WO2012013419A1

WO2012013419A1 - Adhesive seal

Info

Publication number: WO2012013419A1
Application number: PCT/EP2011/060055
Authority: WO
Inventors: Marc Husemann; Werner Kluge-Paletta; Sandra Backhaus
Original assignee: Tesa Se
Priority date: 2010-07-26
Filing date: 2011-06-16
Publication date: 2012-02-02
Also published as: TW201211425A; DE102010038429A1

Abstract

The invention relates to a bridgelike or framelike seal comprising a foam element, a first adhesive, provided on the top side of the foam element, and a second adhesive, provided on the bottom side of the foam element, characterized in that the bridge width of the seal at its narrowest point is not more than 1.5 mm, the foam element has a maximum thickness of 400 µm and consists of one or more closed-pore foams having a density in the range from 100 to 400 kg/m³, the first adhesive having a bond strength to polymethyl methacrylate (PMMA), as measured by ASTM-D 3330 Method C, of at least 3 N/cm, the second adhesive having a bond strength to acrylonitrile-butadiene-styrene copolymer (ABS), as measured according to ASTM-D 3330 Method C, of not more than 1.5 N/cm. The invention further encompasses a method for the sealing of joints between or openings in components made of metal, glass and/or plastic, by means of the aforementioned seal, the compression of the seal amounting to not more than 25 ± 1%, preferably not more than 10%, of its thickness in the free (i.e. unbonded) state.

Description

description

Adhesive seal

The invention relates to a double-sided pressure-sensitive adhesive seal with differentiated adhesive behavior, a method for the production and the use for sealing in portable electronic devices.

In portable electronic devices, a variety of seals are used. With the seals, it should be avoided that e.g. Dust, dirt or moisture enters the device. Particularly affected are portable electronic devices, as they are also used outdoors. A particular area of use is e.g. Mobile phones. There are additional openings here, e.g. Tones (speaker openings or microphone openings). For sealing, foam materials are generally used in portable electronic devices. Very popular are e.g. Polyurethane foams. These foam types have a partially open-cellular and a partially closed cell structure. These are e.g. commercially available under the Trademark Poron ™ from Rogers. To achieve optimum sealing behavior, these foams are used under pressure. Some of these seals are designed to be adhesive on one side to prevent slippage of the seal from the required position. The sealing effect itself is only effected by the compression of the seal in the sealing joint. By compression, all cells close and it can no longer penetrate dust or moisture.

For example, in the bonding of display windows in the housing, the sealing joint is sealed by appropriate seals. For sealing, the display unit is pressed against the seal and housing frame, so that the foam seals. Due to the compression but also reduces the pressure and shock absorbing potential of the foam, since this is already compressed in order to achieve the sealing function. In general, there is a trend that the portable electronic devices are getting smaller and thinner. This reduces the available surfaces and layer heights for sealing. The existing systems can not do this anymore. Furthermore, there is also a cost pressure on the manufacturers. However, the common types of polyurethane are relatively expensive to manufacture. In addition, they must be compressed heavily in order to achieve a good sealing behavior. This place is no longer available.

Furthermore, there is a strong trend in the electronics industry to recycle. Components should also be removable from one another without residue, in order to be separated according to type or even to enable repair processes. This also makes special demands on the bonding of the foams.

There is thus a need for a pressure-sensitive adhesive seal which does not have the list of technical disadvantages or restrictions summarized above.

The object is achieved by a particular web or frame-shaped seal, comprising a foam body, provided on the top of the foam body first adhesive and provided on the underside of the foam body second adhesive, the web width of the seal at its narrowest point not more than 1 , 5 mm, the foam body has a maximum thickness of 400 μηη and consists of one or more closed-cell foams with a bulk density in the range of 100 to 400 kg / m ³ , further wherein the first adhesive has a measured according to ASTM D 3330 bond strength a surface of polymethyl methacrylate (PMMA) of at least 3.0 N / cm (strongly adhesive adhesive), and wherein the second adhesive has an adhesive force measured according to ASTM-D 3330 on an acrylonitrile-butadiene-styrene copolymer (ABS) surface of at most 1.5 N / cm (low-adhesion adhesive).

Preferably, the bond strength measured according to ASTM-D 3330 of the first adhesive on a surface of polymethyl methacrylate (PMMA) is at least 5.0 N / cm; very preferably at least 7.5 N / cm, particularly preferably more than 9.5 N / cm,

More preferably, the adhesive force of the second adhesive measured on a surface of ABS 1, 0 N / cm or less, measured according to ASTM-D 3330. The subclaims relate to preferred further developments, to methods of production and to the use of the pressure-sensitive adhesive seal.

The measurement of the bond strengths given in this document corresponds, unless otherwise stated, to ASTM D 3330 / D 3330M-04 dated 01. October 2004, Test Method C (Adhesion of Double-Coated Tape); Section 13 (also referred to in this document as "ASTM-D 3330 Method C").

As a modification of point 6.2 of the above provision, the following materials were used as panels (measuring substrates), not steel, but the following materials (all values refer to these measuring substrates):

The polymethyl methacrylate used was colorless PMMA XT with a thickness of 3 mm. The material was produced by extrusion.

The ABS sheets are obtainable by extrusion of molten ABS pellets having a composition of 50% by weight of styrene, 30% by weight of acrylonitrile and 20% by weight of butadiene. Sheets were used in 3 mm thickness.

The glass used was soda lime glass with a thickness of 3 mm. The glass is composed of 75.5% silica, 12.9% sodium oxide and 1.6% calcium oxide.

The surfaces of all three materials are smooth (glossy), scratch-free, untreated and cleaned. The surface roughness value given in item 6.3 of ASTM D 3330 / D 3330M -04 is observed for all three substrates.

The seals according to the invention are usually punched out of larger layers. For the measurement of bond strengths, samples are used having the sizes mentioned in the measurement instructions, which have the same layer structure as the seals according to the invention. Thus, the measured sealing material samples may have larger dimensions than the gasket according to the invention per se, without this resulting in a contradiction or a lack of clarity.

For the invention it is very advantageous if the anchoring forces between the first adhesive and the foam body and between the second adhesive and the foam body at a measured according to ASTM-D 3330 method C (peel angle 180 °) measurement are each greater than the bond strength of second adhesive on ABS. The above condition is fulfilled when it is in the implementation of the cited measurement to no failure of the anchorages of the two bond strengths on the foam body, so the adhesive layers do not dissolve from the foam body before the compound of the second adhesive is dissolved on the ABS surface, in particular completely dissolved.

By adhering to the aforementioned condition can be ensured that the seal when detaching the seal of a housing body (in particular ABS or comparable with ABS in its surface properties material) not undesirably splits.

Advantageously, at least one of the anchoring forces between the first adhesive and the foam body and between the second adhesive and the foam body at a measurement carried out according to ASTM-D 3330 method C (peel angle 180 °) by at least 20% greater than the bond strength of the second Adhesive on ABS. This is very preferably the case for both mentioned anchoring forces.

The double-sided pressure-sensitive adhesive seal according to the invention is used in particular for the bonding of components in electronic consumer goods. The details of the bond strengths of the adhesives used on PMMA and on ABS correspond to typical materials usually bonded together in such products.

An alternative solution to the objective problem can be found by the fact that a seal is used, is used as the reference bonding surface glass on both sides. Thus, the invention further relates to a particular web or frame-shaped seal comprising a foam body, provided on the top of the foam body first adhesive and provided on the underside of the foam body second adhesive, wherein the web width of the seal at its narrowest point not more than 1 , 5 mm, the foam body has a maximum thickness of 400 μηη and consists of one or more closed-cell foams with a bulk density in the range of 100 to 400 kg / m ³ , further wherein the first adhesive has a measured according to ASTM D 3330 bond strength a glass surface of at least 5.0 N / cm (strongly adhesive adhesive), and wherein the second adhesive has a measured according to ASTM D 3330 bond strength on a glass surface of at most 1, 5 N / cm (low-adhesion adhesive). The first adhesive (strongly adhesive adhesive) and the second adhesive (weakly adhesive adhesive) in each case have the values indicated in each case both for PMMA or ABS and for glass.

As the first adhesive (strongly adhesive adhesive) and / or as the second adhesive (weakly adhesive adhesive) it is particularly advantageous to use pressure-sensitive adhesives.

