12 Apr Using the Squeegee Efficiently and Effectively
Choose your squeegee wisely. Your choice of the squeegee can have a big impact on your printing – make sure you’re using the right one for the job! Efficient and effective screenprinting requires the proper tools, and the squeegee is very near the top of the list. There are a number of variables to consider when selecting a squeegee, and it’s important to understand how each affects the printing process.
The requirements of ink transfer within the screenprinting technologies are ever-changing. Today, the screenprinting process is used to produce functional devices where a thick ink deposit is a necessity. This is true of displays, fuel cells, high-density inks on wearable apparel, humidity, and biological materials, organic light-emitting diodes (OLEDs), sensors for gases, solar cells, transistors, to name only a few. As well, there is a need for producing intricate features with a high degree of control. Apparel decorators are moving to higher mesh counts, increasing tensions, and lower emulsion over mesh ratios to produce finer halftone images, with a few pushing into the 300-lines per inch (118-lines per centimeter). Others that produce screenprinted items in layers, such as conductive, dielectric, insulating, and light-emitting properties, need a very exacting ink deposit to eliminate any variance.
If you are one of the few who believe that the squeegee stroke is supposed to force the ink into the mesh openings in order to transfer the ink, you have been spending too much time on Wikipedia and YouTube. There is a better way to transfer ink while saving you both time and money. Let’s spend a few moments on the role of the squeegee in the ink transfer process. But first, we need to describe the three strokes that are used in the ink transfer process. The three strokes are the fill stroke, the squeegee stroke, and the flood stroke. If you are a manual press operator, you will use the squeegee for all three strokes, whereas if you are printing on a semi-automatic, or automatic press there are two blades in use; the squeegee and the fill blade, which can serve as both a fill blade and a flood blade.
The first step in the actual printing process is to use the fill stroke to transfer the ink into the mesh openings.
The purpose of the squeegee is to bring the bottom of the ink-filled mesh into contact with the substrate, while shearing the ink from the top of the mesh, providing the opportunity for the ink to more easily and accurately transfer onto the substrate by capillary action. This is due to the intermolecular forces between the ink and the mesh opening. If the diameter of the mesh opening is small enough to counter the surface tension of the walls of the mesh opening and that of the substrate the ink will release onto the substrate.
Once you understand the purpose of a fill stroke and of a squeegee stroke, you begin to understand that…
“The wet ink deposit is equal to the thickness of the stencil; the total thickness of the mesh and emulsion over mesh ratio of the stencil.”
There is really no need to make multiple squeegee passes if the printing process is understood and followed.
There are a number of factors that influence the print quality and ink consistency that is squeegee specific. The process effects determine the choice of squeegee in terms of material composition, edge profile, shore hardness, bulk elastic modulus, and extending into the type of squeegee holder, angle and blade width are extremely important in the consideration of choosing the right squeegee blade for the task. The duration effects, which occur as the squeegee deteriorates during the production run, i.e. absorption of chemicals in the inks and cleaning process, the abrasion as it comes into contact with the inks (especially functional materials such as conductive metallic particles) and the mesh during the printing process, and even with age.
Thus, in terms of producing a consistent, predictable, and reproducible quality of printing, a better understanding of the squeegee and its consequent impact on the printed product is required in choosing the proper squeegee. We will discuss the variables to be considered in this article.
The hardness of a squeegee is referred to as Shore A, or when mentioning a particular hardness; 70 Shore A, or 70sh. The term durometer is often used incorrectly to describe the hardness of the squeegee blade material. Durometer is actually the measurement of hardness, not the hardness itself, which is referred to as Shore A Hardness, as in 70ShA. Some people erroneously refer to the Shore A Hardness gauge as a durometer.
Shore Hardness of a squeegee is measured with an instrument named, what else, Shore A Hardness Gauge. A higher number on the scale depicts a higher resistance to indentation and less flexibility of the squeegee blade.
A harder blade will sheer the ink more completely, while a softer squeegee blate will not sheer as well, leaving ink in the mesh opening, even when producing a heavier ink deposit.
Virtually all squeegee blades used in screenprinting today fall somewhere between 55 and 90 Shore A, with each hardness providing a different ink transfer.
Softer blades (55-65 Shore A) will produce a thicker ink deposit, but with a loss of resolution that comes naturally from an increase in the ink deposit.
Medium blades (70-75 Shore A) will produce a slightly thinner ink deposit, with better resolution than the softer blades.
Harder blades (80-90 Shore A) will produce the thinnest ink deposit, but with great resolution.
One squeegee hardness will not work well on all prints, depending on the expectations of the end effect and quality to be achieved. Often, a print will be produced with two or three different squeegee hardnesses. The large solid areas will be printed with a softer squeegee and the details and/or halftones will be printed with a harder squeegee, producing a superior print than if only one hardness were used. The absorbancy and finish of the surface on the substrate, as well as the mesh count and thread diameter also come into play as to which squeegee will produce the best print.
To better understand the differences in Shore Hardness as it relates to the printed image, consider the prints below, which I worked with Fimor to produce.
