Abstract:
A monofilament is particularly suited for use as a component in an industrial textile such as a papermachine clothing (PMC) fabric. The monofilament is formed from a composition including more than 70 weight % to 99 weight % polyamide and from 1 weight % to less than 30 weight % polyphenylene ether.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0001]    The present invention relates to a monofilament, in particular for use as a component in an industrial textile, such as a papermachine clothing (PMC) fabric. 
         [0002]    Monofilaments formed from polymeric resins are used as yarns in a variety of industrial applications. For example, woven or non-woven fabrics manufactured from polymeric monofilaments are widely used in dryers, conveyors and the like. In particular, endless fabric belts are important constituents of the dryer sections, forming sections and press sections of paper machines. Such fabrics, which are also called paper machine clothings (PMC), are disclosed, for example, in commonly assigned patent application publication US 2012/0214374 A1 and in its counterpart European published patent application EP 2 489 781 A1. 
         [0003]    Monofilaments which are to be used as yarns in an industrial textile are often formed from polyamide (PA). Thermoplastic polyamides generally have a high resiliency, a high abrasion resistance as well as a high toughness. The mechanical properties of monofilaments formed from polyamides are generally sufficient for the above mentioned applications and in particular for the use in the forming sections and press sections of paper machines. In these sections, water based pulp is deposited on a porous forming fabric manufactured from monofilaments. After the deposition of the pulp, water is extracted from the pulp by gravity and suction. During this extraction process, water passes through the pores of the forming fabric. In a further stage of the paper production process, the wet web prepared from the pulp is transported on a press felt. Nip rollers or the like are used to squeeze out water from the web. Finally, the web is dried on a porous dryer fabric by supplying thermal energy. 
         [0004]    The contact between the polyamide yarns and water during a paper production process is problematic, because polyamides tend to absorb a considerable amount of water. This effect is due to the hydrogen bonding capacity of the amide linkages present in the polymer structure. Water absorption affects the mechanical properties of the monofilaments, resulting in dimensional changes of the respective fabric. Therefore, the stability and durability of PMC fabrics made from polyamide yarns is rather poor. 
         [0005]    In order to reduce the water absorption capacity of monofilaments formed from polyamide, chemically modified polyamides and/or additives could be in principle used. However, such approaches are disadvantageous because the tensile and abrasion resistance properties of the monofilaments are reduced and the material costs are increased. On account of these reasons there is a need to enhance the stability of monofilaments for industrial textiles while maintaining the tensile properties. 
       SUMMARY OF THE INVENTION 
       [0006]    It is accordingly an object of the invention to provide a monofilament, a production method and a fabric which overcome the above-mentioned and other disadvantages of the heretofore-known devices and methods of this general type and which provides a monofilament which is easy to produce and which has a high mechanical stability even when intensely exposed to moisture. 
         [0007]    With the foregoing and other objects in view there is provided, in accordance with the invention, a monofilament formed from a composition including more than 70 weight % to 99 weight % polyamide and from 1 weight % to less than 30 weight % polyphenylene ether. 
         [0008]    Polyphenylene ether (PPE) polymers are amorphous and non-polar. Moreover, they have excellent mechanical and thermal properties as well as being dimensional stable. The inventors have surprisingly recognized that it is advantageous to combine the high resiliency and abrasion resistance of polyamide with the high stability and the low water absorption capacity of polyphenylene ether. The aromatic component of the polyphenylene ether lowers the overall polarity of the composition and thus reduces the water uptake of the formed monofilament. 
         [0009]    In principle, polyamide is poorly mixable with polyphenylene ether. Surprisingly, however, it has been found that the compatibility of polyamide and polyphenylene ether at comparatively low loadings of polyphenylene ether is sufficient to produce stable monofilaments. These monofilaments are easy to produce and have excellent tensile and loop properties as well as high abrasion resistance. Simultaneously reduced water absorption capacity should lead to improved dimensional stability. Therefore, the invention enables longer overall fabric life on a paper machine. 
         [0010]    According to a particularly preferred embodiment of the invention, the polymer part of the monofilament completely consists of or at least essentially consists of the polyamide and the polyphenylene ether as polymer ingredients. Specifically, the sum of weights of the polyamide and the polyphenylene ether based on the total weight of the polymer part of the monofilament may be at least 80 weight %, preferably at least 90 weight %, more preferably at least 95 weight %, even more preferably at least 99 weight % and most preferably 100 weight %. Although it is preferred to use only polyamide and polyphenylene ether as polymeric ingredients, the composition may further comprise non-polymeric additives. For certain applications, it may be advantageous to add further polymers to the mixture of polyamide and polyphenylene ether. However, maximizing of the amount of polymer in the composition increases yarn tenacity. 
         [0011]    Preferably, the composition does not include any compatibilizer. 
         [0012]    According to a preferred embodiment of the invention, the composition does not include any compound belonging to the group consisting of fumaric acid, maleic acid, itaconic acid, dimethylmaleate, maleimide, tetrahydrophthalimide, maleic anhydride, itaconic anhydride, glutaconic anhydride, citraconic anhydride and tetrahydrophthalic anhydride. This maximizes ease of processing and reduces the production costs. 
         [0013]    In accordance with another preferred embodiment of the invention, the composition does not include any functionalized olefinic elastomer. 
         [0014]    Notably good results are achieved when the polymer part of the composition is a binary mixture of polyamide and polyphenylene ether. I. e. it is preferred that the composition doesn&#39;t contain any further polymers apart from polyamide and polyphenylene ether. However, as stated above, such a preferred composition may contain additional non-polymeric ingredients. 
