Low Melt Viscosity Polycarbonate Compositions Having Improved Impact Strength

This invention relates to flame retardant, aromatic poly¬ carbonate resins having improved impact strength at low melt viscosities.

Background of the Invention Polycarbonate polymers are known as being excellent mold¬ ing materials since products made therefrom exhibit such pro¬ perties as high impact strength, toughness, high transparency, o wide temperature limits (high impact resistance below -60 C and a UL thermal endurance rating of 115 C with impact), good dimensional stability, good creep resistance, good flame retardance, and the like. However, these properties are generally exhibited in polycarbonate resins having relatively high melt viscosities . such as on the order of about 2400 poises. It would be desirable to add to this list of properties that of improved impact strength when the polycarbonates have relative¬ ly low melt viscosities such as on the order of about 1500- 2000 poises. These low melt viscosity polycarbonate resins having improved impact strength can then be employed to form molded articles requiring long thin wall s ections which are difficult to mold when polycarbonates having high viscosities are employed. Summary of the Invention

It has now been found that improved impact strength can be imparted to low melt viscosity, high molecular weight, aromatic

poly carbonate resins by blending the polycarbonate resin with rubbery acrylic-butadiene copolymer at a weight ratio of poly¬ carbonate to the rubbery copolymer in the range of about 10:1 200: 1. In the practice of this invention, any of the aromatic poly¬ carbonates can be employed that are prepared b reacting a diphenol with a carbonate precursor. Typical of some of the diphenols that can be employed are bisphenol-A (2, 2-bis(4-hyd phenyl)propane), bis (4-hydroxyphenyl) methane, 2, 2-bis(4-hydr 3-methylphenyl)prθpane, 4, -bis(4-hydrόxyphenyl)heptane, 2, 2- (3, 5, 3 ^, ,5'-tetrachloro-4, 4'-dihydroxydiphenyl)propane, 2, 2-(3, 5 3', 5'-tetrabromo-4, 4--dihydroxydiphenyl)propane, (3, 3'-dichlor 4, 4' -dihydroxyphenyl) methane. ' Other diphenols of the bisphen type can also be used such as are disclosed in U. S. Patents 2, 999, 835, 3, 028, 365, and 3, 334, 154.

It is possible to employ two or more different diphenols or a copolymer with a glycol or with hydroxy or acid terminated polyester, or with a dibasic acid in the event a carbonate co¬ polymer or interpolymer rather than a homopolymer is desire for use in preparing the aromatic polycarbonate. Blends of a of these materials can also be used to obtain aromatic poly-

( carbonates.

These diphenols can then be employed to obtain the high mo cular weight aromatic polycarbonates of the invention which can be linear or branched homopolymers or copolymers as we as mixtures thereof or polymeric blends and which generally have an intrinsic viscosity (IV) of about 0. 40-1, 0 dl/g as measured in methylene chloride at 25 C.

The carbonate precursor used can be either a carbonyl halide, a carbonate ester or a haloformate. The carbonyl halides can be carbonyl bromide, carbonyl chloride and mix¬ tures thereof. The carbonate esters can be diphenyl carbonate

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di-(halophenyl) carbonates such as di-(chlorophenyl) carbonate, di-(bromophenyl) carbonate, di-(trichlorophenyl)carbonate, di-

(tribromophenyl) carbonate, etc. , di-(alkylphenyl) carbonate such as di(tolyl) carbonate, etc. , di-(naphthyl) carbonate, di- (chloronaphthyl) carbonate, phenyl tolyl carbonate, chloro- phenyl chloronaphthyl carbonate, etc. , or mixtures thereof.

The halofor ates than can be used include bis -haloformates of dihydric phenols (bischloroformates of hydro.quinone, etc. ) or glycols (bis haloformates of ethylene glycol, neophenyl glycol, polyethylene glycol, etc. ). While other carbonate precursors will occur to those skilled in the art, carbonyl chloride, also known as phosgene, is preferred.

