US3919974A

US3919974A - Hot melt extrusion apparatus

Info

Publication number: US3919974A
Application number: US414519A
Authority: US
Inventors: Peter Herzog
Original assignee: Bolton Emerson SA
Current assignee: Bematec SA; Bolton Emerson Americas Inc
Priority date: 1973-11-09
Filing date: 1973-11-09
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18
Also published as: CA1043559A

Abstract

An apparatus and method for applying hot melt coatings to the under face of a web from the orifice of a coating head. The extrusion pressure preferably lifts the web slightly by overcoming web tension. Uniform heat is achieved by central feed to the head. Smoothing doctor blades are not required and the head is movable relative to a fixed back-up roll so that roll readjustment is not required when rethreading. One extrusion lip is flexible and independently movable relative to the other to permit change in width of the elongated extrusion orifice. A relatively light, distortable lip bearing member is provided.

Description

United States Patent 1191 Herzog 1 51 Nov. 18, 1975 1 1 HOT MELT EXTRUSION APPARATUS [75] Inventor: Peter Herzog, Chemin du Martinet,

[2]] Appl. No.: 414,519

[52] US. Cl. 118/410; 118/253; 118/419 [51] Int. Cl? B05C 3/12 [58] Field of Search 118/410, 424, 419, 429,

Dentch et al. 118/410 Heijnis et a1. 118/410 Primary Examiner-W. C. Reynolds Assistant ExaminerDoug1as Salser Attorney, Agent, or FirmPearson & Pearson [57] ABSTRACT An apparatus and method for applying hot melt coatings to the under face of a web from the orifice of a coating head. The extrusion pressure preferably lifts the web slightly by overcoming web tension. Uniform heat is achieved by central feed to the head. Smoothing doctor blades are not required and the head is movable relative to a fixed back-up roll so that roll readjustment is not required when rethreading. One ex- 56 References Cited I UNITED STATES PATENTS trusion lip is flexible and independently movable relative to the other to permit change in width of the elon- SEI P gated extrusion orifice. A relatively light, distortable een i 3,348,526 10/1967 Ncubaucr i 1 18/410 hp bearmg member 18 provlded' 3,556,832 1/1971 Park 118/410 1 Claim, 4 Drawing Figures l 2 lo I'- L 3O 3O 22 US. Patent Nov. 18, 1975 Sheet10f2 3,919,974

I g) Q52 US. Patent Nov. 18, 1975 Sheet 2 of2 3,919,974

HOT MELT EXTRUSION APPARATUS BACKGROUND OF THE INVENTION U.S. Pat. No. 2,464,771 of Mar. 15, 1949, to Van Guelpen discloses an angularly tiltable extrusion head over which a web under tension is passed for coating the under, face, but no backer roll is used opposite the orifice and a doctor, or smoothing, blade is in rear of the orifice along the web path to actually produce the smooth coating. Such a device is not likely to produce a commercially acceptable, thin, low cost coating from viscous, tacky, hot melt substances which range from 5,000 to 500,000 cps.

One solution to the problem of commercially successfully handling such hot melt coatings at high line speeds and with desired uniformity is found in U.S. Pat. No. 3,556,832 of Jan. 19, 1971 to Park. Apparatus is disclosed in this patent wherein a web to be coated is passed over a stationary, somewhat rounded coating head having an elongate slit. Paper moves over the elongate slit bearing against the rounded coating head. Hot melt material is extruded through the elongate slit onto the paper. An important part of this process is the transverse stretching of the web as it approaches the coating head and the guiding of the web under tension into sliding contact with the coating head itself. The coating process described by Park generally includes the steps of simultaneously controlling the rate of flow of the coating material to exert a pressure that is somewhat greater than an opposing force on the tension web, a force normally achieved with a press roll.

In general, the process disclosed by Park has been a successful and desirable commercial process.

Indeed the process has been found to be so broadly applicable that there has been a need for improved apparatus that will permit full exploitation of the process capabilities.

SUMMARY OF THE INVENTION Therefore, it is an object of the invention to provide an improved extrusion head apparatus which can be used to achieve improved coating precision of hot melt materials and is readily cleaned and adjusted to meet various processing conditions.

It is a further object of the invention to provide apparatus which has an improved self-cleaning characteristic during operation.

Another object of the invention is to provide a more efficient coating apparatus, one characterized by a more dependable maintenance of web tension.

Other objects of the invention will be obvious to those skilled in the art on reading the instant application.

The above objects have been substantially achieved by constructing a coating apparatus comprising a coating head, or extrusion die, wherein the web-support members forming an elongate slit comprise elongate lead-on members and lead-off members at least one of which is adjustably mounted for overall positioned adjustment with respect to the other member and also for adjustment of slit width along the length of the slit by means of adjusting either compression or tension on individual adjusting means spaced along the member.

This adjusting feature, permitting as it does finer control over the slit width, also allows central feed to a plenum chamber from which the elongate slit feeds hot ILLUSTRATIVE EXAMPLE OF THE INVENTION In this application and accompanying drawings there 0 is shown and described a preferred embodiment of the invention and suggested various alternatives and modifications thereof, but it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will be able to modify it in a variety of forms, each as may be best suited in the condition of a particular case.

IN THE DRAWINGS FIG. 1 is a partially diagrammatic section in elevation and showing the relationship of the apparatus of the invention to a web being coated therewith.

FIG. 2 is a section of the extrusion apparatus as defined by section line 2-2 on FIG. 4.

FIG.'3 is a section of the apparatus as defined by section line 33 on FIG. 4.

FIG. 4 is a sectional view of the coating apparatus of the invention taken through a plane which is normal to the direction of the web being coated.

