KR102257234B1 - Process for producing an adhesive tape with foamed psa layer and structuring on the surface - Google Patents

Abstract

The present invention relates to a process for structuring a foamed adhesive tape made of at least one adhesive layer and optionally at least one additional layer. At least one adhesive layer is foamed, wherein the adhesive tape is structured on a surface by a structure embossed through a line with the aid of a roll in the present process.

Description

A method of manufacturing an adhesive tape having a structured surface with a foamed PSA layer {PROCESS FOR PRODUCING AN ADHESIVE TAPE WITH FOAMED PSA LAYER AND STRUCTURING ON THE SURFACE}

The present invention relates to a process for producing an adhesive tape having at least one foamed adhesive layer and a structured surface.

Several small parts, especially those in the field of consumer electronics, are now bonded using adhesive tape. One advantage is that this adhesive tape can be re-divided easily and as far as possible without residue. One of the reasons for this requirement is to try to replace defective parts as simply as possible. Such replacement may be necessary immediately after or during production if there is a problem with production, or else after prolonged use if the consumer finds a defect. In addition, efforts and legal provisions that eager or regulate the recycling of various parts continue to increase.

The term “mobile device” encompasses, for example, devices in the consumer electronics industry, including electronic, optical and precision-mechanical devices, ie, in the context of the present application, more particularly, cell phones, smartphones and tablets.

The literature describes various possibilities for repartitioning pressure-sensitive adhesive tapes. One simple possibility is to heat the adhesive tape and thus reduce the bond strength. The downside of this is that electronic components often do not withstand the desired high temperatures and are damaged. Also, in this process, the adhesive softens and, accordingly, loses its cohesion. In such a case, when the bond breaks, some of the adhesive remains on both surfaces, and cohesive breaks exist. This is where the cleaning operation is important, which is often complex but is necessary to reuse at least one of the two bonding partners.

For this process, various methods of providing heat to the bonding surface are described, for example, by heating the entire device in an oven or by introducing heat into the bonding line in a targeted manner using a laser.

Another possibility to split the adhesive tape is to use a so-called stretch-release adhesive tape. When these tapes are stretched on the bonding surface, their bonding strength decreases. A disadvantage of this technique is that it requires a finger tab that can pull the adhesive tape from the bonding line. These finger tabs sometimes interfere with other components and interfere with the visual effect. In addition, there is a problem that the adhesive tape tends to tear during peeling, since peeling is no longer possible in such a case.

In the bonding of at least one transparent adherend, it is also possible to use an adhesive tape that is cured by UV light and thus loses the bonding strength as it is used in the adhesive tape to produce a silicon wafer. The downside is that it is used only for transparent substrates.

The aim was to develop a pressure-sensitive adhesive product that has high adhesion performance and can nevertheless be peeled back as much as possible without residue.

Here, an attempt has been made to re-segment the adhesive bond by means of a solvent, where the solvent is applied around the bonding area, and thereafter, gradually moves between the adhesive tape and the substrate to achieve a significant decrease in the holding performance. .

For most adhesive tapes, especially when the bonding area is relatively large, this process is very slow and is hardly suitable for industrial procedures.

To speed up this process, an adhesive tape with a rough surface was used, which means that the solvent can move much faster into the bonding zone through the resulting channel.

In this case, the structuring of the adhesive can be realized through different processes. The focus here is on the liner and the subsequent embossing of the adhesive tape after foaming.

The liner (release paper, release film) is not part of the adhesive tape, but instead serves only as a means for its production, storage, or further processing by die-cutting. Also, in contrast to the adhesive tape carrier, the liner is not rigidly connected to the adhesive layer.

In the process according to the invention, the adhesive tape is structured on the surface by means of a structure that is embossed through the liner with the aid of a roll. Typically, at least one outward facing surface of the adhesive layer of the adhesive tape is structured.

Because electronic devices are always intended to be carried by humans, these devices are becoming smaller and lighter. Due to the portability of such mobile devices, such devices can be carried by themselves, for example by impact on corners, by dropping, by contact with other hard objects in the bag, or otherwise simply. By the permanent movement associated with it, it is subjected to increased loads, in particular mechanical loads. However, mobile devices are also generally loaded to a greater degree due to moisture exposure, temperature effects, etc. than such "immobile" devices that are installed inside and do not move little or no.

For such mobile devices, an adhesive tape having a particularly high holding force is required. In part, also the possibility of subsequent elimination is desired. In many applications, an additional requirement is to have a high strength even at elevated temperatures.

However, it is also particularly important that the adhesive tape does not degrade its holding power when the mobile device, i.e., a mobile phone, falls to the ground and is impacted, for example. Accordingly, the adhesive strip or the bonded assembly must have a very high impact resistance.

The foamed adhesive itself has been shown to be suitable for increasing the impact resistance. In this context, the entire adhesive can be foamed, or if there are multiple layers, only one of the layers can be foamed.

Polymer foams can in principle be produced in two ways. First, by the action of the blowing gas, added as a blowing gas or formed by a chemical reaction; Second, by the introduction of hollow spheres into the material matrix. Foams produced in the latter manner are referred to as syntactic foams.

In syntactic foam, hollow spheres, such as glass spheres, or hollow ceramic spheres (microspheres) or microballoons are introduced into the polymer matrix. Accordingly, in the syntactic foam, voids are separated from each other, and substances (gas, air) contained in the voids are separated from the surrounding matrix by the membrane.

Compositions foamed into hollow microspheres are known for their defined cell structure with a uniform size distribution of foam cells. When using hollow microspheres, a closed-cell foam without cavities is obtained, which differs from its open-cell counterpart in quality, including a better sealing effect on dust and liquid media. In addition, chemically or physically foamed materials are more prone to irreversibly decay under pressure and temperature, and often exhibit lower cohesive strength.

Particularly advantageous properties can be achieved when the microspheres used for foaming are expandable microspheres (also referred to as “microballoons”). By virtue of its flexible, thermoplastic polymer shell, this class of foam has a greater capacity to conform than those filled with non-expandable, non-polymeric hollow microspheres (e.g., hollow glass spheres). . This generally has a better suitability for compensation of manufacturing tolerances, for example in the case of injection molding, which can also better compensate for thermal stresses, due to its foaming properties.

In addition, it is possible to further influence the mechanical properties of the foam through the selection of the thermoplastic resin of the polymer shell. Thus, for example, even when the foam has a lower density than the matrix, it is possible to produce a foam with a higher cohesive strength than if only the polymer matrix has. For example, conventional foam properties, such as the ability to adapt to rough substrates, can be combined with high cohesive strength for self-adhesive foams.

A common problem with using expandable microballoons is that after foaming, the microballoons protrude from the adhesive, and thus the bonding strength of the adhesive tape is greatly reduced.

