WO2002004730A1

WO2002004730A1 - Nonwoven for sound-insulating applications

Info

Publication number: WO2002004730A1
Application number: PCT/SE2001/001444
Authority: WO
Inventors: Jörgen BALOGH; Mats Averfalk
Original assignee: Fiberduk Ab
Priority date: 2000-07-07
Filing date: 2001-06-25
Publication date: 2002-01-17
Also published as: SE0002559D0; AU2001266500A1; SE521917C2; SE0002559L

Abstract

The invention relates to a fibrous material for sound insulation in, for example, vehicles. The fibrous material comprises a first layer (2) of a continuous fibrous material, which has a portion of at least 50 % of short fibres having a length below 10 mm, a second layer (3) for free fibres or a fibrous web with a portion of at least 50 % of long libres having a length above 20 mm, and a binder in the form of a polymer which is added as latex and bonding the fibres in the two layers and which has thermoplastic properties after manufacturing the fibrous material. The invention further relates to a method for manufacturing the fibrous material, and using the fibrous material in a sound-insulating material.

Description

NONWOVEN FOR SOUND-INSULATING APPLICATIONS

Field of the Invention

The present invention relates to a fibrous material for sound insulation in, for instance, vehicles. The in- vention further relates to a method for manufacturing a fibrous material for sound insulation in, for example, vehicles .

Technical Background Sound insulation is required in many different applications, such as in dwellings, in offices, in industrial premises and in vehicles .

Since a person's sense of hearing is temporarily blunted or permanently impaired even at relatively low sound levels if staying in noisy environments for a long period of time, it is important to the fullest possible extent to avoid undesirable sound. Another important aspect is that we humans to a high degree use our sense of hearing to avoid danger. For example, it is important for car drivers to be able to hear approaching emergency vehicles, as well as it is important for industrial workers to hear warning signals or warning cries from fellow workers. A conventional sound-insulating material often consists of a relatively thick, airy material similar to the materials which are used in the walls of a house as thermal insulation.

In order to avoid that a motorcar engine gives off disturbing sound levels, the engine is suspended from the chassis with vibration dampening sleeves and the engine compartment is sound-insulated. Conventional insulation of engine compartments, such as bonnet insulation, usually consists of cotton rags which have been put together with a layer of non-woven and which have been condensed under pressure and at an elevated temperature. The pur- pose of the layer of non-woven is to have a joining effect and, to be water and oil repellent and to serve as a flame retardant . By this design, the thicker the cotton rags, the better the sound insulation. However, this means that the insulation becomes too heavy and unnecessarily bulky.

Non-woven is a material that mainly consists of separate textile fibres which are held together by so- called bonding. Bonding is a method of textile technology for holding together fibres or threads mechanically or physicochemically (by gluing or melting) . Non-woven is usually classified as fabric or flexible sheet material and is used in a wide variety of technical fields. For example, non-woven can be used as surgical drapes, outer layers of insulation, or other applications where a thin and light layer of material is desirable but where also considerable tensile strength or tear strength is required. It is also possible to manufacture non-woven type materials with considerably greater thickness and, thus, to use these directly as insulation material. 093/18218 discloses a number of different variants of insulation material of the above-mentioned type. More specifically, an insulation material which is intended for passenger compartments of vehicles and which consists of a sound-absorbing intermediate layer and two outer layers is disclosed, of which the outer layer turned towards the passenger compartment is sound permeable and the outer layer which is turned away from the passenger compartment is sound-reflecting. By this design, the in- sulation material is considered, on the one hand, to receive and absorb sound from the passenger compartment and, on the other, to shut out noise and the like from the road. However, the aim of the WO specification is how to obtain material with sound-permeability and sound- absorption properties, and the sound-reflecting material is not disclosed in more detail. In addition to said WO specification, there are a countless number of documents which, on the one hand, disclose different types of fibrous material that correspond to the cotton rags and, on the other, disclose dif- ferent methods for manufacturing the material at issue.

For example, US-A-2 695 855 discloses a fibrous material which has been impregnated with rubber latex and a curing polymer in such a manner that the material in connection with drying and curing should form an open net- work-like/honeycomb-like pattern with gaps in between.

This material is a variant of the above-mentioned cotton rags and exhibits, just as the cotton rags, sound- absorption properties due to its airy structure.

Further examples of how to use non-woven material with the purpose of sound insulation, are found, inter alia, in GB-1 391 878 which relates to the use of a special copolymer latex for bonding the fibres to one another in the non-woven.

