Air brake tubing and compositions for making the same

Abstract

Air brake tubing is provided having an air brake tube body comprising at least one layer formed from a composition comprising a copolyester, polyethylene terephthalate or polybutylene terephthalate; and a thermoplastic polyurethane.

Claims

1. An air brake tubing comprising: an air brake tube body comprising at least one layer formed from a composition comprising at least one of the group consisting of a copolyester, a polyethylene terephthalate, and a polybutylene terephthalate; a thermoplastic polyurethane; and a polyamide.

2. The air brake tubing of claim 1, wherein the air brake tubing is capable of meeting the performance requirements of SAE J844, SAE J2547 and DOT FMVSS 106.

3. The air brake tubing of claim 1, wherein the tube body comprises a wound or braided reinforcement layer.

4. The air brake tubing of claim 1, wherein the air brake tubing has a multi-layer construction comprising a core inner layer, a reinforcement layer, and a protective outer layer.

5. The air brake tubing of claim 1, wherein the composition comprises about 15-75 wt % by weight of the copolyester.

6. The air brake tubing of claim 5, wherein the copolyester is selected from one or more copolyesters exhibiting hardness of from 63D-74D on the Shore scale.

7. The air brake tubing of claim 1, wherein the composition comprises about 15-75% by weight of the thermoplastic polyurethane.

8. The air brake tubing of claim 1, wherein the composition comprises about 0.1-20% by weight of the polyamide.

9. A reinforced tubing suitable for use in pneumatic or hydraulic applications, the tubing comprising at least one layer formed from a composition comprising about 15-75% by weight copolyester, polyethylene terephthalate or polybutylene terephthalate or combinations thereof; about 15-75% by weight polyurethane, and about 1-15% by weight polyamide.

10. The tubing of claim 9, wherein the tubing is capable of meeting the performance requirements of at least one of SAE J844, SAE 12547 and DOT FMVSS 106.

11. The tubing of claim 9, wherein the tubing comprises a wound or braided reinforcement layer.

12. The tubing of claim 9, wherein the tubing is formed from a composition comprising about 30-60% by weight of the copolyester, polyethylene terephthalate, polybutylene terephthalate or combinations thereof; about 30-60% by weight thermoplastic polyurethane; and about 3-12% by weight polyamide.

13. The air brake tubing of claim 1, wherein the thermoplastic polyurethane is a polyether-based thermoplastic polyurethane.

14. The air brake tubing of claim 1, wherein the polyamide is selected from the group consisting of one or more of PA612, PA6, PA12, PA66, PA610, PA1010, PA1012, PA11, PA12, and PA1212.

15. The air brake tubing of claim 1, wherein the composition is a blend, alloy or copolymer.

16. The air brake tubing of claim 3, wherein the wound or braided reinforcement layer comprises a material selected from the group consisting of polyester, nylon, and aramid.

17. The air brake tubing of claim 1, wherein the at least one layer is selected from the group consisting of an inner layer and an outer layer.

18. The air brake tubing of claim 1, Comprising at least two layers including a polyamide inner layer and an outer layer prepared from a composition comprising about 45-50/45-50/5-10 wt ratio of copolyester/polyurethane/polyamide.

19. The air brake tubing of claim 1, comprising three or more layers including an inner and outer layer prepared from a composition comprising about 45-50/45-50/5-10 wt. ratio of copolyester/thermoplastic polyurethane/polyamide, and a PA6 or PA12 middle layer.

20. The air brake tubing of claim 4, wherein the outer layer comprises a material selected from the group consisting of polyamide, copolyester, polyethylene terephthalate, polybutylene terephthalate, polyurethane blend, and polyolefin blend, or alloys, or co-polymers thereof.

21. The air brake tubing of claim 1, wherein the at least one layer is a single mono-wall layer, an inner layer, or an outer layer.

Description

BRIEF DESCRIPTION OF FIGURES

(1) FIG. 1 is a schematic drawing of an air brake system according to an embodiment.

(2) FIG. 2A shows copolyester/PET/PBT concentration ranges used in compositions for forming an airbrake tubing body layer.

(3) FIG. 2B shows copolyester/PET/PBT hardness ranges used in compositions for forming an airbrake tubing body layer.

(4) FIG. 2C shows thermoplastic polyurethane concentration ranges used in compositions for forming an airbrake tubing body layer.

(5) FIG. 2D shows thermoplastic polyurethane hardness ranges used in compositions for forming an airbrake tubing body layer.

(6) FIG. 2E shows polyamide concentration ranges used in compositions for forming an airbrake tubing body layer.

(7) FIG. 2F shows plasticizer concentration ranges used in compositions for forming an airbrake tubing body layer.

(8) FIG. 3A shows an embodiment of mono-wall air brake tubing.

(9) FIG. 3B shows an embodiment of reinforced air brake tubing.

(10) FIG. 3C shows an embodiment of air brake tubing with multi-layer construction.

(11) FIG. 4 is a schematic drawing of an extrusion system used to make the air brake tubing according to an embodiment.

