Pressure-sensitive adhesive thicknesses

Release coatings are important components of pressure sensitive adhesive (PSA) products such as tapes and labels [1]. Release materials are coated onto the backside of PSA tape backings (often called low adhesion backsizes or LABs in this form) to provide the desired tape roll unwind force. They are also coated onto various substrates to form release liners for PSA products such as labels and transfer tapes. Typically the thickness of the release coating is less than 1 p,m, and often times less than 0.1 jLm. Release coatings can be thought of as the PSA delivery system, providing a controlled unwind or release force and protecting the adhesive from contamination and unintentional contact until it is applied. 

In addition to the petrolatum tapes and those based on a laminate of p.e. or p.v.c. with an elastomeric sealant or pressure-sensitive adhesive layer, recent developments have centred around self-adhesive bituminous laminates. These tapes are commonly constructed with a p.v.c. backing, whose thickness ranges from 0 08 to 0 75 mm and a bituminous adhesive compound layer to provide a total tape thickness of up to 2 mm. In order to maintain conformability without compromising impact values, tapes may also be manufactured with a fabric reinforcement within the bituminous layer. 

A simpler test that is used widely also involves adhesive tape. In this, a sample of the treated film is coated with a controlled thickness of a standard proofing ink and the coating allowed to dry completely. A specified pressure-sensitive adhesive tape then is applied under controlled conditions and stripped away the percentage of the ink removed by the tape is assessed by eye. The test has the merit of being easy to perform and when experience has been acquired of assessing the extent of removal of ink it can be remarkably accurate. 

A number of reviews have appeared on the function of different types of photoinitiators and their future development and applications. A number of articles have targeted interest in photosensitive polyelectrolyte diazo systems," pressure sensitive adhesives and coatings, bonding of epoxy resins, electrodeposition materials, heat transfer in thick films, ring opening metathesis and curing for microelectronics. ... 

The PSA tape is manufactured by Compac Industries, Inc. (manufacturer part number 807). The backing is 51 microns thick aluminum foil with a 31 microns thick acrylic pressiare sensitive adhesive. The surface of each sensor was washed with isopropyl alcohol and then blown dry with nitrogen prior to applying the pressure sensitive adhesive tape. Tests were conducted at room temperature using acetone as the liquid. 

With increasing applied stress, the rectangular cross-section of the adhesive under stress will become increasingly trapezoidal until eventually disentanglement occurs (Fig. 11). The test is now terminated, having provided that force necessary to initiate disentanglement. The test also provides secondary information in that, if the adhesive thickness is known accurately and the distance moved before disentanglement is also known from the recorder chart, then the ratio of these two dimensions is a measure of the deformability of the adhesive, a key factor in pressure-sensitive adhesive behavior. 

Pressure-sensitive adhesives are normaiiy supported on backing materiais and soid as tapes, iabeis or sheet products. Their adhesion properties are often tested in the form of tapes cut directiy from such products. Since most adhesion properties are influenced by the nature and thickness of the adhesives and backing Aim iayers, the resuits obtained cannot be regarded as intrinsic properties of the pressure-sensitive adhesives, but are in fact properties of the composite tape. 

The optimal adhesive layer thickness depends on a number of factors. Some bonds, notably Tensile test specimens, are stronger when the adhesive layer thickness is redn-ced. For fracture specimens, including double cantilever beam specimens bonded with structural adhesives (see Fracture mechanics test specimens), optimal bond thicknesses have been identified, although the optimal thickness depends on the loading rate and test temperature. " Enhanced ductility plays a role in this process, and a sufficient quantity of adhesive is desired to dissipate energy (see Peel tests). This latter mechanism is also important in the peel energy of Pressure-sensitive adhesives and other systems. 

As supplied, adhesives can be found in the form of low viscosity liquids, viscous pastes, thin or thick films, semisolids, or solids. Before application to a substrate, an adhesive need not be sticky or otherwise particularly adherent. A distinct exception is the pressure-sensitive adhesive (PSA), which is inherently tacky when first made. Such an adhesive is applied as a thin film with or without a backing, the combination of the adhesive and the backing defining an adhesive tape. The PSA remains throughout its useful lifetime essentially the same material it was when first made. All other forms and types of adhesives undergo a transformation which is central to their function as an adhesive. This transformation is usually carried out through imposition of time, heat, or radiation, either actively or passively. 

