US3903791A - Small roll, thin belt embossing apparatus - Google Patents

Abstract

A web embossing machine capable of establishing a desired pattern of good quality on both sides of a hard web in a single pass of the embossing nip by engaging the subject web between a relatively small diameter engraved embossing roll and a thin belt of resilient material. The embossing nip may be either of the two nips formed by pressing the embossing roll into nip spreading relation between two larger diameter backing rolls. A thin belt of resilient material runs continuously over one of the backing rolls. The subject web is threaded between the small diameter engraved embossing roll and the thin belt.

Description

United States Patent [191 De Ligt Sept. 9, 1975 [54] SMALL ROLL, THIN BELT EMBOSSING 3,542,353 11/1970 Schuhmann 1. 101/420 X APPARATUS 3,730,080 5/1973 DeLigt 101/23 [75] Inventor: John De Llgt, Covington, Va. Primary Examiner Edgar Burr [73] Assignee: Westvaco Corporation, New York, 145511910"! Examiner-Edward M- C hen NY Attorney, Agent, or Firm-W. Allen Marcontell; Richard L. Schmalz [22] Filed: Aug. 31, 1973 [21] App]. No.: 393,669 [57] ABSTRACT A web embossing machine capable of establishing a 52 0.5. CI. 101/23 desired Patter 0f qualiy both sides a hard 5 I] hit. cm B44B 5/02 web in a single Pass of embossing by engagmg [58] Field of Search". I 01/22 23 420 2) 220 the subject web between a relatively small diameter 101/221 I79 1 5 5 engraved embossing roll and a thin belt of resilient 308/1316 b i 362/1748 material. The embossing nip may be either of the two nips formed by pressing the embossing roll into nip [56] References Cited spreading relation between two larger diameter back ing rolls. A thin belt of resilient material runs continu- UNITED STATES PATENTS ously over one of the backing rolls. The subject web is 389-949 9/1338 Baker 101/23 threaded between the small diameter engraved eml,593,20() 6/1925 Ball r 4 t A i i t 101/23 bossing l and h i belt. 1,669,885 5/1928 Webb et a]. t. 101/23 2,878,778 3/1959 Kusters 101/22 x 6 Claims, 11 ng Figures PATENTEB P 91'975 3,903.791

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SHEET [1F 4 SMALL ROLL, THIN BELT EMBOSSING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous web material embossing and, more particularly, to an appara tus for embossing high density web materials requiring concentrated application of high embossing pressures.

2. Description of the Prior Art For many web materials, such as light weight paper, lastic films and thin metallic foils, embossing is a simple mechanical process comprising the step of passing the subject web through the rolling nip between an embossing roll and a backing roll. The embossing roll has the desired pattern three-dimensionally engraved on and into the surface thereof. The backing roll may have a smooth surface of rubber or other resilient material having a Shore A-85 durometer hardness adhered thereto. With a force of approximately 700 pounds per lineal inch applied to the nip, a pound per ream paper will receive adequate permanent material deformation in a single pass of the nip for good embossing.

More dense materials, such as 60 pound per ream paper, present compounded difiiculties for the embossing process, however. Since the basic embossing objective is to stress the subject material beyond the yield limit along the selective lines of the desired pattern, high density materials, characteristic of fine papers, require considerable pressure applications to achieve the desired result. Such pressures are difficult, if not impossible to attain against a conventional, rubber coated backing roll since higher force applications are merely distributed over a larger nip area. Moreover, to prevent structural distortion of the embossing roll mid-section between a conventional bearing support span of 60 inches, the embossing roll must be fabricated with a substantial diameter of 12 inches or greater. Accordingly, the necessary physical size of the embossing roll further aggravates the nip force distribution area enlargement problem.

Successful but expensive alternatives to resilient coated backing rolls include steel, male/female mating rolls and backing rolls fabricated from extremely dense paper fill, the latter requiring a considerable, 6 to 8 hour run-in time with the steel embossing roll.

