Purple developing toner with reversible thermochromic properties and preparation method thereof

Abstract

The present invention discloses a purple developing toner with reversible thermochromic properties and a preparation method thereof. The toner is made of the following raw materials in parts by weight: 80-90 parts of styrene-acrylic acid copolymer, 4-6 parts of polypropylene wax, 2-4 parts of thermochromic material, 1-3 parts of charge control agent, 2-4 parts of fumed silica, and 1-3 parts of titanium dioxide; the above materials are sequentially subjected to high-speed mixing, mixing, cooling, coarse grinding, airflow crushing classification, micro powder classification, pre-external additive mixing, spheroidization treatment, post-external additive mixing, sieving, and packaging to prepare a toner product. The present invention imparts a thermochromic effect to the toner, showing purple at room temperature and red under a heat source, realizing the anti-counterfeiting function of a printing toner based on the toner, and the printed text can be changed in color by a certain heat source. After removing the heat source for a period of time, the color can be restored; the thermochromic effect is reversible.

Description

Technical Field

[0001] The invention relates to a purple developing toner with reversible thermochromic properties, belonging to the technical field of developers for printers or copiers. Background Art

[0002] With the increasing volume and demand for information processing, high-speed and color-enhanced electrostatic copying and printing have become a trend. Color toners are required to have uniform, pure color, no color cast, and a relatively small particle size to meet high-resolution requirements. The pursuit of personalized printing, coupled with functional demands for vibrant color change, anti-counterfeiting features, and the ability to track environmental changes, is driving increasing technical demands for functional color toners. However, ensuring that the printed substrate does not affect the reversible color change properties is a challenging issue in developer manufacturing. Summary of the Invention

[0003] The present invention aims to provide a developer toner with reversible thermochromic properties. By adding a thermochromic material to the developer toner matrix, the printing toner is endowed with thermochromic properties, and the color change effect is reversible. The present invention also provides a method for preparing the developer toner with reversible thermochromic properties.

[0004] The present invention has a reversible thermochromic toner using the following technical solution: a purple toner with reversible thermochromic properties, which is made of the following raw materials in parts by weight: 80-90 parts of styrene-acrylic acid copolymer, 4-6 parts of polypropylene wax, 2-4 parts of thermochromic material, 1-3 parts of charge control agent, 2-4 parts of fumed silica, and 1-3 parts of titanium dioxide. The thermochromic material uses a YNbO4 matrix and uses Bi 3+ -Eu 3+ The charge control agent is niobium carbide having a Mxene structure.

[0005] In the thermochromic material, the molar ratio of Bi, Eu and Y is 1:1:10.

[0006] Bi was doped into YNbO4 matrix by hydrothermal method with soluble Bi salt and soluble Eu salt. 3+ -Eu 3+ .

[0007] The preparation method of the developer toner with reversible thermochromic properties of the present invention adopts the following technical scheme: A preparation method of a purple developer toner with reversible thermochromic properties, comprising the following steps: (1) preparing materials according to the following weight parts: 80-90 parts of styrene-acrylic acid copolymer, 4-6 parts of polypropylene wax, 2-4 parts of thermochromic material, 1-3 parts of charge control agent, 2-4 parts of fumed silica, and 1-3 parts of titanium dioxide; the thermochromic material adopts YNbO4 as the matrix, and adopts Bi 3+ -Eu 3+ doping; the charge control agent is niobium carbide with a Mxene structure; (2) premixing: the above-mentioned measured materials, styrene-acrylic acid copolymer, polypropylene wax, thermochromic material, and charge control agent are put into a mixer for premixing; (3) mixing: the above-mentioned premixed materials are mixed by a continuous mixer; (4) cooling: the extruded material after mixing in the mixer is cooled by a cooling water-cooled steel belt and crushed into flake materials; (5) coarse grinding: the flake materials are put into a coarse grinder for grinding; (6) air flow grinding and classification: the coarse grinding is carried out. The good materials are placed in the air flow milling and classifying machine for pulverization; (7) Micro powder classification: the air flow milled materials are classified and the unqualified small particles are removed; (8) Spheroidization treatment: the pre-added mixed materials are subjected to surface spheroidization treatment by a micro powder surface modification treatment machine; (9) External addition mixing: the spheroidized materials are put into a high-speed mixer together with the external additives of fumed silica and titanium dioxide for mixing; (10) Screening: the mixed materials are screened using a vibrating screen; (11) Packaging: the screened materials are packaged according to the specified specifications.

