Printing International provides pad printing ink that is specially designed for the pad printing process. We have a pad printing ink suitable for all kinds of applications, such as medical, cosmetic, automotive, promotional, apparel, and electronic objects, as well as appliances, sports equipment and toys. Solvent ink is largely used as a common pad printing ink.
Printing International has built a large library of existing colours, which stores existing matches and ink formulations for all of our pad printing ink ranges. If the colour requested is not an existing colour, our ink technicians will use highly accurate calibrated measurement tools and experience to define the colour and match the target. Multiple technologies from human eye to spectrophotometers will be used to match pad printing inks to nearly any shade on any printable substrate.
FOR DIFFERENT APPLICATIONS
We offer inks for all kinds of industries, but mainly focus on inks for:
- pharma: edible ink
- food: edible natural colors ink
- ecological: exclude polluting components
- medical device: inks for marking medical devices
- toys: exclude 19 elements
- automotive: excludes certain substances
Our inks conform to the most common guidelines worldwide such as: EuPIA, GADSL, RoHS, EN 71/3, REACH, USP CLASS VI, cGMP, GAMP5, FDA.
How to choose the correct pad printing ink?
There is a technical data sheet for each ink, stating what it is suitable for. This sheet also states whether or not pre-treatment or post-treatment is necessary. It can also be deduced from this that several inks are suitable for some products.
The most important selection criteria for an ink are the following:
- coverage power
- adhesion of the ink on the product
- resistance to chemical products, wear resistance
- glossy or matte
- light resistance
What are the most important components of a pad printing ink?
These inks consist of the following components: resins, pigments and thinners. The resin, also called binder, is the most important component, together with the special additives, the binder is responsible for the mechanical properties of the ink film (adhesion, abrasion resistance, scratch resistance and drying). The pigments are the dyes that are mixed in the resin. The thinner (see additives) ensures that the viscosity of the resins and pigments is adjusted to the desired printing properties of the pad printing ink. After printing and curing, only a very thin ink film remains on the product.
Can pad printing ink be used on all materials?
There exist a whole range of different ink types, with this range you are able to print onto almost any kind of material, such as:
- Acrylonitrile butadiene styrene (ABS)
- Acrylonitrile styrene acrylate (ASA)
- Cellulose acetate
- Chromium-plated surfaces
- Coated surfaces
- Duroplastics (phenolic and melamine resins, glass-fibre reinforced polyester and epoxy resins)
- Gold-plated surfaces
- Nickel-plated surfaces
- Rhodium-coated surfaces
- Plasticized PVC
- PMMA (acrylic glass)
- Polyacetal (POM, with flame-drying)
- Polyamide (PA)
- Polycarbonate (PC)
- Polyester (PES)
- Polymer blends like PC/ABS
- Polystyrene (PS)
- Polyurethane (PU)
- Pre-treated polyolefines, i.e. polypropylene (PP), polyethylene (HD-PE, LD-PE)
- Rigid PVC
- Silicone rubber
- Styrene acrylonitrile resin (SAN)
- Synthetic leather
- Thermoplastic elastomers (TPE, TPU, TPS, soft-touch coatings)
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Pad Printing vs. Screen Printing – The Differences Explained
When creating promotional products for your brand, there’s a high chance that your printing company will either use pad printing or screen printing to do it. While it’s best left up to the experts, it’s still beneficial to have an idea of what’s involved with each process. Below we’ve explained some of the key difference between pad printing and screen printing.
The name gives a big clue to how pad printing works. The process involves transferring ink from a silicone pad onto the item you want printed. You could think of it as like those stamps you probably used to make crafts when you were a kid – though obviously professional pad printing is much more sophisticated!
The pad printing machine holds both the pad and the product steady and then presses the pad into an ink plate, which has been tailored to the shape of your logo or artwork. The pad is then pressed onto the object and left to air dry. It’s pretty straightforward.
Pad printing is a relatively modern process, especially when compared to screen printing, which dates back centuries and is often preferred as it makes it easier to print unusual shaped objects.
Pros and cons of pad printing
One of the main advantages of using pad printing is that you can use it to print on three dimensional surfaces and products of all shapes and sizes. It doesn’t matter if your items are curved or have an uneven surface, using this printing method will still achieve a quality print.
Pad printing is also suitable for delicate and mechanically sensitive products. If you need to print fine subjects, you will find that the resolution of pad printing is far better than that of screen printing.
Many companies actually choose to run their own pad printing operations in-house, as set-up costs are fairly low. Not only that but pad printing equipment doesn’t take up much room and the process is fairly simply to learn.