First adhesive (strongly adhesive adhesive)

Acrylic, natural rubber, synthetic rubber, silicone or EVA adhesives are advantageously used as adhesive composition systems, in particular pressure-sensitive adhesive systems, for the inventive double-sided pressure-sensitive adhesive tapes. The adhesives based on polymers and / or copolymers based on Acrylate and / or Methacrylatderiavten (hereinafter referred to as Acrylathaftklebemasse). In principle, depending on the desired bonding conditions, it is also possible to use the other PSAs known to the person skilled in the art. For an overview of suitable PSAs, reference is made to the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, New York 1989).

The strongly adhesive adhesive is selected or further processed in such a way that it has the defined adhesive forces on PMMA or glass.

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.

In the case of rubber / synthetic rubber as the starting material for the adhesive, wide variations are possible, it can be selected, for example, from the group of natural rubbers and / or the group of synthetic rubbers and / or from any blend of natural rubbers and / or synthetic rubbers, the natural rubber or synthetic rubber the natural rubbers in principle from all available qualities such as Crepe, RSS, ADS, TSR or CV types, depending on the required level of purity and viscosity, and the synthetic rubber or the synthetic rubbers from the group of random copolymerized styrene-butadiene Rubbers (SBR), butadiene rubbers (BR), synthetic polyisoprenes (IR), Butyl rubbers (HR), halogenated butyl rubbers (XIIR), acrylate rubbers (ACM), ethylene-vinyl acetate copolymers (EVA) and polyurethanes and / or blends thereof can be selected.

Further, for the purpose of improving the processability, rubbers may preferably be added with thermoplastic elastomers having a weight fraction of 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 particularly preferred design, acrylic PSAs are preferably used.

The acrylate PSAs used are preferably obtainable by free-radical polymerization. The acrylic pressure-sensitive adhesives used advantageously comprise at least 50% by weight of polymers and / or copolymers [hereinafter referred to as (co) polymers] based on one or more acrylic monomers from the group of the compounds of the following general formula:

wherein Ri = 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, especially those having 1 to 30 carbon atoms.

The monomers are preferably chosen such that the resulting polymers can be 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 This can be done, for example, by choosing the appropriate static glass transition temperature. The PSAs used preferably have a static glass transition temperature T _G of not more than 20 ° C. The glass transition temperature is advantageously adjusted by the choice of monomers for the preparation of the (co) polymers and / or the choice of admixed additives which influence the glass transition temperature, in particular resins.

To achieve the desired static glass transition temperature of the (co) polymers, the monomers are very preferably selected in such a way and the quantitative composition of the monomer mixture is advantageously chosen such that according to the Fox equation (G1) (compare TG Fox, Bull. Soc 1 (1956) 123) gives the desired T _G value.

(G1)

T 'G £ - n T' G, n

Here 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. By mixing with resins increases in the Usually the static glass transition temperature. By choosing a suitable static glass transition temperature of the (co) polymers and choosing the type and amount of optionally added resins, the desired glass transition temperature of the PSA can be realized.

The determination of the glass transition temperature T _G can be done by differential scanning calorimetry DDK (English: DSC) according to DIN 53765: 1994-03; The information on the glass transition temperature in the context of this document refers to the extrapolated onset temperature T _g0 ^E according to this standard, cf. Section 2.2.1, unless specified otherwise.

The molar masses M _w (weight average) of the polyacrylates used are preferably M _w > 200,000 g / mol. The molecular weights M _w given in the context of this document refer to the measurement by size exclusion chromatography (GPC).

In a very preferred manner, the monomers used are acrylic and methacrylic acid esters whose hydrocarbon radicals comprise 4 to 14 C atoms, preferably 4 to 9 C atoms, and are in particular alkyl groups. Specific examples of such monomers, 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 advantageously usable classes of compounds are monofunctional acrylates and / or methacrylates of bridged cycloalkyl alcohols having at least 6 C atoms in the cycloalkyl alcohol radical. The cycloalkyl alcohols may also be substituted, e.g. by C 1-6 -alkyl groups, halogen atoms or cyano groups. Specific examples are cyclohexyl methacrylates, isobornyl acrylate, isobornyl methacrylates and 3,5-

Dimethyladamantyl.

In a further preferred procedure, monomers are used which contain polar groups such as carboxyl radicals, sulfonic and phosphonic acids, hydroxyl radicals, lactam and lactone, N-substituted amide, N-substituted amine, carbamate, epoxy, thiol, alkoxy. Cyan radicals, ethers or the like wear.

Moderate basic monomers are e.g. Ν, Ν-dialkyl substituted amides, e.g. N, N-dimethylacrylamide, Ν, Ν-dimethylmethacrylamide, N-tert-butylacrylamide, N-vinylpyrrolidone, N-vinyllactam, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate,

Diethylaminoethyl methacrylate, diethylaminoethyl acrylate, N-methylolmethacrylamide, N- (buthoxymethyl) methacrylamide, N-methylolacrylamide, N- (ethoxymethyl) acrylamide, N-isopropylacrylamide, but this list is not exhaustive.

Further preferred examples are 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, vinylacetic acid, tetrahydrofufuryl acrylate, β-acryloyloxypropionic acid, trichloroacrylic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, although this list is not exhaustive.

In a further very preferred procedure, the (co) 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 the company. 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.

In a further preferred procedure, comonomers whose homopolymers have a high static glass transition temperature are added to the described monomers. Suitable components include aromatic vinyl compounds such as styrene, in which the aromatic nuclei preferably C ₄ - to C ₈ - can comprise blocks and contain heteroatoms. Particularly preferable examples are 4-vinylpyridine, N-vinylphthalimide, methylstyrene, 3,4-dimethoxystyrene, 4-vinylbenzoic acid, benzylacrylate, benzylmethacrylate, phenylacrylate, phenylmethacrylate, t-butylphenylacrylate, t-butylphenylmethacrylate, 4-biphenylacrylate and methacrylate, 2-naphthylacrylate and methacrylate and mixtures of those monomers, this list is not exhaustive.

To achieve stronger adhesive properties resins are optionally added to the PSAs. Tackifying resins which can be used are the previously known adhesive resins described in the literature, in particular those which dissolve homogeneously in the base polymer or base copolymer. The homogeneity of such solutions can advantageously be determined by DSC measurement. In case of incompatibilities, in addition to the static glass transition temperature, melt peaks which originate from undissolved resin are then measured.

Examples of readily soluble and therefore advantageously usable resin types are 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, C5, C9 and other hydrocarbon resins. Any combination of these and other resins may be used to effect the Adjust the properties of the resulting adhesive as desired. In general, all compatible with the corresponding polyacrylate (soluble) resins can be used, the compatibility depends strongly on the polarity of the polyacrylate.

Furthermore, the PSA may optionally be admixed with phosphate plasticizers (plasticizers). These usually reduce the static glass transition temperature and lower the bond strength.

Other useful additives are fillers, microspheres of other materials, silicic acid, silicates, nucleating agents, blowing agents, compounding agents and / or anti-aging agents, e.g. be added in the form of primary and secondary antioxidants or in the form of sunscreens.

In addition to the static glass transition temperature, in particular of less than 20 ° C., the degree of crosslinking is decisive for the properties; in particular, this applies to acrylate PSAs. In order to achieve optimum pressure-sensitive adhesive properties, it is very advantageous if the gel value of the PSA is between 30 and 70% (see method gel value determination). Over-crosslinking leads to a decrease in the bond strength, sub-crosslinking to a cohesive gap. The crosslinking of the PSA can in principle be effected by means of high-energy radiation (electron beams and / or ultraviolet rays), alternatively or additionally also with thermal energy (heat input and / or suitable thermal crosslinkers).

To achieve the desired gel value range 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. For thermal crosslinking metal chelates or metal salts can be added in particular advantageous. Particularly suitable are e.g. Aluminum chelate or titanium chelate. The degree of crosslinking in thermal crosslinking can be controlled by the amount of crosslinker added. Thus, for polyacrylates, between 0.1 and 0.6 parts by weight of metal chelate or epoxy compound or isocyanate compound (data based on 100 parts by weight of base polymer) are generally added in order to achieve the desired degree of crosslinking.

