JP3175352B2 - Electrophotographic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner used for electrophotographic copying.

[0002]

2. Description of the Related Art Toners used in electrophotography are generally produced by melt-mixing a binder resin, a colorant and necessary additives, and pulverizing and classifying the melt-kneaded product. It is a common practice to add waxes that are incompatible with the binder resin as necessary additives in order to prevent the occurrence of high-temperature offset during heat roll fixing.

However, since the added wax is not compatible with the binder resin, it is difficult to uniformly disperse the wax in the binder resin with a small particle size. But easy to separate.

If the size of the wax separated from the toner particles is a fine powder much smaller than the particle size of the toner,
Even if it is removed in the classification process, or even if it is not removed, the fine powder will fate together with the toner in a state where it is stuck to the toner particles and will not adversely affect the photoreceptor and the copied image, etc. When the distance is close, the fine powder is not cut even in the classification step, and is scattered in the toner product. Since the free wax that has entered into the product does not contain a colorant or a charge control agent, the chargeability of the free wax is significantly different from that of the product toner.

[0005] During the copying process, the wax adhered to the electrostatic latent image on the photoreceptor together with the toner particles is not transferred even in the transfer process onto copy paper, and free wax remains on the photoreceptor. The wax remaining on the photoreceptor is not cleaned by the cleaner blade in the cleaning step, and is left as it is on the photoreceptor. This fusion wax is further thinly stretched and filmed on the photoreceptor.

Further, toner adheres to the filmed wax, and black spots (black spots) are formed on the photoreceptor in a streak shape. Since the filming and the black spot fused material do not leak electric charge, fogging occurs in a copied image, or when toner is further developed on them,
The toner is transferred to the paper and causes image noise.

[0007] Recently, the particle size of the toner has been reduced in order to enhance the definition of the image. In the case of such a toner, it is particularly necessary to uniformly disperse the wax with a small particle size.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and in which wax has a small particle diameter and is uniformly dispersed. It is an object of the present invention to provide a toner that does not cause black spots and fog.

[0009]

That is, the present invention relates to an electrophotographic toner for heat roll fixing comprising at least a binder resin and an anti-offset wax, wherein the toner is produced through mixing, kneading, pulverizing and classifying steps. The wax is 1 to 7 parts by weight based on 100 parts by weight of the binder resin.
Weight included, the average of the major axis length of the wax particles contained in the toner is a, and the average of the minor axis length is b,
A / b of the wax particles is 20/1 or less, and at least a / b is
Wax particles with 1/1 to 3/1 and wax with a / b of 5/1 to 20/1
And wax particles having a / b of 1/1 to 3/1, the average diameter of the wax (D _W ) and the average diameter of the toner (D _T ) are expressed as D _W = satisfy the relationship of 0.05D _T ~0.2D _T, for the wax particles a / b is 5 / 1-20 / 1, the following ^{relationship: (ab 2) 1/3 = 0.025D} T ~0.1D T (The average diameter, the major axis and the minor axis length of the wax particles were measured from an electron micrograph of the wax particles collected by treating the toner with a solvent that dissolves the binder resin and does not dissolve the wax particles. Value of the toner for electrophotography).

The toner for electrophotography of the present invention comprises at least a wax which is not compatible with the binder resin.

The binder resin used may be a commonly used thermoplastic resin, for example, a styrene / acrylic copolymer resin or a polyester resin.

As the wax, low molecular weight polypropylene, low molecular weight polyethylene, ethylene bisamide, microcrystalline wax, carnauba wax, paraffin wax such as beeswax are preferably used.
The material is not particularly limited as long as it is not compatible with the thermoplastic resin used as the binder resin of the toner and has a releasing property.

In the present invention, "having no compatibility" refers to a state in which the wax is dispersed in the resin in an island shape when melt-kneaded, and is not taken into the molecular chains of the resin.

In the present invention, the wax is obtained by dispersing substantially spherical particles and / or spindle-shaped particles in a binder resin.

