This discussion reviews conventional doming techniques and reveals methods for applying domed emblems to textiles.
The industry for domed labels and decals has grown enormously in recent years. In fact, polyurethane-resin doming is currently one of the fastest growing markets in the field of industrial graphics and product identification. Domed labels are everywhere: on cars, cameras, microwaves, DVD players, freezers, stereos, and just about every other type of consumer item. One reason for the increase in demand is that doming greatly enhances the appeal of an otherwise conventional, flat, and lifeless label. Doming dramatically transforms graphics into interesting, three-dimensional, decorative items and produces a high-gloss finish that enriches the printed colors (Figure 1). The doming process is particularly effective when used on metalized polyester, where the mirror finish accentuates the light-bending effects of the dome, creating additional depth and interest. In addition to increasing visual impact, the dome also serves to protect the image from damage. Polyurethane domes are very durable, and their self-repair properties enable the surface to recover almost instantly from indentations. Polyurethane doming resins are UV stable and non-yellowing, even when used outdoors for several years. Furthermore, the UV inhibitors used in the polyurethane coating greatly prolong the life of the printed image. Despite the proven popularity of domed labels and decals in the field of product marking, they are rarely seen on garments or other fabric surfaces. This is because the normal method of applying a pre-printed, domed, self-adhesive polyester or vinyl label to the product is only satisfactory if the surface to be marked is rigid and non-porous. The visual impact provided by the contrast of a glossy domed surface with the matte texture of the surrounding fabric holds the promise of enhancing many textile products. Consequently, the practice of applying domed emblems to T-shirts, sports bags, sneakers, baseball caps, raincoats, and a range of other fabric and leather goods is growing in popularity (Figure 2). Producing domed graphics for fabrics requires a few alterations to conventional doming techniques. We'll begin by reviewing those techniques, then consider the limitations fabrics introduce to the process and explore a method for overcoming those limitations. Doming basics A typical doming application involves the dispensing of a liquid polyurethane resin onto a printed label or decal in a measured amount. The liquid resin then flows over the surface until its progress is interrupted, usually by the cut edge of the label. Surface tension then holds the liquid in place, and it begins to cure after seven or eight minutes. Cured resin is dry to the touch after about one hour. These setting times assume a normal room temperature of approximately 70°F (21°C). The curing process can be accelerated by the application of heat; for example, placing trays of freshly domed labels into special cabinets heated to 90-100°F (32-38°C) reduces the cure time to approximately 20 minutes. Alternately, the domes can be cured inline by means of a conveyor equipped with an infrared heat source. Resin-dispensing machines can be either manual or configured to varying degrees of automation. They come in different levels of sophistication, depending on the type and number of labels to be treated. As a guide, you can expect that a semiautomatic machine, such as the unit shown in Figure 3, would dome approximately 50,000-60,000 1-sq-in. labels per day. You could produce considerably more with a fully automatic model. The method of printing employed before doming is not critical. Screen printing, flexography, letterpress, thermal imaging, and inkjet can be used successfully. Water-based inkjet printing can present special problems, however, because the liquid polyurethane can react poorly with the coatings applied to polyesters to make them receptive to the water-based dyes. Only recently have coated polyesters been developed that guarantee compatibility with the doming-grade polyurethane. Challenges in unique applications As explained previously, the label's cut edge acts as a temporary barrier that holds the resin for a vital few moments until it begins to gel. However, problems can arise when no such cut edge is available. Also, because the polyurethane is applied as a liquid, it is essential that the surface of the label be non-absorbent; otherwise, the doming material will not pool on the surface to produce the desired dome effect. Hence, it is generally not possible to dome directly onto woven materials. One method used to overcome this problem is to frequency weld the dome to the fabric. This method presents a number of drawbacks. For example, the label must have a matching piece of weldable plastic positioned on the inside face of the fabric area to be domed. If the backer is not in precise alignment with the domed label on the face of the garment, a satisfactory weld will not be achieved. For this reason, it can be difficult to apply welded domes to finished articles, particularly if they are lined inside, as with some jackets or bags. Furthermore, the welding process can leave the domed area with a slightly rough edge that contrasts noticeably with the smoothness of the dome and can detract from its finished appearance. Another technique uses screen printing for both the background and for the printed image. The drawback with this system seems to be the number of colors that can be incorporated into the design. However, there is now a method of production that will allow the use of digital printing, giving almost total freedom of design and color. In addition, inkjet printing offers the flexibility of profitably handling the short print runs often required in the decorated-garment and ad-specialty markets, as well as being practical and economical for longer run lengths. These digitally printed and domed labels for use on woven fabrics have all the rich, vibrant colors associated with normal domed labels, not the muted effects often produced when digitally printing directly on garments. Applying domed graphics to garments A heat press is a fine tool to use for adhering domed graphics to garments. This method offers the advantage