EP0011688B1 - Electrophotographical developer material and its use - Google Patents

Description

The invention relates to an electrophotographic developer material containing toner and carrier particles.

A photoconductor is charged in electrophotography and then exposed imagewise. In the areas in which the photoconductor has been exposed, the charge is dissipated or the charge decays, while the dark areas retain their electrostatic charge.

Due to the different charging in the exposed and unexposed areas of the photoconductor, electric fields arise between them. The resulting electrostatic latent image is then developed on the photoconductor by depositing small colored particles, called toners, on the photoconductor, which are charged so that the electric fields direct them to the image areas of the photoconductor.

A number of methods for developing latent electrostatic images using toner particles are known. One of these methods is called cascade development and is described, for example, in US Pat. No. 2,368,552. Another method is known as a magnetic brush method and is described in U.S. Patent 2,874,063.

A two-component developer material is used in both cascade and magnetic brush development. The developer material consists of a mixture of small toner particles and relatively large carrier particles. The toner particles are held on the surface of the relatively large carrier particles by electrostatic forces which arise from the contact between the toner and carrier particles with the formation of triboelectric charges with opposite polarities on the toner and carrier. When the developer material is contacted with the electrostatic latent image on the photoconductor, the toner particles are attracted to the latent image.

The toner and carrier particles of the developer material are prepared and treated such that the toner particles are charged with the desired polarity and size to ensure that the toner particles are substantially attracted to the desired image areas of the photoconductor. The toner particles are then electrostatically transferred to a desired copy sheet, and thereafter the transferred image of the toner particles is fixed by heat and / or pressure to obtain the fixed copy of the desired image as a final product.

One of the problems in producing the desired image on the copy sheet is to provide the best possible image quality. This is commonly referred to as copy quality. The copy quality includes properties such as a clear image, that is, a clear recording of lines; uniform darkness of the image areas; Background quality, i.e. gray values or the absence of these values in the background areas and other properties which cannot be precisely determined, all of which are essential for maintaining a good copy quality.

Other factors related to the toner that deserve attention in a development process are the utilization of the toner per copy. Of course, from an economic standpoint, the less toner used for a given image, the better. Also, in a system in which unused toner is discharged from the air using a filter, it is essential to keep the amount of unused toner as low as possible to thereby extend the life of the filter.

When using a heat fixing process, it is desirable to provide an image that has the best possible heat transfer characteristics to minimize the amount of heat necessary to fix the image. This is not only essential for the sake of energy saving, but also because the fixing time or temperature can be reduced if the toner transfers heat faster.

European patent application 78101178.8 (publication number 1785) describes a toner classification with which the aforementioned problems can be essentially solved. However, additional problems arise when the improved toner described therein is used together with a conventional carrier material which is coated with polytetrafluoroethylene (see, for example, US Pat. No. 3,944,721). A problem that arises is contamination of the toner with fluorocarbon. This is due to the transfer of polytetrafluoroethylene from the carrier coating to the surface of the toner. Transfer of this type or lubrication causes a negative change in the triboelectric properties on the surface of the toner particles, which in turn leads to a deterioration in the operation of the toner.

In addition, a coating of pure polytetrafluoroethylene on the carrier particles shows slow, but still substantial wear. While carrier particles coated with polytetrafluoroethylene are very durable compared to other conventional coatings, wear and tear takes place during the making of a few hundred thousand copies.

There is therefore a need for a coated carrier material to be used in conjunction with the improved toner according to European patent application 78 101 178.8, which is not Fluorocarbon pollution causes and is extremely durable. The object of the invention is to provide an electrophotographic developer material containing a coated carrier material which fulfills the requirements stated above and is used together with a classified toner material.

• a) etwa 5 bis 55 Gew.-% Polytetrafluoräthylen (PTFE),
• b) etwa 5 bis 55 Gew.-% fluoriertem Polyäthylen-propylen (FEP) und
• c) etwa 40 bis 80 Gew.-% Poly(amid-imid) (PAI), das bis wenigstens 316°C thermisch stabil und triboelektrisch negativ (relativ zu dem verwendeten Toner) geladen ist;

beschichtet sind, bestehen und der Toner Teilchen mit folgender Größenverteilung enthält:

