Syntactic foam plugs

Abstract

The present invention provides an improved syntactic foam plug for plug assist thermoforming wherein such plug is composed of a thermoplastic material having a relatively high melting and / or glass transition temperature. Accordingly, the subject invention encompasses diminishing or removing the undesirable characteristics of thermoset syntactic plugs while increasing the ease by which these articles may be constructed for a given use, by forming such plugs from syntactic foams containing thermoplastics.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This is a Continuation of International Application No. PCT / NL00 / 00536 filed Jul. 27, 2000 which which designated the U.S. and was published in the English language. This application also claims the benefit of U.S. provisional application 60 / 145,821 filed Jul. 27, 1999. The contents of both the PCT application and the provisional application are incorporated in their entirety by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates to thermoplastic matrix syntactic foam plugs for use in plug assist thermoforming and the process of making and using the same. In particular, the present invention relates to forming syntactic foam plugs from thermoplastic matrix material having a melting temperature and / or glass transition temperature at least 5° C. higher than the operating design temperature of the thermoforming process. [0004] 2. Background Art [0005] A plug, or plug assist, is a male tool u...

AI Technical Summary

Benefits of technology

[0011] A still further advantage of the present invention is achieved when plugs are produced from thermoplastic polyamide compounds which are formed, for instance, from lactams in in situ polymerization. In situ polymerization occurs, for example, when a lactam is combined at an elevated temperature with the hollow filler material and a suitable catalyst directly in a vessel or mold that at least approximates the desired shape of the plug. After polymerization, the mold is removed and a plug is obtained. This process can therefore minimize or avoid the need for additional operations within the manufacturing process, which would normally be necessary if the plug were obtained by conventional extrusion techniques.

[0012] Thus, it is an object of this invention to provide an improved syntactic foam plug for plug assist thermoforming wherein such plug is composed of a thermoplastic material having a relatively high melting and / or glass transition temperature. Accordingly, the subject invention encompasses diminishing or removing the undesirable characteristics of thermoset syntactic plugs while increasing the ease by which these articles may be constructed for a given use, by forming such plugs from syntactic foams having a thermoplastic matrix. Other objects and advantages of this invention will become readily apparent from the following written description and appended claims.

[0013] Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiments which illustrate, by way of example, the principles of the invention.DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0014] The term thermoplastic resin, as used in this description, is to mean any polymeric material capable of being remolded when heated, more preferably it is a material with a melting point, or glass transition temperature, above 180° C., preferably above 200° C., and still more preferably above 210° C.

[0015] The syntactic plug of the present invention may be formed from a syntactic material comprising a thermoplastic resin which serves to bind one or more light-weight hollow fillers. Suitable thermoplastic resins include polyether (including polyetherimide, polyetheretherketone (PEEK), polyetherketoneketone (PEKK)), polyurethane, polyamide (including, for example, polyamideimide), polyacrylates, polycarbonates, polysulphones, copolymers, and mixtures thereof. Preferred resins include polyamides, specifically nylon 6 and nylon 6,6, and polyurethanes.

[0016] Suitable hollow filler materials for use in these syntactic materials include any filler used within the art, and obtained from any commercial source. The filler may include generally any material having a density lighter than the density of the resin, more typically the filler includes glass microspheres, hollow polymeric microspheres, hollow ceramic microspheres, microspheres of urea-formaldehyde resin and / or phenol-formaldehyde resin.

Problems solved by technology

Primarily each of these suffer from their relatively high thermal conductivity which removes heat from the molten web and thus adversely affects the stretching of the molten web to be formed into a high quality part.

These deficiencies may be at least partially overcome through the use of internal or external heating of the plug or employing a multi-component plug but this adds complexity to the device, to the operation and increases the operating cost.

However, these plug assists lack the mechanical toughness desired for the application.

They are easily damaged during the operation or during the frequent tool changes typical of their usage and once a dent or chip occurs in a critical area, the tool is unacceptable and must be reworked or scrapped.

In addition, it is difficult to machine a brittle epoxy form.

The thermoset syntactic foam can chip during machining and the removed materials turn to dust.

Once this occurs, machine wear issues are created.

Also, most often the machinist must wear protective equipment to avoid dust inhalation and spend additional time to clean up the area after machining.

Although there are recognized advantages and disadvantages to using syntactic materials for plugs, it was believed that the relatively high operating temperature demands of thermoforming operations limited the selection of syntactic materials to thermoset matrix syntactic materials.