Patent Application
20050151299
The present invention is generally directed to a method of bonding various materials such as foam materials to polymeric materials and to articles made therefrom. More particularly, the present invention is directed to a method of bonding foam materials to thermoplastic polymers using silane containing compounds.
Many useful articles are constructed by bonding foams to various structural materials. The foam can be incorporated into the product in order to provide thermal insulation, to provide insulation from noise, to act as a filler, to increase the structural integrity of the article, or for many other various reasons. In the past, when bonding foams to plastic materials, the foams have been primarily used with thermosetting polymers and with composite polymers such as fiberglass. Unfortunately, thermoset plastics are difficult to recycle once used.
In many foam and polymer applications, it would be very desirable to replace the non-recyclable plastics with recyclable materials, such as thermoplastic polymers. In the past, however, many difficulties have been encountered in sufficiently bonding the foam materials to the thermoplastic resins. The prior art teaches using cross-linking agents such as peroxides to form the bond. The cross-linking agents, however, render the polymers non-recyclable, thus removing one of the primary advantages of using them.
For instance, one prior art construction is directed to a process for the production of multi-layer moldings from a substrate member. The process includes bonding an elastomer foam to polypropylene containing a cross linking agent. The cross-linkable polypropylene and elastomer foam are combined and compression molded and then stored under hot conditions in order to increase the degree of cross-linking. As discussed above, however, cross-linking agents can render a thermoplastic resin thermoset in character making the polymer very difficult to recycle.
Generally speaking, the present invention is directed to a method for bonding various materials especially foam materials to thermoplastic polymers without using cross-linking agents. In particular, a silane compound is used for bonding a foam to the polymer. Unexpectedly, through the process of the present invention, no cross-linking agents, such as peroxides, are necessary for establishing a bond between the foam and the polymer. As shown in the accompanying figures, the method of the present invention can be used to construct watercrafts, pallets, thermocoolers, and many other useful articles.
The present invention is generally directed to a method of making polymeric and foam articles using a rotational molding technique. According to this method, a mold having an interior surface is first loaded with a predetermined amount of a polymeric material. The amount of the polymeric material added to the mold should be sufficient to cover substantially the entirety of the interior surface. Once loaded, the mold is heated and rotated causing the polymeric material to melt and distribute over the interior surface.
Thereafter, a predetermined amount of mist containing silane solution is sprayed into the mold to dope the polymeric material with silane. The silane solution contained with the silane mist can contain from 0.1% to about 20% silane. The solution can also contain an alcohol having a neutral to basic pH.
Rotation is continued in a manner such that the silane-doped polymeric material distributes over the mold. The molded material is then cooled and bonded to a dissimilar material, such as a foam material.
In particular, the foam material, which can be a polyurethane foam, is bonded to the inner layer comprised of the silane-doped polymeric material. In one embodiment, the polyurethane foam can be formed directly on the shaped polymeric article by reacting a polyol with an isocyanate. It is believed that while the polyurethane is forming it simultaneously bonds with the silane contained within the polymeric material.
In another embodiment, the polymeric shaped article can comprise multiple layers of polymeric materials. The silane-doped thermoplastic resin forms at least one surface on the shaped article for later bonding with the foam material.
Other features and aspects of the present invention are discussed in greater detail below.
A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:
Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous feature or elements of the invention.
It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended to limit the broader aspects of the present invention, which broader aspects are embodied in the exemplary construction.
The present invention is generally directed to a method of bonding various and different materials such as foam materials to recyclable thermoplastic resins. The present invention is also directed to various polymer and foam articles made according to the above method. More particularly, according to the process of the present invention, a thermoplastic resin is doped with a silane compound while the resin is being molded into an article. A different material, such as a polyurethane foam, is then bonded to the article for any desired reason.
As described above, the foam material is bonded to the thermoplastic resin without using a cross-linking agent, such as a peroxide. When cross-linking agents are employed, the thermoplastic resins take on thermoset properties and are no longer easily recyclable. In the present invention, however, the foam materials are bonded to the thermoplastic resins without the resins losing their thermoplastic characteristics.
The resulting polymer and foam articles are lightweight but have substantial structural integrity. Products that can be made according to the process of the present invention include watercrafts, polymeric pallets, polymeric furniture, insulated storage tanks, thermocoolers, children's toys, and many other various items.
Describing the process of the present invention in more detail, first a polymeric material, namely a thermoplastic polymer, is doped with a silane. As used herein, a silane refers to any compound that contains silicon. Preferably, the silane compound used in the present invention is an organosilane having the following general formula:
R—SiX3
wherein R is an organofunctional group and X is a hydrolyzable group that may convert to silanol on hydrolysis. In some embodiments, R can include a propylene group bonded to various other groups such as chlorine, a methacrylate group, or an amino group.
The X in the above formula, on the other hand, is typically an alkoxy group such as a methoxy group. Preferably, the SiX3 group is a trimethoxysilane.
