Cybrid Encyclopedia - Adhesion properties and market applications of pressure-sensitive adhesives
Pressure-sensitive adhesive, is a slight pressure can be instantaneous bonding of an adhesive. Pressure-sensitive adhesive is the manufacture of adhesive tape of an adhesive, divided into solvent-activated, heating and pressure-sensitive three categories, including the most convenient use of pressure-sensitive type, rapid development.
1 classification of pressure-sensitive adhesive
Pressure-sensitive adhesive can be divided into rubber-based pressure-sensitive adhesive and resin-based pressure-sensitive adhesive according to its adhesive type, rubber-based pressure-sensitive adhesive to rubber as a viscous material, adding tackifier, filler, antioxidant and other components. According to the type of rubber can be divided into natural rubber, polyisobutylene rubber, styrene-butadiene rubber pressure-sensitive adhesive and other classes. Resin type pressure-sensitive adhesive viscous material for the synthetic resin, there are homopolymer resin and copolymer resin. The preparation of pressure-sensitive adhesives should be added to the viscosity increase agent, softening agent, filler and antioxidant. According to the type of resin can be divided into polyolefin, vinyl chloride copolymer, acrylic resin, silicone and fluorine resin pressure-sensitive adhesive and other categories.
2 Composition of pressure-sensitive adhesive
Pressure-sensitive adhesive in addition to the viscous material, but also to add auxiliary substances such as tackifiers.
1. The viscous material of pressure-sensitive adhesive is rubber or synthetic resin and other materials, the role is to give the adhesive layer of sufficient cohesive strength and adhesion, the amount of 30% -50%.
2. Tackifier. Tackifier with rosin and its derivatives, petroleum resin, etc., its role is to increase the adhesive layer adhesion. Its dosage is 20%-40%.
3. Plasticizer. The plasticizer used for general plastic processing plasticizer, its role is to increase the quick adhesion of the adhesive layer. The dosage is 0-10%.
4. Anti-aging agent. General rubber, plastic antioxidants are available, the role is to improve the service life, the amount of 0-2%.
5. Filler. The filler used for the general plastic filler, the role is to improve the adhesive layer cohesive strength and reduce costs, the amount of 0-40%. In addition, some pressure-sensitive adhesives, but also need to add viscosity adjusters, vulcanizing agents and solvents.
3 commonly used pressure-sensitive adhesives
Currently used pressure-sensitive adhesive mainly rubber pressure-sensitive adhesive, acrylate pressure-sensitive adhesive and silicone pressure-sensitive adhesive three types.
1. Rubber-based pressure-sensitive adhesive. Rubber-based pressure-sensitive adhesive is the most widely used one of the most widely used pressure-sensitive adhesive, the rubber used in natural rubber, synthetic rubber and recycled rubber. Natural rubber as the viscous material of pressure-sensitive adhesive compatibility, pressure-sensitive, creep resistance are good, aging resistance is poor, and hardness changes. With synthetic rubber as the viscous material of the pressure-sensitive adhesive heat resistance, durability than natural rubber, but the bonding strength is poor. With recycled rubber as the viscous material can only use natural rubber recycled rubber, synthetic rubber recycled rubber effect is very poor, should not be used. For the natural rubber as the viscous material of the pressure-sensitive adhesive, natural rubber and synthetic rubber can be used, partly vulcanized crosslinking, grafting modified or modified by adding appropriate reinforcing filler. These methods can improve the adhesive layer of anti-aging properties, increasing the service life of the adhesive.
2. acrylate pressure-sensitive adhesive. Acrylate pressure-sensitive adhesive is second only to the amount of rubber-based pressure-sensitive adhesive, the adhesive is a copolymer of acrylate and other ethylene monomers. The copolymer monomer is divided into the main monomer, secondary monomer and functional monomer. The main monomer is butyl acrylate, etc., the role is to provide toughness and adhesion. Secondary monomers such as methyl methacrylate, styrene, etc., is a rigid monomer, can provide rigidity and cohesive strength. Functional monomers are monomers containing other functional groups, such as hydroxyethyl methacrylate, etc., which act as cross-linkers in the polymerization process to further improve adhesion, cohesion and heat creep resistance. This scientific monomer coordination provides the copolymer itself with the basic properties of a pressure-sensitive adhesive, so that acrylate pressure-sensitive adhesives are almost one-component. Compared to rubber-based pressure-sensitive adhesives, acrylate pressure-sensitive adhesives offer excellent weather and heat resistance without the addition of antioxidants, good oil resistance, and a transparent adhesive layer with no phase separation or migration. Because the copolymerization can introduce a variety of polar groups, increasing the intermolecular secondary valence force, so it has greater adhesive strength and cohesion strength.
