GB2323608A

GB2323608A - Treatment of fabrics with chemicals

Info

Publication number: GB2323608A
Application number: GB9804797A
Authority: GB
Inventors: Howard Rushworth; Robert Linzey Wilson; Pauline Elizabeth Beedham; Simon Phillip Gay; Roy Arthur Munford
Original assignee: Merlin Dyeing & Finishing Limi
Current assignee: Merlin Dyeing & Finishing Limi
Priority date: 1997-03-22
Filing date: 1998-03-07
Publication date: 1998-09-30
Also published as: GB9804797D0; WO1998042907A1; GB9705993D0; AU6407898A

Abstract

A method of treating a fabric comprises several steps. Firstly, at least a double layer of the fabric is dipped into a treatment chemical to thereby cover the exterior surface of the fabric in a single step and provide a reservoir of treatment chemical between the layers thereof. Secondly, a pressure is exerted on the fabric to thereby impregnate the fabric. The double layers may be discreet or stitched or woven together in the form of a bag. An air bag fabric treatment process comprises the steps of contacting the fabric with a treatment chemical and passing the fabric through a pair of nip rollers wherein at least one of the nip rollers includes absorption means to cause the chemical to impregnate the fabric. A method of treating an air bag comprises the step of dipping the bag into a treatment chemical to thereby cover the exterior surface thereof in a single step.

Description

A FABRIC TREATMENT PROCESS The present invention relates to a fabric treatment process and, in particular, an air bag fabric treatment process.

Some years ago, air bags were developed to reduce the likelihood of injury to the driver or passenger of a vehicle which was involved in a collision. The air bag is generally designed to inflate upon impact so that the vehicle occupant is unable to collide with any hard parts of the vehicle. The nature of the explosion used to inflate the air bag is such that a hot, chemically active gas is produced. Originally, to prevent the gas escaping through the nylon fabric, the fabric was coated with neoprene rubber. Unfortunately, the rubber was not particularly heat resistant or chemically resistant and, as an alternative, air bags coated with silicone were recently developed for the purposes of improving heat and chemical resistance. Usefully, silicone also has the properties of being resistant to moisture and fluctuations in temperature and is also a flame retardant. The coatings are applied to the fabrics using known coating technology. The preferred method of coating is to use either knife on air or knife on roller technology to obtain the thickness of coating required for the application. Typically, the fabric is first coated with the silicone on one side before being cut into the appropriate shape and stitched to other such pieces to form a bag with the coating on the inside thereof. The coating on the inside of the bag is necessary to protect the fabric from the hot explosive gases and to avoid coating layer - fabric adhesion failure due to differential elastic properties if the coating was located on the exterior of the bag in use.

In use, it is necessary to be able to fold the air bag into a very small size so that it can be stored in the car in an unobtrusive manner during ordinary use of the vehicle. As the limit of the explosion is reached, the bag itself is under considerable strain and it is thus necessary to utilise coating compositions with relatively high molecular weights so that the coatings have the appropriate strength and elongation to withstand the explosive force. However, a coated air bag may become too cumbersome to fold into the necessary small dimensions required. Accordingly, a balance has to be struck between the thickness of the air bag which is necessary to permit it to be folded into a small shape and the thickness of coating necessary to withstand the force of the explosion. Recently, pre-formed bags have been used which provide advantages in that there are no stitched seams as such. Unfortunately, such bags provide coating problems as they do not present a flat surface to the coating knife and this results in thicker and thinner areas of coating or even, in the limiting case, no coating at all. Furthermore, it is then necessary to invert the bag so that the coated surface is on the inside and this presents still further problems and additional processing steps. Furthermore, new bag designs are now being developed which are increasingly complex in order to provide additional protection to the vehicle occupants by, for example, the use of large fingers which protect the head and limbs of the passenger in side impact and collisions which cause the car to roll. Such complex shapes present even greater reversal problems during processing. It is one of the objectives of the present invention to overcome the coating problems mentioned above.

