Tow multiaxial non-woven fabric, and method of making the same

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a non-woven fabric made of tows and a method of producing the same. The non-woven fabric has a great basis weight and is high in strength in all directions and can be used in manufacturing three-dimensional moulded products or as geotextile, for instance.

[0003] 2. Description of the Related Art

[0004] In one of the uses thereof, geotextiles have so far been used in the form of woven fabrics in those fields where marked strength characteristics are required, for example in embankment or soft ground reinforcement.

[0005] However, heavy weight woven fabrics can be produced only at a slow rate and require the use of yarns, which increases the cost of production thereof. From the physical properties viewpoint, they are highly strong in the machine and cross-machine directions but are weak in oblique directions at 45°. Therefore, they are not always suited for use as geotextiles, which are required to be strong in every direction. Thus, it becomes necessary to use unreasonably heavy woven fabrics. In this respect, too, increases in cost result. To achieve improvement in this respect, tetraaxially woven fabrics have been developed and the use thereof as geotextiles has been studied (“Sangyo-yo Sen'ishizai Handbook (Handbook of Textile Materials for Industrial Use)”, published 1994 by Maruzen, page 376). However, tetraaxially woven fabrics are still worse in productivity than those woven fabrics produced on ordinary weaving machines, which result in increases in cost. They are thus unsuited for use as geotextiles to which the cost is an important factor. Furthermore, woven fabrics, though high in strength but show a low extension ratio, hence their break energy (strength×extension ratio) is not so high.

[0006] When geotextiles are used in another important field, namely in soaking up water, filtration or drainage, for instance, they are required to have water permeability as an important characteristic. In this field, spunbonded non-woven fabrics and short fiber non-woven fabrics have so far been used. However, spunbonded non-woven fabrics have an average fiber diameter as large as 25 to 30 micrometers, hence their water permeability, which depends on the capillary action of fibers, is not always high. On the other hand, spunbonded non-woven fabrics produced from fibers having a reduced diameter are poor in productivity and cannot avoid increases in cost. Furthermore, the filaments of spunbonded non-woven fabrics are weak in strength, namely their strength is only about 20 mN/tex. Further, the filament alignment in such fabrics are random, hence the capillary action utilization efficiency is low. As for the short fibers non-woven fabrics, the fiber strength is as high as 100 to 200 mN/tex but the strength of the non-woven fabrics, which depends on the strength resulting from entanglement of fibers, is very low since the fibers are short fibers. Furthermore, the fiber alignment in the non-woven fabrics is random, and this is not efficient from the water permeability viewpoint.

[0007] In the above discussion, geotextiles have been taken as an example. The same may be said in solving the prior art problems in other fields where high tenacity and high break energy are required, for example roofing base cloths, carpets and flexible containers.

[0008] The present inventors have been engaged in development works to alleviate the weak strength, in oblique directions of 45°, of conventional woven fabrics and cross laminated non-woven fabrics and develop multiaxially laminated non-woven fabrics, for example triaxially and obliquely laminated or tetraaxially laminated ones (U.S. Pat. Nos. 5,308,424, 5,338,593). Since, however, these are laminates made of yarns, only coarse textures can be realized and the productivity in manufacturing products having a great basis weight is poor. Further, according to these senior inventions, the mutual bonding of yarns depends on an adhesive. This means an increased cost of production. Further, the bonding by means of an adhesive is generally weak in bond strength and the adhesive has not heat resistance and, therefore, the utility of the products is limited in many instances.

[0009] For producing non-woven fabrics having a great basis weight of 1 kg/m2, for instance, from conventional non-woven fabrics such as spunbonded non-woven fabrics or short fiber-based non-woven fabrics, it is necessary to markedly reduce the production speed. Thus, the advent of a technology of efficiently producing non-woven fabrics having a great basis weight at low cost has been desired.

[0010] Meanwhile, in the field of plastics, thermal forming of plastics sheets has moulded three-dimensional products.

[0011] Woven fabrics have no thermal formability and show a low extension ratio, so that they cannot be brought to three-dimensional products.

[0012] Some non-woven fabrics have thermal formability (Japanese Laid-open Patent Publication Nos. Sho 60-199957, Sho 60199961, and Hei 8-291457). However, they are constituted of lowly molecular oriented filaments and therefore the finished products made thereof are low in strength and dimensional stability. These are basically spunbonded non-woven fabrics, hence the productivity in obtaining products with a great basis weight is low.

[0013] Therefore, materials capable of being made into three-dimensional moulded products, such as car sheets or ceilings, office reception room sofas and the like, having a great basis weight and resembling cloths in feel and touch have been demanded in vain.

[0014] Furthermore, in the present state of society, the disposal of waste plastics such as PET bottles is not only a problem in the plastics industry but also a social problem, involving the relevant administrative agencies and distribution sectors. The present invention has an important social significance in that such waste plastics are used as raw material resins to thereby open up a road to the mass use of geotextiles and the like while efficiently utilizing waste plastics.

