As the most commonly used material for packaging and printing, the physical properties of paper will have a direct or indirect impact on the printing quality.Paper Characteristics And Packaging Printing Quality
Correctly understanding and mastering the nature of paper and reasonably using paper according to the characteristics of products will play a positive role in improving the printing quality of products.Paper Characteristics And Packaging Printing Quality
1. Quantitative. It refers to the weight per unit area of paper, expressed in g / ㎡, that is, the gram weight of 1 square meter of face paper. The quantity of paper determines the physical properties of paper, such as tensile strength, tear, tightness, stiffness and thickness. Paper Characteristics And Packaging Printing Quality
This is also the main reason why the high-speed printing machine is difficult to print the paper with a fixed amount of less than 35g / m2, so it is easy to cause abnormal paper continuation and inaccurate overprint. Paper Characteristics And Packaging Printing Quality
Therefore, it is better to reduce the consumption and improve the product quality and the printing efficiency of the equipment by arranging the printing pieces corresponding to the performance according to the characteristics of the equipment.Paper Characteristics And Packaging Printing Quality
2. Thickness. It is the thickness of paper. The unit of measurement is usually used μ M or mm. Thickness is closely related to quantification and compactness. Generally speaking, if the paper thickness is large, its quantification is high, but the relationship between the two is not absolute. Paper Characteristics And Packaging Printing Quality
Although some paper is thin, its weight is equal to or more than that of thicker paper. This shows that the tightness of the fiber structure of the paper determines the quantity and thickness of the paper. Paper Characteristics And Packaging Printing Quality
From the perspective of printing and packaging quality, it is very important that the paper thickness is uniform. Otherwise, automatic paper resuming, printing pressure and ink quality will be affected.Paper Characteristics And Packaging Printing Quality
If the book is printed on paper with different thickness, it will make the finished book have obvious thickness difference.Paper Characteristics And Packaging Printing Quality
3. Tightness. It refers to the weight of paper per cubic centimeter, expressed in g / C ㎡. The tightness of paper is calculated from the weight and thickness according to the following formula: D = g / d × 1000, where: G represents the quantity of paper; D is the thickness of the paper. Tightness is a measure of the density of the paper structure.Paper Characteristics And Packaging Printing Quality
If it is too tight, the paper is easy to crack, the opacity and ink absorption will be significantly reduced, the imprint is not easy to dry, and it is easy to get sticky and dirty.Paper Characteristics And Packaging Printing Quality
Therefore, when printing on paper with high compactness, we should pay attention to reasonably controlling the amount of coated ink, and select the ink with corresponding dryness.Paper Characteristics And Packaging Printing Quality
4. Hardness. It is the performance of paper to resist the collapse of another object, and it is also the coarse and hard performance of paper fiber tissue.Paper Characteristics And Packaging Printing Quality
The paper has low hardness and can obtain clear imprinting. Relief printing process is generally suitable for printing with paper with low hardness, so that the printing ink quality is good and the printing plate resistance is also high.Paper Characteristics And Packaging Printing Quality
5. Smoothness. It refers to the degree of unevenness on the paper surface, expressed in seconds and measurable. The detection principle is: the time taken for a certain volume of air to pass through the gap between the glass plate surface and the sample surface under a certain vacuum and pressure.
When the paper surface is smoother, the air passes slower, on the contrary, the air passes faster. Printing requires the paper to have moderate smoothness, high smoothness, and small dots will be faithfully reproduced.Paper Characteristics And Packaging Printing Quality
However, when printing the full plate on the field, pay attention to prevent the back from sticking dirty.Paper Characteristics And Packaging Printing Quality
If the smoothness of the paper is low, the printing pressure required is large, and the ink consumption is also large.Paper Characteristics And Packaging Printing Quality
6. Dust degree. It refers to the impurity spots on the paper, and the color is obviously different from the paper color. Dust degree is an index to measure paper impurities, which is expressed by the number of dust areas in a certain range per square meter of paper. Paper Characteristics And Packaging Printing Quality
The paper has high dust, poor reproduction effect of printing ink and dot, and many dirty spots, which affect the beauty of the product.
7. Sizing degree. Usually, the paper surface of writing paper, coating paper and packaging paper forms a protective layer with water resistance through sizing. How about the sizing degree? Dip a duck pen into a special standard ink and draw a line on the paper in a few seconds to see the maximum width of non-diffusion and impermeability, in mm. High paper sizing, high brightness of printing ink layer and low ink consumption.
8. Ink absorption. It indicates the ability of paper to absorb ink. The paper with good smoothness and sizing has weak ink absorption, slow drying of ink layer and easy to stick dirty prints. On the contrary, the ink absorption is strong and the printing is easy to dry.
9. Vertical and horizontal. It refers to the arrangement direction of paper fiber tissue. In the process of papermaking, the fiber along the running direction of the paper machine is the longitudinal direction of the paper.
It can be identified from the acute angle of the mesh mark. Perpendicular to the longitudinal direction is transverse, the deformation value of longitudinal paper grain printing is small, the expansion variation in the process of transverse paper grain printing is large, and the tensile strength and tear degree are poor.
10. Expansion rate. It refers to the size variation of paper after moisture absorption or moisture loss. The softer the fibrous tissue of the paper, the lower the tightness, the higher the expansion rate of the paper; On the contrary, the lower the expansion rate. In addition, the paper with good smoothness and sizing has small expansion rate. Such as double-sided coated paper, glass card and a offset paper.
11. Air permeability. Generally speaking, the thinner the paper and the lower the tightness, the greater the air permeability. The unit of air permeability is ml / min (ml / min) or S / 100ml (s / 100ml), Paper Characteristics And Packaging Printing Quality
that is, the amount of air passing through the paper or the time required to pass through 100ml of air in 1 minute. The paper with high air permeability is easy to absorb double paper in the printing process.
12. Whiteness. It refers to the brightness of the paper. If all the light reflected from the paper can be seen by the naked eye, it is white. To determine the whiteness of paper, the whiteness of magnesium oxide is usually specified as 100% as the standard. If the paper sample is irradiated by blue light, the whiteness with low reflectivity is poor.
Photoelectric whiteness meter can also be used to measure whiteness. The unit of whiteness is 11%. High whiteness paper, printing ink appears deep, and easy to produce through printing phenomenon.
13. Front and back. During papermaking, the pulp is attached to the steel mesh and shaped by filtration and dehydration. In this way, if the fine fibers and fillers on one side of the net are lost with water, the net mark is left, and the paper surface is thicker. On the other side, it is fine without a net. Smooth, so that the paper forms a difference between the front and back sides.
Although it is dried and calendered in production, there are still differences between the front and back sides. The gloss of the front and back of paper is different, which directly affects the absorption of ink and the printing quality of products. Paper Characteristics And Packaging Printing Quality
If the relief process uses paper printing with thick reverse side, the plate wear will be significantly increased. The front printing pressure of paper is light, and the ink consumption is also low.Paper Characteristics And Packaging Printing Quality
To sum up, only by correctly understanding and identifying the main physical properties of paper and its impact on printing, and taking corresponding measures in operation and process technology according to the properties and characteristics of paper, can we effectively reduce or avoid the chance of printing failure, so as to ensure production efficiency and product printing quality.