While pad printing is great for achieving accurate results, it is slightly limited in terms of speed. You usually have to apply multiple colours separately, so there is a slight risk of registration. However in terms of reliability and versatility, you really can’t beat it!
The process of screen printing involves creating an ink-blocking stencil and applying it to a woven mesh. The stencil then forms an area through which ink or other substances can be transferred.
While today, screen printing is the most widely used method of t-shirt printing, the technique actually dates back to early China (between 960 and 1279 AD). It was the technique used by Andy Warhol in the sixties for his Marilyn Monroe and Elvis Presley prints and it is still used by many companies today.
Today’s screen printing equipment is highly sophisticated and largely automated. It is ideal for carrying out quick and effective printing on t-shirts and other promotional products; however it’s not the best method for printing items with intricate detail.
While screen printing is ideal for larger designs consisting of just a couple of colours, it can get quite expensive if you require multiple colours, as each has to be applied separately. When using multiple colours, there’s also a risk of registration, however this can usually be resolved by overprinting (printing one colour on top of another).
Screen printing can also be fairly time consuming to set up and clean, which is why most businesses tend to outsource any screen printing, rather than conduct it in-house.
Pad Printing vs. Screen Printing: Which is better?
When choosing between pad printing and screen printing, it’s not really a case of which method is better in general but which method is better for your printing project. Before determining which printing method you are going to use, it’s best to study your product and consider the results you are hoping to achieve.
If your product is small (e.g. bar codes and labels) and features intricate detailing, then pad printing is going to be the best option for you. Pad printing is also excellent for printing on unusual shapes. The same goes for if you are printing on a 3D or uneven surface. Pad printing is quick, cost effective and ideal for achieving high quality, small prints.
If on the other hand the surface area of your item is quite large and you require a big print (say for example on a t-shirt) then screen printing will make much more sense. Also be aware that screen printing can cause inks, enamels and paints to be transferred during the process. If in doubt about which is the best to use then contact an expert like ourselves here at Tampo Canada Inc.
While there are key differences between pad printing and screen printing both boast great advantages, which is why they are the two most popular printing methods used today. For more information about pad printing equipment and consumables, feel free to get in touch.
Technique used for printing images onto 3D surfaces
Pad printing (also called tampography) is a printing process that can transfer a 2-D image onto a 3-D object. This is accomplished using an indirect offset (gravure) printing process that involves an image being transferred from the cliché via a silicone pad onto a substrate. Pad printing is used for printing on otherwise difficult to print on products in many industries including medical, automotive, promotional, apparel, and electronic objects, as well as appliances, sports equipment and toys. It can also be used to deposit functional materials such as conductive inks, adhesives, dyes and lubricants.
Physical changes within the ink film both on the cliché and on the pad allow it to leave the etched image area in favor of adhering to the pad, and to subsequently release from the pad in favor of adhering to the substrate.
The unique properties of the silicone pad enable it to pick the image up from a flat plane and transfer it to a variety of surfaces, such as flat, cylindrical, spherical, compound angles, textures, concave, or convex surfaces.
While crude forms of pad printing have existed for centuries, it was not until the twentieth century that the technology became suitable for widespread use. First gaining a foothold in the watch-making industry following World War II, developments in the late 60s and early 70s, such as silicone pads and more advanced equipment, made the printing method far more practical. The ability to print on formerly unprintable surfaces caught the imaginations of engineers and designers, and as a result pad printing exploded into the mass production marketplace.
Today, pad printing is a well established technology covering a wide spectrum of industries and applications.
- From the home position, the sealed ink cup (an inverted cup containing ink) sits over the etched artwork area of the printing plate, covering the image and filling it with ink.
- The sealed ink cup moves away from the etched artwork area, taking all excess ink and exposing the etched image, which is filled with ink. The top layer of ink becomes tacky as soon as it is exposed to the air; that is how the ink adheres to the transfer pad and later to the substrate.
- The transfer pad presses down onto the printing plate momentarily. As the pad is compressed, it pushes air outward and causes the ink to lift (transfer) from the etched artwork area onto the pad.
- As the transfer pad lifts away, the tacky ink film inside the etched artwork area is picked up on the pad. A small amount of ink remains in the printing plate.
- As the transfer pad moves forward, the ink cup also moves to cover the etched artwork area on the printing plate. The ink cup again fills the etched artwork image on the plate with ink in preparation for the next cycle.
- The transfer pad compresses down onto the substrate, transferring the ink layer picked up from the printing plate to the substrate surface. Then, it lifts off the substrate and returns to the home position, thus completing one print cycle.
