JPS6239427B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic powder toner used for developing electrical latent images in electrophotography, and more specifically, it improves the durability of the developer by several orders of magnitude and is suitable for electrophotographic copying of a large number of sheets. An object of the present invention is to provide a toner composition for electrophotography, which can provide copies with high density and no background fog. Conventionally, various electrophotographic methods have been published in patent specifications such as US Pat. No. 2,297,691, other technical documents, magazines, and the like. Electrophotography is usually
Selenium, zinc oxide, vinyl carbazole compounds,
A photoconductive material such as cadmium sulfide is used as a photoreceptor, an electrical latent image is formed on the photoreceptor by various means, and toner is attached to this latent image by methods such as cascade and magnetic brush development methods to make it visible. This is done by converting the toner image into an image, transferring the toner image to paper, a sheet, etc., and then fixing it using heat, solvent, pressure, etc. The most important thing in such electrophotography is the quality of the final image.
In other words, the most desired characteristics are mainly excellent image contrast, such as high image density, little background fog, and little edge effect, and also good characteristics such as fine line resolution, sharpness, and transferability. is desired next. Therefore, the two points of greatest interest to the engineer are image contrast and maintenance of the characteristics during copying of a large number of sheets, that is, developer durability. By the way, although various toners with excellent image contrast have been studied, toners that also provide excellent developer durability have not yet been proposed. The factors that promote such deterioration of developer durability can be broadly classified into the following two points. That is, firstly, this is due to a change in the polarity of frictional charging due to the adhesion of toner components onto the surface of developer carrier particles, a phenomenon commonly referred to as generation of spent toner. This phenomenon is affected not only by the surface condition of the carrier particles but also by the properties of the toner binding resin. This is due to the abrasiveness when mechanical external pressure is repeatedly applied, the blocking property when the temperature of the developer increases due to stirring and the copying machine itself, and the properties of the binder resin, such as the amount of low molecular weight substances mixed in. becomes a problem. Therefore, in order to suppress the amount of spent toner generated as low as possible, it is necessary to select a suitable binder resin that has high abrasion resistance, a sharp melting point, good blocking properties, and does not contain low molecular weight substances. There is. The second cause of accelerated deterioration of the developer is a change in the amount of charge caused by agitation of the developer due to repeated use of a copying machine. Of course, the amount of charge changes as the polarity of frictional charging changes due to the generation of spent toner, but even when there is virtually no generation of spent toner, the amount of charge changes when copying a large number of sheets. is becoming clear. This variation in the amount of charge is an undesirable phenomenon in actual copying. In other words, if the amount of charge tends to increase when a large number of copies are made, the image density of the copies will gradually decrease, and a measure must be taken to increase the ratio of toner to developer. However, if toner is replenished to a specific toner density such that the toner completely covers the surface of the carrier particles and there is excess free toner, a severe fogging phenomenon will occur in the background of the copy and the density contrast will deteriorate. I'll let you. on the other hand,
If the amount of charge tends to decrease when a large number of copies are made, the image density of the copy will increase, but the fog on the white background will gradually increase when a large number of copies are made, and in the end only a very unsightly image will be obtained. Moreover, toner scattering from the developer increases, resulting in the undesirable result of contaminating the inside of the copying machine. If a measure is taken to reduce the specific toner density of the developer to prevent these phenomena, the image density will decrease and the carrier particles will migrate to the photoreceptor surface, resulting in a black solid image on the copy. This causes a phenomenon of partial transfer failure called white spots on the copying machine, and also causes the inconvenience of carrier particles scattering inside the copying machine. An object of the present invention is to provide an electrophotographic toner which does not have the above-mentioned drawbacks in copying a large number of sheets, that is, the toner in the developer has a stable charge amount. Another object of the present invention is that the toner replenished when copying a large number of sheets can withstand mechanical external pressure such as shearing and impact, has sufficient abrasion resistance, and therefore produces less spent toner, and furthermore, It is an object of the present invention to provide an electrophotographic toner which can be quickly charged by contacting carrier particles and can have a predetermined charge amount value. As a result of intensive research, the present inventors found that the dibasic acid component
At least 60 mol% of the glycol component is obtained from terephthalic acid or its ester and at least 60 mol% of the glycol component is 2,2-dimethyl-1,3-propanediol, acid value 3 to 13 mgKOH/g, softening point 55 by ring and ball method.
