We display forms for flexographic printing

Dr. tech. sciences, prof. MGUP im. Ivan Fedorov

A type of letterpress that is widely used for printing labels and packaging products from paper, foil, plastic films, as well as for printing newspapers, is flexography. Flexographic printing is carried out with elastic rubber or highly elastic photopolymer printing plates with fluid fast-setting inks.


In the printing apparatus of a flexographic printing machine, rather liquid ink is applied to a printing plate fixed on a plate cylinder, not directly, but through an intermediate rolling (anilox) roller. The knurling roller is made of steel pipe, which can be coated with a layer of copper. A raster grid is applied to this surface by etching or engraving, the deep cells of which are made in the form of pyramids with a sharp top. The raster surface of the anilox roller is usually chrome-plated. The transfer of ink from the ink box to the printing plate is carried out by a rubber (ductor) roller to the anilox roller, and from it to the printing elements of the form.

The use of resilient printing plates and low-viscosity fast-setting inks makes it possible to print almost any roll material at high speed, to reproduce not only line elements, but also single- and multi-color images (with screening lineature up to 60 lines/cm). Slight typing pressure ensures b about Greater circulation stability of printed forms.

Flexography is a direct printing method in which ink is transferred from a plate directly onto the printed material. In this regard, the image on the printing elements of the form must be mirrored in relation to the readable image on paper (Fig. 1).

In modern flexographic printing, photopolymer printing plates (FPF) are used, which are not inferior to offset ones in terms of printing and technical and reproduction and graphic properties, and, as a rule, surpass them in run resistance.

Solid or liquid photopolymerizable compositions are used as photopolymer materials. These include solid or liquid monomeric, oligomeric or monomeric-polymer mixtures capable of changing the chemical and physical state under the action of light. These changes lead to the formation of solid or elastic insoluble polymers.

Solid photopolymerizable compositions (SFPs) retain a solid state of aggregation before and after manufacturing printed form. They are delivered to the printing company in the form of photopolymerizable shaped plates of a certain format.

The structure of photopolymerizable plates for flexographic printing is shown in fig. 2.

Liquid photopolymerizable compositions (LFP) are supplied to printing companies in containers in liquid form, or they are made directly at the enterprises by mixing the initial components.

The main technological operation in the manufacture of any FPF, during which a photopolymerization reaction occurs in the photopolymerizable composition and a latent relief image is formed, is exposure (Fig. 3 but) of the photopolymerizable layer. Photopolymerization occurs only in those parts of the layer that are exposed to UV rays and only during their exposure. Therefore, negative photoforms and their analogues in the form of a mask layer are used for exposure.

Rice. Fig. 3. Technological operations for obtaining photopolymer printing plates on solid photopolymerizable plates: a - exposure; b - washing out of gaps; c - drying of the printing plate; d - additional exposure of printing elements

The development of a relief image, as a result of which non-polymerized areas of the photopolymerizable plate are removed, is carried out by washing them out with an alcohol, alkaline solution (Fig. 3 b) or water depending on the type of plates, and for some types of plates - dry heat treatment.

In the first case, the exposed photopolymerizable plate is processed in the so-called solvent processor. As a result of the washout operation (see Fig. 3 b) of non-polymerized sections of the plate, a relief image is formed on the form with a solution. Washout is based on the fact that in the process of photopolymerization, the printing elements lose their ability to dissolve in the wash solution. After washing, drying of photopolymer forms is required. In the second case, processing is carried out in a thermal processor for processing photopolymer forms. Dry heat treatment completely eliminates the use of traditional chemicals and wash solutions, reduces the time of obtaining molds by 70%, since it does not require drying.

After drying (Fig. 3 in) the photopolymer form is subjected to additional exposure (Fig. 3 G), which increases the degree of photopolymerization of printing elements.

After additional exposure, photopolymer plates based on TFP for flexo printing have a shiny and slightly sticky surface. The stickiness of the surface is eliminated by additional processing (finishing), as a result, the form acquires the properties of stability and resistance to various solvents of printing inks.

Finishing can be done chemically (using chloride and bromine) or by exposure to ultraviolet light in the range of 250-260 nm, which has the same effect on the form. With chemical finishing, the surface becomes matte, with ultraviolet - shiny.

One of the most important parameters of photopolymer printing plates is the profile of the printing elements, which is determined by the angle at the base of the printing element and its steepness. The profile determines the resolution of photopolymer printing plates, as well as the adhesion strength of the printing elements to the substrate, which affects the runtime. The profile of the printing elements is significantly affected by the exposure modes and the conditions for washing out white space elements. Depending on the exposure mode, the print elements may have a different shape.

With overexposure, a flat profile of the printing elements is formed, which ensures their reliable fixation on the substrate, but is undesirable due to the possible decrease in the depth of gaps.

With insufficient exposure, a mushroom-shaped (barrel-shaped) profile is formed, leading to instability of the printing elements on the substrate, up to the possible loss of individual elements.

The optimal profile has an angle at the base of 70 ± 5º, which is the most preferable, as it ensures reliable adhesion of the printing elements to the substrate and high image resolution.

The profile of printing elements is also affected by the ratio of exposures of preliminary and main exposure, the duration of which and their ratio are selected for various types and batches of photopolymer plates for specific exposure units.

Currently, for the manufacture of photopolymer printing plates for flexographic printing, two technologies are used: “computer-photoform” and “computer-printing plate”.

So-called analog plates are produced for the “computer-printing plate” technology, and digital plates for the “computer-printing plate” technology.

