Development and Application of Color Measuring Technology for Printing Inks

New technologies help ink manufacturers meet tighter ink tolerances.

For manufacturers, color has become an important means of identifying products. Regardless of where they are, consumers can recognize the red color of Coca-Cola, the orange color of Tide detergent, and the color of many products.

Companies that produce these products attach great importance to protecting the hue of product packaging. No matter which substrate is used, the printed ink must be stable and consistent. Both printers and their customers hope that the ink color can meet the requirements, and ink manufacturers will be more and more stringent requirements for ink solubility. The naked eye is no longer considered a reliable guarantee for determining ink color. Nowadays, various technologies can make up for the naked eye, and the color measurement results are more accurate.

Printing ink stability

The customer wants a stable and consistent printing ink. If the same product is seen in the store as showing two different colors, some of them will not be fresh enough, and companies that produce a variety of products would also like to have a consistent print ink.

Mr. Ess Peck, Product Manager of X-Rite Company, said: “Companies are all asking for brand recognition logos; they want the printing ink to be consistent.”

"I think that customers are increasingly demanding the stability of the ink," said Terry Waynes, who is responsible for the color processing business at Datacolor International. "In the jargon, it is to protect brand equity. Customers are developing product colors." A lot of investment is made. Tide washing powder is an excellent example. We can see that the box or plastic container with printed labels is the same color. Everyone knows that the color of Tide detergent packaging is orange yellow, And the Tide Orange should always be stable and consistent. It should be the same regardless of plastic containers, printing trays or printed labels." Mr. Stan Law, general manager of ColourValid Ltd., said: "Some customer requirements in the printing and packaging department no matter which The substrates should be printed with the same ink color.” As Mr. Loworth points out, if the frozen peas’ outer packaging is blue, people tend to avoid it.

Mr. Richard M. Adams, researcher of digital printing and color reproduction in the United States printing technology, GATF, said: “There are several trends that have played a role in improving the requirements for the stability of black printing, such as the print market. Globalization trends, industry quality trends, trends in the digital control of ink layer thickness (using densitometry and spectrophotometric assays), the decline in the cost of color ink testing, and the increasing awareness of color measurement inks, etc.” Hunter Lab’s Director of Sales Services Mr. Goode said: “The current market demand is more pressing and customers have higher requirements on quality. This includes consistent and stable prints such as packaging and containers.”

Tolerance is a very important aspect of measuring ink consistency. More technical tools (such as the CELAB color matching system) are currently being used to determine whether ink meets customer requirements.

Says Walter Zawachi, Technical Director of Flint Ink and a member of the American Printing Ink Research Association: “More customers require us to comply with professional standards. Some tolerances are very demanding. When determining tolerances for printing ink, you must Considering the proofing system, the substrates, and the differences that can be seen with the naked eye, the researchers tested commonly used sheetfed and gravure proofing methods in the first study, and tested thermal and flexographic proofs in the second study. For example, when using a sheet-fed printing ink, the same ink proofing substrate is sent to the laboratory, and the Prunbau and Little Joe proofers are used to prepare prints in the two laboratories. Ten printed sheets were printed, and one of them was selected as a standard sheet, comparing it with the rest of the sheets. Due to the proofing method, the color of the ink was different from that of the paper used, and the change in the CIELAB value of 10 sheets was gradually reduced. 0.25 units, up to 4.6 units. Even with Profbau proofers, the DE value varies from 0.25 units to 1.20 units. After the room. Only under the circumstances to determine the range of variation proofing mode, the substrate and the operator, in order to know the practical ink allowed tolerance exactly how much. "

Mr. James Forsk, Paul N. Gardner’s technical director, said: “Suppliers do not want the color of the ink to change. The result of each observation of the color is slightly different. The customer needs persuasive data, that is, the color of Quantify the data. They don't want to say that it's blue; they want to say what the L value is, what the A and B values ​​are. The instrument plays an absolute role in quality control and can quantify the color. This is the main requirement."

The development of color measurement technology

Color measurement operations are required for quality control, formulation and standards, and communications. From the naked eye to densitometers, colorimeters, and spectrophotometers, color measurement technology has developed rapidly. Each color measurement method has its advantages, but the newly introduced color measurement technology has greater color measurement accuracy.

Mr. Adams said: "The portable colorimeter developed from the color densitometer of the 1950s to the spectrophotometer of the early 90s. Later it developed into the current benchtop spectrophotometer. Although it is good at distinguishing colors, it is not good at Memory colors, so the instrument shows its unique importance."

Mr. Dauns said: “The naked eye is one of the best color-difference sensors in the world, but if you don't put the products together, you can't accurately measure solid colors.

The role of the densitometer is not to measure the color, but to measure the amount of ink transferred to the paper, which is of great benefit to the control of the printing machinery. The use of a spectrophotometer is a very important trend that can both measure color and measure optical density. The current practice is to use a spectrophotometer to compensate for the lack of densitometer, or simply replace it with a densitometer. ”

Mr. Parker pointed out that there are many different methods of color measurement. The densitometer measures the optical density, and the logarithmic scale is used to measure the color value and the amount of color change. The colorimeter acquires colorimetric data in three dimensions: hue, lightness, and color saturation.

Mr. Parker said that spectrophotometers use 16 to 32 numerical values ​​(or more) to determine the reflective properties of color and substrate combinations. Spectrophotometers are used when the color and substrate requirements are very stringent: Spectrophotometers are also used when determining ink formulations. The three methods mentioned above all play an important role in determining the ink color. The naked eye is the best color measurement tool, but it does not have storage capacity, nor is it a digital instrument, but has a dominant tendency. Everyone's observations are not the same. Some people are color blind, and fatigue is also a factor. The densitometer measures the amount of light reflected and calculates the optical density, which is suitable for some coarse color analysis.

Mr. Parker said that spectrophotometers can give extremely accurate color values ​​and determine the reflective properties of color and substrate combinations. Substrate has a great influence on color. One way to do this is to find the chromaticity value so that you can know if the hue is the same before you turn off the print. In determining the appropriate hue, brightness and color saturation, LAB assay is an effective method of quality control. It can also determine the density value and determine the ink formula. The specific approach is to refer to the actual spectral data obtained, using ink formulation software to find the best match. Science can tell us exactly what it needs. (to be continued)