Diffusion prevention method for digital machine printing material

Abstract

The invention belongs to the technical field of digital printers, and particularly relates to an anti-diffusion method for a printing material of a digital machine, which comprises the following steps: S1, dividing areas on the surface of the printing material, and dividing the surface of the printing material into n equal areas along the conveying direction of the printing material; s2, the first area is coated with a coating; s3, the second area is coated with paint, printing is carried out on the first area, and first curing is carried out; and S4, the third area is coated with paint, printing is conducted on the second area, first curing is conducted, and second curing is conducted on the first area. The surface of the printing material is divided into a plurality of areas, and the paint is sequentially coated in each area, so that the paint in each area can be ensured to have enough time to be cured after being coated. Therefore, the paint can be prevented from being influenced by subsequent printing operation under the condition that the paint is not completely cured, and ink is prevented from permeating into the paint or diffusing on the surface of the paint.

Description

Technical Field

[0001] The invention belongs to the technical field of digital printing machines, and in particular relates to a method for preventing diffusion of printing materials of digital machines. Background Art

[0002] At present, UV digital printers mainly use inkjet technology to spray UV ink onto printing materials, and then quickly cure the ink through ultraviolet irradiation. Since UV ink is a light-curing ink, after printing on the surface of the material, the UV ink is almost not absorbed by the material, but directly forms a solidified film on the surface. Since UV ink cannot penetrate into the material like traditional ink, but is cured or formed through light, this technology performs well on non-diffusion materials (such as coated paper, plastic, metal, etc.), and can provide high-resolution, colorful and durable printing effects.

[0003] However, although UV ink cures quickly, the ink droplets still have a certain degree of fluidity before curing. For diffusion materials, especially materials with strong water absorption (such as writing paper), even if the UV ink is not absorbed by the material, the tiny pores and fiber structure on the surface of the material will still have a certain adsorption effect on the ink droplets, causing the ink droplets to diffuse slightly before curing. This diffusion will make the edges of the text blurred, especially when printing small characters, this effect is more obvious.

[0004] In order to solve the above problems, the commonly used measure is to apply a thin coating on the surface of the diffusive material before printing, such as UV curing polyurethane coating. UV curing polyurethane coating is a coating specially used for UV printers. It can be cured within a few seconds. UV curing polyurethane coating can fill the micropores on the surface of the material, reduce the adsorption of UV ink by the diffusive material, and provide a smooth surface so that the ink can be evenly distributed and quickly cured. This can reduce the diffusion of UV ink before curing, thereby improving the clarity of the edges of small characters.

[0005] However, for larger posters or other larger printed materials, due to their larger size, curing is performed after the entire surface of the printed material is printed. In this case, the diffusion degree of the UV ink layer printed first on the printed material is much different from that of the UV ink printed later. Since UV ink will not penetrate the surface of the coating, the UV ink printed first will still diffuse on the coating, affecting the clarity of the print.

[0006] Therefore, a printing method for large-sized diffusion-type materials is needed to solve the above problems. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a method for preventing diffusion of printed materials by a digital machine, which solves the problem that the UV ink area printed first may diffuse in large-sized printed materials.

[0008] The object of the present invention can be achieved by the following technical solution: A method for preventing diffusion of digital printing materials, comprising the following steps:

[0009] S1: Divide the surface of the printing material into regions, and divide the surface of the printing material into n equal regions along the conveying direction of the printing material;

[0010] S2: applying a coating on the first area;

[0011] S3: coating the second area, printing on the first area and performing the first curing;

[0012] S4: coating the third area, printing and performing a first curing on the second area, and performing a second curing on the first area;

[0013] Repeat S1-S4, so that when coating is applied to the nth area, printing is performed on the n-1th area, and a second curing is performed, and a second curing is performed on the n-2th area, until printing is completed;

[0014] After the coating process is completed, the coating is cured.

[0015] Preferably, the digital machine includes a flexographic printing seat, and the flexographic printing seat is used for applying the coating;

[0016] The flexographic printing seat is arranged at the front end of the digital machine printing area. The flexographic printing seat includes an anilox roller and a UV lamp which are arranged in sequence. The anilox roller abuts against the surface of the printing material to realize coating of the coating, and the UV lamp cures the coated coating.

[0017] Preferably, a UV lamp is used to cure the printed UV ink, and the power density of the UV lamp for the first curing is twice the power density of the UV lamp for the second curing.

[0018] Preferably, in the process of S1-S4, it also includes filling nitrogen gas on the conveying area of ​​the printing material to ensure that the nitrogen gas fully covers the surface of the printing material.

