As the competitiveness of the printing market gradually increases, the share of "hard power" in printing units is becoming more and more obvious, especially a cost-effective printing machine can bring great business opportunities to printing units and can cope with the growing Market demand, but whether the performance of the new printing machine fully meets the needs of the company, how to check and accept the newly purchased printing machine is a very critical issue. I am fortunate to participate in the acceptance of the new printing machine at the printing company. Share the results of the acceptance with your colleagues, hoping to give some inspiration to the industry.
1. Contents of acceptance work
For manufacturers of big-brand offset presses, they have done comprehensive tests before shipment. However, considering the price of the offset press and the factory's requirements for production, some tests before acceptance are necessary, such as checking whether the offset press is in a stable working state after installation and commissioning; check whether the performance and parameters of the offset press are in line with Specification of instructions. The author communicated with the experienced printer chief and the masters who worked in the front line of printing production for many years. It is believed that the acceptance of the new printing press mainly includes the following aspects.
1. Empty vehicle operation
After powering on the offset press, in order to check whether the installation and connection of each part of the equipment is normal, the operation speed of the equipment cannot be opened particularly fast, and it can only be operated at a low speed. Then slowly increase the speed until it runs at the highest speed. One is to listen to the abnormal sound of the offset press; the second is to check the vibration level of the offset press. You can put half a bottle of mineral water on each unit to observe the fluctuation of the water surface due to vibration Is there anything abnormal?
2.50% flat screen printing test
Generally speaking, the perimeter of 50% dots is the largest, and the larger the perimeter, the greater the dots increase, so the dot increase value is also the largest, and because of this, the 50% dot increase value is one of the important indicators to evaluate the performance of offset press . The requirements for a 50% flat screen are: the maximum screen size of the flat screen; the flat screen itself is flat without stripes; the front opening or trailing edge of the flat screen should preferably have a solid plot to use for the amount of ink when the flat screen is tested Basis.
3. Field Beta
The field test version mainly checks whether the printing pressure, roller pressure, etc. have reached a certain standard. You can check whether each unit has a bar (including impact bar, ink bar, water bar, etc.). Since the level of 50% flat net's response to the bars is not obvious, the test in this part is still very necessary.
4. M-shaped overprint
M-shaped overprinting is mainly to check the offset accuracy of the offset press and to reflect the fan-shaped expansion of the paper. The following tests can be done: a single test is performed on the premise that the full-page fine-line overprinting is basically accurate (overprinting accuracy can reach 0.01mm): first, printing is performed at different speeds to check whether the overprinting accuracy changes; then print 100 sheets of about 80g / M2 paper, observe the loose tail printing on thin paper, because the loose tail is related to the performance of the paper itself. Can only be used as a reference.
5. Print standard test version
Although there are various combinations and collocations of the test versions used by various machines, there is no unified provision, but it will definitely contain two parts, namely, objective measurement signal bars and subjective evaluation pictures to complete the comprehensive evaluation of the printed matter. After discussion, considering the actual production situation of our factory, it was decided to take the GATF color copy test chart as a sample, and then add some special images to perform the acceptance of this offset press.
Second, the objective test content of the beta version
1. GATF / system digital layout control
The object is designed to be used along the outer edge of the test format. It is a multi-component inspection and process control tool, including A, B, C, D, E, F and other parts, used to monitor the digital output exposure system, film, printing Version, proof, etc.
Part A includes image device confirmation, interpreter level, horizontal and vertical resolution, image orientation, screen line number, screen dot type, screen line angle.
Part B is the test system resolution.
Part C is the minimum mark and minimum spacing for a given resolution.
Part D is used to detect the exposure conditions of the system. If the arc details of the positive and negative images are clear, it indicates that the system is good.
Part E is the star and ink solid color blocks. The star is composed of a wedge-shaped pattern separated by 5 degrees. It is mainly used to check printing faults such as proofing, expanded and horizontal deformation of the dots during printing, ghosting and paste printing. The two color patches are 1501pi and 2001pi 50% dots, which are used to evaluate the increase in the color value of the system, and can also be objectively evaluated with a reflection densitometer.
