Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
  • D01F6/88—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds
  • D01F6/92—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polycondensation products as major constituent with other polymers or low-molecular-weight compounds of polyesters
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/0027—Screen-cloths

Definitions

• This invention relates to a paper maker's forming fabric made from synthetic plastic fibers.
• a continuous sheet of paper or paper-like material is formed by flowing a water-based slurry of cellulosic fibers onto a travelling continuous woven belt.
• a continuous belt also known as a forming fabric or forming wire
• a typical slurry as delivered to the moving forming fabric can contain as little as 0.5% by weight of cellulosic fibers, can range in temperature from about 30°C to about 85°C, and typically has a pH of from 4 to 9.
• the wet paper web leaving the forming fabric to pass to the press and dryer sections can still contain 80% water by weight.
• the still-wet web After leaving the wet end or forming section over a couch roll, the still-wet web is transferred to a press section where a major proportion of the remaining water is removed, by passing it through a series of pressure nips in sequence. On leaving the press section the web passes to a dryer section, which is heated for final drying. The dried web can then be calendered, to smooth the surface, and is finally collected on a reel.
• This invention is directly concerned with the wet end or forming section of a papermaking machine, and thus is concerned with papermaking fabrics known as "forming fabrics". These fabrics are used to screen a moisture laden mass of cellulose fibers during the initial stage of water removal to transform it into a wet paper web.
• the forming fabric comprised a structure woven from metal wire, as a result of which these fabrics came to be known as fourdrinier wires.
• the preferred metal for these wires was phosphor-bronze.
• These fourdrinier wires were used in all kinds of papermaking machines, and for all qualities of paper. Whilst effective, these wires were not without disadvantages, especially as regards their abrasion resistance capabilities when the cellulose fiber slurry also contained abrasive fillers such as silica and calcium carbonate.
• the synthetic polymers which provide the currently most acceptable monofilaments used in making forming fabrics are polyester, more particularly polyethylene terephthalate, and polyamide, particularly nylon-6(polycaprolactam) and nylon-66(poly-hexamethyleneadipamide). These monofilaments have been mixed with others, such as polyethylene and polyesters based on polybutylene terephthalate, but still such fabrics are far from perfect.
• nylon-6 and nylon-66 in the range of moisture contents found in the paper-making environment, running from fully wet to dry, imposes a restriction on the ratio of nylon monofilaments to polyethylene terephthalate monofilaments which may be used. This is cited as 50% in both U.S. 4,529,013 and 4,289,173; West German OS 2,502,466 similarly gives a figure of 50%, and additionally suggests that the nylon filaments should have at least 4% (the maximum recommended is 25%) larger diameter than the polyester monofilaments.
• a forming fabric containing both a nylon and a polyester provides an acceptable compromise, provided the amount of nylon used is limited.
• Such fabrics also appear to be resistant to the pH which can be expected in use, which may range from about 4 to a value in the 8-9 range. Polyester fibers do not degrade unduly under these conditions, even under the ranges of temperature extending up to about 85°C encountered in modern paper making machines.
• This invention seeks to provide a solution to the problems associated with the use of nylon, by making available an alternative papermakers forming fabric including monofilaments based on a polymer blend which has the weaving and heat setting characteristics of polyethylene terephthalate.
• This fabric also at least approaches the abrasion resistance capabilities of the common nylon-containing fabrics.
• For the remainder of the forming fabric it is preferred to use monofilaments of polyethylene terephthalate, but this invention is not limited to the use of this polymer for the remainder of the fabric, as other yarns or monofilaments could be used.
• this invention is discussed by way of reference to monofilaments as being the woven fibers, it is not so limited, and is applicable to forming fabrics woven from both yarns and monofilaments. It is preferred that the yarn used be a monofilament.
