WO1993022384A1

WO1993022384A1 - Clear copolyester/polycarbonate blends

Info

Publication number: WO1993022384A1
Application number: PCT/US1993/003898
Authority: WO
Inventors: Abraham James Cox; Richard Van Brooks
Original assignee: Eastman Chemical Company
Priority date: 1992-05-07
Filing date: 1993-04-27
Publication date: 1993-11-11

Abstract

This invention relates to a clear thermoplastic molding composition comprising: (a) 60-30 % by weight of a copolyester comprising: repeat units from an acid component consisting essentially of terephthalic acid and a glycol component comprising repeat units from 75 to 60 mole % ethylene glycol and 25-40 mole percent 1,4-cyclohexanedimethanol, said copolyester having an I.V. of at least 0.3 dl/g, the I.V. of said copolyester being determined at 25 °C in a solvent mixture consisting of 60 % by weight phenol and 40 % by weight tetrachloroethane, and 40-70 % by weight of a polycarbonate of 4,4-isopropylidenediphenol, said polycarbonate having a melt flow rate of from 2 to 17 g/10 min. as determined at 300 °C with a 1.2 kilogram load.

Description

_ 2. - CLEAR COPOLYESTER/POLYCARBONATE BLENDS

Field of the Invention

This invention relates to blends of copolyesters of poly(ethylene terephthalate) modified with 25 to 40 mole percent 1,4-cyclohexanedimethanol combined with bisphenol—A polycarbonate based polymers.

Background of the Invention Polyesters based on terephthalic acid, ethylene glycol and 1,4—cyclohexanedimethanol(CHDM) have properties which make them useful as plastic materials. For some applications, these polyesters have suffered from a low heat distortion temperature. This property can be improved by blending with a second polymer such as bisphenol—A polycarbonate which has a high heat deflection temperature. However, it is also desirable to maintain clarity in the blend. For this reason, a polyester which is compatible with polycarbonate must be used.

It is known in the art that blends of polyesters of terephthalic acid with 1,4-cyclohexanedimethanol modified with X mole percent ethylene glycol are compatible with bisphenol—A polycarbonate. X may range from 0 to 60 mole percent. The blends may contain from 5 weight percent to 95 weight percent polymer.

Blends of polycarbonates with other thermoplastic resins have been sought to improve the impact resistance of polycarbonate resins. Typical polymer blends include polycarbonate resins with poly(alkylene terephthalate) resins such as those disclosed in U.S. Patent 4,554,315, U.S. Patent 4,267,096 and EP 0 135 779. Polycarbonate blends with poly(cyclohexylene dimethylene terephthalate) resins (PCT) are also known such as those disclosed in U.S.Patent 4,628,074 and U.S. Patent 4,536,538.

Specifically, U.S. Patent 4,554,312 discloses thermoplastic blends of a polycarbonate resin with a poly(alkylene terephthalate) resin, an acrylic core- shell impact modifier and an epoxide—containing polymer modifier. The preferred poly(alkylene terephthalate) resin is poly(ethylene terephthalate) (PET) .

U.S. Patent 4,267,096 discloses blends comprising 65—97.5 parts by weight of an aromatic polycarbonate resin, 1—30 parts by weight of an amorphous polyester resin and 0.1—6 parts by weight of a partially hydrogenated copolymer of a vinyl aromatic compound and a diolefin. The amorphous polyester resin may be a poly(alkylene terephthalate) or a poly(cyclohexylene dimethylene terephthalate) resin.

U.S. Patent 3,864,428 discloses thermoplastic resins comprising 10—75 weight percent polycarbonate, 25—85 weight percent of an aromatic polyester and 2—35 weight percent of a butadiene polymer—vinyl monomer graft copolymer. These resins do not contain PET.

EP 0 135 779 discloses polycarbonate blends containing a poly(alkylene terephthalate) resin arid an amorphous copolyester copolymer resin which is prepared by reacting terephthalic acid and/or isophthalic acids with a mixture comprising cyclohexanedimethanol and ethylene glycol in a molar ratio of 4:1 to 1:4, respectively.

