JPH0758411B2 - Toner image fixing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an electrophotographic heat fixing method for heating and fixing toner adhered on a recording paper.

[Prior Art] In the electrophotographic method, a desired electrostatic latent image is formed on a recording paper, toner is electrically attached to the electrostatic latent image and developed, and then the toner is heated to form a recording paper. There is a method of fixing. Conventionally, the electrophotographic heat fixing method of heating the toner to fix it on the recording paper is to pass the recording paper on which the electrostatic latent image is formed between a pair of rollers and heat the rollers to melt the toner. Therefore, the method of fixing the toner on the recording paper is adopted.

However, in such an electrophotographic heat fixing method,
The melted toner adheres to the roller to cause so-called offset, which is fixed on the recording paper for the next fixing and causes background stain.

Therefore, a roller is provided with a coating layer that does not easily adhere to toner, or a liquid that does not easily adhere to toner is applied to the roller, but a complicated and expensive device is used, which is not economical.

On the other hand, for the purpose of eliminating the problem of heat fixing, a fixing method using pressure is also known, but this method also requires an extremely large pressure without heating, and it is not possible to sufficiently fix the fixing property. Even if you put up with it, even if you put up with high pressure, fine parts of the toner image will collapse and gloss will occur on the recording paper, and the weight of the device will increase and the cost will increase, and the recording cost will increase. Has many problems.

[Problems to be Solved by the Invention] The present invention eliminates the above problems and provides a toner fixing method capable of performing fixing without offset using a simple and inexpensive apparatus. With the goal.

[Means and Actions for Solving Problems] Specifically, the present invention provides a toner image fixing method including a fixing step of fixing a toner image formed of a toner onto a recording sheet at least twice. Toner has different softening temperature 2
The softening temperature of the binder resin containing at least one kind of binder resin and having the lowest softening temperature is _TL , the pre-fixing pressure and pre-fixing temperature of pre-fixing are P ₁ and T ₁ , and the post-fixing post-fixing pressure and When the fixing temperatures are P ₂ and T ₂ , the binder resin whose softening temperature is lower than the pre-fixing temperature T ₁ is the former binder resin 10
It is contained in an amount of 20 to 90 parts by weight per 0 parts by weight, and the toner image is fixed on the recording paper by pre-fixing and post-fixing under the following conditions: P ₁ <P ₂ , T ₁ > T ₂ , _TL <T _1. And a method for fixing a toner image.

The toner used in the electrophotographic system is mainly composed of a binder made of a thermoplastic resin and a colorant. About 60 to 95% of the toner is a binder, and the thermal behavior is dominated by the properties of the binder. Further, as shown in Comparative Example 2 described later, when the pre-fixing temperature T ₁ is lower than the softening temperature T _{L of the} binder resin having the lowest softening temperature, the fixability of the toner image on the recording paper is deteriorated.

In the present invention, a toner using two or more kinds of binder resins having different softening temperatures is more preferably heat-fixed at a temperature of the minimum softening temperature or higher and the maximum softening temperature or lower among the softening temperatures of the binder resins. After that, a pressure higher than about 7 kg / cm ² which is a pressure for normal heat fixing, and a pressure lower than 200 kg / cm ² which is a pressure for normal pressure fixing, preferably 2
By fixing by applying a pressure of 0 to 100 kg / cm ² , it is possible to prevent melting of the entire binder and to better prevent the occurrence of so-called offset in which toner adheres to the roller. Further, this makes it possible to favorably prevent deterioration of image quality and occurrence of gloss of paper, which are problems of pressure fixing.

If you try to apply the above pressure and temperature at the same time by using the same roller, you cannot use it as a normal heat fixing roller because it is weak against pressure and has no durability. The surface releasability is poor, and it is difficult to obtain sufficient offset resistance. That is, the present invention achieves the above-mentioned object by performing the fixing in two stages using separate heat rollers 3 and light pressure rollers 4 as shown in the example in FIG.