• this invention provides a forming fabric for use in a papermaking machine woven from:
• the yarns used in both the first and the second direction are monofilaments, and it is also preferred that the yarns used in the first direction, together with the remainder of the yarns in the second direction, are polyethylene terephthalate.
• Utilization of the new monofilament of this invention in its broadest aspect is thus independent of the form of weave used. It encompasses those fabrics commonly known as single layer, double layer or duplex, and composite. Descriptions of these generic forming fabric types are provided, amongst other places, in U.S. Patents 3,858,623 and 4,071,050 and in Canadian Patent 1,115,177, respectively.
• this invention also provides a synthetic monofilament comprising a blend consisting essentially of from more than 60% to about 90% by weight of polyethylene terephthalate and from less than 40% to 10% by weight of a thermoplastic polyurethane, together with from zero up to about 5% by weight of a hydrolysis stabilizer for the thermoplastic polyurethane.
• thermoplastic polyurethane Preferably, the percentage range by weight of thermoplastic polyurethane is above about 15%; more preferably 25% to about 35%; and most preferably the amount of thermoplastic polyurethane is about 30%.
• this invention provides a forming fabric for use in a papermaking machine wherein the minor proportion of the yarns making up the face of the forming fabric onto which the cellulose fiber pulp slurry is laid are monofilaments of a blend of polyethylene terephthalate with a thermoplastic polyurethane as defined above, and wherein the major proportion of the yarns making up the machine side of the forming fabric are monofilaments of a blend of polyethylene terephthalate with a thermoplastic polyurethane as defined above.
• the yarns used are monofilaments.
• the yarns comprising the major proportion of the face of the forming fabric and the minor proportion of the machine side of the fabric are polyethylene terephthalate monofilaments.
• machine direction means a direction substantially parallel to the direction in which the forming fabric moves in the paper machine.
• cross-machine direction means a direction substantially at a right angle to the "machine direction", and in the plane of the fabric.
• machine direction corresponds to the warp threads, and "cross-machine direction” to the weft threads.
• the fabrics of this invention are thus comprised of two different yarns, preferably one of which is a polyester monofilament, and the other of which is a monofilament of a polyester - thermoplastic polyurethane blend.
• blends containing from 10% to at most 40% of polyurethane provide a monofilament which has abrasion resistance characteristics approaching those of a nylon monofilament, but without the other attendant problems of such a nylon monofilament deriving from its lack of permanent crimpability.
• certain polyester - thermoplastic polyurethane blends exhibit better crimpability and heat set behaviour than those of the polyester when that polyester is used without any thermoplastic polyurethane in the monofilament.
• This property has a direct bearing on the weaving behaviour of these monofilaments, and is wholly unexpected.
• the use of this blended monofilament also allows further simplification of the weaving process, since it permits the elimination of the nylon monofilaments often used in the cross-machine direction to provide adequate abrasion resistance properties to the machine side of the fabric.
• the polyester - thermoplastic polyurethane blend monofilaments can be used alone as the only cross-machine yarns.
• the polyester component For the blended monofilament, there are some necessary criteria which the polyester component must meet not only to provide a material which can be melt extruded into suitable monofilaments, but also to provide a polymer blend which has adequate properties.
• the polyester In addition to the standard requirements of purity, lack of "dirt", and particularly lack of water (the polyester should be relatively anhydrous with at most 0.007% of water) the polyester should also have a molecular weight similar to that of resins commonly used to provide warp and weft yarns.
• the polymer should have an intrinsic viscosity of between 0.50 and 1.20, when measured in accordance with the procedure set forth below. Preferably, the intrinsic viscosity is in the range of from 0.65 to 1.05.
• Polyethylene terephthalate grades available under the following designations (which include trade marks) have this property: Dupont "Merge 1934" (a product of Du Pont sold under this description) Arnite A06-300 (a trade mark of Akzo) Vituf 9504C (a trade mark of Goodyear) Tenite 10388 (a trade mark of Eastman)