In the manufacture of photopolymer forms of flexographic printing based on TFPK (Fig. 4), the following main operations are performed:

• pre-exposure reverse side photopolymerizable flexographic printing plate (analogue) in the exposure unit;
• the main exposure of mounting the photoform (negative) and the photopolymerizable plate in the exposure unit;
• processing of a photopolymer (flexographic) copy in a solvent (washout) or thermal (dry heat treatment) processor;
• drying of the photopolymer form (solvent washout) in dryer;
• additional exposure of the photopolymer form in the exposure unit;
• additional processing (finishing) of the photopolymer form to eliminate the stickiness of its surface.

Rice. Fig. 4. Scheme of the process of manufacturing photopolymer molds based on TPPC using the “computer-photoform” technology

Exposing the reverse side of the plate is the first step in the manufacture of the form. It represents an even illumination of the reverse side of the plate through a polyester base without the use of vacuum and negative. This is important technological operation, which increases the photosensitivity of the polymer and forms the base of the relief of the required height. Correct exposure of the reverse side of the plate does not affect the printing elements.

The main exposure of the photopolymerizable plate is carried out by contact copying from a negative photoform. On a photoform intended for making molds, the text must be mirrored.

Photoforms must be made on a single sheet of film, since composite montages glued with adhesive tape, as a rule, do not provide a reliable fit of the photoform to the surface of the photopolymerizable layers and can cause distortion of the printing elements.

Before exposure, the photoform is applied to the photopolymerizable plate with the emulsion layer down. Otherwise, a gap equal to the thickness of the base of the film is formed between the plate and the image on the photoform. As a result of the refraction of light in the basis of the film, a strong distortion of the printing elements and copying of the raster areas can occur.

To ensure close contact of the photoform with the photopolymerizable material, the film is matted. Microroughnesses on the surface of the photoform allow you to completely quickly remove air from under it, which creates a tight contact between the photoform and the surface of the photopolymerizable plate. For this, special powders are used, which are applied with a cotton-gauze swab with light circular movements.

As a result of the processing of photopolymer copies based on solvent washout plates, the monomer that has not been exposed and polymerized is washed out - it dissolves and is washed off from the plate. Only areas that have undergone polymerization and form a relief image remain.

Insufficient washout time, low temperature, improper brush pressure (low pressure - bristles do not touch the surface of the plate; high pressure - bristles arch, reduced washout time), low solution level in the wash tank leads to too fine relief.

Excessive washout time, high temperature and insufficient solution concentration lead to too deep relief. The correct washout time is determined experimentally depending on the thickness of the plate.

When washing out, the plate is impregnated with a solution. The polymerized image relief swells and softens. After removing the wash solution from the surface with non-woven napkins or a special towel, the plate must be dried in the drying section at a temperature not exceeding 60 °C. At temperatures above 60 °C, registration difficulties may arise, since polyester base, which under normal conditions maintains stable dimensions, begins to shrink.

Swelling of the plates when washed out leads to an increase in the thickness of the plates, which, even after drying in the dryer, do not immediately return to their normal thickness and must be left for another 12 hours in the open air.

When using heat-sensitive photopolymerizable plates, the manifestation of the relief image occurs by melting the non-polymerized sections of the forms during their processing in a thermal processor. The molten photopolymerizable composition is adsorbed, absorbed and removed with a special cloth, which is then sent for disposal. Such a technological process does not require the use of solvents, and therefore, drying of the developed forms is excluded. In this way, it is possible to produce both analog and digital forms. The main advantage of the technology with the use of heat-sensitive plates is a significant reduction in mold manufacturing time, which is due to the absence of a drying stage.

To give durability, the plate is placed in an exposure unit for additional illumination with UV lamps for 4-8 minutes.

To eliminate the stickiness of the plate after drying, it must be treated with UV radiation with a wavelength of 250-260 nm or chemically.

Analog solvent-washout and heat-sensitive photopolymerizable flexographic plates have a resolution that provides 2-95 percent halftone dots at a screen lineature of 150 lpi, and a print run of up to 1 million prints.

One of the features of the process of manufacturing flat photopolymer forms of flexographic printing using the “computer-photoform” technology is the need to take into account the degree of stretching of the form along the circumference of the plate cylinder when it is installed in the printing machine. The stretching of the mold surface relief (Fig. 5) leads to an elongation of the image on the print compared to the image on the photoform. In this case, the thicker the stretchable layer located on the substrate or stabilizing film (when using multilayer plates), the longer the image.

The thickness of photopolymer forms varies from 0.2 to 7 mm and above. In this regard, it is necessary to compensate for elongation by reducing the image scale on the photoform along one of its sides, oriented in the direction of movement of the paper web (tape) in the printing machine.

To calculate the scale value M photoforms, you can use the stretching constant k, which for each type of plates is equal to k = 2 hc (hc is the thickness of the relief layer).

Print length Lott corresponds to the distance that a certain point on the surface of the mold travels during a complete revolution of the forme cylinder, and is calculated as follows:

where Dfts— diameter of the plate cylinder, mm; hf— thickness of the printing plate, mm; hl— adhesive tape thickness, mm.

Based on the calculated impression length, the necessary shortening of the photoform Δ is determined d(in percent) according to the formula

.

So, the image on the photoform in one of the directions should be obtained with a scale equal to

.

Such scaling of the image on the photoform can be performed by computer processing of a digital file containing information about the imposition or individual pages of the publication.

