Patent Application
20090236030
The present invention relates in general to a molding process and related apparatus and pertains, more particularly, to an improved method and associated apparatus particularly adapted for making rubber soles for boots or shoes.
One flow molding apparatus known in the art for making plastic parts comprises a top electrode and a bottom electrode with top and bottom molds disposed therebetween. The top and bottom molds define a molding cavity in which a plastic material may be placed. Preferably, the current field lines are perpendicular to the plastic material at all points along its surface to thereby provide a uniform temperature throughout the material. In addition, the top and bottom electrodes substantially match the configuration of the plastic part that is being fabricated such that the distance between the electrodes is constant in order to provide uniform heating of the plastic material. In operation, an alternating electric field is applied across the molding cavity to thereby form the plastic part. An example of this type of a flow molding apparatus is disclosed in U.S. Pat. No. 4,268,238 (which is incorporated herein by reference).
Another flow molding apparatus known in the art for making plastic parts comprises a top electrode and a bottom electrode with a mold disposed therebetween. The mold has a non-uniform thickness so as to allow the molding of a non-uniform plastic part from a plastic material placed between the mold and the top electrode. In order to provide uniform heating throughout the plastic material, a constant capacitance is maintained throughout all of the different thickness sections of the plastic part. This may be accomplished by equalizing the relative dielectric constants between the plastic material and the mold, preferably by altering the relative dielectric constant of the mold via the use of additives. Alternatively, the capacitance may be equalized by modifying the spacing between the top and bottom electrodes in the different thickness sections of the plastic part. An example of this type of a flow molding apparatus is disclosed in U.S. Pat. No. 4,441,876 (which is incorporated herein by reference).
Another flow molding apparatus known in the art for making foamed plastic parts comprises a top electrode and a bottom electrode with a mold disposed therebetween. A plastic foam material may be placed in a cavity of the mold and then compressed during the heating cycle. After the heat is terminated, the compressed plastic foam material is permitted to expand as it cools so as to conform to the shape of the mold and thereby form the foamed plastic part. An example of this type of a flow molding apparatus is disclosed in U.S. Pat. No. 4,524,037 (which is incorporated herein by reference).
Yet another flow molding apparatus known in the art for making foamed plastic parts comprises a top electrode and a bottom electrode with a two-piece mold disposed therebetween. The mold supports a diaphragm such that a plastic foam material may be placed between the diaphragm and the bottom mold. A fluid is injected into the mold above the diaphragm so as to initially deflect the diaphragm and thus expel substantially all of the air from the mold. The fluid is then extracted from the mold during the heating cycle, which causes a vacuum in the mold to thereby assist in the expansion of the plastic foam material. An example of this type of an apparatus is disclosed in U.S. Pat. No. 4,851,167 (which is incorporated herein by reference).
Another molding process is used for making a molded article from two or more different formable materials having different molding temperatures and a single heating or molding cycle. An example of this type of an apparatus is disclosed in U.S. Pat. Publication No. 2006/0012083 (which is incorporated herein by reference). Also incorporated by reference in its entirety is US Publication No. 2006/0012082.
There is also schematically illustrated in
In this prior technology the mold is mounted in a hydraulic press (not shown) for applying a pressure in the direction of arrow 15 illustrated in
The process also includes a heating of the mold. In the metal heated mold illustrated in
In the shoe industry, it is common to provide a foamed mid-sole that is placed on top of the rubber bottom sole. The mid-sole is typically formed of polyurethane, polyethylene, or EVA (ethylene vinyl acetate) foams. It has been found quite difficult to bond those mid-soles to the rubber bottom sole. For military applications for boots, there is a request for a pull test where the bond between the mid-sole and the bottom sole has to exceed 100 pounds. Adhesive films do exist that bond suitably to the mid-sole but they do not bond well to the vulcanized rubber.
