Ruban adhésif

The invention describes a self-adhesive tape which is adhesive on both sides and which on the one hand can perform gap-bridging sealing functions and on the other hand achieves adhesive strengths which are typical for commercially available high-performance adhesive tapes. The product is suitable for both cold and heat-resistant bonds.

In order to achieve high strengths against peeling and shear forces, the use of different adhesive tapes is known.

DE-PS 2105877 shows an adhesive tape which consists of a carrier which is coated on at least one side with a microcellular, pressure-sensitive adhesive and the adhesive layer of which contains a nucleating agent, the cells of the adhesive layer being closed and completely distributed in the adhesive layer . This adhesive tape can adapt to the irregular surface to which it is applied and thus lead to a relatively permanent bond, but on the other hand shows only a relatively small recovery when it has been compressed to half its original thickness. The cavities in the adhesive, however, offer approaches for lateral entry of solvents and water into the adhesive joint, which is very undesirable, for example, in the case of glued-on strips in automobile construction. Furthermore, the complete passage of solvents or water through the entire adhesive tape cannot be excluded.

EP 601 582 A describes an adhesive tape which consists of a foamed elastomer core to which a pressure-sensitive adhesive layer has been applied.

Here, too, there are the disadvantages caused by the principle of the cavities that the adhesive tape core can absorb moisture or solvents like a sponge. This can weaken the bond strength. Furthermore, due to the principle of the foamed elastomer core, restoring forces occur in the bonds, which can lead to premature failure of the bonds.

The adhesive tapes mentioned have in common that the absorbable shear forces which act on the bonded connection are inadequate for many applications in order to ensure a permanent connection between the substrate and the object to be mounted by means of the adhesive tape. Thus, in particular at lower temperatures, the use of such adhesive tapes is only possible to a very limited extent because embrittlement of the carrier occurs at low temperatures, so that the adhesive tape is no longer able to maintain the desired bond.

In addition, the adhesive tapes mentioned are unable to bridge and seal gap widths of more than 0.5 cm. Adhesive tapes that are capable of this, for example butyl tapes, have only very low strengths against shear and tilt shear stresses, in particular at elevated temperatures.

A laminate made of a polyurethane and a pressure-sensitive adhesive layer is also known. Such a laminate is disclosed, for example, in WO 86/00536, a description of a tablet packaging or dosage form. A polyester film that has not been further processed is provided with a self-adhesive coating which surrounds a tablet and is simultaneously glued to the tablet on the skin of the user.

From US 5,127,974 a film for the temporary protection of the painted surfaces of automobiles is known, which also suggests the use of polyurethane for the production of the carrier film. A pressure-sensitive adhesive is then applied to the carrier film. This laminate of film and adhesive is applied to the painted surface after removal of a layer protecting the adhesive.

A self-adhesive tape that is adhesive on both sides, based on a polyurethane carrier as described above and a pressure-sensitive adhesive layer laminated on both sides, is not described in the cited documents, but would also have the disadvantage of elastic restoring forces of the carrier, which cannot be absorbed and therefore weaken the bond strength would lead.

The invention has for its object to provide a self-adhesive tape that does not have the disadvantages of the prior art, or at least not to the extent and yet is not limited in its usability similar to the aforementioned products.

To achieve this object, the invention proposes a pressure-sensitive self-adhesive tape coated on both sides with adhesive, the backing of which is formed from a formulated, crosslinked, non-foamed polyurethane.

Formulation components of the carrier are a crosslinked, non-foamed polyurethane, fillers and, if appropriate, further auxiliaries. The proportion of polyurethane in the carrier is up to 50% by weight, preferably 30% by weight to 40% by weight, the polyurethane being free from plasticizers. The fillers make up 50% to 70% by weight of the carrier.

The selection of the isocyanate component of the polyurethane is based on the properties of the carrier to be specifically set. For example, tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, mixtures of the isocyanates mentioned or chemically derived isocyanates, for example dimerized or trimerized types. The selection of the component reacting with the isocyanate also depends on the properties of the carrier to be set depending on the desired profile of requirements. For example, all polyester diols, triols and polyols, polyether diols, triols and polyols, polyether diamines, triamines, polyamines, hydroxyl-functionalized polybutadiene and all monohydric alcohols (mono-ols), monohydric amines (mono-amines) , Polyether-mono-ole, Polyether-mono-amine or products derived from the last four groups.

It has proven to be advantageous if the hydroxyl-functionalized polybutadienes, the polyester diols, the polyester triols, the polyester polyols, the polyether diols, the polyether triols, the polyether polyols, the polyether diamines, the polyether triamines or the polyether polyamines have a molecular weight M._G ≥ 1000 g / mol.