[0008] Between steps (7) and (8), a pre-addition mixing step is performed. The classified material and the external additive fumed silica are put into a mixer for mixing. The fumed silica in the pre-addition mixing step is 0-1 parts, and the fumed silica in the external addition mixing step is 2-3 parts.

[0009] The mixing in the pre-mixing, pre-addition mixing and external addition mixing steps is all carried out in a high-speed mixer. The mixing process in each step is as follows: first, mixing at a low speed for 1 minute, then mixing at a high speed for 2 minutes, and pausing for 1 minute; then repeating the above steps twice, pausing for 1 minute between the two times; the speed of the high-speed mixer for low-speed mixing is 60-80 rpm, and the speed of high-speed mixing is 150-180 rpm.

[0010] In the coarse crushing step, the particle size of the material after coarse crushing is 0.5-1.0 mm.

[0011] In the micro powder classification step, the median particle size D50 of the classified material is 4-6 μm.

[0012] In the spheroidization step, the sphericity of the material after the spheroidization treatment is 0.95-0.98.

[0013] In the sieving step, the mesh size of the sieve of the vibrating sieve machine is 200 meshes.

[0014] The beneficial effects of the present invention are: the present invention uses YNbO4 as the doping ion Bi 3+ -Eu 3+ Support, transition metal Bi 3+ The introduction of a thermochromic material helps improve the sensitivity of individual luminescent centers. This material undergoes thermal color change within 473K, changing from purple to pink and finally to red. After removing the heat source, the color restoration time is short, taking only 15-20 seconds after the temperature drops to room temperature. That is, after printing, the printed image undergoes a reversible color change by applying a heat source. The present invention incorporates a thermochromic material into the developer toner. During the preparation process, by adjusting the composition of the thermochromic material in the developer toner, the printing toner is endowed with the property of thermal color change without affecting the printing effect.

[0015] The present invention uses niobium carbide with a MXene structure as a charge control agent, which has the following advantages: (1) The MXene structure has a large specific surface area, has good adsorption performance with paper, has the characteristics of fast adsorption rate and large adsorption amount, which is beneficial to improving the adhesion of toner, thereby improving the wiping resistance and printing color fastness, etc.; (2) The MXene structure has good electrical conductivity and excellent structural stability under external strain and temperature, which is better than traditional electrolytes, and is also beneficial to further improve image density and fixing fastness, and reduce the amount of waste powder; (3) The charged characteristics of the MXene structure are also beneficial to improving the dispersibility of the system due to the principle of like charges repelling; (4) The niobium carbide with the MXene structure and YNbO4 have certain interactions due to the same niobium atoms, and the layered characteristics of MXene can also ensure that the Bi loaded by YNbO4 3+ -Eu 3+ It is not easy to fall off, ensuring the stability of the system; (5) The compatibility between the MXene structure and the polymer matrix is ​​not too good, so as to ensure the loading of Bi 3+ -Eu 3+ The thermochromic effect of YNbO4 is not masked by the polymer matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 These are the color fastness and discoloration test results of Examples 1-10 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] The following preferred embodiments of the present invention may make it easier to understand the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood in the art to which the present invention belongs. In the event of any conflict, the definitions in this specification shall prevail.

[0019] For example, as used herein, the term "prepared from" is synonymous with "comprising." As used herein, "comprising," "including," "having," or any other variations thereof, is intended to cover a non-exclusive inclusion. For example, a composition, step, method, or apparatus that comprises a list of elements is not limited to only those elements but may include other elements not expressly listed or may inherently include elements.

