WO2007032022A2

WO2007032022A2 - Consolidation of non-woven textile fibres

Info

Publication number: WO2007032022A2
Application number: PCT/IN2006/000249
Authority: WO
Inventors: Lodha Preeti; Kapoor Bir; Mankad Jagrat Maheshprasad; Patil Parag Dilip
Original assignee: Lodha Preeti; Kapoor Bir; Mankad Jagrat Maheshprasad; Patil Parag Dilip
Priority date: 2005-07-13
Filing date: 2006-07-13
Publication date: 2007-03-22
Also published as: WO2007032022A3; WO2007052284A3; WO2007052284A2

Abstract

The present invention concerns a method of bonding a mass of fibres, in which fibres are laid in at least one layer, which is impregnated with a polar hydrophilic cellulose dissolving solvent to dissolve cellulose fibres, the impregnated fibre layer is cured, and then contacted with appropriate regenerating liquid and washed and dried, if required, to obtain a bonded fibre structure.

Description

TITLE

Consolidation of non-woven textile fibres

FIELD OF INVENTION

This invention relates to a method of bonding a mass of fibres, which at least partially contains cellulose, using a solvent system.

INTRODUCTION

A fibrous mass typically needs to be consolidated /bonded to give it strength and structural integrity for most commercial applications. There are various physical and chemical bonding techniques used to achieve the desired bonding. Physical bonding processes include the mechanical and thermal bonding techniques as explained below.

1. Mechanical Processes: It includes needling and hydro entanglement. a. Needling: This process uses barbed needles for reorienting a portion of horizontally located fibres or filaments into the vertical plane in the form of fibre tufts, which get interlocked through repeated needle penetrations. This is effective for materials with higher masses per surface unit (g/m² commonly called as gsm). Webs of lower gsm (<100) tend to get destroyed during this treatment, hence cannot be used on the lower gsm. The webs consolidated by this technique are typically bulkier and lower in strength. The needling process cannot be used at high speeds as the vertical movement of the needles is required for punching. Being a mechanical process, the fibres in the web are also prone to physical damage. The process leaves hole marks in the fabric which increases the pore size and hence permeability and negatively impacts the barrier properties. This may affect aesthetics in some applications and reduce their value. b. Hydro-entangling: (Evans U. S. Patent No. 3,485,706) A system of high pressure fluid (typically water) jets or currents are sprayed onto the webs with a required minimum kinetic energy, so that part of the fibres are seized and reoriented by the striking jets or currents and subsequently entangled, intertwined or even knotted with other fibres. This technique can be used for consolidation of non-woven webs typically in 50-600 gsm range. The process is based on the principle that the fibres form the web by entangling with each other and thus the process cannot be used for lower gsm since the web gets disintegrated. The process cannot be used for low denier fibres due to economical reasons. Hydro-entangled bonded non-woven tend to have higher bulk.

2. Thermal Bonding process: Thermal bonding process involves hot air treatment, calendaring and welding of non-woven web. This technique relies on the presence of thermoplastic fibres or powders in the web for its bonding. Since, cellulose polymers degrade before melting, these binder fibres are essentially synthesized. This technique can be used for a variety of non- woven with masses per surface unit from 20 to 4000 g/m² for uniform and thorough bonding. However, the final non-woven product made using this technique contains synthetic binder material, which has a detrimental effect on some of its performance parameters such as water absorption, natural feel and biodegradability. Thus, this technique cannot be used for making 100% cellulose non-woven products since cellulose polymers degrade before melting.

3. Chemical Bonding: Chemical bonding uses chemicals (e.g. acrylate based, vinyl based, latex based etc.) for bonding the fibres in the non-woven web positively with one another. The chemical binder can be impregnated, sprayed, printed or foamed on to the substrate. This technique can give very strong, compact webs in a wide gsm range. Webs with specific properties can be obtained by choosing the appropriate binder. The obvious disadvantage of this technique is the use of chemicals, which limits its application in various areas such as medical and personal hygiene and gives it poor overall environmental compatibility. Also, the presence of chemicals in the non-woven web negatively affects some of the web properties such as water absorption, natural feel and biodegradability. The final web bonded using this technique can never remain 100% cellulosic due to the presence of the binder. Thus, 100% cellulose webs cannot be prepared using this bonding technique.

