CA2119904C - Monofilament for papermaker's fabric - Google Patents

Abstract

A monofilament having high knot strength and good hydrolytic stability for forming into fabric used in the manufacture of paper and paper products is disclosed. The monofilament is made from a polymer blend of an acid-modified poly(cyclohexane-1,4-dimethylene terephthalate) and a second polymer selected from among polycarbonate and a glycol-modified poly(cyclohexane-1,4-dimethylene terephthalate).

Description

r. 21 19g 0 4 MONOFILAMENT FOR PAPERMAKER'S FABRIC
FIELD OF THE INVENTION
The present invention relates generally to monofilament yarns for industrial fabric, and especially to yarns for use in papermaking fabrics.
BACKGROUND OF THE INVENTION
Generally, in the process for making paper, incremental amounts of liquid are removed from a slurry of pulp in a succession of steps. In a first forming step, the slurry is deposited on a porous fabric which drains much of the liquid by gravity and suction and leaves a wet web of solids on the fabric surface. In a later pressing step, the wet web is typically compressed between fabrics to remove additional liquid. In a still later, drying step more liquid is removed by evaporation, usually by supporting the web by dryer fabrics so that the web is contacted with large diameter, smooth, heated rolls.
Papermaking places considerable demands on the fabrics used in each process step. The fabrics should be structurally strong, flexible, abrasion resistant and able to resist the harsh chemicals and high temperatures to which they can be exposed for extended times.
One major improvement in papermaking fabric technology has been the use of synthetic polymer monofilaments. Use of polymer, however, presents additional design constraints. For example, the polymer must be commercially processable to form monofilament of uniform quality. Furthermore, the polymer must make a monofilament that is sufficiently strong and impact resistant for automated fabric manufacturing techniques, as well as, for running on papermaking machinery at high speed.
Monofilaments have been made from such polymers as polyethylene terephthalate (PET) and polyphenylene sulfide (PPS).
Each has physical properties which affect its suitability for papermaking fabric. PET has good dimensional stability, reasonable resistance to abrasion, is moderately priced but has marginal hydrolytic stability. PPS monofilament has excellent hydrolytic stability but is very expensive, highly crystalline, relatively brittle, and exhibits low knot and loop strengths.
It is desired to provide a low cost, strong, polymeric monofilament for industrial fabrics, which meets the demands of papermaking, including high knot strength and good hydrolytic stability. It is also desired to provide a monofilament which is suitable for use in the automated manufacturing process for such fabrics.
STJMMARY OF THE INVENTION
The present invention provides high knot strength, hydrolysis resistant monofilament for use in papermaker's fabric.
More specifically, there is provided a monofilament of a polymer blend consisting essentially of:
(a) about 1-10 weight percent of a polyester selected from the group consisting of (1) polycarbonate and (2) glycol-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and recurring units of a copolymerized glycol other than cyclohexane-1,4-dimethanol and copolymerized terephthalic acid; and (b) a complementary amount to total 100 weight percent of acid-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized dicarboxylic acid other than terephthalic acid.
There is also provided a papermaker's fabric of yarns including the above-described monofilament.
There is further provided a process for making a papermaker's fabric using the above-described monofilament.
BRIEF DESCRIPTION OF THE DRAWINGS
The Figure is a graph of the percent retained knot strength (A) and the percent coefficient of variation of retained knot _. ~ 119 9 0 ~