[0015] Further, in ordinary tow production, spun and unstretched tows are stored in boxes or cans. And, a multiplicity of unstretched tows are drawn out from a number of such cans and subjected to stretching and crimping to give product tows or to directly give short fibers upon further processing. In such a process, a large number of cans are required for storing spun and unstretched tows and for sending out them to the step of stretching. Thus, a tow manufacturing plant gives an impression of being full of such cans, and the efficiency from the plant space viewpoint is low. Therefore, a rational method of producing tows, which might appropriately be used in the practice of the invention, is demanded.

[0016] Further, opened tow-based cross laminated non-woven fabrics have also been invented which are produced by opening tows to thin webs, cross laying the webs and bonding them (Japanese Laid-open Patent Publication Nos. Sho 52-124976). However, the efficiency of opening tows is not very good. While the opening of tows may be effective in producing non-woven fabrics low in basis weight, it is not efficient in producing non-woven fabrics with a great basis weight or non-woven fabrics strong in many directions.

SUMMARY OF THE INVENTION

[0017] It is an object of the present invention to provide a non-woven fabric having desired characteristics, which cannot have been attained with the conventional woven fabrics or non-woven fabrics, as well as a method of producing the same.

[0018] To accomplish the above object, the multiaxially laminated non-woven fabric of the invention has layers each composed of a multiplicity of parallel tows having a total tex of not less than 1,000 but not more than 30,000, and each of said tows is formed of crimped filaments having an average fineness of not more than 3 tex.

[0019] The above multiaxially laminated non-woven fabric is a tow-based laminated non-woven fabric resulting from bonding by at least one of the techniques or methods (1) to (5) specified below:

[0020] (1) Needle punching, (2) stich bonding, (3) ultrasonic bonding, (4) water jet process, (5) through air method.

[0021] The above multiaxially laminated non-woven fabric shows the tensile strength at 50% elongation not less than 10 mN/tex in each of warp direction and weft direction and oblique direction at 45°.

[0022] The tows constituting the above multiaxially laminated non-woven fabric comprise tows composed of conjugate fibers or bicomponent fibers made of at least two polymers differing in softening point, and are bonded together by thermal embossing or thermal press treatment to give a tow-based laminated non-woven fabric.

[0023] Another object of this present invention is to provide three-dimensional moulded products made of the above tow-based laminated non-woven fabric.

[0024] A further object of this present invention is to provide a method of producing tow-based multiaxial non-woven fabrics according to which the step of multiaxial lamination of tows is followed by interfilament bonding or web heat treatment in a state in which oblique materials multiaxially overlaid with one another and obliquely crossing one another are held, at both side edges thereof, by pins.

[0025] A still further object of this present invention is to provide a method of producing three-dimensional moulded products made of a tow-based laminated non-woven fabric which comprises shaping or moulding the above multiaxially laminated non-woven fabric comprising conjugate fibers or bicomponent fibers made of at least two polymers differing in softening point into a three-dimensional moulded products and then subjecting the three-dimensional moulded products to heat treatment at a temperature not lower than the softening point of that non-woven fabric-constituting polymer which is lower in softening point.

[0026] The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings, which illustrate an example of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]
FIG. 1 is a schematic representation of a tow-based triaxially laminated non-woven fabric according to an embodiment of the invention.

[0028]
FIG. 2A is a schematic representation of a tow-based tetraaxially laminated non-woven fabric according to another embodiment of the invention.

[0029]
FIG. 2B is a view showing a lay pattern of a group of tows constituting the tetraaxial non-woven fabric.

[0030]
FIG. 3A is a schematic representation of a tow-based pentaaxially laminated non-woven fabric according to another embodiment of the invention, with the materials laid in the machine direction being omitted.

[0031]
FIG. 3B is a view showing a lay pattern of a group 4a of tows constituting the pentaaxial non-woven fabric.

[0032]
FIG. 4 is a graphic representation of the strength distribution at 50% elongation in a tow-based multiaxial non-woven fabric according to an embodiment of this invention in comparison with a short fibers non-woven fabric.

[0033]
FIG. 5 is a plan view illustrating the process for producing tow-based multiaxial non-woven fabrics according to an embodiment of the invention.

[0034]
FIG. 6 is a side view illustrating the process for producing two-based multiaxial non-woven fabrics according to an embodiment of the invention.

[0035]
FIG. 7 is a view illustrating an example of the process for the three-dimensional moulded products according to an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] In accordance with the present invention, non-woven fabrics produced by the technology of multiaxially laminated non-woven fabrics, namely obliquely laminated triaxial, tetraaxial, pentaaxial and further multiaxial non-woven fabrics are used. These non-woven fabrics, unlike woven fabrics or cross laminated non-woven fabrics, are characterized by comprising obliquely crossing materials.

[0037] The “triaxial non-woven fabric” or “triaxially laminated non-woven fabric” means a non-woven fabric resulting from lamination and bonding of constituent warp members (especially tows) and oblique members (especially tows) crossing the warp members in two directions crossing each other with the warp members as approximate axes of symmetry. It may also be a non-woven fabric resulting from lamination and bonding of constituent weft members (especially tows) and oblique members (especially tows) crossing the weft members in two directions crossing each other with the weft members as approximate axes of symmetry.

