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Chemic science associated with pressure-sensitive adhesives

The chemistry of pressure-sensitive adhesives describes the chemical science associated with pressure-sensitive adhesives (PSA). PSA tapes and labels accept become an important part of everyday life. These rely on agglutinative material affixed to a backing such as newspaper or plastic pic.

Because of the inherent tackiness of the adhesive material and low surface free energy, these tapes can exist placed onto a diverseness of substrates when low-cal pressure level is applied, including paper, forest, metals, and ceramics.

The design of tapes requires a balance of the need for long service life and accommodation to a variety of environmental and human furnishings, including temperature, UV exposure, mechanical article of clothing, contamination of the substrate surface, and adhesive degradation.^[1]

Composition [edit]

A typical PSA record consists of a pressure-sensitive adhesive (the sticky part of the tape) coated to a backing material. To prevent the agglutinative from sticking to the bankroll when wound in a gyre, a release amanuensis is applied to the backing or a release liner is placed on the adhesive. Sometimes a primer is coated between the agglutinative and backing increasing the bond.

Common adhesives [edit]

Tabular array ane: Glass Transition Temperatures and Surface Energies of Typical Acrylate Monomers Used in Tape Adhesives

Substance	${\displaystyle {T_{chiliad}}}$ (K)	${\displaystyle \gamma }$ ( ${\displaystyle {mJ \over thousand^{two}}}$ )
two-ethylhexyl acrylate	223	29.vii[2]
n-butyl acrylate	219	32.8[two]
methyl acrylate	286[iii]	39.8[two]
t-butyl methacrylate	503	thirty.5[2]

Structure [edit]

Pressure sensitive adhesives are viscoelastic polymers with their rheology tuned to the desired bonding and de-bonding characteristics needed.^[4] Typical materials used to make the adhesive include:

• acrylate polymer,^[5]
• rubber, either natural rubber or synthetic thermoplastic elastomer
• silicone prophylactic
• and others

These materials often are blended with a tackifier to produce permanent tack ("grabbing power") at room temperature,^{[5] [6] [7]} are somewhat deformable, take depression surface energy,^[five] and are moisture resistant.^[8] To come across these requirements, these materials are typically low cantankerous-linking density, depression viscosity (η < 10,000 cP),^[5] and broad molecular weight distribution^[v] to enable deformation of the adhesive material to the crude surface of the substrate under diverse temperatures and peel conditions.

Two components ofttimes comprise the adhesive: a loftier tack and low tack textile. The loftier tack material is a polymer with low glass transition temperature and high entanglement molecular weight, whereas the depression tack polymer has high drinking glass transition temperature and depression entanglement molecular weight.^[5] The high tack material comprises virtually 95% of the adhesive and provides the majority of the agglutinative's tackiness.^[5] In addition to these 2 components, surfactants are frequently added to reduce the surface energy of the adhesive and facilitate adhesion to high surface energy substrates (metals, other polymeric materials).^[9] A list of typical acrylate monomers and their drinking glass transition temperatures ( ${\displaystyle {T_{g}}}$ ) and surface energies ( ${\displaystyle \gamma }$ ) are shown in the Table.^[10] The ${\displaystyle T_{one thousand}}$ of a binary agglutinative mixture of acrylate monomers can be estimated using the Gordon-Taylor equation, where ${\displaystyle {\phi _{1}}}$ and ${\displaystyle {\phi _{2}}}$ are the volume fractions of homopolymers with glass transition temperatures ${\displaystyle {T_{k,1}}}$ and ${\displaystyle {T_{m,two}}}$ , respectively.

${\displaystyle {T_{1000}}={\phi _{one}T_{g,1}}+{\phi _{2}T_{g,two}}}$ [Gordon-Taylor Equation]

Production [edit]

Polyacrylates used in adhesive tapes are readily synthesized by complimentary-radical polymerization.^[five] These polymerizations can exist initiated thermally or photograph catalytically using azo- and peroxide-based initiators.^[v] Such polymerizations are typically carried out in solvent to produce a water-resistant, homogenous coating.^[5] Because h2o-permeable adhesives are undesired, adhesives are not synthesized by emulsion polymerization, which introduces h2o into the adhesive.

