Self-adhesive material

The formulation of the latter contains certain adhesion promoters which allow for enhanced affinity between rubber and the other substrate. The chemical nature of self-adhesive materials in most cases is proprietary information which cannot be disclosed. But, several models for bonding are described in the literature [10]. 

Another similar test is the peel test [11]. A strip of self-adhesive material is peeled off the substrate and the force needed for peeling is recorded. In order not to tear the rubber during the peeling test it is reinforced with a glass fabric. 

Practically, all properties known for LR can be incorporated into a self-adhesive material. Such modifications include LR with enhanced oil, tear and/or heat resistance. 

A viable solution could be the combination of primer and self-adhesive material, or even a combination between self-adhesive and mechanical anchorage. Mechanical anchorage will ensure a residual stability of the composite, and the self-adhesive material will guarantee hermetic sealing. 

Figure 11.7 shows that adhesion increases with the course of time. This property is used as evidence to assume that composites made of self-adhesive materials or materials and primers will not fall apart after anv time under normal circumstances. 

A number of RTVl, RTV2 and HTV self-adhesive materials are available which will not only work as an adhesive at first sight but also in cured in place gasket , a technology of growing importance in the automotive industry and many other areas. 

To measure the shear strength a force is applied parallel to the adhesive bond. For floorcovering adhesives the force per area, which results in fracture of bonded samples, is registered. For PSAs the time is measured required for a certain area of self-adhesive material to slide off a standard surface in parallel direction to the surface with a constant load of 0.5 or 1 kg. Shear strength is determined by destroying a bonded area and is taken as a measure for the cohesive properties, whereas peel strength is the force applied to a bonded length and represents the adhesives properties, in particular when adhesion fracture occurs. In either measurement it is important to know the fracture pattern in order to assess the properties correctly and to be able to improve the adhesive properties. 

Corresponding to FINAT test method No. 8, the shear strength is the time required for a certain area (25 mm x 25 mm) of a self-adhesive material to slide off a standard surface in the parallel direction to the surface with a load of 1 kg (Fig. 8-21). The standard surface used is glass. In PSTC-7, a 12.5 x 12.5 mm adhesive contact area on corrugated or stainless steel is subjected to a 1 kg load and the time to adhesive failure is recorded. 

Constrained-Layer Treatments. Constrained-layer damping treatments consist of a thin layer (/ m) of viscoelastic material sandwiched between a base material and an outer constraining layer of sheet metal or other stmctural material. Some of these treatments are available with self-adhesives on both sides of the viscoelastic material and act as a bonding agent between the base and constraining layers others have the constraining layer already bonded to the inner layer so they need only be appHed to the base material. 

This stock is discharged from the mixer to equipment that allows cooling and a convenient storage form, such as a mill or an extmder/die plate that yields a sheet or pelletized form. Usually the material is coated with a slurry of clay, calcium carbonate, or zinc stearate to prevent self-adhesion. 

The use of coatings applied in the form of tape is also increasing. Polyethylene and polyvinyl chloride films, either self adhesive or else supporting films of butyl adhesive, petrolatum or butyl mastic are in use as materials applied cold at ambient temperatures. Woven glass fibre or nylon bandage is also used to support films of filled asphalt or coal tar and these are softened by propane gas torches and applied to the steel surface hot, cooling to form a thick conforming adherent layer. 

Promote improved elasticity and cold temperature flexibility. Used in cables, self-adhesive products, roadmarking materials, etc. 

Strip packages represent an alternative form of packaging for unit-dose medication. Strips can be produced from single- or multiple-ply laminated materials provided the two inner plies can be sealed by heat or pressure (e.g., cold self-adhesive seals). Materials can range from relatively permeable plies to those that incorporate a foil ply of sufficient thickness and effectiveness of seal so that an individual hermetic seal is produced for each dosage. Strip packages are produced at lower speeds and occupy greater volume than blisters. 

Additional drawbacks to the use of polyimide insulators for the fabrication of multilevel structures include self- or auto-adhesion. It has been demonstrated that the interfacial strength of polyimide layers sequentially cast and cured depends on the interdiffusion between layers, which in turn depends on the cure time and temperature for both the first layer (Tj) and the combined first and second layers (T2) [3]. In this work, it was shown that unusually high diffusion distances ( 200 nm) were required to achieve bulk strength [3]. For T2 > Tj, the adhesion decreased with increasing T. However, for T2 < Tj and Tj 400 °C, the adhesion between the layers was poor irrespective of T2. Consequently, it is of interest to combine the desirable characteristics of polyimide with other materials in such a way as to produce a low stress, low dielectric constant, self-adhering material with the desirable processabiHty and mechanical properties of polyimide. 

The 6th material Is a condensation-cure product which has been previously used for medical Implant protection (I). As verified by lap shear tests, (described below), the first 3 elastomers provide minimal adhesion In the absence of a surface primer. The last 3 are self-prlmlng materials. To permit visual examination, we tried to select clear materials. All of the elastomers are clear except for types 5 and 6. 

Airofom PA 230 is a non-crosslinked PE foam which while having a slightly lower temperature resistance than crosslinked types, is claimed to be substantially cheaper to process. It has a closed-cell structure and is available in rolls, sheets and fabricated products, or as a self-adhesive backed or laminated to other materials. A sample of the foam is included. 