The present invention has been completed by discovering that the above object can be achieved by blending a polyester resin with a number average molecular weight of 2,000 to 12,000 at a temperature of ~160°C in an amount of 60% by weight or more of the total binder resin of the toner. That is, the present invention consists of 1 to 25 parts by weight (hereinafter abbreviated as "parts") of a colorant, 75 to 99 parts of a binder resin, and an auxiliary agent added as necessary, and at least 60 parts of the binder resin. is a polyester resin with an acid value of 3 to 13 mgKOH/g obtained from 60 mol% or more of terephthalic acid as a dibasic acid component and 60 mol% or more of 2,2-dimethyl-1,3-propanediol as a glycol component. An object of the present invention is to provide an electrophotographic toner composition characterized by the following. It has been known that certain polyester resins having appropriate softening points and molecular weights are useful in electrophotographic toners, particularly negatively charged toners. Such resins have been proposed in patent specifications and other literature. However, the toner composition for electrophotography using the polyester resin of the present invention is superior to any of the conventional toner compositions in terms of generation of a small amount of spent toner when copying a large number of sheets and stable charge amount. In order to reduce the occurrence of spent toner, the binder resin must have high shear resistance, impact resistance, and abrasion resistance, be able to be crushed into particles with a particle size of approximately 5 to 20 μm during toner manufacturing, and be crushed during fixing. It is necessary to melt sharply at relatively low temperatures. The polyester resin of the present invention satisfies these conditions and generates little spent toner.
This originates from the fact that the main component is 1,3-propanediol. It is presumed that the linearity of the polymer due to terephthalic acid and the symmetrical glycol and the reduction in crystallinity due to the effects of the side chain methyl groups provide excellent mechanical strength and appropriate friability and meltability. From the above point of view, a polyester resin obtained by using 100 mol% of terephthalic acid as the dibasic acid component and 100 mol% of 2,2-dimethyl-1,3-propanediol as the glycol component is most preferable, but the amounts of each are approximately small. If both amounts are 60 mol%, a practically preferable polyester resin can be obtained. Examples of acid components other than terephthalic acid include phthalic acid,
Isophthalic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, diphenyl-m,
Examples include m-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, etc.
Depending on the case, various monobasic acids such as benzoic acid and acetic acid can also be used in combination. Examples of alcohol components other than 2,2-dimethyl-1,3-propanediol include ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,5-pentanediol, and 2,2,4-trimethyl. -1,
3-pentanediol, 2,2-bis-(4-cyclohexanol)propane, cyclohexanedimethanol, P-dihydroxymethylbenzene,
Examples include glycols such as 2,2'-bis(4-hydroxypropoxyphenyl)propane, and in some cases various monohydric alcohols such as cyclohexanol and benzyl alcohol may also be used in combination. Such acids and alcohols have a polyester resin acid value of 3 to 13 mgKOH/g and a ring and ball softening point of 55 to 160°C.
It is used within the range that does not damage. The polyester resin in the present invention has an acid value of 3 to 13 mg.
