JPH08240924A - Production of electrophotographic toner - Google Patents

Abstract

PURPOSE: To obtain an electrophotographic toner not causing the problem of preservability and fixable at a low temp. by melting a crystalline material having a specified m.p., a bonding resin and a colorant by heating, kneading them and heat-treating the resultant kneaded material. CONSTITUTION: At least a bonding resin and a colorant are added to a crystalline material having 50-90 deg.C m.p., they are melted by heating and kneaded and the resultant kneaded material is heat-treated, pulverized and classified. The amt. of the crystalline material is preferably 3-30 pts.wt. per 100 pts.wt. of the bonding resin and the crystalline material is preferably hardened oil obtd. by hydrogenating triglyceride-based oil, natural wax or ester wax synthesized from fatty acid and alcohol. The objective toner having satisfactory preservability, not causing trouble such as blocking in practical use and fixable at a low temp. is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrophotographic toner for a copying machine or printer which employs heat roll fixing.

[0002]

2. Description of the Related Art In recent years, electrophotographic copying machines and printers have been widely used in general households and the like. (Reduction of power consumption), high speed for the purpose of spreading to so-called gray area located at the boundary between printing machine and copying machine, or low roll pressure for simplification of fixing roll to reduce machine cost. Is desired. In addition, copiers equipped with a double-sided copy function and an automatic document feeder have become widespread with the sophistication of copiers, and therefore the fixing temperature of electrophotographic toner used in copiers and printers is low and There is a demand for a sheet having excellent offset properties and excellent fixing strength on a transfer sheet in order to prevent stains during double-sided copying and stains in the automatic document feeder.

In response to the above requirements, attempts have been made so far to lower the fixing temperature by incorporating a crystalline substance such as natural wax into an electrophotographic toner to lower the melting start temperature of the toner itself. Conventionally, electrophotographic toners containing such crystalline substances have been manufactured by pulverizing and classifying after hot melt kneading. However, in such a conventional manufacturing method, the structure of the crystalline substance contained in the electrophotographic toner is changed by the hot melt kneading, and the melting point of the crystalline substance is the crystal before the hot melt kneading. The melting point of the electrophotographic material is lower than the melting point of the electrophotographic material, and the storage stability of the electrophotographic toner is deteriorated.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a manufacturing method capable of obtaining an electrophotographic toner capable of fixing at a low temperature without causing a problem of storability.

[0005]

The present invention has a melting point of 50 ° C.
At least a binder resin and a colorant are added to a crystalline substance having a temperature of 90 ° C. or higher, and the mixture is melted and kneaded to obtain a kneaded product. Then, the kneaded product is subjected to heat treatment, pulverized and classified. And a method for producing an electrophotographic toner.

The present invention will be described in detail below. The present invention is characterized in that a kneaded product obtained by hot melt kneading is subjected to a heat treatment during toner production. The reason why the kneaded product is subjected to heat treatment is that the crystallinity of the crystalline substance is changed by the hot melt kneading during the toner production, and the melting point is significantly lowered by 10 ° C. or more from the melting point before the kneading to deteriorate the storability of the toner. The purpose is to solve. The heat treatment, which is a feature of the present invention,
A predetermined time according to the heating temperature of the kneaded product after hot melt kneading,
It means to treat with heat. In this case, the predetermined time is not particularly limited, but when the heat temperature is 35 ° C., one day, 40
12 hours is appropriate for the temperature of 50 ° C., or 1 hour is appropriate for the temperature of 50 ° C., and the treatment may be performed until the crystal structure returns to the original state. Further, it is preferable to perform the treatment until the melting point of the toner after classification, that is, the peak temperature of the absorbed heat amount of DSC becomes 60 ° C. or higher. The temperature of heat for treating the kneaded material is preferably not less than the glass transition point of the kneaded material and not more than the melting point of the kneaded material because the melting point can be increased even if the heat treatment time is short and the melting point before the kneading can be easily returned. However, the object of the present invention can be achieved by treating the kneaded product at a temperature below the glass transition point for a long time. The temperature in the heat treatment may be such that the kneaded material is treated at a constant temperature, or may be changed by raising or lowering the temperature over time. Further, the kneaded product immediately after the hot melt kneading may be heat-treated, or the kneaded product once cooled after the hot melt kneading may be subjected to the heat treatment. Further, the heat treatment is preferably performed by applying heat to the kneaded product using a thermostatic bath capable of controlling the heat temperature, but the method is not limited as long as the heat can be applied to the kneaded product such as hot air treatment. . The hot melt kneading in the present invention may be performed by using a single screw extruder, a twin screw extruder, or the like, crushing may be performed by using a hammer mill, a cutter mill, a jet mill, or the like, and classification may be performed by using an airflow classifier or the like. Good.

