UF-printers also UF-blackened (world market)
The UF-printer is the universal device capable to perform printing the specific paints hardening under the influence of ultraviolet both on rolled materials, and on firm surfaces, such as PVC, laminate, metal, etc. The directory of the Office equipment is available on TAdviser.
There are three main configurations of large-format UF-printers. The configuration has a considerable impact on image location accuracy concerning material and also determines the speed of drawing production.
UF-printers for work with rolled carriers
The material feed in these types of machines is performed using capstan idlers in the same way as in all inkjet printers. Such configuration generally for printing on soft (rolled) carriers is used that includes banner PVC-fabrics, a canvas, self-adhesive films, grids. Purchase of such printer is justified at orientation of printing production only on rolled materials.
UF-printers of a pipeline configuration
This configuration of UF-printers is most functional and therefore it is demanded. It allows to print both on rolled carriers, and on the majority of tough (sheet) materials. The pipeline is the mesh tape tense between two shaft. For fixing of material the vacuum system of a clip is used. As a rule, such machines are supplied with the system of giving acceptance (taking-up) of rolled materials. Application of this kind of a configuration is especially effective by drawing productions when the minimum time for giving and for removal of material is an important factor. At printing on tough materials in case of existence of increased requirements to the accuracy of combination of the image and edges of the carrier deviations at a material feed are possible, and than the product is longer, shift will be that more. Such shortcoming is connected with irregularity of a tension of the conveyer belt and material of which it consists. Only the operator of the machine owning experience and skill necessary for this purpose can minimize such shortcoming.
UF-printers of a tablet configuration
This configuration means existence of a motionless horizontal table. All main movements are made by the portal (a superstructure with the carriage). Material is fixed on a table using the vacuum system of a clip or using a bilateral adhesive tape for temporary fixing. Such machines are recommended for the printing productions focused on products from tough (sheet) materials including plastic, glass, metal and wood. The printability on rolled materials is provided only on some models of tablet printers by inclusion in a configuration of additional nodes (options) that conducts to machine value addition. Technology tablet UF-printers are more preferred solution in comparison with a pipeline configuration thanks to existence of a motionless table: the possibility of shift of material, irrespective of its weight is excluded, and, as a result, more exact putting paint on a surface concerning edges of material is provided that is not always possible when using the conveyer belt.
In water ink and ink on the basis of solvents from 50% up to 70% of volume occupy substances which evaporate from a surface after drawing. Unlike them, UF-ink represents polymer which at printing practically for 100% is transferred to a surface and does not evaporate anywhere. UF-ink, despite their higher cost concerning other types of ink, is used to two times more effectively.
UF-otverzhdayemye ink usually consists of the following components:
- special additives.
In the course of UF-curing photoinitiators are principal components. After absorption of ultra-violet light from the source located in the printing carriage, photoinitiators get into reagents which start chemical reaction of polymerization (reaction of connection of separate molecules in long molecular chains). This process will transform liquid ink to a firm film.
These substances define final properties of the cured film, including elasticity, resistance to atmospheric and chemical actions. Oligomera have high molecular weight and are some kind of chemical framework of UF-ink.
Monomer — a uniform molecule which can become chemically connected with other monomers, creating polymer. Monomers are present at composition of ink for giving of special properties to them, increase the hardness and resistance of a film to abrasion, but also can increase viscosity of chemical compound.
In UF-ink the dyes based on paints or pigments are applied. Usually dyes are based on pigments because of their big retroreflective capability and durability in comparison with paints.
Depending on a formula of UF-ink, they can include the potokoobrazuyushchy and liquefying means, antioxidants and stabilizers. For providing a uniform covering of material enter special surfactants into composition of ink. It is very important to manage spraying process that influences the correct formation of a point and it is important for providing a high image quality.
Stabilizers influence storage life of ink and resistance of structure to heating which is important at high temperatures of injection. Stabilizers neutralize or absorb chemically active molecules in ink in the course of storage and prevent their premature polymerization. Art works of course of process of curing of UF-ink are given below.
Under the influence of UV-radiation from a source photoinitiators activate polymerization reaction - intermolecular communications are formed.
Polymerization process continues still some time after the termination of influence of radiation. After inclusion in reaction of all components there is a complete polymerization of ink. Power of an ultraviolet light has a great influence on curing speed. The it is higher, the reaction proceeds quicker.
After the end of chemical reaction the film with strong molecular communications and the fulfilled photoinitiators in structure is formed.