For optional crosslinking with UV light, UV-absorbing photoinitiators may be added to the polyacrylate PSAs. Useful photoinitiators, which are very are good to use are benzoin ethers, such as. 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 - phenylethanone, 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 other usable photoinitiators and others of the type Norrish I or Norrish II may contain the following radicals: benzophenone, acetophenone, benzil, benzoin, hydroxyalkylphenone, phenylcyclohexylketone, anthraquinone, trimethylbenzoylphosphine oxide, methylthiophenylmorpholinketone, aminoketone , Azobenzoin, thioxanthone, hexarylbisimidazole, triazine or fluorenone, each of which may be additionally substituted with one or more halogen atoms and / or one or more alkoxy groups and / or one or more amino groups or hydroxy groups. 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. In the case of UV crosslinking, the degree of crosslinking is controlled by the UV dose and by the irradiated wavelength.

Second adhesive (weak adhesive)

The adhesive composition systems, in particular pressure-sensitive adhesive systems, for the low-adhesion side can basically be based on the same chemical compound classes as have already been specified for the strongly adhesive adhesive; in particular acrylate, natural rubber, synthetic rubber, silicone or EVA adhesive are used, in particular from this group are the EVA adhesive and the acrylic PSAs, the latter being coated either in solution, from the melt or as a dispersion. The adhesive is chosen or processed so that it has an adhesive force on ABS or on glass of not more than 1.5 N / cm. For natural rubber adhesives, the information already given for strong pressure-sensitive adhesives apply accordingly.

In a method which is particularly preferred according to the invention, acrylate PSAs are used as low-adhesion adhesives.

In order to achieve very weakly adhesive properties, three different concepts can be pursued in particular:

Concept 1) Conventional Acrylate PSAs, as already described above, with additives that lower the bond strength,

Concept 2) Conventional Acrylate PSAs, as already described above, but with a gel value greater than 90%,

Concept 3) (meth) acrylate PSAs Which Have a Static Glass Transition Temperature between 25 and 35 ° C.

Konzept.1.)

It is possible to use the (meth) acrylate PSAs described above (see strongly adhesive PSA). The reduction of the bond strength is achieved by additives which themselves have no or only a very low tack.

Examples of suitable additives are resins which are completely or partially incompatible with the PSA. This is e.g. the case when the resins have a different polarity to the poly (meth) acrylate. Thus, especially C5 and C9 hydrocarbon resins with poly (meth) acrylates have only a very low compatibility.

Further suitable additives are aliphatic compounds, e.g. Fatty acid, or long-chain carboxylic acids. These have the following formula

CxHyR where R may preferably be COOH, OH, NH ₂ , S0 ₃ H or their esters or P0 ₃ H or esters thereof. However, other polar groups can also be used. The number of C atoms X varies between 12 and 30, the number H between 9 and 61. The Group C _x H _Y may be saturated or unsaturated, may be unbranched, branched or cyclic.

Furthermore, fillers can be added as additives. As fillers, e.g. the class of fumed silicas are added. You will u. a. used as thickening agents, gelling agents or thixotropic agents in fluids of various kinds, using their influence on the rheological properties of the fluids. Both hydrophilic or hydrophobic silicas can be used.

Furthermore, modified phyllosilicates can also be used. Furthermore, it is possible to use natural, inorganic or organic fillers, such as calcium carbonate, kaolin, talc, dolomite or silicates.

Also, silica, calcium u. Barium sulfate, aluminum hydroxide, glass fibers and - balls and cellulose powders and carbon blacks are used.

It is also possible to distinguish inorganic and organic fillers according to their density. Thus, the inorganic fillers often used in plastics and adhesives, such as chalk, titanium dioxide, calcium and barium sulfate increase the density of the composite, since they themselves have a density which is higher than that of the polymer. For the same layer thickness, the basis weight is then higher.

There are also fillers that can reduce the overall density of the composite. These include hollow microspheres, very voluminous lightweight fillers. The balls are filled with air, nitrogen or carbon dioxide, the spherical shells are made of glass, in some products also from a thermoplastic.

Furthermore, there are polymeric fillers with a density on the order of the

Pressure-sensitive adhesive polymer is located. This includes, for example, polyethylene, polypropylene,

Polyamide, polyacrylonitrile, polyester, polymethacrylate and polyacrylate.

Furthermore, as organic fillers, in particular both vegetable and / or animal raw materials can be used. The organic fillers are very preferably finely divided, in particular in the form of fibers, shot, dust or flour.

Vegetable organic fillers are preferably renewable raw materials

(renewable organic materials), in particular wood, cork, hemp, flax,

Grasses, reeds, straw, hay, cereals, maize, nuts or constituents of the aforementioned

Materials such as trays (e.g., nutshells), cores, awns, or the like.

In particular, there are wood flours, cork flours, cereal flours, corn flours and / or Potato flours are used without wishing to be unnecessarily limited by the list in the inventive teaching.

Particularly suitable animal organic fillers are bones, chitin (for example, crayfish, insect armor), hair, bristles and horn, in particular in finely divided (ground) form.

Filler materials have proven to be particularly advantageous in which the size of at least 99% of the particles (the diameter in the case of almost round particles, such as granular particles, or the maximum length in the case of elongated particles, such as fibers) no longer is 1000 μηη.

The proportion of fillers in the pressure-sensitive adhesive is advantageously greater than 50% by weight, more preferably greater than 70% by weight, very particularly greater than 80% by weight.

Furthermore, surfactants can also be added as additives. Surfactants are defined as substances which reduce the surface tension of a liquid or the interfacial tension between two phases and enable or assist the formation of dispersions or act as solubilizers. Surfactants generally consist of a hydrophobic ("water-repellent") hydrocarbon radical and a hydrophilic ("water-loving") moiety. Surfactants cause two liquids that are not really miscible, such as oil and water, to be finely mixed. Surfactants are also detergent substances (detergents) which are contained in detergents, dishwashing detergents and shampoos.

The nonpolar part is always an alkyl group. The polar part can be constructed differently. For nonionic surfactants, hydroxy, ether or ethoxylates are used as hydrophilic groups. Examples of this are e.g. Alkyl phenol ethoxylates. Anionic surfactants have a carboxylate, sulfonate or sulfate group. Cationic surfactants have a quaternary ammonium group and amphoteric surfactants preferably a carboxylate and quaternary ammonium group.

However, natural surfactants may also be used, e.g. Lecithin.

Other specific surfactants are e.g. Sodium lauryl sulfate or cetyltrimethylammonium bromide.

The proportion of surfactant additives is preferably between 5 and 25%, very preferably between 10 and 20%. Furthermore, rubber elastomers (natural rubber and / or synthetic rubber) can be added as additives to acrylate PSAs. For the pressure-sensitive adhesives, preferably a natural rubber having up to a molecular weight (weight average) is not ground below about 100,000 daltons, preferably not below 500,000 daltons, and is additized. The natural rubber or natural rubbers can in principle be made of all available grades such as Crepe, RSS, ADS, TSR or CV grades, depending on the required level of purity and viscosity, 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 (II R), halogenated butyl rubbers (XIIR), acrylate rubbers (ACM), ethylene Vinyl acetate copolymers (EVA) and the polyurethanes and / or their blends are selected. Particular preference is given to using styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene types (SEBS). The variants are also available in hydrogenated form, as diblock polymers and also with MSA (maleic anhydride) functionalization.

It is also possible to choose blends of natural rubbers and / or synthetic rubbers.

The proportion of rubber additives is between 5 and 50%, very preferably between 10 and 30%.

Concept 2)

Here, modified PSAs are used, starting from the compounds already described for strongly adhesive adhesives. To reduce the bond strengths, however, the monomers are chosen such that the static glass transition temperature is not -20 ° C., preferably less than -30 ° C., and crosslinking is carried out so that the PSA has a gel value of greater than or equal to 90%, preferably greater than or equal to 90% equal to 95%. The desired static glass transition temperature is achieved as described above. The same applies in principle to the adjustment of the required gel value, wherein in the present case generally for polyacrylates with a gel value of 90% or higher at least 1, 5 wt .-% metal chelate or epoxy compound or isocyanate compound, based on the Base polymer are added, more preferably greater than 2.0 wt .-%. Not more than 10% by weight of crosslinker should be added to prevent complete laking.

The degree of crosslinking is controlled by electron beam hardening by the acceleration voltage and the dose, which also depends on the amount of crosslinking agents added and the thickness of the material to be irradiated.

The degree of crosslinking in UV curing is controlled by the wavelength of the UV light, the amount of photoinitiator added, the amount of crosslinking accelerator and the dose.

Concept 3)

The poly (meth) acrylates preferably used for this concept are based on at least 50% by weight of at least one acrylic monomer from the group of the compounds of the following general formula:

wherein Ri = 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 1-30 carbon atoms.

