CA2185928C

CA2185928C - Method of producing a composite web

Info

Publication number: CA2185928C
Application number: CA002185928A
Authority: CA
Inventors: Bernd Kunze; Hans Dieter Ott
Original assignee: Reifenhaeuser GmbH and Co KG Maschinenenfabrik
Current assignee: Reifenhaeuser GmbH and Co KG Maschinenenfabrik
Priority date: 1995-09-19
Filing date: 1996-09-18
Publication date: 2007-01-16
Anticipated expiration: 2016-09-18
Also published as: KR100363452B1; DE19534702A1; EP0764521A3; KR970015825A; DK0764521T3; EP0764521B1; ES2188700T3; MX9604075A; EP0764521A2; CA2185928A1

Abstract

A molten strand of a thermoplastic synthetic resin from a wide-slit nozzle is electrostatically charged before it contacts a fleece of thermoplastic filament and/or fibers, the latter passes onto a drum or roller at a temperature below the~
melting temperature of the filaments and/or fibers so that the electrostatic forces cause bonding of the foil to the fleece, thereby forming a composite web. Because of the electrostatic forces, pressing of the composite, e.g. with a calender, is not necessary.

Description

2~3 METHOD OF PRODITCING A COMPOSITE WEB
FIELD OF THE INVENTION
Our present invention relates to a method of producing a composite web from a nonwoven fleece of synthetic resin (thermoplastic) filaments and/or synthetic-resin (thermoplastic) fibers, and a synthetic resin foil on one side of said fleece and also composed of a thermoplastic synthetic resin. The nonwoven fleece itself can be composed of one or more layers but preferably is a single layer or a layer composed of synthetic resin filaments and a further layer of synthetic resin fibers.
In other words, the fleece can be of one or more layers and each of the layers can be either composed of spun-bond or melt-blown material.
BACKGROUND OF THE INVENTION
A composite web of a fleece and a foil has been made in the past by applying the nonwoven fleece to the synthetic resin foil or vice versa and pressing them together by mechanical pressing forces, with heating, to bond the two materials together or by bonding the two materials through the intermediary of an adhesive. Generally an appropriate calender is provided for 20~ . 2185928 pressing the two materials together and the calender can thus be considered a pressing unit.
The calenders required for this purpose are relatively expensive and the product which is fabricated by the use of such calenders, as well as the produciton rate, can be improved.
It is the principal object ofthe present disclosure, therefore, to provide an improved method of or process for producing a composite web of a nonwoven fleece and a synthetic resin foil which will provide an improved product at lower cost than earlier systems and is also free from drawbacks of earlier systems.
Another object is to provide a method for the continuous production of a composite web in which the nonwoven fleece is composed of spun-bond or synthetic resin filaments and/or of melt-blown or synthetic resin fibers which does not require the use of expensive calenders.
Still another object is to provide a method of forming a composite web in which the bond between the synthetic resin foil and the melt-blown fibers and/or spun-bond filaments of the fleece is enhanced_ More particularly, this disclosure provides a continuous process for producing a composite web of a nonwoven fleece of synthetic resin filaments and/or synthetic resin fibers of a thermoplastic synthetic resin and a synthetic resin foil bonded on one side of the fleece and composed of a thermoplastic synthetic resin, which is characterized by the following features:
the nonwoven fleece is fed at a,temperature which is significantly lower than the melting temperature of the thermoplastified synthetic resin thereof to the station at which it is to be bonded to the foil:
the nonwoven fleece at this temperature is fed onto a roller or drum on which the bonding to the foil is to be effected while the roller is rotated at a peripheral speed corresponding to the feed speed of the fleece, the roller extending at least over the full width of the nonwoven fleece;
the synthetic resin foil is produced by a wide-slit nozzle from a melt of thermoplastic synthetic resin of the foil with the mouth of the nozzle being located in the region at which the nonwoven fleece is fed onto the roller or drum and the synthetic resin foil in a virgin plastic state is directed substantially tangentially into contact with the fleece on the drum so that contact is made between the synthetic resin of the foil and the fleece at approximately the melting or thermoplastified temperature of the foil material and before full solidification thereof; and in the region in which the foil, still in its plastic state, comes into contact with the fleece on the roller or the drum, the foil is electrostatically charged with the aid of at least one electron-generating corona electrode which extends transversely to the direction of travel of the fleece and the foil.
