Abstract:
This invention is a bicomponent meltblown microfiber nonwoven material wherein at least two different polymers have been extruded and spun together in either a side by side or core/sheath configuration and wherein at least one of the polymers is polytrimethylene terephthalate (PTT) and at least one of the polymers is one of but not limited to the following thermoplastics: polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), and polylactide (PLA). The ratio of PTT to the other component ranges from 1:99 to 99:1, based on the weight of the polymers. The preferred weight ratio range of PTT:PP is 25:75 to 75:25 and the most preferred range is 25:75 to 50:50. The present invention also provides a process for making such a bicomponent fiber. The present invention also provides a process for making such a meltblown microfiber nonwoven material.

Description:
CROSS REFERENCE TO PRIOR APPLICATION  
       [0001]    This application claims priority to provisional application No. 60/246,139, filed Nov. 6, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to meltblown microfiber nonwoven materials made from polytrimethylene terephthalate. More particularly, the invention relates to bicomponent nonwoven materials wherein polypropylene and polytrimethylene terephthalate are extruded, spun together, and then meltblown.  
         BACKGROUND OF THE INVENTION  
         [0003]    Thermoplastic resins have been extruded to form fibers and webs for a number of years. The most common thermoplastics for this application are polyolefins and polyesters. Other materials such as polyetheresters, polyamides and polyurethanes are also used for this purpose. Each material has its characteristic advantages and disadvantages vis-a-vis the properties desired in the final product to be made from such fibers. The term “bicomponent” usually refers to fibers which have been formed at least two polymers extruded from separate extruders but spun together to form one fiber. The configuration of such a bicomponent fiber may be a sheath/core arrangement wherein one polymer is surrounded by another or may be a side by side arrangement. It was often desirable that the fabics have the combination of the advantages of different polymers in one spun fiber. In nonwovens industries, the bicomponent (bico) fibers have been developed in the recent years for the meltblown and spunbond processes.  
         SUMMARY OF THE INVENTION  
         [0004]    This invention is a bicomponent meltblown microfiber nonwoven material wherein at least two different polymers have been extruded and spun together in either a side by side or core/sheath configuration and wherein at least one of the polymers is polytrimethylene terephthalate (PTT). The ratio of PTT to the other polymer(s) ranges from 1:99 to 99:1, based on the weight of the polymers. The preferred weight ratio range of PTT to other polymer(s) is 25:75 to 75:25 and the most preferred ratio is 25:75 to 50:50.  
           [0005]    The other polymer(s) in PTT based meltblown nonwoven may be one of the following thermoplastics: polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), and polylactide (PLA).  
           [0006]    The present invention also provides a process for making such a bicomponent fiber. The present invention also provides a process for making such a meltblown microfiber nonwoven material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 shows the dynamic relationship of properties to processing conditions of PTT webs.  
         [0008]    [0008]FIG. 2 shows the fiber diameter and hydrohead for bicomponent meltblown webs wherein the melt throughput was 0.6 grams per whole per minute.  
         [0009]    [0009]FIG. 3 shows the heat shrinkage of PTT mono and PTT/PP bicomponent meltblown webs at 90° C., 110° C., and 130° C. for seven minutes.  
         [0010]    [0010]FIG. 4 shows a comparison of the heat shrinkage for PTT and PET mono meltblown webs at 90° C., 110° C., and 130° C. for seven minutes.  
         [0011]    [0011]FIG. 5 shows a comparison of the heat shrinkage for PTT and PET bicomponent meltblown webs at 90° C. for seven minutes. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Meltblowing is a one-step process to make microfiber nonwovens directly from thermoplastic polymers with the aid of high velocity of air to attenuate the melt filaments. It has become an important industrial technique in nonwovens because of its ability to produce fabrics of microfiber structure suitable for filtration media, thermal insulators, battery separators, oil absorbents and many laminate applications. Polypropylene (PP) is the most widely used polymer for this process. Others such as polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA) can be also used to produce the meltblown webs. A lot of efforts have been made in the last 30 years on the process study, new resin and product development, and process improvement.  
         [0013]    Polytrimethylene terephthalate (PTT) is primarily a linear aromatic polyester which can be prepared from the condensation polymerization of 1,3-propane diol and terephthalic acid. For commercial applications, it is desirable to produce PTT having an intrinsic viscosity greater than 0.7 dl/g and preferably greater than 0.8 dl/g. PTT itself is described more specifically and processes for making it also in U.S. Pat. No. 6,277,947, which is herein incorporated by reference.  