WO 2009/090119 A1 discloses a pressure-sensitive adhesive containing expanded microballoons, wherein peel adhesion of the adhesive including expanded microballoons is of the same surface weight of the adhesive and voids generated by the expanded microballoons. Pressure sensitive adhesives are described that are reduced by up to 30% compared to the peel adhesion of the formulation defoamed by breaking. In this case, the at least partially foamed pressure sensitive adhesive is shaped between the two liners by at least two rolls. In order to create a smooth surface without breaking through, breaking microballoons, high pressure in a roll nip is applied to the microballoons to break through the polymer matrix back from the surface.

1 is a thermogram recording the change in the heat capacity of the block copolymer of the present invention.

The adhesive layer used in the adhesive tape of the present invention is usually a pressure-sensitive adhesive (PSA) layer. PSA is an adhesive that allows durable bonding to virtually any substrate under relatively low application pressure and, where appropriate, can peel back from the substrate after service, substantially without residue. PSA has a permanent pressure-sensitive adhesive force at room temperature, and thus has a sufficiently low viscosity and high touch-tack, and thus it can wet the surface of the individual adhesive base even under low application pressure. The bonding property of an adhesive is derived from its adhesive property, and the re-peelability is derived from its cohesive property. According to the present invention, the terms "pressure-sensitive adhesive" and "self-adhesive" (and terms derived therefrom) are used synonymously.

The adhesives used according to the invention can be based on various polymers or polymer mixtures. Adhesives based on specific polymers (or specific polymer mixtures) typically mean that the elastomeric component of the adhesive consists of at least 50% by weight, and preferably on the order of at least 90% by weight of such polymers or polymer mixtures. In another preferred embodiment, in addition to the base polymer, the adhesive contains no additional elastomer in an amount that substantially affects the essential properties of the base polymer.

Adhesive based on vinyl aromatic block copolymer

Synthetic rubber-based PSAs comprising vinylaromatic block copolymers are well known and used in a variety of applications. The advantage of this class of PSA is the high bonding strength to substrates of different surface energies, especially including those of low surface energies. These are at the same time notable for their very high holding power under normal ambient conditions.

PSAs based on vinylaromatic block copolymers with advantageous impact resistance are likewise described. DE 10 2016 202 018 A1 teaches that improved impact resistance can be achieved by selecting a suitable block copolymer. It is also possible to improve the impact resistance when the PSA is in a foamed form and contains, for example, expanded microballoons for that purpose.

In order to impart pressure-sensitive adhesive properties to the polydiene, it must be mixed with a tackifier resin. This is also the case for vinylaromatic block copolymers containing polydiene blocks.

EP 3 075 775 A1 describes foamed block copolymer blends with tackifier resins or combinations of tackifier resins. In addition to hydrocarbon resins and polyterpene resins, it is possible to use oxygen-containing tackifier resins, but this is not described in more detail.

DE 10 2008 056 980 A1 and DE 10 2008 004 388 A1 teach formulations that exhibit tackiness using tackifier resins, comprising polystyrene-polyisoprene block copolymers and, for example, rosin esters. The formulation is disclosed. The adhesive contains microballoons in a relatively high proportion and therefore has a very low density.

Elastomer component (a)

The elastomeric component typically comprises at least one synthetic rubber in the form of a block copolymer having the structure ABA, (AB) _n , (AB) _n X or (ABA) _{n X, wherein}

Block A represents a polymer formed independently of each other by polymerization of at least one vinylaromatic compound;

Block B represents a polymer formed by polymerization of a conjugated diene having 4 to 18 carbons independently of each other;

-X represents a radical of a coupling reagent or a multifunctional initiator;

-n represents an integer of ≥ 2.

In one embodiment, all synthetic rubbers of the PSA (layer) of the present invention may be block copolymers having the structures described above. Accordingly, the PSA (layer) of the present invention may also comprise a mixture of different block copolymers having the above structure.

Accordingly, at least one suitable block copolymer typically comprises at least one rubbery block B (soft block) and at least two glassy block A (hard block). In addition, the elastomeric component may comprise one or more diblock copolymer ABs. More particularly, the synthetic rubber of the PSA (layer) of the present invention is _{a mixture of block copolymers having the structure AB, ABA, (AB) 3} X or (AB) ₄ X, which is preferably at least diblock copolymer AB And/or triblock copolymer ABA.

Typically, as a PSA or PSA layer, mainly for the polymerization of vinylaromatic compounds (A block), preferably a polymer block formed of styrene, and mainly 1,3-diene (B block), for example butadiene and isoprene. Polymers formed by, or for example, those based on block copolymers comprising copolymers thereof, are used.

The block copolymer of the PSA or PSA layer preferably has polystyrene end blocks.

Instead of the preferred polystyrene blocks, also as vinylaromatic compounds, for example other aromatic compound-containing homopolymers and copolymers (preferably C ₈ to C _{12) having a glass transition temperature of more than 75° C. according to Test IV.} It is possible to use polymer blocks based on aromatic compounds), for example blocks of α-methylstyrene-containing aromatic compounds. It is also possible for the same or different A blocks to be present.

Preferred conjugated dienes as monomers for soft block B are in particular selected from the group consisting of butadiene, isoprene, and also mixtures of these monomers, and also hydrogenated homologues thereof. Block B can also take the form of a homopolymer or copolymer.

The proportion of hard blocks (block A) in the block copolymer is at least 12% and 40% by weight or less, preferably at least 15% and 35% by weight or less.

In one preferred configuration, the proportion of the vinylaromatic block copolymer, in particular the styrene block copolymer, is at least 35% by weight and up to 65% by weight, more preferably, at least 45% by weight, based on the total PSA (layer). % And up to 55% by weight.

Tackifier resin component (b)

The foamable PSA or foamed PSA layer, as well as the PSA or PSA layer with at least one vinylaromatic block copolymer, has at least one tackifier resin to increase adhesion in a desired manner. The tackifier resin should be compatible with the elastomer block of the block copolymer.

"Tackifier resin" is understood as an oligomer or polymer resin that increases the adhesion (adhesion, intrinsic tack) of a PSA compared to other identical PSAs, except that it does not contain a tackifier resin, according to the general understanding of the skilled person .

Tackifier resins are specific compounds with a lower molar mass compared to elastomers, typically with a weight-average molecular weight (Test V) M _W <5000 g/mol. The weight-average molecular weight is usually 400 to less than 5000 g/mol, preferably 500 to 2000 g/mol.

Suitable tackifier resins are preferably non-hydrogenated, partially hydrogenated or fully hydrogenated resins based on rosin or rosin derivatives, hydrogenated polymers of dicyclopentadiene, C-5, C-5/C- Non-hydrogenated, partially, selectively or fully hydrogenated hydrocarbon resins based on 9 or C-9 monomer streams, or polyterpene resins based on α-pinene and/or ß-pinene and/or δ-limonene. Includes. The tackifier resin may be used alone or as a mixture. In addition, the formulation of the adhesive may also include a tackifier resin that is liquid at room temperature.