The production of photopolymer flexographic printing plates using the “computer-printing plate” technology is based on the use of laser methods for processing plate materials: ablation (destruction and removal) of the mask layer from the surface of the plate and direct engraving of the plate material.

Rice. Fig. 5. Stretching of the surface of the printing plate when installed on the plate cylinder: a - printing plate; b - printing plate on a plate cylinder

In the case of laser ablation, the subsequent removal of the non-polymerized layer can be performed using a solvent or thermal processor. For this method, special (digital) plates are used, which differ from traditional ones only in the presence of a mask layer 3-5 μm thick on the surface of the plate. The mask layer is a soot filler in an oligomer solution that is insensitive to UV radiation and thermally sensitive to the infrared range of the spectrum. This layer is used to create the primary image formed by the laser and is a negative mask.

The negative image (mask) is necessary for the subsequent exposure of the shaped photopolymerizable plate with a UV light source. As a result of further chemical processing, a relief image of the printing elements is created on the surface.

On fig. 6 shows the sequence of operations for manufacturing a flexographic plate on a plate containing a mask layer 1 , photopolymer layer 2 and substrate 3 . After laser removal of the mask layer in places corresponding to the printing elements, a transparent substrate is exposed to create a photopolymer substrate. Exposure to obtain a relief image is carried out through a negative image created from a mask layer. Then the usual processing is carried out, consisting of washing out the unpolymerized photopolymer, washing, post-exposure with simultaneous drying and light finishing.

When recording an image using laser systems, the dot size on masked photopolymers is, as a rule, 15–25 μm, which makes it possible to obtain images with a lineature of 180 lpi and higher on the form.

In the manufacture of photopolymer plates in the "computer-printing plate" technology, plates based on solid photopolymer compositions are used, which provide high quality printing plates, the further processing of which occurs in the same way as analog flexo photopolymer plates.

On fig. 7 shows the classification of photopolymerizable plates for flexographic printing based on solid photopolymer compositions.

Depending on the structure of the plate, single-layer and multi-layer plates are distinguished.

Single-layer plates consist of a photopolymerizable (relief-forming) layer, which is located between the protective foil and the lavsan base, which serves to stabilize the plate.

Multi-layer plates designed for high-quality raster printing consist of relatively hard thin-layer plates with a compressible substrate. On both surfaces of the plate there is a protective foil, and between the photopolymerizable layer and the base there is a stabilizing layer, which ensures almost complete absence of longitudinal deformation when the printing plate is bent.

Depending on the thickness, photopolymerizable plates are divided into thick-layer and thin-layer ones.

Thin-layer plates (thickness 0.76-2.84 mm) have high hardness in order to reduce dot gain during printing. Therefore, printing plates made on such plates provide high quality finished products and are used to seal flexible packaging, plastic bags, labels and tags.

Thick-layer plates (thickness 2.84-6.35 mm) are softer than thin-layer ones and provide tighter contact with an uneven printed surface. Printing forms based on them are used for sealing corrugated cardboard and paper bags.

IN Lately when printing on materials such as corrugated cardboard, plates with a thickness of 2.84-3.94 mm are more often used. This is explained by the fact that when using thicker photopolymer forms (3.94-6.35 mm) it is difficult to obtain a high-line multicolor image.

Depending on the hardness, plates of high, medium and low hardness are distinguished.

Plates of high hardness are characterized by less dot gain of raster elements and are used for printing high-line works. Plates of medium rigidity allow you to print raster, line and solid works equally well. Softer photopolymerizable plates are used for ink printing.

Depending on the method of processing photopolymer copies, plates can be divided into three types: water-soluble, alcohol-soluble, and plates processed using thermal technology. To process plates belonging to different types, it is necessary to use different processors.

The method of laser ablation of the mask layer of photopolymerizable plate materials produces both flat and cylindrical printing plates.

Cylindrical (sleeve) flexographic forms can be tubular, put on a plate cylinder from its end, or represent the surface of a removable plate cylinder installed in a printing machine.

The process of manufacturing flat flexographic printing plates based on solvent washout or heat-sensitive digital photopolymerizable plates with a mask layer using the “computer-printing plate” technology (Fig. 8) includes the following operations:

• preliminary exposure of the reverse side of the photopolymerizable flexographic plate (digital) in the exposure unit;
• transferring a digital file containing data on color separation images of stripes or a full-size printed sheet to a raster processor (RIP);
• digital file processing in RIP (reception, interpretation of data, rasterization of the image with a given lineature and raster type);
• writing the image on the mask layer of the plate by ablation in the forming device;
• main exposure of the photopolymerizable layer of the plate through the mask layer in the exposure unit;
• processing (washing out for solvent-washable or dry heat treatment for heat-sensitive plates) of a flexographic copy in a processor (solvent or thermal);
• drying of the photopolymer form (for solvent-washable plates) in a drying device;
• additional processing of the photopolymer form (light finishing);
• additional exposure of the photopolymer form in the exposure unit.

The process of manufacturing sleeve photopolymer flexographic printing plates by the ablation method (Fig. 9) differs from the process of manufacturing flat plates mainly in the absence of the operation of preliminary exposure of the reverse side of the plate material.

The use of the mask layer ablation method in the manufacture of photopolymer flexo plates not only shortens the technological cycle due to the lack of photo plates, but also eliminates the causes of quality degradation that are directly related to the use of negatives in the production of traditional printing plates:

• there are no problems arising due to loose pressing of photoforms in a vacuum chamber and the formation of bubbles during exposure of photopolymer plates;
• there is no loss in the quality of forms due to dust or other inclusions;
• there is no distortion of the shape of the printing elements due to the low optical density of photoforms and the so-called soft point;
• no need to work with vacuum;
• the profile of the printing element is optimal for dot gain stabilization and accurate color reproduction.