Part F consists of two sets of matching gradation scales. The upper one is the compensation program setting without applying RIP, and the lower one is the application compensation setting. The two scales clearly indicate the impact of the compensation procedure. If the two scales are exactly the same, then there is no compensation program for RIP.
2. Gray balance scan object
The gray balance scan object contains a series of gray balance color patches, which have the same values ​​as the color patches in the four areas of the gray balance table. These numbered color patches are designed to be arranged in a straight line to facilitate the scanning of the density meter. The color patch of number 1 is white paper used for density meter calibration; the color patches of numbers 2 to 27 correspond to the signal area of ​​highlights; the number 28 The color patches up to 64 correspond to 1/4 order tone signal areas; the color patches numbered 65 to 101 correspond to mid-tone signal areas; and the color patches numbered 102 to 138 correspond to 3/4 order tone signal areas. In the sequence of highlight signal areas from 2 to 27, the green dots of each color patch are 7%, while the range of magenta and yellow dots is increased from 1% to 6%; the green dots in the 1/4 tone area are 30%, The range of Pin and Yellow dots is 16% to 28%; in the midtone area, the Green dot is 60%, and the range of Pin and Yellow dots is increased from 46% to 58%; in the 3/4 tone area, the green dot is 80 %, Product and yellow outlets increased from 66% to 78%.
3. Scanning step scale
For the six colors in the digital test page 4.1 format, each scan gradation ladder contains 22 halftone ink sticks and one solid ink stick. These color patches can be used to measure the expansion of the dots increased from 5% to 95% at equal intervals of 5%, and add 3% and 7% dots in the light part, and 97% dots in the dark part, as a threshold Additional input for the tone range of the part. The functions of these gradation ladders designed for process standardization are better than those for process control and detection. To obtain valid data from this scale, the printing system must operate within the operating specifications. If a densitometer with microprocessor assistance is used to measure the dot expansion value, it will automatically measure the apparent dot area. After obtaining 23 sets of data points from the scan scale, it is easy to construct a dot expansion curve. Describe the characteristics of the entire printing system. When using halftone color separation printing in this system, it is also necessary to use the dot expansion value tolerance determined by this curve. The advantage of using a scanning gradation scale to create a dot-expanded value curve is that its 23 data points make the curve highly accurate. It is linked to the digital page test format, which may optimize the printing conditions.
4. IT8.7 / 3 basic data setting
Include IT8.7 / 3 standard test draft in the digital page test format. The basic data setting is used for a large number of third-color replication tests, or the composition of the three spot colors of the color plus black. Selecting the color in the IT8 color setting can cover the entire color tone, and facilitate the conversion of color space and the drawing of the full tone curve. The color patches in the basic data list are confirmed by the letters representing the columns and the numbers representing the rows (for example: B13 represents the color patches in the 13th row of column B).
5. Six-color double-row control strip
The six-color double-row control strip is located at the edge of the beginning of the test format page, two small blocks wide and 114 small blocks long, and its size is 0.39 × 22.47 inches (10.0 × 57.1 mm), and the single block measurement size is 0.20 × 0.20 inches (5.0 × 5.0mm), the inked area is 1.18 inches (30mm) long. The upper layer arrangement is composed of solid ink sticks, containing 19 repeated copies of CMYK, while the lower layer arrangement contains a white color block of the original paper, followed by three color colors of CMYK 25%, 50%, 75% The block repeats, then two copies of the CMYK star, two copies of the CMYK dot expansion scale II, then the overprint of blue, green, and red, two copies of the CMKY ghost / highlight target, and the adjacent The blue, green, and red colors are overprinted on the ground and in 50% color.