Plasticizing resin component (c)

Optionally available plasticizing resins or plasticizing resin mixtures typically have a softening temperature ( ^* Ring&Ball, Test VI) of <30°C. The plasticizing resin may be based on rosin, or very preferably based on hydrocarbons or polyterpenes. The plasticizing resin or plasticizing resin mixture is used in fractions of 0% to 15% by weight, and preferably at least 2% by weight and at most 10% by weight, with respect to the total adhesive (layer of). When the fraction of the hydrolyzed resin is too high, the cohesive force is reduced, and the thermal shear strength is adversely affected.

Optional Additional Ingredients (d)

The foamable PSA or foamed PSA layer, or if appropriate, even the non-foamed adhesive layer may have further additives, in particular protective agents, added thereto. These include primary and secondary aging inhibitors, photoprotectants and UV protection agents, and also flame retardants, and also fillers, dyes and pigments. Accordingly, the adhesive (layer of) may have any color, or may be white, gray or black.

These or other additional additives that may be used typically include:

● Preferably, a fraction of 0.2 to less than 5% by weight, based on the total weight of the PSA (layer of), of a plasticizer, for example a low molecular weight liquid polymer, for example a low molecular weight Polybutene,

● Preferably, in a fraction of 0.2 to 1% by weight, based on the total weight of the PSA (layer of), a primary antioxidant, such as, for example, a sterically hindered phenol,

● Preferably, in a fraction of 0.2 to 1% by weight, based on the total weight of the PSA (layer of), of a secondary antioxidant, such as, for example, phosphite or thioether,

● Preferably, in a fraction of 0.2 to 1% by weight, based on the total weight of the PSA (layer of), a process stabilizer, for example a C radical scavenger,

● Preferably, in a fraction of 0.2 to 1% by weight, based on the total weight of the PSA (layer of), a photoprotective agent, for example a UV absorber or a sterically hindered amine,

● Preferably, 0.2 to 1% by weight of a processing aid, based on the total weight of the PSA (layer of),

If desired, preferably, in a fraction of 0.2 to 10% by weight, based on the total weight of the PSA (layer of), the end block reinforcing agent resin, and

Preferably, in a fraction of 0.2 to 10% by weight, based on the total weight of the PSA (layer of), optionally further polymers, preferably elastomers in nature; The elastomers that can thus be used are, among other things, those based on pure hydrocarbons, for example unsaturated polydienes, e.g., naturally or synthetically produced polyisoprene or polybutadienes, chemically substantially saturated. Elastomers such as saturated ethylene-propylene copolymers, α-olefin copolymers, polyisobutylene, butyl rubbers, ethylene-propylene rubbers, and also chemically functionalized hydrocarbons such as , Halogen-containing, acrylate-containing, allyl or vinyl ether-containing polyolefins.

The properties and amounts of the blending ingredients can be selected as needed, the latter can also be higher than the preferred upper limit. It is also part of the present invention when the adhesive layer does not each have a specific described adjuvant or even all described adjuvants.

Nitrile rubber adhesive

Besides vinylaromatic block copolymers, other elastomers can also serve as the basis for PSA. Another very suitable elastomeric group is the elastomeric group of nitrile rubber.

Adhesives based on nitrile rubbers, as their base polymers, include at least one, or two or more solid acrylonitrile-butadiene rubbers and also tackifier resins, wherein the fraction of tackifier resins is 20 to 55 % By weight, and the acrylonitrile content of the solid acrylonitrile-butadiene rubber(s) is 10 to 30% by weight.

The acrylonitrile content of the solid acrylonitrile-butadiene rubber(s) is preferably 10 to 25% by weight.

The acrylonitrile-butadiene rubber may contain added inert release aids such as talc, silicates (talc, clay, mica), zinc stearate and PVC powder, more particularly to the extent of 3% by weight. The release aid is preferably selected from the group consisting of talc, silicates (talc, clay, mica), zinc stearate and PVC powder.

In addition, the acrylonitrile-butadiene rubber can preferably be mixed with a thermoplastic elastomer such as a synthetic rubber for the purpose of improving workability, for example in a fraction of up to 5% by weight. Representative examples thereof may include, in particular, miscible styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) types.

The PSA of the present invention may comprise at least one liquid acrylonitrile-butadiene rubber in addition to one or more solid acrylonitrile-butadiene rubbers, in which case the acrylonitrile of the liquid acrylonitrile-butadiene rubber(s). The content is likewise 10 to 30% by weight.

The fraction of liquid acrylonitrile butadiene rubber is preferably at most 20% by weight.

Compared to solid rubber, the characteristic of liquid rubber is that such liquid rubber has a softening point of <40°C.

Data on the softening point TS of oligomeric and polymeric compounds such as resins can be obtained, for example, in a ring according to DIN EN 1427:2007 with the appropriate application of the regulation (instead of bitumen, analysis of oligomer or polymer samples, procedures remain otherwise). & Ball method, and these measurements are carried out in a glycerol bath.

Preferably, no polymer is present in the PSA other than the acrylonitrile-butadiene rubber. In such a case, the PSA is a composition of solid and liquid acrylonitrile-butadiene rubber, one or more tackifier resins, preferably aging inhibitor(s) and optionally a release aid, which represents a preferred embodiment. In addition, it is also possible that the plasticizers, fillers and/or dyes described below are optionally present in small amounts.

Alternatively, the base polymer contains more than 90% by weight, preferably more than 95% by weight of solid and liquid acrylonitrile-butadiene rubber.

As tackifier resins, in the case of self-adhesive compositions, it is possible, for example, to use especially hydrogenated and non-hydrogenated hydrocarbon resins and polyterpene resins as main components. Suitable ones preferably include hydrogenated polymers of dicyclopentadiene, preferably hydrogenated polymers of C8 and C9 aromatic compounds. This can result from the hydrogenation of the polymer from a pure aromatics stream, or else it can be based through the hydrogenation of a polymer based on a mixture of different aromatic compounds. In addition, some hydrogenated polymers of C8 and C9 aromatic compounds, hydrogenated polyterpene resins, hydrogenated C5/C9 polymers, aromatic-modified, optionally hydrogenated dicyclopentadiene derivatives are suitable. The tackifier resin may be used alone or as a mixture.

Hydrogenated hydrocarbon resins are particularly suitable blending components as described, for example in EP 0 447 855 A1, US 4,133,731 A and US 4,820,746 A, because the absence of double bonds indicates that crosslinking cannot be stopped. Because it means.

However, it is also possible to use a non-hydrogenated resin when a crosslinking accelerator such as, for example, a polyfunctional acrylate is used.

Other non-hydrogenated hydrocarbon resins, non-hydrogenated analogs of the hydrogenated resins described above, may also be used.

Additionally, it is possible to use rosin-based resins.

It is particularly preferred to use polyterpene resins, or terpene-phenolic resins based on α-pinene and/or β-pinene and/or δ-limonene.

