A Method Of Making The Leno Fabric

Field of Invention:

This invention relates to producing bags for packing and storing of goods. More particularly, the invention relates to packing and storing perishable agricultural products (agro-products). Even more particularly, the present invention relates to bag manufactured from flat or tubular fabric which is comprised of at least one bulk yarn as weft and at least one combination of bulk yam and stiff yarn in warp, wherein the weft yarn is held in position to one another by leno weave.

Background of Invention:

In general, the open mesh leno bags used for packing of different agro-products such as potatoes, onions, fruits, flowers and the like, are made from slit film tape of polyethylene or polypropylene material. The slit film tape material imparts the required breathability or openness to the fabric bag, however, has rough edges of the tapes gives a harsh feel upon touch, which could be damaging to more delicate of the perishable agro-products. Also, the dimensional stability of the fabric is compromised due to slippery behaviour of slit film tapes, whereby the bags are unable to hold their shape during handling of the bags.

Further, in order to improve the softness of the fabric and the resulting bag if only multifilament yam is used in making of the leno bag, there is more dimensional stability issue during bag processing, packing of goods and storage of bags. Therefore, there is need to improve upon the structure of bag to provide softness and dimensional stability.

Objects of the invention:

One of the objects of present invention is to provide softness to the bag content and adequate cover with the required breathability/openness.

Another object of present invention is to provide the rigidity to bag structure giving dimensional stability to bag and its contents.

A further object of present invention is to provide a fabric structure suitable for automated bag processing.

Summary of Invention:

This invention relates to producing bags for packing and storing of goods. More particularly, the invention relates to flat or tubular leno weave fabric which is comprised of at least one warp thread (6A) that has one of its strands (6B or 6C) made from bulk yarn as weft and/or at least one of its weft threads (5 A) is made from bulk yarn, and a bag made from such fabric. The invention addresses the problem of harshness of the leno weave fabric made from stiff yarn, particularly on perishable goods and other goods that can get damaged by harsh packaging.

Woven fabrics typically comprise warp and weft structures that formed using warp and weft threads, respectively. Woven slit film tape fabric typically comprises of two sets of threads arranged in warp structure and weft structure. Threads are typically made of multiple slit film tapes. The fabric of the invention has some bulk yarn introduced in the weaving pattern to make the fabric softer than the conventional fabric. This key aspect of the invention has led to bags that are less harsh on the goods, than bags made from conventional leno fabric made from stiff yam.

Brief Description of Figures:

Figure 1 A: Prior art leno tubular fabric

Figure IB: Enlarged view of prior art leno fabric structure

Figure 2: Leno tubular fabric of the invention

Figures 2A, 2B, 2C: some of the weaving patterns that are covered by the scope of the invention

Figures 3A, 3B, 3C: some of the other weaving patterns that are covered by the scope of the invention

Figures 4A and 4B: some more of the weaving patterns that are covered by the scope of the invention

Figures 5 A, 5B, 5C: still more of the weaving patterns that are covered by the scope of the invention

Figures 6A, 6B, 6C: yet more of the other weaving patterns that are covered by the scope of the invention

Figures 7A, 7B, 7C: some other weaving patterns that are covered by the scope of the invention List of Parts:

1 : prior art leno tubular fabric 10 6: Warp structure; 6 A: weft 2: Weft slit film tape (prior art) thread/yarn; 6B and 6C - the two 3 : warp slit film tape warp strands that make up a warp

4: Leno tubular fabric of the thread

invention 7 : Bulk yarn

5: Weft structure 5 A: weft 15 8. Stiffyarn

thread/yam L. Loop

Description of Invention:

Woven fabrics typically comprise warp and weft structures that formed using warp and weft threads, respectively. Woven slit film tape fabric typically comprises of two sets of threads arranged in warp structure and weft structure. Threads are typically made of multiple slit film tapes. Threads from any one set (warp or weft structure) and are arranged in parallel to each other and interlaced with the threads from the second set (weft or warp structure). The threads from one set are oriented substantially at right angle to the threads from the other set. For a simple plain weave, the warp threads cross over and under the weft threads in an alternating pattern. In particular, for a given warp thread crossing over a particular weft thread, the adjacent warp thread will cross under the particular weft thread, thereby locking the weft thread in place. The limitation of plain weave fabric is lack of porosity or openness.