SUMMARY OF THE PRESENT INVENTION It is an object ofthe present invention to teach an apparatus whereby fine, high density paper and other such web materials may be impressed on the two faces thereof with a single pass through an embossing nip.

Another object of the present invention is to teach the construction of a two-face, single pass embossing apparatus for fine papers requiring significantly smaller capital expenditures than prior art apparatus for this purpose.

Another object of the present invention is to teach the construction of a fine paper embossing apparatus having a rapid. pattern change capacity.

These and other objectives of the present invention are accomplished by forming an embossing nip between a relatively small diameter embossing roll and one of two, larger diameter backing rolls. One backing roll is provided with a smooth steel surface whereas the other backing roll surface should be a smooth resilient surface. The axes of the two backing rolls are parallel but selectively free to move within proximate limits. Preferably, the backing rolls are biased to a position of surface element tangency or contact.

The embossing roll is given full transverse support along the axial length thereof by a loading carriage having at least two loading struts. The strut loaded carriage presses the embossing roll between the nip proximity of the two backing rolls to a desired limit position near but short of coplanar tangency.

At the desired limit position, further separation of the backing rolls is positively prevented by mechanical abutments.

Through the nip between the embossing roll and the steel surface backing roll is threaded an endless belt of thin (approximately 0.050 in. thickness or less) polyurethane. This thin belt is of substantially greater periphery than the circumference of the steel surface backing roll and is carried about a closed circuit passing through said nip and around said steel surface backing roll.

Management of belt material extruded from the embossing nip due to the high pressures therein is pro vided by a large discharge area air plenum whereas back circuit support for the thin belt provided by air bearings.

Tendencies of the thin belt to slide to one side or the other of the desired tracking course around the smooth steel backing roll may be corrected by applying small increments of nip loading stress differential from the respective ioading struts. In this respect, the capacity to load one end of the embossing roll more or less than the other represents a mechanism for fine, belt steering trim.

BRIEF DESCRIPTION OF THE DRAWINGS Relative to the drawings wherein like reference characters denominate like parts throughout the several figures:

FIG. 1 is a schematic representation of a side elevation of the present apparatus.

FIG. 2 is a static force vector diagram representative of the loading characteristics of the present apparatus.

FIG. 3 is a sectional elevation of the present apparatus as viewed from cutting plane III-III of FIG. 1.

FIG. 4 is a schematic representation of an elevational side section of an alternative embodiment of the invention.

FIG. 5 is a schematic representation of operational effects of the high pressure nip on the thin belt as viewed normal to the belt plane.

FIG. 6 is a stress profile diagram of the belt along the section S of FIG. 5.

FIG. 7 is a stress profile diagram of the belt along the section S of FIG. 5 under extreme tension conditions.

FIG. 8 is a schematic representation of operational effects on the thin belt by the air plenum as viewed along the belt plane.

FIG. 9 is an enlarged schematic representation of operational effects of the high pressure nip on the thin belt as viewed along the belt plane from the midsection thereof.

FIG. 10 is another enlarged schematic representation of operational effects on the thin belt.

FIG. 11 is another enlarged schematic representation of operational effects on the thin belt in a failure mode.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, the apparatus of the present invention is illustrated in line schematic form showing the frame standards as pivotally supporting backing roll carrying swing arms 12.

Indexing turrets 14 are provided with a number abutments 16 for engaging the swing arms 12 at a precisely predetermined position of relative separation. The several abutments 16 are of different size for convenience in selecting the desired separation position.

Backing roll 20 is preferably a smooth, steel surface cylinder mounted for rotation about the swing arm 12 carried journal axis 21.

Backing roll 22 also is a steel cylinder mounted for rotation about the swing arm 12 carried journal axis 23. The surface of roll 22, however. is preferably coated with a suitable resilient material that is softer than the embossing roll to prevent injury to the surface thereof.