6. GATF / RHEM light indicator
GATF / RHEM light indicator can be placed in the lower part of the test format page. Used to confirm whether ambient light is the recommended standard 5000K color temperature (according to ANSI PH 2.30-1994). The GATF / RHEM light indicator is a pressure-sensitive adhesive with a stripe pattern coated with two formula inks. It is carefully configured to achieve the optimal matching at 5000K color temperature, while at other color temperatures. It can't match under the light of this kind, this kind of light indicator serves as a kind of warning pattern, when the evaluation program can't make the correct color judgment, it gives a warning. Because subjective quality control relies on color matching between different colorants (such as between sublimation dyes and printing inks), all judgments must also be made under standard observation conditions (ANSI standards).
3. Subjective evaluation pictures of the beta version
1. Low profile / red sleeping chair
The red couch is a low-key reference picture. Its main color is dark, including red, green, blue and a variety of perfect wood texture tones. It is located in the middle to low-key area of ​​the tone replication curve. If you want to copy dark images of this level of detail, you need a high-resolution scanner and a larger file, which has higher requirements for color separation and pre-press equipment. There is enough tone compression to make the middle tone The part is shifted towards the tail of the dark tone, and it is printed by flat printing or direct digital printing, so as to have enough contrast to distinguish the dark tone colors.
2. High profile / wedding banquet
The photo of the wedding banquet is a reference picture for bright tone. The main colors are soft light and white, which are located in the high-tone to mid-tone part of the tone reproduction curve. For this type of picture, the smallest printable tone dots (especially 3% dots) should be set, with sufficient tone compression to shift the middle tone to the highlight part, and use flat printing or direct digital printing. To achieve accurate reproduction, only to have enough contrast to distinguish between bright tones.
3. Group portraits / painting teenagers Group portraits / painting teenagers are reference drawings for human skin color. From left to right in the figure are Caucasians, Latinos, Japanese, African Americans, and Indians. The key to how to reproduce all five skin tones equally and perfectly is to choose the correct color correction to maintain these tones without causing a shift in gray balance.
4. Portraits of women
Women's portraits are white female reference pictures, which are common examples of portrait tone reproduction. Women's portraits are the key points emphasized in photo color printing. To maintain the details of the dark tone parts of the hair and clothes, while maintaining the details of the bright tone parts, during the color separation process, the gray balance should be correctly compensated by tilting to the direction of the human body tone replication, then the part from highlight to middle There will be subtle color changes.
5. Neutral gray
Neutral gray In addition to neutral gray, there are some grays with warm or cold tones. The only saturated color is the hue of the emphasis. Accurate reproduction of neutral gray pictures is very difficult. The gray balance reproduction is easily determined by checking the closeness of the tone to neutral gray. In order to maintain a better tone separation effect, the tone reproduction curve of the middle-low tone part needs a greater tone compression. The combination of tone compression and gray balance makes neutral gray photos the most difficult to control in terms of accurate reproduction.
6. Full color tones, fruit pictures
Fruit picture full-tone / fruit picture is a picture taken with a flash in close-up. Its constituent elements are fewer, the purpose is to provide wider colors and tone levels. Therefore, there are more saturated dark areas in the picture, but the number of details is relatively small. It is very difficult to use narrow-tone inks to reproduce these tones.
7. Memory color / Picture of small bridge with roof
The picture of Xiaoqiao is a reference color sample of excellent outdoor natural light scenery. Its actual purpose is to evoke the reader's reaction to the memory color. When the reader sees a picture of such a memory color, it will first judge whether the color it contains is credible. In the process of color reproduction, as long as there is a slight change can be found, therefore, the color reproduction should be very close to the original. The picture of the small bridge with roof is very useful for testing the quality of color reproduction, because most observers have a clear understanding of these tones.
8. Textured pictures
The characteristic of this kind of picture is to evaluate the texture of the printed matter through the highlight and transparency of some metals or glass, and evaluate the reproducibility of the highlight. The typical representative of this kind of picture is "ware".
In short, the acceptance of the newly purchased offset press is a systematic, comprehensive and comprehensive work. Both buyers and sellers should do this work in a scientific and professional manner to achieve mutual benefit.
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