WO1992013033A1

WO1992013033A1 - Miscible polyester blends

Info

Publication number: WO1992013033A1
Application number: PCT/US1992/000336
Authority: WO
Inventors: James Douglas Small, Jr.; Robert William Seymour; Larry Wayne Branscome
Original assignee: Eastman Kodak Company
Priority date: 1991-01-16
Filing date: 1992-01-14
Publication date: 1992-08-06

Abstract

Disclosed are thermoplastic molding compositions comprising a miscible blend of (a) a polyester or copolyester consisting essentially of repeat units of terephthalic acid with Y1 mole percent 1,4-cyclohexanedimethanol and with 100-Y1 mole percent ethylene glycol, where Y1 = 0 to 100 mole percent, and (b) a copolyester consisting essentially of repeat units of terephthalic acid with Y2 mole percent 1,4-cyclohexanedimethanol and with 100-Y2 mole percent ethylene glycol, wherein |Y1 - Y2| is greater than or equal to 18 mol % and is less than or equal to 50 mol %.

Description

MISCIBLE POLYESTER BLENDS

Technical Field

The present invention relates to miscible polyester blends that have improved clarity and a useful balance of mechanical properties.

Background of the Invention

Thermoplastic polyesters and copolyesters of terephthalic acid (TPA) with 1,4-cyclohexanedimethanol (CHDM) and/or ethylene glycol (EG) are useful engineering plastics for injection molding parts requiring chemical resistance, toughness, and good resistance to sterilization by gamma radiation. The use of such polyesters and copolyesters in film, sheet, and packaging applications is well established in the art.

A wide variety of mechanical and thermal properties exist across the compositional spectrum of copolyesters of terephthalic acid with various EG/CHDM ratios. Some typical properties of the homopolymers of terephthalic acid and ethylene glycol, and terephthalic acid and CHDM, and of selected copolymers of terephthalic acid and various ratios of EG/CHDM are given in Table 1.

Table 1

Typical Properties of Polyesters and Copolyesters of TPA with CHDM and/or EG

COMPOSITION

Table 1 (Cont'd.)

Typical Properties of Polyesters and Copolyesters of TPA with CHDM and/or EG

PROPERTIES

Although these polyesters and copolyesters provide a wide range of properties, it is sometimes advantageous to use mixtures or blends of such polymers to either tailor mechanical properties, improve processability, or utilize recycled or reground scrap materials from other processes. However, miscible blends or mixtures are preferred because they are clear and because many of their properties vary smoothly with blend composition. Paul et al ["Encyclopedia of Polymer Science and Engineering," 12, 399 (1988)] have reported such behavior of polymer blends in the literature, and Figure 1 demonstrates the concept.

The most well established and accepted theory for predicting miscibility in polymer blends utilizes the Flory—Huggins equation, which is well known to those familiar with the art. The method involves the calculation of the well known polymer—polymer interaction parameter χ from values of the individual solubility parameters of the polymer components. The solubility parameters are determined by group contribution methods established in the art, an example of which is attributed to Small fJ. Appl. Chem. 3, 71 (1953)]. The upper limit for miscibility of two polymers across the entire compositional range is set by a critical value of the polymer—polymer interaction parameter, χ_CR as discussed by Krause fMacromol. Sci. Revs. Macromol. Chem.. C7(2), 251 (1972)]. For values of X ≤ XCR' m scibili y is predicted at the temperature used to calculate χ. The Flory—Huggins treatment assumes that dispersive forces are the only molecular interactions involved during mixing. Coleman et al [Polymer, 31, 1187 (1990)] have recently extended this approach by accounting for the presence of molecular interactions that are favorable in inducing miscibility, resulting in an expansion of the range of χ_c« for the particular molecular interactions involved. This invention relates to blends comprised of a polyester or copolyester of terephthalic acid with 1,4-cyclohexanedimethanol and/or ethylene glycol and a copolyester of terephthalic acid with 1,4—cyclohexane— dimethanol and ethylene glycol, which were unexpectedly found to be miscible and clear. In addition, the blends show a good balance of properties that would make them useful as molding compositions.