         [0015]    In a further development of the present invention, it is proposed that the composition includes a stabilizer, in particular an antioxidant. 
         [0016]    Particularly good results are achieved when the polyphenylene ether has a number average molecular weight of less than 10000 g/mol. In accordance with the present invention, the number average molecular weight is measured by gel permeation chromatography making use of polystyrene standards. 
         [0017]    In accordance with a still further embodiment of the invention, the polyamide is selected from the group consisting of PA6, PA6.6, PA6.T, PA6.10, PA6.12, PA6,6.6, PA4.10, PA5.6, PA5.10, PA5.12 and mixtures thereof. These polyamides have turned out to provide especially good results. 
         [0018]    Notably good results are achieved when the polyamide is PA6 (polycaprolactam) or PA6.6 (nylon). 
         [0019]    According to a further embodiment of the invention, the monofilament has a loop tenacity which is at least 20% greater than the loop tenacity of a comparative monofilament, wherein the comparative monofilament is formed in an identical manner as the monofilament except that the polyphenylene ether is replaced by polyamide. 
         [0020]    In accordance with the present invention, the loop tenacity is determined by linking two loops of the monofilament or of two respective monofilaments and pulling the loops against each other. 
         [0021]    In accordance with a still further embodiment of the invention, the monofilament has a loop tenacity which is at least approximately 40% greater than the loop tenacity of a comparative monofilament, wherein the comparative monofilament is formed in an identical manner as the monofilament except that the polyphenylene ether is replaced by polyamide. 
         [0022]    According to yet another embodiment of the present invention, the monofilament has a loop tenacity ranging from 4 gf/den to 10 gf/den, preferably from 5.5 gf/den to 8.5 gf/den, wherein “gf/den” means “grams force per denier” and wherein 1 gf/den×8.83 equals 1 cN/tex. 
         [0023]    In accordance with still another embodiment of the present invention, the monofilament has a water absorption which is at least 15% less than the water absorption of a comparative monofilament, wherein the comparative monofilament is formed in an identical manner as the monofilament except that the polyphenylene ether is replaced by polyamide, and wherein the water absorption is determined by immersing the respective monofilament in distilled water at 23° C. for 24 h and weighing the respective monofilament before and after the immersion process. Specifically, the water absorption may be determined according to ASTM D570. 
         [0024]    Preferably, the monofilament has a water absorption which is at least approximately 30% less than the water absorption of a comparative monofilament, wherein the comparative monofilament is formed in an identical manner as the monofilament except that the polyphenylene ether is replaced by polyamide, and wherein the water absorption is determined by immersing the respective monofilament in distilled water at 23° C. for 24 h and weighing the respective monofilament before and after the immersion process. 
         [0025]    According to a further preferred embodiment of the present invention, the monofilament has an abrasion resistance which is at least 50% greater, preferably at least 70% greater, than the abrasion resistance of a comparative monofilament, wherein the comparative monofilament is formed in an identical manner as the monofilament except that the polyphenylene ether is replaced by polyamide. In accordance with the present invention, the abrasion resistance is measured by the squirrel cage method as disclosed in the above-mentioned US 2012/0214374 A1 and EP 2 489 781 A1. 
         [0026]    Particularly good results are achieved when the monofilament has a tenacity which is greater than 5.0 gf/den. In accordance with the present invention, the tenacity is determined according to ASTM D2256-97. 
         [0027]    According to a further preferred embodiment of the present invention, the monofilament has a thermal stability which is at least 10% greater than the thermal stability of a comparative monofilament, wherein the comparative monofilament is formed in an identical manner as the monofilament except that the polyphenylene ether is replaced by polyamide, and wherein the thermal stability is determined as percentage of the tenacity retention after exposing the respective monofilament in an oven at 170° C. for 24 h. 
         [0028]    Moreover, it is preferred that the monofilament has an elongation at break ranging from 10% to 50%, preferably from 20% to 35%. In accordance with the present invention, the elongation at break is measured according to ASTM D2256-97. 
         [0029]    In accordance with still another preferred embodiment of the present invention, the monofilament has a maximum diameter ranging from 0.005 mm to 5 mm, preferably from 0.05 mm to 2 mm. According to the present invention, the term “maximum diameter” means the maximum dimension in the cross-section of the monofilament. Monofilaments having a dimension falling in this numeric value range have been found to be specifically suited for PMC applications. Generally, the monofilament according to the invention may have a circular, oval or rectangular cross section. Specifically, the cross-sectional shape of the monofilament may be selected depending on the type of fabric or felt which is to be produced and depending on the application field of the fabric or felt. 
         [0030]    Moreover, the present invention is directed to a fabric, in particular a papermachine clothing (PMC) fabric, comprising a plurality of woven or non-woven monofilaments, wherein at least some of the monofilaments are formed from a composition including more than 70 weight % to 99 weight % polyamide and 1 weight % to less than 30 weight % polyphenylene ether. 
         [0031]    Such a fabric is easy to produce, cost-effective and sufficiently stable to be used in a high moisture environment, such as the forming and press section of a paper machine. 
         [0032]    Notably good results are achieved when the fabric is completely made up from monofilaments which are formed from a composition including more than 70 weight % to 99 weight % polyamide and 1 weight % to less than 30 weight % polyphenylene ether. 
         [0033]    According to a further preferred embodiment of the present invention, the fabric forms an endless belt. Such an endless belt can be used as a conveyor belt or, preferably, as a dryer belt, forming belt or press belt in a paper machine. 
         [0034]    Therefore, according to still another embodiment of the invention, the fabric has a sufficient mechanical and thermal stability to be used as a dryer belt, forming belt or press belt in a paper machine. 
