US2929544A - Plural-ply paper bag for arctic and tropical climates - Google Patents

Description

March 22, 1960 R. J. HERSCHLER 2,929,544

PLURAL-PLY PAPER BAG FOR ARCTIC AND TROPICAL CLIMATES Filed Sept. 9, 1955 IN V EN TOR. Rebel-i v], Hersclzler BY 6M ATTORNEY United States Patent PLURAL-PLY PAPER BAG FOR ARCTIC AND TROPICAL CLIMATES Robert J. Herschler, Camas, Wash., assignor to the United States of America as represented by the Secretal'y of the Army Application September 9, 1955, Serial No. 533,531 7 Claims. (Cl. 22955) This invention relates to seams formed in containers, and methods of forming them. The invention is particularly useful in (but not limited to) glued seams formed in bags having plastic coated paper liners, and methods of making such seams.

In the manufacture of paper bags and other containers having glued seams, it has been difficult to form seams capable of holding together when subjected to heavy duty usage in arctic and tropical climates as well as temperature climates. Particular diiiiculty has been experienced in the case of seams formed in laminated or plastic coated paper, such as polyethylene coated kraft paper.

An object'of this invention is to provide new and improved container seams capable of holding together over a wide range of temperatures, and methods of forming such seams.

. Another object of the invention is to provide new and improved glued seams in bags having plastic coated paper liners, and methods of making such seams.

A complete understanding of the invention may be had from the following detailed description of a container seam forming a specific embodiment thereof, when studied in connection with the appended drawing, in which:

Fig. 1 is a perspective view of a multiwall paper bag having glued seams embodying the invention;

Fig. 2 is an enlarged transverse section of the multiwall bag illustrated in Fig. 1, and

Fig. 3 is a greatly enlarged section taken along line 3--3 of Fig. 1 showing the seams in detail.

The composite multiwall paper bag illustrated in the drawing is constructed from an inner liner nested within an intermediate folded paper sheet 12, which i? turn is nested within an outer folded paper sheet 14. The sheets 12 and 14 are made of ordinary kraft paper, while the inner liner 10 is made of a plastic coated paper, preferably a polyethylene coated kraft paper.

The multiwall paper bag is provided with a bottom seam 16 which may be formed in any convenient manner. For example, the bottom ends of the liner 10 and the sheets 12 and 14 may be glued together by means of suitable adhesives. As shown in Fig. 1, a reinforcing strip 18 of paper may be folded around these ends and stitched to them by means of a length of strong thread 23.

The outer paper sheet 14 is folded into tubular form and provided with a longitudinal side seam by overlapping its opposite edges 28, 29 and gluing them together with a single glue line or adhesive stripe 22 interposed therebetween. Similarly, a single glue line or adhesive stripe 24 is applied inside the overlapped opposite edges 31,32 of the intermediate sheet 12. Since the sheets 12 and 14 are made of ordinary uncoated and unlaminated kraft paper, sufficient bonding strength over the desired temperature range can be obtained by the use of suitable well known adhesives. For example, adhesives compounded from dextrin and starch, or polyvinyl alcohol borax have demonstrated their suitability. However, when these adhesives alone are applied to laminated or plastic coated kraft paper they fail to perform over the specified temperature range, and particular difi'iculty with seam failures is encountered at arctic temperatures.

'Dow Corning C-269 and C-27l.

F ice In accordance with the present invention the inner liner 10, which has been previously described as being composed of a plastic coated paper and preferably a polyethylene coated kraft paper, is provided with a longitudinal side seam having good adhesive strength over the temperature range -70 F. to F. This objective is achieved by employing two different adhesives applied in two parallel lines or stripes 26 and 27 inside the overlapped opposite edges of the liner 10. Both adhesives are capable of bonding strongly to plastic coated kraft paper under ordinary moderate conditions of temperature and usage, but one of these adhesives is compounded specially to provide good adhesive strength under heavy duty usage over a wide temperature range including extreme arctic and tropical temperatures.

