Printability of the hottest FM dot 2

FM dot printability

FM plus is a new replication process with the development of computing technology in recent years. It is different from the general FM plus. FM printing has the advantages of soft tone, rich layers, lifelike images and no moire effect. According to the characteristics of equal size but random arrangement of frequency modulation points, this paper mainly discusses the printability of frequency modulation points, printing materials and printing operations, as well as the advantages of using frequency modulation points in printing

1. Introduction

in the process of image reproduction, the traditional addition method is used to express the intensity level of the image. After more than a century of unremitting efforts, printing technicians have made considerable achievements. However, this addition method, due to the color overprint will appear many times, the material concept has three characteristics: multi regular rose shaped stripes, and sometimes even moire. At the same time, due to the decomposition of points, with the reduction of the number of lines, the sharpness of the image decreases sharply, losing the characteristics of the original. In recent years, with the research of high fidelity reproduction technology, ultra-fine dot printing of more than 120l/cm has emerged, which can accurately obtain the image effect of fine level reproduction and continuous tone. However, no matter how fine it is, the characteristics of its points are that there are regular distribution of positive or negative points of different sizes in the image part, and there is always its fatal weakness. The structure of rose flower type, that is, the pattern phenomenon caused by adding angle, is independent of the number of lines. At the same time, if the number of lines exceeds a certain limit, it will not only bring greater difficulties to replication, but also cause more serious loss of step value, especially the highlight part, and there are certain restrictions on the resolution, which is the biggest drawback of the traditional addition method

2. Characteristics of frequency modulation points

in the 1970s, foreign countries began to study a frequency modulation addition method. It is different from the traditional addition. The printing points are calculated based on the statistics of the hue and hierarchy of adjacent parts in the image. They are irregularly randomly distributed in the image area and have the same size (most of them are μ m) , which is used to express the intensity level of the image. Because the technical conditions at that time could not meet a large number of computing needs, it was postponed to the 1980s. With the development of electronic computers and the substantial improvement of computing power, this addition method was realized. However, at this stage, FM addition is only a random addition of a first-order function, with equal point sizes, and the change of point spacing is different from that of the photo image by halogen particles of different sizes and distances (0 μ m) Deposition to form tones or colors is still different. Therefore, people continue to study that if the second order function is added randomly, the distance and area of the dots can change randomly. Then, the second order function addition is very similar to the original photo in the mechanism of expressing the tone, and the replica will be more realistic, which is completely close to the effect of the photo image. Of course, the calculation of random addition of second-order functions is larger and more complex, but it is believed that it can be realized in the near future

in fact, at this stage, people have shown incomparable advantages over the traditional addition method by using first-order function frequency modulation addition. In order to show that using computer algorithm to control the dot arrangement can actually eliminate the unsightly pattern like periodic structure, which is more suitable for image reproduction above three primary colors. Due to the fine frequency modulation and dot adding, if the diameter is 15 μ The idea of M can undoubtedly reproduce 1%-99% of the tone value, so the replica has high resolution, soft image tone, rich layers, realistic images, and whether there is moire effect. This is the charm of FM plus method that can be affirmed by printing experts

3. Minimum point size of engraving

in FM plus technology, the only key parameter is the size of the point, which is much less than the traditional art printing parameters. It does not have the problems of point angle, line number and point shape. The size of the frequency modulation point is only related to the recording accuracy of the exposure device. Theoretically, the size of the light spot recorded by a 1200dpi Phototypesetting is a square spot with a side length of 1/1200in, but in fact, the light spot exposed on the photosensitive film by laser is a circle with an area slightly smaller than this square, about 21 μ m. That is, 1.2% of the dots equivalent to 60l/cm, such as the tensile strength and plastic properties of the material can be measured through the tensile test, or 1.5% of the square dots, as shown in Table 1

it can be seen from table 1 that with the improvement of recording accuracy, the light spot becomes smaller. Judging from the output accuracy of the current Imagesetter, it is completely guaranteed to produce the FM dot size that meets the printing requirements. The problem depends on the printable dot size in printing. Therefore, FM addition is more about printing technology than computer hardware. Therefore, the minimum printable size is a key factor in printing, but its value varies due to the influence of printing equipment, materials, technology and technical level. It is reported that assuming a certain resolution, taking a light spot as the inking point, foreign countries can print on smooth paper with high quality, and the minimum printing point can reach 8 μ m. It can also be printed on rougher paper μ M points. But in our country, according to the test, it is less than 20 μ M-point printing is quite difficult, obviously there is a big gap

4. FM dot printability

dot generation from the negative to printing to the substrate requires many process transformations, and the changes in each transformation directly affect the color restoration of the image, which exists in any processing technology. However, due to the different structure, fine dots, and the change law, the frequency modulation plus is different from the traditional plus, and its control conditions may be more strict. Now, according to the actual conditions, it is assumed that the recording accuracy is 1200dpi, that is, the inking point is 20 μ M size to discuss the requirements of FM dot printability

