The pressure-sensitive manufacturing process consists of a series of operations designed to apply a variety of coatings to a continuous moving web or roll of material. The final construction will be made up of a minimum of two or as many as four separate layers that are all laminated together during the manufacturing process.

Pressure-Sensitive Sandwich

The pressure-sensitive product derives its name from the way that the adhesive works. Unlike other types of glues or adhesives that form a bond with the surface that they are applied to, through evaporating or absorbing a solvent to form a solid material, pressure-sensitive adhesives stick to the substrate through the use of slight pressure. No additional outside force is required (water, heat) to allow the product to adhere (see "Adhesives" section).

The total pressure-sensitive construction consists of a variety of layers, each with a specific function and purpose. The typical layers include: top coating, facestock, primer, adhesive, release coating, release liner, anti-block coating. For most applications, the pressure-sensitive material will contain one facestock, adhesive and release liner. However in some applications, multiple layers can be added to produce a label on top of a label, or what is called a piggyback product.

Top Coating is a material that is applied to the surface of the facestock intended to improve or change the surface properties of the label. The intent of the coating is to develop a surface that is more receptive to printing inks or computer imprinting. In most cases the coating increases the ability of the ink to adhere to the surface, preventing smearing or flaking of the image.

Top coatings are used primarily on non-absorbent facestocks such as laminated foils, metallized papers, and film materials (vinyl, polyester). Most paper materials are printable in their natural state and do not require the application of a top coat.

Facestock is the term used to describe the label material. It is the portion of the pressure-sensitive construction that will contain the graphics and be applied to the final object. The facestock will always be the layer with the adhesive permanently bonded to it. In rare cases, a customer may request that a liner be used as a facestock. To avoid confusion, the layer with the adhesive is still described as the facestock.

Facestocks are available in a variety of materials. They can be manufactured from paper, plastic, metal and specialty materials such as cloth and embossed metallized foils that give the effect of a prism. The physical requirements of a facestock are dependent on both the end use and converting requirements of the finished label as well as the need to pull the web through the coater during the manufacturing operation.

Treatments are applied to film facestocks to improve or change the surface properties. The intent of these treatments (i.e., corona- or print-treatments) is to enhance printing ink receptivity or adhesive anchorage.

Primer is a material similar to a top coating that is applied to the back side of the facestock. The application of primer is limited to specific coating lines which are fitted with a priming station. Primers provide three basic functions:

Increase Opacity - The application of a primer to the back side of the facestock will reduce the amount of light that can pass through the label, increasing the opacity of the label. In applications where a high degree of opacity is required of the label to cover-up or prevent the "show through" of preprinted information on the object to be labeled, a gray or black primer (Fascover) can be used.

Adhesive Anchorage - Some of the adhesives used in a pressure-sensitive construction are designed to be removable from the final object. These types of adhesives, by design, develop a low level of adhesion which may not be sufficient to keep the adhesive on the facestock when the label is removed from the final object. A primer can be used to increase the adhesion of the adhesive to the facestock to prevent "adhesive transfer" to the object.

Prevent Adhesive Bleed - The primer acts as a sealer, much like house primer is used when painting a wall. The primer fills the pores in the back side of the facestock, minimizing or eliminating the penetration of the adhesive into the facestock. The nature of a pressure-sensitive adhesive is to flow into the surface of the substrate that it is applied to. In the case of very soft adhesives, a primer may be needed to prevent penetration into the label, which would cause a yellow, oily appearance to the label.

The selection of a primer is not an issue that the customer need consider when purchasing a pressure-sensitive material. The only time a primer must be specifically requested is when additional label opacity is needed for "cover-up" purposes.

Block Plasticizer Migration - When used on some film facestocks such as PVC vinyl, the primer acts as a barrier to prevent the plasticizers in the vinyl facestock from migrating into the adhesive, causing either loss of adhesion or anchorage to the facestock.

Adhesive is the portion the the pressure-sensitive construction that allows the label to adhere to the final object. Adhesives are available in a variety of formulations to provide the desired end use performance. Pressure-sensitive adhesives are classified in three ways: Coating technology (Hot melt, Solvent, Emulsion), Chemistry (Rubber based, Acrylic) and the Type of adhesive (Permanent or Removable). See Adhesive.

Release Coating is a material that is applied to the top side of the release liner (usually called "liner"), which prevents the adhesive from adhering to the liner. The release coating is a silicone-based material (sometimes known as the "lacquer") which is applied either prior to the manufacturing process (prelacquered, or called "PLB") or in line with the adhesive coating operation (called "tandem lacquer"). Release coatings are available in both solvent and solventless versions (cured by heat or radiation).

Solvent release coatings or what are called "solvent silicones" are solutions that contain a high percentage of an organic or petroleum based solvent during the coating process. During coating, the solvents are evaporated leaving the dried silicone behind.

Solventless release coatings or "solventless silicones" use no solvents during the coating process. The fluid material is applied to the release liner and cured through exposure to high heat or radiation. The silicone chemistry crosslinks, forming a hard film. No solvents are evaporated.

Release Liner is the portion of the label that receives the release coating, and provides protection for the adhesive and support for the facestock. Pressure-sensitive label materials are unique in that the release liner provides support for the facestock during the die cutting operation and allows the label to be transported to a label applicator or through a secondary printer (i.e.; thermal transfer, laser, etc).

Release liners are available in a variety of materials depending on the end use requirements. Supercalendered papers are the most widely used liners for both roll to roll and computer printing applications. machine finished liners (MF) provide the added stability and "layflat" required for labels that will be processed in sheet form. Plastic liners (Polyester, Ultraliner) and polycoated liners provide the strength needed in some high speed label applicators to mitigate web breaks.

Anti-Block Coating, or "ABC" is a coating applied to the back side of the release liner (opposite the adhesive) that prevents adhesive, that may have migrated from under the label, from sticking to the release liner as the roll is unwound. ABC coatings are applied to constructions that contain either a very soft adhesive or an excessive amount of adhesive. ABC coatings cannot be applied to all release liners and must be used with caution since they will cause the roll to telescope if improperly wound. ABC coatings cannot be used if back printing is required, unless special inks are used.