[0038] The “tetraaxial non-woven fabric” or “tetraaxially laminated non-woven fabric” means a non-woven fabric resulting from lamination and bonding of constituent warp and weft members and oblique members crossing the warp and weft members in two directions crossing each other with the warp or weft members as approximate axes of symmetry.

[0039] The “pentaaxial non-woven fabric” or “pentaaxially laminated non-woven fabric” corresponds to a combination of warp members and two sets of oblique members which differ in angle of crossing with the warp members in two directions crossing each other with the warp members as approximate axes of symmetry.

[0040] In the above multiaxial non-woven fabrics, it is assumed that the warp members be used in one layer. It is also possible to dispose the warp members on the front and reverse sides.

[0041] The constitution of the multiaxially laminated non-woven fabric may be that of any of those provided by the senior inventions by the present inventors (U.S. Pat. Nos. 5,308,424, 5,338,593) or that of any other non-woven fabric resulting from lamination and bonding of warp, weft and oblique members, without any particular restriction.

[0042] In accordance with the invention, tows are used as at least part of the warp, weft and oblique members.

[0043] A “tow” is defined, according to JIS (Glossary of textile terms in Japanese Industrial Standards), as a “kind of raw spinning materials and a bundle of a very large number of filaments” and, in describing the invention, the term “tow” is used in this sense and thus means “a bundle of a very large number of filaments”.

[0044] The term “filament” means an essentially continuous fine fiber and is distinct from a short fiber not more than about 80 millimeters in length.

[0045] The reason why tows are used is as mentioned below. With multiaxial laminates produced using conventional yarns, products having a great basis weight can be obtained only with poor productivity. By using tows as such as starting materials in accordance with the invention, non-woven fabrics having a great basis weight could be realized, and the non-woven fabric was found best suited for use as geotextile. The present invention provides the non-woven fabric, which has a great basis weight of not more than 500 g/m2, desirably not more than 800 g/m2, most desirably 1 kg/m2. A basis weight means a mass (g) of fabric at square meter.

[0046] In the prior art, there was no technology available of making tows directly into sheets and it was impossible to produce, from tows, heavy non-woven fabrics having a uniform basis weight distribution and showing a sufficient level of strength in every direction. Therefore, non-woven fabrics have so far been produced by using short fibers. However, the production of short fibers non-woven fabrics requires extra steps such as the steps of cutting tows and carding them and, as a result of cutting tows, the strength of fibers can never be fully utilized and the product strength disadvantageously depends on the bonding strength. On the contrary, the present invention has overcome these problems by directly using tows and has made it possible to realize heavy non-woven fabrics strong in multiple directions.

[0047] When tows are used as ordinary raw spinning materials, they have total tex of 50,000 to several hundred thousand. However, the tows to be used as oblique members in the practice of the present invention desirably have a total tex of 1,000 to 30,000, in particular 2,000 to 25,000. Tows having an excessively high total tex are difficult to handle while the special use of tows with a total tex less than several hundred is of no significance, since yarns for industrial use are in general use. In addition, tows small in total tex rather cause an increase in cost in the production of non-woven fabrics.

[0048] The tows to be used as warp members may have a total tex as high as 30,000 to 50,000. In some cases, using them in an opened form may use tows having a fineness (in tex) of 100,000 or more.

[0049] The filaments constituting the tows to be used in accordance with this invention have an average fineness of not more than 3 tex, desirably not more than 1 tex. Experiments revealed that when the single filament fineness is in excess of 3 tex and needle punching effects the bonding, for instance, without using any adhesive, webs would not be entangled to a satisfactory extent, failing to afford sufficient bonding strength.

[0050] The method of producing tows for use in the practice of the invention is not limited to the method of producing the so-called short fibers but the tows can also be prepared by stretching filaments spun from a spunbond-die, meltblow-die, flashspun-die, centrifugal spin die or the like for producing non-woven fabrics. The only essential thing is that each tow is a “bundle of a very large number of filaments”.

[0051] In the multiaxial non-woven fabric according to this invention, conjugate fibers made of at least two polymers differing in softening point or melting point or fibers differing in softening point or melting point may be used in admixture. For attaining such a form, these fibers may be contained in the tows, or another web containing these fibers may be used for lamination with a multiaxial non-woven fabric, followed by bonding by needle punching, for instance.

[0052] The term “fibers” means fibers in a broader sense of the word, including not only short fibers but also filaments.

[0053] The softening point is the temperature at which the fibers in question become soft and, at above that temperature, they begin to adhere together.

[0054] The use of conjugate fibers are effective in providing bulkiness and/or favorable touch and, further, the lower melting component acts as an adhesive component, hence can be used in bonding tow filaments or layers together by thermal embossing or thermal press treatment.

[0055] The mixing of fibers differing in shrinkage percentage is effective in realizing bulkiness or touch owing to the difference in softening point or melting point and, further, the lower softening point component fibers serve as an adhesive component and therefore can be utilized in interfilament or interlayer bonding by thermal embossing or thermal press treatment.

