Abstract:
The present invention is directed to a monofilament made from a blend of a polyester having a polyhydric alcohol of 1,4-cyclohexane-dimethanol, and a polyamide. This blend is useful as an article of paper making machine clothing used in forming, pressing, or drying sections of a paper making machine when the blend is in the form of a fiber structure. The blends usefulness stems from its dry-heat strength and hydrolysis resistance.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a monofilament made from a blend of a polyester having a polyhydric alcohol component of 1,4-cyclohexanedimethanol, and a polyamide. This invention is particularly useful as an article of paper making machine clothing used in the forming, pressing, or drying sections of a paper making machine when the blend is in the form of a fiber structure. 
     BACKGROUND OF THE INVENTION 
     Paper is composed of cellulosic fibers that are formed into a sheet. The majority of paper making machine consists of three main sections: the forming section, the pressing section, and the drying section. 
     In the forming section, the cellulosic pulp slurry or furnish is injected onto a forming fabric which is a long, woven mesh belt. As the forming fabric moves along through the forming section, some of the water in the slurry drains through the fabric and a paper web is formed. As this paper web leaves the forming section, it is composed of about 80% water and about 20% solids. 
     For many years, forming fabrics were woven from metal wires and had a life of about one week on a paper machine. This short life was due to metal fatigue and abrasion caused by contacting the machine parts in the forming section. 
     In the 1960&#39;s, experiments were begun to replace the metal fabrics with woven, synthetic, monofilament yarn fabrics. Today, polyester monofilament is the yarn of choice for this application and typical fabric life is about 60-120 days. 
     After leaving the forming section, the paper web moves into the pressing section where a high compressive force is exerted by a pair of press rolls to remove more water from the paper web. The press fabric serves as cushioning and water removing media between the press rolls. As the paper leaves the pressing section, the paper web contains about 60% water and 40% solids. 
     Traditionally, press fabrics were made of 100% wool due to its resilience and water absorbency. However, synthetics have been developed with good resilience that have longer life than woolen felts. Fabrics of choice today consist of a base fabric, woven from polyamide monofilaments into which polyamide fibers have been needlepunched to form a felt. Typically life of press felts is 30-60 days. 
     The drying section consists of large, steam-heated cylinders that dry the paper web to a level of about 6% moisture. 
     A dryer felt or fabric is needed to hold the paper in contact with the dryer cylinders. Originally, these fabrics were made from cotton, but as paper making developed, higher speed and temperature shortened the life of the cotton dryer felts. 
     Many different fibers and yarns have been used to develop better-performing dryer felts so as to improve the efficiency of the paper making process. Presently, the predominant yarn used in the manufacture of dryer fabrics is polyester monofilament. See, Luciano, B., Albany International Fabric Facts, Volume 38, No. 4-6. Dryer fabrics made from polyester monofilament operating at normal temperatures (300° to 350° F.) last about one year. 
     In order to improve profitability, paper makers desire to increase speeds of the paper making machines. To sufficiently dry the paper at increased throughput, additional heat is used in the dryer section and perhaps in other sections of the paper machine as well. 
     Elevated temperatures tend to adversely affect the hydrolysis resistance of polyester yarns. For this reason manufacturers of dryer fabrics have looked at other fibers and yarns in an effort to increase fabric life at higher temperatures. 
     Moreover, if a fabric has to be replaced at other than scheduled maintenance cycles due to failure or damage, the downtime cost to the paper maker can be significant. For this reason, it is desirable to manufacture dryer fabrics that will run with longer and more predictable times under increased heat and speed conditions. 
     As we move into the next century, an ever increasing emphasis is being put on using recycled paper in the making of new paper. Federal and state laws are being passed which require a certain amount of recycled paper to be used in each pound of paper manufactured. For the environmentalist this is a good law, however, for the paper makers this law poses new challenges because the recycled paper has a high level of contaminants. Contaminants include wood pulp residues, inorganic residues (such as clays and titanium dioxide), adhesives from mailing labels, stickers from hot-melt adhesives, non-paper films, and printing inks. These contaminants may either stick to the paper making fabrics or be carried on through the paper machine in the paper sheet. If these contaminants cannot be easily removed, the fabrics will become plugged and the quality of the paper will decrease to the point that the fabric must be replaced. Due to the ease of cleaning, fabrics made from 100% monofilaments are desired. See: Luciano, B., Ibid. 