• a) weniger als 15 Gew.-% Teilchen größer 16 µm;
• b) 7 bis 15 Gew.-% Teilchen kleiner 5 µm;
• c) Rest Teilchen mit einer Größe zwischen 5 und 16 µm

und daß er einen Medianwert der Teilchengröße nach der Gewichtsverteilung zwischen 8 und 12 J-Lm aufweist.The object of the invention is achieved by an electrophotographic developer material which is characterized in that the carrier particles consist of cores which are made with an abrasion-resistant resin system

• a) about 5 to 55% by weight of polytetrafluoroethylene (PTFE),
• b) about 5 to 55 wt .-% fluorinated polyethylene propylene (FEP) and
• c) about 40 to 80 wt .-% poly (amide-imide) (PAI), which is thermally stable up to at least 316 ° C and triboelectrically negative (relative to the toner used);

coated, exist and the toner contains particles with the following size distribution:

• a) less than 15 wt .-% particles larger than 16 microns;
• b) 7 to 15 wt .-% particles smaller than 5 microns;
• c) rest particles with a size between 5 and 16 microns

and that it has a median particle size by weight distribution between 8 and 12 J-Lm.

The coating preferably also contains a pigment, for example titanium dioxide. Advantageous embodiments are the subject of the dependent claims. The invention also relates to the use of the electrophotographic developer material according to the invention in an electrophotographic development process.

• Fig. 1 ist eine graphische Darstellung, aus der die Breite und bevorzugte Zusammensetzung der Überzüge gemäß der Erfindung für Trägerteilchen ersichtlich ist;
• Fig.2 ist eine graphische Darstellung des Prozentgehalts verunreinigten Toners in einem konventionellen Träger-Tonersystem und dem verbesserten Träger-Tonersystem in Abhängigkeit von der erstellten Kopienzahl und
• Fig. ist eine graphische Darstellung des Gewichtsverlustes eines konventionellen Trägers und eines verbesserten Trägers gemäß der Erfindung als Funktion der Kopienzahl und der Kopienzahl pro Pfund Mischung.

The invention is explained in more detail with reference to the figures and the special description.

• Fig. 1 is a graph showing the width and preferred composition of the coatings according to the invention for carrier particles;
• Figure 2 is a graphical representation of the percentage of contaminated toner in a conventional carrier toner system and the improved carrier toner system as a function of the number of copies made and
• Figure 2 is a graphical representation of weight loss of a conventional carrier and an improved carrier according to the invention as a function of copy number and copy number per pound of blend.

According to the present invention, there is provided an improved developer for electrophotographic copying machines by using the improved toner according to European patent application 78101178.8 together with carrier particles coated with a mixed resin of polytetrafluoroethylene, fluorinated polyethylene-propylene and poly (amide-imide) becomes. The coating of the carrier particles preferably also contains a pigment such as titanium dioxide particles to control the triboelectric charge.

As for the carrier component of the developer, it is made of a core material, preferably about 50 to 500 µm in diameter, the core material being made of a magnetic material if the developer is to be used in a magnetic brush developing device. A coating consisting of a three part resin system is applied to the core to form the carrier particles. The resin system consists of polytetrafluoroethylene, fluorinated polyethylene-propylene and poly (amide-imide), the components of each of these three resins being selected so as to obtain an excellent carrier with an extremely long life and a very low tendency to contaminate the toner particles with fluorocarbons . In Fig. 1 graphically depicts the broad preferred and optimal ranges of the three components of this resin system. In the broadest sense, the composition should be within the limits indicated by the lines between points 1, 2, 3 and 4. Through this area, a composition is represented which consists of approximately 5 to 55% by weight of polytetrafluoroethylene, approximately 5 to 55% by weight of fluorinated polyethylene propylene and approximately 40 to 80% by weight of poly (amide-imide) resin . Fluorinated polyethylene propylene is a copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). It typically consists of about 80 to 85% TFE and 15 to 20% HEP, preferably about 80% TFE and 20% HFP. However, these proportions can also vary somewhat.

The poly (amide-imide) resin is characterized by being stable up to about 316 ° C (600 ° F), triboelectrically negative (in relation to the toner used here), non-splintering, substantially abrasion resistant and non-crumbling and can be dispersed with the other resin components. A typical poly (amide-imide) resin is a copolymer of trimellitic anhydride and an organic diamine, for example 4,4'-bis-aminodiphenylmethane. A polymer of this type typically has a molecular weight in the range of 15,000 to 30,000, preferably 20,000 to 25,000. Other poly (amide-imide) resins can also be used. For example, pyromellitic anhydride or other similar anhydrides can be used either individually or in combination with the above-mentioned diamine or other, preferably aromatic diamines can be used. Examples of these poly (amide-imide) resins are described in U.S. Patent No. 3,179,614.

