GB2149339A

GB2149339A - Manufacturing a composite web of plastic material

Info

Publication number: GB2149339A
Application number: GB08330105A
Authority: GB
Inventors: Arthur A Zufang; Robert Antonius Maria J Fabrie
Original assignee: Stork Brabant BV
Current assignee: Stork Brabant BV
Priority date: 1983-11-11
Filing date: 1983-11-11
Publication date: 1985-06-12
Also published as: GB2149339B; GB8330105D0

Abstract

A web of plastic material having filtering properties comprises a porous layer interconnected with a non woven layer of plastic fibres. The porous layer consists of polyester fibres and the nonwoven layer of polypropylene fibres. An apparatus for manufacturing the web comprises a heated central roller (6), an endless metal band (14) engaging a cooled second roller (17), said heatable central roller (6) and an endless felt band (8) partially surrounding the heatable central roller and a part of the metal band (14), the untreated material (12) being passed between said endless metal band (14) and said felt band (8) for heating by the roller (6), the treated web (18) being cooled by roller (17) on its way to a coiling reel (16). In a modified apparatus, Fig. 3 (not shown), the central roller is cooled and a separate heating member is disposed opposite the outer surface of the roller. <IMAGE>

Description

SPECIFICATION A web of plastic material, more particularly a web of plastic material presenting filtering properties, and a method and apparatus for manufacturing said web This invention relates to a web of plastic material, more particularly a web of plastic material presenting filtering properties obtained by heat treatment while retaining the base material in such a manner that the base material has undergone a controlled stretch or shrinkage.

Such a web of plastic material as obtained by retaining, for example, a polyester or nonwoven sheet material in a tenter, and heating same, for example, up to 200 C, is known in the art.

This heating process provides stability to the material sothat it can be used at a working temperature of up to 200 C without drastic changes in shape or appearance occurring.

A web of plastic material of this kind is relatively expensive, since the base material has to be clamped in a tenter, while heating up to the predetermined temperature also requires very accurate processing conditions.

On the other hand, there is also known a web-shaped plastic nonwoven material obtained by impregnating a plastic nonwoven with plastic resin, and subsequently curing the plastic resin by heat, said treatment being carried out on a roller calender. A drawback of this known web-shaped plastic nonwoven is that the heat treatment must take place within a short time and with high line pressure between the rollers of the roller calender and the base material.

Finally, when subjecting a web-shaped plastic material composed of a laminate of two nonwovens of different plastic materials, the disadvantage arises that, when heating the plastic fibtres having the lowest melting point up to the melting temperature, said plastic fibres will fuse together and form a very small mass, all favourable properties of the webshaped plastic material thus getting lost.

It is therefore an object of the resent invention to provide a web-shaped plastic material which is easier to manufacture and, in addition, has optimum strength properties, without the necessity of using a tenter or roller calender.

This oject is attained according to the invention in that the web of plastic material has been formed by passing the base material through a region formed by a roller and an endless band at least partially slung around said roller, while heat is supplied.

When applying these measures, which can be carried out effectively by using a band calender, it is possible to accurately control the degree of pressure between the band and the roller, and, in addition, to work with relatively low pressure forces, enabling the contact times to be long in comparison with contact times and pressure forces in a roller calender, which results in optimum quality of the final product.

Advantageously, the web of plastic material consists of a first nonwoven layer of plastic fibres having a higher platicizing point than another plastic layer bonded to said nonwoven layer.

Such a web of plastic material is suitable for a wide range of applications, and, in case the other plastic layer is a porous platic layer, the web of plastic material is particularly well adapted for use as a filtering material.

Especially good filtering materials are obtained when one surface of the other porous plastic layer is free from plastic fibres projecting from the first nonwoven layer, and has been obtained by fusing together plastic fibres of another nonwoven layer.

Particularly such a web of plastic material is suitable for filtering compositions of liquid foodstuffs, such as milk, but also for many other types of filtration, as the first nonwoven layer retains its normal properties, and the other plastic layer on the other hand, is provided with specified pores to allow liquid passage.

