WO2001006046A1

WO2001006046A1 - Industrial fabrics having components of polytrimethylene terephthalate

Info

Publication number: WO2001006046A1
Application number: PCT/CA2000/000845
Authority: WO
Inventors: Paul C. Fleri; Samuel M. Baker
Original assignee: Astenjohnson, Inc.
Priority date: 1999-07-19
Filing date: 2000-07-19
Publication date: 2001-01-25
Also published as: AR024795A1

Abstract

Industrial fabrics in which at least a portion of the components, such as mono- or multi-filament yarns or extrusions, are fabricated from polytrimethylene terephthalate having an intrinsic viscosity measured according to ASTM D4603-96 of at least 0.95 dL/g in the finished fabric. Oriented fibers and extrusions produced from the polymer are durable under repetitive compressive stresses, exhibit mechanical properties comparable to polyamide-6, and provide moisture stability similar to yarns and extrusions fabricated from polyamide-6/10 or polyamide-6/12. The fabrics find use in paper making machines, as either forming fabrics or press felt fabrics.

Description

Industrial Fabrics Having Components of Polytrimethylene Terephthalate

Field of the Invention

The present invention relates to industrial fabrics assembled from separate components in which at least one of the components is fabricated from polytrimethylene terephthalate, also known as poly (1, 3-propanediol terephthalate) or PTT, having an intrinsic viscosity, measured according to ASTM D6403-96, in the finished fabric of at least 0.95 dL/g. The fabrics are particularly suitable for use in rigorous environments, where the dimensional stability and mechanical properties of the components and fabrics made therefrom are important .

Background of the Invention

Modern industrial fabrics are commonly assembled by weaving, braiding, knitting, knotting and other known methods from polymeric monofilament or multifilament yarns. It is also known from EP 0 802 280 to assemble such fabrics from a plurality of extruded polymeric strips or panels. The chosen polymers are most frequently polyesters, copolyesters, polyamides, polyphenylene sulfides, pol.yphenylene oxides, fluoropolymers or polyketones. Selection of any particular polymer for a specific application will generally be dictated by the physical and mechanical properties desired in the finished fabric, the cost of the polymer to be used, and the prevailing environmental conditions of the end use.

The present invention is primarily concerned with industrial fabrics intended for environments where the dimensional stability and resistance to repetitive compressive stress of the components used in the fabric are important. The invention is thus particularly relevant to papermaking fabrics which are used to form, drain, dewater and convey a paper web as it is created within a paper making machine.

For the purposes of this invention, the term "fabric" is taken to mean an assembly of components. The term "component" is taken to mean any of the components from which a fabric can be assembled, such as yarns (both monofilament and multifilament) or extrusions. The components forming the fabric can be arranged by interlacing, entangling or engagement so as to form an integrated cohesive structure, such as nets, cloth, felts, batts, textiles and the like, which are created by weaving, braiding, knitting, knotting, joining, felting, needling, spiral winding, bonding, or similar methods. Typical components include individual monofilaments, ultifilaments, staple and spun yarns, spiral coils, and profiled plastics extrusions such as strips, tiles or panels. These components are generally fabricated by an appropriate method from a thermoplastic material, such as melt extrusion, melt spinning, casting or slitting from an extruded film. The fabricated components are then joined to form an integrated cohesive structure.

In a papermaking machine, a paper web is created in three stages. In the forming section, a water based stock of papermaking components is discharged onto a moving continuous forming fabric. As the fabric conveys the stock through the forming section, it is drained and agitated to provide a somewhat self supporting wet paper web. Drainage of the stock is augmented by various stationary elements with which the forming fabric is in moving contact. The web is then transferred to the press section where a major proportion of the remaining water is removed by mechanical pressing in a series of high pressure nips between opposed press rolls. Press fabrics are used both to convey the wet paper web, and to receive expelled water. The web then passes to the dryer section, in which it is conveyed on at least one dryer fabric over a series of heated cylinders where the remaining water is removed by evaporation. The resulting paper is then calendered, slit and wound onto reels.

