NO864926L - NEW SYNTHETIC WATER DISPERSIBLE FIBER. - Google Patents

Abstract

Water-dispersible synthetic fiber of scalloped-oval cross-section to promote dispersibility, and so better uniformity, softer feel and more opacity to the resulting wet-laid fabrics.

Description

The technical area

This invention relates to a new synthetic, polymeric, water-dispersible fiber, especially of poly(ethylene terephthalate), and its production.

The background of the invention

There has been increased interest in recent years for water-dispersible synthetic fibres, especially for polyester fibres. Such a water-dispersible fiber is used for various "non-woven" purposes, including papermaking and wet-laid non-woven fabrics, occasionally as part of a mixture, often with large amounts of wood pulp, or fiberglass, but also for purposes that only require polyester fiber, i.e. .unmixed with other fibres. This application and the requirements for it are completely different from the previous more common application as rope or staple fiber for conversion into textile yarn for end use in woven or knitted fabrics, due to the necessity of dispersing this fiber in water instead of converting the fiber into yarn, e.g. by such processes as carding, e.g. within the cotton system. It is this requirement for water dispersibility that separates the area of the invention from the previously more common polyester staple fiber.

Most such water-dispersible polyester fibers are poly(ethylene terephthalate) and are manufactured in substantially the same general manner as conventional textile polyester staple fibers, except that most water-dispersible polyester fibers are not crimped, whereas any polyester staple fiber for use in textile yarns is generally crimped while in place in the form of a rope, before conversion to staple fiber. Thus, water-dispersible polyester fibers have generally been produced by melt-spinning the polyester into filaments, combining the filaments to form a rope, drawing, applying a suitable coating to impart water-dispersible properties, generally in the same manner as a finish is applied to a rope of ordinary textile filaments,

and then, generally without any ripple (or with the addition of only a few weak waves in some cases to give extra bulk and a three-dimensional base mass),

conversion of the rope into staple. Certain earlier polyester staple fibers have been produced in an uncrimped state, e.g.

for use as fluff in bulk materials, but for such use water dispersibility has not been necessary.

Polyester fibers are naturally hydrophobic so that it is necessary to apply a suitable coating to the polyester, as described by Ring et al. in US Patent No. 4007083, Hawkins in US Patent Nos. 4137181, 4179543 and 4294883, and Viscose

Suisse in British Patent No. 958350, to overcome the inherent hydrophobicity of polyester fibers without foaming or causing the fibers to flocculate. It is this coating that has separated water-dispersible polyester fibers from more common polyester staple fibers rather than any inherent characteristic feature of the polyester itself or of its shape, such as the cross-section. To the best of our knowledge, the cross-section of all commercial water-dispersible polyester fibers to date has been round. In reality, the cross-section of most commercial polyester staple fibers has generally been round because this has been preferred.

Although most synthetic polymeric water-dispersible fibers to date have been made from polyesters which are inexpensive and available in large quantities, increasing amounts of polyolefins and polyamides are beginning to be used for water-dispersible fibers, and thus the invention is not limited only to polyesters, but covers other synthetic polymers.

Summary of the invention

According to the present invention, new synthetic, polymeric, water-dispersible fibres, especially polyester fibres, are provided, characterized in that the fibers have a round-tagged-oval cross-section.

A round-tagged-oval cross-section has so far been used for other polyester fibers, as described here. Apart from the cross-section, the water-dispersible fibers according to the invention can be essentially the same as previous water-dispersible polyester fibers or other synthetic polymer fibers, even if the advantages described later may allow for further modifications. The invention will be described below with special reference to polyester fibres, although it will be understood that other synthetic polymers, such as polyamides and polyolefins, can also be used.

The fibers according to the invention can be conveniently produced by melt spinning and drawing polyester filaments with a suitable denier per filament (dpf) and on these to apply a suitable coating to give water-dispersible properties. The filaments are then generally cut into staples of any desired length for the intended end use.

The use of a round-tagged-oval cross-section for the water-dispersible fiber according to the invention has surprisingly been shown to promote dispersibility compared to a round cross-section, and this gives the obtained wet-laid fibers better uniformity, a softer grip, stronger opacity and good permeability, which will be evident from the example.

Brief description of the drawings

Figure 1 shows a round-tagged-oval cross-section for one

stylized fiber according to the invention.

