EP2398838A1

EP2398838A1 - Pressure-sensitive adhesive mass

Info

Publication number: EP2398838A1
Application number: EP10702873A
Authority: EP
Inventors: Kirstin Weiland; Uwe Schümann; Daniel Klier; Marc Husemann
Original assignee: Tesa SE
Current assignee: Tesa SE
Priority date: 2009-02-20
Filing date: 2010-02-05
Publication date: 2011-12-28
Also published as: CN102348734A; TW201031727A; DE102009009757A1; JP2012518694A; WO2010094585A1; US20110319560A1; KR20110134412A

Abstract

The present invention relates to a pressure-sensitive adhesive mass based on polyurethane, wherein the polyurethane is composed of the following starting materials in the specified proportions, said starting materials being reacted catalytically with each other: a) at least one aliphatic or alicyclic polyisocyanate, wherein the functionality thereof is less than or equal to 3 in each case; b) a combination of at least one polypropylene glycol diol and at least one polypropylene glycol triol, wherein the ratio of the number of hydroxyl groups of the diol component to the number of hydroxyl groups of the triol component is less than 10, wherein the ratio of the number of isocyanate groups to the total number of hydroxyl groups is between 0.65 and 1.2, and wherein the diols and triols are selected and combined alternatively as follows in each case: - diols having a molecular weight of less than or equal to 1000 are combined with triols having a molecular weight greater than or equal to 1000, - diols having a molecular weight of greater than 1000 are combined with triols having a molecular weight less than 1000; c) at least one light stabilizer based on an aromatically substituted triazine having a proportion of 0.2 - 2 wt % and at least one amine-hindered light stabilizer having a proportion of 0.2 - 2 wt %; d) at least one antioxidant based on a sterically hindered phenol having a proportion of 0.2 - 2 wt %; e) a carbodiimide having a proportion of 0.25 - 2.5 wt %.

Description

tesa Aktiengesellschaft Hamburg

description

PSA

The present invention relates to a pressure-sensitive adhesive, in particular for bonding optical components, according to claim 1.

Pressure-sensitive adhesives are used very widely today. For example, there are a wide variety of applications in the industrial sector. Adhesive tapes based on pressure-sensitive adhesives are used in the electronics sector or in the consumer electronics sector. Due to the high number of pieces of pressure-sensitive adhesive tapes can be processed very quickly and easily, so that other processes, such. Riveting or welding, too expensive. In addition to the normal connection function, these pressure-sensitive adhesive tapes may also have to take on additional functions. So this can be e.g. be a thermal conductivity, an electrical conductivity or an optical function. In the latter case, e.g. Pressure-sensitive adhesive tapes are used, which have light-absorbing or light-reflecting functions. Another optical function is, for example, a suitable light transmission. Here are pressure-sensitive adhesive tapes and PSAs are used, which are very transparent, have no intrinsic color and also have high light stability.

In many cases, a pressure sensitive adhesive for optical purposes in addition to the connection function has the function of excluding air, since air has a refractive index of 1 and the optical films or glasses have a generally much higher refractive index. The difference in the refractive indices leads to a reflection during the transition from air to the optical component, which reduces the transmission. One way to solve this problem is to use antireflective coatings, which facilitate the passage of light into the optical component and reduce the reflection. Alternatively or additionally, it is also possible to use an optical pressure-sensitive adhesive which has a similar refractive index as the optical component. As a result, the reflection on the optical component is significantly minimized and the transmission increased. A typical application is, for example, the bonding of touch panels on the LCD or OLED display (indium tin oxide) for capacitive touch panels. Further typical applications are the use as single-sided pressure-sensitive adhesive tape for reinforcing glass as splinter protection, the bonding of ITO films (indium tin oxide) for capacitive touch panels or surface protection films for optical films, such as, for example, polarizer films.

As a rule, optical components, such as films or glasses, have a relatively high refractive index, so that pressure-sensitive adhesives are required which likewise have a high refractive index. This is how most of them are visually bonded

Substrates have a refractive index of 1, 45 - 1, 70 on. Another requirement is the neutrality of the PSA formulation. So should the PSA no

Contain acidic functions, e.g. Contact with ITO films may negatively affect the electrical conductivity over a longer period of time. Another

Requirement is UV stability. Thus, e.g. for outdoor applications also used optical PSAs, but exposed to UV light.

For transparent bonds, a large number of acrylate PSAs are known which are used in the optical range and have very different refractive indices. No. 6,703,463 describes acrylic PSAs which have a refractive index below 1.40. This is achieved by fluorinated acrylate monomers. The refractive index is thus significantly below the desired range. JP 2002-363523 A describes acrylate PSAs having a refractive index between 1.40 and 1.46. Again, fluorinated acrylate monomers are used. Also, this refractive index is well below the desired range. Also commercially available are various acrylic pressure-sensitive tapes, e.g. 3M 8141. These conventional acrylate PSAs are in a refractive index range of 1.47 to 1.48.

US 2002/0098352 A1 describes acrylic PSAs with aromatic comonomers which have a refractive index of 1.49-1.60. This is within the desired range, but there are also disadvantages associated with the aromatics. This allows them to absorb UV light in the short-wave range, which negatively influences the transmission stability and the tendency to yellowing. EP 1 652 889 A1 describes PSA compositions based on polydiorganosiloxanes for optical applications. Silicone compounds generally have a low refractive index, so that these adhesives are not optimally suited for optical applications.

