GB2141045A - Adhesive coated sheet materials - Google Patents

Abstract

Adhesive coated sheet materials particularly adapted for self-releasable adhesive tapes as described. The invention comprises the use of a coated base web and an adhesive layer selected so that the base web coating has a greater affinity for the adhesive than for the base web. The result is an adhesive sheet material that, when bonded to itself by applying the adhesive against the opposite side of the sheet material, may be readily peeled apart by delamination of the coating on the base sheet. This combination may be used as a bander for coiled materials such as rolls of stamps, or for stacks of currency, and the like.

Description

SPECIFICATION Adhesive Coated Sheet Materials The present invention relates to adhesive coated sheet materials, especially those in the form of tapes, strips or the like. In particular, the invention relates to such of those sheet materials as are intended generally for one-time use wherein they are bonded to themselves by contact between the adhesive surface and the opposite surface or back side. Such adhesive coated sheet materials are well known, and provide means for restraining coiled, stacked or gathered items. Familiar examples include tape seal closures for rolls of postage stamps, banders for stacks of currency, skeins of yarn or shoestrings and the like. Due to the high value of many of these items, it is extremely important that the adhesive aggressively maintains the closure. On the other hand, the single use of such strips demands a cost consistent with disposability.

Published patents and literature descriptions of adhesive. coated sheet materials are iegion. It is also well known to use adhesive coated strips for the specific application of banding rolls of stamps, stacks of currency and the like. As above stated, this application demands a delicate balance between the strength and tack properties required to prevent premature release and the cost of the banders themselves. The use of strips of conventional masking tape or a tape comprised of an uncoated Kraft base sheet having a conventional gum coating applied thereto have both proven unsatisfactory because the aggressive nature of the adhesive frequently resulted in the tape base sheet itself prematurely tearing or delaminating all around the strip, thus leaving the contents still banded.Attempts to modify such materials by providing selective coating of the adhesive to reduce the peel strength have proven costly. Other attempts to reduce the bonding by applying release coating to the back side have also been expensive. The use of an adhesive with less tack or bond strength is subject to premature adhesive failure. An alternative approach has been to increase the integrity of the base sheet to prevent delamination, but such stronger base sheets also increase costs and nonwoven base sheets require specially formulated adhesives or extended drying times. To merely illustrate this discussion of prior art adhesive coated materials, the following patents may be identified: U.S. Patent 3,425,968 to Reiling dated 4 February 1969 directed to noncurling gummed products U.S. Patent 4,377,433 to Merz et al. dated 22 March 1983, U.S.Patent 2,978,343 to Russo et al. dated 4 April 1961, U.S. Patent 3,574,1 53 to Sirota dated 6 April 1971, and U.S. Patent 4,192,783 to Bomball et al. dated 11 March 1980. These patents and conventional practice, however, reflect a standard procedure of applying the adhesive coating to uncoated base stock or to the uncoated side of coated base stock, thus leaving the coated side free for accepting printing. Both structures fail to satisfy the adhesive property requirements with ready release. U.S. Patent 3,076,588 to Conway et al. dated 5 February 1963 is directed to an adhesive construction requiring a smooth, film layer component.

The present invention provides a unique and cost effective adhesive coated sheet material particularly adapted for the bander applications above described. In accordance with the invention, it has been found that by selection of a particular coated base sheet web and application of the adhesive coating to a coated side of the base web or otherwise so that in use it will contact the coating, the resulting combination, while aggressively bonded upon contact between the adhesive coated side and the opposite side with activation of the adhesive, may be readily separated without delamination of the base sheet web. Rather, the coating remains with the adhesive and separates from the base sheet web and releases the banded contents.In this manner, use may be made of conventionally available water moistenable, solvent activated or heat sensitive adhesives as well as readily available coated webs as the base sheet. In contrast to prior attempts, however, we have found that it is not necessary to utilize separate release coatings or resort to selective adhesive application. Also contrary to conventional practice, the application of the adhesive to the coated side of the base sheet is preferred to achieve the benefits described.

According to one aspect of the invention there is provided an adhesive sheet material comprising a coated base web and an adhesive layer, the base web coating having a greater affinity for said adhesive than for said base web whereby, after contacting a portion of the adhesive layer with a portion of the opposite side (that is the side remote from said adhesive) of said sheet material to effect adhesion, the adhesive bond between portions of said sheet material which is thereby obtained is readily releasable as a result of delamination from the base web of the base web coating to which said portion of the adhesive layer is adhered.

