Bond strip technology

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/145,600, filed Feb. 4, 2021. The disclosure of the above application is incorporated herein by reference.

The present invention relates to joining of fiber filled thermoplastic parts.

Resistive implant welding (RIW) process to bond together thermoplastic parts molded with a 20% carbon fiber filled nylon resin have been used in the past and present.

The process consists of molding the two separate components of a part and joining them by way of a special mesh that is heated and rolled with force into one of the components. The two components are then nested together and the mesh in between the two components is energized with electricity, which melts a layer of resin on both sides of the mesh, while the combined parts are pressed together in a press, bonding the two components together to make a strong, single part. Such a process is shown in our co-assigned U.S. Pat. No. 9,950,471.

This process is in manufacturing use today for low volume manufacturing programs of approximately 5000 parts a year. Due to the time-consuming nature of rolling the mesh on to the part and the heating up and pressing of the components together along with the precise control needed for the electrical current being put into the mesh, this process is not suitable to be scaled up for a high volume of parts production.

Therefore, it is a goal in the art to provide an improved process suitable for production part capability.

The process of the present invention includes a process for joining polymer molded parts. The process includes:

a. Providing a first part made from a first material and a second part made from a same or different material; b. Attaching an infrared bonding material to at least one of the parts in a place for the parts to be joined; and, c. Heating the at least on infrared bonding material with an infrared heating element and pressing the first part into contact with the second part wherein a bond is formed.

In order to overcome the problem of bonding both the 20% carbon fiber filled and 60% glass filled resins, we conceived the idea to overmold a strip of secondary resin molded locally on the part, where the IR welded bond is needed to take place. This secondary resin strip would typically be made of same base resin as the structural resin used, but without fillers to disrupt the IR welding process. In the case of our nylon filled resins, we would use a nylon resin with no glass or carbon fiber fillers.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a half section of a first molded part to be joined in accordance with the present invention;

FIG. 2 is a perspective view of a second part to be joined to the first part having a compatible IR bonding material overmolded at the joining locations;

FIG. 3 is a sectional view of area 3 showing the part of FIG. 2 ;

FIG. 4 is a sectional view showing the parts of FIG. 1 and FIG. 2 joined together by the process of the present invention;

FIG. 5 is a sectional view of a part bonded without any secondary strips;

FIG. 6 is a sectional view of a part prior to bonding with overmolded material;

FIG. 7 is a sectional view of the part of FIG. 6 bonded together; and

FIG. 8 is a schematic view of the process of the present invention.

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

In order to overcome the problem of bonding both the 20% carbon fiber filled and 60% glass filled resins, we conceived the idea to overmold a strip of secondary resin molded locally on the part, where the IR welded bond is needed to take place. This secondary resin strip is typically be made of the same base resin as the structural resin used, but without fillers to disrupt the IR welding process. In the case of our nylon filled resins, we would use a nylon resin with no glass or carbon fiber fillers.

These strips of secondary resin could be applied to one or both halves of the components being joined. The width and thickness of the strip would vary depending on the bond needed and the resins effectiveness to be joined.

Other methods of joining besides IR welding may be applicable to using this secondary strip of resin to enable bonding such as hot plate welding, ultrasonic welding or vibration welding.

In an alternate embodiment, the process is also used to allow dissimilar plastics to be joined together. The secondary strips made of compatible resins are added to one or both dissimilar plastics to enable their joining.

In an additional embodiment, this method could be used with adhesives if the base resin in a part is unable to be dissolved by an adhesive to create a sufficient bond to another part. A secondary strip of resin can also be added to make a joint between them compatible if necessary.

The process of adding this secondary strip of material to a primary plastic part is typically done through the process of two-shot injection molding or insert molding. The two-shot injection molding process enables the overmolding of the secondary strip resin because it is done immediately after the primary part resin is injected into the mold. While the primary part is still hot but sufficiently solid to manipulate, it can be presented to another cavity and injected with the secondary plastic resin, forming the strip of material to be bonded. Because this secondary injection of plastic occurs while the primary part is still very hot and is being done with plastics that have common base resin, a strong molecular bond occurs between the two resins. Once this occurs, the two parts can be bonded together by the joining process required.

Referring now to the drawings, and in particular to FIG. 8 , there is provided a process for joining polymer molded parts, generally shown at 10 . The process involves the steps of providing a first part 12 and a second part 14 to be joined along cooperative joining portions 16 and 18 . The first part made from a first material and a second part made from a same or different material as the first material. Then an infrared bonding material is overmolded or otherwise bonded to at least one of the parts ( 12 , 14 ) in a place ( 16 or 18 or both) for the parts 12 , 14 to be joined. The parts 12 and 14 are either already in the mold halves 20 , 22 that they were molded in, or they are placed in a mold cavity for joining them together. The molds are separated and an infrared heating element 24 is inserted between the parts 12 and 14 . This heats at least the surface with the infrared bonding material 15 , which can be on one side or both sides. Thereafter the mold is used for pressing the first part 12 into contact with the second part 14 at the joining surface 15 wherein a bond is formed.

When two bonding materials are used the first infrared bonding material and second infrared bonding material are compatible for infrared melt bonding to each other and also to the respective surfaces 16 and 18 on the parts 12 and 14 . Preferably parts 12 and 14 comprise thermoplastic fiber filled thermoplastic resins.

While Nylon and glass filled, or graphite filled polypropylene are preferred polymers. However, the present process is used with any filled resin with a high filler content that makes joining difficult. Generally, this process would be used with fiber filled materials having above about 20% fillers. Typically, the amount of fillers are about 40% and above fiber content, preferably the filler content is from about 40% to about 60% all fiber fillers are by weight. For carbon fiber filled resins it would be useful for amounts of 20% and above filler. This process when other fillers are present in a resin that makes joining difficult. The present process is also useful to bond two parts with differing levels of filler together, if one half needed some special properties or as a cost saving measure.

As an example, the polymer is a 10-30% carbon fiber filled nylon composition and a nylon material is overmolded on the surfaces to be joined prior to infrared heat treatment for joining the parts. Highly filled 30-60% filled long glass fiber compositions are also joinable using the process of the present invention. Typically, the resin is a carbon fiber or glass filled fiber composition.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the essence of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.