Quality control during printing
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In order to ensure the final effect of the printed matter, it is very important to understand the quality problems in the printing production process as well as the quality inspection work. Below we talk about the quality control problems in the printing process according to the basic printing workshops set up by domestic printing companies.
First, the rotation center
In general, the rotation center is a large-scale printing workshop integrating pre-printing, printing and post-pressing. The workshop is mainly used for printing journals, magazines, etc., which are updated quickly and have low quality accuracy requirements. The publication's focus is on the speed and effectiveness of printing, so in this workshop, its main printing equipment is a high-speed rotary press.
For the production process of the rotation center, the IKEA production control process is mainly followed. It mainly includes four processes of prepress, printing, binding and packaging (Figure 1).
Because the rotating center mainly prints some periodicals and magazines, it has unique requirements in terms of printing precision and technology, so it has corresponding characteristics in the quality control in the production process. Mainly involved in printing ink, paper, machine debugging in the printing process and so on.
1. Ink
1.1 offset printing ink (black) should have a tinting strength range of 95% to 110%;
1.2 high-speed offset printing ink (black) fluidity should be in the range of 40 ~ 50mm; medium speed offset printing ink (black) fluidity should be in the range of 35 ~ 40mm; low-speed offset printing ink (black) fluidity should be in the range of 30 ~ 40mm;
1.3 rotation offset ink should be 100-400 Pascal seconds (Pa·s);
2. Paper
2.1 For the web printed by the rotary press, it is necessary to prevent the paper from slack; if the paper is broken, the paper force can be changed by adjusting the relevant components, the braking effect can be changed, the water volume can be reduced, and the parallelism of the paper guide roller can be checked. web;
2.2 In the printing process, it is easy to appear that the ink is not inked or slightly blurred. At this time, the plate can be changed, the pH value of the dampening solution is adjusted, the reducing agent is sprayed or the machine is stopped for cleaning, and the pressure is reset;
2.3 The inked part is completely uninked, and the light print is repeated on the same part of each page, and the reducing agent or the blanket can be applied;
2.4 If ink stains appear on the surface of the printing plate when ink or color is applied, the water supply can be increased to remove the adhesive, check whether the brush needs to be replaced, and whether the pressure needs to be adjusted;
3. Adjustment of the printing press
3.1 The vertical and horizontal limit deviation of the 1 turn machine version shall be ±1.0mm; the difference between the two diagonal lines of the rotary machine version shall be ≤2mm;
3.2 When the printing starts, the non-inking part is stained with paper powder. Stop immediately, wipe the layout, change the setting time, and adjust the ink roller before turning on the machine.
3.3 Ink roller inking failure should adjust the line pressure, make the pressure as small as possible without affecting the printing quality. If the ink roller wears or cracks, it should be repaired immediately, adjust the pH value of the dampening solution or replace the ink;
3.4 When printing, the wheel transfer should have a tracking color mark and be marked correctly.
Second, the prepress center
The prepress center is mainly prepared for printing. It mainly has two functions: one is to process the customer's documents into the graphic information/work program and related resources of the printing plate, and the other is to manage the color management, in addition to the most basic functions. Processes such as document storage, pre-screening, production, screening, and overprinting.
Preflight-Preflight, borrowing the English word Preflighting, refers to the pre-screening work carried out before the plane takes off to ensure the flight safety of the aircraft, and foolproof. Preflighting is used in the printing industry, which means pre-checking work before printing. Pre-printing pre-screening is undoubtedly a vital part of the overall printing process. As the printing industry continues to adopt new technologies, not only color desktop publishing systems (DTP) and computer-to-plate systems (CTP), but also new processes are emerging. In the face of a large number of new technologies, many experts in the electronic publishing industry predict that the final printer will only accept PDF files.
Why do you want to pre-check PDF before printing? The main reason is that the information from 1 customer has changed - electronic file /page layout/image/fonts/PDF; 2 traditionally pay attention to crafts/eyes; 3CTP comparison software and equipment - electronic files should use software to check for errors and omissions; Overprint/picture number; 4 market-wide processes are automatically pre-screened, although fast, but not detailed enough. There are a variety of pre-screening systems available on the market: PDF (Pitstop server is used to check pdf files, there are fixed and effective unified settings), Arcobat comes with software, Application File (original file, Flightcheck is an effective and can be preset Software).