Furthermore, PSAs are known as pressure-sensitive adhesives. Based on polyurethane, hydroxyl-bearing double-bond-containing polyol components are used. Polyurethane pressure-sensitive adhesives based thereon are listed, for example, in JP 02003476 A, WO 98/30648 A1, JP 59230076 A, JP 2001-146577 A, US Pat. No. 3,879,248 A, US Pat. No. 3,743,616 A, US Pat. Nos. 3,743,617, 5,486,570 and 3,515,773 , A disadvantage is the oxidative sensitivity of these pressure-sensitive adhesives, caused by the double bonds in the polymer main chain. This leads after some time to a laking and / or yellowing and / or blunting the pressure sensitive surface.

DE 21 39 640 A describes a pressure-sensitive adhesive based on an aromatic diisocyanate urethane. A disadvantage of this pressure-sensitive adhesive is, above all, the tendency to yellow which is typical of aromatic polyurethanes.

Thus, there is still a need for an improved pressure-sensitive adhesive which does not have the aforementioned disadvantages and is thus particularly suitable for optical applications. In particular, a suitable adhesive should have a high optical transparency and a high UV stability.

The present invention solves the problem described above by a pressure-sensitive adhesive according to claim 1. Preferred embodiments and further developments are the subject of the subclaims.

Accordingly, the invention relates to a pressure-sensitive adhesive based on polyurethane, in which the polyurethane is composed of the following catalytically reacted starting materials in the ratios indicated: a) at least one aliphatic or alicyclic polyisocyanate, the functionality of which is in each case less than or equal to 3 b) a combination of at least one polypropylene glycol diol and at least one polypropylene glycol triol, wherein the ratio of the number of hydroxyl groups of the diol component to the number of hydroxyl groups of the triol component is less than 10, preferably between 0.2 and 5, wherein the ratio of the number of isocyanate groups to the total number of hydroxyl groups is between 0.65 and 1, 2, preferably between 0.95 and 1, 05, more preferably between 1, 0 and 1, 05, and wherein the diols and triols are each alternatively selected and combined as follows:

Diols having a molecular weight of less than or equal to 1000 are combined with triols whose molecular weight is greater than or equal to 1000, preferably greater than or equal to 3000,

Diols with a molecular weight greater than 1000 are combined with triols whose molecular weight is less than 1000. c) at least one light stabilizer based on an aromatically substituted triazine in a proportion of 0.2-2% by weight and at least one amine-hindered light stabilizer with a Proportion of 0.2-2% by weight d) of at least one aging inhibitor based on a sterically hindered phenol with a proportion of 0.2-2% by weight e) a carbodiimide with a proportion of 0.25-2.5 wt .-%

The PSA thus has in particular no aromatic comonomers, yet a high refractive index, in particular greater than 1, 48 is adjustable.

The light transmission of such a PSA formulation is in particular greater than 86% and the haze at less than 5% according to ASTM D 1003. Thus, the

Pressure-sensitive adhesive, in particular suitable for bonding in the optically transparent region. The PSA is characterized by a high refractive index, high transmission and high UV stability. The PSA is preferably used for bonding optical components in consumer electronics goods.

When designing and designing optical components, such as glass windows and foils, the interaction of the materials used with the type of incident light must be taken into account. In a derived version, the energy conservation law takes the form T (λ) + p (λ) + a (λ) = 1 where T (λ) describes the proportion of the transmitted light, p (λ) the proportion of the reflected light and a (λ) the proportion of the absorbed light (λ: wavelength) and wherein the total intensity of the incident light is normalized to 1. Depending on the application of the optical component, it is important to optimize one of these three terms and suppress the other. Optical components designed for transmission should be characterized by values of T (λ) close to unity. This is achieved by reducing p (λ) and a (λ) in magnitude.

Polyurethane-based pressure-sensitive adhesives normally have no appreciable absorption in the visible range, ie in the wavelength range between 400 nm and 700 nm. This can be easily checked by measurements with a UV-Vis spectrophotometer. Of crucial interest is therefore p (λ). Reflection is an interface phenomenon that depends on the refractive indices n _dl of two contacting phases i and is described by the Fresnel equation:

nd 2 - ⁿ d 1 p (λ) = n _{d 2} + n _{d 1}

In the case of isorefractive materials, for which n _{d 2} = n _d i, p (λ) = 0. This explains the necessity to adapt the refractive index of a PSA to be used for optical components to those of the materials to be bonded. Typical values for various such materials are listed in Table 1.

(Source Pedrotti, Pedrotti, Bausch, Schmidt, Optics, 1996, Prentice-Hall, Munich Data at X = 588 nm)

In order to produce polyurethanes with sufficient light stability and high light transmission, it is known that aliphatic or alicyclic polyisocyanates or polyisocyanates with not aromatically bound isocyanate groups be used. Surprisingly, it has been found that aliphatic or alicyclic polyisocyanates are suitable in order to also produce the other desired property profile of the polyurethane PSA in accordance with the requirements of optical applications. Thus, the surface-specific selectivity of the pressure-sensitive adhesive properties can be adjusted by using aliphatic or alicyclic polyisocyanates, but also pressure-sensitive adhesives having high transparency.

In contrast to the aliphatic or alicyclic polyisocyanates, the use of aromatic polyisocyanates leads to discoloration and disadvantageous adhesive properties.