In the prior art shown in
In accordance with the present invention there is provided a method of making a molded article, preferably for making a shoe or boot bottom sole. The mold may be considered as a two part mold that defines a mold cavity therebetween. The method includes positioning a rubber base material in the mold cavity. The rubber base material is constructed and arranged to substantially match the profile of the mold cavity. An adhesive film is formed over the rubber base material. Energy is applied across the mold so as to heat and vulcanize the rubber base material while concurrently adhering the adhesive film to the rubber base material. Thus, in accordance with the present invention, rather than providing a single centrally disposed block of raw rubber material in the mold, the rubber material is formed to conform to the size and shape of the mold cavity. The rubber material preferably covers substantially the entire bottom side of the mold cavity. The rubber base material may be formed either in a single matching profile or may be formed by multiple sheets stacked one on the other to provide the same basic profile. The energy that is applied to the mold may be RF energy applied between respective electrodes or the mold may be a metal mold and the energy is applied by heating the metal mold to vulcanize the rubber base material. There may also be provided a foam mid-sole material over the adhesive film with a blowing agent so that the foam material fills the mold cavity. In one embodiment practiced herein, a bladder may be used over the foam mid-sole material, closing the bladder against the foam material and enabling the bladder to move against the mold as the foam material expands.
In accordance with another aspect of the present invention there is described a method of attaching a shoe or boot upper to a sole construction by using a mold having a mold cavity. This method includes positioning a rubber base material in the bottom of the mold cavity where the rubber base material has an adhesive film attached thereto and providing an upper rubber layer attached to the shoe or boot upper and also having an upper rubber layer having adhesive film attached thereto. The respective films may be considered as defining therebetween a cavity pocket. The final step is injecting a foam material into the cavity pocket so as to form the mid-sole. A polyurethane foam may be injected into the cavity pocket.
In accordance with still another aspect of the present invention there is provided an apparatus for molding an article in which the mold includes separate mold parts that define therebetween a mold cavity. A pair of electrodes is provided, one associated with each of the mold parts. An RF source is coupled to the electrodes to provide RF energy across the mold cavity. A rubber base material is disposed in the mold cavity with the rubber base material being constructed and arranged to substantially match the profile of the mold cavity. An adhesive film is disposed over the rubber base material. The application of the RF energy across the mold heats and vulcanizes the rubber base material while concurrently adhering the adhesive film to the rubber base material. The rubber base material may be either formed as a single matching profile or formed with multiple rubber sheets.
The method and apparatus of the present invention will now be described in greater detail in the following detailed description of the invention as taken in conjunction with the following drawings, in which:
Reference is now made to the drawings for further illustrations of the principles of the present invention. Previously, mention was made of the prior art technique of providing a “hockey puck” size base material along with the use of heat and pressure to form the bottom sole. This has been found to be an inefficient process limiting the number of soles that can be outputted. Now, in accordance with the present invention the raw material, such as typically a rubber material, is formed with a profile that substantially matches the profile of the mold cavity. In this regard, refer to
In accordance with the present invention the molds themselves can be constructed of either a metal material or a non-metal material. If the mold is constructed of a metal material then it is preferably provided with small venting hole 22 (see
A preferred molding technique in accordance with the present invention uses a flow molding process (radio frequency) heating such as is practiced in my previously issued U.S. Pat. No. 4,441,876, particularly where the mold has a non-uniform thickness. In order to provide uniform heating throughout the raw material, a constant capacitance is maintained throughout all of the different thickness sections of the part. This may be accomplished by equalizing the relative dielectric constants between the raw material and the mold, preferably by altering the relative dielectric constant of the mold via the use of additives. Alternatively, the capacitance may be equalized by modifying the spacing between the top and bottom electrodes in the different thickness sections of the part. This provides a heating at the same rate in both thin and thick sections of the bottom sole.
If RF energy is used then the molds are non metallic. For example, the mold can be made out of different materials that may be fiber reinforced such as out of silicone, epoxy, etc. The molds are not preheated. The RF dielectric heats the rubber and does not heat the mold except a small thin skin around the mold to allow curing all the way to the face of the rubber. Refer also to my earlier US Publication No. 2006/0012082 for another example of a non-metal mold. Generally speaking non-metal molds are cheaper than metal mold and thus preferred.
