JP2010175724A - Electrophotographic toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrophotographic toner containing polylactic acid waste as a binder resin, which is excellent in grindability and fixability, and superior in toner concentration stability and preservability. <P>SOLUTION: The electrophotographic toner contains polylactic acid with a molecular weight of 5,000-50,000 and polymethyl methacrylate as a binder resin, the compounding amount of the polymethyl methacrylate being 5-45 mass% to the amount of toner. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic toner, and more particularly to an electrophotographic toner containing a biodegradable resin in a 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, but the toner easily aggregates due to the wax component, so that the productivity due to the lowering of the classification efficiency deteriorates. 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). This proposal blends the toughness of polylactic acid and the terpene phenol copolymer, which has low resin strength but is effective for low-temperature fixability, to achieve 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 limited to about 30% by weight. If the blending amount is further increased, the grindability is deteriorated and it becomes difficult to prepare 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.

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

  The present invention has been made in view of the above circumstances, and provides an electrophotographic toner that contains polylactic acid as a binder resin, has good pulverization properties and fixing properties, and has excellent density stability and durability. With the goal.

  In order to solve the above problems, one embodiment of the present invention contains polylactic acid having a molecular weight of 5,000 to 50,000 and polymethyl methacrylate as a binder resin, and the blending amount of the polymethyl methacrylate is An electrophotographic toner is provided, which is 5 to 45% by mass with respect to the toner amount.

  In such an electrophotographic toner, the polylactic acid having a molecular weight adjusted by a hydrolysis treatment can be used.

  According to the present invention, there is provided an electrophotographic toner that contains polylactic acid as a binder resin, has good pulverization and fixing properties, and has excellent density stability and storage stability.

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.

  As described above, conventionally, a toner containing a biodegradable resin as a binder resin has been mixed and melt-kneaded by mixing the biodegradable resin with a colorant and other additives. As a biodegradable resin, for example, polylactic acid has a melting point of about 170 ° C., and when used alone as a binder resin for toner, the softening temperature is high and the grindability is poor. In order to improve this, when a large amount of a low softening point substance is mixed with the binder resin, the difference in viscosity of the resin in melt-kneading becomes large, and uniform dispersion becomes difficult. As described above, even when the binder resin is added, there is a limit to the amount of biodegradable resin.

  The present inventors have found that the above problem can be solved by using a polylactic acid having a low molecular weight and further blending polymethyl methacrylate with the binder resin.

  That is, the electrophotographic toner according to an embodiment of the present invention contains, as a binder resin, polylactic acid having a molecular weight of 5,000 to 50,000 and polymethyl methacrylate, and the blending of the polymethyl methacrylate. The amount is 5 to 45% by mass with respect to the toner amount.

  Thus, as a binder resin, polymethyl methacrylate is added to polylactic acid having a molecular weight of 5,000 to 50,000, preferably 10,000 to 50,000, and polymethyl methacrylate is 5 to 45% by mass with respect to the toner amount. Preferably, by blending 10 to 40% by mass, it is possible to obtain a toner having good pulverization property, fixing property and storage property.

  When the molecular weight of the polylactic acid is less than 5,000, the storage stability and the fixing property are deteriorated, and when it exceeds 50,000, the grindability is deteriorated. Further, when the amount of polymethyl methacrylate is less than 5% by mass, the storage stability is deteriorated, and when it exceeds 45% by mass, the fixability and grindability are deteriorated.

  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 are a method of fermenting starch such as corn as a raw material, obtaining lactic acid, and then dehydrating and condensing directly from lactic acid monomer, and a method of synthesizing from lactic acid via cyclic dimer lactide and 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. .

  However, as the molecular weight of polylactic acid decreases, the glass transition point tends to decrease. A toner having a decreased glass transition point deteriorates durability and storage stability. In order to improve this, in this embodiment, by adding a polymethyl methacrylate resin, which is known to have high compatibility with polylactic acid, a toner having both pulverizability and storage stability is obtained.

  Polymethyl methacrylate resin is commercially available from Kuraray Co., Ltd., Mitsubishi Rayon Co., Ltd., Sumitomo Chemical Co., Ltd. and the like. There are various grades, but all have a high Tg (glass transition point) of about 90 to 120 ° C. By blending this with polylactic acid, the Tg of the binder resin is increased and the storage stability is improved. effective.