strength (B), plotted against the weight percent polycarbonate in a monofilament of one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polymer blend suitable for the monofilament of this invention consists essentially of two polymers. The term "consists essentially of" as used herein means that the blend can include other components; provided that such components do not significantly detract from the function or operability of the invention. The term "monofilament" as used herein means a single fiber structure and is used interchangeably with the term "yarn" .
One polymer of the blend is an acid-modified copolyester, occasionally hereinafter referred to as PCTA. It is a semicrystalline thermoplastic copolymer substantially of two recurring units. One such recurring unit is of copolymerized cyclohexane-1,4-dimethanol (CHDM) and copolymerized terephthalic acid. The other recurring unit is of copolymerized CHDM and a copolymerized dicarboxylic acid other than terephthalic acid.
Thus, recurring units are according to the following formulae ( I ) and (II), respectively:
O O
(I) -0-CHDM'-O-C-AR1-C-O O
(II) -O-CHDM'-O-C-AR2-C-wherein CHDM' is a radical obtained by dehydroxylation of CHDM;
AR1 is a radical of decarboxylated terephthalic acid;
and AR2 is a radical obtained by decarboxylation of a dicarboxylic acid other than terephthalic acid.
PCTA can be prepared either by direct polyesterification of CHDM with an appropriate mixture of dicarboxylic acids, or by transesterification of dialkyl esters of dicarboxylic acids with an effective amount of CHDM followed by polycondensation.

~ 119 9 0 4~

Preferred other dicarboxylic acids include, for example, isophthalic acid and phthalic acid. Thus, PCTA is seen to be a copolyester of poly(cyclohexane-1,4-dimethylene terephthalate) wherein a portion of the terephthaloyl radical is replaced by isophthaloyl or phthaloyl radicals.
The amount of recurring unit (I) is from about 10-99 mole percent, preferably 50-99 mole percent, and more preferably, about 90-97 mole percent of the total of recurring units (I) and (II) .
The second polymer of the blend is~polycarbonate or a glycol-modified copolyester, occasionally hereinafter referred to as PCTG. PCTG is a semicrystalline thermoplastic copolymer substantially of two recurring units. One such recurring unit is of copolymerized CHDM and copolymerized terephthalic acid in accordance with formula (I). The other recurring unit is of a copolymerized glycol other than CHDM and copolymerized terephthalic acid, according to the following formula (III):

(III) -O-R-O-C-ARl-C-wherein R is an organic radical containing 2-20 carbon atoms obtained by dehydroxylation of a linear, branched or cyclic aliphatic bifunctional glycol or ether glycol.
Illustrative examples of bifunctional glycols suitable for use in the glycol-modified copolyester component are ethylene glycol;
1,4-butanediol; 1,5-pentanediol and 1,10-decanediol.
Illustrative examples of ether glycols are diethylene glycol and triethylene glycol. Ethylene glycol is preferred.
PCTA, PCTG and the method for making them are more fully described in U.S. Patent 2,901,466.
Polycarbonate suitable for use in the present invention includes carbonate polymers of dihydric phenols as well as carbonate copolymers of glycols, such as, for example, ethylene glycol or propylene glycol; dibasic acids, such as, for example, isophthalic or terephthalic acid; and hydroxyl or acid-terminated polyesters, such as, for example, the hydroxyl or acid-terminated polyester of neopentyl glycol and adipic acid. Such polycarbonate resins may be prepared by reacting a dihydric phenol with a carbonate precursor such as phosgene, a haloformate or a carbonate ester. Generally the resulting carbonate polymers may be typified as having recurring units of the following formula (IV):