BACKGROUND OF THE INVENTION

US 6,048,917 (1998) describes a process of fiber-reinforced seamless cellulose casings made of non-woven fibre fabric which are coated on inside and/or outside with an alkaline viscose solution which then treated with an acidic coagulation liquid which precipitates the cellulose xanthogenate and regenerated it to form cellulose hydrate. As a result of the process the resultant product gains additional weight vis-a-vis the original casing material. Further the coating is required to be carried out on dry web at high temperatures to restrict the coagulation of the cellulose solution used for the coating.

In US 3,135,613 1964 the paper webs of relatively strong natural fibers such as manila hemp, flax, and the like have been coated and impregnated with a viscose solution, the cellulose in the viscose solution hereafter bring thereafter regenerated by immersion of the treated paper in a suitable acidic regenerating bath. The regenerated cellulose thus formed as a coating and impregnated on in the fibres of the paper, strengthened the paper web and imparted some degree of resistance to water.

US Patent Nos. 3447393, 3447956 and 3508941 describe the processes of producing cellulose solutions with Cyclic Amino Oxide being used as preferred solvents. A process for strengthening a fibrous material is known from US Patent No. 3447956. The fibrous material is soaked within Amino Oxide and heated to a temperature at which Amino Oxide is able to strengthen the fibrous material. Proposed fibrous materials are woven or non-woven containing natural cellulose. Invention is particularly preferred for treatment of paper with amino oxide, and in doing so NMMO is used as a monohydrate in molten or liquid state or dissolved in a volatile solvent capable of being evaporated.

N-methyl morpholine N-oxide is (NMMO) a cyclic tertiary amine oxide, which is known to dissolve cellulose. Some other cyclic amine oxides known to dissolve cellulose are N-methyl piperidine-N-oxide, N-methyl pyrrolidine-N-oxide. Of these NMMO has been exploited commercially.

Patent No. WO 96/37653 describes fibre assemblies provided with cellulose coat impregnation or sheaths are known. Those fibre assemblies are produced by coating the fibre assembly on one side with a solution of aqueous NMMO whereupon the layer is coagulated in water bath.

US Patent No. 6042890 provides for producing a strengthened fiber assembly containing cellulose II fibrous by contacting the fiber assembly with aqueous solution of NMMO at an elevated temperature between 70 to 130 degree C, with concentration from 70 to 84% by mass and having temperature less than 130⁰C, and subsequently washing the fiber assembly. While working the invention fibrous assembly used is a slightly needle punched.

It is known that cellulose of any type per se is soluble in aqueous solution of NMMO where the concentration of NMMO is greater than 70%. Reference: Ullmann's encyclopaedia of industrial chemistry, Weinheim: Wiley-VCH, 1998 where Phase Diagram of the ternary system NMMO/water/cellulose. Process steps and appropriate range of solubility are indicated and the temperature of solution is greater than 100 ⁰C. This dissolution process is conventionally used in making of cellulosic fibres. At lower concentrations and lower temperatures there is poor solubility of cellulose in NMMO. The US Patent No. 6042890 describes process in which only cellulose II can be used for making fibre assembly and the process requires the use of NMMO at high concentrations and at relatively high temperatures. The use of NMMO at high concentration requires relatively high temperature and is moderately corrosive and requires careful handling.

OBJECT OF THE INVENTION

The object of the invention is to provide a method of bonding a mass of fibres, which at least partially contains cellulose.

SUMMARY OF THE INVENTION

According to this invention, therefore there is provided a method of bonding a mass of fibres, which at least partially contains cellulose, said method comprising the following steps, i. laying the fibres in at least one layer, ii. impregnating the at least one layer, with a polar hydrophilic cellulose dissolving solvent at a temperature ranging from 20 to 50 ⁰C and at a concentration between 20 to 60%. iii. curing the impregnated layer, iv. contacting the said layer with regenerating liquid; and v. washing and optionally drying, to obtain a bonded fibre structure.