The web shaped plastic material according to the present invention particularly possesses very well controlled stretch or shrinkage properties, as a result of which it can be used in an optimum manner as an industrial product so as to manufacture other products.

The invention also relates to a method of manufacturing a web of plastic material, more particularly a web of plastic material with filtering properties, by subjecting a webshaped base material to heat treatment while retaining said base material in such a manner, that said material is subjected to a controlled stretch or shrinkage, the base material passing through a region located between a roller and an endless band at least partially slung around said roller, while heat is supplied.

This method provides a web of plastic material having optimum properties as compared with products manufactured so far on tenters or by means of roller calenders.

Advantageously, the surface pressure during treatment is comprised between 0,05 and 3 kg/cm2, preferably 0,10 and 0,15 kg/cm2, the temperature being comprised between 25 and 300 C at a contact time between 1 and 60 sec, preferably 5 and 15 sec.

The method according to the invention moreover provides particularly great advantages in the event that heat treatment is carried out in several regions located at or in the vicinity of the circumference of a central roller, to wit subsequently a preheating region, a constant-temperature region and a cooling region, preferably around a central roller, which affords optimum properties to be obtained. In this way a web of excellent quality is obtained.

Effectively, a layer of a release agent is applied upon the base product, upon the central roller and/or upon one or several of the bands at least partially slung around the roller and engaging the plastic material, so as to enable easy removal of the finished product, if the product, in the absence of a release agent, would adhere to the surface areas of the roller and/or one several bands being at least partially slung around the roller.

Effectively, the release agent is applied by means of a traversely moving felt strip.

The present invention is further embodied in apparatus for performing the method of the invention, consisting of a central roller which co-operates with an endless band being at least partially, slung around the circumference of the central roller, as well as a guide means provided for the endless band and a tensioning means for pressing the band against the roller surface with controllable force, said apparatus being provided with at least one heat-supply member and at least one cooling member An advantageous embodiment of the apparatus according to the invention is characterised in that, the first endless band consists of a a heat-conducting material and in that at least one heat-supply member is disposed along a portion of the circumference of the central coolable roller covered by the first band which has been partially slung around the central roller.This allows a very high production speed as the coolable roller will rapidly cool the band of heat-conducting material so that the plastic material after heating will easily loosen from said band.

According to another advantageous embodiment of the present invention, at least two bands are slung around a central heatable roller, one of the bands being a band having a low heat resistance and being disposed between the central heatable roller and a heatinsulating, second endless band being said first band, said band with low heat resistance being passed through a cooling region located outside the circumference of the central roller.

Due to the presence of the band of a low heat resistance the heat-treated web will easily loosen from said band after cooling, whilst on the other hand this band will not impair the effectivity of the heat treatment.

The invention will now be illustrated with respect to an embodiment in the accompanying drawings, wherein: Figure 1 is a cross-sectional view of a web of plastic material according to the present invention; Figure 2 is a first embodiment of an apparatus according to the invention; Figure 3 is a second embodiment of an apparatus according to the invention; and Figure 4 is a schematic view of the base material.

Fig. 1 shows a web of plastic material according to the invention, comprising a first polyester nonwoven 1 adhesively bounded with another plastic layer 2 obtained by fusing polyolefin fibres, more particularly polypropylene fibres. Said other plastic layer 2 is fused in such a manner that the layer is provided with pores 3.

As can be seen, the other plastic layer in the form of porous polypropylene sheet material 2 is, on one surface, adhesively bonded with the first polyester nonwoven fabric whose fibres are secured in the polypropylene sheet material 2. The other surface 4 of the webshaped plastic material is free from projecting fibres.

A material of this type lends itself particularly well to being used as a filtering material for milk, but also for other filtration processes.

Fig. 2 illustrates an apparatus according to the invention, comprising a central roller 6 provided with heating coils 7 and/or a supply and discharge means for a heating fluid to bring this central roller to a predetermined temperature.