O
( IV) -O-A-O-C-wherein A is a divalent aromatic radical of the dihydric phenol, preferably 4,4'-isopropylidenebisbenzenol, (bisphenol A), employed in the polymer producing reaction. The dihydric phenols which may be employed to provide such aromatic carbonate polymers are mononuclear or polynuclear aromatic compounds, containing as functional groups, two hydroxyl radicals, each of which is attached directly to a carbon atom of an aromatic nucleus.
Typical dihydric phenols are 2,2-bis-(4-hydroxyphenyl)-propane;
1,3-benzenediol; 1,4-benzenediol; 2,2-bis-(4-hydroxyphenyl)-pentane; 2,4'-dihydroxydiphenyl methane; bis-(2-hydroxyphenyl)-methane; bis-(4-hydroxyphenyl)-methane; bis-(4-hydroxy-5-nitrophenyl)-methane;l,l-bis-(4-hydroxyphenyl)-ethane;3,3-bis-(4-hydroxyphenyl)-pentane; 2,6-dihydroxynapthalene; bis-(4-hydroxyphenyl)-sulfone; 2,2'-dihydroxydiphenyl sulfone; 4,4'-dihydroxydiphenyl ether; and 4,4'-dihydroxy-2,5-diethoxydiphenyl ether. It is, of course possible to employ two or more different dihydric phenols or, as stated above, a dihydric phenol in combination with a glycol, a hydroxy or acid-terminated polyester, or a dibasic acid in the event a carbonate copolymer rather than a homopolymer is desired.
The monofilament of the present invention can be prepared using conventional monofilament production equipment. The components of the polymer blend are typically supplied as particles in granular or pellet form. They should have a low moisture content to avoid degradation during subsequent melt - ~l l gg processing. The particles can be melt blended continuously, in equipment such as single screw and twin-screw extruders, or batchwise in BanburyT"" or BrabenderT"" mixers .
It has been found advantageous to make the monofilament in a two-step process. In such a process, a melt-blended masterbatch containing a conveniently high concentration of the minor component in PCTA is prepared. The masterbatch is pelletized and the pellets are later melt blended with additional PCTA to provide monofilament of desired composition. This two-step process provides good uniformity of composition, particularly when the product contains small amounts of the minor component, i.e., 5 weight percent or less.
Monofilament of this invention should be made by blending the melt at lower shear conditions than is conventional in polymer melt blending operations. Reduced shear averts polymer degradation during melt processing. Low shear can be achieved by known methods such as slowing the processor screw speed or using a low compression ratio screw. Normally, this is accompanied by a compensating reduction in production rate to achieve a uniform blend. The minor component should be uniformly dispersed throughout the composition.
Typically the melt is filtered through a screen pack, extruded through a multihole die, quenched to produce strands, drawn and heat-set to form monofilament. The drawing and heat-setting can include multiple cycles at different draw ratios and temperatures and can include one or more relaxation steps.
Monofilament for papermaker's fabric typically has a diameter in the range of about 0.1 to 1.5 mm.
The monofilament of the present invention can be made into industrial fabric by conventional methods. It can be woven on looms in the traditional warp and fill fabric structure or formed into spiral structure in which parallel spiral monofilaments are intermeshed with pintle yarns. The fabric of this invention can be formed exclusively from the novel monofilament or from the novel monofilament in combination with other materials. A
preferred use for the fabric of this invention is in papermaking machines.

