Achieving Plastisol Cure

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ACHIEVING PLASTISOL CURE ON TEXTILE PRODUCTS Having been a screenprinter for over sixty years, I have witnessed a great number of changes in the screenprinting industry. Perhaps the greatest of these was the advent of plastisol ink for printing on textile substrates. But along with all the benefits of plastisol came the headache of achieving cure. Screenprinters have been troubled with curing plastisol ink since it’s beginning in 1956. Most novice screenprinters are under the mistaken assumption that all that is needed is for the plastisol ink deposit to reach a certain temperature for two minutes to ensure a proper cure. If it were only that simple.

means that the ink is overcured or undercured, depending on which myth you hear. This is a myth and nothing more. Checking for cure by stretching the ink has never been a viable test. There are two substrates here, i.e. the vinyl ink film and the material it is printed on. There is no way that they will have the same molecular structure and stretch the same.

With standard plastisol, there will always be cracking at some point. The woven material will always stretch further than the most pliable ink film. The fact is that the plastisol deposit is nothing more than a vinyl film laid atop a Myths very stretchable fabric. They are two different materials and will never stretch The screenprinting industry is ripe with equally. If a ink separates immediately myths. Screenprint message boards during the stretching process is it are ripe with screenprinters espousing probably overcured as the plasticizers one myth after another. In truth, most have been damaged from the heat and people only know what they know and become a solid non-flexible layer of ink. have never given any time to gaining If the separation take a little longer with the scientific knowledge necessary to more stretch, the ink may be underunderstand the process. They believe cured. that what they are doing is the only, right way to do what ever it is that they Cracking will occur on an undercured do. After all, they have been doing it for ink film just as it will on a cured ink film years and so it must be true. This is as well as a overcured ink film. Try it for what is referred to as TTWWHADI, an yourself and see. Stretching is never a acronym for “That’s the way we have good test for cure. always done it!” But, sooner or later everyone becomes more intelligent and Two Minutes realizes the error of their ways as they grow to realize that they have been do- There is another myth that plastisol ink ing the same thing over and over for must be held at a particular temperayears and were wrong. ture (depending on the resin used by the ink manufacturer) for a certain Stretch Test amount of time, say two minutes. This is a myth based on the fact that dryer The biggest myths concerning plastisol temperature fluctuates as the thermoink cure is that if the ink deposit cracks couple sends a signal to the control when the substrate is stretched it either panel to turn the units on and off. The [1]

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dryer manufacturer and the ink companies want to assure that the ink was in the dryer tunnel long enough to go through one cycle of high versus low heat. The curing of plastisol inks happens instantaneously at a prescribed temperature. The resin opens up, allowing the plasticizer to be enveloped and then as the resin cools a pliable layer of ink is formed. Nothing more than that! Heat Till it Bubbles There is another myth that we should take the ink up until it smokes, or blisters, or bubbles and then back off. This is about as scientific as it gets, right? This reminds me of the T-shirt that I used to wear when I rode motorcycles, "Accelerate until you see the eyes of God, and then stomp on it!" Most likely you are always going to overcure the ink if you are using this as a scientific basis for ink cure. Testing for Cure The only real tests for plastisol cure are the wash test and the chemical test using 99-percent ethyl acetate. However, warning! Ethyl acetate is poisonous and flammable. Always wear butyl or nitrile (not latex) rubber gloves and goggles when handling this chemical. Do not pour directly from the container onto the fabric. Use a glass eyedropper. And, the chemical test can give a false positive due to thick ink deposits and other variables. Getting it Right The greatest error that a screenprinter can make is assuming that the plastisol ink deposit is cured equally on each and every substrate. The first key to cure comes about through an extensive knowledge of the great number of variables in the screenprinting process. The second key is to identify each variable of the curing process to create a standardization of the screenprinting process. The third key is to implement this standardization, while continue to learn more about variables and making small changes as necessary to decrease the likelihood of a failure in the curing process.

cures fine and the plastisol ink washes right out of the next job. Perhaps the plastisol ink deposit almost completely disappears in the laundering process, or it becomes splotchy in some areas and not in others. Other times, the center will disappear and the edges will be fine, albeit in a circular manner. Knowing that the screen, platen, and flash were either square or rectangular in shape this circular pattern perplexes them.

