Apparatus and method for realizing a web of fibrous material

Abstract

An apparatus for producing a web of fibrous material includes a roll having incisions with a depth of 0.01-2.00 mm, a width of 0.01-2.00 mm, and a pitch 0.01-10.00 mm, and rotated at a peripheral velocity v.sub.1 equal to the velocity of an upstream apparatus unit; a belt stretched between transmission rollers that advances at a velocity v.sub.2 less than v.sub.1, wherein v.sub.1/v.sub.2 lies between 1.05 and 1.40; a presser roller rotating at a peripheral velocity v.sub.2, associated with a presser system acting to press the belt against the metal roll with a pressure of 1-200 kg per centimeter; and a system that feeds a sheet of pliable fibrous material between the belt and the roll, the belt having a longitudinal elongation of no more than 5%, dimensional stability along its entire length, a thickness of 1-10 cm, and a hardness 24-70° Shore A.

Claims

1. An apparatus for producing a web of fibrous material, comprising: a metal roll having a peripheral surface defining incisions spaced around the circumference of the roll, where the apparatus is configured to rotate the roll at a peripheral velocity v.sub.1 that is substantially equal to a peripheral velocity of an upstream belt or roller that is configured to advance the web toward the metal roll, the incisions having, a depth of 0.01-2.00 mm, a width of 0.01-2.00 mm, and a pitch 0.01-10.00 mm; a belt of a compressible elastic material, the belt stretched between transmission rollers, where the apparatus is configured to advance the belt at a velocity v.sub.2 that is less than the peripheral velocity v.sub.1 of the metal roll, where v.sub.1/v.sub.2 is between 1.05 and 1.40; a presser roller coupled to a presser system that is configured to compress the belt between the presser roller and the metal roll with a force of between 1 kg and 200 kg per centimeter width of a contact band between the belt and the metal roll; and where the belt has a hardness between 24° Shore A and 70° Shore A, and is longitudinally extensible by an amount not exceeding 5% at least on a side of the belt facing the presser roller, dimensional stability along its entire length, thickness between 1 cm and 10 cm.

2. The apparatus of claim 1, further comprising: a second belt of compressible elastic material, where the apparatus is configured to advance the second belt at a velocity v.sub.3 where v.sub.3<v.sub.2, where v.sub.1/v.sub.3 lies between 1.05 and 1.40, and a second presser roller coupled to the presser system, where the apparatus is configured to rotate the second presser roller with a peripheral velocity v.sub.3, where the presser system is configured to compress the second belt between the second presser roller and the metal roll.

3. The apparatus of claim 1, wherein the metal roll is covered with a layer of ceramic material.

4. The apparatus of claim 1, wherein the incisions are disposed at regular intervals around the entire circumference of the metal roll.

5. The apparatus of claim 1, wherein the incisions extend in spiral form along the peripheral surface of the metal roll.

6. The apparatus of claim 5, wherein the spiral incisions have an inclination not exceeding 45° relative to a line on the peripheral surface extending parallel to a rotational axis of the metal roll.

7. The apparatus of claim 1, wherein the incisions extend continuously across the peripheral surface of the metal roll.

8. The apparatus of claim 1, wherein the incisions extend discontinuously across the peripheral surface of the metal roll.

9. The apparatus of claim 1, wherein the incisions have: a depth of 0.05-0.50 mm, a width of 0.07-0.9 mm, and a pitch of 0.125-1.25 mm.

10. The apparatus of claim 1, wherein the presser system is configured to press said belt toward said metal roll with a force of between 20 kg and 40 kg per centimeter width of the contact band.

11. The apparatus of claim 1, wherein the belt of elastically compressible material has a thickness between 2.5 cm and 5.0 cm.

12. The apparatus of claim 1, wherein the belt of elastically compressible material has a hardness between 29° Shore A and 50° Shore A.

