In the past newspapers used letterpress printing, and now more and more offset printing. The smoothness and opacity of offset printing for newsprint are not as high as for letterpress printing. The main requirement is that the printing process does not lose hair. In offset printing, the sheet is subject to the pressure between the printing cylinders, the adhesion of the blanket, and the adhesion of the printing ink (the viscosity of the offset ink is much greater than the viscosity of the offset ink) when the surface strength of the sheet used for the offset printing reaches Less than required, the surface of the paper will be subject to a certain degree of damage, that is, hair loss and powder fallout will occur, which will make the writing and pictures unclear, and the quality of the prints will be poor. Frequent shutdowns will be required to clean the printing plate and the rubber roller, which will improve printing efficiency. reduce. Therefore, offset newsprint must have a certain surface strength. This article will discuss the problem of powder off and hair loss in newsprint containing mechanical pulp and quality control issues.
1 Offset Offsets Offsets are caused by the combination of loose fiber material that, when leaving the press nip, falls off due to the stresses between the offset and the sheet. This force mainly acts on the vertical sheet surface direction. If the offset plate is not installed properly or the platen is deformed, it may also generate frictional forces parallel to the surface of the paper sheet. The paper that fell off during offset printing consisted primarily of fine fibrous material (through a 200 mesh screen). Some of the coarser paper hairs are composed of medium and long fiber components as well as some stiff fibers in the fiber bundles (fiber bundles) with poor bonding. The laboratory of Nanping Paper Mill Center once analyzed the “compacted matter†of the offset printing newsprint of the factory during the printing of “Ningbo Dailyâ€. The results showed that about 80% of the “compacted matter†is fiber, and about 5% is ash, 15%. About the ink.
The longer the offset printing time is, the more paper hairs fall off. These papers accumulate on the offset plate. Once it enters the ink system, it will affect the transfer of ink to the paper, and the quality of the final print will deteriorate so much that it will be forced to stop cleaning. In this way, in addition to the deteriorating print quality at the end of the run, downtime can cause the printer to have similar consequences such as web breaks or mechanical failures during printing.
2 Factors affecting the paper's ability to direct it in production The two main production factors that have a significant impact on the lint-free of newsprint are the quality of the pulp and the papermaking process.
2.1 Pulp quality The quality of the pulp, especially the components of the mechanical pulp, has a great influence on lint. The decontamination and purification of mechanical pulp is a prerequisite for reducing the loss of newsprint. The quality control of mechanical wood pulp usually uses three indicators of crack length, beating degree, and fiber bundle content to make stone cutting and how to cut stone. The splitting length of the slurry is controlled from k2200 to 2400m, and the beating degree is approximately 70 to 74SR. The control range of the fibers in the grind-milled wood pulp system is that the components remaining on the 50-mesh sieve are less than 26% and pass through 200 mesh components. Less than 40%. According to user requirements, H2O2 is sometimes added to the pulp for bleaching, and the whiteness is controlled at 55% to 58% (ISO). After the bleaching, the pH of the slurry should be stabilized at about 6.5. Newsprint Add 5% of deinked pulp to the blend About 1% of the chemical pulp and the state's groundwood pulp can be reduced. Deinked pulp fiber bundle content is quite low, tensile strength and tearing is better than that of grinding stone. Investigations by newspaper printing houses have shown that the use of deinked pulp to produce newsprint has good printability, opacity, and ink absorbency, and these changes will reduce page pick-up. The amount of filler in the paper stock should be appropriate, and the filler fineness should be above 400 mesh. The reduction of filler particles, and its associated adsorption and other effects will be significantly enhanced, and good results will be obtained after use, which can reduce the phenomenon of powder off in newsprint printing. There are two interrelated factors that need to be considered in the influence of the quality of the chemical pulp, namely the coarseness of the fiber and the degree of increase in the binding force after refining. The greater the fiber thickness, the shorter the total length per unit volume of fiber, which will affect the flexibility, bonding force and paper surface strength of the fiber. After increasing the chemical pulp fiber thickness, the paper sheet cannot be pressed tightly on the paper machine, and at the same time, the bond strength of the paper sheet is reduced, thus making the news paper more hairless. Usually, fine grinding is an effective measure to improve the quality of chemical pulp. Proper beating of chemical pulp in the newsprint ratio (increasing the pulping degree of pulp by 8 to 10 SR) is beneficial in any case.