Commercially available silane coupling agents that can be used in the process of the present invention can be obtained from Dow Corning Corporation, located in Midland, Mich. One preferred silane coupling agent available from Dow Corning Corporation is N-(2-aminoethyl)-3-aminopropyltrimethoxysilane which has the following chemical formula:
NH2CH2CH2NH(CH2)3Si(OCH3)3
As stated above, the chosen silane compound is used as a dopant in being combined with a thermoplastic polymer. As used herein, a silane-doped thermoplastic resin refers to a thermoplastic polymer that has been treated with a silane compound. Generally, any thermoplastic polymer or resin may be used in the process of the present invention. In particular, polyolefins such as homopolymers and copolymers of polypropylene, polyethylene, polybutylene or mixtures thereof, or vinyl polymers such as polyvinyl chloride or a polystyrene may be used. The particular polymer chosen for use in the present invention will depend upon the particular article being made and the physical characteristics that are desired.
Silane compounds are typically commercially available in either a dry form or as a concentrate. It has been found that when used in the present invention, it is preferable to place the silane in an aqueous solution prior to application to the thermoplastic polymers.
The silane solution used in the present invention contains from about 0.1% to about 30% by weight silane and preferably contains about 5% by weight silane. The remainder of the solution can comprise water or can include water and a stabilizer. Preferably, the stabilizer is an alcohol, such as isopropyl alcohol or etherglycol. When present, the stabilizer can be added in amount from about 5% to about 10% by volume.
According to the present invention, during a process for molding a polymeric article, the silane solution is sprayed on to at least one surface of the article during the molding process. For example, in one embodiment, the silane solution can be sprayed on to the molded article after the article has formed but prior to cooling the article. The silane solution serves as a dopant on a surface of the article for later bonding the article to a different material.
Once molded to a particular shape, the polymeric article is then preferably cooled (for instance, below about 125° F.). Silane remains on the surface of the shaped article and provides reactive sights for bonding with various materials such as foam materials. It has been found, that after melting and hardening the resin, the silane groups become much more amenable to reaction with a foam material for bonding the foam material to the polymer. The reasons for this phenomenon, thus far, remain unknown.
In one embodiment, a layered polymeric product can be made using a rotational molding technique. Various embodiments of rotational molding apparatus that may be used in the present invention are disclosed in U.S. Pat. No. 5,358,682 which is incorporated herein in its entirety by reference thereto, and in which the present inventor is also the listed inventor. In addition to rotational molding, however, it is believed that the process of the present invention can also be used in conjunction with blow molding, injection molding, and any other suitable molding process.
Referring to
When rotational molding apparatus 10 is used according to the process of the present invention, a charge of polymeric material is first loaded into mold 12. Rotational molding apparatus 10 is then wheeled into an oven 18 and heated while mold 12 can be rotated about the Y axis and/or the X axis. Mold 12 is heated to a temperature sufficient to cause the polymeric material contained therein to melt and distribute over the inside walls of the mold.
Whether formed through rotational molding, blow molding, injection molding or any other, means, once a polymeric article is formed containing a silane-doped thermoplastic polymer, according to the present invention a dissimilar material such as a foam material can then be bonded to the article as desired. Specifically, the foam material is bonded to a surface of the article comprised of the silane-doped polymer. The silane contained within the polymer acts as a coupling agent between the polymer and the foam.
Although it is believed that other foam materials may be bonded to the silane-doped thermoplastic resin, preferably a polyurethane foam is used. Polyurethanes are versatile polymers that can be used in forming foam products with a wide range of hardnesses and densities.
Polyurethane foams are typically made by reacting two major chemical components together that are metered and mixed in a preselected ratio. The two major chemical components mixed to produce the foam are a polyol and an isocyanate. Other ingredients can be added as needed for producing a specific type of foam. These other additives may include water, auxiliary blowing agents, catalysts, fillers, coloring agents, and surfactants.
The polyol that is used to make polyurethane foams is typically a diol. For instance, in one embodiment, the polyol can be a copolymer of ethylene glycol and adipic acid. The isocyanate used to make the foam, on the other hand, is typically a diisocyanate. One example of a commercially available polyurethane foam that may be used in the process of the present invention can be obtained from Flexible Products Company located in Marietta, Ga. Specifically, the foam product is made by combining a polyol component with an isocyanate component. It is believed that the isocyanate used is a diphenyl methane diisocyanate.
Polyurethane foams are generally formed using a spraying method or a pouring method. Spraying, which is generally used to produce rigid foams, refers to a process by which the chemical reactants are mixed and sprayed onto a surface where the foaming reaction occurs. In the pouring method, the reactants are dispensed and mixed in an open cavity or in a closed mold where the reaction take place and the foam is formed.
When using a polyurethane foam in the process of the present invention, the foam may be formed upon the polymeric article. While the foam is forming, the foam then reacts and bonds to the silane contained within the thermoplastic polymer.
For example, in one embodiment, a liquid resin containing a polyol and a liquid isocyanate initiator can be kept in separate tanks under a nitrogen blanket. The two components can then be shot out through a hose onto or into the formed polymeric article. Although, the amounts will depend upon the particular polyurethane foam used, the polyol resin and the isocyanate can be mixed and dispensed onto the polymeric article in about a one to one ratio. Once the components are applied to the polymeric article, a polyurethane foam will form that simultaneously bonds to the silane-doped thermoplastic polymer.
