Relationship between Thickness and Density of Packaging Printing and Printing Layer (1)

[Abstract] The thickness of packaging printing ink is appropriate or not, and the color quality of printed products is determined to a great extent. The relationship between the thickness of ink layer, the degree of ink agriculture, and the density was studied experimentally, and the relationship between the thickness of the ink layer and the ink volume, and the relationship between the ink density and the concentration were established.

Keywords: ink layer thickness; density; color

The special color measuring instrument used in the packaging and printing industry is a density meter. Density measurement plays an important role in the quality control of printing products in the printing industry. The thickness of printed ink layers has a great influence on color reproduction. Therefore, the experimental study on the relationship between ink layer thickness, ink density and density has not only facilitated the understanding of the color rendering law of printed products and the control of the quality of printed products, but also improved the color matching theory of color inks and the color matching specification. Lay a good foundation.

1 Density measurement

1.1 The role of density measurement in packaging printing

The concept of “density” in physics is to characterize the absorption properties of light on the surface of an object. If the irradiated light flux is φ0 and the reflected light flux is φ, the density is defined as:

Where: D is the density or absorbance; R = φ0/φ is called reflectivity.

As the object absorbs some of the visible light energy, the light intensity weakens. The absorption of light is governed by Lamber's law and Beer's law. Lambert-Beer's law states that at a certain wavelength, the amount of light absorbed is proportional to the concentration of the light-absorbing material, and the light-absorbing material With regard to the thickness, the mathematical expression is:

Where: αλ is the absorbance index or the extinction index, which is related to the molecular structure of the absorbing object, and is related to the wavelength of the irradiated light; l is the thickness of the light-absorbing material; c is the concentration of the color material contained in the light-absorbing material.

According to the Lambert-Beer law, in the printing, the reflection density can be used to easily determine the thickness of the ink layer 1 or the concentration c of the ink, so the reflection density D can be used to control the change in the amount of ink in the printing process. |

In actual printing, the density of the ink not only has a complicated relationship with the nature of the ink itself, but also the density D does not increase infinitely because the thickness of the ink ink layer becomes larger. Most paper inks are saturated at about 10 μm, and the density value no longer increases. When the saturation value is set to D∞, there is an empirical formula:

In the formula: m is a constant related to the smoothness of the printing paper.

The discussion above shows that density is an objective physical quantity that describes the light-absorbing properties of a substance. The spectral density can also be used to describe the spectral absorption properties of a substance. This is what is commonly referred to as selective absorption. The density measurement process referred to here is entirely a physical process, not related to human eyes and subjective feelings; or it is not related to human physical and psychological factors.

Based on the physical property of density, in the modern printing, the density is the detection value to control the ink strength (ink layer thickness or concentration), and to calculate the dot area rate, dot gain, relative contrast, overprint efficiency, etc.; In the ink color quality detection, The density can be used to determine the gray and hue errors of the primary ink. In short, the density and density measurement method has played a significant role in the development of printing technology and is a relatively mature technology. American P. Tobias said at a printing association's annual meeting: "In the printing industry in the United States, the most useful meter in the past 10 years is the density meter."

1.2 Color Density Measurement

A special colorimetric instrument used in the printing industry is a densitometer, which uses red (R) green (G) blue (B) triple filters and a visual color film (L) for measuring lightness. Therefore, For a printed product, four density values ​​can be measured using the four color filters on the color density meter, which are denoted as DR, DG, DB, and DL. The nature of the density measurement still depends on the spectral reflectance of the surface of the object. The above four density values ​​measure the sum of reflectance and absorption in each spectral range, and they are effective data as an objective quantitative parameter characterizing color. Due to the spectrally selective absorption properties of the ink, it plays a major role in determining the color of the ink. Therefore, using the density value to determine the characteristics of the ink and the quality of the print is a more accurate method in the printing industry.