Plate and ink interface technologies
Open inkwell system
Open ink well systems, the older method of pad printing, used an ink trough for the ink supply, which was located behind the printing plate. A flood bar pushed a pool of ink over the plate, and a doctor blade removes the ink from the plate surface, leaving ink on the etched artwork area ready for the pad to pick up.
Sealed ink cup system
Sealed ink cup systems employ a sealed container which acts as the ink supply, flood bar and doctor blade all at the same time. A ceramic ring with a highly polished working edge provides the seal against the printing plate.
Pads are three-dimensional objects typically molded of silicone rubber. They function as a transfer vehicle, picking up ink from the printing plate, and transferring it to the part (substrate). They vary in shape and diameter depending on the application.
There are two main shape groups: "round pads" and long narrow pads called "bar pads". Pads are also made in other shapes, called "loaf pads". Within each group there are three size categories: small, medium, and large size pads. It is also possible to engineer custom-shaped pads to meet special application requirements.
Image plates (also called clichés or print plates) are used to contain the desired artwork "image" etched in its surface. Their function is to hold ink in this etched cavity, allowing the pad to pick up this ink as a film in the shape of the artwork, which is then transferred to the substrate.
There are two main types of printing plate materials: photopolymer and steel. Photopolymer plates are the most popular, as they are easy to use. These are typically used in short to medium production runs. Steel plates come in two forms: thin steel for medium to long runs, and thick steel for very long runs. Both steel plate types are generally processed by the plate supplier as it involves the use of specialized equipment.
Multicolor applications can be executed by the coordinated use of several clichés. One image can contain several contrast colors (monochrome) by applying different engraving depths and/or grid resolutions.
Ink is used to mark or decorate parts. It comes in different chemical families to match the type of material to be printed (please consult the substrate compatibility chart for selection).
Pad printing inks are often "solvent-based" and require mixing with additives before use. They typically seem dry to the touch within seconds although complete drying (cure) might take a substantially longer period of time. There are FDA approved edible variants that have been developed for human consumption and more ecological variants to reduce the environmental impact.
There are many more options. Inks that cure via the use of Ultra Violet light are convenient for certain applications. UV inks will not fully cure until UV light hits the ink. UV curable ink can be wiped off many substrates when mistakes are made. They can be cured with UV light in as fast as 1 second of light exposure. This depends on the ink, substrate and the light power and spectrum. UV inks can be reused as the pot life can be high as long as the ink stays clean, blocked from UV light and hasn't broken down from sitting. This same feature makes it easier to clean than some solvent and epoxy like two part component inks. Also there are heat curable inks, which work in much the same way as UV in the sense that there is a "trigger" that cures the ink when pulled. Two-component inks usually have a pot life of only a few hours or so. They must be disposed of when they cannot be revived (by means of retarders etc.)
Climatic conditions will significantly affect the performance of any pad printing ink, especially the open ink well style printers. Too dry conditions can lead to faster evaporation of solvents causing the ink to thicken prematurely and too much moisture can lead to ink issues of "clumping" or something alike. Also the climate can affect other aspects of the printing process such as ink pick up and release from the plate to the pad to the substrate, as well as polymer plate to blade chattering or binding due to humidity.
Substrate is the technical term used to address any parts or materials to be printed. Fixtures vary in materials and complexity depending on the application. Substrates need to be clean and free from surface contamination to allow proper ink adhesion.
Making of printing plates
There are two main techniques used to create a printing plate. The traditional technique requires a UV exposure unit and involves photo exposure with film positives and chemical etching. A second technique known as "computer to plate" requires a laser engraver and involves automated laser etching. The latter technique is more convenient for short production delays, high precision, stable quality control.
Both techniques can be applied on a specialized polymer or steel plate. The standard cycle life that can be expected out of a polymer plate is quite low (50,000 impressions on the high end). By comparison, a hardened steel plate can easily last for over 1 million impressions.
Printing application examples
Pad printing is typically used for applications where print quality, precision or a complex shape are involved.
- Medical devices (syringes, surgical instruments, etc.)
- Implantable & in body medical items (catheter tubes, contact lenses, etc.)
- Pharmaceutics (pills)
- Cosmetic packaging (eyeliner, perfume bottles, etc.)
- Caps and closures (drink bottle caps, etc.)
- Golf ball logos/graphics
- Hockey pucks
- Decorative designs/graphics appearing on toys (Hot Wheels or Matchbox toy cars, balls, etc.)
- Automotive parts (turn signal indicators, panel controls, etc.)
