US 3018212 A
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Description (OCR text may contain errors)
Jan. 23, 1962 H. G. CHlNN 3,018,212
THERMOPLASTIC BONDING AND COATING Filed July 17, 1958 INVENTOR 40 HYMAN o. CHINN Y r 34 14. BY M 1.5%
A T TORNE Y United States PatentOfiice 3,018,212 THERMOPLASTIC BONDING AND COATING Hyman Chinn, Somerville, NJ., assignor to Union Carbide Corporation, a corporation of New York Filed July 17, 1958, Ser. No. 749,274 4 Claims. (Cl. 156-195) This invention relates to thermoplastic edged webs and thermoplastic lined containers and a method for their manufacture.
Continuous thermoplastic coatings over both the surface and the edges of sheet material have heretofore been generally unsatisfactory and diflicult to obtain. In certain instances, as when the sheet material has been fabIicated into a container, continuous thermoplastic coatings have been impossible to obtain. Coating the flat expanse of sheet material faces is easily accomplished, but the edges of the sheet material Web cannot be successfully coated with thermoplastic by any of the presently known coating techniques.
, The presence of a discontinuity in a coating such as is created by an uncoated and exposed sheet material edge almost completely nullifies the advantages realized from coating the sheet material faces. Uncoated sheet material edges are a point, in an othervn'se completely coated container, at which leakage can develop, if the packaged contents are liquid or even semi-liquid. In addition, contamination of the contents by the elution of chemicals from the sheet material is a distinct possibility. Thus the presence of even one uncoated edge interrupts the inert, chemically resistant, moisture and vapor impermeable barrier which resin coatings, when continuous, provide.
Inaccessibility of the edges, particularly after the sheet material has been fabricated into a container, and coincidence of a sheet material edge with a container edge preclude use of spray coating techniques which are awkward, time consuming, and unreliable in these applications. Further, with thermoplastic resins, such as polyethylene, a problem of adhesion to nonmetallic subtrates arises, rendering spray-coating techniques even less desirable. In other applications, such as coating of sharpedged webs with plastic to prevent their cutting, a convenient, widely adaptable method is not known. Dip coating techniques such as are used with wax coatings are not practicable with thermoplastics,
There are two general types of bonds employed to join or seal webs of sheet material, a butt-joint or edgeto-edge bond, and a lap joint or edge margin-over-edge margin bond wherein the portion of sheet material immediately adjacent to the edge, or edge margin, is lapped over the corresponding portion of the sheet material web. In the fabrication of a paper bag, for example, a web of sheet material is folded lengthwise and the opposite edge margins are brought into contact with one another and bonded with a suitable adhesive. Thus there is a seam running the entire length of the bag. If the bag is fabricated from sheet material coated on the inner side, a continuous thermoplastic lining would be obtained if a suitable bond were made between the edges. Generally a lap joint is employed because it affords greater strength than butt joint bonds, and in many applications the extra bulk at the seam which invariably accompanies lap joints is not harmful. Whether bulky or not, the lap joint exposes an edge of the web inside the container which, if uncoated, breaks the continuity of the thermoplastic lining and defeats the purpose of the coating. Bags with discontinuous-linings are prone to unsightly staining and physical weakening due to seepage of the contents. Because a butt joint generally lacks the necessary strength for most bag making and similar applications, it is not so widely used, although with such a joint adjacent, un-
Patented Jan. 23, 1962 coated edges are coextensive and are thus not exposed to the container contents and a bond of less bulk is obtained.
A bag with a long seam is only one of the many types of containers in which the problem of exposed uncoated edges arises. Others are spiral wound containers and convolute containers which offer greater rigidity and strength but are subject to the same limitations as bags with regard to liquid and semi-liquid goods. Also, in these containers, the bulk of a lap joint can become a serious drawback.
It is an object, therefore, of my invention to provide a method for forming a bond between webs of sheet material which possesses the advantages but not the drawbacks of both the butt joint and the lap joint.
This and other objects are accomplished in accordance with my invention by extruding a bead of a thermoplastic onto the edge margin of a web of sheet material and flattening the extruded bead, as by a pair of pinch rolls, so that a portion of the flattened bead adheres to the web edge margin of the sheet material and the remainder of the flattened bead extends outwardly from the web edge margin as a skirt. Thereafter the sheet material can be fabricated into a container by placing a skirted sheet material edge adjacent to asecond sheet material edge in such manner that the skirt of said skirted sheet material edge overlaps the edge margin of said second sheet material edge and placing adhesive therebetween and simultaneously pressing said skirt and said edge margin against said adhesive to form a joint therebetween.