[0020] When an amount, concentration or other value is expressed as a range, a preferred range or a range limited by a series of upper and lower values, it should be understood that all ranges formed by any pairing of any range limit or preferred value are specifically disclosed, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be understood to include the range of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0021] In addition, the indefinite articles "a" and "an" before the elements or components of the present invention do not limit the number of elements or components. Therefore, "a" and "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms unless the number clearly indicates a singular form.

[0022] A method for preparing a purple developing toner having reversible thermochromic properties according to an embodiment of the present invention comprises the following steps:

[0023] (1) Prepare the following materials in parts by weight: 80-90 parts of styrene-acrylic acid copolymer, 4-6 parts of polypropylene wax, 2-4 parts of thermochromic material, 1-3 parts of charge control agent, 2-4 parts of fumed silica, and 1-3 parts of titanium dioxide; the thermochromic material uses YNbO4 as the matrix and Bi 3+ -Eu 3+ Doping is performed; the charge control agent is niobium carbide having a Mxene structure;

[0024] (2) Premixing: The measured materials of styrene-acrylic acid copolymer, polypropylene wax, thermochromic material, and charge control agent are put into a mixer for premixing. The premixed materials are mixed in a high-speed mixer. The mixing process is as follows: first, mixing at a low speed for 1 minute, then mixing at a high speed for 2 minutes, and pausing for 1 minute; repeating the above steps twice, pausing for 1 minute between the two times;

[0025] (3) Mixing: Mix the pre-mixed materials in a continuous mixer;

[0026] (4) Cooling: The extruded material after mixing in the mixer is cooled by a cooling water cooling steel belt and crushed into flake materials;

[0027] (5) Coarse crushing: Put the flake material into the coarse crusher for crushing. The particle size of the material after coarse crushing is 0.5-1.0mm;

[0028] (6) Airflow crushing and classification: The coarsely crushed material is placed in the airflow crushing and classification machine for crushing;

[0029] (7) Micro powder classification: the material after air flow pulverization is classified to remove unqualified small particles. The median diameter D50 of the classified material is 4-6 μm;

[0030] (8) Pre-addition mixing: put the classified materials and 0-1 parts of external additive fumed silica into a mixer for mixing. Pre-addition mixing is carried out in a high-speed mixer. The mixing process is as follows: first, mix at a low speed for 1 minute, then mix at a high speed for 2 minutes, and pause for 1 minute; repeat the above steps twice, with a pause of 1 minute between the two times;

[0031] (9) Spheroidization treatment: The pre-added mixed material is subjected to surface spheroidization treatment by a micro-powder surface modification machine. The sphericity of the material after spheroidization treatment is 0.95-0.98;

[0032] (10) External addition and mixing: the spherical material is mixed with 2-3 parts of external additives, fumed silica and titanium dioxide, in a high-speed mixer. The external addition and mixing are mixed in a high-speed mixer. The mixing process is as follows: first, mixing at a low speed for 1 minute, then mixing at a high speed for 2 minutes, and pausing for 1 minute; repeat the above steps twice, pausing for 1 minute between the two times;

[0033] (11) Screening: The mixed materials are screened using a vibrating screen with a mesh size of 200 meshes;

[0034] (12) Packaging: Pack the screened materials according to the specified specifications.

[0035] In steps (2), (8) and (10), the rotation speed of the high-speed mixer for low-speed mixing is 60-80 rpm, and the rotation speed of the high-speed mixer for high-speed mixing is 150-180 rpm.

[0036] In the above method, the pre-added fumed silica is Evonik Degussa's R974, the added fumed silica is Degussa's A200, the silica is Cabot's TG-C6020, and the titanium dioxide is Coster's TiONA696. The different flow properties of the two fumed silicas allow for easy control of the toner's fluidity.