Test Print Specifications
- Artwork: 50 LPI / elliptical dot / 61-degree angle, Provided by Fernando Lemus of Lemus Design and CGTex Printers (email@example.com)
- Substrate: 100% Cotton black jersey knit material from Yazbek
- Mesh: 160-threads-per-inch (62-threads-per-centimeter), tensioned to 30Ncm2 on 25 x 36-inch Newman Roller Frames
- Ink: Plastisol
- Press: M&R Sportsman, squeegee angle 94-degrees (4-degrees off of 90-degrees), squeegee pressure 25-psi
- Squeegees: SR1-65sh, SR1-75sh, SR1-85sh, TXS3-55/90/55, SR3-65/90/65, and SR3-75/90/75
All six squeegees were sharpened to the same free height so that when the squeegees were changed from one print to the next, no adjustments would need to be made. This provided a set of printed images that would accurately depict the differences in shore hardness. The examples shown here are at 72-dpi, to see the examples at 300-dpi click here and increase the size to 100-percent in your browser window.
These sample prints were produced under ideal conditions, but in an award-winning print shop that produces some of the finest printing on textiles to be found anywhere. It is recommended that you only take these prints as an example of what has been done, but perform the same or similar test in your own shop with your unique process settings. To that end, Fimor offers the Serilor® Squeegee Evaluation Kit of 6 pre-cut squeegees, each with different hardness for screenprinters to evaluate how the variables of squeegee hardness affect the printed image. This kit allows for the determination of which squeegee will provide the best results, taking into account the variables of the press, print design, ink, mesh, and tension within the particular working environment.
Originally squeegee blades were made of leather, and later of rubber or neoprene. While you can still find rubber and neoprene (synthetic rubber) blades available at hobby stores, they should not be considered for extended use, as they absorb chemicals and break down quickly.
Today virtually all commercial blades are made of polyurethane, a flexible, highly dense plastic. Polyurethane is easily formed yet exhibits a combined resistance to chemicals and abrasion. Polyurethane can be dyed, which allows manufacturers to color-code their blades according to their hardness. However, you should be aware that there is no standard color code for the hardness, and each manufacturer has its own distinctive coloring system.
Most better squeegees are manufactured with a computer-controlled, centrifugal casting process, which guarantees batch to batch consistency. The centrifugal casting method is known for its high quality and to avoid bubbles and craters in the material. The process allows for optimum homogeneity to the finished compound, in the core of the material and after grinding.
Squeegee blades are manufactured in a composite form by blending materials of different hardnesses together into a single dual-layer blade. These are referred to as “composite” blades and are available in a variety of types and profiles. The most common types are shown here.
Triple Layer Blade – This blade is often erroneously referred to as a “triple hardness” despite possessing only two hardnesses, albeit in three layers. The blade is centrifugally cast with a harder center section and a softer hardness on either side. The harder center layer provides rigid support required for precision printing, while the softer outer layers compress at the edge to provide a heavier ink deposit. This allows for a controllable ink deposit with the ability to hold detail and edge resolution at a greater level than with a single hardness squeegee blade. In this way, the center support might be 90 shore hardness and the two print sides might be a 55 shore hardness, which is written as 55/90/55. You will find other configurations such as 65/90/65 or 75/90/75.
Tipped Blade – a harder blade tipped with a softer material. The harder section provides support for the softer section of the blade. This creates a firm squeegee with a printing edge that retains the flexibility to ride over rough-surfaced substrates and still lay down a good thick ink deposit.
Fiberglass Reinforced – a stiff fiberglass blade molded into the center of a softer blade to give support in the core of the blade.
Other types of blade support are external. In some shops, a thin but stout the metal backing plate is attached to the squeegee holder to act as a support for the upper part of the squeegee blade. The metal backing plate extends along the entire length of the squeegee blade.
The squeegee is designed to be positioned so that only the very edge touches the mesh. An angle of 94-degrees (4-degrees off of 90-degrees) will give the sharpest print and prevent the squeegee from bending with the normal pressure of 25-psi.
If you are of the illusion that you need 50 psi or more pressure to transfer ink, you have other problems that need to be resolved. Most of the time on the press the tip of the squeegee blade is covered with ink during printing and thus you cannot see what is happening when you apply excessive force to the squeegee blade. The photos shown here should make you reconsider your thoughts on using more pressure. As you can see there is actually less pressure in the center of the image and more at the outside edges. The more pressure you apply the more severe the gap. Obviously, this is not what you intended.
The edge of the squeegee blade refers to the point that comes into contact with the mesh and there are several shapes to consider:
- Square edged squeegee blades are flat across the bottom and cut at a right angle to the sides. These are the most common types of squeegee blades and are used for most screenprinting work.
- Round edged – also known as ball-nose – squeegees are an older style of squeegee edge that can produce a heavier deposit of ink, albeit with a loss of image edge resolution.
- Beveled edged squeegees are available in several styles. They feature an angle on one or both sides of the blade. Beveled blades are most often used when printing extreme details on very high mesh counts or when printing on substrates that are curved or uneven.
