JP4702460B2 - Method for producing toner for electrophotography - Google Patents

Description

The present invention relates to a toner for electrophotography and a method of manufacturing the same, more particularly, to a method of manufacturing electrophotographic toner over comprising a biodegradable resin in the binder resin.

  Image formation by electrophotography is performed by developing and visualizing an electrostatic image with toner, transferring the obtained toner image onto a sheet, and then fixing it with heat and pressure. As the toner used for such image formation, a toner prepared by kneading a mixture of a binder resin and a colorant or a charge control agent, and adjusting the particle size distribution by pulverization is used.

  Conventionally, petroleum-derived resins such as styrene / acrylic resins and polyester resins have been used as binder resins. In recent years, in consideration of the environment, a method has been proposed in which a biodegradable resin having a low environmental impact at the time of disposal, or a biomass-derived resin made from renewable resources, is used as a toner resin. These biodegradable resins and biomass-derived plastics are called bioplastics and are expected to reduce the consumption of fossil resources and suppress the increase in the concentration of carbon dioxide in the atmosphere.

  One of the most promising resins among bioplastics is polylactic acid. Polylactic acid is a crystalline polyester having a melting point of about 170 ° C., a glass transition point of about 60 ° C., and a molecular weight of about 1 to 150,000. Currently, it is used for food packaging materials and containers. In addition, heat resistance and high durability have been added to polylactic acid, and it has also begun to be used for mobile phone cases and the like.

  However, when polylactic acid is used as a resin for toner as it is, there are problems that it is hard and has poor grindability, and has a high softening temperature and is not suitable for low-temperature fixing.

  In order to solve such a problem, proposals have been made to add a large amount of plant wax to polylactic acid (see, for example, Patent Document 1). However, in this proposal, it is possible to lower the softening temperature of the toner by adding a large amount of wax. As the toner fluidity deteriorates, problems such as inferior toner transportability in the developing machine occur.

  There is also a proposal of blending a terpene phenol copolymer and a specific wax into a polylactic acid-based biodegradable resin (see, for example, Patent Document 2). In this proposal, blending a terpene phenol copolymer that has low toughness of polylactic acid and low resin strength but is effective for low-temperature fixability provides good low-temperature fixability and grindability without sacrificing durability. Both can be achieved.

  However, the blending amount of the polylactic acid-based biodegradable resin is about 30% by mass, and if the blending amount is further increased, the grindability is deteriorated and it becomes difficult to produce a toner. Also, the melt viscosity becomes high, and the low-temperature fixability deteriorates.

  In addition, there is a proposal of blending two types of resins having different softening points into a biodegradable resin for low-temperature fixability and fixing stability (for example, see Patent Document 3). In this proposal, the low softening point resin serves as a bridge between the high softening point resin and the biodegradable resin, and the biodegradable resin is uniformly dispersed in the binder resin. However, the blending ratio of the biodegradable resin in the binder resin is about 13% by mass, and at most 33% by mass is the limit. Although there is no clear description, it is considered that one of the causes is that if the blending ratio of the biodegradable resin is further increased, the biodegradable resin is poorly dispersed and the durability and grindability are deteriorated.

  As described above, there are many problems in using biodegradable resins and biomass plastics as the main component of the binder resin for toners. It is desired that more biodegradable resins and biomass plastics can be blended while maintaining.

  In addition, although the technique which grind | pulverizes after heat-treating biodegradable resin and raising crystallinity is known (for example, refer patent document 4), this raises hardness by raising crystallinity, and is grind | polished. The main use of the obtained powder is an abrasive, and the molecular weight of the biodegradable resin used is also high.

  Although Patent Document 4 also describes use as a resin for toner, it is extremely difficult to pulverize to a particle size of 10 μm or less required by the toner in view of its molecular weight and the like.

Japanese Patent No. 2597452 Japanese Patent No. 3779221 JP 2006-91278 A JP 2007-197602 A

  The present invention has been made in view of the above circumstances, and provides an electrophotographic toner containing polylactic acid as a binder resin and having good transferability, storage stability, fixability, and pulverization properties, and a method for producing the same. With the goal.