The composition of the monomers is preferably chosen so that the resulting polymers can be used as low-adhesion PSAs at room temperature. This can be controlled, for example, by means of the glass transition temperatures of the homopolymers of the monomers used and / or by suitable additive addition, as already described in principle. The static glass transition temperature of the PSA in this concept is between + 25 ° C and + 35 ° C. The molar masses M _{w of} the polyacrylates used here are preferably M _w > 200,000 g / mol, very preferably greater than 600,000 g / mol.

In a very preferred manner, acrylic or methacrylic monomers are selected from the pool which has already been indicated in the case of the strongly adhesive PSA as a pool for (meth) acrylate monomers.

Advantageously used as comonomers are vinyl esters, vinyl ethers, vinyl halides, vinylidene halides, vinyl compounds with 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.

In a further advantageous procedure, the comonomers used are photoinitiators having a copolymerizable double bond, in particular Norrish I and II photoinitiators being suitable. Suitable examples include benzoin 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.

In a further preferred procedure, comonomers are used 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-butylphenylacrylate, t-butylphenylmethacrylate, 4-biphenylacrylate and -methacrylate, 2-naphthylacrylate and methacrylate and mixtures of those monomers, this list is not exhaustive.

Furthermore, resins are optionally added to the PSAs. As the tackifying resins to be added, it is possible to use the previously known adhesive resins described in the literature which dissolve homogeneously in the base polymer. This can be determined eg by a DSC. In case of incompatibilities, in addition to the static glass transition temperature, melt peaks which originate from undissolved resin are then measured. Examples of highly soluble types of resins are 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, 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, the compatibility depends strongly on the polarity of the polyacrylate.

In addition to the suitable static glass transition temperature, the degree of crosslinking is an influencing factor for the properties of the PSA. To achieve optimum tack-adhesive properties, the gel value of the PSA should be between 30 and 70%. Over-crosslinking leads to a decrease in the bond strength, sub-crosslinking to a cohesive gap. To achieve this gel range, the already mentioned crosslinkers and promoters can be used.

Furthermore, the already mentioned crosslinkers can be used for high-energy radiation and / or thermal crosslinking, so that crosslinking by means of UV rays, electron beams and / or by means of thermal energy can be effected. Reference is made to the statements made above on this.

Production process for the PSAs

To prepare the acrylic PSAs of the strongly adhesive side and the weakly adhesive side, conventional free-radical polymerizations are advantageously carried out. Initiator systems which additionally comprise further free-radical initiators for the polymerization, in particular thermally decomposing radical-forming azo or peroxo initiators, are preferably used for the free-radical polymerizations. In principle, however, all acrylates customary to the person skilled in the art are suitable. The production of C-centered radicals is described in Houben Weyl, Methods of Organic Chemistry, Vol. E 19a, pp. 60-147. These methods are preferably applied by analogy.

Examples of radical sources are peroxides, hydroperoxides and azo compounds, as some non-exclusive examples of typical radical initiators are mentioned here Potassium peroxodisulfate, dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, azodiisoic acid butyronitrile, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate, benzpinacol. In a very preferred embodiment, the free-radical initiator used is 1, 1'-azobis (cyclohexanecarbonitrile) (Vazo 88 ™ from DuPont) or azodisobutyronitrile (AIBN).

The polymerization may be carried out neat, in the presence of one or more organic solvents, in the presence of water or in mixtures of organic solvents and water. The aim is to keep the amount of solvent used as low as possible. Suitable organic solvents are pure alkanes (eg hexane, heptane, octane, isooctane), aromatic hydrocarbons (eg benzene, toluene, xylene), esters (eg ethyl acetate, propyl, butyl or hexyl acetate), halogenated hydrocarbons (eg chlorobenzene) , Alkanols (eg, methanol, ethanol, ethylene glycol, ethylene glycol monomethyl ether) and ethers (eg, diethyl ether, dibutyl ether) or mixtures thereof. The aqueous polymerization reactions can be treated with a water-miscible or hydrophilic cosolvent to ensure that the reaction mixture is in the form of a homogeneous phase during the monomer conversion. Advantageously used cosolvents for the present invention are selected from the following group consisting of aliphatic alcohols, glycols, ethers, glycol ethers, pyrrolidines, N-alkylpyrrolidinones, N-alkylpyrrolidones, polyethylene glycols, polypropylene glycols, amides, carboxylic acids and salts thereof, esters, organosulfides, Sulfoxides, sulfones, alcohol derivatives, hydroxy ether derivatives, aminoalcohols, ketones and the like, as well as derivatives and mixtures thereof.

The polymerization time is - depending on the conversion and temperature - between 2 and 72 hours. The higher the reaction temperature can be selected, that is, the higher the thermal stability of the reaction mixture, the lower the reaction time can be selected.

To initiate the polymerization, the entry of heat is essential for the thermally decomposing initiators. The polymerization can be initiated for the thermally decomposing initiators by heating to 50 to 160 ° C, depending on the type of initiator. For the preparation, it may also be advantageous to polymerize the acrylate PSAs in substance. In particular, the prepolymerization technique is suitable here. The polymerization is initiated with UV light, but only led to a low conversion about 10 - 30%. Subsequently, this polymer syrup can be, for example, shrink-wrapped in films (ice cubes in the simplest case) and then polymerized in water to high conversion. These pellets can then be used as acrylate hotmelt adhesives, with film materials which are compatible with the polyacrylate being used with particular preference for the melting process. Also for this preparation method, the thermally conductive material additives can be added before or after the polymerization.

In further design variants of the invention, controlled free-radical or living polymerization processes are used for the preparation of the inventive pressure-sensitive adhesives.

Another advantageous production method for the acrylic PSAs is anionic polymerization. Here, inert solvents are preferably used as the reaction medium, e.g. aliphatic and cycloaliphatic hydrocarbons, or aromatic hydrocarbons.

foams

The double-sided pressure-sensitive adhesive seal according to the invention has at least one foam body (foam carrier layer) which is based on at least one foam. In particular, a foam layer based on a foamed polymer or copolymer, based on a foamed mixture of polymers or copolymers or based on a laminate of two, three or more foam layers, in particular of the aforementioned types, can be used as the foam body. Also, laminates of two, three or more layers, of which not all layers are foamed, but at least one, advantageously at least the two outer layers of the laminate are foamed, can be used, wherein as foam layers of the laminates can be used in particular on the foam layers mentioned above , Advantageously used foam bodies are those in which the foam body is a foam layer of a foamed polymer or foamed copolymer or a foamed (co) polymer mixture; in particular according to the following foam specifications. However, these also apply to the foam layers of the other aforementioned foam body.

Foamed bodies which can be used according to the invention include or are (in particular if the foam body is only a foam layer) preferably foamed homo- and / or copolymers of ethylene, in particular polyethylenes (PE) of low and very low density (LDPE, LLDPE, VLPDE), ethylene-vinyl acetate copolymers (EVA), as well as mixtures of the aforementioned polymers (eg PE-EVA foams); further foamed polyvinyl acetates, polypropylenes, ethylene-propylene-diene rubber (EPDM) and thermoplastic elastomers based on styrene block copolymers. The foams can be used crosslinked or uncrosslinked.

As foam bodies or layers of foam bodies foams of polyethylene, ethyl vinyl acetate (PVA) and polypropylene are particularly advantageously used. In a very preferred embodiment, polymer blends of polyethylene and ethyl vinyl acetate are used, preferably an ethyl vinyl acetate having a vinyl acetate content of up to 15% by weight.

Foamed bodies which are light or dark in color are preferably used according to the invention; especially white, anthracite or particularly advantageous black colored. The coloration may concern the entire foam body or individual layers thereof. The foam carriers used according to the invention can be pretreated for better anchoring of the layers provided on it. Particularly preferred as a pretreatment are the treatment with corona, the etching and / or the finishing with an adhesion promoter, ie a precoat, which improves the anchoring properties of the film. It has been found to be very preferable if the foam carrier layers are both corona treated and etched. The pretreatment of the foam carrier can be done on one or both sides.

The foams according to the invention have a closed-cell structure. Scavenged foams of integral or non-integral structure can be used. Also usable according to the invention are laminates of several foams. Especially for use in portable electronic devices, the cell size is important, since such devices are made ever smaller and according to the components used - as well as seals - should be as small as possible. The maximum cell height (ie the maximum cell extent in the direction of the thickness of the seal) of the foams used is therefore very preferably between 25 and 200 μm. The maximum cell length (ie the maximum cell expansion in any direction perpendicular to the direction of the thickness of the seal) is advantageously between 0.1 and 1 mm, very preferably between 0.2 and 0.6 mm. The expansions of all cells in the areas mentioned are advantageous.

