EP2449048A1 - Use of adhesive tapes for bonding optical components - Google Patents

Abstract

Method for bonding optical components by means of an adhesive tape, characterized in that the adhesive tape comprises at least one layer of a pressure-sensitive adhesive compound on basis of a polyacrylate having a weight-averaged molecular weight M_w in the range of 200000 ≤ M_w ≤ 1000000 g/mol, which can be obtained by radical copolymerization of at least the following components: (a) 55 to 92% by weight of one or more acryl monomers of the general formula CH₂=CH-COOR_1, where R₁ is a hydrocarbon group having 4 to 14 carbon atoms, (b) 5 to 30% by weight of one or more copolymerizable monomers, wherein the glass transition temperature T_G,bH of the homopolymer from the monomer of the component (b) is no less than 0°C, or wherein the glass transition temperature T_G,bH of the copolymer from the monomers of the component (b) is no less than 0°C, (c) 3 to 15% by weight of one or more copolymerizable monomers promoting a cross-linking reaction of the polyacrylate, wherein the polyacrylate is cross-linked, wherein the cross-linked polyacrylate is characterized by a loss factor (tan δ value) ranging between 0.2 and 0.4, wherein the cross-linked polyacrylate has a shear strength characterized by a maximum deflection X_max in the microshear travel test of 200 to 600 μm, and wherein the cross-linked polyacrylate is characterized by an elastic portion in the polyacrylate of at least 60%.

Description

 description

USE OF ADHESIVE TAPES FOR GLUING OPTICAL COMPONENTS

Particularly in the field of electronic consumer devices, but also in the industrial and other areas, electronic data displays take a big

Room. To protect the display modules from any damage due to external mechanical effects such as shocks and also for light management, for

Thermal management, the provision of electrical functions and other tasks, such display systems usually have transparent protective windows that cover the outside of the display modules.

Adhesive tapes which are used for bonding components or substrates which serve optical purposes or are used for optical apparatus must frequently be light-reflecting, light-absorbing, highly transparent and / or light-resistant. Furthermore, it may be important to exclude air This has the advantage that the reflection is reduced, which results from the transition from air to eg optical medium made of glass. For example, in the bonding of glasses or plastic windows for displays, panels or the like even the smallest bubbles inclusions can adversely affect the appearance of the image. For the bonding of optical components with PSAs, the nature of the surfaces of substrate and adhesive is of crucial importance. A particularly smooth PSA surface is required for the bonding of optical components, because perfect lamination of the equally smooth optical substrates is necessary to obtain a defect-free optical component. Until now, the surface quality of the release film used has always had a decisive influence on the surface properties of the adhesive because the adhesive has assumed the surface quality of the release film in the adhesive tape (the profile of the release film pressed into the adhesive surface so that it assumed the negative profile of the release film surface) , For a good bond strength, a high cohesion of the PSA is often required. Especially at very cohesive Adhesive remains but even for a long time a consistent image of the release film surface after deduction of the release film exist. In WO2008 / 149890 A attention is drawn to the great influence of the release film surface roughness on the resulting surface roughness of the pressure-sensitive adhesive surface.

High cohesion of the (adhesive) adhesives used is often required for the stability of the product structure, especially at high temperatures. Low cohesion would indeed promote a flow of the (adhesive) adhesive after removal of a release film and thus lead to a smoothing of the adhesive surface, but the tapes thus obtained would not meet the requirements in the rule.

The object of the invention is to provide a pressure-sensitive adhesive which can be used excellently for the bonding of optical components, meets the high requirements in this area of application and at least largely overcomes the disadvantages of the prior art. Advantageously, cohesive PSAs are to be made available which are suitable for the formation of layers with very smooth surfaces. The object is achieved by an adhesive tape having at least one layer of a pressure-sensitive adhesive based on a polyacrylate having a weight-average molecular weight M _w in the range of 200,000 <M _w <1 000 000 g / mol, which is the polymerization product of at least the following components

 (A) 55 to 92 wt .-% of one or more acrylic monomers of the general formula

CH ₂ = CH-COOR ₁

wherein R _{1 represents} a hydrocarbon radical having 4 to 14 carbon atoms, with particular advantage branched and / or unbranched, saturated and / or unsaturated hydrocarbon radicals are used;

wherein furthermore, when component (a) comprises only one monomer, the glass transition temperature T _{G aH of} the homopolymer of the monomer of

Component (a) [defined as the glass transition temperature T _g according to DIN 53765: 1994-03 (. See section 2.2.1)] is not more than - 20 ⁰ C.

or, if the component (a) comprises more than one monomer, the glass transition temperature T _G , _a c of the copolymer of the monomers of the component (a) according to the Fox equation is not more than - 20 ⁰ C, wherein for the calculation in the Fox equation, the glass transition temperature values T ₉ according to DIN 53765: 1994-03 (see Section 2.2.1) of the homopolymers of the individual monomers of component (a) are used;

 (b) 5 to 30% by weight of one or more copolymerizable monomers,

 when component (b) comprises only one monomer, the

Glass transition temperature T _{G bH} of the homopolymer from the monomer of component (b) [defined as the glass transition temperature value T according to DIN 53765 _9: 1994-03 (. See section 2.2.1)] is not less than 0 ⁰ C

or wherein, when the component (b) comprises more than one monomer, the glass transition temperature T _{G bC of} the copolymer of the

Monomers of the component (b) according to the Fox equation is not less than 0 ⁰ C, wherein for the calculation in the Fox equation the glass transition temperature values T ₉ according to DIN 53765: 1994-03 (see Section 2.2.1) Homopolymers of the individual monomers of component (b) are used;

 (c) 3 to 15% by weight of one or more copolymerizable monomers which promote crosslinking reaction of the polyacrylate,

is

wherein the polyacrylate is crosslinked,

and wherein the crosslinked polyacrylate is characterized by a loss factor (tan δ value) between 0.2 and 0.4,

wherein the crosslinked polyacrylate has a shear strength which is characterized by a maximum deflection x _max in the micro-shear test of 200 to 600 microns, and wherein the crosslinked polyacrylate characterized by an elastic content in the polyacrylate of at least 60%, determined in the micro-shear test.

It has surprisingly been found that in the case of PSAs with suitable elastic and viscous behavior, as is characterized in more detail in the claims, very smooth layer surfaces can be obtained.

But these masses still have a sufficiently high cohesion, which he required for bonding in the optical field, for example, to ensure the punchability or to prevent slippage of the optical components in normal operation. For a more detailed description and quantification of the amount of elastic and viscous portion and the ratio of the proportions to each other can be determined by Dynamic Mechanical Analysis (DMA) sizes storage modulus (G '), loss modulus (G ") and the loss factor tan δ (tan delta) designated quotient G "/ G 'are used. G 'is a measure of the elastic part, G "is a measure of the viscous part of a substance, both of which depend on the deformation frequency and the temperature.

 The loss factor tan δ is a measure of the elasticity and fluidity of the substance under investigation.

The sizes can be determined with the help of a rheometer. The material to be examined is exposed to a sinusoidal oscillating shear stress in a plate-and-plate arrangement, for example. In the case of shear-tension controlled devices, the deformation as a function of time and the time offset of this deformation y (gamma) are compared with the introduction of the shear stress T (tau). This time offset (phase shift between shear stress and deformation vector) is referred to as the phase angle δ (delta).

