泡棉基材压敏胶带的选用(english,来自外国专业网站).doc

Selecting and Using Foam Backed Pressure Sensitive TapesPressure sensitive tape can be manufactured with a foam backing and a pressure sensitive adhesive on either one or both sides of the foam. These products are generally known as mounting tape, double backed foam tape, or very high bond (VHB) tape - a term used by 3M Company, one of the major suppliers of this product.The most recognizable applications are for securing objects such as pictures on walls and attaching plastic body side molding to automobiles. Foam tapes have unique physical characteristics that make them appropriate fasteners in semi-structural applications as well. These important applications include shear wall construction for housing and replacing mechanical fasteners in appliances. Many other sensible structural applications are also possible. Foam backed tapes with PSA on only one side can be used as a cushioning gasket for sealing and insulating objects such as window frames on residential homes and automobiles. They are often found in the do-it-yourself section of local stores for home weather stripping. Whether adhesive is on one or both sides of the foam, these products must have special physical property requirements both for the adhesive as well as for the foam backing. This article will review the various types of foam tapes that are commercially available, their main applications, and considerations that need to be taken into account when using these products. Double sided foam tapes generally consist of four components as shown in Figure 1. These are: The carrier material, which is a foam, A layer of pressure sensitive adhesive on one side of the foam, A layer of pressure sensitive adhesive on the second side of the foam (possibly different from the adhesive on the first side), and A release liner covering one or both of the adhesive layers. (A single release liner is generally used when the foam tape is manufactured in roll form, and two release liners are used when it is manufactured and sold in sheet form.) Double sided foam tapes sometimes use different adhesive types depending on the application. For example, one side may contain a permanent adhesive while the other side uses a removable formulation. Figure 1: Double sided pressure sensitive foam tape. What separates these products from other pressure sensitive products is the foam backing or carrier material. The backing in standard (non-foam) tape constructions includes paper, films, non-wovens, fabrics, and other materials. However, polymeric foam provides good gap filling characteristics, compressibility, and resilience, which contribute to the tapes unique overall performance properties. There are several polymeric foams (see following section) that have been found to be useful in foam tape construction. The choice often depends on the conditions that the final assembled product will experience when in service. The foam carrier comes in various thicknesses to fill the gap between substrates. It also comes in different densities to provide a range of compressibility, strength, and other properties. Lower density foams are generally used for sealing and gasketing, and higher density foams are employed for mounting. Because the foam has a degree of movement or elongation capability, the tape can be applied to substrate that is extensible and conformable without significantly affecting those properties.The adhesive that is used in constructing the foam tape must, of course, have pressure sensitive characteristics. This is provided by the viscoelastic properties such as elongation, stress relaxation, and strain rate dependence of the base polymer used in the adhesive formulation. An optimum combination of these properties is necessary for instantaneous adhesion and adequate tack, peel, and shear strength properties. The adhesive must also have sufficient durability to meet the demands of the application. There are many pressure sensitive adhesives that could be used in foam tape construction and the selection will depend on the application. Although several adhesive systems are used for constructing foam backed tapes, in structural applications only high quality and durable PSAs, such as high-performance acrylic adhesives, are used. The release liner plays an important role in storage, transfer, and application of the adhesive. There are four basic types of release liners used in pressure sensitive tape construction: Kraft paper release liners are generally the least expensive but tend to wrinkle when exposed to humidity. Clay coated paper liners, in contrast, hold their shape in humid conditions and withstand high temperatures but tear easier than Kraft papers. Polycoated paper liners cost more than Kraft or clay coated paper liners but better resist humidity, will not wrinkle, and also lay flatter. However, polycoated paper cant withstand elevated temperatures. Film liners such as LDPE, HDPE, polyester, or polypropylene are generally the most expensive of all but give the highest possible resistance to humidity, and they are the easiest to remove. Foam backed tapes are an attractive bonding method for many applications. They are easier to use than mechanical fasteners or liquid adhesives. For the end-user, there is no polluting or toxic material to encounter, and there is no need for metering and mixing