DETAILED DESCRIPTION

(12) The present application relates to tubing suitable for use in air brake systems and other pneumatic or hydraulic applications and to material compositions for making the same. In particular, the present application relates to materials suitable for Type A (non-reinforced) and Type B (reinforced) air brake tubing.

(13) Polymeric air brake tubing comprising one or more layers formed from a composition comprising (a) one or more of a copolyester, polyethylene terephthalate and/or polybutylene terephthalate; and (b) polyurethane is provided. In some embodiments, the air brake tubing comprises at least one layer formed from a composition comprising (a) one or more of a copolyester, polyethylene terephthalate and/or polybutylene terephthalate; (b) a polyurethane; and (c) a polyamide. The compositions can be used for manufacturing mono-layer tubing, reinforced tubing or multi-layer tubing. The polymeric air brake tubing provided herein meets performance requirements specified in SAE and DOT standards.

(14) FIG. 1 shows an example of an air brake system 10 used in vehicles. Compressed air is generated in the air compressor 11 and dried using an air dryer 12. Dried air can be stored in one or more compressed air storage/supply tanks 13. When brakes are applied by pressing on the foot valve 14, compressed air is led to the brake chambers 18 through air brake hoses 16 (i.e. air brake tubing). Alternatively, brakes can be applied by a hand control valve (e.g., the park brake). The compressed air can also be regulated by various other modulators and valves 15 such as control valves, protection valves, safety release valves and load sensing valves (not shown). The brake system 10 of a vehicle may also be connected to the brake system of another vehicle unit such as a trailer. When in use, air brake hoses are exposed to wear and tear, and the road conditions, such as heat, cold and moisture, and various chemicals such as road salt, oil, etc.

(15) Air brake tubing is typically constructed of a thermoplastic core inner layer that may optionally be reinforced by a layer of wound or braided material and protected by an outer layer that can withstand abrasion and wear. The possible materials and construction used to make air brake tubing are limited by the requirement to withstand multiple stressors, including environmental and mechanical stress factors as articulated in the regulatory requirements set by the SAE (such as SAE Standard J844 and J2547) and DOT (such as DOT FMVSS 106). The test parameters along with the required limits for ¼ inch tubing are listed in TABLE 1. For example, the tubing must meet particular requirements for withstanding extreme temperatures and exposure to moisture and chemicals and yet remain pliable and impact and burst resistant. Some other test parameters include, for example, ambient burst strength, moisture absorption, zinc chloride resistance, stiffness, and tensile strength. In order to pass the requirements for the Boiling Water Conditioning and Tensile Strength (hot pull) test, the test criteria allows for meeting either the minimum 50 lbf(L) or minimum % elongation of 50% (L) specifications. Polyamide (“PA”) 12 is a common material for manufacturing air brake tubing, but when used by itself in a single layer (e.g., a mono-wall tube), PA12 may not have optimal cold temperature impact resistance. On the other hand, copolyester, another popular material for air brake tubing, is relatively inflexible, and a construction using copolyester only may have difficulty meeting the stiffness requirements.

(16) TABLE-US-00001 TABLE 1 DOT/SAE Standard Test Limits. DOT (D)/ Requirements for ¼ inch O.D. tube Test SAE (S) (L = lower limit, U = upper limit) Constriction D I.D. >66% of nominal, Pass/Fail High T. Cond. & Dimensional Stability D Dimensions shall not exceed Boiling Water Cond. & Dimensional Stability specified values, Pass/Fail Ambient Burst Strength D & S 1206 psi (L) Moisture Absorption and Burst Strength, psi D & S 2% (U) and 960 psi (L) Ultraviolet Light Resistance D & S 960 psi (L) Low/Cold T. Flexibility D & S Pass/Fail High T. Flexibility & Burst Strength D & S 960 psi (L) High T. Resistance & Burst Strength D & S 960 psi (L) High T. Cond. (72 h) & Cold T. Impact D 960 psi (L) High T. Cond. (24 h) & Cold T. Impact S 960 psi (L) Boiling Water Cond. & Cold T. Impact D & S 960 psi (L) Zinc Chloride Resistance D & S No visible cracks, Pass/Fail Methyl Alcohol Resistance D & S No visible cracks, Pass/Fail High T. Cond. & Collapse Resistance D & S 20% (U) Ozone Resistance D No visible cracks, Pass/Fail Oil Resistance D 960 psi (L) Tensile Strength D 50 lbf (L) Boiling Water Cond. & Tensile Strength D & S 50 lbf (L) or 50% (L) (hot pull), lbf Thermal Cond. &Tensile Strength D & S 50 lbf (L) and 50% (L) (Conditioned), lbf Vibration Resistance D & S 50 sccm @ 1M cycles, 25 sccm after 1 h rest End Fitting Retention D & S 960 psi (L) Thermal Cond. & End Fitting Retention D & S No rupturing or disconnect, Pass/Fail End Fitting Serviceability D & S Leakage <25 sccm End Fitting Corrosion Resistance D No base metal corrosion, Pass/Fail Stiffness S 2 lbs (U) Adhesion S N/A Heat Aging Adhesion S N/A T. = Temperature, Cond. = Conditioning