Papermaking fabrics must ideally possess multiple characteristics simultaneously:

(a) they must be resistant to abrasive wear caused by their passage over the various stationary elements in the paper making machine, and by contact with solids in the stock which they are to convey;

(b) they must be structurally stable, so as to function as designed within the range of stresses imposed during their use;

(c) they must resist dimensional changes in the plane of the fabric due to moisture absorption over a wide range of moisture conditions;

(d) they must resist stretching under the tension imposed by the powered rolls which drive the fabrics on the machine; and

(e) they must be resistant to chemical degradation caused by the various materials present in both the stock and the materials used to clean the fabrics, at the prevailing temperatures of use.

Press felts must in addition be resistant to compaction and repetitive cyclic compressive stress caused by their repeated passage through the press nips in a rigorous chemical environment .

Of the various polymers available for industrial fabrics applications, those most commonly used in paper making are: - polyesters, in particular polyethylene terephthalate (PET) and various copolymers thereof; and polyamides, particularly polyamide-6 (also known as polycaprolactam) , and polyamide-6/6 (also known as polyhexamethylene adipamide) .

Although components formed from both of these polymer types offer certain advantageous characteristics, there are essentially two difficulties associated with their use:

(i) while PET components generally provide adequate chemical resistance and dimensional stability, and PET yarns are also amenable to weaving, having good crimpability and heatsetting behavior, component abrasion and compaction resistance are not always adequate, especially in higher speed paper machines; and

(ii) although components formed from both polyamide-6 and polyamide-6/6 have adequate abrasion and compaction resistance, they are not dimensionally stable in the moisture range found in the paper making environment, and the mechanical properties of yarns and fabrics made from them are known to change .

US 5,137,601 to Hsu discloses papermaking fabrics, in particular press felts, whose component fibers and filaments are fabricated from what is described as polypropylene terephthalate, hereinafter referred to as PPT. In view of the use of "propylene" in the polymer name, this appears to be a polymer of terephthalic acid and 1, 2-propanediol . The fabrics are alleged to have chemical resistance properties similar to PET, and physical properties comparable to polyamide-6. There is no disclosure of suitable intrinsic viscosities for the PPT, no identification of suitable grades, nor are there any teachings to suggest that components made from this polymer may be suitable to withstand repetitive cyclic compressive stress. Best, in EP 0 844 320, discloses monofilaments for use in paper machine clothing whose principle component is polytrimethylene terephthalate (described by Best as PTMT, and stated to be a polymer of terephthalic acid and 1,3- propanediol) . A preferred embodiment discloses blends of PTT and up to 45% by weight of polyurethane. There is no disclosure of the appropriate grade or intrinsic viscosity of a suitable PTT, nor does the disclosure teach that increasing intrinsic viscosity may improve the service life of the component yarns .

Despite these innovations, neat polyamide yarns are still preferred for many industrial fabric applications. The term "neat" as used herein refers to a polymer system containing only one polymer, e.g. polyamide-6, into which nothing else has been added, other than small amounts of one or more conventional additives suitable for polymer compositions, such as stabilizers, plastic processing aids, colorants, and inhibitors of oxidative, hydrolytic or thermal degradation. The compaction and abrasion resistance of these polyamide based yarns is useful in physically demanding applications, such as paper makers press felts, filtration fabrics, and the like. However, the fact that these polyamide yarns absorb moisture, and thus undergo physical changes in their mechanical properties, dimensions and weight when the environment of use exposes them to different moisture conditions, limits their use in moist environments where such variations often cannot be tolerated. This difficulty is discussed inter alia in US 4,529,013, US 4,289,173 and DE 2,502,466 which teach that fabrics including more than 50% polyamide yarns tend to grow or stretch as they absorb moisture in a wet environment, and will shrink as they dry out, thus rendering the fabric dimensionally unstable on a papermaking machine. To circumvent these dimensional stability problems, fabric manufacturers have turned to substantially more costly polyamides, such as polyamide-6/10 and polyamide-6/12, especially in instances where wet-to-dry dimensional stability is crucial. However, the per-unit cost of these polymer resins is approximately three times greater than either polyamide-6 or -6/6. Further, polyamide-6/10 and -6/12 yarns have comparatively poorer thermal properties, making them attractive for only a limited number of very specific applications.