Embossing roll 30 is a simple steel cylinder having a desired embossing pattern etched, cut or rolled into the surface thereof. No journal supports are required of the roll 30 thereby allowing a number of such rolls 30a, 30b, 300 of different diameters and patterns to be stored conveniently in a magazine carriage 32. The carriage 32 is adapted to position the desired roll 30 within the reciprocation plane of the loading mechanism 40. The primary design criterion of the embossing roll diameter is the repetitive period of the desired pattern. Accordingly, the embossing roll 30 diameter may be substantially less than that of either backing roll 20 or 22.

Loading mechanism comprises loading struts 42 in support of resilient section 44. Between the emboss ing roll 30 and the resilient section 44 is provided a wheel carriage section 46. Rotatably mounted along the length of the carriage section 46 are two rows of closely spaced, freely turning support wheels 47 and 48. Each wheel row 47 and 48 is laterally displaced from a plane passing through the axis of embossing roll 30 and normal to a plane common to backing roll axes 21 and 23. Such lateral displacement of support wheels 47 and 48 provides a measure of positive stability for the embossing roll 30'prior to nip engagement with backing rolls 20 and 22.

Loading struts 42 are illustrated as telescoping hydraulic cylinders but it should be understood that numerous other devices such as screw or rack mechanisms are suitable for the same purpose.

Similarly, resilient section 44 may take numerous forms of mechanical equivalency. The form of resilient section 44. shown in detail by FIG. 4, includes upper and lower channel member 51 and 52 resiliently sepa rated by a series of springs distributed along the length of the channels.

The objective served by resilient section 44 is to uniformly distribute force applications from the two loading struts 44 but this is a matter of design choice and, if desired. resilient section 44 may be completely omitted or accomplished by other, equivalent means.

Web W, the embossed subject, is threaded around lower turning roll 61, through nip 60 between embossing roll 30 and the smooth steel surface backing roll 20 and finally around upper turning roll 62. From upper turning roll 62, web W may be directed to a rewind station or to other web processing stations as desired.

Also passing through nip is a thin (approximately 0.050 in. or less) polyurethane belt B of approximately Shore A-95 durometer hardness. Contrary to prior art teachings of attempting to secure such a thin resilient film to the surface of a steel backing roll, the present invention requires the belt B to be free of any structural attachments. Accordingly, after departing from surface contact with backing roll 20, the back circuit of the endless belt B is coursed around air bearing stations 63 and 64.

Element 65 of the belt control circuit is an elongated, crescent-shaped air plenum having a multiplicity of air discharge orifices 66 (FIGS. 3 and 4) through the wall thereof adjacent the belt B. Although plenum 65 serves an important secondary function as a final turning station for the belt circuit antecedent to entering the nip 60, a more important or primary function of the plenum 65 is that of transverse tension control of the belt in the region proximate of the nip 60 on the immediate in-feed side thereof. The mechanics of such tension control will be explained subsequently relative to FIGS. 7-11.

Rotational power may be delivered to either backing roll 20 or 22 but as shown in FIG. 3 such power is delivered to a driving element 24 of a gear cluster 25 for transfer to a driven element 26. In turn, driven element 26 drives the final drive gear 27 which is rotationally rigid with backing roll 20.

operationally, loading strut 42 is retracted from nip 6O sufficiently to allow clearance for magazine 32 to position the desired pattern embossing roll 30 in line with the wheel carriage section 46. Collaterally, turrets 14 are indexed to position the pair of abutments l6 appropriate for the selected embossing roll.

Upon loading actuation of the struts 42, the desired embossing roll 30 is lifted from its magazine carriage cradle and pressed into the nip between backing rolls 20 and 22. As shown, rolls 20 and 22 are gravity biased to a position of surface element contact or tangency due to the unstable disposition of roll axes 21 and 23 relative to respective swing arm frame journals 28 and 29.

An alternative to the FIG. I unstable disposition between axes 21 and 23 relative to respective journals 28 and 29 is the substantive distinction of FIG. 4. By disposing the swing arm 13 for backing roll 20 to the upper unstable position, the crowded condition of FIG. 1 and 3 lower section may be relieved. In such case the drive cluster 25 would be disposed concentric with journal 28 of FIG. 4.

