MX2008010417A - Press felt for papermaking - Google Patents

Abstract

This invention provides a press felt (10) for papermaking, comprising a substrate (30), a wet paper-side vat layer (20) and a press-side vat layer (23). The wet paper-side vat layer (20) comprises a wet paper contact-side vat layer (21) and a substrate-side vat layer (22). The wet paper contact-side vat layer (21) comprises a core-sheath composite fiber (41) comprising a core component of a high-molecular weight nylon having an absolute viscosity of not less than 80 mPa·s and a sheath component of a nylon having a lower melting point than the core component. The substrate-side vat layer (22) comprises a layer of a nylon fiber (42) free from the core-sheath composite fiber (41). The sheath component of the core-sheath composite fiber (41) is melted to render the wet paper contact-side vat layer (21) dense, and, consequently, moisture in the press-side vat layer (23) is less likely to be moved to the wet paper side, whereby a remoistening phenomenon can be suppressed. Further, since the substrate-side vat layer (22) comprises a nylon layer free from the core-sheath composite fiber, the balance among smoothness, defiber resistance, abrasion resistance, compression fatigue resistance, and water drainage is good.

Description

FELT OF PRESS TO MANUFACTURE PAPER FIELD OF THE INVENTION This invention relates to a press felt for manufacturing paper used in a papermaking machine (hereinafter referred to as "press felt").

BACKGROUND OF THE INVENTION Press machines have been used to dehydrate a wet paper web in a papermaking process. In a press machine, a wet paper web formed with layers therein ie dehydrated within a pressure contact line, sandwiched between a pair of press felts. The press machines generally have a plurality of pressure contact lines. Figure 5 is a schematic view of a pressure contact line in a press machine. A pair of pressure rollers P ', P' and a pair of pressing felts 11 ', 11' form a pressure contact line. The press felts 11 ', 11' and a wet paper web W are compressed within a pressure portion between the pressure rollers P ', P', where the water is removed from the wet paper web W and absorbed by the press felts 11 ', 11'. The volume of the wet paper web W and the press felts 11 ', 11' expand rapidly as they travel through the middle portion of the press portion (contact line) to the exit thereof, when they are released quickly from compression. This expansion generates negative pressure inside the press felts 11 ', 11' which, coupled with the capillary phenomenon within the wet paper web W associated with thin fibers therein, results in a rewet, a phenomenon in which the water is absorbed by the press felts 11 ', 11' back into the wet paper web. Japanese Unexamined Patent Publication No. 143627/2004 (patent document 1) describes an example of a press felt that is intended to prevent rewetting. This felt comprises a base layer, a paper side fluff layer, and a side press fluff layer, with a hydrophilic nonwoven fabric being placed within the paper side fluff layer. According to this invention the water is absorbed and retained in the hydrophilic nonwoven fabric due to its hydrophilic nature, resulting in an effective rewet prevention. In addition, it is also essential for a felt pressing to have a capacity to recover its uncompressed state after compression without flattening (fatigue resistance by compression), an ability to improve the smoothness of the wet paper web by smoothing the felt itself (smoothness), resistance to fraying and abrasion. Japanese Unexamined Patent Publication No. 302584/1996 (Patent Document 2), for example, describes a felt with these capabilities which includes fibers with a core structure in a coating made of a two-component material. According to this invention, the two-component material used for a fiber to form a fluff layer is composed of a coating member with a low melting point and a core with a high melting point. With the heat hardening process of the press felt, the low melting point coating member softens to form a matrix within the fluff layer, which improves the dewatering and compression resistance of the felt. press. In addition, press felts made of a woven fabric with better dewatering and smoothness are used in recent high speed papermaking machines. The fabric is woven with a warp yarn (CMD yarn) and a weft yarn (MD yarn), both of which are individual strands of a single filament (See Japanese Unexamined Patent Publication No. 170086/2000: Patent Document 3).