In particular, a surprising improvement has been noted between double layers of fabric which have been dip coated together so that a reservoir exists between them.

Thus, according to a first aspect of the present invention there is provided a method of treating a fabric comprising the steps of:dipping a double layer of the fabric into a treatment chemical to thereby cover the exterior surface of the fabric in a single step and provide a reservoir of treatment chemical between the layers thereof and exerting a pressure on the fabric to thereby impregnate the fabric.

The double layers may be discreet or stitched or woven together in the form of a bag. The bag may also comprise a third or further layer as the effect of the invention will still be possible with the number of layers being greater than three but will eventually reach a limit.

Preferably, there are between two and six layers, more preferably, between two and five layers, most preferably, between two and four layers of the fabric.

Preferably, the exertion of the pressure is carried out by a pair of nip rollers which may be rubber, steel, fabric and microporous rollers.

Typically, the air bag is woven in one piece.

Preferably, at least one of the rollers includes absorption means to cause the coating chemical to impregnate the fabric.

Preferably, the absorption means exerts a suction force on a fabric passing through the roller.

Advantageously, by dipping the fabric and simultaneously treating both exterior surfaces, the need for a second pass through the process is eliminated. Using coating techniques, such as knife coating means that it is only possible to coat one side of the cloth during each single pass. Thereafter it is still necessary to invert the bag to locate the coating on the inside if inversion is a physical possibility. If not this poses a further technical dilemma which is resolved by impregnation.

A further advantage of the invention is that the bag is uniformly impregnated/coated irrespective of the shape of the bag. This is not possible with knife coating when the bag contours are such that it cannot be laid completely flat thereby producing an uneven coated film thickness on the surface.

It has been noted by the inventors that the chemical in the air bag in the form of a reservoir of chemical available between the layers of the bag improves the impregnation of the fabric. This may be due to the nip pressure forcing the chemical through the fabric or due to the chemical being sucked into the fabric during the exiting phase of the roller step as the nip pressure is reduced or it may be a combination of both these effects.

According to a second aspect of the present invention there is provided a fabric treatment process comprising the steps of:contacting the fabric with a fabric treatment chemical and passing the fabric through a pair of nip rollers, wherein at least one of the rollers includes absorption means to cause the treatment chemical to impregnate the fabric.

Preferably, at least the surface of the roller has a microporous structure to thereby provide the absorption means and to result in both a roller nip pressure and a suction pressure on the fabric as it passes through the rollers.

Preferably, the roller has a fibrous structure and may include cotton, wool or other natural fibres or appropriate synthetic fibres having absorption means and which are suitable to exert the nip pressure on the fabric. Preferably, the fibres of the roller are coated with rubber to produce a resilient microporous structure. Preferably, the fibres of the roller have a capillary suction cavity.

Preferably, the treatment chemical is water based. Typical treatment chemicals are silicones, melamines, polyurethanes and acrylics. Melamines and acrylics are used in sail cloth treatment. Silicones are used in air bag coatings.

It is not entirely clear why the absorption aspect of the roller causes the chemical to pass from the surface of the fabric into its interior matrix to thereby impregnate it. It may be that the rollers and the fabric exert a mutual suction effect as the nip pressure is reduced on exiting causing the chemical to impregnate the interior of the fabric by a form of capillary action caused by the micropores in the rollers, in the fabric or both. Additionally or alternatively, the micropores of the roller will have a capacity for the chemical and due to this store of chemical on the roller the fabric may be able to absorb chemical therefrom, by an internal fabric capillary action, as the nip pressure is reduced during the exit phase of its progress through the rollers.

However, the above are proffered as only possible mechanisms of impregnation and is not intended to limit the invention in any way.

According to a third aspect of the present invention there is provided an air bag fabric treatment process comprising the steps of:contacting the fabric with a treatment chemical; and passing the fabric through a pair of nip rollers wherein at least one of the nip rollers includes absorption means to cause the chemical to impregnate the fabric.

