The picture drum

The image drum as a transmitter of the print image in laser printing and laser copying. At the heart of your printer is the image drum, also known as the photoconductor, known as the Photo Conductor Unit (PCU) in English-speaking countries. The image drum as a central printer accessory transfers the print image of your print job to the substrate in a photoelectric process and thus represents the crucial component of your printing device when converting digital information into a printed image.

At the center of electrophotography - the image drum

The technology used to print an image or text in laser printers and laser copiers is called electrophotography. The process, which is also called xerography or electro-facsimile process, is behind the popular terms laser printing or photocopy.

Electrophotography first transmits a digital image with the help of light into an invisible image, in order to transfer it into an image of toner particles, which is finally pressed onto a carrier material. To transfer the various images of the original image, different rollers and transfer mechanisms are used. The most important of these rollers is the image drum with its exposed photoconductor.

A technically advanced pipe - the image drum

The image drum is a tube of aluminum that is between one to two millimeters thick. Depending on the printer model, the image drum has a different diameter. Their length protrudes a few millimeters on both sides of the substrate, so in A4 printers almost 22 centimeters, in A4 printers almost 30 centimeters long. The image drum is firmly anchored in the printer via hanger and can be removed and replaced depending on the design.

On the entire surface of the image drum is a photosensitive layer - the so-called photoconductor or semiconductor. In the classical printers and copiers of laser technology, twenty years ago inorganic substances for the photoconductor, such as arsenic tellurium, gallium arsenide or amorphous selenium were used. Today, environmentally friendly amorphous organic materials are used for the photoconductor, abbreviated to OPC - Organic Photo Conductor - be designated, such as amorphous silicon or arsenic triselenide.

Information transmission through exposure and development - this is how the image drum works

The image drum is in the inactive state in the dark electrically balanced and non-conductive. The aluminum drum is positively charged, the layer of the photoconductor is negatively charged, whereby the electrical charge is balanced and no current flows.

The exposure - the hidden negative image on the image drum

As soon as light hits the drum, the charges of photoconductor and drum change. Depending on the printer model, different techniques are used for light transmission. The light is transmitted, for example, by light emitting diodes or laser beam as well as with the aid of a lens that projects light onto the image drum. Upon impact of light, electrical charge is generated in the layer of the photoconductor, which transmits a positive charge to the drum at the exposed areas and at the same time causes an electrical discharge.

This creates an invisible image from all those areas that no longer carry any electrical charge. The digital image information is now transmitted as a hidden image in the form of charge-free points, areas and lines on the image drum. From here, the image information is now transferred to a printed image by the toner is used.

Development - the visible picture on the picture drum

With the help of a toner roller, which is brought to the image drum, the toner is now transferred to the image drum. The toner plays a significant role in its transfer to the image drum, for which it is equipped with technically advanced features. The toner knows various technical varieties, with which it is optimally adjusted to the requirements of the printer model in which it is to be used.

Thus, the so-called two-component toner consists of the color particles on the one hand and iron particles on the other hand, which react to the magnet and end up as waste in the waste toner container at the end of the printing process. In the one-component toner, however, the color particles themselves are magnetic, can have a different electrical charge depending on the printing technology and implement different printing processes. The application of the toner is carried out by another drum, which in turn is equipped differently in different technologies.

The first drum to apply toner is the so-called brush - a magnetic roller whose magnetism causes the particles of the toner to rise like bristles. The toner roller of the so-called jump technology, however, makes the brush superfluous. In the jump technology, the toner skips the gap between the toner roller and the image drum due to a higher electrostatic charge to immediately land on the charged areas.

The rollers of both methods come very close to the image drum in the toner transfer, creating an electrostatic charge, which pulls the toner particles to the image drum and transferred to the electrically charged areas of the image drum. Due to its opposite charge, the toner sticks to the charged areas of the image drum and now presents the complete print image.

So the toner comes from the image drum on the paper

When transferring the toner to the paper, the so-called transfer roller or a transfer belt is used. The transfer roller or transfer belt is much more charged at up to 15 kilovolts than the image drum and thus completely attracts the toner. The carrier material is passed through between the two drums and takes over the toner from the transfer roller or the transfer belt, and then again to run through two heated rollers to fix the toner.

Due to their heat, the toner melts and bonds stably with the paper. At the same time, the toner is provided with a fixing agent and pressed by another roller to obtain optimum adhesion to the paper.

Cleaning the image drum - this is how your printer waits

After each printing operation, the image drum must be cleaned of any remaining residues of toner particles just as it must be freed from any remaining electrical charge. For this purpose, the image drum with a rod-shaped light source is fully exposed once to remove all electrical charges. Then another drum with a scraper or a brush is used to remove the remaining toner, which is transferred to the waste toner box and stored there until disposal.

Capacity - that's what a picture drum does

Depending on the print volume, manufacturers offer different image drums. Disposable imaging drums print up to 5,000 pages, depending on the printer model, until they need replacing, while semi-permanent imaging drums are designed to print up to 20,000 pages. The most powerful image drums are the so-called permanent image drums, which can print up to 300,000 pages.

Image drums for color laser printing - turret system and inline system

The turret system is the simplest color printing system. The printing device is equipped with a picture drum, which is responsible for each of the four inks. The paper is passed once per color over the image drum. For this, the image drum is exposed for each individual color. The turret system processes the four colors one after the other, which means that the printing of one page takes a relatively long time and the paper is also pulled four times through the rollers.

The inline system uses four image drums for the four colors in the printing system. The colors are applied one after the other on the paper, whereby the paper runs once through the complete printing system. Prints in the inline system are made much faster than in the revolver system.

Image drum individually or in the toner pack

The manufacturers install the image drums for their various printer models in different variations. There are image drums that are integrated into the printer, work independently of the toner and have to be replaced after their wear. Some image drums are an integral part of the printer-specific toner cartridge and must be replaced as soon as you dispose of your toner.

Printer Test - important information before buying a printer

Before buying your printer, it is worthwhile obtaining the most accurate information possible about the technical characteristics of the respective image drums in order to choose the most suitable technology for you. Printer test reports provide valuable information by examining the different printer models of the manufacturers and giving detailed information about the important printer components.