When exposing a montage consisting of a photoform and a photopolymer plate, in traditional technology, the light passes through several layers before reaching the photopolymer: silver emulsion, frosted layer and film base, and vacuum copy frame glass. In this case, the light is scattered in each layer and at the boundaries of the layers. As a result, the halftone dots have wider bases, resulting in increased dot gain. In contrast, when laser-exposing masked flexographic plates, there is no need to create a vacuum and there is no film. The near-total absence of light scatter means that the high-resolution image on the layer mask is faithfully reproduced on the photopolymer.

In the manufacture of flexographic forms according to digital technology ablation of the mask layer, it must be borne in mind that the formed printing elements, in contrast to exposure through a photoform in traditional (analogue) technology, are somewhat smaller in area than their image on the mask. This is explained by the fact that the exposure takes place in an air environment and, due to the contact of the FPS with atmospheric oxygen, the polymerization process is inhibited (delayed), causing a decrease in the size of the emerging printing elements (Fig. 10).

Rice. Fig. 10. Comparison of printing elements of photopolymer forms: a — analog; b - digital

The result of exposure to oxygen is not only a slight decrease in the size of the printing elements, which affects small raster dots to a greater extent, but also a decrease in their height relative to the height of the plate. In this case, the smaller the raster dot, the smaller the height of the relief printing element.

On a form made using analog technology, the printing elements of raster dots, on the contrary, exceed the die in height. Thus, the printing elements on a plate made by digital mask technology differ in size and height from the printing elements formed by analog technology.

The profiles of the printing elements also differ. So, the printing elements on the forms made by digital technology have steeper side edges than the printing elements of the forms obtained by analog technology.

Direct laser engraving technology includes only one operation. The mold manufacturing process is as follows: the plate without any pre-treatment is mounted on the cylinder for laser engraving. The laser forms the printing elements by removing material from the space elements, that is, the space elements are burned out (Fig. 11).

Rice. Fig. 11. Scheme of direct laser engraving: D and f are the aperture and focal length of the lens; q - beam divergence

After engraving, the form does not require treatment with washable solutions and UV radiation. The form will be ready for printing after rinsing with water and drying for a short time. Dust particles can also be removed by wiping the mold with a damp soft cloth.

On fig. 12 presented structural scheme technological process of manufacturing photopolymer flexographic printing plates using direct laser engraving technology.

The first engraving machines used a 1064nm infrared high-power ND:YAG neodymium yttrium aluminum garnet laser to engrave rubber sleeves. Later, they began to use a CO2 laser, which, due to its high power (up to 250 W), has about performance, and due to its wavelength (10.6 microns) allows you to engrave a wider range of materials.

The disadvantage of CO2 lasers is that they do not provide image recording with lineatures of 133-160 lpi, necessary for modern level flexographic printing, due to the large beam divergence q. For such lineatures, the image should be recorded with a resolution of 2128-2580 dpi, that is, the size of an elementary point of the image should be approximately 10-12 microns.

The spot diameter of the focused laser radiation must correspond in a certain way to the calculated size of the image dot. It is known that with the correct organization of the laser engraving process, the spot of laser radiation should be much larger than the theoretical size of the dot - then there will be no unprocessed material between adjacent lines of the recorded image.

Increasing the spot by 1.5 times gives the optimal diameter of the elementary point of the image: d 0 = 15-20 µm.

In the general case, the diameter of the CO2 laser radiation spot is about 50 μm. Therefore, printing plates obtained by direct CO2 laser engraving are mainly used for printing wallpaper, packaging with simple patterns, notebooks, that is, where high-line raster printing is not required.

Recently, there have been developments that allow increasing the resolution of image recording by direct laser engraving. This can be done through the skilful use of overlapping laser recording points, which make it possible to obtain elements smaller than the spot diameter on the form (Fig. 13).

Rice. 13. Obtaining small details on the form using overlapping laser spots

To do this, laser engraving devices are modified in such a way that it is possible to change from one beam to work with several beams (up to three), which, due to different power, engrave the material to different depths and thus provide better formation of slopes of raster dots. Another innovation in this field is the combination of a CO2 laser for pre-embossing, especially deep areas, with a solid-state laser, which, due to the much smaller spot diameter, can form slopes of print elements of a predetermined shape. The limitations here are set by the mold material itself, since the radiation of the Nd:YAG laser is not absorbed by all materials, in contrast to the radiation of the CO2 laser.

1.Create a print layout:

Draw a print layout with the necessary data on a computer in any program and invert it into a negative (black and white) image.
We offer the program CoralDraw to create a print layout and to help "beginners" a disk - "Seals and stamps. Protective elements" (3000 rubles), with a large selection of layouts, fonts, templates and images.

2.Print layout:

Print to laser printer with a resolution of at least 600 dpi on matte Kimoto film or transparent LOMOND (pay attention to the quality of the negative).

3. Toner the negative:

Process the negative with toner, after which the dark background should darken. Use original cartridges and toner.

4. Place the negative on the glass:

After wetting the reverse side of the film, place the negative face up on the glass, previously moistened with water (for better adhesion).

5. Cover the negative with a protective film (optional):

Cover the negative with a protective film on top (optional). With smoothing movements, drive out the remaining water from under the film (to prevent the formation of air bubbles and better contact).