Figure 2 shows a typical spinning nozzle opening for spinning filaments according to the invention.

Description of the invention

As indicated above, a round-tagged-oval cross-section has already been used for more common polyester staple fibers which have been spun into filaments and drawn, sheared, converted into spun yarn and used in woven or knitted textiles. Such fibers have not had the water-dispersible properties necessary according to this invention. In a similar way, polyester filaments with a round-tagged-oval cross-section are already known from Gorrafa US patent no. 3914488 which proposed use in fur-like textiles. Oriented polyester filaments with a round serrated-oval cross-section have also been described in Frankfort et al. in US patent no. 4134882 and 4195051, in that they have been produced by spinning at a very high speed (5486 m/min), since these high speeds will also be able to be used for the production of oriented polyester filaments as a substrate for this apply a suitable coating to impart water-dispersible properties and thereby obtain water-dispersible fibers according to the invention. Also, Franklin, US Patent Application 664,803 filed October 25, 1984, proposes partially oriented filaments of round-tagged-oval cross-section for use as feed yarns for draft texturing. Nothing within this state of the art relates to the area of the present invention. The polyester filament substrates for the production of the water-dispersible fibers according to the invention can, however, be produced by the methods described there or by suitable modifications thereof or by other known methods for the production of polyester filaments with a non-round cross-section.

Gorrafa US patent no. 3914488 and Franklin US patent application 664803 describe parameters for a round-tagged-oval cross-section, and Figure 1 is essentially as shown there. The round-tagged-oval is essentially oval in shape with a significant difference between the major and minor axis lengths and is significantly different from previously known round and multilobed filaments in this respect so that it would be misleading here to consider all four rounded parts of the round-tagged-oval as lobes (which Gorrafa did) taking into account the terminology used in other prior art for symmetrical, multi-lobed cross-sections. However, preferred dimensions, essentially as described by Gorrafa and by Franklin, can be characterized as follows: Referring to Figure 1, the cross-sectional shape of the fibers can be determined from a photomicrograph of the fiber cross-section.

The length of the cross-section along the main axis X is indicated by A, which is also 2R, i.e. the encircling radius of the cross-section. The width of the cross-section along the minor axis y is indicated by B. The ratio between the length and width of the cross-section is

A/B.

During melt spinning of filaments, the polymer tends to flow so that smooth curves or combinations of smooth curves and straight lines are obtained in the periphery of the cross section. For measurement purposes, the periphery can be considered as composed of straight lines and arcs of circles. When applying this principle, filaments according to the invention have a flap arranged at each end of the cross-sectional main axis, the extreme part of the flap forming an arc of a circle and preferably more than a semicircle. The radius of each tab tip is indicated by r^. Likewise, at each end of the minor axis Y of the cross-section, another arc occurs whose radius is indicated by r^-Although Figure 1 shows the centers of curvature for both arcs at the same point on the minor axis, this is not of significant importance. The centers of curvature may be separated, for example as described by Gorrafa. The tip radius ratio for the lobes on the major axis is r^/R and for the extremities of the minor axis r~/R.

Another distinctive feature of the cross-section is the distance d which is the distance between two serrations measured across the main axis of the fiber cross-section, as described by Gorrafa and by Franklin.

The dimensions are preferably approximated within the following ratios: - the ratio between length and width A/B for the cross section from 1.4 to 2.4, the tip radius ratio r^/R for the tabs on the main axis between 0.20 and 0.45, and the tip radius ratio r ^/R on the minor axis from 0.8 to 2.1 times the tip radius ratio r^/R. The cross-section must be correctly tagged to provide the desired properties according to the invention. For this reason, the ratio d/2r^ is preferably from approx. 0.6 to 1.0.

Although the above features may seem complicated, they are quite easy to measure on enlarged photomicrographs of cross-sectional views.

The manufacture of the polyester staple fiber is otherwise conventional and includes the steps of melt spinning the polymer into filaments, gathering the filaments into a rope, drawing the rope and applying a suitable water dispersive coating to impart characteristics. If low shrinkage is desired, the drawn filaments are generally heat relaxed.

Selection of a suitable coating to promote water dispersibility is important, and more of such a coating is generally required than for comparable weights of round cross section fibers with similar dpf due to the greater surface area of the round serrated-oval cross section periphery. It is particularly important to provide good boundary lubrication properties. For this reason, an ethoxylated coating is preferred.

