EP2220522A1

EP2220522A1 - Optical adhesive tape for light management of keyboards

Info

Publication number: EP2220522A1
Application number: EP08857020A
Authority: EP
Inventors: Marc Husemann
Original assignee: Tesa SE
Current assignee: Tesa SE
Priority date: 2007-12-04
Filing date: 2008-12-03
Publication date: 2010-08-25
Also published as: DE112008003068A5; TW200934849A; CN101889223B; KR20100099259A; CN101889223A; WO2009071569A1; US20100263782A1; JP2011505483A

Abstract

The invention relates to an at least one-sided adhesive tape comprising at least one multi-layer substrate material and at least one layer of an adhesive, characterized by a light transmission of not more than 0.1% and a total light reflection of at least 80% and a diffuse light portion of 30 - 80%, and the use of such adhesive tapes for taping in the production of keyboards.

Description

tesa Aktiengesellschaft Hamburg

description

Optical pressure-sensitive adhesive tapes for light management of keyboards

The invention relates to single-sided or double-sided pressure-sensitive adhesive tapes with multilayer support structures and with light-reflecting properties with high diffuse light content and absorbing properties for backlighting of keyboards.

Pressure sensitive adhesive tapes are widely used processing aids in the age of industrialization. Especially for use in the electronics industry very high demands are placed on pressure-sensitive adhesive tapes. In addition to certain adhesion properties, pressure-sensitive adhesive tapes for certain applications should also fulfill optical properties.

One application area includes keyboards. Thus, keyboards are designed more and more elaborate and lighted for the simplified use at night and their backs. The rear illumination allows the assignment of numbers or letters to each key in the dark. This process is also associated with problems. For reasons of cost, the number of light sources should be limited. In addition, for example, reduced by a variety of light sources, the operating life of the batteries in notebooks, for example.

Therefore, solutions are currently being sought which reduce the number of light sources and, with a few light sources, enable uniform and homogeneous backlighting. For this reason, white films are often used as Lichtguide (light distributor). Another problem is the minimization of interfering light reflections, which also results in non-homogeneous illumination of the light and which reduces the precision of the illuminated letters or numbers. On the other hand, a reflection with a very high proportion of direct light on the reflection side leads to the appearance of light spots.

There is therefore still a need for backlighting of keyboards Pressure-sensitive adhesive tapes, the deficiencies described above, or only in a reduced manner or improve.

The object of the invention is therefore to provide single and / or double-sided pressure-sensitive adhesive tapes which have a high light absorption, which have a high light reflection, high light diffusion on the light-reflecting side and can serve for backlighting the illumination of keyboards.

The object is achieved by pressure-sensitive adhesive tapes, which allow not only a high light absorption but also a high diffuse light component for the backlighting of the keyboard due to certain carrier film properties.

The invention accordingly relates to at least one-sided pressure-sensitive adhesive tapes comprising at least one multilayer support material and at least one layer of a pressure-sensitive adhesive, characterized by a light transmission of not more than 0.1%, in particular less than 0.1%, a total light reflection of at least 80% (DIN 5063 part 3) and a scattered light content of 30 to 80%.

The invention is in particular realized by single- or double-sided pressure-sensitive adhesive tapes which comprise a multilayer carrier material and one or two identical or different pressure-sensitive adhesive mass layers and which have the aforementioned light parameters.

The invention relates in particular to single-sided or double-sided pressure-sensitive adhesive tapes which consist of a multilayer substrate and one or two identical or different PSAs which have a light transmission of less than 0.1% and DIN 5063 part 3 a total light reflection of greater than 80% and a scattered Proportion of light from 30 to 80%.

The invention further relates to the use of pressure-sensitive adhesive tapes according to the invention for optimizing the backlighting of keys (operating keys), keyboards or keypads, in particular electronic devices. Under "optimization" is here in particular an increase in the light output of one or more light sources (in particular LEDs, see the following version) for backlighting the keys, keyboards or keypads, in other words, a gain of in Direction of the keys, keyboards or keypads sent light while maintaining the power of the light sources. For this purpose, the pressure-sensitive adhesive tapes according to the invention can be used as a light guide (also referred to as a light guide or light distributor), in particular by being provided between the keys or the actual keypad and the light diodes.

The invention accordingly also relates, in particular, to the bonding in the production of keyboards or keypads, in particular electronic devices.

Figure 1 schematically shows the backlighting of such a keyboard and is an example of an application of the pressure-sensitive adhesive tapes according to the invention in a keyboard again.

Where:

1 LEDs (LEDs)

2 sensors

3 buttons

4 pressure-sensitive adhesive tape according to the invention

4a light-absorbing pressure-sensitive adhesive tape side

4b light-reflecting pressure-sensitive adhesive tape side

5 housing

# Light

Φs scattered light

As a light source usually LEDs (LEDs) (1) are used. The LEDs (1) distribute the light (Φ) via a light guide (light distributor). This is preferably done with a pressure-sensitive adhesive tape (4), which on one side (4a) is light-absorbing, in particular black and on the other side (4b) light-reflecting, in particular metallic. The light-reflecting side (4b) is preferably aligned to the side of the LEDs (1), reflects the light and increases the light output. The light-absorbing, in particular black side (4a) has the function of light absorption and is advantageously aligned towards the side of the keys (3). Thus, scattered light (φ _s ) is collected here and the precision of the light illumination of the button (3) is increased. The PSAs are used for fixing in the keyboard assembly.