In order to ensure a good tightness, the expansion of the foam cells in any spatial direction - in particular adherence to the above values - should not more than 80%, preferably not more than 70% of the expansion of the foam formed by the cells in this direction. Most preferably, the maximum cell expansion of the cells (ie, typically the largest dimension of the largest cell) should not exceed 80%, preferably not more than 70%, of the smallest ridge width of the seal, the smallest path over which the seal will seal , in order to achieve an optimum sealing effect.

About the thickness of the foam body, the total thickness of the pressure-sensitive adhesive seal can be varied. The maximum layer thickness of the foam body is preferably 400 μm. In order to have a foam effect, the minimum layer thickness should preferably not be less than 50 μm.

The foams used for the foam bodies preferably have a bulk density of from 100 to 400 kg / m ³ .

Optional further layers

The pressure-sensitive adhesive according to the invention can be reinforced in one advantageous development by one or more carrier films. The carrier film (s) cause a stabilization of the pressure-sensitive adhesive seal. It is advantageous, for example, that usually such reinforced sealing materials are punched more easily.

The film supports are advantageously based on polymers that can be extruded or cast into films. Suitable film materials are, for example, polyesters, polymetharylates, polycarbonates, polyamides, polyolefins, polyvinyl chlorides, polyurethanes, Polyimide or nylon. In a particularly preferred embodiment, polyethylene terephthalate (PET) is used.

Advantageously, one or more film support layers of polyethylene terephthalate are used, although other polymers which have film-forming properties could be used. The film carrier may advantageously be transparent, white, anthracite or black colored or coated.

The films preferably have a layer thickness of 4 to 50 μm, more preferably a layer thickness of 12 to 25 μm. The adhesive layers preferably each have a layer thickness of from 10 μm to 100 μm. For the weakly adhering PSA, it may be advantageous to limit the layer thickness to below 50 μm. For some PSA composition, it may also be advantageous to limit the PSA layer thickness to below 20 μηη. For the strongly adhesive pressure-sensitive adhesive side, it may be advantageous, in order to achieve the targeted bond strength range, to set a layer thickness of greater than 50 μm.

The reinforcing film (s) may be pretreated to better anchor the layers provided thereon. Particularly suitable as a pretreatment are the treatment with corona, the etching and / or the finishing with an adhesion promoter, ie a precoat, which improves the anchoring properties of the film. It has been found to be very preferable if the film (s) are both corona treated and etched. Depending on the product structure, it is also possible to use a laminating adhesive for anchoring to the foam. But there is also the possibility that the foaming was made directly on the carrier film, so that can be dispensed with this adhesive.

The laminating adhesive which can be used is that known to the person skilled in the art and suitable for both materials (reinforcing film and foam). Suitable adhesives are, in particular, pressure-sensitive adhesives based on (meth) acrylate or based on rubber. In the case of single-layer (carrierless) laminating tapes and symmetrical double-sided adhesive tapes, it is in particular to be possible to choose a laminating adhesive which has good suitability for both carrier materials.

The laminating adhesive has to ensure the bond strength and should therefore have a bond strength which ensures that the compound caused by it does not dissolve in accordance with a measurement carried out according to ASTM-D 3330 method C (180 ° measurement) before the compound of the second Adhesive dissolved on the ABS surface is, in particular, completely solved. So here is guaranteed that the seal when redetaching from the ground here has no unwanted breakage.

With regard to the total thickness of the seal according to the invention, an advantageous embodiment of the laminating adhesive layer is characterized in that it is kept very thin. Particularly advantageous here layers of not more than 50 μηη, better of not more than 30 μηη used. A laminating adhesive layer of 20 μm has proved to be very advantageous, particularly advantageously based on resin-blended polyacrylates and / or polymethacrylates.

To produce, in particular, strapless, single-layer laminating adhesive layers, the adhesive is preferably applied with a basis weight of not more than 50 g / m ² , more preferably not more than 30 g / m ² .

In the case of a chemical pretreatment, the respective carrier can first advantageously be provided with precoating, reactive primers being used in a particularly preferred embodiment. As precursor materials, e.g. Reactive adhesive.

A pretreatment of the carrier layers (film carrier and / or foam carrier) on the side facing away from the laminating adhesive in each case serves to better anchor the outer adhesive layer.

product structure

As foamed bodies (carrier materials), foams, foams or foamed-film laminates are used in accordance with the statements made above on this, in particular also in the following product constructions. Advantageously, in this case a single-layer foam body is used, so that very thin seals can be realized.

In the simplest case, the pressure-sensitive adhesive tape has the product structure shown in FIG. 1, in which:

1 = strongly adhesive adhesive, in particular pressure-sensitive adhesive (first adhesive)

2 = foam body 3 = weakly adhesive adhesive, in particular PSA (second PSA)

Furthermore, multi-layered structures can be realized. 2 shows an advantageous embodiment in which a carrier film (4) is used for stiffening on the side of the strongly adhesive layer of adhesive. However, the film carrier (4) can also be oriented to the weakly adhesive side, cf. see FIG. 3.

In a further advantageous embodiment, a laminating adhesive is provided between the carrier film (4); see. 4 and 5 (Fig. 4: carrier film and laminating adhesive on the strongly adhesive side; Fig. 5: carrier film and laminating adhesive on the weakly adhesive side).

A further embodiment provides more than one foil carrier (4) for reinforcement, in FIG. 6 is shown by way of example - and without wishing to be limited to this embodiment variant - a variant with two foil carriers (4), wherein one of the foil carriers (4) is fixed by a laminating adhesive (5) on the foam carrier (3).

The seals according to the invention have in particular thicknesses of 500 μm or less (with foam body thicknesses of 400 μm or less). It is also excellent seals even smaller thickness, so about 400 μηη or less, or preferably 300 μηη or less, realize.

Foamed bodies which can be used according to the invention can have thicknesses of 100 μm or less up to 50 μm or less. The thickness of the seals is significantly influenced by the foam body thickness and the penetration depth of the PSA layers into the foam, so that - in typical adhesive compositions orders of 20 to 60, for example 50 g / m ² - seals of the invention down to a thickness of about 100 μηη feasible are.

According to the invention, the seal at its narrowest point on a web width of not more than 1, 5 mm. To ensure sufficient stability, it is advantageous if the web width at the narrowest point of the seal does not fall below 0.5 mm. For example, seals have proven to be very advantageous whose narrowest point is about 0.8 mm. The seals can be frame-shaped (for example round, oval, rectangular, square) and so regularly that the seal has a consistently (constant) web width in the range of 0.5 to 1, 5 mm, very preferably of 0.8 mm, but also so irregular that the web width varies and there are one or more narrowest points with the specified land widths next to wider webs or web sections. As a result, the seal can be optimally adapted to the shape of the point to be sealed or the component.

The sealing material according to the invention can advantageously be offered in rolled-up form; in particular before the punching or packaging to be used seal. For reeling, the sealing material is preferably covered with a release film or a release paper. Suitable release papers are glassine, HDPE or LDPE liners, which in a preferred embodiment have a graduated release effect. In a further embodiment of the invention, a release film is used. The release film should also have a graduated release effect in a preferred design. In addition, however, it is also possible to use two release films or release paper or combinations for covering.

use

The seal according to the invention is used for sealing joints between two components. The seal is particularly suitable for sealing in (untreated, treated and / or painted) articles made of plastic, glass, metal or articles made of several of these materials.

The seal of the invention is particularly preferably used for sealing joints and / or openings between or in components of electronic devices, such as those in the field of consumer electronics, consumer electronics and / or communication electronics (for example, for mobile phones, PDAs, laptops and other computers, digital cameras and Display devices such as displays, digital readers or organic light-emitting diode displays (OLEDs) and for solar cell modules such as electrochemical dye solar cells, organic solar cells or thin-film cells). As structural units are presently understood all components and accumulations thereof, which are used in electronic devices, such as electronic components (discrete and integrated components), housing parts, optical and / or mechanical protection devices (protective screens, grille and etc.), electronic modules, antennas, display panels, bare and / or populated boards, and the like.