• these preferred viscosities correspond to number average molecular weights in the range of from about 1.5 x 104 to about 5.2 x 104.
• the intrinsic viscosity when given herein, is measured on a solution of the polyester in a mixed solvent comprising a 60:40 part by weight mixture of phenol and (1,1,2,2)-tetrachloroethane. The viscosity measurements are carried out at 30°C.
• thermoplastic polyurethane part of the blend it is again necessary that the material used be essentially anhydrous (less than 0.01% water), free from impurities as far as possible, and also free of "dirt", so that it can be processed by normal melt extrusion techniques into a monofilament.
• thermoplastic polyurethanes are of two types; those derived from polyesters, and those derived from polyethers.
• polyester variety is more effective, and hence is preferred.
• the thermoplastic polyurethane is a relatively soft material, the softness being measured in accordance with the standard procedure set forth in ASTM Method D.2240.
• the hardness should be no greater than 95 when measured with a Type A durometer, or no greater than 75 when measured with a Type D durometer.
• Thermoplastic polyurethane grades available under the following designations have been found to be suitable for preparing the blended polymer monofilaments of this invention: Ester-based types: Texin 445D (a trade mark of Mobay) Elastollan C95 (a trade mark of BASF) Pellethane 2102-80AE (a trade mark of Dow Chemical) Ether-based types: Texin 990A (a trade mark of Mobay) Pellethane 2103-80A (a trade mark of Dow Chemical).
• the amount of stabilizer used can thus range from none at all, up to a maximum of about 5% of the total weight, beyond which no further improvement appears to be observed. Where a stabilizer is used, it seems that below about 0.3% the amount of protection given is minimal. We therefore prefer to use the stabilizer in a range of from about 0.3% to 5.0%, with a preferred range being from about 0.7% to about 3%.
• the stabilizer is conveniently incorporated into the blend by way of a "masterbatch" made up in either the thermoplastic polyurethane or the polyester.
• Stabaxol KE7646 (a trade mark of Rhein Chemie)
• Stabaxol P100 (a trade mark of Rhein Chemie)
• Hytrel 10MS (a trade mark of Dupont).
• the monofilaments can be surface coated as produced, for example with a combined antistatic agent and lubricant, to facilitate handling and weaving. Generally speaking such coatings are removed very quickly when the fabric gets used in a paper making machine.
• PET is used to denote polyethylene terephthalate
• TPU is used to denote thermoplastic polyurethane. Where necessary, the TPU is identified as being ether-based or ester-based.
• the PET used was a Du Pont product, sold under the description "Merge 1934". Generally, this material was dried before use, and also post-condensed in the solid state to ensure that the intrinsic viscosity is within the desired range. Similarly, the TPU material was also dried before use. In all cases, the nylon was nylon 66.
• Examples also utilize monofilaments prepared from the specified polymers. Where relevant, the dimensions of these monofilaments are given. Generally, the monofilaments used in forming fabrics will have a size within the range of from about 0.1 mm to about 0.9 mm, and most often in the range of from about 0.127 mm to about 0.4 mm. It should also be noted that the monofilament is not necessarily of circular cross section, and particularly may be in the form of a rectangle or ribbon.
• lengths of monofilament strands are initially weighed and then wound in a single layer around one end of a polyethylene rod.
• a polyester control monofilament is wound around the other end.
• the rod is then mounted on the lower end of a vertical shaft, at right angles to it, so as to immerse the two windings in a slurry of 57% by weight of No. 24 grit sand in water.
• the shaft is rotated by a motor drive above the tank containing the slurry.
• the strands are removed from the slurry, unwound, dried, and weighed.
• the abrasion resistance is determined by calculating the percentage weight loss.
• the time and shaft rotation speed are chosen to give measurable results.
• the abrasion resistance of degraded samples is determined in the same manner after the coils of monofilament have been immersed in solutions of controlled pH and temperature for varying lengths of time.
