Best understanding of different paper characterist

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Understand the characteristics of different paper to improve the quality of packaging and printing

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core tip: 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. Correctly understand and master the properties of paper. According to the characteristics of products,

paper is the most commonly used material for packaging and printing. Its physical properties will have a direct or indirect impact on the printing quality of abs/pcta alloy. Correctly understanding and mastering the nature of paper and using paper reasonably according to the characteristics of products will play a positive role in improving the printing quality of products

1. Quantitative

it refers to the weight of paper per unit area, 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 strength, tightness, stiffness and thickness. This is also the main reason why the high-speed printing machine can't print the paper with a fixed quantity of less than 35g/m2, which is prone to abnormal paper continuation, inaccurate overprinting and other reasons. Therefore, according to the characteristics of the equipment, arrange the printing pieces with a fixed quantity corresponding to its performance for production, so as to better reduce consumption, improve product quality and equipment printing efficiency

2. Thickness

it is the thickness of the paper. The unit of measurement is usually μ M or mm. Thickness is closely related to quantification and tightness. Generally speaking, if the paper thickness is large, its quantification is correspondingly high, but the relationship between the two is not absolute. Although some papers are thin, their weight is equal to or more than that of thicker ones. This shows that the tightness of the fiber structure of paper determines the quantity and thickness of paper. From the perspective of printing and packaging quality, it is very important that the thickness of paper is uniform. Otherwise, automatic paper resuming, printing pressure and ink quality will be affected. If the book is printed on paper with different thickness, the finished book will have obvious thickness differences

3. Tightness

it refers to the weight of paper per cubic centimeter, expressed in g/C ㎡. The tightness of the paper is calculated from the weight and thickness according to the following formula: D = g/D × 1000, where: G refers to the quantity of paper; D is the thickness of the paper. Tightness is a measure of the density of the paper structure. 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 produce the phenomenon of sticking and dirty. Therefore, when printing on paper with high compactness, we should pay attention to the reasonable control of the amount of ink coated, and choose the ink with the corresponding dryness

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. The hardness of paper is low, and a clear impression can be obtained. The blade cutting structure 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

5. Smoothness

it refers to the degree of unevenness on the surface of the paper, expressed in seconds, which can be measured. The detection principle is: under a certain vacuum and pressure, the time taken for a certain volume of air to pass through the gap between the glass plate surface and the sample surface. When the paper surface is smoother, the air passes slower, on the contrary, the air passes faster. The printing requires the paper to have a moderate smoothness, which is high, and the small spots will be faithfully reproduced. However, when printing the full plate on the field, attention should be paid to prevent the back from sticking dirty. If the smoothness of the paper is low, the printing pressure required is large, and the ink consumption is also large

6. Dust degree

it refers to the impurity spots on the paper surface, and there is a significant difference between the color and 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. The paper has high dust degree, poor reproduction effect of ink color and dots, 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-proliferation and impermeability, in mm. The paper has high sizing degree, high brightness of printing ink layer and low ink consumption

8. Ink absorption

it means that the ability of paper to absorb ink is also low when entering the door. Paper with good smoothness and sizing degree has weak ink absorption, slow drying of ink layer, and is easy to stick dirty prints. On the contrary, ink absorption is strong, and printing products are easy to dry

9. Vertical and horizontal direction

it refers to the direction of arrangement 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 mark. Those perpendicular to the longitudinal direction are transverse. The deformation value of longitudinal paper grain printing is small, and the expansion variation is large in the process of transverse paper grain printing, and the tensile strength and tearing degree are poor

10. Expansion ratio

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, etc

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 below the applicable range of the above three scales: ml/min (ml/min) or S/100ml (s/100ml), which refers to the amount of air passing through the paper in 1 minute or the time required to pass through 100ml of air. The paper with high air permeability is prone to double suction in the printing process

12. Whiteness

it refers to the brightness of the paper. If the paper reflects all the light, what can be seen by the naked eye is white. To measure the whiteness of paper, the whiteness of magnesium oxide is usually specified as 100% as the standard. If the paper sample is exposed to 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

when papermaking, the pulp is attached to the steel and shaped in the way of filtration and dehydration. In this way, the fine fibers and fillers on one side of the paper will be lost with water, leaving traces, and the paper surface will be thicker. On the other side, if it is not supported, it is more detailed. Smooth, so that the paper forms a difference between the positive and negative sides. Although it is dried and calendered in production, there are still differences between the positive and negative 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. If the relief process uses paper printing with a thick reverse side, the wear of the printing plate will be significantly increased. The front printing pressure of the paper is light, and the ink consumption is also small. To sum up, only by correctly understanding and identifying the main physical properties of the paper and its impact on printing, and taking corresponding measures in terms of operation and process technology according to the nature and characteristics of the paper, can we effectively reduce or avoid the chance of printing failure, so as to ensure production efficiency and product printing quality

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