By combining a high degree of reflection of the light-reflecting, in particular metallic side (4b) with a high diffuse light component becomes a more uniform illumination of the rear lighting unit achieved.

The adhesive tape according to the invention advantageously has a light-reflecting side and / or a light-absorbing side.

The adhesive tape according to the invention furthermore has, in particular for effecting the reflection of light, a metallically reflecting layer, wherein the metallically reflecting layer alone or supportively can be responsible for the reflection, and / or for effecting the absorption of light a color-carrying layer, ie in particular a colored layer or a colored layer Layer. The light-absorbing layer is in particular a dark, preferably a black layer

In the context of this application, the metallic-reflecting layers of the pressure-sensitive adhesive tapes according to the invention, in particular also in the embodiments of FIGS. 2 to 13 described below (in the sense of the light reflecting layers described above) can be replaced by white layers (for example white colored layers), in particular when the ref lektionsverhalten the white layers for the desired application is sufficient.

Metallic layers white but a better ref lective behavior and are therefore even better suited for the described application.

The pressure-sensitive adhesive tapes described in Figure 1 are described in more detail in the construction in the following figures. They consist of a multilayer substrate each with one or two PSAs, have a light transmission of less than 0.1% and according to DIN 5063 Part 3 a total light reflection of greater than 80% and a scattered light content of 30 to 80%.

product constructions

In a first advantageous embodiment according to FIG. 2, the pressure-sensitive adhesive tape according to the invention consists of a carrier film layer (a), two metallically reflecting layers (b), a color-carrying layer (c) and a PSA layer (d) on the light-reflecting side (b).

In a further advantageous embodiment according to FIG. 3, this consists Pressure-sensitive adhesive tape of the invention comprising a carrier film layer (a), two metallically reflecting layers (b), a color-carrying layer (c) and a PSA layer (d) on the color-carrying layer (c).

In a further advantageous embodiment according to FIG. 4, the pressure-sensitive adhesive tape according to the invention consists of a carrier film layer (a), two metallically reflecting layers (b), a color-carrying layer (c) and two PSA layers (d) and also (d '), the PSAs ( d) and (d ') can be identical or different composition.

In a further preferred embodiment of the invention, the pressure-sensitive adhesive tape according to the invention has the product structure outlined in FIG. Here, the double-sided pressure-sensitive adhesive tape consists of a carrier film (a), a metallically reflecting layer (b), a color-bearing layer (c) and two pressure-sensitive adhesive layers (d) and (d '), wherein the pressure-sensitive adhesives (d) are unjd (d') identical or can differ from each other.

In a next advantageous embodiment according to FIG. 6, the pressure-sensitive adhesive tape according to the invention consists of a carrier film (a), a metallically reflecting layer (b), a color-bearing layer (c) and a pressure-sensitive adhesive layers (d), wherein the pressure-sensitive adhesive (d) adheres to the reflective Side (b) is coated. This embodiment thus represents a single-sided pressure-sensitive adhesive tape.

In a next advantageous embodiment according to FIG. 7, the pressure-sensitive adhesive tape (here also one-sided) consists of a carrier film (a), a metallically reflecting layer (b), a color-carrying layer (c) and a pressure-sensitive adhesive layer (d), the pressure-sensitive adhesive (i.e. ) is coated on the color-bearing layer (c).

In a further preferred embodiment of the invention, the pressure-sensitive adhesive tape according to the invention has the product structure shown in FIG. 8; the double-sided pressure-sensitive adhesive tape consists here of a carrier film (a), a metallically reflecting layer (b), a color-carrying layer (c) and two pressure-sensitive adhesive layers (d) and (d '), wherein the pressure-sensitive adhesives may be identical or different from one another. FIG. 9 shows a further advantageous embodiment of a one-sided pressure-sensitive adhesive tape according to the invention; this consists of a carrier film (a), a metallically reflecting layer (b), a color-carrying layer (c) and a pressure-sensitive adhesive layer (d), wherein the pressure-sensitive adhesive (d) is applied to the reflective side (b).

For the advantageous embodiment of a one-sided pressure-sensitive adhesive tape according to the invention shown in FIG. 10, this consists of a carrier film (a), a metallically reflecting layer (b), a color-carrying layer (c) and a pressure-sensitive adhesive layer (d), wherein the pressure-sensitive adhesive (d) the color-carrying layer (c) is applied.

Also Fig. 1 1 shows an advantageous embodiment of a pressure-sensitive adhesive tape according to the invention, this consists of a carrier film (a), two metallically reflecting layers (b), at least two superimposed color-carrying layers (c) and (c ¹ ) and two pressure-sensitive adhesive layers (d) and (d ¹ ), wherein the PSAs may be identical or different from each other.