- Letters on computer keyboards and calculator keys
- TV and computer monitors
- Identification labels and serial numbers for many applications
- Apparel industry for printing labels directly on clothing
- Promotional gifts and give-aways
- Shoe heels
Pad Printing Inks
711 Series of pad print ink is our most popular universal 1 or 2 component pad-printing ink that is both highly opaque and extremely chemical and abrasion resistant. Our head lab tech says, "711 works on 70% to 80% of all the products we test"… This universal 711 pad printing ink is well suited for pad-printing onto many items including; molded plastics, thermo-plastics and coated materials. This is an excellent pad transfer printing ink for interior automotive components and medical devices alike and it is certified for Class VI Medical use and it also meets several automotive industry certifications.
712 Series of pad print ink is a specially formulated pad printing ink for bonding to untreated Polypropylene and 712 pad printing ink is opaque and provides a semi-matt finished look. This one (1) component pad print ink can be also used with the Printcolor HDI hardener (up to 10% by weight) to improve bonding strength on polypro. This 712 series of solvent based pad print ink is great for pad printing on Advertising Goods made of PP.
747 Series of pad print ink is a new specially formulated UV cured pad printing ink that is highly resistant to chemicals and abrasion resistance. Series 747 UV pad printing ink is very well suited for printing on a wide variety of plastics substrates and coated materials and this product also meets the European and US toy safety standards and we have certification for Class VI Medical grade use.
750 Series of pad print ink is our most popular 2 component pad transfer printing ink for indoor-use and it’s highly opaque and is used to print on plastics such as; Polyolefin's (pre-treated PE and PP), Polyacetal (PA), Polycarbonate (PC), Duro-plastics, Glass, Ceramics, Metals and many coated / painted products. This 750 series pad transfer printing ink is also excellent for printing on Nylon 6/6 and on glassware & ceramic goods such as; tumblers, coffee mugs, wine glasses, souvenir shot glasses, etc. When printing on glass & metal objects you mix series 750 pad print ink with a special glass hardener called 700-GL (20:1).
752 Series of pad print ink is a highly opaque 1 or 2-component pad transfer printing ink system that is based upon highly resistant (to chemicals and abrasion) raw materials. This universal pad printing ink system is used on a wide variety of different plastics, metals and coated products. It is also suitable for printing on Duro-plastics and wood items. This 752 series pad printing ink has been specified for pad-printing on interior and/or exterior automotive components, satellite dishes and meets many different auto manufacturers’ specifications and series 750 is also Class VI Medical grade approved.
784 Series of pad print ink is a quick drying 2-component pad printing ink series that is highly resistant and is suitable for pad printing applications such as metal items, coated materials and a variety of plastics (also cosmetic containers which demand high chemical resistance against the contents ingredients). This series of pad print ink also displays excellent weather-durability and chemical resistance. This ink also meets the US Military Specification # A-A-208B.
Printcolor introduces their newest pad printing ink series 786, which will very soon replace series 784. The new 786 series of ink is a 2-component pad printing ink made from the latest safe & technically advanced ingredients. Series 786 is highly glossy, extremely resistant and highly opaque ink system for printing on many technical components, such as; automotive parts, toys, childcare products (baby bottles and pacifiers), cosmetic packaging, poly bottle caps, plastic wine sleeves and much more. Series 786 is environmentally and user-friendly and 786 series pad printing ink provides the best possible protection for your staff and our environment. Printcolor pad printing ink series 786 complies with the strict requirements of EN 71-3:2013 (reference to safe printing standards on toys). Furthermore, all substances found in Series 786 are listed in the Swiss Ordinance on Materials and Articles.
Protecting your people and environment
An important reason for the launch of Series 786 is to further safe-guard the users who come into contact with the inks. Here are some key bullet points:
- A non-compliant, with the new GHS labeling requirements, raw material that was previously utilized in Series 784 has been removed from the new 786 series.
- Series 786 is also free of PAH and printers as well as end-users will benefit from this new level of safe.
- Series 786 is halogen free which can cause risks to the environment and people.
Series 786 is available in the MS (Mixing System) shades, four process colors CMYK as well as many special colors and special FX and all are free of PAH and halogens.
Swiss Ordinance on Materials and Articles
All substances in Series 786 are listed in the Swiss Ordinance on Materials and Articles (SR 817.023.21).
Safe for pad printing on toys
These days, inks of low emission are an important requirement for use in all sectors of the printing industry. Stricter requirements, contained in the certification EN 71 3:2013 for printing on toys. Printcolor series 786 complies fully with all the required specifications of this world class toy standard.
Request a free sample!
Want to test out Printcolor pad print ink Series 786? Call our order desk at 714-639-DECO to request a free sample pack.