In the first part of the pre-press center - pre-inspection process, it is necessary to follow the pre-press pre-test requirements, which mainly include clear requirements, registration of the manuscript, inspection data, production instructions, production follow-up, revision follow-up, retreat Several aspects of the draft.
Color management is an important part of prepress work. The main color separation equipment used in the prepress center is the round pixel scanner (electronic color separation machine) for the Screen 8060 Scanner, which is the SG-860P Mark II.
Color Management mainly includes three parts: color management, specification file, and color conversion.
1. CMC procedure:
1.1 first set the total ink amount of the printer (Setup Total ink for printer);
1.2 Create a printer basic line (Creat lineasation for printer);
2. Create a print printer profile file (Creat Destination & source Profile)
2.1 print IT8 as standard and measure the Lab Data;
2.2 Set the standard for printers;
2.3 Generate this profile file (Creat a ICC Profile);
3. Color Conversion (Color Conversation)
3.1 directly convert color from RIP (Convert from RIP directly);
3.2 in the application software for picture color conversion (Convert from Application software);
After the electronic color separation is completed, the necessary image and text information is processed, and the next work is to issue a row. The main inspection items in the process of delivery include: finished product size (according to the work order); character error or loss; graphic bleeding (≥3mm) (Wrio is 4 side bleeding); image color block color mode (must be cmyk or grayscale) There is no ultra-fine line (≤0.1mm); whether there is a low picture (≤300dpi); whether the software version is suitable (different languages should correspond to related software); retreat ridge (the end of the book and the post and the quality check must be retired) Ridge); beer line or spot color (with or without special color); whether the Pdf file is centered, whether the font is fully embedded, and whether the corner is outside the positive.
There is also an important link in the prepress process - imposition. Puzzle - Imposition, basically divided into two parts: Template Making and automatic typesetting.
Its main advantages are:
1 Simplify the process flow, increase the degree of automation, replace more manual operations, and reduce the requirements for operators;
2 shorten the production time and preparation time, because the computer imposition speed is much faster than the artificial imposition speed, the original file that needs to be spelled for one day can be completed in one hour;
3 Reduce the waste of raw materials, reduce the material waste during adjustment and reduce the cost of finished products while reducing setup and preparation time. Due to the high error rate of manual imposition, it is often found that the imposition is wrong after the completion of the PS version, resulting in more material waste, and computer imposition is less likely to occur;
4 improve product reliability and consistency. Since the documents handed over to the printing factory have been completed, the quality of the processed products can be consistent at different times and regions, and the stability of the printed matter quality is improved;
5 improve product quality and reduce errors. Since the large version is completed by the computer before the film is released, there is no problem of registration and error, which effectively improves the product quality.
Third, the printing workshop
The lithography workshop mainly prints books and magazines with high printing precision requirements and low timeliness. Most of the printing machines used in the workshop are four-color printing machines produced by Heidelberg, and two printing machines produced by KBA. A domestic printing machine, the ink supply system of the lithography workshop uses system equipment, and the degree of automation is high.
Before starting the printing, check the products to be printed, check the items before and during the printing process: 1 Whether the picture is registered (must be checked with a magnifying glass); 2 Whether the front and back sides, cross lines, page numbers are right ( Clear proof of blue paper or sample book); 3 whether the layout is clean (dirty point removal); 4 front gauge and pull gauge are in place (do the pull rule line, the two sides of the cross line extended to the paper edge position); 5 each ink color is standard (Compared with the sample paper, it must be carefully compared with the density meter); 6 whether the back is dirty or towed; 7 with paper and printed count; 8 whether there is powder on the paper (note the powder machine throat) Blocking, printing large ink position printing, cleaning the powder nozzle, lifting the explosion-proof powder); 9 mixing ink bucket (ink skin is one of the important factors leading to the ink sheet of the printed sheet); 10 to keep the ink color stable, must be the layout Moisture control is at a minimum, usually the faster the speed, the amount of water must be increased in an appropriate amount. When printing is reversed, due to dusting, it is necessary to pay attention to the dirtyness of the printed sheet.