In an advantageous embodiment, aliphatic or alicyclic diisocyanates are used as the polyisocyanates. These form a better network and thus enable an optimization of the adhesive properties in terms of cohesion and reversibility.

Particularly advantageous is the use of aliphatic or alicyclic diisocyanates each having asymmetrical molecular structure, in which therefore the two isocyanate groups each have a different reactivity. In particular, the otherwise typical tendency for tacky polyurethanes to "greasy" is significantly reduced by the use of aliphatic or alicyclic diisocyanates with unsymmetrical molecular structure Unsymmetrical molecular structure means that the molecule has no symmetry elements (for example, mirror planes, symmetry axes, symmetry centers), that is, no symmetry operation can be carried out, which generates a congruent with the starting molecule molecule.

Further examples of the pressure-sensitive adhesive of suitable polyisocyanates are: butane-1,4-diisocyanate, tetramethoxybutane-1,4-diisocyanate, hexane-1,6-diisocyanate,

Ethylene diisocyanate, 2,2,4-trimethyl-hexamethylene diisocyanate, ethylethylene diisocyanate, dicyclohexylmethane diisocyanate, 1,4-diisocyanatocyclohexane, 1, 3

Diisocyanatocyclohexane, 1, 2-diisocyanatocyclohexane, 1, 3-diisocyanatocyclopentane, 1, 2-diisocyanatocyclopentane, 1, 2-diisocyanatocyclobutane, i-isocyanatomethyl-3-isocyanato-1, 5,5-trimethylcyclohexane (isophorone diisocyanate), 1-methyl-2 , 4-diisocyanato-cyclohexane, 1, 6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane, 5-isocyanato-1 - (2-isocyanatoeth-1-yl) -1, 3,3-trimethyl-cyclohexane, 5-isocyanato-1 - (3 isocyanatoprop-1-yl) -1,3,3-trimethylcyclohexane, 5-isocyanato-1 - (4-isocyanatobut-1-yl) -1,3,3-trimethylcyclohexane, 1-isocyanato-2- ( 3-isocyanatoprop-1-yl) cyclohexane, 1-isocyanato-2- (2-isocyanatoeth-1-yl) cyclohexane, 2-heptyl-3,4-bis (9-isocyanatonyl) -1-pentylcyclohexane, Norbonandiisocyanatomethyl, chlorinated, brominated, sulfur or phosphorus-containing aliphatic or alicyclic diisocyanates, and derivatives of the diisocyanates listed, in particular dimerized or trimerized types.

In a particularly preferred embodiment, isophorone diisocyanate is used.

With regard to the material and quantitative composition of the reactants reacted with the polyisocyanate, aliphatic diols are preferably used. A combination of at least one polypropylene glycol diol and at least one polypropylene glycol triol is used to produce high bond strength, high transmission polyurethanes.

As polypropylene glycols, it is possible to use all commercial polyethers based on propylene oxide and a difunctional initiator in the case of the diols and of a trifunctional starter in the case of the triols. These include both the conventional, that is usually prepared with a basic catalyst such as potassium hydroxide, polypropylene glycols, as well as the particularly pure polypropylene glycols, the DMC (double metal cyanide) catalyzed produced, and their preparation, for example, in US 5,712,216 A, US 5,693,584 A, WO 99/56874 A1, WO 99/51661 A1, WO 99/59719 A1, WO 99/64152 A1, US 5,952,261 A, WO 99/64493 A1 and WO 99/51657 A1.

It is characteristic of the DMC-catalyzed polypropylene glycols that the "nominal" or theoretical functionality of exactly 2 in the case of the diols or of exactly 3 in the case of the triols is indeed approximately achieved slightly lower than the theoretical one, especially for higher molecular weight polypropylene glycols. The cause is a rearrangement side reaction of propylene oxide to allyl alcohol.

Furthermore, it is also possible to use all the polypropylene glycol diols or triols in which ethylene oxide is copolymerized in, which is commercially available Polypropylene glycols is the case to achieve an increased reactivity towards isocyanates.

By varying the ratio of the number of hydroxyl groups of the diol to that of the triol within the set limits, the bond strength can be influenced and adjusted in accordance with the application. Surprisingly, it was found that the

Adhesive strength increases, the higher the ratio of the number of diol-OH groups to the

Triol-OH groups is. The bond strength range, which can be adjusted within the specified limits, is approximately in the range of 1.0 to 15.0 N / cm measured on steel according to PSTC-1 (see description of test methods) and in

Dependence on the pressure-sensitive adhesive application.

Particularly advantageous is the use of a bismutcarboxylat- or bismutcarboxylatderivathaltigen catalyst or catalyst mixture, whose use for accelerating polyurethane reactions is known. Such a catalyst substantially controls the pressure-sensitive adhesive properties of the polyurethane in such a way that a surface-specific selectivity of the pressure-sensitive adhesive properties is achieved. Examples of bismuth carboxylates are bismuth trisdodecanoate, bismuth trisdecanoate, bismuth trisneodecanoate, bismuth trisoctanoate, bismuth trisisooctanoate, bismuth trishexanoate, bismuth trispentanoate, bismuth trisbutanoate, bismuth trispropanoate or bismuth trisacetate.

However, it is also possible to use all other catalysts known to the person skilled in the art, such as, for example, tertiary amines or organotin compounds.

In one possible embodiment, the polyurethane-based PSA contains further formulation constituents such as, for example, additional catalysts or rheological additives.