Continued pressing of the embossing roll 30 into the backing roll nip spreads the backing rolls until swing arms 12 engage abutments 16. For maximum force advantage from the loading system, the final or operational position of the embossing roll axis 31 should be as near to the plane common to backing roll axes 2] and 23 as is safe. Safety in this context means those op crational conditions whereunder the roll 30 could be dravm or pressed completely through the backing roll nip.

Such a disposition of the embossing roll is known to the prior art as a high loading position." An example of such prior an may be found in my US. Pat. No. 3,730,080.

The source of the high loading characterization of this loading system is seen from the FIG. 2 vector diagram wherein a relatively small applied force, V from loading mechanism 40, is balanced by large nip forces V and V from respective backing rolls 20 and 22.

By way of example, embossing nip 60 vector V is in the order of 500-700 pounds per lineal inch of nip for a 1.75 inch diameter embossing roll 30 and inch diameter backing roll 20 driven at 230 rpm. The subject web W in the example was a 70 pound per ream, 0.004 caliper, coated and calendered paper. The belt B used in the present example was of 0.015 inch thickness Shore A-95 durometer hardness polyurethane.

To appreciate the operational advantages of the present invention over the prior art of fine paper embossing with steel or paper filled mating rolls, embossing forces in the order of 1,000 to 1,200 pounds per lineal inch of nip are common with such prior art techniques.

Although forces of 500-700 pounds per lineal inch of nip are common to other embossing systems utilizing a resilient backing surface, either as a backing roll coating or as a free running belt, it should be noted that such other systems are incapable of embossing materials having the properties of dense, fine papers. Accordingly, such systems are limited to use wifli light weight, pounds per ream or less papers such as is commonly characterized as crepe paper.

It should be further noted that while good, fine paper embossing may be achieved with 500-700 pounds per lineal inch of nip from the present invention, this is not to say that pressures prevalent in the embossing nip are the same as those found in other resilient backing surface systems. Quite to the contrary, and due predominately to the thin belt dimensions and properties and to some degree, the great diameter differential between the embossing roll 30 and backing roll 20, such nip force distribution is applied to considerably smaller nip areas. Accordingly, the applied embossing pressure in pounds per square inch is more in the order of that prevalent in the prior art mating roll systems. It is due to such high nip pressures required for fine paper embossing that prior art attempts at resilient film coatings for backing rolls such as taught by US. Pat. No. 3,247,785 have failed. No successful bonding or adhesion technique has been found that will hold the film for a practicable operational period.

As an alternative to the coated roll technique of providing a resilient embossing support, a free running belt of dimension and material characteristics taught herein presents formidable obstacles. The relatively high yield, low strength characteristics of such a thin polyurethane belt prohibits the normal prior art techniques for handling the back circuit thereof such as is taught by US. Patent No. 389,949. Polyurethane belt widths commensurate with a width-to-thickness ratio (w/t) of greater than 1000:l simply will not follow a fixed tracking course over dimensionally hard turning rolls. Moreover, apparently due to the high pressures applied to a nip including such thin polyurethane belts, a significant degree of temporary, localized material extrusion takes place to distort the belt form and dimension. If, under the aforedescribed embossing conditions, the belt is allowed to lay against the backing roll 20 surface antecedent to nip entry in substantial excess of 10 of wrap, a destructive standing wave will develop in the belt midsection. Although largely a matter of conjecture, the following explanation of critical belt dynamics has considerable support from observations borne of experience.

Relative first to FlG. 5, compressive stress within the nip has the effect of extrusively distorting the belt shape and thickness within the nip region 60. Since the belt material is essentially incompressible, the stressed portion thereof is merely displaced thereby causing bulges 71 at the web edges due to the absence of lateral restraint. Displaced material within the belt central portions, however, must be displaced along the machine running direction.

On the approach side of the nip, where the total flow of the belt material is toward the nip line C, such machine direction material displacement represents a countercurrent flow of belt material to create a region of compressive stress as represented by the stress profile diagram of FIG. 6 relative to the analytical plane S of FIG. 5. The bounded area on the minus side of the FIG. 6 diagram represents the distribution of tensile forces within the belt sections.

