EP0106775B1 - Method of making synthetic fabrics, in particular for paper-making machines, and synthetic fabric made by the method - Google Patents

Description

Process for manufacturing plastic fabrics, in particular for paper machines, and plastic fabric thus obtained.

The present invention relates to the field of fabrics for forming the paper sheet of paper machines, and relates to a process for manufacturing plastic fabrics intended for this purpose.

The invention also relates to a plastic fabric obtained by applying this method.

In paper machines, the pulp, which is a suspension in water of cellulose fibers and fillers at a concentration of about 1%, is poured over an endless sieve called canvas, through which it must drain quickly and regularly.

Until recently, the fabrics used were metallic fabrics woven in twill weaves of 3, or knitting, these fabrics being rendered endless to the desired length by brazing or joining the canvas, and undergoing a treatment of finish before cutting to the desired width.

These fabrics are constituted by a number N of warp threads per cm called comb number, and by a number 5 of weft threads per cm called duitage, these numbers representing the texture are final after weaving.

Generally the diameter of the weft threads is greater than the diameter of the warp threads by about 2/100 mm.

The warp threads are strongly wavy, while the weft threads remain practically straight, so that the warp threads are prominent in relation to the weft threads. The linking of the warp threads with the weft threads is ensured by their intertwining: the weft threads pass alternately above the ply of warp threads, then below the same ply of warp threads. A weave of fabric is determined by the number of harnesses and the distribution of the warp threads between the points of change of direction of the weft threads, the change of direction being made perpendicular to the plane formed by the web of warp threads. Thus, in the knit weave, which is a 3-harness weave, the weft threads pass over two warp threads, then below the third directly adjacent warp thread, which achieves a 2-1 tying. In practice this corresponds to a float of the warp thread located on the face of the fabric in contact with the machine, and the weft thread has a float on the opposite face of the fabric, in contact with the paper.

As a result, the knitted wire fabrics present prominent chain floats towards the machine, resulting in premature wear of the warp threads causing deterioration of the fabrics as well as the work hardening of the threads subjected to alternating bending as well as corrosion phenomena.

To overcome these drawbacks, it has been proposed to replace the metallic wires with synthetic wires called horsehair or plastic son, in the form of horsehair, in particular polyester, or even polyamide, or others, which are insensitive to hardening and corrosion, and have good abrasion resistance.

The plastic threads used are either multifilament, that is to say constituted by twisted filaments, or monofilament, that is to say formed by a unitary horsehair of the desired diameter.

• - Si un fil de chaîne passe au-dessus d'un fil de chaîne puis en dessous de quatre fils de chaîne directement contigus, il s'agit du mode de liage 1-4.
• - Si un fil de chaîne passe au-dessus de deux fils de chaîne puis en dessous de trois fils de chaîne directement contigus, il s'agit du mode de liage 2-3.
• - Les autres modes de liage possibles sont les modes 4-1 et 3-2, qui se déduisent respectivement du premier et du second ci-dessus par symétrie.

Known plastic canvases are often made on the same trades as metal canvases, hands in armor that most of the time exceed 3 harnesses; the most common armor being with 4 harnesses. This increase in the number of harnesses was imposed, in order to produce fabrics which are dimensionally stable and which sufficiently drip on a paper machine. The more the armor is made with a large number of harnesses, the more the number of variants in the binding modes increases. For example, in a 5-harness fabric, the following binding methods are possible:

• - If a warp thread passes over a warp thread and then below four directly contiguous warp threads, this is binding mode 1-4.
• - If a warp thread passes over two warp threads and then below three directly contiguous warp threads, this is the 2-3 tying mode.
• - The other possible binding modes are modes 4-1 and 3-2, which are deduced respectively from the first and from the second above by symmetry.

These plastic fabrics require a longitudinal and transverse stabilization heat treatment, during which the fabric is strongly stretched, while it retracts in a transverse direction at a temperature between 150 ° C and 180 ° C. Such a treatment called thermofixation is necessary to prevent excessive stretching of fabrics on paper machines. This treatment also has the effect of rendering the longitudinal son less wavy, while the transverse son become significantly, so that they are prominent compared to the longitudinal son. This is one of the reasons which leads to using plastic fabrics with the weft effect on the machine side.

