天津市印刷厂

Discussion on the control techniques of spot color printing in offset printing technology

一、专色的检测

Detection of spot color

目前国内大部分包装印刷企业对专色的测控手段都比较落后，多数依靠工人师傅的经验来调配专色墨。这样做的缺点是专色墨的配比不够精确，调配时间长，主观因素影响大。一些有实力的大型包装印刷企业已采用了专色配墨系统对其进行管理。

At present, most of the packaging and printing enterprises in China are relatively backward in the means of spot color measurement and control, most rely on the experience of workers and masters to prepare spot color ink. The disadvantage of this is that the proportion of spot color ink is not accurate enough, and the deployment time is long. Some powerful packaging printing enterprises have adopted the spot color matching system to manage them.

专色配墨系统由电脑、配色软件、分光光度计、分析天平、匀墨仪、展墨仪组成。用该系统将公司经常使用的纸张、油墨的参数收入数据库中，应用配色软件对客户提供的专色进行电脑自动配色，利用分光光度计测量其CIELab值、密度值、△E，从而可以实现专色配墨的数据化管理。

Spot-color ink matching system consists of computer, color matching software, spectrophotometer, analysis balance, ink leveler, ink developer. The parameters of paper and ink often used by the company are collected in the database by this system. The spot color provided by customers is automatically matched by computer by color matching software. The CIELab value, density value and E are measured by spectrophotometer. Thus the data management of spot color matching can be realized.

目前市场上常见的分光光度计有美国X-Rite和瑞士Gretag两种品牌。不同的分光光度计，测量色差时采用的是不同的计算方法，从而会带来不同的容差。

At present, the common spectrophotometer in the market has two brands: American X-Rite and Swiss Gretag. Different spectrophotometers use different calculation methods to measure chromatic aberration, which will bring different tolerances.

二、影响专色色差的因素

Two, factors affecting spot color difference

在印刷过程中，导致专色油墨生产色差的因素很多，下面对这些因素分别进行探讨。

In the process of printing, there are many factors that lead to color difference in spot-color ink production. The following factors are discussed separately.

1、纸张对颜色的影响

1, the influence of paper on color

纸张对墨层颜色的影响主要体现在3个方面。

The influence of paper on the color of ink layer is mainly reflected in 3 aspects.

1.1 纸张白度：白度不同(或带有一定颜色)的纸张，对印刷墨层的颜色显现有不同的影响。因此，在实际生产中应尽量选用白度相同的纸张印刷，以减小纸张白度对印刷颜色的影响；

1.1 Paper whiteness: Paper with different whiteness (or with a certain color) has different effects on the color of the printing ink layer. 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 in actual production.

1.2 吸收性：同一种油墨在相同条件下印刷到吸收性不同的纸张上时，会有不同的印刷光泽。非涂料纸与涂料纸相比，黑色墨层会显得灰暗、无光泽，并且彩色墨层会产生漂移，由青色墨和品红色墨调配出的颜色表现最明显；

1.2 Absorbability: The same ink in the same conditions when printed to absorb different paper, there will be different printing luster. Compared with the coated paper, the black ink layer will be gray and dull, and the color ink layer will drift. The color of the green ink and magenta ink is the most obvious.

1.3 光泽度与平滑度：印刷品的光泽度取决于纸张的光泽度与平滑度。印刷用纸的表面属于半光泽表面，尤其是涂料纸。

1.3 gloss and smoothness: gloss of printed matter depends on gloss and smoothness of paper. The surface of printing paper belongs to semi glossy surface, especially coated paper.

2、表面处理对颜色的影响

2. The effect of surface treatment on color.

包装类产品的表面处理方式主要有覆膜(亮光膜、亚光膜)、上光(罩亮光油、亚光油、UV光油）等。印品经过这些表面处理后，会有不同程度的色相变化和色密度变化。覆亮光膜、罩亮光油和UV油时，色密度增加；覆亚光膜、罩亚光油时，色密度降低。化学变化主要来自覆膜胶、UV底油、UV油内含有的多种有机溶剂，它们会使印刷墨层的颜色发生变化。

The surface treatment methods of packaging products mainly include coating (bright film, Matt film), polishing (cover bright oil, Matt oil, UV light oil), etc. After these surface treatments, the prints will change to different degrees of hue and color density. The color density increases when coated with bright film, glossy oil and UV oil, and decreases when coated with Matt Film and glossy oil. Chemical changes mainly come from the film coating adhesive, UV base oil, UV oil contains a variety of organic solvents, they will change the color of the printing ink layer.