[0037] The purple developing toner with reversible thermochromic properties prepared according to the above method is made of the following raw materials in parts by weight: 80-90 parts of styrene-acrylic acid copolymer, 4-6 parts of polypropylene wax, 2-4 parts of thermochromic material, 1-3 parts of charge control agent, 2-4 parts of fumed silica, and 1-3 parts of titanium dioxide.

[0038] The purple developing toner having reversible thermochromic properties of the present invention is described below with reference to specific examples:

[0039] Example 1:

[0040] Raw material components: 80 parts of styrene-acrylic acid copolymer; 6 parts of polypropylene wax; 4 parts of thermochromic material; 3 parts of charge control agent; 4 parts of fumed silica (1 part pre-added and mixed, 3 parts added and mixed); 3 parts of titanium dioxide.

[0041] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, sieving and packaging are carried out in sequence to obtain the product.

[0042] Example 2:

[0043] Raw material components: 90 parts of styrene-acrylic acid copolymer; 4 parts of polypropylene wax; 2 parts of thermochromic material; 1 part of charge control agent; 2 parts of fumed silica (0 parts pre-added and mixed, 2 parts added and mixed); 1 part of titanium dioxide.

[0044] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, spheroidization, external addition and mixing, sieving and packaging are carried out in sequence to obtain the product.

[0045] Example 3:

[0046] Raw material components: 85 parts of styrene-acrylic acid copolymer; 5 parts of polypropylene wax; 3 parts of thermochromic material; 2 parts of charge control agent; 3 parts of fumed silica (0.5 parts pre-added and mixed, 2.5 parts added and mixed); 2 parts of titanium dioxide.

[0047] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, sieving and packaging are carried out in sequence to obtain the product.

[0048] Example 4:

[0049] Raw material components: 85 parts of styrene-acrylic acid copolymer; 6 parts of polypropylene wax; 2 parts of thermochromic material; 2 parts of charge control agent; 3 parts of fumed silica (0.5 parts pre-added and mixed, 2.5 parts added and mixed); 2 parts of titanium dioxide.

[0050] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, sieving and packaging are carried out in sequence to obtain the product.

[0051] Example 5:

[0052] Raw material components: 87 parts of styrene-acrylic acid copolymer; 4 parts of polypropylene wax; 3 parts of thermochromic material; 3 parts of charge control agent; 2 parts of fumed silica (0 parts pre-added and mixed, 2 parts added and mixed); 1 part of titanium dioxide.

[0053] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, spheroidization, external addition and mixing, sieving and packaging are carried out in sequence to obtain the product.

[0054] Example 6:

[0055] Raw material components: 83 parts of styrene-acrylic acid copolymer; 6 parts of polypropylene wax; 4 parts of thermochromic material; 2 parts of charge control agent; 3 parts of fumed silica (0.7 parts pre-added and mixed, 2.3 parts added and mixed); 2 parts of titanium dioxide.

[0056] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, sieving and packaging are carried out in sequence to obtain the product.

[0057] Example 7:

[0058] Raw material components: 88 parts of styrene-acrylic acid copolymer; 4 parts of polypropylene wax; 3 parts of thermochromic material; 2 parts of charge control agent; 2 parts of fumed silica (0 parts pre-added and mixed, 2 parts added and mixed); 1 part of titanium dioxide.

[0059] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, spheroidization, external addition and mixing, sieving and packaging are carried out in sequence to obtain the product.

[0060] Example 8:

[0061] Raw material components: 82 parts of styrene-acrylic acid copolymer; 5 parts of polypropylene wax; 3 parts of thermochromic material; 3 parts of charge control agent; 4 parts of fumed silica (1 part pre-added and mixed, 3 parts added and mixed); 3 parts of titanium dioxide.

[0062] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, sieving and packaging are carried out in sequence to obtain the product.

[0063] Example 9:

[0064] Raw material components: 86 parts of styrene-acrylic acid copolymer; 5 parts of polypropylene wax; 2 parts of thermochromic material; 3 parts of charge control agent; 2 parts of fumed silica (0 parts pre-added and mixed, 2 parts added and mixed); 2 parts of titanium dioxide.