The crystalline substance used in the present invention is added to lower the melting start temperature of the toner and to improve the low temperature fixability. The lower the melting point of the crystalline substance, the better the low-temperature fixability, but if the melting point is less than 50 ° C., the storage stability will deteriorate.
Further, if the melting point exceeds 90 ° C., the low-temperature fixability deteriorates, so that the range of the melting point is 50 ° C. or more and 90 ° C. or less. The melting point referred to here is the peak temperature of the amount of absorbed heat measured by DSC. The method of measuring the peak temperature of the absorbed heat quantity by DSC is carried out as follows. For example, differential scanning calorimeter SSC-5200 manufactured by Seiko Instruments Inc.
As a measurement condition, about 10 mg of a crystalline substance is weighed and placed on a DSC, and 50 ml of N 2 is added per minute.
Blow in ₂ gas. Then, the temperature of 20 to 150 ° C. is raised at a rate of 10 ° C. per minute, and the amount of absorbed heat at that time is measured. When a plurality of peaks are obtained, the peak temperature showing the maximum amount of absorbed heat is taken as the melting point. The crystalline substance in the present invention refers to a substance capable of clearly obtaining a peak temperature in the measurement of the amount of heat absorbed by DSC,
Specifically, hydrogenated oil obtained by hydrogenating an oil or fat containing triglyceride of fatty acid and glycerin as a main component, natural wax, ester wax synthesized from fatty acid and alcohol, fatty acid amide, ketone, olefin wax and the like can be exemplified. . Among these, hardened oils, natural waxes and ester waxes having particularly low melting points and excellent low-temperature fixability are preferably used in the present invention. The hydrogenated oil is a triglyceryl ester of an unsaturated fatty acid and glycerin, that is, a fat and oil containing glyceride as a main component, to which about 0.2% of a reduced nickel catalyst is added, and hydrogen is added at a reaction temperature of 150 to 160 ° C. and a reaction pressure of 15 kg / cm ^3. It is obtained by blowing in and stirring for about 3 hours. Various hardened oils can be obtained depending on the type of unsaturated fatty acid. Specific examples of the hardened oil include castor wax (castor hardened oil), rapeseed hardened oil, cottonseed hardened oil, olive hardened oil, and the like. Specific examples of the natural wax include rice wax and carnauba wax. Specific examples of the ester wax include monoester wax synthesized from long-chain linear saturated fatty acid and long-chain linear saturated alcohol, diester wax synthesized from polybasic acid and long-chain linear saturated alcohol, triester wax, Examples thereof include oligoester wax. Also,
As the binder resin used in the present invention, a styrene resin,
Polyacrylic acid ester resin, styrene-methacrylic acid ester copolymer resin, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, phenol resin, epoxy resin, polyester resin and the like can be mentioned, especially for the purpose of improving the fixing performance. The melting start temperature is preferably as low as possible. Further, as the colorant, carbon black, nigrosine dye, aniline blue, chalco oil blue,
Examples include chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, and mixtures thereof. It is necessary that these colorants be contained in a sufficient ratio so that a visible image having a sufficient image density is formed, and the ratio is usually about 1 to 20 parts by weight with respect to 100 parts by weight of the binder resin. Is preferred. Further, a charge control agent, waxes such as polypropylene and the like may be added to the electrophotographic toner of the present invention.