While the moisture stability performance of polyamide-6 and polyamide-6/6 yarns has been improved, yarn manufacturers have as yet been unable to address effectively the special combination of requirements necessary for paper machine clothing applications, in particular: cost, wet-to-dry dimensional stability, and resistance to both abrasive wear and repetitive compressive stress cycling.

Polytrimethylene terephthalate, herein referred to as PTT, also known more accurately as poly (1, 3-propanediol terephthalate) , is a polymer that has recently become commercially available, and which appears to combine a number of the mechanical properties of both polyesters and polyamides . PTT is commercially available from Shell Chemical Co. of Houston, Texas under the trade name CORTERRA™ and is stated to be the polymeric reaction product of purified terephthalic acid and 1, 3-propanediol. This polymer has also been described by Chemical Abstracts Service as poly (1, 3-propylene terephthalate) , terephthalic acid-trimethylene glycol copolymer, and 1, 3-propanediol-terephthalic copolymer.

Two grades of PTT are currently available in bulk: carpet grade, which has an intrinsic viscosity as supplied of about 0.92 dL/g, and a second grade whose intrinsic viscosity as supplied is about 1.3 dL/g. In both cases, the intrinsic viscosity quoted is measured according to ASTM D4063-96 on the bulk resin prior to extrusion into monofilaments; the intrinsic viscosity when measured on the monofilaments is somewhat lower.

The present inventors have discovered that industrial fabrics whose components are fabricated from PTT, and which has an intrinsic viscosity in the finished components greater than 0.95 dL/g when measured according to ASTM D 4603-96, are as resistant to compaction, are dimensionally stable in a moist environment, and are able to withstand cyclic repetitive stresses, as well as components fabricated from polyamide-6/10 or polyamide-6/12. Further, the components are as chemically stable as those formed from PET and are amenable to weaving when formed into monofilament or multifilament yarns. The finished PTT components are thus particularly suitable for use in the assembly of industrial fabrics such as press felts for papermaking machines.

Summary of the Invention

The present invention relates to industrial fabrics formed at least in part from components fabricated from polytrimethylene terephthalate wherein the intrinsic viscosity of the polytrimethylene terephthalate in the finished component in the fabric is at least 0.95 dL/g when measured according to ASTM D4603-96. Components such as yarns and extrusions formed from this polymer and which are used in the fabrics of this invention are resistant to cyclic repetitive compressive stress and fibrillation, as well as to permanent deformation caused by compressive stress, and thus address the aforementioned deficiencies of the prior art.

Preferably, the intrinsic viscosity of the PTT resin from which the component is produced is greater than 0.92 dL/g, when determined according to the procedure described in ASTM D 4603- 96. More preferably, the resin intrinsic viscosity is about 1.3 dL/g. It is well known that the intrinsic viscosity of the polymer will be reduced upon extrusion; we have found that the intrinsic viscosity of the PTT resin prior to extrusion must be greater than 0.92 dL/g so as to obtain satisfactory results from the finished component. It appears that, when the PTT resin is extruded as filaments or as profiled strips, the intrinsic viscosity of the extruded products must be at least 0.95 dL/g or more so as to obtain satisfactory results. If the intrinsic viscosity of the bulk resin is too low, it can be increased by post-condensation polymerization, also known as solid state polymerization. This is a well known method for increasing the intrinsic viscosity of polyester polymers.

The PTT components may also contain from about 0.05% to about 5% by weight based on the total weight of the composition of one or more conventional additives suitable for polyester compositions, such as stabilizers, plastic processing aids, colorants, and inhibitors of oxidative, hydrolytic or thermal degradation. The amount of stabilizer will be dependent upon the intended end use of components made from the polymer.

Preferably, the components of the industrial fabrics of this invention are PTT monofilaments or multifilaments, and the fabric is assembled by weaving. Alternatively, the components are PTT extruded strips, panels or coils, which are assembled by snap/press fitting, spiral winding or by rapier insertion according to the methods described by Baker in EP 0 802 280.