792 Series of pad print ink is a high-gloss and flexible 2 component pad printer ink system for decorative and functional applications for printing on elastic and plasticized (PVC) materials, such as soft-touch coatings and various thermo-set plastics. This is a great pad printing ink for pad printing onto squeeze balls or stress balls.
Pad Printing Ink Additives
Universal Thinner 700-017
Universal Thinner 700-017 is a pad print ink thinner that has been designed to use with all Printcolor 700 series pad printing inks. It has been formulated to work in both open inkwells and closed ink cup systems. Typically the pad print inks are reduced with 700-017 by 10 to 20% (by weight).
Universal Retarder 700-018
Universal Retarder 700-018 is effectively a "slow speed thinner", meaning that it evaporates slower than 700-017 above. This ink retarder has been developed to use with all Printcolor 700 series pad-printing inks. It works well when a slower drying ink is required and it can be blended with the 700-017 thinner above in any ratio to create a custom blend for your work environment. Typically the inks are reduced with this retarder (aka slow speed thinner) by a maximum of 10%.
Universal Accelerator 700-019
Universal Accelerator 700-019 is a "fast speed thinner", meaning that it evaporates faster than the standard 700-017 thinner. This 700-019 accelerator has been formulated to work with all Printcolor brand 700 series pad printing inks. This fast speed thinner (aka accelerator) works well for high-speed applications with closed cup inking systems and rotary pad printing machines. All four thinners 700-017, 018, 019, and 020 can be custom blended to create a special "house blend" for your application and environment. Typically these pad transfer inks are reduced with the 700-019 accelerator or fast speed thinner by 10 to 20%.
Universal Fast Accelerator 700-020
Universal Fast Accelerator 700-020 is a "Super-Fast speed thinner" and it evaporates even faster than the standard 700-017 thinner and faster than the 700-019 Accelerator. This 700-020 fast accelerator has been formulated to work with all Printcolor 700 series inks. This "super fast" speed thinner (accelerator) works well for top-speed production applications as found in motor driven or mechanical cam driven pad printing machines with closed ink cups and in-line high speed rotary pad transfer printing systems. All four thinners 700-017, 018, 019 and 020 can be blended in any ratio to create a custom "house blend" that is perfect for your specific production application. Typically the 700 series Printcolor brand pad printing inks are reduced with 700-020 accelerator by 10 to 15% (by weight).
Special Retarder 10-02637
Special Retarder 10-02637 is a very special retarder formulation that has a slow evaporation rate and it has been designed to use in areas with very high heat (ie: Arizona desert or non-temperature controlled factories). Because this product is so slow in it’s evaporating rate, we recommend only adding a maximum of 10% by weight. Also this special high heat environment retarder can be hot air dried on the silicone pads. An added benefit to this thinner (retarder) is that it has low chemical attack on the silicone pads.
"Adhesion Promoter" Thinner 10-0330
"Adhesion Promoter" Thinner 10-0330 is a special thinner that was designed to improve the adhesion to polystyrene (PS) materials and related plastics such as ABS and SAN. This special thinner has also been used to improve adhesion on PET, PET (A, E & G). The drying characteristics are similar to our universal pad printing ink thinner 700-017, and like all of our thinners/ additives listed above this special adhesion promoting thinner can be custom blended with any of the thinners mentioned herein. Typically the Printcolor pad printing inks are reduced with this thinner by 10 to 20%.
Hardener 700-HDA is a highly reactive universal hardener that offers high chemical resistance and extremely good abrasion resistance. 700-HDA hardener has also been formulated for outdoor usage as this hardener will not cause the printing to yellow over time. Also the 700-HDA hardener gives a nice gloss finish to all of the 700 series inks. See specific ink series technical bulletins for specific mixing ratios and usage instructions.
Hardener 700-HDI is a highly reactive universal hardener that offers high chemical resistance, extremely good abrasion resistance and fast cross-linking. 700-HDI hardener has been formulated for indoor usage only and it may yellow over time if exposed to heavy sunlight. This hardener works well with ink series: 750, 752 and in some cases with series 712. Please review the individual ink technical bulletins for specific mixing ratios.
Hardener 700-HDR is a highly reactive hardener that combines the characteristics of both the 700-HDA & 700-HDI hardeners. This hardener is very innovative because it is a solvent-free product and 700-HDR hardener is well suited for both indoor and outdoor applications, and it delivers a high-gloss sheen when printed. This 700-HDR hardener works best with 752, 754, 784, and 792 and in some cases with 711. See the ink technical bulletin for specific mixing ratios.