To stabilize the PSA, it is common to add primary antioxidants such as sterically hindered phenols, secondary antioxidants such as phosphites, or thioethers, and/or C radical scavengers. to be.

Any desired combination of these can be used to adjust the properties of the obtained PSA according to the requirements. In the literature ["Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, 1989)], the expression of the state of knowledge can be explicitly referred to.

The weight of the resin is 20 to 55% by weight, preferably 30 to 55% by weight, more preferably 35 to 50% by weight.

Acrylonitrile-butadiene rubber-based PSAs are additives to adjust optical and technical adhesion properties, such as fillers, dyes or aging inhibitors (ozone inhibitors, antioxidants (primary and secondary), photoprotective agents, etc.) It may include.

Additives to commonly used adhesives are as follows:

● primary antioxidants, such as sterically hindered phenols

● Secondary antioxidants, for example phosphite or thioether

● Photoprotective agents, such as UV absorbers or hindered amines.

The filler can be a reinforcing or non-reinforcing filler. Of particular note herein are silicon dioxide (spherical, acicular, or irregular, e.g., pyrogenic silica), sheet silicate, calcium carbonate, zinc oxide, titanium dioxide, aluminum oxide or aluminum oxide hydroxide. .

The concentration of additives that affect the optical and technical adhesion properties is preferably at most 20% by weight, more preferably at most 15% by weight, more preferably at most 5% by weight.

In the present invention, the proportion of all substances added (other than acrylonitrile-butadiene rubber and tackifier resin), for example synthetic rubber and/or thermoplastic elastomer and/or filler and/or dye and/or aging inhibitor It should not exceed 5% by weight in total, preferably 2% by weight.

It is advantageous for the nitrile rubber composition to be crosslinked so that the structure is still present after removal of the liner, in order to obtain sufficient cohesive force and suppress the cooling of the adhesive.

There are in principle two pathways for bridging. Chemical crosslinking can take place via double bonds still present, for example by addition reactions or radical crosslinking. In addition, crosslinking by radiation, for example UV rays, or preferably an electron beam, is possible.

Polyacrylate

In addition to the described adhesives, those based on polyacrylates can also be used.

"Polyacrylate" is a polymer in which the monomer base is composed of acrylic acid, methacrylic acid, acrylic acid ester and/or methacrylic acid ester of at least 30% in size, based on the amount of the substance, wherein the acrylic acid ester and/or The methacrylic acid ester is generally present at least proportionally and preferably at least 30%. More particularly, "polyacrylate" is a polymer obtainable by radical polymerization of acrylic and/or methylacrylic monomers, and, optionally, further copolymerizable monomers.

It is preferred to use polyacrylates which can be derived from the following monomer composition:

a) acrylic acid esters and/or methacrylic acid esters of the formula:

CH ₂ =C(R ^I )(COOR ^II )

[Wherein, R ^I is H or CH ₃ and R ^II is an alkyl radical having 4 to 14 carbons],

b) an olifenically unsaturated monomer having a functional group that is reactive, for example reactive toward an epoxide group,

c) Optionally, further acrylate and/or methacrylate and/or olefinically unsaturated monomers copolymerizable with component (a).

For the application of polyacrylates as pressure sensitive adhesives, the corresponding fractions of components (a), (b) and (c) are chosen so that the polymerization product has a glass transition temperature in particular ≤ 15° C. (DMA at low frequencies).

In particular, to produce PSA, 45 to 99% by weight of the monomer of component (a), 1 to 15% by weight of the monomer of component (b), and 0 to 40% by weight of the monomer of component (c) It is very advantageous to select (the numbers are based on a monomer mixture for the "base polymer", ie a monomer mixture in which no possible additives have been added to the complete polymer such as resins, etc.).

The monomers of component (a) are in particular plasticized and/or non-polar monomers. It is preferable to use acrylic acid esters and methacrylic acid esters having an alkyl group consisting of 4 to 14 carbons, more preferably 4 to 9 carbons as the monomer (a). Examples of such monomers include n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-amyl acrylate, n-hexyl acrylate, hexyl methacrylate, n- Heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate, and branched isomers thereof, such as Examples are 2-ethylhexyl acrylate or 2-ethylhexyl methacrylate.

The monomers of component (b) are, in particular, olefinically unsaturated monomers having a functional group, in particular having a functional group capable of reacting with an epoxide group.

Preference is given to the use of monomers having functional groups selected from the group comprising the following compounds for component (b): hydroxyl, carboxyl, sulfonic or phosphonic acid groups, acid anhydrides, epoxides, amines.

Particularly preferred examples of the monomer of component (b) include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, β-acryloyloxypropionic acid, trichloroacrylic acid, vinylacetic acid, Vinylphosphonic acid, itaconic acid, maleic anhydride, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, 6-hydroxyhexyl methacrylate, allyl alcohol, gly Cidyl acrylate and glycidyl methacrylate.

As component (c), in principle, it is possible to use all compounds that have vinyl functionalization and are copolymerizable with components (a) and (b). The monomer of component (c) can serve to adjust the properties of the obtained PSA.

Polyacrylates can be prepared by methods familiar to the person skilled in the art, in particular, advantageously, by conventional radical polymerization or controlled radical polymerization. The polyacrylate can be prepared by copolymerizing the monomer component using a conventional polymerization initiator, and, optionally, a chain transfer agent, and the polymerization is carried out at a conventional temperature, in bulk, in an emulsion, for example, water or It occurs in liquid hydrocarbons or in solution.

The weight-average molecular weight M _W of the polyacrylate is preferably in the range of 20,000 to 2,000,000 g/mol, very preferably in the range of 100,000 to 1,000,000 g/mol, very preferably in the range of 150,000 to 500,000 g/mol. Range [numbers for average molecular weight M _W and polydispersity PD herein are based on determination by gel permeation chromatography (test V; see experiment section)]. For this purpose, it may be advantageous to carry out the polymerization in the presence of suitable polymerization chain transfer agents such as thiols, halogen compounds and/or alcohols to establish the desired average molecular weight.

The poly(meth)acrylate is preferably crosslinked by a linking reaction, i.e., in particular in terms of an addition or substitution reaction, by linking reactions of the functional groups contained therein with a crosslinking agent.

The crosslinking agent is preferably used in an amount of 0.1 to 5% by weight, more particularly 0.2 to 1% by weight, based on the total amount of the polymer to be crosslinked.

It is also possible to crosslink through complexing agents, also referred to as chelates. One preferred complexing agent is, for example, aluminum acetylacetonate.

The acrylates can also be crosslinked using radiation, such as UV rays or electron beams.

In this case, it is important that the adhesive exhibits no or only very little cooling and is crosslinked to the extent that the structure of the adhesive is maintained when the liner is removed.

In order to increase the adhesion, it is also possible to mix the tackifier resin with the polyacrylate.

