Abstract:
A plant serves as a mean for production of a fibre web of synthetic fibres, such as plastic fibres and absorbent fibres, such as viscose and cellulose fibres. The plant includes a forming head preliminary to lay a homogeneously and smoothly distributed fibre layer on a net shaped wire. Furthermore the plant includes a hydro-entangling section with liquid nozzles with powerful liquid jets to treat the in the forming head formed fibre layer, which consists of both synthetic—and absorbent fibres. The plant also includes an oven subsequently to thermal bond the synthetic fibres with cross bonds in the affected areas. Finally the dried web is winded up in a roller. By the help of the plant according to the invention, by higher production speed than known previously a fibre web can be produced, which is far cheaper, and which has a better and more homogeneous structure than similar conventional fibre webs.

Description:
BACKGROUND ART 
     The invention concerns in any case synthetic fibres, such as plastic fibres and absorbent fibres, such as viscose and cellulose fibres to produce a fibre web, which at least include one heat-treatment section for heating up the synthetic fibres at least to one in advance determined temperature, and at least one hydro-entangling section with liquid nozzles to aim a number of powerful liquid jets against one made of synthetic fibres and absorbent fibres combined fibre layer. 
     A such plant is known, where long, carded, synthetic fibres of for instance polypropylene or polyethylene are laid in a web shaped layer on the top side of a net shaped, endless wire&#39;s upper tissue, which while running simultaneously runs in a direction, which points towards the plant&#39;s outlet. On the same or on a following wire the fibre layer hereafter is guided through an oven, where the fibres are heated up to such a high temperature that they will be tied together with cross bonds in the affected areas. 
     A thermal bonding fibre layer has now been formed, serving as a framework and supporting web for absorbent fibres, such as viscose and/or cellulose fibres, which as web can be un-winded from a roller or applied in an air-flow with the help of a known forming head. 
     A close-meshed wire transports hereafter the supporting web with the applicated fibres through a battery of water nozzles, which send a powerful water jets down against the fibres, which hereby are driven effectively into the underlying, frame-like supporting web. 
     When the water jets touch the close-meshed wire, part of the water is hit back against the supporting web, with the help of which the applicated fibres are wound around the cross bonded, synthetic fibres and are laid closely against the web&#39;s lower side, which hereby will be conveyed a smooth and flush surface. 
     The mentioned water exposure is in technical terms called hydro-entangling or spun-lacing. In the following the term hydro-entangling will be used. 
     The hydro-entangled web is dried in an oven, and finally the web is wound up in shape of a roller. 
     Fibre webs, which are manufactured in this way, are for instance used for products as wet wipes, towels, drapes, and gowns. 
     The above described process can be varied in several ways, which however has in common that they all start with a carded fibre layer. Typically the layers will be of polypropylene, polyethylene, or viscose, or a mixture of such fibres. 
     The carded made supporting web is soft and suitable for absorbing and intimately connect with the applicated fibres. In the longitudinal direction besides the web has such a matching strength that the process can proceed without a large risk of web breakage, which could lead to expensive stops of production and losses of materials. 
     Another advantage is that during the hydro-entangling process hydrogen bonds are made between the fibres, to avoid that the finished product flock and mote by use or processing. 
     The carding process however is slower than the following processes, which therefore cannot proceed with optimum capacity, this means the yield is reduced to a level, which is set by the carding process. Since plants of this kind are extremely expensive, it must be considered a serious lack that a great part of the known plant thus is not being used to the full extent. 
     Besides the carding process requiring close supervision and control, and it is difficult and complicated to work with, because for instance during running it is necessary to stretch the carded fibre layer. 
     The synthetic fibres, which make up the supporting web are furthermore considerably more expensive than cellulose fibres, and since the known process requires that approximately equal size quantities are being used of the two fibre types, the resulting product becomes expensive. 
     Even with the above mentioned content of synthetic fibres, the finished fibre web anyhow will suffer from the main lack that there exists an even big difference in the strength respectively in the longitudinal and transverse direction. The strength scale is typically 5:1. Products, which are manufactured of such fibre webs, therefore may tend to part alongside during use. Thus it is easy to stick a finger through the product. 