2.2 Papermaking process Poorly formed paper sheets are not uniform in the content and distribution of fine fibers, and the tightness of the paper sheets is not uniform when passing through the press section and the calender. This will cause newsprint paper to fall off. The forming net used and the total dewatering on the paper machine will affect the structure of the paper sheet. The double-layer forming net used in recent years can better support the sheet and has a lateral dewatering capability, so that more fine fibers can be retained in the sheet. Therefore, the copied paper has a compact structure on both sides, which increases the resistance to lint-free from the surface. The paper-grinding machine is double-sided dewatering. Both sides of the paper sheet have the function of removing potential hair-loss materials (crude fibers and fine fibers), and will produce a paper with a uniform structure and small difference on both sides. Therefore, replacing the newsprint copied from the Fourdrinier paper machine with a net paper machine will inevitably reduce the loss of paper. The press section plays a significant role in sheet lint, and the press load affects the tightness of the sheet and the binding force between the fibers, increases the press load, and can reduce sheet slippage.
In the initial stage of drying, rapidly increasing the temperature of the paper sheet will cause the paper sheet to stick to the surface of the dryer cylinder and cause the paper surface to break, resulting in a decrease in the strength of the surface of the paper sheet, thereby increasing the hair loss phenomenon.
3 Print off hair test There is no standard print off hair test method. The paper mill measured the speed of pulling the newsprint, indicating the surface strength of the paper, and the printer was able to measure the resistance to the printing cycle (indicating that the offset newsprint was not subjected to a continuous print interruption during the printing process). Nanping Paper Factory achieved a record of 0~1 times of paper breaks in the printing cycle of 3h in high-speed offset printing through a series of process control; the speed of paper forming and pulling reached 46cm/s, and the printing cycle reached 40,000 pairs. Open/print record.
In recent years, papermaking and printing workers have used lint as the main quality parameter and end-use performance of offset newsprint in both process and operation. The importance of paper will continue to increase, so the focus of quality control will inevitably shift to this aspect. Offset newsprint should have strict hair loss quality inspection in the production process, so that the printing can not lose hair, can not afford powder, improve the printing performance of the product printing.
1 Offset Offsets Offsets are caused by the combination of loose fiber material that, when leaving the press nip, falls off due to the stresses between the offset and the sheet. This force mainly acts on the vertical sheet surface direction. If the offset plate is not installed properly or the platen is deformed, it may also generate frictional forces parallel to the surface of the paper sheet. The paper that fell off during offset printing consisted primarily of fine fibrous material (through a 200 mesh screen). Some of the coarser paper hairs are composed of medium and long fiber components as well as some stiff fibers in the fiber bundles (fiber bundles) with poor bonding. The laboratory of Nanping Paper Mill Center once analyzed the “compacted matter†of the offset printing newsprint of the factory during the printing of “Ningbo Dailyâ€. The results showed that about 80% of the “compacted matter†is fiber, and about 5% is ash, 15%. About the ink.
The longer the offset printing time is, the more paper hairs fall off. These papers accumulate on the offset plate. Once it enters the ink system, it will affect the transfer of ink to the paper, and the quality of the final print will deteriorate so much that it will be forced to stop cleaning. In this way, in addition to the deteriorating print quality at the end of the run, downtime can cause the printer to have similar consequences such as web breaks or mechanical failures during printing.
2 Factors affecting the paper's ability to direct it in production The two main production factors that have a significant impact on the lint-free of newsprint are the quality of the pulp and the papermaking process.
