The present invention is directed to a dual layer papermaking fabric which provides even drainage throughout and in which both the paper support surface and the machine contact surface are weft dominant surfaces.

Normally, dual layer papermaking fabrics are woven with a single set of warp threads, upper layer weft threads and lower layer weft threads. Normally, the number of upper layer weft threads is twice that of the lower layer weft threads. It is also desirable to have long weft floats on the paper support surface to provide a smooth surface with adequate permeability. The machine contact surface also preferably comprises long weft floats also for adequate permeability and further for protecting the warp threads against wear through excessive contact with the machine rolls.

Papermaking fabrics developed with these features in mind are disclosed in U. S.

Patents 4, 739, 803 ; 4, 709, 732 ; 5, 025, 839 ; 5, 487, 414 ; and 5, 555, 917.

The instant invention has for its object, a papermaking fabric having a paper support surface which is smooth so as to reduce fabric marking on the paper to a minimum.

Another object of the invention is a papermaking fabric having a paper support surface having machine direction crossovers forming balanced twill lines which provide a minimum number of uniform markings on the paper.

Another object of the invention is providing a papermaking fabric having a minimum number of the warp threads exposed on the outer fabric surfaces providing increased wearability and improved uniformity.

Another object of the invention is a papermaking fabric which maintains even drainage during use.

Another object of the invention is a papermaking fabric having stabilized machine contact surface floats.

Another object of the invention is a papermaker's fabric having stabilized support surface floats.

Another object of the invention is a papermaking fabric in which the warp crossovers on the paper support surface and the warp cross-unders on the machine contact surface form diagonal twill lines across each fabric surface.

Another object of the invention is a multi-layer papermaking fabric in which the waves of each fabric layer are balanced.

Summary of the Invention The instant invention is directed to a multi-layer papermaking fabric which utilizes a single set of MD (machine direction) yams. The fabric includes a lower CMD (cross machine direction) layer having a selected number of yarns per inch and an upper CMD layer having a selected number of yams per inch which are at least twice that of the lower CMD layer. A system of MD yams are interwoven with the upper and lower CMD yarns in a repeated weave pattern. Preferably the number of upper CMD yams is twice the number of lower CMD yams.

The weave pattern requires that each MD yam weave to cross-under an even number of lower CMD yams and to crossover an uneven number of upper CMD yams with the number of upper CMD yam crossovers being two-thirds of the CMD yarn crossovers and cross-unders. The MD yam and the CMD yam crossovers and cross-unders are arranged in twill arrays diagonally across the width of the weave pattern.

Selected of the CMD floats of the upper surface are tied in with a single crossover of a MD yam at each end within the weave pattern while other of the CMD yam floats are tied inwith a single crossover of a MD yarn only at one end within the weave pattern. These other of the CMD yarn floats are arragned between the selected CMD yarn floats throughout the weave pattern.

It is preferred that the uneven number of crossovers of each MD yam comprises three. Also, it is preferred that each of these crossovers cross over only one CMD yam. It is also preferred that certain of these crossovers of each of the MD yams are separated by at least ten CMD yams while others of these crossovers are separated by as few as two of the CMD yams per weave pattern repeat.

On the machine or lower surface, each of the CMD yarns forms only one float which passes beneath a majority of the MD yams for each weave pattern repeat. These lower surface CMD floats are tied in with a plurality of consecutive MD yarns which successively pass under, over, under each CMD yarn forming a tie end point at one end of the CMD float. The tie end points form twill lines diagonally across the lower surface of the weave pattern.

The weave requires selected of the upper CMD yarns to cross under selected MD yams and form a cross-under which appears on the lower surface. The weave does not allow a lower CMD yam to appear on the upper surface.

The weave pattern, which produces a CMD yam dominated support and machine surfaces utilizes sixteen MD yams per weave pattern repeat. There are forty-eight CMD yams per weave pattern repeat. It is preferred that the CMD yams are of equal size. The CMD yams forming the support surface may be of a different diameter than the CMD yams forming the contact surface. Also, the CMD yams forming the support surface may be of multiple sizes.