This invention can be used to bond wet fibrous mass also. Preferably, the cellulose content is from 10 to 100% of the total mass.

In accordance with one embodiment of the invention, the cellulosic fibres consists of fibres selected from a group of fibres consisting of Lyocell, cellulose acetate, ethyl cellulose, chitin, viscose rayon, cotton, flax, ramie, hemp, jute, kenaf, abaca, banana, sisal, henequen and sunn.

In accordance with another embodiment of the invention, the at least one layer is impregnated by at least one method selected from a group of methods consisting of padding, spraying, coating, sprinkling, foaming and printing.

In accordance with another embodiment of the invention, the impregnating polar hydrophilic cellulose dissolving solvent consists of a at least one compound selected from a group of compounds consisting of N-methylmorpholine N-oxide (NMMO), Dimethyl acetamide-lithium chloride, dimethyl sulphoxide-paraformaldehyde, calcium thiocyanate- water and Ionic liquids including l-alkyl-3-methylimidazoliurn, 1- alkylpyridinium, 1-methyl-l-alkylpyrrolodinium, l-Butyl-3- methylimidazolium chloride, l-Allyl-3-methylimidazolium chloride, 1- Allyl-3-butylimidazolium chloride, 1,3-diAllylimidazolium chloride, 1- Butyl-2,3-dimethylimidazolium chloride, l-Butyl-2,3- dimethylimidazolium thiocyanate, l-Butyl-3-methylimidazolium saccharinate, l-Butyl-3-methylimidazolium tosylate, l-Butyl-3- methylimidazolium bisulfate, l-Allyl-3-methylimidazolium dicyanamide, l-Allyl-3-Butylimidazolium dicyanamide, l-Allyloxy-3-methylimidazolium dicyanamide, l-Allyloxy-3-methylimidazolium chloride, choline chloride and urea.

In accordance with a preferred embodiment of the invention, the impregnating solvent is a mixture of N-methylmorpholine N-oxide (NMMO) and water.

In accordance with another embodiment of the invention, the impregnating solvent is a mixture of Dimethyl acetamide and lithium chloride in the ratio of 1:0.08.

Preferably, the impregnation is done by a padding mangle at a pressure ranging from 0.1 to 10 kg/cm².

Preferably, curing the impregnated layer is done by passing through a constant environment chamber at a temperature ranging from 70 to 160 ⁰C for a period ranging from 5 sec to 30 minutes. In accordance with another embodiment of the invention, the regenerating liquid consists of at least one compound selected from a group of compounds consisting of Water, Methanol, Acetone and low concentration NMMO solution.

In accordance with an alternative embodiment of the invention, the cured layer is passed through a pair of rollers with a pressure ranging from 1 to 10 kg/cm² to compress the layer.

In accordance with another embodiment of the invention, the cured layer is washed with water to remove impregnating solvent and regenerating liquid.

In accordance with another embodiment of the invention, impregnating solvent contains an anti-oxidant.

In accordance with another embodiment of the invention, the antioxidant consists of anti-oxidants selected from a group of anti-oxidants consisting of n-propyl gallate (Benzoic acid 3,4,5, hydroxyl n-propyl ester), styrene-divinylbenzene copolymer carrying chelate-forming iminodiacetic acid and styrene-divinylbenzene copolymer with covalently- bound phenyl methylamine.

Preferably, the anti-oxidant quantity ranges from 0 to 1% of the total mass of the impregnating solvent.

In accordance with another embodiment of the invention, impregnating solvent contains a colouring pigment.

Preferably, colouring pigment quantity ranges from 0 to 5% of the total mass of the impregnating solvent. DESCRIPTION OF THE FIGURES

The invention will now be described with respect to the accompanying drawing in which figure 1 shows a schematic view of the method of bonding mass of fibers in accordance with this invention.