~11g90 4 Monofilament from PCTA blends of this invention provides high retained knot strength in combination with good hydrolysis resistance at reasonable cost. PCTA, absent added polymer blend components as herein provided, has hydrolysis resistance superior to PET but only moderate knot strength because it is brittle .
Incorporation of small amounts of polycarbonate or glycol-modified copolyester into PCTA dramatically improves retained knot strength, while maintaining hydrolysis resistance, and without substantially adversely affecting other physical properties. It is now also revealed that the coefficient of variation of retained knot strength of the blended composition yarn is, unexpectedly, significantly less than that of wholly PCTA yarn. Consequently, the yarn of this invention is not only more ductile than PCTA yarn, but it can resist breaking during fabric forming and papermaking operations more consistently, and with better predictability, than PCTA yarn.
The present invention can be more fully understood by reference to the following representative examples of certain preferred embodiments thereof, where all parts, proportions and percentages are by weight unless otherwise indicated.
EXAMPLES
In the following examples, tensile strength and related properties were measured on a tensile testing machine operated with 10 inch/minute jaw separation rate and 10 inch initial jaw separation. Modulus was measured as the slope of the stress/strain curve at 1 percent strain. Free shrink was measured as percent dimensional change after unrestrained exposure to 400°F for 15 minutes. Hydrolysis resistance was measured as percent of initial tensile strength at break retained by the sample after 5 hours of exposure to steam at 325°F.
Examples 1 and 2 and Comparative Example Cl LEXANT"' 141 polycarbonate from General Electric, hereinafter "PC" , and KODART"" "THERMXT"" 13319" PCTA from Eastman Chemicals, hereinafter "Polymer A", pellets were mixed to obtain mixtures of 5 % and 10 % PC in Polymer A. In separate runs, each mixture _8_ was fed to a 1.5 inch single screw extruder equipped with a general purpose screw operating at 24.7 rpm and 552°F to obtain a melt blend. The melt blends were filtered through a 250 mesh (70 ~,m) screen pack and extruded through a multihole die. The extrudate was quenched under water and drawn to a ratio of 3.82:1, to produce a yarn of 0.4 mm diameter. Some volatiles generated during extrusion, perhaps from insufficient drying of the materials, caused the yarn to break frequently during quenching and drawing. Extrusion was steady, however. Polymer A, without PC, was similarly processed to produce comparison yarn C1.
Samples of each yarn were tested for retained knot strength by the following method. Tensile strength at break was determined. Knotted breaking strength was measured as the tensile strength at break after placing an overhand knot in~fresh a test sample. Retained knot strength was calculated as the knotted breaking strength expressed as a percentage of the tensile strength at break. Retained knot strengths of Example 1 samples were about 50 0, which compared favorably to only 10-15 0 observed for yarn C1.
Examples 2-5 and Comparative Example C2 PC and Polymer A were dried at 250°F for 6 hours to less than 0.02 o moisture and tumbled to obtain a 30 o PC mixture.
The mixture was continuously melt blended at 225 pounds per hour in a twin-screw extruder equipped with a vacuum vent port and operated at 15 inches Hg, to obtain 400 pounds of masterbatch.
The screw speed was 312 rpm and the extruder zones 1-6, die and melt temperatures were 510, 520, 500, 490, 490, 490, 515 and 495°F, respectively. The melt blend was extruded as strand, quenched and cut to pellets. The masterbatch pellets were crystallized in pans at 350°F for 2.5 hours.
Masterbatch pellets were dried at 250°F for 5 hours then fed to an extruder with polymer A to obtain 0 , 3 . 2 , 4 . 5 , 7 . 3 and 10 . 0 o PC compositions, Examples C2 and 2-5, respectively. The compositions were extruded at 24.8 rpm screw speed in a 3.5 inch single screw extruder operated at exit melt temperature in the ~'~ 1890 4 range of 560-570°F. The compositions were extruded through a multihole spinneret with 2.0 mm diameter and 4.0 mm capillary length holes. The extrudate was quenched in water and dried.
It was then drawn and relaxed in a succession of stages to a ratio of 3.45:1 to provide 0.5 mm diameter monofilaments.
Extrusion and spinning of the low PC concentration yarns went smoothly. At 10 o PC, polymer began to build up on the die and to drip into the yarn. Physical properties of the yarns are shown in Table 1.