In the printing process, a variety of chemical reagents, such as dampening solution, detergent, etc., are used, and these items are dangerous, so safety should be taken during use. Since the printing press is a consumable item, the printing machine is maintained in order to make the printing machine have a longer service life and lower the cost. There are mainly the following aspects: delivery, water tank, wind turbine pump, air compressor, and surrounding.
However, no matter how the machine equipment, the operation of the personnel, and the control of the raw materials are arranged during the printing process, some quality problems may occur. The quality problems and control methods that are easy to appear are similar to the rotary printing machine, mainly involving the printing ink. , paper, machine debugging in the printing process and so on.
1. Ink
1.1 offset resin ink (black) tinting strength should range from 95% to 110%;
1.2 The viscosity of the ink should be moderate, and the viscosity of the single offset ink should be 200-800 Pascal seconds (Pa·s);
1.3 offset ink fineness range should meet the standard, the general ink fineness range should be ≤15;
2. Paper
2.1 wrinkled paper, the paper should be subjected to humidity control before printing, and the pressure of the suction air and the pressure of the paper ball can be adjusted according to the difference of the paper;
2.2 Ink bar, adjust the printing pressure according to the requirements before printing, check whether the printing machine is running normally;
2.3 The lines on the surface of the printed parts are not repaired. At this time, the exposed side of the film should be repaired and treated in time;
3. Machine debugging
3.1 Print double sheets, check whether the double detectors are normal before printing, if they are not normal, they should be repaired in time;
3.2 The part of the graphic part is lost or the color is lightened, and the drying of the first surface ink layer is accelerated, and after the drying, the second side printing is performed;
3.3 The vertical and horizontal limit deviation of the full boot version shall be ±1.0mm; the difference between the two diagonals of the full boot version shall be ≤3mm;
3.4 pairs of the vertical and horizontal limit deviation of the boot version should be ± 1.0mm; the difference between the two diagonals of the boot version should be ≤ 3mm;
In general, there are many problems encountered in the printing process. For the actual operator, there are still many problems that need attention and resolution.
1 The ink prepared by the spot color printing is obtained according to the principle of subtractive color mixing. Color blocks with low color transparency, high saturation, and uniform ink color are usually printed in the field, and the amount of ink is appropriately increased. The color block printed by the four-color printing process, when printing the dot, is easy to change due to the change of the thickness of the ink layer and the change of the printing process conditions, and the comprehensive effect of the subtractive method absorption and color mixing method of the obtained dot;
2 The color version added is inconsistent with the original color version - all color versions are re-exported again (the safest way);
3 EPS map can not save JPEG format, CorelDraw is best not to use PSD through the base map, otherwise it is easy to white line;
4 check the items: whether the text black is black or not; whether the text is garbled, replaced or bolded, whether there is a hollow point in the stroke intersection; whether the size is consistent with the file setting, whether the page is centered; some objects are processed by the front-end application software. Directly posted, not linked, will be lost after RIP;
5 factors affecting the quality of outlets. Prepress: The temperature and speed of the machine have the opportunity to affect the size of the dot, CTP exposure and speed; printing and printing. Printing: the temperature and humidity of the paper; different people have different experience and different judgments; the balance of the drum and the gear when rotating, the vibration generated by it will affect the printing dot; the blanket is too soft or too hard, which will cause the dot to be printed. Expansion on paper;
6 In the printing process, check the condition of the printed sheet, the ink sheet, the pull gauge, the double sheet, the bottoming, and the wind proofing if necessary. The preparation of the bad paper after cleaning and the number of the printed sheets are prepared;
7 The main reason for falling powder is excessive powder or excessive accumulation of powder in the delivery area;
8 In order to avoid the smudging of the back of the printed sheet, the thickness of the printed sheets after printing is not too high, and it is necessary to pay attention to dusting;
9 Printing process inspection work guides its inspection items: print specifications, stains (cleared, keep the layout clean), film edge, tangent, corner line (cleared, or can be cut after writing), print registration, front and back Overprint, blue sample (corrected page number), ink color (in accordance with "printable" color sample / proof or customer requirements), ink relationship (to achieve ink and water balance); other.