Preferably, all of the components of the industrial fabrics of this invention are fabricated from PTT having an intrinsic viscosity in the finished component of at least 0.95 dL/g. Alternatively, at least some of those components that are oriented in the direction within the plane of the fabric substantially perpendicular to the direction of a tensional load placed on the fabric under its conditions of use are fabricated from PTT having an intrinsic viscosity in the finished component of at least 0.95 dL/g.

As a further alternative, at least some of those components that are oriented in the direction of a tensional load placed on the fabric under its conditions of use are fabricated from PTT having an intrinsic viscosity in the finished component of at least 0.95 dL/g. The proportion of the components selected for use in the fabric will be determined at least in part by the level of tensile load placed on the fabric. For example, it appears that PTT yarns having an intrinsic viscosity in the finished component of at least 0.95dL/g should not be used alone in the machine direction in a woven paper making machine fabric.

Brief Description of the Figures

Fig. 1 is a bar graph showing the percent change in length from wet to dry of a polyamide-6 control monofilament, a polyamide-6/10 monofilament and a PTT monofilament having an intrinsic viscosity of 1.17 dL/g;

Fig. 2 is a photomicrograph of a mesh formed from PTT monofilaments having an intrinsic viscosity of 0.86 dL/g following exposure to 9,000 cycles of repetitive compressive stress at 40°C; and

Fig. 3 is a photomicrograph of a mesh formed from PTT monofilaments having an intrinsic viscosity of 1.17 dL/g following exposure to 54,000 cycles of repetitive compressive stress at 40°C. Detailed Description of the Invention

In the following description, all intrinsic viscosity values quoted were obtained according to the procedure set out in ASTM D4603-96.

Components of the industrial fabrics of this invention are produced using known methods of melt extrusion of PTT resin having an initial intrinsic viscosity of greater than 0.92 dL/g using either a single or twin screw extruder under conditions suitable for this polymer. The PTT resin, together with any additives, are mechanically mixed by placing the components in the extruder hopper and feeding to the extruder. Melting and blending of the PTT resin and any additives takes place in the extruder at a temperature of about 280°C. As the extruder screw (s) conveys the components forward, the molten and thoroughly blended resin is fed into a metering pump that drives it through a die to form a molten extrudate. The extrusion temperature range is preferably from about 220°C to about 300°C, and more preferably is from about 240°C to about 280°C.

The molten extrudate can be quenched in air or water; water quenching is preferred. To produce a monofilament yarn, the solid extrudate is drawn into yarn at room or an elevated temperature in a multi-stage draw process. For the compositions disclosed herein, the preferred drawing temperature range is from about 65-260°C, with energy being supplied between independently speed controlled godets that provide a final draw ratio of from about 3:1 to about 6:1. The final yarns are allowed to relax about 0-25% by passing them through a relaxing stage at a temperature within the range of from about 65°C to about 260°C. The yarns are then wound onto spools. The preceding normal processing conditions provide acceptable results; others may prove suitable. We have found that PTT fibers produced from plastics resin whose initial intrinsic viscosity is from about 0.86 to about 0.92 dL/g or less, referred to as carpet grade, do not offer the necessary mechanical integrity required for repetitive compressive stress applications. Although the wet-to-dry dimensional stability of yarns formed from this range of viscosities is excellent, as well as their mechanical properties as measured by traditional tensile test methods (e.g. percent elongation) over that of a neat polyamide-6 system control yarn, their performance under repetitive cyclic compressive stress is poor.

This is demonstrated in the following tests, where the physical performance characteristics of yarns fabricated from neat polyamide-6 and polyamide-6/10 were compared to those formed from a PTT polymeric resin having an intrinsic viscosity of 0.92 dL/g, and yarns formed from a PTT polymeric resin having an intrinsic viscosity of 1.3 dL/g. In these and later tests, the control yarns of neat polyamide-6 resin were extruded from Ultamid® X-301 available from BASF. The control yarns of neat polyamide-6/10 were extruded from polyamide-6/10 available from Rhone Poulenc under the designation 7030. The PTT used was Corterra™ CP509200 and CP51300, having intrinsic viscosities of 0.92 dL/g and 1.3 dL/g respectively prior to extrusion. These grades of PTT resin are available from Shell Chemical Company of Houston, Texas.