U.S. Patent 4,628,074 discloses that polycarbonate compositions containing polycarbonates and a poly—

(cyclohexylene dimethylene terephthalate) resin with an effective amount of an impact modifier such as an olefin diene terpolymer exhibit improved impact strength.

Similarly, U.S. Patent 4,536,538 discloses compositions containing a minor amount of an amorphous polyester derived from cyclohexane dimethanol and an aromatic dicarboxylic acid.

Despite considerable efforts, a need still exists for polyester/polycarbonate blends which exhibit the property of clarity while maintaining good mechanical properties.

Summary of the Invention The invention is directed towards a clear thermoplastic molding blend or composition comprising:

(a) 60—30% by weight of a copolyester comprising: repeat units from an acid component consisting essentially of terephthalic acid and a glycol component comprising repeat units from 75 to 60 mole percent ethylene glycol and 25-40 mole percent 1,4-cyclohexanedimethanol said copolyester having an I.V. of at least 0.3 dL/g, the I.V. of said copolyester being determined at 25°C. in a solvent mixture consisting of 60% by weight phenol and 40% by weight tetrachloroethane, and

(b) 40—70% by weight of a polycarbonate of 4,4—isopropylidenediphenol (bisphenol—A) , said polycarbonate having a melt flow rate of from 2 to 17 g/10 in. at 300°C with a 1.2 kilogram load. These blends exhibit good clarity while maintaining good tensile strength.

Detailed Description of the Preferred Embodiments

Blends of glycol—modified poly(ethylene terephthalate) (PETG) and bisphenol—A polycarbonate have been discovered which offer materials that can be processed over a relatively wide temperature range because of the generally amorphous nature of each of the polymers. These blends exhibit good clarity while maintaining tensile strength. Clear blends are useful for medical devices, display racks, automotive parts, protective eyewear, containers, etc. Clear blends are formed with 25—40 mole percent of 1,4—cyclohexane— dimethanol when processed at 300°C with a 4—minute residence time. The clarity of the blends or compositions can, under certain conditions, depend on the rate of mixing of the blend. One skilled in the art can be expected to be able to adjust these parameters and conditions in preparing the compositions or blends of the invention in order to achieve the appropriate clarity.

The blends also have good tensile strength values which are close to the tensile strength of the polycarbonate itself . The clarity of these blends and the good tensile strength is dependent on a critical range of 1,4-cyclohexanedimethanol.

The invention relates to a clear thermoplastic molding blend or composition comprising:

(a) 60—30% by weight, preferably 60—40% by weight, and more preferably 50% by weight of a copolyester comprising: repeat units from an acid component consisting essentially of terephthalic acid and a glycol component comprising repeat units from 75 to 60 mole percent ethylene glycol and 25—40 mole percent, preferably 30—40 mole %, and more preferably, at 35—40 mole % 1,4-cyclo¬ hexanedimethanol, and

(b) 40—70% by weight, preferably 40—60% by weight, and more preferably 50—50% by weight of a polycarbonate of 4,4—isopropylidene—diphenol (bisphenol A) . The copolyester of component (a) has an I.V. or inherent viscosity of at least 0.3 dL/g. The I.V. of the copolyester of component (a) may preferably range from 0.3 to 1.2 dL/g, and more preferably at a range of 0.5 to 0.8 dL/g. The I.V. of the copolyester is determined at 25°C. in a solvent mixture consisting of 60% by weight phenol and 40% by weight tetrachloroethane.

The polycarbonate portion of the blend consists of the polycarbonate of 4,4'—isopropylidenediphenol

(bisphenol—A) . The polycarbonate based polymers can be modified or branched versions with melt flow rates of from 2 to 17 g/10 min. , preferably, 2 to 11 g/10 min, and more preferably, 2 to 4 g/10 min. The melt flow rate is based on ASTM Method D—1238, condition 300—1.2 (300°C with a 1.2 kilogram load). The level of carbonate used in the blend can range from-40—70 weight percent.

