KR20070061826A - A process for preparing a non-woven cellulosic structure and the non-woven cellulosic structure prepared therefrom - Google Patents

Abstract

The present invention relates to a process for preparing a non-woven cellulosic structure comprising the steps of extruding continuous filaments from a cellulosic solution; passing the extruded filaments through a regenerating liquid to attenuate the filaments and laying the attenuated filaments into a web and to the non-woven cellulosic structure prepared therefrom.

Description

A process for preparing a non-woven cellulosic structure and the non-woven cellulosic structure prepared therefrom

The present invention relates to a method of making a nonwoven cellulose structure and to a nonwoven cellulose structure made by this method. Specifically, the present invention relates to a consolidated comprising at least one layer made from a biodegradable continuous cellulose material. A method for making absorbent, durable or disposable composite nonwoven cellulose structures of multiple / single layers.

More specifically, the present invention is directed to continuous randomized cellulose fibers and composite nonwoven cellulose structures made therefrom.

The consolidated nonwoven structure can be composed of viscose fibers, lyocell fibers, cellulose acetate and / or blends of these with synthetic fibers. Lyocell fibers are artificial fibers based on the process of directly dissolving uninduced cellulose in an organic solvent. Reocell fibers are prepared by regenerating cellulose fibers from a solution in an organic solvent such as N methyl morpholine N oxide.

Methods of making cellulose fibers are known in the prior art. US Patent No. 3600397 describes a method of making viscose fibers using wood pulp as a raw material. It is deposited as a sheet or slurry with 17-22% NaOH. Excess sediment is removed by pressurization. Alkaline cellulose is ground and aged for aging. Aged alkaline cellulose is xanthated with carbon disulfide. Sulfate (xanthate) is dissolved in NaOH to form a viscose solution. Ripening and filtering once or several times during or after ripening. The viscose solution is then spun through a fine orifice in an acidic spin bath to form regenerated cellulose filaments / fibers / tow Since viscose / rayon spinning is a 100-year old technique, we will briefly describe it here. Preparation of the dielectric Drawing cellulose solution through the four routes are also known.

Indian Patent No. 189773 mentions a method for preparing a cellulose solution for fiber / film spinning. This method includes a method for preparing a suspension by introducing a cellulose material into an aqueous solution of a third amine oxide. The suspension is then subjected to high shear equipment heat treatment at low pressure.

U.S. Patent Nos. 4,144,080 and 4,246,221 describe a process for the extrusion of milled third amine oxide solution and cellulose to produce an amine oxide solution. Also described is a method of regenerating cellulose from a solution by passing it through a fine orifice in air to spin the solution and orienting the mechanical stretch and then passing the filament through a bath of nonsolvent.

Once the filaments are formed through the viscose process or by other means, the tow is washed and the fibers are cut to staple length. Staple fibers are usually dried and baled (if the nonwoven is made elsewhere). The dried staple fiber bales are opened, blended if necessary and carded to form a fibrous mat. The mat is bonded directly or after cross lapping to form a nonwoven.

The methods cited in US Pat. Nos. 3,833,438 and 3,906,130 describe methods for making nonwoven perforated textile fabrics from continuous copper ammonia rayon, viscose rayon and similar fiber filaments. In this method, mainly continuous filaments are cast on a conveyor that vibrates laterally with forward motion. The radiating unit describes the parallel and sinusoidal curves respectively. Thereafter, consolidation is achieved by water jet. Copper ammonia rayon is an expensive way to produce absorbent cellulose nonwovens. This method involves moving mechanical parts such as cam / crank mechanisms that are susceptible to failure / maintenance. The limiting vibration rate (cycles / min) limits the filament feed rate, ie the production rate.

U.S. Patent Nos. 3,620,903 and 4,069,563 describe a process for treating a fibrous sheet with a fine essentially one or more columnar liquid streams ejected from an orifice at high pressure to produce lightweight, non-patterned nonwoven fabrics. One layer of the fibrous web is supported on the surface and intersects the stream to weave the fibers in a manner that provides strength and stability without the need for a binder.