2.1 Pulp quality The quality of the pulp, especially the components of the mechanical pulp, has a great influence on lint. The decontamination and purification of mechanical pulp is a prerequisite for reducing the loss of newsprint. The quality control of mechanical wood pulp usually uses three indicators of crack length, beating degree, and fiber bundle content to make stone cutting and how to cut stone. The splitting length of the slurry is controlled from k2200 to 2400m, and the beating degree is approximately 70 to 74SR. The control range of the fibers in the grind-milled wood pulp system is that the components remaining on the 50-mesh sieve are less than 26% and pass through 200 mesh components. Less than 40%. According to user requirements, H2O2 is sometimes added to the pulp for bleaching, and the whiteness is controlled at 55% to 58% (ISO). After the bleaching, the pH of the slurry should be stabilized at about 6.5. Newsprint Add 5% of deinked pulp to the blend About 1% of the chemical pulp and the state's groundwood pulp can be reduced. Deinked pulp fiber bundle content is quite low, tensile strength and tearing is better than that of grinding stone. Investigations by newspaper printing houses have shown that the use of deinked pulp to produce newsprint has good printability, opacity, and ink absorbency, and these changes will reduce page pick-up. The amount of filler in the paper stock should be appropriate, and the filler fineness should be above 400 mesh. The reduction of filler particles, and its associated adsorption and other effects will be significantly enhanced, and good results will be obtained after use, which can reduce the phenomenon of powder off in newsprint printing. There are two interrelated factors that need to be considered in the influence of the quality of the chemical pulp, namely the coarseness of the fiber and the degree of increase in the binding force after refining. The greater the fiber thickness, the shorter the total length per unit volume of fiber, which will affect the flexibility, bonding force and paper surface strength of the fiber. After increasing the chemical pulp fiber thickness, the paper sheet cannot be pressed tightly on the paper machine, and at the same time, the bond strength of the paper sheet is reduced, thus making the news paper more hairless. Usually, fine grinding is an effective measure to improve the quality of chemical pulp. Proper beating of chemical pulp in the newsprint ratio (increasing the pulping degree of pulp by 8 to 10 SR) is beneficial in any case.
2.2 Papermaking process Poorly formed paper sheets are not uniform in the content and distribution of fine fibers, and the tightness of the paper sheets is not uniform when passing through the press section and the calender. This will cause newsprint paper to fall off. The forming net used and the total dewatering on the paper machine will affect the structure of the paper sheet. The double-layer forming net used in recent years can better support the sheet and has a lateral dewatering capability, so that more fine fibers can be retained in the sheet. Therefore, the copied paper has a compact structure on both sides, which increases the resistance to lint-free from the surface. The paper-grinding machine is double-sided dewatering. Both sides of the paper sheet have the function of removing potential hair-loss materials (crude fibers and fine fibers), and will produce a paper with a uniform structure and small difference on both sides. Therefore, replacing the newsprint copied from the Fourdrinier paper machine with a net paper machine will inevitably reduce the loss of paper. The press section plays a significant role in sheet lint, and the press load affects the tightness of the sheet and the binding force between the fibers, increases the press load, and can reduce sheet slippage.
In the initial stage of drying, rapidly increasing the temperature of the paper sheet will cause the paper sheet to stick to the surface of the dryer cylinder and cause the paper surface to break, resulting in a decrease in the strength of the surface of the paper sheet, thereby increasing the hair loss phenomenon.
3 Print off hair test There is no standard print off hair test method. The paper mill measured the speed of pulling the newsprint, indicating the surface strength of the paper, and the printer was able to measure the resistance to the printing cycle (indicating that the offset newsprint was not subjected to a continuous print interruption during the printing process). Nanping Paper Factory achieved a record of 0~1 times of paper breaks in the printing cycle of 3h in high-speed offset printing through a series of process control; the speed of paper forming and pulling reached 46cm/s, and the printing cycle reached 40,000 pairs. Open/print record.
In recent years, papermaking and printing workers have used lint as the main quality parameter and end-use performance of offset newsprint in both process and operation. The importance of paper will continue to increase, so the focus of quality control will inevitably shift to this aspect. Offset newsprint should have strict hair loss quality inspection in the production process, so that the printing can not lose hair, can not afford powder, improve the printing performance of the product printing.
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