Apparatus for folding of a web

Abstract

A web of material is predisposed to folding by being passed through a pair of cooperatively mounted mating rolls; i.e., a male and female roll, which roll along what become the lines of fold of the web, prior to its being manipulated into its folded position. The rolls tend to loosen bonds in the web transverse of the ultimate lines of fold, thereby facilitating folding. Because the mating rolls manipulate the web only slightly, in distinction to the action of conventional folding devices, the web maintains its alignment while passing through the mating rolls relatively well, resulting in accurately located lines along which the web is predisposed to fold. Since the lines of predisposition to folding are accurately located, the ultimate folded structure is more dimensionally consistent than heretofore possible. In the preferred embodiments, the rolls press against the web with constant pressure, rather than being fixedly mounted, thereby providing a built-in adjustment for variations in web thickness.

Parent Case Text

This is a continuation of application Ser. No. 203,806, filed Dec. 1, 1971, and now abandoned.

Description

BACKGROUND OF THE INVENTION

This invention relates to the folding of webs and more particularly to the use of mated rolls to predispose a web to fold.

Webs of material are often provided with lines of fold by the use of a pair of mating male and female rolls with a generally V-shaped periphery which crush and deform the web as it passes through them. Typical of this prior art is U.S. Pat. No. 3,570,841 issued Mar. 16, 1971 to Friedrich Rettig.

With relatively flexible webs such as facial tissues, folding is generally done with structures comprising boards around which a moving web is manipulated by means of guiding members. A folding apparatus of guides and boards has also been used with relatively heavy webs such as a disposable diaper pad with some success. Because of the relative rigidity of such a heavy web, however, control of the web position in such a folding apparatus is relatively difficult; the stiff web has a mind of its own. The result of inadequate control of web position in the folding apparatus, commonly referred to as poor tracking, is dimensional variations in the folded web. This is obviously undesirable.

It has been found that a prefolding step such as described hereinafter will predispose a web to fold along the lines of prefolding and cause the web to track more nearly uniformly on the folding apparatus, resulting in a more dimensionally consistent folded web.

Second only to the dimensional stability problem in a board and guide folder is the problem of longitudinal web stretching in the folder because of the relatively high web tensions normally required in this apparatus. This problem is especially severe with composite webs whose materials have greatly different elasticities such as the creped paper and polyethylene sheet composite web used for making disposable diapers. When such a web is tensioned both materials stretch. When the tension is released the polyethylene springs back a significant amount while the creped paper has little or no spring back. The difference in final lengths of the two components of the web, often referred to as puckering, is obviously undesirable. If the web can be predisposed to fold, and consequentially the tension used in the folding apparatus reduced, this problem may be significantly reduced.

Any solution to the above problem, to be practical, must also avoid materially weakening the web transverse of the lines of fold. This requirement means that many conventional means for folding such as embossing and scoring could not be used.

Accordingly it is an object of this invention to provide an apparatus of predisposing a web to fold along lines of fold which are accurately located.

It is another object of this invention to predispose a web to fold thereby reducing the forces required in the folding operation.

It is still another object of this invention to achieve the above objects without embossing or scoring the web and without materially affecting the strength of the web transverse of the line of fold.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided an apparatus for predisposing a web to fold along a predetermined line of said web comprising a male roll having a convex raised periphery and a female roll having a concave peripheral groove, said groove being substantially wider than said raised periphery, said male and female rolls being co-operatively mounted and adapted to engage said web therebetween and to roll along said predetermined line and to compress said web with about 10 to about 40 pounds force.

BRIEF DESCRIPTION OF THE DRAWINGS

Although the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as forming the present invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view of the prefolding apparatus of this invention.

FIGS. 2 and 3 are elevation views of the preferred configuration of the prefolding rolls.

FIG. 4 is an exaggerated edge view of the web emerging from the apparatus of FIG. 1.

FIG. 5 is a fragmentary perspective view of the board and guide folding portion of the overall folding apparatus.

FIG. 6 is an end view of the web as it is folded by the apparatus of this invention.