Of particular advantage, the foam can be formed and bonded to the polymeric article at lower temperatures, below 100° F. Thus far, it has been found that the foam will adequately form and bond to the polymeric article at temperatures between about 65° F. to about 85° F. and preferably at about 80° F.
Besides foam materials, the silane doping process of the present invention can also be used to bond other various materials to thermoplastic resins. Generally speaking, any material that reacts and bonds with silane can be coupled to the silane-doped thermoplastic resin. More particularly, it is believed that many thermosetting polymers can be bonded to a silane doped thermoplastic resin made in accordance with the present invention. For instance, it is believed that the silane doped thermoplastic resin will bond to epoxies, phenolics, melamines, nylons, polyvinyl chloride, acrylics, urethanes, non-foam polyurethanes, nitrile rubbers, polyesters, polysulfides and others.
When bonding thermosetting polymers and other similar types of materials as listed above to a silane doped thermoplastic resin, preferably the dissimilar material is formed on the surface of the silane doped thermoplastic resin and bonded therewith similar to the process described above using polyurethane foams. Depending upon the material being bonded to the silane doped resin, heat may need to be supplied in order to get the materials to bond together or in order to form the non-doped material.
Many advantages can be realized when bonding thermoplastic resins, especially polyolefins, to different materials, such as thermosetting polymers, rubber-type materials, and other various non-foam materials. For instance, it is now possible through the process of the present invention to coat an article made from a thermosetting polymer with a polyolefin or to coat an article made from a polyolefin with a thermosetting polymer.
Many varieties and types of useful articles can be formed according to the above described process. For instance, articles for use in the building and construction field can be formed, furniture and furniture parts can be constructed, articles for use in motor vehicles can be made, and insulated panels for refrigeration units can be made.
For exemplary purposes only,
A polymer and foam article as exemplified by
Referring to
In a preferred embodiment, outer shell 42 of pallet 40 is made from a silane-doped thermoplastic resin. The thermoplastic resin provides structural support and is completely recyclable. In fact, as stated above, foam material 44 is bonded to shell 42 without the use of a cross-linking agent. Thus, shell 42 retains its thermoplastic characteristics. Further, by having shell 42 securely bonded to foam layer 44, a coherent, lightweight and structurally sound article is produced.
Referring to
Currently, boats and various watercrafts such as illustrated in
The process of doping a thermoplastic resin with a silane can be accomplished by various processes. In one embodiment, the thermoplastic resin is immersed in a silane solution, and the silane-doped resin is then loaded into a molding apparatus, such as a rotational molding apparatus for forming an article. However, in some applications, it may be desirable to apply the silane to the thermoplastic resin while simultaneously molding the resin.
As such, another embodiment of the present invention includes a rotational molding apparatus that can perform the multiple functions of heating a thermoplastic resin, molding the thermoplastic resin into an article, and doping the thermoplastic resin with silane. In accordance with the present invention, the silane may be sprayed into the mold during the molding process for doping the polymeric material.
For instance, referring to
In the embodiment illustrated in
Once formed into small droplets or a mist, the silane solution evenly coats the interior surface of the mold as the mold is rotating along one or more axis.
The amount of silane solution required varies depending on the particular application and the size of the mold. In one embodiment, for example, about one ounce of silane solution is used. When rotational molding apparatus 10 is used to perform the multiple functions of molding and silane doping according to the process of the present invention, a charge of polymeric material is first loaded into mold 12. Rotational molding apparatus 10 is then wheeled into an oven 18 and heated while mold 12 can be rotated about the Y axis and/or the X axis. Mold 12 is heated to a temperature sufficient to cause the polymeric material contained therein to melt and distribute over the inside walls of the mold.
Once the polymeric material has distributed within mold 12, a mist or fog of silane can be released into the mold by injector 20 as described above. The mist dopes the thermoplastic resin with silane.
In one embodiment, approximately one ounce of silane mist is applied to mold 12 near the end of the cycle (at about 12-16 minutes). If the silane is released by the injector 20 at an earlier point in the heating cycle (e.g. 8 minutes), a thicker layer of silane doped resin can form. Likewise, if the silane mist is released by injector 20 after the end of the heating cycle and during the cooling cycle, a thinner layer of silane-doped resin can form. Although it is preferred that the silane mist be released near the end of the heating cycle, the mist can also be released at numerous other points during the heating or cooling cycles, depending on the particular application.
In some embodiments, the silane may be injected into the molding apparatus at higher temperatures to prevent against shock cooling of the polymeric structure. Shock cooling can occur, for instance, at temperatures less than about 280° F., especially during crystallization of the polymer. Shock cooling of the polymer, however, is not a problem at higher temperatures.
In one embodiment, in order to prevent against shock cooling, the silane solution can be released into the mold at lower temperatures if the silane and/or injection gas are preheated prior to being emitted.
Once the thermoplastic resin is doped with silane by injector 20, the interior layer provides a surface for bonding with foam materials. For example, a polyurethane foam can be formed upon and bonded with the silane-doped resin as described above.
In the embodiment illustrated in
These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.