Storage modulus G 'G' = τ / γ 'COs (O)

Loss modulus G "G" = τ / γ ^" sin (ö)

 Loss factor tan δ tan δ = GVG "

The details of the aforementioned parameters in the context of this document refer to the measurement by means of a rheometer in plate-on-plate configuration, based on a round sample with a sample diameter of 8 mm and a sample thickness of 1 mm. Measurement conditions: temperature 25 ⁰ C, otherwise standard conditions, frequency of the oscillating shear stress 0.1 rad / s.

The data concerning the maximum shear path and the elastic part refer to the results of the shear path measurement. The maximum shear path (= the maximum deflection x _max ) is a quantitative quantity for describing the shear strength, and the elastic part is a quantitative measure for describing the resilience of the investigated sample. The measurement principle is shown schematically in FIG. 1 (FIG. 1 a: plan view of the measurement setup, FIG. 1 b: side view of the measurement setup).

Of the polyacrylate to be examined, a 50 μm thick layer is produced and crosslinked. The polyacrylate layer adheres to a stabilizing film, such as a PET Foil. From this composite, a sample pattern [length (L ₁ ) 50 mm, width (B) 10 mm] is cut out.

 The composite of polyacrylate layer (1) and stabilizing film (2) is glued to the polyacrylate layer side in such a manner previously cleaned with acetone steel plate (3) 5 that the steel plate (3) projects beyond the tape right and left and that the adhesive tape ( 1) the steel plate at the top by a distance (a) of 2 mm surmounted. The bonding area of the polyacrylate layer (1) on the steel plate (3) is height (H) x width (B) = 13 mm x 10 mm. The bonding site is then overrolled six times with a 2 kg steel roll, so that there is a firm bond.

 10 The composite strip (1, 2) is flush with a stable reinforcing strip (4), such as cardboard, on top of the film side, on which a distance sensor (deflection sensor) (5) rests. The sample is suspended vertically by means of the steel plate.

The measurement conditions are a temperature of 40 ⁰ C and the rest

15 standard conditions selected. The sample to be measured is provided at the lower end by means of a clamp (7) (weight of the clamp 6.3 g) with a weight (6) of 500 g (total load 506.3 g) and for a period of time (Δti) of 15 min loaded (see Figure 1 c). Due to the firm bonding of the polyacrylate layer (1) on the steel plate (3) and on the stabilizing film (2) act on the polyacrylate layer

20 shearing forces. The shearing distance (maximum deflection of the distance sensor;

Stress shearing _distance x _max ) of the polyacrylate layer after the predetermined duration at constant temperature is given as the result ([x _max ] = μm).

After expiration of the period of time under load (At ₁ ), the weight (6) and the clamp (7) are removed; and there is a return movement of the polyacrylate layer (1)

25 relaxation (see Figure 1d). After a relief period (At ₂ ) of likewise 15 minutes, the shear distance (residual deflection of the displacement sensor, relieving shear distance X _m i _n ) of the polyacrylate layer is again measured ([× _min ] = μm).

The elastic proportion A _e ι _as i of the polyacrylate in percent results according to

_ _π (Xmax ~ Xmm) * 1 00

θ (J Aelast = ~

The data on the weight-average molecular weight M _w refer to the

Determination by gel permeation chromatography (GPC). The eluent was THF

0.1 vol .-% trifluoroacetic acid used. The measurement was carried out at 25 ⁰ C. As a precolumn

35, PSS-SDV, 5μ, 10 ³ Å, ID 8.0 mm x 50 mm was used. For separation, the Columns PSS-SDV, 5 μ, 10 ³ and 10 ⁵ and 10 ⁶ each used with ID 8.0 mm x 300 mm. The sample concentration was 4 g / l, the flow rate 1, 0 ml per minute. It was measured against PMMA standards, (μ = μm, 1 λ = 10 ^{~ 10} m). In the context of this document, if parameters are specified within a range defined between two limits, the specified limit values are deemed to belong to the parameter range, unless stated otherwise.

The invention furthermore relates to the use of such an adhesive tape for bonding optical components, ie a method for bonding optical components by means of an adhesive tape, wherein the adhesive tape comprises at least one layer of a PSA based on a polyacrylate having a weight-average molecular weight M _w in the range of 200,000 <M _w <1 000 000 g / mol, which is obtainable by radical copolymerization of at least the following components:

(A) 55 to 92 wt .-% of one or more acrylic monomers of the general formula

CH ₂ = CH-COORi

 wherein Ri represents a hydrocarbon radical having 4 to 14 carbon atoms, with particular advantage branched and / or unbranched, saturated and / or unsaturated hydrocarbon radicals are used;

 wherein further, when component (a) comprises only one monomer, the

Glass transition temperature T _{G, aH} of the homopolymer from the monomer of component (a) [defined as the glass transition temperature value T ₉ according to DIN 53765: 1994-03 (. See section 2.2.1)] is not more than - is 20 ⁰ C.

or, if component (a) comprises more than one monomer, the glass transition temperature T _{G aC of} the copolymer of the monomers of

Komonente (a) according to the Fox equation is not more than - 20 ⁰ C, wherein for the calculation in the Fox equation glass transition temperature value T ₉ 53765 according to DIN: 1994-03 (see Section 2.2.1.) Of the homopolymers the individual monomers of component (a) are used;

(b) 5 to 30% by weight of one or more copolymerizable monomers,

where, if component (b) comprises only one monomer, the glass transition temperature T _G , b _{H of} the homopolymer of the monomer of component (b) [defined as glass transition temperature value T ₉ according to DIN 53765: 1994-03 (see Section 2.2 .1)] is not less than 0 ^° C or wherein, when the component (b) comprises more than one monomer, the glass transition temperature T _G , bc of the copolymer of the monomers of the component (b) according to the Fox equation is not less than 0 ⁰ C, wherein for the calculation in the Fox equation the glass transition temperature value T _g according to DIN 53765: 1994-03 (see Section 2.2.1) of the homopolymers of the individual monomers of component (b) are used;

 (c) 3 to 15% by weight of one or more copolymerisable ones

Crosslinking reaction of polyacrylate-promoting monomers,

wherein the polyacrylate is crosslinked,

and wherein the polyacrylate prior to the bonding of the optical components by a

Loss factor (tan δ value) is characterized between 0.2 and 0.4,

the polyacrylate having a shear strength which is characterized by a maximum deflection x _max in the micro-shear test from 200 to 600 μm,

and wherein the crosslinked polyacrylate is characterized by an elastic content in the polyacrylate of at least 60%, determined in the micro-shear test.

For the purposes of the present specification, the term "for the bonding of optical components" is understood to mean any bond which serves for optical purposes, in particular adhesions which place high demands on the PSA on account of the light management associated with the bonded substrates.

Exemplary uses which fall in particular under the claimed use are the use of the adhesive tapes according to the invention for the lamination of polarizer films, retarder films, light-enhancement films, lightguide films, antireflection films, antiglare films, shatter-proofing films, on LCD modules, mutually on one of the films mentioned or on transparent substrates with structural function; Furthermore, the bonding of glasses, plastic films, plastic windows and the like in the production of optical data displays (LCDs, liquid crystal displays), OLED displays (organic light-emitting diode displays), other displays, so-called touch panels, screens (monitor windows) and the like.