FIG. 12 shows an advantageous embodiment of a single-sided PSA tape according to the invention comprising a carrier film (a), two metallically reflecting layers (b), at least two color-coated layers (c) and (c ') and a pressure-sensitive adhesive layer (d) Pressure-sensitive adhesive (d) on the reflective side (b) is applied.

In the advantageous embodiment shown in FIG. 13, the one-sided pressure-sensitive adhesive tape according to the invention consists of a carrier film (a), two metallically reflecting layers (b), at least two color-coated layers (c) and (c ¹ ) and a pressure-sensitive adhesive layer (d) painted one above the other. , wherein the pressure-sensitive adhesive (d) is applied to the color-carrying layer (c ').

The carrier film (a) is preferably between 5 and 250 μm, more preferably between 8 and 50 μm, most preferably between 12 and 36 μm thick. The carrier film (a) is very preferably transparent, semitransparent or slightly translucent, for example by coloring. In a preferred embodiment of the invention, the film (a) is vapor-coated on one or both sides with metal, for example with aluminum or silver. The layers (b) are metallic shiny or slightly matt and light-reflecting. The layer thickness of the layers (b) is preferably between 5 nm and 200 nm. The layer or layers (c), (c ¹ ) are the color-carrying lacquer layers, each of which preferably has a layer thickness between 0.01 and 5 microns. In particular, these layers guarantee a good light absorption behavior of the corresponding adhesive tape side. In a very preferred embodiment, a black layer is used as the color-carrying layer (c ¹ ), for example by incorporating black dyes or pigments in the corresponding layer, (c) and (c ') can be of different chemical nature and can have different color-bearing pigments, which have an advantageous effect on the light-absorbing properties.

In the sense of the color-carrying layers, it is also possible to use lacquer layers, in particular black lacquer layers.

The pressure-sensitive adhesive layers (d) and (d ') preferably have a thickness of 5 μm to 250 μm, respectively. According to the invention, the individual layers (b), (c), (c '), (d) and (d ¹ ) within the single-sided or double-sided pressure-sensitive adhesive tape may differ with respect to the layer thickness, so that, for example, different thickness PSA layers can be applied.

Carrier film (a)

In principle, all filmic polymer supports can be used as film carriers. For example, polyethylene, polypropylene, polyethersulfones, polyamides, polyimides, polyetherimides, polyesters, polyphenylsulfides, polyamideimides, polyetherimides, polymethacrylates, styrene-based films, polycarbonates, polyetherketones, polyaryls, polyurethanes, polyacrylates, polybutyrals, polyethylvinyl acetates, polyethylene naphthylates and fluorinated polymers can be used , These types of polymers can be used alone or in combination. In a particularly preferred variant, polyester films are used, particularly preferably PET films (polyethylene terephthalate). For the embodiments shown in FIGS. 8 to 10, the carrier film (a) should be transparent, so that the corresponding design variants with transparent carrier film in each case represent a very preferred inventive embodiment of the particular inventive adhesive tape.

The films may be relaxed or have one or more preferred directions. Preferred directions are achieved by stretching in one or two directions.

For the inventive properties, the roughness profile of the carrier film (a) is crucial. Due to the film roughness, the diffuse component of the light reflection can be controlled after the metallization. For example, very preferably films with a film roughness R _a of greater than 0.05 μm, more preferably greater than 0.10 and very preferably greater than 0.15 μm are used. The preferred maximum film roughness _Ra is 0.35 .mu.m. The film roughnesses are measured according to DIN 4768 and can be quantified by the R _a value. With increasing film roughness, the diffuse light component in the light reflection of the metallic side is increased. The roughness R _{a of} the carrier film (a) should not exceed 0.35 μm, since otherwise the light reflection becomes too low.

The film roughness of the carrier film (a) can be controlled by the manufacturing process. Thus, for example, antiblocking agents, such as silica, chalk or chalk, zeolites, may be added to the film (a) in the manufacturing process. By increasing the anti-blocking agent content, the roughness of the film is increased. Furthermore, the films can also be embossed after extrusion. Here, the roughness of the carrier film can be controlled by an embossing roller.

Through this manufacturing process, it is also possible to make only one of the film sides rougher. In a very preferred variant of the invention, then the rough side is metallized, which is used as a light-reflecting side in the final application. Furthermore, the film roughness can also be controlled by the extrusion process. At the lip exit of the coating nozzle, roughnesses on the surface of the film can be produced by the lip profile. Also can be influenced by the temperature control in the coating nozzle, the surface roughness. Thus, the roughness can be increased by lowering the nozzle lip temperature. The absolute temperature profile depends on the extruded material (glass transition temperature, rheological profile).

Furthermore, the film roughness can be controlled by film additives. For example, nano- and micrometer-scale fillers can be added in order to increase the film roughness.

The roughness of the film is evenly distributed in a particularly preferred form. In a particularly preferred variant, the roughness has a prismatic structure.

