In order to provide a reference sample for the publishing paper and provide reference data for the printing and papermaking enterprises, the printing press has selected five light papers for physical index testing and on-machine printing testing to evaluate its printability and vision under the same printing conditions. effect. In order to realize the evaluation of the printing suitability of paper, the printing press commissioned us to design a printability test version.
In order to achieve a more objective and realistic reflection of the print applicability of the tested paper, when designing printability test versions, the focus is on the visual effects of proofs after printing. In the selection of test items, we mainly selected test items for natural image copying effects, including the typical character skin color, tea tone, dark green tone, high tone, midtones, shadow, subtle levels, sharpness, geometric figures in the image. Visual evaluation items such as gradation tones, non-color structures, etc.
In addition to evaluating visual effects, we also selected some printing process control indicators related to printability, such as reflectance density, dot gain value, overprint rate, chroma value, relative contrast (K value), and dot reproduction. , paper print density and so on. These indicators can be measured with special test instruments. Physical quantities can be used to describe and evaluate the printability of the tested papers, eliminating the errors caused by human factors and being more scientific.
In addition, from the perspective of evaluating the quality of printed products, we also designed tests and evaluation items such as register, geometric deformation, appearance, text, flat screen, gradient mesh synthesis, resolution, etc., in order to evaluate it more comprehensively, objectively and truthfully. Printability of the tested paper.
In the specific design of the printability test version, we selected 8 standard natural images and 10 composite images provided in the ISO1 2640 (GB/T18721-2002) standard. In order to test the printing effect of the flat screen, we also chose the more commonly used 70% deepnet and 30% shallow net superimposed flat grid color blocks (usually two-color superposition main) to meet the printability of light paper Testing requirements.
Taking into account the characteristics of light paper, three sets of printability test versions were selected using dot line counts of 120 lpi, 150 lpi, and 175 lpi. The three sets of printability test versions all use round dots, and the dot angles also use the traditional Y 90. , M 45. , C 75. , BK 15. . Because each color image in the printability test version adopts the electronic file provided by IS012640 (GB/T18721-2002) standard, there is no big deviation in image making. The black-and-white image in the printability test version is made by converting the color image data into grayscale image data. In order to maintain the reproducibility of the data, we have not adjusted the gradation, gradation, etc. of the image, and still use the image data after the color image data is converted to grayscale to maintain a relatively stable reduction effect.
Due to the open size, we adjusted (mainly reduced) the ISO1260 (GB/T1872l-2002) original standard image size during the platemaking process, and recombined individual images. The 8 color natural images selected for the printability test version have their own special features. They are used to perform special evaluations on the visual effects of the printed paper to be tested (for specific functions, see the sample description of the test sample).
The five resolution composite images (icons) selected for the printability test version are used to evaluate the conditions under which the tested paper is relatively fixed in other test conditions, reproducing its resolution, registration accuracy, etc., and moiré (moiré) and imaginary Such as the effect of. The patterns of the selected five resolution composite images (icons) are 1/4 of the neon light pattern, and each radiation angle is separated by four. The dimensions of the figures are all 30 mm x 30 mm, and the values ​​of the four dichroic sheets are the same. Resolving Figure 1 shows that the radiation is sinusoidally changed. It can be used to evaluate the smoothness, gray balance, and midtone reproduction of the tested paper by changing the image's radiation density (this pattern completes every 4 cycles). Printability and visual effects.
Resolution 2 is a binary representation of FIG. In radioactivity, all 50% or less than 50% of the outlet values ​​are recorded as 0%. All site values ​​above 50% are recorded as 100%. Figure 3 and Figure 2 show exactly the opposite, that is, all 50% or less than 50% of the network point value is recorded as 100%, all network values ​​above 50% are recorded as 0%. Figures 4 and 5 are generated in a similar manner to Figures 2 and 3. The difference is that the transformed outlet values ​​are 80% and 40% instead of 100% and O%. The purpose of selecting the resolution map 2-5 is also the same as selecting the resolution chart 1 to evaluate the printability and visual effects of the image resolution of the tested paper under different conditions.