• Example Composition Exposure % Weight Loss A7 64% PET + 36% TPU 71°C for 21 days 2.3 A8 64% PET + 36% TPU 88°C for 7 days 2.3 A9 64% PET + 36% TPU 100°C for 3 days 2.7 A10 62% PET + 37% TPU + 1% Stabilizer 71°C for 21 days 1.2 A11 62% PET + 37% TPU + 1% Stabilizer 88°C for 7 days 1.2 A12 62% PET + 37% TPU + 1% Stabilizer 100°C for 3 days 1.4
• Example Composition Exposure % Weight Loss A13 66% PET + 34% TPU 100°C for 3 days 2.5 A14 73.2% PET + 26% TPU + .8% Stabilizer 100°C for 3 days 1.9 A15 71.8% PET + 26% TPU + 2.2% Stabilizer 100°C for 3 days 1.9
• TPU was Pellethane 80AE and the stabilizer, Staboxyl KE7646.
• a fabric sample is held under tension against the outer surface of a drum comprised of ceramic segments rotating in a horizontal plane.
• a jet of water is continuously applied to the entrance nip of the fabric on the drum so as to keep the fabric and ceramic surface wet.
• the thickness of the fabric is measured at the beginning of the test and thereafter at predetermined times after exposure to the rotating ceramic segment surface.
• the loss of thickness is a measure of abrasion resistance.
• a series of double layer fabric samples were woven with warps of .16 mm diameter at a mesh count of 59/cm.
• the bottom, or machine side set of wefts were woven using PET, alternating PET/nylon, and 75% PET/25% TPU blend. In each case the weft count was 51/cm. All of these samples were woven with a paper side weft diameter of 0.19 mm and a machine side weft diameter of 0.30 mm. All of the samples were heat set identically.
• the results of abrasion tests in which the machine side of the fabric was in contact with the drum are given in the following table.
• the abrasion resistance of fabric samples with blended monofilaments having different concentrations of PET and TPU woven in the bottom layer of a composite fabric was measured.
• the upper mesh count was 25/cm, the lower mesh count 12.5/cm.
• the rectangular-section upper and lower warps were 0.11 mm by 0.19 mm, and 0.19 mm by 0.38 mm respectively.
• the wefts were PET monofilaments, with the upper weft having a diameter of 0.18 mm and the lower weft having a diameter of 0.30 mm.
• a 0.14 mm PET weft binder strand or tie strand was used in all cases.
• the bottom layer of the fabric was in contact with the drum.
• Example Composition Thickness Loss in Millimeters after 75 Minutes B4 100% PET Control .0188 B5 84% PET + 16% TPU .0152 B6 75% PET + 25% TPU .0137 B7 65% PET + 35% TPU .0119 B8 Alternating PET/Nylon 66 .0124
• the TPU used was Texin 445D, and the PET was DuPont Merge 1934, post-condensed in the solid state.
• Forming fabrics are often subjected to cycles of drying and wetting. For example, they are delivered dry to the paper mill and become saturated with water shortly after the paper machine is run to make paper. During its life time a forming fabric may be dried out several times at maintenance shut-downs or week-ends. A forming fabric with a large proportion of nylon monoflaments in the cross machine direction will then suffer from changes in width. In cases where the polyester and nylon monofilaments lie in two separate layers, the forming fabric will curl badly at the edges due to the differential expansion or contraction of the two layers. This behaviour limits the use of nylon monofilaments to 50% of the total cross machine direction filaments.
• the following table shows the length changes occurring in monofilaments made from nylon, polyester, and the blended monofilaments of this invention when subjected to a cycle of wetting (boiling in water) and then drying out. Measurements of length were made at room temperature immediately after the wetting or drying.
• a commonly used measure of crimpability of the weft strands in forming fabrics is the so-called crimp differential.
• the warp monofilaments in the final cloth tend to be straighter than the weft monofilaments, which, to a degree, are simply bent over and under the warp monofilaments.
• the weft monofilaments therefore tend to lie proud of the warp monofilaments, particularly on the machine-side of the fabric. But if the weft is a very stiff monofilament, then it will tend to bend the warp monofilament and thus not lie so proud of the warp.
• the crimp differential By careful measurement of the cloth thickness, it is possible to determine how far the weft thread is out of the plane of the warp threads. This difference in the warp and weft planes is known as the crimp differential. As the crimpability of the weft monofilament increases, so also does the crimp differential, in any given weave construction.
• Example Weft Strand Crimp Differential (mm) D1 0.30 mm PET .014 D2 0.30 mm PET alternating with 0.30 mm nylon .012 D3 0.30 mm 75% PET/25% TPU blend .017
• PET-TPU monofilaments have very high crimpability compared to polyester, whereas nylon has lower crimpability.