Hardener 700-GL is a special hardener designed for use in decorating glass and ceramic items. This hardener is used primarily with our series 750 Printcolor brand pad print ink. This 700-GL hardener provides excellent adhesion and resistance on glass, ceramic and metal objects (including anodized aluminum) and printed parts that have been printed with 750 series ink and 700-GL hardener can be put through a dishwasher (life testing results may vary). 700-GL hardener is not suitable for outdoor usage. Please review the Series 750 and 700-GL technical bulletins for specific mixing ratios and usage instructions.
Adhesion Promoter 700-PP
Adhesion Promoter 700-PP is a special agent that has been designed to improve the adhesion to polypropylene (PP) materials where adhesion results are not satisfactory. 700-PP ink adhesion promoter can be added by 10 to 20% by weight to the inks final mixture. This adhesion promoter is often used on lower grade poly-pro materials that contain a higher amount of regrind.
Flow Agent 700-VMT
Flow Agent 700-VMT is highly concentrated silicon based additive that improves the flow and (sometimes) increases the gloss level of the ink. The 700-VMT flow agent must only be used very sparingly, only adding 0.3 to 0.5% (up to 1% maximum) by weight. This 700-VMT flow agent will help eliminate "pin-holes", bubbling and will smooth out any "orange-peel" effect that happens occasionally when printing. Over dosage can cause deterioration of adhesion characteristics.
Wetting Agent 700-BMT
Wetting Agent 700-BMT is a highly concentrated liquid additive that can be used to improve the wetting and bonding on contaminated substrates, such as found on extruded plastics, silicone mold releases and oxidation on glass and metal parts. This wetting agent is also used very sparingly - only adding 0.5 to 1% (max. 2%) by weight. As with all our additives, prior testing is recommended to determine suitability for your specific application before running full production.
Anti-static Agent 700-AMT
Anti-static Agent 700-AMT is a special anti-stat agent that is added to the ink when there are specific static energy problems. These are most often referred to as "spider-webs" or used when you experience poor and inconsistent ink transfer to the part. To alleviate this problem, 700-AMT is added to the ink mixture sparingly and by only adding 0.5 to 1% (max. 2%) by weight. It is important to remember to always clean your silicone pads with tape - not solvents! This practice will also cut down on static (that gets introduced into the pads) and ensure longer pad life.
Print ink pad
Complicated substrates, irregular shapes and surfaces, greater versatility – these are only a few reasons why pad printing has been, and continues to be, a popular process across a variety of industries. However, while this process has been around for decades, it still poses issues for many printers seeking to utilize its benefits.
Plastics Decorating sat down with industry consultant and Pad Print Pros President John Kaverman to address some of the challenges regarding the pad printing process that he has encountered over the years. According to Kaverman: “While the theory of operation for every pad printing cycle is exactly the same – regardless of whether it’s three parts per minute or 300 being printed – the list of variables that create problems with the process is extensive. As a consultant, I address common misunderstandings of the impact on the process these variables have daily.” When asked about some of the most common issues found in pad printing, Kaverman noted three main issues and their potential cause.
Issue 1: The machine isn’t doctoring the clichés
There are several potential causes for this particular problem, including:
The doctor ring on the ink cup is worn. Most doctor rings are ceramic. When properly handled, they should last several hundred thousand cycles. It is when the sharp end of the doctor rings wear to a flat edge of 0.25mm (~ 0.010″) that they stop shearing and start smearing the ink. Replace the doctor ring.
Poor ink cup maintenance. In most cup designs, a flexible O-ring creates an interference fit between the ink cup body and the doctor ring. This feature allows the doctor ring to stay in intimate contact with the surface of the cliché as it traverses the cliché and changes direction during the cycle. When the cups are not properly cleaned and maintained, the doctor rings lose their ability to “float” or “flex,” and leaks occur.
Skimping on ink. Ink acts like a lubricant for the ink cup during doctoring. With most ink cup designs, there is a minimum amount of ink that will allow the cup to doctor the cliché efficiently.
When people have short run productions, they tend to skimp on ink – especially when using a two-component ink – because two-component ink must be discarded after the pot life has expired. The ink level within the ink cup needs to be enough to completely wet the cliché over the entire inside diameter of the ink cup on each cycle. Without sufficient wetting, the ink cup cannot clean the surface of the cliché sufficiently. To use an analogy, it’s like driving in a light mist, and the windshield wipers smear the windshield. Once it starts raining harder (more lubricant), they clean efficiently – unless they’re worn out or misaligned.
