CA1037653A - Diaper with adhesive tabs - Google Patents

Abstract

ABSTRACT

A disposable diaper of the type having a liquid impervious backing sheet is provided with a pair of adhesive tape tab fasteners, each having a flexible substrate, a coating of tacky, pressure-sensitive adhesive and a release sheet. One end of each fastener is attached to the backing sheet. The other end of each fastener extends beyond the diaper and is covered by a release sheet which adheres to the adhesive coating with an attachment force of between 300 to 700 grams per 2-3/4 inches of width measured by a TLMI
tester. The release sheet is co-extensive in width and length with the substrate and provides a manually grippable portion for removing the sheet from the adhesive coating. The sub-strate has no sizing on its back face, both faces of the sub-strate have surfaces to which the adhesive material will strongly adhere.
The adhesive tape tab fasteners are applied to the backing sheet after being cut as segments from a roll of a laminar assembly of the substrate, the release sheet and the adhesive layer therebetween.

Description

~376~3 Backqround of the Invention Disposable diapers have met with increased commercial acceptance in recent years primarily because of their con-venience, as opposed to cloth diapers, which need to be laundered once soiled. In keeping with the demand for in-creased convenience in the use of diapers, the old-fashioned safety pins commonly used for fastening the diaper about the infant has been abandoned in favor of adhesive tabs. Adhesive tabs are not only more convenient, but are safer in use than safety pins and thus have received wide acceptance in the field.
Although ordinary pressure sensitive tape has been suggested and used as a fastener means with di~posable diapers, most of these conventional tapes have been difficu~t to handle in manufacture, overly expensive, and deficient in functioning.
Conven~ional adhesive tape is supplied in rolls in which the tape, consisting of a substrate layer and an adhesive layer, is rolled onto itself. In such rolls, the back face of the substrate must be coated with a sizing layer to prevent the tape from sticking to itself. The necessary sizing layer adds to the expense of the tape and also adds unnecessary stiffness.
In the use of conventional adhesive tape for ad-hesive tape tabs on diapers, the tape, as it is unwound from the roll is brought into contact (on its adhesive face) with a release sheet, generally made of paper, which is simultane-ously unwound from another roll. Because of the difficulty in high speed manufacture of getting perfect alignment between the rapidly unwinding adhesive tape and the rapidly unwinding release sheet, the release sheet is generally made somewhat 0 wider than the adhesive tape to insure coverage of the latter .
.' ~37t~S;~I
and to avoid having exposed sticky surfaces on the diaper. This is wasteful of material and adds to the expense of the diaper~
It is also disadvantageous in that overla~pping edges of the release paper can give rise to paper cuts during the handling of the diaper.
In addition, certain combinations of adhesive composi-tions and substrate compositions cannot be utilized in conven-tional tape procedures because some adhesive compositions must be applied to substrates in melt form at elevated temperatures and some substrates cannot survive much elevated temperatures.
one useful substrate which cannot be used with melt adhesives in conventional tape procedures is a sheet material made of melt extruded polyethylene fihers, more or less randomly oriented , within a plane and fused together. Such sheet material is sub-stantially isotropic with respect to tensile strength and is particularly useful from a manufacturing standpoint, as will be described in more detail below.
Summary o the Invention The present invention relates to disposable diapers having a water-impervious backing sheet, such as polyethylene film, which utilize pressure-sensitive adhesive tape tab fasten-ers to attach the diaper about an infant. The tape tab fasteners of the present invention are formed from a modified label stock in which the substrate, the pressure-sensitive adhesive layer and release sheet are assembled in a laminar fashion with the adhesive layer being the central layer, and the assembled layers are rolled in a single roll.
Label stock, in its most usual form, suitable for cutting into labels, name tags, etc. which adhere easily and without wetting to most surfaces and which are readily strip-pable therefrom without leaving a residue, consists of a paper substrate, a pressure-sensitive adhesive layer coated on one ~37~S3 surface thereof, and a rel0ase paper covering the adhesive layer. It is usually made with a release paper with a sub-stantial amount of silicone polymer, or other release agent, on its surface so that the release paper can be very easily removed.
In the modification of the usual label stock for use in accordance with this invention the nature and amount of release agent on the surface of the release paper and the nature and amount of the adhesive are adjusted to require moderate force for removal of the release paper from the pressure-sensitive adhesive layer so that the release paper adheres sufficiently strongly to remain in position during the handling of the diapers on high speed production machinery but is still readily removable at the time of use. Preferably, the adhesion between the adhesive layer and the release sheet is maintained at a level so that a force of from about 300 to about 700 grams of force per 2-3/4 inches of width is required to separate the release sheet from the adhesive layer.