It has lately been found that the sound-insulating ability of a material also depends on the air permeability of the material . One way of improving the sound- insulating ability is to coat the thick, airy material with a layer of a material that has considerably lower air permeability. Great demands are made on this layer. For example, it has to be strong, flexible, light, and easy to form, it must be possible to treat it with a flame retardant, it has to be possible to treat it in such a manner that it is made oil repellent and, moreover, it must have low air permeability. The materials described above do not correspond to all these material requirements. The non-woven material in conventional bonnet insulation has air permeability in the range of 3000- 5000 litres/ (m²*s) , which is considered to be too high, and the cotton rags are, as mentioned above, too heavy. Summary of the Invention

An object of the invention is to provide a material which has low air permeability and low weight per unit area. Another object of the invention is to provide a material which corresponds to the above-mentioned demands with respect to strength, flexibility, and ductility.

The present object has been achieved by means of a fibrous material which is characterised in that it com- prises a first layer of a continuous fibrous material which has a portion of at least 50 % of short fibres having a length below 10 mm, a second layer of free fibres or a fibrous web with a portion of at least 50 % of long fibres having a length above 20 mm, and a binder in the form of a polymer which is added as latex and bonding the fibres in the two layers and which has thermoplastic properties after manufacturing the fibrous material.

This material is light. It exhibits a high degree of strength. It is flexible and can easily be formed. Fur- thermore, it can be treated with a flame retardant and be made oil repellent. In addition, the material has low air permeability in relation to its weight per unit area. As will be disclosed in the description of preferred embodiments, for instance, air permeability can be achieved which is as low as about 100 1/ (m²*s) at a weight per unit area of only about 63 g/m². Suitable layers of material which exhibit the convenient portions of fibre of a predetermined length are, for example, non-woven or fibrous web (the layer of long fibres) and tissue material (the layer of short fibres) . Conventional non-woven material and tissue material have air permeability in the range of 3000-5000 l/(m*s) and in the range of 2000 1/ (m²*s) , respectively. By bringing these two layers together and impregnating them, a fibrous material with low air permeability and with maintained low weight per unit area can thus be obtained. The weight relative to the desired parameter (in this case, inter alia, low air

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character of the first layer. A first layer which has a relatively high portion of short fibres and which is relatively dense from the start requires a smaller quantity of polymer compared with a first layer which is relatively airy or non-dense. On the other hand, a first layer with very short fibres may require a certain quantity of polymer in order to make the fibres in the material "stick together" so that the material obtains the requisite strength. Advantageously, the coherent fibrous material is creped. This means that the layer of material with the short fibres can be stretched to a relatively large degree without being torn to pieces . This flexibility gives the layer of short fibres such an extension ability that the resultant fibrous material can be stretched to the same degree as a conventional non-woven material, i.e. notably more than a smooth (non-creped) material of short fibres can.

As mentioned previously, a high portion of short fi- bres in the first layer results in a material with low air permeability, while a high portion of long fibres in the second layer results in a material with the necessary strength. The portion and the current length of the fibres in the different layers can vary with respect to the material requirements as regards different fields of application.

The previously mentioned object is also achieved by a method for manufacturing a fibrous material in accordance with the independent claim of method. Besides, the object of the invention is achieved by using the previously described fibrous material in a sound-insulating material in accordance with the independent claims as regards the use of the fibrous material in a sound-insulating material and the sound-insulating material as such.

According to a preferred embodiment, the sound- insulating material comprises a second layer of a fibrous material with a thickness above about 5 mm. This second layer can, for example, be cotton rags or the like, the resultant sound-insulating material being, for instance, used as bonnet insulation. According to another preferred embodiment, the sound-insulating material comprises a second layer of a fibrous material with a thickness below about 5 mm. This results in a thin material which, for example, can be used as insulation on the floor of a car or the like. This insulation can, for instance, be included in the floor carpet and the ceiling, respectively.

Brief Description of the Drawings

The invention will be described in more detail in the following with reference to the accompanying schematic drawings which by way of example show the embodiments of the invention preferred at present, in which

Fig. 1 shows an enlarged cross-section of a fibrous material according to a preferred embodiment of the in- vention,

Fig. 2 shows the fibrous material according to the invention in a sandwich construction together with one or more additional layers, and

Fig. 3 schematically shows equipment for manufactur- ing a fibrous material.

Description of a Preferred Embodiment

The fibrous material 1 comprises a first layer 2 of a so-called tissue material which has been brought to- gether with a second layer 3 of a non-woven material (see

Fig. 1) . In order to hold the material 1 together, it has been impregnated with latex.

The manufacture takes place according to the following: A. Manufacturing tissue material. B. Manufacturing fibrous web. C. Bringing the tissue material and the fibrous web together.

