How hard is color consistency in digital printing?

How hard is color consistency in digital printing?
From the emergence of Indigo's first digital printing press in 1993 to more than 20 years of development, digital printing equipment has entered the stage of a hundred flowers, imaging technology from electrostatic to inkjet, and the printing format has also developed from A3 to B2 or even B1 format.
Although the growth of digital printing equipment is gratifying, the application scope has been staying in the commercial printing market, among which books, images, labels and signs, personalized customized consumer goods and so on are the mainstream direction, and there are few successful cases of application in the field of packaging and printing. The reason for this is that we test and analyze the printing quality, printability, production efficiency and post-press process.
Print quality
Since the advent of digital printing equipment, printing quality has been attracting much attention, on the one hand, the role model effect of offset printing has set quality standards for digital printing early, and on the other hand, digital printing carries the future and expectations of a generation of printers for the development of printing.
Due to the limitations of material characteristics, imaging technology, software calculation, etc., the resolution of digital printing is generally about 1000dpi, which is far from the effect of offset printing, so the font and line edges are not good, and the jagged shape is obvious, especially the small font, the strokes are sticky and unclear, so the bar code on the packaging box needs to be refined before printing to meet the corresponding grade requirements. This problem has been improved with the development of inkjet technology and FM netting, and barcodes can easily reach class A.
Color has always occupied an important position in the field of packaging printing, and the early digital printing was dominated by electrostatic imaging technology, and color uniformity and stability once became a stumbling block restricting the development of digital printing in the packaging industry. It is not until the emergence of high-speed inkjet printing technology in recent years that the problem of color consistency has been solved in principle, and the current high-profile Heidelberg Primefire, Landa, Fujifilm JetPress, etc. are all using this technology, so color consistency is no longer a difficult fortress to overcome, which is undoubtedly another grand gift for digital printing to enter the packaging industry.

As we all know, spot color is a major feature of offset packaging printing, and spot colors are designed to maintain batch color consistency on the one hand, and to obtain colors outside the normal color gamut to highlight the theme on the other hand. Thanks to the solution of color stability, the problem of spot colors that plague digital printing has also been partially alleviated, and as for spot colors outside the normal color gamut, it is believed that Multi-Color will be the future development direction.
Accurate reproduction of graphics and texts is the primary task of printing, and traditional offset printing takes mechanical transmission as the principle of reproduction, and the interlocking printing process is an important condition to ensure the accuracy of the reproduced content. Generally, the original design draft is used as the standard content, respectively, the key links such as document processing, plate output, and the first printing are proofread, and each link is the inheritance of the results of the previous link. Digital printing, on the other hand, is a challenge in that even if the same original is copied in batches, each sheet is re-imaged, and the uncertainty in this process brings considerable challenges to the batch copying work.
The correlation between the quality of the front and rear printing sheets is reduced, the randomness of printing failures increases, the bottom ash failure of electrostatic equipment, the ink line problem of inkjet equipment, the misalignment of graphics and texts in the imaging link, poor inking, ink droplet smudging and a series of printing faults may randomly appear in bulk goods, so quality inspection is an indispensable link in packaging digital printing.
The packaging industry has strict requirements for the size and needle position of the printing paper, such as the deformation of graphics and texts in the production process, the inaccurate needle position and other problems, which will lead to abnormal positions of the face paper and the knife mold in the die-cutting process and increase the defective rate. After the digital printing ink is transferred to the paper, it often needs to be dried and cured at high temperature, which is easy to cause the paper to deform and cause the distortion of graphics and texts.
On the other hand, the early digital printing machine design paid more attention to the realization of the core part of printing, and there was a lack of attention to the mechanical platform and paper path design, so the design of feeder, transmission, paper delivery and other devices was unsatisfactory, which was reflected in the biggest problem in the packaging industry is the inaccurate needle position. The Primefire presented at Drupa 2016 in Heidelberg is a digital press designed on the basis of a traditional offset press platform, which solves the problem of inaccurate printing needle position. Landa, JetPress and other equipment are also showing their own talents in paper path and conveyor design, and go hand in hand.
Printability for use
I believe that everyone who has been in contact with digital printing machines has a feeling that the scope of application is limited, the advantages and disadvantages of digital printing machines of different brands and models are significant, and the direction of application is not the same, so determine the business type and direction before equipment selection, fully consider the applicability of the equipment, and avoid a lot of unnecessary troubles for subsequent production.