The polycarbonate portion of the invention is prepared in the melt, in solution, or by interfacial polymerization techniques well known in the art. Many such polycarbonates are commercially available and are normally made by reacting bisphenol—A with phosgene or dibutyl carbonate or diphenyl carbonate, etc. The dicarboxylic acid portion of the polyesters and copolyesters useful in this invention consists of terephthalic acid. The acid portion may be modified with up to 20 mole percent of other acids which may contain 3 to 20 carbon atoms and may consist of units of aromatic, aliphatic, or alicyclic dicarboxylic acids or combinations of these dicarboxylic acids. Examples of useful aliphatic dicarboxylic acids are malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, _ sebacic, dodecanedioic, 1,4—, 1,5—, and 2,6—decahydrc— naphthalenedicarbox lic acid, and cis— or trans—1,4—cyclohexanedicarboxylic acid. Examples of useful aromatic dicarboxylic acids are terephthalic acid, isophthalic acid, 4,4'—biphenyldicarboxylic, trans 3,3'— and trans—4,4—stilbenedicarboxylic acid, 4,4'— ibenzyl—dicarboxylic acid, 1,4—, 1,5—, 2,3—, 2,6, and 2,7—naphthalenedicarboxylic acid.

The ethylene glycol and cyclohexanedimethanol portions of the copolyester useful in this invention may be replaced with up to 20 ol % of other aliphatic glycols, containing from 2 to 10 carbon atoms such as 1,3—propanediol, neopentyl glycol, 1,4—butanediol, 1,5—pentanediol or 1,6—hexanediol.

In a preferred embodiment, the cyclohexane¬ dimethanol component is a cis—/trans—mixture of 1,4-cyclohexanedimethanol. It is also preferred that the cyclohexanedimethanol is present at 30—40 mole %, and more preferably, at 35—40 mole % in the blend.

Preferred σopolyesters of the invention comprise repeat units from terephthalic acid, ethylene glycol and 1,4—cyclohexanedimethanol.

The polyesters and copolyesters of the present invention are prepared by conventional polycondensation processes well known in the art, such as the process described in U.S. Patent 2,901,466 dated August 25, 1959. These include direct condensation of the acid(s) with the glycol(s) or by ester interchange using lower alkyl esters.

The polyester/polycarbonate blends of the invention may be made by conventional melt processing techniques. For example, pellets of the polyester may be mixed with pellets of the polycarbonate and subsequently melt blended in either a single or twin screw extruder to form a homogenous mixture. Suitable processes for preparing the polycarbonates of the present invention are described in, for example, U.S. Patents 4,018,750, 4,123,436 and 3,153,008. However, other known processes for producing polycarbonates are suitable.

The blends of the present invention contain from 40-70 weight percent of the polycarbonate resin. In addition to the components discussed hereinabove, the blends of this invention may contain additives commonly employed with polyester resins, such as colorants, flame retardants such as a phosphorous compound, a halogen compound, or a halogen compound in combination with an antimony compound, mold release agents, antioxidants, tougheners, nucleating agents, ultraviolet light, and heat stabilizers and the like.

The blends of this invention are prepared by blending the components together by any convenient means to obtain an intimate blend. Compounding temperatures must be at least the melting point of the polyester. For example, the polyester can be mixed in a dry state in any suitable blender or tumbler with the other components and the mixture melt extruded. The extrudate can be chopped into pellets.