D. Impregnating the combined materials with latex.

E. Removing excess latex. F. Drying the fibrous material.

G. Winding the fibrous material.

H. Using the fibrous material.

Fig. 3 shows the principle of manufacturing the fi- brous material. The tissue layer 2 is conducted on an endless wire or the like. From above, the fibrous web 3 is supplied from an endless wire or the like. The joined layers 2, 3 are conducted to a station of impregnating D and further to a station E, in which excess latex is re- moved. Subsequently, the fibrous material is dried in a drier F and wound on a roll G.

A. Manufacturing the Tissue Material

The first layer 2 has a large portion of short cel- lulose fibres with a length in the range of 1.5-3 mm. The fibres can be brought together by so-called wet laying or by so-called dry laying. The most common thing is to use wet laying when such short fibres are to be handled. Wet laying means that a thin layer of fibres and any binders are spread out by means of nozzles or the like when the fibres are suspended in a liquid. After having been spread out, the layers are dried in such a manner that the desired fibrous material is formed.

The short fibres constitute almost 100 % of the fi- bres in the tissue material.

In connection with the drying, the tissue material is creped to a degree of creping in the range of 20-30 %. The degree of creping is usually defined as the difference in length of the creped material in a creped and a stretched, smooth position, respectively, relative to the stretched length. B . Manuf cturing the Fibrous Web

The fibrous web is manufactured by the desired fibres being mixed and carded to a fibrous web . The fibres in the second layer 3 is a mixture of polyester and vis- cose fibres. These synthetic fibres have a relatively well-defined length which in this case is in the range of 40 mm. The fibrous web can be needled together by hydro- entanglement or the like.

The long fibres constitute almost 100 % of the fi- bres in the fibrous web.

C. Bringing the Tissue Material and the Fibrous Web together

After the two more or less continuous materials have been manufactured, they are continuously brought together in the form of two material webs which run along one another. The fibrous web is conducted above the relatively stronger tissue material since the stronger material can support the weaker fibrous web at open parting locations, if any, in the feeding of the material web.

P. Impregnating the Combined Materials with Latex

After the two materials have been combined, they are impregnated with latex. The impregnation can take place by means of foam impregnation, dip impregnation or the like.

The polymer added as the latex is intended to bond the fibres to one another in the two layers 2, 3. The fibres have to be bonded mutually to one another in the layers, as well as to fibres from the second layer. By bringing two layers of material together in which the fibres are not particularly firmly bonded to one another before the joining, fibres in each of the layers may bond to fibres in the other layer. This means that very strong bonding between the two layers is obtained, whereby it is largely avoided that the two layers let go of one another when forming the end product . > 1x3 DO

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stage of the drying is lower than the curing temperature of the polymer added as latex. However, the drying temperature should be so high that the polymer added as latex, at least partly, melts and bonds the fibres to one another in the different layers.

When selecting drying process, attention should be paid to how the drying air currents are conducted relative to the fibrous material web. Air currents which are passed through the fibrous material will affect the final air permeability of the fibrous material negatively (i.e. the air permeability will be higher and, in all probability, far too high) . Advantageously, a so-called convection dryer is used, in which the drying air currents are conducted parallel to, instead of right through, the the fibrous material web. It becomes more and more important to take this factor into consideration, the drier the fibrous material has had time to become in the dryer. This factor should also be taken into consideration when removing the excess latex.

G. Winding the Fibrous Material

After drying, the fibrous material is usually wound on a roll.

H. Using the Fibrous Material

The fibrous material manufactured in the way described above complies with the requirements which have been mentioned previously: low air permeability relative to the weight per unit area, strong, flexible, light, easy to form. The fibrous material can, for instance, be used as a layer in bonnet insulation, the floor carpet of a car, insulating material within the aircraft industry or the like. The fibrous material can, of course, be used at a large number of other locations, such as industry wall insulation, machine hoods or the like. However, it is within the transport sector that the fibrous material appears to advantage since it unites the desired sound-

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vented from propagating further to the passenger compartment .

According to a preferred embodiment, the fibrous material has a weight per unit area of about 63 g/m², a thickness of about 0.6 mm and air permeability of about 100 1/ (m²*s) . According to another embodiment, the fibrous material has a weight per unit area of about 60 g/m², a thickness of about 0.9 mm and air permeability of about 1200 1/ (m²*s) . Apparently, it is possible to vary the air permeability with maintained weight per unit area. The choice of portion of binder and the choice of tissue material are parameters which affect these properties. To all appearances, the thickness can be easily varied between, for example 0.6 and 0.9 mm, and the air permeability between 100 and 1200 1/ (m²*s) with maintained low weight per unit area.