Conventional pressure-sensitive adhesive tape is made by applying a tacky, pressure-sensitive adhesive composition to a suitable substrate as a layer thereon. Since the ad-hesive tape is wound on itself in roll form, the back side of the substrate is coated with a non-stick sizing to keep the tape from sticking to itself.
Label stock and the modified label stock used in this invention are made by a different procedure in which a tacky, pressure-sensitive adhesive composition is applied to a relsase sheet as a layer thereon and a substrate is then applied to the opposite side of the adhesive layer. The 0 combined layers form a laminar assembly which is then rolled ill~3~
up, the presence of release paper between the adhesive and the next layer of substrate making it unnecessary to treat the bare substrate surface to prevent sticking. In label stock and in the modified label stock used in the tape tabs of this invention, both faces of the substrate are strongly ad~
herent to the adhesive material due to the absence of non-stick sizing on the back face of the substrate.
Since the tape tab fastener used in the diaper of the present invention is in the form of label stock, the cost of the diaper is reduced relative to the cost of diapers made with prior art tape tab fasteners due to the fact that sizing is not required on the back face of the substrate and, in fact, would be undesirable because it would add unnecessary stiffness to the tape tab fastener.
From a broad aspect, the present invention provides a disposable diaper comprising an absorbent pad; a water-impervious backing sheet in juxtaposition with a major surface of said pad; and a pair of tape tab fasteners adhered at end portions thereof to opposite side portions of said backing sheet near one end thereof on the surface opposite said absorbent pad, said Fasteners having free end portions oppnsite said adhered end portions, each of said fasteners including a flexible sub-strate having a normally tacky and pressure-sensitive adhesive coating on one major surface thereof and a release sheet having width and length dimensions equal to those of said substrate and being precisely coterminous with said substrate at said free end portion7 an end portion of said release sheet being adhered to an end portion of said adhesive coating with the ad-hered portions in registry, the other end portion of said re-lease sheet being folded back on itself to provide a pull tab,thus leaving uncovered the adhesive coating at the other end of each of said fasteners to provid~Lthe means for adhering the _~ _ ~37~
tape tab fasteners to the backing sheet of the diaper as afore-said, each of the surfaces of said substrate being receptive to strong adherence by said adhesive coating, said release sheet having an average attachment force to said adhesive coating of between about 300 and about 700 grams per 2-3~4 inches of width, measured by a TLMI tester under the conditions of TAPPI Test Method T402m.
Brief Description of the Drawings FIG. 1 is a perspective view, with certain portions broken away for clarity of illustration, of an open-unfolded diaper, and FIG. 2 is an enlarged perspective view with a portion broken away of the tape tab fastener used on the diaper of the present invention.
Detailed Description of a Preferred Embodiment While this invention is susceptible of embodiment in many forms, there is shown in the drawings and will herein be described in detail only a preferred embodiment of the inven-tion, with the understanding that the present invention is to be considered an an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.
Disposable diaper 10 having the improved tape tab fasteners of this invention applied thereon may be of many - 5a -, iS3 types of construction, and as illustrated include, when fully opened and laid out flat, a lowermost water-impervious sheet 12 which is rectangular in shape, upon which is posi-tioned a fibrous pad 13. Pad 13, as illustrated, includes a highly water-absorbent ~ibrous panel 14, which is also rectangular in shape, but smaller than the impervious sheet and centrally disposed thereon, and an overlying facing layer 16 of fibrous material, which is also rectangular in shape, equal in dimension, and coterminous with the impervious sheet and in contact therewith in the marginal poxtions of the diaper extending peripherally beyond the absorbent panel, i.e., in portions 16b and 12b of facing layer 16 and impervious sheet 12, respectively. Absorbent panel 1~ is adhered to backing sheet 12 by bead lines 22 of adhesive substantially throughout khe interface therebetween. Marginal portions 16b and 12b are also adhered to each other by bead lines 2~.
In the preferred embodiment of the invention, moisture-impervious sheet 12 is formed of polyethylene having a thickness of approximately 0.001 inch. The sheet may be smooth, or may be embossed to improve its drape and feel.
Other suitable flexible moisture-impervious sheets may be used in accordance with this invention, such as, for example, polyethylene terephthalate sheets having a thickness of about 0.0005 inch.
Although the diaper illustrated utilizes a facing sheet which is coterminous with the impervious backing sheet, it will be appreciated that other constructions, such as constructions utilizing a backing sheet which overlaps the end portions of the facing layer may also be utilized without departing from the scope of the present invention.