It is to improve the anchoring of the paint layers or Metallevampfung vorzuillhaft to pretreat the films. The films may be etched (eg, trichloroacetic acid or trifluoroacetic acid), pretreated with corona or plasma, or equipped with a primer (eg, saran).

Reflecting layer (b)

To produce the light-reflecting and absorbing properties, the film (a) is advantageously vapor-coated on one or both sides with a metal, such as, for example, aluminum or silver.

In a very preferred variant of the invention, the film layer (a) is vapor-deposited on both sides with aluminum or silver. In order to achieve particularly excellent reflective properties, the sputtering process must be controlled so that the aluminum or silver is applied very evenly to achieve optimum reflection. Furthermore, in a very preferred embodiment, a plasma-pretreated film is used and vapor-coated on one or both sides with aluminum in one working step. Through the use of the reflective layer (b), on the one hand the light is deliberately reflected and, on the other hand, the transmission of the light through the carrier material is reduced. The surface roughness of film (a) remains after metallization, albeit in somewhat reduced form. The layer thickness of the metal layer must be completely opaque, i. the film (a) must be fully metallised.

For the production process, it may be advantageous if the metallized side is again protected by a clearcoat prior to coating with the PSA.

Color layers (c) and (c ^! )

The color layers (c) and (c ') can fulfill various functions. In a variant of the invention, the color layer has the function of perfect absorption of the external light. Therefore, in this case, for the double-sided pressure-sensitive adhesive tape, the transmittance in a wavelength range of 300 to 800 nm must be <0.5%, more preferably <0.1%, most preferably <0.01%. In a preferred variant of the invention, this is achieved with a black lacquer layer. In a curing binder matrix (preferably thermosetting system, but also radiation-curing system possible) black color pigments are mixed into the paint matrix. As paint materials, for example, polyesters, polyurethanes, Polyacrylates or polymethacrylates are used in conjunction with the paint additives known to the person skilled in the art. In a highly preferred inventive variant of the invention, soot or graphite particles are mixed into the binder matrix as color-carrying particles. In addition to complete light absorption, electrical conductivity is additionally achieved by means of this additivation (> 20% by weight) in addition to the complete light absorption, so that the inventive double-sided pressure-sensitive adhesive tapes likewise have antistatic properties. Furthermore, the layer (c) and (c ') may also have the additional function of an adhesion promoter. Here, the layer can also improve the adhesion of the pressure-sensitive adhesive (d) or (d ') to the carrier film (a) or to the metallic layer (b).

To enhance the absorbing property of the black color layer (c '), the color layer (c) can additionally be filled with white color pigments. As white color pigments are preferably titanium dioxide pigments.

Pressure Sensitive Adhesives (d) and (d)

The pressure-sensitive adhesives (d) and (d ') are identical in a preferred variant of the invention on both sides of the pressure-sensitive adhesive tape. However, in a specific variant of the invention it may also be advantageous if the pressure-sensitive adhesives (d) and (d ') differ from one another by layer thickness and / or chemical composition. Thus, for example, different adhesive properties can be set in this way. As pressure-sensitive adhesive systems for the inventive double-sided pressure-sensitive adhesive tape, acrylate, natural rubber, synthetic rubber, silicone or EVA adhesives are used. For an inventive variant of the invention, in which the double-sided inventive pressure-sensitive adhesive tape has a high reflection on at least one side, it is very advantageous if the pressure-sensitive adhesive preferably has a high transparency on at least this side.

In principle, however, it is also possible to process all other pressure-sensitive adhesives known to the person skilled in the art, as listed, for example, in the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, New York 1989).

For natural rubber adhesives, the natural rubber is not ground to a molecular weight (weight average) below about 100,000 daltons, preferably not below 500,000 daltons, and is additized. For rubber / synthetic rubber as the starting material for the adhesive are wide Variations given. Natural rubbers or synthetic rubbers or any blends of natural rubbers and / or synthetic rubbers can be used, the natural rubber or the natural rubbers in principle from all available qualities such as Crepe, RSS, ADS, TSR or CV types, depending on the required purity and viscosity level, and the synthetic rubber or synthetic rubbers from the group of random copolymerized styrene-butadiene rubbers (SBR), butadiene rubbers (BR), synthetic polyisoprenes (IR), butyl rubbers (NR), halogenated butyl Rubbers (XIIR), the acrylate rubbers (ACM), the ethylene-vinyl acetate copolymers (EVA) and the polyurethanes and / or their blends can be selected.

It is further preferable for rubbers to be added to improve the processability by adding thermoplastic elastomers having a weight fraction of from 10 to 50% by weight, based on the total elastomer content. Representative may be mentioned at this point especially the most compatible styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) types.

In an inventive variant of the invention, preference is given to using (meth) acrylate PSAs. (Meth) acrylate PSAs which are advantageously obtainable by free-radical polymerization and comprise at least 50% by weight of at least one acrylic monomer from the group of compounds of the following general formula:

wherein R ₁ = H or CH ₃ and the radical R ₂ = H or CH ₃ or is selected from the group of branched or unbranched, saturated alkyl groups having 1 to 30 carbon atoms.