The aforementioned uses are particularly relevant in the field of electronic devices, such as for televisions, computer monitors, radars, oscilloscopes, portable computers (notebooks), PDAs (handhelds, organizers), mobile phones, digital cameras, camcorders, navigation devices, clocks, level indicators on storage vessels and the same. The bonding of decorative elements falls under the claimed use, in particular if this demanding bonding are connected.

 In the case of the use of adhesive tapes for optical purposes, these can furthermore advantageously have a filter effect, mechanical protection, suitability for thermal management (eg the regulation of thermal radiation) and / or suitability for electrical management (provision of electrical or electronic functions) as well as the fulfillment of further Ensuring tasks. Advantageously, the elastic portion (micro-shear test) of the polyacrylate of the adhesive tape according to the invention and of the adhesive tape used in accordance with the invention are adjusted to be in the range between 70% and 95%.

The polymerization of the polyacrylate is carried out in particular by free radical polymerization of the comonomers used according to known polymerization.

The Fox equation can be used to determine the glass transition temperature of copolymers (see TG Fox, Bull. Am. Phys Soc., 1 (1956) p. 123), which states that the reciprocal glass transition temperature of the copolymer exceeds the proportions by weight of the copolymers calculated comonomers and the glass transition temperatures of the corresponding homopolymers of comonomers can be calculated:

1 W ₁ w ₂

^{~ ■} +

TG T _G JT _{G 2}

wherein W ₁ and w _{2 represent} the mass fraction of the respective monomer 1 or 2 (wt .-%) and T _G , i and T _{G 2,} the respective glass transition temperature of the homopolymer of the respective monomers 1 and 2 in K (Kelvin).

The equation is generalizable in the case of more than two comonomers

w _r

¹ G n 'G, n

In the general equation, n represents the number of runs via the monomers used, w _n the mass fraction of the respective monomer n (wt .-%) and T _G , _n the respective glass transition temperature of the homopolymer of the respective monomers n in K (Kelvin). The values for the glass transition temperatures of the corresponding homopolymers can also be taken from relevant reference works.

The hydrocarbon radical of the acrylic monomers for component (a) may in particular be a branched or unbranched alkyl or alkenyl group. Particularly advantageous are hydrocarbon radicals having 4 to 10 carbon atoms.

Advantageous examples of acrylic monomers which can be used in the sense of component (a) are n-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-nonyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate, and the like branched isomers, such as Isobutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate.

For component (b), in a preferred procedure, at least partially one or more acrylic and / or methacrylic monomers of the general formula

CH ₂ = C (R ₂ ) -COOR ₃

used, wherein R ₂ = H or R ₂ = CH ₃ , wherein furthermore R _{3 is} a hydrocarbon radical, in particular having 1 to 30 carbon atoms, and wherein the conditions mentioned for component (b) with respect to the glass transition temperatures are met.

The hydrocarbon radical of a respective acrylic monomer for component (b) may be branched or unbranched, saturated or unsaturated, aliphatic or aromatic, substituted or unsubstituted. As advantageous monomers in the sense of component (b) can be, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, use Isooctylmethacrylat.

Further advantageous monomers for component (b) are monofunctional acrylates and / or methacrylates of bridged cycloalkyl alcohols which have at least 6 C atoms. The cycloalkyl alcohols may also be substituted, for example by C 1-6 -alkyl groups, halogen atoms or cyano groups. Advantageous examples of such monomers are cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate and 3,5-dimethyl adamantyl acrylate. Further advantageous monomers for component (b), either as sole monomers of component (b) or in particular also in combination with the already described comonomers of component (b), non-acrylic monomers can be used which have a high static glass transition temperature ( in particular T _G ≥ 0 ° C). For example, aromatic vinyl compounds, such as, for example, styrene, are suitable, where the aromatic nuclei preferably consist of C ₄ - to C ₁₈ -components and may also contain heteroatoms.

 Particularly preferred examples are 4-vinylpyridine, N-vinylphthalimide, methylstyrene, 3,4-dimethoxystyrene, 4-vinylbenzoic acid.

Advantageously, acrylic monomers having aromatic radicals in the sense of component (b) can also be used, for example benzyl acrylate, benzyl methacrylate, phenyl acrylate, phenyl methacrylate, t-butylphenyl acrylate, t-butylphenyl methacrylate, biphenyl A-acrylate and methacrylate, 2-naphthyl acrylate and methacrylate , In particular for enabling and / or promoting crosslinking of the polyacrylate, the compounds of component (c) are added as comonomers. The crosslinking of the polyacrylate can be effected by thermal crosslinking and / or chemical crosslinking and / or by actinic radiation (in particular UV radiation or electron radiation). The setting of the parameters mentioned in the claims can be carried out in particular by a targeted crosslinking. The crosslinking is then carried out to a degree of crosslinking which is characterized by a loss factor (tan δ value) between 0.2 and 0.4, a micro-shear of 200 to 600 microns and an elastic content in the polyacrylate of at least 60%. The setting of such a degree of crosslinking is one of the general knowledge of the skilled person, in particular of those skilled in the field of adhesives and self-adhesives, and is readily practicable by him with his expertise.

In the sense of component (c) may advantageously exclusively or at least partially, in the second case particularly advantageous in combination with copolymerizable photoinitiators, in particular as hereinafter referred to, one or more acrylic and / or methacrylic monomers of the general formula

CH ₂ = C (FU) -COOFt ₅ where R ₄ = H or R ₄ = CH ₃ and wherein R ₅ = H or R _{5 represents} an alkyl group having a functional group capable of or promoting a crosslinking reaction. As functional groups in the above sense, for example, carbonyl groups, acid groups, hydroxy groups, epoxy groups, amine groups, isocyanate groups can be selected.

In a preferred embodiment of the invention, component (c) is employed in an amount such that the amount of substance n _a [in moles] of the monomers of component (a) corresponds to the molar amount n _c [in moles] of the functional groups of component (c). in the ratio 1 <n _a / n _c <20, preferably 5 <n _a / n _c <16, more preferably 6 <n _a / n _c <1 1. Particularly advantageous, but not necessarily, is that when component (c) comprises only an acrylic or methacrylic monomer, the glass transition temperature T _{G, CH of} the homopolymer of the acrylic or methacrylic monomer of component (c) [defined as the glass transition temperature value T ₉ according to DIN 53765: 1994-03 (see Section 2.2.1)] is not less than 0 ° C, or, if component (c) comprises a plurality of acrylic and / or methacrylic monomers, the glass transition temperature T _G , cc of Copolymer of the acrylic and / or methacrylic monomers of component (c) according to the Fox equation is not less than 0 ° C, wherein for the calculation in the Fox equation the glass transition temperature value T ₉ according to DIN 53765: 1994-03 ( see Section 2.2.1) of the homopolymers of the individual monomers of component (c).