6. Paste with curb tape:

Glue around the perimeter with a border tape that limits the space for the polymer, while leaving gaps in the corners.

7.Fill the negative with photopolymer:

Evenly, without interrupting the jet, fill the negative with photopolymer and remove the formed bubbles by blowing air from a rubber bulb or a sharp object (paper clip, toothpick, needle).

8. Cover with a substrate film:

Cover with a film-substrate (On the polymer with a rough side! Glossy outside!), Starting from the middle, as shown in the figure. We touch the center of the polymer with a film without pressing and simply release the edges - they will straighten themselves out and fall on the polymer.

9. Cover with a second glass:

Cover the resulting composition with a second glass and clamp along the edges with clips (stationery clips are bought separately at any stationery store).

10. Place in the exposure chamber:

Place the glass cassette face up in the exposure chamber.

11.Start the timer:

Set the exposure time on the digital timer, which largely depends on the properties of the photopolymer. For polymer grades VX55, ROEHM on the side of the transparent film (first time) it is approximately 20 -30 sec. Start the timer by pressing the CD button. At the same time, the timer will start counting down the time, and a blue glow from the lamps will appear inside.

12. Set the exposure time on the timer:

After the timer counts down and the lamps go out, turn the cassette over with the matte film (negative) up and start the exposure process again (CHANGING THE TIME). For resin grades VX55, ROEHM, the exposure time on the reverse side (second time) is 1 min. A more accurate time is determined empirically by changing the time of both exposures. See the brochure "Technological regulations". When finished, remove the cassette from the camera.

13. Having separated the glass, separate the negative:

After carefully separating the glasses, separate only the negative and the protective thin film from the photopolymer. Do not separate the substrate (transparent) from the print. After removing the hardened polymer from the glasses, some of it remains liquid, so it must then be washed.
ATTENTION!
Very often, novice manufacturers violate the manufacturing technology, namely, the print must necessarily contain a rigid basis for printing - the substrate! This film has two sides, one of which the rough side is superimposed on the photopolymer, and the smooth side is later used for gluing onto adhesive tape (on the tooling, on the body). It does not need to be separated from the photopolymer after the manufacturing process!
For example: if you make a comparison - imagine a person who does not have a bone skeleton, and a print without a substrate.

14. Rinse Cliche:

To remove uncured resin, wash the cliché well with a brush and detergent and degreaser such as Fairy, Cinderella under warm (not hot) running water.

15. Place the cliché into the water:

Place the cliche in a bath of water in the exposure chamber for 7-10 minutes to harden.

16. Cut off excess polymer:

Cut out the cliche, cut off all excess polymer. Cut carefully without touching the sides, otherwise the print will be rejected. This step must be taken very carefully so that you do not have to repeat everything from the beginning.

17. Cliche to stick on the snap:

Glue the finished cliché onto the snap.

In our store, visit the section where you can purchase consumables.

An essential factor in the development of flexographic printing was the introduction of photopolymer printing plates. Their use began in the 1960s, when DuPont introduced the first Dycryl letterpress plates to the market. However, in flexo they could be used to make original cliches, from which matrices were made, and then rubber molds by pressing and vulcanization. A lot has changed since then. . .

Manufacturing methods

Today, the following manufacturers of photopolymer plates and compositions are best known on the global flexographic printing market: BASF, DUPONT, Oy Pasanen & Co and others. pressure generated by the impression cylinder). These include paper, cardboard, corrugated cardboard, various synthetic films (polypropylene, polyethylene, cellophane, polyethylene terephthalate lavsan, etc.), metallized foil, combined materials (self-adhesive paper and film). The flexographic method is used mainly in the field of packaging production, and also finds application in the manufacture of publishing products. For example, in the USA and Italy, about 40% of the total number of all newspapers are printed flexographically on special flexographic newspaper units.

There are two types of plate material for making flexographic plates: rubber and polymer. Initially, the plates were made on the basis of rubber material, and their quality was low, which, in turn, made the quality of flexo prints in general poor. In the 70s of our century, a photopolymerizable (photopolymer) plate was first introduced as a plate material for the flexographic printing method. The plate made it possible to reproduce high-line images up to 60 lip/cm and above, as well as lines with a thickness of 0.1 mm; dots with a diameter of 0.25 mm; text, both positive and negative, from 5 pixels and bitmap 3-, 5-, and 95-percentage points; thus allowing flexography to compete with the "classic" methods, especially in the field of packaging printing. And, naturally, photopolymer plates have taken a leading position as a plate flexographic material, especially in Europe and in our country.

Rubber (elastomer) printing plates can be obtained by pressing and engraving. It should be noted that the molding process itself based on elastomers is laborious and not economical. The maximum reproducible lineature is about 34 lines/cm, i.e. the reproduction capabilities of these plates are low and do not meet modern requirements to the packaging.

Photopolymer forms make it possible to reproduce both complex color and transitions, various tonalities, and raster images with a lineature of up to 60 lines / cm with a rather small spreading (increase in tonal gradations). Currently, as a rule, photopolymer forms are made in two ways: analog - by exposing UV radiation through a negative and removing unpolymerized polymer from gaps using special wash solutions based on organic alcohols and hydrocarbons (for example, using a wash solution from BASF Nylosolv II ) and by means of the so-called digital method, i.e., laser exposure of a special black layer applied over a photopolymer layer, and subsequent washing out of unexposed areas. It is worth noting that recently new developments by BASF have appeared in this area, which make it possible to remove the polymer in the case of analog plates using ordinary water; or directly remove the resin from the gaps using laser engraving in the case of digital mold making.