     A further disadvantage is that the known plant due to the carding process is rather unfit for production of sandwich webs, where the carded fibres become a part of several layers. The known plant can therefore not be used for production of one of today&#39;s strongly demanded products, which consists of two non-woven fibre layers with an intermediate air-laid fibre layer, which is tied together with the two others by the help of hydro-entangling. layer, which is tied together with the two others by the help of hydro-entangling. 
     SUMMARY OF THE INVENTION 
     The purpose of the invention is to assign a plan t of at the opening mentioned character, which has a simple and cheap structure, which is easy to work with and financially favourable while running, and which furthermore can manufacture at a larger transition speed than known so far. 
     Another purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a fibre web with a balanced proportion between the strengths respectively in the longitudinal and transverse direction can be manufactured. 
     A third purpose of the invention consists of assigning a plant of at the opening mentioned character, which is designed to manufacture fibre webs taking price and features into consideration for optimum proportions between the quantities of fibre types used for manufacturing the web. 
     A fourth purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a fibre web can be manufactured, which has a more homogeneous and precise distribution of fibres than formerly known. 
     A fifth purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a fibre web with tighter tolerances than formerly known can be manufactured. 
     A sixth purpose of the invention consists of assigning a plant of at the opening mentioned character, by means of which a sandwich fibre web easily can be manufactured. 
     The new and specific, by means of which this is achieved according to the invention consist of the plant besides include an air-laying section including means during operation to generate a mainly vertical descending air-flow through at any rate the upper tissue on a mainly vertical running net shaped, endless wire, and successively supply the air-flow with at least synthetic fibres and distribute these in a smooth and homogenous, web shaped layer on the upper side of the wire&#39;s upper tissue, which under here runs in one against the plant&#39;s outlet pointing direction. 
     When the known plant&#39;s carding process thus is replaced by a reliable and financially favourable air-laying process the plant&#39;s remaining equipment is now made able to operate at optimum production speed, simultaneously the process becomes easy to control. The fibres can be distributed homogeneously and precisely with an equal orientation in all directions, thus the finished fibre web achieves approximately same strength in longitudinal and transverse direction, and besides manufacturing with tight tolerances becomes possible. 
     Now the process does not require a large strength in the longitudinal direction anymore, and the expensive synthetic fibres can among other things for this reason to a large extent be replaced by cheaper cellulose fibres, by means of which the finished fibre web&#39;s absorbent features are improved favourably, and the cost price is being reduced. 
     It is especially favourable, when the absorbent fibres are added at the same time as the synthetic fibres in the same air-laying section, since the fibres hereby are mixed intimately from start, and the supporting web will be integrated in the forming process. 
     For the purpose a forming head can be used, which include a under the wire&#39;s upper tissue placed suction box, which is connected t o a vacuum air pump, one above the wire placed house with one or more fibre inlets, and one in the house above the wire placed number of rotary wings for while operating to distribute the fibres in a flush layer on the upper side of the wire&#39;s upper tissue. 
     A simple and cheap construction form for the plant can be constructed of a forming head for at a time to form both the synthetic fibres and the absorbent fibres, a hydro-entangling section, and an oven with sufficient high treatment-temperature to thermal bond the synthetic fibres in the affected areas. 
     By this construction the thermal bonding of the synthetic fibres takes place in the same oven, which is used for drying the hydro-entangled fibre web. When a specific thermal bonding oven is inserted between the forming head and the hydro-entangling section, the process can be controlled very precisely, because the temperatures in respectively the thermal bonding oven and the later drying oven can be adjusted to an optimum for the respective processes. Furthermore the fibre web is now stabilised, when it passes through the hydro-entangling process, which therefore can proceed with an optimum effect and without a large waste of loose fibres. 
     When the single forming head in one of the two above mentioned construction forms for the plant according to the invention is replaced with three on one-and-another following forming heads, the plant can be successfully used for production of sandwich fibre webs, since the middle forming head then mainly is supplied with for instance cellulose fibres, while the two other forming heads are supplied with synthetic fibres or both synthetic fibres and cellulose fibres. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention regards also a fibre web, which is manufactured by the help of the above mentioned plant according to the invention, and which contains synthetic fibres as well as absorbent fibres. Due to the production process this web has a structure with a homogenous orientation of the fibres in all directions and a good balance between the strengths respectively in longitudinal and transverse direction. 