(17) The shortcomings of the materials typically used for making air brake hoses can be overcome by combining polymers with different properties in a composition (e.g., a blend, alloy or co-polymer) that fulfills the regulatory requirements set by the SAE and DOT. According to an embodiment, a composition suitable for tubing used in air brake systems and other pneumatic or hydraulic applications may comprise a combination of copolyester, polyethylene terephthalate and/or polybutylene terephthalate and thermoplastic polyurethane and optionally polyamide (e.g., impact modified polyamide). The combination of polymers benefits from the better processability and temperature performance of copolyester, polyethylene terephthalate and/or polybutylene terephthalate and the flexibility and hydrolytic stability of polyurethane. Referring to FIGS. 2A through 2F, ranges of components of compositions according to embodiments are shown.

(18) As shown in FIG. 2A, in some embodiments, the composition comprises approximately 15-75 wt %, or approximately 30-60 wt %, or approximately 40-50 wt % of one or more copolyester, polyethylene terephthalate (PET) and/or polybutylene terephthalate (PBT), compared to the total weight of the unfilled composition.

(19) In some embodiments, the composition comprises one or more copolyesters. Copolyesters are selected from thermoplastic copolyester based elastomers. In some embodiments, the composition comprises a copolyester combination of a hard segment of polyester (PBT) and a soft segment of polyethers or polyester. In some embodiments, the copolyester can impart stiffness under high temperature conditions. In some embodiments, the copolyester does not contain an elastomer. In some embodiments, the copolyester is an extrusion grade copolyester elastomer. In some embodiments, the copolyester is selected from a commercially available copolyester. In some embodiments, the copolyester is selected from a commercially available copolyester, for example, from Dupont or DSM Engineering Plastics, Inc. In some embodiments, the copolyester is selected from EM630-H, 63 Shore D hardness, extrusion grade copolyester elastomer, Arnitel® (DSM Engineering Plastics, Inc.); EM630, 60 Shore D, extrusion grade copolyester elastomer, Arnitel® (DSM Engineering Plastics, Inc.); and EM740, 74 Shore D, extrusion grade copolyester elastomer, Arnitel® (DSM Engineering Plastics, Inc.).

(20) In some embodiments, the composition comprises one or more polybutylene terephthalates (PBT). In some embodiments, the PBT is a partially crystalline saturated polyester based on polybutylene terephthalate (PBT). In some embodiments, the PBT is a commercially PBT such as an Arnite® (DSM) or Ultradur® PBT (BASF). The PBT can be unreinforced, or reinforced, for example, with glass fiber, or mineral reinforced. In some embodiments, the PBT is impact modified.

(21) In some embodiments, the composition comprises one or more polyethylene terephthalates (PET). Polyethylene terephthalate is a copolymer polyester. PET can be prepared from, for example, an esterification reaction between terephthalic acid and ethylene glycol; or by transesterification between, for example, ethylene glycol and dimethyl terephthalate. The polyethylene terephthalate can be a commercially available polyethylene terephthalate. In some embodiments, the composition comprises a polyethylene terephthalate such as Array™ 9921 polyethylene terephthalate (DAK Americas).

(22) Copolyesters, polyethylene terephthalates and/or polybutylene terephthalates of varying hardness can be used as shown in FIG. 2B. In some embodiments, the copolyester, polyethylene terephthalate and/or polybutylene terephthalate exhibits a durometer reading of about 30D-80D on the Shore scale, or about 40D-74D, or about 47D-74D, or about 55D-74D, or about 63D-74D, or about 63D. In some embodiments, the copolyester, polyethylene terephthalate and/or polybutylene terephthalate exhibits a durometer reading of about 74D. In some embodiments, two known durometers of copolyester are combined in the composition, for example, 63D and 74D. Different types of copolyester, polyethylene terephthalate and/or polybutylene terephthalate or blends, alloys or co-polymers including one or more of such materials may be used.

(23) As shown in FIG. 2C, in some embodiments, the composition comprises approximately 15-75 wt %, or approximately 30-60 wt %, or approximately 40-50 wt % polyurethane, compared to the total weight of the unfilled composition. The polyurethane is a thermoplastic polyurethane (TPU) is selected from one or more TPUs. A polyurethane is a polymer composed of organic units joined by carbamate (urethane) links. Polyurethane polymers are generally formed by reacting an isocyanate with a polyol. The isocyanates and polyols contain on average two or more functional groups per molecule. Thermoplastic polyurethanes (TPUs) are thermoplastic elastomers that can exist in a molten state when subject to heat. TPUs consist of linear segmented block copolymers composed of hard and soft segments. TPUs are formed, for example, from three components: (a) diisocyanates, (b) short chain diols (chain extenders); and (3) long chain bifunctional diols (polyols). The hard block is constructed from a chain extender and isocyanate and can impart the TPU with toughness and physical performance properties. The soft block is constructed from a polyol and an isocyanate and can impart flexibility and elastomeric character to the TPU. Various TPU properties can include elasticity, transparency, and resistance to oil, grease, and abrasion. In some embodiments the brake line tubing is formed from a composition comprising copolyester, polyethylene terephthalate and/or polybutylene terephthalate; and a thermoplastic polyurethane. In some embodiments, the polyurethane is a polyether-based polyurethane. In some embodiments, the thermoplastic polyurethane (TPU) is a commercially available TPU. In some embodiments, the TPU is selected from a commercially available polyether-based polyurethane selected from a BASF Elastollan® TPU or a Huntsman TPU. In some embodiments, for example, the TPU is a polyether-based TPU selected from BASF 1164D (Shore D hardness 64), BASF 1154D (Shore D hardness 53), Huntsman D64P4777 (Shore D hardness 62) or Huntsman A98P4535 (Shore D hardness 51). In some embodiments, the polyurethane is a polyester-based polyurethane.