“You don’t understand, we don’t have time to do it THAT way!” Of course, they always have time to reprint the job when it fails. Taking the time to learn about the screenprinting process in depth will greatly benefit the screenprinter who wants to eliminate or decrease the number of variables in the process. The best way to learn anything is to study the process that you use every day. No matter whether you are manual printer working out of your garage or spare bedroom with a one color press and waterbase plastisol ink or a giant facility with three dozen automatics, you have the same ability to learn as everyone. There are many experts in screenprinting that are more than happy to answer your questions and give you the advice you need to excel. Many of them can be contacted by phone, online, at trade shows.

Common sense tells us that surely we can’t be alone on this island of perpetual problems, but where do we turn for the answers? This article will cover the many variables within the screenprinting and curing process that effect the ability of the plastisol ink deposit to properly cure. Even more so, it will provide the reader with the ability to identify and properly diagnose a solution so that the plastisol ink deposit can be cured from job to job with relative ease. Fabric – The Beginning There have been tomes written about the many variables of the screenprinting process and how the variables affect each other. Almost all variables effect the curing process to some (or a great) degree. We will discuss those variables that only affect cure.

The first place to begin our search into knowledge of the curing process begins not with the dryer or plastisol ink, but with the substrates. Yes, the substrate greatly effects the curing process. As we mentioned previously most people overlook this because they believe that it is only necessary to bring Learning the temperature of the plastisol ink to the correct temperature. Unfortunately, Screenprinters have long had a ap- the fabric often dictates the temperaproach of never taking the time to learn ture as much as the plastisol ink. the process well. Fewer than 3-percent of all screenprinters attend any sort of All textile substrates absorb moisture educational seminar, workshop, or to some degree. Again, the plastisol ink class on screenprinting. And of those deposit cannot achieve a full cure until 3-percent that do attend some sort of the reaches this temperature throughtraining, they end up using only 10- out the plastisol ink deposit. It is imporpercent of what they learn. Perhaps it tant to understand that in order for this is the creative spirit of the craft that to happen the substrate must also makes screenprinters want to ignore reach this temperature as well, since the facts and construct their own way the plastisol ink is in direct contact with of doing things. the substrate.

Many times I have shown a screenprinter how to properly coat a screen, only to visit them six-months later and find them doing it backwards. I cannot tell you how many times I have heard of a screenprinter coating screens with one pass on each side of all mesh counts and then thinking that the exposure time for all screens is the same Often, screenprinters experience cur- regardless of the thickness of the mesh ing problems, when nothing has seem- or emulsion. The most often used ingly changed in the process. One job phrase in the screenprinting industry is,

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Yes, the bottom as well as the top of the plastisol ink deposit must reach full cure temperature. Think of trying to cook a pancake as it sits on a block of ice. You may cook the surface, but the bottom will never receive enough heat to cook. This is why we flip pancakes over when cooking on skillet, i.e. to assure heat distribution on both sides. Obviously, we can’t flip the wet plastisol ink deposit over, so we must present an equal heat from above and

below, thus the substrate must be Again, the marketplace will dictate the heated to the same temperature. fabric weight of the substrates we must print on. Screenprinters in colder reFabric variables include fiber content, gions will find themselves printing on moisture content, fabric weight, fabric heavier fabrics than those in the construction and color of the fabric. warmer climates. But, don’t put your business up for sale and start packing Fiber Content your bag yet. There is an easier solution. In many cases the client makes the decision about the fabric content, i.e. The weight of a substrate is deter100-percent cotton or a blend of cotton mined by yarn count of the thread used and polyester. Often they choose 100- and the number of woven stitches per percent cotton based on comfort alone, inch used to manufacturer the subwhen in actuality the blended cotton strate. And, the heavier a substrate is, and polyester substrate give the great- the more moisture it will retain, adest return on investment for them and versely effecting the curing process. the screenprinter. Of course we all The more moisture present in a subknow that a blended substrate usually strate, the more problematic it is to shrinks less, holds it’s shape better remove, in order for the plastisol ink to and wears longer than a 100-percent reach the curing temperature. Lowercotton substrate, but important to the ing the humidity in the facility is often a curing process is that a blended sub- huge undertaking due to the generally strate will better receive, disperse and large area of most screenprinting transmit heat. shops. However, many screenprinters have found great success in lowering A blended cotton and polyester sub- the humidity level of substrates by runstrate will prove better because it’s ning them through a forced air gas non-hydrophilic characteristics. In other dryer just prior to printing them. As a words it doesn’t attract as much mois- general rule, infrared dryers are not as ture as a 100-percent cotton substrate. efficient in removing moisture as most The blended cotton and polyester sub- lack the high concentrations of air flow strate will not absorb moisture and will that are necessary to remove the moisreceive heat faster than a hydrophilic ture from the immediate area of the 100-percent cotton substrate, making substrate and thus the substrates rethe blended cotton substrate a better absorb much the moisture before they substrate for the curing process. leave the tunnel. Moisture Content