As a consequence, there is an electrostatic bonding of the foil to the fleece before the foil is fully cooled, whereupon cooling can be carried out on the drum or roller or thereafter to yield the resulting composite web.
while we have mentioned a synthetic resin foil and indeed the continuous layer bonded to the fleece can be properly described as such following the cooling stage, it will be understood that at the time this "foil" contacts the nonwoven fleece.and until cooling is complete, the continuous strand of the synthetic resin material emerging from the wide slit nozzle and contacting the fleece may not have sufficient coherency to consider it a web, i.e. this strand has not cooled or solidified sufficiently to be fully coherent. It emerges from the wide slit nozzle over the width of the fleece and with the thickness of the foil rather as a molten strand of the thermoplastic material and is deposited as such after being electrostatically charged, on the fleece_ With the new system, mechanical pressure as has been applied in the past in a calender is no longer required to consolidate the nonwoven fleece and the synthetic resin foil. Surprisingly, the electrostatic charging of the foil provides sufficient force to enable the foil to bond to the filaments or fibers and indeed to mold around the filaments and fibers so as to hug them with a substantial contact area between the filaments or fibers and the foil to. provide an improved bond without the mechanical consolidation hitherto deemed to be necessary. The electrostatic charging can be effected with at least one electron=discharging corona electrode which can extend transversely to the feed direction and, if desired, two or more such electrodes can be provided. The electrostatic forces which result have been found to be very high.
The new process can be carried out with the nonwoven fleece at a range of temperatures, depending upon the material used, including ambient or room temperature. When high outputs are desired, it has been found to be advantageous to preheat the fleece before it is fed to the bonding station.
Indeed, optimum temperatures for any particular material can be readily determined empirically by trial techniques with which the effective fleece and foil temperatures, the feed rate, the degree of heating of the roller or drum, the extrusion rate of the synthetic resin foil and the electrostatic charge to be applied can be readily determined.
It has been found to be advantageous to adjust these parameters so that the foil material slumps around the filaments or fibers so that it will lie in contact with the filaments or fibers over an arc length of 900 or more. As a result, the _ 5 _ 20~ 218928 material of thefoil is so intimately intercalated in the fleece.
that an improved bond is obtained over any which can be provided merely by mechanical pressing between two rollers. Indeed, the molten strand emerging from the wide-slit nozzle is sufficiently plastic and its surface tension remains sufficiently effective to promote the flow of the foil material around the individual filaments or fibers of the fleece.
Electron-emitting corona electrodes are widely used for a variety of purposes and any of the material variants thereof can be utilized for the purposes described herein. They are utilized, for example, in electrostatic filters where, in principle, they also promote adhesion, albeit of dust particles to a surface. As far as we are aware, it has not been recognized heretofore that electrostatic forces can promote bonding of a molten strand of synthetic resin from a wide-slit nozzle to a thermoplastic fleece of spun bond and/or melt blown.
It has been found to be advantageous to subject the nonwoven fleece prior to bonding to the foil to a biaxial stretching with a preferred stretching ratio in each of two mutually perpendicular directions of say 1.4. The fleece can be composed of spun bond or melt-blown filaments or fibers which, in the filament-producing or fiber-producing processes can be subjected to stretching at ratios of 1:20 to 1:30.
The speed of the nonwoven fleece at the bonding station and the speed with which the molten strand of thermoplastic is extruded from the wide-slit nozzle can be more or less the same;