To solve the above problems, states like the present invention, a kneading step of kneading a raw material mixture containing a binding Chakujushi, milling step pulverizing the kneaded product obtained by kneading step, and by the milling step An electrophotographic toner production method comprising a heat treatment step of adding an external additive to a finely pulverized powder and then heat-treating at a temperature not lower than a glass transition point and not higher than a melting point of the binder resin. The resin composition contains 50 to 100% of polylactic acid having a number average molecular weight of 5,000 to 50,000, and the heat treatment step is a step of heat treatment at about 70 to 100 ° C. for 1 to 2 hours. A method for producing an electrophotographic toner is provided.

  According to the present invention, an electrophotographic toner containing polylactic acid as a binder resin and having good transferability, storage stability, fixability, and grindability, and a method for producing the same are provided.

It is a schematic diagram which shows the arrangement | sequence of the polylactic acid molecule | numerator after rapid cooling of a kneaded material. It is a schematic diagram which shows the arrangement | sequence of the polylactic acid molecule | numerator after the heat processing of a kneaded material. FIG. 5 is a characteristic diagram in which polylactic acid hydrolysis treatment time is plotted on the horizontal axis and molecular weight is plotted on the vertical axis. It is the characteristic view which plotted the processing time of the hydrolysis of polylactic acid on the horizontal axis | shaft, and the glass transition point (Tg) on the vertical axis | shaft.

  Hereinafter, various embodiments of the present invention will be described.

  An electrophotographic toner according to an embodiment of the present invention is obtained by kneading and pulverizing a raw material mixture containing a binder resin containing polylactic acid having a molecular weight of 5,000 to 50,000, and then binding the glass of the binder resin. The heat treatment is performed at a temperature not lower than the transition point and not higher than the melting point.

  Thus, as a binder resin, a raw material mixture containing a binder resin containing polylactic acid having a molecular weight of 5,000 to 50,000, preferably 10,000 to 50,000, is kneaded and pulverized. By performing a heat treatment at a temperature not lower than the glass transition point and not higher than the melting point of the binder resin, a toner having good transferability and storage stability can be obtained.

  In the electrophotographic toner according to this embodiment, the heat treatment after pulverization is performed to promote crystallization of polylactic acid. Normally, in the kneading step of the raw material mixture in the production of toner, the melted kneaded product is rapidly cooled, so that the polylactic acid molecules in the kneaded product are in an amorphous state in which they are randomly dispersed as shown in FIG. It is thought that there is.

  In the electrophotographic toner according to this embodiment, a polylactic acid contained in the binder resin having a molecular weight of 5,000 to 50,000 is used in order to improve grindability. When polylactic acid having a low molecular weight is used, the glass transition point of the toner is low and is as low as 40 ° C. A toner having a low glass transition point obtained by continuing the toner production process in such a state where the polylactic acid is in an amorphous state is extremely deteriorated in transferability and storage stability when the glass transition point is exceeded. .

  On the other hand, in the electrophotographic toner according to the present embodiment, the kneaded product is finely pulverized and then subjected to a heat treatment, whereby polylactic acid molecules are regularly arranged, that is, crystallized as shown in FIG. And storage stability can be improved. Since polylactic acid is originally a crystalline resin, even if it becomes amorphous by rapid cooling, it is crystallized by heat treatment. Although depending on the crystallinity, the heat resistance can be improved up to a temperature near the melting point of polylactic acid. However, since the purpose is to improve the storability, crystallization should be performed within a range in which the storability is improved. Therefore, it is not necessary to perform heat treatment more than necessary and excessively promote crystallization.

  The heat treatment temperature may be not less than the glass transition point and not more than the melting point. However, since the kneaded material also contains a low melting point release agent, the release agent can be prevented from bleeding during the heat treatment. It is preferable to heat-treat at a temperature below the melting point of the mold.

  The specific heat treatment temperature is in the range of 60 to 100 ° C., more preferably 70 to 80 ° C., although it depends on the type of release agent to be added.

  When heat treatment is performed in a shorter time, it is most preferable to obtain a crystallization peak temperature with a differential scanning calorimeter DSC and perform the heat treatment at this crystallization peak temperature.

  Regarding the heat treatment time, it takes time to obtain the required crystallinity, but it varies depending on the heat treatment temperature and the treatment method and can be arbitrarily adjusted.