A substantially spherical shape has a ratio of the major axis a to the minor axis b of 1/1.
Refers to a - 3/1, average diameter of the wax (D _W) is (a +
b) / 2

When such a substantially spherical wax is dispersed in the resin, the average diameter (D _W ) of the wax and the average diameter (D _T ) of the toner are 0.05 D _T ≦ D _W ≦ The particles are dispersed with a small particle size that satisfies the relationship of 0.2 _DT .

In the case of spindle-shaped particles, the average of the major axis of the spindle is
Where a is the average of the short axis and b is the long axis compared to the short axis.
Too much wax can break free wax into toner products.
The ratio (a / b) of major axis a to minor axis b (a / b) should be less than 20/1
Need to be.

The ratio (a / b) of the major axis a to the minor axis b is 5/1 to 20
In the case of the spindle-shaped wax in the range of / 1 , the dispersion is performed so as to satisfy the following relational expression: (ab ² ) ^1/3 = 0.025D _{T to} 0.1D _T The formula (ab ² ) ^1/3 is statistically obtained from the experimental results and approximately represents the radius of the spindle-shaped wax.

When D _W is less than 0.05 D _T , or when (ab ² ) ^1/3 is less than 0.025 D _{T, the} effect of preventing high-temperature offset is reduced, and free wax is still produced by classification. The toner adheres to the toner and becomes difficult to remove. On the other hand, when D _W is larger than 0.2 D _T or when (ab ² ) ^1/3 is larger than 0.1 D _T , the free wax gets into the product toner and causes filming and black spots. .

The average diameter of the wax, the major axis and the minor axis are as follows:
The obtained toner is treated with a solvent that dissolves the binder resin but does not dissolve the wax, and then centrifuged to collect the wax floating in the solvent, and a scanning electron micrograph (SEM)
To observe an arbitrary region (7.
Approximately 500 substantially spherical and spindle-shaped particles within 3 × 9.5 cm) were arbitrarily extracted, and the average value was obtained.

The average diameter of the toner is a value measured by a volume average diameter of a Coulter counter.

The wax produced in this manner is obtained in a state in which substantially spindle-shaped wax and spherical wax are dispersed at random, and D _W and (ab ² ) ^1/3 satisfy the relationship described above. If so, there is no particular problem.

Further, in the toner of the present invention, it is preferable that the substantially spindle-shaped wax accounts for 70% or less of the wax particles.

The toner of the present invention is produced by mixing a binder resin, a colorant, a wax and other additives, and kneading, pulverizing, and classifying. Wax is toner binder resin 10
1 to 7 parts by weight, preferably 2 to 6 parts by weight, is added to 0 parts by weight. If the amount is less than 1 part by weight, the effect on high-temperature offset is small, and if it is more than 7 parts by weight, free wax increases and filming black spots on the photoreceptor increase. The amount of other additives may be a usual amount.

In order to uniformly disperse the wax with a small particle size as in the present invention, a mixer having a pulverizing ability, such as a ball mill or a Henschel mixer, is used in the mixing step. This is achieved by taking care that the temperature is set as low as possible below the melting temperature of the resin and that the shearing force of the resin is used.

Hereinafter, the present invention will be further described with reference to examples.

[0027]

EXAMPLES Example 1 100 parts by weight of styrene-acrylic copolymer resin Number average molecular weight (Mn): 4500, Mw / Mn: 48 (Mw; weight average molecular weight) Glass transition point (Tg): 62 ° C. Carbon black (MA # 8; manufactured by Mitsubishi Chemical Corporation) 8 parts by weight ・ Nigrosine dye (Bontron N-01; manufactured by Orient Chemical Industries) 3 parts by weight ・ Low molecular weight polypropylene (Viscol 550P; manufactured by Sanyo Chemical Industries) 4 parts by weight

The above materials were charged into a ball mill, and
Mixing and crushing for hours. Further, the mixture was sufficiently kneaded for 15 minutes using three rolls. At this time, the temperature of the two rolls inside and behind the three rolls was set to 140 ° C, and the temperature of the front roll was set to 120 ° C.
Set to.