The PTT and polyamide-6 monofilament samples having a diameter of about 0.20mm were produced according to the method described above. Both grades of resin were used for the PTT monofilaments, which were found to have intrinsic viscosities of 0.86 dL/g (from the 0.92 dL/g resin) and 1.17 dL/g (from the 1.3 dL/g resin) . Figure 1 provides a graphical comparison of the wet-to-dry dimensional stability of the neat polyamide-6 and polyamide- 6/10 monofilament controls compared to a monofilament formed from the PTT of the present invention.

The monofilament samples were first tested to determine their wet-to-dry dimensional stability using the following method. Fiber samples greater than 1 meter in length were obtained from each of the control and test monofilaments. These samples were first conditioned by exposing them to air at 23°C and 50% relative humidity for 24 hours. Each sample was then cut to a convenient length, typically 1 meter. The samples were then immersed in distilled water at room temperature for 24 hours, removed from the water, blotted surface dry, and their wet length accurately measured. The samples were then again exposed to air at 23°C and 50% relative humidity for 24 hours, and their dry length then measured. The wet and dry cycle measurements were then repeated. The changes in length are expressed as a percentage, and the average percent change in length over the two wet to dry cycles is taken as being indicative of the stability of the monofilament under these conditions.

Figure 1 shows that the percent change in the length of the control monofilament made of neat polyamide-6 was about 3.5%, and that of the control filament made of neat polyamide- 6/10 was about 0.8%, while that of the PTT monofilaments was about 0.3%. This test demonstrates that the PTT monofilament has superior wet-to-dry dimensional stability when compared to either of the polyamide monofilaments.

However, we have found from further tests that the resistance to repetitive compressive stress cycling of monofilaments formed from PTT having a bulk intrinsic viscosity of 0.92 dL/g prior to extrusion is poor and their physical response, as determined by their loss in diameter and gross failure by fibrillation, is unacceptable for paper machine clothing applications.

In the test results set out in Table 1, the neat polyamide-6 control, and the monofilaments fabricated from the 0.92 dL/g intrinsic viscosity PTT and from the 1.3 dL/g intrinsic viscosity PTT were subjected to a repetitive cyclic compressive stress test to simulate the repetitive compressive stress cycling experienced by a paper machine press felt passing through a nip under load. In this test, a pressure of approximately 7.3 MPa at 40°C, 60°C and 85°C was applied at a frequency of 300 compressions/minute for 180 minutes using a laboratory scale dynamic compaction tester to simulate 54,000 compression cycles. The samples were each wrapped around a notched crossover plate so as to create a grid which simulates a press felt base weave with a mesh of 16 x 16 yarns per cm. The samples and crossover plate are then placed in the dynamic compaction tester where they are subjected to repeated compression under constant load and recovered under zero load. The samples are removed at specific time intervals and examined for damage. Table 1 shows the physical response of all of the monofilaments, as determined by their percent loss in original diameter following 54,000 cycles of compression and relaxation.

Table 1 shows that, not only is the percent loss in diameter of the 1.17 dL/g intrinsic viscosity PTT monofilament substantially lower than the control at all three temperatures, but the 0.86 dL/g intrinsic viscosity PTT monofilaments experience gross failure, as evidenced by their breakage. This breakage is illustrated in Figure 2, which is a photomicrograph of the yarn sample taken from the previously described crossover plate following only 9,000 compression cycles at 0°C. Figure 3 is a photomicrograph of the PTT monofilaments having 1.17 dL/g intrinsic viscosity PTT following exposure to 54,000 compressive stress cycles at 40°C. It is apparent from these photomicrographs and the data presented in Table 1 that monofilaments formed from the 1.3 dL/g intrinsic viscosity PTT, having an intrinsic viscosity of 1.17 dL/g, surprisingly maintain their physical properties following repetitive compressive stress cycling at various temperatures even better than those formed from the neat polyamide-6 control.

The percentage losses in diameter given in Table 1 are the averages of four tests on each filament at each temperature.

Table 1

Percent Diameter Loss of Various 0.20 mm Monofilaments as Compared to Pure Polyamide-6 Monofilament Following Repetitive Compressive Stress Cycles at Different Temperatures .