A typical leno weave differs from the plain weave In leno type weave, the warp structure (6) is made of warp threads (6A) which in turn have warp strands (6B, 6C) that are grouped in pairs. Weft structure (5) comprises weft threads (5 A) that are interlaced with the warp threads (6A), however, in between each weft thread (5A), the warp strand pairs (6B, 6C) of the individual warp threads (6A) are twisted around one another, reducing distance between them to almost zero in between weft threads (5 A). This type of leno weave, spaces are formed in between the weft threads, giving more openness to the fabric. The empty spaces between weft threads function as pivot points resulting in a flexible fabric which readily conforms to complex contours of the goods they store. The relative effectiveness of pivot points can be augmented or diminished by changing the warp and weft thread/yam structure. As shown in Figure 1 schematic, the prior art leno bag (1) has slit film tapes as warp and weft threads/yarn. Figure IB shows the enlarged views of the traditional leno bag fabric structure, wherein the weft and warp threads/yarn are made from plastic slit film tapes. The denier and width of warp yarn/thread and weft yarn/thread maybe same or different as per the packing requirement. This structure lacks the softness (due to the sharpness or toughness of the tape edges) and less coverage.

Accordingly, the fabric of the invention (see Figure 2) has some bulk yarn introduced in the weaving pattern to make the fabric softer than the conventional fabric. This key aspect of the invention has led to bags that are less harsh on the goods, than bags made from conventional leno fabric made from stiff yam. There are a number of patterns that fall under the scope of the invention such that the weight of the bulk yarn (7) used in the fabric may be up to 100% by fabric weight in gsm and/or the weight of the stiff yarn (8) used in the fabric may be up to 95% by fabric weight in gsm.

A number of weaving patterns are possible depending on the type of yarn that is used to form the weft and warp structures (5, 6).

In a preferred embodiment of the invention (see Figure 2A), bulk yam (7) is used as weft threads/yarn (5A) of the weft structure (5). In this embodiment, in the warp threads/yarn (6A) - which consist of pair of warp strands (6B, 6C) - one strand is made from bulk yam (7) and the other one from stiff yarn (8). Here, the two warp strands (6B, 6C) are weaved by twisting one around the other such that a loop (L) is formed. Through the loops (L) of the twisted pair of the warp strands (6B, 6C), the weft thread (5 A) is passed.

Figures 2B and 2C show some weaving patterns where bulk yam is a part of the warp structure (6) of the fabric. Each warp thread (6A) comprises two warp strands (6B, 6C) - one made from a stiff yarn (8) and the other made from a bulk yarn (7). However, the weft structure (5) may comprise entirely (Figure 2B) stiff yarn (8) or a combination (Figure 2C) of stiff yarn (8) and bulk yarn (7) laid out in a number of arrangements. For example, in the weft structure (5), stiff yarn (8) and bulk yarn (7) may alternate, or there may be only bulk yam (7) or only stiff yarn (8), or any number of consecutively positioned stiff yam (8) followed by any number of bulk yarn (7).

Figure 3 A, 3B, and 3C show a number of other weaving patterns where the warp structure (6) of the fabric is formed entirely using bulk yam (7). However, the weft structure (5) may comprise entirely stiff yarn (8) or a combination of stiff yarn (8) and bulk yarn (7) laid out in a number of arrangements. For example, in the weft structure (5), stiff yam (8) and bulk yarn (7) may alternate, or there may be only bulk yarn (7) or only stiff yam (8), or any number of consecutively positioned stiff yarn (8) followed by any number of consecutively positioned bulk yarn (7).

Figures 4A and 4B show a number of weaving patterns where the warp structure (6) of the fabric is made entirely of stiff yam (8). Here, the weft structure (5) may be either made entirely of bulk yarn (7), or arranged in alternating layout of bulk yarn (7) and stiff yarn (8).

Figures 5A and 5B show a number of weaving patterns where the warp structure

(6) is made such that any single warp thread (6A) may be made of either bulk yarn (7) or stiff yarn (8). Such warp threads (6A) are laid out in a pattern where warp threads (6A) made completely from bulk yam (7) and stiff yam (8) alternate. It is also possible that a number of warp threads (6A) made entirely from bulk yarn (7) are laid out consecutively before introducing warp threads (6A) made entirely from stiff yarn (8). In combination with such warp structure (6) pattern, the weft structure (5) pattern comprises entirely bulk yam (7) or stiff yarn (8). Alternatively, the weft structure (5) may comprise alternatingly laid out threads of bulk yarn (7) and stiff yarn (8).