Suitable coatings are described in Hawkins, US patents

Nos. 4137181, 4179543 and 4294883, and also in the pending US patent application 721344, filed concurrently herewith and in the name of van Issum and Schluter. which describes the use of a synthetic copolyester of poly(ethylene terephthalate) units and poly(oxyalkylene) of groups derived from a poly(oxyalkylene) glycol with an average molecular weight within the range from 300 to 6000, as described e.g. in Mclntyre et al., US Patent Nos. 3,416,952, 3,557,039 and 3,619,269, herein incorporated by reference. Other useful segmented copolyesters are disclosed in Raynolds, US Patent No. 3981807. All of these disclosures

is herein incorporated by reference.

Such polyester fibers are generally first produced in the form of a continuous, filamentous, uncrimped tow or the filaments, if additional bulk is required and a more three-dimensional matrix, can be provided with slight wave-like undulations by a gentle crimping-type process, and the uncrimped or slightly wave-like filaments are cut to the desired cut length, ie to form the water-dispersible fiber, which is generally sold in the form of bales, or other packages of cut fiber. Suitable cut lengths are generally from approx. 5 to approx. 90 mm, generally up to 60 mm, and with a ratio length/diameter (L/D) from approx. 100:1 to approx. 2000:1, preferably from approx. 150:1 to approx. 2000:1, in that it is an advantage of the invention that good behavior has been achievable with preferred water-dispersible fibers according to the invention with a ratio L/D that is higher than what we have considered satisfactory for known water-dispersible polyester fibers. For example, machine manufacturers have generally recommended that the ratio L/D should not exceed 500:1, and a number of operators have considered even this figure to be unrealistically high. A suitable denier per filament is generally from approx. 0.5 to approx. 20. The coating is generally present in an amount from approx. 0.04 to approx. 1.0% of the fiber's weight (OWF%), and it is an advantage that smaller amounts can generally be used than what we have considered satisfactory according to the state of the art.

There is also provided a method for the production of such water-dispersible polyester fibers, comprising the steps of melt-spinning the polyester into filaments of round serrated-oval cross-section, forming a rope of such filaments, stretching and then coating the filaments in the rope with such a synthetic copolyester and, to the right time, ■ conversion of such coated filaments into staple fibres.

The coating is preferably cured on the filaments by heating the coated filaments or, if desired, the obtained staple fiber to a temperature of from approx. 100°C to approx. 190°C to improve durability.

The invention is further illustrated in the example below in which all parts and percentages are based on weight if nothing else is stated and in which OWF

are (solids) "by the weight of the fiber". Reference is made to several measurements of yarn properties, such as tensile properties (tenacity and elongation at break) which are measured in accordance with the methods described in Frankfort et al. US patent no. 4134882. It will be understood that other conditions may be used, e.g. other opening designs, such as those shown by Gorrafa, US Patent No. 3914488.

Example

The following fibers, Fiber A, a comparison with a round cross-section, and Fiber X, a fiber according to the invention with a round-tagged-oval cross-section, were both spun from poly(ethylene terephthalate) with an intrinsic viscosity of 0.64 and containing 0.3% TiO 2 as a anti-glare agent.

Fiber A was spun at 1463 m/min into filaments with conventional radial air quench using a 900 hole spinneret with round holes having a diameter of 0.381 and a capillary length of 0.762 mm, a 270°C block and polymer throughput of 30.9 kg/ hour. Denier per filament was 3.67. The fiber A was then oriented by passing it over a set of feed rollers at 26.8 m/min, followed by a set of draw rollers at 73.1 m/min and delivered to a conveyor by draw rollers at 73.2 m/min. Between the feed roll sections, the filaments were treated in a 45°C water bath. Between the feeding and stretching rollers, the rope was showered with water at 98°C. A commercial water-dispersible coating agent (50/50 mixture of potassium salt of mono- and diacid phosphate esters of lauryl alcohol/tallow alcohol ethoxylated with 25 moles of ethylene oxide) was applied between the stretching and drawing rolls. The filaments were then relaxed freely in an oven at 150°C for 6 minutes.