13. A method for producing a web of fibrous material, comprising: feeding a sheet of pliable fibrous material between a metal roll rotated at a peripheral velocity v.sub.1 and a first side of a belt of elastically compressible material, the belt having a thickness between 1 cm and 10 cm, and hardness between 24° Shore A and 70° Shore A, the metal roll having a peripheral surface defining incisions spaced around a circumference of the metal roll, the incisions having a depth of 0.05-0.50 mm, a width of 0.07-0.9 mm, and a pitch of 0.125-1.25 mm, where the belt is configured to elongate in a longitudinal direction by not more than 5% at least on a second side opposite the first side of the belt; advancing the belt at a velocity v.sub.2 that is less than the peripheral velocity v.sub.1 of the metal roll, where v.sub.1/v.sub.2 lies between 1.05 and 1.40; and compressing the belt between a presser roller and the metal roll at a pressure between 1 kg and 200 kg per each centimeter of width of a band of contact between the belt and the metal roll.

14. The method as claimed in claim 13, wherein the belt is compressed at a pressure between 20 kg and 40 kg per each centimeter of width of the band of contact.

15. The method as claimed in claim 13, wherein the belt has a hardness between 29° Shore A and 50° Shore A.

16. The method as claimed in claim 13, wherein the belt has a thickness between 2.5 cm and 5 cm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is further clarified hereinafter with reference to the accompanying drawings, in which:

(2) FIG. 1 shows schematically an apparatus for producing a web of fibrous material according to the invention,

(3) FIG. 2 is a front view of a roll thereof comprising continuous circumferential incisions,

(4) FIG. 3 is a front view of a roll thereof comprising continuous spiral incisions,

(5) FIG. 4 is a front view of a roll thereof comprising discontinuous circumferential incisions,

(6) FIG. 5 shows an enlarged partial longitudinal section through a portion of incised roll and, in a position corresponding with the incisions, the pattern of the fibres of a portion of paper web obtained by the apparatus according to the invention, and

(7) FIG. 6 shows schematically a variant of the apparatus for producing a web of fibrous material.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(8) An apparatus according to the invention for producing a web of fibrous material of high longitudinal and transverse extensibility, for example of paper material, can be inserted into an in-line plant for paper production, in which case it is fed with a sheet of cellulose fibre (virgin, recovered or mixed) to form the web, or can consist of a self-standing apparatus, in which case it is fed with an already formed paper web previously subjected to wetting to a water content between 82% and 30%.

(9) A similar apparatus and plant can also be used to produced vegetable fibre webs, non-woven fabric webs or synthetic fibre webs; in this case it is not possible to talk of water content of the sheet of cellulose fibre mix or of the rewetted paper web, but of the pliability of the fibrous material web, and essentially of its softening temperature.

(10) Independently therefrom, the apparatus comprises a cylindrical roll 2, of metal material, possibly covered with a layer of material presenting different mechanical characteristics (for example ceramic material), and in any event comprising on its cylindrical surface a series of incisions 4 extending along parallel circumferential lines or along spiral lines, and in any event extending with a pattern having a circumferential component.

(11) FIGS. 2-4 show different arrangements of these incisions, which can be of circumferential pattern (FIG. 2), spiral (FIG. 3) or continuous or discontinuous (FIG. 4).

(12) They can have a depth between 0.01 and 2 mm, preferably between 0.05 and 0.5 mm, width between 0.01 and 2 mm, preferably between 0.07 and 0.9 mm, and pitch between 0.01 and 10 mm, preferably between 0.125 and 1.25 mm. Moreover, in the case of spiral incisions, the angle of inclination can be from the minimum value allowed by the width of the incision to a maximum of 45°, preferably between 5° and 20°, with the spiral pattern being the same along the entire axial length of the roll 2 or be opposing on the two halves of the roll.

(13) As an alternative to the cylindrical shape, the roll 2 can have a convex shape (not shown) which has proved particularly useful for compensating the flexure of its shaft resulting from the forces applied to the ends thereof to exert pressure on the opposing roller, as apparent hereinafter.

(14) The roll 2 is made to rotate at a peripheral velocity v.sub.1 substantially equal to the operative velocity of the upstream station, i.e. at the velocity with which a sheet of fibrous material 6 to be processed is fed.