The results in Table 1 also show that a yarn product having 0.86 dL/g intrinsic viscosity PTT as taught by the prior art is not viable in applications such as press felts. For applications such as these, the intrinsic viscosity of the PTT polymer, which is most easily monitored in the component itself thus avoiding any changes which are known to occur during extrusion, appears to play a crucial role in the ability of the fabric to tolerate exposure to repetitive compressive stress cycling without failure while maintaining the required wet-dry dimensional stability. The data in Table 1 also shows that monofilaments fabricated from a relatively high intrinsic viscosity PTT do not exhibit gross material failure, i.e., fibrillation, when exposed to about 54,000 compaction cycles. It can also be seen that temperature does affect the ability of both the PTT and polyamide-6 filaments to resist compaction; the PTT filaments according to this invention show a lower percentage loss at all three test temperatures.

A number of experimental fabrics were woven from combinations of PTT and polyamide-6 and polyamide-6/10. In these fabrics, PTT and polyamide-6/10 were used as wefts, and PTT and polyamide-6 were used as warps. The elastic modulus of these test fabrics was determined, so as to assess the ability of these fabrics to resist stretching under tensional load, and to remain dimensionally stable on exposure to wet conditions. The details of each test fabric, and the results of these tests, are shown in Table 2.

Table 2

Comparison of the Elastic Moduli of Experimental Fabrics Containing Polyamide- 6 and P Monofilaments in the Machine Direction .

Λ O n

> σi

J -

In Table 2, the terms used to describe the fabric condition have the following meanings: "Not Heatset" refers to the base fabric as woven; "Heatset" refers to the woven base fabric after exposure to normal first heatsetting conditions;

"Batt Needled" refers to the base fabric after the first heatsetting, needling of paper side and machine side layer batt, and second heatsetting; a "dry" fabric is one that has not been immersed in water; and a "wet fabric" is one that has been soaked in room temperature water for at least 2 hours, and which is then tested when wet.

In Table 2 the terms used to describe monofilament polymers have the following meanings:

"PTT" refers to monofilaments extruded from Shell CORTERRA CP15300 polytrimethylene terephthalate resin and having a measured intrinsic viscosity in the finished monofilament of 1.17 dL/g.;

"PA-6/10" refers to monofilaments extruded from polyamide 6/10 obtained from the Shakespeare Company of Columbia, South Carolina under yarn designation NX150; and

"PA-6" refers to monofilaments extruded from polyamide-6 resin obtained from Johnson Filaments of Williston, Vermont under yarn designation N978.

All fabrics above were "endless woven" according to the same double layer 8-shed/4-repeat well known double layer weave pattern in which the MD weft yarn passes over 1 PS warp, between a pair of stacked PS/MS yarns, beneath 1 MS warp, between a pair of stacked PS/MS yarns, and then over 1 PS warp to repeat the pattern. The diameter of all of the CD warp yarns was 0.4 mm. The MD weft yarns in all samples were 0.2/2/3 cabled monofilaments. Two layers of 125 gsm batt consisting of PA-6 fibers were needled to the machine side of the fabric and 4 layers of the same batt were needled to the paper side. All fabric samples were needled according to the same schedule with 12 passes through the needling machine at 400 penetrations/min. at a penetration depth of 12 - 14 mm.

All of the woven base fabrics were exposed to standard heatsetting conditions and temperature of 150°C so as to stabilize them prior to needling. The paper and machine side layer batts were then needled to the base fabric and the resulting fabric exposed to 4 passes through a second heatsetting step at 100°C, 130°C, 140°C and 180°C respectively.

The elastic modulus test results in Table 2 of the samples were determined according to the following procedure. A fabric sample measuring at least 25.4cm in the weft, machine, direction by at least 3.8cm in the warp, cross machine, direction is taken from the fabric. The cross machine direction yarns are stripped out alternately from either edge to provide a band about 2.5cm wide, which contains only machine direction yarns. Each of the two bands is clamped into a constant rate of extension tensile testing apparatus equipped with a 500kg minimum capacity load cell having data outputs to a chart recorder (or other suitable data acquisition device) . The fabric sample is then subjected to an increasing machine direction tensile load, and changes in sample length are measured. The resulting data is converted into a stress-strain curve; the elastic modulus is then defined as the slope of the linear region of the stress-strain curve, located between an initial non-linear portion, and the fabric yield point, also known as the fabric elastic limit.