3. Silicone pressure-sensitive adhesive. Silicone pressure-sensitive adhesive is made of silicone rubber and silicone resin, silicone rubber as the basic components of the pressure-sensitive adhesive, silicone resin as a tackifier. The properties of pressure-sensitive adhesives change with the change of the ratio of the two. In the formulation, the relative molecular mass of raw silicone rubber is about 1.5 × 10, but the silicone resin should be properly selected, requiring an active end group at the end. Commonly used are methyl silicone resins, methyl phenyl silicone resins, and phenyl vinyl silicone resins. They all have good thermal stability, silicone pressure-sensitive adhesive bonding performance is good, bonded to the aluminum sheet, the strength of 21MPa, by 260 ℃, 7d, the strength of the same, as a silicone pressure-sensitive adhesive backing materials are polyester, polyester, etc..
4 pressure-sensitive adhesive composition
Pressure-sensitive adhesive tape is generally made into a ribbon roll, there are three forms: single-sided glue, double-sided glue and adhesive sheet.
1. Single-sided glue in the substrate front coating primer after coating pressure-sensitive adhesive, the reverse side of the brush after the back treatment can be rolled up.
2. Double-sided adhesive tape and single-sided adhesive film does not require a back treatment, but a layer of adhesive surface paste isolation paper. The substrate of the tape is the basic material to support the pressure-sensitive adhesive. As a substrate for pressure-sensitive adhesive, it must have good mechanical strength, uniform thickness, not easily deformed, and better wetting with pressure-sensitive adhesive. Commonly used substrates are cotton, glass cloth, synthetic fibers and other fabrics, polyethylene, polyester, polyvinyl chloride and other plastic films.
3. Primer, also known as primer and primer. The primer coating agent can enhance the adhesion of the pressure-sensitive adhesive to the substrate and prevent degumming. There are two types of primers: mixed and grafted. Mixed primer is a mixture of resin with an affinity for the substrate and resin with an affinity for the pressure-sensitive adhesive. Graft copolymerization primer is made by grafting the resin that has affinity for the pressure-sensitive adhesive onto the main chain and grafting the monomer of the resin that has affinity for the base material. Some pressure-sensitive adhesives can be applied without primer if the adhesion between the adhesive and the substrate is strong.
The so-called backside primer is a layer applied to the backside of a single-sided adhesive tape that acts as a layer separator when the tape is rolled into a circle. This treatment agent can also improve the physical and mechanical properties of the substrate. The choice of the back treatment agent requires a good layer of isolation ability, unmasking the back of the tape can not be with the lower layer of pressure-sensitive adhesive, but also requires a good transparency and non-migration. Commonly used backing agents include polyacrylates, polyvinyl chloride, cellulose derivatives, and silicone compounds. Depending on the substrate or pressure-sensitive adhesive, different primers are used, or several primers can be used together. For double-sided adhesive tapes, labels, stickers, adhesive sheets, etc. should be covered with a layer of isolation paper on the surface of their pressure-sensitive adhesives. Commonly used isolation paper is semi-rigid PVC film, polypropylene film and coated with a back treatment of kraft paper.
5 adhesion properties of pressure-sensitive adhesives
The pressure-sensitive nature of a pressure-sensitive adhesive is a manifestation of its adhesion properties, which are made up of four elements: the fast tack force (A), the adhesive bond force (B), the cohesive force (C) and the adhesive base force (D).
1. Fast adhesive force (A) refers to when the adhesive tape and the sticky material with the lightest pressure, the fastest speed immediately after contact to separate the performance of an interfacial peeling force. It can be understood as the initial adhesion, performance of adhesion and pressure-sensitive adhesive to the sticky material, such as the ability of infiltration, it is difficult to define a strict.
2. Adhesive force (B) refers to the tape after appropriate paste and the surface of the adhesive embodied in the peel force, the size of which determines the adhesive tape adhesion properties.
3. cohesive force (C) that is, the adhesive layer of the cohesive strength, it and intermolecular force, intermolecular bonds, molecular size and intermolecular arrangement of the way.
4. Adhesive base force (D) is the adhesive force between the pressure-sensitive adhesive and the substrate or the adhesive force between the pressure-sensitive adhesive and the primer and the primer and the substrate. Because these four forces should meet between the relationship between A < B < C < D, so in the design of pressure-sensitive adhesive formulation should pay strict attention to the nature and amount of each component and its impact on the adhesion properties.
6 pressure-sensitive adhesive tape preparation process
The preparation process of pressure-sensitive adhesive tapes often adopts different processes and equipment due to different substrates, types of rubber, films and shapes of tapes.
1.Preparation of pressure-sensitive adhesives. Apply to the solvent coating of pressure-sensitive adhesive first viscous material dissolved in the solvent, and then add other components, stir, modulated into a certain viscosity of the adhesive spare. If the viscous material for rubber, it is best to first refine in order to increase the fast adhesion and solubility, and reduce the cohesion of the appropriate. Apply to roll-paste coating pressure-sensitive adhesive, generally according to the first rubber, antioxidant, resin (tackifier), plasticizer, viscosity adjuster and filler in the order of the mixing machine evenly, and then add a small amount of solvent to dilute to a certain viscosity can be.