However, due to the fact that these fabrics are generally woven with a large number of longitudinal threads to increase their resistance to elongation, they have narrow meshes which make it necessary to make them long, therefore with a low inheritance and / or diameters of threads. transverse not exceeding those of the longitudinal wires by 2 to 5/100 mm and exceptionally by 8/100 mm, in order to allow sufficient drainage; in most cases they lead to a reduction in the retention of the fine elements contained in the paper pulp.

The usual fabrics have transverse threads with a long float on the face in contact with the machine, while these same threads only form a bend on the face receiving the paper; the two sides are therefore asymmetrical so that on the one hand the paper side has less resistance to wear than the machine side, this however not being a nuisance in most cases and that, on the other hand, the canvas edges show a tendency to curl up.

To overcome these drawbacks, US-A-4 281 688 proposes a type of symmetrical fabric whose two faces are almost identical to the face defined above, like the machine face. This result is obtained by weaving a first weft as in the usual fabrics, then by weaving a second symmetrical weft of the first, that is to say with the elbow of the second weft on the same face as the float of the first weft and the float of the second frame adjoining the elbow of the first frame. In this case, the third, fifth and seventh frames are identical to the first frame, while the fourth, sixth and eighth frames are identical to the second frame.

In this fabric each of the frames passes above a number P of warp threads and below M other warp threads the sum P + M being constant and equal to the number of harnesses. The term symmetrical means that each pair of consecutive wefts is composed by the weft thread (a) which passes above Pa warp threads and below Ma other warp threads, and by the weft thread (b) which passes above Pb chain son and below Mb other chain son, with Pa + Ma = Pb + Mb, and in addition for the symmetry Pa = Mb and Ma = Pb.

Finally, to obtain good drainage and good retention of the fibers while retaining good mechanical characteristics, double-layer fabrics have been proposed in which the weft threads form a succession of pair of wefts superimposed in the thickness of the fabric. However, this type of fabric is difficult to manufacture and causes cleaning difficulties, in particular when the raw materials introduced into the paper pulp are recovered fibers.

The present invention aims to overcome these drawbacks.

It has, in fact, for its object a process for manufacturing plastic fabrics, in particular for paper machines, in which a weaving is carried out, on an existing machine, by alternating at least two modes of weft tying, each weft passing through - above a number P ₁ , P ₂ warp threads and below M ₁ , M ₂ other warp threads, P ₁ + M ₁ being equal to P ₂ + M ₂ and the number of harnesses with P ₁ ≠ M ₁ and P ₂ ≠ M ₂ , with each pair of consecutive wefts constituted by two weft threads, the first weft thread forming a float on the paper side passing over P ₁ warp threads, then forming a float on the machine side passing below M ₁ warp threads, while the second weft thread forms a float on the paper side passing over P ₂ warp threads, then forms a float on the machine face passing by below M ₂ warp threads, with P ₁ <M ₁ , characterized in that it consists essentially of weaving, with a number of harnesses equal to or greater than four, alternating at least two non-symmetrical weft tying modes, such as P ₁ > P ₂ , P ₂ <M ₁ and P ₂ <M ₂ , so that the warp threads , in the machine direction, no longer remain in the same longitudinal plane.

The invention also relates to a plastic fabric obtained by application of this method, having a weave alternating at least two modes of weft bonding, each frame passing over a number P ₁ , P ₂ warp threads and in below M ₁ , M ₂ other warp threads, P ₁ + M ₁ being equal to P ₂ + M ₂ and to the number of harnesses, with Pt ≠ M ₁ and P ₂ ≠ M ₂ , characterized in that it has a weave with a number of harnesses equal to or greater than four with at least two non-symmetrical alternate weft tying modes, the warp threads of which are strongly waved in the horizontal and vertical planes.