This invention can be further illustrated by the following examples of preferred embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated. The starting materials are commercially available unless otherwise noted. All percentages are by weight unless otherwise indicated. EXAMPLES

Example 1

A pellet/pellet blend of a copolyester of poly— (ethylene terephthalate) (PET) modified with 30 mole percent cyclohexanedimethanol, having an I.V. of 0.75 dL/g, with 50% Makrolon (trademark) HMS—3118 was prepared and dried at 70°C for 16 hours. Makrolon HMS—3118 is a high melt strength polycarbonate having a melt flow rate of < than 3 grams per/10 min. at 300°C with a 1.2 kilogram load. Makrolon HMS—3118 is commercially available from Mobay Chemical Company. The material was extruded at 280°C and 300°C on a .75" (1.91 cm) Brabender extruder equipped with a mixing screw using a 90 rpm screw speed, which has an approximate average residence time of 1.6 min. Material extruded at these conditions was opaque. When extruded at 300°C with a 30 rpm screw speed (average residence time of 4 minutes) the material was clear. Clear specimens were molded from the clear material on either a Boy 22S or Toyo_.90 molding machine using barrel temperature settings Of 280-300°C, 500-550 psig (3548.86-3893.61 kPa) injection pressure, 150 rpm screw speed and 30 sec cycle time. A clear molded sample had a tensile strength value of 11,900 psi (83 MPa), and a flexural strength value of 12,400 psi (86 MPa) and a notched Izod impact strength at 23°C of 2.38 ft.-lb./in. (127 J/M) .

Example 2 A 50/50 blend by weight of a copolyester of PET modified with 30 mole percent eyelohexane—dimethanol having an I.V. of 0.60 dL/g and 120 ppm titanium catalyst with 50% Makrolon HMS-3118, a high melt strength polycarbonate, as described herein, was prepared by pellet to pellet blend. For comparison, a 50/50 blend of a copolyester of PET modified with 30 mole percent cyclohexanedimethanol and 60 ppm titanium catalyst and 50% Makrolon HMS—3118, as described herein, was also prepared. The blends were processed through a .75" (1.91 cm) Brabender single screw extruder with mixing screw at 280, 290 and 300°C and 90 rpm screw speed. The extrudates for all these samples were hazy even after two passes through the extruder. At 30 rpm and 300°C during the first pass, the blend with 60 ppm Ti catalyst became clear, and at 45 rpm and 300°C during the first pass the blend with 120 ppm Ti catalyst became clear.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifi¬ cations can be effected within the spirit and scope of the invention. Moreover, all patents, patent ^'applica¬ tions (published or unpublished, foreign or domestic) , literature references or other publications noted above are incorporated herein by reference for any disclosure pertinent to the practice of this invention.

Claims

Claims We claim:

1. A clear thermoplastic molding composition comprising: (a) 60—30% by weight of a copolyester comprising: repeat units from an acid component consisting essentially of terephthalic acid and a glycol component comprising repeat units from 75 to 60 mole % ethylene glycol and 25—40 mole percent 1,4-cyclohexanedimethanol, said copolyester having an I.V. of at least 0.3 dL/g, the I.V. of said copolyester being determined at 25°C. in a solvent mixture consisting of 60% by weight phenol and

40% by weight tetrachloroethane, and (b) 40—70% by weight of a polycarbonate of 4,4—isopropylidenediphenol, said polycarbonate having a melt flow rate of from 2 to 17 g/10 min. as determined at 300°C with a 1.2 kilogram load.

2. The composition of claim 1 comprising 60—40 weight % copolyester.

3. The composition of claim 1 comprising 60 weight % copolyester and 40 weight % polycarbonate.

4. The composition of claim 1 comprising 50 weight % copolyester and 50 weight % polycarbonate.

5. The composition of claim 1 wherein said copolyester has a notched Izod impact strength of at least 1.5 ft— lb./in. (80.1 J/m) at 23°C.

6. The composition of claim 1 wherein said copolyester has an inherent viscosity of from 0.3 to 1.2 dL/g.

7. The composition of claim 1 wherein said copolyester has an inherent viscosity of from 0.5 to 0.8 dL/g.

8. The composition of claim 1 wherein said polycarbonate is modified or branched with melt flow rates of 2 to 11 g/10 min.

9. An injection molded article made of a composition according to claim 1.

10. The composition of claim 1 characterized by having a tensile strength of at least 8,000 psi (55.16 MPa).