Advantageous examples of corresponding functionalized (meth) acrylic monomers in the sense of component (c) are acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, allyl alcohol, maleic anhydride, itaconic anhydride, itaconic acid, glyceridyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, 2-butoxyethyl methacrylate, 2-butoxyethyl acrylate, cyanoethyl methacrylate, cyanoethyl acrylate, glyceryl methacrylate, 6-hydroxyhexyl methacrylate, vinyl acetic acid, tetrahydrofurfuryl acrylate, β-acryloyloxypropionic acid, trichloroacrylic acid, fumaric acid, crotonic acid, aconitic acid. For the purposes of component (c), copolymerisable photoinitiators may advantageously be used exclusively or else in part, in the latter case in particular in combination of the abovementioned compounds in the sense of component (c). As copolymerizable photoinitiators are Norrish I photoinitiators (photochemically fragmenting, in particular α-cleaving photoinitiators) and

Norrish II photoinitiators (photochemically excited hydrogen-abstracting photoinitiators) are suitable. Advantageous examples of copolymerizable photoinitiators include benzoin and acrylated benzophenones, for example, the commercially available product Ebecryl P 36 ^® from. UCB. In principle, it is possible to use all photoinitiators known to the person skilled in the art which are copolymerisable (in particular have polymerizable double bonds) and can crosslink the polymer via UV irradiation via a radical mechanism. Crosslinkers and promoters can be added to the polyacrylate for the crosslinking reaction. In particular, for the polymerization reaction insensitive (non-reactive) crosslinkers and / or promoters can optionally already be added before or during the polymerization. Suitable crosslinkers for electron beam crosslinking and UV crosslinking are, for example, difunctional or polyfunctional acrylates, difunctional or polyfunctional isocyanates (also in blocked form) or difunctional or polyfunctional epoxides. Furthermore, thermally activatable crosslinkers, such as Lewis acids, metal chelates or multifunctional isocyanates may be added. For optional crosslinking with UV light, it is possible to add to the PSAs instead of the copolymerizable photoinitiators or in addition to these non-copolymerizable UV-absorbing photoinitiators. Useful photoinitiators which are very useful are benzoin ethers, such as benzoin ethers. B. benzoin methyl ether and benzoin isopropyl ether, substituted acetophenones, such as. B. 2,2-Diethoxyacetophenon (available as Irgacure 651 ^® from. Ciba Geigy ^® ), 2,2-dimethoxy-2-phenyl-1-phenyl-ethanone, dimethoxyhydroxyacetophenone, substituted α-ketols, such as. For example, 2-methoxy-2-hydroxypropiophenone, aromatic sulfonyl chlorides, such as. For example, 2-naphthyl sulfonyl chloride, and photoactive oximes, such as. B. 1-phenyl-1,2-propanedione 2- (O-ethoxycarbonyl) oxime. The above-mentioned and / or further advantageously usable, non-copolymerizable Photoinititatioren, in particular those of the type Norrish-I or Norrish-Il, may particularly advantageously contain the following radicals: benzophenone, acetophenone, benzil, benzoin, hydroxyalkylphenone, Phenylcyclohexylketon- , Anthrachinon-, Trimethylbenzoylphosphinoxid-, Methylthiophenylmorpholinketon-, aminoketone, azobenzoin, thioxanthone, Hexarylbisimidazol-, triazine or fluorenone, wherein each of these radicals additionally with one or more halogen atoms and / or one or more alkoxy groups and / or one or may be substituted by a plurality of amino groups or hydroxy groups. The mention of these radicals is given by way of example only for advantageous compounds and is not intended to be limiting.

The comonomer mixture to be polymerized, the polymer present in the polymerization and / or the ready-polymerized polyacrylate may be added, preferably before the crosslinking reaction, in particular to support the setting of the desired product properties, further components and / or additives, in particular those additives which do not enter the Polymer are incorporated and / or not participate in the crosslinking reaction.

 As additives which are advantageous in particular for the use in the optical range for the polyacrylate of the adhesive tape, there may be mentioned, for example, light stabilizers and anti-aging agents.

The presence of tackifier resins and plasticizers can be dispensed with in the case of the pressure-sensitive adhesive used for the adhesive tape of the invention or for the adhesive tape used according to the invention, such that an outstanding variant of the adhesive tape of the invention and the adhesive tape of the invention each have a PSA layer, in particular by a PSA layer are realized (single-layer, carrierless adhesive tape), in which no resins and / or plasticizers are added to the PSA, in particular advantageously neither resins nor plasticizers are added. Such additives often have adverse effects in the optical bonding application. The resins used according to the prior art as tackifier resins for acrylate PSAs are usually polar in nature in order to achieve compatibility with the polyacrylate matrix. This usually leads to the use of aromatic tackifier resins, which turn yellowish upon prolonged storage or under the action of light. The polyacrylate obtainable as described above and optionally additized becomes

Preparation of a PSA Layer applied on one or both sides of a support, wherein a permanent support can be used, which is retained in the adhesive tape construction in the application. However, carrier-less, in particular single-layer adhesive tapes are produced in an especially advantageous manner which, in a very outstanding embodiment, are used in the application from US Pat

Adhesive adhesive layer alone consist (so-called transfer tapes) and are provided on the market on one or both sides with a temporary carrier for previous handling, packaging and offering, in particular wound to the role.

For the preparation of such transfer adhesive tapes, the polyacrylate obtainable as described above is advantageously applied to a temporary support (in particular anti-adhesive and / or anti-adhesive materials (so-called cover materials, release materials, release materials or (release) liners) such as, for example, siliconized papers, films or the like In principle, all release materials suitable for polyacrylate PSAs can be used here.

It is also possible to produce adhesive tapes with two (adhesive) layers of adhesive of different types, of which at least one of the layers is a PSA layer according to the invention (described in the context of this document). The PSA layers can adjoin one another directly (two-layer adhesive tape), and between the two PSA layers optionally one or more further layers can be provided, such as, for example, carrier layers or the like (multilayer structure).

The crosslinking of the polyacrylate is preferably carried out in the layer on the carrier material. The pressure-sensitive adhesive is preferably adjusted so that the pressure-sensitively adhesive properties are suitable for the use of the PSA for the described intended use. According to the invention, this is preferably done by selecting the appropriate degree of crosslinking of the polyacrylate. The polyacrylate is crosslinked in this case to a degree of crosslinking, which requires the realization of the specified parameters. In this way, in particular the cohesion and the adhesion of the PSA and their flow behavior can be regulated. In a very preferred procedure, the crosslinking of the polyacrylate can be effected thermally (ie by the supply of thermal energy), in very preferred cases the crosslinking temperature is at most 90 ° C., very preferably at most 60 ° C., and in particular the residence time to a maximum of 2 minutes , is very preferably limited to a maximum of 1 minute at this temperature. In particular, crosslinking temperatures of not more than 90 ° C. can be combined with crosslinking times of not more than one minute and, advantageously, crosslinking temperatures of not more than 60 ° C. and crosslinking periods of not more than two minutes). For thermal crosslinking, the PSA tapes of the invention are preferably passed through a drying channel. The drying channel fulfills two functions. On the one hand, in the case where the acrylic PSA has been coated from solution, the solvents are removed. This is usually done by a gradual heating to avoid drying bubbles. On the other hand - when a certain degree of drying is achieved - the heat is used to initiate thermal crosslinking. The required heat input depends on the crosslinker system. For example, metal chelate crosslinking can be carried out even at very low temperatures of 90 ° C., very preferably at 60 ° C. and short contact times, in particular in the drying channel (advantageously a maximum of 2 minutes, preferably a maximum of 1 minute).