         [0035]    In addition, the present invention relates to a method for forming a monofilament comprising the steps of preparing a resin composition including more than 70 weight % to 99 weight % polyamide and 1 weight % to less than 30 weight % polyphenylene ether, extruding the resin composition through a spinneret to form a monofilament and drawing the monofilament for one or more times. 
         [0036]    Apart from using a mixture of polyamide and polyphenylene ether having a low loading of polyphenylene ether, the drawing of the monofilament may be performed according to the principles that are generally known in the field of monofilament production. 
         [0037]    In accordance with still another preferred embodiment of the present invention, the resin composition is extruded by means of a standard extruder, such as a single screw extruder or a twin screw extruder. 
         [0038]    Particularly good results are achieved when the step of preparing the resin composition includes the step of melt blending a mixture of polyamide and polyphenylene ether. 
         [0039]    Preferably, the melt blending is carried out without adding any compatibilizer. This maximizes ease of processing and keeps the production costs low. 
         [0040]    Moreover, it is preferred that the step of preparing the resin composition does not involve any chemical modification of the polyamide. 
         [0041]    in accordance with a concomitant feature, the invention is also directed to the use of a monofilament as described above for forming a papermachine clothing (PMC) fabric. 
         [0042]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0043]    Although the invention is illustrated and described herein as embodied in a monofilament, a fabric, and a method of producing the same, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0044]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0045]      FIG. 1  is a fragmentary perspective view of a portion of a fabric made up from monofilaments; and 
           [0046]      FIG. 2  is a flowchart illustrating an embodiment of the method of making monofilaments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a portion of a fabric  10  formed from a plurality of woven monofilaments  12 , or monofilament bodies. The fabric  10  may be formed to provide an endless belt. The monofilament bodies  12  have a diameter ranging from 0.005 mm and 5 mm, depending on the application. The specific weave pattern of the fabric  10  may vary from one application to another. Moreover, fabric  10  need not necessarily be a woven fabric, but may include non-woven monofilaments  12 . The monofilaments  12  shown in  FIG. 1  have a circular cross section, but this may vary depending on the application. In particular, the monofilaments  12  may have an elliptical cross section or a rectangular cross section with slightly rounded corners. 
         [0048]    At least some of the monofilaments  12  and preferably all monofilaments  12  making up the fabric  10  are formed from a resin composition including more than 70 weight % to 99 weight % polyamide and 1 weight % to less than 30 weight % polyphenylene ether, as it is described above and for an exemplary embodiment below. 
       Examples 
       [0049]    Different samples of monofilaments were produced on the basis of a polyamide (PA) resin and a polyphenylene ether (PPE) resin. The polyamide resin was PA6 supplied by BASF. The polyphenylene ether was Noryl SA120-100 supplied by SABIC. Of these two polymers, binary mixtures having different PPE loadings were prepared by melt blending as shown at  14  in  FIG. 2 . No compatibilitizers were added to the mixtures. Monofilaments  12  or yarns were produced by extruding the mixture through a spinneret in a single screw extruder as shown at  16  in  FIG. 2 . The loading of the PPE ranged from 5 weight % to 30 weight % as shown in Table 1 below. A comparative monofilament having a PPE loading of 0 weight % was also prepared. Preblending into pellets was not necessary. The monofilaments  12  were drawn so as to have a diameter of 0.40 mm, as is shown at  18  in  FIG. 2 . 
         [0050]    Tensile properties of the monofilaments  12  thus produced were evaluated according to ASTM D2256-97. The results are indicated in Table 1. 
         [0051]    The abrasion resistance of the monofilaments  12  was measured using the squirrel cage method. This method is described in US 2012/0214374 A1 and EP 2 489 781 A1 and involves the use of a rotating drum of metal wires which are aligned perpendicular to the polymer strands. At the beginning of the test, a load is applied to each strand. During the test the strands are continually abraded by the rotation of the drum and the abrasion resistance is quantified by the number of cycles it takes for the strand to fail. The average number of cycles to break for the monofilaments  12  formed from the PA-PPE-mixture was found to range between 16900 and 22700 (Table 1). In contrast, the comparative monofilament having a PPE loading of 0% processed under similar conditions had an average number of cycles to break of 10000. Hence, the abrasion resistance is increased by more than 1.65 times with the addition of PPE. Increasing the PPE loading above 30% resulted in a phase separation of the components and in unacceptable monofilaments. 
         [0052]    To determine the free shrinkage, the samples were kept in an enclosed hot air oven at 177° C. for 3 minutes in an unrestrained condition. After this hot air treatment, the change in the length of each sample was measured and the free shrinkage percentage was calculated therefrom. 
         [0053]    Apart from the abrasion resistance and the free shrinkage, Table 1 shows further tensile properties of the monofilament samples according to the present invention as well as of the comparative monofilament. Thermal stability of the monofilaments was evaluated by exposing the monofilaments to high temperatures and measuring the tensile properties before and after the heat treatment. Specifically, the samples were exposed to 170° C. for 24 hours in an enclosed hot air oven and retained tensile strength of the monofilaments was expressed in percentage after the heat treatment. 
         [0054]    The water absorption of the monofilament samples was measured according to ASTM D570. Specifically, the samples were emerged in distilled water at 23° C. for 24 hours. The samples were then removed, dried using a lint free cloth and weighed. 
         [0055]    It can be deduced from Table 1 that the use of a PA-PPE-composition having a comparatively low PPE loading enables the production of monofilaments having a high stability, excellent tensile and loop properties and a reduced water absorption at the same time. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Monofilament properties 
               
