Poly (trimethylene terephthalate) based spunbonded nonwovens

Abstract

This invention is a spunbonded nonwoven material which is formed of polytrimethylene terephthalate (PTT). This material may be a microfiber material which is 1 dpf or less in fiber diameter. This nonwoven material is unique in that it has a hydrostatic head of no more than 10 cm, preferably no more than 5 cm.

Description

FIELD OF THE INVENTION

[0001] This invention relates to spunbonded microfiber nonwoven materials made from polytrimethylene terephthalate.

BACKGROUND OF THE INVENTION

[0002] 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.

[0003] In nonwovens industries, fibers have been developed for use in meltblown and spunbond processes to make nonwovens webs. Dupont developed the first commercial spunbond process in the late 1950's. A primary factor in the production of spunbond fabrics is control of four simultaneous integrated operations: filament extrusion, drawing, laydown, and bonding. In its simplest form, a spunbond line consists of the following elements: an extruder for forming filaments; a metering pump; a die assembly; a filament spinning, drawing, and deposition system; a belt for collecting the filaments; a bonding zone; and a winding unit. There are three basic bonding techniques employed in a spunbond process: thermal, adhesive/chemical, and needling. In the former two, point and area bonding are used using heat and pressure to bond in point bonding and usually only heat in area bonding. These are well known and commonly used techniques in the industry.

[0004] 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.

SUMMARY OF THE INVENTION

[0005] This invention is a spunbonded nonwoven material which is formed of polytrimethylene terephthalate (PTT). This material may be a microfiber material which is 1 dpf (denier per filament) or less in fiber diameter. This nonwoven material is unique in that it has a hydrostatic head of no more than 10 cm, preferably no more than 5 cm. Preferably, the liquid strike-through is no more than 25 seconds, more preferably no more than 15 seconds, even more preferably no more than 10 seconds, and most preferably no more than 7 seconds, and thus it is better than that of PET. Thus, the PTT nonwoven web is useful as a stocking for a diaper since it is important that materials for this use have low liquid strike-through time. It is preferable that the web also has good permeability to air. Preferably, the air permeability is at least 200 m3/m2/min.

[0006] This invention also includes bicomponent spunbonded microfiber nonwoven materials made from PTT 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. The other polymer(s) in PTT based spunbonded nonwoven may be one of the following thermoplastics: polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), and polylactide (PLA).

[0007] The present invention also provides a process for making such a bicomponent fiber. The present invention also provides a process for making such a spunbonded microfiber nonwoven material.

DETAILED DESCRIPTION OF THE INVENTION

[0008] Spunbonding is a process to make microfiber nonwovens from thermoplastic polymers wherein the melt filaments are first formed by extrusion and drawing and then are laid on a continuous belt. Bonding is then accomplished by several methods such as hot roll calendaring or by passing the web through a saturated steam chamber at an elevated pressure. 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 spunbonded 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.

[0009] 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.

[0010] 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. 1

[0011] 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.

[0012] Many polymers can be used in this invention as the other polymer fiber in a bicomponent structure 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.

[0013] The bicomponent spunbonded microfiber nonwoven material which is comprised of at least two different polymers may be made by extruding and spinning them together in a core/sheath configuration. The bicomponent fiber material may be made by a process which comprises extruding at least two different polymers and spinning them together in a side by side configuration.

EXAMPLES

[0014] The PTT samples of nonwovens used herein were produced in a Reifenhauser spunbond line. The polyethylene terethphalate (PET) and polypropylene (PP) samples were commercially available materials.

[0015] Like PET and PBT, PTT absorbs moisture which causes thermal degradation of PTT at melt processing temperatures. Drying of the polymer is required before spunbonding 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 spunbonded process.

[0016] Test and Characterization

[0017] Testing of these webs included basis weight (g/cm2), fiber diameter (um), air permeability (ASTM D 737—m3/m2/min), liquid strike-through (seconds), and hydrostatic head (IST 80.4-92—cm). The fiber diameter was measured by optical microscope with the software of Image Pro. Liquid strike-through is measured by using a Lenzing Lister strike-through tester.

[0018] Results

[0019] The PTT spunbonded nonwovens sample had a basis weight of 20.26 and a fiber diameter of 14.99. The PET spunbonded nonwovens sample had a basis weight of 22.68 and a fiber diameter of 10.81. The PP spunbonded nonwovens sample had a basis weight of 20.63 and a fiber diameter of 12.24. The basis weight and fiber diameters of these samples are relatively close for comparative purposes.

[0020] The air permeability of the PTT, PET, and PP nonwovens webs was 240, 135, and 129 m3/m2/min, respectively. The liquid strike-through for the three samples was 7.24, 27.12, and >1000 seconds, respectively, and the hydrostatic head was 5.7, 5.7, and 16.5 cm, respectively. It can be seen that the PTT web exhibits the best combination of hydrostatic pressure and liquid strike-through (both low) of the three webs and is thus the most suitable for use in filtration applications.

Claims

1. A spunbonded nonwoven material with a hydrostatic head of no more than 10 cm which is comprised of polytrimethylene terephthalate.

2. The material of claim 1 wherein the hydrostatic head is no more than 5 cm.

3. The material of claim 1 wherein the liquid strike-through is no more than 25 seconds.

4. The material of claim 3 wherein wherein the liquid strike-through is no more than 15 seconds.

5. The material of claim 4 wherein the liquid strike-through is no more than is 10 seconds.

6. The material of claim 5 wherein the liquid strike-through is no more than 7 seconds.

7. The material of claim 1 wherein the web is a bicomponent web which is comprised of at least two different polymers and the other polymer(s) is (are) selected from the group consisting of polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), and polylactide (PLA).

8. The bicomponent spunbonded nonwoven material of claim 7 wherein the polymers have been extruded and spun together in a core/sheath configuration.

9. The bicomponent spunbonded nonwoven material of claim 7 wherein the polymers have been extruded and spun together in a side by side configuration.