An endless felt band 8 is partially slung around the circumference of the central roller 6 and passes over guide rollers 9 and tension- ing rollers 10 and 11 to press the felt band 8 against the central roller 6 with the desired force, thus enabling the pressure desired to be exerted upon a web-shaped laminate 12 of a nonwoven material of polyolefin fibres, particularly polypropylene fibres, which have been consolidated with a first nonwoven of polyester fibres by needle-punching.

Said laminated composite nonwoven 12 is fed from a reel 13 or other feed mechanism of base material.

Co-operating with the outer surface of the central roller 6 there is a second endless band or follower 14 having a low heat resistance, such as for example, a metal foil band provided with a thin layer of polylester or a thin band of glass-fibre teflon (RTM). This second band 14 passes via a coolable roller 17, past which there is disposed a conveyor belt 15 for guiding the web of plastic material, referenced 18 and obtained according to the invention, to a coiling reel 16 or other type of coiling mechanism.

In using a composite nonwoven of polypropylene fibres and a nonwoven layer of polyester fibres consolidated therwith by needling, the temperature of the central roller 6 may be approximately 1 80 C, the contact time in the heating zone then being 10 sec.

In the path where the web-shaped plastic material formed according to the invention leaves the surface of the central roller 6, the finished product is cooled, the coolable roller 17 cooling it ultimately to a temperature below 1 00 C, for example 60 C. To this effect, the cooled roller 17 is fed with cooling water of for example 20 C by way of the cooling water feed means 19 and cooling-water outlet means 20.

In general, the surface pressure between the felt band 8 and the second or follower band 14 is chosen so as to be comprised between 0,5 and 3 kg/cm2, and preferably between 0,10 and 0,15 kg/cm2. The temperature is preferably comprised between 25 and 300 C at a total contact time of 1 to 60 sec, preferably 5 to 15 sec between the follower band 14 and felt band 8.

Fig. 3 shows still another embodiment of the invention comprising a cooled central roller 6' provided with a central supply means 21 for supplying cooling water so that the circumferential surface of the central roller 6 is cooled to, for example, room temperature.

The web of composite nonwoven 12 likewise supplied from a supply reel 13 and composed of a nonwoven of polyester fibres and a nonwoven of polypropylene fibres consolidated with each other by needling, is pressed against the surface of the cooled central roller 6' by means of a first, endless band 8'. For supplying the heat required for the heat treatment, the apparatus is provided with a heating member 22 disposed oposite the circumferential surface of the central roller 6', but in such a manner that the heat is being supplied from the heating member 22 over part of the portion of the central roller 6', an endless band 8' being slung around this roller.Cooling of the heat-treated composite nonwoven web the fibres of the polypropylene having been fused to a porous layer, takes place after having passed the operative region of the heating member 22, thus in the area indicated by the arrows 24, 24'.

After leaving the central roller 6', the obtained porous polypropylene sheet material 2 along with the polyester nonwoven 5 adhesively bonded therwith, is passed to the coiling reel 16 through conveyor belt 15.

In order to prevent the composite nonwoven product 18 from adhering to the central roller 6' or to the heat-conducting, first endless band 8', it may be advisable to apply a release agent on said surfaces by means of a a release-agent aplicator means 23, for example in the form of a traversely moving felt strip.

It is of course also possible to apply the release agent directly upon the two surfaces of the base material by means of a releaseagent applicator 23', as shown in Fig. 3.

It is obviously also possible to apply the release agent upon the second endless band 14 and upon the felt band 8' by means of release-agent applicators 23.

Fig. 4 is a schematic view of the base product comprising a nonwoven 1 of polyester fibres and a nonwoven 2' of polypropylene fibres consolidated with each other by a needle-punching operation.

During the heat treatment in the apparatus, as illustrated in Fig. 2, the polypropylene nonwoven 2 is guided in such a manner as to abut against the second endless band or follower band 14.

