Plastic hose offset printing and screen printing t

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Plastic hose offset printing and printing technology

in recent 10 years, plastic hose packaging has been favored by the majority of consumers in cosmetics, medicine, food and other industries because of its light weight, convenient use, high quality and low price

as the name suggests, the raw material of plastic hose is plastic, more specifically, it is mainly polyethylene. According to the structure, the packaging hose can be divided into single-layer pipe, multi-layer pipe and composite pipe with various raw materials. As far as packaging is concerned, the part that can attract customers most is the printed pattern. Therefore, this paper mainly introduces the printing processing of plastic hose

hose printing process

at present, the common hose printing process is: dust removal - surface pretreatment - printing (UV ink) - glazing - UV curing (or heat curing) of varnish. A special hose printing machine can basically realize the above process, such as the hose printing machine produced by polytype in Switzerland and hinterkof in Germany

the first step of dust removal

a common problem of plastic raw materials is that they are easy to generate static electricity. In the process of producing hoses, polyethylene raw materials are constantly in contact and friction with metal molds, resulting in static electricity on the surface of the hose. The static electricity gradually approaches the detection load, making the surface of the hose easy to absorb dust. Therefore, dust removal treatment needs to be carried out before printing

second step surface pretreatment

as polyethylene is a non-polar material, surface pretreatment is required before printing. There are two main treatment methods, one is corona treatment, the other is flame treatment, both of which can achieve the purpose of firmly attaching ink and varnish

the main factors affecting the effect of corona treatment are: discharge power, the distance between the electrode and the treated surface, and the speed of the hose passing through the corona processor

the main variables affecting the effect of flame treatment are: air/fuel gas ratio, the distance between the treated surface and the blue top of the visible flame, and the speed of the hose passing through the flame

generally, the tension of the hose after surface treatment is required to reach 3.6 × Above 10-2n/m, the specific value is also related to the characteristics of the ink and varnish used

a simple way to test the surface treatment effect is to put the treated hose into the water, then lift it from the water, and observe whether there is a uniform water film on the hose surface. If the water film is uniform, it indicates that the hose surface treatment is good, otherwise the factors affecting the surface treatment effect should be adjusted appropriately

third step printing

at present, there are two common printing methods for plastic hoses. One is offset printing, which transfers the ink to the printing plate through a set of ink rollers, and then the printing plate transfers the ink on the printing pattern to the blanket, and then the blanket transfers the complete printing pattern to the substrate at one time

offset press for hose printing is different from what we usually call offset press. The offset printing plate is usually referred to as lithography. The ink is supplied to the printing plate based on the principle of immiscibility of water and ink, and then transferred from the printing plate to blanket. Although waterless offset printing has been developed, the printing plate is still lithography or flat intaglio. The offset plate used for hose printing is relief plate, so the more accurate name should be relief offset printing

hose offset printing plate is usually made of light curing resin plate, which is made through main exposure, development, washing, drying, post exposure and other processes. The production time of a printing plate is about 30 ~ 40 minutes, and the printing resistance reaches more than 100000. Because the printing plate is a resin plate, and the protrusion of the graphic part is high (about 0.5 ~ 0.6mm), when making the eye adjustment plate, the highlight part can only retain more than 5% of the points, so the printing pattern on the hose is not as fine as that of offset printing. It is also for this reason that labeling on the hose package replaces the direct printing of trademark and other symbolic patterns on the hose

at present, the speed of hose offset printing has reached 12000 pieces/hour, and the operation process is becoming simpler and simpler. With the increase of production speed and the decrease of offset printing cost, offset printing has been widely used in hose printing

another way of hose printing is traditional silk printing. The multicolor silk printing press produced in China is usually composed of several monochrome silk printing presses connected in series, with large floor area, long hose conveying route, poor positioning accuracy between colors than offset printing, and low printing speed, which makes its cost high. At present, silk screen printing brush machines for hose printing have been developed and produced in Europe, such as isimat company in Germany, hinterkof company and moss company in Italy. The printing accuracy and printing speed have been greatly improved. The production speed has reached 5400 pieces/hour, the overprint accuracy has reached ± 0.2mm, and the printing color can reach 6 colors at most. Due to the thick ink layer of silk printing, it is mainly used for the printing of color hose or some uncovered varnish products

in terms of hose printing methods, the above two printing methods can also be combined. Our company introduced a full-automatic hose production line last year, which realizes the combined production of offset printing and silk printing, so that the printing color number of hose reaches 12 colors

with the popularization and improvement of UV curing technology, UV curing ink is widely used in both hose offset printing and printing, making the control of ink easier

fourth step polishing

a set of polishing device is installed on both hose offset press and silk press, which is composed of two steel rollers and one rubber roller. The adhesion fastness of varnish is also directly related to the tension after plastic surface pretreatment. The varnish used by our company is usually UV curing varnish, including bright varnish and Matt varnish. In addition, there are also heat curing varnish and three in one varnish, which are used for polishing after hose offset printing

The fifth step is that the UV curing intensity of the oil is closely related to the UV curing intensity of the oil. For products with subsequent processing such as hot stamping, the curing degree of varnish will have a great impact on the quality of subsequent processing

common problems

in the process of hose printing, several problems and solutions are as follows

1. The problem is mainly related to the surface pretreatment of printing materials. The surface tension can reach 3.6 by increasing the power of corona treatment and the ratio of flame treated air/combustion gas × 10-2N/m。 However, the greater the surface tension, the better. Some inks have a surface tension of 4.0 × At 10-2n/m, poor adhesion will also occur. Therefore, the best surface tension value should be found for different inks

2. Inking phenomenon appears in pictures and texts

this phenomenon is usually caused by excessive printing pressure. There are two pressures on the hose printing machine that will affect the printing quality of the final product. One is the pressure of the ink roller on the printing plate, and the other is the pressure of the printing plate on the blanket. If the pressure is too high, the ink in the middle of the picture and text will be squeezed to the edge of the picture and text, and the ink and dots on the edge of the printed pattern will become larger. Therefore, the automatic shutdown of the instrument must be ensured; Ensure moderate printing pressure

source: printing technology 2005.1

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