Critical values of the interaction parameter for polymer blends that display dipole-dipole interactions, such as would be for polyesters, range from 0.002 to 0.02 according to Coleman et al. The value of χ from Flory—Huggins theory is <0.002. Blends of the present invention involve polyesters or copolyesters which can be described as TPA(EG)-Y-CHDM where 0 < Y < 100 and where Y is the mole percentage of CHDM in the polymer. Since EG and CHDM are the only glycols present, then (100 — Y) is the mole percentage of EG in the polymer. For Y = 100, the polymer would be PCT and PET would be defined by letting Y = 0. The Flory—Huggins criteria for miscibility of polyester A, defined as TPA(EG) — Y — CHDM, and polyester B, defined as TPA(EG) - Y² - CHDM, dictates that Δ, defined as lY¹ - Y²ι (absolute value), must be less than or equal to 5 mol %. The criteria outlined by Coleman et al suggests that Δ must be less than or equal to 18 mol % in order to insure miscibility at 25°C. Therefore, it is unexpected that blends of such polyesters and copolyesters were indeed clear and miscible if Δ is less than or equal to 50 mol %, a much wider range than predicted by accepted theory.

Mixtures of polyesters and/or copolyesters of poly(ethylene terephthalate) (PET) and of poly(1,4—cyclohexylenedimethylene terephthalate) (PCT), integrally formed together with reinforcing material into a stampable sheet, were disclosed in U.S. Patent 4,263,364; however, since the multilayered sheet was reinforced, no mention was made of clarity or miscibility of any of the polyester mixtures and the utility of such blends as clear molding compositions was not disclosed. Similarly, ternary mixtures of polyesters and copolyesters utilized as part of an oriented composite polyester film were disclosed in U.S. Patent 4,868,051. The present blends are new thermoplastic molding compositions comprised of a polyester or copolyester of terephthalic acid with 1,4-cyclohexanedimethanol and/or ethylene glycol and a copolyester of terephthalic acid with 1,4-cyclohexanedimethanol and ethylene glycol. In their unmodified forms, the blends of this invention are clear. This, combined with their excellent chemical resistance and processability, make them useful in molded medical parts. Additional applications include appliance parts and consumer goods. Brief Description of the Drawings

Figure 1 is a graph illustrating typical properties plotted against compositions wherein blends of Polymer A and Polymer B are shown, the curves in solid lines representing immiscible blends and the curves in broken lines representing miscible blends.

Description of the Invention

According to the present invention, there is provided a clear thermoplastic molding composition comprising a miscible blend of (a) 1-99 weight %, preferably 5-95 weight %, of a polyester or copolyester consisting essentially of repeat units of terephthalic acid with Y mole percent 1,4-cyclohexane¬ dimethanol and with 100—Y mole percent ethylene glycol where Y = 0 to 100 mole percent; and (b) 99-1 weight %, preferably 95-5 weight % of a copolyester consisting essentially of repeat units of terephthalic acid with Y mole percent 1,4-cyclohexanedimethanol and with

100 — Y mole percent ethylene glycol, wherein lY — Y i is greater than or equal to 18 mol % (preferably 20 mol %) and is less than or equal to 50 mol %. The polyesters and copolyesters used in the present invention are prepared by conventional polycondensation procedures well known in the art. The polyesters contain repeat units from a dicarboxylic acid component and a glycol component. The dicarboxylic acid component, a total of 100 mol %, consists essentially of terephthalic acid and the glycol component, a total of 100 mol %, consists essentially of either ethylene glycol or 1,4-cyclohexanedimethanol. The copolyesters contain repeat units from a dicarboyxlic acid component and two glycol components. The dicarboxylic acid component, a total of 100 mol %, consists essentially of terephthalic acid and the glycol components, a total of 100 mol % consist essentially of a mixture of ethylene glycol and 1,4-cyclohexanedimethanol.

Both the polyesters and the copolyesters can be prepared by direct condensation of the acid with the glycol(s) or by ester interchange using a lower alkyl ester such as dimethyl terephthalate. The essential components of the polyesters and copolyesters, e.g., terephthalic acid or dimethyl terephthalate, ethylene glycol, and 1,4—cyclohexanedimethanol, are commercially available. The polyesters and copolyesters described above should have an I.V. (inherent viscosity) of from 0.4 to 1.2.