• the blended PET and TPU are the same as for Example E5, below.
• the mechanical stability of a forming fabric is assessed by measuring its resistance to stretching and narrowing.
• a sample of cloth 25.4 mm long and 50 mm wide is mounted in an Instron (trade mark) tensile tester.
• the load and elongation are recorded as the tension of the sample is increased from zero to 7.16 kg/cm.
• Stretch resistance is derived by measuring the slope of the load-elongation curve. This defines the elastic modulus of the cloth, which for forming fabrics is typically from about 1,100 to about 2,000 kg/cm.
• Narrowing resistance is measured on the same sample, mounted in an Instron, except that the reduction in width is accurately determined as the sample tension is increased from zero to 7.16 kg/cm.
• a narrowing resistance factor is found by dividing the observed width change, expressed in percent, by the total increase in tension. Typical narrowing resistance factors for forming fabrics are .005%/kg/cm to .050%/kg/cm.
• the PET is Dupont Merge 1934, post-condensed in the solid state, and the TPU was Texin 445D.
• the higher molecular weight PET provides a filament with a slightly better abrasion resistance than that of the lower molecular weight PET. Both filaments have significantly better abrasion resistance than the PET control monofilaments. Thus it appears that the molecular weight of the PET is not the critical factor in determining the abrasion resistance of PET-TPU blend monofilaments.
• the polyester and polyurethane resin beads are first dried, then mechanically mixed and loaded into an extruder hopper, which feeds a single screw extruder.
• the desired amount of stabilizer, if used, is also added, conveniently as a master batch or concentrate in either the polyester or the polyurethane.
• the amount of polyester or polyurethane added with the stabilizer is taken into account in determining component quantities.
• the melting and intimate mixing of the resin mixture takes place as the screw conveys the molten mixture forward through a heated barrel at a temperature of about 275°C.
• the molten polymer blend is conveyed to a metering pump which forces the mixture through a die to form monofilaments.
• the extrusion temperature may range from 260° to 285°C, with the range 265° to 275°C being preferred.
• the monofilaments are quenched in a water bath to form solid filaments. These are drawn at elevated temperatures of up to 100°C between a set of draw rolls to a draw ratio of from 3.0:1 to 4.5:1, and optionally further drawn at a higher temperature of up to 250°C to a maximum draw ratio of 6.5:1 and allowed to relax up to about 30% maximum whilst heated in a relaxing stage.
• the finished cooled monofilaments are then wound onto spools.
• the monofilament of the present invention was produced according to the foregoing process.
• a typical example is as follows.
• the extruder die had eight .80mm holes.
• the final monofilament size was .30mm.
• the monofilament was quenched in a water bath at a temperature of 66°C, positioned 2.0 cm under the die.
• the quenched monofilament was drawn in a hot air oven at a temperature of 74°C with a draw ratio of 3.36, drawn further in a hot air oven at a temperature of 230°C to a total draw ratio of 5.0 and allowed to relax 25% at a temperature of 280°C.
• the finished monofilament was then taken up on spools for testing.
• a similar monofilament was prepared using 73% polyester, 26% polyurethane, and 1% stabilizer.
• polyester resin was extruded into a monofilament using the same extrusion conditions described for the polyester-polyurethane blend.
• the physical properties of the three materials were tested and the results are given below.
• Elastic Modulus kg/meter2 0.70 x 109 0.40 x 109 0.44 x 109 Shrinkage at 220°C 10.5% 7.9% 13.6
• Abrasion Resistance * 3.2 1.8 1.8 * As measured by weight loss, according to the method previously described, %.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Paper (AREA)
• Artificial Filaments (AREA)
• Woven Fabrics (AREA)

Applications Claiming Priority (2)

Publications (4)

Family

ID=23264361

Family Applications (1)

Country Status (4)

Cited By (9)

Families Citing this family (3)

Citations (4)

• 1989
  • 1989-08-17 AT AT89115192T patent/ATE115211T1/de not_active IP Right Cessation
  • 1989-08-17 EP EP89115192A patent/EP0387395B2/de not_active Expired - Lifetime
  • 1989-08-17 ES ES89115192T patent/ES2064400T5/es not_active Expired - Lifetime
  • 1989-08-17 DE DE68919827T patent/DE68919827T3/de not_active Expired - Lifetime

Patent Citations (4)

Also Published As

Similar Documents

Legal Events