3、撤淡剂对颜色的影响

3. The effect of the lighter on color.

撤淡剂是一种油膏状的无色透明物质，在专色印刷中主要起冲淡颜色的作用。撤淡剂的加入量不同，对色相的影响也不同，尤其是蓝色表现得最明显。

The diluent is a paste-like colorless transparent substance, which plays a major role in spot-color printing to dilute the color. The influence of the amount of the disintegrating agent on the hue is different, especially the blue is the most obvious.

4、干退密度差异的影响

4. The effect of dry density difference.

刚印出的印品，油墨尚处于湿态，与干态时有一个密度差。湿色密度大于干色密度的现象称为干退密度现象。这是因为刚印出的墨层有一定的流平性，所以表面反射以镜面反射为主，看上去色彩鲜艳，光泽好。当墨层处于干燥状态时，表面反射以漫反射为主，色泽自然比刚印刷出来时显得要暗淡无光。

The printed ink is still wet and has a density difference when it is dry. The phenomenon that wet color density is greater than dry color density is called dry density phenomenon. This is because the ink layer just printed has a certain leveling, so the surface reflection to mirror reflection, looks bright color, good luster. When the ink layer is in a dry state, the surface reflection is mainly diffuse reflection, and the color is naturally dimmer than when printed.

5、系统差异的影响

5, the impact of system differences

用匀墨仪、展墨仪制作色卡的过程是"干印"过程，没有水参与，而印刷是"湿印"过程，有润湿液参与印刷过程，所以在胶印中油墨必然要发生油包水的乳化现象，乳化后的油墨由于改变了颜料粒子在墨层中的分布状态，必然要产生色差，印出的产品也就显得色泽灰暗、不鲜艳。另外，调配专色所用油墨的稳定性、墨层的厚度、称量油墨的准确性、印刷机供墨区的新旧差异、印刷机速、印刷时的上水量等也都会对色差的产生有不同的影响。

The process of making color cards with leveler and developer is a process of "dry printing" without water. Printing is a process of "wet printing" with wetting liquid participating in the printing process. Therefore, the emulsion of oil-in-water must occur in offset printing. The emulsion ink must be produced because it changes the distribution of pigment particles in the ink layer. The color difference between the product and the printed product is dull and not bright. In addition, the stability of the ink used for spot color matching, the thickness of ink layer, the accuracy of weighing ink, the difference between the old and new ink supply area of the printing press, the speed of the printing press, the amount of water used in printing will also have a different impact on the color difference.

三、专色的控制

Three. Control of spot color.

综上所述，为了保证同批和不同批产品的色差符合国家标准和客户要求，我们在印刷过程中对专色进行了这样的控制。

In summary, in order to ensure that the color difference of the same batch and different batch of products meet the national standards and customer requirements, we have carried out such control on spot color in the printing process.

1、制作色卡

1. Make color cards.

首先根据客户提供的颜色标准样，用电脑配色系统给出专色油墨比例，然后再调出油墨小样，用匀墨仪、展墨仪"展示"出不同密度的颜色样；然后根据国家标准(或客户)对色差的要求范围，用分光光度计确定标准、浅限、深限，制作印刷标准色卡(色差超标需进一步修正)。色卡一半是普通颜色样，另一半是经过表面处理的颜色样，这是为了方便质检时使用。

Firstly, according to the color standard sample provided by customers, the proportion of spot-color ink is given by computer color matching system, then the ink sample is adjusted out, and the color samples with different densities are displayed by leveler and developer, then the standard, light limit and depth limit are determined by spectrophotometer according to the range of color difference required by national standards (or customers). Printing standard color cards should be made. Half of the color cards are ordinary color samples, the other half are surface treated color samples, this is to facilitate the use of quality inspection.

2、验证专色

2. Verify spot color.

考虑到纸张是影响色差的主要因素，所以每次印刷前都要用实际印刷用纸"展示"颜色样，对照色卡做微修正，以剔除纸张的影响。

Considering that paper is the main factor affecting the color difference, the actual printing paper should be used before each printing to "display" color samples, slightly corrected against the color card, in order to eliminate the impact of paper.

3、印刷控制

3. Printing control

印刷时领机用印刷标准色卡对专色墨层厚度进行控制，同时辅助以密度计测量颜色的主密度值和Bk值，来克服油墨干、湿色密度差异性。

In order to overcome the difference between dry and wet ink density, a standard color card is used to control the thickness of spot-color ink and a densitometer is used to measure the principal density and Bk of the color.