The basis of a photopolymer plate of any type (both analog and digital) is a photopolymer, or the so-called relief layer, due to which the formation of raised printing and recessed blank elements, i.e. relief, occurs. The basis of the photopolymer layer is a photopolymerizable composition (FPC). The main components of FPC, which have a significant impact on the printing and technical characteristics and quality of photopolymer printing plates, are the following substances.

1) Monomer - a compound of relatively low molecular weight and low viscosity, containing double bonds and, therefore, capable of polymerization. The monomer is a solvent or diluent for the remaining components of the composition. By changing the monomer content, the viscosity of the system is usually controlled.

2) oligomer - capable of polymerization and copolymerization with a monomer, an unsaturated compound of a molecular weight greater than the monomer. These are viscous liquids or solids. The condition for their compatibility with the monomer is solubility in the latter. It is believed that the properties of cured coatings (eg photopolymer printing plates) are determined mainly by the nature of the oligomer.

As oligomers and monomers, oligoether- and oligourethane acrylates, as well as various unsaturated polyesters, are most widely used.

3) Photoinitiator. The polymerization of vinyl monomers under the action of UV radiation can, in principle, proceed without the participation of any other compounds. This process is simply called polymerization and is rather slow. To speed up the reaction, small amounts of substances (from fractions of a percent to percent) are introduced into the composition, capable of generating free radicals and/or ions under the action of light, initiating a polymerization chain reaction.

This type of polymerization is called photoinitiated polymerization. Despite the insignificant content of the photoinitiator in the composition, it plays an extremely important role, which determines both many characteristics of the curing process (photopolymerization rate, exposure latitude) and the properties of the obtained coatings. Derivatives of benzophenone, anthraquinone, thioxanthone, ascilphosphine oxides, peroxy derivatives, etc. are used as photoinitiators.

The best from the BASF

BASF Drucksysteme GmbH (Germany) is one of the leading manufacturers of the world's widest range of photopolymer plates for letterpress, gravure and flexographic printing.

For flexo printing, BASF offers the nyloflex plate series, which includes: label printing plates (nyloflex FAE I, FAH, FAR II, MA III, ACE), corrugated direct printing plates (nyloflex FAC-X and FAII), for printing sausage casings (nyloflex ME), a plate for digital communication (digiflex II), a plate for printing with UV inks (nyloflex Sprint) and a plate for direct laser engraving (nyloflex LD).

Label Printing Plate - nyloflex ACE

The nyloflex ACE plate is designed for high quality flexo screen printing in areas such as:

• - flexible packaging made of film and paper;
• - packaging for drinks;
• - labels;
• - pre-sealing the corrugated cardboard surface.

It has the highest hardness among all nyloflex inserts - 62 ° Shore A (Shore A scales).

Main advantages:

• - change in the color of the plate during exposure - the difference between the exposed / not exposed areas of the plate is immediately visible;
• - large exposure width provides good fixing of halftone dots and clean indentations on reverses, masking is not required;
• - short processing time (exposure, washout, finishing) saves work time;
• - a wide range of tone gradations on the printed form allows you to simultaneously print raster and line elements;
• - good contrast of printed elements facilitates installation;
• - high-quality ink transfer (especially when using water-based inks) allows you to evenly reproduce the raster and solid, and reducing the required amount of transferred ink makes it possible to print smooth raster transitions;
• - high hardness with good stability, transmission of high-line raster transitions when using the technology of "thin printing plates" in combination with compression substrates;
• - resistance to wear, high circulation-resistance;
• - resistance to ozone prevents the formation of cracks.

The plate shows excellent ink transfer, especially when using water-based inks. In addition, it is well suited for printing on rough materials.

Nyloflex ACE can be supplied in the following thicknesses:

ACE 114-1.14mm ACE 254-2.54mm

ACE 170-1.70 mm ACE 284-2.84 mm

FAC-X - Corrugated Printing Plate

The insert has a low hardness (33° Shore A), which provides it good contact with the rough and uneven surface of the corrugated board and minimizes the washboard effect. One of the main advantages of FAC-X is its excellent ink transfer, especially for water-based inks used in printing on corrugated board. Uniform printing of plates without high printing pressure helps to reduce the increase in gradations (dot gain) during raster printing and increase the contrast of the image as a whole.

In addition, the plate has a number of other distinctive features:

• - the violet shade of the polymer and the high transparency of the substrate make it easier to control images and mount forms, using adhesive tapes, on a plate cylinder; - high bending strength of the plate eliminates peeling of the polyester substrate and protective film;
• - the form is well cleared both before, and after the press.

The nyloflex FAC-X plate is single layer. It consists of a photosensitive photopolymer layer deposited on a polyester substrate for dimensional stability.

Nyloflex FAC-X is available in 2.84mm, 3.18mm, 3.94mm, 4.32mm, 4.70mm, 5.00mm, 5.50mm, 6.00mm, 6.35mm .

Relief depth of nyloflex FAC-X plates is set by pre-exposure reverse side plates by 1 mm for plates with a thickness of 2.84 mm and 3.18 mm and in the range from 2 to 3.5 mm (depending on each specific case) for plates with a thickness of 3.94 mm to 6.35 mm.