• la figure 1 est une vue en plan, à échelle fortement agrandie, d'une toile conforme à l'invention;
• la figure 2 est un schéma de principe d'une armure à 5 harnais et 2 modes de liage conforme à l'invention;
• la figure 3 est une vue en coupe suivant un fil de chaîne;
• la figure 4 est une vue en coupe suivant un fil de trame;
• la figure 5 est une vue analogue à celle de la figure 4 montrant un autre mode de liage de trame;
• la figure 6 représente, dans une vue analogue à celle de la figure 2, une variante de réalisation de l'invention;
• la figure 7 montre, en coupe, une ondulation de fil de chaîne d'une toile existante, et
• la figure 8 montre dans une vue analogue à celle de la figure 7, une ondulation d'un fil de chaîne d'une toile conforme à l'invention.

The invention will be better understood from the description below, which relates to a preferred embodiment, given by way of nonlimiting example, and explained with reference to the appended schematic drawings, in which:

• Figure 1 is a plan view, on a greatly enlarged scale, of a fabric according to the invention;
• Figure 2 is a block diagram of a weave with 5 harnesses and 2 binding modes according to the invention;
• Figure 3 is a sectional view along a warp thread;
• Figure 4 is a sectional view along a weft thread;
• Figure 5 is a view similar to that of Figure 4 showing another mode of weft tying;
• Figure 6 shows, in a view similar to that of Figure 2, an alternative embodiment of the invention;
• FIG. 7 shows, in section, a ripple of warp thread of an existing fabric, and
• Figure 8 shows in a view similar to that of Figure 7, an undulation of a warp of a fabric according to the invention.

In accordance with the invention, and as shown more particularly, by way of example, FIG. 1 of the appended drawings, the process for manufacturing plastic fabrics, in particular for paper machines, essentially consists in weaving, on a existing machine with any number of harnesses, for example five, by alternating at least two non-symmetrical weft tying modes. Thus, for example, the weft threads 1 pass over two and below three warp threads 3, that is to say that they carry out a tying 2-3 while the weft threads 2 pass through above one and below four warp threads by making a binding 1-4, the weft threads 1 and 2 being alternated and their binding being offset by a warp thread at each alternation.

By designating the tying 2-3 of the weft thread 1 by P ₁ and M ₁ and that, 1-4, of the weft thread 2 by P ₂ and M ₂ , we could say that the weft thread 1 forms a float on the paper side passing over P ₁ warp thread 3, then forms a float on the machine face passing below M ₁ warp thread 3, while the second weft thread 2 forms a float on the face paper passing over P ₂ warp threads 3 then forms a float on the machine face passing under M ₂ warp threads 3, P ₁ + M ₁ being equal to P ₂ + M ₂ and the number of harness with P ₁ ≠ M ₁ , P ₁ <M ₁ , P ₁ > P ₂ , P ₂ <M ₁ and P ₂ <M ₂ .

Thus, the succession of five wire ties 1 with five wire ties 2 leads to a pitch of ten frames from from which the same motif is renewed identical to itself. A weave thus constituted is represented in FIG. 2 where the ties of the weft yarns 1 are shown diagrammatically by hatched squares 1 'and those of the wires 2 by hatched squares 2', the arrows 1 "and 2" showing the renewal of the pattern. after a step of ten.

The binding of the threads 1 causes the two warp threads 3 to join together, over which they pass, and this bringing together is kept as short as possible by the fact that the next double binding point separated from the first by a weft thread 2, is offset by a warp thread 3 causing an oblique alignment called diagonal, so that a single warp thread from the first bond 2-3 belongs to the second bond 2-3.

The type 1-4 binding of weft threads 2, in which such a thread 2 passes over a single warp thread 3, is carried out on the thread 3 contiguous to the pair of warp threads 3 linked by the previous thread 1, so that this thread 3 is not linked by the next weft thread 1. The simple bonding points of the wires 2 thus follow one another with an offset of a warp wire 3, thus reinforcing the diagonal indicated above.

FIG. 6 schematically represents another mode of armor with five harnesses with a pitch of twenty and alternate tying 2-3 and 1-4.

