Photo-printed Sun-Offset Quality Control Key

Shaiban is the link between prepress technology and proofing, printing process. It needs to faithfully transfer the original graphic information to the PS plate; at the same time, it should make the graphic part hydrophilic and blank part hydrophilic, and make the printing The plate can withstand the enormous long-term pressure between the rollers without changing its hydrophilic properties.

At present, although some printing plants have CTP plates, the utilization rate is still not high, and most printing plants still use the traditional printing methods. Due to the more traditional printing methods, the quality control is more difficult, and many printing The factory often neglects the quality control of the printing section, which leads to the impact on the printing quality and reduces the printing efficiency.

When we manufacture the PS version, we always hope that the sun-dried outlets will be strong and smooth, and the blank part of the printing plate will be clean and free of dirt, and the graphics and text will have a good lipophilicity.
In production, we often encounter the following problems:
1, PS version outlet virtual halo, false, printing color instability.
2. The loss of high-gloss small dots is serious, the printed image is not smooth, and the flat screen is uneven.
3, blank parts more than dirty, eliminate long dirty time.
4, 10% of the following flat-screen drying.
5. The graphic part is not inked.
6, printing plate printing rate is low, can not reach the PS version should be printed.
7, printing plate easy to dirty.

Although the above problems are related to the printing pressure, the use of fountain solution, and the performance of the blanket, most of the troubles are caused by the drying of the PS plate.
Since the occurrence of any failure in printing is not caused by a fixed reason, the operation specification and data standard for each process will help reduce the occurrence of failures.

When you already have a good PS version, if you want to make a PS version that meets quality requirements, you need to have the following conditions:
1, constant light efficiency, uniform illumination.
2. Shaiky glass has no scratches, cleanness and transparency.
3, suitable suction time, vacuum degree is good.
4. The density of the original film meets the standard.
5, the exact exposure time 6, the matching developer, the appropriate development concentration, the development temperature.
7, the appropriate development time.
8, the matching elimination of dirty fluid, the correct way to eliminate dirty.
9, the protective glue coating is uniform, thick and thin.

If we can control each of the above steps one by one and develop good operating practices, we will greatly improve the quality of the PS version.

First, the appropriate form of light

For the same brand of PS version, you must ensure that the total exposure is constant, when the lamp is used for too long, the light efficiency will be reduced, the exposure will be insufficient, need to pass the test to increase the exposure time, in order to stabilize the total exposure, Or replace the lamp.

Different brands of printing machine, the light uniformity is not the same, when the light uniformity is poor, it is easy to lead to different shades of printing plates, especially when drying flat network is very obvious.

Second, the appropriate original film.

The printing plate is usually a violet light source or ultraviolet light source with a wavelength of 400 μm. The penetrating power is strong. In order to completely transfer the original negative film web point to the printing plate, it does not generate the photosensitive layer in the future graphic part. Photochemical reactions require:

1, the original film density in the field to reach 3.5 or more, otherwise it will easily lead to 5% of the following points lost, the network is not clean

2. The fog level of the original film should be low and should be less than 0.05, otherwise it will affect the density contrast on the printing plate.

3, the original film should be clean and dirty, otherwise it will give the printing plate dirty.

The original film does not use the collage tape as much as possible. For stitching, it is recommended to use glue, especially the dot film. At the same time, there must be no boundary phenomenon between the film and the film. In this way, the film and the PS board can be closely combined to avoid light scattering. Caused by the phenomenon of network points, if you use the tape collage, the distance between the tape should be greater than or equal to 7mm. Otherwise, it will cause the network to dry up.

Third, the drying frame glass

The shelf plate glass is clean. Otherwise, dust on the glass can easily make the PS plate dirty. Due to the fact that our current working conditions are difficult to achieve absolute cleanliness of the printing workshop, we must wipe the printing plate glass with alcohol prior to printing, and we must wipe both the front and the back to eliminate the glass. Dirty spots are generated by dust.

Wiping the glass should avoid scratching the glass with hard objects on the hands, and ensure that the cloth or sponge that wipes the glass does not have sand particles, so as not to damage the glass.

When the glass plate of the printing plate is scratched too much and too deep, the glass must be replaced. Otherwise, when drying the flat screen, dirt spots will be generated, resulting in a large number of waste plates.

Fourth, good pumping

Insufficient evacuation vacuum level can cause poor adhesion of the original film and the photosensitive layer of the plate, resulting in voids and severe light penetration, thus changing the size of the dots or even losing them. Therefore, we need to find a suitable pumping time, so that the PS version and the original film can be closely integrated in order to facilitate the correct exposure.

When the air pumping blanket is used for a long time, there will be aging, and there will be a small amount of air leakage in some edge areas. The PS version and the film will not stick tightly, and the printed text will be too weak. At this time, the manufacturers should be contacted. Replace the blanket.

When you inhale, if you can't walk from the middle to the surroundings, you will have local bubbles, and the PS plate will be partially blurred. At this time, check the bottom plate.

V. Accurate exposure time

We only have a good PS version, good exposure conditions are not enough, but also have sufficient and not excessive exposure time to produce a good PS version.

As the use of printing plate will increase part of the production cost, the confirmation of the exposure time of many printing factories is often judged by experience, resulting in extremely unstable printing quality.

If we want to obtain a stable print quality, we must use the print control signal bar (such as: UGRA1982 print control bar), through the print test, to find out the standard exposure time and development time.