Table 1 Example C2 2 3 4 5 PC, 0 0 3.2 4.5 7.3 10 denier 2251 2200 2212 2222 2249 elongation at 1.75 grams 11.1 12.6 13.9 18.1 22.6 per denier, breaking energy, kg-mm 243.9 254.4 275.5 307 321.6 tenacity, grams/denier 2.89 2.81 2.75 2.52 2.33 breaking elongation, a 23.7 25.9 28.3 33.4 37.2 modulus, grams/denier 37.9 37.8 36.9 34.4 32.4 elongation at 1 pound, 0 0.55 0.54 0.54 0.58 0.61 free shrink, 0 4.7 6.1 6.1 5.8 5.9 retained knot strength, 0 40.4 69.7 65.5 74.2 73.3 retained knot strength 37.2 14.2 14.4 9.5 3.1 variability, %COV*

coefficient of variation ~. ~ ~11g90 4 Above 4.5 % PC, tenacity and modulus decrease. However, as the concentration of PC increases, toughness which is indicated by breaking energy and retained knot strength, increases.
Retained knot strength of Examples 2-5 were substantially higher than those of C2. Above 4.5 o PC, retained knot strength remains levels at about 70 %. The coefficient of variation of retained knot strength, calculated by dividing the standard deviation of replicates by the average, drops as PC concentration increases. The smaller coefficients of variation show that retained knot strength of the yarn from blends was less variable than PCTA yarn and that consistency of retained knot strength improves with increasing PC content. Knot strength improvement data from Table 1 is shown graphically in the Figure. The ordinate is percent property value and the abscissa is percent PC in the yarn. Line A represents retained knot strength and Line B represents coefficient of variation.
Examples 6 and 7 A masterbatch of 30 % KODART"" 5445 PCTG from Eastman Chemicals, hereinafter "Polymer G" and 70% Polymer A was prepared as in Examples 2-5. Extruder zones 1-6, die and melt temperatures were 500, 510, 490, 480, 480, 480, 510 and 490°F, respectively. Screw speed was 325 rpm and production rate was 220 pounds per hour.
The masterbatch was processed as in Examples 2-5 except that extruder exit melt temperature was in the range of 545-555°F arid the compositions were 3 and 6o PCTG, Examples 6 and 7, respectively. Analytical results are presented in Table 2.

Table 2 Example 6 7 8 C3 PCTG, % 3 6 3 0 draw ratio 3.8:1 3.8:1 4.2:1 4.2:1 denier 2224 2224 2220 2214 elongation at 1.75 11.6 11.9 8.4 8.1 grams per denier, %

breaking energy, kg-mm 261.7 265.9 219 206.8 tenacity, grams/denier 2.88 2.84 3.23 3.24 breaking elongation, 0 25.4 25.9 19.9 19.0 modulus, grams/denier 38.1 39.3 43.8 44.0 elongation at 1 pound, 0 0.53 0.52 0.48 0.47 free shrink, 0 4.1 3.7 6.1 6.5 retained knot strength, 64.6 59.8 58.9 27.7 %

knot strength 18.0 17.5 6.8 51.5 variability, oCOV*

coefficient of variation 211 g9 0 4 Relative to Comparative Example C2 (Table 1) retained knot strength increased from 40.4 o to about 60 %, representing a 50 improvement. Furthermore, the coefficient of variation of retained knot strength dropped dramatically, indicating that knot strength of the yarn from blends was much more consistent than yarn of PCTA alone. Other yarn properties were not significantly affected by incorporation of PCTG.
Example 8 and Comparative Example C3 The procedures of Examples 6 and C2 were repeated except that the first stage draw ratio was increased from 3.8:1 to 4.2:1. Yarn samples were analyzed and the results are shown in Table 2. Tenacity improvement from about 2.9 of Examples 6 and C2, to about 3.2 grams/denier was observed in both Examples 8 and C3. However, retained knot strength of C3 dropped to 27.7 % and coefficient of variation increased to 51.5 0. Surprisingly, the retained knot strength of Example 8 remained high at 58.9 % and variability improved to 6.8 %, despite the fact that tenacity was increased by raising the draw ratio relative to Example 6.
Examples 9-10 and Comparative Example C4 A masterbatch of 30o Polymer G and 70o Polymer A was prepared as in Example 6. The masterbatch and a separate stream of Polymer A pellets were metered to a yarn extrusion line in proportions to produce yarns of 3.0, 1.5 and 0 o Polymer G.
Samples of the 0.6 mm diameter yarns were tested and the results are shown in Table 3.

Table 3 Example C4 9 10 Polymer G, % 0 3.0 1.5 denier 3136 3071 3050 elongation at 1.75 grams 10.4 10.8 11.0 per denier, o tenacity, grams per denier 2.6 2.67 2.53 breaking energy, kg-mm 308.4 349.5 297.8 breaking elongation, % 22.3 24.9 22.7 modulus, grams per denier 39.4 39.6 40.3 free shrink, % 5.0 4.4 5.3 hydrolysis resistance, 0 95.3 95.3 98.4 retained knot strength, % 52.5 64.6 72.2 knot strength, lbs 9.47 11.4 12.3 Table 3 data confirm that only low concentrations of PCTG
in PCTA were needed to improve retained knot strength and did not adversely affect other properties. Although the unknotted tensile strength (17 pounds) of the yarn of Example 10 dropped relative to C4 (18 pounds), knot strength of the monofilament with only 1.5 % PCTG was much higher than of C4. The hydrolysis resistance of the yarns from blends remained excellent at greater than 95%. A comparable sample of PET yarn was not tested, however, its hydrolysis resistance is expected to be only about SOo.