The monomers are preferably selected such that the resulting polymers are used as pressure-sensitive adhesives at room temperature or higher temperatures in particular such that the resulting polymers have pressure-sensitive adhesive properties according to the Handbook of Pressure Sensitive Adhesive Technology by Donatas Satas (van Nostrand, New York 1989).

In a further inventive variant of the invention, the comonomer composition is selected such that the PSAs can be used as heat-activable PSAs.

The polymers can preferably be obtained by polymerization of a monomer mixture which is composed of acrylic acid esters and / or methacrylic acid esters and / or their free acids having the formula CH ₂ CC (R ₁ ) (COOR ₂ ), where R ₁ = H or CH ₃ and R _{2 is} an alkyl chain of 1-20 C atoms or H.

The molar masses M _{w of} the polyacrylates used are preferably Mw ≥ 200,000 g / mol.

In a very preferred manner, acrylic or methacrylic monomers are used which consist of acrylic and methacrylic acid esters having alkyl groups of 4 to 14 carbon atoms, preferably 4 to 9 carbon atoms. Specific examples, without wishing to be limited by this list, are methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate , Lauryl acrylate, stearyl acrylate, behenyl acrylate, and their branched isomers such as isobutyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isooctyl acrylate, isooctyl methacrylate. Further classes of compounds to be used are monofunctional acrylates or methacrylates of bridged cycloalkyl alcohols, consisting of at least 6 C atoms. The cycloalkyl alcohols may also be substituted, for example by C-1-alkyl groups, halogen atoms or cyano groups. Specific examples are cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate and 3,5-dimethyl adamantyl acrylate.

In one approach monomers are used, the polar groups such as

Carboxyl, sulfonic and phosphonic acid, hydroxy, lactam and lactone,

N-substituted amide, N-substituted amine, carbamate, epoxy, thiol, alkoxy. Cyan radicals, ethers or the like wear. Moderate basic monomers are, for example, N, N-dialkyl substituted amides, such as N, N-dimethylacrylamide, N, N-dimethylmethylmethacrylamide, N-tert-butylacrylamide, N-vinylpyrrolidone, N-vinyllactam, dimethylaminoethylmethacrylate, dimethylaminoethylacrylate, diethylaminoethylmethacrylate, diethylaminoethylacrylate, N Methylolmethacrylamide, N- (buthoxymethyl) methacrylamide, N-methylolacrylamide, N- (ethoxymethyl) acrylamide, N-isopropylacrylamide, but this list is not exhaustive.

Further preferred examples are hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, allyl alcohol, itaconic anhydride, itaconic acid, glyceridyl methacrylate, phenoxyethyl methacrylate, 2-butoxyethyl methacrylate,

Hydroxypropyl acrylate, maleic anhydride, phenoxyethyl acrylate, 2-butoxyethyl acrylate, cyanoethyl methacrylate, cyanoethyl acrylate, glyceryl methacrylate, 6 ~

Hydroxyhexyl methacrylate, vinylacetic acid, tetrahydrofufuryl acrylate, β-

-Acryloyloxypropionsäure, trichloroacrylic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, this list is not exhaustive.

In a further very preferred procedure, the monomers used are vinyl esters, vinyl ethers, vinyl halides, vinylidene halides, vinyl compounds having aromatic rings and heterocycles in the α-position. Here again, not only a few examples are mentioned: vinyl acetate, vinyl formamide, vinyl pyridine, ethyl vinyl ether, vinyl chloride, vinylidene chloride and acrylonitrile.

Furthermore, photoinitiators having a copolymerizable double bond are used in a further procedure. Suitable photoinitiators are Norrish I and II photoinitiators. Examples are, for example, benzoin acrylate and an acrylated benzophenone from UCB (Ebecryl P 36®). In principle, all photoinitiators known to those skilled in the art can be copolymerized, which can crosslink the polymer via UV irradiation via a radical mechanism. An overview of possible usable photoinitiators which can be functionalized with a double bond is given in Fouassier: "Photoinitiation, Photopolymerization and Photocuring: Fundamentals and Applications", Hanser-Verlag, Munich 1995. In addition, Carroy et al. in "Chemistry and Technology of UV and EB Formulation for Coatings, Inks and Paints". Oldring (ed.), 1994. SITA. London used. In a further preferred procedure, monomers are added to the comonomers described. which have a high static glass transition temperature. Suitable components are aromatic vinyl compounds, such as, for example, styrene, wherein the aromatic nuclei preferably consist of C ₄ - to C ₁₈ -components and may also contain heteroatoms. Particularly preferable examples are 4-vinylpyridine, N-vinylphthalimide, methylstyrene, 3,4-dimethoxystyrene, 4-vinylbenzoic acid, benzylacrylate, benzylmethacrylate, phenylacrylate, phenylmethacrylate. t-butylphenyl acrylate, t-butylphenyl methacrylate, 4-biphenyl acrylate and methacrylate, 2-naphthyl acrylate and methacrylate and mixtures of those monomers, this list being not exhaustive.