Examples of rheological additives are fumed silicas, phyllosilicates (for example bentonites), high molecular weight polyamide powders or castor oil derivative powders. When choosing the rheological additives, care must be taken that they are chosen so that they do not adversely affect the transmission of the PSA. This is achieved by having these additives on the order of magnitude (spatial extent) which is in the range of the wavelength of visible light (400-800 nm) or less. When selecting these additives, care must also be taken to ensure that these substances have no tendency to migrate towards the substrate to be bonded so that staining does not occur in this way. For the same reason, the concentration of these substances, in particular the liquid, is to be kept as low as possible in the overall composition. The additional use of plasticizers or tackifier resins should therefore be avoided if possible - in individual cases, however, their use may still be useful.

In order to further accelerate the reaction between the isocyanate component and the isocyanate-reactive component, it is additionally possible to use all the catalysts known to the person skilled in the art, such as, for example, tertiary amines or organotin compounds.

The light stabilizers c) are selected from the group of substituted triazines. The triazines are chosen so that they have a good compatibility with the polyurethanes. This is e.g. achieved by substituents. Thus, preferred embodiments of the triazines have at least one aromatic substituent, more preferably at least 2 aromatic substituents, and most preferably 3 aromatic substituents. These aromatics themselves may in turn be substituted with at least one aliphatic substituent. In the simplest form, this may be a methyl group. But there are also other substituents possible, such as hydroxyl groups, ether groups, aliphatic chains having 2 to 20 C atoms, which are linear, branched or cyclic and in turn may contain one to 5 oxygen atoms in the form of ether groups, hydroxy groups, ester groups, carbonate groups. Examples of commercial nature sunscreens are available from Ciba under the trade name Tinuvin®. Thus, e.g. Tinuvin® 400, Tinuvin® 405, Tinuvin® 479 and Tinuvin® 477 suitable light stabilizers that can be used.

Other light stabilizers used are hindered amines. Particular preference is given to using substituted N-methylpiperidine derivatives. These are sterically hindered, for example in position 1 and 5, by aliphatic groups, such as methyl groups. More preferably, four methyl groups are used for steric hindrance. To achieve good solubility with the polyurethane, as well as to increase the evaporation temperature, become long aliphatic substituents used. The substituents may be linear, cyclic or branched, contain up to 20 carbon atoms, contain up to 8 O atoms, which are for example in the form of ester groups, ether groups, carbonate groups or hydroxyl groups. For the effect compounds with only one N-methylpiperidine can be used. But there are also known dimeric N-methylpiperidine derivatives which have a sunscreen function. These can also be combined with the monomeric compounds.

As anti-aging agent d) sterically hindered phenols are used. Sterically hindered phenols have in a preferred embodiment in both ortho positions to the hydroxy group tert-butyl groups. In order to achieve a good solubility and a high evaporation temperature, the sterically hindered phenols should be additionally substituted. The substituents may be linear, cyclic or branched, contain up to 20 C atoms, contain up to 8 O atoms, e.g. in the form of ester groups, ether groups, carbonate groups or hydroxy groups. Commercially available compounds are e.g. Irganox® 1 135 or Irganox® 1330 from Ciba.

As a further component carbodiimides are added to the polyurethanes. When selecting the carbodiimides, attention must again be paid to the compatibility with the polyurethanes and the boiling or evaporation temperature. Thus, numerous carbodiimides, such as dicyclohexylcarbodiimide (boiling point 122 ° C) or N ₁ N-diisopropylcarbodiimide (boiling point 148 ° C) are not suitable because they have too high a vapor pressure. For example, 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride is preferably used, which has a melting point of about 110 ° C. Furthermore, however, polymeric carbodiimides are also known, as are commercially available, for example, from Rheinhausen as Stabaxol® P 200.

Furthermore, further anti-aging agents can be added. The combination of substituted phenols which have been substituted at least twice and which carry at least one sulfur atom in both substituents and also aromatically substituted phosphites has proven to be particularly advantageous. Commercial examples of S-containing hindered phenols are Irganox® 1520 or Irganox® 1726 from Ciba. Commercial examples of aromatically substituted phosphites are Irgafos® 168, Irgafos® 126, Irgafos® 38, Irgafos® P-EPQ or Irgafos® 12 from Ciba. method

The pressure-sensitive adhesive is produced continuously in a preferred embodiment by the process described below:

Essentially, the premixed polyaliphatic glycol combination (polyol component) and, in a container B, essentially the isocyanate component are initially introduced in a container A, with the other formulation constituents optionally having been previously admixed to these components in a customary mixing process. The polyol and the isocyanate component are conveyed by precision pumps through the mixing head or the mixing tube of a multi-component mixing and dosing, where homogeneously mixed and reacted. The mixed, chemically reactive components are applied immediately thereafter to a web-shaped carrier material, which preferably moves at a constant speed. The type of carrier material depends on the article to be produced. The coated with the reactive polyurethane composition carrier material is passed through a heat channel in which the polyurethane composition cures to PSA. The application weight of the polyurethane compound is freely selectable. It depends on the article to be produced. The coated carrier material is finally wound up in a winding station.

The process described makes it possible to work solvent and water-free. The solvent and water-free working is the preferred method, but not mandatory. For example, to achieve very low application weights, the components can be diluted appropriately.