Another advantage of using the RF technique is that a relatively low pressure is used as the rubber has only to conform to the mold and does not have to flow far away. This enables a speeding up of the overall molding process. The process of the present invention allows the mold to produce up to 8 pairs which are molded at once under a one minute cycle. The rubber is heated at the same rate throughout its thickness. The process of the present invention thus produces 250 to 400 pairs per hour instead of 46 to 72 pairs per hour with the prior art technique.
In accordance with the process of the present invention, another advantage is that one can readily now add a film on top of the rubber raw material of the bottom sole shape. Because the raw material profile matches that of the mold the adhesive is not broken or stretched during the vulcanizing, and thus the adhesive layer stays where it has been placed and bonds very well to the rubber during the vulcanization process. This allows polyurethane injection of the foamed midsole on top of the rubber bottom sole which bonds very well to the rubber using the polyurethane film already bonded to it.
In accordance with the present invention various types of adhesive films or layers may be used. However, the preferred film is a polyurethane film. The film can also be of polyolefin. Polyurethane is used when bonding rubber (bottom sole) to the urethane foam midsole. A co-extrusion polyurethane-polyolefin may be used when bonding the rubber bottom sole to the polyethylene or EVA (Ethylene vinyl acetate) foam midsole. In other applications vinyl, polyester or polyamide films may be used. An adhesive coating on top of the rubber may also be used instead of a film form. This may be applied in any one of a number of different ways. The preferred supplier of the films is Upaco Adhesives of Nashua N.H.
Reference is now made to
In accordance with the present invention there are different options depending on the customer's needs. A first case is illustrated in
Another use of the principles of the present invention relates to the embodiment shown in
The mold structure shown in
In another version of the present invention a single process step can be used with the mold structure of
From the initial position of
In
In
After the boot or shoe upper is in place, then the forming of the midsole is accomplished. A foam material such as urethane is then injected through the port 58 into the mold cavity to make a midsole. Due to the film 57 on top of the rubber bottom sole material, the polyurethane foam midsole bonds to the rubber bottom sole. The polyurethane also bonds to the rubber layer 52 (that is molded with the film 59) that is used under the boot upper. Rubber can also possibly be injected. A machine for the injection molding operation may be the well-known “Desma” machine. This machine is made by a German manufacturer and has many stations, up to as many as 24 stations, thus allowing for an improved quantity of production.
In practicing the principles of the present invention the following prior patents or publications of mine may be used depending on the particular application. For example, US Publication No. 2006/0012083 describes a method of making a molded article from two or more formable materials in a single heating cycle, while US Publication No. 2006/0012082 describes a method of forming a hardened skin on a surface of a molded article. The principles set forth in US Publication No. 2006/0012083 can particularly be used when molding more than one plastic compound at the same time. Thus, in one step one can mold the rubber bottom sole (which will shape and vulcanize) to the EVA midsole (which will be a blowing foam from raw material containing a blowing agent), which decomposes at a certain temperature. Both materials can be brought to their respective molding temperatures, at the same time, even though the molding temperatures are different, as described in '083 publication.
In accordance with the present invention the preferred mold material is non-metallic, although the principles can be practiced with a metal mold. As mentioned previously the mold may be vented with a small hole to let the air escape such as through a hole like that shown in
The embodiments described herein have used primarily RF energy for vulcanizing. However, the principles of the present invention also apply to other mold constructions including both metal and non-metal molds, as well as using other energy forms including a metal mold with accompanying heat and high pressure. A vacuum may also be used which allows molding with a heated metal mold rubber starting from sheets or a profile. This would then allow a film to be placed on top of the rubber without damaging it.
It is noted that in, for example,
Alternate embodiments are now described that are similar to the previously described ones but, instead of a flat bottom sole, a shell of rubber is used which has a film inside that bonds to a foam just as has been described before. The same process is used in
For the athletic shoe, refer to the embodiment shown herein in the schematic diagram of
For a regular shoe, refer to the schematic diagram of
Having now described certain embodiments of the present invention, it should now be apparent to those skilled in the art that numerous our embodiments and modifications thereof are contemplated as falling within the spirit and scope of the present invention. As mentioned before the use of RF energy for curing is preferred, but other types of processes can be used for the vulcanizing. Either metal or non-metal molds can be used, although a non-metal mold is preferred, in conjunction with the use of RF energy for heating and curing.