Fabric Construction

The moisture content of a substrate is important to the ability of the plastisol ink to reach full cure temperature. Moisture present within a substrate is slower than the cotton fibers and thus moisture must be removed from the fibers before the plastisol can be cured. The moisture begins to dissipate at approximately 155-degree Fahrenheit (68.3-degrees Centigrade). Screenprinters working in areas where the humidity levels are high understand this and make adjustments as required. Those working in low humidity areas will find that they can bring the temperature of the substrate up much quicker and more efficiently than when the relative humidity is high.

The construction of the fabric is important to the curing process as a fabric with a tighter (more threads per inch) stitch density will be smoother and require a thinner deposit of plastisol ink. This is good news as a thinner ink deposit will receive, retain and disperse heat better than a thick plastisol ink deposit. A fabric with a loose weave will require a thicker deposit of ink, which will require more time and heat to bring the thicker deposit of ink to a full cure. Keep this in mind as you choose fabrics for printing.

Fabric Weight

and regretted it because of the extreme heat it absorbed from the sun. Since the fabric must be heated to remove the moisture the darker colors will absorb this heat faster than lighter colors and disperse the moisture quicker. Since most darker fabrics are printed with a heavier deposit of plastisol ink they will need the extra heat to assist in the curing of the underside of the ink deposit. Frame Choice Yes, your choice of frame type can make a huge difference as to plastisol ink cure just as it does to all other variables of the screenprinting process. The reasoning is simple. Rigid, stretch and glue frames cannot attain the higher levels of screen tension recommended by the manufacturers of mesh, and they are incapable of holding the screen tension for more than one job. This of course gives the rigid, stretch and glue frames a very poor return on investment, which should be enough to avoid them. However, more important to our discussion of plastisol ink cure is the inability of these rigid, stretch and glue frames to maintain tension. As the mesh tension is lost from use, the necessary shearing of the ink is decreased, off-contact must be increased and additional squeegee pressure is required. As this tension is lost, the additional squeegee pressure will extrude the plastisol ink from the mesh openings as it is pushed down the substrate. This excessive plastisol ink is then driven into the wales of the substrate and acts as an insulator, shielding the plastisol ink from the heat that is applied.

Color of Fabric

And, worse, the tension will never stabilize and thus the screenprinter will find himself chasing these variables as the mesh continues to lose tension. Finding just two matching, rigid, stretch and glue frames required for holding tight register becomes a physical impossibility.

It is well documented and accepted that darker color substrates absorb heat more than lighter colors. Remember the last time you inadvertently wore a dark shirt for a stroll on the beach

Retensionable frames allow the mesh to be brought to optimum screen tension and maintained at that level, which is needed to minimize the ink deposit and prevent it from being