[0056] Generally, tows are subjected to crimping treatment so that filaments may not loosened by static electricity, for instance, but may remain entangled. In the practice of the invention, the crimping is effective not only in entanglement but also in rendering the needle punching or water jet process, for instance, efficient in the mutual bonding of filaments or laminate layers. The crimping treatment is generally carried out using a stuffing box. The techniques of conjugate crimping, edge crimping, gear crimping, three-dimensional crimping and the like are also effective.

[0057] The tows to be used in the practice of this invention are relatively small in total fineness (in tex). The productivity in manufacturing tows small in total tex is generally low in ordinary spinning processes for producing short fibers. However, by employing a tow production process in which the steps of spinning, stretching and crimping are carried out continuously, tows relatively small in total fineness and suited for use in tow-based laminated non-woven fabrics can be produced rather with good productivity and with good efficiency from the plant space viewpoint, since the space for placing a large number of boxes or cans for storing unstretched spun tows and the space for disposing a large number of boxes or cans for sending out unstretched tows to the step of stretching are now unnecessary. For realizing this process, it is necessary to stretch a group of filaments running a spinning speed of several thousand meters per minute at that speed and further to cause the filaments to crimp at that speed, hence a high-speed stretching apparatus and a high-speed crimper are required. When the stuffing box method is employed as the means of crimping, it is necessary for the stuffing box to endure that speed of several thousand meters per minutes. As the apparatus suited for that purpose, those apparatus according to prior inventions (Japanese Laid-open Patent Publication Nos. Sho 59-59931) can be used.

[0058] The step of stretching may also be carried out in the step of spinning for producing filaments from a molten polymer, by increasing the draft ratio.

[0059] In the practice of the invention, it is not always necessary that all filaments or fibers constituting the present invention be tows. When tows are used as at least part of the filaments, the intended purpose can satisfactorily be achieved in some applications. For example, it is also possible to use tows as warp members alone and use ordinary yarns as oblique members.

[0060] It is further possible to unite a tow-based multiaxial laminate according to the invention with another web, for example a spunbonded non-woven fabric, by bonding by means of needle punching, for instance. It is also judicious, on that occasion, to incorporate the other web between the warp member layer and oblique member layer. As that other web, a spunbonded non-woven fabric or the like may be incorporated as an extender for reducing the cost or increasing the thickness, a melt-blown non-woven fabric, which is constituted of ultrafine filaments and therefore can produce a filter effect may be incorporated for utilizing the filter effect, a polyvinyl alcohol or cotton non-woven fabric may be incorporated for obtaining hydrophilicity, a web having an antimicrobial or miticidal action may be used combinedly, or a woven fabric may be incorporated for dimensional stability, for instance.

[0061] Most suited as the means of interfilament or interlayer bonding in the practice of the invention is needle punching. Even for such heavy non-woven fabrics as provided by the invention, needle punching can realize bonding with good efficiency. As compared with the use of an adhesive, it has advantages: the cost is low, the non-woven fabrics will never be rendered rigid and the water permeability required of geotextiles is never impaired.

[0062] Needle punching is an effective method of bonding also for producing non-woven fabrics having a high extension ratio, which is one of the characteristic features of the invention.

[0063] Furthermore, products by needle punching are characterized by their soft feel and suave appearance, which are important factors in using the products of this invention in car seats or ceilings, office chairs and the like. For making good use of this feature, it is effective to use needles capable of attaining not only mere needle locking but also decorativeness and good feel and touch.

[0064] The means of bonding to be employed in the practice of the invention includes not only needle punching but also stich bonding, ultrasonic bonding, the water jet process, the through air method and the like. These means, too, can effect bonding without using any adhesive, hence are suited for treating heavy webs. The water jet process is a non-woven production process, which can realize bonding by water jet at high pressure. The through air is also method for non-woven production, which can realize bonding by hot air through and adhesion of bicomponent fibers.

[0065] Those multiaxial non-woven fabrics, which contain conjugate fibers or mixed fibers consisting of polymers differing in melting point may also be bonded up by such bonding means as embossing, thermal pressing or through air. In that case, it is also possible to employ the above-mentioned embossing or like means while using an adhesive web as the other web so referred to hereinabove.

[0066] These bonding means are desirably used in a state such that those oblique members of a multiaxial laminate which obliquely cross with one another are held, at both side edges, by pins after the step of multiaxial lamination of tows. By carrying out the bonding in that state of oblique members being held by pins, it becomes possible to realize the bonding without disturbing the multiaxial arrangement of tows or without disturbing the intended strength balance. Furthermore, the product width becomes constant and the basis weight fluctuation becomes slight and, accordingly, no portions become low in strength.

[0067] After the above steps of multiaxial lamination and bonding, the multiaxial laminate is desirably heat-treated in a state such that those oblique members thereof, which obliquely cross with one another, are held, at both side edges, by pins. Removing those strains caused by needle punching by such heat treatment can contribute to product stabilization. When a product has internal strains, the product may become twisted or distorted. By carrying out heat treatment in the state of oblique members being held by pins, it becomes possible to provide a non-woven fabric improved in width constancy, flatness and/or dimensional stability.