This resin is preferably a rosin or terpene-phenolic resin as described above. The fraction of the tackifier resin is 5 to 30% by weight, preferably 10 to 25% by weight.

Microballoon

The present invention relates to an expandable, ie non-expandable, foamable pressure-sensitive adhesive comprising microballoons. It also relates to a foamed layer of pressure sensitive adhesive comprising at least partially expanded microballoons.

The term “at least partially expanded microballoons” is typically used in the present invention in which the microballoons as a whole form a reduction in the density of the adhesive to a technically significant degree compared to the same adhesive containing unexpanded microballoons. It is understood to mean to expand to the extent. This means that the microballoons do not necessarily have to be fully expanded. Preferably, the individual microballoons, individually considered in each case, have expanded to at least twice their maximum size in the unexpanded state. In addition, the term “at least partially expanded microballoons” may also refer to the fact that only a portion of the microballoons under consideration is (initial) expanded. In one preferred embodiment of the foamed PSA layer, the microballoons are fully expanded, ie the layer has been foamed so that, for a given microballoon portion, a minimum layer density is achieved.

Foaming is achieved in particular through the introduction of microballoons and subsequent expansion.

"Microballoons" are understood to be hollow microspheres with elastic, thus expandable in their basic state, and thermoplastic polymer shells. These spheres are filled with a low-boiling liquid or liquefied gas. Shell materials used include, in particular, polyacrylonitrile, PVDC, PVC or polyacrylate. Suitable low-boiling liquids are, in particular, hydrocarbons of lower alkanes, examples of which are isobutane or isopentane, which is contained in the form of a liquefied gas under pressure in the polymer shell.

Exposing the microballoons, especially when exposed to heat, softens the outer polymer shell. At the same time, the liquid blowing gas present in the shell transitions to its gaseous state. Here, the microballoon expands irreversibly and expands three-dimensionally. Expansion ends when the internal pressure matches the external pressure. Because the polymer shell is retained, the result is a closed shell foam.

Various types of microballoons are commercially available, differ essentially in their size (6 to 45 μm diameter in the unexpanded state), and at the starting temperature, these are required for expansion (75 to 220° C.). ). An example of a commercially available microballoon is the Expancel ^® DU grade from Nouryon (DU = dry expanded), another example is the Matsumoto Microsphere ^® F/FN from Matsumoto Yushi Seiyaku.

The unexpanded microballoon grade is also in the form of an aqueous dispersion having a solid fraction or microballoon fraction of approximately 40 to 45% by weight and additionally as a polymer-bonded microballoon (masterbatch), for example approximately 65% by weight. It is available as polymer-bound microballoons (masterbatch) in ethylene-vinyl acetate with a microballoon concentration of %. Masterbatches such as DU grade as well as microballoon dispersions can be considered to produce the foamed PSA of the present invention.

The foamed PSA layer of the present invention can also be produced using what is called a pre-bulged microballoon. With these groups, swelling occurs before being introduced into the polymer matrix. Pre-expanded microballoons are, for example, the grade name Expancel DE (dry expanded) from the designation Dualite ^®, or Nouryon from Chase Corp. commercially available.

Preferably, in the present invention, at least 90% of all voids formed by microballoons in the foamed layer of PSA have a maximum diameter of 20 to 75 μm, more preferably 25 to 65 μm. "Maximum diameter" refers to the maximum size of a microballoon in any spatial direction at the cryofracture edge under SEM.

The diameter is determined on the basis of the cold crack edge in a scanning electron microscope (SEM) at 500 times magnification. The diameter of each individual microballoon is identified graphically.

When foaming occurs using microballoons, the microballoons can be supplied to the formulation as a batch, as a paste or as a pure or blended powder. These can also be suspensions in solvents.

The fraction of microballoons in the adhesive (layer of) is, according to the invention, in each case, based on the total composition of the adhesive (layer of), usually from 0.3% to 2.5% by weight, preferably 0.5% by weight. To 2.0% by weight and very particularly from 0.7% to 1.7% by weight. Numbers relating to foamable adhesives are typically based on unexpanded microballoons, and numbers relating to foamed adhesive layers are based on unexpanded or pre-expanded microballoons commonly used.

PSAs that include expandable hollow microspheres and are used in the present invention may also, additionally, include non-expandable hollow microspheres. The only important factor is whether these membranes are made of elastically and thermoplastically stretchable polymer mixtures, or elastic glass that is non-thermoplastic within the temperature spectrum possible, for example in plastic processing, by permanent sealing membranes. Virtually all gas-containing cavities are closed.

Regarding the performance capacity of the PSA layer, more important than the amount of microballoons used is its density. The density of the foamed PSA layer of the invention, determined according to test VII, is at least 600 kg/m3 and at most 920 kg/m3, preferably at least 650 kg/m3 and at most 870 kg/m3, very preferably at least. 700 kg/m3 and maximum 820 kg/m3. For a given amount used, the lower the density, the larger microballoons can be achieved. In order to reach the desired performance capacity in terms of the purposes of the present invention, relatively fewer large microballoons will be used than small microballoons. The usual range of amounts used is particularly advantageous for microballoons with a maximum diameter of less than 40 μm. In the case of microballoons with a diameter of the expanded form of 40 μm, less than 2.0% is used.

The invention also relates to a self-adhesive product, in particular a double-sided adhesive self-adhesive product, ie, in particular, to a double-sided adhesive tape comprising at least one PSA layer of the invention. Adhesive transfer tapes are particularly advantageous. Alternatively, the self-adhesive product may also comprise a (permanent) intermediate carrier.

Accordingly, a self-adhesive tape produced using at least one PSA layer of the present invention can in particular be designed as follows:

-A single layer, double-sided self-adhesive adhesive tape, referred to as a transfer tape, consisting of a single PSA layer of the present invention;

-A multilayer, double-sided self-adhesive adhesive tape, the layers each consisting of an inventive PSA layer, or one inventive PSA layer and one non-inventive PSA layer;

-Double-sided self-adhesive treated adhesive tape with an intermediate carrier (so-called permanent carrier) disposed in the adhesive layer or between two adhesive layers.

Also preferred is one embodiment of a self-adhesive article in which the intermediate carrier consists solely of a single layer, more particularly a polymer film. It is also preferred that the intermediate carrier comprises at least one formulation layer comprising at least one class of vinylaromatic block copolymer and at least one class of tackifier resin. In such a case, the double-sided product, independently of the properties of the intermediate carrier, may have a symmetrical or asymmetric product structure, for example in terms of the properties of the PSA layer such as the composition and/or thickness of the PSA layer.

Typical converted forms of the PSA layer of the present invention are adhesive tape rolls and also adhesive strips in the form of, for example, die-cuts. Preferably, all layers are bonded to each other over their entire area.

