Acceptance test for new offset presses
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As the competitiveness of the printing market gradually increases, the share of “hard power” in the printing unit becomes more and more obvious. In particular, a cost-effective printing machine can bring great business opportunities to the printing unit and can cope with the growing Market demand, but whether the performance of introducing new printing presses is completely in line with the company's needs, how to accept the newly purchased printing press is a key issue. I am fortunate to have participated in the acceptance of the new printing press in the printing company. I will share the results of the acceptance with my colleagues, hoping to give some inspiration to the industry.
First. Acceptance work content
For the manufacturers of large-brand offset presses, they have done relatively comprehensive tests before shipment. However, considering the price of the offset printing machine and the requirements of the factory for production, some tests before the acceptance are necessary, such as testing whether the offset printing machine is in a stable working state after installation and commissioning; checking whether the performance and parameters of the offset printing machine are consistent The provisions of the instructions. The author and the experienced printing captain and long-term work in the print production line of the master exchange. It is believed that the acceptance of the new printing press mainly includes the following aspects.
1. Empty car operation
After the offset press is powered on, in order to check whether the installation and connection of each part of the device is normal, the operation speed of the device cannot be turned up particularly quickly, and it can only be operated at a low speed. Then slowly increase the speed until the highest speed, one is to hear the abnormal sound of the offset press; the other 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 Whether the situation is abnormal.
2.50% flat screen printing test
Generally speaking, the 50% dot is the largest in circumference, and the larger the circumference is, the larger the dot gain is, so the dot gain is also the largest. For this reason, the 50% dot gain is one of the important indicators for evaluating the performance of the offset press. . The requirement for 50% flat net is: the flat screen is the maximum printing size; the flat net itself is flat and has no streaks; the front or the tip of the flat net is best to carry the solid parcel, which is used for the flat net test. Basis.
3. Field test version
The field test version mainly detects whether the printing pressure, roll pressure, etc. reach a certain standard. You can check whether there are any bars (including impact bars, ink bars, water bars, etc.) in each unit. Because the 50% flat net does not reflect the degree of the bar, the testing of this link is very necessary.
4. Meter character overprint
The m-printing is mainly to check the registration accuracy of the offset press and the reflection of the fan-shaped expansion of the paper. It can be tested as follows: Under the premise that the full-page fine-line overprinting is basically accurate (the overprinting precision can reach 0.01mm), the single test is carried out: firstly, printing is performed at different speeds to check whether the overprinting accuracy changes; then 100 pieces of 80g are printed. /m2 paper, observe the spread of thin paper printing, because the tail is related to the performance of the paper itself. Can only be used as a reference.
5. Printing standard test version
Although there are various combinations and combinations of test versions used by various machines, there is no uniform regulation, but it will certainly contain two parts, namely objective measurement signal bars and subjective evaluation pictures, in order to complete the comprehensive evaluation of printed matter. After discussion, taking into account 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 accept the offset press.
Second, the test version of the objective test content
1.GATF/system digital layout control
Designed for use along the outer edge of the test format, this object is a multi-component inspection and process control tool that includes A, B, C, D, E, F, etc. for monitoring digital output exposure systems, film, and printing. Edition, proof, etc.
Part A includes image device confirmation, interpreter level, horizontal and vertical resolution, image orientation, number of screen lines, dot type, and cable 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 details of the positive and negative arcs are clear, the system is good.
Part E is a star mark and ink solid color block. The star mark is composed of a wedge pattern with a 5 degree interval. It is mainly used to check the printing faults such as enlarged vertical and horizontal deformation, ghosting and paste printing of the dots during printing. The two color patches are 1501pi and 2001pi 50% dots for evaluating the increase in system color values and can also be objectively evaluated using a reflection densitometer.
Part F consists of two sets of matching step scales, the upper one is the compensation program setting without RIP applied, and the lower one is the application compensation setting. The two steps are more clearly indicating the impact of the compensation procedure. If the two steps are identical, there is no compensation procedure for RIP.
2. Gray balance scanning object
The gray balance scan object contains a series of gray balance patches that have the same values as the patches in the four regions of the gray balance table. These numbered patches are designed to be arranged in a straight line for easy scanning of the densitometer. The number 1 patch is white for density meter calibration; the number 2 to 27 patches correspond to highlight signal areas; The patches of 64 correspond to the 1/4 tone signal region; the patches of numbers 65 through 101 correspond to the signal regions of the midtone; the patches of numbers 102 through 138 correspond to the 3/4 tone signal regions. In the sequence of high-light signal regions of 2 to 27, the green dot of each patch is 7%, while the range of the product and the yellow dot is increased from 1% to 6%; in the quarter-tone region, the green dot is 30%. The range of products and yellow dots is 16% to 28%; in the middle adjustment area, the green dot is 60%, the product and yellow dot ranges are increased from 46% to 58%; in the 3/4 tone region, the green dot is 80. %, product, yellow network points increased from 66% to 78%.