  The method for the heat treatment is not particularly limited, and may be a continuous type or a batch type.

  As described above, the case where the melt-kneaded product is pulverized and then heat-treated has been described. However, the heat treatment can be performed after adding an external additive to the pulverized powder. Although it is possible to carry out before adding the external additive, the addition after the external additive is preferable because aggregation due to heat treatment can be prevented.

  Polylactic acid is a polymer in which lactic acid is bonded by an ester bond, and has recently attracted attention as an environmentally friendly biodegradable plastic. In other words, in nature, enzymes that cleave ester bonds (esterases) are widely distributed, so polylactic acid is gradually decomposed by such enzymes in the environment and converted into lactic acid, which is a monomer. And eventually carbon dioxide and water.

  It does not specifically limit as a manufacturing method of polylactic acid used by this embodiment, A conventionally well-known method can be used. There is a method of fermenting starch such as corn as a raw material to obtain lactic acid, and then dehydrating and condensing directly from lactic acid monomer, or a method of synthesizing from lactic acid via cyclic dimer lactide by ring-opening polymerization in the presence of a catalyst. .

  The molecular weight of the polylactic acid used in this embodiment can be arbitrarily adjusted by varying the reaction conditions during polymerization. Here, the polylactic acid used as a general-purpose resin needs a high molecular weight of about 100,000 as the number average molecular weight, but the polylactic acid used in this embodiment is 5,000 to 50,000. This is a relatively low-molecular polylactic acid of such a degree, and the low molecular weight makes it possible to pulverize polylactic acid, which has been difficult to pulverize, and add polylactic acid at a high concentration. It becomes possible to do.

  As another method, there is a method of using polylactic acid having a reduced molecular weight by utilizing hydrolysis characteristics of polylactic acid, for example, by allowing polylactic acid to stand in a high-temperature and high-humidity environment for hydrolysis treatment. .

  A conventionally known colorant can be used as the colorant used in the toner according to the exemplary embodiment. For example, as a black colorant, carbon black and as a blue colorant, C.I. I. Pigment 15: 3, and red colorants include C.I. I. Pigment 57: 1, 122, 269, and yellow colorants include C.I. I. Pigment 74, 180, 185 and the like. In consideration of the influence on the environment which is one of the objects of the present invention, a single colorant having high safety is preferable.

  The content of these colorants is preferably 1 to 10% by mass with respect to the whole toner. The colorant may be used in the form of a masterbatch in which a resin and a colorant are dispersed in high concentration in advance.

  A conventionally known release agent can be added to the toner according to the exemplary embodiment as necessary. Examples of such a release agent include olefinic waxes such as polypropylene wax, polyethylene wax, and Fischer-Tropsch wax, natural waxes such as carnauba wax, rice wax, and scale insect wax, and synthetic ester waxes.

  In order to improve low-temperature fixability and high-speed printing performance, a release agent having a relatively low melting point of about 60 to 100 ° C. is preferable, and specifically, carnauba wax and synthetic ester wax are preferable. In consideration of environmental impact, natural product carnauba wax is more preferable.

  The compounding amount of the release agent is preferably 1 to 10% by mass with respect to the whole toner.

  A conventionally known charge control agent of positive charge or negative charge can be added to the toner according to the exemplary embodiment as necessary. Examples of the positive charge control agent include quaternary ammonium salts, resins containing amino groups, and the like. Examples of the negative charge control agent include metal complexes of salicylic acid, metal complexes of benzylic acid, and calixarene type phenolic compounds. Examples include condensates and resins containing carboxyl groups.

  The blending amount of the charge control agent is preferably 0.1 to 5% by mass with respect to the whole toner.

  In addition to polylactic acid, conventionally known toner resins can be added to the toner according to the exemplary embodiment, if necessary. Examples of such resins include styrene / acrylic resins and polyester resins. From the viewpoint of pigment dispersibility and low-temperature fixability, polyester resins developed for toners are preferred. Resin may be individual or may mix 2 or more types.

  The amount of the resin for toner is preferably 0 to 50% by mass with respect to the whole toner in consideration of the influence on the environment which is one of the objects of the present invention.

