Repositionable Adhesives


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Pressure-Sensitive Adhesive products , are usually bonded , firmly to applied surface.
The PSA product peel -of or delamination is not desired or Intended.
However, there are adhesive tapes where in the , adhesive clean and easy removal from substrates after use is desired.
A repositionable adhesive allows a label to be repositioned without damage , to either the label or the substrate. Many applications require that the adhesive holds the label firmly in place, yet does not leave residue behind when the label is removed.

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Repositionable Adhesives

  1. 1. No : PCP 002 Date : 09 JAN 2014 Removable Pressure Sensitive Adhesive Products However, there are adhesive tapes where in the , adhesive clean and easy removal from substrates after use is desired. A repositionable adhesive allows a label to be repositioned without damage , to either the label or the substrate. Many applications require that the adhesive holds the label firmly in place, yet does not leave residue behind when the label is removed. This material holds items firmly, yet lets you remove or reposition your artwork or matting as many times as you want to, even months later. Use on your computerized mat cutters so your mats won't slip. Also used to hold articles in place that requiring stitching. It resists bleeding, staining, or wrinkling. Should only be used for temporary bonding. This pressure sensitive material can be a range of removable adhesive tapes, clean peel and perm/peel products. Both single and double coated, controlled peel products, designed for clean, residue free removal, even after extended periods History In 1968, Dr. Spencer Silver, a scientist at 3M in the United States, was attempting to develop a super-strong adhesive. But he created a "low-tack", adhesive by accident. It was found to be reusable, pressure-sensitive adhesive . For five years, Silver promoted his invention within 3M, both informally and through seminars, but without much success. In 1974, a colleague of his, Art Fry, who had attended one of Silver's seminars, came up with the idea of using the adhesive to anchor his bookmarks. A year later, in 1978, 3M issued free samples to residents of Boise, Idaho, and 94 % of the people who tried them said 1 The PSA product peel -of or delamination is not desired or Intended. removed from paper without lifting fibers or delaminating it. Page Pressure-Sensitive Adhesive products , are usually bonded , firmly to applied surface.
  2. 2. No : PCP 002 Date : 09 JAN 2014 that they would buy the product. On April 6, 1980, the product debuted in US stores as "Post-It Notes". In 1981, Postits were launched in Canada and Europe. The yellow color was chosen by accident; a lab next-door to the Post-it team only had scrap yellow paper, which the team initially used. Often we require a pressure sensitive adhesive (PSA) bond that is not permanent, and the substrates need to be purposely "detached" at a certain time. Uses for such adhesives include nonstructural applications such as removable labels, masking tape, surface protection films, easily replaceable and removable note paper, and bonding credit cards to mailers. Applications can even include structural applications such as tooling placement, prototyping, and the assembly of parts for eventual reuse or recycling. There are various types of removable pressure sensitive adhesives available to the end-user depending on the degree of bond strength required. PSAs that are filled with microspheres are claimed to be the most repositionable of these 2 Standard Post-it Brand notes have only partial adhesive coating on the back, along one edge. Similar products are used for specialized purposes with full adhesive coating; the US Post Office uses such yellow address labels to forward mail. Introduction Page In 2003, the company came out with Post-it Brand Super Sticky notes, with a stronger glue that adheres better to vertical and non-smooth surfaces.
  3. 3. No : PCP 002 systems. Here "repositionable" is defined as the ability of the substrates to be detached and then rebonded repeatedly. This feature is desired when the bond is meant to be repeatedly detached and rebonded or when substrates are commonly misapplied and need to be repositioned. Thus, repositionable adhesives differ from what is referred to as "removable" adhesives. Removable adhesives are generally those providing an adhesive bond that can withstand the rigors of service but in which the substrates can be purposefully detached leaving little or no adhesive residue. The substrates generally cannot be rebonded once they are detached. Date : 09 JAN 2014 These repositionable adhesives have a unique composite-like structure in which micro-sized spheres are held together by a polymeric binder. The binder also serves as the base polymer in the adhesive formulation. Due to the presence of the microspheres and the discontinuous morphology , the adhesive does not completely wet the substrate to which it is applied. As a result, the adhesive strength is less and does not develop with time as in the case of conventional pressure sensitive adhesives. Microspheres are tiny particles measuring between 10 and 250 microns in diameter. Although they are microscopic in size, these spheres are still much larger than the emulsion particles found in conventional adhesives. The size difference has a Page The concept of a repositionable PSA made by incorporating microspheres into a polymeric binder has been around for several decades. For example, 3M Company's famous Post-It™ Notes product, commercialized in the 1980s, consists of tacky, crosslinked acrylic microspheres, which make "point contact" with the paper substrate4. 3 Mechanism