To further complicate analysis, the belt B also exhibits tensile yielding characteristics as manifest by the necking tendency of the belt in regions 72. Since friction drive from the embossing nip provides motive power to the belt 1, tensile strain to overcome the belt inertial, frictional and gravitational resistance would be greatest in the region 72. Although such longitudinal yielding as to cause lateral edge necking is within proportional limits, it is conceivable that coincident lateral stress toward the belt center axis further operates to create an excess of belt material in the region 70. Said excess of material in the region 70 is the substance of a standing wave in the belt course immediately ahead of the nip and is the cause of free running, embossing film belt failures.

As a point of interest, similar failure mechanics occur in the case of coated rolls; notwithstanding firm adherence of the resilient film to the roll surface.

If the amplitude of a standing belt wave is not restrained from maximum critical limits, the entire wave will be drawn into the nip with the consequent ruination of the embossing pattern and destruction of the belt.

Destruction may also occur from attempts to prevent standing wave accumulation by tensioning the belt over the unsupported span so greatly as to assure the stress distribution profile of FIG. 7 where even the midsection of the belt has at least a small degree of tensile stress. Experience with belts of the present description having w/t greater than 1,000 running over conventional cylindrical turning rolls indicates a tendency to develop severe necking in the regions 72 and longitudinal fluting also begins to appear. When drawn into the nip, such longitudinal flutes are equally destructive as the standing wave failures.

A complete analysis of such standing wave mechanics is extremely complicated due to the multiplicity of relevant parameters including; belt speed, average tension, nip pressure, belt width, belt thickness, unsupported span length, frictional coefficients of the backing roll surface and paper web surface, modulus of elasticity, hardness, Poisson's ratio, temperature and humidity. In so far as such a complex dynamic system is susceptible of complete analysis by state-of-the-art analytical techniques, however, it is only necessary, for reliable continuing operation of such a system, to recognize the nature of the failure and deploy the present invention within narrow limits of experimentation obvious to those of ordinary skill in the art.

The first factor to be acknowledged in this empirical approach is the standing period P (FIG. 9) for the particular belt and running conditions. P is that distance, measured along the theoretical plane E of the belt W, from the theoretical nip point A between rollers 20 and 30, to a point D ahead of the nip where the actual plane of the belt E, (the standing wave 90) first crosses or coincides with the theoretical plane E The theoretical nip point A is equidistant between the surface elements of rolls 20 and 30 and within the plane C of smallest separation between said surface elements which is the plane of roll tangency. Nip point A is assumed to lie in the throat of the belt B constriction as it passes between rolls 20 and 30.

Another theoretical plane passing through point A, one that is normal to the plane C, shall be characterized as the nip tangent.

Angle a is the included angle between the nip tangent and the linear portion of the theoretical belt plane E Angle a may also be considered as the circular arc, about the center of backing roller 20, between the point A and the first point of normal coincidence between the theoretical belt plane E and a radii of backing roller 20.

It is not necessary to actually determine the period P in linear units but to merely recognize the substantive relationship between P and the average angle Referring next to FIG. 10, as the angle 0: is increased, assuming a constant value for P, at some degree the belt will come into surface contact with backing roll 20 in the vicinity of point D Notwithstanding further increases of a, the standing wave period P remains constant. Accordingly, if the angle a is increased by a quantity 8 to a point of first prenip contact D the surface of backing roll 20 will frictionally seize the belt over the are 5 and draw it into the nip 60 ahead of the standing wave loop 70 as shown by FIG. 11. The angle a at which a destructive degree of wrap 5 occurs shall be characterized as the critical wrap angle a Solution to the above described problem is won by sustaining sufficient longitudinal tension across the unsupported span of the belt B between the nip 60 and the plenum 65 so as to assure that the critical angle or is not exceeded at any point thereacross.

