HXGH TEMPERATURE FOLYAMIDE COATING FOR FASTENERS

BACKGOUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates generally to fasteners and, more particularly, to a high temperature polyamide coating adhered to at least a portion of threads of a fastener.

2. Description of the Related Art

[0002] It is known to provide a self-locking fastener for fastening parts together. Self-locking fasteners are of a type in which the self-locking characteristic is derived from a coating such as a patch material adhered to all or a portion of a thread defining surface of the fasteners. These self-locking fasteners have proven to be very popular for a wide variety of applications in order to prevent loosening of the fastener due to vibration and the like in various applications.

[0003] Self-locking fasteners have been used in military, aircraft, and automotive applications. However, in some applications, these fasteners are subjected to a high temperature or corrosive environment. As a result, the coating may not withstand the high temperature and therefore loose its self-locking characteristic.

[0004] Therefore, it is desirable to provide a coating for a fastener that can withstand high temperatures and provide self-locking characteristics for the fastener. It is also desirable to provide a polyamide coating for a fastener that can withstand high temperatures and provide self-locking characteristics for the fastener. Thus, there is a need in the art to provide a high temperature polyamide coating for a fastener that meets these desires.

SUMMARY OF THE INVENTION

[0005] It is, therefore, one object of the present invention to provide a high temperature polyamide coating for a fastener.

[0006] It is another object of the present invention to provide a high temperature nylon coating for a fastener that imparts self-locking characteristics to the fastener.

[0007] Accordingly, the present invention is a high temperature polyamide coating for a fastener. The coating is a composition from about 60 wt.% to about 80 wt . % of an aliphatic polyamide having a repeating unit. The composition also includes from about 3 wt.% to about 9 wt.% of an epoxy based resin having a molecular weight in the range from about 525 to about 585. The composition includes from about 4 wt.% to about 10 wt.% of a ceramic microsphere material and from about 2 wt.% to about 5 wt.% of a thermoplastic methacrylate binder. The composition also includes from about 4 wt.% to about 12 wt.% of crushed glass. The composition includes from about 0.1 wt.% to about 1 wt.% of a polyamide with a secondary amino group as a curing agent. The composition further includes a balance comprised of an epoxy based curing agent.

[0008] In addition, the present invention is a fastener including a thread defining surface. The fastener also includes a high temperature polyamide coating adhered to at least a portion of the thread defining surface to lock a fastener in place and be able to withstand temperatures from about -54 ⁰ C (- 65°F) to about 250 ⁰ C (482°F) .

[0009] One advantage of the present invention is that a high temperature polyamide coating is provided for a fastener. Another advantage of the present invention is that the high temperature polyamide coating has a formulation that exhibits high temperature resistance properties, good anticorrosion properties, and is excellent for application to the threads of fasteners to lock the fastener in place in high temperature and corrosive applications. Yet another advantage of the present

invention is that the high temperature polyamide coating is applied to at least a portion of the threads of the fastener to form a self-locking fastener.

[00010] Other objects, features, and advantages of the present invention will be readily appreciated, as the same becomes better understood _/ after reading the subsequent description.

DESCRIPTION OF THE PREFERRED EMBODIMENT (S)

[00011] The present invention is a high temperature polyamide coating or a high temperature resistant polyamide composition for adding corrosion resistance and locking properties to fasteners upon which is applied. The composition has a formulation comprised of an aliphatic polyamide having a repeating unit CuføiON, a glass transition temperature of 42°C, an amorphous density at 25°C of 1.01 g/cm ³ , and a molecular weight of the repeating unit of 183.30 g/mol . The composition includes from about 60 wt.% to about 80 wt . % of the aliphatic polyamide having a repeating unit Ci _α H ₂ iON and more preferably about 73.9 wt.% of such a polyamide. This aliphatic polyamide is a nylon material commonly known as Nylon 11 and is derived from 11 amino undecanoic acid in a manner that is known to those skilled in the art. Nylon 11 is a product that is available from a number of producers such as the Rohm and Hass Company of Flying Hills, Pennsylvania.

