Plates are an important factor in the current printing process. In the printing process, on the one hand, it accepts the ink transmitted by the ink roller, and on the other hand, it transfers the graphic ink to the surface of the substrate or other intermediate carrier. The quality of the printing plate will directly determine the quality of the printed matter. The printing plate used in flexographic printing is higher in graphic and graphic than the non-graphic part and belongs to the category of relief. Therefore, the quality of the printing plate must not only have the quality requirements of the metal letterpress, as shown in the figure, the top surface is flat and uniform, and the edge of the picture and text has a certain slope and relief depth, etc.; and because the printing pressure is small, it is necessary to reach the plate and the substrate. Adhesion is sufficient to allow the ink to transfer well and the printing plate should have adequate softness, so these factors must be taken into account when making the plate. So, how to make a flexible printing plate? I think we should do the following things before we can make a flexible printing plate.

First, the quality control of plate negatives

The current flexographic plate is the same as that of the lithographic plates. It is made by the color desktop publishing system.

of. However, the flexographic plate has its own characteristics, and the film must satisfy these characteristics in order to pay for platemaking.

1. The film density requirements.

Flexographic plate negatives are positive negatives, their opaque non-graphical parts have higher density values ​​and generally should not be smaller than

4.0, this is because the main exposure time of the flexographic plate is longer, and if the density value of the non-graphical part is less than 4.0, light leakage may cause the image relief depth to be shallow. The transparent graphic part should be very transparent, the value of fog should not be greater than 0.05, otherwise it will block the light when exposed, so that the end of the graphic due to insufficient light, the photosensitive resin cross-linking hardening is not enough to cause uneven.

2. Requirements for film graphics.

1 Graphic texts should avoid fine text and fine lines. Otherwise, the exposure to light will be insufficient and the foundation will be narrow, making the printing plate

In the process of developing corrosion, it can not withstand the brush of the plate brush and washed, causing the layout text to be broken or missing, and the lines are incomplete.

2 There should be no bar or solid pattern parallel to the axial direction on the film, otherwise it will cause unevenness in the circumferential height, and the machine is in operation.

When the rotation is beating due to the level of the circumference, it will cause streaks on the product.

3 large areas of field and small print, outlets should not be designed in the same layout. Because printing requires thick ink layers, it must be

Need to increase the pressure of printing to achieve. Small prints and outlets use smaller printing pressures to prevent them from being deformed or even stenciled. If the design of the field and the small print and the outlets are in the same layout, they often miss one another when printing. In order to take care of the field, we must make small prints and outlets more deformed or stenciled; taking care of the small prints and outlets, the lack of pressure on the ground will cause the flowers to become deficiencies.

3. The requirements of the film texture level

1 Texture level requirements

The characteristics of the flexo printing plates are relief printing, so the level of textures it reproduces is not like the lithographic process.

This is rich, because the image reticulation level of the flexographic printing plate can not be netted in the high-profile part, and there must be a small network to support it. In order for small outlets to stand in print, the area of ​​their outlets should not be less than 5%. Secondly, the flexographic printing plate is relatively soft, and it will be deformed and expanded after being pressed. Therefore, the halftone dot area of ​​the screen must not be more than 85%, and it cannot be a real place. Otherwise, the dark tone portion is stuck in the printing. It can be seen that the level of the texture of the flexographic printing is limited by the characteristics of the printing plate and can only be limited to the range of 5% to 85%. If the manuscript level is very rich and the tone level is 0-95%, the plateau must be compressed before processing, and the plateau must be compressed before processing. At the same time, the hardness of the printing plate is controlled at 70° Shore.

2 mesh lines

Flexographic printing uses metallic anilox rollers to transfer ink to the plate. Due to the depth of the ink in the metal anilox roller

Unchanged, it can ensure quantitative and uniform ink transfer to printing plates. In order to ensure that every dot on the flexo plate can get ink, the relationship between the number of screen lines on the plate and the number of metal screen roller lines must be taken into account. It has been proved that when the number of reticulation lines on the printing plate is 1/3 of the number of reticulation lines on the metal anilox roller, it can ensure that every dot on the printing plate gets ink. In order to better get the ink of the printing plate patterns, it is recommended to use the number of printing plate lines: the number of metal screen lines is 1:4.