~L037~3 Near one end of the diaper and at opposite edges thereof are attached tape tab fasteners 30 of a pressure-sensitive type with one end of each extending beyond the respective side edges of the diaper.
Referring to FIG. 2, each tape tab fastener 30 is pro-vided in the form of label stock which is to say that fastener 30 includes a substrate 31, a coating of adhesive 33 (par-tially stripped away in ~IG. 2), and a release sheet 35, folded back on itself to provide pull tab 38 and to expose the adhesive at end 36 of the fastener while opposite end 37 is still covered.
The tape tab fasteners are attached to the underside of imper-vious sheet 12 by khe adhesion thereto of the expose~ adhesive of ends 36.
Substrate 31 in the preferred embodiment is in the form of polyethylene which is melt extruded as fibers 32, fused to each other in a randomly oriented fashion within a plane to produce a film substrate of substantially isotropic tensile strength. In this preferred embodiment in which a material of a substantially isotropic tensile strength is used, the fasten-ers cut from a continuous roll of modified label skock may betransferred and attached to the backing sheet without the necessity of re-orientation which is required of tabs having primary tensile strength in the machine direction, as discussed below.
Since ~asteners 30 are formed from modified label stock, it will be appreciated that sizing is not required on the surface of the substrate opposite the adhesive coating 33 which reduces the cost in the production of the diaper~
Preferably, the adhesive coating 33 is formulated by using a block polymer elastomer in combination with a tackifier. The block polymer is an elastomeric and thermoplastic styrene-1~13'~SS3 isoprene AOA block polymer sold by the Shell Chemical Company under the registered trade name "Kraton". This type of adhe-sive is known in the art, and reference may be made to commonly assigned U.S. Patents Nos. 3,625,752; 3,676,202 and 3,723,170, for a further discussion of the chemical characteristics thereof.
The mass distribution of adhesive 33 on substrate 31 may range from about 1 oz./yd.2 to about 3 oz./yd.2. When backing sheet 16 is smooth, it has been found that 1 oz /yd 2 of adhesive functions to secure the fasteners to the backing sheet without premature separation therefrom. Conversely, when backing sheet 16 is embossed to improve its drape and feel, adhesive mass distribution must be raised due to the decreased area of attachment and it has been found that about 1-1/2 oz./yd.2 functions well to secure fasteners on an embossed backing sheet.
Release sheet 35 may be formed of any suitable material and includes a silicone coating on the surface adjacent adhesive coating 33, the weight of the coating being adjusted so that the force necessary to separate the release sheet from the adhesive is in the range of about 300 to 700 grams per