In addition to the isocyanate components listed above and the components reacting therewith, other starting materials can also be used to form the polyurethane without departing from the inventive concept.

In order to accelerate the reaction between the isocyanate component and the component reacting with the isocyanate, all catalysts known to the person skilled in the art, such as, for example, tertiary amines or organotin compounds, can be used.

Polyurethanes as described above are state of the art in production and are described, for example, in "Ullmann's Encyclopedia of Industrial Chemistry, Vol. A21: Polyurethanes".

The formulation of polyurethane compositions is also state of the art and is used particularly in the production of sealants (cf. "Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 23: Sealing Materials").

In a particularly preferred embodiment of the self-adhesive tape, an NCO / OH ratio of 1.0 to 1.3, preferably 1.0 to 1.1, is set to form the polyurethane.

The preferred mono-ol-OH portion of the total OH portion, ie the preferred chain termination portion, is between 5% and 40%, in particular between 10% and 30%.

Both reinforcing materials such as carbon black and non-reinforcing materials such as chalk or barium sulfate can be used as fillers. Further examples are talc, mica, pyrogenic silicic acid, silicates, zinc oxide, micro full glass balls, micro hollow glass balls and / or micro plastic balls of all kinds. Mixtures of the substances mentioned can also be used.

To increase the aging stability of the adhesive tape, this can be done using conventional anti-aging agents, which, depending on the application, can come from the class of discoloring or non-discoloring anti-aging agents, in the range between 0% by weight and 5% by weight, and known light stabilizers in the range between 0% by weight and 5% by weight or ozone protection agents in the range between 0% by weight and 5% by weight are mixed. In order to achieve freedom from bubbles, drying agents, such as calcium oxide or molecular sieve zeolites, can also be added to the formulation, in particular in the range between 0% by weight and 10% by weight.

Depending on the intended use of the self-adhesive tape, all of the auxiliaries mentioned can be used either alone or in any combination with one another to produce the polyurethane composition in order to obtain an optimal match to the use. Through the use of these additives, black coloring, as is required in particular by the motor vehicle industry, is also possible without problems.

The carrier mixture is preferably prepared in a planetary mixer or dissolver. In order to achieve freedom from bubbles, work is carried out in vacuum mode. The viscosity of the mixture is adjusted so that it is in the range between 10^-1 and 10³ Pa * s lies. Solvent-free processing is preferably carried out.

The mixture can then be spread on commercial coating machines in any thickness between 0.1 mm and 50 mm, preferably between 0.4 mm and 20 mm.

The chemical crosslinking then takes place in the drying tunnel, preferably at temperatures from room temperature to 120 ° C., depending on the polyurethane formulation selected and the amount of catalyst.

Depending on the application, the application weight of the adhesive is also arbitrary within the range of 10 g / m² up to 250 g / m², preferably 40 g / m² up to 150 g / m², selectable.

Generally known rubber or acrylate-based adhesives can be used as adhesives.

Known adhesion promoters or additional layers of lacquer can be used to increase the anchoring of the adhesive on the carrier. The paint preferably comes from the group of polyamide, epoxy, phenol, urea-formaldehyde, melamine-formaldehyde or polyurethane resins. Alternatively, a corona pretreatment can also be carried out. In order to achieve particularly firm anchoring, a combination of the methods listed is also possible.

The adhesive can be applied directly, in the indirect transfer process or by coextrusion with the carrier from the solution, dispersion or melt. This is a particularly preferred form of order<img file="EP0894841A2_D0001.tif" />inverse "application process. In this process, the dried and crosslinked adhesive, which has been spread out on release paper or release film, is placed and coated with the not yet hardened, pasty or liquid polyurethane composition with the aid of the two-component mixing technique in the desired layer thickness. Before curing or Crosslinking of the polyurethane mass is a second adhesive, which is also already spread, dried and crosslinked on release paper or release film, laminated against the spread polyurethane mass. Subsequently, the curing or crosslinking of the polyurethane mass takes place in a dry channel run at a temperature between room temperature and 120 ° C., depending on the polyurethane formulation selected and the amount of catalyst.

A self-adhesive tape as described above, consisting essentially of a laminate of a polyurethane composition formulated according to the invention and a pressure-sensitive adhesive layer and characterized by a three-layer structure of adhesive layer / formulated polyurethane composition / adhesive layer, is not described in the prior art.

The formulation with fillers leads to the excellent product properties described above. The fillers take some of the elastic restoring force from the polyurethane backing and thus contribute to the permanent bond strength of the bonds.

