Adhesive Application System

Abstract

A system for uniformly applying adhesive to a base material comprising a plurality of spaced-apart filaments which are continuously moving forwardly in contact with an applicator roll disposed above a reservoir of liquid adhesive with a portion of the roll surface disposed beneath the surface of the adhesive so that the roll picks up a layer of adhesive on its surface as it is rotated and transfers adhesive to the base material, including a metering bar cooperating with the applicator roll to define a metering nip in which the thickness of the adhesive layer on the applicator roll surface is uniformly established, the metering bar being cooled sufficiently below ambient temperature to cause condensation of moisture on the bar and preclude build-up of solidified adhesive on the bar thereby preventing accumulation of adhesive such as would disrupt the uniformity of the adhesive layer established in the metering nip. The system also includes doctor blade means having a deformable doctoring surface for removing residuary adhesive from the roll surface in a region ahead of the region where the roll surface enters the liquid adhesive.

Description

This invention relates generally to the continuous application of adhesive to a base material, such as a plurality of spaced-apart filaments which are being moved forwardly as in a process of manufacture. More specifically, this invention relates to improved control over the uniformity with which the adhesive is applied to the filaments as they pass over the applicator roll.

Not infrequently in applying adhesive to a base material such as a plurality of filaments, such as in a process for manufacturing a laminated product comprising a web ply reinforced by a filamentary ply bonded thereto in superposed relation, it is desired that the adhesive be applied uniformly to the filaments so as to obtain uniform and continuous bonding of the filaments to the web. For reasons of economy, commonly, the manufacturing process is continuous and the filaments are moved forwardly through an adhesive application station in a continuous manner.

In applying liquid adhesive to such continuously moving base material, it has been a common practice heretofore to contact the traveling base material with a rotating applicator roll which bears a coating of adhesive and effect a transfer of adhesive from the roll to the filaments. In accordance with such prior practice, the applicator roll is mounted above a reservoir containing the liquid adhesive, a portion of its roll surface being submerged beneath the surface of the liquid adhesive so that as the roll rotates it picks up a layer of adhesive on its outer surface, the adhesive being transferred by the rotating roll onto the base material.

Prior to the present invention, the thickness of the layer of adhesive on the applicator roll, hence the quantity of adhesive applied to each filament, has been controlled by adjusting the viscosity of the adhesive and the rotational speed of the applicator roll. This means for controlling the adhesive layer thickness provided poor results because small changes in the adhesive viscosity, which were frequent and not reasonably controllable, yielded large variations in the amount of adhesive picked up on the applicator roll surface as the roll rotated through the adhesive. The quantity of adhesive transferred to each filament likewise varied in an uncontrollable nonuniform manner with resultant insufficient bonding of the superposed plies in some areas and excessive adhesive in other areas.

When using a screeding device to level off the adhesive to a uniform thickness on the surface of the applicator roll, it has been found that an adhesive puddle is created in the nip between the applicator roll and the metering bar as a result of the adhesive affinity for each of the bodies. The marginal portions of such puddled adhesive solidifies after a time of operation of this system, resulting in progressively enlarging accumulations of solid adhesive which eventually bridge the gap between the bar and roll. These accumulations scrape adhesive from the rotating applicator roll thereby disrupting the desired uniformity of the adhesive layer on the applicator roll and causing poor adhesion between the plies of the product. Frequently, flakes or chunks of the solid or semisolid adhesive break away from the screeding device and are carried by the applicator roll to the base material resulting in serious problems during subsequent processing operations.

When passing a plurality of spaced-apart filaments over an applicator roll which carries a layer of adhesive on its surface, the filaments commonly are maintained spaced apart by combs, eyeboards or like devices which cause the filaments to run along respective paths at all times. Consequently, the filaments pick up adhesive from the roll in their respective paths, leaving the adhesive disposed between paths on the roll surface as residuary adhesive. This residuary adhesive between filament paths has been noted to solidify after a period of roll rotation and eventually flake off from the roll and be picked up by a filament with the noted undesirable consequences during subsequent processing.

It is therefore an object of this invention to provide an improved system for applying liquid adhesive to a filamentary base material. It is also an object to provide a system for applying a liquid adhesive to a filamentary base material in a continuous and uniform manner. It is a further object to provide an adhesive application system including means to prevent viscosity changes of the adhesive caused by entrainment of air in the adhesive.

FIG. 1 is a perspective view of the system disclosed herein;

FIG. 2 is a sectional view of the system shown in FIG. 1 and taken along line 2--2 of FIG. 1; and

FIG. 3 is an enlarged fragmentary view, in section, of the metering roll and applicator roll of the system shown in FIG. 2.