In order to improve the anchoring of the polyurethane composition on the web-shaped carrier materials, it is possible to use all known methods of surface pretreatment, such as, for example, corona pretreatment, flame treatment, gas phase treatment (for example fluorination). Likewise, all known methods of primer can be used, wherein the primer layer can be applied both from solutions or dispersions on the carrier material as well as in the extrusion or coextrusion process. In order to improve the unwinding properties of the wound roll, the back side of the sheet material may be precoated with a release varnish or may carry a separating coextruded or extruded backsize coating.

Further details, objects, features and advantages of the present invention will be explained in more detail below with reference to preferred embodiments. In the drawing shows

1 a single-sided pressure-sensitive adhesive tape, FIG. 2 a pressure-sensitive adhesive tape on both sides, FIG.

3 shows a carrier-free pressure-sensitive adhesive tape (transfer adhesive tape).

1 shows a single-sided adhesive pressure-sensitive adhesive tape 1 for use in the bonding of optical components, in particular of optical films. The pressure-sensitive adhesive tape 1 has an adhesive layer 2 which has been produced by coating one of the previously described pressure-sensitive adhesive onto a carrier 3. The PSA coating is preferably between 5 and 250 g / m ² . The pressure-sensitive adhesive has a transmittance of at least 86%, especially in the visible range of light, making it particularly suitable for optical use.

For use in the bonding of optical components, a transparent carrier 2 is also used as carrier 2. The carrier 2 is thus also transparent in the visible light range, and therefore preferably has a transmittance of at least 86%.

In addition (not shown) may still be provided a release film, which covers the adhesive layer 2 before using the pressure-sensitive adhesive tape 1 and protects. The release film is then removed from the adhesive layer 2 prior to use.

The transparent PSA may preferably be protected with a release film. Furthermore, it is possible that the carrier film is provided with one or more coatings.

The product structure shown in FIG. 2 shows a pressure-sensitive adhesive tape 1 with a transparent carrier 3, which is coated on both sides with a pressure-sensitive adhesive and thus has two adhesive layers 2. The PSA per side is again preferably between 5 and 250 g / m ² .

Also in this embodiment, at least one adhesive layer 2 is preferably covered with a release film. If the adhesive tape is rolled up, it can also cover the second adhesive layer 2 if necessary. But it can also be provided more separation films.

Furthermore, it is possible that the carrier film is provided with one or more coatings. Furthermore, only one side of the pressure-sensitive adhesive tape may be provided with the inventive PSA and on the other side another transparent PSA may be used.

The product structure shown in Fig. 3 shows a pressure-sensitive adhesive tape 1 in the form of a transfer adhesive tape, i. a carrier-free pressure-sensitive adhesive tape 1. For this purpose, the

Pressure-sensitive adhesive is coated on one side on a release film 4 and thus forms a

Pressure-sensitive adhesive layer 2 off. The pressure-sensitive adhesive coating is usually between

5 and 250 g / m ² . Possibly. This pressure-sensitive adhesive layer 2 is still covered on its second side with a further release film. To use the pressure sensitive adhesive tape, the release liners are then removed.

As an alternative to release films, for example, release papers or the like. Can be used. In this case, however, the surface roughness of the release paper should be reduced in order to realize the smoothest possible PSA side.

carrier films

As a carrier films, a variety of highly transparent polymer films can be used. In particular, special high-transparency PET films can be used. For example, films from Mitsubishi with the trade name Hostaphan ™ or the company Toray with the trade name Lumirror ™ are suitable. The Haze value, a measure of the haze of a substance, should in a preferred design have a value of less than 5% according to ASTM D 1003. A high haze value means low visibility through the corresponding substance. The light transmission is preferably at 550 nm at greater than 86%, particularly preferably greater than 88%. A other very preferred species of polyesters are the polybutylene terephthalate films.

In addition to polyester films, it is also possible to use highly transparent PVC films. These films may contain plasticizers to increase flexibility. Furthermore, PC, PMMA and PS films can be used. In addition to pure polystyrene, other comonomers, such as styrene, can be used to reduce the tendency to crystallize in addition to styrene. Butadiene, use.

Furthermore, polyethersulfone and polysulfone films can be used as support materials. These are e.g. from BASF under the trade names Ultrason ™ E and Ultrason ™ S. Furthermore, particularly preferably highly transparent TPU films can also be used. These are e.g. commercially available from the company Elastogran GmbH. It is also possible to use highly transparent polyamide and copolyamide films and also films based on polyvinyl alcohol and polyvinyl butyral.

In addition to monolayer films, multilayer films may also be used, e.g. be prepared coextruded. For this purpose, the abovementioned polymer materials can be combined with one another.

Furthermore, the films can be treated. Thus, e.g. Coats may be made, for example with zinc oxide, or it may be applied coatings or adhesion promoters. Another possible additive is UV protection agents, which may be present as additives in the film or may be applied as a protective layer.

The film thickness is in a preferred embodiment between 4 .mu.m and 150 .mu.m, more preferably between 12 .mu.m and 100 .mu.m.

The carrier film may, for example, also have an optical coating. As an optical coating are in particular coatings that reduce the reflection. This is achieved for example by lowering the refractive index difference for the transition air / optical coating.

