Laser printing

The laser printing process consists of five consecutive steps:

1. Photoshaft charging

Photoval is a cylinder with a coating of a photofilament conductor (a material that can change its electrical resistance during illumination). In some systems, instead of a photo cylinder, photovoltaic was used - an elastic looped strip with a photo layer.

Photovoltaic charging - application of uniform electric charge on the surface of the rotating photobarabane (1). The most commonly used photobarabane material - photorganic - requires the use of a negative charge, but there are materials (for example, silicon) that allow the use of a positive charge.

Initially, charging was carried out using a speedron (English scorotron) - a tensioned wire, which is supplied with voltage relative to the photobaraban. A metal grid is typically placed between the wire and the photobarabane to align the electric field.

Later they began to apply charging using a charging roller (English Charge Roller) (2). Such a system allowed to reduce stress and reduce the problem of ozone release in corona discharge (conversion of O2 molecules to O3 under the influence of high voltage), but entails the problem of direct mechanical contact and wear of parts, as well as cleaning from impurities.

2. Laser scanning

Laser scanning (illumination) - the process of passing the negatively charged surface of the photograph under the laser beam. The laser beam (3) is deflected by the rotating mirror (4) and, passing through the distribution lens (5), focuses on the photograph (1). The laser is activated only in places where the magnetic shaft (7) will subsequently have to apply toner.

Under the action of the laser, the portions of the photosensitive surface of the photovoltaic, which have been illuminated by the laser, become electrically conductive, and the charge in these portions "drains" onto the metal base of the photovoltaic. Thus, an electrostatic image of the future imprint in the form of a weakened charge is created on the surface of the photograph.

3. Imposing of a toner

A negatively charged roller when supplying toner gives the toner a negative charge and supplies it to the development roller. The toner in the hopper is attracted to the surface of the magnetic shaft by the magnet from which the core of the shaft [1] is made. During rotation of the magnetic shaft, the toner on its surface passes through a narrow slot formed between the metering blade and the magnetic shaft. After that, the toner comes into contact with the photograph and is attracted to it in those places where the negative charge was removed by illumination.

Thus, the electrostatic (invisible) image is converted to visible (manifested). The toner drawn to the photo moves further on it until it comes into contact with the paper.

4. Transfer of a toner

At the point of contact of the photographer with paper, under the paper is another roller, called a transfer roller. A positive charge is supplied to him, which he reports to the paper with which he contacts. Toner particles, coming into contact with positively charged paper, are transferred to it and held on the surface due to electrostatics.

If you look at the paper at this moment, a fully finished image will be formed on it, which can be easily destroyed by swiping on it, because the image consists of toner powder drawn to the paper, which is not held on the paper by anything other than electrostatics. To get the final print, the image must be pinned.

5. Fixing of a toner

Paper (8) with "filled" toner image moves further to fixing unit (furnace) (11). The image is fixed due to heating and pressure.

The stove consists of two shafts:

• an upper, inside which is a heating element (usually a halogen lamp), called a thermoval;
• lower (pressing roller), which presses the paper to the upper due to the retaining spring.

The temperature of the thermostat is monitored by a temperature sensor (thermistor).

The stove consists of two contacting shafts, between which the paper passes. When the paper is heated (180-220 ° C), the toner drawn to it melts and is pressed into the texture of the paper in liquid form. After leaving the stove, the toner quickly freezes, which creates a constant image that is resistant to external influences. So that the paper on which the toner is applied does not adhere to the thermoval, paper separators are made on it.

However, the thermal is not the only embodiment of the heater. An alternative is a furnace that uses a thermoplastic film: a special flexible material with heating elements in its structure.

Color laser printers

The principle of multicolor laser printing is as follows:

At the initial stage of the printing process, the rendering engine takes a digital document and processes it one or more times, creating its page-by-page bitmap image, spread out according to color components corresponding to the colors of the toners used.

In a second step, the laser or array of LEDs forms a charge distribution on the surface of the rotating photosensitive drum similar to the resulting image. Charged fine particles of toner consisting of coloring pigment, resins and polymers are attracted to charged areas of drum surface.

Then the paper contacts the drum, and the toner is transferred to it. Most color laser printers use four separate passes corresponding to different colors. The paper then passes through a "stove" that melts the resins and polymers in the toner and fixes it to the paper, creating a final image.

Lasers are able to focus accurately, resulting in very thin beams that discharge the necessary areas of the photosensitive drum. Thanks to this, modern laser printers, both color and black and white, have a high resolution.

Main article: Laser printers

Main article: Printing devices (market)

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