FIG. 7 is a front elevation view of a preferred embodiment of the prefolding apparatus of this invention, partially cut away for clarity.

FIG. 8 is a fragmentary side elevation view of the apparatus of FIG. 7 as viewed along section line 8--8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Folder

Referring now to the drawings, FIG. 5 shows the board and guide folder designated generally as 40. Web W enters the folder 40 at the left of the drawing as a flat sheet and is discharged at the right in its folded configuration. Although many different fold patterns may be achieved by the apparatus of this invention, the description will be limited to achieving the fold pattern shown in FIG. 6; and in particular to achieving this fold pattern on a web of materials comprising a disposable diaper such as that shown in U.S. Pat. No. 26,151 issued Jan. 31, 1967 to R. C. Duncan et al. Briefly, this web is typically comprised of about 10 plies of creped tissue having an air dry basis weight of 7-9 pounds per ream of 3,000 square feet, before creping to reduce its length by 60 percent, sandwiched between a 0.001 inch thick sheet of polyethylene and a non-woven fabric web of 1.5-3 denier rayon with 20-35% thermoplastic binder and a basis weight of 15-19 grams per square yard. A "fluff" batt of comminution pulp as described in U.S. Pat. No. 3,612,055, issued Oct. 12, 1971 to F. K. Mesek can be used in place of the creped paper. Such a web has a typical total thickness of 0.100-0.25 inches or more.

Web W is pulled through folder 40 by tension T applied to the web W by subsequent equipment, not shown, and is shown in fragments (for clarity of illustration) at various points along folder 40. Initially the web W is flat and horizontal. Upon reaching the elevating board 41 the web W rises and its outer edges droop downwardly over the edges of elevating board 41 under the force of gravity and the urging of guide rails 42a and 42b. As can be seen, elevating board 41 narrows from its initial width, which is preferably the same as the width of the web, to a final width C which is substantially equal to the width of the central portion of the folded structure as shown in FIG. 6. The horizontal board 43a and the descending board 43b are also substantially equal to C in width.

The guide rails 42a and 42b proceed downwardly and inwardly from their point of initial contact with web W and at the discharge end of horizontal board 43a (i.e., the right end as shown in FIG. 5) are directly below horizontal board 43a and beneath it by the distance I corresponding to the intermediate section I of the folded structure as shown in FIG. 6.

In the direction of travel of web W along the descending board 43b the guide rails 42a and 42b converge at points adjacent the underside of descending board 43b and spaced inwardly from its edges by the distance I. Members 44a and 44b provide support and lateral rigidity to guides 42a and 42b, respectively.

Normally the tension T imparted to the entire width of the web W by the subsequent equipment (not shown) will be sufficient to cause the outer edges E of the web to rise into the desired position as shown. If for some reason, the web W does not rise as desired, the plow 45a (and a corresponding member on the other side, not shown) will urge it into the desired position. Plow 45a consists of a vertical member 46a which prevents inwardly movement of edge E of web W and supports lifting member 47a which urges web W upwardly toward the discharge plate 48a. Since plow 45a serves only to redirect the web W should it go astray, it is not necessary for the discharge plate 48a to be in close proximity to descending board 43b and the two are preferably spaced about one-half inch apart as shown so as to avoid binding problems.

As mentioned previously, the board and guide folding apparatus 40 has previously served as the only means for folding a web W which is later cut into individual lengths to form disposable diapers. Tracking has been a continual problem with this arrangement, however, since there is no assurance that web W will remain centered on the folding apparatus 40. Moreover, any misalignment tends to perpetuate itself rather than correct itself.

Prefolder

The prefolding apparatus shown in the fragmentary perspective view of FIG. 1, and designated generally as 10, located at any point upstream of the folding apparatus 40 (in the direction of web travel), has dramatically improved the tracking of web W on the folding apparatus 40. The prefolding apparatus 10 uses mated pairs of rolls consisting of male rolls 11 and female rolls 12 to flex the web W as it passes between the mated rolls. The preferred geometry of the rolls is shown in more detail in FIGS. 2 and 3. Each pair of rolls (a, b, c, and d) flexes the web W along predetermined lines and the result of this flexing is shown, greatly exaggerated for clarity, in FIG. 4.