2. Pressure-sensitive adhesive coating. The pressure-sensitive adhesive, primer and back treatment agent with a good match, the available solvent method or roll-paste method, such as the way they are coated on the substrate after removing the solvent that is, the thickness of the adhesive layer to 0.02-0.03mm is appropriate. With the solvent method of coating, in the process of the substrate forward will first primer and back treatment agent coated on the substrate of the two different surfaces, after drying and then coated pressure-sensitive adhesive, the whole process is continuous. The solvent method is simple, easy to operate, and has a wide range of coating thicknesses, especially suitable for gluing on substrates with low strength. The disadvantage is the need to consume large amounts of solvent, increasing costs and environmental pollution. Roll method of sizing order and the solvent method is basically the same, but managed to distribute the glue on the roll, so that the substrate to be coated in two rolls (one or both are coated with glue) to complete the gluing through the thickness of the glue layer available between the two rolls to adjust the distance. Roll coating method without or with less solvent, low cost pollution is very small, uniform layer thickness, safe and convenient construction, but the equipment is more complex, only in the higher strength of the substrate glue. After improvement of the roll-off method, such as isolation roll-off method for a wider range of applications, can be used in any substrates on the glue.
7 pressure-sensitive adhesive in the application of electronic and electrical appliances
Pressure-sensitive adhesives are widely used in electronics and electrical appliances, mainly in the following areas.
1. Electrical insulation. Electrical insulation is mainly transformers, electromagnetic coil winding layer insulation and outer envelope, wire and cable joints and end insulation. The most commonly used is polyvinyl chloride tape and polyester tape. For heat resistance, silicone pressure-sensitive adhesive tapes with glass cloth, PTFE or polyimide as substrate are available. Small transformers and low-voltage coil with PVC, polyester, polypropylene or impregnated, coating treatment of paper and cloth and other substrates of pressure-sensitive tape as winding insulation, end fixing and external envelope. For large transformers requiring heat resistance, aramid and glass cloth tapes should be used, or polyimide, PTFE or silicone impregnated glass cloth tapes can be used. In order to improve the electrical insulation properties of the transformer, generally are insulating varnish vacuum impregnation, when the pressure-sensitive adhesive tape should be resistant to insulation varnish impregnation.
2. Welding mask and surface protection. Printed wiring board connectors are to be electroplated in order to improve the contact performance, the circuit board in the wave soldering, the need to not tin parts of the mask; masking tape should be used when spraying. Masking tape is generally used as a substrate for high strength paper, crepe paper or polyester film. The masking tape is also solvent resistant, and wave soldering masking tape is required to withstand temperatures of 230°C or higher instantaneously. Home appliances for advanced nameplate and sprayed surface, cathode ray tube glass screen surface, and electronic calculator surface mostly polyethylene film as the substrate of the protective film (a special pressure-sensitive adhesive tape) for surface protection. It is required to be easy to peel off, and the pressure-sensitive adhesive should not remain and contaminate the protective surface. Semiconductor and integrated circuit silicon wafers also need to use protective film.
3. Cluster fixed. TV deflection coils, demagnetization coils and other electromagnetic coils of the cluster and the end of the treatment of most of the use of flame-retardant polyvinyl chloride tape. Refrigerators, washing machines and other electrical conduits or splints of the fixed and sealed; refrigerators, air conditioners in the production process, foamed polyurethane or foamed polyethylene and other heat-insulating materials when molding the fixed and sealed, cathode ray tube glass and explosion-proof hoop between the buffer are applied a variety of pressure-sensitive adhesive tape. Printed circuit board assembly plug-in automation needs components arranged neatly, the use of paper-based pressure-sensitive adhesive tape can make a single component into a strip of orderly packaging form, the whole plant and then in order on the basis of a variety of components, in accordance with the pre-determined instruction program for the second selection of sequential tape, which is currently the only electronics industry can be the only high speed automatic plug-in method. In addition, the automatic production of ceramic capacitors, polyester capacitors and resistors also require pressure-sensitive tape for taping and fixing. Electronic equipment tends to be ultra-miniaturized, sheet (lead-free) components will increase the production volume, will make lead-free components for packaging pressure-sensitive tape and can be hot melt pressure-sensitive adhesive dosage will be greatly increased.
4. Double-sided paste. Double-sided adhesive tape can greatly improve the workability of the installation of audio equipment scale board, color TV's door indicator sign by adopting double-sided adhesive tape. Foam polyurethane as the substrate of double-sided tape is also widely used in audio-visual equipment for shockproof machine. Double-sided tape is used for the end reinforcement of flexible circuit boards for the miniaturization of electronic computer equipment, for the installation of diaphragm switches on electronic calculator keyboards, and for the installation and fixing of polarizing poles in liquid crystal displays.