The general expression “adhesive tape” in the context of the present invention refers to any sheet-like structure, for example a film or film section extended in two dimensions, a tape having an extended length and a limited width, a tape section, etc., and finally, It also includes die-cuts or labels.

The adhesive tape is more particularly in the form of a web. Web is understood to mean an object that is several times larger in length than its width, and the width over its entire length remains approximately and preferably exactly the same.

The adhesive tape can be produced in the form of a roll, ie in the form of an Archimedean spiral wound over itself.

The foamed PSA layer of the present invention is used in self-adhesive products as described above. Such self-adhesive products can be constructed as adhesive films, adhesive tapes or adhesive die-cuts. The self-adhesive article comprises at least one foamed PSA layer of the present invention. This layer can have a layer thickness of 10 to 2000 μm. The thickness is preferably 15 μm to 250 μm, more preferably 25 μm to 150 μm, and more particularly at most 100 μm. Self-adhesive products are usually bonded on both sides in form. An advantage of the formulation of the present invention is that when two parts are bonded to each other, ie, more particularly in a mobile device, a particularly good effect can be exhibited in a double-sided adhesive self-adhesive product.

Suitable film materials for the ply of at least one optional carrier for this design form are, in particular, polyester films, and in that case more preferably, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT). ) Based on film. The polyester film is preferably biaxially stretched. In addition, films of polyolefin, more particularly polybutene, cycloolefin copolymer, polymethylpentene, polypropylene or polyethylene, such as uniaxially stretched polypropylene, biaxially stretched polypropylene or biaxially stretched polyethylene, may be considered. This list is for illustrative purposes only. Those skilled in the art will recognize additional systems consistent with the inventive concept.

It is also possible to use stretchable carriers, for example carriers based on polyurethane, polyamide or various rubbers.

However, also metal foils, woven fabrics, nonwovens, or other knitted or woven carriers or paper carriers may be contemplated.

Additionally, foams in the form of webs (eg of polyethylene and polyurethane) are suitable.

The intermediate carrier may have a multi-ply configuration.

In addition, the intermediate carrier may have an outer layer that prevents the penetration of components from the adhesive into the intermediate carrier or vice versa, an example of which is a barrier layer. These outer layers may also have barrier properties to prevent diffusion of oxygen and/or water vapor through these layers.

To improve the fixation of the PSA on the intermediate carrier, the intermediate carrier can be pretreated by known means such as corona, plasma, or flame. The use of primers is also possible. However, ideally, no pretreatment is required.

The thickness of the intermediate carrier here is usually in the range of 2 μm to 200 μm, preferably 5 to 100 μm and more particularly 10 to 80 μm.

The adhesive tape preferably does not comprise a film carrier and consists solely of one or more adhesive layers.

The adhesive tape is lined with a liner on one or both sides, which is a temporary carrier with an anti-adhesive coating on one or both sides.

In the case where expandable microballoons are used for the adhesive layer, it is advantageous to fully withstand the foaming operation at high temperatures, for example 150 to 200°C, depending on the microballoons in which the liner is used. Many structured liners have a structured polyethylene coating. However, these PE coatings melt at high temperatures, meaning that silicone or polyethylene can be transferred to the adhesive.

This problem is avoided if the adhesive is coated on a smooth liner preferably made of polyethylene terephthalate (PET) and is covered accurately with such a liner. Thereafter, structuring occurs subsequently.

When expandable microballoons are used, a common problem is that after foaming, the microballoons protrude from the adhesive, thus significantly reducing the bonding strength of the adhesive tape.

One possibility to avoid this is to shape at least some foamed adhesive between the two liners, for example by means of at least two rolls. As a result of the high roll pressure, the microballoons can be pressed back into the adhesive, creating a smooth surface without breaking through the microballoons.

The structuring is then achieved, ideally when the composition is still hot. The assembly of the still hot foamed adhesive between the two liners proceeds onto the structured roll with the corresponding opposing rolls. If the pressure is sufficient, the structure of the roll is pressed into the PET liner and thus also into the composition. Advantageously, the facing rolls are smooth, so that only one side of the adhesive can be structured afterwards. Ideally, the roll is heated. It has proven to be advantageous if the liner during structuring has a temperature of 100 to 200°C, preferably 100 to 170°C. If higher temperatures are provided, structuring can be achieved at lower pressures.

Rather than structured rolls, printing plates can also be used for structuring and applied to the rolls.

The depth at which the structure is pressed into the product is advantageously 5 to 40 μm, preferably 10 to 30 μm.

Regarding re-peelability, the properties of the structure are decisive. In the adhesive, and after bonding, a continuous structure that results in connected channels in the bonding line has been shown to be particularly advantageous. In this case, the solvent can move more easily and quickly to the bonding line. While honeycomb or lattice patterns such as squares or squares are preferred herein, irregular structures such as irregular polygons are also contemplated.

Formulations, namely pressure sensitive adhesives (PSA), and coatings and self-adhesive products produced therefrom, can be produced with or without solvents.

The substrate in the method of the invention is preferably a sheet-like element, more particularly a carrier material, a film, a (release) liner, a transfer material, and/or an external material. The substrate can also be the surface of a fabrication line in a production method. In such a case, the PSA is processed into at least one PSA layer having a thickness of at least 15 μm or even at least 10 μm, and the PSA layer applied in a sheet-like manner is optionally dried and/or the solvent is removed.

In order to apply the PSA, the sheet-like elements used in the present invention can be coated by a method including, among other things, a knife method, a nozzle knife method, a rolling rod die method, an extrusion die method, a casting nozzle method and a caster method. . Likewise, according to the present invention, there are application methods such as a roll application method, a printing method, a screen-printing method, a patterned roll method, an inkjet method and a spray method. The hot melt method (extrusion, die) is preferred.

Additional layers or plies of material are optionally laminated or subsequently coated in-line or off-line, whereby a multi-layer/multi-ply product structure can also be created.

In a further embodiment of the method of the present invention, the resulting combination of a sheet-like element and a PSA is cut into a metric product comprising a tape and/or punched to form a die-cut, and the tape is optionally wound on a roll.

Finally, the invention also extends to an adhesive assembly obtained using a self-adhesive article comprising at least one PSA layer of the invention. In other words, the present invention relates to an assembly consisting of two substrates, for example, in particular parts of a mobile device, typically joined by the double-sided adhesive tape of the present invention and the adhesive tape. Accordingly, the invention also relates to the use of a double-sided adhesive variant of an adhesive tape in an assembly having two substrates.

The adhesive tape structured on the surface is intended to be easily removable again after bonding without residue by applying a solvent around the bonding partner. This solvent then flows into the channel between the adhesive and the substrate resulting from structuring, thereby causing a decrease in the bond strength.

The solvent used can in principle be almost any solvent, but it is preferred that the solvent is not absorbed very well by the adhesive, so that the solvent is not drawn up before it can penetrate the channel.

