Attached are slides for Part two of two outlining the advanced topics of printer mechatronics.
Attached are slides for Part one of two outlining the basic printer mechatronics.Inkjet Printing Mechatronics
SGIA 2017 – New Orleans Part 2 of 3
Ink Development of 2017 – Water-based Applications for Sign and Label by Prism Inks
The booth that really caught our eye for printing on non-porous, semi-porous, or microporous material was Sensient. They have been busy formulating top of the line inks for both mechanical durability as well as UV stability. The exact quote their SGIA representative used was, “For our new SX 3000 inks we are only using pigments with a Blue Wool Value of 6 or higher. This means that all of our pigments in the SX 3000 inks have the highest resistance to color density loss and Delta E color fade.”
The statement from the SX 3000 SensiJet Ink Brochure states:
“SensiJet SX 3000 inks are pigmented, water-based inkjet inks designed for non-porous substrates to generate images with excellent adhesion and fastness properties.”
These inks were developed with the environment in mind. The SX 3000 aqueous inks have been designed to have a low impact on the environment and meet the modern environmental and regulatory requirements.
SensiJet SX 3000 Ink Applications
- Labels, posters, flexible and rigid packaging
- Signage and displays (advertising panels, outdoor and indoor banners, backlit displays, temporary signage, vehicle wraps)
- Decorative industry (wall coverings, photomurals, professional photography and fine arts, glass, ceramics)
- Leather (fashion, automotive)
- Laminated applications (with adhesive or thermal lamination)
SensiJet SX 3000 Print Head Applications
Sensient Printer Integration
Sensient partners with several companies to develop printers and systems solutions. Their specialty lies in the inks and as such they have ensured compatibility with Epson, Kyocera, and Konica print heads. These print heads can be integrated into 3rd party printers or printer solutions.
SensiJet SX 3000 Ink Printing
SensiJet SX 3000 inks have been tested on various industrial prints. The suitability of the inks for individual machines and model’s needs, has to be validated by the 3rd party integrator. Depending on the ink and Piezo print head being used, heat may be required during printing (45C to 60C is recommended), the ink will set immediately.
SensiJet SX 3000 Compatible Substrates
SensiJet SX 3000 inks can be printed directly onto non-porous or semi-porous materials such as: polypropylene, polyethylene, PVC, TPU, window glass, leather, polycarbonate, ABS, polyamide, and various exterior vinyl applications.
SensiJet SX 3000 Curing Conditions of the Aqueous Ink
For the maximum mechanical resistance, prints should be cured at 100C for 1-2 minutes. If lower temperatures are required due to the nature of the substrate, the curing time should be increased by 3 minutes for every 10-degree decrease in temperature. The dry time is most notable for smudging the image, but is truly critical for the exterior and mechanical durability. While an image may appear dry to the touch it can be due to an exterior skin forming at the liquid air interface. If this is not fully dried or cured the image will degrade significantly faster than a fully cured print.
SensiJet SX 3000 Pre and Post Treatment
Depending on the substrate, the surface may need to be optimized for wetting out. Many companies rely on Corona or plasma treatment, but there are specialty coating companies who develop print receptive topcoats or primers to avoid pre-treatments like Corona. Post treatment is never necessary but can be used to improve durability if an over laminate is applied with UV stabilizers or absorbers.
SensiJet SX 3000 Cleaning and Head Maintenance
While this is highly dependent on the print head and the subsequent integration into a printer, it is recommended to use the SensiJet brand cleaning fluid for all preventative maintenance. The SXY 1010 will clean out any residual inks from the print head, as well as to clear out any nozzles which may be misfiring or clogging. Also, if the printer remains idle for longer than 60 minutes or becomes unplugged, the printheads need to be properly capped.
SensiJet SX 3000 Capping of the Printhead when Idle
It is recommended to use a water-filled capping station with the liquid level close to the nozzle plate to ensure that a proper vapor pressure is maintained through the capping periods. Depending on the print head used ask your Sensient representative if a co-solvent such as a glycol can be added to improve the cleaning of the print head and nozzles after the capping session.