Mutual components [edit]

Bankroll [edit]

The agglutinative is coated onto a flexible material (the bankroll) such equally paper, foil, textile, or plastic film (such as biaxially oriented polypropylene or polyvinyl chloride^{[5] [vii]}) to provide strength and protect the adhesive from degradation by environmental factors including humidity, temperature, and ultraviolet light. Backing tensile forcefulness, elongation, stiffness, and tear resistance can be matched to the intended utilise of the tape. The adhesive tin be spring to the backing through surface treatments, primers, heating, or UV curing.^[5]

Release coating [edit]

To allow for the winding and unwinding of the record, the backing is coated with a release agent that somewhat prevents the tape from sticking to itself or the sticking of two adhesive layers (double-sided tapes). This is achieved by using a cloth that enables the easy removal of favorable interactions at the adhesive-backing or adhesive-agglutinative interface, or by making both surfaces immiscible in one another. Two mutual materials used in polyacrylate-based adhesive tapes are fluorosilicones^[7] and vinyl carbamates.^[5] Fluorosilicones are immiscible with the polyacrylates-based adhesive^[7] whereas the long tails of vinyl carbamates form a high crystalline structure that the adhesive cannot penetrate.^[v] Furthermore, during peeling fluorosilicone release liners make no dissonance^[7] whereas vinyl carbamates brand loud noises.^[5]

Adhesive-bankroll interface [edit]

Plastic films tin can have the surface modified by corona treatment or plasma processing to allow increased bonding of the agglutinative. A primer layer tin also exist used for this purpose. Some backings need to be sealed or otherwise treated before adhesive blanket.^[5] This is especially important when the introduction of new materials into the agglutinative can compromise the agglutinative's operation.

Application [edit]

Pressure sensitive adhesive tapes usually require a light pressure to ensure bonding with a substrate. This depression pressure requirement allows easy application to surfaces by simply using fingers or hands to utilize pressure. The pressure applied to the tape allows the tape to have better contact with the surface and allows the physical forces between the two to build up. Usually, increased application pressure increases the bond of the agglutinative to the substrate. PSA record laboratory testing is often conducted with a two kg roller to increase test uniformity.^[11] PSAs are able to maintain their tackiness at room temperature and practice not require the use of additives such as h2o, solvents, or heat activation to exert strong adhesive forces on surfaces. Due to this PSAs are capable of being practical to a variety of surfaces such as newspaper, plastics, wood, cement, and metal. The adhesives have a cohesive holding and are also rubberband allowing PSAs to be manipulated past mitt and also be removed from a surface without leaving behind whatever residual.

Ecology factors [edit]

About PSAs are best suited to be used in moderate temperatures of around 59-95 °F.^{[12] [ unreliable source? ]} Inside this temperature range typical adhesives maintain their residuum in viscous and elastic behavior where optimal surface wetting tin can be achieved. At extremely loftier temperatures the tape may be able to stretch more than it could initially. This could cause issues after application to the surface because if the temperature drops the tape may experience additional stress. This may lead to the tape losing some of its contact area, lowering its shear adhesion or holding power. At lower temperatures the agglutinative polymers go harder and stiffer which lowers the overall elasticity of the tape and begins to react like drinking glass.^[12] The lower elasticity makes information technology harder for the adhesives to be in contact with the surface and lowers its wet-power. An adhesive can be formulated to maintain tack in libation temperatures or a greater amount of adhesive blanket on the tape may exist necessary. The bankroll of the adhesives may likewise be plasticized in order to lower its glass transition temperature and retain its flexibility.^[12]

Substrate-adhesive conditions [edit]

Bonding force [edit]