The aforementioned patent describes how the cellulose solution is spun using solvent spinning. Cellulose fibers are spun and then cut into staple lengths. These are then treated with water and / or other chemicals. These wet fibers are dried. To produce a nonwoven product, the mat is opened using an opener, carded and then hydro entangled to obtain a spun lace product. The product is redried to obtain cellulose nonwoven fibers. This is a conventional widely adopted cellulose nonwoven fiber manufacturing method. However, this method increases the cost by including the process of drying the fibers twice. Also, the strength of the nonwoven fibers is not high, since they consist of short (staple) fibers.

The present invention describes a process for producing continuous cellulose filaments that overcomes the above disadvantages.

The present invention relates to a method for manufacturing a nonwoven cellulose structure, comprising the steps of extruding a filament from a cellulose solution, allowing the extruded filament to pass through the regeneration solution, tapering the filament, and laying the thin filament to web and Preparing a nonwoven cellulose structure made therefrom.

The present invention will now be described with reference to the numbers attached to the specification, wherein like numbers refer to like parts.

1 is an isometric view of an assembly for spinning a nonwoven cellulose material.

FIG. 2 is an exploded isometric view of the radiation box shown in FIG. 2.

3 is an isometric view of the setup showing the laying of the curtains.

4 is a variety of manufacturing options for the composite structure.

The cellulose solution of the temperature and constant flow rate required in FIGS. 1 and 2 is fed into the spinneret assembly 7, preferably the rectangular spinneret assembly. The spinning box 3 is placed under the rectangular spinneret assembly. The spinning box 3 maintains the rectangular arrangement of the web by using it to thin the filaments and to randomly lay down the filaments. The regeneration liquid is supplied using the rectangular liquid supply pipe 4. The regeneration liquid supply pipe may be located below or above the spinning box. The spinning box 3 forms a funnel shape up to a certain length and the rest consists of a funnel side that is straight. The funnel means to allow the regeneration solution to pass from top to bottom. The upper part of the funnel 5 may have a hole drilled in the side plate such that the regeneration solution begins to fill the spinning box 3 so that fluid flows out of the hole and passes through the funnel. The flow from the regeneration liquid supply pipe 4 is adjusted so that the liquid maintains a constant level. The height of the water column in the spinning box makes the liquid flow from the funnel 5 high speed due to gravity acceleration. The high velocity fluid attracts and thins the filament supplied from the spinneret assembly. The stretched filaments fall on the collecting belt conveyor 8 by the self energy obtained by the fluid flow. Since the collecting belt 8 moves slowly relative to the filament dropping speed, the filaments are placed randomly on the belt to form a fairly entangled nonwoven web. The entire conveyor is located in the regeneration liquid collection tank 9. The regeneration liquid flows out of this tank by gravity and reaches the recirculation section following the recovery section. Laying is achieved by a vacuum system 10 under the collection belt just below the filament outlet. The vacuum reduces the force of the water by allowing the filament to maintain its random orientation on the belt.

3 shows a preferred laying option. The curtain 11 formed in this way reaches the supply box 12. The feed box has a mechanically driven twin roll arrangement that pulls the curtain and feeds it down. The feed box 12 is pivoted by a swing arrangement, laying down the curtains on the ply 13 over the moving collecting belt 14. Depending on the required coverage, the speed of swing, drop down speed and belt conveyor speed may be adjusted. Similarly, one or more supply boxes 12 in combination with collection belt 14 may be operated in such a way that a web structure, such as a cross lapper structure, is obtained. The cross wrapped web may have better tensile strength and wider coverage in the transverse direction (CD) compared to the transverse (CD) tensile strength of the web produced as shown in FIG. 3.