         [0014]    PTT, a member of the polyester family, is based upon a three-carbon diol. Its structure is shown below along with those of PET and PBT which are based on two-carbon and four-carbon diols, respectively.  
                         
 
         [0015]    PTT combines the physical properties of PET (strength, toughness, stiffness, heat resistance) with the processing advantages of PBT (low melt and processing temperatures, rapid crystallization, faster production cycles). PTT is less rigid than PET, exhibiting greater elasticity. Other desirable properties of PTT are resilience, softness, elastic recovery, moisture resistance, chemical resistance, dimensional stability, stain resistance, weather/UV resistance and ease of dying or painting into many different colors. PTT does very well in the carpet industry, textiles, films and other thermoplastic applications.  
         [0016]    Many polymers can be used in this invention but polypropylene is preferred. The polypropylene which can be used in the present invention is commercially available crystalline isotactic polypropylene. These products are well known and have been the subject of many patents, including U.S. Pat. Nos. 3,112,300 and 3,112,301, which are herein incorporated by reference. Isotactic polypropylene is a straight chain of propylene units wherein the methyl groups are all aligned on one side of the polymer chain.  
       EXAMPLES  
       [0017]    The Reicofil® side-by-side bicomponent meltblown line at the University of Tennessee&#39;s Textile and Nonwoven Development Center (TANDEC) was used for the process and product development of different polymers. In this research, we focused on the production of the PTT based (both mono and bico) meltblown webs and their attributes for possible applications. Trial Design and Web Preparation Since meltblowing is a highly complex and multi-variable process where knowledge of the mechanistic model is lacking, surface response methodology (SRM) was applied in this research to develop the mono PTT meltblown webs to study the processability of PTT. Melt temperature, melt throughput, air temperature, air flow rate, and DCD (Distance of Collector to Die) were considered as primary control variables in the process. DSC scanning and melt flow rate were measured to determine the proper experimental range of temperature. The heating rate of DSC was 10° C./min. The temperature was set from 50° C. to 350° C. DSC was applied to determine the melting temperature and thermal behavior or stability of the resin. Melt flow rate (MFR) or melt flow index (MFI or MI) was also measured to help determine the processing temperature. MFR is widely used in plastic industry to describe the fluidity of a polymer melt. It is a simple flow value of the amount of material extruded at a standardized temperature through a die under pressure from a set mass over a period of 10 minutes. The melt at the higher temperature is easier to flow and corresponds to higher MFI. The resin usually is not recommended for the meltblown process if the MFR value is too low (&lt;100) at the processing temperature, or increasing temperature should be considered for the production as long as no oxidation occurs.  
         [0018]    Like PET and PBT, PTT absorbs moisture which causes thermal degradation of PTT at melt processing temperatures. Drying of the polymer is required before meltblowing and the MFR measurement. The drying condition was: 120° C. for 3 hours, which reduced moisture content from 0.22% before drying to 0.003% (30 ppm) after drying. The MFR value of PTT was 385 (tested at 270° C.) and 844 (tested at 300° C.) indicating that a melt temperature of 270-300° C. is suitable for the meltblown process.  
         [0019]    Table 1 shows the designed processing conditions with the melt throughput from 0.3-1.5 g/hole/min, melt temperature from 271 to 304° C. (520 to 580° F.), air temperature from 232 to 277° C. (450 to 530° F.), air flow rate from 8495 to 19822 liters per minute (300 to 700 Standard Cubic Foot per Minute [SCFM]) and Die-to-Collector Distance (DCD) 30 to 48 centimeters (11 to 19 inches). Based on preparation of the mono PTT webs, PTT/PP bicomponent meltblown webs were made at weight ratios of 25/75, 50/50, 75/25 (Table 2). The web basis weight was controlled to reach the same target weight at 1 oz/yd 2  (31.0 g/m 2 ). The grades of PTT and PP were Shell VFR 50009 and Exxon 3546G respectively.  
