Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-11-20
2004-02-17
Zacharia, Ramsey (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S338000
Reexamination Certificate
active
06692813
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to bonding and more particularly to the preparation of two surfaces for bonding with a bonding agent.
BACKGROUND OF THE INVENTION
There are numerous methods that have been used for joining together two or more surfaces. The more common methods include welding, joining, or bonding. Two surfaces may be welded together by melting or dissolving them together. Two surfaces may be joined together using a suitable piece of strong material that can be pushed or compressed in some manner. Included in this category are bolts, screws, nails, and rivets. Two surfaces may be bonded together using a bonding agent that forms an adhesive bond to both surfaces. Pressure sensitive adhesives commonly employed for use in labels are a prime example of this type of bonding. Two surfaces may also be mechanically bonded together with a bonding agent that hardens to a strong rigid material. A good example of this bonding is the use of glue to bring two surfaces of wood together.
In the case of welding two surfaces together, if carried out properly with the right materials, very strong bonds result which can be as strong or even stronger than the two substrates themselves. The welding of two metal surfaces is accomplished by employing a small but intense area of heat at the site where the two pieces are to be joined. The heat is so intense that the metal of both pieces melts and flows together. Quite often additional metal is added to the weld during the process. A welding rod of a suitable material (usually the same material as the substrate) is placed in the heated area so that it melts and flows into the weld to build it up. Most metals require very high temperatures and as such only certain conditions are suitable for welding. These include electrical discharge for arc, tig, mig, and spot welding and high temperature gas mixtures such as acetylene-oxygen for gas welding.
Unfortunately, welding cannot always be used to bond two metal surfaces together. In many instances the substrates may not be made of a material that can be welded. In addition, even if the substrate is made of a suitable material it may not be of suitable dimensions for welding. It may be too thin making welding without bum through difficult or even impossible. One surface may be on a thicker substrate than the other resulting in uneven heating or even thermal distortion.
The welding together of two plastic surfaces requires that the plastic is capable of either melting by the application of heat, or dissolving into a solvent. In the case of joining plastic surfaces together by heat, the plastic must have a suitable melting point that allows the material to flow together. Many plastics will soften but not easily melt. In such instances it is often practice to use an alternative method to weld the two pieces together without the need to apply heat. Some plastics are soluble in common solvents. For example polystyrene is substantially soluble in toluene. If a drop of toluene is placed onto a piece of polystyrene and a second piece of polystyrene placed on top, the toluene will dissolve some polystyrene from both surfaces. This layer of polystyrene solution will mix into both surfaces. When the toluene evaporates, the pieces will be firmly joined. Sometimes it is practice to dissolve some of the plastic into the solvent prior to application between the two surfaces to be joined. The familiar plastic model kits sold in hobby shops use this system. The individual model pieces are made from polystyrene, and the glue is a solution of polystyrene dissolved in toluene. This system works well because when the two pieces are bonded together with this glue, the final joint that results is the same material as the substrate (polystyrene). In this respect a true weld has been achieved.
While effective for joining certain types of plastic materials together, welding by heat and/or solvent will not work for the stronger more advanced plastics used in composites. The reason for this is that a weld derives strength by forming a continuous bond of substantially the same material from one substrate to the other. In other words, The two pieces that are welded together literally become one. It is as if the resultant piece was initially made as a single piece. In order for this to take place, the substrate material must become fluid and flow to become at least part of the joint. Advanced polymers commonly employed in composites contain a substantial amount of crosslinking.
The crosslinking keeps the polymer rigid and strong. Crosslinking also prevents the polymer from being welded by heat or solvent. Heavily crosslinked polymers will not melt. If heated they will burn or degrade without melting. Heavily crosslinked polymers will not truly dissolve in solvents. They may swell or even become weak enough to pull apart, however they will not dissolve to form a free flowing liquid.
The joining of two pieces together using a third piece that interconnects both pieces to be joined is a very common practice. A good example of this method of joining is the common nail. A nail is a relatively long and narrow piece of metal having a sharpened end and a blunt end. When joining two pieces together using nails, one piece is placed on top of the other. The sharp end of the nail is positioned into the top piece and directed toward the bottom piece. A hammer is then used to strike the blunt end causing the nail to be driven into both pieces. The result is that the nail holds both the top piece and the bottom piece together. While common for joining two wooden boards together, nails are relatively easily pulled out. Furthermore if nails are to be used for joining two pieces of material together the material must yield to the nail without breaking or shattering. Thus while effective for joining two pieces of wood, nails are not always best suited for joining hard or brittle materials together.
Other examples of this type of fastening include rivets, bolts, and screws. Rivets are fasteners having a wide end and a narrow end that is expandable. Using rivets requires a hole to be drilled through both substrates. The holes are aligned and the rivet pressed into this hole until the wide end rests firmly against the top piece. When the rivet has been pressed all of the way in, the narrow end is expanded so that it cannot work its way out. Rivets are commonly used to join thin sheets of metal together.
Bolts and screws are threaded fasteners that can either be threaded directly into a substrate or alternatively can have a threaded nut screwed onto the free end to tighten the substrates together. In either case, these fasteners join two pieces together by virtue of the fastener itself providing an independent connection between the two pieces.
The bonding of two substrates together with a bonding agent relies on both the strength of the bonding agent as well as adhesion of the bonding agent to both joining surfaces. Adhesive bonding between a bonding agent and a surface relies on molecular attraction and compatibility between the bonding agent and the substrate. If the surface to be bonded and the bonding agent can form true chemical bonds which cross the interface between them, then a strong bond can form based on molecular attraction alone. The nature of this attraction can be that of covalent bonds that result from surface reactions between the bonding substrate and bonding agent, or alternatively, Ionic bonds may form between oppositely charged atoms or groups of atoms. Weaker attractive forces may also play a significant role in adhesion such as hydrogen bonding, polar forces or even the weak attractions that result from the electron clouds in the atoms of one molecule being weakly electrostatically attracted to the positively charged nuclei in the atoms of other molecules.
This type of bonding, while being exceedingly strong, is not easily achieved. In addition, substantial improvements can be obtained by increasing the available surface area. This is usually done by increasing the surface roughness of the substrate. Wit
Satermo Eric K.
Zacharia Ramsey
LandOfFree
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