(24) Polyurethanes of varying hardness can be used as shown in FIG. 2D. For example, in some embodiments, the polyurethane exhibits a durometer reading of about 51D-74D on the Shore scale, or about 60D-70D, or about 64D. Different types of polyurethane may be used, such as for example a polyester or a polyether type or blends, alloys or co-polymers that include polyurethane.

(25) In some embodiments, the composition comprises one or more polyamides (nylon). As shown in FIG. 2E, in some embodiments, the composition may additionally comprise approximately 0-50 wt %, or approximately 0-20 wt %, or approximately 0-10 wt %, or approximately 0-5 wt % polyamide compared to the total weight of the unfilled composition. In other embodiments, the composition comprises polyamide in approximately 0.1-20 wt %, or approximately 1-15 wt %, or approximately 3-12 wt %, compared to the weight of the total weight of the unfilled composition. In some specific embodiments, the composition comprises approximately 5 wt %, or approximately 10 wt % polyamide. Various types of polyamide or blends, alloys or co-polymers that include one or more polyamides may be used. For example, the polyamide may include one or more of the following polyamides: PA612, PA6, PA12, PA66, PA610, PA1010, PA1012, PA11, PA12 or PA1212, and may be either plasticized or unplasticized. In some embodiments, the polyamide is an impact modified polyamide. In some embodiments, the polyamide is selected from PA6, PA612, or PA610. In some embodiments, the polyamide is an impact modified PA612. In some embodiments, the PA is a commercially available PA. In some embodiments, the PA is a commercially available PA612, such as Grilamid® 2D, (EMS-Grivory); In some embodiments, the PA is a commercially available PA610, such as Grilamid® 2S, (EMS-Grivory), or Ultramid® S Balance (BASF). In some embodiments, the PA is a regrind, or recycled PA.

(26) In some embodiments, the composition comprises other additives such as heat and light stabilizers, impact modifiers, lubricants, wetting agents, antioxidants, pigments, dyes, colorants, colorings, or opacifying agents such as for coloring-coding of the tubing, luminescents, light reflectants, chain extending oils, tackifiers, blowing agents, foaming or anti-foaming agents, reinforcements such as glass, carbon, or textile fibers, and fire retardants such as halogenated compounds, metal oxides and salts, The additives may be in liquid, powder, particulate, flake, fiber, or other form. The impact modifier may be a maleic anhydride (MAH) grafted polyolefin (Fusabond®, Dupont), or an ethylene/methacrylic copolymer-based ionomer resin such as Suryln®, (DuPont, Wilmington, Del.), or other ethylene copolymer resin which may be a high-molecular-weight copolymer resin such as an EVACO (ethylene/vinyl acetate/carbon monoxide), EBACO (ethylene/butyl acrylate/carbon monoxide), or EnBAGMA (ethylene/n-butyl acrylate/glycidyl methacrylate) terpolymer resin (Elvaloy®, Dupont). The heat age stabilizer, in turn, may be a hindered amine, or a proprietary additive such as “E1” from DSM Engineering Plastics (Evansville, Ind.). Typically, the optional additives are blended or otherwise admixed with the composition, and may comprise between about 0.01 wt % and 10 wt %; or between about 0.05 wt % and 5 wt %; or between about 0.1 wt % and 3 wt %.

(27) In some embodiments, a plasticizer can be employed to increase flexibility and cold impact resistance. In some embodiments, the concentration of plasticizer in the composition may be very low. For example, as shown in FIG. 2F, the composition may comprise approximately 0-8 wt %, or approximately 0-4 wt %, or as little as approximately 0-1 wt % plasticizer. In some embodiments, the composition comprises a plasticizer at approximately 0.1-8 wt %, or approximately 0.3-6 wt %, or approximately 0.5-4 wt % compared to the weight of the unfilled composition. Conventional plasticizers known in the art may be used.

(28) In some embodiments, the air brake tubing composition is unfilled. In some embodiments, the composition comprises one or more fillers. In some embodiments, the composition comprises one or more fillers selected form intercalated graphite particles, borates, siloxanes, phosphates, glass, hollow or solid glass or elastomeric microspheres, silica, silicates, mica, carbon black and the like. Typically, the optional fillers are blended or otherwise admixed with the base polymeric material, and may comprise between about 0.1% and 80% by weight compared to the weight of the unfilled composition.