[00012] The composition also includes the addition of an effective amount of a ceramic microsphere material. These ceramic microsphere materials are typically used to reduce the VOC levels, increase filler loadings, improve hardness, and add burnish, scrub, and abrasion resistance to the formulation. Preferably, the ceramic microspheres are hollow spheres with thick walls comprised of silica-alumina ceramic material. The ceramic microsphere material has a true-density of about 2.1 to about 2.5 gm/cc and an average particle size distribution of from about 1 to about 200 microns. The ceramic microsphere

material has a surface area of about 2 to about 6 m ² /cc and an

011 absorption of about 60 grα to about 70 grα of oil per 100 cc of microspheres. These ceramic microspheres are added to the formulation to promote smoother powder coating finishes. They are available under a variety of tradenames and are available through the 3M Corporation under the tradename Zeeosphere Ceramic microspheres. Of particular interest is Zeeosphere G- 600. The ceramic microspheres are present in an amount of from about 4 wt. % to about 10 wt.% of the composition and most preferably in an amount of about 7.66 wt.% of the composition.

[00013] The composition further includes from about 2 wt.% to about 5 wt.% of a thermoplastic methacrylate based binder, and preferably about 3.29 wt.% of a methacrylate based binder. The methacrylate based binders may be selected from the group of poly (benzylmethacrylate) , poly (butylmethacrylate) , poly (cyclohexylmethacrylate) , poly (ethylmethacrylate) , poly (hexylmethacrylate) , poly (isobutylmethacrylate) , poly (isopropylmethacrylate) , poly (isopropylmethacrylate) , poly (methylmethacrylate) , poly (phenyl methacrylate), poly (propyl methacrylate) , and mixtures thereof- Most preferably, poly (methyl methacrylate) is used in the present formulation. This thermoplastic methacrylate based binder is available under a number of tradename products, such as Degalan® LP 64/12, available from Degussa Corporation of Parsippany, New Jersey.

[00014] The composition includes from about 4 wt.% to about

12 wt.% of a crushed glass material and preferably about 8.72 wt.% of the crushed glass material. The crushed glass material is used to impart corrosion resistance and temperature resistance properties to the composition.

[00015] The composition further includes from about 3 wt.% to about 9 wt.% of a low molecular weight solid epoxy based resin derived from liquid epoxy resin and bisphenol A. The resin has a micro weight range of about 525 grams per mol to about 585 grams per mol. This material is available under a

number of tradenaraes such as Epon®1001F available from Resolution Performance Products or any other number of providers. The material is useful in polyam'ide cured coatings where chemical resistance, durability, toughness, and adhesion properties of the coating are desired. It is also used to upgrade thermosetting acrylic resins coatings with greatly improved adhesion toughness and detergent resistance. For these reasons, the coating utilizing this material is especially useful in automotive and aircraft applications.

[00016] The composition also includes from about 0.1 wt.% to about 1 wt . % of a polyamide with a secondary amino group as a curing agent. Such curing agents are known under the trade name Ancamine® curing agents and, in particular interest, is Ancamine 2014AS available from Air Products of Allentown, Pennsylvania.

[00017] Finally, the composition includes an effective amount of an epoxy based curing agent and specifically a curing agent in an amount of about 0.37 wt.% of epoxy based curing agent. Of particular interest is Curezol® 2MZ curing agent available from Air Products of Allentown, Pennsylvania.

[00018] The composition as described herein is useful as a coating or patch to be applied to the threads of fasteners for use in high temperature applications such as that encountered in automotive or aircraft applications. A patch would be applied as a powder to the threads of a heated fastener so that the formulation is adhered to the threads of the fastener. The formulation meets MIL-DTL-18240F and serves to lock the fastener in place and further to offer corrosion resistant properties to the threads of the fastener.