The melting start temperature of the electrophotographic toner obtained in the present invention is preferably 60 ° C. or higher and lower than 100 ° C. If it is higher than 100 ° C., the fixing property is not sufficient, and if it is lower than 60 ° C., the blocking property is deteriorated to cause a problem in storage stability. The melting start temperature refers to the temperature at which the plunger starts to fall. Measuring instrument; Shimadzu's advanced flow tester CF-500 Measuring condition: Plunger: 1 cm ² Die diameter: 1 mm Die length: 1 mm Load: 20 KgF Preheating temperature: 50-80 ° C Preheating time: 300 sec Temperature rising rate : 6 ° C / min

The electrophotographic toner obtained by the manufacturing method of the present invention is mixed with a carrier composed of ferrite powder, iron powder or the like to form a two-component developer. When a magnetic substance is contained, it may be used as it is as a one-component developer for developing an electrostatic image without mixing with a carrier, or may be mixed with a carrier and used as a two-component developer. Further, it can be applied to a non-magnetic one-component developing method.

[0010]

EXAMPLES The present invention will be described below based on examples. In the examples, “part” means “part by weight”. <Example 1> The above raw materials were mixed by a super mixer and kneaded by heat to obtain a kneaded product. Then, as a heat treatment, the kneaded product was left in a constant temperature bath at 50 ° C. for 24 hours and cooled to room temperature (about 25 ° C.). Then, after pulverization and classification, negatively chargeable toner base particles having an average particle diameter of 11 μm were obtained. Further, 0.3 part of hydrophobic silica (R-972 manufactured by Nippon Aerosil Co., Ltd.) was adhered to the surface of the toner base particles by a Henschel mixer to obtain an electrophotographic toner according to the present invention. The melting point of the kneaded product before the heat treatment was 52 ° C., but the melting point after the heat treatment was 65 ° C. <Example 2> An electrophotographic toner according to the present invention was prepared in the same manner as in Example 1 using the above raw materials. In this example, the melting point of the kneaded material before heat treatment was 53 ° C, but after the heat treatment, the melting point was 67 ° C.

<Example 3> 1 mol of tetradecanoic acid, 2 mol of heptadecane 1ol and 0.5 mol of sulfuric acid were placed in a round bottom flask equipped with a stirrer and a condenser, and the mixture was placed at 4 ° C at 130 ° C.
Heated to reflux for hours. After removing excess heptadecane 1-ol, the residue was purified with methyl ether to obtain a monoester wax having a melting point of 65 ° C. used in the present invention. An electrophotographic toner according to the present invention was prepared in the same manner as in Example 1 using the above raw materials. In this Example, the melting point of the kneaded product before heat treatment was 58 ° C, but after the heat treatment, the melting point was 63 ° C. <Example 4> An electrophotographic toner according to the present invention was prepared in the same manner as in Example 1 using the above raw materials. In this Example, the melting point of the kneaded product before the heat treatment was 56 ° C, but after the heat treatment, the melting point was 61 ° C.

<Example 5> An electrophotographic toner according to the present invention was prepared in the same manner as in Example 1 using the above raw materials. In this Example, the melting point of the kneaded material before heat treatment was 59 ° C, but after the heat treatment, the melting point was 69 ° C. <Example 6> An electrophotographic toner according to the present invention was prepared in the same manner as in Example 1 using the above raw materials. In this Example, the melting point of the kneaded product before the heat treatment was 79 ° C, but after the heat treatment, the melting point was 83 ° C. Comparative Example 1 A comparative electrophotographic toner was obtained in the same manner as in Example 1 except that the heat treatment step was omitted. The melting point of the kneaded product after hot melt kneading was 52 ° C. <Comparative Example 2> A comparative electrophotographic toner was obtained in the same manner as in Example 2 except that the rapeseed hydrogenated oil was removed from the raw material.