[0019] Preferably, the process of S1-S4 also includes control of the humidity of the conveying area, and the humidity control is achieved by a humidity control device, the humidity control device includes a humidity monitoring device and a drying device, the humidity monitoring device and the drying device are electrically connected, the humidity monitoring device is used to measure the humidity detection value of the air, and a humidity threshold interval is preset in the humidity monitoring device, and the humidity monitoring device controls the humidity value of the conveying area within the humidity threshold interval according to the humidity detection value and the humidity threshold interval.

[0020] Preferably, before step S1, the surface of the printing material is pre-processed, and the pre-processing includes the following steps:

[0021] a: Clean the surface of the printed material;

[0022] b: Corona treatment to ensure that the entire surface of the printed material is covered with electrical charge;

[0023] The corona treatment is completed using a corona treater integrated on the printing press, which is set at the front end of the flexographic printing station.

[0024] Preferably, after a, the step further includes a1: performing heat pressing treatment on the surface of the printing material.

[0025] The beneficial effects of the present invention are:

[0026] By dividing the surface of the printed material into multiple areas and applying the coating in each area in turn, it can be ensured that the coating in each area has enough time to cure after coating. This can prevent the coating from being affected by subsequent printing operations when it is not fully cured, and prevent the ink from penetrating into the coating or spreading on the coating surface; and through the two curing of UV ink, the first curing can make the ink surface solidify quickly to form a thin solid film to prevent the UV ink from continuing to spread; the second curing ensures that the UV ink is fully cured inside to form a solid polymer network, effectively reducing the diffusion of UV ink on diffusive printing materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0028] Figure 1 The figure is a flowchart of the steps of the method of the present invention. DETAILED DESCRIPTION

[0029] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0030] Because the tiny pores and fiber structure on the surface of the diffusive material will have a certain adsorption effect on the UV ink droplets, causing the UV ink droplets to diffuse slightly before curing. This diffusion will make the edges of the text blurred, especially when printing small characters, this effect is more obvious. Therefore, to solve this problem, a layer of UV curing polyurethane coating is formed on the diffusive material. The UV curing polyurethane coating effectively prevents the diffusion of UV ink by forming a dense protective film on the surface of the diffusive material, ensuring clear edges of text and images. The UV curing polyurethane coating can also enhance the adhesion of the ink and prevent the ink from penetrating into the material.

[0031] However, even if a UV-curing polyurethane coating is provided on the diffusive material, when the size of the printed material itself is large, for example, in the printing of large-sized promotional posters required for large-scale events, due to the large size of the printed material, the UV ink cannot be cured in time after printing, and the UV ink will still diffuse slightly on the coating, resulting in poor curing effect of the UV ink, affecting the printing effect.

[0032] See also Figure 1 This embodiment provides a method for preventing diffusion of printed materials by a digital machine, comprising the following steps:

[0033] S1: Divide the surface of the printing material into n equal areas along the conveying direction of the printing material. The size of the area to be divided is selected according to the curing conditions required by the UV ink used and the power of the UV curing lamp used;

[0034] S2: applying a coating on the first area;

[0035] S3: coating the second area, printing on the first area and performing the first curing;

[0036] S4: coating the third area, printing and performing a first curing on the second area, and performing a second curing on the first area;

[0037] Repeat S1-S4, so that when coating is applied to the nth area, printing is performed on the n-1th area, and a second curing is performed, and a second curing is performed on the n-2th area, until printing is completed;

[0038] After the coating process is completed, the coating is cured. The curing time and curing power of the UV-curing polycarbonate coating are determined according to the specific components of the coating used and the coating thickness of the coating. The coating thickness of the UV-curing polycarbonate is

[0039] By dividing the surface of the printed material into multiple areas and applying the paint in each area in turn, it is possible to ensure that the paint in each area has enough time to cure after being applied. This can prevent the paint from being affected by subsequent printing operations when it is not fully cured, and prevent the ink from penetrating into the paint or spreading on the paint surface.

[0040] Naturally, the printing parameters of the printer can also be designed to first cover the entire surface of the printed material with coating and solidify it, then perform partitioning on the surface of the printed material, and then perform the first and second solidification on the surface of the printed material in sequence.

[0041] Since the control of UV lamp and curing time for one-time curing needs to be strictly controlled, too low power density of UV lamp will easily lead to incomplete curing and the ink cannot be fully cross-linked; too high power density may cause the ink surface to cure prematurely, while the inside is still not completely cured, forming a "false curing" phenomenon. Therefore, in order to better set the curing time and power of UV lamp, one-time curing is designed as two-time curing, and in order to further reduce the diffusion of ink on the printed material, especially in the area of ​​small characters or fine patterns that require high definition, UV lamp is used to cure the printed UV ink, and the power density of UV lamp for the first curing is twice that of UV lamp for the second curing;

[0042] Use a UV lamp with a lower power density for the first curing to quickly solidify the surface and edges of the UV ink, because the ink droplets formed on the surface of the coating have a certain curvature, which generally becomes thinner from the middle to the sides. Through the first curing of the UV lamp, the edges and surfaces of the ink droplets are cured to prevent the ink from spreading laterally on the surface of the coating. There is a certain time difference between the second curing and the first curing, so during this time difference, the ink can be fully cross-linked to ensure the stability of the subsequent second curing, thereby ensuring the clear edges of the text and images.