Figures 6A, 6B and 6C show a number of further weaving patterns where the warp structure (6) is made such that at least one warp thread (6A) may be made of a combination of bulk yam (7) and stiff yam (8) - that is any one of the two warp strands (6B or 6C) is made of bulk yam (7) and the other strand (6C or 6B) is made of stiff yarn. The fabric may have any number of such warp threads laid out consecutively or in alternating arrangement with warp threads (6A) that are made entirely of stiff yarn. Such warp threads (6A) are laid out in a pattern where bulk yarn (7) and stiff yarn (8) alternate. In combination with such warp structure (6) pattern, the weft structure (5) pattern comprises entirely bulk yarn (7) or stiff yam (8). Alternatively, the weft structure (5) may comprise alternatingly laid out threads of bulk yarn (7) and stiff yarn (8).

Figures 7A, 7B and 7C show a number of still further weaving patterns where the warp structure (6) is made such that at least one warp thread (6A) may be made of a combination of bulk yam (7) and stiff yam (8) - that is any one of the two warp strands (6B or 6C) is made of bulk yam (7) and the other strand (6C or 6B) is made of stiff yarn. In this embodiment, the warp structure (6) also comprises a warp thread (6A) where both warp strands (6B, 6C) are made from bulk yam (7). The fabric may have warp threads from any one of the aforementioned two types laid out consecutively or in alternating arrangement with warp threads (6A) of the other type. In combination with such warp structure (6) pattern, the weft structure (5) pattern comprises entirely bulk yam (7) or stiff yarn (8). Alternatively, the weft structure (5) may comprise alternatingly laid out threads of bulk yarn (7) and stiff yarn (8).

The stiff yam (8) used in the leno fabric of the invention may be any type of slit film tape or monofilament yarn. The stiff yarn can be fibrillated or folded or simple slit film tape made from polymeric material, preferable polyolefin. Optionally stiff yam can be made from bio-degradable material. The bulking yarns (7), due to their inherent structure, help increase the softness of the fabric made from the yam, yet increase friction with adjacent yarns, which is necessary for structural robustness of the fabric. The unique combination of bulking yam (7) and stiff yam (8) in warp threads (6A) provides better stability and structural integrity to overall material. The denier range of stiff yam (8) used in the invention is 50 to 1200 and width is from 0.5 mm to 12 mm.

A bulk yam (7) is a yam that has been processed to have covering power or apparent volume than that of a conventional yarn of equal linear density and of the same basic material with normal twist often these bulk yarns are referred to as bulk continuous filament yams (BCF). BCF yarns include any continuous filament yarn whose smooth, straight fibres have been displaced from their closely packed parallel position by the introduction of some form of curl, crimp, loop or coil. Bulking gives filaments the aesthetic properties of spun yarns by altering the surface characteristics and creating space between the fibres. Fabrics are more absorbent and comfortable and have better bulk, cover and elasticity. These properties are important in protecting goods during storage/transportation. They are more breathable and permeable to moisture. Static build-up is lower. Bulk yarns do not peel or shed.

In one aspect of the invention, bulk yam (7) can be made from bio-degradable material or its combination with man-made fibres. The individual bulking yam component will typically have a denier of about 100 to 2000, however, it’s preferable to use yarn components of deniers from 150 to 5000.

There are three classes of bulk yams: bulky or bulking yam, stretch yarn, and textured yarns.

Bulk yam formed from inherently bulky fibres such as manufactures fibres that are hollow along part or all of their length, or yarns from fibres that cannot be closely packed because of their cross sectional shape, fibre alignment, stiffness, resilience or natural crimp. Bulky yams are used in a wide array of products from carpeting to lingerie and sweaters to shoelaces. However, their use in the leno fabric for storing perishable and other types of goods is not known. Stretch yams are thermoplastic filament or spun yams with a high degree of potential elastic stretch (30-100%), rapid recovery and high degree of yam curl. Stretch yam have moderate bulk. Stretch yarns (nylon) used extensively in men’s and women’s hosiery, pantyhose, leotards, swim-ware, jerseys, however, these are not known to be used in making leno fabric for storage/transportation of goods.