Next, the following items were tested for the electrophotographic toners obtained in the above Examples and Comparative Examples. (1) Storability After storing 20 g of a toner in a 150 cc bottle and leaving it in a constant temperature bath at 50 ° C. for 8 hours, the caking state of the toner was visually confirmed to evaluate the storability. The judgment conditions are shown below. ○: No problem ×: Toner blocks and does not collapse even when shaken

(2) Non-offset temperature region 4 parts of each of the electrophotographic toners obtained in the above-mentioned Examples and Comparative Examples and 96 parts of a ferrite carrier (product name: FL-1020 manufactured by Powdertech Co., Ltd.) not coated with a resin. Were mixed to prepare a two-component developer. Next, a commercially available copying machine (trade name: SF-980, manufactured by Sharp Corporation) is used using the developer.
In 0), a plurality of belt-shaped unfixed images having a length of 2 cm and a width of 5 cm were formed on an A4 transfer paper. Next, a heat fixing roll having a surface layer made of Teflon and a pressure fixing roll having a surface layer made of silicone rubber are paired and rotated, and a fixing device is rotated at a roll pressure of 1 Kg / cm ² and a roll speed of 50 mm.
/ Sec, and the surface temperature of the heat fixing roll was changed stepwise to fix the toner image on the transfer paper on which the unfixed image was formed at each surface temperature. At this time, it was observed whether or not the toner was smeared in the blank area, and the temperature region in which the toner was not smeared was set as the non-offset temperature region. Further, the difference between the maximum value and the minimum value in the non-offset temperature region was defined as the non-offset temperature width.

(3) Fixing Strength The surface temperature of the heat fixing roll of the fixing device was set to 140 ° C., and the toner image on the transfer paper on which the unfixed image was formed was fixed. Then, the formed fixed image was rubbed with a cotton pad, and the fixing strength was calculated by the following formula to be used as an index of low energy fixing property. As the image density, a reflection densitometer RD-914 manufactured by Macbeth was used. Fixing strength (%) = image density of fixed image after rubbing / image density of fixed image before rubbing × 100 The test results of the above items are shown in Table 1.

[0016]

[Table 1]

From the results shown in Table 1 above, the electrophotographic toner according to the manufacturing method of the present invention has practically no problem in storability and has a non-offset temperature range of 60 to 70 ° C.
And the fixing strength was 90% or more when the fixing temperature was 140 ° C., and good low temperature fixing characteristics were exhibited. However, in Comparative Example 1, there is a problem in storability, and in Comparative Example 2, the fixing strength is 60%.
It was bad and there was a problem in practical use.

[0018]

According to the manufacturing method of the present invention, it is possible to provide an electrophotographic toner which has good storage stability and can be fixed at a low temperature without causing problems such as blocking in practical use.

Claims (6)

[Claims] 1. A crystalline substance having a melting point of 50 ° C. or higher and 90 ° C. or lower is added with at least a binder resin and a colorant, and the mixture is heat-melt kneaded to obtain a kneaded product, which is then heat-treated. A method for producing a toner for electrophotography, which comprises pulverizing and classifying. 2. The method for producing an electrophotographic toner according to claim 1, wherein the content of the crystalline substance is 3 parts by weight or more and 30 parts by weight or less based on 100 parts by weight of the binder resin. 3. The method for producing an electrophotographic toner according to claim 1, wherein the crystalline substance is a hardened oil obtained by hydrogenating an oil or fat containing triglyceride as a main component. 4. The method for producing an electrophotographic toner according to claim 1, wherein the crystalline substance is a natural wax. 5. The method for producing an electrophotographic toner according to claim 1, wherein the crystalline substance is an ester wax synthesized from a fatty acid and an alcohol. 6. The method for producing an electrophotographic toner according to claim 1, wherein the temperature in the heat treatment is not less than the glass transition point of the kneaded product and not more than the melting point of the kneaded product.