  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 release agents 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.

  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. 1 plots treatment time on the horizontal axis and molecular weight on the vertical axis, and FIG. 2 plots treatment time on the horizontal axis and 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) 80 parts by weight Polymethyl methacrylate (Parapet GF, manufactured by Kuraray Co., Ltd.) 10 parts by weight Colorant: Carbon black (MOGUL L manufactured by CABOT Co., Ltd.) 4 parts by weight Release Agent: Carnauba wax No. 1 powder (manufactured by Nippon Wax Co., Ltd.) 5 parts by mass Charge control agent: E-84 (manufactured by Orient Chemical Co., Ltd.) 1 part by mass It extended | stretched, cooled, and coarsely crushed with the Rotoplex (The Hosokawa Micron Corporation make, 2 mm screen). Thereafter, the mixture was pulverized and classified by an impact pulverizer / air classifier so that the average particle diameter of the toner became 9.0 μm, thereby obtaining fine particles.

  As an external additive, 2 parts by mass of “RY200” (manufactured by Nippon Aerosil Co., Ltd .: hydrophobic silica, primary particle size of 12 nm) is added to 100 parts by mass of the obtained fine particles, and a Henschel mixer (with stirring reinforcing wings, Mitsui) is added. (Mine Co., Ltd.) for 3 minutes with stirring to obtain a toner.

Examples 2-5, Comparative Examples 1-4
A toner was 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.

  The fogging, density stability, storage stability, fixability and grindability of the toners of Examples 1 to 5 and Comparative Examples 1 to 4 obtained as described above were tested and evaluated by the following test methods.

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 practical problem ×: Bad fog value of 10 or more Test 2—Concentration stability Using the same device as used in Test 1, a 5% printed image was obtained in a normal environment (25 ° C., 50% RH). 14,000 sheets were continuously printed. In the middle, an A4 solid image was printed every 2,000 sheets, the image density was measured at the four corners and the center, and the average density was determined (in this case, image defect portions due to white stripes and the like were not measured). Among the average concentrations determined at each sampling point, the concentration stability was determined from the maximum value and the minimum value according to the following equation and evaluated according to the following criteria.

Concentration stability (%) = Minimum average density / Maximum average density × 100
◎: Good when the density stability is 95% or more ○: Good when the density stability is 85% or more and less than 95% △: Level where the density stability is 75% or more and less than 85%, and there is no practical problem ×: The density stability is 75 Test 3-Storage stability 10 g of toner is placed in a glass beaker and left in a constant temperature and humidity chamber at 50 ° C. and 90% RH for 24 hours, and then the aggregation state of the toner is visually confirmed and evaluated as follows. Evaluated by 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 part 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 (weight 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 product in the pulverization / classification step, the determination is made based on the yield (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.

  As the binder resin, the electrophotographic toner according to Examples 1 to 5 containing polylactic acid having a molecular weight of 5,000 to 50,000 and polymethyl methacrylate in an amount of 5 to 45% by mass with respect to the toner amount, All of them show excellent results in all the characteristics of fogging, concentration stability, storage stability, fixability, and grindability.

  In contrast, the toner according to Comparative Example 1 in which the molecular weight of polylactic acid is more than 50,000 and 70,000 is excellent in density stability and storage stability, but inferior in fogging, fixing properties, and pulverizing properties. The toner according to Comparative Example 2 in which the binder resin does not contain polymethyl methacrylate is excellent in concentration stability, fixing property, and pulverization property, but is inferior in storage stability. In addition, the toner according to Comparative Example 3 in which the blending amount of polymethyl methacrylate exceeds 50% by mass is excellent in concentration stability and storage stability, but inferior in fogging, fixing property, and grindability. The toner according to Comparative Example 4 in which the molecular weight of polylactic acid is 3,000, which is less than 5,000, is excellent in pulverization property, but it is fogging, fixing property, concentration stability, storage property, and pulverization property. Is inferior.

Claims (2)

  The binder resin contains polylactic acid having a molecular weight of 5,000 to 50,000 and polymethyl methacrylate, and the blending amount of the polymethyl methacrylate is 5 to 45% by mass with respect to the toner amount. An electrophotographic toner characterized by the above.   2. The electrophotographic toner according to claim 1, wherein the polylactic acid has a molecular weight adjusted by hydrolysis treatment.

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