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AssigneeNone recorded
InventorsMarc Husemann, Stephan Zollner
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The invention relates to an adhesive material based on block copolymers of general type P(B)-P(A/C)-P(B). wherein each block copolymer consists of a central copolymer block P(A/C) and terminal polymer block P(B). The invention is characterised in that P(A/C) represents a copolymer from monomers A anid C, which has a glass transition temperature of 0° C.-80° C. wherein component C contains at least one functional group which behaves in an inert manner in a radical polymerisation reaction, and which is used to increase the cohesion of said block copolymer: P(B) represents a polymer from monomers B, which has a glass transition temperature of 20° C.-175° C.; the polymer-block P(B) is insoluble in the copolymer-block P(A/C), and P(A/C) are unmixable.
A pressure sensitive adhesive based on block copolymers of the general type P(B)-P(A/C)-P(B), each block copolymer being composed of one middle copolymer block P(A/C) and two end polymer blocks P/(B), characterized in that
The pressure sensitive adhesive of one of the preceding claims, characterized in that the functional group of the monomers C brings about the enhancement of cohesion by means of dipole/dipole interactions and/or hydrogen bonds.
The pressure sensitive adhesive of one of the preceding claims, characterized in that the functional group of the monomers C is a carboxylic acid group, a hydroxyl group or a tert-butyl group.
The pressure sensitive adhesive of one of the preceding claims, characterized in that as monomers C at least one compound from the following group is used:
The pressure sensitive adhesive of at least one of the preceding claims, characterized in that as monomers C use is made of at least one compound which lowers the glass transition temperature of the copolymer block P(A/C) to Tg<0° C.
The pressure sensitive adhesive of at least one of the preceding claims, characterized in that as monomers A use is made of at least one compound of the general formula
The pressure sensitive adhesive of at least one of the preceding claims, characterized in that as monomers B at least one monomer is used such that the resultant polymer blocks P(B) are capable of forming a 2-phase domain structure with the copolymer blocks P(A/C).
The pressure sensitive adhesive of at least one of the preceding claims, characterized in that the pressure sensitive adhesive possesses an average molecular weight of between 5,000 and 600,000 g/mol, in particular between 10,000 and 300,000 g/mol.
The pressure sensitive adhesive of at least one of the preceding claims, characterized in that the fraction of the polymer blocks P(B) lies between 10 and 60% by weight, in particular between 15 and 40% by weight, of the entire block copolymer.
The pressure sensitive adhesive of at least one of the preceding claims, characterized in that the weight fraction of the monomers C in relation to that of the monomers A lies between 0.1 and 20, in particular between 0.5 and 5.
The pressure sensitive adhesive as claimed in at least one of the preceding claims, characterized in that the block copolymers are mixed with from 0 to 50% by weight, in particular with from 20 to 40% by weight, of a resin.
A process for preparing a pressure sensitive adhesive of at least one of the preceding claims, characterized in that, in the course of the preparation and/or processing operation, additives are added to the pressure sensitive adhesive, such as aging inhibitors, light stabilizers, ozone protectants, fatty acids, plasticizers, nucleators, blowing agents, accelerators and/or fillers.
A process for producing a pressure sensitive adhesive of at least one of the preceding claims, characterized in that the pressure sensitive adhesive is processed further from the melt, in that it is applied in particular to a backing.
The use of the pressure sensitive adhesive of at least one of the preceding claims for adhesive tape, with the acrylic pressure sensitive adhesive being present as a single-side or both-sides film on a backing.
Dependencies are inferred from the claim text.
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Adhesives based on block copolymers containing at least one sequence of a
Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains…:…
Adhesives based on block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon…: modified…
Composition of polymers characterized by a further compound in the blend, being organic macromolecular compounds, natural resins, waxes or and…:…
Term end not estimated
The invention relates to pressure sensitive adhesives based on block copolymers of the general type P(B)-P(A/C)-P(B).
In the field of pressure sensitive adhesives (PSAs) continuing technological developments in the coating technique mean that there is an ongoing need for new developments. Within the industry, hotmelt processes with solventless coating technology are of increasing importance in the preparation of PSAs, since the environmental regulations are becoming ever more stringent and the prices of solvents continue to rise. Consequently, solvents are to be eliminated as far as possible from the manufacturing operation for PSA tapes. The associated introduction of the hotmelt technology is imposing ever-greater requirements on the adhesives. Acrylic PSAs in particular are the subject of very intensive investigations aimed at improvements. For high-level industrial applications, polyacrylates are preferred on account of their transparency and weathering stability. In addition to these advantages, however, these acrylic PSAs must also meet stringent requirements in respect of shear strength and bond strength. This profile of requirements is met by polyacrylates of high molecular weight and high polarity, with subsequent efficient crosslinking. These high shear strength, polar PSAs, however, possess the disadvantage that they are not well suited to the hotmelt extrusion operation, because high application temperatures are necessary and because, furthermore, shearing within the extruder lowers the molecular weight of the polymer. This damage significantly reduces the level of the adhesive properties. The bond strength and the tack are generally low, since owing to the polar fractions in the adhesives the glass transition temperature is relatively high. The shear strengths of the hotmelt-coated acrylic PSAs, in particular, fall distinctly in comparison to the original, solvent-coated PSA. At the present time, therefore, different concepts aimed at reducing the flow viscosity and thereby facilitating extrusion coating of these PSAs are being investigated.
The industry is pursuing a variety of concepts for achieving this objective. One possibility is the highly efficient crosslinking of a low viscosity, apolar acrylic adhesive not until it is on the backing. Acrylates containing electron donating groups are copolymerized and, during crosslinking by UV or EBC (EBC: electron beam curing), they stabilize free radicals that are formed. Examples thereof are tertiary amine monomers [WO 96/35725], tertiary butylacrylamide monomer [U.S. Pat. No. 5,194,455], and tetrahydrofuryl acrylates [EP 0 343 467 B1]. A further efficient crosslinking concept is the copolymerization of UV photoinitiators into the polyacrylate chain. For example, benzoin acrylate has been used as a comonomer and the crosslinking has been conducted on the backing using UV light [DE 27 43 979 A1]. In U.S. Pat. No. 5,073,611, on the other hand, benzophenone and acetophenone are used as copolymerizable monomers.
Test Methods
The following test methods were employed for evaluating the technical adhesive properties of the PSAs prepared. For testing, films made of polyethylene glycol terephthalate (Examples 1 to 6) or siliconized release papers (Examples 7 to 12) were coated with adhesive at a rate of 50 g/m2.
Shear Strength (Test A1, A2, A3)