In general, a distinction can be made between single and multi-layer coatings. In the simplest case, MgF _{2 is used} as a single layer to minimize reflection. MgF ₂ has a refractive index of 1.35 at 550 nm. Furthermore, for example, metal oxide layers in different layers can be used to minimize the reflection. Typical examples are layers of SiO ₂ and TiO ₂ . Other suitable oxides include hafnium oxide (HfO ₂ ), magnesium oxide (MgO), silicon monoxide (SiO), zirconium oxide (ZrO ₂ ) and tantalum oxide (Ta ₂ Os). Furthermore, however, nitrides can also be used, such as SiN _x . Furthermore, fluorinated polymers can also be used as low refractive index layers. These are also very often used in combination with the aforementioned layers of SiO ₂ and TiO ₂ . Furthermore, sol-gel processes can be used. Here, for example, silicones, alkoxides and / or metal alkoxides are used as mixtures and coated therewith. Siloxanes are thus also a widely used basis for reflection-reducing layers.

The typical coating thicknesses are between 2 and 1000 A (0.2 to 100 nm), preferably between 100 and 500 A (10 to 50 nm). In some cases - depending on the layer thickness and chemical composition of the individual or the plurality of optical layers - color changes, which in turn can be controlled or changed by the thickness of the coating. For the solution-coated siloxane process, layer thicknesses greater than 1000 A (100 nm) can also be achieved.

Another way to reduce reflection is to create certain surface structures. Thus, there is the possibility of porous coating and the production of stochastic or periodic surface structures. The distance between the structures should be clearly none other than the wavelength range of the visible light.

In addition to the solvent-coating process already mentioned, the optical layers can be vacuum-coated, such as by vacuum deposition techniques. CVD (Chemical Vapor Deposition) or PIAD (Plasma Ion Assisted Deposition).

release film

To protect the open PSA, it is preferably covered with one or more release films. In addition to release liners, release papers may also be used, although not very preferably, such as, for example, glassine, HDPE or LDPE tow papers, which in one embodiment have siliconization as the release liner. Preferably, however, a release film is used. The release film has in a very preferred design a siliconization as a release agent. Furthermore, the film separator should have an extremely smooth surface, so that no structuring of the PSA by the release liner is made. This is preferably achieved through the use of antiblock-free PET films in combination of solution-coated silicone systems.

Use The pressure-sensitive adhesives and pressure-sensitive adhesive tapes described above are particularly suitable for use in optical applications, wherein preferably permanent bonds with residence times of more than one month are made.

A single-sided pressure-sensitive adhesive tape is particularly suitable for bonding e.g. Glass windows, wherein the pressure-sensitive adhesive tape can take the function of splinter protection or sunscreen has UV and heat-absorbing effect.

Furthermore, double-sided pressure-sensitive adhesive tapes can be used to bond touch panels to displays, membrane touch switches can be provided with protective films, anti-scratch films can be glued on, or ITO films can be bonded for capacitive touch panels.

Test Methods

A ... Brech.ungsi.ndex

The refractive index of the PSA was measured in a 25 μm thick film using the Optronic measuring device from Krüss at 25 ° C. and white light (λ = 550 nm ± 150 nm) according to the Abbe's principle. For temperature stabilization, the device was operated in conjunction with a thermostat from Lauda.

B ,. K ebkraft!

The peel strength (bond strength) was tested according to PSTC-101. The adhesive tape is applied to a glass plate. A 2 cm wide strip of adhesive tape is glued by rolling it twice over twice with a 2 kg roll. The plate is clamped and the self-adhesive strip on its free end to a tensile testing machine subtracted at a peel angle of 180 ° at a speed of 300 mm / min. The force is given in N / cm.

C - .. Tr.. ⁿ .?. ^m J.?siQn The determination of the transmittance at 550 nm in accordance with ASTM D1003. The composite of optically transparent pressure-sensitive adhesive and glass plate was measured.

P.. Haze

Haze is determined according to ASTM D1003.

E .- .. y.?Mbsst.ändigkeit

The composite of pressure-sensitive adhesive and glass plate is irradiated in the size 4 x 20 cm ² for 300 h with Osram Ultra Vitalux 300 W lamps at a distance of 50 cm. After

Irradiation is determined according to test method C, the transmission.

F .-. WechseJklj.matest

The pressure-sensitive adhesive is used as a one-sided pressure-sensitive adhesive tape (50 g / m ² coat, 50 μm

PET film of the type Mitsubishi RNK 50) Glued air-free to a glass plate. Of the

Test strip has the dimension 2 cm wide and 10 cm long. It is determined according to test method B, the bond strength to glass.

At the same time, such a bonding compound is placed in a removable air conditioning cabinet and stored for 1000 cycles. One cycle includes: storage at -40 ° C for 30 minutes heating up to 85 ° C within 5 minutes - storage at 85 ° C for 30 minutes cooling to -40 ° C within 5 minutes

After the climate change test again the bond strength is determined according to test method B.

The PSA is adhesively bonded as a one-sided pressure-sensitive adhesive tape (50 g / m ² , 50 μm PET film of the type Mitsubishi RNK 50) to a glass plate free of air bubbles. The test strip has the dimension 2 cm wide and 10 cm long. It is determined according to test method B, the bond strength to glass. At the same time, such a bonding compound is placed in an alternating climate chamber and stored for 1000 hours at 60 ° C. and 95% relative humidity. Subsequently, the bond strength according to test method B is determined again.

Examples

The coatings were made in the examples on a conventional continuous coating laboratory coating equipment. The coating was carried out in a clean room ISO 5 according to standard ISO 14644-1. The web width was 50 cm. The coating gap width was variably adjustable between 0 and 1 cm. The length of the heat channel was about 12 m. The temperature in the heat channel was divisible into four zones and each freely selectable between room temperature and 120 C.