Preferably, the treatment chemical is silicone.

Preferably, the roller has a fibrous structure and may include cotton, wool or other natural fibres or appropriate synthetic fibres having absorption means and which are suitable to exert the nip pressure on the fabric.

Preferably, the treatment chemical is water based. Other treatment chemicals may be used in place of silicone as long as it has similar characteristics such as film forming properties, resistance to moisture, low heat conductivity, flame retardancy and chemical resistance. The use of a water based treatment chemical may be more easily controlled by the process parameters. Water, due to its surface tension tends to be less likely to strike through compared with other solvents. Thus, impregnation of the water based chemical is substantially effected by roller induced absorption and not by the strike through of a solvent carrier.

Preferably, the silicone is water based.

For the avoidance of doubt, impregnation is intended to refer to the distribution of treatment chemical. In known coating techniques the chemical is mostly coated on the surface of the fabric but in the impregnation process the chemical mostly penetrates into the fabric structure and, preferably, provides a more even coverage throughout the structure of the fabric.

The fabric is contacted with the chemical by any suitable technique such as knife coating, lick roller, brush coating, spraying or a dipping technique.

However, dipping is preferred as the definitive step to achieve the correct distribution and amount of chemical to be applied. This is effected by the nip rollers and therefore a knife coating step, or lick roller, to obtain the correct weight of application prior to passing through the nip rollers, is not necessary and would only increase processing costs. In addition dipping is simpler than spraying or brush coating.

It is perceived that knife coating whether on air or on roller is the most favoured method of applying a coating to the air bag. The knife coating technique allows a fairly precise thickness of coat to be applied to the surface of the fabric as long as the surface of the fabric remains flat. In the case of airbags this presents problems as detailed above. If the air bag is already formed it is preferable to invert the air bag to locate the coating on the inside of the bag. This avoids the problem of adhesion chemical and heat resistance etc.

Consequently, according to a fourth aspect of the present invention there is provided, a method of treating an air bag comprising the step of:dipping the bag into the treatment chemical to thereby cover the exterior surface thereof in a single step.

Preferably, after treatment, the air bag is passed through a pair of nip rollers Preferably, dipping the bag into the treatment chemical covers not only exterior surfaces of the bag as presented but may also penetrate through the structure to be located on the interior surfaces of the bag in a single step.

The preferred range of expressions for the preferred rollers of any of the aspects of the invention is 5 % to 60%. In accordance with any of the aspects of the present invention it is especially preferred to have a range of expressions between 5% and 40%. The percentage solids pick up is a function not only of the pick up expression which establishes the percentage of treatment liquor absorbed by the cloth but also the solids concentration within the treatment liquor. The resultant solids pick up is the product of the two percentage characteristics.

The preferred solids pick up for the preferred rollers of any of the aspects of the invention is between 5 % and 55 % . In accordance with any aspect of the present invention it is especially preferred to have a solids pick up of between 15% and 36%. The percentage pick up from the roller is a function of not only the roller material but also the solids content of the chemical substance being applied to the fabric.

Preferably, the nip pressure of the rollers is between lkg per cm2 and 40kg per cm2, more preferably, it is between 10 and 20 kg per cm2.

Typically, the impregnation rollers are high expression, microporous, rubber/non-woven cellulose fibre composition rollers. However, appropriate rollers having similar performance characteristics would also allow the process to be well controlled. Preferably, a pair of rollers which are substantially identical in composition are used to optimise the process. However, although not preferred, non-identical rollers can be used. Typically, the non-identical roller could be a metal or rubber roller.

The rollers may be defined in terms of the "shore" hardness. Preferably, the shore hardness of the rollers is between 60 and 100 units, more preferably, between 85 and 100 units.