Fiber X was prepared in a similar manner to item A except that 1054 filaments of 2.98 dpf and round-tagged-oval cross-section were spun through capillaries as shown in Figure 2 with a block temperature of 27 4°C and a throughput of 30.4 kg /hour. Roll speeds for the orientation were feed rolls 31.2 m/min, draw rolls 73.3 m/min and pull rolls 72.3 m/min, and a higher concentration of water dispersible coating was used to counteract the round serrated ovals approximately 13% higher surface area .

Cross sections for Fiber X had dimensions within the following average ratios: A/B = 1.57, r^/R=0.38, r2/R=0.42 and d/2 r]L=0.83.

The properties of the drawn, coated filaments are compared in Table 1.

Both types were cut to form water dispersible fibers with cut lengths of 6.35, 9.53, 12.7 and 19.05 mm and were tested on a Fourdrinier inclined wire machine. Fibers were dispersed for three minutes in a small dissolver at 0.75% consistency (kg fiber per 100 kg slurry or batch). The cylindrical dissolver had a diameter of approx. 0.9 m and a depth of approx. 1.8 m. Fibers were then mixed with unrefined sulphite pulp to form a 50% polyester blend and diluted to 0.1% consistency in a 10m storage tank. This supply was further diluted in the machine's inlet box to 0.0143% consistency and converted into a 0.5 meter wide, wet-laid, non-woven web at 20 m/min.

A shower of an acrylic binder, Acronyl 240 D, was applied to the end of the Fourdrinier wire. The web was then cured in a dryer with flowing air at 150°C. The finished web weighed an average of 40 g/m2.

The dispersion quality can be judged from the evenness of the web produced from a given sample. As the cut length increases, the evenness of the path can generally be expected to suffer considerably. However, greater advantages can be obtained by using a longer fiber because, for example, the abrasion resistance of the web increases. In practice, therefore, a textile manufacturer will generally want to use the longest fiber that will satisfy his uniformity standards. A longer fiber with improved or equivalent uniformity would thus be preferred. Textile samples from Fibers A and X were independently shown to a panel of 10 people (equally favored between men and women) who were asked to rank the textiles in terms of visual smoothness, with the results shown in Table 2, the smoothest was ranked with 1, i.e. the lowest score.

It appears that each round-tagged-oval fabric (X) gave better points, i.e. that due to fabric uniformity it was preferred over its round counterpart with the same cut length. The 12.7mm Item X was actually preferred, by a small margin, over its significantly shorter 9.53mm counterpart Item A.

A common defect for wet-laid, non-woven webs is that two clumps of fibers are connected to each other via a single overlength. These defects are called manuals or, if they have a single end, lumps. The number of

such defects were determined for known weights of fabrics for all cut lengths of both fibers. On average, item X, the round-tagged oval, had 44% fewer defects/100g of fabric than the control. This could possibly be due to it

fiber bending module's asymmetric nature which limits the freedom of long round-oval fibers to react to eddies in the wake.

Standard physical properties were measured for the set of textiles at the Herty Foundation, Savannah, GA. Whenever compared to Fiber A as 100%, Fiber X had the following average properties:

On balance, the item X showed advantages in the important areas of higher opacity and higher abrasion resistance, with smaller sacrifices in abrasion resistance and bulk. The textiles of object X also exhibited a pleasingly soft grip.

When they have been used together with the suitable water-dispersible coating agent in the correct quantity, the fibers according to the invention with round-tagged-oval cross-section have produced a textile product with exceptional dispersion evenness, opacity and soft grip.

Fabrics made from 80%/20% blends of kraft pulp with similar round serrated-oval water-dispersible fibers, with a different coating, have consistently shown better opacity than fabrics with varying weights of round cross-section polyester fibers.

Based on theoretical considerations, it was to be expected that water-dispersible fibers with a regular round cross-section would have produced more uniform dispersions and therefore more uniform wet-laid webs. This is because the surface energy required for

to disperse a fiber (or other objects) is given by: Energy = (Surface tension) x (Dispersed surface area -

Undispersed surface area).

The undispersed fiber occurs in sticks or clumps of several hundred fibers, most of which are located on the inside of the sticks. The undispersed surface area is therefore negligible compared to the dispersed area, and the energy expression can be expressed approximately as: Energy: (Surface tension) x (Number of fibres) x (Surface area of a fibre).