Referring to FIG. 1, it is seen that coating apparatus 10 comprises a coating head 12 which is mounted for angular movement by an hydraulic ram 14 by means of a bracket 16 mounted for skewed movement on shaft 18 within arcuate slot 20.

A paper web 22 is passed left-to-right across coating head 12 and receives a layer 24 of a hot melt barrier coating 26. g

A fixed press roll 28 is mounted on the opposite side of web 22 and forms means to support said web against pressure exerted by coating material being forced under pressure onto the web from coating head 12. Idler rolls 30 form means to keep web 22 in snug contact with coating head 12.

FIGS. 3 and 4 show details of coating head 12. The coating head is formed of a primary housing which encloses a plenum, or manifold chamber 32. Coating material is forced into this chamber through a conduit 34 and thence through an elongate slit 36 onto the web to be coated. Slit 36 is formed of two elongate members, each of which comprises a web-contacting surface, one of which we shall refer to as lead-on surface 38, the other as lead-off surface 40. Lead-on surface 38 forms the web supporting surface of static lead-on member 42. Lead-off surface 40 forms the web-supporting surface of the static lead-off member 44.

Lead-on member 42 is fixed by bolt 46 to the housing of plenum chamber 32. However, lead-off member 44 is not so attached.

Lead-off member 44 is mounted for adjustment of its position with respect to member 42 by means of a series of spaced threaded fasteners 48 which form means to push or pull member 44 as is required to adjust the width of slit 36. Member 44 is sufficiently distortable along its length that fasteners 48 can be utilized to, for example, make the extreme ends of slit 36 wider than the center thereof, or make whatever other modification in slit width is made desirable along the length thereof.

Fasteners 48 are held in a support plate 50 which in turn is fastened to plenum chamber housing 51 by fasteners 52. A clamp plate 54 is utilized to hold member 44 snugly against housing 51 with bolts 55.

FIG. 2 shows end plates 56 which are fastened by bolts 58 to housing 51 and thereby form the lateral walls of plenum chamber 32.

More detail of the apparatus is shown in H0. 4. Press roll 28 is equipped with ports 60 and a chamber 62 for accommodating heating or cooling fluids as may be required for a given coating operation.

Unlike prior art coaters, the press, or backing, roll 28 is rotatable in

fixed bearings

64 and 66 in frame 68. Thus the web path and web tension remain constant and are not affected by any displacement of the roll. Because the roll cannot be elevated, flying splice operation is facilitated. The backing roll 28 is not subject to skewing, because skewing is accomplished with the adjustable movable coating head 12. For threading of the web, the coating head may be tilted and compensation may be made for non-parallelism by skewing the coating head in a horizontal plane.

The center feed to the plenum 51 assures uniformity of distribution of coating to both ends of the extrusion slot. It should be noted that there are no gap adjusting screws which cross the extrusion slot to interfere with flow, adjustment of slot opening being accomplished by screws exterior to the slot and outside the coating path.

While the device of the above mentioned Van Guelpen patent relies on a doctor, or smoothing, blade for achieving a thin, smooth, uniform coating of tacky, viscous hot melt substance, the device of this invention achieves a commercially acceptable coating by proper adjustment of the width of the slit, or orifice, 36, together with angular adjustment of the coating head to the web and to the fixed backing, or press roll 28.

The extrusion orifice, slit or nozzle 36 of the apparatus of this invention may also be used to extrude' cold viscous material which includes a predetermined percentage of solvents, such as dispersions, lacquers (nytro-lacquers) and rubber cements with benzine solvents. High viscosity materials of many types may be applied in thinner than conventional layers to thereby save considerable drying time. Capital outlay for drying equipment, such as heat tunnels, ovens and the like, and the floor space for coating apparatus is thus greatly reduced.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which might be said to fall therebetween.

I claim:

1. Apparatus for coating the underside of a web advancing at a predetermined rate along a generally horizontal path, said apparatus comprising:

a press roll mounted at each opposite end in fixed bearings to extend transversely of said web above said path for guiding and supporting said web in an unchanging said path during splicing thereof;

coating head means, mounted at each opposite end in support pivots, to extend transversely of said web under said path, for forming a coating nip therewith, said means including actuating mechanism for independently pivoting one said end relative to the other to skew said head relative to said roll to control coating thickness,

said coating head having an elongated lead-on lip and an elongated, rounded, lead-off lip removably mounted thereon and jointly defining a narrow extrusion slot connecting with a central feed plenum chamber, said slit and chamber being free of obstructions and free of gap adjustment screws in the path of extrudate emerging from said slit;

said lead-off lip being flexible and distortable along its length and said head including a plurality of spaced threaded screws therealong forming means to push and pull said lead-off lip to vary the width of said slit and control the thickness of coating extruded therefrom.

Claims

1. Apparatus for coating the underside of a web advancing at a predetermined rate along a generally horizontal path, said apparatus comprising: a press roll mounted at each opposite end in fixed bearings to extend transversely of said web above said path for guiding and supporting said web in an unchanging said path during splicing thereof; coating head means, mounted at each opposite end in support pivots, to extend transversely of said web under said path, for forming a coating nip therewith, said means including actuating mechanism for independently pivoting one said end relative to the other to skew said head relative to said roll to control coating thickness, said coating head having an elongated lead-on lip and an elongated, rounded, lead-off lip removably mounted thereon and jointly defining a narrow extrusion slot connecting with a central feed plenum chamber, said slit and chamber being free of obstructions and free of gap adjustment screws in the path of extrudate emerging from said slit; said lead-off lip being flexible and distortable along its length and said head including a plurality of spaced threaded screws therealong forming means to push and pull said lead-off lip to vary the width of said slit and control the thickness of coating extruded therefrom.