3. Scanning step scale
For the six colors in the Digital Test Page 4.1 format, each of the scan step scales contains a total of 22 halftone ink blocks and one solid ink block. These patches can be used to measure dot gain from 5% to 95% at 5% equal intervals, and increase 3% and 7% in the light portion, and increase 97% in the dark portion as a critical Additional input for the range of part gradations. These step scales are designed for process standardization and are better than those for process control and inspection. In order to obtain valid data from the ladder, the printing system must operate within the operating specifications. If a microprocessor-assisted densitometer is used to measure the dot gain value, it will automatically measure the apparent dot area. After obtaining 23 sets of data points from the scan step scale, it is easy to construct a dot gain curve. Describe the characteristics of the entire printing system. When using halftone color separation printing in this system, the dot gain value latitude determined by this curve is also used. The advantage of using a scan step scale to create a dot gain curve is that its 23 data points make the curve highly accurate. It is linked to the digital page test format and may optimize printing conditions.
4. IT8.7/3 basic data settings
The IT8.7/3 standard test draft is included in the digital page test format. The base data settings are used for a large number of third-color copy tests, or for the three spot colors of color plus black. Selecting the color in the IT8 color setting can cover the entire color tone and facilitate the conversion of the color space and the drawing of the full-tone curve. The patches in the underlying data list are collectively confirmed by the letters representing the columns and the numbers representing the rows (for example, B13 represents the patch of 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. It is two small blocks each, 114 pieces long, and its size is 0.39×22.47 inches (10.0×57.1 mm). The measurement size of the single block is 0.20×0.20 inches. (5.0 x 5.0 mm), the inking area is 1.18 inches (30 mm) long. The upper layer consists of solid ink blocks containing 19 duplicate copies of CMYK, while the lower layer contains a white color block of the initial paper, followed by CMYK's 25%, 50%, and 75% color colors. The block is repeated, followed by two CMYK star copies, two CMYK dot enlargement scale II copies, then blue, green, and red overprints, two copies of CMKY's ghost/highlight target, and adjacent Blue, green and red are printed on the ground and 50% in color.
6.GATF/RHEM light indicator
The 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 painted with two formulations of ink. It is carefully configured to achieve an optimal match at 5000K color temperature, while at other color temperatures. The light can't be matched. This light indicator acts as a warning pattern and warns when the evaluator cannot correctly determine the color. Because subjective quality control relies on color matching between different colorants (such as between sublimation dyes and printing inks), all judgments must be made under standard viewing conditions (ANSI standards).
Third, the test version of the subjective evaluation picture
1. Low-key / red couch
The red couch is a low-key reference map with a primary hue of dark tones, including red, green, blue, and a variety of perfect wooden grain tones, in the middle of the tone reproduction curve to the low-key area. If you want to copy such a degree of detail, you need a high-resolution scanner and a large file. This has high requirements for color separation and prepress equipment, and there is enough tone compression to make the middletone The part is offset to the dark tail and printed using plain or direct digital printing so that there is enough contrast to distinguish the dark color.
2. High-profile / wedding banquet
The photo of the wedding reception is a bright reference picture whose main color is soft light and white, located in the high-tone to mid-tone part of the tone reproduction curve. For this type of picture, set the smallest printable tone point (especially 3% of the dots), have enough tone compression, shift the middle to the highlights, and use plain or direct digital printing. The way to achieve accurate copying, in order to have enough contrast to distinguish the highlights.
3. Group portrait / painting teenager
The group portrait/painting juvenile is a reference picture for the human skin color. From left to right, the figure is Caucasian, Latino, Japanese, African American, Indian. The key to how to replicate the five skin colors 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 maps, which are common examples of portrait tone reproduction. Women's portraits are the focus of photo coloring. In order to keep the details of the dark parts of the hair and clothes while maintaining the details of the bright parts, in the process of color separation, the gray balance should be tilted to the direction of the human body to be correctly compensated, then the position from the highlight to the middle tone Subtle color changes can occur.
5. Neutral gray
In addition to neutral gray, some grays in neutral gray photos are warm or cool, and the only saturated color is the hue that is emphasized. The exact copying of neutral gray pictures is very difficult, and its gray balance reproduction is easily determined by checking the degree of closeness of the tone and neutral gray. In order to maintain a good tone separation effect, the mid-low key portion of the tone reproduction curve requires a large degree of tone compression. The combination of tone compression and gray balance makes the photo of neutral gray the most difficult quality control in terms of accurate copying.
6. Color full color, fruit picture
Fruit Picture Full Color/Fruit Picture is a picture taken with a flash in close shot. It has fewer constituent elements and is designed to provide a wider range of colors and tones. Therefore, there are more saturated dark areas in the picture, and the number of detail parts is relatively small. It is difficult to use narrow-tone inks to copy these colors.
7. Memory color / roofed bridge picture
The bridge picture is a reference color proof of the excellent outdoor natural light scenery. The actual purpose is to evoke the reader's reaction to the color of memory. When the reader sees a picture of such a memory color, it first judges whether the color it contains is credible. In the color copying process, as long as there is a slight change, it can be found, so the color reproduction should be very close to the original. The picture of the small bridge with a roof is very useful for testing the quality of color reproduction, as most observers have a clear understanding of these tones.
8. Texture picture
The characteristics of this type of picture are that the texture of the printed matter is evaluated by the high light and transparency of some metals or glass, and the reproducibility of the highlight portion is evaluated. A typical representation of this type of picture is the "ware".
In short, the newly purchased offset press acceptance 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.