This energy expression describes both the energy required to disperse the fiber and the free energy driving force for reagglomeration. For any given coating and fiber dpf, it was therefore to be expected that fibers with a lower area would give a more uniform dispersion and thus a more uniform fabric. The smallest surface area per unit weight for a given fiber occurs when the cross-section is round, which would therefore be expected to be preferred.

However, these gave roundtag<g>et-oval fibers despite an approx. 15% larger surface area surprisingly smoother

without limiting the invention to any theory, this may be due to the hydrodynamic shape of the fiber which will be able to more effectively utilize the energy available in the shear field of the mixer.

Claims (20)

1. Water-dispersible, synthetic polymer fiber, characterized in that the fibers have a round serrated-oval cross-section. 2. Fiber according to claim 1 with a cut length of from 5 to 90 mm, and in which the length/diameter ratio is from 100:1 to 2000:1. 3. Polymer filaments substantially as claimed in claim 1, except that they are in the form of a continuous, filamentous, uncrimped rope. 4. Water-dispersible polyester fiber, characterized in that the fibers have a round-tagged-oval cross-section. 5. Fiber as claimed in claim 4, wherein the denier is from 0.5 to 20. 6. Fiber as claimed in claim 4, with cut length from 5 to 90 mm. 7. Fiber as claimed in claim 6, in which the length/diameter ratio is from 100:1 to 2000:1. 8. Water-dispersible fiber as claimed in claim 7, in the form of a package of chopped fiber. 9. Water-dispersible fiber as claimed in claim 1, in the form of a package of chopped fiber. 10. Polyester fiber according to claim 4 consisting essentially of poly(ethylene terephthalate). 11. Water-dispersible poly(ethylene terephthalate) fiber as claimed in claim 4, wherein the fiber is substantially uncrimped with a cut length of from 5 to 90 mm, a length/diameter ratio from 100:1 to 2000:1 and with a denier from 0 .5 to 20, and an ethoxylated water-dispersing coating is present in an amount of from 0.04 to 1.0% of the total weight of the fiber. 12. Water-dispersible fiber as claimed in claim 11, in the form of a package of chopped fiber. 13. Polyester filaments substantially as claimed in claim 11, except that they are in the form of a continuous, filamentous, uncrimped rope. 14. Polyester fiber according to claim 4, coated with a water-dispersing coating consisting essentially of a segmented copolyester of repeating poly(ethylene terephthalate) units and poly(oxyalkylene) groups derived from a poly(oxyalkylene) glycol with an average molecular weight in the range from 300 to 6000. 15. Polyester filaments substantially as claimed in claim 14, except that they are in the form of a continuous, filamentous rope. 16. Water-dispersible fiber according to claim 1, in which the round-jagged-oval cross-section is characterized as follows: a. at major and minor symmetry axes that are perpendicular to each other, b. at a ratio between length A and width B, measured along the axes of symmetry, of from 1.4 to 2.4, c. at a flap which is located at each extremity of the main axis and which has a tip radius ratio r^ /R of from 0.20 to 0.45, where is the radius of the tip of the flap and R is the radius of a circle circumscribing the oblong cross-section, d. at a tip radius f orhold^/ R ve<^ nver extremity of the minor axis of from 0.8 to 2.1 times the tip radius ratio r^/ R for the tabs on the major axis, e. by sinking between the extremities for the main and minor axes, and f. in that the shortest distance d between two recesses on opposite sides of the main axis is from 1.2 to 2.0 times the radius r^ for the tabs on the main axis. 17. Process for the production of water-dispersible polyester fiber, comprising the steps of melt-spinning the polyester into filaments with round serrated-oval cross-section, forming a rope from such filaments, stretching the rope, coating the filaments in the rope with a segmented synthetic copolyester of repeating poly(ethylene terephthalate) units and poly(oxyalkylene) groups derived from a poly(oxyalkylene) glycol having an average molecular weight in the range of 300 to 6000, and the coated filaments are converted into fibers with a cut length of 5 to 90 mm. 18. A method as claimed in claim 17, wherein the filaments are coated with the copolyester in an amount of from 0.04 to 1.0% of their weight. 19. Method as claimed in claim 17, wherein the coating is cured on the filaments by heating the coated filaments to a temperature of from 100°C to 190°C. 20. A method as claimed in claim 19, wherein the filaments are coated with the copolyester in an amount of from 0.04 to 1.0% of their weight.