The web W of FIG. 4 is shown as it would appear emerging from the prefolding apparatus 10 of FIG. 1; i.e., looking into the arrow 50 of FIG. 1 showing the direction of movement of the web W through the prefolding apparatus 10. The ridges shown in FIG. 4 from left to right are formed by rolls 11a and 12a, 11b and 12b, 11c and 12c, 11d and 12d respectively. The arrows on FIG. 4 show the direction in which each portion of the web is predisposed to fold as a result of passing the prefolding apparatus 10.

Returning to FIG. 1, all of the rolls 11 and 12 are preferably driven in synchronism by a mechanism which will be described in connection with FIGS. 7 and 8 which show the complete assembly of the preformer 10. Male rolls 11a and 11d are mounted on fixed rotatable shaft 13a and female rolls 12b and 12c are similarly mounted on fixed rotatable shaft 13b. Female rolls 12a and 12d which mate with male rolls 11a and 11d respectively are mounted on floating rotatable shaft 14a. Male rolls 11b and 11c which mate with female rolls 12b and 12c respectively are mounted on floating rotatable shaft 14b.

Floating rotating shafts 14a and 14b are similarly mounted, although the only mounting shown is a portion of that for shaft 14b. Air cylinder 18a is used to provide a constant upward force on shaft 14b via pin 17a, pivot linkage 16a, bearing block 19a and bearing 20. Pivot linkage 16a rotates about fixed shaft 15a. Similar piston and linkage assemblies are used to provide constant upward force on each end of each of the floating rotatable shafts 14a and 14b.

To predispose the web of diaper material to folding on the folding apparatus 40, the web is compressed to a point just short of embossing as will be discussed later. This can be accomplished by having a suitably adjusted fixed spacing between the male and female roll of a pair or by use of a constant force moving the male and female rolls of a pair toward one another. If the constant force approach is used, each of the four pairs of rolls should be urged together with a force of from about 10 to about 40 pounds. The use of constant force between the pairs of mating rolls is superior to the use of constant spacing between the rolls in many applications as it provides automatic adjustment for variations in web thickness. This is especially important when folding disposable diapers as they are comprised of a plurality of layers of creped paper, each layer being provided by a separate stock roll. Rolls of creped paper stock are continually being exhausted and new ones added, consequently the exact number of layers, and hence the web thickness, is continually varying. Each of the four air cylinders must therefore exert 10 to 40 pounds upward force plus whatever is required to overcome the force of gravity on the shaft, gears, rolls, bearings, etc. which it is lifting. Each of the male rolls 11 preferably has a diameter A of about 41/2 inches with a width B of 0.188 inches and a semicircular periphery of 0.188 inches diameter. The female roll 12 preferably has a diameter C of about 43/4 inches and a width D of about 1/2 inch. The segment shaped groove in its periphery, as shown in FIG. 3, has a radius E of 0.218 inches with an offset F of 0.083 inches. The web contacting portions of the rolls (i.e., the outside diameter of the male roll and the inside diameter of the groove) should be the same diameter, thus allowing the peripheral speed of these portions to be matched to the web speed by simple gearing as will be shown later. The otherwise sharp corners circumferentially about the female roll 12 are machined to a 0.03 radius to minimize the potential for the web hanging-up on the edges and being pulled apart.

There is some tendency for the web to be drawn inwardly by the pairs of mating rolls; i.e., to be gathered between two pairs of mating rolls. Because of this, when four pairs of mating rolls are being used as shown the web preferably first contacts the two outermost pairs of rolls. In this way, a small, but controlled, amount of excess material is gathered between these rolls to provide some "play" at the inner two pairs of rolls.

It should be noted that it is almost imperative to mount no more than two preforming rolls on each of the floating shafts as shown. This coupled with the floating mounting of each end of each floating shaft allows each pair of preforming rolls to adjust individually.

Machine Details

FIGS. 7 and 8 show a complete machine, cut away in places for clarity, used to perform the prefolding steps described earlier with reference to the partial perspective view of FIG. 1.

