Learn about the adhesive

Words and phrases to explain features and functionality of adhesives and adhesive tapes

Adhesive tapes and glues: types of products

Variations based on nytrilic rubber, neoprene rubber, synthetic copolymer, synthetic elastomer. These polymers are melted in a solvent. These adhesives work through a wet bonding, a partial evaporation or through contact.
Acrylic and neoprene based variations. The resins are melted into a water solution. They work through a wet bonding and through contact.
EVA, polyolefins and polyamides based variations. These are all solid adhesives (without a solvent) which are activated melting them at an activation temperature. The speed of cooling determines the open time of the adhesive. There are also reactive polyurethane based versions and, through this variation, they supply structural performances: shear resistance ≥ 100 Kg/cm².
Variations on synthetic elastomers, polychloroprene basis. Adhesives for a quick assembly of light weight materials or for repositionable bonds. They work through a wet bonding or through contact.
Variations on polyurethane (solvent free), cianoacrylic (butyl, methyl, ethyl solvent). They supply bonds with structural performances: shear ≥ 100 kg/cm².

Epoxy adhesives, they polymerize through heat. They supply bonds with structural defined performances: shear resistance ≥ 100 kg/cm².
Variations on polyurethane, acrylic and epoxidic basis. They are composed by two products which are mixed between them in proportions established before application. They supply bonds with defined structural performances: Shear ≥ 100 kg/cm².
Silicones (acetics, oximes), butyles, nitriles, polyurethans, synthetics. They are used in different formulations according to the materials to be sealed and to the use conditions.

Characteristics of the surfaces to be bonded

Process which leads a liquid in contact with a solid. It is obtained with the contact angle, thermodynamic measure defined as the angle got from the interface liquid/fluid (air) with the relative liquid/solid interface.
The application of an adhesive to any substrate must be always preceded by an accurated cleaning of the surface to be bonded. The dirty on the surfaces reduces the direct contact between the adhesive and the surface limiting the efficiency of the bonds. To stick together plastics on which waxes or mould release agents are present, it is important to use a degreasing product as isopropyl alcohol, or acetone for a proper cleaning. Sometimes an abrasion of the substrate s needed, namely the surface removal of material due to repeated friction actions. Surfaces can also be treated with a primer. The primer is a substance which bonds to the substrate tenaciously and it exposes molecules very similar to the adhesive to be applied on the free side.
An irregular or not planar surface - for example lightly curved as a car hood - the more it is irregular the more it is difficult to be bonded. Thicker adhesives ensure best performances in this case because they are able to compensate gaps better adhering to surfaces. For the same reason, referring to acrylic foams, "soft" adhesives are more efficient compared to those defined " firm".
Temperature is a physical property linked to the state of the motion of the particles which build up a substance. The temperature of a substrate can be different from the room one according to its thermal capacity, to its insulation property and to its absorbing capacity of solar radiation. It means that, given a specific application temperature of an adhesive tape, it could happen that the room temperature is compatible with the product but the substrate one could not. For example, let's think to a metal foil exposed to the sun - then heated through radiation up to a temperature much higher than environmental air one- or for the opposite situation, let's think to an insulating material component which is moved from a cold environment to a hot one and that it will take much time to get back to the equilibrium temperature.
The roughness is a property of a body constituted by microimperfections normally present on a surface. Such imperfections present themselves generally as wrinkles and scratches with different shape, depth and direction. The rough surfaces request the use of adhesive of higher thickness and "softness", characteristics which allow to the adhesive to adapt itself to the surface filling the cracks.
It expresses the surface forces of materials and it is marker of the ability of a surface to bond with an adhesive. It is defined as the necessary energy to increase the surface of a given volume of a liquid of a unitary quantity. In case of solid surfaces, not being the surface variable for a given volume, it is measured as wettability (practically with the reaction of a liquid in contact with the solid surface itself).