In contrast, epoxy crosslinks require longer crosslinking times and temperatures of 100 ° C. and higher in order to achieve efficient crosslinking in the drying channel. Furthermore, the heat input is controlled by the drying channel length and the Bahngeschindigkeit. It has been found that adhesive tapes according to the invention can be produced with outstanding suitability for use for optical bonds, if exclusively or partially aluminum chelate compounds are used as crosslinkers. In contrast to other crosslinkers, these compounds do not tend to yellow and therefore lead to very clear products. Crosslinked with aluminum chelates polyacrylates also tend over time (for example, during prolonged storage) for post-crosslinking or aging, so that the product properties are retained over a very long period of time. For the crosslinking reaction with aluminum chelates only very moderate temperatures for activation are necessary (see above), so that no risk of adversely affecting adhesive tape building blocks such as carriers, liners or is the same (higher temperatures, for example, lead to damage of carriers and / or liners, such as shrinkage, warping or the like). Therefore, high-quality, homogeneous products can be produced (especially with high optical quality).

In principle, adhesive tapes according to the invention can also be obtained by crosslinking by means of UV irradiation, wherein this crosslinking can be carried out alternatively or in addition to other crosslinking methods.

For UV crosslinking is irradiated by short-wave ultraviolet radiation in a wavelength range of 200 to 400 nm, depending on the UV photoinitiator used, in particular using high-pressure mercury or - medium pressure lamps at a power of 80 to 400 W / cm , The irradiation intensity is adapted to the respective quantum efficiency of the UV photoinitiator and the degree of crosslinking to be set. The irradiation conditions (in particular type of irradiation, intensity, dose and duration) are adapted to the particular chemical composition of the polyacrylates to be crosslinked in particular such that the required parameter values of the crosslinked polyacrylate are achieved and the polyacrylate has the required suitability for the desired applications. The following information is used as a guide for parameter ranges in which a control is advantageous.

It is advantageous to irradiate with a UV-C dose of 50 to 200 mJ / cm ² , preferably of 75 to 150 mJ / cm ² . The dose was measured with a UV dosimeter from Eltosch. The dose can be varied by the power of the UV lamp, or by the irradiation time, which in turn is controlled by the web speed. In the inventive sense, preferably low irradiation intensity (less than 200 mJ / cm ² UV-C) is irradiated. As a result, a laking of the PSA surface is avoided and in the irradiated areas, the elasticity is maintained, which is needed for the inventive effect. On the other hand, too low radiation doses lead to undercrosslinking of the PSA. The web speed for a UV crosslinking is preferably between 1 and 50 m / min, depending on the irradiation intensity of the UV lamp.

 In order to set the correct UV dose, it may be appropriate to adapt the radiator output to the web speed and / or the type of pressure-sensitive adhesive tape.

In order to regulate the crosslinking reaction of the UV-crosslinked adhesive, the hard UV-C radiation in a wavelength range of less than 300 nm is preferred limited. The main use of hard UV-C radiation results in a high crosslinking yield on the PSA surface. Lower pressure-sensitive adhesive layers are less strongly crosslinked by the short wavelength radiation. Therefore, the UV irradiation for the inventive method in addition to the UV-C radiation very preferably also contains portions of UV-A and UV-B radiation.

 In addition, it is possible to irradiate with the exclusion of atmospheric oxygen. For this purpose, the pressure-sensitive adhesive tape can be covered before the UV irradiation or the irradiation channel is covered with an inert gas, such as e.g. Nitrogen, flooded.

 Suitable UV radiation devices, for example, the companies Eltosch, Fusion and IST ago. Furthermore, doped glasses can be used to filter out certain radiation areas.

It has been possible to produce very smooth adhesive tapes, in particular with the abovementioned methods, and here in particular by means of thermal crosslinking. The adhesive tape according to the invention and the adhesive tape used according to the invention permit a simple and error-free processing without formation of optical defects, largely independent of the substrate and release material surface quality. It has a good flowability, so that it can be perfectly adapted to the surface of the substrates to be bonded. Nevertheless, the cohesion is sufficiently high to ensure a good bond strength. The elastic portion A _e ι _as t of the polyacrylate is at least 60% (Scherwegmessung).

The surface of the adhesive layer of the adhesive tape according to the invention and of the adhesive tape used according to the invention which is exposed on stripping of an applied release material preferably has a mean roughness R _a, io _s equal to or less than 70% within a time of 10 s after removal of the applied release material. preferably 60%, the average roughness R _{a, 0 of} the surface of the release material which has been applied to the layer of adhesive, assuming that the average roughness R _{a, 0 of} the adhesive layer exposed by the release of the release material at time 0 (immediately after withdrawal of the release material, "initial value") and that of the surface of the release material which has been applied to the adhesive layer are the same.

Adhesive tapes according to the invention and adhesives used according to the invention are particularly preferred if the surface roughness of the exposed PSA layer over a period of 24 hours after removal of the release film to a mean roughness R _a , _{24 h} of at most 55%, preferably at most 50%, more preferably at most 45%, even more preferably at most 40% of the initial value decreases.

 Preferred adhesives can assume both of the aforementioned states in the time sequence shown.

Adhesive tapes according to the invention and adhesive tapes used according to the invention are preferably covered on one or both sides with release materials whose mean roughness R _a does not exceed 350 nm, preferably 300 nm, more preferably 150 nm exceeds. In this way it can be ensured that the adhesive layer has a sufficient smoothness for optical applications in the application. By using very smooth release materials, which can have an average roughness R _a of up to 1 nm or even less, the smoothness of the adhesive film can be optimized. In particular, for optical applications, the PSA is preferably adjusted so that it as a layer up to a layer thickness of 250 .mu.m, preferably up to a layer thickness of 300 .mu.m, a transparency corresponding to a transmission (emitted light intensity based on irradiated light intensity, in%) of at least 95% (after previous deduction of the reflection losses at the interface transitions air / adhesive and adhesive / air) or of at least 89% (emitted light intensity in relation to the absolutely irradiated light intensity, without deduction of the portions of air / adhesive and adhesive / air the incident light intensity, white light C according to standard CIE 13.3-1995). Further advantageously, the pressure-sensitive adhesive has a Haze value (ASTM D 1003) of at most 5% or less.

The adhesive tape according to the invention is particularly well suited for permanent adhesive bonds, in particular adhesions in which the adhesive bond is to be permanently retained. The bonds can also be carried out over a large area and also be loaded with high weights. This is an advantage for many applications, such as the bonding of glass plates, since the bonded objects or substrates often have a high weight. Furthermore, the adhesive tapes according to the invention have good resistance at elevated temperatures. The adhesive tapes according to the invention are also outstandingly suitable for use in applications in which the bonding surface is not horizontally planar, for example, is oriented vertically planar, so for example for the bonding of glasses and glass in LCD and plasma TVs. Here, in particular, a sufficiently high cohesion is required, since these devices are operated in a vertical form and can be heated to temperatures of 40 ° C and more over a longer period.