Claims (11)

1. A monofilament of a polymer blend consisting essentially of:
(a) about 1 to about 10 weight percent of a polyester selected from the group consisting of (1) polycarbonate having recurring units that include a divalent aromatic radical, and (2) glycol-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid and recurring units of copolymerized glycol having no more than 20 carbon atoms, selected from the group consisting of linear, branched and cyclic aliphatic glycols and ether glycols, and copolymerized terephthalic acid; and (b) a complementary amount to total 100 weight percent of acid-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized dicarboxylic acid other than terephthalic acid.

2. A monofilament according to claim 1, wherein said polyester is a glycol-modified copolyester comprising about 50 to about 95 mole % of recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and a complementary amount to total 100 mole % of recurring units of a copolymerized bifunctional glycol having 2-20 carbon atoms, selected from the group consisting of linear, branched and cyclic aliphatic glycols and ether glycols;
and copolymerized terephthalic acid; and wherein said acid-modified copolyester comprises:
about 50 to about 95 mole % recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and a complementary amount to total 100 mole % of recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized isophthalic acid.

3. A monofilament according to claim 2, wherein said bifunctional glycol is ethylene glycol.

4. A monofilament according to claim 3, wherein the glycol-modified copolyester is present at about 1 to about 6 weight percent.

5. A monofilament according to claim 3, wherein the glycol-modified copolyester is present at about 1.5 to about 3 weight percent.

6. A monofilament according to claim 1, wherein said polyester is polycarbonate having recurring units of the following formula:
wherein A is a divalent aromatic radical of bisphenol A; and wherein said acid-modified copolyester comprises:
about 50 to about 95 mole % recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and a complementary amount to total 100 mole % of recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized isophthalic acid.

7. A monofilament according to claim 6, wherein the polycarbonate is present at about 1 to about 5 weight percent.

8. A papermaker's fabric comprising monofilaments of a polymer blend consisting essentially of:
(a) about 1 to about 10 weight percent of a polyester selected from the group consisting of (1) polycarbonate having recurring units that include a divalent aromatic radical, and (2) glycol-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and recurring units of copolymerized glycol having no more than 20 carbon atoms, selected from the group consisting of linear, branched and cyclic aliphatic glycols and ether glycols; and copolymerized terephthalic acid; and (b) a complementary amount to total 100 weight percent of acid-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized dicarboxylic acid other than terephthalic acid.

9. A papermaker's fabric according to claim 8, wherein (a) is present from about 1 to about 6 weight percent and is a glycol-modified copolyester comprising:
about 50 to about 95 mole % of recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and a complementary amount to total 100 mole % of recurring units of copolymerized ethylene glycol and copolymerized terephthalic acid; and wherein said acid-modified copolyester comprises:
about 50 to about 95 mole % recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and a complementary amount to total 100 mole % of recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized isophthalic acid.

10. A papermaker's fabric according to claim 8, wherein (a) is present from about 1 to about 5 weight percent and is polycarbonate having recurring units of the following formula:
wherein A is a divalent aromatic radical of bisphenol A; and wherein said acid-modified copolyester comprises about 50 to about 95 mole % recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and a complementary amount to total 100 mole % of recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized isophthalic acid.

11. A method for making papermaker's fabric comprising forming said fabric from yarns including monofilament of a polymer blend consisting essentially of:
(a) about 1 to about 10 weight percent of a polyester selected from the group consisting of (1) polycarbonate having recurring units that include a divalent aromatic radical, and (2) glycol-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and recurring units of copolymerized glycol having no more than 20 carbon atoms, selected from the group consisting of linear, branched and cyclic aliphatic glycols and ether glycols; and copolymerized terephthalic acid; and (b) a complementary amount to total 100 weight percent of acid-modified copolyester comprising recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized terephthalic acid, and recurring units of copolymerized cyclohexane-1,4-dimethanol and copolymerized dicarboxylic acid other than terephthalic acid.