A conventional multicomponent mixing and dosing plant with a dynamic mixing system was used. The mixing head was designed for two liquid components. The mixing rotor had a variable speed up to max. about 5000 rpm. The metering pumps of this plant were gear pumps with a delivery capacity of max. about 2 l / min.

The polyol components were manufactured in a conventional heated and evacuated mixing vessel. During the approximately two-hour mixing process, the temperature of the mixture was adjusted to about 70 ° C, vacuum was applied to degas the components.

The following table lists the base materials used to make the polyurethane pressure-sensitive adhesives, each with trade names and manufacturer. The raw materials mentioned are all freely available on the market.

Table 1: Base materials used for the production of the polyurethane pressure-sensitive adhesives with trade names and manufacturers

COMPARATIVE EXAMPLES

Comparative Example 1 (VD Polyurethane composition: NCO / OH ratio: 0.95

Ratio number of diol OH / number of triol OH: 5.0

The test samples were coated with 50 g / m ² polyurethane pressure-sensitive adhesive on a 75 micron thick polyester release film. Comparative Example 2 (V2) Polyurethane composition: NCO / OH ratio: 0.95

Ratio number of diol OH / number of triol OH: 5.0

The test samples were coated with 50 g / m ² polyurethane pressure-sensitive adhesive on a 75 micron thick polyester release film.

Comparative Example 3 (V3) Polyurethane composition: NCO / OH ratio: 0.95

Ratio number of diol OH / number of triol OH: 5.0

The test samples were coated with 50 g / m ² polyurethane pressure-sensitive adhesive on a 75 micron thick polyester release film. Comparative Example 4 (V4) Polyurethane composition: NCO / OH ratio: 0.99

Ratio number of diol OH / number of triol OH: 4.8

Comparative Example 5 (V5) Polyurethane composition: NCO / OH ratio: 0.99

Ratio number of diol OH / number of triol OH: 4.8

Comparative Example 6 (V6) Polyurethane composition: NCO / OH ratio: 0.99

Ratio number of diol OH / number of triol OH: 4.8

Comparative Example 7 (V7) Polyurethane composition: NCO / OH ratio: 0.99

Ratio number of diol OH / number of triol OH: 4.8

Comparative Example 8 (V8) Polyurethane Composition: NCO / OH Ratio: 0.7

Ratio number of diol OH / number of triol OH: 2.5

Comparative Example 9 (V9) Polyurethane composition: NCO / OH ratio: 1.02

Ratio number of diol OH / number of triol OH: 1, 0

Comparative Example 10 (V10) Polyurethane composition: NCO / OH ratio: 1.0

Ratio number of diol OH / number of triol OH: 4.0

Comparative Example 1 1 (V1 1) Polyurethane composition: NCO / OH ratio: 1.0

Ratio number of diol OH / number of triol OH: 1, 0

Inventive examples

All inventive examples were chosen so that no acid functions are included.

Example 1 Polyurethane composition: NCO / OH ratio: 0.99

Ratio number of diol OH / number of triol OH: 4.8

The test samples were coated with 50 g / m ² polyurethane pressure-sensitive adhesive on a 75 micron thick polyester release film. Example 2 Polyurethane composition: NCO / OH ratio: 0.99

Ratio number of diol OH / number of triol OH: 4.8

Example 3 Polyurethane composition: NCO / OH ratio: 0.99

Ratio number of diol OH / number of triol OH: 4.8

Example 4

Polyurethane composition: NCO / OH ratio: 0.74

Ratio number of diol OH / number of triol OH: 2.5

The test samples were coated with 50 g / m ² polyurethane pressure-sensitive adhesive on a 75 micron thick polyester release film. Example 5 Polyurethane composition: NCO / OH ratio: 1.0

Ratio number of diol OH / number of triol OH: 4.0

Results

After the test sample preparation of all examples and comparative examples of the refractive index according to test method A were determined. The results are summarized in Table 2.

It can be seen from the measured values that all the inventive examples have reached the desired range of greater than 1.49, as do the comparative examples V1 to V10. Only Comparative Example 1 1 was too hazy and no refractive index was determined. For the resin blended variants V10 and 5 slightly higher refractive indices were measured.

In the following step, the instant adhesives on glass were determined from all examples and comparative examples. This was measured at 180 ° angle. In the following Table 3, the results are shown. Table 3

Example adhesive strength (test B)

1 5.7 N / cm

2 5.8 N / cm

3 5.6 N / cm

4 6.0 N / cm

5 6.6 N / cm

V1 5.8 N / cm

V2 5.8 N / cm

V3 5.6 N / cm

V4 5.5 N / cm

V5 5.7 N / cm

V6 5.7 N / cm

V7 5.8 N / cm

V8 6.1 N / cm

V9 0.2 N / cm

V10 6.8 N / cm

V1 1 0.1 N / cm

Table 3 shows that all the inventive examples are suitable for permanent bonding. By contrast, comparative examples V9 and V1 1 clearly show too low adhesive forces. V9 is an example of the fact that the right composition of the polycyanates and polyols is crucial to achieve a sufficiently high bond strength. V1 1 is again an example of the microphase separation produced by the incompatibility of the resin, which reduces the bond strengths that can be achieved.