By increasing the aromatic content of the refractive index of the PSA increases and the dispersion between the LCD glass and PSA by, for example, extraneous light is minimized.

For further development, the PSAs may be mixed with resins. As the tackifying resins to be added, it is possible to use all of the previously known adhesive resins described in the literature. Mention may be made representative of the pinene, indene and rosin resins, their disproportionated, hydrogenated, polymerized, esterified derivatives and salts, the aliphatic and aromatic hydrocarbon resins, terpene resins and terpene phenolic resins and C5, C9 and other hydrocarbon resins. Any combination of these and other resins can be used to adjust the properties of the resulting adhesive as desired. In general, all compatible with the corresponding polyacrylate (soluble) resins can be used, in particular reference is made to all aliphatic, aromatic, alkylaromatic hydrocarbon resins,

Hydrocarbon resins based on pure monomers, hydrogenated hydrocarbon resins, functional hydrocarbon resins and natural resins. The presentation of the state of knowledge in the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, 1989) is expressly pointed out.

Here, too, transparent and very well compatible with the polymer resins are preferably used to improve the transparency. Hydrogenated or partially hydrogenated resins often have these properties. In addition, plasticizers (plasticizers), further fillers (such as, for example, fibers, carbon black, zinc oxide, chalk, solid or hollow glass spheres, microspheres made from other materials, silicic acid, silicates), nucleating agents, electrically conductive materials, such as, for example, conjugated polymers, may optionally be used , doped conjugated polymers, metal pigments, metal particles, metal salts, graphite, etc., blowing agents, compounding agents and / or anti-aging agents, for example in the form of primary and secondary antioxidants or in the form of light stabilizers.

In a further possible variant of the invention, the pressure-sensitive adhesive (d ') applied to the black layer (c) contains light-absorbing particles, such as, for example, black color pigments or carbon black or graphite particles as filler.

In addition, crosslinkers and promoters can be mixed for crosslinking. 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, it is also possible to add thermally activatable crosslinkers, such as, for example, Lewis acid, metal chelates or multifunctional isocyanates.

For optional crosslinking with UV light, UV-absorbing photoinitiators can be added to the PSAs. Useful photoinitiators which are very useful are benzoin ethers such as benzoin methyl ether and benzoin isopropyl ether, substituted acetophenones such as 2,2-diethoxyacetophenone (available as Irgacure 651® from Ciba Geigy®, 2,2-dimethoxy-2-one). phenyl-1-phenylethanone, dimethoxyhydroxyacetophenone, substituted α-ketols such as 2-methoxy-2-hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthylsulfonyl chloride, and photoactive oximes such as 1-phenyl-1,2-propanedione; 2- (Oethoxycarbonyl) oxime.

The above-mentioned and other usable photoinitiators and others of the Norrish-I or Norrish-II type may contain the following radicals: benzophenone, acetophenone, benzil, benzoin, hydroxyalkylphenone, phenylcyclohexylketone, anthraquinone, trimethylbenzoylphosphine oxide, methylthiophenylmorpholine ketone -, 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 more amino groups or hydroxy groups may be substituted. A representative overview is given by Fouassier: "Photoinitiation, Photopolymerization and Photocuring: Fundamentals and Applications", Hanser-Verlag, Munich 1995. In addition, Carroy et al., Chemistry and Technology of UV and EB Formulation for Coatings, Inks and Paints ", Oldring (ed.), 1994, SITA, London.

Coating process, equipment of the carrier material

To produce pressure-sensitive adhesive tapes according to the invention, in a preferred procedure, the pressure-sensitive adhesive is coated from solution onto the support material. To increase the anchoring of the pressure-sensitive adhesive, it is optionally possible to pretreat the layers (b) or (c) and (c ¹ ). For example, can be pretreated with corona or with plasma, it can be applied from the melt or solution, a primer or it can be chemically etched.

Especially with a black lacquer layer but the corona power should be minimized, since otherwise pinholes (optical defects, impurities) are burned into the film. For the coating of the PSA from solution, the solvent is removed by way of heat supply, for example in a drying tunnel, and optionally the crosslinking reaction is initiated.

The polymers described above can furthermore also be coated as hotmelt systems (ie from the melt). For the production process, it may therefore be necessary to remove the solvent from the PSA. In principle, the methods known to those skilled in the art can be used here. A very preferred method is concentration over a single or twin screw extruder. The twin-screw extruder can be operated in the same direction or in opposite directions. The solvent or water is preferably distilled off over several vacuum stages. In addition, depending on the distillation temperature of the solvent is heated counter. The residual solvent contents are preferably <1%, more preferably <0.5% and very preferably <0.2%. The hotmelt is processed from the melt.

For coating as a hotmelt different coating methods can be used. In one embodiment, the PSAs are over Roll coating process coated. Different roll coating methods are described in the Handbook of Pressure Sensitive Adhesive Technology by Donatas Satas (van Nostrand, New York 1989). In a further embodiment is coated via a melt nozzle. In another preferred method is coated by extrusion. The extrusion coating is preferably carried out with an extrusion die. The extrusion dies used can advantageously come from one of the following three categories: T die, fishtail die and ironing nozzle. The individual types differ in the shape of their flow channel. The coating can also give the PSAs orientation.