Each of the CMD yams forming the contact surface is stacked beneath selected of the CMD yams forming the support surface. These selected CMD yams are each separated from each other by a single support surface CMD yam.

Description of the Drawings The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof, wherein examples of the invention are shown : Figure 1 is a sectional top view of the paper support surface of the papermaking fabric of the invention through a single repeat of the weave pattern ; Figure 2 is a sectional bottom view of the machine contact surface of the papermaking fabric of the invention through a single repeat of the weave pattern ; Figure 3 is a side sectional view showing the relationship of each warp and weft yarn throughout a single repeat of the weave pattern ; Figure 4 is a weave diagram for the papermaking fabric of the invention through a repeat of the weave pattern ;

Figure 5 is a sectional top view of the paper support surface of an alternative arrangement of the papermaking fabric of the invention through a single repeat of the weave pattern ; Figure 6 is a sectional bottom view of the machine contact surface of the alternative arrangement of the papermaking fabric of the invention through a single repeat of the weave pattern ; Figure 7 is a side sectional view showing the relationship of each warp and weft yam of the altemative arrangement throughout a single repeat of the weave pattern ; Figure 8 is a weave diagram for the alternative arrangement of the papermaking fabric of the invention through a repeat of the weave pattern ; Figure 9 is a sectional top view of the paper support surface of a second alternative arrangement of the papermaking fabric of the invention through a single repeat of the weave pattern ; Figure 10 is a sectional bottom view of the machine contact surface of the second alternative arrangement of the papermaking fabric of the invention ; Figure 11 is a side sectional view showing the relationship of each warp and weft yam throughout a single repeat of the weave pattern of the second alternative arrangement ; and, Figure 12 is a weave diagram for the second alternative arrangement of the papermaking fabric of the invention through a repeat of the weave pattern.

Description of a Preferred Embodiment Turning now to the drawings ; Figure 1 shows a full repeat of the weave pattern forming the paper support surface 10 of papermaking fabric A of the invention. As shown

there are sixteen warp yams 12, numbered 1-16, which are controlled by sixteen harness frames in the usual manner to weave with upper layer weft yam 14 to form the upper fabric layer which forms the paper support surface 10. Figure 2 shows the same warp yarns 12 weaving with lower layer weft yam 18 to form the lower fabric layer which forms the machine contact surface 16.

The complete weave pattern, as shown in Figure 4, depicts sixteen warp yams weaving with forty-eight picks of weft yam to form the complete repeat of the weave pattern.

Preferably the warp and weft yams are formed of monofilament polyester yams ranging in diameters of between 0. 0032 to 0. 0450 inches. Preferably, the diameter of the warp yarn is about 0. 0050 inches and the diameter of weft yams 14 and 16 is about the same.

Optionally, upper weft yams 14 forming support surface 10 may be smaller or larger than the warp yams by about 0. 0020 inches while lower weft yarns 18 forming contact surface 16 may be larger in diameter than the warp yams by about 0. 020 inches. The upper weft yams may be of a single diameter or of plural diameters.

Other materials are acceptable for forming the warp yarns and one or both of the weft yarns may comprise as polyamide, plyetherketone or blends thereof. Also, multi- filament may be used.

Turning now to Figures 1, 2, and 3, it can be seen that warp yarns 12 are arranged as a single set which weaves with both the upper layer weft yarn 14 to form the paper support surface 10 and the lower layer of weft yarns 18 to form the machine contact surface 16. Figure 3 clearly shows that each warp yarn 12 of the weave pattern repeat weaves over only three spaced picks of weft yarn 14 on the paper support surface per repeat of the weave pattern. By way of example warp yam 01 of warp yams 12 weaves to crossover only picks 1, 16, and 33 of the weft yarns, while passing beneath the remaining

upper layer weft yams 14. Warp yam 1 also weaves to pass over all lower weft yams 18 through the weave pattern, except where it weaves twice to pass beneath lower layer picks 11 and 41. Likewise warp yam 2 of warp yams 12 is controlled to pass over only upper layer picks 10, 25, and 42 and to pass under only lower layer picks 2 and 29 through a repeat of the weave pattern. Warp yams 3-16 weave in similar manner as shown in the drawing.

