JP2010169764A - Electrophotographic toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic toner containing a biodegradable resin as a binder resin, having favorable pulverizing property and fixing property and excellent density stability and durability. <P>SOLUTION: The electrophotographic toner contains an amorphous polylactic acid as a binder resin and has a D-lactic acid concentration of 10 to 40 mol% in the binder resin. <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 circumstances as described above, and provides an electrophotographic toner that includes a biodegradable resin as a binder resin, provides good pulverization and fixing properties, and has excellent density stability and durability. The purpose is to do.

  In order to solve the above problems, one embodiment of the present invention includes an amorphous polylactic acid as a binder resin, and the concentration of D-lactic acid in the binder resin is 10 to 40 mol%. Provide photographic toner.

  In such an electrophotographic toner, amorphous polylactic acid and crystalline polylactic acid can be contained as the binder resin. In this case, the amount of the amorphous polylactic acid in the binder resin can be set such that the D-lactic acid concentration in the binder resin is 10 to 40 mol%.

  According to the present invention, there is provided an electrophotographic toner that includes a biodegradable resin as a binder resin, provides good pulverization properties and fixing properties, and is excellent in density stability and durability.

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

  The electrophotographic toner according to an embodiment of the present invention includes amorphous polylactic acid as a binder resin, and a D-lactic acid concentration in the binder resin is 10 to 40 mol%.

  In this specification, the amorphous polylactic acid refers to polylactic acid having a D-lactic acid concentration of 10 mol% or more or an L-lactic acid concentration of less than 90 mol%.

  When the binder resin does not contain amorphous polylactic acid, that is, when only crystalline polylactic acid is contained as the polylactic acid, the pulverizability when pulverizing the kneaded material containing the binder resin is poor, and the toner Is difficult to form.

  In addition, when the D-lactic acid concentration in the binder resin is less than 10 mol%, naturally, there is no amorphous polylactic acid in the binder resin, and the kneaded material containing the binder resin is pulverized. The grindability is poor and it is difficult to form a toner.

  On the other hand, when the concentration of D-lactic acid in the binder resin exceeds 40 mol%, the durability and fixability of the toner deteriorate.

  The polylactic acid contained in the binder resin does not have to be all amorphous polylactic acid, and may contain both amorphous and crystalline polylactic acid. In this case, the ratio of the amorphous polylactic acid to the crystalline polylactic acid is such that the D-lactic acid concentration in the binder resin is 10 to 40 mol%, and thus, good crushability and durability. And fixing ability can be obtained.

  The polylactic acid resin is a resin having the following structural formula.

(OCH (CH ₃ ) CO) _n
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.

  The method for producing polylactic acid used in the present invention is not particularly limited, and a conventionally known method can be used. For example, fermenting starch such as corn as a raw material to obtain lactic acid, then dehydrating and condensing directly from lactic acid monomer, or synthesizing from lactic acid via cyclic dimer lactide and synthesizing by ring-opening polymerization in the presence of a catalyst There is.

  Here, there are optical isomers in lactic acid, and there are L-lactic acid and D-lactic acid, and L-lactic acid is industrially used. Recently, the industrialization of D-lactic acid production has been promoted. It has been.

  In the amorphous polylactic acid used in the present invention, the constituent molar ratio of L-lactic acid units and D-lactic acid units is important, and L-lactic acid is less than 90 mol%, and is amorphous without crystallinity. It is a feature. As a method of adjusting the L-lactic acid concentration, there are a method of blending at the time of the monomer and a method of adjusting with a polymerized product, and any method may be used.

  Considering environmental issues and considering replacing the general-purpose resin with polylactic acid, increasing the molecular weight of polylactic acid and further increasing the optical purity of lactic acid increases the crystallinity and improves heat resistance and impact resistance. Usually improvements are made. On the other hand, when considering the application of polylactic acid to a toner binder resin, the present inventors do not need heat resistance and impact resistance unlike general-purpose resins, but rather have a low molecular weight and optical properties. It has been found that an amorphous resin having a low purity has a lower melt viscosity, is easily pulverized, and further has good dispersibility of the material, and is suitable as a binder resin for toner.

