Industrial PSA

The age of pressure swing adsorption (PSA) began so far as air separation is concerned in the late 1950s. The first process patent was that of Skarstrom [12]. The scientists and engineers of the Linde Laboratories were very active in this field. It is worth mentioning that the discovery of synthetic zeolite molecular sieves was 

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The purity of Ar in the high pressure cycles was limited to 50%. The purity and recovery were improved in subadnospheric cycles with a consequent loss of productivity. In blowdown steps, oxygen product was also concentrated to %-98% with recovery up to 90%. It is noted that 3 and 1 atm are the pressures of product in the two main industrial PSA air... 

Failures or weakening of barriers are frequent causes of undesirable incidents in the petroleum sector. The Petroleum Safety Authority in Norway therefore states in the Management Regulations that the relationship between risk assessments and barrier management must be clarified by the industry (PSA, 2010). This relationship is essential for the successful risk management of operations. 

As mentioned in the background section, barrier management has been highly focused in the Norwegian petroleum industry lately. Safety barriers are implemented to avoid hazards or accidents. When several barriers are in place to prevent an undesirable event or accident, this is often referred to as defence in depth . The principles apply to safety in rig move operations as well. Severd barriers must fail simultaneously in order for an accident to occur. This is often illustrated by the Swiss cheese model (Reason, 1997). The following barrier definitions are based on the memo Principles for barrier management in the petroleum industry (PSA, 2013) ... 

The sedimentation methods of particle size analysis, both gravitational and centrifugal, have, over the years, generated many contributions and are still extensively used in many traditional industries. PSA 91 saw however only three such contributions [Allen (2) Bernhardt], one which was a Keynote lecture reviewing the historical developments of this fundamental method. The Andreasen sedimentation technique and sieving continue as essential methods used for the characterisation of many certified reference materials. 

DPA), or by reducing the total pressure, as in pressure swing adsorption (PSA). Industrially, PSA is the predominant type of adsorption cycle used for gas separation, although TSA is also quite common. These processes are alternatives to other traditional and more energy-intensive cryogenic and distillation processes. 

Pressure sensitive adhesives typically employ a polymer, a tackifier, and an oil or solvent. Environmental concerns are moving the PSA industry toward aqueous systems. Polymers employed in PSA systems are butyl mbber, natural mbber (NR), random styrene—butadiene mbber (SBR), and block copolymers. Terpene and aUphatic resins are widely used in butyl mbber and NR-based systems, whereas PSAs based on SBR may require aromatic or aromatic modified aUphatic resins. 

There is second shear adhesion test that is now being reported with increasing frequency, the so-called SAFT, or shear adhesion failure temperature test. It is particularly popular among block copolymer PSA developers. In this test [15], a shear specimen with an overlap area of 2.54 cm x 2.54 cm is prepared and suspended in a circulating air oven. A 1-kg weight is attached to the tape and the oven temperature is raised continuously 5.5°C per 15 min until failure. An industry wide standard has not yet been written for this test. 

Acrylics are some of the most common and most versatile materials used in the PSA industry. Although the basic monomers and some of the acrylic polymers have been known for about a century, their commercial application as pressure sensitive adhesives did not happen until after the Second World War. 

A significant step towards commercial success came with a discovery in the late 1950s by E. Ulrich at 3M when he found that copolymerization of hydrogen bonding monomers, like acrylic acid with alkyl acrylates resulted in cohesively strong, yet tacky materials [63]. Since then, newer developments in such areas as polymer crosslinking, and the synthesis and copolymerization of new monomers, have led to a rapid penetration of acrylics throughout the PSA industry. 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

An example of the contribution of polar interactions between an acrylic PSA and a substrate is shown in Fig. 6. By copolymerizing iso-octylacrylate and acrylic acid, using a monomer ratio of, respectively, 95/5 and 90/10, two otherwise identical PSAs were made. The PSAs were laminated to both sides of a foam core to make an attachment tape as used in the automotive industry for the application of body side moldings to a car. One side of the foam tape was laminated against an aluminum foil backing. The other side was laminated against an automotive paint-coated panel to make the final test sample. The test sample was allowed to... 