THE INVENTION However, the press felts described in Patent Document 1 and 2 tend to be vulnerable to repetitive compression by a pressing machine. further, the press felt with the lint layer made of the two-component material, as described in patent document 2, tends to require short-term replacement due to cuts of the fibers during use, fraying or abrasion, due to Thermal pressurization in the felt manufacturing process that produces deterioration of mechanical strength or chemical degradation. On the other hand, the press felt described in the patent document 3 is known to be far inferior to conventional felts which use braided yarns in terms of the resistance to fraying and abrasion, because the fluff fibers and the woven fabric they are not firmly integrated by the seam. Thus, there is a need for a press felt not only with an anti-wetting capability but with a balanced combination of advantages such as compressive strength, smoothness, resistance to fraying and abrasion, and dehydration capacity. In view of the above problems, the aim of the present invention is to provide a papermaking press felt which is capable of preventing rewetting and arresting superior smoothness, abrasion resistance and compression fatigue, and dewatering capability. The present invention solves the aforementioned problems with a press felt comprising a base body and fluff layers having a side layer of wet paper web and a side pressure layer, characterized in that the side layer of wet paper web is composed of a wet paper web in contact with the side fluff layer and a side fluff layer of the base body, the wet paper web in contact with the lateral fluff paper layer having a core fiber in coating comprising a central member made of high molecular weight nylon with an absolute viscosity of 80m Pa.s or more and a cladding member made of nylon with a melting point lower than that of the central member, and the side fluff layer of the base body being Made of nylon without the core fiber in coating. The "absolute viscosity" of 80 mPa.s or more was measured at the temperature of 25 ° C after dissolving the nylon in 100 ml of 0.5 g / 95% sulfuric acid, which was measured using an oscillating viscometer.

The percentage of the content of the core fibers in coating within the wet paper web in contact with the fluff layer is preferably in the range of 25-75%. The wet paper web in contact with the side fluff layer can be multilayer, in which the content percentage of core fibers in coating increases with the increase of the pressure side towards the paper side thereof. In addition, the base body (hereinafter also referred to as the "base layer") is preferably a woven fabric with a warp yarn (CD yarn) and a weft yarn (MD yarn), both of which are individual yarns of a single yarn. filament. According to the invention, the wet paper web in contact with the side fluff layer becomes dense due to the melting of the coating member of the core fiber in coating. As a result, the wet paper web in contact with the side fluff layer functions as a barrier to block water within the pressure side layer so that it moves towards the wet paper web side, thus avoiding Rewetting Furthermore, the invention successfully improves the resistance to fraying, abrasion and compression fatigue of the press felt by providing the central member the core fiber in high viscosity coating, ie using high molecular weight nylon. As a result, the press felt of this invention becomes more durable reducing the need for replacement, which contributes to improving the quality of the finished paper with fewer fibers bound thereon due to fraying and abrasion and is able to maintain the smoothness of the finished paper. the wet paper web in contact with the surface. Further, since the wet paper web in contact with the side blot layer is made of the core fiber in the liner while the side body blot layer formed on the side surface of the wet base paper network is made of nylon without the core fiber in coating, the press felt of this invention is provided with a balanced combination of smoothness and resistance to fraying, abrasion, compression fatigue and dewatering capacity. Furthermore, the present invention improves the dewatering capacity of the felt by using a woven fabric with individual single filament yarns for the base body and thereby improves the permeability thereof.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view of one embodiment of the press felt of the present invention.

Figure 2 is a sectional view of another embodiment of the press felt of the present invention. Figure 3 - is a schematic view of an apparatus for evaluating the effects of the press felt of the present invention. Figure 4 is a schematic view of an apparatus for evaluating the effects of the press felt of the present invention. Figure 5 is a schematic illustration of a pressing apparatus of a papermaking machine.

PREFERRED MODALITIES OF THE INVENTION A press felt of this invention will be detailed hereinafter. Figure 1 is a sectional view CMD of a press felt 10 of the present invention. The "machine direction" (MD) refers to the longitudinal direction in which a press filter is transferred in a papermaking machine while "cross machine direction (CMD)" refers to the lateral direction that crosses the machine's direction. As shown in Figure 1, the press felt 10 comprises a base body 30, a side eraser layer of the wet paper web 20 and a side pressure eraser layer 23, the side eraser layer having the wet paper web 20 in contact with the side eraser layer 21 and a side eraser layer of base body 22 which is formed on the inner side of the eraser layer on the contact side of the wet paper web 21. The lint layer in contact with the wet paper web 21, the side body liner layer 22, and the pressure side liner layer 23 are made of staple fibers, with the side body liner layer 22 and the backing layer 22. pressure side eraser layer 23 integrally intermeshed by sewing with the side of the wet paper web and the pressure side of the base body 30 respectively. The side fluff layer in contact with the wet paper web 21 is integrated by interlacing with the side fluff layer 22 of the base body by sewing. In the press felt 10 of this invention, the side fluff layer in contact with the wet paper web 21 is made of a core fiber in coating 41, a cut fiber, which has a central member made with a yarn of high molecular weight nylon with an absolute viscosity of 80mPa.s or more and a cladding member made of nylon with a melting point lower than that of the central member, while the side fluff layer of the base body 22 is made of a fiber cut from a conventional nylon fiber 42 without the core fiber in coating 41.