The surface energy of the substrate decides how well the adhesive bonds to the surface. Substrates that accept low surface energy prevent the adhesives from wetting out while substrates with high surface energies will allow the adhesives to spontaneously wet out.^[thirteen] Surfaces with high energy take greater interactions with the agglutinative, allowing it to spread out and increase its contact area. Surfaces with depression surface energies may undergo corona or flame treatment in order to enhance its surface energy.^[13] However even if a surface has loftier free energy, contaminants on the surface can interfere with the adhesive's ability to bond to the surface. The presence of contaminants such as dust, paper, and oils will reduce the contact expanse for the adhesives and lower the adhesives bonding force. If contaminants are present it may exist necessary to clean the surface with a suitable solvent such as benzene, alcohols, esters, or ketones.^[xiv] Surfaces with textures may besides lower the bonding force of an adhesive. Textures create an uneven surface which will brand it harder for the adhesives to be in contact with the surface thus lowers its wetting ability.^[13] H2o or moisture of any form volition reduce surface adhesion and reduce record tackiness. Wet can be removed off the surface by any physical methods or chemical methods likewise. However, silicon based removal of moisture will also cause lowering of adhesion and thus failure.

Lifetime [edit]

Schematic of the forces present due to thermal expansion/contraction of the agglutinative tape

A force per unit area-sensitive adhesive will experience a range of weather throughout its lifetime. These conditions affect i of the following parts of the tape: the surface or the majority. The surface is only the part of the tape that is exposed to the environment through the whole of its lifetime. The bulk is everything nether the surface of the tape, that is the interactions that occur betwixt the substrate and the adhesive office of the tape.

Surface exposure conditions [edit]

The surface of the tape will experience various conditions imposed on it such as varying temperatures, humidity levels, UV exposure levels, mechanical article of clothing, or even degradation of adhesive exposed to the surface. While the bulk will experience mechanical wear and adhesive degradation, these effects are not as widespread or equally large in magnitude inside the majority equally they are inside the surface. The response of the tape to varying weather is largely due to the adhesive and backing composition too as adhesive properties such as the Glass Transition Temperature and adhesive-substrate interactions due to adhesion forcefulness.

Environmental atmospheric condition [edit]

Many factors within the environs tin can bear upon the surface vesture of adhesive record.^[15] Even the prospect of rapidly irresolute ecology conditions tin can be plenty to cause a failure in the substrate. For instance, rapid cooling tin can cause the substrate to shrink dramatically while the adhesive remains stationary. This pulling forcefulness can be enough to cause tears in the substrate decreasing the substrate's adhesion. Thus, substrate failure is predicated on the response of the substrate to diverse ecology atmospheric condition equally well as the rate at which those conditions change. An adhesive tape practical in a moderate setting will experience a smaller range of temperatures than one practical in a hot desert. Substrate failure is largely predicated on Temperature changes every bit these are the near likely to occur and the most likely to affect the substrate in whatever big way.

However, the substrate tin still exist affected by humidity and UV exposure^[15] if the substrate is practical in an environment that information technology was non designed for.^[16] For instance, one could get substrate failure by using a tape that was made to exist used in a desert in a identify such equally Florida. The departure in temperature might not be very big, but there is a huge deviation in humidity. Any environmental upshot on the substrate is dependent on the identity and purpose of the substrate.^[16]

Schematic of the forces present due to mechanical wear of the adhesive tape

Mechanical article of clothing [edit]

Mechanical wear is largely dependent on the amplitude and direction of the forces exerted on the system.^[17] These forces could exist directly applied to the adhesive record itself as in attempting to peel the tape off or could be applied indirectly to the record through manipulation of the substrate to which the adhesive tape is adhered. The latter is demonstrated in the figure to the right. It must exist noted that the figure is assuming the adhesive record is property two separate substrate pieces together and that twisting of both pieces in reverse directions has not been noted.

