Background of the Invention Field of the Invention An improved connector module for splicing together corresponding wire-ends of opposing sections of communications cables in an assembly station is formed from a polycarbonate alloy which exhibits improved resistance to stress cracking and solvents.

Description of the Related Art Various types of modular connectors are known in the telecommunications art.

U.S. Patent 3,713,214, (Enright et al.), discloses an apparatus and method for splicing together the corresponding wire-ends of opposing sections of communications cables using solderless U-connector multiple-layer modules in an assembly station including module supporting means, wire-guiding and wire-separating means, and wire retaining means. It is disclosed that the assemblies are made from an electrically insulative material; polycarbonate is the sole material listed.

U.S. Patent 3,858,158 discloses a connector module made from materials "such as polycarbonate, polyamide, or related polymer such as ABS resin."

U,S. Patent 4,262,985 discloses a connector module wherein it is stated that the components of the connector module and cap are made by conventional plastic molding techniques from materials such as polycarbonate. Improvements to such connectors have generally focused on mechanical design changes, e.g., to permit accommodation of greater size range of conductors, or to increase electrical isolation of the conductors.

However, the specifications for such assemblies have contained increasingly stringent requirements for solvent resistance, and temperature stability. Polycarbonate modules have encountered problems with stress-cracking after exposure to environmental stresses such as organic

solvents and the like. With a possible lifetime of between 20 and 40 years, improved aging and resistance characteristics would be highly desirable. However, the modules must also be flexible, sonically weldable, and highly resistant to pressure. Further, because the modules are reenterable, and may have new covers at some point, the new parts must meet certain standards for processibility and good dimensional stability in order to insure proper mating of such covers with existing product bases. The expense of molding tools makes it preferable that any changes in material have similar injection molding properties, e.g., shrinkage, to minimize need for new tooling, handling or extrusion equipment.

Polymer blends containing polycarbonates are well known in the chemical arts. Many patents exist which disclose one or more improved characteristics of polymer blends over either polymer alone. Polycarbonates are high temperature, high performance thermoplastics having generally good thermal and mechanical properties, especially the aromatic polycarbonates. Polycarbonate resins have been blended with various types of other polymers and copolymers to improve properties such as impact resistance, solvent resistance, and the like. The blends disclose improvements ranging from impact resistance to resistance to mild solvents and improved resistance to environmental stress crazing.

U.S. Patent 4,522,979 discloses thermoplastic molding compositions which comprise a blend of a polycarbonate resin a thermoplastic polyester, an impact modifier and a locked polyisocyanate prepolymer. U.S. Patent 4,968,756, discloses a thermoplastic resinous blend comprising 50 to 97 percent aromatic carbonate polymer; 2 to 25 percent polyacetal, and 0.5 to 40 percent thermoplastic urethane. The blend is disclosed to have improved environmental stress crazing and cracking, and improved impact strength. The blend is disclosed to useful as an injection molded component for

automobiles, appliances, electrical machinery and the like. However, the flex moduli and percentage elongation exhibited by the polymers are low, indicating that the blends would not be flexible enough to allow the reentry and reuse required by telecommunications modules.

U.S. Patent 4,562,222, discloses a solvent resistant resin mixture having improved impact strength, and extraordinary resistance to environmental stress cracking. The resin mixture comprises specific aromatic polycarbonates and a modifier combination comprising a coupled resinous block copolymer, e.g., SBS, and a copolymer of an olefin and a Cj-Cjβ alkyl acrylate.

U.S. Patent 4,743,650 discloses a thermoplastic molding blend of polycarbonate and polyurethane. The resins have a flex modulus of at least 1.05 x 10 ⁴ kg/cm ² , and a heat deflection temperature of at least 50°C at 18.6 kg/cm ² .

U.S. Patent 4,859,738 discloses environmental stress failure resistant and impact resistant thermoplastic molding compositions prepared from an aromatic polycarbonate, an aromatic polyester, and a copolymer of ethylene and carbon monoxide. The blend is disclosed to exhibit high impact resistance, chemical resistance, temperature stability and excellent thermoplastic engineering properties.

However, none of these polycarbonate blends is disclosed to be useful for a telecommunications splice assembly, modular connector, or any telecommunications applications. Also, while many patents on thermoplastic molding materials claim improved solvent resistance, most of these materials would not withstand the solvents in which these assemblies must be tested, e.g., lubricants, filling compounds, insecticides and herbicides.

Further, many of the polycarbonate blends taught therein would not have the physical properties required of such an assembly, e.g., flexibility for reentry, complete reclosure, ultrasonic weldability, ability to

withstand crimping pressure, etc. Also, some blends have improved certain properties at the expense of other properties such as softening temperature.