3 Netting angle

Flexographic metal anilox rolls typically have an angle of 45° (also 60°). To avoid metal mesh

The splay angle of the roller is overlapped with the splay angle of the plate pattern, resulting in a moiré pattern. Therefore, the angle of the stencil pattern of the plate negative film should avoid a 45 degree angle. The reticulate angle of the film can be yellow 90°, magenta 15°, cyan 60° and black 30°. Alternatively yellow 82.5°, magenta 67.5°, cyan 97.5° and black 37.5° are used.

The shape of 4 dots and the number of screen lines added to the screen

At present, the vast majority of printing processes use printing pressure to transfer the graphic ink on the printing plate to the surface of the printing material.

Because of the pressure, network expansion is inevitable. As long as the expanded value of outlets is within the effective control range, normal printing can be considered. The expanded value of the outlets is often related to the shape of the outlets and the number of screened screens:

The expansion value of the outlets is proportional to the perimeter of the outlets. Because outlets expand to four weeks when printing, in the same conditions

Under the square, the perimeter of the edge of the square dot is the largest, so the dot enlargement value is also the largest; the perimeter of the edge of the circle dot is the smallest, so the dot gain value is also the smallest. The flexible printing plate is relatively soft, and the dot enlargement value during printing is large, and the use of circular dots is the most ideal choice.

The expansion value of the outlets is inversely proportional to the size of the outlets. Within a unit area, the higher the number of screen lines, the smaller the area of ​​the network points.

The greater the number of outlets, the greater the total perimeter of outlets, and the larger the outlet expansion. On the contrary, if the number of screen lines in the screen is low, the screen area is large, and the number of screen points is small. Therefore, the total perimeter of the screen points is also small, and the value of the screen points is also small. It can be seen that the number of lines of the flexible version is more advantageous when the number of lines is 133 lines/inch or less.

Second, the requirements of the plate operation

1. Exposure control

1 Determine the exposure

Different batches of flexible sensitized plates have different raw and auxiliary materials due to different production dates and storage time

Different, so the exposure is also different. In order to correctly grasp the exposure of the flexible photographic plate, an exposure test should be performed before use to obtain the correct exposure parameters. The test can be performed on a small flexible photographic plate divided equally into several pieces, each with a proportional increase in exposure time. After the sample was exposed and developed and eroded, look at the sample stage, compare the dot layer and size of the film and the layout, and the relief depth to determine the ideal exposure parameters.

2 exposure control of exposure time

a back exposure. The main effect of back exposure is to increase the thickness of the plate base, determine the depth of the graphic relief, and increase the resistance to printing force. Back

Exposure exposure time is generally controlled in 1-2 minutes. If the exposure time is too long, it will cause the printing plate to be too thick, the relief of the picture and text is too shallow, and the non-graphic part is easy to print in the wild ink; on the contrary, the exposure time is too short, the graphic relief is too deep, the text, dot, thin line The supporting force is not enough, it is easy to flush away when the printing plate develops corrosion, resulting in incomplete graphics.

b. Main exposure, also known as front exposure. Its role is to form graphics on the layout. The main exposure time can be appropriately longer, generally

Control in 5-8 minutes. Since the negative film is of a negative type, the exposure is excessive, resulting in the text, lines, and screen lines becoming thicker and thicker, the graphic articulation being degraded, and even being smeared. Exposure time is too short, text, lines, dots become smaller and thinner, the hardening degree of the photosensitive layer is not enough, it is easy to cause the printing plate in the development of corrosion, the small print, dot missing, the lines are incompletely bent.

c After exposure. The effect of post-exposure is to cross-link and harden the polymer resin without cross-linking hardening inside the printing plate, so that

The hardness of the plate is increased to improve the corrosion resistance and wear resistance of the plate to the ink solvent. The exposure time for post-exposure is generally around 10 minutes. Less exposure time, printing can not reach the purpose of thick exposure, excessive exposure time makes the plate too hard.