Scooping. Scooping sometimes happens with magnetic ink cups on thin photopolymer and laser engraved clichés. Depending on the cup design, the magnetic pull on the clichés can deflect the cliché, causing the doctor ring to “scoop” ink out of the image area where the magnets cause the highest degree of deflection. Sometimes, this can be alleviated or eliminated by using a spacer on the ink cup to increase the distance from the magnets to the cliché surface.
Issue 2: The ink isn’t sticking to the parts
The surface energy of the material is too low. For ink to adhere to a part, the surface energy (dyne level) needs to be 38 dyne/cm minimum. Forty-two or better is optimal. Polyolefins such as polypropylene and polyethylene are typically below the minimum and need to be pre-treated to raise the surface energy. Sometimes an adhesion modifier can be added to the ink, but it is only effective when the material has a borderline minimum surface energy.
Contamination is another culprit. Residual oils from upstream processes, mold-release or even oils and perspiration from human handlers can act as a barrier to efficient ink transfer and adhesion. Stay away from mold-release agents and avoid touching the image area of parts in handling.
Using the wrong ink and/or testing too soon. It is imperative to test inks and associated additives for adhesion, as well as chemical and mechanical resistance, long before production is initiated. No single pad printing ink sticks to everything or meets all performance requirements across the board. Printers should ask their suppliers for help with conducting test prints for evaluation.
Testing too soon is a common problem, especially when two-component inks are part of the equation. All inks are post-curing, meaning that while they might be dry, they have not cured to the point of having maximum adhesion and/or chemical and mechanical resistance.
Even UV-cured inks can post-cure for 24 hours or more after being applied. Two-component inks can range from 72 hours to five days or more, depending on the specific formulation. Follow the ink manufacturer’s drying and curing recommendations before performing quality control tests.
Issue 3: Print quality is poor
This can be a tough one to diagnose without photos of the defects and, preferably, video of the printing cycle and information about ink, additives, cliché specifications and pads. Some of the most common issues include:
Proper manipulation of solvent evaporation. The clever manipulation of solvent evaporation is what makes pad printing work. If the ink is too wet (has too much thinner or a thinner that evaporates too slowly), it won’t pick up and transfer efficiently. Depending on the machine’s capabilities, it might be possible to program short delays within the cycle to allow the ink more time to undergo the physical changes necessary to allow it to transfer completely.
If it’s not possible to program delays where necessary, speed up the evaporation of solvent by blowing low-pressure, low-volume air at the pad(s) between image pick-up and transfer. Blowing low-pressure, low-volume air at the part is also helpful when double printing or printing multiple color wet-on-wet within the cycle. If neither delays nor air are an option, try using a thinner that has a faster evaporation rate. When fast (45 ppm) or really fast (100+ ppm) cycles are required, air and fast thinner might be needed, along with a specific cliché etch depth.
Cliché is incorrect. A bad cliché can cause a multitude of issues. Etch depth and consistency are important. A typical straight etch is between 22 and 25 microns. If deeper than 28 microns, there will probably be issues with too much ink film thickness on the pad. If it is below 18 microns in depth, the ink might dry in the cliché before it is picked up or on the pad before it can be transferred (unless using a UV-curable ink).
If using a photopolymer cliché, the line screen might be wrong. Typical line screens are 150, 120, 100 and 80 lines/cm. 120 lines/cm are used about 90% of the time. If a little more ink film thickness is needed, use 100 line/cm. If there are finer details, use 150 line/cm for better resolution.
With laser engraved clichés, the angle with which the beam engraves and the frequency with which it removes material can cause issues. If the laser is fixed, the further it goes out from 90° vertical, the higher the potential for the laser to create sidewalls within the etch that are off vertical. This makes it difficult for the doctor ring to cleanly shear the ink at the edges of the image during doctoring and for the pad to pick up the image without the sidewalls of the etch interfering.
Incorrect or worn pad. When picking a pad, try starting with the pad that has the most mass, steepest angle and hardest material, then work down. More mass equals less distortion. The pad’s image area should be at least 20% larger than the image in all dimensions. Of course, if the machine cannot efficiently compress a pad, it is too large.
The higher the angle with which the pad compresses during transfer, the more efficient it is at displacing air from between the ink and the product. This is especially important when printing textured substrates and products having spherical, cylindrical and compound angled geometries.
Hard pads provide sharper image resolution (less distortion, better displacement of air), a more consistent ink film thickness and better penetration of textured surfaces than soft pads. Soft pads, having more oil, are more pliable and, therefore, last a little longer. So, try to save moving toward a softer pad as a last result when out of printing force to compress a harder pad with the same geometry.