Surprisingly, it has now been discovered, that a splice module comprising a alloy or blend containing at least one aromatic polycarbonate, said alloy having a flex modulus of at least 2.1 xlO ⁴ kg/cm ² , a tensile strength of at least 280 kg/cm ² , an elongation of at least 130%, and a heat deflection temperature of at least 117°C at 455 kPascals (kPa) will show improved chemical resistance, improved resistance to stress cracking, while retaining the temperature resistance and molding capabilities required of such a module.

Other benefits of preferred systems herein include improved uniformity in depth of cutoff blades, and resultant increased wire retention, especially during reuse of modules in the field.

Summary of the Invention The invention provides a splice connector module having improved resistance to stress cracking formed of a composition comprising at least one non-silicone polycarbonate alloy having a flex modulus of at least 2.1 xlO ⁴ kg/cm ² , a tensile strength of at least about 280 kg/cm ² , an elongation of at least 130%, and a heat deflection temperature of at least 117°C at 455 kPa.

Preferred modules of the invention are formed of a polycarbonate blend comprising at least 40% of an aromatic polycarbonate polymer, and at least one polymer selected from the group consisting of aromatic polyesters, and copolyesters, and have a flex modulus of at least 2.3 xlO ⁴ kg/cm ² , a tensile strength of at least 350 kg/cm ² , and an elongation of at least 200% and a heat deflection temperature. In one highly preferred embodiment, the blend also contains at least one thermoplastic elastomer.

Connector modules are variously referred to in the

art as "splice assemblies", "splice modules", "connector assemblies" , "joint modules", and so on. It is understood herein that such terms are interchangeable, and are used to refer to any of such devices.

Detailed Description of the Invention Modules of the invention must meet many specific requirements in order to satisfy the Bellcore specifications. Rural Electrical Associations specifications, and various international tests required by telecommunications companies. They must be resistant to fungi, heat, solvents and stress cracking agents as well as meeting various electrical insulation resistance requirements, temperature cycling tests and the like. They must also be injection moldable, have good dimensional stability, uniformity in depth of cutoff blades, and have the ability to withstand the 280 kg/cm ² (4000 psi) of pressure used to crimp the cover onto the module, while retaining the uniformity of blade depth. Modules according to the invention are injection molded from non-silicone polycarbonate alloys containing at least one aromatic polycarbonate and having a flex modulus of at least 2.1 xlO ⁴ kg/cm ² , a tensile strength of at least 280 kg/cm ² , an elongation of at least 130%, and a heat deflection temperature of at least 117°C at 455 kPa.

Preferred polycarbonate alloys in devices of the invention comprise at least one aromatic polycarbonate polymer and at least one polyester or copolyester such that the final alloy or blend has the above cited properties. Polycarbonate alloys having less than the required flex modulus or tensile strength will fa.il at least one of the required tests. Surprisingly, polycarbonate alloys having the required flex, tensile and heat deflection temperatures will exhibit the required resistance to solvents, stress cracking, and the

like while also being easily cold molded in similar tools to those used for polycarbonate. The modules also show aging results similar or better than those of polycarbonate. Aromatic polycarbonate resins suitable for use in the instant invention may be prepared by any of the conventional processes known in the art for manufacture of polycarbonates. Generally, aromatic polycarbonates are prepared by reacting an aromatic dihydric phenol with a carbonate precursor, such as a carbonyl halide, a carbonate ester or the like.

One preferred method for preparing the aromatic polycarbonates suitable for use in the present invention involves the use of a carbonyl halide, such as phosgene. The phosgene gas is passed into a reaction mixture containing an activated dihydric alcohol, or a dihydric phenol and an acid acceptor, such as aniline, pyridine, quinoline and the like. Generally, one mole of phosgene will react with one mole of dihydric alcohol to form the polycarbonate and two moles of hydrochloric acid, which will be taken up by the acid acceptor. The acid acceptor may be used with inert organic solvents such as methylene chloride, 1,2-dichloroethane and the like. Tertiary amines are particularly preferred since they provide good solvents as well as good acid acceptors during the reaction. The reaction may be carried out at temperatures of room temperature to 50°C. The rate of phosgene addition is used to control the temperature of the reaction. In other methods, phosgene may be added to an alkaline aqueous suspension of dihydric phenols in the presence of inert solvents, or added to the suspension of an anhydrous alkali salt of an aryl diol in a nonaqueous medium. Such methods are described in U.S. Patents

3,028,365, 3,148,172, 3,153,008, 3,248,414, 3,271, 367. Aromatic polyesters and copolyesters suitable for

use may be prepared by condensing aromatic dicarboxylic acids with diols or by condensing precursors which contain both an alcohol or phenol and a carboxylic acid. Suitable diols include ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, and 1,6-hexanediol. Examples of suitable aromatic dicarboxylic acids are terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyletherdicarboxylic acid, and the like. Examples of precursors containing both an alcohol and a carboxylic acid include 4-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, and the like.