The method of my invention utilizes one and preferably two extruders. The first extruder places a bead of resin upon a travelling web of sheet material near the edge. The head after flattening adheres firmly'to the sheet material and is sufficiently solidified to extend outwardly without outside support as a skirt. The second extruder places a head of hot resin between said skirt and a second web edge margin andsaid skirt and edge margin are then pressed against the hot bead and become firmly bonded together thereby. Additionally, in .those instances in which the two web edges are aligned in substantially abutting relation, some of theresin from the second extruder may be squeezed between said edges and form a bond therebetween as well. The bond, when formed, possesses the valuable attributes of both an overlap seal and a butt joint seal and also avoids the disadvantages of both. The bond possesses great strength, is uniform, does not leak, does not expose an uncoated surface, is easily .applied, is not bulky, and is universally adaptable. "This combination of qualities has not'been attained before. The joint produced by the method of my invention is ideal in containers which are to package liquid, semi-liquid, and/or chemically active goods.
The method is extremely versatile in that the extruded head can be any thermoplastic composition and can be applied to virtually any web of sheet material, regardless of thickness, whether single or multi-ply, e.g., paper, metal foil, coated paper, and laminates. The width and thickness of both the portion of the flattened bead adhering to the web and the portion protruding outwardly from the web, i.e., the skirt, can be exactly controlled during the process.
Additional advantages will become apparent from a consideration of the detailed description below of one embodiment of the invention which is described in conjunction with the attached drawings in which:
FIGURE 1 is a diagrammatic isometric View of the apparatus according to and for carrying out the method of the preferred embodiment of the present invention,
FIGURE 2 is a section taken along the line 22 of FIGURE 1,
FIGURE 3 is a pictorial view of the preferred embodiment of a product of the method of my invention, and
FIGURE 4 is a section taken along the line 44 of FIGURE 3. V
The method of my invention as particularly adapted to the formation of spiral wound containers is shown in FIGURE 1. From a consideration of the figure, it will be seen that sheet material is withdrawn from a supply roll 12 at a constant rate along a predetermined path. An extruder, not shown, with nozzle 14 is positioned above the travelling web of sheet material 10 so as to be approximately M; inch from the edge of the sheet material 10. A bead of molten resin 16 is forced from the nozzle 14 onto the sheet material 10 which advances with the resin bead 16 through the nip of a pair of pinch rolls 18. The pinch rolls 18 serve to flatten the resin bead 16, causing it to adhere to the sheet material 10 and to extend outwardly from the sheet material '10 in a self-supporting manner as a skirt 20. The relation of the skirt 20 and the sheet material 10 is best shown in FIGURE 2.
In order to form a spiral wound container such as shown in FIGURE-3, the sheet material 10 with skirt 20 is wound around fixed mandrel 22. A paraffin-waxed paper slip sheet 24 is wound simultaneously with and slightly ahead of the sheet material 10 to ensure easy removal of the tube formed. A second extruder or sealer with nozzle 26 places adhesive bead 28 on the skirt 20 of sheet material 10. Winding of sheet material 10 about the mandrel 22 is accomplished in a manner which places edge margin 34 adjacent to edge margin 36. In the specific embodiment shown, the edges of the respective edge margins 34 and 36 are in abutting relation, however, it is within the scope of my invention for edge margins 34 and 36 to be in overlapping relation. In
' FIGURE 1, as the sheet material 10 is wound, skirt 20 margin 36 of sheet material 10 in overlapping relation with skirt 20. The nozzle 26 places a bead of adhesive between skint 20 and the next turn of sheet material 10. The pressure induced by the winding action forces edge margin 36 against skirt 20 to form a bond such as shown in FIGURE 4. The bond hardens and the spiral wound container is cut as withdrawn from the mandrel and appears in FIGURE 3.
Various modifications such as formation of two skirts simultaneously and alternate embodiments of our invention such as bag and convolute wound container manufacture are obvious to those skilled in the art.
The scope of my invention, therefore, is not limited except as defined in the appended claims.
What is claimed is:
1. A method of forming a strong, moisture-proof bond comprising the steps of placing a head of thermoplastic melt onto the edge margin of a sheet material Web, flattening the bead causing a portion of the head to adhere to said edge margin and another portion of the head to extend outwardly from said edge margin as a skirt, placing a second sheet material web in contact with the skirted sheet material web, and supplying thermoplastic melt between the skirt and the adjacent second web forming a bond.
2. A method of forming spiral wound containers com prising the steps of placing on one edge margin of a sheet material web a bead of thermoplastic melt, flattening the bead causing a portion to extend outwardly from said edge margin as a skirt, wrapping the skirted web around a mandrel, placing the edges of successive turns of said web in abutting relation, and placing a head of adhesive between the skirt and the adjacent edge margin of the web to form a joint between successive turns of sheet material web.
3. A method of forming spiral wound containers comprising the steps of placing on one edge margin of a sheet material web a bead of thermoplastic melt, flattening the bead causing a portion to extend outwardly from said edge margin as a skirt, wrapping the skirted web around a mandrel, placing the edges of successive turns of said web in abutting relation, and placing a head of thermoplastic adhesive between the skirt and the adjacent edge margin of the web to form a joint between successive turns of sheet material web.
4. A method of forming a skirted sheet material web which comprises the steps of placing a bead of thermoplastic melt on the surface of a sheet material Web near the edge of said web, and by application of pressure fiattening said bead, causing a portion of the head to adhere to the web surface and another portion to extend out wardly past the said edge of the web as a self-supporting skirt.
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