System of curing of paint
One of the most important nodes of the UF-printer is the system of curing of ink. Since the beginning of emergence of the first UF-devices powerful ultra-violet lamps acted as the only means of curing of ink. Rather recently there were full-fledged UF-printers using LEDs (UV-LED) radiating ultra-violet light.
Such radiation sources are established on the printing carriage of the printer. From a reverse side of rather printing field to a lamp the aluminum reflector and the powerful cooling system are installed. In the majority of models of printers material at return motion of the carriage is protected from influence of radiation by special blinds which open and closed automatically depending on the selected printing modes.
Use of UF-lamps assumes obligatory existence in the printer of the cooling system of lamps, and for printing on materials, sensitive to temperature, as well existence of the cooling system of material after radiation.
Minuses of this type of sources of ultraviolet are selection of a large amount of heat during operation of lamps, big energy consumption, rather small service life of lamps (from 600 to 1500 hours). Despite it, UF-lamps are installed more than in 95% of all equipment for the UV printing. One more shortcoming is added to rather small life of lamps: unsafeness of the cooling system of lamps. As a rule, in the majority of constructive solutions in UF-printers the air cooling system is installed. At operation of the equipment in the conditions differing from recommended by the manufacturing plant, fast failure of cooling fans is possible. To avoid similar breakdowns of the equipment, it is regularly necessary to carry out prevention of cooling systems of the printer and to comply operating conditions according to technical data sheet of the machine.
From the very beginning of creation of UF-printers producers tried to find an alternative to UF-lamps. The LEDs radiating ultraviolet were the only option at that time, but the complexity was that then LEDs had very low power (measured in milliwatts) and high cost. But the LED industry develops enough in high gear, and today there are already full-fledged printers in which LED UV sources are used. There is a lot of advantages at this technical solution: high efficiency of LED levels, lack of strong heating of material, low power consumption and inclusion of LEDs for milliseconds. For that time at which service life of LEDs is estimated during the work with the printer on two UF-lamps (for bidirectional printing) you should replace each lamp of more than 40 times.
Now the complexity in operation of UF-printers on LEDs is connected not so much with diodes because of their insufficient emissive power how many with need for special chemical composition of UF-ink and lack of enough suppliers of paint. Therefore upon purchase of the LED UF-printer it is necessary to approach the choice of the supplier of supplies seriously. So, the situation at which at a certain and most responsible moment the user can appear without supplies to the machine is quite possible.
Undoubtedly, LEDs proved advantage of the technology in all respects, but the main criterion for many producers of commercial graphics is the criterion of economic feasibility of use of this or that technology for the printing production.
Feed system of ink
The feed system of ink is intended for uninterrupted supply of paint to printing heads. The main nodes of a system are: tanks for storage of ink, superchargers (pumps), the system of recirculation of white color, pumps of return pressure (not in all models of printers), subtanks (tanks with paint in front of printing heads) and printing heads. Let's consider separately main nodes of this system.
Tanks for UF-ink are executed of opaque material. It is caused by property of ink to harden under the influence of ultra-violet light. The intensity of sunlight is not enough for fast curing of ink, but during long influence this influence can affect properties of paint. For the same reasons all tubes of UF-printers on which paint proceeds are executed of material of black color.
For supply of paint from the main tanks to the printing carriage special pumps for ink of each of flowers which works depending on indications of sensors in tanks on the printing carriage (subtanks) are used.
System of recirculation of white color
For white color the special system of recirculation of paint is provided in modern models of UF-printers. It is caused by property of white paint at long idle standing in tanks to be stratified on components. The system of recirculation provides homogeneous composition of paint throughout all operation mode of the printer. Capacity with white paint is also supplied by the supercharger, as well as basic colors, for supply of paint in subtanks.
System of negative pressure
At switching off of the mode of printing paint should not flow from nozzles of printing heads. For this purpose it is necessary to create return pressure in subtanks. At the moment there are two methods of adjustment of return pressure: adjustment by provision of a subtank and forced creation of return pressure. These methods have advantages and shortcomings. Let's dwell upon them. Adjustment by provision of a subtank is performed by change of vertical position of a subtank of rather printing head, thereby creating return pressure. Such construction is cheaper and has no additional nodes. The main lack of this method is the complexity of pressure control under the unstable and changing conditions. There is a probability of failures of supply of ink in printing heads at high speeds of printing.
Pressure adjustment by a pump means existence of the separate system creating negative pressure in subtanks. Main advantage of such system is simplicity of regulation at different operating conditions. Besides, in this case uninterrupted supply of ink in subtanks at high speeds of printing is provided.
Printing heads for UF-printers essentially do not differ from the heads used in modern printers using paints on the basis of solvent (solvent and ecosolvent ink). Therefore it is possible to consider characteristics of heads generally.