Furthermore, it may be necessary for the pressure-sensitive adhesive composition to be crosslinked. In a preferred embodiment, crosslinking is effected with electron and / or UV radiation.

For UV crosslinking is irradiated by brief 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 240 W / cm. The irradiation intensity is adapted to the respective quantum efficiency of the UV photoinitiator and the degree of crosslinking to be set.

Furthermore, it is possible in a variant of the invention to crosslink the PSAs with electron beams. Typical irradiation devices which can be used are linear cathode systems, scanner systems or segment cathode systems, if they are electron beam accelerators. A detailed description of the prior art and key process parameters can be found at Skelhorne, Electron Beam Processing, in Chemistry and Technology of UV and EB formulation for Coatings, Inks and Paints, Vol. 1, 1991, SITA, London. The typical acceleration voltages are in the range between 50 kV and 500 kV, preferably 80 kV and 300 kV. The applied waste cans range between 5 to 150 kGy, in particular between 20 and 100 kGy.

Both crosslinking methods or other methods enabling high-energy irradiation can also be used.

Furthermore, the subject of the invention is the use of the one- and double-sided Pressure-sensitive adhesive tapes for bonding backlighting units for keyboards. The bonding is shown as an example in Figure 1. For use as a pressure-sensitive adhesive tape, the single-sided or double-sided pressure-sensitive adhesive tapes may be covered with one or two release films or release papers. In a preferred variant of the invention, siliconized or fluorinated films or papers, such as glassine, HPDE or LDPE coated papers are used, which in turn are provided with a release layer based on silicones or fluorinated polymers or fluorinated silicones.

Accordingly, the pressure-sensitive adhesive tapes according to the invention can be used in particular for optimizing the backlighting of the keyboards.

Examples

The invention will be described below without wishing to be unnecessarily limited by the choice of examples.

The following test methods were used.

Test Methods

A..Transmissjon

The transmission was measured in the wavelength range from 190 to 900 nm using a Uvikon 923 from the company Biotek Kontron. The Absolute Transmission is given as the value at 550 nm in%.

ß _.. - _. _R. auhjρ _A speed

The roughness of the film is determined and specified according to DIN 4768. The roughness is given in terms of the R _a value in μm.

C, .Reflekti.on

The reflection test is carried out according to DIN standard 5063 part 3. The measuring instrument used was an Ulbrecht sphere type LMT. The reflectance and the scattered light components are given in%. PoJy m er.1.

A 200 L reactor conventional for radical polymerizations was charged with 2400 g of acrylic acid, 64 kg of 2-ethylhexyl acrylate, 6.4 kg of N-isopropylacrylamide and 53.3 kg of acetone / isopropanol (95: 5). After 45 minutes, passing nitrogen gas while stirring, the reactor was heated to 58 ⁰ C and 40 g of 2,2'-azoisobutyronitrile (AIBN) was added. Subsequently, the outer heating bath was heated to 75 ⁰ 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 (95: 5). After 6 h and 8 h, in each case 100 g of dicyclohexyl peroxydicarbonate (Perkadox 16®, from Akzo Nobel) dissolved in 800 g of acetone in each case were added. The reaction was stopped after 24 h reaction time and cooled to room temperature.

Networking

The pressure-sensitive adhesives are coated from solution onto a siliconized release paper (PE-coated release paper from. Loparex), dried for 10 minutes in a drying oven at 100 ⁰ C and then crosslinked with 25 kGy dose at an accelerating voltage of 200 kV. The mass application was in each case 50 g / m ² .

Foils (AI evaporation):

The PET films were coated on both sides with aluminum until a full-surface aluminum layer was applied on both sides. The film was vapor-deposited at a width of 300 mm by the sputtering method. In this case, positively charged, ionized argon gas is passed into a high-vacuum chamber. The charged ions then strike a negatively charged Al plate and dissolve aluminum particles at the molecular level, which then deposit on the polyester film passed over the plate.

Foils (color painting):

Production of the black color:

The black paint was made from 4 parts Hardener CVL no. 10 (from Dainippon Ink and Chemieals, Inc.) and 35 parts Daireducer ™ V No. 20 (by Dainippon Ink and Chemieals, Inc.) and 100 parts of Panacea ™ CVL-SPR805 paint (from Dainippon Ink and Chemieals, Inc.), a vinyl chloride-vinyl acetate based paint.

Slide 1 (black / silver):

On one side of the Al-coated film SO 15 (base polyester film SKC SO 15, R _a = 0.221 microns to Test Method B), the black color is applied evenly and dried for 48 hours at 45 ⁰ C. The black lacquer coated side is completely and evenly black. The application is about 2 g / m ² .