2.03 although it is also possible to subject the foil to some elongation upon contact with the web or to cause the foil material to bunch up at contact with the fleece.
According to one feature of this disclosure the nonwoven fleece is heated to a laminating temperature lower than the melting temperature of thermoplastified synthetic resin of the fleece but higher than ambient temperature. -Preferably the temperature of the nonwoven fleece on the roller, the speed with which the thermoplastic foil is extruded from the wide-slit nozzle and the electrostatic charge applied to the thermoplastic foil are so selected that the thermoplastic foil has a contact angle with thermoplastic synthetic resin fibers or filaments of the nonwoven fleece of 900 to in excess of 1800.
Of course, the parameters with which the new process operates will depend upon the materials used. It has been found to be most advantageous, however, to operate with a nonwoven flesce with a basis weight of 15 to 25 g/m', preferably 17 g/m', and a synthetic.resin foil with a melting point temperature of 80oC to 160°G and with foil thicknesses of 12 to 18 ~Cm, preferably about 14 um, with the nonwoven fleece being preheated to a bonding temperature of about 60°C and the drum or roller 7 _ ~2,~~9~8 2 0~3 , held at a temperature of about 50°C so that at least partial cooling is effected on the drum or roller.
The nonwoven fleece can be composed of polypropylene fibers and/or.filaments while the synthetic resin foil can be an ethylene-acrylic acid ester thermoplastic-to which the aforementioned parameters are especially applicable. The foil can also be composed of PP (polypropylene), LPDE (low-density polyethylene), LLDPE and HDPE (high-density polyethylene) or mixtures thereof.
The electrostatic charging must, of course, be sufficient to effect the bonding previously described and, of course, the maximum possible electrostatic charge should thus be applied for that purpose. This can be achieved by providing the bonding roller or drum with a metallic surface or making the drum or roller of metal and connecting the drum surface with respect to the corona electrode as an anode. It is, however, also possible to provide at least the surface of the drum or roller of a dielectric material.
Between the corona electrode and the synthetic resin strand forming the foil, a further nonwoven fleece can be fed so that it is additionally bonded electrostatically to the foil_ _ g _ 20~~ ' 2ls~s~s This additional nonwoven fleece can be composed of cellulosic filaments and/or fibers.
More particularly, in accordance with the invention, there is provided a process forthe continuous production of a composite web comprising the steps of.
(a) continuously supplying a nonwoven fleece of thermoplastic synthetic resin fibers or filaments to a laminating station at a temperature substantially below a melting temperature of thermoplastified synthetic resin of the fleece;
(b) passing the nonwoven fleece of thermoplastic synthetic resin fibers or filament at the temperature substantially below the melting temperature of the thermoplastified synthetic resin of the fleece over a laminating roller rotating at aperipheral speed at the station IS corresponding to a speed with which the nonwoven fleece is fed to the station and of a length at least equal to a width of the nonwoven fleece;
(c) extruding a thermoplastic foil directly onto one side of the nonwoven fleece on the roller from a wide-slit nozzle supplied with a thermoplastic melt at a region at which the nonwoven fleece runs onto the roller and in a direction which is generally tangential to the nonwovenfleece on the roller upon contact of the thermoplastic foil with the nonwoven fleece, _ g _ ~ ~~.~~~~8 whereby the foil contacts the nonwoven fleece in a virgin plastic state of the thermoplastic foil;
(d) electrostatically charging the thermoplastic foil while the thermoplastic foil is in the plastic state in a region in which the thermoplastic foil initially contacts the nonwoven fleece with a corona electrode extending transversely of a direction of advance of the nonwoven fleece and the foil whereby the foil bonds intimately to the nonwoven fleece to form a laminate web on the roller; and {e) cooling the laminate web.
The advantages of the process include the elimination of any need for-mechanical pressing and hence of the calenders hitherto utilized for the purpose while nevertheless obtaining an improved bond. The new process-therefore also facilitates mass production.
Embodiments of the invention will now be described, reference being made to the accompanying drawings in which:
FIG_ 1 is a diagram of an apparatus for carrying out a process embodying theinvention;