[0043] The first curing can make the ink surface solidify quickly to form a thin solid film to prevent the UV ink from spreading further; the second curing ensures that the UV ink is completely cured inside to form a solid polymer network. The specific power and curing time should be adjusted according to the ink type, material properties and printing content to achieve the best curing effect. Of course, the light irradiation range of the UV curing lamp can be adjusted according to the size of the area to ensure the curing effect.

[0044] In order to make the coating more uniform, in one embodiment, the digital machine includes a flexographic printing seat, which is used to apply the coating;

[0045] The flexo printing station is set at the front end of the digital printing area, that is, the flexo printing station is integrated into the production line of the digital printing machine, and the coating and curing process can be completed before the material enters the printing area. This ensures that the material has a stable coating when it enters the printing area, avoiding printing quality problems caused by incomplete curing of the coating.

[0046] The flexographic printing station includes an anilox roller and a UV lamp, which are arranged in sequence. The anilox roller and the surface of the printing material are in contact to achieve the coating of the paint, and the UV lamp solidifies the coated paint. The anilox roller is a metal roller with a tiny texture, which can accurately control the thickness of the paint. By adjusting the texture depth and pressure of the anilox roller, the thickness of the paint in each area can be ensured to be uniform. The texture on the anilox roller can transfer the paint evenly to the surface of the printing material during the coating process, avoiding the phenomenon of local over-thickness or over-thinness.

[0047] During the UV ink curing process, if the UV ink surface contacts oxygen in the air, an oxide layer may be formed on the surface. This oxide layer will hinder the direct contact between the ink and the coating, and reduce the adhesion of the UV ink on the coating. Although the time for the UV ink to drip from the nozzle to the coating and the time for the ink to wait for curing on the coating are very short, the contact area between the ink droplets and the air will increase because the nozzle sprays very fine ink droplets. Although the oxidation reaction produces very little oxide layer, the impact on the extremely small contact area between the UV ink and the coating cannot be ignored. Therefore, in one embodiment, it also includes filling nitrogen on the transmission area of ​​the printing material to ensure that the nitrogen can cover the surface of the printing material, isolate the UV ink from the oxygen in the air, and thus avoid the generation of oxides. Of course, nitrogen can also be replaced by other inert gases. In this process, it is necessary to ensure the uniformity of nitrogen filling, not to affect the operation of the printer nozzle, and to ensure that the location of the printing area is relatively closed to enhance the effect of nitrogen.

[0048] Due to the rainy weather in the south or the high humidity in spring, during the printing process of printing materials, UV ink is easy to absorb moisture in the air in a high humidity environment, resulting in a decrease in the performance of UV ink. Moisture will affect the fluidity, viscosity and curing speed of UV ink, and then affect the adhesion between UV ink and materials. In addition, moisture may also cause a water film to form on the surface of UV ink, hindering the direct contact between UV ink and materials and reducing adhesion.

[0049] Therefore, it is necessary to monitor the humidity in the environment during the printing process, and when the humidity exceeds the standard value, adjust the humidity of the printing area to reduce the impact of the high humidity environment on the curing of UV ink. In one embodiment, in the process of S1-S4, it also includes the control of the humidity of the transmission area, and the humidity control is achieved by a humidity control device, the humidity control device includes a humidity monitoring device and a drying device, the humidity monitoring device and the drying device are electrically connected, the humidity monitoring device is used to measure the humidity detection value of the air, and the humidity monitoring device is preset with a humidity threshold interval, the humidity monitoring device controls the humidity value of the transmission area within the humidity threshold interval according to the humidity detection value and the humidity threshold interval, and the humidity control device can be used to achieve the humidity of the space required to be adjusted according to the set humidity control.

[0050] The general standard humidity range is 40%-60% RH (relative humidity). This range can effectively prevent UV ink from absorbing moisture, avoid moisture absorption and deformation of the coating, and ensure the flatness and stability of the printed material. However, the specific standard humidity range for different printing materials needs to be tested and adjusted to best suit the current printing material and UV ink.