With nyloflex FAC-X plates, it is possible to obtain screen lineature up to 48 lines / cm and a gradation interval of 2-95% (for plates with a thickness of 2.84 mm and 3.18 mm) and a screen lineature of up to 40 lines / cm and a gradation interval of 3-90% (for inserts with a thickness of 3.94 mm to 6.35 mm). The choice of plate thickness is guided both by the type of printing machine and the specifics of the printed material and the reproduced image.

Sausage casing sealing plate - nyloflex ME

This sample differs from others in the multilayer structure. The nyloflex ME plate is designed for printing with inks containing esters and also for pre-printing films with a two-component white ink.

Its advantages include excellent ink transfer, high run time, short washout time, wide exposure interval and good swelling resistance with all inks.

The nyloflex ME plate consists of a photosensitive photopolymer layer deposited on a stabilizing film, which, in turn, is deposited on an elastic substrate. Plates are supplied with a thickness of 2.75 mm.

Relief depth of nyloflex ME plates

is set by the thickness of the relief layer. The relief is washed out to a stabilizing film. The depth of the relief is always about 0.7 mm. With nyloflex ME plates, it is possible to obtain a raster lineature of up to 60 lines / cm with a gradation interval from 2 to 95%.

A large exposure interval contributes to the excellent fixation of such relief elements as lines with a width of 55 microns or 2% raster tones with a relief depth of up to 0.7 mm.

Nyloflex ME does not require masking. The information contained on the negative, down to the smallest detail and with optimal transmission of gradations, is transferred to the nyloflex ME photopolymer plate. So, for example, negative elements (reverse) are formed open, with good intermediate depths. The bitmap areas are copied with sharp edge angles.

Plate for digital transmission of information

The digiflex II photopolymer plate was developed from the first generation of digiflex plates and combines all the advantages of digital communication with even simpler and easier processing.

Benefits of the digiflex II plate:

1) No photographic film, which enables direct transfer of data to the printing plate, protecting the environment and saving time. After removing the protective film, a black layer becomes visible on the surface of the plate, which is sensitive to infrared laser radiation. Image and text information can be written directly on this layer using a laser. In places that are affected by the laser beam, the black layer is destroyed. After that, the printing plate is exposed to UV rays over the entire area, washed, dried, and the final illumination occurs.

2) optimal transfer of gradations, allowing to recreate the slightest shades of the image and providing high quality printing;

3) low installation costs;

4) highest quality print. The basis of laser-exposed photopolymer printing plates are nyloflex FAH printing plates for highly artistic raster flexographic printing, which are covered with a black layer. The laser and subsequent conventional exposures are chosen such that significantly lower gradation increments are achieved. You get exceptionally high quality print results.

5) reduced load on environment. No film processing not used chemical compositions for photo processing, closed exposure and washing units with closed regeneration devices lead to a reduction in the harmful impact on nature.

The scope of plates for digital transmission of information is wide. These are paper and film bags, corrugated cardboard, films for automatic machines, flexible packaging, aluminum foil, film bags, labels, envelopes, napkins, beverage packaging, cardboard products.

UV printing plate - nyloflex Sprint

Nyloflex Sprint is a new plate from the nyloflex series for the Russian market. Currently being tested at a number of production printing companies Russia.

This is a special water washable plate for printing with UV inks. Washing with ordinary water makes sense not only from a nature protection point of view, it also significantly reduces the processing time compared to the technology using an organic wash solution. The nyloflex sprint plate requires only 35-40 minutes for the entire deprinting process. Due to the fact that only clean water is needed for flushing, nyloflex sprint also saves on additional operations, because the used water can be poured directly into the sewer without filtration or additional treatment. And those who already work with nyloprint water-washable plates and letterpress processors do not even need to purchase additional equipment.

Nyloflex sprint features very good ink transfer as well as outstanding results in high quality line and screen printing. Its fields of application are flexible packaging, bags and labels.

With a resolution of up to 60 lines/cm, even the thinnest lines and small fonts are printed clearly. Ideally prints nyloflex sprint on all smooth materials such as bags, labels or flexible film packaging. To make the truth, the usual steps are necessary, like the analogous traditional way of making molds.

Plate for direct laser engraving - lylollexLD

The nyloflex LD plate was introduced by BASF in May this year. at the Drupa fair in Düsseldorf. This is the latest innovation created by BASF specifically for direct laser engraving. During processing, the image and information are applied directly to the plate by laser engraving of the polymer, bypassing the stages of pre-exposure, washing, drying and finishing.

The advantages of this plate are in the reduction of processing steps, in high-quality ink transfer, the contrast of printed elements, in high abrasion resistance and resistance to UV inks and circulation resistance.

On the Russian market plate has not yet been used.

Final stage - printing form

The production of printing plates takes place on BASF plate equipment and includes the following steps:

1. Preliminary exposure of the reverse side of the plate, which determines the depth of the relief and serves to better fix the fine details of the relief.

2. Basic exposure - polymerization of the printed relief by exposing UV light of the A range at a wavelength of 360 nm through a frosted negative under vacuum.

3. Washing out of unexposed areas. The non-polluting Nylosolv II is recommended as a wash solution. However, any other solution on the market can be used for flushing.

4. Drying, during which the remnants of the solution contained in the printing plate evaporate. The mold must then be kept at room temperature before further processing.

5. Additional exposure, providing a guarantee of complete polymerization of all small parts. The duration corresponds to the time of the main exposure.

6. Final processing - irradiation of the form with UV light of the C range, with a wavelength of 254 nm to eliminate the stickiness of the form.

Untreated nyloflex sheets are stored in a cool and dry place at 15 to 20°C and about 55% relative humidity.