The most important characteristics of printing heads are the speed provided with them and printing quality. I want to pay your attention to the word "quality": this concept which all of us can interpret in different ways and at everyone a concept of quality is individual. In its direct determination it sounds so: "The quality is a compliance of actually received values (characteristics, detailing, etc.) set previously". Therefore I suggest not to use this concept, and to replace with specific descriptive characteristics - for example, high detailing or uniform filling.
So, we will consider what influences a print speed? First, the speed of the printing head or frequency of clock periods of work of piezoelements, vypryskivayushchy paint from nozzles. The frequency of clock periods, the bigger quantity of points is higher the printing head will be able to put per unit length with the identical traverse speed of the printing carriage. Respectively, heads with high frequency of printing require use of more hi-tech servicing electronics that considerably affects increase in their cost. The number of printing heads multiply increases possibilities of fast printing by one paint. So, when installing two heads on every color we receive twice bigger section of a coverage for one pass of the carriage.
When installing three and more printing heads for one color the result will be even higher, but there is one important nuance - preset tuning of the machine, or "data of heads". At acquisition of the equipment with several printing heads of one color you need to pay attention to services of training of your operators by the service engineer of supplier company, otherwise installation and setup of the equipment will demand a lot of time and forces. It is easy to reduce two-three printing heads, but configure work more than four heads already rather difficult. Data are necessary for the correct arrangement of printing heads of one color among themselves and still concerning three and more groups of printing heads of other flowers. At imperfect tuning you will observe "lumbago" of flowers within one step of printing (print pass).
The existing high-frequency drivers in a pair combination for one color are capable to provide a print speed to 140 sq.m/h for outside application and up to 70 sq.m/h at printing in the mode of interior quality.
Detailing of the image ("quality" of printing)
The following characteristics of printing heads are responsible for high detailing of the image, smoothness of color transitions: the drop size (in picolitres) and the number of printing nozzles per unit length. High-speed machines for printing of outdoor advertizing use printing heads with drop value from 80 pl to 40 pl. At a high print speed such size of a drop provides the saturation and uniformity of filling of uniform colors (die fillings). Big drops, without having managed to be absorbed in material, spread, merging with the next drops that leads to ensuring more uniform colors without granularity. Heads with a size of drop less than 40 pl are suitable more for ensuring interior image quality where soft junctions of flowers and high detailing are necessary.
It was told about certain values of the sizes of a drop of printing heads above. Many heads are characterized by the fixed size of a drop. Purchasing a printing head with a big drop, we lose interior image quality and, on the contrary, purchasing a head with a small drop, we lose in a print speed of advertizing of outside application. For situations when it is necessary to connect a high print speed of outdoor advertizing and high detailing of interior images in one press, use of printing heads with a dynamic drop as well as possible will approach (with technology of formation of a drop of ink of variable volume). Heads with a dynamic drop allow to change its size depending on type of the sealed area. For example, if it is homogeneous filling, the big size of a drop is used, and, on the contrary, upon color transitions - smaller size of drops. The example of printing static drops and dynamic is given in drawings below.
One more characteristic of the printing head which is responsible for detailing of the image is physical permission of a printing head, or the number of printing nozzles per unit length (1 inch). Nozzles are very small openings in the printing head through which the piezoelement vypryskivat paint. The it is more nozzles, the printing head can apply bigger quantity of drops on a surface for one pass and the more so densely drops will lie on the relation to each other, providing uniform filling. There are several configurations of arrangement of printing nozzles: single-row, double-row, arrangement in chessboard order and turn of the printing head with single-row arrangement of nozzles that increases density of drops, but reduces the size of a printing field for one pass of a head by a certain corner.
Some printing heads are supplied with the system of heating of ink before injection on a surface. Such technical solution is caused by properties of paints and need of their preliminary preparation for ensuring uniform drawing. There are heads with a single system of heating for all heads of the printing carriage where uniform temperature for all subtanks and also heads with individual heating on each subtank is set. You should not forget that in paint of any shade chemical dyes which in turn are different chemicals are used and have an impact on properties of all paint. Paint temperature monitoring separately of each subtank allows to reach more granular control for every color that is especially important in UF-printers.
According to Rusnano, the volume of the world market of UF-printers in 2008 was 2,766 units (the forecast of growth by 2013 — 85%) and $607 million (growth by 2013 — 63%).
In turn, the size of the market of UF-ink in 2008 reached 1,638 thousand liters (the forecast of growth by 2013 — 117%) and $248 million (growth by 2013 — 64%).
Main article: Printer