According to a further aspect of the invention there is provided a method of restraining coiled, stacked or gathered items which comprises using as restraining means an adhesive sheet material as defined above.

Examples of preferred embodiments include a clay coated Kraft stock base sheet to which is applied on the coated side a water moistenable adhesive formulation. Others include the use of a coated latex saturated base sheet or a coated Kraft base sheet as well as other conventional coated base sheets such as 60 lbs./3300 ft2 (0.09 kg/m2) coated litho webs. In use as a bander, the strips of the present invention produce a strong seal since an aggressive adhesive may be used in combination with a smooth backing and yet are readily and quickly releasable when desired. In general, the peel strength under such conditions will be at least in the range of about 0.01 to 10.0 Ibs./inch (0.18 to 180 kg/m) width and, preferably,0.2 to 3.0 Ibs/inch (3.6 to 54 kg/m) width.The coating should have an affinity for the adhesive that is greater than its affinity for the base sheet web or itself as measured by microscopic examination of separated bands in the previously bonded area. The clay coating originally on the stock will be found predominantly adhered on the surface of the adhesive. A useful independent measure with moistenable adhesives involves moistening the adhesive coat on a one-inch (2.54 cm) strip and bonding it to a 99 lbs./3300 ft2 (0.1 5 kg/m2) Kraft paper. After drying for 1/2 to 1 minute, the strip is slowly hand peeled from the paper at an angle of about 1200 at a rate of about 20 inches/minutes (50.8 cm/minute). Useful materials will exhibit a substantial amount of clay coating deposited on the surface of the adhesive layer on the paper.

In accordance with the present invention, the base sheet material may be selected from a wide variety of available coated webs. These webs include those that have been previously employed as adhesive backings by applying the adhesive coating to the uncoated side. Suitable base materials include for example clay coated bleached Kraft stock (35-60 Ibs./3300 ft2) (0.05-0.09 kg/m2) such as is available from Watervliet Paper Company, smudgeproof coated latex saturated sheet as is available from Kimberly-Clarke Corporation under the designation Munising Division Grade C-32714, and treated synthetic nonwoven webs such as spunbonded polyolefin as is available from duPont under the trademark Tyvek designation 1073D. Other base web materials will suggest themselves to those skilled in the art.The base web material is coated or treated whereby the fibers on at least one side of the web have a substantially continuous film formed thereon on at least one side thereof. Coatings or treatments of the base web can conveniently be those which are normally employed for improved printability, generally clay and other pigment coatings. These are low cost coatings and may be applied directiy on the paper making machine or as an off machine coating step. For most purposes, a clay coating of about 10 to 25 libs./3300 ft2 (0.01 to 0.04 kg/m2) and, preferably 1 5 to 20 lbs./3300 ft2 (0.02 to 0.03 kg/m2) will be suitable for purposes of the present invention while falling within the scope of commercial paper production.Examples of other coatings or treatments which may be used include sizing or holdout coatings conventionally employed to reduce requirements for subsequent print or other coatings as well as antistatic and others which form a film on the web or fibers.

Any of a wide variety of adhesives may be employed in the present invention. These include, without iimitation, water moistenable adhesives such as are described in the above mentioned U.S. Patent 3,425,968 to Reiling dated 4 February 1969, for example, heat seal coatings such as are taught in U.S. Patent 2,625,287 to Holt, Jr., et. al., dated 13 January 1 953 and solvent activatable adhesive coatings such as are described in U.S. Patent 3,531,316 to Sternasty dated 29 September 1970. Selection of a particular coating for the purposes of the present invention will depend upon the desired end use as well as the nature of the coated base sheet web.