Consistent with achieving such sufficient tension is to position the plenum 65 relative to the nip 60 for as low an angle a as possible. A smaller angle a requires less tensile exertion on the belt to keep the critical angle orC within tolerable limits. parallel axis turning rolls, cylindrical or crowned, are unsatisfactory for this purpose as having only fixed geometry for tensile distribution. In high w/r embossing film belts (w/t greater than 1,000) of the nature described herein, it is necessary to apply a smoothly distributed force, independent of position, to draw the standing wave period out from critical contact with the backing roll as localized accumulations of material develop.

Referring next to FIG. 8 it may further be seen why such flexibility in web tension management is essential to the successful practice of the invention. As the belt 8 passes over the plenum 65. escaping pressurized air therefrom tends to balloon the belt midsection B,,,. As already explained. the natural dynamics of the nip on the belt sustains a certain degree of tension in the belt edges 8,. Accordingly in the belt midsection, where the quantity of longitudinally extruded material is greatest, such ballooning efiectively reduces the nip approach angle a relative to the edge nip approach angle 04 Such is the substance of differential angle A. Since differential angle A may vary from moment to moment it necessarily follows that an extremely compliant tensioning mechanism is required. The plenum 6S taught herein is such a mechanism.

Although the fluid bearing between the underside of belt B and the proximate surface elements of plenum 65 offer a relatively frictionless pivot station for the belt circuit, the more significant contribution of the fluid bearing is to provide, within tolerable limits, a uniformly distributed tensioning force across the belt width that is independent of fixed position. As the bearing space becomes larger coincident with a localized increase in the standing wave period or amplitude, the longitudinal belt tension remains constant to restrain the wave from further increasing.

To contrast this operation with a fixed geometry turning roll, as a localized standing wave before the nip grows, no localized compliance of the tensioning surface is available to attenuate the growth. To the contrary, the wave provides an effective decoupling of the nip tractor force to the belt length opposite from the wave. Accordingly, belt tension along the longitudinal elements including the wave diminishes. With the diminution of tension, the wave further increases in amplitude until the critical angle at is exceeded whereupon the entire wave is drawn into the nip to destruction.

Since belt tension and the angle a are so critically interrelated, it is obvious that the magnitude of tension necessary to control a standing wave may be minimized in the embossing machine design by reducing the angle a to a tolerable minimum. Ideally, the belt B should approach the nip tangentially. However, for the belt and operating conditions described above, a theoretical approach angle a of 10 has been found tolerable.

A final point to be considered in the operation of the present invention relates to belt steerage and the particular technique of embossing roll loading taught herein.

Due to the lack of normal lateral restraints effective to sustain an endless belt in track with the desired circuit, belts having air bearing turning stations tend to slide to one side or the other in the course of running. In other words, belt track is relatively unstable. Dimensional flexibility of the belt further aggravates a difiicult problem.

It is a physical impossibility at the present state of the art to build a machine of the complexity described herein with all components having and sustaining perfect parallelism of alignment. Accordingly, alignment defects are a major cause of lateral drift in the belt.

Other factors affecting belt tracking are the static uniformity of thickness and squareness of the beit periphery.

Although machines and belts of the character described may be fabricated reasonably close to perfect, the near frictionless lateral support of an air bearing circuit magnifies the effect of even small defects thereon. Conversely, only small correcting forces are necessary to laterally hold such a belt that is otherwise reasonably close to a true running track.

Accordingly, by applying small differentials in roll 30 loading forces from struts 42, small lateral force may be applied to the belt at the nip to oppose the built-in forces of instability.

While certain embodiments of the invention have been described for purposes of illustration, it will be apparent that modifications thereof will occur to those skilled in the art within the scope of the appended claims.