"An absolute viscosity of 80mPa.s or more" was measured at the temperature of 25 ° C after dissolving the nylon in 100ml of 0.5g / 95% sulfuric acid, which can be measured using an oscillating viscometer. In Figure 1, the core fiber in coating 41 was amplified for purposes of illustration. Conventionally, attention has not been paid to the viscosity of a central member, or its molecular weight, when a fiber with a core structure in coating constituted of a two-component material is used for a layer of fluff of a press felt. However, the present invention successfully achieved a balance of advantages such as smoothness, fraying and abrasion resistance, and resistance to compression fatigue by providing the central member with a higher viscosity compared to conventional practices, ie using nylon of high molecular weight, and placing a layer made of this core material in coating (the side fluff layer in contact with the wet paper web) on the outer side of the side fluff layer of the base body formed on the lateral surface of the wet paper web of the base body. The nylon used for the core member of the core fiber in cladding 41 shall be high molecular weight nylon with an absolute viscosity of 80mPa.s or more at 25 ° C and with a melting point higher than that of the coating member. When nylon with a high viscosity (80mPa.s or more) is used for the central member, the resistance to fraying, abrasion and compression of the felt can be improved. This is likely because the high molecular weight nylon has a longer molecular chain, which improves the mechanical strength (intensity or durability such as resistance to abrasion and attrition) as a result of the entanglement of these molecular chains. The nylon with an absolute viscosity of less than 80mPa.s (moderate viscosity) can not be sufficiently advantageous to improve the resistance to fraying, abrasion and compression. The preferred nylon used for the core member includes high molecular weight nylon 6, high molecular weight nylon 66, high molecular weight nylon 46, high molecular weight nylon 610, and high molecular weight nylon 612. More specifically, nylon obtained by means of polycondensation of nylon salt is preferable, such as the polymerization of e-caprolactam (nylon 6), polycondensation of hexamethylenediamine adipate (nylon 66), polycondensation of 1,4-diaminobutane adipate (nylon 46), polycondensation of hexamethylenediamine sebacate (nylon 610), polycondensation of diacid hexamethylenediamine dodecandioic (nylon 612), and aliphatic nylon can also be included, which has a melting point of 200 ° C or more as measured by DSC (differential scanning calorimetry). Preferably, an absolute viscosity of the higher molecular weight nylon in 100ml of 0.5g / 95% sulfuric acid is 80mPa.s. or more. This high molecular weight nylon is produced with a well known polymerization process or a solid phase polymerization process in which the polymerized nylon slides are placed in an atmosphere of 120-200 degrees C inert gas without oxygen (for example , Japanese Unexamined Patent Publication No. 529604/2002). The nylon used for the coating member of the core fiber in coating 41 should have a melting point lower than that of the core member. Preferred nylon includes binary copolymerized nylon such as nylon 6/12, nylon 6/610, nylon 66/6, nylon 66/12, nylon 66/610, and ternary copolymerized nylon such as nylon 6/66/12 and nylon 6 / 66/610. As is known in the art, a melting point of that copolymerized nylon fluctuates depending on its composition (or percentages by weight of copolymerized elements), and only those with a melting point of 180 ° C or less is useful for this invention. The coating member is melted by thermal pressurization in the manufacturing process of the press felt, which leads to the construction of the core fiber in coating 41, thereby making the side fluff layer in contact with the denser wet paper web 21 and adding smoothness to the surface of the felt. The side fluff layer in contact with the wet paper web 21 with additional density is also effective to prevent rewetting, because it blocks the water of the base body 30, the base body side fluff layer 22 formed on the lateral surface of the wet paper web of the base body, and the pressure side fluff layer 23 of moving there, when the press felt 10 is released from the contact line pressure. In the present invention, only the side fluff layer in contact with the wet paper web 21 is composed of core fiber in shell 41, with the side fluff layer of base body 22 being made of normal nylon fiber 42 without the core fiber in coating 41. This composition allows the press felt to have a balanced combination of smoothness, fraying and abrasion resistance, compressive fatigue resistance, and dewatering capability. When the side fluff layer of the base body 22 has the core fiber in coating 41, the fluff layers formed on the side surface of the wet core paper web become incompressible as a all due to the melting of the cladding member. Consequently, that pressing felt exhibits better resistance to fraying and abrasion, but the dewatering capacity in a pressure section is degraded. The side fluff layer in contact with the wet paper web 21 is preferably made of a blend with a predetermined percentage of the core fiber in coating 41 and the normal nylon fiber 42 to achieve a better balance of smoothness, abrasion resistance and compression. Preferably, the blend consists of 75-25% of the core fiber in coating 41 and 25-75% of the nylon fiber 42. When the content percentage of the core fiber in coating 41 is less than 25%, the felt is lacking of smoothness due to the insufficient density of the layer of the side fluff layer in contact with the wet paper web 21 and is unable to effectively prevent rewetting. On the other hand, when the content percentage of the core fiber in coating 41 exceeds 75%, the felt tends to flatten with the side fluff layer in contact with the wet paper web 21 susceptible to compression fatigue, although it has smoothness , resistance to abrasion and is effective in preventing rewetting. The side eraser layer in contact with the network of wet paper 21 can be multi-layer, in which the content percentage of the core fiber in coating 41 increases increasingly from the side of the paper-side pressure thereof to provide additional improvements in smoothness and strength to the abrasion. Figure 2 illustrates an embodiment in which the side fluff layer in contact with the wet paper web 21 comprises a first layer 21a and a second layer 21b, the first layer 21a having more core fibers in coating 41 than the second layer 21a. 21b. This structure allows the side wiper layer in contact with the wet paper web 21 to achieve a balance between the anti-wetting and the anti-wetting capabilities. Dehydration More specifically, the first layer 21a with a relatively higher content percentage of core fiber in coating 41 has anti-wetting and smoothness due to its density, while the second layer 21b with a relatively low content percentage of core fiber in coating 41 is provided with a better dewatering capacity due to its additional compressibility in exchange for a lower density, thereby providing the side fluff layer in contact with the wet paper web 21 with anti-wetting and dehydrating capabilities. In this way, in comparison with the modality in the layer of eraser Lateral in contact with the wet paper web 21 is a single layer, the felt has the advantage of achieving a plurality of effects: better anti-wetting and dewatering capabilities due to doubly dense layers in addition to better smoothness and resistance to fraying and abrasion. On the other hand, when the side fluff layer in contact with the wet paper web 21 is formed with a decreasing percentage content of the core fiber in coating 41 of the paper side pressure side, the smoothness, strength the fraying and abrasion, and anti-wetting property of the felt are degraded, as compared to the manner in which the side eraser layer in contact with the wet paper web 21 is a single layer. Although the side fluff layer in contact with the wet paper web 21 is two layers in Figure 2, it may comprise three or more layers. The ratio of the volume of the core and facing members of the core fiber in coating 41 has no limitation, but may range from 5: 1 to 1: 5, with a preferred ratio of 1: 1. The nylon fiber 42 used for the side fluff layer in contact with the wet paper web 21, the pressure fluff layer 23, and for mixing with the fiber Coating core 41 is preferably nylon 6, nylon 66, nylon 46, nylon 610, and nylon 612, etc. Preferably, the base body 30 is a non-woven fabric with a warp yarn 31 (CMD yarn) and a weft yarn 32 (MD yarn) which are individual single filament yarns. It can be a double cloth like [2 / 1,1 / 2], [3/1, 1/3], and [5/1, 1/5], a triple cloth, or a multilayer texture like [a single cloth + a double cloth], [a double cloth + a double cloth]. The single thread of a single filament can be one with a diameter of 0. lmm - 0.6mm and a thread density of the texture can be 10-100 threads / 25mm. However, the base body 30 need not be a woven fabric, and other structures and methods may be employed as appropriate, such as simply overlaying an MD yarn and a CMD yarn, a film, a knitted fabric, or winding a yarn. body in the form of a narrow band to produce a body in the form of a band of relatively large width. In addition, the materials to be used for the base body 30 include natural fibers such as wool, and synthetic fibers such as polyester, nylon 6, and nylon 66 which have superior abrasion and fatigue resistance, compliance, and anti-pollution property. The preferred fineness of the core fiber in coating 41 is 15-25 dtex for a felt of pickup used in a first press in a press section of a papermaking machine, 10-20dtex for a felt in a second and third press, and 5-20dtex for a felt in a fourth press and a shoe press. The preferred fineness of the nylon fiber 42 is 10-25dtex and 15-25dtex for the paper side fluff layer 20 and the pressure side fluff layer 23 of the pick-up felt used in the first press respectively, while which is 10-15dtex and 10-20dtex for the corresponding layers of the felt used in the second and third press, and 5-15dtex and 5-20dtex for the corresponding layers of the felt used in the fourth press and the shoe press.

