Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-06-20
2003-01-28
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000, C428S356000, C442S149000, C442S151000
Reexamination Certificate
active
06511745
ABSTRACT:
The invention relates to the development of pressure sensitive adhesive tapes based on butadiene/acrylate latices having a high butadiene content and resin dispersions.
In the patent literature there exists a large number of applications on the production of adhesive packaging tapes.
The time honored adhesive composition systems for adhesive packaging tapes are based essentially on natural rubber, styrene block copolymers and polyacrylates.
The natural rubber systems are commonly used as solutions in an aliphatic solvent mixture. Water based natural rubber compositions based on centrifuge latex are likewise known. For the required adhesive properties it is vital to add resins, fillers and aging inhibitors. Crosslinking takes place either chemically by way of added crosslinking agents or physically by way, for example, of electron beam curing.
Synthetic rubbers based on styrene block copolymers have also been described in the past as adhesive compositions for adhesive packaging tapes. These are 100% systems, which, after blending with resins and further coagents, may be applied in the melt state in the absence of solvents or water.
The use of polyacrylates as adhesive compositions for adhesive packaging tapes is likewise known. Besides solutions of polyacrylates, there have also been descriptions in the past of polyacrylate dispersions, which, after compounding with resin dispersions and further coagents, meet the requirements of an adhesive packaging tape composition. Acrylate dispersions exhibit relatively poor tack to cartons, especially when the substrate originates from papers which have been recycled a number of times, which is increasingly the case with packaging cartons. By adding resin dispersions this deficiency can be eliminated. Since natural resin dispersions based on rosin derivatives often have an undesirable influence on the cohesion of acrylate compositions, there is a tendency to use the more cohesive hydrocarbon resin dispersions, which are offered by a variety of resin producers.
Backing materials commonly used for adhesive packaging tapes are monoaxially or biaxially oriented polyolefins, PVC types or papers.
In the pressure sensitive adhesives field, butadiene/styrene latices have been used for many years to impregnate and stabilize backing materials. These backing materials include, primarily, papers, wovens, and nonwovens. Because of the application, the impregnation or coating must in no case be tacky. The butadiene/styrene copolymers used for this application must therefore contain a relatively high fraction of hardening monomers, but on the other hand must include sufficient softening monomer that the copolymer overall remains elastic. Butadiene/styrene latices with a butadiene content of about 25-50% fulfill this requirement very effectively. Depending on the butadiene content, films of these copolymers have an elasticity ranging from moderate to good and are not tacky. Such monomers have been available on the raw materials market for many years now (Butofan® grades from BASF, various grades from Dow and Synthomer). Because of their preparation, such latices and dispersions include emulsifier systems in order to bring about compatibility between the organic phase and the aqueous phase.
In the past, butadiene/styrene copolymers have also been used as base polymers for label compositions. In the labels segment, cohesion is frequently of secondary importance, so that, following compounding with customary tackifiers, weakly adhering systems exhibit properties which are sufficient in many cases.
As a framework polymer for adhesive packaging tape compositions, butadiene/styrene based copolymers with little or no tack are often poorly suited, since they can be made tacky only with considerable quantities of tackifier resins, which in turn is associated with a substantial loss of cohesion. This rules out their use as adhesive compositions for adhesive packaging tapes.
Butadiene/styrene copolymers or butadiene/methyl methacrylate copolymers having a high butadiene content, on the other hand, are of great interest as framework polymers for adhesive packaging tapes.
Butadiene copolymers having a high butadiene content and containing a hard and thus cohesive segment as copolymerization partner are suitable as framework polymers for high performance pressure sensitive adhesive compositions, but exhibit only moderate tack on critical substrates. It is an object of the invention to provide adhesive compositions based on butadiene copolymers which do not have the aforementioned deficiencies and with which it is possible to make a pressure-sensitive adhesive tape which meets the requirements of an adhesive packaging tape.
This object has been achieved through the use of butadiene/acrylate dispersions having a high butadiene content which have been blended with suitable resin dispersions.
The group of the butadiene/acrylate copolymers comprises framework polymers of butadiene and a moderately hard comonomer such as butyl acrylate, for example. Butadiene/acrylate copolymers have markedly lower glass transition points than butadiene/styrene or butadiene/methyl methacrylate copolymers. At a butadiene content of about 75%, the glass transition point may be lowered by about 15° C. to −70° C. by passing from styrene to, for example, butyl acrylate as comonomer.
The compound formulations comprising framework polymer and resin dispersion may be admixed, if desired, with further coagents such as, for example, aging inhibitors or further emulsifiers, in order to improve the protection against aging, or to further adapt the unrolling properties to the application. After the adhesive composition has been coated onto a polymer or paper backing it is possible to obtain a pressure sensitive adhesive tape which entirely meets the requirements of an adhesive packaging tape in respect of tack, bond strength, cohesion, and unrolling properties.
Adhesive compositions:
The copolymerization of butadiene with acrylates such as butyl acrylate, for example, in an aqueous medium provides copolymers which are film forming and which have a glass transition point which is suitable for pressure sensitive adhering. Butadiene/acrylate dispersions are generally stabilized by incorporating small amounts of carboxyl-containing groups, which at the same time improves the adhesion to many substrates.
As adhesive compositions for the invention it is possible in particular to use carboxylated butadiene/acrylate copolymer dispersions having a butadiene fraction of 50-95%, preferably 60-85%, based on the overall butadiene and acrylate solids fraction, which in a mixture with resin dispersions exhibit outstanding suitability as adhesive compositions for adhesive packaging tapes. Carboxylated copolymers of this kind contain in particular below 10%, preferably below 5%, based on the monomer content, of carboxyl-containing comonomer, especially acrylic acid, in the copolymer.
Butadiene/acrylate dispersion types of the invention having a butadiene content >60% are available, for example, from Dow.
As the resin component it is possible to use not only dispersions of synthetic resins (e.g. hydrocarbon resins, terpene phenolic resins, etc.) but also natural resin dispersions (e.g., rosin derivatives, polyterpenes etc.).
Owing to their high cohesion, there is a distinct preference for hydrocarbon resin dispersions. The melting point of the base resins should be situated in the range 50-120° C., preferably 60-100° C. Based on the overall solids content in terms of butadiene/acrylate copolymer and resin, the resin fraction should be situated in the range 5-60%, preferably 10-40%. To tailor the adhesive properties it is also possible to use mixtures of different resins. To improve the aging behavior it is possible to add dispersions of customary aging inhibitors which are well known from the field of elastomers.
Furthermore, as and when required, it is possible to add further additives to modify the product properties, such as fillers, soft resins, oils or emulsifiers, for example, of the alkoxylated alkylphen
Norris & McLaughlin & Marcus
tesa AG
Zirker Daniel
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