[00019] The following examples describe the present invention in more detail. The parts and percentages unless otherwise indicated are parts and percentages by weight of the composition.

EXAMPLES

[00020] Examples I through V are offered to illustrate the torque used to remove fasteners that were treated with the composition as previously described. For each of the Examples I through V, the indicated number of threaded fasteners were coated with a composition comprised of 73.9 wt.% of Nylon 11, 8.72 wt.% crushed glass, 7.66 wt.% Zeeospheres G-600, 3.29 wt.% Degalan LP 64/12, 5.51 wt.% Epon 1001F, 0.55 wt.% Ancamine, and 0.37 wt.% Curezol 2MZ. Samples of coated fasteners were baked at 482° F (250° C) for three (3) hours and allowed to cool for a minimum of one (1) hour. The samples of coated fasteners were mated with threaded receivers to simulate actual fastener systems. The samples of coated fasteners were subjected to five (5) removal processes from the threaded receivers, and the torque necessary to remove the fasteners was recorded. Torque was measured in foot-pounds .

EXAMPLE I

[00021] Example I illustrates the prevailing take off torque through five (5) reuses of the coated fasteners set forth above, applying a maximum torque of 7.5 and a minimum torque of 0.5.

[00022] The prevailing off torque is given in Table 1 below:

TABLE 1

EXAMPLE II

[00023] Example II illustrates the prevailing take off torque through five (5) reuses of the coated fasteners set forth above, applying a maximum torque of 12.0 and a minimum torque of 1.0. The prevailing off torque is given in Table 2 below:

TABLE 2

EXAMPLE III

[00024] Example III illustrates the prevailing take off torque through five (5) reuses of the coated fasteners set forth above, applying a maximum torque of 18.0 and a minimum torque of 1.5. The prevailing off torque is given in Table 3 below:

TABLE 3

EXAMPLE IV

[00025] Example IV illustrates the prevailing take off torque through five (5) reuses of the coated fasteners set forth above, applying a maximum torque of 60.0 and a minimum torque of 3. The prevailing off torque is given in Table 4 below:

TABLE 4

EXAMPLE V

[00026] Example V illustrates the prevailing take off torque through five (5) reuses of the coated fasteners set forth above, applying a maximum torque of 165 and a minimum torque of 9-0. The prevailing off torque is given in Table 5 below:

TABLE 5

In the following Examples VI through X, the fasteners were coated with the same composition or formulation as the fasteners of previous Examples I through V. However, the fasteners of Examples VI through X were baked for one (1) hour at 500° F. While the fasteners were at this temperature, the prevailing off torque in foot-pounds was measured.

EXAMPLE VI

[00027] Example VI illustrates the prevailing take off torque of the coated fasteners set forth above, applying a maximum torque of 7.5 and a minimum torque of 0.5. The prevailing off torque is given in Table 6 below:

TABLE 6

EXAMPLE VII.

[00028] Example VII illustrates the prevailing take off torque of the coated fasteners set forth above, applying a maximum torque of 12.0 and a minimum torque of 1.0. The prevailing off torque is given in Table 7 below:

TABLE 7

EXAMPLE VIII

[00029] Example VIII illustrates the prevailing take off torque of the coated fasteners set forth above, applying a maximum torque of 18.0 and a minimum torque of 1.5. The prevailing off torque is given in Table 8 below:

TABLE 8

EXAMPLE IX

[00030] Example IX illustrates the prevailing take off torque of the coated fasteners set forth above, applying a maximum torque of 60.0 and a minimum torque of 3. The prevailing off torque is given in Table 9 below:

TABLE 9

EXAMPLE X

[00031] Example X illustrates the prevailing take off torque of the coated fasteners set forth above, applying a maximum torque of 165 and a minimum torque of 9.0. The prevailing off torque is given in Table 10 below:

TABLE 10

[00032] The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation and the examples are intended to illustrate and not limit the scope of the present invention.

[00033] Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.