UGRA1982 measurement and control bar consists of five parts:
A, highlights and dark tone control area, usually in the sun print pattern: to ensure that 98% outlets do not paste, 2% outlets to be preserved: In the printing on the printing machine: to ensure that 97% outlets do not paste, 3% outlets to Reservations.
B. Test ghost area.
C. The dot area used to measure dot gain and print contrast.
D. Twelve Yin Yang patterns with a diameter of 4.5 mm. The width of the line is between 4 μm and 70 μm. This section can be used to determine the correct exposure time and resolution of the PS plate.
E. Gray scale used to test whether the development is normal.

(a), test steps:

Exposure: The UGRA control strip is placed on a PS plate to be tested. The PS plate is exposed using a T, 1.4T, 1.42T, 1.43T, 1.44T, 1.45T,... 1.4 times for the previous stage, such as: the first exposure is 10 exposure units, the second is 1.4 x 10 exposure units, until the last exposure exceeds the normal exposure.

Development: Use the developer stock matched with the PS plate and dilute it according to the developer's standard ratio. Put the exposed PS plate flat on the developer tank. Use the manual development method. Take about 0.5-1 minute and then take it out and wash it. Plate platform flush with water.

The method of manual development is to avoid inaccurate development time and unfavorable developer concentration.

Exposure time T 1.4T 1.42T 1.43T 1.44T 1.45T
Reproducible female line width 20μ 8μ 6μ 6μ 4μ 4μ
The smallest reproducible width of the male line 4μ 4μ 6μ 10μ 15μ 20μ

(B) The resolution of the PS version resolution

The most important factor affecting the virtual reality of printing plates is the resolution of printing plates. The higher the resolution of printing plates, the better the performance of small outlets and the more real the outlets. At the same time, if you want to determine the exact exposure time, you must first confirm the PS version of the resolution.

Observe the reproduction of the yin and yang lines of the yin and yang loop area of ​​the UGRA control strip using a 10x magnifier (at least 50% can be clearly reproduced).

According to the regulations of the UGRA1982 measurement and control strip, at a certain exposure time, the same level of the Yin and Yang lines in the yin and yang circle area can be clearly observed at the same time. This level is the resolution of the printing plate, as shown in the above table Edition resolution is 6μm.

(three) the appropriate exposure time judgment

We only have a high-resolution PS version, good exposure conditions are not enough, but also there is sufficient and not excessive exposure time in order to produce a good PS version.

The following table is a list of parameters recommended by UGRA manufacturers to find suitable exposure time: (The yellow area in the table is what we can do in real production)

The minimum reproducible width of the male line in the yin and yang circle area after printing is printed on the plate at the same exposure time, and the actual spot size on the plate
7% Network Area 20% Network Area 40% Network Area 80% Network Area
4μm ca.7% ca.10% ca.40% ca.80%
6μm 6.5% 9.5% 39.0% 79.0%
8μm 6.0% 9.0% 38.0% 78.0%
10μm 5.5% 8.5% 37.0% 77.5%
12μm 5.5% 8.0% 36.0% 77.0%
15μm 5.0% 7.5% 35.0% 76.0%
20μm 4.0% 6.0% 33.5% 74.5%
25μm 3.0% 5.0% 32.0% 74.0%

Table 1: Plates with resolution <5μm

The minimum reproducible width of the male line in the yin and yang circle area after printing is printed on the plate at the same exposure time, and the actual spot size on the plate
7% Network Area 20% Network Area 40% Network Area 80% Network Area
6μm ca.7% ca.10% ca.40% ca.80%
8μm 6.5% 9.5% 39.5% 79.5%
10μm 6.5% 9.0% 38.5% 79.0%
12μm 6.0% 8.5% 37.5% 78.5%
15μm 5.5% 8.0% 36.0% 77.5%
20μm 4.5% 7.0% 34.5% 76.0%
25μm 4.0% 6.0% 33.0% 74.5%

Table 2: Plates for resolution from 5μm to 8μm

The minimum reproducible width of the male line in the yin and yang circle area after printing is printed on the plate at the same exposure time, and the actual spot size on the plate
7% Network Area 20% Network Area 40% Network Area 80% Network Area
10μm ca.7% ca.10% ca.40% ca.80%
12μm 6.5% 9.5% 38.5% 79.5%
15μm 6.0% 8.5% 37.0% 78.5%
20μm 5.0% 7.5% 35.5% 77.0%
25μm 4.5% 6.5% 34.5% 76.5%
30μm 3.5% 5.5% 33.0% 75.0%

Table 3: Plates for Resolutions from 8 μm to 12 μm
According to the results of the previous stepwise exposure, the resolution of this printing plate is 6 μm. It is a PS plate with a resolution between 5μm and 8μm. The exposure time that should be used is the range of exposure time required for the minimum reproducible popliteal width listed in Table 2 between 12 μm and 15 μm.

Observe the reappearance of the positive line of the yin and yang loop area at all levels of exposure, and the exposure with 10 μm remnant, 12 μm full, and 15 μm clear is the appropriate exposure time. Exposure time can be slightly longer for linework

Six , matching the developer and its optimal concentration

There are roughly two types of developer materials used with the PS plate: solid state developer and liquid developer concentrate. Regardless of which type of developer material is used, the developer must first be adjusted to a suitable concentration before being used for development.

Different types of positive PS plates have their associated developing materials. To obtain the best development results, try not to use other brands of developer. Otherwise, it may result in opaque or excessive development.

The development medicine has a shelf life. When it is used, its production date should be confirmed. Expired development medicine should be avoided. The shelf life provided by most manufacturers is one year, but try not to store the developer for too long.

The manufacturer will also provide the corresponding ratio of formulated developer. Such as a certain grade of developer powder in the instructions for use suggested "a bottle of toner with 5