Spot color ink is a kind of new ink in china printing, which is made up of one
or more kinds of ink mixed together and some auxiliary materials, compared with
traditional CMYK four-color ink. Spot color performance gamut is largely beyond
the scope of RGB and CMYK performance gamut. Many colors that CMYK four-color
printing ink can not 
present can be realized with spot color ink. Spot color
printing uses a large area of field color block to print color, with good color
effect, which reduces the color difference caused by dot overprint and dot
deformation, with stable color and wide color gamut. Therefore, in order to
achieve special artistic effect, spot color ink is widely used in cigarette
label, wine label and package. Spot color printing can not only solve the
problems of overprinter and ink balance in four-color printing, but also meet
the quality requirements of innovative design, and the ink balance in the
printing process is easy to control. There are many factors to produce spot
color ink printing color difference, but they are mainly: material properties,
ink properties, printing conditions, printing surface finishing. These factors
will affect the color reproduction in spot color printing.
1. Smoothness and glossiness of
paper
From the perspective of the influence on
the quality of printed matter, there is a very direct relationship between the
glossiness of paper and that of printed matter. No matter what type of ink, the
glossiness of printed matter increases with the improvement of the glossiness
of paper itself. The glossiness of paper is directly related to the inking
efficiency of paper. The paper with high glossiness can obtain higher printing density
when the paper surface has the same ink film thickness than the paper with low
glossiness. Therefore, there is a close relationship between the gloss of
printed matter and the gloss of paper itself.
2. Ink acceptance and absorption of paper in china printing
Ink receptivity refers to the ability of
paper surface to receive transfer ink at the moment of printing on the press.
It is closely related to three aspects of paper performance: the ability of
paper surface to receive printing ink wetting; the ability of paper surface to
absorb certain ink components; the ability of paper surface to fix and retain
uniform ink film. However, the ink absorption performance of paper occurs in a
long time from the contact of ink and paper to the complete curing on the paper
surface. It is related to the absorption of low viscosity components in the ink
by the paper pores and the permeation of some components in the ink into the
paper. Printing pressure, printing time, ink viscosity, paper capillary radius
will affect the paper's ability to absorb ink. When the same ink is printed on
paper with different absorbency under the same conditions, it will have
different printing density. The paper surface has the pore structure formed by
the anisotropic multiphase complex structural elements. In order to make the
paper surface obtain good uniformity and smoothness, it is generally necessary
to coat different thickness of coating on the paper surface. The properties and
thickness of the coating determine the absorption capacity of the paper surface
to the ink. Different absorptive capacity leads to different color of printing
ink layer.
3. Paper whiteness China printing
The factors that affect the whiteness of
paper are:
� Whiteness of size: the most important
factor.
� Dye: select the dye so that it does not affect its reflectivity
near the main wavelength of whiteness measurement, that is, it does not affect
the whiteness of paper.
� Filler: depending on its type and grade.
� Coating: the whiteness of coating printing
paper is determined by the whiteness of base paper, coating whiteness and
coating amount. Different whiteness and paper with a certain color (such as
some paper is blue and the latter is yellow) have different effects on the
color presentation of the printing ink layer. For the same kind of white board
paper, the whiteness is different, especially for the color with higher
brightness value, the influence is particularly obvious, resulting in a great
difference in the proportion of spot color ink. Therefore, in order to reduce
the influence of paper whiteness on printing color, the paper with the same
whiteness should be selected as far as possible.