As shown in FIG. 4, the simple tying points of the weft threads 2 give a float of the weft 2 below four warp threads 3 on the face of the fabric which will be in contact with the machine, this float supporting the abrasion during machine walking and allowing an extension of the service life of the fabric thus obtained due to the large volume to be abraded.

On the other hand, the double tying points of the weft threads 1 (FIG. 5) give, on the machine side, a float of the weft below only three warp threads 3, the tying above two warp threads 3 allowing to retain a greater number of paper fibers and thus improve retention.

Thanks to these methods of tying the weft threads 1 and 2, the warp thread 3 passes, as shown in FIG. 3, over four weft threads, under a thread, over a thread, under a thread, then on two threads, and again under a thread at each step, i.e. a 4/1/1/1/2/1 tying, so that the greatest chain float is carried out above four weft yarns preventing premature wear or the risk of impact rupture against an external element of the machine. The warp thread 3 is thus protected, both on the machine side and on the paper side by the prominent weft threads, so that its diameter can be chosen to ensure only the essential mechanical resistance.

The weaving method according to the invention makes it possible to obtain meshes of variable length due to the undulation of the wefts 1 in the horizontal plane. This small desired displacement is beneficial, since the paper side of the fabric tends to form a pseudo-alignment of the binding points of the weft promoting the deposition of paper fibers and thereby improving retention.

The extent of displacement of the weft threads is limited, and the retention improved, thanks to the invention by the fact that the weaving is carried out with a strong duitation, that is to say with a large number of weft threads per cm, and / or with weft threads of a diameter clearly greater than normal, and which can advantageously exceed the diameter of the warp threads by a value of the order of 70%. Such an embodiment allows a short average mesh length and improved retention.

The weaving mode in accordance with the invention makes it possible to obtain a slight difference in level between the consecutive weft threads. Indeed, the weft thread 2 is lifted by a single warp thread 3 and pulled down by four warp threads 3 so that on the paper side and on the machine side, it is slightly below the level. The weft thread 1 is, on the other hand raised by two threads 3 and pulled down by only three warp threads 3, thus lying slightly above the average level, both on the paper side and on the machine side.

This embodiment combining a particular mode of binding of numerous weft threads and / or of large diameter, as well as a difference in level between wefts, therefore makes it possible to obtain a thicker fabric than that obtained with a 5H weaving. classic, and thus, a more dynamic draining.

In accordance with another characteristic of the invention, in order to obtain a small difference in level of the weft threads, in particular on the paper side, the insertion tension of the weft threads 1 is adjusted differently depending on the mode of tying. (1-4 or 2-3 in the example described), or else, these wires 1-2 are of different natures, for example, one made of polyester, and the others made of polyamide.

• N = numéro de peigne
• S = duitage
• C = chaîne
• T = trame
  

The increase in dynamic drainage due to the increase in thickness of the fabric, expressed in free volume in the thickness in mm ³ / cm ² , of the fabric according to the invention compared to existing fabrics is shown in the table below, in which:

• N = comb number
• S = duitage
• C = string
• T = frame
  

As this table shows, the weft threads have a diameter very much greater than that of warp threads, so that their diameter ratio is at least equal to 1.7 while in existing fabrics this ratio is always less than 1.6.

As a result, as shown in FIG. 7, in the known fabrics, the amplitude a of the residual undulation of the warp threads after heat-fixing, between the crossing points of a warp thread C with two weft threads T consecutive is relatively small and is not significantly larger than the diameter of the warp threads, the protrusion beyond this diameter never exceeding 5/100 mm, so that all the warp threads remain substantially in the same longitudinal secant plane.

On the other hand, in the fabrics according to the invention (FIG. 8), the amplitude a of the undulation between the crossing points of a warp thread C with two weft threads T is large and may exceed the value of 1.5 times the diameter of warp wire C, so that no secant longitudinal plane shows a continuous section. The fabric obtained after stabilization heat treatment becomes practically non-deformable, having a low longitudinal elongation and negligible transverse shrinkage for service tensions which can reach 10 to 15 kg / cm in width. The increase in transverse rigidity results in a significant improvement in the characteristics of the fabrics, which become comparable to those of double-layer fabrics and approach those of metallic fabrics.