Various definitions of adhesive products

Flexible molecular structure, more suitable to the dynamic load, to repeated stresses, such as vibrations, thermal expansions and shocks.
It is an adhesive with a rigid molecular structure, high resistant to dynamic load and shear.
It is an adhesive which shows dynamic shear values ≥ 100 kg/cm², at the temperature of 24°C.
It combines the advantages of the rigid adhesives - of which it mantains the very high mechanical endurance - with those of the flexible ones.
It is used to facilitate the positioning of logos or signs on the surface to be decorated and to provide more solidity to the adhesive film: it can be made of paper or transparent film to favour the graphics assembly.
Adhesive which does not adapt to the roughness of the surfaces, defined "low tack". On the contrary, it is easy to get converted and it has got an excellent wheather and solvent resistance.
Adhesive able to adapt quickly to a given surface roughness of the substrate, conforming to its interstices, ensuring a good initial adhesion (high tack).
The strapping consists of the application of the tape on packed products to ensure, reinforce and bundle them.
It is a small tab which is applied on a tape liner to facilitate its peel off.
The tear strip tape is a thin one which is used for the easy, quick and safe opening of the carton boxes, of the plastic film or corrugated board.

Risk factors on bondings

UV rays modify the chemical structure of the adhesives getting worst their properties. This effect comes along the time. The more is high the resistance to UV the more an adhesive will be capable to mantain its "linking" properties whether exposed to the light of the sun.
Plasticizers are chemical additives used in the manufacturing of plastic polymers. They can modify their characteristics, for instance making them more plastic and workable at low temperatures. Plasticizers may transfer themselves from a plastic to an adhesive along the time, changing the adhesive fiber properties and weakening its bond with the substrate.
Water or other hydrophilic liquids may penetrate inside the adhesive mass weakening the adhesive and inactivating a bond. Some adhesives, particularly those solvent based and the acrylic foams, have got higher characteristics of resistance to the action of the water since their chemical structure makes them waterproof.
Solvents can melt the adhesive and inactivate its linking strengths. Some adhesives - particularly those in water dispersion and acrylic foams - have got a higher resistance to solvents since their chemical structure makes them waterproof and invulnerable.
The application of an adhesive at temperatures different from those established by the producer may get the product useless. Specifically, the adhesive (in particular the hot melt ones) lose their initial tack and tend to crystallize at a low temperature. they become too "liquid" at high temperature resulting in a quick lowering of its static shear.
Range of temperature within which an applied adhesive keeps unchanged its adhesive performances (at the end of its waiting time phase).

The adhesive tapes liner

Paper obtained through a further lamination process in a supercalander at the end of the process of production of a standard paper. The process makes it thinner, translucent and water resistant.
It is the polymer of vinyl chloride. In its pure version it is rigid; it owes its application versatility to the possibility to be mixed also at high proportions with plasticizer products or with inorganic compounds which make it flexible and mouldable.
Polyesters are a class of polymers obtained through a step-growth polymerization via condensation which contains the functional group of esters along the main carbonaceous chain.
It's a version of polypropylene film with tensile and break resistance much larger than the standard one along both the axis.
Paper made with a cellulose pulp purified from lignin through a chemical treatment (kraft treatment). It is highly resistant, so it is suitable to be a carrier for the adhesive.
It's a paper which is coated with a particular blend of substances to give it specific further physical characteristics as gloss, coating, resistance to humidity, permeability to inks, etc.
It's a paper which is coated on one or both sides with a thin layer of polyethylene or polypropylene which confers to it higher resistance to humidity.
It's a low branched polyethylene, with high intermolecular strenghts and a superior rigidity compared to LDPE.
It is composed by very much branched polymers. So it is a ductile and flexible material.
It's a version of polypropylene film with tensile and break resistance much larger than the standard one along an axis.