  One example of such a commercial product of amorphous polylactic acid is Viro Ecole (trade name, manufactured by Toyobo Co., Ltd.). Viro Ecole is an amorphous polylactic acid resin whose D-lactic acid concentration is increased to about 20 mol%, and is characterized by being easily dissolved in a general-purpose solvent as compared with crystalline polylactic acid. It is used as a resin for paints such as lactic acid film and as an adhesive.

Depending on the grade, Viro Ecole has a number average molecular weight of about 50,000 and a molecular weight lower than that of conventional polylactic acid. Therefore, it has sufficient grindability as a binder resin for toner.

  Viro Ecole also has a high D-lactic acid concentration and is amorphous, so it has a low melt viscosity and a softening point of about 110 ° C., which is optimal as a binder resin for toner. In addition, the dispersibility of the material is excellent as compared with crystalline polylactic acid.

  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, a binder resin containing amorphous polylactic acid, a colorant, and, if necessary, a raw material containing other additives are mixed and then kneaded in a kneader such as a biaxial kneader, a pressure kneader, or an open roll. A kneaded product is obtained. 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. The following 6 types were prepared as polylactic acid used in Examples and Comparative Examples.

In addition, polylactic acid resins other than commercially available products are ring-opening polymerization using a mixture of L-form lactide and D-form lactide as a monomer at a predetermined ratio and 2-ethylhexane tin as a catalyst so as to have a predetermined molecular weight. Was obtained.

Polylactic acid resin commercial product A: REVODE101B manufactured by Kaisho Biological Co., Ltd.
Polylactic acid resin commercial product B: Toyobo Co., Ltd. Bailo Ecole BE-400.

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.

90 parts by weight of polylactic acid 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 weight Charge control agent: E- 84 (manufactured by Orient Chemical Co., Ltd.) 1 part by mass The mixed powder was melted and kneaded with a pressure kneader, then stretched, cooled, and coarsely crushed with a rotoplex (manufactured by Hosokawa Micron Co., Ltd., 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 1-3
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 fog, density stability, durability, fixability, and grindability of the toners of Examples 1 to 5 and Comparative Examples 1 to 3 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 problem in practical use ×: A fog value of 10 or more is bad.

Test 2-Concentration stability Using the same apparatus as used in Test 1, 14,000 sheets of 5% print images were continuously printed in a normal environment (25 ° C., 50% RH). 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
A: Good when the density stability is 95% or more. B: Good when the density stability is 85% or more and less than 95%. Less than% is bad.

Test 3-Durability Using the same apparatus as used in Test 1, 16,000 sheets of 5% print images were continuously printed in a normal environment (25 ° C, 50% RH). In the middle, solid images and halftone images were printed every 2,000 sheets, and the number of white stripes generated by blade fusion was evaluated.

◎: Not generated up to 16,000 sheets ○: Generated after 14,000 sheets and less than 16,000 sheets (practically acceptable level)
Δ: Generated after 12,000 sheets and less than 14,000 sheets x: Generated when less than 12,000 sheets.

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 3 below.

  From Table 3 above, the following is clear.

  Each of the electrophotographic toners according to Examples 1 to 5 containing amorphous polylactic acid as the binder resin and having a D-lactic acid concentration of 10 to 40 mol% in the binder resin is fogging and concentration stable. Excellent results were obtained in all the properties of durability, durability, fixability and grindability.

  In particular, the toners according to Examples 1, 2, and 5 using only amorphous polylactic acid as the binder resin showed excellent results in terms of fogging, density stability, and fixability.

  On the other hand, the toner according to Comparative Example 1 which does not contain amorphous polylactic acid and uses only crystalline polylactic acid as a binder resin is difficult to grind and abandoned as a toner. Further, in the toner according to Comparative Example 2, since the D-lactic acid concentration in the binder resin was 50 mol% and exceeded 40 mol%, durability and fixability were deteriorated. The toner according to Comparative Example 3 used polylactic acid with a reduced molecular weight. However, since it was crystalline polylactic acid, the fixability was insufficient.

Claims (3)

  An electrophotographic toner comprising amorphous polylactic acid as a binder resin, wherein the D-lactic acid concentration in the binder resin is 10 to 40 mol%.   2. The electrophotographic toner according to claim 1, wherein the binder resin contains amorphous polylactic acid and crystalline polylactic acid.   2. The electrophotographic image according to claim 1, wherein the amount of the amorphous polylactic acid in the binder resin is an amount such that the D-lactic acid concentration in the binder resin is 10 to 40 mol%. Toner.