In today’s fast-changing, on-demand marketplace, the economic benefits and flexibility of digital printing technology cannot (and should not) be disputed. These presses are “on their feet” with minimal set-up required, empowering them to produce short runs and customized work with fast turnaround times. The computerized process delivers perfectly aligned images with crisp edges and no color overlapping. Traditional flexo technology, on the other hand, is fast, cost-effective for large runs, versatile with regard to substrate options, and offers numerous choices for decoration. While each printing method has its strengths, the possibilities increase exponentially when the two are used together.
Flexo printing
In a mechanical process like flexo printing, an anilox roll, metered by a doctor blade, delivers ink to the substrate by way of a printing plate. How the anilox roll and doctor blade interact has a large impact on the quality of the finished print. Factors such as anilox cell configuration, doctor blade material and tip, and dyne levels of the components throughout the ink delivery system play key roles.
Digital printing
Digital printing presses deliver an electronic image directly to the media using either inkjet or electrophotographic technology. In digital inkjet presses, the ink is delivered through a print head and jetted onto the substrate in an on-demand or continuous basis. The inks are engineered with lo w viscosity formulations, to prevent clogging of the print head nozzles, and specific adhesion properties to control dot spread and image quality.
Electrophotography, or laser printing, technology uses electrostatic energy to apply charged wet (HP Indigo) or dry (Xeikon) toner particles to the substrate. Electrical charges attract or repel the particles from the areas to be printed. The particles are then permanently adhered or “fused” using heat, pressure, light or a combination.
Applying digital printing technology to packaging
As the demand for customization and shorter runs crosses into the flexo packaging industry, there are obvious benefits to adopting digital printing. But there are disparities that have to be overcome. The two printing processes require different ink characteristics in order to execute a clean replication of the image in print, for example. Also, consumer packaging substrates have to meet requirements such as strength, barrier and resistance while holding up to print, finishing and conversion.
Digital inks and toners are not always compatible with packaging substrates such as labels, plastic film, folding carton and corrugated board. The heat used to fix dry toner to the substrate can dehydrate the media. When it comes to wet toner, ink wetting, or how the toner droplets interact with the surface of the substrate, has to be precise. If wetting is too low, the ink droplets spread too little, and the printed image contains gaps that appear as lines or bands in the image. If wetting is too high, the droplets merge with one another and the image loses edge definition. When applied to a substrate such as paper or board, the ink or toner can penetrate the material, leaving less on the surface and reducing color strength. With non-porous substrates, such as plastic and metallic films, the ink or toner tends to sit on top and not adhere properly to the material. This printed surface is left vulnerable to rubbing and scratching.
底漆、清漆和特殊效果涂料
数字加工商可以使用柔印技术涂上多层涂层，以弥合包装基材与数字油墨之间的差距，或增加点缀。
底漆
To prepare materials – both paper and plastics – for digital printing, a “priming layer” is applied to the surface of the substrate to improve its adhesion properties and make it more receptive to ink or toner. Primers fix surface tension to improve adhesion and hold-out, reduce bleed and mottle, and provide a foundation for specialty coatings. Primed surfaces can support higher-quality graphics with sharper images and more vibrant colors. A coating of primer also seals the substrate for a consistent, finished look and enables faster drying.
Priming solutions are formulated based on the properties of both the substrate and the ink and can be applied inline, offline or by the supplier before the stock arrives in the pressroom. Equipment producers and consumables suppliers are working together to simplify this process. Some press manufacturers, such as HP, are providing inline priming units to optimize the performance of their equipment. Ink companies are engineering formulas for specific use with primers, and materials producers are innovating substrates suited to digital printing.
清漆（保护涂料）
We know that digital printing technology is capable of transferring a high-quality image and that substrates can be treated to “accept” the image flawlessly. However, digital inks are not as resistant as flexo inks, and digitally-printed surfaces are vulnerable to dirt, smudges, fingerprints, rubbing, scratching, scuff, moisture, heat and other damage from their environment.