As shown in. figure 1, at least one unbonded fibre layer 1 coming from web forming machine not shown is figure 1 is passed through a padding mangle 2 filled with impregnating solvent. In the padding mangle 2 impregnating solvent wets and soaks the fibre layer. Then the fibre layer enters the constant environment chamber 3 where curing operation takes place. The fibre layer is made to pass through this constant environment chamber 3 kept at a specified temperature and at predetermined speed to achieve desired residence time. Fibre layer may be allowed to pass through pressing rolls if further compaction at curing temperature is desired. Later the cured fibre layer is allowed to pass through various steps of regeneration 5 and other after treatment zones, if required. Wet bonded structure 7 thus obtained is sent for further processes like drying 8, slitting, winding and the like.

DETAILED DESCRIPTION OF THE INVENTION

The technique according to the invention for producing consolidated textile structure containing cellulose fibres from 10 to 100% by weight, by impregnating at least one layer evenly with a polar hydrophilic cellulose dissolving solvent, treating the impregnated textile structure enabling solvent to selectively dissolve the cellulose, curing the impregnated layer, contacting with the regenerating liquid, washing and drying the cured layer if desired to obtain a bonded fibre structure.

Process

Step 1: Laying the textile structure: The textile structure can be of unbonded fibers or continuous filament. The structure can be a single layer or could be multi layered and may consist of woven fabric as well. The said textile structure is laid on a conveyer belt to form at least one fibre layer. Step 2: The at least one layer formed in step one is impregnated with a polar hydrophilic cellulose dissolving solvent selected from a group of solvents consisting of N-methylmorpholine N-oxide (NMMO), Dimethyl acetamide-lithium chloride, dimethyl sulphoxide- paraformaldehyde, calcium thiocyanate-water and Ionic liquids including l-alkyl-3- methylimidazolium, 1-alkylpyridinium, 1-methyl-l-alkylpyrrolodinium, 1- Butyl-3-methylimidazolium chloride, l-Allyi-3-methylimidazolium chloride, l-Allyl-3-butylimidazolium chloride, 1,3-diAllylimidazolium chloride, l-Butyl-2,3-dimethylirnidazoliurn chloride, l-Butyl-2,3- dimethylimidazolium thiocyanate, l-Butyl-3-methylimidazolium saccharinate, l-Butyl-3-methylimidazolium tosylate, l-Butyl-3- methylimidazolium bisulfate, l-Allyl-3-methylimidazolium dicyanamide, l-Allyl-3-Butylimidazolium dicyanamide, l-Allyloxy-3-methylimidazolium dicyanamide, l-Allyloxy-3-methylimidazolium chloride, choline chloride and urea.

The preferred solvent is NMMO/water solution. The impregnating solvent optionally consists of additives like anti-oxidants to prevent oxidation of NMMO solution and optionally consists of colouring pigments to colour the fibres.

The said layer is impregnated by any suitable method such as padding, spraying, coating, sprinkling, foaming and printing.

A preferred method of impregnation is done by a padding mangle 2 shown in figure 1 at a pressure ranging from 0.1 to 10 kg/cm². Preferably the temperature of the impregnating solvent ranges from 20 to 50 ⁰C and concentration between 10 to 60%.

Step 3: The one or more impregnated layers obtained from step 2 is cured by passing through a constant environment chamber at a temperature ranging from 70 to 160 ⁰C for a period ranging from 5 sec to 30 minutes. The impregnated fibre layer is collected on the conveyer belt (higher the temperature, lower is the time required for dissolution of cellulose in solvent). Step 4: As an additional step, if required, the said cured mass while it is still at the curing temperature is optionally passed through a pair of rollers with a pressure ranging from 1 to 10 kg/cm² to compress the impregnated and cured mass to enhance bonding which leads to superior bonding strengths and relatively denser structures.

Step 5: The cured pressed or unpressed mass is passed through a tank containing appropriate regenerating liquid which regenerates the cellulose and forms the bonding. The regenerating liquid could be any one of the liquids selected from Water, Methanol, Acetone, acrylonitrile and low concentration NMMO solution.

Step 6: The regenerated fiber mass is washed to remove the solvent and the regenerating liquid.

Step 7: The washed fiber mass is dried.