I claim:

1. Apparatus for high pressure embossing a continuous high density material web of indefinite length comprising:

a. a pair of substantially cylindrical backing rolls having axes movably mounted to sustain relative parallelism therebetween;

b. a substantially cylindrical embossing roll;

c. support means to selectively engage the cylindrical surface of said embossing roll along the length thereof, said support means comprising loading means to press said embossing roll into the proximity between said backing rolls to form respective roll nips therebetween, each of said toll nips having a material in-flow and out-flow side respective thereto;

d. selectively positionable abutment means to limit the axial separation between said backing rolls to a magnitude less than the sum of the diameter of said embossing roll and the radii of said backing rolls;

e. an endless, thin, resilient material belt of appreciably greater periphery than the circumference of one of said backing rolls disposed for traveling about said one backing roll in a closed course passing through the roll nip comprising an embossing nip between said embossing roll and said one backing roll;

f. means to direct a continuous web of indefinite length through said embossing nip between said embossing roll and said endless belt;

g. means to deliver rotational power to one of said backing rolls; and.

h. endless belt tensioning means disposed on the inflow side of said embossing nip, proximate thereof, and comprising fluid discharge means disposed within a curvilinear portion of said closed course for applying a substantially constant longitudinal tensile stress to said belt regardless of reasonable dimensional variations in the proximity between said belt and said fluid discharge means.

2. Apparatus for embossing a continuous web as described by claim 1 wherein said loading means comprises at least two selectively extensible elements for applying a force differential to said embossing roll along the length thereof from one axial end to the other.

3. Apparatus for embossing a continuous web as described by claim 1 wherein the diameter of said embossing roll is substantially less than the diameter of said one backing roll.

4. Apparatus for embossing a continuous web as described by claim I wherein said endless belt is of polyurethane composition having a thickness of less than 0.05 inches and hardness of approximately Shore A-95.

5. Apparatus for embossing a continuous web as described by claim I wherein said fluid discharge means comprises an air plenum extending across the width of said belt, said plenum having a perforated wall adjacent said closed belt course.

6. Apparatus for embossing a continuous web as described by claim 5 further comprising air support bearings supporting said belt along additional portions of said closed course.

Claims (6)

1. Apparatus for high pressure embossing a continuous high density material web of indefinite length comprising: a. a pair of substantially cylindrical backing rolls having axes movably mounted to sustain relative parallelism therebetween; b. a substantially cylindrical embossing roll; c. support means to selectively engage the cylindrical surface of said embossing roll along the length thereof, said support means comprising loading means to press said embossing roll into the proximity between said backing rolls to form respective roll nips therebetween, each of said roll nips having a material in-flow and out-flow side respective thereto; d. selectively positionable abutment means to limit the axial separation between said backing rolls to a magnitude less than the sum of the diameter of said embossing roll and the radii of said backing rolls; e. an endless, thin, resilient material belt of appreciably greater periphery than the circumference of one of said backing rolls disposed for traveling about said one backing roll in a closed course passing through the roll nip comprising an embossing nip between said embossing roll and said one backing roll; f. means to direct a continuous web of indefinite length through said embossing nip between said embossing roll and said endless belt; g. means to deliver rotational power to one of said backing rolls; and, h. endless belt tensioning means disposed on the in-flow side of said embossing nip, proximate thereof, and comprising fluid discharge means disposed within a curvilinear portion of said closed course for applying a substantially constant longitudinal tensile stress to said belt regardless of reasonable dimensional variations in the proximity between said belt and said fluid discharge means.

2. Apparatus for embossing a continuous web as described by claim 1 wherein said loading means comprises at least two selectively extensible elements for applying a force differential to said embossing roll along the length thereof from one axial end to the other.

3. Apparatus for embossing a continuous web as described by claim 1 wherein the diameter of said embossing roll is substantially less than the diameter of said one backing roll.

4. Apparatus for embossing a continuous web as described by claim 1 wherein said endless belt is of polyurethane composition having a thickness of less than 0.05 inches and hardness of approximately Shore A-95.

5. Apparatus for embossing a continuous web as described by claim 1 wherein said fluid discharge means comprises an air plenum extending across the width of said belt, said plenum having a perforated wall adjacent said closed belt course.

6. Apparatus for embossing a continuous web as described by claim 5 further comprising Air support bearings supporting said belt along additional portions of said closed course.

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