FIG. 7 is a front elevation of the prefolding apparatus 10. The web (not shown) is moving toward the viewer. The male rolls 11a, 11b, 11c, and 11d, and female rolls 12a, 12b, 12c and 12d each has a split collar extension 35 to allow it to be secured to one of the shafts 13a and 13b and 14a and 14b as shown. Shafts 13a and 13b and 14 a and 14b are supported in bearings 20 which in turn are supported by side plates 30a and 30b. The side plates 30a and 30b are supported on base plate 21 which also supports depending support members 22a and 22b. Depending support members 22a and 22b hold the piston support plate 23 which in turn supports piston mounting yokes 28a, 28b, 28c and 28d to provide a pivoted mounting for air cylinders 18a, 18b, 18 c and 18d respectively via piston mounting brackets 29a, 29b, 29c and 29d respectively.

The drive mechanism will be described subsequently with reference to FIG. 8, however it should be noted with reference to FIG. 7 that the floating rotatable shafts 14a and 14b are driven by gears 31a and 31b respectively. As was stated earlier, the upward force exerted by the air cylinders 18 preferably equals the weight of the rolls, shafts, etc. plus about 10 to about 40 pounds. To simplify adjustment of the upward forces exerted by each air cylinder 18 counterweights 32a and 32b are provided. By making the counterweights 32a and 32b exactly like gears 31a and 31b respectively and by locating them symmetrically with respect to said gears, the air cylinders 18 may more easily be adjusted as desired.

FIG. 8 is a side elevation of the prefolding apparatus 10 taken along section line 8--8 of FIG. 7. Gears 31a, 31b, 31c, 31d, 31e and 31f provide the requisite synchronization of the pairs of mated rolls. Sprocket 33a is driven by chain 34 and a suitable drive means (not shown). Chain 34 also drives sprocket 33b which is connected to conveyor belt roll 37. The interconnection of the preformer 10 with the preceding conveyor belt 38 via conveyor belt roll 37, sprockets 33a and 33b, and chain 34 allows the preformer 10 to be synchronized with the web speed on the preceding equipment as exempified by conveyor belt 38.

Sprocket 33a drives shaft 13a, and thereby male rolls 11a and 11d, and gear 31d which is also mounted on shaft 13a. Gear 31d engages gear 31a, thereby driving shaft 14a and the female rolls 12a and 12d, and gear 31f, thereby driving the overhung shaft 39 and gear 31e. The overhung shaft 39 is supported by bearing 20' specifically suited to the overhung load and retained by shaft retainer 39'. Gear 31e drives gear 31c, thereby driving shaft 31b and female rolls 12b and 12c. Gear 31c in turn drives gear 31b, thereby driving shaft 14b and male rolls 11b and 11c.

Pivot shafts 15a and 15b are mounted between side plates 30a and 30b. Connected to pivot shaft 15a is pivot linkage 16a and 16d (not shown) and connected to pivot shaft 15b is pivot linkage 16b (partially shown in FIG. 8) and 16c (not shown). The function of each pivot linkage 16 and the associated parts is identical; for simplicity only pivot linkage 16a will be described. Pivot linkage 16a is pivotally mounted to both pivot shaft 15a and, via pivot pin 17a, to air cylinder 18a. Bearing block 19a rests on pivot linkage 16a and contains bearing 20 which in turn supports one end of floating shaft 14b. Thus air cylinder 18a provides upward support for and pressure on male roll 11b. Pivot linkage 16a is tapped to accommodate stop bolt 26b which is held in place by lock nut 27b. Stop bolt 26b is adjusted such that, in the absence of a web, the male roll 11b cannot be driven against the female roll 12b because of the stop 24b which is supported by member 25b. Member 25b is in turn supported from base plate 21.

Work table 36 is supported from side plates 30a and 30b and serves to support the web W and guide it into the nip of the mating rolls.

Roll Geometry Considerations

FIGS. 2 and 3 show the male roll 11 and the female roll 12 respectively in the preferred configuration for prefolding the web of a disposable diaper.