[0051] In order to improve the adhesion between the coating and the printed material surface, in one embodiment, the surface of the printed material is pre-treated before step S1, and the pre-treatment includes the following steps:

[0052] a: Clean the surface of the printing material to completely remove dust, oil and other impurities on the surface of the printing material to ensure that the surface is clean and smooth. This can not only improve the adhesion of the ink, but also avoid printing defects caused by impurities;

[0053] a1: As mentioned above, in an environment with high humidity, the bonding between the printing material itself and the coating will be affected. In order to prevent the presence of fine creases or indentations on the surface of the printing material and reduce the stability of the bonding between the coating and the surface of the printing material, the printing material is subjected to heat pressing treatment before the coating is applied. The printing material is smoothly passed through the hot pressing roller, which abuts against the surface of the printing material to improve the flatness of the surface of the printing material.

[0054] The hot pressing roller set on the conveying mechanism of the printing material can heat and press the upper surface of the printing material by the hot pressing roller. The hot pressing eliminates the tiny wrinkles and unevenness on the surface of the printing material by heating and pressurizing. The hot pressing roller applies uniform pressure, and the heat can soften the surface of the material, making it easier to flatten. When the material passes through the hot pressing roller, the unevenness on the surface will be flattened to form a smoother and flatter surface. Reducing the influence of the fine unevenness on the printing material on the coating effect of the subsequent coating, and then affecting the curing effect of the subsequent ink.

[0055] b: Corona treatment, ensuring that the entire surface of the printed material is covered with electrical charge;

[0056] Corona treatment is generally achieved by a corona treatment machine, which contains a pair of electrodes, one of which is connected to a high voltage power supply and the other electrode is in contact with the printed surface. When a high voltage is applied, the oxygen and nitrogen in the air are ionized to form a plasma, i.e., corona discharge, which activates the activity of the printed material surface and can effectively improve the tightness of the connection between the printed material and the applied coating.

[0057] The corona treatment is completed using a corona treater integrated in the printing press or in a separate corona treater. If the corona treater needs to be integrated in the printing press, the corona treater is set at the front end of the flexographic printing seat, so that the printed material after corona treatment is coated with paint. The coating can be performed when the corona effect is best, thereby improving the bonding between the paint and the surface of the printed material.

[0058] The printing material processing device used in this application can be selectively integrated on the digital printing machine body, and the processing device and the digital printing machine body are combined through the conveying mechanism of the printing machine, and controlled by an intelligent control system or a manual debugging system to meet the functions required by this solution.

[0059] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preventing diffusion of printed materials by a digital machine, characterized in that: The following steps are involved: S1: Divide the surface of the printing material into regions, and divide the surface of the printing material into n equal regions along the conveying direction of the printing material; S2: applying a coating on the first area; S3: coating the second area, printing on the first area and performing the first curing; S4: coating the third area, printing and performing a first curing on the second area, and performing a second curing on the first area; Repeat S1-S4, so that when coating is applied to the nth area, printing is performed on the n-1th area, and a second curing is performed, and a second curing is performed on the n-2th area, until printing is completed; After the coating process is completed, the coating is cured.

2. The method for preventing diffusion of digital printing materials according to claim 1, characterized in that: The digital machine includes a flexographic printing base, and the flexographic printing base is used for applying paint; The flexographic printing seat is arranged at the front end of the digital machine printing area. The flexographic printing seat includes an anilox roller and a UV lamp which are arranged in sequence. The anilox roller abuts against the surface of the printing material to realize coating of the coating, and the UV lamp cures the coated coating.

3. The method for preventing diffusion of printed materials by a digital machine according to claim 1, characterized in that: The UV ink is cured, and the power density of the UV lamp for the first curing is twice the power density of the UV lamp for the second curing.

4. The method for preventing diffusion of digital printing materials according to claim 1, characterized in that: The process of S1-S4 also includes filling nitrogen gas on the conveying area of ​​the printing material to ensure that the nitrogen gas fully covers the surface of the printing material.

5. The method for preventing diffusion of digital printing materials according to claim 3, characterized in that: The process of S1-S4 also includes controlling the humidity of the conveying area. The humidity control is achieved by a humidity control device. The humidity control device includes a humidity monitoring device and a drying device. The humidity monitoring device and the drying device are electrically connected. The humidity monitoring device is used to measure the humidity detection value of the air, and a humidity threshold interval is preset in the humidity monitoring device. The humidity monitoring device controls the humidity value of the conveying area within the humidity threshold interval according to the humidity detection value and the humidity threshold interval.

6. The method for preventing diffusion of digital printing materials according to claim 4, characterized in that: Before step S1, the surface of the printing material is pre-processed, and the pre-processing includes the following steps: a: Clean the surface of the printed material; b: Corona treatment to ensure that the entire surface of the printed material is covered with electrical charge; The corona treatment is completed using a corona treater integrated on the printing press, which is set at the front end of the flexographic printing station.

7. The method for preventing diffusion of digital printing materials according to claim 6, characterized in that: After a, a1 is also included: performing heat pressing treatment on the surface of the printing material.

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