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driven into the wales of the fabric during the printing process. Additionally, the increase in tension levels reduced the amount of off-contact between the bottom of the screen and top of the substrate. As this space is decreased, so is the pressure needed to push the fabric to the mesh. This decrease in pressure affects the ink deposit to a great degree as it allows the plastisol ink to be printed onto the surface of the substrate in a thinner deposit which is more readily cured. This improved “surface printing” where the ink is applied to the surface of the substrate, in lieu of into the substrate, cannot be accomplished with undertensioned, rigid, stretch and glue frames. With the massive amount of written literature touting the many benefits of retensionable frames it is incomprehensible that manufacturers and distributors continue to make and sell these type of frames to screenprinters. No one tool in the screenprinting process has done more to lower the productivity and profitability of the industry than the rigid, stretch and glue frame. Retensionable frames are favored over rigid, stretch and glue frames for their increased control over tension, offcontact, shear characteristics, squeegee pressure, squeegee speed and registration. Any screenprinter who has studied his bottom line knows the importance of retensionable frames and uses them to his benefit. Yes, you can achieve a level of salable printed work from using rigid, stretch and glue frames, but you will never realize how much more efficient, productive and profitable your shop can be until you decide to print with retensionable frames. Mesh All too often, screenprinters will choose two or three mesh counts based on what they believe to be true and never consider switching to a mesh count that might better achieve a greater degree of detail and lay down a thinner deposit of ink that will easier to cure. Mesh Count Go on any industry message board and you’ll find hundreds of posts stat-

ing that one should always use 110 thread per inch (43 threads per centimeter) mesh to get sufficient coverage when printing white ink on black substrates. Some recommend using an 83 thread per inch (33 threads per centimeter) mesh. Once they begin printing with the recommended mesh counts, they stick with them until one day they attend an industry awards presentation and note that most of the white ink printed on black garments are printed with much finer mesh counts and have a much softer hand. Mesh Selection The object of mesh selection is too choose the best mesh for the individual job. To do so, we must take into consideration the minimum ink deposit that will achieve the coverage that is desired. All that is necessary to achieve the right coverage is to allow for three of the largest particles in the plastisol ink to be passed through one mesh opening. The hard work is already done for you if you will only consult the mesh specifications of the ink manufacturer. They will know how fine they ground the inks and in knowing the largest particle size will make recommendations as to the best possible mesh counts.

place. You measure an inch then, through the loupe, count the threads with your pointer. After two or three tries, most people use the short-cut method of counting a quarter of an inch and multiplying by four to save time. The odd mesh count numbers (305, 330, 355) stem from the fact that mesh is woven in Europe and based on the metric system. An obvious question when troubleshooting a problem print on the press is: "What's the mesh count?" To often, nobody knows and we have to guess or try to find enough open area in the screen to count, which wastes time. To make matters worse, even if they write it on the mesh, many screen makers cover the mesh count label with tape. Don't let them do it. Insist on visible mesh counts! Mesh count is probably the most oftenused screen modification. Choosing a higher or lower mesh count usually creates the most measurable change in ink deposit or ink flow, but we should first consider mesh that will support our stencil before considering ink deposit and flow. Theoretical Ink Volume

Theoretical ink volume is a number assigned to a particular mesh that denotes the amount of ink that will be The thread measurements on manu- transferred by this mesh in comparison facturer’s charts reflect the diameter to other mesh counts. after extrusion, rather than after the tortures of the manufacturing process. The theoretical ink volume is calcuTo measure true thread diameter, use lated from the combination of the open a microscope or loupe with a measur- area and mesh thickness. The volume ing reticle. Measure the thread at the of the open mesh governs the actual center of its span from intersection to amount of ink that a screenprinting intersection. You can also measure a mesh can accept. The calculated acsingle thread with a micrometer. tual ink volume is always higher, but is proportional to the theoretical ink volFor any screen-printing application, a ume. mesh should be selected with ink deposit and ink flow in mind, but chosen Always remember that under ideal according to both mesh count and conditions how the mesh is filled with thread diameter, the combination of ink depends on the squeegee speed, which will define open area squeegee blade characteristics – hardness, angle and finish – and the To measure a mesh count, use a consistency of the ink itself. But make commercial mesh tester. This can be a no mistake about it; if you don’t fill the test-film-positive with a design that mesh opening with ink, the ink transfer makes a distinctive moiré pattern that process is not going to happen well. will indicate the count of the mesh being measured. A slower but more accu- The TIV is a particularly important rate method requires a linen loupe and number in that if after choosing a mesh something pointy to help you keep your count and realizing that an additional Measuring

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15-percent more ink build up is needed, you can refer to the mesh specification chart of the manufacturer to locate a mesh with a TIV that is 15percent higher than the chosen mesh. Given the difficulty of calculating a value based on so many variables, theoretical ink volume provides a more practical alternative for determining ink consumption and the thickness of the printed volume. The Fill Stroke

Granted this whole process is assisted by a careful study of the various components of the ink transfer system – mesh opening, thread diameter, mesh tension, rheology of the ink, completeness of the fill, the angle, pressure and speed of the fill stroke, completeness of fill, and the angle, pressure and speed of the squeegee. While that appears to be a big list, it really is very simple to create a better print than you might think possible.