[0068] In the prior art, in carrying out needle punching, for instance, of short fiber non-woven fabrics, a woven fabric called carpet backing is often used as a backing material for attaining the above-mentioned dimensional stability and width constancy and further producing reinforcement effects. On the contrary, the present invention is also characterized in that sufficient levels of strength, dimensional stability and width constancy, among others, can be attained without using such a backing material.

[0069] The non-woven fabric of the invention is particularly suited for use as a geotextile. Geotextiles are required to have high absolute strength and break energy values and further required to be strong in every direction. Since they are buried in the ground, they are required to be as inexpensive as possible. Therefore, it is necessary to use a minimum amount of fibers as efficiently as possible. The ground, which is the target of use of geotextiles, is full of variety, differing in geographical features, containing obstacles such as stones and rocks, and/or consisting of mixed firm and soft grounds, for instance, and, therefore, it is not sufficient for geotextiles to have strength alone; they are required to have a sufficient level of extension ratio, too. The direction in which strength or tenacity is required cannot be anticipated and, therefore, they are generally required to have sufficient levels of strength and break energy in every direction. According to the invention, tows consisting of continuous fibers or filaments are directly used, so that the non-woven fabric of the invention has strength and crimps and shows a high elongation before break, hence the break energy is great. The non-woven fabric of the invention is a multiaxial one, hence is strong in every direction and thus is best suited for use as a geotextile.

[0070] Further, the multiaxial non-woven fabric of the invention is very slight in basis weight irregularity or in the content of portions low in strength or other irregularities, so that the objects of the invention can be accomplished using a minimum calculated amount of fibers, which leads to cost reduction.

[0071] The multiaxial non-woven fabric of the invention can be used as a geotextile for the purpose of reinforcement, drainage or filtration, for instance. Thus, for example, it can be used in or for soft ground improvement, packed sand drain, sandwich method, soft subgrade soil bearing capacity improvement, slope reinforcement, railway embankment, railway cobble stone stabilization, road pavement reinforcement, subgrade-base separation, and the like.

[0072] Since fine filaments are arranged continuously in each tow in the non-woven fabric of the invention, the capilarity can function effectively and the non-woven fabric is effective in removing water in drainage, separation, filtration and so forth.

[0073] The multiaxial non-woven fabric of the invention has the above-mentioned advantages from the performance and production viewpoint and therefore can be used not only as geotextile but also as roofing base cloth, carpet, car interior, flexible container base cloth, civil engineering base cloth, waterproof sheet, or machinery or furniture protecting cover.

[0074] In the case of roofing base cloth, the non-woven fabric of the invention has a great absolute value of strength×extension ratio and particularly effective in stretchable roofing base cloth (JIS A 6022, JIS A 6013).

[0075] Flexible containers are required to be greater in size and safer by recent demands for distribution rationalization. The high break energy realized by the invention greatly contributes to that end.

[0076] Carpets are required to have high functionality. The soft and high-strength non-woven fabric of this invention can be a quality product.

[0077] Further, combinations of the multiaxial non-woven fabric of the invention with another material or other materials can give bases for various applied processed goods.

[0078] Another characteristic feature of the multiaxial non-woven fabric of the invention is that the elongation at break can be increased. This owes to the fact that tows have crimps. The extent to which crimps of tows are to be retained in the multiaxial non-woven fabric depends on the tension applied to tows in the step of lamination and/or the extent of needle punching and/or heat treatment. A high elongation at break means that the break energy (strength at break×elongation at break) is great, and this is important not only in the use as geotextile or roofing base cloth, as mentioned above, but also in other applications, for example the production of three-dimensional moulded products by deep drawing.

[0079] Further, the occurrence of crimps gives not only mechanical features but also soft feel and touch and this may become a remarkable feature from the sensibility viewpoint.

[0080] The three-dimensional moulding in the practice of this invention comprises making the non-woven fabric of the invention into a three-dimensional structure by a mechanical shape-modifying action, typically by deep drawing.

[0081] The three-dimensional structure of the invention is characterized in that the moulded product is mechanically tough and, at the same time, retains the soft feel of the non-woven fabric. Another feature is that a heavy moulded product can be formed at once. In moulding thick plastics sheets, the thick sheets must be heated uniformly and this involves losses of energy and technological difficulties in uniform heating. On the contrary, in moulding the multiaxial non-woven fabric of this invention, heating is not always involved and therefore, in many instances, no heat energy is lost and no technological difficulties in uniform heating are encountered in spite of the moulding of heavy products.

[0082] The tows to be used in the practice of the invention are made of organic synthetic fibers consisting of polypropylene, polyester, polyamide, polyacrylonitrile, polyvinyl alcohol or the like. Tows made of high performance or high function fibers, such as ultrahigh strength polyethylene, aramid or polyarylate fibers, may also be used.