  4. 4. No : PCP 002 Repositionable adhesives have relatively good coat ability but a low degree of tack and peel strength. If the microspheres are resilient and there is sufficient binder concentration, the adhesive bond results in an even peel strength during separation with little adhesive transfer. Table 1 shows the tack and peel strength of representative permanent, removable, and repositionable (microsphere) adhesive system. Shear strength of a microsphere PSA is very low and generally not measured. Peel Strength gm/25 mm Permanent >2000 Removable 250-275 Repositionable 90-100 Loop Tack gm/25 mm 1400 400 250 Shear High Med Low The Performance Challenges To ensure perfect placement should offer highest degree of repositionability To protect fragile substrate clean removal from varies surfaces like , newsprint, paper, drywall and glass, with no adhesive residue, transfer or ghosting. Durability Reusability like paper tab markers to be used again and again. 4 A repositionable adhesive allows a label to be repositioned without damage to either the label or the substrate. Many applications require that the adhesive hold the label firmly in place, yet does not leave residue behind when the label is removed. PSA Type Page dramatic impact on adhesive tack. By forming a discontinuous film, microsphere adhesives limit physical contact, resulting in low peel, removability and stable tack over time. Emulsion adhesives, on the other hand, use smaller particles, which coalesce into a continuous film and do not allow for easy removal or repositioning. Date : 09 JAN 2014
  5. 5. Most repositionable microsphere PSAs are made from acrylic emulsion base polymers that serve as the "binder" as well as the microspheres. It is important that the microspheres (measuring 10-250 microns) are significantly larger than the emulsion binder particles. The binder concentration must be optimized to the particle size of the microspheres in order to provide the surface morphology that will achieve the best adhesive performance. Microsphere adhesives can be produced via one of two processes. Typically they are formed by a water based free radical suspension polymerization using two acrylic monomers. In this case, the microspheres are acrylic and form together with the base polymer emulsion particles. Another method of production can be to form the base polymer and the microspheres separately and then mix them together in the formulating process. This technique is used in specialized applications as it provides somewhat more control of the end-properties due to the variety of microspheres that can be produced. The adhesive properties of microsphere PSAs are controlled by a number of factors. Most significant are coating weight, particle size, concentration of binder, and monomer characteristics such as glass transition temperature (Tg) and molecular weight. Table 2 provides information on how these factors can be used to control adhesive performance. These factors must be balanced by the formulator and / or converter to provide adhesive properties that are optimized for the specific application. Factor Adhesive coating weight Microsphere particle size and amount of binder Performance Contribution Peel adhesion strength is increased by increasing coating weight. This is not unlike other PSAs. However, with microsphere adhesives too much adhesive on a smooth facestock can cause layering of spheres on top of each other leading to poor cohesive strength. Large particle size microspheres and low binder levels provide rough coatings (lowest adhesion level). High levels of binder and small particle size will lead to smoother coatings and better wetting of the adhesive on the substrate. Smoothest coatings give the highest peel strength and peel values that build over time. The roughest surface will provide the 5 Materials, Handling, and Application Date : 09 JAN 2014 Page No : PCP 002
  6. 6. Molecular weight In addition to lowering the tack and peel strength, repositionable adhesives must also provide a mechanism that counteracts the peel strength development with time noticed with all PSAs. To tackle this, formulators have replaced petrochemical based acrylate esters with esters made from alcohols found in vegetable oils. In general, microsphere PSAs can be used much like conventional PSAs. However, certain Precautions should be observed due to the composite nature of the product. General Avoid high shear forces. Small pumps operating at slow speed and gentle mixing are preferred. Microspheres rise to the top of their container. Gently stir before each use or transfer. Microsphere adhesives are pH sensitive. A pH of 7.9 to 9.5 is recommended. pH can be adjusted with 21% aqueous ammonia. Once microspheres are coagulated, the adhesive is unrecoverable. Storage Shelf life is six months. Store between 10°- 30° C do not freeze. Use partial drums quickly. Pumping and Filtration Be sure to eliminate air from adhesive lines as this will create foam. Do not use felt filter bags. Fine filtration removes spheres; Do not use filters finer than 60 mesh or 250 microns. Change filter bags when pressure exceeds 30 psi. Handling Add all formulating ingredients slowly under gentle agitation. 6 Glass transition temperature, Tg Date : 09 JAN 2014 lowest and most stable peel values. Monomers that form low Tg polymers (e.g., 2-ethylhexyl acrylate provide good tack and flexibility). Comonomers with higher Tg (e.g., methyl or ethyl acrylate) provide higher cohesion and shear strength. This is not unlike other PSAs. Lower molecular weight microspheres adhesive offer higher tack, while higher molecular weights provide better shear strength. Very low molecular weights can produce cohesive strength problems. Page No : PCP 002