     Figure 4 (a) shows a typical unconsolidated laid mat made from viscose continuous filament 1 randomized by a fluid assisted randomizer. 4 (b) shows a typical non-consolidated laid mat made from lyocell continuous filaments 2 randomized by a fluid assisted randomizer. The two structures can be consolidated by the known methods described above. Figure 4 (c) is a representative sketch of a nonwoven composite structure produced by the above method before consolidation. In this case the bottom layer may be a cellulose nonwoven viscose or lyocell (1) or (2) or the like prepared by the above method and the top layer may be a cellulose nonwoven or a synthetic nonwoven web (x). The structure may be consolidated by the known method described above to produce a compacted structure. Fig. 4 (d) is a representative sketch of a nonwoven composite structure produced by the above method before consolidation. In this case the bottom layer may be a cellulose nonwoven or a synthetic nonwoven web (x), the top layer may be a cellulose nonwoven viscose or lyocell (1) or (2) or the like prepared by the above method. The structure can be consolidated by known methods. 4 (e) is a composite structure consisting of a plurality of layers of cellulose or synthetic nonwovens (x1, x2 ...), at least one of which is a cellulose or synthetic nonwoven viscose or lyocell (1) Or (2) or the like. The presence or absence of layer (1) or (2) depends on the required performance of the composite structure. The structure can then be consolidated by known methods.

         Solvent Spinning Route (Reocell)

Preferred pulp for preparing solutions is soft wood pulp with a high alpha cellulose content (89-93%) and a low hemicellulose content. The degree of polymerization (DP) of the pulp is in the range of 600 to 1100, with a preferred range of 700 to 1000. The cellulose concentration from which the spinnable solution can be obtained can be 5 to 28%, preferably 7 to 20%, most preferably 10 to 15%. Commercially available N-Methyl Morpholine N-Oxide (NMMO) has a concentration of 50% and must be preconcentrated to 77% by conventional distillation before dissolution. Blending a small piece of pulp with a preconcentrated solvent is performed at about 100 ° C. in a double blade sigma mixer with a vacuum of 400 mm Hg. After 1.5 hours a homogeneous solution is obtained and cooled to a solid state. Other methods of preparing the cellulose solution on a continuous basis are possible using high shear blenders, thin film devices or devolatalizing type counter rotating twin screw blenders. The method described in Indian Patent No. 189773 may also be followed.

The filament can be extruded using a plurality of holes (spinning hole diameter 50 to 150 μ, preferably 55 to 100 μ) arranged in a rectangular shape with an aspect ratio of length to width of about 1.2: 200. have. The aspect ratio makes it possible to provide a row of 10 to 60 holes.

Provide sufficient air gap and air flow in the transverse direction while spinning the lyocell polymer at 90-110 ° C. Depending on the size of the spinneret, filaments of 5 to 5 denier below the denier thickness may be spun.

The filaments coming out in the form of curtains can be held in the form of rectangles by means of special instruments including regeneration baths. The central portion of the box may be a funnel arrangement. The funnel may be drilled from the top and flat below a certain distance. The interior may be provided at the bottom of the funnel with a slit that serves as the outlet of the regeneration liquor as well as the outlet of the spinning filament. The funnel is sealed and isolated on its side so that regeneration liquid from the bottom of the box cannot enter the funnel. An inlet for the regeneration solution is provided at the bottom. If the liquid fills the box and the water level rises above the flat part of the funnel, the liquid reaches the perforations of the funnel. The liquid goes into the funnel. The flow in the box is adjusted so that the outflow level is aligned with the inflow level so that the liquid is always full up to the edge of the regeneration box. The extrusion rate of the filament is 8 to 80 m per minute.

Liquid flow within the narrow width accelerates the filament velocity from the spinneret. The regeneration solution is sent to a solvent recovery process.

The speed of the regeneration liquid obtained at the outlet of the spinning box is controlled as follows.

V ² = 2 xgxh

Where g is gravity acceleration (m / sec ² ),

            h is the height (m) of regeneration liquid from the bottom of the funnel,

            V is the speed (m / sec) of the regeneration solution.

The speed of the regeneration solution is maintained at 50 to 250 m / min, preferably 100 to 200 m / min.