In accordance with the invention disclosed herein, a metering roll, preferably a hollow cylinder, is disposed adjacent to a rotating applicator roll disposed above a reservoir of liquid adhesive and having a portion of its outer surface submerged beneath the surface of the liquid adhesive so as to pick up a layer of liquid adhesive on its outer surface as it rotates. The metering roll preferably is disposed with its longitudinal axis generally parallel to the longitudinal axis of the applicator roll and is spaced from the applicator roll so as to define a metering nip or gap therebetween. As disclosed herein, the metering roll is cooled to a temperature below ambient temperature so as to cause condensation of moisture onto the outer surface of the metering bar. This layer of condensation on the outer surface of the metering bar has been found to function in at least two roles; namely, first, the layer of condensate on the outer surface of the metering roll functions as a release agent thereby precluding adherence of the liquid adhesive to the metering roll, and, second, in the preferred geometry of the metering roll, a quantity of condensate flows by gravity toward the puddle of adhesive formed in the metering nip between the metering roll and applicator roll thereby continuously adding a small amount of moisture to the puddle edges to inhibit drying of the puddle edges and replenishing moisture lost from the adhesive by evaporation.

In a preferred system, the surface of the rotating applicator roll is cleared of residuary adhesive as the roll rotates. Desirably, this clearing function occurs in a region on the surface of the applicator roll just ahead of the region where the surface of the applicator roll enters the reservoir of liquid adhesive. In the illustrated embodiment, the residuary adhesive is removed from the surface of the applicator roll by means of a doctor blade preferably having a deformable doctoring surface so as to provide a means to contact the surface of the applicator roll and doctor off the adhesive without encountering the dangers attending the positioning of a rigid object against the smooth surface of the applicator roll. The residuary adhesive doctored from the applicator flows from the doctor blade into a collector. In an adhesive application system wherein the viscosity of the adhesive is altered by entrainment of air as the adhesive flows from the doctor blade into a collector, the disclosed invention includes a skirt element depending from the doctor blade to a point immediately above the surface level of adhesive in the collector thereby providing a means for transfer of the adhesive from the blade to the collector with minimal entrainment of air.

In the embodiment of the invention illustrated in the drawings, a plurality of parallelly aligned, spaced-apart filaments 10 are fed forwardly from a creel (not shown) over and in partially wrapping contact with the top surface 12 of an applicator roll 14. After having passed over the applicator roll, these filaments are further directed forwardly to be deposited upon a forwardly moving continuous fibrous web 16, for example, which advantageously may be fed upwardly from a supply roll 18 over an idler roll 20 to receive the spaced filaments. This base web 16, with the filaments 10 deposited thereon, may be directed to additional processing stations such as a drying over or the like (not shown) and may be collected as by winding the filament-bearing web into a roll by appropriate means (not shown).

As illustrated, the applicator roll 14 is preferably disposed above a reservoir 22 of liquid adhesive 24 with the lower portion 26 of the outer surface of the applicator roll 14 submerged beneath the surface 28 of the liquid adhesive 24 within the reservoir so that as the applicator roll is rotated by conventional means (not shown), the outer surface of the applicator roll picks up a quantity of adhesive from the reservoir 22 for transfer to the filaments which contact the upper portion 12 of the rotating applicator roll.

As illustrated in FIG. 3, liquid adhesive picked up on the outer surface of the applicator roll 14 as it rotates through the liquid adhesive 24 is adjusted in thickness by means of a stationary metering roll 32 disposed adjacent, but spaced apart from, the outer surface of the applicator roll so as to define a metering nip 34 therebetween. As the applicator roll 14 rotates past the metering roll 32, adhesive in excess of a layer thickness approximately equal to the nip distance is screeded from the surface of the applicator roll thereby establishing a uniformly thick layer of adhesive 30 on the roll surface. The filaments 10 which partially wrap the applicator roll 14 each pick up a quantity of this adhesive as they are immersed in the layer of adhesive during their passage over the roll while in contact therewith, (see FIG. 2). The preferred adhesive layer is of a thickness at least equal to the diameter of the filament which is passed over the roll thereby causing each filament to be fully immersed in the adhesive and receive a complete and uniform coating of adhesive.