~~$~~~8 FIG. 2 is a diagram of another embodiment of the apparatus;
FIG. 3 is a diagram of a third embodiment for practicing the method of the-invention; and FIG. 4 is a diagram illustrating the bond formed between the foil and the filaments or fibers of the web.
SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIGS. 1-3 of- the drawing, corresponding elements have been identified with the same reference numerals. In all of these embodiments, a nonwoven fleece 2, is withdrawn from a supply unit 1 which can be a supply coil, a fabricating machine for the nonwoven fleece, a system for biaxial stretching thereof, an arrangement for combining a spun bond (filaments) fleece with a melt-blown (fiber) fleece or the like. A synthetic resin molten strand 3 which can be cooled to form a foil, is extruded from a wide-slit nozzle 4 extending over the entire width of the fleece 2 in the same direction as that in which the fleece is fed. In-all cases, moreover, just upstream of the location at which the strand of molten thermoplastic synthetic resin of the foil meets the fleece, there is an electron-emitting corona electrode 5 extending transversely to the direction of feed of ~~~~~2~

the fleece and the foil and perpendicular to the plane of the paper in FIGS. 1-3 to electrostatically charge the foil 3.
The fleece 2 can be heated to a bonding temperature which is substantially less than the melting temperature of the fibers or filaments of the fleece which can be about 250°C. The preheated fleece 2 is fed to the receiving region 6 of a bonding roller or drum 7 which is rotated, e.g. in the clockwise sense in FIGS. 1-3 at a peripheral speed that can correspond to the speed with which the nonwoven fleece 2 is fed to the roller which extends over the full width of the fleece. The rotation of the roller or drum 7 has been indicated by a curved arrow.
In the embodiment of FIG. l, the supply 1 can be a coil of the nonwoven fleece 2 which is drawn from this coil and passed over a heating roller 8 on which the nonwoven fleece is preheated to the bonding temperature of 60°C. The roller or drum 7 itself is heated to the temperature of 50°C and the mouth or slit 9 of the nozzle 4 is located in the receiving region 6 of the roller or drum 7 and the virgin plastic material from the wide nozzle contacts the fleece 2 in the still at least partially molten form of the plastic material which has been previously charged. The electrostatic forces which result from charging of the foil draw the fbil around the filaments or fibers so that contact between the foil material and the fibers or filaments can extend over ~~~8~~28 arcs in excess of 90°. On the roller 7 or downstream of the roller 7, the composite web 2, 3 is cooled.
From FIGS. 2 and 3, it will be apparent that an additional nonwoven fleece 10 can be passed between the corona electrode 5 and the contact point of the foil with the fleece 2 so that the electrostatic forces also draw the additional fleece against the foil and produce a sandwich composite in which the foil is sandwiched between the thermoplastic fiber and/or filament fleece 2 and the fleece 10 which can be composed of a 10 cellulose, fluff, fiber or filament product.
From FIG. 4, it can be seen that the contact with the fibers or filaments 1l of the foil material 3 can be in the form of loops or undulations around the fibers or filaments with arc lengths up to 180° and more, the preferred arc length of contact being 90° to 180°.

Claims

CLAIMS:

1. A process for the continuous production of a composite web, comprising the steps of:

(a) continuously supplying a nonwoven fleece of thermoplastic synthetic resin fibers or filaments to a laminating station at a lamination temperature substantially below a melting temperature of thermoplastified synthetic resin of said fleece but above ambient temperature;

(b) passing said nonwoven fleece of thermoplastic synthetic resin fibers or filament at said lamination temperature substantially below said melting temperature of the thermoplastified synthetic resin of said fleece over a laminating roller rotating at a peripheral speed at said station corresponding to a speed with which said nonwoven fleece is fed to said station and of a length at least equal to a width of said nonwoven fleece;