The bulking yarns can be used from two major categories: i) continuous multifilament textured yarn and ii) staple fibre spun yarns. Textured yams are produced from conventional raw texturing or air texturing process. The air texturing process uses compressed air to change the texture of yarn by disarranging and looping the filaments that make up the yam bulk structure. Air texturing bulking yarn are generally made from low cost polypropylene, polyethylene or polyester or the like. Textured yarns is a general term for any continuous filament yarn whose smooth straight fibres have been displaced from their closely packed, parallel position by the introduction of some form of crimp, curl, loop or coil. Textured yams can be made from either filament fibre or staple fibres cut from filaments that have been given textured configuration of some type. The majority of textured yarn are made from filament fibres. Texturing yarns may be uniform in shape and smooth in appearance- like simple yarns, they may be irregular so that they have some resemblance to complex yam structure. Texturing gives slippery filaments the aesthetic properties of the spun yams by altering the surface characteristics and creating space between the fibres. This gives the fabric more breathability, permeability to moisture more absorbency, more comfortable and has less static build-up. Textured yarn is a generic term for filament(s) that have been given notably greater apparent volume or bulk than conventional yams of similar filament count or which have been made more extensible by filament distortion through physical, chemical or heat treatment or a combination of these. Texturing introduces permanent distortions, crimps, loops, coils, or crinkles without destroying the essential continuity of the filaments. This improves the texture of the yarns. Texturing gives yarns a soft and woolly feel and increases the warmth and comfort of fabrics. The loops and crimps entrap a multitude of small pockets of air. The filaments prevent air movement and hold the fabric together. In the case of Leno type fabrics that are used in storage of perishable goods in particular, softness of the fabric is of great importance towards reducing the damage to the goods during storage and/or transportation.

The primary purpose of texturing filament yams is to create bulky structure which is desirable for the following reasons:

- The voids in the structure cause the materials to have good insulation

properties.

The voids in the structure change the density of the material which makes it to have light weight with good covering properties. The disorganized surface of the yarn gives dispersed light reflection which in turn gives a desirable mat appearance.

The sponge like structure feels softer than the lean twisted flat yam.

The crimp filament structure gives lower effective modulus of elasticity to the structure as compared to a flat yam.

Man-made Textured Yarn is a fully drawn, fully oriented multifilament yam with soft crimp, high bulk and texture with cotton feel and very high durability and retention properties. This is manufactured by texturizing partially oriented yam using high speed texturizing machines. Textured Filament Yam can be draw- textured or air-textured yarn. Yarns produced by the air-jet texturizing are called Air Textured Yams (ATY). Air-jet texturizing process is a purely mechanical method that uses a cold air-stream to produce bulked yams of low extensibility. ATY is very bulky with permanent crimps and loops. In ATY man-made yarn can be combined with natural fibre yam.

Various effects may be provided to a yam, these are curled, stretched-and-relaxed, lofted using air jet, peaked crimp, rounded crimp, crimping using heated gears, and crimping using stuffing box method.

The other type of bulking yarn maybe from staple fibres. Staple fibres are shorter lengths, usually only a few inches long. They are twisted together to form longer strands. The two major types of staple fibre yam are conventional ring spun yam and friction spun yarn. The friction spun yam are produced by friction spinning process like Dref which produces large diameter, bulky yarns.

The dimensional rigidity to the inventive bag structure is provided by the stiff yarn (8) (see Figure 2A) which can be monofilament, slit film tape or folded slit film tape or bonded yarn or like.

The bag fabric can be made using conventional flat loom or circular loom design for leno weave.

The woven improved open mesh structure of the fabric obtained by the disclosure made here may be further enhanced by use of number of different yarns/fibres (geometry, type, cross-section and combination thereof) as well as textile structure, arranged in particular pattern or alternatively. The engineered placement of radically different yarn types directly facilitates enhanced dimensional structure and mechanical properties.

Further, during the cyclic load testing the conventional leno fabric made from plastic tape showed around 4 to 12% dimensional distortions whereas the inventive leno fabric having combination of bulk yam and stiff yarn in warp showed negligible dimensional distortion, leading to more stable structure.

Some other aspects of the invention are now disclosed. In one aspect, the stiff yarn and the bulk yam may be produced using man-made yarn. In another aspect, either the bulk yarn or the stiff yam, or both, may be biodegradable. In a further aspect of the invention, any one yam may contain colour or additive or inorganic filler or processing aid or UV stabiliser.

Overall weight of the leno fabric of the invention is below 120 gsm.

While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.