The term Impregnating used in this specification means fully or partially filling fully or partially saturation, permeation, soaking, infusion, imbibing and otherwise introducing a liquid into a porous mass. Similarly curing is defined to mean any process of curing by chemical or physical process.

TABLE - A

EXAMPLES

Example 1

A 50 gsm fibrous structure of 100% Lyocell fibers of 350 mm width, produced by a pilot-scale carding machine supplied by Cormatex, Prato, Italy, Mod 38/50 at 8.8 m/min. The textile structure was collected on a conveyor belt made of nylon mesh of 50 mesh pore size of width 400 mm.

The said structure was deposited in the hold above padding mangle ( by Ernst Benz AG, Switzerland, model KTF HV 500 at 0-10 m/min) containing the reagent A ( NMMO solution with NMMO concentration of 27.5% and water 72.5%). The said structure was soaked with the NMMO solution at 250% by weight of the textile structure. The soaked structure is passed thru the padding mangle (Padding rollers are Teflon coated set of rollers where roller 1 (on top) is positively driven and roller 2 is driven by pressure contact with the roller 1. The two rollers are in line contact at compressed air pressure loading of 3.5 kg force / cm² where the pressure of the rollers is maintained at 3.5 kg force / cm².

The evenly soaked structure was collected on another conveyer belt of the same specifications as mentioned above and is passed thru a curing machine (by Werner Mathis AG, Niederhasli-Zurich, Switzerland and model KTF 1796, of the chamber width and length of 500 mm and 900 mm) set at a temperature of 80⁰C with a speed allowing the structure to be cured and heated for about 20 minutes. The atmospheric temperature and humidity of this room, where the curing machine is kept, during the experiment was 35-38°C and 65-70%, respectively. The heated structure is passed thru a pair of rollers (5 kg pressure) to compress the structure coming out of the heating chamber. The Textile structure is then washed in regenerating liquid (Water) to ensure that the reagent content of the washed bonded textile structure is 0.05% or lower by weight. Testing Procedure:

1. Samples were tested on an Instron tensile testing machine, Model 4204.

Cross head speed of testing: 300 mm/min

Gauge length: 75 mm

Sample width: 25 mm

Tenacity was calculated as per ASTM D-5035-1995 procedure and reported in newtons per square millimeter

2. Coverage was measured in grams per squared meters (gsm) as per ISO 3801-1977 procedure

Example 2:

The said structure was sprayed with Reagent A (NMMO solution with NMMO concentration of 12.5% and water 87.5%) such that the solution sprayed and absorbed by the textile structure was 500% by weight of the textile structure.

The soaked structure was passed through a curing machine (by Werner Mathis AG, Niederhasli-Zurich, Switzerland and model KTF 1796, of the chamber width and length of 500 mm and 900 mm) set at a temperature of 90⁰C with a speed allowing the structure to be cured for about 10 minutes. The atmospheric temperature and humidity of this room, where the curing machine is kept, during the experiment was 35-38°C and 65- 70%, respectively. The Textile structure is then washed with regenerating liquid (Water) to ensure that the reagent content of the washed bonded textile structure is 0.05% or lower by weight.

Similar procedure was repeated with the following combinations

Add on of 100% means 1 g of solvent was added to 1 g of unbonded web.

Thus it is apparent that there has been provided, in accordance with the invention, a process that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

Claims

Claims:

1. A method of bonding a mass of fibres, which at least partially contain cellulose, said method comprising the following steps, a) laying the fibres in at least one layer, b) impregnating the at least one layer, with a polar hydrophilic cellulose dissolving solvent at a temperature ranging from 20 to 50 ⁰C and at a concentration between 10 to 60%. c) curing the impregnated layer, d) Contacting the said layer with regenerating liquid e) washing and optionally drying, to obtain a bonded fibre structure.

2. A method of bonding fibres as claimed in claim 1, wherein the cellulose content of the mass is from 10 to 100%.

3. A method of bonding fibres as claimed in claim 1, wherein the cellulosic fibres consists of fibres selected from a group of fibres consisting of Lyocell, cellulose acetate, ethyl cellulose, chitin, viscose rayon, cotton, flax, ramie, hemp, jute, kenaf, abaca, banana, όisal, henequen and sunn.