Conventional non-woven and tissue material have air permeability in the range of 3000-5000 1/ (m²*s) and in the range of 2000 1/ (m²*s) , respectively. It will be understood that a large number of modifications of the described embodiments of the invention are possible within the scope of the invention, which will be defined in the appended claims.

For example, the fibrous web 3' can be put together with the tissue layer 2 after the step of impregnating D

(see the dashed line in Fig. 3) . In addition, the layer of tissue material can be placed above the fibrous web instead.

The different fibres and the latex can be replaced by other materials which have similar properties. In some applications, it may be possible to ignore a certain property, thus making it possible to use another type of fibre or another latex.

Claims

1. A fibrous material for sound insulation in, for example, vehicles, c h a r a c t e r i s e d in that it comprises a first layer (2) of a continuous fibrous material which has a portion of at least 50 % of short fibres having a length below about 10 mm, a second layer (3) of free fibres or a fibrous web with a portion of at least 50 % of long fibres having a length above about 20 mm, and a binder in the form of a polymer which is added as latex and bonding the fibres in the two layers (2, 3) and which has thermoplastic properties after manufacturing the fibrous material .

2. A fibrous material as claimed in claim 1, which has a thickness below about 2 mm.

3. A fibrous material as claimed in claim 1 or 2 , in which the polymer added as latex constitutes at least

15 %, preferably at least 20 % by dry weight of the fibrous material .

4. A fibrous material as claimed in any one of the preceding claims, in which the continuous fibrous mate- rial in the first layer (2) is creped.

5. A fibrous material as claimed in claim 4, in which the first layer (2) has a degree of creping above 10 %, preferably between 20 and 30 %.

6. A fibrous material as claimed in any one of the preceding claims, in which the first layer (2) has a portion of at least 50 %, and preferably 75 %, of cellulose fibres .

7. A fibrous material as claimed in any one of the preceding claims, in which the first layer (2) has a por- tion of at least 75 % of short fibres having a length below about 10 mm.

8. A fibrous material as claimed in any one of the preceding claims, in which the first layer (2) has a portion of at least 50 % of short fibres having a length below about 5 mm.

9. A fibrous material as claimed in any one of the preceding claims, in which the first layer (2) has a portion of at least 75 % of short fibres having a length below about 5 mm.

10. A fibrous material as claimed in any one of the preceding claims, in which the second layer (3) has a portion of at least 75 % of long fibres having a length above about 20 mm.

11. A fibrous material as claimed in any one of the preceding claims, in which the second layer (3) has a portion of at least 50 % of long fibres having a length above about 30 mm.

12. A fibrous material as claimed in any one of the preceding claims, in which the second layer (3) has a portion of at least 75 % of long fibres having a length above about 30 mm.

13. A fibrous material as claimed in any one of the preceding claims, in which the second layer (3) has a portion of at least 50 %, and preferably 75 %, of polyester and viscose fibres.

14. A method for manufacturing a fibrous material for sound insulation in, for example, vehicles, c h a r a c t e r i s e d in that it comprises the steps of manufacturing a continuous fibrous material, which has a portion of at least 50 % of short fibres having a length below about 10 mm, bringing the continuous fibrous material and fibres in the form of free fibres or a fibrous web together with a portion of at least 50 % of long fibres having a length above about 20 mm, impregnating the continuous fibrous material and the added fibres with latex, and drying the combined and impregnated fibrous material .

15. A method as claimed in claim 14, in which the drying takes place at a temperature which is lower than the curing temperature or degradation temperature of the polymer added as latex.

16. A method as claimed in claim 14 or 15, in which the step of manufacturing a continuous fibrous material comprises the step of creping the fibrous material .

17. A method as claimed in any one of claims 14-16, in which the free fibres or the fibrous web are/is placed above the continuous fibrous material during the step of bringing the fibres together.

18. A method as claimed in any one of claims 14-17, in which the step of bringing the fibres together is carried out before the step of impregnating.

19. A method as claimed in any one of claims 14-18, which further comprises a step of removing an excess of impregnation, which is carried out after the step of im- pregnating and before the step of drying.

20. A method as claimed in any one of claims 14-19, in which the step of removing an excess of impregnation comprises the step of removing by suction an excess of impregnation from the fibrous material which is brought together.

21. Use of a fibrous material as claimed in any one of claims 1-13 in a sound-insulating material.

22. A sound-insulating material c h a r a c t e r i s e d in that it comprises a first layer (1) of a fibrous material as claimed in any one of claims 1-13.

23. A sound-insulating material as claimed in claim 22, which further comprises a second layer (4) of a fibrous material with a thickness above about 5 mm.

24. A sound-insulating material as claimed in claim 22, which further comprises a second layer (4) of a fibrous material with a thickness below about 5 mm.