The determining factors will be the compatibility of the base web sheet and the adhesive; for example, the adhesive should not cause undue deterioration of the base web sheet nor should the coating of the base web sheet interfere unduly with the adhesive action of the adhesive composition. A second important factor will be the degree of bonding obtained when the adhesive side is placed in contact with the opposite side of the sheet material and the adhesive activated by solvent, water, heat or the like, the requirement being that the coating bond more aggressively to the adhesive than to its web substrate or to itself such that the coating will delaminate when peel stress is applied. This may be readily determined by weighing samples before and after peeling and comparing the amount of coating adhering to the peeled components.Examples of adhesive which may be used include water moistenable adhesives as described in the above mentioned U.S. Patent 3,425,968 to Reiiing dated 4 February 1969, heat seal adhesives such as homopolymers and copolymers of ethylene and vinyl acetate, solvent activatable adhesives such as acrylic and styrene polymers and copolymers and nitrile or chloraprene elastomers. The amount of adhesive required will also depend upon the nature of the base web and the desired end use. In general, the amount should be sufficient to provide a peel strength of at least about 0.01 to 10 Ibs./inch (0.1 8 to 180 kg/m) width, preferably about 0.2 to 3.0 Ibs./inch (3.6 to 54 kg/m) width.For example, for the application as a bander for coiled stamps and using a base sheet of a 62 Ibs./3300 ft2 (0.1 kg/m2) latex saturated paper web having one side clay coated, the amount of dry gum water moistenable adhesive will be generally in the range of from about 6 to 14 Ibs./3300 ft2 (0.09 to 0.021 kg/m2) and preferably about 10 to 12 lbs./3300 ft2 (0.015 to 0.018 kg/m2).

The invention will now be further described with reference to the accompanying drawings, in which: Figure 1 illustrates in schematic form one process for producing an improved releasable adhesive sheet of the present invention; Figure 2 illustrates, in cross section, one form of the improved releasable adhesive sheet of the invention; Figure 3 illustrates a similar view of a second form of the releasable adhesive sheet material of the present invention; Figure 4 illustrates the adhesive sheet material of the present invention illustrated in Figure 2 in use as a bander; Figure 5 illustrates the bander of Figure 4 peeled away with certain portions greatly exaggerated for clarity; and Figure 6 is an enlarged view similar to that of Figure 5 showing the embodiment of Figure 3.

Referring first to Figure 1, a method for preparing a preferred embodiment of the invention will now be described. As shown, base sheet 10 having coated side 12 is unwound from roll 14 supported by stand 1 5 and directed over idler and guide rolls 17 to adhesive coating station 16 where adhesive 18 is applied by means of roll 20 or other suitable means such as a rod, blade, or the like. The adhesive coated sheet 22 is then dried by passing through forced air dryer 24 over guide rolls 25, cooled and rewound by means of chilled rolls 27 or the like into roll 26 over idler rolls 29. The resultant stock may be slit into desired widths by slitting, wound into rolls or sheeted as desired. Various support means required (only partially illustrated) will be apparent to those skilled in this art.

Turning to Figure 2, coated sheet 22 is shown in cross-section. As illustrated, it shows the combination of base sheet 10 with adhesive 1 8 applied to the coating 12 on one side thereof.

Turning to Figure 3, a similar view is shown wherein a different base sheet 30 is employed and the coating and adhesive are on opposite sides.

Turning to Figures 4 and 5, the adhesive sheet of the invention in tape form is illustrated in cross section as a bander for a coil of postage stamps.

As shown, tape 32 encircles stamp coil 34 and is bonded to itself by means of contact between activated adhesive 1 8 and the opposite side 36 at overlap area 38. Thus, a stamp coil 34 is retained in a compact, rolled condition. As shown in Figure 5, when it is desired to open the coil of stamps, the adhesive tab 35 is pulled away, and coating 40 delaminates as shown in exaggerated detail. Thus, the stamp package may be conveniently and quickly opened without premature tearing and without delamination of bander web 10.

Turning to Figure 6, there is shown an enlarged and exaggerated cross-sectional view of the embodiment of Figure 3 in use. In this case, bander 42 comprises base sheet 30 having adhesive 44 on one side and a surface sizing 46 on the other. Such a composite may utilize webs as disclosed in Louden U.S. Patent 4,058,648 dated 1 5 November 1977, for example. As shown in Figure 6, in use, the adhesive layer 44 will contact sizing 46. When peeled away, although the sizing 46 may not totally and cleanly adhere to adhesive layer 44, the preferential adhesion is sufficient to result in pulling away at areas 47 and opening the band without delamination of base sheet 30.

The invention will now be illustrated by the following Examples.