The self-adhesive tape shows excellent properties that could not have been predicted in this way even by a person skilled in the art. Due to the high flexibility of the carrier, the adhesive tape adapts very well to uneven surfaces when it is pressed onto it with a certain pressure. This creates a very permanent connection between the adhesive tape and the substrate, which does not fail even with high shear forces that act on the self-adhesive tape. Because of the lack of laterally open cavities in the carrier, the possible penetration of solvents or water into the adhesive tape with all its known disadvantages is prevented. Since the adhesive tape according to the invention can be produced in thicknesses of 2 cm and more, it can also be used as a self-adhesive, gap-bridging sealing tape.

Due to the very low glass point of the adhesive tape, low-temperature applications down to - 40 ° C are possible, because the otherwise observed embrittlement of known adhesive tapes does not occur, so that optimal adhesion of the adhesive tape is guaranteed even at these extreme temperatures.

The good heat and aging stability of the adhesive tape, caused by the non-foamed backing consistency, which prevents moisture and atmospheric oxygen from penetrating, also enables use at higher temperatures from 70 ° C to 100 ° C.

Cold and heat loads are required, for example, when gluing trim strips or mirrors in automobile construction because the vehicles are sometimes driven in very cold zones or very warm regions of the world with high levels of solar radiation.

In addition to the automotive industry, the invention is also used in the furniture and construction industries, where mirrors, strips or panels are also to be permanently anchored to the substrate.

Because of the excellent product properties, the use of the invention is not limited to the examples mentioned. Rather, the use of the adhesive tape as mounting material is possible in many industrial areas if it is important to create a secure connection between two parts of different materials on a relatively uneven surface.

In the following, the invention will be explained in more detail by means of exemplary embodiments, without wishing to restrict the invention unnecessarily.

Examples

Table 1 lists the materials used to manufacture the carrier, each with its trade name and manufacturer. The chemicals mentioned are all freely available on the market. The raw materials are used in different mixing ratios depending on the application of the self-adhesive tape.<tables id="tabl0001" num="0001"><img file="EP0894841A2_D0002.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0894841A2_D0003.tif" /></tables>

In the following, 11 recipes for the production of carriers according to the invention are presented in the form of a table. The materials used are always prepared in the way described below.<tables id="tabl0003" num="0003"><img file="EP0894841A2_D0004.tif" /></tables><tables id="tabl0004" num="0004"><img file="EP0894841A2_D0005.tif" /></tables><tables id="tabl0005" num="0005"><img file="EP0894841A2_D0006.tif" /></tables><tables id="tabl0006" num="0006"><img file="EP0894841A2_D0007.tif" /></tables>

The components in the examples mentioned are mixed with one another in a commercially available planetary mixer or dissolver for two hours, with the exception of the isocyanate, which is added only immediately before coating using a commercially available two-component mixing technique. In order to obtain a bubble-free product, the mixture is degassed during the last 10 minutes of the mixing process by applying a vacuum of less than 15 torr. In each case, a structurally viscous paste that can be processed at room temperature is obtained in the viscosity range from 1 Pa * s to 300 Pa * s.

After the isocyanate has been metered in, the pastes are spread onto a commercially available coating system on commercially available paper that has been siliconized on both sides to form a web of 1 mm thickness and then pass through an drying channel at a temperature of from room temperature to 120 ° C. and a residence time of 10 minutes to 30 minutes to form an elastomer networked. After curing and subsequent storage for one week at room temperature, the supports have a Shore A hardness of 10 to 60, a glass transition temperature in the range from -60 ° C to -30 ° C and a tensile strength of greater than 1 N / mm² with an elongation at break of less than 500%.

Then the material is applied in two steps on both sides with 50 g / m each² the polyacrylate composition Durotac 280-1753 from National Starch. The coating with the solvent mass takes place after an in-line corona treatment directly on the carrier. It is dried and crosslinked at 100 ° C. The double-sided adhesive tape thus obtained is covered on one side with release paper.

In a particularly preferred production process, the polyacrylate composition is first spread on release paper or release film and dried and crosslinked at 100 ° C. The polyurethane mixture is coated directly onto the coated polyacrylate compound. Before hardening or Crosslinking the polyurethane mass, a second polyacrylate mass, which has also already been spread out, dried and crosslinked on release paper or release film, is laminated against the polyurethane mass. Subsequently, the curing or crosslinking of the polyurethane mass takes place in a dry channel run at a temperature between room temperature and 120 ° C., depending on the polyurethane formulation selected and the amount of catalyst.

The double-sided adhesive tape is characterized by high adhesive strength and high shear strength at the same time, and the bonds produced with it have excellent cold impact resistance. The material seals well against moisture.