             
          
           
               
                   
                   
                   
                   
                   
                 Abrasion 
                 Tenacity 
                   
               
               
                   
                   
                   
                   
                 Free 
                 Resistance 
                 Retention 
               
               
                 PPE 
                   
                 Elongation 
                 Loop 
                 Shrinkage 
                 (number of 
                 (Thermal 
                 Water 
               
               
                 Loading 
                 Tenacity 
                 at Break 
                 Tenacity 
                 (177° C.; 
                 cycles to 
                 Stability 
                 Absorption 
               
               
                 (%) 
                 (gf/den) 
                 (%) 
                 (gf/den) 
                 3 min) 
                 break) 
                 Test) (%) 
                 (%) 
               
               
                   
               
             
          
           
               
                 0 
                 6.42 
                 24.08 
                 5.89 
                 12.9 
                 10000 
                 14.64 
                 6.29 
               
               
                 5 
                 6.47 
                 26.12 
                 7.52 
                 13.5 
                 16900 
                 24.57 
                 6.00 
               
               
                 10 
                 6.23 
                 25.23 
                 6.86 
                 13.7 
                 19400 
                 35.63 
                 4.55 
               
               
                 15 
                 5.79 
                 25.17 
                 7.97 
                 13.7 
                 22700 
                 49.05 
                 5.31 
               
               
                 20 
                 5.81 
                 25.59 
                 8.03 
                 13.5 
                 17800 
                 42.51 
                 5.32 
               
               
                 30 
                 5.81 
                 31.85 
                 6.56 
                 13.4 
                 20500 
                 55.77 
                 5.00 
               
               
                   
               
             
          
         
       
     
         [0056]    While this invention has been described with respect to a preferred embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.