The obtained kneaded material was taken out, gradually cooled to 90 ° C., and further cooled to 40 ° C. or less with cold air. Cooling is 2
It was coarsely pulverized to a size of not more than an mm square.

Next, the coarsely pulverized product was pulverized with a jet pulverizer to an average diameter of 8.4 μm, and coarse and fine powders were cut with a DS classifier to obtain particles having an average diameter of 9.1 μm.

Finally, hydrophobic silica (H
-2000; manufactured by Hoechst Co.) and subjected to a surface treatment to obtain a toner A.

Example 2 100 parts by weight of polyester resin Number average molecular weight (Mn): 6800, Mw / Mn: 32 (Mw; weight average molecular weight) Glass transition point (Tg): 65 ° C. Carbon black (# 44; Mitsubishi) 8 parts by weight ・ Cr-containing oil-soluble dye (Bontron S-34; manufactured by Orient Chemical Industries) 2 parts by weight ・ Low molecular weight polypropylene (Viscol TS-200; manufactured by Sanyo Chemical Industries) 4 parts by weight

The above material was converted into a toner in the same manner as in Example 1 to obtain a toner B having an average diameter of 8.2 μm.

Examples 3 to 5 Toners C to E having the particle diameters shown in Table 1 below were obtained in the same manner as in Example 1 except that the amount of the surface treating agent was changed as follows.

[0035]

[Table 1] Particle size (μm) Surface treated toner C 5.4 H-2000 0.3% by weight Toner D 12.1 H-2000 0.15% by weight Toner E 14.8 H-2000 0.1% by weight

Example 6 Toner F having an average diameter of 8.4 μm was prepared in the same manner as in Example 1 except that the low molecular weight polypropylene was changed to Viscol 660P.
I got

Example 7 In the same manner as in Example 1 except that the low molecular weight polypropylene was added in the following amount, toners G to G having particle sizes shown in Table 2 below were prepared.
H was obtained.

[0038]

[Table 2] Low molecular weight polypropylene particle size Toner G 1 part by weight 8.7 μm Toner H 5 parts by weight 9.2 μm7 parts by weight of toner I 8.6 μm

Comparative Example 1 The materials used in Example 1 were charged into a V blender with the same composition, and the V blender was rotated for 15 minutes to uniformly mix the materials. Next, the mixture was charged into a continuous extrusion kneader and kneaded at a set temperature of 160 ° C. The temperature of the kneaded material discharged is 178.
° C. The obtained kneaded material was rapidly cooled to 40 ° C. or less with a cooling belt, and then pulverized to 2 mm square or less. Example 1 below
In the same manner as in the above, a toner J having an average diameter of 8.6 μm was obtained.

Comparative Example 2 The same composition as in Example 2 was used, and Comparative Example 1 was used.
In the same manner as in the above, a toner K having an average diameter of 8.5 μm was obtained.

Comparative Example 3 A toner L having an average diameter of 8.8 μm was obtained by using the same material and the same composition as in Example 3 except that 8 parts by weight of low molecular weight polypropylene was used.

Comparative Example 4 During the solution polymerization reaction of a styrene acrylic copolymer resin, 4 parts by weight of low molecular weight polypropylene (Viscol 330P; manufactured by Sanyo Chemical Industries) was melted and dispersed. Next, the obtained melt was desolvated in a high vacuum to obtain a resin. The number average molecular weight of the obtained resin is 5,200 and the degree of dispersion (Mw / Mn) is 4
6. The glass transition point was 61 ° C.

100 parts by weight of the above resin 8 parts by weight of carbon black (MA # 8; manufactured by Mitsubishi Kasei Kogyo Co., Ltd.) 3 parts by weight of a nigrosine dye (Bontron N-01; manufactured by Orient Chemical Co., Ltd.) 3 parts by weight The average diameter is 8.4 μ as in Example 1.
m of toner M was obtained.