[0083] It is a characteristic feature of the present invention that tows spun from a main resin material recovered from waste plastics can be used as the raw material tows. The use as geotextile or the like according to the invention is free of such problems as unevenness in fineness of constituent filaments and dyeability thereof, the filament diameter is not required to be fine, and no feel or like features are required. Accordingly, waste plastics comprising various materials can be used as a raw material on condition that the material do not cause frequent filament breakage in the process of spinning. The use of waste plastics contributes to cost reduction and thus renders the non-woven fabric best suited, for example, as a geotextile to which the cost is an important factor, and serves for effective utilization of waste plastics.

[0084] As described hereinabove, the present invention has made it possible to produce, efficiently and at low cost, multiaxial non-woven fabrics strong in many directions and showing a high extension ratio, hence showing a high level of break energy in every direction, and having a high basis weight.

[0085] In this way, it has become possible for the multiaxial laminated non-woven fabric of the invention to have a markedly increased level of break energy as compared with those short fibers non-woven fabrics or spunbonded non-woven fabrics which have so far been used as heavy or thick non-woven fabrics.

[0086] The non-woven fabric of this invention is much less expensive than tetraaxial woven fabrics, which are strong in many directions and further can have an increased thickness, hence is high in absolute tenacity and in extension ratio. Making good use of such characteristics, it can be used as a tow-based laminated non-woven fabric for use as geotextile, roofing base cloth, carpet, car interior, flexible container base cloth, civil engineering sheeting base cloth or waterproof sheeting base cloth.

[0087] Since the individual filaments constituting the tow-based multiaxial non-woven fabric of the invention have crimps, the non-woven fabric can be high in extension ratio, have a soft touch and be readily changed in shape. Making good use of this high extension ratio characteristic, it is now possible to realize three-dimensional moulding, such as deep drawing and thus conduct one-piece moulding of car seats or ceilings, office chair coverings and the like.

[0088] The tow-based multiaxial non-woven fabric of the invention, when coated or impregneated with a resin or laminated with a certain sheet, can be used also as waterproof sheet or civil engineering sheet.

[0089] Now, referring to the drawings, several embodiment of this invention are described.

[0090]
FIG. 1, FIG. 2 and FIG. 3 each schematically illustrate the manner of lamination of the tow-based multiaxially laminated non-woven fabric of the invention.

[0091]
FIG. 1 shows an example of triaxial lamination. The multiplicity of tows la shown by dotted lines in the longitudinal direction are warp member tows occurring on the reverse side of a triaxial non-woven fabric, which is an example of the multiaxial non-woven fabric of the invention. The multiplicity of tows 1b shown by dash-and-dot lines is warp member tows occurring on the front side of the non-woven fabric. Tows 2a constitute one of the two groups of oblique tows, which cross obliquely with each other. Tows 2b constitute the other group of oblique tows crossing with the group of tows 2a. It is not always necessary that these members' 1a, 1b, 2a and 2b be all tows. It is sufficient if tows account for at least part thereof.

[0092] In that figure, a line for easier understanding shows the course of a certain tow. However, the tow is not a yarn but has a width. Thus, although the tow-based laminated non-woven fabric is shown as a net-like structure composed of crossing lines in the figure, the whole non-woven fabric is filled with filaments.

[0093]
FIG. 2 shows an example of tetraaxial lamination. FIG. 2A shows a mode of tetraaxial lamination. FIG. 2B shows the pattern of running of one group of tows 3a. In this FIG. 2B, one tow is shown in thick line for easier understanding of the travelling pattern thereof.

[0094] The tetraaxial laminate further comprises a group of tows 3b symmetrically crossing the group of tows 3a as well as the warp member tows 1a and 1b shown in FIG. 1.

[0095]
FIG. 3 shows an example of pentaaxial lamination. In FIG. 3A, those longitudinal warp members out of the five axial members are omitted. FIG. 3B shows the pattern of traveling of one tow of one group 4a, wherein the angles, α and β, of turning around each pin are different. The pentaaxial laminate is comprised of this group 4a, a group 4b of tows obliquely and symmetrically crossing the group 4a as well as the warp member tows 1a and 1b shown in FIG. 1. All of these materials need not be tows. Providing tow-feeding guides in multiple stages can also produce Hexaaxial and further multiaxial laminates.

[0096]
FIG. 4 illustrates the strength of examples of the multiaxial non-woven fabrics of this invention, wherein the experimental results of strength distribution at 50% elongation testing in a plane are shown in comparison with the results obtained with a short fiber non-woven fabric. The details will be mentioned later in an example.

[0097]
FIG. 5 and FIG. 6 illustrate an example of the equipment for laminating tows according to the invention. FIG. 5 is a plan view and FIG. 6 is a side view.