[Examples] The press felt of this invention will be described using the following examples. However, the scope of the present invention is not limited to those examples. Production of the core fiber in coating; The refined nylon 6 (caprolactam, melting point: 220 degrees C) and copolymerized nylon 6/12 (caprolactam / laurolactam, melting point: 140 degrees C) are individually placed in an extruder with a vent to remove volatiles. The cast nylon 6 of the central member and the copolymerized nylon 6/12 of the member of coating are quantified by a metering gear pump and sent to the respective spinning nozzles. The spunbond core fibers of the spinning nozzles are subjected to cooling in a spin stack and oiling processes, which are then rolled at a natural stretching ratio, stretched, deformed and cut to a fixed length. In the above procedure, a MODELO-EMF spinning machine made by Toyo Seimitsu Kogyo Co can be used. , Ltd. which can be used with an extruder, a multistage stretching machine of a Nelson roller system, and slicer. In the examples, high molecular weight nylon 6 (absolute viscosity: 85mPa.s at 25 degrees C, melting point: 220 degrees C) and nylon 6 of average molecular weight (absolute viscosity: 70mPa.s at 25 degrees C, point) are used. of fusion: 220 degrees C) for central member and copolymerized nylon 6/12 (melting point: 140 degrees C) is used for the cladding member to produce two types of sheared core cut fibers in which the volume ratio of the core and the coating member is 1: 1. A fiber with the central member made of high molecular weight nylon 6 is hereinafter referred to as a composite fiber A, while one with a central member made of nylon 6 of The average molecular weight is referred to as a composite fiber B. The absolute viscosities of 85mPa.s and 70mPa.s are 4.5 and 3.0nr respectively in the relative viscosity (nr) measured by the generally used measurement method (Ubbelohde viscometer). As a reference, the absolute viscosity of 80 mPa.s is equal to 4.0 nr.