In the embodiment of the apparatus of Fig.

3, however, the polypropylene nonwoven 2' is guided so as to abut against the metal foil band 8' provided with a polyester layer.

The endless band 8' may, however, also consist of silicone paper or teflon (RTM) foil material, the smoothness of the surface of the laminated propylene layer 2' obviously also depending upon the smoothness of said endless band 8'.

In the embodiment of Fig. 2, the central roller 6 has a surface temperature of at least 190 C; in any event the temperature should be below 225 C, as, at the latter temperature, the polyester would melt.

In the foregoing, the application of a release agent by means of a traversely moving felt strip is described, but said release agent may obviously also be applied by spraying or by means of a roller applicator.

The invention will now be further explained with respect to some exemplified embodiments.

EXAMPLE I A band calender as shown in Fig. 3 is fed with a composite nonwoven layer consisting, for 20% of its weight, of a nonwoven layer of polypropylene and, for 80% of its weight, of a nonwoven layer of polyester, said two layers being consolidated with each other by needlepunching.

To obtain a filtering material in which the polypropylene is fused to a smooth porous layer and the polyester nonwoven adhering thereto as a voluminous filtering layer, the composite web of nonwovens is heated, by means of a heating element 22, to a temperature of 180 C. A heat-conducting band 8' of coper foil is used which, on its side being in contact with the nonwoven layer, of polypropylene, is provided with a coating of polyester.

The contact time in the heating region, heated by the heating member 22, is 10 sec, whereas subsequent cooling to a temperature of 80 C proceeds by means of the cooled central roller 6'. Hereupon the conveyor belt 18 carries the web-shaped material as obtained according to the invention to coiling reel 16.

The web of plastic material thus obtained and presenting excellent filtering properties consists of a polyester nonwoven whose polyester fibres are firmly secured in a polypropylene layer 2 provided with pores and formed by a fusing of the polypropylene fibres of the polyprolylene nonwoven 2'.

The pore structure in the layer 2 is such that polyester fibres possibly becoming disen gaged during the use of the web material according to the invention, are retained by the polypropylene filter material 2.

EXAMPLE II A web of composite nonwoven fabric is treated as described in example I in a felt band calender according to Fig. 2. The central roller 6 has a surface temperature of 190 C.

The copper-foil band 14 having low heat resistance then melts the fibres of polypropylene to a porous layer and conveys the sheet material 18 as obtained to the cooling roller 17 where the coper foil band 14 is cooled by water. Due to the cooling the copper will contract and thus the composite web material having a temperature of 80 C is separated from the copper band 14. Subsequently, the web of plastic material according to the invention, presenting excellent filtering propoerties will be coiled.

Claims

1. A web of plastics material obtained by heat treatment while retaining the base material in such a manner that the base material has undergone a controlled stretch or shrinkage, wherein the web of plastics material has been formed by passing the base material through a region formed by a roller and an endless band at least partially slung around said roller, while heat is supplied.

2. A web of plastics material according to Claim 1, which web has filtering properties.

3. A web of plastics material according to Claim 1 or 2, wherein the web consists of a first nonwoven layer of plastics fibres having a higher plasticizing point than another plastics layer consolidated with said nonwoven layer.

4. A web of plastics material according to Claim 3, wherein the other plastics layer is a porous plastics layer.

5. A web of plastics material according to Claim-4, wherein one surface of the porous plastics layer is free from plastics fibres projecting from the first nonwoven layer.

6. A web of plastics material according to any of Claims 3 to 5, wherein the other plastics layer has been obtained by fusing together plastics fibres of another nonwoven layer.

7. A web of plastics material according to Claim 6, wherein the other plastics layer has been formed by fusing together a second nonwoven layer of polyolefin fibres, whilst the first nonwoven layer consists of polyester fibres.