In particular, the preferred ranges of the components of the resin system should be within the limits of the lines connecting points 5, 6, 7, 8, 9 and 10 of the diagram. This range represents a composition of about 5 to 30% by weight of polytetrafluoroethylene, of about 5 to 30% by weight of fluorinated polyethylene propylene and of about 50 to 70% by weight of poly (amide) imide. The optimum The composition is about 20% by weight of polytetrafluoroethylene, about 20% by weight of fluorinated polyethylene propylene and about 60% by weight of poly (amide-imide).

In view of compliance with these ranges, it has been found that prior art 100% polytetrafluoroethylene shows a significant tendency to fluorocarbon contaminate the toner particles, that is, the carrier coating material is transferred to the surface of the toner particles while changing the triboelectric properties of the toner particles. whereby the properties of the toner particles deteriorate. Adding the poly (amide-imide) resin alone to polytetrafluoroethylene does not sufficiently reduce this tendency of the coating to contaminate, and if only small proportions of the poly (amide-imide) resin are used alone with polytetrafluoroethylene, poor coating adhesion is prevented Shear stress observed. The use of fluorinated polyethylene propylene in combination with poly (amide-imide) resin alone results in a coating on which toner film formation occurs to a high degree. This is a condition in which the toner material (a system based on methyl methacrylate and n-butyl methacrylate) tends to transfer or smear on the surface of the carrier coating. This adversely affects the ability of the carrier to hold electrostatic toner particles and causes the properties of the developer to deteriorate. Toner filming also occurs on poly (amide-imide) alone, and this resin also has an excessive electrical surface charge. Conversely, if less than 40% poly (amide-imide) is used, the surface charge is too low. Furthermore, when this 40% limit of poly (amide-imide) is undershot and polytetrafluoroethylene prevails, the material tends to contaminate the toner with fluorocarbon; and when fluorinated polyethylene propylene prevails, there is a tendency for toner film formation.

In order to obtain the desired behavior of the developer, it is necessary to use all three resins in the specified range. To control the charge and monitor the toner film formation, poly (amide-imide) must be present in an amount between 40 and 80%. There must be at least 5% fluorinated polyethylene-propylene to reduce the tendency for fluorocarbon contamination and at least 5% polytetrafluoroethylene to likewise reduce the tendency for toner film formation. Within this range, the poly (amide-imide) is a component that is so resistant to wear that the coating is essentially abrasion resistant. Even better control of these properties is possible within the specified narrow limits, and optimal monitoring is obtained at the optimal values.

To monitor the triboelectric charge, it is desirable to add a pigment to the resin. For this purpose, titanium dioxide is preferably used, which is added in an amount of about 3 to 15% by weight, based on the total coating weight. Titanium dioxide is preferably used in an amount of 7 to 9% and optimally in an amount of 8%. As is known, titanium dioxide can also be used for the purpose of activating sensors which trigger the addition of toner if the toner supply is too low.

In accordance with this invention, the improved carrier coating gives greatly improved copy quality results when used with the toner described in European Patent Application 78101 178.8. This toner is classified and has a particle size distribution with less than 15% by weight greater than 16 µm; from 7 to 15% by weight less than 5 µm and the rest with a particle size between 5 and 16 µm, the median of the particle size according to the weight distribution being between 8 and 12 µm. Preferably there is a distribution with less than 2% by weight greater than 16 (9 to 15% by weight less than 5 µm and a median particle size according to the weight distribution between 8.5 and 9.5 µm. If the developer mixture in the Equilibrium is after a start-up period, which is generally the case after about 10,000 copies, the toner particles should have a size distribution of 15 to 30% by weight less than 5 µm, less than 12% by weight greater than 16 µm and the rest with a Particle size between 5 and 16 microns, the median particle size by weight is between 6.5 and 9.5 microns.

Table I shows the results of the inventive combination of the improved toner and carrier compared to conventional polytetrafluoroethylene coated carrier and conventional toner. Example I represents a developer with a prior art toner and carrier coated with pure polytetrafluoroethylene, and Examples II, 111 and IV represent toners and carriers according to the present invention. Table II gives the particle size distribution of the toner and the nominal coating composition of the carrier particles. Conventional magnetic brush development with feedback was used to perform these tests.