Foil 2 (black / silver):

On one side of the Al-coated film SC 44 (base polyester film SKC SC 44, R _a = 0,1 1 micron by test method B) (based on Hostaphan ™ 5210), the white color applied evenly and for 48 hours at 45 ⁰ C. dried. The application is 2 g / m ² . Then it is painted again on the same side with the black color. It is dried again at 45 ^° C. for 48 hours. The double coated side is completely and evenly black. The application of both colors is 4 g / m ² .

Foil 3 (black / silver):

On one side of the Al-coated film SC 42 (base SKC polyester film SC 42, R _a = 0.08 microns to test method B), the black color is applied flat and dried for 48 hours at 45 ⁰ C. The black lacquer coated side is completely and evenly black. The application is about 2 g / m ² .

Reference film 1 (black / white):

On one side SW083 (SKC polyester film 23 microns), the black color is applied flat and dried at 45 ⁰ C for 48 hours. The black lacquer coated side is completely and evenly black. The application is about 2 g / m ² .

Reference foil 2 (black / silver):

On one side of the Al-coated film (PET film R _a = 1, 00 microns according to test method B), the black color is applied flat and dried for 48 hours at 45 ⁰ C. The black lacquer coated side is completely and evenly black. The application is about 2 g / m ² . example 1

The film 1 is coated in the laminating with the polymer 1 on one side with 50 g / m2.

Example 2

The film 1 is coated in the lamination process with the polymer 1 on both sides with 50 g / m ² .

Example 3

The film 2 is coated in the lamination process with the polymer 1 on one side with 50 g / m2.

Example 4

The film 2 is coated in the lamination process with the polymer 1 on both sides with 50 g / m ² .

Example 5

The film 3 is coated in the lamination process with the polymer 1 on one side with 50 g / m ² .

Example 6

The film 3 is coated in the lamination process with the polymer 1 on one side with 50 g / m2.

Reference Example 1

The reference film 1 is coated in the lamination process with the polymer 1 on both sides with 50 g / m ² .

Reference Example 2

The reference film 2 is coated in the lamination process with the polymer 1 on both sides with 50 g / m ² . Results

Examples 1 to 6 were tested together with Reference Examples 1 and 2 according to Test Method A. The results are shown in Table 1. From the results of Table 1 it can be seen that Examples 1 to 6 and Reference Examples 1 and 2 have a very low transmission of less than 0.1%. The measurements prove that both the composition of the paint and the metallization can achieve a very low light transmission for the adhesive tapes.

To study the reflection behavior, optical measurements were taken from the metallized side. For this purpose was glued as a reference against glass.

The values are shown in Table 2.

The results show that with increasing roughness the diffuse fraction in the

Reflection increases significantly. At the same time, the reflection values are still at a very high level. Reference Example 1 demonstrates that only a small reflection value can be achieved with a white and smooth film having an R _a value of 0.05 μm.

Reference Example 2 with an R _a value of greater than 0.35 μm proves that with very high roughness the diffuse fraction is very high (greater than 80%), but the entire

Reflection (total) has fallen significantly and is well below 80%. Thus, the Luminous efficiency at the gluing of the backlight unit of keyboards too low.

Examples 1, 3, 5, 6 and Reference Example 2 were fixed on the rear side of a back-lit keyboard for the performance testing. The keyboard has buttons in the size 1 x 1 cm and a total size of about 8 cm x 28 cm.

In contrast, occur when using the reference example 1 light spots in the bonding of the backlight unit with the LC display in the display, which must be avoided. It was backlit with 8 LED units (each 3 mm diameter / 8000 med / white / 3.4 volts operating voltage / 20 ° opening angle). Subsequently, the total luminous efficacy of the keyboard was determined by the numbers and letters in the dark. By using Examples 1, 3, 5 and 6, in contrast to Reference Example 2, the luminous efficacy of the overall membrane keyboard could be increased by 2.5%.

Claims

claims

1. At least one-sided pressure-sensitive adhesive tape comprising at least one multilayered support material and at least one layer of a pressure-sensitive adhesive, characterized by a light transmission of not more than 0.1% and a total light reflection of at least 80% and a scattered light fraction of 30 to 80%.

2. Pressure-sensitive adhesive tape according to claim 1, characterized in that it is a double-sided adhesive tape ..

3. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that it has a light-reflecting side and a light-absorbing side.

4. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that the light absorption of the light-absorbing side is wholly or partly caused by a black-colored layer of the adhesive tape.

5. Pressure-sensitive adhesive tape according to one of the preceding claims, characterized in that the light reflection of the light-reflecting side is wholly or partly caused by a metallically reflecting layer of the adhesive tape.

6. Use of an at least one-sided pressure-sensitive adhesive tape comprising at least one multilayer support material and at least one layer of a pressure-sensitive adhesive, wherein the pressure-sensitive adhesive tape has a light transmission of not more than 0.1% and a total light reflection of at least 80% and a scattered light component of 30 to 80% has, for optimizing the backlighting of keyboards or keypads especially electronic devices.

7. Use according to claim 6, characterized in that a pressure-sensitive adhesive tape according to one of claims 2 to 5 is used.