The glue line 26 is designated the primary glue line, and it contains the specially compounded adhesive. This adhesive is composedessentially of an adhesive silicon resin mixed with a rubbery elastomer. It cures or sets slowly to form an adhesive bond functional at extreme temperatures. A highly effective composition was compounded successfully from about 50% by weight of a pressure sensitive silicone adhesive containing 40% solids in a xylene solvent, and about 50% by weight of Buna S (G.R.S.) butadiene-styrene copolymer resin contain invention; they are characterized by the following physical properties (40% solution in xylene):

Viscosity at 25 C. cp 10004000 Flash point F 60-75 Specific gravity .94

These adhesives are described in Dow Corning Corporations Silicone Notes, Reference No. 4-602, dated February 1953, entitled Properties and Applications of However, it will be understood that other curable organosilicon polymers (silicones) in organic solvents, which are available on the commercial chemical market, may be likewise used, provided they have the property of curing to a coldand heat-resistant adhesive film; for a basic discussion of the chemistry and properties of polymeric curable organosilicon compounds see, e.g. US. Patents Nos. 2,386,467 and 2,438,478, Hyde; assignor to Corning Glass Works.- Other elastomers could be substituted for the .Buna S (G.R.S.) in this composition. For example, Hycar smoked sheets, or neoprene could be used successfully. However, since the Buna S (G.R.S) is one of the least expensive and most readily available elastomers suitable for the purposes of the invention, it is preferred. It is usually desirable to work such elaston'iers as Buna S (G.R.S.) sheet stock on a roll mill to effect depolymerization, thus greatly increasing the solution rate in hydrocarbons and lowering the solution viscosity at a given solids content.

The glue line 27 is designated the secondary line. It-

comprises a commercial adhesive which sets rapidly and bonds readily to polyethylene and other plastic coated.

papers under ordinary temperature conditions. Goo'd results have been obtained from the Naugatuck Chemical Co. adhesive product Naugatuck 1789, and theNational: Adhesives Co. product Polylok. In general these prodner, the adhesives forming the secondary glue line may be applied to the'paper bags by means of an ordinary" paste wheel.

like.

The adhesive composition. comprising. the primary glue line is so viscous that it may be necessary to employ a paste pump to apply the composition to the paperbags. For this purpose, a commercial gear pump powered'by a. quarter horsepower motor through a variable speed. torque converter delivers a. uniform stream of adhesive for theprimary bag seam. It is desirable; for this composition to have 'a minimum viscosity of about 20,000

centipoises to minimize strike in. Due to the slow rate. at which the adhesive in the pri- "mary glue line sets or cures, the primary glue, line must be aged for at least fifteen days at room temperature before it. sets sufiiciently to form an effective adhesive bond;

assau t 7 hesive. silicone resin and a rubbery elastomer, said adhesive having the characteristic of requiring several days at room temperature to set and form a strong adhesive bond efiective over a temperature range of from -.-70 F. to +140 F., and the! other glue line. beingv composed of an adhesive compound which sets. rapidly and forms a strong adhesive bond effective at ambient temperatures;

- whereby said, paper bag may be shipped in the, temperate The principal'purpose of the fast setting secondary glue line is to provide a temporary adhesive bond during the time required for the. primary glue line to set, thereby a.voiding; interference with the manufacture and the'ship 'ment of the bags.

, In the'manufacture of multiwall paper bags, the inner liner and the outer sheets are, folded: into tubular form with their opposite edges overlapping; Depending upon 7 the size of. the bag being manufactured, the opposite edges 28, 29 and 31, 32 of the paper sheets overlap to an extent which may vary in width from about inch up to 7 about 2 inches. The edges 30, 33 of the inner liner 10 may overlap somewhat more, and'the two parallel glue lines 26 and 27 applied thereto should preferably be spaced apart about Mt inch.

- In the formation of theglue lines, the amount of ad-- hesiveapplied should be limited to the minimum quantity required to obtain a strong bond. It was observedthat the primary and secondary glue lines formed in aczone upon the quick setting of said second-named ad-' hesive, and whereby said first-named adhesive is permitted to set slowly and form a permanent glue line.

2. A plural-ply paper bag according to claim 1, wherein said rubbery elastomer is a butadiene styrene resin.

3'. A plural-ply paper bag according to claim 2,, wherein said first-named adhesive is'compounded from aboutequal portions by weight of said adhesive silicone resinand of said butadiene styrene resin.