3 light sources

The plate-making light source of the flexographic printing plate generally uses 365 nm ultraviolet light. Due to the different lighting fixtures, the luminous intensity

Different, usually just for the new light-emitting intensity of a strong, you can reduce the exposure time exposure; after a period of use of the lamp, the luminous intensity has weakened, plate-making exposure time may be appropriate to extend some.

2, the operation of the plate making process

1 Unexposure to the dried flexographic plate, the surface has a certain degree of viscosity, after close contact with a smooth film, it is difficult to extract the air between them to form spacer bubbles, causing the graphic text to be deformed, thickened or blurred after plate making. . Ideally, the surface of the flexographic plate should be matte, which facilitates the derivation of the air after it has been bonded to the flexographic plate. This requires the use of specially made matte polyester film-based photographic materials to make films. If a smooth offset plate is used, a fine layer of fine powder can be applied to the surface of the film to solve the problem of poor air conduction. However, the thinner the powder, the better, otherwise it will increase the fog of the film.

2 If the unexposed flexo is softer, it is better not to apply pressure to the plate before exposure, even if the vacuum is flattened.

Also do not press with your hand, but use roller to roll gently, otherwise it will leave indentation marks.

3 When the protective film is peeled off before the exposure of the plate, the film should be removed in one go. Do not pause in the middle, otherwise it will be

A trace is left on the layout, which causes the amount of ink deposited at the printing area to be larger than the other areas to form the ink mark.

4 For back exposure of a flexographic plate, use a semi-vacuum and front exposure. Use a full vacuum.

At the same time, attention should also be paid to the presence or absence of remaining air bubbles between the film and the plate, if any.

5Development Corrosion should control the pressure of the developing board brush, the concentration of developer and the speed of washing. Usually developing brush

The pressure depends on the distance between it and the platen. When the distance is small, the pressure of the plate brush on the plate is large. Although the development and corrosion time can be shortened, due to the pressure, the small print, thin lines and dots of the plate can be easily brushed away; The pressure is small, the development and corrosion time is long, and the printing plate expands due to excessive absorption of the developing solution, resulting in bending and deformation of the text lines and the loss of small dots. The concentration of the developer is controlled. Usually, a certain amount of new solvent is added for every corrosion of the developing, so that the solvent concentration of the developer can be controlled within a valid range. If it is not added in time or the amount of replenishment is not enough, the photosensitive resin monomers remaining on the plate will be too sticky and the surface smoothness will be deteriorated. The development and corrosion of the washing speed should be appropriate, otherwise the speed of the developing washing plate is too fast, and the residual unexposed polymer resin monomer on the plate is too much, so that the depth of relief of the graphic and text after exposure is affected; if the plate washing speed is too slow, It is easy for the printing plate to absorb the solvent to swell, resulting in excessive solvent residue in the baking process, and the fine part of the graphic is deformed or even dropped off.

Third, the quality of the check plate

Inspection of plate quality should be checked by comparing the graphic quality of the negative plate with the graphic quality of the plate surface.

Good board quality should be consistent with the printing plate's text, lines, texture levels and dot size and the film, with a certain depth of relief. The borders of the images are smooth, no burrs, smooth lines and flat layout. Graphic lines, dots, text strokes are complete, narrow and wide, and have a solid foundation. If found:

1 Dots and text gaps are too shallow, indicating that the depth of relief is not enough. This is due to overexposure and insufficient development corrosion.

2 Dots, texts, and lines with steep sides, or large or small, indicate that the printing plate is poorly printed and poorly printed. This is caused by insufficient exposure time or excessive development.

3 The picture is not smooth on the end face, or there are strange patterns or scars. This is a part of the graphic transparency of the film. The fog becomes bigger and the powder is not even.

There are missing strokes in the 4 layout drawings, indicating that there are dirty spots on the negative film or vacuum film, or the pressure of the pattern brush is too large when washing.

There are pinholes and pits in the 5 layouts, indicating that the platemaking environment is poor in sanitation and dust; there are stains on the vacuum film.