[0098] Referring to FIG. 5 and FIG. 6, a conveyer 12 having, along the left and right edges relative to the travelling direction thereof, pin arrays 11a and 11b for guiding tows at a predetermined pitch is going round. On the upper side of the conveyer 12, there are disposed a pair of cylindrical cams 13a and 13b parallel to each other and crossing the conveyer at right angles. As the cams rotate, a tow feeding guide 15 connected to the rail 14 between both cams by means of bearings (not shown) goes back and forth between the cams in the direction crossing the pins 11a and 11b on the conveyer 12. Another rail 16 is held on the tow feeding guide 15 by means of bearings (not shown) above the conveyer at a height differing from that of the rail 14 (guide rail), making a certain predetermined angle. The angle of crossing to tows in products can be altered according to the angle of that rail 16. When the angle is 63.5 degrees relative to the longitudinal direction of the conveyer 12, the tetraaxial lamination shown in FIG. 2 can be realized. When that angle is 90 degrees, namely when the rail is parallel to the cylindrical cams, the triaxial lamination shown in FIG. 1 can be realized. For the tetraaxial lamination shown in FIG. 2, one more pair of tow feeding guides 20 are required and, in this case, a rail 21 is disposed at an angle of −63.5 degrees, which is symmetrical to the angle of the rail 16. These two feeding guides 15 and 20 have a number of thin guide tubes 17 and 22, grespectively. The rotation of the cylindrical cams 13 and 18 and of a nip roll 24 is controlled in synchronization with the conveyer 12 driven by a motor 23.

[0099] A multiplicity of tows stored in a number of boxes (cans) are sent out, adjusted with respect to tension and fed, as tows 25, 26, to the multiaxial overlaying machine. The tows are distributed into the tow feeding tubelets 17 and 22, respectively. The respective tows fed to the two feeding tubelets 17 and 22 on the tow feeding guides 15 and 20 shuttling to and fro crossing above the conveyer are held by the right and left pins 11a and 11b on the conveyer and the tows are intersectingly overlaid on the conveyer.

[0100] A large number of tows 28 and 29 are fed from cans 27a and 27b as warp members. Tows 28 of one group are placed side by side on the conveyer, while tows 29 of the other group are fed onto the group of cross-overlaid tows. The group of cross-overlaid tows is sandwiched between the groups of tows 28 and 29 by means of the nip roll 24. The groups of tows thus overlaid are subjected to needling on a needle-punching machine 30 in a state such that the group of cross-overlaid tows is held by the arrays of pins 11a and 11b. The subsequent heat treatment on a hot air heat treatment apparatus 31 gives a tow-based multiaxially laminated non-woven fabric 32.

[0101] Another non-woven fabric, such as a short fiber non-woven fabric or spunbonded non-woven fabric, may be laid between those two groups or on the surface thereof and integrated with the tow-based multiaxial laminate by needle punching, for instance. When, in that case, the other non-woven fabric contains fibers lower in softening point in the form of conjugate fibers or mixed fibers, then the three-dimensional product obtained by moulding can maintain its three-dimensional shape as a result of fusion of the low-softening component.

[0102]
FIG. 7 illustrates an example of the production of a three-dimensional moulded product.

[0103] On a conveyer 41, there are sections 42a and 42b of the multiaxial non-woven fabric of the invention as cut to a predetermined size. They travel while being heated by infrared heaters 43a and 43b. A thus-heated non-woven fabric 42c is placed on a mold 45a of a press 44 and press-formed between the mold 45a and a countermold 45b, to give a three-dimensional moulded product 42d. In this case, it is desirable that the multiaxial non-woven fabric 42 contains low-softening fibers.

[0104] When the molds 45a and 45b of the press 44 are each equipped with a heater and can heat the laminate, the heating by means of the heaters 43 can be omitted. In some cases, the laminate can be moulded by press treatment alone while omitting the heating.

[0105] In the following, typical examples of the invention are described together with a comparative example.

EXAMPLE 1

[0106] The equipment shown in FIG. 5 and FIG. 6 was used. The distance between the pin arrays 11a and 11b was 40 mm, the angle of the rail 16 relative to the machine direction was 90 degrees and the second tow-feeding guide 20 was not used. Tows having a total tex of 5,500 (50,000 denier) and composed of filaments having an average fineness of 0.66 tex (6 denier) as produced by spinning of pellets recovered from waste PET bottles, followed by stretching and crimping, were used as the raw material. The tows were crosswise overlaid, the warp tows were fed to above and below the layer of cross overlaid tows at a pitch of 40 mm to thereby sandwich the layer of cross overlaid tows. The subsequent needle punching and heat treatment at 185° C. gave a triaxially laminated tow-based non-woven fabric (weighing 0.95 kg/m2 and 3.2 mm in thickness).

[0107] Table 1 shows experimental results of example 1.

1TABLE 1Strength atStrength50% elongationExtension ratioBreak energymN/texmN/tex%% · mN/texWarp direction46.730.172.53385.8At angle of 15°46.924.788.93636.0At angle of 30°38.721.892.13564.3At angle of 45°37.524.691.63435.0Weft direction40.228.895.43835.1

[0108] The methods of measuring the above properties are as follows. Samples, 30 cm in length and 10 cm in width, are cut out for each angle. The tenacity of the samples are determined by carrying out tensile testing at a test specimen width of 10 cm, a testing length of 10 cm and a pulling rate of 100% per minute. The strength of the samples is calculated by dividing the tenacity value by the fineness (in tex) calculated from the sample weight. The number of test specimens is 5 for each direction.

