Whether ordinary paper can be smoothly and of high quality used for sample printing depends on the printing suitability of the paper. The requirements for paper in sample printing are as follows: the color tone of the paper should be as close as possible to the color purity of the same texture, the dustiness of the paper should not exceed the allowable range, it should have the minimum light transmittance, and it should have the mechanical strength to ensure normal printing. The thickness, tightness, structural characteristics of the paper should remain the same in each printing batch, the paper edges should be right angles and the slope error should not exceed ±3mm.
Paper smoothness: The smoothness of the paper directly determines the printing quality of the printed product. Paper with high smoothness can better come into contact with the printing plate during pressing, allowing the ink layer on the printing plate to be evenly transferred to the paper surface. Paper with low smoothness, however, will have uneven contact between the printing plate surface and the paper surface during pressing, causing the ink layer to be transferred to the paper surface unevenly. In such cases, when using paper with low smoothness, it is advisable to appropriately increase the printing pressure during the printing process to appropriately compensate for the phenomenon of weak printing marks caused by the uneven surface.
The ink absorption property of paper: The absorption of ink by paper mainly depends on the tightness of the fibers in the paper (the size of the gaps). When the gaps between the paper fibers are small, due to the insufficient fibrillation of the fibers, the action of the fiber capillaries is affected, resulting in a decrease in the paper's ink absorption capacity; if the gaps between the paper fibers are too large, excessive absorption of the binder will cause the ink pigment to be absorbed together, resulting in the phenomenon of through-printing in the printed product.
The elasticity and plasticity of paper: During various processes such as storage and printing, paper will undergo various changes due to different surrounding environments. For example, under the action of external forces, it will instantly change its shape and size, and when the external forces stop, the paper will return to its original shape and size. This deformation process is called sensitive elastic deformation; when the paper is subjected to external forces and changes its shape and size within a certain period of time, and then returns to its original shape and size when the external forces stop, this deformation process is called sluggish elastic deformation; when the external forces are removed, the paper still remains in the state of shape and size deformation caused by the external forces, this is called plastic deformation. Sensitive elastic deformation and sluggish elastic deformation are reversible deformations, while plastic deformation is irreversible.
Surface strength of paper: The surface strength of paper plays a decisive role in determining the wear resistance, anti-falling-off of powder, and anti-fuzzing of the paper surface during printing. To obtain clearer dots during printing, some ink with higher viscosity is used. If the surface strength of the paper is insufficient, it will easily cause powder and fuzz to fall off, and these will adhere to the surface of the plate. If lower viscosity ink is used, in offset printing, the ink and the developer solution will emulsify, resulting in dirtiness in the blank areas of the printing plate.
The moisture content of paper: The amount of moisture in paper directly affects the quality of the printed samples. Excessive moisture content will reduce the strength of the paper. Under the action of external forces, the paper fibers will be pulled out, which will enhance the plastic deformation and affect the drying speed of the print marks. If the moisture content is too low, the paper will become brittle and prone to damage, and static electricity may occur. Since the moisture content of paper has a significant correlation with the surrounding environment, it is necessary to appropriately arrange the humidity and temperature in the printing room to maintain the balance of the paper's moisture content.