The wear of an agglutinative tape as it slides across a substrate can be estimated using Archard's Police of Adhesive Wear, where ${\displaystyle H}$ and ${\displaystyle k_{westward}}$ are the hardness and wear coefficients of the agglutinative tape, ${\displaystyle \nu }$ is the distance the adhesive is dragged beyond the substrate surface, ${\displaystyle F_{Fifty}}$ is the total normal load interim on the adhesive record, and ${\displaystyle \Psi }$ is the volume of the adhesive tape lost during dragging.^[18] ${\displaystyle \Psi =k_{w}{F_{L}\nu \over H}}$ [Archard'south Law of Adhesive Article of clothing]

Bulk exposure atmospheric condition [edit]

The predominant factors affecting the bulk of the adhesive tape are temperature and mechanical wear. Temperature changes and extremes could cause degradation of the substrate and the adhesive, while mechanical wear could crusade delamination of the agglutinative tape depending on the magnitude and direction of the applied forces. Substrate degradation, while unlikely, could besides result in delamination though this will be instance and surround specific.

Adhesive degradation [edit]

The adhesive is largely affected by the temperature equally polymeric adhesives are commonly used today. Polymeric materials used today are viscoelastic materials, which enables easy application and quick adherence to the substrate. Adhesive degradation in the bulk is largely due to temperature effects, which reduce adhesion causing delamination of the agglutinative tape.^[17] Too low a temperature can cause the polymeric adhesive to enter its drinking glass land condign very brittle and reducing adhesion.^[12] Raising the temperature, on the other hand, causes the polymer to become more fluid and mobile. Equally the mobility increases, the polymer adhesion is reduced as the polymer starts to flow as opposed to adhere. Both temperature extremes ultimately results in delamination. The ideal temperature range is largely dependent on the adhesive identity,^[17] which comes down to polymer structure. The more rigid the polymer chain is, the stronger the Intermolecular Forces betwixt polymer bondage, and the stronger the interactions between the substrate and the adhesive will ultimately consequence in a potent adhesion and, every bit a event, a college ideal temperature range for adhesion.

That being said, in order to avoid delamination, selection of an adhesive tape needs to exist based upon the weather that the tape will experience over its lifetime.^[16] This option process will reduce the chains of agglutinative tape degradation and failure occurring during the lifetime of the tape though there is non guarantee that this process will completely avoid the possibility.

Furnishings on recycling [edit]

Used PSA tapes are composite materials and not recycled into new tapes. Their possible effects on the recyclability of the products they have been used on, all the same, is important. Reuse or recycling are sometimes aided past a tape being removable from a surface.

Effects on recyclability are particularly of import when record is applied to paper surfaces, such equally corrugated fiberboard and other packaging. When taped corrugated boxes are recycled, moving-picture show-backed box sealing tapes practise not hinder box recycling: the adhesive stays with the backing and is easily removed.^{[xix] [20]}

Tapes used in paper manufacturing plants are sometimes designed to be repulpable. A repulpable adhesive disperses when put into the hot slurry of lurid.

References [edit]