The seal should in particular be suitable for being decoupled in the bonded state on at least one of its bonded sides, in particular without residues remaining here. In particular, the suitability for a reversible, multiple use is desired. Thus, the corresponding seal can not only remove, for example, for a recycling process, but the sealing effect is maintained even if replaceable parts, such as mobile phone shells, are equipped with the seal (preferably by means of strongly adhesive side) and repeatedly removed, rerun or ., whereby the seal with the weakly adhesive side adheres to the housing and thereby guarantees the sealing effect to this side.

The seal is realized in particular by means of a method in which the seal according to the invention, double-sided pressure sensitive adhesive sealant is adhesively bonded on both sides with the components forming the joint. Due to the closed-pored design and the seal of the bonding sites caused by the bonding, the entire joint is sealed, without the need for any pressure beyond the effect of the pressure-sensitive adhesive bond. Preferably, the seal is compressed in the state of use to not more than 25 ± 1% of its thickness in the free (ie not bonded) state, more preferably not more than 10 ± 1%. Particularly preferably, the seal is not compressed in the application state (ie pressure-free), so that the compression (within the error accuracy, see deviation) is 0% ± 1%% (as compression, the thickness difference = [(thickness (not compressed) - thickness (upset) / thickness (not compressed)], where "upset" refers to the condition of use, "unbent" to the state of free, unconsolidated and non-compressed seal).

At least the adhesive bond on one of the sides, preferably the housing side in the bonding of small parts such as display windows, speaker covers (grids) or the like, is reversible, as by means of the weakly adhesive adhesive (second adhesive), in particular PSA causes. The seal as a whole is designed such that upon release of the sealing point, the inner structure of the seal is substantially retained, the weakly adhesive side thus dissolves before inner layer cohesion (eg between foam and adhesive, Foam and laminating compound, foam and film, laminating compound and film, film and adhesive or the like) are broken or before the foam structure is destroyed. The latter can be achieved by the chosen density of the foam, as this stable foams are present.

The cohesion of sealed by means of the gasket components of the invention is preferably not effected by the adhesive layers of the seal, but by other structural devices of the corresponding device itself, for example by mechanical latching devices or the use of adhesive tapes that need not be designed to be sealed. The adhesive layers of the seal therefore serve primarily to anchor the seal on the joining partners that form the joint seal, and only optional and then support their cohesion. The seal therefore does not need to be configured in such a way that it would have to be suitable as the adhesive tape structurally effecting the connection of the parts to be joined. Therefore, it can be realized that the weakly adhesive adhesive forms correspondingly low bond strengths on ABS or on glass, which increases the removability and, if appropriate, the reversibility suitability on this side.

The advantage of the seal according to the invention and the corresponding sealing method over the prior art are shown in FIGS. 7a and 7b. Fi. 7a shows a seal according to the prior art, FIG. 7b shows a seal according to the invention. By way of example, without wishing to be unnecessarily limited by this choice, the fixing and sealing of a display window (12) (in particular of PMMA) on a housing frame (13) (in particular of ABS) of an electronic device are shown. The display window (12) protects the electronic display device (1 1), for example, an LED, the display. Between the window (12) and the housing (13) is due to the design of a joint (F) through which moisture, dirt, dust or the like could penetrate into the device. Therefore, it is necessary to seal this joint (F). According to the prior art, the fixing of the window is effected by a double-sided, conventional pressure-sensitive adhesive tape (14), below which a foam gasket (15) is provided. The sealing effect of this seal (15) comes about by pressure. As a result, however, the pressure-absorbing effect of the foam is lost, since this is the higher, the more deformation energy of the foam can absorb. Due to the design, the sealing effect is irreversibly lost when the window detached from the housing and thus the pressure between the window (12), housing (13) and display device (1 1) decreases. When using the seal (D) according to the invention (see Fig. 7b), the fixing of the window (12) on the housing (13) by other devices causes, for example by a double-sided pressure-sensitive adhesive tape (16), which fixes these components together ( Alternatively, a mechanical connection, for example a snap-in connection, is available for exchangeable or repeatedly detachable parts. The sealing effect is effected directly between the window (12) and the display device (1 1) by means of the seal (D) according to the invention and does not or not significantly contributes to the fixation of the components. By both-sided equipment with PSAs, the seal (D) on both the window (12) and on the display device (1 1) fixed, and the sealing effect comes about due to this fixation and the closed-pore design of the seal (D) already without substantial pressure ,

The strongly adhesive side is oriented in this case to the window (12), the weak adhesive side to the display device (1 1). The fact that both sides of the seal (D) are designed adhesive, the sealing function is enhanced. The seal (D) no longer has to be compressed so much or so much, and therefore a variety of sealing materials could be used, which would not be suitable for compression.

Thus, the connection of the components can be repeatedly opened and restored without the need for an exchange of the seal and without the sealing effect is lost (for example, in the event that the device, such as a mobile phone repaired must be, the case of The weakly adhering PSA side can be removed without residue from the glass of the display unit for this case.) This principle can be applied analogously to the sealing of joints between components other than those shown when using the gasket according to the invention.

FIG. 8 shows by way of example how the seal according to the invention can be used in a display window (12) fastened mechanically, eg in the housing (D), eg by latching. The seal (D) is mounted between the display window (12) and display device (1 1) without pressure or substantially without pressure and attached to both the fixed (12) and on the display device (1 1) by means of the adhesive layers. Thus, between the housing (13), window (12) and display device (1 1) extending joint (F) Even without pressure influence excellent sealed and reversible the connection without the seal (D) would be destroyed.

In portable electronic devices there are a variety of seals that can be replaced in this way. For example, only the openings for the microphone or for the speaker are mentioned here, which are usually provided with seals to keep water, moisture and dust from the inside of the portable electronic device.

The gasket is usually used in such a way that the strongly adhesive side is oriented toward components made of PMMA, polycarbonate, glass or the like, while the weakly adhesive side is fixed on ABS, in particular untreated ABS, polyamide, in particular glass fiber reinforced polyamide, or the like. The specified bond strengths are excellently adapted to the use according to the invention for these materials.

The seal according to the invention is advantageously used in the form of a web or preferably in the form of a frame, which can surround the opening to be sealed accurately. Due to the ever smaller components of electronic devices seals must be offered, which are at least at its narrowest point 1, 5 mm wide or narrower. For example, seals are possible, which are round or polygonal, for example, square or rectangular, and the web width uniformly smaller throughout / equal to 1, 5 mm, or even in square frame such that at least two opposite webs have this web width throughout. Even these narrow bars must not be permeable to water, moisture, dust or other interfering substances that disturb the device. Such narrow webs, however, according to an embodiment according to the prior art are regularly not feasible, since the narrow webs deform strongly uncontrolled under the influence of pressure, therefore can not be uniformly compressed and therefore do not guarantee a sufficient sealing effect. The pressure-free seal could be remedied in the present case. According to the invention, it is thus also possible to use gaskets of small thickness, which-in particular also in the case of the web widths mentioned-have an outstanding sealing effect. experiments

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

The following test methods were used.

.180 ° Kl ebk rafflest. (Test A)

The bond strength test in the examples was performed according to ASTM D 3330 Method C. As a modification of point 6.2 of the above provision, the panels used were not steel, but polymethylmethacrylate (PMMA), acrylonitrile-butadiene-styrene copolymers (ABS) and glass in each case in accordance with the above-mentioned specifications. The surfaces of all three materials are smooth (glossy), scratch-free, untreated and cleaned. The surface roughness value given in item 6.3 of ASTM D 3330 / D 3330M -04 is observed for all three substrates. The substrates were cleaned in the case of ABS and PMMA with ethanol and in the case of glass with acetone.

The bond strength was determined in each case after 7 days of wind-up time during storage (wind-up conditions: 23 ° C. and 50% relative atmospheric humidity). All measurements were carried out at room temperature under conditioned conditions (23 ° C, 50% relative humidity). The values given are averaged from the results of three measurements and expressed in N / cm.

In addition to the measurement of the bond strength, it was assessed whether the PSA leaves residues on the glass surface.