         [0020]    Test and Characterization  
         [0021]    Testing of these mono- and bi-component webs included basis weight, bulk density, fiber diameter, air permeability (ASTM D 737), tensile properties (ASTM D 1117), and hydrostatic head (IST 80.4-92). The fiber diameter was measured by optical microscope with the software of Image Pro. SEM (Scanning Electrical Microscope) was applied to examine the fiber structure of mono and bicomponent webs. Heat resistance was evaluated by heat shrinkage of the web, determined by geometric average of heat shrinkage in the machine direction (MD Shrinkage) and heat shrinkage in the cross-machine direction (CD Shrinkage) showing as following equation:  
         Average Heat Shrinkage=( MD Shrinkage× CD Shrinkage) 1/2    
         [0022]    Results  
         [0023]    Table 3 shows the measured web properties of all the mono PTT webs. Based on all the processing conditions and corresponding web properties, a dynamic relationship of web properties to the processing conditions was built by SRM. Our previous research showed that it is an effective and efficient statistical method for systematically studying and modeling of the mono meltblown process FIG. 1 shows the relationship of the response characteristics to the processing conditions at melt temperature and throughput of 288° C. (550° F.) and 0.8 g/hole/min, air temperature of 249° C. (480° F.) and flow rate of 17,840 liters per minute (630 SCFM), and DCD of 33 centimeters (13 inches). As seen from first column in FIG. 1, an increase in melt temperature (MELTTEMP) for this case results in decrease in fiber diameter (FIBDIA), air permeability (AIRPERM), breaking elongation (BRKEXT), and hydrostatic head (HH). An increase of tenacity (TENACITY) was observed as melt temperature increased. The second column shows the effect of melt throughput (THRPUT). As the melt throughput increases, fiber diameter increases, and bulk density (BULKDEN) and hydrostatic head decrease. The third and fourth columns illustrate that as air temperature (AIRTEMP) and flow rate (AIRFLOW) increase, fiber diameter decreases and tenacity increases.  
         [0024]    Table 4 shows the measured web properties of bico PTT/PP webs. Fine meltblown fabrics of fiber diameter from 1.71 to 2.41 μm were produced at melt throughput of 0.6 g/hole/min for mono PTT and bico PP/PTT as shown in FIG. 2. The bico PTT/PP showed better barrier properties than mono PTT meltblown webs at the fiber diameter range of 1.71 to 2.41 μm. The hydrostatic head of bico PTT/PP webs were about four time higher than PTT mono webs. Compared to PET mono and bico webs, the hydrostatic head of PTT/PP bico webs were also higher than that of mono PET and bico PET/PE webs. The higher barrier properties of PTT/PP bico webs may result from the structure and morphology of the bico fiber.  
         [0025]    Scanning electron microscope (SEM) photographs of PTT mono meltblown webs show that the PTT mono meltblown fibers have a round and smooth morphology the same as conventional meltblown fibers. In SEM pictures of PTT/PP bico meltblown webs, non-round cross-sectional, more crimped or twisted fibers are observed, which might be due to thermal properties and Theological gradients of the melts on each side of the bico fiber in the web forming process. Some curly fibers have been observed for bico PTT/PP webs. This may be the cause of the better barrier properties of the webs. The curly fibers (crimped or twisted) would result in a longer and more tortuous path for gas to pass through.  
         [0026]    As shown in FIG. 3, the bico 75PP/25PTT web resulted in negligible shrinkage when subjected to heat without any tension at temperatures of 90, 110, and 130° C., respectively for 7 minutes. This was followed by 50PP/50PTT web which resulted in only slight shrinkage over the temperature/exposure conditions of 90 to 130° C. and only less than 2% shrinkage at 130° C. On the other hand, the 25PP/75PTT also showed enhanced heat resistance and the heat shrinkage notably reduced compared to mono PTT.  
         [0027]    [0027]FIG. 4 compares the heat shrinkage of mono PET and PTT meltblown webs. PET web, when subjected to heat without any tension at temperatures of 90, 110 and 130° C. respectively for 7 minutes, showed higher shrinkage (16-28%) than that of PTT (6.4-14%). The high shrinkage of 100% PET may be readily explained by theory. Since PET crystallizes relatively slowly, meltblown process solidification occurs before the small amount of stress induced orientation can result in significant crystallization, as occurs in conventional high speed melt spinning and in some spunbond processes.  