Also included are the polymeric derivatives of a dihydric phenol, ^' a dicarboxylic acid and carbonic acid such as are dis- closed in U. S. Patent 3, 169, 121 which is incorporated herein by reference, and which are particularly preferred. This class of compounds is generally referred to as copolyestercarbonates..

Molecular weight regulators, acid acceptors and catalysts can also be used in obtaining the aromatic polycarbonates of this invention. The useful molecular weight regulators include monohydric phenols such as phenol, chroman-I, paratertiary- - butylphenol, parabromophenol, primary and secondary amines, etc. Preferably, phenol is employed as the molecular -weight regulator. A suitable acid acceptor can be either an organic or an inorganic acid acceptor. A suitable organic acid acceptor is a tertiary amine such as pyridine, triethylamine, dimethylaniline, tributylamine, etc. The inorganic acid acceptor can be either a hydroxide, a carbonate, a bicarbonate, or a phosphate of an alkali or alkaline earth metal.

The catalysts which can be employed are those that typically aid the polymerization of the diphenol with phosgene. Suitable

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catalysts include tertiary amines such as triethylamine, tri- propyla ine, N,N-dimethylaniline, quaternary ammonium com¬ pounds such as, for example, tetraethylammonium bromide, cetyl triethyl ammonium bromide, tetra-n-heptylammonium iodid tetra-n-propyl ammonium bromide, tetramethylammonium chlor tetramethyl ammonium hydroxide, tetra-n-butyl ammonium iodi benzyltrimethyl ammonium chloride and quaternary phosphonium compounds such as, for example, n-butyltriphenyl phosphonium bromide and methyltriphenyl phosphonium bromide. Also ^' included herein are branched polycarbonates wherein a polyfunctional aromatic compound is reacted with the diphenol and carbonate precursor to provide a thermoplastic randomly branched polycarbonate. These polyfunctional aromatic com¬ pounds contain at least three functional groups which are carbo carboxylic anhydride, haloformyl, or mixtures thereof. Illustra tive of polyfunctional aromatic compounds which can be employe include trimellitic anhydride, trimellitic acid, trimellityl tri¬ chloride, 4-chloroformyl phthalic anhydride, pyromellitic acid, pyromellitic dianhydride, mellitic acid, mellitic anhydride, tri- esic acid, benzophenonetetracarboxylic acid, benzophenonetetr carboxylic anhydride, and the like. The preferred polyfunctiona aromatic compounds are trimellitic anhydride and trimellitic ac or their acid halide derivatives.

Blends of linear and branched aromatic polycarbonates are also included within the scope of this invention.

Other well known materials can also be employed for their intended function and include such materials as anti- static agent mold release agents, thermal stabilizers, ultraviolet light stabi lizers, reinforcing fillers such as glass and other inert fillers, foaming agents, and the like.

Preferably, the polycarbonate resins employed are those that exhibit improved flame retardance. Typical of the flame retard

polycarbonates that can be used in the practice of this inven¬ tion are those that are derived from halogenated diphenols such as are disclosed in U. S. Patent 3, 062, 781, German Patent P25 317. 2 and in copending applications Serial No s. 882, 242; 882, 191; and, 882, 193, all of which -were filed on

February 28, 1978. These copending applications are assigned to the same assignee as this application and are incorporated herein by reference thereto.

The rubbery acrylic-butadiene copolymers that can be em- ployed are those which are commercially available such as those offered by Rohm and Haas Company under their product identifications KM-228, KM-607 and KM-611.

The rubbery copolymer can be blended with the low melt viscosity polycarbonate in amounts of about 0. 5 to 10%, pre- ferably 1 to 5% and optimumly 2 to 4% based upon the weight of the polycarbonate. Preferred Embodiment of the Invention

The following examples are set forth to more fully and clearly illustrate the present invention and are intended to be, and should be construed as being, exemplary and not limitative of the invention. Unless otherwise stated, all parts and percentages are by weight.