  As other resin materials, a low molecular weight resin can be added to improve grindability, fixability and the like. Here, the low molecular weight resin is a resin in an oligomer region having a molecular weight of several hundred to several thousand, and examples thereof include rosin and rosin derivatives, polyterpene resins, terpene phenol resins, and petroleum resins that are commercially available as tackifiers.

  A conventionally known hydrolysis inhibitor can be added to the toner according to the exemplary embodiment as necessary. Examples of the hydrolysis inhibitor include carbodiimide compounds, isocyanate compounds, and oxazoline compounds. By such a hydrolysis inhibitor, the residual monomer and the hydroxyl group and carboxyl terminal produced by decomposition can be blocked, and the hydrolysis chain reaction can be suppressed. In this embodiment, by adding a hydrolysis inhibitor, in addition to improving the original hydrolysis resistance, an effect can be obtained for adjusting the molecular weight of the biodegradable resin.

  As a specific hydrolysis inhibitor, “Carbodilite LA-1” manufactured by Nisshinbo Co., Ltd., which is a polycarbodiimide compound, is commercially available. It is preferable that the addition amount of a hydrolysis inhibitor is 0.01-10 mass% with respect to biodegradable resin, and 0.05-5 mass% is more preferable. When the amount is too large, the transparency is deteriorated and the color of the toner tends to be deteriorated.

  A conventionally known crystal nucleating agent can be added to the toner according to the exemplary embodiment as necessary. Examples of the crystal nucleating agent include inorganic nucleating agents such as talc, organic carboxylic acid metal salts such as sodium benzoate, phosphoric acid ester metal salts, organic nucleating agents such as benzylidene sorbitol, and carboxylic acid amide.

  The electrophotographic toner described above can be produced by a conventionally known method.

  For example, after mixing raw materials containing a binder resin containing polylactic acid and polymethyl methacrylate, a colorant, and other additives as necessary, a kneader such as a biaxial kneader, a pressure kneader, or an open roll Kneading to obtain a kneaded product. After cooling this kneaded material, the toner can be obtained by pulverizing with a pulverizer such as a jet mill and classifying with an air classifier.

  Here, the particle size of the toner is not particularly limited, but is usually adjusted to be 5 to 10 μm. An external additive can be added to the toner thus obtained in order to improve fluidity, adjust chargeability, and improve durability.

  As the external additive, inorganic fine particles are generally used, and examples thereof include silica, titania, alumina, etc. Among them, silica subjected to hydrophobic treatment (commercially available from Nippon Aerosil Co., Ltd., CABOT Co., Ltd.) is preferable. The particle diameter of the inorganic fine particles is preferably 7 to 40 nm as the primary particle diameter, and two or more kinds may be mixed for improving the function.

  Examples of the present invention and comparative examples are shown below, and the present invention will be described more specifically.

  1. The measuring method of each physical property value of the components used in Examples and Comparative Examples is as follows.

(Measurement of softening point)
Apparatus: Flow tester (manufactured by Shimadzu Corporation, CFT-500D)
Sample: 1g
Temperature increase rate: 6 ° C / min Load: 20kg
Nozzle: 1mm diameter, 1mm length
1/2 method: The temperature at which half of the sample flowed out was taken as the softening point.

(Measurement of toner particle size)
Equipment: Multisizer II (manufactured by Coulter, Inc.)
Sample: A small amount of sample, purified water, and a surfactant were placed in a beaker and dispersed with an ultrasonic cleaner.

  Measurement: The aperture was 100 μm, the count was 50,000, and the volume average particle size was obtained.

(Measurement of glass transition point (Tg))
Apparatus: Differential scanning calorimeter (manufactured by Shimadzu Corporation: DSC-60)
Sample: 8mg
Temperature raising conditions: The temperature is raised to 160 ° C. at 10 ° C./min, cooled to 35 ° C. at a temperature lowering rate of 10 ° C./min, and then raised again to 160 ° C. at 10 ° C./min.

  At the second temperature increase, the intersection of two tangents of the curve portion obtained by the transition was taken as the glass transition point.

(Measurement of melting point of release agent)
The same measurement as the glass transition point was performed, and the peak temperature of the endothermic curve due to the release agent at the second temperature increase was taken as the melting point.