Highly preferred modules comprise a polycarbonate blend comprising from 40% to 85% of an aromatic polycarbonate polymer, from 2% to 60% of an aromatic polyester or copolyester, and from about 1% to 25% of a thermoplastic elastomer.

Suitable thermoplastic elastomers such as acrylonitrile-butadiene-styrene copolymers (ABS) , EPDM copolymers, polybutadiene, ethylene-butylene copolymers, polyisoprene, and the like.

Suitable commercial polycarbonate alloys include Sabre™ 1647, available from Dow Chemical Company, Texin™ 1091, available from Miles Polymers, and the like. Various additives may also be present in the compositions, e.g., pigments and dyes, fillers, flame retardants, foaming agents, impact modifiers, mold release agents, antistatic agents ultraviolet radiation absorbers, plasticizers and the like, in conventional amounts, to the extent to which they do not affect the critical physical properties, e.g., typically 10% or less.

Such alloys may be colored or colorless in appearance, and may be opaque or translucent. Polymeric blends which will exhibit translucence after forming processes are preferred, as they give ready visual access to the connections without opening the cover of the module.

The method of forming the polycarbonate blend is not critical. Any conventional blending technique is generally suitable. One preferred method is to blend the polymers and additives before extruding the blend and chopping into pellets suitable for molding to shape by means conventionally used to mold thermoplastic conditions.

Injection molding methods for splice assemblies of the invention are well known in the art. Connector modules typically contain multiple parts which are formed of a plastic resin, such as the base, the body or bodies, and the cover. For maximum improvements, all of such parts will be formed from a polycarbonate alloy according to this invention. However, if desired, e.g., for economical reasons, any single or combination of these parts may be formed of the polycarbonate alloy.

Modules of the invention can be pluggable, hardwired, branched splice, two-wire or three-wire, or other known variations.

Preferred modules of the invention are those which typically consist of elongate interfitting bases, body and cover members. The body member carries a double row of contact elements, the elements being disposed alternately close to and distant from one edge, and the body is multiperforate along such edge, each perforation providing access to a corresponding element. Wire ends of a first cable bundle of wire pairs are supported across the base and beneath the body and wire-ends from the opposing cable bundle of wire-pairs are supported across the upper surface of the body and beneath the cover, with each wire in position for contacting an appropriate contact element; and the several members are then forcefully pressed together to complete the modular connection. Such modules are available commercially from Minnesota Mining and Manufacturing Company (3M) as "the 4000 Series "Super Mini" and 4005 Series "Super Mate"

modules .

Such modules are described in U.S. Patent Nos. 3,699,501; 3,708,779; 3,713,214; 3,945,745; 3,717,334; 3,897,129, and 3,897,129.

Test Methods Tensile Strength The tensile strength of the polycarbonate alloy is tested according to American Society of Test Methods (ASTM) Test Method "D638-86".

Flex Modulus The flex modulus of the polycarbonate alloy is tested according to ASTM Test Method "D790-86".

Elongation The elongation of the polycarbonate alloy is tested according to ASTM Test Method "D638-86".

Heat Deflection Temperature

The heat deflection temperature under load is tested according to ASTM Test Method "D638-86".

Chemical Resistance

Test bar samples 0.317 cm thick x 1.27 cm wide x 6.35 long, supported on 5.08 cm centers, are deflected and loaded to induce an outer fiber strain of 0.0075 inches/inch. Each sample is then immersed in a stated chemical for 24 hours. The samples are placed in a glass jar to discourage evaporation. Samples should be free from visible cracks.

Electrical Contact Integrity Test A module injection molded from a polycarbonate alloy. The module is wired and circuit board mounted. The insulation resistance is measured before and after

cycling from -195°C (-321°F) to 82°C (180°F) every twelve minutes for 100 cycles (about 8 hours) . The insulation resistance should not vary more than 2 milliohms.

Sonic Welding Test The welding strength of a polycarbonate alloy module is tested by molding from the alloy, a 4000 Super Mini™ module, a type of module available from 3M, on standard production assembly equipment. The module is then placed in a test fixture which compressively pushes down on the bottom of the body member which tends to tear the body bottom free of the body top. The test fixture used comprises two steel blocks each having about 50 pins pointed to the interior of the fixture when the two blocks are placed together, and a space for the module. A module is placed therebetween, perpendicular to the pins. The fixture is then compressed in a Chatillon™ gauge, and compressed until the module pops apart. The maximum force required to force the modules apart at the weld is recorded.