The adhesive tapes carrier

The term "acetate" is used to indicate more polymers. The most known one is the cellulose triacetate which characteristics of dimensional stability make it suitable to production of low deformability films (it was used for movie films in the past). A peculiar characteristic of triacetate is its resistance to high temperatures.
Thermally treated aluminium. It is heated up to 350° C and it is cooled at room temperature. The hardening structure recrystallizes in new grains without internal strengths and a soft and ductile structure is obtained.
There are metallic adhesive tapes which carrier can be made with partcular metals, useful on the base of specific purpose situations. E.g. lead can be used to make tinsmithery works in the building field; the zinc tape has got anticorrosive properties whereas problems connected to corrosion phenomena on electrolytic processes may arise; the copper tape may be used as conductor.
Polypropylene film with tensile strength and elongation at break, much higher than the standard version on both the axis.
The creaped paper is obtained through the raw paper processing. The degree of corrugation can reach 150%. The degree of corrugation is the percentage increase of the grammage caused by the corrugation itself. Through the corrugation the extensibility and the elasticity of the paper are increased and the degree of protection of the packaging is increased as well.
Paper in different grammages, used as a carrier of adhesive tapes. To suit the physical characteristics for this usage it is impregnated before the adhesive coating. The treatment is used to avoid that the paper absorbs a relevant part of the coated adhesive.
The Kapton® is a polyimide film, developed by DuPont™, formed for polymerization of imide monomers. It can stay stable in a huge range of temperatures, from -269° C up to +400° C.
Polypropylene film with tensile strength and elongation at break, much higher than the standard version on an axis.
It's a synthetic elastomer (synthetic rubber) formed by polymerization of chloroprene. It shows as a closed cell foam which main characteristics are: elasticity, shear and flattening resistance, resistance to wheater aging and to heat. It is also inert against many chemicals, oils and solvents. The polymer is used in the mixture of some adhesives as well.
Through "nylon" we identify a family of synthetic aliphatic polyammide, formed through a polimerization process. Nylon fibers are composed by linear macromolecules containing repeated amide bonds, the 85% of which have got bonds with aliphatic chains. Its typical characteristics are: elasticity, hardness and abrasion resistance.
A thermoplastic resin which looks like a trasparent solid (amorphuos form) or as white one (crystalline form) with very good insulating properties and a chemical stability.
The polyethylene terephthalate belongs to the family of polyesters. It is a thermoplastic resin suitable to food contact. According to its production processes and to its thermic history it can be in amorphous form (transparent) or in semi-crystalline form (white and opaque). It is used also for its electrical properties, its chemical resistance, its performances at high temperatures, its self-extinguishing properties, its moulding rapidity. Polyesters are flammable, but, due to their intrinsic thermoplasticity, they are apt to burn with a self-extinguishing flame. The PET decomposes at 340° C.
Polymer including monomers bonded by a peptide bond, either they are natural as proteins, wool or silk, or artificial as nylon or aramid fibre as well. Polyamide fibres are used for their resistance and ageing features.
Semi-crystalline polymer characterized by a high elongation at break, by a low density, by a good thermal and abrasion resistance in its isotactic configuration.
Huge family of polymers in which the polymeric chain is composed by urethane bonds. These materials have got a wide range of properties and they are available in the industrial field like foams, elastomers and solids.
It is the polymer of vinyl chloride. In its pure version it is rigid; it owes its application versatility to the possibility to be mixed also at high proportions with plasticizer products or with inorganic compounds which make it flexible and mouldable. It is considered stable and safe at room-temperature in technological applications, but highly dangerous if burnt or heated at high temperatures for the possibility of release of dioxin.
It is the polymer of vinyl fluoride. It is structurally similar to PVC. PVF has got a low permeability to gasses, it burns very slowly and has got an excellent weatherability and a resistance to chemicals and to dust. The film known as Tedlar®, pruduced by DuPont™, is one of the most relevant products made of PVF.
Rayon or viscose is a fiber which stems from the manufacturing of cellulose. It is defined as semi-synthetic fiber, being obtained from natural polimers artificially. Rayon is a fiber which gives a fabric with characteristics very similar to the natural silk ones. This is why it is defined as an "artificial silk".
The foams are an important class of light-structured cellular materials. They may be divided into two macro categories on the base of the nature of the pores which compose them:open cell foams and closed cell foams.The open cell foams have got interconnecting pores which form a network of interconnections that can be filled with any sorrounding fluid. The closed cell foams have got separated pores, one from another, which do not form an interconnected network and consequently get waterproofed to fluids.
The polytetrafluoroethylene (PTFE) is the polymer of the tetrafluoroethylene. It is normally more known through its trade names Teflon™, Fluon, Algoflon, Hostaflon, to which polymers are added other stabilizers and fluidizers to improve their applications possibilities. It is a smooth plastic material and it is resistant to high temperatures (up to 300° C), It has got a good chemical inertia and the lowest known friction coefficient.
The cloth is a fabric, of every kind of material, built with the simpliest frame with which the yarns of warp and weft can be plotted. The frame of the cloth shows itself the same on the right and on the reverse.
The fabric is a product composed by a plot of yarns perpendicular among them.
The non woven is in general an industrial product similar to a tissue but obtained through different processings from weaving. The manifacturing uses normally piled fibers or mechanically cross-joined, with adhesives or thermal processes.

