As is known to us, specialty paper printing is more difficult than normal paper because of great difference of surface flatness and ink absorption. When print on specialty paper, the printing press operator must make preparations in advance, so what are the difficulties of specialty paper printing and how to solve them?
Adding drying oil to ink
Specialty paper with a particularly smooth surface has poor ink absorption and will stick to dirt if you don’t pay attention to it during printing. Therefore, it is best to choose fast-drying inks, and add drying oil to each color ink that can promote the rapid drying, increase the drying speed and avoid the sticky surface of the paper during printing.
Strictly control plant temperature and humidity
Compared with art paper and matte paper, the filler and composition of specialty paper are different. If the temperature and humidity of the workshop are not well controlled, it is easy to cause paper deformation and inaccurate overprinting. Generally, when using specialty paper for printing, the temperature of the workshop should be controlled at 20-24°C and the humidity at 60%-70%. When the humidity in the workshop is less than 40%, some paper will curl up in about 10 minutes, which may cause difficulty in printing and feeding. Therefore, the paper should be wrapped with plastic film and placed in a warehouse with suitable temperature and humidity immediately after cutting. At the same time, attention should be paid to keeping the temperature and humidity of the printing workshop stable and suitable.
Different ink supply for different specialty paper
For special papers with a high degree of surface smoothness, such as pearl paper, ice white paper, metallic paper, etc., ink color should not be too saturated during printing, and the normal ink supply can be used. Because the smoother the surface of the paper, the worse the ink absorption, and the greater the amount of ink supplied, the easier it is to stick to the back of the paper.
Specialty papers with a rough surface, such as color paper, rice paper, kraft paper, etc., have textures and are not smooth to touch. When printing, this paper has good ink absorption, and the ink will penetrate into the lines of the paper. After ink dries, color of the printed product will become lighter and printing quality will also be reduced. Therefore, for this specialty paper, the amount of ink supplied during printing is larger than usual, and the requirement for saturation is higher.
Pay attention to the dirt on the back
Compared with ordinary paper, specialty paper has a little more static electricity, and it is easy to absorb dust and dirt on the transfer roller. Therefore, the press operator must pay attention to the back of the paper during printing. If dirt is adsorbed, the paper transfer roller and conveyor belt of the machine must be cleaned according to the location of the dirt.
Appropriate amount of powder spraying
Different specialty papers have different ink absorption properties and have different requirements for powder spraying. The smoother the surface of the paper, the worse the ink absorption, and the greater the amount of powder spray required; the rougher the paper, the stronger the ink absorption and the smaller the amount of powder spray required. In order to prevent the paper from sticking and dirty during printing, some captains will adjust the amount of powder spraying very large, but this approach is wrong. Because under normal circumstances, special paper printing needs to go through multiple post-printing processes, such as embossing, hot stamping, embossing, laminating, etc. If the amount of powder sprayed during printing is too large, it will cause post-press processing. Impact, such as the film can not be covered. Therefore, based on experience, make sure that the amount of powder sprayed is as small as possible while ensuring that the paper is not sticky to facilitate post-press processing.
Paper stoppers on delivery side should not be clamped too tightly
In order to keep the printing sheets neatly, paper stoppers on delivery side are usually clamped a little tightly. Regular papers such as coated paper and matte paper can be operated in this way, but for specialty paper is easy to stick and dirty. Clamped the stopper too tightly will make back of specialty paper sticky when moving back and forth. Therefore, the stoppers should not be clamped too tightly, as long as the paper can be neatly packed.
Boards are needed when stacking printing sheets
Because specialty paper is easy to stick and dirty, back of the bottom paper is always sticky when it is piled up after printing, so specially designed wooden boards and foot blocks of suitable size for stacking printing sheets. When thickness of printing sheets is around 15-20 cm, a piece of wood board is placed to keep away printed matter, which reduces load-bearing of bottom paper and avoids sticking and dirty. The board is very convenient and no need to update the stopper, which improves the printing efficiency.
Uses other white paper for trial printing
During specialty paper printing, printing press is vibrated when turn on and turn off, which makes the first 10 printing sheets darker and unstable. Due to high price of the paper, material margin given by engineer is very small when place order. In addition, printing requirements for the paper are higher than that of ordinary ones. If follow the usual printing habits, it is difficult for operator to guarantee the printed quantity and quality. Therefore, operator’s assistant must place about 10 more sheets of white paper or single-sided white paper on specialty paper (even printed ones could turn upside down and the white side could be used for color matching). The leftovers are white on the back and can be used to run ink on a printing press.) In this way, after turning on the machine, the paper on top will be printed first. When specialty paper is to be printed, color can be stabilized and unified, thus ensuring the printing quality.
Maintain color consistency
Specialty paper is generally used as covering wrapper of a book and requires higher color consistency than ordinary paper. Therefore, when adjusting the ink color, operator must master amount of water and adjust ink color accurately. Be sure to maintain color consistency and print strictly according to the signature.
Ensure accurate position of layout paper
Because there are several post-press processes, thickness of specialty paper is different from ordinary paper and with high positioning requirements. Therefore, assistant of operator must adjust paper layout to ensure printing effect.
There must be enough time to dry after printing
Different specialty papers have different ink absorption properties. Smooth surface of the paper is not easy to dry. It must be left for a long time, and then can be sorted after drying, otherwise it will easily cause the back side to be smeared.
Specialty paper printing is not easy, according to smoothness of paper surface, adsorption capacity of ink and size of electrostatic, it is necessary to do preparation in advance, especially to avoid the emergence of sticky and dirty problems before printing. As a printing press operator, it is required to know performance of paper well, and then could control all aspects of printing to ensure quality of post-press processes.