It should be noted that no lower layer weft yams 18 appear on support surface 10 as each pick of weft yam 18 is stacked beneath alternate picks of upper weft yam 14.

Also, substantially all of the picks of upper weft yam 14 appear only on support surface 10 and not on machine contact surface 16. However, each pick of upper layer weft yam 14 includes an uncovered cross-under 15 which appears at a single point along each warp yam on contact surface 16. While these weft yam cross-unders 15 appear on the machine contact surface 16 they remain elevated above cross-unders of warp yams 12 and the lower weft yams 16 and are, therefore, not engaged when the contact surface is in machine contact. Examples of upper layer weft cross-unders 15 which appear on the machine contact surface are at warp 01, pick 33 ; warp 02, pick 42 ; and warp 03, pick 3.

The weave pattern provides a balanced construction in which the warp yams form a plurality of inner floats 20 along each of warp yarns 1-16 of warp 12. As best seen in Figure 3, these inner floats are relatively short, passing beneath four and above two picks of lower weft yam 18 ; beneath five and above two picks of lower weft yarn ; beneath ten and above five picks of lower weft yarn ; beneath three and above one pick of lower weft yarn along each warp yam of warp 12 throughout the weave pattern.

The weave pattern, as shown in Figures 1-4, provides an upper paper support surface 10 in which the warp crossovers, indicated at 28, are arranged in diagonal rows or twill lines 32 across the support surface. The weave pattern also provides that alternative

picks of weft yam 14 forming the upper layer form a pair of weft floats 36, 37 across the width of the weave pattern. Intermediate picks of weft yam 14 are woven with warp yams 12 to form extended floats 39 which pass over fifteen warp yams 12 and are tied in with only a single crossover 28 per weave pattern repeat. Floats 36, 37 which pass over eight and six adjacent warp yams respectively along with floats 39 form twill lines 33 across the fabric width.

By locating the warp crossovers 28, which tie down opposed ends of the weft floats 36, 37, and 39, in staggered positions located along opposite sides of intermediate sections of weft floats 39. These weft floats are stabilized aiong their length and are retained along their transverse axis in substantially parallel positions relative the other floats. In addition to promoting even drainage, the stabilized floats provide for a more even or uniform support surface which reduces marking of the paper product supported thereon. Likewise, the twill lines 32 produce minimal markings while forming a pleasing pattern.

The warp cross-unders 30, 31 on the machine contact surface 16 are positioned along diagonal rows forming twill lines 34 across the weave pattern. The weft floats 38, are of extended length with only one float being formed for each pick across the width of the weave pattern, are arranged in diagonal rows forming twill lines 42. Each float is anchored at one end in each weave patterns by a pair of warp cross-unders 30, 31 which are separated by warp crossover 40. These tie in points are formed by adjacent warp yams 12 and securely anchor an end of the extended floats. Again, cross-unders 30, 31 are arranged to be positioned along intermediate portions of opposing sides of floats 38 further stabilizing and maintaining the floats in position.

Turning now to Figures 5-8, a second arrangement is shown for forming the papermaking fabric of the invention. Figure 5 shows a full repeat of the weave pattern

forming the paper support surface 10'of papermaking fabric B. Again, there are sixteen warp yams 12', numbered 01-16, which are again controlled by sixteen harness frames to weave with upper layer weft yam 14'to form upper layer of support surface 10'of fabric B.

Figure 6 shows warp yams 12'weaving with lower layer weft yams 18 forming lower or contact surface 16.