     One solution is to use polyphenylene sulfide (PPS) monofilaments in the manufacture of dryer felts. PPS has very good hydrolysis resistance, but unfortunately, the polymer is difficult to extrude into monofilaments and is quite expensive. Also, PPS monofilaments are very brittle which can cause problems on the paper machine. An example of a PPS monofilament is found in U.S. Pat. No. 5,162,151, which is incorporated herein by reference. 
     Another fiber solution to the harsh environment of the paper making process is the use of poly(2-methyl-1,5-pentylene) terephthalamide. See U.S. Pat. No. 5,162,152, which is incorporated herein by reference. Yet another fiber solution is the use of a copolymer of terephthalic acid, isophthalic acid, and 1,4-dimethylocyclohexane (also referred to as 1,4-cyclohexanedimethanol). See: U.S. Pat. No. 5,169,499, which is incorporated herein by reference. 
     Accordingly, there is a need in the paper making industry to develop new fibers for use in paper making clothing. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a monofilament made from a blend of a polyester having a polyhydric alcohol of 1,4-cyclohexane-dimethanol, and a polyamide. This blend is useful as an article of paper making machine clothing used in forming, pressing, or drying sections of a paper making machine when the blend is in the form of a fiber structure. The blends usefulness stems from its dry-heat strength and hydrolysis resistance. 
     DESCRIPTION OF THE INVENTION 
     The inventive blends disclosed herein include a polyester having a polyhydric alcohol component of 1,4-cyclohexane-dimenthanol, and a polyamide. The blend may include about 70 to about 95 percent by weight of the polyester and about 5 to about 20 percent by weight of the polyamide. The blend preferably includes about 85 to about 95 percent by weight of the polyester and about 5 to about 10 percent by weight of polyamide. Additionally, the blend may include a hydrolysis stabilizing agent. The hydrolysis stabilizing agent may comprise about 0.5 to about 5 percent by weight of the blend, preferrably it comprises about 1.0 percent by weight of the blend. The blend may also include a thermo-oxidative stabilizing agent. The thermo-oxidative stabilizing agent may comprise about 0.05 to about 10 percent by weight of the blend, preferrably it comprises about 5 percent by weight of the blend. 
     The term &#34;monofilament&#34;, as used herein, is directed to any single filament of a manufactured fiber usually of a denier higher than 14. The term &#34;shaped article&#34;, as used herein, is directed to articles which are made by extrusion or molding techniques, including, but not limited to, fibers, films, injection molded articles, and blow molded articles. 
     The term &#34;polyester having polyhydric alcohol component of 1,4-cyclohexanedimethanol&#34;, as used herein, is directed to, but not limited by the polyester material disclosed and claimed in U.S. Pat. No. 2,901,466, which is incorporated herein by reference. The polyfunctional acid component may be selected from, but is not limited to, the group of: isophthalic acid; terephthalic acid; derivatives of isophthalic acid; derivatives of terephthalic acid; and combinations thereof. These polyester may be referred to as polycyclohexlandymethanol terephthalate (PCT)-a polyester from the condensation reaction of cyclohexanedimethanol (CHDM) and terephthalatic acid or its derivatives, or PCTA--the condensation product of CHDM, terephthate acid and isothalic acid. Each of the foregoing products are commercially available from the Eastman Chemical Co., of Kingsport, Tenn. under the tradename Eastman 3879 (the PCT product) and &#34;KODAR&#34; THERMX Copolyester Type 13319 (the PCTA product). The PCTA material is preferred. The fiber processability of these materials may be improved by the addition of a minor portion of polyethylene terephthalate. See: British Patent Specification No. 1,040,470 incorporated herein by reference. 
     The term &#34;polyamide&#34;, as used herein, is directed to any of the known polyamide polymers. The polyamide appears to improve the dry-heat strength and hydrolysis resistance of the yarns made from the blend. Exemplary polyamides include, but are not limited to: nylon 6; nylon 6,10; nylon 6,12; nylon 11; nylon 12; nylon 4,6; nylon 6,T; nylon 6,6; and combinations thereof. Nylon 6,6 is preferred. The foregoing nylon materials are commercially available from the Engineering Plastic Division of the Hoechst Celanese Corporation, Summit, N.J. 