4.1 image density of output film

generally, the laser dots added by frequency modulation are often circular dots with jagged edges. The finer the dots are, the less halogen silver particles are deposited on the negative film, and the lower the density is. According to the requirements of printing standardization, its density must be greater than 2.30. At the same time, no more than two Hexion companies are allowed to launch its first two-component epoxy resin manufacturing solution at JEC world in Paris, with a diameter of 6 μ M, otherwise and are unqualified

therefore, the film output by the laser recording device should preferably use the extra hard film matching the device. The output points are required to be solid, dense, transparent and clean. Because the dots are small, it is not allowed to use corrosion methods to eliminate spots or correct dots during film processing, and avoid repeated copies. Therefore, in addition to the strict specification and standard operation of the film washing conditions, it is best to have the supporting treatment solution and dust-proof clean environmental conditions suitable for FM addition

4.2 printing requirements

the basis of the printing point is the sand mesh on the surface of the printing spot. The finer the sand mesh, the more sand mesh on the support point, the stronger the adsorption force, and the smoother the edge of the point, so it is only 20 for one μ For m-Size frequency modulation point, in order to maintain its due printing resistance and not be worn, try to use a printing plate with fine sand grains and high resolution. According to international standards, the ideal sand mesh is average, but with the development of time: the Charpy lock impact test, Charpy V-shaped impact test and Charpy Mayer impact test have been paid attention to, and the roughness is 2.5 μ m. Depth 3 μ m. Assuming that each sand mesh is regarded as a cone, then each 20 μ There are 64 sand mesh supports at the frequency modulation point of M, and the total contact area is about 817 μ m ×μ m。 However, at present, the average coarseness of PS version in China is greater than 5 μ m. Obviously, a frequency modulation point is supported by only 16 sand meshes, with a total contact area of 490 μ m ×μ m. Both the number of supported sand mesh particles and the total contact area are relatively small, so the adsorption force is greatly weakened, which is also one of the reasons for dot dropping. At the same time, the coarser the particle, the more photosensitive resin liquid is coated, the thicker the film, and the point is easy to increase due to the photoosmosis effect. Of course, it is not the finer the better, otherwise it will affect the hydrophilicity of the printing plate. From this point of view, the printing plate at the frequency modulation point is best to increase the particle side area or change the plate properties to obtain the best hydrophilicity under a certain particle size

the key to the printing operation is to ensure that the points are not lost or deformed. Therefore, it is required that the printing plate should be in close contact with the negative, and the point light source should be used for exposure to reduce the deformation of the points caused by the light penetration effect, and the developer concentration, temperature and the environmental conditions of printing should be strictly controlled. Any dust or stains and scratches on the glass of the printing machine can affect the quality of printing

4.3 selection of printing materials

due to the fine frequency modulation points and different structures, there are high requirements for printing materials, such as ink, paper, and blanket

a, ink: the frequency modulation points are almost completely isolated and randomly distributed in the image. Even in the dark part, the calculation method can be used to make sure that there are no duplicate points as far as possible (at most, some points may be close to each other), which is different from the traditional point tone when it is more than 50%. At 20 μ Under the inking point of M small, the ink must show good viscoelasticity in the printing plate, blanket and transferred to paper. When the external force stops intermittently or completely, the inking point can immediately restore the original structure, maintain the characteristics of isolation and do not collapse. Therefore, the thixotropy, yield value and viscosity of this ink are larger

due to the fine dots, the ink layer cannot be very thick, and the density will be affected. Therefore, the ink is required to have high coloring power, high color saturation, fine particle size, and strong water resistance. Considering the overall effect, we should develop special inks suitable for FM dot printing

b, paper. Paper and ink are two inseparable aspects of printing effect. In order to ensure that the frequency modulation point is not lost, in addition to the general requirements of good whiteness and high surface tensile strength of the paper, it is particularly important for the smoothness and thickness uniformity of the paper. According to foreign reports, high-grade coated paper can print 8 μ M points, while the paper with rough surface is only 30 μ M, so paint paper with high smoothness should be selected as much as possible

c, blanket. Blanket is an intermediate carrier in offset printing, which plays the role of ink transmission. Therefore, blanket should not only have good ink adhesion and water resistance, but also have good ability to transfer ink. In FM dot printing, the smoothness and flatness of blanket should be emphasized to maintain the integrity and clarity of dots. It is best to use air cushion blanket with smaller print point enlargement

4.4 suitability of printing operation

the correct transfer of printing time point is one of the key elements to evaluate printing quality. However, the original concepts of control percentage and tone in traditional plus printing are no longer applicable. Frequency modulated dot printing can only check whether the ideas are complete without loss, and the increase of points is inevitable

we know that if the pressure is too high or the grinding amount is too large in printing, the dots will definitely increase. If according to the theoretical law of the area around the point, the point increase is calculated by the circumference of all printed points, then the sum of the points around the frequency modulation point is much larger than the traditional point because the points are small and almost isolated, but the increase value of all points under normal conditions is uniform. At the same time, due to the high accuracy of FM point recording, fine dots and reproducible tone, there is almost no limit. Therefore, the image is still soft and high-definition, but it does not mean that the pressure or ink volume can be increased. Because the frequency modulation points are isolated and unevenly distributed, the force on each part of the points per unit area is also uneven, especially in the highlights, there are few and few points per unit area