(c) extruding a thermoplastic foil directly onto one side of said nonwoven fleece on said roller from a wide-slit nozzle supplied with a thermoplastic melt at a region at which said nonwoven fleece runs onto said roller and in a direction which is generally tangential to said nonwoven fleece on said roller upon contact of said thermoplastic foil with said nonwoven fleece, whereby said foil contacts said nonwoven fleece in a virgin plastic state of the thermoplastic foil;
(d) electrostatically charging said thermoplastic foil while said thermoplastic foil is in said plastic state in a region in which said thermoplastic foil initially contacts said nonwoven fleece with a corona electrode extending transversely of a direction of advance of said nonwoven fleece and said foil whereby said foil bonds intimately to said nonwoven fleece to form a laminate web on said roller; and (e) cooling said laminate web, whereby the temperatures, the feeding speed, the speed of extrusion of the thermoplastic foil from the wide slit nozzle and the electrostatic charging are selected such that the thermoplastic foil in the region of contact surrounds the synthetic resin filaments and/or fibers at an enclosure angle in the range of 90 to 180 degrees or more.

2. The method defined in claim 1 wherein said laminate web is cooled on said roller in step (e).

3. The method defined in claim 1 wherein said laminate web is cooled downstream of said roller in step (e).

4. The method defined in claim 1 wherein said nonwoven fleece is heated in step (a) to a laminating temperature lower than the melting temperature of thermoplastified synthetic resin of said fleece but higher than ambient temperature.

5. The method defined in claim 1 wherein the temperature of the nonwoven fleece on said roller, the speed with which said thermoplastic foil is extruded from said wide-slit nozzle and the electrostatic charge applied to said thermoplastic foil are so selected that the thermoplastic foil has a contact angle with thermoplastic synthetic resin fibers or filaments of said nonwoven fleece of 90°to in excess of 180°.

6. The method defined in claim 1 wherein said thermoplastic synthetic resin of said nonwoven fleece is a polyolefin or a mixture containing a polyolefin.

7. The method defined in claim 4 wherein said thermoplastic foil is a polyolefin or a mixture containing a polyolefin.

8. The method defined in claim 4 wherein said nonwoven fleece has a basis weight of 6 to 25 g/m2 and said thermoplastic foil has a thickness of 3 to 20 µm, said laminating temperature is about 60°C and said roller is maintained at a temperature of about 50°C.

9. The method defined in claim 8 wherein said nonwoven fleece is composed of polypropylene and said thermoplastic foil is a foil of a polyethylene-acrylic acid ester.

10. The method defined in claim 1 wherein said roller has at least an outer surface onto which said nonwoven fleece is applied and composed of metal, said method further comprising the step of grounding said outer surface.

11. The method defined in claim 10 wherein the roller is composed of metal and is grounded.

12. The method defined in claim 1 wherein said roller has at least an outer surface onto which said nonwoven fleece is applied and composed of metal, said method further comprising the step of connecting said outer surface as an anode with respect to said corona electrode.

13. The method defined in claim 1 wherein said roller has at least an outer surface onto which said nonwoven fleece is~
applied and composed of a dielectric.

14. The method defined in claim 9 wherein the temperature of the nonwoven fleece on said roller, the speed with which said thermoplastic foil is extruded from said wide-slit nozzle and the electrostatic charge applied to said thermoplastic foil are so selected that the thermoplastic foil has a contact angle with thermoplastic synthetic resin fibers or filaments of said nonwoven fleece of 90° to in excess of 180°.

15. The method defined in claim 14 wherein said roller has at least an outer surface onto which said nonwoven fleece is applied and composed of metal, said method further comprising the step of grounding said outer surface.

16. The method defined in claim 14 wherein the roller is composed of metal and is grounded.

17. The method defined in claim 14 wherein said roller has at least an outer surface onto which said nonwoven fleece is applied and composed of metal, said method further comprising the step of connecting said outer surface as an anode with respect to said corona electrode.

18. The method defined in claim 14 wherein said roller has at least an outer surface onto which said nonwoven fleece is applied and composed of a dielectric.

19. The method defined in claim 1 wherein a cellulosic fleece is fed between said electrode and said foil for bonding to said composite web.