The fill stroke is my neologism for flood stroke. The flood stroke is actually a misnomer that has caused considerable problems for screenprinters over the years. Flooding the screen with ink will not assist in the ink transfer to any great degree. And, it makes the squeegee have to do the work of what should have been done with the fill stroke.

<strong>Fill Stroke Needed

By filling the screen’s mesh openings completely with a fill stroke you will find that you can achieve a significant deposit with a single squeegee stroke. Why? Because the ink deposit should always be equal to the thickness of the stencil. Read that last sentence again. I don't want you to miss that. The ink deposit should always be equal to the thickness of the stencil.

Squeegee

The fill stroke is the most overlooked tool in the screenprinting process. So much so that many manual press operators mistakenly believe that the fill stroke is not needed. This couldn't be further from the truth. A hard fill stroke is needed to force the ink into the mesh openings to fill the stencil with ink. Too light of a fill stroke will result in Thickness of Stencil = Wet Ink De- mesh openings that are not sufficiently posit filled with ink and a light print.

Ink Transfer

Most screenprinters know that squeegee have a limited lifespan, that can be drastically reduced if the squeegee blade is not cared for. Excessive pressure, chemicals and soaking in ink degradient will soften the squeegee blade. Soft Squeegees

A softer squeegee requires more pressure to push the mesh down to the substrate to allow for the ink transfer to take place. Again, just as with excessive off-contact this excessive pressure drives the ink into the mesh openings as the mesh is pushed down to the substrate and subsequently the excessive ink is pushed into the wales of the substrate. Because the ink is pushed into the fabric the opacity will be lacking and a second or third pass must be made to achieve a sufficient opacity. The squeegees job is to simply push This increase in plastisol ink will not the mesh down to the substrate, allow- only have a harsh hand, it will be exing the wet ink to adhere to the surface tremely difficult to cure. of the substrate. Once the thixotropic ink begins to move it will bond with the Tension Changes Squeegee Choice substrate and when the squeegee passes the tension of the mesh cou- Over the years, tension has been impled with the off contact will pull the proved greatly within the screenprinting mesh from the ink and leave the ink industry. Today, the average tension of deposited on the substrate. screens has increased to a minimum of When you fill the mesh openings with ink you are giving the ink every chance to lay down on the shirt during the ink transfer process. Yes, the ink transfer process – not print stroke. You see the squeegee really isn’t the printing tool that we believe it to be. The ink deposit is controlled first by the stencil thickness (think about thick high density screens for a minute) and second by the fill stroke.

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20-N/cm2. Many printers will print at double that when the mesh can hold such tension. And, as the tension levels have increased, so has the durometer of the squeegees we use to transfer ink. With the higher tension levels, we have an increase in the shear rate and we have found that a harder squeegee blade will produce a thinner ink deposit but lay it on the surface of the substrate, which in effect increases opacity. Just 10 years ago, textile screenprinters were printing with squeegees that hardly registered in durometer. Today, most have understood the need for a harder squeegee and a sharp or slightly rounded edge. The sales of squeegee sharpeners has risen over the past ten years as this understanding has increased. In the past, screenprinters choose a 60, 70 or 80 single durometer squeegee. Today, we find more screenprinters choosing a 70/90/ 70, so called triple durometer squeegee for most work and an 80/90/80 when they print process color, high-end simulated printing or for printing great detail. Squeegee Pressure Excessive squeegee pressure is the curse of screenprinters everywhere. However, few realize the implications of the pressure used on the final print. The most important lesson a screenprinter can ever learn is the ink deposit is control by the stencil – not the squeegee. The squeegee is not the printing tool – the mesh serves this purpose. The sole purpose of the squeegee is to push the ink laden mesh openings down to the substrate so that the wet ink is transferred to the substrate in a capillary action. The Big Error Press manufacturers have pushed the fact that their platen arms do not “give” during printing, or that their automatics will produce more pressure per square inch, further exacerbating the idea that more pressure is better. Squeegee manufacturers have not done better in their advertising that their blades will not flex under pressure. The whole industry has for too many years believed that excessive pressure is the answer to producing a more opaque