Toners A to A prepared in Examples and Comparative Examples
M was dissolved in chloroform and centrifuged. Ten minutes later, the wax floating on the surface was collected, and a SEM photograph was taken to measure the particle size of the wax. The results are shown in Table 3 below.

[0045]

[Table 3]

The obtained toners A to M were sufficiently mixed with a separately prepared binder type carrier (average diameter: 62 μm) and charged. Copier EP8600 for negatively charged toner
(Minolta Camera Co., Ltd.), and in the case of a positively chargeable toner, a copying machine EP860 in which the photosensitive member is changed to an organic laminated photosensitive member
A printing durability test was performed using 0. The results are shown in Table 4 below.

[0047]

[Table 4]

The ranking in the above table was performed as follows. Filming of photoreceptor ；: No filming at all ○: Slight filming but no problem in practical use ×: Filming occurs and fog occurs Black spot fusion (black spot (BS)) ；; Black spot fusion No adhesion Δ: Black spot fusion is observed on the photoreceptor, but does not occur in the copy image. ×: Black point appears in the copy image.

The obtained toners A to M were sufficiently mixed with a separately prepared binder type carrier (average diameter: 62 μm) and charged. Copier EP8600 for negatively charged toner
(Minolta Camera Co., Ltd.), and in the case of a positively chargeable toner, a copying machine EP8600 was modified, and a printing durability test was performed by changing the photoconductor to an organic laminated photoconductor. Further, the fixing test was performed at a system speed of 13 cm / sec, and images having the density of ID 1.2 and ID 0.6 were copied.
The copied image was shaved with an eraser rubber under a load of 1 kg and three reciprocations, and the ratio to the reflection density before shaving was expressed in%. At the same time, the hot offset occurrence temperature was measured. The results are shown in Table 5 below.

Practically, the reflection density ratio is required to be 80% or more for an image with ID 1.2 and 65% or more for an image with ID 0.6. The temperature at which the hot offset occurs is practically 230
Temperatures above ℃ are required.

[0051]

[Table 5]

According to the toner of the present invention, the wax is uniformly dispersed with a small particle diameter, and filming on the photoreceptor due to the separation of the wax, and the resulting black spot,
No fogging or the like occurs.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroyuki Fukuda 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd. In-house (56) References JP-A-3-168649 (JP, A) JP-A-2-27363 (JP, A) JP-A-4-255865 (JP, A) JP-A-3-296067 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) G03G 9/08

Claims (2)

(57) [Claims] 1. An electrophotographic toner for heat roll fixing comprising at least a binder resin and an anti-offset wax, wherein the toner is produced through mixing, kneading, pulverizing and classifying steps, and the wax is mixed with the binder resin 100.
1 to 7 parts by weight relative to parts by weight, the average of the major axis length of the wax particles contained in the toner is a, and the average of the minor axis length is b, the wax particles a / b is not more than 20/1, and at least a / b is 1/1 to 3/1 with wax particles and a / b
And wax particles that are 5/1 to 20/1, a / b
The average diameter of the wax (D _W ) and the average diameter of the toner (D _T ) satisfy the relationship of D _W = 0.05 D _{T to} 0.2 D _T. For wax particles having a / b of 5/1 to 20/1, the following relational expression: (ab ² ) ^1/3 = 0.025D _{T to} 0.1D _T (average diameter, long axis and short axis of the wax particles) The length of the shaft is a value measured from an electron micrograph of the wax particles collected by treating the toner with a solvent that dissolves the binder resin but does not dissolve the wax particles.) Electrophotographic toner. 2. The method according to claim 1, wherein the mixing step is performed using a mixer having a pulverizing ability, and the kneading step disperses the wax particles in the binder resin by a shearing force of the binder resin. The toner for electrophotography according to the above.