     An effectively tied and therefore strong fibre web is achieved, when the synthetic fibres are bi-component fibres, which each consists of a core of at first plastic and then of another one of plastic with a higher melting point than the first. When this form of synthetic fibres are being used, bonding is secured in all places, where the fibres meet, without a simultaneous risk of the core to melt, by which the bonding feature would be lost. 
     With the help of the plant according to the invention manufactured fibre web can favourably have a percentage content of cellulose fibres of between 50 and 95, mainly between 60 and 90, and especially between 75 and 85, at which the web becomes substantially cheaper than the conventional fibre webs of this type. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows schematically a first construction form for a plant according to the invention 
     FIG. 2 shows schematically a second construction form for a plant according to the invention. 
     FIG. 3 shows schematically a third construction form for a plant according to the invention, and 
     FIG. 4 shows schematically a fourth construction form for a plant according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIG. 1 a first construction form for a plant according to the invention can be seen. The main components are a forming head  1 , a conveyor  2 , a hydro-entangling section  3 , an oven  4 , and a winder section  5 . 
     The forming head  1  consists of a house  6  with a fibre inlet  7  for synthetic fibres, for instance plastic fibres, and a fibre. inlet  8  for instance cellulose fibres 
     Below the house a net shaped wire  9 , having an upper tissue  10  and a lower tissue  11  runs above roller  12 . 
     Close under the wire&#39;s upper tissue  10  a suction box  13  is placed, which is connected to a vacuum pump  14 , and above the wire&#39;s upper tissue  10  a number of rotating wings  15  are placed. 
     During operation the vacuum pump  14  provides via the suction box  13  and the house  6  an air-flow, which from an unshown source for synthetic fibres and likewise an un-shown source for absorbent fibres, as for instance cellulose fibres, leads synthetic fibres and absorbent fibres into the house  6  via respectively the fibre inlet  7  and the fibre inlet  8 . 
     The air-flow flows down through the wire&#39;s upper tissue  10 , while the fibres are kept back on the tissue&#39;s upper side, where those are mixed and distributed by the rotating wings  15  in an flush and homogeneous fibre layer  16  with a random and even orientation of the fibres in all directions. 
     Simultaneously the wire runs  9 &#39;s upper tissue  10  in the arrow shown direction against the plant&#39;s outlet at the winder section  5 , and delivers under here the fibre web  16  to the conveyor  2 . 
     This conveyor  2  consists of a wire  17 , which overlaps the forming head&#39;s wire  9  and runs over rollers  18 . The wire  17  has a lower tissue, which is placed on the upper side of the fibre layer  16 . 
     The suction box  20 , which is connected to a vacuum air pump  21  and is placed above the wire  17 &#39;s lower tissue, generates a negative pressure, which holds the fibre layer  16  on to the wire  17 &#39;s lower tissue  19 , which thereby will be able to transport the fibre layer  16  to the hydro-entangling section  3  in the with the arrow shown direction. 
     This hydro-entangling section  3  consists of a relatively close-meshed wire  22 , which overlaps the wire  17  of the conveyor  2  and runs above rollers  23 . The wire  22  has an upper tissue  24 , which is placed on the lower side of the fibre layer  16 . 
     A number of water nozzles  25  are placed above upper tissue  24  of the wire  22 , sending powerful water jets  26  down against the fibre layer  16 , which are held to the web by an underlying suction box  27 , which is connected to a vacuum air pump  28 . Water and loose fibres will be removed from the suction box  27  by the pump  28 . 
     The water jets wind the fibre web&#39;s different fibres together in a strong bond. A portion of the water fights at the meeting with the close-meshed wire  22 &#39;s upper tissue  24  besides back against the fibre web&#39;s lower side, supplying a flush and smooth surface. 
     Furthermore the hydro-entangling treatment effects that between the fibres, hydrogen bonds will be formed, which prevent flocculation and dust by use and during processing. 
     After the hydro-entangling treatment, the now relatively strong and well coherent fibre web runs into an oven  4 , which works at a sufficient high temperature to thermal bond the synthetic fibres in the affected area. Simultaneously the web will be dried. 
     In the oven  4  a rotating roll  29  is equipped with a perforated wall, which allows a warm flow of air to pass. The air-flow will be re-circulated as shown by the help of fans  30 . 