as with many liquid adhesives. Due to the tapes pressure sensitive characteristics, the bond strength is instantaneous and occurs with only the application of hand pressure. There is no need for complicated application or fixturing equipment.The key features with foam backed pressure sensitive tapes is that the foam distributes the stress and acts as a gap filler to take up the space substrates caused by uneven or non-parallel surfaces. The foam also acts as a shock absorber for reducing noise and vibration and providing outstanding impact resistance. What separates these products from other pressure sensitive products is the foam backing or carrier material. The backing in standard (non-foam) tape constructions includes paper, films, non-wovens, fabrics, and other materials. However, polymeric foam provides good gap filling characteristics, compressibility, and resilience, which contribute to the tapes unique overall performance properties. There are several polymeric foams (see following section) that have been found to be useful in foam tape construction. The choice often depends on the conditions that the final assembled product will experience when in service. The foam carrier provides strong support and reinforcement to the holding power of the aggressive pressure sensitive adhesive that is on both sides of the foam. With foam tapes, a significant amount of energy is dissipated by plastic deformation as shown in Figure 2. As a result the stored energy changes if the foam tape is elastically stretched. In addition to having an impact on the stored energy, this deformation also reduces the peel rate and, therefore because of the viscoelastic nature of the adhesive also the fracture energy. The amount of energy dissipated depends on the adhesion of the foam-adhesive-substrate combination, and also on the foam properties such as conformability and ductility.Figure 2: Plastic deformation of foam tape distributes stress over a large area, thereby increasing strength properties. As a result of these processes, the measured strength of an assembly bonded with foam backed tape can be surprisingly high. For example, tensile-shear, peel, and tensile strengths are significantly higher than can be realized with other pressure sensitive products. Table 1 shows typical physical properties and performance characteristics of an acrylic foam tape. This opens the possibility of using pressure sensitive adhesives in semi-structural applications such as replacing fasteners on appliances, bonding architectural fa?de material to frames, and structural glazing. cTest ConditionsValuePeel adhesionASTM D3330 on stainless steel20 pli (350 N/100mm)Normal tensile strengthASTM D897 on aluminum t-block70 psi (480 kPa)Dynamic overlap shearASTM D1002 on stainless steel65 psi (450 kPa)Static shearASTM D3654 at 22C 66C 93C 1000 g/0.5 in2 (holds 10,000 min)500 g/0.5 in2 (holds 10,000 min)500 g/0.5 in2 (holds 10,000 minSolvent resistanceExcellentUV resistanceExcellentTemperature resistance Short term (mins to hrs) Long term (days to weeks)149C 93C Table 1: Physical Properties and Performance Characteristics of Acrylic Foam Tape 1 Because of the compressibility and deformability of the foam backing, these products are capable of bonding to rough or irregular surfaces and filling gaps between the substrates. Conventional pressure sensitive tapes cannot do that because of their thin construction and relatively still nature. As a result, foam backed tapes can be used to provide a sealing function as well as a joining function. Pressure sensitive foam tapes, for example, can be used to seal the glass windows to air flow (Figure 3). Figure 3: Typical assembly configuration of structural glazing using an acrylic foam glazing tape. Selecting between the various types of pressure sensitive adhesive products (i.e., single coated tapes, transfer films, double coated tapes, and double coated foam tape) is generally a straightforward decision. All of these products have ease of application and high initial bond strength. Transfer films and double coated tapes will bond two surfaces together. But only double coated tapes can use two different adhesive systems. However, double coated foam tapes should be considered when the application requires: two different adhesives; dimensional stability; gap-filling; sealing; ease of application; or special properties, such as noise and vibration reduction or thermal isolation. The performance properties of a PSA foam tape depend on several parameters: Type of adhesive Adhesive coating thickness Type and nature (polymer, grade, density, etc.) of the foam carrier Thickness of the carrier Interactions between the carrier material and the adhesive. The interactions of these parameters have been studied for the purpose of developing a general mode. As a result there are many types and configurations of pressure sensitive foam tapes. Table 2 provides properties of only a small selection of the tapes that are possible. Foam Adhesive Density, kg/m 3Thickness,mmTensile Strength, kg/cm2Elongation, %Peel Adhesion, gm/cmTemp Limit, CPVCAcrylic2560.790.68150500-18 to 711.56PUAcrylic4000.790.50350710-35 to 931.591.343.122.06Rubber0.790.505351.591.343.122.06PERubber960.700.89250557-29 to 821.52Table 2: Properties of Pressure Sensitive Foam Mounting Tapes2 Although other adhesives can be used in