One of the highlights for signs, labels, and printing every year is the SGIA expo. This year it was hosted in New Orleans, at the Ernest N. Memorial Convention Center from October 9th through the 12th. This year there are over 500 exhibitors (closer to 540) displaying their technologies ranging from, graphics, garments, wide format printing, printed electronics, signs, industrial, commercial packaging, and ink in the form of UV inkjet, Solvent based inkjet, and water based inkjet (including latex).
PIAMS primarily focuses on the ink development for DOD and CIJ printing techniques. Here we will highlight:
Ink Developments of 2017
UV Applications – Wide format for Glass and thick substrates (Kao Collins)
Water-based Applications – Sign and label (Prism Inks)
Media Developments of 2017 – Inkjet Media by Durico C&T, Inc.
UV Applications – Glass and Thick Substrates by Kao Collins
Kao Collins has developed a wide-variety of high-speed UV curable inks for use in Piezo print heads. D and H bulb curing CMYKLcLmW ink sets are available for substrates ranging from thin films to glass. Several of these inks have received approval from print head manufacturers, while other inks have been formulated to target specific end-user requirements.
After discussing the new ink portfolio, the Kao Collins representative, they have developed inks for specialty applications in order to provide enhanced performance characteristics for customized solutions. They released a statement in their brochures stating:
“Kao Collins is currently developing a variety of inorganic inks designed for applications that require longer light fastness and durability from inkjet fluids. Targeted applications include a range of architectural design products and exterior construction materials: windows, shutters, siding, facades, flooring, and other industrial material.”
We discussed their upcoming product portfolio and confirmed that their products were mainly for the home improvement sector and they have already begun to partner with what they referred to as a well-known window contractor and exterior remodeling company.
LED Curable Tesla Inks
Kao Collins has developed a wide-variety of high-speed LED curable inks for use in Piezo print heads. LED curing optimized CMYKLcLmW ink sets are available for substrates ranging from thin films to glass.
Fibra – Textile Inks for Piezo Inkjet
Kao Collins shocked us once again this year by improving their textile line by offering pigment-, reactive dye-, acid dye-, and dye sublimation-based textile inks for direct to garment (DTG) and direct to fabric (DTF) printing. They had a floor unit to demonstrate the new textile printing ink and applications thereof.
Targeted substrates range from natural fibers to polyester and ever clothing material in between, according to the representative at the SGIA booth.
Quanta – EB Curable Inks for Piezo Inkjet
The material that they have published in their brochures states the following:
“EB curing occurs by a similar polymerization process as UV and LED curing, but without the requirement of photo initiators. Kao Collins embarked on this project after seeing that the prices of beam curing units were approaching those of high-end LED curing units. Without photo initiators, the inks are safer, less costly, more stable, more reliable, and most importantly nearly odorless.
The EB process also offers a more complete cure than UV/LED and does so without generating as much heat as other curing technologies. This opens the door for printing on very thin films and foils. E-beam provides advantages for companies wanting to print low migration labels, packaging for food applications, and other consumer products. “– KAO Collins Quanta Brochure
What EB Curable Inks Mean for the Future of Inkjet
Over the past couple of years, Kao Collins has been formulating and validating e-beam inkjet inks to provide a niche solution to the industrial printing industry that current UV/LED curable inks do not offer. Concerns regarding material variability, potential migration, print integrity, complete and consistent cure are obsolete with EB technology. After working closely with e-beam equipment manufacturer, PCT, to conduct multiple printing trials, they’ve experienced all of the above first hand. The results are what they are here at SGIA to demonstrate, and I must say they are exceptional.
Kao Collins is able to formulate inks that are far superior to anything previously available to the market with other technologies. Kao Collins has an e-beam curing unit mounted to a web transport for in house ink development and testing. Kao Collins states that they are the first inkjet ink company to have such a novel set up, and they are really pushing to show off their wonderful creations. They are also challenging and encouraging customers to take advantage of the opportunity to explore the possibilities of e-beam curing.
After our previous post on Piezo and thermal print head technology we have had several of our customers stop in and ask about the working principles of the Piezo inkjet print head. In fact one of our largest customers, a siding contractor, places posters printed with this technology for window advertisements because they are durable and resistant to the elements.
Diving into the working principles of how these work can be summarized at a very high level of a deformation mode of either: squeeze, bend, shear, or push.