Production of press felt for making paper; The examples and comparative examples are all provided with a basic structure as follows to be compared under the same conditions; Base body: Woven fabric A [a double cloth of (3/1, 1/3) using folded yarns made of double braided yarns made of thin nylon monofilaments of 240 dtex of an MD yarn and a CMD yarn], basis weight : 300 g / m2. : Woven fabric B [a double cloth of (3/1, 1/3) using individual threads of thin nylon monofilaments of 1100 dtex for an MD yarn and a CMD yarn], basis weight: 300 g / m2. Epoxy layers: cut fibers of nylon 6 of 17dtex and composite fibers A or B of 17 dtex for the layers of lateral fluffs in contact with the wet paper layer [the first layer, "layer of fiber in contact with the paper web wet "in Table 1), total basis weight: 120g / m2: cut fibers of nylon 6 of 17dtex and fibers Composite A of 17 dtex for the side fluff layer in contact with the wet paper layer [the second layer), total basis weight: 120g / m2: cut fibers of nylon 6 of 17dtex and composite fibers A of 17 dtex for the layer of lateral erasing of the base body, total basis weight: 120g / m2: cut fibers of nylon 6 of 17dtex for the side lining layer of the press, total basis weight: 100g / m2 Sewing frequency: 700 times / cm2 Thermal pressurization: a stitched felt was submitted to a 5 times compression between a pair of calendering rolls (heated to 160 degrees C, with a pressure of 30 kg / cm) at a speed of 5 m / min to have a density of 0.5 g / cm3 The compositions of the examples 1-8 and Comparative Examples 1-6 are shown in Tables 1 and 2, respectively.