(29) The FIGS. 3A through 3C show various embodiments of air brake tubing 20. The composition can be used to make one or more layers or wall thicknesses to be used in tubing. A tubing layer comprised of the composition can be used to make a mono-wall tube/hose or can be incorporated into a hose having multiple layers. For example, referring to FIG. 3A, tubing 20 made from the composition can be constructed as mono-wall (i.e. single layer) tubing 21 that meets the size and performance requirements of SAE Standards J844 and J2547, and DOT FMVSS 106. According to embodiments, the tubing may comprise a single layer of the composition and may be formed from a composition comprising, for example, approximately 15-75 wt %, 30-60 wt %, or 40-50 wt % copolyester, polyethylene terephthalate and/or polybutylene terephthalate; approximately 15-75 wt %, 30-60 wt %, or 40-50 wt % polyurethane; and approximately 0-50 wt %, 0-20 wt %, 0-10 wt %, or 0-5 wt % polyamide.

(30) In embodiments, air brake tubing is provided with outer diameter (O.D.) ⅛ inch, 5/32 inch, 3/16 inch, ¼ inch, 5/16 inch, ⅜ inch, ½ inch, ⅝ inch and ¾ inch, with corresponding nominal inside diameter (I.D.) of 0.156, 0.187, 0.218. 0.281. 0.343, 0.406, 0.531, 0.656 and 0.800 inches. Typically, air brake tubing with an O.D.< 5/16 inch is type A non-reinforced tubing, and above ⅜ inch O.D. is type B reinforced tubing. In some embodiments, the air brake tubing is a monolayer, or comprises two or more, three or more, four or more, or five or more layers. In some embodiments, the air brake tubing is non-reinforced. In some embodiments, the air brake tubing comprises a reinforcement layer.

(31) Air brake tubing is provided comprising at least one layer formed from a composition comprising copolyester, polyethylene terephthalate and/or polybutylene terephthalate; and polyurethane. In certain embodiments, the composition can be a co-polymer, alloy or blend. In some embodiments, the composition comprises one or more of a copolyester, polyethylene terephthalate and/or polybutylene terephthalate of different Shore A hardness. For example, the copolyester, polyethylene terephthalate and/or polybutylene terephthalate may have a durometer reading of about 30D-80D on the Shore scale, or about 40D-74D, or about 47D-74D, or about 55D-74D, or about 63D-74D, or about 63D and the polyurethane may have a durometer reading of about 54D-74D on the Shore scale, or about 60D-70D, or about 64D, or about 74D. In some embodiments, the composition comprises a medium hardness polymer. In some embodiments, the composition comprises two or more polymers selected from copolyester, polyethylene terephthalate and/or polybutylene terephthalate and the polyurethane, such that one polymer with a higher durometer reading can be used to compensate for another polymer with a lower durometer reading. For example, in some embodiments, the composition comprises a copolyester of 63D hardness and a copolyester of 74D Shore D hardness.

(32) In some embodiments, the brake line tubing is prepared from a composition comprising about 40-50 wt % copolyester, polyethylene terephthalate and/or polybutylene terephthalate; and about 40-50 wt % polyurethane. In some embodiments, the brake line tubing is prepared from a composition comprising about 40-50 wt % copolyester polybutylene terephthalate and/or polyethylene terephthalate; about 40-50 wt % polyurethane; and about 1-15 wt % of a polyamide.

(33) In specific embodiments, the brake line tubing is prepared from a composition comprising about 45-47.5 wt % copolyester, polyethylene terephthalate and/or polybutylene terephthalate; about 45-47.5 wt % polyurethane; and about 5-10 wt % of polyamide 612.

(34) In some embodiments, brake line tubing comprising at least one layer formed from a composition comprising polybutylene terephthalate and polyurethane is provided.

(35) In some embodiments, the brake line tubing comprises at least one layer formed from a composition comprising between about 25-40 wt % polybutylene terephthalate; about 50-65 wt % polyurethane; and about 3-12 wt % of a polyamide; and about 0.1-3 wt % of a heat and/or light stabilizer.

(36) In some specific embodiments, the brake line tubing comprises at least one layer formed from a composition comprising between about 35 wt % polybutylene terephthalate; about 55 wt % polyurethane; about 10 wt % of a polyamide; and about 0.1-3 wt % of a heat and/or light stabilizer.

(37) In some embodiments, the brake line tubing comprises two or more layers. In some embodiments, the brake line tubing comprises at least two layers including a polyamide inner layer and an outer layer prepared from a composition comprising about 45-50/45-50/0-10 wt ratio of copolyester/polyurethane/polyamide. In some specific embodiments, the brake line tubing includes two layers including a polyamide inner layer and an outer layer prepared from a composition comprising 47.5/47.5/5 wt % ratio of copolyester/polyurethane/polyamide.

(38) In some embodiments, the brake line tubing includes three or more layers including an inner and outer layer prepared from a composition comprising about 45-50/45-50/0-10 wt. ratio of EM740 copolyester/Hunt 64D/PA612 and a PA6 or PA12 middle layer.