The test procedure is intended to determine the resistance to stretch of the fabric. From the data reported in Table 2, it is apparent that the elastic modulus of the wet fabrics containing PTT yarns oriented in the machine direction is much greater than that of the control and test fabrics. Also, the percent difference in the elastic modulus between the dry fabric and the wet fabric is much smaller for the fabrics having PTT yarns in the machine direction.

Elastic modulus is a measure of the ability of a fabric to resist stretch and remain dimensionally stable in the machine direction. The test results reported in Table 2 above demonstrate that the elastic modulus of press fabrics whose woven base structure includes PTT yarns in at least the machine direction is higher, and more predictable, than fabrics containing polyamide yarns in the same direction.

The dimensional stability of yarns used in the manufacture of a papermakers' press felts is important. When a new press felt is installed in the press section of a paper making machine, the fabric is usually first "broken in" by saturating it with water and running it under normal loads before beginning to make paper. It is well known in the industry that a press felt containing polyamide-6 yarns oriented in the machine direction of its base fabric will tend to stretch in this direction as it is tensioned and wetted. The elastic modulus of the fabric will provide an indication of the amount of stretch the fabric can be expected to exhibit under running conditions. Table 2 shows that the elastic modulus of fabrics containing PTT yarns in the machine direction will change less than that of fabrics containing polyamide-6 yarns; press felts containing PTT yarns as at least a portion of the machine direction yarns will thus be more dimensionally stable under wet-to-dry conditions than fabrics containing polyamide-6 yarns oriented in the same direction. Wet-to-dry dimensional stability in the cross machine direction is also important because press felts whose base fabrics contain PTT yarns in the cross machine direction will tend to resist widening under the compaction of the press rolls. Press felts containing polyamide-6 yarns in the cross machine direction will tend, in some instances, to spread out beyond the width of the press roll due to the polyamide-6 yarns swelling as they absorb water, which is undesirable, while those containing PTT yarns generally will not.

In general, the elastic modulus tests show that press felt base fabrics including PTT yarns as at least a proportion of the machine direction strands will be more resistant to stretch when wet, and will be more dimensionally stable under wet-to- dry conditions, than fabrics woven from polyamide-6 yarns.

We have also found that fabrics made from PTT components having an intrinsic viscosity in the finished component of at least 0.95 dL/g may not possess sufficient tensile strength to allow their use alone in the direction in which a tensile load is applied to the fabric in its environment of use, for example in the machine direction of paper making machine fabrics. In such fabrics, it is recommended that the fabric include a proportion of components formed from other polymers, such as the polyamides discussed above, or another polymer, or polymers, suitable for the conditions of use, so as to enhance the load bearing capability of the fabric. Both the polymer (or polymers) to be used with the PTT, and the relative proportions of PTT components to components fabricated from the other polymer (or polymers) will need to be determined for each fabric taking into account both the load to be sustained, and the environment of use. Example 1 .

Pellets of Shell CORTERRA™ CP509200 PTT resin having an intrinsic viscosity of 0.92 dL/g were added to the feed port, then mixed and formed into monofilament using a 19.0 mm single screw extruder operated at about 280 °C. The material was drawn using multi-stage godets and ovens. The overall draw ratio was 4:1, and the operating temperatures of the ovens were approximately 200°C; the finished monofilament size was about 0.20 mm in diameter. The PTT in the resulting monofilament was found to have an intrinsic viscosity of 0.86 dL/g. The monofilament was found to exhibit good wet-to-dry dimensional stability but extremely poor repetitive compaction resistance characteristics .

Example 2.

