The pressure sensitive adhesive ( PSA , self-adhesive , self-stick adhesive ) is an adhesive that forms bonds when pressure is applied to marry adhesives with adherend. There is no solvent, water, or heat required to activate the adhesive. It is used in pressure-sensitive cassettes, labels, glue points, note pads, car trims, and a variety of other products.
As the name "pressure sensitive" suggests, the bonding rate is affected by the amount of pressure used to apply the adhesive to the surface.
Surface factors such as smoothness, surface energy, contaminant removal, etc. are also important for proper bonding.
ILM is usually designed to form bonds and survive well at room temperature. PSAs usually reduce or lose their spikes at low temperatures and reduce their shear-retention capabilities at high temperatures; Special adhesives are made to function at high or low temperatures. It is important to choose an adhesive formulation designed for the intended use conditions.
Video Pressure-sensitive adhesive
Structural and pressure-sensitive adhesive
Adhesives can be broadly divided into two classes: structural and pressure-sensitive. To form a permanent bond, the structural adhesive hardens through a process such as evaporation of the solvent (eg, white glue), reaction with UV radiation (as in the dental adhesive), chemical reactions (such as two parts epoxy), or cooling (as in hot melt). In contrast, pressure-sensitive adhesives (PSAs) form bonds only by applying light pressure to mating adhesives with adherents. Pressure-sensitive adhesives are designed with a balance between flow and flow resistance. The bonding form because the adhesive is soft enough to flow, or wet, is attached. The bond has strength because the adhesive is hard enough to withstand the flow when the voltage is applied to the bond. Once adhesives and adherents are in proximity, there are also molecular interactions such as van der Waals forces involved in bonding, which contribute significantly to the ultimate bonding strength. ILM exhibits viscoelastic (viscous and elastic) properties, both of which are used for proper bonding.
In contrast to the structural adhesive, whose strength is evaluated as the lap shear strength, pressure-sensitive adhesives are characterized by their shear and skin resilience as well as their initial tactics. These properties depend, inter alia, on formulations, coating thickness, under-rub and temperature.
"Permanent " pressure sensitive adhesives are initially sensitive to pressure and can be released (eg to recover mislabeled items) but after hours or days change their properties, by becoming less or less viscous, or by increasing the bond strength, so the bond becomes permanent.
Shape effect
The adhesive bond of the tape or label may be affected by its shape. Bands with sharp corners began to slip out at the corners; adhesive strength can be increased by rounding the corners.
Maps Pressure-sensitive adhesive
Apps
Pressure-sensitive adhesive is designed for permanent or removable applications. Examples of permanent applications include safety labels for electrical equipment, foil tapes for HVAC channel work, automotive interior trim assembly, and sound/vibration film. Some high performance permanent PSAs exhibit high adhesion values ​​and can support kilogram weight per square centimeter of contact area, even at high temperatures. This builds adhesion to a permanent bond after a few hours or days.
Deletion
The removable adhesive is designed to form a temporary bond, and ideally can be removed after months or years without leaving residue on its adherents. Removable adhesive is used in applications such as surface protective films, masking tape, bookmarking paper and notepaper, price tags, promotional graphic materials, and for skin contact (wound care, ECG electrodes, athletic, analgesic and transdermal bands, etc.). Some removable adhesive is designed to be repeatedly sticky and non-sticky. They have low adhesions and generally can not support much weight.
Sometimes the clean removal of the pressure sensitive band can be difficult without damaging the substrate being obeyed. Pulling at a slow rate and with a low skin angle helps reduce surface damage. PSA residues can be softened with certain organic solvents or heat. Extreme cold (dry ice, frozen spray, etc.) May cause viscoelastic material to turn into glass phase; so it is useful to remove many types of ILM.
Producing
Pressure-sensitive adhesives are produced with a liquid carrier or in solid form 100%. Articles such as tapes and labels are made from liquid PSA by coating the adhesive on the support and evaporation of organic solvents or water carriers, usually in hot air dryers. The dry adhesive can be further heated to initiate crosslinking and increase the molecular weight. 100% solid PSA may be a coated low viscosity polymer and then reacted with radiation to increase the molecular weight and form an adhesive (radiation that cures the PSA); or they may be heated high viscosity materials to reduce the viscosity sufficient to allow coatings, and then cooled to their final form (hot melted PSA, HMPSA).
Composition
ILM is usually based on an aggravated elastomer with an appropriate tackifier (eg, rosin ester). Elastomers can be based on acrylics, which can have sufficient tactics on their own and do not require a tackifier. bio-based acrylate - more recently, biologically based macromonomers are grafted onto the acrylic spine so that the resulting PSA uses 60% bio-based materials, butyl rubber, ethylene-vinyl acetate (EVA) with high vinyl acetate content; can be formulated as a hot melt PSA, natural rubber, nitrile, silicone rubber, requiring a special propellant based on silicate resin "MQ", composed of trimethyl silane monofrillation ("M") reacted with quadrafunctional silicon tetrachloride ("Q").
Styrene block copolymers (SBC), also called styrene copolymer adhesives and rubber-based adhesives, have good low temperature flexibility, high elongation, and high heat resistance. They are often used in hot melt adhesive applications, where the composition retains tactics even when compacted; However non-pressure-sensitive formulations are also used. High heat resistance, good low temperature flexibility. The strength is lower than the polyester. They usually have A-B-A structures, with elastic rubber segments between two rigid plastic endblocks. High-strength film formers as standalone, enhancing cohesion and viscosity as additives. Waterproof, soluble in some organic solvents; cross-linking increases solvent resistance. Resins associated with endblocks (cumarone-indene,? -methyl styrene, vinyl toluene, aromatic hydrocarbons, etc.) Improve adhesion and alter viscosity. Resins associated with the midblock (aliphatic olefin, rosin resin, polterpene, terpene phenolate) enhance the adhesion, processing and pressure sensitive properties. The addition of plasticizer reduces costs, increases pressure sensitive spikes, reduces melt viscosity, lowers hardness, and increases low temperature flexibility. The structure of A-B-A promotes phase separation of the polymer, binding together the endblock, with the central elastic member acting as a cross link; SBCs do not require any additional cross-linking, styrene-butadiene-styrene (SBS), used in high styrene-ethylene/butylene styrene (SEBS) PSA applications, used in low non-woven, styrene-ethylene/propylene ( SEP), styrene-isoprene-styrene (SIS), used in high-viscosity high PSA applications, vinyl ether.
See also
- Blu-Tack
- Contact mechanic
- Glue points
- Gaffer tape
- Post-it
- Rheology
- Automatic adhesive stamp
- Viscoelasticity
- Pressure sensitive paper
References
Further reading
Source of the article : Wikipedia
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