Examples are given of the use of extruded PE foam sections in conjunction with other polymeric materials in the production of triangular, semicircular, rectangular and trapezoidal profiles, e.g. beam-like structures in which the rigid support may be of GRP. The foam can be bonded with thermally-fusible adhesives or two-sided self adhesive tape affixed to the foam prior to fabricating. A standard range of the foam prodncts is available, but other types can be tailor-made. 

Self-Adhesive or Pressure-Sensitive Labels. It is preferable to call these pressure-sensitive labels, as both the pregummed and heat-sensitive labels are self-adhesive (i.e., the adhesive is already there). They consist of a suitable label facing material (usually paper or polymer), the reverse side of which is coated with a permanently tacky adhesive that is in contact with a backing paper (occasionally plastic) that protects it prior to use. The backing paper is coated with a special release coating that permits the label to be removed easily. Labels may be provided on roll or sheet form both can have the label laid on that is, the unprinted area has been cut and removed. 

The windows in EPROM chips are used during the erasure process. When you open a computer case, make sure they are covered with a small piece of opaque material (part of a self-adhesive mailing label works well) to prevent light (either sunlight or light from fluorescent lamps) from inadvertently erasing these chips. 

Acetyltributyl citrate is used in oral pharmaceutical formulations and films intended for direct food contact. It is also used in self-adhesive thin films used for topical delivery systems. It is generally regarded as a relatively nontoxic and nonirritating material. However, ingestion of large quantities may be harmful. 

It has generally been observed that urethane systems, which are cured on the surface of some low energy materials, are also free from adhering to them, i.e. they are self-releasing. Materials which show this characteristic relative to urethanes in a very effective way include at least three different types of plastics polytetrafluoroethylene, polyethylene, and polypropylene. These materials all have a defined critical surface tension sc less than about 30 dynes/cm. Assuming that this value is near, the liquid vapor surface tension lv value of an effective IMR urethane systems, then the work of adhesion as given by Equation 4 is as follows ... 

Corn and callus caps and plasters contain high concentrations (usually 40%) in a semisolid base spread on to a suitable backing material, contained within a ring that is either self-adhesive or attached to an adhesive plaster. They should be changed every 1-2 days for about a week, after which the callosity should lift away easily. 

During the last decade many new roofing materials were introduced which are applied in the form of weldable membranes, liquid curable materials, self-adhesive products, and torchable materials. These materials are produced from numerous polymers such as, PVC, chlorinated polyethylene, chlorosulfonated polyethylene, EPDM, acrylics, bitumen, polymer-reinforced bitumen and several other materials. It is beyond the scope of this book to analyze compositional changes in these materials. We will provide a brief overview. 

The exposed area of woodbased panels and other materials were 1.0 m. Thus the loading factor in the chamber is 1.0 m /m. The air change rate was 1.0 airchange per hour. Since the emission from the edges of the board often are higher, the edges are consequently sealed with self-adhesive aluminium tape. For preconditioned test pieces the steady state concentration will be reached within a week. 

Self-adhesive labels can be applied to most materials wood, plastic, metal, glass, paper and board. As the adhesives are resin-based (plasticised thermoplastics), migration problems can occur when they are applied to certain plastics (PVC, LDPE, etc.). Adhesive systems for pressure sensitive labels include latex and acrylic bases and adhesives which may be applied as a hot melt, or via a solvent, emulsion or dispersion base. Water-based adhesives are currently increasing in use. 

Exchange between product and pack can occur in both directions, e.g. certain labelling materials such as heat sensitive and self-adhesive labels when in contact with plastic materials. Both the plastic and the adhesives may contain plasticisers or migratory constituents. Most cellulosics use phthalate, sebacate, phosphate-type plasticisers (e.g. methyl phthalate (DMP) may be used in cellulose acetate). Plasticisers may also be found in poly vinyl chloride/acetate copolymers, polyvinyl acetate and polyvinyl alcohol formulations, polymethyl methacrylate, nylon and certain thermosetting resins. 

Achieved by aqueous, solvent, hot melt, etc., adhesives or self-adhesives, cold seal materials. Solder is a metallic adhesive system. Solvent bonding is a chemical adhesive system. 

Print adhesion on plastics (and foil) is normally checked using a self-adhesive tape peel test. A few inches of a suitable standard tape is firmly pressed onto the print area then pulled off, slowly at first, then more rapidly. An assessment of print adhesion can be made from the quantity (ideally none) removed. Adhesion can vary according to the type and colour of the ink, the degree of pretreatment, the surface involved and the printing process, etc. In order to test print under likely use conditions, product immersion tests may be necessary 60°C (140°F) is a frequently used condition, for 3 to 6 h. If product-pack may be used with soapy hands, a solution of soap can be employed. A print adhesion test, as above, can then be carried out, on the washed material, after it has been cooled to room temperature. 

Although 10 years ago the US pharmaceutical industry predominantly used heat seal labels, the UK was rapidly moving to the more expensive self-adhesive labelling systems. Since Europe is now predominantly using self-adhesive, there appears to be an international trend even though it is a more expensive label process. It has the advantage, with the correct choice of materials, that it will adhere to most substrates. 

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