8. A web of plastics material according to Claim 7, wherein the polyolefin fibres are polypropylene fibres.

9. A method-of manufacturing a web of plastics material by subjecting a web-shaped base material to heat treatment while retaining said base material in such a manner that said base material undergoes a controlled stretch or shrinkage, wherein the base material passes through a region located between a roller and an endless band at least partially slung around said roller, while heat is sup plied.

10. A method according to Claim 9, wherein the base material comprises a first nonwoven layer consisting of plastics fibres having a higher plasticizing point than another plastics layer consolidated with said nonwoven layer.

11. A method according to Claim 10, wherein the other plastics layer is transformed into a porous plastics layer.

12. A method according to Claim 11, wherein the porous plastics layer is formed in such a manner that one surface thereof is free from plastics fibres projecting from the first nonwoven layer.

13. A method according to any one of Claims 10 to 12, wherein the platics fibres of another nonwoven layer are fused to form said other plastics layer.

14. A method according to Claim 13, wherein the other plastics layer is formed by fusing together a second nonwoven layer of polyolefin fibres and the first nonwoven layer consists of polyester fibres, the base layers being consolidated with each other by needle punching.

15. A method according to Claim 14, wherein the polyolefin fibres are polypropyl ene fibres.

16. A method according to any one of Claims 9 to 15, wherein the surface pressure during heat treatment is between 0.5 and 3 kg/cm2 (4.9 X 104 and 2.9 x 105 N/m2) and the temperature is between 25 and 300 C at a contact time between 1 and 60 seconds.

17. A method according to Claim 16, wherein the surface pressure is between 0.1 and 0.15Kg/cm2 (9.8 x 103 and 1.5 x 104 N/m2).

18. A method according to Claim 16 or 17, wherein the contact time is between 5 #and 15 seconds.

19. A method according to any one of Claims 9 to 18, which includes a cooling step.

20. A method according to any one of Claims 9 to 19, wherein the heat treatment is carried out in several regions located at or in the vicinity of the circumference of the roller.

21. A method according to Claim 20, wherein the base material is pased succes sively through a heating region, a constant temperature region and a cooling region.

22. A method according to any one of Claims 9 to 21, wherein a layer of a release agent is applied to the base material, the roller and/o,r the band at least partially slung around the roller.

23. A- method according to Claim 22, wherein the release agent is continuously ap plied by means of a transversely moving felt strip.

24. An apparatus suitable for manufacturing a web of plastics material by subjecting a web-shaped base material to heat treatment while retaining said base material in such a manner that said base material undergoes a controlled stretch or shrinkage, the apparatus comprising a roller cooperating with a first endless band which is at least partially slung around the circumference of the roller, at least one guide roller and/or at least one pressure adjusting roller for pressing the band against the surface of the roller with controllable force, at least one heat-supply means and at least one cooling means.

25. An apparatus according to Claim 24, wherein the first endless band comprises a heat-conductng material and at least one heatsupply means extends along a part of the circumference of the roller which is covered by the first endless band, the roller being coolable.

26. An apparatus according to Claim 24, wherein the first endless band comprises a heat-insulating material, a second endless band comprising a heat-conducting material is disposed between the roller and the first endless band, the roller is heatable and the second endless band passes through a cooling region.

27. An apparatus according to Claim 26, wherein the cooling region comprises a cooling roller.

28. A web of plastics material, substantially as hereinbefore described with reference to, and as shown in, Fig. 1 of the accompany- ing drawings.

29. A method of manufacturing a web of plastics material, substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

30. A method of manufacturing a web of plastics material, substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

31. A method of manufacturing a web of plastics material, substantially as hereinbefore described with reference to Example I.

32. A method of manufacturing a web of plastics material, substantially as hereinbefore described with reference to Example II.

33. An apparatus for manufacturing a web of plastics material, substantially as hereinbefore described with reference to, and as shown in, Fig. 2 of the accompanying drawings.

34. An apparatus for manufacturing a web of plastics material, substantially as hereinbefore described with reference to, and as shown in Fig. 3 of the accompanying drawings.

35. Any novel feature or combination of features described herein.