formed of any suitable material.

Accordingly, the toner of the present invention can be used in admixture with conventional carriers to develop electrostatic latent images on any suitable electrostatic latent image-bearing surface, including conventional photoconductive surfaces. Ru.

The following examples specifically show embodiments of the toner according to the present invention, but it goes without saying that the present invention is not limited to these examples only. In addition, comparative examples are shown to further clarify the excellent effects of the toner according to the present invention.

Comparative Example 1 63 parts of a polyester resin consisting of bisphenol A and maleic anhydride (glass transition point 50°C, melt index 100 (110°C), number average molecular weight 2000),
Styrene-butadiene copolymer (number average molecular weight
20000, weight average molecular weight 1.5 million, glass transition point 40
℃) 27 parts and 10 parts of carbon black were mixed well, and the oil pressure was 7.0Kg/cm ² in an intensive mixer.
The mixture was press-fitted at a compressor pressure of 5.0 kg/cm ² and kneaded for 5 minutes at a mixer internal temperature of 80°C.

After taking it out from the mixer, it is cooled, crushed appropriately, and coarsely crushed into several hundred micrometers using a free mill, and then crushed using a dietmizer (Nippon Neumatic Kogyo KK).
The powder was finely pulverized with an air pressure of 6.3 Kg/cm ² and a supply rate of 1.0 Kg/hr to obtain a fine powder with an average particle size of 12 μm, which was used as a toner.

Mix the toner obtained above with DSP iron powder carrier,
When we measured the fusing point and offset point using a Xerox Model 720 copying machine, we found that it fusing at an extremely low temperature of 125°C, and no offset occurred up to 200°C.

Comparative Example 2 72 parts of a polyester resin consisting of bisphenol A and maleic anhydride (glass transition point 50°C, melt index 100 (110°C), number average molecular weight 2000),
Styrene-butadiene copolymer (number average molecular weight
20000, weight average molecular weight 1.5 million, glass transition point 40
C.) and 10 parts of carbon black were thoroughly mixed and then press-fitted into an intensive mixer at a hydraulic pressure of 7.0 Kg/cm ² and a compressor pressure of 5.0 Kg/cm ² , and kneaded for 5 minutes at a mixer internal temperature of 80° C.

After taking it out of the mixer, it is cooled, crushed appropriately, and roughly pulverized to several hundred micrometers in a free mill, and then used in a jettomizer at an air pressure of 6.3Kg/cm ² and a feed rate of 3.0Kg/hr.
When finely pulverized with
A grinding speed three times higher than that of Comparative Example 1 was achieved.

However, when the toner obtained above was mixed with a DSP iron powder carrier and the fusing point and offset point were measured using a 720 Xerox copier, the minimum fusing temperature was
Although a minimum fixing temperature of 115°C, which is 10°C lower than that of Comparative Example 1, was obtained, an offset occurred at 165°C, and the fusing gradient was even narrower than that of Comparative Example 1. Ivy.

Comparative example 3 Epoxy resin E-1004 (manufactured by Ciel Chemical KK) 63
and styrene-butadiene copolymer (number average molecular weight 15,000, weight average molecular weight 2 million, glass transition point
40°C) and 10 parts of carbon black were thoroughly mixed together and press-fitted into an intensive mixer at a hydraulic pressure of 7.0 kg/cm ² and a compressor pressure of 5.0 kg/cm ² , and kneaded for 5 minutes at a mixer internal temperature of 80°C.

After taking it out from the mixer, it is cooled, crushed appropriately, and coarsely pulverized into several hundred micrometers using a free mill.Then, it is processed using a dietmizer at an air pressure of 6.3 Kg/cm ² and a feed rate of 3.0 Kg/cm 2 .
By pulverizing with hr, a fine powder with an average particle size of 12μ could be obtained.

However, when the toner obtained above was mixed with a DPS iron powder carrier and the fixing point and offset point were measured using a Model 720 Xerox copying machine, it was found that the fixing point and offset point were sufficient at 125°C, but an offset was observed at 160°C.

Comparative example 4 Styrene-allyl alcohol copolymer RP-450
(manufactured by Ciel Kagaku KK), 18 parts of styrene-butadiene copolymer (number average molecular weight 18,000, weight average molecular weight 2.3 million, glass transition point 40°C), and 10 parts of carbon black were mixed thoroughly and placed in an intensive mixer. Oil pressure 7.0Kg/cm ² , compressor pressure 5.0
Kg/cm ² was press-fitted and kneaded for 5 minutes at a mixer internal temperature of 80°C.

After taking it out from the mixer, it is cooled, crushed appropriately, and coarsely pulverized to several hundred micrometers in a free mill, and then used in a jettomizer at an air pressure of 6.3Kg and a feed rate of 6.0Kg/hr.
A fine powder with an average particle size of 12μ could be obtained by pulverization, but the pulverization speed was six times that of Comparative Example 1 and twice that of Comparative Examples 2 and 3. achieved.