EXAMPLE I One hundred (lOO )parts of an aromatic polycarbonate, pre- pared by reacting 2, 2-bis(4-hydroxyphenyl)propane and phos gene in the presence of an acid acceptor and a molecular weight regulator and having a melt viscosity of about 1650 poises was mixed with 4. 3 parts of each of two rubbery acrylic- butadiene copolymers by tumbling the ingredients together in a laboratory tumbler. The resulting mixture was then fed through an extruder -which -was operated at about 265 C and the extruder was comminuted into pellets.

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-6- The pellets were than injection molded about 315°C into test bars of about (5 in.) 12.7 cm by 1/2 in.) 1.27 cm by about (1/16-1/8 in.) 0.16-0.32 cm thick and into test squares of about (2 in. by 2 in.) 5 cm x 5 cm by about (1/8 in.) 0.32 cm thick. The test bars (5 for each test listed in the Tables) were subject to the notched Izod impact test in accordance with ASTM D-256 on test ^" bars as molded and after the test bars had been subjected to accelerated heat aging at 125°C for periods set forth in Table 1 below wherein the acrylic-butadiene copolymers are those obtained from Rohm and Haas Company and are shown by their product identifica¬ tions.

Table I notched Izod Impact Test on Molded and Heat Aged Test Bars

Formulation

Polycarbonate (parts by weight) 100 100 100

Acrylic-Butadiene Copolymer:KM-607 0 4.3 (parts by weight) KM-611 ^' 0 4.3

Properties

Melt Viscosity (poises) 1620 1680 1620

Notched Izod Impact (ft.lbs/inch of notch) kg-cm/cm

As Molded ( (1144..55))7788..9 (13.8) 75.1 (13. 9) 75

Aged at 125°C for:

1 hr. (1.6)8.7 (11.6) 63.1 U3) 71

2 hrs. (10. 9) 59.3 (11.6) 63 __ 8 hrs. (5.9) 32 (10.5) 57

16 hrs. (5 , 1) 28 (10.1) 54

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As can be seen from the results, shown in Table 1 above, the unmodified polycarbonate at this low melt viscosity lost its ductile impact strength in less than one hour. The formulation containing M-607 retained its ductile impact strength up to about 8 hours at 125°C whereas the formulation containing KM-611 retained its ductile impact strength after being heat aged at 125°C for over 16 hours.

Example 2

The procedure of Example i was repeated except that the polycarbonate obtained had a melt viscosity of 1970 poises. This polycarbonate was also formulated with the acrylic-butadiene copolymer^ as in Example 1 and subjected to the same tests. The results obtained are set forth in Table II.

Table II

Notched Izod Impact on Molded and Heat Aged. Test Bars

Formulation

Polycarbonate (parts by weight) 100 100 100

Acrylic-Butadiene Copolymer:KM-607 0 4.3 (parts by weight) KM-611 0 4 .3

Properties

Melt Viscosity (poises) 1970 1880 1830

Notched Izod Impact (ft.lbs/inch of notch) kg-cm/cm

As Molded 15.4 11.8 12.7

-8- Table II (continued) Aged at 100°C for:

4 hrs. (1.6)8,7 (.12,7)69.1 (12,2)66 32 hrs. - (11.8)64.2 (12.3)66

Aged at 125°C for:

_ 1 hr. (1.6)8.7

^• - 8 hrs. - (9.7)53 (11) 60

16 hrs. - (3.3)18 (7.7) 42

24 hrs. - - (11.9) 65

The results in Table II above reveal that the formulations containing the acrylic-butadiene 0 ^• copolymers retained their ductile impact strength for prolonged periods even after being heat aged.