  When the endothermic curve is two or more peaks, the average value of each peak was taken as the peak.

(Measurement of molecular weight)
Equipment: GPC (manufactured by Shimadzu Corporation), detector RI
The molecular weight Mn is a number average molecular weight measured by GPC (gel permeation chromatography) using a calibration curve prepared with a polystyrene sample having a known molecular weight as a standard.

  2. As the polylactic acid used in the examples and comparative examples, hydrolyzed commercial polylactic acid was used as follows.

  Hydrolysis treatment was performed by leaving polylactic acid (REVODE101B manufactured by Kaisho Biological Co., Ltd.) in a constant temperature and humidity chamber set at a temperature of 80 ° C. and a humidity of 90% RH. Hydrolysis treatment was performed by changing the treatment time to obtain polylactic acid having different molecular weights.

Table 1 below shows the treatment time of the hydrolysis treatment, the molecular weight of the hydrolyzed polylactic acid, and the glass transition point (Tg).

  As shown in Table 1 above, it can be seen that the molecular weight and the glass transition point (Tg) of the hydrolyzed polylactic acid decrease as the treatment time increases.

  A graph of the results shown in Table 1 is shown in FIGS. FIG. 3 plots the treatment time on the horizontal axis and the molecular weight on the vertical axis, and FIG. 4 plots the treatment time on the horizontal axis and the glass transition point (Tg) on the vertical axis.

Example 1
Each component of the following blending amount was put into a Henschel mixer (standard feather mounted, manufactured by Mitsui Mining Co., Ltd.) and mixed.

Low molecular weight polylactic acid (molecular weight: 50,000) 90 parts by weight Colorant: Carbon black (MOGUL L manufactured by CABOT Co., Ltd.) 4 parts by weight Mold release agent: Carnauba wax No. 1 powder (manufactured by Nippon Wax Co., Ltd.) 5 Part by mass Charge control agent: E-84 (manufactured by Orient Chemical Co., Ltd.) 1 part by mass The mixed powder was melt-kneaded with a twin screw extruder (screw diameter 43 mm, L / D = 34), then stretched and cooled, A kneaded product was obtained. The obtained kneaded material is coarsely crushed with a rotoplex (manufactured by Hosokawa Micron Co., Ltd., 2 mm screen). Were pulverized and classified so that the average particle size of the toner was 9.0 μm.

  After the obtained fine particles were treated with a hot air dryer at 70 ° C. for 2 hours, “RY200” (manufactured by Nippon Aerosil Co., Ltd .: hydrophobic silica, primary particle size 12 nm) as an external additive to 100 parts by mass of the fine particles. 2 parts by mass was added, and the mixture was stirred and mixed for 3 minutes with a Henschel mixer (equipped with stirring reinforcement blades, manufactured by Mitsui Mining Co., Ltd.) to obtain a toner.

Examples 2-4, Comparative Examples 1-3
Toners were obtained in the same manner as in Example 1 except that various polylactic acids shown in Table 2 below were used as the binder resin, and predetermined heat treatment conditions were adopted or heat treatment was not performed.

  The toners of Examples 1 to 4 and Comparative Examples 1 to 3 thus obtained were tested and evaluated by the following test methods for fogging, transferability, storage stability, fixability, and grindability.

Test 1-Fog Mount toner on a non-magnetic one-component developing device "Casio Page Presto N-5" (Casio Computer Co., Ltd .: 29 color printers per minute (A4 horizontal) machine, process speed 129 mm / sec), In a normal environment (25 ° C., 50% RH), after printing 10,000 sheets of 5% print images continuously using plain paper (XEROX-P paper A4 size), printing on blank paper and printing Printing was forcibly terminated by opening the front door, and the fog toner on the OPC drum at that time was copied onto a mending tape and affixed to white paper, and compared with a tape from which fog toner was not collected. In the measurement, the maximum value of the difference before and after fogging was determined as the fog value from the XYZ value obtained using a spectroscopic color difference meter “SE-2000” manufactured by Nippon Denshoku Co., Ltd., and evaluated according to the following criteria.