[0109] The above test results of the strength at 50% elongation shown in FIG. 4 by open circle marks.

EXAMPLE 2

[0110] The equipment shown in FIG. 5 and FIG. 6 was used. The distance between the pin arrays was 40 mm, the angle of the rail 16 relative to the machine direction was 63.5 degrees and the second tow-feeding guide 20 was also used at an angle of −63.5 degrees between the second rail 21 and the machine direction. Tows having a total tex of 5,500 (50,000 denier) and made of filaments having an average fineness of 0.66 tex (6 denier) as produced by spinning of pellets recovered from waste PET bottles, followed by stretching and crimping, were used as the raw material. The tows were crosswise overlaid, the warp tows were fed to above and below the layer of cross overlaid tows at a pitch of 40 mm to thereby sandwich the layer of cross overlaid tows. The subsequent needle punching to the same extent as in Example 1 and heat treatment at 150° C. gave a tetraaxially laminated tow-based non-woven fabric (weighing 1.05 kg/m2 and about 3.5 mm thickness).

[0111] Table 2 shows experimental results of example 2.

2TABLE 2Strength atStrength50% elongationExtension ratioBreak energymN/texmN/tex%% · mN/texWarp direction51.135.982.74226.0At angle of 15°33.520.8119.84013.1At angle of 30°29.712.1111.23558.0At angle of 45°50.230.5107.15376.4Weft direction50.733.181.24116.8

[0112] The methods of measuring the above properties are the same as mentioned in Example 1.

[0113] The above test results of the strength at 50% elongation are shown in FIG. 4 by the black circles marks.

COMPARATIVE EXAMPLE

[0114] Short fibers having a length of 65 mm were prepared by cutting the same tows as used in Example 1. They were treated on a carding engine to give short fibers webs. These short fiber webs were made into a laminated web by the crosslaying method. Eight laminated webs prepared in that manner were overlaid with one another and subjected to needle punching to the same extent as in Example 1 or 2, to give a short fibers non-woven fabric (weighing 1.02 kg/m2 and about 5 mm in thickness).

[0115] Table 3 shows experimental results of comparative example.

3TABLE 3Strength atStrength50% elongationExtension ratioBreak energymN/texmN/tex%% · mN/texWarp direction17.74.2107 1893.9At angle of 15°18.95.1971833.3At angle of 30°19.94.6981950.2At angle of 45°18.76.8941757.8Weft direction32.69.7912966.6

[0116] The methods of measuring the above properties are the same as mentioned in Example 1.

[0117] The above test results of the strength at 50% elongation are shown in FIG. 4 by the marks X.

[0118] As is seen from the results of Examples 1 and 2 and the comparative example, the multiaxial non-woven fabrics have at least a strength of 12 mN/tex and show an elongation of at least 70%, a strength at 50% elongation of 18 mN/tex, the break energy being at least 3000 %mN/tex. On the contrary, in the comparative example, the strength is 17 mN/tex, the extension 91%, a strength at 50% elongation of 4 mN/tex, and the break energy about 1700%.mN/tex. Thus, the strength and break energy all could markedly be improved. The strength at 50% elongation, in particular, could be improved very widely.

[0119] In FIG. 4, the triaxial laminate shows a low strength value at the angle 45 degrees and the tetraaxial one shows a low strength value at the angle 30 degrees. In the actual use of such products, however, the width thereof is not so narrow as the sample width of 10 cm and, therefore, values higher than the data values can be obtained. For example, the properties with sample width 20 cm of at angle 30 degrees of example 2 show follows; the strength is 38 mN/tex, the extension 135%, a strength at 50% elongation of 18 mN/tex, and the break energy about 5130%.mN/tex.

EXAMPLE 3

[0120] A short fiber non-woven fabric weighing 100 g/m2 was inserted between the warp members 28 and the cross-overlaid layer and the same one between the warp members 29 and the cross overlaid layer (i.e. into the inside of the laminate) in carrying out the procedure of Example 1 using the apparatus shown in FIG. 5. The warp members, oblique members and inserted short fiber non-woven fabric were all subjected to needle punching to give a multiaxial non-woven fabric (non-woven fabric A).

[0121] In that case, the short fiber non-woven fabric was prepared by submitting Unitika's bicomponent polyester fibers (Melty 1680, cut length 55 mm, the softening point of the low-softening component of the bicomponent fibers 110° C.) to a carding engine.

[0122] This multiaxial non-woven fabric A was cut to the size of the mold 45a shown in FIG. 7 and pressed between the molds 45a and 45b. In this case, the molds 45a and 45b were heated to 150° C. The non-woven fabric A was heat-treated by the heat of the heated molds under the pressing action and, after releasing from the molds and cooling, successfully gave a three-dimensional moulded product.

[0123] Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications might be made without departing from the spirit or scope of the appended claims. The teachings of Japanese Patent Application Number 377350, filed Dec. 28, 1999, are incorporated herein in their entirety, inclusive of the claims, specification and drawings.

Tow multiaxial non-woven fabric, and method of making the same

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