The average elementary meshes obtained by applying the method according to the invention have an almost square shape, even rectangular, the longest side being oriented in the direction of the weft.

In addition, the use of a greater number of weft yarns and / or weft yarns of larger diameter allows better resistance of the fabric to abrasion, and therefore a longer service life on the machine. to paper.

Finally, this process results in a strong residual undulation of the warp threads, in particular at the level of the simple tying points, which notably improves the resistance of the spliced junctions.

Thanks to the invention, it is possible to produce fabrics for forming the sheet of paper, single layer, used in the manufacture of papers, wadding papers, or the like, as well as cardboard boxes based on old paper, and possibly neighboring products such as asbestos panels, chemical fiber panels, particle boards, etc., having qualities of transverse rigidity, thickness, and dynamic draining significantly better than those of the usual single layer fabrics and substantially comparable to those of a double layer canvas, while being less susceptible to fouling.

Of course, the invention is not limited to the embodiment described and shown in the accompanying drawings. Modifications remain possible, in particular from the point of view of the constitution of the various elements, or by substitution of technical equivalents, without thereby departing from the scope of protection of the invention.

Claims (7)

1. A method of making synthetic cloths, particularly for paper-making machines, wherein weaving is effected, on an existing machine, by alternating at least two methods of weft-binding (1-2), each weft (1-2) passing over the number P₁, P₂ of warp threads and under M₁, M₂ of other warp threads, P₁ + M₁ being equal to P₂ + M₂ and to the number of harnesses with P₁ ≠ M₁ and P₂ ≠ M₂, with each pair of consecutive wefts consisting of two weft threads (1-2), the first weft thread (1) forming a float on the paper face by passing over P₁ warp threads (3) then forming a float on the machine face by passing under M₁ warp threads (3), while the second weft thread (2) forms a float on the paper face by passing over P₂ warp threads (3), then forms a float on the machine face by passing under M₂ warp threads (3), with P₁ < M₁, characterised in that it consists essentially in effecting weaving, with a number of harnesses equal to or greater than four, by alternating at least two non-symmetrical methods of weft binding (1-2), such that P₁ > P₂, P₂ < M₁ and P₂ < M₂, in such a manner that the warp threads (3), in the machine direction, no longer remain in one and the same longitudinal plane.

2. A method, according to claim 1, characterised in that the weaving is effected with a high density of weft threads, that is to say with a large number of weft threads per cm, and/or with weft threads having a diameter distinctly larger than normal, and which may advantageously exceed the diameter of the warp threads by a value of about 70 %.

3. A method according to either one of claims 1 and 2, characterised in that, in order to obtain a slight difference in the level of the weft threads, in particular on the paper face, the insertion tension of the weft threads (1-2) is adjusted in a different manner according to the method of binding, or further, these threads (1-2) are of different kinds.

4. A method according to any one of claims 1 to 3, characterised in that the amplitude (a) of the undulation between the points of intersection of a warp thread (C) with two weft threads (T) is high and may exceed the value of 1.5 times the diameter of a warp thread (C), so that no secant longitudinal plane causes a continuous section to appear.

5. A synthetic cloth obtained by using the method, according to any one of claims 1 to 4, and having a weave alternating at least two methods of weft binding (1-2), each weft (1-2) passing over a number P₁, P₂ of warp threads and under M₁, M₂ of other warp threads, P, + M₁ being equal to P₂ + M₂ and to the number of harnesses, with P₁ ≠ M, and P₂ ≠ M₂, characterised in that it has a weave with a number of harnesses equal to or greater than four with at least two alternate non-symmetrical methods of weft binding (1-2), and wherein the warp threads (3) are greatly undulated in the horizontal and vertical planes.

6. A cloth, according to claim 5, characterised in that it comprises floats of warp threads over at most five weft threads, in order to keep said warp threads distinctly above the upper level of the weft threads and to avoid any risk of premature damage thereto.

7. A cloth, according to claim 5, characterised in that it has a great residual undulation of the warp threads in order to achieve a greater thickness of cloth than normal and to make spliced joins of great reliability.

Images