     The term &#34;hydrolysis stabilizing agent&#34;, is used herein, refers to an &#34;endcapping agent&#34;. Endcapping agents are used to prevent degregation of the polyester polymer. This particular form of degradation results from hydrolysis. Exemplary hydrolysis stabilizing agents include the class of chemicals known as carbodiimides. A preferred carbodiimide is known chemically as 2,6-diisopropylphenyl carbodiimide. Such carbodiimides are commercially available under the tradename &#34;STABAXOL&#34; from the Rhein Chemie GmbH of Rheinau, Federal Republic of Germany. &#34;STABAXOL I&#34; is preferred. These materials are also sold, by Rhein Chemie, in a polymeric form &#34;STABAXOL P&#34; and &#34;STABAXOL P-100&#34;. 
     The term &#34;thermo-oxidative stabilizing agent&#34;, as used herein, refers to a material added to prevent degredation of the polyester when subjected to hot dry heat. The preferred material is sold under the commercial name of &#34;KODAR&#34; THERMX 13319 L0001 from the Eastman Chemical Co. of Kingsport, Tenn. 
    
    
     Other details and aspects of the invention are more fully described in the examples set forth hereinafter. Weights are given as weight percent unless otherwise noted. 
     EXAMPLES 
     In the following examples, the manufacture of the present invention is illustrated, and a physical property and performance comparison of the present invention to other materials is made. The components and weight percentages of the tested blends are identified in TABLE 1. 
     The polyester resins are dried to remove moisture. The moisture content of the dried resins should be less than 0.007%. The resins are then transferred into an oxygen free hold vessel located above a three heated zone, single screw extruder. The resins are gravity fed into the extruder. Other components of the blend are added by including the polyamide resins, of the blend are added by metering devices when the resins are gravity fed into the extruder. While in the extruder, all components of the blend are melted and intimately mixed. The set temperatures for each zone are given in TABLE 2. The blend is then melt spun through a spin die or spinnerette to produce monofilaments having a diameter of 0.50 mm. The spin die temperature and blend temperature at extrusion are given in TABLE 2. After leaving the spin die, the monofilaments are quenched in a water bath located beneath the spin die. After quenching, the monofilaments are drawn and heat set. The heat setting occurs in an oven located in the third draw zone. The draw ratios and heat set oven temperatures are given in TABLE 2. 
     The physical properties of the foregoing monofilaments are given in TABLE 3. &#34;Denier&#34; was calculated by weighing one meter lengths of the monofilament. &#34;Hot air shrinkage&#34; was calculated by placing a sample (one meter in length, coiled into a loop of about 10-11 cm in diameter) into a forced hot air oven set at 200° C. for 15 minutes, then removing the sample from the oven, letting the sample cool and finally measuring the length of the sample. &#34;Relative elongation at one gram per denier&#34; (Rel. Elong. @ 1G/D); &#34;elongation at break&#34; (Elong @ Break); and &#34;tenacity&#34; are measured using an Instron Tensile Tester Model #4201 set with a 500 mm gauge length, a cross head speed of 500 mm/minute, and using flat faced clamps (the monofilament running over the top of the top clamp to below the bottom of the bottom clamp). &#34;Loop strength&#34; and &#34;knot strength&#34; are measured using the Instron setup noted above, the exceptions being: for &#34;loop&#34;--two monofilaments are joined by intersecting loops; and for &#34;knot&#34;--the monofilament is tied with an overhand knot. &#34;Abrasion cycles to failure&#34; was measured by utilizing a squirrel cage apparatus to abrade weighted monofilament samples. The squirrel cage (diameter 83/8 inches; with fifteen 0.2024 inch Precision Brand Product Ind. T302 stainless steel spring tempered wire equally spaced about the periphery of the cage). The squirrel cage is rotated at 60 revolutions per minute. The monofilaments are draped over the squirrel cage from a bar located above top dead center of the cage and weighted with either 50 grams (monofilament diameter less than 0.50 mm) or 100 gram (monofilament diameter 0.50 mm or more). The results are reported as the number of cycles lapsed at the moment of monofilament breakage. 
     In TABLE 4, &#34;hydrolysis resistance&#34; of the examples is set forth. The hydrolysis resistance is measured as the percent strength retention as a function of days in a hydrolysis pot. Samples (about one meter in length) are coiled into 3 inch diameter loops. Samples are needed for the initial and each sample day. Samples are placed on a rack inside a consolidated sterilizer autoclave. The autoclave is set to 15 psi and 250° F. (121° C.) for continuous operation with a 60 minute exhaust time (cool down cycle). On days when samples are to be tested, the autoclave is cooled down and samples are removed and allowed to cool and equilibrate for one day prior to Instron testing. Samples for future test days are reheated in the autoclave as discussed above. Measurement of the &#34;load to break&#34; on samples is performed on an Instron Tensile Tester Model #4201, gauge length-500 mm, cross head speed-500 mm/min, and using flat, leather faced clamps. The percent strength retention is calculated against the initial load to break. 