4. A method of bonding fibres as claimed in claim 1, wherein at least one layer is impregnated by at least one method selected from a group of methods consisting of padding, spraying, coating, sprinkling, foaming and printing.

5. A method of bonding fibres as claimed in claim 1, wherein the impregnating polar hydrophilic cellulose dissolving solvent consists of compound selected from a group of compounds consisting of IM- methylmorpholine N-oxide (NMMO), Dimethyl acetamide-lithium chloride, dimethyl sulphoxide-paraformaldehyde, calcium thiocyanate-water and Ionic liquids including l-alkyl-3- methylimidazolium, 1-alkylpyridinium, 1-methyl-l- alkylpyrrolodinium, l-Butyl-3-methylimidazolium chloride, 1-Allyl- 3-methylimidazolium chloride, l-Allyl-3-butylimidazolium chloride, 1,3-diAllylimidazolium chloride, l-Butyl-2,3-dimethylimidazolium chloride, l-Butyl-2,3-dimethylimidazolium thiocyanate, l-Butyl-3- methylimidazolium saccharinate, l-Butyl-3-methylimidazolium tosylate, l-Butyl-3-methylimidazolium bisulfate, l-Allyl-3- methylimidazolium dicyanamide, l-Allyl-3-Butylimidazolium dicyanamide, l-Allyloxy-3-methylimidazolium dicyanamide, 1- Allyloxy-3-methylimidazolium chloride, choline chloride and urea.

6. A method of bonding fibres as claimed in claim 1, wherein the impregnating solvent is a mixture of N-methylmorpholine N-oxide (NMMO) and water.

7. A method of bonding fibres as claimed in claim 1, wherein the impregnating solvent is a mixture of Dimethyl acetamide and lithium chloride in the ratio of 1:0.08.

8. A method of bonding fibres as claimed in claim 1, wherein the impregnation is done by a padding mangle at a pressure ranging from 0.1 to 10 kg/cm².

9. A method of bonding fibres as claimed in claim 1, wherein curing the impregnated layer is done by passing through a constant environment chamber at a temperature ranging from 70 to 160 ⁰C for a period ranging from 5 sec to 30 minutes.

10. A method of bonding fibres as claimed in claim 1, wherein the regenerating liquid consists of compound selected from a group of compounds consisting of Water, Methanol, Acetone, acrylonitrile and low concentration NMMO solution.

11. A method of bonding fibres as claimed in claims 9 and 10, wherein the cured layer is passed through a pair of rollers with a pressure ranging from 1 to 10 kg/cm² to compress the at least one layer.

12. A method of bonding fibres as claimed in claim 1, wherein the cured layer is washed with water to remove impregnating solvent and regenerating liquid.

13. A method of bonding fibres as claimed in claim 5, wherein impregnating solvent contains an anti-oxidant.

14. A method of bonding fibres as claimed in claim 13, wherein the anti-oxidant consists of anti-oxidants selected from a group of anti-oxidants consisting of n-propyl gallate (Benzoic acid 3,4,5, hydroxyl n-propyl ester), styrene-divinylbenzene copolymer carrying chelate-forming iminodiacetic acid and styrene- divinylbenzene copolymer with covalently-bound phenyl methylamine.

15. A method of bonding fibres as claimed in claim 13, wherein the anti-oxidant quantity ranges from 0 to 1% of the total mass of impregnating solvent.

16. A method of bonding fibres as claimed in claim 5, wherein impregnating solvent contains a colouring pigment.

17. A method of bonding fibres as claimed in claim 16, wherein colouring pigment quantity ranges from 0 to 5% of the total mass of the impregnating solvent.

18. A method of bonding fibres substantially as herein described with reference to the examples and figures accompanying the specification.

19. A product prepared by the method of bonding fibres as claimed in claim 1 to 18, substantially as herein described with reference to the examples and figures accompanying the specification.