Contrary to the prior art, long periods of operation of the disclosed adhesive application system with good bonding between the filaments and fibrous web has been found possible by cooling the metering roll 32 to a temperature sufficiently below ambient temperature as will promote condensation of moisture 36 on the outer surface of the metering roll 32. As illustrated, such cooling may be accomplished by flowing cold water through the hollow cylindrical metering roll along the length thereof as by means of a pump 38 which circulates a quantity of water by means of conduits 40, 42 through a cooler 44 thence through the hollow roll 32. The metering roll 32 preferably is restrained against movement and in any event is held against rotation thereof so as to insure that the outer surface of the bar remains free of any covering, such as a layer of adhesive, which would preclude the desired condensation of moisture from the ambient atmosphere onto the roll surface.

The preferred roll geometry includes a portion 46 which slopes downwardly toward the metering nip 34 along which condensate 36 will flow to the edges of the adhesive puddle 48 formed on the upper side of the metering nip 34. The quantity of condensate 36 which forms on the roll surface and flows to the puddle of adhesive desirably is sufficiently small as will not appreciably dilute the adhesive but is sufficiently large as will maintain the puddle margin moist and replenish moisture lost from the puddle adhesive by evaporation. In this manner, the puddled adhesive is prevented from solidifying by drying and the heretofore troublesome accumulations of solidified adhesive are eliminated thereby enhancing the uniformity of the adhesive layer on the applicator roll surface and eventually resulting in good uniform bonding of the filaments to the web. As indicated hereinbefore, the metering roll preferably comprises a hollow cylinder. Such a cylindrical geometry provides the desired downwardly sloping surface and in addition provides a strong roll which does not bow in its central unsupported surface and therefore retains its alignment with the applicator roll.

The condensate on the metering roll surface also has been noted to reduce the affinity of the adhesive for the roll surface, the condensate appearing to function in the manner of a release agent to cause the adhesive to not be drawn to the metering roll. Accordingly, when the metering roll is cooled sufficiently to promote condensation thereon, the puddle tends to be restricted more to the nip region thereby reducing the stagnant volume of the puddle and decreasing the tendency of the marginal areas thereof to solidify. Reduction of the solidification tendency of the puddle also reduces the presence of chunks or flakes of solid or semisolid adhesive, hence reduces the deleterious effects during subsequent processing as referred to hereinbefore.

In addition to the beneficial effects realized from the condensate, the cooled metering roll also lowers the temperature of the adhesive adjacent the metering roll, particularly in the nip puddle, thereby reducing the rate of moisture evaporation from the adhesive and retarding solidification of the adhesive. The cooled adhesive also becomes slightly more viscous which also reduces the rate of moisture escape from the adhesive and aids in keeping it from solidifying.

Residuary adhesive 50 remaining on the applicator roll 14 after the filaments 10 have been contacted is preferably removed from the surface of the roll to prevent this adhesive from remaining on the rotating roll so long that a coating of solidified or semisolidified adhesive commences to form on the roll surface. Such a coating of hardened adhesive roughens the roll surface and causes variations in the adhesive layer carried by the roll. Also, as noted hereinbefore, the residuary adhesive between filament paths and in other areas on the roll become another source of the undesirable chunks and flakes of solid or semisolid adhesive. Accordingly, in the illustrated embodiment, the residuary adhesive 50 is cleared from the applicator roll surface during each rotation of the applicator roll by means of a doctor blade 52 preferably disposed adjacent the roll just ahead of the region where the surface of the rotating roll enters the reservoir of liquid adhesive.

Referring to FIG. 2, the illustrated doctor blade 52 preferably is provided with a covering 54 which extends at least over the doctoring or leading edge 56 of the blade 52 and preferably depends from the trailing edge 58 of the blade to form a skirt 60 whose lower edge 62 terminates near the surface of liquid adhesive in a collector compartment 68 of the reservoir 22. Desirably, the covering 54 is deformable so as to permit the covered doctor blade to be adjustably positioned in good doctoring contact with the roll surface with relatively uncomplicated and inexpensive adjusting apparatus and without undue concern for damaging the roll surface through inordinate contact between the blade and roll surface. One suitable covering is a nonwoven spunbonded polyester synthetic fabric distributed by E. I. DuPont de Nemours of Wilmington, Delaware under the trademark REEMAY. This fabric may be held in place by the doctor blade forcing it against the applicator roll. It is readily replaceable if damaged or if it becomes unusable due to accumulation of adhesive thereon as during shut-down of the system. When held in contact with the applicator roll, this fabric thoroughly cleans the roll surface of residuary adhesive and possesses satisfactory drape characteristics so that the covering will depend from the blade in the desired position for the flow of adhesive therealong to the collector. Due to the stiffness of the covering, no external support is required for maintaining the skirt portion in place. Further, because of its hydrophobic nature the fabric does not absorb moisture from the adhesive flowing over it and does not in this manner appreciably alter the viscosity of the adhesive. Other sheet material may be employed to cover the doctor blade such as Teflon, rubber or fabrics other than Reemay. As illustrated, the depending skirt 60 preferably terminates just above the surface level of the liquid adhesive in the collector so as to prevent the doctored adhesive from falling freely through air and thereby entraining air to change its viscosity with resultant change in the quantity of adhesive picked up by the applicator roll as it rotates through the adhesive.