ink deposit, when nothing could be further from the truth. Fabric Absorbency

opaque ink deposit, especially when printing on coarse mesh counts. This slightly rounded edge will keep the screenprint operator from applying exThe pressure used during the squee- cessive force, as it wants to glide more gee stroke greatly effects the curing of easily across the surface of the mesh. the plastisol ink deposit. When printing on an absorbent material that will com- When we speak of a slightly rounded press under pressure, one must used edge, we are not referring to what is the lightest possible pressure to pre- called a bull-nose edge, but one in vent the ink from penetrating into the which the sharp edge is only slightly wales of the fabric and down into the feathered. What we are looking for is a material. The ink that penetrates the blade which glides across the surface fabric will be difficult to cure as it is pro- and not one which spreads the ink tected from the heat by the cotton fi- onto the surface like spreading butter bers of the substrate. This was ad- onto bread. A blade edge that is too dressed in a previous section on fabric rounded will cause an excessive choice, as to how fabric density and amount of plastisol ink to be applied weave can have a profound effect on and will cause more curing problems plastisol ink cure. than it appears to resolve. Squeegee pressure is determined by other forces, i.e. that tension of the mesh, off-contact distance and the tack of the chosen plastisol ink. More pressure does not mean more ink deposit – never has, never will. The absorbency of the substrate also comes into play. The more absorbent the material the lighter the squeegee pressure should be to prevent the compression of the fabric, which will only increase the chances of the ink being pushed into the fabric. Squeegee Profile For years it was believed that a rounded edge was needed to place more ink on the substrate. This was before the advent of higher tension levels, increased shear and a better understanding of the ink transfer process. It is true that a slightly rounded edge on the squeegee will cause the squeegee to glide across the surface of the mesh without unnecessary pressure and thus with less pressure the ink deposit will not penetrate the material, but there is much more going on here than meets the eye at first glance. The edge of the squeegee blade has an all important effect on the transfer of plastisol ink onto the surface of the substrate. Most educated screenprinters and squeegee manufacturers agree that a sharp edge on the squeegee blade will give the sharpest print possible when printing fine detail. However, when you want to lay down a significant amount of ink a slightly rounded edge will produce a more

Platens The platen is the object upon which the substrate sits during printing. Far too little concern has been paid to this tool of the ink transfer process. That’s right, it serves more than just a holder for the substrate. The platen construction affects the ink deposit and thus the ink cure in several ways. Platen Composition The manufacturers of presses who use composite wood platens are doing a great disservice to the screenprinting industry. They use these platens to cut costs, just as the car companies no longer place a full size tire in the trunk of inexpensive automobiles. The composite wood will never remain flat and create problems due to the curving of the wood. This curve takes place naturally as the wood absorbs moisture and dries. All wood will warp, even the best Medium Density Overlay (MDO) platens are subject to this warping effect. As the outer edges of the wood, which are not supported, flex upward the surface of the platen is no longer flat. It is true that the squeegee is flexible to a degree, but few squeegees can adequately apply an even pressure across a platen that has been allowed to flex. The result is that the mesh will touch the outside edges of the platen long before the middle of the mesh has reached the surface of the substrate in the middle. As more force is applied to allow the squeegee to come into con-