The flow rate of the regeneration liquid required to maintain the water level in the spinning box is controlled as follows.

           Q = L x W x V

Where L is the length of the funnel measured in the bottom (m),

            W is the hole size (m) at the bottom of the funnel,

Q is the amount of regeneration liquid (m ³ / Hr) required to maintain the water level.

In the above relation, it can be observed that for a spinneret of a given width, the flow rate depends on two parameters: height and funnel bottom hole. As a result of tests on various funnels, the higher the liquid level, the greater the retardation force (extension force) applied to the filament. On the other hand, the higher the flow rate, the greater the water energy at the funnel outlet location. The greater the water energy, the more disturbing the filament. Therefore, these two factors must be taken into account when designing the spinning box. The examples cited show different funnel shapes.

When the extruded filament passes through the regeneration solution, the filament becomes thin.

When the filaments formed in this way reach the belt conveyor, they are further randomized due to the flow of regeneration solution. The web may be collected on a rotating vacuum drum system in place of the belt conveyor. The feed box may have a twin roll arrangement that is mechanically driven to pull the web and feed it down. The feed box is pivoted by a swing arrangement that varies in drive speed and lays down the web over the moving collection belt. Stepless adjustment of swing amplitude and swing speed can also be provided. Depending on the required coverage, the swing amplitude, drop down speed and belt conveyor speed are adjusted to achieve coverage of 10 to 600 gsm. The filament mat can also be formed without swinging the supply box. The only variable would then be the conveyor and curtain drop down speed.

Another laying option is cross wrapping. The method is similar to the method in FIG. However, there are one or more boxes that feed the belt conveyor in the transverse direction. The swing box not only lays down the web along the width of the conveyor to provide cross-lapping laying, but also if necessary lays along the direction of the moving belt conveyor shown in FIG. 3, which web depends on the CD tensile strength shown in FIG. It can show higher coverage and better tensile strength in the transverse direction. The laying option cited above is particularly beneficial when the cellulose fibers are mixed with other fibers. When a composite structure is required, a web of one or more fibers is taken to form a multi-layered structure. The resulting web will be a composite structure of cellulose fibers and other fibers.

The unbonded web is then subjected to a consolidation step, which may include hydroentanglement, chemical bonding, needle punching systems, etc., which consolidate the mat fibers together to form a bonded consolidated nonwoven.

The wet bonded nonwoven is subjected to post-treatment such as bleaching, further cleaning, dyeing and soft finishing, and then passed through a dryer to remove excess moisture. The web is then rolled up on a winder to roll. The web has a soft handle, good strength and can be used for a variety of applications, either semi-durable or disposable.

                  Viscose spinning route

The appropriately aged, filtered, aged and deaerated viscose is fed to the radiator at a suitable temperature. The spinneret holder is either left intact or adapted to a cluster plate with round precious metal eyes mounted and arranged in a rectangular shape. Each eye is drilled into the required number of spinning orifices according to conventional triangular pitch and arrangement.

The spinneret is immersed in a spinning bath maintained at the required temperature and concentration in an inverted position, i.e., in a position with the spinning orifice face down. The only difference between the lyocell route and the viscose route is that the lyocell route maintains an air gap between the regeneration solution and the spinneret, whereas for the viscose route the spinneret is immersed in the regeneration bath because the viscose spinning is a wet spinning process. In this way, a viscose web is formed. The cross section of cellulose fibers can be changed to tri-lobal, Y-shaped, or other shapes to impart specific properties to the structure using different spinnerets. Subsequent steps are the same as the solvent spinning route mentioned above to form the nonwoven. For viscose only hydroentanglement / consolidation actuation parameters are different.

You need to understand the filament's behavior when laying down. Here we consider the similarity of threads. When the thread is laid down perpendicular to the moving belt, the shape laid down by the thread is determined by the properties of the filament (linear density, bending stiffness and torsional stiffness, feed point height and feed rate ratio to the belt). In addition, important parameters separate from the properties of the filament in the laying down process are the filament speed, belt speed, water speed, the height of the spinning box from the belt, the design of the vacuum and spinning box under the collecting belt.