When processing photopolymer plates, windows must be covered with a special film to protect against UV radiation from the sun. Lighting fixtures in the room should also be shielded from UV radiation.

The production of digiflex printing plates differs from the classical plate process by the presence of an additional stage - laser evaporation of the masking layer of the plate on special equipment (for example, Alfa's Lazer Graver equipment),

The plate then goes through the usual steps of back side pre-exposure, main exposure, washing, drying, post-exposure and plate finishing.

Modern photopolymer forms (FPF). General scheme manufacturing FPF

The use of photopolymer printing plates began in the 60s. An essential factor in the development of flexographic printing was the introduction of photopolymer printing plates. Their use began in the 1960s, when DuPont introduced the first Dycryl letterpress plates to the market. However, in flexo they could be used to make original cliches, from which matrices were made, and then rubber molds by pressing and vulcanization. A lot has changed since then.

Today, the following manufacturers of photopolymer plates and compositions are best known on the global flexographic printing market: BASF, DUPONT, Oy Pasanen & Co and others. pressure generated by the impression cylinder). These include paper, cardboard, corrugated cardboard, various synthetic films (polypropylene, polyethylene, cellophane, polyethylene terephthalate lavsan, etc.), metallized foil, combined materials (self-adhesive paper and film). The flexographic method is used mainly in the field of packaging production, and also finds application in the manufacture of publishing products. For example, in the USA and Italy, about 40% of the total number of all newspapers are printed flexographically on special flexographic newspaper units. There are two types of plate material for making flexographic plates: rubber and polymer. Initially, the plates were made on the basis of rubber material, and their quality was low, which, in turn, made the quality of flexo prints in general poor. In the 70s of our century, a photopolymerizable (photopolymer) plate was first introduced as a plate material for the flexographic printing method. And, naturally, photopolymer plates have taken a leading position as a plate flexographic material, especially in Europe and in our country.

Production of the FPF.

In the manufacture of photopolymer forms of flexographic printing, the following main operations are performed:

• 1) preliminary exposure of the reverse side of the photopolymerizable flexographic plate (analogue) in the exposure unit;
• 2) the main exposure of mounting the photoform (negative) and the photopolymerizable plate in the exposure unit;
• 3) processing of a photopolymer (flexographic) copy in a solvent (washout) or thermal (dry heat treatment) processor;
• 4) drying of the photopolymer form (solvent-washable) in a drying device;
• 5) additional exposure of the photopolymer form in the exposure unit;
• 6) additional processing (finishing) of the photopolymer form to eliminate the stickiness of its surface.

Polymer molds

This means that some kind of polymer reacts to light. There are 2 types of polymers: either they "crosslink", i.e. polymerize or solidify under the influence of light, or vice versa - they become soluble. This is what the whole technology of production of printing forms is built on.

The scope of photopolymer printing plates is any printed matter.

Application advantages:

– good registration (since the accuracy of ink application, which determines the quality of prints of a color image)

– reproduction of images with lineature up to 120 l/cm (high lineature) is possible

– simple production of printing forms

– high circulation resistance

– repeated use

Disadvantages:

– unstable to some components of printing inks (printing inks, if not in accordance with the requirements, can corrode the printing plate)

General requirements for flexo printing plates

1) Uniformity of the printing surface with good ink acceptance and ink release

2) Small deviations in plate thickness (plate thickness uniformity)

3) High circulation resistance

Classification of Photopolymer Printing Plates(only 2 varieties)

1. Hard polymer, so-called. TPFM (hard polymer photographic materials)

2. Liquid polymer forms - ZhFPM

Solid polymer molds are single-layer and multi-layer

Hardness, surface, information properties.

The structure of hard polymer printing plates,

single layer consists of 4 layers:

- protective film

- anti-adhesion layer (i.e., it comes off together with the protective film, does not allow it to stick strongly to?)

- photopolymer layer

– film-substrate

multilayer:

- protective film

- anti-adhesive layer

- photopolymer layer

- stabilizer film

- substrate layer

- anti-adhesive layer

- protective film

The photopolymer strongly interacts with oxygen (loses its photosensitive properties, hardens in air, etc.), so there is a film on both sides.

The substrate is needed so that during the manufacture a thin layer of a photopolymer is poured onto it, which hardens. Then the whole thing is still cut into pieces we need.

Single layer plate. This photopolymer under the influence of UV hardens let it (polymerization occurs). If we put a photoform on top and put the whole thing under ultraviolet light, then roughly speaking, molecular bonds will be destroyed under the transparent areas of the photoform, which are then very easily removed (by washing, blowing with air, mechanically with brushes - it doesn’t matter). We are left with printing elements, and the whitespace element has such properties that it can be easily removed.

The composition of the photopolymerizing layer includes monomers (i.e. what is a "polymer" - roughly - a very long molecule), photoinitiators (a substance that is the source of a further chain reaction, i.e. a substance, when it receives a dose of UV, starts the reaction - it changes itself and causes the surrounding molecules to also change), elastomeric binder, stabilizers and additives.

The polymer itself is not photosensitive (it doesn’t care what kind of light shines on it), but the photoinitiator doesn’t care, and when ultraviolet is shined on the photoinitiator, it changes itself and causes nearby polymer molecules to also change (domino principle - it itself fell and others fell down) .

Production process: a roll with a film-substrate is unwound, a polymer is poured onto it in a uniform layer, a protective film is placed on top so that there is no exposure to oxygen. Further it is cut on the necessary format.