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tract in the middle, the ink is extruded through the mesh openings and is pushed down into the wales of the substrate. Aluminum Platens The only cure for this is to use aluminum platens, which will remain flat much longer than the wood platens. If you were unfortunate enough to have purchased a press from a manufacturer who uses wood platens you should consider upgrading to high grade aluminum platens. Although the aluminum platens will not stand the rigors of excessive flashing, they will last years longer than their wood counterparts. Rubber Surface The best aluminum platens will have a high density rubber surface mounted with heat resistant glue. The rubber surface helps keep the ink on the surface of the substrate by allowing a little more cushion for the compression of the substrate should the force of the squeegee be too great. Platen Parallelism By platen parallelism we are speaking of the parallelism between the platen and the screen. This is easily adjusted on most professional presses. If you are in the market for a new press, be sure that this parallelism is adjustable. The parallelism effects the ink deposit if the distance at one side or one end of the platen is further away from the mesh. The farther distance will be presented with a thicker deposit of ink, where the closer distance will get a much thinner deposit of ink. These two different thicknesses will not cure the same. While the thinner deposit may be completely cured and launder well, the thicker deposit will be undercured and will fail during the laundering process. When working with a multi-color rotary press the problem is exacerbated by the fact that not all platens may be aligned with any one screen holder properly. You may achieve a good parallel on platen one at head number one, but poor parallelism on head number two. This presents the same problem of differing thicknesses of ink deposit and poor curing.

It is important that the parallel of the press be checked often to assure that the platens and screen holders are parallel with one another. Parallel is not a one time fix. While the press manufacturer may have paralleled the press when it was installed, you are responsible for maintaining that parallel over the lifetime of the press. Some printers check parallel each week or each month depending on the ability of the press and the shop personnel to hold this parallel over time. An article is available from the author on how to achieve this on both manual and automatic presses in the resource list at the end of this article. Platen Plane While parallelism effect the distance between the differing points of the mesh to substrate, the platen plane effects the plane of one platen to another. If one platen is just a bit further away from the screen holder than another platen, the subsequent ink deposit will be thicker on all substrates printed on that platen and thus the cure is affected. Assure that all platens are on the same plane by moving each under a tightly tensioned screen located in any one screen holder. The distance should be the same on each platen. Dryer At last we come to the tool that we once thought to be solely responsible for the curing of plastisol ink. By now, surely you have come to realize that curing is more than running the substrates though the dryer for two minutes at the temperature suggested by the ink manufacturer.

create a sauna, which further complicates the gelling of the ink.

Which Dryer

The selection of a dryer is one of the An infrared dryer with forced air will do most fundamental issues in consider- a slightly better job of helping to reing the productivity and profitability of move the moisture. The addition of the the shop, as well as ensuring the cur- forced air also allows the moisture to ing of the substrates. All too be removed from the tunnel, but a often an owner will choose loss of radiant heat. the press first and then have the salesperson Gas Dryer suggest which dryer matches up to the press. A screenprinter who desires Visit Us Online The real problem begins to achieve maximum effiwhen a shop starts out as ciency, productivity and profa manual shop and then itability will do well to begin grows to an automatic press. with a gas dryer with sufficient The dryer is often not replaced air to drive off the moisture present and becomes a bottleneck in the proc- in the substrates. Not only does the ess. As revenues are not met and the gas dryer with it’s reflective panels problem identified, the dryer is re- provide a more even and consistent placed, but because of a lack of reve- temperature across the surface of the nue an inexpensive dryer that barely substrate and the entire tunnel area, meets the need is purchased. Econom- the gas dryer provide the screenprinter ics should never take a back seat to with the ability to print a wider range of efficiency when looking at production ink systems, such as water-based inks equipment. and solvent-based inks, which do not cure well in an infrared dryer. Infrared Dryer About the Author An infrared (IR) dryer do a very poor job of driving off moisture. As noted in Bill Hood is the author of over a twenty the section on fabric, the dryer that books on screenprinting and in excess would be right for a screenprinter in a of 750 technical articles, which are high humidity area will never work well published at Bill Hood Books. He has for a screenprinter in a low humidity visited and consulted with over 7,500 area. Radiant heat dryers work on the clients worldwide and due to his vast premise of heat absorption though ra- background and knowledge is the most diation. This is why flash units do a sought after consultant in the screenvery poor job of gelling the ink in an printing industry. Hood is a popular and efficient manner. The cost to run a frequent speaker at industry trade flash unit is increased as the moisture shows and open houses throughout content of the fabric increases. The the world. He can be reached through moisture attempted to rise up from the his website at Bill Hood Consulting substrate and is trapped by the flash, http://billhoodconsulting.com. which sits just above the surface of the substrate. This does little more than

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