     In TABLE 5, &#34;dry heat strength&#34; of the examples is set forth. The dry heat strength is measured as the percent strength retention as a function of days in a forced air circulation oven. Samples (about one meter in length) are coiled into 3 inch diameter loops. Samples are needed for the initial and each sample day. Samples are hung from a steel sample holder located eight inches from the top of the inside of the chamber of the forced air circulation oven. The oven is set at a temperature of 175° C. for continuous operation. Samples are removed on test days and allowed to cool. Measurement of the &#34;load to break&#34; on samples is performed on an Instron Tensile Tester Model #4201, gauge length-500 mm, cross head speed 500 mm/min, and using flat, leather faced clamps. The percent strength retention is calculated against the initial load to break. 
     
                       TABLE 1______________________________________SAMPLE     A      B     C    D   E   F    G   H   I______________________________________% polyester      100    90    99   95  94  89   84  79  74(CHDM).sup.1% polyamide.sup.2      --     10    --   --  --   5   10  15  20% hydrolysis      --     --    .9   --  .9  .9   .9  .9  .9stabilizer.sup.3% thermo-oxidative      --     --    --    5   5   5    5   5   5stabilizer.sup.4______________________________________ Notes: .sup.1 Polyester (CHDM)  &#34;KODAR&#34; THERMX copolyester type 13319 by Eastman Chemical Co., Kingsport, TN. .sup.2 Polyamide  nylon 6,6 by Engineering Plastics Division, Hoechst Celanese Corporation, Summit, NJ. .sup.3 Hydrolysis stabilizer  Stabaxol ® 1 by Rhein Chemie GmbH, Rheinau, Federal Republic of Germany. .sup.4 Thermooxidative stabilizer  &#34;PCTA 13319 L0001&#34; by Eastman Chemical Co., Kingsport TN. 
    
     
                                           TABLE 2__________________________________________________________________________SAMPLE            A  B  C  D  E  F  G  H  I__________________________________________________________________________Extruder Temp (° C.):ZONE 1            306                308                   303                      305                         304                            304                               300                                  305                                     305ZONE 2            306                305                   304                      304                         304                            305                               305                                  304                                     304ZONE 3            300                302                   302                      302                         302                            302                               302                                  302                                     302SPIN DIE TEMP (° C.)             300                299                   300                      300                         300                            300                               300                                  300                                     300BLEND TEMP (° C.) AT EXTRUSION             312                311                   309                      310                         308                            309                               310                                  310                                     311HEAT SET OVEN TEMP (° C.)             200                200                   200                      200                         200                            200                               200                                  200                                     200DRAW RATIO:ZONE 1            3.33                3.33                   3.33                      3.33                         3.33                            3.33                               3.33                                  3.33                                     3.33ZONE 2            1.02                1.02                   1.02                      1.02                         1.02                            1.02                               1.02                                  1.02                                     1.02ZONE 3            0.98                0.98                   0.98                      0.98                         0.98                            0.98                               0.98                                  0.98                                     0.98TOTAL             3.33                3.33                   3.33                      3.33                         3.33                            3.33                               3.33                                  3.33                                     3.33__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________SAMPLE      A  B  C  D  E  F  G  H  I  CONTROL.sup.1__________________________________________________________________________DENIER      2233          2140             2143                2159                   2150                      2145                         2139                            2133                               2117                                  2421HOT AIR SHRINKAGE @       8.9          9.1             8.9                9.0                   8.0                      8.9                         9.1                            9.5                               9.7                                  5.9200° C. (%)REL. ELONG  4.1          4.2             4.2                4.4                   4.3                      4.3                         4.2                            3.9                               3.8                                  1.7@ 1 G/D - (%)ELONG @ BREAK - (%)        26           25              27                 25                    26                       27                          28                             24                                25                                   36TENACITY (G/D)       2.66          2.73             2.73                2.63                   2.65                      2.71                         2.71                            2.73                               2.84                                  4.14LOOP STRENGTH (G/D)       1.60          1.38             1.97                1.41                   1.50                      2.69                         2.07                            1.53                               1.53                                  6.22KNOT STRENGTH (G/D)       1.90          1.63             1.89                1.57                   1.91                      1.71                         1.65                            1.63                               1.72                                  3.39ABRASION CYCLES       1438          2684             1461                1484                   1311                      1370                         1525                            2257                               2725                                  2518TO FAILURE__________________________________________________________________________ Note: .sup.1 Control  PET monofilament, TREVIRA ® MONOFIL 9 EA from Hoechst Celanese Corporation of Spartanburg, SC. 