The squeeze type of piezo print head works by heating a metal plate which transfers heat to the nozzles on two sides to create pressure gradient which forces the droplets out of the print head.
The bend and push methods are similar and work by heating a plate which transfers heat to a reservoir of ink. This increase in pressure again will force the ink out of the print nozzle. The main difference is that bend will apply to the center of a reservoir, while the push will apply to the bottom of a reservoir.
The shear method has separate cavities split by metallic plates. These vertical plates are heated and create a pressure gradient to force the ink out of the print head.
When choosing between the different methods, print head manufacturers have to decide whether or not the ink can withstand different temperatures and pressures, because that is the main difference in applications between these methods.
How Piezo Print Heads Function
A commonality between each of these methods of piezo printing is that the heating of metal plates around the nozzles heats the ink to a point where the ink creates a pressure gradient in the print head. The above examples only differentiate as to where the heat is applied and where the pressure gradient originates. All of the piezo printing technologies creates a pressure gradient so as to expel the ink out of the nozzles at each burst of heat applied.
After the heat is applied in the form of an electric voltage, a drop is fired. A wave of ink equal to the expelled is then reflected back at the reservoir to create a wave of positive pressure, which is then amplified by the second waveform that is created when the next droplet is fired out of the print head.
An actuator for each piezo print head is the electrical element that applies the voltage across the channel.
An electric voltage on a piezo heating element enlarges a channel to generate a large negative pressure in the printing lines and the print head itself. After reflection at the reservoir, this becomes a positive-pressure wave. The positive-pressure wave is amplified by the second slope of the driving waveform to obtain a large positive-pressure peak at the nozzle, which fires a droplet. There are many mathematical equations that can adequately describe this nature, but what can be taken away from this type of printing is the following:
- The charging of a piezo element will enlarge the cross sectional channel, which initiates the negative pressure wave. The negative pressure wave will propagate through the print head and bounce back to the front of the nozzles.
- The reservoir acts as an opene ended channel in order to send a return wave to the front of the nozzles.
- Upon discharge of the piezo printing element amplifies the wave thus increasing the positive pressure.
- The channels are designed to handle a large incoming positive pressure peak at the nozzle.
- The above combine together to release a droplet of ink from the print head.
When conceptualizing inkjet technology, it is incredibly easy because it is essentially a digitally controlled ejection of drops of fluid from a print head onto a film or substrate. The manner in which the ejection happens, varies in two primary ways. The first being industrial inkjet, and is most commonly referred to as CIJ or Continuous Inkjet, where the second way to classify it is drop-on-demand inkjet. Variants of each of these styles are numerous and generally are only initiated for unique solutions.
Continuous inkjet ejects drops continuously, where the droplets are directed directly to the substrate, or in some instances to a collection tank for recirculation, recycling, or reuse. Drop-on-demand only produces and ejects droplets when required.
Continuous inkjet is stigmatized in the printing industry as a primitive or amateur type of printing. Continuous inkjet printers account for roughly 10% of the printer sales in North America in 2016. This is primarily and almost exclusively used in the marking and coding of products and packages, where high volumes and fast line speeds are critical to manufacturing process performance. CIJ utilizes a pump which pushes fluid from a reservoir through small nozzles to produce a continuous stream of droplets between (50kHz and 175kHz) via vibrating piezo print head crystals. The print quality and resolution is determined by how the droplets are charged through an electrostatic field, and deflected using a magnetic plate or field. The charge on the droplet, the magnetic field strength both determine where the droplet lands on the substrate, or if not charge is applied, the droplet will be directed to reflow through the reservoir conserving and recycling the unused ink. One of the unique benefits of CIJ printing is the fact that the droplets are pumped through the system at speeds often ten times faster than other methods which enables the substrate to be printed upon from a further distance away. Finally, the benefit of using a solvent based ink, allows for compatibility with a wider range of substrates including those with high surface energies.
The main drawback of CIJ is that most people consider this technology to be bad for the environment due to solvent being driven off in the curing process. While, this may be true, often times the alternative method of printing these labels or specialty signage have a far worse impact on the environment.
In the above image, pressure (red arrow) is applied to the heating plate (orange outline) in order to force the droplet of ink out through the print head nozzles.