Papermaking fabric B is also woven in a weave pattern which requires forty-eight picks of weft yam 14'numbered 1-48 and sixteen ends of warp yam 12'numbered 01-16.

The weave also provides three crossovers for each warp yam 12'through a repeat of the weave pattern at 44 on support surface 10'. Warp yam crossovers 44 are separated by warp yam cross-unders 20'of four, five, nine, and ten picks of weft yam 14'.

Weft yam 14'form weft floats 36'and 37'on the support surface on alternate picks over the weave pattern. Weft floats 36', 37'each pass over seven warp yams 12'with two floats being formed on first picks through the weave pattern. Weft floats 39'pass over fifteen warp yams and, are formed on second or alternate picks. There is only a single weft float 39'per pick in the weave pattern.

Crossovers 44 form diagonal or twill lines 32'across the weave pattern and weft floats 36', 37', and 39'for diagonal twill lines 33'across the weave pattern. Crossovers 44 are arranged adjacent intermediate portions of weft floats 39'and act to help stabilize the position of these floats in the fabric.

Contact surface 16, as shown in Figure 6, is substantially identical of contact surface 16 of Figure 2. The only difference is the location of support surface weft cross- unders 15'as they appear along each pick of upper weft 14'as indicated.

Figure 7, as in Figure 3, shows the interrelationship of each warp yarn 12'and each weft yam 14'throughout the weave pattern.

Figure 8 is the weave diagram for forming papermaking fabric B.

Turning now to Figures 9-13 a third arrangement of the papermaking fabric of the invention is illustrated at C. Figure 9 is a complete repeat of the weave pattern showing the outer or support surface 10"formed of sixteen ends of warp yams 12"which are numbered 01-16 and which weave with upper layer weft yam 14". The lower layer weft yarn 18 weaves also with warp yams 12"to form lower or machine contact surface 16. The weave pattern includes forty-eight picks, numbered 1-48, of weft yam 14"and sixteen ends of warp yam numbered 01-16.

Each warp yam 12"weaves over three and under twenty-nine picks of upper weft yam 14"in each weave pattern repeat forming three crossovers 46. Crossover 46 are separated by fifteen, two, and twelve picks respectively. Crossovers 46 are arranged over support surface 10"in such a manner that diagonal or twill lines 32"are formed across the width of the fabric.

Support surface 10"is a weft dominated surface with first picks forming weft floats 36"and 37"which pass over seven warp yams 14"and are tied in with a pair of crossovers 46. Second picks which form weft floats 39"pass over fifteen warp yams 14" and are tied in with a single crossover 46 per repeat of the weave pattern. The first and second picks are arranged in alternative manner over the support surface with crossovers 46 being positioned to engage and stabilize intermediate portions of weft floats 39". Again weft floats 36", 37", and 39"form diagonal twill lines 33"across the weave pattern and fabric.

Figure 10 shows the contact surface 16 of papermaking fabric C which again is substantially identical with the surface of papermaking fabric A & B. Again, the difference is

the location of crossovers 15"as the upper layer weft 14"which appears on the contact surface.

Figure 11 shows the interrelationship of each warp yam and each weft yarn throughout the weave pattern for fabric C.

Figure 12 shows the weave pattern.

The papermaking fabric structure as described provide even drainage throughout and the paper support surface and also forms a support surface which is even and smooth.

The fabrics exhibit good stability due to the balanced weave patterns, provide a minimal number of evenly even distributed anchoring points, those points where the warp yams pass over the upper weft yams or under the lower weft yarns weft yams, over both the paper support and machine surfaces.

The fabric, which is preferably a papermaking forming fabric, has been described as being woven flat with the warp yams extending in the machine direction (MD) and the weft yams extending in the cross machine direction (CMD). It is within the scope of the invention to weave the fabric continuous in which case the weft yams would extend in the MD and the warp yams in the CMD.

While preferred aspects of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.