If you’re a manual screenprinter, your squeegee handle will be a major consideration. You want a handle that holds up well to the rigors of printing, but one that feels comfortable in your hand.
Wooden handles are a perennial favorite because they are warm and comfortable in the hand. However, they also absorb moisture and solvents, making them difficult – if not impossible – to clean. The method of swapping out squeegee blades also is usually more difficult with wooden handles.
Plastic or aluminum handles are easy to clean, and blades can usually be swapped out quickly and easily. You can look for handles with an ergonomic design that feels comfortable in your hand.
Blade width – The squeegee blade should extend about one inch beyond your artwork on each side; however, the blade shouldn’t come too near the frame, as this can destroy the tension of the mesh.
Squeegee blades can develop nicks or warp. Because of the abrasiveness of the mesh, they will dull over time. Make sure your squeegee is in good condition and free from warping or damage, as this can affect your print quality.
Blades absorb moisture and solvents. Don’t let blades sit in a solution, clean blades quickly after use and have enough squeegee blades on hand that you can rotate your blades, giving each blade enough time to dry out between jobs.
When you understand how each squeegee variable affects your overall print, you can choose the right squeegee for each screenprinting job. The right squeegee, and the proper squeegee care, will help you to improve your screenprinting.
When the ink hits the shirt, you need a good squeegee to keep your print quality high. Here are some squeegee maintenance tips!
There are many variables that can affect the quality of your printing. One tool that has a profound effect is your squeegee. If your squeegee isn’t in good shape, your prints will suffer.
When your squeegee is sharp and in good shape, it will fill the details of your stencil fully, allow you to better control the flow of the ink and sheer the ink cleanly away from the mesh as your print. In short, a well-maintained squeegee will help you to produce crisp, clear prints.
In contrast, a worn-down squeegee will mean degraded prints. If your squeegee has dulled, it will leave heavy ink deposits, blur the edges of your prints and obscure print details. A nicked squeegee blade can leave a long, heavy streak of ink through your image. A squeegee that has broken down can begin to “skip” over portions of the ink and mesh, leaving flaws in your image. Dull squeegees cause you to use more ink, which costs you extra money.
A well-maintained squeegee is a key to good print quality.
It’s inevitable that squeegees will break down over time. Exposure to inks and solvents causes blades to swell and warp. The pressure of pushing the squeegee across the mesh can weaken the blade, and the constant drag of the squeegee over the rough surface of the mesh dulls the edges of the blade.
Proper squeegee care can help to mitigate the effects of a bad squeegee. It can also save your shop money: Caring for your blades properly can save you from overusing ink and from having to purchase replacement blades as frequently. There are a few simple guidelines to follow to keep your squeegees in good shape.
The rubber squeegee material swells and warps when exposed to the moisture of inks and solvents. Cleaning your squeegees immediately after each use can help to minimize this warping. Never leave your squeegees soaking in a solvent, as that can lead to excessive swelling and warping, and a premature breakdown of squeegee blades. Allowing ink to dry on squeegees can also prove harmful: Squeegee blades are easily nicked and damaged in the process of chipping off dried ink.
Because the moisture in ink causes squeegee blades to swell and soften during use, it’s important to limit your use of each individual squeegee. It’s recommended that you change out your squeegee after 4 to 6 hours of printing, or a day of printing if it’s a lower production day. Have a rotating supply of squeegees so each squeegee can rest for 24 to 48 hours between each use. That gives the squeegee time to dry out and return to its original shape.
Squeegees work hard, give them a break every now and then!
Storing your squeegees properly can help them retain their shape and extend their lifespan. For squeegees that have been fitted into the handle, store the squeegee with the blade up in a squeegee holder or on a shelf; make sure that there is no pressure on the squeegee blade during storage. For squeegee blade that has not been fitted into a handle, store it flat — never leave it coiled. It is shipped in a coil to save money on shipping. Once you receive it, you should immediately uncoil it and lay it out flat. You can cut your new stock of squeegee blade to your preferred printing length before storage to make storage easier. The reason for laying it flat is that all polyurethane will harden over time and the blade will become permanently deformed if left in a coil.
Squeegee Blade Sharpening
You could throw out and replace squeegee blades as they wear down, or you can extend the life of your squeegee blades by sharpening them. There are a variety of squeegee sharpeners available for the job, and each squeegee blade can be sharpened between 25 and 50 times before it needs to be thrown away. Each squeegee will have a recommended blade height, and it’s usually acceptable to sharpen away ½ inch of squeegee blade before the blades should be replaced — the squeegee manufacturer should provide recommendations on squeegee height and sharpening allowances.
Squeegee maintenance may be simple, but it is necessary! By maintaining your squeegees you’ll maintain the crispness and quality of your printing, and you’ll ultimately save your shop money on both replacement squeegee blades and ink.
When choosing a squeegee for a particular task these are main considerations:
- Material composition
- Bulk elastic modulus
- Age of the material
- Edge profile
- Blade Width
- Solvent Absorption
- Edge Indentation
- Squeegee Wear