[0065] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, spheroidization, external addition and mixing, sieving and packaging are carried out in sequence to obtain the product.

[0066] Example 10:

[0067] Raw material components: 84 parts of styrene-acrylic acid copolymer; 4 parts of polypropylene wax; 4 parts of thermochromic material; 1 part of charge control agent; 4 parts of fumed silica (1 part pre-added and mixed, 3 parts added and mixed); 3 parts of titanium dioxide.

[0068] According to the above preparation method, the steps of premixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, sieving and packaging are carried out in sequence to obtain the product.

[0069] Comparative Example 1:

[0070] Raw material components: 88 parts of styrene-acrylic acid copolymer; 5 parts of polypropylene wax; 3 parts of thermochromic material; 2 parts of fumed silica; and 2 parts of titanium dioxide.

[0071] According to the above preparation method, the steps of pre-mixing, kneading, cooling, coarse pulverization, air flow pulverization classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, and sieving are carried out in sequence to obtain a toner.

[0072] Comparative Example 2:

[0073] Raw material components: 88 parts of styrene-acrylic acid copolymer; 5 parts of polypropylene wax; 3 parts of charge control agent; 2 parts of fumed silica; and 2 parts of titanium dioxide.

[0074] According to the above preparation method, the steps of pre-mixing, kneading, cooling, coarse crushing, air flow crushing classification, fine powder classification, pre-external addition mixing, spheroidization treatment, external addition mixing, sieving and packaging are carried out in sequence to obtain a toner.

[0075] Color fastness test: The products obtained in the above Examples 1-10 and Comparative Examples 1-2 were tested using a Dutch Oce engineering drawing duplicator TDS-400 for a distance of 1 km, and the image density remained above 1.40.

[0076] Color change test: Cut the copy into 2cm wide strips, put them into a crucible, and then put the crucible into a muffle furnace. Heat it to 100℃ within 2 minutes, keep it warm for 2 minutes and then take it out. It was found that the color changed from purple to red. When it was cooled in the air, the color changed from red to purple.

[0077] The results of the color fastness and color change tests are as follows Figure 1 As shown in the table in . It can be seen from the above test results that the purple developing toners with reversible thermochromic properties of Examples 1-10 of the present invention have high color fastness, change color when heated, and have anti-counterfeiting effects.

[0078] The present invention utilizes reversible thermochromic materials. When heated, the visible absorption spectrum changes, that is, its color changes significantly, showing a new color. When cooled, the color will also be restored. The color change is a functional material with reversible color.

[0079] Reversible thermochromic material using Bi loaded 3+ -Eu 3+ YNbO4, a transition metal-based coordination polymer, is very suitable for use as a thermochromic anti-counterfeiting material because: (1) Various inorganic compound coordination compounds exist in transition metal element complexes. When complexes of transition elements with d1-9 electronic configurations are exposed to light, they selectively absorb visible light and undergo dd transitions, thereby exhibiting different colors. (2) The splitting of energy levels in the crystal of transition metal ions is closely related to the coordination environment of the transition metal ions and is easily affected by external stimuli.

[0080] The present invention adds an anti-counterfeiting material to the developer toner, and the resulting printing toner, produced using the aforementioned preparation method, features simple technology, low cost, rich color variations, and an early warning anti-counterfeiting function. Introducing intelligent stimulus responsiveness into the printing field offers new application directions and significantly broadens its scope of use.

[0081] The foregoing examples are merely illustrative, serving to illustrate certain features of the present invention. The appended claims are intended to be as broad as conceivable. Therefore, applicants intend that the appended claims be not limited by the selection of examples illustrating the features of the present invention. Certain numerical ranges used in the claims also include subranges therein, and variations within these ranges are also to be construed as being covered by the appended claims.