         [0028]    [0028]FIG. 5 compares heat shrinkage for three different weight ratios of PTT/PP and PET/PP bico meltblown webs conditioned at 90° C. for 7 minutes. PTT/PP bico webs show lower heat shrinkage than PET/PP bico webs. As shown in FIG. 5, 50% PP may result in shrinkage free for PTT/PP bico meltblown webs, which may expand the application of PTT in some areas requiring dimension stability.  
         [0029]    Mono- and bi-component PTT meltblown fiber webs were produced on the Reicofil® side-by-side bicomponent meltblown line. SRM was applied for the web. The obtained fiber diameter was in the range of 1.71 to 4.76 μm. PTT and bico PTT/PP nonwovens exhibited excellent meltblown processability and web quality. Compared to conventional (mono) round and smooth meltblown fibers, the bico PTT/PP webs showed the structure of non-round cross-sectional and twisted fibers. The air, gas, or liquid barrier properties and heat shrinkage resistance of the bico webs were notably improved.  
                                                                                                                                     TABLE 1                           Processing Conditions for PTT                                Air Flow               Sample   Melt Temp   Throughput   Air Temp   Air Flow Rate (Std.   Rate   DCD   DCD            No.   (° F.)   (° C.)   (g/hole/min.)   (° F.)   (° C.)   Liters per minute)   (SCFM)   (in.)   (cm)                    1   520   271   0.9   490   254   14,159   500   15   38.1       2   535   279   0.6   470   243   11,327   400   17   43.2       3   535   279   0.6   510   266   16,990   600   13   33       4   535   279   0.6   470   243   11,327   400   13   33       5   535   279   0.6   510   266   16,990   600   17   43.2       6   535   279   1.2   470   243   11,327   400   13   33       7   535   279   1.2   510   266   16,990   600   17   43.2       8   535   279   1.2   470   243   11,327   400   17   43.2       9   535   279   1.2   510   266   16,990   600   13   33       10   550   288   0.3   490   254   14,159   500   15   38.1       11   550   288   0.9   490   254   14,159   500   15   38.1       12   550   288   0.9   490   254     8495   300   15   38.1       13   550   288   0.9   490   254   19,822   700   15   38.1       14   550   288   0.9   450   232   14,159   500   11   28       15   550   288   0.9   530   277   14,159   500   19   48.3       16   550   288   0.9   490   254   14,159   500   15   38.1       17   550   288   0.9   490   254   14,159   500   15   38.1       18   550   288   1.5   490   254   14,159   500   15   38.1       19   565   296   0.6   470   243   11,327   400   13   33       20   565   296   0.6   510   266   16,990   600   17   43.2       21   565   296   0.6   470   243   11,327   400   17   43.2       22   565   296   0.6   510   266   16,990   600   13   33       23   565   296   1.2   470   243   11,327   400   17   43.2       24   565   296   1.2   510   266   16,990   600   13   33       25   565   296   1.2   470   243   11,327   400   13   33       26   565   296   1.2   510   266   16,990   600   17   43.2       27   580   304   0.9   490   254   14,159   500   15   38.1                  
 
         [0030]    [0030]                                                                                               TABLE 2                           Processing Conditions for Bico PTT/PP Webs                                            Air Flow                                   Air Flow   Rate (Std.       Sample       Melt Temp ° F. (° C.)   Air Temp   Throughput   DCD   DCD   Rate   Liters per            No.   PTT/PP Ratio   PTT   PP   ° F. (° C.)   (g/hole/min.)   (in.)   (cm)   (SCFM)   minute)               bico1a   75/25   550   520   500   06   12   30.5   400   11,327               (288)   (271)   (260)       bico1b   75/25   550   520   500   0.6   14   35.6   500   14,159               (288)   (271)   (260)       bico1c   75/25   550   520   500   0.6   12   30.5   600   16,990               (288)   (271)   (260)       bico1d   75/25   550   520   500   0.6   19   48.3   500   14,159               (288)   (271)   (260)       bico2a   50/50   550   520   500   0.6    8   20.3   300     8495               (288)   (271)   (260)       bico2b   50/50   550   520   500   0.6   10   25.4   400   11,327               (288)   (271)   (260)       bico2c   50/50   550   520   500   0.6   12   30.5   500   14,159               (288)   (271)   (260)       bico3a   25/75   550   520   500   0.6   10   25.4   400   11,327               (288)   (271)   (260)       bico3b   25/75   550   520   500   0.6   10   25.4   300     8495               (288)   (271)   (260)       bico3c   25/75   550   520   500   0.6    8   20.3   300     8495               (288)   (271)   (260)                    
         [0031]    [0031]                                                                                                                             TABLE 3                           Characterization of PTT Mono Webs                                        Hydro-       Sample   Bulk Den.   Fiber Diameter   Break Ext.   Tenacity   Air Perm.   Air Perm.   head            ID   (g/cm 3 )   Ave. (μm)   C.V. (%)   (%)   (mN/tex)   (ft 3 /ft 2 /min)   (m 3 /m 2 /min)   (cm)                    1   0.115   4.76   27.4   58.54   1.08   314.6   95.9   12.03       2   0.085   3.84   18.1   88.10   0.71   318.8   97.2   13.10       3   0.117   2.86   25.6   30.95   2.15   128.6   39.2   19.20       4   0.103   2.88   30.8   49.04   0.59   161.6   49.3   15.93       5   0.112   2.87   22.8   33.18   1.61   132.8   40.5   17.07       6   0.098   3.77   28.2   52.98   1.41   321.0   97.8   9.43       7   0.101   2.87   26.6   40.28   1.78   266.0   81.1   10.23       8   0.083   3.83   25.4   68.06   1.12   411.6   125.5   9.13       9   0.112   2.41   23.6   34.58   2.50   212.2   64.7   9.60       10   0.110   2.56   40.9   29.80   2.00   85.8   26.2   13.77       11   0.101   2.98   22.3   41.64   1.20   186.2   56.8   9.97       12   0.083   3.99   27.5   81.60   1.26   346.6   105.6   9.13       13   0.116   2.39   21.6   26.50   3.23   132.4   40.4   11.23       14   0.111   2.99   28.8   27.06   2.39   149.0   45.4   11.53       15   0.088   2.67   31.0   50.88   1.09   201.2   61.3   9.90       16   0.105   3.24   19.7   38.18   1.22   170.0   51.8   10.00       17   0.104   3.18   20.0   33.22   1.56   168.8   51.5   9.93       18   0.101   3.22   29.6   34.60   1.73   239.4   73   9.67       19   0.110   3.04   22.4   20.36   1.34   158.4   48.3   9.50       20   0.113   2.02   25.2   26.98   2.07   110.5   33.7   11.40       21   0.106   3.36   19.0   25.14   0.92   112.8   34.4   9.90       22   0.118   2.21   22.1   15.52   3.65   71.4   21.8   11.77       23   0.087   3.00   23.2   32.02   0.90   192.8   58.8   9.13       24   0.112   2.22   22.4   24.70   3.33   133.4   40.7   11.03       25   0.099   2.83   20.5   32.72   1.55   203.4   62   9.53       26   0.101   2.51   27.4   30.26   2.15   150.8   46   10.30       27   0.099   3.01   20.0   30.18   2.62   128.2   39.1   10.50                    
         [0032]    [0032]                                                                                                                             TABLE 4                           Properties of Bicomponent PTT/PP Webs.                                        Hydro-       Sample   Bulk Den.   Fiber Diameter   Break Ext.   Tenacity   Air Perm.   Air Perm.   head            ID   (g/cm 3 )   Ave. (μm)   C.V. (%)   (%)   (mN/tex)   (ft 3 /ft 2 /min)   (m 3 /m 2 /min)   (cm)                    bico1a   0.110   3.00   22.5   12.10   2.33   110.2   33.6   38.77       bico1b   0.109   2.47   26.4   10.42   2.87   90.2   27.5   40.37       bico1c   0.111   1.71   21.4   11.82   3.39   80.3   24.5   42.00       bico1d   0.092   2.27   25.6   20.32   1.45   82.3   25.1   31.77       bico2a   0.112   2.22   24.9   37.02   5.97   95.6   29.1   41.30       bico2b   0.103   2.12   23.9   15.74   3.81   82.2   25.5   45.87       bico2c   0.098   1.92   24.1   14.04   2.90   85.2   26   45.17       bico3a   0.107   1.98   26.1   10.96   3.58   53.1   16.2   59.10       bico3b   0.111   2.34   30.7   15.10   4.60   73.5   22.4   52.10       bico3c   0.116   2.20   23.4   12.32   12.84   62.5   19.1   59.17