Adhesive packaging tape

Details Adhesive packaging tape Adhesive packaging tape

2002-09-30

2004-03-16

Dawson, Robert (Department: 1712)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

C428S336000, C428S337000, C428S341000, C428S219000, C428S220000

Reexamination Certificate

active

06706392

ABSTRACT:

The invention relates to solvent-free adhesive tapes with a film based on polyolefins and an adhesive based on acrylic dispersion, and to their use as adhesive packaging tape.
Solvent-based adhesive tapes with a film based on polyolefins, especially on biaxially oriented polypropylene, and an adhesive based on acrylic dispersion are known and are available from known manufacturers of adhesive packaging tapes.
A description is given, for example, in “Packaging Tapes”, Stefan Roeber in Handbook of Pressure Sensitive Adhesive Technology, Third Edition, edited by Donatas Satas, Satas&Associates, Warwick, R.I., pp. 787-814. Further descriptions can be found in European Adhesives & Sealants 10 (4), 1993, 29, by G. Pedala and European Adhesives & Sealants 2 (2), 1985, 18 by R. W. Andrew.
The known adhesive packaging tapes with a film based on biaxially oriented polypropylene and an adhesive based on acrylic dispersion are used for numerous packaging tasks, especially in the sealing of cartons. In comparison to commercial adhesive tapes with adhesive based on solventborne natural rubber compositions blended with appropriate resins, the adhesive tapes with adhesive based on acrylic dispersion have the disadvantage of a sealing effect which is often unsatisfactory. This means that the sealed cartons open again a few minutes or hours after sealing. This unwanted opening generally affects not all of the sealed cartons but only a relatively small fraction, which then, however, leads to disruptions and extra work in the automatic conveying and packaging lines that are nowadays the norm. The problem occurs to an increased extent when using cartons which have been manufactured from recycled paper. For some years there has been a continual increase in the fraction of cartons made from recycled paper.
The failure of the adhesive tapes based on acrylic dispersions is caused by the inadequate tack of the adhesive to the surfaces of cartons made from recycled paper and by the stretch introduced into the adhesive tape as a result of excessive unwind force during processing. Given the sufficient lid-flap tension in the cartons, caused by the pressure of the material packed in the carton or by the tension of the packing material, which acts counter to the sealing, the adhesive tape detaches from the surface of the carton, and the carton opens.
One known means of improving the tack is to add resins to acrylic dispersions. The resins may be added in the form of an aqueous dispersion.
An overview of possible resin dispersions can be found, for example, in “Resin Dispersions”, Anne Z. Casey in Handbook of Pressure Sensitive Adhesive Technology, Second Edition, edited by Donatas Satas, Van Nostrand Reinhold New York, pp. 545-566. Results of the blending of acrylic dispersions with resin dispersions are described in “Modification of Acrylic Dispersions”, Alexander Zettl in Handbook of Pressure Sensitive Adhesive Technology, Second Edition, edited by Donatas Satas, Van Nostrand Reinhold New York, pp. 457-493.
The company Hercules BV proposes a mixture of acrylic dispersions (Acronal 85D, BASF), 33% by weight of resin dispersions based on a hydrocarbon resin (Tacolyn 4177) and about 4% by weight (2% based on the mixture of the aqueous dispersions) of an isocyanate crosslinker (Basonat F DS 3425X, BASF) (“Tacolyn 4177 and Tacolyn 153 Resin Dispersions, use in WBPSA technical tapes for high temperature application”; Hercules BV product information dated 06.01.1995, pages 1-4).
By this means, an improved thermal stability, improved cohesion, and improved tack to steel are obtained. The anchoring of the composition to a film of biaxially oriented polypropylene, however, is not sufficient. Moreover, sufficiently quiet and easy unwinding cannot be achieved by means of the proposed adhesives, and use of the isocyanate crosslinker results in increased effort for workplace safety, since Basonat F DS 3425X is classed as a hazardous material under German regulations and may give rise to sensitization by inhalation or skin contact and to heath damage on inhalation (Basonat F DS 3425 safety data sheet in accordance with 91/155/EEC dated 20.07.1994, BASF). The means proposed is therefore considerable for obtaining adhesive tapes with improved tack to recycled paper in conjunction with quiet and easy unwinding plus sufficient composition anchoring.
Another possibility for improving the tack to cardboard packaging made from recycled paper is described in DE 196 11 501 A1 and EP 0 796 906 A2. Here, an adhesive based on a mixture of acrylic dispersion, special resin dispersions based on hydrocarbon resins, alkoxylated alkylphenols, and, optionally, a suitable crosslinker is used.
For preparing acrylic dispersions, anionic, nonionic, and, less often, cationic or amphoteric components are used as emulsifiers. Anionic emulsifiers comprise sodium, potassium or ammonium salts of fatty acids and sulfonic acids, alkali metal salts of C 12-16 alkyl sulfates, ethoxylated and sulfonated fatty alcohols or alkylphenols.
The emulsifiers are frequently used at concentrations of 0.2-5% based on the acrylic monomers.
Owing to emulsifiers, but also to wetting agents added additionally, the dried acrylic dispersion films exhibit a more or less pronounced sensitivity to water.
The water sensitivity is frequently determined by the time taken for the dried self-adhesive composition to develop a white coloration after it has been wetted with water. In certain label applications, where great value is placed on optical qualities, the degree of whitening does play a certain part. In the case of adhesive packaging tapes, however, its significance is low. Possibly much more serious, however, is the water sensitivity or moisture sensitivity in adhesive tapes with acrylic dispersions which have been physically treated (corona/flame treatment) on both sides, when at high atmospheric humidity these adhesive tapes display a tendency for the adhesive, during unwind from the roll, to transfer to the other side. Polypropylene adhesive tapes which have been given a surface treatment on both sides are described, inter alia, by G. Pedala in European Adhesives & Sealants 10 (4), 1993, 29. Double-sided surface-treated PP adhesive tapes are on the market as low-noise adhesive packaging tapes. A description can be found, for example, in the “Handbook of Pressure Sensitive Adhesive Technology” by Donatas Satas, Third Edition, p. 797.
In many cases, however, only the reverse of the adhesive tape is subjected to corona treatment in a printing machine in order to apply flexographic printing inks to PP adhesive tapes. Suitable flexographic printing inks are, for example, the inks from the series “15 PAA” from Michael Huber GmbH, D 85551 Kirchheim-Heimstetten.
In order to have reduced water sensitivity, the literature sets out processes which start right from the preparation of the dispersion, with the selection of the emulsifiers. Thus there are emulsifiers which are sufficiently volatile at relatively high temperatures or which decompose on drying. For instance, U.S. Pat. No. 2,680,111 to United States Rubber Co. sets out ammonium soaps which are used in synthetic rubber polymerization to improve the water resistance of rubber coatings.
U.S. Pat. No. 3,847,855 to Union Carbide Corp. recommends vinyl chloride copolymer emulsions comprising ammonium salts of fatty acids. Since the migration of emulsifiers is often held responsible for the water sensitivity, the literature contains references which use copolymerizable emulsifiers in order to lessen the migration.
Through a selection of certain comonomers in acrylic polymerization it is also possible to increase the water resistance: for example, ethylene glycol dimethacrylate is proposed as a comonomer by T. Ono in U.S. Pat. No. 3,983,297 with the aim of improving the water resistance.
The known adhesive tapes unwind relatively noisily when used in practice, i.e., at unwind speeds of between 20 and 200 m/min, and lead to a deterioration in working conditions as a result of increased noise levels.
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