Rosin and its derivates have shown wide compatibility with a broad range of acrylics and other PSA polymer precursors. This property has made them one of the most common tackifiers in the industry. 

One of the important breakthroughs in the silicone PSA industry has been the development of new release liners based on fluorosilicones [116]. These new materials significantly improve the release characteristics of the silicone PSAs, something that has been difficult to achieve because of the high adhesion silicone PSAs show to low energy substrates, including silicone rubbers and liners. 

Besides the higher volume pressure sensitive adhesives discussed above, the industry also uses other synthetic elastomers as the base component for PSA formulation. Most of these elastomers require some form of tackification to make the materials tacky. However, a few materials are low enough in Tg and sufficiently compliant to be useful without requiring compounding with tackifiers. 

One class of materials with some inherent PSA properties includes polyvinyl-ethers. Vinyl ether monomers are industrially derived from the reaction of acetylene with alcohols [117]. The most common alcohols used are methanol, ethanol or isobutanol. A generic structure of the vinyl ether is shown below ... 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Because of their ease of use and their cost-effectiveness relative to other methods of assembly, pressure sensitive adhesives continue to penetrate all kinds of industrial applications. Some of the main reasons PSAs and PSA coated articles are prime candidates for industrial applications include the following ... 

PSA coated tapes are used for a variety of applications in the electrical industry, but they have to meet additional requirements to be accepted in this industiy The adhesive are typically expected to be non-corrosive, they need to have good dielectric properties, they need to hold out moisture, and they need to show good flame retardaney. Espeeially for eleetronic applieations, little or no outgassing is aeceptable, and the adhesive should not introduce migratory contaminants resulting from exposure to release coatings or the presence of additives. 

Another important application area for PSAs in the electronic industry focuses on the manufacturing, transport and assembly of electronic components into larger devices, such as computer disk drives. Due to the sensitivity of these components, contamination with adhesive residue, its outgassing products, or residue transferred from any liners used, needs to be avoided. Cleanliness of the whole tape construction becomes very critical, because residuals like metal ions, surfactants, halogens, silicones, and the like can cause product failures of the electronic component or product. Due to their inherent tackiness, acrylic PSAs are very attractive for this type of application. Other PSAs can be used as well, but particular attention has to be given to the choice of tackifier or other additives needed in the PSA formulation. The choice of release liner also becomes very critical because of the concern about silicone transfer to the adhesive, which may eventually contaminate the electronic part. 

Pressure sensitive labels and tapes for the consumer markets form a very significant portion of the PSA industry. Whereas the original products were rather simple in construction and use, today s products often perform unique functions that result from more sophisticated assembly of a label or tape product. Examples of these unique functions include the monitoring of food or drug storage conditions, or the ability to monitor the charge status of a battery. 

Most types of PSAs have found some application in the label industry. Block copolymer-based adhesives are perhaps the most popular because of their high adhesion to a variety of surfaces, their low cost, their good performance over a range of temperatures and peel rates, and their ease of processing. For applications where high temperature performance is required, block copolymers have been formulated with high T end block associating resins or polymers. 

Significant advances in the synthesis, design and fundamental understanding of these viscoelastic materials have fueled the tremendous growth of the PSA product industry and opened up a variety of often demanding new product applications. There is every reason to believe this growth will continue since these products provide convenience and versatility for both the industrial and consumer market. 

It is noteworthy that an important industrial application is based on pure silicone network [9]. This is the organic PSA release technology where an uncured silicone is deposited as a thin coating to a flexible substrate. Strong adhesion develops at the silicone-substrate interface whilst the coating cures. 

Because most plastic bottles are recycled, it is necessary to separate the label and adhesive from the bottle. The label is contaminated with ink and not recyclable. The adhesive is also not recycled. Ideally the adhesive will stick tenaciously to the film, but release cleanly from the bottle during the recycling operation. Adhesives designed to aid in recycling have been developed for this market. They incorporate conventional surfactants in place of some or all of the oil in PSA compositions [69] or use ingredients such as rosin which when neutralized by base can function as surfactants. A goal of the recycling industry is to eliminate the need to use base in the process. 

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