A: The fog value is less than 2 and good. B: The fog value is 2 or more and less than 5. Δ: The fog value is 5 or more and less than 10. Level at which there is no problem in practical use: Poor fog value of 10 or more Test 2—Transferability Using the same apparatus as used in Test 1, a solid image was formed in a normal environment (25 ° C., 50% RH). Printing was forcibly terminated by opening the front door in the middle of printing. At that time, the amount of transferred toner per unit area transferred to the paper and the amount of residual toner transferred per unit area on the OPC drum were measured. . The transfer rate was determined by the following formula and evaluated according to the following criteria.

Transfer rate (%) = (transfer toner amount / (transfer toner amount + transfer residual toner amount)) × 100
○: Transfer rate is 80% or more, good △: Transfer rate is 75% or more and less than 80%, practically no problem ×: Transfer rate is less than 75%, bad Test 3-Preservability 10 g of toner is contained in a glass beaker Then, after being left in a constant temperature and humidity chamber of 50 ° C. and 90% RH for 24 hours, the aggregation state of the toner was visually confirmed and evaluated according to the following evaluation criteria.

(Evaluation criteria)
A: No toner aggregation is observed.

  ○: Almost no aggregation of toner is observed.

  Δ: Slight aggregation of toner is observed.

  X: Aggregation of toner is clearly recognized.

Test 4-Fixability A fixing tester is prepared by changing the temperature of the fixing portion of the same apparatus as used in Test 1 so that the temperature can be varied. After obtaining an unfixed image with this apparatus, the fixing temperature of the upper roll was varied in a range of 100 to 200 ° C. every 10 ° C., and the unfixed image was passed through a fixing device. At that time, the lower roll was set at a temperature 10 ° C. lower than the set temperature of the upper roll. The cold offset, hot offset, and peeled nail trace of the image sample were visually evaluated, and a non-offset area was obtained and evaluated. The process speed was 129.3 mm / sec, and the paper was XEROX P paper A4 size (mass 64 g / m ² ). The oil supply roll of the fixing device was removed.

  (Double-circle): A non-offset area | region is 30 degreeC or more.

  ○: The non-offset region is 20 ° C. or higher and lower than 30 ° C.

  (Triangle | delta): A non-offset area | region is 10 degreeC or more and less than 20 degreeC.

  X: A non-offset area | region is less than 10 degreeC.

Test 5-Crushability When pulverizing and classifying the kneaded and crushed material in the pulverization / classification step, the determination is made based on the yield (% by mass) of the particles serving as the toner base. In reality, there is no problem if the yield is 70% or more. At this time, the pulverization conditions are adjusted so that the volume average particle diameter of the toner is 9 μm, the number ratio of particles of 3 μm or less as fine powder is 5% or less, and the volume ratio of particles of 16 μm or more as coarse powder is 3% or less. .

○: Yield 65% or more X: Yield less than 65% The results of the above tests 1 to 5 are shown in Table 2 below.

  From Table 2 above, the following is clear.

  Each of the toners according to Examples 1 to 3 in which a kneaded product containing polylactic acid having a molecular weight of 5,000 to 50,000 was roughly pulverized and finely pulverized and then heat-treated at 70 ° C. for 2 hours was fogged. It shows excellent transferability and pulverization, and almost satisfactory results in storage. In addition, the toner according to Example 4 in which the heat treatment condition was changed to 100 ° C. for 1 hour showed almost satisfactory results, although the evaluation in the characteristics other than fogging was lowered.

  On the other hand, it can be seen that the toners according to Comparative Examples 1 to 3 that were not heat-treated were inferior in transferability and storage stability.

Claims (1)

A kneading step for kneading the raw material mixture containing the binder resin, a fine pulverizing step for finely pulverizing the kneaded product obtained by the kneading step, and after adding an external additive to the finely pulverized powder by the fine pulverizing step A method for producing an electrophotographic toner comprising a heat treatment step of heat-treating at a temperature not lower than the melting point and not higher than the glass transition point of the binder resin ,
The binder resin contains 50 to 100% polylactic acid having a number average molecular weight of 5,000 to 50,000, and the heat treatment step is a step of heat treatment at about 70 to 100 ° C. for 1 to 2 hours. A method for producing an electrophotographic toner, which is characterized.

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