The blends of the present invention may be made by either melt compounding the components, for example, in a single or twin screw extruder, or by introducing an admixture of the components directly into the feed hopper of an injection molding machine (salt and pepper blending) .

Of course, it should be understood that the compositions may also contain other additives such as impact modifiers, colorants, stabilizers, processing aids, flame retardants, fillers, and the like.

The following examples are submitted for a better understanding of the invention. Example 1

Blends of a number of polymers of the invention were prepared by dry mixing the two components in the ratios 25:75, 50:50, and 75:25% and extruding them into film on a Brabender single screw extruder. Miscibility was judged by the presence or absence of haze in the film, clear film being indicative of miscibility.

Table 2 shows that, unexpectedly, the blends of the polymers are miscible only if the difference in CHDM content between the two components, Δ, is less than or equal to 50 mol %. If Δ is greater than 50 mol %, then hazy, immiscible blends result.

Table 2

Miscibility of Blends of CHDM/EG Containing Polyesters and Copolyesters

Blends of two copolyesters were prepared by dry mixing the components and then subsequently adding the mixture to the feed hopper of a Boy 50S injection molding machine. The difference in CHDM content between the two components of the blend was 27.5 mol %, and all of the compositions tested yielded clear parts. Further, a useful balance of properties was exhibited by the blends, and key properties are reported in Table 3.

Table 3

Properties of Blends of Copolyesters with CHDM Difference (Δ) of 27.5 Mol %.

Copolyester A: 100 mol % terephthalic acid 95 mol % ethylene glycol 5 mol % 1,4-cyclohexane¬ dimethanol

Copolyester B: 100 mol % terephthalic acid 70 mol % ethylene glycol 30 mol % 1,4-cyclohexane¬ dimethanol

Exam le

Tensile strength § yld. , 10³ psi 8.07 8.03 7.96 7.96 7.89 7.10

Flexural modulus 10³ psi 3.56 3.55 3.52 3.46 3.49 2.90

As used herein, the inherent viscosity (I.V.) is measured at 25^βC using 0.50 g of polymer per 100 mL of a solvent consisting of 60% by weight phenol and 40% by weight tetrachloroethane.

The following tests are used herein: Flexural Modulus: ASTM-D790 Tensile Strength: ASTM—D638 Izod Impact Strength: ASTM—D256 Unless otherwise specified, all percentages, parts, ratios, etc. are by weight.

The invention has been described in detail with particular reference to preferred embodiments thereof. but it will be understood that variations and modifications can be affected within the spirit and scope of the invention.

Claims

1. A thermoplastic molding composition characterized as being a miscible blend of

(a) a polyester or copolyester consisting essentially of repeat units of terephthalic acid with Y¹ mole percent 1,4-cyclohexane¬ dimethanol and with 100—Y mole percent ethylene glycol, where Y¹ = 0 to 100 mole percent, and

(b) a copolyester consisting essentially of repeat units of terephthalic acid with Y mole percent 1,4-cyclohexanedimethanol and with

100 — Y² mole percent ethylene glycol, wherein lY¹ — Y ι is greater than or equal to 18 mol % and is less than or equal to 50 mol %,

said composition being clear when containing only said polyester and copolyester.

2. A molding composition according to Claim 1 wherein the I.V. of the polyesters or copolyesters is 0.4-1.2.

3. A molding composition according to Claim 1 comprising 1—99 weight % of polyester or copolyester (a) and 99—1 weight % of copolyester (b) .

4. The method of forming a miscible polymer blend which is characterized thoroughly mixing

(a) a polyester or copolyester consisting essentially of repeat units of terephthalic acid with Y mole percent, 1,4-cyclohexanedimethanol and with 100—Y mole percent ethylene glycol, where Y = 0 to 100 mole percent, and

(b) a copolyester consisting essentially of repeat units of terephthalic acid with

Y mole percent 1,4-cyclohexanedimethanol and with 100 — Y mole percent ethylene glycol, wherein lY¹ — Y²ι is greater than or equal to 18 mol % and is less than or equal to 50 mol %.