The softer the pad, the more silicone oil it contains. There is no magic number for how long pads last. With each cycle, the pick-up and transfer of the ink depletes silicone oil from the pad. It is entirely possible for a pad with no visible wear (cuts, abrasions, etc.) to be worn out due to the depletion of silicone oils having reached the point where the surface energy of the pad is high enough that the ink won’t want to leave the cliché during pick-up or the pad during transfer.
When in doubt, change the pad (break it in first).
John Kaverman is president of Pad Print Pros, an independent consulting firm specializing in pad printing. Kaverman, who holds a degree in printing, has 32 years of experience in the plastics decorating industry in capacities including production, supervision, process engineering, technical training and sales. For more information, visit www.padprintpros.com.
Innovative Pad Printing Inks in Best Quality
Pad printing lends itself particularly well to printing two and three dimensional objects.
Pad printing lends itself particularly well to printing two and three dimensional objects. Advertising goods of every type - even with difficult shapes - as well as panels, housings, switches and consoles for use in the interiors of automobiles and telecommunication sector can be printed with pad printing inks with precision.
Proell offers one and two-component pad printing inks covering the whole range of printable materials.
High opaque color shades and process inks for pad printing are available as well.
Our solvent-based, quick drying universal and customized pad printing inks can be used in both open and closed cup pad printing machines.
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Fast drying pad printing ink for printing on rigid PVC, polystyrene, ABS, SAN, acrylics, polycarbonate and pretreated polyolefines
- Promotional Items & Writing Utensils
One or two-component screen printing ink for PVC, pretreated polyester films and polyolefines, acrylics, polycarbonate, leather, wood, metal, paper and cardboards (NoriPUR replaces PUR®-ZK)
- Bottle Crates
- Graphical Screen Printing
- Paper & Card Boards
Norifin® PP N
Physically drying one-component solvent based ink system for printing on untreated polypropylene.
- Promotional Items & Writing Utensils
- Medical Equipment
Two-component pad printing ink for the decoration of glass, metal* and coated metal substrate after pre-tests.
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Pad Print Thinners and Hardeners
Pad printing’s smooth transfer of an image from the inked cliché to the subtrates is facilitated by additives used in the ink’s mix. Pad Print thinners and hardeners are additives critical in handling ink adjustments for better adhesion and extending image life.
Transferring pad printing inks requires that a percentage of thinner be mixed into the ink. Thinners are volatiles; that is, they evaporate quickly (“flash off”) to dry out the ink mixture so it becomes “tacky.”
This “tackiness” is what enables the silicone pad to pick up an image/ink and transfer it to the part.
Ink manufacturers provide special, chemically-formulated thinners to work with their inks. They usually provide thinners in different.” The “speeds” refers to how fast the thinner evaporates. Typically, you’ll find fast, medium and slow (sometimes referred to as “retarder”) options.
As you may know, there are different ink “series” that adhere best to specific substrates. Manufacturers will provide charts that cross-reference different substrates and which inks work best with them. Each of these inks may utilize one (or many) different thinners, depending on the application. Here is a link to the Ink & Materials Table from the website.
Another important function of a pad printing thinner is it also cross-links the ink/pigment to the surface of the part while the thinner is evaporating, also aiding adhesion. Some substrates are more porous than others, which makes it easier for ink to bond, so the cross-linking happens quickly. Other substrates require more time, so you’ll use a “slower” thinner. In any case, once the ink transfer (print cycle) is complete, the thinner continues to evaporate and perform its cross-link duties simultaneously, eventually leading up to a “cured” image.
Images pad printed with solvent-based inks are usually “dry to the touch” in a matter of seconds, which means you can handle the parts relatively quickly. However, most pad print inks don’t achieve a full cure until at least 24 hours, sometimes longer.
Where do hardeners fit into this, you may ask? They have very little effect on ink adhesion, but have a huge influence on image durability.
Again, ink manufacturers provide hardeners that are formulated specifically to their inks. Some hardeners work with more than one ink series. This formulation also includes different ink-to-hardener ratios. Some are 4:1 (ink-to-hardener), some are 10:1 and others as much as 20:1. Technical data sheets on inks will detail all of that for you.
Hardeners are always added for inks used on metal, glass and ceramics, as well as parts (regardless of substrate) that may face exposure to abrasives, chemicals, sterilization procedures, etc.
The good thing about hardeners is they enhance image durability. The bad thing about hardeners is that they decrease the “pot life” in an ink cup (normally 8–10 hours max). The important thing is your customer gets a quality, long-lasting image.
Join the conversation! Our dedicated ink experts can get your ink problems solved and your printer up and running in no time!