The crosslinked polyacrylate of the adhesive tapes according to the invention and the adhesive tapes according to the invention has an elasticity which is characterized by a loss factor (tan δ value) between 0.2 and 0.4, furthermore a shear strength which is determined by a maximum deflection x _max in the micro-shear test of 200 to 600 microns, and a resilience, which is characterized by an elastic content in the polyacrylate of at least 60%, determined in the micro-shear test. It is possible according to the invention to provide pressure-sensitive adhesives and adhesive tapes produced therefrom which have high cohesion and high flowability and which are surprisingly able to compensate for the negative effect of surface roughness caused by the application of a release material. The products thus allow excellent gluing in the optical range as well as very good laminations.

Experimental part

Polvmersationen of Polvacrylates

Example 1 .. (according to the invention)

A 200 L reactor conventional for free-radical polymerizations was charged with 4900 g of acrylic acid, 51 kg of 2-ethylhexyl acrylate, 14 kg of methyl acrylate and 53.3 kg of acetone / gasoline / isopropanol (48.5: 48.5: 3). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 40 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time again 40 g of AIBN was added. After 5 h and 10 h each was diluted with 15 kg acetone / isopropanol (90:10). After 6 and 8 h each 100 g of dicyclohexyl peroxydicarbonate (Perkadox 16 ^® , Fa. Akzo Nobel) were dissolved in each added 800 g of acetone. The reaction was stopped after 24 h reaction time and cooled to room temperature. GPC analysis showed an M _w of 507000 g / mol. Bejspiel.2.ierfjndunasgemäß)

A 200 L reactor conventional for radical polymerizations was charged with 4900 g of acrylic acid, 51 kg of 2-ethylhexyl acrylate, 14 kg of methyl acrylate and 53.3 kg of acetone / gasoline / isopropanol (48.5: 48.5: 2). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 40 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time again 40 g of AIBN was added. After 5 h and 10 h each was diluted with 15 kg acetone / isopropanol (90:10). After 6 and 8 h 100 g dicyclohexyl peroxydicarbonate (Perkadox ^® 16, Fa. Akzo Nobel) was added dissolved in each 800 g of acetone. The reaction was stopped after 24 h reaction time and cooled to room temperature. GPC analysis showed an M _w of 812,000 g / mol. ß.ejspjeJ.S.Xerfindunflsciernäß)

The procedure was analogous to Example 2 of the invention. ß. eispjej.4 _ (compulsory)

 The procedure was analogous to Example 2 of the invention. B.ejspjeJ.S. ^ Erfindunflsciernäß)

The procedure was analogous to Example 2 of the invention.

Bejspiel..6. (Erfjnduηasgemäß _ι i

 A conventional for radical polymerizations 200 L reactor was 2.4 kg

Acrylic acid, 38.8 kg of 2-ethylhexyl acrylate, 38.8 kg of n-butyl acrylate and 60 kg

Acetone / isopropanol (99: 4). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 20 g of 2,2'-azoisobutyronitrile

(AIBN) added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time 20 g of AIBN was added again. The reaction was stopped after 72 hours reaction time by cooling to room temperature. According to the test method GPC, the molecular weight M _w = 780,000 g / mol.

BsJspJ6l..7 (erfjndun≤ [SJQ [ernäß).

 A conventional for radical polymerizations 200 L reactor was 9.6 kg

Acrylic acid, 45.4 kg of 2-ethylhexyl acrylate, 25.0 kg of n-butyl acrylate and 60 kg of acetone / isopropanol (99: 4). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 20 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time 20 g of AIBN was added again. The reaction was stopped after 72 hours reaction time by cooling to room temperature. According to the test method GPC, the molecular weight M _w = 786000 g / mol.

Ref e re nzbe i spi ej.1

A 200 L reactor conventional for free-radical polymerizations was charged with 3.2 kg of acrylic acid, 38.4 kg of 2-ethylhexyl acrylate, 38.4 kg of n-butyl acrylate and 60 kg of acetone / isopropanol (99: 1). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 20 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time 20 g of AIBN was added again. The reaction was stopped after 72 hours reaction time by cooling to room temperature. According to test method GPC, the molecular weight M _w = 1625000 g / mol. Ref e re nzb.ej spj ej.2

 A conventional for radical polymerizations 200 L reactor was 9.6 kg

Acrylic acid, 35.2 kg of 2-ethylhexyl acrylate, 35.2 kg of n-butyl acrylate and 60 kg

Acetone / isopropanol (99: 1). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 20 g of 2,2'-azoisobutyronitrile

(AIBN) added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time 20 g of AIBN was added again. The reaction was stopped after 72 hours reaction time by cooling to room temperature. According to the test method GPC, the molecular weight M _w = 1710000 g / mol.

Ref e re nzbej spj e.l.3

 A conventional for radical polymerizations 200 L reactor was 5.6 kg

Acrylic acid, 16 kg of methyl acrylate and 58.4 kg of 2-ethylhexyl acrylate and 60 kg of acetone / isopropanol (90:10). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 40 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time again 40 g of AIBN was added. The reaction was stopped after 12 hours reaction time by cooling to room temperature. According to test method GPC, the molecular weight M _w = 188000 g / mol.

Refere nce s e c e 1.4

A 200 L reactor conventional for radical polymerizations was charged with 5.6 kg of acrylic acid, 16 kg of methyl acrylate and 58.4 kg of 2-ethylhexyl acrylate and 60 kg of acetone / isopropanol (98: 2). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 20 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time 20 g of AIBN was added again. The reaction was stopped after 72 hours reaction time by cooling to room temperature. According to the test method GPC, the molecular weight M _w = 1580000 g / mol.

Ref e re nzbej spj el5 A 200 L reactor conventional for radical polymerizations was charged with 2800 g of acrylic acid, 10.5 kg of cyclohexyl methacrylate, 56.7 kg of butyl acrylate and 53.3 kg of acetone / gasoline / isopropanol (48.5: 48.5: 2). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 40 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time again 40 g of AIBN was added. After 5 h and 10 h each was diluted with 15 kg acetone / isopropanol (90:10). After 6 and 8 h 100 g dicyclohexyl peroxydicarbonate (Perkadox ^® 16, Fa. Akzo Nobel) was added dissolved in each 800 g of acetone. The reaction was stopped after 24 h reaction time and cooled to room temperature. GPC analysis showed an M _w of 1230,000 g / mol.

Ref e re .nzbei spi ej.6

A 200 L reactor conventional for free-radical polymerizations was charged with 1400 g of acrylic acid, 58.8 kg of 2-ethylhexyl acrylate, 9.8 kg of isobornyl acrylate and 53.3 kg of acetone / gasoline / isopropanol (49.5: 49.5: 1) , After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 40 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After 1 h reaction time again 40 g of AIBN was added. After 5 h and 10 h each was diluted with 15 kg acetone / isopropanol (90:10). After 6 and 8 h 100 g dicyclohexyl peroxydicarbonate (Perkadox ^® 16, Fa. Akzo Nobel) was added dissolved in each 800 g of acetone. The reaction was stopped after 24 h reaction time and cooled to room temperature.

GPC analysis showed an M _w of 1840,000 g / mol.