Claims

1. A purple developing toner having reversible thermochromic properties, characterized in that: The thermochromic material is made of the following raw materials in parts by weight: 80-90 parts of styrene-acrylic acid copolymer, 4-6 parts of polypropylene wax, 2-4 parts of thermochromic material, 1-3 parts of charge control agent, 2-4 parts of fumed silica, and 1-3 parts of titanium dioxide. The thermochromic material adopts YNbO4 matrix and adopts Bi 3+ -Eu 3+ The charge control agent is niobium carbide having a Mxene structure.

2. The violet developing toner having reversible thermochromic properties according to claim 1, wherein: In the thermochromic material, the molar ratio of Bi, Eu and Y is 1:1:

10.

3. The violet developing toner having reversible thermochromic properties according to claim 1, wherein: Doping Bi into YNbO4 matrix 3+ -Eu 3+ It is a hydrothermal method using soluble Bi salt and soluble Eu salt.

4. A method for preparing a purple developing toner having reversible thermochromic properties, characterized in that: It includes the following steps: (1) Prepare the following materials in parts by weight: 80-90 parts of styrene-acrylic acid copolymer, 4-6 parts of polypropylene wax, 2-4 parts of thermochromic material, 1-3 parts of charge control agent, 2-4 parts of fumed silica, and 1-3 parts of titanium dioxide; the thermochromic material uses YNbO4 as the matrix and Bi 3+ -Eu 3+ doping; the charge control agent is niobium carbide with a Mxene structure; (2) premixing: the above-mentioned measured materials, styrene-acrylic acid copolymer, polypropylene wax, thermochromic material, and charge control agent are put into a mixer for premixing; (3) mixing: the above-mentioned premixed materials are mixed by a continuous mixer; (4) cooling: the extruded material after mixing in the mixer is cooled by a cooling water-cooled steel belt and crushed into flake materials; (5) coarse grinding: the flake materials are put into a coarse grinder for grinding; (6) air flow grinding and classification: the coarse grinding is carried out. The good materials are placed in the air flow milling and classifying machine for pulverization; (7) Micro powder classification: the air flow milled materials are classified and the unqualified small particles are removed; (8) Spheroidization treatment: the pre-added mixed materials are subjected to surface spheroidization treatment by a micro powder surface modification treatment machine; (9) External addition mixing: the spheroidized materials are put into a high-speed mixer together with the external additives of fumed silica and titanium dioxide for mixing; (10) Screening: the mixed materials are screened using a vibrating screen; (11) Packaging: the screened materials are packaged according to the specified specifications.

5. The method for preparing a purple developing toner having reversible thermochromic properties according to claim 4, wherein: Between steps (7) and (8), a pre-addition mixing step is performed. The classified material and the external additive fumed silica are put into a mixer for mixing. The fumed silica in the pre-addition mixing step is 0-1 parts, and the fumed silica in the external addition mixing step is 2-3 parts.

6. The method for preparing a purple developing toner having reversible thermochromic properties according to claim 5, wherein: The mixing in the pre-mixing, pre-addition mixing and external addition mixing steps is all carried out in a high-speed mixer. The mixing process in each step is as follows: first, mixing at a low speed for 1 minute, then mixing at a high speed for 2 minutes, and pausing for 1 minute; then repeating the above steps twice, pausing for 1 minute between the two times; the speed of the high-speed mixer for low-speed mixing is 60-80 rpm, and the speed of high-speed mixing is 150-180 rpm.

7. The method for preparing a purple developing toner having reversible thermochromic properties according to claim 4, wherein: In the coarse crushing step, the particle size of the material after coarse crushing is 0.5-1.0 mm.

8. The method for preparing a purple developing toner having reversible thermochromic properties according to claim 4, wherein: In the micro powder classification step, the median particle size D50 of the classified material is 4-6 μm.

9. The method for preparing a purple developing toner having reversible thermochromic properties according to claim 4, wherein: In the spheroidization step, the sphericity of the material after the spheroidization treatment is 0.95-0.

98.

10. The method for preparing a purple developing toner having reversible thermochromic properties according to claim 4, wherein: In the sieving step, the mesh size of the sieve of the vibrating sieve machine is 200 meshes.

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