A double-coated, pressure-sensitive adhesive tape fixes the panel in place until the one-part polyurethane adhesive has fully cured. As a result of its foam core, the pressure-sensitive adhesive tape is 3 mm thick and ensures the uniform thickness of the adhesive layer. Because the bond of the adhesive tape is highly dependent on temperature, it is advisable not to do the bonding work at high or low temperatures. 

A double-coated, 3 mm thick pressure-sensitive adhesive tape which serves as a mounting aid and spacer to ensure the correct adhesive layer thickness is installed before application of the adhesive. The adhesive bead is extruded parallel to the tape at a distance of about 10 mm onto the top surface of the substructure and the steps are then positioned on the adhesive beads (Fig. 113). 

Six micrometre PEEK film has recently replaced polyethylene terephthalate (PET) as a cover film for thermal-acoustic and burn-through insulation. PET failed the new FAA flame performance tests and alternative materials such as PVDF and polyimides were too dense or not available in the required film thicknesses. The film is installed using PEEK tape coated in an acrylic pressure-sensitive adhesive. PEEK fibre also finds application in high-temperature acoustic blankets based on the Helmholtz resonator effect [2]. 

The U.S. Postal Service has also turned to plastic, to develop a new stamp that could be sold by twenty-four-hour automatic teller machines anywhere. One of the two nonlick postage stamps developed uses a new proprietary Fasson-brand polymer-based pressure-sensitive adhesive. It was developed by the U.S. Materials Group of Avery in Painesville, Ohio. These stamps are printed on a sheet the size of a dollar bill. With the cooperation of banks, consumers would buy stamps and the cost would be deducted from their accounts. Plastic is the only material that could meet the thickness tolerances of automatic bank teller machines. With this stamp, including its adhesive and backing sheet, plastic... 

The form factor for a 25-mm-diameter disk, 2-mm thick, is too high at about 20,000. It is satisfactory for maximum modulus values of about 10 dyn/cm. The usual approach to accurately measure modulus values greater than 10 dyn/cm is to obtain measurements on long samples, such as rods or bars, which allow significant deformation at reasonable forces. The rectangular sample, which is approximately 2i" x i" wide, has a form factor of about 1. This can be used to measure samples in the modulus range greater than 10 dyn/cm. However, it is very difficult to prepare a bar of a pressure-sensitive adhesive at room temperature. Therefore, a small parallel-plate fixture, one which is only about 8 mm in diameter, was employed for all our measurements. 

Double-sided tapes are used for a vast diversity of applications in industry and household. Further important applications are laminating narrow profiles and wide substrates like foams and thick mats to endow them with pressure-sensitive adhesion. Two special applications are ... 

Bond strength is relatively low due to the surface energy of polytetrafluoroethylene. The range of bond strength is 0.1-1.8 kg/cm depending on the type of adhesive. The adhesive can be applied in the form of a fluid by working it on the surface to achieve an even thickness. A more convenient alternative is two sided tapes to which the pressure sensitive adhesive has already been applied. All bubbles should be removed to lessen the chance of delamination and peeling. 

PVC Pressure-Sensitive Tapes. Formulated PVC plastisols are used in automotive applications. A pressure-sensitive adhesive-coated closed-cell PVC tape has replaced butyl glazing tape in some glazing applications. Other applications include automotive, trucks and trailers, mobile homes, steel building erection, metal door gasketing, and sound deadening. Both single-face and double-face tapes are available in various thicknesses, widths, and densities. The pressure-sensitive adhesive is believed to be of the acrylic type. 

This is the ability of the adhesive coat to grab the other part and prevent it from moving immediately after assembly. For pressure-sensitive adhesives, it is the ability to stick immediately after application of the tape or label. Tack develops during waiting time and also it may be provided by a thick and sticky adhesive so that there will be a suction effect, for instance, in mastics. Tack may be measured with many different test methods according to the industries. We will just mention a few of these methods. 

The properties that determine whether a product can be labelled as a pressure sensitive adhesive are tack, peel and creep. Tack is the property related to bond formation. Peel defines the tension or force necessary to remove the adhesive tape. Creep is the property describing the flow characteristics of the PSA. Formulators need to be aware of any factors that can directly affect these three properties such as temperature, aging, film thickness, cure rate and post-cure parameters. There are also several formulation variables - these include oligomer selection, tackifier addition, monomer structure, molecular weight and glass transition - that directly impact tack, peel and creep. 

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