(Table 1) (Table 1 below) (Table 2) (Table 2 below) Tests were conducted with the following conditions and methods for evaluating anti-wetting and dewatering capabilities, compressive fatigue resistance, fraying and abrasion resistance, and smoothness, using the examples and comparative examples listed above. Evaluation of antirrehumectant and dehydration capabilities; Tests to evaluate the anti-wetting and dehydrating capabilities were conducted using the apparatuses shown in Figures 3 and 4. In Figures 3 and 4, P is a pressure roller, 110 is a top side filter, 10 is a bottom side felt , SC is a suction tube, and SN is a shower nozzle. The above examples and comparative examples are all used as the bottom side filter 10, while Comparative Example 2 is used for the upper side felt. The apparatuses shown in figures 3 and 4 operate the felt at a speed of 800m / min with a pressure of 80kg / cm. In the apparatus of Figure 3, a wet paper web released from the compression within the contact line is placed on and is transferred by the bottom side felt 10. Accordingly, the water content data of a network of rewet paper can be collected by measuring the moisture of the wet paper web when it passes through the contact line and is placed on and transferred through the bottom side filter 10 (at an outlet of the press 1). On the other hand, in the apparatus of Figure 4, the felt of the lower side 10 comes into contact with the pressure roller over a larger area, which means that the wet paper web released from the pressure of the contact line it is in contact with the pressure felts 10 and 110 only briefly. Therefore, the water content data of a lightly rewetted paper web can be collected by measuring the moisture of the wet paper web immediately after it leaves the contact line (at a press outlet 2).

The degree of rewet and dehydration capacity were determined on the basis of the data collected using the apparatus of Figures 3 and 4. The evaluation of the dehydration capacity, a felt with a water content in the 48% lower range that 49% was evaluated as good, while one with a water content of 49% or more was evaluated as "failed". The degree of rewet was determined on the basis of the difference in the water content data collected with the apparatuses of Figures 3 and 4; a felt with the difference of less than 0.5% was considered not to be rewetted (evaluated as "good"), while one with a difference of 0.5% less than 1.0% was considered as slightly rewetted (evaluated as "failed"), and one with the difference of more than 1% was considered as rehumidified (evaluated as "failed").

Test for fatigue resistance by compression; The felts are subjected 300,000 times to a pulse load of 5 Hz to 120 kg / cm2. Compression fatigue strength is evaluated on the basis of a test ratio after density to that of the finished felt, where the ratio of less than 1.3 was evaluated as "excellent", 1.30-1.39 as "good", " and 1.40 or more "failed".

Test of resistance to fraying and abrasion; The resistance to fraying and abrasion of the felts was determined by means of a Taber abrasion tester based on JIS1023-1992. The amount of detached fiber was measured by placing a discoidal sample piece on a rotating turntable and applying a rotating roller with intense resistance on the sample piece (load: 0.5 kg, wheel: CS-17, rotation: 3000 times, unit of measurement : mg). The amount of less than 40 mg was evaluated as "good" and more than 40 mg was evaluated as "failed".

Surface roughness test; The smoothness of the felt surfaces is determined by measuring the average roughness Rz (μ ??) of 10 points of finished felts (JIS-B0601) before the fraying and abrasion test. The average roughness is less than 60 μt? it was evaluated as "excellent", with 60 um-99 um evaluated as "good" and 100 um or more evaluated as "failed". The results of the measurement and evaluation are shown in Table 3.