DOD inkjet is by far the most common and broadest classification of inkjet printing. This is most commonly used by companies such as Hewlett-Packard, Fujifilm, Lexmark, and Canon. As the large brand names suggest, these are most commonly used in consumer products such as desktop printers, but in the recent history has been proving to be useful in industrial printing as well. DOD print heads such as, thermal, piezo, and electrostatic use large pulses of pressure, with the differentiating factor being how the pressure is generated. Many companies may consider MEMS to be a unique method of drop-on-demand printing, but in the end it is still a subcategory based upon piezo or thermal architecture.
DOD droplets can be formed by rapidly heating a resistive element in a small enclosed chamber containing the ink. In this scenario the heated element is increased to 350°C to 400°C, which will cause a thin film of ink above the heater to vaporize. The vaporization causes a bubble to create a pressure pulse that forces a droplet of the ink through the print heads nozzle. Upon relaxation, the small chamber is then backfilled with more of the ink which will then be jetted through the nozzle onto the substrate as well.
The greatest advantages of DOD inkjet are the ability to create extremely fine droplet sizes which translate to resolutions observed greater than 1000p. Additionally, the high nozzle density due to the creation of droplets via pressure allows for more compact devices, lower print head prices, and reduced production costs. The main disadvantage is most commonly stated to be the limited inks available for vaporization. Each of the components in an inkjet droplet must be able to withstand high temperatures during vaporization without being adversely impacted upon solidification on the printed surface.
After the 1990’s inkjet had worked its way into nearly all households through its printing presence in consumer benchtop printers as a low cost, reliable, fast, and convenient method for printing anything from digital files, photos, or screen shots. It has come a significant distance since its advent in the 1950s, in commercial products such as medical strips and chart recorders. As the industry has seen success the technology spread throughout the 1970s, into the widely recognized printing technique that exists today.
In theory, inkjet printing is simple. A print head ejects micro droplets of ink, carrier, and water onto a substrate (paper, vinyl, PET, etc.). When executing these techniques, companies have spent decades and countless millions practicing their disciplines in this skill. Piezo and thermal print heads are the most common when it comes to jetting UV inkjet or water based latex inkjet ink.
Taking into account the complexity of the practice of inkjet printing, what drives the industry to adopt these techniques is the wide range of applications that are available. Initially, it was seen as a drop on demand product, which can produce any color gamut available without pre-blended colors or a unique colored thermal transfer ribbon. As this technology continues to develop, it is turning into a wider range of applications including educational and industrial where professionals need to accurately deposit precise amounts of materials. Additionally, inkjet printing laid the ground work for the 3d printing technology that is still premature and developing today. The list of industrial uses for inkjet technology appears endless and is only being improved by reduced manufacturing costs, higher quality materials (such as outdoor durable jetted materials, 3d printed materials, and accurate doses), printing on difficult surfaces, reduction of waste, and rapid prototyping.
Benefits of Inkjet
|Automotive coatings||Replaces spraying or dipping, thereby reducing waste and increasing coating uniformity.|
|Plastic part decoration||Non-contact accommodates curved surfaces. Improved print quality over pad or screen printing. Digital eliminates requirement for inventory of screens or pads, resulting in faster prototyping and wider variety of designs. Process color capability reduces the number of ink colors that must be stocked.|
|Conductive patterns||Minimizes waste of costly materials; very suitable for short runs.|
|Rapid Prototyping||Rapid formation of three-dimensional structures designed by using computer software.|
|Variable information||Allows fast changing of the printed information, unlike analogue printing methods which require formation of new hardware (e.g., screens in silk screen printing).|
|Ceramics||Minimizes setup time, eliminates requirement for inventory of screens.|
The introduction of inkjet printing in industrial markets has proven to increase manufacturing environments with often more than a modest improvement, or in some cases revolutionize the production and identification of materials and products.
Pardon our mess, we are currently remodeling out website. Check back this week for news and updates regarding Thermal transfer printing. Our expert staff is preparing a fantastic article about the fundamentals of thermal transfer printing, as well as improving chemical resistance of the THT print.
From there, we will have our most senior staff provide us with an article on ink jet applications and the current limitations of eco-solvent inks.