  7. 7. Coating Certain microsphere products are capable of being coated by rod, roll, or slot-die coated. Avoid free-fall of the adhesive during the recirculation process. Polymeric microspheres are now helping deliver enhanced performance in many of these areas. Larger than particles found in conventional emulsion adhesives, these spheres have a big impact on adhesive tack. They create a discontinuous adhesive surface that limits physical contact with a substrate, making removability easier. The microsphere adhesive holds labels firmly in place on most substrates yet is permanently repositionable. Typically microsphere adhesives are formed directly from raw materials by a water-based free-radical suspension polymerization using two acrylic monomers. However, for specialized applications the microspheres are sometimes formed by dispersion polymerization in an organic solvent, and then added to a separately-formed adhesive. Component Deionized water Crosslinked acrylic acid Sulfocarboxylic acid anionic surfactant Ethoxylated oleil alcohol nonionic surfactant Ethyl acrylate/2-ethylhexyl acrylate Dibenzoyl peroxide initiator Amount (g) 242.3 8.4 Total proportion 60.57% 2.10% 4 1.00% 3.2 0.80% 141.6 35.39% 0.56 0.14% Suspension polymerizations are heated until the initiators thermally decompose to generate a sufficient number of free radicals to begin the reaction, with nitrogen bubbled through the reaction mixture to deoxygenate it. Monomers are typically already present when the reaction is initiated. Stirring time and speed parameters can be used to control monomer droplet size, with average particle size tending to decrease with increased and prolonged agitation of the reaction mixture. 7 Defoamer can be added to minimize foam (typically 0.1-0.2% if oil based and 0.1% if silicone based). Premix defoamer at a ratio of 1:1 with water. Date : 09 JAN 2014 Page No : PCP 002
  8. 8. Controlling microsphere adhesive performance The adhesive properties of microsphere PSAs are most often modified by varying glass transition temperature (Tg) using different types and amounts of comonomers. Monomers that form low Tg polymers like 2-ethylhexyl acrylate provide adhesive tack and flexibility. Comonomers giving higher Tg polymers like methyl or ethyl acrylate enhance the adhesive's cohesion and shear strength. Varying polymer molecular weight is another way in which microsphere PSA properties can be controlled, especially tack and shear strengths. This can be done through process control, for example by changing polymerization temperature, or by chemical control, by changing initiator concentration or adding chain transfer agents. Lower molecular weight microsphere adhesives show higher tack strength, while higher polymer molecular weights provide better shear strength. Low polymer molecular weights can produce major microsphere cohesivity problems when larger amounts of chain transfer agents are used. The Ethyl Acrylate % ( Increase Ethyl Acrylate and Decrease 2 Ethyl hexyl Acrylate ) is useful in altering the Adhesive Properties . 8 This process yields a process that stable aqueous suspension of microspheres can be used immediately as an adhesive. Alternatively it can be compounded with tackifiers, plasticizers, rheology modidiers, colourants, latex binders and other additives. Date : 09 JAN 2014 Page No : PCP 002
  9. 9. Date : 09 JAN 2014 9 While microsphere pressure sensitive adhesives have proven to be repositionable, the strength of their bonds increases over time. To tackle this, scientists have replaced the petrochemical-based acrylate esters with esters made from alcohols found in vegetable oils. These are produced by reacting acrylic acid with heptanol, octanol or decacnol from sources like coconut oil and palm kernel oil, or animal fats such as tallow and lard. Page No : PCP 002
  10. 10. Carpet tape for Aero Plane. The carpet tape is a double-sided, differentially coated adhesive tape with one clean peel removable side and one very high adhering side. The modified acrylic adhesive on the carpet side provides very high levels of initial tack and adhesion. The unique, clean peel removable acrylic on the floor side provides very secure adhesion to composite floor panels and easy, controlled peel removal with the carpet. Masking of parts during powder coating Masking for Abrasive or Sand Blasting During preparation, items are abrasive blasted to remove oils, dirt, rust and mill scale. Threaded portions of parts are masked to prevent damage. Because of the extreme pressure applied during blasting, duct tape is used to mask for this step. Duct tape is sticky and thick enough to stand up to the heat caused by the friction of blasting parts. Masking for Curing Oven Parts can then be masked to prepare for baking in the curing oven using a hightemperature tape. Temperature-resistant tape comes in many sizes and formulations. These tapes are made from polyester or fiberglass with special silicone-based adhesives able to withstand extended periods at high temperatures. Protection of bright parts Mounting of protection pads 10 Suitable Applications Date : 09 JAN 2014 Page No : PCP 002
  11. 11. No : PCP 002 Date : 09 JAN 2014 as an application tape for auto badges More Applications Ultra Removable Stickers and Labels Mounting of shop front and window graphics Temporary fixing in print finishing and direct mail companies Page Adhesive tape technology is seen as the most flexible, clean and easy solution for the smart card market’s manufacturing process. Adhesive use for module embedding guarantees both card quality and long term resistance, which in turn reinforce the Smart Card security. 11 Mounting of smart cards