Pellets of Shell CORTERRA™ CP51300 PTT resin having an intrinsic viscosity of 1.3 dL/g were added to the feed port, then mixed and formed into monofilament using a 19.0 mm single screw extruder operated at about 280°C. The material was drawn using multi-stage godets and ovens. The overall draw ratio was 4:1, and the operating temperatures of the ovens were approximately 200°C; the finished monofilament size was about 0.20 mm in diameter. The PTT in the resulting monofilament was found to have an intrinsic viscosity of 1.17 dL/g. The monofilaments exhibit good wet-to-dry dimensional stability and excellent repetitive compaction resistance characteristics.

Example 3.

Pellets of Shell CORTERRA™ CP51300 PTT resin having an intrinsic viscosity of 1.3 dL/g were added to the feed port, then mixed and formed into monofilament using a 19.0 mm single screw extruder operated as described in Example 1. The finished monofilament size was about 0.40 mm in diameter. The PTT in the resulting monofilament was found have an intrinsic viscosity of 1.10 dL/g. The monofilament was found to exhibit good wet-to-dry dimensional stability and excellent compaction resistance characteristics.

Claims

What is claimed is:

1. An industrial fabric formed at least in part from components fabricated from neat polytrimethylene terephthalate wherein the intrinsic viscosity of the polytrimethylene terephthalate in the finished component used in the fabric is at least 0.95 dL/g when measured according to ASTM D4603-96.

2. An industrial fabric according to Claim 1 wherein the components are chosen from the group consisting of yarns and extrusions.

3. An industrial fabric according to Claim 2 wherein the components are polytrimethylene terephthalate yarns chosen from the group consisting of monofilaments, multifilaments, spun yarns and mixtures thereof.

4. An industrial fabric according to Claim 2 wherein at least some of the components are polytrimethylene terephthalate yarns chosen from the group consisting of monofilaments, multifilaments, spun yarns and mixtures thereof, and the fabric is assembled by weaving.

5. An industrial fabric according to Claim 2 wherein all of the components are polytrimethylene terephthalate yarns chosen from the group consisting of monofilaments, multifilaments, spun yarns and mixtures thereof, and the fabric is assembled by weaving.

6. An industrial fabric according to Claim 4 which is a papermaking machine fabric.

7. An industrial fabric according to Claim 6 wherein the papermaking machine fabric is chosen from the group consisting of a forming fabric and a press felt fabric.

8. An industrial fabric according to Claim 4 wherein at least some of those components that are oriented in the direction of a tensional load placed on the fabric under its conditions of use are fabricated from PTT having an intrinsic viscosity in the finished component of at least 0.95 dL/g.

9. An industrial fabric according to Claim 4 wherein at least some of those components that are oriented in the direction within the plane of the fabric substantially perpendicular to the direction of a tensional load placed on the fabric under its conditions of use are fabricated from PTT having an intrinsic viscosity in the finished component of at least 0.95 dL/g.

10. An industrial fabric according to Claim 1 wherein the polytrimethylene terephthalate in the components has an intrinsic viscosity of at least 1.17 dL/g, when determined according to the procedure described in ASTM D 4603-96 carried out on the finished component.

11. An industrial fabric according to Claim 1 wherein the intrinsic viscosity of the bulk resin prior to component fabrication has been increased by post-condensation polymerization.

12. An industrial fabric according to Claim 1 wherein the polytrimethylene terephthalate further contains an effective amount of at least one additive chosen from the group consisting of stabilizers, plastic processing aids, colorants, and inhibitors of oxidative, hydrolytic or thermal degradation.

13. An industrial fabric according to Claim 12 containing from about 0.05% to about 5.0% by weight, based on the total weight of the component, of additive or additives.

14. An industrial fabric according to Claim 1 wherein the components are chosen from at least one member of the group consisting of extruded strips, panels or coils, which are assembled into a fabric by snap/press fitting, spiral winding or by rapier insertion.

15. A finished component for use in an industrial fabric according to Claim 1 wherein the intrinsic viscosity of the polytrimethylene terephthalate in the finished component is at least 0.95 dL/g when measured according to ASTM D4603-96.

16. A finished component for use in an industrial fabric according to Claim 15 wherein the components are chosen from the group consisting of yarns and extrusions.

17. A finished component for use in an industrial fabric according to Claim 16 wherein the components are yarns chosen from the group consisting of monofilaments, multifilaments, spun yarns and mixtures thereof.