However, when the toner obtained above was mixed with a DSP iron powder carrier and the fixing point and offset point were measured using a 720 model Xerox copying machine, it was found that it was fixed at 120°C, but offset occurred at 160°C.

Example 72 parts of a polyester resin consisting of bisphenol A and maleic anhydride (glass transition point 50°C, melt index 100 (110°C), number average molecular weight 2000),
Styrene-butadiene copolymer (number average molecular weight
20000, weight average molecular weight 1.5 million, glass transition point 40℃)
1 part of Teflon K-10J (manufactured by Mitsui Fluorochemical KK) was added as a polytetrafluoroethylene fine powder to 100 parts of a polymer colorant mixture consisting of 18 parts of carbon black and 10 parts of carbon black, and after thorough premixing, the mixture was mixed in an intensive mixer. Hydraulic pressure 7.0
Kg/cm ² , compressor pressure 5.0Kg/cm ² ,
The mixture was kneaded for 5 minutes at a mixer internal temperature of 80°C. After taking it out of the mixer, it is cooled, crushed appropriately, and coarsely pulverized in a free mill to several hundred micrometers, and then finely pulverized in a jettomizer at an air pressure of 6.3 Kg/cm ² and a feed rate of 3.0 Kg/hr to have an average particle size. A fine powder of 12μ was obtained, but Teflon K-
The crushability was the same as when 10J was not added.

When the toner obtained above was mixed with a DSP iron powder carrier and the fixing point and offset point were measured using a 720 model Xerox copying machine, the minimum fixing temperature was 115°C, which was the same as when Teflon K-10J was not added. No offset was observed up to 200℃.
The improvement of the fusing temperature by Teflon K-10J was remarkable.

Example For 100 parts of a mixture consisting of 63 parts of epoxy resin E-1004, 27 parts of styrene-butadiene copolymer (number average molecular weight 15,000, weight average molecular weight 2 million, glass transition point 40°C) and 10 parts of carbon black,
After adding 1 part of Teflon K-10J and premixing well, the mixture was press-fitted into an intensive mixer at a hydraulic pressure of 7.0 kg/cm ² and a compressor pressure of 5.0 kg/cm ² and kneaded for 5 minutes at a mixer internal temperature of 80°C.

After taking it out from the mixer, it is cooled, crushed appropriately, coarsely pulverized to several hundred μ in a free mill, and then used in a jettomizer at an air pressure of 6.3 Kg/cm ² and a feed rate of 3.0
By pulverizing at a rate of Kg/hr, a fine powder with an average particle size of 12 μm could be obtained, and the pulverization properties were the same as when Teflon K-10J was not added.

When the toner obtained above was mixed with DSP iron powder carrier and the fixing point and offset point were measured using a 720 model Xerox copying machine, it was found that it was sufficiently fixed at 125°C and 195
No offset occurred up to ℃. Teflon K
-10J was found to increase the hot offset temperature without affecting the minimum fixing temperature.

Example Styrene-allyl alcohol copolymer RP-450
(manufactured by Ciel Chemical KK), 18 parts of styrene-butadiene copolymer (number average molecular weight 18,000, weight average molecular weight 2.3 million, glass transition point 40°C), and 10 parts of carbon black. K-10J (manufactured by Mitsui Fluorochemical KK) 1
After pre-mixing thoroughly, mix the oil pressure in an intensive mixer at a pressure of 7.0Kg/cm ² and a compressor pressure of 5.0.
Kg/cm ² was press-fitted and kneaded for 5 minutes at a mixer internal temperature of 80°C.

After taking it out from the mixer, it is cooled, crushed appropriately, and coarsely pulverized to several hundred micrometers in a free mill, and then used in a jettomizer at an air pressure of 6.3 Kg/cm ² and a feed rate of 6.0 μg.
Kg/hr, it was possible to obtain a fine powder with an average particle size of 12 μm by pulverization, and the same pulverization speed as when Teflon K-10J was not added was achieved.

When the toner obtained above was mixed with DSP iron powder carrier and the fixing point and offset point were measured using a 720 model Xerox copier, it was found that the toner was sufficiently fixed at 120°C.
No offset occurred up to 195°C.

Although the present invention has been described above in detail with particular reference to its preferred embodiments, it goes without saying that changes and improvements can be made within the spirit and scope of the present invention.

Claims (1)

[Scope of Claims] 1. An electrophotographic toner comprising 5% by weight or less of fibrous polytetrafluoroethylene inside toner particles consisting of a binder resin and a colorant. 2 Into the mixture consisting of binder resin and colorant,
After mixing polytetrafluoroethylene that can be made into fibers in an amount of 5% by weight or less based on the mixture,
A method for producing an electrophotographic toner, characterized in that the polytetrafluoroethylene is made into fibers during the toner production process by melt-kneading.