Production of the adhesive films for the sample samples

To the solution containing the polyacrylate were in each case the following amounts (in parts by weight) of crosslinker (tris (2,4-pentanedionato) aluminum (III) = aluminum (III) acetylacetonate), in each case based on 100% by weight. Parts of polyacrylate (solid), added (use of the crosslinker as a 3% solution in isopropanol). It was then diluted with isopropanol to a solids content of 30%. The polymer solutions thus obtained were each spread on a 50 μm thick siliconized polyester film. After the solvent was flashed off at room temperature, it was dried in the drying oven under the following conditions, whereby crosslinking took place.

Drying and curing conditions:

 based on 100 parts by weight of polyacrylate (solid)

The adhesive layer thickness after drying was 50 μm in each case. On the free

Side of the polyacrylate layer was then laminated a 50 micron thick siliconized polyester film.

 As side B of the polyacrylate layer, the surface is referred to, which rests on the first siliconized polyester film, as side A of the polyacrylate layer is the

Surface on which the second siliconized polyester film was laminated.

For the examination of the examples according to the invention, samples having two different films were produced with respect to each of the adhesive tape sides as shown above (one sample each with the films A1 and B1 and one with the films A2 and B2 per example): Separating films pointing to the side A of the adhesive, R _a [nm]:

Release film A1: R _a = 10.4 nm;

Release film A2: R _a = 28.7 nm

Separating films pointing to the side B of the adhesive, R _a [nm]:

Release film B1: R _a = 13.6 nm

Release film B2: R _a = 31, 3 nm

Analytical methods

^A ... Scherweg

 From the adhesive film to be examined, a sample sample [length 50 mm, width 10 mm] is cut out. From the sample sample one of the siliconized polyester films is peeled off.

The sample sample is glued with the exposed polyacrylate layer side onto a steel plate previously cleaned with acetone in such a way that the steel plate projects beyond the adhesive tape to the right and left and the adhesive tape projects beyond the steel plate by a distance of 2 mm at the upper edge. The bonding surface of the polyacrylate layer on the steel plate is height x width = 13 mm x 10 mm. The bonding site is then overrolled six times with a 2 kg steel roll, so that there is a firm bond.

 The sample pattern is flush with a sturdy cardboard backing strip on top of the film side, on which a displacement sensor (deflection sensor) rests. The sample is suspended vertically by means of the steel plate.

As measuring conditions a temperature of 40 ° C and otherwise norm conditions are chosen. The sample to be measured is provided at the lower end by means of a clamp (weight of the clamp 6.3 g) with a weight of 500 g (total load 506.3 g) and loaded for a period of time At ₁ of 15 min. Due to the firm adhesion of the polyacrylate layer on the steel plate and on the stabilizing film, shear forces act on the polyacrylate layer. The maximum deflection x _{max of} the position sensor after the predetermined duration at constant temperature is indicated as the result in μm.

After expiration of the period of time Δti under load, the weight and the clamp are removed; and there is a return movement of the polyacrylate layer by relaxation. After a relief period At ₂ of also 15 min, the residual deflection x _mιn of

Distance sensor measured.

The elastic proportion A _e ι _as t of the polyacrylate in percent results according to

(Xmax ~ Xmm) * 1 00

 Aelast =

B ^ Rh-someter measurements

 The measurements were carried out in a plate-on-plate configuration using a "RDA II" rheometer manufactured by Rheometrics Dynamic Systems and measuring a round sample with a sample diameter of 8 mm and a sample thickness of 1 mm.

The sample was obtained by laminating together 20 layers of the adhesive films prepared as above, which were for this purpose freed from the respective carrier material, so that a carrier-free 1 mm thick adhesive film was obtained, from which the round sample could be punched out.

 Measurement conditions: temperature 25 ° C, otherwise standard conditions, frequency of the oscillating shear stress 0.1 rad / s.

Q _.: Optical. evaluation

The siliconized release film was removed from the adhesive film to be examined on page A. A 175 μm thick polymethyl methacrylate (PMMA) film was laminated to the exposed side of the adhesive film. Subsequently, the second siliconized release film from side B of the adhesive film was peeled off and a second 175 micron thick PMMA film (Plexiglas Superclear®) also laminated on this side.

From the thus prepared composite of the polyacrylate layer and the PMMA films, 25 square sample samples (edge length of 20 cm each) were cut out and examined visually (naked eye) for the top side and for the bottom side for optical defects. Every discernible irregularity was registered and counted. From the results of the 25 sample patterns, the mean number of errors (arithmetic mean of the counted errors on top and bottom together) was formed and normalized to the number of errors per square meter (normalized mean error number n ^* ). Errors include all irregularities, such as streaks, air pockets, dents, grooves and the like, which are still visible to the human eye. D, .MolekuJargewichtsbestjrnmuηgen The weight-average molecular weight M _w was determined by gel permeation chromatography (GPC). The eluent used was THF containing 0.1% by volume of trifluoroacetic acid. The measurement was carried out at 25 ° C. The precolumn used was PSS-SDV, 5 μ, 10 ³ Å, ID 8.0 mm × 50 mm. For separation, the columns PSS-SDV, 5 μ, 10 ³ and 10 ⁵ and 10 ^{6 were used} , each with ID 8.0 mm x 300 mm. The sample concentration was 4 g / l, the flow rate 1, 0 ml per minute. It was measured against PMMA standards, (μ = μm, 1 λ = 10 ¹⁰ m).

E ,. Obecf! Ächen.rauhigkeit

The release material was removed from the adhesive film surface to be examined and, if necessary, the sample was stored open for long-term measurements for the specified period of time in such a manner that the exposed side pointed upward (clean room environment under

Standard conditions).

Regarding the diagonal of an area of 320 μm x 320 μm as the reference section, the surface profile was determined with a confocal microscope (type Nanofocus μscan) and from this the average roughness R _a for the characterization of the surface roughness was determined.

The average roughness R _a indicates the average distance of a measuring point on the surface to the center line. The center line intersects the true profile within the reference line so that the sum of the profile deviations with respect to the center line becomes minimal, and thus corresponds to the arithmetic mean of all deviations from the

Centerline.

The mean roughness values R _a were measured after a time t of 10 s and after a

Storage time t of 24 hours (each time after deduction of the release material) determined. The relative roughness R 1, after the time t, corresponds to the measured mean roughness R _{a, t} after the time t, relative to the average roughness R _{a 0} (time t = 0) in the covered one

Condition corresponding to the roughness of the release film:

The temporal change ΔR _{a of} the average roughness is defined as cn)

The adhesive tape according to the invention has a low weight average

Molecular weight, but still a high cohesion. The reference examples generally have a very high molecular weight (> 1000000 g / mol), so that the cohesion is relatively high. This results in sufficiently high shear strengths in the micro-shear test, but also only in a very high retention of the surface roughness. By the high

Molecular weight, the elastic fraction is also above 60%. An exception is Reference Example 3, since this has a very low molecular weight

(<200,000 g / mol) and thus the cohesion level is very low. Here, due to the high fluidity, no elastic component could be determined.

The optical assessment of the PMMA-laminated sample samples showed for the adhesive tapes of the invention a very low number of errors in the range of 10 errors / m ² . Even though this assessment is qualitatively relatively coarse, it can be clearly seen from the measurement results that the error numbers of the reference patterns are significantly different, in particular at least twice as high. It can also be seen from the results that the aluminum chelate crosslinking can be carried out even at very low temperatures. The cohesion level in the micro-shear test almost does not change and also the elastic component remains relatively constant and above 60%. Furthermore, it can be seen that the result can be improved even further by gentle thermal crosslinking. In particular, Examples 3, 4 and 5 show a very small number of errors / m ² (<10 errors / m ² ).