foam tape constructions, acrylic and synthetic rubber (generally styrene block copolymers) have been used in most applications. Within these two types of PSAs, there are many variants and a significant range of properties is possible. Table 3 shows a general comparison of acrylic and synthetic rubber adhesives.PropertyAcrylicRubberTackLow / moderate / highTypically high180 peel adhesionLow / moderate / highModerate to highStatic shear strengthLow / moderate / highLow / moderate / highHumidity resistanceExcellent ExcellentAged peel adhesion Increases with timeConstant with timeService temperature range-40 to 122C+30 to 66CEnvironmentIndoor and outdoorIndoor onlyUV resistanceExcellentPoorAdhesive colorClear to strawYellow (discolors with time)Solvent / chemical resistanceVery goodGoodPlasticizer resistancePoor to fairGenerally poorTable 3: Comparison of Pressure Sensitive Acrylic and Synthetic Rubber Adhesives 3 Rubber based adhesive generally exhibits a higher initial level of adhesion (tack) than acrylic PSAs, but in the long run they offer significantly less ultimate shear strength. Acrylic based adhesives are also better for permanent bonds due to their relatively good temperature and aging resistance. They also provide increased UV and solvent/chemical resistance when compared to rubber adhesives. Proper adhesive must be chosen not only based on their adhesion to the substrate but also based on their adhesion to the foam backing. For example, the adhesive must not be affected by plasticizer migration from the foam material.Polyethylene (partially crosslinked), vinyl, urethane, and polychloroprene (neoprene) foams are generally used in most mounting tapes. However, acrylic and elastomeric foams can also be used. Table 4 offers a summary of the different types of foams that are conventionally used in mounting tapes.Type of FoamCharacteristicsPolyurethane Tend to swell in contact with oils and solvents, especially with an open cell structure Low density used for sealing, insulation, and general purpose mounting High density used for high strength mounting application Can be open or closed cell Vinyl Good resistance to oils and water. Appropriate for general purpose applications Plasticizers tend to migrate into the adhesive interface causing lower bond strength Close cell structure of limited compressibility Neoprene Very resistant to oils, solvents, and water Relatively expensive Tend to have closed cell structure with limited compressibility Polyethylene Generally partially crosslinked via radiation processing Relatively inexpensive Closed cell structure tends to limit compressibility Lower resistance to heat than the other types of foam Acrylic Excellent weathering resistance Good balance of properties; most often used in structural glazing applications Foam can be clear or white Closed cell structure Table 4: Summary of Foams Used in Pressure Sensitive Mounting Tapes The foam is available in several configurations: cell size, bulk density, and thickness. High density foams with a well adhered skin are generally used for mounting foams. Low density foams are used for sealing and insulation purposes and also for miscellaneous general purpose uses where the low cost of such foams becomes an important advantage. For rough surfaces, softer foams will offer higher peel strength values because they are more conformable and adjust better to uneven surfaces. The pressure needed to fix a soft or thick foam to a substrate is generally lower than for a hard and/or thin foam. Double sided foam tape can bond similar or dissimilar surfaces. It is often used in an intermediate step where it bonds a single substrate that then gets processed (e.g., die-cut). Double sided foam tape can be the primary means of fastening or used to temporarily hold substrates together during assembly, machining operations, or other processes. Double sided foam pressure sensitive tapes have become a mainstay in the automotive industry. Double coated tapes attach exterior trim, emblems, nameplates, mirror assemblies, and carpet. Double coated foams dampen vibration and attenuate sound. Single coated foam can be applied as a pre-formed gasket or seal. Appliance manufacturers also use foam PSA tapes as assembly aids. Because of their ability to adhere to irregular surfaces, they help secure door handles, gasketing, microwave door linings, and affix wire and cable clips. Foam tapes are also used for attaching nameplates, emblems, and graphic mountings because of their good edge bonding capabilities. A large application of double backed foam tape is the application to traffic signs. Signs constructed with foam tape have withstood winds of 153 km/hr and high speed auto crash tests.4 However, the main benefit over mechanical fasteners is that through-holes are prevented, thus, decreasing the opportunity for corrosion and increasing sign visibility. Heitman performed one of the largest published studies on the possible engineering use of foam tapes . This research studied the structural engineering properties of acrylic foam tapes used to attach glazing elements in curtain wall applications. The results of this study indicated that short term strength requirements in shear and tension were easily met or exceeded. The adhesive tape also performed well in environmental tests. Creep endurance was the limiting factor for th