(39) Tubing 20 made from the composition may also be reinforced as shown in FIG. 3B. The reinforcement 24 may comprise conventional reinforcement materials, such as a wound or braided layer of polyester, nylon or aramid. The composition is also suitable for use in multi-layer tubes as shown in FIG. 3C. Multi-layer tubes may include two or more layers and may comprise, for example, a core 22 comprised of the composition, a wound reinforcement layer 24 and a protective outer layer 26. The outer layer may be constructed of materials such as polyamide, copolyester, polyethylene terephthalate, polybutylene terephthalate, polyurethane or polyolefin or blends, alloys or co-polymers thereof. Other compositions and constructions of multi-layer tubes are also possible.

(40) According to exemplary embodiments, tubing may be made of various compositions as shown in TABLES 2-4. For example, air brake tubing of varying compositions representing Type A, ¼-inch mono-wall construction may be prepared and tested according to SAE J844 and DOT FMVSS 106 testing protocols.

(41) Referring to TABLE 2, sample 1 is formed from a composition comprising between 45-55 wt % thermoplastic polyurethane with a hardness of 64D (available from Huntsman Corp., Salt Lake City, Utah; BASF Corp., Florham Park, N.J.; Lubrizol Corp., Wickliffe, Ohio; Bayer, Morristown, N.J.; or DuPont, Wilmington, Del.) and 45-55 wt % copolyester with a hardness of 74D (available from DSM Engineering Plastics, Birmingham, Mich.; or DuPont). Sample 2 is formed from a composition comprising between 42-52 wt % thermoplastic polyurethane with a hardness of 64D, 42-52 wt % copolyester with a hardness of 74D, and 3-8 wt % polyamide PA612 (available from DuPont; EMS-CHEMIE Inc., Sumter, S. C.; A. Schulman, Inc., Akron, Ohio; or Arkema, King of Prussia, Pa.). Sample 3 is formed from a composition comprising between 40-50 wt % thermoplastic polyurethane with a hardness of 64D, 40-50 wt % copolyester with a hardness of 74D, and 5-15 wt % polyamide PA612.

(42) Referring to TABLE 3, test sample 4 is prepared from a composition comprising between 50-60 wt % of a polyether-based thermoplastic polyurethane (TPU) of Shore D hardness 53 (BASF) and approximately 40-50% polybutylene terephthalate (PBT)(BASF).

(43) Referring to TABLE 4, test sample 5 is formed from a composition comprising between 40-50 wt % TPU, polyether-based thermoplastic elastomer of Shore D hardness 64 (BASF), 40-50 wt % 74 Shore D, extrusion grade copolyester elastomer, Arnitel® (DSM Engineering Plastics, Inc.) and 5-15 wt % polyamide 612. Test sample 6 is formed from a composition comprising between 50-60 wt % TPU, 30-40 wt % thermoplastic copolyester elastomer, stabilized, of 72D Shore D hardness (Hytrel®, DuPont), and 5-15 wt % polyamide 612. Test sample 7 is formed from a composition comprising between 45-52 wt % TPU, polyether-based thermoplastic elastomer (Shore D hardness 64)(BASF), 45-52 wt % 74 Shore D, extrusion grade copolyester elastomer, Arnitel® (DSM Engineering Plastics, Inc.), and 3-8 wt % polyamide 612. The test results of 14 of the most critical test parameters for the exemplary compositions are shown in TABLES 2-4.

(44) TABLE-US-00002 TABLE 2 Air Brake Tubing Performance: Test Samples. Specification (U = upper limit, Test Test Test L = lower limit) SAMPLE 1 SAMPLE 2 SAMPLE 3 Polyurethane 45-55 wt % 42-52 wt % 40-50 wt % Copolyester 45-55 wt % 42-52 wt % 40-50 wt % Polyamide —  3-8 wt %  5-15 wt % Ambient Burst Strength 1206 psi (L) 1768 psi 1682 psi 1587 psi Moisture Absorption, % 2% (U) 0.60% 0.60%  0.50%  Moisture Absorption, psi 960 psi (L) 1514 psi 1515 psi 1416 psi Low/Cold T. Flexibility Pass/Fail Pass Pass Pass High T. Flexibility & Burst 960 psi (L) 1464 psi 1560 psi 1462 psi Strength High T. Cond. (72 h) & Cold 960 psi (L) 1484 psi 1536 psi 1461 psi T. Impact High T. Cond. (24 h) & Cold 960 psi (L) 1580 psi 1650 psi 1513 psi T. Impact Boiling Water Cond. & Cold 960 psi (L) 1435 psi 1516 psi 1418 psi T. Impact Zinc Chloride Resistance Pass/Fail Pass Pass Pass High T. Cond. & Collapse 20% (U)  7.1%  8.8%   6.1%  Resistance Stiffness 2 lbs (U) 1.88 lbs 1.78 lbs 1.83 lbs 120° F. Burst 600 psi (L) 704 psi 920 psi 893 psi 260° F. Burst 250 psi (L) 479 psi 781 psi 815 psi Tensile Strength 50 lbf (L) 117 lbf 106 lbf 95 lbf Boiling Water Cond. & 50 lbf (L) 37 lbf 37 lbf 37 lbf Tensile Strength (hot pull), lbf Boiling Water Cond. & 50% (L)   91%  84%  82% Tensile Strength (hot pull), % Thermal Cond. & Tensile 50 lbf (L) 122 lbf 132 lbf 130 lbf Strength (Conditioned), lbf Thermal Cond. & Tensile 50% (L)  310% 311% 294% Strength (Conditioned), % End Fitting Retention 960 psi (L) 1675 psi 1623 psi 1434 psi T. = Temperature, Cond. = Conditioning