KOH/g, preferably 5 to 11 mgKOH/g, and this acid value is an extremely important factor as a constituent factor of the binding polyester resin regarding developer durability. That is, toners using polyester resins with an acid value lower than 3 mgKOH/g as a binder resin component have poor triboelectric charging properties with carrier particles, and despite this, the developer is repeatedly used when using a copying machine. The amount of charge increases temporarily due to stirring,
Eventually, the amount of charge reaches several times the value initially set as the optimum amount of charge. As a result, the image density decreases, and if toner replenishment is increased in an attempt to prevent this, a problem arises in that a large amount of fogging occurs in the white background area. On the other hand, toners using polyester resins with an acid value exceeding 13 as the binder resin component have good triboelectric charging properties with carrier particles;
Due to repeated agitation of the developer, the amount of charge decreases for a while, and eventually drops to a fraction of the value initially set as the optimum amount of charge. As a result, a large amount of fogging occurs in the white background area, and the inside of the copying machine is contaminated by toner scattering from the developer. If toner supply is reduced in order to prevent this, the image density will decrease and white spots will occur in the solid black areas of the copy. However, when a polyester resin consisting of a specific component and an acid value as in the present invention is used as a binder resin component in a toner, the amount of charge even after copying a large number of sheets remains the same as the amount of charge of the initially prepared developer. In comparison, a constant level of image density is always obtained with almost no change, and a copy with almost no fog in the white background area can be obtained. In addition, the polyester resin used in the present invention usually has a softening point of 55 to 160 according to the ring and ball method (ASTM E-28).
℃, preferably 80-130℃, number average molecular weight 2000
~12000, preferably 4000-12000,
The molecular weight has an effect on friability, and the softening point has an effect on reducing the generation of spent toner. It is preferable that the polyester resin according to the present invention accounts for all of the binder resin, but if necessary, it may be reduced to about 60 parts out of 75 to 99 parts of the binder resin, that is, 15 to 39 parts. Can be other resins. Resins other than polyester resins can be those normally used in electrophotographic toners, specifically polystyrene,
Examples include styrene-acrylic resin, alkyd resin, epoxy resin, phenol resin, polyvinyl chloride, polyvinyl acetate, coumaron-indene resin, and the like. The colorant used in the present invention is normally used in electrophotographic toners, and one or more of carbon black, organic pigments, inorganic pigments, and dyes are used, and the amount thereof is determined according to the toner composition. 1 to 25 copies. However, it is not preferable to use strong polar dyes that reverse the toner polarity, such as nigrosine dyes and methylene blue chloride. When used in the toner for electrophotography according to the present invention, it is used together with carrier particles, and the carrier particles at that time become positive polarity by frictional charging operation with the above-mentioned toner, and have a particle size of 10 to 5000 microns, preferably 50 to 150 microns.
Micron ones are usually used. The ratio of the carrier particles to the toner is such that the weight ratio of the carrier particles to the toner is 5 to 250 times, preferably 10 to 100 times.
It's double. Such carrier particles can usually be those produced by electrophotography, such as iron oxide powder,
Examples include reduced iron powder, carbonyl iron powder, glass beads, and inorganic salts, but it is not preferable to use carrier particles that reverse the toner polarity, such as Teflon-coated carriers. Next, the present invention will be specifically explained using examples. Example 1 Terephthalic acid was placed in a four-necked flask equipped with a stirring bar, condenser, inert gas inlet tube, and thermometer.
Add 166 g of 2,2-dimethyl-1,3-propanediol, 208 g of dibutyltin oxide, and 0.1 g of sodium acetate, and react with stirring at 200 to 220°C while blowing nitrogen gas to obtain an acid value of 3 mg.
Terephthalic acid is added when it becomes below KOH/g.
130g was added, the temperature was raised to 240-260℃ and the reaction was carried out to give an acid value of 5.1mgKOH/g and a hydroxyl value of 17.3mg.
A polyester resin having KOH/g, a softening point of 119°C, and a number average molecular weight of 5100 was obtained. 10 parts of carbon black (Morgan A, manufactured by CABOT Co., Ltd.) was blended with 90 parts of the resin, melted and kneaded at 140°C, cooled and solidified, and then finely pulverized with a jet mill to form a powder toner for electrophotography with an average particle size of 10 microns. A) was obtained. Example 2 Using the same equipment as in Example 1, terephthalic acid 265
g, 218 g of 2,2-dimethyl-1,3-propanediol, 1.5 g of dibutyltin oxide, and 0.1 g of sodium acetate, and while blowing nitrogen gas.