2-3/~ inches of width, as measured by a TLMI test (Tag and Label Manufacturers Institute) on a tester manufactured by Testing Machines, Inc. of Amityville, New York, subject to conditions of TAPPI test method T~02m. It has been found that the combination of adhesive and release sheet having a combined attachment force in this range functions satisfactorily to maintain the release sheet on the fastener during production and handling while also allowing the release sheet to be re-moved from the fastener when the diaper is to be used without tearing of the water-impervious sheet on which the attached end of the fastener is secured. Ideally, the release sheet ,_. ~`, ~a~76~3 should have an attachment force to the adhesive coating of about 400 grams per 2-3/4 inches of width.
In the preferred embodiment fasteners 30 are cut from a continuous supply of a laminar assembly of a substrate, a release sheet and an adhesive layer therebetween, which is 2-3/4 inches in width and the individual fasteners are cut transversely from the supply to provide fasteners which are one inch wide. The release sheet at one end of the fastener is folded back out of contact with the adhesive coating so that one end 36 of the fastener may be attached to impervious sheet 16 while the other end 37 extends outwardly from the diaper as illustrated in FIG. 1. The folded back portion 38 of the cover sheet functions as a manually grippable portion for re-moving the cover sheet to expose the adhesive coating when the diaper i9 to be fastened about an infant. A speciFic method and apparatus for the attachment of tape tab fasteners is - disclosëd in the co-pending and co-assigned patent application Serial No. 206,708 of Donald Oabcock, filed on August 9, 1974.
The fasteners of the preferred embodiment of the pre-sent invention may be cut from a modified label stock having asubstrate sold under the registered trade name "TYVAC" consist-ing of melt extruded polyethylene fibers, randomly oriented in a plane. Since conformability of the diaper as a whole is a de-sired characteristic, the fasteners should be as flexible as pos-sible and still stiff enough to maintain their outwardly extend-ing orientation without curling during the production of the diaper and handling. It has been found that a substrate of sufficient stiffness to function properly during production and ,~ , ~(~3~6~ii3 handling and sufficient flexibility to remain conformable during use is obtained at an average stiffness in the range of about 80 to 300 milligrams, as tested on a Gurley stiffness tester under the conditions specified in rrAPPI Method T~02m.
Preferably, the average stiffness should be about 200 mil-ligrams.
While the invention has been described above in connection with its preferred embodiment in which the sub-strate material is substantially isotropic in tensile strength, it is not limited thereto. Other substrates, including sub-strates substantially stronger in the machine direction than in the transverse direction may be used, including paper sub-strates.
, Where a substrate is used which has inadequate strength in the transverse direction to function in the long dimension of the tape tab, it is preferable to supply the label stock laminar assembly in a width corresponding to the width of the desired tape tabs and then to re-orient the cut end segments therefrom by 90 before adhering the end segments to the water-impervious sheet of the diaper.
Suitable apparatus for carrying out such re-orienting is disclosed in U.S. Patent No. 3,728,191, issued April 17, 1973, to A. R. Wierzba et al., except that in the present invention, the laminar assembly of the substrate and release sheet is payed out from a single roll rather than from two separate rolls, thereby eliminating the problem of alignment of the two rolls and avoiding the necessity of an anti-stick siæing on the back of the substrate.
As stated above, the elimination of the anti-stick sizing on the back side of the substrate leaves the bac~ side ~37~Si3 capable of being adhered to strongly by the adhesive coating adherence of the same order of magnitude as the adherence on the side to which the adhesive is applied and substantially greater than the adherence by the release sheet, as described above.
From the foregoing discussion, it will be appre-ciated that the present invention provides a new improvement in disposable diapers, and particularly to the tape tab fasteners thereon, which are more economical from a fabri-cation and production standpoint as well as being more suit-able functionally than prior art diapers. Accordingly, others skiLled in the art may make modifications to the disclosed embodiment without departing from khe spirit and scope of the invention as pointed out in the appended claims.

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A disposable diaper comprising an absorbent pad; a water-impervious backing sheet in juxtaposition with a major surface of said pad; and a pair of tape tab fasteners adhered at end portions thereof to opposite side portions of said back-ing sheet near one end thereof on the surface opposite said absorbent pad, said fasteners having free end portions opposite said adhered end portions, each of said fasteners including a flexible substrate having a normally tacky and pressure-sensi-tive adhesive coating on one major surface thereof and a release sheet having width and length dimensions equal to those of said substrate and being precisely coterminous with said substrate at said free end portion, an end portion of said release sheet being adhered to an end portion of said adhesive coating with the adhered portions in registry, the other end portion of said release sheet being folded back on itself to provide a pull tab, thus leaving uncovered the adhesive coating at the other end of each of said fasteners to provide the means for adhering the tape tab fasteners to the backing sheet of the diaper as afore-said, each of the surfaces of said substrate being receptive to strong adherence by said adhesive coating, said release sheet having an average attachment force to said adhesive coating of between about 300 and about 700 grams per 2-3/4 inches of width, measured by a TLMI tester under the conditions of TAPPI Test Method T402m.

2. The diaper of claim 1 wherein said substrate is formed from melt extruded fibers, randomly oriented within a plane.

3. The diaper of claim 2 wherein said substrate is formed from polyethylene.

4. The diaper of claim 1 wherein said adhesive attach-ment force is about 400 grams per 2-3/4 inches of width.

5. The diaper of claim 1 wherein said adhesive is present on said substrate in the range of 1 oz./yd.2 to about 3 oz./yd.2.

6. The diaper of claim 5 wherein said backing sheet is embossed and said adhesive is present on said substrate in the amount of about 1-1/2 oz./yd.2.

7. The diaper of claim 5 wherein said backing sheet is smooth and said adhesive is present on said substrate in the amount of about 1 oz./yd.2.

8. The diaper of claim 1 wherein said substrate has a stiffness, measured by a Gurley stiffness tester, in the range of 80 to 300 milligrams under the conditions of TAPPI Test Method T402m.

9. The diaper of claim 8 wherein said substrate has a stiffness of about 200 milligrams.