Advantageously, the reservoir 22 in which the liquid adhesive is contained is divided into a central compartment 64 into which the applicator roll extends for picking up an adhesive layer. Adhesive screeded from the roll 14 by the metering roll 32 is collected in a separate compartment 66 flanking the central compartment 64 along one of its sides and disposed beneath the metering nip 34. Residuary adhesive 50 doctored from the applicator roll 14 is collected in a further separate compartment 68 flanking the central compartment 64 on its other side and disposed generally beneath the doctor blade 52. Adhesive collected in the two flanking compartments 66, 68 may be directed to a makeup station where its viscosity is adjusted prior to reintroducing the adhesive to the central compartment 64. However, commonly the adhesive reclaimed in the present system is not so changed in viscosity but what it can be injected directly into a stream of freshly-mixed adhesive and fed into the central compartment for reuse without reconstitution. As depicted in FIG. 1, freshly-mixed adhesive from an adhesive makeup station 70 is pumped through a conduit 72 by a pump 74 and further caused to flow through a conduit 76 into the top of the central compartment 64. At the same time, the pump 74 withdraws adhesive through a conduit 78 from the bottom of the central compartment 64 for recirculating to the top of the compartment 64. Also simultaneously, the reclaimed adhesive is withdrawn through conduits 80 and 82 from the flanking compartments 66 and 68, respectively, and into the conduit 72 along with the freshly-mixed adhesive for eventual return to the central compartment 64.

Whereas this invention has been described in terms of applying adhesive to a plurality of filaments, it will be recognized that the invention is also useful in other applications such as applying adhesive to an expanded tow. Likewise, various adhesives may be employed, the invention being particularly useful with those adhesives which tend to solidify upon the loss of moisture therefrom. It will be understood, therefore, that there is no intent to limit the disclosure, but rather, it is intended to cover all modifications and constructions falling within the spirit and scope of the invention as defined in the appended claims.

Claims

What is claimed is:

1. In a system for transferring a controlled quantity of liquid adhesive from a reservoir of such adhesive to a base material including an applicator roll having a portion of its outer surface disposed beneath the surface of said liquid adhesive in said reservoir and having a further portion of its outer surface exposed for contact by said base material, said roll being rotated to pick up a layer of adhesive on its outer surface and carry such adhesive to the region of contact with said base material and thereby transfer at least a portion of said adhesive from said roll to said base material, the improvement comprising

nonrotating meter roll means having a longitudinal axis, said meter roll means being disposed contiguous to the outer surface of said applicator roll with its longitudinal axis generally parallel to the longitudinal axis of said applicator roll at a position intermediate the region on said rotating applicator roll where said applicator roll exits from beneath the surface of said liquid adhesive and the region on said rotating applicator roll which is contacted by said base material, said meter roll means and said applicator roll defining a metering nip therebetween whereby adhesive in excess of a predetermined quantity is screeded from said applicator roll in said nip to provide a uniform layer of adhesive on the outer surface of said rotating applicator roll, and

means maintaining said metering roll at a temperature sufficiently less than ambient temperature so that moisture from ambient atmosphere is condensed on said meter roll means and said adhesive is thereby prevented from accumulating on said meter roll means in a nonfluid state.

2. The system of claim 1 wherein said meter bar includes a surface portion which is exposed to ambient atmosphere and which slopes downwardly to said metering nip so that condensate formed on said surface flows toward said metering nip.

3. The system of claim 1 and including doctor blade means contacting said cylindrical roll along the length of its outer surface in a region intermediate the region where said base material contacts said roll and the region on said rotating roll where its outer surface enters the liquid adhesive in said reservoir, said doctor blade means including a compressible covering on at least the leading edge thereof.

4. The system of claim 3 wherein said covering on said doctor blade comprises a nonwoven synthetic fabric.

5. The system of claim 3 wherein said covering includes a portion depending from the trailing edge of said doctor blade means and forming a transport means for doctored adhesive wherein said adhesive does not fall freely through air in the interval between doctoring thereof from said applicator roll and collection thereof for reuse.