Table I shows, in terms of the copying results, the superiority of the combination of the improved toner and the coated carrier according to the present invention. The reasons for these improvements are not fully known. However, it is believed that the very long-lasting quality of the carrier coating imparted by the poly (amide-imide) resin, in conjunction with the fluorinated polyethylene-propylene / polytetrafluoroethylene resin mixture in the system, which tends to be very low in fluorocarbon contamination, is significantly among those in the system contribute to improved results. A comparison of the fraction of a contaminated toner using conventional toner (similar to that of Example I) and conventional carrier with a pure polytetrafluoroethylene coating with toner and carrier (similar to that of Example VI) according to the invention is shown in graphical form in FIG. 2. In this figure, the fraction contaminated with fluorocarbon toner is plotted against the number of copies. As can be seen, less contaminated toner is increasingly produced with the present invention, whereas with conventional, previously known toner / carrier the amount of contaminated toner remains the same and is at a level which is substantially higher than that with the improved toner and carrier coating according to the invention. This substantial reduction in contaminated toner contributes significantly to the improved results listed in Table I.

• 1. 3 bis 5 ml einer geeigneten Flüssigkeit oder Lösung, beispielsweise einer 0,1%igen Lösung von Triton X-100 in deionisiertem Wasser werden in eine flache Schale gegossen.
• 2. Eine bekannte Menge Toner-Trägermischung (beispielsweise 0,25 g) werden auf die Oberfläche der Flüssigkeit gegossen.
• 3. Man wartet, bis der Träger benetzt wird und absinkt und der Toner auf der Flüssigkeitsoberfläche zurückbleibt.
• 4. Die Lösung wird dann vom Grund der Schlüssel her bewegt, indem man den Träger mit einem Magnet rührt. Das Rühren wird so lange fortgesetzt, bis eine einheitliche Farbe erhalten wird.
• 5. Der Träger wird mit einem Magnet festgehalten und der Toner und die Lösung werden in ein enghalsiges Glasfläschchen gegossen, das bis etwa 5 mm unterhalb seines Randes mit der gleichen Flüssigkeit gefüllt ist. Es muß darauf geachtet werden, daß möglichst wenig Blasen vorhanden sind.
• 6. Das Glasfläschchen wird dann sorgfältig gefüllt, damit die Oberflächenspannung bewirkt, daß sich die Flüssigkeitsoberfläche über den oberen Rand des Glasfläschchens hinaus erstreckt.
• 7. Ein gewogenes, starres Stück Kunststoff wird auf den oberen Rand des Glasfläschchens gelegt, so daß die Flüssigkeit dieses benetzt und auf letzterer schwimmender Toner an ihm anhaftet. Das Stück Kunststoffmaterial wird dann entfernt und getrocknet und gewogen.
• 8. Der Prozentgehalt verunreinigten Toners ist gleich der Gewichtszunahme des Stücks Kunststoff, dividiert durch das Produkt aus dem Gewicht der Mischung und der Tonerkonzentration, welche als Bruchteil ausgedrückt wird.

The percentage of contaminated toner is determined as follows:

• 1. 3 to 5 ml of a suitable liquid or solution, for example a 0.1% solution of Triton X-100 in deionized water, are poured into a flat dish.
• 2. A known amount of toner carrier mixture (for example 0.25 g) is poured onto the surface of the liquid.
• 3. Wait until the carrier is wetted and sinks and the toner remains on the liquid surface.
• 4. The solution is then moved from the bottom of the key by stirring the carrier with a magnet. Stirring is continued until a uniform color is obtained.
• 5. The carrier is held in place with a magnet and the toner and the solution are poured into a narrow-necked glass vial which is filled with the same liquid up to about 5 mm below its edge. Care must be taken to ensure that there are as few bubbles as possible.
• 6. The glass vial is then carefully filled so that the surface tension causes the liquid surface to extend beyond the top of the glass vial.
• 7. A weighed, rigid piece of plastic is placed on the top edge of the glass vial so that the liquid wets it and toner floating on the latter adheres to it. The piece of plastic material is then removed and dried and weighed.
• 8. The percentage of contaminated toner is equal to the weight increase of the piece of plastic divided by the product of the weight of the mixture and the toner concentration, which is expressed as a fraction.

Fig. Is a graphical representation showing the carrier coating weight as a function of the number of copies. With the conventional toner / carrier (coating made of pure polytetrafluoroethylene) known to date, a considerable loss of carrier coating material is continuously observed. However, with the backing of the present invention (which in this example is nominally the composition of Example IV) only a very, very low loss of backing is observed, so that the backing can be said to be essentially abrasion resistant, which property is due to the proportion of the poly (amide-imide) resin is effected.

