Toner Production via Controlled Recrystallization for Fixability
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Solution Overview
Problem
Existing toner production methods face challenges in achieving low-temperature fixability while maintaining high-temperature storability and preventing density unevenness of images, particularly due to issues with crystalline resin compatibility and surface resistance.
Innovation Solution
A process involving an emulsion aggregation method where a dispersion containing a binder resin with a crystalline resin is heated to a temperature above its melting point, followed by maintaining the dispersion at a specific temperature range (Rc−25° C. to Rc−5° C.) for 30 minutes or longer, with a pH between 5.5 and 9.0, to control the domain diameter and presence state of the crystalline resin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a crystalline resin is added to enhance low-temperature fixability, then the melting temperature and melt viscosity of the binder resin are lowered, but the high-temperature storability deteriorates due to compatibility between the crystalline resin and amorphous resin
Solution Approach 1:
Heat treatment is performed in advance during the toner production process to establish a stable crystalline resin structure before the toner is put into storage or use. This preliminary action ensures that the crystalline resin domains are properly formed and stabilized, preventing subsequent compatibility issues with the amorphous resin during storage.
Solution Approach 2:
The heat treatment temperature is precisely controlled within a specific range (above the glass transition temperature of the amorphous resin but below the melting point of the crystalline resin) to achieve optimal crystallization. By adjusting this temperature parameter, the crystalline resin structures are stabilized without causing excessive compatibility with the amorphous resin, thus resolving the contradiction between low-temperature fixability and high-temperature storability.
2Reliability
If heat treatment is performed to recrystallize the crystalline resin and enhance high-temperature storability, then the storability is improved, but the domain diameter of the crystalline resin increases and low-temperature fixability deteriorates
Solution Approach 1:
The heat treatment temperature is precisely controlled within a specific range (above the glass transition temperature of the amorphous resin but below the melting point of the crystalline resin) to achieve optimal crystallization. By adjusting this temperature parameter, the crystalline resin structures are stabilized without causing excessive domain growth that would harm low-temperature fixability.
Solution Approach 2:
The heat treatment is applied partially in terms of temperature intensity - enough to promote crystallization and improve storability, but not excessive enough to cause significant domain growth. This controlled partial action achieves the desired recrystallization while maintaining the fine domain structure necessary for low-temperature fixing performance.
3Stability of the object's composition
If the crystalline resin is exposed on the surface of the toner through heat treatment in an aqueous medium, then the dispersion is improved, but the surface resistance is lowered and charging characteristics deteriorate, resulting in image noise
Solution Approach 1:
The heat treatment process creates local quality differences within the toner particles - the interior undergoes crystallization to improve storability, while the surface maintains its original composition and properties. This localized effect ensures that the surface resistance and charging characteristics are preserved while the interior structure is stabilized.
Solution Approach 2:
The heat treatment temperature is controlled to be below the melting point of the crystalline resin, which prevents excessive surface exposure of the crystalline resin. By adjusting this temperature parameter, the crystallization occurs primarily within the particle interior while the surface composition remains stable, avoiding the harmful effects of surface crystalline resin exposure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a toner with excellent low-temperature fixability and suppressed density unevenness, effectively managing the crystalline resin's dispersion and surface properties to enhance image quality.
Implementation Method 1
heating a dispersion containing an aqueous medium and a binder resin containing a crystalline resin to a temperature higher than or equal to a melting point of the crystalline resin
Implementation Method 2
maintaining the dispersion at temperature T (° C.) for 30 minutes or longer... where the temperature T satisfies: Rc−25≤T≤Rc−5 (Rc represents a recrystallization temperature (° C.) of the crystalline resin)
Implementation Method 3
in dry heat treatment, the elevation of the glass transition temperature, the increase of the domain diameter of a crystalline resin in a toner, etc., are caused due to the change of the moisture adsorption state of a toner
Data Source
AI summary
A process for producing a toner of the present invention includes: a first step of heating a dispersion containing an aqueous medium and a binder resin containing a crystalline resin to a temperature higher than or equal to a melting point of the crystalline resin; and a second step of maintaining the dispersion at temperature T (° C.) for 30 minutes or longer in a state where a pH of the dispersion is maintained at 5.5 or higher and 9.0 or lower, in which the temperature T satisfies the following expression, Rc−25≤T≤Rc−5, where the Rc represents a recrystallization temperature (° C.) of the crystalline resin.