    
     
                                           TABLE 4__________________________________________________________________________                                         CONTROLSAMPLE.sup.1 A    B    C    D    E    F    G  H   I  (PET).sup.2__________________________________________________________________________DAY: 4    95.7 96.3 99.0 94.7 98.6 98.1 99.1                                  99.1                                      97.6                                         93.7 7    91.8 92.8 98.9 91.6 97.3 96.6 99.6                                  98.6                                      97.0                                         87.810    84.9 86.5 98.2 85.2 94.8 95.2 99.0                                  98.0                                      96.9                                         61.012    76.4 81.8 96.8 55.6 93.0 94.7 99.2                                  100.5                                      96.6                                          7.914    60.8 75.0 95.6 19.4 91.3 95.6 99.0                                  98.8                                      96.6                                         FAILED17    FAILED      25.4 90.9 FAILED                     81.9 88.1 95.8                                  98.3                                      94.719         FAILED           86.9      77.7 87.3 96.4                                  95.6                                      94.821              82.7      56.1 84.0 89.5                                  88.6                                      88.524              56.2       8.7 73.8 84.9                                  83.0                                      85.325              62.4      FAILED                          76.9 85.4                                  83.5                                      67.626              35.2           66.9 78.5                                  81.2                                      76.827              33.2           51.7 78.4                                  79.0                                      75.128              18.2           46.6 79.5                                  81.0                                      76.429              FAILED         32.7 69.0                                  76.8                                      76.230                             32.7 75.8                                  76.9                                      71.931                             12.6 72.4                                  71.3                                      69.632                             27.0 47.6                                  58.8                                      63.433                              9.5 38.4                                  64.8                                      53.934                             FAILED                               32.7                                  47.3                                      63.935                                  30.0                                  62.9                                      46.836                                  27.1                                  57.3                                      60.4__________________________________________________________________________ Note: .sup.1 All tested monofilaments have a diameter of 0.50 mm. .sup.2 Control  PET monofilament, TREVIRA ® MONOFIL 9 EA from Hoechst Celanese Corporation of Spartanburg, SC. 
    
     
                                           TABLE 5__________________________________________________________________________                                  CONTROLSample.sup.1    A    B  C    D    E    F  G  H  I  (PET).sup.2__________________________________________________________________________DAY: 4  82.8 98.9       92.3 96.8 97.9 96.6                         99.3                            97.4                               96.0                                  93.3 7  71.5 95.1       84.7 94.2 94.0 92.8                         96.8                            94.3                               92.7                                  87.910  55.4 86.4       78.4 88.2 88.6 89.1                         90.1                            88.1                               86.3                                  82.112  37.3 82.2       70.8 81.4 82.1 84.4                         86.0                            81.0                               79.3                                  79.114  23.1 78.1       62.6 69.2 70.9 79.9                         83.7                            80.0                               75.7                                  75.917  12.7 72.8       37.5 60.5 50.0 75.7                         81.6                            76.5                               75.6                                  74.319  FAILED    63.8       31.1 49.7 48.7 72.3                         75.4                            73.6                               71.9                                  71.321       59.7       29.5 30.1 30.3 64.1                         66.5                            66.3                               64.3                                  69.924       60.6       20.3  6.1  6.2 38.6                         52.3                            51.7                               52.0                                  63.925       49.3       12.0 16.6  7.9 47.9                         54.4                            55.6                               56.8                                  67.726       55.7        8.1 FAILED                  6.2 30.6                         43.1                            52.7                               49.4                                  66.527       57.0       FAILED    FAILED                      25.0                         50.9                            52.7                               46.1                                  60.628       30.7              28.7                         42.8                            43.2                               46.7                                  64.029       39.2              25.0                         44.3                            45.6                               52.7                                  62.930       40.9               8.1                         28.9                            30.0                               39.1                                  58.3__________________________________________________________________________ Note: .sup.1 All tested monofilaments have a diameter of 0.50 mm. .sup.2 Control  PET monofilament, TREVIRA ® MONOFIL 9 EA from Hoechst Celanese Corporation of Spartanburg, SC. 
    
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.