Performance test (test B);

A PMMA sheet 1 mm thick, 75 mm long and 60 mm wide is bonded to an ABS sheet having outer dimensions of 75 mm in length and 60 mm in width at a thickness of 3 mm (specifications of PMMA and ABS as above; Exception of deviating dimensions). The sealing materials according to the invention are used as stamped parts for bonding. The outer dimensions of the frame-shaped (rectangular) die-cut are 72 mm x 56 mm. Punchings with uniform ridge widths of 2 mm on all sides and those with uniform ridge widths of 1.5 mm on all sides and those with uniform ridge widths were used examined on all sides of 1 mm. The bond area is therefore 496 mm ² (for 2 mm web width), 375 mm ² (for 1, 5 mm web width) or 244 mm ² (for 1 mm web width). First, the diecut on the ABS side with a pressure of 5 kg for 6 sec. Glued. The materials used were previously acclimated for 24 hours at 23 ° C and 50% relative humidity. Subsequently, 0.25 g of feinpulvriges and pre-dried calcium chloride is introduced into the interior, then the release liner removed from the blank, the PMMA plate symmetrically applied to the ABS plate and then the bonding of the two plates with a pressure of 5 kg for 6 s carried out. The low-adhesion side of the sealant is applied to the ABS side, the strongly adhesive side to the PMMA. The seal in the specimen is pressure-free (compression 0 ± 1%) within the scope of the error accuracy.

It is conditioned for 24 hours at 23 ° C and 50% relative humidity and the total weight of the unit determined. Subsequently, the sample is subjected to a water-tightness test with a 1 m high water column in accordance with standard IEC 60529 (the test piece is placed in a vessel with a 1 m high water column above it). After 24 hours, the sample is removed from the water column, pre-dried with a rag, and then acclimated for 24 h at 23 ° C and 50% relative humidity. Then again the total weight of the unit is determined. The calcium chloride acts as a drying agent and can absorb any incoming water. The increase in weight due to water absorption is determined by the weight measurement of the bonded unit before and after the hydrohead test and the difference determined. The difference in weight correlates with the amount of water or moisture which has entered the interior through the gasket and has been taken up by the calcium chloride. The measurement was carried out with a Mettler Toledo PM 100 balance. The measurement accuracy at 23 ° C and 50% relative humidity is 0.0001 g.

The test is passed, so the seal as waterproof, if the weight gain is less than 0.01 g.

Abi ös ba rkej tstest. (Test C) .:

A PMMA sheet 1 mm thick, 45 mm long and 35 mm wide is bonded to an ABS frame with outer dimensions of 50 mm length and 40 mm width at a thickness of 3 mm. The ABS frame is cut centrally inside with the dimensions 25 mm x 35 mm. The seal samples according to the invention are used as diecuts for bonding. The outer dimensions of the diecut are 46 mm x 36 mm. The web width to all sides is 2 mm. The low-adhesion side is applied on ABS, the strong-adhesive side on PMMA. The bond area is 304 mm ² . The bonding is carried out with a pressure of 5 kg for 6 s. It is then conditioned for 72 hours at 23 ° C and 50% humidity. Then the ABS frame is removed manually from the PMMA plate. The pressure-sensitive adhesive tape should leave no residue on the ABS frame.

With a web width of 2 mm, it is guaranteed that all narrower webs can be removed without residue.

Preparation of the samples

P.Qjy. rn.sr .1 .. (Heft kjebmasse strong. adhesive)

A 200 L reactor conventional for radical polymerizations was charged with 3 kg of acrylic acid, 10 kg of methyl acrylate, 35 kg of 2-ethylhexyl acrylate, 35 kg of butyl acrylate and 53.3 kg of acetone / isopropanol (85:15). After passing through nitrogen gas with stirring for 45 minutes, the reactor was heated to 58 ° C and 40 g of 2,2'-Azoisobuttersäurenitril (AI BN) was added. Subsequently, the outer heating bath was heated to 75 ° C and the reaction was carried out constantly at this external temperature. After a reaction time of 1 h, 40 g of Al BN were again added. After 5 h and 10 h, each was diluted with 15 kg acetone / isopropanol (85:15). 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.

Subsequently, 20 wt .-% of a C5-C9 KW resin from VFT Rüttgers (TK 90 H) was mixed in solution and then freed in the heat at 120 ° C in vacuo from the solvent. Subsequently, it was mixed with 0.2% by weight of aluminum (III) acetylacetonate (dissolved as a 10% solution in isopropanol) with vigorous stirring. The entire solution is then diluted to 25% solids with acetone and coated with a comma bar. After drying at 120 ° C. for 10 minutes, complete crosslinking of the pressure-sensitive adhesive is achieved.

P.Qlyrner 2. (Heftkjebmasse weak ... sticking)

The procedure was analogous to polymer 1. After completion of the polymerization reaction, 10% by weight of stearic acid dissolved in gasoline was added. Subsequently, on 25% solids content diluted with gasoline, 0.4% by weight of aluminum (III) acetylacetonate (dissolved as a 10% solution in isopropanol) with intensive stirring.

After drying at 120 ° C. for 10 minutes, complete crosslinking of the pressure-sensitive adhesive is achieved.

Pole 3. (Hard-tacky Aceks)

The procedure was analogous to polymer 1. After completion of the polymerization reaction, 5% by weight of aluminum (III) acetylacetonate (dissolved as a 10% solution in isopropanol) was added with intensive stirring.

Poly mer 4 _ (H aftkjebem aces weakly adherent)

A 200 L reactor conventional for free-radical polymerizations was charged with 3 kg of acrylic acid, 40 kg of stearyl acrylate, 37 kg of butyl acrylate and 53.3 kg of acetone / gasoline / isopropanol (40: 57: 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 (AI BN) 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 of benzine (60/95). After 6 and 8 h 100 g dicyclohexyl peroxydicarbonate (Perkadox ^® 16, Fa. Akzo Nobel) was added dissolved in each 800 g special boiling point spirit (60/95). The reaction was stopped after 24 h reaction time and cooled to room temperature.

Subsequently, it was mixed with difunctional isocyanate (Demodur L75, Bayer AG) 0.6 wt .-% with vigorous stirring. The entire solution is then diluted to 25% solids with acetone and coated with a comma bar. After drying at 120 ° C. for 10 minutes, complete crosslinking of the pressure-sensitive adhesive is achieved.

Kasc _{"hjerkjebemass} _^

A mixture of 5 g of acrylic acid and 95 g of 2-ethylhexyl acrylate degassed and saturated with nitrogen was filled into a polyethylene bag with oxygen exclusion. The PE Bag has a siliconized inner layer and is coated with aluminum on the outside. Then the reactor was irradiated with a Co60 source at 100 Krad / h and a total dose of 10 Krad. The syrup was mixed with 0.5% by weight of Esacure KIP 150 ™ (α-hydroxyketone oligo [2-hydroxy-2-methyl-1- [4- (1-methylvinyl) phenyl] propanone]; Lamberti) and blended used as a laminate adhesive. The laminate adhesive is coated on a transparent PET carrier film by means of a doctor blade. It was then laminated with the foam. For UV polymerization and curing of the laminate adhesive, a UV system from Eltosch was used. The system is equipped with a Hg undoped UV emitter with a wavelength of 250 nm and an intensity of 200 W / cm.

The Kaschierverklebung was driven at 10 m / min through the system, which were irradiated to increase the dose per sample in several rounds.

Production of the double-sided pressure-sensitive adhesive seal

Polymers 1 to 4 were coated from solution via a brush bar onto a 1.5 g / m ² silicone coated (polydimethylsiloxane) glassine release paper. Subsequently, the polymer was in a drying tunnel with max. Dried 120 ° C. The coated PSAs were then laminated to the corresponding backing (foam or reinforcing film).

To improve anchoring, the foams used were freshly coronazed beforehand. This also applies to the case of the PET reinforcing film used.

Intensifying Screens:

The following film was used:

Mitsubishi RNK12: polyethylene terephthalate film with 12 μηη thick foams:

Foam 1: Sekisui Volara XLIM 0.2 mm soft (closed-cell PE foam with 0.2 mm thickness). By means of SEM recording a maximum cell length of 330 μηη, a maximum cell height of 50 μηη and a maximum cell width of 160 μηη was found.

Foam 2: Sekisui Volara XLIM 0.3 mm medium (closed cell PE foam with

0.3 mm thickness). By SEM recording was a maximum cell length of 370 μηη, a maximum cell height of 70 μηη and a maximum cell width of 190 μηη found.

Foam 3: Rogers Corp. PORON ™ 4701-15 (mixed cellular polyurethane foam with

0.53 mm thickness)

Foam 4: Rogers Corp. PORON ™ 4701 -50 Firm Supported (mixed cell

Polyurethane foam with 0.3 mm thickness including PET reinforcement film)

example 1

Foam 2 is coated on one side with polymer 1 (50 g / m ² ) and on the other side with polymer 2 (25 g / m ² ).