The amount of binder resin whose softening point is lower than that under the pre-fixing temperature is
The total amount of the binder is preferably 20 to 90 parts by weight, more preferably 40 to 70 parts by weight, based on 100 parts by weight. It is difficult to obtain sufficient fixability at the end of 20 parts by weight, and it is difficult to obtain sufficient offset resistance when it exceeds 90 parts by weight.

[Examples] Examples will be described below. The softening temperature was measured by the ring and ball method.

Toner Production Example 1 Volume average particle size 8.0μm by kneading, crushing and classifying the above components
Toner was obtained.

Toner Production Example 2 The above components were mixed with an attritor at a temperature of 80 ° C. for 4 hours to prepare a monomer composition.

254 parts by weight of the obtained monomer composition, 20 parts by weight of amino-modified silica (100 parts by weight of Aerosil 200 treated with 5 parts by weight of aminopropyltriethoxysilane) and 0.
Distilled water 1200 containing 25 parts by weight of 1N hydrochloric acid and heated to 85 ° C
Add to a part by weight of an aqueous medium under stirring with a TK homomixer,
After charging, the mixture was stirred for 15 minutes at 10,000 rpm to carry out dispersion granulation.

After granulation, the liquid temperature was lowered to 60 ° C, and 3 parts by weight of 2,2'-azobis- (2,4-dimethylvaleronitrile) and 1.5 parts by weight of 2,2'-azobisisobutyronitrile were used as a polymerization initiator. Added to the aqueous medium and stirred for 30 minutes. Further, the stirring was changed to a paddle blade stirring, and stirring was carried out at 60 ° C. for 10 hours to complete the polymerization.

The obtained polymerized toner-containing aqueous medium is cooled and dehydrated,
Washing with sodium hydroxide solution to dissolve and remove amino-modified silica, washing with water, dehydration, and drying (if necessary, fine particles of unnecessary component particles are removed to remove them) Volume average particle size
A 6.5 μm (measured with a Coulter counter using a 100 μm aperture) toner was obtained. The resulting polymerized toner contained about 100 parts by weight of paraffin wax with respect to 100 parts by weight of polystyrene. Further, the obtained toner did not cause blocking even when left in an environment of 50 ° C. for one day. From this, it was found that the paraffin wax was encapsulated inside the polymerized toner particles.

The softening temperature (polystyrene softening temperature) of the toner obtained by melt-kneading a toner polymerized by the same method as in Toner Production Example 2 except that paraffin wax was not used was 155 ° C.

Examples 1 and 2 and Comparative Examples 1, 2 and 3 The toners obtained in Toner Production Examples 1 and 2 were developed by an ordinary two-component developing method, and the following fixing test was conducted.
The paper traveling speed was 300 mm / sec. The results are shown in Table 1.

[Advantages of the Invention] As described above, according to the fixing method of the present invention, it is possible to obtain an excellent fixing property without causing an offset.

Further, the fixing temperature can be lowered as compared with the usual heat fixing method, and the energy can be saved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a fixing device used in the present invention. 1 ... paper, 2 ... toner 3 ... heat roller, 4 ... light pressure roller

Claims (2)

[Claims] 1. A toner image fixing method comprising a fixing step of fixing a toner image formed of a toner onto a recording paper twice or more, wherein the toner contains two or more kinds of binder resins having different softening temperatures and is softened. Let T _{L be} the softening temperature of the lowest binder resin, P ₁ and T ₁ be the pre-fixing pressure and the pre-fixing temperature of the pre-fixing, and P ₂ and T ₂ are the post-fixing pressure and the post-fixing temperature of the post-fixing. , The binder resin having a softening temperature lower than the pre-fixing temperature T ₁ is 2 per 100 parts by weight of the total binder resin.
It is contained in an amount of 0 to 90 parts by weight, and is characterized in that the toner image is fixed on the recording paper by performing pre-fixing and post-fixing under the following conditions P ₁ <P ₂ , T ₁ > T ₂ , T _L <T _1. Toner image fixing method. 2. The method for fixing a toner image according to claim 1, wherein the post-fixing pressure P ₂ is ₂₀ to 100 kg / cm ₂ .