(15) The apparatus according to the invention also comprises a belt 8 of rubber or of different elastic material stretched between motorized rollers 10 and having a thickness between 1 cm and 10 cm, preferably between 2.5 cm and 5 cm, and hardness between 24° Shore A and 70° Shore A, preferably between 29° Shore A and 50° Shore A.

(16) The rollers 10 present a degree of friction against the rubber belt 8 sufficient to ensure its driving at a velocity v.sub.2 less than the peripheral velocity v.sub.1 of the roll 2. In particular, the ratio v.sub.1/v.sub.2 varies between 1.05 and 1.40.

(17) The belt 8 is substantially inextensible longitudinally (during operation it presents a maximum elongation of 5%) at least on that side adhering to the rollers 10, which inextensibility can be achieved, for example, by incorporating longitudinal steel wires into the belt or applying an inextensible fabric to the belt.

(18) Moreover the belt 8 must have a dimensional stability along its entire length, to prevent possible deformations, given that on one side it is in contact with the roll 2, having a peripheral velocity v.sub.1, while on the other side it is made to advance at a velocity v.sub.2<v.sub.1, and is hence braked longitudinally.

(19) The belt 8 is maintained pressed against the roll 2 by a presser roller 12, made preferably of steel, possibly covered with a surface layer of suitable mechanical characteristics. It can be idle or motorized, but in any event it must have a peripheral velocity of v.sub.2. The pressure with which the roller 12 presses the belt 8 against the roll 2 is controlled by suitable mechanical, pneumatic or hydraulic known means. This pressure is between 1 kg and 200 kg per centimetre of width of the belt 8, and is preferably between 20 kg and 40 kg.

(20) The apparatus according to the invention operates in the following manner.

(21) In the initial stage, i.e. before the apparatus is fed with the fibrous material sheet 6, the roll 2 and the rollers 10, 12 rotate at the same peripheral velocity v.sub.1 with the roller 12 simply resting on the roll 2.

(22) Under these conditions, the fibrous material sheet 6, having a water content between 82% and 30% in the case of cellulose or vegetable fibre in general, or at a temperature not less than the initial softening temperature in the case of synthetic fibres, and advancing at the velocity v.sub.1, is introduced between the rubber roller 8 and the roll 2; the rollers 10 and 12 are progressively raised to the velocity v.sub.2<v.sub.1, and the roller 12 is pressed with increasing pressure against the roll 2, to squeeze the belt 8 and the sheet 6 of fibrous material adhering to it.

(23) The combined effect of the longitudinal braking and the squeezing in the thickness direction is to cause the sheet 6 to locally fill the incisions 4 of the roll 2, and become accumulated longitudinally in bands corresponding to the incisions and with curved compaction lines 14, of the type illustrated in FIG. 5.

(24) In its turn, this longitudinal accumulation and the particular arrangement of the fibres, determine the longitudinal and transverse extensibility of the formed fibrous material web, when this reaches the final moisture content of the paper in the case of vegetable fibres, or its dimensional stability in the case of synthetic fibres.

(25) The degree of both longitudinal and transverse extensibility depends on the ratio between the velocities v.sub.1 and v.sub.2, on the force with which the belt 8 is pressed against the roll 2, on the characteristics of the incisions 4 on the roll 2, on the pliability of the sheet 6 at the commencement and termination of treatment, and on the physical and geometrical characteristics of the rubber belt 8.

(26) Experimental tests carried out to test the effectiveness of the method have enabled paper to be obtained with a degree of longitudinal extensibility of about 20% and transverse extensibility of about 15%.

(27) If the apparatus according to the invention is inserted into a paper web production line, the plant also comprises, in traditional manner, stations for tensioning the rubber belt 8, for its centring, for its cooling, and for its grinding to maintain its thickness uniform.

(28) Before the fibrous material sheet 6 is engaged between the rubber belt 8 and the roll 2, it is impregnated with specific additives able to provide particular characteristics and properties to the final web obtained.

(29) Finally the roll 2 and/or rollers 10 and/or 12 are subjected to cooling or heating during operation, according to specific technological requirements and/or to the properties which the web of fibrous material is required to present.