of overcoming the absorbency of the fabric, while simultaneously making the application of the finished dome almost foolproof and virtually eliminating risk of damage to expensive, completed items. In addition, the garment's fabric integrity is retained, because the labels are securely attached to the garments without the need for any stitching. This is a particular advantage when applying domed graphics to waterproof materials, where stitching can open routes for moisture to penetrate the garment's protective coating. The apparent simplicity of this heat-press solution is, however, complicated by the fact that the heat required to secure a satisfactory bond to the fabric damages normal doming-grade polyurethane. One way around this is to use adhesive products that work at lower temperatures to bond the emblem to the garment. But these adhesives can sometimes adversely affect the strength of the bond of the dome to the fabric. Also, certain fabrics can be difficult to bond to satisfactorily, unless a high enough temperature is used in the heat press. Similarly, some rubberized fabrics can present problems if the heat is not sufficient. The key is that the dome be able to withstand the heat of the press at the point of application, for a sufficient time, without the process degrading the pristine surface of the dome. In addition to heat resistance, the polyurethane used for garment doming should be formulated to be much softer when cured than the domes produced for application to rigid surfaces. This also presents special problems for the chemist, because the softer the material, the more susceptible it is to heat damage. The good news is that extensive research and development have yielded a doming-grade polyurethane that is capable of weathering all of these extremes. Designing graphics for fabric doming It's important to consider the size of the domed graphic that you want to apply to garments. Domes are so eye-catching that the best effect is often obtained by using quite small and discreet domed images. Small domes add a look of quality to the product, but the effect can be diminished by the use of domes that are too large. Smaller domes are also very cost effective in use. You can, and indeed you should, expect to use much smaller images than you would with embroidery or screen-printed heat transfers. You will find that your customers will typically choose to have much smaller images with domes than they would with other methods of garment decoration. In addition to determining the appropriate size, you should also give careful consideration to the shape of the domed emblems for application to garments. It used to be that square labels had to have rounded corners to be domed satisfactorily. Improvements in the flow characteristics of the latest doming polyurethanes remove such restrictions from many general doming applications. However, I strongly recommend that you limit the shapes for garment-bound domes to round and elliptical shapes or rectangles with rounded corners. Sharp corners can be uncomfortable for the wearer, and they can decrease wash resistance. You can give your customers an idea of what to expect by producing conventional, domed labels as samples, or even create short production runs of domed labels by using small, twin-pack cartridges of polyurethane resin and a hand-held dispenser (Figure 4). This method is popular in the field of ad specialties, for example, where small quantities of many different sizes of labels are required. It also has the advantage of allowing the production of high-grade domed labels with virtually no capital expenditure. Kits that contain all of the necessary equipment and supplies are available for as little as $160 (Figure 5). The subject of adhesion is rarely discussed when it comes to conventional domed badges and decals that are applied to rigid surfaces. Customers take it for granted that the dome will stick to their product and stay there. The situation is somewhat different when doming for fabrics. Expect customers to ask how many washes a domed garment can withstand. The answer depends on a number of variables, so you need to ascertain the following. * What is the fabric type to which the domed decal will be applied? For example, adhesion will normally be better to cotton than to a monofilament synthetic fabric. However, bathroom towels are normally made of cotton, but they can present particular challenges, depending on the length of the surface pile on a the particular towel. * What temperature and dwell time will be used for the heated press at the point of application of the dome? It is tempting to cut corners to save time at the point of application, but this can result in reduced bond to the fabric. * What is the temperature and time of the wash cycle? Compare the rigors of a commercial laundry, processing rented work wear that is aggressively washed every week, to a domestic washing machine doing the weekly wash. In the final analysis, only actual wash tests will determine the true answer, and if you are offered a large contract, you should give serious consideration to conducting rigorous wash tests before going into production. But, purely as a guide, I have tested a cotton T-shirt decorated with a domed label for 50 washes and didn't notice any fading of the print or conspicuous lifting of the of the dome from the fabric. Just dome it As with any printing and finishing process, there are variables inherent to domed garment graphics that you must sort out. You also may need to contract the doming work to avoid potentially costly investments in high-output machines. But whether you send out your doming work or invest in the equipment to do it yourself, one thing is for sure: You can boost the appeal of printed garments when you permanently attach a domed decal to the fabric. About the author Mike Mockridge is president and CEO of Mockridge Doming Systems Ltd., which is a division of Mockridge International Ltd., Greater Manchester, England. Mockridge is a Freeman of the City of London, as well as a director of the SGIA. He has lectured and advised on the subject of doming in many countries throughout the world. Mockridge can be contacted through his company's Website at www.mockridge.com.
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