4. A plural-ply paper bag according to claim 1, where in the outside edge of the overlap ofsaid inner liner is adhesively secured to said surrounding paper ply; and" wherein said second-narned adhesive is applied proximate the other edge of said overlap. and said first-named ad'- hesive is applied intermediate said edges of said overlap, whereby the setting of said first-named adhesive is fa cilitated.

l 5. A plural-ply paper bag according to claim I, wherein said first-named adhesive has a viscosity of at leastabout 20,000 centipoisesprior to setting. a

6. A plural-ply paper bag for shipment to an'arctic. or tropical climate, said paper bag having a tubular inner -liner made from a sheet of plasticsrcoated,- paper, andat.

' least one tubular paper ply surrounding said inner liner;

eordance with this method formed continuous films on w the paper. In each case the glue line should be applied to the flap which is inside the overlapped portions of the edges of the sheets. Oneedge 30 of the liner 10 may be interposed bet-ween the overlapped opposite edges 31, 32 .oflthe intermediate sheet 12, as is bestshown in Fig. 3.

The primary glue line 26 is located nearer to the outside edge 30 of the overlapped edges 30, 33 of the liner 10, while the secondary glue line 27is positioned nearer the inside edge 33 thereof. The reason for this arrangement V is' 'to facilitate the evaporation of the solvent from the adhesive in the, primary glue line, thereby'shortening the setting time required.

tested by subjecting them to a standard drop test at the extreme limits of the'temperature range 70 F; to

V j Bags having'seams embodying the invention werei +140" F. They were filled with approximately 85.,

pounds of navy beans; some bags were stored' for a number of hours at elevated temperatures, and others at very low temperatures before being dropped None said inner liner being formed byoVerlapping the edges of said liner, the outside edge of the overlap of said inner liner being adhesively secured to said surrounding paper ply, and the overlapped edges of said liner being secured together by two. parallel glue lines. interposed therebetween and parallel thereto, one of said glue lines being composed of an adhesivecompounded fromabout, equal parts by weight of an adhesivesilicone. resin and a butadiene styrene resin, said adhesive having the characteristic of requiring several'days at room temperature to set and form a strong adhesive bond efiective over-a ternperaturerange of from 70 F. to +140 F., and the other glue line being composed of an adhesive compound which sets rapidly and forms a strong adhesive bond;

efiective at ambient temperatures; said second-named adhesive being applied proximate the free. edge, of said overlap, and said first-named adhesive being applied intermediate the glue'line formedby said: secondrnam ed adhesive and the outside edge, of the overlap which is.

of the bags tested failed attheir seams, and the only 7 failures observed occurred in the paper fibers.

"Although the invention has been illustrated and d'e scribed in connection with tubular multi-ply paper bags, it should be understood that the invention'may also be embodied in'parallel seam structures for other types of containers, such as single-ply bags (of coated or uncoated material), envelopes, pasteboard boxes, and the 1 Furthermore, the shape, size and purpose of such' containers are unrelated to the invention. -Numerous' changes and modifications maybe made to suit special requirements without departingfrom the'spirit and the scope of the invention. a

What Iclaimis: 7 I I 1. A plural-ply paper bag for shipment to an arctic or tropical climategsaid paper bag having a tubular inner liner made from a sheet of plastics-coated paper, and at 7 least one tubular paper ply surrounding said ,inner liner; :saidinner liner being fo'rmed by overlapping the edges of said liner,g=;the overlapped edges of said linerlbeing secured together by two parallelglue lines interposed being composed of an adhesive'c'ompounded from an ad- 'therebetween and parallel thereto, one of said glue lines I V adhesively secured to said surrounding paper ply so as to facilitate the setting of said first-named adhesive; whereby said paper bagmay be shipped in the temperate zone upon the quick setting of saidsecond-named adhesive, andwhereby said first-named adhesive is permitt to set slowly, and form a permanent glue line.

7; 'AfpluraI-ply paper bag, according to claim ,6, wherein said first-named adhesive fhas dviscosity of at least about 20,000 ceutipoises prior to setting. 1

References Cited in the file of this patent UNIT ED v STATES PATENTSv Dexter Feb. 28, I956 sands j; Man 15,1898

Images