Preferably, the fabric is under the minimum tension necessary to present a uniform flat surface to the rollers and is, therefore, under tension during the step of feeding the fabric through the rollers. Preferably, the tension of the fabric is between 0 and 120 kg per metre width of the fabric, more preferably, between 20 and 80 kg per metre width.

Advantageously, due to the nature of the microporous or natural fibre roller, the minimum tension necessary using the present invention is lower than that for a corresponding fabric using the knife coating technique.

The temperature of the chemical to be applied to the fabric may be varied to suit requirement and to optimise absorption. Preferably, the temperature of the chemical is between 1 and 99"C, more preferably, between 15 and 35"C.

Preferably, the fabric is cleaned prior to contact with the chemical.

Preferably, the process includes a drying or curing step.

The impregnation process will now be more specifically described, by way of example, with reference to the accompanying drawings in which figure 1 shows a schematic diagram of the process.

Referring to figure 1, a prepared fabric acts as the in-feed during the impregnation phase of the process. The impregnation phase involves passing the fabric through a bath of chemical to be impregnated. The cloth is then passed between nip rollers under a specific nip pressure of 15kg per cm2. The absorption capacity of the nip rollers is such that a 20% pick up of the chemical takes place. The fabric web tension as the fabric passes through the rollers is 50kg per metre width of the fabric and the temperature of the chemical bath is 25"C. The roller is composed of a non-woven cellulose fibre composition of the type known for the removal of water during fibre finishing. The roller comprises a steel shaft at its core and a series of annular pieces of fibre which are coaxial with the shaft and pressed together along the length thereof. Currently available rollers which are useful for this purpose are the "Roberto" roller and the "Resilio" roller. After passing the fabric through the nip rollers, the fabric is dried and cured in separate steps. The process results in an even impregnation of the chemical across the length, width and depth of the cloth. This is rendered possible in the case of the length and width of the cloth by means of a cambered roller. As the roller pressure is applied at each end the camber is removed and the surface of the roller applies an even pressure across the width and length of the fabric. The even distribution across the depth of the fabric is possibly achieved as a result of the microporous nature of the roller in combination with the nip pressure.

It is found that an even distribution through the depth of the cloth is found irrespective of whether the cloth is a single sheet or a double sheet as in the case of a pre-formed air bag.

Additionally, as the process does not result in a thick surface coasting, the interior surfaces of an air bag will not tack together during the drying or curing step.

The process is particularly useful where the pre-formed air bag design is such that the fabric will not "lie flat". As air bag technology improves, this kind of design of air bag is becoming increasingly common. By varying the nip pressure, speed of rollers, solids content of the chemical bath and temperature of the process it is possible to accurately control the quantity of the chemical substance which is impregnated into the fabric.

Drying phase The parameters of drying are merely a function of the moisture content required to be driven off. This can be manipulated by many factors including process speed, process temperature, dryer path length and percentage solid content of chemical substance applied.

Curing phase The curing phase will require different characteristics depending upon the curing requirements of the substance applied to the cloth. Usually the most relevant aspects of curing substances are the exposure temperature required and the exposure time required at that temperature.

Cloth take off The cloth is collected at the take off end of the process in the standard manner.

In addition to the advantages detailed above there are some additional advantages to the process for one piece woven air bags which include:1. Single Pass:a) Greater Potential For Quality Control: i) Single pass exposure to heat - less opportunity for thermal variation of any sort.

ii) Simultaneous exposure to heat on both sides of fabric - less opportunity for differential shrinkage between the two layers of fabric.

iii) Simultaneous impregnation of the identical chemical substrate bilaterally - less opportunity for substrate variation between the two layers of fabric.

iv) Simultaneous, and therefore identical, physical conditions of process - less opportunity for variation of physical characteristics between the two layers of fabric.

b) Potential for Reduced Process Time - process not repeated on same batch of fabric as in knife coating.

c) More Energy Efficient: i) both sides of fabric cured simultaneously - less opportunity for energy losses due to wastage, greater proportion of the energy used for the purpose intended.

ii) heavy fabric only moved through the machine once - reasoning as for 1b above.