The adhesive of the tapes

Adhesive made of acrylic resins in water dispersion. During the coating process, the water is evaporated. Good heat resistance, medium adhesion, good resistance to solvents and ageing. Low humidity resistance.
Adhesive made of acrylic resins in solvent solution which evaporates during the coating process. It has got a very good heat resistance, a medium adhesion, a very good resistance to ageing and to humidity. Recommended for outdoor applications.
Adhesive made of natural rubber and resins.
Adhesive made of natural rubber and resins melted in a solvent (hexane) which is evaporated during the coating process. Good tack, medium adhesion, heat resistant. Moderate resistance to solvents. It is easily removable and it has got a fair adhesion even on difficult substrates.
It deals with a kind of adhesive obtained throught the melting of synthetic resins and thermoplastic rubbers. It has got good adhesive features up to 50-60°C. It is solvent-free and enviromentally friendly. It has got a high initial tack, it is resistant to humidity but it has got a limited resistance to temperature, to ageing and low resistance to solvents.
High density resin acrylic adhesive foam, characterized by very good adhesion properties.. It has got a very good resistance to weather agents.
Silicone rubber based adhesive, an elastomer made of silicone.chains. This chemical frame supplies to the silicone and to the silicone rubbers peculiar characteristics of stability, softness and resistance to high temperatures. The silicone adhesive is suggested for applications on anti-adhesive surfaces as for example silicone papers and applications where the clean removal is important and a constant adhesivity in the time as well.
Not active room-temperature adhesive. It must be heated at a specific temperature to get the bond with the surface. There are two versions : a) irreversible adhesive: once heated and cooled to get the bond, there are no more effects from a further heating at high temperatures. b) reversible adhesive: it solidifies itself creating a bond but it becomes soft if re-heated allowing the detachment of the sticked parts.

The adhesive tapes structure

Internal cylinder usually produced in cardboard or plastic on which the adhesive tape is winded.
Peelable material protecting the adhesive part/parts of the tape.
Chemical solution spread on a surface before positioning the adhesive tape. It favourites the adhesion between both of them.
Antiadhesive layer coated on the backing of the liner or on the backing of the single sided tapes carrier. It permits to the tape to be self-wounded avoiding that the adhesive sticks together with the underneath layer.
Type of support consisting of warp and weft which supplies dimentional stability of the adhesive.
Peelable protective material applied to the closed side of the tape.
Coating which permits the liner removing from the adhesive. It is generally obtained throught the coating of a thin silicon or PTFE layer.
Basic carrier on which the adhesive is coated.
Electric treatment of the carrier that increases its receptivity to the adhesive temporarely.

The adhesive tapes converting

To cut adhesive tapes in sheets of defined dimensions.
To produce shaped adhesive tapes according to a draw, cut as single pieces, starting from rolls or master rolls.
To accomplish a discontinous cut on the primary liner or on the secondary one of an adhesive tape to facilitate the split of rolls segments or the continuous die-cut on a roll.
To couple an adhesive tape to another material.
To produce shaped adhesive tapes according to a draw, laminating them on a secondary liner which is not cut and make them available in continuos patterns on sheets or rolls.
To make an adhesive tape with an extended liner or with fingerlift in order that it is possible to facilitate the removal when used.
To unwind an adhesive tape roll to wind it againg according to the defined length or on a core with different dimensions.
Removal of waste material during the production of die-cut as draw.
To get rolls of a defined measure starting from a master roll or from bigger rolls.