     During the passage of the oven  4  the fibre web  16  runs around rollers  31  and the in arrow pointing direction rotating roll  29 , by means of which the warm air will be forced through the fibre web, which dries, simultaneously a cross bond in the contact points will be formed mutually between the synthetic fibres and to a certain extent also between the synthetic fibres and the absorbent fibres. 
     Finally the finished fibre web will be wound up into a roller of fibre web  32  in the roller section  5 , which fundamentally consists of a winder  33  with a driven roller  34  and an idler roller  35 . 
     FIG. 2 shows other construction form for a plant according to the invention and separates itself from the above described and shown in FIG. 1 first construction form by, a special thermal bonding oven  36  being inserted between the conveyor  2  and the hydro-entangling section  3 . Similar parts are therefore indicated with the same reference numbers. 
     The thermal bonding oven  36  is a continuos oven, which the upper tissue  37  passes through on a wire  38 , which runs above roller  39 . The fans  40  serve the purpose of re-circulating the air across through the fibre web  16  and the upper tissue  37  of the wire  38 , which carries the fibre web. 
     The thermal bonding oven  40  works with a temperature, which is sufficiently high to bond the synthetic fibres together in the affected areas, however not that high that the fibres melt noticeably. 
     The process in the thermal bonding oven is easiest controlled, when bi-component fibres are used. When the core for example has a melting point of 180 Celsius and the shell a melting point of for example 135 Celsius, the temperature in the oven must be kept in a spot between these two temperatures to efficiently cross bond the synthetic fibres in the affected areas without risking the core to melt simultaneously. 
     One of the advantages, which is obtained by using this special thermal bonding oven  36 , consists of the fibre web  16  is stabilised in advance, thus the following hydro-entangling process can proceed with increased certainty and less fibre waste, which must be lead away in the wastewater. 
     Another advantage consists of the oven  4 , now just needs to work as a drying oven, and therefore can work with a here fore fitted lower temperature, which size furthermore is uncritical. 
     FIG. 3 shows third construction form for a plant according to the invention and separates itself from the above described and shown in FIG. 1 first construction form by, instead of only one forming head three exists placed after one-another  41 ,  42 , and  43 . Each of these forming heads are constructed in the same way as the first constructions form&#39;s forming head  1 . Similar parts are therefore indicated with the same reference numbers. 
     When the plant in this way is supplied with three forming heads, it can be used for production of sandwich-fibre web, which typically consist of a soft thermal bonded top- and bottom layer with an absorbent core. The sandwich-fibre web can for example have following combination. 
     EXAMPLE  1   
     Bottom layer  15  GSM 
     The proportions between the synthetic fibres and the absorbent fibres, such as cellulose fibres  10 - 5 . This means that 67% of the bottom layer consists of synthetic fibres and 33% of absorbent fibres. 
     Middle layer  30  GSM 
     The proportions between the synthetic fibres and the absorbent fibres, such as cellulose fibres  3 - 27 . This means that 10% of the middle layer consists of synthetic fibres and 90% of absorbent fibres. 
     Top layer  15  GSM 
     The proportions between the synthetic fibres and the absorbent fibres, such as cellulose fibres  7 - 8 . This means that 47% of the top layer consists of synthetic fibres and 53% of absorbent fibres. 
     The process processes in a way that the first forming head  41  will be supplied with the fibres for the bottom layer, the other forming head  42  with the fibres for the middle layer, and the third forming head  43  with the fibres for the top layer, thus the three layers will be formed in each layer&#39;s separate forming head  41 ,  42 ,  43  and successively will be laid on top of one-another. Subsequently the process continues in the same way as described for the first construction form. 
     The in FIG. 3 shown fourth construction form for a plant according to the invention separates itself from the above mentioned and in FIG. 3 shown third construction form by, now similar to the other construction form, and as shown in FIG. 2, a special continuous thermal bonding oven  36  is inserted between the conveyor and the hydro-entangling section  3 . Similar parts are therefore also in this case indicated with the same reference numbers. 
     With this setting of the plant according to the fourth construction form the same advantages will be achieved as described in connection with the description of the other construction form. 
     In the below table indicated data respectively for a card based product and a product according to the invention serves the purpose of making the advantages clear, which can be achieved by the invention. 
     EXAMPLE  2   
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Product 
               