(45) TABLE-US-00003 TABLE 3 Air Brake Tubing Performance: Comparative and Test Samples. Specification (U = upper limit, Comparative Comparative Test L = lower limit) SAMPLE A SAMPLE B SAMPLE 4 Polyurethane — — 50-60 wt % Copolyester — 90 wt % — PBT — — 40-50 wt % Polyamide 100 wt % 10 wt % — Ambient Burst Strength 1206 psi (L) 1373 psi 1490 psi 1357 psi Moisture Absorption, % 2% (U)  1.0%  0.4% 1.04%  Moisture Absorption, psi 960 psi (L) 1485 psi 1475 psi 1303 psi Low/Cold T. Flexibility Pass/Fail Pass Pass Pass High T. Flexibility & Burst 960 psi (L) 1614 psi 1501 psi 1270 psi Strength High T. Cond. (72 h) & Cold 960 psi (L) 1691 psi 1473 psi NT T. Impact High T. Cond. (24 h) & Cold 960 psi (L) 1493 psi 1335 psi 1348 psi T. Impact Boiling Water Cond. & Cold 960 psi (L) 1307 psi 1296 psi 1212 psi T. Impact Zinc Chloride Resistance Pass/Fail Pass Pass Pass High T. Cond. & Collapse 20% (U)  3.4%  6.8% NT Resistance Stiffness 2 lbs (U) 1.79 lbs 1.84 lbs 2.53 lbs 120° F. Burst 600 psi (L) 894 psi 875 psi 755 psi 260° F. Burst 250 psi (L) 459 psi 493 psi 425 psi Tensile Strength 50 lbf (L) 87 lbf 92 lbf 118 lbf Boiling Water Cond. & 50 lbf (L) 46 lbf 46 lbf 46 lbf Tensile Strength (hot pull), lbf Boiling Water Cond. & 50% (L)  86% 106%    73% Tensile Strength (hot pull), % Thermal Cond. & Tensile 50 lbf (L) 97 lbf 101 lbf 113 lbf Strength (Conditioned), lbf Thermal Cond. & Tensile 50% (L) 159% 296%   205% Strength (Conditioned), % End Fitting Retention 960 psi (L) 1390 psi 1326 psi 1309 psi T. = Temperature, Cond. = Conditioning, NT = Not yet Tested

(46) TABLE-US-00004 TABLE 4 Air Brake Tubing Performance: Test Samples. Specification (U = upper limit, Test Test Test L = lower limit) SAMPLE 5 SAMPLE 6 SAMPLE 7 Polyurethane 40-50 wt % 50-60 wt % 45-52 wt % Copolyester 40-50 wt % 30-40 wt % 45-52 wt % PBT — — — Polyamide  5-15 wt %  5-15 wt %  3-8 wt % Ambient Burst Strength 1206 psi (L) 1412 psi 1285 psi 1297 psi Moisture Absorption, % 2% (U) 1.13%  1.30%  1.14%  Moisture Absorption, psi 960 psi (L) 1190 psi 1160 psi 1274 psi Low/Cold T. Flexibility Pass/Fail Pass Pass Pass High T. Flexibility & Burst 960 psi (L) 1524 psi 1342 psi 1337 psi Strength High T. Cond. (72 h) & Cold 960 psi (L) 1583 psi 1461 psi 1240 psi T. Impact High T. Cond. (24 h) & Cold 960 psi (L) 1685 psi 1425 psi 1395 psi T. Impact Boiling Water Cond. & Cold 960 psi (L) 1241 psi 1069 psi 1112 psi T. Impact Zinc Chloride Resistance Pass/Fail Pass Pass Pass High T. Cond. & Collapse 20% (U)  9.3%  12.5%  10.0%  Resistance Stiffness 2 lbs (U) 1.61 lbs 0.95 lbs 1.75 lbs 120° F. Burst 600 psi (L) 697 psi 673 psi 701 psi 260° F. Burst 250 psi (L) 406 psi 356 psi 519 psi Tensile Strength 50 lbf (L) 98 lbf 89 lbf 103 lbf Boiling Water Cond. & 50 lbf (L) 37 lbf 34 lbf 35 lbf Tensile Strength (hot pull), lbf Boiling Water Cond. & 50% (L)  74%  84%  75% Tensile Strength (hot pull), % Thermal Cond. & Tensile 50 lbf (L) 105 lbf 108 lbf 115 lbf Strength (Conditioned), lbf Thermal Cond. & Tensile 50% (L) 258%  288%  234%  Strength (Conditioned), % End Fitting Retention 960 psi (L) 1428 psi 1338 psi 1225 psi T. = Temperature, Cond. = Conditioning