(30) From the aforegoing it is apparent that the apparatus and method for obtaining webs of fibrous material according to the invention are particularly advantageous, in that they enable webs to be obtained with characteristics of high extensibility both longitudinally and transversal by simple apparatuses of low installation, running and maintenance costs, and with the facility for modifying the extensibility characteristics of the web obtained, on the basis of specific requirements.

(31) In order to obtain fibrous material webs of different characteristics and performance, the fibrous material sheet 6 can be subjected to more than one compaction treatment of the described type, in the sense that the web leaving one apparatus can be inserted, after being possibly subjected to other intermediate treatments, into another apparatus in which the rubber belt 8 and/or the incisions on the surface of the roll 2 and/or the velocities in play and/or the pressures in play can be different.

(32) In the variant illustrated in FIG. 6, an apparatus comprising a single roll 2 having on its surface a plurality of incisions 4 is provided with two rubber belts 8, 8′ made to adhere to said roll 2 along different generating lines. In particular, a first rubber belt 8 is made to adhere to the roll 2, having its peripheral velocity v.sub.1, by a first presser roller 12 which at the same time is made to advance at a velocity v.sub.2<v.sub.1. A second rubber belt 8′ is made to adhere to the same roll 2 by a second presser roller 12′ made to advance at a velocity v.sub.3<v.sub.2. Again in this case the velocity ratios v.sub.1/v.sub.2 and v.sub.1/v.sub.3 independently lie between 1.05 and 1.40.

(33) The fibrous material sheet 6, which enters along a first contact generating line between the first rubber belt 8 and the roll 2 at the velocity v.sub.1 leaves these at the velocity v.sub.2<v.sub.1, compacted in both the longitudinal and traverse directions. The said sheet 6, which is withdrawn at its exit along this first contact generating line at the velocity v.sub.2, is made to enter along a second contact generating line between the second rubber belt 8′, which advances at a velocity v.sub.3<v.sub.2, and the said roll 2, and is subjected to a second compaction treatment.

(34) As there is only one roll 2 there is only a single set of incisions 4 to determine the two compaction treatments on the fibrous material sheet 6.

(35) However, as the two rubber belts 8, 8′ can be different, the pressures with which they are pressed against the roll 2 can be different and the velocities in play are different, the second treatment will give the sheet 6 characteristics and performance which are different from those obtained by the first treatment.

(36) From the aforegoing it is apparent that the apparatus and method for producing extensible paper according to the present invention are much more advantageous than those of the state of the art, and in particular of U.S. Pat. No. 2,624,245, WO2005/100686 and GB 868391, in that:

(37) they enable high values of longitudinal and transverse extensibility to be achieved, together with a high degree of paper smoothness,

(38) they enable high production rates (of the order of 1000 m/min) to be achieved, hence enabling the apparatus to be inserted into modern papermaking plants,

(39) because of the use of a rubber belt instead of a rubber-coated roller, its replacement in the case of wear, besides being much less frequent, is very quick and easy and can be carried out in the actual papermaking works, i.e. where the apparatus is actually used,

(40) again because of the use of the belt, which comprises large portions far from the working zone and free on both sides, this can be subjected, if requested, to a series of treatments (cooling, cleaning, grinding, suction, etc.) which in the case of a rubber-coated roller would be difficult if not impossible; in particular the cooling, often required because of the large quantity of heat which can develop during operation, can be carried out very simply, without having to use the complicated systems otherwise required inside rubber-coated rollers,

(41) the diameter of the roller which presses the rubber belt against the steel roll is made independent of variations in the apparatus operating velocity, meaning that the nip between the rubber and steel can be of constant width as this velocity varies, in contrast to what occurs in the case of a rubber-coated roller, in which, as stated, the diameter of the rubber-coated roller must be increased as the apparatus velocity varies,

(42) the belt can be easily and quickly replaced on site, without having to use specialized outside industries, and lengthy apparatus shut-downs,

(43) replacement belts kept in store take up little space and are easily replaced,

(44) the width of the nip between rubber and steel can be modified depending on the characteristics of the paper web to be produced.