Preparation of the surfaces for bonding

Adhesive tapes must be stored in their original package in a dry place, shelted from sun rays and at temperature no higher than 30 ° C and not lower than 15° C.
Pressure to be applied on the tape perpendicularly to the substrate for the best adhesion of the adhesive tape.
Temperature range (from min. to max.) within which an adhesive could be applied reaching the nominal performances.
The necessary time for the stabilization of the bond between adhesive and substrate - to reach the best adhesive performance.
The application surfaces must be cleaned and degreased with proper products. It is possible to use the isopropyl alcohol to make the cleaning. This product does not require a forced aspiration because it does not generate toxic gases. There are specific more complex cases - as for instance the contamination with mould release agents of a component to be stuck - for which the isopropyl alcohol would not be sufficient and for which the use of powerful solvents is needed, as for example the acetone. In this case all the current working security rules must be adopted.
Surfaces must be dry, free from dust, oil, oxides, release agents and other contaminants. A sufficient surface energy is important to get good bonding forces.

Adhesive systems and stress factors

Dynamic loads differ from the static ones for the variable nature of the applied forces. The eliciting of the dynamic loads is overcome more easily from a "flexible" carrier adhesive, able to smooth the action, expanding or compressing, compensating it.
Vibrations act in a degenerative manner on the adhesive bonds. Their mechanical actions may break the bonds. "Soft" adhesives, low density adhesive foams and acrylic foams have got a better resistance to vibrations since they have intrinsec absorbing properties of smoothing. As a secondary effect, they soften the effects on the substrate as well.
The adhesives react to static loads according to their physical properties. The bond can "break" because the adhesive delaminates either from the carrier, or from the substrate, or from the overcoming of the specific physical resistance characteristics of the carrier, whereas the adhesive is provided with it.

Solvents and cleaning products

Acetone is a ketone. Ketones are compounds characterized by the presence of functional carbonyl group. It has got a very high polarity which gives it a determinated chemical reactivity. Acetone is a colorless and a flammable liquid with a characteristic smell. It is miscible with water, ethanol and ether and it is mainly employed as a solvent.
Isopropyl alcohol is a colorless alcohol with a strong characteristic smell. It is usually used as a cleaner, solvent and as an industrial additive; it is also an excellent degreaser.

Technical specifications of adhesives

Adhesion is the state through which two surfaces are kept together by connection strengths. It is defined as "PEEL at 180°C" when the detachment strength is applied along the contact surface between the tape and the substrate and as "PEEL at 90°C" when the detachment strength is perpendicular to the contact surface between the tape and the substrate.
Referring to heat-activated adhesives, it is the temperature at which their state changes making them active ones.
Range of temperature within which an applied adhesive keeps unchanged its adhesive performances (at the end of its waiting time phase).
Temperature range (from min. to max.) within which an adhesive could be applied reaching the nominal performances.
The necessary time for the stabilization of the bond between adhesive and substrate - to reach the best adhesive performance.
Pressure to be applied on the tape perpendicularly to the substrate for the best adhesion of the adhesive tape.
Measure of the initial adhesion of the adhesive determined through the necessary detachment strength - according to the 300mm/min established speed - of a specific portion of tape from a given surface to which it's got stuck without a relevant pressure.
Measure of the initial adhesion of a specific adhesive determined by the distance accomplished by a little steel ball of a given weigth and energy got roll on the adhesive side of the tape up to the stop of the ball.
It measures the capacity of a tape to resist to the application of a static shear (a specific weigth applied on its free far end). It is measured in mm of slipping of the sample of the tape from the substrate where it is applied or as a time in which the full detachment of the sample is achieved -if the full detachment is achieved before the end of the test.
It is the measure of capacity of resistance of double-sided tape to a dynamic shear. The force is applied pulling two aluminium plates bonded together with a double-sided tape of 25 mm width and 25 mm heigth (total surface 625 mm²). Its value is given from the peak reached before the time in which the bond breaks and the plates detach.
It is the necessary strength to unwind an adhesive tape from its backing with an angle of 180°.
Percentage of increase of the original length of the tape which measures its breaking point.
Weight per surface unit, it could be referred to the carrier, the adhesive or to the liner.
Tape thickness, understood as carrier + adhesive layers.
Strength applied to a tape of a determined width in order to reach its breaking point.

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