(Table 3) As indicated by the test results of examples 1-8 in Table 3, it was determined that the press felt of this invention not only avoids rewetting but achieves a balanced combination of compressive fatigue resistance, fraying and abrasion resistance, smoothness and dehydration capacity. Although the comparative examples 1, in which the layer of lint on the side of the base body is made of core fiber in lining, is superior in terms of fatigue resistance by compression, fraying and abrasion, it lacks smoothness of the surface. Example 3 and comparative example 3, with less than 25% of the core fiber in coating, in the side-on-board layer in contact with the wet paper web and comparative example 2 without those fibers, on the other hand, it has compression fatigue resistance but no anti-moisture property. In addition, comparative example 4, in which the content percentage of the core fiber in coating decreases increasingly from the side of the paper side pressure of the side fluff layer in contact with the wet paper web, is lower in smoothness, although it exhibits resistance to fatigue due to compression and anti-re-wetting capacity. The explanation may be that the first layer of the fluff layer comes into contact with the wet paper web with fewer core fibers in the coating constituting the surface of the felt. In addition, comparative example 5, in which it is used nylon of average molecular weight for the core member of the core fiber in coating, is lower than example 1, with high molecular weight nylon in terms of resistance to fatigue by compression, fraying and abrasion. And finally, example 8, in which the fabric B woven with single strands of a single strand is used for the base layer, is greater than example 1, in which the base body is the woven fabric A with braided strands of a only filament, in terms of dehydration capacity as indicated by the low percentage of water content in both outputs of press 1 and 2.

INDUSTRIAL APPLICABILITY In accordance with the present invention, the natural fluff layer in contact with the wet paper web functions as a barrier to prevent rewetting. The invention successfully improves the resistance to fraying, abrasion and compression fatigue of the press felt by improving the viscosity of the core member of the core fiber in coating, i.e. using high molecular weight nylon. As a result, the press felt of this invention becomes more durable, reducing the need for replacement, contributes to improving the quality of the finished paper with fewer fibers bonded on it due to the fraying and abrasion and is able to maintain the smoothness of the surface with contact on paper. Further, since the side fluff layer in contact with the wet paper web is made of core fiber in coating while the side fluff layer of the base body formed on the lateral surface of the wet paper web or narrower body of nylon without the core fiber in coating the press felt of this invention is provided with a balanced combination of smoothness, fraying resistance, abrasion and compression fatigue, and dewatering capability. In addition, the present invention provides a press felt with better dewatering capability by using a woven fabric with single single filament yarns for the base layer and thereby improving the water permeability thereof.

Claims (4)

1. CLAIMS 1. Press felt for making paper comprising a base body and a layer of fluff having a side layer to the wet paper web and a side layer to the press, characterized in that the side layer to the wet paper web is composed of a side fluff layer in contact with the wet paper web and a fluff layer lateral to the base body, the side fluff layer in contact with the wet paper web having a core fiber in shell comprising a core consisting of high molecular weight nylon with an absolute viscosity of 80 mPa. s or more and a coating member made of nylon with a melting point lower than that of the central member; and being in the side fluff layer of the base body made of nylon without the core fiber in coating. The press felt according to claim 1, wherein a content percentage of the core fiber in the coating in the side fluff layer in contact with the wet paper web ranges from 25% to 75%. The press felt according to claim 1 or claim 2, wherein the side fluff layer in contact with the wet paper web has a plurality of layers in which the content percentage of the core fiber in the coating is increased. Increasingly on the side of the press towards the paper side thereof. 4. Pressing felt according to claim 1 to claim 3, wherein the base body is a woven fabric made of a warp yarn and a weft yarn which are individual strands of a single filament. SUMMARY This invention provides a press felt (10) for making paper, comprising a substrate (30), a wet paper side fluff layer (20) and a fluff layer on the side of the press (23). The lint layer on the wet paper side (20) comprises a side liner layer in contact with the paper (21) and a lint layer on the substrate side (22). The lint layer on the side in contact with the wet paper (21) comprises a composite fiber of the liner core (41) comprising a core component of a high molecular weight nylon having an absolute viscosity of not less than 80 mPa.sy a nylon cladding component having a melting point lower than that of the core component. The substrate side fluff layer (22) comprises a layer of nylon fiber (42) free of the core composite fiber in coating (41). The coating component of the composite core fiber in coating (41) is melted to transform the contact-side fluff layer with the dense paper (21), and consequently, the moisture in the fluff-side layer of the press (23) is less likely to be moved next to wet paper, so a rewet phenomenon can be suppressed. In addition, since the layer of lint on the substrate side (22) comprises a layer of free nylon core composite fiber in coating, the balance between smoothness, fraying resistance, abrasion resistance, resistance to compression fatigue, and water drainage is good.