2. Greater Preservation of Fibre Surface Area eg If a second, subsidiary, application (eg KEY COATING) to the cloth is ever considered this may help improve the relevant properties achieved by that second process - for example - adhesion.

3. More Economic Use of Chemicals: a) low weight of substrate applied b) one pass - therefore less potential for wastage c) less chemical placed at a more relevant site.

4. Thinner End Product - relevant chemical substrate is introduced into the fabric structural integrity to a much greater degree than is the case with coating. Therefore, for the installation of the equivalent quantity of substrate the impregnated fabric must be thinner. This is useful where space is of a premium eg the housing module of an air bag.

5. More flexible End Product (easier to fold) - as the chemical substrate is introduced into the fabric structural integrity to a much greater degree than is the case in coating it also allows the fabric to be less stiff than the equivalent coated product (Beam Effect).

6. Potential Ability To Even Offer Protection To Those Bags That Cannot Be Easily Reversed - the greatest technical advantage that one piece woven air bag production possesses over "cut and sew" air bag production is probably its ability to faithfully reproduce complex technical designs. As such designs become ever more sophisticated it is ever more likely that complex air bags will not be capable of reversal to allow the coating to protect the fabric integrity by acting as an internal barrier between gases and fabric.

The invention provides relatively straight forward means of offering the fabric some protection without reversal being necessary as the chemical substrate is introduced into the fabric structural integrity to a much greater degree than is the case in coating, as outlined above.

7. May Remove The Requirement To Reverse Some Bags At All - even those air bags that are simple enough in design to allow reversal may be cheaper to produce without reversal, thus promoting cost reduction without compromising safety.

8. Easier And More Natural Dimensional Control - current one piece woven air bag coating techniques require fabric to be as flat as possible at the point of presentation of the substrate. To achieve this there are considerable amounts of tension applied to the fabric. This tension in turn results in dimensional changes. The invention will allow the fabric to be processed at minimal tensions thus reducing the tendency to alter one piece woven air bag dimensions. It will also allow greater potential for dimensional manipulation should that ever be required.

9. Weave Change Compensation - one piece woven air bag technology requires changes of weave within fabric in order to construct designs.

On certain occasions changes of weave result in some parts of the cloth standing proud above the flat plane of the cloth. This phenomena may be exaggerated by the currently used knife coating techniques. The invention will not exaggerate these occurrences, it is rather more likely to compensate for them and hence further facilitate complex design structures.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s).

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of treating a fabric comprising the steps of: dipping a double layer of the fabric into a treatment chemical to thereby cover the exterior surface of the fabric in a single step and provide a reservoir of treatment chemical between the layers thereof and exerting a pressure on the fabric to thereby impregnate the fabric.

2. A method of treating a fabric as claimed in claim 1, wherein the fabric has a third or further layer.

3. A method of treating a fabric according to claim 1 or 2, wherein the exertion of the pressure is carried out by a pair of nip rollers.

4. A method of treating a fabric according to any preceding claim, wherein at least one of the rollers includes absorption means to cause the coating chemical to impregnate the fabric.

5. A method of treating a fabric according to claim 4, wherein the absorption means exerts a suction force on a fabric passing through the roller.

6. A fabric treatment process according to any preceding claim, comprising the steps of: contacting the fabric with a fabric treatment chemical and passing the fabric through a pair of nip rollers, wherein at least one of the rollers includes absorption means to cause the treatment chemical to impregnate the fabric.

7. A fabric treatment process according to claim 6, wherein the absorption means exerts a suction force on a fabric passing through the roller.

8. A fabric treatment process according to claim 6 or 7, wherein at least the surface of the roller has a microporous structure to thereby provide the absorption means and to result in both a roller nip pressure and a suction pressure on the fabric as it passes through the rollers.