1. ^ Werner Karmann and Andreas B. Kummer "Tapes, Adhesive" in Ullmann's Encyclopedia of Industrial Chemical science, Wiley-VCH, Weinheim, 2000. doi:10.1002/14356007.a26_085
2. ^ ^{a b c d} "Critical Surface Tension, Surface Free energy, Contact Angles with Water, and Hansen Solubility Parameters for Various Polymers". Accu Dyne Test. Diversified Enterprises. 2014. Retrieved 3 June 2014.
3. ^ Guice, K. B. (2008). Synthesis and Characterization of Temperature- and pH-responsive Nanostructures Derived from Block Copolymers Containing Statistical Copolymers of HEMA and DMAEMA. ProQuest. p. 29. ISBN978-0-549-63651-9.
4. ^ Ozawa, Takehiro; Ishiwata, Kano (2001). "Adhesive Properties of Ultraviolet Curable Pressure-Sensitive Adhesive Tape for Semiconductor Processing (I) - Interpretation via Rheological Viewpoint" (PDF). Furukawa Review. 20: 83–88. Archived from the original (PDF) on 12 June 2018. Retrieved 18 April 2015.
5. ^ ^{a b c d e f g h i j k fifty m n o p} Silva, L. F. M. (2011). Handbook of Adhesion Technology. Frg: Springer. pp. 337, 342–372.
6. ^ Tse, Mun Fu (1989). "Studies of triblock copolymer-tackifying resin interactions past viscoelasticity and agglutinative performance". Journal of Adhesion Scientific discipline and Technology. 3 (i): 551–570. doi:ten.1163/156856189x00407.
7. ^ ^{a b c d east} Habenicht, G. (2009). Applied Adhesive Bonding. Germany: WILEY-VCH.
8. ^ "The Fundamentals of Selecting Pressure-Sensitive Adhesives". Medical Device and Diagnostic Industry. Medical Plastics and Biomaterials. 1998. Retrieved 5 June 2014.
9. ^ Veselovsky, R. A. (2002). Adhesion of Polymers. New York: McGraw-Hill.
10. ^ Zajaczkowski, Grand. J. (2010). "Force per unit area Sensitive Adhesives in High Functioning Applications" (PDF). adhesives.org. The Adhesive and Sealant Council, Inc. Retrieved 3 June 2014.
11. ^ ASTM D3330
12. ^ ^{a b c d} "The Furnishings of Low Temperatures on Pressure-Sensitive Adhesives". world wide web.tesatape.com. Tesa Tape. Archived from the original on xiv July 2014. Retrieved four June 2014.
13. ^ ^{a b c} "Pressure level Sensitive Adhesive Information". www.chemsultants.com. Chemsultants International. Archived from the original on 14 July 2014. Retrieved 4 June 2014.
14. ^ Nagel, Christoph (2014). "A Candid Look at Record Backings". tesatape. Tesa Record, Inc. Archived from the original on 29 April 2014. Retrieved 5 May 2014.
15. ^ ^{a b} Broughton, Due west.R.; Mera, R.D. "Environmental Deposition of Adhesive Joints Accelerated Testing" (PDF). Eye for Materials Measurement & Engineering National Physical Laboratory. Retrieved 8 June 2014.
16. ^ ^{a b c} "Jobsite System Failures Involving Pressure Sensitive Agglutinative Masking Tape over Gypsum Board Substrates" (PDF). Drywall Finishing Council.
17. ^ ^{a b c} Ojeda, Cassandra Due east.; Oakes, Eric J.; Colina, Jennifer R.; Aldi, Dominic; Forsberg, Gustaf A. "Temperature Furnishings on Adhesive Bond Strengths and Modulus for Commonly Used Spacecraft Structural Adhesives" (PDF). Jet Propulsion Laboratory, California Institute of Technology. Archived from the original (PDF) on 14 July 2014. Retrieved 8 June 2014.
18. ^ Butt, H.; Graf, K.; Kappl, Thou. (2013). Physics and Chemistry of Interfaces: 3rd, Revised, and Enlarged Edition. Germany: WILEY-VCH. p. 319.
19. ^ Jensen, Timothy B. (Apr 1999). "Packaging Tapes: To Recycle Or Non, And If And so, How?". Adhesives and Sealants Quango. Archived from the original on 2007-11-09. Retrieved 2007-11-06 .
20. ^ Gruenewald, L. E.; Sheehan, R. Fifty. (1997). "Consider box closures when considering recycling". J. Applied Manufacturing Systems. nine (1): 27–29. ISSN 0899-0956.

Encounter too [edit]

• Dynamic mechanical assay

Farther reading [edit]

• "Pressure-Sensitive Adhesives and Applications", Istvan Benedek, 2004, ISBN 0-8247-5059-4
• "Pressure Sensitive Adhesive Tapes", J. Johnston, PSTC, 2003, ISBN 0-9728001-0-seven
• "Pressure Sensitive Formulation", I. Benedek, VSP, 2000, ISBN 90-6764-330-0

External links [edit]

• How it's Made: Adhesive Tape, [1]

Source: https://en.wikipedia.org/wiki/Chemistry_of_pressure-sensitive_adhesives

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