Example ^• 3

An aromatic polycarbonate was prepared by reacting 2,2-bis (4-hydroxyphenyl)propane and phosgene in the presence of an acid acceptor and a molecular weight regulator to-obtain a poly¬ carbonate having a melt viscosity of about 4000 poises. A copolycarbonate was also prepared by reacting 2,2-bis (4-hydroxyphenyl) propane and 2,2- (4-hydroxy-3,5-dibromophenyl) ropane and phosgene the presence of an acid acceptor and a molecular

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weight regulator to obtain a copoly carbonate having a melt vis¬ cosity of about 3500 poises. A sufficient amount of the poly¬ carbonate was blended with the copolycarbonate by tumbling them together in laboratory tumbler to obtain a composition having a bromine content of 4. %. This composition was made opaque by adding to it 2% titanium dioxide pigment and tumbling the ingredients together in the same manner. The pigmented and blended composition was divided into equal half portions and 4% of KM-611 acrylic-butadiene copolymer was blended with one of the portions by tumbling them together. Each portion was then extruded into pellets, the pellets molded into test bars and the test bars subjected to the notched Izod impact test all as descri¬ bed in Example 1. Test squares were also obtained as described in Example 1 and the flame retardancy of these test squares was also determined according to the test procedure set forth in

Underwriter's Laboratories, Inc. Bulletin UL-94, Burning Test for Classifying Materials. In accordance with this test proce¬ dure, materials so investigated are rated either V-0, V-I or V-II based on the results of 5 specimens. The criteria for each V (for vertical) rating per UL-94 is briefly as follows:

••V-0": Average flame and/or glowing after removal of the igniting flame shall not exceed 5 seconds and none of the specimens shall drip flaming particles which ignite absorbent cot .t. on.

"V-I": Average flaming and/or glowing after remo¬ val of the igniting flame shall not exceed 25 seconds and the flowing does not travel vertically for more than ( 1 /8") 0. 32 cm of the specimen after flaming ceases and glowing is incapable of igniting absorbent cotton. φREAl OMPI

-10- "V-II": Average flame and/or glowing after removal of the igniting flame shall not exceed 25 seconds and the speci¬ mens drip flaming particles which ignite absorbent cotton. In addition, a test bar which continues to burn for more than 25 seconds after removal of the igniting flame is classified, not by UL-94, but by the standards of the instant invention as "burns". 0 The results of these tests are shown in Table III,

^• Table III

Notched Izod Impact and Flame Retardancy Formulation 5 Polycarbonate blend

(parts by weight) 100 100

Acrylic-Butadiene Copolymer: KM-611 (parts by weight) 0

Properties Q Melt Viscosity (poises) 3200 3490

UL-94 Rating V-II V-II

ULτ94 Flame out (seconds) 1.5 5.5

Notched Izod Impact (ft.lbs/inch of notch) kg-cm/cm 5 As Molded (2.4) 13 (13.6)74

Aged at 125°C for:

2 hrs. (11.8)64

6 hrs. (6.7)36

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From the results shown in Table III above, it can be seen that the polycarbonate blend containing the acrylic-butadiene copolymer retained its ductile impact strength over a prolonged period, even after being heat aged, despite the presence of a pigment and the halogenated copolycarbonate, Furthermore, this was achieved without detrimentally affecting its UL-94 rating.

Example 4 The procedure of Example 3 was repeated except that the polycarbonate obtained had a melt viscosity of 1900 poises, the amount of titanium dioxide pigment added was increased to 2.5% and the KM-611 acrylic-butadiene copolymer level was increased to 6%. The same tests were run as in Example 3, the results of which are shown in Table IV.

Table IV Notched Izod Impact and Flame Retardancy Formulation Polycarbonate blend (parts by weight) 100 100

Acrylic-Butadiene Copolymer: KM-611 (parts by weight)

Properties

Melt Viscosity (poises) 1250 1260

UL-94 Rating V-II V-II

UL-94 Flame out (seconds) 2.2 3.7

Notched Izod Impact (ft.lbs/inch of notch) kg-cm/cm

As Molded (1.4)7.6 (10.4)56.6

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The results in Table IV show that the poly ^* - carbonate blend containing the acrylic-butadiene copolymer retained its ductile impact strength, despite the increased amount of pigment and its relatively low melt viscosity, with no sacrifice o its UL-94 rating.

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