Technical application of UV curing system of the m

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Technical application of UV curing system of water printing machine II

3 curing of varnish

the purpose of coating varnish is to provide gloss to the final print and protect the surface of the print

the types of varnish include water-based varnish, UV varnish, oily op (over print) varnish, UV OP varnish, etc. their drying and curing are briefly introduced

1) water based varnish that evaporates water to achieve drying

water based varnish is composed of water and resin. The heat generated by the IR drying device evaporates the water to achieve a/d conversion to one body drying. Generally, it is mostly used for the polishing of printing products with oily inks. In addition to increasing gloss and protecting the surface of printed products, it can also shorten the transition time to the next process (promoting the solidification of the film on the ink surface, the polymerization and powder spraying operation, and reducing the use of anti sticking and dirty diaphragms, etc.)

in addition, because water-based varnish itself contains more water, it should be evaporated during the drying process. In terms of gloss and surface protection, its effect is not as good as UV varnish, but its price is much cheaper than UV varnish

2) UV varnish with high gloss

uv varnish is composed of UV curing resin. Like UV ink, it is cured instantly by UV irradiation through UV curing device. Unlike water-based varnish, the evaporation component is very small, so according to the different coating amount of varnish, its gloss may reach about 80. UV varnish has the property of instant curing, and the surface state (smoothness) of the ink film during curing is very important

3) container coating device

the main device for coating varnish is the sealed container coating device. The cavity of the wrinkle roller (for glazing) of the device is full of varnish. The varnish is first printed on the blanket, and then transferred to the substrate through the blanket. The main factors that determine the coating amount of substrate varnish are the transfer rate of varnish and the volume of holes. Here we will introduce the relationship between the number of lines on the roller and the gloss. The so-called number of lines of the roller is expressed by the number of lines per inch, which only affects the appearance and performance of the material. The lines of the roller of the coating device of the sheet fed offset press are generally lines. The smaller the number of lines, the larger the cavity volume, and the larger the area of the opening on the surface of the roller. Therefore, the smaller the number of lines, the more the varnish accumulates, and the smoothness of the varnish coating surface will become worse. From the perspective of printing materials, although the gloss coating has a sense of thickness, the gloss has decreased

as one of the methods to improve the smoothness (and finally improve the gloss), it is to increase the distance between the coating varnish process and the UV irradiation process, which can make the surface of the varnish printed on the substrate smooth and finally improve the gloss. The varnish coating amount on the substrate varies according to the transfer rate of Guangshan, but the general data is about 7.5/m2 (under the condition of 80 lines)

4 curing device between units

all the above are drying problems after printing, but there are also methods of drying in the printing process. Generally speaking, there is no drying device in the printing unit for oily inks, and a curing device must be set in the unit for UV printing

There are two kinds of curing devices for UV ink between units: deck installation and special drying unit (DU)

1) deck installation method

the deck installation method is to install a UV lamp on the deck (foot springboard) between the units, and the printing surface is cured during the printing process after being irradiated by the UV lamp. The advantage of this method is that the printing machine can be processed and transformed in advance, and the position of UV lamp in the unit can be changed freely. Compared with Du method, the initial investment of the equipment is small. The disadvantage is that there is only one UV lamp, and the curing efficiency is poor compared with Du mode. In addition, the reflected light generated by the ultraviolet light shining on the printing surface will harden the UV ink on the blanket, so it is necessary to take countermeasures such as reducing the liner paper of the blanket, especially when changing the work or changing the paper size, the liner thickness of the blanket must be changed every time, which brings difficulties to the operation

2) Du mode

the so-called Du mode is to set a special curing unit equipped with a UV lamp between the printing units to complete the curing of ink during the printing process. Advantages of this method: due to the large number of UV lamps, the curing efficiency is higher than that of the deck method. In addition, because it is a special unit, it has the ability to prevent UV reflection, and will not cure the ink on the blanket. Its disadvantage is that it is set as a special device, which increases the total length of the machine and cannot change its position among the units. The initial investment is high

either method has advantages and disadvantages. The low-cost deck mode can be selected for the occasions requiring less curing work between units, and the Du mode with higher production efficiency should be considered for the occasions requiring more curing work between units

5 various UV printing materials

compared with the melt blown resin and basic mixture currently available on the market, many printing materials around us are printed with four-color ink. At present, there is only four-color printed matter with fierce price competition among printing companies, and it is difficult to make profits even if orders are obtained. In order to avoid price competition, it is an ideal way to sign orders by printing methods different from other printing companies

even so, it does not mean that the company can do anything printed, but should decide which products to print according to the equipment of its own company

1) transparent substrate printing

transparent substrate printing is generally characterized by printing from the back of the film. When printing four primary color inks that express color on this transparent substrate, a transparent printing effect is obtained. To prevent this, a layer of white ink is usually printed after four-color printing

after four-color printing, printing white ink on this kind of wet ink sometimes has the problem of printing failure (overprint problem), at this time, the drying device in the unit is required to play a role. In addition, if the effect of white ink printing is not good, it will be printed again

2) vacuum aluminized paper printing

refers to printing on vacuum aluminized paper (paper with metallic luster on the surface) and other materials such as holographic film. Printing four primary color inks on the substrate with metallic luster can obtain the processing effects of various metallic senses

when the designed metallic color effect cannot be achieved, a layer of white ink can be printed first, and then four primary colors can be printed. Printing four primary colors on the wet white ink is difficult to achieve a good overprint effect, so it is necessary to configure the drying device between the units. Like transparent substrates, white ink can sometimes be printed twice

3) print metallic effect on ordinary paper

Komori company used metalfx ink of Wolstenholme company in England on drupa 2004 to print promotional materials with various metallic color effects on the surface of the substrate with metallic effect. As mentioned above, printing on a metal substrate can obtain various metal effects, but the price of the substrate is on the high side

now there has been a process of using metalfx ink to simulate the above metallization on cheap ordinary paper. The initial practice was to print silver ink on plain paper and dry it, and then print four primary colors. As a result, prints with various metallic feelings were obtained. On drupa2004, Komori company demonstrated this product with six color offset printing machine

(compiled by Yang Zhigang)

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