                 Consolidation

Once a curtain of randomized / laying continuous cellulose filaments is obtained, the next process is to consolidate the curtain into a nonwoven web. Once randomized / laying continuous cellulose filaments are obtained, the nonwovens manufacturer can use a number of options (shown in Figures 4 (a) -4 (e)). Monolayers of melt blown or spunbonded single-component / bicomponent melt-spun thermoplastic polymers (eg, polyethylene, polypropylene, ethyl vinyl acetate, polyester, polyurethane, ethyl methyl acrylate, nylon, etc.) Multiple layers can be used. Single / multiple layers are selected according to the required end product performance characteristics. In addition, a carded staple fiber mat formed from the aforementioned viscose, lyocell, or other melt-spun thermoplastic polymer to form a nonwoven structure with at least one or more layers of curtains produced by the method described herein. Can be used. After laying the layers all to the intended position, the unbonded nonwoven structure is consolidated using various processes known in the art. Processes may include hydroentanglement, needle punching, thermal bonding, melt stabilization, latex or chemical bonding. The bonding / consolidation process used may depend on the intended final product / product properties.

          exam

Test procedures used to determine the properties of compacted nonwoven structures and products made by the described processes are known to those skilled in the nonwovens art.

The tensile strength

A 200 mm long, 2.5 cm wide sample is drawn on an Instron instrument at a speed of 100 mm / min to find the yield point of the structure. The numerical values represent the tensile strength values of the nonwovens when expressed in N / 2.5 cm. The values are shown in Table 1 below.

Fiber orientation distribution

This test measures the randomization of filaments in nonwoven structures. Below is a graph showing two examples: Graph 1 represents a nonwoven structure with a high number of filaments in a particular direction, that is, a low degree of randomization, and graph 2 shows a nonwoven structure with a high degree of randomization. In this way, the randomization amount of the web structure can be measured.

Other tests essential to understanding the performance of the product include: basic weight, breaking point elongation, tear strength, web wear durability test, drop absorption test, absorbent capacity test, vertical wicking rate, immersion capacity (drip) capacity test, dry lint release test. Procedures for these tests can be found in the Nonwovens Handbook.

                                  Example 1

A 12% cellulose lyocell polymer solution is fed at a rate of 0.06 g / hole / min through a rectangular spinneret with 20 rows of holes with a diameter of 80μ to obtain an extrusion rate of 10 m / min. A spinning box holding a 510 mm regeneration column below the spinneret is installed such that the gap between the top water surface and the bottom of the spinneret is 15 to 25 mm. The bottom of the funnel is provided with a 5 mm gap. A regeneration liquid flow rate of 10 to 15 m ³ / hr is sufficient to maintain a sufficient water level in the spinning box. The speed of the liquid is maintained at 190 mm / min. The water velocity at the outlet of the funnel is much higher, but the retardation force on the filament tapers the filament, providing a draw ratio of 4-6. (The draw ratio is the ratio of filament speed to extrusion speed.) A collection belt operating at 10 m / min below the spin box maintains a distance of 120 mm from the spin box. Provide a vacuum of 400 mm water column below the laying section. The web obtained on the belt cleans the solvent and sends it to a multi-layering device for bonding. Different samples are prepared by varying the number of layers to obtain nonwoven samples with different coverage. The resulting nonwovens are good in strength, soft and absorbent. Samples are measured in gsm-grams / square meter, water absorption (g / g) and tensile strength in the machine direction (MD) and transverse direction (CD) for both dry and wet conditions.