Example 2

Foam 2 is coated on one side with polymer 1 (50 g / m ² ) and on the other side with polymer 3 (25 g / m ² ).

Example 3

Foam 2 is coated on one side with polymer 1 (50 g / m ² ) and on the other side with polymer 4 (25 g / m ² ).

Example 4

Foam 1 is coated on one side with polymer 1 (50 g / m ² ) and on the other side with polymer 3 (25 g / m ² ).

Example 5

Foam 2 is glued to the 12 μηη PET film with the laminating adhesive. Subsequently, on the PET side polymer 1 is laminated with 50 g / m ² and on the foam side polymer 3 with 25 g / m ² .

Example 6

Foam 2 is glued to the 12 μηη PET film with the laminating adhesive. Subsequently, polymer 3 is laminated on the PET side with 25 g / m ² and on the foam side polymer 1 with 50 g / m ² .

Reference Example 1

Foam 1 is coated on both sides with polymer 1 (50 g / m ² ). Reference Example 2

Foam 1 is coated on one side with polymer 1 (50 g / m ² ). Reference Example 3

Foam 3 is coated on both sides with polymer 1 (50 g / m ² ). Reference Example 4

Foam 3 is coated on one side with polymer 1 (50 g / m ² ). Reference Example 5

Foam 4 is coated on the open foam side and on the PET film side in each case with polymer 1 (50 g / m ² ).

results

In a first step, the bond strengths of the examples and the reference examples according to test A were determined. The bond strengths were measured on glass. In addition to the bond strength, the residual materials were also evaluated.

The results are shown in the following Table 1.

Table 1 a. Overview of bond strengths (Test A).

Table 1 b. Overview of bond strengths (Test A).

It can be seen from Tables 1 a and 1 b that all examples have similar bond strengths on the strongly adhesive side, since the reference examples were also coated with polymer 1. On the weak adhesive side of all inventive examples, the adhesive strength criterion is less than 1.5 N / cm complied. Reference Examples 1 and 3 were also provided with Polymer 1 on the low adhesion side. Therefore, the bond strengths of greater than 10 N / cm are significantly higher. Reference Examples 2 and 4 have no low adhesion mass and are coated on one side only. Therefore, the bond strength is 0. Furthermore, the glass plate was examined for ground remnants of this weakly adhesive ground side. The results are summarized in Table 2.

Table 2. Overview of low-stick residues (Test A).

Examples of ground residues (Test A)

Weakly adhesive S.

1 None

2 None

3 None 4 None

5 None

6 None

Reference Example 1 Strong residues

Reference Example 2 None

Reference Example 3 Strong residues

Reference Example 4 None

Reference Example 5 Columns of the foam

Table 2 demonstrates that the inventive pressure-sensitive adhesives leave no residue on the glass substrate. Only reference examples 1 and 3 have strong residues.

In a second test, the sealing effect according to test method B was investigated. The results are summarized in Table 3.

Table 3. Tightness test (Test B).

Examples of tightness test (test B)

2 mm web width

1 0.0004 g

2 0.0002 g

3 0.0002 g

4 0.0002 g

5 0.0003 g

6 0.0003 g

Reference Example 1 0.0002 g

Reference Example 2 0.4254 g

Reference Example 3 0.0005 g

Reference Example 4 0.0034 g

Reference Example 5 0.0004 g

Examples of tightness test (test B)

1.5 mm web width

1 0.0004 g

2 0.0004 g

3 0.0003 g

4 0.0003 g

5 0.0005 g 6 0.0005 g

Reference Example 1 0.0005 g

Reference Example 2 0.4483 g

Reference Example 3 0.0129 g

Reference Example 4 0.0165 g

Reference Example 5 0.0136 g

Examples of tightness test (test B)

1 mm web width

1 0.0021 g

2 0.0013 g

3 0.0017 g

4 0.0018 g

5 0.001 1 g

6 0.0010 g

Reference Example 1 0.0013 g

Reference Example 2 0.4547 g

Reference Example 3 0.0363 g

Reference Example 4 0.0429 g

Reference Example 5 0.0434 g

The results show that all examples according to the invention have a very good sealing effect. The weight gain is very low with a web width of 2.0, 1, 5 and 1 mm and is well below 0.01 g. The slight increase could result from increased humidity or residual amounts of water outside the specimen. The reference examples behave differently. With a web width of 2 mm, the sealing behavior in Reference Examples 1, 3, 4 and 5 still remains intact. The weight gains are very low and are below 0.01 g. Only reference example 2 already shows slight water ingress. The weight gain is 0.4254 g and is thus already well above the 0.01 g mark.

At 1, 5 mm web width, the result of the reference examples deteriorates. Here, in addition to the reference example 2, the reference examples 3, 4 and 5 show a significant increase in water, and the tightness is no longer present. All the examples according to the invention furthermore show only a very slight increase in weight of less than 0.01 g and thus a very good sealing effect. With 1.0 mm web width, the sealing effect for reference examples 2, 3, 4 and 5 remains poor. All inventive examples continue to show only a very small increase in weight of less than 0.01 g and thus a very good sealing effect.

For verification, the composite of Reference Example 4 was also compressed again by 10% (fixation with several staples). The compression and fixation could not prevent the ingress of water under the 1 m high water column. With a web width of 1 mm, a weight gain of 0.3931 g was measured.

Furthermore, the removability of the seals was tested (Test C). The results are summarized in Table 4.

Table 4. Removability (Test C).

The results from Table 4 show that all the examples according to the invention can be removed without residue. There are no residues left on the ABS. The same applies to Reference Examples 2 and 4, since they are only provided on one side with a pressure-sensitive adhesive. In contrast, the reference examples 1, 2 and 5 show a very high adhesion, so that they can be detached only by splitting the foam.

Overall, the practical statements show that the described inventive seals without compression also have a very good sealing effect and the existing concepts, such as one-sided pressure-sensitive adhesive seal and sealing under compression, are superior.

Claims

claims

1 . Web-shaped or frame-shaped seal comprising a foam body, a first adhesive provided on the upper side of the foam body and a second adhesive provided on the underside of the foam body,

characterized in that

the web width of the seal at its narrowest point is no longer 1.5 mm, the foam body has a maximum thickness of 400 μm and consists of one or more closed-cell foams with a bulk density in the range from 100 to 400 kg / m ³ ,

wherein the first adhesive has a bond strength to polymethyl methacrylate (PMMA) of at least 3 N / cm measured according to ASTM-D 3330 method C, the second adhesive having a bond strength to acrylonitrile-butadiene-styrene copolymer (ASTM-D 3330 method C) ( ABS) of at most 1.5 N / cm.

2. Seal according to claim 1, characterized in that

the anchoring forces between the first adhesive and the foam body and between the second adhesive and the foam body in a measurement carried out according to ASTM-D 3330 Method C are each greater than the adhesive force of the second adhesive on ABS.

3. Seal according to one of precede the claims, characterized in that

the bond strength of the first adhesive to polymethylmethacrylate (PMMA) measured according to ASTM-D 3330 method C at least 5.0 N / cm; very preferably at least 7.5 N / cm, more preferably more than 9.5 N / cm.

4. Seal according to one of the preceding claims, characterized in that

the bond strength of the second adhesive to acrylonitrile-butadiene-styrene copolymer (ABS) measured according to ASTM-D 3330 method C 3330 is 1.0 N / cm or less.

5. Seal according to one of the preceding claims, characterized in that

the cells are designed so that their maximum diameter is not more than 70% of the web width of the seal at its narrowest point.

6. Seal according to one of the preceding claims, characterized in that

the cell height of the foams used, ie the cell expansion in the direction of the thickness of the seal, is between 25 and 200 μm.

7. Seal according to one of the preceding claims, characterized in that

the cell length of the foams used, ie the cell expansion in any direction perpendicular to the direction of the thickness of the seal, between 0.1 and 1 mm, very preferably between 0.2 and 0.6 mm.

8. Use of a seal according to one of the preceding claims for the sealing in consumer electronics items.

9. A method for sealing joints between or openings in components made of metal, glass and / or plastic, characterized in that

a seal according to any one of claims 1 to 5 is used, wherein the compression of the seal is not more than 25 ± 1%, preferably not more than 10% of its thickness in the free (ie non-bonded) state.

10. The method according to claim 9, characterized in that

the compression of the seal is 0 ± 1%.