Attempts have also been made to compare the improved carrier coating and conventional toner known to date with the improved carrier coating and toner classified. These results are shown in Table 111 below. In Example V, previously known toner is used and in Example VI the improved, classified toner is used.

In Example V above, the size distribution of the toner in the developer mixture (in equilibrium) was as follows:

In Example VI, the size distribution in the developer mixture was as follows:

In each case, the support was coated with a nominally 60/20/20 mixture of poly (amide-imide) / polytetrafluoroethylene / fluorinated polyethylene-propylene with an addition of about 9% titanium dioxide.

As can be seen, background, cleaner throughput, toner yield, development and fusing quality are all significantly improved with the toner / carrier combination according to the invention.

The reason why the special carrier coating interacts so well with the toner described in European patent application 78 101 178.8 is not completely clear. However, it is believed that even the very slight tendency of the carrier coating of the present invention to contaminate the toner with fluorocarbon in the prior art toner in which there is a large percentage of large particles (i.e., greater than 16 microns) is important plays. The charge-to-mass ratio in these particles is very low and is a limit for maintaining a useful copy quality. Therefore, even a low level of contamination can significantly reduce this charge, causing poor copy quality. In any case, the combination according to the invention of the improved poly (amide-imide) / polytetrafluoroethylene / fluorinated polyethylene-propylene system in combination with the toner described in European patent application 78 101 178.8 results in an extraordinary improvement in the copying behavior.

Claims (10)

1. Electrophotographic developer material containing toner and carrier particles, characterized in that the carrier particles consist of cores coated with an abrasion-proof resin system comprising

a) approximately 5 to 55% by weight polytetrafluoroethylene,

b) approximately 5 to 55% by weight fluoronated polyethylenepropylene, and

c) approximately 40 to 80% by weight poly(amide-imide) which is thermally stable up to at least 316° C and of a triboelectrically negative charge;

and that the toner comprises particles with the following size distribution:

a) less than 15% by weight particles smaller than 16 µm;

b) 7 to 15% by weight particles smaller than 5 µm;

c) the remaining particles with a size between 5 and 16 µm,

and that it has a median size by weight between 8 and 12 µm.

2. Electrophotographic developer material as claimed in claim 1, characterized in that the cores of the carrier particles are coated with a resin system comprising

a) approximately 5 to 30% by weight polytetrafluoroethylene,

b) approximately 5 to 30% by weight fluorinated polyethylenepropylene, and

c) approximately 50 to 70% by weight poly(amide-imide).

3. Electrophotographic developer material as claimed in claims 1 and 2, characterized in that the cores of the carrier particles are coated with a resin system comprising

a) approximately 20% by weight polytetrafluoroethylene,

b) approximately 20% by weight fluorinated polyethylenepropylene, and

c) approximately 60% by weight poly(amide-imide).

4. Electrophotographic developer material as claimed in any one of claims 1 to 3, characterized in that the resin system additionally contains a pigment to modify the triboelectrical properties of the resin.

5. Electrophotographic developer material as claimed in claim 4, characterized in that the resin system additionally contains approximately 3 to 15% by weight, preferably 7 to 9% by weight titanium dioxide.

6. Electrophotographic developer material as claimed in claims 4 and 5, characterized in that the resin system additionally contains 8% by weight of titanium dioxide.

7. Electrophotographic developer material as claimed in any one of claims 1 to 3, characterized in that the poly(amide-imide) component of the resin system is a copolymer of at least one anhydride and an organic bis-amine.

8. Electrophotographic developer material as claimed in any one or several of claims 1 to 3 and 7, characterized in that the poly(amide-imide) component of the resin system is a copolymer of a trimellitic anhydride and/or pyromellitic anhydride, and 4.4-bis-amino-diphenylmethane.

9. Electrophotographic developer material as claimed in claim 1, characterized in that the toner contains particles with the following size distribution:

a) less than 2% by weight particles greater than 16 µm;

b) 9 to 15% by weight particles smaller than 5 µm;

c) the remaining particle with a size between 5 and 16 µm,

and that it has a median size by weight between 8.5 and 9.5 µm.

10. Use of the electrophotographic developer material as claimed in any one or several of claims 1 to 9, in an electrostatic copying process.

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