Traditional printers are accustomed to cutting the paper directly on the offset printing machine after the size, which is not feasible in digital printing, most of the digital printing equipment requires the paper to go through the coating process before printing, and the coating solution is evenly coated on the surface of the paper, so as to improve the adhesion ability of the ink on the surface of the paper. It seems to be a simple process, but the production process needs to add a lot of control links: the selection of applicability of coating solution, the selection of coating equipment, coating quality testing standards, the shelf life of the coated material and the impact on printing quality, etc., are all factors that have to be considered in production.
Coating fluids can solve most of the ink adhesion problems of materials, but they are not omnipotent, and the printability of non-absorbent materials remains a major challenge.
In the early stage of the development of digital printing, the application market was concentrated in graphic stores, and a large part of the factors stemmed from the limitation of printing format.
Before the introduction of wide-format digital printing equipment on the market, the digital printing format was mainly A3 size, which greatly limited the attempt of digital printing of packaging products. The four-format B2 digital printing equipment represented by the HP Indigo 10K has only become popular in recent years, while the two-panel B1 format equipment has only become popular after the Drupa exhibition in 2016. The popularity of wide-format equipment has brought benefits and more possibilities to the digital printing market, and more and more packaging companies have begun to try digital printing.
On the other hand, the limitations of equipment consumables such as the life of blankets on paper size are also slowly highlighted, frequent replacement of substrate size will accelerate the loss of blankets, and suction transmission equipment does not support arbitrary changes of paper size, in short, relatively fixed substrate size will make digital printing run more smoothly. As for the thickness of the substrate, the design style of the paper path will be different according to the digital printing machine, and the compatibility of thick paper and thin paper is not high in general, so more and more equipment is designed with different models and modes to meet the printing needs of thick and thin paper.
Productivity
Digital printing has always appeared in the public eye with the advantages of "short, flat and fast", a print, quick change, immediate and short, pre-press preparation time is short, are digital printing labels.
What exactly is the production efficiency?
Since there is no need for plate making, digital printing no longer requires high printing costs, and truly realizes one printing and quick order change. Pre-press preparation time depends on the quality requirements of the printing sheet, the general commercial printing that does not require high printing quality, does not need to prepare for too long a long time, for the appearance, color and other packaging and printing with strict consistency requirements, it takes a lot of time to calibrate the color correction, especially the electrostatic equipment with poor stability, and it is necessary to frequently run various correction and correction procedures to ensure that the printing quality is maintained on the same level. From this point of view, the "fast" of digital printing will be greatly reduced.
In addition to the proofreading preparation time, the most direct factor affecting production efficiency is the speed of equipment operation. The description of the printing speed of the offset press is simple, e.g. 15,000 sheets/hour. The printing speed parameters of the digital press are much more complex to describe: 3450 sheets per hour; 3000 sheets/hour for single side, 1500 sheets/hour for double side; 38 ppm (A3 format), etc.
The running speed of digital printing equipment is affected by the number of colors, single and double-sided, substrate thickness and other factors, in general, the net speed of single-sided four-color printing is about 3000 sheets / hour, if the proofreading preparation, appearance quality inspection, equipment failure rate and other factors are taken into account, the high requirements of packaging and printing production efficiency can be maintained at 1500 sheets / hour is a good result.
Post-press process
Packaging and printing products are almost inseparable from the post-press surface finishing process, which can not only improve the artistic effect of printed matter, but also play a protective role in printing products to avoid damage to packaging and printing products in the process of transportation and sales.
Lamination and glazing is a commonly used surface process in ordinary packaging printing, which mainly protects packaging products, especially surface inks, so surface wear-resistant, waterproof, explosion-proof color and other parameters are important indicators to measure whether the process is qualified or not. In addition, common finishing processes such as hot stamping, local UV, and concave and convex are also the focus of packaging and printing. Different digital printing equipment uses different materials and consumables, and their compatibility and adaptability with the paper surface and process materials directly affect the process quality and performance results, so they cannot be generalized and need to be analyzed according to the actual situation. In general, for the collocation and application of surface finishing technology, traditional printing has reached the realm of perfection, and digital printing still has limitations.
The development of digital post-press equipment is more sluggish than digital printing equipment, and as early as seven or eight years ago, we began to experiment with the possibility of combining digital printing with traditional post-press on the A3 format machine Indigo.
The combination of traditional post-press and digital printing not only limits the play of the advantages of digital printing personalization, but also cannot solve the problems of digital printing needle beating. In recent years, digital post-press equipment has appeared one after another, among which Scodix, MGI and other digital surface efficiency equipment are relatively mature, constantly exploring innovative application directions, and Evergreen, KAMA Procut and other equipment also solve problems for the digital die-cutting process. More and more digital post-press equipment has entered the market and has been recognized by the industry, and continues to develop in the direction of quality refinement.