The Gradient Stripe composite image selected for the printability test version consists of eight consecutive transitional gradient mesh images with a gradient range of 100% to O%. The eight color versions are C, M, Y, K, R, G, B, and BK. Among them, the latter four are the combined color strips of two-color and three-color superposition of C, M, Y three primary colors. These color stripe images are used to evaluate the effect of printing a gradient mesh on the tested paper. A total of four chromatogram synthesis images were selected for the printability test version. The chromatogram synthesis image 1 has 6 rows of color patches, 13 color patches in each row; the chromatograph synthesis image 2 has 8 rows of color patches, 13 color patches in each row; the chromatogram synthesis image 3 includes 12 area blocks, each area block has 36 The color blocks; chromatogram synthesis image 4 includes 14 area blocks, of which, each of the 10 area blocks is 25 color blocks, and each of the other 4 area blocks is 16 color blocks. The chromatogram colors reflected by these chromatographic composite images have met the requirements for evaluating the printability and visual effects of the tested paper.
In order to complete the physical index testing requirements for the tested paper printing, we selected the first, second, and third color blocks in the first row of the chromatogram synthesis image 1 (C 100%, M 100%, Y 100%, respectively) and The twelfth color patch (BK 100%) in the second row is a reference color patch for measuring the print density and chromaticity of the test sample. The third color patches (80% of C, M, Y, and BK) of the 3rd, 4th, 5th, and 6th rows in the image 1 with the above four color patches are respectively measured for the relative printing of the respective measured papers. Contrast value (K value); Match 3 color blocks of the 5th (C 100%, BK 100%), 6 (M 100%, BK 100%), 7 (Y 100%, BK 100%) of the second row , Measure the two-color overprint rate of each tested paper. In addition, we chose the 2nd (80% for each color), 5th (50% for each color), and 8th (25% for each color) color blocks of rows 3, 4, 5 and 6 to measure each The dot enlargement rate of the measured paper also selected the 11th (100% of each color) color block in the second row to measure the backside print density of each tested paper. (For details on the four chromatogram composite images, see attached figure).
In order to reflect the effect of a large area of ​​flat screen printing, the printability test version intentionally spreads the commonly used flat screen in the caption part of the natural image. Figure 1, 2, 3, and 4 show the shallow nets of about 30% of different colors. Figures 5, 6, 7, and 8 show the depth of about 70% of different colors (mainly two-color and three-color overlays). The complex color) is used to evaluate the effect of the tested paper on reproduction of colors after printing. Due to the influence of space, the printability test version failed to use the text and a variety of fonts, font size layout test items, in particular to explain.
Based on the principle of scientific rigorousness and impartiality, we carried out serious tests on the printing test samples of the five types of light papers provided by the Press Association. The test items mainly involved the printability index of the print proofs, including visual effects and visual effects. The natural image embodies the features of the printing effect, tone reproduction, uniformity, dot recovery, color density, overprint, through the situation, etc., a total of 5l items. After nearly a month of intense testing, various testing indicators and results have been completed. From the test results, No. 2 and No. 4 of the tested five types of paper are more suitable for low-grade color printing, and No. 3, No. 1, and No. 5 are more suitable for single printing. Color printing (monochrome prints based on text), see the attachments (test records) for all actual measurement conditions.
First, test item description
Since the purpose of the inspection is to test the printability of various lightweight papers, we focus on the content to be tested on the inspection items, namely, the reproduction visual effects of tone tone, print uniformity, dot reproduction and reproducibility. , Backside penetration, dryness, overprinting of prints, changes in geometry, and field printing effects. In addition, printing conditions such as powder-off lint, print-feeding, and wrinkling are not within the detection range. Due to the lack of detection methods, certain indicators (such as glossiness of prints) could not be evaluated with quantitative values.
Second, testing equipment and testing environment
In order to make the detection parameters truly reflect the actual conditions of the measured object, we will send all the testing instruments and equipment used to measure and calibrate. The testing equipment includes:
(1) Sx40 times light source reading microscope (Zhejiang Wenzhou)
(2) X-Rite 418 Color Reflectance Densitometer (USA)
(3) TCS color analyzer (Beijing Oyke) Test environment: temperature 20 °C, relative humidity 45%, light source natural light (equivalent to 5500 K), in line with visual evaluation standards.
(to be continued)