Reacted at 200-240℃ with stirring to give an acid value of 10mg.
When the level is below KOH/g, add 40g of maleic acid.
was added and the reaction continued until the acid value was 10.3mgKOH/g.
A polyester resin having a hydroxyl value of 10.1 mgKOH/g, a softening point of 103° C., and a number average molecular weight of 5,600 was obtained. Toner (B) was obtained in the same manner as in Example 1 using this resin. Comparative Example 1 Using the same equipment as in Example 1, terephthalic acid 332
After adding 312 g of 2,2-dimethyl-1,3-propanediol and 2 g of dibutyltin oxide and stirring at 200 to 220°C while blowing nitrogen gas, the acid value reached about 30 mgKOH/g. Gradually reduce the pressure in the flask and proceed with the reaction while distilling the glycol to obtain an acid value of 0.8mgKOH/g and a hydroxyl value of 23.8mg.
A polyester resin having KOH/g, a softening point of 117° C., and a number average molecular weight of 4,600 was obtained. Toner (A) was obtained in the same manner as in Example 1 using this resin. Comparative Example 2 18 g of phthalic anhydride was added to 300 g of the polyester resin obtained in Comparative Example 1 and reacted at 210°C for 2 hours to give an acid value of 19.8 mgKOH/g and a hydroxyl value of 4.3 mgKOH/
A polyester resin having a softening point of 118° C. and a number average molecular weight of 4,700 was obtained. A toner (b) was obtained in the same manner as in Example 1 using this resin. Example 3 9 g of phthalic anhydride was added to 300 g of the polyester resin obtained in Comparative Example 1, and the mixture was reacted at 210°C for 2 hours to give an acid value of 9.4 mgKOH/g and a hydroxyl value of 14.2 mgKOH/g.
A polyester resin having a softening agent of 118° C. and a number average molecular weight of 4,700 was obtained. Toner (C) was obtained in the same manner as in Example 1 using this resin. Example 4 Using the same apparatus as in Example 1, 388 g of dimethyl terephthalate, 312 g of 2,2-dimethyl-1,3-propanediol, and 1.5 g of lead oxide were added, and a transesterification reaction was carried out while introducing nitrogen gas. . After about 95% of the theoretical amount of methanol has been distilled off, the pressure in the flask is reduced and the deglycol condensation reaction is carried out at 220°C. When the softening point of the polyester resin reaches 110°C, 6 g of maleic anhydride is added and the temperature is kept constant. pressure,
After reacting at 210℃ for 2 hours, the acid value was 6.4mgKOH/
A polyester resin having a hydroxyl value of 19.4 mgKOH/g, a softening point of 112° C., and a number average molecular weight of 4,300 was obtained. Toner (D) was obtained in the same manner as in Example 1 using this resin. Example 5 In Example 4, the glycol component was changed to 270 g of 2,2-dimethyl-1,3-propanediol, 2,
2'-bis[4-hydroxypropoxy (3 mol)
Phenyl] Acid value 5.8mg instead of 160g propane
KOH/g, hydroxyl value 17.4mgKOH/g, softening point 108
A polyester resin having a number average molecular weight of 4800 was obtained. Toner (E) was obtained in the same manner as in Example 1 using this resin. Comparative Example 3 Using the same equipment as in Example 1, 388 g of dimethyl terephthalate, 228 g of 1,2-propylene glycol
g and 1.2 g of lead oxide were added, and a transesterification reaction was carried out while introducing nitrogen gas. After about 95% of the theoretical amount of methanol was distilled off, the flask was depressurized and heated to 220 methanol.
The deglycol reaction was carried out at 110°C, and the reaction was terminated when the softening point reached 110°C. Acid value 0.4mgKOH/
A polyester resin having a hydroxyl value of 22.4 mgKOH/g, a softening point of 110° C., and a number average molecular weight of 4,900 was obtained.