For further optical determination, transmission and haze measurements were made of all the inventive and comparative examples. The results are listed in Table 4.

From Table 4 it can be seen that all examples have a water-clear transparency typical for polyurethanes and thus also a high transmission. In the measurement, the transmission is about 92% to 93%, limited by reflection losses due to the transition of air to the adhesive. Only Comparative Example 1 1 (V1 1) is well below the requirements due to the very high turbidity. These results are again confirmed by measurements of Haze values and are due to resin incompatibility.

In the following, various aging studies were continued. First, a light resistance test according to Test Method E was carried out. Here it is checked whether by long sunlight Irradiation discoloration or yellowing occurs. This is especially important for optical applications that require one Permanent exposure, such as exposed by a display, or used outdoors. The results are summarized in Table 5.

Table 5 shows that the comparative examples V1 to V4 as well as V7 to V1 1 show a significant drop in transmission. In all these examples, different light stabilizers based on sterically hindered amines were used, but obviously they did not achieve adequate stabilization, even in different combinations and with different proportions. Due to the yellowing after the light resistance test, such adhesive formulations are not suitable for optical applications. By contrast, all inventive examples show a very good stability and no or only a very small drop in transmission. This also applies to Comparative Examples V4 and V5, which additionally contain sterically hindered phenols with sulfur in the side groups. Another aging test involves an alternating climate test. Here, the situation is simulated that the adhesive is exposed to a very different climate, which in turn may be the case in outdoor optical applications. The climate change test was carried out according to test method F. The results are shown in Table 6.

* The samples showed a brown color after the change climate test

The measurements from Table 6 illustrate that, in particular, the comparison samples V9 and V11 show very low bond strengths after the climate change test. However, V9 and V1 1 already had very low bond strengths at the beginning. V10, however, also shows a significant loss. As a last measurement, a humidity test was again carried out with all examples and comparative examples. This is to clarify whether the PSA is stable in outdoor applications or in the tropical climate at high humidity. The measurement results for these investigations are shown in Table 7.

The measurement results show that all comparative examples have a very low bond strength after moisture storage. In contrast, the inventive examples show a very high moisture resistance.

In summary, the measurement results show that only very specific pressure-sensitive adhesives with very defined adhesive formulations can meet all requirements. It turned out that also anti-aging agents show efficacy in certain combinations. Also carbodiimide additives required to achieve moisture resistance. In addition, all of the inventive examples meet the requirements with regard to optical transparency and bond strengths also for permanent applications.

The inventive examples are thus very well suited for use in optical applications. Typical applications are e.g. glass window gluing for splinter protection or as sunlight protection, or the bonding of touch panels or membrane touch switches or the bonding of anti-scratch films or the bonding of ITO films for capacitive touch panels. To test these properties, adhesions were once again made to an ITO film from Nitto Denko and then, in contact with Examples 1 to 5, the electrical conductivity as a function of time and at 60 ° C. storage was determined. The measurements showed that the electrical conductivity remained constant within a range of ± 10% at 60 ° C for 4 weeks. Thus, the inventive examples show a very good neutrality towards ITO and do not damage the electrical conductivity of this material.

Claims

claims

1. Pressure-sensitive adhesive based on polyurethane, in which the polyurethane is composed of the following catalytically reacted starting materials in the ratios indicated: a) at least one aliphatic or alicyclic polyisocyanate, whose functionality is in each case less than or equal to 3 b) a combination of at least a polypropylene glycol diol and at least one polypropylene glycol triol, wherein the ratio of the number of hydroxyl groups of the diol

Component to the number of hydroxyl groups of the triol component is less than 10, preferably between 0.2 and 5, wherein the ratio of the number of isocyanate groups to the total number of hydroxyl groups is between 0.65 and 1.2, preferably between 0, 95 and 1, 05, more preferably between 1, 0 and 1, 05, and wherein the diols and triols are each alternatively selected and combined as follows:

Diols with a molecular weight of greater than 1000 are combined with triols whose molecular weight is less than 1000. c) at least one light stabilizer based on an aromatically substituted triazine with a proportion of 0.2-2% by weight and at least one amine-hindered light stabilizer with one

Proportion of 0.2-2% by weight d) of at least one aging inhibitor based on a sterically hindered phenol with a proportion of 0.2-2% by weight e) a carbodiimide with a proportion of 0.25-2.5 wt .-%.

2. Pressure-sensitive adhesive according to claim 1, characterized in that as starting material aliphatic or alicyclic diisocyanates, in particular isophorone diisocyanate, is contained as polyisocyanate and / or that the polyisocyanate has an asymmetrical molecular structure.

3. Pressure-sensitive adhesive according to claim 1 or 2, characterized in that the polyurethane is prepared using a catalyst, in particular a bismutcarboxylat- or bismutcarboxylatderivathaltigen catalyst or catalyst mixture.

4. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that as starting material 1-ethyl-3- (3-dimethyl aminopropyl) carbodiimide hydrochloride is contained as carbodiimides.

5. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the pressure-sensitive adhesive is formed free of acid functions.

6. Pressure-sensitive adhesive according to one of the preceding claims, characterized in that the pressure-sensitive adhesive has a light transmission according to ASTM D 1003 of at least 86% and / or a haze value according to ASTM D 1003 of not more than 5%.

7. Use of a pressure-sensitive adhesive according to one of the preceding claims for bonding optical components, in particular optical films.