The following table shows the measured values of the tests on the adhesive surface roughnesses as a function of time (Analytical Method E) for the examples according to the invention.

Investigations on the adhesive surface roughness as a function of time (Analytical Method E) for the reference examples

O

Investigations on the adhesive surface roughness as a function of time (Analytical Method E) for the

reference Examples

w

From the table it can be seen that all examples according to the invention have a significant decrease in the surface roughness (average roughness R _a ). Thus, the value is 60% or less directly after peeling off the release film (10-second values). If you wait 24 hours, the value drops to 50% or less. By contrast, the reference examples in the following table all show significantly higher values after immediate removal of the release film or after 24 hours. Only Reference Example 3 achieves the target values of the inventive examples. This can be explained by the low viscosity of this reference example. However, the shear strength measurements described above also demonstrated that Cohesion was too low for Reference Example 3 to perform very good and stable optical bonds.

Claims

claims

1. A method for bonding optical components by means of an adhesive tape, characterized in that

 the adhesive tape at least one layer of a pressure-sensitive adhesive based on a

Polyacrylate having a weight-average molecular weight M _w in the range of 200000≤M _w <1 000 000 g / mol, which is obtainable by radical copolymerization of at least the following components:

 (A) 55 to 92 wt .-% of one or more acrylic monomers of the general formula

CH ₂ = CH-COORi

 wherein Ri represents a hydrocarbon radical having 4 to 14 carbon atoms, in particular

further wherein the glass transition temperature T _G , _{aH of} the homopolymer of the monomer of component (a) [defined as

Glass transition temperature value T according to DIN 53765 _9: 1994-03] not more than - 20 ⁰ C is

or wherein the glass transition temperature T _G , _a c of the

Copolymers of the monomers of Komonente (a) according to the Fox equation is not more than - 20 ⁰ C,

(b) 5 to 30 wt .-% of one or more copolymerizable monomers, wherein the glass transition temperature T _G , b _{H of} the homopolymer of the monomer of component (b) [defined as glass transition temperature T ₉ according to DIN 53765: 1994-03] is not less than 0 ⁰ C or wherein the glass transition temperature T _G , bc of

Copolymers is not less than 0 ⁰ C from the monomers of Komonente (b) according to the Fox equation,

 (c) 3 to 15% by weight of one or more copolymerizable monomers which promote crosslinking reaction of the polyacrylate, the polyacrylate being crosslinked,

 wherein the crosslinked polyacrylate by a loss factor (tan δ value) between

0.2 and 0.4 is characterized

 wherein the crosslinked polyacrylate has a shear strength which is characterized by a

Maximum deflection x _{max is characterized} in the micro-shear test from 200 to 600 μm, and wherein the crosslinked polyacrylate is characterized by an elastic content in the polyacrylate of at least 60%, determined in the micro-shear test.

2. The method according to claim 1, characterized in that

 as component (b) at least partially one or more acrylic and / or

Methacrylic monomers of the general formula

CH ₂ = C (R ₂ ) -COOR ₃

be used, wherein R ₂ = H or R ₂ = CH ₃ and wherein R _{3 represents} a hydrocarbon radical having at least 6 carbon atoms and for the conditions mentioned for component (b) with respect to the

Glass temperatures are met.

3. The method according to claim 1, characterized in that

 the tape is strapless.

4. The method according to claim 3, characterized in that

 the adhesive tape is formed by the PSA layer.

5. The method according to any one of the preceding claims, characterized in that

 as component (c) at least partially one or more acrylic and / or methacrylic monomers of the general formula

CH ₂ = C (R ₄ ) -COOR ₅

 be used

wherein R ₄ = H or R ₄ = CH ₃ and wherein R ₅ = H or R _{5 represents} an alkyl group having a functional group capable of and / or promoting a crosslinking reaction of the polyacrylate.

6. The method according to claim 5, characterized in that

wherein the glass transition temperature T _{G, CH of} the homopolymer from the

Monomer of component (c) [defined as the glass transition temperature value T according to DIN 53765 _9: 1994-03] not less than 0 ⁰ C.

or wherein the glass transition temperature T _G , _c c of the copolymer of the monomers of component (c) according to the Fox equation is not less than 0 ⁰ C.

7. The method according to any one of the preceding claims, characterized in that

 the crosslinking is thermally initiated.

8. The method according to claim 7, characterized in that

 aluminum chloride is added as the crosslinking initiator.

9. The method according to any one of claims 7 or 8, characterized in that the temperature in the crosslinking 90 °, preferably 60 ⁰ C does not exceed.

10. The method according to any one of the preceding claims, characterized in that

 as component (c) at least partially one or more copolymerizable photoinitiators are used.

1 1. adhesive tape having at least one layer of a pressure-sensitive adhesive based on a polyacrylate having a weight-average molecular weight M _w in the range of 200,000 <M _w <1 000 000 g / mol, wherein the polyacrylate is the polymerization of at least the following components

 (A) 55 to 92 wt .-% of one or more acrylic monomers of the general formula

CH ₂ = CH-COORi

 wherein Ri represents a hydrocarbon radical having 4 to 14 carbon atoms,

furthermore, if component (a) comprises only one monomer, the glass transition temperature T _G , _{aH of} the homopolymer of the monomer of component (a) [defined as glass transition temperature value T ₉ according to DIN 53765: 1994-03 (see Section 2.2 .1)] is not more than - 20 ⁰ C or, if component (a) comprises more than one monomer, the glass transition temperature T _G , _a c of the copolymer of the monomers of the component (a) according to the Fox equation no longer as - 20 ⁰ C, wherein for the calculation in the Fox equation, the glass transition temperature value T ₉ according to DIN 53765: 1994-03 (see. Section 2.2.1) of the homopolymers of the individual monomers of component (a) are used;

(B) 5 to 30 wt .-% of one or more copolymerizable monomers, wherein, when the component (b) comprises only one monomer, the glass transition temperature T _G , b _{H of} the homopolymer of the monomer of component (b) [defined as glass transition temperature value T ₉ to DIN 53765: 1994-03 (. see section 2.2.1)] is respectively not less than 0 ⁰ C wherein the glass transition temperature T _G, bc of the copolymer of the monomers of Komonente (b) according to the Fox equation is not less than 0 ⁰ C, wherein for the calculation in the

Fox equation the glass transition temperature value T ₉ according to DIN 53765: 1994-03 (see Section 2.2.1) of the homopolymers of the individual monomers of component (b) are used;

 (c) 3 to 15% by weight of one or more copolymerizable monomers which promote crosslinking reaction of the polyacrylate,

is

wherein the polyacrylate is crosslinked,

wherein the crosslinked polyacrylate by a loss factor (tan δ value) between

0.2 and 0.4 is characterized

wherein the crosslinked polyacrylate has a shear strength which is characterized by a

Maximum deflection x _{max is characterized} in the micro-shear test from 200 to 600 μm,

and wherein the crosslinked polyacrylate is characterized by an elastic content in the polyacrylate of at least 60%, determined in the micro-shear test.