               
                   
                 Card based 
                 according to 
               
               
                 Product features 
                 product 
                 the invention 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Content of thermal 
                 50% 
                   
                 5%-45% 
                   
               
               
                 bonding fibres 
               
               
                 Content of cellulose 
                 50% 
                   
                 95%-55% 
               
               
                 fibres 
               
               
                 Length of thermal 
                 12-60 
                 mm 
                 2-25 
                 mm 
               
               
                 bonding fibres 
               
               
                 Length of viscose 
                 6-60 
                 mm 
               
               
                 fibres 
               
               
                 Length of cellulose 
                 0-6 
                 mm 
                 0-6 
                 mm 
               
               
                 fibres 
               
               
                 Length of alternative 
                   
                   
                 2-25 
                 mm 
               
               
                 fibres (for example 
               
               
                 absorbent fibres) 
               
               
                 Dry strength, longitu- 
                 100 
                 N/50 mm *) 
                 25-50 
                 N/50 mm *) 
               
               
                 dinal direction 
               
               
                 Dry strength, trans- 
                 20 
                 N/50 mm *) 
                 15-30 
                 N/50 mm *) 
               
               
                 verse direction 
               
               
                 Wet strength, longitu- 
                 100 
                 N/50 mm *) 
                 19 
                 N/50 mm *) 
               
               
                 dinal direction 
               
               
                 Wet strength, trans- 
                 20 
                 N/50 mm *) 
                 11 
                 N/50 mm *) 
               
               
                 verse direction 
               
               
                 *) gram weight 
                 65 
                 g/sqm 
                 65 
                 g/sqm 
               
               
                   
               
             
          
         
       
     
     As it can be seen, a great part of the expensive synthetic fibres in the conventional card based product has been replaced by cheaper cellulose fibres in the inventive product, which in this way can manufacture at a far lower price than the conventional product. 
     Simultaneously the inventive product&#39;s strength is favourable fairly identical in the longitudinal and transverse direction, while the conventional product&#39;s corresponding strength ratio is as 5-1. 
     It must be noted that the above described and on the drawing shown constructions forms only serve as considerate examples of, how a plant according to the invention can be arranged. 
     In this way the plant can, within the frame of the invention&#39;s protection scale after need be supplied with two, four, or a bigger number of forming heads, which besides do not necessarily need to be placed in a row just after one-another. 
     Furthermore in the production line one or several further sections can be inserted to in dependency of the wished quality to treat the fibre web.