                             Table 1

                             Example 2

An 11% cellulose lyocell polymer solution is fed at a rate of 0.01 g / hole / min through a rectangular spinneret with 20 rows of holes with a diameter of 80μ to obtain an extrusion rate of 1.72m / min. The spinning box is held on a 170 mm regeneration column. The bottom of the funnel is provided with a 4mm gap. A regeneration liquid flow rate of 7 m ³ / hr is sufficient to maintain sufficient water level in the spinning box. The speed of the liquid is maintained at 109 mm / min. The water velocity at the outlet of the funnel is much higher, but the retardation force on the filament tapers the filament to 8 m / min, giving a draw ratio of 4.6. The web laying speed is maintained at 1 to 3 m / min to obtain a uniform nonwoven. Provide a vacuum of a water column of 255 mm below the laying section. The web obtained on the belt cleans the solvent and sends it to a multi-layering device for bonding. Different samples are prepared by varying the number of layers to obtain nonwoven samples with different coverage. The nonwoven obtained is very similar to the nonwoven described above.

The present invention can also be applied to viscose to obtain similar comparison results.

              Advantage of the present invention

a) Cellulose nonwoven fabrics for the same coverage are 1.5 to 2 times higher in strength than staple fiber carded spun racing fabrics and significantly higher than lyocell meltblown fabrics. This means that the material input can be kept the same to obtain a fabric of high strength or the same purpose can be achieved even by lowering the use of material for the same strength.

b) Unlike lyocell melt blowing, the process of the present invention does not involve the use of expensive high temperatures for spinning. The entire process is operated at low temperatures, which reduces the total energy consumption per kg of fabric.

c) No expensive high pressure air is needed to thin the filament.

d) High pressure fluid injection and high vacuum levels are not required for the randomization of filaments. A small amount of low speed regenerative fluid can be used.

e) nonwovens made of staple fiber-carded spun lacing routes, since the process of making viscose to web or from lyocell dope to web includes only one drying step (in the final step after spun lacing). One complete drying step can be reduced compared to the web. This process also does not require toe cutting, fiber opening and carding steps.

f) Once a randomized mat is produced, other processes for consolidating the web, such as needle punching and binder use, may be employed without using additional equipment such as cross wrappers.

g) The process of the present invention is ideal for making wipes for clean rooms, by eliminating the possibility of short fibers generating lining by using only continuous fibers.

The present invention has the advantages described above to solve the disadvantages of existing fibers.

Claims (19)

Nonwoven cellulose structure manufacturing method comprising the following steps: a) extruding the filament from the cellulose solution, b) tapering and randomizing the extruded filament through a regeneration solution; and c) laying the tapered and randomized filaments to obtain a web. The method of claim 1 wherein said filament is a continuous filament. The method of claim 2, wherein the structure is uniform. The method of claim 3, wherein the nonwoven cellulose structure is consolidated by known methods. The method according to any one of claims 1 to 3, wherein the regeneration solution and the extruded filaments pass through a gap of 3 to 7 mm. The method of claim 5, wherein the regeneration solution and the extruded filaments pass through a gap of 4 to 6 mm. The production method according to any one of claims 1 to 6, wherein the regeneration solution has a speed of 150 m / min to 330 m / min. The production method according to claim 7, wherein the regeneration solution has a speed of 200 m / min to 216 m / min. The manufacturing method according to claim 7 or 8, wherein the speed is achieved by gravity. The manufacturing method according to any one of claims 1 to 9, wherein the filament is 1 to 5 denier filaments. The production method according to any one of claims 1 to 10, wherein a speed at which the extruded filaments leave the regeneration solution is 8 to 80 m / min. The manufacturing method according to any one of claims 1 to 11, wherein the speed of the extruded filaments provides a draw ratio of up to six. The manufacturing method according to any one of claims 1 to 12, wherein the laying is performed by a vacuum assisted process. The method of claim 13, wherein the vacuum assisted process is achieved by a rotary vacuum drum system. A nonwoven cellulose structure made by the method of claim 1. The nonwoven cellulose structure of claim 15, wherein the nonwoven cellulose structure is lyocell, viscose, or a combination thereof. A nonwoven consolidation structure comprising at least one layer of the nonwoven cellulose structure of claim 15. Method for producing a nonwoven cellulose structure described with reference to the examples and figures attached to the specification. Nonwoven cellulose structure described with reference to the examples and figures attached to the specification.

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