Accelerated Aging Test The modules to be tested fully wired with 22 AWG oversized PIC wires representing the largest gauge specified. They are placed in aluminum trays measuring about 23cm x 28cm x 3.8cm. The tray is then filled with a reenterable encapsulant; "126" by Caschem Company, High Gel™, available from 3M, and "D1000", available from American Telephone and Telegraph Company. The encapsulants were then cured at room temperature for 24 hours. The trays were tapped frequently during this period to prevent trapping air bubbles in the encapsulant. The trays were then baked at 60°C for the number of days specified in the table. The modules were then opened using the 3M Popapart™ tool specified for the

module tested (#4053 for 4000D Super Mini™ modules and . #4053-PM for 4005 DPM Super Mate™ modules. The hooks latches and cutoff blade pockets and elements were inspected using a microscope at 3X. The following examples are for illustrative purposes only, and do not limit the scope of the invention, which is that of the claims. Variations within the claimed scope may easily be rendered by one skilled in the art. The improved connector modules are specifically not limited to the designs and assemblies described in the examples below. They may be any varied as is known in the telecommunications art, e.g., the number of connections may vary, the size of the connector may vary, the pair count may vary, and the like. The modules can be pluggable or hardwired, single splice or branched splice, two-wire or three-wire, or fiber optic connectors.

Examples Various polycarbonate alloys were subjected to stress cracking performance. Bar samples (0.32cm thick, 1.26cm in width and 6.35cm in length) of each alloy were wet with Black Flag™ wasp spray, available from Oulen Company, until dripping and maintained in a sealed glass jar for 24 hours. If the initial sample cracked, two additional samples were tested with the same chemical. Two of three samples with cracks were considered a failure. Treated samples were then tested for 30 days; the spray was reapplied each day. Alloys tested include polybutylene terephthalate and aromatic polycarbonate blends; polycarbonate/polyethylene terephthalate blends; polycarbonate/acrylonitrile-butadiene-styrene blends, and a polycarbonate polyurethane blend.

'Polycarbonate/polybutylene terephthalate ² Polycarbonate/polyethylene terephthalate ³ Polycarbonate/acrylonitrile-butadiene-styrene ⁴ Polycarbonate/polyurethane Polycarbonate/ elastomer ic polyurethane

The alloys of Table I which passed the 30 day test were then molded into modules. The blends were dried to remove moisture in dehumidifying hopper ovens. The dried materials were injection molded in a standard production injection molding machine with reciprocating screws. Plastic melt temperatures for the blends ranged from approximately 215°C to approximately 360°C, varying with the polymers used in the blend. Mold surface temperatures likewise ranged from approximately 10°c to approximately 135°C. Molding cycles were from 5 seconds to about 50 seconds.

The modules were then tested for wire crimping and wire cutting over a temperature range of -40°C to 60°C. The results are shown in Table II.

As can be seen from the above data, polycarbonate alloys having the required physical characteristics exhibited good wire cutting properties. Those with lower tensile strengths or lower flex moduli exhibited poor wire cutting. The alloy having a combination of low tensile strength and high elongation showed the highest change in the position of the cutting blades.

Alloys with modules successful in the crimping test then had modules wired, circuit board mounted and tested for electrical insulation integrity.

A second test procedure showed the performance retention of modules under accelerated aging conditions. Modules containing 26 to 22 AWG PIC wires

are directly encapsulated in three solvents; Caschem™ 126, available from Caschem Corp, "D-1000", available from AT&T, and 4442 High Gel™, available from 3M, and then stored at 140°F for thirty and ninety days.

Table III

MODULE % 00S ¹

1 outside specification limits

2 module covers of Example 12 alloy/module bases control

3 tested for 20 hours at 82°C

As the data above show, the polycarbonate alloys showing the required properties perform equally to the polycarbonate controls. Those modules marked with an asterisk had wires come completely undone from the modules, which rendered the change in insulation resistance meaningless. Covers made of these blends also unlatched from module bodies made of either the blend polycarbonate, allowing wires to fail.

Polycarbonate/polyester alloy modules which performed well in the wire retention test were then tested for weld strength, when ultrasonic welded. The maximum force of disruption weld strength is reported in kilograms in Table IV.

TABLE IV

As can be seen, the polycarbonate control module weld strengths started much higher, but dropped 15-50% whereas the module formed of the polycarbonate alloy of the invention actually had weld strengths increase on the average.