Particularly preferred solvents are those that do not react with other components in the electronic device and are not harmful to personnel or the environment. Accordingly, in order to reduce the surface tension of the water and to make the solvent flow more easily into the channel, ethanol and water are particularly preferred, and also water containing various detergents, such as soapy water, is particularly preferred.

Test Methods

Unless specified to the contrary, all measurements were made to determine adhesion properties at 23° C. and 50% relative atmospheric humidity.

Test I-Peel Adhesion

Peel adhesion was determined as follows (according to AFERA 5001). The specified substrate used is a polished steel sheet with a thickness of 2 mm. The bondable sheet-like element under test (with a 36 μm etched PET support film on the back side) was cut to a width of 20 mm and a length of about 25 cm, providing a handling section, and immediately after, at a rate of 10 m/min. Using an advancing 4 kg steel roller, it was pressed 5 times on each selected substrate. Immediately after, the bondable sheet-like elements were peeled using a tensile tester (from Zwick) at an angle of 180° at a speed v = 300 mm/min, and the force required to achieve this at room temperature was measured. The measured value (N/cm) was obtained as an average value from three individual measurements.

For the measurement of peel adhesion after ethanol exposure, the test was modified as follows:

After the substrates were bonded and rolled down with a steel roller, an overstuck steel plate was briefly immersed in ethanol for 2 seconds. Thereafter, the overstuck grater was taken out of ethanol and stored on a horizontal bench for 1 minute. After that, the measurement was carried out as described above.

Test II-penetrating impact toughness; z-plane (DuPont test)

A square, frame-shaped sample was cut from the adhesive tape under test (external dimension 33 mm x 33 mm; rim width 2.0 mm; internal dimension (window open) 29 mm x 29 mm). These samples were bonded onto a polycarbonate (PC) frame (external dimension 45 mm×45 mm; rim width 10 mm; inner dimension (window open) 25 mm×25 mm; thickness 3 mm). On the other side of the double-sided adhesive tape, a 35 mm x 35 mm PC window was bonded. The PC frame, adhesive tape frame and PC window were joined so that each of the geometric centers and diagonals were on top of each other (corners on the edges). The bonding area was 248 mm 2. The junction was pressed at 248 N for 5 seconds and stored for 24 hours while conditioned at 23° C./50% relative humidity.

Immediately after storage, the adhesive assembly consisting of the PC frame, adhesive tape and PC window was clamped in the sample holder by the protruding edge of the PC frame in such a way that the assembly is aligned horizontally. In this arrangement, the PC frame is laid flat on the sample holder by the protruding edge, allowing the PC window to float freely under the PC frame (fixed by the adhesive tape specimen). Thereafter, the sample holder was inserted centrally into the holder provided on the DuPont Impact Tester. An impact head weighing 150 g was inserted so that a circular impact geometry with a diameter of 24 mm was centered and abutted horizontally with the freely accessible PC window surface from above.

A weight guided on two guide rods and having a weight of 150 g was dropped vertically at a height of 5 cm on the assembly of the sample holder, sample and impact head arranged as above (measurement condition 23° C., 50% relative Humidity). The height of the falling weight was increased in 5 cm steps until the impact energy introduced as a result of penetrating impact loading destroyed the sample, and the PC window was divided from the PC frame.

To compare experiments with different samples, energy was calculated as follows:

E[J] = Height [m] * Weight of weight [kg] * 9.81 kg/m*s²

For each product, 5 samples were tested and the average energy was reported as a characteristic of the penetration impact toughness.

Test III-Push-out

Rectangular specimens measuring 10 cm x 6 cm were cut from the adhesive tape under test. These specimens were bonded onto a rectangle of the same size made of polyvinyl chloride having a thickness of 2 mm. The outer substrate is an aluminum body with an indentation 0.5 cm larger than the PVC plate in both directions. The aluminum body has a 3 × 3 cm hole in the center of the groove. The PVC plate was then bonded to the center of the groove.

The two bonding partners were pressed together at 100 kg for 5 seconds, and the test structures were stored at room temperature (23° C.) and 50% rh for 24 hours and 336 hours (or 14 days).

Subsequently, using a plunger, the PVC plate was pushed out of the metal body through the hole and the force was measured.

In the test after ethanol exposure, just before the measurement, 1 ml of ethanol was allowed to flow around the PVC plate into the grooves of the aluminum body. After a 1 minute dwell time, the test was carried out as described above.

Test IV-Glass Transition Temperature (DSC)

The glass transition temperature of the polymer block in the block copolymer was determined using dynamic scanning calorimetry (DSC). For this purpose, approximately 5 mg of an untreated block copolymer sample was weighed into a small aluminum crucible (25 μl volume) and the crucible was closed with a perforated lid. Measurements were carried out using DSC 204 F1 from Netzsch, working under nitrogen for inactivation. The sample was first cooled to -150°C, heated to +150°C at a rate of 10 K/min, and cooled again to -150°C. The subsequent second heating curve was again performed at 10 K/min and the change in heat capacity was recorded. The glass transition appeared as a step in the thermogram. The glass transition temperature was evaluated as follows (in this regard, see FIG. 1). The tangent line was applied to the baseline of the thermogram before and after step 1 and 2, respectively. Specifically, in order to form two regions 4 and 5 of the same area (between each tangent, the line of the top pit, and the measurement plot), the line 3 of the best fit is intersected in a way that the two tangents intersect. Placed parallel to the ordinate in the area. The intersection of the line of the best pit positioned accordingly with the measurement plot gives the glass transition temperature.

Test V-Molar Mass (GPC)

(i) peak molar mass of individual block copolymer mode

GPC is a suitable technical measurement method for determining the molar mass of an individual polymer mode in a mixture of different polymers. For block copolymers that can be used for the purposes of the present invention, prepared by living anionic polymerization, the molar mass distribution is usually assigned to triblock copolymers, diblock copolymers or multiblock copolymers. The polymer modes are narrow enough to occur with sufficient resolution to each other in an elugram. The peak molar mass for each polymer mode can then be read out from the illugram.

The peak molar mass M _P was determined by gel permeation chromatography (GPC). The eluent used is THF. Measurements were carried out at 23°C. The precolumn used was PSS-SDV, 5 μ, 10 ³ Å, ID 8.0 mm × 50 mm. Separation was carried out using columns PSS-SDV, 5 μ, 10³Å and also 10 ⁴ Å and 10 ⁶ Å (each having an ID of 8.0 mm×300 mm). The sample concentration was 4 g/l and the flow rate was 1.0 ml per minute. Measurements were performed on PS standards (μ = μm; 1 Å = 10 ^-10 m).

(ii) in particular the weight-average molecular weight of the tackifier resin

The weight-average molecular weight M _w (MW) was determined by gel permeation chromatography (GPC). The eluent used is THF. Measurements were carried out at 23°C. The precolumns used were PSS-SDV, 5 μ, 10³Å, ID 8.0 mm × 50 mm. Separation was performed using columns PSS-SDV, 5 μ, 10 ³ Å and also 10 ⁴ Å and 10 ⁶ Å (each having an ID of 8.0 mm×300 mm). The sample concentration was 4 g/l and the flow rate was 1.0 ml per minute. Measurements were performed on PS standards (μ = μm; 1 Å = 10 ^-10 m).