Using this resin, toner (c) was prepared in the same manner as in Example 1.
I got it. Comparative Example 4 9 g of phthalic anhydride was added to 300 g of the polyester resin obtained in Comparative Example 3 and reacted in the same manner as in Example 3 to obtain an acid value of 10.4 mg KOH/g and a hydroxyl value of 11.8 mg.
A polyester resin having KOH/g, a softening point of 112° C., and a number average molecular weight of 5,000 was obtained. Toner (d) was obtained in the same manner as in Example 1 using this resin. Comparative Example 5 Using the same equipment as in Example 1, phthalic anhydride 296
g, 156 g of 2,2-dimethyl-1,3-propanediol, and 144 g of 2,2-bis(4-cyclohexanol)propane were added and reacted at 200 to 210°C to obtain an acid value of 10.9 mgKOH/g and a hydroxyl value of 15.6. mg
A polyester resin having KOH/g, a softening point of 115° C., and a number average molecular weight of 4,200 was obtained. A toner (e) was obtained in the same manner as in Example 1 using this resin. Example 6 60 parts of the polyester resin obtained in Example 2, polystyrene (manufactured by Etsuo Petrochemical Co., Ltd.: Picolastic)
Toner (F) was obtained in the same manner as in Example 1 using 30 parts of E125) and 10 parts of carbon black (Morgan A, manufactured by Caboto). Example 7 3 g of phthalic anhydride was added to 300 g of the polyester resin obtained in Comparative Example 1 and reacted for 2 hours to obtain an acid value of 3.7 mgKOH/g, a hydroxyl value of 20.3 mgKOH/g,
A toner (G) was obtained in the same manner as in Example 1 using a polyester resin having a softening point of 118°C and a number average molecular weight of 4650. Example 8 10g of phthalic anhydride was added to the polyester resin obtained in Example 7 and reacted to give an acid value of 12.1mgKOH/
A polyester resin having a hydroxyl value of 11.3 mgKOH/g, a softening point of 119° C., and a number average molecular weight of 4,800 was obtained. Toner (H) was obtained in the same manner as in Example 1 using this polyester resin. Application Example A developer was prepared by blending 100 parts of surface oxidized iron powder with a particle size of 100 to 250 mesh to 3 parts of each toner of Examples and Comparative Examples. Various characteristics of the developer were tested using a commercially available electronic copying machine that uses a selenium drum as a photoreceptor. The results are shown in the table below.

【table】

[Table] As is clear from the above table, the developer using the toner of the example based on the present invention generated less spent toner even when copying 20,000 sheets, and exhibited a stable charge amount. No increase or decrease in image density or increase in background smudge was observed. On the other hand, the developers using the toners of Comparative Examples 1 and 2 produced a small amount of spent toner, but the change in the amount of charge was large;
In particular, the image density was significantly reduced when using the toner of Comparative Example 1, and the background smudge was significantly increased when using the toner of Comparative Example 2. In addition, the developers obtained using the toners of Comparative Examples 3 to 5 had a large amount of spent toner, and in all cases, the image density decreased and a large amount of background smear occurred, resulting in extremely unsightly images.

Claims (1)

[Scope of Claims] 1 Consists of 1 to 25 parts by weight of a coloring agent, 75 to 99 parts by weight of a binder resin, and an auxiliary agent added as necessary, and at least 60 parts by weight of the binder resin is dibasic. 60 mol% or more of terephthalic acid as an acid component and 60 mol% or more of 2,2-dimethyl-1 as a glycol component.
Acid value 3-13 obtained from 3-propanediol
An electrophotographic toner composition characterized in that it is a polyester resin of mg·KOH/g. 2 Polyester resin has a softening point of 55~ by ring and ball method.
2. The electrophotographic toner composition according to claim 1, wherein the electrophotographic toner composition has a temperature of 160° C. and a number average molecular weight of 2,000 to 12,000.