在印刷后可以涂上一层透明的涂层，以 "密封 "图像，并在运输、储存和处理过程中对其进行保护。保护涂层也称为套印光油 (OPV)，本质上是由耐久性树脂、抗擦伤剂和其他添加剂组成的透明溶液层，可在线或离线使用。在整张纸上进行泛涂，可以保护表面免受损坏，增加创意维度，或创造出所需的外观或表面效果。点涂层可用于为设计的某些区域增添光彩和深度。保护涂层还有助于保持基材的完整性，例如防止卷曲，最好涂在涂有底漆的纸张上，其表面可支撑面漆并防止吸收。
特效涂层
In recent years, consumer packaging has taken on the role of marketing in addition to containing, protecting and describing what’s inside. Manufacturers look for ways to differentiate their brands and improve the shelf-appeal of their products over competitors’. A large variety of special effect coatings can be used to add tactical, visual or olfactory dimensions to packaging and improve sales:
| 闪光 | 五彩 | 噼啪声 |
| 柔软触感 | 光泽度 | 刮开 |
| 珠光 | 亚光 | 勇气 |
| 沙子 | 冰霜 | 气味 |
| 金属 | 夜光 | 缎面 |
| 纹理 | 热变色 | 无趣 |
涂层配方
水性涂料是最常见、最经济、最环保的选择。水性涂料有亮光和哑光两种，只能用于水浸场合。水性涂料可以在线喷涂，并使用热风和红外线烘干机烘干。水性涂料具有良好的耐磨性和耐摩擦性，可防止变黄并保护金属油墨不变色。水性涂料通常使用更安全，清理也更安全，而且更容易在城市垃圾处理系统中回收利用。
紫外线涂料是一种更昂贵的选择，也可以在线喷涂，并提供额外的保护和引人注目的装饰效果。紫外线涂料通过紫外线照射固化，通常含有限制黄变、开裂、擦伤和长期剥落的成分。紫外线涂料有亮光、哑光或有色表面，可用于覆盖整个板材或突出设计的某些区域（称为点涂层）。
选择涂料配方
When selecting a coating formula, there are several factors that should be considered according to Kurt Hudson, an independent consultant to the printing industry and founder of Solutions Logic. “More times than not, the question is – ‘What is the object to be coated, in what environment will it need to be used, what are the specific requirements for the printed product to be effective in the end use environment, and what is the cheapest way to get there?’” Generally, Hudson believes the packaging use should drive the decision: “If one is producing for direct contact food packaging, then aqueous is the only choice. If one needs exterior durability, then UV is the only choice.” Beyond that, he suggests using cost as a guideline: “One uses UV coatings when aqueous products can no longer provide the required benefits,” said Hudson. He believes that look or feel is rarely the deciding factor as good mattes, textures and gloss can be achieved with aqueous and UV (with the exception of 3D tactile which requires a UV formula). He acknowledges that sometimes, but not often, productivity, ease of use and residual odor are considerations.
涂层应用
The application of primer, protective coatings and special effects coatings is done via a flexo process which uses an anilox roll and doctor blade. The application of these formulas can be challenging and using the right doctor blade will have a big impact on quality and efficiency.
Primers and special effects coating formulas tend to have high viscosities – up to 5-7 times that of water and solvent-based ink formulas – or contain large particulates which can make it difficult for the printer to accurately control the amount being applied. The mass of the highly-viscous coating applies extra pressure to a steel metering blade as the anilox roll turns, especially at high press speeds. The result is hydroplaning or “spitting,” which wastes materials and requires downtime for clean-up. A customized blade product with sufficient stiffness and abrasion-resistance is recommended to control the lay-down of coating and prevent spitting.
TruPoint Orange® doctor blade with MicroTip®
上述粘性和磨蚀性涂层配方的苛刻化学成分，以及输送涂层所需的粗糙网纹表面，会很快磨损钢刮刀片。在这些应用中，需要一种耐用材料制成的刮刀，以适应涂层的苛刻特性。通过在一种先进的聚合物材料上设计一种改良的薄片刀尖（称为 "MicroTip"），Flexo Concepts 创造出了一种创新的塑料刀片解决方案 - TruPointOrange - 这种刀片在打底和涂层应用中被证明是非常有价值的。该刀片与所有涂层配方兼容，对网纹辊和印刷机操作员安全，并且具有塑料刀片的最大优点：使用寿命更长。
TruPoint Orange blades can be engineered to a full range of size and profile combinations to optimize metering performance with higher viscosity and large particulate formulas. They range in thickness from .027”/.7mm to .050”/1.25mm to offer varying degrees of stiffness, rigidity and deflection. These properties combined with the innovative MicroTip edge allow the blades to achieve a fine contact area with the anilox roll and deliver a fluid transfer of coating to the plate with no spitting or slinging – even at high press speeds. With a range of MicroTip options (M10, M15 and M25), the blades can be customized for a “perfect fit.”
Doctor blade optimization
The choice of blade thickness and tip will be determined by the anilox configuration, which is driven by the viscosity and solid load of the coating. Typically, higher line screens and lower cell volumes will require a smaller MicroTip (an M10 or M15 for dull/satin/gloss coatings for example). But, as line screens decline and volumes increase, a MicroTip providing a larger contact area (M15 or M25) will perform better. By selecting the appropriate MicroTip for a particular application, printers are able to achieve longer blade life than with steel blades.
支持 TRUpoint 的原始设备制造商Orange
A number of digital finishing and hybrid press producers have found that their press productivity and output quality are optimized when using a TruPoint Orange doctor blade:
- A B 制图国际公司
- AzTech Converting Systems
- 条形制图机械
- Cartes Srl
- 焦点标签机械
- Gonderflex 国际公司
- Grafisk Maskinfabrik
- 马克-安迪
- 精加工
- 温州瑞冠机械有限公司
Many of these manufacturers have chosen Orange to demonstrate the effectiveness of their equipment at Labelexpo shows worldwide, and a number are shipping their equipment standard with the blade.
摘要
As the package printing sector continues to embrace customization and personalization, combining the power of flexo and the versatility of digital will deliver strong competitive advantage to the converter. The use of primers, varnishes and special effects coatings aligns the two processes, bringing efficiencies and almost unlimited design possibilities to the pressroom. Industry suppliers have rallied to support this evolution; manufacturers have introduced new innovations ranging from hybrid presses, new substrates, state-of-the-art coating formulas and an advanced polymer doctor blade called TruPoint Orange with MicroTip edge technology.