9. A fabric treatment process or a method of treating a fabric according to any of claims 3-8, wherein at least one of the rollers has a fibrous structure and may include cotton, wool or other natural fibres or appropriate synthetic fibres having absorption means and which are suitable to exert the nip pressure on the fabric.

10. A fabric treatment process or a method of treating a fabric according to any of claims 3-9, wherein the fibres of at least one of the rollers are coated with rubber to produce a resilient microporous structure.

11. A fabric treatment process or a method of treating a fabric according to any of claims 3-10, wherein the fibres of at least one of the rollers have a capillary suction cavity.

12. A fabric treatment process or a method of treating a fabric according to any preceding claim, wherein the treatment chemical is water based.

13. An air bag fabric treatment process comprising the steps of: contacting the fabric with a treatment chemical; and passing the fabric through a pair of nip rollers wherein at least one of the nip rollers includes absorption means to cause the chemical to impregnate the fabric.

14. An air bag fabric treatment process according to claim 13, wherein the absorption means exerts a suction force on a fabric passing through the rollers.

15. An air bag fabric treatment process according to any of claims 13 or 14, wherein at least the surface of at least one of the rollers has a microporous structure to thereby provide the absorption means and to result in both a roller nip pressure and a suction pressure on the fabric as it passes through the rollers.

16. An air bag fabric treatment process according to any of claims 13-15, wherein at least one of the rollers has a fibrous structure and may include cotton, wool or other natural fibres or appropriate synthetic fibres having absorption means and which are suitable to exert the nip pressure on the fabric.

17. An air bag fabric treatment process according to any of claims 13-16, wherein the treatment chemical is water based.

18. A method of treating an air bag comprising the step of: dipping the bag into the treatment chemical to thereby cover the exterior surface thereof in a single step.

19. A method of treating an air bag according to claim 18, wherein after treatment, the air bag is passed through a pair of nip rollers.

20. A method of treating an air bag according to any of claims 18 or 19, wherein dipping the bag into the treatment chemical covers not only exterior surfaces of the bag as presented but may also penetrate through the structure to be located on the interior surfaces of the bag in a single step.

21. A method of treating an air bag, a fabric treatment process or a method of treating a fabric according to any of claims 3-17, 19 or 20, wherein the nip pressure of the rollers is between lkg per cm2 and 40kg per cm2.

22. A method of treating an air bag, a fabric treatment process or a method of treating a fabric according to any of claims 3-17 or 19-21, wherein the fabric is under the minimum tension necessary to present a uniform flat surface to the rollers and is, therefore, under tension during the step of feeding the fabric through the rollers.

23. A method of treating an air bag, a fabric treatment process or a method of treating a fabric according to any of claims 3-17 or 19-22, wherein the tension of the fabric is between 0 and 120 kg per metre width of the fabric.

24. A method of treating an air bag, a fabric treatment process or a method of treating a fabric according to any of claims 19-23 wherein the shore hardness of at least one of the rollers is between 60 and 100 units.

25. A method of treating an air bag, a fabric treatment process or a method of treating a fabric according to any of claims 19-24, wherein the range of expressions for the rollers is between 5% and 60%.

26. A method of treating an air bag, a fabric treatment process or a method of treating a fabric according to any of claims 19-25, wherein the solids pick up for the rollers is between 5 % and 55 %.

27. A method of treating an air bag, a fabric treatment process or a method of treating a fabric according to any preceding claim, wherein the temperature of the chemical to be applied to the fabric is varied to suit requirements and to optimise absorption.

28. A method of treating an air bag according to any preceding claim, wherein the fabric is cleaned prior to contact with the chemical.

29. A method of treating an air bag according to any preceding claim, wherein the process includes a drying or curing step.

30. A method of treating an air bag as hereinbefore described.

31. A fabric treatment process as hereinbefore described.

32. A method of treating a fabric as hereinbefore described.

33. A fabric having been treated in accordance with any of claims 1-32.

34. An air bag comprising a fabric having been treated in accordance with any of claims 1-33.