(47) TABLE 2 shows performance of Test Samples 1-3 monolayer tubing samples formed from different compositions comprising copolyester and polyurethane with or without polyamide. Test Samples 1-3, as shown in Table 2, exhibit similar or improved performance in standard tests compared to current marketed brake line tubing Comparative Sample A (PA12) or Comparative Sample B (Polyester/PA blend), as shown in Table 3. In particular, Test Samples 1-3, formed from a composition comprising 40-55 wt % thermoplastic polyurethane, 40-55 wt % copolyester and 0-15 wt % polyamide, exhibited improved end fitting retention, improved performance in boiling water conditioning and cold temperature impact, and improved tensile strength compared to Comparative Samples A and B.

(48) TABLE 3 shows performance of Test Sample 4 shown in Table 3, a monolayer tubing sample formed from a composition comprising 50-60 wt % polyurethane and 40-50 wt % polybutylene terephthalate (PBT) compared to control current marketed Comparative Sample A (ECLIPSE®; Eaton, 100% polyamide) or Comparative Sample B (SOLSTICE®; 90 wt % copolyester blend/10 wt % polyamide), as shown in Table 3. Test Sample 4 approaches the performance of Comparative Sample A and Comparative Sample B in several criteria in the standard tests, as shown in Table 3. In particular, Test Sample 4, formed from a composition comprising 50-60 wt % thermoplastic polyurethane and 40-50 wt % PBT, exhibited improved tensile strength, and improved performance in thermal conditioning and tensile strength (conditioned, lbf) tests compared to Comparative Samples A and B.

(49) TABLE 4 shows performance of Test Samples 5-7 monolayer tubing samples formed from different compositions comprising copolyester and polyurethane with polyamide. Test Samples 5-7, as shown in Table 4, exhibit similar or improved performance in standard tests compared to current marketed brake line tubing Comparative Sample A (PA12) or Comparative Sample B (Polyester/PA blend), as shown in Table 3. In particular, Test Samples 5-7, formed from compositions comprising 40-60 wt % thermoplastic polyurethane; 30-52 wt % copolyester; and 3-15 wt % polyamide exhibit improved performance in boiling water conditioning and cold temperature impact test compared to Comparative Samples A and B.

(50) As shown in TABLES 2-4, improved tensile strength was exhibited by Test Samples 1-3, 5 and 7 as compared to Comparative Samples A and B. Improved end fitting retention was exhibited by Test Samples 1-3 and 5 as compared to Comparative Samples A and B.

(51) As shown in TABLES 2-4, improved performance in Thermal Conditioning & Tensile Strength (conditioned)(lbf) was exhibited by Test Samples 1-7 compared to Comparative Samples A and B.

(52) An exemplary method for preparing air brake tubing is illustrated in FIG. 4. Tubing 20 comprised of the composition may be manufactured on an extrusion system 100 as shown in FIG. 4. The extrusion system 100 may include, among other components, a conveyor 110, a hopper 112, an extruder 114 (e.g., an auger or screw type extruder), a control system 116, a heating system 118 and a crosshead 120. The components (polyurethane pellets 102, copolyester, polyethylene terephthalate and/or polybutylene terephthalate pellets 104, and optional polyamide pellets 106) used to make the tubing 20 can be metered into a hopper 112 using the conveyor 110 controlled by the control system 116. The components 102, 104, 106 may be in pellet form or any other suitable form. The components 102, 104, and optional 106 can be at least partially mixed in the hopper 112 and then fed into the extruder 114 where the components 102, 104, and optional 106 are further mixed and heated with heat supplied by one or more heating elements of the heating system 118. The components 102, 104, and optional 106 may be under pressure prior to or when exiting the extruder 114 into the cross head 120. The cross head 120 may include a tip and a die (not show) to form the body of the tubing 20. After the extrusion process the tubing 20 may be cooled (e.g., by using a cooling bath) and gathered on a take-up reel. Mixing the components 102, 104, and optional 106 and extruding them directly into tubing 20 without additional heating steps may be beneficial because an additional heating step and therefore degradation of the composition can be avoided. Alternatively it may be desirable in some circumstances to mix and extrude the components 102, 104, and optional 106 to form pellets comprising the composition that can then be formed into tubing 20 at a later time using the extrusion system 100. In certain examples, the composition can be a co-polymer, alloy or blend.

(53) Air brake tubing of the present embodiments may possess superior qualities as compared to existing products by having increased burst strength, reduced moisture absorption, improved impact resistance, increased elevated temperature burst strength, increased tensile strength both before and after thermal conditioning, better fitting retention, lower cost, and may enable the elimination of plasticizers from the product.

(54) From the forgoing detailed description, it will be evident that modifications and variations can be made without departing from the spirit and scope of the disclosure.