EXAMPLE 1 Using the process described with respect to Figure 1, a 77 Ib. per 3000 sq ft. (0.11 kg/m2) Kraft stock coated with about 1 5 lbsj3300 ft2 (0.022 kg/m2) of a clay coating (the composite being available from Watervliet Paper Co. under designation "Envelope Kraft-coated one side") was coated on the clay coated side with about 10 Ibs. per 3300 sq.ft. (0.015 kg/m2) of a water moistenable adhesive formulation dispersed in a water-organic solvent system of the type described in the above mentioned Reiling U.S.

Patent 3,425,968 dated 4 February 1 969 and offered commercially by Kimberly-Clark Corporation as the adhesive on its Pancake (Trade Mark) dry gum label and business form paper. The coated web was then dried free of solvent, the adhesive coating moistened with water over a 1 in.2 (6.45 cm2) area and the web bonded to its reverse side. Quick tack ranged about 23 sec. This was determined by separating the moistened stock immediately after application to its reverse side. Separation was obtained by hand pulling at an angle of about 1200 and a rate of about 20 in./min (0.5 m/min). The end point was defined as the time at which coating separation occured.

After ageing for 24 hours, the shear bond strength of the construction prepared was greater than the tensile strength of the stock [shear bond strength about 30-38 Ibs./in. (535-680 kg/m) width]; however, the bond readily separated as desired upon application of a peel force of about 0.27 to 0.78 Ibjinch (4.8 to 13.9 kg/m) width with the stock remaining essentially intact. This and other data contained in the Examples were obtained using an Instron Model 11 30 tester with a jaw separation speed of 12 in./min (0.3 m/min).

EXAMPLE 2 Example 1 was repeated with a base sheet of 62 Ibs. per 3300 sq. ft (0.1 kg/m2) of a clay coated latex saturated sheet (available from Kimberly-Clark Corporation under the designation Munising Grade C-32714), and the result was shear bond strength exceeding the tensile strength of the base stock [shear bond strength about 29 to 37 Ibs./in. (517 to 660 kg/m) width] and a web band that was also readily separated when a peel force of about 0.35 to 0.65 Ib./in. (65 to 11.6 kg/m) width was applied. The quick tack results for this construction were 90 to 120 sec.

EXAMPLE 3 Example 1 was repeated using a 11 2 lb./3300 ft2 (0.16 kg/m2) latex saturated base sheet with a clay coating on both sides (available from Kimberly-Clark Corporation under designation Munising Grade M31415). The result was a shear bond strength exceeding the tensile strength of the stock [shear bond strength about 42 to 49 Ibs./inch (750 to 875 kg/m) width]. The bond, However, was readily separated when a peel force of about 0.6 to 1.1 Ib./inch (10.7 to 19.6 kg/m) width was applied. The quick tack of this construction was about 300 sec.

EXAMPLE 4 Example 1 was repeated using a base sheet of 47 Ibs. per 3300 sq.ft. (0.07 kg/m2) of a densified Kraft stock coated with 8 lbs./3300 ft2 (0.01 kg/m2) of polyvinyl alcohol resin (Gelva grade 20-30 from Monsanto) applied by Meyer rod from a 72% aqueous methanol mixture. For this Example, the moistenable adhesive was applied to the side opposite the polyvinyl alcohol resin coating. In this case, the shear bond strength of the construction was about 7.5 Ibs./inch (133 kg/m) width and the bond readily separated by applying a peel force of about 0.14 to 14 Ibs./inch (2.5 to 250 kg/m) width.

EXAMPLE 5 The base stock of Example 2 was coated on the clay coated side with 12 lbs./3300 ft2 (0.018 kg/m2) of a blend of polymers and copolymers of ethylene and vinyl acetate (offered by Kimberly Clark Corporation, Brown-Bridge Division on coated stock as adhesive 808-PP). The coated web was dried free of water and the adhesive activated at 3200F (1 600C) for 5 seconds with a heating iron supplied over a 1 in.2 (6.45 cm2) area in contact with the reverse side. After 24 hours, the shear bond strength exceeded the tensile strength of the stock [shear bond strength about 26 to 32 Ibs./inch (464 to 571 kg/m) width].

However, the bond readily separated as desired upon application of a peel force of about 0.45 to 0.8 Ib./inch (8.0 to 14.2 kg/m) width with the stock remaining essentially intact.