Test VI-(Tackifier) Resin Softening Temperature

(Tackifier) The (Tackifier) resin softening temperature, also referred to as the resin softening point, was performed according to a related method, known as Ring & Ball and standardized according to ASTM E28.

Test VII-Density

The density of the adhesive or adhesive layer, ie, the absolute density, was confirmed by forming the ratio of the coat weight to the thickness to the adhesive layer applied to the carrier or liner.

The coat weight is the mass of the section, having the same dimensions, of the carrier or liner used, in the mass of the section, defined in terms of its length and its width, of this class of adhesive (layer of) applied to the carrier or liner. It may be determined by subtracting (known or may be identified separately).

The thickness of the adhesive (layer of) has the same dimensions of the carrier or liner used, at the thickness of the section, defined in terms of its length and its width, of this class of adhesive (layer of) applied to the carrier or liner. , Can be determined by subtracting the thickness of the section (known or can be identified separately). The thickness of the adhesive (layer of) can be checked by a commercial thickness tester (gauge test instrument) with an accuracy of deviation of less than 1 μm. In this application, the precision thickness tester Mod. 2000 F was used, which has a circular gauge with a diameter of 10 mm (flat). The measuring force is 4 N. Values were read 1 second after loading. In cases where variations in thickness were found, the average of the measurements was reported at three or more representative sites, thus not measuring, in particular, in wrinkles, folds, nips, etc.

Example

The pressure-sensitive adhesive tape of the present invention is described in a preferred practice below with reference to a number of examples, which are not intended to limit the present invention in any way.

Further listed are comparative examples showing unsuitable adhesive tapes.

The components of the pressure-sensitive adhesive are dissolved at 40% in special-boiling point spirit/toluene/acetone for vinylaromatic block copolymer compositions, or 30% in butanone for nitrile rubber compositions, where both compositions are appropriate. E, mixed with microballoons in suspension in spirit or butanone, respectively, and then coated with a coating rod on a PET film provided with a silicone release system, structured or unstructured at the desired layer thickness. The solvent was subsequently evaporated at 100° C. for 15 minutes to dry the layer of the composition. In the examples listed, this is possible, because, in this case, microballoons with an expansion temperature in excess of 100° C. were used. In the case of using different microballoons, one skilled in the art will select a suitable production temperature accordingly without departing from the scope of the present invention.

After performing drying, if the adhesive contains microballoons, the adhesive layer is lined with a second PET liner ply as defined above, without any air inclusions, and forced air drying at 170° C. for 30 seconds. While hanging from the cabinet, it was foamed between the two liners.

Table 1 shows the raw materials used.

Table 1: Raw materials used

Tables 2 and 3 show the formulations used and their characteristics.

Table 2: Formulation and its features

Table 3: Additional formulations and their features

From this adhesive, it was produced by coating the adhesive tapes of Examples 1 to 3 below on a liner, foaming and optionally subsequently structuring.

The liner is a 50 μm liner with a relatively high release force, and a 36 μm liner with a relatively low release force.

In this case the adhesive was coated from solution onto a 50 μm liner and dried, and the dried composition had a coat weight of approximately 38 g/m 2. A 36 μm liner was then laminated thereon and the adhesive tape was foamed at 160° C. to give a thickness of approximately 50 μm. Immediately after foaming, the adhesive tape was embossed while still maintaining a high temperature between the two rolls and adhered to the plate, which is a printing plate. The printing plate has a diamond pattern with diamonds 5 mm in the length direction and 3 mm in the transverse direction. The interconnect width was approximately 150 μm. The pressure was set so that the embossing depth was approximately 25 μm.

In Example 3, the adhesive tape was subsequently crosslinked at a dose of 30 kGy using an electron beam of 250 kV.

Comparative Example 1

The same composition as in Example 1 (Adhesive 1) was used, but no microballoons were added, and as a result, the composition could not be foamed. Accordingly, the composition was coated in a straight line at about 50 g/m 2 (after drying).

Comparative Example 2

It was the same as in Comparative Example 1 except that the adhesive 2 was used.

Comparative Example 3

At this time, structuring was omitted, and it was the same as in Example 1 except that the adhesive tape had a smooth surface after creation.

Comparative Example 4

It was the same as in Example 3 except that the specimen was not crosslinked with an electron beam.

Tables 4 and 5 show test results for Examples and Counter-Examples (Comparative Examples) of the present invention.

Table 4: Test results for Examples of the present invention

Table 5: Test results for counter-examples (i.e., comparative examples)

It is clear that the impact performance can be significantly improved through the foaming of the adhesive.

The structuring of the surface of the adhesive tape helps re-peel. If it is not structured, it is not possible to achieve a lowering of peel adhesion or a push-out value of 40% or more. In the case of unstructured, delamination occurs from the PVC in part as well as on the metal side.

It is desirable that the peelability is maintained even after long-term storage. A very soft adhesive such as Comparative Example 4 loses its structuring and thus loses immediately available re-peelability over time.

Claims (14)

A method of structuring a foamed adhesive tape made of at least one adhesive layer and optionally at least one additional layer, wherein the at least one adhesive layer is foamed, wherein the adhesive tape comprises a liner with the aid of a roll. Wherein the structure is structured on at least one ourward-pointing surface of the adhesive layer of the adhesive tape by the structure embossed through. The method according to claim 1, characterized in that an adhesive tape is used for the adhesive bonding and possible re-release of electronic components. The method of claim 1, wherein the embossing takes place at a temperature of at least 100°C. The method of claim 1, wherein the resulting structure creates channels in the adhesive through which the solvent can penetrate the bonding line so that the adhesive tape can be peeled back. The method according to claim 1, characterized in that the depth of the structure is 10 to 50 μm deep. The method of claim 1, wherein the structure is still recognizable after at least two weeks after application and storage at room temperature (23° C.). The method of claim 1, wherein the adhesive tape consists of at least one adhesive layer. The method of claim 1, wherein the adhesive layer is a pressure sensitive adhesive layer. The method of claim 1, wherein the adhesive tape is double-sided. The method according to claim 1, characterized in that the foaming of the at least one adhesive layer is carried out with the aid of microballoons. The method according to claim 1, characterized in that the at least one adhesive layer is based on a vinylaromatic block copolymer. The method according to claim 1, characterized in that the at least one adhesive layer is based on nitrile rubber. An adhesive tape according to any one of claims 1 to 12, wherein the adhesive tape comprises a film or a woven fabric carrier. An adhesive tape according to any one of claims 1 to 12, wherein the adhesive tape does not contain a film or a woven fabric carrier.

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