While applicant does not wish to be bound by a description of the mechanisms involved in the prefolding step described, it is believed that the prefolding step has the effect of loosening the fibrous bonds transverse of the lines of ultimate fold without materially weakening the web, thereby facilitating folding along these lines.

More specifically, two mechanisms are thought to be involved. First is the bending of the web around the male roll which is a comparatively gentle and distributed action. Second is application of a relatively high force along a narrow line where the male and female rolls meet. To separate these effects, the male roll has a smaller radius protrusion than the radius of the groove in the female. This provides a narrow line of greatest proximity thus providing a narrow line of application of the high force.

The width B of the male roll largely determines the sharpness of the ultimate fold; the narrower the roll the sharper the fold. The female roll is chosen based on the width of the male roll and the thickness of the web. In the application described above the width B of male roll is about 1.7 times the thickness of the web being prefolded and the width G of the groove in the female roll is such that there is essentially no compression of the web in the region between the sides of the male roll and the essentially vertical walls of the arcuate groove in the female roll (i.e., G = B + 2X web thickness). Thus, the periphery of the male roll meets the base of the groove in the female roll along a narrow line to compress the web. Beyond the narrow line of compression, the groove in the female roll provides a means to wrap the web around the semicircular periphery of the male roll.

With the above mentioned geometries, materials, and forces, the web is compressed to a minimum thickness of about 0.004 to about 0.008 inches and it springs back after passing through the prefolder to essentially its initial thickness of about 0.100-0.250 inches. This same web could be embossed by compression with much higher pressures to about 0.001 to 0.003 inches thickness at which point it would have very limited spring back.

It can be appreciated that, while the preferred geometry for the rolls of the prefolding apparatus utilizes a male roll having an arcuate convex raised periphery and a female roll having a concave arcuate peripheral groove as described above, other roll shapes selected with the above considerations could perform satisfactorily. For example the male roll could have a V-shaped edge portion and the female groove could be rectangular with a V- or truncated V-shaped bottom.

Many modifications of the invention can be made and it is not intended to limit the invention to the particular structures described, all reasonable equivalents thereof being intended to fall within the scope of this invention.

Claims

What is claimed is:

1. An apparatus for folding a moving web of disposable diaper material or the like having an initial thickness, prior to compression, of from about 0.100 to about 0.250 inches along a multiplicity of predetermined fold lines oriented parallel to the direction of movement of said web, the innermost pair of said predetermined fold lines defining the central portion of said web, said apparatus comprising:

a. a male roll for each of said lines, each male roll having a convex raised periphery, said convex raised periphery having a minimum width approximately 1.7 times greater than the thickness of said web prior to compression;

b. a mating female roll for each male roll, each female roll having a concave peripheral groove, said groove having a minimum width approximately equal to the sum of the width of said raised convex periphery plus twice the thickness of said web prior to compression;

c. means for engaging said web between a mating pair of male and female rolls along each of said predetermined fold lines;

d. means for driving said male and said female rolls in synchronization with the movement of said web;

e. means for urging each mating pair of rolls against said web to compress said web to a minimum thickness of between about 0.004 inches and about 0.008 inches while said web is engaged between said rolls, thereby predisposing said web to fold along saud predetermined fold lines;

f. a board folder having an uppermost surface and a lowermost surface, the infeed width of said board folder being at least equal to that of said web prior to folding, said board folder tapering to a width substantially equal to the width of the central portion of said web lying between the innermost pair of said predetermined fold lines; and

g. guide means for directing the lateral edge portions of said web inwardly into superposition with the lowermost surface of said board folder along said predetermined fold lines.

2. The apparatus of claim 1, wherein said means for urging each mating pair of rolls against said web is comprised of a constant force generating mechanism.

3. The apparatus of claim 1, wherein said means for urging each mating pair of rolls against said web is comprised of a fixed gap spacing between said rolls, said fixed gap spacing being between about 0.004 inches and about 0.008 inches, as measured between said mating rolls at the highest point on said raised convex periphery and the lowest point on said concave peripheral groove.