EXAMPLE 6 The base stock of Example 2 was coated on the clay coated side with about 12 lbs./3300 ft2 (0.01881 kg/m2) of a blend of styrene and acrylic ester polymers and copolymers applied from a water dispersion (offered by Kimberly-Clark Corporation, Brown-Bridge Division on coated stock as adhesive SA-354). The coated stock was dried free of water, and the adhesive activated over a 1 in2 (6.45 cm2) area by treating with toluene and bonded to its reverse side. After 24 hours, the shear bond strength was between 14 and 32 Ibs./inch (250 to 571 kg/m) width.

However, the bond readily separated as desired upon application of a peel force of about 0.1 to 0.3 Ib./inch (1.8 to 5.4 kg/m) width with the stock essentially intact. The quick tack after solvent activation with toluene, averaged 1 50 sec.

For comparison, two samples of coiled stamps obtained from the U.S. Post Office banded by a web of 38.5 lbs./3300 ft2 (0.06 kg/m2) bleached Kraft coated with 1 6 lbs./3300 ft2 (0.02 kg/m2) or a vegetable based water moistenable adhesive were also tested. These hands had a shear bond strength in excess of the tensile strength of the paper [shear bond strength about 20 to 23 Ibs./inch (360 to 410 kg/m) width] and both delaminated within the base web itself, upon hand peeling by grasping the finger tab, thus hindering unwrapping of the coil stamps. The same result occurred upon mechanical testing of laboratory prepared samples using a peel force of 0.25 to 0.45 ibs./inch (4.5 to 8.0 kg/m) width.

While the invention has been demonstrated with respect to specific adhesives, it will be apparent that by following the criteria defined above, suitable adhesive coated sheets in accordance with the invention may be made with other types of adhesives as well.

Claims (18)

1. An adhesive sheet material comprising a coated base web and an adhesive layer, the base web coating having a greater affinity for said adhesive than for said base web whereby, after contacting a portion of the adhesive layer with a portion of the opposite side (that is the side remote from said adhesive) of said sheet material to effect adhesion, the adhesive bond between portions of said sheet material which is thereby obtained is readily releasable as a result of delamination from the base web of the base web coating to which said portion of the adhesive layer is adhered.

2. An adhesive sheet material according to claim 1 wherein the adhesive layer is on a coated side of said base web.

3. An adhesive sheet material according to either of claims and 2 wherein, after contacting a portion of the adhesive layer with a portion of the opposite side (that is the side remote from said adhesive) of said sheet material to effect adhesion, the shear bond strength between said portion of the adhesive layer and said portion of the opposite side of said sheet material is at least 5 Ibs/in. (90 kg/m) width and the peel strength is in the range of from 0.01 to 101bs./inch (0.18 to 180 kg/m) width.

4. An adhesive sheet material according to any of the preceding claims wherein said peel strength is in the range of from 0.2 to 3.0 Ibs./inch (0.18 to 18 kg/m) width.

5. An adhesive sheet material according to any of the preceding claims wherein the adhesive is a water moistenable adhesive.

6. An adhesive sheet material according to any of claims 1 to 4 wherein the adhesive is a heat sealable adhesive.

7. An adhesive sheet material according to any of claims 1 to 4 wherein the adhesive is a solvent activatable adhesive.

8. An adhesive sheet material according to any of the preceding claims wherein the coated base web is a clay coated pauper.

9. An adhesive sheet material according to any of claims 1 to 7 wherein the coated base web is a latex saturated sheet.

1 0. An adhesive sheet material according to any of claims 1 to 7 wherein the base web is nonwoven sheet material.

11. An adhesive sheet material according to any of the preceding claims in the form of a tape.

12. An adhesive sheet material according to any of thepreceding claims in a form suitable for use as a bander for restraining coiled, stacked or gathered items.

1 3. An adhesive sheet material according to claim 12 in the form of a coil bander.

14. An adhesive sheet material as claimed in claim 1 substantially as herein described.

1 5. An adhesive sheet material substantially as herein described in any of the Examples.

1 6. An adhesive sheet material as herein described with reference to any of Figures 2 to 6 of the accompanying drawings.

1 7. A method of restraining coiled, stacked or gathered items which comprises using as restraining means an adhesive sheet material as claimed in any of the preceding claims.

18. A method as claimed in claim 1 7 wherein said items comprise a coiled strip of material wound upon itself or upon a core, a stack of sheets or a skein.